Environmental Evolution and Risk Assessment of Perry Canyon AML in Washoe County, Nevad

The Perry Canyon abandoned mine land hosts acid mine drainage (AMD) that is forming in underground abandoned mine workings. This AMD may be causing high concentrations of As and Pb in the surface water, soils, and groundwater of Perry Canyon. Samples were collected and analyzed to determine the degree of contamination of the natural resources. Due to elevated concentrations and potential for negative health impacts, As and Pb were identified as contaminants of concern. A MODFLOW model was developed using the hydraulic gradient and monitored meteorological conditions to identify transport pathways for potential contamination sourced from adit effluent and waste rock piles. Samples of groundwater collected downstream of the adit seeps were compared to groundwater samples from locations upstream to determine the effects of AMD inflows on groundwater quality. As and Pb contamination in the groundwater seems to remain proximate to the adits with limited increases in downstream concentration. During periods of intense precipitation, it is likely that contamination from discharging adit effluent flows towards Perry Creek and is carried by increased surface flows towards the alluvial fan. Erosion of soils from the waste rock would also transport contamination towards the mouth of the canyon. Contamination mobilized from infiltration into waste rock would likely flow to the aquifer and remain proximate to the source. Transport of contamination can be reduced by controlling erosion of contaminated soils and transport of adit effluent during large precipitation events. Minimizing infiltration into waste rock piles will reduce AMD formation in the waste rock and prevent contamination from infiltrating to the aquifer.