Lower Duwamish Source Control
The City's program to keep pollution from entering the Lower Duwamish Waterway (LDW) is an important element of the watershed-wide source control strategy led by Ecology. Learn more about Ecology's Source Control Strategy.
The City’s program has three elements: source tracing, business inspections, and pipe cleaning.
Source tracing/characterization sampling
The City 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
The City has a Source Control Implementation Plan (SCIP) that describes our work to control pollution sources over the next five years. 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 Washington Department of Ecology’s website.
The Source Control Implementation Plan Documents are available for review:
- 2021-2026 Lower Duwamish Waterway Source Control Implementation Plan (PDF)
- 2021-2026 Lower Duwamish Waterway Source Control Implementation Plan Appendices (PDF)
- 2021-2026 Lower Duwamish Waterway Source Control Implementation Plan Map Atlas (PDF)
Below are the 2015-2021 Source Control Implementation Plan Documents: