New C.3 Requirements

The San Francisco Bay Regional Water Quality Control Board has adopted the third reissuance of the Municipal Regional Stormwater Permit, or MRP 3.0.  This reissuance includes significant changes and additional requirements in Provision C.3.  Summary of key changes below. 

Effective July 1, 2023:

  • Impervious surface threshold for most projects will drop from 10,000 to 5,000 sq ft, including for new roads and the addition of a travel lane to an existing road.​
  • New categories of regulated projects include:
    • Road and sidewalk repair projects ≥ 5,000 contiguous sq ft
    • Road reconstruction and pavement widening ≥ 1 contiguous acre
    • Detached single family home that creates or replaces ≥ 10,000 sq ft

Please note that the C.3 Guidebook and related resources referenced in this site have been updated to reflect new permit requirements.

*To obtain Word document versions of templates (like the Stormwater Control Plan Template) or other documents marked with an asterisk, please contact the CCCWP at cleanwater@pw.cccounty.us or 925-313-2360

Provision C.3 requires site designs for new developments and redevelopments to minimize the area of new roofs and paving. Runoff should be dispersed to landscaping where possible. Where feasible, pervious pavements can be used so that runoff can infiltrate to the underlying soil. Remaining runoff from roofs and pavement must be treated using bioretention. In some developments, the rates and durations of site runoff must also be controlled.

In addition, project applicants must execute agreements to maintain stormwater treatment and flow-control facilities in perpetuity.

The C.3 requirements are separate from, and in addition to, Provision C.6 requirements for erosion and sediment control and for pollution prevention measures during construction.

Contra Costa municipalities have adopted the Contra Costa Clean Water Program’s Stormwater C.3 Guidebook to establish criteria and to assist applicants through the process of submittals and reviews.

Most publications accessible from the C.3 pages are formatted for both on-line navigation and 2-sided printing. 

What’s New  

  • Updates to the C.3 Guidebook page, to reflect new and updated resources for land development projects, including the following:
    • ​(NEW!) Stormwater C.3 Guidebook 9th Edition (PDF) (April 17, 2024).  This edition reflects Contra Costa Permittees’ adoption of the Bay Area Hydrology Model (BAHM) and updated resources for land development and redevelopment projects.  Supersedes the 8th Edition, published 2022.
    • (NEW!) Updated Stormwater Control Plan Template (PDF)* (April 17, 2024).  This template helps applicants prepare the required project submittal (updated per 9th Edition Guidebook updates).
    • (NEW!) New Development Review Checklist (Excel file) (April 17, 2024).  This checklist was adapted from the San Mateo Countywide Pollution Prevention Program’s checklist.
    • (NEW!) Links to the Bay Area Hydrology Model (BAHM) and BAHM Trainings (clearcreeksolutions.info).  BAHM is required to be used for HM compliance demonstration purposes, for applicable projects submitted for review on or after April 17, 2024.  BAHM was created by Clear Creek Solutions and was updated in 2023 to incorporate Contra-Costa specific environmental data.
    • (NEW!) IMP Calculator Updates (Apr 17, 2024). The IMP Calculator was updated per the 9th Edition Guidebook updates, including the adoption of BAHM for HM compliance.
    • Updated CCCWP 2023 HM Applicability Map, Web Application Format (CCCWP.maps.arcgis.com) (February 1, 2024).  This map was created for rapid initial determination of whether location-based HM requirements apply to proposed land development projects in jurisdictions across Contra Costa County.
  • MRP 3.0 (PDF at waterboards.ca.gov), adopted May 11, 2022 by the San Francisco Bay Regional Water Quality Control Board.  Order No. R2-2022-0018 NPDES Permit No. CAS612008.