The Rush Springs aquifer, in western Oklahoma, is equivalent to the Permian-age Rush Springs Formation. It is composed of very fine-grained to fine-grained sandstone that is massive to highly cross-bedded and is underlain by less-permeable Marlow Formation. Reported irrigation well yields exceed 1,000 gallons per minute; yields reported on 89 drillers' logs ranged from 11 to 850 gallons per minute. Transmissivities range from 670 to 1,870 feet squared per day. Specific yields for core samples range from 0.13 to 0.34. Estimates of hydraulic conductivities at one site ranged from 1.05 to 5.62 feet per day. The Rush Springs aquifer is recharged by infiltration of precipitation, ranging from 0.2 to more than 2 inches per year. Discharge is primarily to streams and rivers where the Rush Springs aquifer crops. Estimated total withdrawal was 54.7 million gallons per day in 1990. Over 42 million gallons per day, or 77.8 percent of water withdrawn, was used for irrigation of crops.
Thirty-five of the 64 wells sampled produced nitrate concentration that equaled or exceeded drinking water standards. Sulfate concentration also exceeds the drinking water standards in some areas. Two major water types occur in the aquifer, a calcium-magnesium bicarbonate type and a calcium sulfate type. Dissolved solids concentrations in water samples from the aquifer ranged from 52 to 1,840 milligrams per liter.
The chemical composition of ground water in the Rush Springs aquifer is the result of chemical reactions between the recharge waters and minerals in the overlying soils and rocks in the Rush Springs and Marlow Formations. Saturation indices of minerals were calculated for 64 water-quality analyses using the geochemical computer model WATEQF. Mass transfer rates were calculated using the mass-balance model NETPATH.