CCCWP’s Stormwater C.3 Guidebook and resources below have been updated to reflect new stormwater permit requirements (MRP 3.0 Provision C.3).
The Municipal Regional Stormwater NPDES Permit (MRP) Provision C.3 concerns New Development and Redevelopment. The goal of MRP Provision C.3 is, “…[To] address stormwater runoff pollutant discharges and prevent increases in runoff flows from new development and redevelopment projects. This goal is to be accomplished primarily through the implementation of low impact development (LID) techniques” (MRP 1.0-3.0, page C.3-1).
In 2022, the San Francisco Bay Regional Water Quality Control Board adopted the third reissuance of the MRP, or MRP 3.0, which was later amended in October 2023. This reissuance includes significant changes and additional requirements in Provision C.3.
To learn more, visit our webpages: NPDES Permit and New in MRP 3.0
Please refer to this latest Guidebook for projects subject to MRP 3.0 and Regulated Projects (C.3.b.) submitted for review on or after April 17, 2024.
(NEW!) Download the Stormwater C.3 Guidebook 9th Edition, Revised June 2025 (PDF).
The 9th Edition reflects Contra Costa Permittees’ adoption of the Bay Area Hydrology Model (BAHM). This edition was approved April 17, 2024 and now includes minor revisions to improve ease of use. Please refer to this latest Guidebook for projects subject to MRP 3.0 and Regulated Projects (C.3.b.) submitted for review on or after April 17, 2024.
Note: The new C.3 Development Review Checklist, updated Stormwater Control Plan template, link to BAHM, updated IMP Calculator, and updated Hydromodification Management (HM) Applicability Map information can be found further on this webpage.
For projects approved between July 1, 2023 – April 16, 2024, and for projects subject to MRP 2.0, see the 8th and 7th Edition C.3 Guidebooks in the Older Resources section (bottom of this webpage)
Municipality-specific procedures, policies and submittal requirements should be obtained from the municipality’s planning and community development department.
Follow the link to the local municipality website:
(NEW!) Download the Development Review Checklist (Excel file) (April 17, 2024). This checklist was adapted from the San Mateo Countywide Pollution Prevention Program’s checklist.
View the Frequently Asked Questions (FAQs) for Development Projects (PDF) (April 2024).
Please note that the resources below may be updated periodically to reflect changes to the MRP and/or Stormwater C.3 Guidebook. To obtain Word document versions of templates (like the Stormwater Control Plan Template) or other documents, please contact the CCCWP at cleanwater@pw.cccounty.us or 925-313-2360
The purpose of the template is to help applicants prepare the required project submittal.
(NEW!) Download the updated Stormwater Control Plan Template, based on the 9th Edition (PDF) (April 17, 2024).
The following documents may be incorporated into Stormwater Facilities O&M Plans.
BAHM is required to be used for Hydromodification Management (HM) compliance demonstration purposes, for applicable projects submitted for review on or after April 17, 2024.
Download BAHM 2023 (clearcreeksolutions.info). BAHM was created by Clear Creek Solutions and was updated in 2023 to incorporate Contra-Costa specific environmental data.
View the BAHM 2023 Training Videos (clearcreeksolutions.info). The trainings & materials are free, but you must first create a log-in in (Click “Log In”, “Create Account”, and then Fill in your information). You can also get access by sending Clear Creek Solutions a request here.
BAHM Training videos without the materials are available on Clear Creek Solutions’ Youtube channel:
CCCWP’s HM Applicability Map should be used for rapid initial determination of whether location-based HM requirements apply to proposed land development projects.
View the CCCWP 2023 HM Applicability Map, Web Application Format (CCCWP.maps.arcgis.com) (approved February 1, 2024). The CCCWP 2023 HM Applicability Map should be used for rapid initial determination of whether location-based HM requirements apply to proposed land development projects in jurisdictions across Contra Costa County.
The 2023 HM Applicability Map was created for Contra Costa Permittees in compliance with Provision C.3.g. of the Municipal Regional Stormwater Permit issued by the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB). The 2023 HM Applicability Map was approved by the SFBRWQCB on February 1, 2024.
Methodology and data sources used to create the 2023 HM Applicability Map are explained in the following addendum (2023) to the technical memorandum (2017, see Archive at bottom of page):
CCCWP’s IMP Calculator is a free tool to assist in the design and sizing of IMPs.
Download the Updated IMP Calculator, Version 1.4.1, September 2024 (.zip file).
This version, released September 27, 2024, includes the following fix to the updated calculator that was released April 2024: for Road Reconstruction projects, if the user changes the mean annual precipitation the minimum sizing now automatically recalculates. Both the April and the September 2024 versions are compatible with the 9th Edition Guidebook.
