Prepared in cooperation with the 

City of Lawrenceville 

Methods and Hydrogeologic Data from 

Test Drilling and Geophysical Logging Surveys 

in the Lawrenceville, Georgia, Area 

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Fo at on 

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Boreho e-camera mages show ng 

down-ho e v ew ( eft) and s de v ew (r ght) 

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Open-File Report 2004-1366 

U.S. Department of the Interior 

U.S. Geological Survey 

Methods and Hydrogeologic Data from Test Drilling 

and Geophysical Logging Surveys in the 

Lawrenceville, Georgia, Area

By Lester J. Williams, Phillip N. Albertson, Donna D. Tucker, and Jaime A. Painter

U.S. Department of the Interior

U.S. Geological Survey

In cooperation with the City of Lawrenceville, Georgia

Open-File Report 2004-1366
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.

Suggested citation: Williams, L.J., P.N. Albertson, D.D. Tucker, and J.A. Painter, 2004, Methods and hydrogeologic data 

from test drilling and geophysical logging survey in the Lawrenceville, Georgia, area: U.S. Geological Survey, Open-File 

Report 2004-1366, p. 38.
 iii

Contents

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

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

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of the Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Water Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Geologic Setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Hydrogeologic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Well-Naming System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Supplemental Data on CD–ROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Methods of Data Collection and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Test-Well Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Air-Percussion Rotary Drilling and Well Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Lithologic Sampling and Determination of Rock Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Well Development and Short-Term Yield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Geophysical Logging and Borehole-Camera Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Caliper Logging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Natural-Gamma Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Resistivity Logging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Fluid-Temperature and Fluid-Resistivity Logging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Borehole-Televiewer Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Borehole-Camera Surveys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Characterization of Fractures in Open Boreholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Determination of Type, Depth, and Orientationof Fractures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Identification of Water-Bearing Fractures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Estimating Yield Contribution from Individual Water-Bearing Fractures. . . . . . . . . . . . . . . . . . . . . . . . . . 14

Estimating Yield during Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Flowmeter Surveys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Aquifer Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Packer Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Water-Level Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Hydrogeologic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Fracture Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Individual Fracture Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Joints, Open Joints, and Zones of Joint Concentration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Foliation Partings and Major Foliation Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Dissolution Openings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Irregular-Shaped Voids and Fractures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Flowmeter Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Aquifer-Test Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Aquifer-Test Yield, Drawdown, and Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Direction and Magnitude of Drawdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
iv 

Packer-Test Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Water-Level Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figures

1. Map showing location of study area in Gwinnett County and well locations in 

Lawrenceville, Georgia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Lithologic map showing distribution of principal lithologic units and bedrock well locations,

Lawrenceville, Georgia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

3. Schematic diagrams illustrating how the strike and dip of a planar feature intersecting a borehole 

are determined. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4. Down-hole packer assembly used during the study showing schematic of packer assembly, and 

photos of pressure transducers secured to top of packer assembly, conductor pipe and perforated

pump sleeve, and lowering packer assembly into well 14FF59, Lawrenceville, Georgia . . . . . . . . . . . . 16

5. Example lithologic units and geophysical log figure showing caliper, gamma, lateral resistivity, 

fluid temperature, and fluid resistivity, Lawrenceville, Georgia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6. Example structure log figure showing rock types, lithologic units, tadpole plots, borehole images, 

and borehole deviation, Lawrenceville, Georgia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7. Flowmeter logs for well 13FF23, showing inflow and outflow from borehole, 

Lawrenceville, Georgia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8. Partial record of water-level hydrograph for well 14FF08 showing effect of pumping at the 

Rhodes Jordan Wellfield, Lawrenceville, Georgia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Tables

1. Description of principal lithologic units in the Lawrenceville, Georgia, area. . . . . . . . . . . . . . . . . . . . . . . . . .6

2. Location and well construction information for the Lawrenceville. Georgia, area . . . . . . . . . . . . . . . . . . . .8

3. Description of borehole geophysical tools used in the Lawrenceville, Georgia, area. . . . . . . . . . . . . . . 10

4. Geophysical logs collected in the Lawrenceville, Georgia, area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5. Depth, yield, and structural features of water-bearing fracture zones in the Lawrenceville, 

Georgia, area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6. Observations from ambient and pumping flowmeter surveys, Lawrenceville, Georgia, area . . . . . . . 23

7. Drawdown, pumping rate, and specific capacity of wells during aquifer tests in the 

Lawrenceville, Georgia, area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

8. Fracture depth, straddle depths, and hydraulic response observed during packer testing of 

well 14FF59, Lawrenceville,Georgia, area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

9. Water levels in wells, October 31, 2001, Lawrenceville, Georgia, area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

10. Range of dates where continuous water-level data are available and influence from pumping,

Lawrenceville, Georgia, area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
 v

Conversion Factors and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

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

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Specific capacity

gallon per minute per foot [(gal/min)/ft)] 0.2070 liter per second per meter [(L/s/m]

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32) / 1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 (NGVD 29).

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

Altitude, as used in this report, refers to distance above the vertical datum.
Methods and Hydrogeologic Data from Test Drilling 

and Geophysical Logging Surveys in the 

Lawrenceville, Georgia, Area

By Lester J. Williams, Phillip N. Albertson, Donna D. Tucker, and Jaime A. Painter

Abstract

Thirty-two wells, ranging in depth from 180 to 630 feet, 

were used to study the bedrock lithology, fracture, and wateryielding characteristics in the Lawrenceville, Georgia, area. 

These data were compiled to determine what geologic structures, if any, contribute to the development of increased permeability and high ground-water yield in the area. Methods used in 

this study include test-well drilling, geophysical logging and 

borehole-camera surveys, flowmeter surveys, aquifer testing, 

packer testing, and water-level monitoring.

Water-bearing fractures identified in open boreholes of 

wells include: joints, open joints, and zones of joint concentration; foliation partings and major foliation openings along foliation and layering of the rock; dissolution openings along mineral 

infillings; and irregular voids and fractures. Most of the joints 

observed in the boreholes appeared as tight hairline fractures 

and typically were not significant water-bearing zones. Moderate to small amounts of water—from 1 to 5 gallons per minute 

(gal/min)—are produced from open, steeply-dipping joints and 

zones of joint concentration. Foliation partings and major foliation openings, which form “foliation parallel-parting systems” 

in the area, yielded large quantities of water to open boreholes. 

Foliation partings typically yielded from 1 to 15 gal/min, with a 

maximum value of about 63 gal/min. In some boreholes, groups 

of foliation partings form significant water-bearing zones yielding as much as 50 gal/min. Major foliation openings yield substantially more water than the smaller foliation partings, with a 

typical range from 50 to 100 gal/min. Major foliation openings 

are the primary water-producing features responsible for highyield wells in the area. In a few wells, dissolution openings 

along mineral infilled joints or veins had yields as much as 

35 gal/min, indicating the potential importance of dissolution 

features in the bedrock.

Flowmeter surveys, aquifer tests, packer tests, and waterlevel monitoring provided additional hydrologic information on 

water-bearing fractures in the study area. These data were used 

to help confirm the depth and yield contribution from various 

types of water-bearing fractures, indicate the hydraulic characteristics of these fractures, and show the hydraulic response of 

the aquifer system to pumping.

Collectively, the data from this study indicate that foliation 

parallel-parting systems, consisting of discontinuous zones of 

foliation partings and major foliation openings, strongly influence the yields of wells in the Lawrenceville area. Wells tapping 

these systems are capable of sustaining large ground-water 

withdrawals for extended periods of time, as indicated from the 

continuous operation of the Rhodes Jordan Wellfield since 1995. 

Open-hole water levels, flowmeter surveys, and preferential 

drawdown parallel to foliation and compositional layering all 

indicate a general hydraulic confinement of foliation parallelparting systems, and indicate a strong lithologic and structural 

control on the development of these water-bearing fracture systems.

Foliation parallel-parting systems are easily identified in 

boreholes using geophysical methods described in this report. 

The yield potential of foliation parallel-parting systems within 

an individual topographic basin or several topographic basins 

can be large, depending on the areal extent of the waterbearing zones and the interconnectivity of these zones with 

sources of recharge.

Introduction

There is a great need to assess the ground-water resources 

of the crystalline-bedrock aquifer in the Piedmont and Blue 

Ridge physiographic provinces of Georgia (fig. 1). Ground 

water in this region could be used to supply water to small communities or supplement the larger surface-water systems in 

times of drought, for emergency supplies, or as a long-term continuous source to increase the capacity of these systems to meet 

future supply demands. In any given area, however, little information generally is available to assess the potential of developing a water supply from these complex aquifer systems. Despite 

this lack of information, large ground-water supplies1

 have 

been developed in many parts of the region (Carter and Herrick, 

1951; Cressler and others, 1983; Herrick and LeGrand, 1949; 

Radtke and others, 1986; Thomson and others, 1956).

1

Large ground-water supplies typically have been defined in the literature as 25 gallons per minute (gal/min) or greater. 

In this report, 75 gal/min or greater generally is used to indicate a large supply.
14FF10,14FF16,14FF17

14FF18,14FF26,14FF3614FF37,14FF39

13FF23

13FF22 13FF21

13FF20

13FF19

13FF18

13FF17

14FF58

14FF57

14FF55 14FF56

14FF54

14FF53

14FF52

13FF16

13FF15

14FF50

14FF49

14FF47

14FF46

13FF13

14FF

14FF27

13FF12

13FF24

13FF25

14FF61

13FF14 Rhodes Jordan Wellfield

14FF08

Maltbie Street Wells

84°02' 84° 83°58'

33°56'

33°58'

Gwinnett

County

Lawrenceville

GEORGIA YELLOW RIVER BASIN ALCOVY RIVER 

Sugarloaf Parkway

124

20

20

29

29

120

316

AIRPORT

Lawrenceville-Suwanee Rd

LAWRENCEVILLE

Redland Creek

Pew Creek

Yellow

Rive

r

Shoal

0 1 

0.5 1

0 1 2 KILO

0.5 1.5

Base from U.S. Geological Survey 1:24,00Lawrenceville city limit from City of Lawren

EXPLANATION

River basin divide

13FF13 Well and site name

Figure 1. Location of study area in Gwinnett County and well locations in Lawrenceville, Georgia.
Introduction 3

The U.S. Geological Survey (USGS), in cooperation with 

the City of Lawrenceville, began collecting lithology, fracture2, 

yield, and water-level data from bedrock wells during December 1994 to investigate the geology and ground-water resources 

of the Lawrenceville area. Major objectives of the Lawrenceville study were to: (1) evaluate the regional hydrogeologic setting, (2) delineate and characterize subsurface discontinuities 

and fractures that control aquifer permeability, and (3) monitor 

the response of the bedrock ground-water system to local 

ground-water pumping. To accomplish these objectives, the 

USGS completed local- and site-specific studies between 1995 

and 2002. The local studies entailed compiling detailed hydrogeologic information on private and publicly owned wells in the 

vicinity of Lawrenceville and preparing a 1:24,000 geologic 

map of the study area (Chapman and others, 1999). The sitespecific studies included a test-well drilling program and collection of geophysical logging data needed to characterize the 

distribution of lithology and fractures in the subsurface. Detailed

subsurface lithology, fracture, and yield data—which are a 

focus of this report—were compiled to determine what geologic 

structures, if any, contribute to the development of increased 

permeability and high ground-water yield3

 in the area.

Purpose and Scope

This report describes the methods used and data resulting 

from test drilling and geophysical logging surveys conducted 

between December 1994 and October 2001. Included in this 

report are:

• methods of collecting and analyzing data;

• fracture data showing the depth, nature, and yield 

of different types of water-bearing fractures;

• aquifer-test data showing the yield of wells and the 

direction and magnitude of drawdown;

• packer-test data showing the hydraulic response 

among high-yield fractures; and

• water-level data showing fluctuations in ground-water 

levels in response to seasonal variations in precipitation 

and from local ground-water withdrawals.

The test-drilling program included field observations during 

drilling, lithologic sampling, and descriptions of rock samples. 

Geophysical logging and borehole-imaging techniques were 

used extensively to characterize lithology and fractures in openbedrock wells. The scope of this report includes lithologic and 

borehole geophysical logs from 32 wells, flowmeter surveys 

from 12 wells, aquifer-test data from 9 wells (total of 10 tests), 

packer-test data from 1 well, and continuous water-level data 

from 26 wells. Images of subsurface fractures and other structures are included to document the types of bedrock fractures 

and small-scale structural features common in the study area.

Description of the Study Area

The 44-square mile (mi2) study area includes the City of 

Lawrenceville and adjacent areas in Gwinnett County (fig. 1). 

The study area is in the Piedmont physiographic province—an 

area underlain by igneous and metamorphic crystalline rocks. 

