San Mateo County, CA Environmental Rules: Erosion Control (2026)

The County's erosion control requirements implement NPDES MRP Provision C.6 (Construction Site Controls) and state Construction General Permit (SWRCB Order 2022-0057-DWQ) for sites 1+ acre. An Erosion and Sediment Control Plan (ESCP) must be submitted with building permit applications for any project involving ground disturbance. Required BMPs per the County ESC Manual: silt fence along downslope property perimeter, straw wattles on contour for sheet flow control, stabilized construction entrance (rock pad) to prevent tracking onto roads, gravel bag checks in swales, erosion control blankets on disturbed slopes, inlet protection at storm drain catch basins, stockpile covers. Wet-season work (Oct 1 - Apr 30) requires enhanced inspections and stabilization before each storm event; active grading on slopes steeper than 3:1 may be restricted. Disturbed areas must be stabilized (via vegetation, hydroseed, or mulch) within 14 days of disturbance cessation. Final stabilization with 70% vegetation cover or paved/landscaped finish is required before project closeout. Steep-slope projects may also trigger Geotechnical Review. Pre-site inspections for erosion control and tree protection are now required on specific site types.