Lower Duwamish Waterway Project

The last five miles of the Duwamish River is contaminated; it is a United States Superfund Site. The City of Seattle is part of the Lower Duwamish Working Group (LDWG) who is working to clean up the river. Currently we are working on scientific studies and design planning for river cleanup and controlling sources of pollution to the river. Future cleanup construction will include dredging and capping of contaminated river mud (sediments). Learn more about sediment cleanup at LDWG.org and pollution source control below.

Learn more about the United States Environmental Protection Agency (EPA) and the Washington Department of Ecology’s (DOE) oversight of Lower Duwamish Waterway cleanup: 

Learn more about citywide work to control sources of pollutionhow to report a pollution problem, or how you can prevent pollution.

Lower Duwamish Waterway Pollution Source Control Program

The City’s program to keep pollution from entering the Lower Duwamish Waterway (LDW) has three elements: business inspections, source tracing, and pipe cleaning.

Source Tracing/Characterization Sampling

The City’s collects and tests sediment samples from area catch basins and pipes. When elevated contaminant levels (arsenic, copper, lead, mercury, and zinc, semi-volatile organic compounds, PCBs, and total petroleum hydrocarbons) are found, additional sampling and inspections are conducted upstream to locate the source.

Business Inspections

The City inspects and works with businesses to ensure that they are using best management practices to keep stormwater pollution, including hazardous materials and industrial waste, out of storm drains that flow to the LDW. We inspect businesses based on identified or potential pollution risk.

Pipe Cleaning

When the City finds elevated contaminant levels in storm drain sediment, it cleans the pipes to remove the sediment and stop pollution from reaching the waterway. Material removed from the pipe is collected, dewatered, and shipped offsite for disposal. The pipe is then checked periodically to see whether the contamination comes back. If it does, the whole process starts over again with more sampling and business inspections to find and control the source.


Source Control Implementation Plan

The City has a Draft Source Control Implementation Plan (SCIP) that describes our work to control pollution sources over the next five years. The Washington Department of Ecology SCIP for potential into the the City’s Municipal Stormwater Permit. More information can be found on the Washington Department of Ecology’s website.

The Source Control Implementation Plan Documents are available for review: