AGENDA REPORT
City Council
MEETING
DATE:
August 19, 2026
PREPARED
BY:
Ben Stryker, PE
Principal Engineer
Jaylee McDowell, PE
Principal Engineer
DEPARTMENT
DIRECTOR:
Dan Nutter, PE
DEPARTMENT: Engineering CITY
MANAGER:
Jennifer Campbell
SUBJECT:
Adopt the 2026 Update to the City Stormwater BMP Design Manual RECOMMENDED ACTION:
1) Adopt City Council Resolution No. 2026-62 titled, “A Resolution of the City Council of the City of Encinitas, California, Adopting the 2026 Update to the Stormwater Best Management Practice (BMP) Design Manual” (Attachment 1) ENVIRONMENTAL CONSIDERATIONS:
The action being considered by the City Council is exempt from the California Environmental Quality Act (CEQA) because it is not a “project” under Section 15061(b)(3) of the CEQA Guidelines because it can be seen with certainty that there is no possibility that the activity in question may have a significant effect on the environment. The action is also exempt from CEQA under Section 15378(b)(5) of the CEQA Guidelines because it involves an organizational or administrative activity of government that will not result in the direct or indirect physical change in the environment.
This item does not relate to the Climate Action Plan.
GENERAL PLAN/CITY COUNCIL FOCUS AREAS:
The recommended action aligns with the Effective & Reliable City Services, Infrastructure, and Communications City Council Focus Area by publishing a Stormwater BMP Design Manual that accurately reflects current engineering permitting processes and standards for residents and developers.
2026-08-19 Item #12D Page 1 of 816
FISCAL CONSIDERATIONS:
There is no fiscal impact associated with the recommended action. The updated Engineering Design Manual included internal staff administrative changes and updates and did not require the use of a consultant contract to prepare the changes and updates.
BACKGROUND:
On May 8, 2013, the San Diego Regional Water Quality Control Board (RWQCB) adopted Water Quality Order No. R9-2013-0001, National Pollutant Discharge Elimination System (NPDES) Permit and Waste Discharge Requirements for Discharges from the Municipal Separate Storm Sewer Systems (MS4s) Draining the Watersheds within the San Diego Region (2013 Municipal Stormwater Permit). Provision E.3 of the 2013 Municipal Stormwater Permit requires local agencies, including the City of Encinitas, to implement stormwater requirements for new development and redevelopment projects. The City’s BMP Design Manual implements these requirements locally by identifying applicable BMP requirements based on project type. In general, these requirements include:
1. Source Control and Low Impact Development (LID)/Site Design BMPs for development projects where local permits are issued.
2. Additional pollutant control and structural BMP requirements for projects classified as Priority Development Projects (PDPs).
3. Hydromodification management requirements for applicable PDPs.
4. Long term operation and maintenance requirements for structural BMPs where they are required.
5. Alternative compliance options where allowed under the NPDES Permit.
On January 27, 2016, City Council adopted the 2016 Stormwater BMP Design Manual. The 2016 Manual replaced the prior framework and implemented the current 2013 Municipal Stormwater Permit requirements.
On October 18, 2023, City Council adopted the 2023 Stormwater BMP Design Manual. The 2023 BMP Design Manual included technical updates and clarifications intended to provide applicants with additional compliance flexibility, streamline the review process, and reflect current regional stormwater design practices. The update included revised guidance and fact sheets, additional post-construction stormwater compliance pathways, and a new definition for Routine Pavement Maintenance Projects.
Since the adoption of the 2023 BMP Design Manual, updates to industry best practices warrant administrative cleanup to maintain consistency with standards implemented throughout the County.
On June 1, 2026, a public comment period opened on the City’s website to begin soliciting public input. Comments are being solicited through an online feedback form and direct contact with industry stakeholders. On June 5, 2026, a Public Notice was made available through Coast News inviting public comments. On June 30, 2026, the public comment period closed.
On June 11, 2026, Environmental Commission was presented the proposed changes by staff and unanimously recommended the updated manual be brought to City Council for approval. 2026-08-19 Item #12D Page 2 of 816
ANALYSIS:
The proposed changes to the Stormwater BMP Design Manual ensure that the City’s standards remain consistent with industry practice throughout the County. The primary change to the 2 involves requiring projects that add less than 5,000 square feet (SF) of impervious area, currently characterized in the manual as a Standard Project, to utilize site design BMPs only, rather than requiring structural BMPs. With this change, a stronger emphasis on thoughtful site design and low impact development can be achieved for projects that propose less than 5,000 SF of impervious surface.
The intent of this update is to streamline compliance pathways for small-scale development while ensuring that water quality protection remains fully consistent with the 2013 Municipal Stormwater Permit and consistent with countywide stormwater model practices and water quality standards.
This change does not reduce the level of treatment or performance expected; rather, it clarifies that non‑PDP projects may meet compliance using established site design principles that achieve equal or greater effectiveness, when applied appropriately.
Site design BMPs are particularly well‑suited for smaller projects because they integrate stormwater management directly into the layout, grading, and landscape features of the site.
These measures tend to be more practical, cost‑effective, and space‑efficient for projects creating less than 5,000 square feet of impervious area. For these project types, small structural BMPs can be disproportionately burdensome without providing commensurate environmental benefit, while site design BMPs often yield improved infiltration, reduced runoff volumes, superior site aesthetics, and enhanced long‑term sustainability with simpler maintenance for the homeowner or property manager. No changes have been proposed for PDP requirements, key definitions, maintenance requirements or performance standards.
Tracked change versions of the 2023 City of Encinitas BMP Design Manual and Appendices are included in Attachments 2 & 3, and a full summary of all specific proposed changes can be found in Attachment 4 of this report.
ATTACHMENT(S):
1. Resolution No. 2026-62 titled, “A Resolution of the City Council of the City of Encinitas, California, Adopting the 2026 Update to the City of Encinitas Stormwater Best Management Practice (BMP) Design Manual”
2. 2026 Update to the City of Encinitas Stormwater BMP Design Manual – Tracked Changes
3. 2026 Update to the City of Encinitas Stormwater BMP Design Manual Appendices – Tracked Changes
4. Summary of Changes - 2026 Update to the City of Encinitas Stormwater BMP Design Manual
2026-08-19 Item #12D Page 3 of 816
ATTACHMENT 1
RESOLUTION 2026-62
A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF ENCINITAS, CALIFORNIA, ADOPTING THE 2026 UPDATE TO THE STORMWATER BEST MANAGEMENT PRACTICE (BMP) DESIGN MANUAL
WHEREAS, on May 8, 2013, the San Deigo Regional Water Quality Control Board (RWQCB) issued National Pollutant Discharge Elimination System (NPDES) Order No. R9-2013- 0001 (2013 Municipal Stormwater Permit); and
WHEREAS, Provision E.3 of the 2013 Municipal Stormwater Permit requires Copermittees, including the City of Encinitas, to use local land use authority to implement a development planning program in compliance with detailed standards; and WHEREAS, per City Council Resolution 2013-120, the City Council for the City of Encinitas adopted the 2023 Stormwater BMP Design Manual; and WHEREAS, administrative updates have been made by the Engineering & Development Services Departments to reflect current standards and processes and have been made available for review by members of the public and the professional community; and WHEREAS, the City Council has reviewed the tracked changes versions of the 2026 Updates to the 2023 Stormwater BMP Design Manual and understands that adoption of the 2026 Updates to the 2023 Stormwater BMP Design Manual constitutes approval of all the tracked changes.
NOW, THEREFORE, BE IT RESOLVED, by the City Council of the City of Encinitas, California, that: the foregoing recitals are true and correct, and the 2026 Updates to the 2023 City of Encinitas Stormwater BMP Design Manual are hereby adopted, effective immediately, superseding the original 2023 Stormwater BMP Design Manual.
NOW, THEREFORE, BE IT FURTHER RESOLVED, that this action is exempt from the provisions of the California Environmental Quality Act (CEQA) pursuant to Section 15378(b)(5) of the CEQA Guidelines, as an organizational or administrative activity of government that will not result in a direct or indirect physical change in the environment.
PASSED, APPROVED AND ADOPTED this 12th day of August, 2026 by the City Council of the City of Encinitas, State of California:
______________________________
Bruce Ehlers, Mayor
ATTEST:
______________________________
Peter Weichers, City Clerk
2026-08-19 Item #12D Page 4 of 816
ATTACHMENT 1
APPROVED AS TO FORM:
_____________________________
Ajit Thind, City Attorney
CERTIFICATION: I, Peter Weichers, City Clerk of the City of Encinitas, California, do hereby certify under penalty of perjury that the foregoing Resolution was duly adopted at a regular meeting of the City Council on the 12th day of August, 2026 by the following vote:
AYES:
NOES:
ABSENT:
ABSTAIN:
______________________________
Peter Weichers, City Clerk
2026-08-19 Item #12D Page 5 of 816
2026 BMP DESIGN MANUAL
Adopted tbd
Effective _______
2026-08-19 Item #12D Page 6 of 816
2023
2026-08-19 Item #12D Page 7 of 816
i 2023
Encinitas BMP Design Manual
This manual was adapted from the Model BMP Design Manual for the San Diego Region. 2026-08-19 Item #12D Page 8 of 816
City of Encinitas BMP Design Manual
ii 20236
In May 2013, the California Regional Water Quality Control Board for the San Diego Region (SDRWQCB) reissued the National Pollutant Discharge Elimination System permit for Municipal Separate Storm Sewer Systems (MS4s) for the San Diego Copermittees.
The reissued MS4 Permit updates and expands stormwater requirements for new developments and redevelopments. The MS4 Permit reissuance to the San Diego County Copermittees went into effect in 2013 (Order No. R9-2013-0001) and was amended in February 2015 by Order No. R9-2015-0001.
As required by the reissued MS4 Permit, the City of Encinitas has adopted this Best Management Practices (BMP) Design Manual (from here in referred to as the “manual”) to replace the Encinitas Stormwater Manual (Chapter 7 of the Engineering Design Manual), which was based on the requirements of the 2007 MS4 Permit. The effective date of this manual was February 16, 2016.
Following the adoption and implementation of the February 2016 Manual, regional efforts were made to update the model manual to address practical application issues experienced by jurisdictions across the region, clarifications from the SDRWQCB, and evolved BMP sizing, maintenance, and design guidance. This updated manual is consistent with the approved Regional BMP Design Manual and any subsequent updates, and replaces and supersedes the February 2016 City of Encinitas BMP Design Manual and is effective _______
This Manual is intended to address:
This Manual addresses updated onsite post-construction stormwater requirements for Standard Projects and Priority Development Projects (PDPs), and provides updated procedures for planning, preliminary design, selection, and final design of permanent stormwater BMPs based on the performance standards presented in the MS4 Permit. The intended users of the BMP Design Manual include project applicants for both private and public developments, their representatives responsible for preparation of Stormwater Quality Management Plans (SWQMPs), and City personnel responsible for review of these plans.
The following are significant updates to stormwater requirements of the MS4 Permit compared to the 2007 MS4 Permit and 2011 Countywide Model SUSMP:
• PDP categories have been updated, and the minimum threshold of impervious area to qualify as a PDP has been reduced.
• Many of the low impact development (LID) requirements for site design that were applicable only to PDPs under the 2007 MS4 Permit are applicable to all projects (Standard, Basic and Exempt Projects and PDPs) under the MS4 Permit. • The standard for stormwater pollutant control (formerly treatment control) is retention of the 24-hour 85th percentile storm volume, defined as the event that has a precipitation total greater than or equal to 85 percent of all daily storm events larger than 0.01 inches over a given period of record in a specific area or location. • For situations where onsite retention of the 85th percentile storm volume is technically not feasible, biofiltration must be provided to satisfy specific “biofiltration standards”.
These standards consist of a set of siting, selection, sizing, design, and operation and maintenance (O&M) criteria that must be met for a BMP to be considered a “biofiltration BMP” – see Section 2.2.1 and Appendix F. • Exemptions from hydromodification management are reduced, and certain categories of exemptions that are not identified in the MS4 Permit must be identified in a 2026-08-19 Item #12D Page 9 of 816
City of Encinitas BMP Design Manual
iii 20236
Watershed Management Area Analysis (WMAA).
• The flow control performance standard for hydromodification management is based on controlling flow to pre-development (natural) condition rather than pre-project condition.
• Hydromodification management requirements are expanded to include requirements to protect critical coarse sediment yield areas.
• Alternative (offsite) compliance approaches are provided as an option to satisfy pollutant control or hydromodification management performance standards if a Copermittee implements an alternative compliance program. Copermittees are given discretion by the MS4 Permit to allow the project applicants to participate in an alternative compliance program without demonstrating technical infeasibility of retention and/or biofiltration BMPs onsite.
This manual is organized in the following manner:
An introductory section titled “How to Use this Manual” provides a practical orientation to intended uses and provides examples of recommended workflows for using the manual.
Chapter 1 provides information to help the manual user determine which of the stormwater management requirements are applicable to the project: source controls/site design BMPs, pollutant controls, and/or hydromodification management. This chapter also introduces the procedural requirements for preparation, review, processing, and approval of project submittals.
Chapter 2 defines the performance standards for source control and site design BMPs, stormwater pollutant control BMPs, and hydromodification management BMPs. This chapter also presents information on the underlying concepts associated with these performance standards to provide the project applicant with technical background, explains why the performance standards are important, and gives a general description of how the performance standards can be met.
Chapter 3 describes the essential steps in preparing a comprehensive stormwater management design and explains the importance of starting the process early during the preliminary design phase. By following the recommended procedures in Chapter 3, project applicants can develop a design that complies with the complex and overlapping stormwater requirements. This chapter is intended to be used by Standard, Basic and Exempt Projects and PDPs; however, certain steps will not apply to Standard, Basic and Exempt Projects (as identified in the chapter).
Chapter 4 presents the source control and site design requirements to be met by all development projects and is therefore intended to be used by all projects.
Chapter 5 applies to PDPs only. It presents the specific process for determining which category or combination of onsite pollutant control BMPs is most appropriate for the PDP site and explains how to design the BMP(s) to meet the stormwater performance standards. The prioritization order of onsite pollutant control BMPs begins with retention, then biofiltration, and finally flow-thru treatment control (in combination with offsite alternative compliance).
Chapter 6 applies only to PDPs that are subject to hydromodification management requirements.
This chapter provides guidance for meeting the performance standards for the two components of 2026-08-19 Item #12D Page 10 of 816
City of Encinitas BMP Design Manual
iv 20236
hydromodification management: protection of critical coarse sediment yield areas and flow control for post-project runoff from the project site. Chapter 6 incorporates applicable requirements of the "Final Hydromodification Management Plan (HMP) Prepared for County of San Diego, California," dated March 2011, with modifications based on updated requirements in the MS4 Permit. Chapter 6 does not apply to Standard Projects or to PDPs with only pollutant control requirements.
Chapter 7 addresses the long term O&M requirements of structural BMPs presented in this manual and discusses mechanisms to ensure O&M in perpetuity. Chapter 7 applies to PDPs only and is not required for Standard Projects; however Standard Projects may use this chapter as a reference.
Chapter 8 describes the specific requirements for the content of project submittals to facilitate local jurisdictions' review of project plans for compliance with applicable requirements of the manual and the MS4 Permit for both Standard Projects and PDPs. This chapter pertains specifically to the content of project submittals, and not to specific details of jurisdictional requirements for processing of submittals; it is intended to complement the requirements for processing of project submittals that are included in Chapter 1.
Appendices to this manual provide detailed guidance for BMP design, calculation procedures, worksheets, maps, and other figures to be referenced for BMP design. These Appendices are not intended to be used independently from the overall manual – rather they are intended to be used only as referenced in the main body of the manual.
This manual is organized based on project category. Requirements that are applicable to all projects are presented in Chapter 4. Additional requirements applicable only to PDPs are presented in Chapters 5 through 7.
Throughout this manual, the term "structural BMP" is a general term that encompasses the pollutant control BMPs and hydromodification management BMPs required for PDPs under the MS4 Permit.
A structural BMP may be a pollutant control BMP, a hydromodification management BMP, or an integrated pollutant control and hydromodification management BMP. Hydromodification management BMPs are also referred to as flow control BMPs in this manual. 2026-08-19 Item #12D Page 11 of 816
City of Encinitas BMP Design Manual
v 20236
1. POLICIES AND PROCEDURAL REQUIREMENTS 1-1
1.1 INTRODUCTION TO STORMWATER MANAGEMENT POLICIES ................................................................ 1-1
1.2 PURPOSE AND USE OF THE MANUAL ........................................................................................................... 1-2
1.2.1 Determine Applicability of Construction BMP Requirements ............................................................................1-2
1.2.2 Determining Applicability of Permanent BMP Requirements ............................................................................1-3
1.3 DEFINING A PROJECT ..................................................................................................................................... 1-4
1.3.1 Routine Maintenance Determination for Pavement Projects ..............................................................................1-7
1.4 IS THE PROJECT A PDP? ............................................................................................................................... 1-11
1.4.1 PDP Categories ......................................................................................................................................................... 1-12
1.4.2 Local Additional PDP Categories and/or Expanded PDP Definitions ......................................................... 1-15
1.4.3 Local PDP Exemptions or Alternative PDP Requirements ............................................................................. 1-15
1.5 DETERMINING APPLICABLE STORM WATER MANAGEMENT REQUIREMENTS ........................ 1-161-16
1.6 APPLICABILITY OF HYDROMODIFICATION MANAGEMENT REQUIREMENTS ........................... 1-181-18
1.7 SPECIAL CONSIDERATIONS FOR REDEVELOPMENT PROJECTS (50% RULE) ............................. 1-201-20
1.8 ALTERNATIVE COMPLIANCE PROGRAM ............................................................................................ 1-211-21
1.9 RELATIONSHIP BETWEEN THIS MANUAL AND WQIPS .................................................................. 1-241-24
1.10 STORM WATER REQUIREMENT APPLICABILITY TIMELINE ........................................................... 1-251-25
1.11 PROJECT REVIEW PROCEDURES .......................................................................................................... 1-261-26
1.12 PDP STRUCTURAL BMP VERIFICATION ............................................................................................ 1-261-26
2. STANDARDS AND CONCEPTS .................................................................................... 2-1
2.1 SOURCE CONTROL AND SITE DESIGN REQUIREMENTS FOR ALL DEVELOPMENT PROJECTS ......... 2-4
2.1.1 Performance Standards ...............................................................................................................................................2-4
2.1.2 Concepts and References ..............................................................................................................................................2-7
1.1 STORM WATER POLLUTANT CONTROL REQUIREMENTS FOR PDPS ............................................... 2-82-9
1.1.1 Storm Water Pollutant Control Performance Standard .................................................................................. 2-82-9
1.1.2 Concepts and References ........................................................................................................................................ 2-10
2.2 HYDROMODIFICATION MANAGEMENT REQUIREMENTS FOR PDPS ................................................. 2-13
2.2.1 Hydromodification Management Performance Standards ................................................................................ 2-13
2.2.2 Hydromodification Management Concepts and References ............................................................................ 2-15
2.2.3 Avoidance and Bypass of Critical Coarse Sediment ........................................................................................... 2-17
2.3 RELATIONSHIP BETWEEN PERFORMANCE STANDARDS ....................................................................... 2-17
3. DEVELOPMENT PROJECT PLANNING AND DESIGN .......................................... 3-1
3.1 COORDINATION BETWEEN DISCIPLINES .................................................................................................... 3-2
3.2 GATHERING PROJECT SITE INFORMATION ................................................................................................ 3-3 2026-08-19 Item #12D Page 12 of 816
City of Encinitas BMP Design Manual
vi 20236
3.3 DEVELOPING CONCEPTUAL SITE LAYOUT AND STORM WATER CONTROL STRATEGIES................ 3-4
3.3.1 Preliminary Design Steps for All Development Projects .....................................................................................3-4
3.3.2 Evaluation of Critical Coarse Sediment Yield Areas .............................................................................................3-5
3.3.3 Drainage Management Areas .....................................................................................................................................3-5
3.3.4 Developing Conceptual Storm Water Control Strategies .....................................................................................3-8
3.4 DEVELOPING COMPLETE STORM WATER MANAGEMENT DESIGN ...................................................... 3-9
3.4.1 Steps for All Development Projects ...................................................................................................................... 3-10
3.4.2 Steps for PDPs with only Pollutant Control Requirements .............................................................................. 3-10
3.4.3 Steps for Projects with Pollutant Control and Hydromodification Management Requirements ............... 3-11
3.5 PROJECT PLANNING AND DESIGN REQUIREMENTS SPECIFIC TO LOCAL JURISDICTION .............. 3-12
3.5.1 Maximum Ponding Depth ....................................................................................................................................... 3-12
3.5.2 SCCWRP Analysis .................................................................................................................................................... 3-13
3.5.3 Location of BMPs on the project site ................................................................................................................... 3-13
3.5.4 Centralized Facilities ................................................................................................................................................. 3-13
3.5.5 Impervious area calculations for subdivisions ..................................................................................................... 3-13
3.5.6 Infiltration Testing .................................................................................................................................................... 3-13
3.5.7 Temporary Improvements ...................................................................................................................................... 3-13
3.5.8 City Engineer has the final discretion ............................................................................................................ 3-143-14
3.6 PHASED PROJECTS ........................................................................................................................................ 3-14
4. SOURCE CONTROL AND SITE DESIGN REQUIREMENTS FOR ALL
DEVELOPMENT PROJECTS ............................................................................................. 4-1
4.1 GENERAL REQUIREMENTS (GR) ................................................................................................................... 4-1
4.2 SOURCE CONTROL (SC) BMP REQUIREMENTS .......................................................................................... 4-2
4.3 SITE DESIGN (SD) BMP REQUIREMENTS ................................................................................................... 4-5
5. STORM WATER POLLUTANT CONTROL REQUIREMENTS FOR PDPS ............ 5-1
5.1 STEPS FOR SELECTING AND DESIGNING STORM WATER POLLUTANT CONTROL BMPS ................. 5-1
5.2 DMAS EXCLUDED FROM DCV CALCULATION / OPTIONS FOR MEETING STRUCTURAL PERFORMANCE STANDARDS .......................................................................................................................... 5-2
5.2.1 Self-mitigating DMAs .................................................................................................................................................5-2
5.2.2 De Minimis DMAs ......................................................................................................................................................5-3
5.2.3 Self-retaining DMAs via Qualifying Site Design BMPs ........................................................................................5-3
5.3 BMP SELECTION AND DESIGN ..................................................................................................................... 5-6
5.4 DOCUMENTING STORM WATER POLLUTANT CONTROL BMP COMPLIANCE WHEN HYDROMODIFICATION MANAGEMENT APPLIES ...................................................................................... 5-7
6. HYDROMODIFICATION MANAGEMENT REQUIREMENTS FOR PDPS ........... 6-1 2026-08-19 Item #12D Page 13 of 816
City of Encinitas BMP Design Manual
vii 20236
6.1 HYDROMODIFICATION MANAGEMENT APPLICABILITY AND EXEMPTIONS ....................................... 6-1
6.2 PROTECTION OF CRITICAL COARSE SEDIMENT YIELD AREAS .............................................................. 6-3
6.3 FLOW CONTROL FOR HYDROMODIFICATION MANAGEMENT ............................................................... 6-4
6.3.1 Point(s) of Compliance ...............................................................................................................................................6-6
6.3.2 Offsite Area Restrictions ...................................................................................................................................... 6-86-7
6.3.3 Requirement to Control to Pre-Development (Not Pre-Project) Condition ....................................................6-8
6.3.4 Determining the Low Flow Threshold for Hydromodification Flow Control .......................................... 6-96-8
6.3.5 Designing a Flow Control Facility .................................................................................................................... 6-106-9
6.3.6 Integrating HMP Flow Control Measures with Pollutant Control BMPs .............................................. 6-116-10
6.3.7 Drawdown Time ....................................................................................................................................................... 6-12
6.4 IN-STREAM REHABILITATION..................................................................................................................... 6-13
7. LONG TERM OPERATION & MAINTENANCE ....................................................... 7-1
7.1 NEED FOR PERMANENT INSPECTION AND MAINTENANCE ................................................................... 7-1
7.1.1 MS4 Permit Requirements .........................................................................................................................................7-1
7.1.2 Practical Considerations ..............................................................................................................................................7-1
7.2 SUMMARY OF STEPS TO MAINTENANCE AGREEMENT ............................................................................. 7-2
7.3 MAINTENANCE RESPONSIBILITY .................................................................................................................. 7-2
7.4 LONG-TERM MAINTENANCE DOCUMENTATION ..................................................................................... 7-3
7.5 INSPECTION AND MAINTENANCE FREQUENCY ........................................................................................ 7-4
7.6 MEASURES TO CONTROL MAINTENANCE COSTS ...................................................................................... 7-4
7.7 MAINTENANCE INDICATORS AND ACTIONS FOR STRUCTURAL BMPS ................................................. 7-6
7.7.1 Maintenance of Vegetated Infiltration or Filtration BMPs ..................................................................................7-7
7.7.2 Maintenance of Non-Vegetated Infiltration BMPs ...............................................................................................7-8
7.7.3 Maintenance of Non-Vegetated Filtration BMPs ..................................................................................................7-9
7.7.4 Maintenance of Detention BMPs ..................................................................................................................... 7-107-9
8. SUBMITTAL REQUIREMENTS .................................................................................... 8-1
8.1 SUBMITTAL REQUIREMENT FOR STANDARD PROJECTS ........................................................................... 8-1
8.1.1 Standard Project SWQMP..........................................................................................................................................8-1
8.2 SUBMITTAL REQUIREMENTS FOR PDPS ...................................................................................................... 8-2
8.2.1 PDP SWQMP ...............................................................................................................................................................8-2
8.2.2 Requirements for Construction Plans ......................................................................................................................8-3
8.2.3 Design Changes During Construction and Project Closeout Procedures .........................................................8-3
8.2.4 Additional Requirements for Private Entity O&M ...............................................................................................8-4 BIBLIOGRAPHY ..................................................................................................................... I 2026-08-19 Item #12D Page 14 of 816
City of Encinitas BMP Design Manual
viii 20236
Appendices
Appendix A: Submittal Templates
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control Appendix D: Geotechnical Engineer Analysis
Appendix E: BMP Design Fact Sheets
Appendix F: Biofiltration Standard and Checklist
Appendix G: Guidance for Continuous Simulation and Hydromodification Management Sizing Factors Appendix H: Guidance for Investigating Potential Critical Coarse Sediment Yield Areas Appendix I: Significant Site Design BMP (SSD-BMP) Sizing Methods and Calulations Appendix J: Forms and Checklists
Appendix K: Guidance on Green Infrastructure
Glossary of Key Terms
2026-08-19 Item #12D Page 15 of 816
City of Encinitas BMP Design Manual
ix 20236
Figures
FIGURE 1-1. Procedural Requirements for a Project to Identify Storm Water Requirements ......................... 1-3 FIGURE 1-3. Applicability of Hydromodification Management BMP Requirements ...................................... 1-18 FIGURE 1-3. Pathways to Participating in Alternative Compliance Program ................................................... 1-23 FIGURE 1-4. Relationship between this Manual and WQIP ............................................................................... 1-25 FIGURE 3-1. Approach for Developing a Comprehensive Storm Water Management Design ....................... 3-1 FIGURE 3-2. DMA Delineation .................................................................................................................................. 3-6 FIGURE 3-3. Tributary Area for BMP Sizing ............................................................................................................ 3-7 FIGURE 5-1. Self-Mitigating Area ............................................................................................................................... 5-3 FIGURE 5-2. Self-retaining Area .................................................................................................................................. 5-4 Tables
TABLE 1-1. Applicability of Permanent, Post-Construction Storm Water Requirements ................................. 1-6 TABLE 1-2. Applicability of Manual Sections for Different Project Types ....................................................... 1-16 TABLE 2-1. Applicability of Performace Standards for Different Project Types ................................................ 3-4 TABLE 3-1. Applicability of Section 3.3 Sub-sections for Different Project Types ............................................ 3-4 TABLE 3-2. Applicability of Section 3.4 Sub-sections for Different Project Types ............................................ 3-9 TABLE 5-1. Permanent Structural BMPs for PDPs .............................................................................................. 5-13 TABLE 6-1. Mean Annual Precipitation .................................................................................................................. 6-12 TABLE 7-1. Schedule for Developing O&M Plan and Agreement ........................................................................ 7-2 TABLE 7-2. Permanent BMP Maintenance Verification and Inspection Requirements .................................... 7-4 TABLE 7-3. Maintenance Indicators and Actions for Vegetated BMPs ............................................................... 7-7 TABLE 7-4. Maintenance Indicators and Actions for Non-Vegetated Infiltration BMPs ................................. 7-9 TABLE 7-5. Maintenance Indicators and Actions for Filtration BMPs ................................................................. 7-9 TABLE 7-6. Maintenance Indicators and Actions for Detention BMPs ............................................................ 7-10 2026-08-19 Item #12D Page 16 of 816
City of Encinitas BMP Design Manual
x 20236
303(d) Refers to Clean Water Act Section 303(d) list of impaired and threatened waters ASTM American Society for Testing and Materials
BF Biofiltration (BMP Category)
BMPs Best Management Practices
CEQA California Environmental Quality Act
DCV Design Capture Volume
DMA Drainage Management Area
ESA Environmentally Sensitive Area
FT Flow-thru Treatment Control BMP (BMP Category)
GLUs Geomorphic Landscape Units
GR General Requirements
HMP Hydromodification Management Plan
HSPF Hydrologic Simulation Program-FORTRAN
HU Harvest and Use
INF Infiltration (BMP Category)
LID Low Impact Development
MEP Maximum Extent Practicable
MS4 Municipal Separate Storm Sewer System
NRCS Natural Resource Conservation Service
O&M Operation and Maintenance
PDPs Priority Development Projects
POC Point of Compliance
PR Partial Retention (BMP Category)
SC Source Control
SCCWRP Southern California Coastal Water Research Project SD Site Design
SDHM San Diego Hydrology Model
SDRWQCB San Diego Regional Water Quality Control Board
SIC Standard Industrial Classification
SUSMP Standard Urban Stormwater Mitigation Plan
SWMM Storm Water Management Model
SWQMP Storm Water Quality Management Plan
TN Total Nitrogen
TSS Total Suspended Solids
USEPA United States Environmental Protection Agency
USGS United States Geological Survey
WMAA Watershed Management Area Analysis
WQIP Water Quality Improvement Plan
This manual is intended to help a project applicant develop a Stormwater Quality Management Plan (SWQMP) for a development project (public or private) that complies with local and MS4 Permit requirements. Most applicants will require the assistance of a qualified civil engineer, architect, and/or landscape architect to prepare a SWQMP.
2026-08-19 Item #12D Page 17 of 816
City of Encinitas BMP Design Manual
xi 20236
Beginning Steps for All Projects: What requirements apply? Start by reviewing Chapter 1 to determine whether the proposed project is a “Standard Project”, “Basic Project”, “Exempt Project” or a “PDP”, the primary factor affecting which stormwater quality requirements apply.
Not all of the requirements and processes described in this manual apply to all projects. Therefore, it is important to begin with a careful analysis of which requirements apply and to verify with City staff, since every project is different. Chapter 1 provides an overview of the process of planning, design, construction, operation and maintenance, with associated jurisdictional review and approval steps leading to compliance. The flow chart below shows how to categorize a project in terms of applicable post-construction stormwater requirements. The flow chart is followed by a table that lists the applicable section of this manual for each project type.
Once an applicant has determined which requirements apply, Chapter 2 describes the specific performance standards associated with each requirement. For example, an applicant may learn from Chapter 1 that the project must meet stormwater pollutant control requirements. Chapter 2 describes what these requirements entail, why thesey requirements are in place, and how they can be met. Refer to the list of acronyms and glossary as guidance to understanding the meaning of key terms within the context of this manual.
Next Steps for All Projects: How should an applicant approach a project stormwater management design?
Most projects will then proceed to Chapter 3 to follow the step-by-step guidance to prepare a stormwater project submittal for the site. This chapter does not specify any regulatory criteria beyond those already specified in Chapter 1 and 2 – rather it is intended to serve as a resource for project applicants to help navigate the task of developing a compliant Stormwater Quality Management Plan submittal. Note that the first steps in Chapter 3 apply to all projects, while other steps in Chapter 3 only apply to PDPs.
The use of a step-by-step approach is highly recommended because it helps ensure that the right information is collected, analyzed, and incorporated into project plans and submittals at the appropriate time in the jurisdictional review process. It also helps facilitate a common framework for discussion between the applicant and the reviewer. However, each project is different, and it may be appropriate to use a different approach as long as the applicant demonstrates compliance with the MS4 Permit requirements that apply to the project.
Final Steps in Using This Manual: How should an applicant design BMPs and prepare documents for compliance?
Standard and Basic Projects PDPs
Standard and Basic Projects will proceed to
Chapter 4 for guidance on implementing
source control and site design requirements.
PDPs will proceed to Chapter 4 for guidance
on implementing source control and site
design requirements.
2026-08-19 Item #12D Page 18 of 816
City of Encinitas BMP Design Manual
xii 20236
After Chapter 4, Standard Projects shall
provide BMPs based on Section 1.4.3.1 and
then will proceed to Chapter 8 for project
submittal requirements.
PDPs will use Chapters 5 through 7 and
associated Appendices to implement pollutant
control and hydromodification management
requirements for the project site, as
applicable. These projects will proceed to
Chapter 8 for project submittal requirements.
Plan Ahead to Avoid Common Mistakes
The following list identifies strategies to avoid some common errors that delay or compromise development approvals with respect to stormwater compliance. • Plan for compliance as a first step. The strategy for stormwater quality compliance should be considered before completing a conceptual site design or sketching a layout of project site or subdivision lots (see Chapter 3). Planning early is crucial; for example, LID/Site Design is required for all development projects and onsite retention of stormwater runoff is required for PDPs. Additionally, collection of necessary information early in the planning process (e.g. geotechnical conditions, groundwater conditions) can help avoid delays resulting from redesign.
• Know that proprietary stormwater treatment facilities and strategies acceptable under previous MS4 Permits may not be sufficient to achieve compliance. Under the MS4 Permit, the standard for pollutant control for PDPs is retention of the 85th percentile storm volume (see Chapter 5). Flow-thru treatment cannot be used to satisfy permit requirements unless the project also participates in an alternate compliance program. Under some conditions, certain proprietary BMPs may be classified as “biofiltration” according to Appendix F of this manual and can be used for primary compliance with storm water pollutant treatment requirements (i.e. without alternative compliance). • Plan for on-going inspections and maintenance of PDP structural BMPs in perpetuity. It is essential to select structural BMPs that can be effectively operated and maintained by the ultimate property owner, to ensure access for maintenance, to control maintenance costs, and to secure a mechanism for funding of long term Operation & Maintenance of structural BMPs, (see Chapter 7).
2026-08-19 Item #12D Page 19 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L 1-1 2023
Chapter
1 1 Policies and Procedural
Requirements
This chapter introduces stormwater management policies and is intended to help categorize a project, determine the applicable stormwater management requirements, and provide options for achieving compliance. This chapter also introduces the procedural requirements for preparation, review, and approval of project submittals.
1.1 Introduction to Stormwater Management Policies
MS4 Permit Provision E.3.a-c; E.3.d.(1)
Stormwater management requirements for development projects are derived from the MS4 Permit and implemented by local jurisdictions.
On May 8, 2013, the California Regional Water Quality Control Board San Diego Region (referred to as “San Diego Water Board”) reissued a municipal stormwater permit titled “National Pollutant Discharge Elimination System Permit and Waste Discharge Requirements for Discharges from the MS4s Draining the Watersheds within the San Diego Region” (Order No. R9-2013-0001; referred to as MS4 Permit) to the municipal Copermittees. The MS4 Permit was issued by the San Diego Water Board pursuant to section 402 of the federal Clean Water Act, implementing regulations (Code of Federal Regulations Title 40, Part 122) adopted by the United States Environmental Protection Agency, and Chapter 5.5, Division 7 of the California Water Code. The MS4 Permit, in part, requires each Copermittee to use its land use and planning authority to implement a development planning program to control and reduce the discharge of pollutants in stormwater from new development and significant redevelopment to the maximum extent practicable (MEP). MEP is defined in the MS4 Permit.
Different requirements apply to different project types.
The MS4 Permit requires all development projects to implement source control and site design practices that will minimize the generation of pollutants. While all development projects are required to implement source control and site design/LID practices, the MS4 Permit has additional requirements for development projects that exceed size thresholds and/or fit under specific use categories. These projects, referred to as PDPs, are required to incorporate structural BMPs into the project plan to reduce the discharge of pollutants and to address potential hydromodification impacts 2026-08-19 Item #12D Page 20 of 816
Chapter 1: Policies and Procedural Requirements
1-2 2023
from changes in flow and sediment supply.
1.2 Purpose and Use of the Manual
This manual presents a “unified BMP design approach”.
To assist the land development community, streamline project reviews, and maximize cost-effective environmental benefits, the Copermittees developed a unified BMP design approach1 that meets the
performance standards specified in the MS4 Permit. By following the process outlined in this manual, project applicants (for both private and public developments) can develop a single, integrated design that complies with the complex and overlapping MS4 Permit source control and site design requirements, stormwater pollutant control requirements (i.e. water quality), and hydromodification management (flow-control and sediment supply) requirements.
1.2.1 Determine Applicability of Construction BMP Requirements Figure 1-1 below presents a flow chart of the decision process that the manual user should use to:
1. Categorize a project;
2. Determine stormwater requirements; and
3. Understand how to submit projects for review and verification.
This figure also indicates where specific procedural steps associated with this process are addressed in Chapter 1.
Refer to appendix J-1 for a step-by-step checklist that will aid in determining applicability of permanent, post-construction stormwater BMP requirements to your project. 1 The term “unified BMP design approach” refers to the standardized process for site and watershed investigation, BMP selection, BMP sizing, and BMP design that is outlined and described in this manual with associated appendices and templates. This approach is considered to be “unified” because it represents a pathway for compliance with the MS4 Permit requirements that is anticipated to be reasonably consistent across the local jurisdictions in San Diego County. In contrast, applicants may choose to take an alternative approach where they demonstrate to the satisfaction of the Copermittee, in their submittal, compliance with applicable performance standards without necessarily following the process identified in this manual
2026-08-19 Item #12D Page 21 of 816
Chapter 1: Policies and Procedural Requirements
1-3 2023
FIGURE 1-1. Procedural Requirements for a Project to Identify Storm Water Requirements
1.2.2 Determining Applicability of Permanent BMP Requirements All projects and phases of projects, even if exempted from meeting some or all of the Permanent BMP Requirements, are required to implement temporary erosion, sediment, good housekeeping and pollution prevention BMPs to mitigate stormwater pollutants during the construction phase. 2026-08-19 Item #12D Page 22 of 816
Chapter 1: Policies and Procedural Requirements
1-4 2023
Refer to the City’s Stormwater Standards Manual for detailed information on these requirements.
1.3 Defining a Project
Not all site improvements are considered “development projects” under the MS4 Permit.
This manual is intended for new development and redevelopment projects, inclusive of both private and public projects. Development projects are defined by the MS4 Permit as "construction, rehabilitation, redevelopment, or reconstruction of any public or private projects". Development projects are issued local permits to allow construction activities. To further clarify, this manual applies only to development or redevelopment activities that have the potential to contact stormwater and contribute an anthropogenic source of pollutants, or reduce the natural absorption and infiltration abilities of the land.
A project must be defined consistent with the California Environmental Quality Act (CEQA) definitions of "project."
CEQA defines a project as: a discretionary action being undertaken by a public agency that would have a direct or reasonably foreseeable indirect impact on the physical environment. This includes actions by the agency, financing, grants, permits, licenses, plans, and regulations or other entitlements granted by the agency. CEQA requires that the project include “the whole of the action” before the agency. This requirement precludes "piecemealing," which is the improper (and often artificial) separation of a project into smaller parts in order to avoid triggering requirement thresholds.
In the context of this manual, the "project" is the "whole of the action" which has the potential for adding or replacing or resulting in the addition or replacement of roofs, pavement, or other impervious surfaces and thereby resulting in increased flows and stormwater pollutants. "Whole of the action" means the project may not be segmented or phased into small parts either onsite or offsite if the effect is to reduce the quantity of impervious area and fall below thresholds for applicability of stormwater requirements.
When defining the project, the following questions are considered:
• What are the project activities?
• Do they occur onsite or offsite?
• What are the limits of the project (project boundary)? • What is the whole of the action associated with the project (i.e. what is the total amount of new or replaced impervious area considering all of the collective project components through all phases of the project)?
• Are any facilities or agreements to build facilities offsite in conjunction with providing service to the project (street widening, utilities)?
For subdivisions where homes, driveways, hardscape, and other impervious surfaces will be created, the “whole of the action” consists of grading and build out of the approved new homes and any proposed hardscape. Installation of any new and/or replaced hardscape by a subsequent new homeowner will be considered a separate project for purposes of determining relevant stormwater 2026-08-19 Item #12D Page 23 of 816
Chapter 1: Policies and Procedural Requirements
1-5 2023
management requirements.
For subdivisions where homes are not proposed, but home construction is anticipated in the near future, the “whole of the action” shall include the subdivision project and anticipated future homes, roads, driveways and any other related impervious surface. An estimate of total impervious surface created and/or replaced shall be included in the permanent BMP sizing calculations.
For subdivisions where no homes are proposed, and the lots are intended to be sold separately to individual owners for custom home builds, the “whole of the action” shall be considered the proposed subdivision only. Any future homes or other improvements built by a separate owner will be considered a separate project.
If a project applicant plans on developing and constructing homes or other impervious surfaces on more than one lot in a subdivision, the entire scope of work proposed shall be considered the “whole of the action”. Likewise, projects proposed by a single person or entity on adjacent lands at the same time shall not be piecemealed into separate projects.
Table 1-1 is used to determine whether stormwater management requirements defined in the MS4 Permit and presented in this manual apply to the project.
If a project meets one of the exemptions in Table 1-2 then permanent BMP requirements do not apply to the project; i.e. requirements in this manual are not applicable. If permanent BMP requirements apply to a project, Sections 1.4 to 1.7 will further define the extent of the applicable requirements based on the MS4 Permit. The MS4 Permit contains standard requirements that are applicable to all projects (Standard, Basic and Exempt Projects and PDPs), and more specific requirements for projects that are classified as PDPs.
2026-08-19 Item #12D Page 24 of 816
Chapter 1: Policies and Procedural Requirements
1-6 2023
TABLE 1-1. Applicability of Permanent, Post-Construction Storm Water Requirements Do permanent stormwater requirements apply to your project? Requirements DO NOT apply to:
Replacement of impervious surfaces that are part of a routine maintenance activity, such as:
• Replacing roof material on an existing building
• Restoring pavement or other surface materials affected by trenches from utility work • Resurfacing existing roads and parking lots, including milling, slurrying, overlaying, and restriping
• Routine replacement of damaged pavement, if the sole purpose is to repair the damage
• Constructing new sidewalk, pedestrian ramps or bike lanes on existing roads (within existing street right-of-way) if designed as described in damaged pavement. See Section 1.3.1 for additional details on common damaged pavement replacement scenarios.
• Restoring a historic building to its original historic design • Installation of ground mounted solar arrays over existing impermeable surface.
Note: Work that creates impervious surface outside of the existing impervious footprint is not considered routine maintenance.
Repair or improvements to an existing building or structure that do not alter the size:
• Plumbing, electrical and HVAC work
• Interior alterations including major interior remodels and tenant build-out within an existing commercial building
• Exterior alterations that do not change the general dimensions and structural framing of the building (does not include building additions or projects where the existing building is demolished).
Development project type determination and permanent BMP requirement applicability shall be at the sole discretion of the City Engineer.
2026-08-19 Item #12D Page 25 of 816
Chapter 1: Policies and Procedural Requirements
1-7 2023
1.3.1 Routine Maintenance Determination for Pavement Projects Table 1-2 provides additional detail about whether several types of projects that typically occur in or along street, alleys, and similar areas can be considered routine maintenance. This table reflects guidance provided by the San Diego Water Board to the City of Lemon Grove in March 2022, to the City of San Diego in October 2020, and the City of Poway in September 2021. Based on this guidance, public projects and private projects both may be considered routine maintenance as described in this section, as long as they meet all criteria described in the numbered list following Table 1-2.
TABLE 1-2. Applicability of Routine Maintenance Exemption for Pavement Projects Project Scenarios Routine
Maintenance
1. Full depth replacement of over 5,000 sf of contiguous, impervious damaged pavement that includes one or more of the following:
a. Includes disturbance of native soil
b. Includes disturbance of uncompacted subgrade
c. Includes disturbance of compacted subgrade
Yes1
2. Replacing an entire concrete panel as a result of utility trenching projects that includes one or more of the following:
a. Includes disturbance of native soil
b. Includes disturbance of uncompacted subgrade
c. Includes disturbance of compacted subgrade
Yes1
3. Full depth replacement of several damaged, non-contiguous, impervious patches with each individual patch under 5,000 sf, but cumulatively the patches result in over 5,000 sf of impervious area, that includes one or more of the following:
a. Includes disturbance of native soil
b. Includes disturbance of uncompacted subgrade
c. Includes disturbance of compacted subgrade
Yes1
4. Replacing a sidewalk that otherwise based on its condition does not require replacement. Replacement occurs for ADA compliance only, within the same footprint, with over 5,000 sf of replaced impervious area, and includes one or more of the following:
No2
(But see note at left
about sidewalk work
2026-08-19 Item #12D Page 26 of 816
Chapter 1: Policies and Procedural Requirements
1-8 2023
Project Scenarios Routine
Maintenance
a. In the public right-of-way
b. Within a property
Note: as noted in Table 1-2, routine sidewalk repair or replacement that is necessary based on the condition of the sidewalk (e.g. broken concrete) is generally considered routine maintenance.
that is considered
routine maintenance)
5. Replacing a sidewalk outside an existing impervious footprint with a meandering walkway, resulting in over 5,000 sf of new and replaced impervious area for ADA compliance.
No2
6. Creating new walkways (i.e. new impervious area) that must be ADA compliant that includes one or more of the following:
a. Ingress/egress to the building/feature
b. All ADA walkways within a project
No2
7. Creating new, shared use pathways wider than the minimum width required for ADA compliance that includes one or more of the following:
a. Entire width of shared ADA walkway and pedestrian/vehicle access pathway
b. Only the minimum ADA width portion of the pathway (i.e. 5 feet)
c. Entire width of any pathway greater than the minimum ADA width
No2
8. Creating a new sidewalk triggered by an ADA complaint that includes one or more of the following:
a. All projects of this nature regardless of size
b. Projects of this nature over 5,000 sf but only up to a given size threshold
No2
9. Creating and replacing curb ramps in any of the following situations, with the disturbed area being the minimum footprint needed to meet ADA requirements, that includes one or more of the following:
Yes1
2026-08-19 Item #12D Page 27 of 816
Chapter 1: Policies and Procedural Requirements
1-9 2023
Project Scenarios Routine
Maintenance
a. Curb ramp replacement completely within existing curb ramp footprint
b. Curb ramp replacement encroaches into the street without creating new impervious area
c. Curb ramp replacement encroaches into the pervious parkway and creates new impervious area
d. New curb ramp that encroaches into street without creating new impervious area
e. New curb ramp encroaches into pervious parkway and creates new impervious area
10. Replacing driveway aprons, with the disturbed area being the minimum footprint needed to meet ADA requirements that includes one or more of the following:
a. Driveway apron replacement completely within existing driveway apron footprint
b. Driveway apron replacement encroaches into the street as needed without creating new impervious area
c. Driveway apron replacement encroaches into the pervious parkway as needed and creates new impervious area
Yes1
11. Creating driveway aprons, with the disturbed area being the minimum footprint needed to meet ADA requirements that include one or more of the following:
a. New driveway apron encroaches into the street as needed without creating new impervious area
b. New driveway apron encroaches into pervious parkway as needed and creates new impervious area
No2
1 Must also meet all of the numbered criteria described in the discussion following this table to be considered routine maintenance.
2 Project may use the PDP exemptions described in section 1.4.3 if designed in a way that meets the requirements necessary to qualify for those exemptions. These PDP exemptions include, for example, hydraulically disconnected sidewalks and street improvements that follow Green Street guidance. 2026-08-19 Item #12D Page 28 of 816
Chapter 1: Policies and Procedural Requirements
1-10 2023
To qualify as routine maintenance, project scenarios identified as routine maintenance in Table 1-3 must also meet all of the requirements in the numbered list below.
1. The project is identified as part of the City’s regularly scheduled pavement maintenance on existing facilities or is an existing private road or parking lot that requires scheduled maintenance only.
2. The project is not part of, or associated with, development project mitigation requirements, development project construction, development project construction agreement, or conditions of approval.
3. No street widening or other enhancements are occurring in association with the damaged pavement project that would normally trigger PDP requirements or be PDP exempt per MS4 Permit Provision E.3.b.(3) – Green Streets Exemption (see “PDP Exemption Category 2” in Section 1.4.3 for more information).
4. The project would normally be CEQA exempt.
5. Construction BMPs must be implemented to control sediment and other pollutants associated with construction activity in accordance with the requirements the City of Encinitas Stormwater Standards Manual . More detail about construction BMPs is provided in Section
1.3.1.1 below.
6. The City shall maintain a list of projects that fall under this category. The City’s project manager is responsible for documenting that the project qualifies as routine maintenance per Section 1.3.1 and satisfies all the criteria in this numbered list. The City’s project manager shall keep this documentation in the project file.
Different routine maintenance scenarios combined together still are considered routine maintenance as long as they are not combined with an activity type that is not routine maintenance.
For example, a project that includes full depth pavement replacement that disturbs native soil (scenario 1a) and curb ramp replacement that encroaches into the street (scenario 9b) but no other activities would be considered routine maintenance.
Note, however, that if an activity that otherwise would be considered routine maintenance per Section 1.3.1 is combined with other activities that are classified as a PDP or use the Green Streets Exemption, then the activities that would have been considered routine maintenance are no longer considered routine maintenance since they are part of a PDP. They require treatment in that case; see Section 1.4.1 for additional information.
1.3.1.1 Construction BMP Requirements for Routine Maintenance Pavement Projects
As noted in item 6 in Section 1.3.1 above, construction BMP requirements must be met for a routine maintenance exemption to apply. All applicable BMPs from the City of Encinitas Stormwater Standards Manual must be implemented. The following highlights the construction (temporary) BMPs most likely to be applicable for routine maintenance work that occurs along streets:
• Cover and berm (perimeter controls) stockpiles at the end of each work day. Stockpiles must be placed at least 18 inches from the face of curb and are prohibited where they obstruct flow. • Implement at least one of the following at the end of each work day for demolished curbs, 2026-08-19 Item #12D Page 29 of 816
Chapter 1: Policies and Procedural Requirements
1-11 2023
gutters, ribbon gutters, and any other concentrated flow pathways that re impacted by the project even when there is no forecasted rain. These BMPs help prevent sediment transport from non-stormwater discharges such as irrigation runoff, water main breaks, water line flushing, etc.
o Install check dams along the impacted concentrated flow pathways. o Install run-on controls (e.g. gravel bag berms) to divert water around the impacted concentrated flow pathways.
o Cover and secure the impacted concentrated flow pathways with an erosion control product such as mats, plastic sheeting (e.g. Visqueen), or equivalent. • Implement erosion control for disturbed areas (any areas where pavement has been removed, soil or base is exposed, and any other areas where project work has disturbed soil, such as landscaping adjacent to the work area) when either (a) there is a 50% chance of rain within 24 hours, OR (b) the disturbed area is inactive (no soil disturbing activities for a period of 7 days or greater).
o Use pavement replacement approach that results in no exposed disturbed soil at the end of the work day (e.g. full depth reclamation, or applying compacted cold mix or hot mix at the end of the day to areas where pavement has been removed). Note: Contractors must obtain written approval from the City Engineer to utilize a full depth asphalt restoration method(s) if it differs from the approved construction plans, Standard Drawings, and/or Special Provisions.
OR
o Implement and effective combination of one or more of the following:
Install run-on controls (e.g. gravel bag berms) and/or use by-pass method(s) to prevent run-on to areas where soil has been disturbed. Cover the areas where pavement has been removed, soil or base is exposed, and any other areas where project work has disturbed soil with an erosion control product or technique such as steel traffic plates in conjunction with cold patches around the edges, mats, plastic sheeting (e.g. Visqueen), or an equivalent method.
Cover and secure demolished curb gutter, ribbon gutters, and any other impacted concentrated flow pathway with an erosion control product such as mats, plastic sheeting (e.g. Visqueen), or equivalent.
1.4 Is the Project a PDP?
MS4 Permit Provision E.3.b.(1)
This section presents the PDP categories defined in the MS4 Permit and describes the limited exemption categories available.
2026-08-19 Item #12D Page 30 of 816
Chapter 1: Policies and Procedural Requirements
1-12 2023
1.4.1 PDP Categories
In the MS4 Permit, PDP categories are defined based on project size, type and design features.
Projects shall be classified as PDPs if they are in one or more of the PDP categories presented in the MS4 Permit, which are listed below. Review each category, defined in (a) through (f), below. A PDP applicability checklist for these categories is also provided in Appendix J-2. If any of the categories match the project, the entire project is a PDP. For example, if a project feature such as a parking lot falls into a PDP category, then the entire development footprint including project components that otherwise would not have been designated a PDP on their own (such as other impervious components that did not meet PDP size thresholds, and/or landscaped areas), shall be subject to PDP requirements. Note that size thresholds for impervious surface created or replaced vary based on land use, land characteristics, and whether the project is a new development or redevelopment project.
Therefore, all definitions must be reviewed carefully. Also, note that categories are defined by the total quantity of “added or replaced” impervious surface, not the net change in impervious surface.
For example, consider a redevelopment project that adds 7,500 square feet of new impervious surface and removes 4,000 square feet of existing impervious surface. The project has a net increase of 3,500 square feet of impervious surface. However, the project is still classified as a PDP because the total added or replaced impervious surface is 7,500 square feet, which is greater than 5,000 square feet. "Collectively" for the purposes of the manual means that all contiguous and non-contiguous parts of the project that represent the whole of the action must be summed up. For example, consider a residential development project that will include the following impervious components:
• 3,600 square feet of roadway
• 350 square feet of sidewalk
• 4,800 square feet of roofs
• 1,200 square feet of driveways
• 500 square feet of walkways/porches
The collective impervious area is 10,450 square feet.
PDP Categories defined by the MS4 Permit:
(a) New development projects that create 10,000 square feet or more of impervious surfaces (collectively over the entire project site). This includes commercial, industrial, residential, mixed-use, and public development projects on public or private land. (b) Redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site on an existing site of 10,000 square feet or more of impervious surfaces). This includes commercial, industrial, residential, mixed-use, and public development projects on public or private land.
(c) New and redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site), and support one or more of the following uses:
2026-08-19 Item #12D Page 31 of 816
Chapter 1: Policies and Procedural Requirements
1-13 2023
(i) Restaurants. This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared foods and drinks for immediate consumption (Standard Industrial Classification (SIC) code 5812).
Information and an SIC search function are available at https://www.osha.gov/pls/imis/sicsearch.html.
(ii) Hillside development projects. This category includes development on any natural slope that is twenty-five percent or greater.
(iii) Parking lots. This category is defined as a land area or facility for the temporary parking or storage of motor vehicles used personally, for business, or for commerce. (iv) Streets, roads, highways, freeways, and driveways. This category is defined as any paved impervious surface used for the transportation of automobiles, trucks, motorcycles, and other vehicles.
(d) New or redevelopment projects that create and/or replace 2,500 square feet or more of impervious surface (collectively over the entire project site), and discharging directly to an Environmentally Sensitive Area (ESA). “Discharging directly to” includes flow that is conveyed overland a distance of 200 feet or less from the project to the ESA, or conveyed in a pipe or open channel any distance as an isolated flow from the project to the ESA (i.e. not commingled with flows from adjacent lands).
Note: ESAs are areas that include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas designated as Areas of Special Biological Significance by the State Water Board and San Diego Water Board; State Water Quality Protected Areas; water bodies designated with the RARE beneficial use by the State Water Board and San Diego Water Board; and any other equivalent environmentally sensitive areas which have been identified by the Copermittee (see Section 1.4.2 below to determine if any other local areas have been identified).
For projects adjacent to an ESA, but not discharging to an ESA, the 2,500 sq-ft threshold does not apply as long as the project does not physically disturb the ESA and the ESA is upstream of the project.
(e) New development projects, or redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface, that support one or more of the following uses:
(i) Automotive repair shops. This category is defined as a facility that is categorized in any one of the following SIC codes: 5013, 5014, 5541, 7532-7534, or 7536-7539.
Information and an SIC search function are available at https://www.osha.gov/pls/imis/sicsearch.html.
(ii) Retail gasoline outlets. This category includes Retail gasoline outlets that meet the following criteria: (a) 5,000 square feet or more or (b) a projected Average Daily Traffic of 100 or more vehicles per day.
2026-08-19 Item #12D Page 32 of 816
Chapter 1: Policies and Procedural Requirements
1-14 2023
(f) New or redevelopment projects that result in the disturbance of one or more acres of land and are expected to generate pollutants post construction.
Exclusions that apply to this category only: Projects creating less than 5,000 square feet of impervious surface and where any added landscaping does not require regular use of pesticides and fertilizers, such as a slope stabilization project using native plants, are excluded from this category. Calculation of the square footage of impervious surface need not include linear pathways that are for infrequent vehicle use, such as for emergency or maintenance access or for bicycle or pedestrian use, if they are built with pervious surfaces or if they sheet flow to surrounding pervious surfaces. See Section 1.4.2 for additional guidance.