In Georgia, the Piedmont lies between the Valley and Ridge and 

Blue Ridge provinces to the north and the Coastal Plain province to the south (fig. 1). Topography consists of low hills and 

moderately entrenched stream valleys that range in altitude 

from 780 feet (ft) to 1,170 ft. Lawrenceville is on a major drainage divide that separates the Yellow and Alcovy River Basins 

(fig. 1). To the west, the Lawrenceville area is drained by Redland Creek, Pew Creek, and tributaries of the Yellow River. 

To the east, the Lawrenceville area is drained by Shoal Creek 

and tributaries of the Alcovy River.

Water Use

In Gwinnett County, water use totaled about 90.5 million 

gallons per day (Mgal/d) during 2000 (Fanning, 2003). Of 

this amount, only about 0.5 Mgal/d were withdrawn from 

ground-water sources. Of the 0.5 Mgal/d withdrawn from 

ground-water sources, 80,000 gallons per day (gal/d) were 

used for commercial purposes, 390,000 gal/d for public supply, 

and 10,000 gal/d for livestock. From the surface-water sources, 

only 80,000 gal/d were used for livestock and the remainder 

(90 Mgal/d) was used for public supply.

Lawrenceville currently (2003) uses about 2.5 Mgal/d for 

public supply, of which about 120,000 to 140,000 gal/d is 

obtained from ground-water sources (Mike Bowie, City of 

Lawrenceville, oral. commun., 2002). The Rhodes Jordan 

Wellfield (fig. 1) currently (2003) is the only operating active

wellfield in the Lawrenceville area, and has two production 

wells that are alternately pumped at rates of 200–250 gallons 

per minute (gal/min) for 10 or more hours per day. The wellfield was refurbished in the early 1990s and has been in continuous operation since 1995. Historically, ground water also was 

withdrawn from another well site located on Maltbie Street 

(fig. 1). A replacement well for the Maltbie Street well was 

drilled in the late 1990s but was never put into production 

because of local ground-water contamination near that site. 

More recently, six of the test wells drilled for this study were 

converted into production wells by the City of Lawrenceville. 

These new production wells, combined with wells at the Rhodes 

Jordan Wellfield, are capable of producing a combined estimated yield of approximately 2 Mgal/d (Mike Bowie, City of 

Lawrenceville, oral commun., 2002).

2In this report, “fractures” refer to openings along foliation planes, joints, and brittle fractures related to faulting.

3

In this report, “high ground-water yield” refers to areas where wells have a reported yield of 70 gal/min or greater. 

Cressler and others (1983) defined “high-yield” as 25 gal/min or greater.
4 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Geologic Setting

The geologic setting of the Lawrenceville area varies substantially from location to location, primarily because of the 

complex structural deformation of the bedrock. The general 

history of structural deformation includes thrust faulting, largescale folding and faulting, partial melting of preexisting rocks 

forming migmatites, and syntectonic to post-tectonic intrusion 

of granitic bodies. Atkins and Higgins (1980), Higgins and others (1984, 1988, 1998), McConnell and Abrams (1984), and by 

Chapman and others (1999) described the geology of the region. 

Crawford and others (1999) described the revision of the stratigraphic nomenclature for the geologic units in the study area.

Chapman and others (1999) divide the various rock types in 

the Lawrenceville area into seven principal lithologic units: 

amphibolite, biotite gneiss, button schist, granite gneiss, magnetite quartzite, quartzite/aluminous schist (quartzite/schist), 

and diabase dikes (fig. 2, table 1). The principal lithologic units 

represent mappable rock groups correlated based on dominant 

rock types. Differences in weathering and fracturing in the principal lithologic units produce a wide variation in the hydrologic 

properties of these units.

The principal lithologic units penetrated in wells drilled in 

the study area include amphibolite, biotite gneiss, button schist, 

granite gneiss and quartzite/schist (fig. 2). For the most part, all 

of these units, excluding the granite gneiss, are compositionally 

layered, consisting of several to many rock types in each unit. 

The compositional layering varies from finely laminated (individual layers only tenths of inches thick) to thinly layered (typically less than 6 inches) and, in fewer instances, thickly layered 

(typically greater than 6 inches). All of these units also may be 

massive; in particular, large bodies of massive granite gneiss 

and biotite gneiss crop out throughout the area.

The amphibolite consists of fine- to medium-grained, darkgreen to greenish-black, massive to finely laminated, hornblende-plagioclase and plagioclase-hornblende amphibolite 

(Chapman and others, 1999). This unit, interlayered with biotite 

gneiss, is penetrated by many high-yield wells in Lawrenceville 

and forms a significant water-bearing unit.

The biotite gneiss consists of medium- to coarse-grained, 

gray to grayish-brown, to dark-gray biotite-rich gneiss (Chapman and others, 1999) and forms a significant water-bearing 

unit where it is interlayered with amphibolite. This unit generally is schistose in texture and locally contains lenses and pods 

of hornblende-plagioclase amphibolite.

The button schist consists of medium- to coarse-grained, 

dark-gray to brownish-gray garnet schist with interlayered 

biotite gneiss and scarce amphibolite (Chapman and others, 

1999). This unit generally has a sheared texture, and there is 

evidence that the button schist was derived from shearing of 

biotite gneiss (Higgins and others, 1998). The button schist is 

named for its weathering characteristic that yields mica concentrations that resemble “buttons.” The button schist generally is 

not considered a significant water-bearing unit in the 

Lawrenceville area; however, several high-yield wells derive 

water from this unit.

The granite gneiss consists of a light gray to white, mediumgrained, muscovite-biotite-feldspar-quartz gneiss. This unit 

generally is a poor water-bearing unit in the area.

The quartzite/schist consists of quartz-rich schist, muscovite schist, and layers of resistant quartzite. The quartzite/schist 

is penetrated by only two wells. No large water-bearing zones 

were identified in the quartzite/schist at these two wells. 

Diabase and magnetite quartzite are not penetrated by any 

wells used in this study and are not discussed further.

Large-scale structural features in the Lawrenceville area 

include a northeast-southwest trending, doubly-plunging 

synform in the central and eastern part of the study area, and an 

east-west-trending synform in the western part of the study area 

(fig. 2). Through the main part of the city, the lithologic units 

generally strike east-west and dip gently to the south. Each 

principal lithologic unit shown in figure 2 is bounded by thrust 

faults; the outcrop patterns are typical of those that result from 

eroded open folds.

Hydrogeologic Setting

Ground water fills joints, fractures, and other secondary 

openings in bedrock and pore spaces in the overlying mantle of 

soil, saprolite, alluvium, and weathered rock. In this report, the 

soil, saprolite, alluvium, and weathered rock are collectively 

referred to as regolith.

Ground-water recharge to the regolith and underlying bedrock is mainly through infiltration of precipitation at the land 

surface. The infiltrating water collects in the regolith and 

recharges the bedrock fracture system underlying it. Because 

regolith has a much higher storage capacity than bedrock, the 

regolith can be conceptualized as a ground-water reservoir or 

“sponge” that feeds the underlying bedrock. Joints, weathered 

zones, dissolution openings, and zones of brittle faults in bedrock and combinations of these features also can store a substantial quantity of water.

The storage capacity and depth of weathering of the 

regolith/bedrock fracture system is influenced largely by differences in the weathering character of various rock types. These 

variations in weathering are most apparent from geologic field 

mapping; rocks more resistant to weathering were observed to 

form pavement rock outcrops in streams and some hilltops; 

whereas, rocks less resistant to weathering were observed to 

form thick saprolite. The depth of casing of bedrock wells 

(table 2) also is a general indication of the depth of weathering. 

In the Lawrenceville area, saprolite generally is thicker on feldspar-rich rocks and thinner on quartz-rich rocks. The biotite 

gneiss unit (Chapman and others, 1999) is particularly susceptible to deep weathering and typically forms a thick saprolite 

above the bedrock. Mafic rocks (such as amphibolite), because 

of the general lack of feldspar, typically are characterized by 

thin saprolite development. In layered rocks, saprolite forms 

between layers of otherwise hard bedrock. In the Lawrenceville 

area, this occurs where chemically less resistant rock (such as 

biotite gneiss) is compositionally layered with more resistant 

rock (such as amphibolite).
34°

84° 83°56'

33°56'

0

0

1 2 MILES

1 2 KILOMETERS

14FF59

14FF42

14FF58

14FF52

14FF46

13FF15

13FF21

13FF23

13FF19

14FF57

14FF47

13FF22

13FF18

14FF55

14FF56

14FF53

13FF20

13FF16

13FF12

14FF49

13FF17

14FF08

14FF50

14FF27

13FF14

13FF13 14FF26

14FF17 14FF18

14FF39

14FF16

14FF10

LAWRENCEVILLE

Maltbie Street 

wells

Rhodes Jordan

Wellfield

Base modified from U.S. Geological Survey 1:24,000-scale digital data

Lawrenceville and Luxomni, 1992

Airport

Amphibolite

Biotite gneiss

Button schist

Granite gneiss

Quartzite/schist

Diabase dike

EXPLANATION

Principal lithologic unit

Well—Only bedrock wells shown

Synform

General strike and dip 

 of foliation parallel to 

 compositional layering

Double plunging

Yield of 100 gallons per minute or more 

Yield of less than 100 gallons per minute

Gwinnett

County

Lawrenceville

GEORGIA

Introduction 5

Figure 2. Distribution of principal lithologic units and bedrock well locations, Lawrenceville, Georgia 

(modified from Chapman and others, 1999). See table 1 for description of principal lithologic units.
6 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Table 1. Description of principal lithologic units in the 

Lawrenceville, Georgia, area (from Chapman and others, 1999).

Amphibolite unit (a) – Fine- to medium-grained, dark green to 

greenish-black, ocher weathering, massive to finely layered, locally 

laminated, locally pillowed, locally chloritic, commonly garnetiferous, locally magnetite-bearing, generally pyrite-bearing, generally 

epidotic, hornblende-plagioclase and plagioclase-hornblende 

amphibolites with minor amounts (generally less than a very small 

fraction of 1 percent) of fine- to medium-grained, generally amphibole-bearing, granofels. The final weathering product of the amphibolite is a very characteristic dark red clayey soil.

Biotite Gneiss unit (bg) – Gray to grayish-brown to dark gray, 

medium- to coarse-grained, commonly schistose, generally pegmatitic (biotite-muscovite-quartz-potassium-feldspar pegmatites), 

biotite-rich gneiss with generally rare but locally fairly common 

layers, lenses, and pods of hornblende-plagioclase amphibolite. 

Characteristically and commonly contains small pods and lenses of 

altered meta-ultramafic rocks. The biotite gneiss weathers to a 

uniform, slightly micaceous, dark-red saprolite and clayey dark red 

soil; vermiculitic mica is characteristic of soils formed from the 

biotite gneiss.

Button Schist unit (bs) – Dark gray to brownish-gray, mediumto coarse-grained, lustrous (where fresh), (± chlorite)-garnetbiotite-muscovite-plagioclase-(± microcline)-quartz button schist 

with tiny black opaques. In most outcrops the schist contains large 

muscovite fish that weather to buttons. The button schist is resistant 

to weathering.

Diabase (dia) – Fine- to medium-grained, dark gray to black augite 

diabase, in dikes generally 16 to 66 feet wide. The diabase weathers 

to a dark red clayey soil containing speheroidal boulders with fresh 

rock inside an armoring, ocherous rind. 

Granite Gneiss unit (gg) – Complex of granite and granitic gneiss. 

Light gray to whitish-gray, medium-grained muscovite-biotitemicrocline-oligoclase-quartz gneiss having well defined gneissic 

layering. Most commonly is poorly foliated. Pavement outcrops, 

“whale-back” outcrops, and boulder outcrops are characteristic of 

this granite gneiss. Where deeply weathered, the gneiss forms thin 

light whitish-yellow sandy soils.

Magnetite quartzite (mq) – Thinly layered (0.4 inch) to laminated, 

medium-grained, magnetite quartzite in units about 1 to 20 feet 

thick. Commonly has thin (from 0.4 to 1.6 inches) quartz-magnetite 

layers, with magnetite crystals as much as 0.4 inch in size, but commonly about 0.04 inch. The quartz-magnetite layers alternate with 

quartz layers without magnetite, or quartz layers with a small percentage of magnetite, from about 1.6 to 3.2 inches thick. Magnetite 

clumps that generally disrupt the layering are locally as large as 

8 inches, but are commonly about 0.4 inch.

