King County planning follow-up sediment cleanup in lower Duwamish River

King County in early 2005 plans to use an environmental cleanup method called enhanced natural recovery to reduce the impact of contaminated sediment washed into the Duwamish River during dredging a year ago. This follow-up action, to take place by March 1, 2005, will help protect fish, the environment and public health.

The action will spread 5,500 tons of clean sand evenly over an area outside the southwest part of the 7-acre dredging site in the lower Duwamish. That area had the largest increase in contaminant concentration after the dredging.

An average of 7 inches of sand will cover the area and immediately reduce the exposure to organisms living in the Duwamish to polychlorinated biphenyls, or PCBs. Also, that amount of sand should not be enough to affect organisms that live in the sediment.

The contractor for King County's Wastewater Treatment Division removed an estimated 66,000 cubic yards of contaminated sediment from the dredging area between November 2003 and March 2004. The project resulted in the cleanup of 7 acres of the Duwamish and removal of about 400 pounds of PCBs from the river ecosystem.

In the early stages of the cleanup, actions by the contractor dredging in the highly contaminated southwest part of the site caused excessive contaminated dredged material to escape. The contractor corrected its dredging practices, and the project continued. As planned, the contractor then placed a cap of clean material on top of the dredged area.

After the cleanup, monitoring results showed some higher levels of contamination outside the dredged and capped area-especially around the southwest part of the site. King County notified state and federal regulatory agencies and explained the results. The county also notified organizations interested in the cleanup, and possible remedies were discussed during the summer of 2004.

King County proposed the enhanced natural recovery remedy to reduce contamination levels faster. The regulatory agencies and King County are planning this work to take place before March 1, 2005.

The follow-up action will extend into the Duwamish navigation channel. But the 7-inch layer of sand will not significantly change the depth of the channel and affect navigation nor will it trigger more dredging to maintain the depth of the channel.

This project will also be studied as a possible alternative for the clean up of other lightly contaminated sites in the river. This alternative and others will be considered during a cleanup feasibility study under way as part of the Lower Duwamish Superfund process.

This project is considered an interim action under the Washington State Model Toxics Control Act (WAC 173-340). The continuing Superfund investigation will include evaluation of the need for more cleanup in this area of the river that may take place after completion of the Superfund investigations.

King County's regional wastewater treatment utility is managing the cleanup for the Elliott Bay/Duwamish Restoration Program. Other members of the program panel are the state Department of Ecology, U.S. Fish and Wildlife Service, National Oceanic and Atmospheric Administration, Muckleshoot and Suquamish tribes, and City of Seattle.

The dredging removed contaminated sediment from a stretch of the Lower Duwamish Waterway just north of Kellogg Island. The Duwamish flows northwest from Tukwila, splitting around Harbor Island and emptying into Elliott Bay south of the Seattle waterfront. The lower waterway has been heavily industrialized for more than 80 years, getting discharges from a large industrial, urban area.

A 1991 consent decree settled a 1990 lawsuit filed by NOAA against the City of Seattle and the former Municipality of Metropolitan Seattle (Metro), now the county's Wastewater Treatment Division. The lawsuit alleged injuries to natural resources in Elliott Bay and the lower Duwamish River.

For more information about the follow-up action, contact John Phillips of the Wastewater Treatment Division, at 206-263-6543 or e-mail; or Rick Huey of the state Department of Ecology at 425-649-7256 or e-mail. Information is also available on the project Web site.

Copies of the plan are available for review at these locations:

• Georgetown Gospel Chapel, 6606 Carleton Ave. S., Seattle. Call Pastor Leroy Hedman for an appointment, 206-767-3207.
• State Department of Ecology, 3190 160th Ave. S.E., Bellevue. Call 425-649-7190 for an appointment.

The county's Wastewater Treatment Division protects public health and the environment by serving 18 cities, 16 local sewer agencies and more than 1.4 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional utility operated by King County has been preventing water pollution for more than 40 years.