The Effects on Water Quality by Mining Activity in the Miami, Arizona Region

Abstract

Intensive strip and leach mining activity within a confined region usually causes environmental impacts both on the land and on water quality. Adverse water quality effects could be realized long after any mining activity has ceased due to the continuous leaching by precipitation of contaminants from spoils piles and leach dumps. The Miami, Arizona region is unique in its surface and subsurface hydrology. Two unconnected aquifers underlay the region with both serving as domestic (private and municipal) and industrial (mining) supply sources. The shallow floodplain alluvial aquifer is hydraulically connected to surface drainage from mine tailings and leach dumps. Several wells drawing from this aquifer have been abandoned as a municipal supply source due to severe water quality degradation. Water quality in these wells varies directly with precipitation indicating a correlation between surface drainage over and through tailings and leach piles. Expansion of spoils dumps into natural recharge pathways of the deeper Gila Conglomerate aquifer has raised concern that this aquifer may also be subjected to a long term influx of mine pollutants. Questions have also been raised concerning the potential effects of a proposed in situ leaching operation on the water quality of the conglomerate aquifer.