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Toxics Cleanup Program

Lower Duwamish Waterway
Site History

Until the 20th century, the Duwamish River meandered widely through a valley consisting of floodplains, freshwater wetland, and tidal marshes before emptying into Elliott Bay, Puget Sound, near Seattle, Washington. In the early 1900’s, the lower portion of the Duwamish River was straightened and dredged to improve navigation and industrial development. The material dredged up from the bottom of the river was used to create Harbor Island. Since 1916, parts of the river have been regularly dredged to support ship navigation.

Click here to view Historical Maps of the Duwamish River from 1945 and 1955.

1945 (a) historical sites
1945 (b) historical sites

1955 (a) historical sites

1955 (b) historical sites

The River Today

The Lower Duwamish Waterway Superfund site is made up of approximately 5.5 miles of the downstream portion of the Duwamish River which flows into Elliott Bay. 

For decades much of the land adjacent to the Lower Duwamish Waterway has been industrialized.  Current commercial and industrial operations include cargo handling and storage, marine construction, boat manufacturing, marina operations, concrete manufacturing, paper and metals fabrication, food processing, and airplane parts manufacturing.

Duwamish Waterway (Ecology)

This waterway serves as a major shipping route for containerized and bulk cargo. Common shoreline features within the Lower Duwamish Waterway include constructed bulkheads, piers, wharves, buildings extending over the waters, and steeply sloped banks armored with fill materials.

Although the Lower Duwamish Waterway is viewed primarily as an industrial corridor, two residential neighborhoods  border the banks of the river: South Park and Georgetown.

There are also small patches of inter-tidal habitats where birds, fish, and marine invertebrates live. Kellogg Island is the largest continuous area of inter-tidal habitat remaining in the Lower Duwamish Waterway.  Over the past 20 years, public agencies and volunteer organizations have worked to restore intertidal and subtidal habitat to the river. Some of the largest restoration projects are at Herring House Park/Terminal 107, Turning Basin 3, Hamm Creek, and Terminal 105.

Kellogg Island (Ecology)

Sediment Contamination

Contaminants in the Lower Duwamish sediments include, but are not limited to, PCBs (polychlorinated biphenyls) PAHs (polycyclic aromatic hydrocarbons), mercury, other metals, and phthalates. In September 2001, the U.S. Environmental Protection Agency (EPA) added the LDW to the Superfund or National Priorities List. In February 2002 the Washington State Department of Ecology (Ecology) listed the LDW under the authority of the Washington Model Toxics Control Act (MTCA).

Many sources have contributed to the contamination, such as marina operations, shipyard and aircraft operations, combined sewer overflows (CSOs) more than 100 storm drains, and other industrial uses.

Early Action Areas

The concentrations of sediment contamination in the Lower Duwamish Waterway vary widely. Many areas exceed the Washington Sediment Management Standards and/or regional Dredged Material Management Program criteria.

As part of the first phase of the remedial investigation, seven priority areas of the waterway that had higher contamination levels were identified for early cleanup.

Cleanup Work

Sediment removals took place at the Duwamish/Diagonal Way (Combined Sewer Overflow/Storm Drain (CSO/SD).  The Norfolk CSO sediment removal was completed before the Superfund work began in the waterway.

Cleanup at Duwamish/Diagonal Early Action Area (Ecology)

Preparation for sediment cleanup is currently in progress at the following early action areas: Slip 4, Boeing Plant 2, and Terminal 117.  Work at other early action areas will be considered as additional information is gathered in the second phase of the remedial investigation, and as resources become available. Source control action plans are complete for Duwamish/Diagonal and Terminal 117.  The source control action plan for Slip 4 is in development.  These plans will contain information on the source areas, the source control work, and monitoring that are needed, and how progress for each early action site will be reported.