USGS Washington Water Science Center
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Lake Roosevelt was formed on the Columbia River by the construction of the Grand Coulee Dam, and extends a total of 217 km to within 24 km of Canada The lake is heavily contaminated with trace elements that were discharged as slag material from a smelter in Canada; approximately 360 metric tons were discharged per day from 1900 to 1998. A study by the USGS reported that Lake Roosevelt bed sediments were contaminated based upon high concentrations, impaired benthic invertebrate communities, and laboratory sediment bioassays. While the majority of studies have focused on contaminants in water, sediment, and fish, there is recent concern over the potential threat of airborne contaminants to human health. Trace metal concentrations associated with the fine-grained fraction have high potential for entrainment into the lower atmosphere by wind gusts. Once airborne, the dust particles are carried downwind various distances depending on their size and the magnitude and duration of the prevailing winds. During the spring, the reservoir water level decreases substantially and exposes extensive reaches of contaminated sediments that, upon drying, may easily be transported via the prevailing wind throughout the Lake Roosevelt area. The U.S. EPA recently stated that airborne contaminants in Lake Roosevelt area may be of concern to human health and has recommended additional studies.