California Water Code sections 13260 and 13383 implement the federal Clean Water Act through statewide MS4 NPDES permits issued by the State and Regional Water Boards, binding all municipal stormwater dischargers uniformly.
Water Code 13260 requires anyone discharging waste into state waters to file a Report of Waste Discharge. Section 13383 authorizes the State Water Resources Control Board to issue NPDES permits enforcing federal Clean Water Act requirements. Statewide MS4 Phase I and Phase II General Permits regulate municipal separate storm sewer systems, requiring construction site BMPs, post-construction stormwater retention, and illicit discharge controls. Local agencies must adopt ordinances at least as stringent as their NPDES permits; they cannot weaken the standards. The Construction General Permit (Order 2022-0057-DWQ) covers projects disturbing one acre or more.
Water Code 13385 authorizes administrative civil liability up to $10,000 per day per violation plus $10 per gallon of unauthorized discharge. Willful violations are misdemeanors. EPA and Regional Water Board enforcement actions are common.
See how Sonoma's stormwater management rules stack up against other locations.
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