Contaminated Elliott Bay sediment clean-up begins

King County is cleaning up Elliott Bay and improving habitat for fish and wildlife by removing an estimated 4,000 dump truck loads of contaminated material from the bottom.

Beginning Nov. 27, dredging barges working just offshore Myrtle Edwards Park in Seattle will start to remove contamination from combined sewer overflows (CSO) and restore habitat in local water bodies. Dredged material will be disposed in an approved landfill.

The contaminated sediment accumulated over decades from stormwater and sewage overflows discharged through an outfall pipe known as the Denny Way CSO, at 3165 Alaskan Way.

A variety of chemicals and metals washed out and collected in adjacent sediments. The old outfall pipe has since been removed, and sewage and stormwater overflows are now controlled by a $139 million King County project that was completed in 2005.

The cleanup stems from an agreement with the Washington State Department of Ecology to remove sediments that do not meet state sediment quality limits.

About 20,000 cubic yards of material contaminated with PCBs and mercury will be removed from the nearshore area. Future projects are also expected farther offshore to remove a smaller amount of contamination.

King County's contractor, American Civil Constructors, is using a mechanical dredge on a barge to excavate the area and load a second barge with contaminated sediment. The second barge will transfer the sediment to trucks and trains for transport to a landfill.

The excavated area will be backfilled with clean sand and gravel to match the seabed's existing grade and improve the site as shallow-water nearshore habitat for fish and wildlife.

King County project managers will oversee contractor operations to ensure careful dredging methods are used to limit sediment disturbances. King County inspectors will regularly monitor water quality around the work area to verify that the environment is protected. American Civil Constructors' crew has years of experience in removing contaminated sediment.

King County worked closely with the Department of Ecology, the Muckleshoot Tribe, NOAA Fisheries and other agencies in planning the project. Stakeholders also weighed in on best management practices, cleanup methods and restoration.

Work is expected to last approximately 10 weeks at a cost of $3.6 million.

The project will require some minor construction staging near the King County facilities and plaza in Myrtle Edwards Park. Although park users are not expected to be significantly impacted by the cleanup, community members can call the project's 24-hour construction hotline at 206-205-9305 to share comments or inquires about the project.

People enjoy clean water and a healthy environment because of King County's wastewater treatment program. The county's Wastewater Treatment Division protects public health and water quality by serving 17 cities, 17 local sewer districts and more than 1.4 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional clean-water agency now operated by King County has been preventing water pollution for more than 40 years.