Managing stormwater from state highways

Learn how we manage stormwater runoff from paved surfaces like highways, rest areas, park-and-ride lots, ferry terminals and maintenance facilities in urban areas throughout the state.

In spring 2019, the Washington State Department of Ecology issued us a Municipal Stormwater Permit (permit) that regulates stormwater runoff from our paved surfaces. The permit requires us to implement a Stormwater Management Program comprised of the program requirements listed in the permit.

Our Stormwater Management Program Plan (SWMPP) fulfills that obligation and describes how we will implement the 2019 permit’s requirements. The SWMPP is updated annually and submitted with the Stormwater Report.

Send feedback to the Stormwater Permit Program

We want to hear from you! Please provide feedback on the 2022 Stormwater Management Program Plan (SWMPP) (PDF 580KB).We will consider all comments received by October 1, 2023, before finalizing the 2023 plan.

Municipal Stormwater Permit Reports

Annual Stormwater Report

Read the 2022 Annual Stormwater Report (PDF 1.7MB) for an update on our compliance with the permit from July 1, 2021, to June 30, 2022, our reporting period. This document serves as the annual report required by the permit. Read the 2021 Annual Stormwater Report (PDF 1.6MB) to get an update on our compliance during the previous reporting period.

To request copies of Annual Stormwater Reports from previous years, contact Garrett Starks at

Annual Stormwater Monitoring Reports

In 2022 we submitted the Monitoring Status Report Water Year 2021 (PDF 1.1MB). As required by Special Condition S7.D. of the permit, the report summarizes monitoring activities completed in Water Year 2020 (WY20) from October 1, 2020, through September 30, 2021.

In 2021 we submitted the Monitoring Status Report Water Year 2020 (PDF 884KB)

To request copies of Annual Stormwater Monitoring Reports from previous years, contact Brad Archbold at

Total Maximum Daily Load (TMDL) Programmatic Implementation Summary Reports

Read these reports to learn about highway discharge locations and potential pollutant sources within each TMDL, as well as how we followed up to address potential pollutant sources identified. To request copies of these reports, contact Elsa Pond at Reports are available for the following TMDLs:

  • Bear-Evans Creek
  • Green River
  • Hangman Creek
  • Issaquah Creek Basin
  • Little Bear Creek
  • Newaukum Creek
  • Oakland Bay
  • Palouse River
  • Puyallup River
  • Salmon Creek
  • Snoqualmie River
  • South Fork Palouse
  • Swamp Creek Basin
  • Stillaguamish River
  • Totten/Eld and Skookum Inlets Tributaries
  • Upper Naches River and Cowiche Creek
  • Whatcom Creek Watershed

Construction Stormwater Permit Reports

Monthly Discharge Monitoring Reports (DMRs) – Use Ecology’s Permit and Reporting Information System (PARIS) to find submitted discharge monitoring reports.

Stormwater research

Stormwater research projects help identify state-of-the-art, cost-effective solutions for designing, constructing, and maintaining stormwater management systems. Visit our Research reports webpage to find information on past research. We are currently working on two stormwater research projects:

  • Steep Slope Ksat Study – quantify runoff volume loss over roadway embankments as stormwater flows down the slope.
  • CAVFS vs Compost Blanket over a VFS application for BMP runoff treatment effectiveness.

To comply with the permit, we also contribute funds to Stormwater Action Monitoring (SAM) for research related to the status and trends of water quality in receiving water bodies.

Quality assurance project plans (QAPPs)

A QAPP describes the objectives of a monitoring study and the procedures to follow to ensure the quality and integrity of collected data and ensure the results are representative, accurate and complete. To request copies of our stormwater monitoring QAPPs, contact Brad Archbold at

Standard operating procedures (SOPs)

SOPs describe procedures to follow for completing specific tasks. To request copies of our SOPs, email the contact related to the tasks below.

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