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.

On September 23, 2021, the City of Seattle, King County and the Port of Seattle sent a letter to the Environmental Protection Agency about the Lower Duwamish Waterway and East Waterway (at the mouth of the Duwamish River) cleanup plans and our continued dedication to reducing unacceptable risks to human health and the environment. View the letter in full. 

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 Source Control Implementation Plan (SCIP) that describes our work to control pollution sources over the next five years. The Washington State Department of Ecology approved the City of Seattle's 2021-2026 SCIP on December 17,2020 to fulfill the requirements contained in Appendix 13 of the 2019 NPDES 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:

Below are the 2015-2021 Source Control Implementation Plan Documents: