Ambient Groundwater Quality of the Lower San Pedro Basin: A 1999-2000 Baseline Study

The Lower San Pedro Groundwater Basin (LSP) baseline groundwater quality study was conducted by the Arizona Department of Environmental Quality in 2000. Located in southeastern Arizona, this semiarid basin is drained by the San Pedro and Gila Rivers. The LSP is a rural landscape with scattered towns and two
extensive copper mining and processing operations. Groundwater from three aquifers (floodplain, unconfined basin-fill, and confined basin-fill or artesian) and fractured mountain hardrock is the principle source of water supply. For this study, 63 groundwater sites were sampled for inorganic constituents. In addition, fewer sites were also sampled for Volatile Organic Compounds (25), radiochemistry (19), radon (19), and pesticide (2) analyses. Eighteen (18) percent of sample sites had concentrations of at least one constituent that exceeded a health-based, Federal or State water-quality standard.