Quartzite/Schist unit (qs) – White to yellowish, sugary, to vitreous, 

slightly graphitic to nongraphitic quartzite with accessory muscovite, garnet and aluminosilicate minerals (kyanite, staurolite, or sillimanite), in layers from about 1 to 4 feet thick, interlayered with 

feldspathic quartzite and garnetiferous quartz-muscovite or muscovite-quartz schist. The aluminous schist part of the unit is commonly 

a tan to yellow weathering, sheared or button-textured, commonly 

quartzose, garnet-biotite-plagioclase-muscovite-quartz schist that 

generally contains kyanite or staurolite.

Well-Naming System

In this report, wells are named using a system based on USGS 

71⁄2-minute topographic quadrangle maps. Each topographic map 

in Georgia has been assigned a number and letter designation beginning at the southwestern corner of the State. Numbers increase eastward through 39; letters advance northward through “Z,” then doubleletter designations “AA” through “PP” are used. The letters “I,” 

“O,” “II,” and “OO” are not used. Wells inventoried in each quadrangle are named sequentially beginning with “1.” Thus, the 55th 

well inventoried in the Lawrenceville 7.5 minute quadrangle (designated 14FF) in Gwinnett County is designated as well 14FF55.

Supplemental Data on CD–ROM

Supplemental data on this CD–ROM include detailed lithology, fracture, yield, and water-level data collected at various wells 

in the study area. These data are presented in a nonproprietary 

Geographic Information System (GIS) database file format that 

includes geographic and tabular data. A copy of ArcExplorer®, a 

free GIS data viewer developed by Environmental Systems 

Research Institute, is included on this CD–ROM for use with the 

GIS database and allows a user to view the data spatially and query 

the data of interest. In addition, much of the data are linked to a 

hypertext markup language (HTML) document to allow a user to 

access and view the data tables through text and Adobe® Portable 

Document Format (PDF) files. A description of the GIS data and 

figures contained on this CD–ROM is provided in the section 

“Organization and Presentation of Hydrogeologic Data.”

Acknowledgments

The authors gratefully acknowledge former Mayor Bartow 

Jenkins, former Director of Public Works Don Martin, City Clerk 

Bob Baroni, and the Lawrenceville City Council for their support 

during the cooperative water-resource investigations. We thank 

Lawrenceville Water Department Superintendent Jim Steadman, 

and Water Plant Operators Mike Bowie and Robert Paul for their 

valuable assistance in constructing roads, obtaining digging permits, 

and their continued day-to-day support during this study. Many 

USGS employees were involved with data collection during this 

study. We are especially grateful to Melinda Chapman, who made 

large contributions to the study from 1995 to 2000. Other USGS 

employees who contributed substantially to the study include Adrian 

Addison, Dianna Crilley, Joshua Lawson, Chris Leeth, Kristen 

McSwain Bukowski, Michael Peck, and Todd Tharpe. We also are 

very grateful to Thomas J. Crawford, Professor Emeritus of Geology, and Randy L. Kath, Associate Professor of Geology at the 

Department of Geological Sciences, State University of West 

Georgia, whose concepts and knowledge were extremely valuable 

in developing a better understanding of geology and the hydrogeology of the area; each spent numerous days working either directly 

or indirectly with the authors. Finally, we thank Caryl Wipperfurth 

who prepared the report figures and spent many hours compiling 

and editing data included on the CD–ROM, Steve Craigg who provided technical and editorial reviews, and Patricia Nobles who 

carefully edited and prepared the final manuscript for publication.
Introduction 7

Table 2. Location and well construction information for the Lawrenceville, Georgia, area. 

[ft, foot; in., inch; gal/min, gallons per minute; —, data not collected. Geologic units: a, amphibolite; bg, biotite gneiss; bs, button schist; gg, granite gneiss; 

qs, quartzite/schist. Casing type: stl, steel; PVC, polyvinyl chloride. Source: Coordinates and altitudes, E&C Consulting Engineers, Inc.]

Well

name Latitude Longitude

Land surface 

altitude 

(ft)

Top of casing 

altitude 

(ft)

Well 

depth 

(ft)

Casing 

depth 

(ft)

Casing 

diameter 

(in.) and type

Ream 

depth

(ft)

Well

 yield 

(gal/min)

Geologic 

units 

penetrated

Bedrock wells

13FF12 33°57'50.33" -83°59'54.40" 1,040.0 1,040.12 265.0 54.0 6–stl — 1254 bg, bs, bg, a

13FF13 33°57'21.06" -84°00'24.96" 972.3 976.13 448 19 6–PVC — 1135 a, bg, a, qs, bs, a

13FF14 33°57'41.77" -84°00'06.77" 987.9 991.09 285 22.8 10–stl — 1140 a, bg

13FF15 33°58'12.01" -84°00'24.10" 1,053.2 1,054.61 605 55 10–stl 250 1250 bg

13FF16 33°57'44.97" -84°00'39.10" 1,004.7 1,006.32 605 32 10–stl 252 175 a, bs, a, bg

13FF172 33°57'11.05" -84°01'19.08" 990.9 994.04 480 15 6–PVC — 390 a

13FF182 33°57'21.14" -84°00'48.13" 953.8 955.76 550 55 8–stl 200 3100

4150

a

13FF192 33°56'02.62" -84°01'04.11" 921.8 923.58 477 65 8–stl 275 3250 4

350–400

a

13FF202 33°57'43.95" -84°01'16.52" 990.1 992.06 455 69 6–PVC — 335 a, bs

13FF212 33°56'40.90" -84°02'11.03" 889.4 891.5 505 40 8–stl 277 3130

4

125

bg, a

13FF222 33°56'45.88" -84°01'07.44" 929.7 932.99 600 23 6– PVC — 3100 a, bg

13FF232 33°56'22.72" -84°01'43.98" 906.2 908.04 498 30 8–stl 270 3250 4

350–400

a, bg, bs

14FF08 33°57'39.24" -83°59'39.62" 1,019.8 1,020.89 352 28 8–stl — 1400 a, bs, bg, gg

14FF10 Not available Not available 994.2 996.09 386 20 8–stl — 1270 a

14FF16 Not available Not available 994.2 998.69 320 30.5 10–stl 210 1471 a, bs

14FF17 33°57'33.49" -83°58'46.47" 990.9 992.07 212 25 6–stl — 3150 a

14FF18 33°57'32.62" -83°58'42.65" 999.3 1,001.09 180 24 6–stl — 3100 a

14FF26 33°57'33.97" -83°58'44.76" 993.4 996.14 380 33 6–stl — — a, bg, bs, a, bg

14FF27 33°57'20.32" -83°59'42.65" 1,048.3 1,050.7 600 59 6–stl — 3150 gg, bg, qs, a, bs

14FF39 33°57'34.12" -83°58'44.81" 993.4 996.09 180 36 6–stl — 3150 a

14FF42 33°58'38.81" -83°57'23.55" 1,028.2 1,029.67 599.0 35 8–stl — 110.0

5

0.1

a, bs, bg

14FF46 33°57'52.51" -83°58'47.58" 1,022.9 1,028.46 301 9 6–stl — 370 a, bs, bg

14FF47 33°56'34.71" -83°59'43.20" 1,004.2 1,006.07 300 39.5 6–PVC — 325 bg

14FF49 33°57'47.63" -83°59'49.41" 1,041.7 1,044.79 400 80.5 6–PVC — 310 bg, gg

14FF50 33°57'40.32" -83°59'43.13" 1,019.3 1,023.31 387 77.5 10–stl 275 1300 a, bs, bg, gg

14FF52 33°58'06.16" -83°58'11.22" 1,082.3 1,083.57 630 22 6–PVC — 340 a, bs, bg

14FF53 33°56'57.58" -83°57'07.96" 967.7 969.43 605 29 6–PVC — 350 bs, a, gg

14FF552 33°57'06.68" -83°58'21.28" 969.6 971.87 450 63 8–stl 301 3250

4

325

bg, a

14FF562 33°57'12.09" -83°57'41.11" 936.3 937.86 600 25 6–PVC — 360 a, bs, bg

14FF572 33°55'15.22" -83°59'41.63" 954.1 956.47 380 35.5 6–PVC — 33 bg

14FF582 33°58'43.29" -83°59'31.79" 1,030.2 1,031.98 550 34 6–PVC — 31 gg

14FF592 33°59'02.07" -83°56'58.91" 952.1 954.19 470 35 8–stl 400 3180 4350–400a, bs, bg
8 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Methods of Data Collection 

and Analysis

A variety of methods were used to collect and analyze 

data during this study. These methods consisted of indirect and 

direct measurement of various hydrologic and geologic properties by test-well drilling, geophysical logging and boreholecamera surveys, flowmeter surveys, aquifer testing, packer 

testing, and water-level monitoring.

Test-Well Drilling

Test-well drilling was used to obtain detailed subsurface 

information about rock types, fracture zone(s), rock fabrics, and 

hydrologic characteristics of water-bearing zones. Many of the 

wells were drilled using air-percussion rotary methods and constructed as open-hole wells. Two existing wells, 14FF10 and 

14FF08, reportedly were drilled using the cable-tool method. 

A list of wells, locations, and construction details is provided 

in table 2. Well locations are shown in figures 1 and 2.

Air-Percussion Rotary Drilling and 

Well Construction

Air-percussion rotary drilling was used for constructing test 

wells during the study. This drilling technique, which uses a 

down-hole air hammer, is the most suitable drilling method in 

crystalline-rock formations and also is rapid and inexpensive. 

The method uses air as a circulating medium to cool the air 

hammer, bring drill cuttings to the surface, and maintain borehole integrity. When drilling, the cuttings are removed from the 

borehole using high-pressure air. The air that is circulated also 

cools the drill bit as it circulates from inside the drill rod and out 

and around the bit. Water is added to the air stream when the 

borehole does not produce sufficient amounts of water to carry 

rock cuttings to land surface.

Test wells were constructed by (1) advancing an 8- to 

12-inch-diameter borehole through unconsolidated soil, 

saprolite and the upper portion of bedrock; (2) grouting a 

polyvinyl chloride (PVC) surface casing to seal off the upper 

zones; and (3) drilling a 6-inch-diameter borehole into the 

underlying bedrock. When discussing fractures, yield, or 

other physical features within the open portion of the test well 

(below the surface casing) the term borehole is used hereafter. 

The term well is used to describe the performance characteristics of water- bearing zones intersecting the entire length of 

the test well.

Field observations made at the time of drilling included the 

depth, drilling rate, size of cuttings, changes in lithology, and 

color of the drilling fluid. The rate of ground-water production 

from the test well also was monitored to determine the depths of 

water-bearing fractures.

Lithologic Sampling and Determination of Rock Type

Rock cuttings collected during drilling were used to determine subsurface lithology and estimate the approximate depth 

of lithologic contacts. Samples were collected in a wire-mesh 

basket placed below the rotary table where water and cuttings 

were returned to the land surface. The wire-mesh basket was 

emptied every 10 ft that the hole was drilled, and the samples 

were washed, cleaned, and dried on a preparation board. Rock 

cuttings were then examined with a hand lens to determine 

approximate mineral and rock-type percentages.

Regolith wells

13FF245 33°56'40.89" -84°02'11.13" 889.4 891.60 16.5 11.5 2–PVC — — Regolith

13FF255 33°56'02.71" -84°01'04.00" 921.6 923.89 16.3 10.3 2–PVC — — Regolith

14FF36 33°57'34.47" -83°58'44.12" 993.4 996.63 — — — — — Regolith

14FF37 33°57'32.67" -83°58'42.66" 1,000 999.98 — — — — — Regolith

14FF605 33°59'02.17" -83°56'59.08" 952.8 955.57 9.3 4.3 2–PVC — — Regolith

14FF615 33°57'06.76" -83°58'20.93" 970.6 972.76 14 9 2–PVC — — Regolith

Table 2. Location and well construction information for the Lawrenceville. Georgia, area. —Continued

[ft, foot; in., inch; gal/min, gallons per minute; —, data not collected. Geologic units: a, amphibolite; bg, biotite gneiss; bs, button schist; gg, granite gneiss; 

qs, quartzite/schist. Casing type: stl, steel; PVC, polyvinyl chloride. Source: Coordinates and altitudes, E&C Consulting Engineers, Inc.]