IMP Calculator Help Documentation (.pdf)
Consistent with the 9th Edition. Be sure to review and follow Guidebook instructions for preparing a complete Stormwater Control Plan.
To view the 2009 version of the IMP Calculator and troubleshooting information for the 2009 IMP Calculator, see the Archive section below.
The plant palette below is an independent, stand-alone resource that may be used by development professionals who are considering plants with low or very low irrigation needs, for use in GSI facilities.
Download the GSI Low Irrigation Plant Palette (4/23/25) (.xlsx)
Prepared by: John Steere (Watershed Planner, Contra Costa County Watershed Program). Additional input and review by: Connie Goldade (Community Design Consultants), Peter Schultz-Allen (EOA), Erin Lennon (Contra Costa Clean Water Program, CCCWP), Yvana Hrovat (Haley and Aldrich), and various members of the Bay Area Stormwater Collaborative (BAMSC) Development Subcommittee and its Work Groups.
Important Notes: This palette is not directly affiliated with the CCCWP C.3 Guidebook, nor any of the guidebooks, resources, and organizations it references. Users should cross-check their plant selection with any relevant local requirements and resources based on case-by-case conditions, limitations, and considerations. Please note that the selection of plants with lower water or maintenance needs does not preclude the need for on-site irrigation and maintenance. Each GSI facility should be designed, constructed, and operated and maintained in a manner appropriate for its intended functionality.
The links below lead to external resources to assist with the use of soil media and mulch in stormwater biotreatment areas. Copies of the PDFs referenced are in the Archive section below.
(New!) Download CCCWP Bioretention Detail Sheets (.zip) and SMC GI Detail Sheets (.zip)
San Mateo County GI Details and Specifications sheets were modified with permission by Lotus Water and reviewed by CCCWP member agencies during FY2023-2024. The final modified versions are available starting on page 192 of the 9th Edition C.3 Guidebook. AutoCAD (ACAD) drawings of the typical GI details are provided in the zip files above, such that the design professionals must modify the plan, sections, call-outs, and/or construction notes to address the project’s site-specific conditions and local permitting agency requirements.
The San Mateo County GI Details file contains ACAD files of all of the unmodified SMC detail sheets.
The CCCWP Bioretention Details file contains the ACAD files of all of the modified detail sheets:
(LEGACY) View the previous Stormwater C.3 Guidebook 8th Edition (PDF) (December 23, 2022). For projects subject to MRP 3.0 and Regulated Projects (C.3.b.) approved between July 1, 2023 – April 16, 2024. This edition reflected the new requirements in MRP 3.0 and superseded the 7th edition in effect since 2017.
(LEGACY) View the previous Stormwater C.3 Guidebook, 7th Edition (PDF) (June 21, 2017). For projects subject to MRP 2.0.
(LEGACY) View the previous Stormwater Control Plan Template, based on the 8th edition (PDF)* (February 2023), consistent with the Stormwater C.3. Guidebook 8th Edition.
(LEGACY) View the previous Stormwater Control Plan Template, based on 7th Edition (PDF)*
Please note that the 7th and 8th Edition Stormwater C.3 Guidebooks and Templates are legacy documents. For projects subject to MRP3.0 (published May 11, 2022, amended October 2023) and for Regulated Projects (C.3.b.) submitted for review on or after April 17, 2024, please refer to the 9th Edition Guidebook and Template.
The 2017 HM Applicability Mapping Methodology Technical Memorandum, with 2023 Addendum (PDF) includes background information and context for the updated 2023 HM Applicability Map addendum.
The soil specification approved April 18, 2016 (PDF) includes the following statement: “Local soil products suppliers have expressed interest in developing ‘brand-name’ mixes that meet these specifications. At their sole discretion, municipal construction inspectors may choose to accept test results and certification for a ‘brand-name’ mix from a soil supplier.”
For the convenience of the land development community, the Contra Costa Clean Water Program invited local soil suppliers to request listing here. The following suppliers submitted test results and certifications. Listing does not imply or guarantee that the mix as designed or delivered meets all requirements of the soil specification. Contractors and construction inspectors should independently obtain and review the required information before approving installation of a ‘brand-name’ soil mix.
Policies and content of the following memoranda were incorporated into the 7th Edition. The memoranda include some additional background and explanatory material.
Please note that the 7th and 8th Edition Stormwater C.3 Guidebooks and Templates are legacy documents. For projects subject to MRP3.0 (published May 11, 2022, amended October 2023) and for Regulated Projects (C.3.b.) submitted for review on or after April 17, 2024, please refer to the 9th Edition Guidebook and Template.
To obtain Word document versions of templates (like the Stormwater Control Plan Template) or other model documents marked with an asterisk, please contact the CCCWP at 925-313-2360
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