Economic Development Committee
August 4, 2025

CML 5059 (264) Sisk Road Signal Coordination
Item # Item Description Units Quantity Unit Price Extension

2. Clearing, Grubbing, and Mobilization LS 1 $24,471.00 $24,471.00

3. Conduit Installation LF 3,600 $116.00 $417,600.00

4. Fiber Optic Cable Installation-96 Strand LF 18,400 $6.00 $110,400.00

5. Fiber Optic Cable Installation-12 Strand LF 325 $11.00 $3,575.00

6. Pull Boxes EA 10 $2,000.00 $20,000.00

7. Fiber Splice Boxes EA 6 $3,500.00 $21,000.00

8. 144 Fiber Splice Tray EA 3 $16,802.00 $50,406.00

9. Fusion Splice-12 Strand Fiber With 24 EA 7 $4,033.00 $28,231.00 Splice Enclosure

10. Fusion Splice Hub Termination-96 Strand Fiber EA 4 $18,280.00 $73,120.00

11. Water Pollution Control Plan (WPCP) LS 1 $9,700.00 $9,700.00

12. Restoration LS 1 $26,521.00 $26,521.00

13. Monument Preservation LS 1 $4,860.00 $4,860.00
Total: $829,884.00
Percent From Engineer's Estimate: -0.59%
Tennyson Electric LLC
(925) 606-1038 7275 National Drive, Suite A2, Livermore, CA 94550 Base Bid

1. Traffic Control, Barricades, and Other Related Fees LS 1 $102,500.00 $102,500.00

2. Clearing, Grubbing, and Mobilization LS 1 $42,000.00 $42,000.00 3 Conduit Installation LF 3,600 $115.00 $414,000.00

4. Fiber Optic Cable Installation-96 Strand LF 18,400 $7.37 $135,608.00

5. Fiber Optic Cable Installation-12 Strand LF 325 $17.40 $5,655.00

6. Pull Boxes EA 10 $7,145.00 $71,450.00

7. Fiber Splice Boxes EA 6 $5,130.00 $30,780.00

8. 144 Fiber Splice Tray EA 3 $7,630.85 $22,892.55

9. Fusion Splice-12 Strand Fiber With 24 EA 7 $3,061.10 $21,427.70 Splice Enclosure

10. Fusion Splice Hub Termination-96 Strand Fiber EA 4 $8,410.30 $33,641.20

11. Water Pollution Control Plan (WPCP) LS 1 $10,670.00 $10,670.00

12. Restoration LS 1 $135,000.00 $135,000.00

13. Monument Preservation LS 1 $2,500.00 $2,500.00
Total: $1,028,124.45
Percent From Engineer's Estimate: 23.15%
MP Nexlevel of California, Inc
(320) 963-2400 500 County Rd 37, Maple Lake, MN 55358
Base Bid

1. Traffic Control, Barricades, and Other Related Fees LS 1 $260,000.00 $260,000.00

2. Clearing, Grubbing, and Mobilization LS 1 $15,000.00 $15,000.00

3. Conduit Installation LF 3,600 $80.00 $288,000.00

4. Fiber Optic Cable Installation-96 Strand LF 18,400 $8.10 $149,040.00

5. Fiber Optic Cable Installation-12 Strand LF 325 $33.30 $10,822.50

6. Pull Boxes EA 10 $6,190.00 $61,900.00

7. Fiber Splice Boxes EA 6 $12,450.00 $74,700.00

8. 144 Fiber Splice Tray EA 3 $6,785.00 $20,355.00

9. Fusion Splice-12 Strand Fiber With 24 EA 7 $2,330.00 $16,310.00 Splice Enclosure

10. Fusion Splice Hub Termination-96 Strand Fiber EA 4 $7,170.00 $28,680.00 #3..
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CML 5059 (264) Sisk Road Signal Coordination
Item # Item Description Units Quantity Unit Price Extension

11. Water Pollution Control Plan (WPCP) LS 1 $7,000.00 $7,000.00

12. Restoration LS 1 $150,000.00 $150,000.00

13. Monument Preservation LS 1 $2,500.00 $2,500.00
Total: $1,084,307.50
Percent From Engineer's Estimate: 29.88%
Engineer's Estimate
Base Bid

1. Traffic Control, Barricades, and Other Related Fees LS 1 $50,000.00 $50,000.00

2. Clearing, Grubbing, and Mobilization LS 1 $35,000.00 $35,000.00

3. Conduit Installation LF 3,600 $73.00 $262,800.00

4. Fiber Optic Cable Installation-96 Strand LF 18,400 $12.00 $220,800.00

5. Fiber Optic Cable Installation-12 Strand LF 325 $10.00 $3,250.00

6. Pull Boxes EA 10 $4,000.00 $40,000.00

7. Fiber Splice Boxes EA 6 $9,000.00 $54,000.00

8. 144 Fiber Splice Tray EA 3 $10,000.00 $30,000.00

9. Fusion Splice-12 Strand Fiber With 24 EA 7 $4,500.00 $31,500.00 Splice Enclosure

10. Fusion Splice Hub Termination-96 Strand Fiber EA 4 $10,000.00 $40,000.00

11. Water Pollution Control Plan (WPCP) LS 1 $2,500.00 $2,500.00

12. Restoration LS 1 $40,000.00 $40,000.00

13. Monument Preservation LS 1 $25,000.00 $25,000.00
Total: $834,850.00
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CITY OF MODESTO

COMMITTEE AGENDA REPORT
DATE OF MEETING:

August 4, 2025
Date: July 10, 2025
TO: Economic Development Committee
Eric Alvarez, Chair
Sue Zwahlen, Vice-Chair
Nick Bavaro, Member
THROUGH: Joseph P. Lopez, City Manager
FROM: William Wong, Director of Utilities
SUBJECT: Prequalified Local Consultant List Civil Engineering Services CONTACT: Edgar Vargas, Senior Civil Engineer, [email protected], 209-577-5424 DESCRIPTION:

Consider a Prequalified Local Consultant List for Civil Engineering Services for a period of five (5) years and forwarding to Council for approval. (Funding Source: Various Capital/Non-Capital Projects)
STRATEGIC PLAN ELEMENT:

The recommended action supports the 2025-2026 City’s Strategic Plan Initiatives, Goal D:

Provide safe, efficient, and reliable infrastructure through proactive community investment, maintenance, and sustainability efforts.

BACKGROUND:

On April 12, 2022, by Resolution No. 2022-191, Council approved a Prequalified Local Consultant List for Civil Engineering Services for a period of up to three (3) years. This list expired on April 11, 2025 and Staff is seeking to have it reestablished as it has proven to be beneficial to the Utilities Department to have expedited access to Local Civil Engineering Services for efforts that require consultant services for efficient project delivery. Retaining a prequalified consultants list also eliminates the need to send out repetitive Requests for Qualifications (RFQ) for projects of similar scope and/or type, saving Staff time and project costs.

DISCUSSION:

In accordance with Administrative Directive 3.1, Selection Procedures for Professional Consultants Who Provide Architectural & Engineering Services for Capital Projects, which follows State of California Government Code, Sections 4526-4529, Staff solicited and formally advertised an RFQ.
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Economic Development Committee, August 4, 2025
Prequalified Local Consultant List
Civil Engineering Services

On February 25, 2025, the Engineering Division of the Utilities Department issued RFQ 2025-03 notifying prospective consultants of the opportunity to participate in the selection process to establish a Prequalified Local Consultants List for Civil Engineering Services on the City’s OpenGov public bidding website under the following commodity codes:
90735 – Designing Services
90738 – Drafting Services
91842 – Engineering Consulting
92500 – Engineering Services, Professional
92596 – Wastewater Treatment Engineering
Seventy-Six (76) companies downloaded the RFQ document from OpenGov, nine (9) chose to respond, and seven (7) local proposals were received.

After careful review of the Statements of Qualifications by a committee composed of four (4) members of the Utilities Department Staff, the following firms were selected as most qualified:

BKF Engineers
Black Water Consulting Engineers, Inc.

NorthStar Engineering Group, Inc.

Siegfried Engineering, Inc.

Services to be provided will include, but are not limited to:

Topographic Survey
Design Drawings
Specifications
Construction Cost Estimates
Project Management
Permitting
Environmental Clearance
Engineering Support During Construction
Grant Research, Writing and Management
When consultant services are required, a Request for Proposals (RFP) with a specific scope of work will be issued to these firms. Following evaluation of the proposals, interviews may be necessary to select the most qualified firm for the job in question. Once a firm has been selected an Agreement for Engineering Services will be presented to Committee and Council for approval.

This process is consistent with Modesto Municipal Code section 8-3.204(a), which exempts contracts for professional services from the City’s formal bidding requirements, as long as proposals are sought from at least three (3) qualified entities.

Staff is requesting that this prequalified list be in effect for five (5) years from the date of Council approval. In the event the firms listed on the prequalified list are deemed to lack experience or expertise for specific projects, the City retains the right to recruit consultants for individual projects through its standard purchasing procedures.
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Economic Development Committee, August 4, 2025
Prequalified Local Consultant List
Civil Engineering Services

FISCAL IMPACT:

There are no fiscal impacts at this time; Consultant Agreements resulting from the use of this Prequalified List will be project specific and encumbered against their associated budgets.

RECOMMENDED COMMITTEE ACTION:

Staff Recommendations:

Motion recommending a Prequalified Local Consultant List for Civil Engineering Services for a period of five (5) years and forwarding to Council for approval.

Approved by:

William Wong, Director of Utilities
Joseph P. Lopez, City Manager
Attachments:

1. Evaluation Criteria
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CITY OF MODESTO

COMMITTEE AGENDA REPORT
DATE OF MEETING:

August 4, 2025
Date: July 1, 2025
TO: Economic Development Committee
Eric Alvarez, Chair
Sue Zwahlen, Vice-Chair
Nick Bavaro, Member
THROUGH: Joseph P. Lopez, City Manager
FROM: Jessica Hill, Director of Community and Economic Development SUBJECT: Tivoli Catch Basin Engineering Design Agreement CONTACT: Edgar Garcia, Community Development Manager
[email protected], 209-577-5211
DESCRIPTION:

Consider an Agreement for Engineering Design Services for the Tivoli dual use basin and park with Westwood Professional Services, Inc., Plano, TX, for a total amount not to exceed $446,674. (Funding Source: General Fund Loan and Community Facilities District Bonds) STRATEGIC PLAN ELEMENT:

The recommended action supports the City Council’s 2025-2026 Strategic Plan, Goal D:

Provide Safe, Efficient, and Reliable Infrastructure through proactive community investment, maintenance and sustainability efforts.

BACKGROUND:

The Tivoli Specific Plan (TSP) approved by City Council in 2008 by Ordinance No. 3479-C.S., is a 454-acre area located in an unincorporated area of Stanislaus County. The project is located within the City of Modesto’s Sphere of Influence. The site is bounded by the planned Claratina Avenue on the north, Oakdale Road on the west, Sylvan Avenue on the south, and Roselle Avenue on the east.

On August 13, 2024, by Resolution No. 2024-279, the Council approved the Resolution of Intention to form City of Modesto Community Facilities District (CFD) No. 2024-1 (Tivoli) to establish improvement area No. 1, designate a future annexation area and authorize the levy of special tax within said Community Facilities District. The City Council also approved a Resolution to Incur Debt by Resolution No. 2024-280. It is the sole discretion of CFD No. 2024-1 as to if and when Bonds will be issued. During the formation of the CFD, it may be determined that there is a need for the issuance of bonds to pay for the facilities required for the CFD. If bonds are required, documents relating to the issuance and sale of the bonds will be brought to the Council for approval. The proposed maximum CFD bond authorization is $120 million, and #5..
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Economic Development Committee, August 4, 2025
Tivoli Catch Basin Engineering Design Agreement

this serves as a “not to exceed” bond amount for the CFD and is based on the cost of financing the associated facilities. The maximum Annual Facilities Special Tax includes a buffer to prevent the possible authorization of bonds from limiting the capacity of the CFD to pay for ongoing services. The CFD is a separate legal entity and the land within the CFD secures the bonds, and any sale of CFD bonds will not impact the City’s bonding capacity.

On September 24, 2024, by Resolution No. 2024-354, the Council approved the formation of City of Modesto Community Facilities District No. 2024-1 (Tivoli) (“CFD No. 2024-1”) pursuant to the Mello-Roos Community Facilities Act of 1982 and conditionally authorized staff to levy special taxes therein and conditionally establishing annual appropriations limits.

DISCUSSION:

The TSP proposes an approximately 19 acre dual-use basin and neighborhood park that will serve as a centralized focal point and recreational open space asset for future residents. South of the park is an area designated for an elementary school site. The TSP may include small neighborhood common open space in some residential districts. The paseos located along primary collector streets will offer appealing pedestrian links to the centrally located basin and park. The City of Modesto has begun to receive several developer inquires and planning projects for the Tivoli area including tentative subdivision map applications. On July 22, 2025, the Council approved the first set of final subdivision maps for the TSP area. These maps call for the construction of 284 single family dwellings. The design and eventual construction of the dual use catch basin will be crucial as new TSP subdivisions continue through the entitlement process. Given that the basin will be constructed by several TSP property owners, the City will work towards creating a single set of designs that are compliant with City standards which will inform the new development in Tivoli.

On March 4, 2025, the City Manager executed an authorization to purchase form to authorize staff to issue a Request for Proposals (RFP) to search for qualified engineering design firms.

The City released the RFP through the OpenGov platform on February 28, 2025. Four (4) firms were notified of the opportunity, Westwood Professional Services, NorthStar Engineering Group, Blackwater Consulting Engineers, and Siegfried Engineering. Following the close of the RFP on March 21, 2025, the City received only one response from Westwood Professional Services Inc. of Plano Texas. Westwood Professional Services, previously known as O’Dell Engineering, as the sole respondent is also qualified to design the Tivoli Catch basin given that O’Dell Engineering assisted the City in the development of the original Tivoli Specific Plan in 2008.

Modesto Municipal Code Section 8-3.203 generally requires all purchases, which meet or exceed $100,000 for material, equipment, or contractual services to follow formal bid procedures. However, exceptions to the formal bidding process are granted in MMC 8-3.204(a) for contracts for professional services as defined in Section 8-3.103, if competitive quotations or proposals have been sought informally from at least three (3) qualified entities. Given that proposals were requested from four (4) qualified engineering design firms, staff recommends the award of this Engineering Services Agreement to Westwood Professional Services Inc. as the sole responsive bidder.

FISCAL IMPACT:

As part of this item, an interfund loan from the Water Fund has been included to the Tivoli CFD fund 3255 in an amount of $446,674 to fully fund the anticipated agreement expenditures. As #5..
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Economic Development Committee, August 4, 2025
Tivoli Catch Basin Engineering Design Agreement

previously mentioned, the Tivoli CFD is authorized to issue bonds to reimburse the costs of eligible activities, including the development of the basin. Following the issuance of CFD bonds, the Water Fund will be reimbursed immediately for this initial loan which is needed to proceed with the basin’s design in a timely manner. As required by the City’s Operating Budget policy, the interfund loans will accrue interest based on the actual rate of return earned by the City’s investment portfolio during the 12-month period immediately preceding a payment date. The cost of the Agreement is allocated to the following tasks:

Project Management $ 23,110
Survey and Topographic Mapping
Design Development
$ 9,570
$ 53,500
Design Services $247,980
Specialized Technical Services $ 77,314
Construction Support $ 35,200
Total cost not to exceed $446,674
RECOMMENDED COMMITTEE ACTION:

Staff Recommendations:

Motion recommending the Award of Proposal and Agreement for Engineering Design Services for the Tivoli dual use basin and park to Westwood Professional Services, Inc., Plano, TX, for a total amount not to exceed $446,674, and forwarding to Council for approval.

Motion recommending the issuance of an interfund loan in an amount not to exceed $446,674 from the Water Fund 4100 to the Tivoli CFD Fund 3255 for the purchase of Engineering Design Services for the Tivoli dual use basin and forwarding to Council for approval.

Approved by:

Jessica Hill, Director of Community and Economic
Development
Joseph P. Lopez, City Manager
Attachments:

1. Standard Agreement-Tivoli Basin Design Services

2. Exhibit A-Scope of Services

3. Tivoli Basin Design RFP

4. Westwood Professional Services Proposal

5. Levine Act Disclosure Form
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1 STANDARD AGREEMENT

FOR CONSULTANT SERVICES
THIS AGREEMENT made and entered into in the City of Modesto, State of California, this ______ day of __________________, 20___, (“Effective Date”) by and between the CITY OF MODESTO, a municipal corporation of the State of California, hereinafter referred to as "CITY", and WESTWOOD PROFESSIONAL SERVICES, Inc., a Texas corporation, hereinafter referred to as "CONSULTANT".

This AGREEMENT is made with regard to the following recitals:
a. The Tivoli Specific plan area is beginning to have the first initial housing developments nearing the beginning of the construction phase.
b. The CITY has determined that there is a need for engineering design services of a dual use catch basin and park due to the upcoming housing projects nearing completion. c. CONSULTANT represents that it is qualified, willing, and able to provide the services to prepare said document(s).

NOW, THEREFORE, in consideration of this AGREEMENT, and the mutual promises, covenants, and stipulations hereinafter contained, the parties agree as follows:

1. TERM OF AGREEMENT.

This Agreement is effective as of the date first written above and will continue in effect until City’s acceptance of and payment for all services authorized by City and Performed by Consultant, unless terminated earlier in accordance with the provisions of the termination clause in this Agreement.

Pricing shall remain firm for the first two (2) years of the agreement. #5..
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2 Price increases for subsequent AGREEMENT years shall not exceed the Consumer Price Index (CPI) for West Urban Area in any one AGREEMENT year and shall be negotiated through the Purchasing Division. Requests for price increases shall be submitted by CONSULTANT in writing, ninety (90) days prior to the annual anniversary date of the AGREEMENT to be effective for the subsequent year.

2. SCOPE OF SERVICES.

CONSULTANT shall undertake and complete the preparation of the scope of work as set forth and described in the documents attached hereto and referred to as Exhibit (A) or “Project” with the exception of task 7 which is not required at this time. The CONSULTANT shall perform the services as described in Exhibit (A) in a manner compatible with the standards of its profession and shall produce a fully complete project that is acceptable to the CITY.

3. COMPENSATION.

CONSULTANT agrees to accept a sum not to exceed $446,674 (maximum compensation) as full remuneration for performing all services and furnishing all staffing and materials for CITY in accordance with Exhibit (A).

The Compensation shall be paid pursuant in the manner and at the times set forth below:

CITY shall pay CONSULTANT on a time and materials basis for CONSULTANT’s actual costs for all work called for in Exhibit (A) to this AGREEMENT. All work to be performed under this AGREEMENT shall be billed at the hourly rates set forth in Exhibit (A) attached hereto.

CONSULTANT shall submit monthly invoices to CITY which include detailed tasks, hours worked, and billable rates for all work completed, and detailed receipts for any reimbursable expenses paid by CONSULTANT and identified in Exhibit (A) or approved by the CITY in writing.

CITY shall pay CONSULTANT Net 45 Days via manual check
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3 4. OBLIGATIONS OF CONSULTANT.

Throughout the term of this AGREEMENT, CONSULTANT shall possess, or secure all licenses, permits, qualifications and approvals legally required to conduct business. CONSULTANT represents that it has all of the necessary professional capabilities and experience, as well as all tools, instrumentalities, facilities and other resources necessary to provide the CITY with the services contemplated by this AGREEMENT. CONSULTANT further represents that it will follow the best current, generally accepted and professional practices to make findings, render opinions, prepare factual presentations, and provide professional advice and recommendations regarding this project.

5. PERFORMANCE BY KEY EMPLOYEE.

CONSULTANT has represented to CITY that Chad Kennedy will be the person primarily responsible for the performance of the services referred to in this AGREEMENT. The project manager responsible for daily coordination of the project will be Tyler Fay. CITY has entered into this AGREEMENT in reliance on that representation by CONSULTANT. CONSULTANT therefore agrees that twenty-five percent (25%) or more of the time to be devoted to the project that is the subject of this AGREEMENT will be that of the above-named person.

6. OWNERSHIP OF DOCUMENTS/TITLE TO DATA.

Ownership of Documents
Upon payment in full for CONSULTANT’s services under this Agreement, all reports, drawings, designs, graphics, working papers and other incidental work or materials furnished hereunder shall become and remain the property of the CITY, and may be used by CITY as it may require without any additional cost to CITY. No reports shall be used by the CONSULTANT for purposes other than this AGREEMENT without the express prior written consent of CITY.
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4 Title to Data
If, as a part of the AGREEMENT, CONSULTANT is required to produce data such as, but not limited to, drawings, plans, specifications, calculations, models, flow diagrams, visual aids and other related materials, the originals of all such data generated under this AGREEMENT will be delivered to CITY upon the completion or termination of services under the AGREEMENT. It is understood and agreed that the documents and other materials, including but not limited to those described above, prepared pursuant to this AGREEMENT are prepared specifically for the CITY and are not necessarily suitable for any future or other use by CITY.

All materials, documents, data or information obtained from the CITY data files or any CITY medium furnished to CONSULTANT in the performance of this AGREEMENT will at all times remain the property of the CITY. Such data or information may not be used or copied for direct or indirect use by CONSULTANT after termination of this AGREEMENT without written consent of the CITY.

7. NEWS AND INFORMATION RELEASE.

CONSULTANT agrees that it will not issue any news releases in connection with either the award of this AGREEMENT, or any subsequent amendment of or efforts under this AGREEMENT, without first obtaining review and approval of said news releases from CITY through the CITY Manager.

8. CONFLICT OF INTEREST.

CONSULTANT warrants that it presently has no interest and shall not acquire any interest, direct or indirect, which would create a “conflict of interest”, as that term is defined in the Political Reform Act (Gov. Code § 81000 et seq), for the CONSULTANT in the performance of this AGREEMENT.

CONSULTANT warrants that, in performance of this AGREEMENT, CONSULTANT shall not employ any person having any such interest. CONSULTANT understands that, if this AGREEMENT is made in violation of Government Code § 1090 et seq., the entire AGREEMENT is void and CONSULTANT will #5..
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5 not be entitled to any compensation for services performed. CONSULTANT agrees to file a Statement of Economic Interests with the City Clerk at the start and end of this AGREEMENT if so, required at the option of CITY.

9. AMENDMENTS.

This AGREEMENT, including the Exhibits attached hereto, may be amended only by a writing signed by both Parties. CITY will not be responsible to pay any charges CONSULTANT may incur in performing services not identified in Exhibit (A) unless first authorized by the CITY in writing.

10. INDEPENDENT CONTRACTOR.

All acts of CONSULTANT, its agents, officers, and employees and all others acting on behalf of CONSULTANT relating to the performance of this AGREEMENT, shall be performed as independent contractors and not as agents, officers, or employees of CITY. Except as CITY may specify in writing, CONSULTANT has no authority to bind or incur any obligation on behalf of CITY. CONSULTANT has no authority or responsibility to exercise any rights or power vested in the CITY. It is understood by both CONSULTANT and CITY that this AGREEMENT shall not under any circumstances be construed or considered to create an employer-employee relationship or a joint venture. CONSULTANT, its agents, officers and employees are and, at all times during the terms of this AGREEMENT, shall represent and conduct themselves as independent contractors and not as employees of CITY.

CONSULTANT shall determine and control the method, details and means of performing the work and services to be provided by CONSULTANT under this AGREEMENT. CONSULTANT shall be responsible to CITY only for the requirements and results specified in this AGREEMENT, and, except as expressly provided in this AGREEMENT, shall not be subjected to CITY's control with respect to the physical action or activities of the CONSULTANT in fulfillment of this AGREEMENT. CONSULTANT is permitted to provide services to others during the same period service is provided to CITY under this #5..
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6 AGREEMENT. If necessary, CONSULTANT has the responsibility for employing other persons or firms to assist CONSULTANT in fulfilling the terms and obligations under this AGREEMENT.

If in the performance of this AGREEMENT any third persons are employed by CONSULTANT, such persons shall be entirely and exclusively under the direction, supervision, and control of CONSULTANT. All terms of employment including hours, wages, working conditions, discipline, hiring, and discharging or any other term of employment or requirement of law shall be determined by the CONSULTANT.

It is understood and agreed that as an independent contractor and not an employee of CITY neither the CONSULTANT or CONSULTANT's assigned personnel shall have any entitlement as a CITY employee, right to act on behalf of the CITY in any capacity whatsoever as an agent, or to bind the CITY to any obligation whatsoever. It is further understood and agreed that CONSULTANT must issue W-2 forms or other forms as required by law for income and employment tax purposes for all of CONSULTANT's personnel. As an independent CONSULTANT, CONSULTANT hereby indemnifies and holds CITY harmless from any and all claims that may be made against CITY based upon any contention by any third party that an employer-employee relationship exists by reason of this AGREEMENT.

11. ASSIGNMENT.

Neither this AGREEMENT nor any portion thereof shall be subcontracted or assigned, without the express prior written consent of the CITY in each and every instance.

12. PATENT/COPYRIGHT MATERIALS.

Unless otherwise expressly provided in the AGREEMENT, CONSULTANT shall be solely responsible for obtaining the right to use any patented or copyrighted materials in the performance of this #5..
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7 AGREEMENT. CONSULTANT shall furnish a warranty of such right to use to CITY at the request of CITY.

13. NOTICES.

Notice required by this AGREEMENT shall be given in writing and shall be deemed given and effective upon delivery provided that such are delivered in accordance with the provisions of this Section. Notices shall be delivered either by: (a) personal delivery; (b) overnight courier service which obtains confirmation of delivery; or (c) certified mail, return receipt requested, if delivery is confirmed by a return receipt; or (d) by electronic transmission subject to reasonable proof that the notice was both transmitted and received. Each such notice shall be sent to the parties at the address respectively set forth below or to such other address as a party may designate by written notice given in accordance with the provisions of this Section:

FOR CONSULTANT: Name: Westwood Professional Services, Inc.

Address: 1165 Scenic Drive, Suite A
Modesto, CA 95350
Attention: Chad Kennedy
Email: [email protected]
WITH A COPY TO Name: Westwood Professional Services, Inc.

Address: 2805 Dallas Parkway Suite 150
Plano, TX 75093
Attention: Legal
email: [email protected]
FOR CITY: Name: City of Modesto
Address: P.O. Box 642
Modesto, CA 95353
Attention: Jessica Hill
Phone: (209) 577-5321
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8 14. INSURANCE REQUIREMENTS.

The Consultant shall provide at its own expense and maintain at all times the following insurance with insurance companies authorized to do business in the State of California and shall provide evidence of such insurance to the City as may be required by the Risk Manager of the City. The policies or certificates thereof shall provide that, thirty (30) days prior to cancellation or material change in the policy and ten (10) days prior if cancellation due to nonpayment of premium, notices of same shall be given to the Risk Manager of the City via PINS Advantage Insurance Program, for all of the following stated insurance policies.

In the event the certificates of insurance required hereunder do not provide for notice of cancellation to the certificate holder and/or additional insureds, the Consultant shall provide, and shall require its subcontractors to provide, as an express condition precedent to payment hereunder, an endorsement from their insurers providing that the additional insureds identified herein shall be provided 30 days’ notice of the cancellation on the policies of insurance required hereunder (10 days’ notice if the policies are cancelled for non-payment of premium). In addition, the named insured on all such policies shall provide to the additional insureds identified herein any notices of cancellation of said insurance policies within 5 business days of receipt of such notice. The Consultant shall, as a further express condition precedent to payment for work performed, affirm under penalty of perjury that the required insurance on the project remains in place and said insurance has not been cancelled. (a) General Liability insurance with a limit of liability per occurrence of $1,000,000 for bodily injury and property damage. If Commercial General Liability Insurance or other form with a general aggregate limit is used, either the general aggregate limit shall apply separately to this project/location or the general aggregate limit shall be twice the required occurrence limit. This insurance shall indicate on the certificate of insurance the following coverages and indicate the policy #5..
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9 aggregate limit applying to: premises and operations; broad form contractual; vicarious liability for independent consultants and subcontractors; products and completed operations as applicable. (b) Automobile Liability insurance with limit of liability per occurrence of $1,000,000 for bodily injury and property damage. This insurance shall cover any automobile for bodily injury and property damage.
(c) Worker's Compensation - in compliance with the statutes of the State of California, plus employer's liability with a limit of liability of $1,000,000. (d) Professional Liability insurance with a limit of $1,000,000 per claim and policy aggregate. If coverage is on a claim made basis it shall be maintained for at least three (3) years following completion of the work.

If at any time any of said policies shall be unsatisfactory to the City, as to form or substance, or if a company issuing such policy shall be unsatisfactory to the City, the Consultant shall promptly obtain a new policy, submit the same to the Risk Manager for approval and submit a certificate thereof as hereinabove provided. Upon failure of the Consultant to furnish, deliver or maintain such insurance and certificates as above provided, this Agreement, at the election of the City, may be forthwith declared suspended or terminated. Failure of the Consultant to obtain and/or maintain any required insurance shall not relieve the Consultant from any liability under this Agreement, nor shall the insurance requirements be construed to conflict with or otherwise limit the obligations of the Consultant concerning indemnification. The City, its agents, officers, employees, and volunteers shall be named as an additional insured on all insurance policies required herein, except Workers' Compensation and Professional Liability. The Workers' Compensation insurer shall agree to waive all rights of subrogation against the City, its agents, officers, employees, and volunteers for losses arising from work performed by Consultant for the City. The Consultant's insurance policy(ies) shall include a provision that the #5..
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10 coverage is primary as respects the City; shall include no special limitations to coverage provided to additional insured; and, shall be placed with insurer(s) with acceptable Best's rating of A: VII or with approval of the Risk Manager. The Consultant must deliver certificates evidencing existence of the insurance listed above to the City prior to the time the contract is signed.

CONSULTANT shall provide CITY with separate endorsements evidencing proof of the CITY’s additional insured status as to both the general liability and automobile liability insurance policies. In addition, CONSULTANT shall provide CITY with a Workers Compensation subrogation waiver by way of a separate endorsement. All endorsements referenced above must include the applicable policy number.

For any claims related to this project, the CONSULTANT’S insurance coverage shall be primary insurance as respects the Entity, its officers, officials, employees, and volunteers except for worker’s compensation and professional liability coverages. Any insurance or self-insurance maintained by the Entity, its officers, officials, employees, or volunteers shall be excess of the CONSULTANT’S insurance and shall not contribute with it.

15. TERMINATION OF AGREEMENT.

Termination by CITY for Default of CONSULTANT
Should the CONSULTANT default in the performance of this AGREEMENT or materially breach any of its provisions, at its option, CITY may terminate this AGREEMENT by giving written notification to CONSULTANT. The termination date shall be the effective on the date it is mailed by CITY or sent via electronic mail, as described in Section 13.. For the purposes of this section, material breach of this AGREEMENT shall include, but not limited to, any of the following: failure to perform required services or duties, willful destruction of City's property by CONSULTANT, dishonesty or theft. #5..
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11 Termination by CITY for Convenience
The City may also terminate the CONSULTANT's performance under the AGREEMENT, either in whole or in part, at its own discretion, or when conditions encountered during the services make it impossible or impracticable to proceed, or when the City is prevented from proceeding with the AGREEMENT by act of God, by law, or by official action of a public authority, or upon a determination by the City that such termination is in the best interest and convenience of the City, or whenever the City is prohibited from completing the services for any reason. The City shall provide no less that ten (10) calendar days written notice of its intent to terminate the AGREEMENT for convenience and shall endeavor to provide the CONSULTANT with consultation with the City prior to termination.

Post-Termination Procedure
Upon receipt of a written notice of termination pursuant to either of the foregoing paragraphs, the CONSULTANT shall:

A. Cease its work as directed in the notice of termination as of the termination date and see to it that its employees, subconsultants and agents are notified of such termination and act as specified in the notice of termination;
B. Terminate all orders and subconsultants except as necessary to complete any portion of the work that is not terminated;
C. If directed in writing by the CITY to do so, assign all right, title and interest in subcontracts and materials in progress to CITY, in which case the CITY will have the right at its discretion to settle, or pay any or all claims arising out of the termination of such subconsultants, but in no event shall recovery by any CONSULTANT or subconsultant include lost profits for portions of the work not completed or undertaken, including materials not delivered; #5..
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12 D. Upon final payment to CONSULTANT, make available to the CITY all data, drawings, specifications, reports, estimates, summaries and such other information and material as may have been accumulated by the CONSULTANT in performing the work whether completed or in process;
E. Settle outstanding liabilities and claims, subject to the approval of CITY; F. Complete performance of such part of the work as has not been terminated; G. Take such other actions as may be necessary, or as may be directed by the CITY for the protection and preservation of the work and/or property related to the work; H. If CITY so requests, and at CITY's cost, CONSULTANT shall provide sufficient oral or written status reports to make CITY reasonably aware of the status of CONSULTANT's work on the project.

I. The CONSULTANT understands and agrees that CITY may, in CITY's sole discretion, refuse to pay CONSULTANT for that portion of CONSULTANT's services which were performed by CONSULTANT on the project prior to the termination date and which remain unacceptable and/or not useful to CITY as of the termination date.

CITY will pay CONSULTANT an amount based on the percentage of satisfactory work completed in accordance with the notice or termination. The final payment to the CONSULTANT after termination for convenience shall be limited to amounts due and owing under the AGREEMENT at time of termination, including the following:

J. The cost of settling and paying valid claims arising out of the termination of the work such as subconsultant AGREEMENTs or contracts for materials;
K. The AGREEMENT price allocable to the portion of the work properly performed, or goods supplied to the work site by the CONSULTANT as of the date of termination, as determined in #5..
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13 accordance with the notice of termination, reduced by any sums previously paid to the CONSULTANT.

Authorization to Terminate Agreement
Termination of the AGREEMENT may be invoked by the City Manager, or his/her designee, subject to the right of the CONSULTANT to appeal the City Manager, or his/her designee's, decision to the City Council. The CONSULTANT shall appeal by notifying the City Clerk in writing within ten (10) calendar days of receipt of written notification from City of termination of the AGREEMENT. In the event that termination of this AGREEMENT is upheld by the City Council, any cessation of payment of delay claims, extended claims, Eichleay claims, or any other claims for delay shall be retroactive to the date of termination selected by the City Manager, or his/her designee.

16. INDEMNITY.

The Consultant shall hold the City, its officers, agents and employees, harmless from and save, defend (except for professional liability claims) and indemnify them against any and all claims, losses, liabilities, judgments or damages arising from third parties, including but not limited to injury to person or property or wrongful death, including reasonable costs and expenses of defense of any judicial or administrative action, to the proportional extent caused by any negligent or intentional act or omission of Consultant, or its agents, officers, employees, or volunteers relating to or during the performance of its obligations under this Agreement except for professional liability claims, for which Consultant shall have no reimbursement obligation for defense of professional liability claims. In no event shall the cost to defend charged to the Consultant exceed the design professional’s proportionate percentage of fault. Notwithstanding the previous sentence, in the event one or more defendants is #5..
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14 unable to pay its share of defense costs due to bankruptcy or dissolution of the business, the Consultant shall meet and confer with other parties regarding unpaid defense costs.

Consultant's obligation to defend (except for professional liability claims), indemnify, and hold the City, its agents, officers, and employees harmless under the provisions of this paragraph is not limited to or restricted by any requirement in this Agreement for Consultant to procure and maintain a policy of insurance.

In the event that Consultant or any employee, agent, or subcontractor of Consultant providing services under this Agreement is determined by a court of competent jurisdiction or the California Public Employees Retirement System (PERS) to be eligible for enrollment in PERS as an employee of City, Consultant shall indemnify, defend, and hold harmless City for the payment of any employee and/or employer contributions for PERS benefits on behalf of Consultant or its employees, agents, or subcontractors, as well as for the payment of any penalties and interest on such contributions, which would otherwise be the responsibility of City.

17. DISPUTE RESOLUTION.

Venue for all claims, controversies, or disputes arising out of, or relating to the formation of this AGREEMENT, or the breach, termination execution, enforcement, interpretation, or validity of this AGREEMENT, including the determination of the scope or applicability of this AGREEMENT provision shall be in the Superior Court of Stanislaus County or the United States District Court for the Eastern District of California.

18. ATTORNEY'S FEES.

If a party to this AGREEMENT brings any action, including an action for declaratory relief, to enforce or interpret the provision of this AGREEMENT, the prevailing party shall be entitled to reasonable attorneys’ fees in addition to any other relief to which that party may be entitled. The #5..
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15 court may set such fees in the same action or in a separate action brought for that purpose. A “prevailing party” need not assert affirmative claims to be considered a prevailing party, and a party that successfully defends against a claim in relative terms to the amount of the claim asserted shall be considered a prevailing party for the purposes of this section. In claims for money damages, the total amount of recoverable attorney’s fees, expenses, and costs shall not exceed the net monetary award or judgment of the prevailing party, if the prevailing party was the party seeking a monetary award or judgement.

19. ENTIRE AGREEMENT.

This AGREEMENT and its exhibits contain the entire understanding between CONSULTANT and CITY. All previous proposals, offers and communications related to this AGREEMENT, whether oral or written, are hereby superseded except to the extent that they have been incorporated into this AGREEMENT. No future waiver of or exception to any of the terms, conditions, and provisions of this AGREEMENT shall be considered valid unless specifically agreed to in writing by all the parties.

20. PARTIAL INVALIDITY.

If any provision in this AGREEMENT is held by a court of competent jurisdiction to be invalid, void, or unenforceable, the remaining provisions shall nevertheless continue in full force without being impaired or invalidated in any way.

21. WAIVER.

The waiver by any party to this AGREEMENT of a breach of any provision hereof shall be in writing and shall not operate or be construed as a waiver of any other or subsequent breach hereof unless specifically stated in writing.
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16 22. AUDIT.

The CITY's duly authorized representative shall have access at all reasonable times to all reports, contract records, contract documents, contract files, and personnel necessary to audit and verify CONSULTANT's charges to CITY under this AGREEMENT.

CONSULTANT agrees to retain reports, records, documents, and files related to charges under this AGREEMENT for a period of four (4) years following the date of final payment for CONSULTANT services. CITY's representative shall have the right to reproduce any of the aforesaid documents.

23. GOVERNING LAW.

This AGREEMENT shall be governed according to the laws of the State of California.

24. HEADINGS NOT CONTROLLING.

Headings used in the AGREEMENT are for reference purposes only and shall not be considered in construing this AGREEMENT.

25. COMPLIANCE WITH LAWS.

CONSULTANT shall insure compliance with all safety and hourly requirements for employees, in accordance with federal, state, and county safety and health regulations and laws. CONSULTANT shall fully comply with all applicable federal, state, and local laws, ordinances, regulations and permits.

26. CITY BUSINESS LICENSE.

CONSULTANT will have a City of Modesto business license. #5..
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17 IN WITNESS WHEREOF, the City of Modesto, a municipal corporation, has authorized the execution of this AGREEMENT by its City Manager and attestation by its City Clerk under authority of Resolution No. 20___ - ______, adopted by the Council of the City of Modesto on the ______day of ______, ______, and Westwood Professional Services, Inc has caused this AGREEMENT to be duly executed as of the Effective Date.
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Scope of Services
Included in this section is the technical scope of work to complete the project as we interpret it. It is organized a bit differently than the scope in the RFP document to help streamline the process and include key scope assignments that may have been overlooked.

Task 1: Meetings and Project Management

1.1 Kick-off Organization & Scoping Meeting
A well-run organizational meeting at the beginning of the project will clear up any unexpected issues before they arise. A meeting will be held with staff, during which our proprietary client communication program is started and the following typical items are discussed:
y Introduce staff and project partners to the design consulting team. y Review objectives of the project, scope of services, deliverable expectations, project schedule, and milestones. y Confirm project parameters and limits of work. (Conduct a site review and photo document site conditions.) y Collect available data and published material (GIS data, aerial photography, right-of-way maps, as-built plans, and record maps).
y Establish meeting and presentation schedules and communication channels with all parties involved. y Review and list all applicable design/planning standards, opportunities, and/or challenges anticipated. y Coordinate with agency departments, other agencies, and stakeholders. y Review project budget and billing requirements.
y Complete custom client communications program.

1.2 Progress Meetings
After each submittal and subsequent staff review period, a progress meeting with the design team will be held. An agenda will be prepared prior to, and minutes will be provided after, each meeting. It is anticipated that there will be a progress meeting each month during the design period and ideally held at the following stages:
y Following the Basis of Design Report submittal
y Following the 30%, 60%, 90%, and 100% PS&E submittals

1.3 Management
Management of all project design aspects will be covered by the team. The following will be provided:
y A comprehensive design schedule
y Monthly progress update meetings and minutes
y Correspondence between City, Modesto Irrigation District (MID), and design team y Management of the consultant team quality control measures

1.4 Site Visits
y Perform site reconnaissance visits to evaluate site conditions and identify potential conflicts and design challenges. y Meet with City, MID, and design team on-site to review and discuss potential conflicts and design challenges.

Deliverables
y Meeting agendas and Minutes in PDF format
y Customized Client Communication Program in PDF format y Preliminary project schedule with critical path milestones in Microsoft Project and PDF format y Monthly progress reports and invoices
Task 2: Site Analysis/Data Collection & Review
Research objectives will include a detailed review of project history and existing park site information including topographic surveys and soil studies. A site visit will be conducted and site photographs will be taken.

2.1 Contextual Analysis
Analyze existing elements within the proposed site to guide design. Items including but not limited to prevailing winds, soil type, local demographics, utilities, and so forth will be reviewed.

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2.2 Topographic Survey Base Mapping
Surveying services in support of this project will include topographic surveying of the existing site. The topographic survey data will be collected using the City’s existing horizontal and vertical survey control and benchmarks. All information will be collected with the input and collaboration of both internal and external subconsultant specialty disciplines to guarantee a focused, but well-rounded product that rises to meet the needs of each of the project’s objectives. y Perform cross-section survey of linear corridor at 50-foot intervals. y Perform topographic survey of all hardscape and softscape, including grade breaks, high points, and low points. In flat areas, measure spot elevations in a grid pattern at 50-foot intervals. y Locate surface-visible utility features and improvements, including but not limited to signs, fences, walls, buildings, striping, driveways, walkways, drainages, structures, lights, poles, bollards, general limits of vegetated or landscaped areas, USA markings, vaults, valves, meters, boxes, pedestals, cleanouts, manholes, drain inlets, catch basins, culverts, outfalls, and standpipes.
y All trees 6” in diameter or larger will be located.
y At manholes and accessible structures, measure invert elevation of all gravity storm drains and sewer pipes. Annotate topographic survey drawing with invert elevation, approximate diameter, and orientation of each pipe visible at the time of the survey. Where access is not practical, Westwood shall indicate by notation on the mapping deliverable. y Create existing ground Civil 3D TIN surface model.
y Prepare topographic map at a 1” = 20’ scale.

2.3 Resolved Boundary
Having a resolved boundary will provide definitive information that can be used to make precise determinations about the subject property, including matters including but not limited to gross/net parcel area, setbacks, encroachments, etc.

It is a critical part of the planning and design process because it brings clarity to the often uncertain nature of property boundaries, easements, and road rights-of-way, which rarely lie exactly where they are presumed to. A resolved boundary is also essential if improvements are being built close to property lines or near setback minimums. y Resolve the location of property boundaries, road rights-of-way, and easements as defined by an analysis of available record maps, title report(s), supporting documents, and physical evidence. y Reset missing or damaged property corner monuments as required.

2.4 Utility Investigation & Coordination
A comprehensive utility investigation will be completed to determine what utilities are available, their locations, and utility depth within the project limits of work. Available as-built and original design drawings will be reviewed, utility request letters will be sent to all applicable utility companies, and site investigation will be used to make determinations. We will work with utilities as necessary to prepare the site for construction efforts. Where feasible, utilities infrastructure will be installed and or relocated prior to beginning construction.

Deliverables
y Topographic survey base map drawing in AutoCAD Civil 3D 2023 format y Resolved boundary linework drawing in AutoCAD Civil 3D 2023 format y Site plan of topographic survey in PDF format
Task 3: Design Development

3.1 Preliminary Site Plan Development
Following site analysis efforts, the design team will prepare two concept plans illustrating alternative designs for the park. The preliminary site plan will be developed to reflect the guidelines for the dual-use basin park as outlined in the Tivoli Specific Plan. After the designs have been presented to the City for review and comment, a final rendered master plan will be prepared for inclusion in the Basis of Design Report. In addition, a preliminary layout of new sewer mains and connections will be prepared based on the location of proposed street improvements and other utilities. This is a crucial step to limit revisions later in the process and to avoid inefficient uses of time and resources. This site plan will be drawn with actual topographic data, to scale, and will be a rendered drawing depicting all proposed park features and amenities.

3.2 Basis of Design Report
In conjunction with the preliminary site plan, the primary purpose of the Basis of Design report is to convey the design intent early in the design process. This report will help identify, clarify, and simplify any major design decisions early. It will Project Understanding and Approach
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be developed with a mix of communication styles including visual and written, and will include tables and charts. Typical information in the report might include:
y Contextual information for the project site
y Conceptual plans to illustrate design concepts and alternatives y Enlargements of the special areas within the park
y Discussions of maintenance requirements and potential life cycle costs y Renderings and sections to convey design intent in a three-dimensional manner y Sample imagery of site furnishings and features, plant types, and irrigation methods y Planning level construction cost estimates

3.3 Design Development Drawings (30% PS&E)
The Design Development Drawing package includes drawings to convey general engineering and design concepts. This service will include the following preliminary plan sheets at a minimum:
y Cover sheet and project information
y Site plan
y General and project specific notes
y Existing conditions plan
y Grading, drainage, and utilities plan
y Plan and profile sheets
y Site finishes and furnishings plans
y Irrigation plans
y Planting plan
y Electrical plans
y Major construction details
y Technical specifications table of contents
Deliverables
y Rendered site plan in PDF format
y Basis of Design Report
y 30% drawings in PDF format
y 30% estimates and quantities in PDF format
y Technical specifications TOC in PDF format
y Updated project schedule with critical path milestones in Microsoft Project and PDF format Task 4: Construction Documentation

4.1 Construction Documents (PS&E)
Following the approval of a final site plan, the team will prepare final site improvement plans for permitting.

Improvement plans include routine information normally required by governing agencies. The scope of work will include three packages: 60% construction documents with draft specifications, 90% construction documents with updated specifications, and 100% documents including final specifications. This service will include the following tasks:
y Improvement Plans - Plans may include the following sheets but are subject to change as the parameters, needs, and existing conditions of the project formalize:
y Cover sheet
y General and project specific notes and conditions
y Site plan
y Existing conditions and demolition plan
y Underground utilities plan
y Plan and profile sheets
y Grading and drainage plans
y Erosion control plans
y Horizontal control plan
y Site finishes and furnishings plans
y Enlargement plans (playground, etc.)
y Irrigation plans and water use calculations
y Planting plan
y Electrical plans
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y Construction details
y Shade Structure sections and plans
y As-built drawings as appropriate for reference
y Construction quantities and estimates
y Draft & final technical specifications (City will provide boilerplate and Front-End specifications) y Draft & final stormwater pollution prevention plan (SWPPP & NPDES permit coordination)

4.2 Bid Package
Following the approval of the 100% PS&E drawings, the team will prepare a final bid package. The bid package will include:
y Front end documents (provided by the City)
y Stamped and signed cover sheet
y Bid forms
y Bid item descriptions
y Final stamped and signed PS&E
y Final stamped and signed technical specifications booklet y Final cut sheets for important features and materials y Geotechnical Report
Deliverables
y Final Geotechnical Report in PDF format
y 60%, 90%, & 100% drawings in PDF format
y 60%, 90%, & 100% estimates and quantities in PDF format y Technical specifications TOC in PDF format
y 60% & 90% updated project schedule with critical path milestones in Microsoft Project and PDF format y SWPPP document in PDF format
y Final bid package in PDF and AutoCAD
Task 5: Specialized Technical Services
Westwood will provide specialized technical services to ensure that the basin meets City, State, and Federal requirements. These services include preparing comprehensive basin calculations and geotechnical investigations to evaluate subsurface soil conditions.

5.1 Basin Calculations
The Westwood team will conduct comprehensive basin calculations to evaluate stormwater management requirements for the project area. These calculations will assist with the following:
y Development of a model to estimate stormwater generation based on local rainfall patterns and land use characteristics. y Designing systems for stormwater detention and retention and assessing percolation rates for infiltration systems. y Creating a hydrological model to simulate water flow and evaluate various stormwater management strategies.

5.2 Geotechnical Investigation
The geotechnical investigation will occur early in the design process to ensure that the team has the information needed to make recommendations early and aid in preparing accurate cost estimates throughout the design process. y To characterize the subsurface conditions and obtain soil samples for laboratory testing, six (6) soil borings throughout the proposed park of varying depths will be drilled.
y An Engineer/Geologist will direct the sampling and log the borings. The samples will be delivered to the laboratory for evaluation and testing. Field penetration tests will be used to evaluate relative density, strength, and compression characteristics of native soils. The borings will be backfilled according to the City/County permit requirements. y Following the completion of subsurface exploration, percolation testing will be conducted in support of the park basin.

Borehole percolation tests will be performed to measure infiltration/percolation rates boring logs. It is anticipated that these tests will occur in five (5) locations.
y Laboratory tests will be performed on representative soil samples obtained from the exploratory borings, which may include unit weight, moisture content, sieve analysis, Atterberg Limits, direct shear, soluble sulfate and soluble chloride contents, pH and minimum resistivity, R-Value, and landscape suitability. y Engineering analysis will be prepared and a Geotechnical Report containing the following (but not limited to):
y Project description
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y Summary of subsurface exploration and subsurface conditions y Infiltration rates
y Laboratory test results
y CBC seismic design parameters for structures (non-site specific) y Summary of groundwater conditions encountered and potential impact on design and construction y Foundation recommendations for structures
y Recommendations for over-excavation of unsuitable soils y Recommendations for grading and construction
y Recommendations to aid in the design of slabs-on-grade and exterior concrete hardscape y Pavement section recommendations
y Site Plan with current boring and infiltration/percolation test locations y Boring logs with laboratory test results
Deliverables
y Basin calculation report summarizing findings and methodologies. y Stormwater generation model with peak flow rates and volume calculations. y Design calculations and specifications for detention and retention systems, including percolation assessment results. y Hydrological model report detailing the simulation results and validation against historical data. y Draft and final geotechnical investigation report.
y Operations and maintenance manual, including guidelines for routine maintenance and emergency procedures.

Task 6: Construction Support Services

6.1 Site Visits & Construction Communications
Westwood will perform construction support services throughout the project’s completion. Services include the following: (We can provide additional support as requested.) y Assist City Staff in bidding process.
y Attend pre-bid meeting.
y Respond to RFIs.
y Prepare Addenda and Transmittals (as needed).
y Attend pre-construction meeting.
y Review and approve Contractor’s schedule, shop drawings, RFIs, and submittals. y Perform site review and prepare reports on construction progress. y Prepare as-built drawings from contractor maintained field drawings. y Construction observation site visits to review site finishes, at irrigation installation phase, for plant review and approval prior to planting, during playground installation, following structural installations but prior to final surface covering, a final punch list walk, etc. Includes the following site visits:
y Site progress visits to review rough grading, site finishes (concrete, surfacing, etc.), irrigation installation, for plant review and approval prior to planting, following playground retrofits, following structural installations but prior to final surface covering
y Final project site review and report
Deliverables
y Meeting agenda and minutes in PDF format
y Bidding RFI and addenda in PDF format
y Construction progress reports in PDF format
y Construction RFI, shop drawing, and submittal responses in PDF format y As-built drawings in PDF format
Task 7: Pump Station Design

7.1 Stormwater Pump Station Design (If Required)
If it is determined during the design phase of the project that a stormwater pump station is required, Westwood can provide this service as an additional scope item. This service includes the following:
y Develop a Preliminary Design Memorandum to outline the design criteria, alternative designs, equipment specifications, operational criteria, and a recommended design approach with preliminary cost estimates. It is anticipated that this Project Understanding and Approach
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memorandum will establish the basis and consensus for the final design with an emphasis on maintenance requirements and life-cycle costs of the pump station.
y Prepare improvement plans for the pump station, force main, and discharge structures at MID Lateral 6. Improvement plans will be prepared for the “inside the fence” pump station facilities.

Deliverables
y Preliminary Design Memorandum in PDF format
y 30%, 60%, 90%, & 100% drawings in PDF format
y 30%, 60%, 90%, & 100% estimates and quantities in PDF format y Technical specifications TOC in PDF format
y Conformed plans and record drawings in PDF Format
Limitations and Understandings:
y All governmental/regulatory fees to be provided by the City. y It is assumed that building permits will be obtained by the contractor. y It is assumed that all structures will be pre-fabricated and considered deferred submittals for building permit purposes. y It is assumed that environmental planning for the project is complete and that there is no coordination needed for such planning efforts.
y Scope does not include any adjustments to City standard details. y Scope does not include any utility work within the roads. y Scope does not include utility relocation.
y Scope does not include right-of-way or easement acquisition services. y Scope does not include QSP services but can be added at client’s request. y Scope does not include construction management or inspection services. y Scope does not include traffic control plans.
y Scope does not include dust control plans.
y Scope does not include joint trench (dry utility) plans. y Scope does not include off-site utility design or coordination. y Survey deliverables will be based on the NAD83 horizontal datum and the NAVD88 vertical datum using Agency benchmarks. A survey control statement will be provided, including the location, elevation, and description of the benchmark utilized, as well as a horizontal survey coordinate table with the point number, northing, easting, and description for at least three (3) points.
y Obstructed or inaccessible areas may not be mapped.
y Scope does not include mapping of small trees, shrubs, or other minor vegetation. Utility locations will be based off of as-built drawings and information from utility departments and companies. y Scope does not include potholing, subsurface utility research, or locating. y Scope does not include boundary surveying as defined in Section 8726(c) of the Professional Land Surveyors’ Act. y Scope does not include preparation of a Record of Survey map or corner record. y Scope does not include monument preservation as defined and required by Section 8771 of the Professional Land Surveyors’ Act.
y Scope does not include public outreach or correspondence with property owners. y Scope does not include soil management report — soil fertility testing and reports (to be performed by landscape contractor after mass grading has been completed).
y Scope does not include structural engineering.
y Scope does not include environmental approvals and permitting as Environmental Impact Report is posted on City’s website for project.
y Scope assumes that plans will be based on City of Modesto Standard Specifications and Drawings and Caltrans Standard Plans and Specifications.
y This scope does not include revisions to the plans due to site plan changes, and/or significant client requested changes at 60% submittal stage or later, including revisions due to bid results or resulting value engineering efforts.

Organization Chart
The organization chart can be found in the Qualifications of Consultant Staff and Subconsultant Staff section.

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Version: 1.0
5/16/2025
Project Fees by Task
PROJECT #: P0061067
PROJECT: Modesto Tivoli Specific Area Storm Basin
CLIENT: City of Modesto
DATE: 3/21/2025
Director
(Kennedy)
Project Manager IV
(Persak)
Graduate Engineer III
(Beyronneau)
Graduate Engineer II
(Hamed)
Engineering Tech IV
(Humphrey)
Surveyor V
(Roberts)
Surveyor IV
(Miller)
Surveyor II
(Munoz)
Survey Tech III
(Bloodgood)
Survey Field III (Crew
Chief) **PREVAILING
WAGE**
(Ahart)
Survey Field II
(Instrument Operator)
**PREVAILING WAGE**
(Pyle)
Landscape Architect V
(Nash)
Landscape Architect III
(Fay, Grafton, Lewis)
Graduate Landscape
Designer III
(Cordova, Honeck,
Samarripa)
Graduate Landscape
Designer II
(Latina, Olea, Wu,
Senior Electrical
Engineer (Engineer V)
(Murtcher)
Project Electrical
Engineer (Engineer II)
(Jeffries)
Staff Electrical
Engineer (Engineer I)
(Pattison)

SWPPP/QSD
(Garcia, Ramirez)
Admin III
(Schmall, Ramos)
Reproduction Costs
Reimbursable costs
Geotechnical Engineer
- Krazan
Pump Station -
Blackwater
Hours
Task Subtotal
Task Total Fee
$315.00 $280.00 $180.00 $170.00 $165.00 $250.00 $235.00 $190.00 $145.00 $240.00 $200.00 $230.00 $190.00 $175.00 $165.00 $275.00 $205.00 $195.00 $325.00 $140.00 108 $23,110 $23,110

1.1 Kick-Off and Scoping Meeting 2 2 2 2 4 12 $2,490 $2,490

1.2 Progress Meetings (4) 4 4 4 12 $2,600 $2,600

1.3 Management 20 48 68 $14,720 $14,720

1.4 Site Visits with City Staff (2 Field Visits) 4 4 4 4 16 $3,300 $3,300 48 $9,570 $9,570

2.1 Topographic Survey 2 2 4 7 9 6 6 2 38 $7,655 $7,655

2.2 Resolved Boundary 1 2 4 3 10 $1,915 $1,915
288 $53,500 $53,500

3.1 Basis of Design Report 2 4 20 4 2 8 36 4 80 $14,870 $14,870

3.2 Basis of Design Estimate 1 2 2 4 12 21 $3,840 $3,840

3.3 30% Improvement Plans 2 4 16 8 32 4 8 48 10 2 2 2 138 $25,110 $25,110

3.4 30% Design Cost Estimate 1 2 2 2 4 1 1 13 $2,460 $2,460

3.5 30% Specifications (TOC Only) 1 2 1 2 1 1 8 $1,580 $1,580

3.6 Value Engineering 4 8 4 4 8 28 $5,640 $5,640
1273 $246,330 $247,980

4.1 60% Improvement Plans 2 4 56 48 88 8 36 88 48 2 8 8 2 500 398 $71,040 $71,090

4.2 60% Design Cost Estimate 1 2 2 2 8 2 2 19 $3,560 $3,560

4.3 60% Specifications 2 32 4 36 2 2 78 $14,180 $14,180

4.4 Constructability Review, Constructability Analysis & Report 4 20 4 8 24 60 $11,360 $11,360

4.5 90% Improvement Plans 2 2 44 24 44 6 24 64 32 2 12 4 2 500 262 $47,440 $47,490

4.6 90% Design Cost Estimate 1 2 2 2 8 2 2 19 $3,560 $3,560

4.7 90% Specifications 1 16 2 24 2 2 47 $8,540 $8,540

4.8 100% Improvement Plans 1 24 24 36 4 20 40 24 2 16 8 32 2 500 233 $46,870 $46,920

4.8 100% Design Cost Estimate 1 4 1 2 8 1 1 18 $3,350 $3,350

4.10 100% Specifications 1 8 2 16 1 1 29 $5,300 $5,300

4.11 Bid Documents 2 12 4 2 4 12 8 2 46 $8,390 $8,390

4.12 Site Visits with City Staff (2 Field Visits) 4 4 4 4 16 $3,300 $3,300

4.13 Building Permit 8 16 8 16 $10,000 48 $19,440 $20,940 100 $69,640 $77,314

5.1 Basin Calculations
a Stormwater Generation 2 12 20 4 38 $6,680 $6,680
b Detention/Retention/Percolation 4 8 12 24 $4,600 $4,600 c Develop Hydrological Modeling 2 20 8 30 $5,520 $5,520

5.2 Geotechnical Investigations 2 2 4 $51,160 8 $52,840 $60,514

5.3 Operations and Maintenance Manual 0 $0 $0
187 $35,175 $35,200

6.1 Assist City Staff in Bidding Process 2 4 2 2 4 14 $2,570 $2,570

6.2 Attend Pre-Bid Meeting 2 2 2 2 2 10 $2,280 $2,280

6.3 Review and Process all RFI's and Bid Addenda 2 12 2 2 12 30 $5,660 $5,660

6.4 Attend Pre-Construction Meeting 2 2 2 2 8 $1,650 $1,650

6.4 Reivew & Process all RFI's, Shop Drawings, and Submittals 4 16 4 2 4 16 1 2 2 51 $9,775 $9,775

6.6 Provide Site Review & Prepare Reports on Construction Progress 8 2 2 4 8 4 28 $4,930 $4,930

6.7 Make Final Review & Report on Completed Project 1 8 4 1 8 22 $3,970 $3,970

6.8 Prepare As-Built Drawings from Contractor's Field Drawings 1 2 8 1 8 4 250 24 $4,340 $4,365 14 100 395 169 214 3 6 11 12 6 6 38 227 520 130 9 52 36 32 24 443 $4,410 $28,000 $71,100 $28,730 $35,310 $750 $1,410 $2,090 $1,740 $1,440 $1,200 $8,740 $43,130 $91,000 $21,450 $2,475 $10,660 $7,020 $10,400 $3,360 $1,750 $10,000 $51,160 $0 $437,325 $446,674 $175 $1,500 $7,674 $0
$4,410 $28,000 $71,100 $28,730 $35,310 $750 $1,410 $2,090 $1,740 $1,440 $1,200 $8,740 $43,130 $91,000 $21,450 $2,475 $10,660 $7,020 $10,400 $3,360 $1,925 $11,500 $58,834 $0 $446,674 Base Scope 3.16% 117.38% 29.35% #DIV/0! #DIV/0! 5.42%
6 $236,380 $271,642

7.1 Pump Station Design 2 2 2 $235,080 6 $236,380 $271,642 0 2 2 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 14
$0 $560 $360 $0 $0 $0 $0 $0 $0 $0 $0 $0 $380 $0 $0 $0 $0 $0 $0 $0 $0 $0 $0 $235,080 $236,380 $271,642 $0 $0 $35,262
$0 $560 $360 $0 $0 $0 $0 $0 $0 $0 $0 $0 $380 $0 $0 $0 $0 $0 $0 $0 $0 $0 $0 $270,342 $718,316

GRAND TOTAL WITH INCLUDED TASKS

TOTAL COST INCLUDED TASKS
CONSULTANT MARK-UP 10% - 15%

TOTAL HOURS
GRAND TOTAL with PHASE 7
TASK 7 - PUMP STATION DESIGN (IF REQUIRED)

TOTAL HOURS

TOTAL COST OPTIONAL TASKS
CONSULTANT MARK-UP 15%
TASK 4 - DESIGN SERVICES
TASK 3 - DESIGN DEVELOPMENT
TASK 6 - CONSTRUCTION SUPPORT
TASK 5 - SPECIALIZED TECHNICAL SERVICES
Tasks
Westwood Professional Services

TASK/DESCRIPTION
TASK 1 - PROJECT MANAGEMENT
Subcons.

