U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2010–1066

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

Summary of Hydrologic Testing of the Floridan Aquifer 

System at Hunter Army Airfield, Chatham County, Georgia

Note: Distance between well HAAF 11 and well HAAF 8 is 176 feet

5,298 feet

3,600 feet

1,995 feet

2,020 feet

Upper Floridan

 aquifer

Lower Floridan 

aquifer

Confining

unit

Confining

unit

Surficial aquifer

100

200

300

400

500

600

700

800

900

1,000

1,100

Land

surface

DEPTH BELOW LAND SURFACE, IN FEET

Morrison Plantation Well

(36Q020)

Aquifer

test

period Well HAAF 8

(36Q292)

Tidal stage Barometric 

pressure

FEBRUARY 2009

12 13 14 15 16 17 18 19 20 21 22 24 25

TIDAL STAGE, IN FEET 

BELOW OR ABOVE (–) 

NAVD 88 –8

–6

–4

–2

0

2

4

750

755

760

765

770

775

780

BAROMETRIC PRESSURE,

IN MILLIBARS

60.9

44.7

44.9

45.1

45.3

45.5

45.7

45.9

59.7

59.9

60.1

60.3

60.5

60.7

WATER LEVEL IN WELL 36Q292WATER LEVEL IN WELL 36Q020

BELOW LAND SURFACE, IN FEETBELOW LAND SURFACE, IN FEET

Well HAAF 9

36Q391

Well HAAF 8

36Q292

Well HAAF 11

36Q392

(pumped well)

Well HAAF 5

(36Q288)

Well HAAF 5Well HAAF 11Well HAAF 8Well HAAF 9
Cover. See figures 11 and 13 of this report.
Summary of Hydrologic Testing of the Floridan Aquifer 

System at Hunter Army Airfield, Chatham County, Georgia

By Lester J. Williams

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

Open-File Report 2010–1066

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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reproduce any copyrighted materials contained within this report.

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.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Site Description.....................................................................................................................................2

Hydrogeologic Units.............................................................................................................................2

Acknowledgments................................................................................................................................5

Flowmeter Surveys........................................................................................................................................6

Ambient Flowmeter Survey—Open Interval from 333 to 1,168 Feet.............................................6

Pumping Flowmeter Survey—Open Interval from 333 to 1,168 Feet............................................6

Ambient and Pumping Flowmeter Surveys—Open Interval from 703 to 1,112 Feet ..................8

Packer-Slug Tests........................................................................................................................................10

571- to 575-Foot Test...........................................................................................................................11

641- to 645-Foot Test...........................................................................................................................12

688- to 692-Foot Test...........................................................................................................................13

698- to 702-Foot Test...........................................................................................................................14

802- to 806-Foot and 812- to 816-Foot Tests....................................................................................15

Aquifer Testing .............................................................................................................................................17

Upper Floridan Aquifer Tests ............................................................................................................18

Analytical Method .....................................................................................................................18

Test 1: February 17–18, 2009.....................................................................................................19

Drawdown Estimation......................................................................................................20

Aquifer-Test Analysis .......................................................................................................22

Test 2: August 10, 2009 ..............................................................................................................23

Lower Floridan Aquifer Test: August 13–16, 2009 ..........................................................................24

Test Procedure ...........................................................................................................................24

Drawdown Estimation...............................................................................................................26

Aquifer-Test Analysis ................................................................................................................28

Combined Upper and Lower Floridan Aquifer Test .......................................................................29

Summary and Conclusions.........................................................................................................................30

References....................................................................................................................................................30
iv

Figures

1. Maps showing location of study area, selected wells, and tidal station at 

Hunter Army Airfield and vicinity, Georgia...............................................................................3

2. Borehole geophysical logs from well HAAF 11 (36Q392), Hunter Army Airfield, 

Chatham County, Georgia............................................................................................................4

3. Pumping and ambient flowmeter surveys completed on June 17, 2009, in 

well HAAF 11 (36Q392), Hunter Army Airfield, Chatham County, Georgia. 

Pumping survey through the 333–1,168 foot interval and ambient survey 

through the 333–1,168 foot interval ...........................................................................................7

4. Pumping and ambient flowmeter surveys following completion of well HAAF 11 

(36Q392), Hunter Army Airfield, Chatham County, Georgia. Pumping survey 

through the 333–1,112 foot interval collected on August 15, 2009, while pumping 

747 gallons per minute, and ambient survey through the 333–1,112 foot interval 

collected on September 29, 2009 ...............................................................................................9

5–10. Graphs showing test data and analysis for packer-slug test in well HAAF 11 

(36Q392), Hunter Army Airfield, Chatham County, Georgia—

5. Depth interval 571–575 feet, conducted on June 26, 2009..........................................11

6. Depth interval 641–645 feet, conducted on June 26, 2009..........................................12

7. Depth interval 688–692 feet, conducted on June 25, 2009..........................................13

8. Depth interval 698–702 feet, conducted on June 25, 2009..........................................14

9. Depth interval 802–806 feet, conducted on June 26, 2009..........................................15

10. Depth interval 812–816 feet, conducted on June 25, 2009..........................................16

11. Location and construction characteristics of wells used for aquifer tests at 

Hunter Army Airfield, Chatham County, Georgia. Map showing aquifer test layout 

and schematic section showing the open intervals of the wells in relation to 

major hydrogeologic units.........................................................................................................18

12–16. Graphs showing—

12. Water-level data for well HAAF 9 (36Q391) during 24-hour aquifer test 

conducted February 17–18, 2009, Hunter Army Airfield, Chatham County, 

Georgia ................................................................................................................................19

13. Comparison of water levels at well HAAF 8 (36Q292) to background 

water levels at Morrison Plantation observation well (36Q020) and to 

stage and barometric pressure at tidal gage 021989773 (U.S. Army Corps 

of Engineers Dock, Savannah, Georgia), Hunter Army Airfield, 

Chatham County, Georgia, February 12–26, 2009..........................................................20

14. Effects of different time series components on development of a synthetic 

water level used to filter out extraneous trends for well HAAF 8 (36Q292), 

Hunter Army Airfield, Chatham County, Georgia..........................................................21

15. Logarithmic plot of drawdown and time for observation well HAAF 8 

(36Q292) located 2,020 feet from pumping well HAAF 9 for Upper Floridan 

aquifer test conducted February 17–18, 2009, Hunter Army Airfield, 

Chatham County, Georgia.................................................................................................22

16. Logarithmic plot of drawdown and time for observation well HAAF 8 (36Q292) 

located 2,020 feet from pumping well HAAF 9 for Upper Floridan aquifer test 

conducted August 12, 2009, Hunter Army Airfield, Chatham County, Georgia........23
v

17–20. Graphs showing—

17. Drawdown response in Upper Floridan wells HAAF 8 (36Q292) and 

HAAF 5 (36Q288) during a 72-hour aquifer test of Lower Floridan well 

HAAF 11 (36Q392) conducted August 13–16, 2009, Hunter Army Airfield, 

Chatham County, Georgia.................................................................................................25

18. Estimated drawdown in Upper Floridan aquifer wells HAAF 8 (36Q292) 

and HAAF 5 (36Q288) during a 72-hour aquifer test of Lower Floridan 

well HAAF 11 (36Q392) conducted August 13–16, 2009, Hunter Army Airfield, 

Chatham County, Georgia.................................................................................................27

19. Aquifer-test plots for 72-hour aquifer test of Lower Floridan aquifer 

conducted August 13–16, 2009, Hunter Army Airfield, Chatham County, 

Georgia. Log-log plot of drawdown and time and semi-logarithmic plot 

of residual drawdown and t/t'..........................................................................................28

20. Aquifer-test plots for 6-hour aquifer test of combined Upper and 

Lower Floridan aquifers in well HAAF 11 conducted June 19, 2009, 

Hunter Army Airfield, Chatham County, Georgia. Log-log plot of drawdown 

and time and semi-logarithmic plot of residual drawdown and t/t'...........................29

Tables

1. Location and completion intervals of wells used in the aquifer test analyses,

Hunter Army Airfield, Chatham County, Georgia.....................................................................2

2. Horizontal hydraulic conductivity determined from packer-slug tests at 

well HAAF 11 (36Q392), Hunter Army Airfield, Chatham County, Georgia.........................10

3. Summary of transmissivity and storage cofficients determined from aquifer tests 

conducted in the Upper and Lower Floridan aquifers, Hunter Army Airfield,

Chatham County, Georgia, 2009......................................................................................................17
vi

Conversion Factors

Multiply By To obtain

Length

inch 2.54 centimeter (cm)

inch 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

gallon (gal) 3.785 cubic decimeter (dm3

) 

million gallons (Mgal) 3,785 cubic meter (m3

)

Flow rate

foot per minute (ft/min) 0.3048 meter per minute (m/min)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

Vertical coordinate information is referenced to the North American Vertical datum of 1988 

(NAVD 88). Historical data collected and stored as National Geodetic Vertical Datum of 1929 

have been converted to NAVD 88 for this publication. 

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). 

Historical data collected and stored as North American Datum 1927 have been converted to 

NAD 83 for this publication.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.
Summary of Hydrologic Testing of the Floridan Aquifer 

System at Hunter Army Airfield, Chatham County, Georgia

By Lester J. Williams

Abstract

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 waterbearing 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 waterbearing 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.

Introduction 

A 1,168-foot-deep test well was drilled at Hunter Army 

Airfield to investigate the potential of using the Lower Floridan aquifer as a source of water supply to satisfy increase 

needs due to base expansion. Hydrologic testing conducted in 

the test hole and the completed test well included flowmeter 

surveys, packer-slug tests, and aquifer tests of the Upper and 

Lower Floridan aquifers.

Well drilling was completed by Sam Martin Well Drilling 

of Dublin, Georgia, construction oversight and engineering 

was completed by AECOM of Raleigh, North Carolina, and 

geophysical logging and well testing was overseen by the 

U.S. Geological Survey (USGS). The test well was completed 

to a total depth of 1,168 feet (ft) on July 30, 2009. Hydrologic testing was completed to obtain data needed to develop 

a groundwater flow model that could be used to estimate 

the amount of leakage from the Upper Floridan aquifer that 

would result from the proposed withdrawal from the Lower 

Floridan well as required by Georgia Environmental Protection Division requirements for managing saltwater encroachment in the coastal areas of Georgia (Georgia Environmental 

Protection Division, 2003). 
2 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Site-specific hydrologic testing was conducted in the 

summer of 2009 to determine the hydraulic characteristics of 

the Upper Floridan aquifer, middle-confining unit, and Lower 

Floridan aquifer at the test site. This report summarizes: 

• Flowmeter surveys conducted in the Lower Floridan 

aquifer test well,

• Packer-slug tests conducted in the middle confining 

unit and intra-aquifer confining units of the Lower 

Floridan aquifer, 

• A 24-hour aquifer test and a shorter-term (6-hour) 

aquifer test of the Upper Floridan aquifer, 

• A 72-hour aquifer test of the Lower Floridan 

aquifer, and 

• A 6-hour aquifer test on the combined Upper and 

Lower Floridan aquifers. 

Location and construction details for the wells used as 

part of the hydraulic testing at HAAF are included in table 1.

