Stormwater MS4 Permit

The State Water Resources Control Board under the Municipal Storm Water Permitting Program regulates storm water discharges from municipal separate storm sewer systems (MS4s).

MS4 Permits are issued under two phases; individual Phase I which started in 1990, the Regional Water Quality Control Boards have adopted National Pollutant Discharge Elimination System General Permit (NPDES) storm water permits for medium and large municipalities. Most of these permits are issued to a group of co-permittees encompassing an entire metropolitan area and Phase II permit for smaller municipalities:

  • Phase I MS4 permits require the discharger to develop and implement a Storm Water Management Plan/Program with the goal of reducing the discharge of pollutants to the maximum extent practicable (MEP). MEP is the performance standard specified in Section 402(p) of the Clean Water Act. The management programs specify what best management practices (BMPs) will be used to address certain program areas. The program areas include public education and outreach; illicit discharge detection and elimination; construction and post-construction; and good housekeeping for municipal operations.
  • Phase II MS4 permits On April 30, 2003 as part of Phase II, the State Water Resources Control Board issued a General Permit for the Discharge of Storm Water from Small MS4s (WQ Order No. 2003-0005-DWQ) to provide permit coverage for smaller municipalities.  Phase II Small MS4 General Permit covers Phase II Permittees statewide.

The City was previously designated as a Small Phase II MS4 in 2003. The City of Santa Rosa, County of Sonoma and the Sonoma Water were jointly issued their first NPDES permit in 1997. In early 2013, Phase II municipalities within the Russian River Watershed were provided an option to align with the Phase I program in an effort for watershed wide consistency and collaboration among the Phase I and Phase II Co-Permittees. The City of Cloverdale, the City of Cotati, the City of Rohnert Park, the City of Healdsburg, the City of Sebastopol, the City of Ukiah, the Town of Windsor, and the Phase II designated portions of the County of Sonoma elected to participate in the Phase I program. The current NPDES permit was adopted by the North Coast Regional Water Quality Control Board on January 6, 2016.