New Development / C.3

Provision C.3 in the Municipal Regional Permit (MRP) requires site designs for new developments and redevelopments to minimize the area of new roofs and paving. Where feasible, pervious surfaces should be used instead of paving so that runoff can infiltrate to the underlying soil. Remaining runoff from impervious areas 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 allow municipalities to verify that stormwater treatment and flow-control facilities are maintained in perpetuity.

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 76 local government entities, including those in western and central Contra Costa County. The Central Valley Regional Water Quality Control Board has adopted permit requirements, similar to those in the MRP, that apply to eastern Contra Costa cities and the eastern portion of the unincorporated area. 

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

Most publications accessible from the C.3 pages are formatted for both on-line navigation and 2-sided printing. Many require Adobe Acrobat Reader 7.0 or later, available free at

What’s New

  • The PowerPoint presentation from the June 7, 2016 training, “Low Impact Development Planning, Design, and Construction,” is available here.
  • The Stormwater C.3 Guidebook, 6th Edition, has been amended by a March 2016 “Stormwater C.3 Update,” available here.
  • Effective December 1, 2012, projects that create or replace 2,500 square feet or more, but less than 10,000 square feet, of impervious surface must implement site design measures to reduce stormwater runoff. “Preparing a Stormwater Control Plan for a Small Land Development Project,” a November 28, 2012 addendum to the Stormwater C.3 Guidebook, is available for download on the C.3 Guidebook page.
  • Stormwater C.3 Guidebook 6th Edition, approved February 15, 2012. Supersedes the 5th Edition in effect since October 2010.
  • Stormwater Control Plan template, in MS Word format, to assist applicants in preparing the required project submittal.
  • Suppliers of bioretention soil mix are listed here.
  • IMP Sizing Calculator available at the C.3 Guidebook page. It includes a help document.

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