Attachment D - Appendix F-2 - Storm Water Quality Management Plan — San Marcos City Council, June 25, 2024 (part 1 of 2)

ATTACHMENT D

ENVIRONMENTAL IMPACT REPORT
APPENDIX F-2
SWQMP

APPENDIX F-2
Stormwater Quality Management Plan

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022

CITY OF SAN MARCOS

PRIORITY DEVELOPMENT PROJECT (PDP)

STORM WATER QUALITY MANAGEMENT PLAN (SWQMP)
FOR

SOUTH PACIFIC

SOUTH PACIFIC STREET
SAN MARCOS , CA 92078

ASSESSOR'S PARCEL NUMBER(S):
219-223-20&22
ENGINEER OF WORK:

___________________________________________________________________________________

Robert Dentino, PE 45629

PREPARED FOR:

Hughes Circuits, Inc.
546 South Pacific Street
El Cajon, CA 92078
Contact Person: Joe Hughes
Phone: (760) 744-0300x304
E-mail: [email protected]

PDP SWQMP PREPARED BY:

Excel Engineering
440 State Place
Escondido, CA 92029
(760) 745-8188

DATE OF SWQMP:
2/24/2022

SDP22-0002
PLANS PREPARED BY:

Excel Engineering
440 State Place
Escondido, CA 92029
(760) 745-8188

AMMENDED:
11/13/2023
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 9/21/2021
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City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 9/21/2021

TABLE OF CONTENTS

Acronym Sheet
PDP SWQMP Preparer's Certification Page
PDP SWQMP Project Owner's Certification Page
Submittal Record
Project Vicinity Map
FORM I-1 Applicability of Storm Water BMP Requirements
FORM I-2 Project Type Determination Checklist (Standard Project or PDP) FORM I-3B Site Information Checklist for PDPs
FORM I-4 Source Control BMP Checklist for All Development Projects FORM I-5 Site Design BMP Checklist for All Development Projects FORM I-6 Summary of PDP Structural BMPs
Attachment 1: Backup for PDP Pollutant Control BMPs
Attachment 1a: DMA Exhibit
Attachment 1b: Tabular Summary of DMAs and Design Capture Volume Calculations Attachment 1c: Harvest and Use Feasibility Screening (when applicable) Attachment 1d: Categorization of Infiltration Feasibility Condition (when applicable) Attachment 1e: Pollutant Control BMP Design Worksheets / Calculations Attachment 2: Backup for PDP Hydromodification Control Measures Attachment 2a: Hydromodification Management Exhibit
Attachment 2b: Management of Critical Coarse Sediment Yield Areas Attachment 2c: Geomorphic Assessment of Receiving Channels Attachment 2d: Flow Control Facility Design
Attachment 3: Structural BMP Maintenance Plan
Attachment 3a: B Structural BMP Maintenance Thresholds and Actions Attachment 3b: Draft Maintenance Agreement (when applicable) Attachment 4: Copy of Plan Sheets Showing Permanent Storm Water BMPs

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 9/21/2021

ACRONYMS

APN Assessor's Parcel Number
BMP Best Management Practice
HMP Hydromodification Management Plan
HSG Hydrologic Soil Group
MS4 Municipal Separate Storm Sewer System
N/A Not Applicable
NRCS Natural Resources Conservation Service
PDP Priority Development Project
PE Professional Engineer
SC Source Control
SD Site Design
SDRWQCB San Diego Regional Water Quality Control Bo ard SIC Standard Industrial Classification
SWQMP Storm Water Quality Management Plan
`

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022

PDP SWQMP PREPARER'S CERTIFICATION PAGE

Project Name: South Pacific
Permit Application Number:

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 PDP requirements of the City of San Marcos BMP Design Manual, which is a design manual for compliance with local City of San Marcos 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 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 of Work's Signature, PE Number & Expiration Date

Robert D. Dentino, RCE 45629, 12-31- 22_______________________ Print Name

Excel Engineering__________________________________________ Company

____________________________
Date
Engineer's Seal:

11/3/2023
-
No. 45629
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 9/21/2021
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City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022

PDP SWQMP PROJECT OWNER'S CERTIFICATION PAGE

Project Name: South Pacific
Permit Application Number:

PROJECT OWNER'S CERTIFICATION

This PDP SWQMP has been prepared for Hughes Circuit s, Inc. by Excel Engineering. The PDP SWQMP is intended to comply with the PDP requirements of the City of San Marcos BMP Design Manual, which is a design manual for compliance with local City of San Marcos 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 trans fers its interests in the property, its successor-i n- interest shall bear the aforementioned responsibili ty to implement the best management practices (BMPs) described within this plan, including ensuri ng 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

Hughes Circuits, Inc. ________________________________________ Company

____________________________
Date

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 9/21/2021
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City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 9/21/2021

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 column 4 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

□
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022

PROJECT VICINITY MAP

Project Name: South Pacific
Permit Application Number:

VICINITY MAP
~

NOT TO SCALE
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Applicability of Storm Water Best Management Practices (BMP) Requirements (Storm Water Intake Form for all Development Permit Applications) For detailed information please visit:
http://www.san-marcos.net/departments/development-services/stormwater/development-planning Form I -1
[March 15, 2016]
Project Identification
Project Name: South Pacific
Description: Proposed project is an industrial project that will include driveways, a single building, structural BMPs, parking and all amenities.

Permit Application Number (if applicable): N/A Date:

Project Address:

Determination of Requirements
This form is required as part of the City’s application process. The purpose of this form is to identify potential land deve lopment planning storm water requirements that apply to development projects.

Development projects are defined as construction, rehabilitation, redevelopment, or reconstruction of any public or private projects. In addition, the identification of a development project, as it relates to storm water regulations, would truly apply to development and redevelopment activities that have the potential to contact storm water and contribute a source of pollutants, or reduce the natural absorption and infiltration abilities of the land.

To access the BMP Design Manual, Storm Water Quality Management Plan (SWQMP) templates, and other pertinent information related to this program please refer to:
http://www.san-marcos.net/departments/development-services/stormwater/development-planning

Please answer each of the following steps below, starting with Step 1 and progressing through each step until reaching "Stop".

Step Answer Progression
Step 1: Based on the above, Is the project a
"development project" (See definition above)?
See Section 1.3 of the BMP Design Manual for
further guidance if necessary.
 Yes Go to Step 2.
 No Permanent BMP requirements do not apply. No
SWQMP will be required. Provide brief discussion
below.

STOP.

Discussion / justification if the p roject is not a "development project" (e.g., the project includes only interior remodels within an existing building):

Step 2: Is the project a Standard Project, Priority
Development Project (PDP), or exception to PDP
definitions?

To answer this item, complete Form I-2, Project
Type Determination. See Section 1.4 of the BMP
Design Manual in its entirety for guidance.

In addition to Section 1.4, please refer to the
City’s SWQMP Submittal Requirements form.

 Standard Project Only Standard Project requirements apply, including Standard Project SWQMP. STOP.
 PDP Standard and PDP requirements apply, including
PDP SWQMP. Go to Step 3 on the following page.
 Exception to PDP
definitions
Standard Project requirements apply, and any
additional requirements specific to the type of
project. Provide discussion and list any additional
requirements below. Prepare Standard Project
SWQMP. STOP.

Discussion / justification, and additional requirements for exceptions to PDP definitions, if applicable:
2/24/2022
NE Corner of South Pacific Street , San Marcos, CA 92078 City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Form I -1 Page 2 , Form Date: March 15, 2016
Step 3 (PDPs only) . Please answer the list of questions in this section to determine if hydromodification requirements reply to the proposed PDP. Does the project:

Step 3a. Discharge storm water
runoff directly to the Pacific Ocean?
 Yes STOP . Hydromodification requirements do not apply.  No Continue to Step 3b.

Step 3b . Discharge storm water
runoff directly to an enclosed
embayment, not within protected
areas?
 Yes STOP . Hydromodification requirements do not apply.  No Continue to Step 3c.

Step 3c . Discharge storm water
runoff directly to a water storage
reservoir or lake, below spillway or
normal operating level?
 Yes STOP . Hydromodification requirements do not apply.  No Continue to Step 3d.

Step 3d . Discharge storm water
runoff directly to an area identified in
WMAA?
 Yes STOP . Hydromodification requirements do not apply.  No Hydromodification requirements apply to the project. Go to Step

4. Discussion / justification if hydromodification control requirements do not apply:

Step 4 (PDPs subject to
hydromodification control
requirements only). Does protection
of critical coarse sediment yield areas
apply based on review of WMAA
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).

Stop.
 No Management measures not required for protection of critical coarse sediment yield areas.

Provide brief discussion below.

Stop.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022
No Potential Critical Coarse Sediment Yield areas nearby that will influence the project.

Potential Critical Coarse Sediment
Proposed Project
Proposed Project
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021

Project Type Determination Checklist Form I-2
[March 15, 2016]
Project Information
Project Name/Description: South Pacific
Permit Application Number (if applicable): Date:

Project Address:

Project Type Determination: Standard Project or Priority Development Project (PDP) The project is (select one):  New Development  Redevelopment The total proposed newly created or replaced impervious area is: _ _ ft2 (__ __) acres Is the project in any of the following categories, (a) through (f)? Yes

No

(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.

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 on public or private land.

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 (Standard Industrial Classification (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 is defined as any paved impervious surface used for the transportation of automobiles, trucks, motorcycles, and other vehicles.

2/24/2022
NE Corner of South Pacific Street , San Marcos, CA 92078 106214.09

2.44 I
I
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Form I -2 Page 2 , Form Date: March 15, 2016
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 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 Copermittees. See BMP Design 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 (RGOs). This category includes RGOs that meet the following criteria: (a) 5,000 square feet or more or (b) a projected Average Daily Traffic (ADT) of 100 or more vehicles per day.

Yes

No

(f) New or redevelopment projects that result in the dis turbance of one or more acres of land and are expected to generate pollutants post construction.

Note: See BMP Design Manual Section 1.4.2 for additional guidance.

Does the project meet the definition of one or more of the Priority Development Project categories (a) through (f) listed above?
 No – the project is not a Priority Development Project (Standard Project).  Yes – the project is a Priority Development Project (PDP).

The following is for redevelopment PDPs only:

The area of existing (pre-project) impervious area at the project site is: ________ ft 2 (A)
The total proposed newly created or replaced impervious area is ________ ft 2 (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 impervious areas are considered PDP OR
greater than fifty percent (50%) – the entire project site is a PDP

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Site Information Checklist
For PDPs
Form I-3B (PDPs)
[March 15, 2016]
Project Summary Information
Project Name South Pacific
Project Address

Assessor's Parcel Number(s) (APN(s))
Permit Application Number
Project Hydrologic Unit Select One:
 Santa Margarita 902
 San Luis Rey 903
 Carlsbad 904
 San Dieguito 905
 Penasquitos 906
 San Diego 907
 Pueblo San Diego 908
 Sweetwater 909
 Otay 910
 Tijuana 911
Project Watershed
(Complete Hydrologic Unit, Area, and Subarea
Name with Numeric Identifier)
The project is located in the Richland Hydrologic Sub
Area of the San Marcos Hydrologic Area of the
Carlsbad Hydrologic Unit (904.52).

Parcel Area
(total area of Assessor's Parcel(s) associated
with the project)

_ _ Acres (_ _____ Square Feet)
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.

NE Corner of South Pacific Street ,
San Marcos, CA 92078
219-223-20&22

2.926
127456.56

2.926
127456.56
106214.09

2.44 0.49
21242.47
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 2 of 10, Form Date: March 15, 2016
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

Existing Natural Hydrologic Features (select all that apply):
 Watercourses
 Seeps
 Springs
 Wetlands
 None

Description / Additional Information:

The existing site condition is undeveloped natural area with soil type D.

Note: At the upper northwest corner of the
project site the GW depth is 4'. At the rest
portion of the project site the GW depth is
between 6'-10'.



□
✓
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 3 of 10 , Form Date: March 15, 2016
Description of Existing Site Drainage Patterns
How is storm water runoff conveyed from the site? At a minimum, this description should answer:
(1) whether existing drainage conveyance is 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:

The majority of the existing offsite surface slopes generally from the north to the south. When the water reaches South Pacific Street along the west border of the project, it flows into the existing dual 48 inches pipes then flow through vacant property before entry the project area.

The site is currently undeveloped. The existing onsite surface slope is approximately 2% and runs generally from the north to the south. When the water from offsite reaches to the north edge of the project, it flows along the slope until it reaches the project’s POC at the south edge of the property. According to the Web Soil Survey, the entire existing site is Soil Type D.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 4 of 10 , Form Date: March 15, 2016
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):

Does the project include grading and changes to site topography?  Yes
 No

Description / Additional Information:

The project is proposing to build a building, parking lots with landscape area, and structural Biofiltration BMPs (BF-2) along with a Modular Wetlands proprietary biofiltration (BF-3).

The proposed impervious areas of the project will include a building, the associated parking lot, and the paved road.

The proposed pervious areas of the project will include two biofiltration BMPs (BF-2), pervious pavers in the parking stalls, and minor landscaped areas around the building's footprint.

The current site has a slight upward slope from South Pacific then drops down to a lower elevation that creates an entire channel that conveys waters from the north. The proposed project will raise the site and allow the water to convey through the site through proposed Reinforced Concrete Pipes.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022
Form I-3B Page 5 of 10 , Form Date: March 15, 2016
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:

The project proposes to build a building, parking and landscape areas. The proposed parking slopes to the project’s biofiltration basin (BMP-A) at 0.5%. To decrease impervious area on the site, the parking stalls will be installed with pervious concrete. The proposed building is approximately 1.298 acres. The 1.024 acres of the building will discharge roof water into BMP-A, another 0.274 acres of the building will discharge roof water into BMP-B. After all stormwater from parking lot and roof get collected and treated in BMP-A and BMP-B, it flows into the 48 inches storage tank, which is located at the north and east edge of the project site. This storage tank is used for detaining post-developed onsite water. At the end of the storage tank, a weir plate with two orifices is used for regulating low flow. Each of the biofiltration basins have an emergency spillway that will ultimately allow water to go to the street. It should be noted this is a last attempt emergency spillway for safety; these spillways should not have water actually going through them.

A 24 inches pipe connect the storage tank with two proposed new 66 inches culverts. These two new 66 inches culverts run from the north to the south and meet with the existing two 66 inches culvert at south pacific street. These two 66 inches culverts route storm water through the site and finally collects into the POC at the South Pacific Street.

At the west and south edge of the project site, there is approximately 0.497 acres which include pervious and landscaped slope that will not flow to the basins. This section drains surface water from the north to the south and collects in an existing 18 inches storm drain pipe which ties to an existing 27 inches storm drain to the POC.

At the south side of the project site, there is BMP-C which is a modular wetland system to convey storm water from north to south. The proposed 18 inches outlet pipe of the modular wetland is connecting with the existing 18 inches RCP pipe where the headwall used to be. Storm water drains southernly to the modular wetland system and get treated, then drains into the existing 18 inches storm drain pipe to the POC.

At the southeast corner of the project site, there is a dispersion area to route surface runoff from impervious street area to the adjacent pervious area. This is to slow surface runoff and reduce discharge by infiltration and evapotranspiration.

BMP-D is the dispersion area for DMA-4. 100% of the impervious will be going to the dispersion area.

At the east part of the project site, the parcel APN 219-223-20, water is intercepted at the south easterly corner at a headwall which connects to dual 24 inches pipes. These two new 24 inches pipes goes under BMP-B and connect with the two proposed new 66 inches culverts to route storm water to the POC at the South Pacific Street.

For more information on these flows, see the Drainage Study of this project.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021

Form I-3B Page 6 of 10, Form Date: March 15, 2016
Identify whether any of the following features, activities, and/or pollutant source areas will be present (select all that apply):
 On-site storm drain inlets
 Interior floor drains and elevator shaft sump pumps
 Interior parking garages
 Need for future indoor & structural pest control
 Landscape/Outdoor Pesticide Use
 Pools, spas, ponds, decorative fountains, and other water features  Food service
 Refuse areas
 Industrial processes
 Outdoor storage of equipment or materials
 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

Description / Additional Information:

□
□
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 7 of 10 , Form Date: March 15, 2016
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:
303(d) Impaired Water Body Pollutant(s)/Stressor(s)
TMDLs / WQIP Highest Priority
Pollutant
San Marcos Creek
Lake San Marcos
Batiquitos Lagoon Pathogen
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
Pesticides

*
*Note: Only Applies to BMP-C (Modular Wetlands Flow Through) Indicator Bacteria, Phosphorus,
Selenium
Ammonia (N), Copper, Nutrients,
Phosphorus
Nutrients
X
X
X
X
X
X
X
X
X
The flow path of storm water from the project site discharge the upper of San Marcos Creek then to the Lake San Marcos and ultimate discharge to the Pacific Ocean.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 8 of 10 , Form Date: March 15, 2016
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 Based on the maps provided within the WMAA, do potential critical coarse sediment yield areas exist within the project drainage boundaries?
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 is 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:

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 9 of 10 , Form Date: March 15, 2016
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.

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 the low flow threshold is 0.1Q2
 Yes, the result is the low flow threshold is 0.3Q2
Yes, the result is the low flow threshold is 0.5Q2

If a geomorphic assessment has been performed, provide title, date, and preparer:

Discussion / Additional Information: (optional)

There is one POC at the southeast corner of the property. Water flows from biofiltration basins and storage tank to the street at this point.




San Marcos Creek Specific Plan, Master Water Quality and Hydromodification Management Plan, Final December 15, 2011, City of San Marcos.

See Attachment 2C for the geomorphic assessment.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/22/2021
Form I-3B Page 10 of 10 , Form Date: March 15, 2016
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.

There is a section constraint at the street that makes sizing an appropriate biofiltration system work, in this case Modular Wetlands bio clean was chossen.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Source Control BMP Checklist
for All Development Projects
(Standard Projects and Priority Development Projects)
Form I-4
[March 15, 2016]
Project Identification
Project Name: South Pacific
Permit Application Number:

Source Control BMPs
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 Model BMP Design 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 Model BMP Design 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 Discussion / justification if SC-1 not implemented:

SC-2 Storm Drain Stenciling or Signage  Yes  No  N/A Discussion / justification if SC-2 not implemented:

SC-3 Protect Outdoor Materials Storage Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
 Yes  No  N/A
Discussion / justification if SC-3 not implemented:

SC-4 Protect Materials Stored in Outdoor Work Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
 Yes  No  N/A
Discussion / justification if SC-4 not implemented:

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City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Form I-4 Page 2 of 2, Form Date: March 15, 2016
Source Control Requirement Applied?
SC-5 Protect Trash Storage Areas from Rainfall, Run-On, Runoff, and Wind Dispersal
 Yes  No  N/A
Discussion / justification if SC-5 not implemented:

SC-6 Additional BMPs Based on Potential Sources of Runoff Pollutants (must answer for each source listed below)
 On-site storm drain inlets
 Interior floor drains and elevator shaft sump pumps
 Interior parking garages
 Need for future indoor & structural pest control
 Landscape/Outdoor Pesticide Use
 Pools, spas, decorative fountains, and other water features  Food service
 Refuse areas
 Industrial processes
 Outdoor storage of equipment or materials
 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-6 not implemented. Clearly identify which sources of runoff pollutants are discussed. Justification must be provided for all "No" answers shown above.

✓ ✓ □
□ □
-
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Site Design BMP Checklist
for All Development Projects
(Standard Projects and Priority Development Projects)
Form I-5
[March 15, 2016]
Project Identification
Project Name: South Pacific
Permit Application Number
Site Design BMPs
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 Model BMP Design 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 Model BMP Design 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.

Site Design Requirement Applied?
SD-1 Maintain Natural Drainage Pathways and Hydrologic Features  Yes  No  N/A Discussion / justification if SD-1 not implemented:

SD-2 Conserve Natural Areas, Soils, and Vegetation  Yes  No  N/A Discussion / justification if SD-2 not implemented:

SD-3 Minimize Impervious Area  Yes  No  N/A
Discussion / justification if SD-3 not implemented:

SD-4 Minimize Soil Compaction  Yes  No  N/A
Discussion / justification if SD-4 not implemented:

SD-5 Impervious Area Dispersion  Yes  No  N/A
Discussion / justification if SD-5 not implemented:

There are no significant areas of level vegetation to implement this BMP. All impervious areas are directed to a biofiltration pond.

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City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Form I-5 Page 2 of 2, Form Date: March 15, 2016
Site Design Requirement Applied?
SD-6 Runoff Collection  Yes  No  N/A
Discussion / justification if SD-6 not implemented:

SD-7 Landscaping with Native or Drought Tolerant Species  Yes  No  N/A Discussion / justification if SD-7 not implemented:

SD-8 Harvesting and Using Precipitation  Yes  No  N/A Discussion / justification if SD-8 not implemented:

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City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Summary of PDP Structural BMPs Form I-6 (PDPs)
[March 15, 2016]
Project Identification
Project Name: South Pacific
Permit Application Number:

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, and the local jurisdiction must confirm the maintenance (see Section 7 of the BMP Design Manual).

Use this form 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.

Step 1, the project was divided up and evaluated at the DMA scale. Each DMA area was classified as Self- Treating, Self-Retaining or Draining to a Best Management Practice (BMP).

Step 2, For the DMAs that drain to BMPs, the appropriate runoff factors were applied to each area and the required Design Capture Volume (DCV) of each sub area calculated. For this project, Harvest and reuse is not considered feasible.

Step 3, due to the impermeability of the underlying soils, (soil type D), infiltration BMPs are not feasible.

Step 3A&B for the no infiltration condition leads to section 5.5.3 which is the Biofiltration BMP category.

The various sizing methods included in Appendix B.5 were followed and the entire DCV can be treated within the proposed BMPs.

Step 4, each Biofiltration area is sized in accordance with the fact sheet BF- found in appendix E of the BMP design manual. This project requires hydromodification controls, so the Biofiltration units accomplish both storm water treatment and flow control mitigation in an integrated design.

(Continue on page 2 as necessary.)

2 Step 4, each Biofiltration BMP area is sized in accordance with the fact sheet BF 2 or Proprietary biofiltration with BF3 found in appendix E of the BMP design manual. This project requires hydromodification controls, so the Biofiltration units accomplish both storm water treatment and flow control mitigation in an integrated design.

I
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Form I -6 Page 2 of 4, Form Date: March 15, 2016
(Page reserved for continuation of description of general strategy for structural BMP implementation at the site)
(Continued from page 1)

DMA 5 and DMA 6 are self mitigating area and drain to
natural areas; therefore they not a part of sizing calculations.

City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
Form I -6 Page 3 of 4 (Copy as many as needed) Form Date: March 15, 2016 Structural BMP Summary Information
(Copy this page as needed to provide information for each individual proposed structural BMP) Structural BMP ID 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)  Proprietary Biofiltration (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)

Who will certify construction of this BMP?
Provide name and contact information for the
party responsible to sign BMP verification forms if
required by the [City Engineer] (See Section 1.12 of
the BMP Design Manual)
The Engineer o f Work
Robert Dentino
Excel Engineering
440 State Place
Escondido, CA 92029

Who will be the final owner of this BMP?

Project Owner
Who will maintain this BMP into perpetuity?

Project Owner
What is the funding mechanism for maintenance?

Project Owner

BMP-A




City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021

Form I -6 Page 4 of 4 (Copy as many as needed) Form Date: March 15, 2016 Structural BMP Summary Information
(Copy this page as needed to provide information for each individual proposed structural BMP) Structural BMP ID No.

Construction Plan Sheet No.

Who will be the final owner of this BMP?

Project Owner
Who will m aintain this BMP into perpetuity?

Project Owner
What is the funding mechanism for maintenance?

Project Owner

BMP-B




City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021

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) Proprietary Biofiltration (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)

Who will be the final owner of this BMP?

Project Owner
Who will m aintain this BMP into perpetuity?

Project Owner
What is the funding mechanism for maintenance?

Project Owner

BMP-C (Modular Wetlands)








City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021

Form I-6 Page 4 of 4 (Copy as many as needed) Form Date: March 15, 2016 Structural BMP Summary Information
(Copy this page as needed to provide information for each individual proposed structural BMP) Structural BMP ID 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) Proprietary Biofiltration (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 con trol  Pre-treatment/forebay for another structural BMP
 Other (describe in discussion section below)

Who will certify construction of this BMP?
Provide name and contact information for the
party responsible to sign BMP verification forms if
required by the [City Engineer] (See Section 1.12 of
the BMP Design Manual)
The Engineer of Work
Robert Dentino
Excel Engineering
440 State Place
Escondido, CA 92029
Who will be the final owner of this BMP?

Project Owner
Who will maintain this BMP into perpetuity?

Project Owner
What is the funding mechanism for maintenance?

Project Owner



BMP-E (Storage Pipe)






Hydromodification and Hydrology Detention

Hydromodification and Hydrology Detention
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
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
Sequence
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 I -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 I-7.

 Included
 Not included because the entire
project will use infiltration BMPs

Attachment 1d Form I -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 I-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

Attachment 1A
DMA Exhibit
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
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 self-mitigating)  Potential pollutant source areas and corresponding required source controls (see Chapter 4, Appendix E.1, and Form I-3B)
 Structural BMPs (identify location, type of BMP, and size/detail)

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WAlER OIJAL/TY BASIN INSTALLAllON NOlES:
!. J INCHES OF 1/El.L -AGtZJ, SHREOOEO HARO/fOOO N(JLCH.

2. AN (JNOERORAIN Cl.EANot/T llflH A NINIJl(JN 6-/NCH 0/ANE!ER ANO LOCKABLE CAP IS PLACEO £/,£RY 250 TO .JOOFEET AS REot/lREO BASEO ON (JNIJERORAIN LENGTH.

3. 1£GETARON (JSEO SHot/LO BE S(JITABLE FOR lHE Cl.lNA!E PER LANOSCAPE PLANS

4. RL !ER COARSE IS A NIN/N(JN OF 6 INCHES PR0/40EO IN TWO SEPARA 1E 3 INCH LA IV?S. lHE TOP LA}ER SHA!.L BE NAOE OF ASlY CJJ CHOKER SANO ANO lHE BOTTOl,I LAIV? BE OF ASlY Na 8 ACGRECAlE NARKERS STAKES SHALL BE (JS£0 TO ENS/JRE (JNIFORN LIFT lH/CKNESS.

5. AASHTO Na 57 STONE OR Cl.ASS 2 PERNEABLE PER CAL 1RANS SPEClflCARON 68-1.025 IS REC(JA(NENOElJ FOR lHE AGQl?ECA 1E STORACE LA }ER. WASHEO, OPEN-GRAOEO CRLISHEO ROCK NAY BE (JSEO, HOHEVER, A ,f. INCH AHN/N(JN WASHEO PEA GRA ill flL !ER Cot/RSE LA IV? AT lHE TOP OF THE CR(JSHEO ROCK IS REot/lREO.

6. INPERAIEABLE UNER SHALL BE INSTALLEO /#HEN lHE 8/0flL 1RA RON BASIN IS llflH/N 10 ITET OF RETAINING WALLS OR B(J/LOING Fot/NOARONS, OR AS RECOl.fNENOElJ BY lHE .%¥LS ENGINEER, OR REot/lRElJ BY THESE PLANS. IJIPERNEABLE UNER SHALL BE JO AHL lH/CI( (PER COfJNTY OF SAN 0/EGO GREEN S1l?E£1S OES/GN STANOARO ORA/lfNG GS-3.00 ANO Cot/NTY GREEN S1l?E£1S S/JPPLEMENT TO CAL 1RANS SPEClflCARONS 20-/1.088) CONRG//REO TO ENRl?El.Y ENCOl.fPASS lHE S/OES OF !HE WA 1ER ot/ALITY BASIN.

7. /JIPERl,/EABLE LINER BE CONS1R(JC1EO IN COl.fPLIANCE llflH lHE COfJNTY OF SAN 0/EGO GREEN S1REE1S Sl/PPLEJIENT TO CAL 1RANS SPECIRCARONS 20-11.088.

