Washington Department of Transportation Municipal Stormwater Permit

This permit specifically covers the Washington State Department of Transportation (WSDOT). Through this permit, we require the agency to manage and control polluted stormwater runoff to protect downstream waters from pollution.

Besides covering state highways and transportation-related facilities, this permit also covers stormwater discharges from rest areas, park and ride lots, ferry terminals, and maintenance facilities within urban areas of Washington.

The current permit went into effect April 5, 2019, and expires April 5, 2024.

Why does WSDOT need to control stormwater?

Statewide, WSDOT oversees more than 7,000 miles of highway. When rest areas, ferry terminal holding lots, and park and ride lots are included, they manage over 40,000 acres of paved surfaces. Paved surfaces do not allow water to penetrate into the ground where it can be naturally filtered and treated before entering streams or underground water supplies. This lack of infiltration results in excess stormwater running off state highway facilities each year.

Current permit and related documents

WSDOT Municipal Stormwater General Permit (Effective April 5, 2019)
Fact Sheet with Response to Comments
Application for Coverage (Notice of Intent)
Highway Runoff Manual (HRM)
Implementing Agreement between WSDOT and Ecology regarding application of the HRM

WSDOT permit compliance

See the WSDOT water resources and erosion control page for information on permit-related activities such as:

  • Stormwater research
  • Annual reports
  • Monitoring reports
  • Total Maximum Daily Load (TMDL) implementation reports

Previous permit documents

WSDOT Municipal Stormwater General Permit (Effective April 5, 2014)
Fact Sheet