Area that may be excluded from impervious area calculations for determining if the project is a PDP:
(a) Based on guidance from the San Diego Water Board, activities defined as routine maintenance per Section 1.3.1 cannot be combined with work that is a PDP or uses the Green Streets Exemption. If combined with work that is a PDP or uses the Green Streets Exemption, work described in Section 1.3.1 that would be routine maintenance if done on its own is no longer routine maintenance, and it requires treatment as described in Section 1.3.1 for work that does not qualify as routine maintenance. For additional guidance, see Example 1 below, following this list. (b) Except as described in item (a), areas of a project that are considered exempt from storm water requirements (e.g., routine maintenance activities such as resurfacing, interior repair or improvements to an existing building, etc.) shall not be included as part of “added or replaced” impervious surface in determining project classification. For additional guidance, see Example 2, following this list.
Example 1: A project includes reconfiguration of an existing road for traffic calming and pedestrian improvements. This project includes creation or replacement of 15,000 square feet of pavement, and the replaced pavement areas are not damaged. This work does not qualify as routine maintenance per Section 1.3.1 but does qualify to use the Green Streets Exemption. The project also includes full depth replacement of several patches of damaged pavement in adjacent parts of the road; these full depth replacement patches are a total of 6,000 square feet. While if done by itself the 6,000 square feet of full depth damaged pavement replacement would qualify to be considered routine maintenance per Section 1.3.1, in this case it is also subject to Green Streets standards since it is combined with work that is using the Green Streets Exemption.
Example 2: A project includes replacing the roof on a 10,000 square foot commercial building. The project also includes building a new trash enclosure (150 square feet). The roof replacement work does not expose underlying soil and is routine maintenance per Table 1-2, so the roof replacement area is not included in determining whether the project is a PDP. Because the trash enclosure work is 150 square feet of impervious area, it is considered a Standard Project. Standard Project requirements apply to the trash enclosure work, and the roof replacement work is considered routine maintenance.
Redevelopment projects may have special considerations with regards to the total area required to be treated. Refer to Section 1.7.
2026-08-19 Item #12D Page 33 of 816
Chapter 1: Policies and Procedural Requirements
1-15 2023
1.4.2 Local Additional PDP Categories and/or Expanded PDP Definitions To determine whether your project discharges directly to an Environmentally Sensitive Area, begin by referring to the map of ESAs in Appendix J. This map includes all locally known ESAs as defined by the MS4 Permit. Additionally, if a site-specific open space area and/or wetland area has been identified on the property or downstream of the property, this must be considered when determining whether the project is a PDP. Consult with City staff for additional guidance.
1.4.3 Local PDP Exemptions or Alternative PDP Requirements
1.4.3.1 Requirements for Standard and Basic Projects
The City of Encinitas, in addition to the PDPs categorized in section 1.4.1, categorizes non-PDP projects as Standard or Basic Projects. Projects that create and/or replace 500 square feet or more of impervious surface but are not classified as one of the PDP categories described above are considered Standard Projects. Projects that create and/or replace less than 500 square feet of impervious surface and are not classified as one of the PDP categories described above are considered Basic Projects.
Standard projects shall provide natural bioretention BMPs or document equivalent volume reduction via site design or other structural BMP, for stormwater pollution control based on the following sizing calculation method or the DCV calculation method described in Chapter 5 and Appendix B. The total surface area shall include new and replaced impervious areas of the proposed project. If it is determined that bioretention BMPs are not feasible, at the discretion of the City Engineer, partial retention BMPs, biofiltration BMPs or other source control BMPs may be used. The DCV calculation method may be used to determine volume reduction needed for Standard Projects. The following sizing calculation may be used for sizing natural bioretention BMPs. All Standard Projects must also implement source control and site design measures as described in Chapter 4. Consult Chapter 5 for structural BMP design options.
MINIMUM BMP AREA = 0.03 Σ (Surface Type SF X Surface Type Runoff Factor) Basic Projects must also implement source control and site design measures as described in Chapter 4 but are not required to provide structural BMPs.
In situations with uncontrolled cross lot drainage that do not drain into a controlled, engineered drainage conveyance system the City Engineer may require additional or upsized stormwater treatment and flow control facilities. These facilities shall be designed for the greater surface area and volume of either treatment sizing required for new or removed and replaced impervious surface areas OR sizing for Hydromodification based on the net new impervious surface area. Special attention shall be made to design the overflow of these facilities to maintain the historical drainage pattern to the maximum extent practical.
1.4.3.21.4.3.1 Local PDP Exemptions
As defined in the MS4 Permit, projects that meet the following criteria may qualify for an exemption from PDP requirements:
1) New or retrofit paved sidewalks, bicycle lanes, or trails that meet the following criteria:
a) Designed and constructed to direct stormwater runoff to adjacent vegetated areas, 2026-08-19 Item #12D Page 34 of 816
Chapter 1: Policies and Procedural Requirements
1-16 2023
or other non-erodible permeable areas; OR
b) Designed and constructed to be hydraulically disconnected from paved streets or roads; OR
c) Designed and constructed with permeable pavements or surfaces in accordance with current USEPA Green Streets guidance, "Managing Wet Weather with Green Infrastructure – Municipal Handbook: Green Streets" (USEPA, most recent edition).
2) Retrofitting or redevelopment of existing paved alleys, streets or roads that are designed and constructed in accordance with the current USEPA Green Streets guidance, "Managing Wet Weather with Green Infrastructure – Municipal Handbook: Green Streets" (USEPA, most recent edition).
Consult City staff if you think your project may qualify for an exemption based on the above definitions. Note that the source control and site design stormwater requirements that are applicable to all projects will still apply even if a project is exempt from PDP requirements.
1.5 Determining Applicable Storm Water Management
Requirements
MS4 Permit Provision E.3.c.(1)
Depending on project type and receiving water, different stormwater management requirements apply.
New development or redevelopment projects that are subject to this manual requirement pursuant to Section 1.3, but are not classified as PDPs based on Section 1.4, include Standard Projects, Basic Projects and Exempt projects. Source control and site design requirements apply to all projects including Standard Projects, Basic Projects, Exempt Projects and PDPs. Additional structural BMP requirements (i.e. pollutant control and hydromodification management) apply to PDPs and Standard projects (on a more limited basis). Stormwater management requirements for a project, and the applicable sections of this manual, are summarized in Table 1-3.
TABLE 1-4. Applicability of Manual Sections for Different Project Types Project Type
Project
Development
Process
(Chapter 3
and 8)
Source Control
and Site
Design
(Section 2.1 and
Chapter 4)
Structural
Pollutant Control
(Section 2.2 and
Chapter 5 and 7)
Structural
Hydromodification
Management
(Section 2.3, 2.4 and
Chapter 6 and 7)
Not a Development Project The requirements of this manual do not apply Basic Project* NA NA
Standard Project* NA NA
2026-08-19 Item #12D Page 35 of 816
Chapter 1: Policies and Procedural Requirements
1-17 2023
PDP with only Pollutant Control
Requirements** NA
PDPs with Pollutant Control and
Hydromodification Management
Requirements
* Standard Projects refer to Section 1.4.3.1 for designing required structural BMPs. ** Some PDPs may be exempt from Structural Hydromodification Management BMPs, refer to Section 1.6 to determine. 2026-08-19 Item #12D Page 36 of 816
Chapter 1: Policies and Procedural Requirements
1-18 2023
Figure 1-2. Applicability of Hydromodification Management BMP Requirements
1.6Applicability of Hydromodification Management
Requirements
MS4 Permit Provision E.3.c.(2)
Hydromodification management requirements apply to PDPs only. 2026-08-19 Item #12D Page 37 of 816
Chapter 1: Policies and Procedural Requirements
1-19 2023
If the project is a Standard, Basic or Exempt Project, hydromodification management requirements do not apply. Hydromodification management requirements apply to PDPs (both new and redevelopment) unless the project meets specific exemptions discussed below.
PDP exemptions from hydromodification management requirements are based on the receiving water system.
The City has the discretion to exempt a PDP from hydromodification management requirements where the project discharges stormwater runoff to:
(i) Existing underground storm drains discharging directly to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean;
(ii) Conveyance channels whose bed and bank are concrete lined all the way from the point of discharge to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean; or
(iii) An area identified by the Copermittees as appropriate for an exemption by the optional WMAA incorporated into the Water Quality Improvement Plan (WQIP) pursuant to Provision B.3.b.(4) of the MS4 permit.
As allowed by the MS4 Permit, projects discharging directly to the Pacific Ocean, by either existing underground storm drain systems or conveyance channels whose bed and bank are concrete-lined all the way from the point of discharge to the Pacific Ocean, are exempt. This exemption is subject to the following additional criteria defined by this manual:
a) The outfall must be located on the beach (not within or on top of a bluff), b) A properly sized energy dissipation system must be provided to mitigate outlet discharge velocity from the direct discharge to the ocean for the ultimate condition peak design flow of the direct discharge,
c) The invert elevation of the direct discharge conveyance system (at the point of discharge to the ocean) should be equal to or below the mean high tide water surface elevation at the point of discharge, unless the outfall discharges to quay or other non-erodible shore protection.
o For cases in which the direct discharge conveyance system outlet invert elevation is above the mean high tide water surface elevation but below the 100-year water surface elevation, additional analysis is required to determine if energy dissipation should be extended between the conveyance system outlet and the elevation associated with the mean high tide water surface level.
o No exemption may be granted for conveyance system outlet invert elevations located above the 100-year floodplain elevation.
As allowed by the MS4 Permit, projects discharging directly to a water storage reservoir or lake, by either existing underground storm drain systems or conveyance channels whose bed and bank are concrete-lined all the way from the point of discharge to the water storage reservoir or lake, are exempt. This exemption is subject to the following additional criteria defined by this manual:
a) A properly sized energy dissipation system must be provided in accordance with local design standards to mitigate outlet discharge velocity from the direct 2026-08-19 Item #12D Page 38 of 816
Chapter 1: Policies and Procedural Requirements
1-20 2023
discharge to the water storage reservoir or lake for the ultimate condition peak design flow of the direct discharge,
b) The invert elevation of the direct discharge conveyance system (at the point of discharge to the water storage reservoir or lake) should be equal to or below the lowest normal operating water surface elevation at the point of discharge, unless the outfall discharges to quay or other non-erodible shore protection. Normal operating water surface elevation may vary by season; contact the reservoir operator to determine the elevation. For cases in which the direct discharge conveyance system outlet invert elevation is above the lowest normal operating water surface elevation but below the reservoir spillway elevation, additional analysis is required to determine if energy dissipation should be extended between the conveyance system outlet and the elevation associated with the lowest normal operating water surface level.
c) No exemption may be granted for conveyance system outlet invert elevations located above the reservoir spillway elevation.
As allowed by the MS4 Permit, projects discharging directly to an area identified as appropriate for an exemption in the WMAA for the watershed in which the project resides, by either existing underground storm drain systems or conveyance channels whose bed and bank are concrete-lined all the way from the point of discharge to the designated area, are exempt. Consult the WMAA within the WQIP for the watershed in which the project resides to determine areas identified as appropriate for an exemption. Exemption is subject to any criteria defined within the WMAA, and criteria defined below by this manual:
a) A properly sized energy dissipation system must be provided to mitigate outlet discharge velocity from the direct discharge to the exempt river reach for the ultimate condition peak design flow of the direct discharge, b) The invert elevation of the direct discharge conveyance system (at the point of discharge to the exempt river reach) should be equal to or below the 10-year floodplain elevation. Exceptions may be made at the discretion of the City Engineer, but shall never exceed the 100-year floodplain elevation. The City Engineer may require additional analysis of the potential for erosion between the outfall and the 10- year floodplain elevation.
c) No exemption may be granted for conveyance system outlet invert elevations located above the 100-year floodplain elevation.
1.7 Special Considerations for Redevelopment
Projects (50% Rule)
MS4 Permit Provision E.3.b.(2)
Redevelopment PDPs (PDPs on previously developed sites) may need to meet storm water management requirements for ALL impervious areas (collectively) within the ENTIRE project site.
If the project is a redevelopment project, the structural BMP performance requirements and 2026-08-19 Item #12D Page 39 of 816
Chapter 1: Policies and Procedural Requirements
1-21 2023
hydromodification management requirements apply to redevelopment PDPs as follows:
(a) Where redevelopment results in the creation or replacement of impervious surface in an amount of less than fifty percent of the surface area of the previously existing development, then the structural BMP performance requirements of Provision E.3.c [of the MS4 Permit] apply only to the creation or replacement of impervious surface, and not the entire development; or
(b) Where redevelopment results in the creation or replacement of impervious surface in an amount of more than fifty percent of the surface area of the previously existing development, then the structural BMP performance requirements of Provision E.3.c [of the MS4 Permit] apply to the entire development.
These requirements for managing stormwater on an entire redevelopment project site are commonly referred to as the "50% rule". For the purpose of calculating the ratio, the surface area of the previously existing development shall be the area of impervious surface within the previously existing development. The following steps shall be followed to estimate the area that requires treatment to satisfy the MS4 Permit requirements:
1. How much total impervious area currently exists on the site?
2. How much existing impervious area will be replaced with new impervious area?
3. How much new impervious area will be created in areas that are pervious in the existing condition?
4. Total created and/or replaced impervious surface = Step 2 + Step 3.
5. 50% rule test: Is step 4 more than 50% of Step 1? If yes, treat all impervious surface on the site. If no, then treat only Step 4 impervious surface and any area that comingles with created and/or replaced impervious surface area.
Note: Step 2 and Step 3 must not overlap as it is fundamentally not possible for a given area to be both “replaced” and “created” at the same time. Also activities that occur as routine maintenance shall not be included in Step 2 and Step 3 calculation.
For example, a 10,000 sq. ft. development proposes replacement of 4,000 sq. ft. of impervious area.
The treated area is less than 50% of the total development area and only the 4,000 sq. ft. area is required to be treated.
1.8 Alternative Compliance Program2
MS4 Permit Provision E.3.c.(1).(b); E.3.c.(2).(c); E.3.c.(3) PDPs may be allowed to participate in an alternative compliance program.
Copermittees have the discretion to independently develop an alternative compliance program for their jurisdiction. The alternative compliance program allows PDPs to participate in this program in 2 The City of Encinitas does not currently have an Alternative Compliance Program. 2026-08-19 Item #12D Page 40 of 816
Chapter 1: Policies and Procedural Requirements
1-22 2023
lieu of meeting either the PDP structural BMP performance requirements for retention or a portion of DCV that is not retained onsite in conjunction with onsite mitigation.
At this time, the City of Encinitas does not have an Alternative Compliance Program. Project based (i.e. on a case-by-case basis) Alternative Compliance may be approved by the City provided that the proposed design has added water quality and hydromodification benefits for the City compared to on-site stormwater management. The proposed design for Alternative Compliance shall be in accordance with the Water Quality Equivalency Guidance approved by Water Quality Control Board, Region 9. If the City establishes an Alternative Compliance Program in the future, this section of the BMP Design Manual will be updated.
Participation in an alternative compliance program would allow a PDP to fulfill the requirement of providing retention and/or biofiltration pollutant controls onsite that completely fulfill the performance standards specified in Chapter 5 (pollutant controls) with onsite flow-thru treatment controls and offsite mitigation of the DCV not retained onsite.
PDPs may be allowed to participate in an alternative compliance program by using onsite BMPs to treat offsite runoff. The PDP utilizing the alternative compliance program would (at a minimum) provide flow-thru treatment control BMPs onsite, then fund, contribute to, or implement an offsite alternative compliance project deemed by the jurisdiction-specific alternative compliance program to provide a greater overall water quality benefit for the portion of the pollutants not addressed onsite through retention and/or biofiltration BMPs. Offsite alternative compliance program locations for the purpose of this manual are defined as location within the same watershed management area as the PDP. Participation in an alternative compliance program would also potentially relieve hydromodification management flow control obligations that are not provided onsite (see Chapter 6 for hydromodification management requirements). PDPs must consult the local jurisdiction for specific guidelines and requirements for participation in potential alternative compliance programs.
Figure 1-2 generally represents two potential pathways for participating in alternative compliance (i.e. offsite projects that supplement the PDPs onsite BMP obligations). • The first pathway (illustrated using solid line, left side) ultimately ends at alternative compliance if the PDP cannot meet all of the onsite pollutant control obligations via retention and/or biofiltration. This pathway requires performing feasibility analysis for retention and biofiltration BMPs prior to participation in an alternative compliance project.
• The second pathway (illustrated using dashed line, right side) is a discretionary pathway along which jurisdictions may allow for PDPs to proceed directly to an alternative compliance project without demonstrating infeasibility of retention and/or biofiltration BMPs onsite.
Participation in an alternative compliance program also requires onsite flow-thru treatment control BMPs.
Participation in an offsite alternative compliance project and the obligation to implement flow-thru treatment controls for the DCV not reliably retained or biofiltered onsite, are linked and cannot be separated. Therefore, if a jurisdiction either does not have an alternative compliance program or does not allow the PDP to participate in the program or propose a project-specific offsite alternative 2026-08-19 Item #12D Page 41 of 816
Chapter 1: Policies and Procedural Requirements
1-23 2023
compliance project, then the PDP may not utilize flow-thru treatment control. The PDP should consult with the jurisdiction regarding processing requirements if this is the case.
PDPs may be required to provide temporal mitigation when participating in an alternative compliance program.
Finally, if the PDP is allowed to participate in an offsite alternative compliance project that is constructed after the completion of the development project, the PDP must provide temporal mitigation to address this interim time period. Temporal mitigation must provide equivalent or better pollutant removal and/or hydrologic control (as applicable) as compared to the case where the offsite alternative compliance project is completed at the same time as the PDP.
Water Quality Equivalency calculations must be accepted by the Regional Board The Water Quality Equivalency (WQE) calculation must be accepted by the San Diego Water Board’s Executive Officer prior to administering an alternative compliance program. The Water Quality Equivalency provides currency calculations to assess water quality and hydromodification management benefits for a variety of potential offsite project types and provides regional and technical basis for demonstrating a greater water quality benefit for the watershed.
Figure 1-3. Pathways to Participating in Alternative Compliance Program *PDP may be allowed to directly participate in an offsite project without demonstrating infeasibility of retention and/or biofiltration BMPs onsite. Consult the local jurisdiction for specific guidelines. 2026-08-19 Item #12D Page 42 of 816
Chapter 1: Policies and Procedural Requirements
1-24 2023
An Applicant Implemented Alternative Compliance Project may be allowed.3 3 The City may allow an applicant to implement an alternative compliance project in lieu of complying on site. In this scenario, the applicant is fully responsible for the alternative compliance project design, construction, operation and long-term maintenance. Applicant proposed alternative compliance projects shall not be authorized by the City prior to acceptance of the water quality equivalency calculations by the Regional Water Quality Board.
1.9 Relationship between this Manual and WQIPs
This manual is connected to other permit-specified planning efforts.
The MS4 Permit requires each Watershed Management Area within the San Diego Region to develop a WQIP that identifies priority and highest priority water quality conditions and strategies that will be implemented with associated goals to demonstrate progress towards addressing the conditions in the watershed. The MS4 Permit also provides an option to perform a WMAA as part of the WQIP to develop watershed specific requirements for structural BMP implementation in the watershed management area. PDPs should expect to consult either of these separate planning efforts as appropriate when using this manual as follows:
1. For PDPs that implement flow-thru treatment BMPs, selection of the type of BMP shall consider the pollutants and conditions of concerns. Among the selection considerations, the PDP must consult the highest priority water quality condition as identified in the WQIP for that particular watershed management area.
2. There may be watershed management area specific BMPs or strategies that are identified in WQIPs, for which PDPs should consult and incorporate as appropriate.
3. As part of the hydromodification management obligations that PDPs must comply with, PDPs shall consult the mapping of potential critical coarse sediment yield areas provided in the WMAA attachment to the WQIPs and design the project according to the procedures outlined in this manual if these sediments will be impacted by the project.
4. PDPs may be exempt from implementing hydromodification management BMPs (Chapter 6) based on the exemptions indicated in Section 1.6, and potentially from additional exemptions recommended in the WMAA attachment to the WQIPs. PDPs should consult the WMAA for recommended hydromodification management exemptions to determine if the project is eligible.
5. PDPs may have the option of participating in an alternative compliance program. Refer to Section 1.8.
These relationships between this manual and WQIPs are presented in Figure 1-3. 3 The City of Encinitas does not currently have an Alternative Compliance Program. 2026-08-19 Item #12D Page 43 of 816
Chapter 1: Policies and Procedural Requirements
1-25 2023
FIGURE 1-4. Relationship between this Manual and WQIP
The City of Encinitas is a Copermittee within the Carlsbad WMA. The Carlsbad WMA WQIP may be accessed at the Project Clean Water website (www.projectcleanwater.org).
1.10 Storm Water Requirement Applicability Timeline
MS4 Permit Provision E.3.e.(1)(a)
The City must require and confirm that all Priority Development Projects implement the requirements of Provision E.3 of the MS4 Permit. For project applicants that have received prior lawful approval before the effective date of this manual, the City has the discretion to allow previous land development requirements to apply under certain conditions. At the discretion of the City Engineer, the City will 2026-08-19 Item #12D Page 44 of 816
Chapter 1: Policies and Procedural Requirements
1-26 2023
allow previous land development requirements to apply to a Priority Development Project if the conditions of Provision E.3.e.(1) of the MS4 Permit are met.
1.11 Project Review Procedures
Local jurisdictions review project plans for compliance with applicable requirements of this manual and the MS4 Permit.
The project applicant must provide sufficient documentation to demonstrate that applicable requirements of the BMP Design Manual and the MS4 Permit will be met.
For Standard and Basic Projects, a Standard Project SWQMP must be completed prior to first plan check to document that the following general requirements of the MS4 Permit are met, and showing applicable features onsite grading, building, improvement and landscaping plans:
• BMP Requirements for All Development Projects, which includes general requirements, source control BMP requirements, and narrative (i.e. not numerically-sized) site design requirements (MS4 Permit Provision E.3.a).
For PDPs, a PDP SWQMP must be completed prior to first plan check to document that the following general requirements of the MS4 Permit are met, and showing applicable features onsite grading and landscaping plans:
• BMP Requirements for All Development Projects, which includes general requirements for siting of permanent, post-construction BMPs, source control BMP requirements, and narrative (i.e. not numerically-sized) site design requirements (MS4 Permit Provision E.3.a); • Stormwater Pollutant Control BMP Requirements, for numerically sized onsite structural BMPs to control pollutants in stormwater (MS4 Permit Provision E.3.c.(1)); and • Hydromodification Management BMP Requirements, which includes protection of critical sediment yield areas and numerically sized onsite BMPs to manage hydromodification that may be caused by stormwater runoff discharged from a project (MS4 Permit Provision E.3.c.(2)).
Detailed submittal requirements are provided in Chapter 8 of this manual. Documentation of the permanent, post-construction stormwater BMPs must be provided with the first submittal of a project.
Stormwater requirements will directly affect the layout of the project. Therefore stormwater requirements must be considered from the initial project planning phases, and will be reviewed with each submittal, beginning with the first submittal.
1.12 PDP Structural BMP Verification
MS4 Permit Provision E.3.e.(1)
Structural BMPs must be verified by the local jurisdiction prior to project occupancy.
Pursuant to MS4 Permit Provision E.3.e.(1), each Copermittee must require and confirm the following with respect to PDPs constructed within their jurisdiction:
(a) Each Copermittee must require and confirm that appropriate easements and ownerships 2026-08-19 Item #12D Page 45 of 816
Chapter 1: Policies and Procedural Requirements
1-27 2023
are properly recorded in public records and the information is conveyed to all appropriate parties when there is a change in project or site ownership. (b) Each Copermittee must require and confirm that prior to occupancy and/or intended use of any portion of the PDP, each structural BMP is inspected to verify that it has been constructed and is operating in compliance with all of its specifications, plans, permits, ordinances, and the requirements of the MS4 Permit.
For PDPs, this means that, the City inspector for the project will require the project owner’s engineer to inspect and provide a certification that the site improvements for the project have been constructed in conformance with the approved stormwater management documents and drawings. A note stating this requirement must be placed on project plans.
Inspection of structural BMPs is required at each significant construction stage and at completion. If the need arises to modify a BMP during construction, the proposed change must be submitted to City plan check engineers for review and approval. Modifications must meet the permanent BMP sizing requirements in order to be approved. Following construction, the City may require an addendum to the SWQMP and As Builts to address any changes to the structural BMPs that occurred during construction that were approved by the City Engineer. The City may also require a final update to the O&M Plan, and/or execution of a maintenance agreement that will be recorded for the property. A maintenance agreement that is recorded with the property title can then be transferred to future owners.
Certification of structural BMPs, updates to reports, and recordation of a maintenance agreement must occur prior to project final and occupancy and/or intended use of the project. Specific procedures are provided in Chapter 8 of this manual.
2026-08-19 Item #12D Page 46 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L 2-1 2023
Chapter
2 2 Standards and Concepts
Projects must meet four separate performance standards, as applicable.
Performance standards are specific design objectives to be achieved through the implementation of BMPs. The MS4 Permit establishes separate performance standards for source control and site design practices; storm water pollutant control BMPs; and hydromodification management BMPs. Each development project must be designed to satisfy any of several potentially applicable performance standards. Four types of standards are addressed in this manual; the first applies to all development projects, while the remaining three apply only to PDPs. The specific applicability of all standards may vary depending on specific site conditions and design choices. Table 2-1 provides an overview of these standards and their potential applicability.
1. Baseline BMP Implementation (Sections 2.1.1.2 and 2.1.1.3) Baseline Source Control and Site Design BMPs must be implemented for all development projects wherever it is applicable and feasible to do so. These BMPs help to prevent the onsite generation of pollutants and flows and to keep them from leaving the site. For example, covering trash storage areas prevents wastes from being washed into the MS4. Likewise, directing runoff from an impervious surface (e.g., a rooftop) to a pervious dispersion area (landscaping, etc.) provides infiltration of pollutants and flows into the soil.
Baseline BMP requirements are qualitative in that strict compliance with BMP sizing and/or specific design criteria is not required. Their selection and design should be guided by the feasibility of implementing them at all applicable locations. They include each of the BMPs described in BMPDM Sections 4.2 and 4.3, as well as any additional practices specified in applicable SWQMP Forms and instructions. Both the Standard and PDP SWQMP Forms require consideration of specific Baseline BMPs for each of the following categories:
• Existing Natural Site Features. This category addresses water bodies, drainage corridors, and other natural features with the following BMPs: Conserve Natural Features (SD-G), and Provide Buffers Around Waterbodies (SD-H)
• Outdoor Impervious Areas. This category addresses streets, sidewalks, driveways, and other common outdoor impervious features with the following BMPs: Direct runoff to pervious areas (SD-B), Construct Surfaces From Permeable Materials (SD-I), and Minimize the Size of Impervious Areas
2026-08-19 Item #12D Page 47 of 816
Chapter 2: Performance Standards and Concepts
2-2 2023
TABLE 2-2-1. Applicability of Performance Standards for Different Project Types
1. Baseline BMP Implementation
2. DCV
Reduction
through
Enhanced Site
Design BMPs
3. Compliance with Structural
Performance Standards 4. Avoidance &
Bypass of
Critical Coarse
Sediment
a. Source Control
BMPs
b. Site Design
BMPs
a. Pollutant
Control
b. Hydromod.
Management
Sections 2.1.1.2 &
4.2 Sections 2.1.1.3
& 4.3
Sections 2.1.1.4,
2.2.2.2 &
Appendices B.1
& I.1
Sections 2.2 &
5 Sections 2.3,
2.4 & 6
Sections 2.3.3, 6.2
& Appendix H
Basic Projects
Required where applicable and
feasible
NA NA NA NA
Standard Projects Required per Section 1.4.3.1NA NA NA PDP-exempted Projects • New or retrofit paved NA NA NA NA
sidewalks, bicycle lanes, or trails (Section 1.4.3)
• Retrofitting or redevelopment
of paved alleys, streets or roads (Section 1.4.3)
NA Required NA NA
PDPs
Optional Required Required Required • Without HMP Exemption (Section 1.4)
• With HMP Exemption
(Section 6.1) Optional Required NA NA
2026-08-19 Item #12D Page 48 of 816
Chapter 2: Performance Standards and Concepts
2-3 2023
• Rooftop Areas. This category addresses permanent impervious coverings on buildings and/or other structures such as patios or decks with the following BMPs: Direct Runoff to Pervious Areas (SD-B), Install Green Roofs (SD-C), Install Rain Barrels (SD-E) • Landscaped Areas. This category addresses planting areas, turf areas (artificial or natural), and water features in a landscape design with the following BMP: Use Sustainable Landscaping (SD-K)
• Work and Storage Areas: This category addresses trash storage, materials and equipment storage, loading and unloading, fueling, maintenance and repair, vehicle and equipment cleaning, and other areas that have the potential to generate pollutants with the following BMPs: Overhead Covering (SC-A), Berms and Grade Breaks (SC-B), and Wind Protection (SC-C)
• Management of Stormwater Discharges: This category addresses management of discharges from outdoor work areas and where runoff may be routed to with the following BMPs:
Sanitary Sewer (SC-D), Containment Areas (S-D), Stormwater S-BMP or SSD-BMP • Management of Non-Stormwater Discharges: This category addresses non-stormwater discharges to prevent illicit discharges from entering the storm drain system with the following BMPs: Storm Drain Signage (SC-F), Educational BMP Signage (SC-G), and practices for interior work surfaces, floor drains and sumps, drain lines, and fire sprinkler test water
2. DCV Reduction through Enhanced Site Design BMPs (Sections 2.1.1.4, 2.2.2.2, & Appendix B.1) An Enhanced Site Design BMP is any site design BMP used specifically to reduce the Design Capture Volume (DCV) within a Drainage Management Area (DMA). This can be achieved either by adjusting the impervious runoff factor of one or more surfaces (Attachment B.2.1) or by implementing BMPs that receive and mitigate a portion of the DCV (Attachment B.2.2). Since DCV reduction is not required, this performance standard is optional. However, implementation of Enhanced Site Design BMPs is strongly encouraged for all PDPs as a means of reducing or eliminating the need for other, more complex or costly BMPs needed to satisfy Structural Performance Standards for the remaining DCV (see below).
Examples of BMPs that can be used as Enhanced Site Design BMPs include Tree Wells (Fact Sheet SD-A), Impervious Area Dispersion (Fact Sheet SD-B), Green Roofs (Fact Sheet SD-C), Permeable Pavement (Fact Sheet SD-D) and Rain Barrels (Fact Sheet SD-E). These BMPS must be sized and constructed in accordance with applicable guidance provided in their respective Fact Sheets or as otherwise specified. DCV reductions may be determined using the DCV Worksheet B.1.1 in Appendix B or any other methodology acceptable to the City.
3. Compliance with Structural Performance Standards (Sections 2.2, 2.3, 2.4, 5; Chapters 5 and 6) Structural Performance Standards are numeric design standards for reducing or eliminating stormwater flows and pollutant loads from Priority Development Project sites. They specifically address the remaining volume of runoff within a DMA (either the DCV or a greater volume) after the application of all other site design and source control BMPs described above.
Projects that are exempt from hydromodification management requirements must only satisfy the Pollutant Control Structural Performance Standard. All other projects must satisfy both the Pollutant 2026-08-19 Item #12D Page 49 of 816
Chapter 2: Performance Standards and Concepts
2-4 2023
Control Structural Performance Standard and the Hydromodification Management Structural Performance Standard. The latter must mitigate an adjusted volume greater than the DCV.
Subject to all applicable design requirements, either standard may be fully satisfied through a variety of design approaches, including Structural BMPs (S-BMPs) and Significant Site Design BMPs (SSDBMPs). SSD-BMPs are site design BMPs designed to fully retain the DCV for the DMA (Section
5.2.3). Tree Wells (Fact Sheet SD-A), Impervious Area Dispersion (Fact Sheet SD-B), or any other SSD-BMP acceptable to the City may be used. See Appendix I for more information on sizing SSDBMPs.
4. Avoidance and Bypass of Critical Coarse Sediment (Sections 2.3.1, 6.2, & Appendix H) For many Priority Development Project sites, additional BMPs may be needed to preserve the supply of critical coarse sediment to water bodies. Any PDP that is not exempt from hydromodification management requirements must either comply with critical coarse sediment requirements or demonstrate that they do not apply.
Performance standards can be met through an integrated approach.
While performance standards are defined separately in this Manual, an overlapping set of design features can be used as part of demonstrating conformance to each standard. Further discussion of the relationship between performance standards is provided in Section 2.4.Source Control and Site Design Requirements for All
Development Projects
2.1.1 Performance Standards
MS4 Permit Provision E.3.a
MS4 Permit Provision E.3.a defines performance standards for general, source control, and site design practices that are applicable to all projects (regardless of project type or size; both Standard Projects and PDPs) when City permits are issued.
2.1.1.1 General Requirements
All projects must meet the following general requirements:
(a) Onsite BMPs must be located so as to remove pollutants from runoff prior to its discharge to any receiving waters, and as close to the source as possible; (b) Structural BMPs must not be constructed within waters of the United States (U.S.); and (c) Onsite BMPs must be designed and implemented with measures to avoid the creation of nuisance or pollution associated with vectors (e.g. mosquitos, rodents, or flies). 2026-08-19 Item #12D Page 50 of 816
Chapter 2: Performance Standards and Concepts
2-5 2023
2.1.1.2 Baseline Source Control Requirements
Baseline pollutant source control BMPs are features that must be implemented to address specific sources of pollutants.
The following source control BMPs must be implemented at all development projects where applicable and feasible:
(a) Prevention of illicit discharges into the MS4;
(b) Storm drain system stenciling or signage;
(c) Protection of outdoor material storage areas from rainfall, run-on, runoff, and wind dispersal; (d) Protection of materials stored in outdoor work areas from rainfall, run-on, runoff, and wind dispersal;
(e) Protection of trash storage areas from rainfall, run-on, runoff, and wind dispersal; and (f) Use of any additional BMPs determined to be necessary by the City to minimize pollutant generation at each project.
Further guidance is provided in Section 2.1.2 and Chapter 4.
2.1.1.3 Baseline Site Design Requirements
Baseline site design requirements are qualitative requirements that apply to the layout and design of ALL Development Project sites (Standard Projects and PDPs).
Site design performance standards define minimum requirements for how a site must incorporate LID BMPs, including the location of BMPs and the use of integrated site design practices. The following site design practices must be implemented at all Development Projects, where applicable and feasible:
(a) Maintenance or restoration of natural storage reservoirs and drainage corridors (including topographic depressions, areas of permeable soils, natural swales, and ephemeral and intermittent streams3F
4 ;
(b) Buffer zones for natural water bodies (where buffer zones are technically infeasible, require project applicant to include other buffers such as trees, access restrictions, etc.); (c) Conservation of natural areas within the project footprint including existing trees, other vegetation, and soils;
(d) Construction of streets, sidewalks, or parking lot aisles to the minimum widths necessary, provided public safety is not compromised;
(e) Minimization of the impervious footprint of the project; (f) Minimization of soil compaction to landscaped areas; (g) Disconnection of impervious surfaces through distributed pervious areas; 4 Development Projects proposing to dredge or fill materials in waters of the U.S. must obtain a Clean Water Act Section 401 Water Quality Certification. Projects proposing to dredge or fill waters of the state must obtain waste discharge requirements.
2026-08-19 Item #12D Page 51 of 816
Chapter 2: Performance Standards and Concepts
2-6 2023
(h) Landscaped or other pervious areas designed and constructed to effectively receive and infiltrate, retain and/or treat runoff from impervious areas, prior to discharging to the MS4; (i) Small collection strategies located at, or as close as possible to, the source (i.e. the point where stormwater initially meets the ground) to minimize the transport of runoff and pollutants to the MS4 and receiving waters;
(j) Use of permeable materials for projects with low traffic areas and appropriate soil conditions; (k) Landscaping with native or drought tolerant species; and (l) Harvesting and using precipitation.
A key aspect of this performance standard is that these design features must be used where applicable and feasible. Responsible implementation of this performance standard depends on evaluating applicability and feasibility. Further guidance is provided in Section 2.1.2 and Chapter 4.
Additional site design requirements may apply to PDPs.
Site design decisions may influence the ability of a PDP to meet applicable performance standards for pollutant control and hydromodification management BMPs (as defined in Section 2.2 and 2.3). For example, the layout of the site drainage and reservation of areas for BMPs relative to areas of infiltrative soils may influence the feasibility of capturing and managing stormwater to meet stormwater pollutant control and/or hydromodification management requirements. As such, the City may require additional site design practices, beyond those listed above, to be considered and documented as part of demonstrating conformance to stormwater pollutant control and hydromodification management requirements.
Appendix K (Guidance for Green Infrastructure Projects) includes County of San Diego guidance for implementing green street and other green infrastructure project features and types. Applicants are encouraged to utilize Appendix K as a basis for designing and constructing low impact design and sustainable infrastructure features for their projects.
2.1.1.4 DCV Reduction through Enhanced Site Design BMPs (Sections 2.2.2.2 & Appendix B.1)
Enhanced site design BMPs reduce or eliminate the DCV within a DMA. Using them can decrease the number or size of other, more complex or costly BMPs needed to satisfy Structural Performance Standards.
Examples of Enhanced Site Design BMPs include Tree Wells (Fact Sheet SD-A), Impervious Area Dispersion (Fact Sheet SD-B), Green Roofs (Fact Sheet SD-C), Permeable Pavement (Fact Sheet SDD), and Rain Barrels (Fact Sheet SD-E). Each BMP must be sized and constructed in accordance with applicable guidance provided in its respective Fact Sheet or as otherwise specified. DCV reductions are typically determined for larger projects using the DCV Worksheet B.1.1 in Appendix B and Worksheet J.1.1 in Appendix J. However, other worksheets, tables, calculators, or methods acceptable to the City may also be used. See section 2.2.2.2 for additional guidance on DCV calculation, and Appendices B.1 and J.1. for specific options and methodologies for achieving DCV reductions.
2026-08-19 Item #12D Page 52 of 816
Chapter 2: Performance Standards and Concepts
2-7 2023
2.1.2 Concepts and References
Land development tends to increase the amount of pollutants in stormwater runoff.
Land development generally alters the natural conditions of the land by removing vegetative cover, compacting soil, and/or placement of concrete, asphalt, or other impervious surfaces. These impervious surfaces facilitate entrainment of urban pollutants in stormwater runoff (such as pesticides, petroleum hydrocarbons, heavy metals, and pathogens) that are otherwise not generally found in high concentrations in the runoff from the natural environment. Pollutants that accumulate on impervious surfaces and actively landscaped pervious surfaces may contribute to elevated levels of pollutants in runoff relative to the natural condition.
Land development also impacts site hydrology.
Impervious surfaces greatly affect the natural hydrology of the land because they do not allow natural infiltration, retention, evapotranspiration and treatment of stormwater runoff to take place. Instead, stormwater runoff from impervious surfaces is typically and has traditionally been directed through pipes, curbs, gutters, and other hardscape into receiving waters, with little treatment, at significantly increased volumes and accelerated flow rates over what would occur naturally. The increased pollutant loads, stormwater volume, discharge rates and velocities, and discharge durations from the MS4 adversely impact stream habitat by causing accelerated, unnatural erosion and scouring within creek beds and banks. Compaction of pervious areas can have a similar effect to impervious surfaces on natural hydrology.
Site Design LID involves attempting to maintain or restore the predevelopment hydrologic regime.
LID is a comprehensive land planning and engineering design approach with a goal of maintaining and enhancing the pre-development hydrologic regime of urban and developing watersheds. LID design seeks to control stormwater at the source, using small-scale integrated site design and management practices to mimic the natural hydrology of a site, retain stormwater runoff by minimizing soil compaction and impervious surfaces, and disconnecting stormwater runoff from conveyances to the storm drain system. Site Design LID BMPs may utilize interception, storage, evaporation, evapotranspiration, infiltration, and filtration processes to retain and/or treat pollutants in stormwater before it is discharged from a site. Examples of Site Design LID BMPs include using permeable pavements, rain gardens, rain barrels, grassy swales, soil amendments, and native plants.
Site design must be considered early in the design process.
Site designs tend to be more flexible in the early stages of project planning than later on when plans become more detailed. Because of the importance of the location of BMPs, site design should be considered as early as the planning/tentative design stage. Site design is critical for feasibility of storm water pollutant control BMPs (Section 2.2) as well as coarse sediment supply considerations associated with hydromodification management (introduced in Section 2.3).
Source control and site design (LID) requirements help avoid impacts by controlling pollutant sources and changes in hydrology.
Source control and site design practices prescribed by the MS4 Permit are the minimum management practices, control techniques and system, design and engineering methods to be included in the 2026-08-19 Item #12D Page 53 of 816
Chapter 2: Performance Standards and Concepts
2-8 2023
planning procedures to reduce the discharge of pollutants from development projects, regardless of size or purpose of the development. In contrast to stormwater pollutant control BMPs and hydromodification control BMPs which are intended to mitigate impacts, source control and site design BMPs are intended to avoid or minimize these impacts by managing site hydrology, providing treatment features integrated within the site, and reducing or preventing the introduction of pollutants from specific sources. Implementation of site design BMPs will result in reduction in stormwater runoff generated by the site. Methods to estimate effective runoff coefficients and the stormwater runoff produced by the site after site design BMPs are implemented are presented in Appendix B.2.
This methodology is applicable for PDPs that are required to estimate runoff produced from the site with site design BMPs implemented so that they can appropriately size stormwater pollutant control BMPs and hydromodification control BMPs.
The location of BMPs matters.
The site design BMPs listed in the performance standard include practices that either prevent runoff from occurring or manage runoff as close to the source as possible. This helps create a more hydrologically effective site and reduces the requirements that pollutant control and hydromodification control BMPs must meet, where required. Additionally, because sites may have spatially-variable conditions, the locations reserved for structural BMPs within the site can influence whether these BMPs can feasibly retain, treat, and/or detain stormwater to comply with structural pollutant control and hydromodification control requirements, where applicable. Finally, the performance standard specifies that onsite BMPs must remove pollutants from runoff prior to discharge to any receiving waters or the MS4, be located/constructed as close to the pollutant generating source as possible and must not be constructed within waters of the U.S.
The selection of BMPs also matters.
The lists of source control and site design BMPs specified in the performance standard must be used “where applicable and feasible.” This is an important concept – BMPs should be selected to meet the R9-2013-0001 permit requirements and are feasible with consideration of site conditions and project type. By using BMPs that are applicable and feasible, the project can achieve benefits of these practices, while not incurring unnecessary expenses (associated with using practices that do not apply or would not be effective) or creating undesirable conditions (for example, infiltration-related issues, vector concerns including mosquito breeding, etc.).
Methods to select and design BMPs and demonstrate compliance with source control and site design requirements are presented in Chapter 4 of this Manual. Source control and site design fact sheets are also provided in Appendix E.
2.2Storm Water Pollutant Control Requirements for
PDPs
2.2.1 Storm Water Pollutant Control Performance Standard MS4 Permit Provision E.3.c.(1)
Per MS4 Permit Provision E.3.c.(1), Storm Water Pollutant Control BMPs for PDPs must meet the following performance standards:
2026-08-19 Item #12D Page 54 of 816
Chapter 2: Performance Standards and Concepts
2-9 2023
(a) Each PDP shall implement BMPs that are designed to retain (i.e. intercept, store, infiltrate, evaporate, and evapotranspire) onsite the pollutants contained in the volume of stormwater runoff produced from a 24-hour, 85th percentile storm event (Design Capture Volume (DCV)). The 24-hour, 85th percentile storm event shall be based on Figure B.1-1 in Appendix B or an approved site-specific rainfall analysis.
(i) If it is not technically feasible to implement retention BMPs for the full DCV onsite for a PDP, then the PDP shall utilize biofiltration BMPs or approved equivalent proprietary biofiltration systems for the remaining volume not reliably retained. Biofiltration BMPs must be designed as described in Appendix F to have an appropriate hydraulic loading rate to maximize stormwater retention and pollutant removal, as well as to prevent erosion, scour, and channeling within the BMP, and must be sized to:
[a]. Biofiltration BMPs must be designed as described in Appendix F to have an appropriate hydraulic loading rate to maximize storm water retention and pollutant removal, as well as to prevent erosion, scour, and channeling within the BMP, and must be sized to:
1. Treat 1.5 times the DCV not reliably retained onsite, OR
2. Treat the DCV not reliably retained onsite with a flow-thru design that has a total volume, including pore spaces and pre-filter detention volume, sized to hold at least 0.75 times the portion of the DCV not reliably retained onsite.
[b]. Approved equivalent proprietary biofiltration systems use a combination of treatment devices and additional site design BMPs that, as a system, have an equal or greater effectiveness than biofiltration BMPs. While these systems, unlike biofiltration BMPs, do not provide the full required amounts of both treatment and retention in the same device or site feature, because they are equally effective to biofiltration they meet the MEP standard as defined in Attachment C of the MS4 Permit. Approved equivalent compact proprietary biofiltrations systems must be designed as described below:
1. Demonstrate that the BMP meets applicable effectiveness certifications, e.g., Washington (State) Technology Acceptance Protocol-Ecology (TAPE), and the proposed use of the BMP is in accordance with criteria in the certification (e.g., treatment flow rate), as described in Appendix F.2.1, AND
2. Treat the DCV no reliably retained onsite with a flow-based sizing in accordance with Appendix F.2.2, AND
3. Incorporate additional site design BMPs as necessary to achieve stormwater retention equivalent to what would have been achieved using biofiltration BMPs as described earlier in this section, and as described in Appendices B and F.
(b) The City of Encinitas does not have an Alternative Compliance Program. Therefore, an applicant of a PDP may not participate in an alternative compliance program.
Demonstrations of feasibility findings and calculations to justify BMP selection and design must be provided by the project applicant in the SWQMP to the satisfaction of the City. Methodology to 2026-08-19 Item #12D Page 55 of 816
Chapter 2: Performance Standards and Concepts
2-10 2023
demonstrate compliance with the performance standards, described above, applicable to stormwater pollutant control BMPs for PDPs is detailed in Chapter 5.
2.2.2 Concepts and References
Retention BMPs are the most effective type of BMPs to reduce pollutants discharging to MS4s when they are sited and designed appropriately.
Retention of the required DCV will achieve 100 percent pollutant removal efficiency (i.e. prevent pollutants from discharging directly to the MS4). Thus, retention of as much stormwater onsite as technically feasible is the most effective way to reduce pollutants in stormwater discharges to, and consequently from the MS4, and remove pollutants in stormwater discharges from a site to the MEP.
However, in order to accrue these benefits, retention BMPs must be technically feasible and suitable for the project. Retention BMPs that fail prematurely, under-perform, or result in unintended consequences as a result of improper selection or siting may achieve performance that is inferior to other BMP types while posing other issues for property owners and the City. Therefore, this manual provides criteria for evaluating feasibility and provides options for other types of BMPs to be used if retention is not technically feasible.
Biofiltration BMPs or approved equivalent compact proprietary biofiltrations systems can be sized to achieve approximately the same pollutant removal as retention BMPs.
In the case, where the entire DCV cannot be retained onsite because it is not technically feasible, PDPs are required to use biofiltration BMPs with specific sizing and design criteria listed in Appendices B and F or approved equivalent compact proprietary biofiltration systems. Sizing and design criteria for approved equivalent compact proprietary biofiltration systems are also included in Appendices B and F, and specific details included in Appendix F.2. These sizing and design criteria are intended to provide a level of long term pollutant removal that is reasonably equivalent to retention of the DCV.
Flow-thru treatment BMPs are required to treat the pollutant loads in the DCV not retained or biofiltered onsite to the MEP.
If the pollutant loads from the full DCV cannot feasibly be retained or biofiltered onsite, then PDPs are required to implement flow-thru treatment control BMPs to remove the pollutants to the MEP for the portion of the DCV that could not be feasibly retained or biofiltered. Flow-thru treatment BMPs may only be implemented to address onsite storm water pollutant control requirements if coupled with an offsite alternative compliance project that mitigates for the portion of the pollutant load in the DCV not retained or biofiltered onsite.
Offsite Alternative Compliance Program may be available.
The MS4 Permit allows the City the discretion to grant PDPs permission to utilize an offsite alternative compliance program for meeting the pollutant control performance standard. Onsite and offsite mitigation is required when a PDP is allowed to use an offsite alternative compliance program. The specific parameters of an offsite alternative compliance program will be specific to each jurisdiction if one is available (Refer to Section 1.8 and Appendix J).
Methods to design and demonstrate compliance with stormwater pollutant control BMPs are 2026-08-19 Item #12D Page 56 of 816
Chapter 2: Performance Standards and Concepts
2-11 2023
presented in Chapter 5 of this Manual. Definitions and concepts that should be understood when sizing stormwater pollutant control BMPs to be in compliance with the performance standards are explained below:Best Management Practices
To minimize confusion, this Manual considers all references to “facilities,” “features,” or “controls” to be incorporated into development projects as BMPs.
2.2.2.2 DCV
The MS4 Permit requires pollutants be addressed for the runoff from the 24-hour 85th percentile storm event (“DCV”) as the design standard to which PDPs must comply.
The 85th percentile, 24-hour 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, the following steps would be followed:
• Obtain representative precipitation data, preferably no less than 30-years period if possible. • Divide the recorded precipitation into 24-hour precipitation totals. • Filter out events with no measurable precipitation (less than 0.01 inches of precipitation). • Of the remaining events, calculate the 85th percentile value (i.e. 15 percent of the storms would be greater than the number determined to be the 85th percentile, 24-hour storm).
The 85th percentile, 24-hour storm event depth is then used in hydrologic calculations to calculate the DCV for sizing storm water pollutant control BMPs. An exhibit showing the 85th percentile, 24-hour storm depth in the City of Encinitas is included in Appendix B.1.1. Guidance to estimate the DCV is presented in Appendix B.1.
See also Section 2.1.1.4 for description of options for reducing the DCV.
2.2.2.3 Implementation of Storm Water Pollutant Control BMPs The MS4 Permit requires that the PDP applicants proposing to meet the performance standards onsite implement storm water pollutant control BMPs in the order listed below. That is, the PDP applicant first needs to implement all feasible onsite retention BMPs needed to meet the storm water pollutant control BMP requirements prior to installing onsite biofiltration BMPs, and then onsite biofiltration BMPs prior to installing onsite flow-thru treatment control BMPs.
PDP applicants may be allowed to participate in an offsite alternative compliance program. Refer to Section 1.8 for additional guidance.
Retention BMPs: Structural measures that provide retention (i.e. intercept, store, infiltrate, evaporate and evapotranspire) of storm water as part of pollutant control strategy. Examples include infiltration BMPs and cisterns, bioretention BMPs and biofiltration with partial retention BMPs.
Biofiltration BMPs: Structural measures that provide biofiltration of storm water as part of the pollutant control strategy.
Approved equivalent compact proprietary biofiltration systems: Approved equivalent compact 2026-08-19 Item #12D Page 57 of 816
Chapter 2: Performance Standards and Concepts
2-12 2023
proprietary biofiltration systems that use a combination of treatment devices and additional site design BMPs that, as a system, have an equal or greater effectiveness than biofiltration BMPs. While theses systems, unlike biofiltration BMPs, do not provide the full required amounts of both treatment and retention in the same device or site feature, because they are equally effective to biofiltration they meet the MEP standard as defined in Attachment C of the MS4 Permit. The treatment devices in an approved equivalent compact proprietary biofiltration system must meet the requirements in Appendices B and F.
Flow-thru treatment control BMPs: Structural measures that provide flow-thru treatment as part of the pollutant control strategy. Examples include vegetated swales and media filters.
2.2.2.4 Technical Feasibility
MS4 Permit Requirement E.3.c.(5)
Analysis of technical feasibility is necessary to select the appropriate BMPs for a site.
PDPs are required to implement pollutant control BMPs in the order of priority in Section 2.2.2.3 based on determinations of technical feasibility. In order to assist the project applicant in selecting BMPs, this Manual includes a defined process for evaluating feasibility. Conceptually, the feasibility criteria contained in this Manual are intended to:
• Promote reliable and effective long term operations of BMPs by providing a BMP selection process that eliminates the use of BMPs that are not suitable for site conditions, project type or other factors;
• Minimize significant risks to property, human health, and/or environmental degradation (e.g. geotechnical stability, groundwater quality) as a result of selection of BMPs that are undesirable for a given site; and
• Describe circumstances under which regional and watershed-based strategies, as part of an approved WMAA and an offsite alternative compliance program developed by the jurisdiction where the project resides, may be selected.
Specific guidance related to geotechnical investigation guidelines for feasibility of stormwater infiltration and groundwater quality and water balance factors is provided in Appendices B and D, respectively.
2.2.2.5 Biofiltration BMPs
The MS4 Permit requires Biofiltration BMPs be designed to have an appropriate hydraulic loading rate to maximize stormwater retention and pollutant removal, as well as to prevent erosion, scour, and channeling within the BMP. Appendix F of this Manual has guidance for hydraulic loading rates and other biofiltration design criteria to meet these required goals. Appendix F also has a checklist that will need to be completed by the project SWQMP preparer during plan submittal. Guidance for sizing Biofiltration BMPs is included in Chapter 5 and Appendices B and F. 2026-08-19 Item #12D Page 58 of 816
Chapter 2: Performance Standards and Concepts
2-13 2023
2.2.2.6 Flow-thru Treatment Control BMPs (for use with Offsite Alternative Compliance5
)
MS4 Permit Requirement E.3.d.2-3
The MS4 Permit requires that the flow-thru treatment control BMP selected by the PDP applicant be ranked with high or medium pollutant removal efficiency for the most significant pollutant of concern.
Steps to select the flow-thru treatment control BMP include:
• Step 1: Identify the pollutant(s) of concern by considering the following at a minimum a) Receiving water quality; b) Highest priority water quality conditions identified in the Watershed Management Areas Water Quality Improvement Plan; c) Land use type of the project and pollutants associated with that land use type and d) Pollutants expected to be present onsite.
• Step 2: Identify the most significant pollutant of concern. A project could have multiple most significant pollutants of concerns and must include the highest priority water quality condition identified in the watershed WQIP and pollutants expected to be presented onsite/from land use.
• Step 3: Effectiveness of the flow-thru treatment control BMP for the identified most significant pollutant of concern.
Methodology for sizing flow-thru treatment control BMPs and the resources required to identify the pollutant(s) of concern and effectiveness of flow-thru treatment control BMPs are included in Chapter 5 and Appendix J.5.
2.3 Hydromodification Management Requirements for
PDPs
2.3.1 Hydromodification Management Performance Standards MS4 Permit Provision E.3.c.(2)
This section describes performance standards for hydromodification management, including flow control of post-project storm water runoff and protection of critical sediment yield areas, that must be met by all PDPs unless exempt from hydromodification management requirements per Section 1.6 of this Manual. Each PDP must implement onsite BMPs to manage hydromodification that may be caused by storm water runoff discharged from a project as follows:
(a) Post-project runoff conditions (flow rates and durations) must not exceed pre-development runoff conditions by more than 10 percent (for the range of flows that result in increased potential for erosion, or degraded instream habitat downstream of PDPs). (i) In evaluating the range of flows that results in increased potential for erosion of natural (non-hardened) channels, the lower boundary must correspond with the critical channel 5 The City of Encinitas does not currently have an Alternative Compliance Program. 2026-08-19 Item #12D Page 59 of 816
Chapter 2: Performance Standards and Concepts
2-14 2023
flow that produces the critical shear stress that initiates channel bed movement or that erodes the toe of channel banks.
(b) Each PDP must avoid and allow bypass of critical sediment yield areas known to the City or identified by the optional WMAA pursuant to Provision B.3.b.(4) [of the MS4 Permit], or implement measures that allow critical coarse sediment to be discharged to receiving waters, such that there is no net impact to the receiving water. Refer to Section 6.2 and Appendix H for additional guidance.
(c) A PDP may be allowed to utilize offsite alternative compliance under Provision E.3.c.(3) [of the MS4 Permit] in lieu of complying with the performance requirements of Provision E.3.c.(2)(a). The PDP must mitigate for the post-project runoff conditions not fully managed onsite if Provision E.3.c.(3) is utilized. Refer to Section 1.8 and Appendix J for additional guidance.
Hydromodification management requirements apply to both new development and redevelopment PDPs, except those that are exempt based on discharging to downstream channels or water bodies that are not subject to erosion, as defined in either the MS4 Permit (Provision E.3.c.(2).(d)) or the WMAA for the watershed in which the project resides. Exemptions from hydromodification management requirements are described in Section 1.6 of this Manual.
For undisturbed sites, the existing condition should be taken to be the pre-development runoff condition. For redevelopment PDPs or sites that have been previously disturbed, pre-development runoff conditions must be approximated by applying the parameters of a pervious area rather than an impervious area to the existing site, using the existing onsite grade and assuming the infiltration characteristics of the underlying soil.
For San Diego area watersheds, the range of flows that result in increased potential for erosion or degraded instream habitat downstream of PDPs and the critical channel flow must be based on the "Final Hydromodification Management Plan Prepared for County of San Diego, California March 2011" (herein, "March 2011 Final HMP"). For PDPs subject to hydromodification management requirements, the range of flows to control depends on the erosion susceptibility of the receiving stream and must be:
• 0.1Q2 to Q10 for streams with high susceptibility to erosion (this is the default range of flows to control when a stream susceptibility study has not been prepared); • 0.3Q2 to Q10 for streams with medium susceptibility to erosion and which has a stream susceptibility study prepared and approved by the City; or • 0.5Q2 to Q10 for streams with low susceptibility to erosion and which has a stream susceptibility study prepared and approved by the City.