8. B/OflL1RARON sm NEO/A LAIV? (BSI.I) SHALL CONSIST OF 60% TO 80% BY VOl.(JJIE SANO, (Ip TO 20% BY VOl.(JNE TOPSO'L, ANO (JP 20% BY VOl.(JNE C(JA(POST (PER Cot/NTY OF SAN 0/EGO 81,/P OES/GN NAN(JAL SEP!ENBER 2020 APPENO/% F.2 SECRON 80J-2 BLENOElJ BSI.I CRl!ERIA ANO lESRNG REot/lREI.IENlS) PLACEO IN 6' LIFTS ANO C&PAC1EI) llflH WATER PRIOR TO lHE NEXT

WATER QUALITY SIGN- PLACED AT

EACH BIOFILTRATION BASIN SOURCE CONTROL
L/Fl IN/HAL PERAIEABILITY SHALL BE 8' PER Hot/R (llflH ASSLINEO STABIL/ZEO PERJIEABILITY OF 5• PER Hot/R)
J Jj
NOTE: ALL BIOFlLlRATION AREAS WILL

HAVE A SIGN POSTED TO BE
VISIBLE AT ALL TIMES.

IAIPEHAIEABL.E LINEN £OGE ANCHIR OETAIL

NOT TO SCALE
---CATCH BASIN

PER PLAN
SCH 40 PW: NALE
AOAP!ER (NilPKSoC)
SCH 40 PW: lHREAOEO

ENO CAP (FPT)
_________ J-..w.i.,--ORJLL OR/flCE HOI.E AT
I lli.--AHN. J4'), cl(_ ROHt.lNE OF ENO CAP
ld'J,'. •• \_;~: ; (SIZE PER BIO-BASIN OETAIL)
Na 57 STONE
LOH£'R ORIFICE OETAIL

NOT TO SCALE
.m'L NI% ~
LAIV?
GRAill
LAIV? !'::i
I
I

1. I
I
I
• :::::J \~;W:S~CTOR
LOI/ER OR!flCE

SIZE PER TABLE
CA,r;HIJAS/N DETAIL SEE ORlflCE OETAIL

NOT TO SCALE
OETA/L
iVO OUI.IP/NC" AT CATCH BASINS
NOlE· ALL CATCH BASINS llflH GRATES SHALL
BE SlENC/LEO llflH CITY REot/lREO llEI,/ PER
ABO/£ OETAIL (OAS NAN(JFACTlJRING /S/)0 OR
Eot/lVALENT).

SOURCE CONTROL REQUIREMENT
SC-1 PREVIENTION OF ILLICIT DISCHARGES
SC-2 STORM DRAIN STENCILING OR SIGNAGE
SC-5 PROTECT TRASH STORAGE

NODE IMPLEMENTAION

EFFECTIVE IRRIGATION WILL BE IMPLEMENTED AND

VIEHICLE WASHING IS PROHIBITED
STENCIL EVERY INLET WITH PROHIBITIVE WORDS: "NO
DUMPING! DRAINS TO WATERWAYS" AND "NO CONTAMINE"
IN SPANISH.

TRASH ENCLOSURE WILL BE PROTECTED BY LID OR BE

WALLED WITH ROOF TO AVOID STORMWATER GET

CONTAMINATED
SCALE· 1:50

9. lHE AGCRECA!E STORACE LAYE'R SHALL BE COl.fPAClEO IN ACCOROANCE llflH .%¥LS ENGINEER's RECOl.fNENOA RONS.
ta 01£RROW SlRtlCTlJRE TO HA/£ A AHN/N(JN OF 2 INCHES OF fREEBOARO.

If. ALL UNER INSTALLA 110NS, flELO JIEZO/NG OF SEANS, ANO OBSE'RVA RON OF SO'L AH% PLACEI.IENT SHALL REWIRE SPECIAL INSPECRON BY lHE PROECT CEO!ECHNICAL ENGINEER OR OTHER (){IAUREO PERStw. A LET!ER CERRFYING PROPER INSTALLARON SHALL BE PROl40EO TO lHE ENGINEER OF RECORO TO ACCEPTANCE OF lHE FAC/LIRES.

12. SPECIAL INSPECRON SHALL BE REot/lRElJ FOR CONS1R(JC110N OF ALL 8/0flL 1RA RON BASINS.

INSPEC110N SHALL BE PERFORNEO BY A ot/AL/flEO IN0/140/IAL (Sl/CH AS.· ENGINEER OF RECORO, OSO}. INSPECRON SHALL INCJ.(JOE:
• /,£/?/flCARON OF 01£RALL OINENS/ONS PRIOR TO PLACENENT OF NA!ERIALS,· • PLACEI.IENT OF lHE LINER, IF REot/lRElJ;ANO SEANS OR PENE1RA110NS • PLACEI.IENT OF lHE GRA ill, flL !ER NA lERIALS, ANO flL 1ER NEOIA; • ALL INLET ANO ot/llET SlRtlCTlJRES INCJ.(JOING (JNOERORA/NS, IF REot/lREO. • CONTRACTOR SHALL TAKE P/CllJRES AT EACH STAGE OF INSTALLARON ANO S(JBN/TlEO TO ENGINEER FOR 1£R/flCA110N OF INSTALL.

INSPECTOR SHALL BE GIIIEN A NIN/N(JN OF ,f.8 Hot/RS PRIOR TO INSPEClltw. (JPON COl.fPLERON lHE INSPECTOR SHALL PR0/40E A CERllflCARON TO lHE ENGINEER OF /#ORK. !3. PROPOSEO NA !ERIALS, S(JCH AS AGCREGA IE, fll !ER NA !ER/AL, ANO flL !ER JIEO/A SHALL BE S/JBl,I/TlEO TO lHE ENGINEER OF IHJRK FOR APPROVAL.

SOUTH PACIFIC STREET -- -- - - -0 50 100 150 200 OMA EXHIB/ T Attachment 1B
Tabular Summary of DMA's
1 85th percentile 24-hr storm depth from Figure B.1-1 d= 0.67 0.67 0.67 inches 2 Area tributary to BMP (s) A= 1.82 0.47 0.50 Acres
3 Area weighted runoff factor (estimate using Appendix B.1.1 and B.2.1) C= 0.77 0.80 0.64 unitless
4 Street trees volume reduction TCV= cubic-feet
5 Rain barrels volume reduction RCV= cubic-feet
6 Calculate DCV=
(3630 x C x d x A) - TCV -RCV DCV= 3,411.00 922.00 774.00 cubic-feet Worksheet B-2.1 Design Capture Volume
Drainage Basin ID or NameDMA-1 DMA-2 DMA-3 UNITS
85th Percentile 24-hr Storm Depth 0.67 0.67 0.68 INCHES Impervious Surfaces 66,908 17,980 14,565 SQFT
Engineered Pervious Surfaces 12,444 2,662 7,094 SQFT
Total Tributary Area 79,352 20,643 21,659 SQFT
Total Tributary Area 1.82 0.47 0.50 ACRE
Attachment 1C
Harvest and Use Feasibility
Screening Checklist
Appendix I: Forms and Checklists

I-26 February 2016
Harvest and Use Feasibility Checklist Form I-7

1. Is there a demand for harvested water (check all that apply) at the project site that is reliably present during the wet season?
Toilet and urinal flushing
Landscape irrigation
Other:______________

2. If there is a demand; estimate the anticipated average wet season demand over a period of 36 hours.

Guidance for planning level demand calculations for toilet/urinal flushing and landscape irrigation is provided in Section B.3.2.
[Provide a summary of calculations here]

3. Calculate the DCV using worksheet B-2.1.

DCV = __________ (cubic feet)
3a. Is the 36 hour demand greater
than or equal to the DCV?
 Yes /  No
3b. Is the 36 hour demand greater than

0.25DCV but less than the full DCV?
 Yes /  No

3c. Is the 36 hour demand
less than 0.25DCV?
 Yes
Harvest and use appears to be
feasible. Conduct more detailed
evaluation and sizing calculations
to confirm that DCV can be used
at an adequate rate to meet
drawdown criteria.

Harvest and use may be feasible.

Conduct more detailed evaluation and
sizing calculations to determine
feasibility. Harvest and use may only be
able to be used for a portion of the site,
or (optionally) the storage may need to be
upsized to meet long term capture targets
while draining in longer than 36 hours.

Harvest and use is
considered to be infeasible.

Is harvest and use feasible based on further evaluation?  Yes, refer to Appendix E to select and size harvest and use BMPs.  No, select alternate BMPs.

DCV = 4333

0.25xDCV=1083.25
Flushing: (72 employees)x(9.3 gal/emp) = 669.6 gallons (669.6 gal)(1.5 days)/(7.48 gal/cu. ft.) = 134.3 cu. ft.

Irrigation: 36-hr Mod. Water per Table B.3-3 = (1,470 gal days/acre)(0.49 acres)/(7.48 gal/cu feet) = 96.3 cu ft.

Total Demand = 230.6 cu. ft.
4333
~
~
□
~ C3 i C3 CD
~
Attachment 1D
Categorization of Infiltration
Feasibility Condition
I-8
I-8
X
X
The NRCS soils across the site are all Type D soils. the site soils are consistent with the NRCS mapped soil types based on site explorations and percolation testing. According to soil report, the approximate depth to groundwater is between 4-10 feet, which should have an infiltration rate is 0.

Worksheet : Categorization of Imtltration Feasibility Condition 111 lfil ■ llln1 ■ -.••••11 l~•t1lln.•n-n11uun 11
...

Part 1 - Full Infiltration Feasibility Screening Criteria Would infiltration of the full design volume be feasible from a physical perspective without any undesirable consequences that cannot be reasonably mitigated?
Criteria Screening Question
1 Is the estimated reliable infiltration rate below proposed facility locations greater than 0.5 inches per hour? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D.

Provide basis:

Yes No
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability. 2 Can infiltration greater than 0.5 inches per hour be allowed without increasing risk of geotechnical hazards (slope stability, groundwater mounding, utilities, or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2.

Provide basis:

Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability.

C-11
I-8
I-8
X
X
The NRCS soils across the site are all Type D soils. the site soils are consistent with the NRCS mapped soil types based on site explorations and percolation testing. According to soil report, the approximate depth to groundwater is between 4-10 feet, which should have an infiltration rate is 0.

The NRCS soils across the site are all Type D soils. the site soils are consistent with the NRCS mapped soil types based on site explorations and percolation testing. According to soil report, the approximate depth to groundwater is between 4-10 feet, which should have an infiltration rate is 0. - - -'-l.fljTiil""l~i
Criteria Screening Question
3 Can infiltration greater than 0.5 inches per hour be allowed without increasing risk of groundwater contamination (shallow water table, storm water pollutants or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3.

Provide basis:

Yes No
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability. 4 Can infiltration greater than 0.5 inches per hour be allowed without causing potential water balance issues such as change of seasonality of ephemeral streams or increased discharge of contaminated groundwater to surface waters? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3.

Provide basis:

Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability.

Part 1
If all answers to rows 1 - 4 are "Yes" a full infiltration design is potentially feasible. The feasibility screening category is Full Infiltration
Result* If any answer from row 1-4 is "No", infiltration may be possible to some extent but would not generally be feasible or desirable to achieve a "full infiltration" design .

Proceed to Part 2
*To be completed using gathered site information and best professional judgment considering the definition of MEP in the MS4 Permit . Additional testing and/ or studies may be required by City Engineer to substantiate findings.

C-12
I-8
X
Duetositesoilsnotpercolatingandthesignificantamountofclayeysoils,itisunlikelythatany appreciablevolumeofwaterwillinfiltrate.

X
The NRCS soils across the site are all Type D soils. the site soils are consistent with the NRCS mapped soil types based on site explorations and percolation testing. According to soil report, the approximate depth to groundwater is between 4-10 feet, which should have an infiltration rate is 0. - - -'-l.fljTiil""l~i ~ I ' ....

Part 2 - Partial Infiltration vs. No Infiltration Feasibility Screening Criteria Would infiltration of water in any appreciable amount be physically feasible without any negative consequences that cannot be reasonably mitigated?
Criteria Screening Question
5 Do soil and geologic conditions allow for infiltration in any appreciable rate or volume? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2 and AppendixD .

Provide basis:

Yes No
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability and why it was not feasible to mitigate low infiltration rates .
6 Can Infiltration in any appreciable quantity be allowed without increasing risk of geotechnical hazards (slope stability, groundwater mounding, utilities, or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2.

Provide basis:

Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability and why it was not feasible to mitigate low infiltration rates.

C-13
I-8
No
Inf.

X
X
The NRCS soils across the site are all Type D soils. the site soils are consistent with the NRCS mapped soil types based on site explorations and percolation testing. According to soil report, the approximate depth to groundwater is between 4-10 feet, which should have an infiltration rate is 0.

The NRCS soils across the site are all Type D soils. the site soils are consistent with the NRCS mapped soil types based on site explorations and percolation testing. According to soil report, the approximate depth to groundwater is between 4-10 feet, which should have an infiltration rate is 0. - - -'-l.fljTiil""l~i
Criteria Screening Question
7 Can Infiltration in any appreciable quantity be allowed without posing significant risk for groundwater related concerns (shallow water table, storm water pollutants or other factors)? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3.

Provide basis:

Yes No
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability and why it was not feasible to mitigate low infiltration rates.
8 Can infiltration be allowed without violating downstream water rights? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3.

Provide basis:

If all answers from row 1-4 are yes then partial infiltration design is potentially feasible.

Part 2 The feasibility screening category is Partial Infiltration.

Result* If any answer from row 5-8 is no, then infiltration of any volume is considered to be infeasible within the drainage area. The feasibility screening category is No Infiltration. *To be completed using gathered site information and best professional judgment considering the definition of MEP in the MS4 Permit . Additional testing and/ or studies may be required by City Engineer to substantiate findings C-14
Attachment 1E
Pollutant Control BMP Design
Worksheets & Calculations
0 1 DCV Start with 0 if no Carry over from Another
DMA DCV 0 cubic-feet
2 DCV retained DCV retained 0 cubic-feet
3 DCV biofiltered DCV biofiltered 0 cubic-feet
4 DCV requiring flow-thru
(Line 1 — Line 2 —0.67*Line 3) DCV flow-thru 0 cubic-feet 5 Adjustment factor (Line 4 / Line 1) AF= 1 unitless
6 Design rainfall intensity i= 0.2 in/hr
7 Area tributary to BMP (s) A= 1.5369 acres
8 Area-weighted runoff factor (estimate using
Appendix B.2) C= 0.800 unitless
9 Calculate Flow Rate = AF x (C x I x A)*1.5 Q= 0.37 cfs Worksheet B-6.1Flow-thru Design Flows
BMP-C Sizing for MWS
L-8-12-5'6"-C
Category # Description i ii iii Units
1 Drainage Basin ID or Name BMP-A BMP-B BMP-D unitless
2 85th Percentile 24-hr Storm Depth 0.67 0.67 0.67 inches 3 Impervious Surfaces Not Directed to Dispersion Area (C=0.90) 66,908 17,980 sq-ft 4 Semi-Pervious Surfaces Not Serving as Dispersion Area (C=0.30) sq-ft 5 Engineered Pervious Surfaces Not Serving as Dispersion Area (C=0.10) 12,444 2,662 sq-ft 6 Natural Type A Soil Not Serving as Dispersion Area (C=0.10) sq-ft 7 Natural Type B Soil Not Serving as Dispersion Area (C=0.14) sq-ft 8 Natural Type C Soil Not Serving as Dispersion Area (C=0.23) sq-ft 9 Natural Type D Soil Not Serving as Dispersion Area (C=0.30) sq-ft 10 Does Tributary Incorporate Dispersion, Tree Wells, and/or Rain Barrels? No No Yes yes/no 11 Impervious Surfaces Directed to Dispersion Area per SD-B (Ci=0.90) 6,575 sq-ft 12 Semi-Pervious Surfaces Serving as Dispersion Area per SD-B (Ci=0.30) sq-ft 13 Engineered Pervious Surfaces Serving as Dispersion Area per SD-B (Ci=0.10) 4,773 sq-ft 14 Natural Type A Soil Serving as Dispersion Area per SD-B (Ci=0.10) sq-ft 15 Natural Type B Soil Serving as Dispersion Area per SD-B (Ci=0.14) sq-ft 16 Natural Type C Soil Serving as Dispersion Area per SD-B (Ci=0.23) sq-ft 17 Natural Type D Soil Serving as Dispersion Area per SD-B (Ci=0.30) sq-ft 18 Number of Tree Wells Proposed per SD-A #
19 Average Mature Tree Canopy Diameter ft
20 Number of Rain Barrels Proposed per SD-E #
21 Average Rain Barrel Size gal
22 Total Tributary Area 79,352 20,642 11,348 sq-ft
23 Initial Runoff Factor for Standard Drainage Areas 0.77 0.80 0.00 unitless 24 Initial Runoff Factor for Dispersed & Dispersion Areas 0.00 0.00 0.56 unitless 25 Initial Weighted Runoff Factor 0.77 0.80 0.56 unitless 26 Initial Design Capture Volume 3,411 922 355 cubic-feet 27 Total Impervious Area Dispersed to Pervious Surface 0 0 6,575 sq-ft 28 Total Pervious Dispersion Area 0 0 4,773 sq-ft
29 Ratio of Dispersed Impervious Area to Pervious Dispersion Area n/a n/a 1.40 ratio 30 Adjustment Factor for Dispersed & Dispersion Areas 1.00 1.00 0.00 ratio 31 Runoff Factor After Dispersion Techniques 0.77 0.80 0.00 unitless 32 Design Capture Volume After Dispersion Techniques 3,411 922 0 cubic-feet 33 Total Tree Well Volume Reduction 0 0 0 cubic-feet
34 Total Rain Barrel Volume Reduction 0 0 0 cubic-feet
35 Final Adjusted Runoff Factor 0.77 0.80 0.00 unitless 36 Final Effective Tributary Area 61,101 16,514 0 sq-ft 37 Initial Design Capture Volume Retained by Site Design Elements 0 0 355 cubic-feet 38 Final Design Capture Volume Tributary to BMP 3,411 922 0 cubic-feet False
False
Automated Worksheet B.1: Calculation of Design Capture Volume (V2.0) Dispersion
Area, Tree Well
& Rain Barrel
Inputs
(Optional)
Standard
Drainage Basin
Inputs
Results
Tree & Barrel
Adjustments
Initial Runoff
Factor
Calculation
Dispersion
Area
Adjustments
No Warning Messages
Category # Description i ii Units
1 Drainage Basin ID or Name BMP-A BMP-B sq-ft
2 Design Infiltration Rate Recommended 0.000 0.000 in/hr 3 Design Capture Volume Tributary to BMP 3,411 922 cubic-feet 4 Is BMP Vegetated or Unvegetated? Vegetated Vegetated unitless 5 Is BMP Impermeably Lined or Unlined? Lined Lined unitless 6 Does BMP Have an Underdrain? Underdrain Underdrain unitless 7 Does BMP Utilize Standard or Specialized Media? Standard Standard unitless 8 Provided Surface Area 1,920 759 sq-ft
9 Provided Surface Ponding Depth 6 6 inches
10 Provided Soil Media Thickness 18 18 inches
11 Provided Gravel Thickness (Total Thickness) 15 15 inches 12 Underdrain Offset 3 3 inches
13 Diameter of Underdrain or Hydromod Orifice (Select Smallest) 0.50 0.50 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 0 0 cubic-feet
19 Ponding Pore Space Available for Retention 0.00 0.00 unitless 20 Soil Media Pore Space Available for Retention 0.05 0.05 unitless 21 Gravel Pore Space Available for Retention (Above Underdrain) 0.00 0.00 unitless 22 Gravel Pore Space Available for Retention (Below Underdrain) 0.40 0.40 unitless 23 Effective Retention Depth 2.10 2.10 inches
24 Fraction of DCV Retained (Independent of Drawdown Time) 0.10 0.14 ratio 25 Calculated Retention Storage Drawdown Time 120 120 hours 26 Efficacy of Retention Processes 0.12 0.16 ratio
27 Volume Retained by BMP (Considering Drawdown Time) 412 148 cubic-feet 28 Design Capture Volume Remaining for Biofiltration 2,999 774 cubic-feet 29 Max Hydromod Flow Rate through Underdrain 0.0113 0.0113 cfs 30 Max Soil Filtration Rate Allowed by Underdrain Orifice 0.25 0.64 in/hr 31 Soil Media Filtration Rate per Specifications 5.00 5.00 in/hr 32 Soil Media Filtration Rate to be used for Sizing 0.25 0.64 in/hr 33 Depth Biofiltered Over 6 Hour Storm 1.53 3.87 inches 34 Ponding Pore Space Available for Biofiltration 1.00 1.00 unitless 35 Soil Media Pore Space Available for Biofiltration 0.20 0.20 unitless 36 Gravel Pore Space Available for Biofiltration (Above Underdrain) 0.40 0.40 unitless 37 Effective Depth of Biofiltration Storage 14.40 14.40 inches 38 Drawdown Time for Surface Ponding 24 9 hours
39 Drawdown Time for Effective Biofiltration Depth 56 22 hours 40 Total Depth Biofiltered 15.93 18.27 inches
41 Option 1 - Biofilter 1.50 DCV: Target Volume 4,498 1,160 cubic-feet 42 Option 1 - Provided Biofiltration Volume 2,549 1,156 cubic-feet 43 Option 2 - Store 0.75 DCV: Target Volume 2,249 580 cubic-feet 44 Option 2 - Provided Storage Volume 2,249 580 cubic-feet 45 Portion of Biofiltration Performance Standard Satisfied 1.00 1.00 ratio 46 Do Site Design Elements and BMPs Satisfy Annual Retention Requirements? Yes Yes yes/no 47 Overall Portion of Performance Standard Satisfied (BMP Efficacy Factor) 1.00 1.00 ratio 48 Deficit of Effectively Treated Stormwater
0 0 cubic-feet
Retention
Calculations
Automated Worksheet B.3: BMP Performance (V2.0)
False
False
BMP Inputs
Biofiltration
Calculations
False
False
False
False
Result
False
False
No Warning Messages

CURB OPENING

STANDARD DETAIL

STORMWATER BIOFILTRATION SYSTEM
MWS-L-8-16-5'-6"-C

SITE SPECIFIC DATA
INTERNAL BYPASS DISCLOSURE:

PLAN VIEW

ELEVATION VIEW

RIGHT END VIEW

LEFT END VIEW

GENERAL NOTES

INSTALLATION NOTES
PROJECT NUMBER 15339

PROJECT NAME SOUTH PACIFIC STREET

PROJECT LOCATION SAN MARCOS, CA

STRUCTURE ID BMP-C

TREATMENT REQUIRED
VOLUME BASED {CF) FLOW BASED {CFS)
N/A 0.3695

TREATMENT HGL AVAILABLE (FT) N/K
PEAK BYPASS REQUIRED {CFS) - IF APPLICABLE 7.0
PIPE DATA I.£ MATERIAL DIAMETER d
INLET PIPE 1 N/A N/A N/A
INLET PIPE 2 N/A N/A N/A
d
OUTLET PIPE 521.37 RCP 18" <I

PRETREATMENT BIOFILTRA TION DISCHARGE
RIM ELEVATION 526.95 526.95 526.95
SURFACE LOAD H-20 DIRECT N/A H-20 DIRECT
FRAME & COVER 2EA ¢30" OPEN PLANTER ¢30"
WETLANDMEDIA VOLUME (CY) 11.15
ORIFICE SIZE {DIA. INCHES) ¢2.90"
NOTES: PRELIMINARY NOT FOR CONSTRUCTION. ENGINEER TO CONFIRM ELEVATIONS AND PEAK FLOW RAT£ ALL MANHOLE CASTINGS TO BE ADA COMPLIANT.

1. CONTRACTOR TO PROVIDE ALL LABOR, EQUIPMENT, MATERIALS AND

INCIDENTALS REQUIRED TO OFFLOAD AND INSTALL THE SYSTEM AND

APPURTENANCES IN ACCORDANCE WITH THIS DRAWING AND THE

MANUFACTURERS' SPECIFICATIONS, UNLESS OTHERWISE STATED IN MANUFACTURER'S CONTRACT.

2. UNIT MUST BE INSTALLED ON LEVEL BAS£ MANUFACTURER
RECOMMENDS A MINIMUM 6" LEVEL ROCK BASE UNLESS SPECIFIED BY THE PROJECT ENGINEER. CONTRACTOR IS RESPONSIBLE FOR VERIFYING PROJECT ENGINEER's RECOMMENDED BASE SPECIFICATIONS.
<I
4 <I :
• <I·
,i

PEAK HGL
-
/ifo;ALL
--71/£RS
C/L

VERTICAL

UNDERDRAJN

MANIFOLD
d
.a
'A1
<I d
_ll
526.95
RIM/FG
~ ~~~~~~~ h!l --------- -i----W--~
. <!

4. CONTRACTOR TO SUPPLY AND INSTALL ALL EXTERNAL CONNECTING PIPES. ALL PIPES MUST BE FLUSH WITH INSIDE SURFACE OF
CONCRETE (PIPES CANNOT INTRUDE BEYOND FLUSH). INVERT OF OUTFLOW PIPE MUST BE FLUSH WITH DISCHARGE CHAMBER FLOOR.

ALL PIPES SHALL BE SEALED WATERTIGHT PER MANUFACTURER'S STANDARD CONNECTION DETAIL.

5. CONTRACTOR RESPONSIBLE FOR INSTALLATION OF ALL PIPES, RISERS, MANHOLES, AND HATCHES. CONTRACTOR TO USE GROUT AND/OR

BRICKS TO MATCH COVERS WITH FINISHED SURFACE UNLESS SPECIFIED

OTHERWISE
6"~ .------------~;:=g:----------. r-6·

6. VEGETATION SUPPLIED AND INSTALLED BY OTHERS. ALL UNITS WITH

VEGETATION MUST HAVE DRIP OR SPRAY IRRIGATION SUPPLIED AND INSTALLED BY OTHERS.

7. CONTRACTOR RESPONSIBLE FOR CONTACTING BIO CLEAN FOR
ACTIVATION OF UNIT. MANUFACTURER'S WARRANTY IS VOID WITHOUT

PROPER ACTIVATION BY A BIO CLEAN REPRESENTATIVE

1. MANUFACTURER TO PROVIDE ALL MATERIALS UNLESS OTHERWISE NOTED.

2. ALL DIMENSIONS, ELEVATIONS, SPECIFICATIONS AND CAPACITIES ARE SUBJECT TO CHANG£ FOR PROJECT SPECIFIC DRAWINGS DETAILING EXACT DIMENSIONS, WEIGHTS AND ACCESSORIES PLEASE CONTACT BIO CLEAN.

THE DESIGN AND CAPACITY OF THE PEAK CONVEYANCE METHOD TO BE REVIEWED AND APPROVED BY THE ENGINEER OF RECORD. HGL(S) AT PEAK FLOW SHALL BE ASSESSED TO ENSURE NO UPSTREAM FLOODING. PEAK HGL AND BYPASS CAPACITY SHOWN ON DRAWING ARE USED FOR GUIDANCE ONLY.
~' " 0 D U 1., ,A R
~ETLAND5 THE INFORIIATION CONTAINED IN THIS OOCUl,fENT IS THE SOLE PROPERTY OF FORTERRA ANO ITS COMPANIES. THIS OOCUMENT.
7l: ::::0:/,/fJ; =-~~ ~,:_:: o,, NOR ANY PAlff THEREOF, A44Y BE USED, REPRODUCED OR l,f(){)(flED PROPRIETARY AND CONFIDENTIAL:

Bio~ Clean

7.67"11': =14- 1EA1ED F1J/IE1(//( PA1ENIS OR IN ANY A44NNER WITH OUT THE WRITTEN CONSENT OF FORTERRA. 0/HER PA1ENIS - AFortemCom
TREATMENT FLOW (CFS) 0.3695
OPERATING HEAD {FT) 2.7
PRETREATMENT LOADING RATE {GPM/SF) 1.6
WETLAND MEDIA LOADING RATE (GPM/SF) 1.0
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
ATTACHMENT 2

BACKUP FOR PDP HYDROMODIFICATION CONTROL MEASURES

This is the cover sheet for Attachment 2.

Mark this box if this attachment is empty because the project is exempt from PDP hydromodification management requirements.

