C3 Guidance: Development

The California Regional Water Quality Control Board for the San Francisco Bay Region reissued the MRP in November 2015 (MRP 2.0). MRP 2.0 governs discharges from municipal storm drains operated by 79 local government entities, including those in Contra Costa County. MRP 2.0 requires municipalities to protect our local creeks, reservoirs, watersheds, Delta, and Bay from contamination and pollution. Construction activities and businesses need to implement Best Management Practices to prevent pollutants from running off into storm drains. 

Provision C.3 in the MRP 2.0 requires site designs for new developments and redevelopments to minimize the area of new roofs and paving and treat runoff, and in some cases, control the rates and durations of site runoff. Where feasible, pervious surfaces should be used instead of paving so that runoff can infiltrate to the underlying soil. Runoff should be dispersed to landscaping where possible. Remaining runoff from impervious areas must be treated using bioretention. In some developments, the rates and durations of site runoff must also be controlled.

The C.3 requirements are separate from, and in addition to, requirements for erosion and sediment control and for pollution prevention measures during construction. In addition, project applicants must execute agreements to allow municipalities to verify that stormwater treatment and flow-control facilities that are approved as part of new development are maintained in perpetuity.

Provision C.6 in the MRP 2.0 requires construction projects to implement erosion controls, sediment controls, and good housekeeping practices to prevent the release of sediment (dirt) and construction materials during the active phases of construction. 

Through the Contra Costa Clean Water Program, Contra Costa municipalities have prepared a Stormwater C.3 Guidebook to assist applicants through the process of submittals and reviews.

Quick Links

  • Stormwater C.3 Guidebook 7th Edition, approved June 21, 2017. Supersedes the 6th Edition in effect since 2012.

  • Example Stormwater Control Plans for a Commercial Project and for a Residential Subdivision on the C.3 Guidebook page.

  • Stormwater Control Plan template, in MS Word format, to assist applicants in preparing the required project submittal (based on the 7th Edition).

  • Stormwater Facilities Operation and Maintenance Plan template.

  • Example Stormwater Facilities Operation and Maintenance Plans for a Commercial Project and for a Residential Subdivision on the C.3 Guidebook page.

  • Suppliers of bioretention soil mix are listed here.

  • IMP Sizing Calculator available at the C.3 Guidebook page. It includes a help document.