Tools for assessing stream susceptibility to erosion have been developed by Southern California Coastal Water Research Project (SCCWRP). The tools are presented in the March 2011 Final HMP and also available through SCCWRP's website. If a PDP applicant intends to select the 0.3Q2 or 0.5Q2 threshold, the SCCWRP screening tool must be completed and submitted with other project documentation.
The March 2011 Final HMP does not provide criteria for protection of critical sediment yield areas.
The standard as presented in the MS4 Permit and shown above is: avoid and allow bypass of critical 2026-08-19 Item #12D Page 60 of 816
Chapter 2: Performance Standards and Concepts
2-15 2023
sediment yield areas or implement measures that allow critical coarse sediment to be discharged to receiving waters, such that there is no net impact to the receiving water.
Methods to demonstrate compliance with hydromodification management requirements, including protection of critical coarse sediment yield areas and flow control for post-project runoff from the project site, are presented in Chapter 6 of this Manual. Hydromodification management concepts, theories, and references are described below.
2.3.2 Hydromodification Management Concepts and References
2.3.2.1 What is Hydromodification?
The MS4 Permit defines hydromodification as the change in the natural watershed hydrologic processes and runoff characteristics (i.e. interception, infiltration, overland flow, 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, such as stream channelization, concrete lining, installation of dams and water impoundments, and excessive streambank and shoreline erosion are also considered hydromodification, due to their disruption of natural watershed hydrologic processes.
Typical impacts to natural watershed hydrologic processes and runoff characteristics resulting from new development and redevelopment include:
• Decreased interception and infiltration of rainfall at the project site due to removal of native vegetation, compaction of pervious area soils, and the addition of impervious area; • Increased connectivity and efficiency of drainage systems serving the project site, including concentration of project-site runoff to discrete outfalls; • Increased runoff volume, flow rate, and duration from the project site due to addition of impervious area, removal of native vegetation, and compaction of pervious area soils; • Reduction of critical coarse sediment supply from the project site to downstream natural systems (e.g. streams) due to stabilization of developed areas, stabilization of streams, and addition of basins that trap sediment (either by design as a permanent desilting basin or stormwater quality treatment basin that settles sediment, or incidentally as a peak flow management basin); and
• Interruption of critical coarse sediment transport in streams due to stream crossings such as culverts or ford crossings that incidentally slow stream flow and allow coarse sediment to settle upstream of the crossing.
Any of these changes can result in increased potential for erosion, or degraded instream habitat downstream of PDPs. The changes to delivery of runoff to streams typically modify the timing, frequency, magnitude, and duration of both storm flows and baseflow. Changes to delivery of coarse sediment and transport of coarse sediment result in increased transport capacity and the potential for adverse channel erosion.
Note that this Manual is intended for design of permanent, post-construction BMPs, therefore this discussion is focused on the permanent, post-construction effects of development. The process of construction also has impacts, such as an increase in sediment load produced from surfaces exposed 2026-08-19 Item #12D Page 61 of 816
Chapter 2: Performance Standards and Concepts
2-16 2023
by vegetation removal and grading, which is often deposited within stream channels, initiating aggradation and/or channel widening. Temporary construction BMPs to mitigate the sediment delivery are outside the purview of this Manual.
Channel erosion resulting from PDP stormwater discharge can begin at the point where runoff is discharged to natural systems, regardless of the distance from the PDP to the natural system. It could also begin some distance downstream from the actual discharge point if the stream condition is stable at the discharge point but more susceptible to erosion at a downstream location. The March 2011 HMP defines a domain of analysis for evaluation of stream susceptibility to erosion from PDP stormwater discharge.
2.3.2.2 How Can Hydromodification be Controlled?
In the big picture, watershed-scale solutions are necessary to address hydromodification. Factors causing hydromodification are watershed-wide, and all of San Diego's major watersheds include some degree of legacy hydromodification effects from existing development and existing channel modifications, which cannot be reversed by onsite measures implemented at new development and redevelopment projects alone. As recommended by SCCWRP in Technical Report 667, "Hydromodification Assessment and Management in California," dated April 2012, "management strategies should be tailored to meet the objectives, desired future conditions, and constraints of the specific channel reach being addressed," and "potential objectives for specific stream reaches may include: protect, restore, or manage as a new channel form." Development of such management strategies and objectives for San Diego watersheds will evolve over successive MS4 Permit cycles. The current MS4 Permit requires the Copermittees to prepare WQIPs for all Watershed Management Areas within the San Diego Region. The WQIPs may include WMAAs which would assess watershed-wide hydrologic processes. These documents may be used to develop watershed-specific requirements for structural BMP implementation, including watershedscale hydromodification management strategies.
This Manual addresses development and redevelopment project-level hydromodification management measures currently required for PDPs by the MS4 Permit. Until optional watershed-specific performance recommendations or offsite alternative compliance programs are developed, hydromodification management strategies for new development and redevelopment projects will consist of onsite measures designed to meet the performance requirements of Provisions E.3.c.(2).(a) and (b) of the MS4 Permit shown in Section 2.3.1. While development project-level measures alone will not reverse hydromodification of major streams, onsite measures are a necessary component of a watershed-wide solution, particularly while watershed-wide management strategies are still being developed. Also, development project-level measures are necessary to protect a project's specific stormwater discharge points, which are typically discharging in smaller tributaries not studied in detail in larger watershed studies. Typical measures for development projects include:
• Protecting critical sediment yield areas by designing the project to avoid and allow bypass of them or implementing measures that would allow coarse sediment to be discharged to receiving waters, such that the natural sediment supply is unaffected by the project; • Using site design/LID measures to minimize impervious areas onsite and reduce post-project runoff; and
2026-08-19 Item #12D Page 62 of 816
Chapter 2: Performance Standards and Concepts
2-17 2023
• Providing structural BMPs designed using continuous simulation hydrologic modeling to provide flow control of post-project runoff (e.g. BMPs that store post-project runoff and infiltrate, evaporate, harvest and use, or discharge excess runoff at a rate below the critical flow rate).
Structural BMPs for hydromodification management provide volume to control a range of flows from a fraction of Q2 to Q10. The volume determined for hydromodification management is different from the DCV for pollutant control. Methodology to demonstrate compliance with hydromodification management requirements are presented in Chapter 6 of this Manual. See Section 2.4 regarding the relationship between pollutant control and hydromodification management performance standards.
2.3.3 Avoidance and Bypass of Critical Coarse Sediment
For many Priority Development Project sites, additional BMPs may be needed to preserve the supply of critical coarse sediment to water bodies. Any PDP that is not fully exempt from hydromodification management requirements must either comply with critical coarse sediment requirements or demonstrate that they do not apply. Documentation of applicability and compliance options is required in SWQMP forms and corresponding attachments. See Section 6.2 and Appendix H for additional description of these requirements.
2.4Relationship between Performance Standards
An integrated approach can provide significant cost savings by utilizing design features that meet multiple standards.
Site design/LID, stormwater pollutant control, and hydromodification management are separate requirements to be addressed in development project design. Each has its own purpose and each has separate performance standards that must be met. However, effective project planning involves understanding the ways in which these standards are related and how single suites of design features can meet more than one standard.
Site design features (aka LID) can be effective at reducing the runoff to downstream BMPs.
Site design BMPs serve the purpose of minimizing impervious areas and therefore reducing postproject runoff, and reducing the potential transport of pollutants offsite and reducing the potential for downstream erosion caused by increased flow rates and durations. By reducing post-project runoff through, site design BMPs, the amount of runoff that must be managed for pollutant control and hydromodification flow control can be reduced.
Single structural BMPs, particularly retention BMPs, can meet or contribute to both pollutant control and hydromodification management objectives.
The objective of structural BMPs for pollutant control is to reduce offsite transport of pollutants, and the objective of structural BMPs for hydromodification management is to control flow rates and durations for control of downstream erosion. In either case, the most effective structural BMP to meet the objective are BMPs that are based on retention of stormwater runoff where feasible. Both stormwater pollutant control and flow control for hydromodification management can be achieved within the same structural BMP(s). However, demonstrating that the separate performance requirements for pollutant control and hydromodification management are met must be shown 2026-08-19 Item #12D Page 63 of 816
Chapter 2: Performance Standards and Concepts
2-18 2023
separately.
The design process should start with an assessment of the feasibility to retain or partially retain the DCV for pollutant control, then determine what kind of BMPs will be used for pollutant control and hydromodification management.
A typical design process for a single structural BMP to meet two separate performance standards at once involves (1) initiating the structural BMP design based on the performance standard that is expected to require the largest volume of stormwater to be retained, (2) checking whether the initial design incidentally meets the second performance standard, and (3) adjusting the design as necessary until it can be demonstrated that both performance standards are met. 2026-08-19 Item #12D Page 64 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L 3-1 2023
Chapter
3 3 Development Project Planning and
Design
Compliance with source control/site design, pollutant control, and hydromodification management BMPs, as applicable, requires coordination of site, landscape, and project stormwater plans. It also involves provisions for operation and maintenance of structural BMPs. This chapter outlines a stepwise, systematic approach (Figure 3-1) to preparing a comprehensive stormwater management design for Standard, Basic and Exempt Projects and PDPs.
STEP 1:
Coordinate Between Disciplines
Refer to Section 3.1
Purpose: Engage and coordinate with owner and other project disciplines (e.g. architect, engineer) early in the design and throughout the design process to support appropriate project decisions.
STEP 2:
Gather Project Site Information
Refer to Section 3.2
Purpose: Gather information necessary to inform overall storm water planning process and specific aspects of BMP selection; determine the applicable storm water requirements for the project.
STEP 3:
Develop Conceptual Site Layout and
Storm Water Control Strategies
Refer to Section 3.3
Purpose: Use the information obtained in Step 2 to inform the preliminary site design and storm water management strategy. The scope of this step varies depending on whether the project is a Standard Project or a PDP.
STEP 4:
Develop Complete Storm Water
Management Design
Refer to Section 3.4
Purpose: Develop the complete storm water management design by incorporating the site design and storm water management strategies identified in Step 3 and conducting design level analyses. Integrate the storm water design with the site plan and other infrastructure plans.
FIGURE 3-1. Approach for Developing a Comprehensive Storm Water Management Design Use of this step-wise approach is encouraged and has a number of advantages. First, it helps ensure that applicable requirements and design goals are identified early in the planning process. Second, it helps ensure that key data about the site, watershed, and project are collected at the appropriate time in the project development process, and the analyses are suited to the decisions that need to be made at each phase. Third, taking a systematic approach helps identify opportunities for retention of 2026-08-19 Item #12D Page 65 of 816
Chapter 3: Development Project Planning and Design
3-2 2023
stormwater that may not be identified in a less systematic process. Finally, a systematic approach helps ensure that constraints and unintended consequences are considered and used to inform BMP selection, design, and related project decisions.
3.1 Coordination Between Disciplines
Stormwater management design will affect the site layout and should therefore be coordinated among the project team as necessary from the start. The following list describes entities/disciplines that are frequently involved with stormwater management design and potential roles that these entities/disciplines may play.
Owner:
• Engage the appropriate disciplines needed for the project and facilitate exchange of information between disciplines.
• Identify who will be responsible for long term O&M of stormwater management features and initiate maintenance agreements when applicable.
• Ensure that whole lifecycle costs are considered in the selection and design of stormwater management features and a source of funding is provided for long-term maintenance. • Identify the party responsible to inspect structural BMPs at each significant construction stage and at completion in order to provide certification of structural BMPs following construction.
Planner:
• Communicate overall project planning criteria to the team, such as planned development density, parking requirements, project-specific planning conditions, conditions of approval from prior entitlement actions (e.g. CEQA, 401 certifications) etc., and locations of open space and conservation easements, and environmentally sensitive areas that are protected from disturbance.
• Consider location of stormwater facilities early in the conceptual site layout process. • Assist in developing the site plan.
Architect:
• Participate in siting and design (architectural elements) of stormwater BMPs.
Civil Engineer:
• Determine stormwater requirements applicable to the site (e.g. Standard, Basic, or Exempt Project or PDP).
• Obtain site-specific information (e.g. watershed information, infiltration rates) and develop viable stormwater management options.
• Reconcile stormwater management requirements with other site requirements (e.g. fire access, Americans with Disabilities Act accessibility, parking, open space). • Develop preliminary and final design documents.
• Select and design BMPs; conduct and document associated analyses; prepare BMP design 2026-08-19 Item #12D Page 66 of 816
Chapter 3: Development Project Planning and Design
3-3 2023
sheets, details, and specifications.
• Prepare project SWQMP submittals.
Landscape Architect and/or Horticulturist/Agronomist:
• Select appropriate plants for vegetated stormwater features and prepare planting plans. • Develop specifications for planting, vegetation establishment, and maintenance. • Assist in developing irrigation plans/rates to minimize water application and nonstormwater runoff from the project site.
Geotechnical Engineer
• Assist in preliminary infiltration feasibility screening of the site to help inform project layout and initial BMP selection, including characterizing soil, groundwater, geotechnical hazards, and any other factors, as applicable for the site.
• Conduct detailed analyses at proposed infiltration BMP locations to confirm or revise feasibility findings and provide design infiltration rates.
Geomorphologist and/or Geologist
• Provide specialized services, as needed, related to sediment source assessment and/or channel stability or sensitivity assessment.
3.2 Gathering Project Site Information
In order to make decisions related to selection and design of stormwater management BMPs, it is necessary to gather relevant project site information. This could include physical site information, proposed uses of the site, whether the project is a Standard, Basic, or Exempt Project or a PDP, proposed stormwater discharge locations, potential/anticipated stormwater pollutants based on the proposed uses of the site, receiving water sensitivity to pollutants and susceptibility to erosion, hydromodification management requirements, and other site requirements and constraints.
The amount and type of information that should be collected depends whether the project is a Standard, Basic or Exempt Project, a PDP subject to all requirements, or a PDP with only pollutant control requirements. Refer to Figure 1-1 in Chapter 1 to identify the project type.
Information should only be gathered to the extent necessary to inform the stormwater management design. In some cases, it is not necessary to conduct site specific analyses to precisely characterize conditions. For example, if depth to groundwater is known to be approximately 100 feet based on regional surveys, it is not necessary to also conduct site specific assessment of depth to groundwater to determine whether it is actually 90 feet or 110 feet on the project site. The difference between these values would not influence the stormwater management design. In other cases, some information will not be applicable. For example, on an existing development site, there may be no natural hydrologic features remaining, therefore these features do not need to be characterized. The lack of natural hydrologic features can be simply noted without further effort required.
Checklists (in Appendix J) and submittal templates (in Appendix A) are provided to facilitate gathering information about the project site for BMP selection and design. As part of planning for site 2026-08-19 Item #12D Page 67 of 816
Chapter 3: Development Project Planning and Design
3-4 2023
investigation, it is helpful to review the subsequent steps (Section 3.3 and 3.4) to gain familiarity with how the site information will be used in making decisions about site layout and stormwater BMP selection and design. This can help prioritize the data that are collected.
3.3 Developing Conceptual Site Layout and Storm
Water Control Strategies
Once preliminary site information has been obtained, it is essential to identify potential locations for stormwater management features at a conceptual level during the site planning phase. Preliminary design of permanent stormwater BMPs is partially influenced by whether the project is a Standard Project or a PDP. Table 3-1 presents the applicability of different subsections in this chapter based on project type and must be used to determine which requirements apply to a given project.
TABLE 3-3-1. Applicability of Section 3.3 Sub-sections for Different Project Types *Shall provide BMPs based on Section 1.4.3.1
3.3.1 Preliminary Design Steps for All Development Projects All projects must incorporate source control and site design BMPs. The following systematic approach outlines these site planning considerations for all development projects:
1 Review Chapter 4 of this manual to become familiar with the menu of source control and site design practices that are required.
2 Review the preliminary site information gathered in Section 3.2, specifically related to:
a. Natural hydrologic features that can be preserved and/or protected; b. Soil information;
c. General drainage patterns (i.e. general topography, points of connection to the storm drain or receiving water);
d. Pollutant sources that require source controls; and
e. Information gathered and summarized in the Site Information Checklist for Standard, Basic and Exempt Projects (Appendix J-3A).
Project Type Section 3.3.1 Section 3.3.2 Section 3.3.3 Section 3.3.4 Basic and Exempt
Projects*
NA NA NA
Standard Project NA NA NA *
PDP with only Pollutant
Control Requirements NA
PDP with Pollutant and
Hydromodification
Management Requirements
2026-08-19 Item #12D Page 68 of 816
Chapter 3: Development Project Planning and Design
3-5 2023
3 Create opportunities for source control and site design BMPs by developing an overall conceptual site layout that allocates space for site design BMPs and promotes drainage patterns that are effective for hydrologic control and pollutant source control. For example:
a. Locate pervious areas down gradient from buildings where possible to allow for dispersion.
b. Identify parts of the project that could be drained via overland vegetated conveyance rather than piped connections.
c. Develop traffic circulation patterns that are compatible with minimizing street widths.
4 As part of Section 3.4, refine the selection and placement of source control and site design BMPs and incorporate them into project plans. Compliance with site design and source control requirements shall be documented as described in Chapter 4.
3.3.2 Evaluation of Critical Coarse Sediment Yield Areas For PDPs that are required to meet hydromodification management requirements, evaluate whether critical coarse sediment yield areas exist within or upstream of the project site. Identification of critical coarse sediment yield areas is discussed in Chapter 6 of this manual, additional guidance on identification and protection of critical coarse sediment yield areas is provided in Appendix H.
Conceptual layout of the project site must consider the following items:
a. Have critical coarse sediment areas been identified within the project site? Does the proposed project impact these onsite critical coarse sediment areas? What measures are necessary to avoid impacts to these areas? What measures are necessary to convey critical coarse sediment from these areas through the site? b. Have critical coarse sediment areas been identified upstream of the project site? Does the proposed project impact upstream critical coarse sediment areas? What measures are necessary to avoid impacts to these areas or convey critical coarse sediment from these areas through the site?
c. If impacts to onsite and offsite critical course sediment areas are not avoided, what mitigation practices will be implemented to ensure no net impact to the receiving water?
3.3.3 Drainage Management Areas
Drainage management areas (DMAs) provide an important framework for feasibility screening, BMP prioritization, and stormwater management system configuration. BMP selection, sizing, and feasibility determinations must be made at the DMA level; therefore delineation of DMAs is highly recommended at the conceptual site planning phase and is mandatory for completing the project design and meeting submittal requirements. This section provides guidance on delineating DMAs that is intended to be used as part of Section 3.3 and 3.4.
DMAs are defined based on the proposed drainage patterns of the site and the BMPs to which they drain. On site DMAs should not overlap and should be similar with respect to BMP opportunities and feasibility constraints. More than one DMA can drain to the same BMP, or to another DMA.
However, because the BMP sizes are determined by the runoff from the DMA, a single DMA may not drain to more than one BMP. See Figure 3-2.
2026-08-19 Item #12D Page 69 of 816
Chapter 3: Development Project Planning and Design
3-6 2023
FIGURE 3-2. DMA Delineation
In some cases, in early planning phases, it may be appropriate to generalize the proposed treatment plan by simply assigning a certain BMP type to an entire planning area (e.g. Parking lot X will be treated with bioretention) and calculating the total sizing requirement without identifying the specific BMP locations at that time. This planning area would be later subdivided for design-level calculations.
Section 5.2 provides additional guidance on DMA delineation. A runoff factor (similar to a “C” factor used in the rational method) should be used to estimate the runoff draining to the BMP. Appendix B.1 provides guidance in estimating the runoff factor for the drainage area draining to a BMP.
BMPs must be sized to treat the DCV from the total area draining to the BMP, including any offsite or onsite areas that comingle with project runoff and drain to the BMP. To minimize offsite flows treated by project BMPs, consider diverting upgradient flows subject to local drainage and flood control regulation. An example is shown in Figure 3-3.
2026-08-19 Item #12D Page 70 of 816
Chapter 3: Development Project Planning and Design
3-7 2023
FIGURE 3-3. Tributary Area for BMP Sizing
2026-08-19 Item #12D Page 71 of 816
Chapter 3: Development Project Planning and Design
3-8 2023
3.3.4 Developing Conceptual Storm Water Control Strategies This step applies to PDPs only. The goal of this step is to develop conceptual stormwater control strategies that are compatible with the site conditions, including siting and preliminary selection of structural BMPs. The end product of this step should be a general, but concrete understanding of the stormwater management parameters for each DMA, the compatibility of this approach with the site design, and preliminary estimates of BMP selection. For simpler sites, this step could be abbreviated in favor of skipping forward to design-level analyses in Section 3.4. However, for larger and/or more complex sites, this section can provide considerable value and help allow evaluation of stormwater management requirements on common ground with other site planning considerations.
The following systematic approach is recommended:
1. Review the preliminary site information gathered in Section 3.2, specifically related to information gathered and summarized in the Site Information Checklist for PDPs (Appendix J-3B).
2. Identify self-mitigating, de minimis areas, and/or potential self-retaining DMAs that can be isolated from the remainder of the site (See Section 5.2).
3. Estimate DCV for each of the remaining DMAs (See Appendix B.1).
4. Determine if there is a potential opportunity for harvest and use of stormwater from the project site. See Section 5.4.1 for harvest and use feasibility screening, which is based on water demand at the project site. For most sites, there is limited opportunity; therefore evaluating this factor early can help simplify later decisions.
5. Estimate potential runoff reduction and the DCV that could be achieved with site design BMPs (See Appendix B.1).
6. Based on the remaining runoff after accounting for steps 2 to 5, estimate BMP space requirements. Identify applicable structural BMP requirements (i.e. stormwater pollutant control versus hydromodification management) and conduct approximate sizing calculations to determine the overall amount of storage volume and/or footprint area required for BMPs. Use worksheets presented in Appendices B.4 and B.5 to estimate sizing requirements for different types of BMPs.
7. Conduct preliminary screening of infiltration feasibility conditions as part of site planning to identify areas that are more or less conducive to infiltration. Recommended factors to consider include:
a. Soil types (determined from available geotechnical testing data, soil maps, site observations, and/or other data sources)
b. Approximate infiltration rates at various points on the site, obtained via approximate methods (e.g. simple pit test), if practicable c. Groundwater elevations
d. Proposed depths of fill
e. New or existing utilities that will remain with development f. Soil or groundwater contamination issues within the site or in the vicinity of the site g. Slopes and other potential geotechnical hazards that are unavoidable as part of site development
2026-08-19 Item #12D Page 72 of 816
Chapter 3: Development Project Planning and Design
3-9 2023
h. Safety and accessibility considerations
This assessment is not intended to be final or account for all potential factors. Rather, it is intended to help in identifying site opportunities and constraints as they relate to site planning.
After potential BMP locations are established, a more detailed feasibility analysis is necessary (see Section 3.4 and 5.4.2). Additionally, Appendix C provides methods for geotechnical and groundwater assessment applicable for screening at the planning level and design-level requirements. The jurisdiction may allow alternate assessment methods with appropriate documentation at the discretion of the City Engineer.
8. Identify tentative BMP locations based on preliminary feasibility screening, natural opportunities for BMPs (e.g. low areas of the site, areas near storm drain or stream connections), and other BMP sites that can potentially be created through effective site design (e.g. oddly configured or otherwise unbuildable parcels, easements, and landscape amenities including open space and buffers which can double as locations for bioretention or biofiltration facilities). Centralized stormwater management BMPs that treat runoff from all portions of the project are required unless otherwise authorized by the City Engineer.
9. Based on the results of feasibility screening and tentative DMA and BMP locations, determine the general infiltration feasibility condition at these locations. Categories are described in Section 5.4.2 and include:
a. Full infiltration condition;
b. Partial infiltration condition; and
c. No infiltration condition.
Adapt the site layout to attempt to achieve infiltration to the greatest extent feasible.
10. Consider how stormwater management BMPs will be accessed for inspection and maintenance and provide necessary site planning allowances (access roads, inspection openings, setbacks, etc.). On private projects, stormwater management BMPs are only allowed within the bounds of the private property unless otherwise authorized by the City Engineer.
11. In the SWQMP document site planning and opportunity assessment activities as a record of the decisions that led to the development of the final stormwater management plan. The SWQMP primarily will show the complete design rather than the preliminary steps in the process. However, to comply with the requirements of this manual, the applicant is required to describe how stormwater management objectives have been considered as early as possible in the site planning process and how opportunities to incorporate BMPs have been identified.
3.4 Developing Complete Storm Water Management
Design
The complete stormwater management design consists of all of the elements describing the BMPs to be implemented as well as integration of the BMPs with the site design and other infrastructure. The scope of this step varies depending on whether the project is an Exempt Project, a Basic Project, a Standard Project, a PDP with only pollutant control BMP requirements, or a PDP with pollutant 2026-08-19 Item #12D Page 73 of 816
Chapter 3: Development Project Planning and Design
3-10 2023
control and hydromodification management requirements. The following systematic approach is recommended to develop a final site layout and stormwater management design. Table 3-2 presents the applicability of different subsections based on project type and must be used to determine which requirements apply to a given project.
TABLE 3-3-2. Applicability of Section 3.4 Sub-sections for Different Project Types *Shall provided BMPs based on section 1.4.3.1
3.4.1 Steps for All Development Projects
Standard, Basic and Exempt Projects only need to satisfy the source control and site design requirements of Chapter 4 of this manual, and then proceed to Chapter 8 of this manual to determine submittal requirements.
1. Identify general requirements applicable to the selection and design of BMPs. See Section
4.1. 2. Select, identify and detail specific source control BMPs. See Section 4.2.
3. Select, identify and detail specific site design BMPs. See Section 4.3.
4. Document that all applicable source control and site design BMPs have been used. See Chapter 8.
3.4.2 Steps for PDPs with only Pollutant Control Requirements The steps below primarily consist of refinements to the conceptual steps completed as part of Section
3.3, accompanied by design-level detail and calculations. More detailed instructions for selection and design of stormwater pollutant treatment BMPs are provided in Chapter 5.
1. Select locations for stormwater pollutant control BMPs, and delineate and characterize DMAs using information gathered during the site planning phase.
2. Determine retention requirements per Appendix B.2.
3. Based on the results of step 2, select the BMP category that is most appropriate for the Project Type Section 3.4.1 Section 3.4.2 Section 3.4.3
Basic and Exempt Projects NA NA
Standard Projects NA * NA
PDP with only Pollutant Control
Requirements NA
PDP with Pollutant Control and
Hydromodification Management
Requirements
NA
2026-08-19 Item #12D Page 74 of 816
Chapter 3: Development Project Planning and Design
3-11 2023
site.
4. Calculate required BMP sizes and footprints. See Appendix B (sizing methods) and Appendix E (design criteria).
5. Evaluate whether the required BMP footprints will fit within the site considering the site constraints; if not, then document infeasibility and move to the next step.
6. If using biofiltration BMPs, document conformance with the criteria for biofiltration BMPs found in Appendix F, including Appendix F.1.
7. If needed, implement flow-thru treatment control BMPs (for use with Alternative Compliance7
) for the remaining DCV. See Section 5.5.4 and Appendix B.6 for additional guidance
8. If flow-thru treatment control BMPs (for use with Alternative Compliance6) were implemented, refer to Section 1.8.
9. Prepare SWQMP documenting site planning and opportunity assessment activities, final site layout, and stormwater management design. See Chapter 8.
10. Determine and document O&M requirements. See Chapters 7 and 8.
3.4.3 Steps for Projects with Pollutant Control and Hydromodification Management Requirements
The steps below primarily consist of refinements to the conceptual steps completed as part of Section
3.3, accompanied by design-level detail and calculations7 . More detailed instruction for selection and
design of stormwater pollutant treatment and hydromodification control BMPs are provided in Chapters 5 and 6, respectively.
1. If critical coarse sediment yield areas were determined to exist within or upstream of the project site (Section 3.3.2), incorporate on-site mitigation measures when applicable (Section
6.2).
2. Determine the point of compliance and evaluate the susceptibility to erosion of the downstream channel.
3. Select locations for stormwater pollutant control and hydromodification management BMPs.
Delineate and characterize DMAs using information gathered during the site planning phase.
4. Conduct feasibility analysis for harvest and use BMPs. See Section 5.4.1.
5. Conduct feasibility analysis for infiltration to determine the infiltration condition. See Section
5.4.2. 6
The City of Encinitas does not currently have an Alternative Compliance Program. 7 Steps 8-10 only apply if the City of Encinitas has implemented an Alternative Compliance Program or approved a project based Alternative Compliance design.
2026-08-19 Item #12D Page 75 of 816
Chapter 3: Development Project Planning and Design
3-12 2023
6. Based on the results of steps 3 and 4, select the BMP category for pollutant treatment BMPs that is most appropriate for the site. See Section 5.5.
7. Develop the design approach for integrating stormwater pollutant treatment and hydromodification control. The same location(s) can serve both functions (e.g. a biofiltration area that provides both pollutant control and flow control), or separate pollutant control and flow control locations may be identified (e.g. several dispersed retention areas for pollutant control, with overflow directed to a single location of additional storage for flow control).
8. Calculate BMP sizing requirements for pollutant control and flow control. See Appendix B (sizing methods) and Appendix E (design criteria).
a. When the same BMP will serve both functions, Section 6.3.6 of this manual provides recommendations for assessing the controlling design factor and initiating the design process.
9. Evaluate whether the required BMP footprints will fit within the site considering the site constraints:
a. If they fit within the site, design BMPs to meet applicable sizing and design criteria.
Document sizing and design separately for pollutant control and hydromodification management even when the same BMP is serving both functions. b. If they do not fit the site, document infeasibility and move to the next step.
10. Implement flow-thru treatment control BMPs (for use with Alternative Compliance8 ) for the
remaining DCV. See Section 5.5.4 and Appendix B.6 for additional guidance.
11. If flow-thru treatment control BMPs (for use with Alternative Compliance) were implemented, refer to Section 1.8. 9
12. Prepare a SWQMP documenting site planning and opportunity assessment activities, final site layout, stormwater pollutant control design, and hydromodification management design. See Chapter 8.
13. Determine and document O&M requirements. See Chapters 7 and 8.
3.5Project Planning and Design Requirements
Specific to Local Jurisdiction
For projects within the City of Encinitas, the following local project planning and design requirements must be met.
3.5.1 Maximum Ponding Depth
For all bioretention, partial retention and flow through BMPs, a maximum ponding depth of 18 inches must not be exceeded. The ponding depth is measured from the top opening of the grate inlet to the 8The City of Encinitas does not currently have an Alternative Compliance Program. 2026-08-19 Item #12D Page 76 of 816
Chapter 3: Development Project Planning and Design
3-13 2023
top of finished grade of the BMP. BMPs with ponding depths that exceed 18 inches tend to lose effectiveness more quickly over time and therefore are not allowed.
3.5.2 SCCWRP Analysis
SCCWRP analysis that was conducted for a nearby project may be used for your project at the discretion of the City Engineer on a case by case basis.
3.5.3 Location of BMPs on the project site
When water quality treatment and hydromodification management is deemed to be technically infeasible within given DMA, the City Engineer may authorize BMPs to be located within an alternate DMA on the within the project site, as long as both DMAs are tributary to the same downstream point of compliance and as long as the water quality benefit is equal to or greater than the treatment necessary for the of the infeasible area. For example, a project that is required to provide road widening along the property frontage where treatment of the runoff from the additional pavement is deemed infeasible, may be authorized to treat the runoff from another portion of the site in-lieu of the actual pavement being created, as long there is an equal or greater water quality benefit.
3.5.4 Centralized Facilities
Centralized structural BMPs that treat runoff from all portions of the project are required unless otherwise authorized by the City Engineer. Where BMPs are authorized on individual residential lots, BMPs must be located in the front yards unless otherwise authorized by the City Engineer. Centralized facilities must be maintained by a Homeowner’s Association, unless otherwise authorized by the City Engineer. Adequate access for maintenance and inspection of the centralized facility shall be provided.
Centralized facilities and their corresponding maintenance access shall be deed restricted to prevent future development of the land for any other purpose.
3.5.5 Impervious area calculations for subdivisions
When calculating the proposed impervious area on a proposed residential subdivision, a 15 percent contingency for hardscape added by future homeowners must be included in the proposed impervious area measurement.
3.5.6 Infiltration Testing
Infiltration testing on the existing site must be conducted at the discretionary review phase of PDPs.
Results of infiltration testing must be included in the SWQMP submittal.
3.5.7 Temporary Improvements
Unforeseen circumstances may cause temporary improvements to be installed for much longer than anticipated. Examples of temporary improvements include parking lots for model home visitors and construction site management offices. At the discretion of the City Engineer, temporary improvements may require stormwater treatment to avoid downstream water quality impacts. 2026-08-19 Item #12D Page 77 of 816
Chapter 3: Development Project Planning and Design
3-14 2023
3.5.8 City Engineer has the final discretion
The City Engineer has the ultimate discretion to determine the project category (PDP, Standard, Basic or Exempt) and approve proposed stormwater management BMP sizing and design.
3.6Phased Projects
Phased projects typically require a conceptual or master PDP SWQMP followed by more detailed submittals. See section 1.3 for more details regarding the definition of a project. 2026-08-19 Item #12D Page 78 of 816
M O D E L B M P D E S I G N M A N U A L
4-1 2023
Chapter
4 4 Source Control and Site Design
Requirements for All Development
Projects
This chapter presents the source control and site design requirements to be met by Exempt Projects, Basic Projects, Standard Projects and PDPs. Checklists J-4 for source control and J-5 for site design included in Appendix J can be used by all project types to document conformance with the requirements.
4.1 General Requirements (GR)
GR-1: Onsite BMPs must be located so as to remove pollutants from runoff prior to its discharge to any receiving waters, and as close to the source as possible.
The location of the BMP affects the ability of the BMP to retain and/or treat the pollutants from the contributing drainage area. BMPs should be placed as close to the pollutant source as possible.
How to comply: Projects shall comply by implementing source control (Section 4.2) and site design BMPs (Section 4.3) that are applicable to the project and site conditions.
GR-2: Structural BMPs must not be constructed within the Waters of the United States The definition of Waters of the U.S. can be found in Clean Water Rule 40 CFR 230.2. Structural BMPs must not be constructed within navigable waters, impoundments, tributaries to navigable waters, wetlands, vernal pools, and the 100-year floodplain.
Construction, operation, and maintenance of a structural BMP in a water body can negatively impact the physical, chemical, and biological integrity of the water body, as well as its beneficial uses.
However, alternative compliance9 opportunities involving restoration of areas within Waters of the U.S. may be identified by local jurisdictions.
How to comply: Projects shall demonstrate compliance with this requirement by showing 9 The City of Encinitas does not currently have an Alternative Compliance Program. 2026-08-19 Item #12D Page 79 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-2 2023
the location of structural BMPs on project plans and describing or depicting the location of receiving waters.
GR-3: Onsite BMPs must be designed and implemented with measures to avoid the creation of nuisances or pollutants associated with vectors (e.g. mosquitos, rodents, and flies).
According to the California Department of Health, site design features and structural BMPs that retain standing water for over 96 hours may facilitate mosquito breeding.
How to comply: Projects shall comply by incorporating design, construction, and maintenance principles to minimize standing water and to drain retained water within 96 hours. Design calculations shall be provided to demonstrate that the potential for surface water ponding accessible to mosquitos has been addressed. This criterion is not applicable to ponding water that is not accessible to vectors, such as water retained in the amended soil of a biofiltration facility.
4.2Source Control (SC) BMP Requirements
Source control BMPs avoid and reduce pollutants in stormwater runoff. Everyday activities such as recycling, trash disposal, and irrigation generate pollutants that have the potential to drain to the stormwater conveyance system. Source control BMPs are defined as activities that reduce the potential for stormwater runoff to come into contact with pollutants. An activity could include an administrative action, design of a structural facility, usage of alternative materials, and operation, maintenance and inspection of an area. Where applicable and feasible, all development projects are required to implement source control BMPs. Applicability and feasibility determinations and selection of source control BMPs will be reviewed and approved by the City during the plan check process. Source control BMPs are discussed below.
How to comply: Projects must implement all source control BMPs that are applicable to their project. Applicability should be determined through a consideration of the development project’s proposed features and the anticipated pollutant sources associated with them. Appendix D provides guidance for identifying source control BMPs applicable to a project. Table 2 “Baseline BMPs for Pollutant-Generating Sources” located in Standard and PDP SWQMPs must be used to document compliance with these requirements. Table 2 applies to all projects except for Small Residential Projects. Small Residential Projects are those requiring either: a Building Permit, Minor Residential Grading Permit, or site Plan Permit for a single family home; or a Tentative Parcel Map Permit for up to 4 single family homes and a remainder parcel.
Prevent illicit discharges into the MS4
An illicit discharge is any discharge to the MS4 that is not composed entirely of stormwater except discharges pursuant to a National Pollutant Discharge Elimination System permit and discharges resulting from emergency firefighting activities. Projects must effectively eliminate discharges of nonstormwater into the MS4.
For outdoor areas, exposure reduction generally requires work areas and storage areas to be covered to prevent rain exposure; graded to prevent stormwater run-on and run-off; and protected from the wind so that materials are not dispersed. See Fact Sheet BL-5 (Work and Storage Areas) in Appendix 2026-08-19 Item #12D Page 80 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-3 2023
C. If there are storm water discharges from outdoor areas work areas or storage areas, Fact Sheet BL6 (Management of Stormwater Discharges) in Appendix C provides practices to prevent discharge of materials from these areas. For interior work surfaces, floor drains and sumps, drain lines, and fire sprinkler test water, exposure reduction generally requires directing the discharge to the sanitary sewer.
See Fact Sheet BL-7 (Management of Non-Stormwater Discharges) in Appendix C. Fact Sheet BL-7 also discusses education for prevention of illicit discharges, which is discussed in more detail below in Section 4.2.2.
Identify the storm drain system using stenciling or signage Storm drain signs and stencils are visible source controls typically placed adjacent to the inlets. Posting notices regarding discharge prohibitions at storm drain inlets can prevent waste dumping. Stenciling shall be provided for all stormwater conveyance system inlets and catch basins within the project area.
Inlet stenciling may include concrete stamping, concrete painting, placards, or other methods approved by the local municipality. In addition to storm drain stenciling, projects are encouraged to post signs and prohibitive language with graphical icons which prohibit illegal dumping at trailheads, parks, building entrances and public access points along channels and creeks within the project area.
Language associated with the stamping (e.g. “No Dumping-Drains to Ocean”) must be satisfactory to the City Engineer. See Appendix E, fact sheet BL-7 for additional guidance.
Protect outdoor material storage areas from rainfall, run-on, runoff, and wind dispersal Materials with the potential to pollute stormwater runoff shall be stored in a manner that prevents contact with rainfall and stormwater runoff. Contaminated runoff shall be managed for treatment and disposal (e.g. secondary containment directed to sanitary sewer). All development projects shall incorporate the following structural or pollutant control BMPs for outdoor material storage areas, as applicable and feasible:
• Storage areas must be paved and sufficiently impervious to contain leaks and spills, where necessary.
• The storage area must be sloped towards a sump or another equivalent measure that is effective to contain spills.
• Runoff from downspouts/roofs must be directed away from storage areas. • The storage area must have a roof or awning that extends beyond the storage area to minimize collection of storm water within the secondary containment area. A manufactured storage shed may be used for small containers.
• Use other methods approved by the City.
See Fact Sheet BL-5 (Work and Storage Areas) in Appendix C for more information.
Protect materials stored in outdoor work areas from rainfall, run-on, runoff, and wind dispersal
Outdoor work areas have an elevated potential for pollutant loading and spills. All development projects shall include the following structural or pollutant control BMPs for any outdoor work areas with potential for pollutant generation, as applicable and feasible:
2026-08-19 Item #12D Page 81 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-4 2023
• Create an impermeable surface such as concrete or asphalt, or a prefabricated metal drip pan, depending on the size needed to protect the materials.
• Cover the area with a roof or other acceptable cover. • Berm the perimeter of the area to prevent water from adjacent areas from flowing on to the surface of the work area.
• Directly connect runoff to sanitary sewer or other specialized containment system(s), as needed and where feasible. This allows the more highly concentrated pollutants from these areas to receive special treatment that removes particular constituents. Approval for this connection must be obtained from the appropriate sanitary sewer agency. • Locate the work area away from storm drains or catch basins. • Use other methods approved by the City.
See Fact Sheets BL-5 (Work and Storage Areas) and BL-6 (Management of Stormwater Discharges) in Appendix C for more information.
Protect trash, grease, and manure storage areas from rainfall, run-on, runoff, and wind dispersal
Stormwater runoff from areas where trash, cooking grease and horse manure is stored or disposed of can be polluted. In addition, loose trash and debris can be easily transported by water or wind into nearby storm drain inlets, channels, and/or creeks. All development projects shall include the following structural or pollutant control BMPs, as applicable:
• Trash enclosure areas and manure storage areas must be walled and covered with a waterproof roof to prevent offsite transport of trash or manure and rainwater intrusion. Provide an impervious, non-combustible roof, on all trash enclosures and manure storage areas to minimize direct precipitation and prevent rainfall from entering the area. If there is an open area between the roof and the perimeter wall, the roof overhang shall be equal or larger than the opening width.
• Design trash enclosures areas and manure storage areas so that drainage from adjoining roofs and pavement is diverted around the area(s) to avoid run-on. Use a berm or wall to prevent run-on of stormwater. A berm or wall shall be installed at all openings to hold in any liquids that escape from the area and to prevent any flow of storm water through the containment area. The berm can be designed wide and flat to allow rolling of the dumpster in and out. • The trash enclosure shall be lockable and locked when not in use. • The trash enclosure shall have a drain that discharges through an adequately sized oil/ grease separator (if an oil/ grease separator is required by building code) and then is filtered through a City-approved hydrocarbon filter and discharged into the public sanitary sewer system and not to planters or the storm drain system. The trash enclosure finish floor shall be at least six inches higher than 100-year storm water surface elevation. The finished floor shall also be sloped at 2%, minimum, to the middle of the enclosure or the back wall, wherever the drain is located. A separate building permit may be required for this structure. • Locate used grease storage bins inside restaurant facilities, if permitted by the City of Encinitas.
If the grease bin must be located outside for health purposes, the bin must have secondary 2026-08-19 Item #12D Page 82 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-5 2023
containment for any potential spills and overhead coverage large enough to cover the bin and the secondary containment unit.
• Locate storm drains away from immediate vicinity of the trash storage, grease storage and manure storage areas and vice versa.
• Post signs on all dumpsters informing users that hazardous material are not to be disposed. • Use other methods approved by the City.
See Fact Sheets BL-5 (Work and Storage Areas) and BL-6 (Management of Stormwater Discharges) in Appendix C for more information.
Use any additional BMPs determined to be necessary by the Copermittee to minimize pollutant generation at each project site
At its discretion, the City may determine that additional on-site controls are necessary to minimize pollutant generation. These determinations will be made on a project-specific basis. Appendix D provides guidance on permanent controls that are applicable at a project site based on potential sources of runoff pollutants at the project site. Applicants must implement all applicable and feasible source control BMPs listed in Appendix D.
4.3Site Design (SD) BMP Requirements
Site design BMPs (also referred to as LID BMPs) are intended to reduce the rate and volume of stormwater runoff and associated pollutant loads. Site design BMPs include practices that reduce the rate and/or volume of stormwater runoff by minimizing surface soil compaction, reducing impervious surfaces, and/or providing flow pathways that are “disconnected” from the storm drain system, such as by routing flow over pervious surfaces. Site design BMPs may incorporate interception, storage, evaporation, evapotranspiration, infiltration, and/or filtration processes to retain and/or treat pollutants in stormwater before it is discharged from a site.
Appendix C also provides the following fact sheets to assist project applicants with designing BMPs to meet Site Design Requirements:
• BL-1 – Existing Natural Site Features
• BL-2 – Outdoor Impervious Areas
• BL-3 – Rooftop Areas
• BL-4 – Landscaped Areas
In addition, Appendix E also provides the following fact sheets to assist project applicants in Design Capture Volume (DCV) reduction using Enhanced Site Deign BMPs:
• SD-A – Tree Well;
• SD-B – Impervious Area Dispersion;
• SD-C – Green Roofs;
• SD-D – Permeable Pavement (Site Design BMP);
• SD-E – Rain Barrels; and
2026-08-19 Item #12D Page 83 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-6 2023
Source:
• SD-F – Amended Soil.
Site design BMPs shall be applied to all development projects as appropriate and practicable for the project site and project conditions. Site design BMPs are described in the following subsections.
How to comply: Projects must comply with this requirement by using all of the site design BMPs listed in this section that are applicable and practicable to their project type and site conditions. Applicability of a given site design BMP should be determined based on project type, soil conditions, presence of natural features (e.g. streams), and presence of site features (e.g. parking areas). Applicants must provide an explanation for any site design BMP they do not consider to be applicable and feasible. Site plans must identify site design BMPs and provide adequate supporting detail to ensure their effective implementation. Table 1 “ Baseline BMPs for Existing and Proposed Site Features” which is part of both the Standard SWQMP and the PDP SWQMP listed in Appendix A, should be used to document compliance with site design BMP requirements. Table 1 applies to all development projects.
Maintain natural drainage pathways and hydrologic features Maintain or restore natural storage reservoirs and drainage corridors (including topographic depressions, areas of permeable soils, natural swales, and ephemeral and intermittent streams) Buffer zones for natural water bodies (where buffer zones are technically infeasible, require project applicant to include other buffers such as trees, access restrictions, etc.) During the site assessment, natural drainages must be
identified along with their connection to creeks and/or streams, if any. Natural drainages offer a benefit to
stormwater management as the soils and habitat already
function as a natural filtering/infiltrating swale. When determining the development footprint of the site,
natural drainages should be avoided. By providing a
development envelope set back from natural drainages,
the drainage can retain some water quality benefits to
the watershed. In some situations, site constraints,
regulations, economics, or other factors may not allow
avoidance of drainages and sensitive areas. Projects
proposing to dredge or fill materials in Waters of the
U.S. must obtain Clean Water Act Section 401 Water Quality Certification. Projects proposing to dredge or fill waters of the State must obtain Waste Discharge Requirements. Both the 401 Certification and the Waste Discharge Requirements are administered by the San Diego Water Board.
The project applicant shall consult the local jurisdiction for other specific requirements.
Per Encinitas Municipal Code Section 30.34.040, when planning out your project, a buffer of 100 feet in width shall be maintained around all identified coastal lagoons and wetland areas. In addition, all riparian areas require a minimum 50-foot-wide buffer.
Projects can incorporate this into a project by implementing the following planning and design phase techniques as applicable and practicable:
• Evaluate surface drainage and topography in considering selection of Site Design BMPs that 2026-08-19 Item #12D Page 84 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-7 2023
will be most beneficial for a given project site. Where feasible, maintain topographic depressions for infiltration.
• Optimize the site layout and reduce the need for grading. Where possible, conform the site layout along natural landforms, avoid grading and disturbance of vegetation and soils, and replicate the site’s natural drainage patterns. Integrating existing drainage patterns into the site plan will help maintain the site’s predevelopment hydrologic function. • Preserve existing drainage paths and depressions, where feasible and applicable, to help maintain the time of concentration and infiltration rates of runoff, and decrease peak flow. • Structural BMPs cannot be located in buffer zones if a State and/or Federal resource agency (e.g. SDRWQCB, California Department of Fish and Wildlife; U.S. Army Corps of Engineers, etc.) prohibits maintenance or activity in the area.
• See Fact Sheet BL-1 (Existing Natural Site Features) in Appendix C for more information.
Conserve natural areas, soils and vegetation
Conserve natural areas within the project footprint including existing trees, other vegetation, and soils
To enhance a site’s ability to support source control and reduce runoff, the conservation and restoration of natural areas must be considered in the site design process. By conserving or restoring the natural drainage features, natural processes are able to intercept stormwater, thereby reducing the amount of runoff.
The upper soil layers of a natural area contain organic material, soil biota, vegetation, and a configuration favorable for storing and slowly conveying stormwater and establishing or restoring vegetation to stabilize the site after construction. The canopy of existing native trees and shrubs also provide a water conservation benefit by intercepting rain water before it hits the ground. By minimizing disturbances in these areas, natural processes are able to intercept stormwater, providing a water quality benefit. By keeping the development concentrated to the least environmentally 2026-08-19 Item #12D Page 85 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-8 2023
sensitive areas of the site and set back from natural areas, stormwater runoff is reduced, water quality can be improved, environmental impacts can be decreased, and many of the site’s most attractive native landscape features can be retained. In some situations, site constraints, regulations, economics, and/or other factors may not allow avoidance of all sensitive areas on a project site. Project applicant shall consult the local municipality for jurisdictional specific requirements for mitigation of removal of sensitive areas.
When a proposed project is reviewed by the Encinitas Planning Department, the project must comply with regulations identified in the following policies:
• Hillside Bluff Overlay Zone: EMC 30.34.030
• General Plan Resource Management Element Policies
• Urban Forest Management Plan
• Multiple Habitat Conservation Program
• Draft Encinitas Subarea Plan
• CEQA
Projects can incorporate this by implementing the following planning and design phase techniques as applicable and practicable:
• Identify areas most suitable for development and areas that must be left undisturbed.
Additionally, reduced disturbance can be accomplished by increasing building density and increasing height, if possible.
• Cluster development on least-sensitive portions of a site while leaving the remaining land in a natural undisturbed condition.
• Avoid areas with thick, undisturbed vegetation.
Soils in these areas have a much higher capacity
to store and infiltrate runoff than disturbed
soils,
• and reestablishment of a mature vegetative
community can take decades. Vegetative cover
can also provide additional volume storage of
rainfall by retaining water on the surfaces of
leaves, branches, and trunks of trees during
and after storm events.
• Preserve trees, especially native trees and
shrubs, and identify locations for planting
additional native or drought tolerant trees and large shrubs. Refer to Appendix E, factsheet SD-A Tree Wells, for additional guidance on implementing this as a site design BMP. • In areas of disturbance, topsoil should be removed before construction and replaced after the project is completed. When handled carefully, such an approach limits the disturbance to 2026-08-19 Item #12D Page 86 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-9 2023
native soils and reduces the need for additional (purchased) topsoil during later phases. • Sensitive areas, such as wetlands, biological open space areas, biological mitigation sites, streams, floodplains, or particular vegetation communities, such as coastal sage scrub and intact forest must be avoided. Areas that are habitat for sensitive plants and animals— particularly those State or federally listed as endangered, threatened or rare—must be avoided. Development in these areas is restricted by federal, state and local laws.
• See Fact Sheet BL-1 (Existing Natural Site Features) in Appendix C for more information.
Minimize impervious area
Construct streets, sidewalks or parking lots aisles to the minimum widths necessary, provided public safety is not compromised
Minimize the impervious footprint of the project
One of the principal causes of environmental impacts by development is the creation of impervious surfaces. Imperviousness links urban land development to degradation of aquatic ecosystems in two ways:
• First, the combination of paved surfaces and
piped runoff efficiently collects urban pollutants and
transports them, in suspended or dissolved form, to
surface waters. These pollutants may originate as
airborne dust, be washed from the atmosphere
during rains, or may be generated by automobiles and
outdoor work activities.
• Second, increased peak flows and runoff
durations typically cause erosion of stream banks and
beds, transport of fine sediments, and disruption of
aquatic habitat. Measures taken to control stream
erosion, such as hardening banks with riprap or
concrete, may permanently eliminate habitat.
Impervious cover can be minimized through identification of the smallest possible land area that can be practically impacted or disturbed during site development. Reducing impervious surfaces retains the permeability of the project site, allowing natural processes to filter and reduce sources of pollution.
Projects can incorporate this by implementing the following planning and design phase techniques as applicable and practicable:
• Decrease building footprint through (the design of compact and taller structures when allowed by local zoning and design standards and provided public safety is not compromised. • Construct walkways, trails, patios, overflow parking lots, alleys and other low-traffic areas with permeable surfaces. Refer to Appendix E, factsheet SD-D Permeable Pavement for guidance on implementing this as a Site Design BMP.
• Construct streets, sidewalks and parking lot aisles to the minimum widths necessary, provided that public safety and alternative transportation (e.g. pedestrians, bikes) are not compromised. 2026-08-19 Item #12D Page 87 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-10 2023
• Consider the implementation of shared parking lots and driveways where possible. • Landscaped area in the center of a cul-de-sac can reduce impervious area depending on configuration. Design of a landscaped cul-de-sac must be coordinated with fire department personnel to accommodate turning radii and other operational needs. • Design smaller parking lots with fewer stalls, smaller stalls, more efficient lanes. • Design indoor or underground parking.
• Minimize the use of impervious surfaces in the landscape design.
See Fact Sheets BL-2 (Outdoor Impervious Area), BL-3 (Rooftop Areas), and BL-4 (Landscaped Areas) in Appendix C for more information.
In addition, the following Fact Sheets provided in Appendix E describe ways to reduce impervious areas:
• SD-B – Impervious Area Dispersion;
• SD-C – Green Roofs; and
• SD-D – Permeable Pavement (Site Design).
Minimize soil compaction
• Minimize soil compaction in landscaped areas
The upper soil layers contain organic material, soil biota, and a configuration favorable for storing and slowly conveying stormwater down gradient. By protecting native soils and vegetation in appropriate areas during the clearing and grading phase of development the site can retain some of its existing beneficial hydrologic function. Soil compaction resulting from the movement of heavy construction equipment can reduce soil infiltration rates. It is important to recognize that areas adjacent to and under building foundations, roads and manufactured slopes must be compacted with minimum soil density requirements in compliance with local building and grading ordinances.
Projects can incorporate this by implementing the following planning and design phase techniques as applicable and practicable:
• Avoid disturbance in planned green space and proposed landscaped areas where feasible.
These areas that are planned for retaining their beneficial hydrological function should be protected during the grading/construction phase so that vehicles and construction equipment do not intrude and inadvertently compact the area.
• In areas planned for landscaping where compaction could not be avoided, re-till the top 8 inches of soil surface to allow for better infiltration capacity. Soil amendments are recommended and may be necessary to increase permeability and organic content. Soil stability, density requirements, and other geotechnical considerations associated with soil compaction must be reviewed by a qualified landscape architect or licensed geotechnical, civil or other professional engineer. Refer to factsheet SD-F in Appendix E for additional guidance on implementing amended soils within the project footprint. 2026-08-19 Item #12D Page 88 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-11 2023
• See Fact Sheets BL-1 (Existing Natural Site Features) and BL-4 (Landscaped Areas) in Appendix C for more information.
Disperse impervious areas
• Disconnect impervious surfaces through distributed pervious areas • Design and construct landscaped or other pervious areas to effectively receive and infiltrate, retain and/or treat runoff from impervious areas prior to discharging to the MS4 Impervious area dispersion (dispersion) refers to the practice of disconnecting impervious areas from directly draining to the storm drain system by routing runoff from impervious areas such as rooftops, walkways, and driveways onto the surface of adjacent pervious areas. The intent is to slow runoff discharges and reduce volumes while achieving incidental treatment. Volume reduction from dispersion is dependent on the infiltration characteristics of the pervious area and the amount of impervious area draining to the pervious area. Treatment is achieved through filtration, shallow sedimentation, sorption, infiltration, evapotranspiration, biochemical processes and plant uptake.
The effects of imperviousness can be mitigated by disconnecting impervious areas from the drainage system and by encouraging detention and retention of runoff near the point where it is generated.
Detention and retention of runoff reduces peak flows and volumes and allows pollutants to settle out or adhere to soils before they can be transported downstream. Disconnection practices may be applied in almost any location, but impervious surfaces must discharge into a suitable receiving area for the practices to be effective. Information gathered during the site assessment will help determine appropriate receiving areas.
Project designs should direct runoff from impervious areas to adjacent landscaping areas that have higher potential for infiltration and surface water storage. This will limit the amount of runoff generated, and therefore the size of the mitigation BMPs downstream. The design, including consideration of slopes and soils, must reflect a reasonable expectation that runoff will soak into the soil and produce no runoff of the DCV. On hillside sites, drainage from upper areas may be collected in conventional catch basins and piped to landscaped areas that have higher potential for infiltration.
Or use low retaining walls to create terraces that can accommodate LID areas. 2026-08-19 Item #12D Page 89 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-12 2023
Projects can incorporate SD-5 by implementing the following planning and design phase techniques as applicable and practicable:
• Implement design criteria and considerations listed in impervious area dispersion fact sheet (SD-B) presented in Appendix E.
• Drain rooftops into adjacent landscape areas.
• Drain impervious parking lots, sidewalks, walkways, trails, and patios into adjacent landscape areas.
• Reduce or eliminate curb and gutters from roadway sections, thus allowing roadway runoff to drain to adjacent pervious areas.
• Replace curbs and gutters with roadside vegetated swales and direct runoff from the paved street or parking areas to adjacent LID facilities. Such an approach for alternative design can reduce the overall capital cost of the site development while improving the stormwater quantity and quality issues and the site’s aesthetics.
• Plan site layout and grading to allow for runoff from impervious surfaces to be directed into distributed permeable areas such as turf, landscaped or permeable recreational areas, medians, parking islands, planter boxes, etc.
• Detain and retain runoff throughout the site. On flatter sites, landscaped areas can be interspersed among the buildings and pavement areas. On hillside sites, drainage from upper areas may be collected in conventional catch basins and conveyed to landscaped areas in lower areas of the site.
• Pervious area that receives run on from impervious surfaces should have a minimum width of 2026-08-19 Item #12D Page 90 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-13 2023
10 feet and a maximum slope of 5%.
See Fact Sheets BL-2 (Outdoor Impervious Areas), BL-3 (Rooftop Areas) and BL-4 (Landscaped Areas) in Appendix C for more information.
