Environmental Rules in San Mateo County, CA (2026)
5 county-level rules, plus city-specific rules for 1 city in San Mateo County, California.
Verified from official government sources
Stormwater Management
Unincorporated San Mateo County bans dumping anything but rainwater into the county storm drain system under its Stormwater Pollution Prevention Ordinance.
San Mateo County Illicit Discharge Ban
Significant RestrictionsSan Mateo County Code § 4.100.120
The discharge of Non-Stormwater to the County Storm Drain System is prohibited. All discharges of material other than Stormwater must be with a NPDES Permit and this ordinance. It is unlawful for any Person to commence or continue any Illicit Discharge to the County Storm Drain System. This prohibition applies to all connections made to the County Storm Drain System. Alteration is inclusive of ...
Erosion Control
Grading and construction sites in unincorporated San Mateo County must keep BMPs in place to stop erosion and sediment from reaching roads or storm drains.
San Mateo County Construction Erosion Control
Some RestrictionsSan Mateo County Code § 4.100.210
Any Person engaged in construction or grading work in the County shall install, maintain, and replace controls and BMPs in order to prevent Non-Stormwater Discharges including, but not limited to, Target Pollutants, erosion and sediment runoff onto roadways or into the County Storm Drain System, as outlined in the County Drainage Manual, is required for any construction and/or grading for which...
Coastal Development
San Mateo County administers its own certified Local Coastal Program (LCP) and issues Coastal Development Permits (CDPs) for projects in the Coastal Zone, which covers roughly 240 sq miles from Devil's Slide south through Pescadero, Año Nuevo, and the Santa Cruz County line. Projects in the Coastal Zone typically require a CDP from County Planning; certain appealable areas (near the shoreline, in sensitive habitat, or in rural areas) can also be appealed to the California Coastal Commission. ESHA (Environmentally Sensitive Habitat Area) buffers, public access, and view corridors are key LCP policies.
environmental/coastal-development
Some RestrictionsCA Coastal Commission - Coastal Zone Boundary (Coastal Act of 1976, PRC Sec. 30103)
Coastal Act of 1976). PRC Section 30103(b) directed the Coastal Commission to prepare and adopt more detailed 1:24,000 scale Coastal Zone Boundary (CZB) maps, which occurred March 1, 1977. These 161 adopted maps provide the official basis for all other representations of the landward CZB. The digital version of the CZB created by developing this data is a conformed copy of the official boundary...
Flood Zones
Unincorporated San Mateo County bars grading, filling, new construction or any other development in a mapped Area of Special Flood Hazard, Floodway or Coastal High Hazard Area until the Director of Planning and Building issues a development permit under Zoning Chapter 8.300, which applies only outside the county's 20 incorporated cities.
San Mateo County Floodplain Development Standards
Some RestrictionsSan Mateo County Zoning Regulations § 8.300.060(1)
The areas of San Mateo County subject to flood discharge, flood or flooding, as established by Chapter 8.300 are hereby divided into Areas of Special Flood Hazards, Floodways and Coastal High Hazard Areas. Development located in Areas of Special Flood Hazards, which includes Floodways and Coastal High Hazard Areas, is required to meet applicable regulations of the County Subdivision Regulations...
Flood Elevation Requirements
Unincorporated San Mateo County requires the lowest floor of any new or substantially improved structure in an Area of Special Flood Hazard to sit at or above the regulatory flood-protection elevation, which is set from the base flood: the flood with a 1% annual chance of occurring, commonly called the 100-year flood.
San Mateo County Base Flood Elevation Rule
Some RestrictionsSan Mateo County Zoning Regulations § 8.300.060(1)(a)
Base Flood. The flood having a one percent chance of being equaled or exceeded in any given year, sometimes referred to as the 100-year flood. The base flood is the basis for the regulatory flood protection elevation used throughout this Chapter. Lowest Floor. The lowest floor of the lowest enclosed area, including basement areas. The lowest floor does not include (a) an unenclosed area or floo...
Environmental Rules by City in San Mateo County
1 cities in San Mateo County have their own environmental rules rules. Each link goes to that city's dedicated page with code citations.
All San Mateo County ordinances
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