TASK 2 - SURVEY AND TOPOGRAPHIC MAPPING
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1 INF-RFP-00003 - REQUEST FOR PROPOSALS:

TIVOLI SPECIFIC AREA STORM BASIN DESIGN
PROPOSAL RELEASE: FRIDAY, FEBRUARY 28, 2025
PROPOSAL DUE: BEFORE 5:00 PM ON MARCH 21, 2025
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2 PROJECT OVERVIEW
NOTICE IS HEREBY GIVEN that the City of Modesto, County of Stanislaus, State of California (“City”), will receive proposals (each, a "Proposal") electronically through its OpenGov Procurement portal from qualified Proposers (each, a “Proposer”) for the furnishing of TIVOLI SPECIFIC AREA STORM BASIN DESIGN services (the “Services”) for the City of Modesto, Community and Economic Development Department, Land Development Engineering Division. Proposals are due before 5:00 pm on Friday, March 21, 2025. Proposals received in any other format will not be accepted.

The project site is a 454-acre area located in the City of Modesto, within Stanislaus County, in the central San Joaquin Valley. Stanislaus County is bounded by San Joaquin County to the north, Calaveras, Tuolumne, and Mariposa Counties to the east, Merced County to the south, and Santa Clara and Alameda Counties to the west.

The Tivoli Specific Plan (TSP) includes a mixture of various types of residential development and associated densities, regional, general and neighborhood oriented commercial sites, professional office space, neighborhood and linear park spaces, and a proposed school site. The primary goals for the TSP are to foster attractive and distinctive development, to ensure public facilities and services are adequately provided and planned including funding mechanisms, to provide a range of housing types in compliance with the Housing Element, to ensure a circulation system that is consistent with traffic policies, and to provide for new regional commercial development opportunities on the east side of Modesto. The TSP is presently designated as predominantly Residential in the General Plan. that allows for predominantly single-family residential uses, but also with multi-family and senior housing, schools, and parks. Existing small-scale commercial and office uses are deemed compatible.
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3 Figure 1: Tivoli Specific Plan Area
The TSP proposes an approximately 19 acre dual-use basin and neighborhood park (as seen in the exhibit above) that will serve as a centralized focal point, as a recreational open space asset. South of the park is an area designated for an elementary school site. The TSP may include small neighborhood common open space in some residential districts. The paseos located along primary collector streets will offer appealing pedestrian linkages to the centrally located basin/park. The City of Modesto is beginning to receive many new developer inquires and planning projects for the Tivoli area including several tentative map applications, the design and eventual construction of the dual-use catch basin will be crucial as the development process progresses in the area.
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4 TRANSMITTAL LETTER
Proposer shall provide a letter containing an expression of the proposer's interest in the work, a summary statement regarding the qualifications of the proposer to do the work, and a brief summary of any information about the project team or the proposer that may be useful or informative to the City.

The proposal should be signed by an officer authorized to bind the proposing firm. Indicate the name of the organization submitting the proposal, its mailing address, telephone number, and identify the primary point of contact.

Acknowledge that the proposer agrees to be bound by the representations in their proposal during the term of the agreement in addition to a statement that the proposal is valid for a period of one hundred twenty (120) days.

SCOPE OF WORK

PURPOSE OF RFQ
The City of Modesto (the City) is seeking to retain the Professional Engineering Services of one qualified licensed engineering firm to perform design of Tivoli Specific Area Detention Basin, which includes, but not limited to, the preparation and calculations to design the dual-use basin, park features and landscaping design, technical specifications, and full bid package construction documents, if needed.

SCOPE OF WORK OR PROJECT DETAILS
The scope of the project is to provide Construction Documents such as plans, specifications, and estimates for the construction of a Tivoli Specific Area Detention Basin as indicated in the project area map. The Project scope includes, but not limited to, perform hydraulic calculations for storm water generation, detention/retention, and percolation, preparing detailed engineering drawings and specifications for the dual-use basin, compliance with all Local, State and Federal regulations of storm water, landscape architecture designs including landscaping and irrigation etc. The selected consultant will design and support construction of the basin.
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5 The following tasks are identified for the scope of services and may include but shall not necessarily limited to:

Project Management
This task includes project management responsibilities including progress monitoring, scheduling and meetings:
• Monitor and direct work activities in accordance with contracted scope of work, schedule and budget. Maintain open communication with the City regarding progress monitoring, inform the City within a reasonable time and prior to work be conducted if contracted scope of work, schedule and budget need to be changed.
• Provide a milestone schedule prior to start of Preliminary Engineering for City Approval. Schedule to include a list of tasks, estimated completion dates, and responsible party. • Maintain the project schedule throughout the duration of the project Surveys and Topographic Mapping
The Consultant shall perform a topographic survey of the project limits which shall include:
• Location of items necessary to complete the design and construction of the project, including but not limited to, roadway improvement features, pavement, concrete, slopes, grade breaks, drainage features, signs, existing striping, structures, driveway features, house walks and trees; • Location of visible above ground utility features such as manholes, valves, vaults and utility poles; • Measurements to accessible sewer and storm drain manholes and inlets/catch basins to include approximate size, depth and direction;
• Sufficient temporary benchmarks (TBMs) to provide adequate control during the construction phase but placed to not be demolished as part of the construction process; • Identification of existing survey monuments, file corner records, benchmarks to be preserved during construction;
• Datum to be derived from the City of Modesto datum and no GPS surveying is allowed; • Coordination with City of Modesto Survey Division and Transportation Engineering Division during design;
• Additional trips for supplemental topography and/or potholing support if needed.

Design Services
Prepare Basis of Design and estimates, and 30%, 60%, 90%, and 100% plans and specifications. Basis of Design and estimates shall have an emphasis on maintenance requirements and potential life cycle costs. Assist with permitting and design-related approvals. Provide constructability review. Anticipated design disciplines #5..
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6 include Civil, Drainage and Water Quality, Roadway, Hydrogeology, Landscape Architecture, Electrical and Geotechnical Analysis.
• Consultant shall schedule field visits with City staff as needed to analyze existing site condition. • Value engineering techniques should be identified to decrease cost wherever possible. Consultant shall propose unique engineering solutions and costs saving analysis where possible. • Consultant shall prepared a Preliminary Estimate of Probable Costs Engineering Services During Construction
Provide engineering services to support construction activities, including responding to Requests for Information, Change Order requests, and reviewing submittals as required.

Specialized Technical Services
Provide modeling support to confirm drainage basin design meets City and all applicable State and Federal requirements.

Permitting Services
Develop and submit permits and environmental approvals required to authorize construction of the project through all required agencies, if required.

Anticipated deliverables include:
• Survey base mapping markups, geotechnical and environmental characterization reports as needed • Project management, quality assurance, and progress reporting • 30%, 60%, 90% Design Plans, Specifications & Cost Estimate • Final Design Plans, Specifications & Cost Estimate
• Basis of Design Report
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7 • Bid Plans and Special Provisions for Bid Project Manual • Constructability Analysis and Report
• Operations and Maintenance Manual
• Hydraulic Modeling Report
• Construction support deliverables, including submittal review, RFI responses, Design Change issuance, etc.
• As-builts record drawings in PDF and AutoCAD format.

The following documents are available as reference material:
• Tivoli Facilities Master Plan
• Tivoli Infrastructure Financing Program (IFP)

PROPOSAL EXPECTATIONS

CITY OF MODESTO EXPECTATIONS
The City reserves the right to amend, withdraw and cancel this RFP. The City reserves the right to reject all responses to this RFP at any time prior to contract execution. The City reserves the right to request or obtain additional information about any and all proposals.

The selected Consultant is expected to have a complete understanding of City, State, and Federal procedures and manuals and all applicable laws and regulations necessary to complete the Scope of Work.

This RFP provides guidance but may not represent the exact form of the final project scope, pending negotiations between the selected Consultant and the City. Experience in performing similar services will be a heavily weighted factor in the selection process. Quality of performance on public relation and marketing services, ability to meet schedules and budgets, and ability to communicate effectively with City staff, other consultants, community members and the public will be some of the attributes and factors considered.

COST OF RFP PREPARATION
The City shall not be liable for any pre-contractual expenses incurred by any consultant preparing a submittal or portions thereof or by any selected consultant. Each consultant shall protect, defend, indemnify, and hold #5..
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8 harmless the City from any and all liability, claims, or expenses whosoever incurred by, or on behalf of, the entity participating in the preparation of its response to this RFP. Pre-contractual expenses are defined as expenses incurred by consultants, if any, in:

1. Preparing the Proposal and related information in response to this RFP.

2. Negotiations with the City of any matter related to this procurement.

3. Costs associated with interviews, meetings, travel, or presentations.

4. All other expenses incurred by a proposer/consultant prior to the date of award and a formal notice to proceed.

PROPOSAL FORMAT
Proposals should be submitted through the City's OpenGov Procurement portal. The Proposal shall contain an acknowledgment of receipt of all amendments and/or addenda to the RFP.

PROPOSAL EXPECTATION
The City requires the proposer to submit a concise proposal clearly addressing all the requirements outlined in this RFP; it must contain information covering the following topics:

COVER LETTER
The cover letter shall be signed by a person authorized by the Proposer to execute an agreement with the City. It shall include: the legal name of the company; the name, address and telephone number of the principal person representing the firm; the firm’s current annual dollar volume of work; and a summary of the Proposal, including a brief description of the proposed team. It shall make a commitment to accept the terms and conditions in the RFP and the Standard Agreement for Professional Services (Attachment A), including acknowledgment of receipt of all amendments and/or addenda to the RFP.

The letter shall also identify a single person for possible contact during the RFP review process regarding agreement language.
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9 PROJECT UNDERSTANDING AND APPROACH
This section should demonstrate an understanding of the scope of services. It should describe the general approach, organization, and staffing required for the services requested. Also, describe the firm’s understanding of key issues and its approach to resolving those issues. All sub-consultants and their roles must be identified.

The consultant shall include an organizational chart identifying key personnel responsible for accomplishing all aspects of the work.

QUALIFICATIONS OF CONSULTANT STAFF AND SUBCONSULTANT STAFF This section should include a list of key personnel to be assigned to the proposed RFP and qualifications for each person to be used, including sub-consultant personnel. An organizational chart or similar graphic shall also be provided that clearly shows the function each person will be expected to fulfill. It is imperative that the key personnel providing the requested services have the background, experience, and qualifications to provide the services described in this RFP. The City reserves the right to approve all key personnel individually and all subconsultants for work on this agreement.

If sub-consultants or joint consultants are proposed, describe any relevant association with the proposed subconsultants. Provide examples of past projects on which the lead firm has worked with each sub-consultant.

Indicate the percentage of the fee allocated for each participating consultant and/or sub-consultant.

After the agreement is signed, the consultant may not replace key staff without written agreement by the City.

EXPERIENCE OF FIRM
This section should include the relevant experience of the principal firm. Include project descriptions, status of the services, costs and dollar value of services provided. Clearly identify the role of key staff identified herein and identify a minimum of ten (10) current and recent client references including contact information (phone numbers and emails). The focus shall be on experience, analysis, and documentation for similar services. Only recent similar services completed in the past ten (10) years should be included in this section. During evaluation of proposals, completed services on which the key staff proposed for this RFP had a significant role in the #5..
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10 project will be considered to have more weight than those that did not include such personnel. Any other details that the principal firm wishes to convey about itself or its proposed subcontractors should be placed in this section.

COST, SCHEDULE & DEADLINES
The following elements shall be included in describing the budget allocation in the Consultant Proposal:

1. An overall cost proposal, including a breakdown of costs by Activity listed in the scope of work section of this RFP;

2. Person hours allocated to each step and total hours allocated for services objectives and overall services (including sub-contractors), or flat costs by tasks with a “not to exceed” figure for each task;

3. A breakdown of the employees and professionals to be assigned to each project objective and the hourly rates and person-hour costs assigned (please indicate total number of hours for each project team member along with total hours for each project objective and the entire project), or flat costs by tasks with a “not to exceed” figure for each task;

4. Personnel charge rates of the firm;

5. Classification as to whether or not employees are reimbursed by hourly rate or salary; and,

6. List of any subcontractors who may provide technical or other assistance and breakdown of hours/costs associated with the sub-consultants;

7. Any proposals for additions to, modifications of or exceptions from the Scope of Work shall be clearly stated in the proposal and fully explained in the appropriate section(s), with costs specifically broken out in this section. The City is open to innovative and/or customized measures, but reserves the right to evaluate such proposals in full prior to execution of a contract in order to ensure that all the needs of the project and the City are met; and,

8. A detailed schedule, listing sufficient activities to demonstrate an understanding of the process involved in delivering the services of this type.
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11 SAMPLE CITY AGREEMENT
A sample of the City agreement is included in Exhibit A which defines the City’s terms and conditions for these contractual services. Include in your proposal any proposed changes to these terms and conditions as part of your proposal.

INSURANCE REQUIREMENTS
Proposer, if awarded an agreement, will be required to hold harmless, defend and indemnify the city, its agents, officers, employees, and volunteers, against any and all claims, losses, liabilities, judgements or damages from every cause, including but not limited to injury to person or property or wrongful death, including reasonable costs and expenses of defense of any judicial or administrative action, arising directly or indirectly out of any negligent or intentional act or omission of Proposer, its agents, officers, employees, and volunteers relating to or during the performance of its obligations under this Proposal. Consultants obligation to defend, indemnify, and hold the city, its agents, officers, and employees harmless under the provisions of this paragraph is not limited to or restricted by any requirement in this Proposal for Proposer to procure and maintain a policy of insurance. With reference to the foregoing, the parties agree that all risk of loss, including but not limited to damages, property losses and defense of third-party suits, arising out of or relation to the operation of city-owned vehicles by Consultant’s employees is apportioned to Consultant in accordance with the provisions contained in indemnity.

During the term of the Agreement, CONSULTANT shall maintain in full force and effect at its own cost and expense the insurance coverage as set forth in the attached Exhibit (C) to the Agreement and shall otherwise comply with the other provisions of Exhibit (C) to the Agreement. The city utilizes a software program “PINS Advantage” where vendor is responsible for uploading and maintaining updated insurance.

Insurance Type or Requirement Requirement
General Liability $1,000,000
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12 Automobile $1,000,000
Worker's Compensation (if there are employees
of the business)
$1,000,000
Professional Liability or Errors and Omissions $2,000,000 and $2,000,000 aggregate Waiver of Subrogation Form Required
Additional Insured Endorsement Additional Named Insured language required: The City of Modesto, its officers, officials, employees, agents and volunteers are to be covered as additional insureds.

FINANCIAL INTEREST DISCLOSURE AND FINANCIAL REVIEW
Any agreement award to result from this RFP process and Proposer’s submission of a Proposal therewith will require approval by a majority vote of the City of Modesto’s City Council. In order to have full transparency in any City of Modesto commercial actions, the City Council may not approve an agreement between the City and the Proposer until all persons with a direct or indirect financial interest of greater than $2,000 in the Proposer are identified by name.

Proposer must therefore complete this Financial Interest Disclosure Form listing by name all parties that have a material financial interest in the agreement, contract, or development right. This signed form must be submitted with the final proposal.

PLEASE NOTE, any Council action that requires a Financial Interest Disclosure cannot be considered by the City Council until the required reporting is made. That means that City Council agenda items without the disclosure will be removed from the Council agenda.

City staff will request financial statements from the proposer whose proposal is determined to best meet the City’s needs, as determined by the selection committee. Within two (2) business days of City request, proposer shall provide a copy of their company’s most recent professionally prepared Financial Statements (Income #5..
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13 Statement and Balance Sheet). These statements, if un-audited, shall be accompanied by a cover letter that states the name and title of the preparer, the basis of the financial statement presentation (cash or accrual) and whether these statements have been prepared in accordance with Generally Accepted Accounting Principles for the most recent fiscal year end of the proposer. Audited financial statements shall be submitted in their entirety, including the auditor’s opinion and notes to the financial statements.

CONFIDENTIALITY
If any of the submittals, or any portion of the submittals, are considered confidential by the respondent, such uploads should be submitted in the space provided for Additional Information with the word "Confidential" in the file name(s).

All information and documents, excluding the confidential financial information, submitted in response to this RFP are subject to the California Public Records Act, https://www.ftb.ca.gov/your-rights/california-publicrecords-act.html, California Government Code §§ 6250 through 6276.48) (“CPRA”), which mandates the disclosure of documents in the possession of the City upon the request of any person, unless the content of the document falls within a specific exemption category of the CPRA. On each page that contains information that the respondent believes is exempt from mandatory disclosure under CPRA, respondent shall include the following separate legend:
“CONFIDENTIAL – NOT FOR PUBLIC DISTRIBUTION”
“THIS PAGE CONTAINS INFORMATION THAT IS EXEMPT

FROM MANDATORY DISCLOSURE UNDER THE CALIFORNIA
PUBLIC RECORDS ACT.”
Should the City receive a request to review confidentially labeled information, the City will notify the respondent of the request and delay the access to the materials for seven (7) days after notification to respondent to allow respondent to act in protection of its labeled information. Failure to so act shall constitute a complete #5..
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14 waiver.

All responses will be considered public records that are subject to public disclosure. In the event a respondent considers its submittal as a proprietary trade secret or otherwise exempt from disclosure under the CPRA, the respondent must designate its submittal as confidential. The City will withhold designated applications from public disclosure only if permitted by applicable law. The City will not be responsible or liable for disclosure of any information, including without limitation those marked confidential, if disclosure is deemed by the City to be required by law, or by a court of competent jurisdiction.

PROPOSAL EVALUATIONS
The following is an outline of the procedures the City will use in the selection process:

1. Establish a Screening and Selection Committee.

2. Screening and Selection Committee reviews and evaluates the proposals submitted by the prospective consultants.

3. Proposers may be required to participate in an oral interview. The oral interview will be a panel comprised of members of the selection committee.

4. Negotiations may take place with the primary firm on the final scope of work, the final contract proposal, and the proposal price.

5. If an agreement cannot be negotiated for this service, the negotiations with the designated consultant shall be terminated in writing and negotiations shall be started with the next highest rated consultant.

6. The selection committee will make a recommendation to the awarding authority.

CONSULTANT EVALUATION CRITERIA
The City intends to engage the most qualified consultant available for this assignment. It is imperative the consultant’s proposal fully address all aspects of the RFP. It must provide the City staff with clearly expressed information concerning the consultant’s understanding of the City’s specific requirements and qualifying the proposer to conduct this study in a thorough and efficient manner.

The selection committee will make a recommendation to the awarding authority. The acceptance of the #5..
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15 proposal will be evidenced by written Notice of Award from the City’s Director of Community and Economic Development to the successful Proposer.

The following criteria shall be used in evaluation of the proposer’s offer of services:

No. Evaluation Criteria Scoring Method Weight (Points)

1. Experience
• Years of experience of firm and/or its
principals in working with public
utilities infrastructure.
• Broad character and scope of past
projects.
• Experience, education, certification
and licenses of key proposed team
members.
• Experience of proposed team
members in projects of similar
magnitude, requirements and
complexity, within the past five
years. Identify each team member’s
involvement in the specific project
listed and with which firm they were
employed when the work was done.
• History of repeat business with
clients. Stipulate the previous (within
the past five years) contracts with the
City of Modesto.

Points Based 40
(40% of Total)
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16 2. Analysis and Approach
• Originality, creativity, and soundness
of approach to problem solving and
analysis of school safety
transportation requirements.
• Demonstrated management and
organizational ability as relates to
time management, scheduling, City
staff/client relationships, etc., and the
ability to meet deadlines.
• Ability to execute complete, clear and
concise construction documents, and
produce a quality work product.
• Ability to prepare project
recommendations and preliminary
cost estimates appropriate to the size
and complexity of the project.

Points Based 50
(50% of Total)

3. General
• Size of firm and available staff as
appropriate for the required services.
• General comprehension of the
potential assignments and
responsiveness to the special project
requirements.
• Demonstrated understanding of
community economic and social
relationships, such as citizen and
environmental concerns, energy
conservation, ecological and
economic considerations.
• Firm reputation as relates to
principles, credibility, and attitude.

Points Based 10
(10% of Total)

PROPOSAL

PROPOSAL INFORMATION
PROPOSAL (WITHOUT COST)*
Please Upload your Proposal here formatted in the manner required by this RFP. This upload here should NOT INCLUDE any pricing information as that will be uploaded separately. #5..
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17 *Response required
PAYMENT TERMS AND METHODS*
Proposer is able to choose from either of the following payment methods and associated timings:

Option A (Preferred): City of Modesto ePay Payment: This secure payment methodology is preferred by an increasing number of the City’s suppliers. On Net 30-day timing, you will receive a single-use Master Card number with a detailed remittance for each payment. You will process the payment though your POS/Card terminal. The payment remittance will be sent from [email protected] via email and will contain the following information:
• 16-digit credit card number
• Expiration date
• Security code
• Total dollar amount of invoices to be paid
• Invoices reference numbers and corresponding amounts
ePay results in small percentage rebate of 1.0% to the City through the card issuer. That rebate amount will be considered by the City in its evaluation of Proposer’s pricing proposal hereunder. Information about enrolling in MasterCard ePay program can be obtained from the City’s contact listed on the Cover Page of this RFP.

Option B – Manual Check: On Net 45 Day timing, the City will mail a hardcopy check to Bidder. The payment will be deemed to have been made when the check envelope is mailed via US Postal Service First Class Mail. The timing of the mailing will be at the end of the Net 45 Day period. Additional time should be estimated by the Bidder for the check to be in transit, and to await deposit and clearance by Bidder staff.

Please select which option for payment terms and method you accept. ☐ Option A (Preferred)
☐ Option B
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18 *Response required
SEPARATE COST FILE*
Please upload a breakdown of your pricing information here. This information should not be part of your main proposal upload which is why it is requested separately here. *Response required

FINANCIAL INTEREST DISCLOSURE
Any contract award to result from this RFP process and Proposer’s submission of a Proposal therewith will require approval by a majority vote of the City of Modesto’s City Council. In order to have full transparency in any City of Modesto commercial actions, the City Council may not approve an agreement between the City and the Proposer until all persons with a direct or indirect financial interest of greater than $2,000 in the Proposer are identified by name.
• Financial_Interest_Disclosu...

CALIFORNIA LEVINE ACT DISCLOSURE*
Please download the below documents, complete, and upload. • Modesto_Levine_Act_Statemen...
*Response required

ADDITIONAL INFORMATION (IF NEEDED)
For any additional information requested or required by any of your previously provided answers or as stated within this RFP please upload the additional documentation here.

SUBMITTAL CONFIRMATION*
Proposer hereby certifies that all information provided within this proposal is accurate to the best of their knowledge. Proposer acknowledges that they have examined and carefully studied all Contract Documents and #5..
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19 any Addenda and that they have provided any necessary proof of their authority to submit a proposal on behalf of the Company Name stated on the proposal thereby committing the Company to the information contained within.

By checking the "please confirm" box below, you certify the above statement. ☐ Please confirm
*Response required

PROPOSED TIMELINE
RFP Issued: February 28, 2025
Questions Due via City's OpenGov
Procurement portal:

March 5, 2025, 12:00pm
Addendum Issued (if required): March 6, 2025
Proposal Due Date & Time: March 21, 2025, 5:00pm
Approximate Award Date: Q2 2025
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20 The City of Modesto assumes no responsibility for delay in upload or submittal of any proposal(s). All costs associated with the preparation and upload/submittal of any proposal(s) shall be borne by the proposer(s).

Each proposal shall be submitted electronically through the City's OpenGov Procurement portal before 5:00 pm on Friday, March 21, 2025.

All questions regarding the RFP shall be submitted through the Questions & Answer area of the City's OpenGov Procurement portal prior to 12:00 pm on Wednesday, March 5, 2025. The City will respond to questions through the OpenGov portal where answers can be found in the Question & Answer tab; however, if a response to a question elicits a change to the bid documents, an addendum will be posted through the OpenGov portal under the Addenda & Notices tab. All contact between Proposer and the City regarding the Proposal process shall be through the City Contact. Attempts by the Proposer to contact other City personnel regarding this RFP and associated process may result in disqualification of the Proposer. Notwithstanding the foregoing, information intentionally or unintentionally provided by any person other than the City Contact may not be correct and will be not be binding upon the City.

I hope this opportunity will be of interest to you and look forward to your response.

Sincerely,
Mark Bolden
Buyer
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21 EXHIBIT A: SAMPLE AGREEMENT

STANDARD AGREEMENT

FOR CONSULTANT SERVICES
THIS AGREEMENT made and entered into in the City of Modesto, State of California, this ______ day of _______________, 20___, (“Effective Date”) by and between the CITY OF MODESTO, a municipal corporation of the State of California, hereinafter referred to as "CITY", and (CONSULTANT), a California corporation, hereinafter referred to as "CONSULTANT".

This AGREEMENT is made with regard to the following recitals:
a. The CITY has determined that an _______________ should be prepared for the CITY to _________________.
b. CONSULTANT represents that it is qualified, willing, and able to provide the services to prepare said document(s).

NOW, THEREFORE, in consideration of this AGREEMENT, and the mutual promises, covenants, and stipulations hereinafter contained, the parties agree as follows:

1. SCOPE OF SERVICES
CONSULTANT shall undertake and complete the scope of work as set forth and described in the documents attached hereto and referred to as Exhibit (A) or "Project". The CONSULTANT shall perform the services as described in Exhibit (A) in a manner compatible with the standards of its profession and shall produce a fully complete project that is acceptable to the CITY.

2. TERM OF AGREEMENT
The term of the AGREEMENT shall be for a period of two (2) years, with three (3) one-year extension options at the sole discretion of CITY, for a total of up to five (5) years. #5..
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22 Year 1: MONTH DD, 20___ through MONTH DD, 20___
Year 2: MONTH DD, 20___ through MONTH DD, 20___
Year 3: MONTH DD, 20___ through MONTH DD, 20___
Year 4: MONTH DD, 20___ through MONTH DD, 20___
Year 5: MONTH DD, 20___ through MONTH DD, 20___
Pricing shall remain firm for the first two (2) years of the AGREEMENT.

Price increases for subsequent AGREEMENT years, three, four and, five shall not exceed the Consumer Price Index (CPI) for West Urban Area in any one AGREEMENT year and shall be negotiated through the Purchasing Division. Requests for price increases shall be submitted by CONSULTANT in writing, ninety (90) days prior to the annual anniversary date of the AGREEMENT to be effective for the subsequent year.

3. COMPENSATION
CONSULTANT agrees to accept a sum not to exceed $_________ (maximum compensation) as full remuneration for performing all services and furnishing all staffing and materials for CITY in accordance with Exhibit (A) attached hereto and performance by CONSULTANT of all its duties and obligations under this AGREEMENT.

The Compensation shall be paid pursuant in the manner and at the times set forth below:

CITY shall pay CONSULTANT on a time and materials basis for CONSULTANT’s actual costs for all work called for in Exhibit (A) to this AGREEMENT. All work to be performed under this AGREEMENT shall be billed at the hourly rates set forth in Exhibit (B) attached hereto, CONSULTANT shall submit monthly invoices to CITY which include detailed tasks, hours worked, and billable rates for all work completed, and detailed receipts for any out-of-pocket costs paid by CONSULTANT in connection with work performed on this project.

CITY shall pay CONSULTANT [TO BE DETERMINED BY RFQ RESPONSE IN FINAL AGREEMENT, EITHER “Net 30 terms via CITY’s ePay Program” or “Net 45 Days via manual check”.] #5..
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23 4. OBLIGATIONS OF CONSULTANT
Throughout the term of this AGREEMENT, CONSULTANT shall possess, or secure all licenses, permits, qualifications and approvals legally required to conduct business. CONSULTANT warrants that it has all of the necessary professional capabilities and experience, as well as all tools, instrumentalities, facilities and other resources necessary to provide the CITY with the services contemplated by this AGREEMENT. CONSULTANT further warrants that it will follow the best current, generally accepted and professional practices to make findings, render opinions, prepare factual presentations, and provide professional advice and recommendations regarding this project.

5. PERFORMANCE BY KEY EMPLOYEE
CONSULTANT has represented to CITY that ______ will be the person primarily responsible for the performance of the services referred to in this AGREEMENT. CITY has entered into this AGREEMENT in reliance on that representation by CONSULTANT. CONSULTANT therefore agrees that ____ percent (___%) or more of the time to be devoted to the project that is the subject of this AGREEMENT will be that of the abovenamed person.

6. OWNERSHIP OF DOCUMENTS/TITLE TO DATA
Ownership of Documents
All reports, drawings, designs, graphics, working papers and other incidental work or materials furnished hereunder shall become and remain the property of the CITY, and may be used by CITY as it may require without any additional cost to CITY. No reports shall be used by the CONSULTANT for purposes other than this AGREEMENT without the express prior written consent of CITY.

Title to Data
If, as a part of the AGREEMENT, CONSULTANT is required to produce data such as, but not limited to, drawings, plans, specifications, calculations, models, flow diagrams, visual aids and other related materials, the #5..
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24 originals of all such data generated under this AGREEMENT will be delivered to CITY upon the completion or termination of services under the AGREEMENT.

All materials, documents, data or information obtained from the CITY data files or any CITY medium furnished to CONSULTANT in the performance of this AGREEMENT will at all times remain the property of the CITY. Such data or information may not be used or copied for direct or indirect use by CONSULTANT after termination of this AGREEMENT without written consent of the CITY.

7. NEWS AND INFORMATION RELEASE
CONSULTANT agrees that it will not issue any news releases in connection with either the award of this AGREEMENT, or any subsequent amendment of or efforts under this AGREEMENT, without first obtaining review and approval of said news releases from CITY through the CITY Manager.

8. CONFLICT OF INTEREST
CONSULTANT warrants that it presently has no interest and shall not acquire any interest, direct or indirect, which would create a “conflict of interest”, as that term is defined in the Political Reform Act (Gov. Code § 81000 et seq), for the CONSULTANT in the performance of this AGREEMENT. CONSULTANT warrants that, in performance of this AGREEMENT, CONSULTANT shall not employ any person having any such interest.

CONSULTANT understands that, if this AGREEMENT is made in violation of Government Code § 1090 et seq., the entire AGREEMENT is void and CONSULTANT will not be entitled to any compensation for services performed. CONSULTANT agrees to file a Statement of Economic Interests with the City Clerk at the start and end of this AGREEMENT if so, required at the option of CITY.

9. AMENDMENTS
Both parties to this AGREEMENT understand that it may become desirable or necessary during the execution of this AGREEMENT, for CITY or CONSULTANT to modify the scope of services provided under this AGREEMENT. Any material extension or change in the scope of work shall be discussed with CITY and the #5..
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25 change and cost shall be memorialized in a written amendment to the original AGREEMENT prior to the performance of the additional work.

10. INDEPENDENT CONSULTANT
All acts of CONSULTANT, its agents, officers, and employees and all others acting on behalf of CONSULTANT relating to the performance of this AGREEMENT, shall be performed as independent CONSULTANTS and not as agents, officers, or employees of CITY. CONSULTANT, by virtue of this AGREEMENT, has no authority to bind or incur any obligation on behalf of CITY. CONSULTANT has no authority or responsibility to exercise any rights or power vested in the CITY. No agent, officer, or employee of the CITY is to be considered an employee of CONSULTANT. It is understood by both CONSULTANT and CITY that this AGREEMENT shall not under any circumstances be construed or considered to create an employer-employee relationship or a joint venture. CONSULTANT, its agents, officers and employees are and, at all times during the terms of this AGREEMENT, shall represent and conduct themselves as independent CONSULTANTS and not as employees of CITY.

CONSULTANT shall determine and control the method, details and means of performing the work and services to be provided by CONSULTANT under this AGREEMENT. CONSULTANT shall be responsible to CITY only for the requirements and results specified in this AGREEMENT, and, except as expressly provided in this AGREEMENT, shall not be subjected to CITY's control with respect to the physical action or activities of the CONSULTANT in fulfillment of this AGREEMENT. CONSULTANT has control over the manner and means of performing the services under this AGREEMENT. CONSULTANT is permitted to provide services to others during the same period service is provided to CITY under this AGREEMENT. If necessary, CONSULTANT has the responsibility for employing other persons or firms to assist CONSULTANT in fulfilling the terms and obligations under this AGREEMENT.

If in the performance of this AGREEMENT any third persons are employed by CONSULTANT, such persons shall be entirely and exclusively under the direction, supervision, and control of CONSULTANT. All terms of #5..
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26 employment including hours, wages, working conditions, discipline, hiring, and discharging or any other term of employment or requirement of law shall be determined by the CONSULTANT.

It is understood and agreed that as an independent CONSULTANT and not an employee of CITY neither the CONSULTANT or CONSULTANT's assigned personnel shall have any entitlement as a CITY employee, right to act on behalf of the CITY in any capacity whatsoever as an agent, or to bind the CITY to any obligation whatsoever. It is further understood and agreed that CONSULTANT must issue W-2 forms or other forms as required by law for income and employment tax purposes for all of CONSULTANT's personnel. As an independent CONSULTANT, CONSULTANT hereby indemnifies and holds CITY harmless from any and all claims that may be made against CITY based upon any contention by any third party that an employer-employee relationship exists by reason of this AGREEMENT.

11. ASSIGNMENT
Neither this AGREEMENT nor any portion thereof shall be subcontracted or assigned without the express prior written consent of the CITY in each and every instance.

12. PATENT/COPYRIGHT MATERIALS
Unless otherwise expressly provided in the AGREEMENT, CONSULTANT shall be solely responsible for obtaining the right to use any patented or copyrighted materials in the performance of this AGREEMENT.

CONSULTANT shall furnish a warranty of such right to use to CITY at the request of CITY.

13. NOTICES
Notice required by this AGREEMENT shall be given in writing and shall be deemed given and effective upon delivery provided that such are delivered in accordance with the provisions of this Section. Notices shall be delivered either by: (a) personal delivery; (b) overnight courier service which obtains confirmation of delivery; or (c) certified mail, return receipt requested, if delivery is confirmed by a return receipt; or (d) by electronic transmission subject to reasonable proof that the notice was both transmitted and received. Each such notice shall #5..
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27 be sent to the parties at the address respectively set forth below or to such other address as a party may designate by written notice given in accordance with the provisions of this Section:

FOR CONSULTANT: Name:

Address:

Attention:

Phone: ()
Email:

CITY: Name:

Address:

Phone:

Email:

City of Modesto
Purchasing Division
P.O. Box 642
Modesto, CA 95353
(209)

14. INSURANCE REQUIREMENTS
During the term of this AGREEMENT, CONSULTANT shall maintain in full force and effect at its own cost and expense the insurance coverage as set forth in the attached Exhibit (C), attached hereto and incorporated herein, and shall otherwise comply with the other provisions of Exhibit (C). CONSULTANT is responsible for uploading updated insurance documentation to the City's "PINS Advantage" program.

15. TERMINATION OF AGREEMENT
Termination by CITY for Default of CONSULTANT
Should CONSULTANT default in the performance of this AGREEMENT or materially breach any of its provisions, at its option, CITY may terminate this AGREEMENT by given written notification to #5..
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28 CONSULTANT. The termination date shall be the effective date of the notice. For the purposes of this section, material breach of this AGREEMENT shall include, but not limited to, any of the following: failure to perform required services or duties, willful destruction of CITY's property by CONSULTANT, dishonesty or theft.

Termination by City for Convenience
The CITY may also terminate the CONSULTANT's performance under the AGREEMENT, either in whole or in part, at its own discretion, or when conditions encountered during the service make it impossible or impracticable to proceed, or when the CITY is prevented from proceeding with the AGREEMENT by act of God, by law, or by official action of a public authority, or upon a determination by the CITY that such termination is in the best interest and convenience of the CITY, or whenever the CITY is prohibited from completing the work for any reason. The CITY shall provide no less than ten (10) calendar days written notice of its intent to terminate the AGREEMENT for convenience and shall endeavor to provide the CONSULTANT with consultation with the CITY prior to termination.

Post-Termination Procedure
Upon receipt of a written notice of termination pursuant to either of the foregoing paragraphs, the CONSULTANT shall:
a. Cease its work as directed in the notice of termination as of the termination date and see to it that its employees, subconsultants and agents are notified of such termination and act as specified in the notice of termination;
b. Terminate all orders and subconsultants except as necessary to complete any portion of the work that is not terminated;
c. If directed in writing by the CITY to do so, assign all right, title and interest in subconsultants and materials in progress to CITY, in which case the CITY will have the right at its discretion to settle, or pay any or all claims arising out of the termination of such subconsultants, but in no event shall recovery by any CONSULTANT or subconsultant include lost profits for portions of the work not completed or undertaken, including materials not delivered; d. Deliver or otherwise make available to the CITY all data, drawings, specifications, reports, estimates, summaries and such other information and material as may have been accumulated by #5..
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29 the CONSULTANT in performing the work whether completed or in process; e. Settle outstanding liabilities and claims, subject to the approval of CITY; f. Complete performance of such part of the Service as has not been terminated; g. Take such other actions as may be necessary, or as may be directed by the CITY for the protection and preservation of the Services and/or property related to the Services; h. If CITY so requests, and at CITY's cost, CONSULTANT shall provide sufficient oral or written status reports to make CITY reasonably aware of the status of CONSULTANT's work on the project.
i. The CONSULTANT understands and agrees that CITY may, in CITY's sole discretion, refuse to pay CONSULTANT for that portion of CONSULTANT's services which were performed by CONSULTANT on the project prior to the termination date and which remain unacceptable and/or not useful to CITY as of the termination date.

CITY will pay CONSULTANT an amount based on the percentage of satisfactory work completed in accordance with the notice of termination. The final payment to the CONSULTANT after termination for convenience shall be limited to amounts due and owing under the AGREEMENT at time of termination, including the following:
j. The cost of settling and paying valid claims arising out of the termination of the work such as subconsultant AGREEMENTS or AGREEMENTS for materials;
k. The AGREEMENT price allocable to the portion of the work properly performed, or goods supplied to the work site by the CONSULTANT as of the date of termination, as determined in accordance with the notice of termination, reduced by any sums previously paid to the CONSULTANT.

Authorization to Terminate Agreement
Termination of the AGREEMENT may be invoked by the City Manager, or his/her designee, subject to the right of the CONSULTANT to appeal the City Manager, or his/her designee's, decision to the City Council. The CONSULTANT shall appeal by notifying the City Clerk in writing within ten (10) calendar days of receipt of written notification from CITY of termination of the AGREEMENT. In the event that termination of this AGREEMENT is upheld by the City Council, any cessation of payment of delay claims, extended claims, #5..
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30 Eichleay claims, or any other claims for delay shall be retroactive to the date of termination selected by the City Manager, or his/her designee.

16. INDEMNITY
If CONSULTANT is Design Professional performing design professional services, as defined California Civil Code 2782.8, CONSULTANT agrees to indemnify, defend, and hold harmless the CITY, its agents, officers, officials, employees and volunteers, from and against any and all claims, demands, costs, or liability that arise out of, or pertain to, or relate to the negligence, recklessness, or willful misconduct of CONSULTANT and its employees, officials, officers, agents or agents in the performance of services under this AGREEMENT, but this indemnity does not apply to liability for damages arising from the sole negligence, or willful misconduct of the CITY. The CITY agrees that in no event shall the cost to defend charged to the CONSULTANT exceed that CONSULTANT’s proportionate percentage of fault. However, notwithstanding the previous sentence, in the event one or more defendants is unable to pay its share of defense costs due to bankruptcy or dissolution of the business, the CONSULTANT shall meet and confer with other parties regarding unpaid defense costs. This duty to indemnify shall not be waived or modified by contractual AGREEMENT or acts of the parties.

If CONSULTANT is not a Design Professional performing Design Professional Services, the CONSULTANT shall hold the CITY, its agents, officers, employees, and volunteers harmless from and save, defend and indemnify them against any and all claims, losses, liabilities, judgments or damages from every cause, including but not limited to injury to person or property or wrongful death, including reasonable costs and expenses of defense of any judicial or administrative action, arising directly or indirectly out of any negligent or intentional act or omission of CONSULTANT, or its agents, officers, officials, employees, or volunteers relating to or during the performance of its obligations under this AGREEMENT, except for claims arising from the sole negligence of the CITY.
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31 CONSULTANT's obligation to defend, indemnify, and hold the CITY, its agents, officers, and employees harmless under the provisions of this paragraph is not limited to or restricted by any requirement in this AGREEMENT for CONSULTANT to procure and maintain a policy of insurance.

In the event that CONSULTANT or any employee, agent, or subconsultant of CONSULTANT providing services under this AGREEMENT is determined by a court of competent jurisdiction or the California Public Employees Retirement System (PERS) to be eligible for enrollment in PERS as an employee of CITY, CONSULTANT shall indemnify, defend, and hold harmless CITY for the payment of any employee and/or employer contributions for PERS benefits on behalf of CONSULTANT or its employees, agents, or subconsultants, as well as for the payment of any penalties and interest on such contributions, which would otherwise be the responsibility of CITY.

17. DISPUTE RESOLUTION
Venue for all claims, controversies, or disputes arising out of, or relating to the formation of this AGREEMENT, or the breach, termination execution, enforcement, interpretation, or validity of this AGREEMENT, including the determination of the scope or applicability of this contract provision shall be in the Superior Court of Stanislaus County or the United States District Court for the Eastern District of California.

18. ATTORNEY'S FEES
If a party to this AGREEMENT brings any action, including an action for declaratory relief, to enforce or interpret the provision of this AGREEMENT, the prevailing party shall be entitled to reasonable attorneys’ fees in addition to any other relief to which that party may be entitled. The court may set such fees in the same action or in a separate action brought for that purpose.

19. ENTIRE AGREEMENT
This AGREEMENT and its exhibits contain the entire understanding between CONSULTANT and CITY. Additional or new terms contained in this AGREEMENT which vary from CONSULTANT's proposal are controlling and are deemed accepted by CONSULTANT by shipment of any article or other commencement #5..
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32 of performance hereunder. All previous proposals, offers and communications relative to this AGREEMENT, whether oral or written, are hereby superseded except to the extent that they have been incorporated into this AGREEMENT. No future waiver of or exception to any of the terms, conditions, and provisions of this AGREEMENT shall be considered valid unless specifically agreed to in writing by all the parties.

20. PARTIAL INVALIDITY
If any provision in this AGREEMENT is held by a court of competent jurisdiction to be invalid, void, or unenforceable, the remaining provisions shall nevertheless continue in full force without being impaired or invalidated in any way.

21. WAIVER
The waiver by any party to this AGREEMENT of a breach of any provision hereof shall be in writing and shall not operate or be construed as a waiver of any other or subsequent breach hereof unless specifically stated in writing.

22. AUDIT
The CITY's duly authorized representative shall have access at all reasonable times to all reports, contract records, contract documents, contract files, and personnel necessary to audit and verify CONSULTANT's charges to CITY under this AGREEMENT.

CONSULTANT agrees to retain reports, records, documents, and files related to charges under this AGREEMENT for a period of four (4) years following the date of final payment for CONSULTANT services. CITY's representative shall have the right to reproduce any of the aforesaid documents.

23. GOVERNING LAW
This AGREEMENT shall be governed according to the laws of the State of California. #5..
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33 24. HEADINGS NOT CONTROLLING
Headings used in the AGREEMENT are for reference purposes only and shall not be considered in construing this AGREEMENT.

25. COMPLIANCE WITH LAWS
CONSULTANT shall insure compliance with all safety and hourly requirements for employees, in accordance with federal, state, and county safety and health regulations and laws. CONSULTANT shall fully comply with all applicable federal, state, and local laws, ordinances, regulations and permits.

26. CITY BUSINESS LICENSE
CONSULTANT will have a City of Modesto business license. #5..
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34 IN WITNESS WHEREOF, the City of Modesto, a municipal corporation, has authorized the execution of this AGREEMENT by its City Manager and attestation by its City Clerk under authority of Resolution No. 20___- ______, adopted by the Council of the City of Modesto on the ______ day of ________________, 20___, and (CONSULTANT) has caused this AGREEMENT to be duly executed as of the Effective Date.

CITY OF MODESTO
a municipal corporation
(CONSULTANT)
a California corporation*
By ________________________________ By ________________________________ JOSEPH P. LOPEZ, City Manager Name Title
By ________________________________
ATTEST: Name Title
By ________________________________ (Seal)
DIANE NAYARES-PEREZ, CMC, City Clerk
CONSULTANT's Federal ID# ___________
APPROVED AS TO FORM:

By ________________________________
JOSE M. SANCHEZ, City Attorney
APPROVED AS TO FORM:

By ________________________________
MATHEW BRALEY, Risk Manager
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35 EXHIBIT C: INSURANCE REQUIREMENTS FOR PROFESSIONAL SERVICES Consultant shall procure and maintain for the duration of the contract insurance against claims for injuries to persons or damages to property which may arise from or in connection with the performance of the work hereunder and the results of that work by the Consultant, his agents, representatives, employees or subcontractors.

MINIMUM SCOPE AND LIMIT OF INSURANCE
Coverage shall be at least as broad as:

1. Commercial General Liability (CGL): Insurance Services Office Form CG 00 01 covering CGL on an “occurrence” basis, including products and completed operations, property damage, bodily injury and personal & advertising injury with limits no less than $1,000,000 per occurrence. If a general aggregate limit applies, either the general aggregate limit shall apply separately to this project/location (ISO CG 25 03 or 25 04) or the general aggregate limit shall be twice the required occurrence limit.

2. Automobile Liability: ISO Form Number CA 00 01 covering any auto (Code 1), or if Contractor has no owned autos, hired, (Code 8) and non-owned autos (Code 9), with limit no less than $1,000,000 per accident for bodily injury and property damage.

3. Workers’ Compensation: as required by the State of California, with Statutory Limits, and Employer’s Liability Insurance with limit of no less than $1,000,000 per accident for bodily injury or disease.
(Not required if consultant provides written verification, it has no employees)

4. Professional Liability (Errors and Omissions) Insurance appropriates to the Consultant’s profession, with limit no less than $2,000,000 per occurrence or claim, $2,000,000 aggregate.

If the Consultant maintains broader coverage and/or higher limits than the minimums shown above, the City of Modesto requires and shall be entitled to the broader coverage and/or the higher limits maintained by the contractor. Any available insurance proceeds in excess of the specified minimum limits of insurance and coverage shall be available to the City of Modesto.

Umbrella or Excess Coverage
The Consultant may use Umbrella or Excess Policies to provide the liability limits as required in this agreement.

This form of insurance will be acceptable provided that all of the Primary and Umbrella or Excess Policies shall #5..
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36 provide all of the insurance coverages herein required, including, but not limited to, primary and non-contributory, additional insured, Self-Insured Retentions (SIRs), indemnity, and defense requirements. The Umbrella or Excess policies shall be provided on a true “following form” or broader coverage basis, with coverage at least as broad as provided on the underlying Commercial General Liability insurance. No insurance policies maintained by the Additional Insureds, whether primary or excess, and which also apply to a loss covered hereunder, shall be called upon to contribute to a loss until the Consultant's primary and excess liability policies are exhausted.

The insurance policies are to contain, or be endorsed to contain, the following provisions:

Additional Insured Status
The City of Modesto, its officers, officials, employees, and volunteers are to be covered as additional insureds on the CGL policy with respect to liability arising out of work or operations performed by or on behalf of the Consultant including materials, parts, or equipment furnished in connection with such work or operations. General liability coverage can be provided in the form of an endorsement to the Consultant's insurance with coverage equal to ISO form CG 2010. If Completed Operations endorsement is required, a separate endorsement equal to ISO form CG 2037 is required.

Primary Coverage
The Additional Insured coverage under the Consultant's policy shall be “primary and non-contributory” and will not seek contribution from the City’s insurance or self-insurance and shall be at least as broad as CG 20 01 04 13.

The City of Modesto does not accept endorsements limiting the Consultant's insurance coverage to the sole negligence of the Named Insured.

Notice of Cancellation
Each insurance policy required above shall provide that coverage shall not be canceled, except with notice to the City of Modesto.
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37 Waiver of Subrogation
Consultant hereby grants to City of Modesto a waiver of any right to subrogation which any insurer of said Consultant may acquire against the City of Modesto by virtue of the payment of any loss under such insurance.

Consultant agrees to obtain any endorsement that may be necessary to affect this waiver of subrogation, but this provision applies regardless of whether or not the City of Modesto has received a waiver of subrogation endorsement from the insurer.

Self-Insured Retentions
All Self-insured retentions must be disclosed to Risk Management for approval and shall not reduce the limits of liability. The City of Modesto may require the Consultant to purchase coverage with a lower retention or provide proof of ability to pay losses and related investigations, claim administration, and defense expenses within the retention. Any and all deductibles and SIRs shall be the sole responsibility of Consultant or subcontractor who procured such insurance and shall not apply to the Indemnified Additional Insured Parties.

Acceptability of Insurers
Insurance is to be placed with insurers with a current A.M. Best’s rating of no less than A:VII, unless otherwise acceptable to the City of Modesto.

Claims Made Policies (applicable to Professional Liability only) If any of the required policies provide claims-made coverage:

1. The Retroactive Date must be shown and must be before the date of the contract or the beginning of contract work.

2. Insurance must be maintained, and evidence of insurance must be provided for at least five (5) years after completion of the contract of work.

3. If coverage is canceled or non-renewed, and not replaced with another claims-made policy form with a Retroactive Date prior to the contract effective date, the Consultant must purchase “extended reporting” coverage for a minimum of five (5) years after completion of work. #5..
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38 Verification of Coverage
Consultant shall furnish the City of Modesto with original certificates and amendatory endorsements or copies of the applicable policy language effecting coverage required by this clause and a copy of the Declarations and Endorsements Pages of the CGL and any Excess policies listing all policy endorsements. All certificates and endorsements are to be received and approved by the City of Modesto Risk Services before work commences.

However, failure to obtain the required documents prior to the work beginning shall not waive the Consultant's obligation to provide them. The City of Modesto reserves the right to require complete, certified copies of all required insurance policies, including endorsements required by these specifications, at any time. City reserves the right to obtain a full certified copy of any insurance policy and endorsements. Failure to exercise this right shall not constitute a waiver of right to exercise later.

Subconsultants
Consultant shall require and verify that all subconsultants, or other parties hired for this work, purchase and maintain coverage for indemnity and insurance requirements as least as broad as specified in this agreement to the extent they apply to the scope of the subconsultant’s work with the same certificate of insurance requirements and naming as additional insureds all parties to this contract.

Special Risks or Circumstances
City of Modesto reserves the right to modify these requirements, including limits, based on the nature of the risk, prior experience, insurer, coverage, or other special circumstances.

Certificate Holder Address
Proper address for mailing certificates, endorsements and notices shall be:

City of Modesto
Attn: Risk Management
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39 1010 10th Street
Modesto, CA 95354
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CITY OF MODESTO
Proposal of Services
Tivoli Specific Area Storm Basin Design
March 21, 2025
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March 21, 2025
Re: City of Modesto Tivoli Specific Area Storm Basin Design To Whom It May Concern,
Stormwater basin parks, like the proposed Tivoli Specific Plan (TSP) dual-use basin and neighborhood park, provide a unique opportunity to efficiently capture and utilize water resources while maximizing land use for recreation and community engagement. By integrating stormwater detention and retention systems within this 19-acre open space, the project will enhance flood control, support groundwater recharge, and improve water quality—all while creating a vibrant recreational hub for residents. Strategically located, the basin park will serve as a focal point, seamlessly connecting neighborhoods and an adjacent elementary school, offering safe and accessible green space for play, exercise, and community gatherings. Thoughtful landscape design, walking trails, and multi-use play areas will ensure the basin is not just a functional necessity but a true community asset. Additionally, this dual-purpose approach supports urban sustainability, mitigates heat island effects, and fosters biodiversity by incorporating native vegetation and habitat-friendly elements. As development interest in the Tivoli area grows, the careful planning and execution of this project will be crucial in balancing growth with environmental stewardship, ensuring long-term benefits for both water management and community well-being.

Westwood is uniquely qualified to deliver this project due to our unmatched experience and deep familiarity with the Tivoli Specific Area. As a trusted local firm, we have successfully completed over 100 projects for the City of Modesto, building a strong partnership based on reliability, innovation, and high-quality solutions that enhance the community. Our in-depth knowledge of Modesto’s regulatory framework, geographic landscape, and infrastructure priorities allows us to seamlessly navigate project complexities while ensuring efficiency and sustainability. Our in-house multidisciplinary team—specializing in civil engineering, land surveying, landscape architecture, and stormwater management—has the expertise to design and implement the Tivoli Basin as a high-functioning, dual-use space. Additionally, our active involvement in six developments within the Tivoli Neighborhood Master Plan, covering approximately 257 acres, gives us invaluable insight into the area’s infrastructure needs. Our work on the Sonoma Sewer Trunk Phases 3 and 4a, along with the upcoming Phase 4b design, further demonstrates our ability to integrate stormwater solutions within the existing system. With a proven track record of delivering successful public space and stormwater projects, we are uniquely positioned to ensure that the Tivoli Basin becomes both an essential water management facility and a thriving community gathering place.

Leading this project will be Tyler Fay, PLA, whose extensive experience in dual-use basin parks across the Central Valley makes him the ideal project lead. As Project Manager for seven dual-use basin parks in the City of Manteca, he successfully guided projects from concept to construction, integrating sports courts, fields, walking trails, playgrounds, picnic areas, and exercise stations into functional stormwater basins. His expertise extends to high-profile parks such as Mary E.

Grogan Park in Modesto, where he played a key role in delivering a premier recreational space for the community. Tyler’s leadership will ensure the Tivoli Basin is designed to maximize both stormwater management and recreational benefits.

Supporting him is Mike Persak, who has managed six developments within Tivoli and brings in-depth knowledge of the area’s infrastructure, including the Sonoma Sewer Trunk. Additionally, Scott Roberts will provide technical survey oversight, having led survey efforts for multiple projects within the Tivoli Specific Plan, ensuring seamless integration with Modesto’s control systems. Our team is further strengthened by two trusted subconsultants: Kleinfelder, a long-standing partner with previous Tivoli experience, will provide geotechnical engineering, while Black Water Consulting Engineers, a highly respected local firm with over 15 years of partnership with Westwood, will lead the pump design. Together, this expert team is ready to deliver a well-integrated, high-functioning dual-use basin park that enhances both water management and community recreation.

Our commitment to Modesto runs deep. For decades, we have partnered with the City to shape vibrant neighborhoods, sustainable infrastructure, and meaningful public spaces that improve the lives of residents. The Tivoli Basin Project is more than just a stormwater solution—it represents an opportunity to create a lasting community asset that harmonizes functionality with beauty, resilience with recreation. By blending insightful engineering with thoughtful landscape design, we will transform this basin into a place where Modesto’s future generations can connect with nature, stay active, and build a stronger community. Notes: Regarding the sample agreement, we respectfully request to utilize the negotiated version of the contract that was executed for the TRRP Master Plan Update. I, Chad Kennedy, am authorized to bind the firm (legal name: Westwood Professional Services) and will serve as the primary contact during the proposal and negotiation process. We agree to be bound by the representations in this proposal and certify that the proposal is valid for 120 days. Our current annual dollar volume of work, as relevant to our California offices, exceeds $22 million.

Sincerely,
Chad Kennedy, PLA #5426, Principal Landscape Architect
1165 Scenic Drive, Suite A, Modesto, CA 95350
209.571.1765 - [email protected]
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Project Understanding and Approach
Project Understanding
Tivoli Dual-Use Basin Neighborhood Park
The Tivoli Dual-Use Basin Neighborhood Park project is a pivotal component of the broader Tivoli Specific Plan, which encompasses a 454-acre area within the City of Modesto’s sphere of influence in Stanislaus County. The project site, located between Claratina Avenue, Roselle Avenue, Sylvan Avenue, and Oakdale Road, will be transformed into a mixed-use development, including residential, commercial, educational, and recreational spaces. A central feature of this development will be a 19-acre dual-use basin park designed to integrate both stormwater management and recreational spaces, providing an essential amenity to the surrounding neighborhoods.

Project Overview
The Tivoli Dual-Use Basin Neighborhood Park will be situated at the heart of the Tivoli development, strategically placed to serve as both a recreational space and an essential stormwater management facility. The basin park will be designed in three tiers:
y The Lowest Tier: Dedicated entirely to stormwater management, this area will play a critical role in capturing and storing water during heavy rainfall events, ensuring that runoff is appropriately managed. y The Middle Tier: This area will function as an auxiliary stormwater management zone during the rainy season but will also serve as an informal recreational space during dry months, offering flexibility in its use. y The Upper Tier: Primarily designated for recreational use, this space will provide active and passive recreation areas, with minimal to no involvement in stormwater management.

Westwood’s team, with its extensive experience working with the City of Modesto, will oversee the development and construction of the park, ensuring that the design supports both recreational opportunities and environmental sustainability.

Throughout the design process, the team will collaborate closely with City staff to refine the recreational aspects of the park while maintaining the essential functionality of the basin.

Goals and Opportunities
The Tivoli dual-use basin park represents a unique opportunity to merge environmental stewardship with community recreation. By utilizing the park’s design to manage stormwater, the project will not only enhance the neighborhood’s resilience to storm events but also provide a space that encourages biodiversity and wildlife habitats. The park’s planting palette will feature species that can withstand prolonged inundation, creating a habitat conducive to birdwatching, wildlife observation, and the exploration of natural ecosystems not commonly found in traditional parks.

Furthermore, the park will offer approximately five acres of active recreation space, providing facilities for sports courts (basketball, tennis, pickleball, futsal), children’s play structures, picnic areas, shade structures, and passive recreational spaces. This diverse range of amenities will ensure the park serves as a vibrant community hub for residents of all ages.

Constraints and Challenges
Despite the exciting opportunities, there are several constraints that must be carefully navigated throughout the design and construction process:
y Balancing Recreational Space with Stormwater Management: Given that roughly two-thirds of the park will be dedicated to stormwater management, the challenge lies in maximizing the recreational value of the remaining space while ensuring sufficient capacity for managing stormwater during high-volume events, including but not limited to a 100-year storm event.

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y Maintenance of Dual-Use Basin: Unlike traditional parks, the dual-use basin will require ongoing maintenance of stormwater management facilities to ensure their continued performance, adding a layer of complexity to the park’s upkeep. y Safety: The integration of stormwater management features requires heightened attention to safety, particularly in ensuring that the park is safe for visitors during and after a storm event. Special consideration will be given to the design of recreational spaces adjacent to stormwater areas, with safety features incorporated into the park’s layout.

Westwood’s approach will be multidisciplinary, integrating landscape architects and civil engineers to develop innovative solutions that address these constraints while maintaining the park’s functional and aesthetic goals.

