A proactive approach to addressing mine environmental issues

The Bonanza Mining District is located at the north-eastern edge of the San Juan Mountain Range of Southern Colorado, near the head of the San Luis Valley. Gold, silver, lead, and zinc were discovered in the District in 1880. Mining activities continued sporadically in the area until the late 1960's with the most intensive production occurring during the 1920s. The roughly 2,000-acre mining district is located within the Kerber Creek watershed. Prior to 1993, the U.S. Environmental Protection Agency (EPA), Colorado Department of Public Health and Environment (CDPHE) and the USDA Forest Service (USFS) evaluated the Bonanza Mining District for possible listing on the National Priorities List (NPL) as a Superfund site. The identified environmental issues were impacts to surface water and potential impacts to groundwater, air, and soil from historic mining and milling activities. The private parties with potential historic involvement at the Bonanza District formed a group known as the Bonanza Mining District Group (Bonanza Group), and held discussions with the CDPHE, USES and EPA regarding deferral of the NPL process in favor of a proactive approach to addressing the environmental concerns at the Bonanza District. As a result, the EPA agreed to postpone potential listing of the site on the NPL as long as efforts to address the environmental issues in the Bonanza District proceeded in accordance with preliminary plans. This paper summarizes the historical and regulatory perspectives associated with the removal program, water chemistry, development of water quality goals, remedy development, and remedy implementation. Completed and proposed work involves tailings consolidation and closure, mine adit rehabilitation and plugging, passive water treatment, storm water controls, revegetation, and riparian zone enhancements.