Stormwater Management: San Mateo vs South San Francisco

What stormwater rules apply to my project?

Projects creating or replacing 5,000+ square feet of impervious surface must implement permanent stormwater BMPs reviewed during the permit process.

Can I wash my car in the driveway?

Car wash runoff containing soap and chemicals should not enter the storm drain. Use a commercial car wash or wash over permeable surfaces.

Where does San Mateo's stormwater go?

The city's storm drain system discharges to San Francisco Bay without treatment, which is why pollution prevention is critical.

Does adding a patio or new driveway trigger stormwater treatment?

If your project creates or replaces 2,500 or more square feet of impervious surface (cumulative over 5 years), yes — you trigger Provision C.3 and must implement on-site stormwater treatment (typically a bioretention area sized to the project). Permeable pavers receive 50% credit. Below 2,500 sq ft, source control and site design still apply but full treatment is not required.

How do I report oil or paint being dumped down a storm drain?

Call the San Mateo County Stormwater Pollution Hotline: (650) 599-1420, or report online at smcsustainability.org/report-pollution. For immediate hazards (large spill, chemicals reaching a creek) call 911. Illicit discharges carry federal Clean Water Act penalties.