Summary

Description

Several open pit mines in Nevada lower groundwater to mine ore below the water table. After mining, the pits partially fill with groundwater to form pit lakes. Water quality in the pit lakes may be affected by a variety of factors including the quality of inflowing groundwater, atmospheric precipitation, sulfide oxidation in surrounding rock, dissolution of metals, precipitation of metals, and evaporative concentration. Oxidation reactions on exposed pit walls may release sulfate, acid, and metals into the pit lake. In some cases, water contained in the pit lakes may be of poor quality and may contain concentrations of metals or other inorganic constituents that greatly exceed water quality standards and published wildlife effect levels. Two types of pit lakes may form. The first type has a circumneutral pH and may develop a complex food web. The second type is highly acidic and will remain relatively sterile. While this second type may be less attractive to wildlife, it is highly toxic if water is consumed. Geochemical modeling to predict water quality in some future pit lakes has predicted longterm degradation of pit lake water quality. Wildlife use and the degree of threat presented by inorganic contaminants in pit lakes are uncertain, although at least limited riparian and aquatic communities will become established in most pit lakes where pH remains circumneutral. In these circumneutral pH pit lakes, wildlife use and fish introductions over the longterm are uncertain. Wildlife exposure to contaminants through drinking water and consumption of contaminated foods in the lakes may occur. Constituents that bioaccumulate or biomagnify in the food chain, such as selenium and mercury, are of greatest concern. Currently, little is known about biological characteristics of mine pit lakes. This investigation was designed to provide information on habitat and community development, habitat quality, wildlife use, inorganic contaminants behavior and partitioning, and the potential for wildlife exposure to inorganic contaminants in mine pit lakes.