A widespread environmental problem associated with abandoned mines and their tailings is acid mine<br>drainage @MD). AMD typically has low pH and elevated metal concentrations that are toxic to<br>aquatic life. In Northern California, Iron Mountain and other mines in the Shasta mining districts are<br>the largest sources of AMD. Additional sources lie to the south along a discontinuous belt of copper<br>and zinc mineralization in the western Sierra foothills. Between these areas lies a remote group of<br>copper mines in northeastern Plumas County including the Walker, Engels and Superior mines. Of<br>this group, AMD from Walker Mine has caused the most severe water quality impairment.<br>This paper describes the history and environmental setting of Walker Mine and the approaches used<br>by the Central Valley Regional Water Quality Control Board, a state regulatory agency, to improve<br>water quality at the site. Both the mine and its tailings contribute pollutants to the watershed. The<br>mine has a portal discharge with depressed pH and high copper concentrations. The tailings add fine<br>grained sediment to the creek and generate low but significant concentrations of dissolved copper.<br>The mine is on private property and the tailings are on land managed by the U. S. Forest Service.<br>Because of these differences in pollution problems and ownership, the methods employed by the<br>Regional Board to improve conditions at the mine and tailings have been on different, but parallel<br>tracks. Monitoring shows these efforts have significantly improved water quality in the watershed<br>over the last 10 years.


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