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New Development/Provision C.3.

In February 2003, the California Regional Water Quality Control Boards for the San Francisco Bay Region and the Central Valley Region revised Provision “C.3″ in the NPDES permit governing discharges from the municipal storm drain systems of Contra Costa County and cities and towns within the County. The permit provision was phased in from 2004 through 2006.

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

Project site designs must minimize the area of new roofs and paving. Where feasible, pervious surfaces should be used instead of paving so that runoff can percolate to the underlying soil. Runoff from impervious areas must be captured and treated. The permit specifies ways to calculate the required size of treatment devices.

Projects may also be required to detain or infiltrate runoff so that peak flows and durations match pre-project conditions.

In addition, project applicants must prepare plans and execute agreements to ensure the stormwater treatment and flow-control facilities are maintained in perpetuity.

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 this page are formatted for both on-line navigation and 2-sided printing. Many require Adobe Acrobat Reader 5.0 or later, available free at www.adobe.com.

What’s New

  • Stormwater C.3 Guidebook Updates and Errata include recommended specifications for the soil and gravel layers in planter boxes, swales, and bioretention areas (Latest update May 30, 2007)
  • Construction Workshops September 25-26, 2007. Includes instructions and calculations for the “bucket test” to measure the infiltration rate of soil mixes for bioretention facilities.
  • Policy on Selection of Stormwater Treatment Facilities for Maximum Extent Practicable Effectiveness in Compliance with NPDES Provision C.3 (March 21, 2007, 146 KB .pdf).
  • The Alameda County Clean Water Program’s C.3 Technical Guidance includes a detailed Plant List and Planting Guidance for Landscape-Based Treatment Measures
  • Appendix I includes the Program IMP Sizing Calculator, which may be used to size Low Impact Development Integrated Management Practices (IMPs) to meet treatment-only requirements or treatment-plus-flow-control requirements in Contra Costa municipalities. Appendix I also includes detailed instructions for sizing IMPs using a manual calculation method. (updated December 5, 2006)
  • “Stormwater C.3 Update” (July 2006, 227 KB .pdf)
  • “Stormwater Control Plan Required” Fact Sheet
    to accompany the Stormwater C.3 Guidebook (Updated October 2006, 4 pp., 250 KB .pdf). 11″ x 17″ version.
  • Stormwater C.3 Guidebook, Third Edition approved by the Contra Costa Program Management Committee, October 18, 2006.
  • Stormwater Treatment and Flow-Control Requirements for New Developments workshops for land development design professionals and municipal planners, engineers and development review staff, October 24 and 26, 2006. Agenda, handouts, and presentations.
  • New Example Stormwater Control Plan in Appendix G to the Stormwater C.3 Guidebook (Almondridge East Stormwater Control Plan posted October 4, 2006).