Years of mining for heavy metals has resulted in abandoned mines that are a source of ground- and surface-water contamination in many areas of the United States. To gain an understanding of the controlling processes in the transport of heavy-metal contaminants, which can be applied at other sites, the U.S. Geological Survey's Toxic Substances Hydrology Program initiated an investigation of the fate of heavy-metal contamination from abandoned lead and zinc mines in the Tar Creek drainage basin in northeastern Oklahoma and southeastern Kansas. Investigators from several disciplines studied the geochemical and microbiological reactions that mobilize iron, zinc, cadmium, lead, manganese, and nickel in the underground mine workings and the effect of transport and deposition of these metals in the surface-water drainage. Specific studies included modeling to determine the important geochemical reactions that control mine- and surface-water composition, investigating microbiological activity in surface water, and studying the biological uptake of metals by plants. This research was conducted initially during the late 1980’s and early 1990’s. Increased interest in the site has resulted in activities being restarted in 2004. Current research is being conducted in collaboration with the University of Oklahoma.