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Open-File Report 2010–1066

Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

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

Lester J. Williams

ABSTRACT

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A 1,168-foot deep test well was completed at Hunter Army Airfield in the summer of 2009 to investigate the potential of using the Lower Floridan aquifer as a source of water supply to satisfy increased needs as a result of base expansion and increased troop levels. The U.S. Geological Survey conducted hydrologic testing at the test site including flowmeter surveys, packer-slug tests, and aquifer tests of the Upper and Lower Floridan aquifers.

Flowmeter surveys were completed at different stages of well construction to determine the depth and yield of water-bearing zones and to identify confining beds that separate the main producing aquifers. During a survey when the borehole was open to both the upper and lower aquifers, five water-bearing zones in the Upper Floridan aquifer supplied 83.5 percent of the total pumpage, and five water-bearing zones in the Lower Floridan aquifer supplied the remaining 16.5 percent. An upward gradient was indicated from the ambient flowmeter survey: 7.6 gallons per minute of groundwater was detected entering the borehole between 750 and 1,069 feet below land surface, then moved upward, and exited the borehole into lower-head zones between 333 and 527 feet below land surface. During a survey of the completed Lower Floridan well, six distinct water-producing zones were identified; one 17-foot-thick zone at 768-785 feet below land surface yielded 47.9 percent of the total pumpage while the remaining five zones yielded between 2 and 15 percent each.

The thickness and hydrologic properties of the confining unit separating the Upper and Lower Floridan aquifers were determined from packer tests and flowmeter surveys. This confining unit, which is composed of rocks of Middle Eocene age, is approximately 160 feet thick with horizontal hydraulic conductivities determined from four slug tests to range from 0.2 to 3 feet per day. Results of two separate slug tests within the middle confining unit were both 2 feet per day.

Aquifer testing indicated the Upper Floridan aquifer had a transmissivity of 40,000 feet squared per day, and the Lower Floridan aquifer had a transmissivity of 10,000 feet squared per day. An aquifer test conducted on the combined aquifer system, when the test well was open from 333 to 1,112 feet, gave a transmissivity of 50,000 feet squared per day. Additionally, during the 72-hour test of the Lower Floridan aquifer, a drawdown response was observed in the Upper Floridan aquifer wells.

First posted April 19, 2010

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

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Suggested citation:

Williams, L.J., 2010, Summary of hydrologic testing of the Floridan aquifer system at Hunter Army Airfield, Chatham County, Georgia: U.S. Geological Survey Open-File Report 2010–1066, 30 p.



Contents

Abstract

Introduction

Site Description

Hydrogeologic Units

Acknowledgments

Flowmeter Surveys

Ambient Flowmeter Survey—Open Interval from 333 to 1,168 Feet

Pumping Flowmeter Survey—Open Interval from 333 to 1,168 Feet

Ambient and Pumping Flowmeter Surveys—Open Interval from 703 to 1,112 Feet

Packer-Slug Tests

571- to 575-Foot Test

641- to 645-Foot Test

688- to 692-Foot Test

698- to 702-Foot Test

802- to 806-Foot and 812- to 816-Foot Tests

Aquifer Testing

Upper Floridan Aquifer Tests

Analytical Method

Test 1: February 17–18, 2009

Drawdown Estimation

Aquifer-Test Analysis

Test 2: August 10, 2009

Lower Floridan Aquifer Test: August 13–16, 2009

Test Procedure

Drawdown Estimation

Aquifer-Test Analysis

Combined Upper and Lower Floridan Aquifer Test

Summary and Conclusions

References


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