In addition, the following fact sheet in Appendix E describes ways to reduce the impact of runoff from impervious areas:
• SD-B- Impervious area dispersion
Collect runoff
• Use small collection strategies located at, or as close to as possible to the sources (i.e. the point where stormwater initially meets the ground) to minimize the transport of runoff and pollutants to the MS4 and receiving waters
• Use permeable material for projects with low traffic areas and appropriate soil conditions.
Refer to factsheet SD-D in Appendix E for additional guidance on implementing permeable pavement as a Site Design BMP.
Distributed control of stormwater runoff from the site can be accomplished by applying small collection techniques (e.g. SD-C Green Roofs), or integrated management practices, on small subcatchments or on residential lots. Small collection techniques foster opportunities to maintain the natural hydrology provide a much greater range of control practices. Integration of stormwater management into landscape design and natural features of the site, reduce site development and longterm maintenance costs, and provide redundancy if one technique fails. On flatter sites, it typically works best to intersperse landscaped areas and integrate small scale retention practices among the buildings and paving.
Permeable pavements contain small voids that allow water to pass through to a gravel base. They come in a variety of forms; they may be a modular paving system (concrete pavers, grass-pave, or gravel-pave) or poured in place pavement (porous concrete, permeable asphalt). Project applicants should identify locations where permeable pavements could be substituted for impervious concrete or asphalt paving. The O&M plan for the site must ensure that permeable pavements will not be sealed in the future. In areas where infiltration is not appropriate, permeable paving systems can be fitted with an under drain to allow filtration, storage, and evaporation, prior to drainage into the storm drain system.
Projects can incorporate this by implementing the following planning and design phase techniques as applicable and practicable:
• Implementing distributed small collection techniques to collect and retain runoff • Installing permeable pavements (see SD-D in Appendix E) See Fact Sheets BL-2 (Outdoor Impervious Areas) and BL-3 (Rooftop Areas) in Appendix C for more information.
Landscape with native or drought tolerant species
All development projects are required to select a landscape design and plant palette that minimizes required resources (irrigation, fertilizers and pesticides) and pollutants generated from landscape areas. 2026-08-19 Item #12D Page 91 of 816
Chapter 4: Source Control and Site Design Requirements for All Development Projects 4-14 2023
Native plants require less fertilizers and pesticides because they are already adapted to the rainfall patterns and soils conditions. Plants should be selected to be drought tolerant and not require watering after establishment (2 to 3 years). Watering should only be required during prolonged dry periods after plants are established. Final selection of plant material needs to be made by a landscape architect experienced with LID techniques. Microclimates vary significantly throughout the region and consulting local municipal resources will help to select plant material suitable for a specific geographic location.
Projects can incorporate SD-7 by landscaping with native and drought tolerant species. Recommended plant list is included in Appendix E (Fact Sheet PL) as well as by referring to Fact Sheet BL-4 (Landscaped Areas) in Appendix C.
Harvest and use precipitation
Harvest and use BMPs capture and store stormwater
runoff for later use. Harvest and use can be applied
at smaller scales (Standard Projects) using rain
barrels or at larger scales (PDPs) using cisterns. This harvest and use technique has been successful in
reducing runoff
discharged to the storm drain system conserving
potable water and recharging groundwater. PDPs
would still need to meet hydromodification
management requirements, as applicable.
Rain barrels are above ground storage vessels that
capture runoff from roof downspouts during rain
events and detain that runoff for later reuse for
irrigating landscaped areas. The temporary storage
of roof runoff reduces the runoff volume from a
property and may reduce the peak runoff velocity for
small, frequently occurring storms. In addition, by
reducing the amount of stormwater runoff that
flows overland into a stormwater conveyance system (storm drain inlets and drain pipes), less pollutants are transported through the conveyance system into local creeks and the ocean. The reuse of the detained water for irrigation purposes leads to the conservation of potable water and the recharge of groundwater. SD-E fact sheet in Appendix E provides additional detail for designing Harvest and Use BMPs. Projects can incorporate SD-8 by installing rain barrels or cisterns, as applicable.
2026-08-19 Item #12D Page 92 of 816
M O D E L B M P D E S I G N M A N U A L
5-1 2023
Chapter
5 5 Storm Water Pollutant Control
Requirements for PDPs
PDPs are required to implement storm water pollutant control BMPs to maximize retention of stormwater and reduce the quantity of pollutants in storm water discharges. This chapter outlines the process for PDPs to demonstrate compliance with these requirements.
This chapter should be followed after referencing project planning elements and site design/source control elements discussed in Chapters 3 and 4 respectively. The steps in this chapter pertain specifically to storm water pollutant control BMPs. These criteria must be met regardless of whether hydromodification management applies; however, the overall sequencing of project development may be different if hydromodification management applies. For guidance on how to integrate both hydromodification management and pollutant control BMPs (in cases where both requirements apply), see Sections 3.4.3, 5.4 and Chapter 6.
5.1 Steps for Selecting and Designing Storm Water
Pollutant Control BMPs
Step 1. Determine DCV per Appendix B.1
A. Determine rainfall depth per Appendix B.1.1.
B. Delineate tributary areas per Appendix B.1.2.
C. Determine runoff factors per Appendix B.1.3.
D. Determine site design volume reductions per Appendix B.1.4 Step 2. Determine Retention Requirements Appendix B.2
A. Determine if capture and use analysis is required per Appendix B.2.1 B. Evaluate infiltration restrictions per Appendix B.2.2 C. Determine design infiltration rate per Appendix B.2.3 D. Determine retention requirements per Appendix B.2.4
Step 3. Determine BMP Performance per Appendix B.3
A. Identify proposed BMP characteristics per Appendix B.3.1. 2026-08-19 Item #12D Page 93 of 816
Chapter 5: Storm Water Pollutant Control Requirements for PDPs 5-2 2023
B. Calculate retention processes per Appendix B.3.2
C. Calculate biofiltration processes per Appendix B.3.3 D. Satisfaction of pollutant control requirements per Appendix B.3.4 E. Satisfaction of minimum retention requirements per Appendix B.3.5
5.2 DMAs Excluded from DCV Calculation / Options
for Meeting Structural Performance Standards
Applicants may exclude DMAs from DCV calculations if they meet the criteria specified below.
However, each DMA must implement source control and site design BMPs as applicable and feasible.
These exemptions will be evaluated on a case-by-case basis at the discretion of the City.
5.2.1 Self-mitigating DMAs
Self-mitigating DMAs consist of natural or landscaped areas that drain directly offsite or to the public storm drain system. Self-mitigating DMAs must meet ALL of the following to be eligible for exclusion:
• Vegetation in the natural or landscaped area is native and/or non-native/non-invasive drought tolerant species that do not require regular application of fertilizers and pesticides. • Soils are undisturbed native topsoil, or disturbed soils that have been amended and aerated to promote water retention characteristics equivalent to undisturbed native topsoil. • The incidental impervious areas are less than 5 percent of the self-mitigating area. • Impervious area within the self-mitigated area should not be hydraulically connected to other impervious areas unless it is a storm water conveyance system (such as a brow ditch). • The self-mitigating area is hydraulically separate from DMAs that contain permanent storm water pollutant control BMPs.
Figure 5-1 illustrates the concept of self-mitigating DMAs.
FIGURE 5-1. Self-mitigating Area
Proposed project
2026-08-19 Item #12D Page 94 of 816
Chapter 5: Storm Water Pollutant Control Requirements for PDPs 5-3 2023
5.2.2 De Minimis DMAs
De minimis DMAs consist of areas that are very small, and therefore are not considered to be significant contributors of pollutants, and are considered by the City not practicable to drain to a BMP.
It is anticipated that only a small subset of projects will qualify for a de minimis DMA exclusion.
Examples include driveway aprons connecting to existing streets, portions of sidewalks, retaining walls at the external boundaries of a project, and similar features. De minimis DMAs must meet ALL of the following to be eligible for exclusion:
• Areas abut the perimeter of the development site.
• Topography and land ownership constraints make BMP construction to reasonably capture runoff technically infeasible.
• The portion of the site falling into this category is minimized through effective site design. • Each DMA should be less than 250 square feet and the sum of all de minimis DMAs should represent less than 2 percent of the total added or replaced impervious surface of the project.
Except for projects where 2 percent of the total added or replaced impervious surface of the project is less than 250 square feet, a de minimis DMA of 250 square feet or less may be allowed.
• Multiple de minimis DMAs cannot be adjacent to each other and hydraulically connected.
The SWQMP must document the reason that each de minimis area could not be included in DMA calculations.
5.2.3 Self-retaining DMAs via Qualifying Site Design BMPs Self-retaining DMAs are areas that utilize qualifying site design BMPs to retain runoff to a level determined to constitute full retention of, at a minimum, the entire DCV. Figure 5-2 illustrates the concept of self-retaining DMAs.
FIGURE 5-2. Self-retaining Site
2026-08-19 Item #12D Page 95 of 816
Chapter 5: Storm Water Pollutant Control Requirements for PDPs 5-4 2023
To satisfy pollutant control requirements only, self-retaining means retention of the entire DCV.
However, under some circumstances, a DMA may also satisfy hydromodification management requirements by implementing BMPs that retain a greater volume of runoff. BMPs used to satisfy either standard within a DMA are classified as Significant Site Design BMPs, or SSD-BMPs. Sizing requirements for SSD-BMPs both for pollutant control and hydromodification management are addressed in their respective BMP Fact Sheets as applicable.
Two types of site design BMPs may currently be used in the design of self-retaining DMAs. Basic performance criteria are summarized below.
1. Tree Wells (SD-A in Appendix E),
A DMA can be designed using tree wells to satisfy both pollutant control and hydromodification management performance standards.
• For pollutant control only, the DMA must retain the entire DCV. • For hydromodification management, the DMA must retain the required retention volume (RRV), where RRV is DCV increased by a DCV multiplier provided in SD-A.
Appendix I provides additional information for design of tree wells as SSD-BMPs.
2. Impervious Area Dispersion (SD-B in Appendix E)
The following apply if the dispersion area is native soil (SD-B in Appendix E):
• For pollutant control only, the DMA is considered self-retaining if the impervious to pervious ratio is:
o 2:1 when the pervious area is composed of Hydrologic Soil Group A o 1:1 when the pervious area is composed of Hydrologic Soil Group B The following applies if the dispersion area includes amended soil (SD-B in Appendix E):
• DMAs using impervious area dispersion can be considered to meet both pollutant control and hydromodification flow control requirements if the impervious to pervious area ratio is 1:1 or less and all other design requirements of SD-B are satisfied, including 11 inches of amended soil.
Appendix I provides additional information for design of native soil or amended soil dispersion areas as SSD-BMPs.
Permeable pavement may also be used as dispersion area to satisfy pollutant control requirements only. The following apply if the dispersion area is permeable pavement (SD-D in Appendix E):
• For pollutant control only, a DMA is considered self-retaining if the ratio of total drainage area (including permeable pavement) to area of permeable pavement is 1.5:1 or less, and all other design requirements of SD-D are satisfied.
• Hydromodification management performance standards can be satisfied using permeable pavement only if constructed to Structural BMP specifications. In this case, the permeable pavement must be sized and constructed in accordance with the requirements of INF-3.
All of the criteria described above are conservatively developed to anticipate potential changes in 2026-08-19 Item #12D Page 96 of 816
Chapter 5: Storm Water Pollutant Control Requirements for PDPs 5-5 2023
DMA characteristics with time. Each BMP must de designed in accordance with the requirements and limitations described in its applicable BMP Fact Sheet (Appendix E). The City may accept or reject a proposed self-retaining DMA meeting these criteria at its discretion. Examples of rationales for rejection may include the potential for negative impacts (such as infiltration or vector issues), potential for significant future alteration of this feature, or inability to visually inspect and confirm the feature.
A project may use more than one type of SSD-BMP across the project to satisfy requirements.
However, the SSD-BMPs must be sized individually by DMA because their sizing factors cannot be combined. Each DMA’s requirements must be fully satisfied by either the proposed dispersion area or the proposed tree well(s). Dispersion areas meeting the SSD-BMP criteria do not need an additional downstream BMP. Dispersion areas not meeting the SSD-BMP criteria can be used as regular site design BMPs to reduce the DCV draining to a downstream BMP such as a tree well sized as an SSDBMP or a structural BMP. Tree wells meeting the SSD-BMP criteria do not need an additional downstream BMP. Tree wells not meeting the SSD-BMP criteria can be used as regular site design BMPs to reduce the DCV draining to a downstream structural BMP. See Appendix I for additional information about sizing dispersion areas and/or tree wells as SSD-BMPs. See Appendix B for additional information about using dispersion areas and/or tree wells to reduce DCV draining to a downstream structural BMP.
Site design BMPs used as part of a self-retaining DMA or as part of reducing DCV draining to a downstream BMP must be clearly called out on project plans and in the SWQMP.
For PDPs subject to hydromodification requirements and using structural BMPs to satisfy hydromodification flow control requirements, please note that Self-retaining DMAs not designed as SSD-BMPs must be included in the hydromodification analysis. When a project uses a combination of SSD-BMPs and structural BMPs to meet hydromodification requirements, the SSD-BMPs need not be included in the hydromodification analysis if the DMAs served by the SSD-BMPs are hydraulically separate from, not draining through, the structural BMPs.
Other site design BMPs can be considered self-retaining for meeting storm water pollutant control obligations if the long-term annual runoff volume (estimated using continuous simulation following guidelines listed in Appendix G) from the DMA is reduced to a level equivalent to pervious land and the applicant provides supporting analysis and rationale for the reduction in long term runoff volume.
Analysis of proposals for satisfying applicable hydromodification management requirements may also be considered if supported by continuous simulation analysis. Approval of other self-retaining areas is at the discretion of the City.
2026-08-19 Item #12D Page 97 of 816
Chapter 5: Storm Water Pollutant Control Requirements for PDPs 5-6 2023
5.3 BMP Selection and Design
The BMP designs described in the BMP Fact Sheets (Appendix E) constitute allowable storm water pollutant control BMPs for the purpose of meeting storm water management requirements. Table 5- 1 maps the BMP category to the fact sheets provided in Appendix E. Criteria specifically described in these fact sheets override guidance contained in outside referenced source documents. Where criteria are not specified, the applicant and the project review staff should use best professional judgment based on the recommendations of the referenced guidance material or other published and generally accepted sources. When an outside source is used, the preparer must document the source in the SWQMP.
TABLE 5-5-1. Permanent Structural BMPs for PDPs
BMP
Category Components BMPs Generic Illustration
Harvest &
Use
(HU)
HU-1: Cistern
Infiltration
(INF)
Soil Media: Optional
Underdrain: No
Bottom Liner: No
INF-1: Infiltration basin
INF-2: Bioretention
INF-3: Permeable pavement
Unlined
Biofiltration
Soil Media: BSM
Underdrain: Yes
Bottom Liner: No
PR-1: Biofiltration with partial
infiltration
Lined
Biofiltration
Soil Media: BSM
Underdrain: Yes
Bottom Liner: Yes
BF-1: Biofiltration
BF-2: Nutrient Sensitive Media
Design
BF-3: Proprietary Biofiltration
Flow-thru
treatment
FT-1: Vegetated swales
FT-2: Media filters
FT-3: Sand filters
FT-4: Dry extended detention
basins
FT-5: Proprietary flow-thru
treatment control
2026-08-19 Item #12D Page 98 of 816
Chapter 5: Storm Water Pollutant Control Requirements for PDPs 5-7 2023
5.4 Documenting Storm Water Pollutant Control BMP
Compliance when Hydromodification
Management Applies
The steps and guidance presented in Chapter 5 apply to all PDPs for demonstrating conformance with stormwater pollutant control requirements regardless of whether hydromodification management applies. However, when hydromodification management applies, the approach for project design may be different. The following process can be used to document compliance with stormwater pollutant control BMPs in cases when hydromodification management also applies:
1. Develop a combined BMP or treatment train (BMPs constructed in series) based on both stormwater pollutant control and hydromodification management requirements. Appendix E provides specific examples of how stormwater pollutant control BMPs can be configured to also address hydromodification management.
2. Dedicate a portion of the combined BMP or treatment train as the portion that is intended to comply with stormwater pollutant control requirements.
3. Follow all of the steps in this chapter related to demonstrating that the dedicated portion of the BMP or treatment train meets the applicable stormwater pollutant control criteria.
4. Check BMP design criteria in Appendix E and F to ensure that the hydromodification management design features (additional footprint, additional depth, modified outlet structure, lower discharge rates, etc.) do not compromise the treatment function of the BMP.
5. On project plans and in the maintenance plan, clearly denote the portion of the BMP that serves the stormwater pollutant control function.
Alternative approaches that meet both the stormwater pollutant control and hydromodification management requirements may be acceptable at the discretion of the City and must be documented in the SWQMP. Also refer to Section 6.3.6 for additional guidance. 2026-08-19 Item #12D Page 99 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L 6-1 2023
Chapter
6 6 Hydromodification Management
Requirements for PDPs
The purpose of hydromodification management requirements for PDPs is to minimize the potential of stormwater discharges from the MS4 from causing altered flow regimes and excessive downstream erosion in receiving waters. Hydromodification management implementation for PDPs includes two components: protection of critical coarse sediment yield areas and flow control for post-project runoff from the project site. For PDPs subject to hydromodification management requirements, this chapter provides guidance to meet the performance standards for the two components of hydromodification management.
Within this chapter, Appendix G, and the WMAA, the civil engineer preparing the hydromodification management study for a project will find and all the information necessary to meet the MS4 Permit standards. Should unique project circumstances require an understanding beyond what is provided in this manual, then consult the March 2011 Final HMP, which documents the historical development of the hydromodification management requirements.
Guidance for flow control of post-project runoff is based on the March 2011 Final HMP, with modifications in this manual based on updated requirements in the MS4 Permit. The March 2011 Final HMP was prepared based on the 2007 MS4 Permit, not the current MS4 Permit that drives this manual. In instances where there are changes to hydromodification management criteria or procedures based on the MS4 Permit, the criteria and procedures presented in this manual supersede the March 2011 Final HMP.
Protection of critical coarse sediment yield areas is a new requirement of the MS4 Permit and is not covered in the March 2011 Final HMP. The standards and management practices for protection of critical coarse sediment yield areas are presented here in this manual.
6.1 Hydromodification Management Applicability and
Exemptions
As noted in Chapter 1, Section 1.6 a project may be exempt from hydromodification management requirements if it meets any one of the following conditions:
• The project is not a PDP;
2026-08-19 Item #12D Page 100 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-2 2023
• The proposed project will discharge runoff directly to existing underground storm drains discharging directly to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean;
• The proposed project will discharge runoff directly to conveyance channels whose bed and bank are concrete lined all the way from the point of discharge to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean; or
• The proposed project will discharge runoff directly to an area identified by the Copermittees as appropriate for an exemption by the WMAA for the watershed in which the project resides.
The above criteria reflect the latest list of exemptions that are allowed under the MS4 Permit and therefore supersede criteria found in earlier publications.
To qualify for the potential exemption, the outlet elevation of the stormwater conveyance system discharging to the water storage reservoir or lake must be at or below either the normal operating water surface elevation, the reservoir spillway elevation, or at the elevation of the beach sand and properly designed energy dissipation must be provided.
DMAs Excluded from Hydromodification Management Flow Control Requirements When hydromodification management requirements apply to a project, protection of critical coarse sediment yield areas applies to all of the project area (all DMAs); however, certain DMAs may be excluded from the hydromodification management flow control analysis, pursuant to the criteria below.
Self-mitigating DMAs (defined in Section 5.2.1) must be evaluated on a case by case basis. Even when self-mitigating DMAs do not add impervious area, increased flow rates and durations can occur if the project’s drainage layout increases the total area draining to a natural system, or if the project creates a new concentrated discharge point in natural terrain in a location where runoff is not concentrated in the pre-development condition (e.g., a new outfall located on a hillside without defined natural channels). Additionally, if the self-mitigating area is contributing runoff to a flow control point of compliance, POC, (see Section 6.3.1 for guidelines to identify POCs), then it must be included in the sizing factor analysis or project-specific continuous simulation model. This is necessary to ensure accurate accounting of area draining to the POC and calculation of total flow rates and durations at the POC. Self-mitigating DMAs may only be excluded from flow control analyses if the following conditions are met:
• The self-mitigating area does not contribute runoff to a flow control POC. • The self-mitigating DMA does not concentrate runoff in a new location where runoff is not concentrated in the pre-development condition.
• The self-mitigating DMA does not increase the total area draining to the same discharge point compared to the pre-development condition.
De minimis DMAs meeting the restrictions defined in Section 5.2.2 may always be excluded from the flow control analysis. Subtract the de minimis area from both the pre-development and post-project footprint when conducting sizing factor calculations (Section 6.3.5.1) or project-specific continuous simulation modeling (Section 6.3.5.2).
Self-retaining DMAs via qualifying site design BMPs (defined in Section 5.2.3) must be included in 2026-08-19 Item #12D Page 101 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-3 2023
the hydromodification management analysis. Reductions in DCV realized through site design BMPs are applicable to pollutant control only and do not relax hydromodification management requirements. The self-retaining area geometry may be included in a project-specific continuous simulation model as it may provide some flow control benefit that would reduce the size of flow control structural BMP(s). Sizing factor calculations do not consider self-retaining area geometry; therefore any flow control benefit from the self-retaining area will not be realized in the sizing factor results. The exception to this rule is for DMAs that are self-retaining through the use of impervious area dispersion when the ratio of impervious to pervious area is 1:1 or less and the DMA meets all the requirements of fact sheet SD-B: Impervious Area Dispersion (Appendix E.7). These DMAs are considered to meet both the pollutant control and hydromodification flow-duration control performance standard and shall be subtracted from both the pre-development and post-project area when performing hydromodification sizing calculations.
6.2Protection of Critical Coarse Sediment Yield
Areas
When hydromodification management requirements are applicable, the applicant must determine if the project will impact any areas that are determined to be critical coarse sediment yield areas (CCSYAs). A CCSYA is an area that has been identified as an active or potential source of coarse sediment to downstream channel reaches. The process for demonstrating that the PDP does not impact CCSYAs is illustrated in Figure 6-1 below, and supplemented with detailed methodologies presented in Appendix H of this manual. PDPs complying with this MS4 Permit requirement are not subject to the provisions of the Total Maximum Daily Load for Sediment in Los Peñasquitos Lagoon, post construction. However, PDPs may be subject to Total Maximum Daily Load requirements during construction.
2026-08-19 Item #12D Page 102 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-4 2023
Figure 6-1 . Pathways to meet CCSYA requirements
Description of Steps:
Step 1. Applicants must identify CCSYAs located onsite and/or upstream of the project’s property boundary per the guidance presented in Appendix H.1. If no CCSYAs are identified in this step, no further consideration of critical coarse sediment supply is necessary.
Step 2. Applicants should avoid impacts to onsite CCSYAs through effective site design techniques discussed in Appendix H.2.
Step 3. Applicants should bypass bed sediment from onsite and/or upstream CCSYAs to downstream receiving waters per guidance presented in Appendix H.3.
Step 4. When impacts to CCSYAs are not avoided or bypassed through the site, the applicant must demonstrate that the project generates no net impact to the receiving water per guidance presented in Appendix H.4
6.3Flow Control for Hydromodification Management
PDPs subject to hydromodification management requirements must provide flow control for post-project runoff to meet the flow control performance standard.
This is typically accomplished using structural BMPs that may include any combination of infiltration basins; bioretention, biofiltration with partial retention, or biofiltration basins; or detention basins.
This section will discuss design of flow control measures for hydromodification management. This section is intended for use following the source control and site design processes described in Chapter 4 and the stormwater pollutant control design process described in Chapter 5. 2026-08-19 Item #12D Page 103 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-5 2023
The flow control performance standard is as follows (adapted from the March 2011 Final HMP, with modifications to meet the requirements of the MS4 Permit):
1 For flow rates ranging from 10 percent, 30 percent or 50 percent of the pre-development 2- year runoff event (0.1Q2, 0.3Q2, or 0.5Q2) to the pre-development 10-year runoff event (Q10), the post-project discharge rates and durations shall not deviate above the pre- development rates and durations by more than 10 percent over and more than 10 percent of the length of the flow duration curve. The specific lower flow threshold will depend on the erosion susceptibility of the receiving stream for the project site (see Section 6.3.4).
In this context, Q2 and Q10 refer to flow rates determined based on continuous simulation hydrologic modeling or the following approved regression equation:
= 3.60 ×
.
×
.
= 6.56 ×
.
×
.
where:
Q2 = 2-year recurrence interval discharge in cubic feet per second Q10 = 10-year recurrence interval discharge in cubic feet per second A = Drainage area in square miles
P = Mean annual precipitation in inches (Refer to Table 6-1) When determining Q2 and Q10 the same methodology must be applied to determination of both flow rates (i.e. cannot mix and match methods at a POC), and be consistent across all POCs for the project (i.e. cannot mix and match methods between multiple POCs).
TABLE 6-6-1. Mean Annual Precipitation
Gage Latitude Longitude Mean Annual Precipitation
(inches)
Oceanside 33.2105556 -117.353333 12.29
Encinitas 33.044567 -117.277213 10.73
Kearney Mesa 32.835118 -117.128456 11.43
Fashion Valley 32.7652778 -117.1758333 10.75
Bonita 32.6561111 -117.0341667 10.88
Poway 32.9522222 -117.0472222 13.08
Fallbrook AP 33.354669 -117.251279 16.18
Lake Wohlford 33.166423 -117.004955 16.63
Ramona 33.0480556 -116.8608333 16.57
Lake Henshaw 33.2386111 -116.7616667 21.58
Borrego 33.2211111 -116.3369444 4.00
Lindbergh 32.7337 -117.1767 10.75
2026-08-19 Item #12D Page 104 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-6 2023
Gage Latitude Longitude Mean Annual Precipitation
(inches)
Escondido 33.1197222 -117.095 14.67
Flinn Springs 32.847104 -116.857801 15.55
Lake Cuyamaca 32.9894 -116.5867 31.30
Lower Otay 32.6111 -116.9319 11.90
San Onofre 33.3513889 -117.5319444 11.13
San Vicente 32.912082 -116.926513 16.47
Santee 32.839016 -117.024857 13.15
The range from a fraction of Q2 to Q10 represents the range of geomorphically significant flows for hydromodification management in San Diego. The upper bound of the range of flows to control is pre-development Q10 for all projects. The lower bound of the range of flows to control, or "lower flow threshold" is a fraction of pre-development Q2 that is based on the erosion susceptibility of the stream and depends on the specific natural system (stream) that a project will discharge to. Tools have been developed in the March 2011 Final HMP for assessing the erosion susceptibility of the stream (see Section 6.3.4 below for further discussion of the lower flow threshold).
When selecting the type of structural BMP to be used for flow control, consider the types of structural BMPs that will be utilized onsite for pollutant control.
Both stormwater pollutant control and flow control for hydromodification management can be achieved within the same structural BMPs. For example, a full infiltration BMP that infiltrates the DCV for pollutant control could include additional storage volume above or below ground to provide either additional infiltration of stormwater or control of outflow for hydromodification management.
If possible, the structural BMPs for pollutant control should be modified to meet flow control performance standards in addition to the pollutant control performance standards. See Section 6.3.6 for further discussion of integrating structural BMPs for pollutant control and flow control.
6.3.1 Point(s) of Compliance
For PDPs subject to hydromodification management requirements, the flow control performance standard must be met for each natural or un-lined channel that will receive runoff from the project.
This may require multiple structural BMPs within the project site if the project site discharges to multiple discrete outfalls. When runoff is discharged to multiple natural or un-lined channels within a project site, each natural or un-lined channel must be considered separately and points of compliance (POCs) for flow control must be provided for each natural or un-lined channel, including situations where the channels will confluence before leaving the project boundary. When runoff from the project site does not meet a natural or un-lined channel onsite, instead traveling some distance downstream of the project in storm drain systems or lined channels prior to discharge to natural or un-lined channels, the POC(s) for flow control analysis shall be placed at the project boundary (i.e., comparing 2026-08-19 Item #12D Page 105 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-7 2023
the pre-development and post-project flows from the project area only, not analyzing the total watershed draining to the offsite POC), unless the project is draining to and accommodated by an approved master planned or regional flow control BMP.
For projects with multiple POCs, care should be taken to avoid the diversion of flow from one POC to another. In addition to water balance issues, flow diversion between points of compliance increases the size of the required flow control measures because the post-project drainage area is larger than the pre-development area. Consider the effect of grading changes and conveyances on potential diversions.
For individual projects draining to approved central or regional flow control BMPs, the POC for flow control analysis may be offsite of the specific project application.
In these instances, the individual project draining to a central or regional flow control BMP shall reference the approved design documents for the BMP, and shall demonstrate that either (a) the individual project design is consistent with assumptions made for imperviousness and features of the project area when the central or regional BMP was designed, or (b) the central or regional BMP still meets performance standards when the actual proposed imperviousness and features of the project area are considered.
Guidelines for Drainage Layout for Effective Hydromodification Management The following guidelines for drainage layout will assist PDPs in effectively managing site runoff for more efficient hydromodification flow control management. By following these guidelines, the total number and size of structural BMPs necessary for flow control can be minimized. • Identify existing (pre-development) drainage concentration points and use the existing concentration points for storm water discharge in the proposed design. • Avoid creating new concentrated discharge points (storm drain outfalls) on hillsides or other locations where drainage is not naturally concentrated. • Avoid diversion. Diversion means changing the discharge location of storm water runoff from a given land area from one concentration point to another (i.e., change in POC drainage area between pre-development and post-project condition). In the context of hydromodification management, diversion is measured with respect to each natural drainage system that is subject to erosion (i.e., at each POC), rather than at a property boundary. A diversion area is created when area that originally drains to one discharge location (e.g., “POC A”) is changed to discharge to a different location (e.g., “POC B”) as a result of grading and land development.
Note that when the proposed project design will create a diversion area, the project must provide mitigation to match the pre-development runoff from the existing (pre-development) area. This means that if the proposed project will discharge runoff from 5 acres to a location that had a pre-development drainage area of 4 acres, the proposed project must provide mitigation to match the pre-development runoff flow rates and durations from the predevelopment drainage area of 4 acres. When there is a diversion area, project-specific continuous simulation modeling is required to demonstrate that the flow control performance standard is met (Section 6.3.5.2). Sizing factor calculations (Section 6.3.5.2) are not applicable when there is a diversion area.
2026-08-19 Item #12D Page 106 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-8 2023
6.3.2 Offsite Area Restrictions
Runoff from offsite undeveloped areas should be routed around structural BMPs for flow control whenever feasible.
Methods to route flows around structural BMPs include designing the site to avoid natural drainage courses, or using parallel storm drain systems. If geometric constraints prohibit the rerouting of flows from undeveloped areas around a structural BMP, a detailed description of the constraints must be submitted to the [City Engineer].
Structural BMPs for flow control must be designed to avoid trapping sediment from natural areas regardless of whether the natural areas are critical coarse sediment yield areas or not.
Reduction in coarse sediment supply contributes to downstream channel instability. Capture and removal of natural sediment from the downstream watercourse can create "hungry water" conditions and the increased potential for downstream erosion. Additionally, coarse or fine sediment from natural areas can quickly fill the available storage volume in the structural BMP and/or clog a small flow control outlet, which can cause the structural BMP to overflow during events that should have been controlled, and will require frequent maintenance. Failure to prevent clogging of the principal control orifice defeats the purpose of a flow control BMP, since basin inflows would simply overtop the control structure and flow unattenuated downstream, potentially worsening downstream erosion.
6.3.3 Requirement to Control to Pre-Development (Not Pre-Project) Condition
The MS4 Permit requires that post-project runoff must be controlled to match predevelopment runoff conditions, not pre-project conditions, for the range of flow rates to be controlled.
Pre-development runoff conditions are defined in the MS4 Permit as "approximate flow rates and durations that exist or existed onsite before land development occurs." • Redevelopment PDPs: Use available maps or development plans that depict the topography of the site prior to development; otherwise use existing onsite grades if historic topography is not available. Assume the infiltration characteristics of the underlying soil. Use available information pertaining to existing underlying soil type such as soil maps published by the Natural Resource Conservation Service (NRCS). Do not use runoff parameters for concrete or asphalt to estimate pre-development runoff conditions. • New development PDPs: The pre-development condition typically equates to runoff conditions immediately before project construction. However if there is existing impervious area onsite, as with redevelopment, the new development project must not use runoff parameters for concrete or asphalt to estimate pre-development runoff conditions.
When it is necessary for runoff from offsite impervious area (not a part of the project) to co-mingle with project site runoff and be conveyed through a project's structural flow control BMP, the offsite impervious area may be modeled as impervious in both the pre- and post- condition models. A project is not required to provide flow control for stormwater from offsite. This also means that for redevelopment projects not subject to the 50% rule (i.e., redevelopment projects that result in the creation or replacement of impervious surface in an amount of less than 50% of the area of impervious 2026-08-19 Item #12D Page 107 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-9 2023
surface of the previously existing development), comingled runoff from undisturbed portions of the previously existing development (i.e., areas that are not a part of the project) will not require flow control. Flow control facilities for comingled offsite and onsite runoff would be designed to process the total volume of the comingled runoff through the facility, but would provide mitigation for the excess runoff (difference of developed to pre-developed condition) based on onsite impervious areas only. The project applicant must clearly explain why it was not feasible or practical to provide a bypass system for stormwater from offsite. The City Engineer may request that the project applicant provide a supplemental analysis of onsite runoff only (i.e., supplemental model of the project area only).
6.3.4 Determining the Low Flow Threshold for Hydromodification Flow Control
The range of flows to control for hydromodification management depends on the erosion susceptibility of the receiving stream.
The range of flows to control is either:
• 0.1Q2 to Q10 for projects discharging to streams with high susceptibility to erosion (and this is the default range of flows to control when a stream susceptibility study has not been prepared),
• 0.3Q2 to Q10 for projects discharging to streams with medium susceptibility to erosion as determined by a stream susceptibility study approved by the City Engineer, or • 0.5Q2 to Q10 for projects discharging to streams with low susceptibility to erosion as determined by a stream susceptibility study approved by the City Engineer.
The project applicant may opt to design to the default low flow threshold of 0.1Q2, or provide assessment of the receiving stream ("channel screening" a.k.a. "geomorphic assessment"), which may result in a higher low flow threshold of 0.3Q2 or 0.5Q2 for project hydromodification management.
Use of a higher low flow threshold of 0.3Q2 or 0.5Q2 must be supported by a channel screening report. Channel screening is based on a tool developed by the Southern California Coastal Water Research Project (SCCWRP), documented in SCCWRP's Technical Report 606 dated March 2010, "Hydromodification Screening Tools: Field Manual for Assessing Channel Susceptibility." The SCCWRP channel screening tool considers channel conditions including channel braiding, mass wasting, and proximity to the erosion threshold. SCCWRP's Technical Report 606 is included in Appendix B of the March 2011 Final HMP, and can also be accessed through SCCWRP's website.
The result of applying the channel screening tool will be classification of high, medium, or low susceptibility to erosion, corresponding to low flow thresholds of 0.1Q2, 0.3Q2, and 0.5Q2, respectively, for the receiving stream. Note that the City Engineer may require that the channel screening study has been completed within a specific time frame prior to their review, and/or may apply a sunset date to their approval of a channel screening study. Other projects may rely on previously approved SCCWRP analyses at the discretion of the City Engineer.
The receiving stream is the location where runoff from the project is discharged to natural or un-lined channels.
The receiving stream may be onsite or offsite. The POC for channel screening is the point where 2026-08-19 Item #12D Page 108 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-10 2023
runoff initially meets an un-lined or natural channel, regardless of whether the POC for flow control facility sizing is at or within the project boundary or is offsite. A project may have a different POC for channel screening and flow control facility sizing if runoff from the project site is conveyed in hardened systems from the project site to the un-lined or natural channel. The erosion susceptibility of the receiving stream must be evaluated at the POC for channel screening, and for an additional distance known as the domain of analysis, defined in SCCWRP's Technical Report 606.
6.3.5 Designing a Flow Control Facility
Flow control facilities for hydromodification management must be designed based on continuous simulation hydrologic modeling.
Continuous simulation hydrologic modeling uses an extended time series of recorded precipitation data and evapotranspiration data as input and generates hydrologic output, such as surface runoff, groundwater recharge, and evapotranspiration, for each model time step. Using the continuous flow output, peak flow frequency and duration statistics can be generated for the pre-development and post-project conditions for the purpose of matching pre-development hydrologic conditions in the range of geomorphically significant flow rates. Peak flow frequency statistics estimate how often flow rates will exceed a given threshold. Flow duration statistics determine how often a particular flow rate is exceeded. To determine if a flow control facility meets hydromodification management performance standards, peak flow frequency and flow duration curves must be generated and compared for predevelopment and post-project conditions.
Flow control facilities may be designed using either sizing factors presented in Appendix B of this manual, or using project-specific continuous simulation modeling. The sizing factors were developed based on unit-area continuous simulation models. This means the continuous simulation hydrologic modeling has already been done and the project applicant needs only to apply the sizing factors to the project's effective impervious area to size a facility that meets flow control performance standards.
The sizing factor method is intended for simple studies that do not include diversion, do not include significant offsite area draining through the project from upstream, and do not include offsite area downstream of the project area. Use of the sizing factors is limited to the specific structural BMPs for which sizing factors were prepared. Project-specific continuous simulation modeling offers the most flexibility in the design, but requires the project applicant to prepare and submit a complete continuous simulation hydrologic model for review.
6.3.5.1 Sizing Factor Method
A project applicant may use sizing factors that were created to facilitate sizing of certain specific BMPs for hydromodification management.
The sizing factors included in G.2 have been updated based on the requirements in the 2013 MS4 permit and are different than the sizing factors presented in previous manuals. These updated values replace the previous sizing factors which shall no longer be used for sizing of hydromodification flow control BMPs. A discussion of the rational for the update is included in Appendix G.2.
The sizing factor method is intended for simple studies that do not include diversion, do not include significant offsite area draining through the project from upstream, and do not include offsite area downstream of the project area. Use of the sizing factors is limited to the specific structural BMPs described in Appendix G.2.
2026-08-19 Item #12D Page 109 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-11 2023
6.3.5.2 Project-Specific Continuous Simulation Modeling A project applicant may prepare a project-specific continuous simulation model to demonstrate compliance with hydromodification management performance standards.
This option offers the most flexibility in the design. In this case, the project applicant shall prepare continuous simulation hydrologic models for pre-development and post-project conditions, and compare the pre-development and post-project (with hydromodification flow control BMPs) runoff peaks and durations until compliance with the flow control performance standards is demonstrated.
The project applicant will be required to quantify the long-term pre-development and post-project runoff response from the site and establish runoff routing and stage-storage-discharge relationships for the planned flow control BMPs. There are several available hydrologic models that can perform continuous simulation analyses. Refer to Appendix G.1 of this manual for guidance for continuous simulation hydrologic modeling.
6.3.6 Integrating HMP Flow Control Measures with Pollutant Control BMPs
Both stormwater pollutant control and flow control for hydromodification management can be achieved within the same structural BMP(s) or by a series of structural BMP(s).
The design process should start with an assessment of the controlling design factor, then the typical design process for an integrated structural BMP or series of BMPs to meet two separate performance standards at once involves (1) initiating the design based on the performance standard that is expected to require the largest volume of stormwater to be retained, (2) checking whether the initial design incidentally meets the second performance standard, and (3) adjusting the design as necessary until it can be demonstrated that both performance standards are met. The following are recommendations for initiating the design process:
• Full infiltration condition: retention for pollutant control performance standard is the controlling design factor. For a system that is based on full retention for stormwater pollutant control, first design an initial retention area to meet stormwater pollutant control standards for retention, then check whether the facility meets flow control performance standards. If the initial retention facility does not meet flow control performance standards: increase the volume of the facility, increasing retention if feasible or employing outflow control for runoff to be discharged from the facility; as needed to meet the flow control performance standards. • Partial infiltration condition: retention for pollutant control performance standard is the controlling design factor. For a system that is based on partial retention for stormwater pollutant control, first design the retention area to maximize retention as feasible. Then design an additional runoff storage area with outflow control for runoff to be discharged from the facility; as needed to meet the flow control performance standards. Then address pollutant control needs for the portion of the stormwater pollutant control DCV that could not be retained onsite.
• No infiltration condition: flow control for hydromodification management standard is the controlling design factor. For a system that is based on biofiltration with no infiltration for stormwater pollutant control, first design the facility to meet flow control performance standards, then check whether the facility meets biofiltration design standards for stormwater pollutant control. If the flow control biofiltration facility does not meet performance standards 2026-08-19 Item #12D Page 110 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-12 2023
for stormwater pollutant control by biofiltration, increase the volume of the biofiltration facility as needed to meet pollutant control performance standards, or identify other methods to address pollutant control needs for the portion of the stormwater pollutant control DCV that could not be processed with biofiltration onsite.
When an integrated structural BMP or series of BMPs is used for both stormwater pollutant control and flow control for hydromodification management, separate calculations are required to demonstrate that pollutant control performance standards and hydromodification management standards are met.
When an integrated structural BMP or series of BMPs is proposed to meet the stormwater pollutant control and flow control for hydromodification management obligations, the applicant shall either:
• Perform separate calculations to show that both hydromodification management and pollutant control performance standards are met independently by using guidance from Appendices B and G. Calculations performed shall be documented in the SQWMP. or • Develop an integrated design that meets the separate performance standards presented in Chapter 2 for both hydromodification management and pollutant control. In this option the BMP requirements to meet the pollutant control performance standard are optimized to account for the BMP storage provided for flow control, and vice versa. Calculations performed to develop an integrated design shall be documented in the SQWMP. Project approval when this option is selected is at the discretion of the City Engineer.
6.3.7 Drawdown Time
The maximum recommended drawdown time for hydromodification management facilities is 96 hours based on Section 6.4.6 of the March 2011 Final HMP.
This is based on instruction from the County of San Diego Department of Environmental Health for mitigation of potential vector breeding issues and the subsequent risk to human health. This standard applies to, but is not limited to, detention basins, underground storage vaults, and the aboveground storage portion of LID facilities. When this standard cannot be met due to large stored runoff volumes with limited maximum release rates, a vector management plan may be an acceptable solution if approved by the governing municipality.
In cases where a Vector Management Plan is necessary, it shall be incorporated into the SWQMP as an attachment. A Vector Management Plan will only be accepted after the applicant has proven infeasibility of meeting the required drawdown time using any and all allowable BMPs. The information included in the plan will vary based on the nature, extent and variety of potential vector sources. It is recommended that preparers consult with the Department of Environmental Health Vector Control Program for technical guidance. Plans should include the following information at a minimum:
• Project identification information;
• A description of the project, purpose of the report, and existing environmental conditions; • A description of the management practices that will be employed to minimize vector breeding sources and any associated employee education required to run facilities and operations; 2026-08-19 Item #12D Page 111 of 816
Chapter 6: Hydromodification Management Requirements for PDPs 6-13 2023
• A discussion of long term maintenance requirements;
• A summary of mitigation measures;
• References; and
• A list of persons and organizations contacted (project proponents are expected to obtain review and concurrence of proposed management practices from Department of Environmental Health Vector control program staff prior to submission).
The property owner and applicant must include and sign the following statement: “The measures identified herein are considered part of the proposed project design and will be carried out as part of project implementation. I understand the breeding of mosquitoes in unlawful under the State of California Health and Safety Code Section 2060-2067. I will permit the Vector Surveillance and Control program to place adult mosquito monitors and to enforce this document as needed.” Refer to the sources below for additional guidance:
Report Guidance: http://www.sandiegocounty.gov/dplu/docs/Vector_Report_Formats.pdf Department of Environmental Health Vector Control Program:
http://www.sandiegocounty.gov/deh/pests/vector_disease.html It should be noted that other design factors may influence the required drawdown when hydromodification management BMPs are integrated with stormwater pollutant control BMPs. Since hydromodification flow control BMPs are designed based on continuous simulation modeling, which is based on a continuous rainfall record and analyzes a continuous inflow and outflow of the BMPs, inter-event drawdown time and availability of the BMP for subsequent event inflow has been accounted for in the sizing. Therefore, drawdown recommendations for hydromodification management are based on public safety, not availability of the BMP for the next inflow event.
Stormwater pollutant control BMPs are designed on a single-event basis for a DCV (the 85th percentile storm event). Some of the design standards presented in Chapter 5 or Appendix B require that the pollutant control portion of the BMP drain within a specific time frame to ensure the pollutant control portion of the BMP is available for subsequent storm events. When hydromodification management BMPs are integrated with stormwater pollutant control BMPs, the designer must evaluate drawdown time based on both standards.
6.4 In-Stream Rehabilitation
An alternative to onsite flow control for post-project runoff may be in-stream rehabilitation.
Project applicant may be allowed to participate in an in-stream rehabilitation project in lieu of implementing onsite flow control BMPs. Refer to section 1.8 to determine if this option is available in the project watershed10.
10 The City of Encinitas does not currently have an Alternative Compliance Program. 2026-08-19 Item #12D Page 112 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L 7-1 2023
Chapter
7 7 Long Term Operation & Maintenance
Permanent structural BMPs require on-going inspection and maintenance into perpetuity to preserve the intended pollution control and/or flow control performance.
This chapter addresses procedural requirements for implementation of a long-term Stormwater Maintenance Agreement and an Operation & Maintenance (O&M) Plan. This chapter also explains the typical maintenance requirements of structural BMPs presented in the manual. Specific requirements for O&M Plans will be discussed in Chapter 8 with the Submittal Requirements.
7.1 Need for Permanent Inspection and Maintenance
7.1.1 MS4 Permit Requirements
The MS4 Permit requires that each Copermittee implement a program that requires and confirms structural BMPs on all PDPs are designed, constructed, and maintained to remove pollutants in stormwater to the MEP.
Routine inspection and maintenance of BMPs will preserve the design and MS4 Permit objective to remove pollutants in stormwater to the MEP. The MS4 Permit requirement specifically applies to PDP structural BMPs; however, poor maintenance of source control, site design, or LID BMPs can lead to clogging or failure of structural BMPs due to greater delivery of runoff and pollutants than intended. Therefore, the City Engineer may also confirmation of maintenance of source control BMPs and site design / LID BMPs as part of the PDP structural BMP maintenance documentation requirements, as applicable (see Section 7.4).
7.1.2 Practical Considerations
Why do permanent structural BMPs require on-going inspection and maintenance into perpetuity?
By design, structural BMPs will trap pollutants transported by stormwater. Structural BMPs are subject to deposition of solids such as sediment, trash, pollutants, and other debris as well as to vegetation overgrowth. All components of the BMP, including both the surface and any sub-surface components, must be properly maintained to ensure ongoing pollutant capture capacity and to prevent flooding, standing water, and associated vector issues.
2026-08-19 Item #12D Page 113 of 816
Chapter 7: Long Term Operation and Maintenance
7-2 2023
Vegetated structural BMPs, including vegetated infiltration or partial infiltration BMPs, and above ground detention basins, also require routine maintenance so that they don't inadvertently become wetlands, waters of the state, or sensitive species habitat under the jurisdiction of the United States Army Corps of Engineers, SDRWQCB, California Department of Fish and Wildlife, or the United States Fish and Wildlife Service. A structural BMP that is constructed in the vicinity of, or connected to, an existing jurisdictional water or wetland could inadvertently result in creation of expanded waters or wetlands. Proper placement and routine maintenance of structural BMPs are key to preventing this scenario and the need for specific resource agency permits and costly mitigation to perform maintenance of the structural BMP.
7.2 Summary of Steps to Maintenance Agreement
Ownership and maintenance responsibility for structural BMPs should be discussed at the beginning of project planning, typically at the pre-application meeting with the planning and zoning agency.
Structuring provisions to finance and implement maintenance of BMPs can be a major stumbling block to project approval. A maintenance agreement must be completed prior to the issuance of any construction, grading, building permit, site development permit, or any other applicable permit. The Operation and Maintenance plan is an attachment to the Stormwater Maintenance Agreement. Below are the typical steps and schedule for establishing a plan to ensure on-going maintenance of structural BMPs.
Table 7-1. Schedule for Developing O&M Plan and Agreement Item Description Time Frame
1 Determine structural BMP ownership, party
responsible for permanent O&M, and
maintenance funding mechanism.
Prior to first submittal of a project
application – discuss with staff at preapplication meeting. 2 Identify expected maintenance actions. First submittal of a project application – identify in SWQMP.
3 Develop detailed O&M Plan and submit to
City for review and approval.
Prior to issuance of construction, grading,
building, site development, or other
applicable permits.
4 Prepare and record a Stormwater Maintenance
Agreement (legal agreement to be recorded
against the property by the County Recorder)
with the O&M Plan attached.
Prior to issuance of permit and/or
recordation of parcel/final map.
5 Upon completion of construction, at the
discretion of the City Engineer, the
Stormwater Maintenance Agreement may be
revised and rerecorded if conditions warrant.
Prior to final and release of securities.
7.3 Maintenance Responsibility
The property owner is responsible for the maintenance of the permanent structural BMPs into 2026-08-19 Item #12D Page 114 of 816
Chapter 7: Long Term Operation and Maintenance
7-3 2023
perpetuity.
The property owner is responsible to ensure inspection and O&M of permanent structural BMPs on their property unless responsibility has been formally transferred to an agency, community facilities district, homeowners association, property owners association, or other special district. When property ownership changes (i.e. the property is sold or otherwise transferred to a new owner), maintenance responsibility runs with the land and automatically transfers to the new owner. For structural BMPs that will be transferred to an agency, community facilities district, homeowners association, property owners association, or other special district, there may be an interim period during which the property owner is responsible until maintenance responsibility is formally transferred.
In the City of Encinitas, a Stormwater Maintenance Agreement must be prepared for all PDPs. The Stormwater Maintenance Agreement and attached O&M Plan must document the following:
• Property ownership and maintenance responsibility,
• Transfer of ownership/maintenance responsibility upon sale of the property, • Structural BMPs that were installed per plan, and
• Required maintenance activities and frequency.
The Stormwater Maintenance Agreement is a legal agreement to be recorded against the property by the County Recorder. The City of Encinitas maintains four different maintenance agreement templates, depending on the property ownership arrangement. The four types of maintenance agreements include:
• Agreement for Maintenance by a Homeowner
• Agreement for Maintenance by a Homeowners’ Association • Agreement for Maintenance by an Agent
• Agreement for Maintenance by an Agent of a Commercial Facility
7.4 Long-Term Maintenance Documentation
As part of on-going structural BMP maintenance into perpetuity, property owners are required to provide documentation of maintenance for the structural BMPs on their property on an annual basis to support the Copermittees' reporting requirements to the SDRWQCB.
The MS4 Permit requires each Copermittee to verify that structural BMPs on each PDP "are adequately maintained, and continue to operate effectively to remove pollutants in stormwater to the MEP through inspections, self-certifications, surveys, or other equally effective approaches." Based on these MS4 Permit requirements, the City Engineer requires that all permanent structural BMPs installed at PDPs be inspected by the property owner and maintained as necessary.
Inspection and proper maintenance of all permanent structural BMPs shall be verified annually by the party responsible for maintenance. The City sends annual reminder letters to the responsible party for each site in the City’s PDP inventory. Annual verification documentation can conveniently be submitted via a specially designed City website, http://cleanwaterbmp.cityofencinitas.org/. Maintenance verification submitted via email, mail or 2026-08-19 Item #12D Page 115 of 816
Chapter 7: Long Term Operation and Maintenance
7-4 2023
in person are also accepted.
In addition to the mandatory annual self-verifications, the City conducts inspections of all permanent structural BMPs at the PDP site to verify that each BMP is working, being maintained properly, and is in compliance with all applicable City ordinances and permits. Inspection frequencies vary with the established project inspection priority. Table 4-3 below presents structural BMP priorities and their corresponding inspection frequencies. For instance, all PDPs designated as High priority for inspection, as determined in Section 4.5.2, are inspected by City staff on an annual basis prior to October 1.
Table 7-2. Permanent BMP Maintenance Verification and Inspection Requirements Project
Inspection
Priority
Maintenance Verification Inspection Frequency
High Required from all projects annually 100% inspected annually by City staff prior to the start of the rainy season (October 1)
Low Required from all projects annually Inspected by City staff if verification documentation is not provided or is not adequate.
7.5 Inspection and Maintenance Frequency
How often is a property owner required to inspect and maintain permanent structural BMPs on their property?
The minimum inspection and maintenance frequency is once per year, reported annually. However, maintenance needs depend on the amount and quality of runoff delivered to the structural BMP, and annual maintenance is not always sufficient. Maintenance must be performed each time the maintenance threshold for removal of materials (sediment, trash, debris or overgrown vegetation) is met; maintenance indicators are presented in Section 7.7. If the annual inspection reveals that the maintenance threshold has already been exceeded, then the structural BMP has been operating at a reduced capacity; more frequent inspections and maintenance will be necessary in the future to avoid expensive rehabilitation of such inadequately maintained BMPs.
During the first year of normal operation of a structural BMP (i.e. when the project is fully built out and occupied), inspection is recommended at least once prior to August 31 and then monthly from September through May. Inspection during and after a storm event is also recommended to verify proper BMP function. After the initial period of frequent inspections, the minimum inspection and maintenance frequency can be determined, based on the results of the first year inspections.
7.6 Measures to Control Maintenance Costs
Because structural BMPs must be maintained into perpetuity, it is essential to include measures to control maintenance costs.
The most effective way to reduce maintenance of structural BMPs is to reduce the pollutants they 2026-08-19 Item #12D Page 116 of 816
Chapter 7: Long Term Operation and Maintenance
7-5 2023
receive by implementing source control and site design BMPs onsite, as required and described in Chapter 4. In addition, structural BMPs should include design features to facilitate maintenance, as listed below.
Considerations for placement of vegetated BMPs:
• Locate structural BMPs outside of floodway, floodplain, and other jurisdictional areas. • Avoid direct connection to a natural surface water body. • Discuss the location of the structural BMP with a wetland biologist to avoid placing a structural BMP in a location where it could become a jurisdictional wetland or be connected to a jurisdictional wetland area.
Measures to facilitate collection of the trapped pollutants:
• Design a forebay to trap gross pollutants in a contained area that is readily accessible for maintenance. A forebay may be a dedicated area at the inlet entrance to an infiltration BMP, biofiltration BMP, or detention basin, or may be a gross pollutant separator installed in the storm drain system that drains to the primary structural BMP.
Measures to access the structural BMP:
• The BMP must be accessible to equipment needed for maintenance. Access requirements for maintenance will vary with the type of facility selected. • Infiltration BMPs and biofiltration BMPs typically require routine landscape maintenance using the same equipment that is used for general landscape maintenance. At times these BMPs may require excavation of clogged media (e.g. bioretention soil media, or sand for the sand filter), and should be accessible to appropriate equipment for excavation and removal/replacement of media.
• Above-ground detention basins should include access ramps for trucks to enter the basin to bring equipment and to remove materials.
• Underground BMPs such as detention vaults, media filters, or gross pollutant separators used as forebays to other BMPs, typically require access for a vactor truck to remove materials.
Proprietary BMPs such as media filters or gross pollutant separators may require access by a forklift or other truck for delivery and removal of media cartridges or other internal components. Access requirements must be verified with the manufacturer of proprietary BMPs.
• Vactor trucks are large, heavy, and difficult to maneuver. Structural BMPs that are maintained by vactor truck must include a level pad adjacent to the structural BMP, preferably with no vegetation or irrigation system (otherwise vegetation or irrigation system may be destroyed by the vactor truck).
• The sump area of a structural BMP should not exceed 20 feet in depth due to the loss of efficiency of a vactor truck. The water removal rate is three to four times longer when the depth is greater than 20 feet. Deep structures may require additional equipment (stronger vactor trucks, ladders, more vactor pipe segments).
• All manhole access points to underground structural BMPs must include a ladder or steps.
Measures to facilitate inspection of the structural BMP:
2026-08-19 Item #12D Page 117 of 816
Chapter 7: Long Term Operation and Maintenance
7-6 2023
• Structural BMPs shall include inspection ports for observing all underground components that require inspection and maintenance.
• Silt level posts or other markings shall be included in all BMP components that will trap and store sediment, trash, and/or debris, so that the inspector may determine how full the BMP is, and the maintenance personnel may determine where the bottom of the BMP is. Posts or other markings shall be indicated and described on structural BMP plans. • Vegetation requirements including plant type, coverage, and minimum height when applicable shall be provided on the structural BMP and/or landscaping plans as appropriate or as required by the City Engineer.
• Signage indicating the location and boundary of the structural BMP is recommended.
When designing a structural BMP, the engineer should review the typical structural BMP maintenance actions listed in Section 7.7 to determine the potential maintenance equipment and access needs.
When selecting permanent structural BMPs for a project, the engineer and project owner should consider the long-term cost of maintenance and what type of maintenance contracts a future property owner, homeowners association or property owners association will need to manage. The types of materials used (e.g. proprietary vs. non-proprietary parts), equipment used (e.g. landscape equipment vs. vactor truck), actions/labor expected in the maintenance process and required qualifications of maintenance personnel (e.g. confined space entry) affect the cost of long term O&M of the structural BMPs.
7.7 Maintenance Indicators and Actions for
Structural BMPs
This section presents typical maintenance indicators and routine and corrective maintenance actions for typical structural BMPs.
Structural BMPs are grouped into four categories based on common maintenance requirements:
• Vegetated infiltration or filtration BMPs
• Non-vegetated infiltration BMPs
• Non-vegetated filtration BMPs
• Detention BMPs
The components of the structural BMP will determine its maintenance category and therefore the applicable maintenance indicators. Maintenance indicators and actions shall be shown in the projectspecific O&M Plan.
