About 5,000 cubic yards of material unsuitable for open water placement is being dredged from the Duwamish River by a U.S. Army Corps of Engineers contractor beginning Jan. 25.
The contractor will use a specially-designed clamshell bucket and approved dredging procedures designed to minimize sediment resuspension and remove the unsuitable material. The Corps’ Seattle District awarded a $650,000 contract to Federal Way-based Kiewit Infrastructure West Co., to remove the material. The dredging will take about two weeks to complete and material will be disposed of at the Roosevelt Regional Landfill in Klickitat County.
In December 2011 the Seattle District contracted Kiewit to remove sedimentation from Seattle Harbor and the Duwamish River. The portion containing this 5,000 cubic yards was found unsuitable for open water placement and not dredged during those operations. The material deemed suitable at that time was placed at an approved Elliott Bay open-water site.
The unsuitable material not dredged in 2011 was within acceptable chemical contaminant levels, but found to exceed open-water placement limits during bioassay tests. It is unknown why the material exceeds those limits, but bioassay tests override chemical contaminant levels making it unsuitable for open water placement under the Dredged Material Management Program, or DMMP, guidelines. The DMMP, implemented by the Corps’ Seattle District, is a partnership between the U.S. Environmental Protection Agency and Washington state departments of Ecology and Natural Resources. These four agencies collaboratively work to manage and regulate disposal of dredged material from dredging projects in Washington state.
Corps officials worked with the EPA, Washington Departments of Ecology and Natural Resources, Port of Seattle and Muckleshoot Indian Tribe to ensure the dredging was environmentally responsible. In addition, the Corps prepares a biological evaluation in accordance with the Endangered Species Act and assures full compliance with the act prior to starting.
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Press Release, January 28, 2013