EVALUATION OF POLLUTION FATE AND TRANSPORT RISKS AND IMPLICATIONS FOR MANAGEMENT ON ABANDONED MINE LANDS: CASE STUDIES FOR THE PERRY CANYON AND CASELTON WASH ABANDONED MINE LANDS

Environmental risks from abandoned mine lands (AMLs) are largely based on the potential for transport of contaminated materials off-site via wind or water-based mechanisms. The Perry Canyon AML (Washoe County, NV) and Caselton Wash AML (Lincoln County, NV) provide case studies to evaluate environmental fate and transport risks from AMLs and serve as examples for management and agency-academy partnership opportunities. Perry Canyon includes two filled in adits and re-graded waste-rock dumps capped with an erosional protection layer. Since closure and capping activities, minimal vegetation has re-grown and the closed adits continue to drain groundwater from underground workings. Groundwater, surface water, and sediments in Perry Canyon continue to have elevated levels of As, Pb, and Cu. XRF surveys have indicated that sediments contain metals possibly associated with on-going erosion of the capped waste-rock dumps and mass loading from the adit drains. Transport and exposure pathways for heavy metals and acid mine drainage hazards exist in surface water, groundwater, and sediments. The transport of sediments poses additional long-term risks associated with climate change as increased runoff and erosional events may occur in Perry Canyon. The Caselton Wash AML is an abandoned tailings disposal site from the Caselton Mill which was last operational in the 1960s. The Caselton Wash AML includes two tailings units, a sulfide/acid-generating tails and a manganese-oxide tails, deposited over 10 disposal cells. The ponds were constructed in an un-lined alluvial channel and may pose risks to groundwater. Hydrologic modeling of the tailings indicates steady-state percolation rates between 0.1-10 mm/year. In addition to percolation risks, observed surface-water runoff and wind erosion has been observed. The size and scope of the Caselton Wash AML, as well as the uncertainty in hydrologic properties and system geometry presents significant management challenges. A risk-based approach to long-term management of Caselton Wash has been proposed based on limited data. An evaluation approach for quantifying natural attenuation capacity and stability for Perry Canyon and Caselton Wash is presented.