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 captured and used or 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 adopted the MRP in October 2009. The MRP governs discharges from municipal storm drains operated by 76 local government entities, including those in western and central Contra Costa County.

The MRP supersedes C.3 requirements in the preceding permit, which were in effect from 2005 until 2009. The additional MRP requirements are being phased over the 5-year permit term. In September 2010, the Central Valley Regional Water Quality Control Board adopted requirements, similar to those in the MRP, that apply to eastern Contra Costa cities. The San Francisco Bay RWQCB amended the MRP C.3 Provisions on November 28, 2011.

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

  • Slides from the June 12, 2014 training, Low Impact Development Planning, Design, and Construction, are available on the C.3 Workshops and Conferences page.
  • A March 20, 2013 addendum to the Stormwater C.3 Guidebook, 6th Edition, Contra Costa Clean Water Program Technical Criteria for Non-LID Facilities, details requirements that apply to tree-box-type high-flowrate biofilters and vault-based high-flowrate media filters when proposed for use on Special Projects (see the Guidebook 6th Edition, page 58).
  • A new 2-page C.3 Update handout (February 2013) summarizes thresholds and requirements for small development projects and Regulated Projects.
  • 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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