San Mateo County, CA Environmental Rules: Erosion Control (2026)
Key Facts
- Governing section
- County Code § 4.100.210
- Who enforces
- Planning and Building Dept. Director
- Scope
- Unincorporated county only
- Stop-work power
- Yes, for inadequate BMPs
Summary
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.
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 such a plan is deemed necessary by the Planning and Building Department. The Planning and Building Department Director, or Director's designee, shall have the authority to stop construction and/or grading work on a site where adequate controls and/or BMPs are not in place. Grading shall also adhere to the County of San Mateo Regulations for Excavating, Grading, Filling and Clearing on Lands in Unincorporated San Mateo County, and all other applicable County regulations.
(Ord. No. 4913, § 1, 11-4-2025)
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 47).
Full Breakdown
Section 4.100.210 requires anyone doing construction or grading work in the unincorporated county to install, maintain and replace controls under the County Drainage Manual to prevent erosion and sediment runoff onto roadways or into the county storm drain system. The Planning and Building Department Director can halt work on any site where adequate BMPs are not in place. Applies only outside incorporated cities.
Violations & Fines
The Director can stop construction/grading work immediately for missing controls; separate violations enforced under Chapter 1.40 (Administrative Remedies).
Frequently Asked Questions
Who can stop my construction site for erosion issues?
What standard governs the required BMPs?
Sources & Official References
Other rules in San Mateo County
California rules heatmap·Compare San Mateo County to another location·View the California environmental rules overview
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