C3 Guidance: Development
Provision C.3 in the Municipal Regional Stormwater Permit (MRP) 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.
In addition, project applicants must exectue agreements to allow municipalities to verify tht stormwater treatment and flow-control facilities are maintained 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.
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 www.adobe.com.
Guidebook Update, May 20, 2020: Bioretention Sizing (treatment only). 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).
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.
Stormwater C.3 Guidebook 7th Edition, approved June 21, 2017. Supersedes the 6th Edition in effect since 2012.
Suppliers of bioretention soil mix are listed here.
- IMP Sizing Calculator available at the C.3 Guidebook page. It includes a help document.