During inspection, the inspector checks the maintenance indicators. If one or more thresholds are met or exceeded, maintenance must be performed to ensure the structural BMP will function as designed during the next storm event. At a minimum, maintenance shall be performed once annually.
Table 7-3 to Table 7-6 present generalized maintenance actions based on the BMP categories.
Additional guidance is provided in Appendix E in the factsheets for each BMP. 2026-08-19 Item #12D Page 118 of 816
Chapter 7: Long Term Operation and Maintenance
7-7 2023
7.7.1 Maintenance of Vegetated Infiltration or Filtration BMPs "Vegetated infiltration or filtration BMPs" are BMPs that include vegetation as a component of the BMP. Applicable Fact Sheets may include INF-2 (bioretention), PR-1 (biofiltration with partial retention), BF-1 (biofiltration) or FT-1 (vegetated swale). The vegetated BMP may or may not include amended soils, subsurface gravel layer, underdrain, and/or impermeable liner. Maintenance indicators and associated actions for vegetated infiltration and filtration BMPs are presented below.
Table 7-3. Maintenance Indicators and Actions for Vegetated BMPs Typical Maintenance
Indicator(s) for Vegetated BMPs Maintenance Actions
Accumulation of sediment, litter, or
debris
Remove and properly dispose of accumulated materials,
without damage to the vegetation. Examine the DMA draining to the BMP to determine the source of the sediment.
Implement corrective measures as applicable to minimize the sediment supply.
Poor vegetation establishment Re-seed, re-plant, or re-establish vegetation per original plans.
Evaluate proper functioning of irrigation system, if applicable.
Overgrown vegetation Mow or trim as appropriate, but not less than the design height of the vegetation per original plans when applicable (e.g. a vegetated swale may require a minimum vegetation height).
Erosion due to concentrated
irrigation flow
Repair/re-seed/re-plant eroded areas. If necessary, perform minor re-grading to restore proper drainage according to the original plan. Adjust the irrigation system to prevent further erosion.
Erosion due to concentrated storm
water runoff flow
Repair/re-seed/re-plant eroded areas, and make appropriate corrective measures such as adding erosion control blankets, adding stone at flow entry points, or minor re-grading to restore proper drainage according to the original plan. If the issue is not corrected by restoring the BMP to the original plan and grade, contact the City Engineer prior to any additional repairs or reconstruction.
Standing water in vegetated swales Make appropriate corrective measures such as adjusting the irrigation system, removing obstructions of debris or invasive vegetation, loosening or replacing top soil to allow for better infiltration, or minor re-grading, to restore proper drainage according to the original plan. If the issue is not corrected by restoring the BMP to the original plan and grade, contact the City Engineer prior to any additional repairs or reconstruction.
Repair/re-seed/re-plant per the original plans any damaged vegetation in need of replacement.
2026-08-19 Item #12D Page 119 of 816
Chapter 7: Long Term Operation and Maintenance
7-8 2023
Typical Maintenance
Indicator(s) for Vegetated BMPs Maintenance Actions
Standing water in bioretention,
biofiltration with partial retention, or
biofiltration areas, or flow-through
planter boxes for longer than 96
hours following a storm event*
Make appropriate corrective measures such as adjusting the irrigation system, removing obstructions of debris or invasive vegetation, loosening or replacing top soil to allow for better infiltration, clearing any underdrains, or minor re-grading to restore proper drainage according to the original plan. If the issue is not corrected by restoring the BMP to the original plan and grade, contact the City Engineer prior to any additional repairs or reconstruction. Repair/re-seed/re-plant per the original plans any damaged vegetation in need of replacement.
Obstructed inlet or outlet structure Clear obstructions.
Damage to structural components
such as weirs, inlet or outlet
structures
Repair or replace as applicable.
*These BMPs typically include a surface ponding layer as part of their function which may take 96 hours to drain following a storm event.
7.7.2 Maintenance of Non-Vegetated Infiltration BMPs
"Non-vegetated infiltration BMPs" are BMPs that store stormwater runoff until it infiltrates into the ground, and do not include vegetation as a component of the BMP (refer to the "vegetated BMPs" category for infiltration BMPs that include vegetation). Non-vegetated infiltration BMPs generally include non-vegetated infiltration trenches and infiltration basins, dry wells, underground infiltration galleries, and permeable pavement with underground infiltration gallery. Applicable Fact Sheets may include INF-1 (infiltration basin) or INF-3 (permeable pavement). The non-vegetated infiltration BMP may or may not include a pre-treatment device, and may or may not include above-ground storage of runoff. Maintenance indicators and associated actions for non-vegetated infiltration BMPs are presented below.
2026-08-19 Item #12D Page 120 of 816
Chapter 7: Long Term Operation and Maintenance
7-9 2023
Table 7-4. Maintenance Indicators and Actions for Non-Vegetated Infiltration BMPs Typical Maintenance
Indicator(s) for Non-Vegetated
Infiltration BMPs
Maintenance Actions
Accumulation of sediment, litter, or
debris in infiltration basin,
pretreatment device, or on
permeable pavement surface
Remove and properly dispose accumulated materials.
Examine the DMA draining to the BMP to determine the
source of the sediment. Implement corrective measures as applicable to minimize the sediment supply.
Standing water in infiltration basin
without subsurface infiltration
gallery for longer than 96 hours
following a storm event
Remove and replace clogged surface soils.
Standing water in subsurface
infiltration gallery for longer than 96
hours following a storm event
This condition requires investigation of why infiltration is not occurring. If feasible, corrective action shall be taken to restore infiltration (e.g. flush fine sediment or remove and replace clogged soils). BMP may require retrofit if infiltration cannot be restored. If retrofit is necessary, the City Engineer shall be contacted prior to any repairs or reconstruction.
Standing water in permeable paving
area
Flush fine sediment from paving and subsurface gravel.
Provide routine vacuuming of permeable paving areas to
prevent clogging.
Damage to permeable paving
surface Repair or replace damaged surface as appropriate.
Note: When inspection or maintenance indicates sediment is accumulating in an infiltration BMP, the DMA draining to the infiltration BMP should be examined to determine the source of the sediment, and corrective measures should be made as applicable to minimize the sediment supply.
7.7.3 Maintenance of Non-Vegetated Filtration BMPs
"Non-vegetated filtration BMPs" include media filters (FT-2). These BMPs function by passing runoff through the media to remove pollutants. Maintenance indicators and associated actions for nonvegetated filtration BMPs are presented below.
Table 7-5. Maintenance Indicators and Actions for Filtration BMPs Typical Maintenance Indicator(s)
for Filtration BMPs Maintenance Actions
Accumulation of sediment, litter, or
debris
Remove and properly dispose accumulated materials.
Examine the DMA draining to the BMP to determine the
source of the sediment. Implement corrective measures as applicable to minimize the sediment supply.
Obstructed inlet or outlet structure Clear obstructions.
Clogged filter media Remove and properly dispose filter media, and replace with fresh media.
2026-08-19 Item #12D Page 121 of 816
Chapter 7: Long Term Operation and Maintenance
7-10 2023
Damage to components of the
filtration system Repair or replace as applicable.
Note: For proprietary media filters, refer to the manufacturer's maintenance guide.
7.7.4 Maintenance of Detention BMPs
"Detention BMPs" include basins, cisterns, vaults, and underground galleries that are primarily designed to store runoff for controlled release to downstream systems. For the purpose of the maintenance discussion, this category does not include an infiltration component (refer to "vegetated infiltration or filtration BMPs" or "non-vegetated infiltration BMPs" above). Applicable Fact Sheets may include HU-1 (cistern) or FT-4 (extended detention basin). Maintenance indicators and associated actions for detention BMPs are presented below.
Table 7-6. Maintenance Indicators and Actions for Detention BMPs Typical Maintenance
Indicator(s) for Detention
Basins
Maintenance Actions
Poor vegetation establishment Re-seed, re-plant, or re-establish vegetation per original plans.
Evaluate proper functioning of irrigation system, if applicable.
Overgrown vegetation
Mow or trim as appropriate, but not less than the design height of the vegetation per original plans when applicable (e.g. effective function may require a minimum vegetation height).
Erosion due to concentrated
irrigation flow
Repair/re-seed/re-plant eroded areas. If necessary, perform minor re-grading to restore proper drainage according to the original plan. Adjust the irrigation system to prevent further erosion.
Erosion due to concentrated storm
water runoff flow
Repair/re-seed/re-plant eroded areas and make appropriate corrective measures such as adding erosion control blankets, adding stone at flow entry points, or minor re-grading to restore proper drainage according to the original plan. If the issue is not corrected by restoring the BMP to the original plan and grade, contact the City Engineer prior to any additional repairs or reconstruction.
Accumulation of sediment, litter, or
debris
Remove and properly dispose of accumulated materials.
Examine the DMA draining to the BMP to determine the
source of the sediment. Implement corrective measures as applicable to minimize the sediment supply.
Standing water
Make appropriate corrective measures such as adjusting the irrigation system, removing obstructions of debris or invasive vegetation, or minor re-grading to restore proper drainage according to the original plan. If the issue is not corrected by restoring the BMP to the original plan and grade, contact the City Engineer prior to any additional repairs or reconstruction.
Repair/re-seed/re-plant per the original plans any damaged 2026-08-19 Item #12D Page 122 of 816
Chapter 7: Long Term Operation and Maintenance
7-11 2023
vegetation in need of replacement.
Obstructed inlet or outlet structure Clear obstructions.
Damage to structural components
such as weirs, inlet or outlet
structures
Repair or replace as applicable.
2026-08-19 Item #12D Page 123 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L 8-1 2023
Chapter
8 8 Submittal Requirements
The City Engineer will review project plans for compliance with applicable requirements of this manual and the MS4 Permit.
The review process must verify that stormwater management objectives were considered in the project planning process and that opportunities to incorporate BMPs have been identified. The review process must confirm the site plan, landscape plan, and project stormwater documents are congruent.
Therefore, the City of Encinitas requires a submittal documenting the stormwater management design for every project that is subject to the requirements of this manual. Herein the submittal is called a Stormwater Quality Management Plan (SWQMP). A complete and thorough project submittal will facilitate and expedite the review and approval, and may result in fewer submittals by the applicant.
The sections below discuss submittal requirements. The project applicant must provide sufficient documentation to demonstrate that applicable requirements of this manual and the MS4 Permit will be met.
8.1 Submittal Requirement for Standard Projects
8.1.1 Standard Project SWQMP
For Standard Projects, the project submittal shall include a "Standard Project SWQMP." The Standard Project SWQMP is a compilation of checklists that document that all permanent source control and site design BMPs have been considered for the project and implemented where feasible.
All applicable features shall be shown on site plans and landscaping plans. The Standard Project SWQMP shall consist of the following forms and/or checklists included in Appendix J of this manual:
• Form J-1: Applicability of Permanent BMP Requirements • Form J-2: Project Type Determination (Standard Project or PDP) • Form J-3A: Site Information for Standard Projects
• Form J-4: Source Control BMP Checklist
• Form J-5: Site Design BMP Checklist
The Standard Project SWQMP shall also include copies of the relevant plan sheets showing source 2026-08-19 Item #12D Page 124 of 816
Chapter 8: Submittal Requirements
8-2 2023
control and site design BMPs.
8.2 Submittal Requirements for PDPs
8.2.1 PDP SWQMP
For PDPs, the project submittal shall include a "PDP SWQMP." The PDP SWQMP shall document that all permanent source control and site design BMPs have been considered for the project and implemented where feasible; document the planning process and the decisions that led to the selection of structural BMPs; provide the calculations for design of structural BMPs to demonstrate that applicable performance standards are met by the structural BMP design; identify O&M requirements of the selected structural BMPs; and identify the maintenance mechanism (see Sections 7.2 and 7.3) for long term O&M of structural BMPs. PDPs shall use the PDP SWQMP Template provided in Appendix A, which will include forms and/or checklists included in Appendix J of this manual as well as checklists for documentation of pollutant control and hydromodification management structural BMP design. The PDP SWQMP shall include copies of the relevant plan sheets showing site design, source control, and structural BMPs, and structural BMP maintenance requirements.
A PDP SWQMP must be provided with the first submittal of a project application, including all backup documentation. If a project’s stormwater treatment design relies on continuous simulation modeling or a SCCWRP channel assessment, the corresponding reports must be included with the first project submittal.
Stormwater requirements will directly affect the layout of the project. Stormwater requirements must be considered from the initial project planning or in project concept stage, and will be reviewed upon each submittal, beginning with the first submittal. The process from initial project application through approval of the project plans often includes design changes to the site layout and features. Changes may be driven by stormwater management requirements or other site requirements. Each time the site layout is adjusted, whether the adjustment is directly due to stormwater management requirements identified during the City Engineer's review of the stormwater submittal, or is driven by other site requirements, the stormwater management design must be revisited to ensure the revised project layout and features meet the requirements of this manual and the MS4 Permit. An updated PDP SWQMP must be provided with each submittal of revised project plans. The updated PDP SWQMP should include documentation of changes to the site layout and features, and reasons for the changes.
In the event that other site requirements identified during plan review render certain proposed stormwater features infeasible (e.g. if fire department access requirements were identified that precluded use of certain surfaces or landscaping features that had been proposed), this must be documented as part of the decisions that led to the development of the final stormwater management design.
8.2.1.1 PDP O&M Plan
While the PDP SWQMP must include general O&M requirements for structural BMPs, the PDP SWQMP may not be the final O&M Plan.
The O&M requirements documented in the PDP SWQMP must be sufficient to show that O&M requirements have been considered in the project planning and design. However, a final O&M Plan 2026-08-19 Item #12D Page 125 of 816
Chapter 8: Submittal Requirements
8-3 2023
should reflect actual constructed structural BMPs to be maintained. Photographs and as-built plans for the constructed structural BMPs should be included. See Section 8.2.3 for project closeout procedures including local requirements for final O&M Plans, and Section 8.2.4 for additional requirements for private entity O&M of structural BMPs.
8.2.2 Requirements for Construction Plans
8.2.2.1 BMP Identification and Display on Construction Plans Plans for construction of the project (grading plans, improvement plans, and landscaping plans, as applicable) must show all permanent site design, source control, and structural BMPs, and must be congruent with the PDP SWQMP.
8.2.2.2 Structural BMP Maintenance Information on Construction Plans Plans for construction of the project must provide applicable detail to support maintenance activities for structural BMPs.
For the purpose of long term O&M, the project plans must identify the following:
• How to access the structural BMP to inspect and perform maintenance; • Features that are provided to facilitate inspection (e.g. observation ports, cleanouts, silt posts, or other features that allow the inspector to view necessary components of the structural BMP and compare to maintenance thresholds);
• Manufacturer and part number for proprietary parts.
8.2.3 Design Changes During Construction and Project Closeout Procedures
8.2.3.1 Design Changes During Construction
Prior to occupancy and/or intended use of any portion of a PDP, the site must be in compliance with the requirements of this manual and the MS4 Permit.
During construction, any changes that affect the design of stormwater management features must be reviewed and approved by the City Engineer prior to implementation of any changes during construction. This might include changes to drainage patterns that occurred based on actual site grading and construction of stormwater conveyance structures or modifications to stormwater management features. The proposed changes will be reviewed to ensure the revised project layout and features meet the requirements of this manual and the MS4 Permit.
8.2.3.2 Certification of Constructed BMPs
As part of the "Structural BMP Approval and Verification Process" required by the MS4 Permit, each structural BMP must be inspected by the City inspector and the project owner’s engineer to verify that it has been constructed and is operating in compliance with all of its specifications, plans, permits, ordinances, and the requirements of the MS4 Permit.
The City inspector for the project will require the project owner’s engineer to inspect and provide 2026-08-19 Item #12D Page 126 of 816
Chapter 8: Submittal Requirements
8-4 2023
certification that the site improvements for the project have been constructed in conformance with the approved stormwater management documents and drawings. A note stating this requirement must be placed on project plans.
Since some portions of the structural BMP will not be readily visible after completion of construction (e.g. subsurface layers), the City Engineer will require inspections at each significant phase of construction, photographs taken during construction, and certification by the project owner’s engineer that the BMP has been constructed in conformance with the approved plans. The City Engineer may require forms or other documentation be submitted prior to the City inspection in order to facilitate the structural BMP inspection. Specific requirements for this process during construction may vary by project. Typical documentation that may be required includes: certified engineered soil specification, proprietary BMP activation report, proof of washed rock size install, etc.
8.2.3.3 Final O&M Plan
If any approved construction changes will result in modifications to O&M procedures, the City Engineer will require a revised final O&M Plan to be submitted.
A final O&M Plan shall reflect project-specific constructed structural BMPs with project-specific drawings, photographs, and maps, and identify specific maintenance requirements and actions for the constructed structural BMPs. Project bonds will not be released until the final O&M Plan is submitted and approved.
8.2.4 Additional Requirements for Private Entity O&M
This section discusses private structural BMPs to be operated and maintained on private property by the property owner or manager.
8.2.4.1 Agreements for Private Structural BMP Maintenance For privately owned and operated structural BMPs, the local jurisdiction requires execution of a Stormwater BMP Maintenance Agreement.
A Stormwater BMP Maintenance Agreement is a recorded document signed by the property owner committing the property owner and any future property owners to maintain the permanent structural BMPs into perpetuity. Prior to final approval of the project a BMP maintenance agreement will have been required to be recorded. If any approved construction changes will result in modifications to structural BMPs or O&M procedures, the City Engineer may require an updated BMP Maintenance agreement to be recorded with the County Recorder.
8.2.4.2 Interim Security Period of Maintenance Funding for Private Structural BMP Maintenance
At the discretion of the City Engineer, an interim security period of maintenance funding may be required. Prior to project final and security release, the developer shall notify the City of the person or party responsible for long-term BMP maintenance. The following information must be provided to the City, including:
• HOA Name
• Property Management Company Name
2026-08-19 Item #12D Page 127 of 816
Chapter 8: Submittal Requirements
8-5 2023
• Contact Person
• Mailing Address
• Phone Number
• Email
2026-08-19 Item #12D Page 128 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L i 2023
Bibliography
ASTM International.. 2009. ASTM Standard D3385-09. Retrieved from http://www.astm.org/Standards/D3385.htm
Breuer, L., Eckhardt, K, and Frede, H. 2003. Plant Parameter Values for Models in Temperate Climates. Ecological Modelling. 169:237-293. November.
California Department of Water Resources. 1947. Evaporation from Water Surfaces in California, A Summary of Pan Records and Coefficients, 1881 to 1946. Bulletin No. 54. California State Printing Office.
California Department of Water Resources. 2012. California Irrigation Management Information System Reference Evapotranspiration Zones.
Caltrans. 1986. Method for Determining the Percolation Rate of Soil Using a 6-inch-diameter Test Hole. California Test 750.
http://www.dot.ca.gov/hq/esc/sdsee/wwe/documents/Test_750.pdf Cedergren, H.R. 1997. Seepage, drainage, and flow nets, third ed. John Wiley and Sons, Inc., New York.
Cities and County of Riverside. 2012. Water Quality Management Plan for the Santa Margarita Region of Riverside County.
City of Los Angeles. 2011. Development Best Management Practices Handbook. Low Impact Development Manual.
City of Portland. 2008. Storm water Management Manual
City of San Diego. 2011. Guidelines for Geotechnical Reports.
City of San Diego. 2011. San Diego Low Impact Development Design Manual.
City of San Diego. 2012. Storm Water Standards.
City of Santa Barbara. 2013. Storm Water BMP Guidance Manual.
Clear Creek Solutions, Inc. 2012. San Diego Hydrology Model User Manual.
County of Los Angeles Department of Public Works. 2014. Low Impact Development, Standards Manual.
County of Orange. 2011. Model Water Quality Management Plan (Model WQMP).
County of Orange. 2011. Technical Guidance Document for the Preparation of Conceptual/Preliminary and/or Project Water Quality Management Plans (WQMPs).
County of San Bernardino. 1992. Suitability of Lots and Soils for Use of Leachlines or Seepage Pits, Soil Percolation (PERC) Test Report Standards, Onsite Waste Water Disposal System, August 1992.
County of San Diego. 2007. Low Impact Development Handbook: Stormwater Management 2026-08-19 Item #12D Page 129 of 816
Bibliography
ii 2023
Strategies.
County of San Diego. 2011. Final Hydromodification Management Plan County of San Diego. 2012. County of San Diego SUSMP: Standard Urban Stormwater Mitigation Plan Requirements for Development Applications.
County of San Diego. 2014. Low Impact Development Handbook: Stormwater Management Strategies.
County of San Diego. 2003. Stormwater Standards Manual.
County of Ventura. 2011. Ventura County Technical Guidance Manual for Stormwater Quality Control Measures.
Darcy, H, 1856. Les fontaines publiques de la Ville de Dijon (The public fountains of the City of Dijon). Trans. Patricia Bobeck. Paris: Dalmont. (Kendall/Hunt, 2004) 506 p Double Ring Infiltrometer Test (ASTM 3385)-ASTM International. 2009.
Emerson, C. 2008. Evaluation of Infiltration Practices as a Means to Control Stormwater Runoff.
Civil and Environmental Engineering. Villanova University.
Emerson, C.H. 2008. Evaluation of Infiltration Practices as a Means to Control Stormwater Runoff.
Doctoral dissertation, Villanova University. May 2008.
Galli, J. 1992. Analysis of urban stormwater BMP performance and longevity in Prince George’s County, Maryland. Metropolitan Washington Council of Governments, Washington, D.C.
Gobel, P. et al. 2004. Near-Natural Stormwater Management and its Effects on the Water Budget and Groundwater Surface in Urban Areas Taking Account of the Hydrogeological Conditions.
Journal of Hydrology 299, 267-283.
Gulliver, J., Erickson, A., and Weiss, P. 2010. Optimizing Stormwater Treatment Practices: A Handbook of Assessment and Maintenance.
Hazen, A. 1892. Some Physical Properties of Sands And Gravels, With Special Reference To Their Use In Filtration. 24th Annual Rep., Massachusetts State Board of Health, Pub. Doc. No. 34, 539-556.
Hazen, A. 1911. Discussion of Dams On Sand Foundations’ by A.C. Koenig. Trans. Am. Soc. Civ.
Eng., 73, 199-203
Hazen, A., 1892. Some Physical Properties of Sands and Gravels, With Special Reference to their Use in Filtration. 24th Annual Rep., Massachusetts State Board of Health, Pub. Doc. No. 34, 539-556.
Hazen, A., 1911. Discussion of Dams on Sand Foundations’ by A.C. Koenig. Trans. Am. Soc. Civ.
Eng., 73, 199-203
King County Department of Natural Resources and Parks. 2009. King County, Washington Surface Water Design Manual. Retrieved from http://your.kingcounty.gov/dnrp/library/water-andland/stormwater/surface-water-design-manual/SWDM-2009.pdf 2026-08-19 Item #12D Page 130 of 816
Bibliography
iii 2023
Lindsey, G., L. Roberts, and W. Page. 1991. Storm Water Management Infiltration. Maryland Department of the Environment, Sediment and Storm Water Administration.
Lindsey, P. and Bassuk, N. 1991. Specifying Soil Volumes to Meet the Water Needs of Mature Urban Street Trees and Trees in Containers. Journal of Arboriculture 17(6): 141-149.
Minnesota Pollution Control Agency (MPCA). (n.d.). Minnesota Stormwater Manual. Retrieved October 2014 from:
http://stormwater.pca.state.mn.us/index.php/Calculating_credits_for_tree_trenches_and_tree _boxes
Orange County Watersheds Protection Program. 2011. Project-Specific Alternatives to the Interim Sizing Tool.
Philips C. and W. Kitch 2011. A review of methods for characterization of site infiltration with design recommendations. California State Polytechnic University-Pomona. http://www.csupomona.edu/~wakitch/arts/Philips_&_Kitch_2011.pdf Phillips, E., and Kitch, W. 2011. A Review of Methods for Characterization of Site Infiltration with Design Recommendations. Journal of the Nevada Water Resources Association, Summer 2011, Vol. 6, No. 1, pp. 29-46.
Pitt, R., Chen, S., Clark, S., Lantrip, J., and C. Ong. 2008. Compaction’s Impacts on Urban Stormwater Infiltration, J. Irr. and Drainage Eng., January 2008.
Pitt, R., Chen, S., Clark, S., Swenson, J., and Ong, C. 2008. ”Compaction’s Impacts on Urban StormWater Infiltration.” J. Irrig. Drain Eng. 134, SPECIAL ISSUE: Urban Storm-Water Management, 652–658.
Riverside County. 2011. Riverside County - Low Impact Development BMP Design Handbook – Appendix A – Infiltration Testing
http://rcflood.org/downloads/NPDES/Documents/LIDManual/Appendix%20A_Infiltratio n_Testing.pdf
Riverside County Copermittees. 2014. Santa Margarita Region Hydromodification Management Plan.
Riverside County Flood Control and Water Conservation District. 2011. Design Handbook for Low Impact Development Best Management Practices.
Riverside County Percolation Test (2011), California Test 750 (1986), San Bernardino County Percolation Test (1992); USEPA Falling Head Test (1980).
Rossman, Lewis A. 2010. Storm Water Management Model User's Manual Version 5.0.
EPA/600/R-05/040.
San Diego County Copermittees. 2002. Model Standard Urban Storm Water Mitigation Plan for San Diego County, Port of San Diego, and Cities in San Diego County.
San Diego County Copermittees, 2011. Countywide Model SUSMP San Diego County Copermittees. 2012. San Diego BMP Sizing Calculator Methodology 2026-08-19 Item #12D Page 131 of 816
Bibliography
iv 2023
San Diego County Copermittees. 2014. San Diego County Regional Watershed Management Area Analysis
San Diego County Copermittees. 2008. Countywide Model SUSMP.
SCCWRP. 2010. Hydromodification Screening Tools: Field Manual for Assessing Channel Susceptibility. Brian P. Bledsoe; Robert J. Hawley; Eric D. Stein; Derek B. Booth. Technical Report 606.
SCCWRP. 2012. Hydromodification Assessment and Management in California. Eric D. Stein; Felicia Federico; Derek B. Booth; Brian P. Bledsoe; Chris Bowles; Zan Rubin; G. Mathias Kondolf and Ashmita Sengupta. Technical Report 667.
Schwab, G., Fangmeier, D., Elliot, W., and Frevert, R. 1993. Soil and Water Conservation Engineering. Fourth Edition. John Wiley & Sons, Inc.
Scurlock, J., Asner, G., and Gower, S. 2001. Global Leaf Area Index from Field Measurements, 1932-2000. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/584.
U.S. Department of the Interior, Bureau of Reclamation. 1990. “Procedure for Performing Field Permeability Testing by the Well Permeameter Method (USBR 7300-89)” in Earth Manual, Part
2. Materials Engineering Branch Research and Laboratory Services Division, Denver, Colorado.
U.S. Department of the Interior, Bureau of Reclamation. 1993. Drainage Manual: A Water Resources Technical Publication. Retrieved from
http://www.usbr.gov/pmts/wquality_land/DrainMan.pdf
United States Environmental Protection Agency. 2000. BASINS Technical Note 6 – Estimating Hydrology and Hydraulic Parameters for HSPF. EPA-823-R00-012.
Urban Drainage and Flood Control District, Denver, CO. (2010). Urban Storm Drainage Criteria Manual. Volume 3, Best Management Practices.
US Department of Interior Bureau of Reclamation. 1993. Drainage Design Manual.
USEPA. 1980. Onsite Wastewater Treatment and Disposal Systems (EPA No. 625/1-80-012).
Retrieved from nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=300043XO.txt USEPA. 1999. Preliminary data summary of urban storm water best management practices. EPA821-R-99-012, U. S. Environmental Protection Agency, Washington, D.C.
Washington Department of Ecology. 2012. Stormwater Management Manual for Western Washington.
Washington State Department of Ecology. 2012. Stormwater Management Manual for Western Washington - Volume 3: Hydrologic Analysis and Flow Control BMPs. Retrieved from https://fortress.wa.gov/ecy/publications/summarypages/1210030.html 2026-08-19 Item #12D Page 132 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L v 2023
2026-08-19 Item #12D Page 133 of 816
2026 BMP DESIGN MANUAL
APPENDICES
Adopted tbd
Effective ________
2026-08-19 Item #12D Page 134 of 816
i 2023
Table of Contents
Appendix A Submittal Templates ...................................................................................... A-1 A.1 Standard SWQMP ...................................................................................................................................... A-2 A.2 PDP SWQMP .......................................................................................................................................... A-14 Appendix B Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs ........................................................................................ B-1 B.1 Step 1 – Determine DCV .......................................................................................................................... B-2 B.1.1 Step 1A – Rainfall Depth .................................................................................................................... B-5 B.1.2 Step 1B – Tributary Area .................................................................................................................... B-5 B.1.3 Step 1C – Runoff Factor ..................................................................................................................... B-6 B.1.4 Step 1D – Site Design Volume Reductions ..................................................................................... B-7 B.2 Step 2 - Determine Retention Requirements ....................................................................................... B-10 B.2.1 Step 2A - Capture and Use Analysis ................................................................................................ B-10 B.2.2 Step 2B – Infiltration Restrictions ................................................................................................... B-11 B.2.3 Step 2C – Design Infiltration Rate .................................................................................................. B-12 B.2.4 Step 2D - Retention Requirements .................................................................................................. B-13 B.3 Step 3 - Determine BMP Performance ................................................................................................. B-15 B.3.1 Step 3A - BMP Characteristics ......................................................................................................... B-18 B.3.2 Step 3B - Retention Processes .......................................................................................................... B-18 B.3.3 Step 3C - Biofiltration Processes...................................................................................................... B-21 B.3.4 Step 3D - Satisfaction of Pollutant Control Requirements ......................................................... B-23 B.3.5 Step 3E - Satisfaction of Minimum Retention Requirements ..................................................... B-24 B.4 Less Common Pollutant Control Calculations .................................................................................... B-25 B.4.1 Major Maintenance Intervals for Reduced Size BMPs ................................................................. B-25 B.4.2 Capture and Use Evaluation ............................................................................................................. B-29 B.4.3 BMPs Downstream of a Storage Unit............................................................................................. B-31 B.4.4 Onsite Alternative Compliance ........................................................................................................ B-32 B.4.5 Offline BMPs ...................................................................................................................................... B-32 B.5 Backup Information on Pollutant Control Standards ......................................................................... B-34 B.5.1 Pollutant Control Performance Standard Backup ......................................................................... B-34 B.5.2 Retention Requirement Backup ....................................................................................................... B-35 B.5.3 Rainfall Depth Backup ...................................................................................................................... B-35 2026-08-19 Item #12D Page 135 of 816
ii 2023
B.5.4 Tree Well Backup ............................................................................................................................... B-36 B.5.5 Sediment Clogging Backup ............................................................................................................... B-37 Appendix C Baseline BMP Fact Sheets for Site Design and Source Control .................... C-1 BL-1: Existing Natural Site Features ...................................................................................................................... C-3 BL-2: Outdoor Impervious Area........................................................................................................................... C-10 BL-3: Rooftop Areas ............................................................................................................................................... C-15 BL-4: Landscaped Areas ......................................................................................................................................... C-18 BL-5: Work and Storage Areas .............................................................................................................................. C-21 BL-6: Management of Storm Water Discharges ................................................................................................. C-30 BL-7: Management of Non-Storm Water Discharges ....................................................................................... C-36 Appendix D Geotechnical Engineer Analysis .................................................................... D-1 D.1 Analysis of Infiltration Restrictions ........................................................................................................ D-2 D.2 Determination of Design Infiltration Rates .......................................................................................... D-3 D.2.1 Initial Infiltration Rate ........................................................................................................................ D-3 D.2.2 Corrected Infiltration Rate ................................................................................................................. D-7 D.2.3 Safety Factors ..................................................................................................................................... D-10 D.3 Geotechnical Reporting Requirements ................................................................................................ D-12 Appendix E BMP Design Fact Sheets ................................................................................ E-1 E.1 Fact Sheet Quick Guide ............................................................................................................................. E-3 E.2 Source Control BMP Requirements ........................................................................................................ E-4 E.3 SC-Q Large Trash Generating Facilities ............................................................................................... E-16 E.4 SC-R Animal Facilities ............................................................................................................................. E-20 E.5 SC-S Plant Nurseries and Garden Centers ........................................................................................... E-21 E.6 SC-T Automotive Facilities ..................................................................................................................... E-22 E.7 SD-A Tree Well ......................................................................................................................................... E-24 E.8 SD-B Impervious Area Dispersion ........................................................................................................ E-32 E.9 SD-C Green Roofs ................................................................................................................................... E-40 E.10 SD-D Permeable Pavement (Site Design BMP) .................................................................................. E-47 E.11 SD-E Rain Barrels .................................................................................................................................... E-53 E.12 SD-F Amended Soils ................................................................................................................................ E-57 E.13 HU-1 Cistern ............................................................................................................................................. E-60 E.14 INF-1 Infiltration Basin ........................................................................................................................... E-68 E.15 INF-2 Bioretention ................................................................................................................................... E-78 2026-08-19 Item #12D Page 136 of 816
iii 2023
E.16 INF-3 Permeable Pavement (Pollutant Control) ................................................................................. E-90 E.17 INF-4 Dry Wells .................................................................................................................................... E-104 E.18 PR-1 Biofiltration with Partial Retention ........................................................................................... E-105 E.19 BF-1 Biofiltration ................................................................................................................................... E-118 E.20 BF-2 Nutrient Sensitive Media Design .............................................................................................. E-133 E.21 BF-3 Proprietary Biofiltration Systems .............................................................................................. E-136 E.22 FT-1 Vegetated Swales .......................................................................................................................... E-137 E.23 FT-2 Media Filters ................................................................................................................................. E-148 E.24 FT-3 Sand Filters ................................................................................................................................... E-156 E.25 FT-4 Dry Extended Detention Basin ................................................................................................. E-164 E.26 FT-5 Proprietary Flow-Thru Treatment Control BMPs ................................................................. E-174 E.27 PL Plant List ........................................................................................................................................... E-175 Appendix F Biofiltration Standard and Checklist .............................................................. F-1 F.1 Pollutant Treatment Performance Standard ........................................................................................... F-9 F.2 Guidance on Sizing and Design of Approved Equivalent Proprietary Biofiltration Systems ...... F-13 F.2.1 Guidance on Design per Conditions of Certification/Verification ........................................... F-13 F.2.2 Sizing of Flow-Based Biofiltration BMP ........................................................................................ F-13 F.3 Bioretention Soil Media (BSM) ............................................................................................................... F-16 Appendix G Guidance for Continuous Simulation and Hydromodification Management Sizing Factors ................................................................................................. G-1 G.1 Guidance for Continuous Simulation Hydrologic Modeling for Hydromodification Management Studies in San Diego County Region 9 .................................................................................................. G-2 G.1.1 Introduction ......................................................................................................................................... G-2 G.1.2 Software for Continuous Simulation Hydrologic Modeling ......................................................... G-2 G.1.3 Climatology Parameters ...................................................................................................................... G-3 G.1.4 Land Characteristics and Loss Parameters ...................................................................................... G-7 G.1.5 Modeling Structural BMPs (Ponds and LID Features) ............................................................... G-16 G.1.6 Flow Frequency and Duration ........................................................................................................ G-25 G.2 Sizing Factors for Hydromodification Management BMPs ............................................................. G-29 G.2.1 Unit Runoff Ratios and Low Flow Control Orifice Design ....................................................... G-34 G.2.2 Sizing Factors for "Infiltration" BMP ............................................................................................ G-37 G.2.3 Sizing Factors for Biofiltration with Partial Retention ................................................................ G-40 G.2.4 Sizing Factors for Biofiltration ........................................................................................................ G-43 G.2.5 Sizing Factors for "Cistern" BMP ................................................................................................... G-46 2026-08-19 Item #12D Page 137 of 816
iv 2023
Appendix H Guidance for Investigating Potential Critical Coarse Sediment Yield Areas H-1 H.1 Step 1: Identify CCSYAs .......................................................................................................................... H-2 H.1.1 Identification Methods ....................................................................................................................... H-2 H.1.2 Refinement Options ............................................................................................................................ H-3 H.2 Step 2: Avoidance of Onsite CCSYAs ................................................................................................... H-3 H.2.1 Avoidance Metrics ............................................................................................................................... H-4 H.3 Step 3: Bypass Onsite and Upstream CCSYAs ..................................................................................... H-4 H.3.1 Bypass CCSYAs from Hillslopes ...................................................................................................... H-4 H.3.2 Bypass CCSYAs from Channels ....................................................................................................... H-5 H.3.3 De Minimis Upstream CCSYA ......................................................................................................... H-5 H.4 Step 4: Demonstrate No Net Impact ..................................................................................................... H-6 H.4.1 Background ........................................................................................................................................... H-6 H.4.2 Management Standard ........................................................................................................................ H-9 H.4.3 Types of Mitigation Measures ......................................................................................................... H-10 H.5 References H-12
H.5.1 Terms of Reference ........................................................................................................................... H-14 H.6 PCCSYAs: Regional WMAA Maps ...................................................................................................... H-15 H.6.1 Site-Specific GLU Analysis .............................................................................................................. H-18 H.6.2 Assumptions for Regional WMAA PCCSYA Maps .................................................................... H-36 H.6.3 Encroachment Allowance for Regional PCCSYA WMAA Map ............................................... H-37 H.7 PCCSYAs: Refinement Options ........................................................................................................... H-38 H.7.1 Depositional Analysis........................................................................................................................ H-38 H.7.2 Threshold Channel Analysis ............................................................................................................ H-39 H.7.3 Coarse Sediment Source Area Verification ................................................................................... H-44 H.8 Calculation Methodology for Ep and Sp ............................................................................................. H-48 H.8.1 Calculation of Ep ............................................................................................................................... H-48 H.8.2 Calculation of Sp................................................................................................................................ H-63 H.9 Mitigation Measures Fact Sheets ........................................................................................................... H-71 H.9.1 Additional Flow Control .................................................................................................................. H-71 H.9.2 Stream Rehabilitation ........................................................................................................................ H-76 H.10 IntroductionStep 1: Identify CCSYAs .................................................................................................. H-78 H.10.1 Identification Methods ..................................................................................................................... H-78 Appendix I Appendix Significant Site Design Significant Site Design BMP (SSD-BMP) 2026-08-19 Item #12D Page 138 of 816
v 2023
Sizing Methods and Calculations .................................................................... I-1 I.1 Significant Site Design BMPs (SSD-BMPs) ............................................................................................ I-2 I.2 Step 1: Determine DCV ............................................................................................................................. I-2 I.3 Step 2: Dispersion Areas............................................................................................................................. I-5 I.4 Step 3: Tree Wells ........................................................................................................................................ I-8 I.4.1 Step 3.1: Determine DCV or RRV as applicable ........................................................................... I-12 I.4.2 Step 3.2: Select a tree species and tree well soil depth ................................................................... I-13 I.4.3 Step 3.3: Determine the minimum soil volume required in the tree well ................................... I-13 I.4.4 Step 3.4: Determine tree well soil installation area and show on plans ...................................... I-13 Appendix J Forms and Checklists ...................................................................................... J-1 Appendix K Guidance on Green Infrastructure ................................................................. K-1 K.1 Guidance on Green Infrastructure ......................................................................................................... K-3 K.2 Green Streets .............................................................................................................................................. K-8 K.2.1 Green Streets Performance Standard ............................................................................................... K-9 K.2.2 Green Streets Guidelines .................................................................................................................. K-20 K.2.3 Green Parking Lots Guidelines ....................................................................................................... K-83 Glossary of Key Terms ............................................................................................................... i 2026-08-19 Item #12D Page 139 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L A-1 2023
Appendix
A
Appendix A Submittal Templates
The following templates were developed to assist the project applicant and the plan reviewer:
• Standard SWQMP
• PDP SWQMP
2026-08-19 Item #12D Page 140 of 816
Appendix A: Submittal Templates
A-2 2023
A.1Standard SWQMP
City of Encinitas Standard Project SWQMP (Stormwater Intake Form for All Development Projects)
Project Identification
Project/Applicant Name:
Permit/Application Number: Date:
Scope of work/project description:
Determination of Project Status and Requirements
This form will identify permanent, post construction BMP requirements. Refer to City of Encinitas Stormwater BMP Design Manual for guidance.
Step 1: Is the project a "development project"?
Development projects are defined as
"construction, rehabilitation, redevelopment, or
reconstruction of any public or private projects".
See Section 1.3 and Table 1-2 of the manual for
guidance. For example, interior remodels, roof
replacements, electrical and plumbing are not
development projects.
Yes Go to Step 2.
No
Stop.
Permanent BMP requirements do
not apply. No SWQMP will be
required. Provide discussion below.
2026-08-19 Item #12D Page 141 of 816
Appendix A: Submittal Templates
A-3 2023
If “No”, provide discussion / justification explaining why the project is not a "development project":
Step 2: Complete questions below for Project Type Determination.
The project is (select one): New Development Redevelopment The total proposed, newly created and/or replaced impervious area is: ft2 Is the project in any of the following categories, (a) through (f) below? Yes
No
(a) New development projects or redevelopment projects that create and/or replaced 10,000 square feet or more of impervious surfaces (collectively over the entire project site). This includes commercial, industrial, residential, mixed-use, and public development projects.
Yes
No
(b) Redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site on an existing site of 10,000 square feet or more of impervious surfaces). This includes commercial, industrial, residential, mixed-use, and public development projects.
Yes
No
(c) New and redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site), and support one or more of the following uses:
(i) Restaurants. This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared foods and drinks for immediate consumption (SIC code 5812).
(ii) Hillside development projects. This category includes development on any natural slope that is twenty-five percent or greater.
(iii) Parking lots. This category is defined as a land area or facility for the temporary parking or storage of motor vehicles used personally, for business, or for commerce.
2026-08-19 Item #12D Page 142 of 816
Appendix A: Submittal Templates
A-4 2023
(iv) Streets, roads, highways, freeways, and driveways. This category is defined as any paved impervious surface used for the transportation of automobiles, trucks, motorcycles, and other vehicles.
Yes
No
(d) New or redevelopment projects that create and/or replace 2,500 square feet or more of impervious surface (collectively over the entire project site), and discharge directly to an Environmentally Sensitive Area (ESA). “Discharge directly to” includes flow that is conveyed overland a distance of 200 feet or less from the project to the ESA, or conveyed in a pipe or open channel any distance as an isolated flow from the project to the ESA (i.e. not commingled with flows from adjacent lands).
Note: ESAs are areas that include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas designated as Areas of Special Biological Significance by the State Water Board and SDRWQCB; State Water Quality Protected Areas; water bodies designated with the RARE beneficial use by the State Water Board and SDRWQCB; and any other equivalent environmentally sensitive areas which have been identified by the Copermittees. See manual Section 1.4.2 for additional guidance.
Yes
No
(e) New development projects, or redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface, that support one or more of the following uses:
(i) Automotive repair shops. This category is defined as a facility that is categorized in any one of the following SIC codes: 5013, 5014, 5541, 7532- 7534, or 7536-7539.
(ii) Retail gasoline outlets. This category includes retail gasoline outlets that meet the following criteria: (a) 5,000 square feet or more or (b) a projected Average Daily Traffic of 100 or more vehicles per day.
Yes
No
(f) New or redevelopment projects that result in the disturbance of one or more acres of land and are expected to generate pollutants post construction.
Note: See manual Section 1.4.2 for additional guidance. 2026-08-19 Item #12D Page 143 of 816
Appendix A: Submittal Templates
A-5 2023
Does the project meet the definition of one or more of the PDP categories (a) through (f) listed above? Yes – The project is a Priority Development Project, the applicant shall provide PDP Post Construction BMPs and provide a PDP SWQMP. Stop here and complete PDP SWQMP. No – Does the project propose 500 SF or more of new and/or replaced impervious surface area? Yes – The project is a Standard Project, the applicant shall implement Structural Post Construction BMPs or demonstrate equivalent Design Capture Volume via site design/source control BMPs baseline BMPs, (site design and source control BMPs.)
Complete Step 3, 4, & 5 and Tables 1, 2, and 3.
No – The project is a Basic Project, the applicant shall implement site design and source control measures. Complete Step 3 & 4.
Step 3: Source Control BMP Checklist – All “Development Projects” Must Complete All development projects must implement source control BMPs SC-1 through SC-6 where applicable and feasible. See Chapter 4 and Appendix E of the manual for information to implement source control BMPs shown in this checklist.
Answer each category below pursuant to the following.
• "Yes" means the project will implement the source control BMP as described in Chapter 4 and/or Appendix E of the manual. Discussion / justification is not required. • "No" means the BMP is applicable to the project but it is not feasible to implement. Discussion / justification must be provided.
• "N/A" means the BMP is not applicable at the project site because the project does not include the feature that is addressed by the BMP (e.g., the project has no outdoor materials storage areas). Discussion / justification may be provided.
Source Control Requirement Applied?
SC-1 Prevention of Illicit Discharges into the MS4 Yes No N/A SC-2 Storm Drain Stenciling or Signage Yes No N/A SC-3 Protect Outdoor Materials Storage Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
Yes No N/A
SC-4 Protect Materials Stored in Outdoor Work Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
Yes No N/A
2026-08-19 Item #12D Page 144 of 816
Appendix A: Submittal Templates
A-6 2023
SC-5 Protect Trash Storage Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
Yes No N/A
SC-6 Additional BMPs Based on Potential Sources of Pollutants Answer for each source listed below:
Onsite storm drain inlets
Interior floor drains and elevator shaft sump pumps drain to sewer Interior parking garages drain to sewer
Need for future indoor & structural pest control
Landscape/outdoor pesticide use
Pools, spas, ponds, decorative fountains, and other water features Food service
Refuse/Trash areas must be covered
Industrial processes
Outdoor storage of equipment or materials must be covered Vehicle and equipment cleaning
Vehicle/equipment repair and maintenance
Fuel dispensing areas
Loading docks
Fire sprinkler test water
Miscellaneous drain or wash water
Plazas, sidewalks, and parking lots
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Discussion / justification if SC-1 through SC-6 not implemented. Justification must be provided for ALL "No" answers shown above.
2026-08-19 Item #12D Page 145 of 816
Appendix A: Submittal Templates
A-7 2023
Step 4: Site Design BMP Checklist – All “Development Projects” Must Complete All development projects must implement site design BMPs SD-1 through SD-8 where applicable and feasible. See Chapter 4 and Appendix E of the manual for information to implement site design BMPs shown in this checklist.
Answer each category below pursuant to the following.
• "Yes" means the project will implement the site design BMP as described in Chapter 4 and/or Appendix E of the manual. Discussion / justification is not required. • "No" means the BMP is applicable to the project but it is not feasible to implement. Discussion / justification must be provided.
• "N/A" means the BMP is not applicable at the project site because the project does not include the feature that is addressed by the BMP (e.g., the project site has no existing natural areas to conserve). Discussion / justification may be provided.
Source Control Requirement Applied?
SD-1 Maintain Natural Drainage Pathways and Hydrologic Features Yes No N/A
SD-2 Conserve Natural Areas, Soils, and Vegetation
Yes No N/A
SD-3 Minimize Impervious Area
Yes No N/A
SD-4 Minimize Soil Compaction
Yes No N/A
SD-5 Impervious Area Dispersion - Directly Connected Impervious Areas (e.g. roof downspouts connected to street) are not allowed Yes No N/A
SD-6 Runoff Collection
Yes No N/A
SD-7 Landscaping with Native or Drought Tolerant Species Yes No N/A
SD-8 Harvesting and Using Precipitation
Yes No N/A
2026-08-19 Item #12D Page 146 of 816
Appendix A: Submittal Templates
A-8 2023
Discussion / justification if SD-1 through SD-8 not implemented. Justification must be provided for ALL "No" answers shown above.
Step 5: Standard Project BMP Sizing for ≥500sf New/Replaced Impervious Surface Areas Projects that create and/or remove and replace 500sf or greater of impervious surface collectively over the entire project site shall provide natural biofiltration and/or bioretention BMPs or document equivalent volume reduction via site design or other structural BMP based on the DCV method described in Chapter 5 and Appendix B. The following sizing calculation may be used for sizing natural bioretention BMPs:
_ _
MINIMUM EFFECTIVE BMP AREA = 0.03 x Σ (Surface Type SF X Surface Type Runoff Factor) Describe the selected Structural BMP Design including type, location, size, etc. below:
2026-08-19 Item #12D Page 147 of 816
Appendix A: Submittal Templates
A-9 2023
TABLE 1 – BASELINE BMP CHECKLIST FOR EXISTING AND PROPOSED SITE FEATURES A. BMPS for Existing Natural Site Features (See Fact Sheet BL-1)
1. Check the boxes below for each existing feature on the site
2. Select the BMPs to be implemented for each identified feature. Explain why any BMP not selected is infeasible in Table 3.
Conserve
natural features
(SD-G)
Provide buffers around waterbodies
(SD-H)
Natural Waterbodies
Natural storage reservoirs & drainage corridors
--
Natural areas, soils, & vegetation (incl. trees)
--
B. BMPs for Common Impervious Outdoor Site Features (See Fact Sheet BL-2)1. Check the boxes below for each proposed feature.
2. Select the BMPs to be implemented for each proposed feature. If neither BMP SD-B, nor SD-I is selected for a feature, explain why both BMPs are infeasible in Table 3. a. Direct runoff
to pervious
areas (SD-B)
b. Construct surfaces from
permeable materials (SD-I)
c. Minimize the size
of impervious areas
Streets and roads
2026-08-19 Item #12D Page 148 of 816
Appendix A: Submittal Templates
A-10 2023
Sidewalks & walkways Check this box to confirm
that all impervious areas on the site will be minimized where feasible. If this box is not checked, identify the surfaces that cannot be minimized, and explain why it is infeasible to do so in Table 3, Parking areas & lots Driveways Patios, decks, & courtyards Hardcourt recreation areas Other: C. □ BMPs for Rooftop Areas: Check this box if rooftop areas are proposed and select at least one BMP below.If no BMPs are selected, explain why they are infeasible in Table 3. (See Fact Sheet BL3)
1. Direct runoff to pervious
areas (SD-B)
2. Install green roofs (SD-C)
3. Install rain barrels (SD-E)
D. BMPs for Landscaped Areas: Check this box if landscaping is proposed and select at least one BMP below. If no BMPs are selected, explain why they are infeasible in Table 3. (See Fact Sheet BL4)
1. Sustainable Landscaping (SD-K)
2026-08-19 Item #12D Page 149 of 816
Appendix A: Submittal Templates
A-11 2023
TABLE 2 – BASELINE BMPS FOR POLLUTANT-GENERATING SOURCES If this is a Small Residential Project, check this box and skip the rest of this table.
A. Management of Stormwater Discharges
1. Identify all proposed outdoor work
areas below
2. Which BMPs will be used to prevent materials
from contacting rainfall or runoff?
(See Fact Sheet BL-5)
3. Where will runoff from the work area
be routed?
(See Fact Sheet BL-6)
(Check here if none are proposed) (Select all feasible BMPs for each work area1) (Select one or more for each work area) Overhead
covering
(rooftops, etc.)
(SC-A)
Separation of
flows from
adjacent areas
(berms, etc.)
(SC-B)
Wind
protection
(screens,
etc.)
(SC-C)
Sanitary
sewer2
(SC-D)
Contain
ment
system
SC-E)
Stormwater
S-BMP or
SSD-BMP3
Other
4 Trash & Refuse Storage Materials & Equipment Storage Loading & Unloading -- Fueling -- Maintenance & Repair -- Vehicle & Equipment Cleaning -- Other: -- B. Prevention of Non-stormwater Discharges (See Fact Sheet BL-7) Select on option for each feature below: •Storm drain inlets and catch basins… are not proposed.
will be labeled with stenciling or signage to discourage dumping (SC-F).
•Educational BMP Signage… are not
proposed.
will be labeled with educational signage for BMP (SCG). •Interior work surfaces, floor drains, & sumps… are not proposed.
will not discharge directly or indirectly to the MS4 or receiving waters.
•Drain lines (e.g. air conditioning, boiler, etc.)… are not proposed.
will not discharge directly or indirectly to the MS4 or receiving waters.
•Fire sprinkler test water… are not
proposed.
will not discharge directly or indirectly to the MS4 or receiving waters.
Note: All features and BMPS must be shown on applicable construction plans. See applicable Fact Sheets in Appendix D of the BMP Design Manual for additional Information. Use Table 3 to explain BMP feasibility or inapplicability, or to describe features not listed in this form.
Additional explanation may be required by City Staff.
2026-08-19 Item #12D Page 150 of 816
Appendix A: Submittal Templates
A-12 2023 1Each BMP is required where feasible. If none are selected for any feature, explain why in Table 3 2Separate wastewater agency approvals may be required 3Permanent BMPs (PBMPs) and Significant Site Design BMPs (SSD-BMPs) may not receive discharges from work areas that concentrate pollutants in a manner that will impair their functioning. Discharges from proposed work area must also be included in DCV calculations for the applicable BMP.
4Describe other proposed options for managing stormwater discharges in Table 3. 2026-08-19 Item #12D Page 151 of 816 Appendix A: Submittal Templates
A-13 2023
Table 3 – Explanations and Justifications for Table 1 and 2 Baseline BMPs Check here if no explanations or justifications for Table 1 or 2 BMPs are required. • Required Justifications: Provide explanations of BMP inapplicability and/or infeasibility as indicated per Tables 1 and 2.
• If Requested: Justify why individual BMPs will not be implemented or will only be partially implemented.
• Additional Explanation: Describe any proposed features and or BMPs not listed in Tables 1 and 2.
BMP-Feature Combination Explanation
Feature
BMP
Feature
BMP
Feature
BMP
Feature
BMP
Feature
BMP
Feature
BMP
2026-08-19 Item #12D Page 152 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-14
A.2PDP SWQMP
CITY OF ENCINITAS
STORMWATER INTAKE FORM AND PRIORITY DEVELOPMENT PROJECT
STORMWATER QUALITY MANAGEMENT PLAN (SWQMP)
FOR:
[PROJECT NAME] [APPLICATION/PERMIT NUMBER(S)]
[SITE ADDRESS] [ENCINITAS, CA 92024] [APN]
PREPARED BY:
[NAME OF ENGINEER OF RECORD] [ENGINEERING FIRM]
[ADDRESS] [CITY, STATE, ZIP] [PHONE NUMBER]
PREPARED FOR: [APPLICANT/OWNER] [ADDRESS]
[CITY, STATE, ZIP] [PHONE NUMBER]
DATE OF SWQMP: [MM/DD/YY] [REVISION #]
GRADING PLAN PREPARED BY: [NAME OF ENGINEER OF RECORD]
[ENGINEERING FIRM]
[ADDRESS] [CITY, STATE, ZIP] [PHONE NUMBER]
2026-08-19 Item #12D Page 153 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-15
PREPARER'S CERTIFICATION ............................................................................................................... 9 PROJECT OWNER'S CERTIFICATION ................................................................................................. 10 SUBMITTAL RECORD ........................................................................................................................... 11 PROJECT IDENTIFICATION .................................................................................................................. 12 DETERMINATION OF PROJECT STATUS AND REQUIREMENTS .................................................... 12 SITE INFORMATION CHECKLIST ......................................................................................................... 15 SOURCE CONTROL BMP CHECKLIST ................................................................................................ 24 SITE DESIGN BMP CHECKLIST ........................................................................................................... 25 PDP STRUCTURAL BMPS .................................................................................................................... 26 STRUCTURAL BMP SUMMARY INFORMATION ................................................................................. 27 ATTACHMENT 1 - BACKUP FOR PDP POLLUTANT CONTROL BMPS ............................................. 28 ATTACHMENT 2 - BACKUP FOR PDP HYDROMODIFICATION CONTROL MEASURES ................. 30 ATTACHMENT 3 - STRUCTURAL BMP MAINTENANCE INFORMATION........................................... 32 ATTACHMENT 4 - COPY OF PLAN SHEETS SHOWING PERMANENT STORM WATER BMPS...... 34
2026-08-19 Item #12D Page 154 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-16
PREPARER'S CERTIFICATION
I hereby declare that I am the Engineer in Responsible Charge of design of storm water best management practices (BMPs) for this project, and that I have exercised responsible charge over the design of the BMPs as defined in Section 6703 of the Business and Professions Code, and that the design is consistent with the Priority Development Project (PDP) requirements of the City of Encinitas BMP Design Manual, which is a design manual for compliance with local City of Encinitas and regional MS4 Permit (California Regional Water Quality Control Board San Diego Region Order No. R9-2015- 0100) requirements for storm water management.
I have read and understand that the City Engineer has adopted minimum requirements for managing urban runoff, including storm water, from land development activities, as described in the BMP Design Manual. I certify that this PDP Storm Water Quality Management Plan (SWQMP) has been completed to the best of my ability and accurately reflects the project being proposed and the applicable BMPs proposed to minimize the potentially negative impacts of this project's land development activities on water quality. I understand and acknowledge that the plan check review of this PDP SWQMP by the City Engineer is confined to a review and does not relieve me, as the Engineer in Responsible Charge of design of storm water BMPs for this project, of my responsibilities for project design.
Engineer's Seal
Engineer of Work's Signature, PE Number
Print Name
Company
Date
2026-08-19 Item #12D Page 155 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-17
PROJECT OWNER'S CERTIFICATION
This PDP SWQMP has been prepared for [INSERT PROJECT OWNER'S COMPANY NAME] by [INSERT SWQMP PREPARER'S COMPANY NAME]. The PDP SWQMP is intended to comply with the PDP requirements of the City of Encinitas BMP Design Manual, which is a design manual for compliance with local City of Encinitas and regional MS4 Permit (California Regional Water Quality Control Board San Diego Region Order No. R9-2015-0100) requirements for storm water management.
