Lower Duwamish Waterway Sediment Cleanup
Dredging to remove contaminated sediment in the Lower Duwamish Waterway
Project Description
In 2001, United States Environmental Protection Agency (EPA) listed the last five miles of the Duwamish River as the Lower Duwamish Superfund Site due to contaminated river sediment. The Lower Duwamish Waterway Group (LDWG) (the City of Seattle, King County, and the Boeing Company) work together to implement EPA’s cleanup plan for contamination.
The Lower Duwamish Waterway will be cleaned up in three segments: the upper, middle, and lower reaches. Cleanup began in the upper reach and will continue downstream towards Harbor Island over the next decade. Each section will have its own design and cleanup schedule.
Cleanup construction season is typically October through February each year. In-water construction activities are restricted to these months to protect certain fish species.
Current and detailed information about this project is available at the LDWG website.
View the enlarged Duwamish Superfund Project map. (PDF)
Location
The entire Lower Duwamish Superfund site extends from approximately from 102nd Street Bridge (south end) to the East Waterway (north end).
What’s happening now
Upper reach construction takes place October through February of each year. Construction is finished for the 2024-2025 season and is expected to start again in October 2025.
Cleanup work on the Lower Duwamish Waterway during the 2024-2025 construction season (photo credit: King County)
Background
More than 100 years of industrial and urban use polluted the sediments (mud on the river bottom), water, and marine life in the Lower Duwamish Waterway. Contamination from polychlorinated biphenyls (PCBs) and other industrial chemicals including arsenic, polycyclic aromatic hydrocarbons (PAHs), and dioxins and furans poses risk to people and wildlife, with PCBs posing the greatest risk.
PCBs are toxic chemicals that were commonly used from 1929 to 1979 for numerous industrial activities and in some household products and building materials. They were widely used in hydraulic oils, electrical transformers, electrical equipment, caulk, and oil-based paint. PCBs can be harmful when released into the environment, in part because they persist and travel up through the food chain where people and wildlife can then be exposed to PCBs through eating contaminated fish and shellfish.
In 2001, EPA listed the last five miles of the Duwamish River as a Superfund Site. As such, EPA is the lead agency for the cleanup of the Lower Duwamish Waterway. The Lower Duwamish Waterway Group (LDWG) is a collaboration between the City of Seattle, King County, and the Boeing Company, who are working together with EPA to study contamination levels, design and implement detailed cleanup plans, and educate and involve the community in the EPA-led process.
Between 1999 and 2015, five “early action” efforts cleaned up about 29 acres of some of the most contaminated sediment in the site. On September 23, 2021, the City of Seattle, King County, and the Port of Seattle sent a letter to EPA about the Lower Duwamish Waterway and East Waterway cleanup plans and our continued dedication to reducing unacceptable risks to human health and the environment. View the EPA letter in full. In early 2025 the Environmental Protection Agency and the Washington State Department reached an agreement with LDWG partners on the consent decree that will govern cleanup.
You can find more information at the LDWG website, including project documents, recent activities, and project schedules.
Shipping Activity at Terminal 30 in the East Waterway
Lower Duwamish Waterway and the East Waterway
The Lower Duwamish Waterway and the East Waterway are economically, ecologically, and culturally significant for the residents of Seattle. More than a century of urbanization and industrial activity polluted the sediments in both waterways, posing risks to people and the environment, and prompted the U.S. Environmental Protection Agency (EPA) to list both areas as Superfund sites.
Though the two waterways are physically connected, they are two separate, active cleanup projects led by the EPA. The City of Seattle is involved with two separate working groups that have collaborated to fund and clean up these contaminated waterways.
Learn more about EPA and Washington Department of Ecology's (DOE) oversight of Lower Duwamish Waterway cleanup: