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Scientific Investigations Report 2012–5082

Hydrogeologic Characteristics and Water Quality of a Confined Sand Unit in the Surficial Aquifer System, Hunter Army Airfield, Chatham County, Georgia

Prepared in cooperation with the U.S. Department of the Army

Gerard J. Gonthier

ABSTRACT

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An 80-foot-deep well (36Q397, U.S. Geological Survey site identification 320146081073701) was constructed at Hunter Army Airfield to assess the potential of using the surficial aquifer system as a water source to irrigate a ballfield complex. A 300-foot-deep test hole was drilled beneath the ballfield complex to characterize the lithology and water-bearing characteristics of sediments above the Upper Floridan aquifer. The test hole was then completed as well 36Q397 open to a 19-foot-thick shallow, confined sand unit contained within the surficial aquifer system. A single-well, 24-hour aquifer test was performed by pumping well 36Q397 at a rate of 50 gallons per minute during July 13–14, 2011, to characterize the hydrologic properties of the shallow, confined sand unit. Two pumping events prior to the aquifer test affected water levels. Drawdown during all three pumping events and residual drawdown during recovery periods were simulated using the Theis formula on multiple changes in discharge rate. Simulated drawdown and residual drawdown match well with measured drawdown and residual drawdown using values of horizontal hydraulic conductivity and specific storage, which are typical for a confined sand aquifer. Based on the hydrologic parameters used to match simulated drawdown and residual drawdown to measured drawdown and residual drawdown, the transmissivity of the sand was determined to be about 400 feet squared per day. The horizontal hydraulic conductivity of the sand was determined to be about 20 feet per day. Analysis of a water-quality sample indicated that the water is suitable for irrigation. Sample analysis indicated a calcium-carbonate type water having a total dissolved solids concentration of 39 milligrams per liter. Specific conductance and concentrations of all analyzed constituents were below those that would be a concern for irrigation, and were below primary and secondary water-quality criteria levels.

First posted May 25, 2012

For additional information contact:
Director, Georgia Water Science Center
U.S. Geological Survey
3039 Amwiler Rd.
Suite 130
Atlanta, GA 30360-2824
http://ga.water.usgs.gov/

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Suggested citation:

Gonthier, G.J., 2012, Hydrogeologic characteristics and water quality of a confined sand unit in the surficial aquifer system, Hunter Army Airfield, Chatham County, Georgia: U.S. Geological Survey Scientific Investigations Report 2012–5082, 14 p., available online at http://pubs.usgs.gov/sir/2012/5082/



Contents

Abstract

Introduction

Purpose and Scope

Site Description

Hydrogeologic Setting

Method of Study

Hydrogeology

Hydrogeologic Units

Aquifer Test

Pumping History

Estimating Drawdown

Aquifer-Test Analysis

Water Quality

Summary and Conclusions

References Cited


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