Solano County, CA Environmental Rules: Stormwater Management (2026)

Solano County's stormwater program is implemented by Resource Management — Public Works to comply with the federal Clean Water Act, the California Porter-Cologne Water Quality Control Act, and the State Water Board's Phase II Small MS4 General Permit (Order No. 2013-0001-DWQ as amended). Solano County Code Chapter 31 (Grading, Drainage, Land Leveling, and Erosion Control) is the implementing local ordinance: any grading permit with one acre or more of land disturbance must comply with NPDES Construction General Permit requirements, and any project creating 2,500+ square feet of impervious surface must obtain coverage under the County's Municipal NPDES Permit through the grading-permit process. SWPPPs must identify best management practices (BMPs) — desilting basins, fiber rolls, silt fences, stabilized construction entrances, hydroseeding — to control sediment and other construction-related pollutants. Post-construction, certain new and redevelopment projects must include Low Impact Development (LID) features such as bioretention, infiltration trenches, or pervious pavement to manage runoff onsite. The MS4 permit also prohibits non-stormwater discharges to the County storm-drain system: car-washing soap, paint, motor oil, pet waste, pool drainage, and similar contaminants may not enter gutters, catch basins, or roadside ditches.