Site Description

The U.S. Department of the Army (U.S. Army) Garrison 

Fort Stewart and Hunter Army Airfield (HAAF), Georgia, 

is located in central Chatham County, Georgia (fig. 1). The 

study area is characterized by flat topography and sandy 

topsoil typical of the Georgia coastal area. The study area has 

a mild climate with warm, humid summers and mild winters. 

During 1971–2000, precipitation at the Savannah Airport 

averaged about 49 inches per year. Maximum monthly rainfall 

(exceeding 4 inches per month) generally occurs during June–

September, with monthly rainfall totals typically less than 

4 inches during the rest of the year. 

Hydrogeologic Units

The Savannah area is underlain by a thick sequence of 

unconsolidated to semiconsolidated sands, clays, and limestone/dolomite rock units ranging in age from Cretaceous to 

recent. These formations have varying degrees of porosity and 

permeability and form multiple aquifer systems, including, 

from shallowest to deepest, the surficial, Brunswick, and 

Floridan aquifer systems. The Floridan aquifer system is subdivided into the Upper and Lower Floridan aquifers (Miller, 

1986; Falls and others, 2005). The Floridan aquifer system is 

confined by overlying clay layers and is separated into several 

permeable water-bearing zones by layers of denser limestone/

dolomite that act as semiconfining units allowing vertical 

leakage of groundwater to enter the Upper or Lower Floridan 

aquifers, depending on the vertical hydraulic conductivity 

and head gradient (Miller, 1986; Clarke and others, 1990). In 

the Savannah area, current-meter (flowmeter) tests conducted 

in deep wells indicate there are at least five permeable zones 

within the Floridan aquifer system (McCollum and Counts, 

1964). A generalized correlation of hydrogeologic and geologic units to borehole geophysical logs and flowmeter data 

at HAAF is shown in figure 2. 

Geophysical logs and flowmeter surveys indicate the 

Upper Floridan aquifer is 309 ft thick at the test well location. The Upper Floridan aquifer is overlain by a 187-ft-thick 

confining layer consisting mostly of clay of the Hawthorn 

Formation and underlain by an approximately 160-ft-thick 

semiconfining layer consisting mostly of fine-grained limestone and dolomitic limestone of the Avon Park Formation. 

This interpretation is supported by the evaluation of drill 

cuttings, flowmeter logs, and geophysical logs completed 

for the test well. 

Table 1. Location and completion intervals of wells used in the aquifer test analyses, Hunter Army Airfield, Chatham County, Georgia. 

[See fig. 1 for site locations; UF, Upper Floridan; LF, Lower Floridan; —, no HAAF number, not located on base] 

HAAF 

number

USGS 

identification Site number Land elevation** Latitude Longitude

Values, in feet below land surface

Static Aquifer

water level*

Top

opening

Bottom

opening

5 36Q288 320001081110401 11 32.00047 –81.18453 49.3 85 380 UF

8 36Q292 320003081102301 22 32.00086 –81.17257 63.12 255 375 UF

9 36Q391 320018081100601 16.3 32.00512 –81.16831 59.02 295 425 UF

11 36Q392 320005081102101 22 32.00132 –81.17257 63.23 703 1,100 LF

— 36Q020*** 320021081124801 13 32.00604 –81.21317 47.78 330 336 UF

* Measured 8/10/2009

** Datum is NGVD 29

*** Located at Morrison Plantation; used as a background monitoring well
Introduction 3

36Q285

36Q286

36Q287

36Q290

36Q289

36Q391

36Q284 36Q020 

(Morrison Plantation)

36Q292 (HAAF 8)

36Q288

(HAAF 5)

36Q391

(HAAF 9)

36Q392 (HAAF 11)

FORT STEWART

BULLOCH

BRYAN

LIBERTY

EFFINGHAM

CHATHAM

TATTNALL

EVANS JASPER

LONG

GA

SC

BEAUFORT 16

95

95

Savannah

Hinesville

Richmond 

Hill

COASTAL

PLAIN

GEORGIA

SOUTH

CAROLINA

81°0' 80°45'

 Hilton

 Head

Island

81°45' 81°30' 81°15'

32°0'

32°15'

31°45'

021989773

35P110

35P125

36Q330

0 0.5 1 1.5 MILES

0 0.5 1 1.5 KILOMETERS

516

Image from U.S Geological Survey High Resolution Orthoimagery 

 for Coastal Georgia, 0.5-meter pixel resolution, 2007

Hunter Army Airfield

EXPLANATION

Groundwater well

 and name

Tidal station

 and number

Hunter Army Airfield ATLANTIC

OCEAN

Figure 1. Location of study area, selected wells, and tidal station at Hunter Army Airfield and vicinity, Georgia.

Location

 of map

 below

Base map from U.S. Geological Survey 1:2,000,000-scale digital data 

Roads from TIGER 1:100,000-scale digital data (2000)

36Q020

021989773 0 5 10 15 MILES

0 5 10 15 KILOMETERS

516

Figure 1. Location of study area, selected wells, and tidal station at Hunter Army Airfield and vicinity, Georgia.
4 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

RESISTIVITY

0 0 500 OHM-M

GAMMA

100 API-GR

DEPTH BELOW LAND SURFACE, IN FEET

0

300

600

700

100

200

400

500

800

900

1,000

1,100

GEOLOGY

HYDROLOGIC

UNITS FORMATION LITHOLOGY

T.D. = 1,168 ft

Figure 2. Borehole geophysical logs from well HAAF 11 (36Q392), Hunter Army Airfield, Chatham County, Georgia. 

Black bars denote water-bearing zone and percentage of flow determined from pumping flowmeter test while pumping 

847 gallons per minute. [LN, long normal resistivity; SN, short normal resistivity; LA, lateral resistivity; *zones 1 through 5

correlate to water-bearing zones previously defined in the area by McCollum and Counts, 1964]

LN

LA

SN

ZONES*

2

3

4

1

5

Packer test 

 location

POSTMIOC. MIOCENE OLIGO- CENE UPPER EOCENE MIDDLE EOCENE

UPPER

FLORIDAN 

AQUIFER

LOWER

FLORIDAN 

AQUIFER

SURFICIAL

AQUIFER

UPPER 

CONFINING

UNIT

MIDDLE

CONFINING 

UNIT

AGE

Undifferentiated

Hawthorn

Formation

Tiger Leap

Formation

Suwanee

Limestone

Ocala

Limestone

Avon Park

Formation

Quartz 

sand

Clay

Phosphatic sand

Phosphatic sand

Clay

Limestone

sand and clay

Sandy 

Limestone

Limestone

(calcarenite)

Glauconitic

Limestone

(calcilutite 

and 

calcarenite)

Glauconitic

Limestone

(calcarenite)

Cherty

Limestone

(calcilutite)

6.7 %

44.9 %

27.2 %

1.8 %

3 %

4.3 %

1.5 %

5.4 %

1.8 %

3 %

0.6 %

Figure 2. Borehole geophysical logs from well HAAF 11 (36Q392), Hunter Army Airfield, Chatham County, Georgia. 

Black bars denote water-bearing zone and percentage of flow determined from pumping flowmeter test while 

pumping 847 gallons per minute. [LN, long normal resistivity; SN, short normal resistivity; LA, lateral resistivity; 

*zones 1 through 5 correlate to water-bearing zones previously defined in the area by McCollum and Counts, 1964]
Introduction 

5

Acknowledgments

Many people participated in the successful comple-

tion of this study. Stanley Thomas with the U.S. Department 

of the Army is gratefully acknowledged for his help with 

the overall coordination between the U.S. Army, USGS, 

and civilian contractors. He provided assistance whenever 

needed and was a large part of the success of this project. 

Numerous people from the base’s water department helped 

during the project, including Nathanial Williams, Donald 

Highsmith, and Terry Howard who helped with coordination 

and modification of pumping schedules needed to complete 

the tests. From AECOM, Robert McManus, Peter Thibodeau 

and John Funk are acknowledged for their work with on-site 

coordination, engineering, safety, and provided assistance 

when needed during the completion of the testing program. 

Dwight Robertson and Beth Mitchell of Oak Ridge National 

Laboratory are acknowledged for their work with the con-

tracting performed for the project. Many thanks is given to 

Owen (Gary) Holloway of the USGS who helped to design 

and construct the packer assembly used in this study and was 

present throughout the fieldwork portion of the study. 
6 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Flowmeter Surveys

Flowmeter surveys were performed at different stages of 

well construction to identify the depth intervals and yields of 

water-bearing zones and confining beds that separate the main 

producing aquifers. Ambient and pumping surveys also were 

performed to obtain information about hydraulically active 

zones in the open portion of the borehole. 

Ambient Flowmeter Survey—Open Interval 

from 333 to 1,168 Feet

The first flowmeter survey, conducted on June 17, 2009, 

was used to traverse the borehole under ambient (nonpumping) 

conditions. The goal of this survey was to determine the flow 

conditions (up or down) in the borehole under ambient conditions. During this stage of construction, the well was open 

from 333 to 1,168 ft, an interval that includes both the Upper 

and Lower Floridan aquifers. 

To conduct this survey, a rubber skirt was attached to the 

outside of an electromagnetic (EM) flowmeter to divert flow 

through the center of the tool and, thus, increase sensitivity 

of the tool. The skirt prevents flow from bypassing the tool 

except in areas of borehole enlargement where the skirt is not 

fully sealed against the borehole wall. Using this “skirt-on” 

configuration, the EM flowmeter is capable of measuring flow 

rates of between 0.01 and 10 gallons per minute (gal/min). 

The results of the flowmeter survey indicate that, under 

ambient conditions, groundwater enters the borehole from 

higher-head zones of the Lower Floridan aquifer, moves 

upward, and then exits into lower-head zones of the Upper 

Floridan aquifer. Water inflows, or gains, were observed 

between the 1,069 ft and 750 ft interval at specific zones, 

reaching a maximum upward flow rate of 7.6 gal/min at a 

depth of 750 ft. The increase in flow through this section of the 

borehole is illustrated by a stair-step pattern that indicates flow 

contribution from several discrete zones rather than contribution from the entire thickness of the Lower Floridan aquifer 

(fig. 3B). This interpretation is consistent with the observed 

response during the pumping flowmeter survey (described 

below). Above 750 ft, within the interval of the confining 

unit, several of the flowmeter measurements plot to the left 

of the interpreted profile. These points suggest that a significant amount of water was likely bypassing the tool at these 

flow-measurement stations. Flow bypass was interpreted to 

occur along sections of enlarged borehole where the skirt was 

not fully fit across the borehole. Between the 333 ft and 527 ft 

depth interval, flow decreased back toward zero, indicating 

that groundwater exits the borehole along permeable sections 

of limestone in the Upper Floridan aquifer. 

Pumping Flowmeter Survey—Open Interval 

from 333 to 1,168 Feet

A pumping flowmeter survey was performed on June 19, 

2009, to determine relative contribution of the water-bearing 

zones under a stressed condition and to assist in identifying 

low or “no flow” zones that may correlate to regional or local 

confining units within the aquifer system. To conduct this 

survey, the EM flowmeter was run in a “skirt-off” configuration, allowing some of the flow to bypass the tool to allow for 

greater flow-rate ranges. 

