C.3 Requirements: Development
New C.3 Requirements
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 are in the process of being updated to reflect new permit requirements. Stay tuned!
*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 email@example.com 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.
(NEW) Updates to Stormwater Control Plan Template (PDF)*, to help applicants prepare the required project submittal (updated per 8th Edition Guidebook updates).
- (NEW) Stormwater C.3 Guidebook 8th Edition (PDF), published December 23, 2022. This edition reflects the new stormwater compliance requirements in MRP 3.0. Supersedes the 7th Edition, published 2017.
(NEW) Updates to the C.3 Guidebook page, to reflect new requirements for land development projects in MRP 3.0.
(NEW) 2-page C.3 Factsheet/Handout for Developers, Engineers, Planners, and Project Applicants on the New in MRP 3.0 page.
(NEW) 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.
Example Stormwater Control Plans for a Commercial Project and for a Residential Subdivision on the C.3 Guidebook page.
Example Stormwater Facilities Operation and Maintenance Plans for a Commercial Project and for a Residential Subdivision on the C.3 Guidebook page.
Stormwater Facilities Operation and Maintenance Plan template (PDF)*.
Suppliers of bioretention soil mix are listed here.
- IMP Sizing Calculator available at the C.3 Guidebook page. It includes a help document.