The undersigned, while it owns the subject property, is responsible for the implementation of the provisions of this plan. Once the undersigned transfers its interests in the property, its successorin- interest shall bear the aforementioned responsibility to implement the best management practices (BMPs) described within this plan, including ensuring on-going operation and maintenance of structural BMPs. A signed copy of this document shall be available on the subject property into perpetuity.
Project Owner's Signature
Print Name
Company
Date
2026-08-19 Item #12D Page 156 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-18
SUBMITTAL RECORD
Use this table to keep a record of submittals of this PDP SWQMP. Each time the PDP SWQMP is re- submitted, provide the date and status of the project. In the fourth column, summarize the changes that have been made or indicate if response to plancheck comments is included. When applicable, insert response to plancheck comments behind this page.
Submittal
Number
Date Project Status Summary of Changes
1 Preliminary Design /
Planning/ CEQA
Final Design
Initial Submittal
2 Preliminary Design /
Planning/ CEQA
Final Design
3 Preliminary Design /
Planning/ CEQA
Final Design
4 Preliminary Design /
Planning/ CEQA
Final Design
2026-08-19 Item #12D Page 157 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-19
PROJECT IDENTIFICATION
Project/Applicant Name:
Permit/Application Number: Date:
Site Address: APN:
Scope of work/project description:
DETERMINATION OF PROJECT STATUS AND REQUIREMENTS
This form will identify permanent, post construction BMP requirements. Refer to City of Encinitas Stormwater BMP Design Manual for guidance.
Step 1: Is the project a "development project"?
Development projects are defined as "construction,
rehabilitation, redevelopment, or reconstruction of any public or private projects". See Section 1.3 and Table
1-2 of the manual for guidance. For example, interior
remodels, roof replacements, and electrical and
plumbing work are not development projects.
Yes Go to Step 2.
No
Stop.
Permanent BMP requirements do
not apply. No SWQMP will be
required. Provide discussion below.
If “No”, provide discussion / justification explaining why the project is not a "development project":
Step 2: Complete questions below for Project Type Determination.
The project is (select one): □New Development □ Redevelopment The total proposed, newly created and/or replaced impervious area is: ft2 Is the project in any of the following categories, (a) through (f) below? 2026-08-19 Item #12D Page 158 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-20
Yes
□
No
□
(a) New development projects or redevelopment projects that create and/or replaced 10,000 square feet or more of impervious surfaces (collectively over the entire project site). This includes commercial, industrial, residential, mixed-use, and public development projects.
Yes
□
No
□
(b) Redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site on an existing site of 10,000 square feet or more of impervious surfaces). This includes commercial, industrial, residential, mixed-use, and public development projects.
Yes
□
No
□
(c) New and redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site), and support one or more of the following uses:
(i) Restaurants. This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared foods and drinks for immediate consumption (SIC code 5812).
(ii) Hillside development projects. This category includes development on any natural slope that is twenty-five percent or greater. (iii) Parking lots. This category is defined as a land area or facility for the temporary parking or storage of motor vehicles used personally, for business, or for commerce.
(iv) Streets, roads, highways, freeways, and driveways. This category isdefined as any paved impervious surface used for the transportation of automobiles, trucks, motorcycles, and other vehicles.
Yes
□
No
□
(d) New or redevelopment projects that create and/or replace 2,500 square feet or more of impervious surface (collectively over the entire project site), and discharge directly to an Environmentally Sensitive Area (ESA). “Discharge directly to” includes flow that is conveyed overland a distance of 200 feet or less from the project to the ESA, or conveyed in a pipe or open channel any distance as an isolated flow from the project to the ESA (i.e. not commingled with flows from adjacent lands).
Note: ESAs are areas that include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas designated as Areas of Special Biological Significance by the State Water Board and SDRWQCB; State Water Quality Protected Areas; water bodies designated with the RARE beneficial use by the State Water Board and SDRWQCB; and any other equivalent environmentally sensitive areas which have been identified by the 2026-08-19 Item #12D Page 159 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-21
Copermittees. See manual Section 1.4.2 for additional guidance.
Yes
□
No
□
(e) New development projects, or redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface, that support one or more of the following uses:
(iii) Automotive repair shops. This category is defined as a facility that is categorized in any one of the following SIC codes: 5013, 5014, 5541, 7532- 7534, or 7536-7539.
(iv) Retail gasoline outlets. This category includes retail gasoline outlets that meet the following criteria: (a) 5,000 square feet or more or (b) a projected Average Daily Traffic of 100 or more vehicles per day.
Yes
□
No
□
(f) New or redevelopment projects that result in the disturbance of one or more acres of land and are expected to generate pollutants post construction.
Note: See manual Section 1.4.2 for additional guidance.
Does the project meet the definition of one or more of the PDP categories (a) through (f) listed above? □ Yes – The project is a Priority Development Project, the applicant shall provide PDP Post Construction BMPs and continue to Step 3.
□No – The project is a Standard or Basic Project. Stop here and complete the “City of Encinitas Stormwater Intake Form for All Developments and Standard Projects SWQMP”.
The following is for redevelopment PDPs only:
The area of existing (pre-project) impervious area at the project site is: ft2 (A) The total proposed newly created or replaced impervious area is: ft2 (B) Percent impervious surface created or replaced (B/A)*100: _% The percent impervious surface created or replaced is (select one based on the above calculation):
□ Less than or equal to fifty percent (50%) – only new and/or replaced impervious areas are considered PDP subject to treatment and HMP criteria OR □ Greater than fifty percent (50%) – the entire site is a PDP; treatment and HMP criteria apply to entire site regardless of whether it is replaced
Step 3 (PDPs only):
Do hydromodification
control requirements
Yes
PDP structural BMPs required for pollutant control
(Chapter 5) and hydromodification control (Chapter 6).
2026-08-19 Item #12D Page 160 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-22
apply?
See Section 1.6 of the BMP
Design Manual for guidance.
Go to Step 4.
No
PDP structural BMPs required for pollutant control
(Chapter 5) only.
Provide brief discussion of exemption to
hydromodification control below.
Go to “Site Information Checklist”
Discussion / justification if hydromodification control requirements do not apply:
Step 4 (PDPs subject to
treatment and
hydromodification controls):
Does protection of critical coarse
sediment yield areas apply based
on review of the City of Encinitas
Potential Critical Coarse Sediment
Yield Area Map?
See Section 6.2 of the BMP Design
Manual for guidance.
Yes
Management measures required for protection of
critical coarse sediment yield areas (Chapter 6.2).
Go to “Site Information Checklist”
No
Management measures not required for protection of
critical coarse sediment yield areas.
Provide brief discussion below.
Go to “Site Information Checklist”
Discussion / justification if management measures not required for protection of critical coarse sediment yield areas:
Project’s Watershed
(Complete Hydrologic Unit, Area, and Subarea
Name with Numeric Identifier)
Parcel Area
(Total area of Assessor's Parcel(s) associated with
the project) _ Acres ( Square Feet)
2026-08-19 Item #12D Page 161 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-23
Area to be Disturbed by the Project
(Project Area)
_ Acres ( Square Feet)
Project Proposed Impervious Area
(Subset of Project Area)
_ Acres ( Square Feet)
Project Proposed Pervious Area
(Subset of Project Area)
_ Acres ( Square Feet)
Note: Proposed Impervious Area + Proposed Pervious Area = Area to be Disturbed by the Project.
This may be less than the Parcel Area.
Description of Existing Site Condition
Current status of the site (select all that apply):
Existing development
Previously graded but not built out
Demolition completed without new construction
Agricultural or other non-impervious use
Vacant, undeveloped/natural Description / Additional Information:
Existing Land Cover includes (select all that apply):
Vegetative Cover
Non-Vegetated Pervious Areas
Impervious Areas
Description / Additional Information:
Underlying soil belongs to Hydrologic Soil Group (select all that apply):
NRCS Type A
NRCS Type B
NRCS Type C
NRCS Type D
Approximate Depth to Groundwater (GW):
GW Depth < 5 feet
5 feet < GW Depth < 10 feet
10 feet < GW Depth < 20 feet
GW Depth > 20 feet
2026-08-19 Item #12D Page 162 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-24
Existing Natural Hydrologic Features (select all that apply):
Watercourses
Seeps
Springs
Wetlands
None
Description / Additional Information:
Description of Existing Site Drainage Patterns
How is storm water runoff conveyed from the site? At a minimum, this description should answer:
1) Is existing drainage conveyance natural or urban?
2) Is runoff from offsite conveyed through the site? If yes, quantify all offsite drainage areas, design flows, and locations where offsite flows enter the project site, and summarize how such flows are conveyed through the site.
3) Provide details regarding existing project site drainage conveyance network, including any existing storm drains, concrete channels, swales, detention facilities, storm water treatment facilities, natural or constructed channels. And
4) Identify all discharge locations from the existing project site along with a summary of conveyance system size and capacity for each of the discharge locations. Provide summary of the pre-project drainage areas and design flows to each of the existing runoff discharge locations.
Describe existing site drainage patterns:
Description of Proposed Site Development
Project Description / Proposed Land Use and/or Activities:
List/describe proposed impervious features of the project (e.g., buildings, roadways, parking lots, courtyards, athletic courts, other impervious features):
List/describe proposed pervious features of the project (e.g., landscape areas):
2026-08-19 Item #12D Page 163 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-25
Does the project include grading and changes to site topography? Yes
No
Description / Additional Information:
Description of Proposed Site Drainage Patterns
Does the project include changes to site drainage (e.g., installation of new storm water conveyance systems)?
Yes
No
If yes, provide details regarding the proposed project site drainage conveyance network, including storm drains, concrete channels, swales, detention facilities, storm water treatment facilities, natural or constructed channels, and the method for conveying offsite flows through or around the proposed project site. Identify all discharge locations from the proposed project site along with a summary of the conveyance system size and capacity for each of the discharge locations. Provide a summary of pre- and post-project drainage areas and design flows to each of the runoff discharge locations. Reference the drainage study for detailed calculations.
Describe proposed site drainage patterns:
Identification and Narrative of Receiving Water and Pollutants of Concern Describe flow path of storm water from the project site discharge location(s), through urban storm conveyance systems as applicable, to receiving creeks, rivers, and lagoons as applicable, and ultimate discharge to the Pacific Ocean (or bay, lagoon, lake or reservoir, as applicable):
List any 303(d) impaired water bodies within the path of storm water from the project site to the Pacific Ocean (or bay, lagoon, lake or reservoir, as applicable), identify the pollutant(s)/stressor(s) causing impairment, and identify any TMDLs and/or Highest Priority Pollutants from the WQIP for the impaired water bodies:
2026-08-19 Item #12D Page 164 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-26
303(d) Impaired Water Body Pollutant(s)/Stressor(s) TMDLs / WQIP Highest Priority Pollutant
Identification of Project Site Pollutants*
*Identification of project site pollutants is only required if flow-thru treatment BMPs are implemented onsite in lieu of retention or biofiltration BMPs (note the project must also participate in an alternative compliance program unless prior lawful approval to meet earlier PDP requirements is demonstrated)
Identify pollutants expected from the project site based on all proposed use(s) of the site (see BMP Design Manual Appendix B.6):
Pollutant Not Applicable to
the Project Site
Expected from the
Project Site
Also a Receiving
Water Pollutant of
Concern
Sediment
Nutrients
Heavy Metals
Organic Compounds
Trash & Debris
Oxygen Demanding
Substances
Oil & Grease
Bacteria & Viruses
2026-08-19 Item #12D Page 165 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-27
Pesticides
Hydromodification Management Requirements
Do hydromodification management requirements apply (see Section 1.6 of the BMP Design Manual)? Yes, hydromodification management flow control structural BMPs required. No, the project will discharge runoff directly to existing underground storm drains discharging directly to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean. No, the project will discharge runoff directly to conveyance channels whose bed and bank are concrete-lined all the way from the point of discharge to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean.
No, the project will discharge runoff directly to an area identified as appropriate for an exemption by the WMAA for the watershed in which the project resides.
Description / Additional Information (to be provided if a 'No' answer has been selected above):
Critical Coarse Sediment Yield Areas*
*This section only required if hydromodification management requirements apply 2026-08-19 Item #12D Page 166 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-28
Based on the maps provided within the WMAA, do potential critical coarse sediment yield areas exist within the project drainage boundaries?
Yes
No, no critical coarse sediment yield areas to be protected based on WMAA maps If yes, have any of the optional analyses presented in Section 6.2 of the BMP Design Manual been performed?
6.2.1 Verification of Geomorphic Landscape Units (GLUs) Onsite 6.2.2 Downstream Systems Sensitivity to Coarse Sediment 6.2.3 Optional Additional Analysis of Potential Critical Coarse Sediment Yield Areas Onsite No optional analyses performed, the project will avoid critical coarse sediment yield areas identified based on WMAA maps
If optional analyses were performed, what was the final result? No critical coarse sediment yield areas to be protected based on verification of GLUs onsite Critical coarse sediment yield areas exist but additional analysis has determined that protection is not required. Documentation attached in Attachment 2.b of the SWQMP. Critical coarse sediment yield areas exist and require protection. The project will implement management measures described in Sections 6.2.4 and 6.2.5 as applicable, and the areas are identified on the SWQMP Exhibit.
Discussion / Additional Information:
Flow Control for Post-Project Runoff*
*This section only required if hydromodification management requirements apply List and describe point(s) of compliance (POCs) for flow control for hydromodification management (see Section 6.3.1). For each POC, provide a POC identification name or number correlating to the project's HMP Exhibit and a receiving channel identification name or number correlating to the project's HMP Exhibit.
2026-08-19 Item #12D Page 167 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-29
Has a geomorphic assessment been performed for the receiving channel(s)? No, the low flow threshold is 0.1Q2 (default low flow threshold) Yes, the result is low flow threshold 0.1Q2
Yes, the result is low flow threshold 0.3Q2
Yes, the result is low flow threshold 0.5Q2
If a geomorphic assessment has been performed, provide title, date, and preparer:
Discussion / Additional Information: (optional)
Other Site Requirements and Constraints
When applicable, list other site requirements or constraints that will influence storm water management design, such as zoning requirements including setbacks and open space, or local codes governing minimum street width, sidewalk construction, allowable pavement types, and drainage requirements.
Optional Additional Information or Continuation of Previous Sections As Needed This space provided for additional information or continuation of information from previous sections as needed.
2026-08-19 Item #12D Page 168 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-30
SOURCE CONTROL BMP CHECKLIST
All development projects must implement source control BMPs SC-1 through SC-6 where applicable and feasible. See Chapter 4 and Appendix E of the manual for information to implement source control BMPs shown in this checklist.
Answer each category below pursuant to the following.
• "Yes" means the project will implement the source control BMP as described in Chapter 4 and/or Appendix E of the manual. Discussion / justification is not required. • "No" means the BMP is applicable to the project but it is not feasible to implement. Discussion / justification must be provided.
• "N/A" means the BMP is not applicable at the project site because the project does not include the feature that is addressed by the BMP (e.g., the project has no outdoor materials storage areas). Discussion / justification may be provided.
Source Control Requirement Applied?
SC-1 Prevention of Illicit Discharges into the MS4 Yes No N/A SC-2 Storm Drain Stenciling or Signage Yes No N/A SC-3 Protect Outdoor Materials Storage Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
Yes No N/A
SC-4 Protect Materials Stored in Outdoor Work Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
Yes No N/A
SC-5 Protect Trash Storage Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
Yes No N/A
2026-08-19 Item #12D Page 169 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-31
SC-6 Additional BMPs Based on Potential Sources of Runoff Pollutants (must answer for each source listed below)
Onsite storm drain inlets
Interior floor drains and elevator shaft sump pumps drain to sewer Interior parking garages drain to sewer
Need for future indoor & structural pest control
Landscape/outdoor pesticide use
Pools, spas, ponds, decorative fountains, and other water features Food service
Refuse/Trash areas must be covered
Industrial processes
Outdoor storage of equipment or materials must be covered Vehicle and equipment cleaning
Vehicle/equipment repair and maintenance
Fuel dispensing areas
Loading docks
Fire sprinkler test water
Miscellaneous drain or wash water
Plazas, sidewalks, and parking lots
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Discussion / justification if SC-1 through SC-6 not implemented. Justification must be provided for ALL "No" answers shown above.
2026-08-19 Item #12D Page 170 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-32
SITE DESIGN BMP CHECKLIST
All development projects must implement site design BMPs SD-1 through SD-8 where applicable and feasible. See Chapter 4 and Appendix E of the manual for information to implement site design BMPs shown in this checklist.
Answer each category below pursuant to the following.
• "Yes" means the project will implement the site design BMP as described in Chapter 4 and/or Appendix E of the manual. Discussion / justification is not required. • "No" means the BMP is applicable to the project but it is not feasible to implement. Discussion / justification must be provided.
• "N/A" means the BMP is not applicable at the project site because the project does not include the feature that is addressed by the BMP (e.g., the project site has no existing natural areas to conserve). Discussion / justification may be provided.
Source Control Requirement Applied?
SD-1 Maintain Natural Drainage Pathways and Hydrologic Features Yes No N/A SD-2 Conserve Natural Areas, Soils, and Vegetation Yes No N/A SD-3 Minimize Impervious Area Yes No N/A
SD-4 Minimize Soil Compaction Yes No N/A
SD-5 Impervious Area Dispersion - Directly Connected Impervious Areas (e.g. roof downspouts connected to street) are not allowed Yes No N/A
SD-6 Runoff Collection Yes No N/A
SD-7 Landscaping with Native or Drought Tolerant Species Yes No N/A SD-8 Harvesting and Using Precipitation Yes No N/A Discussion / justification if SD-1 through SD-8 not implemented. Justification must be provided for ALL "No" answers shown above.
2026-08-19 Item #12D Page 171 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-33
PDP STRUCTURAL BMPS
All PDPs must implement structural BMPs for storm water pollutant control (see Chapter 5 of the BMP Design Manual). Selection of PDP structural BMPs for storm water pollutant control must be based on the selection process described in Chapter 5. PDPs subject to hydromodification management requirements must also implement structural BMPs for flow control for hydromodification management (see Chapter 6 of the BMP Design Manual). Both storm water pollutant control and flow control for hydromodification management can be achieved within the same structural BMP(s).
PDP structural BMPs must be verified by the local jurisdiction at the completion of construction. This may include requiring the project owner or project owner's representative and engineer of record to certify construction of the structural BMPs (see Section 1.12 of the BMP Design Manual). PDP structural BMPs must be maintained into perpetuity (see Section 7 of the BMP Design Manual). The local jurisdiction will confirm the maintenance annually.
Use this section to provide narrative description of the general strategy for structural BMP implementation at the project site in the box below. Then complete the PDP structural BMP summary information sheet (page 3 of this form) for each structural BMP within the project (copy the BMP summary information page as many times as needed to provide summary information for each individual structural BMP).
Describe the general strategy for structural BMP implementation at the site. This information must describe how the steps for selecting and designing storm water pollutant control BMPs presented in Section 5.1 of the BMP Design Manual were followed, and the results (type of BMPs selected). For projects requiring hydromodification flow control BMPs, indicate whether pollutant control and flow control BMPs are integrated or separate.
2026-08-19 Item #12D Page 172 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-34
STRUCTURAL BMP SUMMARY INFORMATION
Copy this page as necessary to provide information on each individual proposed structural BMP Structural BMP ID No: DMA No:
Construction Plan Sheet No:
Type of structural BMP:
Retention by harvest and use (HU-1)
Retention by infiltration basin (INF-1)
Retention by bioretention (INF-2)
Retention by permeable pavement (INF-3)
Partial retention by biofiltration with partial retention (PR-1) Biofiltration (BF-1)
Biofiltration with Nutrient Sensitive Media Design (BF-2) Approved Equivalent Proprietary Biofiltration Systems (BF-3) meeting all requirements of Appendix F Flow-thru treatment control with prior lawful approval to meet earlier PDP requirements (provide BMP type/description in discussion section below)
Flow-thru treatment control included as pre-treatment/forebay for an onsite retention or biofiltration BMP (provide BMP type/description and indicate which onsite retention or biofiltration BMP it serves in discussion section below)
Flow-thru treatment control with alternative compliance (provide BMP type/description in discussion section below)
Detention pond or vault for hydromodification management Other (describe in discussion section below)
Purpose:
Pollutant control only
Hydromodification control only
Combined pollutant control and hydromodification control Pre-treatment/forebay for another structural BMP
Other (describe in discussion section below)
2026-08-19 Item #12D Page 173 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-35
Who will inspect and certify construction of this
BMP? Provide name and contact information for the
party responsible to sign BMP verification forms
required by the City Engineer (See Section 1.12 of
the BMP Design Manual)
Who will be the final owner of this BMP?
Who will maintain this BMP into perpetuity?
What is the funding mechanism for maintenance?
Discussion (as needed):
2026-08-19 Item #12D Page 174 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-36
ATTACHMENT 1 – BACKUP FOR PDP POLLUTANT CONTROL BMPS
This is the cover sheet for Attachment 1.
Indicate which items are included behind this cover sheet:
Attachment Contents Checklist
Attachment 1a DMA Exhibit (Required)
See DMA Exhibit Checklist on the back of
this Attachment cover sheet.
Included
Attachment 1b Tabular Summary of DMAs Showing DMA
ID matching DMA Exhibit, DMA Area, and
DMA Type (Required)*
*Provide table in this Attachment OR on
DMA Exhibit in Attachment 1a
Included on DMA Exhibit in
Attachment 1a
Included as Attachment 1b, separate
from DMA Exhibit
Attachment 1c Form J-7, Harvest and Use Feasibility
Screening Checklist (Required unless the
entire project will use infiltration BMPs)
Refer to Appendix B.3-1 of the BMP
Design Manual to complete Form J-7.
Included
Not included because the entire
project will use infiltration BMPs
Attachment 1d Form J-8, Categorization of Infiltration
Feasibility Condition (Required unless the
project will use harvest and use BMPs)
Refer to Appendices C and D of the BMP
Design Manual to complete Form J-8.
Included
Not included because the entire
project will use harvest and use BMPs
Attachment 1e Pollutant Control BMP Design
Worksheets / Calculations (Required)
Refer to Appendices B and E of the BMP
Design Manual for structural pollutant
control BMP design guidelines
Included
2026-08-19 Item #12D Page 175 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-37
Use this checklist to ensure the required information has been included on the DMA Exhibit:
The DMA Exhibit must identify:
Underlying hydrologic soil group
Approximate depth to groundwater
Existing natural hydrologic features (watercourses, seeps, springs, wetlands) Critical coarse sediment yield areas to be protected
Existing topography and impervious areas
Existing and proposed site drainage network and connections to drainage offsite Proposed demolition
Proposed grading
Proposed impervious features
Proposed design features and surface treatments used to minimize imperviousness Drainage management area (DMA) boundaries, DMA ID numbers, and DMA areas (square footage or acreage), and DMA type (i.e., drains to BMP, self-retaining, or selfmitigating) Potential pollutant source areas and corresponding required source controls (see Chapter 4, Appendix E.1, and Form J-3B)
Structural BMPs (identify location, type of BMP, and size/detail) 2026-08-19 Item #12D Page 176 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-38
ATTACHMENT 2 – BACKUP FOR PDP HYDROMODIFICATION CONTROL
MEASURES
This is the cover sheet for Attachment 2.
Mark this box if this attachment is not included because the project is exempt from PDP hydromodification management requirements.
Indicate which items are included behind this cover sheet:
Attachment Contents Checklist
Attachment 2a Hydromodification Management Exhibit
(Required)
Included
See Hydromodification Management
Exhibit Checklist on the back of this
Attachment cover sheet.
Attachment 2b Management of Critical Coarse Sediment
Yield Areas (WMAA Exhibit is required,
additional analyses are optional)
See Section 6.2 of the BMP Design
Manual.
Exhibit showing project drainage
boundaries marked on WMAA Critical
Coarse Sediment Yield Area Map
(Required)
Optional analyses for Critical Coarse
Sediment Yield Area Determination
6.2.1 Verification of Geomorphic
Landscape Units Onsite
6.2.2 Downstream Systems Sensitivity
to Coarse Sediment
6.2.3 Optional Additional Analysis of
Potential Critical Coarse Sediment
Yield Areas Onsite
Attachment 2c Geomorphic Assessment of Receiving
Channels (Optional)
See Section 6.3.4 of the BMP Design
Manual.
Not performed
Included
Submitted as separate stand-alone
document
Attachment 2d Flow Control Facility Design, including
Structural BMP Drawdown Calculations
and Overflow Design Summary
(Required)
See Chapter 6 and Appendix G of the
BMP Design Manual
Included
Submitted as separate stand-alone
document
Attachment 2e Vector Control Plan (Required when
structural BMPs will not drain in 96 hours)
Included
Not required because BMPs will drain
in less than 96 hours
2026-08-19 Item #12D Page 177 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-39
Use this checklist to ensure the required information has been included on the Hydromodification Management Exhibit:
The Hydromodification Management Exhibit must identify:
Underlying hydrologic soil group
Approximate depth to groundwater
Existing natural hydrologic features (watercourses, seeps, springs, wetlands) Critical coarse sediment yield areas to be protected
Existing topography
Existing and proposed site drainage network and connections to drainage offsite Proposed grading
Proposed impervious features
Proposed design features and surface treatments used to minimize imperviousness Point(s) of Compliance (POC) for Hydromodification Management Existing and proposed drainage boundary and drainage area to each POC (when necessary, create separate exhibits for pre-development and post-project conditions) Structural BMPs for hydromodification management (identify location, type of BMP, and size/detail) 2026-08-19 Item #12D Page 178 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-40
ATTACHMENT 3 - STRUCTURAL BMP MAINTENANCE INFORMATION
This is the cover sheet for Attachment 3.
Indicate which items are included behind this cover sheet:
Attachment Contents Checklist
Attachment 3a Structural BMP Maintenance Thresholds and Actions (Required)
Included
See Structural BMP Maintenance
Information Checklist on the back of this
Attachment cover sheet.
Attachment 3b Draft Maintenance Agreement (when
applicable)
Included
Not Applicable
2026-08-19 Item #12D Page 179 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-41
Use this checklist to ensure the required information has been included in the Structural BMP Maintenance Information Attachment:
Preliminary Design / Planning / CEQA level submittal:
Attachment 3a must identify:
Typical maintenance indicators and actions for proposed structural BMP(s) based on Section 7.7 of the BMP Design Manual
Attachment 3b is not required for preliminary design / planning / CEQA level submittal. Final Design level submittal:
Attachment 3a must identify:
Specific maintenance indicators and actions for proposed structural BMP(s). This shall be based on Section 7.7 of the BMP Design Manual and enhanced to reflect actual proposed components of the structural BMP(s)
How to access the structural BMP(s) to inspect and perform maintenance Features that are provided to facilitate inspection (e.g., observation ports, cleanouts, silt posts, or other features that allow the inspector to view necessary components of the structural BMP and compare to maintenance thresholds)
Manufacturer and part number for proprietary parts of structural BMP(s) when applicable Maintenance thresholds specific to the structural BMP(s), with a location-specific frame of reference (e.g., level of accumulated materials that triggers removal of the materials, to be identified based on viewing marks on silt posts or measured with a survey rod with respect to a fixed benchmark within the BMP)
Recommended equipment to perform maintenance
When applicable, necessary special training or certification requirements for inspection and maintenance personnel such as confined space entry or hazardous waste management Attachment 3b: For private entity operation and maintenance, Attachment 3b shall include a draft maintenance agreement in the local jurisdiction's standard format (PDP applicant to contact the City Engineer to obtain the current maintenance agreement forms). 2026-08-19 Item #12D Page 180 of 816
Appendix A: Submittal Templates
Preparation Date: [INSERT DATE] Page A-42
ATTACHMENT 4 – COPY OF PLAN SHEETS SHOWING PERMANENT STORM
WATER BMPS
This is the cover sheet for Attachment 4.
Use this checklist to ensure the required information has been included on the plans: The plans must identify:
Structural BMP(s) with ID numbers matching Form J-6 Summary of PDP Structural BMPs The grading and drainage design shown on the plans must be consistent with the delineation of DMAs shown on the DMA exhibit
Details and specifications for construction of structural BMP(s) Signage indicating the location and boundary of structural BMP(s) as required by the City Engineer How to access the structural BMP(s) to inspect and perform maintenance Features that are provided to facilitate inspection (e.g., observation ports, cleanouts, silt posts, or other features that allow the inspector to view necessary components of the structural BMP and compare to maintenance thresholds)
Manufacturer and part number for proprietary parts of structural BMP(s) when applicable Maintenance thresholds specific to the structural BMP(s), with a location-specific frame of reference (e.g., level of accumulated materials that triggers removal of the materials, to be identified based on viewing marks on silt posts or measured with a survey rod with respect to a fixed benchmark within the BMP)
Recommended equipment to perform maintenance
When applicable, necessary special training or certification requirements for inspection and maintenance personnel such as confined space entry or hazardous waste management Include landscaping plan sheets showing vegetation requirements for vegetated structural BMP(s) All BMPs must be fully dimensioned on the plans
When proprietary BMPs are used, site-specific cross section with outflow, inflow, and model number shall be provided. Photocopies of general brochures are not acceptable.
2026-08-19 Item #12D Page 181 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L B-1 2023
Appendix
B
Appendix B Storm Water Pollutant
Control Hydrologic Calculations
and Sizing Methods for Structural
BMPs
Table of Contents:
B.1. Step 1: Determine DCV
B.2. Step 2: Determine Retention Requirements
B.3. Step 3: Determine BMP Performance
B.4. Less Common Pollutant Control Calculations
B.5. Backup Information on Pollutant Control Standards
2026-08-19 Item #12D Page 182 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-2 2023
B.1Step 1 – Determine DCV
The first step in performing storm water pollutant control calculations is to calculate the Design Capture Volume (DCV). The DCV represents the volume of storm water runoff that must be retained and/or biofiltered in order to satisfy pollutant control requirements. The DCV can be calculated through use of automated Worksheet B.1 depicted on the following page, or can be calculated manually by following Steps 1A through 1D presented in this section. =
12 −
Where:
DCV: Design Capture Volume (ft3)
D: Rainfall Depth (inches), refer to section B.1.1.
A: Tributary Area (ft2), refer to Section B.1.2.
C: Runoff Factor (unitless), refer to section B.1.3.
R: Site Design Volume Reductions (ft3), refer to Section B.1.4. 2026-08-19 Item #12D Page 183 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-3 2023
Worksheet B.1 Calculation of Design Capture Volume
2026-08-19 Item #12D Page 184 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-4 2023
Worksheet B.1 Line Item Notes
1. User Input from stormwater plans.
2. User input from BMPDM Figure B.1-1.
3. User Input from stormwater plans.
4. User Input from stormwater plans.
5. User Input from stormwater plans.
6. User Input from stormwater plans.
7. User Input from stormwater plans.
8. User Input from stormwater plans.
9. User Input from stormwater plans.
10. User Input. Default is "No". Select Yes if any of the referenced elements are proposed.
11. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
12. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
13. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
14. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
15. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
16. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
17. User Input from stormwater plans. Must satisfy criteria from Fact Sheet SD-B.
18. User Input. Must satisfy criteria from Fact Sheet SD-A.
19. User Input. Must satisfy criteria from Fact Sheet SD-A. Acceptable range from 0-30 feet.
20. User Input. Must satisfy criteria from Fact Sheet SD-E. Cannot provide more than a 25% reduction to initial DCV.
21. User Input. Must satisfy criteria from Fact Sheet SD-E. Acceptable range 0-100 gallons for generic volume reductions.
22. Sum of Lines 3 through 17.
23. [0.9(Line 3) + 0.3(Line 4 + Line 9) + 0.1(Line 5 + Line 6) + 0.14(Line 7) + 0.23(Line 8)] /(Sum of Lines 3 through Line 9)
24. [0.9(Line 11) + 0.3(Line 12 + Line 17) + 0.1(Line 13 + Line 14) + 0.14(Line 15) + 0.23(Line 16)] /(Sum of Lines 11 through Line 17)
25. [(Line 23 x (Sum of Lines 3 through 9) + Line 24 x (Sum of Lines 11 through 17)) / Line 22]
26. (Line 2/12) x Line 22 x Line 25
27. Line 11
28. Summation of Lines 12-17.
29. [Line 27 / Line 28]. If greater than 4.0 dispersion benefits are not quantified.
30. Lookup values from Table B.1-1 weighted with respect to distribution of dispersion areas specified in Lines 12-17.
31. [Line 23 x (Sum of Lines 3 through Line 9) + Line 24 x Line 30 x (Sum of Lines 11 through Line 17)] / Line 22
32. (Line 2/12) x Line 22 x Line 31
33. [Line 18 x Lookup value from Section B.1.4 of BMP Design Manual]
34. [Line 20 x Line 21/7.48]. If Line 21>100 or Line 10 is "n/a" or "no", then this value must be zero.
35. Line 31 x [1 - ((Line 33 + Line 34)/(Line 32))]. Value must be between zero and one.
36. Line 22 x Line 35
37. [(Line 26 - Line 32) + Line 33 + Line 34]
38. [Line 26 - Line 37]. Minimum result of 0.
2026-08-19 Item #12D Page 185 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-5 2023
B.1.1 Step 1A – Rainfall Depth
The 85th percentile, 24-hour isopluvial map is provided as Figure B.1-1. The rainfall depth to estimate the DCV shall be determined using Figure B.1-1. The methodology used to develop this map is presented below:
B.1.1.1 Gauge data and calculation of 85th percentile
The method of calculating the 85th percentile is to produce a list of values, order them from smallest to largest, and then pick the value that is 85 percent of the way through the list. Only values that are capable of producing run off are of interest for this purpose. Lacking a legislative definition of rainfall values capable of producing runoff, Flood Control staff in San Diego County have observed that the point at which significant runoff begins is rather subjective, and is affected by land use type and soil moisture. In highly-urbanized areas, the soil has a high impermeability and runoff can begin with as little as 0.02" of rainfall. In rural areas, soil impermeability is significantly lower and even 0.30" of rain on dry soil will frequently not produce significant runoff. For this reason, San Diego County has chosen to use the more objective method of including all non-zero 24-hour rainfall totals when calculating the 85th percentile. To produce a statistically significant number, only stations with 30 years or greater of daily rainfall records are used.
B.1.1.2 Mapping the gauge data
A collection of 56 precipitation gauge points was developed with 85th percentile precipitation values based on multiple years of gauge data. A raster surface (grid of cells with values) was interpolated from that set of points. The surface initially did not cover the County's entire jurisdiction. A total of 13 dummy points were added. Most of those were just outside the County boundary to enable the software to generate a surface that covered the entire County. A handful of points were added to enforce a plausible surface. In particular, one point was added in the desert east of Julian, to enforce a gradient from high precipitation in the mountains to low precipitation in the desert. Three points were added near the northern boundary of the County to adjust the surface to reflect the effect of elevation in areas lacking sufficient operating gauges.
Several methods of interpolation were considered. The method chosen is named by Environmental Systems Research Institute as the Natural Neighbor technique. This method produces a surface that is highly empirical, with the value of the surface being a product of the values of the data points nearest each cell. It does not produce peaks or valleys of surface based on larger area trends, and is free of artifacts that appeared with other methods.
B.1.2 Step 1B – Tributary Area
Determine the total tributary area through evaluation of the drainage area delineations performed as outlined in Section 3. These areas will be analyzed in additional detail in Step 1C below. 2026-08-19 Item #12D Page 186 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-6 2023
B.1.3 Step 1C – Runoff Factor
Runoff factors (C) represent the ratio of storm water runoff over rainfall that is anticipated for a particular surface type. Impervious surfaces typically have high runoff factors (0.90) as nearly all rainfall is converted into runoff. Pervious surfaces typically have low runoff factors (0.10) as much of the rainfall is retained in natural surface features. Applicants should evaluate all of the surface coverages within a drainage area and assign runoff factors consistent with the values in Table B.1-1.
Table B.1-1: Runoff factors for surfaces draining to BMPs – Pollutant Control BMPs Category Surface Type Runoff Factor (C)
Impervious
Surfaces Roofs, Concrete, Asphalt, Unit Pavers (grouted) 0.90 Semi-Pervious
Surfaces
Decomposed Granite, Cobbles, Crushed Aggregate,
Compacted soil (unpaved parking) 0.30
Engineered
Pervious
Surfaces
Green Roofs per SD-C
Permeable Pavement per SD-D,
Amended Soils per SD-F,
Landscaped/Mulched Soils,
Permeable Pavement per INF-3
0.10 Natural
Pervious
Surfaces
Type A Soil 0.10
Type B Soil 0.14
Type C Soil 0.23
Type D Soil 0.30
Impoundments Swimming pools, fountains, ponds, etc. 0.00 Dispersion
Areas
Areas routed to or serving as a dispersion area per
SD-B
See Dispersion Area
Text Below
If a drainage area is comprised of more than one surface type, an area-weighted runoff factor must be calculated per the following equation where C represents the runoff coefficient and A represents the area of each surface.
=
∑
+
+
∑
Dispersion Area Runoff Factor Adjustments
Adjustment to runoff factors may be permitted when storm water runoff from impervious surfaces is dispersed through pervious dispersion areas in accordance with the SD-B fact sheet located in Appendix E. Note that pervious dispersion areas may be used to eliminate the DCV requiring treatment and thereby fully satisfy pollutant control requirements when designed as significant site 2026-08-19 Item #12D Page 187 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-7 2023
design BMPs (SSD-BMPs). Refer to Appendix I for sizing methods and criteria to use dispersion areas as SSD-BMPs.
Runoff factor adjustments may be applied to drainage areas with a 4:1 maximum ratio of impervious to pervious area. In order to be eligible for runoff factor adjustments, impervious areas must have a runoff factor of 0.90 and must be directed towards a pervious dispersion area with a runoff factor of
0.30 or less.
Table B.1-2 presents runoff factor adjustments as a function of the ratio of impervious to pervious area and the hydrologic soil group of the pervious dispersion area. Applicants applying runoff factor adjustments must identify appropriate factors in the table below and multiply that factor by the original composite runoff factor of the impervious area and the dispersion area.
Table B.1-2: Impervious area adjustment factors that account for dispersion Characteristics of
Pervious Area
Ratio = Impervious area/Pervious area
<=1 2 3 4
Type A or
Amended Soils 0.00 0.00 0.21 0.32
Type B Soils 0.00 0.24 0.38 0.48
Type C Soils 0.31 0.50 0.60 0.67
Type D Soils 0.77 0.84 0.87 0.90
When using adjustment factors from Table B.1-2:
a) The underlying soil group need not be considered if amended soils implemented per SD-F. b) Linear interpolation must be performed if the impervious to pervious area ratio of the site is in between one of ratios for which an adjustment factor was developed; c) Use adjustment factor for a ratio of 1 when the impervious to pervious area ratio is less than 1 B.1.4 Step 1D – Site Design Volume Reductions
Site design volume reductions (R) account for the effects of incorporating non-structural BMPs such as tree wells and rain barrels into the site design. Effective use of these site design elements can significantly reduce the DCV requiring treatment through structural BMP strategies. Note that tree wells may be used to eliminate the DCV requiring treatment and thereby fully satisfy pollutant control requirements when designed as significant site design BMPs (SSD-BMPs). Refer to Appendix I for sizing methods and criteria to use tree wells as SSD-BMPs.
Tree wells designed per the SD-A fact sheet provide the following volume reductions to the DCV.
The maximum volume reduction for any individual tree is 420 cubic feet.
Table B.1-3: Tree Well Volume Reductions
Mature Tree Canopy
Diameter (ft)
Volume Reduction
(cubic feet/tree)
2026-08-19 Item #12D Page 188 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-8 2023
0 0
5 10
10 40
15 100
20 180
25 290
30 420
Rain barrels designed per SD-E fact sheet can also provide limited volume reductions to the DCV.
The effects of rain barrels are typically less substantial than tree wells and are subject to the following restrictions: 1) individual rain barrel volumes are no greater than 100 gallons, 2) the total rain barrel volume is no greater than 0.25 DCV, and 3) the site must have landscape areas of at least 30% of the project footprint. If the proposed rain barrels do not meet these criteria, design volume reductions may still be achieved through Cistern criteria presented in fact sheet HU-1.
Table B.1-4: Rain Barrel Volume Reductions
Rain Barrel Size
(gallon)
Volume Reduction
(cubic feet)
0 0.0
20 2.7
40 5.3
60 8.0
80 10.7
100 13.4
2026-08-19 Item #12D Page 189 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs B-9 2023
Figure B.1-1: 85th Percentile 24-hour Isopluvial Map
2026-08-19 Item #12D Page 190 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control B-10 2023
B.2Step 2 - Determine Retention Requirements
The second step in performing storm water pollutant control calculations is to determine the retention requirements for each drainage area. Retention requirements can be calculated through use of the automated Worksheet B.2 depicted below, or can be calculated manually by following Steps 2A through 2D presented in this section.
Worksheet B.2 Retention Requirements
B.2.1 Step 2A - Capture and Use Analysis
Projects that do not propose habitable structures over 9 stories tall may skip this step (proceed to Step 2B).
Category # Description i Units
1 Drainage Basin ID or Name uniless
2 85th Percentile Rainfall Depth inches
3 Predominant NRCS Soil Type Within BMP Location unitless 4 Is proposed BMP location Restricted or Unrestricted for Infiltration Activities? unitless 5 Nature of Restriction unitless
6 Do Minimum Retention Requirements Apply to this Project? yes/no 7 Are Habitable Structures Greater than 9 Stories Proposed? yes/no 8 Has Geotechnical Engineer Performed an Infiltration Analysis? yes/no 9 Design Infiltration Rate Recommended by Geotechnical Engineer in/hr 10 Design Infiltration Rate Used To Determine Retention Requirements in/hr 11 Percent of Average Annual Runoff that Must be Retained within DMA percentage 12 Fraction of DCV Requiring Retention ratio
13 Required Retention Volume cubic-feet
Advanced
Analysis
Basic
Analysis
Result
Worksheet B.2 Line Item Notes
1. User input from stormwater plans.
2. User input from BMPDM Figure B.1-1.
3. User input from stormwater plans.
4. User input from BMPDM Section B.2.2.
5. User input from BMPDM Section B.2.2.
6. Default value of "Yes" for Priority Development Projects.
7. User input from BMPDM Section B.2.1. If "Yes", separate capture and use evaluation must be provided.
8. User input from BMPDM Section B.2.3. If "Yes", geotechnical report excerpts must be provided.
9. User input from BMPDM Section B.2.3.
10. Rates of 0.300, 0.200, 0.100, 0.025, or 0.000 for A, B, C, D, or Restricted soils respectively. Or rate from Geotechnical Engineer.
11. Determined Per BMPDM Section B.2.4.
12. Determined Per BMPDM Section B.2.4.
13. Determined Per BMPDM Section B.2.4.
2026-08-19 Item #12D Page 191 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-11 2023
Projects that propose habitable structures over 9 stories tall are required to perform a capture and use analysis to identify whether the DCV from the project site can be utilized for onsite toilet flushing and/or irrigation within 36 hours of the storm. If the results indicate capture and use is possible, then the project is required to implement capture and use. Guidance for performing this analysis is provided in B.3.8.
B.2.2 Step 2B – Infiltration Restrictions
The SWQMP Preparer is responsible for evaluating the infiltration restrictions in Table B.2-1 below and characterizing each drainage area as Restricted or Unrestricted for infiltration.
Restriction elements are divided into Mandatory Considerations and Optional Considerations.
Mandatory Considerations include elements that may pose a significant risk to human health and safety. These elements must always be evaluated and discretion regarding the setbacks is not permitted.
Optional Considerations include elements that are not necessarily associated with human health and safety, so analysis is not mandated through this guidance document.
Analysis of these elements is outside of the scope of typical geotechnical engineering investigations; therefore, it is the responsibility of the SWQMP Preparer to perform this evaluation. If a geotechnical engineer is consulted to complete this portion of the analysis, additional discretion on the mandatory considerations may be permitted if supported by the geotechnical reporting.
Table B.2-1: Infiltration Restrictions
Restriction Element
Is Element
Applicable?
(Yes/No)
Mandatory
Considerations
BMP is within 100’ of Contaminated Soils
BMP is within 100’ of Industrial Activities Lacking Source Control BMP is within 100’ of Well/Groundwater Basin
BMP is within 50’ of Septic Tanks/Leach Fields
BMP is within 10’ of Structures/Tanks/Walls
BMP is within 10’ of Sewer Utilities
BMP is within 10’ of Groundwater Table
BMP is within Hydric Soils
BMP is within Highly Liquefiable Soils and has Connectivity to Structures BMP is within 1.5 Times the Height of Adjacent Steep Slopes (≥25%) County Staff has Assigned “Restricted” Infiltration Category Optional
Considerations
BMP is within Predominantly Type D Soil
BMP is within 10’ of Property Line
BMP is within Fill Depths of ≥5’ (Existing or Proposed) BMP is within 10’ of Underground Utilities
BMP is within 250’ of Ephemeral Stream
2026-08-19 Item #12D Page 192 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-12 2023
Other (Provide detailed geotechnical support)
Result
Unrestricted. None of the restriction elements above are applicable.
Restricted. One or more of the restriction elements above are applicable.
The following table summarizes public data sources available for the infiltration restriction analysis.
Table B.2-2: Public Data Sources for Infiltration Restriction Analysis Resources Description
Geotracker Website: geotracker.waterboards.ca.gov
Reference Layers: Groundwater Depths, Contaminated Sites/Soils SANGIS Website: sangis.org
Reference Layers: Land Use Current, Gas Stations, Wells, Groundwater Basins, Flowlines, Liquefaction, Soils, Steep Slopes, Sewer, Topography, Elevation Grids Web Soil Survey
(NRCS Soil Type)
Website: websoilsurvey.sc.egov.usda.gov/App
Reference Layers: Hydrologic Soil Group, Map Unit Names Watershed
Management Area
Analysis
Website: projectcleanwater.org/watershed-management-area-analysis-wmaa Reference Layers: Electronic Data from Appendix C of WMAA Survey Records
System
Website: srs.sandiegocounty.gov
Reference Layers: Grading Plans, Surveys, Drainage Plans, Topography Maps, Tentative Parcel Maps
Applicant Plans Website: n/a
Reference Layers: Utility Plans, Grading Plans, Existing Site Conditions, Proposed Site Conditions, Nearby geotechnical reports.
Geotechnical
Engineer
Website: n/a
Reference Layers: At discretion of Geotechnical Engineer B.2.3 Step 2C – Design Infiltration Rate
The design infiltration rate for each drainage area must be determined through either a basic or advanced analysis. The basic analysis allows the SWQMP Preparer to assign a default design infiltration rate based on the predominant NRCS soil type present within the proposed BMP footprint.
The advanced analysis allows for a geotechnical engineer to assign a more specific design infiltration rate based on field testing outlined in Appendix D. Table B.2-3 below identifies the design infiltration rates that can be used for each analysis. Please note that the basic analysis is not permitted for BMPs that lack an underdrain.
Table B.2-3: Design Infiltration Rate
Infiltration Restrictions
Design Infiltration Rate (in/hr)
Option 1: Basic Analysis Option 2: Advanced Analysis
Unrestricted Type A Soil = 0.300
Rate recommended
by geotechnical engineer
(Reference Appendix D)
Unrestricted Type B Soil = 0.200
Unrestricted Type C Soil = 0.100
Unrestricted Type D Soil = 0.025
2026-08-19 Item #12D Page 193 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-13 2023
Restricted Any Soil = 0.000 0.000
B.2.4 Step 2D - Retention Requirements
Using information determined in previous steps, the retention requirements for each drainage area can now be determined. Retention requirements can be expressed as a function of the DCV or as a percentage of annual runoff that must be retained within the drainage area.
Part 1) Using Figure B.2-1, locate the applicable Design Infiltration Rate (determined in Step 2A) along the x-axis. Trace vertically from the x-axis result to the intersect with the plot representing the project’s 85th Percentile Rainfall Depth (determined in Step 1A).
Note: Data presented in Figure B.2-1 represents ranges of rainfall depth. Users should choose the range that includes their specific rainfall depth rather than interpolating or extrapolating discrete values between the plotted lines.
Part 2) Trace horizontally from the intersect result to the right hand y-axis to identify the fraction of the DCV that must be retained to satisfy retention requirements (F).
Note: Retention requirements can also be expressed as a fraction of annual runoff by tracing horizontally from the intersect result to the left hand y-axis. This method is appropriate if the proposed retention elements have drawdown times significantly different than 36-hours.
Part 3) Determine the total volume required to be retained for the drainage as follows. !" = #$%&
Where:
VREQ: Total volume that must be retained within the drainage area (ft3 )
DCV: Design capture volume (ft3)
FDCV: Fraction of DCV requiring retention (unitless)
Retention requirements can be satisfied at the project-scale if DMA scale is not achieved. 2026-08-19 Item #12D Page 194 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs B-14 2023
Figure B.2-1: Retention Requirements
2026-08-19 Item #12D Page 195 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-15 2023
B.3Step 3 - Determine BMP Performance
The third step in performing stormwater pollutant control calculations is to design a structural BMP with the characteristics that provide stormwater treatment for the DCV and meet the minimum retention requirements for the drainage area. Demonstration of appropriate BMP design can be calculated through use of automated Worksheet B.3 on the next page, or can be calculated manually by following Steps 3A through 3E presented in this section. 2026-08-19 Item #12D Page 196 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-16 2023
Worksheet B.3: BMP Performance
Category # Description i Units
1 Drainage Basin ID or Name sq-ft
2 Design Infiltration Rate Recommended in/hr
3 Design Capture Volume Tributary to BMP cubic-feet
4 Is BMP Vegetated or Unvegetated? unitless
5 Is BMP Impermeably Lined or Unlined? unitless
6 Does BMP Have an Underdrain? unitless
7 Does BMP Utilize Standard or Specialized Media? unitless 8 Provided Surface Area sq-ft
9 Provided Surface Ponding Depth inches
10 Provided Soil Media Thickness inches
11 Provided Gravel Thickness (Total Thickness) inches
12 Underdrain Offset inches
13 Diameter of Underdrain or Hydromod Orifice (Select Smallest) inches 14 Specialized Soil Media Filtration Rate in/hr
15 Specialized Soil Media Pore Space for Retention unitless 16 Specialized Soil Media Pore Space for Biofiltration unitless 17 Specialized Gravel Media Pore Space unitless
18 Volume Infiltrated Over 6 Hour Storm cubic-feet
19 Ponding Pore Space Available for Retention unitless
20 Soil Media Pore Space Available for Retention unitless 21 Gravel Pore Space Available for Retention (Above Underdrain) unitless 22 Gravel Pore Space Available for Retention (Below Underdrain) unitless 23 Effective Retention Depth inches
24 Fraction of DCV Retained (Independent of Drawdown Time) ratio 25 Calculated Retention Storage Drawdown Time hours
26 Efficacy of Retention Processes ratio
27 Volume Retained by BMP (Considering Drawdown Time) ratio 28 Design Capture Volume Remaining for Biofiltration cubic-feet 29 Max Hydromod Flow Rate through Underdrain CFS
30 Max Soil Filtration Rate Allowed by Underdrain Orifice in/hr 31 Soil Media Filtration Rate per Specifications in/hr
32 Soil Media Filtration Rate to be used for Sizing in/hr 33 Depth Biofiltered Over 6 Hour Storm inches
34 Ponding Pore Space Available for Biofiltration unitless 35 Soil Media Pore Space Available for Biofiltration unitless 36 Gravel Pore Space Available for Biofiltration (Above Underdrain) unitless 37 Effective Depth of Biofiltration Storage inches
38 Drawdown Time for Surface Ponding hours
39 Drawdown Time for Effective Biofiltration Depth hours 40 Total Depth Biofiltered inches
41 Option 1 - Biofilter 1.50 DCV: Target Volume cubic-feet 42 Option 1 - Provided Biofiltration Volume cubic-feet
43 Option 2 - Store 0.75 DCV: Target Volume cubic-feet
44 Option 2 - Provided Storage Volume cubic-feet
45 Portion of Biofiltration Performance Standard Satisfied ratio 46 Do Site Design Elements and BMPs Satisfy Annual Retention Requirements? yes/no 47 Overall Portion of Performance Standard Satisfied (BMP Efficacy Factor) ratio 48 Deficit of Effectively Treated Stormwater cubic-feet Retention
Calculations
BMP Inputs
Biofiltration
Calculations
Result
2026-08-19 Item #12D Page 197 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-17 2023
Worksheet B.3 Line Item Notes
1. Populated per user input from Worksheet B.1.
2. Populated per user input from Worksheet B.1.
3. Populated per result of Worksheet B.1.
4. User input. Unvegetated may be permitted in full infiltration conditions and/or Green Infrastructure Projects.
5. User input in reference to the bottom of the BMP.
6. User input.
7. User input. Default is "Standard" If specialized media is proposed, refer to BMPDM Sections F.1 - F.3 for guidance.
8. User input.
9. User input.
10. User input, 18 inches minimum.
11. User input. Value represents the total gravel thickness above and below the underdrain.
12. User input. Offset represents the distance between the bottom of the gravel layer to the invert of the underdrain.
13. User input. Select underdrain diameter or hydromod orifice diameter, whatever is smallest.
14. User input. If specialized media is proposed, refer to BMPDM Sections F.1 - F.3 for guidance.
15. User input. If specialized media is proposed, refer to BMPDM Sections F.1 - F.3 for guidance.
16. User input. If specialized media is proposed, refer to BMPDM Sections F.1 - F.3 for guidance.
17. User input. If specialized media is proposed, refer to BMPDM Sections F.1 - F.3 for guidance.
18. For unlined BMPs: Minimum of Line 3 or [Line 8 x (Line 2/12) x 6.00]. For Lined BMPs use zero.
19. Populated per Table B.3-1 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
20. Populated per Table B.3-1 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
21. Populated per Table B.3-1 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
22. Populated per Table B.3-1 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
23. (Line 9 x Line 19) + (Line 10 x Line 20) + ((Line 11-Line12) x Line 21) + (Line 12 x Line 22)
24. [(Line 23/12) x Line 8 + Line 18 / Line 3]. Maximum value of 1.
25. [Line 23 / Line 2]. Assume 120 hours for all lined biofiltration BMPs.
26. Look up value from Retention Percent Capture Curves, and divide by 0.80. Maximum of 1.00.
27. Line 26 x Line 3
28. Line 3 - Line 27
29. If flow controls are provided, calculate per orifice equation: Q=CA√2gh
30. If flow controls are provided, calculate as [(Line 29 x 12 x 3600)/Line 8]
31. Default = 5.00. If specialized media is proposed, refer to BMPDM Section Sections F.1 - F.3 for guidance.
32. Minimum of Line 30 or Line 31
33. [Line 32 x 6]
34. Populated per Table B.3-2 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
35. Populated per Table B.3-2 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
36. Populated per Table B.3-2 of BMPDM. Values vary with respect to BMP elements such as vegetation, underdrain, liners.
37. [(Line 9 x Line 34) + (Line 10 x Line 35) + ((Line 11 - Line 12) x Line 36))]
38. For lined basins use [Line 9/Line 32]. For unlined basins use [Line 9/(Line 32 + Line 2)]
39. For lined basins use [Line 37/Line 32]. For unlined basins use [Line 37/(Line 32 + Line 2)]
40. [Line 33 + Line 37]
41. [1.50 x Line 28]
42. [Minimum of Line 41 or ((Line 40/12) x Line 8))]
43. [0.75 x Line 28]
44. [Minimum of Line 43 or [(Line 37/12) x Line 8]]
45. [Maximum of (Line 42/Line 41) or (Line 44/Line 43)]
46. Yes/No. Determined per BMPDM Section B.3.5.
47. [Line 26 + Line 45]. Maximum of 1.00.
48. [Line 47 x Line 3] - Line 3
2026-08-19 Item #12D Page 198 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-18 2023
B.3.1 Step 3A - BMP Characteristics
The performance of a BMP is a function of its retention and biofiltration processes, which are directly related to the proposed BMP geometry and design components. The SWQMP Preparer should design the BMP characteristics summarized below to satisfy pollutant control performances standards for treatment of the DCV and minimum retention requirements. BMP geometries identify the area and depth over which retention and/or biofiltration processes occur. Critical BMP geometries include: BMP surface area, surface ponding depth, biofiltration soil media depth, gravel depth, underdrain depth, and underdrain diameter. BMP components dictate how retention and biofiltration processes occur over the BMP footprint. Critical BMP components include: vegetation vs no vegetation, standard biofiltration soil media vs non-standard biofiltration soil media, impermeable liner vs no impermeable liner, underdrain vs no underdrain, and design infiltration rates.
The most common BMPs proposed for storm water compliance are infiltration BMPs, bioretention BMPs, and biofiltration BMPs. By default, these BMPs must be sized to provide a surface area that is equal to at least 3% of the tributary effective impervious area. If a smaller BMP surface area is desired, the applicant must complete Major Maintenance Interval calculations presented in Appendix B.4.1.
B.3.2 Step 3B - Retention Processes
BMP retention processes include infiltration and evapotranspiration occurring within the BMP. This section presents how to calculate the retention processes.
Part 1) Determine the volume of infiltration occurring within the BMP during a 6 hour storm event.
This volume is a function of the design infiltration rate, BMP surface area, and duration of the storm event as shown below.