On June 18, 2009, an electric submersible pump was 

installed in the test well to a depth of 120 ft. A 4-inch polyvinyl chloride (PVC) stilling well was also installed at this 

time to provide access for the EM flowmeter and a pressure 

transducer to be placed below the depth of the pump in the test 

well. On the next day (June 19, 2009), the pump was started 

at 07:28 a.m. Eastern Standard Time (EST) at a constant flow 

rate of 847 gal/min. This rate was held steady throughout 

the next 6 hours, the time that it took to complete the flowmeter surveys. A pressure transducer in the stilling well inside 

the test well was used to monitor water-level stabilization 

after pump startup. Following water-level stabilization, two 

separate logs were collected. The first log was collected in a 

“trolling mode,” moving the tool down hole at a constant rate 

of 10 feet per minute (ft/min). This log provided a continuous flow profile along the length of the open borehole. The 

trolling log was started inside the casing, to obtain a baseline 

EM-tool response in counts per second (CPS) at a known 

casing diameter and known pumping rate. Once in the open 

portion of the borehole, the flowmeter was used to traverse 

and quantify the relative contribution from each water-bearing 

zone. The percentage of total pumpage attributed to any one 

zone was calculated by using the ratio of the gain in CPS 

(corrected for casing diameter) across the zone tested to the 

counts per minute in the casing. Corrections for irregular 

borehole diameter were made from the caliper log. 

The exaggerated flow (above the actual flow rate of 

847 gal/min) identified below the casing was determined to 

be an artifact of turbulent flow and borehole enlargements in 

this portion of the borehole and was not used for quantifying 

borehole flow (fig. 3A). 

An additional pumping flowmeter survey was performed 

in a stationary-point mode whereby the tool was positioned at 

specific depths and allowed to stabilize before the flow measurement was made. The resulting stationary point log consisted 

of single measurements along the borehole that were used to 

calibrate and adjust the readings from the trolling log produced 

from the first flowmeter survey (see open circles in figure 3). 
Flowmeter Surveys 7

Pumping flowmeter test—

Upper and Lower Floridan aquifers

333–1,168 feet

A

Percent (%) 

contribution

B

Figure 3. Pumping and ambient flowmeter surveys completed on June 17, 2009, in well HAAF 11 (36Q392), Hunter Army 

Airfield, Chatham County, Georgia. (A) Pumping survey through the 333–1,168 foot interval, (B) Ambient survey through 

the 333–1,168 foot interval. Open circles are stationary point measurements taken during pumping survey. Solid circles 

are stationary point measurements taken during ambient (nonpumping) survey. [LN, long normal resistivity; SN, short 

normal resistivity; LA, lateral resistivity]

100

200

300

400

500

600

700

800

900

1,000

1,100

Lower Floridan aquifer Upper Floridan aquifer

Water zone

Water zone

Water

zones

Bottom of 

16-inch casing 

is at 333 feet

Borehole flow (gallons per minute)

0 500 7 23 0 2,000 0 200

Caliper

(inches)

SN

LN

LA

Resistivity

(ohm-meters)

Confining unit Upper confining unit

Ambient flowmeter test—

Upper and Lower Floridan aquifers

333–1,168 feet

Borehole flow 

(gallons per minute)

847 gal/min

DEPTH BELOW LAND SURFACE, IN FEET

0

Total depth = 

1,168 feet

Flow is exaggerated

through this zone 

probably due to 

turbulence resulting 

from variable borehole 

diameter in this interval

Same flowmeter

log plotted at

different scales

MAJOR 

INFLOW

MAJOR

INFLOW

0 30

Low values due to

underfit diverter

in enlarged hole

6.7%

44.9%

27.2%

1.8%

3%

4.3%

1.5%

5.4%

1.8%

3%

0.6% Packer test 

location

Figure 3. Pumping and ambient flowmeter surveys completed on June 17, 2009, in well HAAF 11 (36Q392), Hunter Army 

Airfield, Chatham County, Georgia. (A) Pumping survey through the 333–1,168 foot interval, (B) Ambient survey through 

the 333–1,168 foot interval. Open circles are stationary point measurements taken during pumping survey. Solid circles 

are stationary point measurements taken during ambient (nonpumping) survey. Arrows indicate water-producing zones. 

[LN, long normal resistivity; SN, short normal resistivity; LA, lateral resistivity]
8 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

The trolling flowmeter log is represented on two scales 

to emphasize zones of groundwater inflow into the borehole 

during pumping (fig. 3). Two major and several minor inflow 

zones were identified within the Upper Floridan aquifer, as 

shown on the 0–2,000 gal/min scale on the left side of figure 3; 

five separate zones can be distinguished, which together 

supply 83.5 percent of the total pumpage or 707 gal/min. 

Deeper water-bearing zones in the confining unit and Lower 

Floridan aquifer are denoted with left-facing arrows along the 

log on the 0–200 gal/min scale (fig. 3). The depth intervals for 

each of these zones are denoted by the black bars in figure 3. 

Collectively, the deeper zones in the confining unit and Lower 

Floridan aquifer supply the remaining 16.5 percent of the total 

pumpage or 140 gal/min. 

The depth and thickness of confining bed(s) separating 

the Upper and Lower Floridan aquifers were determined by 

identifying vertically continuous sections that exhibited little 

to no flow contribution on the flowmeter logs (fig. 3). The 

interpreted confining unit is indicated by gray shading in 

figure 3. Two primary confining beds were identified in the 

flowmeter survey logs: a 94-ft-thick section between 560 and 

654 ft, and a 55-ft-thick section between 665 and 720 ft. These 

two zones combine to form a semiconfining bed that is correlated to other nearby wells. One water-producing zone was 

identified inside the confining bed, which produced 4.3 percent 

of the total pumpage during the flowmeter survey. Based on 

interpretation of the flowmeter logs, the confining layer was 

estimated to be approximately 160 ft thick at the test site.

Ambient and Pumping Flowmeter Surveys—

Open Interval from 703 to 1,112 Feet

Information gathered from the flowmeter surveys, along 

with examination of drill cuttings and correlation of the 

confining bed to nearby wells, was used to make decisions on 

the final well construction. The initial test hole was completed 

with 8-inch steel casing, set to a depth of 703 ft, with an open 

interval from 703 to 1,112 ft. Following well completion, 

additional flowmeter surveys were run in the well to further 

evaluate the depth and location of the water-bearing zones. 

These surveys were run to verify the hydraulic characteristics of the previously identified water-bearing zones in the 

completed well, because these zones may change after the 

completion of the well. 

A pumping flowmeter survey was conducted on 

August 15, 2009, during the last day of the 72-hour pumping 

test (described below). The pumping rate during this survey 

was 747 gal/min. The ambient flowmeter survey was 

performed on September 29, 2009.

During the pumping flowmeter survey, both trolling and 

stationary point logs were collected (fig. 4). The trolling log 

was started inside the casing to obtain initial readings representative of the maximum pumping rate. Once in the open 

portion of the borehole, the flowmeter was used to traverse 

and quantify the relative contribution from each water-bearing 

zone along the open interval. Exaggerated flow identified 

below the casing is likely an artifact of turbulent flow and 

borehole enlargements in that portion of the borehole and 

was not used for quantifying borehole flow. The stationary 

point log consisted of collecting single measurements along 

the borehole and was used to calibrate and adjust the readings 

from the trolling log (see open circles in figure 4).

The trolling flowmeter log is represented on two scales 

to emphasize zones of groundwater inflow into the borehole 

during pumping (fig. 4). Several major and minor inflow zones 

were identified within the Lower Floridan aquifer, as shown 

on the 0–1,000 gal/min scale on the left side of figure 4; 

three zones are distinguished in the upper part of the aquifer, 

which together produce 73.4 percent of the total pumpage 

or 550 gal/min. One of these zones, a 17-ft-thick waterbearing interval from 768 to 785 ft, produced 47.9 percent or 

359 gal/min of the 747 gal/min being pumped. Two deeper 

zones that were identified supply the remaining 19.7 percent 

of the total pumpage or 147.8 gal/min. The depth and relative 

yield of the water-bearing zones in the completed well are 

consistent with flowmeter logs collected earlier in the study. 

The location and approximate contribution from waterproducing zones detected in the flowmeter survey completed 

from 703 to 1,112 ft compares fairly well to the survey that 

was completed in the interval from 333 to 1,168 ft. The only 

large difference is the water-producing zone at 818–837 ft, 

which produced about 11 percent of the total amount of water 

from the well, but did not produce any water during the earlier 

test. The reason for this change may be related to the fact 

that in the final well completion the well is pumped with a 

larger drawdown, thus changing the hydraulics of the waterproducing zones in the open interval.
Flowmeter Surveys 9

Percent (%) 

contribution

Figure 4. Pumping and ambient flowmeter surveys following completion of well HAAF 11 (36Q392), Hunter Army Airfield, 

Chatham County, Georgia. (A) Pumping survey through the 333–1,112 foot interval collected on August 15, 2009, while 

pumping 747 gallons per minute, (B) Ambient survey through the 333–1,112 foot interval collected on September 29, 2009. 

Open circles are stationary point measurments taken during pumping survey. Solid circles are stationary point measurements taken during ambient (nonpumping) survey. Black bars denote the major inflow zones and percent of the total 

pumpage each zones produces. [LN, long normal resistivity; LA, lateral resistivity]

A B

Water zone

Water zone

Water

 zones

Borehole flow (gallons per minute) Resistivity

(ohm-meters)

Ambient Flowmeter Test—

Upper and Lower Floridan aquifers

333–1,100 feet

Borehole flow 

(gallons per minute)

100

200

300

400

500

600

700

800

900

1,000

1,100

0

0 500 0 15

LN

LA

Lower Floridan aquifer Upper Floridan aquifer Confining unit Upper confining unit

DEPTH BELOW LAND SURFACE, IN FEET

Same flowmeter

log plotted at

different scales

SN

MAJOR

INFLOW

Bottom of 8-inch

casing at 703 feet

Flowmeter test—

Lower Floridan aquifer

703–1,100 feet

0 1,000 0 300

Caliper

(inches)

Gaining flow

into borehole

Losing flow

from borehole

MAJOR

INFLOW

MAJOR

INFLOW

MAJOR

INFLOW

Bottom of open portion 

of hole during flowmeter 

test = 1,112 feet

0 5

14.7%

47.9%

10.8%

6.7%

18.0%

1.7%

Low value possibly

attributed to

underfit diverter

in enlarged 

portion of hole

Cased portion of well

Confining unit

within Lower

Floridan aquifer

Figure 4. Pumping and ambient flowmeter surveys following completion of well HAAF 11 (36Q392), Hunter Army Airfield, 

Chatham County, Georgia. (A) Pumping survey through the 333 –1,112 foot interval collected on August 15, 2009, while 

pumping 747 gallons per minute, (B) Ambient survey through the 333–1,112 foot interval collected on September 29, 2009.

Open circles are stationary point measurments taken during pumping survey. Solid circles are stationary point measurements taken during ambient (nonpumping) survey. Arrows indicate water-producing zones. Black bars denote the major 

inflow zones and percent of the total pumpage each zones produces. [LN, long normal resistivity; LA, lateral resistivity]
10 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Packer-Slug Tests

Hydraulic conductivity estimates of the middle 

confining unit and lower permeability material of the Lower 

Floridan aquifer were obtained by conducting packer-slug 

tests at six depth intervals in well HAAF 11 (36Q392): 

571–575 ft, 641–645 ft, 688–692 ft, 698–702 ft, 802–806 ft, 

and 812–816 ft (fig. 2). The four uppermost intervals are 

located within the middle confining unit, and the two lower 

intervals are located within the Lower Floridan aquifer. Each 

interval was isolated using straddle packers, then a slug of 

water was injected into the interval, and the rate of head 

decline was recorded. Data were analyzed for horizontal 

hydraulic conductivity using the Bouwer and Rice (1976) 

method. Pressure transducers were used to monitor waterlevel response within the isolated interval as well as above 

and below the zone being tested. The general procedures for 

conducting these tests were as follows:

1. Lower packer assembly to the target depth.

2. Attach pressure transducers to dataloggers and start 

recording at 2-second intervals.

