Stormwater C.3 Guidebook

Stormwater C.3 Guidebook 7th Edition

Guidebook Update, May 20, 2020: Bioretention Sizing (treatment only). "With justification--to the satisfaction of the municipal reviewer and documented as detailed below--the facility area may be smaller than 4% of tributary impervious area, but must be as large as feasible for the specific application. All facilities must be at least as large as the minimum sizes determined by the following equation..." Redline text with staff report and presentation slides (1.7 MB .pdf).

Click on this link to download the Stormwater C.3 Guidebook 7th Edition (June 21, 2017, 2.6 MB .pdf formatted for 2-sided printing).

Here is a memorandum describing changes from the Guidebook 6th Edition.

Additional Guidebook Resources

Stormwater Control Plan Template

The template is consistent with the Stormwater C.3 Guidebook 7th Edition (40KB .docx).

Example Stormwater Control Plans

Bioretention Soil Media Specification

Click here to download the updated bioretention soil media specification approved April 18, 2016. (See BASMAA and Executive Officer letters for an explanation of the changes.)

IMP Sizing Calculator

Released October 2009. Consistent with the 7th Edition. Be sure to review and follow Guidebook instructions for preparing a complete Stormwater Control Plan. Calculator and setup file (3MB .zip).

NOTE (November 2020): A recent Chrome update added a security feature to prevent users from downloading self-executing .zip files. The workaround (using Chrome) is to right-click on the link and select “Save link as.” This will open a file manager window to allow you to select the location on your computer where the downloaded file will go. Click “Save” and Chrome will give you a notification (at the bottom of the browser window) that the file can’t be downloaded securely and invite you to discard. Click the up-arrow to the right of the “discard” button and select “Keep”. So far, the download seems to work fine using the Microsoft Edge and Firefox browsers.

After installing the calculator, read the help file. If attempting to run the calculator results in an error message, try right-clicking the icon and selecting “Run as Administrator.” If you can't run as administrator, talk to your IT department. If you get a response stating that you need to install .net Framework 2.0, the information on this page may be useful.

Appendix A: Local Exceptions and Requirements

Municipality-specific procedures, policies and submittal requirements should be obtained from the municipality’s planning and community development department.

Follow the link to the local municipality website:

Appendix B: Soils, Plantings, and Irrigation for Bioretention Facilities

The soil specification approved April 18, 2016 includes the following statement: “Local soil products suppliers have expressed interest in developing ‘brand-name’ mixes that meet these specifications. At their sole discretion, municipal construction inspectors may choose to accept test results and certification for a ‘brand-name’ mix from a soil supplier.”

For the convenience of the land development community, the Contra Costa Clean Water Program invited local soil suppliers to request listing here. The following suppliers submitted test results and certifications. Listing does not imply or guarantee that the mix as designed or delivered meets all requirements of the soil specification. Contractors and construction inspectors should independently obtain and review the required information before approving installation of a ‘brand-name’ soil mix.


Policies and content of the following memoranda have been incorporated into the 7th Edition. The memoranda include some additional background and explanatory material.

Contra Costa Hydrology Data

Operation and Maintenance of Stormwater Facilities

Stormwater Facilities Operation and Maintenance Plan Template

Example Stormwater Facilities Operation and Maintenance Plans

Forms and Fact Sheet

The following documents are in MS Word and may be incorporated into Stormwater Facilities Operation and Maintenance Plans. See Chapter 5 of the Stormwater C.3 Guidebook, 7th Edition