Water Quality Permits

A municipal separate storm sewer system, commonly called an MS4, is a conveyance or system of conveyances, such as roads with drainage systems, municipal streets, catch basins, curbs, gutters, constructed channels or storm drains, owned or operated by a governmental entity that discharges to waters of the state. Municipalities that need to obtain an MS4 permit are classified as either "Phase I" or "Phase II". Phase I MS4s cover areas with populations greater than 100,000 (or large and medium0, while regulated Phase II (or "small") MS4s serve populations less than 100,000 located within Census Bureau-defined Urbanized Areas. Federal regulations also provide EPA and the states the discretion to require other MS4s outside of Urbanized Areas to apply for a permit.

MS4 Phase I NPDES permits

​Clackamas County Group

Reissued March 16, 2012

Clackmas County Group (Clackamas County DTD, City of Gladstone, City of Johnson City, City of Lake Oswego, City of Milwaukie, City of Oregon City, City of West Linn, City of Wilsonville, Oak Lodge Sanitary District, CCSD #1, City of Happy Valley, SWMACC and City of Rivergrove)

Portland Group

Reissued Jan. 31, 2011
Portland Group (City of Portland and Port of Portland)

Multnomah County, Gresham Group, City of Salem, City of Eugene

Reissued Dec. 30, 2010
Multnomah County
Gresham Group (Cities of Gresham and Fairview)
City of Salem
City of Eugene

Oregon Department of Transportation

Issued June 9, 2000
•    Permit
•    Permit Evaluation Report
Stormwater Management Plans
•    ODOT Stormwater Management Plan  

MS4 Phase II NPDES permits

​Currently, there are 15 individual Phase II Municipal Separate Storm Sewer System (MS4) permits that obtained individual permit coverage by being Automatically Designated. The permits cover 19 jurisdictions, as there is one set of co-permittees (Rouge Valley Sewer Services-RVSS) that includes four communities.
City of Ashland
City of Bend
Benton County
City of Corvallis
City of Keizer
Lane County
Marion County
City of Medford
City of Philomath Polk County Rogue Valley Sewer Services-Co-Permittees (Jackson County, City of Central Point, City of Phoenix, City of Talent)

City of Springfield

City of Troutdale

City of Turner

City of Wood Village

Jurisdiction maps

​EPA Region 10 developed an Online Map to view the census-identified “Urbanized Areas” for current permittees and new communities identified for permit coverage.

These maps are provided for informational purposes only. If you are uncertain whether a specific area is covered by a particular permit, please contact the permitted community or DEQ.

Enter the R10 Census Boundaries-WA, OR, ID Web page.
Click “Using Your ARCGIS Account”
Enter Username/Password:
Username: oregondeq1
  • Password: OregonDEQ2017ms4


Willamette Basin mercury monitoring

Willamette Basin Mercury Monitoring Memo 
This memo applies to Multnomah County, Gresham, Eugene, Salem and Portland MS4 permits. Mercury data was needed from MS4 permittees in the Willamette Basin to complete Phase 2 of the Willamette Mercury Total Maximum Daily Load. DEQ incorporated this data collection into monitoring requirements in Schedule B of the renewed permits..


For general information about NPDES MS4 Stormwater Discharge Permits, contact Mark Riedel,  503-229-5185.