3. Inflate upper packer to full seating pressure. 

4. Inflate lower packer to full seating pressure.

5. Allow water level in the test interval to stabilize 

(typically 10 minutes).

6. Inject water into the isolated interval through the drill 

stem to raise the water level within the test interval.

7. Monitor the falling water level until water levels return 

to pre-test conditions.

8. Review pressure data from upper and lower intervals 

to check for indications of leakage across the straddle 

packers; re-inflate or reposition packers if necessary.

9. Deflate packers and move to the next depth interval. 

Table 2. Horizontal hydraulic conductivity determined from 

packer-slug tests at well HAAF 11 (36Q392), Hunter Army 

Airfield, Chatham County, Georgia.

Hydrogeologic 

unit

Interval 

(feet below 

land surface)

Horizontal 

hydraulic 

conductivity 

(feet per day)*

Middle confining unit 571–575 1.1

641–645 3.1

688–692 0.16

698–702 0.20

Lower Floridan 

aquifer

802–806 1.7

812–816 1.7

* Estimated using Bouwer and Rice (1972) method

The caliper log was used to position the packers, 

selecting smooth sections of the borehole that would be more 

likely to have the greatest potential for good packer seating. 

Vugs, solution cavities, and irregular borehole enlargements 

were identified so that the rubber packers would not be inflated 

along these irregular surfaces.

Slug test data were analyzed with the Bouwer and Rice 

(1976) method to obtain estimates of hydraulic conductivity 

(table 2). The Bouwer and Rice (1976) method assumes the 

aquifer has an infinite areal extent, is homogeneous, and has a 

uniform thickness; the test well is fully or partially penetrating; 

effects of storage are negligible; flow to the well is quasi-steady 

state; and the slug is introduced into the well instantaneously. 

AQTESOLVTM version 4.5 was used to analyze the tests; the 

resulting plots are shown in figures 5 through 10, and a summary of the test results is listed in table 2. The following were 

specified in the analysis of each test:

• well-screen length: 4 ft (distance measured 

between packers)

• well radius: 0.375 ft (measured from caliper log)

• casing radius: 0.10 ft (drill-rod radius)
Packer-Slug Tests 11

571- to 575-Foot Test

The first slug test was completed at a depth interval 

of 571–575 ft, within the upper part of the Lower Floridan 

aquifer confining bed. To initiate the test, a 5.8-gallon (gal) 

slug of water was introduced into the isolated interval through 

the drill stem, which caused a water-level displacement of 

12 ft within the first 20 seconds followed by a slow decline 

of the water level back to within 0.01 ft of the initial water 

level within approximately 4 minutes (fig. 5). Because of the 

non-instantaneous test initiation, the translation method of 

Pandit and Miner (1986) was applied prior to analyzing the 

50

52

54

56

58

60

62

64

9:43 9:50 9:57 10:04 10:12 10:19 10:26

62.5

63

63.5

64

64.5

Inflate 

lower 

packer

Inflate 

upper

packer Inject

slug

Expanded view showing response in head during packer inflation

Lower

interval

Middle

interval

Upper interval

0.001

0.01

0.1

1.0

10

100

0 60 120 180 240 300

TIME (SEC)

DISPLACEMENT (FT)

Interval: 571–575 ft

Date tested: 6/26/2009

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level data

Analysis

Casing radius: 0.1 ft

Screen length: 4.0 ft

Well radius: 0.375 ft

Aquifer model: Confined

Solution method: Bouwer-Rice

K = 1.1 ft/day

Static water level: 64.01

Shut-in water levels:

Zone WLBLS

Upper 64.14

Middle 63.80

Lower 63.42

WLBLS = water level below land surface

data. (This same correction was applied to all tests described 

below.) A semi-logarithmic plot of the falling-head data produced a straight-line fit, with a calculated horizontal hydraulic 

conductivity of 1.1 feet per day (ft/d) for this test. 

Water levels in the upper and lower intervals were steady 

throughout the test, indicating no observable leakage during 

slug injection or decline. Total water-level displacement across 

the interval after achieving full seating pressure was a positive 

0.72 ft (upper zone water level of 64.14 ft minus lower zone 

water level of 63.42 ft), indicating an upward flow gradient 

across this depth interval.

Figure 5. Test data and analysis for packer-slug test of depth interval 571–575 feet in well HAAF 11 

(36Q392), Hunter Army Airfield, Chatham County, Georgia, conducted on June 26, 2009.
12 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

641- to 645-Foot Test

The second slug test was completed at the 641- to 645-ft 

depth interval, located within the upper part of the middle 

confining unit. For this interval, a 5.8-gal slug of water caused 

a water-level displacement of 6 ft within the first 35 seconds, 

and then a rapid decline of the water level back to within 

0.01 ft of the initial water level within 1.5 minutes. The best 

fit for the data on the semi-logarithmic plot was selected 

57

58

59

60

61

62

63

64

65

8:38 8:45 8:52 9:00 9:07 9:14 9:21

62.5

63

63.5

64

64.5

0.001

0.01

0.1

1.0

10

DISPLACEMENT (FT)

Static water Level: 64.15

Shut-in water levels:

Zone WLBLS

Upper 64.28

Middle 63.75

Lower 63.49

WLBLS = water level below land surface

0 40 80 120 160 200

TIME (SEC)

Analysis

Expanded view showing response in head during packer inflation

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level data

Aquifer model: Confined

Solution method: Bouwer-Rice

K = ft/day

Interval: 641–645 ft

Date tested: 6/26/2009

Inflate 

lower 

packer

Inflate 

upper

packer Inject

slug

Lower interval

Middle interval

Upper interval

Casing radius: 0.1 ft

Screen length: ft

Well radius: 0.375 ft

4.0

3.1

between 10 and 60 seconds, resulting in a calculated horizontal hydraulic conductivity of 3.1 ft/d for this test (fig. 6). 

Water levels in the upper and lower intervals were steady 

throughout the test, indicating no observable leakage during 

slug injection or decay. Total water-level displacement across 

the interval after achieving full seating pressure was a positive 

0.79 ft (upper zone water level of 64.28 ft minus lower zone 

water level of 63.49 ft), indicating a slight increase in the upward 

flow gradient compared to the previously described test interval.

Figure 6. Test data and analysis for packer-slug test of depth interval 641–645 feet in 

well HAAF 11 (36Q392), Hunter Army Airfield, Georgia, conducted on June 26, 2009.
Packer-Slug Tests 13

688- to 692-Foot Test

The third slug test was completed at the 688- to 692-ft 

depth interval, located within the lower part of the middle 

confining unit. For this interval, the 5.8-gal slug of water introduced into the isolated interval through the drill stem caused 

a water-level displacement of 16 ft within the first 40 seconds 

followed by a slow decay of the water level back to within 

0.01 ft of the initial water level within approximately 15 minutes. After translating the data to account for the test initiation, 

a straight line fit to the data between 0 and 400 seconds on 

the semi-logarithmic plot resulted in a calculated horizontal 

hydraulic conductivity of 0.16 ft/d for this test (fig. 7). 

Water levels in the upper and lower intervals were steady 

throughout the test, indicating no observable leakage during 

slug injection or decay. Total water-level displacement across 

the interval after achieving full seating pressure was a positive 

0.65 ft (upper zone water level of 63.71 ft minus lower zone 

water level of 63.06 ft), indicating a decreased flow gradient 

across this depth interval compared to the previous depth interval.

Static water level: 63.53

Shut-in water levels:

Zone WLBLS

Upper 63.71

Middle 63.6

Lower 63.06

Note: shut-in water levels from slug test done

at 09:07

WLBLS = water level below land surface

45

50

55

60

65

10:04 10:07 10:10 10:13 10:16 10:19 10:22 10:24 10:27 10:30

62

62.5

63

63.5

64

K = ft/day

0.001

0.01

0.1

1.0

10

100

DISPLACEMENT (FT)

0.16

Analysis

Expanded view showing response in head during packer inflation

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level data

Interval: 688–692 ft

Date tested: 6/25/2009

Inject

slug

Lower interval

Middle interval

Upper interval

Aquifer model: Confined

Solution method: Bouwer-Rice

Casing radius: 0.1 ft

Screen length: ft

Well radius: 0.375 ft

4.0

0 180 360 540 720 900

TIME (SEC)

Figure 7. Test data and analysis for packer-slug test of depth interval 688–692 feet in 

well HAAF 11 (36Q392), Hunter Army Airfield, Georgia, conducted on June 25, 2009.
14 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

698- to 702-Foot Test

The fourth slug test was completed at the 698- to 702-ft 

depth interval, located in the middle confining unit and near 

the bottom contact with the Lower Floridan aquifer. For this 

interval, the 5.8-gal slug of water introduced into the isolated 

interval through the drill stem displaced the water level 21 ft 

within the first 45 seconds followed by a slow decay of the 

water level back to within 0.02 ft of the initial water level 

within approximately 18 minutes. The best fit is a straight 

line between 0 and 940 seconds on the semi-logarithmic plot, 

giving a horizontal hydraulic conductivity of 0.2 ft/d for this 

test (fig. 8). 

Water levels in the upper and lower intervals were steady 

throughout the test, indicating no observable leakage during 

slug injection or decay. Total water-level displacement across 

the interval after achieving full seating pressure was a positive 

0.82 ft (upper zone water level of 63.67 ft minus lower zone 

water level of 62.85 ft), indicating an increased flow gradient 

at this depth compared to the previous interval.

40

45

50

55

60

65

13:09 13:12 13:14 13:17 13:20 13:23 13:26 13:29 13:32 13:35

62

62.5

63

63.5

64

12:14 12:21 12:28 12:36 12:43 12:50 12:57 13:04 13:12 13:19

0.01

0.1

1.0

100

100

DISPLACEMENT (FT)

Static water level: 63.53

Shut-in water levels:

Zone WLBLS

Upper 63.67

Middle 63.20

Lower 62.85

WLBLS = water level below land surface

0 400 800 1.2E+3 1.6E+3 2.0E+3

TIME (SEC)

Analysis

Expanded view showing response in head during packer inflation (just prior to test shown above)

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level data

Aquifer model: Confined

Solution method: Bouwer-Rice

K = ft/day

Interval: 698–702 ft

Date tested: 6/25/2009

Inflate 

lower 

packer

Inflate 

upper packer

Inject

slug

Lower

interval

Middle interval

Upper interval

Casing radius: 0.1 0.20 ft

Screen length: ft

Well radius: 0.375 ft

4.0

Figure 8. Test data and analysis for packer-slug test of depth interval 698–702 feet in 

well HAAF 11 (36Q392), Hunter Army Airfield, Georgia, conducted on June 25, 2009.
Packer-Slug Tests 15

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

The fifth and sixth slug tests were completed at depth 

intervals of 802–806 ft and 812–816 ft across beds of 

lower permeability within the Lower Floridan aquifer. For 

these intervals, the 5.8-gal slug introduced into the isolated 

interval through the drill stem caused an initial water-level 

displacement of 10 ft and 12 ft, respectively, with rapid 

decay of the water level back to within 0.01 ft of the initial 

water level within about 3 minutes for each test (figs. 9, 10). 