' =
(
12 ) 6 ℎ,-./
Where:
VR6: Volume infiltrated during a 6 hour storm event (ft3) I: Design infiltration rate (in/hr)
B: BMP surface area (ft2)
Part 2) Determine the static retention capacity of the BMP assuming it is entirely full. This volume is a function of the BMP surface area and the effective retention depth as shown below. 0 = ) 1$
Where:
VRS: Static retention capacity of the BMP (ft3)
B: BMP surface area (ft2)
ED: The effective retention depth within all layers of the BMP (ft). This depth is calculated by multiplying the geometric depth (ft) of each BMP layer by the appropriate retention pore space factor in Table B.3-1 below and summing all of the layers. 2026-08-19 Item #12D Page 199 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-19 2023
Table B.3-1: Retention Pore Space Factors
BMP Characteristics
Unlined BMPs
Without Underdrain
All Other Biofiltration/Retention
BMPs
Ponding Pore Space 1.00 0.00
Media Pore Space 0.25 vegetated
0.40 non-vegetated 0.05
Gravel Pore Space Above Underdrain 0.40 0.00
Gravel Pore Space Below Underdrain n/a 0.40*
*BMPs with an impermeable liner, must provide 3” of gravel beneath the underdrain invert (no more or no less is permitted in this case).
Part 3) Determine the fraction of the DCV retained by the BMP. This value is a function of the DCV, volume infiltrated during the 6 hour storm event, and static retention capacity of the BMP as shown below.
#$%& =
' + 0
Where:
FDCV: Fraction of the DCV retained by the BMP (decimal) VR6: Volume infiltrated during a 6 hour storm event (ft3) VRS: Static retention capacity of the BMP (ft3)
DCV: Design Capture Volume (ft3
)
Part 4) Determine the drawdown time for the effective retention depth. This value is a function of the effective retention depth and the design infiltration rate of the BMP as shown below. 2 =
1$
(/12
Where:
TR: Drawdown time for effective retention depth (hrs)
ED: The effective retention depth within all layers of the BMP (ft).
I: Design infiltration rate (in/hr). If this rate is 0.000 (i.e. lined BMP), a 120 hour drawdown time for the effective retention depth may be assumed.
Part 5) Determine the average annual percent capture provided by the BMP using Figure B.3-1 on the next page.
a) Identify the fraction of the DCV retained by the BMP (FDCV) on the x axis. b) Trace vertically from the x-axis result to the intersect with the plot representing the drawdown time for the effective retention depth (TR). Interpolation between the plotted drawdown times may be necessary.
c) Trace horizontally from the intersect result to identify the average annual percent capture of the proposed BMP.
2026-08-19 Item #12D Page 200 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-20 2023
Figure B.3-1: Percent Capture Nomograph
Part 6) Determine the efficacy of the retention processes provided by the BMP. This value represents the portion of the pollutant control performance standard that is satisfied through retention processes of the BMP and is calculated as follows.
1 =
4%
80%
Where:
ER: Efficacy of retention processes (decimal)
PC: Average Annual Percent Capture (%)
Part 7) Determine the total volume retained by the proposed BMP. 89: = DCV x 1
Where:
VRBMP: Total volume retained by BMP (ft3)
DCV: Design capture volume (ft3)
ER: Efficacy of retention processes (decimal)
2026-08-19 Item #12D Page 201 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-21 2023
Part 8) Determine the volume of storm water runoff still available for biofiltration treatment as shown below. If the entire volume is retained, then consideration of biofiltration processes in the next step are not required.
? = DCV − 89:
Where:
VA: Volume of storm water runoff still available for biofiltration treatment (ft3 )
DCV: Design capture volume (ft3)
VRBMP: Total volume retained by BMP (ft3
)
B.3.3 Step 3C - Biofiltration Processes
Any portion of the DCV that has not been retained within site design or structural BMP elements must be biofiltered. BMP biofiltration processes include filtration, sedimentation, sorption, biochemical processes and/or vegetative uptake. This section presents how to calculate the biofiltration processes occurring within the proposed BMP.
Part 1) Determine the filtration rate (in/hr) of the proposed BMP. This is the rate at which storm water biofilters through the BMP and exits through the underdrain. Filtration rates can be governed by characteristics of the biofiltration soil media or by flow restrictions experienced due to the design of the BMP underdrain/orifice. Applicants must evaluate the rates associated with each of these components per the equations below and then select the lowest filtration rate for use in determining the BMP performance.
#@
@ = A43,200 E√2GHI/)
#J = 5 LM/ℎ.
#89: = NLMLO-O (#@
@, #J )
Where:
Funderdrain: The filtration rate (in/hr) accommodated by the proposed BMP underdrain/orifice.
C: Orifice Coefficient (default 0.60)
Ao: Area of Underdrain/Orifice (ft2)
G: Gravitational acceleration (32.2 ft/sec2)
H: Height of water from underdrain invert to top of surface ponding (ft) B: BMP Surface Area (ft2
)
Fsoil: The filtration rate (in/hr) accommodated by the proposed biofiltration soil media in typical conditions. The default soil media filtration rate is 5 in/hr; however, a higher rate may be used if supported per criteria in Section F.2.
FBMP: The filtration rate (in/hr) of the proposed BMP
2026-08-19 Item #12D Page 202 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-22 2023
Part 2) Determine the volume of biofiltration occurring within the BMP during a 6 hour storm event.
This volume is a function of the BMP filtration rate, BMP surface area, and the rainfall duration as shown below.
8' =
#89:
12 ) 6 ℎ,-./
Where:
VB6: Volume of water (ft3
) biofiltered during a 6 hour storm event.
FBMP: Filtration rate (in/hr) of the proposed BMP.
B: BMP surface area (ft2)
Part 3) Determine the static biofiltration capacity of the BMP assuming it is entirely full. This volume is a function of the BMP surface area and the effective biofiltration depth as shown below. 80 = ) 1$8
Where:
VBS: Static biofiltration capacity of the BMP (ft3)
B: BMP surface area (ft2)
EDB: The effective biofiltration depth within all layers of the BMP (ft). This depth is calculated by multiplying the geometric depth (ft) of each BMP layer by the appropriate biofiltration pore space factor in Table B.3-2 below and summing all of the layers.
Table B.3-2: Biofiltration Pore Space Factors
BMP Characteristics
Unlined BMPs
Without Underdrain All Other Biofiltration/Retention BMPs Ponding Pore Space n/a 1.00
Media Pore Space n/a 0.20 vegetated; 0.35 non-vegetated Gravel Pore Space Above Underdrain n/a 0.40
Gravel Pore Space Below Underdrain n/a 0.00
Part 4) Determine the drawdown time (hours) for surface ponding. This is the ponding depth divided by the sum of the design infiltration rate and BMP filtration rate. Surface ponding depths of 24 hours or less are typically required; however, longer drawdown times up to 96 hours may be proposed if supported by a landscape architect/agronomist and no safety hazards are anticipated due to excessive ponding. Surface ponding drawdown times over 96 hours are not permitted due to vector concerns. 2: =
:
( + #89:
Where:
Tp: Time (hours) for the BMP surface ponding depth to draw down.
DP: Surface ponding depth (inches) of the proposed BMP.
I: Design infiltration rate (in/hr)
FBMP: BMP filtration rate (in/hr)
Part 5) Determine the efficacy of the biofiltration processes provided by the BMP. This value represents the portion of the pollutant control standard that is satisfied through the biofiltration 2026-08-19 Item #12D Page 203 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-23 2023
processes of the BMP. There are two options available for establishing the biofiltration performance standard. Applicants may select the option of their choice. Option 1 requires that the BMP treat 1.5 times the portion of the DCV not reliably retained onsite (assuming a 6 hour routing period). Option 2 requires that the BMP treat 1.0 times the portion of the DCV not reliably retained onsite; and additionally check that the system has a total static (i.e., non-routed) storage volume, including pore spaces and pre-filter detention volume, equal to at least 0.75 times the portion of the DCV not reliably retained onsite.
18 =
8' + 80
1.50 − S
18 =
80
0.75 − S
18 = NULO-O (18, 18
)
Where:
EB1: Efficacy of biofiltration processes under option 1 (decimal).
VB6: The volume biofiltered (ft3) during the 6 hour storm event.
VBS: The static biofiltration capacity (ft3) of the BMP.
DCV: Design capture volume (ft3) delivered to BMP.
VRT: The volume retained (ft3) within the BMP.
EB2: Efficacy of biofiltration processes under option 2 (decimal).
EB: Efficacy of biofiltration processes provided by the BMP (decimal).
B.3.4 Step 3D - Satisfaction of Pollutant Control
Requirements
The performance of a BMP with respect to the pollutant control performance standards is referred to as the BMP efficacy. The total BMP efficacy is a function of the previously calculated retention efficacy and biofiltration efficacy as shown below.
1S = 1 + (1.00 − 1
) 18
Where:
ET: Total BMP Efficacy (decimal)
ER: Efficacy of retention processes (decimal)
EB: Efficacy of biofiltration processes (decimal)
To satisfy pollutant control performance standards, the total BMP efficacy must be 100%. If this level of efficacy is not achieved, applicants should consider reconfiguring drainage layout and/or BMP designs as needed. If this level of efficacy still can’t be achieved, applicants may elect to implement flow-thru treatment control at the project site and also participate in the County’s Offsite Alternative Compliance Program outlined in Appendix J.
2026-08-19 Item #12D Page 204 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-24 2023
B.3.5 Step 3E - Satisfaction of Minimum Retention
Requirements
Minimum retention requirements can be satisfied by demonstrating that the all of the retention elements incorporated within a drainage area (rain barrels, tree wells, dispersion areas, and BMPs) retain a volume of water that is greater than or equal to what is required.
Part 1) Determine the total volume retained through site design and structural BMP elements as follows.
S = 8 + SV + $ + 89:
Where:
VRT: Total volume retained within the drainage area (ft3 )
VRRB: Volume retained by rain barrels (ft3
)
VRTW: Volume retained by tree wells (ft3)
VRD: Volume retained by dispersion areas (ft3)
VRBMP: Volume retained by the BMP (ft3)
Part 2) Demonstrate that the total volume retained through site design and structural BMP elements meets retention requirements.
S ≥ !"
Where:
VRT: Total volume retained within the drainage area (ft3) VREQ: Total volume that must be retained within the drainage area (ft3 )
2026-08-19 Item #12D Page 205 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-25 2023
B.4Less Common Pollutant Control Calculations
This section presents methodologies for performing less common pollutant control calculations including: determination of BMP major maintenance intervals, capture and use evaluation, use of offline BMPs, and BMPs located downstream of a storage unit.
B.4.1 Major Maintenance Intervals for Reduced Size BMPs BMPs with a surface area sized at less than 3% of the tributary effective impervious area must perform additional calculations to determine the anticipated major maintenance intervals.
Major maintenance activities include items such as rehabilitation and/or replacement of the entire BMP or BMP components, which are independent of regularly scheduled annual maintenance. BMP major maintenance intervals can be calculated through use of automated Worksheet B.4 below, or can be calculated manually by following Steps 4A-4C presented in this section.
Worksheet B.4: Major Maintenance Intervals for Reduced Size BMPs 2026-08-19 Item #12D Page 206 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-26 2023
B.4.1.1 Annual Sediment Load Delivered to BMP
The annual sediment load delivered to a BMP is a function of the average annual storm water runoff, land use characteristics, and pretreatment elements applicable to the drainage area.
Part 1) Determine the average sediment concentration in storm water runoff from the land uses present within the drainage area by referring to the total suspended solid (TSS) concentrations listed for various land uses in Table B.4-1 below.
Table B.4-1: TSS Concentrations by Land Use
Land Use TSS Concentration (mg/L) C Source
Single Family Residential 123 0.40
San Diego SBPAT EMC
Dataset
Commercial 128 0.80
Industrial 125 0.90
Education (Municipal) 132 0.50
Multi-family Residential 40 0.60
Open Space 216 0.10
Transportation/Pavement 78 0.90 LA SBPAT EMC Dataset
2026-08-19 Item #12D Page 207 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-27 2023
Roof Runoff 14 0.90 Charters et al. (2015)
Low Traffic Areas/Sidewalk 50 0.50 Davis and McCuen (2005) Steep Hillslopes 797 0.30 Model BMPDM
If a drainage area is comprised of more than one land use type, a runoff-weighted TSS concentration must be calculated per the following equation.
2XX?&Y =
∑ 2XX # + 2XX
#
+ 2XX
#
∑ # + #
+ #
Where:
TSSAVG: Average sediment concentration in storm water from all tributary land uses (mg/L) TSS1: TSS concentration from land use 1 (mg/L)
F1: Fraction of total DCV from land use 1 (%)
TSS2: TSS concentration from land use 2 (mg/L)
F2: Fraction of total DCV from land use 2 (%)
TSSx: TSS concentration from land use x (mg/L)
Fx: Fraction of total DCV from land use x (%)
Part 2) Determine the average sediment concentration in storm water runoff as it enters the BMP.
This is the concentration of TSS determined in part 1 after consideration of any “pretreatment” elements incorporated as shown below.
2XX89: = 2XX?&Y (1 − 4)
Where:
TSSBMP: Average sediment concentration in runoff entering the BMP (mg/L) TSSAVG: Average sediment concentration in storm water from all tributary land uses (mg/L) P: Pretreatment removal efficiency (%).
• P value of 0.00 should be used if there is no pretreatment. • P value of 0.25 should be used when pretreatment is included. • P value of 0.50 should be used if pretreatment consistent with Washington TAPE “Pretreatment” BMP performance criteria are satisfied (>50% TSS removal) • P value of 0.80 should be used if pretreatment consistent with Washington TAPE “Basic Treatment” performance criteria are satisfied (>80% TSS removal) Part 3) Determine the average annual runoff volume entering the BMP. This is a function of the average annual precipitation, runoff factor, and drainage area as shown below.
@@
=
@@
12
Where:
Vannual: Average annual runoff volume entering the BMP (ft3 /year)
2026-08-19 Item #12D Page 208 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-28 2023
Dannual: Average annual precipitation (inches/year)
A: Tributary Area (ft2)
C: Runoff factor (unitless)
Part 4) Determine the annual sediment load delivered to the BMP. This is a function of the average annual runoff volume and the average sediment concentration in stormwater from all tributary land uses as shown below.
Z
@@
= 2XX89:
@@
0.0000624
Where:
Lannual: Annual sediment load delivered to the BMP (lbs/year) TSSBMP: Average sediment concentration in runoff entering the BMP (mg/L) Vannual: Average annual runoff volume entering the BMP (ft3 )
B.4.1.2 BMP Sediment Capacity
The BMP sediment capacity is the weight of sediment (lbs) that can be stored within the BMP before significant clogging impacts begin to occur. The BMP sediment capacity can be determined as follows.
Part 1) Determine the appropriate load to clog value by referencing Table B.4-2 below and identifying the BMP configuration that best characterizes the proposed BMP design.
Table B.4-2: Guidance for Selecting Load to Clog (Lc)
BMP Configuration Load to Clog, Lc,
lb/sq-ft
Default Load to Clog Value 2
≥75% vegetative cover 3
≥20 in/hr media permeability and outlet flow control 3
≥75% vegetative cover, ≥30 in/hr media permeability, and outlet control 4 Part 2) Determine the BMP Sediment Capacity (lbs) by multiplying the BMP Load to Clog by the BMP surface area.
89: = ) Z
Where:
CBMP: BMP sediment capacity (lbs)
B: BMP Surface Area (ft2)
Lc: BMP load to clog value (lbs/ft2)
B.4.1.3 Major Maintenance Frequency
The major maintenance frequency can be calculated by dividing the BMP sediment capacity by the annual sediment load delivered to the BMP as shown below.
N89: =
89:
Z
@@
2026-08-19 Item #12D Page 209 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-29 2023
Where:
MBMP: Major maintenance frequency for BMP (years)
CBMP: BMP sediment capacity (lbs)
Lannual: Annual sediment load delivered to the BMP (lbs/yr) The calculated major maintenance frequency must be 10 years or greater. If the calculated major maintenance frequency is less than 10 years, the applicant must take steps to increase the BMP sediment capacity and/or reduce the annual sediment load delivered to the BMP. In limited circumstances, frequencies of less than 10 years may be acceptable if supported to the satisfaction of the County plan reviewer.
B.4.2 Capture and Use Evaluation
If the proposed project includes habitable structures over 9 stories in height, the applicant must perform a capture and use evaluation as outlined herein.
The capture and use evaluation should be performed at the project-scale, and not be limited to a single DMA. This evaluation must identify the potential demand for using stormwater for indoor toilets and outdoor irrigation use and determine if this demand is sufficient to drawdown the DCV within a 36 hour time period.
B.4.2.1 Toilet and Urinal Flushing Demand Calculations* The following guidelines should be followed for computing harvested water demand from toilet and urinal flushing:
If reclaimed water is planned for use for toilet and urinal flushing, then the demand for harvested storm water is equivalent to the total demand minus the reclaimed water supplied, and should be reduced by the amount of reclaimed water that is available during the wet season.
Demand calculations for toilet and urinal flushing should be based on the average rate of use during the wet season for a typical year.
Demand calculations should include changes in occupancy over weekends and around holidays and changes in attendance/enrollment over school vacation periods. For facilities with generally high demand, but periodic shut downs (e.g., for vacations, maintenance, or other reasons), a project specific analysis should be conducted to determine whether the long term storm water capture performance of the system can be maintained despite shut downs.
Such an analysis should consider the statistical distributions of precipitation and demand, most importantly the relationship of demand to the wet seasons of the year.
Table B.4-3 provides planning level demand estimates for toilet and urinal flushing per resident, or employee, for a variety of project types. The per capita use per day is based on daily employee or resident usage. For non-residential types of development, the “visitor factor” and “student factor” 2026-08-19 Item #12D Page 210 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-30 2023
(for schools) should be multiplied by the employee use to account for toilet and urinal usage for nonemployees using facilities.
Note: At the time of publication of this document, there is not a program in place to permit the use of storm water for indoor use. Check with PDS prior to calculating indoor water use.
Table B.4-3: Toilet and Urinal Water Usage per Resident or Employee Land Use Type Toilet User
Unit of
Normalization
Per Capita Use per
Day
Visitor
Factor4
Water
Efficiency
Factor
Total Use
per
Resident
or
Employee
Toilet
Flushing1,
2 Urinals3
Residential Resident 18.5 NA NA 0.5 9.3
Office Employee
(non-visitor) 9.0 2.27 1.1 0.5
7 (avg)
Retail
Employee
(non-visitor)
9.0 2.11 1.4 0.5
Schools
Employee
(non-student) 6.7 3.5 6.4 0.5 33
Various Industrial
Uses (excludes
process water)
Employee
(non-visitor)
9.0 2 1 0.5 5.5
1 - Based on American Waterworks Association Research Foundation, 1999. Residential End Uses of Water. Denver, CO:
AWWARF
2 - Based on use of 3.45 gallons per flush and average number of per employee flushes per subsector, Table D-1 for MWD (Pacific Institute, 2003)
3 - Based on use of 1.6 gallons per flush, Table D-4 and average number of per employee flushes per subsector, Appendix D (Pacific Institute, 2003)
4 - Multiplied by the demand for toilet and urinal flushing for the project to account for visitors. Based on proportion of annual use allocated to visitors and others (includes students for schools; about 5 students per employee) for each subsector in Table D-1 and D4 (Pacific Institute, 2003) 5 - Accounts for requirements to use ultra low flush toilets in new development projects; assumed that requirements will reduce toilet and urinal flushing demand by half on average compared to literature estimates. Ultra low flush toilets are required in all new construction in California as of January 1, 1992. Ultra low flush toilets must use no more than 1.6 gallons per flush and Ultra low flush urinals must use no more than 1 gallon per flush. Note: If zero flush urinals are being used, adjust accordingly.
B.4.2.2 Planning Level Irrigation Demands
To simplify the planning process, the method described above has been used to develop daily average wet season demands for a one-acre irrigated area based on the plant/landscape type. These demand estimates can be used to calculate the drawdown of harvest and use systems for the purpose of LID BMP sizing calculations.
Table B.4-4: Planning Level Irrigation Demand by Plant Factor and Landscape Type 2026-08-19 Item #12D Page 211 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-31 2023
General Landscape Type
36-Hour Planning Level Irrigation Demand
(gallons per irrigated acre per 36 hour period)
Hydrozone – Low Plant Water Use 390
Hydrozone – Moderate Plant Water Use 1,470
Hydrozone – High Plant Water Use 2,640
Special Landscape Area 2,640
B.4.3 BMPs Downstream of a Storage Unit
Incorporation of upstream storage units (cisterns, vaults, etc) into a project’s design can regulate flows to downstream biofiltration BMPs and potentially optimize the required BMP footprints. Use of this approach is not supported by County automated worksheets, but compliance with stormwater pollutant control requirements can be demonstrated through the following steps. Step 1) Determine the flow rate from the upstream storage unit o Use the orifice equation to determine outflow from the storage unit when it is filled to the depth associated with the DCV.
Step 2) Demonstrate that the proposed BMP can accommodate flows from the storage unit o Multiply the BMP surface area (ft2) by the filtration rate of the biofiltration soil media (in/hr) and divide by 43,200 to convert the units into CFS. For proprietary BMPs, this rate should correspond with the rates from certified testing the manufacturer has performed.
Step 3) Demonstrate that the proposed BMP biofilters 92% of the annual runoff volume o If continuous simulation modeling has been performed, provide output reports from SWMM or SDHM modeling.
o If continuous simulation modeling has not been performed, reference the percent capture nomographs in Figure B.3-1 to determine the percentage of annual runoff that is biofiltered. To use the nomographs, applicants must represent the BMP storage capacity as a fraction of the DCV along the x-axis, trace a line vertically to the colored line representing the drawdown time of the system, and then determine the percentage of annual runoff biofiltered by tracing horizontally to the y-axis. Step 4) If the downstream biofiltration BMP is <3% of the effective tributary area, provide information supporting use of compact biofiltration as generally outlined below. o Retention Requirements: Demonstrate that minimum retention requirements from Section B.2 are satisfied.
o Maintenance Requirements: Demonstrate that the BMP design is expected to last 10 years before major maintenance is anticipated per Appendix B.4.1. 2026-08-19 Item #12D Page 212 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-32 2023
o Proprietary Requirements (if applicable): Provide proprietary information demonstrating that the device meets biofiltration criteria outlined in Appendices F.1- F.2.
B.4.4 Onsite Alternative Compliance
If desired, a PDP applicant may generate stormwater pollutant control and/or hydromodification flow control benefits by managing stormwater flows from “excess areas” that are conveyed to the site.
Management of flows from these excess areas may be used to offset flows from “required areas” that lack management.
Required areas are the areas of a project for which the Permit mandates pollutant control and/or HMP flow control requirements. Excess areas are the areas of a project for which the Permit does not mandate pollutant control and/or HMP flow control requirements. Areas of offsite run-on to the PDP site may always be considered excess areas. Additionally, for redevelopment projects falling under the 50% redevelopment threshold, onsite areas that are not being redeveloped may also be considered excess areas.
Compliance with stormwater pollutant control requirements using this onsite alternative compliance approach can be demonstrated as outlined below.
Step 1) Determine the untreated DCV from the required area Step 2) Determine the treated DCV from the excess area o If required areas and excess areas contain different land uses, a land use factor must be applied to account for variations in pollutant concentrations. In most cases, this factor results in a lower treatment volume being credited. Refer to the Water Quality Equivalency (WQE) document for guidance on determining a land use factor and note that the WQE terms “ACP tributary” and “reference tributary” correlate with “excess areas” and “required areas” respectively.
Step 3) Demonstrate compliance
o Show that the treated DCV from the excess area is greater than or equal to the untreated DCV from the required area (Step 2 ≥ Step 1). o Use of this onsite alternative compliance approach does not mandate flow-thru treatment of untreated flows from required areas; however, applicants are encouraged to do so where feasible.
B.4.5 Offline BMPs
Diversion flow rates for offline BMPs must be sized to convey the maximum flow rate of runoff produced from a rainfall intensity of 0.2 inch of rainfall per hour, for each hour of every storm event.
The following hydrologic method must be used to calculate the diversion flow rate for off-line BMPs:
[ = × L ×
2026-08-19 Item #12D Page 213 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-33 2023
Where:
Q = Diversion flow rate in cubic feet per second
C = Runoff factor, area weighted estimate using Table B.1-1 i = Rainfall intensity of 0.2 in/hr
A = Tributary area (acres)
2026-08-19 Item #12D Page 214 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-34 2023
B.5Backup Information on Pollutant Control
Standards
This sections presents backup information describing the rationale for the following elements relating to pollutant control: establishment of the pollutant control performance standard, establishment of retention requirements, establishment of 85th percentile rainfall depths, backup information on tree well retention values, and backup information on BMP major maintenance frequency calculations.
B.5.1 Pollutant Control Performance Standard Backup
Storm water BMPs can be conceptualized as having a storage volume and a treatment rate, in various proportions. Both are important in the long-term performance of the BMP under a range of actual storm patterns, depths, and inter-event times. Long-term performance is measured by the operation of a BMP over the course of multiple years, and provides a more complete metric than the performance of a BMP during a single event, which does not take into account antecedent conditions, including multiple storms arriving in short timeframes. A BMP that draws down more quickly would be expected to capture a greater fraction of overall runoff (i.e., long-term runoff) than an identically sized BMP that draws down more slowly. This is because storage is made available more quickly, so subsequent storms are more likely to be captured by the BMP. In contrast a BMP with a long drawdown time would stay mostly full, after initial filling, during periods of sequential storms. The volume in the BMP that draws down more quickly is more “valuable” in terms of long term performance than the volume in the one that draws down more slowly. The MS4 permit definition of the DCV does not specify a drawdown time, therefore the definition is not a complete indicator of a BMP's level of performance. An accompanying performance-based expression of the BMP sizing standard is essential to ensure uniformity of performance across a broad range of BMPs and helps prevents BMP designs from being used that would not be effective.
An evaluation of the relationships between BMP design parameters and expected long term capture efficiency has been conducted to address the needs identified above. Relationships have been developed through a simplified continuous simulation analysis of precipitation, runoff, and routing, that relate BMP design volume and storage recovery rate (i.e., drawdown time) to an estimated long term level of performance using United States Environmental Protection Agency (USEPA) SWMM and parameters listed in Appendix G for Lake Wohlford, Lindbergh, and Oceanside rain gages.
Comparison of the relationships developed using the three gages indicated that the differences in relative capture estimates are within the uncertainties in factors used to develop the relationships. For example, the estimated average annual capture for the BMP sized for the DCV and 36 hour drawdown using Lake Wohlford, Lindbergh, and Oceanside are 80%, 76% and 83% respectively. In an effort to reduce the number of curves that are made available, relationships developed using Lake Wohlford are included in this manual for use in the whole San Diego County region.
Figure B.4-1 demonstrated that a BMP sized for the runoff volume from the 85th percentile, 24-hour storm event (i.e., the DCV), which draws down in 36 hours is capable of managing approximately 80 percent of the average annual. There is long precedent for 80 percent capture of average annual runoff as approximately the point at which larger BMPs provide decreasing capture efficiency benefit (also 2026-08-19 Item #12D Page 215 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-35 2023
known as the “knee of the curve”) for BMP sizing. The characteristic shape of the plot of capture efficiency versus storage volume in Figure B.3-1 illustrates this concept.
As such, this equivalency (between DCV draw down in 36-hours and 80 percent capture) has been utilized to provide a common currency between volume-based BMPs with a wide range of drawdown rates. This approach allows flexibility in the design of BMPs while ensuring consistent performance.
B.5.2 Retention Requirement Backup
In May 2016, the RWQCB provided clarification on the 2013 MS4 Permit requirement for the BMPDM to “…provide guidance for hydraulic loading rates and other biofiltration design criteria necessary to maximize the storm water retention and pollutant removal of treatment control BMPs.” Through coordination with the RWQCB, a quantifiable minimum retention requirement for treatment control BMPs was established based on the assumption that BMPs would be sized at 3% of the effective tributary area and be unlined where feasible.
The retention curves presented in Figure B.2-1 were developed using Version 1.4 automated pollutant control worksheets assuming various rainfall depths (0.60 to 1.20 inches) and design infiltration rates (0.000 to 0.500 in/hr). BMPs were sized at 3% of the effective impervious tributary area, provided 18” soil media depth, 3” of gravel above the underdrain, 6” underdrains with no hydromodification management orifices, 3” of gravel beneath the underdrain, and varied surface ponding depths as needed to fully satisfy pollutant removal standards.
B.5.3 Rainfall Depth Backup
The method of calculating the 85th percentile is to produce a list of values, order them from smallest to largest, and then pick the value that is 85 percent of the way through the list. Only values that are capable of producing run off are of interest for this purpose. Lacking a legislative definition of rainfall values capable of producing runoff, Flood Control staff in San Diego County have observed that the point at which significant runoff begins is rather subjective, and is affected by land use type and soil moisture. In highly-urbanized areas, the soil has a high impermeability and runoff can begin with as little as 0.02" of rainfall. In rural areas, soil impermeability is significantly lower and even 0.30" of rain on dry soil will frequently not produce significant runoff. For this reason, San Diego County has chosen to use the more objective method of including all non-zero 24-hour rainfall totals when calculating the 85th percentile. To produce a statistically significant number, only stations with 30 years or greater of daily rainfall records are used.
A collection of 56 precipitation gage points was developed with 85th percentile precipitation values based on multiple years of gage data. A raster surface (grid of cells with values) was interpolated from that set of points. The surface initially did not cover the County's entire jurisdiction. A total of 13 dummy points were added. Most of those were just outside the County boundary to enable the software to generate a surface that covered the entire County. A handful of points were added to enforce a plausible surface. In particular, one point was added in the desert east of Julian, to enforce a gradient from high precipitation in the mountains to low precipitation in the desert. Three points were added near the northern boundary of the County to adjust the surface to reflect the effect of elevation in areas lacking sufficient operating gages.
2026-08-19 Item #12D Page 216 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-36 2023
Several methods of interpolation were considered. The method chosen is named by Environmental Systems Research Institute as the Natural Neighbor technique. This method produces a surface that is highly empirical, with the value of the surface being a product of the values of the data points nearest each cell. It does not produce peaks or valleys of surface based on larger area trends, and is free of artifacts that appeared with other methods.
B.5.4 Tree Well Backup
Tree Well credit volume is estimated based on typical characteristics of Tree Wells as follows:
It is assumed that each tree is considered a single BMP, with calculations based on the soil media reservoir volume and/or the individual tree within the tree BMP as appropriate. Tree Well credit volume is calculated as:
]^_` = ]a` + ]_a` + ]b]`
Where:
TWCV = Tree Well credit volume (ft3
)
TIV = Total infiltration volume of all storage layers within tree BMPs (ft3) TCIV = Total canopy interception volume of tree BMPs (ft3 )
TETV = Total evapotranspiration volume, sums the media evapotranspiration storage within each tree BMP (ft3)
Total infiltration volume is calculated as the total volume stored within the tree BMP soil media reservoir. Infiltration volume was assumed to be 20% of the total BMP soil media reservoir volume, the available pore space in the soil media reservoir (porosity – field capacity).
Total canopy interception volume was calculated as the average interception capacity for the entire mature tree canopy projection area. Interception capacity was determined to be 0.04 inches per square foot for all tree sizes, an average from the findings published by Breuer et al (2003) for coniferous and deciduous trees.
Total evapotranspiration volume is the available evapotranspiration storage volume (field capacity – wilting point) within the BMP storage layer media. TEVT is assumed to be 10% of the minimum soil volume. The minimum soil volume as required by SD-A fact sheet of 2 cubic feet per unit canopy projection area was assumed for estimating reduction in DCV.
There may be rain events that generate more runoff than the tree well can handle. Installing an overflow above the design storm water retention level of the reservoir can prevent system failure during extreme weather events. Placement of the overflow should be determined based on the infiltration rate of the subsoil. If infiltration is not adequate to remove water from the rooting zone (the top 18 to 24 inches of soil media reservoir) within 48 hours, the depth of the soil media reservoir may be increased, and the overflow should be placed such that if water rises to the level of the rooting zone it will drain in less than 48 hours.
2026-08-19 Item #12D Page 217 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-37 2023
B.5.5 Sediment Clogging Backup
Under the 2011 Model SUSMP, a sizing factor of 4 percent was used for sizing biofiltration BMPs.
This value was derived based on the goal of treating the runoff from a 0.2 inch per hour uniform precipitation intensity at a constant media flow rate of 5 inches per hour. While this method was simple, it was considered to be conservative as it did not account for significant transient storage present in biofiltration BMPs (i.e., volume in surface storage and subsurface storage that would need to fill before overflow occurred). Under this manual, biofiltration BMPs will typically provide subsurface storage to promote infiltration losses; therefore, typical BMP profiles will tend to be somewhat deeper than those provided under the 2011 Model SUSMP. A deeper profile will tend to provide more transient storage and allow smaller footprint sizing factors while still providing similar or better treatment capacity and pollutant removal. Therefore, a reduction in the minimum sizing factor from the factor used in the 2011 Model SUSMP is supportable. However, as footprint decreases, issues related to potential performance, operations, and/or maintenance can increase for a number of reasons:
1) As the surface area of the media bed decreases, the sediment loading per unit area increases, increasing the risk of clogging. While vigorous plant growth can help maintain permeability of soil, there is a conceptual limit above which plants may not be able to mitigate for the sediment loading. Scientific knowledge is not conclusive in this area. 2) With smaller surface areas and greater potential for clogging, water may be more likely to bypass the system via overflow before filling up the profile of the BMP. 3) As the footprint of the system decreases, the amount of water that can be infiltrated from subsurface storage layers and evapotranspire from plants and soils tends to decrease. 4) With smaller sizing factors, the hydraulic loading per unit area increases, potentially reducing the average contact time of water in the soil media and diminishing treatment performance.
The MS4 Permit requires that volume and pollutant retention be maximized. Therefore, a minimum sizing factor was determined to be needed. This minimum sizing factor does not replace the need to conduct sizing calculations as described in this manual; rather it establishes a lower limit on required size of biofiltration BMPs as the last step in these calculations. Additionally, it does not apply to alternative biofiltration designs that utilize the checklist in Appendix F (Biofiltration Standard and Checklist). Acceptable alternative designs (such as proprietary systems meeting Appendix F criteria) typically include design features intended to allow acceptable performance with a smaller footprint and have undergone field scale testing to evaluate performance and required O&M frequency.
Sediment Clogging Calculations
As sediment accumulates in a filter, the permeability of the filter tends to decline. The lifespan of the filter bed can be estimated by determining the rate of sediment loading per unit area of the filter bed.
To determine the media bed surface area sizing factor needed to provide a target lifespan, simple 2026-08-19 Item #12D Page 218 of 816
Appendix B: Storm Water Pollutant Control Hydrologic Calculations and Sizing Methods for Structural BMPs
B-38 2023
sediment loading calculations were conducted based on typical urban conditions. The inputs and results of this calculation are summarized in Table B.5-1.
Table B.5-1: Inputs and Results of Clogging Calculation Parameter Value Source
Representative TSS Event Mean
Concentration, mg/L 100
Approximate average of San Diego Land Use Event
Mean Concentrations from San Diego River and San
Luis Rey River WQIP
Runoff Coefficient of Impervious Surface 0.90 Table B.1-1 Runoff Coefficient of Pervious Surface 0.10 Table B.1-1 for landscape areas Imperviousness 40% to 90% Planning level assumption, covers typical range of single family to commercial land uses
Average Annual Precipitation, inches 11 to 13 Typical range for much of urbanized San Diego County Load to Initial Maintenance, kg/m2 10 Pitt, R. and S. Clark, 2010. Evaluation of Biofiltration Media for Engineered Natural Treatment Systems.
Allowable period to initial clogging, yr 10 Planning-level assumption Estimated BMP Footprint Needed for
10-Year Design Life 2.8 to 3.3% Calculated
This analysis suggests that a 3 percent sizing factor, coupled with sediment source controls and careful system design, should provide reasonable protection against premature clogging. However, there is substantial uncertainty in sediment loading and the actual load to clog that will be observed under field conditions in the San Diego climate. Additionally, this analysis did not account for the effect of plants on maintaining soil permeability. Therefore, this line of evidence should be considered provisional, subject to refinement based on field scale experience. As field scale experience is gained about the lifespan of biofiltration BMPs in San Diego and the mitigating effects of plants on long term clogging, it may be possible to justify lower factors of safety and therefore smaller design sizes in some cases.
If a longer lifespan is desired and/or greater sediment load is expected, then a larger sizing factor may be justified.
Generally, the purpose of a minimum sizing factor is to help improve the performance and reliability of standard biofiltration systems and limit the use of sizing methods and assumptions that may lead to designs that are less consistent with the intent of the MS4 Permit.
Ultimately, this factor is a surrogate for a variety of design considerations, including clogging and associated hydraulic capacity, volume reduction potential, and treatment contact time. A prudent design approach should consider each of these factors on a project-specific basis and identify whether site conditions warrant a larger or smaller factor. For example, a system treating only rooftop runoff in an area without any allowable infiltration may have negligible clogging risk and negligible volume reduction potential – a smaller sizing factor may not substantially reduce performance in either of these areas. Alternatively, for a site with high sediment load and limited pre-treatment potential, a larger sizing factor may be warranted to help mitigate potential clogging risks. County staff has discretion to accept alternative sizing factor(s) based on project-specific or jurisdiction-specific considerations. Additionally, the recommended minimum sizing factor may change over time as more experience with biofiltration is obtained.
2026-08-19 Item #12D Page 219 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L C-1 2023
Appendix
C
Appendix C Baseline BMP Fact
Sheets for Site Design and Source
Control
2026-08-19 Item #12D Page 220 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-2 2023
The following fact sheets were developed to assist the project applicants with designing BMPs to meet Site Design and Source Control MS4 Permit requirements.
MS4 Category Baseline BMP Fact
Sheet BMP ID Page
Site Design
BL-1: Existing Natural
Site Features
SD-G: Conserve Natural
Features
SD-H: Buffers
C-2
Site Design BL-2: Outdoor
Impervious Areas
SD-B: Impervious Area
Dispersion
SD-I: Permeable Surfaces
C-8
Site Design BL-3: Rooftop Areas
SD-B: Impervious Area
Dispersion
SD-C: Green Roofs
SD-E: Rain Barrels
C-13
Site Design BL-4: Landscaped Areas SD-K: Sustainable
Landscaping C-16
Source Control BL-5: Work and Storage
Areas
SC-A: Overhead Covering
SC-B: Berms and Grade
Breaks
SC-C: Wind Protection
C-19
Source Control BL-6: Mgt of Storm
Water Discharges
SC-D: Sanitary Sewer
SC-E: Containment Areas C-28
Source Control BL-7: Mgt of NonStorm Water
SC-F: Storm Drain Signage
SC-G: Educational BMP
Signage
C-35
*BMP IDs in italics have a standalone fact sheet in Appendix E 2026-08-19 Item #12D Page 221 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-3 2023
BL-1: Existing Natural Site Features
Applicable Site Features
The Project requires baseline BMPs where feasible and applicable for the following types of natural site features:
Natural waterbodies
1 can include any significant accumulation of water on a project site. This includes both larger bodies, such as lakes and rivers, and smaller features such as intermittent and ephemeral streams, creeks, swales, springs, ponds, and wetlands. Applicants should account for any feature containing water for any portion of the year -- even if the feature is usually dry.
Note: If existing waterbodies can’t be avoided, consultations with the US Army Corps of Engineers, Regional Water Quality Control Board, and California Department of Fish and Wildlife may be required along with their respective permits. Development in or near Waters of the U.S. may be subject to Clean Water Act Section 401 Water Quality Certification requirements. Consult the Army Corps of Engineers regarding any work potentially impacting Waters of the U.S. or for determining if a waterbody is a Water of the U.S.
1 For PDPs, Structural BMPs may not be located within a waterbody. 2026-08-19 Item #12D Page 222 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-4 2023
Natural storage reservoirs and drainage corridors. Storage reservoirs are areas where rainfall and runoff flow downhill and collect in low points such as valleys, basins, and other depressions in the landscape. Storage reservoirs can also include areas of permeable soils in topographic depressions. These features may or may not also be waterbodies. Drainage corridors are areas where concentrated or channelized runoff flows from higher elevation to lower elevation on the site. Examples include channels, creeks, swales and gullies. Flows can also concentrate around grade breaks (steep changes in elevation) such as banks and hillsides. Natural areas, soils, and vegetation (including trees) include undisturbed areas with beneficial soils and vegetation such as undeveloped hillsides, meadows, other non-agricultural vegetated areas, or riparian habitat. Preserving natural features such as existing trees, other vegetation, and soils will decrease the amount of storm water that leaves the project site and reduce its long-term impacts.
SWQMP Baseline BMP Requirements
The following baseline BMPs are required where applicable and feasible for the features described above:
SD-G: Conserve natural features
SD-H: Buffers
These baseline BMPs are documented in Table 1, Section A of the PDP and Standard SWQMP Templates as shown below.
2026-08-19 Item #12D Page 223 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-5 2023
SD-G: CONSERVE NATURAL AREAS
Description
Conservation means preserving, maintaining, or enhancing existing natural areas and features. For example, avoiding the removal of trees, or incorporating an existing stream or other open space area(s) into the project design. Leaving soil, vegetation, and other natural features in place promotes natural processes that help reduce runoff and aid in pollutant uptake. Natural areas are often well suited to retain rainwater through infiltration and evapotranspiration, allowing the project to maintain the predevelopment time of concentration and peak flow rate of runoff. Designs that emphasize natural features are often environmentally preferable and can be more appealing to buyers.
Design Considerations
Identify and avoid natural features: Identify features as early as possible to allow the development to be designed around them. This limits overall impacts during and after construction and can avoid unnecessary redesign costs.
Natural features have formed over time in response to existing conditions (location, climate, soil type, etc.). Allow them to function naturally by avoiding removal or modification. o Locate buildings, driveways, and other impervious features away from natural features.
Where possible concentrate development in the least sensitive portions of the site. o Avoid areas containing sensitive plant or animal species. Areas such as wetlands, biological open space areas, biological mitigation sites, streams, floodplains, and vegetation communities (coastal sage scrub, intact forest, etc.) may require additional regulatory protections.
Where possible, conserve areas with the highest ecological or water quality value. Avoid development in areas with thick, undisturbed vegetation because these areas tend to foster ecological diversity and protect water quality. Likewise, native trees and shrubs provide aesthetic, recreational, and air quality benefits.
2026-08-19 Item #12D Page 224 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-6 2023
Maintain existing site drainage and hydrology: Maintain existing drainage patterns and pathways, topographical depressions, and potential storage areas to maximize natural infiltration and preserve the predevelopment hydrologic characteristics of the site. Avoid creating new concentrated discharge points on hillsides or other locations where drainage is not naturally concentrated. Diversion (changing the discharge location of stormwater runoff from a given land area from one concentration point to another, thereby increasing the area draining to an existing feature) can significantly impact drainage, even without the addition of new impervious area. Even small modifications can significantly impact drainage. Pay special attention to changes in the rates, duration, and volume of flows directed to storage reservoirs and drainage corridors. Increased flows can overwhelm existing natural features, potentially causing flooding, oversaturation, or other unintended consequences in downstream areas. Restore or improve impacted features: In some cases, existing features are impacted or degraded prior to development of the site. For example, previous use of the site may have caused a loss of vegetation and subsequent erosion of open space areas. Even if these areas are conserved in the final design, replanting or restoration may be necessary to ensure they function properly.
Prevent construction phase impacts to soils: Natural site features can be particularly vulnerable during grading and construction. Isolate these features as necessary to prevent access by construction equipment and personnel (e.g., by staking or fencing off areas). Also consider minimizing grading as practicable.
Plan Requirements
For each required construction plan, provide the information indicated below for each applicable feature or BMP.
SD-G: Conserve Natural Areas
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) to be conserved • Label features with BMP ID: SD-G
Detail Sheets
N/A
Typical Construction Notes
• USE A CONSTRUCTION FENCE OR SILT FENCE AROUND THE CONSERVED AREAS TO PREVENT CONSTRUCTION EQUIPMENT FROM ENTERING.
Maintenance Considerations
During construction of the project, fences that have been placed to prevent construction equipment from entering conserved areas must be maintained. After construction of the project is complete, generally conservation and protection of natural features does not require routine maintenance 2026-08-19 Item #12D Page 225 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-7 2023
because the features are intended to remain in their natural condition. The following may be required in accordance with applicable maintenance plans or observations:
Removal of trash and debris;
Landscaping only when necessary to restore or improve impacted features; and Other maintenance activities indicated in applicable maintenance plans or in accordance with observations.
Also consider the following:
Maintenance of areas with sensitive plants and animals may be subject to restrictions or requirements imposed by federal, state, and local laws
SD-H: BUFFERS
Description
Buffers are measures to limit access or prevent impacts to natural features. They are encouraged for all features but required for conserved waterbodies where feasible. Buffers can be effective in protecting resources from pollutants; increased runoff flows; physical disturbances from pedestrian use; vehicle parking; or equipment storage; or other potential stressors. Depending on site characteristics and the project layout, the following options should be considered.
Design Considerations
Buffer zones provide physical separation between natural features and adjacent land uses or pollutant sources. Buffer zones such as a strip of landscape between a development and protected feature can effectively retain or transform pollutants and flows to produce a more favorable environment for natural systems. Buffer zones must be provided for natural water bodies whenever technically feasible. When buffer zones are not technically feasible, other types of buffers, such as access restrictions must be considered. Setbacks are buffer zones that establish minimum distances between pollutant sources and resources. For example, Waters of the U.S. typically require from 50 to 200 feet of separation from potential sources. Setbacks can be maintained landscaping or vegetated areas that provide passive treatment of runoff from a development before it reaches the protected feature.
Access restrictions are buffers that protect an area from intrusion or activity (walking, driving, parking, etc.) either through physical barriers such as fences, walls, or vegetation (trees, etc.), or through legal restrictions such as easements or covenants. Physical barriers can be styled to suit the development architecture while providing the desired level of restriction. Hydraulic disconnection uses curbs, berms, grading, etc. to prevent natural areas from receiving storm water or non-storm water flows from upgradient sources. However, 2026-08-19 Item #12D Page 226 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-8 2023
stormwater runoff that has been redirected from a natural area via hydraulic disconnection must ultimately be returned to the system in a safe, non-erosive manner, such as an outfall placed downstream of the protected area in a location that the runoff would have naturally arrived at without redirection. The design of these features should be part of the site drainage plan, with structures appropriately sized for the anticipated runoff. Different buffer types or combinations of those listed above may be proposed.
Plan Requirements
For each required construction plan, provide the information indicated below for each applicable feature or BMP.
SD-H: Buffers
Plan View Requirements
• Show locations and boundaries of buffers
• Label features with BMP ID: SD-H
Detail Sheets
N/A
Typical Construction Notes
• A SETBACK OF 50 TO 200 FEET IS REQUIRED FOR DEVELOPMENT ADJACENT TO WATERS OF THE U.S.. NO STRUCTRAL BMPS ARE TO BE PLACED IN BUFFER AREAS.
• USE A CONSTRUCTION FENCE OR SILT FENCE AROUND THE BUFFER ZONE TO PREVENT CONSTRUCTION EQUIPMENT FROM ENTERING.
Maintenance Considerations
During construction of the project, fences that have been placed to prevent construction equipment from entering buffer zones must be maintained. After construction of the project is complete, the following may be required in accordance with applicable maintenance plans or observations:
Removal of trash and debris;
Landscaping; and
Other maintenance activities indicated in applicable maintenance plans or in accordance with observations.
Also consider the following:
Maintenance of areas with sensitive plants and animals may be subject to restrictions or requirements imposed by federal, state, and local laws; Buffer areas may be maintained as part of normal landscaping practices unless other requirements apply;
2026-08-19 Item #12D Page 227 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-9 2023
Maintenance of physical structures associated with buffers (fences, walls, curbs, berms, etc.) can be addressed as part of the normal facilities maintenance. 2026-08-19 Item #12D Page 228 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-10 2023
BL-2: Outdoor Impervious Area
Source: County of San Diego’s Green Street Guidelines
Applicable Site Features
The Project requires baseline BMPs to minimize impervious areas where applicable and feasible for the following common types of outdoor impervious features. Streets and roads include public or private access routes used to transport automobiles, trucks, motorcycles, bicycles, and other vehicles. Surfaces in this category include alleys and street parking, but not driveways. They are traditionally paved with concrete or asphalt. Sidewalks & walkways include surfaces intended for pedestrian uses (walking, wheelchairs, etc.). Sidewalks are often at the side of a street, road, or structure, while walkways (including paved footpaths and trails) may occur throughout a property. Parking areas & lots includes any area, space, or lot designated for the temporary or longterm parking or storage of automobiles or other vehicles. They do not include parking areas within streets or roads.
Driveways are surfaces that provide vehicles access from offsite to a building or other portion of the property. Unlike streets and roads, driveways normally serve a single property and are privately owned.
Patios, decks, & courtyards are outdoor areas, typically unroofed, associated with a building, and supporting outdoor use (walking, gathering, leisure, etc.). They may be adjacent to or independent of other structures. They are normally exposed to the elements Hardcourt recreation areas are impermeable surfaces intended primarily for sports or recreation. Examples include basketball, tennis, or volleyball courts, and playgrounds.
MS4 Permit Category
Site Design
BMP IDs
SD-B: Impervious Area
Dispersion
SD-I: Permeable Surfaces
2026-08-19 Item #12D Page 229 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-11 2023
Other proposed outdoor impervious features not otherwise listed.
SWQMP Baseline BMP Requirements
The following baseline BMPs are required where applicable and feasible for the features described above:
SD-B: Impervious Area Dispersion
SD-I: Permeable Surfaces
These baseline BMPs are documented in Table 1, Section B of the PDP and Standard SWQMP Templates as shown below.
a. Direct runoff to pervious areas (SD-B)
For impervious surfaces covered in this Fact Sheet, impervious area dispersion refers to the practice of effectively disconnecting impervious areas from directly draining to the storm drain system by routing runoff from impervious areas such as walkways, and driveways onto the surface of adjacent pervious areas. The intent is to slow runoff discharges and reduce volumes and sources of pollutants.
Dispersion with partial or full infiltration results in significant volume reduction by means of infiltration, retention and evapotranspiration. PDPs may claim Design Capture Volume (DCV) reductions if dispersion areas meet specific design criteria described in Fact Sheet SD-B. However, dispersion should still be implemented where applicable and feasible even when the area available for dispersion does not meet the criteria to claim DVC reduction.
Typical dispersion components include:
An impervious surface from which runoff flows will be routed with minimal piping to limit concentrated inflows;
Splash blocks, flow spreaders, or other means of dispersing concentrated flows and providing energy dissipation as needed;
2026-08-19 Item #12D Page 230 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-12 2023
Dedicated pervious area, typically vegetated, with soil infiltration capacity for partial or full infiltration;
Mulch, compost and/or soil amendments to improve water retention, vegetation support, maintain infiltration rates and enhance treatment of routed flows; and Overflow route for excess flows to be conveyed from dispersion area to the storm drain.
Impervious area dispersion primarily functions as a site design BMP for reducing the effective imperviousness of a site by providing partial or full infiltration of the flows that are routed to pervious dispersion areas and otherwise slowing down excess flows that eventually reach the storm drain system. For PDPs, this can significantly reduce the DCV and flow control requirements for the site. b. Construct surfaces from permeable materials (SD-I)
See BMP ID SD-I Permeable Surfaces below.
c. Minimize the size of impervious areas
Minimizing the overall impervious area created by a development project can reduce the impacts of environmental degradation on receiving waterbodies. Implementing this practice limits the potential for both transportation of pollutants in runoff and increased risk of erosion due to increased flows associated with impervious development.
This BMP applies broadly to any traditionally impervious areas associated with land development including streets and roads, sidewalks and walkways, parking lots, driveways, patios, decks, courtyards, hardcourt recreation areas, and the building footprints. 2026-08-19 Item #12D Page 231 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-13 2023
SD-I: PERMEABLE SURFACES
Description
This BMP consists of substituting permeable (or pervious) materials in the place of traditionally impervious materials in a development. Using permeable materials on a development site helps reduce the overall effective impervious area, thereby decreasing total runoff volume and better mimicking predevelopment hydrologic characteristics when compared to the same development using traditional impervious materials. Limiting the total runoff volume from a site has a significant impact on storm water quality by limiting the total amount of pollutants transported offsite to receiving waterbodies.
Design Considerations
Features constructed of materials like concrete, asphalt, and grouted pavers have higher runoff factors (C) causing a higher percentage of rain falling on them to become runoff. Substituting other more porous materials such as decomposed granite, cobbles, crushed aggregate, and soils (natural, compacted, or amended), which have lower runoff factors than impervious materials, can greatly reduce the amount of runoff from a project. See Appendix B, Section B.1.3 for runoff factors (C) for a variety of different construction materials. For PDPs, use of more porous materials with lower runoff factors where feasible within the project can reduce the total design capture volume (DCV) for the project.
Permeable materials should be used for outdoor hard surfaces wherever it is feasible to do so.
Applicants should consider the feasibility of using permeable materials for all impervious surfaces proposed as part of the project. All permeable surfaces that have potential traffic loading shall be designed by a civil engineer.
Typical non-engineered permeable surfaces that shall be designed and labeled with SD-I are the following:
Decomposed Granite
Cobbles
Crushed Aggregate
Reinforced Geotextile Features
Typical engineered permeable surfaces that shall be designed and labeled with SD-D (Existing Fact Sheet in Appendix E) are the following:
Modular Paver Units or Paver Blocks
Pervious Concrete
Porous Asphalt
Turf Pavers
2026-08-19 Item #12D Page 232 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-14 2023
Plan Requirements
For each required construction plan, provide the information indicated below for each applicable feature or BMP.
SD-I: Permeable Surfaces
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) constructed of permeable material.
• Label non-engineered permeable surfaces with BMP ID: SD-I • Label engineered permeable surfaces with BMP ID: SD-D Detail Sheets
• Varies depending on permeable surface.
• Engineered permeable surfaces must include a cross section showing and clearly labeling all required layers (e.g., paver blocks, bedding, filter course, etc.) from pavement surface to subgrade; and include specifications for each material layer that is required as part of the engineered permeable surface.
Typical Construction Notes
• Varies depending on permeable surface
Maintenance Considerations
Routine maintenance of permeable surfaces includes: removal of materials such as trash and debris accumulated on the surface, inspect tributary area for exposed soil or other sources of sediment and apply stabilization measures to sediment source areas. Apply source control measures as applicable to sources of litter or debris. Engineered permeable pavement surfaces (SD-D) require routine preventive vacuum/regenerative air sweeping.
2026-08-19 Item #12D Page 233 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-15 2023
BL-3: Rooftop Areas
Source: County of San Diego’s Climate Action Plan
Applicable Site Features
The Project requires baseline BMPs for common outdoor impervious features. Rooftop Areas include all permanent, impervious coverings on buildings or other structures (e.g., patios or decks) within the project footprint. Rooftops normally account for much of the runoff generated on a typical project. Coverings need only be counted as rooftops if rainfall will flow over or across them rather than passing through to the ground (e.g., permeable shade coverings need not be considered as rooftops).
SWQMP Baseline BMP Requirements
The following baseline BMPs are required where applicable and feasible for the features described above:
SD-B: Impervious Area Dispersion
SD-C: Green Roofs
SD-E: Rain Barrels
These baseline BMPs are documented in Table 1, Section C of the PDP and Standard SWQMP template as shown below:
MS4 Permit Category
Site Design (SD)
BMP IDs
SD-B: Impervious Area
Dispersion
SD-C: Green Roofs
SD-E: Rain Barrels
2026-08-19 Item #12D Page 234 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-16 2023
a. Direct Runoff to Pervious Areas (SD-B)
For rooftop areas, impervious area dispersion refers to the practice of effectively disconnecting the rooftop from directly draining to the storm drain system by routing runoff onto the surface of adjacent pervious areas. The intent is to slow runoff discharges and reduce volumes. Dispersion with partial or full infiltration results in significant volume reduction by means of infiltration, retention and evapotranspiration. Priority Development Projects (PDPs) may claim Design Capture Volume (DCV) reductions if dispersion areas meet specific design criteria described in Fact Sheet SD-B. However, dispersion should still be implemented where applicable and feasible even when the area available for dispersion does not meet the criteria to claim DCV reduction.
Typical dispersion components for rooftop areas include:
A rooftop surface from which runoff flows will be routed using downspout disconnection to limit concentrated inflows;
Splash blocks, flow spreaders, or other means of dispersing concentrated flows and providing energy dissipation as needed;
Dedicated pervious area, typically vegetated, with soil infiltration capacity for partial or full infiltration;
Optional mulch, compost and/or soil amendments to improve water retention, vegetation support, maintain infiltration rates and enhance treatment of routed flows; and Overflow route for excess flows to be conveyed from dispersion area to the storm drain.
Impervious area dispersion primarily functions as a site design BMP for reducing the effective imperviousness of a site by providing partial or full infiltration of the flows that are routed to pervious dispersion areas and otherwise slowing down excess flows that eventually reach the storm drain system. For PDPs, this can significantly reduce the DCV and flow control requirements for the site. b. Install Green Roofs (SD-C)
Green Roofs are rooftops covered with vegetation and a growing medium over a waterproofing membrane. They reduce runoff volumes and rates, treat storm water pollutants through filtration and plant uptake, provide additional landscape amenity, and create wildlife habitat. Additionally, green roofs reduce the heat island effect and provide acoustical control, air filtration and oxygen production.