Well

name Latitude Longitude

Land surface 

altitude 

(ft)

Top of casing 

altitude 

(ft)

Well 

depth 

(ft)

Casing 

depth 

(ft)

Casing 

diameter 

(in.) and type

Ream 

depth

(ft)

Well

 yield 

(gal/min)

Geologic 

units 

penetrated

1

Values for wells 13FF12, 14FF08, 14FF10, and 14FF16 are reported from 

aquifer tests conducted by well driller. Other values are the estimated yield 

from air-lift tests

2Well drilled as part of recent (2001) investigation

3

Reported air-lift yield from 6-inch well

4

Reported air-lift yield from 8-inch well after reaming

5

Five feet of slotted screen used below casing
Methods of Data Collection and Analysis 9

If the sample contained more than 50 percent of a specific 

rock constituent, then the dominant component was listed first, 

followed by the minor component (separated by the “w/” code, 

which is short for “with”). For example, if a sample contained 

between 60 and 80 percent amphibolite with the remainder 

being biotite gneiss, the interval would be identified with the 

code: a-w/bg. Likewise, a sample with predominantly biotite 

gneiss and lesser amounts of amphibolite would be identified 

with the code bg-w/a. Samples with approximate equal 

amounts of different rock types were separated with a dash, 

with the rock types not listed in any specific order of predominance. A sample with equal amounts of amphibolite, biotite 

gneiss, and button schist, for example, would be assigned the 

code a-bg-bs. Samples with more than one minor rock type 

component were identified following the dominant rock code 

and the “w/.” For example, a sample with predominantly 

amphibolite with some biotite-hornblende gneiss and biotite 

gneiss would have the code a-w/bhg-bg.

Using the lithologic unit definitions of Chapman and others 

(1999), the rock types were grouped into one of the seven principal lithologic units (table 1). In general, this grouping was 

based on the dominant rock type identified in the rock-cutting 

samples. If the dominant rock type was amphibolite, for example, with layers and lenses of other rock types, it would be 

assigned to the amphibolite unit. Some weight also was given to 

the gamma log response; a distinctive gamma response in some 

wells was associated with a specific rock unit, such as the button 

schist unit, to define contacts. Most lithologic contacts, however, 

were defined based on rock-cutting samples from the wells.

Determining the precise depth of lithologic contacts was 

complicated by cuttings sloughed off from shallower portions 

of the test well and by having a 10-ft-long sampling interval. In 

the absence of any definitive contact data, such as a distinct 

color change of the return water, the depths of contacts were 

located at the end of the 10-ft-long sampling interval. Two wells 

(14FF26 and 14FF42) were cored, which is the most precise 

method of defining the depths of lithologic contacts.

Some wells did not have any rock cuttings from which to 

produce lithologic logs. For these wells, geophysical logs were 

used to correlate to the lithology observed in nearby wells. 

Lithologic contacts in wells 14FF10, 14FF16, 14FF17, and 14FF18 

(all located in the Rhodes Jordan Wellfield) were based on the 

corehole at well 14FF26 and correlated using geophysical logs. 

Similarly, the depths of lithologic contacts in 14FF08 and 

13FF12 were estimated by correlating to nearby well 14FF50.

Well Development and Short-Term Yield

Drilled, open-hole test wells do not require extensive cleaning or development to prepare them for permanent use. The test 

wells were developed at the end of drilling to clean the open 

portion of the boreholes of drill cuttings and debris and to provide 

a driller’s estimate of short-term yield (the short-term yield is 

estimated by the well driller at the end of the drilling and/or 

development process and is the reported discharge rate that can 

be sustained from the well during a relatively short period of 

time). After drilling to total depth in each well, the driller continued to air lift and discharge water entering the well until the 

return water was relatively clear and did not contain appreciable 

sand or rock fragments. This development process was completed quickly for low-yielding wells but took considerable 

time (3 hours or more) for high-yield wells.

Following well development the driller estimated the shortterm yield. For most test wells, the water being discharged from 

the well was conveyed along a ditch into a 55-gallon drum or a 

calibrated container for measurement. The rate at which water 

was air lifted out of the well was carefully monitored to determine 

the maximum discharge that could be sustained (i.e., short-term 

yield). Well drillers routinely measure short-term yield, and these

measurements are considered reliable indicators of yield compared to short-term aquifer tests (Paillet and Duncanson, 1994).

In some test wells, the drilling rig was “drowned out” before 

reaching the target drilling depth. Air-percussion rotary drilling 

rigs are drowned out when ground water enters the well faster 

than the drilling rig can air lift the water out of the well—typically the result of a bottom-hole fracture. Hence, in drownedout wells, the reported yield at the time of drowning typically is 

less than the actual yield.

Geophysical Logging and Borehole-Camera Surveys

Wells in the Lawrenceville area were logged using various 

geophysical tools and inspected with a submersible borehole 

camera to aid in characterizing the lithology and identifying 

water-bearing zones. Geophysical logs were collected in waterfilled 6- to 10-inch-diameter open boreholes. Table 3 lists the 

logging tools used, types of measurements made, and uses of 

these data. A typical suite of logs from each well consisted of a 

caliper log, natural-gamma log, resistivity logs (short normal, 

long normal, and lateral), fluid resistivity and temperature logs, 

and borehole televiewer image logs. Electromagnetic-conductivity logs also were collected in 21 wells but were not used to 

characterize lithology or identify water-bearing zones. Data 

from the electromagnetic-conductivity logs, however, are 

included on this CD–ROM. The types of logs collected in each 

well are summarized in table 4.

Caliper Logging

Caliper logs were used to measure hole diameter and 

identify open fractures, voids, and other distinct openings in the 

bedrock. The caliper has three spring-mounted arms that 

measure the average diameter of the borehole and, hence, is 

used to identify zones of borehole enlargement typically 

associated with bedrock fractures. Borehole enlargements also 

occur in zones of weaker or more friable rock and, therefore, 

were examined visually using a borehole televiewer and a 

borehole camera to verify the character of the fracture. 

Hairline4 “tight” joints generally could not be distinguished 

using caliper logs.

4

In this report the term hairline is used to describe joints with little to no aperture or physical opening.
10 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Natural-Gamma Logging

Natural-gamma logs were used to help characterize rock 

types in wells. Chapman and others (1999) noted a characteristic lower baseline response (from 0 to 292 American Petroleum 

Institute units [API units]) for the amphibolite unit compared to 

the button schist and biotite gneiss (from 200 to 400 API units).

Resistivity Logging

Resistivity logs were used to detect potential water-bearing 

fracture zones in the bedrock. Resistivity is a measure of the 

bedrock formation’s electrical resistance (expressed in square 

ohmmeters per meter [ohm/m]). Water-bearing fracture zones 

in highly resistive igneous and metamorphic rocks commonly 

are associated with a zone of decreased resistivity. Resistivities 

of igneous and metamorphic rocks penetrated by wells in this 

study area ranged from 1,000 to 4,000 ohm/m for unfractured 

rock, and from 100 to 500 ohm/m for fractured rock having 

water-bearing zones. Three types of resistivity logs were collected: (1) 16-inch normal (measures the formation resistivity 

within a roughly 3-ft spherical zone around the borehole), 

(2) 64-inch normal (measures the formation resistivity within a 

10-ft spherical zone or less), and (3) lateral (measures the resistivity of a small volume of bedrock material in the formation 

without involving the material nearest to the borehole). Both 

16- and 64-inch normal resistivity logs are sensitive to variations in borehole diameter. Because of the similar response of 

these logs, only the lateral log is shown in figures in this report.

Fluid-Temperature and Fluid-Resistivity Logging

Fluid-temperature and fluid-resistivity logs were used to 

detect changes in water temperature and water chemistry. 

Changes in fluid temperature and resistivity usually indicate 

inflow or outflow of water from the borehole; and, hence, 

inflections on fluid temperature and resistivity logs can be used 

to help identify water-bearing zones. The fluid temperature and 

resistivity logs typically are used in combination with other logs 

to verify a water-bearing zone at the inflection point.

Borehole-Televiewer Imaging

Two types of borehole-televiewer imaging techniques were 

used during the study: acoustic televiewer (ATV) and optical 

televiewer using the Borehole Image Processing System 

(BIPS). The ATV uses sound waves to collect a magnetically 

oriented (to magnetic north) image of the borehole wall. Features such as simple fractures, voids, foliation, and layering can 

be identified in the acoustic image. Unlike the ATV, which uses 

sound waves, the BIPS tool records an optical image of the 

borehole wall. The BIPS log has a substantially higher resolution and allows for more subtle features to be identified. The 

BIPS log was used in the same manner as the ATV log.

Borehole-Camera Surveys

Table 3. Description of borehole geophysical tools used in the Lawrenceville, Georgia, area.

Geophysical tools Measures Uses

Caliper Borehole diameter Identify breakouts and potential fractures

Multiparameter log Natural gamma, 64-inch normal resistivity, 16-inch normal 

resistivity, lateral resistivity, spontaneous potential, fluid 

resistivity, fluid temperature

Identify lithology, water-bearing zones, changes 

in water chemistry and temperature

Borehole acoustic televiewer Oriented image of borehole wall, borehole deviation Calculate orientation of subsurface features, calculate borehole deviation

Electromagnetic flowmeter Fluid movement in borehole Identify zones of inflow and outflow from the 

borehole during static or pumping conditions

Heat Pulse Flowmeter Low-velocity fluid movement Identify flow directions in static or low-flow 

pumping conditions

Borehole Image Processing 

System (manufactured by 

RaaX Company Ltd.)

High-resolution oriented optical images of borehole wall Calculate orientation of subsurface features

A borehole camera was used to visually inspect and document joints, fractures and other structures intersecting the borehole wall. A GeovisionTM high-resolution camera was used to 

collect the video images in most of the open boreholes of wells. 

Because the GeovisionTM camera has a fixed head, a survey first 

was made with the camera head pointed downward and a second survey with the camera head horizontal. The downward 

survey provided the best view of steeply-dipping5 fractures and 

large open fractures intersecting the borehole wall. The horizontal survey allowed viewing of small-scale rock fabric, open 

fractures, and other small voids and openings.

5

In this report, “steeply dipping” refers to angles typically greater than 70 degrees from horizontal.
Table 4. Geophysical logs collected in the Lawrenceville, Georgia, area.

[EM, electromagnetic; BIPS, Borehole Image Processing System; —, data not collected]

Well 

name Caliper Combi- nation1 Acoustic televiewer 2 EM flowmeter Heat pulse flowmeter BIPS2 Gamma EM induction Borehole camera Long normal Short normal Spontaneous potential Fluid resistivity Flu

temper

13FF12 x x x — — x x x — — — — — 13FF13 x x x — — x x x — — — — — 13FF14 x x x — — x x x — — — — — 13FF15 x x x — — x — x — — — — — 13FF16 x x x — — x — x — — — — — 13FF17 x x x x x — x x — — — — — 13FF18 x x x x — — x x — — — — — 13FF19 x x x x x — x x — — — — — 13FF20 x x x x — — x x — — — — — 13FF21 x x x x x — x x — — — — — 13FF22 x x x x x — x x — — — — — 13FF23 x x x x — — x x — — — — — 14FF08 x — — — — 3x — x — — — x x 14FF10 x x — — — — — x — — — — — 14FF16 x — x — — — — x x x x x x 14FF17 x — x — — x — x x x x x x 14FF18 x x x — — x x x x x x x x 14FF26 x x x — — 3x x x x x x x x 14FF27 x — x — — x — x x x x — x 14FF39 x x x — — x — x x x x x x 14FF42 x — x — — x — x x x x — x 14FF46 x x x — — x x x — — — — — 14FF47 x x x — — x x x — — — — — 14FF49 x x x — — x x x — — — — — 14FF50 x x x — — x x x — — — — — 14FF52 x x x — — 3x — x — — — — — 14FF53 x x x — — x — x — — — — — 14FF55 x x x x — — x x — — — — — 14FF56 x x x x x — x x — — — — — 14FF57 x x x — x — x x — — — — — 14FF58 x x x — x — x x — — — — — 14FF59 x x x x — — x x — — — — — 

1Combination log includes: long-normal resistivity, short-normal resistivity, lateral resistivity, natural gamma fluid temperature, fluid resistivity, single-point resistance, and s2Logs, include borehole deviation 3Partial, incomplete, or poor visibility log
12 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Characterization of Fractures in Open Boreholes

Imaging techniques used in this study permitted direct 

observation of lithology, compositional layering, foliation, and 

other structures in relation to the depth and nature of the intersecting fracture plane. When viewing fractures, some interpretation was required to separate them into several main types. 

Determination of Type, Depth, and 

Orientation of Fractures

ATV and BIPS logs, in combination with borehole-camera 

surveys, were used to determine the type of fractures in open 

boreholes. The strike and dip of intersecting fractures were 

compared to surrounding foliation and compositional layering 

and classified as “joints” where fractures crosscut rock foliation 

and compositional layering, “open joints” for fractures with visible openings that could be seen intersecting the borehole wall, 

“foliation partings” for small openings formed parallel to foliation or compositional layering, and “major foliation openings” 

for large openings formed parallel to foliation or compositional 

layering. Irregular openings, for which a category was not 

readily apparent, were classified into the primary feature being 

weathered. For example, weathered and dissolutioned joints 

were included in the open joint category and irregular openings 

along foliation planes were included as a foliation parting or a 

major foliation opening depending on the size of the fracture.

