The proposed consent decree requires the Lower Duwamish Waterway Group—Boeing, the City of Seattle, and King County—to design and implement the in-water cleanup remedy selected by EPA in its 2014 Record of Decision, with the federal agency maintaining oversight authority. The decree also keeps EPA’s authority to step in and perform the work if required cleanup obligations are not met.

“This settlement finally ensures full-scale cleanup of the Lower Duwamish Waterway,” Jeffrey A. Hall, assistant administrator for EPA’s Office of Enforcement and Compliance Assurance, said in announcing the agreement. 

“The cost-sharing agreement resulting from negotiations among many parties shows that this administration will make good on its promise to expedite cleanup of hazardous pollutants while ensuring responsible parties are held accountable,” Hall added.

EPA estimates the cleanup will take at least 10 years to complete. The agency’s 2014 cleanup plan estimated the selected remedy would cost about $342 million, with the larger settlement reflecting cost sharing among responsible parties as well as long-term implementation and oversight. 

The consent decree was filed in the U.S. District Court for the Western District of Washington and must go through a 30-day public comment period before a federal judge can approve the settlement.

Large-Scale Sediment Remediation

EPA’s cleanup plan targets contaminated sediments across roughly 412 acres of the Lower Duwamish Waterway, with active remediation planned on about 177 acres of riverbed.

The agency has identified at least 41 hazardous substances in river sediments, including polychlorinated biphenyls, arsenic, carcinogenic polycyclic aromatic hydrocarbons, dioxins and furans.

Emma Pokon, EPA's Region 10 administrator, said the effort is expected to deliver both environmental and economic benefits for Seattle's industrial waterfront.

“Cleaning up this waterway will enhance residents’ use, support safer fishing, protect wildlife and foster a vibrant industrial core in the heart of Seattle,” Pokon said.

The plan combines dredging, engineered sediment capping and enhanced natural recovery to tackle pollution accumulated over more than a century of industrial activity. Dredging or partial dredging will take place over approximately 105 acres of contaminated sediment, while engineered sediment caps will be installed across another 24 acres. Enhanced natural recovery measures are planned for about 48 acres, and around 235 acres of riverbed will be treated through monitored natural recovery as cleaner sediments gradually bury remaining contaminants over time.

EPA identified contamination from decades of shipbuilding, aircraft manufacturing, steel production, municipal outfalls, and other industrial activities along the river corridor and estimates the cleanup will remove roughly 960,000 cu yards of contaminated sediment from the waterway. 

RELATED

Lessons From the Hudson River PCB Cleanup Project

Construction Already Underway

Cleanup construction started in the upper reach of the waterway in late 2024 and is expected to continue through early 2027 as part of a phased remediation plan that divides the river into upper, middle and lower cleanup reaches. The cleanup will move downstream through these segments as dredging, capping and monitoring activities advance.

Diagram illustrates how a clamshell dredge mounted on a barge removes contaminated sediment from a riverbed and transfers it to a bottom-dump barge during environmental cleanup operations.

Diagram courtesy of the Federal Remediation Technologies Roundtable

King County is overseeing the upper-reach project, which covers approximately two miles between Duwamish Waterway Park and the South 102nd Street bridge. Seattle-based Pacific Pile & Marine is the construction contractor for the phase, conducting dredging operations, installing sediment caps and placing clean material to help accelerate natural recovery of the riverbed.

Because the Lower Duwamish provides habitat for migrating salmon and other fish species, in-water construction activities are restricted to seasonal windows from October to February. Cleanup work must also be coordinated with ongoing navigation and industrial operations along the waterway.

Earlier sediment-removal projects addressed some of the river’s most polluted areas, including a 2003-04 dredging effort near the Diagonal/Duwamish combined sewer outfall that removed about 68,000 cu yards of PCB-contaminated sediments and capped a seven-acre section of the riverbed.

Washington State Department of Ecology Director Casey Sixkiller emphasized that resolving how cleanup costs would be divided among responsible parties is key as the project progresses.

“Settling the question of who will pay for the work is critical, especially now that the final stages of active cleanup have begun,” Sixkiller said.

RELATED

NYC's Gowanus Canal Superfund Site Cleanup Begins in Earnest

Industrial Corridor Legacy

The Lower Duwamish has served as Seattle’s primary industrial waterway since the early 20th century, supporting shipyards, aircraft manufacturing, steel fabrication and chemical production facilities.

EPA added the waterway to the Superfund National Priorities List in 2001 after investigations confirmed widespread sediment contamination linked to decades of industrial activity.

The cleanup is paired with a broader source-control program led by the Washington Department of Ecology to reduce the the level of contaminants entering the waterway from the surrounding watershed, a drainage basin of roughly 20,000 acres that contribute runoff to the Lower Duwamish.

Acting Deputy Assistant Attorney General Justin Heminger of the Justice Department’s Environment and Natural Resources Division said the settlement marks a major milestone in the long-running cleanup effort.

“The Duwamish is a vital asset to Seattle and the surrounding community,” Heminger said. “By lodging this settlement with the court today and seeking public comment, we take a big step toward restoring the Lower Duwamish.”