San Joaquin County, CA Environmental Rules: Stormwater Management (2026)

San Joaquin County regulates stormwater under the California General Construction NPDES Permit and its own Phase II Municipal Separate Storm Sewer System (MS4) permit issued by the Central Valley Regional Water Quality Control Board. Any land-disturbing activity of 1 acre or more (or less if part of a larger common plan of development) requires a Stormwater Pollution Prevention Plan (SWPPP), electronic filing through the SMARTS system, a Qualified SWPPP Developer/Practitioner, and a Notice of Intent. Post-construction stormwater management applies to Priority Development Projects that create or replace 2,500 square feet or more of impervious surface in specified categories — these must include Low Impact Development (LID) features: bioretention cells, vegetated swales, pervious pavers, underground retention, and treatment-train BMPs designed to capture the 85th-percentile storm. Owners must record a stormwater facilities operation and maintenance agreement. Illicit non-stormwater discharge (washing concrete, dumping chlorinated pool water, oil, soap, paint) into storm drains or directly to Delta sloughs, the San Joaquin River, the Mokelumne, or the Calaveras Rivers is strictly prohibited and carries significant fines. Agricultural discharges fall under the Irrigated Lands Regulatory Program (ILRP) through coalition groups (e.g., San Joaquin County & Delta Water Quality Coalition).