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

Solano County Code Section 31-31 applies National Pollutant Discharge Elimination System (NPDES) requirements to every grading plan and permit covering one acre or more of land disturbance. Before the Department of Resource Management can issue a grading and drainage permit for such a project, the applicant's plans must include a Storm Water Pollution Prevention Plan detailing best management practices, such as desilting basins or other temporary drainage and control measures, sufficient to control construction-related pollutants leaving the site. Section 31-31(b) requires that all best management practices be installed before grading begins, and that they stay maintained in good working order to the Director's satisfaction throughout construction, unless the Director has already granted final grading approval and all permanent drainage and erosion control systems required by the permit are in place.

The standards applicants must follow are drawn from the Storm Water Quality Handbooks, Construction Site Best Management Practices Manual, defined in Section 31-12 as the Caltrans-prepared manual of best conventional and best available technology BMPs consistent with the Clean Water Act. Section 31-26(b) requires major-permit applicants to submit an engineered erosion, sediment and runoff control plan, prepared and sealed by a registered civil engineer, that incorporates the Handbook's recommendations and addresses vegetative measures, drainage protection, sediment control, runoff control, cut and fill construction, and dust control. Section 31-30(j) separately requires that runoff from impervious surfaces created by grading be treated with biofiltration, or another Director-approved alternative, before it leaves the property or enters any state or federal waters. Section 31-30(i) further requires that any development creating more than 5,000 square feet of new impervious surface retard post-development runoff to no more than predevelopment rates using structural or vegetative measures maintained annually.

Because these BMP and NPDES obligations attach to the grading and drainage permit itself, the Department of Resource Management enforces them alongside the rest of Chapter 31: a stop-work order can issue under Section 31-42(d) if a project falls out of compliance with its approved erosion and sediment control plan, and the Director may require remedial work at the applicant's expense under Section 31-42(g) to protect completed work or prevent further damage.