The US Army Corps of Engineers is responsible for the dredging and disposal of large volumes of sediment each year. Navigable waterways of the United States have a vital role in the Nation's economic growth. For the present study, Duwamish River sediments were removed by a mechanically operated more » clamshell dredge, deposited in barges, and transported to an experimental disposal site in Elliott Bay for disposal. The primary mode of disposal has been pipeline discharge to a shore disposal area. Historically, maintenance dredging of the Duwamish River has required the removal of approximately 230,000 to 305,000 cubic meters of sediment every 3 to 5 yr. Recent studies have shown that another factor makes this site important for study purposes-the potentially adverse biological consequences that may result because of an accidental spill of 984 l of polychlorinated biphenyls (PCB's) in September 1974 into the Duwamish River where maintenance dredging is required.
The study site in Puget Sound represents the only estuarine site where the environmental effects of dredged material disposal by barges (instead of other disposal modes) are being studied. The other sites include Lake Erie off Ashtabula, Ohio the mouth of the Columbia River and the Gulf of Mexico off Galveston, Texas. The Duwamish Waterway study is one of four regional aquatic disposal field investigations sponsored by the DMRP. The biological and water-sediment quality effects of open-water disposal of dredged material are being evaluated under the Environmental Impacts and Criteria Development Project (EICDP) of the DMRP in Task 1A: Aquatic Disposal Field Investigations.
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