Depths of fractures identified from the ATV and/or BIPS 

logs were depth corrected to align vertically with the caliper and 

other geophysical log data. In order to make the correction, the 

caliper log and the image logs first were plotted on the same 

scale, and then prominent fractures on the image logs were 

matched to peaks on the caliper log. An average depth offset 

was then computed to make the depth correction. For example, 

if the caliper log indicated fracture openings at 10 ft, 100 ft, and 

245 ft that corresponded to fractures observed on the image log 

at 11 ft, 101 ft, and 246 ft, then a depth correction of 1 ft was 

used for the ATV or BIPS log. In this manner, the fractures and 

other structural features identified with geophysical tools were 

shifted to a common reference point—that being the caliper log, 

which is referenced to land surface. Small offsets in vertical 

alignment commonly occur because of different tool sizes and 

shifts in the reference point used for logging.

Overall, the caliper log, in combination with the borehole 

ATV and/or BIPS logs, provided ample information to locate 

most of the fractures in the open boreholes of wells. In many 

wells, however, the borehole-camera log was used to aid in 

identifying less obvious joints and fractures that were difficult 

to see in the ATV or BIPS log. Correlating between the highresolution camera log and the image logs was an effective 

means for identifying less obvious intersecting joints and fractures. Small openings, such as foliation partings, rarely were 

accompanied by an observable caliper peak; therefore, camera 

logs were necessary for identifying these small features.

The orientation (strike and dip) of fractures was determined 

from the ATV and BIPS logs. The strike and dip indicate the 

orientation of the layer or planar feature relative to a horizontal 

plane. Strike is the compass direction of a line formed by the 

intersection of the surface of an inclined feature with an imaginary horizontal plane (fig. 3). Dip is the tilt or angle, perpendicular to strike, of an inclined feature measured downward from a 

horizontal plane. In figures included in this report, the structural 

orientation of features is shown in terms of the dip angle (measured from horizontal) and the dip azimuth (using 360-degree 

compass direction) using a tadpole plot (fig. 3). 

WellCad©, a commercial log processing program from 

Advanced Logic Technology (ALT), was used to calculate the 

strike and dip of structural features identified in televiewer logs. 

When viewed in a two-dimensional projection of the borehole 

wall, planar-dipping features form an ellipse across the borehole,

which appears as a sinusoidal wave on a two-dimensional depiction of the borehole wall (fig. 3). The lowest point on the sinusoidal wave gives the direction of the dipping plane. The true 

strike and dip were calculated using the WellCad© image-processing module, which corrects for borehole deviation (fig. 3). 

A rotation of 3.5 degrees west of “true” north also was applied 

to the data to correct for magnetic declination in the study area. 

Identification of Water-Bearing Fractures

Water-bearing fractures in open boreholes of wells were 

identified by comparing the depth and yield of individual waterbearing zones identified during drilling to fracture data compiled from geophysical logs, ATV and BIPS televiewer image 

logs, borehole-camera images, and flowmeter logs. Water-bearing fractures were confirmed using multiple lines of evidence, 

such as a caliper peak (indicating a physical opening), lowresistivity response on resistivity logs, and inflections on fluid 

temperature and fluid resistivity logs. The geophysical log data 

were used in combination with “visual” observations of the 

fracture trace in the ATV or BIPS log, and borehole-camera log. 

Using these sources of data, the main water-bearing fractures 

were interpolated and denoted on geologic logs for each well. It 

should be noted that the water-bearing zones identified in this 

study represent primary water-bearing fractures in each well. 

Joints and fractures not contributing substantially to the yield of 

a well (much less than 1 gal/min) were not of concern unless the 

well was low yielding.

In some cases, water-bearing fractures were identified, but 

the yield from individual fractures could not be quantified with 

the available data. For example, in some wells the yield gained 

along a vertical section of borehole could not be attributed to a 

specific zone. In these vertical sections, the water-bearing zones 

were called potential production zones to indicate the relative 

uncertainty of the exact depth of the production zone. The term 

potential production zone also was applied to the most likely 

production zones in some of the older existing wells for which 

drilling observations were not available.
N

Strike

S

E

W

N N ESW

dip = tan –1 amplitude

C. The trace of an intersecting plane makes 

a sinusoidal wave on a two-dimensional projection of the borehole wall. The amplitude of the 

wave and diameter of the borehole are used to 

calculate dip angle and dip direction.

A. Diagram showing logging winch and 

geophysical sonde used to collect image 

of borehole wall.

B. The orientation of a planar feature intersecting a borehole is described by the strike 

(azimuth direction a straight line would make 

from the intersection of an inclined plane with 

the horizontal) and dip angle (tilt from horizontal). In this diagram dip direction is south.

D. Tadpole plots are used to show the dip direction 

and dip angle. The “tail” of the tadpole points in 

the dip direction (similar to a plan view on a map). 

From left to right, the symbols are plotted with 

increasing dip angle. Horizontal = 0, vertical = 90.

0 30 60 90

Increasing dip angle

Dip angle

Conductor cable

Borehole

wall

Logging winch 

used to raise 

and lower tools

Acoustic or optical 

televiewer sonde

Structures 

intersecting 

borehole

Collects magnetically 

oriented image of 

borehole wall

Dip direction

Fracture

trace

Amplitude

diameter

Low point on 

curve indicates 

dip direction

Direction: 180 degrees

Angle: 45 degrees 

Tadpole plot Corrections

Vertical

borehole

Borehole

deviation

Magnetic

declination

Deviated

borehole

True north

3.5 degrees

Methods and Data Collection and Analysis 13

Figure 3. Schematic diagrams illustrating how the strike and dip of a planar feature intersecting a borehole are 

determined. The calculation assumes the feature is planar (not curved). Corrections are made for borehole deviation 

and magnetic declination.
14 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Estimating Yield Contribution from Individual 

Water-Bearing Fractures

The yield contribution from individual water-bearing fractures was estimated from air-lift yield tests at the time of drilling 

and then confirmed later with flowmeter surveys. The combination of these two methods provided the most effective means of 

characterizing the yield contribution from individual waterbearing fractures intersecting the open boreholes of wells.

Estimating Yield during Drilling

The depth and yield of fractures were initially estimated 

during drilling by carefully observing the drilling rate, identifying “drilling breaks,” and measuring the amount of water being 

evacuated from the test well during air-percussion rotary drilling. A drilling break occurs when the down-hole air hammer 

penetrates an open void, a zone of increased fracturing, or 

weakness in the rock. An increase in “chattering” of the drill 

rod, followed by a distinct drop, and an almost immediate 

increase in the return volume were indicative of large, open, 

water-bearing fractures. Small openings and/or low-yielding 

fractures typically corresponded with small drilling breaks, 

chattering, and small rod drops, but without an increase in 

return volume.

The color and size of the rock cuttings also were used as an 

indicator of potential water-bearing fracture zones. Water-bearing fracture zones commonly are accompanied by an increase in 

the size of the drill cuttings, iron-oxide staining on the cuttings, 

and large angular rock fragments broken out of fracture zones.

The air-lift yield was checked after each potential waterbearing zone was penetrated to determine any increase in yield 

from the zone. The yield measurement generally was made by 

conveying the return water into a bucket or 55-gallon drum and 

using a stopwatch to compute the discharge rate. At well sites 

where there was no practical means to convey the water into a 

bucket, the air-lift yield was estimated by the driller. After making the measurement, the increase in air-lift yield was attributed 

to the zone penetrated. For example, if the well was blowing 

“dry” down to 150 ft and “chattering” and a rod drop was 

observed at 151 ft, followed by an increase in yield of 5 gal/min, 

then a 5-gal/min water-bearing fracture was noted at a depth of 

151 ft. If another zone was penetrated at 200 ft, with a total discharge of 20 gal/min (increase of 15 gal/min), then a 15-gal/min 

fracture zone was noted at 200 ft. This process was repeated for 

all potential water-bearing fracture zones in the well.

The yield contribution of individual fractures and fracture 

zones was later estimated by carefully correlating air-lift yield 

increases observed during drilling (described above) with the 

depth of fracture zones identified using geophysical logging. In 

some zones, the correlation was clear and unambiguous—an 

increase in air-lift yield, for example, may have been observed 

within 5 ft of a large fracture opening or fracture zone observed 

in an ATV log. In other zones, increases in yield could not be 

correlated with a specific fracture observed in the borehole geophysical logs. In these cases, the increase in air-lift yield was 

attributed to one or more previously penetrated (shallow) fracture zones near the depth of yield increase. A shallow fracture 

zone, within 15–25 ft of the increase, often was identified as the 

most likely water-bearing fracture zone. The yield estimated in 

this manner should be regarded only as a rough estimate of the 

yield from the fracture or fracture zone. Limitations of this 

method are: (1) accurately measuring the amount of water being 

lifted out of the well during drilling—some were measured and 

others estimated; (2) identifying the precise location of slight 

increases—increases of 1 to 10 gal/min may not be recognized 

until starting a new segment of drilling rod; and (3) detecting 

small increases in yield below one or two major producing 

zones—for example, an increase from 1 to 5 gal/min may be 

indistinguishable from a shallow (previously penetrated) fracture zone producing 100 gal/min.

Flowmeter Surveys

Flowmeter surveys, conducted under ambient and pumping 

conditions, were used to identify water-producing and waterlosing fracture zones in open-bedrock wells. Water-producing 

zones are defined in this report as discrete zones that yield measurable amounts of water to the borehole when pumped or 

where water is flowing into the borehole during ambient conditions. Water-losing zones are defined as zones where water 

exits the well through fractures or zones of lower hydraulic head.

The technique of locating water-producing and water-losing 

zones involves using a flowmeter to measure the flow velocity 

(up or down) along segments of open borehole or at discrete 

depths, such as above or below previously identified fractures. 

Data are obtained by either measuring flow at a stationary point 

or by trolling along sections of a borehole to produce a flow profile (Johnson and Williams, 2003). Differences in flow rate 

detected with the flowmeter along the borehole are attributed to 

water-producing or water-losing zones. For this study, the stationary-point method was found to be the most reliable method 

for measurement of borehole flow, and those are the data reported.

Two types of flowmeters were used for flow measurement: 

a heat-pulse flowmeter (HPFM) and an electromagnetic (EM) 

flowmeter. The HPFM can measure flow rates as small as 

0.01 gal/min and was used for wells having a borehole flow of 

less than 2 gal/min. The EM flowmeter has a larger operating 

range and was used for wells having a borehole flow of greater 

than 2 gal/min.

With the exception of well 14FF59, two separate flowmeter 

surveys were conducted in each well: (1) a nonpumping “ambient” survey and (2) a pumping survey. In each well, an ambient 

survey was first conducted to document the ambient flow into 

or out of the borehole prior to pumping. These surveys provided 

information on whether there was any ambient flow resulting 

from differences in head and hydraulic conductivity of the 

water-bearing fractures intersecting the well. The rate of flow 

from higher head fractures to lower head fractures is largely 

controlled by the hydraulic conductivity of the fracture and by 

differences in hydraulic head between fractures. Following the 

ambient survey, a submersible pump was installed near the top 
Methods and Data Collection and Analysis 15

of the well and the well was pumped at rates ranging from several gallons per minute to as much as 60 gal/min. After the 

drawdown in the well had stabilized, a second flowmeter survey 

was completed, measuring the flow at similar depths recorded 

during the ambient survey. The results of the ambient and 

pumping surveys then were plotted to show the relative contribution of water-bearing fractures with depth. An interpretive 

line was drawn through the data points to produce a best fit for 

the data, stepping the graph at interpreted inflow or outflow 

points. The depths of water-bearing zones determined from geophysical logs were taken into consideration in determining 

where to designate the inflow or outflow for each log.

Aquifer Testing

The City of Lawrenceville, or its contractor, conducted 

aquifer tests to determine pumping drawdown and yield for 

water-production engineering. Because the goal of these tests 

was for engineering purposes without determination of hydraulic properties, typical aquifer-test procedures and protocols 

were not used. Close attention was paid, however, to the drawdown in the pumped well, pumping rate, and drawdown in 

observation wells.

For the aquifer tests, pressure transducers and water-level 

data recorders were installed in both the pumped well and 

nearby observation wells. These water-level recording devices 

were left in place for a period of time ranging from a few days 

to several weeks, depending on the amount of time required for 

recovery of the water level after pumping. Barometric pressure 

and rainfall gages were used during some of the tests so that 

barometric changes and rainfall recharge effects could be 

accounted for, where necessary. Discharge was regulated using 

gate valves and measured with a flowmeter or an orifice weir. 

