Geohydrology and water resources of the Papago Farms-Great Plain area, Papago Indian Reservation, Arizona, and the upper Rio Sonoyta area, Sonora, Mexico

The Papago Farms-Great Plain and upper Rio Sonoyta study area includes about 490 square miles in south-central Arizona and north-central Sonora, Mexico. In the study area 23,700 acre-feet of ground water from the basin-fill deposits was used to irrigate more than 5,000 acres in 1981. Surface water is not a reliable source for irrigation or public supply. Ground water enters the area as underflow from the north and east and as recharge from the mountains, moves through basin-margin sediments, around the basin-center clays, and exits the area to the west beneath the Rio Sonoyta. Ground-water withdrawals in the upper Rio Sonoyta area do not appear to have an effect on water levels in the Papago Farms-Great Plain area. Depth to water ranges from 500 feet near the southern boundary to 150 feet in the center of study area. About 10 million acre-feet of recoverable ground water is stored in the upper 400 feet of the aquifer. Storage is being depleted at a rate of 19,000 acre-feet per year. The ground water is a sodium and bicarbonate type and has an anomalously high content of arsenic and fluoride. (USGS)