Straight-line fits on the semi-logarithmic plots produced 

calculated horizontal hydraulic conductivities of 1.7 and 

1.2 ft/d, respectively. 

Water levels in the upper interval for each test were steady 

throughout the test, indicating no observable leakage during 

slug injection or decay. The water level in the lower zone was 

not monitored because the pressure exceeded the transducer’s 

calibrated pressure range and, thus, could not be reported. Total 

water-level displacement across the interval could not be calculated. The water-level differences between the test interval and 

the upper interval still remained positive, suggesting upward 

flow gradients across the two depth intervals. 

0.001

0.01

0.1

1.0

10

100

DISPLACEMENT (FT)

62.5

63

63.5

64

64.5

53

55

57

59

61

63

65

7:35 7:37 7:40 7:43 7:46 7:49 7:52 7:55 7:58 8:00

Static water level: 64.03

Shut-in water levels:

Zone Wlbls

Upper 64.14

Middle 63.8

Lower Over range

Wlbls = water level below land surface

Analysis

Casing radius: 0.1 ft

Screen length: ft

Well radius: 0.375 ft

Expanded view showing response in head during packer inflation 

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level data

Aquifer model: Confined

Solution method: Bouwer-Rice

K = ft/day

Interval: 802–806 ft

Date tested: 6/26/2009

Inflate 

upper

packer Inject

slug

Note: Lower interval graph not shown because

over calibrated pressure range.

Middle interval

Upper interval

Inflate 

lower packer

1.7

4.0

0 60 120 180 240 300

TIME (SEC)

Figure 9. Test data and analysis for packer-slug test of depth interval 802–806 feet in 

well HAAF 11 (36Q392), Hunter Army Airfield, Georgia, conducted on June 26, 2009.
16 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Static water level: 63.93

Shut-in water levels:

Zone WLBLS

Upper 63.95

Middle 63.26

Lower over range

WLBLS = water level below land surface

0.001

0.01

0.1

1.0

10

100

DISPLACEMENT (FT)

Figure 10. Test data and analysis for packer-slug test of depth interval 812-816 ft in well HAAF 11 (36Q392) 

conducted on June 25, 2009, Hunter Army Airfield, Chatham County, Georgia.

Analysis

Expanded view showing response in head during packer inflation 

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level data

Aquifer model: Confined

Solution method: Bouwer-Rice

K = ft/day

Interval: 812–816 ft

Date tested: 6/25/2009

Inflate 

upper

packer

Inject

slug

Middle interval

Upper interval

1.2

Casing radius: 0.1 ft

Screen length: ft

Well radius: 0.375 ft

4.0

Note: Lower interval graph not shown because

over calibrated pressure range.

0 60 120 180 240 300

TIME (SEC)

50

52

54

56

58

60

62

64

66

14:38 14:41 14:44 14:47 14:49 14:52 14:55 14:58 15:01 15:04 15:07

62

62.5

63

63.5

64

Figure 10. Test data and analysis for packer-slug test of depth interval 812–816 feet in 

well HAAF 11 (36Q392), Hunter Army Airfield, Georgia, conducted on June 25, 2009.
Aquifer Testing 17

Aquifer Testing

Aquifer tests were conducted at HAAF to estimate 

transmissivity of the Upper and Lower Floridan aquifers and 

storage coefficient of the Upper Floridan aquifer. Details on 

these tests are provided in subsequent sections, and results are 

summarized in table 3. Site layout and a schematic diagram 

showing hydrogeologic units and open intervals in the wells 

are shown in figure 11.

An important factor in the analysis of water-level data in 

the vicinity of HAAF is filtering out interferences that can create 

water-level fluctuations that may obscure relatively small drawdown response. Major interferences include tidal fluctuations, 

barometric pressure changes, and local and regional pumping 

effects. Halford (2006) developed a procedure to filter out 

interferences by use of simple models for estimating unpumped 

water levels that are referred to as synthetic water levels. These 

models sum multiple time series, such as barometric pressure, 

tidal potential, and background water-level trends, to simulate 

non-pumping water levels. The procedure involves adjustment 

of the amplitude and phase of each time series so that synthetic 

water levels match measured water levels during periods unaffected by an aquifer test. Differences between synthetic and 

measured water levels are minimized with a sum-of-squares 

objective function. This procedure was applied to water levels 

for each of the aquifer tests conducted at HAAF. 

Table 3. Summary of transmissivity and storage cofficients determined from aquifer tests conducted in the Upper and Lower Floridan 

aquifers, Hunter Army Airfield, Chatham County, Georgia, 2009.

[ft2/d, square foot per day; —, not applicable]

Test location Hydrologic unit Dates tested

Coefficents

Transmissivity Remarks

(ft2/d)

Storage

(dimensionless)

HAAF 9 

(36Q391)

Upper Floridan 2/17–18/2009 40,000 2.50E–4 Transmissivity and storage calculated 

from drawdown response in well 

No. 8 located 2,020 feet away. Used 

Hantush, 1960, leaky aquifer solution. 

Drawdown was corrected for tidal and 

other fluctuations prior to analysis.

HAAF 9 

(36Q391)

Upper Floridan 8/10/2009 41,000 2.28E–4 Repeat of 2/17–18/2009 test using a 

slightly lower pumping rate. Used 

Hantush, 1960, leaky aquifer solution. 

Drawdown was corrected for tidal and 

other fluctuations prior to analysis.

HAAF 11 

(36Q392)

Lower Floridan 8/13–16/2009 10,000 from 

drawdown data;

12,000 from 

recovery data

— Single well test conducted upon 

completion of Lower Floridan well 

open from 703 –1,100 feet. Analysis 

used Theis, 1935, solution. Drawdown 

was corrected for tidal and other 

fluctuations prior to analysis.

HAAF 11 

(36Q392)

Upper and Lower 

Floridan

6/19/2000 50,000 from 

drawdown data;

49,000 from 

recovery data 

— Single well test conducted during flowmeter survey. Both the upper and lower 

Floridan aquifer open to borehole during 

test; well open from 333 to 1,164 feet.
18 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Note: Distance between well HAAF 11 and well HAAF 8 is 176 feet

5,298 feet

3,600 feet

1,995 feet

2,020 feet

Figure 11. Location and construction characteristics of 

wells used for aquifer tests at Hunter Army Airfield, Chatham 

County, Georgia: (A) diagram showing aquifer test layout and 

(B) schematic section showing open intervals of the wells in 

relation to major hydrogeologic units.

A. Aquifer test layout

B. Schematic cross section

Upper Floridan

 aquifer

Lower Floridan 

aquifer

Confining

unit

Confining

unit

Surficial 

aquifer

100

200

300

400

500

600

700

800

900

1,000

1,100

Land

surface DEPTH BELOW LAND SURFACE, IN FEET

NOT TO SCALE

Well HAAF 9

36Q391

Well HAAF 8

36Q292

Well HAAF 11

36Q392

(pumped well)

Well HAAF 5

(36Q288)

Well HAAF 5(36Q288)Well HAAF 11(36Q392)Well HAAF 8(36Q292)Well HAAF 9(36Q391)

Well open interval

EXPLANATION

Water-producing interval

Upper Floridan Aquifer Tests

Multi-well aquifer tests were conducted in Upper Floridan aquifer wells on February 17–18, 2009, and August 12, 

2009. For each test, well HAAF 9 was pumped, and water 

levels in well HAAF 8 were observed (fig. 11; table 3). Well 

HAAF 8 is located 2,020 ft southwest of the pumped well 

(well HAAF 9). Well HAAF 9 was drilled in 2004 (replacing an older well at that same location) and is currently used 

as a water supply to support operation activities in this area 

of the base (Stanley Thomas, U.S. Department of the Army, 

Ft. Stewart, written commun., 2009). This well is operated 

intermittently, depending on water-supply needs. Under 

normal backpressure conditions, well HAAF 8 is pumped at 

a rate of 400–470 gal/min for several hours at a time until 

demand is reduced and the nearby water storage tank is 

brought to full capacity. Well HAAF 8 is used mostly as a 

supplemental supply during times of high demand and also 

when well HAAF 9 is being serviced.

Well construction information for wells HAAF 8 and 

HAAF 9 is provided in table 1 and illustrated in figure 11. 

Both wells are open to the Upper Floridan aquifer; however, 

both wells partially penetrate the confining unit. Because both 

the pumping and observation wells are only open to the upper 

portion of the Upper Floridan aquifer, the effects of partial 

penetration were considered in the test analysis.

Analytical Method

For each Upper Floridan aquifer test, aquifer properties 

were estimated using drawdown data from the observation 

well only; no aquifer properties were estimated from the 

pumped well because of partial-penetration effects. The 

Hantush (1960) leaky aquifer solution was selected for the 

analysis because this solution most closely matches aquifer 

site conditions compared to other analytical solutions provided 

in AQTESOLVTM. This solution assumes that (1) the aquifer 

is infinite in areal extent, homogeneous, and isotropic, (2) the 

pumping well is fully or partially penetrating, and flow to the 

pumping well is horizontal, (3) the aquifer is leaky, and flow 

is unsteady, (4) water is released from storage instantaneously, 

(5) the diameter of the pumping well is very small, and the 

storage in the well can be neglected, (6) the confining bed 

is infinite in areal extent and has a uniform vertical hydraulic conductivity and thickness, (7) the confining bed has an 

adjacent constant-head source, and (8) flow in the confining 

bed is vertical. While all of these conditions are not perfectly 

met at this test site, this model most closely matches actual 

field conditions and for this reason was selected for use in the 

analysis. The Hantush-Jacob (1955) solution also was evaluated; however, because it does not take into account storage in 

the confining layer, it was not believed to be the best method 

for determining the aquifer coefficients for the Upper Floridan 

aquifer at this test site. 

Figure 11. Location and construction characteristics 

of wells used for aquifer tests at Hunter Army Airfield, 

Chatham County, Georgia. (A) Map showing aquifer 

test layout, (B) Schematic section showing the 

open intervals of the wells in relation to major 

hydrogeologic units.
Aquifer Testing 19

Test 1: February 17–18, 2009

The first Upper Floridan aquifer performance test was 

conducted on February 17–18, 2009, using well HAAF 9 as 

the pumping well. Pressure transducers and manual waterlevel measurements were used to monitor water levels during 

the aquifer test. The production and observation wells were 

monitored from February 12, 2009, through February 24, 

2009, which encompassed a pre-test background period of 

5 days and post-test monitoring of 6 days. The post-test monitoring record for well HAAF 9 is not included in the dataset 

because the wireless data logger used in this well became 

lodged and could not be retrieved following the conclusion 

of the test. Manual measurements, therefore, are used for the 

pumped well. 

490

50

55

450

470

60

430

65

PUMPING

DEPTH TO WATER LEVEL, IN FEET

RATE, IN GALLONS PER MINUTE (GAL/MIN)

390

410

70

Water level

Rate (gal/min)

370

350

75

80

Figure 12. Water-level data for well HAAF 9 (36Q391) during 24-hour aquifer test February 17–18, 2009, 

Hunter Army Airfield, Chatham County Georiga.

