Aquifer compaction and ground-water levels in south-central Arizona

As of 1998, the U.S. Geological Survey is monitoring water-level fluctuationa dn aquifer compaction at 19 wells that are fitted with borehole extensometers in the Eloy Basin, Stanfield Basin, Avra Valley, and Upper Santa Cruz Basin. Decreased ground-water pumping has resulted in water-level recoveries of more than 100 feet at a well near Eloy and almost 200 feet at a well in Avra Valley. Aquifer compaction has continued in both areas despite the large water-level recoveries in Eloy and the stable water levels in Avra Valley. Extensometer sites in the Upper Santa Cruz Basin have recorded as much as 50 feet of water-level decline and 0.2 feet of aquifer compaction during 1980 to 1996. Rates of compaction vary throughout the extensometer network, with the greater rates of compaction being associated with the more compressible sediments of Eloy and Stanfield Basins.