Regional MS4 Permit

 

Santa Ana Regional MS4 Permit

Municipal Separate Storm Sewer System permits, commonly called MS4 permits, regulate discharges of pollutants in stormwater and urban runoff from municipal storm drain systems. An MS4 is a system used to collect or convey stormwater. MS4s can include roads with drainage systems, city streets, catch basins, curbs, gutters, ditches, man-made channels, and storm drains. MS4s are usually owned or operated by a city, county, or other public agency.


On September 11, 2026, the Santa Ana Regional Water Quality Control Board adopted Order R8-2026-0034, NPDES Permit No. CAS618000 (Regional MS4 Permit). The Regional MS4 Permit regulates discharges from MS4s operated by the counties of Orange, Riverside, and San Bernardino, their cities within the Santa Ana Region, and the Flood Control Districts. The Regional MS4 Permit also regulates certain discharges from the cities of Claremont and Pomona. The Regional MS4 Permit becomes effective on March 10, 2027.


The adopted Regional MS4 Permit, including all attachments and appendices, is available below:

Regional MS4 Permit – Order R8-2026-0034, NPDES Permit No. CAS618000

Transmittal Letter for Order R8-2026-0034

Staff Report Summary of the Permit

Announcements and Documents

Announcements, approved documents, and opportunities for public review and comment related to implementation of the Regional MS4 Permit will be posted here as they become available. They will be posted in order of most recent to least recent. They will also be announced to the email updates list. Subscribe to Regional MS4 Permit email updates.
Current Announcements:
• There are no current announcements

Upcoming Announcements:

The following documents are required to be submitted by the following dates. They will then be posted for public review and comment prior to approval as they become available:

  • Notice of Intent to develop a proactive Watershed Management Plan by June 8, 2027
  • Program Monitoring and Reporting Plan by September 11, 2028
  • Uniform Technical Guidance Documents by March 10, 2029
  • Final Watershed Management Plans by June 8, 2029
  • Reactive Watershed Management Plans as submitted
  • Credit trading programs as submitted
  • Waivers of treatment control measures as submitted
  • Certain TMDL related submissions as required in the permit appendices


Previous Permit Information

Before adoption of the Regional MS4 Permit, the Santa Ana Water Board regulated municipal stormwater through separate permits for Orange, Riverside, and San Bernardino Counties and their cities. The countywide MS4 permits were first issued in the 1990s and have been renewed four times. The Regional MS4 Permit replaces the separate countywide permits with a single regional permit.

These permits remain in effect until the Regional MS4 Permit becomes effective on March 10, 2027. On that date, the previous permits are rescinded except for enforcement purposes for violations that occurred while they were in effect.

Orange County MS4 Permit: The previous Orange County MS4 Permit is Order No. R8-2009-0030, NPDES Permit No. CAS61830, as amended by Order No. R8-2010-0062, which replaced Order R8-2002-0010.

Riverside County MS4 Permit: The previous Riverside County MS4 Permit is Order No. R8-2010-0033, NPDES Permit No. CAS618033, which replaced Order R8-2002-0011.

San Bernardino County MS4 Permit: The previous San Bernardino County MS4 Permit is Order No. R8-2010-0036, NPDES Permit No. CAS618036, which replaced Order R8-2002-0012.

Claremont and Pomona: The cities of Claremont and Pomona are located within the geographic jurisdiction of the Los Angeles Regional Water Quality Control Board. Under an agreement between the Regional Water Boards, the Santa Ana Water Board has been responsible for regulating certain discharges from Claremont and Pomona associated with implementation of the bacterial indicator Total Maximum Daily Load (TMDL) for the Middle Santa Ana River watershed. The Santa Ana Water Board issued Order R8-2013-0043, NPDES Permit No. CA8000410 for these requirements. The applicable requirements are now incorporated into the Regional MS4 Permit.

Existing Water Quality Management Plans and Technical Guidance Documents for New Development and Significant Redevelopment: Under the previous countywide MS4 permits, Permittees developed Model Water Quality Management Plans (WQMPs) and Technical Guidance Documents (TGDs) for post-construction stormwater requirements. These documents govern the development and implementation of post-construction pollution controls for certain new development and significant redevelopment as defined in the Orders. The Orders, WQMP, and TGD emphasize the use of controls that support Low Impact Development (LID).

The Regional MS4 Permit establishes a process for replacing these documents with Uniform Technical Guidance Documents. The Uniform Technical Guidance Documents are required to be submitted to the Santa Ana Water Board by March 10, 2029, and will be made available for public review and comment before approval. This page will be updated as those documents are submitted.

The existing requirements under Order R8-2009-0030 for Orange County, Order R8-2010-0033 for Riverside County, and Order R8-2010-0036 for San Bernardino County, including the Model WQMPs and TGDs, continue to apply to initial project applications received by Permittees until 90 days after the Executive Officer approves the applicable Uniform Technical Guidance Documents pursuant to sections VIII.C.4 and VIII.C.5 of the Regional MS4 Permit.

Contact and Additional Information:



Additional Regional MS4 Permit program records are available upon request. Available records include:

  • Previous permits
  • Reports of Waste Discharge
  • Annual Reports
  • Monitoring Plans
  • Water Code section 13383 Orders implementing statewide Trash Provisions
  • Designation agreements for entities that lie within the jurisdiction of multiple regional water boards
  • Administrative record for the adoption of orders

To request these or any other documents, contact the Santa Ana Water Board file review desk at FileReview8@waterboards.ca.gov

Keep up to date on the Regional MS4 Permit by subscribing to the Santa Ana Water Board's email list. Select "Region 8-Stormwater-Regionwide MS4 Permit" when choosing your subscription topics. Subscribe to Regional MS4 Permit email updates

Permit and reporting information is also available through the Stormwater Multiple Application and Report Tracking System (SMARTS)

For additional information regarding the MS4 program, please contact Hero Alexander at (951) 782-4419

For questions, comments, or concerns, email: r8_stormwater@waterboards.ca.gov


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