2/17/09 0:00 2/17/09 12:00 2/18/09 0:00 2/18/09 12:00 2/19/09 0:00 2/19/09 12:00 2/20/09 0:00

Average pumping rate

430 gal/min

Drawdown in pumped well

is approximatly 25.5 feet

Start

pumping

Stop

pumping

Pumping period Recovery period

Well HAAF 9 was pumped for 24 hours starting on February 17, 2009, at 1:40 PM EST and stopping on February 18, 

2009, at 1:41PM EST. Cumulative pumpage during this period 

was 621,000 gal with an average pumping rate of 430 gal/min 

during the 24-hour test. Because this well was operated against 

water-system pressure, the pumping rate varied slightly 

throughout the test (fig. 12). The largest variations occurred 

within the first hour of pumping; pumping then stabilized 

between 428 and 435 gal/min. During a 40-minute period on 

February 17, 2009, at 9:00 PM EST, pumping temporarily 

dropped to 400 gal/min in response to a pressure change in the 

system. Following pump shutdown, well HAAF 9 was kept 

offline for the remainder of the monitoring period to observe 

background fluctuations. 

Figure 12. Water-level data for well HAAF 9 (36Q391) during 24-hour aquifer test conducted 

February 17–18, 2009, Hunter Army Airfield, Chatham County, Georgia.
20 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Figure 13. Comparison of water levels at well HAAF 8 (36Q292) to background water levels 

at Morrison Plantation observation well (36Q020) and to stage and barometric pressure 

at tidal station 02198773 (U.S. Army Corps of Engineers Dock, Savannah, Georgia), 

February 12–25, 2009.

Morrison Plantation Well

(36Q020)

Aquifer

test

period Well HAAF 8

(36Q292)

Tidal stage Barometric 

pressure

FEBRUARY 2009

12 13 14 15 16 17 18 19 20 21 22 24 25

TIDAL STAGE, IN FEET 

BELOW OR ABOVE (–) 

NAVD 88

–8

–6

–4

–2

0

2

4

750

755

760

765

770

775

780

BAROMETRIC PRESSURE,

IN MILLIBARS

60.9

44.7

44.9

45.1

45.3

45.5

45.7

45.9

59.7

59.9

60.1

60.3

60.5

60.7

WATER LEVEL IN WELL 36Q292WATER LEVEL IN WELL 36Q020

BELOW LAND SURFACE, IN FEETBELOW LAND SURFACE, IN FEET

The hydrograph for well HAAF 8 shows barometric and 

tidally influenced fluctuations similar to that observed in the 

background monitoring well (fig. 13). The larger-scale fluctuations on the hydrographs are attributed to barometric-pressure 

changes, and smaller cyclic fluctuations are in response to 

changes in tidal stage. An influence of nearby pumping and 

the regional water-level trend can be seen in the hydrograph 

for well HAAF 8. These external influences tended to mask 

the drawdown response related to the pumping well alone and 

were filtered out of the raw data prior to aquifer-test analysis. 

The process of correcting water-level data to determine the 

pumping-induced drawdown estimates is described below. 

Drawdown Estimation

Using the filtering spreadsheet provided by Halford (2006), 

the amplitude and phase of each time series (background, 

tide, barometric pressure) were adjusted to create a composite 

synthetic water-level hydrograph spanning the period of the 

test. Adjustments to these individual time series were made 

to minimize the differences between synthetic and measured 

water levels. Estimated pumpage-induced drawdowns were then 

derived from differences between measured and synthetic water 

levels during pumping and recovery periods.

The effect of each time series on the development of 

a synthetic water level for the aquifer test was determined 

by using a trial-and-error approach, adding each component 

sequentially and then evaluating the effect of that series on the 

filtering process. Several components were combined and then 

the components that improved the fit were eventually used in 

the final filtering process. Representative time series and the 

effects on the filtering process are shown in figure 14.

Using the background water-level time series alone 

yielded a root-mean-square (RMS) of 0.0432 ft and a relatively poor fit to the tidal-loading effects (fig. 14A). Using a 

6-hour moving average of the background time series, the fit 

improved, but still showed obvious effects of tidal loading that 

were not removed (fig. 14B). Combining the raw background 

time series with the 6-hour moving average greatly improved 

the fit, reducing differences between the synthetic and 

observed water levels down to an RMS of 0.0270 ft (fig. 14C).

 Adding the barometric pressure time series to the 

analysis slightly improved the fit down to an RMS of 0.0263 ft 

(fig. 14D). Attempts were made to use barometric pressure 

alone, without any other time series, but were unrealistic, 

failed to improve the fit, and are not shown here. Similar 

attempts were made using the tidal stage time series alone, but 

this did not produce satisfactory results. Combining tidal stage 

and barometric pressure time series, however, did provide a 

fairly good fit, giving an RMS of 0.0386 ft (fig. 14E).

Finally, all of the time series were combined, including 

the raw and 6-hour moving-average time series from background well 36Q020, tidal stage, barometric pressure, gravity 

tides, and earth tides. This combination created a composite 

synthetic water level that yielded the lowest RMS of 0.0138 ft, 

the best fit of all of the various combinations attempted during 

the filtering procedure (fig. 14F). 

Figure 13. Comparison of water levels at well HAAF 8 (36Q292) to background water levels 

at Morrison Plantation observation well (36Q020) and to stage and barometric pressure at 

tidal gage 021989773 (U.S. Army Corps of Engineers Dock, Savannah, Georgia), Hunter Army 

Airfield, Chatham County, Georgia, February 12–26, 2009.
Aquifer Testing 21

Pumping

Fitting period

Recovery

Estimation period

RMS = 0.039

RMS = 0.043

RMS = 0.033

RMS = 0.027

RMS = 0.026

RMS = 0.014

WATER-LEVEL CHANGE, IN FEET

A

B

C

D

E

F

FEBRUARY 2009

–0.6

–0.4

–0.2

0

12 13 14 15 16 17 18 19

0.2

0.4

0.6

0.8

1.0

–0.6

–0.4

–0.2

0

0.2

0.4

0.6

0.8

1.0

–0.6

–0.4

–0.2

0

0.2

0.4

0.6

0.8

1.0

–0.6

–0.4

–0.2

0

0.2

0.4

0.6

0.8

1.0

–0.6

–0.4

–0.2

0

0.2

0.4

0.6

0.8

1.0

–0.6

–0.4

–0.2

0

0.2

0.4

0.6

0.8

1.0

Figure 14. Effects of different time series components on development of a synthetic water level used to filter out extraneous 

trends for well HAAF 8 (36Q292), Hunter Army Airfield, Chatham County, Georgia: (A) raw water-level data for Morrison Plantation 

well 36Q020, (B) 6-hour moving average water level for well 36Q020, (C) raw and 6-hour moving average water-level data for well 

36Q020, (D) raw and 6-hour moving-average water level for well 36Q020 and barometric pressure, (E) raw barometric pressure 

and raw tidal stage data, and (F) raw and 6-hour moving average water-level data for well 36Q020, tidal stage, barometric 

pressure, gravity tides, and earth tides. [RMS, root mean square of differences between measured and synthetic water levels]

Measured well HAAF 8 (36Q392)

Synthetic well HAAF 8 (36Q392)

Difference between measured and synthetic 

Background Morrison 

Plantation well (36Q020)

Moving average in background 

Morrison Plantation well (36Q020)

Water-level change

Figure 14. Effects of different time series components on development of a synthetic water level used to filter 

out extraneous trends for well HAAF 8 (36Q292), Hunter Army Airfield, Chatham County, Georgia. (A) raw waterlevel data for Morrison Plantation well 36Q020, (B) 6-hour moving average water level for well 36Q020, (C) raw 

and 6-hour moving average water-level data for well 36Q020, (D) raw and 6-hour moving-average water level 

for well 36Q020 and barometric pressure, (E) raw barometric pressure and raw tidal stage data, and (F) raw and 

6-hour moving average water-level data for well 36Q020, tidal stage, barometric pressure, gravity tides, and 

earth tides. [RMS, root mean square of differences between measured and synthetic water levels]
22 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Aquifer-Test Analysis

The resulting logarithmic plot of drawdown data for 

observation well HAAF 8 showed a response that is characteristic of a leaky artesian aquifer with storage of water in the 

semiconfining bed (fig. 15). In particular, the late-time data did 

not fit the Theis (1935) type curve of an ideal confined aquifer. 

The flattening of the curve after approximately 40 minutes 

indicates appreciable amounts of water are being released 

from storage, probably from the underlying semiconfining 

layer and the Lower Floridan aquifer.

0.001

1 10 100 1,000 1.0E+4

0.01

0.1

1.0

TIME (MIN)

DRAWDOWN (FT)

Aquifer model: Leaky

Solution method: Hantush

T = 40,000 ft2

/day

S = 0.00025

r/B' = 0.27

ß' = 0.044

Drawdown data point filtered 

 for tidal, barometric, and 

 other influences

Q = 430 gal/min

r = 2,020 ft

Note: influence

of nearby pumping

that was not able 

to be filtered out 

of the raw data

Theis (1935)

Leaky

solution

where:

b' is thickness of first aquitard [ft]

K' is vertical hydraulic conductivity of first aquitard [ft/d]

Q is pumping rate [gal/min]

r is radial distance [ft]

s is drawdown [ft]

S is storativity [dimensionless]

S' is storativity of first aquitard [dimensionless]

t is time [d]

T is transmissivity [ft2

/d]

Figure 15. Logarithmic plot of drawdown versus time for observation well HAAF 8 (36Q292) 

located 2,020 feet from pumping well HAAF 9 for Upper Floridan aquifer test conducted 

February 17–18, 2009, Hunter Army Airfield, Chatham County, Georgia. 

Using the Hantush (1960) solution, acceptable curve 

matches were obtained by using combinations of the leakance terms r/B’ and β and varying the storativity within a 

reasonable range of values. The early time data, from 3 to 

300 minutes, matched fairly well to the solution, while the 

latter part of the measured field data departed from the type 

curve (shifted upward), possibly due to a nearby pumping 

influence of well HAAF 9. The best match with the Hantush 

(1960) analysis gives a transmissivity of 40,000 feet squared 

per day (ft2/d) and a storage coefficient of 0.00025 (fig. 15). 

Figure 15. Logarithmic plot of drawdown and time for observation 

well HAAF 8 (36Q292) located 2,020 feet from pumping well HAAF 9 

for Upper Floridan aquifer test conducted February 17–18, 2009, 

Hunter Army Airfield, Chatham County, Georgia.
Aquifer Testing 23

Test 2: August 10, 2009

A second multi-well Upper Floridan aquifer performance 

test was conducted on August 10, 2009, during the first stage 

of the Lower Floridan aquifer test, using well HAAF 8 as 

the test observation well. This test was designed in a similar 

manner as the previous test. Well HAAF 9 was pumped at an 

average rate of 400 gal/min, and drawdown was monitored at 

well HAAF 8, located 2,020 ft to the southwest of the pumped 

well (well HAAF 9). Pumping for this test began at 5:30 PM 

on August 10, 2009, and continued throughout the next day. 

