Sediment Contamination Guide:
Background
SEVERAL STUDIES SHOW THAT LAKE ROOSEVELT’S SEDIMENT IS CONTAMINATED with elevated levels of metals (including arsenic, cadmium, copper, lead, mercury, and zinc). Studies also show elevated levels of dioxins, furans and PCB (polychlorinated biphenyl) contaminants. These contaminants are largely the legacy of upstream smelting and pulp operations. Whether, or to what degree, contaminated sediments are adversely impacting the environment or human health is currently being investigated.
Sediments are fragmented material such as gravel, sand, silt and clay that are deposited on the bottoms and banks of rivers and lakes. Beginning in 1988, a series of studies by the Washington Department of Ecology, the United States Geological Survey (USGS), the U.S. Environmental Protection Agency (EPA) and the Spokane Indian Tribe resulted in our present understanding of sediment contamination in Lake Roosevelt. What is known from historical records and these studies includes:
- A smelter in Trail, Canada that has operated since 1896 and is currently owned by Teck Cominco is the primary source of metals contamination. Contaminants were transported to Lake Roosevelt as slag and liquid effluent, byproducts of smelting operations that discharged into the Columbia River. Estimates are that over 10 million tons of slag was discharged from 1942 until 1995, when slag discharge to the river ceased. Discharges of
metals in effluent began declining in the 1980s with changes in operations, processing techniques and plant modernization. Metal loads to the river between 1995 and 1999 were reduced by seventy six to ninety six percent, depending on the metal. - The concentration of metals in sediment samples varies from 5 to 10 fold. Although found throughout the length of the reservoir, some studies show the highest concentrations of copper and zinc are located in the upper sections of the lake. Concentrations of cadmium, lead and mercury were higher in the mid and lower regions.
- Most recent sediment deposits (with the exception of copper) show decreasing concentrations of metals. Further, the highest concentrations of metals are found deeper in the sediments (the lower half of core samples).
- There is weathering and movement of slag that shows ongoing physical and chemical breakdown of contaminated sediments. Further study, however, is needed to determine if this process is causing contaminants to leach into the overlying water column and associated organisms.
- Surface water sampling shows long term effects on organisms, particularly from lead and copper toxicity.
- Dioxins, furans and PCBs are the organic contaminants of greatest concern. The predominant source of dioxins and furans in Lake Roosevelt sediments came from effluent discharge from Celgar, a pulp mill in Canada. Celgar’s operational changes and plant modernization in the mid 1990s were designed to end discharges of furans and dioxins into the river. A point source for PCBs is not yet apparent.
The U.S. EPA began investigating human health and environmental risks of sediment contamination in 1999. EPA has now launched a Remedial Investigation and Feasibility Study to assess these risks, including what (if any) clean up action is needed. This site, however, is not designated as a federal superfund cleanup site.