Indicate which Items are Included behind this cover sheet:

Attachment
Sequence
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




Attachment 2A:

Hydromodification Management Exhibit
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 7/20/2021
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)

NO CURB OPTIONNOTES:
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OR/flC£S

PERMANENT WATER QUALITY

TREATMENT FACILITY
0/MIEllR Mlf'flrl,f£A8t£
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WATER QUALITY SIGN- PLACED AT

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NOTE: ALL BIOFILTRATION AREAS WILL

HAVE A SIGN POSTED TO BE
VISIBLE AT ALL TIMES.
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6" PVC PIPE PERFORATION

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NO!F: ALL CATCH BASINS HflH CRA!ES SHALL
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• lHERE ARE NO NAlVRAL HYOROI.OC/C fEAlVRES ON lHE
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PLIBL/C STORA/ DRAIN S/'SlD,I LOCA1EO IN lHE SOLllH
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• BASED ON WA!ERSHEO l,IAPP/NC OF P07EN11AL CR/11CAL
COARSE SElJIAIENT YIELO AREAS (XSYA) lHERE ARE NO
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lR/BLllARY TO lHE RLINOfF BW'ASSEO AROI.INO lHE SITE
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CUTOFF WALL AT
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MATERIAL AND

COMPACTION PER
PROJ::CT PLANS AND

SPECIFICATIONS

AMENDED SOIL
6" SCARIFIED SOIL
30 MIL

PLASTIC
LINER

1. REFER TO GS-2.00 FOR ALL DETAILS NOT SHOWN HERE.

2. CURB CUT WIDTH PER DESIGN PLANS.

MATERIAL

AND COMPACTION

PER PROJECT

PLANS AND

SPECIFICATIONS

THICKENED

SIDEWALK W/

EDGE TREATMENT
3" SHREDDED HARDWOOD

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PER DESIGN PLANS

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S£ClltW B-B

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SOUTH PACIFIC STREET
HYOROMOOIFICA 1/0N

MANAGEMENT EXHIBIT
Attachment 2B:

Management of Critical Coarse Sediment Yield Areas
City of San Marcos PDP SWQMP Template Date: March 15, 2016 PDP SWQMP Preparation Date: 2/24/2022
No Potential Critical Coarse Sediment Yield areas nearby that will influence the project.

Potential Critical Coarse Sediment
Proposed Project
Proposed Project
Attachment 2C:

Geomorphic Assessment of Receiving Channels

CITY OF SAN MARCOS
FINAL December 15, 2011
San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

Final December 15, 2011

TABLE OF CONTENTS
Page

STORMWATER PROGRAM MANAGER APPROVAL OF MASTER WQTR ............. i-ii

OBJECTIVES OF MASTER WATER QUALITY AND HYDROMODIFICATION MANAGEMENT PLAN (MASTER WQ/HMP MANAGEMENT PLAN .......................... iii

1.0 PROJECT DESCRIPT ION & PHASING............................................................ 1-1

1.1 San Marcos Creek Specific Plan ............................................................ 1-1 Figure: San Marcos Creek Project Vicinity .......................................... F1-1

1.2 Alternative Assessment For Order R9 2007-0001 Compliance .............. 1-3

1.3 Project Planning ..................................................................................... 1-3 Figure: San Marcos Creek Project Vicinity Future Land Use ................ F1-2 Figure: San Marcos Creek Projec t Vicinity Land Use (2009 SANDAG Designatio ns ......................................................................................... F1-3 Figure: San Marcos Creek Impr ovements Alternative 7 ...................... F1-4

2.0 EXISTING CO NDITIONS .................................................................................. 2-1

2.1 Watershed .............................................................................................. 2-1

2.2 303(d) Listings for San Marc os Creek/Lake San Marcos ....................... 2-1 Table 2-1 2010 303(d) Listings for San Marcos Creek/ Lake San Marcos 2-1
Table 2-2 Basin Plan Inland Surfac e Waters Beneficial Uses For San Marcos Creek/Lak e San Marcos ............................................................ 2-2 Figure: San Marcos Creek Specific Plan HAS Map .............................. F2-1 Figure: Lake San Marcos Area ........................................................................ F2-2

2.3 Existing Treatment Controls In Specific Plan Area ................................. 2-5 Figure: San Marcos Creek Vicinity Existing MS4 System/Water Quality ~~
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

Final December 15, 2011
BMP's Marc os ...................................................................................... F2-3 Table 2-3 Estimated Existing Land Use Pollutant Concentrations .......... 2-7

2.4 SWAMP Assessments in San Marcos Creek ......................................... 2-8 Table 2-4 Summary of SWAMP 2002/2007 Physical Habitat
Assessment for San Marcos Creek in Specific Plan Area ........................................ 2-8

2.5 Existing Water Quality in Specific Plan Area .......................................... 2-9 Figure: San Marcos Creek Monitoring Stations .................................... F2-4

3.0 WATER QUALITY / HYDROM ODIFICATION COMPLIANCE
REQUIREMENTS ............................................................................................. 3-1

3.1 Drainage Managem ent Areas ................................................................. 3-1 Figure 3-1 DMA Areas ............................................................................ 3-2

3.2 Hydromodificati on Assessment .............................................................. 3-3

3.3 Hydromodification Criteria Used For Specific Plan Analysis ................... 3-4

3.4 San Marcos Creek Channel Susceptability Analysis .............................. 3-6

3.5 Summary of Chang and Consulta nts June 2011 HMP/Water Quality Analysis .................................................................................................. 3-6 Figure 3-2 Proposed IBI and DMA Locatoi ns ......................................... 3-7

3.6 Hydromodification Facility Sizing ............................................................ 3-8 Table 3-1 Bioretention Basin Si zing to Treat Public Areas ..................... 3-9 Table 3-2 Bioretention Basin Sizing to Treat All Areas (100% of Public and 100% of Pr ivate) ............................................................................ 3-10

3.7 Conclusion ............................................................................................ 3-11

4.0 WATER QUALITY POLLUTANT RE MOVAL EFFECTIVENESS .................... 4-12

4.1 Study Fi ndings ...................................................................................... 4-12 Table 4-1 Bioretention Polluta nt Removal Effectiveness ...................... 4-12 Table 4-2 Comparison Between Existing and Proposed Pollutant Concentrations-With Treatment (B ioretention) for Entire Study Area ...................................................................................................... 4-13 ~~
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

iii

Final December 15, 2011

Table 4-3 Percent Difference Between Existing and Pr oposed Pollutant Concentrations- With Treatment (Bioretention) by Drainage Management Ar ea ................................................................................ 4-14 Table 4-4 Comparison Between Ex isting, Proposed with Treatment, and Literature Pollutant Concentra tions For Entire Study Area ............ 4-15 Table 4-5 Comparison Between Ex isting, Proposed with Treatment, and Literature Pollutant Concentrations by Drainage Management Area ...................................................................................................... 4-16

4.2 Larry Walker and Associat es Independent Validation .......................... 4-16

4.3 Las Posas/San Marcos Creek Restoration Expected Water Quality Benefits ................................................................................................ 4-17

4.4 Recommended Fiel d Validation ............................................................ 4-17

4.5 Conclusions
.......................................................................................... 4-18

5.0 PRIVATE DEVELOPMEN T REQUIREMENTS ................................................. 5-1

5.1 Model Block Development ...................................................................... 5-1

5.2 Basic Guidelines For Model Bloc k Private Development For Permit Compli ance ............................................................................................ 5-1

5.3 Temporary Water Quality Impac ts (Construction/Biological) .................. 5-3

APPENDICES
A. Preliminary Water Q uality Treatment Analysis
B. Water Quality/HMP Analysis
C. Water Quality/HMP Calculation Summary
D. Water Quality Uptake of Restoration Projects
E. Existing Water Quality Baseline Data

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Administration
1 Civic Center Drive
San Marcos, CA 92069-2918
December 15, 2011
Mike Porter
San Diego Regional Water Quality Control Board
917 4 Sky Park Court, Suite 100
San Diego, CA. 92123-4340
Tel: 760.744.1050
Fax: 760.744.9520
Web: www.San-Marcos.net
Re: WQTR 401 Permit Condition for City of San Marcos - San Marcos Creek Specific Plan - City of San Marcos Stormwater Program Manager Letter Confirmation of Final Master Water Quality and Hydromodification Management Plan (Final Master WQTR Dated December 15, 2011) Meets Local SUSMP Requirements
Dear Mr. Porter:

This letter serves to confirm to the San Diego Regional Water Quality Control Board in the determination that the subject project will comply with certain 401 Certification conditions requiring priority development projects to confirm that their project design meets local SUSMP requirements.

The adopted San Marcos Creek Specific Plan and the Final Master WQTR dated December 15, 2011 are framework plans for guiding development in a 135-acre specific plan area. A Final Master Water Quality and Hydromodification Management Plan (Master WQTR) has been completed to guide development and ensure that hydromodification (HMP) effects and Water Quality Requirements can be met under Order R9 2007-0001 at a master plan level and project specific level.

The Final Master WQTR has provided a technical assessment of permit compliance for meeting water quality and HMP requirements for 100 percent of the public facilities and a minimum percentage of private development in shared bioretention facilities in the Promenade. Private development will be required to implement LID and other water quality/HMP facilities for any remainder treatment required onsite.

In addition, the Final Master WQTR includes recommendations for monitoring the efficacy of the BMP effectiveness as part of a 401 permit conditions as requested.

The City is attaching the Final Master Water Quality Technical Report (WQTR) to this letter. By way of my signature below and my signature on each individual development project Water Quality Improvement Plans (WQIPs) in the Specific Plan Area, I certify that the both the attached Final Master WQTR and each individual development project in the Specific Plan Area meets the following Local SUSMP Requirements of the City of San Marcos and that the measures being taken are protective of water quality:
• 85th percentile capture of the 24 hour storm;
• LID Requirements;
• Site Design Requirements;
• Source Control Requirements; and
• Hydromodification Requirements
Any revisions made hereafter will continue to comply with the local SUSMP requirements and will not result in any decreases in water quality treatment or capacity. This Final Master WQTR is signed by way of this letter by the City of San Marcos Stormwater Program Manager and provided to the San Diego Water Board to fulfill the condition of the 401 Certification for this project.

Erica Ryan
Stormwater Program Manager
City of San Marcos
FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

Final December 15, 2011
Objectives of Master Water Qu ality and Hydromodification Management Plan (Master WQ/HMP Management Plan)

This Master WQ/HMP Management Plan for t he San Marcos Creek Specific Plan is intended to:

1. Provide a master management plan fo r water quality and hydromodification facilities within the specific plan development area;

2. Meet the Municipal Sto rmwater Permit Requirements for development in the San Diego Regional Wate r Quality Control Boar d (SDRWQCB) Order R9 2007-0001 (Permit) for water quality and hydromodification (HMP) development requirements as of January 14, 2011;

3. Implement shared and managed water qua lity and HMP facilities for each of the eight designated drainage management areas (DMAs);

4. Identify the required surface storage bioretention capacity in each of the eight DMA WQ/HMP facilities to adequately treat urban runoff and retain and release the natural rainfall rate for all public facilities and a designated portion of private development;

5. Identify a framework to be implemented and submitted annually with the 401 permit Mitigation and Monitoring Reporting Program (MMRP) to:
a. Ensure achievement of antici pated pollutant removal rates by treatment controls to implement a net reduction of current urban runoff load to water bodies downstream (S an Marcos Creek, Lake San Marcos, Batiquitos Lagoon, and the Pacific Ocean);
b. Ensure HMP capacity is adequate for each DMA;
c. Ensure improving IBI/BMI scores over time; and
d. Ensure water quality improvement over time in San Marcos Creek. e. Coordinate with required annual biological MMRP reporting requirements.
f. Provide baseline framework for 401 certification compliance.

6. Identify a consistent application of water quality treat ment design, review and construction implementation for private development projects; In addition to ensuring consistency in t he application of WQ/H MP within a private development project located in the San Marcos Creek Specific Plan area, the Master WQ/HMP Management Plan also ensures that the Specific Plan area functions within ongoing watershed planning so that eac h project takes into consideration its ~~
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

vii

Final December 15, 2011
role within the Specific Plan area as well as within the SAN MARCOS Creek watershed.
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

1-1

Final December 15, 2011

1.0 PROJECT DESCRIPTION AND PHASING

1.1 SAN MARCOS CREEK SPECIFIC PLAN

Figure 1-1 shows the project location in the City of San Marcos. The San Marcos Creek adopted Specific Plan represents an effort to create a managed planning framework for future growth and redev elopment of the approximately 214-acre area along San Marcos Creek in central San Marcos between Discovery Street and SR 78. Approximately 124 acres are proposed for development.

The overall goals of the Specific Plan are to:

1. Create a smart growth downtown area which is currently absent in San Marcos; and

2. Restore San Marcos Creek/Las Posas Creek in the Specific Plan Area.

The Specific Plan provides a comprehensive vision for a creekside district along with goals, policies and development standards to guide future public and private actions relating to the area’s development and conservation of open space and natural resources. The Spec ific Plan also serves as the mechanism for insuring that future development wi ll be coordinated and occur in an order ly and well- planned manner. The vision for the Specif ic Plan area is a generally more urbanized feel.

The proposed land-use is a sm art growth based mixed-use commercial core and “downtown” for San Marcos. The proposed Specific Plan land-uses will balance retail and entertainment uses with a mix of residential, office, and service uses to neighborhoods with both active and passi ve elements. The proposed land-use within the Specific Plan consists of the following:
 Streets: 42.6 acres
 Mixed-Use: 75.6 acres
 Improved Parks: 17.3 acres
Subtotal Development Area: 135.54 acres
 Natural Open-Space:78.5 acres
Total Area: 214.00 acres
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

1-2

Final December 15, 2011
Figure 1-1 Vicinity Map
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San Marcos Creek
Project Vicinity
~ San Marcos Creek
0 Lakes
D San Marcos Creek Specific Plan Arc.i
• - - Discovery Street ROW 1, ___ ~ (lnduded in mnster WQTR analysis) D San Marcos City Limits
Source of Data: SanGIS, 07/10 and City of
San Marcos, 2/11
Created By: City of San Marcos GIS
Every effort has been made to assure the accuracy of
the maps and data provided: however, some information
may not be accurate or current The City of San Marcos
assumes no responsibility arising from use of this
Information and incorporates by rererence its disclaimer regarding the lack of any warranties, 'Nhether expressed or implied, concerning the use of the same. For
additional information see the Disclaimer on the City's website.

FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

1-3

Final December 15, 2011

1.2 ALTERNATIVE ASSESSMENT FOR ORDER R9 2007-0001 COMPLIANCE

The proposed project used as the basis fo r the assessment and development of the Master WQ/HMP Management Plan is the City’s preferred Alternative 7 to be consistent with the Army Corps of Engi neers 404(b) analysis and the selected LEDPA for the project. Alternative 7 was evaluated for compliance with the January 14, 2011 Order R9 2007-0001 requirements.

Figure 1-2 shows the current Alternative 7 concept plan developed by WRT in September 2011. Figure 1 was used as t he basis by Mikhail Ogawa Engineering (MOE) and Wayne Chang Consul tants for the Water Qua lity and HMP Order R9 2007-0001 compliance assessments
Other alternatives developed by the City, including Alternatives 1-6, 8, 8a, and 9, were also assessed for Order R9 2007- 0001 water quality and hydromodification compliance. All other alternatives we re found to be permi t compliant or the development footprints were adjusted to accommodate required bioretention acreages for water quality and hydromodification.

1.3 P

ROJECT PHASING

The project will be constructed in two primary phases:

Phase I - Near Term (by 2014): By 2014, the City plans to have constructed and placed into operat ion the promenade, the shared bioretention water quality and hydromodification facilities located in the promenade, restoration of San Marcos Creek and Las Posas Creek, floodwall improvements, primary utility infrastructure, and critical circulation element improvements in the Specific Plan Area.

It is important to note that by 2014 immediate water quality and hydromodification benefits to San Marcos Creek and Lake San Marcos would occur due to:

o The restoration of San Marcos Creek and Las Posas Creek into balanced creek systems within a key location within the subwatershed; and

o The immediate implementatio n and operation of the shared bioretention facilities in the promenade in advance of any ~~
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

1-4

Final December 15, 2011
development anticipated over the estimated long term buildout of the specific plan area.

Phase II – Long Term (20 Year Estimated Buildout): Private development of the specific plan area (predominately mixed use areas) is required by the specific plan to be developed in model blocks to ensure development consistency. It is anticipated that buildout of the remainder of the Specific Plan Area would occur based primarily on economic factors over a 20 year time frame.
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

1-5

Final December 15, 2011
Figure 1-2 September 2011 Alternative 7, WRT
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NATURAL OPEN SPACE
w N >
~ ~ ~
~ ~ ---~- ~ - - ~ , , - ---,z_
~ _ > . SAN MARCOS Bl:':'_
7 "' - ,r--c; :,;;')· [~ ~---~ - - >~~~~~-~ ~~,. ~ 1
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PARK LAND WATER QUALITY
I 1:
\ -\-~- ~~~4 ~~~9~~4P~77/ , --::: ;:- ; _-:, •1 ,r --
1 ! ; _ ~ f,;;::;: 1[ / ,; _;. . .:--:)L /_--: ~
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I
,~= ~7

AT-GRADE STREET AND FLOODWALL

PARK LAND PARK LAND

SAN MARCOS CREEK IMPROVEMENTS
ALTERNATIVE 7: REALIGNMENT OF LAS POSAS CREEK, DEVELOPMENT REDUCTION

BETWEEN MCMAHR AND VIA VERA CRUZ ,AT-GRADE DISCOVERY STREET WITH FLOODWALL,

ELIMINATION OF CHANNEL EXCAVATION WEST OF VIA VERA CRUZ, BRIDGE CROSSING AT BENT AVENUE LEGEND
[Z::2j PADS

ROADWAYS

PARK LAND

ARMY CORPS

JURISDICTIONAL AREA
September 12, 2011 / WRT
~

ADOPTED PLAN
ALT. 7 PLAN

DIFFERENCE

LAND USE COMPARISON

NEW DEVELOPMENT AREA RETAIL OFFICE
(AC) (SF) (SF)

81.30 1,284,703 598,205
75,55 1,193,841 555,897
-5,75 -90,862 -42,308

RESIDENTIAL PARK
(UNIT} (AC)
---------
AREA
(AC)
2,341 20,64 ROAD 14.76
2,175 16.45 PARK LAND 16.45 ,_
-1 66 -4,19 NATURAL OPEN SPACE 60.66
COMMERC IAL/RESIDENTIAL 75,55
TOTAL 167.42
SCALE: 1"=800 '
San Marcos Creek
Project Vicinity
Future Land Use
'"'-' San Marcos Creek
0 Lakes
LJ Parcels
(:J San Marcos Cr<:'Ck Specific Plan Arca
r; -.- Discovery Stre et ROW
J __ ] {Included in master WQTR. analys is)
c:J San Marcos City limits
Source of Data: WRT. 07/07, SanG IS, 07/11,
and City of San Marcos , 2/11
Created By: City of San Marcos GIS
Every effort has been made to assure the accuracy of
the maps and data provided; however , some information
may not be accurate or current. The City of San Marcos
assumes no responsibility arising from use of this
information and Incorporates by reference its disclaimer regarding the lack ot any warranties, wtiether·expressed or implied, concerning the use of the same. For
additional information see the Disclaimer on the City's i,vebsite.

Cumn\em~J.mdOfflo.•
li.xtrilctivr. Industry
1111 Tra,\Sport.:ition, Communk.1ti on$. Utilities:
l;ducolti1,m
h~tltut.Jora
M i\11..lry

L'ARKS AND RECREATIO N
Rt.'l;'re2tlon
Open Sp,,« Parb

ACRJCULTURE
Inte11slvc-Agriculture
F.:w.teru.iv~ Agrfrultul'I!

UNDEVELO PED
r
San Marcos Creek
Project Vicinity Land Use
(2009 SANDAG Designations)
I""""-..., San Marcos Creek
0 Lakes
CJ Parcels
D San Marcos Creek Specific Plan Area
- - . Discovery Street ROW
f .. _ a (Included in master WQTR analysis)
D San Marcos City Limits
Source of Data: SANDAG, 10/09, SanGIS, 07/11,
and City of San Marcos, 2111
Created By: Clty of San Marcos GIS
Every effort has been made to assure the accuracy of
the maps and data provided; however, some information
may not be accurate or current The City of San Marcos
assumes no responsibility arising from use of this
information and incorporates by reference its disclaimer regarding the lack of any warranties, 'Mhether expressed or implied, concerning the use of the same. For
additional information see the Disclaimer on the City's website.

FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

2-1

Final December 15, 2011

2.0 EXISTING CONDITIONS

2.1 WATERSHED
Figure 2-1 shows that the San Marcos Creek S pecific Plan area is located in the Upper San Marcos Creek (USMC) Watershed of the Carlsbad Hydrographic Unit (HU 904). The USMC Watershed is appr oximately 29 square miles and is comprised of two sub-watersheds. The primary water bodies in the USMC watershed are Upper San Marcos Creek and Lake San Marcos. The Specific Plan Area discharges into both the San Marcos Creek above Lake San Marcos, Lake San Marcos, and ultimately to the Batiquitos Lagoon and Pacific Ocean.

The Specific Plan Area is located in the Richland HSA (HSA 904.52) which comprises the lower portion of the USMC Watershed, and comprises 69% of the total land area of the USMC Waters hed or 12, 863 acres. The proposed development area of the Specific Pl an area is approxim ately 1.0% (135 developed acres) of the total area of the Richland HSA.

2.2 303(

D) LISTINGS AND TMDLS
Table 2-1 summarizes current water quality impairments in San Marcos Creek and Lake San Marcos as identified on the current State of California’s 303(d) List of Impaired Water Body Segments. Table 2-2 lists the beneficial uses of San Marcos Creek, Lake San Marcos, and unna med intermittent streams that are established in the Water Quality Contro l Plan for the San Die go Basin (Basin Plan).

Table 2-1
2010 303(d) Listings for San Marcos Creek/Lake San Marcos 303(d) Listed Water Body 2010
San Marcos Creek DDE, phosphorous,
selenium, sediment toxicity
Lake San Marcos Ammonia as N, Nutrients,

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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

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Final December 15, 2011
Table 2-2
Basin Plan Inland Surface Waters
Beneficial Uses for San Marcos Creek/Lake San Marcos
Water Body Beneficial Uses
San Marcos Creek/Lake San Marcos (904.52 - Richland) MUN (excepted), AGR, REC1, REC2, WARM, WILD

There are two TMDLs in place or underwa y in the Speciic Plan Area. Currently the San Marcos HA is under the Bacteria I TMDL (adopted 2010) with designated load allocations. This TMDL is applicable to the entire San Marcos HA including the Specific Plan area. The City of San Ma rcos is participating in the Bacteria I TMDL. The Lead Agency for this effort is the City of Encinitas.

The Upper San Marcos Creek is also und er a Voluntary Nutrient TMDL which commenced in June 2011. Load allocations have not yet been identified. The City of San Marcos is t he lead agency for the Upper San Marcos Voluntary Nutrient TMDL (See Figure 2-2). The City of San Marcos is also the designated lead in the USMC Watershed Nutrient Management Plan effort.

The Specific Plan Area is just upstream of Lake San Marcos and must consider as the primary pollutants of concern the reduction of bacteria, phosphorous, nitrogen, selenium and other metals, and sediments into the Creek and Lake.

DDE has been in use for dec ades and is attached to soil particulates. Regulatory bans and phase outs on the us e of DDE pesticides over the last several years will take into effect along with increased soil stabilization practices. DDE derivatives are no longer commercially available and the concentrations are anticipated to reduce over time coupled with appropria te best management practices from existing development, proposed development and soil stabilization practices required during construction.

The Specific Plan Area is located in a key point in the USMC watershed.

Because the Specifc Plan Area is located at the western most part of the USMC where drainage areas from t he Richland and Twin Oaks Valley HSA converge, it is poised to provide a significant net positive change to water quality through two primary objectives of the Specific Plan and the this Master WQ/HMP Management Plan:

1. Restoration and Enhancement to a balanced creek system of Las Posas Creek and San Marcos Creek; and

2. Implementation by a pproximately 2014 of shared hydromodification and water quality bioretention facilities in the promenade.

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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

2-3

Final December 15, 2011
Figure 2-1 Watershed Map

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Evt-,y dfo,t NI~ b~n made 14) assur11 I.hf am,ncy ol
t}wm,JK lllldih:.a provlded;h~ somt inf.;,nT1•U0t1
m:ay flOI bt .-ttur.1lr o,- CVrf'tnL The Oty o( ~n :\~"1"('()9. fiS\l ma no =ponRbiility u 1smg from uM of th.is
wom,arlon :and lfw;:orpor•"'~ by ,..,.,...,....,,;i.. di"'l~ilm't f'tgnding the lid ot :any watnnDCS, whcll'ter oprHSN
Of Implied,. C'Ollotming the-u w o( the~- For
~i6on.1l W'onn.1tl1J11 M't' tM' O~iMCr Ofl the C,tv:.
w.!b,i!~ . •
San Marcos Creek Specific Plan
HSAMAP
-- Freeway or Highway
-- Major Road
B Lakes and Reservoirs
~ Important Streams
"'-....,. Other Streams
c:J San Marcos City Limits
D Other Cities
GJ San Marcos Creek Specific Plan Area
RWQCB Hydrologic Sub-Units
(J 1.000 2,000 .i.ooo
H H E---3~
CR£ATED8~ Oty1Jf~ ~,.,ru, CIS
SOt:RCESOF DATA: ~IS, 10/09;
CityotS...~&JWt,2!1l l
FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

2-4

Final December 15, 2011

Figure 2-2 USMC Management Plan and Voluntary Nutrient TMDL Area ~~
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Master Water Quality and Hydromodification
Management Plan

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Final December 15, 2011

2.3 EXISTING TREATMENT CONTROLS IN SPECIFIC PLAN AREA
The Study Area consists of 135.5
acres on the north and south side of
San Marcos Creek between Grand
Avenue and Discovery Street in the
City of San Marcos (See Figure 1-
1). Existing development is
generally located closer to San
Marcos Boulevard.

Existing development in the area
between Grand Avenue and McM ahr Road consists prim arily of commercial and legal nonconforming industrial uses, includ ing neighborhood “strip” retail centers, two gas stations, a lumberyard, three stor age facilities, a construction material storage yard, auto services, a bowling alley, office uses, and a fast food restaurant (San Marcos Creek Specific Plan, 2007). Additionally, there are several residential uses in the study area.

The existing land-use acreages within the Study Area consist of the following:
 Streets 12.65 ac
 Commercial Acreage: 28.02 ac
 Industrial Acreage: 17.57 ac
 Residential Acreage: 12.66 ac
 Vacant Acreage: 64.4 ac

Figure 2-3 shows that there are no treatment controls or hydromodification facilities in the specific plan area. All treatment controls implemented since 2001 are located outside of t he Specific Plan Area and consist predominately of filters installed during t he 2001 Municipal Stormwater Permit cycle which have since been established as a last resort treatment control and not as effective as infiltration and/ or bioretention facilities.

Table 2-3 represents existing water qu ality conditions within the Specific Plan area under existi ng land use conditions (See Appendix A, MOE 2011). Without water quality treatment in the proposed Specific Plan Area, th e pollutant concentrations estimated in Table 2- 3 would continue for 1 - bacteria (fec al coliform), 2-oil and grease, 3- sediment (TSS), 4- nutrients (NH3, No2+NO3, Nitrogen Total Kjeldahl, phosphorous (Total), and 5 – metals (Cd, Cu,Pb, Ni, Zn).

c;
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

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Final December 15, 2011
Figure 2‐3 Existing Treatment Controls in SP Area
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San Marcos Creek Vicinity
Existing MS4 System I
Water Quality BMPs
I} BMP
/'../ Brow Ditch
'-✓ Channel wider th(ln 5 ft
Ditch less than 5 ft wide
Storm Mains
Detention B.1sins
0 Lakes
CJ S;m M.>rcos Crt>ek Specific Plan Arc.>
CJ San Marcos City Limits
Source of Data: SanGIS, 07110 and City of
San Marcos, 2/11
Created By: City of San Marcos GIS
Every effort has been made to assure the accuracy of
the maps and data provided; how-ever, some Information
may not be accurate or current The City of San Marcos
I assumes no responsibility arising from use of this
; information and incorporates by reference Its disclalmer : regarding the lack of any warranties, whether expressed I
Of implied, concerning the use of the same. For
addit[onal informat ion see the Dlsclaimer on the City's webs ite.

FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

2-7

Final December 15, 2011

Table 2-3
Estimated Existing Land Use Pollutant Concentrations

Constituent Units
Estimated Existing
Concentrations of
Pollutants in
Specific Plan Area
TSS (mg/L) 90.07
COD (mg/L) 109.59
Fecal Coliform (mpn/100 mL) 4,962.7
NH3 (mg/L) 0.73
NO2+NO3 (mg/L) 0.74
Nitrogen, Total Kjeldahl (mg/L) 1.71
Phosphorous, Total (mg/L) 0.45
Cd, Total (ug/L) 0.84
Cu, Total (ug/L) 21.77
Pb, Total (ug/L) 29.66
Ni, Total (ug/L) 7.63
Zn, Total (ug/L) 190.74
Oil and Grease (mg/L) 2.57

The estimated existing pollutant concent rations were calculated using land use types from the National Stormwater Quality Database EPA rainfall Zone 6 (see Appendix A, MOE Preliminary Water Quality Treatment Analysis, July 2011) . .... .... .... --~ -.. .. __
FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

2-8

Final December 15, 2011

2.4 2002/2007 SWAMP ASSESSMENTS IN SAN MARCOS CREEK
In 2002 and 2007, the Stormwater Ambi ent Monitoring Program (SWAMP) conducted a physical habitat as sessment in the San Marcos Creek in just south of McMahr (see results for 2002/2007 SWAMP 904CBSAM3). The SWAMP assessment compared physical habitat component ranges for 10 physical habitat components. Numeric ratings from 0 ( poor rating - heavily impacted habitat) to 20 (best rating - unimpacted habitat) were given to each component. The ability of a creek to perform natural water qual ity functions and its susceptability to hydromodification are inherent in the physical habitat components. In general, the concept is that a bal anced physical stream system provides the maximum water quality benefit and resistance to hydromodification. Table 2-4 summarizes the individual physical habitat ratings for San Marcos Creek in the Specific Plan area and provides a generalized assessment of those features that relate most to water quality and those physical habitat features that relate most to hydromodification. The 2002 SWAMP mean rating for San Marcos Creek was

11.5 based on all component s and was rated a moderat ely altered habitat ( greater than 10). Good bank stability is achieved for scores over 15.

Table 2-4
Summary of SWAMP 2002/2007 Physical Habitat Assessment for San Marcos Creek in Specific Plan Area
Physical Habitat
Component
Description
Score Generalized
WQ or HMP
Component
of Natural
Creek
System
Epifaunal Cover 11 WQ
Embeddedness 2 WQ
Velocity Depth Regime 11 HMP/WQ
Sediment Deposition 20 HMP/WQ
Channel Flow 19 HMP/WQ
Channel Alteration 2 WQ
Riffle Frequency 6 WQ
Bank Stability 20 HMP
Vegetation Protection 18 HMP/WQ
Riparian Zone 6 WQ
Source: 2002 and 2007 SWAMP Reports on the Carlsbad Hydrologic Unit The overall summary rating for San Marc os Creek in the Specific Plan Area was rated poor based on three ecological health indicators. Water Chemistry (High severity of impact; 6+ exceedences of aquatic life), Toxicity (Low severity of Impact; Frequency of toxicity between 0. 0 and 0.1) and Bi oassessment (High ~~
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Master Water Quality and Hydromodification
Management Plan

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Final December 15, 2011
Severity of impact, IBI score between 0 and 40). This result was also identified for two locations assessed from 1998 through 2002 and included in the SDRWQCB 2002 Biological Assessment Repor t where site IDs 44 and 46 ( one near McMahr and one near Rancho Santa Fe Road) al so had poor IBI scores (both between 10 and 45) and BMI (bio assessment metrics and benthic macroinvertebrate) assessments which supported the poor rating.

The San Marcos Creek in t he Specific Plan Area, while it has relatively stable banks, is in effect not a balanced stream system and is currently functioning at a substantially diminished capacity to naturally uptake water quality constituents.

DUDEK and associates c onfirmed during focused biological resource assessments for the Specific Plan proposed corridor of restoration for Las Posas Creek and San Marcos Creek that of the estimated 43.54 acres of existing wetlands, that roughly 35 acres (90%) were disturbed wetlands with inclusions of between 20% to 100% weeds. Undistur bed wetlands (wetlands with less than 20% weeds) comprised only 8.61 acres (10%) of the natural creek systems in the specific plan area.

2.5 EXISTING WATER QUALITY IN SPECIFIC PLAN AREA

Figure 2-4 shows ongoing water quality mo nitoring stations that are conducted annually in the specific plan area for two purposes:
MS4 dry weather monitoring; and
Upper San Marcos Creek Nutri ent Management Plan and Voluntary Nutrient TMDL data gathering efforts.

There are currently five monitoring stations in the Specific Pl an Area. Like the rest of the Calrsbad Watershed and County -wide, urban runoff for nutrients and bacteria are above the Basin Plan Water Q uality Objectives and generally below the Order R9 2007-0001 actionable levels.

Data gathered from these monitoring st ations will be used to identify existing baseline water quality for the specific plan area.

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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

2-10

Final December 15, 2011
Figure 2-4 Existing Water Quality Moni toring Stations in Specific Plan Area
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San Marcos Creek
Monitoring Stations
• Mass Loading (TWAS) Site
Q Dry Weather Sites
Q Lake San Marcos Quarterly Monitoring Siles
~ San Marco.s Creek
[;) Lakes
CJ San Marcos Creek Specific Pl.In Areil
- - - Discovery Street ROW
1 _ --~ (Jnd uded in master WQTR analysis)
CJ San Marcos City Limits
Source of Data: SanGIS , 07/10 and City of
San Marcos, 7/11
Created By: City of San Marcos GIS
Eve,y effort has been made to assure the accuracy of
the maps and data provided: however , some information
may not be accurate or current. The City of San Marcos
assumes no responsibility arising from use of this
information and incorporates by reference its disclaimer regarding the lack of any warranties , whethe r expressed or impl1ed, concerning the use of lhe same. For
additiona l informa tion see the Disclaimer on the City's website.

FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

3-1

Final December 15, 2011

3.0 WATER QUALITY/HYDROMODIFICATION COMPLIANCE

REQUIREMENTS

3.1 DRAINAGE MANAGEMENT AREAS

Specific Plan DMA Concept

The Specific Plan area wa s divided into a total of eight Drainage Management Areas (DMAs) with correspo nding discharge points. Each of these eight DMAs was designated to share common hydrology and be constructed with backbone drainage systems in Phase I to correspond to function both individually and collectively in the sp ecific plan area. (See Figure 3-1). It is intended that each DMA wi ll have its own distinct water quality treatment and hydromodification facilities to address runoff and pollutants generated by all of the public streets and a designated portion of the private development land us es in each DMA. Each DMA in the Specific Plan area will be construct ed with a shared water quality and HMP bioretention facility sized to meet the approved HMP plan adopted by the SDRWQCB and treat the 2-year storm fo r water quality required under the March 25, 2010 SU SMP requirements. The concept of shared facilities for a master plan area is allowed in the permit and is in fact preferred by the SDRWQCB. The City of San Marcos discussed the DMA approach and shared facility management approach for permit compliance with the SDRWQCB and gained concept ual approval as an acceptable approach to permit compliance.

DMA1DMA2 DMA3DMA4DMA5DMA6 DMA 7
DMA8
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

3-2

Final December 15, 2011
Figure 3-1 DMA areas wayne chang
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GRAPHIC SCALE
0 250 500
~
INCH = 500 FEET
t:mIE;_

DMA'S ARE BASED ON THE
ALTERNATIVE 7 SITE PLAN.

DRAINAGE
L
'y
L
1 ~
'fl
(/)
<t, ca
:i:.
~ ';.
~
(II
srMa.QL. DEVELOPMENT
c=J MIXED-USE
- MIXED-USE
c=J PAVING
c=J PAVING
\ i
c=J PARKING AISLE PAVING
~ PARKING AISLE PAVING
c=J LANDSCAPING
- LANDSCAPING

SUBAREA BOUNDARY

EXISTING FIELD

CONDITION

PERVIOUS AREA

IMPERVIOUS AREA

PERVIOUS AREA

IMPERVIOUS AREA

PERVIOUS AREA

IMPERVIOUS AREA

PERVIOUS AREA

IMPERVIOUS AREA
Poe a POINT oF coNc ENTRATioN FOR suBAREA

MANAGEMENT AREAS
FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

3-3

Final December 15, 2011
Shared facilities for public and priv ate development for each of the DMAs ensures that water quality and HMP facilities and requirements are appropriately maintained and met by placing the shared facilities under a City managed community facilities district (CFD). The CFD will include monitoring and maintenance costs t hat will be required under the 401 permit for this project for water quality.

Compliance with the January 2011 Or der R9 2007-0001 permit is based on each of the DMAs meeting the r equired sizing for water quality treatment and HMP in the shared facilities in the promenade. In order to be in compliance with Order R9 2007-0001, each individual DMA must:

1. Meet permit compliance requirem ents at the designated discharge points for each DMA; and

2. The entire Specific Plan must meet permit compliance requirements in its entirety.

Water Quality/HMP Shared Facility Concept

In short, the DMAs function and meet expected permit compliance requirements independently from eac h other but also must collectively achieve permit compliance for the entire specific plan area.

3.2 HYDROMODIFICATION ASSESSMENT
Chang Consultants prepared a hydromodification and water quality facility analysis in accordance with the adopted City SUSMP and HMP plan approved by the SDRWQCB. The study identified the re quired bioretention facilities to meet --------------------
FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

3-4

Final December 15, 2011
HMP and water quality facilities for public and private shared facilities. Bio retention facilities were selected as t he permit required treatment control facility for DMAs 1-8 for the following reasons:

Pollutants of concern mu st be treated by a medi um pollutant efficiency removal rate or better;
Bioretention facilities provide the appropriate pollutant removal efficiency rate for metals (selenium), nutrients, and bacteria.

The analyses were performed to prov ide base numerics for permit compliance over the development life of the Specific Plan ar ea to ensure that permit compliance, water quality, and HMP effects were properly mitigated over the life of the project.

The City of San Marcos will construct hy dromodification facilities to serve 100 percent of their infrastruc ture improvements a portion of the facilitieswill have excess capacity allowing some treatment and HMP capacity for private development projects. In most cases, an in dividual developer wi ll be required to address their hydromodification needs as part of their project design and in accordance with this document and the current SUSMP requiremnts. Detailed hydromodification analyses must be prepar ed for each development project and submitted to the City for review and approval.

In addition, the percent capacity outlin ed for each DMA will be reported on an annual basis to the SDRWQCB under t he 401 permit MMRP process to ensure that permit compliance has been continually met.

The following is a summary of the analysis contained in Appendix A:

3.3 H

YDROMODIFICATION CRITERIA USED FOR SPECIFIC PLAN ANALYSIS

Hydromodification must be implemented to ensure that post -development peak flows and durations do not exceed pre- development peak fl ows and durations.

The SUSMP criteria are genera lly defined as follows (see Appendix A for a more detailed description of the criteria):

1. The post-project discharge rates and durations shall not deviate above the pre-project rates and durations by more than 10 percent over and more than 10 percent of the length of the flow duration curve. ~~
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Master Water Quality and Hydromodification
Management Plan

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Final December 15, 2011

2. For flow rates ranging from the lower flow threshold to Q5, the post-project peak flows shall not exceed pre-project peak flows.

3. Tables 7-1 through 7-5 in the HMP (See Appendix B ) were used for sizing factors for various preferred fa cilities including bioretention. The sizing factors will yield similar results as the County of San Diego’s BMP Sizing Calculator. Appendix A also has for the overall specific plan area. the results of the BMP sizing calculator

4. The sizing factor sele ction depends on the applicable lower flow threshold (0.1Q
2, 0.3Q2, or 0.5Q2).

5. SCWWRP’s Hydromodification Screeni ng Tool for Southern California was conducted for the San Marcos Creek in the Specific Plan Area (See Appendix B) and the analysis resulted in a 0.5Q
2 lower flow threshold.

6. The HMP analysis used a conservative approach to ensure that the water quality/ HMP bioretention facilities were conservatively sized. Assumptions included:

a. Type D soils for the ent ire Specific Plan area;
b. Building setbacks;
c. Proximity to the floodwall;
d. Backbone underground utility clearances;
e. Geotechnical information;
f. Groundwater levels in the promenade;
g. Specific Plan recreat ional requirements; and
h. Street right of way requirements.

Underground systems were evaluated; however, due to proximity to the floodwall and the high groundwater in the promenade area (5 feet to 10 feet below grade), vault systems were deemed infeasible at the preliminary assessment level. In addition, Order R9 2007-0001 specifies t hat infiltration methods must be considered first and foremost before going to non-infiltration methods. Therefore, all HMP and water quality facilities in the promenade are bioretention facilities. ~~
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

3-6

Final December 15, 2011

3.4 SAN MARCOS CREEK CHANNEL SUSCEPTABILITY ANALYSIS
A channel screening st udy has been performed for the pr oject and is included in Appendix B . The study determined that the receiving waterbody, San Marcos Creek, has a low susceptibility to erosi on. Consequently, t he hydromodification analyses are based on a 50 percent lower flow threshold, or .5 Q2. See Figure 3-2.

3.5 SUMMARY OF CHANG AND CONSULTANTS JUNE 2011 HMP/WATER

QUALITY ANALYSIS
Approach and Factors
The Alternative 7 Specific Plan area was subdivided into eight subareas for independent hydromodification analyses ( see Figure 3-1). Each subarea has a hydromodification point of compliance at its discharge point into San Marcos Creek. Seven subareas cover the primar y Specific Plan development area (mixed-use, streets, Prom enade, etc.) north of San Marcos Creek, while the eighth subarea covers the Discovery Str eet widening and park land south of San Marcos Creek (see Figure 3-1).

The DMA’s define indivi dual areas of mixed-us e development, paving, and landscaping.

The proposed mixed-use development wa s assumed to contain 85 percent impervious surfaces and 15 percent pervi ous surfaces. The proposed streets consist of standard (asphalt or concrete) paved surfaces in the travel lanes as well as in the diagonal parking areas and in the widened parallel parking aisles.

Figure 3-1 delineates the post-project mixed-use, paving, and landscaping DMA’s within each subarea. Under pre- project condition s, development (commercial, retail, industrial, streets, etc.) exists in po rtions of the Specific Plan area.

The pre-project developed areas were del ineated in a general manner using aerial photographs, topographic mapping, and a field investigation. The pre- project developed areas were assumed to contain 90 percent impervious surfaces and 10 percent pervious surf aces based on the document review and field investigation. Each DMA categor y was further refined to reflect areas supporting pre-project development (90 percent impervious area) or with no pre- project development (pervious area).
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Final December 15, 2011
Figure 3-2 – Proposed IBI and DMA Locations
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kj Site-Specific HMP Channel Susceptibility Assessment = Low Discovery
Lake
San Marcos Creek
San Marcos Creek
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Mcmahr Rd
Mcmahr Rd
M
cm
ahr Rd
!(1
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4 !(
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7 !(
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S Rancho Santa Fe Rd
W San Marcos Blvd
W San Marcos Blvd
S Pacific St
Grand Ave
Discovery St
Grand Ave Knoll Rd
Discovery St
La Mirada Dr
Craven Rd
S Bent Ave
S Las Posas Rd
S Las Posas Rd
Via Vera Cruz
S Pacific St
S Pacific St
Via Vera Cruz
Los Vallecitos Blvd
S Bent Ave
Via Vera Cruz
Every effort has been made to assure the accuracy of
the maps and data provided; however, some information
may not be accurate or current. The City of San Marcos
assumes no responsibility arising from use of this
information and incorporates by reference its disclaimer regarding the lack of any warranties, whether expressed or implied, concerning the use of the same. For
additional information see the Disclaimer on the City’s website.

Created By: City of San Marcos GIS
Source of Data: City of San Marcos, 7/2009 & 12/2011
²
0 800 1,600400
Feet
1 inch = 800 feet
!(1 Drainage Management Areas ID#
kj Discharge Points
Lakes
HMP SCWRP Analysis
Drainage Management Areas (DMA)
Proposed IBI Monitoring Locations
San Marcos Creek Specific Plan Area
Discovery Street ROW
(Included in master WQTR analysis)
San Marcos City Limits
San Marcos Creek
Proposed Master WQTR
IBI Monitoring Locations
and
HMP Drainage Management Areas
X:\Projects\Stormwater\Projects\SMCreek_WaterQualityMasterPlan\Maps\Fig6_ProposedDMAandIBILocations.mxd 12/12/2011 FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

3-8

Final December 15, 2011

Appendix C contains a spreadsheet summarizing the DMAs tributary to each point of compliance for Subareas 1 through 8. The spreadsheet defines individual DMAs for the post-project mixed-us e development, paving, and landscaping categories. During final engineering of any future development projects in the Specific Plan area, these assumptions will need to be verified and adjusted by each project, as appropriate.

3.6 HYDROMODIFICATION FACILITY SIZING
The DMA results are used for hydromodification facility sizing within each of the eight subareas. Each DMA is multiplied by a runoff fa ctor, which provides an area reduction due to infiltration through the DMA surface. (See Appendix B , Table 1).

The final step in the hydromodification sizing is to determine the necessary treatment areas and volumes for each DMA. The City of San Marcos intends to include bioretention basins in the Promenade within each subarea DMA.

Spurlock Poirier determined the bioretent ion area available in the Promenade within each subarea (see Figure 3-3). The bioretention basin sizing is calculated by multiplying the total subarea DMA by the appropriate sizing factors from Table 7-1 of the County of San Diego HMP ( see Appendix B).

The sizing factors in Table 7-1 were chos en based on the following values: lower flow threshold (0.5Q2), soil group (D), existing ground slope (flat), and rain gauge (Oceanside).

For these values, the
surface area, surface
volume, and subsurface
volume sizing factors are

0.065, 0.0542, and

0.0390, respectively. The
bioretention basins will
treat the public areas
(streets and sidewalks
within the public right-of-way and the Promenade).

Therefore, the mixed-use areas were subtracted
from the DMAs for the sizing. The bioretention basin results are summarized in Table 3-1. The sizing will provide the required flow control and will also satisfy the treatment control needs for the public areas.

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Final December 15, 2011
Table 3-1
Bioretention Basin Sizing to Treat Public Areas

DMA
Adjusted
DMA, ac
Surface
Area, ac
Surface
Volume,
ac-ft
Subsurface
Volume, ac-ft
Bio retention
Area
Available in
Promenade (
Alt 7)
Surface
Area, ac
Permit
Compliance
Met HMP/WQ
1 2.30 0.15 0.12 0.09 0.18 YES
2 3.92 0.25 0.21 0.15 0.30 YES
3 3.43 0.22 0.19 0.13 0.32 YES
4 3.61 0.23 0.20 0.14 0.31 YES
5 3.39 0.22 0.18 0.13 0.20 YES
6 3.29 0.21 0.18 0.13 0.37 YES
7 0.06 0.0038 0.0032 0.0023 0.0032 YES
8 3.28 0.21 0.18 0.13 0.18 YES

A comparison of the requir ed bioretention basin surfac e area in Ta ble 3-1 with the available surface area by Spurlock Poirier (See Figure 3-3 ) reveals that the available area is sufficient. Spurlock Po irier did not determine the available bioretention area in Subarea 8, but this is primarily park land, so sufficient area is available.

An additional analysis was performed to determine the bioretention basin sizing assuming each entire subarea is treated (i ncluding the mixed use areas). The results are provided in Table 3-2.

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Final December 15, 2011

Table 3-2
Bioretention Basin Sizing to Treat All Areas
(100% Public and100% Private)

DMA
Adjusted
DMA, ac
Surface
Area, ac
Surface
Volume, ac-
ft
Subsurface
Volume, ac-ft
%
Remainder
in Shared
Faclities
Available for
Private
Development
( see Table
3-1)
1 9.32 0.61 0.51 0.36 7
2 11.15 0.72 0.60 0.43 11
3 10.21 0.66 0.55 0.40 23
4 9.12 0.59 0.49 0.36 22
5 11.10 0.72 0.60 0.43 4
6 8.86 0.58 0.48 0.35 44
7 1.33 0.09 0.07 0.05 0
8 3.28 0.21 0.18 0.13 n/a

The available bioretention ar ea in the Promenade is not sufficient for the entire subarea. The available bior etentin area constructed in the promenade would be constructed to provide 100% of the su rface area for each DMA from Table 3-1 and for 100% of the public facilities and between 7% to 44% of the private development surface area in Table 3-2. Consequently, the private development areas will need to provide s upplemental treatment systems on site to make up the difference.

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Final December 15, 2011

MASTER WQTR DMA COMPLIANCE POINTS

FOR DEVELOPMENT IN SPECIFIC PLAN AREA
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CREEKSIQE PROMENADE

CONCEPTUAL BIO-INFILTRATION TAKEOFFS
ALTERNATIVE 7
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(NOT INCLUDED IN

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(D I 2' WIDE MULTI-USE TRAIL

PROMENADE
45'
, , , ,
2 (l} INFILTRATION BAND, I 0% WIDTH Of PROMENADE 14.5' SWALE AS SHOWN! Q) MINOR OPEN SPACE AMENITY AREA [22' AS SHOWN!
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@ SIDEWALK ZONE / UTILITY EASEMENT
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CRIEK DISTRICT REVISIONS

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CREEKSIDE PROMENADE
ALTERNATIVE 7

SECTION C
CREEK

SLOPED BUFFER
(NOT INCLUDED IN
PROMENADEl
(D 12' WIDE MULTHJSE TRAIL

PROMENADE AND MAJOR OPEN SPACE AMENITY
WIDTH VARIES, 105' AS SHOWN
J
{2) INFILTRATION BAND, l 0% WIDTH OF PROMENADE [IWO 6' SWALES AS SHOWN!

G) MAJOR OPEN SPACE AMENITY AREA
@ SIDEWALK ZONE / UTILITY EASEMENT
~ STREET R.O.W. PER SPECIFIC PlAN
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2 SIDEWALK
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46'
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Master Water Quality and Hydromodification
Management Plan

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Final December 15, 2011

3.7 CONCLUSION

The hydromodification analyses demonstr ate that the Promenade bioretention area for flow and treatment control of r un off generated with t he required percent provides by the public areas to meet permit compliance. Private development will need to supplement this with LID to maximize infiltration onsite as required by the permit and specific plan (See Appendix C). The analyses contained herein are part of the Master Water Quality/HMP Management Plan and intended to provide general guidelines for BMPs in the Spec ific Plan area. More detailed analyses will be required for each fina l engineering project in t he Specific Plan area. The detailed analyses should in clude confirmation of the downstream lower flow threshold and conditions in the project area. These conditions should be reassessed on an annual monitoring schedule to ensure accuracy of the results. ~~
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Final December 15, 2011

4.0 WATER QUALITY POLLUTANT REMOVAL EFFECTIVENESS

4.1 STUDY FINDINGS
MOE made a water quality pollutant remova l effectiveness for the overall specific plan area and on a DMA basis to provide a preliminary effectiveness assessment. (See Appendix A). MOE assumed that 20% of the urban runoff from the proposed impervious developm ent (110 ac.) would be treated via engineered Bioretention Units, and the remaining 80% of the site will be treated via other BMPS or combinat ions of BMPs available. The City intends to implement the most effective BMPs fo r the uses that are permitted by the Specific Plan to achieve the removal efficiencies required by the current municipal stormwater permit. Table 4-1 shows the general pollutant removal effectiveness of bioretention units which are listed as water quality treatment objectives for the Specific Plan Area, in cluding flow- through planters, bioswales, and porous pavers.

Table 4-1
Bioretention Pollutant Removal Effectiveness

Pollutant Removal Rate* Removal Rate for Analysis
Total Suspended Solids 90% 90%
COD N/A 82%
Bacteria 90% 90%
NH3 N/A 70% - low end of phosphorous
NO2+NO3 N/A 70% - low end of phosphorous
TKN 68% - 80% 74%
Total Phosphorous 70% - 83% 76%
Metals (Cu, Zn, Pb) 93% - 98% 95%
Metals (Cd, Ni) N/A 93% - low end of metals
*Source: EPA, 1999
The pollutant removal effectiveness of the Bioretenti on Units has been documented in various locations, e.g ., EPA, CASQA, LID manuals, etc. The following table lists the Removal Rate s for properly designed and constructed Bioretention Units. For the Specific Plan, a conserva tive approach to pollutant removal effectiveness is taken. Table 4- 1 also includes the % removal rates ~~
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Final December 15, 2011
applied to the portion of urban runoff that is to be treated by Bioretention Units.

Tables 4-2 and 4-3 show that for all po llutants of concern overasll and at each DMA level, a reduction and effective remova l rate of medium or better would be achieved for the project.

Table 4-2
Comparison between Existing and Proposed Pollutant Concentrations – With Treatment (Bioretention) for Entire Study Area
Constituent Units Existing Proposed with Treatment Difference TSS (mg/L) 90.07 9.92 -80.14
COD (mg/L) 109.59 4.13 -105.47
Fecal Coliform (mpn/100 mL) 4,962.73 296.04 -4666.69
NH3 (mg/L) 0.73 0.54 -0.19
NO2+NO3 (mg/L) 0.84 0.63 -0.21
Nitrogen, Total Kjeldahl (mg/L) 1.71 0.75 -0.96
Phosphorous, Total (mg/L) 0.45 0.11 -0.34
Cd, Total (ug/L) 0.84 0.08 -0.77
Cu, Total (ug/L) 21.77 3.03 -18.74
Pb, Total (ug/L) 29.66 2.94 -26.72
Ni, Total (ug/L) 7.63 0.85 -6.78
Zn, Total (ug/L) 190.74 19.02 -171.72
Oil and Grease (mg/L) 2.57 0.10 -2.47

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Final December 15, 2011

Table 4-3
Percent Difference between Existing and Proposed Pollutant Concentrations – With Treatment (Bioretention) by Drainage Management Area
Pollutant
DMA
Total
Project
Area
BMP
1 BMP
2 BMP
3 BMP
4 BMP
5 BMP
6 BMP
7 BMP
8 TSS -90.6% -91.4% -86.7% -89.7% - 85.6% -86.6% -78.5% -88.7% -89.0% COD -96.8% -96.9% -95.7% -96.6% -95.0% -95.5% -88.5% -96.5% -96.2% Fecal Coliform -94.3% -94.3% -94.4% -94.0% -94.9% -93.7% -95.6% -91.4% -94.0% NH3 -34.7% -11.6% -31.6% -37.8% -12.6% -14.8% 222.3% -43.9% -26.4% NO2+NO3 -31.1% -41.1% -11.6% -28.1% -8.7% -19.9% 41.9% -26.7% -25.3% Nitrogen, Total
Kjeldahl -61.4% -63.0% -49.6% -59.4% -43.9% -51.1% 11.6% -58.5% -56.1% Phosohorous, Total -78.7% -81.9% -68.7% -76. 3% -67.3% -69.4% -56.1% -71.1% -75.0% Cd, Total -92.1% -93.1% -88.0% -91.1% -87.5% -89.5% -78.4% -90.6% -90.7% Cu, Total -88.0% -90.3% -79.6% -85.9% -80.4% -83.4% -69.1% -89.8% -86.1% Pb, Total -91.7% -94.3% -81.0% -89.8% -83.5% -89.0% -63.4% -90.7% -90.1% Ni, Total -91.0% -92.7% -82.6% -89.7% -81.2% -87.5% ND -86.7% -88.9% Zn, Total -91.8% -93.3% -85.2% -90.6% -84.4% -88.5% -45.5% -89.4% -90.0% Oil and Grease -96.3% -96.1% -95.7% -96.3% -95.1% -95.4% -91.4% -96.4% -95.9%

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Final December 15, 2011
Table 4-4
Comparison between Existing, Proposed with Treatment, and Literature Pollutant Concentrations for Entire Study Area
Constituent Units Literature* Existing Proposed with
Treatment
TSS (mg/L) TSS=10 90.07 9.92
COD (mg/L) 109.59 4.13
Fecal Coliform (mpn/100 mL) 4,962.73 296.04
NH3 (mg/L) 0.73 0.54
NO2+NO3 (mg/L) 0.84 0.63
Nitrogen, Total Kjeldahl (mg/L) 1.1<[N T]<1.69 1.71 0.75 Phosphorous, Total (mg/L) 0.048<[P]<1.3
98 0.45 0.11
Cd, Total (ug/L) 0.84 0.08
Cu, Total (ug/L) [Cu]<10 21.77 3.03
Pb, Total (ug/L) [Pb]<5 29.66 2.94
Ni, Total (ug/L) 7.63 0.85
Zn, Total (ug/L) [Zn]<50 190.74 19.02
Oil and Grease (mg/L) 2.57 0.10
Note:

Irreducible concentrations reported fo r TSS, Cu, Pb, and Zn. Values for NO 3, Total N, and P represented as a range of values reported in same measurement units from literature. * Barrett and Limonuzin, 2009.

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Final December 15, 2011

Table 4-5
Comparison between Existing, Proposed with Treatment, and Literature Pollutant Concentrations by Drainage Management Area
Constituent Units Literature*
DMA
BMP
1 BMP
2 BMP
3 BMP
4 BMP
5 BMP
6 BMP
7 BMP
8 TSS (mg/L) TSS=10 10.41 10.01 10.15 10.14 10.32 10.10 10.44 6.76 COD (mg/L) 4.45 4.17 4.27 4.25 4.37 4.26 4.83 2.03
Fecal Coliform (mpn/100 mL) 262.5 288.6 280.2 278.6 266.9 286.7 317.4 512.2 NH3 (mg/L) 0.59 0.55 0.56 0.56 0.58 0.56 0.58 0.25
NO2+NO3 (mg/L) 0.66 0.63 0.64 0.63 0.65 0.65 0.84 0.38
Nitrogen, Total
Kjeldahl (mg/L) 1.1<[N T]<1.69 0.80 0.76 0.77 0.77 0.79 0.77 0.83 0.43 Phosohorous,
Total (mg/L) 0.048<[P]<1.398 0.12 0.11 0.11 0.11 0.12 0.12 0.14 0.08 Cd, Total (ug/L) 0.08 0.08 0.08 0.08 0.08 0.08 0.08 0.05 Cu, Total (ug/L) [Cu]<10 3.23 3.07 3.12 3.13 3.20 3.10 3.09 1.77 Pb, Total (ug/L) [Pb]<5 3.20 2.97 3.05 3.03 3.13 3.05 3.66 1.22 Ni, Total (ug/L) 0.94 0.86 0.89 0.88 0.92 0.88 1.00 0.27 Zn, Total (ug/L) [Zn]<50 20.67 19.28 19.77 19.69 20.31 19.64 21.81 8.26 Oil and
Grease (mg/L)

0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.06
Note:

4.2 LARRY WALKER AND ASSOCIATES INDEPENDENT VALIDATION
The SDRWQCB requested independent third party validation of the water quality analysis and removal rates. This was conducted by Larry Walker and Associates (LWA) and is included in Appendix A.

LWA validated the pollutant removal rates for the project and provided recommendations for monitoring. LWA concluded that:
The MOE assessment was conservative and therefore protective of water quality;
The analysis provides a reasonable assessment and would result in a reduction of pollutant loads.
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Final December 15, 2011
Representative outfalls are acceptable
Two stations would be adequate;
Either flow weighted composites or grab samples
Continuous flow measures
Storms greater than .25 inches and 72 hour separation 9 storms for stat istical variation.

4.3 L

AS POSAS/SAN MARCOS CREEK RESTORATION EXPECTED WATER

QUALITY BENEFITS
Under the Phase I portion of the project, the Las Po sas Creek and San Marcos Creek would be restored, enhanced, or additional wetlands created. Othe similar projects were researched to determi ne what additional benefits could be achieved with the restorati on. A literature review of available data sets were conducted By DMAX Engineering and are included in Appendix D.

The added water quality benefit of the creek restoration in the specific plan area cannot be used for development water qua lity and HMP compliance, however, it would provide an added water quality benefit.

Four similar restorations were review ed, including one lo cally in San Diego:

Forrestor Creek. While it is difficult to compare projects, in general, the data suggests that under wet and dry weather conditions that a reduction in key pollutants (nitrogen, phosphorous, and bacteria) creek restorations would occur.

In addition, Forrestor Creek showed an impr oved IBI score from 11 to 28. It is expected that the creek restorations will result in a similar if not better results.

4.4 RECOMMENDED FIELD VALIDATION
Based upon the results presented above, it is anticipated that future monitoring is implemented to validate the re sults. There are two types of monitoring that are expected:

1. Assess impacts of the specific plan area development on the watershed and;

2. Assess the discharge result s from the specific plan area.

To determine the impacts of the SPA on the watershed, it is anticipated that upstream and downstream monitoring locati ons are utilized. It is important to capture baseline data to support potent ial changes in habitat, bioassessments ~~
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Final December 15, 2011
and water quality. Figure 3-1 shows three potential bioassesment location areas in the specific plan area.

At the discharge level, each DMA and th e study area as a whole could be monitored individually to determine the range of effluent concentrations generated from each area or su mmarized in a study area co llective result. It is important to distinguish run-on flow and pollutant concentrations while conducting monitoring of the discharges. The mo nitoring protocols, frequency, baseline conditions will be specifically address ed through the development of a Quality Assurance Plan that will be required under the 401 Permit and reviewed and approved by the SDRWQCB.

It is also encouraged to implement project (i.e., each development) specific monitoring locations to allow for invest igations to occur when discharge runoff concentrations warrant such upstream investigations.

4.5 C

ONCLUSIONS
The San Marcos Creek Specific Plan calls for many opportunities to use planned surface areas as low impact development site design/treatment control BMPs.

There are also opportunities to design and construct bioretention BMPs within the Specific Plan Area that meet the conceptual design of the Specific Plan.

The analyzed treatment systems consider not only the expected pollutant concentrations from the built-out Spec ific Plan Area, but also the expected treatment runoff quantities based on t he regionally accepted treatment requirements (85th percentile rain events for flow and volume based treatment).

This analysis demonstrates an expecte d decrease in pollutant loading when comparing the existing site conditions to the permit compliant built-out Specific Plan for the Study Area.

It is important to note that the levels of the constituents expected to be generated are below the action levels for municipal permit monitoring activities and, at those levels, are not considered risks to human health or the environment.

Comparison of the propos ed pollutant concentrations based on the percent removal with those from performance-bas ed effluents show similar results. The pollutant concentrations from the lit erature validate the methods and the proposed post-treatment effluent concentrations presented in the study.

4-20

Final December 15, 2011
land use and new design and construction, and relocating pollutant activities indoors, supports this statement. T he monitoring program approved by the SDRWQCB will be designed to confirm the preliminary analysis. ~~
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Final December 15, 2011

5.0 PRIVATE DEVELOPMENT REQUIREMENTS

5.1 MODEL BLOCK DEVELOPMENT
Private development in the
specific plan area is required to
be developed in model blocks.

This assures a managed and
cohesive development pattern
within each DMA.

It also assures that permit
compliance onsite and in the
shared WQ/HMP facilities can
be tracked and reported on an annual basis

5.2 BASIC GUIDELINES FOR MODEL BLOCK PRIVATE DEVELOPMENT FOR

PERMIT COMPLIANCE
The following are the gui ding elements of the
Master WQ/HMP Management Plan which a project
specific WQTR will be developed for each project in
addition to the Current SUSMP/HMP
Requirements, project type requirements, and LID,
Site Design, and Source Control requirements in
Order R9 2007-0001:

 All projects in the San Marcos Creek Specific Plan Area are categorized as SUSMP Priority projects and must adhere to the source control, site design, and treatment control requirements and criteria of the SUSMP.  All projects in the Specific Plan Area must follow the City of San Marcos SUSMP in effect January 14, 2011 for WQ/HMP.
 All projects in the Specif ic Plan Area must show pre-project pollutant load and HMP calculations and post project pollutant load reduction and HMP calculations for all pollutants generat ed by land uses and potential land uses.
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FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

5-2

Final December 15, 2011
 All projects in the specific plan ar ea must show a pollutant load reduction over existing condition land uses th rough the selecti on of appropriate BMPs and design criteria for wet weather conditions and dry weather conditions.
 All projects must assume the worst case land use for the plan view acreage:

 The primary pollutants of concern are Nu trients, Bacteria ( all) , selenium, DDE/DDT, sediment toxicity,
 All private development projects in the Specific Plan Area must develop a preliminary and final WQ/HMP plan for submittal and approval by the City.  All projects must show and meet a ll TMDL load alloca tions on a project specific basis in place at the time the TMDL is in place.  Projects in the Specific Plan area WILL NOT be granted waivers for site design, source control, LID, or treatment control requirements.  All connections from the project pr ivate storm drain system to the City MS4 must have monitoring manholes installed and labeled;  Projects must participate in the CFD.
 Projects must demonstrate maxi mum utilization of LID features:
permeable pavement, landscape, flow through planters, and other viable runoff reduction measures allowed by t he specific plan or technologically available at the time of development.

REFERENCE DOCUMENTS
Documents intended to be used in the pr eparation of project specific Water quality improvement plans in the Specific Plan Area include:
 City of San Marcos Current St ormwater Standards Manual and SUSMP  Current City of San Marcos Water Quality Ordinance 14.15  CASQA Current Treatment Control BMP Design Requirements FINAL San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

5-3

Final December 15, 2011
 January 2010 Upper San Marcos Creek Nutrient Management Plan  Bacteria I TMDL (SDRWQCB Region 9)
 Upper San Marcos Creek Nu trient TMDL and Management Plan(SDRWQCB Region 9)
 Final Regional Hydromodification Management Plan
 2011 San Marcos Creek Specific Plan Area Preliminary Water Quality Treatment Analysis (MOE, 2011)
 2011 San Marcos Creek Specific Plan HMP Analysis (Wayne Chang & Associates, 2011)

5.3 T

EMPORARY WATER QUALITY IMPACTS
(CONSTRUCTION/BIOLOGICAL)

For all phases of the project the current General Construction Permit (GCP) requirements will be followed on a project by project basis. Order R9 2008-0002 (Dewatering Permit for construction activi ties) may also need to be implemented for project specific construction activities.

The GCP requires the prepar ation of a SWPPP. The Cit y requires that this document and coverage under the GCP is completed prior to the issuance of grading permits. A risk level assessment and BMP sheets based on anticipated pollutants being generated during the construction phas e will have pollutant specific BMPs for each of the four stages of construc tion (Demolition, grading, vertical construction, and landscaping). Pe rmit coverage will be required prior to the start of any work and an effectiv e combination of erosion and sediment controls, rain event action plans, test ing of runoff, and enhanced inspections are required. Mobilization of BMPs 48 hours in advance of a predicted rain event is also required.

Biological resources impacts are also addressed during construction and are considered in the impacts on habitat. Anticipated BMPs include biological monitoring and placing visual barrier s (i.e. orange fencing) to prevent construction activities in habitat areas will be included and coordinated with the MMRP.

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San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

APPENDIX A
September 15, 2011 Page 4-1
San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment
Analysis
Prepared by
Mikhail Ogawa Engineering
)1
,
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Revised July 2011
Study Purpose
San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
The City of San Marcos (City) has prepared a Specific Plan for the San Marcos Creek area. The San Marcos Creek Specific Plan (Specific Plan) represents an effort to create a planning framework for future growth and redevelopment of the approximately 214-acre area along San Marcos Creek in central San Marcos (Figure 1). The Specific Plan has been developed with a thorough analysis of environmental conditions and input from City decision-makers, landowners, neighbors, and the community-at-large. It provides a comprehensive vision for this creekside district along with goals, policies and development standards to guide future public and private actions relating to the Area's development and conservation of open space and natural resources. The Specific Plan also serves as a mechanism for ensuring that future development will be coordinated and well-planned.

Figure1: Not to Scale - Specific Plan and Study Area: red dashed line represents the Specific Plan Area and the blue shaded area is the Study Area (modified from San Marcos Creek Specific Plan, 2007) During a 401 Certification pre-application meeting with the San Diego Regional Water Quality Control Board (RWQCB), the RWQCB staff requested that a study be conducted to compare pre project1 impacts on water quality to post-project1 impacts to determine how much impact the completed Specific Plan Area would have on water quality and the beneficial uses of the receiving waters. The comparison is between (1) the existing land use with no existing treatment control Best Management Practices (BMPs) and (2) the completed Specific Plan Area with expected treatment control BMPs in place and operating.

Study Area
The Study Area consists of 135.5 acres on the north and south sides of San Marcos Creek between Grand Avenue and Discovery Street in the City of San Marcos (Figure 1 ). Existing development is generally located near San Marcos Boulevard. Development in the area between Grand Avenue and McMahr Road consists primarily of commercial and legal nonconforming industrial uses, including neighborhood "strip" retail centers, two gas stations, a lumberyard, three storage facilities, a construction material storage yard, auto services, a bowling alley, office uses, 1 For the purposes of this report discussion , the term "project" refers to the completely built-out Specific Plan area .

San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
and a fast food restaurant (San Marcos Creek Specific Plan, 2007). Additionally, there are several residential uses within the Study Area.

For the purposes of this analysis, existing land use means the current site conditions as they exist. The Vacant land use category is a combination of developable acreage that remains vacant in an undisturbed state and open space that is not developable. The existing land use within the Study Area consists of the following approximate acreages:

Streets:

Commercial Acreage:

Industrial Acreage:

Residential Acreage:

Vacant Acreage:

12.65 ac

28.02 ac

17.57 ac

12.66 ac

64.64 ac
The proposed land use is a mixed-use commercial core and "downtown" for San Marcos. The proposed land use will balance retail and entertainment uses with a mix of residential, office, and service uses to create a new "24-hour'' neighborhood with active/passive use.

The proposed land use within the Study Area consists of the following:

Streets
Mixed-Use
2 :

Improved Park Space3:

42.6 ac

75.6 ac

17.3 ac
Figure 2: Not to Scale - Proposed Land Use for Specific Plan and Study Area (San Marcos Creek Specific Plan, 2007)
As seen in Figures 2 and 4, there are planned pervious surface areas within the mixed use areas (shaded in green) that may be used for low impact development site design/treatment control BMPs. Per the specific plan those areas are described as courtyards, plazas and parks. The intent is to create community gathering spac;;es that have pervious surfaces.

The Study Area is within the San Marcos Hydrologic Area (904.5) of the Carlsbad Hydrologic Unit as defined by the RWQCB. Downstream of the Specific Plan Area is San Marcos Lake, a man made lake (by way of a dam) that is surrounded by two golf courses and residential housing. 2 For the purposes of the discussion and of this report, the term "mixed-use" includes hardscape, building coverage. and ~arking typically associated with commercial/residential/parking land uses The Study Area Improved Park Space consists of linear greenways , multi-use trail, and urban parks. 2 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Downstream of the lake, San Marcos Creek meanders through various land use areas and discharges into the Batiquitos Lagoon prior to ultimate discharge to the Pacific Ocean.

The approved State Water Resources Control Board (SWRCB) 2010 303(d) list provides information about waters that are determined to be impaired for certain pollutant types. The following is a list of waterbodies that the SWRCB has determined to be impaired that the San Marcos Creek Specific Plan Area is tributary to:

Table 1 - 2010 Approved 303(d) Listings Related to Specific Plan Area Water Body Name Pollutant/Stressor
San Marcos Creek DDE, Phosphorus , Sediment toxicity, Selenium San Marcos Lake
Methods and Results
Drainage Management Areas
Ammon ia (as N), Nutrients
The proposed project will have a total of eight Drainage Management Areas (DMAs); delineated areas that share common hydrology and drainage systems - see Figure 3 below. It is intended that each OMA will have its own distinct treatment and flow controls to address runoff and pollutants generated within them. The analyses, and results presented below, were conducted on both the OMA level and the entire specific plan area.

Pollutant Concentrations
This study uses a median concentration approach. Urban runoff contaminant concentrations have substantial variability based on the types of land use. In general, land use defines the imperviousness and types and amounts of pollutants that are present within the area of land use.

The approach estimates the existing concentrations of contaminants based on existing land use.

The study uses the concentration values (Table 2) for the land use type from the National Stormwater Quality Database (NSDQ) Version 1.1 (Pitt et al., February 2004). This database represents monitoring data collected from over 3,750 individual storm events over nearly a ten year period from more than 65 agencies throughout the country. The data characterize the median concentrations from specific land use types including, streets, residential, commercial, industrial and open space. A smaller subset of the data from sites within EPA Rainfall Zone 6 (southwestern US) was extracted from the national database as it better characterizes the study area. Medians were generated from this dataset for all land uses except Vacant, where only 2 events were recorded and the data was insufficient. Vacant concentrations were therefore 3 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
characterized from the national database. The N02 + N03 median concentration for streets land use was also characterized from the national database due to lack of data within Zone 6.

Table 2 - NSDQ Median Concentrations
Constituent Units Streets Residential
TSS (mg/l) 99 94.5
COD (mg/l) 110 135
Fecal Colifonn (mpn/100 ml) 1700 2450
NH3 (mg/l) 1.39 0.865
NO2+NO3 (mg/l) 0.3* 1.1
Nitrogen, Total Kjeldahl (mg/l) 2 2.25
Phosphorous. Total (mg/l ) 0.2385 0.455
Cd, Total (ug/l) 1 1.1
Cu, Total (ug/l) 42 25
Pb, Total (ug/l) 24 50
Ni, Total (ug/l) 8.9 14
Zn, Total (ug/l) 207.5 300
Oil and Grease (mg/l) 3.5 3
(NSDQ Database, EPA Rainfall Zone 6 - Pitt et al., 2004) • NO2 + NO3 value for Streets land use based on entire NSDQ dataset. •· Vacant land use values based on entire NSQD dataset.

Commercial Industrial Vacant**
111 200 48.5
175 235 42 .1
2700 4500 7200

1.6 0.83 0.18
1 1.7 0.59

2.55 3.35 0.74

0.47 1.1 0.31
1 2 0.38

17.5 55 10
23 102 10
11 .5 24 ND
250 560 40
4 4 1.3
Based on the NSDQ and the existing land use information, the expected pre-project constituent concentrations are calculated by prorating and combining the NSDQ concentrations based on the representative land use area for each of the four categories (streets, residential, commercial, industrial and open space). The resulting concentrations are shown in the Table 3 below.

Table 3 - Estimated Existing Land use and Pollutant Concentrations for Entire Study Area Area Streats Residential Commercial Industrial Vacant Total Acres 12.65 12.66 28.02 17.57 64.64 135.54
% of Total 9.33% 9.34% 20.67% 12.96% 47.69% 100%
Constituent Units Pollutant Concentrations
TSS (mg/l) 9.24 8.83 22.95 25.93 23.13 90.07
COD (mg/l) 10.27 12.61 36.18 30.46 20.08 109.59
Fecal Colifom, (mpn/100 ml) 158.6 228.4 558.2 583.3 3,433.7 4,962.7 NH3 (mg/l) 0.13 0.08 0.33 0.11 0.09 0.73
NO2+NO3 (mg/l) 0.03 0,10 0.21 0.22 0.28 0.84
Nitrogen, (mg/l) 0.19 0.21 0.53 0.43 0.35 1.71 Total Kieldahl Phosphorous, (mg/l) 0.02 0.04 0,10 0.14 0.15 0.45 Total Cd, Total (ug/l) 0.09 0.10 0.21 0.26 0.18 0.84
Cu, Total (ug/l) 3.92 2.34 3.62 7.13 4.77 21 .77
Pb, Total (ug/l) 2.24 4.67 4.75 13.22 4.77 29.66
Ni, Total (ug/l) 0.83 1.31 2.38 3.11 ND 7.63
Zn, Total (ug/l) 19.37 28.02 51.68 72.59 19.08 190.74
Oil and (mg/l) 0.33 0.28 0.83 0.52 0.62 2.57 Grease
Using the same method, the proposed contaminant concentrations are calculated based on the proposed land use. Because the planned land use is a mixed-use concept (residential/commercial/parking), the most impactful median concentration values for each constituent are selected from the NSDQ database for the Residential, Commercial, and Parking (i.e. Streets) land use categories. Table 4 represents the median concentration values used to determine the proposed constituent concentrations (Table 5). 4 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Table 4 - Proposed NSDQ Median Concentrations - Worst Case for Mixed Use Category for Entire Study Area
Constituent Units Streets Mixed Use Improved Park Space TSS (mg/L) 99 111 48.5
COD (mg/L) 110 175 42.1
Fecal Coliform (mpn/100 ml) 1700 2700 7200
NH3 (mg/L) 1.39 1.6 0.18
NO2+NO3 (mg/l ) 0.3 1.1 0.59
Nitrogen, Total Kjeldahl (mg/l) 2 2.55 0.74
Phosphorous, Total (mg/l) 0.2385 0.47 0.31
Cd, Total (ug/l) 1 1.1 0.38
Cu, Total (ug/L) 42 42 10
Pb, Total (ug/l) 24 50 10
Ni, Total (ug/l) 8.9 14 ND
Zn, Total (ug/l) 207.5 300 40
Oil and Grease (mg/l) 3.5 4 1.3
(NSDQ Database, EPA Rainfall Zone 6 - Pitt et al., February 2004) Mixed Use areas composed of Residential, Commercial, and Parking land uses.

Table 5 - Estimated Proposed Land Use and Pollutant Concentrations for Entire Study Area Pervious
, n
Improved Area Streets Streets Mixed Use Park Space Total Acres 39.02 3.58 75.62 17.31 135.54
% of Total 28.79% 2.64% 55.80% 12.77% 100%
Constituent Units Pollutant Concentrations
TSS (mg/L) 28.50 2.61 61.94 6.19 99.25
COD (mg/l) 31.67 2.91 97.65 5.38 137.60
Fecal Coliform (mpn/100 ml) 489.4 44.9 1,506.6 919.5 2,960.4 NH3 (mg/l) 0.40 0.04 0.89 0.02 1.35
NO2+NO3 (mg/l) 0.09 0.01 0.61 0.08 0.78
Nitrogen, Total Kjeldahl (mg/l) 0.58 0.05 1.42 0.09 2.15 Phosphorous, Total (mg/l) 0.07 0.01 0.26 0.04 0.38
Cd, Total (ug/l) 0.29 0.03 0.61 0.05 0.98
Cu, Total (ug/l ) 12.09 1.11 23.44 1.28 37.91
Pb, Total (ug/l ) 6.91 0.63 27.90 1.28 36.72
Ni, Total (ug/l) 2.56 0.24 7.81 ND 10.61
Zn, Total (ug/l) 59.74 5.48 167.40 5.11 237.73
Oil and Grease (mg/l) 1.01 0.09 2.23 0.17 3.50
Mixed Use areas composed of Residential, Commercial, and Parking land uses.

Based on this study approach and available data sets, without treatment for the proposed built out Specific Plan Area, the pollutant loading for ten of the thirteen constituents would likely increase. Additionally, the reduction in Phosphorous and the sum of Nitrite and Nitrate would be negligible. Table 6 below represents the comparison between existing and proposed conditions.

I
5 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analys is
Table 6 - Comparison Between Existing and Proposed Pollutant Concentrations - No Treatment for Entire Study Area
Constituent Units Existing Proposed No Treatment Difference TSS (rng/L) 90.07 99.25 9.18
COD (mg/L) 109.59 137.60 28.01
Fecal Coliform (mpn/100 ml) 4,962.7 2,960.4 -2,002.3
NH3 (mg/L) 0.73 1.35 0.62
NO2+NO3 (mg/L) 0.84 0.78 -0.06
Nitrogen , Total Kjeldahl (mg/L) 1.71 2.15 0.43
Phosphorous, Total (mg/L} 0.45 0.38 -0.08
Cd, Total (ug/L) 0.84 0.98 0.13
Cu, Total (ug/L) 21.77 37.91 16.14
Pb, Total (ug/L) 29.66 36.72 7.06
Ni, Total (ug/L) 7.63 10.61 2.98
Zn, Total (ug/L) 190.74 237.73 46.99
Oil and Grease (mg/L) 2.57 3.50 0.93
Treatment Controls Preliminary Design
The overall Specific Plan Area design phase is in a preliminary stage and selection of the final treatment systems has not yet been made. However, for purposes of this analysis, it is assumed that 100% of the urban runoff from the proposed development (118.2 ac.) will be treated via engineered bioretention best management practices (BMPs) including bioretention units, flow through planters, etc. There are many BMPs and combinations available and the City intends to implement or require the implementation of the most effective BMPs for the uses that are permitted by the Specific Plan.

Based on current local practice and guidelines - San Diego County LID Handbook and Model Standard Urban Stormwater Mitigation Plan - the amount of surface area required for the bioretention systems is 4% of the tributary impervious surface area.

The make up of the Specific Plan Area is conducive for meeting the 4% area required for the LID BMPs to be utilized for both the mixed use (highly developed) public right-of-ways and designated open space park areas. This study assumes that the necessary minimum of 4% area will be required through the City's regulatory development requirements.

It is important to note that of the 135.5 ac. within the Study Area, 17.3 acres are expected to be open space parks that will accommodate the use of bioretention BMPs to treat the runoff that is generated from these areas (Figures 2 and 5) and some public impervious surfaces, e.g. some streets and sidewalks.

The pollutant removal effectiveness of bioretention is published in various documents (e.g. EPA, CASQA, LID manuals, etc.). Table 7 lists the removal rates for bioretention BMPs. For this study, a conservative approach to pollutant removal effectiveness is taken, i.e., the lower estimates of available data ranges are used in the approach. The table also includes the percent(%) removal rates applied to the urban runoff that is to be treated by bioretention. 6 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Table 7 - Bioretention Pollutant Removal Effectiveness
Pollutant Publistiei:j Removal Removal Rate for
Rate
TSS 90%*
COD 97%**
Bacteria 90%*
NH3 (ammonia) 60% - 80%***
NO3 (nitrate) 20%
0 *
0 Nitrogen, Total Kjeldahl 65% - 75%***
Total Phosphorous 70% - 83%*
Metals (Cu, Zn, Pb) 92%***
Metals (Cd' Ni) NIA
Oil and Grease > 97%****
*EPA, 1999
**Low Impact Development Center
***Davis, et al, 2001
****Hsieh et al., 2003
*****Davis , et al., 2006
Figure 4: Example of system that meet
conceptual plans of Specific Plan
(WSUD.org)
Analysis
90%
97%
90%
60%
20%
65%
70%
92%
92% - comparable to other
heavv metals
97%
Applying the treatment control BMPs discussed above,
Table 8 below represents the built-out status with
treatment controls applied. The negative numbers
demonstrate a reduction in pollutant concentrations from existing conditions to proposed built-out conditions with treatment. Similarly, Table 9, is a summary of the results when analyzed on a OMA level. It is important to note, that for several of the pollutant comparisons in the BMP7 OMA area, the comparison in concentrations are shown as a
significant increase - this is due to the initial
concentrations being completely open space in its existing conditions and having relatively low or no expected
pollutant generation.

Additionally, as shown in Figure 6, the Specific Plan calls for plazas, park areas and thus, opportunities for site design and pervious surfaces that can be used as
treatment control BMPs.
7 San Marcos Boulevard
San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Pacific Street Main Street
Discovery Street McMahr
West End Gateway Park Creekside Promenade
Figure 5: Not to Scale - Figure showing opportunities for alternative pervious surfaces (San Marcos Creek Specific Plan, 2007)
I
- ----'----,
']' -~rkr~- .· , I 1: ;.i"'.'·-uu. t.m. .-r1i .

