King County Cleans Up Elliott Bay Sediment

Nearshore water quality and fish habitat off Myrtle Edwards Park will substantially improve following King County, Washington's completion of a $3.6 million project to clean up about an acre of contaminated sediment in Elliott Bay.

More than 14,000 cubic yards of contaminated sediment – enough to fill 1,400 dump trucks – was removed and transported to Rabanco's Landfill in Roosevelt, Wash., for safe disposal.

Clean sand and gravel was added to replace the sediment, which had been contaminated with polychlorinated biphenyls, hydrocarbons, and mercury. King County will monitor sediment quality at the site over the next 10 years.

The contamination had accumulated during decades of stormwater and sewage overflows discharged through an outfall pipe known as the Denny Way CSO at 3165 Alaskan Way.

In 2005, King County completed a $139 million project to control combined sewer overflows at this location. The investments include a wet weather treatment plant capable of treating up to 250 million gallons of stormwater and sewage during heavy rains and a 7.2-million-gallon tunnel to store wet weather flows.

King County worked closely with the Washington Department of Ecology, state Department of Natural Resources, the Muckleshoot Tribe, NOAA Fisheries and other stakeholders in planning the project.