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Arkansas River Near Leadville, CO. Credit: USFWS.
Background: The Leadville Mining District (California Gulch) has hundreds of abandoned mines, many miles of underground tunnels and shafts, large waste rock and tailings deposits and numerous processing facilities (some 75 mills and 44 smelters). Waste products including mill tailings, slag, and dust were frequently placed in piles or tailings ponds; often in or adjacent to flood plain locations. Over 2,000 waste rock piles cover approximately 627 acres. Many of these exposed dumps remain as metal sources to the Arkansas River and other Basin tributaries. In addition, blow outs of mine drainage tunnels combined with heavy spring runoff have transported an estimated 115,000 cubic yards of fluvial tailings to the flood plain of the Arkansas River. These fluvial tails are being actively eroded by the river and result in ongoing metals releases.
The Arkansas River is used for recreation, irrigation of agricultural and range lands, and municipal drinking water. Irrigation of rangeland and agricultural land with high metal content water may contribute to elevated levels of metals in animals and plants. High metals concentrations along riverbanks can reduce or eliminate riverside vegetation, which increases erosion potential. High metals concentrations in stream water can cause degradation of fish habitat, recreational areas, and agricultural land. The Arkansas River seasonally exceeds state aquatic life standards for several metals including zinc, lead, cadmium, and copper.
The Department of the Interior (DOI), State of Colorado (State), Environmental Protection Agency (EPA), U.S. Department of Justice (DOJ), and two of the primary potentially responsible parties (PRPs) have signed a Memorandum of Understanding (MOU) which sets up a two part process to restore the Upper Arkansas River Basin. The first part of the process is to determine natural resource injury based on data and information currently available. Upon Completion of injury determination, restoration alternatives will be developed. The second part of the process will set up a facilitated negotiation intended to resolve the PRPs potential liability.