In terms of building design, they can protect against ultraviolet rays and extend the roof lifetime, as well as increase the building insulation, thereby decreasing heating and cooling costs. 2026-08-19 Item #12D Page 235 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-17 2023
Typical green roof components include, from top to bottom:
Vegetation that is appropriate to the type of green roof system, climate, and watering conditions;
Media layer (planting mix or engineered media) capable of supporting vegetation growth; Filter fabric to prevent migration of fines (soils) into the drainage layer; Optional drainage layer to convey excess runoff;
Optional root barrier;
Optional insulation layer;
Waterproof membrane; and
Structural roof support capable of withstanding the additional weight of a green roof.
See Fact Sheet SD-C for additional detailed information on Green Roofs. c. Install Rain Barrels (SD-E)
Rain barrels are containers that can capture rooftop runoff and store it for future use. With controlled timing and volume release, the captured rainwater can be used for irrigation or alternative grey water between storm events, thereby reducing runoff volumes and associated pollutants to downstream waterbodies. Rain barrels tend to be smaller systems, less than 100 gallons, and have low installation costs. Treatment can be achieved when rain barrels are used as part of a treatment train along with other BMPs that use captured flows in applications that do not result in discharges into the storm drain system. Rooftops are the ideal tributary areas for rain barrels.
Rain barrels can be used as a site design feature to reduce the effective impervious area of the site by removing roof runoff from the site discharge. This can reduce the DCV and flow control requirements for the site.
See Fact Sheet SD-E for additional detailed information on Rain Barrels. 2026-08-19 Item #12D Page 236 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-18 2023
BL-4: Landscaped Areas
Source: San Diego Sustainable Landscapes Guidelines
Applicable Site Features
The Project requires baseline BMPs for
landscaped areas. A landscape includes all
planting areas, turf areas (artificial or
natural), and water features in a landscape
design. The landscape area does not include footprints of buildings or structures, sidewalks, driveways, parking lots, decks, patios, gravel or stone walks, other pervious or non-pervious hardscapes and other non-irrigated areas designated for non-development (e.g., open spaces and existing native vegetation).
Landscaped Areas includes SWQMP Baseline BMP Requirements The following baseline BMPs are required where applicable and feasible for the features described above:
SD-K: Sustainable Landscaping
These baseline BMPs are documented in Table 1, Section D of the PDP and Standard SWQMP template as shown below:
MS4 Permit Category
Site Design (SD)
BMP IDs
SD-K: Sustainable Landscaping
2026-08-19 Item #12D Page 237 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-19 2023
SD-K: SUSTAINABLE LANDSCAPING
Description
Sustainable landscaping uses native and drought tolerant plant species to limit the total water demand of landscaped areas and create a living sponge to soak up rainfall. Native and drought tolerant plants are well suited to the long-term climate in San Diego County; able to withstand extended dry periods and typically require less water to remain healthy compared to non-native alternatives. An additional benefit is reduced need for fertilizer and/or pesticides.
Sustainable landscaping must be evaluated for all landscaped areas of a project to meet Storm Water Quality Management Plan (SWQMP) requirements and should also be considered for any plantings associated with natural areas or areas identified for revegetation.
Design Considerations
The San Diego Sustainable Landscape Guidelines provide a detailed watershed friendly approach to landscaping. These guidelines will guide you through important principles such as:
Selecting drought tolerant and native plants for San Diego County. Creating healthy soils to encourage moisture retention. Designing water efficient irrigation systems that reduce the likelihood of irrigation runoff.
The City’s Water Efficent Landscape Regulations generally appliy to any new construction for which the City issues a building permit or a discretionary review where the aggregate landscaped area is 500 square feet or more. The Water Efficient Landscape Design Manual, is a County developed resource that may assist applicants meet the City’s landscape requirements by detailing water efficient irrigation systems, drought tolerant plant selection, fire-resistant designs, and other considerations.
Plan Requirements
For each required construction plan, provide the information indicated below for each applicable feature or BMP.
SD-K: Sustainable Landscaping
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) designed as Sustainable Landscaping.
• Label Sustainable Landscaping with BMP ID: SD-K
Detail Sheets
• Shall be shown on Landscape Plans if applicable.
Typical Construction Notes
2026-08-19 Item #12D Page 238 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-20 2023
• Grading plans need to refer to the approved landscape plan for construction notes.
Maintenance Considerations
Routine maintenance of the landscaped areas is essential to making them sustainable. The following are some maintenance considerations after installation:
Maintain 2” – 4” of mulch and/or compost add more annually Practice Integrated Pest Management
Check and adjust irrigation to eliminate runoff
Regularly flush drip irrigation lines.
Move drip irrigation and add emitters as tree growth occurs in order to maintain the wetting zone at outside edge of tree canopy (Dripline)
2026-08-19 Item #12D Page 239 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-21 2023
BL-5: Work and Storage Areas
Applicable Site Features
The Project requires baseline BMPs for the following common types of outdoor work areas. Trash and refuse storage,
Materials and equipment storage,
Loading and unloading,
Fueling,
Maintenance and repair,
Vehicle and equipment cleaning, and
Other areas, not identified above, that have the potential to generate pollutants.
SWQMP Baseline BMP Requirements
The following baseline BMPs are required where applicable and feasible for the features described above. All three of these BMPs should be implemented together in all areas where storage of materials and trash will be located:
SC-A: Overhead Covering
SC-B: Berm and Grade Breaks
SC-C: Wind Protection
MS4 Permit Category
Source Control (SC)
BMP IDs
SC-A: Overhead Covering
SC-B: Berms and Grade Breaks
SC-C: Wind Protection
2026-08-19 Item #12D Page 240 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-22 2023
These baseline BMPs are documented in Table 2, Section A of the PDP and Standard SWQMP templates as shown below:
A typical isometric and plan view of a trash enclosure is shown on the next page. 2026-08-19 Item #12D Page 241 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-23 2023
Typical Isometric and Plan View of a Trash Enclosure BMP 2026-08-19 Item #12D Page 242 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-24 2023
SC-A: OVERHEAD COVERING
Description
The Roofs or other permanent covers can be constructed over outdoor areas where pollutantgenerating materials or activities are concentrated. This helps prevent rainfall from contacting materials and carrying pollutants with it into the storm drain system.
This BMP can be applied to any material or activity that will regularly be located in the same place on a site and contact with rainfall would result in pollutants being transported by storm water.
Temporary covers, such as tarps, are not considered part of this BMP but may also be an effective solution for preventing contact with rainwater when permanent covers are not feasible. For example, for pollutant-generating materials or activities that are not regularly located in the same place on a site.
Note: Permanent overhead structures must comply with the City of Encinitas Fire Code.
Design Considerations
When initially planning a site, identify any area on the site where a pollutant-generating activity will regularly be occurring in a specific location or where pollutant-generating materials will be stored in a designated area. Consider constructing permanent overhead coverage for these areas, if feasible.
Typical structures include roofs, awnings, and permanent canopies. Design covers with sufficient overhang to help prevent rain from contacting materials even when there are moderate winds.
When designing permanent overhead coverage for these areas, the cover must extend at least to the edge of the berm or grade break and ideally will extend slightly beyond it. Projects are required to construct trash enclosures meeting various design requirements, one of which is a roof that fully covers the enclosure and is sufficiently high to allow dumpster lids to open to the full 90-degree position.
If a downspout is used to drain a rooftop or cover over a designated washing, fueling, or trash area, it should be routed away from the designated area to avoid run-on.
Many food service facilities have storage bins for used cooking oil (i.e. “grease bins”). Storing these bins indoors, when done in accordance with County Health Department regulations, is preferable from a storm water pollution perspective. When grease bins must be stored outdoors, permanent roofs or awnings may be used when compliant with the fire code. Outdoor cooking areas may be designed with fire code compliant roofs or awnings as well.
Plan Requirements
SC-A: Overhead Covering
2026-08-19 Item #12D Page 243 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-25 2023
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) designed with overhead covering
• Label with BMP ID: SC-A
Detail Sheets
• Provide details in the applicable plan set where the feature is being designed and constructed.
Typical Construction Notes
• Storage of non-hazardous liquids must be covered by a roof and be contained by berms, dikes, liners, or vaults.
• Storage of hazardous materials and wastes must be in compliance with local, state and federal hazardous materials regulations, ordinances and hazardous materials management plan for the site.
Maintenance Considerations
Repair permanent covers as needed should any damage occur. 2026-08-19 Item #12D Page 244 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-26 2023
SC-B: BERMS AND GRADE BREAKS
Description
Berms and grade breaks can be used to physically separate designated storage and activity areas and prevent storm water surface flows from transporting pollutants from these areas to the storm drain system. A berm or grade break can prevent run-on from flowing through a pollutant generating area and becoming contaminated. Additionally, berms and grade breaks can effectively prevent contaminated water or spilled liquids from leaving a designated pollutant-generating area when the area is designed with a sump or sewer connection; reducing the likelihood of an illicit discharge of pollutants.
This BMP can be applied to any material or activity that will regularly be located in the same place on a site and where storm water surface flows would be likely to pick up pollutants from the work or storage area and transport them to the storm drain system.
Areas for activities, such as washing or fueling, must be designed with berms or grade breaks around their perimeters to ensure that runoff from these activities does not drain to the storm drain system or receiving waters.
Design Considerations
When initially planning a site, identify any area on the site where a pollutant generating activity will regularly be occurring in a specific location or where pollutant-generating materials will be stored in a designated area. If storm water run-on flowing through this area would be likely to pick up pollutants and carry them to a storm drain, consider modifying the site grading or construct a berm around the area to route run-on around the area.
Constructing concrete slab and curbing around an area is often an effective way to prevent run-on from contacting materials. Lower, rounded berms can also be constructed and are often better suited for areas where vehicular access is needed. Alternatively, strategic grading of a site may achieve the same benefits without requiring construction of berms. For example, locating an activity or storage area on an elevated pad or other high point can prevent run-on from entering the area. Whether using berming or grading, the feature should be designed with sufficient height to be able to redirect anticipated flows at the site. Strategically designing surface drainage features, such as ribbon gutters, in conjunction with the planned berms and/or grade breaks can help minimize the risk of breaching.
Berms and grade breaks should also be considered for areas where water or other liquids are meant to be contained within a designated space. Designing a berm or grade break around such an area is important not only for keeping run-on out of the area, but also for ensuring that any water within the area flows to the designated sewer drain or sump rather than flowing to a storm drain outside the area. When designing washing areas, ensure that the berm or grade break has sufficient height to contain the anticipated volumes of wash water. Also ensure that the berm or grade break is positioned far enough away from the anticipated wash area so that all incidental sprays fall within the designated area. For drive-thru style car washes, consider that incidental sprays and drips are likely to fall on the 2026-08-19 Item #12D Page 245 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-27 2023
areas immediately adjacent to the car wash entrance and exit. Design the car wash entrance and exit areas with grade breaks or berms to ensure that incidental drips and spills are directed back to the car wash clarifier rather than flowing to nearby storm drains. Berms can also be used around designated liquid storage areas. These berms should be constructed with sufficient height to contain the volume of liquids that could potentially be spilled in the area.
Plan Requirements
SC-B: Berms and Grade Breaks
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) designed with Berm and Grade Breaks
• Label with BMP ID: SC-B
Detail Sheets
• Provide details in the applicable plan set where the feature is being designed and constructed.
Typical Construction Notes
• [Related to Berms]: Varies depending on type of berm. • [Related to Grade Breaks]: Where designated on plan, grade breaks shall be provided around activity areas to prevent storm water run-on.
Maintenance Considerations
Minimal maintenance is typically required for berms and grade breaks. Periodically clean bermed areas to reduce the chance of contaminated storm water discharges.
Inspect and repair or reconstruct berms if they are damaged or begin to deteriorate. 2026-08-19 Item #12D Page 246 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-28 2023
SC-C: WIND PROTECTION
Description
Windbreaks are physical barriers that block wind, preventing it from impacting designated areas.
They can be used to protect storage or collection areas where materials might be transported by wind. This prevents wind from blowing lightweight materials out of the designated storage area to adjacent areas where they would be more likely to be washed into a storm drain.
This BMP can be implemented wherever there is a designated area for storage of a material that is light enough to be blown away by wind. Trash storage areas are the most common areas for implementation of this BMP, as litter around trash receptacles can easily be transported by wind. Windbreaks should also be considered for protecting material storage areas whenever the stored material is lightweight. Windbreaks can also be used around outdoor work areas where work activities may generate powders or dust or where extremely lightweight materials, such as expanded polystyrene foam may be present.
Design Considerations
Identify whether the materials anticipated to be on the site can be transported by wind. If these materials will be used or stored in a designated outdoor location, consider building windbreaks to protect the area. Windbreaks can be solid walls that completely block wind, or they may be semJsolid barriers such as fences or screens that allow airflow but still trap and prevent transport of materials when used to create an enclosure around the materials. Privacy windscreens can be added to chain link fences to provide wind protection. Solid walls can also serve a dual purpose as both a windbreak and as protection against run-on. All areas shall have secured lids and/or coverings to close when not in use.
Since wind may come from different directions, it is optimal to place wind breaks on all sides of a storage area. This can be accomplished by placing fixed walls on three sides and having a gate on the fourth side. Where it is not feasible to place windbreaks on all sides of a storage area, it is often still possible to place them on three sides, leaving one side open to allow access. For example, designated stockpile storage areas may be designed with walls on three sides and one open side to allow clear access for vehicles or equipment.
At large trash-generating facilities, trash areas should be designed with three solid-sided walls and a solid gate on the fourth side.
Plan Requirements
SC-C: Wind Protection
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) designed with Wind Protection
2026-08-19 Item #12D Page 247 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-29 2023
• Label Wind Protection with BMP ID: SC-C
Detail Sheets
• Provide details in the applicable plan set where the feature is being designed and constructed.
Typical Construction Notes
• Varies depending on type of enclosure.
Maintenance Considerations
Windbreaks should be repaired or reconstructed if they are damaged or begin to deteriorate. 2026-08-19 Item #12D Page 248 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-30 2023
BL-6: Management of Storm Water Discharges
Applicable Site Features
The Project requires baseline BMPs to prevent illicit discharge into the storm drain system. This Fact Sheet describes baseline Best Management Practices (BMPs) for managing storm water discharges originating from outdoor work areas. While the baseline BMPs described in Fact Sheet BL-5, Work and Storage Areas (Baseline BMPs for Outdoor Work Areas) are intended to effectively minimize pollutant generation from work areas, projects must also be designed to ensure that storm water runoff generated from these areas is properly managed.
The discharge options described below apply to the following types of outdoor work areas:
Trash and refuse storage,
Materials and equipment storage,
Loading and unloading,
Fueling,
Maintenance and repair,
Vehicle and equipment cleaning, and
Other areas, not identified above, that have the potential to generate pollutants.
SWQMP Baseline BMP Requirements
The following baseline BMPs are required where applicable and feasible for the features described above:
MS4 Permit Category
Source Control (SC)
BMP IDs
SC-D: Sanitary Sewer
SC-E: Containment Areas
2026-08-19 Item #12D Page 249 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-31 2023
SC-D: Sanitary Sewers
SC-E: Containment Areas
Storm Water S-BMP or SSD-BMP
These baseline BMPs are documented in Table 2, Section A.3 of the PDP and Standard SWQMP template:
2026-08-19 Item #12D Page 250 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-32 2023
SC-D: SANITARY SEWER
Description
One option for eliminating pollutant discharges to the MS4 or receiving waters is to route storm water flows from the work area to the sanitary sewer. Discharges to the sanitary sewer are treated at a publicly owned treatment facility.
This option should be considered for any pollutant source (e.g., material storage area or activity) that has the potential to routinely generate liquid waste with a high concentration of storm water pollutants.
Connections to sanitary sewer may only be allowed with approval by Sanitary Sewer Agency with authority over the proposed receiving sanitary sewer. See additional information below.
Design Considerations
Unless otherwise noted, the following guidelines assume that discharges to the sanitary sewer are approved.
Pollutant sources with piping and/or collection systems designed to convey waste, waste byproducts, or wash water, or with a defined discharge point, should be connected to sanitary sewer through a direct connection to the facility sanitary plumbing. Pollutant sources that are permanent with passive discharge systems, such as interior floor drains and sumps, drain lines, and water feature overflows should be connected to sanitary sewer through a direct connection to the facility sanitary plumbing. Pollutant sources occupying a defined area, such as trash and refuse areas, material and equipment storage, loading and unloading areas, fueling, maintenance and repair, vehicle and equipment cleaning, and outdoor food preparation areas may drain to a sump within the area that is connected to sanitary sewer through a direct connection to the facility sanitary plumbing. Every effort should be made to prevent discharges of storm water to the sanitary sewer. Therefore, outdoor areas connected to sewer should be protected from direct rainfall and from storm water run-on.
Note: Work areas should not be discharged to an onsite wastewater treatment system (e.g. septic) unless the system is specifically designed to accommodate them. This includes being designed to handle the increased flow volumes and rates as well as being designed to process the particular type of pollutant in its anticipated concentrations. These systems are typically designed specifically for household waste. Introduction of additional flows or pollutant types outside the originally intended design can result in failure of the onsite wastewater treatments system and lead to significant public health issues.
All approved connections are subject to the design and pretreatment requirements (e.g. clarifiers or oil-water separators for wash racks and interior floor drains) of the applicable approving agency. A list of agencies is provided below for reference.
2026-08-19 Item #12D Page 251 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-33 2023
City of Encinitas Sanitary Sewer Agencies
Water District and Address Telephone and Website
City of Encinitas Utilities Department
160 Calle Magdalena
Encinitas, CA 92024
(760)-943-2214
www.encinitasca.gov
Leucadia Wastewater District
1960 La Costa Ave.
Carlsbad, CA 92009
(760)-728-1125
www.lwwd.org
Olivenhain Municipal Water District
(Including 4S Ranch and Rancho Cielo)
1966 Olivenhain Rd.
Encinitas, CA 92024
(760)-753-6466
www.olivenhain.com
Plan Requirements
SC-D: Sanitary Sewer
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) discharging to Sanitary Sewer
• Label with BMP ID: SC-D
Detail Sheets
• Provide details in the applicable plan set where the feature is being designed and construction.
Typically shown on utility sheet on building plan
Typical Construction Notes
• “FEATURE (E.G. FUELING AREA, ETC)” SHALL BE PLUMBED TO SANITARY SEWER WITH APPROVAL FROM LOCAL SANITARY SEWER AGENCY [INSERT NAME OF LOCAL SANITARY SEWER AGENCY].
Maintenance Considerations
All approved connections are subject to the design, pretreatment and maintenance requirements (e.g. clarifiers or oil-water separators for wash racks and interior floor drains) of the applicable approving agency.
2026-08-19 Item #12D Page 252 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-34 2023
SC-E: CONTAINMENT AREAS
Description
Containment areas are specifically designed storage or activity areas that prevent spills, leaks, and other discharges, that would otherwise pollute storm water, from leaving the designated area. Spills leaks and other discharges from storage and activity areas can have high concentrations of pollutants that will contaminate storm water and impact receiving waterbodies if allowed to discharge from the site.
This BMP can be applied to any material or activity that will regularly be located in the same place on a site that could reasonably experience or result in spills, leaks, or other discharges.
Design Considerations
When initially planning a site, identify any area on the site where a pollutant generating activity will regularly be occurring in a specific location or where pollutant-generating materials will be stored in a designated area. If these pollutant-generating activities or materials could result in spills, leaks, or other discharges consider constructing or providing containment for the area.
Containment areas should be designed to hold the entire volume of spilled, leaked, or discharged material without overflowing.
Containment of a pollutant-generating activity can be accomplished by berming the area with a concrete curb, or other sealed linear barrier that prevents all material from flowing out of the area.
Individual liquid storage containers can be effectively contained using manufactured containment pallets or sheds.
Containment areas should be completely isolated from storm drains. Do not construct storm drain inlets within containment areas, and do not allow site drainage to be directed through a containment area. If approved by the permitting sanitary sewer agency (refer to SC-D: Discharge to Sanitary Sewer), a containment area may be drained to the facility sanitary sewer plumbing. Designing containment around a pollutant-generating area is important for ensuring that any water within the area flows to the designated sewer drain rather than flowing to a storm drain outside the area.
Design of washing areas should ensure that containment has sufficient height to accommodate the anticipated volumes of wash water. Also ensure that the containment barrier is positioned far enough away from the anticipated wash area so that all incidental sprays fall within the designated area. For drive-thru style car washes, consider that incidental sprays and drips are likely to fall on the areas immediately adjacent to the car wash entrance and exit. Design the car wash entrance and exit with grade breaks or berms to ensure that incidental drips and spills are directed back to the car wash clarifier rather than flowing to nearby storm drains.
Plan Requirements
SC-E: Containment Areas
2026-08-19 Item #12D Page 253 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-35 2023
Plan View Requirements
• Show locations and boundaries of the features (or portions of features) that discharge to containment areas.
• Label with BMP ID: SC-E
Detail Sheets
• Provide details in the applicable plan set where the feature is being designed and constructed.
Typical Construction Notes
• VARIES DEPENDING ON TYPE OF CONTAINMENT.
Maintenance Considerations
Containment areas should be kept clean of spills, leaks and debris as they occur and repaired or reconstructed if they are damaged or begin to deteriorate. 2026-08-19 Item #12D Page 254 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-36 2023
BL-7: Management of Non-Storm Water Discharges
Applicable Site Features
The Project requires baseline BMPs for the management of non-storm water discharges to prevent illicit discharges from entering the storm drain system. This Fact Sheet describes baseline BMPs for the labeling of all storm drain inlets and catch basins; educational signage; and practices for interior work surfaces, floor drains and sumps, drain lines, and fire sprinkler test water.
SWQMP Baseline BMP Requirements
The following baseline BMPs are required where applicable and feasible for the features described above:
a. Storm Drain Inlets and Catch Basins (SC-F)
See BMP ID SC-F: Storm Drain Signage (SC-F) below.
b. Educational BMP signage (SC-G)
See BMP ID SC-G: Educational BMP Signage (SC-G) below.
c. Interior work surfaces, floor drains & sumps
All interior work surfaces, floor drains and sumps shall not be directly connected to the MS4 or receiving waters. All discharges should be directed to sanitary sewer, if feasible, and with approvals by the Sanitary Sewer Agency with authority over the proposed receiving sanitary sewer.
MS4 Permit Category
Source Control (SC)
BMP IDs
SC-F: Storm Drain Signage
SC-G: Educational BMP Signage
2026-08-19 Item #12D Page 255 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-37 2023
d. Drain lines (e.g., air conditioning, boiler, etc.)
All drain lines shall not be directly connected to the MS4 or receiving waters. All discharges should be directed to sanitary sewer, if feasible, and with approvals by the Sanitary Sewer Agency with authority over the proposed receiving sanitary sewer, or discharge to landscaped areas on site. e. Fire sprinkler test water
Fire sprinkler test water shall not be directly connected to the MS4 or receiving waters. Please click on the following fact sheet for additional information:
https://www.sandiegocounty.gov/content/dam/sdc/dpw/WATERSHED_PROTECTION_PRO GRAM/watershedpdf/IndustComm/English/Fire_Sprinkler_Maintenance.pdf These baseline BMPs are documented in Table 2, Section B of the PDP and Standard SWQMP template as shown below:
2026-08-19 Item #12D Page 256 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-38 2023
SC-F: STORM DRAIN SIGNAGE
Description
Storm drain signs and stencils are visible source controls typically placed adjacent to inlets. Posting notices regarding discharge prohibitions at storm drain inlets can prevent waste dumping. Storm drain signage must be provided for all storm water conveyance system inlets and catch basins within the project area. Storm drain signage may include concrete stamping, concrete painting, placards, or other methods approved by the City. These may be modified and used as educational pieces promoting improved water quality. In addition to storm drain signage at storm water conveyance system inlets and catch basins, applicants are encouraged to post signs and prohibitive language (with graphical icons) which prohibit illegal dumping at trailheads, parks, building entrances, and public access points along channels and creeks within the project area.
Design Considerations
Storm drain stenciling and signage may be implemented using a painted stencil or a sign or placard affixed to the structure. Signage should be located in plain sight of someone observing a storm drain inlet. The signage may include a combination of graphics and prohibitive language that identifies the inlet as a storm drain, prohibits dumping, and explains that storm drains discharge directly to receiving waterbodies.
Stencils and placards can be purchased from a number of suppliers. In the San Diego area, the nonprofit organization, I Love A Clean San Diego, loans out stencil sets for labeling storm drains. They can be contacted at (619) 291-0103 or found online at https://ilacsd.org.
Plan Requirements
SC-F: STORM DRAIN SIGNAGE
Plan View Requirements
• Label each storm drain with BMP ID: SC-F
Detail Sheets
• Provide details on grading or improvement plans associated with the construction of applicable inlet or drainage feature.
Typical Construction Notes
• MARK ALL INLETS WITH THE WORDS “NO DUMPING DRAINS TO WATERWAYS” OR SIMILAR. SEE STENCIL TEMPLATE PROVIDED ON THE SHEET.
Maintenance Considerations
Signage should be repainted or replaced if it is damaged or begins to deteriorate. 2026-08-19 Item #12D Page 257 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-39 2023
SC-G: EDUCATIONAL BMP SIGNAGE
Description
Educational BMP Signage are visible source controls typically placed adjacent to a source control, site design, or structural BMP. Signage educates workers, homeowners and/or the public to raise awareness of storm water issues and educate about the benefits of these watershed protection measures.
Educational BMP Signage is an effective source control BMP to alert the public of the function and maintenance requirements of the BMPs. Below are some typical types of Educational BMP Signage:
1. Temporary BMP Signage: The purpose of temporary BMP signage is to alert contractors during construction that this permanent BMP has been completed and to ensure this BMP does not get disturbed during subsequent grading and building construction activities. It is good practice to divert sediment-laden water to temporary construction BMPs (e.g., sediment traps, etc.) around the permanent structural BMP until all drainage areas have been stabilized. If sediment and/or construction activities infringe on the permanent BMP, the facility will most likely need to be rehabilitated prior to project close-out. Figure 1 below provides a typical temporary BMP signage for use during the construction process that reads “Boundary of Structural Best Management Practice: Bioretention Basin. DO NOT DISTURB”
2. Model Home BMP Signage: Educational BMP Signage for model homes provides future homeowners a description of the benefits and responsibilities of the BMPs constructed on their property. It also provides the maintenance requirements to ensure long-term function of the BMP. Educational BMP Signage for permanent BMPs should include the following; vegetation type, maintenance requirements, design components and link to the City website with resources on maintenance for permanent BMPs. .
https://www.encinitasca.gov/government/departments/public-works/stormwatermanagement/permanent-bmp-program
3. Interpretive BMP Signage: This type of signage provides permanent Educational BMP Signage for the public to detail how BMPs benefit the local waterways. Figure 2 below provides an example of this type of interpretative BMP signage for a permanent BMP. This type of signage would be typically beneficial in public areas and applicable to municipal facilities (such as parks and public buildings), as well as commercial and industrial facilities to educate the public. 2026-08-19 Item #12D Page 258 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-40 2023
Figure 1: Temporary Structural BMP Signage
Figure 2: Permanent Interpretive BMP Signage
Design Considerations
Temporary BMP Signage should be designed to be highly visible to construction crews. Materials should ensure the sign is effective through planned construction activities within the drainage area to the permanent BMP.
Model Home Signage would typically be designed by the homebuilder to incorporate the characteristics of the development project. Signs should clearly provide the function of the permanent BMP and maintenance requirements of the prospective buyers of the property.
Interpretive BMP Signage should be constructed of materials that can withstand long-term placement for the lifecycle of the permanent BMP. Language should emphasize the positive impacts these facilities have to local receiving waters along with design renderings of the facility. Local partnerships and owner information are also important design considerations for this type of signage.
Signage should alert the private owner or public of the function of the permanent BMP, indicate prohibited activities that cause premature clogging, and provide typical maintenance requirements.
Plan Requirements
SC-G: PERMANENT BMP SIGNAGE
Plan View Requirements
2026-08-19 Item #12D Page 259 of 816
Appendix C: Baseline BMP Fact Sheets for Site Design and Source Control C-41 2023
• Label with BMP ID: SC-G
Detail Sheets
• Provide details in the applicable plan set of signage design and language.
Typical Construction Notes
• TEMPORARY BMP SIGNAGE SHALL BE INSTALLED WITH THE WORDS “ BOUNDARY OF STRUCTURAL BEST MANAGEMENT PRACTICE. DO NOT DISTURB” OR SIMILAR. SEE SIGNAGE TEMPLATE PROVIDED ON SHEET [INSERT SHEET NUMBER]
• MODEL HOME BMP SIGNAGE SHALL BE INSTALLED WITH THE WORDS “A STRUCTURAL BMP IS A
PERMANENT STORM WATER QUALITY FEATURE OF THIS PROPERTY THAT REQUIRES MAINTENANCE AND ANNUAL REPORTING REQUIREMENTS WITH THE CITY OF ENCINITAS” OR SIMILAR. SEE SIGNAGE TEMPLATE PROVIDED ON SHEET [INSERT SHEET NUMBER]
• INTERPRETIVE BMP SIGNAGE REQUIRES APPROVAL BY OWNER PRIOR TO INSTALLATION.
Maintenance Considerations
Signage should be repainted or replaced if it is damaged or begins to deteriorate.
Temporary BMP Signage may be removed once all contributing drainage areas have been completed and stabilized and all permits within the drainage area have been closed out. Signage should only be removed with the approval of City staff.
Model Home BMP Signage may be removed once occupancy of model homes have been granted by PDS Building. Signage shall only be removed with the approval of City staff. 2026-08-19 Item #12D Page 260 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L D-1 2023
Appendix
D
Appendix D Geotechnical Engineer
Analysis
2026-08-19 Item #12D Page 261 of 816
Appendix D Geotechnical Engineer Analysis
D-2 2023
D.1Analysis of Infiltration Restrictions
This section is only applicable if the analysis of infiltration restrictions is performed by a licensed engineer practicing in geotechnical engineering. The SWQMP Preparer and Geotechnical Engineer must work collaboratively to identify any infiltration restrictions identified in Table D.1-1 below. Upon completion of this section, the Geotechnical Engineer must characterize each DMA as Restricted or Unrestricted for infiltration and provide adequate support/discussion in the geotechnical report. A DMA is considered restricted when one or more restrictions exist which cannot be reasonably resolved through site design changes.
Table D.1-1: Considerations for Geotechnical Analysis of Infiltration Restrictions Restriction Element
Is Element
Applicable?
(Yes/No)
Mandatory
Considerations
BMP is within 100’ of Contaminated Soils
BMP is within 100’ of Industrial Activities Lacking Source Control BMP is within 100’ of Well/Groundwater Basin
BMP is within 50’ of Septic Tanks/Leach Fields
BMP is within 10’ of Structures/Tanks/Walls
BMP is within 10’ of Sewer Utilities
BMP is within 10’ of Groundwater Table
BMP is within Hydric Soils
BMP is within Highly Liquefiable Soils and has Connectivity to Structures BMP is within 1.5 Times the Height of Adjacent Steep Slopes (≥25%) City Staff has Assigned “Restricted” Infiltration Category Optional
Considerations
BMP is within Predominantly Type D Soil
BMP is within 10’ of Property Line
BMP is within Fill Depths of ≥5’ (Existing or Proposed) BMP is within 10’ of Underground Utilities
BMP is within 250’ of Ephemeral Stream
Other (Provide detailed geotechnical support)
Result
Based on examination of the best available information, I have not identified any restrictions above. Unrestricted Based on examination of the best available information, I have identified one or more restrictions above. Restricted Table D.1-1 is divided into Mandatory Considerations and Optional Considerations. Mandatory Considerations include elements that may pose a significant risk to human health and safety and must always be evaluated. Optional Considerations include elements that are not necessarily associated with human health and safety, so analysis is not mandated through this guidance document. All elements presented in this table are subject to the discretion of the Geotechnical Engineer if adequate supporting information is provided.
Applicants must evaluate infiltration restrictions through use of the best available data. A list of resources available for evaluation is provided in Section B.2. 2026-08-19 Item #12D Page 262 of 816
Appendix D Geotechnical Engineer Analysis
D-3 2023
D.2Determination of Design Infiltration Rates
This section is only applicable if the determination of design infiltration rates is performed by a licensed engineer practicing in geotechnical engineering. The guidance in this section identifies methods for identifying observed infiltration rates, corrected infiltration rates, safety factors, and design infiltration rates for use in structural BMP design. Upon completion of this section, the Geotechnical Engineer must recommend a design infiltration rate for each DMA and provide adequate support/discussion in the geotechnical report.
Table D.2-1: Elements for Determination of Design Infiltration Rates Item Value Unit
Initial Infiltration Rate: Identify per Section D.2.1 in/hr Corrected Infiltration Rate: Identify per Section D.2.2 in/hr Safety Factor: Identify per Section D.2.3 unitless
Design Infiltration Rate: Corrected Infiltration Rate ÷ Safety Factor in/hr D.2.1 Initial Infiltration Rate
For purposes of this manual, the initial infiltration rate is the infiltration rate that has been identified based on the initial testing methods. Some of the acceptable methods for determining initial infiltration rates are presented in Table D.2-2 below, though other testing methods may be acceptable as evaluated by the geotechnical engineer. This table identifies what methods require application of correction factors, safety factors, and what BMPs types are ultimately acceptable for each testing method. The geotechnical engineer should use professional discretion when selecting a testing method as it may ultimately impact the types of BMPs that are permitted.
Table D.2-2: Acceptable Initial Infiltration Rate Methods Category Test Correction
Factor Safety Factor Suitable for Following BMPs
Desktop Methods* NRCS Soil Survey Maps Not Applicable Not Applicable BMPs with Underdrains
Correlation
Methods
Grain Size Analysis
Not Applicable
Required
(See Section
D.2.3)
BMPs with
Underdrains Cone Penetrometer Testing
Laboratory Permeability Tests
Percolation Tests
Simple Open Pit Test
Required
(See Section
D.2.2)
Required
(See Section
D.2.3)
Any BMP Type
Open Pit Falling Head Test
Well Permeameter Method
Borehole Percolation Tests
Infiltration Tests
Double Ring Infiltrometer Test
Not Applicable
Required
(See Section
D.2.3)
Any BMP Type
Single Ring Infiltrometer Test
Large-scale Pilot Infiltration Test
Smaller-scale Pilot Infiltration Test
2026-08-19 Item #12D Page 263 of 816
Appendix D Geotechnical Engineer Analysis
D-4 2023
*Desktop methods may be performed without a geotechnical engineer. Refer to Basic Infiltration Analysis guidance in Section B.2.3 for more information.
NRCS Soil Survey Maps: NRCS Soil Survey maps can be used to establish approximate infiltration rates for use in BMP design. Under this method, default design infiltration rates may be applied based on the predominant NRCS soil type present within a proposed BMP location. Default design infiltration rates (in/hr) for each NRCS soil type are: A=0.300, B=0.200, C=0.100, D=0.025, Restricted=0.000. Use of these default design infiltration rates does not require application of any correction factors or safety factors.
Grain Size Analysis Testing: Hydraulic conductivity can be estimated indirectly from correlations with soil grain-size distributions. While this method is approximate, correlations have been relatively well established for some soil conditions. One of the most commonly used correlations between grain size parameters and hydraulic conductivity is the Hazen (1892, 1911) empirical formula (Philips and Kitch, 2011), but a variety of others have been developed. Correlations must be developed based on testing of site-specific soils. For purposes of this manual, saturated hydraulic conductivity and infiltration rate can be assumed to be equal.
Cone Penetrometer Testing: Hydraulic conductivity can be estimated indirectly from cone penetrometer testing (CPT). A cone penetrometer test involves advancing a small probe into the soil and measuring the relative resistance encountered by the probe as it is advanced. The signal returned from this test can be interpreted to yield estimated soil types and the location of key transitions between soil layers. If this method is used, correlations must be developed based on testing of sitespecific soils. For purposes of this manual, saturated hydraulic conductivity and infiltration rate can be assumed to be equal.
Laboratory Permeability Testing: Laboratory testing can be performed to help evaluate the infiltration rates. The laboratory tests should be in accordance with ASTM or other approved procedures (e.g. ASTM D 5084 or D 5856). Several tests may be required from samples at different elevations to help evaluate the permeability characteristics of the soil strata.
Simple Open Pit Test: The Simple Open Pit Test is a falling head test in which a hole at least two feet in diameter is filled with water to a level of 6” above the bottom. Water level is checked and recorded regularly until either an hour has passed or the entire volume has infiltrated. The test is repeated two more times in succession and the rate at which the water level falls in the third test is used as the infiltration rate. This test identifies a percolation rate that should be converted to an infiltration rate using the Porchet method.
Open Pit Falling Head Test: This test is similar to the Simple Open Pit Test, but covers a larger footprint, includes more specific instructions, returns more precise measurements, and generally should be overseen by a geotechnical professional. Nonetheless, it remains a relatively simple test.
To perform this test, a hole is excavated at least 2 feet wide by 4 feet long (larger is preferred) and to a depth of at least 12 inches. The bottom of the hole should be approximately at the depth of the proposed infiltrating surface of the BMP. The hole is pre-soaked by filling it with water at least a foot above the soil to be tested and leaving it at least 4 hours (or overnight if clays are present). After presoaking, the hole is refilled to a depth of 12 inches and allow it to drain for one hour (2 hours for 2026-08-19 Item #12D Page 264 of 816
Appendix D Geotechnical Engineer Analysis
D-5 2023
slower soils), measuring the rate at which the water level drops. The test is then repeated until successive trials yield a result with less than 10 percent change.
Well Permeameter Method (USBR 7300-89): Well permeameter methods were originally developed for purposes of assessing aquifer permeability and associated yield of drinking water wells.
This family of tests is most applicable in situations in which infiltration facilities will be placed substantially below existing grade, which limits the use of surface testing methods.
In general, this test involves drilling a 6 inch to 8 inch test well to the depth of interest and maintaining a constant head until a constant flow rate has been achieved. Water level is maintained with downhole floats. A smaller diameter boring may be adequate, however this then requires a different correction factor to account for the increased variability expected. The Porchet method or the nomographs provided in the USBR Drainage Manual (United States Department of the Interior, Bureau of Reclamation, 1993) are used to convert the measured rate of percolation to an estimate of vertical hydraulic conductivity.
While these tests have applicability in screening level analysis, considerable uncertainty is introduced in the step of converting direct percolation measurements to estimates of vertical infiltration.
Additionally, this testing method is prone to yielding erroneous results cases where the vertical horizon of the test intersects with minor lenses of sandy soils that allow water to dissipate laterally at a much greater rate than would be expected in a full-scale facility. To improve the interpretation of this test method, a continuous bore log should be inspected to determine whether thin lenses of material may be biasing results at the strata where testing is conducted. Consult USBR procedure 7300-89 for more details.
Source: (United States Department of the Interior, Bureau of Reclamation, 1990, 1993) Borehole Percolation Tests: Borehole percolation tests were originally developed as empirical tests to estimate the capacity of onsite sewage disposal systems (septic system leach fields), but have more recently been adopted into use for evaluating storm water infiltration. Similar to the well permeameter method, borehole percolation methods primarily measure lateral infiltration into the walls of the boring and are designed for situations in which infiltration facilities will be placed well below current grade. The percolation rate obtained in this test should be converted to an infiltration rate using a technique such as the Porchet method.
This test is generally implemented similarly to the USBR Well Permeameter Method. Per the Riverside County Borehole Percolation method, a hole is bored to a depth at least 5 times the borehole radius.
The hole is presoaked for 24 hours (or at least 2 hours if sandy soils with no clay). The hole is filled to approximately the anticipated top of the proposed infiltration basin. Rates of fall are measured for six hours, refilling each half hour (or 10 minutes for sand). Tests are generally repeated until consistent results are obtained.
The same limitations described for the well permeameter method apply to borehole percolation tests, and their applicability is generally limited to initial screening. To improve the interpretation of this test method, a continuous soil core can be extracted from the hole and below the test depth, following testing, to determine whether thin lenses of material may be biasing results at the strata where testing is conducted.
2026-08-19 Item #12D Page 265 of 816
Appendix D Geotechnical Engineer Analysis
D-6 2023
Sources: Riverside County Percolation Test (2011), California Test 750 (Caltrans, 1986), San Bernardino County Percolation Test (1992); USEPA Falling Head Test (USEPA, 1980).
In comparison to a double-ring infiltrometer, this test has the advantage of measuring infiltration over a larger area and better resembles the dimensionality of a typical small scale BMP. This test identifies a percolation rate that should be converted to an infiltration rate using the Porchet method. However, if this method is used to identify rates for a drywell BMP, the correction factor can be omitted at the discretion of the geotechnical engineer.
Double Ring Infiltrometer Test (ASTM 3385): The Double Ring Infiltrometer was originally developed to estimate the saturated hydraulic conductivity of low permeability materials, such as clay liners for ponds, but has seen significant use in storm water applications. The most recent revision of this method from 2009 is known as ASTM 3385-09. The testing apparatus is designed with concentric rings that form an inner ring and an annulus between the inner and outer rings. Infiltration from the annulus between the two rings is intended to saturate the soil outside of the inner ring such that infiltration from the inner ring is restricted primarily to the vertical direction.
To conduct this test, both the center ring and annulus between the rings are filled with water. There is no pre-wetting of the soil in this test. However, a constant head of 1 to 6 inches is maintained for 6 hours, or until a constant flow rate is established. Both the inner flow rate and annular flow rate are recorded, but if they are different, the inner flow rate should be used. There are a variety of approaches that are used to maintain a constant head on the system, including use of a Mariotte tube, constant level float valves, or manual observation and filling. This test must be conducted at the elevation of the proposed infiltrating surface; therefore application of this test is limited in cases where the infiltration surface is a significant distance below existing grade at the time of testing.
This test is generally considered to provide a direct estimate of vertical infiltration rate for the specific point tested and is highly replicable. However, given the small diameter of the inner ring (standard diameter is 12 inches, but it can be larger), this test only measures infiltration rate in a small area.
Additionally, given the small quantity of water used in this test compared to larger scale tests, this test may be biased high in cases where the long term infiltration rate is governed by groundwater mounding and the rate at which mounding dissipates (i.e., the capacity of the infiltration receptor). Finally, the added effort and cost of isolating vertical infiltration rate may not necessarily be warranted considering that BMPs typically have a lateral component of infiltration as well. Therefore, while this method has the advantages of being technical rigorous and well standardized, it should not necessarily be assumed to be the most representative test for estimating full-scale infiltration rates. Source: American Society for Testing and Materials (ASTM) International (2009).
Single Ring Infiltrometer Test: The single ring infiltrometer test is not a standardized ASTM test, however it is a relatively well-controlled test and shares many similarities with the ASTM standard double ring infiltrometer test (ASTM 3385-09). This test is a constant head test using a large ring (preferably greater than 40 inches in diameter) usually driven 12 inches into the soil. Water is ponded above the surface. The rate of water addition is recorded and infiltration rate is determined after the flow rate has stabilized. Water can be added either manually or automatically.
The single ring used in this test tends to be larger than the inner ring used in the double ring test.
Driving the ring into the ground limits lateral infiltration; however some lateral infiltration is generally 2026-08-19 Item #12D Page 266 of 816
Appendix D Geotechnical Engineer Analysis
D-7 2023
considered to occur. Experience in Riverside County (CA) has shown that this test gives results that are close to full-scale infiltration facilities. The primary advantages of this test are that it is relatively simple to conduct and has a larger footprint (compared to the double-ring method) and restricts horizontal infiltration and is more standardized (compared to open pit methods). However, it is still a relatively small scale test and can only be reasonably conducted near the existing ground surface.
Large Scale Pilot Infiltration Test: As its name implies, this test is closer in scale to a full-scale infiltration facility. This test was developed by Washington State Department of Ecology specifically for storm water applications.
To perform this test, a test pit is excavated with a horizontal surface area of roughly 100 square feet to a depth that allows 3 to 4 feet of ponding above the expected bottom of the infiltration facility.
Water is continually pumped into the system to maintain a constant water level (between 3 and 4 feet about the bottom of the pit, but not more than the estimated water depth in the proposed facility) and the flow rate is recorded. The test is continued until the flow rate stabilizes. Infiltration rate is calculated by dividing the flow rate by the surface area of the pit.
This test has the advantage of being more resistant to bias from localized soil variability and being more similar to the dimensionality and scale of full scale BMPs. It is also more likely to detect long term decline in infiltration rates associated with groundwater mounding. As such, it remains the preferred test for establishing design infiltration rates in Western Washington (Washington State Department of Ecology, 2012). In a comparative evaluation of test methods, this method was found to provide a more reliable estimate of full-scale infiltration rate than double ring infiltrometer and borehole percolation tests (Philips and Kitch 2011).
The difficulty encountered in this method is that it requires a larger area be excavated than the other methods, and this in turn requires larger equipment for excavation and a greater supply of water.
However, this method should be strongly considered when less information is known about spatial variability of soils and/or a higher degree of certainty in estimated infiltration rates is desired.
Smaller-Scale Pilot Infiltration Test: The smaller-scale PIT is conducted similarly to the large-scale PIT but involves a smaller excavation, ranging from 20 to 32 square feet instead of 100 square feet for the large-scale PIT, with similar depths. The primary advantage of this test compared to the fullscale PIT is that it requires less excavation volume and less water. It may be more suitable for smallscale distributed infiltration controls where the need to conduct a greater number of tests outweighs the accuracy that must be obtained in each test, and where groundwater mounding is not as likely to be an issue.
D.2.2 Corrected Infiltration Rate
For purposes of this manual, the corrected infiltration rate is the initial infiltration rate as modified by appropriate correction factors needed to convert from percolation to infiltration or to correct for effects of water temperature. The sections below present discussion on correction factors that should be considered by the Geotechnical Engineer.
2026-08-19 Item #12D Page 267 of 816
Appendix D Geotechnical Engineer Analysis
D-8 2023
D.2.2.1 Percolation Rate Correction Factor
A common misunderstanding is that the “percolation rate” obtained from a percolation test is equivalent to the “infiltration rate” obtained from tests such as a single or double ring infiltrometer test which is equivalent to the “saturated hydraulic conductivity”. In fact, these terms have different meanings. Saturated hydraulic conductivity is an intrinsic property of a specific soil sample under a given density. It is a coefficient in Darcy’s equation (Darcy 1856) that characterizes the flux of water that will occur under a given gradient. The measurement of saturated hydraulic conductivity in a laboratory test is typically referred to as “permeability”, which is a function of the density, structure, stratification, fines, and discontinuities of a given sample under given controlled conditions. In contrast, infiltration is the downward entry of water into the soil. The velocity at which water enters the soil is infiltration rate. Infiltration rate is typically expressed in inches per hour. For the purposes of this manual, saturated hydraulic conductivity and infiltration rate can be assumed to be equal.
Similarly, to permeability, infiltration rate can be limited by a number of factors including the layering of soil, density, discontinuities, and initial moisture content. These factors control how quickly water can move through a soil. However, infiltration rate can also be influenced by mounding of groundwater, and the rate at which water dissipates horizontally below a BMP – both of which describe the “capacity” of the “infiltration receptor” to accept this water over an extended period. For this reason, an infiltration test should ideally be conducted for a relatively long duration resembling a series of storm events so that the capacity of the infiltration receptor is evaluated as well as the rate at which water can enter the system. Infiltration rates are generally tested with larger diameter holes, pits, or apparatuses intended to enforce a primarily vertical direction of flux.
In contrast, percolation is tested with small diameter holes, and it is mostly a lateral phenomenon. The direct measurement yielded by a percolation test tends to overestimate the infiltration rate, except perhaps in cases in which a BMP has similar dimensionality to the borehole, such as a dry well.
Adjustment of percolation rates may be made to an infiltration rate using a technique such as the Porchet Method. For drywell BMPs this adjustment may be determined per other methods, (i.e. USBR 7300-89), or may be omitted entirely at the discretion of the geotechnical engineer.
Percolation Rate Conversion Example
Problem:
Apply the Porchet Method (Inverse Borehole Method) to determine the corrected infiltration rate from the following inputs:
• Total depth of test hole, DT = 60 inches
• Initial depth to water, DO = 12.25 inches
• Final depth to water, Df = 13.75 inches
• Test hole radius, r = 4 inches
• Time interval, ∆t = 10 minutes
Solution:
1. Solve for the height of water at the beginning of the selected time interval, HO:
2026-08-19 Item #12D Page 268 of 816
Appendix D Geotechnical Engineer Analysis
D-9 2023
HO = DT - DO = 60 - 12.25 = 47.75 inches
2. Solve for the height of water at the end of the selected time interval, Hf:
Hf = DT - Df = 60 -13.75 = 46.25 inches
3. Solve for the change in height of water over the selected time interval, ∆H:
∆H = HO - Hf = 47.75 - 46.25 = 1.50 inches
4. Calculate the average head over the selected time interval, Havg:
Havg = (Ho + Hf)/2 = (47.75 + 46.25)/2 = 47.00 inches
5. Calculate the tested infiltration rate, It, using the following equation:
It= (∆H*60*r) /(∆t*(r+2Havg))
It = (1.50 in * 60 min/hr * 4 in) / (10 min * (4 inch + (2 * 47 in))) = 0.37 in/hr D.2.2.2 Temperature Correction Factor
The rate of infiltration through soil is affected by the viscosity of water, which in turn is affected by the temperature of water. As such, infiltration rate is strongly dependent on the temperature of the infiltrating water (Cedergren, 1997). For example, Emerson (2008) found that wintertime infiltration rates below a BMP in Pennsylvania were approximately half their peak summertime rates. As such, it is important to consider the effects of temperature when planning tests and interpreting results.
If possible, testing should be conducted at a temperature that approximates the typical runoff temperatures for the site during the times when rainfall occurs. If this is not possible, then the results of infiltration tests should be adjusted to account for the difference between the temperature at the time of testing and the typical temperature of runoff when rainfall occurs. The measured infiltration can be adjusted by the ratio of the viscosity at the test temperature versus the typical temperature when rainfall occurs (Cedergren, 1997), per the following formula:
×=
Typical
Test KK TestTypical
µ
µ
Where:
KTypical = the typical infiltration rate expected at typical temperatures when rainfall occurs KTest = the infiltration rate measured or estimated under the conditions of the test µTypical = the viscosity of water at the typical temperature expected when rainfall occurs µTest = the viscosity of water at the temperature at which the test was conducted 2026-08-19 Item #12D Page 269 of 816
Appendix D Geotechnical Engineer Analysis
D-10 2023
D.2.3 Safety Factors
A safety factor between 2.0 and 9.0 must be applied to the infiltration rates determined above2 .
Application of a safety factor reduces initial or corrected infiltration rates in order to account for various considerations that can impact infiltration rates measured rates over time. In order to minimize safety factor impacts, applicants should consider performing rigorous site investigation, incorporating pretreatment and resiliency into the site design, and taking steps to reduce incidental compaction within BMP footprints.
If the proposed BMP utilizes an underdrain, a default safety factor of 2.0 may be applied or a more detailed safety factor may be determined per Table D.2-3. If the proposed BMP does not utilize an underdrain, then the safety factor must be determined through completion of Table D.2-3. 2 Use of default design infiltration rates based on NRCS soil type does not require application of safety factor. 2026-08-19 Item #12D Page 270 of 816
Appendix D Geotechnical Engineer Analysis
D-11 2023
Table D.2-3: Determination of Safety Factor
Consideration Assigned
Weight (w)
Factor
Value (v)
Product (p)
p = w x v
Suitability
Assessment
(A)
Infiltration Testing Method 0.25
Refer to
Table D.2-4
Soil Texture Class 0.25
Soil Variability 0.25
Depth to Groundwater/Obstruction 0.25
Suitability Assessment Safety Factor, SA = Σp
Design
(B)
Pretreatment 0.50
Refer to
Table D.2-4 Resiliency 0.25
Compaction 0.25
Design Safety Factor, SB = Σp
Safety Factor, S = SA x SB
(Must be always greater than or equal to 2)
The geotechnical engineer should reference Table D.2-4 below in order to determine appropriate factor values for use in the table above. The values in the table below are subjective in nature and the geotechnical engineer may use professional discretion in how the points are assigned.
Table D.2-4: Guidance for Determining Individual Factor Values Consideration High Concern
(3 points)
Medium Concern
(2 points)
Low Concern
(1 point)
Infiltration
Testing
Method
Any At least 2 tests of any kind
within 50’ of BMP.
At least 4 tests within BMP
footprint, OR Large/Small Scale
Pilot Infiltration Testing over at
least 5% of BMP footprint.
Soil Texture
Class
Unknown, Silty, or
Clayey
Loamy Granular/Slightly Loamy
Soil Variability Unknown or High Moderately Homogeneous Significantly Homogeneous Depth to
Groundwater/
Obstruction
<5’ below BMP 5-15’ below BMP >15’ below BMP
Pretreatment None/Minimal
Provides good pretreatment OR
does not receive significant
runoff from unpaved areas
Provides excellent pretreatment
OR only receives runoff from
rooftops and road surfaces.
Resiliency None/Minimal
Includes underdrain/backup
drainage that ensures ponding
draws down in <96 hours
Includes underdrain/backup
drainage AND supports easy
2026-08-19 Item #12D Page 271 of 816
Appendix D Geotechnical Engineer Analysis
D-12 2023
restoration of impacted
infiltration rates.
Compaction Moderate Likelihood Low Likelihood Very Low Likelihood D.3Geotechnical Reporting Requirements
This section is only applicable if a licensed engineer practicing in geotechnical engineering has performed the determination of infiltration restrictions and/or design infiltration rates. The geotechnical report must document the following items in the geotechnical report. Date of site analysis
Scope and results of testing
Public health and safety requirements that affect infiltration locations o Must address Mandatory Considerations presented in Appendix D.1 Conclusions
o Characterize DMAs as Restricted or Unrestricted for Infiltration o Identify Design Infiltration Rates for DMAs
Correspondence between City Staff and Geotechnical Engineer (if applicable) o Development status of site prior to the project application (i.e. new development with raw ungraded land, or redevelopment with existing graded conditions) o The history of design discussions for the site proposed project o Site design alternatives considered to achieve infiltration or partial infiltration on site o Physical impairments and public safety concerns (i.e. fire road egress, sewer lines, etc) o The extent low impact development BMP requirements were included in the project design
It is ultimately the responsibility of the SWQMP Preparer (not the geotechnical engineer) to interpret the conclusions made in the geotechnical report and ensure they are appropriately supported/reflected in associated SWQMP submittal materials such as checklists, narratives, calculations, exhibits, and supplemental reports.
2026-08-19 Item #12D Page 272 of 816
C I T Y O F E N C I N I T A S B M P D E S I G N M A N U A L E-1 2023
Appendix
E
Appendix E BMP Design Fact
Sheets
2026-08-19 Item #12D Page 273 of 816
Appendix E: BMP Design Fact Sheets
E-2 2023
The following fact sheets were developed to assist the project applicants with designing BMPs to meet the storm water obligations.
MS4 Category Manual Category Design Fact Sheet
Source Control Source Control
SC: Source Control BMP Requirements
SC-Q: Large Trash Generating Facilities
SC-R: Animal Facilities
SC-S: Plant Nurseries and Gardens
SC-T: Automotive Facilities
Site Design Site Design
SD-A: Tree Wells
SD-B: Impervious Area
Dispersion
SD-C: Green Roofs
SD-D: Permeable Pavement (Site Design BMP)
SD-E: Rain Barrels
SD-F: Amended Soils
Retention
Harvest and Use HU-1: Cistern
Infiltration
INF-1: Infiltration Basins
INF-2: Bioretention
INF-3: Permeable Pavement (Pollutant Control)
INF-4: Dry Wells
Partial Retention PR-1: Biofiltration with Partial Retention Biofiltration Biofiltration
BF-1: Biofiltration
BF-2: Nutrient Sensitive Media Design
BF-3: Proprietary Biofiltration
FT-1: Vegetated Swales
Flow-thru
Treatment Control
Flow-thru Treatment
Control with Alternative
Compliance
FT-2: Media Filters
FT-3: Sand Filters
FT-4: Dry Extended Detention Basin
FT-5: Proprietary Flow-thru Treatment Control
PL: Plant List
2026-08-19 Item #12D Page 274 of 816
Appendix E: BMP Design Fact Sheets
E-3 2023
E.1Fact Sheet Quick Guide
BF-1 Biofiltration
Location: 43rd Street and Logan Avenue, San Diego, California Description
Biofiltration (Bioretention with underdrain) facilities are vegetated surface water systems that filter water through vegetation, and soil or engineered media prior to discharge via underdrain or overflow to the downstream conveyance system.
Fact Sheet Key
1 Best Management Practice (BMP) Title
2 Categories, Standards, and Benefits
3 BMP Image
4 Main Content; Categories Include:
•Description
•Design Adaptations for Project Goals
•Recommended Siting Criteria
•Recommended BMP Component Dimensions
•Design Criteria and Considerations
•Conceptual Design and Sizing Approach for
o Site Design
o Storm Water Pollutant Control Only
o Integrated Storm Water Pollutant Control and Flow Control •Maintenance Overview
•Summary of Standard Inspection and Maintenance
1 3
MS4 Permit Category
Biofiltration
Manual Category
Biofiltration
Applicable Performance
Standard
Pollutant Control
Flow Control
Primary Benefits
Treatment
2 4
2026-08-19 Item #12D Page 275 of 816
Appendix E: BMP Design Fact Sheets
E-4 2023
E.2Source Control BMP Requirements
Worksheet E.1-1: Source Control BMP Requirements
How to comply: Projects shall comply with this requirement by implementing all source control BMPs listed in this section that are applicable to their project. Applicability shall be determined through consideration of the development project’s features and anticipated pollutant sources. Appendix E.1 provides guidance for identifying source control BMPs applicable to a project. Checklist I.4 in Appendix I shall be used to document compliance with source control BMP requirements. How to use this worksheet: