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Stormwater Discharges from Municipal Sources in Idaho and Washington

Public Notices:

Questions?

For questions about MS4 permits in Region 10, contact Misha Vakoc (vakoc.misha@epa.gov), 206-553-6650.

Join our mailing list: Contact Misha Vakoc to receive notification when the draft MS4 permits are available for review and comment.

On this page:

General Information

Under the National Pollutant Discharge Elimination System (NPDES) stormwater program, operators of large, medium and regulated small municipal separate storm sewer systems (MS4s) require authorization to discharge pollutants under an NPDES permit.

In Region 10, EPA is the NPDES stormwater permitting authority for:

  • Facilities in Idaho.
  • Facilities on Indian Country lands in Oregon and Washington.
  • Federal operators in Washington.

If your facility is not within one of the categories listed above, contact your state's municipal stormwater program:

Learn more:

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MS4 Permits in Idaho

The EPA approved Idaho's application to administer and enforce the Idaho Pollutant Discharge Elimination System (IPDES) program. Under EPA’s approval, authority to issue stormwater permits will transfer to the Idaho Department of Environmental Quality in July 2021.

Visit Idaho NPDES Program Authorization to learn more about EPA's approval.

Which Idaho MS4s are regulated?

All MS4s in U.S. Census-defined Urbanized Areas of Idaho are regulated under the NPDES program (refer to the maps in the table below). See Individual MS4 Permits in Idaho for MS4 operators that have previously obtained individual MS4 permits from EPA.

Area Maps for Regulated MS4s in Idaho
Census Urbanized Area (UA) Map Regulated MS4 Operator
Boise City UA (PDF) (1 pg, 2.5MB)Exit Ada County Highway District, Boise State University, Ada County Drainage District #3, City of Boise, City of Garden City, Idaho Transportation Dept. District #3
Coeur d'Alene UA (PDF) (1 pg, 972K)Exit Lakes Highway District, Post Falls Highway District, City of Coeur d'Alene, City of Post Falls, Idaho Transportation Dept. District #1
Idaho Falls UA (PDF) (1 pg, 735K)Exit City of Idaho Falls, Idaho Transportation Dept. District #6
Lewiston UA (PDF) (1 pg, 446K)Exit City of Lewiston, Idaho Transportation Dept. District #2
Nampa UA (PDF) (1 pg, 1.3MB)Exit Canyon Highway District #4, Nampa Highway District #1, City of Caldwell, City of Middleton
Pocatello UA (PDF) (1 pg, 640K)Exit Bannock County, City of Chubbuck, City of Pocatello, Idaho Transportation Dept. District #5, Idaho State University

Individual MS4 Permits in Idaho

See the table below for MS4 permits currently issued or under development.

MS4 Stormwater Permits Issued by EPA in Idaho
Facility or Permit Name Permit Number Effective Date Expiration Date
Ada County Highway District MS4 IDS028185 2021-02-01 2026-01-31

Boise-Garden City Area MS4s (Ada County, Boise State University, City of Boise, City of Garden City, Drainage District #3, Idaho Transportation Dept. District #3)
(EPA is proposing to reissue the Boise-Garden City Area MS4s permit.)

IDS027561 2012-02-01 2018-01-30
Idaho Transportation Dept. District #3 MS4 IDS028177 2021-02-01 2026-01-31
Caldwell MS4 IDS028118 2020-12-01 2025-09-30
Coeur d'Alene MS4 IDS028215 2020-12-01 2025-09-30
East Side Highway District MS4 (see North Idaho Highway Districts MS4s) IDS028207 2020-10-01 2025-09-30
Idaho Transportation Dept. District 1 MS4 IDS028223 2020-12-01 2025-09-30
Lakes Highway District MS4 (see North Idaho Highway Districts MS4s) IDS028207 2020-10-01 2025-09-30
Idaho Falls and Idaho Transportation Dept. District #6 MS4s IDS028070 2020-10-01 2020-09-30
Middleton MS4 IDS028100 2020-10-01 2025-09-30
Canyon Highway District No. 4 MS4 IDS028134 2021-02-01 2026-01-31
Nampa Highway District #1 MS4 IDS028142 2009-10-15 2014-10-14
Nampa MS4 IDS028126 2021-02-01 2026-01-31
Notus-Parma Highway District #2 MS4 IDS028151 2009-10-15 2014-10-14
Pocatello Urbanized Area MS4s (Pocatello, Chubbuck, Bannock County, Idaho Transportation Dept. District #5, and Idaho State University) IDS028053 2019-10-01 2024-09-30
Post Falls MS4 IDS028231 2020-11-01 2025-09-30
Post Falls Highway District MS4 (see North Idaho Highway Districts MS4s) IDS028207 2020-10-01 2025-09-30
City of Moscow MS4 IDS028398 2019-10-01 2024-09-30
City of Lewiston and Lewis-Clark State College MS4s IDS028061 2020-11-01 2025-09-30
Idaho Transportation Dept. District #2 MS4 IDS028258 2020-11-01 2025-09-30
University of Idaho MS4 IDS028576 2021-03-01 2026-02-28

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MS4 Permits in Washington

EPA Region 10 is the NPDES permitting authority for MS4 discharges operated by federal entities in Washington, regulated MS4s located in Indian Country, and/or regulated MS4s discharging to waters subject to tribal water quality standards.

If your facility is not within one of these categories, visit Washington Stormwater General PermitsExit for permitting information.

MS4 Permits Under Development for Areas of Washington under Federal and Tribal Jurisdiction
Facility or Permit Name Permit Number Effective Date Expiration Date
Naval Station Everett MS4 WAS026640 02-01-2020 01-31-2026
Naval Base Kitsap MS4 WAS026646 02-01-2020 01-31-2026
Naval Air Station Whidbey Island MS4 WAS02661 02-01-2020 01-31-2026
City of Tacoma MS4 Discharges to Puyallup Tribal Waters WAS026680 Draft N/A
Pierce County MS4 Discharges to Puyallup Tribal Waters WAS026875 Draft N/A
Washington State Department of Transportation MS4 Discharges to Puyallup Tribal Waters WAS026743 Draft N/A
Tulalip Tribes MS4 WAS026654 N/A N/A

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