In pursuing its mandated mission to characterize groundwater quality in the state, the Arizona Department of Environmental Quality has collected samples from 1,477 sites over a 15-year period between 1995 and 2009. The sample sites consisted mainly of domestic, stock, irrigation and municipal wells and, to a lesser extent, springs used predominantly for watering stock and wildlife. Sampling activity was conducted within 35 of the state’s 51 officially designated groundwater basins and covered much of Arizona with the exception of Native American tribal lands. The data provide comprehensive and reliable information on the occurrence and concentrations of groundwater contaminants. This is critical knowledge for the estimated 100,000 private domestic wells in the state whose owners represent about 5 percent of Arizona’s population.

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.