The Central City-Clear Creek site is an active mining facility in Central City, Clear Creek and Gilpin counties, Colorado. The site lies within the 400-square mile drainage basin of Clear Creek, which serves as a drinking water source for several municipalities. Presently, six major mine drainage tunnels are thought to be principal discharge sources of acid mine water containing high concentrations of metals to surface waters including Clear Creek and its tributaries. In addition, over 21 mine tailings piles with an estimated total volume of over 2,000,000 cubic yards at numerous locations throughout the site are thought to be major sources of contamination. In response to site contamination, EPA has conducted three removal actions since 1987. The ROD supersedes the remedy provided for OU1 in the 1987 ROD by including active treatment of the Argo Tunnel and delaying a decision on treating the discharge from the Big Five, National and Quartz Hill tunnels, and the Gregory Incline. The primary contaminants of concern affecting the ground water are metals including arsenic, cadmium, chromium, and lead. The selected remedial action for the site is included.