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 of potential pollution pathways.
Source Control Strategy:
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
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.
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;
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
The intent of the implementation plans is to:
- Set each agency's priorities for source control for the near-term (5
- Establish long-term expectations for source control activities
during and following construction of the in-waterway cleanup under the
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
This page last updated March 24, 2017