Hydrogeology, water quality, and geochemistry of the Rush Springs aquifer, western Oklahoma

Abstract

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 Over 42 million gallons per day, or 77.8 percent of water withdrawn, was used for irrigation of crops.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. INTRODUCTION The purpose of this project was to fulfill a legislative mandate for the Oklahoma Water Resources Board (OWRB) to describe the hydrogeology, water quality, and geochemistry and to prepare a numerical model on the ground-water flow of the Rush Springs aquifer in west-central Oklahoma (fig. 1). The Rush Springs aquifer is an important source of water for irrigation, livestock, industrial, municipal, and domestic use. Agriculture is the primary industry in the study area. The Rush Springs aquifer is composed primarily of sandstone and is capable of supporting irrigated agriculture through most of the study area. Soils derived from the Rush Springs Formation are well drained and well-suited for growing crops such as cotton, peanuts, grain sorghum, wheat, alfalfa, and melons. The study began in 1986 and data collection was completed in 1991. Information provided in this report was collected and compiled through a cooperative project between the Oklahoma Geological Survey (OGS), OWRB, and U.S. Geological Survey (USGS). Purpose and Scope The purpose of this report is to describe the hydrogeology, water quality, and geochemistry of the Rush Springs aquifer in western Oklahoma (fig. 1). The hydrogeology is described in terms of the aquifer boundaries, hydrologic properties, recharge, discharge, and water-use. Sources of hydrogeologic data for this report include previously published and unpublished reports, borehole geophysical logs, base-flow discharge measurements of streams, water-level measurements of existing wells, and lithologic descriptions of cores and of surficial exposures of the geologic units. The sources of water quality and geochemical data are chemical analyses of dissolved ions in water samples taken from wells completed in the Rush Springs aquifer, petrographic descriptions of the rock matrix and cements, and analyses of minerals present in the Rush Springs Formation cores. Water samples were collected by the i i I ? I 2. f 10 3° 10 2° 10 1° 10 0 99 ' 98 ° 97 ° 96 95 « 37 36 ° 35 3 4 . 33 C O LO R A D O