Green-Duwamish watershed pollutant loading assessment

The Green-Duwamish pollutant loading assessment (PLA) will identify sources of pollution in the Green-Duwamish watershed and strategies to reduce those sources. We're partnering with the U.S. Environmental Protection Agency (EPA) to conduct this multi-year project.

The PLA will provide information on:

  • What pollutants enter the river.
  • Where pollution comes from.
  • How much comes from different sources.

The information will help us develop strategies so the basin's water and sediments meet environmental quality standards.

Technical advisory committee and community engagement

We're working closely with a technical advisory committee made up of surface water experts from local and tribal governments. We also hold meetings for interested parties — people from businesses, non-profit groups, local and tribal governments, and the general public — to provide updates on the project and get feedback.

We're committed to these relationships and believe this public involvement will help ensure we protect the environment of the Green-Duwamish watershed.

For all current and previous meeting information (2014- current), please visit our Technical Advisory Committee Page.

Pollutants entering the Duwamish River

We work with the EPA to identify, clean up, and control sources of pollution to the lower 5.5 miles of the Green-Duwamish River, also known as the Lower Duwamish Waterway (LDW). We and EPA began a comprehensive assessment of the pollutants entering the watershed from the Howard Hansen Dam in the Cascade Mountains to Elliott Bay. The assessment will lay a foundation for future work to protect human health and the environment in the Green-Duwamish basin.

The pollutant loading assessment is needed to protect and improve the effectiveness of the Lower Duwamish cleanup of contaminated sediments.

The assessment will:

  • Create tools to identify upstream pollution sources.
  • Identify strategies to reduce pollution sources.
  • Combine direct measurements with advanced custom models of how pollutants interact with the basin's surface water, sediments, and its fish and shellfish.

Existing models completed for the cleanup indicate that sediments may still exceed target levels after cleanup because of pollutant concentrations in sediment coming from upstream.

Broad involvement supports the project

A technical advisory committee and interested parties are helping us develop the modeling tools we'll use to conduct the PLA. We expect the PLA will require many years to complete, and that the project will be conducted in phases. We will continue to work with the technical advisory group throughout the assessment. 

How can I stay informed?

Join our Duwamish River Updates email list for announcements about interested parties meetings and other work about our Lower Duwamish Waterway source control actions.

Project documents