The U.S. Geological Survey evaluated the feasibility of utilizing 8,000 acre-feet (9.9 cubic hectometres) of sewage effluent per year to recharge the ground water in a 25-square mile (65-square kilometre) area northwest of Indio, Calif. The depth to water in the area studied ranged from about 50 feet (15 metres) to more than 200 feet (61 metres). Dissolved-solids concentrations greater than 500 milligrams per litre exist in the shallow aquifers in the eastern and southern parts of the study area. The permeability of the shallow sediments ranges from 15 to 50 feet per day (5 to 15 metres per day). The eastern part of the area is underlain by fine-grained sediments that effectively separate the deep and shallow aquifers and would not be conducive to artificial recharge. In the western part of the area, sediments in the upper 100 feet (30 metres) are primarily sand. Considering all but economic factors, the most hydrologically favorable area for recharge is west of Washington Street and north of the Whitewater River.
Using three spreading pits on a rotating basis and assuming long-term infiltration rates of 2 feet per day (0.6 metre per day), an area of 33 acres (13 hectares) would be required to infiltrate 8,000 acre-feet (9.9 cubic hectometres) per year. At the recharge site, a water-level rise of about 36 feet (11 metres) due to recharge is expected.
