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 a "Phase I" or "Phase II" MS4. Phase I MS4s cover areas with populations greater than 100,000 (large and medium) while regulated Phase II (small) MS4s serve populations less than 100,000 and are located within a Census Bureau designated "urbanized area" (UA). Federal regulations also provide the EPA and the states the discretion to require other MS4s outside of UAs to apply for a permit.

Current Action

On November 30, 2018, DEQ issued a NPDES general permit for discharges from small MS4s. This permit is Oregon’s first MS4 Phase II general permit issued after EPA’s revision to the Phase II Stormwater Rule in 2016.
The permit became effective on March 1, 2019.

Final Documents


MS4 Phase I NPDES permits

Clean Water Services

Reissued 2016

Watershed-based NPDES Permit: covers four wastewater treatment facilities operated by Clean Water Services; regulates the discharge of treated domestic, commercial and industrial wastewater from the four facilities to the Tualatin River; authorizes discharge of stormwater from the urban areas of the Tualatin River watershed to the Tualatin River and its tributaries.

Clackamas County Group

Reissued 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 2011
Portland Group (City of Portland and Port of Portland)

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

Reissued 2010
Multnomah County
Gresham Group (Cities of Gresham and Fairview)
City of Salem
City of Eugene

Oregon Department of Transportation

Issued 2000
•    Permit

MS4 Phase II NPDES permits

​Currently, there are 4 individual Phase II Municipal Separate Storm Sewer System (MS4) permits that obtained individual permit coverage by being Automatically Designated.

City of Bend City of Corvallis

City of Springfield

City of Turner

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, email  MS4Stormwater@deq.state.or.us, or call 503-229-5347 or 503-229-6826