Unincorporated San Mateo County is a permittee under the San Francisco Bay Area Municipal Regional Stormwater Permit (MRP 3.0, Order R2-2022-0018) which imposes NPDES Phase I stormwater requirements. Projects creating/replacing 2,500+ sq ft of impervious surface trigger C.3 post-construction stormwater treatment requirements (LID, biofiltration). Illicit discharges to storm drains are prohibited. Construction sites disturbing 1+ acres require SWPPPs and monthly wet-season inspections.
The County operates under the San Francisco Bay Regional Water Quality Control Board's MRP (Municipal Regional Stormwater NPDES Permit), which regulates municipal discharges from the County's MS4 (municipal separate storm sewer system). Provision C.3 (New Development and Redevelopment) applies to 'Regulated Projects' creating/replacing 2,500 sq ft or more of impervious surface — these projects must implement Low-Impact Development (LID) site design, source control, and stormwater treatment. Treatment options include bioretention (rain gardens), flow-through planters, pervious pavement, and infiltration trenches. Provision C.6 (Construction Site Controls) requires Erosion & Sediment Control Plans and monthly wet-season (Oct 1-Apr 30) inspections of construction sites 1+ acre. Illicit discharges of pollutants (paint, oil, soap, chemicals, gray water, pool chlorine) to storm drains are prohibited under Provision C.5 and County Code. Residents and contractors can report illicit discharges to the County stormwater hotline. All new development in unincorporated County must follow the SMC Green Infrastructure Plan's LID approach.
Illicit discharge to storm drain: Clean Water Act civil penalties up to $56,460/day plus County Code $500-$10,000 per incident. C.3 non-compliance: permit denial, required retrofit, $1,000-$25,000. SWPPP violation: stop-work order plus daily $250-$2,500. Sediment entering waterway: RWQCB enforcement up to $25,000/day.
San Mateo County, CA
Amplified music in unincorporated San Mateo County is regulated by County Code Chapter 4.88 Noise Control, which caps exterior noise at 55-75 dBA daytime and...
San Mateo County, CA
Unincorporated San Mateo County enforces CVC §22651(k) for vehicles on public streets (72 hours) and Ordinance Code Chapter 4.48 for inoperable vehicles on p...
San Mateo County, CA
Unincorporated San Mateo County has no general overnight parking ban on most streets. Specific residential neighborhoods may have permit parking. California ...
San Mateo County, CA
Unincorporated San Mateo County enforces California Swimming Pool Safety Act (H&S Code §115920-115929) and CBC Chapter 31B. Minimum 60-inch barrier, self-clo...
San Mateo County, CA
Unincorporated San Mateo County requires building permits for retaining walls over 4 feet measured from bottom of footing to top of wall, per California Buil...
San Mateo County, CA
Unincorporated San Mateo County allows backyard chickens on residential parcels of at least 2,500 sq ft under the County Zoning Regulations. 2,500 to 7,500 s...
See how San Mateo County's stormwater management rules stack up against other locations.
Help us keep this page accurate. If you notice an error or outdated information, let us know.