This study was a cooperative effort between the USGS and and the Arizona Department of Water Resources. A total of eight drivepoints were installed along the San Pedro River by personnel associated with the cooperative study. Of the eight drivepoints, five produced water when pumped with a peristaltic pump. Ground water is predominantly a calcium bicarbonate type near the mountain fronts and trends toward a mixed anion or sodium bicarbonate type at lower elevations near the river. This change in water type can be observed along a ground-water flowpath from the mountains to the river.
Surface water is consistently a calcium bicarbonate type.
Stable isotope values of the surface water in a downstream direction tend to get lighter, which indicates that the surface water is receiving input from the ground water. The upper Santa Cruz River subbasin includes the Santa Cruz River and the metropolitan area of Tucson. Continued population growth and changes in land use may also affect water quality. The present land-use types primarily are urban and rangeland. Subunit Survey Sampling in fiscal year 1998 will include approximately 30 wells selected randomly from existing wells that are open to the basin fill hydrogeologic unit.