The discharge from the aquifer tests was conveyed away from 

the pumped well by routing the flow along a ditch or piped to 

the nearest stream or water body. The discharge rate was 

checked by taking a volumetric measurement using a stopwatch 

and a bucket. These “bucket checks” routinely were taken several times during the test for quality-assurance purposes.

To avoid dewatering fractures, most of the aquifer tests were 

conducted by pumping at a rate large enough to draw the water 

level in the pumped well down to a few feet above the uppermost water-bearing zone and holding the level above that zone 

for the remainder of the test. As each test proceeded, the pumping rate was decreased, if necessary, to maintain the pumping 

water level above the uppermost water-producing fracture zone. 

A small-diameter stilling well (typically 1 inch) was used to 

make manual water-level measurements in the pumped well. 

The stilling well prevented cascading water in the pumped well 

from interfering with water-level measurements.

Analysis of the data consisted of plotting the drawdown in 

the pumped well with respect to time and evaluating if the 

pumping water level stabilized. From these observations, the 

pumping rate and pumping water level were determined. Drawdown in observation wells also was evaluated to see if any 

anisotropic response could be identified. Quantitative analysis 

for determination of aquifer coefficients using the drawdown 

and recovery data is beyond the scope of this report.

Packer Testing

Inflatable straddle packers were used to isolate and 

hydraulically test individual discrete fractures in well 14FF59 

(figs. 1, 4). To conduct each test, the packers were inflated to 

isolate a section of borehole, water was pumped from the isolated section, and pressure transducers were used to monitor the 

hydraulic response within, above, and below the pumped zone.

A special packer system (fig. 4) was designed to conduct 

packer tests in the Lawrenceville area. The packer system consisted of two inflatable rubber packers, a submersible pump, and 

pressure transducers for monitoring above and below the packers (top and bottom transducers) and the isolated interval (middle transducer). Pass-through tubes connect pressure transducers to monitoring intervals. Because the pass-through tubes are 

open ended and trap air when lowered into the borehole, an airactuated valve was used to evacuate trapped air in the passthrough tubes. The rubber packers were inflated using nitrogen 

delivered through a 1⁄4-inch polyethylene air line. The pressure 

in the packers was monitored using a pressure gage. The pumping rate was monitored at the land surface with a flowmeter and 

checked with a calibrated bucket and stopwatch.

Following inflation of packers and stabilization of the water 

levels in the three zones, the submersible pump was used to 

pump water from the isolated interval. Each test continued until 

the water level in the pumped interval was static or nearly static. 

Following the pumping phase of the test, the pump was stopped 

and water-level recovery was monitored.

The data were analyzed by plotting the water-level response 

in the three zones with respect to time. This allowed a qualitative analysis of the data to determine the hydraulic response 

within and between discrete water-bearing fractures.

Water-Level Monitoring

Water levels were measured synoptically, where many wells 

were measured during a short period of time, and continuously 

to monitor the water-level fluctuation in response to seasonal 

variations in rainfall and pumping.

Synoptic water levels were measured in 30 wells throughout 

the study area on October 31, 2001. An electronic water-level 

tape was used to measure the depth of water below land surface 

and a pressure transducer was used to measure water levels in 

flowing wells. Water levels above land surface are expressed as 

negative numbers. Continuous water levels were measured 

using data recorders installed in 26 wells for periods of time 

ranging from more than 1 month to several years. Water-level 

recorders were installed and operated using standard procedures 

of the USGS. All data were entered into the USGS National 

Water Information System database.
A

C

E

D

B

Air line

Top transducer

Middle transducer

Bottom transducer

Electrical

D

B

B,C,D

B

C

D

Open end of pass- 

 through tubes

Note: Air-actuated valve is triggered using a separate air line; trapped air 

in the pass-through tubes is released after assembly is below water level

A. B.

C.

D.

Conductor-pipe 

discharge at surface

Pressure transducers

Air-actuated valve

Pass-through tubes

Upper

packer

C

E

A C D

Open

Conductor pipe

Pump

Lower 

packer

Perforated

sleeve

EXPLANATION

Transducer

Perforated

sleeve

Conductor pipe

16 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Figure 4. Down-hole packer assembly used during the study showing (A) schematic of packer assembly, 

and photos of (B) pressure transducers secured to top of packer assembly, (C) conductor pipe and 

perforated pump sleeve, and (D) lowering packer assembly into well 14FF59, Lawrenceville, Georgia.
Hydrogeologic Data 17

Hydrogeologic Data

Thirty-two bedrock wells, ranging in depth from 180 to 

630 ft, were used to characterize the lithology, yield, and fracture characteristics in the Lawrenceville area. In addition, several shallow regolith wells were used as observation wells during aquifer tests and for long-term monitoring. For each well, 

the latitude, longitude, land-surface altitude, top of casing altitude, well depth, casing depth, casing diameter and type, ream 

depth, well yield, and geologic units are listed in table 2. Well 

locations are shown in figures 1 and 2.

Fracture Data

Fracture data, compiled from geophysical and boreholecamera logs in 32 bedrock wells, were used to determine the 

depth, nature, and yield of bedrock fractures in the Lawrenceville area. These data were plotted on standard figures for each 

well as illustrated in figures 5 and 6. Typically, two or three 

main water-bearing fractures were detected in each well during 

drilling. Although geophysical surveys indicated numerous 

fractures in each well, flowmeter surveys and packer tests identified only a few of these as water bearing—typically the larger 

“open” fractures intersecting boreholes.

Using borehole imaging data and correlating these data to 

individual fracture yield, two main systems of water-bearing 

fractures were identified: (1) joints, open joints, and zones of 

joint concentration consisting mostly of steeply-dipping lowyielding fractures; and (2) small and large openings along foliation planes and layering consisting of discontinuous but highyield fractures, which are defined in this report as “foliation parallel-parting systems” and originally described by Williams 

(2003) as “foliation fracture systems.” Water-bearing zones 

also are formed from the dissolution of preexisting crosscutting 

mineralized joints, which form irregular openings that cross 

foliation and layering. Chemical dissolution along joints, foliation planes, and contacts between compositional layers also 

form a variety of irregular-shaped voids and irregular fractures.

Individual Fracture Yield

Yield of individual water-bearing fractures and fracture 

zones was estimated by carefully correlating air-lift yield increases

observed during drilling with identified subsurface fractures. 

Yields determined for individual fractures and fracture zones in 

32 wells, ranged from less than 1 gal/min to 240 gal/min (table 5).

In general, increases in yield during drilling were found to 

be associated with one or more of the following features:

• joints, open joints, and zones of joint concentration;

• foliation partings and major foliation openings along 

foliation and layering of the rock; 

• dissolution openings of mineral infilling of a joint 

or vein; and 

• irregular-shaped voids and fractures.

Joints, Open Joints, and Zones of Joint Concentration

Joints generally are complex “crisscrossing” fractures that 

break up the rock into blocks and slabs of differing dimensions. 

In boreholes, joints are differentiated from other fractures by 

their occurrence in sets, common planar geometry, and orientation cutting across rock foliation and layering. Most joints 

observed in boreholes appeared as hairline fractures and typically were not significant water-bearing zones.

Open joints and zones of joint concentration typically were 

associated with increases in air-lift yield from 1 to 5 gal/min, 

although slightly higher or lower yields are common for these 

types of fractures. Several wells intercept zones of intensely 

jointed rock. One such well, 14FF58, penetrates multiple zones 

of joint concentration. Despite these many zones of joint concentration, however, only three open joints were identified for a 

combined yield of about 1 gal/min. In other wells, high yields 

were obtained from zones of joint concentration and open 

joints: the highest yielding zone was found in well 13FF22, 

where a yield of about 30 gal/min was reported for a zone of 

concentrated jointing and multiple open joints (table 5). This 

zone of concentrated jointing showed extensive dissolution 

around the joint faces, which apparently has enhanced the yield 

from this specific zone. Other wells producing water from 

joints, open joints, or zones of joint concentrations include 

wells 13FF15, 13FF23, and 14FF17.

Foliation Partings and Major Foliation Openings

Foliation partings and major foliation openings are fractures 

formed nearly parallel to foliation and compositional layering; 

thus, they occur only in layered metamorphic rock sequences 

such as the amphibolite, biotite gneiss, button schist and quartzite/schist units. A foliation parting is defined in this report as a 

small fracture with an aperture typically less than 0.5 inch. A 

major foliation opening is a much larger fracture with an aperture typically ranging from 1 to 8 inches, with some larger.

Individual foliation partings were associated with increases 

in air-lift yield from 1 to 15 gal/min (table 5). In some wells, 

groups of foliation partings or single partings yielded substantial amounts of water. A zone of water-bearing foliation partings in well 14FF52, from a depth of 158 to 159 ft, yielded 

30 gal/min; and a single foliation parting in well 13FF23, from 

a depth of 82.5 to 83.5 ft, yielded 33 gal/min. In another well, 

14FF27, a yield of 50 gal/min was estimated for a group of foliation partings and one open joint in a zone between 410 and 

435 ft (table 5).

Major foliation openings yielded substantially more water 

than the smaller foliation partings described above. A range in 

yield from 50 to 100 gal/min is typical for these larger fracture 

openings (table 5), making these the primary water-bearing features responsible for high-yield wells in the Lawrenceville area. 

All the high-yield wells studied in the Lawrenceville area penetrate at least one major foliation opening. In some wells, such 

as wells 13FF16 and 13FF21, only one major foliation opening 

was penetrated; whereas, in other wells such as well 13FF23, 

multiple foliation openings were penetrated.
0 100 200 300 400 500 0 1,000 2,000 3,000 4,000 60 62 64 

Caliper, 

in inches

Gamma, in APIU

(American Petroleum Institute Units)

Lateral resistivity,

in ohm meters

Fluid temperatu

in degrees Faren

5.5 6.0 6.5 7.0 7.5 

Amphibolite Amphibolite

Total depth

448 feet

Rock type

EXPLANATION

0

100

200

300

400

DEPTH BELOW LAND SURFACE, IN FEET

Well

13FF13

Water level in well

Total air-lift yield for 6-inch hole is 35 gal/min

Amphibolite Button schist Biotite gneiss

20 gal/min

15 gal/min

Quartzite/ schist

Fracture opening

sapsbg

qs

a-w/bg

aaaa

a-w/bga-w/bga-w/bg

qs

bg-sbg

bg

bg-sbgbg-sbgbg-sbg

bg-w/sbg

sbgsbg

bhg-sbg

a-w/bhg-bg

a-bhga-bhg

bhg-w/a

a-bg

bg-w/qs

sbg-bssbg-bsbg-w/abg-w/a

a

a-bg

a-w/bg

a-bhg

a-w/bhg-bg

bg

bg-sbg

bg-w/a

bg-w/qs

bg-w/sbg

sapsbg

bhg-sbg

bhg-w/a

qs

sbg-bs

6-inchpolyvinylchloridecasing to19-feet

Water level

is 6.7 feet

below

land

surface

AmphiboliteEqual amounts of 

amphibolite and biotite gneiss

Equal amounts of 

amphibolite and biotitehornblende gneiss

Predominantly 

amphibolite with some biotite gneiss

Predominantly 

amphibolite with some biotite-hornblende gneiss and biotite gneiss

Biotite gneissEqual amounts of biotite 

gneiss and schistose biotite gneiss

Predominantly biotite 

gneiss with some amphibolite

Predominantly biotite 

gneiss with some quartzite/schist

Predominantly biotite 

gneiss with some schistose biotite gneiss

Equal amounts of biotite 

hornblende gneiss and schistose biotite gneiss

Predominantly biotitehornblende gneiss with 

some amphibolite

Quartzite/schistSaproliteSchistose biotite gneissEqual amounts of 

schistose biotite gneiss and button schist

Individual fracture

airlift yield,

in gallons per

minute (gal/min)

Figure 5. Example lithologic units and geophysical log figure showing caliper, gamma, lateral resistivity, fluid temperature, and fluid resistivity, 
Amphibolite Amphibolite

Image

A shows a late metamorphic, high-angle, mineral-filled joint 

land surface. Image B shows a water-producing foliation opening ju

between the lighter rock below and the darker rock above at about 8surface. Image C shows a 2-foot-long virtual core of the borehole sh

layering of the metamorphic rock. Light and dark areas represent diImage D shows a foliation parting at about 203 feet below land surf

0 30 60

Well Degrees Degrees 13FF13

Biotite gneiss

Quartzite/ 

schist

0 30 60 

Azimuth: 32 Angle: 3 

Azimuth: 28 Angle: 12 

Azimuth: 178 Angle: 86 

Note: structures determined from Borehole Image Processing System log and corrected for magnetic declination and borehole deviation