I i
-'--+ ~
n ..
. ' ..,
Figure 6: Rendering showing opportunities for alternative pervious surfaces (San Marcos Creek Specific Plan, 2007)
8 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Table 8 - Comparison between Existing and Proposed Pollutant Concentrations - With Treatment (Bioretention) for Entire Study Area
Constituent Units Existing Proposed with Treatment Difference TSS (mg/L) 90.07 9.92 -80.14
coo (mg/L) 109.59 4.13 -105.47
Fecal Coliform (mpn/100 ml) 4,962.73 296.04 -4666,69
NH3 (mg/L) 0.73 0.54 -0,19
N02+N03 (mg/L) 0.84 0.63 -0.21
Nitrogen, Total Kjeldahl (mg/L) 1.71 0.75 -0.96
Phosphorous , Total (mg/L) 0.45 0.11 -0.34
Cd, Total (ug/L) 0.84 0.08 -0.77
Cu, Total (ug/L) 21.77 3.03 -18.74
Pb, Total (ug/L) 29.66 2.94 -26.72
Ni, Total (ug/L) 7.63 0.85 -6.78
Zn, Total (ug/L) 190.74 19.02 -171.72
Oil and Grease (mg/L) 2.57 0.10 -2.47
Table 9 - Percent Difference between Existing and Proposed Pollutant Concentrations - With Treatment (Bioretention) by Drainage Management Area
OMA Total
BMP BMP BMP BMP BMP BMP BMP BMP Project
Pollutant 1 2 3 4 5 6 7 8 Area
TSS -90.6% -91.4% -86.7% -89.7% -85.6% -86.6% -78.5% -88,7% -89.0% coo -96.8% -96.9% -95.7% -96.6% -95.0% -95.5% -88.5% -96.5% -96.2% Fecal Colifonn -94.3% -94.3% -94.4% -94.0% -94.9% -93.7% -95.6% -91.4% -94.0% NH3 -34.7% -11.6% -31.6% -37.8% -12.6% -14.8% 222.3% -43.9% -26.4% N02+ N03 -31.1% -41.1% -11.6% -28.1% -8,7% -19.9% 41 .9% -26.7% -25.3% Nitrogen, Total -61.4% -63.0% -49.6% -59.4% -43.9% -51.1% 11.6% -58.5% -56.1% Kieldahl Phosohorous, Total -78.7% -81.9% -68.7% -76.3% -67.3% -69.4% -56.1% -71.1% -75.0% Cd, Total -92.1% -93.1% -88.0% -91.1% -87.5% -89.5% -78.4% -90.6% -90.7% Cu, Total -88.0% -90.3% -79.6% -85.9% -80.4% -83.4% -69.1% -89,8% -86,1% Pb, Total -91.7% -94.3% -81.0% -89.8% -83,5% -89.0% -63.4% -90.7% -90.1% Ni, Total -91.0% -92.7% -82.6% -89.7% -81.2% -87.5% ND -86.7% -88.9% Zn, Total -91.8% -93.3% -85.2% -90.6% -84.4% -88.5% -45.5% -89.4% -90,0% Oil and Grease -96.3% -96.1% -95.7% -96.3% -95.1% -95.4% -91.4% -96.4% -95.9% As an alternative to using median concentrations and percent removal to calculate proposed pollutant concentrations, expected effluent concentrations can be located in published literature for a variety of BMPs. These performance-based effluents have been documented for the some BMPs, although the literature is somewhat limited in respect to bioretention.

In order to perform a desktop validation of the results of the study, the proposed pollutant concentrations following bioretention treatment were compared with irreducible pollutant concentrations located in published studies. As the data is limited, some of the concentrations from the literature appear as ranges and not as absolute values. The pollutant concentrations presented in this study using the percent removal method are within reasonable range of the irreducible concentrations proposed by the literature. Table 10 presents the comparison between the existing, proposed, and literature pollutant concentrations. Similarly, Table 11, is a summary of the results when analyzed on a OMA level.
9 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Table 10 - Comparison between Existing, Proposed with Treatment, and Literature Pollutant Concentrations for Entire Study Area
Constituent Units Literature* Existing Proposed with
Treatment
TSS (mg/L) TSS=10 90.07 9.92
COD (mg/L) 109.59 4.13
Fecal Coliform (mpn/100 ml) 4,962.73 296.04
NH3 (mg/L) 0.73 0.54
NO2+NO3 (mg/L) 0.84 0.63
Nitrogen, Total Kjeldahl (mg/L) 1.1 <[Nr]<1.69 1.71 0.75 Phosphorous, Total (mg/L) 0.048<[P]<1.3 0.45 0.11 98
Cd, Total (ug/L) 0.84 0.08
Cu, Total (ug/L) [Cu]<10 21.77 3.03
Pb, Total (ug/L) [Pb]<5 29.66 2.94
Ni, Total (ug/L) 7.63 0.85
Zn, Total (ug/L) [Zn]<50 190.74 19.02
Oil and Grease (mgll) 2.57 0.10
Note:

Irreducible concentrations reported for TSS , Cu, Pb, and Zn. Values for NO3, Total N, and P represented as a range of values reported in same measurement units from literature. • Barrett and Limonuzin, 2009.

Table 11 - Comparison between Existing, Proposed with Treatment, and Literature Pollutant Concentrations by Drainage Management Area
OMA
Constituent Units Literature• BMP BMP BMP BMP BMP BMP BMP 1 2 3 4 5 6 7
TSS (mg/L) TSS=10 10.41 10.01 10.15 10.14 10.32 10.10 10.44 COD (mg/L) 4.45 4.17 4.27 4.25 4.37 4.26 4.83
Fecal Coliform (mpn/100 ml) 262.5 288.6 280.2 278.6 266.9 286.7 317.4 NH3 (mg/L) 0.59 0.55 0.56 0.56 0.58 0.56 0.58
NO2+NO3 (mg/L) 0.66 0.63 0.64 0.63 0.65 0.65 0.84
Nitrogen, Total (mg/L) 1.1 <[Nr]<1.69 0.80 0.76 0.77 0.77 0.79 0.77 0.83 Kjeldahl Phosohorous, (mg/L) 0.048<[P]< 1.398 0.12 0.11 0.11 0.11 0.12 0.12 0.14 Tota l Cd, Total (ug/L) 0.08 0.08 0.08 0.08 0.08 0.08 0.08
Cu, Total (ug/L) [Cu]<10 3.23 3.07 3.12 3.13 3.20 3.10 3.09 Pb, Total (ug/L) [Pb]<5 3,20 2.97 3.05 3.03 3.13 3.05 3.66 Ni, Total (ug/L) 0.94 0.86 0.89 0.88 0.92 0.88 1.00
Zn. Total (ug/L) [Zn]<50 20.67 19.28 19.77 19.69 20.31 19.64 21.81 Oil and (mg/L) 0.11 0.11 0.11 0.11 0.11 0.11 0.11 Grease Note:

Irreducible concentrations reported for TSS, Cu, Pb, and Zn. Values for NO3, Total N, and P represented as a range of values reported in same measurement units from literature. • Barrett and Limonuzin, 2009.

Recommended Field Validation
Based upon the results presented above, it is anticipated that future monitoring is implemented to validate the results. There are two types of monitoring that are expected: that to determine impacts of the specific plan area development on the watershed and that to determine the discharge results from the specific plan area.

BMP
8 6.76

2.03 512.2

0.25 0.38

0.43 0.08

0.05 1.77

1.22 0.27

8.26 0.06
10 San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
To determine the impacts of the SPA on the watershed, it is anticipated that upstream and downstream monitoring locations are utilized. It is important to capture baseline data to support potential changes in habitat, bioassessments and water quality. As each new phase is developed within the SPA, monitoring could take place to determine if cumulative changes to the watershed are occurring and to what extent.

At the discharge level, each OMA and the study area as a whole could be monitored individually to determine the range of effluent concentrations generated from each area or summarized in a study area collective result. It is important to distinguish run-on flow and pollutant concentrations while conducting monitoring of the discharges.

It is also encouraged to implement project (i.e., each development) specific monitoring locations to allow for investigations to occur when discharge runoff concentrations warrant such upstream investigations.

Conclusions
The San Marcos Creek Specific Plan calls for many opportunities to use planned surface areas as low impact development site design/treatment control BMPs. There are also opportunities to design and construct bioretention BMPs within the Specific Plan Area that meet the conceptual design of the Specific Plan. Figures 4 and 7 show examples of such BMPs.

The analyzed treatment systems consider not only the expected pollutant concentrations from the built-out Specific Plan Area, but also the expected treatment runoff quantities based on the regionally accepted treatment requirements (85th percentile rain events for flow and volume based treatment).

This analysis demonstrates an expected decrease in pollutant loading when comparing the existing site conditions to the built-out Specific Plan for the Study Area, when implementation of the example treatment control BMPs are included. It is important to note that the levels of the constituents expected to be generated are below the action levels for municipal monitoring activities and, at those levels, are not considered risks to human health or the environment.

Comparison of the proposed pollutant concentrations based on the percent removal with those from performance-based effluents show similar results. The pollutant concentrations from the literature validate the methods and the proposed post-treatment effluent concentrations presented in the study.

The analysis is considered conservative in nature because it does not consider the differences between the existing facilities, with their pollutant-generating activities exposed to rainfall, and the built-out conditions, which will likely be much less outdoor pollutant generating activities. A combination of changes in land use and new design and construction, and relocating pollutant activities indoors, supports this statement.
11 ud.,grq
San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis
Figure 7: Example of system that meets conceptua l plans of Specific Plan (WSUD.org) 12 References:

San Marcos Creek Specific Plan Area
Preliminary Water Quality Treatment Analysis

1. City of San Marcos, 2007. San Marcos Creek Specific Plan. City of San Marcos, San Marcos, California

2. Dahlenberg, John, 2006. Water Sensitive Urban Design - www.wsud.org Accessed on October 28, 2007

3. Davis, Allen P., Mohammad Shokouhian, Himanshu Sharma, and Christie Minami. 2001.

Laboratory study of biological retention (bioretention) for urban storm water management.

Water Environment Research 73: 5-14.

4. Davis, AP, et al. 2006. Water quality improvement through bioretention media: Nitrogen and phosphorus removal. Water Environment Research, 78 (3): 284-293.

5. Hsieh, et al., 2003. Multiple-Event Study of Bioretention for Treatment of Urban Storm Water Runoff. University of Maryland, College Park, Maryland.

6. Pitt, Robert et al., 2004. Findings from the National Stormwater Quality Database. Center for Watershed Protection, Ellicott City, Maryland.

7. United States Environmental Protection Agency, 1999. Storm Water Technology Fact Sheet - Bioretention. Office of Water, Municipal Technology Branch, Washington D.C.

8. Michael Barrett and Maelle Limonuzin, Center for Research in Water Resources, University of Texas, September 2009. Literature Review of Extended Detention and Biofiltration Systems prepared for the City of Austin.
13 707 4th Street, Suite 200
Davis, CA 95616
530. 753.6400
530. 753.7030 fax
www.lwa.com

L A R R Y
WALKER
i
June 1, 2010
To: Mikhail Ogawa, MOE
~ I
. ..... !
. ~
From: Malcolm Walker, LWA )~
Cc: Erica Ryan, City of San Marcos
Subject: Technical Review of San Marcos Creek Specific Plan Area Preliminary Water Quality Treatment Analysis by MOE, April 2010

ASSOC IATES
Consistent with a request from the City of San Marcos I have provided an independent review of the subject report. The objectives of my review were two-fold : (1) to crit ique the technical assumptions used in the analysis and to provide recommendations, if necessary, for improvements to the analysis and (2) to provide a framework for validating the analysis. This memorandum is organized to respond to each objective.

Technical Review
The City of San Marcos is currently preparing a Specific Plan for the San Marcos Creek. The Specific Plan represents the City's efforts to provide a planning framework for the 214 acre area along San Marcos Creek. The Regional Board, in review ing the plan and considering 401 certific atio n, requested to City to assess the difference in wate r qual ity impacts that would occur. Thus the purpose of the subject analysis was to compare pre-project water quality with post-project water quality . The approach taken in the analysis reflected a spreadsheet analysis using event mean concentrations and land use designation. The fundamental idea was to estimate the runoff quality (based on constit uent concentrations) from current development without the use of BMPs versus the runoff quality from future development using BMPs (in thi s analysis bioretention was the BMP of choice). Such an approach is appropriate and has been used in other environmental analysis including CEQA. Although a more detailed loading model may better characterize water quality conditions, to perform such an analysis would requ ire more site specific data and would be more resource inten sive. The analysis described in the MOE report appears conservative (i.e. protective) and adequate for a planning level assessment of water quality impacts. That being said I have provided in the follow ing sections recommendations to corroborate the analysis. My recommendations are not intended to replace the MOE analysis but rath er to either validate or not the conclusion by using different assumptions and databases.

In conducting the analysis there are two critical assumptions that were used to assess the pre and post development water quality impacts. These two include:
• Event Mean Concentration s from desig11ated land uses (Table 2)

Page 1 ends

Memo: Technical Review of Water Quality Analysis
June 1, 2010
• BMP Pollutant Removal Effectiveness (Table 7)
Each is addressed below.

Event Mean Concentrations
The analysis uses EMCs from the National Stormwater Quality Database (NSQD) Version 1.1 {Pitt, et.al, February 2004). This database reflects a comprehensive compilation of outfall monitoring data for the entire nation. The database presents an accurate picture of runof f quality from a national perspective, As a result the database includes data from areas with considerably more rainfall than what occurs in the San Diego area. A more representative subset of this database that would reflect San Diego is the data from USE PA rainfall region 6. This region includes California, Nevada and Arizona. This same dataset is currently being used by the Regional Board (Los Angeles and San Diego) in developing stor m water action ~vets-amh:on-se-quentty-i•s-!Jeiri1fC~~tt~represen'fat1ve -ofarierT!Ym ates. 1 wo u I arecom menatn2i this subset be used to characterize the runoff quality from development. The dataset is not as large as the National Dataset but it's more relevant and representative of San Marcos.

Another comment that I would like to make regarding the EMCs is the use of a single value. Stormwater quality will vary based on a number of factors -days since last rainfall, rainfall intensity, time of year of the rainfall event, and rainfall amount. The use of the large dataset allows one to capture a range of events and develop a central tendency of the data but the reality is that EM Cs will vary and more likely a range of values will provide a more accurate assessment. That being said th e use of median EM Cs as used in the MOE analysis is reasonable for making a prel iminary assessment.

And finally although the analysis is EMC based (i.e. concentration based) one could compare pollutant loadings. The use of bioretention has the additional benefit of reducing the volume of discharge. Thus instead of using storm water concentration to assess effectiveness, one could use loading to assess water quality improvements. As noted previously this type of assessment wou ld be more accurate but also require more site specific data and resources to complete. The use of EMCs is a conservative approach since it does not account for the volume reduction aspect of bioretention BMP.

BMP Pollutant Removal Effectiveness
The analysis in Table 7 provides the expected pollutant removal effectiveness (as a percentage) for bioretention BMPs. The estimate effectiveness is based on a number of different references. Although the use of removal efficiency is a common engineering approach for unit process evaluation, the variability of stormwater (see above discussion) makes the use of removal efficiency limited. In fact the ASCE/EPA BMP Database (http://www.bmpdatabase.org/) recommends that percent removal efficiency not be used to assess BMP performance but rather a performance based effluent1. For most BMPs the 1 Wright Water Engineers and Geosyntec Consultants, 2007. Frequently Asked Questions Fact Sheet for the International Stormwater BMP Database: Why does the Internat ional Stormwater BMP

Page 2 ends

Memo: Technical Review of Water Quality Analysis
June 1, 2010
ASCE/EPA database provides a comprehensive review of performance. However, for bioretention the database is inadequate. Bioretent ion is a subset of the BMP category of biofiltration. Furthermore a closer review of the biofiltrat ion catego ry shows that there are few bioretention BMP performance studies. This issue has been noted and the database in the future will be modified to distinguish the performance of bioretention. In the meantime and in lieu of using the ASCE/EPA database I wou ld recommend that the perfo rmance data from a comprehensive literature review conducted by the City of Austin
2 be used.

Summary
The analysis conducted for the City of San Marcos provides a reasonable preliminary evaluation of the water quality changes that would occur with the implemen tation of the Specific Plan. Even with the recommendations suggested in this memorandum to corroborate the analysis, the fundamental conclusion that pollutant loads after the implementation of the Specific Plan will be less than the current pollutant loadings will likely not change.

Validation of Assessment
The subject analysis is a reasonable assessment of the changes in water quality impacts from the Specific Plan. However, the assessment could be validated to confirm some of the basic assumptions (e.g. EM Cs and/or BMP performa nce). The validation of the EMC would be a costly effort because of the need to capture a range of storms for the different land uses presented in the Specific Plan. Instead the more reasonable and cost effec tive validation effort would be to measure the overall effectiveness of bioretention BMPs. Since the BMPs wi ll be applied across the entire area in the Specific Plan the selection of representative outfalls will provid e confirmation of the overall effectivenes s of the BMPs. With that in mind it is recommended that the following monitoring program be considered to validate the preliminary assessment.

Monitoring Locations. Select outfalls in which the developed area draining to the outfall has implemented bloretention BMPs consistent with City requi rements . Care should be provided to ensure that the outfalls do not include runoff from up gradient areas not subject to the BMP requirements.

Number of Stations. 2
Type of monitoring. Optimally a flow weighted composite sampler should be installed to capture represent ative samples. Alternatively, grab samples could be collected timed to capture the full Database Project omit percent removal as a measure of BMP performance? {as posted on www.bmpdatabase.org)
2 Michael Barrett and Mael\e Limonuzin, Center for Research in Water Resources, University ofTexas, September 2009. Literature Review of Extended Detention and Biofiltration Systems prepared for the City of Austin.

Page 3 ends

Memo: Technical Review of Water Quality Analysis
June 1, 2010
hydrographs and then composite d. ft is also recommended that flow be measure, preferably continuously. As previously noted assessing load reductions is relevant for bioretentio n BMPs and thus the need for measuring flow.

List of Constituents. Obviously the constituent list should include the constituents considered in the Specific Plan assessment. Alternatively only constituents that have been identified as problematic in the watershed such sediment and phosphorus and constituents typically present in stormwater such as meta ls and specifically copper and zinc.

Storm Criteria. Mobilizat ion for storms can be difficu lt and expensive. In order to help focus storm collection activities it is suggested the following criteria be used • Storms greater than 0.25 inches. This value may need to be adjusted to reflect site specific conditions (drainage area, slope, soils) and rainfall conditions. This criterion should be established to allow adequate opportunity to collect at least two storms per year.
• 72 hour separation between storm events
Number of storms. Suggest that at least 9 storms are monitored to allow statist ical comparison with BMP performance. Given the variability of storms it is important to have a sufficient number.

And finally by identifying the need to establish monitoring stations early in the planning process, the cost, ease of installati on, and effectiveness of the monitoring station can be optim ized.

Page 4 ends

San Marcos Creek Specific Plan
Master Water Quality and Hydromodification
Management Plan

APPENDIX B
September 15, 2011 Page 4-2

SAN MARCOS SPECIFIC PLAN

MASTER WATER QUALITY

TECHNICAL REPORT

HYDROMODIFICATION AND CHANNEL

SUSCEPTIBILITY ANALYSIS
August 12, 2011
Wayne W. Chang, MS, PE
Chanuffim~[ruOO
Civil Engineering • Hydrology • Hydraulics • Sedimentation P.O. Box 9496
Rancho Santa Fe, CA 92067
(858) 692-0760
Hydromodification Criteria
As of January 14, 2011, the Standard Urban Stormwater Mitigation Plan (SUSMP) expands water quality regulations to include hydromodification (flow control). Hydromodification applies to priority development projects and must be implemented to ensure that post-development peak flows and durations do not exceed pre-development peak flows and durations.

Hydromodification will cause a project to mitigate potential erosion in downstream recei ving waterbodies for a range of lower flow events. The SUSMP criteria are defined as follows:

I. For flow rates ranging from 10, 30, or 50 percent of the pre-project 2-year runoff event (0.1 Q2, O.3Q2, or O.5Q2) to the pre-project 10-year runoff event (Q10), the post-project discharge rates and durations shall not deviate above the pre-project 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 results from the Southern California Coastal Water Research Project's (SCCWRP) channel screening study and the critical flow calculator.

2. For flow rates ranging from the lower flow threshold to Q5, the post-project peak flows shall not exceed pre-project peak flows. For flow rates from Q5 to Q10, post-project peak flows may exceed pre-project flows by up to 10 percent for a I-year frequency interval.

For example, post-project flows could exceed pre-project flows by up to 10 percent for the interval from Q9 to Q10 or from Qs.s to Q6.s, but not from Qs to Qio- The County of San Diego's January 13, 2011, Final Hydromodification Management Plan (HMP), outlines methodology for sizing facilities to meet the SUSMP hydrornodification criteria. Tables 7-1 through 7-5 in the HMP contain sizing factors for various preferred facilities including bioretention, bioretention plus cisterns, bioretention plus vaults, flow-through planters, and infiltration. Facility design using these sizing factors will provide surface areas and volumes needed to satisfy hydromodification. The sizing factors will yield similar results as the County of San Diego 's BMP Sizing Calculator. The sizing factor selection depends on the applicable lower flow threshold (0.1 Q2, O.3Q2, or O.5Q2) mentioned in the first bullet criteria. The lower flow threshold evaluation is described in SCCWRP's "Hydromodification Screening Tool for Southern California" included in Appendix B of the HMP. Alternatively, a threshold of 0.1 Q2 is selected if a channel screening study is not performed, but will result in the most conservative (greatest) facility sizing.

The San Marcos Creek Specific Plan is a priority development project, so it must meet hydromodification requirements. A channel screening study bas been performed for the project and is included in Appendix A. The study determined that the receiving waterbody, San Marcos Creek, has a low susceptibility to erosion. Consequently, the hydromodification analyses are based on a 50 percent lower flow threshold. The following sections outline the hydromodification analyses for the Specific Plan project based on this threshold. The analyses were performed to provide guidelines and regulations for future development in the Specific Plan area. The City of San Marcos may construct hydromodification facilities to serve their infrastructure improvements . In some instances, the City's facilities might have excess capacity allowing some treatment for private development projects. In most cases, an individual developer will be required to address their hydromodification needs as part of their project design and in accordance with this document. Detailed hydromodification analyses must be prepared for each development project and submitted to the City for review and approval.

Specific Plan Hydromodification Analyses
The overall (Alternative 7) Specific Plan area was subdivided into eight subareas for independent hydromodification analyses. Each subarea has a hydromodification point of compliance at its discharge point into San Marcos Creek. Seven subareas cover the primary Specific Plan development area (mixed-use, streets, Promenade, etc.) north of San Marcos Creek, while the eighth subarea covers the Discovery Street widening and park land south of San Marcos CTeek (see Figure 1). The first subarea is located between Grand Avenue and South Bent Avenue. The second subarea is generally the easterly half of the project between South Bent Avenue and Via Vera Cruz. The third subarea is generally the westerly half of the project between South Bent Avenue and Via Vera Cruz. The fourth subarea is the generally the easterly half of the project between Via Vera Cruz and McMahr Road. The fifth subarea is generally the westerly half of the project between Via Vera Cruz and McMahr Road. The sixth subarea is between McMahr Road and Las Posas Creek. The seventh subarea is between Las Posas Creek and Discovery Street.

The eighth subarea is the project area south of San Marcos Creek.

Subareas 1 through 6 support generally rectangular mixed-use development blocks bounded by north-south and east-west aligned streets. The southerly strip along San Marcos Creek will contain a landscaped Promenade with a multi-use trail. Drainage Management Areas (DMA) were delineated within each subarea. The DMA's define individual areas of mixed-use development, paving, and landscaping. The proposed mixed-use development was assumed to contain 85 percent impervious surfaces and 15 percent pervious surfaces. The proposed streets consist of standard (asphalt or concrete) paved surfaces in the travel lanes as well as in the diagonal parking areas and in the widened parallel parking aisles. The landscaping areas include the Promenade, landscape medians, park land, and the 15 percent pervious surfaces within the mixed-use development.

Proposed development in Subareas 7 and 8 varies somewhat from Subareas 1 through 6. Subarea 7 will support a triangular mixed-use area as well as a strip of park land along San Marcos Boulevard. Subarea 8 will include widening of a portion of Discovery Street from South Bent Avenue to Via Vera Cruz and an adjacent floodwall along San Marcos Creek. Subarea 8 will also include park land with trails along the south side of San Marcos Creek between Via Vera Cruz and McMahr Road.

Figure l delineates the post-project mixed-use, paving, and landscaping DMA's within each subarea. Under pre-project conditions, development (commercial, retail, industrial, streets, etc.) exists in portions of the Specific Plan area. The pre-project developed areas were delineated in a general manner using aerial photographs, topographic mapping, and a field investigation. The pre-project developed areas were assumed to contain 90 percent impervious surfaces and 10 percent pervious surfaces based on the document review and field investigation. Each DMA category was further refined to reflect areas supporting pre-project development (90 percent impervious area) or with no pre-project development (pervious area).

Appendix B contains a spreadsheet summanzmg the DMAs tributary to each point of compliance for Subareas 1 through 8. The spreadsheet defines individual DMAs for the post project mixed-use development, paving, and landscaping categories. The spreadsheet includes an adjusted area column that accounts for the post-project mixed-use development comprised of 85 percent impervious area and 15 percent pervious (landscaping) area as well as the pre-project developed areas containing 90 percent impervious surfaces and 10 percent pervious surfaces.

Dming final engineering of any future development projects in the Specific Plan area, these assumptions will need to be verified and adjusted by each project, as appropriate.

Hydromodification Facility Sizing
The DMA results are used for hydromodification facility sizing within each of the eight subareas. Each DMA is multiplied by a runoff factor, whkh provides an area reduction due to infiltration through the DMA surface. Typical runoff factors from the County of San Diego SUSMP are listed in Table 1 for a variety of surface types.

Surface Runoff Factor
Roofs 1.0
Concrete 1.0
Pervious Concrete 0.1
Porous Asphalt 0.1
Grouted Unit Pavers 1.0
Solid Unit Pavers on Granular Base 0.2
Crushed Ag:g-regate 0.1
Turfblock 0.1
Amended, mulched soil 0.1
Landscape 0.1
Table 1. Typical DMA Runoff Factors
A runoff factor of 1.0 was used for the in1pervious portion of the mixed-use areas and for the paving. A runoff factor of 0.1 was used for the pervious portion of the mixed-use areas and landscaping . The spreadsheet in Appendix B includes the runoff factor-adjusted DMAs.

The final step in the hydromodification sizing is to determine the necessary treatment areas and volumes. The City of San Marcos intends to include bioretention basins in the Promenade within each subarea. Spurlock Poirier detennined the bioretention area available in the Promenade within each subarea (see Figure 2). The bioretention basin sizing is calculated by multiplying the total subarea DMA by the appropriate sizing factors from Table 7-1 of the County of San Diego HMP. The portion of the DMA's within the footprint of a pre-project impervious surface are excluded from the overall DMA because these areas are a source of pollutants in the baseline condition. Table 7-1 contains sizing factors for the basin area, surface volume (assuming 10 inches of ponded depth), and subsurface volume (assuming 1.5 feet of growing medium with 40 percent porosity over 2.5 feet of gravel with 40 percent porosity). The sizing factors in Table 7-1 were chosen based on the following values: lower flow threshold (0.5Q2), soil group (D), existing ground slope (flat), and rain gauge (Oceanside). For these values, the surface area, surface volume, and subsurface volume sizing factors are 0.065, 0.0542, and 0.0390, respectively. The bioretention basins will treat the public areas (streets and sidewalks within the public right-of-way and the Promenade). Therefore, the mixed-use areas were subtracted from the DMAs for the sizing. The bioretention basin results are summarized in Table 2. The sizing will provide the required flow control and will also satisfy the treatment control needs for the public areas.

Adjusted Surface Surface Subsurface
Subarea DMA, ac Area, ac Volume, ac-ft Volume, ac-ft
1 2.30 0.15 0.12 0.09
2 3.92 0.25 0.21 0.15
3 3.43 0.22 0.19 0.13
4 3.61 0.23 0.20 0.14
5 3.39 0.22 0.18 0.13
6 3.29 0.21 0.18 0.13
7 0.06 0.0038 0.0032 0.0023
8 3.28 0.21 0.18 0.13
Table 2. Bioretention Basin Sizing to Treat Public Areas A comparison of the required bioretention basin surface area in Table 2 with the available surface area by Spurlock Poirier reveals that the available area is sufficient. Spurlock Poirier did not determine the available bioretention area in Subarea 8, but this is primarily park land, so sufficient area is available.

An additional analysis was performed to determine the bioretention basin sizing assuming each entire subarea is treated (including the mixed use areas). The results are provided in Table 3.

Adjusted Surface Surface Subsurface
Subarea DMA, ac Area, ac Volume, ac-ft Volume, ac-ft
1 9.32 0.61 0.51 0.36
2 11.15 0.72 0.60 0.43
3 10.21 0.66 0.55 0.40
4 9.12 0.59 0.49 0.36
5 11.10 0.72 0.60 0.43
6 8.86 0.58 0.48 0.35
7 1.33 0.09 0.07 0.05
8 3.28 0.21 0.18 0.13
Table 3. Bioretention Basin Sizing to Treat All Areas
The available bioretention area in the Promenade is not sufficient for the entire subarea.

Consequently, the mixed-use areas will need to provide supplemental ti·eatment systems.

Hydromodification Criteria
The hydromodification analyses demonstrate that the Promenade has sufficient bioretention area for flow and treatment control of runoff generated by the public areas. Private development will need to supplement this will additional best management practices. The analyses contained herein are pait of the Master Water Quality Management Plan and intended to provide general guidelines for BMPs in the Specific P1an area. More detailed analyses will be required for each final engineering project in the Specific Plan area. The detailed analyses should include confirmation of the downstream lower flow threshold and conditions in the project ai·ea. These conditions should be reassessed on a 2-year monitoring schedule to ensure accuracy of the results.

