NPDES Stormwater Permit for Ada County Highway District MS4 in Idaho

Transfer of permitting authority to Idaho. As of July 1, 2021, EPA has transferred authority to administer and enforce this permit to the Idaho Department of Environmental Quality. For more information, visit Idaho Pollutant Discharge Elimination System (IPDES) Program.

Below are EPA's National Pollutant Discharge Elimination System (NPDES) municipal separate storm sewer system (MS4) final permit and supporting documents for the Ada County Highway District (ACHD) in Idaho.

Permit number: IDS028185
Effective date: February 1, 2021
Modified: June 25, 2021
Permit expires: January 31, 2026

NPDES Stormwater Permit, Ada County Highway District MS4, #IDS028185 (pdf) (June 22, 2021)
Final modified stormwater permit.
Appendix B1: Stormwater Management Program Template, MS4 Permit #IDS028185 (pdf)
Optional template for creating or revising Stormwater Management Program (SWMP) document.
Appendix B2: Annual Report Form, MS4 Permit #IDS028185 (pdf)
Format for annual report. Due no later than April 4 of each year.
NPDES Permit Modification Fact Sheet, Ada County Highway District MS4, #IDS028185 (pdf) (May 2021)
Technical basis for permit modification.
NPDES Permit Fact Sheet for Ada County Highway District MS4, Canyon Highway District No. 4 MS4, and Idaho Transportation Department District 3 MS4 (pdf) (September 2020)
Technical basis for NPDES stormwater permits: #IDS028185, #IDS028134, #IDS028177.
Response to Comments on Draft NPDES Permit for Ada County Highway District MS4, Idaho, #IDS028185 (pdf) (December 2020)
EPA's responses to public comments on the September 2020 draft permit.