Borehole deviation— Diagram to right shows the borehole is deviated 38.9 feet to the northwest

Increasing dip angle

EXPLAN

Rock type

a

a-bg

a-bhg

a-w/bg

a-w/bhg-bg

bg

bg-sbg

bg-w/a

FoliationJointMajor foliation opening

Tadpole—Shows azimuth directio

Foliation parting

Offset in layering (fault)

50

100

150

200

0

sapsbg

qs

a-w/bg

aa

a-w/bga-w/bg

bg-sbg

bg

bg-w/sbg

bhg-sbg

a-w/

bhg-bg

a-bhga-bhg

bhg-w/a

a-bg

qs

03 6 90

End BIPS log

250

300

350

400448

aa

a-w/bg

bg-sbgbg-sbgbg-sbg

sbgsbg

bg-w/qs

sbg-bssbg-bsbg-w/abg-w/a

qs

Quartzite/ 

schist Button schist Amphibolite

S W N E SS W N E S S W N E S

A. 27 feet

B. 84 feet

C. 145 feet

D. 203 feet

N

Joint

Foliation

parting

Fracture

End 

W 

90

Rock types

Lithologic units

Rock types (continued)

Lithologic units (continued)

Tadpole plot Tadpole plot

(continued)

Borehole images Explanation and b

AmphiboliteEqual amounts of amphibolite  and biotite-hornblende gneissPredominantly biotite gneiss  with some amphibolitePredominantly amphibolite  with some biotite gneiss Predominantly amphibolite  with some biotite-horneblende  gneiss and biotite gneissEqual amounts of amphibolite and biotite gneissEqual amounts of biotite gneiss and schistose biotite gneissBiotite gneiss

Fracture 

DEPTH BELOW LAND SURFACE, IN FEET

DEPTH BELOW LAND SURFACE, IN FEET

Figure 6. Example structure log figure showing rock types, lithologic units, tadpole plots, borehole images, and borehole deviation, Lawre
20 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Table 5. Depth, yield, and structural features of water-bearing fracture zones in the Lawrenceville, Georgia, area.

[ft, foot; BLS, below land surface; PPZ, potential production zone; PZ, production zone; do, ditto; gal/min, gallons per minute; —, data not collected. Geologic units: a, amphibolite; bg, biotite gneiss; bs, button schist; gg, granite gneiss; qs, quartzite/schist; +, plus]

 Well name Depth (ft BLS) Yield Structural features

13FF12

Total yield: 111.0–111.5 PPZ Foliation parting + joint

254 gal/min 116.5–117.5 PPZ Joints

(bg, bs, bg, a) 123–123.5 PPZ Foliation parting

 128.5–132.3 PPZ Multiple joints

 208.8–209.8 PZ Major opening along foliation/layering

 212.2–213.8 PZ Do.

13FF13

Total yield: 87.2–88.2 20 gal/min Major opening along foliation/layering + foliation parting opening

35 gal/min 380–381.5 15 gal/min Major opening along foliation/layering

(a, bg, a, qs, bs, a)

13FF14

Total yield: 231–232 PPZ Dissolution along mineral-filled joint

140 gal/min 269–270 PZ Foliation parting

(a, bg) 271–273 140 gal/min Major opening along foliation/layering

 13FF15

Total yield: 115–116 5 gal/min Joints and open joint

250 gal/min 129–130 PPZ Open joint

(bg) 139–140 5 gal/min Do.

199.5–201 240 gal/min Major opening along foliation/layering

13FF16

Total yield: 169.5–170 10 gal/min Foliation parting

75 gal/min 179.5–180.5 PZ Do.

(a, bs, a, bg) 182.5–184 65 gal/min Major opening along foliation/layering + foliation parting

13FF17

Total yield: 48–49 6 gal/min Major opening along foliation/layering

90 gal/min 64.5–65 60 gal/min Major opening along foliation/layering + joints

(a) 197–198 24 gal/min Foliation parting

13FF181

Total yield: 38–39 — 10 gal/min, sealed off

1002/1503 gal/min 54.5–55 — 18 gal/min, sealed off 

(a) 82.25–83.25 63 gal/min Foliation parting

 100.8–101.8 83 gal/min Major opening along foliation/layering

 159.1–160.1 4 gal/min Foliation parting

13FF194

Total yield: 35–37.5 5 gal/min — 2

250/3350–400 gal/min 58–61 20 gal/min Do.

(a) 198–199 15 gal/min Foliation parting

245.5–246.5 100 gal/min Major opening along foliation/layering

356–357 10 gal/min Foliation parting

13FF20

Total yield: 373.5–374.5 1 gal/min Major opening along foliation/layering

35 gal/min 392.25–393 34 gal/min Do.

(a, bs)

13FF211

Total yield: 240.5–241.5 125 gal/min Major opening along foliation/layering 2

130/

3

125 gal/min

(bg, a)

13FF22

Total yield: 23–25 5 gal/min Multiple joints

100 gal/min 47.5–48.5 10 gal/min Foliation parting

(a, bg) 154–155 50 gal/min Major opening along foliation/layering

368–369 5 gal/min Foliation parting

468–475 30 gal/min Multiple open joints + foliation parting, dissolution along joints

13FF234

Total yield: 40–41 0.5 gal/min Foliation parting 2

250/

3

350–400 gal/min 50–51 1.5 gal/min Open joint

(a, bg, bs) 77.5–78.5 PPZ Foliation parting

82.5–83.5 33 gal/min Do.

101–102 PZ Do.

142–143 65 gal/min Major opening along foliation/layering

164–165 PZ Do.

179–180 PZ Do.

242.75–243.75 150 gal/min Do.

256.5–257.5 PZ Do.
Hydrogeologic Data 21

14FF08

Total yield: 49–50 PPZ Foliation parting

400 gal/min 51–52 PPZ Multiple openings along foliation/layering

(a, bs, bg, gg) 101–113 PPZ Major opening along foliation/layering

185–187 PZ Do.

 206–207.5 PZ Multiple small openings along foliation/layering

222–226 PZ Major opening along foliation/layering

231–233 PZ Do.

14FF10 24–30 PPZ Cavernous, dewatered during pumping

Total yield: 37–39 PPZ Cavernous fracture along foliation, dewatered during pumping

270 gal/min 88–89.5 PPZ Do.

(a) 107–108 PPZ Open vertical fracture

129–131 PZ Major opening along foliation/layering

175.5–178 PZ Do.

14FF16 41.5–43.5 Dry Cavernous, dewatered during pumping

Total yield: 72–76.5 Dry Do.

471 gal/min 91.5– 93 PPZ Foliation parting

(a, bs) 133.5–135.5 PZ Major opening along foliation/layering

169–170 PZ Do.

178–180 PZ Do.

208.5–209.5 PZ Do.

14FF17

Total yield: 34–35 2 gal/min Major opening along foliation/layering

150 gal/min 67–69 PPZ Open joint

(a) 70–71 3 gal/min Do.

142–143 4 gal/min Major opening along foliation/layering

182–183 8 gal/min Do.

210–212 133 gal/min Not determined, bottom hole fracture covered with silt

14FF18

Total yield: 30.5–32.5 1 gal/min Foliation parting, dewatered during pumping

100 gal/min 51–52 2 gal/min Several minor openings along foliation/layering, cascading water during pumping

(a) 105.5–106 27 gal/min Major opening along foliation/layering, no cascading water when pumped below

149.5–151 70 gal/min Major opening along foliation/layering

14FF26

Total yield: 67–68 PPZ Foliation parting

— 85.5–86.5 PPZ Multiple minor openings along foliation/layering

(a, bg, bs, a, bg) 93–94 PPZ Open joint and multiple joints

114–115 PZ Major opening along foliation/layering + foliation parting

161–162 PZ Two separate major openings along foliation/layering

14FF27

Total yield: 62–86 42 gal/min Not determined, water-bearing zone detected while drilling

150 gal/min 103–104 4 gal/min Do.

(gg, bg, qs, a, bs) 112–113 4 gal/min Foliation parting

163–164 PPZ Foliation parting + open joint

zone at 62 ft yielded 42 166–168 PPZ Multiple foliation partings

 gal/min, but sealed 174.5–175.5 10 gal/min Foliation parting

 behind casing 296–299 PPZ Multiple open joints + foliation parting below

335–345 50 gal/min Do.

410–435 50 gal/min Open joint at 433 ft BLS + multiple foliation parting

571–572 25 gal/min Major opening along foliation/layering

14FF39

Total yield: 36.8–38.8 — Joint + foliation parting, dewatered during pumping

150 gal/min 119–120 75 gal/min Major opening along foliation/layering

(a) 170–171 75 gal/min Do.

14FF42

Total yield: 76–77 not determined Joint, cascading water observed

10 gal/min

(a, bs, bg)

14FF46

Total yield: 10–11 10 gal/min Not determined, detected during drilling

70 gal/min 62–63 35 gal/min Major opening along foliation/layering

(a, bs, bg) 145.5–146.5 20 gal/min Do.

227–228 5 gal/min Joint

Table 5. Depth, yield, and structural features of water-bearing fracture zones in the Lawrenceville, Georgia, area.—Continued

[ft, foot; BLS, below land surface; PPZ, potential production zone; PZ, production zone; do, ditto; gal/min, gallons per minute; —, data not collected. Geologic units: a, amphibolite; bg, biotite gneiss; bs, button schist; gg, granite gneiss; qs, quartzite/schist; +, plus]

 Well name Depth (ft BLS) Yield Structural features
22 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

14FF47

Total yield: 26–35 10 gal/min Leakage from partially weathered rock, later cased of 

25 gal/min 51–52 1 gal/min Foliation parting

(bg) 172.5–176 PPZ Multiple joints

204–205 PPZ Foliation parting

235.5–236.5 14 gal/min Do.

274–275 PPZ Foliation parting + joints

14FF49

Total yield: 86–88 PPZ Foliation parting

10 gal/min 111–112 PPZ Do.

(bg, gg) 128–129 PPZ Multiple minor openings along foliation/layering

135–136 PPZ Do.

14FF50

Total yield: 185.5–187.5 PZ Major opening along foliation/layering + foliation parting

300 gal/min gal/min 210.5–212.5 PZ Two separate major openings along foliation/layering 

(a, bs, bg, gg) 213.5–214.5 PZ Irregular opening along foliation

14FF52

Total yield: 158–159 30 gal/min Multiple foliation partings

40 gal/min 186–187 10 gal/min Do.

(a, bs, bg)

14FF53

Total yield: 95–96 3 gal/min Joint

50 gal/min 186–187 12 gal/min Partial foliation parting on one side of borehole

(bs, a, gg) 298–301 35 gal/min Dissolution along mineral-filled joint

14FF554

Total yield: 14–17 15 gal/min Cavernous, mostly along foliation 2

250b/

3

325 gal/min 31–32 PPZ Weak friable rock and openings along layering

(bg, a) 50.5–51.5 PPZ Multiple openings along foliation/layering

64–65 PPZ Opening along foliation

individual fracture yield 100.5–101.5 5 gal/min Foliation parting

based on 6-inch 172.5–173.5 PZ Major opening along foliation/layering

air-lift yield 181–182 20 gal/min Do.

251–252 110 gal/min Do.

305.5–306.5 PPZ Foliation parting

416–417 100 gal/min Major opening along foliation/layering

14FF56

Total yield: 43.5–44.5 30 gal/min Major opening along foliation/layering

60 gal/min 57.5–58.5 10 gal/min Do.

(a, bs, bg) 138–139 20 gal/min Do. 

14FF57

Total yield: 45.5–46.5 2.9 gal/min Major opening along foliation/layering

3 gal/min 196.5–197.5 0.1 gal/min Foliation parting

(bg) 340–341 PPZ Major opening along foliation/layering

14FF58

Total yield: 42–43 PZ Open joint

1 gal/min 287.5–288.5 PZ Do.

(gg) 498–499 PZ Do.

14FF59d

Total yield: 17.5–18.5 30 gal/min Opening along layering 2

180/

3

350-400 gal/min 266.5–267 20 gal/min Major opening along foliation/layering

(a, bs, bg) 281–282 45 gal/min Do.

296–297 30 gal/min Do.

324.5–325 5 gal/min Do.

347–348 50 gal/min Do.