GRAPHIC SCALE
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DMA'S ARE BASED ON THE
ALTERNATIVE 7 SITE PLAN.

DRAINAGE
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i==J MIXED-USE
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i==J PAVING
i==J PARKING AISLE PAVING
c=J PARKING AISLE PAVING
i==J LANDSCAPING
--- LANDSCAPING

SUBAREA BOUNDARY

EXISTING FIELD
CQt:IQIIlQt:1

PERVIOUS AREA

IMPERVIOUS AREA

PERVIOUS AREA

IMPERVIOUS AREA

PERVIOUS AREA

IMPERVIOUS AREA

PERVIOUS AREA

IMPERVIOUS AREA
POC 8 POINT OF CONCENTRATION FOR SUBAREA

MANAGEMENT AREAS
Section 7 Hydromodification Management Plan
Sizing factors have been developed by the consultant team throu gh the use of continuous simulation hydro logic modeling and these factors will be built .into the San Diego LID /HMP Siz.ing Calculator to assist with HMP implementation. Siz.ing factors are ratios of the required mitigation size (.in area or volume) as compared to the contributing developed area. The same concepts used to develop siz.ing factors .in Contra Costa County are be.ing used to develop siz.ing factors based on conditions .in the San Diego area. Tables 7-1 through 7-5 detail sizing factors which have been determined to ensure compliance with peak flow and flow duration criteria as outlined in this HMP.

Table 7-1. Sizing Factors for Bioretention Facilities
Lower Flow Soil Group Slope Rain Gauge A Y1 Y2 Threshold

0.5O2 A Flat Lindbergh 0.060 0.0500 N/A

0.5O2 A Moderate Lindbergh 0.055 0.0458 N/A

0.5O2 A Steep Lindbergh 0.045 0.0375 N/A

0.5O2 B Flat Lindbergh 0.093 0.0771 N/A

0.5O2 B Moderate Lindbergh 0.085 0.0708 N/A

0.5Q2 B Steep Lindbergh 0,065 0.0542 N/A

0.5O2 C Flat Lindbergh 0,100 0.0833 0.0600

0.502 C Moderate Lindbergh 0.100 0.0833 0.0600

0.5O2 C Steep Lindbergh 0.075 0.0625 0.0450

0.5Q2 D Flat Lindbergh 0.080 0.0667 0.0480

0.502 D Moderate Lindbergh 0.080 0.0667 0.0480

0.5O2 D Steep Lindbergh 0.060 0.0500 0.0360

0.5O2 A Flat Oceanside 0,070 0.0583 N/A

0.5O2 A Moderate Oceanside 0,065 0.0542 N/A

0.5O2 A Steep Oceanside 0,060 0.0500 N/A

0.5O2 B Flat Oceanside 0.098 0.0813 N/A

0.5O2 B Moderate Oceanside 0.090 0.0750 N/A

0.5O2 B Steep Oceanside 0.075 0.0625 N/A

0.5O2 C Flat Oceanside 0.075 0.0625 0.0450

0.5O2 C Moderate Oceanside 0.075 0.0625 0.0450

0.5O2 C Steep Oceanside 0.060 0.0500 0.0360

0.5Q2 D Flat Oceanside 0.065 0.0542 0.0390

0.5O2 D Moderate Oceanside 0.065 0.0542 0.0390

0.5O2 D Steep Oceanside 0.050 0.0417 0.0300

0.5O2 A Flat L Wohlford 0.050 0.0417 N/A
0502 A Moderate L Wohlford 0.045 0.0375 N/A

0.5O2 A Steep L Wohlford 0.040 0.0333 N/A

0.5O2 B Flat LWohlford 0,048 0.0396 N/A

0.5O2 B Moderate L Wohlford 0,045 0.0375 N/A

0.5O2 B Steep L Wohlford 0.040 0.0333 N/A
1-iMfoW:!iMIII
7-2
Use of contents on lhls sheet Is subJect to lhe hmita1ions specified a t !he end of this docun1eni S 1Projects\San Diego County\ 133904 • SDCo Hyd1omod Management Plan\WP\HMP\08_Final HMP Jan2011\104720 FIN.~ L_ San D1e1io HMP _ Ja n2011.docx Section 7 Hydromodification Management Plan
Table 7-2. Sizing Factors for Bioretention Plus Cistern Facilities Lower Flow Soil Group Slope Rain Gauge A Threshold

0.1O2 B Moderate L Wohlford 0.020

0.1Qz B Steep L Wohlford 0.020

0.102 C Flat L Wohlford 0.020

0.1O2 C Moderate L Wohlford 0.020

0.1Qz C Steep L Wohlford 0.020

0.102 D Flat L Wohlford 0.020

0.102 D Moderate L Wohlford 0.020

0.1Q2 D Steep L Wohlford 0.020
02 = 2-year pre-project flow rate based upon partial duration analysis of long-term hourly rainfall records 010 = 10-year pre-project flow rate based upon partial duration analysis of long-term hourly rainfall records A = Bioretention surface area sizing factor
V, = Cistern volume sizing factor
Table 7-3. Sizing Factors for Bioretention Plus Vault Facilities Lower Flow Soll Group Slope Rain Gauge A Threshold

0.5Qz A Flat Lindbergh N/A

0.502 A Moderate Lindbergh N/A

0.5O2 A Steep Lindbergh N/A

0.5O2 B Flat Lindbergh 0.040

0.5O2 B Moderate Lindbergh 0.040

0.5Q2 B Steep Lindbergh 0.040

0.5Q2 C Flat Lindbergh 0.040

0.5O2 C Moderate Lindbergh 0.040

0.5O2 C Steep Lindbergh 0.040

0.5O2 D Flat Lindbergh 0.040

0.5O2 D Moderate Lindbergh 0.040

0.5O2 D Steep Lindbergh 0.040

0.5O2 A Flat Oceanside N/A

0.5O2 A Moderate Oceanside N/A

0.5O2 A Steep Oceanside N/A

0.5O2 B Flat Oceanside 0.040

0.5O2 B Moderate Oceanside 0.040

0.5O2 B Steep Oceanside 0.040

0.5O2 C Flat Oceanside 0.040

0.5O2 C Moderate Oceanside 0.040

0.5O2 C Steep Oceanside 0.040

0.5O2 D Flat Oceanside 0.040
1-iMfoW-tMMII
7-8
Use of contents on this sheet is subject to the limitations specified al !he end of !his document V1

0.4000

0.3200

0.2200

0.2400

0.1800
V1
N/A
N/A
N/A

0.3600

0.2400

0.1400

0.1600

0.1200

0.1400

0.1000
N/A
N/A
N/A

0.2100

0.1800

0.1400

0.1200

0.1400
V2
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
V2
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
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S \ProIecIs\San Diego County'133904 - SDCo Hyctromod Management Plan1WP\HMP\08_Final HMP _Jan2011\104 i20_FINAL_Sa11 Dlego HMP _Jan2011.docx

APPENDIX A

SCCWRP INITIAL DESKTOP ANALYSIS

INTRODUCTION
This report provides hydromodification screening analyses for the San Marcos Specific Plan project. The project has been divided into seven drainage subareas north of the creek and one subarea south of the creek (see Figure 1). Each subarea will contain a flow (and treatment) contrnl facility and be served by a storm drain system that discharges into San Marcos Creek.

The flow control facility sizing is dependent on the flow threshold in the receiving waterbody.

The County of San Diego's January 13, 2011, Final Hydromodification Management Plan (HMP) outlines low flow thresholds for hydromodification analyses. The thresholds are based on a percentage of the pre-project 2-year flow (Q2), i.e., 0.1Q2 (low), 0.3Q2 (medium), or 0.5Q2 (high). A threshold of 0.1 Q2 represents a downstream receiving conveyance system with a high susceptibility to erosion. This is the default value used for hydromodification analyses and will result in the most conservative (greatest) on-site facility sizing. A threshold of 0.3Q2 or 0.5Q2 represents downstream receiving conveyance systems with a medium or low susceptibility to erosion, respectively. In order to qualify for a medium or low susceptibility threshold, a project must perform a channel screening analysis based on a "hydromodification screening tool" procedure developed by the Southern California Coastal Water Research Project (SCCWRP).

The SCCWRP results are compared with the critical shear stress calculator results from the County of San Diego's BMP Sizing Calculator to establish the appropriate susceptibility threshold of low, medium, or high.

The SCCWRP screening tool requires both office and field work to establish the vertical and lateral susceptibility of a downstream receiving channel to erosion. The vertical and lateral assessments are performed independently of each other although the lateral results can be affected by the vertical rating. The screening was performed to assess San Marcos Creek near the Specific Plan project, which extends from Discovery Street on the downstream end to Grand A venue on the upstream end.

The initial step in performing the SCCWRP screening analysis is to establish the domain of analysis and the study reaches within the domain. This is followed by office and field components of the screening tool along with the associated analyses and results. The following sections cover these procedures in sequence.

DOMAIN OF ANALYSIS
SCCWRP defines an upstream and downstream domain of analysis, which establish the required study area. The County of San Diego's HMP specifies the downstream domain of analysis based on the SCCWRP criteria with some refinements . The HMP indicates that the downstream limit is defined when one of these is reached:
• at least one reach downstream of the first grade control point • tidal backwater/lentic waterbody
• equal order tributary
• accumulation of 50 percent drainage area for stream systems or 100 percent drainage area for urban conveyance systems (storm drains, hardened channels, etc.) The upstream limit is defined as:
• proceed upstream for 20 channel top widths or to the first grade control point, whichever comes first. Identify hard points that can check headward migration and evidence of active headcutting.

SCCWRP defines the maximum spatial unit, or reach (a reach is circa 20 channel widths), for assigning a susceptibility rating within the domain of analysis to be 200 meters (656 feet). If the domain of analysis is greater than 200 meters, the study area should be subdivided into smaller reaches for analysis.

Downstream Domain o[Analysis
The downstream domain of analysis for the study area has been determined using the bullet items above. The downstream-most discharge location from the project will be just upstream of the Discovery Street crossing of San Marcos Creek. The first permanent grade control below this discharge location is the Lake San Marcos dam, which is approximately 1.6 miles downstream of the Discovery Street crossing. The Lake San Marcos dam is a concrete arch dam, so it will act as a permanent grade control along San Marcos Creek.

The nearest lentic waterbody is Lake San Marcos. The upper (northerly) end of Lake San Marcos begins approx.imately 1,900 feet downstream of the Discovery Street crossing. Lake San Marcos then extends for another 1.3 miles to the dam.

The equal order tributary or accumulation of 50 percent drainage area will be significantly further downstream than Lake San Marcos or its dam because the watershed area tributary to the study reach covers over 20 square miles (see discussion in Initial Desktop Analysis section below). The urban conveyance system does not apply since San Marcos Creek is primarily a natural conveyance system.

Based on this information, the downstream domain of analysis is defined by the upper end of Lake San Marcos. This lentic waterbody is the closer to the project site than the other downstream domain of analysis locations.

Upstream Domain of Analysi s
Echo Lane crosses San Marcos Creek approximately 900 feet upstream of the upstream project limit at Grand Avenue. The roadway is at the elevation of the creek bed and contains a culvert along the tbalweg. The culvert can convey low flow, but during moderate to high storm events the creek flow will overtop the roadway. Since Echo Lane is a non-erodible asphalt crossing spanning the entire creek width, it functions as a grade control and is the first grade control point upstream of the project. Echo Lane is further upstream than the 200 meter limit, but was selected as the upstream domain of analysis because it is a well-defined grade control.

Study Reaches within Domain of Analvsis
2 The domain of analysis along San Marcos Creek extends from the upper end of Lake San Marcos to Echo Lane. The domain of analysis was subdivided into four study reaches with similar characteristics (see the Study Area Exhibit in Appendix A). Reach 1 extends from the upper end of Lake San Marcos to the confluence of San Marcos Creek with Las Posas Creek. The reach length along the creek thalweg is approximately 2,550 feet. Reach 2 extends from the Las Posas Creek confluence to a point nearly 2,350 feet upstream along the thalweg. Reach 3 extends from the upper end of Reach 2 approximately 3,890 feet along the creek tbalweg to South Bent Avenue. Reach 4 extends approximately 2,130 feet along the thalweg from South Bent Avenue to Echo Lane.

Reaches 1, 2, 3, and 4 are longer than the 656 feet maximum reach length specified by SCCWRP. The four reach locations were selected based on consistency within each reach.

Review of topographic mapping, aerial photographs, and field conditions reveals that the physical ( channel geometry and slope), vegetative, hydraulic, and soil conditions within each of these reaches is relatively uniform. Subdividing the reaches into smaller subreaches of less than 656 feet will not yield significantly varying results within a reach. Consequently, the screening tool was applied across Reach 1, 2, 3, and 4, and the results will be the same within each reach.

INITIAL DESKTOP ANALYSIS
After the domain of analysis is established, SCCWRP requires an "initial desktop analysis" that involves office work. The initial desktop analysis establishes the watershed area, mean annual precipitation, valley slope, and valley width. These terms are defined in Form 1 included in Appendix A. SCCWRP recommends the use of National Elevation Data (NED) to determine the watershed area, valley slope, and valley width. A review of the NED for San Marcos determined that it is equivalent to USGS quadrangle maps. The topographic resolution on USGS maps is low and typically on a 25-foot contour interval. For this report, recent topographic mapping along San Marcos Creek was used to establish the valley slope and valley width because the topography is at a I-foot contour interval, which is much greater detail than NED. The I-foot contour mapping did not cover the area near Lake San Marcos or the south creek bank between South Bent A venue and Echo Lane. For these areas, the City of San Marcos ' 2-foot contour topographic mapping was used.

The watershed area tributary to San Marcos Creek was established in the March 27, 199 I, San Marcos Creek Flood Control Improvement Project - Design Development Study, by Willdan Associates. This report contains hydrologic analyses that determined the San Marcos Creek watershed area upstream of the Discovery Street bridge to be 17,003 acres (26.57 square miles).

This area was used for Reach 1. The watershed area upstream of the Las Posas Creek confluence was determined to 13,427 acres (20.98 square miles). This area was used for Reach 2 through 4.

A summary table from the report identifying the watershed areas is included in Appendix A.

The mean annual precipitation is provided by the County of San Diego's BMP Sizing Calculator (see Appendix A) and is 13.3 inches. The valley slope of Reach 1 through 4 was determined from the 1-foot contour interval topographic mapping in the Study Area Exhibit in Appendix A.

This is the longitudinal slope measured along the thalweg. The valley width was estimated from 3 the topographic mapping. This is the valley bottom width defined by clear breaks in the surface slope on the topographic mapping. The valley slope and valley width at each reach is summarized in Table I.
-- -----~
Reach Valley Slope, m/m I Valley Width, m
I--, 0.0033 - 30
2 ' 0.0049 -, 40
3 r--- 0.0042 I s2
-- - ---
4 0.0038 79 - ---
Table 1. Summary of Valley Slope and Width
These values were input to a spreadsheet to calculate the simulated peak flow, screening index, and valley width index outlined in Form 1. The input data and results are included in Appendix A. This completes the initial desktop analysis.

FIELD SCREENING
After the initial desktop analysis is done, a field assessment must be performed. The field assessment is used to establish a natural channel's vertical and lateral susceptibility to erosion.

SCCWRP states that although they are admittedly linked, vertical and lateral susceptibility are assessed separately for several reasons. First, vertical and lateral responses are primarily controlled by different types of resistance, which, when assessed separately, may improve ease of use and lead to increased repeatability compared to an integrated, cross-dimensional assessment. Second, the mechanistic differences between vertical and lateral responses point to different modeling tools and potentially different management strategies. Having separate screening ratings may better direct users and managers to the most appropriate tools for subsequent analyses.

The field screening tool uses combinations of decision trees and checklists. Decision trees are typically used when a question can be answered fairly definitively and/or quantitatively (e.g., d50 < 16 mm). Checklists are used where answers are relatively qualitative ( e.g., the condition of a grade control). Low, medium, high, and very high ratings are applied separately to the vertical and lateral analyses. When the vertical and lateral analyses return divergent values, the most conservative value shall be selected as the flow threshold for the hydromodification analyses.

Visual observation reveals that each study reach contains a densely vegetated, natural watercourse (see Figures 2 to 16). The vegetative cover extends across the creek bottoms and sides. The cover was so dense that most areas were difficult to access by foot, and some areas were only possible to access if the vegetation was trimmed. Due to the dense cover and flat valley slopes calculated through Form I, the vertical and lateral stability was anticipated to have a limited susceptibility to erosion.

Vertical Stability
4 The purpose of the vertical stability decision tree (Figure 6-4 in the County of San Diego HMP) is to assess the state of the channel bed with a particular focus on the risk of incision (i.e., down cutting). The decision tree is included in Figure 20. The first step is to assess the channel bed resistance. There are three categories defined as follows:

1. Labile Bed - sand-dominated bed, little resistant substrate.

2. Transitional/Intermediate Bed - bed typically characterized by gravel/small cobble, Intermediate level of resistance of the substrate and uncertain potential for armoring.

3. Threshold Bed (Coarse/Armored Bed) - armored with large cobbles or larger bed material or highly-resistant bed substrate (i.e., bedrock).

Channel bed resistance is a function of the bed material and vegetation. Figures 17 through 19 show photographs of the larger bed material in the study reaches. A gravelometer is included in the photographs for reference . Each square on the gravelometer indicates grain size in millimeters (the gravelometer squares range from 2 to 180 millimeters). The larger material in the figures was discovered in some isolated locations and generally ranges from 16 to 32 millimeters (mm). The channel bed material in the reaches is generally of smaller size.

Figures 2 through 16 show dense vegetation throughout Reaches 1 through 4. Vegetation prevents bed incision because its root structure binds soil and because the aboveground vegetative growth can greatly reduce flow velocities. Table 5-13 from the County of San Diego's Drainage Design Manual outlines maximum permissible velocities for various channel linings (Table 5-13 is included in Appendix B). Maximum permissible velocity is defined in the manual as the velocity below which a channel section will remain stable. Table 5-13 indicates that a fully-lined channel with unreinforced vegetation has a maximum permissible velocity of 5 feet per second (fps). Due to the dense cover and large vegetation, the permissible velocity is likely greater than 5 fps in most reach areas. Table 5-13 indicates that 5 fps is equivalent to an unvegetated channel containing cobbles (grain size from 64 to 256 mm) and shingles (rounded cobbles). In comparison, coarse gravel (19 to 75 mm) has a maximum permissible velocity of 4 fps. Based on this information, the heavily vegetated San Marcos Creek channel bas an equivalent grain size of at least 64 mm.

Vegetation in a watercourse can be dynamic, i.e., the vegetation size and density can change over time. An increase in vegetation will further reduce the potential for vertical incision, while a decrease can allow greater incision. A primary cause for a reduction in vegetation is removal due to hydraulic forces and shear stress dming periods of high flow. Detailed hydraulic analyses of San Marcos Creek along Reaches 1 through 4 show that the flow velocities are primarily non erosive within the range of hydromodification flows. Therefore, the vegetative condition will not be adversely impacted by these flows. A review of historic aerial photos covering nearly the past 20 years indicates that the vegetative growth has tended to increase over time.

Based on the photographs and site investigation, the bed resistance is within the transitional/intermediate bed category. Dr. Eric Stein from SCCWRP, who co-authored the Hydromodification Screening Tool in the Final Hydromodification Management Plan (HMP), 5 indicated that a transitional/intennediate bed requires the most rigorous analysis steps and will generate appropriate results for the size range. Transitional/intermediate beds cover a wide susceptibility/potential response range and need to be assessed in greater detail to develop a weight of evidence for the appropriate screening rating. The three primary risk factors used to assess vertical susceptibility for channels with transitional/intermediate bed materials are:

1. Armoring potential - three states (Checklist 1)

2. Grade control - three states (Checklist 2)

3. Proximity to regionally-calibrated incision/braiding threshold (Mobility Index Threshold - Probability Diagram)
These tlu·ee risk factors are assessed using checklists and a diagram (see Appendix B), and the results of each are combined to provide a final vertical susceptibility rating for the intermediate/transitional bed-material group. Each checklist and diagram contains a Category A, B, or C rating. Category A is the most resistant to vertical changes while Category C is the most susceptible.

Checklist l determines armoring potential of the channel bed. The channel bed along each of the four reaches is within category B, which represents intermediate bed material within unknown armoring potential due to a surface veneer and dense vegetation. The soil was probed and penetration was relatively difficult through the underlying layer. Due to the dense vegetative growth, the armming potential could have been rated higher, but Category B was conservatively (i.e., more potential for channel incision) chosen.

Checklist 2 determines grade control characte1istics of the cham1el bed. Grade controls can be improvements such as the roadway crossings at Via Vera Cruz1 South Bent A venue, and Echo Lane. Each of these crossings consists of a non-erodible surface in a well-maintained condition as well as culve1is, which together prevent degradation of the upstream channel bed. Tlris combined with the relatively flat valley slope means that each grade control's influence will extend over a large upstream distance. SCCWRP also states that grade controls can be natural.

Examples are vegetation or confluences with a larger waterbody such as Lake San Marcos. As indicated above and verified with photographs, each reach contains dense vegetation (see Figures 2 through 16). The plant roots and fallen tree trunks serve as a natural grade control. The spacing of these is much closer than the 50 meters identified in the checklist. Further evidence of the effectiveness of the natural grade controls is the absence of headcutting, mass wasting (large vertical erosion of a channel bank), or undercutting of existing drainage facilities. Based on this infonnation , each reach is within Category A on Checklist 2.

The Mobility Index Threshold is a probability diagram that depicts the risk of incising or braiding based on the potential stream power of the valley relative to the median particle diameter. The threshold is based on regional data from Dr. Howard Chang of Chang Consultants and others. The probability diagram is based on d50 as well as the Screening Index determined in the initial desktop analysis (see Appendix A). d50 is derived from field conditions. As discussed above, the gravelometer revealed particles at 16 mm and greater, while the equivalent grain size 6 for the densely vegetated channel is at least 64 mm. The Screening Index for each reach calculated in Appendix A varies from 0.0089 to 0.0274. The Mobility Index Threshold diagram shows that the 50 percent probability of incising or braiding for a d50 of 16 and 64 mm has indexes of 0.049 and 0.101, respectively. Since the Screening Index values for each reach are less than these values, each reach falls well within Category A.

The overall vertical rating is determined from the Checklist 1, Checklist 2, and Mobility Index Threshold results. The scoring is based on the following values:

Category A= -1, Category B = 0, Category C = 1
The vertical rating score is the sum of the armoring potential score, grade control score, and Mobility Index Threshold score (0 + -1 + -1 = -2). The combined score of -2 is considered a low threshold for vertical susceptibility.

Lateral Stabilitv
The purpose of the lateral decision tree (Figure 6-5 from County of San Diego HMP included in Figure 21) is to assess the state of the channel banks with a focus on the risk of widening.

Channels can widen from either bank failure or through fluvial avulsions such as chute cutoffs and braiding. Widening through fluvial avulsions/active braiding is a relatively straightforward observation. If braiding is not already occurring, the next logical step is to assess the condition of the banks. Banks fail th.rough a variety of mechanisms; however, one of the most important distinctions is whether they fail in mass (as many particles) or by fluvial detachment of individual particles. Although much research is dedicated to the combined effects of weakening, fluvial erosion, and mass failure, SCCWRP found it valuable to segregate bank types based on the inference of the dominant failure mechanism (as the management approach may vary based on the dominant failure mechanism). A decision tree (Form 4 in Appendix B) is used in conducting the lateral susceptibility assessment. Definitions and photographic examples are also provided below for terms used in the lateral susceptibility assessment.

The first step in the decision tree is to determine if lateral adjustments are occurring. The adjustments can take the form of extensive mass wasting (greater than 50 percent of the banks are exhibiting planar, slab, or rotational failures and/or scalloping, undermining, and/or tension cracks). The adjustments can also involve extensive fluvial erosion (significant and frequent bank cuts on over 50 percent of the banks). Neither mass wasting nor extensive fluvial erosion was evident within any of the reaches. The banks are intact in the photographs included in the figures. The dense vegetation supports the absence of large lateral adjustments.

The next step is to assess the consolidation of the bank material. The banks were moderate to well-consolidated . This determination was made because the banks were difficult to penetrate with a probe. In addition, the banks showed limited evidence of crumbling and were composed of tightly-packed particles (see figures).

Fo1m 6 (see Appendix B) is used to assess the probability of mass wasting. Form 6 identifies a 10, 50, and 90 percent probability based on the bank angle and bank height. The 1- and 2-foot contour interval topographic mapping indicates that the maximum bank angle is 2 to 1 7 (horizontal to vertical) or 26.6 degrees in any of the reaches. The majority of the banks are flatter than this. Form 6 shows that the probably of mass wasting and bank failure has less than 10 percent risk for a 26.6 degree bank angle or less regardless of the bank height.

The final step is based on the braiding risk determined from the Mobility Index Threshold in the vertical rating. The braiding risk for each reach is less than 50 percent per the Vertical Stabibty analysis above. From this, the lateral susceptibility rating is low (red circles are included on the Form 4 Decision Tree in Appendix B showing the decision path).

CONCLUSION
The SCCWRP channel screening tools were used to assess the downstream channel susceptibility for the San Marcos Creek Specific Plan project. The project will discharge into San Marcos Creek at several locations between Discovery Street and Grand A venue. The assessment was made for San Marcos Creek from the upper end of Lake San Marcos to Echo Lane. The assessment was performed based on office analyses and field work. The results indicate a low threshold for vertical and lateral susceptibilities in all four reaches.

The HMP requires that these results be compared with the critical stress calculator results incorporated in the County of San Diego's BMP Sizing Calculator. The BMP Sizing Calculator results for a typical creek section returns a low susceptibility. Therefore, the SCCWRP analyses and critical stress calculator demonstrate that the project can be designed assuming a low susceptibility, i.e., 0.5Q2.

The SCCWRP results are consistent with the physical condition of San Marcos Creek, which has a low longitudinal slope, supports dense vegetative growth, and contains a series of grade controls. The growth is so dense that travel by foot was very difficult in most areas. None of the four study reaches exhibits signs of extensive, ongoing erosion. 8 INTRODUCTION
This repo1t provides hydromodification screening analyses for the San Marcos Specific Plan project. The project has been divided into seven drainage subareas north of the creek and one subarea south of the creek (see Figure 1). Each subarea will contain a flow (and treatment) control facility and be served by a storm drain system that discharges into San Marcos Creek.

The flow control facility sizing is dependent on the flow threshold in the receiving waterbody.

The County of San Diego's January 13, 2011, Final Hydromodification Management Plan (HMP) outlines low flow thresholds for hydromodification analyses. The thresholds are based on a percentage of the pre-project 2-year flow (Q2), i.e., 0.1 Q2 (low), 0.3Q2 (medium), or 0.5Qi (high). A threshold of 0.1 Q2 represents a downstream receiving conveyance system with a high susceptibility to erosion. This is the default value used for hydromodification analyses and will result in the most conservative (greatest) on-site facility sizing. A threshold of 0.3Q2 or 0.5Q2 represents downstream receiving conveyance systems with a medium or low susceptibility to erosion, respectively. In order to qualify for a medium or low susceptibility threshold, a prnject must perform a channel screening analysis based on a "hydromodification screening tool" procedure developed by the Southern California Coastal Water Research Project (SCCWRP).

The SCCWRP screening tool requires both office and field work to establish the vertical and lateral susceptibility of a downstream receiving channel to erosion. The ve1tical and lateral assessments are performed independently of each other although the lateral results can be affected by the vertical rating. The screening was performed to assess San Marcos Creek near the Specific Plan project, which extends from Discovery Street on the downstream end to Grand A venue on the upstream end.

DOMAIN OF ANALYSIS
SCCWRP defines an upstream and downstream domain of analysis, which establish the required study area. The County of San Diego's HMP specifies the downstream domain of analysis based on the SCCWRP criteria with some refinements. The HMP indicates that the downstream limit is defined when one of these is reached:
• at least one reach downstream of the first grade control point • tidal backwater/lentic waterbody
• equal order tributary
• accumulation of 50 percent drainage area for stream systems or 100 percent drainage area for urban conveyance systems (storm drains, hardened channels, etc.) The upstream limit is defined as:
• proceed upstream for 20 channel top widths or to the first grade control point, whichever comes first. Identify hard points that can check headward migration and evidence of active headcutting.

