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 Water Quality Permit Program

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NPDES Phase II Permits and Permittees

Stormwater discharges that need to obtain permits are classified as either "Phase I" or "Phase II" municipal separate storm sewer systems (MS4s). Phase I MS4s are those with populations greater than 100,000, while Phase II (or "small") MS4s are those communities with populations less than 100,000. Permit coverage is determined in one of three ways:

  • Automatic Designation: the small MS4 is located within U.S. Census Bureau-defined “Urbanized Areas”.
  • Required Evaluation: an operator of a small MS4 located outside of an Urbanized Area is designated for permit coverage if the permitting authority (DEQ) determines that the discharges cause, or have potential to cause, an adverse impact on water quality. (Population of at least 10,000 and population density of at least 1,000 people/square mile)
  • Physically Interconnected: DEQ is required to designate any small MS4 located outside of a UA that contributes substantially to the pollutant loadings of physically interconnected MS4 regulated by the NPDES stormwater program.

For more details, please see the EPA Fact Sheet: “Who’s Covered? Designation and Waivers of Regulated Small MS4s” and CFR 40 Part 123.35.

Permits and Permittees

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.

Current Phase II permittees  
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

The 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.

Enter the R10 Census Boundaries-WA, OR, ID Web page.
Click “Using Your ARCGIS Account”
Enter Username/Password:
Username: oregondeq1
Password: OregonState17

What is a MS4?

A municipal separate storm sewer system is a conveyance or system of conveyances (e.g., roads, ditches, municipal streets, catch basins, curbs, gutters, channels or storm drains) owned or operated by a public entity that discharges to waters of the state. What constitutes an MS4 is often misinterpreted and misunderstood. The term MS4 does not solely refer to municipally owned storm sewer systems, but rather is a term of art with a much broader application that can include, in addition to local jurisdictions, state departments of transportation, universities, local sewer districts, hospitals, military bases and prisons. An MS4 also is not always just a system of underground pipes – it can include roads with drainage systems, gutters and ditches.


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For stormwater-related questions, contact the appropriate DEQ regional office.

For general information about NPDES Stormwater Discharge Permits, contact Mark Riedel by phone at 503-229-5185 or by email.

Oregon Department of Environmental Quality
Headquarters: 700 NE Multnomah Street, Suite 600, Portland, OR 97232
Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

The Oregon Department of Environmental Quality is a regulatory agency authorized to protect Oregon's environment by
the State of Oregon and the Environmental Protection Agency.

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