Acidic water that contains elevated concentrations of metals has contaminated a stream and alluvial aquifer in a mining district near Globe, Arizona. The contaminated aquifer is a narrow layer of unconsolidated alluvium along Miami Wash and Pinal Creek. The alluvium overlies basin fill, which extends throughout most of the Pinal Creek basin. The alluvium and basin fill compose the primary aquifer in the basin. Horizontal hydraulic con- ductivities were estimated at about 200 meters per day in the alluvium, and average linear ground- water flow velocities are about 5 meters per day. Water levels in the aquifer respond rapidly to periods of extended runoff in the basin and variable rates of ground-water pumping. Fluctuations of as much as 2.5 meters in 6 months have been measured. Ground-water levels were near record highs during spring 1985 and declined as much as 13 meters by spring 1989. Measured hydraulic gradients indicate that flow is generally upward from the basin fill to the alluvium. From 1980 to 1984, seepage of 155 liters per second from Webster Lake and 279 liters per second streamflow infiltration were estimated to be the two largest sources of inflow to the regional aquifer. Major outflows from the aquifer were 166 liters per second of pumpage and 240 liters per second of natural ground-water discharge to Pinal Creek.
