Source control

Source control is the process of finding sources of contamination, then stopping or reducing them before they reach the Lower Duwamish Waterway (LDW). We must make sure that sources of contamination to the LDW are sufficiently controlled before in-waterway cleanup begins. This means we must investigate more than 20,000 acres of land that drains into the river.

Source control includes site investigation and cleanup, business inspections, controlling stormwater runoff and combined sewer overflows, coordination among agencies, and education. Find out how YOU can help keep stormwater clean.

How does pollution get into the river?

Contaminants in the soil and groundwater in the area around the river can find their way into the sediments through storm runoff and other routes (as shown below). The sediments contain a wide range of contaminants due to decades of industrial activity and runoff from urban areas.

Conceptual site model

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.

Ecology has defined 24 source control areas. View the Source Control Area Map to read more about the work we've done in these areas.

The short-term goal is to control sources sufficiently to allow in‑waterway cleanup to begin. The long-term goal is to minimize recontamination of the river sediment and restore water quality in the river. However, finding and controlling sources is difficult in an urban environment. Even with aggressive source control, some recontamination will likely occur.

Source Control Work Group

Ecology leads the interagency Source Control Work Group. Much coordination is needed between agencies to control sources of pollution within the 24 source control areas. This group of regulatory professionals meets monthly to share information, discuss strategy, develop action plans, implement source control measures, and track progress.

The Source Control Work Group includes:

  • Ecology: Lead for source control at properties that discharge directly to the waterway, as well as at upland contaminated properties.
  • City of Seattle: Lead for source control within their storm drain system.
  • King County: Lead for source control for discharges to wastewater or combined wastewater and stormwater systems.
  • EPA: Provides technical assistance, source control coordination with EPA sediment investigation and cleanup activities.

Upstream to downstream approach

We've determined that 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 24 source control areas 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 we will prioritize site cleanups in the upper reach, we will continue to move forward with our work in the middle and lower reaches.

Lower Duwamish Waterway showing the upper, middle, and lower reaches for source control planning.