The analysis of this test provided additional confirmation of 

the aquifer-test results obtained from the previously described 

24-hour test during February 17–18, 2009.

Using the same procedures described above, raw waterlevel data from well HAAF 8 were first filtered to remove the 

effects of barometric pressure, tidal influences, and regional 

trends and then analyzed with the Hantush (1960) analytical 

solution. The results of this analysis produced a transmissivity 

of 41,000 ft2/d and a storage coefficient of 2.3E-04 (fig. 16). 

These results are a close match to the values determined from 

the first aquifer performance test described above. 

where:

b' is thickness of first aquitard [ft]

K' is vertical hydraulic conductivity of first aquitard [ft/d]

Q is pumping rate [gal/min]

r is radial distance [ft]

s is drawdown [ft]

S is storativity [dimensionless]

S' is storativity of first aquitard [dimensionless]

t is time [d]

T is transmissivity [ft2/d]

Theis (1935)

Leaky

solution

Figure 16. Logarithmic plot of drawdown versus time for observation well HAAF 8 (36Q292) 

located 2,020 feet from pumping well HAAF 9, for Upper Floridan aquifer test conducted 

August 12, 2009, Hunter Army Airfield, Chatham County, Georgia.

0.001

0.01

0.1

1.0

1 10 100 1,000

TIME (MIN)

DISPLACEMENT (FT)

Aquifer model: Leaky

Solution method: Hantush

T = 41,000 ft2

/day

S = 0.00023

r/B' = 0.36

ß' = 0.056

Drawdown data point filtered 

 for tidal, barometric, and 

 other influences

Q = 400 gal/min

r = 2,020 ft

Figure 16. Logarithmic plot of drawdown and time for observation 

well HAAF 8 (36Q292) located 2,020 feet from pumping well HAAF 9 for 

Upper Floridan aquifer test conducted August 12, 2009, Hunter Army 

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

Lower Floridan Aquifer Test: 

August 13–16, 2009

A 72-hour aquifer performance test was completed 

August 13–16, 2009, to estimate the transmissivity of the 

Lower Floridan aquifer and to document pumping-induced 

drawdown in the Upper Floridan aquifer. Although the 

analysis of this test was treated as a single-well test with 

only the transmissivity of the pumped well being estimated, 

drawdown data from the Upper Floridan observation wells 

were collected so that leakage could be simulated in the 

numerical model (not presented here). The pumped well fully 

penetrates the entire thickness of the Lower Floridan aquifer, 

with an open interval from 703 ft to 1,112 ft. Upper Floridan 

aquifer observation wells are located 176 ft to the southeast 

(well HAAF 8), 1,995 ft to the northeast (well HAAF 9), and 

3,600 ft to the west (well HAAF 5; fig. 11). Well-construction 

information is provided in table 1, and a site layout and a 

schematic diagram showing hydrogeologic units and well 

open intervals are shown in figure 11.

Test Procedure

Because of the length of time that was anticipated to 

complete the Lower Floridan aquifer test, HAAF required 

that Upper Floridan aquifer well HAAF 9, which is located 

2,020 ft from the new Lower Floridan aquifer well, be kept 

operational to supply water to this part of the base during the 

test. To minimize the effects of the nearby pumping on the 

aquifer test, a continuous constant-rate pumping schedule was 

maintained for HAAF 9, starting 2 days before the start of the 

aquifer test and continuing throughout the duration of the test. 

Background water levels were monitored in well 36Q020 

located at Morrison Plantation west of HAAF (fig. 1). Tidal 

stage and barometric pressure were monitored at USGS tidal 

gage station 021989773 located at the U.S. Army Corps of 

Engineers Dock in Savannah, Georgia. These data were used 

to filter out background fluctuations and estimate pumpinginduced drawdown in the two observation wells. 

All of the wells used in this test, including the two 

pumped and two observation wells, were monitored with 

pressure transducers beginning July 30, 2009, and ending 

September 2, 2009. This period encompassed 11 days of pretest background monitoring and 12 days of post-test monitoring. Manual water-level measurements were made periodically 

in the pumped and observation wells. The major stages/events 

during the test included:

• Pre-test monitoring began on July 30, 2009 

• Startup of well HAAF 9 (400 gal/min) at 

August 10, 2009 5:07 PM EST

• Temporary shutdown of well No 9 at 

August 11, 2009 9:04 PM EST

• Restart of well HAAF 9 (400 gal/min) at 

August 12, 2009 10:05 AM EST

• Startup of well HAAF 11 (754 gal/min) at 

August 13, 2009 9:10 AM EST

• At well HAAF 11, the generator stalled for 

1 minute, and flow readjusted (747 gal/min) at 

August 14, 2009 1:12 AM EST

• Shutdown of well HAAF 11 at 

August 16, 2009 9:09 AM EST
Aquifer Testing 25

Figure 17. Drawdown response in Upper Floridan 

wells HAAF 8 (36Q292) and HAAF 5 (36Q288) during a 

72-hour aquifer test of Lower Floridan well HAAF 11 

(36Q392) conducted on August 13–16, 2009, Hunter 

Army Airfield, Chatham County, Georgia.

12 14 16 18

49.0

49.5

50.0

63.5

64.0

64.5

65.0

60

70

80

90

100

110

50.5

WATER LEVEL BELOW LAND SURFACE, IN FEET

Well HAAF 8 (36Q292; 176 feet from pumping well)

Well HAAF 5 (36Q288; 3,600 feet from pumping well)

Well HAAF 11 (36Q392)

Pump on 

(747 gallons 

per minute) 

Pump off

AUGUST 2009

• Shutdown of well HAAF 9 at 

August 21, 2009 10:01AM EST

• Post-test monitoring ends and transducers 

were pulled on September 2, 2009 

Cumulative pumpage for well HAAF 11 was 

3.23 million gallons with an average pumping rate of 

747 gal/min during the 72-hour test. Other than one slight 

adjustment as a result of a temporary mechanical issue that 

lasted for 1 minute, the pumping rate remained relatively 

constant throughout the duration of the 72-hour test. The 

pumping rate at well HAAF 9 averaged 400 gal/min with a 

fluctuation of 10–15 gal/min in response to pressure changes 

in the HAAF water system at various times of the day.

During the 72-hour test, a drawdown response was 

observed in the Upper Floridan aquifer wells (fig. 17). The 

water level in well HAAF 8, located 176 ft from the pumping 

well, began drawing down within approximately 1 hour of the 

start of the pumping test. Drawdown in well HAAF 5, located 

3,600 ft away, was less evident because of the decreasing 

water-level trend at the beginning of the test. Barometric 

pressure changes, tidal fluctuations, and regional water-level 

trends all combined to partially mask the pumping-induced 

drawdown in observation well HAAF 5. 

Figure 17. Drawdown response in Upper Floridan wells 

HAAF 8 (36Q292) and HAAF 5 (36Q288) during a 72-hour 

aquifer test of Lower Floridan well HAAF 11 (36Q392) 

conducted August 13–16, 2009, Hunter Army Airfield, 

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

Drawdown Estimation

The effects of background water-level trends, barometric 

pressure, and tidal loading were removed from the raw waterlevel data series using the Halford (2006) filtering spreadsheet 

method. The amplitude and phase of each time series were 

adjusted to create a composite synthetic water-level hydrograph spanning the period of the test. Estimated pumpageinduced drawdowns were then derived from the differences 

between measured and synthetic water levels during the 

pumping and recovery periods. This process was applied only 

to wells HAAF 11, HAAF 5, and HAAF 8. Variations in the 

pumping rate at well HAAF 9 caused water levels to fluctuate 

greater than pumping-induced drawdown; therefore, this well 

was excluded from the analysis.

The raw water-level hydrographs from the 72-hour 

Lower Floridan aquifer test and the response at the two Upper 

Floridan aquifer observation wells are shown in figure 17. 

Even without filtering, pumping-induced drawdown at well 

HAAF 8 is evident in the hydrograph while the drawdown in 

well HAAF 5 is less evident, but distinguishable.

The effects of pumping well HAAF 9 on water levels in 

the area were included in the filtering process. To accommodate this effect, the fitting period for filtering was expanded 

to encompass 1 week before and 2 weeks after the test was 

completed (fig. 18). For well HAAF 8, synthetic and measured 

water levels matched fairly well during the week prior to 

starting to pump well HAAF 9 (fig. 18A). During this pretest period, well HAAF 9 was taken offline to obtain natural 

background fluctuations. Pumping from well HAAF 9 was 

started 2 days prior to the startup of the aquifer test and was 

maintained at an average pumping rate of 400 gal/min until 

5 days following the end of the Lower Floridan aquifer test. 

The drawdown and recovery response of pumping both wells 

HAAF 9 and HAAF 11 is shown in figure 18A. After removing 

the pumping effects for well HAAF 9, the total drawdown 

and recovery response attributed to well HAAF 11 pumping 

alone was estimated to be 0.76 ft (fig. 18A, lower graph). At 

well HAAF 5, located 3,600 ft away from the Lower Floridan 

well, the total pumping-induced drawdown attributed to well 

HAAF 11 pumping was estimated to be 0.32 ft (fig. 18B, 

lower graph).
Aquifer Testing 27

Figure 18. Estimated drawdown calculated in Upper Floridan wells (A) HAAF 8 (36Q292) and (B) HAAF 5 

(36Q288) during the 72-hour aquifer test of Lower Floridan aquifer in well HAAF 11 (36Q392) conducted 

August 13–16, 2009, Hunter Army Airfield, Chatham County, Georgia.

AUGUST 2009

AUGUST 2009

13

3 4 5 6 7 8 9 13

14

14

15

15

16

10 11 12 16 20 21 22 23 24 25 26 27

17

17

18

AUGUST 2009

13 14 15 16 17 18 19

18 19

AUGUST 2009

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

0

0

0

–0.6

–0.4

–0.8

–1.0

–0.2

0.2

0.4

0.6

0.8

1.0

0.2

0.4

0.6

0.8

1.0

–1.5

–1.0

–0.5

0.5

–0.6

–0.4

–0.8

–1.0

–0.2

0

1.0

–1.5

–1.0

–0.5

0.5

1.0

0.76 foot of drawdown

0.43 foot of drawdown

A. Well HAAF 8 (36Q292)

B. Well HAAF 5 (36Q288)

RMS = 0.1990

RMS = 0.4039

RMS = 0.4535

RMS = 0.8211

EXPLANATION

WATER-LEVEL CHANGE, IN FEET WATER-LEVEL CHANGE, IN FEET

Measured 

Synthetic

Difference between 

 measured and synthetic

Water-level change

HAAF 9 pump on

HAAF 11

HAAF 9 Pump on Pump on

HAAF 11

pump on HAAF 11 

pump off HAAF 9 pump off

HAAF 11 

pump off

HAAF 9 pump off

Figure 18. Estimated drawdown in Upper Floridan aquifer wells (A) HAAF 8 (36Q292) and (B) HAAF 5 

(36Q288) during a 72-hour aquifer test of Lower Floridan well HAAF 11 (36Q392) conducted August 13–16, 

2009, Hunter Army Airfield, Chatham County, Georgia.
28 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Aquifer-Test Analysis

The transmissivity of the Lower Floridan aquifer was 

estimated from the drawdown and recovery data obtained from 

the pumped well (well HAAF 11) because no other nearby 

Lower Floridan wells were available for drawdown observations. Similar to the Upper Floridan aquifer tests described 

previously, the Lower Floridan aquifer test also shows a leaky 

artesian aquifer response with the flattening of the drawdown 

starting several hundred minutes into the test (fig. 19). The 

transmissivity calculated using the Theis (1935) solution was 

10,000 ft2/d (fig. 19A). The Theis (1935) solution assumes 

the aquifer has an infinite areal extent, is homogeneous and 

isotropic, and has a uniform thickness; the pumping well is 

fully penetrating; flow to the well is horizontal; the aquifer 

is confined; flow is unsteady and water is released instantaneously from storage with decline of hydraulic head; and the 

effects of borehole storage are small enough to be neglected. 

