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Toxics Cleanup Program


Lower Duwamish Waterway
Source Control Investigation

What is source control?

Source control is the process of finding sources of contamination, then stopping or reducing them before they reach the river. The US Environmental Protection Agency (EPA) will oversee cleanup of sediments in the Lower Duwamish Waterway (LDW). Ecology must ensure that sources of pollution to the LDW are sufficiently controlled before in-waterway work begins.

The goal of source control is to keep sediments from becoming polluted again after being cleaned up. However, finding and controlling sources is difficult. Even with aggressive source control, some recontamination will occur.

The near-term goal is to control sources sufficiently to allow EPA to begin in‑waterway cleanup. The long-term goal is to minimize recontamination of the river sediment and restore water quality in the river.

Source control includes a variety of actions. Investigation and cleanup of contaminated sites are key pieces. Controlling stormwater runoff is crucial, requiring coordination between agencies for permitting and inspections. Education is important too – find out how YOU can help keep stormwater clean!

Illustration showing storm water and combined sewer system overflow pollutants and their sources.

Illustration of potential pollution pathways.

Source Control Strategy:

Our 2016 Source Control Strategy describes the goals, priorities and processes for controlling sources of pollution to the LDW. It provides a framework for identifying source control issues and implementing effective controls for the Lower Duwamish Waterway.

The basic strategy is to identify and manage sources of chemicals to site sediments in coordination with sediment cleanups.

Source Control Areas

The land area around the river is divided into 24 Source Control Areas (SCAs) based on storm drainage. Contaminated sites are located within these areas.

Upstream to downstream approach

Ecology has determined the most efficient way to manage site cleanups for source control is an upstream to downstream approach. This reduces the problem of contamination from an upstream site moving into a downstream site that has already been cleaned up.

The SCAs are grouped into Upper, Middle, and Lower Reaches. The river flows northward, so the Upper Reach (upstream) starts in Tukwila, and the Lower Reach (downstream) ends at the southern tip of Harbor Island.

While Ecology will prioritize site cleanups in the Upper Reach, we will continue to move forward with our work in the Middle and Lower Reaches.

Map:  Upper, middle and lower reaches for Source Control Planning

Source Control Work Group

Effective source control requires an enormous amount of coordination and cooperation. Ecology leads a Source Control Work Group (SCWG) made up of local, state, and federal regulatory partners. They share information, discuss strategy, develop action plans, implement source control measures, and track progress.

The SCWG includes:

Ø Ecology: Lead for source control at properties that discharge directly to the waterway and for source control work at upland contaminated properties;

Ø City of Seattle: Lead for source control within their storm drain system;

Ø King County: Lead for source control for discharges to wastewater or combined wastewater and storm water systems;

Ø EPA: Provides technical assistance, source control coordination with EPA sediment investigation and cleanup activities.

Source Control Implementation Plans

As the lead agency for Source Control, Ecology has asked the city of Seattle, King County, and EPA to develop agency-specific implementation plans. These plans will be considered part of the Source Control Strategy following their completion.

The intent of the implementation plans is to:

  1. Set each agency's priorities for source control for the near-term (5 years).
  2. Establish long-term expectations for source control activities during and following construction of the in-waterway cleanup under the ROD.

City of Seattle Implementation Plan

Source Control Status Reports:

These reports summarize source control activities conducted by the Lower Duwamish Waterway (LDW) Source Control Work Group. 

They provide an overview of the LDW site, the strategy for controlling sources of pollutants to the LDW, the process for developing Source Control Action Plans (SCAPs), the methods and process for implementing the SCAPs, issues associated with permitted discharges, and a summary of source control actions during the period of the report. 

This page last updated March 24, 2017