Previous Experience and Local Knowledge
Westwood’s familiarity with the Tivoli area and its ongoing projects in Modesto provides a distinct advantage in terms of efficiency and cost-effectiveness. The team has completed several survey assignments in the vicinity, providing valuable topographic data that will minimize the need for additional fieldwork. Previous work in the area has also addressed boundary discrepancies, ensuring that the project can proceed smoothly and without delays. This deep local knowledge, combined with Westwood’s extensive experience working with the City of Modesto, will facilitate a seamless design and implementation process.

Infrastructure Considerations
Several infrastructure elements will need to be considered during the development of the park, including:
y Stormwater Detention/Retention: The basin will be designed in accordance with the City of Modesto’s Design Standards for Dual Use Flood Control/Recreational Facilities. Given the limited percolation rates at the site, a pump station and force main will be incorporated to ensure that the basin can evacuate stormwater within the required 48-hour period. y Irrigation and Electrical Facilities: The project site contains existing Modesto Irrigation District (MID) irrigation and electrical infrastructure, including a 30” Davis pipeline and overhead electrical lines. These facilities will need to be carefully integrated into the park design, with possible realignments and coordination with MID. to maintain service during construction. y Relocation of Water Main: A portion of the City’s 16” water main located along Mable Avenue will need to be relocated in accordance with the Tivoli Specific Plan. Westwood will work closely with the City’s Utilities Department to determine the optimal alignment for the water main.
y Farming Operations: The park’s construction will impact adjacent farming operations, including access roads and irrigation facilities.

Westwood will collaborate with property owners to ensure that the necessary infrastructure adjustments are made to minimize disruption to agricultural activities during and after construction.

Conclusion
The Tivoli Dual-Use Basin Neighborhood Park is an exciting and transformative project that will provide a vital green space for the community while also addressing important stormwater management needs. With Westwood’s expertise in landscape architecture, civil engineering, stormwater design, and collaboration with City staff, the project is poised to create a sustainable and dynamic park that balances recreational opportunities with environmental function. The park’s thoughtful design will ensure that it serves as a central and cherished space within the Tivoli development for generations to come.

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Scope of Services
Included in this section is the technical scope of work to complete the project as we interpret it. It is organized a bit differently than the scope in the RFP document to help streamline the process and include key scope assignments that may have been overlooked.

Task 1: Meetings and Project Management

1.1 Kick-off Organization & Scoping Meeting
A well-run organizational meeting at the beginning of the project will clear up any unexpected issues before they arise. A meeting will be held with staff, during which our proprietary client communication program is started and the following typical items are discussed:
y Introduce staff and project partners to the design consulting team. y Review objectives of the project, scope of services, deliverable expectations, project schedule, and milestones. y Confirm project parameters and limits of work. (Conduct a site review and photo document site conditions.) y Collect available data and published material (GIS data, aerial photography, right-of-way maps, as-built plans, and record maps).
y Establish meeting and presentation schedules and communication channels with all parties involved. y Review and list all applicable design/planning standards, opportunities, and/or challenges anticipated. y Coordinate with agency departments, other agencies, and stakeholders. y Review project budget and billing requirements.
y Complete custom client communications program.

1.2 Progress Meetings
After each submittal and subsequent staff review period, a progress meeting with the design team will be held. An agenda will be prepared prior to, and minutes will be provided after, each meeting. It is anticipated that there will be a progress meeting each month during the design period and ideally held at the following stages:
y Following the Basis of Design Report submittal
y Following the 30%, 60%, 90%, and 100% PS&E submittals

1.3 Management
Management of all project design aspects will be covered by the team. The following will be provided:
y A comprehensive design schedule
y Monthly progress update meetings and minutes
y Correspondence between City, Modesto Irrigation District (MID), and design team y Management of the consultant team quality control measures

1.4 Site Visits
y Perform site reconnaissance visits to evaluate site conditions and identify potential conflicts and design challenges. y Meet with City, MID, and design team on-site to review and discuss potential conflicts and design challenges.

Deliverables
y Meeting agendas and Minutes in PDF format
y Customized Client Communication Program in PDF format y Preliminary project schedule with critical path milestones in Microsoft Project and PDF format y Monthly progress reports and invoices
Task 2: Site Analysis/Data Collection & Review
Research objectives will include a detailed review of project history and existing park site information including topographic surveys and soil studies. A site visit will be conducted and site photographs will be taken.

2.1 Contextual Analysis
Analyze existing elements within the proposed site to guide design. Items including but not limited to prevailing winds, soil type, local demographics, utilities, and so forth will be reviewed.

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2.2 Topographic Survey Base Mapping
Surveying services in support of this project will include topographic surveying of the existing site. The topographic survey data will be collected using the City’s existing horizontal and vertical survey control and benchmarks. All information will be collected with the input and collaboration of both internal and external subconsultant specialty disciplines to guarantee a focused, but well-rounded product that rises to meet the needs of each of the project’s objectives. y Perform cross-section survey of linear corridor at 50-foot intervals. y Perform topographic survey of all hardscape and softscape, including grade breaks, high points, and low points. In flat areas, measure spot elevations in a grid pattern at 50-foot intervals. y Locate surface-visible utility features and improvements, including but not limited to signs, fences, walls, buildings, striping, driveways, walkways, drainages, structures, lights, poles, bollards, general limits of vegetated or landscaped areas, USA markings, vaults, valves, meters, boxes, pedestals, cleanouts, manholes, drain inlets, catch basins, culverts, outfalls, and standpipes.
y All trees 6” in diameter or larger will be located.
y At manholes and accessible structures, measure invert elevation of all gravity storm drains and sewer pipes. Annotate topographic survey drawing with invert elevation, approximate diameter, and orientation of each pipe visible at the time of the survey. Where access is not practical, Westwood shall indicate by notation on the mapping deliverable. y Create existing ground Civil 3D TIN surface model.
y Prepare topographic map at a 1” = 20’ scale.

2.3 Resolved Boundary
Having a resolved boundary will provide definitive information that can be used to make precise determinations about the subject property, including matters including but not limited to gross/net parcel area, setbacks, encroachments, etc.

It is a critical part of the planning and design process because it brings clarity to the often uncertain nature of property boundaries, easements, and road rights-of-way, which rarely lie exactly where they are presumed to. A resolved boundary is also essential if improvements are being built close to property lines or near setback minimums. y Resolve the location of property boundaries, road rights-of-way, and easements as defined by an analysis of available record maps, title report(s), supporting documents, and physical evidence. y Reset missing or damaged property corner monuments as required.

2.4 Utility Investigation & Coordination
A comprehensive utility investigation will be completed to determine what utilities are available, their locations, and utility depth within the project limits of work. Available as-built and original design drawings will be reviewed, utility request letters will be sent to all applicable utility companies, and site investigation will be used to make determinations. We will work with utilities as necessary to prepare the site for construction efforts. Where feasible, utilities infrastructure will be installed and or relocated prior to beginning construction.

Deliverables
y Topographic survey base map drawing in AutoCAD Civil 3D 2023 format y Resolved boundary linework drawing in AutoCAD Civil 3D 2023 format y Site plan of topographic survey in PDF format
Task 3: Design Development

3.1 Preliminary Site Plan Development
Following site analysis efforts, the design team will prepare two concept plans illustrating alternative designs for the park. The preliminary site plan will be developed to reflect the guidelines for the dual-use basin park as outlined in the Tivoli Specific Plan. After the designs have been presented to the City for review and comment, a final rendered master plan will be prepared for inclusion in the Basis of Design Report. In addition, a preliminary layout of new sewer mains and connections will be prepared based on the location of proposed street improvements and other utilities. This is a crucial step to limit revisions later in the process and to avoid inefficient uses of time and resources. This site plan will be drawn with actual topographic data, to scale, and will be a rendered drawing depicting all proposed park features and amenities.

3.2 Basis of Design Report
In conjunction with the preliminary site plan, the primary purpose of the Basis of Design report is to convey the design intent early in the design process. This report will help identify, clarify, and simplify any major design decisions early. It will Project Understanding and Approach
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be developed with a mix of communication styles including visual and written, and will include tables and charts. Typical information in the report might include:
y Contextual information for the project site
y Conceptual plans to illustrate design concepts and alternatives y Enlargements of the special areas within the park
y Discussions of maintenance requirements and potential life cycle costs y Renderings and sections to convey design intent in a three-dimensional manner y Sample imagery of site furnishings and features, plant types, and irrigation methods y Planning level construction cost estimates

3.3 Design Development Drawings (30% PS&E)
The Design Development Drawing package includes drawings to convey general engineering and design concepts. This service will include the following preliminary plan sheets at a minimum:
y Cover sheet and project information
y Site plan
y General and project specific notes
y Existing conditions plan
y Grading, drainage, and utilities plan
y Plan and profile sheets
y Site finishes and furnishings plans
y Irrigation plans
y Planting plan
y Electrical plans
y Major construction details
y Technical specifications table of contents
Deliverables
y Rendered site plan in PDF format
y Basis of Design Report
y 30% drawings in PDF format
y 30% estimates and quantities in PDF format
y Technical specifications TOC in PDF format
y Updated project schedule with critical path milestones in Microsoft Project and PDF format Task 4: Construction Documentation

4.1 Construction Documents (PS&E)
Following the approval of a final site plan, the team will prepare final site improvement plans for permitting.

Improvement plans include routine information normally required by governing agencies. The scope of work will include three packages: 60% construction documents with draft specifications, 90% construction documents with updated specifications, and 100% documents including final specifications. This service will include the following tasks:
y Improvement Plans - Plans may include the following sheets but are subject to change as the parameters, needs, and existing conditions of the project formalize:
y Cover sheet
y General and project specific notes and conditions
y Site plan
y Existing conditions and demolition plan
y Underground utilities plan
y Plan and profile sheets
y Grading and drainage plans
y Erosion control plans
y Horizontal control plan
y Site finishes and furnishings plans
y Enlargement plans (playground, etc.)
y Irrigation plans and water use calculations
y Planting plan
y Electrical plans
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y Construction details
y Shade Structure sections and plans
y As-built drawings as appropriate for reference
y Construction quantities and estimates
y Draft & final technical specifications (City will provide boilerplate and Front-End specifications) y Draft & final stormwater pollution prevention plan (SWPPP & NPDES permit coordination)

4.2 Bid Package
Following the approval of the 100% PS&E drawings, the team will prepare a final bid package. The bid package will include:
y Front end documents (provided by the City)
y Stamped and signed cover sheet
y Bid forms
y Bid item descriptions
y Final stamped and signed PS&E
y Final stamped and signed technical specifications booklet y Final cut sheets for important features and materials y Geotechnical Report
Deliverables
y Final Geotechnical Report in PDF format
y 60%, 90%, & 100% drawings in PDF format
y 60%, 90%, & 100% estimates and quantities in PDF format y Technical specifications TOC in PDF format
y 60% & 90% updated project schedule with critical path milestones in Microsoft Project and PDF format y SWPPP document in PDF format
y Final bid package in PDF and AutoCAD
Task 5: Specialized Technical Services
Westwood will provide specialized technical services to ensure that the basin meets City, State, and Federal requirements. These services include preparing comprehensive basin calculations and geotechnical investigations to evaluate subsurface soil conditions.

5.1 Basin Calculations
The Westwood team will conduct comprehensive basin calculations to evaluate stormwater management requirements for the project area. These calculations will assist with the following:
y Development of a model to estimate stormwater generation based on local rainfall patterns and land use characteristics. y Designing systems for stormwater detention and retention and assessing percolation rates for infiltration systems. y Creating a hydrological model to simulate water flow and evaluate various stormwater management strategies.

5.2 Geotechnical Investigation
The geotechnical investigation will occur early in the design process to ensure that the team has the information needed to make recommendations early and aid in preparing accurate cost estimates throughout the design process. y To characterize the subsurface conditions and obtain soil samples for laboratory testing, six (6) soil borings throughout the proposed park of varying depths will be drilled.
y An Engineer/Geologist will direct the sampling and log the borings. The samples will be delivered to the laboratory for evaluation and testing. Field penetration tests will be used to evaluate relative density, strength, and compression characteristics of native soils. The borings will be backfilled according to the City/County permit requirements. y Following the completion of subsurface exploration, percolation testing will be conducted in support of the park basin.

Borehole percolation tests will be performed to measure infiltration/percolation rates boring logs. It is anticipated that these tests will occur in five (5) locations.
y Laboratory tests will be performed on representative soil samples obtained from the exploratory borings, which may include unit weight, moisture content, sieve analysis, Atterberg Limits, direct shear, soluble sulfate and soluble chloride contents, pH and minimum resistivity, R-Value, and landscape suitability. y Engineering analysis will be prepared and a Geotechnical Report containing the following (but not limited to):
y Project description
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y Summary of subsurface exploration and subsurface conditions y Infiltration rates
y Laboratory test results
y CBC seismic design parameters for structures (non-site specific) y Summary of groundwater conditions encountered and potential impact on design and construction y Foundation recommendations for structures
y Recommendations for over-excavation of unsuitable soils y Recommendations for grading and construction
y Recommendations to aid in the design of slabs-on-grade and exterior concrete hardscape y Pavement section recommendations
y Site Plan with current boring and infiltration/percolation test locations y Boring logs with laboratory test results
Deliverables
y Basin calculation report summarizing findings and methodologies. y Stormwater generation model with peak flow rates and volume calculations. y Design calculations and specifications for detention and retention systems, including percolation assessment results. y Hydrological model report detailing the simulation results and validation against historical data. y Draft and final geotechnical investigation report.
y Operations and maintenance manual, including guidelines for routine maintenance and emergency procedures.

Task 6: Construction Support Services

6.1 Site Visits & Construction Communications
Westwood will perform construction support services throughout the project’s completion. Services include the following: (We can provide additional support as requested.) y Assist City Staff in bidding process.
y Attend pre-bid meeting.
y Respond to RFIs.
y Prepare Addenda and Transmittals (as needed).
y Attend pre-construction meeting.
y Review and approve Contractor’s schedule, shop drawings, RFIs, and submittals. y Perform site review and prepare reports on construction progress. y Prepare as-built drawings from contractor maintained field drawings. y Construction observation site visits to review site finishes, at irrigation installation phase, for plant review and approval prior to planting, during playground installation, following structural installations but prior to final surface covering, a final punch list walk, etc. Includes the following site visits:
y Site progress visits to review rough grading, site finishes (concrete, surfacing, etc.), irrigation installation, for plant review and approval prior to planting, following playground retrofits, following structural installations but prior to final surface covering
y Final project site review and report
Deliverables
y Meeting agenda and minutes in PDF format
y Bidding RFI and addenda in PDF format
y Construction progress reports in PDF format
y Construction RFI, shop drawing, and submittal responses in PDF format y As-built drawings in PDF format
Task 7: Pump Station Design

7.1 Stormwater Pump Station Design (If Required)
If it is determined during the design phase of the project that a stormwater pump station is required, Westwood can provide this service as an additional scope item. This service includes the following:
y Develop a Preliminary Design Memorandum to outline the design criteria, alternative designs, equipment specifications, operational criteria, and a recommended design approach with preliminary cost estimates. It is anticipated that this Project Understanding and Approach
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memorandum will establish the basis and consensus for the final design with an emphasis on maintenance requirements and life-cycle costs of the pump station.
y Prepare improvement plans for the pump station, force main, and discharge structures at MID Lateral 6. Improvement plans will be prepared for the “inside the fence” pump station facilities.

Deliverables
y Preliminary Design Memorandum in PDF format
y 30%, 60%, 90%, & 100% drawings in PDF format
y 30%, 60%, 90%, & 100% estimates and quantities in PDF format y Technical specifications TOC in PDF format
y Conformed plans and record drawings in PDF Format
Limitations and Understandings:
y All governmental/regulatory fees to be provided by the City. y It is assumed that building permits will be obtained by the contractor. y It is assumed that all structures will be pre-fabricated and considered deferred submittals for building permit purposes. y It is assumed that environmental planning for the project is complete and that there is no coordination needed for such planning efforts.
y Scope does not include any adjustments to City standard details. y Scope does not include any utility work within the roads. y Scope does not include utility relocation.
y Scope does not include right-of-way or easement acquisition services. y Scope does not include QSP services but can be added at client’s request. y Scope does not include construction management or inspection services. y Scope does not include traffic control plans.
y Scope does not include dust control plans.
y Scope does not include joint trench (dry utility) plans. y Scope does not include off-site utility design or coordination. y Survey deliverables will be based on the NAD83 horizontal datum and the NAVD88 vertical datum using Agency benchmarks. A survey control statement will be provided, including the location, elevation, and description of the benchmark utilized, as well as a horizontal survey coordinate table with the point number, northing, easting, and description for at least three (3) points.
y Obstructed or inaccessible areas may not be mapped.
y Scope does not include mapping of small trees, shrubs, or other minor vegetation. Utility locations will be based off of as-built drawings and information from utility departments and companies. y Scope does not include potholing, subsurface utility research, or locating. y Scope does not include boundary surveying as defined in Section 8726(c) of the Professional Land Surveyors’ Act. y Scope does not include preparation of a Record of Survey map or corner record. y Scope does not include monument preservation as defined and required by Section 8771 of the Professional Land Surveyors’ Act.
y Scope does not include public outreach or correspondence with property owners. y Scope does not include soil management report — soil fertility testing and reports (to be performed by landscape contractor after mass grading has been completed).
y Scope does not include structural engineering.
y Scope does not include environmental approvals and permitting as Environmental Impact Report is posted on City’s website for project.
y Scope assumes that plans will be based on City of Modesto Standard Specifications and Drawings and Caltrans Standard Plans and Specifications.
y This scope does not include revisions to the plans due to site plan changes, and/or significant client requested changes at 60% submittal stage or later, including revisions due to bid results or resulting value engineering efforts.

Organization Chart
The organization chart can be found in the Qualifications of Consultant Staff and Subconsultant Staff section.

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Qualifications of Consultant Staff and Subconsultant Staff Proposal of Services Tivoli Specific Area Storm Basin Design | 11 Qualifications of Consultant Staff &
Subconsultant Staff
Meet the Team!
Westwood Professional Services is honored to lead the design of this transformative project as the Prime Consultant.

Tyler Fay, PLA, a Landscape Architect and Project Manager with deep expertise in community improvement, park master planning, and sports park development, will guide the design with a focus on optimization, funding, and regional impact.

Our team of landscape architects, planners, recreation specialists, designers, ADA experts, grant coordinators, and public outreach professionals will collaborate closely to deliver exceptional results. Together, our team offers unparalleled expertise in park planning across Northern California, ensuring that the Tivoli Specific Area Detention Basin will enhance recreation opportunities, reflect community needs, and promote long-term sustainability.

Chad
Kennedy,
PLA
Tyler Fay,
PLA
Yasmine
Cordova
Scott
Roberts,
PLS
Mike
Persak, PE
Doug
Mutcher,
PE
Jeff M.

Black, PE
Stephen
Plauson,
GE
Role
Principal-inCharge
Project
Manager/
Landscape
Architecture
Lead
Assistant
Project
Manager
Lead
Surveyor Lead Civil Electrical Pump Lead Lead Geotechnical License
Landscape
Architect No.
5426, CA;
LEED AP;
ISA Certified
Landscape
Architect No.
6049, CA
N/A
PLS No.
9235, CA;
FAA Remote
Pilot
Registered
Civil Engineer
No. 44908,
CA
Registered
Electrical
Engineer No.
20135, CA
Registered
Professional
Engineer No.
66645, CA
Registered
Civil Engineer
No. 61926,
CA
Education
MS,
Landscape
Architecture,
Utah State
BS,
Landscape
Architecture,
Ball State
University
BS,
Landscape
Architecture,
UC Davis
BS,
Geomatics
Engineering,
Fresno State
BS, Civil Eng.,
Cal Poly
BS, Electrical
Engineering,
University of
North Dakota
MS, Civil
Engineering,
University of
Utah
BS, Civil
Engineering,
Fresno State
Firm Exp
20 Years
4 Years
5 Years
10 Years
12 Years
12 Years
12 Years
6 Years
Industry
Exp
23 Years
14 Years
5 Years
14 Years
39 Years
25 Years
21 Years
29 Years
Local
Exp
       
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Qualifications of Consultant Staff and Subconsultant Staff 12 | City of Modesto

EXPERIENCE
23+ Years in the Landscape
Architecture Industry
20+ Years with Westwood

EDUCATION
Master of Landscape
Architecture, Utah State
University
BS, Horticulture, Brigham Young
University

REGISTRATIONS
Landscape Architect No. 5426,
CA
LEEDAP
ISA Certified Arborist
NRPA Certified Playground
Safety Inspector

PROFESSIONAL AFFILIATIONS
American Society of Landscape
Architects: Past Chair, Council of
Professional Practice Networks
California Parks and Recreation
Society
Chad Kennedy, PLA
Principal-in-Charge
Chad is passionate about creating customized community recreation and assessment plans. He has supported communities such as North Highlands, Ceres, Hollister, Stockton, Lathrop, Stanislaus County, and Calaveras County, among others, to develop, refine, and utilize amazing planning documents. In every project he completes, his design is focused on positively impacting the community through innovative, sustainable, and inclusive design principles. He is a pioneer in the field of socially inclusive design and has created inclusive play spaces throughout the world.

TIVOLI WELL LANDSCAPE PLANS: MODESTO, CA
Chad served as Project Manager for this project, which included complete landscape improvement plans, technical specifications, and construction phase services for the Tivoli well site in Modesto, CA, located at Sylvan Avenue and Litt Road. Plans submitted to the City included project information, water efficient landscape worksheet with hydrozone tables and water budget calculations, soil management chart, irrigation design plans, planting design plans, construction details, and cost opinion.

NEEL PARK DUAL-USE BASIN: CERES, CA
Westwood provided visioning documents through construction documentation for this neighborhood stormwater retention basin dual-use municipal park in the City of Ceres. The park included the addition of a large playground area with multiple play structures, picnic facilities, a basketball court, outdoor exercise equipment, additional grass open space, shade structures, site lighting, a .6-acre fenced off-leash dog park, and a parking lot with ADA accessible parking stalls and pathways. Westwood assisted the City with preparing materials for grant applications. Following award of grant monies, the Westwood team developed construction documentation and assisted the City with bidding and construction management. Chad served as Principal-in-Charge.

MARY E. GROGAN PARK PHASE 2: MODESTO, CA
Mary E. Grogan Park is a 43-acre master planned community park in northeast Modesto.

Phase 2 is a 17-acre continuation of the updated master plan for the park. The project includes rough grading and stormwater pollution prevention; ADA concrete pathways; a multi-use open turf area of additional soccer fields, cricket, and team sports; a playground; picnic pavilions with picnic tables and group BBQs; a pre-fabricated restroom; security lighting and cameras; landscape and irrigation for drainage swales; an automatic irrigation system with central control; utility connections; drinking fountains; site furnishings and signage; entry signage and plaza; flag and flag poles; and parking lot improvements. Chad is serving as Principal-in-Charge.

CÉSAR E. CHAVEZ PARK: MODESTO, CA
César E. Chavez Park is a 6.25-acre City-owned park located in the heart of a diverse urban community in West Modesto. The park renovation includes an aquatic center, a building expansion, a skate plaza, sports fields, basketball courts, playgrounds, a picnic pavilion, and outdoor fitness station areas. Chad is serving as Principal-in-Charge.

VALLEY CHILDREN’S HOSPITAL PARK: MADERA, CA
Chad served as Principal-in-Charge for this project, which included utilizing an existing master plan to develop this recreation space. It included a complete amphitheater with stage, concrete pathways, a multi-use sports field, site lighting, upgraded parking, an automatic irrigation system with central control, utility connections, drinking fountains, site furnishings, and signage.

ADDITIONAL EXPERIENCE
y The Awesome Spot Socially Inclusive
Playground: Modesto, CA
y Centennial Park: Madera, CA
y South Tower Park: Fresno, CA
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Qualifications of Consultant Staff and Subconsultant Staff Proposal of Services Tivoli Specific Area Storm Basin Design | 13

EXPERIENCE
14+ Years in the Landscape
Architecture Industry
4+ Years with Westwood

EDUCATION
BS, Landscape Architecture, Ball
State University

REGISTRATION
Landscape Architect No. 6049,
CA
Tyler Fay, PLA
Project Manager/Landscape Architecture Lead
Tyler is passionate about creating spaces that provide recreational opportunities to deserving communities. He has supported parks throughout Northern California, many of which have included dual-use basins, trails, sports fields, picnic areas, open spaces for community events, irrigation, and landscape improvements. He has supported park projects for Modesto, Manteca, Fresno, Merced, Ceres, Avenal, and more.

DUAL-USE BASIN PARKS: MANTECA, CA
Tyler served as Project Manager for seven dual-use basin parks in the City of Manteca.

He supported the projects from conceptual plans to construction documents for these new basin neighborhood parks. Amenities included sports courts/fields, walking trails, playgrounds, picnic areas, and exercise stations.

MARY E. GROGAN PARK PHASE 2: MODESTO, CA
Mary E. Grogan Park is a 43-acre master planned community park in northeast Modesto.

Phase 2 is a 17-acre continuation of the updated master plan for the park. The project includes rough grading and stormwater pollution prevention; ADA concrete pathways; a multi-use open turf area of additional soccer fields, cricket, and team sports; a playground; picnic pavilions with picnic tables and group BBQs; a pre-fabricated restroom; security lighting and cameras; landscape and irrigation for drainage swales; an automatic irrigation system with central control; utility connections; drinking fountains; site furnishings and signage; entry signage and plaza; flag and flag poles; and parking lot improvements. Chad is serving as Landscape Architect.

THE AWESOME SPOT PLAYGROUND: MODESTO, CA
The Awesome Spot Socially Inclusive Playground brings research based sensory integration, technologically advanced, socially inclusive, and physically accessible play to the heart of California’s Central Valley. This playground exceeds standard “accessible” play. In addition to exceeding ADA standards, it serves as an opportunity for community members of all ages and all abilities (physical, sensory, or cognitive) to play and interact easily and effectively. The Westwood team performed the site topographic investigation, designed the play space, created the sponsorship packet, was involved in fundraising efforts, maintains the website, managed the funding, and has run every public outreach meeting for this project all on a pro-bono basis. Tyler served as Landscape Architect.

BRIDGING HORIZONS INCLUSIVE PARK (PROP 68): VISALIA, CA Westwood is currently supporting the City of Visalia with the development of Bridging Horizons Inclusive Park. Funded by the Prop 68 program, this park project will improve the open space acreage to population ratio and provide local residents with additional access to both open space and recreational amenities. The playground and pedestrian circulation system is designed to be inclusive for all community members, with no limitations regarding accessibility. The park’s Sequoia Grove playground, River Bottom Water Play Zone, sensory wall, and lawns provide extensive spinning, sliding, rocking, sensory engagement, and respite opportunities for people of all abilities and ages.

The park will also provide substantial shade and green areas, and a community stage.

Westwood previously supported the City of Visalia with their Prop 68 grant application including the park master plan, community outreach, and cost estimating. Tyler is serving as Assistant Project Manager.

ADDITIONAL EXPERIENCE
y Community Park 42: Merced, CA
y South Tower Park: Fresno, CA
y San Pablo Park: Fresno, CA
y Ted C. Willis Park: Fresno, CA
y Cannery Park: Stockton, CA
y Riverway Park: Visalia, CA
y Patterson Sports Complex: Patterson,
CA
y Islanders Field: Lathrop, CA
y Champions Field: Lathrop, CA
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Qualifications of Consultant Staff and Subconsultant Staff 14 | City of Modesto

EXPERIENCE
5+ Years in the Landscape
Architecture Industry
5+ Years with Westwood

EDUCATION
BS, Landscape Architecture,
University of California, Davis
Yasmine Cordova
Assistant Project Manager
Yasmine is dedicated to creating fun, intriguing, and interactive play spaces for all to enjoy. She has supported the outreach and design of inclusive play spaces and parks. Her park experience includes features such as trails, sports fields, picnic areas, open spaces for community events, irrigation, and landscape improvements, lighting, and more.

EMPOWERMENT PARK: SACRAMENTO, CA
Yasmine is serving as Landscape Designer. Westwood provided Prop 68 Grant assistance to the Sacramento Parks Foundation in 2019. The Westwood team developed a master plan, an outreach program (Placemaking through Play) to maximize grant points, and the actual grant package submitted to the State of California. The project was awarded $6.28M in Prop 68 funds, and the Westwood team is currently providing design and construction services for the park.

COMMUNITY PARK 42: MERCED, CA
The Westwood team is supporting this ARPA-funded park in Merced, CA. Phase 1 will proceed through bid documents and includes two natural turf athletic fields, on-site parking, a concession building, sports courts, walking paths, site furnishings, a stormwater basin, and park landscaping. Yasmine is serving as Landscape Designer.

SMYRNA PARK: CERES, CA
The Westwood team led this project, which included the renovation of existing walkways, ramps and ingress routed for ADA compliance, renovation of sanitary sewer lines, and the addition of an approximately 520 s.f. restroom. The restroom is a pre-engineered building built to withstand vandals but maintain aesthetic appeal. The structure is constructed from entirely non-flammable materials and is fully equipped with secure plumbing, vandal resistant stainless steel fixtures, industrial strength doors, metal trusses, concrete siding, a rock facade, and electrical lighting. Yasmine served as Landscape Designer.

PLAY STRUCTURE IMPROVEMENTS (12): FRESNO, CA
The Westwood team is renovating 12 parks for the City of Fresno concurrently.

Improvements include ADA accessibility, replacing or repairing play equipment, and adding new amenities such as splash pads, exercise equipment, shade structures, benches, fencing, and concrete. Westwood is providing civil engineering, landscape architecture, and land surveying to support these renovations. For each of the 12 playgrounds, a slope study was created. These heat maps highlight out of compliance sections of pathways that need improvement through color mapping imagery. Yasmine is serving as Landscape Designer.

MILBURN OVERLOOK: FRESNO, CA
Westwood is currently supporting the City of Fresno with the reconstruction of the existing Milburn Overlook. The scope includes the removal of the existing parking lot, concrete drive approach, removal of unhealthy trees, and removal of existing trellis.

New trellis, binoculars, benches, picnic tables, site lighting, fencing, accessible paths of travel, landscaping, and irrigation will be designed. The Westwood team is providing environmental compliance, public outreach, schematic design, design development, construction documentation, permitting, bidding support, and construction support.

Yasmine is serving as Landscape Designer.

ADDITIONAL EXPERIENCE
y Eastside Community Park: Kerman,
CA
y Northeast Neighborhood Park:

Turlock, CA
y River Islands High School Football
Field: Lathrop, CA
y Youth Baseball Complex: Patterson,
CA
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Qualifications of Consultant Staff and Subconsultant Staff Proposal of Services Tivoli Specific Area Storm Basin Design | 15

EXPERIENCE
14+ Years in the Land Surveying
Industry
10+ Years with Westwood

EDUCATION
BS, Geomatics Engineering,
Fresno State University

REGISTRATIONS
Land Surveyor No. 9235, CA
sUAS Remote Pilot
Scott Roberts, PLS
Land Surveying Manager
Scott brings extensive land surveying experience in health care, master planning, and largescale development projects, with a strong background in both public and private sector work. Scott’s technical proficiency includes AutoCAD Civil 3D, Trimble GNSS & Robotic TS, Trimble Business Center, Trimble RealWorks, and Terrestrial LiDAR, allowing him to execute precise topographic and boundary surveys, underground utility locating, construction staking, and GIS mapping.

TIVOLI NEIGHBORHOOD MASTER PLAN: MODESTO, CA
This 454-acre master plan village area is located in the northeastern region of the City of Modesto. This project has a Specific Plan that was approved in 2008 and updated in 2016. Scott has provided technical survey oversight of multiple private development projects and a sewer trunk project in the Tivoli specific plan area, including design level topographic survey base mapping and boundary resolution to support the engineering design of backbone infrastructure, grading, and subdivision design from feasibility through construction, as well as subdivision mapping, support for easement dedications, and construction staking. Work for all projects was coordinated so that they shared a common reference frame and control network that was tied to the City of Modesto horizontal and vertical control systems, making for the seamless expansion and integration of other public and private datasets.

VALLEY CHILDREN’S HOSPITAL PARK: MADERA, CA
Scott served as Project Surveyor for this project, which included utilizing an existing master plan to develop this recreation space. It included a complete amphitheater with stage, concrete pathways, a multi-use sports field, site lighting, upgraded parking, an automatic irrigation system with central control, utility connections, drinking fountains, site furnishings, and signage.

THE AWESOME SPOT PLAYGROUND: MODESTO, CA
The Awesome Spot Socially Inclusive Playground brings research based sensory integration, technologically advanced, socially inclusive, and physically accessible play to the heart of California’s Central Valley. This playground exceeds standard “accessible” play. In addition to exceeding ADA standards, it serves as an opportunity for community members of all ages and all abilities (physical, sensory, or cognitive) to play and interact easily and effectively. The Westwood team performed the site topographic investigation, designed the play space, created the sponsorship packet, was involved in fundraising efforts, maintains the website, managed the funding, and has run every public outreach meeting for this project all on a pro-bono basis. Scott served as Project Surveyor.

NEEL PARK PLAYGROUND: CERES, CA
Westwood was involved from early concept and visioning through construction administration and playground safety inspections on this neighborhood park. Scott supported the design and completed constructions inspections. The project included a large playground area with multiple play structures, picnic facilities, a basketball court, outdoor exercise equipment, open turf play space, shade structures, site lighting, a dog park, pathways, and parking. The playground and additional amenities were thoughtfully prepared with socially inclusive principals as a core design strategy. Scott served as Project Surveyor.

ADDITIONAL EXPERIENCE
y Bridging Horizons Inclusive Park: Visalia,
CA
y Earlimart Neighborhood Park: Earlimart,
CA
y Hoover Park: Redwood City, CA
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Qualifications of Consultant Staff and Subconsultant Staff 16 | City of Modesto

EXPERIENCE
39+ Years in the Civil
Engineering Industry
12+ Years with Westwood

EDUCATION
BS, Civil Engineering, California
Polytechnic State University,
San Luis Obispo

REGISTRATIONS
Civil Engineer No. 44908, CA
QSD/QSP No. 23311, CA
Mike Persak, PE
Lead Civil Engineer
Mike brings extensive experience in civil engineering design, infrastructure master planning, and project management, making him a valuable asset to this project. His expertise spans grading, street improvements, utilities design, cost estimating, and permit acquisition.

With a strong track record in Modesto, Mike has played a key role in numerous local infrastructure and improvement projects, providing engineering solutions for roadways, utilities, site development, and public facilities.

TIVOLI NEIGHBORHOOD MASTER PLAN: MODESTO, CA
This 454-acre master plan village area is located in the northeastern region of the City of Modesto. This project has a Specific Plan that was approved in 2008 and updated in 2016. The project includes various density residential areas, commercial parcels, professional office space, and public uses (parks and open space). Work included detailed planning, as well as infrastructure analysis. Westwood’s is currently working on six developments within Tivoli, totaling approximately 257 acres. We have also designed the Sonoma Sewer Trunk, Phases 3 and 4a for the City, which runs through the project area, and are about to start the design of the Phase 4b portion of the sewer trunk. Our responsibilities included: land planning, infrastructure concept development, boundary and topographic survey, infrastructure master planning, interim storm basin design, civil engineering design, landscape architecture design, joint trench (dry utilities) design, and interface with existing infrastructure. Mike served as project manager for the six developments within Tivoli, as well as the Sonoma Sewer Trunk.

CÉSAR E. CHAVEZ PARK: MODESTO, CA
César E. Chavez Park is a 6.25-acre City-owned park located in the heart of a diverse urban community in West Modesto. The park renovation includes an aquatic center, a building expansion, a skate plaza, sports fields, basketball courts, playgrounds, a picnic pavilion, and outdoor fitness station areas. Mike is serving as Civil Project Manager.

NEEL PARK DOG PARK: CERES, CA
Mike served as Lead Civil Engineer for the master plan and construction documentation for Neel Park, which included a dog park, in the City of Ceres. The plan included development of an inclusive playground and active recreation components on one-half of the park, and a .6-acre off-leash dog park including separate fenced areas for large and small dogs, shade, seating, and a small parking lot with ADA accessible parking and paths on the other half of the park.

EQUINOA PARK: STOCKTON, CA
Mike served as Project Manager/Engineer for this 10-acre project in Stockton, CA.

The project included a tennis court, basketball court, baseball field, tot lot, walkways, lighting, and a water booster pump station. Responsibilities included site grading design, utilities design, and coordination with the landscape architect, City, and developer.

ADDITIONAL EXPERIENCE
y Amtrak Station North Parking Lot:

Modesto, CA
y Northeast Corporation Yard: Modesto,
CA
y County Corporation Yard Security
Wall: Modesto, CA
y Sparkles Auto & Pet Wash: Modesto, CA
y Kiernan Business Park: Modesto, CA
y Sports Park: Patterson, CA
y Skate Park: Patterson, CA
y Dog Park: Patterson, CA
y Strengthen & Replace Water System
Highway Village: Modesto, CA
y Ladd Road and St. John Road Intersection
Safety Improvement: Modesto, CA
y Crows Landing/Whitmore Water Main
Extension: Ceres, CA
y Sutter Trunk Rehabilitation: Modesto, CA
y Downtown Master Plan: Modesto, CA
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Qualifications of Consultant Staff and Subconsultant Staff Proposal of Services Tivoli Specific Area Storm Basin Design | 17

EXPERIENCE
35+ Years in the Electrical
Engineering Industry
12+ Years with Westwood

EDUCATION
BS, Electrical Engineering,
University of North Dakota

REGISTRATION
Professional Electrical Engineer,
No. 20135, CA
Doug Mutcher, EE
Electrical Engineer
Doug brings extensive electrical engineering expertise to improvement projects, including parks. His diverse background spans multiple industries, such as renewable energy generation, EV charging infrastructure, transportation, campus environments, industrial and commercial facilities, educational institutions, corporate settings, data centers, medical facilities, retail spaces, and manufacturing plants. This wide-ranging experience allows him to deliver innovative and reliable electrical solutions tailored to the unique needs of each project.

CONFIDENTIAL EV FLEET CHARGING FACILITY: CALIFORNIA
Westwood provided the preliminary development design for a large-scale EV charging facility in California with solar canopies and backup generators. Doug served as Lead Electrical Engineer.

PARKS, RECREATION & OPEN SPACE MASTER PLAN: WILLOW PARK, TX The City of Willow Park never had a Parks, Trails, Recreation and Open Space Master Plan. The Westwood team collaborated with City staff in the master planning process at three primary levels: master planning at a parks system-wide level, concept site planning for trails, parks and recreational opportunities, and general evaluation of operational/ maintenance planning. The project included forming a steering committee as the foundation of engaging stakeholders and guiding the framework of the master plan.

The group was comprised of diverse members which included elected and appointed members of City Council, as well as boards and commissions of the city. A city-wide survey of the citizens was preformed to integrate their thoughts and opinions into the master plan. The steering committee also extensively participated in discussions and supplemented our findings with important input during the planning process. Doug served as Lead Electrical Engineer.

RE TRANQUILITY AND TRANQUILITY 8 SOLAR PROJECTS: FRESNO COUNTY, CA Final design for (2) 200MWac linear axis tracking photovoltaic solar plant in Fresno County, CA. Project responsibilities included PV plant layout utilizing multiple wattage PV modules, PVsyst production modeling used for project performance guarantees, medium voltage underground collection design coordinated with project Substation Engineer, BOS equipment specification, electrical engineering, coordination of security/tracker/ monitoring systems, and production verification. Doug served as Lead Electrical Engineer.

BEAUMONT ENERGY STORAGE PROJECT: CALIFORNIA
Engineer of Record final design for a 100MWac / 457MWh AC coupled energy storage facility located in Riverside County, CA. At Beginning of Life, the BESS facility features (124) 4-hour battery containers and (31) PCS enclosures. The design accounted for augmentation to allow for a future addition of (32) 4-hour battery containers and (8) PCS enclosures. Project services include project management, electrical engineering design, and construction support services. The design services included scopes, i.e., MVac collection, auxiliary power, LV DC, and grounding. Doug served as Lead Electrical Engineer.

ADDITIONAL EXPERIENCE
y Sanborn-Edwards Solar + Energy
Storage Project: California
y Canyon Country Energy Storage
Project: California
y LAX Airport Rental Car Facility: Los
Angeles, CA
y Wurzbach Parkway and Traffic
Support: San Antonio, TX
y ATW Microgrid Projects: Appleton,
WI
y Ables Springs Solar + Energy Storage
Project: Texas
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Qualifications of Consultant Staff and Subconsultant Staff 18 | City of Modesto

EXPERIENCE
21+ Years in the Industry
12+ Years with Black Water

EDUCATION
MS, Civil Engineering, University
of Utah
BS, Civil/Environmental

REGISTRATIONS
Registered Professional
Engineer No. 66645, CA
Registered Professional
Engineer No. 136672, TX

AFFILIATIONS
Water Environment Federation
(WEF)
California Water Environment
Association (CWEA)
American Society of Civil
Engineers (ASCE)
Jeff M. Black, PE
Pump Lead
Jeff Black has over 30 years of experience in public water and wastewater systems.

Jeff’s thorough understanding of the construction and operation of hydraulic systems is a valuable benefit to his clients and the operators of these facilities. Throughout his career, he has actively participated in planning, design, permitting, and construction oversight of various public and private water, wastewater, and water resources projects, pipe lines, pump stations, and treatment works. He is proficient in all aspects of project management, design, water and wastewater engineering, and system modeling.

INDUSTRIAL TANK 13 AND BOOSTER PUMPING STATION: MODESTO, CA Project Manager for the preliminary and final design of a 4.0-mg pre-stressed concrete reservoir and 12-mgd booster pumping station. The preliminary design included a life-cycle cost analysis of various tank materials and construction methods. The facility includes a pump station control building, piping and connections to the City distribution system, disinfection equipment, surge control, and standby power facilities.

COLORADO WATER MAIN PROJECT: CITY OF MODESTO, CA
Project Manager. Provided engineering, design, bid assistance, and engineering services during construction for a new water main line in Colorado Avenue. The water main provides water service to the lots fronting Colorado Avenue and connects to existing water mains along the alignment.

GALAS WATER IMPROVEMENTS: MODESTO, CA
Engineering design and specifications for a new domestic well, a 2.5-mgd water booster station, and 1.4 mg of water storage to serve the City of Modesto. Design included site work, pump station, reservoirs, disinfection system, and appurtenant piping and site work for connection to a treatment system for the removal of nitrates and manganese.

SMYRNA WELL AND PUMP STATION PROJECT: CERES, CA
Project Manager responsible for the design of a new well site and pumping station.

The project involved extensive coordination with the City staff, hydro geologist, and engineering team to provide a site assessment, test well, production well, and site design. The ultimate design included two wells each capable of producing 1,000 gpm.

Other improvements included chlorination facilities, site piping to allow the isolation and blending of each well, standby power, and integration with the City’s SCADA system.

CERES RIVER BLUFF RESERVOIR AND PUMPING FACILITY: CITY OF CERES, CA Project Manager. This project includes civil design modifications for an existing City well, connections to the future surface water delivery and distribution systems, design of pumping facilities, and a new water storage tank.

LAUREL AVENUE BOOSTER PUMP STATION, TWAIN HARTE COMMUNITY SERVICES DISTRICT: TWAIN HARTE, CA
Project Manager. Conducted a detail inspection to determine the most effective option to provide adequate domestic water pressure and flow to the residents of Cedar Pine Avenue.

ADDITIONAL EXPERIENCE
y OID Parks Irrigation Project: City of
Oakdale, CA
y Reynolds Ranch Water Storage Tank
Project: City of Lodi, CA
y Well #14: City of Patterson, CA
y Thornton Water System and Storage
Facility Project, San Joaquin County:

Thornton, CA
y Meadow Well Pumping Plant & Main
Extension, Twain Harte Community
Services District: Twain Harte, CA
y Water Distribution and Storage
System: Diablo Grande, CA
y Cedar Pines Tank and Booster
Pumping Station: Twain Harte, CA
y On-Call Water Analyses: Tracy, CA
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Qualifications of Consultant Staff and Subconsultant Staff Proposal of Services Tivoli Specific Area Storm Basin Design | 19

EXPERIENCE
29+ Years in the Geotechnical
Engineering Industry
6+ Years with Kleinfelder

EDUCATION
BS, Civil Engineering, Fresno
State University

REGISTRATIONS
Registered Civil Engineer No.
61926, CA
Registered Geotechnical
Engineer No. 2731, CA
Stephen Plauson, PE, GE
Lead Geotechnical Engineer
Stephen’s project experience includes highways, bridges, flexible and rigid pavements, commercial and industrial developments, schools and hospitals, pipelines, tanks, treatment facilities, power facilities, and forensic studies. He is responsible for managing and conducting geotechnical investigations including site reconnaissance, field classification of soils, sampling, design and report preparation, and review. He performs field inspections and testing, data analysis, laboratory testing, and construction special inspections.

MCNAMARA PARK: MERCED, CA
Stephen served as Principal Geotechnical Engineer for this project involving a new park facility. The improvements included two artificial turf soccer fields, one natural turf soccer field, field lighting, a new restroom, a playground, splash pad, relocation of an existing memorial, and a new raised pavilion. Project challenges included expansive soils and potential heaving of the synthetic fields due to increased moisture in the subgrade below synthetic turf due to interruption of natural vapor transmission.

Kleinfelder provided a geotechnical investigation report to support the design of the park improvements, synthetic fields, and associated site improvements.

TRUNK SEWER AND PRINCE ROAD SEWER LINE PROJECT: NEWMAN, CA Stephen served as Project Manager and Lead Geotechnical Engineer for the preparation of a Geotechnical Investigation Report for the design of approximately 2 miles of new 36-inch diameter trunk sewer line and 2,100 lineal feet of new 12-inch diameter sewer line.

FRIANT KERN CANAL TURNOUT STRUCTURE & PUMPING PLANT: KERN COUNTY, CA
Stephen served as the Project Manager and Lead Geotechnical Engineer for the preparation of a Geotechnical Investigation Report for the design of new turnout structure and pumping plant for Cawelo Water District. The improvements included a reinforced concrete turn out, 60-inch diameter pipeline, and connection to the pump station wet well and pump structure. Recommendations were provided for temporary excavations including soil type and shoring.

WATER TRANSMISSION LINE PROJECT: WINTON, CA
Stephen served as the Project Manager and Lead Geotechnical Engineer for the preparation of a Geotechnical Investigation Report for the design of approximately 16,000 lineal feet of new 18-inch diameter PVC water line. The design included recommendations for jack and bore crossings at four (4) canals with comments on trench stability, temporary slopes, shoring parameters, thrust blocks, and friction along the pipe.

YETTEM-SEVILLE WATER SYSTEM IMPROVEMENTS: TULARE COUNTY, CA Stephen served as the Project Manager and Lead Geotechnical Engineer for the preparation of a Geotechnical Investigation Report for the design of an approximately

1.7-mile-long interconnection water pipeline between the Yettem and Seville communities. The project was necessary to solve water deficiencies by sharing resources between the communities. Additionally, the project included well site improvements involving transformer, electrical panel, and stand-by generator. Water system improvements also included a new 200,000-gallon water storage tank supported on a reinforced concrete ringwall footing.

ADDITIONAL EXPERIENCE
y Lacey Boulevard Widening/
Realignment and Roundabout at SR
43: Hanford, CA
y Martin Ray Reilly Park: Fresno, CA
y East Side Regional Park: Visalia, CA
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Qualifications of Consultant Staff and Subconsultant Staff 20 | City of Modesto
Tyler Fay, PLA
(Project Manager/Lead
Landscape Architect)
Organizational Chart
Assistant Project Manager
Yasmine Cordova
City of
Modesto
Chad Kennedy,
PLA
(Principalin-Charge)
Land Surveying
Scott Roberts, PLS (Lead)
Additional Internal
Services
California Westwood Resources
National Westwood Resources
Subconsultants
Subconsultants
Electrical
Doug Mutcher, EE
Geotechnical
Stephen Plauson, PE (Kleinfelder)
Pump Lead
Jeff M. Black, PE (Black Water)
Civil Engineering
Mike Persak, PE (Lead)
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Qualifications of Consultant Staff and Subconsultant Staff Proposal of Services Tivoli Specific Area Storm Basin Design | 21 Team Introduction
We are proud to partner with the trusted team shown below to ensure every aspect of this planning effort is carefully considered. Each identified subconsultant had deep ties to the Westwood team, a passion for community improvement projects, and the availability and responsiveness needed to support this project in a timely manner. We will work together as a cohesive team led by Tyler Fay to design the best plans possible for the Tivoli Specific Area Storm Basin.

Westwood
Professional Services Kleinfelder Black Water
Role
Prime Consultant Subconsultant Subconsultant
Services
Provided
Landscape Architecture,
Land Surveying, Civil
Engineering, Electrical
Engineering
Geotechnical Engineering Pump
Location
Modesto Fresno Modesto
Number of
Staff
1,900+
Team Members
47 Geotechnical/Geology
Professionals
20 Team Members
Firm
Experience
52 Years
60 Years
13 Years
Modesto
Experience
  
Westwood Project
Experience
N/A
Fresno Dickey Park, Ceres
Moffett Road Rehabilitation,
Visalia Riverway Sports
Park, HSIP Cycle 11 Hanford,
Stockton Cannery Park,
Modesto Sutter Trunk
Rehabilitation, Modesto
Tivoli Storm, Modesto SR132
West Freeway, Fresno E Street
Complete Streets
Ceres Lift Station Modification,
Stevinson Hagaman Park
Restrooms, River Islands in
Lathrop
Percentage of
Fee
55% 8% 37%
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Experience of Firm
Proposal of Services Tivoli Specific Area Storm Basin Design | 23 Experience of Firm
We Love Recreation!
Established in 1972, Westwood is a full service, multi-discipline professional design firm providing services to public and private clients. With over 1,900 staff located across the United States and registrations in most states, Westwood is recognized as one of the top design and engineering firms in the country. Westwood provides quality professional landscape architecture, planning, public outreach, civil engineering, structural engineering, traffic engineering, electrical engineering, land surveying, roundabout design, and environmental planning services to support public improvement projects. In 2024, O’Dell Engineering merged with Westwood Professional Services.

O’Dell had provided public improvement services in California since 1994, including landscape architecture, civil engineering, and land surveying. The Westwood California team currently employs over 95 professionals with offices in Fresno, Merced, Modesto, and Pleasanton.

We support California districts, agencies, and communities with park planning and design services, including system-wide parks master plans, public outreach, inclusive play, and much more! Our Purpose Is Play!
Westwood is passionate about creating recreational amenities that make a difference in the lives of our community members. We partner with public agencies to deliver amazing landscape design and landscape consulting services, including parks, playgrounds, dog parks, trails, athletic fields, aquatics facilities, skate parks, streetscapes, and more. We support public agencies with planning, design, engineering, surveying, and drafting. Our projects range from concepts to construction administration. We support new infrastructure, upgrades, and aesthetic improvements. We also provide plan review services, arborist reviews, and landscape inspection on a regular basis.

A New Take on Public Outreach
We’ve all seen it: boring community outreach that results in less than ideal results. Our team understands how absolutely critical outreach is, especially in park renovations and additions. We create customized outreach approaches that guarantee results. Our fun and innovative approach to outreach gets all different types of community members to contribute in ways that feel comfortable to them. With methods such as online polling, social media interaction, interactive events (indoor and outdoor), and much more, we aim to make our public outreach as fun and interactive as possible. We believe this leads to more authentic responses, a deeper and more thoughtful evaluation of public perspectives, and designs that best represent the community’s desires.

Meet Our
California Team!
30 Number of
Years
in California
Type of Organization
Corporation
8,000+
Acres of Master
Planned Parks
Space
95+ Total California
Staff
9 Licensed
Landscape
Architects
9 Licensed
Land
Surveyors
9 Licensed
Civil
Engineers
6 Certified
QSDs/
QSPs
3 Certified
Playground
Safety
Inspectors
2 ISA
Certified
Arborists
7 LEED
Accredited
Professionals
1 Qualified
Water
Efficient
Landscaper
1 ReScape
Qualified
Professional
800+
Acres of
Designed Parks
Space
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Experience of Firm
24 | City of Modesto
Tivoli Neighborhood Master Plan
Modesto, CA
y Civil Engineering
y Landscape Architecture
y Joint Trench (Dry Utilities)
Design
y Land Planning
y Infrastructure Concept
Development
y Boundary & Topographic Survey
y Infrastructure Master Planning
y Interim Storm Basin Design
y Interface with Existing
Infrastructure
y 454-acre Master Plan Village
Area
y Residential Areas
y Commercial Parcels
y Professional Office Space
y Parks and Open Spaces
Project Features
y Status: Current Project
y Cost: $1,013,623
y Key Staff Involved: Mike Persak,
Scott Roberts
Project Details
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Experience of Firm
Proposal of Services Tivoli Specific Area Storm Basin Design | 25 Mary E. Grogan Park Phase 2
Modesto, CA
y Civil Engineering
y Landscape Architecture
y Land Surveying
y 43-Acre Master Planned
Community Park
y 17-Acre Phase 2 Continuation
y Master Planned Space
y Grading & Drainage
y ADA Pathways
y Plazas
y Multi-Use Open Turf Area of
Additional Soccer Fields
y Cricket
y Team Sports
y Playground
y Picnic Pavilion
y Restroom
y Security Lighting/Cameras
y Drainage Swales
y Automatic Irrigation System
with Central Control
y Drinking Fountains
y Site Furnishings/Signage
y Entry Signage/Plaza
y Flag/Flag Poles
y Parking Lot Improvements
y Master Planning
y Design Development
y Construction Documentation
y Construction Support Services
Project Features
y Status: Under Construction
y Cost: $211,603
y Key Staff Involved: Chad
Kennedy, Tyler Fay, Yasmine
Cordova, Scott Roberts, Mike
Persak
Project Details
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Experience of Firm
26 | City of Modesto
César E. Chavez Park
Modesto, CA
y Civil Engineering
y Landscape Architecture
y Land Surveying
y 6.25 Acres
y Park Renovation
y Low-Income/Underserved
Community
y Crime Prevention
y Aquatic Center
y Community Center Expansion
y Skate Plaza
y Sports Fields
y Basketball Courts
y Playgrounds
y Picnic Pavilion
y Outdoor Fitness Stations
y Landscape Design
y Irrigation Design
y Lighting
y Grading & Drainage
y Refined Master Plan
y Design Development
y Construction Documentation
y Construction Support Services
Project Features
y Status: Under Construction
y Cost: $800,801
y Key Staff Involved: Chad
Kennedy, Tyler Fay, Yasmine
Cordova, Scott Roberts, Mike
Persak
Project Details
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Experience of Firm
Proposal of Services Tivoli Specific Area Storm Basin Design | 27 Valley Children’s Hospital Park
Madera, CA
y Shade Structures
y Amphitheater/Stage
y Open Play
y Field Play
y Walking Path
y Lighting
y Grading & Drainage
y Design Development
y Construction Documentation
y Construction Support Services
y Electrical Engineering
Project Features
y Status: Constructed
y Cost: $1M
y Key Staff Involved: Chad
Kennedy, Tyler Fay, Yasmine
Cordova, Scott Roberts
Project Details
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Experience of Firm
28 | City of Modesto
City of Fresno
[email protected]
559.621.5300
Nathan Sanchez, Projects Administrator
Sacramento Parks Foundation
[email protected]
916.927.3802
Mike Grace, Executive Director
City of Modesto
[email protected]
209.571.5526
Nathan Houx, Parks Planning & Devel.

City of Stockton
[email protected]
Victor Machado, Program Specialist
City of Los Banos
[email protected]
209.827.7034
Joe Heim, Parks & Operations Manager
Livermore Area Recreation and Park District
925.373.5711
Fred Halderman, Parks & Facilities
City of Tracy
[email protected]
209.456.8615
Michael Rosales, Landscape Architect
Cordova Recreation and Park District
[email protected]
916.842.3300 ext. 3319
Laura Taylor, Park Planning & Devel. Mgr.

City of Tracy
[email protected]
209.831.6235
Richard Joaquin, Park Planning & Devel. Mgr.

City of Ceres
[email protected]
209.538.5617
Samir (Sam) Royal, Associate Engineer
References
The following references have worked closely with the Westwood team in projects similar to this one. These professionals have extensive experience collaborating with our identified key staff, including Tyler Fay, to ensure effective coordination and successful project outcomes.
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westwoodps.com
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CITY OF MODESTO

COMMITTEE AGENDA REPORT
DATE OF MEETING:

August 4, 2025
Date: July 16, 2025
TO: Economic Development Committee
Eric Alvarez, Chair
Sue Zwahlen, Vice-Chair
Nick Bavaro, Member
THROUGH: Joseph P. Lopez, City Manager
FROM: Toby Wells, Director of Engineering Services/City Engineer SUBJECT: 2025 Guidance Manual for Development Stormwater Quality Control Measures CONTACT: Jaspreet Mangat, Senior Civil Engineer, [email protected], 209-577-5253
DESCRIPTION:

Consider a 2025 Guidance Manual for Development Stormwater Quality Control Manual and forwarding to Council for approval. (Funding Source: Stormwater Fund) STRATEGIC PLAN ELEMENT:

The recommended action supports the City’s 2025-2026 Strategic Goal D to provide safe, efficient, and reliable infrastructure through proactive community investment, maintenance, and sustainability efforts.

BACKGROUND:

In 1972, the Federal Clean Water Act (CWA) was amended to prohibit discharge of pollutants to water of the United States from any point source, unless the discharge is in compliance with a National Pollutant Discharge Elimination System (NPDES) permit. In 1990, Phase I regulations promulgated, required metropolitan areas with population greater than one hundred thousand to obtain an NPDES permit for stormwater discharges.

In 1993, the City established a Stormwater Program to address urban runoff from the greater Modesto area. This program was created in response to new federal laws and regulations governing stormwater discharges from municipal storm systems (MS4).

In 1994, the Central Valley Regional Water Quality Control Board (RWQCB) issued the City’s first National Discharge Elimination Stormwater Permit (Order No. 94-163). City was required to develop and implement Development Standards that require source and treatment control Best Management Practices (BMPs) to reduce pollutants from the new development and #6..
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2025 Guidance Manual for Development Stormwater Quality Control Measures

redevelopment areas. To address this requirement, City developed the Guidance Manual for New Development Stormwater Quality Control measures.

The RWQCB subsequently reissued this permit in 2002, and then in 2008 (Order No. R5-2008- 0092) to address the effectiveness of the program and a strong emphasis to encourage and incorporate low impact development (LID) measures into public and private projects. As a result, the 2011 Revised Guidance Manual was approved by the City Council on August 7, 2013, which was last revised in 2015.

In 2016, (RWQCB) adopted the regionwide municipal stormwater NPDES permit (Order No. 2016-0040) in June 2016 which emphasizes LID implementation strategies for new development and redevelopment project. Also in 2015, The Statewide Trash Amendments which require the implementation of trash full capture systems or equivalent trash control measures in certain land use areas.

DISCUSSION:

The 2025 Guidance Manual for Development Stormwater Quality Control is an update to the 2011 Development Guidance Manual.

The 2025 Modesto Stormwater Guidance Manual introduces several key updates and policy shifts compared to the 2011 version. The updated manual aligns with the Regionwide NPDES Permit (Order R5-2016-0040) and incorporates the Statewide Trash Amendments, requiring trash full capture systems for specific land use categories. The new version refines project classifications by adding “Priority Land Use” (PLU) projects and clarifying exclusions for minor or routine developments. The manual separates Low Impact Development (LID) strategies into two categories: Volume Retention Measures (VRMs) and LID-based Treatment Measures, each with dedicated design and sizing guidance. It also expands on hydromodification requirements, offering clear exemptions and alternatives for on-site retention. The 2025 manual reorganizes content for clarity, adds new BMPs like infiltration vaults and porous pavement filters, and streamlines integration with the City’s flood control design standards, providing more comprehensive and enforceable development guidance.

The 2025 Modesto Stormwater Guidance Manual was shared with developers, consultants, and other key stakeholders during the update process. Feedback was actively solicited through meetings, review periods, and written comments. Input received from these groups was carefully considered, and several suggested revisions were incorporated to improve clarity, technical feasibility, and alignment with real-world development practices. This collaborative approach helped ensure the manual reflects both regulatory requirements and practical implementation needs.

Upon Council approval, the updated 2025 Guidance Manual will be formally implemented and applicable to all qualifying projects effective September 1, 2025.

FISCAL IMPACT:

There is no fiscal impact to the City as a result of this action. The improved manual is expected to be slightly less costly for the development process. However, the activities detailed in this Guidance Manual may slightly increase expenses to the Storm Drain Fund for oversight of the implemented measures. The fee programs associated inspection and related fees are under #6..
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Economic Development Committee, August 4, 2025
2025 Guidance Manual for Development Stormwater Quality Control Measures

review to ensure adequate coverage the costs associated with the oversight of the required treatment measures.

