Lower Duwamish Waterway

Last updated: August 2023

Fact Sheets

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The Lower Duwamish Waterway site is an approximately 5.5-mile portion of the Lower Duwamish River, which flows into Elliott Bay. The Washington State Department of Ecology (Ecology) and the U.S. Environmental Protection Agency (EPA) are working to clean up contaminated sediments and control sources of recontamination in the Lower Duwamish Waterway. Ecology and EPA have joined a legal agreement (Administrative Order on Consent) with the City of Seattle, King County, the Port of Seattle, and The Boeing Company to begin work in the waterway and upland areas.

The sediments along the river contain a wide range of contaminants due to years of industrial activity and run off from residential areas. These contaminants include PCBs (polychlorinated biphenyls), PAHs (polycyclic aromatic hydrocarbons), chlorinated dioxins & furans, metals, and phthalates.

EPA is leading the sediment contamination cleanup for the Lower Duwamish Waterway site with support from Ecology. Ecology is leading the efforts to control sources of sediment pollution in the Lower Duwamish Waterway in cooperation with the City of Seattle, the Port of Seattle, King County, the City of Tukwila, and EPA.

Source control is the process of working to find and control releases of pollution to waterway sediments to prepare for cleanup and prevent sediment recontamination. Finding and controlling sources is difficult, and even with aggressive source control some recontamination may occur.

The sediment cleanup sites are grouped together by Reach (stretch of river), and the Upper Reach (the upstream end of the LDW) will be the first on the schedule, with cleanup expected to begin in late 2024.  

During the summer of 2023, we submitted a report to EPA that reviewed source control efforts in the Upper Reach of the LDW. Together with our source control and cleanup partners, we’ve made solid progress on controlling sources of pollution. We’re recommending that EPA begin cleanup at 28 out of 29 active sediment cleanup locations in the Upper Reach. 

The one sediment area in the Upper Reach where we are not recommending the EPA to proceed is located next to one contaminated upland cleanup Site where source control is still in progress. This cleanup Site is called Boeing Isaacson Thompson. While the upland source will not be controlled prior to the start of sediment cleanup in the Upper Reach, we are confident that the Site will be cleaned, and sources controlled, shortly after. The Feasibility Study for the Boeing Isaacson Thompson Site cleanup was completed in July 2023, and there will be opportunity for the public to comment on the document later this year.


Read more about the cleanup progress in the 2023 factsheet

View more information about cleanup and source control work in the Lower Duwamish Waterway!