Cleaning up the Lower Duwamish

Cleanup challenges

The Lower Duwamish is affected by significant historic pollution from war time manufacturing, shipping activities and the disposal of raw sewage. It runs through a 32 square-mile drainage area through highly urbanized terrain. The waterway remains affected by ubiquitous contaminants including PCBs and phthalates.

Removing this historic contamination is only the start. Additional measures will be necessary to identify and control ongoing sources. Sediment continues to get contaminated when toxic chemicals enter flowing water and settle on the bottom of large waterways. The toxic chemicals typically come from industrial discharges, upstream inputs, air /dust, stormwater, tidal cycles and combined sewer overflows.

Some of the challenges we face:

• The impacts of the cleanup could have a big effect–positive or negative–on the region’s economic health. For more information read The Economics of Cleaning Up the Lower Duwamish Waterway (PDF).
• The waterway receives inputs from 32 square miles of urban runoff and industrial drainage.
• Water and sediment quality is affected by inputs from a 492 square mile watershed.
• Some of the contamination found in the waterway comes from products commonly used by businesses and consumers, and can therefore still be found throughout our environment
• Some sources of contamination are still unidentified
• Other sources of contamination, including runoff and air deposition are still unchecked.
• Urban background levels of contamination do not allow any cleanup alternative to fully achieve the cleanup's risk reduction goals.

Lower Duwamish Waterway drainage area (PDF), April 2004

Lower Duwamish Waterway Watershed (PDF), September 2000