RECOMMENDED COMMITTEE ACTION:

Staff Recommendations:

Motion recommending a 2025 Guidance Manual for Development Stormwater Quality Control Manual and forwarding to Council for approval.

Approved by:

Toby Wells, Director of Engineering Services/City
Engineer
Joseph P. Lopez, City Manager
Attachments:

1. 2025 Guidance Manual for Development Stormwater Quality Control Manual #6..
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MAY 2025

CITY OF MODESTO
Guidance Manual for Development Stormwater Quality
Control Measures
PREPARED BY:

PREPARED FOR :
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Development Guidance Manual i May 2025

TABLE OF CONTENTS
Section Page

1. INTRODUCTION 1-1

1.1 Purpose & Goals…………………………………….……………………………....................................... 1-1

1.2 Overviews…………………………………………..…………………………………………………………….…..…. 1-2

1.2.1 Hydromodification Requirements…………………………………………………………….….….. 1-2

1.3 Low Impact Development Strategies……………..……………………………………………………..….. 1-3

1.4 Low Impact Development Strategies and the Stormwater Quality Control Criteria Plan: Key Concepts……………………………………………….…………………………………………………… 1-5

1.5 Trash Control Requirements...…………………………………………………………………………………… 1-6

1.6 Flood Control Requirements…………………………………………….………………………………………. 1-6

1.7 Implementation Schedule……………………………………………………..………………………………….. 1-7

2. STORMWATER MANAGEMENT STANDARDS FOR NEW DEVELOPMENT AND

SIGNIFICANT REDEVELOPMENT
2-1

2.1 Process to Comply with City and County Standards…………………………………………………… 2-1

3. SITE ASSESSMENT 3-1

3.1 Assessing Site Conditions and Other Constraints…………………………………………...………… 3-1

3.1.1 Project Location……………………………………………………………………………………………….. 3-1

3.1.2 Site Conditions……………………………………………………………………………………………….… 3-2

3.2 Pollutants of Concern….………………………………………………………………..…………………….….. 3-4

4. SOURCE CONTROLS 4-1

4.1 Introduction……………………………………………………………………………………..……..………….……. 4-1

4.2 Description…………………………………………………………….…………………………..………………….…. 4-1

5. SOURCE CONTROL MEASURES 5-1

5.1 Introduction……………………………………………………………………………………….……………….…… 5-1

5.2 Description………………………………………………………………………………………..…………………….. 5-1

6. VOLUME RETENTION MEASURES 6-1

6.1 Introduction………………………………………………………………………………………………………. 6-1

6.2 Volume Retention Requirement……………………………………………………………………….. 6-2

6.3 Selection of Volume Retention Measures………………………………………..……………….. 6-7

7. TREATMENT CONTROL MEASURES 7-1

7.1 Introduction……………………………………………………………………………………………………… 7-1

7.2 Selection of Treatment Control Measures…………………………………………………………. 7-3

7.3 Description of Treatment Control Measures……………………………………………………… 7-5

7.4 Calculation of Water Quality Design Flow and Water Quality Design Volume…… 7-8

8. CONTROL MEASURE MAINTENANCE 8-1

8.1 Maintenance Plan……………………………………………………………………………………………… 8-1

8.2 Maintenance Agreement………………………………………………………………………………….. 8-4 #6..
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Development Guidance Manual ii May 2025

APPENDICES
Appendix A: Glossary of Terms and List of Acronyms
Appendix B: Site Design Control Measure Fact Sheets (G1-G4) Appendix C: Source Control Measure Fact Sheets (S1-S7)
Appendix D: Volume Retention Measure Fact Sheets (V1-V5) Appendix E: LID-based Treatment Control Measure Fact Sheets (L1-L11) Appendix F: Conventional Treatment Control Measure Fact Sheets (C1-C6) Appendix G: Volume Retention Requirement Worksheet
Appendix H: Volume Retention Requirement Waiver Application Appendix I: Maintenance Agreements and Forms
I-1: Stormwater Treatment Device Access and Maintenance Agreement Template I-2: SWQCP Owner’s Certification Statement
Appendix J: SWQCP and Maintenance Plan Submittal Guidance J-1: Stormwater Quality Control Plan Guidance
J-2: Stormwater Quality Control Plan Template
J-3: Stormwater Maintenance Plan Guidance
J-4: Stormwater Maintenance Plan Template
Appendix K: Hydrologic Soil Groups
Appendix L: Plants Suitable for Vegetative Control Measures Appendix M: Standard Calculations for Diversion Structure Design Appendix N: Approved Proprietary Control Measures
Appendix O: Example Calculation
Appendix P: References
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Development Guidance Manual iii May 2025

FIGURES
Figure 1-1. Pre vs. Post Project Hydrograph…………………………………………………………………….. 1-4 Figure 1-2. Hydrograph with Conventional BMPs……………………………………………………………. 1-4 Figure 1-3. Goal of LID is to Mimic Pre-Project Hydrography through Reduction in Peak Runoff Volume and Flow…………………………………………………………………………………………….…… 1-5 Figure 2-1. Process for Meeting New Development & Significant Redevelopment Stormwater Standards for PLU-Only Projects……………………………………….…………………………. 2-4 Figure 2-2. Process for Meeting New Development & Significant Redevelopment Stormwater Standards for Priority Projects ………………………………………………....................... 2-5 Figure 2-3. Stockton Urbanized Area ………………………………………………………………………………. 2-7 Figure 2-4. City SWQCP Review Process Flowchart …………………………………………………………. 2-14 Figure 2-5. County SWQCP Review Process Flowchart…………………………………………………….. 2-15 Figure 4-1. Storm Drain Message Location………………………………………………………………………. 4-4 Figure 5-1a. Suggested Applications of Runoff VRMs ……………………………………………………… 5-2 Figure 5-1b. Suggested Applications of Runoff VRMs………………………………………………………. 5-3 Figure 5-2. Rain Garden …………………………………………………………………………………………….……. 5-11 Figure 5-3. Rain Barrel Schematic …………………………………………………………………………………... 5-13 Figure 5-4. Importance Of Forest and Trees in Sustaining Water Supply and Rainfall………. 5-15 Figure 6-1. Unit Basin Storage Volume vs. Weighted Runoff Coefficient…………….…………..… 6-12 Figure 6-2a. Bioretention Schematic………………………………………………………............................ 6-20 Figure 6-2b. Bioretention Schematic………………………………………………………………………………… 6-20 Figure 6-3. Infiltration Stormwater Planter Configuration………………………………………………… 6-27 Figure 6-4. Flow-through Stormwater Planter Configuration. "Stormwater Planters."……… 6-27 Figure 6-5. Tree-well Filter Schematic……………………………………………………............................ 6-34 Figure 6-6. Water Quality Infiltration Basin………………………………………………………………......... 6-36 Figure 6-7. Infiltration Trench……………………………………………………………………………………….….. 6-48 Figure 6-8. Infiltration Vault. Adapted from NAHB………………………………………………………….… 6-49 Figure 6-9. Leach Field…………………………………………………………………….................................... 6-49 Figure 6-10. Porous Pavement Filter………………………………………………………………………………… 6-56 Figure 6-11. Vegetated Swale…………………………………………………………………………………………... 6-65 Figure 6-12. Vegetated Street Swale with Underdrain…………………………………….................... 6-66 Figure 6-13. Grassy Swale…………………………………………………………………………………………………. 6-74 Figure 6-14. Grassy Filter Strip………………………………………………………………………………………….. 6-80 Figure 6-15. Conceptual Layout of Constructed Wetland…………………………………………………. 6-83 Figure 6-16. Extended Detention Basin Conceptual Layout………………………………................. 6-92 #6..
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Development Guidance Manual iv May 2025
Figure 6-17. Perforated Pipe Outlet Structure………………………………………………………………….. 6-99 Figure 6-18. Orifice Plate Outlet Configuration…………………………………………………………………. 6-100 Figure 6-19. Conceptual Layout of Wet Pond……………………………………………………………………. 6-106 Figure 6-20. Depth Zones for Wet Pond……………………………………………………………………………. 6-111 Figure 6-21. Outlet Works for Wet Pond…………………………………………………………………………… 6-111 TABLES
Table 2-1. Priority Project and PLU Project Categories and Associated Pollutants of Concern…………………………………………………………………………………….......................................... 2-6 Table 2-2. Control Measure Selection Matrix for New Development and Significant Redevelopment Project Categories…………………………………………………………………………………… 2-12 Table 2-3. Control Measure Selection Matrix for Meeting Low Impact Development and Treatment Requirements…………………………………………………………………………………………………. 2-13 Table 4-1. Summary of Source Control Design Features………………………………….................... 4-2 Table 5-1. Summary of Volume retention and LID Treatment Controls…….………................ 5-1 Table 5-2. Site Constraints for VRMs…………………………………………………….………………………….. 5-6 Table 5-3. Rain Garden Design Criteria…………………………………………………………………………….. 5-8 Table 5-4. Rain Garden Volume and Tributary Impervious Area Credit Calculation………….. 5-9 Table 5-5. Rain Barrel/Cistern Volume and Tributary Impervious Area Credit Calculation… 5-14 Table 5-6. Inspection and Maintenance Requirements for Rain Barrels and Cisterns……….. 5-14 Table 5-7. Interception Tree Volume and Impervious Area Credit Calculation………………….. 5-16 Table 5-8. Inspection and Maintenance Requirements for Interception Trees……………....... 5-17 Table 5-9. Grassy Channel Design Criteria and Reference Values……………………………………… 5-19 Table 5-10. Grassy Channel Volume and Tributary Impervious Area Credit Calculation……. 5-21 Table 5-11. Vegetated Buffer Strips Design Criteria and Reference Values……………………….. 5-26 Table 5-12. Vegetated Buffer Strip Volume and Impervious Area Credit Calculation………… 5-28 Table 6-1. LID Treatment Controls and Conventional Treatment Controls……………….......... 6-2 Table 6-2. Efficiency of Treatment Controls for Reduction of Pollutants of Concern……...... 6-3 Table 6-3. Site Constraints for Treatment Controls…………………………………………………………… 6-6 Table 6-4. Sizing Criteria for Treatment Controls………………………………………………………………. 6-7 Table 6-5. Values of Runoff Coefficients for Typical Site Elements……………………………………. 6-8 Table 6-6. Example Calculation Table for Weighted Runoff Coefficient…………………………….. 6-9 Table 6-7. Example Calculation Table for Effective Tributary Area……………………………………. 6-9 Table 6-8. Bioretention Design Criteria…………………………………………………………………………….. 6-15 Table 6-9. Bioretention Volume retention Calculation……………………………………………………. 6-18 Table 6-10. Inspection and Maintenance Requirements for Bioretention Areas………………. 6-19 Table 6-11. Stormwater Planter Design Criteria……………………………………………………………….. 6-23 Table 6-12. Stormwater Planter Volume Retention Calculation……………………………………….. 6-25 #6..
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Development Guidance Manual v May 2025
Table 6-13. Inspection and Maintenance Requirements for Stormwater Planters……………. 6-26 Table 6-14. Tree-well Filter Design Criteria……………………………………………….......................... 6-30 Table 6-15. Tree-well Filter Volume retention Calculation…………………………………….….…..…. 6-32 Table 6-16. Inspection and Maintenance Requirements for Tree-well Filters………..……….… 6-33 Table 6-17. Water Quality Infiltration Basin Design Criteria……………………………………...……… 6-37 Table 6-18. Inspection and Maintenance Requirements for Water Quality Infiltration Basins………………………………………………………………………………………………………………………………. 6-41
Table 6-19. Infiltration Trench Design Criteria………………………………………………………………….. 6-44 Table 6-20. Geotextile Fabric Specifications……………………………………………………………………… 6-44 Table 6-21. Inspection and Maintenance Requirements for Infiltration Trenches…………….. 6-51 Table 6-22. PPF Design Criteria…………………………………………………………………………………………. 6-54 Table 6-23. PPF Volume retention Calculation………………………………………………………………..… 6-55 Table 6-24. Inspection and Maintenance Requirements for PPF………………………………………. 6-57 Table 6-25. Vegetated Swale and Vegetated Street Swale Design Criteria………………………… 6-60 Table 6-26. Vegetated Swale Volume Retention Calculation…………………………………………….. 6-63 Table 6-27. Inspection and Maintenance Requirements for Vegetated Swales………………… 6-64 Table 6-28. Grassy Swale Design Criteria………………………………………………………………………….. 6-69 Table 6-29. Grassy Swale Volume Retention Calculation………………………………………………….. 6-72 Table 6-30. Inspection and Maintenance Requirements for Grassy Swales……………….……... 6-73 Table 6-31. Grassy Filter Strip Design Criteria…………………………………………………………………… 6-76 Table 6-32. Grassy Filter Strip Volume Retention Calculation……………………………………….... 6-78 Table 6-33. Inspection and Maintenance Requirements for Grassy Filter Strips…………....... 6-79 Table 6-34. Constructed Wetland Basin Design Criteria……………………………………………………. 6-84 Table 6-35. Inspection and Maintenance Requirements for Constructed Wetland Basins… 6-89 Table 6-36. Extended Detention Basin Design Criteria……………………………………………………… 6-93 Table 6-37. Non-woven Geotextile Fabric Specifications………………………………………………….. 6-97 Table 6-38. Inspection and Maintenance Requirements for Extended Detention Basins….. 6-102 Table 6-39. Wet Pond Design Criteria………………………………………………………………………………. 6-105 Table 6-40. Inspection and Maintenance Requirements for Wet Ponds…………………………… 6-112 Table 6-41. Example Inspection and Maintenance Requirements for Trash Capture Devices…………………………………………………………………………………………………………………………….. 6-117 #6..
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Development Guidance Manual 1-1 May 2025

1. INTRODUCTION

1.1 PURPOSE & GOALS
The 2025 Guidance Manual for Development Stormwater Quality Control Measures (2025 Development Guidance Manual or Guidance Manual) for the City of Modesto (City) is an update to the 2011 Development Guidance Manual (last revised in 2015). The 2025 update aligns the Development Guidance Manual with:
1) The municipal stormwater National Pollutant Discharge Elimination System (NPDES) permit (Order R5-2016-00401; Regionwide Permit) requirements, which emphasizes low impact development (LID) implementation strategies for new development and redevelopment projects (adopted in 2016); and
2) The Statewide Trash Amendments, which require the implementation of trash full capture systems (FCS) or equivalent trash control measures in certain land use areas (adopted in 2015).

The Guidance Manual and requirements contained herein are applicable to both private and public parcel-based projects and is a "living document", which will be periodically updated to reflect new information, findings, and experience. The overarching goal of the Guidance Manual is to minimize the potential long-term impacts on receiving water quality from new development and redevelopment projects2 and to streamline the water quality-based design standards with the City’s storage-based design standards (Section 1.4).

The Manual has been prepared to achieve the following:
 Protect water resources within the City’s jurisdiction from the potential adverse impacts associated with runoff from development projects;
 Implement development design standards consistent with the City’s municipal stormwater permit and other State requirements, including trash control;  Integrate and streamline the City’s water quality-based development standards with the storage-based development standards;
 Emphasize the implementation of low-impact development (LID)-based strategies;  Provide clear development standards for developers, engineers, and planners to use in the selection and implementation of appropriate control measures; and  Provide maintenance procedures to ensure that the selected control measures will be maintained to provide effective, long-term pollution control.

Section 2 of the Manual identifies what requirements apply to which types of projects. A list of the key terms and acronyms used within the Guidance Manual is provided in Appendix A. 1 The Central Valley Regional Water Quality Control Board (Regional Water Board) adopted a Regionwide municipal stormwater NPDES Permit (Regionwide Permit; Order No. R5-2016-0040) in June 2016. https://www.waterboards.ca.gov/centralvalley/water_issues/storm_water/municipal_permits/#regwidepermit 2 The City first developed the Development Guidance Manual in January 2001 as required by Order No. 94-163. The 2001 Guidance Manual was updated in 2011 to ensure that it was consistent with Order No. R5-2008-0092. #6..
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Development Guidance Manual 1-2 May 2025

1.1.1 Hydromodification Requirements
The Regionwide Permit requires the development of a Hydromodification Plan to mitigate the potential impacts of stormwater runoff flows on and within receiving waters. However, Priority Projects may be exempt from the implementation of hydromodification controls where “assessments of downstream channel conditions and proposed discharge hydrology indicate that adverse hydromodification effects to beneficial users of natural drainage systems are unlikely.”
Example types of projects that may be exempted include, but are not limited to the following:
1) Redevelopment Projects (e.g., infill) that do not increase the effective impervious area or decrease the infiltration capacity of pervious areas compared to the pre-project conditions.
2) Projects that have any increased discharge directly or via a storm drain to a sump, drainage pump station, lake, area under tidal influence, or into a waterway (e.g., perennial river) that is not susceptible to hydromodification impacts. 3) Projects that discharge directly or via a storm drain into concrete or otherwise engineered (not natural) channels (e.g., channelized or armored with rip rap, shotcrete, concrete lined, etc.), which, in turn, discharge into a receiving water that is not susceptible to hydromodification impacts.

As is described in additional detail in Section 1.4 and Figure 2-1, the City requires new development and most redevelopment projects to retain the stormwater onsite, which protects the receiving waters from potential hydromodification impacts. Alternatively, development projects may be required to discharge into centralized retention or detention basins. These detention basins then typically discharge into engineered channels. As such, the City is exempt from requiring additional hydromodification controls for development projects and is not developing a corresponding Hydromodification Management Plan. 3 However, this Development Guidance Manual emphasizes the broader concept of LID, which works to replicate pre-project hydrology in a post-project environment through the volume reduction requirement (VRR) as well as requirements to implement best management practices (BMPs) that promote retaining rainfall on-site through infiltration, evapotranspiration, or harvest and use. These requirements will reduce or eliminate the volume of stormwater runoff from a post-project site that is discharged to the receiving water and thereby mitigate potential hydromodification impacts. In cases where the VRR cannot be fully met, the project applicant must apply alternative compliance methods for the remaining stormwater volume that is not retained on-site.

As such, the 2025 Development Guidance Manual is consistent with and meets the requirements for hydromodification within Attachment J4. 3 Page 2 of Order No. R5-2015-0024.
4 Finding 16 of the 2016 Regionwide Permit notes “Properly designed, installed, and maintained LID measures are a primary method to address the causes of hydromodification.”
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Development Guidance Manual 1-3 May 2025

1.2 LOW-IMPACT DEVELOPMENT STRATEGIES
Stormwater management has historically consisted of a network of impervious surfaces (e.g., rooftops, walkways, driveways, parking lots, and roads) connected to a storm drain system that was designed to quickly convey stormwater off-site to prevent flooding and protect life and property. Dozens of studies have documented the impacts of connected impervious cover on the natural hydrologic cycle (CWP, 2003). In a natural setting, most rainfall is either infiltrated into the soil or lost to evapotranspiration. However, with urbanization, pervious surfaces (such as forests and meadows) are converted into impervious surfaces such that the rainfall is conveyed off-site. This leads to an increase in the volume and flow of stormwater runoff to downstream water bodies (Figure 1-1). If not managed correctly, this increased stormwater runoff may adversely impact local water bodies.

Figure 1-1. Pre vs. Post Project Hydrograph. Modified from Source: Haltiner, Jeffrey, Philip Williams & Associates, Ltd. Hydromodification: An Introduction and Overview Presentation. (2006, May).

To mitigate these impacts, conventional BMPs (e.g. detention basins) were implemented to detain stormwater runoff by releasing the volume over a period of time (Figure 1-2).

Figure 1-2. Hydrograph with Conventional BMPs. Modified from Source: Haltiner, Jeffrey, Philip Williams & Associates, Ltd. Hydromodification: An Introduction and Overview Presentation. (2006, May).

To enhance pollutant removal and groundwater recharge benefits, LID-based strategies have been required and incorporated into an overall stormwater management approach. LID is defined as, “a stormwater management and land development strategy that emphasizes conservation and the use of on-site natural features integrated with engineered, small-scale #6..
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Development Guidance Manual 1-4 May 2025
hydrologic controls to more closely reflect pre-project hydrologic functions… LID strategies include retention practices that do not allow runoff, such as infiltration, rain-water harvesting and use, and evapotranspiration.”5
LID is a decentralized approach to stormwater management that mimics the site's natural hydrology by retaining rainfall onsite. The goal is to eliminate the shaded areas, as shown in Figure 1-3, by reducing the peak volume and flow duration through site design and volume reduction measures (VRMs). The benefits of the reduced stormwater volume include reduced pollutant loading and increased groundwater recharge and evapotranspiration rates.

Figure 1-3. Goal of LID is to Mimic Pre-Project Hydrography through Reduction in Peak Runoff Volume and Flow. Modified from Source: Haltiner, Jeffrey, Philip Williams & Associates, Ltd. Hydromodification: An Introduction and Overview Presentation. (2006, May).

Additionally, LID strategies can decrease the cost associated with stormwater management and treatment by reducing the number of materials needed for pavement, the need for curbs and gutters, and by reducing stormwater volume, which will correspond to smaller flood-control structures.

1.3 TRASH CONTROL REQUIREMENTS
On April 7, 2015, the State Water Resources Control Board (State Water Board) adopted an Amendment to the Water Quality Control Plan for Ocean Waters of California to Control Trash and Part 1 Trash Provision of the Water Quality Control Plan for Inland Surface Waters, Enclosed Bays, and Estuaries. Together, they are collectively referred to as “the Trash Amendments.”
The Trash Amendments require agencies with regulatory authority over priority land uses (PLUs) to comply with the prohibition of trash discharge to receiving waters. As defined in the Statewide Trash Amendments, PLU areas include high-density residential, industrial, commercial, mixed urban, and public transportation stations (Section 2). As such, development and redevelopment projects within these PLU categories will be required to implement trash full capture controls (Section 7).

In addition to the State Water Board requirements, the City Engineer may mandate the installation of trash full capture controls at facilities that will be dedicated to the City for 5 2016 Regionwide Permit, Attachment C.
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Development Guidance Manual 1-5 May 2025
maintenance. The specific location of these devices will be determined based on the project design, ensuring ease of maintenance activities.

1.4 FLOOD CONTROL DESIGN STANDARDS
This Development Guidance Manual is intended to assist project proponents understand how to apply the City’s stormwater quality-based requirements to new and redevelopment projects.

Although not a part of this manual, it is important to understand how the City’s flood control design standards (which are focused on storage) also apply to development projects.

The City’s Standard Specifications details the multiple criteria for drainage system design (collection, conveyance, storage/disposal) within the City6. Any discussion or references to the flood control requirements within this Guidance Manual is provided to assist project proponents in understanding how the flood control and stormwater quality-based requirements are applied. However, this Guidance Manual is not intended to provide flood control design criteria. The City Engineer shall be the final authority for all questions that may arise as to the interpretation of this Guidance Manual and City Standard Specifications. Appeals of the City Engineer’s decisions may be made to the City Council.

For the purposes of the Flood Control Design Standards:
• Greenfield New Development is considered to be development of buildings or other facilities on undeveloped land with no existing structures or infrastructure. • Infill Development is considered to be development of buildings or other facilities on land located within the City’s existing developed area. Infill development can consist of unused or underutilized land, redevelopment, or new development.

All new development and redevelopment projects are required to provide collection, conveyance and storage/disposal as required by the current City Standard Specifications and stormwater quality-based controls as required by this Guidance Manual.

For infill development, the parcel(s) being improved may currently or have previously been served by the City’s stormwater collection system. If the proposed project improvements will be generating more flows than preexisting, it is the project proponent’s responsibility to demonstrate adequacy of existing improvements (including downstream conveyance and storage/disposal) or store and dispose of all on-site drainage on-site with an approved method.

Infill projects in areas without positive gravity storm drainage system shall utilize horizontal drains for street right-of-way and all on-site drainage shall be stored and disposed of on-site with an approved method.

Once the City’s Standard Specifications requirements for stormwater collection, conveyance and storage/disposal have been met, the project proponent must also ensure that the stormwater quality-based requirements detailed within this Development Guidance are also met, as applicable. If the Volume Reduction Requirements are met through the City Standard Specifications by retaining all the stormwater on site, then the project(s) will not need to meet the VRR as specified within this Guidance Manual. Where this is not the case, the projects will 6 Refer to the current version of the City’s Standard Specifications at www.modestogov.com. #6..
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need to meet the volume retention and other requirements specified within the Guidance Document.

1.5 IMPLEMENTATION SCHEDULE
Effective September 1, 2025, the 2025 Development Guidance Manual is applicable to all Priority Projects and Priority Land Use Projects or phases of these Projects as described below:
• Tentative maps or vested tentative maps.
• Extensions of approved tentative maps or vested tentative maps. • Improvement plans approved by the City Engineer.
• Permits for development or construction issued on or after September 1, 2025. • Infill Priority Projects that require a Use Permit from the City on or after September 1, 2025.

The requirements within this Development Guidance Manual do not apply if approval of a tentative map or vested tentative map was “deemed complete” prior to September 1, 2025. In that case, the design standards within the 2011 Development Guidance Manual apply.
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2. STORMWATER MANAGEMENT STANDARDS FOR NEW

DEVELOPMENT AND SIGNIFICANT REDEVELOPMENT
This section provides an overview of the stormwater management standards for new development and significant redevelopment projects, the controls that are required for each type of project, and the process that must be used to identify and incorporate stormwater control measures.

The standards set forth in the Development Guidance Manual shall apply to all new development and significant redevelopment projects falling under the Priority Project and/or PLU Project categories as specified within this section. Compliance with the Manual should be discussed as early as possible in the design process. The project engineer and other design professionals (including architects) should be involved during the City’s Tentative Map stage.

If a project is being developed on a parcel(s) where a previous project was already subject to the City’s Stormwater Development Guidance Manual, it is possible that some of the stormwater control measures currently onsite may be able to be used to prevent, infiltrate, or treat stormwater from the new project. However, every project subject to this Manual must show how the required stormwater controls will be incorporated, that the requirements are met, and submit the required documentation.

In addition to the requirements prescribed within this Development Guidance Manual, development projects must also adhere to applicable drainage standards as specified in the most current City Standard Specifications (Section 1.4). In the event of a conflict between the requirements of this Guidance Manual and the City’s Standard Specifications, the City Engineer will make the determination as to which of the requirements apply and/or how to resolve the conflict.

For applicable projects, the planning permit application submittal must show how the required stormwater controls will be incorporated in the project.

2.1 EXCLUSIONS
Projects that are located outside of the City of Modesto and the following specific types of projects are not required to comply with the City’s Development Guidance Manual, however these types of project may be subject to other requirements:
a. Interior remodels and interior tenant improvements which do not include any soil disturbance.
b. Second-story additions that do not increase the building footprint or include any soil disturbance.
c. Roof repairs, exterior wall repairs and foundation repairs. d. Raised (not built directly on the ground) decks, stairs, or walkways designed with spaces to allow water drainage.
e. Vegetation and landscaping maintenance.
f. Above-ground fuel storage tanks and fuel farms with spill containment system. #6..
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g. Public and private projects only replacing curb, gutter, and drive approaches (this exception does not apply to offsite improvements associated with private development).
h. Underground utility projects that replace the ground surface with in-kind material or materials similar runoff characteristics.
i. Electrical and utility vaults, lift station wet wells, backflows and other utility devices.

Note: if these types of projects are part of a larger liner utility project (LUP) they will be subject to the Development Guidance Manual if they have a discrete location that has 5,000 square feet or more of a newly constructed contiguous impervious surfaces. j. Photovoltaic systems installed on/over existing roof or other impervious surfaces, and panels located over pervious surfaces with maintained grass or vegetated groundcover, or panel arrays with a buffer strip at the most down gradient row of panels. k. Emergency housing projects undertaken by the government agencies for people experiencing unsheltered homelessness, when those projects are constructed pursuant to and consistent with Government Code § 8698.4, including the definition of “homeless shelter” in subdivision (c), and that are temporary7. These projects must implement relevant best management practices such as provision of trash collection and sanitary sewage services. In addition, the managing entity of such housing projects assumes full responsibility for the quality and quantity of runoff from these properties.

The City Engineer reserves the right to impose the provisions of this manual on such projects, depending on factors such as project location, size, and compliance with applicable regulations.
l. Routine maintenance and repair activities that are conducted to maintain original line and grade, hydraulic capacity, or emergency construction activities required to immediately protect public health and safety. If the activity significantly disturbs the soil under the base then it is not considered routine maintenance. Examples of these types of activities include:
a. Road surface repair including crack sealing, slurry sealing, fog sealing, pavement markings/striping, potholing and square cut patching.
b. Overlaying existing asphalt or concrete pavement with asphalt or concrete with no increase in area.
c. Shoulder grading.
d. Applying pavement treatment such as chip seal or cape seal to existing asphalt or concrete pavement with no increase in area and less than 5,000 cumulative square feet of base repair.
7 Examples of temporary emergency housing include: formal “community cabin” or tent communities; RV safe parking areas; and homeless “navigation centers” with housing, that are temporary and provide housing for people experiencing unsheltered homelessness. #6..
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e. Repair and reconstruction of the road because of slope failures, natural disasters, acts of God or other man-made disaster.

The City Engineer may modify the above listed categories to provide clarity as long as it does not conflict with Section 2.2. As needed, the City Engineer will evaluate projects and provide guidelines to follow and to meet all the applicable requirements.

2.2 IDENTIFICATION OF PROJECT TYPE AND PROCESS TO COMPLY

WITH CITY STANDARDS
The steps, Figures 2-1, 2-2 and 2-3, and process outlined below will assist in determining which requirements apply to a specific project.

In general, all new development and significant redevelopment projects which are determined to be “Priority Projects” must apply all four categories of stormwater pollution controls measures, which include:
 Site Design Control Measures (Section 3)
 Source Control Measures (Section 4)
 LID-Based Volume Retention Measures (Section 5)
 Treatment Control Measures (Section 6)
In addition, all Priority Projects and PLU Projects must apply trash control measures (Section 6). #6..
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Development Guidance Manual 2-4 May 2025
Step 1: Determine Project Type and Requirements
Step 1A: Determine if the Project is New Development or Significant Redevelopment The first step is to determine if the project is categorically “new development” or “significant redevelopment” as defined below (see Figure 2-1).

A. New Development: Land disturbing activities; structural development, including construction or installation of a building or structure, creation of impervious surfaces; and land subdivision.

OR
New Development Infill: development of buildings or other facilities on undeveloped land located within the City’s existing developed area.

B. Significant Redevelopment: Land disturbing activity that results in the creation, addition, or replacement of at least 5,000 square feet of impervious surface area on an already developed site, which may include, but is not limited to the following types of projects:
• Expansion of a building footprint or addition or replacement of a structure; • Structural development including an increase in gross floor area and/or exterior construction or remodeling;
• Replacement of impervious surface that is not part of a routine maintenance activity; and
• Land disturbing activities related with structural or impervious surfaces.

Replacement of impervious surfaces includes any activity where impervious materials are removed, exposing underlying soil during construction.

Significant redevelopment does not include “routine maintenance”, which includes activities that are conducted to maintain original line and grade, hydraulic capacity, or emergency construction activities required to immediately protect public health and safety. If the activity significantly disturbs the soil under the base then it is not considered routine maintenance.

Step 1B: Determine if the Project is Priority Land Use Project, Priority Project or Both The next step is to determine if the project is, by definition:

A. A Priority Land Use (PLU) Project;
B. A Priority Project; or
C. Both a Priority Project and a PLU Project.

The types of land uses and categories of development for both types of projects are defined below.
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Development Guidance Manual 2-5 May 2025
A. PLU Projects include the following:

1. High-density residential – All land uses with at least 10 developed dwelling units per acre.

2. Industrial – Land uses where the primary activities on the developed parcels involve product manufacture, storage, or distribution (e.g., manufacturing businesses, warehouses, equipment storage lots, junkyards, wholesale businesses, distribution centers, or building material sales yards).

3. Commercial – Land uses where the primary activities on the developed parcels involve the sale or transfer of goods or services to consumers (e.g., business or professional buildings, shops, restaurants, theaters, vehicle repair shops, etc.).

4. Mixed urban – Land uses where high-density residential, industrial, and/or commercial land uses predominate collectively (i.e., are intermixed).

5. Public transportation stations – Facilities or sites where public transit agencies’ vehicles load or unload passengers or goods (e.g., bus stations and stops).

B. Priority Projects8 include the following:

1. Residential subdivision of 10 housing units or more – This category includes singlefamily homes, multi-family homes, condominiums, and apartments, as well as the related street and road paved surfaces that are used for the transportation of automobiles, trucks, motorcycles, and other vehicles (not including parking lots, see separate parking lot requirement below). A housing unit is also defined as a dwelling unit.

2. Commercial and industrial developments greater than or equal to 10,000 square feet of impervious area – This category is defined as any development on private land that is not for residential uses, where the land area for development is greater than or equal to 10,000 square feet of impervious area (not including the parking lot, see separate parking lot requirement below). The category includes but is not limited to, hospitals, laboratories and other medical facilities, office commercial, retail commercial, educational institutions), recreational facilities, commercial retail nurseries, car wash facilities, mini-malls, and other business complexes, shopping malls, hotels, office buildings, public warehouses, and other industrial facilities. 8 Priority Development Projects are defined within Attachment C of the Regionwide Permit. It should be noted that the Attachment C category “Single-family hillside residences (includes development on any natural slope that is twenty five percent or greater)” does not apply within the City’s jurisdictional area. #6..
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Development Guidance Manual 2-6 May 2025

3. Automotive repair shops – This category is defined as a facility that is categorized in any of the following Standard Industrial Classification (SIC) codes: 5013, 5014, 5541, 7532- 7534, 7536-7539, or 7549.

4. Retail gasoline outlets (RGOs) – An RGO is defined as any facility engaged in selling gasoline and lubricating oils.

5. Restaurants – This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling foods and drinks for immediate consumption (SIC code 5812), where total impervious area for development is greater than or equal to 5,000 square feet. For restaurants less than 5,000 square feet, the development must meet all development standards except for treatment control measures and numeric sizing criteria.

6. Parking lots 5,000 square feet or more or with 25 or more parking spaces and potentially exposed to urban runoff – A parking lot is defined as a land area or facility for the temporary parking or storage of motor vehicles used personally, for business, or commerce.

7. Significant redevelopment – Land disturbing activity that results in the creation, addition, or replacement of at least 5,000 square feet of impervious surface area on an already developed site, which may include, but is not limited to the following types of projects:
• Expansion of a building footprint or addition or replacement of a structure; • Structural development including an increase in gross floor area and/or exterior construction or remodeling;
• Replacement of impervious surface that is not part of a routine maintenance activity; and
• Land disturbing activities related with structural or impervious surfaces9 .

Replacement of impervious surfaces includes any activity where impervious materials are removed, exposing underlying soil during construction.

Significant redevelopment does not include “routine maintenance”10, which includes activities that are conducted to maintain original line and grade, hydraulic capacity, or emergency construction activities required to immediately protect public health and safety. If the activity significantly disturbs the soil under the base then it is not considered routine maintenance. In the case of an addition, if the addition constitutes less than 50 percent of the original development, post-construction stormwater requirements only apply to the addition.11
9 Replacement of impervious surfaces includes any activity where impervious materials are removed, exposing underlying soil during construction.
10 Routine maintenance includes activities that are conducted to maintain original line and grade and/or hydraulic capacity. If the activity significantly disturbs the soil under the base then it is not considered routine maintenance. 11 For example, if a 6,000 sq-ft addition is built for an existing 15,000 sq-ft building, post-construction stormwater requirements only apply to the 6,000 sq-ft addition.
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Development Guidance Manual 2-7 May 2025
After reviewing the PLU and Priority Project criteria above, determine if the project is:

A. A Priority Land Use (PLU) Project;
B. A Priority Project; or
C. Both a Priority Project and a PLU Project.

Table 2-1 may assist with this determination.

Table 2-1. Determination of Project Type
Type of
Development
Priority Land Use
Project
Priority Project Only OR
Priority Project AND Priority Land Use Project
Residential
High density
(10 dwelling units/acre)
Priority Project Only
Medium or Low Density (< 10 units)
Priority Land Use Project and Priority Project
High-density (10 dwelling units/acre & >10 units)
Industrial Any size Priority Land Use Project and Priority Project > 10,000 sq ft
Commercial Any size Priority Land Use Project and Priority Project > 10,000 sq ft or Auto Repair or RGO or Restaurant
Mixed Urban Any size Priority Land Use Project and Priority Project > 10,000 sq ft
Public
Transportation
Stations
Any facility or site ---
Parking Lots ---
Priority Project Only
> 5,000 sq ft or
> 25 exposed parking spaces
Significant
Redevelopment ---
Priority Project Only
Creation, addition, replacement > 5,000 sq ft
impervious surface
Step 2: Collect Site Information [Applies to PLU Projects and/or Priority Projects] If the project is a PLU and/or Priority Project, site information needs to be collected that is critical for the selection of appropriate stormwater control measures. Section 3 identifies the types of information that must be documented and submitted to the City at the onset of the application process.

Step 3: Apply Site Design Control Measures [Applies to Priority Projects] The third step is to apply the required Site Design Control Measures as specified in Table 2-2.

Site Design Controls protect sensitive environmental features such as riparian areas, wetlands and steep slopes. Development should be located on the least sensitive portion of the site.

Additionally, the project should minimize impervious cover and soil compaction. These controls #6..
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Development Guidance Manual 2-8 May 2025
will help reduce runoff volume and is the first step (and possibly the most inexpensive control measure) in meeting the VRR (see Step 5). Additional guidance on Site Design Controls can be found in Section 3. Minimizing or eliminating the use of curb and gutter so that roadway runoff drains to swales and other VRMs or LID Treatment Controls is strongly encouraged where the slope and density permit.

Step 4: Apply Source Control Measures [Applies to Priority Projects] All Priority Projects must implement applicable Source Control Measures. Source Control Measures are operational practices that prevent pollution by reducing potential pollutants at the source and/or prevent pollutants from coming into contact with stormwater runoff. The Priority Projects must implement the source control measures specified in Table 2-2. Additional Guidance on Source Control Measures can be found in Section 4.

Step 5: Apply LID-based Volume Retention Measures [Applies to Priority Projects] [As noted in Figure 2-1, if a project is required to comply with Section 1.4 of the 2025 Development Guidance Manual consistent with the City Standards by retaining all of the stormwater on site, then the Volume Reduction Requirement Calculations are not required and are considered to have been met.]
All Priority Projects must apply VRMs (Table 2-2 and 2-3). VRMs are BMPs that can direct, retain, reuse, and/or infiltrate stormwater runoff (e.g., rain gardens, rain barrels). Guidance for implementing VRMs is presented in Section 5. As a part of Step 5, projects must calculate their VRR, which drives the need for and application of VRMs.

Stormwater Quality-based Design Storm
The VRR specifies that post-project runoff volumes must match pre-project runoff volumes for the

0.50-inch storm depth, the average 85th percentile 24-hour storm depth estimated for the City’s jurisdictional area1. In other words, the VRR equals the post-project runoff volume (without VRMs) minus the pre-project runoff volume. New Development Priority Projects can combine VRMs and LID Treatment Controls (see Step 6) to meet the VRR.

Additional information on the VRR is provided in Section 5; additional information on the Flood Control Design Standards is provided in Section 1.4.

VRMs also provide treatment benefits recognized through tributary impervious area credits.

These credits can be applied to reduce the effective design area used to calculate the water quality volume (WQV) or water quality flow (WQF), which are the primary design criteria used to size Treatment Control Measures. The WQV is calculated by multiplying the effective impervious area by the unit basin volume (measured in inches). The WQF is calculated by multiplying the effective impervious area by the design rainfall intensity (measured in inches 1 The 85th percentile storm event is the event that has a precipitation total greater than or equal to 85 percent of all storm events over a given period of record in a specific area or location. For example, to determine what the 85th percentile storm event is in a specific location, all 24- hour storms that have recorded values over a 30-year period would be tabulated and a 85th percentile storm would be determined from this record (i.e., 15 percent of the storms would be greater than the number determined to be the 85th percentile storm) [Region-wide Permit pg F63]. For the City of Modesto this has been determined to be 0.5 inches. #6..
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Development Guidance Manual 2-9 May 2025
per hour). Implementation of VRMs reduces the effective impervious area and, thereby, the volume of water to be treated.

The VRM fact sheets (Section 5) detail how volume retention and tributary impervious area credits are calculated for each measure. The application of credits to determine effective area for design of Treatment Controls is described in Section 6.

Volume Retention Requirement Credit for Significant Redevelopment Significant Redevelopment Priority Projects must also comply with the VRR; however, an incentive in the form of credits may be applied based on the type of redevelopment. A maximum credit of 0.25 inch from the 0.50-inch VRR may be applied to any of the following types of redevelopment. Credits are issued in 0.05-inch increments based on five criteria:
 Significant Redevelopment (as defined in Step 1);
 Brownfield redevelopment;
 High density (>22 units per acre);
 Vertical Density (2 or more stories); or
 Mixed-use and Transit Oriented Development (within ½ mile of public transit, such as a bus stop)
Step 6: Apply Treatment Control Measures [Applies to PLU Projects and/or Priority Projects] Treatment control measures are required for all Priority Projects and PLU Projects (Table 2-2 and 2-3). Treatment controls are engineered technologies designed to remove pollutants from stormwater runoff and must be designed to treat the WQF or WQV. All Treatment Controls, except those controls specifically implemented for trash, are designed to treat the runoff from the smaller storms and the first flush of large storms, which comprise 80-85 percent of annual runoff volumes.

For trash, the following types of controls may be implemented as long as they are designed to treat the peak flow rate from a one-year, one-hour storm for the Modesto area (0.32 inches2):
 Full Capture Systems (FCS)3;
 Multi-Benefit Projects4; and
 Other Treatment Controls5.
2 This value was determined by using Basin Sizer, which is a software tool developed by Caltrans to determine what the 1-year, 1-hour storm size is for different areas within California. This information is used for the sizing of full trash capture devices. The value may be modified over time due to changing climate or other conditions. https://svctenvims.dot.ca.gov/basinsizer/ 3 Full Capture System: A treatment control, or series of treatment controls, including but not limited to, a Multi-Benefit project or a LID control that traps all particles that are 5 mm or greater and has the design treatment capacity that is either: a) of not less than the peak flow rate, Q, resulting from a one-year, one-hour storm in the sub-drainage area, or b) appropriately sized to, and designed to carry at least the same flows as the corresponding storm drain.
4 Multi-Benefit Project: A treatment control project designed to achieve any of the benefits set forth in section 10562, subdivision (d) of the Water Code.
5 Treatment Controls: Structural BMPs to either (a) remove pollutants and/or solids from stormwater runoff, wastewater, or effluent, or (b) capture, infiltrate or reuse stormwater runoff, wastewater, or effluent. Treatment Controls include FCS and LID controls. #6..
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Development Guidance Manual 2-10 May 2025
Trash controls shall be installed and maintained by the property owner for all storm drains, catch basins, or inlets located within the parcel's boundaries and operated and maintained by the property owner. Trash controls shall only be installed in storm drains, catch basins, or inlets within the Public Right of Way (RoW) if the City has agreed to enter into a maintenance agreement with the property owner.

The volume or flow in excess of the treatment design values is typically bypassed. Guidance on sizing the Treatment Controls is provided in Section 6. The selection of Treatment Controls should be based on their ability to reduce runoff volumes and remove the pollutants of concern. See Table 6-2 for the typical removal efficiency of treatment controls.

As indicated in Step 5, New Development Priority Projects must meet the VRR. If the VRR has not been met through the use of VRMs, LID Treatment Controls must be used to reduce runoff volume further to meet the Requirement. If the VRR is fully met through VRMs, then a treatment control may be chosen from the lists of LID-based Treatment Controls or Conventional Treatment Controls.

If the VRR cannot be fully met due to site constraints, see “Alternative Compliance Option” in Section 5. Priority Projects that cannot fully meet the VRR must select Treatment Controls with a medium to high removal efficiency for the pollutants of concern (Tables 2-2 and 6-2).

Guidance on Volume Retention is provided throughout the Fact Sheets provided in Sections 5 and 6.

Step 7: Select Additional Treatment Controls as Needed to Meet Treatment Requirement [Applies to Priority Projects]
If the Treatment Requirement is not entirely met through a combination of VRMs and LID Treatment Controls, the project must apply Conventional Treatment Controls to meet the requirement. Guidance on the selection and design of Conventional Treatment Controls is provided in Section 6.

Regional Stormwater Facilities
Priority Projects that discharge stormwater runoff to City-approved, regional stormwater treatment control facilities that comply with the WQV/WQF requirements are not required to provide separate treatment controls. However, such projects are required to meet the VRR and provide site design, source, and VRMs consistent with the Development Guidance Manual.

Step 8: Submit Project Stormwater Quality Control Measures Plan and Maintenance Plan [Applies to PLU Projects and/or Priority Projects]
Priority and PLU Projects are required to submit a Project Stormwater Quality Control Measures Plan (SWQCP) that adequately demonstrates that the proposed project will conform to all requirements of the Development Guidance Manual.

The SWQCP must be approved by the City prior to the issuance of building or use permits for the project. The SWQCP must be submitted in addition to any other required submittals such as a Stormwater Pollution Prevention Plan (SWPPP), which is required for all construction projects subject to the State Construction General Stormwater Permit. #6..
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Development Guidance Manual 2-11 May 2025
Project SWQCPs should conform to the content and format requirements pursuant to the Development Guidance. The City’s review and approval process is as follows:
• Receive Project SWQCP from applicant.
• Send Project SWQCP to plan reviewer.
• Send comment letter, as needed, to applicant outlining steps needed to be taken to obtain plan approval.
• Receive requested item(s) from applicant.
• Check resubmittal.
• Send second comment letter to applicant, if necessary. • Approve Project SWQCP through the City’s permitting system. • Send approved Project SWQCP to the City Environmental Compliance Section for use by inspectors.

The City also requires the submittal of a Maintenance Plan and execution of a Maintenance Agreement with the owner/operator of stormwater control measures prior to the final acceptance of a private project for projects using any of the Structural Source Controls that require maintenance (Section 4), VRMs (Section 5) and Treatment Controls (Section 6).

Maintenance Plans must include guidelines for how and when inspection and maintenance should occur for each control. Section 7 provides additional information and guidance on compliance with maintenance requirements.

Review Figures 2-1, 2-2, and 2-3 to determine what water quantity and water quality requirements apply to the project.
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Development Guidance Manual 2-12 May 2025
Figure 2-1. Determination of Project Type and Requirements #6..
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Development Guidance Manual 2-13 May 2025
Figure 2-2. Development Standards for PLU Projects
Step 2
Collect Site
Information
Step 8(1)
Submit Project Stormwater
Quality Control Plan and
Maintenance Plan
Continue Project Design
Process
Step 6(1)
Apply Trash Controls
(Section 6)
START
From Flow Chart
2-1
Note: Descriptions of the “Steps” is provided in Section 2. (1) Steps 3-5 and Step 7 do not apply to PLU projects.
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Development Guidance Manual 2-14 May 2025
Figure 2-3. Development Standards for Priority Projects and PLU/Priority Projects Step 5: Apply LID -based Volume
Reduction Measures
And Calculate Volume Reduction
Requirement
Volume
Reduction
Requirement
Met?
Step 6: Apply LID -based Treatment
Control Measures to Further Reduce
Volume and Meet WQ V/WQF
and
Apply Trash Control Measures
Volume Reduction
Requirement Met?
Step 7: Apply Additional
Treatment Controls, As Needed,
to Meet WQV/WQF
No
Yes
No

WQV/WQF
Met?
No
START
From Flow Chart
2-1
Step 3: Apply Site Design
Control Measures
Step 4: Apply Source Control
Measures
Step 8: Submit Project
Stormwater Quality Control
Plan and Maintenance Plan
Yes
Alternative Compliance Option
- Submit Volume Reduction
Waiver Form
- Identify Amount of Volume
Reduction Possible
Development Guidance
Does Not Apply
Continue Project Design
Process
No
Yes
Yes
Step 6: Apply LID -based
Treatment Controls and/or
Conventional Treatment Controls
to Meet WQ V/WQF
and
Apply Trash Control Measures
Is it a
Priority
Project?
Step 2:

Collect Site
Information
City Review
Stormwater
Quantity
Measures
Required?
Continue Project
Design Process
Provide Specific
Stormwater
Quantity Control
Measures
No
Yes
Note: Descriptions of the “Steps” is provided in Section 2. #6..
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Development Guidance Manual 2-15 May 2025
Table 2-2. Control Measure Selection Matrix for New Development and Significant Redevelopment Project Categories1 Project Category
Site Design
Control
Measures
Source Control Measures VRMs Treatment Control Measures Conserve Natural Areas (G-1)Protect Slopes and Channels (G-2)Minimize Soil Compaction (G-3)Minimize Impervious Area (G-4)Storm Drain Message and Signage (S-1)Outdoor Material Storage Area (S-2)Trash Storage and Waste Handling Area (S-3)Outdoor Loading/ Unloading Dock Area (S-4)Outdoor Repair/ Maintenance Area (S-5)Outdoor Vehicle/ Equipment Wash Area (S-6)Fueling and Maintenance Area (S-7) Rain Garden
(V-1)
Rain
Barrel/Cistern
(V-2)
Interception
Trees (V-3)
Grassy
Channel (V-4)
Vegetated
Buffer Strip
(V-5)
LID Treatment Controls
Bioretention (L-1)t
Stormwater Planter (L-2)
Tree-well Filter (L-3)
Water Quality Infiltration Basin (L-4)t
Water Quality Infiltration Trench (L-5)t, 2
Porous Pavement Filter (L-6)
Vegetated Swale (L-7)
Grassy Swale (L-8)
Grassy Filter Strip (L-9)
Infiltration Well (L-10)
Dry Well (L-11)
Conventional Treatment Controls
Constructed Wetland (C-1)
Extended Detention Basin (C-2)t
Wet Pond (C-3)
Proprietary Control Device (C-4)
Trash Controls (C-5)
Media Filter (C-6)
Residential Subdivisions (≥ 10 units) R R R R R R1 - - - - - S S/T High-Density Residential (> 10 DU/acre) T
Commercial/Industrial (any size)
(including auto repair, RGO, restaurants) R R R R R R1 R1 R1 R1 R1 R1 S S/T Parking Lots (≥ 5,000 SF or 25 spaces) R R R R R R1 R1 - - - - S S/T Mixed Urban / Public Transport Stn - - - - - - - - - - - - T Significant Redevelopment (≥5,000 SF) R R R R R R1 R1 R1 R1 R1 R1 S S/T R: required; R1: required if outdoor activity is included in the project S: select one or more applicable controls
t: can be modified to meet trash control requirements
S/T: select one or more applicable controls; trash control required; T: trash control required 1: VRMs and Treatment Controls can be used individually or in combination 2: Also known as a French Drain or a Horizontal Drain #6..
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Table 2-3. Control Measure Selection Matrix for Meeting Low Impact Development and Treatment Requirements
Control Measure
Assists in Meeting Requirements for:

Low Impact
Development(1)
Volume Retention/
Reduction
Treatment
Rain Garden (V-1)  
Rain Barrel/Cistern (V-2)  (2)
Interception Tree (V-3)  (2)
Grassy Channel (V-4)  (2)  (3)
Vegetated Buffer Strip (V-5)  (2)  (3)
Bioretention (L-1)  
Stormwater Planter (L-2)  
Tree-Well Filter (L-3)  
Water Quality Infiltration Basin (L-4)  
Water Quality Infiltration Trench (L-5)(4)  
Porous Pavement Filter (L-6)  
Vegetated Swale (L-7)  
Grassy Swale (L-8)  
Grassy Filter Strip (L-9)  
Infiltration Well (L-10)  
Dry Well (L-11)  
Constructed Wetland (C-1)  
Extended Detention Basin (C-2) 
Wet Pond (C-3) 
Proprietary Control Devices (C-4)(5)  
Trash Capture Devices (C-5) 
Media Filter (C-6) 
(1) This Manual emphasizes LID (which works to replicate pre-project hydrology in a post-project environment) by retaining rainfall on-site through infiltration, evapotranspiration, or harvest and use. These requirements mitigate or eliminate the volume of stormwater runoff from a post-project site that is discharged to the receiving water, thereby mitigating potential hydromodification impacts. (2) Control measures may provide some LID benefits by mitigating some stormwater runoff volume. However, it must be coupled with other LID control measures to meet LID requirements. (3) Control measures may provide some pollutant treatment to reduce pollutant load discharged off-site. (4) Also known as a French Drain or Horizontal Drain
(5) Some types of priorietary control devices may assist in retaining and/or infiltrating stormwater. #6..
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Development Guidance Manual 2-17 May 2025
Figure 2-4. City SWQCP Review Process Flowchart
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Development Guidance Manual 3-1 May 2025

3. SITE ASSESSMENT
During the initial project planning and design, the project site should be evaluated to generate a hydrologically functional site that maximizes volume retention and integrates the necessary stormwater management throughout the site. Some of the principles that should be used during this phase of the project include:
• LID-Based Volume Retention Control Measures should be considered as early as possible in the site planning process. Hydrology should be an organizing principle that is integrated into the initial site assessment planning phases.
• Individual control measures should be distributed throughout the project site, and may influence configuration of roads, buildings, and other infrastructure. • Consider flood control early in the design stages. Even sites with LID-based Volume Retention Control Measures will still have stormwater runoff that occurs during large storm events. Look for opportunities to simultaneously address flood control requirements.

This section presents the steps for assessing sites during the planning and design phase of a project to determine the existing site conditions and what control measures are feasible. This step is important for identifying site constraints that may limit or reduce the ability of a site to meet volume retention or treatment requirements. Conducting this step early in the planning process reduces the chance of having to re-design the site if proposed control measures are not technically feasible.

3.1 ASSESSING SITE CONDITIONS AND OTHER CONSTRAINTS
Assessing a site’s potential for implementation of volume retention and treatment control measures requires the review of existing information as well as the collection of sitespecific measurements. Available information regarding site layout and slope, soil type, geotechnical conditions, and local groundwater conditions should be reviewed as discussed below. In addition, soil and infiltration testing must be conducted to determine if stormwater runoff infiltration is feasible, and to determine the appropriate design infiltration rates for infiltration-based treatment control measures. For PLU-only Projects, information is only necessary for Section 3.1.1.

3.1.1 Project Location
Once the project location has been identified, it is necessary to conduct initial field investigations of the project site to determine site conditions and other constraints that may limit the ability to apply stormwater quality control measures. As part of this initial assessment, the developer must identify the following:
• Project area size (acres);
• Drainage area (acreage and location via site map);
• Impervious area (acreage and location via site map);
• Location of discharge point(s) (to the storm drain system or local receiving water); and #6..
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Development Guidance Manual 3-2 May 2025
• Activities expected on-site.

The project area size and drainage area are important factors in determining the sizing and placement of stormwater runoff control measures. Identifying the point(s) of discharge of stormwater runoff off the project site is necessary to determine where stormwater runoff conveyance and/or control measures need to be located. Determining the activities expected to be conducted on-site before, during, and after construction is important in assessing what potential pollutants may be present in stormwater runoff.

3.1.2 Site Conditions
Topography
Assess site topography to evaluate surface drainage, identify topographic high and low points, and locate the presence of steep slopes. Each of these site characteristics can impact the type of volume retention or treatment control measure that will be most beneficial for a given project site. For example, stormwater runoff infiltration is more effective on level or gently sloping sites than steeply-sloped sites. Flows applied to slopes steeper than 15% may runoff as surface flows rather than infiltrate.

Soil Type and Geology
Identify site soil types and geologic conditions to evaluate the infiltration capacity at the site to determine the areas where infiltration is suitable as well as unsuitable for the purpose of locating infiltration-based control measures. Modesto area soil types are:
• Type A Soil – typically sands, loamy sands, or sandy loams. Type A soils have low stormwater runoff potential and high infiltration rates even when thoroughly wetted.

They consist chiefly of deep and well to excessively drained sands or gravels, and have a high rate of water transmission.
• Type B Soil – typically silt loams or loams. They have moderate infiltration rate when thoroughly wetted and consist chiefly of moderately-deep to deep and moderately-wellto well-drained soils with moderately fine to moderately coarse texture. • Type C Soil – typically sandy clay loams. They have low infiltration rates when thoroughly wetted, consist chiefly of soils with a layer that impedes downward movement of water, and/or have moderately-fine to fine soil structure. • Type D Soil – typically clay loams, silty clay loams, sandy clays, silty clays, or clays. They have very low infiltration rates when thoroughly wetted and consist chiefly of clay soils with high swelling potential, permanent high water table, claypan or clay layer at or near the surface, and/or shallow soils over nearly impervious material.

If site-specific data are available, soils with infiltration rates of 0.5 in/hr or greater are considered feasible for infiltration-based control measures. Early identification of soil types throughout the project footprint can reduce the number of test pit investigations and infiltration tests needed by narrowing potential test sites to locations with those that are most likely to be amenable to infiltration.
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Development Guidance Manual 3-3 May 2025
Available geologic or geotechnical reports on local geology should be reviewed to identify relevant features such as depth to bedrock, rock type, lithology, faults, or hydrostratigraphic or confining units. These geologic investigations, which may also identify shallow water tables and past groundwater issues, provide important information for control measure design.

Groundwater Considerations
Site groundwater conditions must be considered prior to volume retention or treatment control measure siting, selection, sizing, and design. The depth to groundwater beneath the project during the wet season may preclude infiltration because ten (10) feet of separation to the seasonal high groundwater level is required. In areas with known groundwater pollution, infiltration should be avoided because it may potentially contribute to the movement or dispersion of groundwater contamination.

Where soils have very high infiltration rates, groundwater quality may be impacted by infiltration-based control measures. Prior to use of infiltration-based control measures, consult with the City to identify if unconfined aquifers are located beneath the project site to determine the appropriateness of infiltration-based control measures.

Geotechnical Considerations
Water infiltration can cause geotechnical issues, including settlement through collapsible soil, expansive soil movement, and slope instability. Stormwater infiltration temporarily increases the groundwater level near the infiltration control measure, such that the potential geotechnical conditions are likely to be of greatest significance near the infiltration area and diminish with distance. A geotechnical investigation must be performed for the infiltration-based control measure to identify potential geotechnical issues.

Increased water pressure in soil pores reduces soil strength. Decreased soil strength can make foundations more susceptible to settlement and slopes more susceptible to failure. In general, control measures must be set back from building foundations or steep slopes.

Recommendations for each site must be determined by a licensed geotechnical engineer based on soils boring data, drainage patterns, and current requirements for stormwater treatment.

Managing Off-Site Drainage
Locations and sources of off-site run-on onto the project site must be identified early in the design process. Off-site drainage must be considered when determining appropriate control measures for the site so that the drainage can be managed. Concentrated flows from off-site drainage may cause extensive erosion if not properly conveyed through or around the project site or otherwise managed. By identifying the locations and sources of off-site drainage, the volume of run-on may be estimated and factored into the siting and sizing of on-site control measures. Vegetated swales or storm drains may be used to intercept, divert, and convey off-site drainage through or around the project site to prevent flooding or erosion that might otherwise occur.
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Development Guidance Manual 3-4 May 2025
Existing Utilities
Existing utility lines that are on-site will limit the possible locations of certain control measures. For example, infiltration-based control measures should not be located near utility lines where the increased amount of water could damage utilities. Stormwater runoff should be directed away from existing underground utilities and project designs that require relocation of existing utilities should be avoided, if possible.

3.1.3 Pollutants of Concern
The pollutants of concern for a site depend on the type of land use and project category. The pollutants of concern should be identified for the site based on Table 3-1.

Table 3-1. Priority Project and PLU Project Categories and Associated Pollutants of Concern Project Category
Pollutant Category of Concern
SedimentNutrientsMetalsTrash Oxygen DemandToxic OrganicsBacteria Residential X X X1 X X X
Commercial/Industrial (any size)
(including auto repair, RGO, restaurants) X X X X X X X Parking Lots (≥ 5,000 SF or 25 spaces) X X X X X
Mixed Urban X X X X X X X
Public Transportation Stations X
X = Pollutant assumed to be present in stormwater runoff from project area unless applicant demonstrates otherwise. 1 – Metals are a pollutant category of concern for the street and road infrastructure portion of the residential development. #6..
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Development Guidance Manual 4-1 May 2025

4. SITE DESIGN CONTROL MEASURES

4.1 INTRODUCTION
The principal objective of the Site Design Control Measures is to reduce stormwater runoff peak flows and volumes through appropriate site design. The benefits derived from this approach include:
 Reduction in size of downstream Treatment Control Measures and conveyance systems;  Reduced pollutant loading to Treatment Control Measures; and  Reduced hydraulic impact on receiving waters.

Site Design Control Measures include the following design features and considerations designated as G-1 through G-4:
 Conserve Natural Areas (G-1)
 Protect Slopes and Channels (G-2)
 Minimize Soil Compaction (G-3)
 Minimize Impervious Area (G-4)
The Site Design Control Measures described in this section are required for all Priority Projects unless the project applicant demonstrates to the satisfaction of the City Engineer that the particular control measures do not apply to the proposed project or the project site conditions; making it infeasible to implement the site design control measure in question. The applicability of specific controls outlined within this section should be confirmed with the City Engineer.

4.2 DESCRIPTION
Detailed descriptions and design criteria for each Site Design Control Measures are presented in fact sheets in Appendix B.
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Development Guidance Manual 5-1 May 2025

5. SOURCE CONTROL MEASURES

5.1 INTRODUCTION
Source control measures are BMPs designed to prevent pollutants from contacting stormwater runoff or to prevent the discharge of contaminated stormwater runoff to the storm drain system and ultimately, the receiving waters. This section describes source control measures for activities identified as potentially significant sources of pollutants in stormwater runoff and is primarily focused on structural measures. The City may require additional source control measures not included in this Development Guidance Manual for specific pollutants, activities, or land uses.

Non-structural source controls, such as good housekeeping and employee training, are not included in this Development Guidance Manual. Each measure specified in this section should be implemented with appropriate non-structural source controls to optimize pollution prevention. The California Stormwater Quality Association BMP Development Handbook may be consulted for information on non-structural source controls (CASQA, 2021)21.

The source control measures apply to both stormwater and non-stormwater discharges. Nonstormwater discharges include any runoff that is occurring on site that is not composed entirely of stormwater. Examples of non-stormwater discharges include cooling water, excess irrigation water, process wastewater, etc.

Some source control measures require a connection to the sanitary sewer system. Connection and discharge to the sanitary sewer system without prior approval or obtaining the required permits is prohibited. Contact the City to obtain information regarding sanitary sewer discharges and/or permits.

5.2 DESCRIPTION
Source control measures and associated design features specified for various sites and activities are summarized in Table 5-1. Detailed descriptions and design criteria for each Source Control Measure are presented in fact sheets in Appendix C. These fact sheets include design criteria established by the City to ensure the effective implementation of the required source control measures.
21 Available through a subscription at www.casqa.org
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Development Guidance Manual 5-2 May 2025
Table 5-1. Summary of Source Control Measure Design Features Source Control Measure1
Design Feature or Element
Signs, placards, stencils, stampsSurfacing (compatible, impervious)Covers, screensGrading/berming to prevent run-onGrading/berming to provide secondary containmentSanitary sewer connectionEmergency Storm Drain Seal Storm Drain Message and Signage (S-1) X
Outdoor Material Storage Area (S-2) X X X X X
Outdoor Trash Storage and Waste Handling Area
(S-3) X X X X X
Outdoor Loading/Unloading Dock Area (S-4) X X X X X
Outdoor Repair/Maintenance Area (S-5) X X X X X
Outdoor Vehicle/Equipment/ Wash Area (S-6) X X X X X X
Fueling and Maintenance Area (S-7) X X X X X
1Refer to Fact Sheets in Section 4 for detailed information and design criteri #6..
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Development Guidance Manual 6-1 May 2025

6. VOLUME RETENTION MEASURES

6.1 INTRODUCTION
The City’s approach to minimize potential water quality impacts from stormwater runoff is implementing a volume retention requirement. By retaining a portion of stormwater runoff onsite, the City expects to reduce and/or eliminate the pollutant loads, which are typically higher during the beginning of storm events, from reaching the receiving waters.

VRMs are required to minimize potential water quality impacts from stormwater. VRMs are BMPs used to direct, retain, reuse and/or infiltrate stormwater runoff (e.g., rain gardens and rain barrels). The type of VRM to be implemented at a site depends on several factors, including the type of potential pollutants in the stormwater runoff, the quantity of stormwater runoff to be treated, project site conditions (e.g., soil type and permeability, groundwater levels); and receiving water conditions. Land area requirements and costs to design, construct and maintain VRMs vary.

The Design Engineer can utilize the listed and/or any other California Water Board approved VRMs and Treatment Controls individually or in combination to achieve the project requirements.

6.2 VOLUME RETENTION REQUIREMENT
The application of VRMs is driven, in part, by the VRR. The VRR is a requirement developed in response to the recent municipal stormwater permits specifying the use of LID and a combination of site design, source control, and treatment control measures.

The VRR specifies that post-project runoff volumes be reduced to match pre-project levels for the 0.50-inch storm depth, the average 85th percentile/24-hour storm depth estimated for the City’s jurisdictional area. This calculated stormwater runoff volume for retention and treatment is different from the flood control retention requirements. The retention and treatment requirements are for water quality purposes, while the flood control retention requirements are for flood control purposes. The procedures for calculating the volume of stormwater runoff that must be retained on-site is presented in Fact Sheet C-1.

New Development Priority Projects may apply a combination of VRMs and LID Treatment Controls (see Step 6) to meet the VRR. Detailed descriptions and design criteria for each VRM are presented in fact sheets in Appendix D.

As indicated in Table 6-1, some controls are better suited for reducing the volume associated with rooftop runoff (e.g., Rain Barrels). In contrast, others are more suited for reducing the volume associated with pavement runoff (e.g., Interception Trees). Suggested applications of VRMs are illustrated in Figures 6-1a and b.
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Development Guidance Manual 6-2 May 2025
Table 6-1. Summary of Volume Retention and LID Treatment Controls Control
Function Disconnection Application
Volume Retention Treatment Rooftop Pavement
VRMs (Section 5)
Rain Garden (V-1) Primary Secondary X X
Rain Barrel/Cistern (V-2) Primary Secondary X
Interception Trees (V-3)1 Primary Secondary X
Grassy Channel (V-4)1 Primary Secondary X X
Vegetated Buffer Strip (V-5)2 Primary Secondary X X
LID-based Treatment Controls (Section 6)
Bioretention (L-1) 1 Primary Secondary X X
Stormwater Planter (L-2) Secondary Primary X X
Tree-well Filter (L-3) Secondary Primary X
Water Quality Infiltration Basin (L-4) 1 Primary Secondary X X Water Quality Infiltration Trench (L-5) 1,3 Primary Secondary X X Porous Pavement Filter (L-6) Primary Secondary X
Vegetated Swale (L-7) Secondary Primary X X
Grassy Swale (L-8) Secondary Primary X X
Grassy Filter Strip (L-9) Secondary Primary X X
Infiltration Well (L-10) Primary Secondary X X
Dry Well (L-11) Primary Secondary X X 1 This control may be modified to meet the trash control design criteria. 2 Disconnected rooftops (rooftops allowed to drain to lawn as opposed to impervious area) should utilize the Vegetated Buffer Strip (V-6) in order to receive credit towards the VRR. 3 Also known as a French Drain or Horizontal Drain. #6..
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Development Guidance Manual 6-3 May 2025
Figure 6-1a. Suggested Applications of Runoff VRMs. Source: Home. Low Impact Development. (2002, November). Retrieved October 5, 2021, from https://lowimpactdevelopment.org/. #6..
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Development Guidance Manual 6-4 May 2025
Figure 6-1b. Suggested Applications of Runoff VRMs. Source: Home. Low Impact Development. (2002) November). Retrieved October 5, 2021, from https://lowimpactdevelopment.org/. TREE WELL FILTER #6..
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Development Guidance Manual 6-5 May 2025
To assist Priority Projects, Appendix G provides additional information on calculating and meeting the VRR. Projects may use the worksheet to help track compliance with the VRR.

Compliance with the VRR can be demonstrated through the following steps:

1. Determine the volume of runoff from the site under pre-project conditions and the volume of runoff from the site under post-project conditions for the 0.50-inch storm depth.

Appendix G provides additional information on calculating and meeting the VRR.

Runoff Volume Retention Calculation Procedure:

Runoff Volume (ft3) = 0.50”/12” x Site weighted runoff coefficient (Cra) x Site area (ft2)  Significant Redevelopment Priority Projects must also comply with the VRR; however, an incentive in the form of credits may be applied based on the type of redevelopment. A maximum credit of 0.25 inch from the 0.50-inch VRR may be applied to any of the following types of redevelopment. Credits are issued in 0.05-inch increments based on five criteria:
a. Significant Redevelopment (as defined in Section 2.1) b. Brownfield redevelopment
c. High density (>22 units per acre);
d. Vertical Density (2 or more stories); or
e. Mixed-use and Transit Oriented Development (within ½ mile of public transit, such as a bus stop)

2. Calculate the VRR as the difference between the pre-project runoff volume and the postproject runoff volume (i.e., post–pre).

3. Select applicable VRMs (e.g., Interceptor Trees, Rain Barrels). Each VRM has a certain volume retention “credit” that can be applied toward the VRR. The VRM fact sheets detail the calculation procedure for volume retention.

4. Determine the remaining VRR not met by the VRMs, if any. This remaining VRR must be met by the application of LID Treatment Controls as described in Step 6.

5. Determine tributary impervious area credits associated with the selected VRMs. These area credits can be applied to reduce the effective design area for treatment controls described in Step 6. Note that these credits must be applied to treatment controls that are in the same tributary drainage area as the VRMs for which the credits are determined and the credits cannot be greater than the tributary drainage areas of the treatment controls to which they are applied.

6. Apply LID Treatment Controls
 If the VRR is not entirely met using VRMs, the project must apply LID Treatment Controls to reduce further the runoff volume to meet the VRR. LID Treatment Controls must be designed to treat the WQV or WQF as discussed in Section 6. The WQV or WQF is calculated using the effective tributary drainage area, which is determined by subtracting area credits (see Step 5) from the actual tributary drainage area for the treatment control under design. #6..
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Development Guidance Manual 6-6 May 2025
 If the VRR is met through the use of VRMs, the project may meet the Treatment Control requirement through the use of LID Treatment Controls and/or Conventional Treatment Controls.

7. If the VRR is not entirely met through the combination of VRMs and LID Treatment Controls, the project must demonstrate technical infeasibility and submit a VRR Waiver Form as described below. Priority Projects that cannot fully meet the VRR must select Treatment Control Measures with a Medium to High removal efficiency for the pollutant of concern (Table 6-2 in Section 6).

Volume Retention Technical Infeasibility and Alternative Compliance Alternative designs may be allowed if the VRR cannot be fully met due to site constraints.

However, even if the project cannot meet the full VRR, the project must still reduce the volume to the MEP. Meeting the VRR is an iterative process. Designers should return to prior steps to explore alternative combinations of VRMs and LID Treatment Controls. The burden of proof is on the project applicant to show that it is technically infeasible to meet the VRR. Economic hardship is not an acceptable reason for infeasibility.

In order to demonstrate technical infeasibility, the applicant must show that the project cannot reliably meet the VRR. Technical infeasibility may result from conditions including the following:
 The corrected in-situ infiltration rate is less than 0.3 inch per hour, and it is not technically feasible to amend the in-situ soils to improve it;
 Locations with shallow groundwater, with less than 10 feet separation between the bottom of the infiltration device and the seasonal high groundwater elevation;  Locations within 100 feet of a groundwater well used for drinking water;  Brownfield development sites where infiltration poses a risk of pollutant mobilization or other locations where pollutant mobilization is a documented concern (e.g., at or near properties that are contaminated or store hazardous substances underground);  Locations with potential geotechnical hazards;
 Historic sites, structures, or landscapes that cannot alter their original configuration in order to maintain their historical integrity;
 Locations where infiltration may adversely impact biological resources; or  Locations where infiltration may cause health and safety concerns.

If meeting the VRR is infeasible, the Applicant must propose an alternative compliance design.

Under all such designs, the portion of the design volume that cannot be reliably retained onsite must be stored on-site, treated, and released once the storm event passes.

Projects that are not able to fully meet the VRR must fill out and submit the VRR Waiver Form, (Appendix H). The Waiver must demonstrate technical infeasibility and describe the alternative compliance design.

The VRR Waiver is primarily available for priority redevelopment or infill projects where site constraints, such as available land, may limit the ability to implement VRMs and LID Treatment #6..
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Development Guidance Manual 6-7 May 2025
Controls to retain and/or treat the WQF or WQV. In general, the City does not expect to grant VRR Waivers for new development projects.

Priority Projects that are not able to fully meet the VRR must fill out and submit the VRR Waiver (Appendix H). The City can reject a VRR Waiver request if VRMs and/or LID Treatment Controls are considered feasible at the project site or if adequate alternative compliance design is not proposed.

6.3 SELECTION OF VOLUME RETENTION MEASURES
Various factors must be considered when selecting VRMs. In addition to reducing volume, site considerations such as the size of the drainage area, depth between the water table and the control, soil type and permeability, slope and need for vegetation irrigation are important factors in selecting the proper VRMs. Vector breeding considerations must also be addressed because of nuisance and potential human health effects. The site constraints used to select VRMs are provided in Table 6-2.

Table 6-2. Site Constraints for VRMs
VRM
Drainage
Area
(acres)
Depth to
Water
Table (ft)
Soil Type1
Slope
(%)
Irrigation
Required
Vector
Control
Frequency
Maintenance
Frequency A/B C/D
Rain Garden (V-1) <0.05 10 ft(2) X X n/a Y L M
Rain
Barrel/Cistern (V2)<0.25 n/a n/a n/a n/a N H3 L
Interception
Trees (V-3) n/a n/a X X n/a Y L L
Grassy Channel
(V-4) <1 n/a X X ≤4% Y L M4
Vegetated Buffer
Strip (V-5) <1 n/a X X <5% Y L M4
X: Control Measure is suitable for listed site condition 1: Type A soils are sands and gravels with typical infiltration rates of 1.0-8.3 inch/hour. Type B soils are sandy loams with moderately fine to moderately coarse textures and typical infiltration rates of 0.5-1.0 inch/hour. Type C soils are silty loams or soils with moderately fine to fine texture and typical infiltration rates of 0.17-0.27 inch/hour. Type D soils are clays with infiltration rates of 0.02-

0.10 inch/hour.
2: Applies if rain garden is allowed to infiltrate
3: Concerns may be mitigated through design features; see the corresponding fact sheet. 4: Once vegetation is established, maintenance is low.
n/a: Not applicable – this site condition does not affect the applicability of this VRM Y = Yes; N = No
H= High; M = Medium; L = Low
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Development Guidance Manual 7-1 May 2025

7. TREATMENT CONTROL MEASURES

7.1 INTRODUCTION
Treatment Control Measures are required in addition to Site Design Control Measures, Source Control Measures and VRMs to reduce pollutants in stormwater runoff to the MEP. Treatment Control Measures are engineered technologies designed to remove pollutants from stormwater runoff. The type of Treatment Control(s) to be implemented at a site depends on several factors, including:
• Type of pollutant(s) in the stormwater runoff;
• Quantity of stormwater runoff to be treated;
• Project site conditions (e.g., soil type and permeability, slope, etc.); • Receiving water conditions; and
• Other regulatory requirements that apply (e.g, Statewide Trash Amendments, State Industrial General Permit).

The Design Engineer is responsible to demonstrate that the treatment requirements are met by utilizing the listed LID-based and/or conventional treatment control measures or any other approved measures.

Land requirements and costs to design, construct and maintain treatment control measures vary by type of treatment control, location, and site constraints.

Unlike flood control measures that are designed to handle peak flows, stormwater treatment control measures are designed to treat the more frequent, lower-flow storm events or the firstflush portions of stormwater runoff from larger storm events (typically referred to as first-flush events). Small, frequent storm events represent most of the total average annual rainfall for the area. The flow and volume from such small events, referred to as the WQF and WQV, are targets for treatment. In addition, Trash Controls are designed to treat the peak flow rate from a one-year, one-hour storm (0.32 inches22).

The Treatment Control Measures presented in this Development Guidance Manual are designed based on flow rates or stormwater runoff volume. • Treatment Control Measures designed based on flow are designed for the WQF • Treatment Control Measures designed based on stormwater runoff volume are designed for the WQV.

Definitions and calculation procedures to determine design flows and volumes are presented in this Section. Stormwater runoff in excess of the WDF or WQV must be diverted around the Treatment Control Measure to prevent overloading or may be diverted through the Treatment Control Measure if it will not cause overloading.
22 This value was determined by using Basin Sizer, which is a software tool developed by Caltrans to determine what the 1-year, 1-hour storm size is for different areas within California. This information is used for the sizing of full trash capture devices. The value may be modified over time due to changing climate or other conditions. https://svctenvims.dot.ca.gov/basinsizer/ #6..
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Development Guidance Manual 7-2 May 2025
Treatment Controls are categorized as either LID Treatment Controls or Conventional Treatment Controls (Table 7-1).
• LID-based Treatment Controls can reduce stormwater runoff volumes and may be used in combination with the VRMs described in Section 5 to meet the VRR. • Conventional Treatment Controls typically do not reduce stormwater runoff volumes. #6..
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Development Guidance Manual 7-3 May 2025
Table 7-1. LID-based and Conventional Treatment Control Measures LID-based Treatment Control
Measures
Conventional Treatment Control Measures
Bioretention (L-1)1
Stormwater Planter (L-2)
Tree-well Filter (L-3)
Water Quality Infiltration Basin (L-4)1
Water Quality Infiltration Trench (L-5)1,2
Porous Pavement Filter (L-6)
Vegetated Swale (L-7)
Grassy Swale (L-8)
Grassy Filter Strip (L-9)
Infiltration Well (L-10)
Dry Well (L-11)
Constructed Wetland (C-1)
Extended Detention Basin (C-2)1
Wet Pond (C-3)
Proprietary Control Device (C-4)
Trash Capture Device (C-5)
Media Filter (C-6)
1 These treatment controls may be designed to also meet the trash control requirements. 2 Also known as a French Drain or Horizontal Drain.

The relative effectiveness of the Treatment Control Measures in reducing pollutants of concern is shown in Table 7-2.

The selection of the Treatment Control Measures should be based on their ability to reduce runoff volumes and/or remove pollutants of concern. Priority Projects that cannot fully meet the VRR must select Treatment Control Measures with a Medium to High removal efficiency for the pollutants of concern (Table 2-1 and Table 7-2). All PLU and Priority Projects must include trash Treatment Controls.
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Development Guidance Manual 7-4 May 2025
Table 7-2. Efficiency of Treatment Control Measures for Reduction of Pollutants of Concern Treatment Control Measures
Pollutant of Concern1
Bacteria Pesticides
Oxygen
Demanding
Substances
Sediments Trash
LID-based Treatment Controls
Bioretention (L-1) M M M H HT
Stormwater Planter (L-2) M M M H --
Tree-well Filter (L-3) M M M H --
Water Quality Infiltration Basin (L-4) H M M H HT
Water Quality Infiltration Trench (L-5)4 H M M H HT
Porous Pavement Filter (L-6) M M M H --
Vegetated Swale (L-7) L2 L2 M M --
Grassy Swale (L-8) L2 L2 M M --
Grassy FIlter Strip (L-9) M M M H --
Infiltration Well (L-10) H M M H --
Dry Well (L-11) H M M H --
Conventional Treatment Controls
Constructed Wetland (C-1) M M M M --
Extended Detention Basin (C-2) M M M M HT
Wet Pond (C-3) M M M H --
Proprietary Devices(C-4)3 − − − − -
Trash Full Capture Systems (C-5) L L M M H
Media Filter M M H H HT
1 H = >75% expected pollutant removal efficiency for typical urban stormwater runoff; M = 25% to 75% expected removal efficiency for typical urban stormwater runoff; L = <25% expected removal efficiency for typical urban stormwater runoff.

T = Treatment Control can be modified to meet trash control requirements. 2 If the pollutants of concern (Table 2-1) are bacteria or pesticides, swales should only be used in combination (e.g., used in a treatment train) with Treatment Controls with a Medium to High removal efficiency for bacteria or pesticide removal efficiency. 3 Effectiveness of proprietary devices varies depending on the manufacturer and type of device. Limited performance data are available.
4 Also known as a French Drain or Horizontal Drain.

7.2 SELECTION OF TREATMENT CONTROL MEASURES
Various factors must be considered when selecting Treatment Control Measures. In addition to reducing target pollutants of concern, site considerations such as the size of the drainage area, depth between the water table and the treatment control, soil type and permeability, site slope, hydraulic head, size of the Treatment Control Measure, and need for vegetation irrigation are important factors in selecting the appropriate Treatment Control Measure. Vector breeding considerations must also be addressed due to the potential nuisance and human #6..
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health effects. The applicability of specific controls outlined within this Section should be confirmed with the City. Site constraint considerations are presented in Table 7-3.

Volume Retention Requirement
All Priority Projects must meet the VRR through a combination of VRMs and LID Treatment Controls.
• Project applicant does not fully meet the VRR through VRMs - LID Treatment Controls must be used to further reduce stormwater runoff volumes and treat the WQF or WQV. • Project applicant does meet the VRR through VRMs - a treatment control may be chosen from the LID-based Treatment Control or Conventional Treatment Control list.

Calculation procedures for determining the volume retention for LID-based Treatment Control Measures are provided within each fact sheet.

If the VRR cannot be fully met due to site constraints, see “Technical Infeasibility and Alternative Compliance” in Section 5. Projects that do not fully meet the VRR must select Treatment Controls with a Medium to High removal efficiency for the pollutant of concern (Table 2-1 and Table 7-2).

7.3 DESCRIPTION OF TREATMENT CONTROL MEASURES
Detailed descriptions and design criteria for each Treatment Control Measure are presented in fact sheets in Appendices E [LID-Based Treatment Controls] and F [Conventional Treatment Controls]. The fact sheets for the Treatment Control Measures include siting considerations, design criteria, calculation fact sheets and worksheets to aid in the design of water quality treatment controls, and maintenance requirements to ensure optimal performance of the measures.

Bioretention LID-based Treatment Controls (L-1) that maximize infiltration to the underlying soils are highly encouraged even if it is infeasible to infiltrate the full amount of runoff (if there are no other conditions that would make infiltration unsafe).

If infiltration is precluded due to site constraints (see “Technical Infeasibility and Alternative Compliance” in Section 5), flow-through treatment controls must be utilized.

It should be noted that proprietary device (C-4) vault systems should be avoided since they are typically equipped with high-flow rate media filters and are thus, less effective at pollutant removal and more challenging to maintain compared to the landscape-based LID type treatment controls. Therefore, proprietary device (C-4) vault systems should be considered only as a last resort, after all other viable alternatives have been thoroughly evaluated. #6..
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Development Guidance Manual 7-6 May 2025
Table 7-3. Site Constraints for Treatment Control Measures Treatment Control Measure
Drainage Area Depth to
Groundwater Soil Type2 Maximum Slope
Hydraulic
Head
Vegetation
Irrigation
Vector
Control
Frequency
Maintenance
Frequency <10
acres
>10
acres
<10
feet
>10
feet
A or
B
only
A, B,
C or D ~0% <15%
LID-based Treatment Controls
Bioretention (L-1)1 X X X X M Y M M
Stormwater Planter (L-2) X X X X X M Y M M
Tree-well Filter (L-3) X X X X X M Y M M
Water Quality Infiltration Basin
(L-4)1 X X X X H Y* L M
Water Quality Infiltration Trench
(L-5)1,5 X X X X H N L L
Porous Pavement Filter (L-6) X X X X X M N L L
Vegetated Swale (L-7) X X X X X L Y L L
Grassy Swale (L-8) X X X X X L Y M L
Grassy Filter Strip (L-9) X X X X X L Y L L
Infiltration Well (L-10) X X X X H N L M
Dry Well (L-11) X X X X H N L M
Conventional Treatment Controls
Constructed Wetland (C-1) X X X X X L Y H H
Extended Detention Basin (C-2)1 X X X X X L Y* M M
Wet Pond (C-3) X X X X X L Y* H M
Proprietary Devices3(C-4)
Trash Full Capture Systems4 (C-5)
Media Filter (C-6) X X X X X X H N L M
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Development Guidance Manual 7-7 May 2025
X: Treatment Control Measure is suitable for listed site condition. H= high; M = medium; L = low; Y= yes; Y* = yes if vegetated; N= no

1. Treatment Control can be modified to meet trash control requirements

2. Type A soils are sands and gravels with typical infiltration rates of 1.0-8.3 inches/hour. Type B soils are sandy loams with moderately fine to moderately coarse textures and typical infiltration rates of 0.5-1.0 inches/hour. Type C soils are silty-loams or soils with moderately fine to fine texture and typical infiltration rates of 0.17-0.27 inches/hour.

Type D soils are clays with infiltration rates of 0.02-0.10 inches/hour.

3. Suitability of proprietary devices varies depending on the manufacturer and type of device.

4. Trash Full Capture Devices are proprietary devices and their suitability depends on the manufacturer and type of device.

5. Also known as a French Drain or Horizontal Drain.
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Development Guidance Manual 7-8 May 2025

7.4 CALCULATION OF WATER QUALITY DESIGN FLOW AND WATER

QUALITY DESIGN VOLUME
Purpose
With the exception of Trash Full Capture Systems (FCS) (C-5), the primary control strategy for all of the treatment control measures is to treat the water quality flow (WQF) or water quality volume (WQV). This section presents calculation procedures and design criteria necessary to determine the WQF and WQV, which are distinct and separate parameters from the VRR discussed in Section 5. The WQF and WQV are required design parameters used to size treatment control measures.

The treatment control measures are listed in Table 7-4, along with the basis of design (WQF or WQV) and the design drawdown periods for those treatment control measures that use the WQV as the basis for design (Figure 7-1).

Table 7-4. Sizing Criteria for Treatment Control Measures Treatment Control Measure Design Basis Design Drawdown2 Bioretention (L-1)1 WQV 12 hours
Stormwater Planter (L-2)1 WQV 12 hours
Tree-well Filter (L-3)1 WQV 12 hours
Water Quality Infiltration Basin (L-4) WQV 48 hours
Water Quality Infiltration Trench (L-5)1,3 WQV 48 hours Porous Pavement Filter (L-6) WQV 12 hours
Vegetative Swale (L-7) WQV 12 hours
Grassy Swale (L-8) WQF N/A
Grassy Filter Strip (L-9) WQF N/A
Infiltration Well (L-10) WQV 48 hours
Dry Well (L-11) WQV 48 hours
Constructed Wetland (C-1) WQV 24 hours
Extended Detention Basin (C-2) WQV 48 hours
Wet Pond (C-3) WQV 12 hours
Proprietary Control Measures (C-4) WQV or WQF 48 hours
Trash Full Capture Devices (C-5) Flow rate for
1-hr, 1-yr storm N/A
Media Filter (C-6) WQV or WQF 48 hours
1 Can be modified to meet trash control requirements.
2 Design drawdown period used to determine Unit Basin Storage Volume (Figure 7-1). 3 Also known as a French Drain or Horizontal Drain. #6..
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Development Guidance Manual 7-9 May 2025
Determining Design Imperviousness, Runoff Coefficient and Effective Area Calculation of the WQV and WQF requires the determination of the following parameters associated with the drainage area tributary to the treatment control under design:
 Weighted stormwater runoff coefficient (Cr) (without application of impervious area credits)  The effective tributary area following the application of area credits (Aeff) Weighted Imperviousness and Stormwater Runoff Coefficient Calculations Projects typically comprise a variety of site elements that have variable values of imperviousness and associated stormwater runoff coefficients. The runoff coefficient is a function of imperviousness and the permeability of the soil if the runoff contacts the soil.

Values of imperviousness and runoff coefficients to be used for calculating WQV and WQF are listed in Table 7-5 for typical site elements. The weighted runoff coefficient value for a particular drainage area is determined as follows:

1. Determine area associated with each site element (Aelement)

2. Determine sum of site element areas (Asite)

3. Determine fraction of total area associated with each site element (Aelement/Asite)

4. Determine the runoff coefficient (Cr) associated with each site element from Table 7-5.

5. Calculate weighted imperviousness (Ia) or runoff coefficient (Cra):

I Ia = Σ Ii × Aelement(i) /Asite
Cra = Σ Cr × Aelement(i) /Asite
Table 7-5. Stormwater Runoff Coefficients for Typical Site Elements1,2 Site Element
Runoff Coefficient (Cr)
Type A and B Soils Type C and D Soils
Asphalt/concrete pavement 0.95 0.95
Roofs 0.95 0.95
Gravel pavement 0.35 0.35
Permeable pavement Variable3 Variable3
Managed turf 0.18 0.25
Disturbed soils 0.18 0.25
Vegetated areas w/ amended Type A soil 0.03 N/A
Forest/undisturbed open space 0.03 0.05
1 Adapted from Center for Watershed Protection, Ellicott City, MD. 2 Not for design of storm drain system piping.
3 Variable with product type. Consult manufacturer for appropriate design values.

Example calculations for weighted stormwater runoff coefficients for a site with Type D soils are shown in Table 7-6.
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Development Guidance Manual 7-10 May 2025
Table 7-6. Example Calculation Table for Weighted Stormwater Runoff Coefficient Site Element
Element
Area(a),
ft2
(Aelement)
Fraction of
Total Area
(Aelement/Asite)
Element
Runoff
Coefficient
(Cr)
Weighted
Runoff
Coefficient (Cra)
Asphalt/concrete pavement 40,000 0.40 0.95 0.38
Roofs 30,000 0.30 0.95 0.29
Permeable pavement 5,000 0.05 0.35 0.17
Managed turf 20,000 0.20 0.25 0.05
Forest/undisturbed open
space
5,000 0.05 0.03 0.01
Total Site (Asite) 100,000 0.90
1 Actual area without adjustment for tributary impervious area credits from VRMs Effective Tributary Area Calculations
The effective tributary area is defined as the effective area to be used in calculations for WQV and WQF for a specific treatment control measure and is determined by subtracting the tributary impervious area credits earned for VRMs from the actual tributary drainage area served by the treatment control (Aeff = Atributary – Acredit).

Note that a tributary impervious area credit for a VRM must be applied to a treatment control that serves the same tributary drainage area as the VRM for which the credit is earned. The credits cannot be greater than the tributary drainage areas of the treatment controls to which they are applied. Example calculations for the effective area are shown in Table 7-7.

Table 7-7. Example Calculation Table for Effective Tributary Area Site Element Element
Area, ft2
Area Credit1
(Acredit), ft2
Effective Area
(Aeff), ft2
Asphalt/concrete pavement 40,000 10,000 30,000
Roofs 30,000 15,000 15,000
Permeable pavement2 5,000 0 5,000
Managed Turf 20,000 0 20,000
Forest/undisturbed open space 5,000 0 5,000
1 Area Credit from VRMs (e.g. rain gardens, rain barrels, interception trees, grassy channel, or vegetated buffer strip) 2 Credit for permeable pavement has already been provided in the form of a reduced runoff coefficient (Tables 7-5 and 7-6).

Water Quality Flow (WQF) Calculation
Hydrologic calculations for design of flow-based treatment control measures in Modesto shall be in accordance with the most current City of Modesto Standard Specifications. #6..
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The WQF is defined to be equal to the maximum flow rate of stormwater runoff produced by the 85th percentile hourly rainfall intensity, as determined from the local historical rainfall record, multiplied by a factor of two. The 85th percentile hourly rainfall intensity for the Modesto area is estimated to be approximately 0.10 inches/hour, based on California State University, Sacramento Office of Water Programs’ Basin Sizer, Version 1.45 (2007) (not to be confused with the 85th percentile, 24-hour storm depth associated with the VRR).

Calculation Procedure

1. Determine the 85th percentile hourly rainfall intensity for the Modesto area. Use 0.10 in/hr.

2. Multiply the 85th percentile hourly rainfall intensity by a factor of two to obtain design rainfall intensity. Use i = 0.10 x 2 = 0.20 in/hr.

3. Determine the weighted runoff coefficient for the project area using the procedure illustrated in Table 7-6.

4. Determine the effective area (Aeff) of the drainage area using the procedure illustrated in Table 7-7.

5. Calculate the WQF using the following equation.

WQF = i x Cra x Aeff = 0.20 x Cra x Aeff
Where
WQF = Stormwater Quality Design flow, cfs
i = Design storm intensity = 0.20 in/hr
Cra = Weighted stormwater runoff coefficient for project area Aeff = Effective project drainage area, acres (Note: Area converted to acres for ease of calculation. Resulting conversion factor is approximately equal to 1.0) Example Calculation
Project site conditions from previous example: Aeff = 75,000 ft2; Cra = 0.90 WQF = 0.20 x 0.90 x 75,000/43,560 = 0.31 cfs
Water Quality Volume (WQV) Calculation
Hydrologic calculations for the design of volume-based treatment control measures in Modesto shall be in accordance with the most current City of Modesto Standard Specifications.

The WQV is defined as the volume necessary to capture and treat 80 percent or more of the average annual stormwater runoff volume from the site at the design drawdown period specified for each treatment control measure. The WQV volume should not be confused with the VRR, which is a separate requirement as defined in Section 5. #6..
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Development Guidance Manual 7-12 May 2025
Calculation Procedure

1. Review the drainage area of the proposed treatment control measure. Determine the weighted stormwater runoff coefficient (Cra) using the procedure illustrated in Table 7-

6. 2. A direct reading of Unit Basin Storage Volumes (Figure 7-1) is required for 80% annual capture of stormwater runoff for values of “Cra” determined in Step 1. A direct reading from Figure 7-1 is conducted as follows:
• Enter the horizontal axis with the “Cra” value from Step 1. • Move vertically up the figure until the appropriate drawdown period line is intercepted. • Move horizontally across the figure from this point until the vertical axis is intercepted. • Read the Unit Basin Storage Volume along the vertical axis.

3. Determine the effective area of the drainage area using the procedure illustrated in Table 7-7.

4. The WQV for the proposed treatment control measure is calculated by multiplying the Unit Basin Storage Volume by the effective drainage area. Due to the mixed units that result (e.g., acre-inches, acre-feet), it is recommended that the resulting volume be converted to cubic feet for use during design.

WQV = Vu × Aeff
Where:

Vu = Unit basin storage volume (ft); and
Aeff = Effective drainage area (acres).
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Example Calculation
Project site conditions from previous example: Aeff = 75,000 ft2; Cra = 0.90

1. Determine design drawdown period for proposed control measure.

Example: L-1: Bioretention x Drawdown period = 12 hrs

2. Determine the Unit Basin Storage Volume for 80% Annual Capture, Vu using Figure 7-1.

Example: for Cra = 0.90 and drawdown = 12 hrs x Vu = 0.31 in

3. Calculate the WQV for the basin.

WQV = Vu ×Aeff = (0.31 in) × (75,000 ft2) × (1 ft/12 in) = 1,938 ft3 Figure 7-1. Unit Basin Storage Volume vs. Weighted Runoff Coefficient Computing Stormwater Runoff Rates and Volumes. NJDEP New Jersey Department of Environmental Protection. (2004).

Retrieved October 7, 2021, from https://www.njstormwater.org/bmp_manual2.htm.

Based on California Stormwater Quality Association
(CASQA) California Stormwater BMP Handbook approach
calculated using Basin Sizer program developed by Office of Water Programs, California State University Sacramento #6..
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Development Guidance Manual 8-1 May 2025

8. CONTROL MEASURE MAINTENANCE
The continued effectiveness of the control measures specified in this Development Guidance Manual depends on diligent ongoing inspection and maintenance. To ensure that such maintenance is provided, the City requires the submittal of a Maintenance Plan and execution of a Maintenance Agreement with the owner/operator of stormwater control measures prior to the issuance of the Building Permit for a private development project, which may include one or more of the control measures detailed in Sections 3,4, 5, and 6.

Unless otherwise agreed to by the City, the landowner, developer, site operator, or successorsin-interest (e.g., homeowner’s association) is responsible for the operation and maintenance of the treatment controls and for complying with the Maintenance Agreement. The maintenance agreement and plan will provide the City designee with complete access to the Device and its immediate vicinity at any time. Requirements for the Maintenance Plan and Maintenance Agreement are presented in this section. A template agreement is provided in Appendix I, however it is recommended that the project proponent use the most recent template agreement available on the City website23.

8.1 MAINTENANCE PLAN
A post-construction Maintenance Plan shall be prepared and submitted to the City as part of the Project Stormwater Quality Control Measures Plan (SWQCP) submittal. The Maintenance Plan should include:
 Operation plan and schedule;
 Site map;
 Operations, maintenance and cleaning activities, including; a. A schedule;
b. Equipment and resources required; and
c. Responsible party(ies).

This section identifies the basic information that shall be included in a Maintenance Plan. Refer to Fact Sheets for individual control measures regarding device-specific maintenance requirements.

A. Site Map

1. Provide a site map showing the boundaries of the site, acreage, and drainage patterns/contour lines. Show each discharge location from the site and any drainage flowing onto the site. Distinguish between soft and hard surfaces on the map.

2. Identify locations of existing and proposed storm drain facilities, private sanitary sewer systems, and grade breaks for purposes of pollution prevention.

3. With legend, show locations of expected sources of pollution generation (e.g., outdoor work and storage areas, heavy traffic areas, delivery areas, trash enclosures, fueling areas, industrial clarifiers, and wash-racks). Identify any areas 23 https://www.modestogov.com/1263/Forms
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having contaminated soil or where toxins are stored or have been stored/disposed of in the past.

4. Within the legend, indicate types and locations of stormwater control measures that will be built to permanently control stormwater pollution. Distinguish between pollution prevention, treatment, sewer diversion, and containment devices.

B. Baseline Descriptions

1. List the property owners and persons responsible for the operation and maintenance of the stormwater control measures on-site. Include phone numbers and addresses.

2. Identify the intended method of providing financing for operation, inspection, routine maintenance, and upkeep of stormwater control measures.

3. List all permanent stormwater control measures. Provide a brief description of stormwater control measures selected and, if appropriate, facts sheets or additional information.

4. As appropriate for each stormwater control measure, provide:
a. A written description and checklist of all maintenance and waste disposal activities that will be performed. Distinguish between the maintenance appropriate for a 2-year establishment period and expected long-term maintenance. For example, maintenance requirements for vegetation in a Constructed Wetland may be more intensive during the first few years until the vegetation is established. The post-establishment maintenance plan shall address maintenance needs (e.g., pruning, irrigation, weeding) for a larger, more stable system. Include maintenance performance procedures for facility components that require relatively unique maintenance knowledge, such as specific plant removal/replacement, landscape features, or constructed wetland maintenance. These procedures shall provide enough detail for a person unfamiliar with maintenance to perform the activity or identify the specific skills or knowledge necessary to perform and document the maintenance.
b. A description of site inspection procedures and documentation system, including record-keeping and retention requirements.
c. An inspection and maintenance schedule, preferably in the form of a table or matrix, for each activity for all facility components. The schedule shall demonstrate how it will satisfy the specified level of performance and how the maintenance/inspection activities relate to storm events and seasonal issues.
d. Identification of the equipment and materials required to perform the maintenance.

5. List all housekeeping procedures for prohibiting illicit discharges or potential illicit discharges to the storm drain. Identify housekeeping BMPs that reduce maintenance of treatment control measures.

C. Spill Plan (not required for PLU Only Projects)
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1. Provide emergency notification procedures (phone and agency/persons to contact).

2. As appropriate for the site, provide emergency containment and cleaning procedures.

3. Note downstream receiving water bodies which may be affected by spills or chronic untreated discharges.

4. Create an emergency sampling procedure for spills. Emergency sampling can protect the property owner from erroneous liability for downstream receiving area cleanups.

D. Facility Changes
Operational or facility conditions or changes that significantly affect the character or quantity of pollutants discharging into the stormwater control measures may require modifications to the Maintenance Plan and/or additional stormwater controls.

E. Training

1. Identify appropriate persons to be properly trained and ensure documentation of training.

2. Training to include:
a. Good housekeeping procedures defined in the Maintenance Plan b. Maintenance of all pollution mitigation devices
c. Identification and cleanup procedures for spills and overflows d. Large-scale spill or hazardous material response
e. Safety concerns when maintaining devices and cleaning spills F. Basic Inspection and Maintenance Activities

1. Create and maintain an on-site log for inspector names, dates, and stormwater control measure devices to be inspected and maintained. Provide a checklist for each inspection and maintenance category.

2. Perform and document annual testing of any mechanical or electrical devices prior to wet weather.

3. Report any significant changes in stormwater controls to the site management. As appropriate, ensure mechanical devices are working properly and/or landscaped BMP plantings are irrigated and nurtured to promote thick growth.

4. Note any significant maintenance requirements due to spills or unexpected discharges.

5. Perform maintenance and replacement as scheduled and as needed in a timely manner to ensure stormwater controls are performing as designed and approved.

6. Assure unauthorized low-flow discharges from the property do not bypass stormwater controls.
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Development Guidance Manual 8-4 May 2025

7. Perform an annual assessment of each pollution-generating operation and its associated stormwater controls to determine if any part of the pollution reduction train can be improved.

G. Revisions to Pollution Mitigation Measures:

1. If future correction or modification of past stormwater control measures or procedures is required, the owner shall obtain approval from the City prior to commencing any work. Corrective measures or modifications shall not cause discharges to bypass or otherwise impede existing stormwater control measures.

H. Monitoring & Reporting Program

1. The City may require a Monitoring & Reporting Program to ensure the stormwater control measures approved for the site are performing according to design.

2. If required by the City, the Maintenance Plan shall include performance testing and reporting protocols specified by the City.

8.2 MAINTENANCE AGREEMENT
Verification of maintenance provisions is required for all structural controls specified in this Development Guidance Manual, whether Site Design Controls (Section 3), Source Controls (Section 4), VRMs (Section 5), or Treatment Controls (Section 6). Verification, at a minimum, shall include:

1. The owner/developer's signed statement accepts responsibility for inspection and maintenance until the responsibility is legally transferred. A sample Owners Certification statement is provided in Appendix I, and either

2. A signed statement from the public entity assuming responsibility for structural control measure inspection and maintenance and certifying that it meets all City design standards; or

3. Written conditions in the sales or lease agreement that require the recipient to assume responsibility for inspection and maintenance activities and to conduct a maintenance inspection at least once a year; or

4. Written text in project conditions, covenants, and restrictions for residential properties that assign maintenance responsibilities to the Homeowners Association for the inspection and maintenance of the structural controls; or

5. A legally enforceable maintenance agreement that assigns responsibility for the inspection and maintenance of post-construction structural controls to the owner/operator. A Maintenance Agreement with the City must be executed by the owner/operator before occupancy of the project is approved. A template agreement is provided in Appendix I, however it is recommended that the project proponent use the most recent template agreement available on the City website24.

Owners, developers, and/or successors-in-interest (ODS) must establish a maintenance entity acceptable to the City that will be responsible for funding and performing the long-term operation, maintenance, replacement, and administration of the proposed treatment controls.

Maintenance entities may be either private or public, depending on the ownership of facilities. 24 https://www.modestogov.com/1263/Forms
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Private Maintenance Entity
The ODS of treatment controls constructed and located in private facilities must execute a Maintenance Agreement with the City before obtaining a building permit for a development project. The ODS will remain responsible for funding and performing the long-term operation, maintenance, replacement, and administration of the treatment controls.

Public Maintenance Entity
The ODS of any subdivision project that includes treatment controls pursuant to the SWQCCP and that will be annexed to the City is required to form a Storm Drainage Maintenance Assessment District to provide funding for the long-term operation, maintenance, replacement, and administration of the treatment controls and all assets of the distribution system (e.g., pump stations, inlets, outlets) constructed for the project. The Assessment District must be formed prior to the recording of a Final Map and requires submittal to and approval by the City of an Engineer’s Report that shall contain a boundary map and an allocation of the costs referenced above.
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Appendices
A: Glossary of Terms and List of Acronyms
B: Site Design Control Measure Fact Sheets (G1-G4)
C: Source Control Measure Fact Sheets (S1-S7)
D: Volume Retention Measure Fact Sheets (V1-V5)
E: LID-based Treatment Control Measure Fact Sheets (L1-L12) F: Conventional Treatment Control Measure Fact Sheets (C1-C6) G: Volume Retention Requirement Worksheet
H: Volume Retention Requirement Waiver Application
I: Maintenance Agreements and Forms
I-1: Stormwater Treatment Device Access and Maintenance Agreement Template I-2: SWQCP Owner’s Certification Statement
J: SWQCP Submittal Guidance
J-1: Stormwater Quality Control Plan Guidance
J-2: Stormwater Quality Control Plan Template
J-6: Stormwater Maintenance Plan Guidance
J-7: Stormwater Maintenance Plan Template
K: Hydrologic Soil Groups
L: Plants Suitable for Vegetative Control Measures
M: Standard Calculations for Diversion Structure Design N: Approved Proprietary Control Measures
O: Example Calculation
P: References
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APPENDIX A

GLOSSARY OF TERMS AND LIST OF ACRONYMS
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Development Guidance Manual A-1 May 2025
APPENDIX A. GLOSSARY OF TERMS AND LIST OF

ACRONYMS
Automotive Repair Shop: A facility that is categorized in any one of the following Standard Industrial Classification (SIC) codes: 5013, 5014, 5541, 5511, 7532-7534, or 7536- 7539.

Berm: An earthen, asphalt, or concrete mound used to direct the flow of stormwater runoff around or through a structure.

Best Management Practices (BMPs): Methods, measures, or practices designed and selected to reduce or eliminate the discharge of pollutants to surface waters from point and nonpoint source discharges including stormwater. BMPs include structural and nonstructural control measures, and operation and maintenance procedures, which can be applied before, during, and/or after pollution producing activities.

Buffer Strip or Zone: Strip of erosion-resistant vegetation over which stormwater runoff is directed.

Catch Basin (also known as Inlet or Drain Inlet): Box-like underground concrete structure with openings in curbs and gutters designed to collect stormwater runoff from streets and pavements.

Clean Water Act (CWA): (33 U.S.C. 1251 et seq.) requirements of the National Pollutant Discharge Elimination System program are defined under Sections 301, 307, 402, 318 and 405 of the CWA.

Commercial Development (for a Priority Project): This category is defined as any development on private land that is not for residential uses, where the land area for development is greater than or equal to 10,000 square feet of impervious area (not including the parking lot, see separate parking lot requirement below). The category includes but is not limited to, hospitals, laboratories and other medical facilities, office commercial, retail commercial, educational institutions), recreational facilities, commercial retail nurseries, car wash facilities, mini-malls, and other business complexes, shopping malls, hotels, office buildings, public warehouses, and other industrial facilities.

Conduit: Any channel or pipe for directing the flow of water.

Construction Activity: Includes clearing, grubbing, grading, excavation, demolition, and contractor activities that result in soil disturbance.

Construction General Permit5: A National Pollutant Discharge Elimination System permit issued by the State Water Resources Control Board for the discharge of stormwater associated with construction activity from soil disturbance of one (1) acre or more.

Conventional Treatment Control Measures: A subset of Treatment Control Measures that can be designed to treat the WQV/WQF. These control measures do not reduce stormwater runoff 5 https://www.waterboards.ca.gov/water_issues/programs/stormwater/construction.html #6..
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volumes and cannot be used to help meet the Volume Retention Requirement. For the purpose of this Guidance Manual, these are treatment control measures identified as C-1 through C-6.

Conveyance System: Any channel or pipe for collecting and directing stormwater runoff.

Culvert: A covered channel or a large diameter pipe that crosses under a road, sidewalk, etc.

Detention: The temporary storage of stormwater runoff to allow treatment by sedimentation and metered discharge of stormwater runoff at reduced peak flow rates. The capture and subsequent release of stormwater runoff from the site at a slower rate than it is collected the difference being held in temporary storage.

Development: Any construction, rehabilitation, redevelopment or reconstruction of any public or private residential project (whether single-family, multi-unit or planned unit development); industrial, commercial, retail and other non-residential projects, including public agency projects; or mass grading for future construction. It does not include routine maintenance to maintain original line and grade, hydraulic capacity, or original purpose of facility, nor does it include emergency construction activities required to immediately protect public health and safety.

Discharge of a Pollutant: Addition of any pollutant or combination of pollutants to waters of the United States from any point source or, any addition of any pollutant or combination of pollutants to the waters of the contiguous zone or the ocean from any point source other than a vessel or other floating craft which is being used as a means of transportation. The term discharge includes additions of pollutants into waters of the United States from:
 Surface runoff which is collected or channeled through a man-made structure;  Discharges through pipes, sewers, or other conveyances owned by a State, municipality, or other person which do not lead to a treatment works; and  Discharges through pipes, sewers, or other conveyances, leading into privately owned treatment works.

Disturbed Area: Area that is altered as a result of clearing, grubbing, grading, demolition, and/or excavation.

Erosion: The wearing away of land surface by wind or water. Erosion occurs naturally from weather or runoff but can be intensified by land-clearing practices relating to farming, residential, commercial, or industrial development, road building, or timber cutting.

Excavation: The process of removing earth, stone, or other materials, usually by digging.

Filter Fabric: Geotextile of relatively small mesh or pore size that is used to: (a) allow water to pass through while keeping sediment out (permeable); or (b) prevent both runoff and sediment from passing through (impermeable).

Full Capture System (FCS): A treatment control, or series of treatment controls, including but not limited to, a Multi-Benefit projects or a low impact development control that traps all particles that are 5 mm or greater, and has a design treatment capacity that is either: a) of not less than the peak flow rate, Q, resulting from a one-year, one-hour storm in the subdrainage #6..
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Development Guidance Manual A-3 May 2025
area (0.31 inches/hour)6, or b) appropriately sized to, and designed to carry at least the same flows as, the corresponding storm drain.

Grading: The cutting and/or filling of the land surface to a desired shape or elevation.

Hazardous Substance: (1) Any material that poses a threat to human health and/or the environment. Typical hazardous substances are toxic, corrosive, ignitable, explosive, or chemically reactive; (2) Any substance named by EPA to be reported if a designated quantity of the substance is spilled in the waters of the United States or if otherwise emitted into the environment.

Hazardous Waste: A waste or combination of wastes that, because of its quantity, concentration, or physical chemical, or infectious characteristics, may either cause or significantly contribute to an increase in mortality or an increase in serious irreversible illness; or pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, disposed of, or otherwise managed. Possesses at least one of four characteristics (ignitability, corrosivity, reactivity, or toxicity) or appears on special EPA or state lists. Regulated under the federal Resource Conservation and Recovery Act and the California Health and Safety Code.

Hydromodification: The change in the natural watershed hydrologic processes and runoff characteristics (i.e., interception, infiltration, overland flow, interflow and groundwater flow) caused by urbanization or other land use changes that result in increased stream flows and sediment transport. In addition, alteration of stream and river channels, installation of dams and water impoundments, and excessive stream bank and shoreline erosion are also considered hydromodification, due to their disruption of natural watershed hydrologic processes.

Illicit Connection: Any man-made conveyance that is connected to the storm drain system without a permit, excluding roof drains and other similar type connections. Examples include channels, pipelines, conduits, inlets, or outlets that are connected directly to the storm drain system.

Illicit Discharge: Any discharge to the storm drain system that is prohibited under local, state, or federal statutes, ordinances, codes, or regulations. The term “illicit discharge” includes all non-stormwater discharges except discharges pursuant to a National Pollutant Discharge Elimination System permit, discharges that are identified in Discharge Prohibitions of this Order, and discharges authorized by the Regional Board.

Impermeable Liner: Filter fabric of relatively small mesh or pore size that is used to prevent both water and sediment from passing through.

Impervious Surface/ Cover: A hard surface area that impede the natural infiltration of stormwater and causes water to runoff the surface in greater quantities or at an increased rate of flow from the flow present under pre-project conditions. Impervious surfaces include, but 6 Determined using the tool Basin Sizer (ca.gov)
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Development Guidance Manual A-4 May 2025
are not limited to, rooftops, walkways, patios, driveways, parking lots, roads or concrete and asphalt paving.

Industrial General Permit7: A National Pollutant Discharge Elimination System Permit issued by the State Water Resources Control Board for the discharge of stormwater associated with industrial activity.

Infiltration: The downward entry of water into the surface of the soil.

Inlet: An entrance into a ditch, storm sewer, or other waterway.

Integrated Pest Management (IPM): An ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties.

Pesticides are used only after monitoring indicates they are needed according to established guidelines, and treatments are made with the goal of removing only the target organism.

Low Impact Development (LID): A stormwater management and land development strategy that emphasizes conservation and the use of on-site natural features integrated with engineered, small-scale hydrologic controls to more closely reflect pre-development hydrologic functions.

Low Impact Development-based Treatment Control Measures: A subset of Treatment Control Measures that can be designed to treat the WQV/WQF and reduce runoff volumes. The runoff reduction achieved by these controls can be used to help meet the Volume Retention Requirement.

Material Storage Areas: On site locations where raw materials, products, final products, byproducts, or waste materials are stored.

Multi-Benefit Project: A treatment control project designed to achieve any of the benefits set forth in section 10562, subdivision (d) of the Water Code. Examples include projects designed to: infiltrate, recharge or store stormwater for beneficial reuse; develop or enhance habitat and open space through stormwater and non-stormwater management; and/or reduce stormwater and non-stormwater runoff volume.

Municipal Separate Storm Sewer System (MS4): A conveyance or system of conveyances (including roads with drainage systems, municipal streets, alleys, catch basins, curbs, gutters, ditches, manmade channels, or storm drains) owned by a State, city, county, town or other public body, that is designed or used for collecting or conveying stormwater runoff, which is not a combined sewer, and which is not part of a publicly owned treatment works, and which discharges to Waters of the United States.

National Pollutant Discharge Elimination System (NPDES): The national program for issuing, modifying, revoking and reissuing, terminating, monitoring and enforcing permits, and imposing and enforcing pretreatment requirements, under CWA §307, 402, 318, and 405. 7 https://www.waterboards.ca.gov/water_issues/programs/stormwater/industrial.html #6..
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Development Guidance Manual A-5 May 2025
New Development: Land disturbing activities; structural development, including construction or installation of a building or structure, creation of impervious surfaces; and land subdivision.

Non-Stormwater Discharge: Any discharge to municipal separate storm drain system that is not composed entirely of stormwater (e.g., discharges containing process wastewater, non-contact cooling water, or sanitary wastewater).

Non-Structural Best Management Practice (BMP): Low technology procedures or management practices designed to prevent pollutants associated with site functions and activities from being discharged with stormwater runoff. Examples include reducing impervious cover, rain barrels, good housekeeping practices, employee training, standard operating practices, inventory control measures, etc.

Outfall: The point where stormwater runoff discharges from a pipe, channel, ditch, or other conveyance to a waterway/receiving water.

Parking Lot: Land area or facility for the temporary parking or storage of motor vehicles used personally, for business or for commerce with an impervious surface area of 5,000 square feet or more, or with 25 or more parking spaces.

Permeability: A property of soil that enables water or air to move through it. ;Usually expressed in inches/hour or inches/day.

Point Source: Any discernible, confined, and discrete conveyance from which pollutants are or may be discharged. This term does not include return flows from irrigated agriculture or agricultural stormwater runoff.

Pollutant: A substance introduced into the environment that adversely affects the usefulness of a resource.

Pollution Prevention: Practices and actions that reduce or eliminate the generation of pollutants.

Post-project: The land use condition as a result of the proposed development activity.

Precipitation: Any form of rain or snow.

Pre-project: The existing land use condition prior to the proposed development activity.

Priority Land Uses (PLU): Those developed sites, facilities, or land uses (i.e., not simply zoned land uses) within the municipal jurisdiction from which discharges of trash are regulated

1. High-density residential: all land uses with at least ten (10) developed dwelling units/acre.

2. Industrial: land uses where the primary activities on the developed parcels involve product manufacture, storage, or distribution (e.g., manufacturing businesses, warehouses, equipment storage lots, junkyards, wholesale businesses, distribution centers, or building material sales yards).

3. Commercial: land uses where the primary activities on the developed parcels involve the sale or transfer of goods or services to consumers (e.g., business or professional buildings, shops, restaurants, theaters, vehicle repair shops, etc.) #6..
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Development Guidance Manual A-6 May 2025

4. Mixed urban: land uses where high-density residential, industrial, and/or commercial land uses predominate collectively (i.e., are intermixed).

5. Public transportation stations: facilities or sites where public transit agencies’ vehicles load or unload passengers or goods (e.g., bus stations and stops).

Priority Project: Any project that meets the following project types or thresholds (where applicable):

1. Residential subdivision of 10 housing units or more.

2. Commercial and industrial developments greater than or equal to 10,000 square feet of impervious area.

3. Automotive repair shops.

4. Retail gasoline outlets.

5. Restaurants.

6. Parking lots 5,000 square feet or more or with 25 or more parking spaces and potentially exposed to urban runoff.

7. Significant redevelopment.

Receiving Water: A “water of the United States” into which pollutants are or may be discharged.

Redevelopment (Significant): Land disturbing activity that results in the creation, addition, or replacement of at least 5,000 square feet of impervious surface area on an already developed site. Significant redevelopment includes, but is not limited to, expansion of a building footprint or addition or replacement of a structure; structural development including an increase in gross floor area and/or exterior construction or remodeling; replacement of impervious surface that is not part of a routine maintenance activity; and land disturbing activities related with structural or impervious surfaces. It does not include routine maintenance to maintain original line and grade, hydraulic capacity, or emergency construction activities required to immediately protect public health and safety.

Regional Stormwater Management Facilities: A regional stormwater management facility is defined as a facility that provides detention of stormwater runoff typically for the entire upstream watershed.

Residential (Priority Project): (subdivision of 10 housing units or more) Includes single-family homes, multi-family homes, condominiums, and apartments, as well as the related street and road paved surfaces that are used for the transportation of automobiles, trucks, motorcycles, and other vehicles (not including parking lots, see separate parking lot requirement below). A housing unit is also defined as a dwelling unit.

Restaurant (Priority Project): This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling foods and drinks for immediate consumption (SIC code 5812), where total impervious area for development is greater than or equal to 5,000 square feet. For restaurants less than 5,000 #6..
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Development Guidance Manual A-7 May 2025
square feet, the development must meet all development standards except for treatment control measures and numeric sizing criteria.

Retail Gasoline Outlet: Any facility engaged in selling gasoline and lubricating oils.

Retention: The storage of stormwater to prevent it from leaving the development site.

Runoff: Water originating from rainfall, melted snow, and other sources that flows over the land surface to drainage facilities, rivers, streams, springs, seeps, ponds, lakes, wetlands, and shallow groundwater.

Run-on: Stormwater surface flow or other surface flow which enters areas other than that where it originated.

Secondary Containment: Structures, usually dikes or berms, surrounding tanks or other storage containers and designed to catch spilled material from the storage containers.

Sedimentation: The process of depositing soil particles, clays, sands, or other sediments that were transported by runoff.

Sediments: Soil, sand, and minerals washed from land into water, usually after rain, that accumulate in reservoirs, rivers, and harbors.

Significant Redevelopment (Priority Project): Land disturbing activity that results in the creation, addition, or replacement of at least 5,000 square feet of impervious surface area on an already developed site. Significant redevelopment includes, but is not limited to, expansion of a building footprint or addition or replacement of a structure; structural development including an increase in gross floor area and/or exterior construction or remodeling; replacement of impervious surface that is not part of a routine maintenance activity; and land disturbing activities related with structural or impervious surfaces . It does not include routine maintenance to maintain original line and grade, hydraulic capacity, or emergency construction activities required to immediately protect public health and safety.

In the case of an addition, if the addition constitutes less than 50 percent of the original development, post-construction stormwater requirements only apply to the addition.

Source Control Measures: Any schedules of activities, structural devices, prohibitions of practices, maintenance procedures, managerial practices or operational practices that aim to prevent stormwater pollution by reducing the potential for contamination at the source of pollution.

Storm Drains: Above- and below-ground structures for transporting stormwater runoff to streams or outfalls for flood control purposes.

Storm Event: A rainfall event that produces more than 0.1 inch of precipitation and is separated from the previous storm event by at least 72 hours of dry weather.

Stormwater: Stormwater runoff, snow-melt runoff, surface runoff, and drainage, excluding infiltration and irrigation tailwater. Urban runoff and snowmelt runoff consisting only of those discharges, which originate from precipitation events. Stormwater is that portion of precipitation that flows across a surface to the storm drain system or receiving waters. #6..
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Development Guidance Manual A-8 May 2025
Stormwater Pollution Prevention Plan (SWPPP): A written plan that documents the series of phases and activities that, first, characterizes your site, and then prompts you to select and carry out actions which prevent the pollution of stormwater discharges.

Structural BMP: Any structural facility designed and constructed to mitigate the adverse impacts of stormwater and urban runoff pollution (e.g. canopy, structural enclosure). The category may include both Treatment Control BMPs and Source Control BMPs.

Trash: All improperly discarded solid material from any production, manufacturing, or processing operation including, but not limited to, products, product packaging, or containers constructed of plastic, steel, aluminum, glass, paper, or other synthetic or natural materials.

Trash Amendments: Amendment to the Water Quality Control Plan for Ocean Waters of California to Control Trash and Part 1 Trash Provision of the Water Quality Control Plan for Inland Surface Waters, Enclosed Bays, and Estuaries they are collectively referred to as “the Trash Amendments”. The State Water Quality Control Board adopted these on April 7, 2015.

Treatment: The application of engineered systems that use physical, chemical, or biological processes to remove pollutants. Such processes include, but are not limited to, filtration, gravity settling, media adsorption, biodegradation, biological uptake, chemical oxidation and ultraviolet radiation.

Treatment Control Measures: Any engineered system designed to remove pollutants by simple gravity settling of particulate pollutants, filtration, biological uptake, media adsorption or any other physical, biological, or chemical process. Treatment Controls, for the purposes of this Plan have been divided into two types: LID Treatment Controls and Conventional Treatment Controls.

Treatment Control Measures (Trash Amendments): Structural best management practices to either
a) remove pollutants and/or solids from STORMWATER runoff, wastewater, or effluent, or b) capture, infiltrate or reuse stormwater runoff, wastewater, or effluent.

Treatment controls include full capture systems and low impact development controls.

Volume Retention Measures: BMPs that can be used to direct, retain, reuse and/or infiltrate stormwater runoff (e.g., rain gardens and rain barrels).

Volume Retention Requirement: Priority Projects must reduce post-project runoff volume to pre-project runoff volumes for the 0.50” rainfall event (85th percentile, 24-hour storm depth) using a combination of Volume Retention Measures and LID Treatment Controls. #6..
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Development Guidance Manual A-9 May 2025

LIST OF ACRONYMS
ASTM American Society for Testing Materials
BMPs Best Management Practices
CASQA California Stormwater Quality Association
CWA Clean Water Act
FCS Trash Full Capture System
IPM Integrated Pest Management
LID Low Impact Development
MEP Maximum Extent Practicable
MS4 Municipal Separate Storm Sewer System
NPDES National Pollutant Discharge Elimination System
NRCS Natural Resources Conservation Service
O&M Operations and Maintenance
PCC Portland Cement Concrete
PLU Priority Land Use
PPF Porous Pavement Filter
SIC Standard Industrial Classification
WQF Water Quality Flow
WQV Water Quality Volume
SWPPP Stormwater Pollution Prevention Plan
SWQCP Stormwater Quality Control Plan
USDA United States Department of Agriculture
USEPA United States Environmental Protection Agency
VRM Volume Retention Measures
VRR Volume Retention Requirement
WPCP Water Pollution Control Plan
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APPENDIX B
Site Design Control Measures Fact Sheets (G1 – G4)
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Site Design Control Measures Fact Sheet G-1: Conserve Natural Areas Development Guidance Manual B-1 May 2025
Purpose
Each project site possesses unique topographic, hydrologic and vegetative features, some of which are more suitable for development than others. Locating development on the least sensitive portion of a site and conserving naturally vegetated areas can minimize environmental impacts in general and stormwater runoff impacts in particular.

Design Criteria
If applicable and feasible for the given site conditions, the following site design features or elements are required and should be included in the project site layout, consistent with applicable General Plan and Local Area Plan policies:

1. Preserve riparian areas and wetlands.

2. Concentrate or cluster development on least-sensitive portions of a site while leaving the remaining land in an undisturbed natural state.

3. Identify and avoid areas susceptible to erosion and sediment loss.

4. Limit clearing and grading of native vegetation at a site to the minimum amount needed to build lots, allow access, and provide fire protection. This area may be defined as the development envelope.

5. Maintain existing topography and existing drainage divides to encourage dispersed flow.

6. Maximize trees and other vegetation at each site by planting additional vegetation, clustering tree areas, and promoting native and/or drought-tolerant plants.

7. Promote natural vegetation by using parking lot islands and other landscaped areas. #6..
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Site Design Control Measures Fact Sheet G-2: Protect Slopes & Channels Development Guidance Manual B-2 May 2025
Purpose
Erosion of slopes and channels can be a major source of sediment and associated pollutants, such as nutrients, if not properly protected and stabilized.

Design Criteria
Slope Protection
Slope protection practices must conform to design requirements or standards set forth in the most recent City Standard Specifications. The design criteria described in this fact sheet are intended to enhance and be consistent with these local standards.

1. Slopes must be protected from erosion by safely conveying stormwater runoff from the tops of slopes.

2. Slopes must be vegetated (full-cover) with first consideration given to use of native or drought-tolerant species.

Channel Protection
The following measures should be implemented to provide erosion protection of unlined receiving waters. Activities and structures must conform to applicable standards and specifications of agencies with the jurisdiction (e.g., U.S. Army Corps of Engineers (COE), California Department of Fish and Wildlife).

1. Utilize natural drainage systems where feasible but minimize stormwater runoff discharge rate and volume to avoid erosive flows.

2. Stabilize permanent channel crossings.

3. In cases where beds and/or banks of receiving streams are fragile and particularly susceptible to erosion, special stabilization may be required. a. Small-grade control structures (e.g., drop structure) may be used to reduce the slope of the channel.
b. Severe bends or cut banks may need to be hardened by lining them with grass or rock. c. Rock-lined, low-flow channels may be appropriate to protect fragile beds.

4. Install energy dissipaters, such as rock riprap, at the outlets of storm drains, culverts, conduits, or channels that discharge into unlined channels to lessen erosion potential.

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Site Design Control Measures Fact Sheet G-3: Minimize Soil Compaction Development Guidance Manual B-3 May 2025
Purpose
This control protects water quality by preserving some of the natural hydrologic functions of the site. Existing soils may contain organic material and soil biota that are ideal for storing and infiltrating stormwater. Clearing and grading equipment can remove existing compact soils and limit their infiltrative capacity. The design criteria presented below are not intended to supersede compaction requirements
associated with building codes.

Design Criteria

1. Delineate and flag the development envelope for the site (e.g., identify the minimum area needed to build lots,
allow access, and provide fire protection).

2. Restrict equipment access and storage of construction equipment to the development envelope.

3. Restrict storage of construction equipment within the development envelope.

4. Avoid the removal of existing trees and valuable vegetation as feasible.

5. It may be difficult for infill and redevelopment developments to avoid soil disturbance. The project should consider soil amendments to restore permeability and organic content in these cases.

Figure 3-1: Dynamic modelling of a single-stage highrate anaerobic reactor—I. Model derivation.

Water Research. Source: Costello, D.J.,
Greenfield, P.F., & Lee, P.L. (1991).
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Site Design Control Measures Fact Sheet G-4: Minimize Impervious Area Development Guidance Manual B-4 May 2025
Purpose
The potential for the discharge of pollutants in
stormwater runoff from a project site increases as the
percentage of the impervious area within the project site increases since the resulting volume and rate of runoff flow also increase. Pollutants deposited on impervious
areas tend to be easily mobilized and transported by
runoff flow. Minimizing impervious areas through site
design is an important means of minimizing stormwater
pollutants of concern. In addition to the environmental and aesthetic benefits, a highly pervious site may allow a reduction in the size of downstream conveyance and
treatment systems, yielding savings in development
costs.

Minimizing impervious area will also reduce the
stormwater runoff coefficient, which is directly
proportional to the volume retention requirement
(VRR). Therefore, lowering the stormwater runoff
coefficient will lower the amount of stormwater
runoff that must be retained on-site and treated.

Design Strategies
Some aspects of site design are directed by City building and fire codes and ordinances. These design strategies are intended to enhance and be consistent with the local codes and ordinances. Strategies for minimizing impervious surfaces through site design include:

1. Use minimum allowable roadway and sidewalk cross sections, driveway lengths and parking stall widths (refer to City Standard Specifications).

2. Minimize or eliminate the use of curb and gutter, so that roadway runoff drains to swales and other volume retention measures (VRMs) or Low Impact Development (LID) Treatment Controls are strongly encouraged where slope and density permit.

3. Use two-track/ribbon driveways or shared driveways.

4. Include landscape islands in cul-de-sacs (where approved).

5. Reduce the footprints of buildings and parking lots.

6. Cluster buildings and paved areas to maximize pervious area.

7. Maximize tree preservation or tree planting.

8. Avoid compacting or paving over soils with high infiltration rates (see G-3).

9. Use pervious pavement materials where appropriate, such as modular paving blocks, turf blocks, porous concrete and asphalt, brick, and gravel or cobbles.

10. Use grass-lined channels or surface swales to convey runoff instead of paved gutters. existing trees and Water Quality
Infiltration Basins preserved
shared driveway
clustered buildings
vegetated swale
narrow street
Source: Low Impact Development Handbook Stormwater
Management Strategies. (2014, July).
https://www.sandiegocounty.gov/content/dam/sdc/dpw/WATERS HED_PROTECTION_PROGRAM/watershedpdf/SBMP/Filtration_O&amp;M_Form.pdf. #6..
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APPENDIX C
Source Control Measures Fact Sheets (S1 – S7)
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Source Control Measures Fact Sheet S-1: Storm Drain Message and Signage Development Guidance Manual C-1 May 2025
Purpose
Waste material dumped into storm drain inlets can adversely impact surface and ground water.

Storm drain messages have become a popular method of alerting the public about the effects of and the prohibitions against waste disposal into the storm drain system. The signs are typically stenciled or affixed near the storm drain inlet. The message simply informs the public that dumping wastes into storm drain inlets is prohibited and/or the drain that discharges to local receiving waters.

Design Criteria
Signs with language and/or graphical icons, which prohibit illegal dumping, shall be posted at designated public access points along channels and streams within a project area. Consult with City staff to determine specific signage requirements.

Storm drain message markers, placards, or concrete stamps are required at all storm drain inlets within the boundary of the development project. Markers should be placed in clear sight adjacent to inlets (Figure S-1.1). All storm drain inlet locations must be identified on the development site map.

All storm drain catch basins and drain inlets must be labeled with the City’s approved stormwater quality message, prior to acceptance by the City.

Maintenance Requirements
Legibility of markers and signs shall be maintained.
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Source Control Measures Fact Sheet S-1: Storm Drain Message and Signage Development Guidance Manual C-2 May 2025
Figure S-1.1. Storm Drain Message Location
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Source Control Measures Fact Sheet S-2: Outdoor Material Storage Area Development Guidance Manual C-3 May 2025
Purpose
Materials (i.e., raw, finished, or waste products) stored outdoors can become sources of pollutants in stormwater runoff if not handled or stored properly. The type of pollutants associated with the materials will vary depending on the type of activities conducted onsite.

Some materials are more of a concern than others. Toxic and hazardous materials must be prevented from coming into contact with stormwater. Non-toxic or non-hazardous materials, such as debris and sediment, can significantly impact surface waters if discharged in significant quantities.

Applicability
Materials are classified into three categories based on the potential risk for pollutant release associated with stormwater contact – high risk, low risk, and non-risk. The general types of materials under each category are listed in Table S-2.1. The City will make final determinations regarding category listings, if necessary.

Table S-2.1. Classification of Materials for Potential Pollutant Risk High-Risk Materials Low-Risk Materials Non-Risk Materials • Recycled materials with
discharge potential
• Corrosives
• Food items
• Chalk/gypsum products
• Scrap or salvage goods
• Feedstock/grain
• Fertilizer
• Pesticides
• Compost
• Asphalt
• Lime/lye/soda ash
• Animal/human wastes
• Rubber or plastic pellets or
other small pieces
• Uncured concrete/cement
• Lead and copper, and any
metals with oil/grease coating
• Clean recycled materials
without effluent potential
• Metal (excluding lead and
copper, and any metals with
oil/grease coating)
• Sawdust/bark chips
• Sand/soil
• Unwashed gravel/rock
• Washed gravel/rock
• Finished lumber (nonpressure treated)
• Rubber or plastic products
(excluding small pieces)
• Clean, precast concrete
products
• Glass products (new)
• Inert products
• Gaseous products
• Products in containers that
prevent contact with
stormwater (fertilizers and
pesticides excluded)
Metal buildings, roofing, and fencing materials may be significant sources of metals in stormwater runoff. Minimizing the use of copper and galvanized (zinc coated) metals on buildings and fencing can help reduce leaching of these constituents into stormwater runoff.

Materials that are conventionally made of galvanized metals include metal roofs, chain-link fencing, metal downspouts, and metal vents of roofs.
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Source Control Measures Fact Sheet S-2: Outdoor Material Storage Area Development Guidance Manual C-4 May 2025
To reduce the risk of metals pollutant release, alternatives to copper and galvanized materials can be used such as coated metal products which are available for both roofing and gutter application. Vinyl-coated fencing is an alternative to traditional galvanized chain-link fences.

These products eliminate contact of bare metal with precipitation. There are also roofing materials made of recycled rubber and plastic.

Design Criteria
Design requirements for material storage areas are governed by current City Building and Fire Codes, ordinances, and zoning requirements. Source control measures described in this fact sheet are intended to enhance and be consistent with these code and ordinance requirements.

The design features presented in Table S-2.2 should be incorporated into the design of outdoor material storage areas when stored materials could potentially contribute significant pollutants if the materials came into contact with stormwater runoff.

Accumulated Stormwater and Non-stormwater
Stormwater and non-stormwater may accumulate in containment areas and sumps with impervious surfaces. Contaminated accumulated water must be disposed of per applicable laws and cannot be discharged directly to the storm drain or sanitary sewer system without the appropriate permission and/or permit. Contact the City regarding permits for the discharge of contaminated accumulated water.

Table S-2.2. Design Criteria for Outdoor Material Storage Areas Design Feature Design Criteria
Surfacing
• High-Risk Materials:
o Construct or pave the storage area base with a material that is chemically resistant to the materials being stored and impervious to leaks and spills. • Low-Risk and Non-Risk Materials:
o No requirement for surfacing
Covers
• High-Risk Materials:
o Cover the storage area with a permanent canopy, roof, or awning to prevent precipitation from directly contacting the storage area. Direct runoff from the cover away from the storage area to a stormwater disposal point that meets all applicable code requirements and applicable requirements of this manual. o Covers 10 feet high or less shall have a minimum overhang of 3 feet measured from the perimeter of the hydraulically isolated storage area. o Cover higher than 10 feet shall have a minimum overhang of 5 feet measured from the perimeter of the hydraulically isolated storage area. • Low-Risk Materials:
o At a minimum, completely cover erodible material with temporary plastic sheeting during rainfall events.

Hydraulic Isolation
and Drainage
• High-Risk Materials:
o Hydraulically isolate the storage area by means of grading, berms, or drains to prevent run-on of stormwater from surrounding areas or roof drains. #6..
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Source Control Measures Fact Sheet S-2: Outdoor Material Storage Area Development Guidance Manual C-5 May 2025
Design Feature Design Criteria
o Direct runoff from surrounding areas away from the hydraulically isolated storage area to a stormwater disposal point that meets all applicable requirements of this manual and codes.
o Drainage facilities are not required for the hydraulically isolated storage area.

However, if drainage facilities are provided, drainage from the hydraulically isolated storage area must be directed to an approved City sanitary sewer or approved collection point.
• Low-Risk Materials:
o Drainage from storage area may be to an approved treatment control measure or possibly to an approved standard stormwater drain(s). o For erodible material, provide grading and a structural containment barrier on at least three sides of each stockpile to prevent run-on of stormwater from the surrounding area and to prevent migration of material due to wind erosion.

Maintenance Requirements
The integrity of structural elements that are subject to damage (e.g., screens, covers, and signs) must be maintained by the owner/operator as required by the City’s Municipal Code. Failure to properly maintain building and property may subject the property owner to enforcement.

Maintenance agreements between the City and the owner/operator may be required (Appendix I).
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Source Control Measures Fact Sheet S-3: Outdoor Trash Storage & Waste Handling Development Guidance Manual C-6 May 2025
Purpose
Stormwater runoff from areas where trash is stored or disposed of can convey pollutants. In addition, loose trash and debris can be easily transported by water or wind into nearby storm drain inlets, channels, and/or receiving waters. Waste handling operations that may be sources of pollutants include dumpsters and waste piles.

Design Criteria
Design requirements for waste handling areas are governed by Building and Fire Codes as well as current City ordinances and zoning requirements. The design criteria described in the fact sheet are meant to enhance and be consistent with these code and ordinance requirements.

Hazardous waste should be handled under legal requirements established in Title 22 of the California Health and Safety Code.

Wastes from commercial and industrial sites are typically hauled away for disposal by either public or commercial carriers that may have design or access requirements for waste storage areas. The design criteria listed below are recommendations and are not intended to conflict with requirements established by the waste hauler. The waste hauler should be contacted prior to the design of your site trash collection area. Conflicts or issues should be discussed with the City.

The trash storage area design features presented in Table S-3.1 were developed to enhance the City codes and ordinances and should be implemented depending on the type of waste and the type of containment.

Table S-3.1. Design Criteria for Outdoor Trash Storage and Waste Handling Areas Source Control
Design Feature Design Criteria
Surfacing • Construct storage area base with a material impervious to leaks and spills.

Screens/Covers
• Install a screen or wall around the trash storage area to prevent off-site transport of loose trash.
• Use lined bins or dumpsters to reduce the leaking of liquid wastes. • Use water-proof lids on bins/dumpsters or provide a roof to cover the enclosure (City discretion) to prevent rain from entering containers.

Grading/Drainage • Berm or grade the waste handling area to prevent run-on of stormwater. • Locate storm drains at least 35 feet from the waste handling area.

Signs • Post signs inside enclosure and/or on all dumpsters prohibiting the disposal of liquids and hazardous materials therein.
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Source Control Measures Fact Sheet S-3: Outdoor Trash Storage & Waste Handling Development Guidance Manual C-7 May 2025
Accumulated Stormwater and Non-stormwater
Stormwater and non-stormwater may accumulate in containment areas and sumps with impervious surfaces. Contaminated accumulated water must be disposed of per applicable laws and cannot be discharged directly to the storm drain or sanitary sewer system without the appropriate permission and/or permit. Contact the City regarding permits for the discharge of contaminated accumulated water.

Maintenance Requirements
The integrity of structural elements that are subject to damage (e.g., screens, covers, and signs) must be maintained by the owner/operator as required by the City’s Municipal Code. Failure to properly maintain the building and property may subject the property owner to enforcement.

Maintenance agreements between the City and the owner/operator may be required (Appendix I).
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Source Control Measures Fact Sheet S-4: Outdoor Loading/Unloading Dock Area Development Guidance Manual C-8 May 2025
Purpose
Materials spilled, leaked, or lost during loading or unloading may collect on impervious surfaces or in the soil and be carried away by stormwater runoff or when the area is cleaned. Also, rainfall may wash pollutants from machinery used to load or unload materials. Depressed loading docks (truck wells) are contained areas that can accumulate stormwater runoff.

Discharges of spills or contaminated stormwater runoff to the storm drain system is prohibited.

Design Criteria
Design requirements for outdoor loading/unloading materials are governed by Building and Fire Codes and current City ordinances and zoning requirements. Source control measures described in the fact sheet are meant to enhance and be consistent with these code and ordinance requirements. The design criteria presented in Table S-4.1 should be followed when developing construction plans for outdoor material loading/unloading areas and are not intended to be in conflict with requirements that may be established by individual companies.

Conflicts or issues should be discussed with City staff.

The following design criteria should be followed when developing construction plans for material loading/unloading areas.

Table S-4.1. Design Criteria for Outdoor Loading/Unloading Dock Area Design Feature Design Criteria
Surfacing
• Construct floor surfaces with paving material that is impervious and chemically resistant to materials being handled in the loading/unloading area.

Covers
• Cover outdoor loading/unloading areas to a distance of at least 10 feet beyond the loading dock or building face if there is no raised dock. • For interior transfer bays, provide a 10-ft minimum “no obstruction zone” to allow trucks or trailers to extend at least 5 feet inside the building.

Identify “no obstruction zone” clearly on building plans and paint zone with high visibility floor paint.
• If covers or interior transfer bays are not feasible, install a seal or door skirt and provide a rain cover to shield all material transfers between trailers and building.
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Source Control Measures Fact Sheet S-4: Outdoor Loading/Unloading Dock Area Development Guidance Manual C-9 May 2025
Design Feature Design Criteria
Hydraulic Isolation
and Drainage
• For outdoor loading/unloading areas, hydraulically isolate the first 6 feet of paved area measured from the building or dock face by means of grading, berms, or drains to prevent run-on of stormwater from surrounding areas or roof drains. Direct runoff and drainage from surrounding areas away from hydraulically isolated area to a stormwater discharge point that meets all applicable requirements of this manual.
• For interior transfer bays or bay doors, prevent stormwater runoff from surrounding areas from entering the building by means of grading or drains.

Do not install interior floor drains in the “no obstruction zone”.

Hydraulically isolate the “no obstruction zone” from any interior floor drains.
• Direct drainage from the hydraulically isolated loading/unloading area to an approved sediment/oil/water separator system connected to an approved City sanitary sewer or other approved collection point. Provide a manual emergency spill diversion valve upstream of the separator system to direct flow in the event of a spill to an approved spill containment vault sized to contain a volume equal to 125% of largest container handled at the facility.

Accumulated Stormwater and Non-stormwater
Stormwater and non-stormwater may accumulate in containment areas and sumps with impervious surfaces. Contaminated accumulated water must be disposed of per applicable laws and cannot be discharged directly to the storm drain or sanitary sewer system without the appropriate permission and/or permit. Contact the City regarding permits for the discharge of contaminated accumulated water.

Maintenance Requirements
The integrity of structural elements that are subject to damage (e.g., screens, covers, and signs) must be maintained by the owner/operator as required by the City’s Municipal Code. Failure to properly maintain the building and property may subject the property owner to enforcement.

Maintenance agreements between the City and the owner/operator may be required (Appendix I).
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Source Control Measures Fact Sheet S-5: Outdoor Repair/Maintenance Area Development Guidance Manual C-10 May 2025
Purpose
Activities that can contaminate stormwater at outdoor vehicle and equipment repair/maintenance areas include engine repair, service and parking (leaking engines or parts).

Oil and grease, solvents, car battery acid, coolant and gasoline from the repair/maintenance bays can contaminate stormwater runoff.

Design Criteria
Design requirements for vehicle and equipment maintenance and repair areas are governed by Building and Fire Codes and current City ordinances and zoning requirements. The design criteria described in the fact sheet are meant to enhance and be consistent with these code requirements.

The design criteria required for vehicle and equipment maintenance and repair are presented in Table S-5.1. All hazardous and toxic waste must be prevented from entering the storm drainage system. Conflicts or issues should be discussed with City staff.

Table S-5.1. Design Criteria for Outdoor Vehicle/Equipment Repair/Maintenance Areas Design Feature Design Criteria
Surfacing • Construct the vehicle/equipment maintenance/repair floor area with Portland cement concrete (PCC).

Covers • Cover areas where parts and fluids are stored. • Cover or enclose all maintenance/repair areas.

Grading/Contouring
• Berm or grade the maintenance/repair area to prevent run-on and runoff of stormwater or runoff of spills.
• Direct runoff from downspouts/roofs away from
maintenance/repair areas.
• Grade the maintenance/repair area to drain to a dead-end sump for collection of all wash water, leaks, and spills. Direct connection of maintenance/repair area to the storm drain system is prohibited.
• Do not locate storm drains in the immediate vicinity of the maintenance/repair area.

Emergency Storm Drain Seal
• Provide means, such as isolation valves, drain plugs, or drain covers, to prevent spills or contaminated stormwater from entering the storm drainage system.

Accumulated Stormwater and Non-stormwater
Stormwater and non-stormwater may accumulate in containment areas and sumps with impervious surfaces. Contaminated accumulated water must be disposed of per applicable laws and cannot be discharged directly to the storm drain or sanitary sewer system without the appropriate permission and/or permit. Contact the City regarding permits for the discharge of contaminated accumulated water.
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Source Control Measures Fact Sheet S-5: Outdoor Repair/Maintenance Area Development Guidance Manual C-11 May 2025
Maintenance Requirements
The integrity of structural elements that are subject to damage (e.g., screens, covers, and signs) must be maintained by the owner/operator as required by the City’s Municipal Code. Failure to properly maintain the building and property may subject the property owner to enforcement.

Maintenance agreements between the City and the owner/operator may be required (Appendix I).
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Source Control Measures Fact Sheet S-6: Outdoor Vehicle/Equipment Wash Area Development Guidance Manual C-12 May 2025
Purpose
Washing vehicles and equipment in areas where the wash water flows onto the ground can adversely impact receiving waters. Wash waters can contain high concentrations of oil and grease, solvents, phosphates, and high suspended solids loads that can be transported to the storm drain system or receiving water.

Design Criteria
Design requirements for vehicle and equipment washing areas are governed by Building and Fire codes and current City ordinances and zoning requirements. The design criteria described in Table S-6.1 are intended to enhance and be consistent with these code requirements.

Hazardous and toxic wastes cannot enter the storm drain system. Conflicts or issues should be discussed with City staff.

Table S-6.1. Design Criteria for Outdoor Vehicle/Equipment Wash Areas Design Feature Design Criteria
Surfacing • Construct the vehicle/equipment wash area floors with Portland Cement Concrete (PCC).

Covers
• Provide a cover that extends at least 3 feet beyond the hydraulically isolated area for cover heights less than or equal to 10 feet. • Provide a cover that extends at least 5 feet beyond the hydraulically isolated area for cover heights greater than 10 feet.

Grading/Drainage
• Hydraulically isolate the maintenance/repair area using berms or grading to prevent run-on and runoff of stormwater or runoff of spills. • Grade or berm the wash area to contain the wash water within the covered area and direct the wash water to treatment and recycle or pretreatment and proper connection to the sanitary sewer system.

Obtain approval from the City before discharging to the sanitary sewer.
• Direct stormwater runoff from downspouts/roofs away from wash areas.
• Do not locate storm drains in the immediate vicinity of the wash area.

Emergency Storm Drain Seal
• Provide means, such as isolation valves, drain plugs, or drain covers, to prevent spills or contaminated stormwater from entering the storm drainage system.

Accumulated Stormwater and Non-stormwater
Stormwater and non-stormwater may accumulate in containment areas and sumps with impervious surfaces. Contaminated accumulated water must be disposed of per applicable laws and cannot be discharged directly to the storm drain or sanitary sewer system without the appropriate permission and/or permit. Contact the City regarding permits for the discharge of contaminated accumulated water.
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Source Control Measures Fact Sheet S-6: Outdoor Vehicle/Equipment Wash Area Development Guidance Manual C-13 May 2025
Maintenance Requirements
The integrity of structural elements that are subject to damage (e.g., screens, covers, and signs) must be maintained by the owner/operator as required by the City’s Municipal Code. Failure to properly maintain the building and property may subject the property owner to enforcement.

Maintenance agreements between the City and the owner/operator may be required (Appendix I).
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Source Control Measures Fact Sheet S-7: Fuel and Maintenance Area Development Guidance Manual C-14 May 2025
Purpose
Spills at vehicle and equipment fueling areas can be a significant source of pollutants because fuels contain toxic materials and heavy metals that are not easily removed by stormwater treatment control measures. When stormwater mixes with fuel spilled or leaks onto the ground, it becomes contaminated with petroleum-based materials that can harm humans, fish and wildlife.

Design Criteria
Design requirements for fueling and maintenance areas are governed by Building and Fire Codes and by current City ordinances and zoning requirements. The design criteria described in Table S-7.1 are intended to enhance and be consistent with these code requirements.

Hazardous and toxic wastes cannot enter the storm drain system. Conflicts or issues should be discussed with City staff.

Table S-7.1. Design Criteria for Fuel and Maintenance Areas Design Feature Design Criteria
Surfacing
• Pave fuel dispensing and maintenance area with Portland cement concrete. The fuel dispensing area is defined as extending 6.5 feet from the corner of each fuel dispenser, or the length at which the hose and nozzle assemble may be operated plus 1 foot, whichever is greater. The paving around the fuel dispensing area may exceed the minimum dimensions of the “fuel dispensing area” stated above. • Use asphalt sealant to protect asphalt paved areas surrounding the fuel dispensing or maintenance area.

Covers
• Cover the fuel dispensing or maintenance area with a permanent canopy, roof, or awning to prevent precipitation from directly contacting the area. Direct stormwater runoff from the cover away from the area to a stormwater disposal point that meets all applicable code requirements and applicable requirements of this manual.
o Covers 10 feet high or less shall have a minimum overhang of 3 feet measured from the perimeter of the hydraulically isolated fuel dispensing area. o Cover higher than 10 feet shall have a minimum overhang of 5 feet measured from the perimeter of the hydraulically isolated fuel dispensing area. • For facilities designed to accommodate very large vehicles or equipment that would prohibit the use of covers, hydraulically isolate the uncovered fuel dispensing or maintenance area and direct drainage from the area through upstream controls to a sanitary sewer as described below.

Hydraulic
Isolation and
Drainage
• Design the area pad with zero slope (flat) to keep minor spills and leaks on the pad and encourage use of proper cleanup methods, which consist of dry cleanup, such as sweeping for removal of litter and debris and use of absorbents for liquid spills and leaks.
• Hydraulically isolate the paved fuel dispensing or maintenance area to prevent runon of stormwater from surrounding areas or roof drains by one of the following methods. Design should conform to applicable American Disabilities Act requirements for disabled access:
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Source Control Measures Fact Sheet S-7: Fuel and Maintenance Area Development Guidance Manual C-15 May 2025
Design Feature Design Criteria
• Berms: Design the berm height four (4) inches above the surface of the area pad such that the pad will serve as spill containment area. • Perimeter trench drains: Locate trench drains around the perimeter of the pad.

Direct drainage from the perimeter drains to one of the following:
o An approved City sanitary sewer. Provide an approved automatic shutoff valve installed upstream of the sanitary sewer connection and below grade in a manhole or similar concrete containment structure. The valve shall be designed to close automatically when the structure's maximum oil/fuel storage capacity is reached.
o An approved below-grade containment vault with at least 60 ft3 of storage capacity. The vault must be emptied, as required, and the contents disposed of by applicable laws.
• Elevated fueling pad: Elevate the grade of the fueling pad such that it is high enough to prevent run-on from surrounding areas. The fueling pad should be flat in order to contain small spills and prevent stormwater runoff.
• Direct runoff and drainage from surrounding areas away from hydraulically isolated area to a stormwater discharge point that meets all applicable requirements of this manual. Locate stormwater drains for surrounding areas at least 10 feet from the hydraulically isolated fuel dispensing or maintenance area.

Accumulated Stormwater and Non-stormwater
Stormwater and non-stormwater may accumulate in containment areas and sumps with impervious surfaces. Contaminated accumulated water must be disposed of per applicable laws and cannot be discharged directly to the storm drain or sanitary sewer system without the appropriate permission and/or permit. Contact the City regarding permits for the discharge of contaminated accumulated water.

Maintenance Requirements
The integrity of structural elements that are subject to damage (e.g., screens, covers, and signs) must be maintained by the owner/operator as required by the City’s Municipal Code. Failure to properly maintain the building and property may subject the property owner to enforcement.

Maintenance agreements between the City and the owner/operator may be required (Appendix I).
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APPENDIX D
Volume Retention Measures Fact Sheets (V1 – V5)
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Volume Retention Measure Fact Sheet V-1: Rain Garden
Development Guidance Manual D-1 May 2025
Description
A rain garden is a planted depression designed to receive, retain, and infiltrate stormwater runoff from impervious areas, such as rooftops and pavement. Stormwater runoff is initially captured in a ponding zone above the vegetated surface. Captured runoff infiltrates the surface layer of the garden and filters through a planting soil layer before entering the groundwater or being collected by an underdrain system. The garden may include a gravel retention zone below the planting soil layer to facilitate infiltration.

Treatment of the runoff occurs through various natural
mechanisms as the runoff filters through the root zone of the vegetation. Part of the water held in the root zone of the garden is returned to the atmosphere through
transpiration by plants. Rain gardens are typically
planted with native, drought-tolerant vegetation that
does not require fertilization and can withstand wet
soils for at least 24 hours, such as wildflowers,
sedges, rushes, ferns, shrubs and small trees. Root
systems of the plants enhance infiltration, moisture
redistribution, and diverse microbial populations
involved in biofiltration. Rain gardens may also
include an underdrain pipe, but they may reduce the
retention capabilities of the Rain Garden.

Other Names: Micro-bioretention, biofiltration
Advantages
• Low installation cost.
• Enhances site aesthetics.
• Reduces stormwater volume and pollutant discharge.
• Potential water conservation.
• Easy to maintain.

Limitations
• Volume retention may be limited by available space.
• Requires underdrains for low permeability soils.
• Requires individual owners/tenants to perform maintenance. • Not suitable for industrial sites or sites where spills may occur unless an impermeable liner prevents infiltration.

RAIN GARDEN
A rain garden is similar to a
bioretention area but differs in
the level of engineering design
criteria specified for
subsurface soil matrix and
construction and, thus the
level of treatment provided.

ISource: Hinman, C. (2007). (rep.). Rain Garden
Handbook for Western Washington Homeowners
(p. 9).

Source: Rain Gardens &amp; Rebate
program. Flows to Bay. (n.d.). Retrieved
October 5, 2021, from
https://www.flowstobay.org/preventingstormwater-pollution/at-home/rain-gardens/. #6..
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Volume Retention Measure Fact Sheet V-1: Rain Garden
Development Guidance Manual D-2 May 2025
Planning and Siting Considerations
• Locate Rain Gardens at least 10 feet from the building foundations. • Maintain a slope of at least one (1) percent from the impervious surface to Rain Garden inlet.
• Provide for overflow discharge that drains away from building foundations to the storm drain system or, if possible, to vegetated surfaces (e.g., grassy buffers, grassy swales/channels) or more suitable infiltration areas.
• For parking lot design, stalls can be shortened if tire curbs are provided around the perimeter of the Rain Garden, and cars are allowed to overhang the Rain Garden. • Irrigation is typically required to maintain viability of the Rain Garden vegetation.

Coordinate design of general landscape irrigation system with that of the Rain Garden, as applicable.

Design Criteria
Design criteria for Rain Gardens are listed in Table V-1.1. A schematic showing the basic elements of a typical Rain Garden is presented in Figure V-1.1.

Table V-1.1. Rain Garden Design Criteria
Design Parameter Criteria Notes
Surface area of ponding zone 20-30%
Typical percentage of impervious area draining to
Rain Garden. Smaller percentages are acceptable
with overflow drainage provided
Maximum depth of ponding zone (DRG) 6 inches Depth above top of mulch layer Depth of top mulch layer 2-3 inches Shredded hardwood or softwood or compost Depth of planting media 12-18 inches Mix: 60-65% loamy sand + 35-40% compost or 30% loamy sand + 30% coarse sand + 40 % compost
Depth of retention zone (optional) 9-12 inches Washed drain rock (0.5 – 1.5 inch diameter). Use with under drain
Under drainpipe (optional) 4 inches Perforated PVC or HDPE. Use with Type C and D soils
Excavation side slope of (H:V) 3:1 Maximum steepness
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Volume Retention Measure Fact Sheet V-1: Rain Garden
Development Guidance Manual D-3 May 2025
Figure V-1.1. Example Rain Garden. Source: Oregon State University. (n.d.). Choose the right Rain Garden.

Retrieved October 6, 2021, from https://extension.oregonstate.edu/node/119221/printable/print.

Volume Retention and Tributary Impervious Area Credit Calculation Rain Gardens provide volume retention by capturing water in the pore spaces of the planting soil layer (detention/filtration zone) and infiltrating it into the underlying soil. Rain Gardens may be used to help meet the volume retention requirement (VRR) and can also be used to reduce the size of required treatment control measures (Section 6). The volume retention credit calculation for Rain Gardens is presented in Table V-1.2. Appendix G provides additional information on calculating and meeting the VRR.

Rain Gardens can also be used to reduce the size of required treatment control measures through the application of the tributary impervious area credits. These credits can be applied to reduce the effective design area used to calculate the water quality volume (WQV) or water quality flow (WQF), which are used to size the treatment control measures.

Implementing Rain Gardens reduces effective impervious area and, thereby, the volume of water that needs to be treated. The credit is based on the ratio of the volume retention to the WQV for the Rain Garden drainage area. Note that these credits must be applied to treatment control measures that are in the same tributary drainage area as the Rain Garden for which the credits are determined and that the credits cannot be greater than the tributary drainage area #6..
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Volume Retention Measure Fact Sheet V-1: Rain Garden
Development Guidance Manual D-4 May 2025
of the Rain Garden. Table V-1.2 details how the tributary impervious area credit is calculated for Rain Gardens.

Construction Considerations
• Divert stormwater runoff during the period of vegetation establishment. Where stormwater runoff diversion is not feasible, cover graded and seeded areas with suitable temporary erosion control materials, such as silt fences.
• Install sediment controls, such as silt fences, around the Rain Garden to prevent high sediment loads from entering the area during ongoing construction activities. • Avoid compaction of native soils below planting media layer or gravel zone. • Repair, seed, or re-plant damaged areas immediately.
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Volume Retention Measure Fact Sheet V-1: Rain Garden
Development Guidance Manual D-5 May 2025
Table V-1.2. Rain Garden Volume Retention and Tributary Impervious Area Credit Calculation Design Parameter Design Criteria Notes
Rain Garden without Subsurface Drain

1. Volume retention for Rain Garden
(Volretenttion)
a) Depth of ponding zone (DPZ)
b) Area of ponding zone (APZ)
c) Depth of detention zone (DDZ)
d) Area of detention zone (ADZ)
e) Volretention= (DPZ
x APZ x 1) + (DDZ x ADZ x 0.1)
DPZ =___________ ft
APZ = ____________ ft2
DDZ =___________ ft
ADZ =____________ ft2
Volretention = __________ ft3
Infiltration allowance for water
in ponding zone water = 1.0
Available Water Holding
Capacity of soil in detention
zone = 0.1 x volume
Rain Garden with Subsurface Drain

2. Volume retention for Rain Garden
(Volretention)
a) Depth of ponding zone (DPZ)
b) Area of ponding zone (APZ)
c) Depth of detention zone (DDZ)
d) Area of detention zone (ADZ)
e) Depth of retention zone (DRZ)
f) Area of retention zone (ARZ)
g) Volretention= (DPZ x APZ x 0.25) +
(DDZ x ADZ x 0.10) +
(DRZ x ARZ x 0.30)
DPZ =___________ ft
APZ =___________ ft2
DDZ =_________ ft
ADZ =____________ ft2
DRZ =_________ ft
ARZ =____________ ft2
Volretention =__________ ft3
Infiltration allowance for water
in ponding zone water = 0.25
Available Water Holding
Capacity of soil in detention
zone = 0.10 x volume
Retention zone is optional.

Porosity of retention zone =

0.30 3. Impervious area tributary to Rain Garden
(Aimp)
Aimp =________ ft2

4. WQV for Aimp based on 12-h drawdown
WQV = 0.32 in x Aimp / 12 in/ft
WQV =__________ ft3
Unit basin storage volume for
12-h drawdown at 100%
imperviousness (0.95 Runoff
Coefficient) = 0.32 in.

Adjust value for Aimp < 100%
impervious

5. Tributary Impervious Area Credit for Rain
Garden (Areacredit)
Areacredit = Aimp x Volretention / WQV
Areacredit =_____ ft2 Maximum allowable Areacredit =
Aimp
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Volume Retention Measure Fact Sheet V-1: Rain Garden
Development Guidance Manual D-6 May 2025
Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, including volume retention measures (VRMs) such as Rain Gardens. Such agreements typically include requirements like those outlined in Table V-1.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement must provide the City with complete access to the VRM and its immediate vicinity at any time. Maintenance is the sole responsibility of the owner.

A sample maintenance agreement is presented in Appendix I.

Table V-1.3. Inspection and Maintenance Requirements for Rain Gardens Activity Schedule
Remulch void areas As needed
Treat diseased trees and shrubs As needed
Use Integrated Pest Management practices As needed
Water plants daily for two weeks At project completion
Inspect soil and repair eroded areas Monthly
Remove litter and debris Monthly
Remove and replace dead and diseased vegetation Twice per year Add additional mulch Once per year
Replace tree stakes and wire Once per year
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Volume Retention Measure Fact Sheet V-2: Rain Barrel/ Cistern Development Guidance Manual D-7 May 2025
Description
Rain Barrels and Cisterns collect and store rainwater runoff from rooftop drainage systems that would otherwise be lost to runoff and diverted to storm drains.
• Rain Barrels are placed above-ground beneath a shortened downspout next to a home or building and typically range in size from 50 to 180 gallons.
• Cisterns are larger storage tanks that may be sited above or below ground.

Rain Barrels are equipped with a removable cover to allow access for maintenance, a screened inlet opening to trap debris and exclude mosquitoes, an outlet spigot typically fitted for garden hose attachment, and an overflow outlet with discharge pipe or hose (Figure V-2.1). Stored rainwater is typically used for landscape irrigation but can be used for washing. Water stored in Rain Barrels and Cisterns should not be discharged to the storm drain system.

Advantages
• Low installation cost.
• Small footprint.
• Reduces stormwater volume and pollutant discharge.
• Potential water conservation.
• Easy to maintain.

Limitations
• Storage volume may be limited.
• Stored water is not suitable for human or pet consumption. • Contact of stored water with fruits and vegetables should be avoided due to unknown risks. • May not be compatible with site aesthetics.
• Potential for mosquito breeding if not properly covered and maintained. • Requires individual owners/tenants to perform maintenance and empty Rain Barrels between storms.

Planning and Siting Considerations
• Locate Rain Barrels and Cisterns to allow easy access for maintenance. • Elevate Rain Barrels above-ground with a sturdy platform to provide spigot clearance.

Source: Communications, I. F. A. S. (n.d.).

Rain barrels. Rain Barrels - UF/IFAS
Extension. Retrieved October 6, 2021, from
http://sfyl.ifas.ufl.edu/sarasota/gardeningand-landscaping/horticultureresidential/florida-yards-andneighborhoods/rain-barrels/.

Source: Chesapeake Bay Foundation
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Volume Retention Measure Fact Sheet V-2: Rain Barrel/ Cistern Development Guidance Manual D-8 May 2025
• Provide screens or deflectors on rain gutters to minimize the discharge of debris to Rain Barrels.
• Direct Cistern overflow discharge to drain away from building foundations and to vegetated areas.

Figure V-2.1 Rain Barrel Schematic. Source: Home. Low Impact Development. (2002, November). Retrieved October 5, 2021, from https://lowimpactdevelopment.org/.

Volume Retention and Tributary Impervious Area Credit Calculation Rain Barrels and Cisterns reduce volume by storing water in a container. Rain Barrels and Cisterns may be used to help meet the VRR and reduce the size of required treatment control measures (Section 6). The volume retention credit calculation for Rain Barrels and Cisterns is presented in Table V-2.1.

Rain Barrels and Cisterns can also be used to reduce the required treatment control measure size by applying for tributary impervious area credits. These credits can be applied to reduce the effective design area used to calculate the WQV or WQF, which are used to size Treatment Control Measures (Section 6).

Implementation of Rain Barrels and Cisterns reduces effective impervious area and thereby the volume of water to be treated. The credit is based on ratio of the volume retention to the WQV for the Rain Barrel or Cistern drainage area. Note that these credits must be applied to treatment control measures that are in the same tributary drainage area as the Rain Barrel or Cistern for which the credits are determined, and the credits cannot be greater than the Linking Kit
90° Overflow
Coupler
Brass
Nipples
Corrugat
ed Hose
Garden Hoses
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Volume Retention Measure Fact Sheet V-2: Rain Barrel/ Cistern Development Guidance Manual D-9 May 2025
tributary drainage areas of the Rain Barrel or Cistern. Table V-2.1 details how the tributary impervious area credit is calculated.

Table V-2.1. Rain Barrel/Cistern Volume and Tributary Impervious Area Credit Calculation Design Parameter Criteria Notes

1. Volume retention (Volretention)
a. Total storage volume of Rain
Barrel/Cistern (Vs)
b. Effectiveness factor (Eff) = 75%
c. Volretention = Vs x Eff
Vs = ____ __ft3
Eff = 0.75 __
Volretention = ft3
The effectiveness factor considers
that storage container may not
be emptied between each storm

2. Total roof area (Aroof) Aroof =_________ft2

3. WQV for roof area based on 12-h
drawdown
WQV = 0.32 in x Aroof / 12 in/ft WQV =________ft3
Unit basin storage volume for 12-
h drawdown at 100 %
imperviousness (Cr= 0.95) = 0.32
in

4. Tributary Impervious Area Credit
(Areacredit)
Areacredit = Aroof x Volretention / WQV Areacredit = ___ ft2 Maximum allowable Areacredit = Aroof
Construction Considerations
Stormwater runoff should not be diverted to the Rain Barrel or Cistern until the overflow discharge area has been stabilized.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, including VRMs such as Rain Barrels and Cisterns.

Such agreements typically include requirements like those outlined in Table V-2.2. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement must provide the City with complete access to the VRM and its immediate vicinity at any time. Maintenance is the sole responsibility of the owner. A sample maintenance agreement is presented in Appendix I.

Table V-2.2. Inspection and Maintenance Requirements for Rain Barrels and Cisterns Activity Schedule
Inspect: roof connection; gutter; downspout, Rain Barrel/ Cistern, mosquito screen, and overflow pipes for leaks and obstructions. Twice per year. Repair as required Inspect insect and debris screens. Clean as required. Following significant rainfall events #6..
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Volume Retention Measure Fact Sheet V-3: Interception Trees Development Guidance Manual D-10 May 2025

Description
Interception Trees are used in residential and
commercial settings to reduce stormwater runoff
volume. Tree canopies can intercept a significant
fraction of rainfall (10-40%) depending on the type
of tree and climate. Tree canopies that project over
impervious areas provide the greatest volume
retention benefit. The rainfall interception and
evaporation benefits are received through a tree’s
hydrologic cycle.

Advantages
• Reduces stormwater runoff volume and pollutant
discharge.
• Enhances site aesthetics.
• Increases property values.
• Provides shading and cooling.
• Improves air quality.
• Can also be used to meet landscaping requirements.

Limitations
• Fire safety may be a consideration for sites with
increased fire risk.

Planning and Siting Considerations
• Trees should be selected that maximize tree canopy, are low maintenance, drought tolerant, and appropriate for local soil conditions.
• Locate trees at appropriate distances from buildings and infrastructure to avoid damage by roots and interference by branches.
• Locate trees such that canopies project over impervious areas, if possible. • Irrigation is typically required to maintain viability of Interception Trees. Coordinate design of general landscape irrigation system with that of Interception Trees, as applicable.

Source: Stringham, T.K., Snyder, K.A., Snyder, D.K.,
Lossing, S.S., Carr, C.A., and Stringham, B.J. (2018).

Rainfall interception by singleleaf piñon and Utah
juniper: implications for stand-level effective
precipitation. Rangeland Ecology & Management
71(3):327-335.

Source: Ekhuemelo, David. (2016).

Importance Of Forest and Trees in Sustaining
Water Supply And Rainfall. Nigeria Journal of
Education, Health And Technology Research
(Njehetr).
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Volume Retention Measure Fact Sheet V-3: Interception Trees Development Guidance Manual D-11 May 2025
Volume Retention and Tributary Impervious Area Credit Calculation Interception Trees provide volume retention through the storage of water in the leaves, branches, and stem of the tree. Interception Trees may be used to help meet the VRR and reduce the size of required treatment control measures (Section 6). The calculation procedure for volume retention and tributary impervious area credit for Interception Trees is presented in Table V-3.1.

Interception Trees can also be used to reduce the required treatment control measure size through the application of tributary impervious area credits. These credits can be applied to reduce the effective design area used to calculate the WQV or WQF, which are the primary design criteria used to size Treatment Control Measures (Section 6).

Implementing Interception Trees reduces effective impervious area and, thereby the volume of water that needs to be treated. The credit is based on the area of canopy projection over impervious areas and the percentage of rainfall interception allowed for the type of tree selected. Table V-3.1 details how the tributary impervious area credit is calculated for Interception Trees.

Table V-3.1. Interception Tree Volume and Impervious Area Credit Calculation Design Parameter Criteria Notes

1. Percent rainfall interception by tree
(Int)
a. Evergreen tree Int = 40%
b. Deciduous tree Int = 20 %
Int = ____________ %

2. No. of trees No. of trees = _________ Provide separate total for each type of tree

3. Canopy projected over impervious
area/tree Areap =______ _____ ft2

4. Design storm depth (d) d= _______ in d = 0.50 inch

5. Volume retention for interception
(Volretention)
Volretention = d x Areap x Int x No. of trees
/12 in/ft
Volretention = ______ ft3
Provide separate calculation for
each type of tree with different
canopy and Int value

6. Tributary Impervious Area Credit for
tree interception
Areacredit = Areap x Int
Areacredit = ______ft2
Provide separate calculation for
each type of tree with different
canopy and Int value.
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Volume Retention Measure Fact Sheet V-3: Interception Trees Development Guidance Manual D-12 May 2025
Construction Considerations
Urban tree mortality can be high. The following construction considerations can help to increase the life expectancy of urban trees:
• Utilize planting arrangements that allow shared rooting spaces • Provide at least 400-cubic (optimally 1,000) feet of soil for large trees (Urban Forestry, 1999)
• Limit the use of heavy equipment in planting areas to prevent soil compaction • Use tree cages to protect trees from lawnmowers, heavy foot traffic and vehicles • Select drought-tolerant tree species
Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, including VRMs such as Interception Trees. Such agreements typically include requirements like those outlined in Table V-3.2. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement must provide the City with complete access to the VRM and its immediate vicinity at any time. Maintenance is the sole responsibility of the owner. A sample maintenance agreement is presented in Appendix I.

Table V-3.2. Inspection and Maintenance Requirements for Interception Trees Activity Schedule
Remove and replace any diseased or dying trees Annually Maintain trees (watering, pruning) As needed
Use Integrated Pest Management Practices As needed
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-13 May 2025
Description
Grassy Channels are densely vegetated
drainage ways with gentle side slopes and
gradual longitudinal slopes in the direction of
flow that receives stormwater runoff from
impervious areas and slowly conveys the
runoff to downstream points of treatment or
discharge. Grassy Channels allow infiltration,
reduce peak flows from impervious areas, and
provide a degree of pollutant removal. Where
development density, topography and soils
permit, Grassy Channels are a preferable
alternative to curb and gutter and storm drains
as a stormwater conveyance system. The
features and function of Grassy Channels are
similar to the full treatment Grassy Swale.

Grassy Channels are appropriate for use in residential, commercial, industrial, and institutional settings for drainage areas typically less than five (5) acres. They can be used in conjunction with Grassy Filter Strips and are located adjacent to impervious areas to be mitigated. Several Grassy Channels may be used on a single site, each designed to receive stormwater runoff from different impervious areas. Grassy Channels can also provide pretreatment for other stormwater treatment control measures, such as
bioretention areas. Irrigation and regular mowing are
required to maintain the grass cover. Options for the types of vegetation that can be used are provided in Appendix L.

Other Names: Grassy Swale, Bioswale
Advantages
• Low installation cost.
• Compatible with site landscaping.
• Reduces stormwater volume and pollutant discharge.
• Easy to maintain.
• A preferred alternative to curb and gutter, where feasible.

Limitations
• Not suitable for areas that receive substantial to full shade. • Not suitable for industrial sites or sites where spills may occur unless infiltration is prevented by an impermeable liner.
• Requires individual owners/tenants to perform maintenance.

A Grassy Channel is similar in
most respects to a grassy
swale, but differs in the level
of engineering design criteria
specified contact time, depth
of flow, and flow velocity.

amento
Grassy channel. Source: Fairfax County Virginia. (n.d.). Control Heavy Runoff - Solving Drainage and Erosion Problems.

Retrieved October 6, 2021, from
https://www.fairfaxcounty.gov/soil-water-conservation/drainageproblem-control-runoff. #6..
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-14 May 2025
Planning and Site Considerations
• Select location where site topography allows for design of a Grassy Channel with sufficiently mild slopes and enough surface area to maintain non-erosive velocities in the channel. • Integrate Grassy Channels into open space buffers and other landscape areas when possible.
• For parking lot design, stalls can be shortened if tire curbs are provided around the perimeter of the Grassy Channel, and cars are allowed to overhang the channel. • Irrigation is typically required to maintain viability of Grassy Channel vegetation. • Coordinate design of general landscape irrigation system with that of the Grassy Channel, as applicable.
• The potential for mosquitoes due to standing water will be greatly reduced or eliminated if the Grassy Channel is properly designed, constructed, and operated.

Design Criteria
Design elements, construction considerations and maintenance requirements of Grassy Channels are similar in most respects to those of full treatment Grassy Swales. Grassy Channels typically differ in terms of the values used for the three principal design parameters that govern treatment performance:
• Contact time, which is a function of swale length
• Depth of flow
• Flow velocity
Key design criteria and reference values for Grassy Channels are listed in Table V-4.1, along with reference values for use in the calculation of credits for reducing the effective impervious area. The design and reference value ratios are used in the calculation of credits for reducing effective impervious area.

Table V-4.1. Grassy Channel Design Criteria and Reference Values Design Parameter Criteria Notes
Longitudinal slope (flow direction) 4%

0.5%
Maximum
Minimum
Maximum bottom width 6 ft
Maximum side slopes (H:V) 4:1 Side slopes to allow for ease of mowing.

Roughness coefficient (n) for treatment
design

0.2 Reflects the roughness of swale when
depth of flow is below the height of the
grass.

Roughness coefficient (n) for
conveyance design

0.1 Reflects the roughness of swale when
depth of flow is above the height of the
grass. Used to determine capacity of
swale to convey peak hydraulic flows.
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-15 May 2025
Design Parameter Criteria Notes
Vegetation – Turf grass (irrigated, not artificial)
Vegetation height (typical) 4 to 6 in. Vegetation should be maintained at a height greater than the depth of flow at
design flow rate but sufficiently low to
prevent lodging or shading of the
vegetation.

Reference Values for Credit Calculation Design Criteria Notes Reference Design Flow (WQFref) WQF WQF = 0.20 in/hr x C x A (Section 6) Reference Contact Time (tref) 7 min
Reference Flow Depth (Dref) 3 in In flow direction
Reference Flow Velocity (vref) 1 ft/sec In flow direction Volume Retention and Tributary Impervious Area Credit Calculation Grassy Channels provide volume retention through water infiltration during conveyance and retaining water in the vegetative layer. Grassy Channels may also be used to help meet the VRR and reduce the size of required treatment control measures (Section 6). Volume retention achieved with Type C and D soils is less than that achieved with Type A and B soils because less infiltration will occur with Type C and D soils. The volume retention credit calculation for Grassy Channels is presented in Table V-4.2.

Grassy Channels can also be used to reduce the size of the required treatment control measures by applying tributary impervious area credits. These credits can be applied to reduce the effective design area used to calculate the WQV or WQF, which are the primary design criteria used to size Treatment Controls (Section 6).

Implementation of Grassy Channels reduces effective impervious area and, thereby the volume of water to be treated. The credit is based on the ratio of volume retention to the WQF for the Grassy Channel drainage area. Note that these credits must be applied to treatment control measures that are in the same tributary drainage area as the Grassy Channel for which the credits are determined and the credits cannot be greater than the tributary drainage areas of the Grassy Channel. Table V-4.2 details how the tributary impervious area credit is calculated for Grassy Channels.
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-16 May 2025
Table V-4.2. Grassy Channel Volume Retention and Tributary Impervious Area Credit Calculation Design Parameter Criteria Notes

1. Determine reference WQF
a. Impervious tributary area
b. Impervious area runoff coefficient
(Cimp)
c. WQFFref= 0.2 x Aimp x Cimp / 43,560
Aimp =___________ ft2
Cimp =_________
WQFref = __________ cfs
Cimp= 0.95

2. Design bottom width of Grassy Channel (WGC) WGC =_______________ ft

3. Design longitudinal slope (sGC) sGC =______________ ft/ft

4. Design length of Grassy Channel (LGC) LGC =________________ ft

5. Flow geometry @ WQF from Manning
equation
a. Design flow depth (DGC)
b. Design flow area (AGC)
c. Design flow velocity (vGC)
DGC =_________ ft
AGC =____________ ft2
vGC =_________ ft/sec

6. Contact time @ WQF (tGC)
tGC = LGC / vGC / 60 sec tGC =__________ min

7. Impervious Area credit for Grassy Channel
(Acredit)
i) Acredit = (Daref/DGC)
2 x (Vref/VGC) 2 x
(tGC/tref) x Aimp
Acredit =_________ ft2
If calculated values of
(qaref/qa), (Vref/VGC), or
(tGC/tref) are > 1.0, the
value is set to 1.0

8. Volume retention for Grassy Channel
(Volretention)
a. Vsoils for A and B soils = 0.50
b. Vsoils for C and D soils = 0.25
c. Volretention = (Acredit) x Vsoils x (0.50/12)
Vsoils =__________ ft3
Volretention = ______ ft3
Vsoils is volume retention
factor allowed for
infiltration, which varies
with soil permeability
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-17 May 2025
Credit Calculation Examples
An example of volume retention and tributary impervious area credit calculations are presented below.

Step 1 – Calculate WQF for impervious area tributary to Grassy Channel Using procedures described in Section 6, determine WQF for area tributary to Grassy Channel.

WQFref = i x Cimp x Aimp
where
WQFref = Stormwater Quality Design Flow, cfs
i = Design storm intensity = 0.20 in/hr
Cimp = Stormwater runoff coefficient for impervious area tributary to Grassy Channel Aimp = impervious area tributary to Grassy Channel, acres Example:

Cimp = 0.95
Aimp = 4,000 ft2
WQFref = 0.20 x 0.95 x 4,000/43,560 = 0.0174 cfs
Step 2 – Determine design bottom width of Grassy Channel (WGC) Note: Design width of Grassy Channel is not restricted to any value, but the ease of mowing and maintenance should be considered.

Example:

WGC = 0.5 ft
Step 3 – Determine longitudinal design slope of Grassy Channel (sGC) and side slope (H:V) sGC = 4% maximum; 0.5% minimum
H:V = 4:1
Example:
sGC = 1% = 0.01ft/ft
Step 4 – Determine design length of Grassy Channel (LGC) Note: Design length of Grassy Channel is not restricted to any minimum value Example:

LGC = 20 ft
Step 5 – Calculate design depth of flow and flow velocity at WQF using Manning’s Equation #6..
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-18 May 2025

Q =

1.49 n
A5 / 3
P2 / 3 × s1/ 2
where
Q = WQFref
A = Cross sectional area of flow
P = Wetted perimeter of flow
s = Bottom slope in flow direction
n = Manning’s n (roughness coefficient) = 0.2 for depth < 6 in Solve Manning’s equation by trial and error to determine the depth of flow, flow area, and flow velocity at the WQF and the design channel geometry.

Example:

DGC = 1.5 in
AGC = 0.0625 ft2
vGC = QWQF / AGC = 0.0174 cfs / 0.0625 ft2
vGC =0.28 ft/sec
Step 6 – Calculate contact time for Grassy Channel (tGC) tGC = LGC / vGC
tGC = 20 ft/ 0.28 ft/sec / 60 sec
tGC = 1.19 min
Step 7 – Calculate impervious area credit for Grassy Channel (Acredit) Acredit = (Dref/DGC)
2 x (vref/vGC)2 x (tGC/tref) x Aimp
Note: The ratios, (Dref/DGC) and (vref/vGC) are squared to account for reduced efficiency of full treatment systems at higher hydraulic loading rates.

If calculated values of (Dref/DGC), (vref/vGC),or (tGC/tref) are > 1.0, the value is set to 1.0 The maximum allowable value of Acredit = Aimp
Example:

Acredit = (3/1.5)2 x (1/0.28)2 x (1.19/7)  4,000
Acredit = (1)2 x (1)2 x 0.17 x 4,000 ft2
Acredit = 680.3 ft2
Step 8 – Calculate volume retention credit for 0.50-inch storm depth Volreduction = (Acredit) x Vsoils x (0.50/12)
Example:
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-19 May 2025
Vsoils = 0.25 for C and D soils
Volreduction= 680.3 x 0.25 x (0.50/12) = 7.2 ft3
Construction Considerations
• Divert stormwater runoff during period of vegetation establishment. Where stormwater runoff diversion is not feasible, cover graded and seeded areas with temporary erosion control materials.
• Install sediment controls around the Grassy Channel to prevent high sediment loads from entering the Grassy Channel during ongoing upstream construction activities. • Repair, seed, or re-plant damaged areas immediately.
• Apply erosion control measures as needed to stabilize side slopes and inlet areas.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, including VRMs such as Grassy Channels. Such agreements typically include requirements like those outlined in Table V-4.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement must provide the City with complete access to the VRM and its immediate vicinity at any time. Maintenance is the sole responsibility of the owner. A sample maintenance agreement is presented in Appendix I.
#6..
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Volume Retention Measure Fact Sheet V-4: Grassy Channel Development Guidance Manual D-20 May 2025
Table V-4.3. Inspection and Maintenance Requirements for Grassy Channels Activity Schedule
Mow grass to maintain height of 4-6 inches or above flow depth at WQF. As required
Remove grass clippings. As required
Use Integrated Pest Management practices. As required
Remove trash and debris from Grassy Channel. As required Inspect Grassy Channel for signs of erosion, vegetation damage/coverage, channelization problems, debris build-up, and excess sedimentation in bottom of channel. Correct
problems or remove debris and sediment as soon as possible.

At least twice annually.

One inspection at the end of wet season
so that summer maintenance can be
scheduled.

Additional inspections after periods of
heavy stormwater runoff are desirable.

Remove sediment in inlet areas, the channel, culverts, and outlets whenever flow into the channel is slowed or blocked.

As required
Repair ruts or holes by removing vegetation, adding and tamping soil, and reseeding. Replace damaged vegetation.

As required
Inspect Grassy Channel for obstructions and pools of standing water that can provide mosquito-breeding habitat.

At least twice during wet season after
significant storm events. Additional
inspections after periods of heavy
stormwater runoff are desirable.
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Volume Retention Measure Fact Sheet V-5: Vegetated Buffer Strip Development Guidance Manual D-21 May 2025
Description
A Vegetated Buffer Strip for rooftop and pavement
disconnection is a gently sloped soil surface planted with dense turf grass or groundcover designed to receive and convey flow from rooftop drainage systems and adjacent
paved areas. Runoff volume retention is achieved through the retention of a portion of the flow in the surface soil and thatch layer of the strip and infiltration. Some pollutant removal is also achieved as the stormwater runoff flows through the vegetation and over the soil surface at a shallow depth by a variety of physical, chemical, and biological mechanisms.

For rooftop drainage disconnection, direct stormwater
runoff away from the building foundation and disperse flow to the strip. Buried extensions with pop-up outlets can be used for the same purpose. To increase the effectiveness of a Vegetated Buffer Strip, the concentrated flow from the roof drain should be dispersed across the top of the strip to the extent possible to maximize the width of flow down the length of the strip. A pea gravel level spreader can be used for this purpose if the slope of the strip exceeds 4 percent.

Other Names: Vegetated Filter Strips, Grassy Buffer Strips, Grassy Filter Strips Advantages
• Relatively inexpensive when used to replace part of a conventional storm drainage system and integrated into site landscaping.
• Reduces peak flows and runoff volume.
• Easy to maintain.

Limitations
• Not suitable for industrial sites or sites where spills may occur unless an impermeable liner prevents infiltration.

Planning and Siting Considerations
• Select a location where site topography allows for the design of buffer strips with proper slopes in the flow direction.
• Integrate Vegetated Buffer Strips into open space buffers, undisturbed natural areas, and other landscape areas when possible.
• Irrigation is typically required to maintain the viability of the buffer strip vegetation.

Coordinate the design of the general landscape irrigation system with the Vegetated Buffer Strip, as applicable.

A Vegetated Buffer Strip is
similar in most respects to a
Grassy Filter Strip (L-9), but
differs in the level of
engineering design criteria
specified for minimum flow
length and maximum
application rates.

#6..
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Volume Retention Measure Fact Sheet V-5: Vegetated Buffer Strip Development Guidance Manual D-22 May 2025
Design Criteria
Design elements, construction considerations, and maintenance requirements of Vegetated Buffer Strips are similar in most respects to those of full-treatment Vegetated Filter Strips presented in Fact Sheet L-9. Vegetated Buffer Strips typically differ in terms of the values used for the two principal design parameters that govern treatment performance:
• Length of the strip in the direction of flow
• Application rate across the top of the strip
Key design criteria and reference values for Vegetated Buffer Strips are listed in Table V-5.1, along with reference values for use in the calculation of credits for reducing the effective impervious area. The ratio of design and reference values are used in calculating credits for volume retention and effective impervious area reduction.

Table V-5.1. Vegetated Buffer Strips Design Criteria and Reference Values Design Parameter Criteria Notes
Minimum design length (LVBS) 3 ft In flow direction
Slope (flow direction) 4%

0.5%
Maximum
Minimum
Vegetation – Turf grass or dense ground cover
(irrigated)
Vegetation height (typical) 1 – 3 in.

Reference Values for Credit Calculation Criteria Notes
Reference Design Flow (WQFref) WQF WQF = 0.20 in/hr x C x A (Section 6) Reference linear application rate (qaref) 0.005 cfs/ft
width
Width for normal to flow (default value) 3 ft Greater flow widths will increase credit values and can be achieved with flow
spreader devices.

Reference length (in flow direction) (Lref) 20 ft Maximum length for credit. Longer lengths receive no additional credit
Runoff coefficient for VBS 0.18

0.25 A and B soils
C and D soils
#6..
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Volume Retention Measure Fact Sheet V-5: Vegetated Buffer Strip Development Guidance Manual D-23 May 2025
Volume Retention and Tributary Impervious Area Credit Calculation Vegetated Buffer Strips provide volume retention through water infiltration during conveyance and retaining water in the vegetative layer. Vegetated Buffer Strips may be used to help meet the VRR and can also be used to reduce the size of required treatment controls (Section 6). The calculation procedure for volume retention and tributary impervious area credit for Vegetated Buffer Strips is presented in Table V-5.2.

Vegetated Buffer Strips can also be used to reduce the required treatment control size by applying for tributary impervious area credits. These credits can be applied to reduce the effective design area used to calculate the WQV or WQF, which are the primary design criteria used to size Treatment Controls (Section 6).

Implementing Vegetated Buffer Strips reduces effective impervious area and, thereby, the volume of water to be treated. The credit is based on the ratio of volume retention for the Vegetated Buffer Strip to the volume retention estimated for reference Vegetated Buffer Strip that would provide full treatment for the drainage area (see L-9: Grassy Filter Strip). Note that these credits must be applied to treatment controls in the same tributary drainage area as the Vegetated Buffer Strip for which the credits are determined and the credits cannot be greater than the tributary drainage areas of the Grassy Vegetated Buffer Strip. Table V-5.2 details how the tributary impervious area credit is calculated for Vegetated Buffer Strips. #6..
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Volume Retention Measure Fact Sheet V-5: Vegetated Buffer Strip Development Guidance Manual D-24 May 2025
Table V-5.2. Vegetated Buffer Strip Volume and Impervious Area Credit Calculation Design Parameter Criteria Notes

1. Determine reference WQF
a. Impervious tributary area
b. Impervious area runoff coefficient (Cimp)
c. WQFref = 0.2 x Aimp x Cimp / 43,560
Aimp =________ ft2
Cimp =________
WQFref = ________cfs
Cimp= 0.95

2. Design width of Vegetated Buffer Strip (Wvbs) WVBS = _________ ft Minimum default width =

3.0 ft

3. Design linear application rate (qa)
qa = WQFref / WVBS
qa =__________
cfs/ft Reference qa = 0.005 cfs/ft

4. Design length of Vegetated Buffer Strip (LVBS) LVBS =________ ft Reference LVBS = 20 ft,
which is max length allowed
for credit

5. Tributary Impervious Area credit for Vegetated
Buffer Strip (Acredit)
Acredit = (qaref/qa)
2 x (LVBS/Lref) x Aimp
Acredit =_______ ft2
If calculated values of
(qaref/qa) or (LVBS/Lref) are
> 1.0, the value is set to 1.0.

Maximum allowable credit =
Aimp

6. Volume retention for Vegetated Buffer Strip
(Volretention)
Volretention = (Acredit) x (Cimp – CVBS) x (0.51/12) Volretention = ___ ft3 CVBS = 0.18 for A and B soils
CVBS = 0.25 for C and D soils
Credit Calculation Examples
Examples of volume and area credit calculations are presented below.

Step 1 – Calculate WQF for impervious area tributary to Vegetated Buffer Strip Using Fact Sheet T-0 in Section 6, determine WQF for impervious area tributary to Vegetated Buffer Strip.

WQFref = i x Cimp x Aimp
where
WQFref = Stormwater Quality Design Flow, cfs
i = Design storm intensity = 0.20 in/hr
Cimp = Runoff coefficient for impervious area tributary to Vegetated Buffer Strip Aimp = impervious area tributary to Vegetated Buffer Strip, acres Example:

C = 0.95
#6..
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Volume Retention Measure Fact Sheet V-5: Vegetated Buffer Strip Development Guidance Manual D-25 May 2025
Aimp = 3,600 ft2
WQFref = 0.20 x 0.95 x 3,600/43,560 = 0.0157 cfs
Step 2 – Determine design width of Vegetated Buffer Strip (WVBS) Note: Design width of Vegetated Buffer Strip is not restricted to any value but runoff flow must be distributed uniformly across the width of the strip. The minimum default width is 3 feet. Wider values can be used if flow is dispersed with a spreader device.

Example:

WVBS = 3.0 ft
Step 3 – Calculate design linear application rate (qa)
qa = WQFref/ WVBS
Example:
qa = 0.0157 cfs/3.0 ft = 0.005 cfs/ft
Step 4 – Determine design length of Vegetated Buffer Strip (LVBS) Note: Design length of Vegetated Buffer Strip is not restricted to any maximum, but 20 feet is the maximum length for credit calculation.

Example:

LVBS = 12.0 ft
Step 5 – Calculate impervious area credit for Vegetated Buffer Strip (Acredit) Acredit = (qaref/qa)
2 x (LVBS/Lref)  Aimp
Note: The ratio, (qaref/qa) is squared to account for reduced efficiency of full treatment systems at higher hydraulic loading rates.

If calculated values of (qaref/qa) or (LVBS/Lref) are > 1.0, the value is set to 1.0 The maximum allowable value of Acredit = Aimp
Example:

Acredit = (0.005/0.005)2 x (12/20) x 3,600 ft2
Acredit = (1.0)2 x (12/20) x 3,600 ft2
Acredit = 0.6 x 3,600 ft2 = 2,160 ft2
Step 6 – Calculate Volume retention for 0.50-inch storm depth Volretention = (Acredit) x Cimp – CVBS) x (0.50/12)
Example:

CVBS = 0.25 for C and D soils
Volreduction = 2,160 x (0.95 – 0.25) x (0.51/12) = 64.3 ft3 #6..
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Volume Retention Measure Fact Sheet V-5: Vegetated Buffer Strip Development Guidance Manual D-26 May 2025
Construction Considerations
• Divert stormwater runoff during period of vegetation establishment. Where stormwater runoff diversion is not feasible, cover graded and seeded areas with suitable temporary erosion control materials, such as silt fences.
• Install sediment controls, such as silt fences, around the Vegetated Buffer Strip to prevent high sediment loads from entering the Vegetated Buffer Strip during ongoing upstream construction activities.
• Repair, seed, or re-plant damaged areas immediately.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, including VRMs such as Vegetated Buffer Strips.

Such agreements typically include requirements like those outlined in Table V-5.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement must provide the City with complete access to the VRM and its immediate vicinity at any time. Maintenance is the sole responsibility of the owner. A sample maintenance agreement is presented in Appendix I.

Table V-5.3. Inspection and Maintenance Requirements for Vegetated Buffer Strips Activity Schedule
Mow grass to maintain height of 2-4 inches. As required Remove grass clippings. As required
Use Integrated Pest Management practices. As required
Remove trash and debris from Grassy Channel. As required Inspect for signs of erosion, vegetation damage/coverage, channelization problems, debris build-up, and excess
sedimentation in bottom of channel. Correct problems or remove debris and sediment as soon as possible.

At least twice annually.

One inspection at the end of wet
season so that summer maintenance
can be scheduled.

Additional inspections after periods of
heavy stormwater runoff are desirable.

Remove sediment in inlet areas, the channel, culverts, and outlets whenever flow into the channel is slowed or blocked.

As required
Repair ruts or holes by removing vegetation, adding and tamping soil, and reseeding. Replace damaged vegetation.

As required
Inspect Grassy Channel for obstructions and pools of standing water that can provide mosquito-breeding habitat.

At least twice during wet season after
significant storm events. Additional
inspections after periods of heavy
stormwater runoff are desirable.
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APPENDIX E
LID-based Treatment Control Measure Fact Sheets
(L1 – L11)
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-1 May 2025
Description
A Bioretention area is a vegetated shallow
depression that is designed to receive, retain, and
infiltrate stormwater runoff from downspouts,
piped inlets, or sheet flow from adjoining paved
areas. A shallow surcharge or ponding zone is
provided above the vegetated surface for the
temporary storage of the captured runoff. During
stormwater events, runoff accumulates in the
surcharge zone and gradually infiltrates the
surface and filters through the engineered soil
matrix, filling the void spaces of the matrix before
infiltrating the underlying soil or being collected
by an underdrain system. Treatment of the runoff
occurs through various natural mechanisms as the
runoff filters through the vegetation root zone and is detained in the pore spaces of the engineered soil matrix. A portion of the water held in the root zone of the soil media is returned to the atmosphere through transpiration by the plants.

Bioretention areas are typically planted with native, drought-tolerant plant species that do not require fertilization and can withstand wet soils for at least 24 hours, such as wildflowers, sedges, rushes, ferns, shrubs and small trees. Root systems of the plants enhance infiltration, moisture redistribution, and diverse microbial populations involved in biofiltration. • No Underdrain - If the underlying soil is permeable (typically Type A or B soil with a permeability greater than the engineered soil layers), the Bioretention area can be constructed without an underdrain pipe, in which case all of the captured runoff will infiltrate into the underlying soil profile. An impermeable liner cannot be used for a Bioretention area without an underdrain system in order to receive a volume retention credit.
• Use of Underdrain - If the underlying soil is less permeable (typically Type C or D soils) or the site slopes are steep, an underdrain is required to prevent excessive ponding. If an underdrain is present, only a portion of the captured stormwater runoff will be retained onsite through vegetation uptake In this case, all captured stormwater runoff will infiltrate into the underlying soil profile.1

1 Bioretention facilities are sometimes referred to as biofiltration (Bioretention facility with an underdrain or elevated underdrain) or bioinfiltration (Bioretention facility with no underdrain) facilities. These types of facilities are designed for partial or full infiltration and treatment of stormwater. The terminology continues to be further refined. https://stormwater.pca.state.mn.us/index.php/Bioretention_terminology Roadway Bioretention Areas in Raleigh, NC. Source:

Raleighnc.gov. (n.d.). Retrieved October 6, 2021, from
https://raleighnc.gov/SupportPages/roadway-Bioretentionareas. #6..
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-2 May 2025
Advantages
• Low installation cost.
• Enhances site aesthetics.
• Reduces or retains stormwater volume and
pollutant discharge.
• Potential water conservation.
• Easy maintenance.
• Can be designed to meet trash control
requirements.

Limitations
• Not appropriate for industrial sites or locations
with contaminated soils or where spills may occur because of the potential threat to groundwater contamination.
• Requires underdrains for low permeability soils or steep slopes. • Will require individual owners/tenants to perform maintenance. • Not appropriate for areas with steep slopes or high groundwater.

Planning and Siting Considerations
• Locate Bioretention areas sufficiently far from structure foundations to avoid damage to structures (as determined by a structural or geotechnical engineer). • Maintain a slope of at least 1 percent from the impervious surface to the Bioretention areas inlet.
• Provide for overflow discharge that drains away from building foundations to a storm drain system or more suitable infiltration area.
• Provide impermeable liners in areas subject to spills or pollutant hot spots. • Provide underdrain pipe in areas with C and D soils.
• For parking lot design, stalls can be shortened if tire curbs are provided around the perimeter of the Bioretention area, and cars are allowed to overhang the Bioretention area. • Irrigation is typically required to maintain viability of Bioretention area vegetation.

Coordinate design of general landscape irrigation system with that of the Bioretention area, as applicable.

Bioretention Systems Source: Bioretention
System. New Jersey Future Green Infrastructure
Developers Guide. (2020, May 7). Retrieved
October 6, 2021,
https://developersguide.njfuture.org/bmp/bioretenti
on-system/.
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-3 May 2025
Design Criteria
Design criteria for Bioretention are listed in Table L-1.1. A typical cross-section illustrating design features is shown in Figure L-1.1a and b.

Table L-1.1. Bioretention Design Criteria
Design Parameter Design Criteria Notes
Maximum depth of ponding zone (DPZ) 12 inches Depth above top much layer Depth of top mulch layer 2 - 3 inches Shredded hardwood or softwood or compost
Depth of planting media 18 - 24 inches
Mix: 60-65% loamy sand + 35-40%
compost or 30% loamy sand + 30%
course sand + 40 % compost
Depth to groundwater >10 feet
The depth to seasonal high
groundwater level should be at least
10 feet from the bottom of the
structure.

Excavation side slope of (H:V) 2:1 Maximum steepness
For Bioretention with Underdrains
Aggregate filter blanket 9 - 12 inches For use with subsurface drainpipe Subsurface drainpipe 4 - 8 inch
Slotted PVC per American Society for
Testing Materials (ASTM) D1785 SCH

40. (Use with C and D soils)
Design Procedure (for Trash Control see below)
Step 1 – Calculate Water Quality Volume (WQV)
Using the procedures presented in Section 7.4, determine the WQV based on a 12-hour drawdown period and the effective contributing area after allowance for impervious area credits.

Step 2 – Design Average Ponding Depth (DPZ)
Select the average WQV depth between six (6) and twelve (12) inches. The average depth is defined as water volume divided by the water surface area of the planter.

Step 3 – Calculate Planter Surface Area (AS)
The design surface area of the planter is determined from the design WQV and DPZ as follows:

AS = WQV/ DPZ
Where
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-4 May 2025
WQV = water quality volume (ft3)
DPZ = average ponding depth (ft)
Step 4 – Design Planting Media Layer
Planting media layer – Provide a mix of 60-65% loamy sand + 35-40% compost or 30% loamy sand + 30% coarse sand + 40 % compost. The long-term hydraulic conductivity of the mix should be ≥ 1.0 in/hr at 80 percent compaction. This layer should be a minimum of 18 inches deep, but a deeper layer is recommended to promote healthy vegetation and improve nutrient removal.

For bioretention with underdrains - Gravel envelope – Place drainpipe on a 3- ft wide, 6- inch-deep bed of gravel (Class 2 Permeable Material per Caltrans Spec 68-1.025). Cover the top and sides of the pipe with gravel to a minimum depth of 12 inches. Do not wrap pipe or gravel envelope with filter fabric to prevent clogging.

Step 5 – Select Subbase Liner (For Bioretention with Underdrains) If expansive soils or rocks are a concern, chemical or petroleum products are handled or stored within the tributary catchment, or infiltration is not desired for any reason, use an impermeable liner at the bottom of the Bioretention facility.

Step 6 – Design Subsurface Drainpipe (For Bioretention with Underdrains) If C or D soils are present or infiltration is not desired, provide a subsurface drainpipe with a diameter sized for the required hydraulic capacity (4-in minimum). Use a heavy-walled, slotted PVC pipe (ASTM D1785 SCD 40) to allow pressure water cleaning and root cutting, if necessary. Connect the subsurface drainpipe to the downstream open conveyance (e.g., swale), another Bioretention cell, a dispersion area, or to the storm drain system.

Step 7 – Select Vegetation
Select vegetation that:
• Is identified on the list of approved plants – Appendix L; • Is suited to well-drained soil;
• Will be dense and strong enough to stay upright, even in flowing water; • Has a minimum need for fertilizers;
• Is not prone to pests and is consistent with Integrated Pest Management practices; • Will withstand being inundated for periods of time; and • Is consistent with local water conservation ordinance requirements.

Avoid the use of bark or similar buoyant material that will tend to float when the vegetated area is inundated.

Step 8 – Design Irrigation System
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-5 May 2025
Provide irrigation system to maintain viability of vegetation, if applicable. The irrigation system must include a City-approved automatic timer.

Step 9 – Design Overflow Device
Provide an overflow device with an inlet to open conveyance or to storm drainage system.

Set the overflow inlet elevation above the WQV surcharge water level. A drop inlet or an overflow standpipe with an inverted opening is an appropriate overflow device).

Design Criteria – Trash Control1
The Bioretention treatment area consists of a ponding layer, a vegetated and mulched layer, an engineered soil layer, and a supporting bed layer of sand or gravel. The vegetated and mulched layer must have a surface area large enough to trap trash and reduce the risk of trash and other debris (e.g.; vegetation) interfering with the hydraulic capacity of the Bioretention system. The subsurface may include perforated pipes, chambers, open bottom concrete galleries, or other high voids structures designed to temporarily store water prior to infiltration.

The Bioretention system must be designed, constructed, and maintained in accordance with the following six (6) requirements: :

1. Trap trash particles that are 5 millimeters or greater at any time during a storm event for the following:
a. The peak flow rate generated by the region specific one-year, one-hour storm event from the applicable sub-drainage area (0.31 inches/hour); or b. The peak flow rate of the corresponding storm drain (if the Bioretention system is designed to treat flows from the corresponding storm drain that is designed for less than the peak flow rate generated from a one-year, one-hour storm event).

2. Bioretention systems may include either or both of the following to trap particles for either flow described above in section 1.a or 1.b:
a. A screen at the system’s inlet, overflow, or bypass outlet; or b. An up-gradient structure designed to bypass flows exceeding the flows as described in section 1.a or 1.b2.

3. The peak flow rates references in section 1.a shall be calculated using one of the following methods:
a. For small drainage areas (generally less than 50 acres) - the Rational Equation Method, which is expressed as Q = CiA, where:

Q = design flow rate (cubic feet per second),
C = runoff coefficient (dimensionless),
1 Based on the State Water Resources Control Board Categorically Certified Multi-Benefit Trash Treatment Systems – Bioretention information sheet June 2023 and any subsequent revisions.
2 Upon approval by the appropriate Regional Water Quality Control Board Executive Officer, a 5 millimeter screen and/or upgradient structure may not be required if the Bioretention System is designed for flood control from flows generated by very large storm events #6..
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-6 May 2025
i = design rainfall intensity (0.31 inches/hour), and
A = subdrainage area (acres).
b. For large drainage areas (generally 50 acres or more) – Other accepted hydrologic mathematical methods that more accurately calculate peak flow rates from large drainage areas, provided a registered California-licensed professional engineer documents the calculations within the design plans.

4. Permittees that have developed a Stormwater Resource Plan (SWRP) pursuant to California Water Code Section 10562 shall only install or approve Bioretention System designs with groundwater recharge functionality at locations suitable for groundwater recharge.

5. For Bioretention Systems that incorporate groundwater recharge capacity into the sizing of the Bioretention System for the purpose of requirements related to the peak flow rates in item 1, above, the percolation rate below the Bioretention System must either be measured directly or estimated employing conservative hydrogeologic assumptions.

6. A registered California licensed Professional Engineer shall stamp and sign Bioretention System design plans as required by California Business & Professions Code section 6700, et seq.

Vector breeding considerations must also be addressed due to the potential nuisance and human health effects.

Trash controls shall be installed and maintained by the property owner for all storm drains, catch basins, or inlets located within the parcel's boundaries and operated and maintained by the property owner. Trash controls shall only be installed in storm drains, catch basins, or inlets within the Public RoW if the City has agreed to enter into a maintenance agreement with the property owner (Appendix I).

Volume Retention Calculation
Bioretention may be used to achieve the VRRs in addition to treatment control requirements. A Bioretention area without an underdrain provides volume retention for the entire WQV calculated in Step 1 of the Design Procedure. The volume retention for a Bioretention area is less if a subsurface drainpipe is provided because less infiltration will occur. The calculation procedure for volume retention for Bioretention is presented in Table L-1.2. #6..
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-7 May 2025
Table L-1.2. Bioretention Volume Retention Calculation
Design Parameter Criteria Notes
Bioretention with Subsurface Drainpipe Required for C and D soils

1. Ponding Zone
Depth of ponding zone (DPZ)
Area of ponding zone (APZ)
DPZ =_______________ ft
APZ =_______________ ft2
Infiltration allowance for water in
ponding zone water = 0.25

2. Planting Media Layer
Depth of planting media layer (DPM)
Area of planting media layer (APM)
DPM =_______________ft
APM =_______________ft2
Available Water Holding Capacity
of planting media layer = 0.1 x
volume

3. Gravel Zone
Depth of gravel below pipe (DGZ)
Area of gravel below pipe (AGZ)
DGZ =_______________ ft
AGZ =_______________ ft2
Porosity of gravel zone = 0.30
Minimum depth below pipe = 6 in
Minimum width of gravel = 3 ft

4. Volume retention for Bioretention
(Volretention)
Volretention = (DPZ x APZ x 0.25) +
(DPM x APM x 0.1) +
(DGZ x AGZ x 0.3)
Vretention = __________ ft3
Bioretention without Subsurface Drainpipe Recommended for A and B soils

1. Ponding Zone
Depth of ponding zone (DPZ)
Area of ponding zone (APZ)
DPZ =________________ ft
APZ =________________ ft2

2. Planting Media Layer
Depth of planting media layer (DPM)
Area of planting media layer (APM)
DPM =_______________ ft
APM =_______________ ft2 Minimum depth = 18 inches

3. Volume retention for Bioretention
(Volretention)
Volretention = (DPZ x APZ) + (DPM x APM x 0.10) Volretention= __________ ft3 Available Water Holding Capacity
of planting media layer = 0.1 x
volume
Construction Considerations
• Divert runoff (other than necessary irrigation) during vegetation establishment. Where stormwater runoff diversion is not feasible, cover graded and seeded areas with suitable temporary erosion control materials.
• Install sediment controls around the Bioretention area to prevent high sediment loads from entering the area during ongoing construction activities. • Avoid compaction of native soils below the planting media layer or gravel zone. #6..
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-8 May 2025
• Repair, seed, or re-plant damaged areas immediately.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, including treatment controls such as Bioretention. Such agreements will typically include requirements such as those outlined in Table L-1.3. The property owner or his/her designee is responsible for compliance with the agreement. Maintenance agreements and plans with shared controls or controls located on more than one property must address shared maintenance responsibilities. The maintenance agreement and plan will provide the City designee with complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.

Table L-1.3. Inspection and Maintenance Requirements for Bioretention Areas Activity Schedule
Remulch void areas As needed
Treat diseased trees and shrubs As needed
Use Integrated Pest Management practices As needed
Water plants daily for two weeks At project completion
Inspect soil and repair eroded areas Monthly
Remove trash Monthly
Remove and replace dead and diseased vegetation Twice per year Add additional mulch Once per year
Replace tree stakes and wire Once per year
Trash Considerations
Because regular maintenance of the Bioretention System is required to maintain adequate trash capture capacity and to ensure that captured trash does not migrate offsite, the Permittee shall establish a maintenance schedule based on:
a. The maintenance frequency as required in the applicable State/Regional Water Board stormwater permit; and b.
b. Site-specific factors including the design trash capture capacity of the Bioretention System, local storm frequency, and characterization of trash and vegetation accumulation in the corresponding sub-drainage area.
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Treatment Control Measure Fact Sheet L-1: Bioretention
Development Guidance Manual E-9 May 2025
Figure L-1.1a. Bioretention Schematic.

Source: Tom Schueler. (n.d.). (tech.). Urban Stormwater Retrofit Practices (3rd ed., Vol. 1, p. 184).

Figure L-1.1b. Bioretention Schematic. Source: Curtis Hinman. (2012). (rep.). Low Impact Development: Technical Guidance Manual for Puget Sound. Puyallup, WA.
#6..
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Treatment Control Fact Sheet L-2: Stormwater Planter
Development Guidance Manual E-10 May 2025
Description
A Stormwater Planter is a vegetated in-ground or
above-ground planter box containing an engineered
soil matrix consisting of layers of topsoil, a sand/peat mixture, and gravel that is designed to receive and
capture stormwater runoff from downspouts or
piped inlets or sheet flow from adjoining impervious
areas. A shallow ponding zone is provided above the
vegetated surface to temporarily store the captured
runoff. During rainfall events, runoff accumulates in
the ponding zone, gradually infiltrates the surface,
and filters through the engineered soil matrix, filling the void spaces of the matrix before infiltrating the
underlying soil or being collected by an underdrain
system.

Treatment of the stormwater runoff occurs through
a variety of natural mechanisms as the runoff
infiltrates through the root zone of the vegetation
and during the detention of the runoff in the
underlying sand/peat bed. Stormwater Planters are
typically planted with native, drought-tolerant
vegetation that does not require fertilization and can
withstand wet soils for at least 24 hours, such as
wildflowers, sedges, rushes, ferns, shrubs and small
trees.

If Stormwater Planters are used, the volume of runoff can be retained through infiltration into underlying soils. For planters underlain with expansive soils or located next to buildings where infiltration of runoff is undesirable, a flow-through Stormwater Planter with an impermeable bottom liner should be employed. This type of planter features an impermeable bottom liner to prevent infiltration and a perforated underdrain pipe to collect treated stormwater runoff. The underdrain gradually dewaters the sand/peat bed over the drawdown period and discharges the runoff to downstream conveyance. However, a Stormwater Planter with an underdrain pipe reduces the amount of water retained and may not allow the site to meet the volume retention requirement.
• If underlying soils are rapidly permeable with permeability greater than the sand/peat layer (typically types A or B soils), the planter can be installed without an underdrain pipe, in which case the WQV will infiltrate into the underlying soil profile. • If less permeable underlying soils (types C or D) are present, an underdrain is required, but a portion of the infiltrated runoff will infiltrate into the underlying soil.

See Figures L-2.1 and L-2.2 for typical Stormwater Planter configurations.

Image 1. Sidewalk Stormwater Planter
Source: California, S. of. (n.d.). Erosion control toolbox:

Sidewalk Stormwater Planter. Erosion Control Toolbox:

Sidewalk Stormwater Planter | Caltrans. Retrieved
October 6, 2021, from
https://dot.ca.gov/programs/design/lap-erosion-controldesign/tool-1-lap-erosion-control-toolbox/tool-1kk-37- sidewalk-stormwater-planter.
#6..
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Treatment Control Fact Sheet L-2: Stormwater Planter
Development Guidance Manual E-11 May 2025
Other Names: Bioretention, Infiltration Planter, Flow-through Planter, Biofilter, Porous Landscape Detention, Rain Garden
Advantages
• Relatively inexpensive when integrated into site landscaping. • Suitable for parking lots and sites with limited open areas for stormwater detention. • Reduces peak flows during small storm events.
• Enhances site aesthetics.
• Easy maintenance.

Limitations
• Irrigation is typically required to maintain vegetation. • Not appropriate for industrial sites or locations where spills may occur unless infiltration is prevented. An impermeable liner may be used, but the benefit of volume retention will be eliminated.
• Not suitable for steeply sloping areas.
• Potential increased cost associated with waterproofing of exterior building walls, if needed.

Planning and Siting Considerations
• Select a location where site topography is relatively flat and allows stormwater runoff drainage to the Stormwater Planter.
• Integrate Stormwater Planters into other landscape areas when possible. • Stormwater Planters may have a non-rectangular footprint to fit the site landscape design. • Irrigation is typically required to maintain viability of Stormwater Planter vegetation.

Coordinate design of general landscape irrigation system with that of a Stormwater Planter, as applicable.
• In expansive soils, locate Stormwater Planters far enough from structure foundations to avoid damage to structures (as determined by a structural or geotechnical engineer).

Design Criteria
Design criteria for Stormwater Planters are listed in Table L-2.1. #6..
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-12 May 2025
Table L-2.1. Stormwater Planter Design Criteria
Design Parameter Design Criteria Notes
Drainage area ≤ 1 acre
Ideally suited for small areas such as parking
lot islands, perimeter building planters,
street medians, roadside swale features, and
site entrance or buffer features. Can be
implemented on a larger scale.

Design volume WQV See Section 7.4
Design drawdown time 12 hrs Period of time over which WQV drains from planter.

Design average surcharge depth (ds) 6-12 in.

Depth to groundwater > 10 ft From planter soil surface (without underdrain).

Topsoil layer 6 in. (minimum)
Sandy loam topsoil. Deeper layer
recommended for better vegetation
establishment. Note: planting media
specified for Bioretention (L-1) may be used
as an alternate for the topsoil and sand and
peat layers.

Sand-peat layer 18 in. (minimum) 75% ASTM C-33 Sand + 25% peat.

Gravel layer 9 in. Class 2 Aggregate per Caltrans Spec 68-1.025 Design Procedure
Step 1 – Calculate Water Quality Volume (WQV)
Using the procedures presented in Section 7.4, determine the contributing area and WQV based on a 12-hour drawdown period.

Step 2 – Design average ponding zone depth (DPZ)
Select the average WQV depth between six (6) and twelve (12) inches. The average depth is defined as water volume divided by the water surface area of the planter.

Step 3 – Calculate planter surface area (AS)
The design surface area of the planter is determined from the design WQV and DPZ as follows:

AS = WQV/DPZ
Where
WQV = water quality volume (ft3); and
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-13 May 2025
DPZ = average ponding depth (ft).

Step 4 – Design base courses
Topsoil layer – Provide a sandy loam topsoil layer above the sand-peat mix layer. This layer should be a minimum of six (6) inches deep, but a deeper layer is recommended to promote healthy vegetation.

Sand/Peat layer – Provide an 18-inch (minimum) sand and peat layer over a 9-inch gravel layer as shown in Figures L-2.1 and L-2.2. Thoroughly mix 75% sand (ASTM C-33) with 25% peat for filtration and adsorption of contaminants. Note: The planting media mix specified for Bioretention (Fact Sheet L-1) may be used as an alternative to the topsoil and sand/peat mix.

Gravel envelope (for subsurface drainpipe) – Place drainpipe on a 3- ft wide, 3-inch-deep bed of gravel (Class 2 Permeable Material per Caltrans Spec 68-1.025). Cover the top and sides of the pipe with gravel to a minimum depth of 6 inches. Place a strip of non-woven filter fabric on top of the gravel layer that extends 18 inches on either side of the drainpipe.

Do not wrap the drainpipe or gravel envelope with filter fabric to prevent potential clogging.

Step 5 – Select sub-base liner
If expansive soils or rocks are a concern, chemical or petroleum products are handled or stored within the tributary catchment, or infiltration is not desired for any reason, use a Flow-through Stormwater Planter with an impermeable liner.

Step 6 – Design subsurface drainpipe (if required)
If C or D soils are present or impermeable liner is used, provide a subsurface drainpipe with a diameter sized for the required hydraulic capacity (4-in minimum). Use a heavy-walled, slotted PVC pipe (ASTM D1785 SCD 40) to allow pressure water cleaning and root cutting, if necessary. Connect subsurface drainpipe to the downstream open conveyance (e.g. swale) or to the storm drain system.

Step 7 – Select vegetation
Select vegetation that:
• Is identified on the list of approved plants – Appendix L; • Is suited to well-drained soil;
• Will be dense and strong enough to stay upright, even in flowing water; • Has a minimum need for fertilizers;
• Is not prone to pests and is consistent with Integrated Pest Management practices; • Will withstand being inundated for periods of time; and • Is consistent with local water conservation ordinance requirements. #6..
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-14 May 2025
Avoid the use of bark or similar buoyant material that will tend to float when the vegetated area is inundated.

Step 8 – Design Irrigation System
Provide irrigation system to maintain viability of vegetation, if applicable. The irrigation system must include a City-approved automatic timer.

Step 9 – Design overflow device
Provide an overflow device with an inlet to storm drainage system. Set the overflow inlet elevation above the WQV surcharge water level. A drop inlet or an overflow standpipe with an inverted or grated opening is appropriate overflow devices.

Volume Retention Calculation
Stormwater Planters may be used to achieve the VRRs in addition to treatment control requirements. The volume retention for a Stormwater Planter is less if a subsurface drainpipe is provided because less infiltration will occur. The calculation procedure for volume retention for Stormwater Planters is presented in Table L-2.2.
#6..
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-15 May 2025
Table L-2.2. Stormwater Planter Volume Retention Calculation Stormwater Planter with Subsurface Drainpipe Required for C and D soils and impermeable liners

1. Ponding Zone
a. Depth of ponding zone (DPZ)
b. Area of ponding zone (APZ)
DPZ =____________ ft
APZ =____________ ft2
Infiltration allowance for water in
ponding zone water = 0.25

2. Planting Media Layer
a. Depth of planting media layer (DPM)
b. Area of planting media layer (APM)
DPM =_____________ ft
APM =____________ ft2
Available Water Holding Capacity
of planting media layer = 0.1 x
volume

3. Gravel Zone
a. Depth of gravel below pipe (DGZ)
b. Area of gravel below pipe (AGZ)
DGZ =____________ ft
AGZ =____________ ft2
Porosity of gravel zone = 0.30
Minimum depth below pipe = 6 in
Minimum width of gravel = 3 ft

4. Volume retention for planters
(VolRetention)
VolRetention = (DPZ x APZ x 0.25) +
(DPM x APM x 0.1) +
(DGZ x AGZ x 0.3)
VolRetention = _________ ft3
For planters with impermeable
liners, volume retention credit is
only given for retention in the
planting media layer:

VolRetention = (DPM x APM x 0.1)
Stormwater Planter without Subsurface Drainpipe Recommended for A and B soils

1. Ponding Zone
a. Depth of ponding zone (DPZ)
b. Area of ponding zone (APZ)
DPZ =____________ ft
APZ =____________ ft2
Infiltration allowance for water in
ponding zone water = 1.0

2. Planting Media Layer
a. Depth of planting media layer (DPM)
b. Area of planting media layer (APM)
DPM =____________ ft
APM =____________ ft2 Minimum depth = 18 inches

3. Volume retention for planters
(VolRetention)
VolRetention = (DPZ x APZ) + (DPM x APM x

0.10)
VolRetention= _________ ft3
Available Water Holding Capacity
of planting media layer = 0.1 x
volume
Construction Considerations
• Divert stormwater runoff (other than necessary irrigation) during the period of vegetation establishment. Where runoff diversion is not possible, cover graded and seeded areas with suitable erosion control materials.
• Install sediment controls (e.g., staked straw wattles) around the planter to prevent high sediment loads from entering the planter during ongoing construction activities. #6..
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-16 May 2025
• Avoid compaction of native soils below the planting media layer or gravel zone for infiltration planter.
• Repair, seed, or re-plant damaged areas immediately.
• For planters next to buildings, provide waterproofing of exterior building walls as directed by an architect or structural engineer.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner before final acceptance of a private development project, including treatment controls such as Stormwater Planters. Such agreements will typically include requirements such as those outlined in Table L2.3. The property owner or his/her designee is responsible for compliance with the agreement.

The maintenance agreement and plan will provide the City designee with complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-17 May 2025
Table L-2.3. Inspection and Maintenance Requirements for Stormwater Planters Activity Schedule
Trim vegetation (as applicable) and remove weeds
to limit unwanted vegetation As required
Remove litter and debris from landscape area As required Use Integrated Pest Management techniques As required
Inspect the planter to determine if runoff is
infiltrating properly
At least twice per year during storm events.

Additional inspections after periods of heavy runoff
are desirable.

If infiltration is significantly reduced, remove and
replace topsoil and sand/peat layer
May be required every 5 to 10 years or more
frequently, depending on sediment loads
Figure L-2.1. Stormwater Planter Configuration. Source: Urban Drainage and Flood Control District (UDFCD). (1999, rev. 2008). Drainage Criteria Manual (Vol 3). Denver, CO. #6..
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Treatment Control Measure Fact Sheet L-2: Stormwater Planter Development Guidance Manual E-18 May 2025
Figure L-2.2. Flow-through Stormwater Planter Configuration. "Stormwater Planters." Source: Stormwater Management Manual. [Eugene, Or.]: City of Eugene. (2008). 2-58--62. Print. http://ceppcontent.eugene1.net;7087/publishedcontent/publish/pw/stormwater/docs/ch2e.pdf #6..
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-19 May 2025
Description
A Tree-well Filter is similar to the Bioretention (L-1) and Stormwater Planters (L-2) and consists of one
or multiple chambered pre-cast concrete boxes
with a small tree or shrub planted in a bed filled
with engineered soil media. A Tree-well Filter is
installed along the edge of a parking lot or
roadway, where street trees might normally be
installed, and is designed to receive, retain, and
infiltrate stormwater runoff from adjoining paved
areas. During rain events, runoff flows into the
chamber and gradually infiltrates the surface and
filters through the engineered soil matrix, filling the void spaces of the matrix before infiltrating the
underlying soil or being collected by an underdrain
system.

Treatment of the stormwater runoff occurs through
a variety of natural mechanisms as the runoff filters
through the root zone of the vegetation and during
the detention of the runoff in the pore space of the
engineered soil matrix. A portion of the water held
in the root zone of the soil media is returned to the
atmosphere through transpiration by the
vegetation.

A Tree-well Filter may be installed in open or closed
bottom chambers.

If underlying soils have a permeability greater than
the engineered soil layers (typically types A or B
soils), the Tree-well Filter can be constructed with
an open bottom with an underdrain pipe. If less
permeable underlying soils (types C or D) are
present, an underdrain pipe is required. If
infiltration must be avoided due to site constraints,
an impermeable liner or concrete bottom should be
provided as well as an underdrain pipe.

Other Names: Stormwater Tree Pit, Tree Box Filter
(Top) A tree box installed with a speed bump to
assist the flow of water towards the inlet. Source
Photo: Pat Rector Rutgers, The State University of New
Jersey, U.S. Department of Agriculture, and County
Boards of Chosen Freeholders. Rutgers Cooperative
Extension, a unit of the Rutgers New Jersey Agricultural Experiment Station, is an equal opportunity program
provider and employer
(Bottom) Tree Box. Source: MSD. (n.d.). Retrieved
October 7, 2021, from https://louisvillemsd.org/complyconsent-decree. #6..
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-20 May 2025
Advantages
• Enhances site aesthetics.
• Integrates well with street landscapes.
• Takes up very little space, may be ideal for highly developed sites. • Adaptable, may be used in a variety of site conditions. • Reduces stormwater volume and pollutant discharge.

Limitations
• May require individual owners/tenants to perform maintenance. • Irrigation is typically required to maintain vegetation. • Not appropriate for industrial sites or locations where spills may occur unless infiltration is prevented.

Planning and Siting Considerations
• Select a location where site topography is relatively flat and allows runoff drainage to the Tree-well Filter.
• Integrate Tree-well Filters into other landscape areas when possible. • Tree-well Filters may have a non-rectangular footprint to fit the site landscape design. • Irrigation is typically required to maintain viability of Tree-well Filters. Coordinate design of general landscape irrigation system with that of tree well-filters, as applicable. • Connect underdrain into storm drain system.

Design Criteria
Design criteria for Tree-well Filters are listed in Table L-3.1. A Design Data Summary Sheet is provided at the end of this fact sheet.
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-21 May 2025
Table L-3.1. Tree-well Filter Design Criteria
Design Parameter Design
Criteria Notes
Drainage area ≤ 1 acre
Ideally suited for small areas such as parking lot
islands, perimeter building planters, street
medians, roadside swale features, and site
entrance or buffer features.

Design volume WQV Section 7.4
Design drawdown time 12 hrs Period of time over which WQV drains from tree well.

Design average ponding depth (ds) 6-12 in.

Depth to groundwater > 10 ft From tree-well soil surface (without underdrain).

Topsoil layer 6 in.
(minimum)
Sandy loam topsoil. Deeper layer recommended
for better vegetation establishment.

Sand-peat layer 18 in.
(minimum)
75% ASTM C-33 Sand + 25% peat. Note: planting
media specified for Bioretention (L-1) may be
used as an alternate for the topsoil and sand and
peat layers.

Gravel layer 9 in. Class 2 Aggregate per Caltrans Spec 68-1.025.

Design Procedure
Step 1 – Calculate Water Quality Volume (WQV)
Using the procedures presented in Section 7.4, determine the contributing area and WQV based on a 12-hour drawdown period.

Step 2 – Design average surcharge depth (ds)
Select the average WQV depth between six (6) and twelve (12) inches. The average depth is defined as water volume divided by the water surface area of the planter.

Step 3 – Calculate Tree-well Filter surface area (AS)
The design surface area of the planter is determined from the design WQV and ds as follows:

AS = WQV/ds
Where:

WQV = water quality volume (ft3); and
ds = average ponding depth (ft).
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-22 May 2025
Step 4 – Design base courses
Sand/Peat layer – Provide a 24-inch (minimum) sand and peat layer over a 9-inch gravel layer, as shown in Figure L-3.1. Thoroughly mix 75% sand (ASTM C-33) with 25% peat for filtration and adsorption of contaminants. Note: The planting media mix specified for Bioretention (Fact Sheet L-1) may be used as an alternative to the topsoil and sand/peat mix.

Gravel envelope (for subsurface drainpipe) – Place drainpipe on a 3- ft wide, 3-inch-deep bed of gravel (Class 2 Permeable Material per Caltrans Spec 68-1.025). Cover the top and sides of the pipe with gravel to a minimum depth of 6 inches. Place a strip of non-woven filter fabric on top of the gravel layer that extends 18 inches on either side of the drainpipe.

Do not wrap the drainpipe or gravel envelop with filter fabric to prevent potential clogging.

Step 5 – Select subbase liner
If expansive soils or rocks are a concern, chemical or petroleum products are handled or stored within the tributary catchment, or infiltration is not desired for any reason, use a Tree-well Filter with an impermeable liner.

Step 6 – Design subsurface drainpipe (if required)
If Type C or D soils are present or an impermeable liner is used, provide a subsurface drainpipe with a diameter sized for the required hydraulic capacity (4-in minimum). Use a heavy-walled, slotted PVC pipe (ASTM D1785 SCD 40) to allow pressure water cleaning and root cutting, if necessary. Connect the subsurface drainpipe to the downstream open conveyance (e.g., swale) or the storm drain system.

Step 7 – Select tree
Select a tree that:
• Is identified on the list of approved plants – Appendix L; • Is suited to well-drained soil;
• Will be dense and strong enough to stay upright, even in flowing water; • Has minimum need for fertilizers;
• Is not prone to pests and is consistent with Integrated Pest Management practices; • Will withstand being inundated for periods of time; and • Is consistent with local water conservation ordinance requirements.

Avoid the use of bark or similar buoyant material that will tend to float when the vegetated area is inundated.

Step 8 – Design Irrigation System
Provide irrigation system to maintain viability of vegetation, if applicable.

Step 9 – Design overflow device
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-23 May 2025
Provide an overflow device with an inlet to storm drainage system. Set the overflow inlet elevation above the WQV surcharge water level. A drop inlet or an overflow standpipe with an inverted or grated opening is appropriate overflow devices.

Volume Retention Calculation
Tree-well Filters may be used to achieve the VRRs in addition to treatment control requirements. The volume retention for a Tree-well Filter is less if an impermeable bottom is used because less infiltration will occur. The calculation procedure for volume retention for Tree-well Filter is presented in Table L-3.2.

Table L-3.2. Tree-well Filter Volume Retention Calculation Design Parameter Design Criteria Notes
Tree-well Filter with Subsurface Drainpipe Required for Type C and D soils and impermeable bottoms

1. Ponding Zone
a. Depth of ponding zone (DPZ)
b. Area of ponding zone (APZ)
DPZ = ___________ ft
APZ = ___________ ft2
Infiltration allowance for water in
ponding zone water = 0.25

2. Planting Media Layer
a. Depth of planting media layer
(DPM)
b. Area of planting media layer (APM)
DPM = ___________ ft
APM = ___________ ft2 Available Water Holding
Capacity of planting media layer
= 0.1 x volume

3. Gravel Zone
a. Depth of gravel below pipe (DGZ)
b. Area of gravel below pipe (AGZ)
DGZ = ____________ ft
AGZ = ____________ft2
Porosity of gravel zone = 0.30
Minimum depth below pipe = 6 in
Minimum width of gravel = 3 ft

4. Volume retention for tree wells
(VolRetention)
VolRetention = (DPZ x APZ x 0.25) +
(DPM x APM x 0.1) +
(DGZ x AGZ x 0.3)
VolRetention = ft3
For tree wells with impermeable
liners, volume retention credit is
only given for retention in the
planting media layer:

VolRetention = (DPM x APM x 0.1)
Tree Well Filters without Subsurface Drainpipe Recommended for Type A and B soils

1. Ponding Zone
a. Depth of ponding zone (DPZ)
b. Area of ponding zone (APZ)
DPZ = ____________ft
APZ = ____________ft2
Infiltration allowance for water in
ponding zone water = 1.0

2. Planting Media Layer
a. Depth of planting media layer
(DPM)
b. Area of planting media layer (APM)
DPM = ____________ft
APM = ____________ft2
Minimum depth = 18 inches

3. Volume retention for tree wells
(VolRetention)
VolRetention= ____________ft3 Available Water Holding
Capacity of planting media layer
= 0.1 x volume
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-24 May 2025
VolRetention = (DPZ x APZ) + (DPM x APM
x 0.10)
Construction Considerations
• Divert runoff (other than necessary irrigation) during vegetation establishment. Where runoff diversion is not possible, cover graded and seeded areas with suitable erosion control materials.
• Install sediment controls (e.g., staked straw wattles) around the tree well to prevent high sediment loads from entering the planter during ongoing construction activities. • Avoid compaction of native soils below the planting media layer or gravel zone. • Repair, seed, or re-plant damaged areas immediately.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner before final acceptance of a private development project, including treatment controls such as Tree-well Filters. Such agreements will typically include requirements such as those outlined in Table L3.3. The property owner or his/her designee is responsible for compliance with the agreement.

The maintenance agreement and plan will provide the City designee with complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.

Table L-3.3. Inspection and Maintenance Requirements for Tree-well Filters Activity Schedule
Trim vegetation (as applicable) and remove weeds
to limit unwanted vegetation As required
Remove litter and debris from landscape area As required Use Integrated Pest Management techniques As required
Inspect the planter to determine if runoff is
infiltrating properly
At least twice per year during storm events.

Additional inspections after periods of heavy runoff
are desirable.

If infiltration is significantly reduced, remove and
replace topsoil and sand/peat layer
May be required every 5 to 10 years or more
frequently, depending on sediment loads
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Treatment Control Measure Fact Sheet L-3: Tree-well Filter Development Guidance Manual E-25 May 2025
Figure L-3.1. Tree-well Filter Schematic. Source: University of New Hampshire, Stormwater Center. (2009) 2009 Biannual Report. p.22.
#6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-26 May 2025
Description
A Water Quality Infiltration Basin is a shallow
earthen basin constructed in naturally pervious
soils (type A or B) designed for infiltrating
stormwater runoff. This type of basin retains the
WQV and. allows the retained runoff to percolate
into the underlying native soils and into the
groundwater table over a specified drawdown
period. Infiltration Basins are similar to the City’s
Water Quality Infiltration Basins but differ in that
they are designed for the purpose of stormwater
runoff treatment and retention as opposed to
drainage.

The bottom of the basin is typically vegetated with
dryland grasses or irrigated turf grass. Treatment
of the runoff occurs through a variety of natural
mechanisms as the water flows through the soil
profile. To ensure adequate treatment, the depth
of unsaturated soil between the basin bottom and the seasonal maximum groundwater surface level should be a minimum of ten (10) feet. A typical layout of a Water Quality Infiltration Basin is shown in Figure L-4.1.

Other Names: Percolation Basin
Advantages
• Reduces or eliminates stormwater runoff discharge to surface waters during most storm events.
• Reduces peak stormwater runoff flows during small storm events. • Can be incorporated into site landscape features or multi-use facilities, such as parks or athletic fields.
• Can be designed to meet trash control requirements.

Limitations
• Not appropriate for areas with low permeability soils or high groundwater. • Not appropriate for industrial sites or locations with contaminated soils or where spills may occur because of the potential threat to groundwater contamination. • Must be protected from high sediment loads. Once clogged with sediment, restoration of basin infiltration capacity may be difficult.
• Potential for mosquito breeding due to standing water. This can be greatly reduced and/or eliminated if the basin is properly designed, constructed, and operated to maintain its infiltration capacity.

Source: Ball Field Water Quality Infiltration Basin.

Stormwater Discovery Tours. (2019, March 28). Retrieved October 7, 2021, from https://stormwater.cob.org/toursqualicum-creek-park/site-ball-field-infiltration-basin/. #6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-27 May 2025
• Not appropriate on fill or sites with steep slopes.

Planning and Siting Considerations
• A qualified geotechnical engineer or geologist should determine soil permeability, and depth to groundwater and design safety factors to ensure that conditions conform to the criteria listed in Table L-4.1.
• Integrate Water Quality Infiltration Basins into open space buffers, undisturbed natural areas, and other landscape areas when possible.
• Pretreatment using Grassy Channels, Vegetated Buffer Strips, Vegetated Swales, Grassy Swales, and/or Vegetated Filter Strip is required to protect Water Quality Infiltration Basins from high sediment loads.
• Irrigation may be required to maintain the viability of vegetation on the slopes and bottom of the basin if vegetation is included in the design. Coordinate the design of the general landscape irrigation system with that of the basin, as applicable. • Plan for setback requirements.

Figure. L-4.1. Example Water Quality Infiltration Basin. Source: Henao Casas, Jose & Walther, Marc & Kalwa, Fritz & Rausch, Randolf. (2019). Numerical and Analytical Assessment of Stormwater Infiltration via Vadose Zone Wells and Infiltration Trenches. 10.13140/RG.2.2.14098.07368. #6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-28 May 2025
Design Criteria and Procedure
Principal design criteria for Water Quality Infiltration Basins are listed in Table L-4.1.

Table L-4.1. Water Quality Infiltration Basin Design Criteria Design Parameter Unit Design Criteria
Drawdown time for WQV hrs 48
WQV ac-ft 80% annual capture; 48-hr drawdown
Soil permeability range in/hr 0.6 - 2 (Saturated vertical permeability) Bottom Basin Elevation ft 10 ft above seasonally high groundwater table minimum.

Freeboard (minimum) ft 1.0
Setbacks ft
ft
100 ft from wells, tanks, fields, springs
20 ft down slope or 100 ft up slope from foundations
Inlet/outlet erosion control – Energy dissipater to reduce inlet/outlet velocity Embankment side slope (H:V) – ≥ 4:1 inside/ ≥3:1 outside (without retaining walls) Maintenance access ramp slope (H:V) – 10:1 or flatter
Maintenance access ramp width ft 16.0 – approach paved with asphalt concrete Vegetation – Side slopes and bottom (may require irrigation during summer)
Design Criteria (for Trash Control see below)
Step 1- Calculate Water Quality Volume (WQV)
Using the procedures presented in Section 7.4, determine the tributary drainage area and WQV for 48-hour drawdown.

Step 2– Calculate Design Maximum Depth of Water Surcharge in the Water Quality Infiltration Basin (Dmax)
s12
It
D max
max ×
× =
Where
tmax = Maximum drawdown time = 48 hrs
I = Site infiltration rate (soil permeability) (in/hr)
s = Safety factor
In the formula above, the safety factor accounts for possible inaccuracies in the infiltration rate measurement. A larger safety factor should be used when the infiltration rate is less certain. Safety factors typically range between two (2) and ten (10) and should be determined by a qualified geotechnical engineer or geologist based on field measurements of saturated vertical permeability at the proposed site. #6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-29 May 2025
Note that soils with a permeability greater than two (2) inches per hour may be used if full pretreatment is provided using one of the approved treatment controls.

Step 3- Calculate Minimum Surface Area of the Water Quality Infiltration Basin Bottom (Amin) Amin = WQV/Dmax
Where
Amin = minimum area required (ft2)
Dmax= maximum allowable depth (ft)
Step 4 – Design Forebay Settling Basin
The forebay provides a zone for the removal of course sediment by sedimentation. The volume of the forebay should be five (5) to ten (10) percent of the WQV. The forebay should be separated from the basin by a berm or similar feature. An outlet pipe connecting the bottom of the forebay and the basin should be provided and sized to allow the forebay volume to drain within 45 minutes.

Step 5 – Design Embankments
Interior slopes (H:V) should be no steeper than 4:1 and exterior slopes no steeper than 3:1.

Flatter slopes are preferable.

Step 6 – Design Maintenance Access
Provide all-weather access for maintenance vehicles to the bottom and outlet works. The maximum grades of access ramps should be ten (10) percent and the minimum width should be ten (10) feet. Ramps should be paved with concrete colored to blend with the surroundings.

Step 7 – Design Security Fencing
Provide aesthetic security fencing around the basin to protect habitat except when specifically waived by the City. Fencing design shall adhere to the City of Modesto Standard Specifications and be approved by the City.

Step 8 – Design Bypass
Provide for bypass or overflow of runoff volumes in excess of the WQV. Provide spillway or overflow structures, as applicable.

Step 9 – Design Relief Drain
Provide 4-inch diameter perforated plastic relief underdrain with a valved outlet to allow removal of standing water in the event of loss of soil infiltration capacity.

Step 10 – Select Vegetation
Select vegetation from the list of approved plants – Appendix L. Plant basin bottoms, berms, and side slopes with native grasses or with irrigated turf. Vegetation provides erosion protection and sediment entrapment.

Step 11 – Design Irrigation System
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-30 May 2025
Provide an irrigation system to maintain the viability of vegetation, if applicable.

Design Procedure – Trash Control8
Water Quality Infiltration Basins may be backfilled with porous media such as gravel, sand, soil, or various locally earthed rocks (assuming such media does not generate pollutants of concern).

These Basins store water for infiltration to underlying soils. The subsurface of the Basin may include perforated pipes, chambers, open bottom concrete galleries, or other high voids structures designed to temporarily store water prior to infiltration. The surface of the Basin must have a surface area large enough to trap trash and reduce the risk of trash and other debris (e.g., vegetation) interfering with the hydraulic capacity.

The Water Quality Infiltration Basin must be designed, constructed, and maintained in accordance with the following five (5) requirements:

1. Trap trash particles that are 5 millimeters or greater at any time during a storm event for the following:
a. The peak flow rate generated by the region specific one-year, one-hour storm event from the applicable sub-drainage area (0.31 inches/hour); or b. The peak flow rate of the corresponding storm drain (if the Basin is designed to treat flows from the corresponding storm drain that is designed for less than the peak flow rate generated from a one-year, one-hour storm event).

2. Water Quality Infiltration Basins may include either or both of the following to trap particles for either flow described above in section 1.a or 1.b:
a. A screen at the system’s inlet, overflow, or bypass outlet; or b. An up-gradient structure designed to bypass flows exceeding the flows as described in section 1.a or 1.b9

3. The peak flow rates references in section 1.a shall be calculated using one of the following methods:
a. For small drainage areas (generally less than 50 acres) - the Rational Equation Method, which is expressed as Q = CiA, where:

Q = design flow rate (cubic feet per second),
C = runoff coefficient (dimensionless),
i = design rainfall intensity (0.31 inches/hour), and
A = subdrainage area (acres).
b. For large drainage areas (generally 50 acres or more) – Other accepted hydrologic mathematical methods that more accurately calculate peak flow rates from large 8 Based on the State Water Resources Control Board Categorically Certified Multi-Benefit Trash Treatment Systems – Infiltration Basin information sheet June 2023 and any subsequent revisions. 9 Upon approval by the appropriate Regional Water Quality Control Board Executive Officer, a 5 millimeter screen and/or upgradient structure may not be required if the Basin is designed for flood control from flows generated by very large storm events. #6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-31 May 2025
drainage areas, provided a registered California-licensed professional engineer documents the calculations within the design plans.

4. For the purpose of requirements related to the peak flow rates in item 1, above, the percolation rate below the Water Quality Infiltration Basin must either be measured directly or estimated employing conservative hydrogeologic assumptions.

5. A registered California licensed Professional Engineer shall stamp and sign Bioretention System design plans as required by California Business & Professions Code section 6700, et seq.

Vector breeding considerations must also be addressed due to the potential nuisance and human health effects.

Trash controls shall be installed and maintained by the property owner for all storm drains, catch basins, or inlets located within the parcel's boundaries and operated and maintained by the property owner. Trash controls shall only be installed in storm drains, catch basins, or inlets within the Public RoW if the City has agreed to enter into a maintenance agreement with the property owner (Appendix I).

Volume Retention Calculation
Water Quality Infiltration Basins may be used to achieve VRRs in addition to treatment control requirements. The volume retention allowed is equal to the WQV calculated in Step 1 of the design procedure.