Because of these assumptions (and the observed leakage 

response), the type curve was only matched to early-time 

data between 7 and 90 minutes. The observed values plotting 

below the Theis (1935) curve between 1 and 7 minutes were 

attributed to borehole storage, and these time-series data were 

included in this analysis.

The Theis (1935) solution for recovery data in a confined aquifer was also used to calculate transmissivity for 

the aquifer test. In the Theis recovery method, the residual 

drawdown is plotted against t/t’ (time over elapsed time 

since pumping began) on a semi-logarithmic plot (fig. 19B). 

A straight-line fit through the observed residual drawdown 

produced a calculated transmissivity of 12,000 ft2/day, which 

is comparable to the value determined using the drawdown 

data. Considering the transmissivity values obtained from 

the pumping and recovery phases, a value of 11,000 ft2/d was 

estimated to represent the Lower Floridan aquifer’s transmissivity at this test site. 

0

4

8

12

TIME, t/t'

RESIDUAL DRAWDOWN (FT)

Aquifer model: Confined

T = 12,000 ft2/day

Solution method: Theis (Recovery)

B.

A.

t = time

t' = time since pumping began

10

100

90

80

70

60

50

40

30

20

DRAWDOWN (FT)

Aquifer model: Confined

Solution method: Theis

T = 10,000 ft2/day

Drawdown data point filtered for 

tidal, barometric, and other influences

Q = 747 gal/min

r = 0.33 ft

Testing period: 8/13–16/2009

Figure 19. Aquifer-test plots for 72-hour aquifer test of 

Lower Floridan aquifer conducted August 13–16, 2009, 

Hunter Army Airfield, Chatham County, Georgia: (A) 

Log-log plot of drawdown versus time and (B) semilogarithmic plot of residual drawdown versus t/t'. [Note: 

Storativity is not computed for single-well test]

1 10 100 1,000

TIME (MIN)

1 10 100 1000 1.0E+4

Figure 19. Aquifer-test plots for 72-hour aquifer test of 

Lower Floridan aquifer conducted August 13–16, 2009, 

Hunter Army Airfield, Chatham County, Georgia. (A) Loglog plot of drawdown and time and (B) semi-logarithmic 

plot of residual drawdown and t/t'. [Note: Storativity is 

not computed for single-well test]
Aquifer Testing 29

Combined Upper and Lower Floridan 

Aquifer Test

A combined Upper and Lower Floridan aquifer performance test was completed on June 19, 2009, conducted at the 

same time as the pumping flowmeter tests. The aquifer test 

provided an opportunity to obtain a transmissivity estimate for 

the combined aquifer system while the well was open to both 

aquifers. During this test, the open borehole (333–1,112 ft) of 

well HAAF 11 was pumped at a constant rate of 847 gal/min 

for 6 hours; water levels were recorded in the pumped well 

and in well HAAF 8. At the time of this test, the well casing in 

well HAAF 11 extended to 333 ft; both the Upper and Lower 

Floridan aquifers were open to the borehole between depths 

of 333 ft and 1,112 ft. Well HAAF 8 served as an observation 

well; however, as shown in figure 11, this well is open only to 

the Upper Floridan aquifer and, therefore, was not used in the 

aquifer-test analysis.

The aquifer-test analysis for the combined Upper and 

Lower Floridan aquifers was treated as a fully penetrating 

single-well test of a confined aquifer system. The resulting 

logarithmic plot of the drawdown data for the pumping well 

discharging 847 gal/min indicates a response along the Theis 

(1935) type curve of an ideal confined aquifer (fig. 20). The 

small shift in the drawdown data shown in figure 18 was 

attributed to the startup of well HAAF 9 and was not matched 

for the aquifer-test analysis.

The Theis (1935) method was applied to both the drawdown and recovery periods (fig. 20) with a calculated transmissivity of 50,000 and 49,000 ft2

/d, respectively. Given these 

results, the transmissivity of the combined Upper and Lower 

Floridan aquifers is estimated to be 50,000 ft2/d. 

Figure 20. Aquifer-test plots for 6-hour aquifer test of 

combined Upper and Lower Floridan aquifers in well HAAF 

11 conducted June 19, 2009, Hunter Army Airfield, Chatham 

County, Georgia: (A) Log-log plot of drawdown versus time 

and (B) semi-logarithmic plot of residual drawdown 

against t/t'. [Note: Storativity is not computed for singlewell test]

0

0.8

1.6

2.4

Slight shift in drawdown 

 is attributed to nearby 

 pumping

RESIDUAL DRAWDOWN (FT)

B.

A.

Aquifer model: Confined

T = 49,000 ft2/day

Solution method: Theis (Recovery)

t = time

t' = time since pumping began

1

10

9

8

7

6

5

4

3

2

DRAWDOWN (FT)

Aquifer model: Confined

Solution method: Theis

T = 50,000 ft2/day

Drawdown data point filtered 

 for tidal, barometric, and 

 other influences

Q = 847 gal/min

r = 0.33 ft

Testing period: 6/19/2009

0.1 1 10 100 1,000

TIME (MIN)

TIME, t/t'

1 10 100 1,000

Figure 20. Aquifer-test plots for 6-hour aquifer test of 

combined Upper and Lower Floridan aquifers in well 

HAAF 11 conducted June 19, 2009, Hunter Army Airfield, 

Chatham County, Georgia. (A) Log-log plot of drawdown 

and time and (B) semi-logarithmic plot of residual 

drawdown and t/t'. [Note: Storativity is not computed 

for single-well test]
30 Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia

Summary and Conclusions

A 1,168-foot deep test well was constructed at Hunter 

Army Airfield to investigate the potential of using the Lower 

Floridan aquifer as a source of water supply to satisfy increased 

needs caused by base expansion and increased troop levels. 

Hydrologic testing was completed to obtain data needed for 

development of a groundwater flow model that could be used to 

determine the contribution from the Upper Floridan aquifer that 

would result from the proposed additional withdrawal from the 

Lower Floridan well. The testing at this site included flowmeter 

surveys, packer-slug tests in the test borehole, 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 waterbearing 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-producing zones were identified in the Upper Floridan 

aquifer that supply 83.5 percent of the total pumpage, and five 

water-producing zones in the Lower Floridan aquifer supply 

the remaining 16.5 percent. An upward gradient was indicated 

from the ambient flowmeter survey. Under ambient conditions, 7.6 gallons per minute of groundwater was detected 

entering the borehole between 750 and 1,069 feet (ft) below 

land surface, then moved upward, and exited the borehole 

into lower-head zones located between 333 and 527 ft. During 

a survey of the completed Lower Floridan well, six distinct 

water-producing zones were identified; one 17-ft-thick zone at 

768–785 ft yielded 47.9 percent of the total pumpage while the 

remaining five zones yielded between 2 and 15 percent each.

The following aquifer characteristics were determined 

on the basis of evaluation of the packer-slug tests and aquifer 

performance tests conducted at the test site:

• The transmissivity of the Upper Floridan aquifer is 

estimated to be 40,000 square feet per day (ft2/day) 

based on analysis of data from two separate multiwell aquifer tests. Storativity values from these tests 

ranged from 0.000228 to 0.000250.

• The transmissivity of the Lower Floridan is estimated 

to be 10,000 ft2/day based on analysis of drawdown 

and recovery data from a single-well test of the 

completed Lower Floridan well.

• The transmissivity of the combined Upper and Lower 

Floridan aquifer is estimated to be 50,000 ft2/day 

based on analysis of data from drawdown and recovery 

data collected during a flowmeter survey.

• The confining unit separating the Upper and Lower 

Floridan aquifers is approximately 160 ft thick, as 

determined from pumping flowmeter surveys.

• Horizontal hydraulic conductivity measurements range 

from 0.2 to 3 feet per day (ft/d) from four separate 

packer-slug tests of the middle confining unit, and 

2 ft/d from two separate packer-slug tests of the 

Lower Floridan aquifer.

References

Bouwer, H., and Rice, R.C., 1976, A slug test method 

for determining hydraulic conductivity of unconfined 

aquifers with completely or partially penetrating wells: 

Water Resources Research, v. 12, p. 423–428.

Clarke, J.S., Hacke, C.M., and Peck, M.F., 1990, Geology 

and ground-water resources of the coastal area of Georgia: 

Georgia Geologic Survey Bulletin 113, 106 p.

Falls, W.F., Harrelson, L.G., Conlon, K.J., and 

Petkewich, M.D., 2005, Hydrogeology, water quality, 

and water-supply potential of the Lower Floridan aquifer, 

coastal Georgia 1999–2002: U.S. Geological Survey 

Scientific Investigations Report 2005–5124, 98 p.

Georgia Environmental Protection Division, 2003, Interim 

strategy for permitting Lower Floridan withdrawals in 

coastal Georgia: Memorandum issued January 28, 2003, 

Nolton Johnson, Chief, EPD Water Resources Branch.

Halford, K.J., 2006, Documentation of a spreadsheet for timeseries analysis and drawdown estimation: U.S. Geological 

Survey Scientific Investigations Report 2006–5024, 38 p.

Hantush, M.S., 1960, Modification of the theory of leaky 

aquifers: Journal of Geophysical Resources, v. 65, 

p. 3713–3725.

Hantush, M.S., and Jacob, C.E., 1955, Non-steady flow in 

an infinite leaky aquifer: Transactions of the American 

Geophysical Union, v. 36, p. 95–100. 

McCollum, M.J., and Counts, H.B., 1964, Relation of saltwater encroachment to the major aquifer zones Savannah 

area, Georgia and South Carolina: U.S. Geological Survey 

Water-Supply Paper 1613–D, 26 p.

Miller, J.A., 1986, Hydrogeologic framework of the Floridan 

aquifer system in Florida and in parts of Georgia, Alabama, 

and South Carolina: U.S. Geological Survey Professional 

Paper 1403–B, 91 p.

Pandit, N.S., and Miner, R.F., 1986, Interpretation of slug test 

data: Ground Water, v. 24, p. 743–749.

Theis, C.V., 1935, The relation between the lowering of the 

piezometric surface and the rate and duration of discharge 

of a well using groundwater storage: Transactions of the 

American Geophysical Union, v. 16, p. 519–524.
Manuscript approved on March 23, 2010

For more information about this publication, contact:

USGS Georgia Water Science Center

3039 Amwiler Road

Atlanta, GA 30360

telephone: 770-903-9100

http://ga.water.usgs.gov/

Edited by Kay E. Hedrick

Layout by Caryl J. Wipperfurth
Williams—Summary of Hydrologic Testing of the Floridan Aquifer System at Hunter Army Airfield, Chatham County, Georgia—Open-File Report 2010–1066