Our MS4 Permit
Regional Phase I Municipal Separate Storm Sewer System (MS4) National Pollutant Discharge Elimination System (NPDES) Permit
The Los Angeles Regional Water Quality Control Board (Regional Board) adopted a new regional permit, Order R4-2021-0105 (Regional Permit), on July 23, 2021, that covers Ventura and Los Angeles Counties and all the incorporated cities therein. As of its effective date, September 11, 2021, the Regional Permit superseded the three separate Orders that covered the Permittees in the region: R4-2010-0108 (Ventura County), R4-2012-0175 (Los Angeles County except for the City of Long Beach), and R4-2014-0024 (City of Long Beach).
The Watershed Management Program (WMP) page has a link to the WMP’s main document, which includes a comprehensive characterization of water quality, pollutant reduction targets within each watershed, and potential pathways to implementation. The Coordinated Integrated Monitoring Program (CIMP) page details the monitoring being conducted to meet Permit requirements.
As required by the Permit for permit renewal, a Report of Waste Discharge (ROWD) detailing the Program’s challenges and accomplishments under R4-2021-0105 was submitted to the Regional Board on March 16, 2026, 180 days before the permit expires.
The Regional Permit and its attachments are included below.
Regional Phase I Municipal Separate Storm Sewer System (MS4) Permit, Order R4-2021-0105, effective September 11, 2021
- Regional NPDES Municipal Stormwater Permit (R4-2021-0105)
- Attachment A Definitions
- Attachment B Watershed Management Area Maps
- Attachment C MS4 Maps
- Attachment D Standard Provisions
- Attachment E Monitoring and Reporting Program
- Attachment F Fact Sheet
- Attachment G Aquatic Toxicity
- Attachment H-a Reporting Forms (PDF)
- Attachment H-b WMP Progress Report Form (MS Word zip)
- Attachment H-c Annual Report Form (MS Word zip)
- Attachment I-a Trash Reporting Forms (PDF)
- Attachment I-b Trash Reporting Forms (MS Excel zip)
- Attachment I-c Trash Reporting Forms (MS Excel zip)
- Attachment J Permittees & TMDL Matrix
- Attachment K Ventura River TMDLs (Ventura County)
- Attachment L VC Miscellaneous Coastal Watersheds (MCW) TMDLs (Ventura County)
- Attachment M SCR TMDLs (Ventura and Los Angeles Counties)
- Attachment N Calleguas Creek TMDLs (Ventura County)
- Attachment O SMB TMDLs (Ventura and Los Angeles Counties)
- Attachment P Dominguez Channel TMDLs (Los Angeles County)
- Attachment Q Los Angeles River TMDLs (Los Angeles County)
- Attachment R San Gabriel River TMDLs (Los Angeles County)
- Attachment S LCC-AB TMDLs (Los Angeles County)
Ventura Countywide MS4 Stormwater Permit, R4-2010-0108, (2010 - September 11, 2021)
Ventura Countywide Stormwater Permit Order No. R4-2010-0108 was adopted in 2010 for a five year term. The Permit expired on July 8, 2015, but continued on administrative extension until the new Regional Permit effective date: September 11, 2021. As required by the Permit, Ventura County Permittees submitted a Report of Waste Discharge (ROWD) to the Los Angeles Regional Water Quality Control Board (Regional Board) in January 2015. The ROWD summarizes the accomplishments and challenges of the Permittees under this permit.
Documents regarding the Ventura Countywide Stormwater Permit are available at the Regional Board website here: Ventura Countywide Municipal Stormwater Permit
- Countywide NPDES Municipal Stormwater Permit (R4-2010-0108)
- Attachment A (Watershed Management Areas)
- Attachment B (Pollutants of Concern)
- Attachment C (Treatment BMP Performance Standards and Effluent Concentrations as Median Values)
- Attachment D (Critical Sources Categories)
- Attachment E (Determination of Erosion Potential)
- Attachment F (Monitoring Program)
- Attachment G (Constituents with Associated Minimum Levels)
- Attachment H (Major Outfall Stations)
- Attachment I (Reporting Program Requirements)