Construction Considerations
• If possible, stabilize the entire tributary area to the Water Quality Infiltration Basin before construction begins. If this is not possible, divert flow around the basin to protect it from sediment loads during construction or remove the top two inches of soil from the basin floor after the entire site has been stabilized.
• Once construction is complete, stabilize the entire tributary area to the basin before allowing runoff to enter the infiltration facility.
• Divert runoff (other than necessary irrigation) during the period of vegetation establishment.
• Construct basin using equipment with extra wide, low-pressure tires. Prevent construction traffic from entering basin to avoid compaction of the surface. • Final grading shall produce a level basin bottom without low spots or depressions. • After final grading, deep till the basin bottom.
• Repair, seed, or re-plant damaged areas immediately.

Long-Term Maintenance
The City requires the execution of a maintenance agreement with the property owner before final acceptance of a private development project, including treatment control measures. Such agreements will typically include requirements such as those outlined in Table L-4.2. The #6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-32 May 2025
property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement and plan will provide the City designee with complete access to the treatment control measure and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.

Trash Considerations
Because regular maintenance is required to maintain adequate trash capture capacity and to ensure that captured trash does not migrate offsite, the Permittee shall establish a maintenance schedule based on:
a. The maintenance frequency as required in the applicable State or Regional Water Board stormwater permit; and
b. Site-specific factors including the design trash capture capacity of the Water Quality Infiltration Basin, local storm frequency, and characterization of trash and vegetation accumulation in the corresponding sub-drainage area.
#6..
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Treatment Control Measure Fact Sheet L-4: Water Quality Infiltration Basin Development Guidance Manual E-33 May 2025
Table L-4.2. Inspection and Maintenance Requirements for Water Quality Infiltration Basins Activity Schedule
If erosion occurs within the basin, re-vegetate
immediately and stabilize with erosion control mulch or mat until vegetation cover is established.

As required
Monitor infiltration rate in basin after storms by recording the drop in water depth versus time using a calibrated rod or staff gauge.

Several times during first year following
installation. During subsequent seasons, at
the beginning and end of wet season.

Additional monitoring after periods of heavy
runoff is desirable.

If drawdown time is observed to have increased
significantly over the design drawdown time, clean, regrade, and till basin bottom to restore infiltrative capacity.

This maintenance activity is expensive and the need for it can be minimized through prevention of upstream
erosion.

As required
Trim vegetation to prevent the establishment of woody
vegetation and for aesthetic and vector control reasons. At the beginning and end of the wet season Monitor health of vegetation and replace. As required
Remove litter and debris from the area. As required
Inspect basin to identify potential problems such as
erosion of the basin side slopes and invert, standing
water, trash and debris, and sediment accumulation.

At beginning and end of the wet season.

Additional inspections after periods of heavy
runoff are desirable.

Remove accumulated sediment and re-grade when the
accumulated sediment volume exceeds ten (10) percent
of the basin volume. Note: scarification or other activities creating disturbance should only be performed when
there are actual signs of clogging, rather than on a routine basis.

As required for both forebay and basin
Maintain pretreatment control measures in accordance to its respective “Long-Term Maintenance” section. As required #6..
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-34 May 2025
Description
A Water Quality Infiltration Trench (also known
as a French Drain or Horizontal Drain) is a narrow
trench constructed in naturally pervious soils
(Type A or B soils) and filled with gravel and sand,
although use of manufactured percolation tank
modules may be considered in place of gravel fill.

Stormwater runoff is stored in the trench until it
infiltrates into the soil profile over a specified
drawdown period. Overflow drains are often
provided to allow drainage if the trench becomes
clogged. Water Quality Infiltration Trenches are
similar to the City’s infiltration trenches but differ
in that they are designed for the purpose
stormwater runoff treatment and retention as
opposed to drainage.

Infiltration Vaults and Infiltration Leach Fields are subsurface variations of the Water Quality Infiltration Trench concept in which stormwater runoff is distributed to the upper zone of the subsurface gravel bed utilizing perforated pipes.

A Water Quality Infiltration Trench is designed to retain the WQV in the trench and allow that volume to infiltrate into the native soil profile over the design drawdown period. Infiltrated water typically reaches the underlying groundwater. Treatment of the stormwater runoff occurs through various natural mechanisms as the water flows through the trench media and the soil profile. To ensure adequate treatment and protect groundwater, the depth of unsaturated soil between the trench bottom and the maximum groundwater surface level should be a minimum of 10 feet.

A typical Water Quality Infiltration Trench configuration is shown in Figure L-5.1.

Other Names: Percolation Trench, Dispersal Trench, French Drain Advantages
• Provides effective treatment through settling and filtering while requiring relatively small space.
• Can be placed below ground.
• Suitable for use when water is not available for irrigation or base flow. • Reduces peak flows during small storm events.
• Can be designed to meet trash control requirements.

Limitations
• Potential for clogging of media. Upstream treatment control measures to remove large sediment may be required to prevent or minimize media clogging. The cost of restorative and
Infiltration Trench. Source: AWWA. (2019, February 1).

Infiltration trench: Do-it-yourself conservation practices.

Acton Wakefield Watersheds Alliance. Retrieved October 7, 2021, from https://awwatersheds.org/infiltration-trench-do-ityourself-conservation-practices/. #6..
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-35 May 2025
maintenance can be high if the soil infiltration rates are significantly reduced due to sediment deposition.
• Not appropriate for areas with slowly permeable soils (C and D type) or high groundwater. • Not appropriate for industrial sites or locations with contaminated soils or where spills may occur because of the potential threat to groundwater contamination.

Planning and Siting Considerations
• Integrate Water Quality Infiltration Trenches into open space buffers, undisturbed natural areas, and other landscape areas when possible.
• Plan for setback requirements as listed in Table L-5.1. • Do not locate trenches under tree drip lines.
• Pretreatment using Grassy Channels, Vegetated Buffer Strips, Vegetated Swales, Grassy Swales, and/or Vegetated Filter Strip is required to protect Water Quality Infiltration Trenches from high sediment loads.
#6..
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-36 May 2025
Design Criteria
Design criteria for Water Quality Infiltration Trenches are listed in Table L-5.1.

Table L-5.1. Water Quality Infiltration Trench Design Criteria Design Parameter Criteria Notes
Tributary Drainage Area ≤ 5 acres
Design volume WQV Section 7.4
Maximum drawdown time for WQV 48 hrs Based on WQV
Soil permeability range 0.6-2 in./hr Saturated vertical permeability Minimum groundwater separation 10 ft Between trench bottom and seasonally high groundwater table
Maximum trench surcharge depth (Dmax) 10 ft
Setbacks
100 ft
20 ft
100 ft
–
From wells, tanks, fields, springs
Downslope from foundations
Upslope from foundations
Do not locate under tree drip-lines
Trench media material size/type 1-3 in. Washed gravel
Trench lining material – Geotextile fabric (Table L-5.2) prevents clogging
Observation well size 4-6 in. Perforated PVC pipe with removable cap Pretreatment vegetated buffer strip
length/slope 10 ft/5% Minimum length/maximum slope in flow direction #6..
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-37 May 2025
Table L-5.2. Geotextile Fabric Specifications
Property Test Method Unit Specification
Material Nonwoven geotextile fabric
Unit Weight oz/yd3 8 (min.)
Filtration Rate in/sec 0.08 (min.)
Puncture Strength ASTM D-751 (Modified) lbs. 125 (min.) Mullen Burst Strength ASTM D-751 psi 400 (min.)
Tensile Strength ASTM-D-1682 lbs. 300 (min.)
Equiv. Opening Size US Standard Sieve No. 80 (min.)
Design Procedure (for Trash Control see below)
Step 1 – Calculate Water Quality Volume (WQV)
Using the procedures presented in Section 7.4 determine the effective tributary drainage area and WQV for 48-hour drawdown.

Step 2 – Calculate Minimum Surface Area of Trench Bottom (Amin) Areamin=
WQVxsx12
𝑡𝑡𝑚𝑚𝑚𝑚𝑚𝑚𝑥𝑥1
Where
WQV = water quality volume (ft3)
tmax = Maximum drawdown time = 48 hrs
I = Site infiltration rate (soil permeability) (in/hr)
s = Safety factor
The safety factor accounts for the variability in soil permeability at the site and the relative uncertainty in the infiltration rate measurements. The more variable the soil conditions and the less certain the infiltration rate, the higher the safety factor should be. Safety factors typically range between two (2) and ten (10) and should be determined by a qualified geotechnical engineer or geologist based on field measurements of saturated vertical permeability at the proposed site. Note that soils with a permeability greater than two (2) inches per hour may be used if full pretreatment is provided using one of the approved treatment controls.

Step 3 – Calculate Design Depth of Water Surcharge in Trench (Dmax) Dmax= WQV
𝑃𝑃 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-38 May 2025
Where
WQV = water quality volume (ft3)
P = Porosity of gravel material (use 0.30) (Note: use of manufactured percolation tank modules can provide greater porosity than gravel.) Areamin = minimum area required (ft2)
Note: Dmax should not exceed ten (10) feet. Increase Amin as necessary to keep Dmax ≤ 10 ft Step 4 – Design Observation Well
Provide a vertical section of perforated PVC pipe, four (4) to six (6) inches in diameter, installed flush with the top of the trench on a footplate and with a locking, removable cap.

The observation well is needed to monitor the infiltration rate and is useful for marking the location of the Water Quality Infiltration Trench.

Step 5 – Design Bypass
Provide for bypass or overflow of runoff volumes in excess of the WQV by means of a screened overflow pipe connected to downstream storm drainage or a grated overflow outlet.

Design Procedure – Trash Control6
Water Quality Infiltration Trenches may be backfilled with porous media such as gravel, sand, soil, or various locally earthed rocks (assuming such media does not generate pollutants of concern). These Trenches store water for infiltration to underlying soils. The subsurface of the Trench may include perforated pipes, chambers, open bottom concrete galleries or other high voids structures designed to temporarily store water prior to infiltration. The surface of the Trench must have a surface area large enough to trap trash and reduce the risk of trash and other debris (e.g., vegetation) interfering with the hydraulic capacity.

The Water Quality Infiltration Trench must be designed, constructed, and maintained in accordance with the following five (5) requirements:

1. Trap trash particles that are 5 millimeters or greater at any time during a storm event for the following:
a. The peak flow rate generated by the region specific one-year, one-hour storm event from the applicable sub-drainage area (0.31 inches/hour); or b. The peak flow rate of the corresponding storm drain (if the Trench is designed to treat flows from the corresponding storm drain that is designed for less than the peak flow rate generated from a one-year, one-hour storm event).

2. Water Quality Infiltration Trenches may include either or both of the following to trap particles for either flow described above in section 1.a or 1.b:
6 Based on the State Water Resources Control Board Categorically Certified Multi-Benefit Trash Treatment Systems – Infiltration Trench information sheet.
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-39 May 2025
a. A screen at the system’s inlet, overflow, or bypass outlet; or b. An up-gradient structure designed to bypass flows exceeding the flows as described in section 1.a or 1.b7.

3. The peak flow rates references in section 1.a shall be calculated using one of the following methods:
a. For small drainage areas (generally less than 50 acres) - the Rational Equation Method, which is expressed as Q = CiA, where:

Q = design flow rate (cubic feet per second),
C = runoff coefficient (dimensionless),
i = design rainfall intensity (0.31 inches/hour), and
A = subdrainage area (acres).
b. For large drainage areas (generally 50 acres or more) – Other accepted hydrologic mathematical methods that more accurately calculate peak flow rates from large drainage areas, provided a registered California-licensed professional engineer documents the calculations within the design plans.

4. For the purpose of requirements related to the peak flow rates in item 1, above, the percolation rate below the Water Quality Infiltration Trench must either be measured directly or estimated employing conservative hydrogeologic assumptions.

5. A registered California licensed Professional Engineer shall stamp and sign Bioretention System design plans as required by California Business & Professions Code section 6700, et seq.

Vector breeding considerations must also be addressed due to the potential nuisance and human health effects.

Trash controls shall be installed and maintained by the property owner for all storm drains, catch basins, or inlets that are located within the boundaries of the parcel and that are operated and maintained by the property owner. Trash controls shall only be installed in storm drains, catch basins, or inlets within the Public RoW if the City has agreed to enter into a maintenance agreement with the property owner (Appendix I).

Volume Retention
Water Quality Infiltration Trenches may be used to achieve the VRR in addition to treatment control requirements. The volume retention allowed is equal to the WQV calculated in Step 1 of the design procedure.
7 Upon approval by the appropriate Regional Water Quality Control Board Executive Officer, a 5 millimeter screen and/or upgradient structure may not be required if the Basin is designed for flood control from flows generated by very large storm events. #6..
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-40 May 2025
Figure L-5.1 Infiltration Trench. Source: Adapted from Urban Storm Drain Criteria Manual Vol 3. – Best Management Practices, Urban Drainage and Flood Control District. (1999, November)

PERFORATED PVC PIPES MAY

BE USED TO INCREASE VOID

SPACE AND STORAGE
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-41 May 2025
Construction Considerations
• If possible, stabilize the entire tributary area to the trench before construction begins. If this is not possible, divert flow around the trench site to protect it from sediment loads during construction.
• Once construction is complete, stabilize the entire tributary area to the trench before allowing runoff to enter the trench facility.
• Install geotextile fabric on the sides, bottom, and one foot below the surface of the trench.

Provide generous overlap at all seams.
• Store excavated material at least 10 feet from the trench to avoid backsliding and cave-ins. • Clean, washed gravel should be placed in the excavated trench in lifts and lightly compacted with a plate compactor. The use of unwashed gravel can result in clogging.

Long-term Maintenance
The City requires the execution of a maintenance agreement with the property owner prior to the final acceptance of a private development project, which includes treatment controls such as Water Quality Infiltration Trenches. Such agreements will typically include requirements such as those outlined in Table L-5.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement and plan must provide the City designee with complete access to the device and its immediate vicinity at any time.

Maintenance of the device is the sole responsibility of the owner.

Trash Considerations
Because regular maintenance is required to maintain adequate trash capture capacity and to ensure that captured trash does not migrate offsite, the Permittee shall establish a maintenance schedule based on:
a. The maintenance frequency as required in the applicable State or Regional Water Board stormwater permit; and
b. Site-specific factors including the design trash capture capacity of the Water Quality Infiltration Trench, local storm frequency, and characterization of trash and vegetation accumulation in the corresponding sub-drainage area.
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Treatment Control Measure Fact Sheet L-5: Water Quality Infiltration Trench Development Guidance Manual E-42 May 2025
Table L-5.3. Inspection and Maintenance Requirements for Water Quality Infiltration Trenches Activity Schedule
If erosion is occurring within the tributary area, re-vegetate immediately and stabilize with erosion control mulch or mat until vegetation cover is established.

As required
Monitor the infiltration rate in trench during and after storms by recording the drop in water depth versus time using a calibrated rod or staff gauge.

Several times during first year
following installation. During
subsequent seasons, near the
beginning and end of wet season.

Additional monitoring after periods
of heavy runoff is desirable.

Clean trench when loss of infiltrative capacity is observed. If infiltration rate is observed to have decreased significantly over the design rate, removal of sediment from the trench and replacement of the upper layer of filter fabric may be necessary. Clogging is most likely to occur near the top foot of the trench, between the upper gravel layer and the protective layer of filter fabric. Cleaning can be accomplished by removing the top layer of gravel and clogged filter fabric, installing a new layer of filter fabric, and replacing the gravel layer with washed gravel. This maintenance activity is expensive, and the need for it can be minimized through prevention of upstream erosion.

As required
Remove pioneer trees that sprout in the vicinity of the trench to prevent root puncture of filter fabric that could allow sediment to enter the trench.

As required
Trim adjacent trees to prevent drip lines from extending over surface of trench. As required
Remove litter and debris from trench area. As required
Inspect trench to identify potential problems such as standing water, trash and debris, and sediment accumulation.

At beginning and end of the wet
season. Additional inspections
after periods of heavy runoff are
desirable.

Maintain grassy buffer strip in accordance with requirements listed in the Vegetated Filter Strip Fact Sheet. As required
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Treatment Control Measure Fact Sheet L-6: Porous Pavement Filter Development Guidance Manual E-43 May 2025
Description
Porous Pavement Filter (PPF) consists of an
installation of permeable interlocking concrete
pavers, pervious concrete, or porous asphalt
pavement that is flat in all directions and is provided with a surcharge zone to temporarily store the
stormwater runoff draining from an adjacent area.

Stormwater runoff infiltrates into the porous
pavement and the sublayers of sand and gravel and
slowly exits through an underdrain.

Permeable interlocking concrete pavement is
comprised of a layer of durable concrete pavers or
blocks separated by joints filled with small stones.

Pervious concrete is made from carefully controlled
amounts of water and cementitious materials used
to create a paste that forms a thick coating around
aggregate particles. Unlike conventional concrete,
the mixture contains little or no sand, creating a
substantial void content between 15% and 25%.

Porous asphalt, or "open-graded" asphalt, pavement
contains no fine aggregate particles, thereby
creating void spaces in the pavement, which allows
water to collect within and drain through the
pavement. An alternative approach is to use
stabilized grassy porous pavement consisting of
grass turf reinforced with plastic rings and filter
fabric underlain by gravel. A typical cross-section of
a PPF system is shown in Figure L-6.1.

Advantages
• Reduces stormwater runoff volume and peak flow during small storm events. • Can serve functional and aesthetic purposes.
• Creates dual use for limited spaces.

Limitations
• The cost of restorative maintenance can be somewhat high if the system seals with sediment and can no longer function properly as permeable pavement. • Uneven driving surfaces and potential traps for high-heeled shoes.

Note: the pavement design needs to meet the project-specific loads, which must be reviewed and accepted by the City.

Pervious Pavers. Source: Bay, A. for the C. (n.d.).

Reduce your stormwater. Pervious Pavers. Retrieved
October 7, 2021, from
https://www.stormwater.allianceforthebay.org/takeaction/installations/pervious-pavers.

Porous Asphalt. Source: Cornell University Urban
Horticulture Institute. (2007). Using Porous Asphalt and CU-Structural Soil®. Retrieved October 7, 2021, from
http://www.hort.cornell.edu/uhi/outreach/pdfs/cu_porous _asphalt.pdf.
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Treatment Control Measure Fact Sheet L-6: Porous Pavement Filter Development Guidance Manual E-44 May 2025
Planning and Siting Considerations
• Should only be installed on relatively flat surfaces. • May be used in low vehicle-movement zones. Potential applications may include the following:
o Low vehicle movement airport zones;
o Parking aprons and maintenance roads;
o Crossover/emergency stopping/parking lanes on divided highways; o Residential street parking lanes;
o Residential driveways;
o Sidewalks, walkways, patios;
o Maintenance roads and trails; and
o Emergency vehicle and fire access lanes in apartment/multi-family/complex situations. • Vehicle movement lanes that lead up to the porous pavement parking pads should be solid asphalt or concrete pavement.
• Grass can be used in block voids, but it may require irrigation and lawn care. • Should be located far enough from foundations in expansive soils so as to limit damage to potential structures.
• When a commercial or industrial site may be handling chemicals and petroleum products that may spill to the ground, an impermeable liner with an underdrain is required to prevent groundwater and soil contamination.
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Treatment Control Measure Fact Sheet L-6: Porous Pavement Filter Development Guidance Manual E-45 May 2025
Design Criteria
The design Criteria for the PPF are summarized in Table L-6.1.

Table L-6.1. PPF Design Criteria
Design Parameter Design Criteria Notes
Drawdown time for WQV 12 h Minimum
WQV 80% annual capture 12-hr drawdown
Surcharge storage volume above
pavement WQV
Depth of surcharge zone 2 in Maximum depth above pavement Imperviousness <60% Variable with pavement type
Permeable Paver Infill ASTM No. 8 crushed aggregate
Base courses 1-inch ASTM No. 8 over 9-inch
ASTM No. 57
Design Procedure
Step 1 – Determine Stormwater Quality Design Volume (WQV) Using the procedures presented in Section 7.4, determine the tributary drainage area and WQV for a 12-hour drawdown period.

Step 2 – Determine Filter Ponding Zone Storage Volume (VPZ) The ponding zone storage volume above the pavement is equal to:

VPZ = C x WQV
Where
WQV = water quality volume (ft3)
C = Use 1.0 for soil types A and B; use 0.25 for soil types C and D (see Table L-6.2) Step 3 – Determine Filter Surface Area (AS)
Calculate the minimum required surface area based on a surcharge depth of 2 inches above the pavement as follows:

Surface Area (AS) = WQV (ft3)/0.17 (ft)
Where
WQV = water quality volume (ft3).
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Treatment Control Measure Fact Sheet L-6: Porous Pavement Filter Development Guidance Manual E-46 May 2025
Step 4 – Select Pavement Type
For permeable pavers, select appropriate modular blocks that have no less than 40 percent of the surface area open. The manufacturer’s installation requirements shall be followed with the exception that porous pavement infill material requirements and base course dimensions are adhered to.

Step 5 – Porous Pavement Infill
The Modular Block Pavement openings should be filled with ASTM No. 8 crushed stone.

Step 6 – Provide Base Courses
Provide 1-inch ASTM No. 8 crushed stone over 9-inch ASTM No. 57 aggregate base courses.

Step 7 – Provide Perimeter Wall
Provide a concrete perimeter wall to confine the edges of the PPF area. The wall should be, at the minimum, 6 inches wide and at least 6 inches deeper than all the porous media and modular block depth combined.

Step 8 – Install Subbase
If expansive soils or rocks are a concern or the tributary catchment has chemical or petroleum products handled or stored, install an impermeable membrane below the base course. Otherwise, install a non-woven geotextile membrane to encourage filtration.

Step 9 – Provide Overflow
Provide an overflow, possibly with an inlet to a storm sewer, set at a maximum of 2 inches above the level of the porous pavement surface. Make sure the 2-inch ponding depth is contained and does not flow out of the area at ends or sides.

Volume Retention Calculation
PPF may be used to achieve the VRR in addition to treatment control requirements. The volume retention for a PPF is less if a subsurface drainpipe is provided because less infiltration will occur. If the PPF is constructed with an impermeable liner, no volume retention credit is given.

The calculation procedure for volume retention for PPF is presented in Table L-6.2. #6..
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Treatment Control Measure Fact Sheet L-6: Porous Pavement Filter Development Guidance Manual E-47 May 2025
Table L-6.2. PPF Volume Retention Calculation
Design Parameter Design Criteria Notes
PPF with Subsurface Drainpipe Required for C and D soils

1. Volume retention for PPF (Volreduction)
Volreduction = (WQV x 0.25) Volreduction =___ ft3

Infiltration allowance for water in
ponding zone = 0.25
No volume retention credit is
given for PPFs with impermeable
liners
PPF without Subsurface Drainpipe Use with A and B soils only

1. Volume retention for PPF (Volreduction)
Volreduction = (WQV x 1.0)
Volreduction = __ ft3

Infiltration allowance for water in
ponding zone water = 1.0
Figure L-6.1. Porous Pavement Filter. Source: Infiltration Stormwater Planter Configuration. Urban Drainage and Flood Control District (UDFCD). (1999, rev. 2008). Drainage Criteria Manual (Vol 3).

Denver, CO.
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Treatment Control Measure Fact Sheet L-6: Porous Pavement Filter Development Guidance Manual E-48 May 2025
Construction Considerations
• Before the entire site is graded, the area planned for the PPF should be cordoned off to prevent heavy equipment from compacting the underlying soils. • Install geotextile fabric under the base course. Provide generous overlap at all seams. • Both prior to and during construction, diversions should be installed around the perimeter of the PPF as needed to prevent runoff and sediment from entering the site until the PPF is in place.

Maintenance Requirements
The City requires the execution of a maintenance agreement with the property owner prior to the final acceptance of a private development project, which includes treatment controls such as PPFs. Such agreements will typically include requirements such as those outlined in Table L6.3. The property owner or his/her designee is responsible for compliance with the agreement.

The maintenance agreement and plan will provide the City designee with complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.

Table L-6.3. Inspection and Maintenance Requirements for PPF Activity Schedule
Inspect pavements to determine if runoff is
infiltrating properly. If infiltration is significantly reduced, remove surface aggregate by vacuuming.

Dispose of and replace old aggregate with fresh
aggregate.

At least twice during the wet season after
significant storm events. Additional inspections
after periods of heavy runoff are desirable.

If stabilized grassy porous pavement is used, trim
vegetation and remove weeds to limit unwanted
vegetation.

As required.

Remove litter and debris from the pavement area. As required. #6..
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-49 May 2025
Description
Vegetated Swales are long, narrow,
landscaped depressions used to collect
and convey stormwater runoff. Pollutants
are removed via settling and filtration as
the water flows over the surface of the
swale or infiltrates into the ground. Check
dams are provided every 12 to 20 feet to
slow flow and pool water to enhance
treatment and infiltration. Vegetated
Swales reduce the volume of runoff from
a site through infiltration into underlying
soils. The Vegetated Street Swale
variation can be employed in a street
setting. This type of swale is constructed
between a standard sidewalk and a standard street curb with curb-cut spillways and features an underdrain system. See Figures L-7.1 and L-7.2 for typical Vegetated Swale configurations.

Advantages
• Relatively inexpensive when integrated into site landscaping. • Suitable for parking lots and sites with the limited open area available for stormwater runoff retention.
• Reduces peak flows during small storm events.
• Enhances site aesthetics.
• Easy to maintain.

Limitations
• Irrigation is typically required to maintain vegetation. • Not appropriate for industrial sites or locations where spills may occur unless infiltration is prevented.
• Not suitable for steeply sloping areas.

Planning and Siting Considerations
• Can receive runoff from parking lots, rooftops, and streets. • Integrate Vegetated Swales into the overall site design. • Connection to the storm drain system or another treatment control measure must be provided at the end of the swale and possibly at points along the swale to allow the discharge of high flows and runoff that does not infiltrate. • Slopes and depth should be kept as mild as possible to avoid safety risks and prevent erosion within the Vegetated Swale.

Image 6-10. Vegetated Swale, Maria Cahill. Water-quality swales:

Low-impact development fact sheet. (2018, June 1). OSU Extension Catalog,Oregon State University. Retrieved October 7, 2021, from https://catalog.extension.oregonstate.edu/em9209/html.
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-50 May 2025
• Irrigation is typically required to maintain viability of the Vegetated Swale vegetation.

Coordinate design of general landscape irrigation system with that of Vegetated Swale, as applicable.
• When Vegetated Street Swales are used, all applicable requirements for other street elements (e.g., curbs, sidewalks, trees) must be met.

Design Criteria
Design criteria for Vegetated Swales are listed in Table L-7.1. Note that the sizing of the Vegetated Swale is volume-based.
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-51 May 2025
Table L-7.1. Vegetated Swale and Vegetated Street Swale Design Criteria Design Parameter Design
Criteria Notes
Design volume WQV Based on 12-hour drawdown. See Section 7.4 for calculation of WQV.

Side slopes 3:1 H:V, Maximum
Flat bottom width 2 ft
4 ft
Minimum
Minimum (Street Swale)
Top width 5 ft
7 ft
Minimum
Minimum (Street Swale)
Longitudinal slope 6% Maximum
Setbacks 5 ft
10 ft
From centerline of swale to property lines
From building foundations (unless lined with impermeable fabric or approved by City
Check Dams
Length
Width
Height
Spacing interval
12 in.

Width of
swale
3 to 6 in.
12 to 20 ft
Use 12 ft for Street Swale
Water storage depth above
bottom
6 in.
12 in.

Minimum
Maximum
Distance from tire stops or
curb cut 6 in. Minimum
Curb cut clear flow area 12 in. x 12
in.

Curbs for street swales should be designed for stability by a structural or geotechnical engineer
Topsoil layer 12 in. Minimum
Permeable filter fabric – Optional for Vegetated Swale below top soil layer. Required for Street Swale below topsoil and gravel layers.

Overflow device – Required
Underdrain layer Required for Street Swales and C and D soils Bottom Slope 10:1 Slope to drain away from street (minimum) Gravel layer depth 12 in. Use 3/4” diameter drain rock
Permeable filter fabric – Use under gravel layer
Impermeable fabric – Use along street edge side of swale #6..
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-52 May 2025
Design Parameter Design
Criteria Notes
Perforated PVC pipe
diameter 6 in.

Vegetation No./100
ft2 Trees, shrubs, grasses, and groundcover. Quantity based on surface area of swale facility. See Design Procedure for minimum quantities.

Design Procedure
Step 1 – Calculate Water Quality Volume (WQV)
Using the procedures presented in Section 7.4, determine the WQV based on a 12-hour drawdown time, the contributing area, and the imperviousness of the contributing area.

Step 2 – Determine Swale Geometry
Based on criteria in Table L-7.1 and site conditions, determine appropriate values for the following swale geometry design elements:
• Bottom width
• Side slope
• Ponding zone storage depth (DPZ)
• Top width
• Longitudinal slope
Step 3 – Determine Cross-Sectional Area of Swale Storage

Astorage = DPZ × Wbottom + Wtop
2 Where
Dpz = ponding zone storage depth (ft);
Wbottom = bottom width of Vegetated Swale (ft); and
Wtop = top width of Vegetated Swale (ft).

Step 4 – Determine Swale Length
Lswale
𝑊𝑊𝑊𝑊𝑊𝑊
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑠𝑠𝑠𝑠
Where
WQV = water quality volume (ft3); and
Astorage = cross-sectional area of Vegetated Swale storage. #6..
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-53 May 2025
Step 5 – Design Inlet Controls
For flow introduced along the length of the swale through curb cuts, provide minimum curb cut widths of 12 inches. For swales that receive direct concentrated runoff at the upstream end, provide an energy dissipater, as appropriate, and a flow spreader such as a pea gravel diaphragm flow spreader at the upstream end of the swale.

Step 6 – Select Vegetation
Select vegetation from the list of approved plants – Appendix L. Choose vegetation to cover the surface area of the swale, including the bottom and side slopes. Turf grass may be used to cover the entire swale surface area. At least 50 percent of the swale surface shall be planted with grasses or grass-like plants. If plantings are chosen to landscape the swale, the minimum plant material quantities per 100 square feet of swale area should be as follows:

Vegetation Type Number Containers Notes
Large shrubs or small
trees
4 3-gallon containers Or equivalent
Shrubs or large grasslike plants 6 1-gallon containers Or equivalent Ground cover plants 1 per foot 4-inch pot (minimum)
On the center, triangular spacing,
for the ground cover planting area
only, unless seed or sod is specified
Wildflowers, native grasses, and ground covers used for Vegetated Swales should be designed to not require mowing. Where mowing is necessary, Vegetated Swales should be designed to require only annual mowing.

Step 7 – Design irrigation system
Provide an irrigation system to maintain the viability of Vegetated Swale landscaping.

Volume Retention
Vegetated Swales may be used to achieve the VRR in addition to treatment control requirements. The volume retention for Vegetated Swale is less if a subsurface drainpipe is provided because less infiltration will occur. The calculation procedure for volume retention for a Vegetated Swale is presented in Table L-7.2.
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-54 May 2025
Table L-7.2. Vegetated Swale Volume Retention Calculation Design Parameter Design Criteria Notes
Vegetated Swale with Subsurface Drainpipe Required for Type C and D soils and Street Swales

1. Ponding Zone
a. Depth of ponding zone (DPZ)
b. Surface Area of ponding zone
(APZ)
DPZ = _____________ ft
APZ = _____________ ft2
Infiltration allowance for water in
ponding zone water = 0.25

2. Planting Media Layer
a. Depth of planting media layer
(DPM)
b. Area of planting media layer (APM)
DPM = ______________ ft
APM = _____________ ft2
Available Water Holding Capacity
of planting media layer = 0.1 x
volume

3. Gravel Zone below drainpipe
a. Depth of gravel below pipe (DGZ)
b. Area of gravel below pipe (AGZ)
DGZ = ______________ ft
AGZ = _____________ ft2
Porosity of gravel zone = 0.30
Minimum depth below pipe = 6 in
Minimum width of gravel = 3 ft

1. Volume retention for Swale
(VolRetention)
VolRetention = (DPZ x APZ x 0.25) +
(DPM x APM x 0.1) +
(DGZ x AGX x 0.3)
VolRetention = _____________ ft3
Vegetated Swale without Subsurface Drainpipe Recommended for Type A and B soils

1. Ponding Zone
a. Depth of ponding zone (DPZ)
b. Area of ponding zone (APZ)
DPZ = ______________ ft
APZ = _____________ ft2
Infiltration allowance for water in
ponding zone water = 1.0

2. Planting Media Layer
a. Depth of planting media layer
(DPM)
b. Area of planting media layer (APM)
DPM = ______________ ft
APM = __________ ft2
Minimum depth = 18 inches

3. Volume retention (VolRetention)
VolRetention = (DPZ x APZ) + (DPM x APM x

0.10)
VolRetention= ____________ ft3
Available Water Holding Capacity
of planting media layer = 0.1 x
volume
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-55 May 2025
Construction Considerations
• Areas to be used for Vegetated Swales should be clearly marked before site work begins to avoid soil disturbance and compaction during construction. • No vehicular traffic, except specifically used to construct the Vegetated Swale, should be allowed within 10 feet of swale areas.
• Divert runoff (other than necessary irrigation) during the period of vegetation establishment. Where runoff diversion is not possible, cover graded and seeded areas with suitable erosion control materials.
• Install sediment controls (e.g., staked straw wattles) around the planter to prevent high sediment loads from entering the planter during ongoing construction activities. • Repair, seed, or re-plant damaged areas immediately.

Long-Term Maintenance
The City requires the execution of a maintenance agreement with the property owner prior to the final acceptance of a private development project, which includes treatment controls such as Vegetated Swales. Such agreements will typically include requirements such as those outlined in Table L-7.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement and plan will provide the City designee with complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.

Table L-7.3. Inspection and Maintenance Requirements for Vegetated Swales Activity Schedule
Trim vegetation and remove weeds (as applicable) to limit unwanted vegetation As required
Remove litter and debris from the landscape area As required Use Integrated Pest Management techniques As required
Inspect the swale to determine if runoff is infiltrating properly
At least twice per year during storm
events. Additional inspections after
periods of heavy runoff are desirable.

If infiltration is significantly reduced, remove and replace topsoil and (for Vegetated Street Swale) drain rocks
May be required every 5 to 10 years or
more frequently, depending on sediment
loads
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-56 May 2025

Figure L-7.1. Vegetated Swale. Source: Vegetated Swale Specifications. City of Sandy, Oregon. (2021, October 23). Retrieved October 7, 2021, from https://www.ci.sandy.or.us/publicworks/page/vegetated-swalespecifications. #6..
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Treatment Control Measure Fact Sheet L-7: Vegetated (Dry) Swale Development Guidance Manual E-57 May 2025
Overflow facility at
downstream end of swale to
approved disposal point
(Class 2 Permeable Material
per Caltrans spec. 68-1.025)
Figure L-7.2. Vegetated Street Swale with Underdrain. Source: Vegetated Swale Specifications. City of Sandy, Oregon. (2021, October 23). Retrieved October 7, 2021, from https://www.ci.sandy.or.us/publicworks/page/vegetated-swale-specifications. #6..
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-58 May 2025
Description
A Grassy Swale is a shallow, open channel
planted with dense, sod-forming
vegetation and designed to accept
stormwater runoff from adjacent surfaces.

As the runoff slows and travels through the
vegetation and over the soil surface,
pollutants are removed by a variety of
physical, chemical, and biological
mechanisms, including sedimentation,
filtration, adsorption, precipitation, and
microbial degradation and conversion.

A Grassy Swale differs from a conventional
drainage channel or roadside ditch due to
the incorporation of specific features that
enhance stormwater pollutant removal
effectiveness. A Grassy Swale is designed
to control flow velocities and depth
through the vegetation in the swale and to provide sufficient contact time to promote settling and filtration of the runoff flowing through it. Greater surface area and contact time promote greater runoff treatment efficiencies. The volume of runoff can also be reduced through infiltration into underlying soils. See Figure L-8.1 for a typical Grassy Swale configuration.

Other Names: Vegetated Swale, Bioswale
Advantages
• Relatively inexpensive when used to replace
part of a conventional storm drainage system
and integrated into site landscaping.
• Provides both stormwater treatment and
conveyance.
• Reduces peak flow rates during small storm
events.
• Easy maintenance.

Limitations
• May not be appropriate for industrial sites or locations where spills may occur unless liner is provided to prevent infiltration.

Do not confuse a Grassy Swale
with a Grassy Filter Strip (L-9),
Vegetated Swale (L-7) or Grassy
Channel (V-5), which is used as
primarily as volume retention
practice. The latter provides only
limited pollutant removal because
of higher application rates, and it
requires downstream treatment
controls.

Grassy Swale. Source: Ekka, S., &amp; Hunt, B. (n.d.). Swale terminology for urban stormwater treatment: NC state extension publications. Swale Terminology for Urban Stormwater Treatment, NC State Extension Publications. Retrieved October 7, 2021, from https://content.ces.ncsu.edu/swale-terminology-for-urbanstormwater-treatment. #6..
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-59 May 2025
Planning and Siting Considerations
• Select a location where site topography allows for the design of a channel with a sufficiently mild slope (unless small drop structures are used) and enough surface area to maintain nonerosive velocities in the channel. • Integrate swales into open space buffers, undisturbed natural areas, and other landscape areas when possible.
• For parking lot design, stalls can be shortened if tire curbs are provided around the perimeter of the swale and cars are allowed to overhang the swale. • The required swale length to meet treatment criteria for a 1-acre project site is typically in the range of 75 to 100 feet. The length will vary depending on several variables, including the geometry of the swale and the runoff coefficient for the site. • Liners may be required in areas where swales may be impacted by hazardous materials or where spills may occur (e.g., retail gasoline outlets, auto maintenance businesses, and processing/manufacturing areas).
• Surface flow into the swale is preferred over underground conveyance. • Irrigation is typically required to maintain the viability of the swale vegetation. Coordinate the design of the general landscape irrigation system with that of the Grassy Filter Strip, as applicable.
• Vector Considerations: The potential for mosquitoes due to standing water will be greatly reduced or eliminated if the Swale is properly designed, constructed, and operated.

Design Criteria
The design criteria for the Grassy Swale are listed in Table L-8.1. #6..
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-60 May 2025
Table L-8.1. Grassy Swale Design Criteria
Design Parameter Design Criteria Notes
Tributary drainage area ≤ 10 acres
For larger areas, break up into sub-watersheds
of 10 acres or less, with a swale for each subwatershed.

Design flow WQF See Section 7.4
Roughness coefficient (n) for
treatment design 0.2 Reflects the roughness associated with shallow flow through dense vegetation.

Roughness coefficient (n) for
conveyance design 0.1
Reflects the roughness of swale when depth of
flow is above the height of the grass. Used to
determine capacity of swale to convey peak
hydraulic flows
Minimum contact time for
treatment of the WQF 7 minutes Provide sufficient length to yield minimum contact time for the WQF Minimum bottom width 0.5 ft
Maximum bottom width 10 ft
Swales wider than 10 feet can be divided by
internal berms to conform to maximum width
criteria.

Maximum side slopes 3:1
Side slopes to allow for ease of mowing. Steeper
slopes may be allowed with adequate slope
stabilization.

Longitudinal slope 1-4%
Check dams As required
For longitudinal slope > 4% and as a means of
promoting more infiltration. Space dams as
required to maintain maximum longitudinal
bottom slope ≤ 4%.

Underdrains As required For longitudinal slope < 1%
Maximum depth of flow at WQF 3-5 in. 1 inch below top of vegetation Maximum flow velocity
(treatment) 1 ft/sec Based on Manning’s n = 0.20. Concentrated inlet flow must be spread Inlet Design/Curb cuts ≥ 12 in. wide
To prevent clogging and promote flow
spreading. Pavement should be slightly higher
than swale. Include energy dissipaters.
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-61 May 2025
Design Procedure
Step 1 – Determine the Grassy Swale’s Function
The Grassy Swale can be designed to function as both a treatment control for the WQF and as a conveyance system to pass the peak hydraulic design flows if the swale is located “online”.

Step 2 – Calculate Stormwater Quality Design Flow (WQF) Using the procedures presented in Section 7.4, determine the contributing area and WQF.

Step 3 – Provide for peak hydraulic design flows
Using the Standard Calculations for Diversion Structure Design, calculate flows greater than WQF to be diverted around or flow through the swale. Design the diversion structure, if needed.

Step 4 – Design the Grassy Swale Using Manning’s Equation Swales can be trapezoidal (as illustrated in Figure L-8.1) or parabolic in shape. While trapezoidal channels are the most efficient channel for conveying flows, parabolic configurations provide good water quality treatment and may be easier to mow since they don’t have sharp breaks in slope.
a. Use a roughness coefficient (n) of 0.20 with Manning’s Equation to design the treatment area of a swale to account for the flow through the vegetation. To determine the capacity of the swale to convey peak hydraulic flows, use a roughness coefficient (n) of 0.10 with Manning’s Equation.

Manning’s Equation

Q =

1.49 n
A5 / 3
P2 / 3 × s1/ 2
Where
Q = WQF
A = Cross-sectional area of flow
P = Wetted perimeter of flow
s = Bottom slope in flow direction
n = Manning’s n (roughness coefficient)
For treatment design of a trapezoidal swale, solve Manning’s equation by trial and error to determine a bottom width that yields a flow depth of 3 to 5 inches at the design WQF and the swale geometry (i.e., side slope and s value) for the site under design. The minimum design bottom width is 0.5 ft.
b. Determine length necessary to provide the desired contact time (7 minutes minimum) for treatment of the WQF.
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-62 May 2025
L = (tc) x (flow velocity) x 60
Where
L = Length of swale, ft
tc = Contact time, 7 minutes minimum
Step 5 – Design Inlet Controls
For flow introduced along the length of the swale through curb cuts, provide minimum curb cut widths of 12 inches and avoid short-circuiting the swale by providing a minimum contact time of 7 minutes.

For swales that receive direct concentrated runoff at the upstream end, provide an energy dissipater, as appropriate, and a flow spreader such as a pea gravel diaphragm flow spreader at the upstream end of the swale. (See Figure L-9.1 in L-9: Grassy Filter Strip for a schematic of pea gravel flow spreader.)
Step 6 – Select Vegetation
A full, dense cover of sod-forming vegetation is necessary for the Grassy Swale to provide adequate treatment.

Select vegetation that:
• Will be dense and strong enough to stay upright, even in flowing water; • Has a minimum need for fertilizers;
• Is not prone to pests and is consistent with IPM practices; • Will withstand being inundated for periods of time; and • Is consistent with local water conservation ordinance requirements.

See Appendix L for recommended grasses for Grassy Swales. Do not use bark or similar buoyant material in the swale or around drain inlets or outlets.

Step 7 – Design irrigation system
Provide an irrigation system to maintain viability of Grassy Swale vegetation.

Volume Retention
Grassy Swales may be used to achieve the VRR in addition to treatment control requirements.

The calculation procedure for volume retention for Grassy Swales is presented in Table L-8.2. #6..
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-63 May 2025
Table L-8.2. Grassy Swale Volume Retention Calculation
Design Parameter Design Criteria Notes

1. WQV for contributing area WQV = ______________ ft3 See Section 7.4

2. Volume retention factor for
Grassy Swale (Vsoils) Vsoils = ______________ Vsoils for A and B soils = 0.50 Vsoils for C and D soils = 0.25

3. Volume retention for Grassy
Swale (VolRetention)
VolRetention = (WQV x Vsoils) VolRetention = ___________ ft3 Construction Considerations
• Divert runoff (other than necessary irrigation) during the period of vegetation establishment. Where runoff diversion is not possible, cover graded and seeded areas with suitable erosion control materials.
• Install sediment controls (e.g., staked straw wattles) around the swale to prevent high sediment loads from entering the swale during ongoing upstream construction activities. • Repair, seed, or re-plant damaged areas immediately.
• Apply erosion control measures as needed to stabilize side slopes and inlet areas.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to the final acceptance of a private development project, which includes treatment controls such as Grassy Swales. Such agreements will typically include requirements such as those outlined in Table L-8.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement and plan will provide the City designee with complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-64 May 2025
Table L-8.3. Inspection and Maintenance Requirements for Grassy Swales Activity Schedule
Mow grass to maintain a height of 4 to 6 inches or
above depth of flow at WQF. As required
Remove grass clippings. As required
Use Integrated Pest Management techniques. As required
Remove trash and debris from the swale. As required
Inspect swale at for signs of erosion, vegetation
damage/coverage, channelization problems, debris
build-up, and excessive sedimentation in bottom of
channel. Correct problems or remove debris and
sediment as soon as possible.

At least twice annually. Schedule one inspection at
the end of the wet season so that summer
maintenance can be scheduled to prepare swale for
wet season. Additional inspections after periods of
heavy runoff are desirable.

Remove sediment in inlet areas, the channel,
culverts, and outlets whenever flow into the swale
is retarded or blocked.

As required
Repair ruts or holes in the channel by removing
vegetation, adding and tamping suitable soil, and
reseeding. Replace damaged vegetation.

As required
Inspect swale for obstructions (e.g., debris
accumulation, invasive vegetation) and pools of
standing water that can provide mosquito-breeding
habitat. Correct observed problems as soon as
possible.

At least twice during the wet season after
significant storms. Additional inspections after
periods of heavy runoff are desirable.
#6..
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Treatment Control Measure Fact Sheet L-8: Grassy Swale
Development Guidance Manual E-65 May 2025
Figure L-8.1. Grassy Swale. Source: Adapted from Urban Storm Drain Criteria Manual Vol. 3 – Best Management Practices, Urban Drainage and Flood Control District. (1999, November). #6..
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Treatment Control Measure Fact Sheet L-9: Grassy Filter Strip Development Guidance Manual E-66 May 2025
Description
A Grassy Filter Strip is a gently sloped
soil surface planted with dense, sodforming vegetation and designed to receive and treat sheet flow runoff
from adjacent surfaces. As the
stormwater runoff flows through the
vegetation and over the soil surface at
a shallow depth, pollutants are
removed by a variety of physical,
chemical, and biological mechanisms,
including sedimentation, filtration,
adsorption, precipitation, and
microbial degradation and conversion.

Greater surface area and contact time
promote greater runoff treatment efficiencies. The volume of runoff can be reduced through infiltration into underlying soils. See Figure L-9.1 for a typical Grassy Filter Strip configuration.

Other Names: Vegetated Filter Strips, Biofilter
Advantages
• Relatively inexpensive when used to replace part of a conventional storm drainage system and integrated
into site landscaping.
• Reduces peak flows during small storm events.
• Easy to maintain.

Limitations
• Not appropriate for industrial sites or locations where spills may occur.

A Grassy Filter Strip should not
be confused with a Grassy
Swale (L-8) or Vegetated
Buffer Strip (V-6), which is
used as volume retention
practice. The latter provides
only limited pollutant removal
because of higher application
rates, and, consequently,
requires downstream
treatment controls.

Source: Filter strips/grassed riparian buffers (NRCS 393 & 390). AgBMPs. (n.d.). Retrieved October 7, 2021, from https://agbmps.osu.edu/bmp/filterstripsgrassed-riparian-buffers-nrcs-393-390. #6..
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Treatment Control Measure Fact Sheet L-9: Grassy Filter Strip Development Guidance Manual E-67 May 2025
Planning and Siting Considerations
• Select a location where site topography allows for the design of filter strips with proper slopes in the flow direction.
• Integrate Grassy Filter Strips into open space buffers, undisturbed natural areas, and other landscape areas when possible.
• For parking lot design, stalls can be shortened if tire curbs are provided around the perimeter of the filter strip and cars are allowed to overhang the filter strip. • Irrigation is typically required to maintain the viability of the filter strip vegetation.

Coordinate the design of the general landscape irrigation system with that of the Grassy Filter Strip, as applicable.
• Vector Considerations: The potential for mosquitoes due to standing water will be greatly reduced or eliminated if the strip is properly designed, constructed, and operated.

Design Criteria
Design criteria for Grassy Filter Strips are listed in Table L-9.1.

Table L-9.1. Grassy Filter Strip Design Criteria
Design Parameter Design Criteria Notes
Drainage area ≤ 5 acres
For larger areas, break up into subwatersheds of 5 acres or less with a filter strip for each.

Design flow WQF See Section 7.4
Maximum linear application rate
(qa) 0.005 cfs/ft of width
Rate at which runoff is applied across the
top width of filter strip. This rate, combined
with the design flow, will define the design
width of filter strip.

Minimum slope in flow direction 1% Gentler slopes are prone to ponding of water on surface
Maximum slope in flow direction 4% Steeper slopes are prone to channeling.

Terracing may be used for slopes > 4%.

Minimum length in flow direction 20 ft
Most treatment occurs in the first 20 feet of
flow. Longer lengths will typically provide
somewhat higher levels of treatment
Vegetation height (typical) 2 – 4 in.

Vegetation should be maintained at a height
greater than the depth of flow at design flow
rate but sufficiently low to prevent lodging
or shading of the vegetation.
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Treatment Control Measure Fact Sheet L-9: Grassy Filter Strip Development Guidance Manual E-68 May 2025
Design Procedure
Step 1 – Calculate Water Quality Flow (WQF)
Using the procedures presented in Section 7.4, determine the contributing area and WQF.

Step 2 – Calculate minimum width of Grassy Filter Strip (WGFS) The design minimum width of the Grassy Filter Strip (WGFS) normal to flow direction is determined from the design WQF and the minimum application rate (qa), as follows:

WGFS = (WQF)/(qa)
WGFS = (WQF)/0.005 cfs/ft (minimum)
Where
WQF = water quality flow (ft3/s); and
qa = linear application rate (ft3/s/ft).

Step 3 – Determine the minimum length of Grassy Filter Strip in the flow direction The length of the filter strip in the flow direction must be a minimum of 20 feet. Greater lengths are desirable, as somewhat better treatment performance can typically be expected.

Step 4 – Determine design slope
The slope of the filter strip surface in the direction of flow should be between one (1) and four (4) percent to avoid ponding and channeling of flow. Terracing may be used to maintain a slope of four (4) percent in steeper terrain.

Step 5 – Design inlet flow distribution
Incorporate a device such as slotted curbing, modular block porous pavement, or other spreader devices at the upstream end of the filter strip to distribute flow evenly along the top width. Concentrated flow delivered to the filter strip must be distributed evenly by means of a level spreader as shown in Figure L-9.1.

Step 6 – Select vegetation
A full, dense cover of sod-forming vegetation is necessary for the filter strip to provide adequate treatment.

Select vegetation that:
• Will be dense and strong enough to stay upright, even in flowing water; • Has a minimum need for fertilizers;
• Is not prone to pests and is consistent with IPM practices; • Will withstand being inundated for periods of time; and • Is consistent with local water conservation ordinance requirements. #6..
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Treatment Control Measure Fact Sheet L-9: Grassy Filter Strip Development Guidance Manual E-69 May 2025
See Appendix L for recommended grasses for Grassy Filter Strips. Do not use bark or similar buoyant material in the filter strip or around drain inlets or outlets.

Step 7 – Design outlet flow collection
Provide a means for outflow collection and conveyance (e.g., grassy channel/swale, storm drain, gutter).

Step 8 – Design irrigation system
Provide an irrigation system to maintain the viability of filter strip grass.

Volume Retention Calculation
Grassy Filter Strip may be used to achieve the VRR in addition to treatment control requirements. The calculation procedure for volume retention for Grassy Filter Strip is presented in Table L-9.2.

Table L-9.2. Grassy Filter Strip Volume Retention Calculation Design Parameter Criteria Notes

1. WQV for contributing area WQV = ____________ ft3 See Section 7.4

2. Volume retention factor for
Grassy Filter Strip (VRF) VRF = ______
VRF for A and B soils = 0.95 – 0.18
= 0.77
VRF for C and D soils = 0.95 – 0.25
= 0.70

3. Volume retention for Grassy
Filter Strip (VolRetention)
VolRetention = (WQV x VRF)
VRetention= ________________ ft3
Construction Considerations
• Divert runoff (other than necessary irrigation) during the period of vegetation establishment. Where runoff diversion is not possible, cover graded and seeded areas with suitable erosion control materials.
• Install sediment controls (e.g., staked straw wattles) around the filter strip to prevent high sediment loads from entering the filter strip during ongoing upstream construction activities.
• Repair, seed, or re-plant damaged areas immediately.

Long-Term Maintenance
The City may require execution of a maintenance agreement with the property owner prior to the final acceptance of a private development project, which includes treatment controls such as Grassy Filter Strips. Such agreements will typically include requirements such as those outlined in Table L-9.3. The property owner or his/her designee is responsible for compliance with the agreement. The maintenance agreement and plan will provide the City designee with #6..
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Treatment Control Measure Fact Sheet L-9: Grassy Filter Strip Development Guidance Manual E-70 May 2025
complete access to the device and its immediate vicinity at any time. Maintenance of the device is the sole responsibility of the owner.

Table L-9.3. Inspection and Maintenance Requirements for Grassy Filter Strips Activity Schedule
Mow grass to maintain a height of 2 to 4 inches (typical). As required Remove grass clippings. As required
Use Integrated Pest Management techniques. As required
Remove trash and debris from the filter strip. As required Inspect filter strip for signs of erosion, vegetation
damage/coverage, channel formation problems, debris buildup, and excessive sedimentation on the surface of the strip.

Correct problems or remove debris and sediment as soon as possible.

At least twice annually. Schedule one
inspection at the end of the wet season so
that summer maintenance can be
scheduled to prepare filter strip for wet
season. Additional inspections after
periods of heavy runoff are desirable.

Remove sediment in inlet areas, the channel, culverts, and outlets whenever flow into the filter strip is retarded or blocked.

As required
Repair ruts or holes in the strip by removing vegetation, adding and tamping suitable soil, and reseeding. Replace damaged vegetation.

As required
Inspect filter strip for obstructions (e.g., debris accumulation, invasive vegetation) and pools of standing water that can provide mosquito-breeding habitat. Correct observed
problems as soon as possible.

At least twice during the wet season after
significant storms. Additional inspections
after periods of heavy runoff are
desirable.
#6..
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Treatment Control Measure Fact Sheet L-9: Grassy Filter Strip Development Guidance Manual E-71 May 2025
Figure L-9.1. Grassy Filter Strip. Source: Adapted from Urban Storm Drain Criteria Manual Vol 3. – Best Management Practices, Urban Drainage and Flood Control District. (1999, November). #6..
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Treatment Control Measure Fact Sheet L-10: Infiltration Well Development Guidance Manual E-72 May 2025
Description
[Note: Infiltration wells cannot be used in City
maintained areas]
An Infiltration Well, which is classified as Class V
underground injection wells by USEPA, is
typically a vertical bore, which contains a
perforated vertical pipe, filled with gravel.

Stormwater runoff is typically conveyed to a
covered concrete catch basin containing the
Infiltration Well. An overflow pipe conveys water
from the catch basin into the Infiltration Well.

Water infiltrates through the gravel media and
into the underlying soil over a design drawdown period. Infiltration Wells are similar to the City’s rockwells, but differ in that they are designed for the purpose of stormwater runoff treatment and retention as opposed to drainage.

Stormwater runoff treatment is primarily filtration as the stormwater runoff flows through the gravel media and into the underlying soil profile. To ensure adequate treatment and protect groundwater quality, the depth of the unsaturated soil between the Infiltration Well bottom and the maximum groundwater surface level should be a minimum of ten (10) feet. A schematic of an Infiltration Well configuration is presented in Figure L-10.1.

Other Names
Injection Well
Advantages
• Provides effective treatment through filtration while requiring a small space. • Is placed below ground.
• Reduces peak stormwater runoff flows during small storm events. • Can be incorporated into site landscape features
Disadvantages
• Cannot be used in City maintained areas.
• Not appropriate for areas with low permeability soils (Type C or D soil) or high groundwater. • Not appropriate for industrial sites or locations with contaminated soils or where spills may occur because of the potential threat to groundwater contamination. • Must be protected from high sediment loads. Once clogged with sediment, restoration of infiltration capacity may be difficult.
• Not appropriate on fill or steep slopes.

Photo Credit - Laura Roll
#6..
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Treatment Control Measure Fact Sheet L-10: Infiltration Well Development Guidance Manual E-73 May 2025
Figure L-10.1. Infiltration Well Schematic (see City standard specifications) Planning and Site Considerations
• Soil permeability, depth to groundwater, and design safety factors should be determined by a qualified geotechnical engineer or geologists to ensure that conditions conform to Table L10.1. • Pretreatment using Grassy Channels, Vegetated Buffer Strips, Vegetated Swales, Grassy Swales, and/or Vegetated Filter Strip is required to protect Infiltration Wells from high sediment loads.
• Plan for appropriate setback distances.

Weepholes are required
At the base of the catch basin
#6..
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Treatment Control Measure Fact Sheet L-10: Infiltration Well Development Guidance Manual E-74 May 2025
Design Criteria
Principal design criteria for Infiltration Wells are listed in Table L-10.1.

Table L-10.1. Infiltration Well Design Criteria
Design Parameter Design Criteria Notes
Drawdown time 48 hr (maximum)
Water Quality Volume 80% annual capture (acre-ft) Use Figure 6-1 at 48-hr drawdown.

Tributary drainage area 10,000 ft2 (maximum) Per Infiltration Well Bore diameter 36 in
Groundwater separation 10 ft (minimum)
Between Infiltration Well bottom
and historical seasonally high
groundwater table
Soil permeability range 0.6-2.0 in/hr Saturated vertical permeability Slope 0%
Core pipe diameter 8 in Perforated PVC pipe with
removable cap
Core pipe length 20 ft Maximum length
Core pipe perforations
(diameter) 0.5 in Every 90° around the pipe
Core pipe perforations (number of
rows) 4
Gravel size (diameter) 1-2.5 in
Setbacks
150 ft (minimum) From domestic water supply wells
20 ft (minimum)
Between all other vertical
Infiltration Wells or rockwells
20 ft Down slope from foundation
100 ft Up slope from foundation
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Treatment Control Measure Fact Sheet L-10: Infiltration Well Development Guidance Manual E-75 May 2025
Design Procedure
Step 1 – Calculate WQV
Calculate the effective tributary drainage area and WQV based on a 48-hour drawdown period.

Step 2 – Calculate Minimum Surface Area of Infiltration Well Bottom (Amin) Where
WQV = water quality volume (ft3);
tmax = maximum drawdown time = 48 hours;
I = site infiltration rate (soil permeability, in/hr); and s = safety factor.

In the formula above, the safety factor accounts for possible inaccuracies in the infiltration rate measurement. A larger safety factor should be used when the infiltration rate is less certain. Safety factors typically range between two (2) and ten (10) and should be determined by a qualified geotechnical engineer or geologist based on field measurements of saturated vertical permeability at the project site. Multiple Infiltration Wells may be necessary at a site to achieve the required total infiltration bottom area.

Step 3 – Design Overflow Pipe
An overflow pipe connecting the Infiltration Well to the catch basin must be installed to convey stormwater runoff from the tributary drainage area to the Infiltration Well. The overflow pipe entering the Infiltration Well should be a minimum of 12 inches above the top of the gravel layer.

Step 4 – Design Core Pipe
The core pipe should be a perforated-C900, Class 200 PVC pipe with an eight- (8-) inch diameter and 20 feet maximum length.

Step 5 – Design Gravel Layer
The washed gravel layer should be composed of 1-2.5-inch diameter stone.

Step 6 – Design Screen Cover
A screen cover is required on top of the core pipe. See the applicable City of Modesto Standard Specifications for details.
#6..
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Treatment Control Measure Fact Sheet L-10: Infiltration Well Development Guidance Manual E-76 May 2025
Volume Retention Calculation
Infiltration Wells may be used to achieve both the volume retention and treatment requirements. An Infiltration Well provides volume retention for the entire WQV calculated in Step 1 of the Design Procedure.

Construction Considerations
• Once construction is complete, stabilize the entire tributary area to the Infiltration Well before allowing stormwater runoff to enter the Infiltration Well. • Store excavated material at least ten (10) feet from the Infiltration Well to avoid backsliding and cave-ins.
• Clean, washed gravel should be placed in the bore hole in lifts and lightly compacted. Use of unwashed gravel can result in clogging.
• Minimize compaction near the Infiltration Well to the maximum extent practicable during construction to prevent loss of infiltrative capacity.

Long-Term Maintenance
The City requires execution of a maintenance agreement with the property owner prior to final acceptance of a private development project, which includes treatment control measures such as Infiltration Wells. Such agreements typically include requirements such as those outlined in Table L-10.2. The property owner or property owner’s designee is responsible for compliance with the agreement. The maintenance agreement must provide the City with complete access to the treatment control measure and its immediate vicinity at any time.

Table L-10.2. Inspection and Maintenance Requirements for Infiltration Wells Activity Schedule
Monitor infiltration rate in Infiltration Well after
storm events by recording the drop in water depth
versus time using a calibrated rod or staff gauge.