Effects of municipal ground-water withdrawals on the Arbuckle-Simpson Aquifer, Pontotoc County, Oklahoma

Water-Resources Investigations Report 93-4230




The Arbuckle-Simpson aquifer in south-central Oklahoma consists of a thick sequence of folded and faulted carbonate and clastic rocks of Upper Cambrian to Middle Ordovician age. Fractures and karst features locally increase the aquifer's capacity to transmit and store ground water. The aquifer is a principal source of water for municipal and rural users. A hydrologic study was conducted to evaluate the effects of municipal ground-water withdrawal from the Arbuckle-Simpson aquifer on local ground-water levels and discharge from nearby springs and streams in south-central Pontotoc County. A municipal well was pumped for 63 hours at an average rate of 1,170 gallons per minute. A maximum observed drawdown of 0.3 feet was recorded half a mile from the pumping well. Drawdown was observed as far as 1.2 miles from the pumping well. No measurable response was observed at any of the surface-water-discharge measurement sites; however, recharge from precipitation may have masked any decreases in discharge caused by the pumping. Simultaneous pumping of two municipal wells for 241 hours at average rates of 1,170 and 2,730 gallons per minute resulted in a maximum observed drawdown of 1.3 feet recorded at an average distance of 0.80 miles from the pumping wells. The most distant drawdown observed was at an average distance 1.1 miles from the pumped wells. Less that 2 days after pumping stopped, increases in springflow were recorded at two springs; it is unknown whether these discharge responses reflect the effects of recharge from precipitation, or the combined effects of precipitation and the cessation of ground-water withdrawal. The effects of the stress tests on the hydrologic system were offset by recharge from concurrent precipitation. The maximum observed drawdown represents about 6 percent of the median natural water-level fluctuation during the study period. The effect of drawdown could become critical during extended periods of low precipitation, if water levels are already near the bottom of domestic wells in the area. However, a comparison of maximum observed drawdown (1.3 ft) with the minimum saturated thickness of fresh ground water (1,500 ft) suggests that municipal pumping had little effect on the amount of ground water stored in the Arbuckle-Simpson aquifer in the study area. This evaluation is based on the limited pumping rates and times of the stress tests.

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Effects of municipal ground-water withdrawals on the Arbuckle-Simpson Aquifer, Pontotoc County, Oklahoma
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Water-Resources Investigations Report
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U.S. G.P.O. ; USGS Earth Science Information Center, Open-File Reports Section [distributor],
iv, 37 p. :ill., maps ;28 cm.