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.

Six MS4 Phase I Individual NPDES Permits Issued​

The MS4 permits for the Portland Group, the Gresham Group, the Clackamas Group, Multnomah County, and the cities of Salem and Eugene were renewed on September 15, 2021. The summary of comments received and responses to comments are posted below. The Stormwater Management Plans developed under the previous permit remain in effect until DEQ approves the Stormwater Management Program Documents required by the new permits.​

Modification to Phase II General Permit complete

DEQ issued this permit on Nov. 30, 2018. It became effective on March 1, 2019 and expires on Feb. 29, 2024. The modification is in effect as of March 12, 2021. The intent of the modified permit is to maintain overall environmental protections while providing additional clarity to and flexibility for regulated communities. Specifically, the modifications correct the typographical errors in the current version of the permit, update the general requirement that permittees investigate known exceedances of water quality standards, adjust the language of schedule A.3.e. which addresses the requirements for post-construction site runoff control for new development and redevelopment, and clarify various permit conditions and definitions.

  • Application for MS4 Phase II General Permit Coverage​ - Coming soon

MS4 Phase I NPDES permits 

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


Portland Group (City of Portland and Port of Portland)

Clackamas 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, WES, City of Happy Valley and City of Rivergrove)

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

Oregon Department of Transportation


Clean Water Services


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.

MS4 Phase II NPDES permits

​Currently, there is 1 Individual Phase II Municipal Separate Storm Sewer System Permit.

City of Bend

MS4 Phase II Individual Permit Application Form - Coming soon

On Nov. 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

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 the program by email  or by phone, 503-229-5347.


Coming Soon: MS4 Permit Newsletter!

The Oregon DEQ MS4 staff will be launching a newsletter aimed at providing information for current and potential MS4 Permit Registrants. These Newsletters will be distributed periodically and will contain infromation about useful resources, hot topics, and general technical assistance information. 

If you have questions about this Newsletter, feel free to reach out to the MS4 Staff at MS4Stormwater@deq.state.or.us​ for more informaiton.