Downstream Domain of Analysis
The downstream domain of analysis for the study area has been determined using the bullet items above. The downstream-most discharge location from the project will be just upstream of the Discovery Street crossing of San Marcos Creek. The first permanent grade control below this discharge location is the Lake San Marcos dam, which is approximately 1.6 miles downstream of the Discovery Street crossing. The Lake San Marcos dam is a concrete arch dam, so it will act as a permanent grade control along San Marcos Creek.

The nearest lentic waterbody is Lake San Marcos. The upper (northerly) end of Lake San Marcos begins approximately 1,900 feet downstream of the Discovery Street crossing. Lake San Marcos then extends for another 1.3 miles to the darn.

Upstream Domain ofAnalys is
Echo Lane crosses San Marcos Creek approximately 900 feet upstream of the upstream project limit at Grand Avenue. The roadway is at the elevation of the creek bed and contains a culvert along the thalweg. The culvert can convey low flow, but during moderate to high storm events the creek flow will overtop the roadway. Since Echo Lane is a non-erodible asphalt crossing spanning the entire creek width, it functions as a grade control and :is the first grade control point upstream of the project. Echo Lane is further upstream than the 200 meter limit, but was selected as the upstream domain of analysis because it is a well-defined grade control.

Study Reaches within Domain of Analysis
2 The domain of analysis along San Marcos Creek extends from the upper end of Lake San Marcos to Echo Lane. The domain of analysis was subdivided into four study reaches with similar characteristics (see the Study Area Exhibit in Appendix A . Reach 1 extends from the upper end of Lake San Marcos to the confluence of San Marcos Creek with Las Posas Creek. The reach length along the creek thalweg is approximately 2,550 feet. Reach 2 extends from the Las Posas Creek confluence to a point nearly 2,350 feet upstream along the thalweg. Reach 3 extends from the upper end of Reach 2 approximately 3,890 feet along the creek thalweg to South Bent A venue. Reach 4 extends approximately 2,130 feet along the thalweg from South Bent Avenue to Echo Lane.

Reaches 1, 2, 3, and 4 are longer than the 656 feet maximum reach length specified by SCCWRP. The four reach locations were selected based on consistency within each reach.

Review of topographic mapping, aerial photographs, and field conditions reveals that the physical (channel geometry and slope), vegetative, hydraulic, and soil conditions within each of these reaches is relatively uniform. Subdividing the reaches into smaller subreaches of less than 656 feet will not yield significantly varying results within a reach. Consequently, the screening tool was applied across Reach 1, 2, 3, and 4, and the results will be the same within each reach.

INITIAL DESKTOP ANALYSIS
After the domain of analysis is established, SCCWRP requires an "initial desktop analysis" that involves office work. The initial desktop analysis establishes the watershed area, mean annual precipitation, valley slope, and valley width. These terms are defined in Form 1 included in Appendix A. SCCWRP recommends the use of National Elevation Data (NED) to determine the watershed area, valley slope, and valley width. A review of the NED for San Marcos determined that it is equivalent to USGS quadrangle maps. The topographic resolution on USGS maps is low and typically on a 25-foot contour interval. For this report, recent topographic mapping along San Marcos Creek was used to establish the valley slope and valley width because the topography is at a I-foot contour interval, which is much greater detail than NED. The I-foot contour mapping did not cover the area near Lake San Marcos or the south creek bank between South Bent Avenue and Echo Lane. For these areas, the City of San Marcos' 2-foot contour topographic mapping was used.

The watershed area tributary to San Marcos Creek was established in the March 27, 1991, San Marcos Creek Flood Control Improvement Project - Design Development Study, by Willdan Associates. This report contains hydrologic analyses that detennined the San Marcos Creek watershed area upsh·eam of the Discovery Street bridge to be 17,003 acres (26.57 square miles).

This area was used for Reach 1. The watershed area upstream of the Las Posas Creek confluence was determined to 13,427 acres (20.98 square miles). This area was used for Reach 2 through 4.

A summary table from the rep01t identifying the watershed areas is included in Appendix A.

The mean annual precipitation is provided by the County of San Diego's BMP Sizing Calculator (see Appendix A) and is 13.3 inches. The valley slope of Reach 1 through 4 was determined from the I-foot contour interval topographic mapping in the Study Area Exhibit in Appendix A.

I Reach I Valley Slope, m/m I Valley Width, m
I 1 I 0.0033 I 30
I 2 I 0.0049 I 40
I 3 I 0.0042 I 52
I 4 I 0.0038 I 79
Table 1. Summary of Valley Slope and Width
These values were input to a spreadsheet to calculate the simulated peak flow, screening index, and valley width index outlined in Form 1. The input data and results are included in Appendix A. This completes the initial desktop analysis.

The field screening tool uses combinations of decision trees and checklists. Decision trees are typically used when a question can be answered fairly definitively and/or quantitatively ( e.g., d50 < 16 mm). Checklists are used where answers are relatively qualitative (e.g., the condition of a grade control). Low, medium, high, and very high ratings are applied separately to the vertical and lateral analyses. When the vertical and lateral analyses return divergent values, the most conservative value shall be selected as the flow threshold for the hydromodification analyses.

Visual observation reveals that each study reach contains a densely vegetated, natural watercow-se (see Figures 2 to 16). The vegetative cover extends across the creek bottoms and sides. The cover was so dense that most areas were difficult to access by foot, and some areas were only possible to access if the vegetation was trirnmed. Due to the dense cover and flat valley slopes calculated through Form 1, the vertical and lateral stability was anticipated to have a limited susceptibility to erosion.

1. Labile Bed - sand-dominated bed, little resistant substrate.

2. Transitional/Intermediate Bed - bed typically characterized by gravel/small cobble, Intermediate level ofresistance of the substrate and uncertain potential for armoring.

3. Threshold Bed (Coarse/Armored Bed) - armored with large cobbles or larger bed material or highly-resistant bed substrate (i.e., bedrock).

Channel bed resistance is a function of the bed material and vegetation. Figures 17 through 19 show photographs of the larger bed material in the study reaches. A gravelometer is included in the photographs for reference. Each square on the gravelometer indicates grain size in millimeters (the gravelometer squares range from 2 to 180 millimeters). The larger material in the figures was discovered in some isolated locations and generally ranges from 16 to 32 millimeters (mm). The channel bed material in the reaches is generally of smaller size.

Figures 2 through 16 show dense vegetation throughout Reaches 1 through 4. Vegetation prevents bed incision because its root structure binds soil and because the aboveground vegetative growth can greatly reduce flow velocities. Table 5-13 from the County of San Diego's Drainage Design Manual outlines maximum permissible velocities for various channel linings (Table 5-13 is included in Appendix B). Maximum permissible velocity is defined in the manual as the velocity below which a channel section will remain stable. Table 5-13 indicates that a fully-lined channel with unreinforced vegetation has a maximum permissible velocity of 5 feet per second (fps). Due to the dense cover and large vegetation, the permissible velocity is likely greater than 5 fps in most reach areas. Table 5-13 indicates that 5 fps is equivalent to an unvegetated channel containing cobbles (grain size from 64 to 256 mm) and shingles (rounded cobbles). In comparison, coarse gravel (19 to 75 mm) has a maximum permissible velocity of 4 fps. Based on this infommtion, the heavily vegetated San Marcos Creek channel has an equivalent grain size of at least 64 mm.

Vegetation in a watercourse can be dynamic, i.e., the vegetation size and density can change over time. An increase in vegetation will further reduce the potential for vertical incision, while a decrease can allow greater incision. A primary cause for a reduction in vegetation is removal due to hydraulic forces and shear stress during periods of high flow. Detailed hydraulic analyses of San Marcos Creek along Reaches 1 through 4 show that the flow velocities are primarily non erosive within the range of hydromodification flows. Therefore, the vegetative condition will not be adversely impacted by these flows. A review of historic aerial photos covering nearly the past 20 years indicates that the vegetative growth has tended to increase over time.

Based on the photographs and site investigation, the bed resistance is within the transitional/intermediate bed category. Dr. Eric Stein from SCCWRP, who co-authored the Hydromodification Screening Tool in the Final Hydromod(fication Management Plan (HMP), 5 indicated that a transitional/intermediate bed requires the most rigorous analysis steps and will generate appropriate results for the size range. Transitional/intermediate beds cover a wide susceptibility/potential response range and need to be assessed in greater detail to develop a weight of evidence for the appropriate screening rating. The three primary risk factors used to assess vertical susceptibility for channels with transitional/intermediate bed materials are:

1. Armoring potential - three states (Checklist 1)

2. Grade control - three states (Checklist 2)

3. Proximity to regionally-calibrated incision/braiding threshold (Mobility Index Threshold - Probability Diagram)
These three risk factors are assessed using checklists and a diagram (see Appendix B), and the results of each are combined to provide a final ve1tical susceptibility rating for the intermediate/transitional bed-material group. Each checklist and diagram contains a Category A, B, or C rating. Category A is the most resistant to vertical changes while Category C is the most susceptible.

Checklist 1 determines armoring potential of the channel bed. The channel bed along each of the four reaches is within category B, which represents inte1mediate bed material within unknown armoring potential due to a surface veneer and dense vegetation. The soil was probed and penetration was relatively difficult through the underlying layer. Due to the dense vegetative growth, the armoring potential could have been rated higher, but Category B was conservatively (i.e., more potential for channel incision) chosen.

Checklist 2 determines grade control characteristics of the channel bed. Grade controls can be improvements such as the roadway crossings at Via Vera Cruz, South Bent A venue, and Echo Lane. Each of these crossings consists of a non-erodible surface in a well-maintained condition as well as culverts, which together prevent degradation of the upstream channel bed. This combined with the relatively flat valley slope means that each grade control's influence will extend over a large upstream distance. SCCWRP also states that grade controls can be natural.

Examples are vegetation or confluences with a larger waterbody such as Lake San Marcos. As indicated above and verified with photographs, each reach contains dense vegetation (see Figures 2 through 16). The plant roots and fallen tree trunks serve as a natural grade control. The spacing of these is much closer than the 50 meters identified in the checklist. Further evidence of the effectiveness of the natural grade controls is the absence of headcutting, mass wasting (large vertical erosion of a channel bank), or undercutting of existing drainage facilities. Based on this information, each reach is within Category A on Checklist 2.

The Mobility Index Threshold is a probability diagram that depicts the risk of incising or braiding based on the potential stream power of the valley relative to the median particle diameter. The threshold is based on regional data from Dr. Howard Chang of Chang Consultants and others. The probability diagram is based on d50 as well as the Screening Index determined in the initial desktop analysis (see Appendix A). d50 is derived from field conditions. As discussed above, the gravelometer revealed paiiicles at 16 mm and greater, while the equivalent grain size 6 for the densely vegetated channel is at least 64 mm. The Screening Index for each reach calculated in Appendix A varies from 0.0089 to 0.0274. The Mobility Index Threshold diagram shows that the 50 percent probability of incising or braiding for a d50 of 16 and 64 mm has indexes of 0.049 and 0.101, respectively. Since the Screening Index values for each reach are less than these values, each reach falls well within Category A.

The overall vertical rating is determined from the Checklist 1, Checklist 2, and Mobility Index Threshold results. The scoring is based on the following values:

Category A = -1 , Category B = 0, Category C = 1
The vertical rating score is the sum of the armoring potential score, grade control score, and Mobility Index Threshold score (0 + -1 + -1 = -2). The combined score of -2 is considered a low threshold for vertical susceptibility.

Lateral Stability
The purpose of the lateral decision tree (Figure 6-5 from County of San Diego HMP included in Figure 21) is to assess the state of the channel banks with a focus on the risk of widening.

Channels can widen from either bank failure or through fluvial avulsions such as chute cutoffs and braiding. Widening through fluvial avulsions/active braiding is a relatively straightforward observation. If braiding is not already occurring, the next logical step is to assess the condition of the banks. Banks fail through a variety of mechanisms; however, one of the most important distinctions is whether they fail in mass (as many particles) or by fluvial detachment of individual particles. Although much research is dedicated to the combined effects of weakening, fluvial erosion, and mass failure, SCCWRP found it valuable to segregate bank types based on the inference of the dominant failure mechanism (as the management approach may vary based on the dominant failure mechanism). A decision tree (Form 4 in Ap endix B) is used in conducting the lateral susceptibility assessment. Definitions and photographic examples are also provided below for terms used in the lateral susceptibility assessment.

The first step in the decision tree is to dete1mine if lateral adjustments are occurring. The adjustments can take the form of extensive mass wasting (greater than 50 percent of the banks are exhibiting planar, slab, or rotational failures and/or scalloping, undermining, and/or tension cracks). The adjustments can also involve extensive fluvial erosion (significant and frequent bank cuts on over 50 percent of the banks). Neither mass wasting nor extensive fluvial erosion was evident within any of the reaches. The banks are intact in the photographs included in the figures. The dense vegetation supports the absence of large lateral adjustments.

The next step is to assess the consolidation of the bank material. The banks were moderate to well-consolidated. This determination was made because the banks were difficult to penetrate with a probe. In addition, the banks showed limited evidence of crumbling and were composed of tightly-packed particles (see figures).

Fom1 6 (see A_Qpendix B) is used to assess the probability of mass wasting. Form 6 identifies a 10, 50, and 90 percent probability based on the bank angle and bank height. The 1- and 2-foot contour interval topographic mapping indicates that the maximum bank angle is 2 to 1 7 (horizontal to vertical) or 26.6 degrees in any of the reaches. The majority of the banks are flatter than this. Form 6 shows that the probably of mass wasting and bank failure has less than 10 percent risk for a 26.6 degree bank angle or less regardless of the bank height.

The final step is based on the braiding risk determined from the Mobility Index Threshold in the vertical rating. The braiding risk for each reach is less than 50 percent per the Vertical Stability analysis above. From this, the lateral susceptibility rating is low (red circles are included on the Form 4 Decision Tree in Appendix B showing the decision path).

DMA'S ARE BASED ON THE
ALTERNATIVE 7 SITE PLAN.

DRAINAGE
L
'p
L
'
9i '?,
"' ~ ;..\
~
%
~
'L
~ .. , -
WzEt:jQ;_
--~,
". G). -.
· ~ - ,,.
{;
C=:J MIXED-USE ON PERVIOUS AREA
- MIXED-USE ON IMPERVIOUS AREA
C=:J PAVING ON PERVIOUS AREA
C=:J PAVING ON IMPERVIOUS AREA
[:=J PERVIOUS PAVING ON PERVIOUS AREA

CJ PERVIOUS PAVING ON IMPERVIOUS AREA
C=:J LANDSCAPING ON PERVIOUS AREA
~ LANDSCAPING ON IMPERVIOUS AREA

SUBAREA BOUNDARY
Poe a POINT oF coNcENTRATioN FOR suBAREA

MANAGEMENT AREAS
Figure 2. Looking East towards Discharge of Reach 1 to Lake San Marcos Figure 3. Looking Upstream at West Edge of Reach 1
10 \,,
Figure 4. Looking Downstream at East Edge of Reach 1
Figure 5. Looking Downstream at Reach 1 from Discovery Street Crossing 11 Figure 6. Looking Upstream at Reach 1 from Discovery Street Crossing Figure 7. Looking Upstream along Reach 2 near Las Posas Creek Confluence 12 Figure 8. Looking Upstream along South Edge of Reach 2 Figure 9. Looking Upstream along North Edge of Reach 2
13 Figure 10. Looking Downstream at Reach 3 from Via Vera Cruz Figure 11. Looking Upstream at Reach 3 from Via Vera Cruz 14 Figure 12. Looking Downstream along South Edge of Reach 3 Figure 13. Looking Downstream towards North Edge of Reach 3 15 l•uat:Ui..;u
Figure 14. Looking Upstream at Reach 4 from South Bent Avenue Figure 15. Looking Downstream towards North Edge of Reach 4 16 Figure 16. Looking towards North Edge of Reach 4 from Echo Lane Figure 17. Channe l Material near Via Vera Cruz
17 Figure 18. Channel Material near South Bent Avenue
Figure 19. Channel Material near Echo Lane
18 LABILE BED
• Seno-dominl?led
•dso-<16 mm
• ¾ surface sand > 25¾
• Loosoly-i)OOk.Gd

CHANNEL BED RESISTANCE - ----- - - ---

INTERMEDIATE BED
• Moderately-to loQssfy
p.!ltked eobblc J gr.1\lel
• Hardpan al uncertain
depth, "41Klonl Orcxitliil','

EXAM INE RISK FACTORS
• grade oon trol
• armoring poten tial
• J:.Ymiimily lo incision thre:shokl

COARSE/ARMORED BED
•d...11 :> 128mm
• 8-0ulder / large cobble
• tightly-packed
• '-5'11i sand
• ConUnuous boorock
• Continuous concmte
go to bed erodibility
checklists and incision
diagram check list
Fill out SCCWRPsa;mg
criteria to determine if'lhe
r4;!c1,!lving channel has a HIGH,
IJEOIUM, or LOW susceplibi 'iy
Figure 6-4. SCCWRP Vertical Susceptibility
Figure 20. SCCWRP Vertical Channel Susceptibility Matrix .:,) hkel 110cd al
COi~ rouuro
b) Pf""l mJly lo
braidm!J
J.2'!>:.

NO
• F\Jly 8m'Ored J OOdroc~ !laflX
~f;.lbll26'01 in 0000 ClY>lltla,
•· N-!> e-11denc;;e• d chuM!
l'DIT"'1bon / ll\lUl&IOns
• Fvry c,:,,,f,ol!<l, dlt!Clly
r,c;»Yl~<hlid 10 h,tsida. vu,1-1
Bartkh!t!;lhl
-<10'r. logstc:
r_ak f<Y~
- - - ... - ~
85"1)." ~~
>10% logslc
,s:~~•an~•
ANOVWI > '2
None, or ns..ai C1'1lr ln-.mrl lo
ber>d& ml OO!t!tllct~
AU. BANK STRATA
Cot4SOLIDA1cD
INtJ.UOl tlK. TOE7
C~tft~l
1 nos,st,r, I loo, d
,. 64 '11111
NO

MASS WASTING OR
EXTEX.SIVE FWVIAL
EROSION OR CHUlE
CUTOFF FORW, Tl<lN
PD01y or Jra:noolmlctll
F-tl8
unc..,.,..old-"lled
AtlD VVt ~ 2
F"'G
ul"ICOn!!aldali,d
AHDVWI > 2
___________ ..,..,.. ..... __ ..._ ______ _
Figure 6-5. Lateral Channel Susceptibility
Figure 21. SCCWRP Lateral Channel Susceptibility Matrix

APPENDIX A

SCCWRP INITIAL DESKTOP ANALYSIS
November, 2009 Revised Draft for Field Testing/TAC Review 6 FORM 1: INITIAL DESKTOP ANALYSIS
IF required at multiple locations, circle one (applicant site, upstream extent, downstream extent)
Location: Latitude: 33• 1363 Longitude:. __ -1_1_7._1_71_6 ____ _ Description (river name, crossing streets, etc.):. __ s_a_n_M_a_r_co_s_c_r_e_ek_ fro_m __ _ upper end of Lake San Marcos to Echo Lane
GIS Parameters: US Customary units used for contributing drainage area (A) and mean annual precipitation (P) to apply regional flow equations after the USGS Symbol
A VI "C (/) .~
(l) (l) C
.c ·- :::J <flt
~ (l) .c
p * g-~ S
~ Ol
C. C
w
Sv
<fl
(l)
t VI
~'E e ::::i
c.- Wv 2~
u5
Table 2.1: Initial desktop analysis in GIS
Variable
(units
Area
(mi2)
Mean annual
precipitation
(in.)
Valley slope
(m/m)
Valley width
(m)
Value Description and Source
contributing drainage area to location via published Hydrologic Unit Codes (HUCs) and/ors 30 m National Elevation Data (NED) , USGS seamless server
area-averaged annual precipitation via USGS delineated
polygons using records from 1900 to 1960 (Natural Resources Conservation Service (NRCS) shape file using records from 1961 to 1990 was less accurate in hydrologic models)
geomorphically-defined valley slope at site via NED, dictated by watershed configuration , confluences , consistent valley widths, etc., over a distance of up to ~500 m or 10% of the main-channe l length from site to drainage divide (whichever is smaller) valley bottom width at site from natural valley wall to valley wall, dictated by clear breaks in surface slope on NED raster, irrespective of potential armoring from floodplain encroachment , levees, etc.

Table 2.2: Simplified peak flow (Hawley and Bledsoe, In review), screening index, and valley width index
Symbol Dependent Variable Value Equation
(units)
01octs 10-yr peak flow (ft3/s) O1octs = 18.2 *Ao.a ?* P 0•77 010 10-yr peak flow (m3/s) 010 = 0.0283 * O1octs
INDEX 10-yr screening index (m 1 5/s0•5) INDEX= S/O 10 0.5 Wref Reference width (m) W,et = 6.99 * 010 0.438
VWI Valley width index (m/m) VWI = W./W,er
Note: Gray highlighting indicates values directly used in field assessments Required
units
A (mi2)
P (in .)
O1oc1s (cfs)
Sv (m/m)
O,o (m3/s)
010 (m3/s)
Wv (m)
Wre1 (m)
(Sheet 1 of 1)
SCCWRP FORM l ANALYSES
Area Mean Annual Precip. Valley Slope Valley Width 10-Year Flow 10-Year Flow 10-Year Screening Ind ex Reference Width Valley Width Index Study Reach A, sq. mi. P, inches Sv,m/m Wv,m Q10ds, cfs Q10, ems INDEX Wref, m VWl, m/m Reach 1 26.57 13.3 0.0033 30 2,315 65.5 0.0267 43.66 0.69 Reach 2 20.98 13.3 0.0049 40 1,885 53.4 0.0358 39.90 1.00 Reach 3 20.98 13.3 0.0042 52 1,885 53.4 0 .0307 39.90 1.30 Reach 4 20.98 13.3 0.0038 79 1,885 53.4 0.0278 39.90 1.98 ~ -
SMC-U/S Discovery St. Bridge and ...

D/S L.P. & Discovery S.D. Confluence
SMC-U/S Las Posas & Discovery S.D. Confluence
SMC-U/S Of S.R. 78 Crossing
SMC-DJS North & East Branch Confluence
SMC-East Branch-UIS North Branch Confluence
SMC East Branch - 1700' E/O Valpreda Rd.

SMC East Branch - N/O A.T.&S.F. R.R.,
1100' W/O Woodland Prkwy. / Ricliland
SMC East Branch - S/O Mission @ Woodland
Prkwy/Richland
SMC East Branch - Rock Springs Rd. @
Knob Hill Rd.

SMC North Branch - U/S E. Branch Confluence
SMC North Branch - 1300' U/S Of Mission
SMC Norlh Branch - 1500' U/S Of Borden Ad.

SMC Norlh Branch - U/S Of La Cienega Rd.

SMC North Branch - 1500' U/S Of Olive Dr.

Las Posas Branch - U/S Of SMC Confluence
Las Posas Branch - U/S Of San Marcos Blvd.

Las Posas Branch - U/S Of Grand Ave.

Las Posas Branch - Las Posas Ad., 500' N/O Fwy
las Posas Branch - @ Proposed Detention Basin
Proposed Discovery St. S.D. System • • •
East Barham Area S.D. System (Confluence Pt.
1700' E/O T.O. Vly Rd.)
Vineyard Rd. S.D. System
NOTES
TSM 339
TSM 302
CONC. PT
291-2
221-0
231-0
241-1
161-0
-
261-0
-
151-0
241-0
181-0
101-0
71-0
41-0
-
211-0
-
191-0
91-0
291-0
271-0
171-0
• • • No Detention Taken For Proposed Discovery Hills Dev't

CONTRIBUTING
AREA (Acres)
17,003
13,427
12,638
11,775
4,660
3,600
3,010
2,516
7,115
6,975
6,145
4,786
3,376
2,113
936
542
1,464
315
377
1990 SAN MARCOS CREEK DESIGN DEVELOPMENT STUDY

ULTIMATE BUILDOUT CONDITION

WILLDAN ASSOCIATES
100 YEAR FREQUENCY 10 YEAR FREQUENCY
24 HOUR DURATION 6 HOUR DURATION 24 HOUR 6 HOUR
(AVERAGE) (AVERAGE)
AMC2 AMC 2.5 AMC 3 AMC 2 AMC 2.5 AMC 3 AMC 2 AMC2
13,400 14,775 16,150 13,850 18,050 22,250 7,100 6,650
10,450 11,625 12,800 11,200 14,875 18,550 5,500 5,200
9,850 11,000 12,150 11,150 14,750 18,350 5,300 5,250
9,150 10,250 11,350 10,250 13,625 17,000 4,900 4,800
4,000 4,400 4,800 5,950 7,500 9,050 2,200 2,950
3,100 3,400 3,700 5,000 6,150 7,300 1,700 2,600
2,200 2.400 2,600 3,550 4,350 5,150 1,250 1,850
5,350 6,025 6,700 5,050 6,975 8,900 2,800 2,350
5,250 5,900 6,550 4,950 6,875 8,800 2,700 2,300
4,600 5,200 5,800 4,550 6,400 8,250 2,400 2,100
3,500 4,025 4,550 3,650 5,225 6,800 1,800 1,700
2,500 2,875 3,250 2,900 4,000 5,100 1,250 1,300
2,000 2,075 2,150 3,350 3,725 4,100 1,200 2,050
800 850 900 1,150 1,325 1,500 500 700
550 575 600 950 1,075 1,200 300 550
1,300 1,400 1,500 1,800 2,200 2,600 750 950
250 300 350 400 525 650 150 200
350 375 400 600 700 BOO 200 350
Compliance Basin Summary
Basin Name: San Marcos SP Basin
Receiving Water: San Marcos Creek
Rainfa ll Basin Oceanside
Mean Annual Precipitation (inches) 13.3

MEAN ANNUAL PRECIPITATION FROM

COUNTY OF SAN DIEGO BMP CALCULATOR

APPENDIX B

SCCWRP FIELD SCREENING DATA
Chapter 5. Open Channels
Table 5-13 Maximum Permissible Velocities for Lined and Unlined Channels Material or Lining
Natural and Improved Unlined Channels
Maximum Permissible
Average Velocity• (ft/sec)
Fine Sand, Colloidal .................................................................... ................................................ 1.50 Sandy Loam , Noncolloidal ····································· ····································-················· ·············· 1·75 Silt Loam , Noncollo idal.. ............................ ................................. _ ................................. .............. 2.00 Alluvial Silts, Noncolloidal ······························-··-···· ··-································ ······························· 2.00 Ordinary Firm Loam ······· ········-··· ··········· ·······························•····•················································ 2.50 Volcanic Ash .................................. ............................................................. ................................ 2.50 Stiff Clay, Very Colloidal ....................................................................................... ....................... 3.75 Alluvial Silts, Collo·dal ............................................................................ ..................................... 3.75 Shales And Hardpans ··········································· ············ ················· ·······························-········ 6.00 Fine Grave l ...........•............. •················· ···································· ······••··•···-··································· 2.50 Graded Loam To Cobbles When Noncolloidal ........................................................................... 3.75 G1m.J1:1d Sills Tu ColJI.Jlt:1!:i Wl11:111 Collu iuc1I.. .................................. ............... _ .............. ................. 4.00 Coarse Grave l, Noncollo idal ............ .......................................... ................................................. 4.00 Cobbles And Shingles ................ ............... ....................... ........................................... =~····· 5.00 Sandy Silt ........................................................................ ...................................... ..................... 2.00 Silty Clay ······································-········-····················-·· ···············································•··········· 2.50 Clay ············· ·································-··· ············································································ ············· · 6.00 Poor Sedimentary Rock ............... ............. ................................................. ................................. 10.0 Fully-Lined Channels
Unreinfo rced Vegetation ........................................................................... ................................... 5.0 Reinforced Turf ···························-········· ······································ ·············· ···········- ········•·•········ '10.0 Loose Riprap .......................................................... .......................................... ............ per Table 5-2 Groute d Riprap ......................... .................... ........................................................................ ...... 25.0 Gabions ............................................... ....................................................................................... 15.0 Soil Cement .................. ........................................................... ................................................... '15.0 Concrete ....................... ......................................... ..................................................................... 35.0 • Maximum permissible veloeily llsfed here is basic guideline; hlgner design velocities may be used, provided approprfare technical documentatio.1 from manufacturer.

San Diego County Drainage Design Manual
July 2005

Page 5 ends

San Marcos City CouncilJune 25, 2024

San Marcos City Council
June 25, 2024