Duwamish Waterway

Cleaning up an urban waterway

Duwamish dredging

The City of Seattle, King County, the Port of Seattle, and The Boeing Company-collectively known as the Lower Duwamish Waterway Group (LDWG)-have been conducting cleanup investigation of the Lower Duwamish Waterway since 2001. The U.S. Environmental Protection Agency and the Washington State Department of Ecology have provided oversight of these efforts

More than 4,000 samples of sediment, soils, water and fish tissue from more than 2,000 locations have been collected and analyzed.

The four main contaminants of concern are:

  • Polychlorinated Biphenyls (PCBs); previously used in many industrial operations, including as a fire retardant and as an insulating fluid for electrical transformers.
  • Polyaromatic Hydrocarbons (PAHs); present in petroleum products and a byproduct of burning fuel.
  • Arsenic; a semi-metallic element that is both naturally occurring and has many industrial, medical and agricultural uses.
  • Dioxins and furans; produced by incomplete burning of carbon-based products including wood, metal, and coal.

Duwamish wildlife

Research concluded that most of the waterway's sediments pose low risk to human or environmental health. EPA has determined that some areas may have elevated risks due to the potential consumption of large quantities of resident fish and shellfish. Migratory fish such as salmon are safe to eat following standard precautions, according to the Washington State Department of Health.

The Lower Duwamish Waterway Group is proposing a cleanup strategy that will:

  • Reduce human health risks as quickly as possible,
  • Minimize impacts to neighborhoods, businesses and the environment, and
  • Employ best-fit technology to ensure an effective cleanup of the Lower Duwamish Waterway.

The EPA is reviewing several cleanup options for the Duwamish Waterway. While each option varies in duration and cost, they all reduce about 90 percent of the sediment contaminants through a combination of dredging, source control and monitored natural recovery. The construction time associated with each option ranges from 4 to 38 years, while cost estimates range from $210 million to $1.35 billion.

Addressing decades of historical contamination will require regional solutions and we will all pay for the cleanup. Public agencies will likely pass along the cost of cleanup through taxes or utility rates. Private companies will need to factor cleanup costs into their business costs.

Plant 2 demolition

The demolition of Plant 2 precedes cleaning up the adjacent waterway and restoring wetlands and habitat.

In addition to the cleanup of the Waterway, Boeing is undertaking the cleanup of Plant 2 and adjacent sediment contamination. When Plant 2 was originally built, portions of the building needed to be constructed on pilings over the Lower Duwamish Waterway. Boeing is removing more than 53,000 square feet of over-water structures. More than 85 percent of the building's materials including steel and wood beams, copper wiring, concrete and other miscellaneous metals are being recycled or reused.

After the environmental cleanup of its property is completed, Boeing will restore the shoreline where Plant 2 once stood and create nearly five acres of intertidal wetlands and habit for migratory fish.