Phase I Regional Municipal Separate Storm Sewer System (MS4) Program

Regional MS4 Permit

The San Diego Water Board regulates discharges from Phase I municipal separate storm sewer systems (MS4s) in the San Diego Region under the Regional MS4 Permit. The Regional MS4 Permit covers 39 municipal, county government, and special district entities (referred to jointly as Copermittees) located in San Diego County, southern Orange County, and southwestern Riverside County who own and operate large MS4s which discharge storm water runoff and non-storm water runoff to surface waters throughout the San Diego Region.

Development of Proposed Changes to the Regional MS4 Permit

The Regional MS4 Permit expired on June 27, 2018, but remains in effect under an administrative extension until it is reissued by the San Diego Water Board. The San Diego Water Board has begun the development of proposed changes to the Regional MS4 Permit and will hold public workshops on focus topics and proposed changes. In application for NPDES permit reissuance of the Regional MS4 Permit, the Copermittees submitted a Report of Waste Discharge (ROWD) on December 27, 2017. The ROWD summarizes the Copermittees' existing storm water programs and makes recommendations for updates and other modifications to the Regional MS4 Permit.

Water Quality Improvement Plans

Pursuant to Provision B of Order No. R9-2013-0001, as amended, the Copermittees must develop a Water Quality Improvement Plan (WQIP) for each of the Watershed Management Areas in the San Diego Region. The WQIPs guide the Copermittees' jurisdictional runoff management programs towards achieving improved water quality in MS4 discharges and receiving waters.

Statewide Trash Amendments

On June 2, 2017, the San Diego Water Board's Executive Officer signed Order No. R9-2017-0077. The Order directs owners and operators of Phase I MS4s draining the watersheds within the San Diego Region to submit reports pertaining to the control of trash in discharges from Phase I MS4s to ocean waters, inland surface waters, enclosed bays, and estuaries in the San Diego Region.

Regional Clearinghouse

Pursuant to Provision F.4 of Order No. R9-2013-0001, as amended, the Copermittees have developed an internet-based Regional Clearinghouse to store permit-required documents and data. The Project Clean Water web site provides a centralized point of access to water quality information and resources for the Regional MS4 Permit Copermittees.

Water Quality Equivalence Guidance (WQE)

On March 15, 2019, the 2018 Water Quality Equivalency Guidance Document was accepted by the San Diego Water Board's Executive Officer. Water Quality Equivalency calculations were developed to establish a regional consistent technical basis for determining water quality benefits associated with alternative compliance projects.

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