Table 5. Depth, yield, and structural features of water-bearing fracture zones in the Lawrenceville, Georgia, area.—Continued

[ft, foot; BLS, below land surface; PPZ, potential production zone; PZ, production zone; do, ditto; gal/min, gallons per minute; —, data not collected. Geologic units: a, amphibolite; bg, biotite gneiss; bs, button schist; gg, granite gneiss; qs, quartzite/schist; +, plus]

 Well name Depth (ft BLS) Yield Structural features

1

Individual fracture yield based on air-lift yield from 8-inch borehole

2Air-lift yield from 6-inch borehole

3Air-lift yield from 8-inch borehole

4Individual fracture yield based on air-lift yield from 6-inch borehole

NOTE: Unless otherwise noted, total yield is from completed well as reported by driller.
Hydrogeologic Data 23

Dissolution Openings

Mineral-filled joints, veins, and possibly other features, such 

as dikes and sills of pegmatite or aplite, appear be susceptible to 

chemical dissolution, depending on the mineralogy. In several 

wells, dissolution features along mineral-filled joints or veins 

were associated with increases in air-lift yield up to 35 gal/min 

(table 5). This amount exceeds the typical range in yield for open 

joints and zones of joint concentration described above, indicating the potential importance of dissolution features in the bedrock. One such feature, at well 14FF53 at a depth from 298 to 

301 ft, yielded 35 gal/min from a single opening (table 5). These 

features also were observed in well 14FF26 at a depth of 93-94 ft 

and in well 13FF14 at a depth of 231–232 ft (table 5). It should 

be noted that dissolution features may be more common than 

indicated by the data because their identification requires a clear, 

high-quality image that shows remnants of the mineral infilling 

around the edges of the joint or vein. These types of high-quality 

images were not available in most of the wells studied.

Irregular-Shaped Voids and Fractures

Under close examination, irregular-shaped voids and fractures appear to originate as joints, foliation partings/openings, 

or a combination of different types of fracture openings that are 

widened through chemical weathering and dissolution. These 

features indicate that chemical weathering and dissolution probably are important processes in widening and enhancement of 

water-bearing fractures in the Lawrenceville area. One example 

is from a zone of steeply-dipping joints in well 13FF22 at a 

depth from 468 to 475 ft. In this zone, extensive dissolution 

around steeply-dipping joints is evident, creating irregular 

voids around the joints (see well-data summary for well 13FF22 

on CD–ROM). Drusy crystalline cement also was observed in 

this zone, indicating physical openings in the bedrock. Many of 

the foliation fractures measured in boreholes also showed 

rounded and irregular forms indicating substantial dissolution 

of rock materials around the fracture face.

Flowmeter Surveys

Flowmeter surveys were used to confirm the yield from various types of fractures intersecting open boreholes (table 6). In 

several of the wells—including 13FF23, 14FF55, and 14FF59— 

these surveys were used to identify confined/semiconfined 

water-bearing zones. Water from the confined/semiconfined 

zones flowed from the fracture, flowed up the borehole, and 

typically exited from the borehole through shallow fractures.

Table 6. Observations from ambient and pumping flowmeter surveys, Lawrenceville, Georgia, area.

[Discharge rate is for pumping survey only; gal/min, gallons per minute; ft, foot]

Well 

name

Survey 

date

Discharge

(gal/min)

Flow observations

Ambient survey Pumping survey

13FF17 2/4/2001 30 Flow near static entire borehole Producing from single fracture at 64.5– 65.5 ft

13FF18 12/3/2001 46 Upward flow above 100 ft, static flow below 100 ft Producing from multiple fractures between 82 and 102 ft

13FF19 11/30/2001 48 Flow nearly static between 0 and 250 ft, upward flow 

between 250–350 ft, nearly static flow below 350 ft

Producing from single fracture at 245.5– 246.5 ft

13FF20 12/5/2001 10 Flow nearly static entire borehole Producing from two fractures between 373 and 392 ft

13FF21 12/5/2001 25 Upward flow above 175 ft, downward flow below 175 ft Producing from single fracture at 240–241.5 ft

13FF22 12/5/2001 48 Upward flow above 450 ft, static below 450 ft Producing from fracture at 154–155 ft and zone of 

fractures from 468 to 475 ft

13FF23 12/4/2001 50 Upward flow above 100 ft; approximately 15–20 gal/min 

exiting borehole at base of casing

Producing from multiple fractures between 100 and 250 ft; 

water exiting borehole into fractures between 35 and 50 ft

14FF55 11/30/2001 48 Upward flow (8–10 gal/min) from 415 ft; water exits from 

borehole along small fracture at 64–65 ft

Producing from fracture at 172.5– 173.5 and at 416– 417 ft; 

water exiting from borehole along fracture at 64– 65 ft

14FF56 12/5/2001 46 Upward flow above 150 ft; near static flow 

below 150 ft

Producing from fractures at 43.5– 44.5, 57.5–58.5, and 138– 139 ft

14FF57 8/17/2001 1.2 Downward flow above 200 ft; upward flow below 200 ft Producing from fractures at 45.5–46.5 and 196.5– 197.5 ft

14FF58 8/6/2001 2 Upward flow above 300 ft; near static flow 

below 300 ft

Producing from multiple fractures including 42–43, 

287.5– 288.5, and 498–499 ft

14FF59 12/3/2001 58 Upward flow above 350 ft, increasing in flow up to 

58 gal/min above 250 ft

Producing from multiple fractures between 250 and 350 ft; 

well flowing 58 gal/min
24 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Well 13FF23 is one example where water from confined/

semiconfined water-bearing zones flows up the borehole and 

exits out into shallow fractures. In this well, multiple waterbearing zones were detected between 100 and 250 ft using a 

flowmeter (fig. 7). Under ambient conditions, water flowed 

from fractures with high hydraulic head into the borehole, up 

the borehole, and exited through fractures with lower head 

below the bottom of the casing (fig. 7a). During pumping conditions, using a pumping rate of 50 gal/min, water entered the 

borehole at water-bearing fractures with high head and flowed 

up the borehole; however, the pumping did not reverse the 

ambient flow regime, and water continued to exit the borehole 

into fractures near the base of casing (fig. 7b, top arrows). 

Although beyond the scope of this report, quantitative techniques could be used to infer the interval transmissivity and 

interval hydraulic head (Paillet, 2000) from these data.

Overall, flowmeter data indicate that ground water, under 

ambient and pumping conditions, appears to be derived from 

discrete fractures intersecting the boreholes, rather than evenly 

distributed along open sections of the boreholes (table 6). Most 

of the inflow typically was concentrated within two or three 

intervals, corresponding to the depth of water-bearing fractures 

identified through other geophysical methods.

Aquifer-Test Data

Aquifer tests were used to determine the long-term yield 

from the wells, which is the yield of all water-bearing fractures 

contributing water to the borehole during the period of the test. 

Data from the aquifer tests also provided information on the 

direction and magnitude of drawdown resulting from pumping, 

which is an indicator of the contributing areas to the pumped 

wells, and potential interference among wells.

Figure 7. (A) Flowmeter logs for well 13FF23, showing inflow and outflow from borehole, Lawrenceville, 

Georgia. Top left-facing arrows indicate fractures where water is flowing out of the borehole. Right-facing 

arrows show water entering borehole along factures between 100 and 250 feet. (B) Caliper log shown for 

reference. Flowmeter survey conducted on December 4, 2001.

5 7 9 11 13

UPWARD FLOW, IN GALLONS PER MINUTE

DEPTH BELOW LAND SURFACE, IN FEET

0 10 20 30 40 50 60 70 80

0

50

100

150

200

250

300

350

400

Casing to 30 feet, well not flowing

A. B.

Ambient flow conditionsPumping at 50 gallons per minute

Measured flow

Interpretation

INCHES

Outflow

Inflow
Hydrogeologic Data 25

Aquifer-Test Yield, Drawdown, and Recovery

Yields from aquifer tests ranged from 75 gal/min for well 

13FF16 to 600 gal/min for well 14FF50 for the period of the test 

(table 7). In several wells, such as 13FF19 and 14FF55, the 

aquifer-test yield was substantially less than the reported air-lift 

yield (table 2). Well 13FF19 had an air-lift yield of 350-400gal/min 

compared to an aquifer-test yield of 177 gal/min with about 

141 ft of drawdown. Well 14FF55 had an air-lift yield of 

325 gal/min compared to an aquifer-test yield of about 

241 gal/min with about 92 ft of drawdown. On the other hand, 

well 13FF21, with an air-lift yield of 125 gal/min was only 

18 gal/min less than the yield of 107 gal/min determined from 

the aquifer test. In other wells, the aquifer-test yield was greater 

than the air-lift yield; well 14FF50 had an air-lift yield of 

300 gal/min, which is half of the aquifer-test yield of 600 gal/min.

Collectively, data from the aquifer tests indicate that the 

pumped wells were able to sustain large pumping rates6 for the 

period of the tests. The recovery of water levels following 

pumping varied from slow, indicating a small recharge rate to 

the fracture(s) supplying the well, to fast, indicating a large 

recharge rate to the fracture(s) supplying the well. One aquifer 

test, indicating slow recovery, was conducted in well 13FF23. 

During that test, a pumping rate of 449 gal/min was used for the 

first 53 hours of the 72-hour test, causing a drawdown of about 

65 ft, approximately 18 ft above the uppermost water-bearing 

fracture. For the remainder of the test, the pumping rate was 

reduced to 342 gal/min to maintain the pumping water level at 

about 65 ft. Although the water level stabilized at 342 gal/min, 

the slow recovery following the end of the test indicated a small 

recharge rate supplying the well. Another well showing slow 

recovery was 13FF15, a 605-ft-deep well that was reamed to 

250 ft and had about 144 ft of available drawdown to the shallowest water-bearing fracture. The first aquifer test conducted 

in this well used pumping rates of 210 gal/min for the first 

24 hours, from 240 to 290 gal/min for the next 24 hours, and 

from 175 to 184 gal/min for the remainder of the 96-hour test. 

Although the water level was nearly stable at the end of the test, 

it took more than 10 days for the water level to recover 143 ft, 

which was still about 8.5 ft lower than the initial static water 

level. Water levels during a second aquifer test conducted in 

well 13FF15, with a pumping rate of 200 gal/min for 48 hours, 

never stabilized and required a similar amount of time to 

recover as that observed in the first test.

In contrast to the wells showing slow recovery, water levels 

in several other wells recovered rapidly after pumping. Well 

13FF21 was pumped at a rate of about 107 gal/min for 72 hours 

and recovered to 99 percent of the prepumping level in about 

35 hours. In another aquifer test, well 14FF59 was pumped for 

72 hours using a pumping rate ranging between 301 and 

444 gal/min, and the water level recovered in about 6 hours. 

The rapid recovery in these two wells indicates a large recharge 

rate into the bedrock fracture system supplying these wells in 

comparison to other wells in the area.

Table 7. Drawdown, pumping rate, and specific capacity of wells during aquifer tests in the Lawrenceville, Georgia, area.

[hrs, hours; ft, foot; gal/min, gallons per minute; gal/min/ft, gallons per minute per foot; do, ditto]

Well

name

Date 

start

Date 

end

Duration 

(hrs)

Drawdown

(ft)

Ending pumping rate

(gal/min)

Specific capacity1

(gal/min/ft)

13FF15 11/15/1999 11/19/1999 96 153.9 177.0 1.1

13FF15 12/20/1999 12/22/1999 48 99.7 200 2.0

13FF16 2/1/2000 2/2/2000 24 123.5 75 0.6

13FF18 9/4/2001 9/7/2001 70 87.3 135.4 1.6

13FF19 10/2/2001 10/5/2001 72 140.8 177 1.3

13FF21 8/21/2001 8/24/2001 do. 186.7 107 0.6

13FF23 9/18/2001 9/21/2001 do. 66.4 341.8 5.2

14FF50 2/22/1999 2/27/1999 116 82.3 600 7.3

14FF55 8/14/2001 8/17/2001 72 91.8 240.9 2.6

14FF59 10/10/2001 10/13/2001 do. 84.3 301.5 3.6

1Calculated by dividing ending pumping rate by drawdown.

6

In this report, “large pumping rates” refer to discharge rates generally greater than 70 gal/min.
26 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Direction and Magnitude of Drawdown

Ground-water level data collected from observation wells 

during the aquifer tests were used to determine the direction and 

magnitude of drawdown and to provide a general indication of 

potential interference among production wells. The drawdown 

in the observation wells varied depending on the distance and 

direction from the pumped well.

One aquifer test was conducted in well 13FF21 located on 

the floodplain of the Yellow River (fig. 1). During that test, the 

greatest drawdown occurred in a northwest-southeast direction 

from the pumped well. A drawdown of 0.75 ft was observed in 

well 13FF19, located about 6,800 ft from the pumped well and 

parallel to the strike of lithologic units. No drawdown was 

observed in well 13FF22 located about 5,400 ft away and perpendicular to the strike of lithologic units. No drawdown was 

observed in a shallow regolith well located 8 ft from the pumped 

well, indicating no apparent hydrologic connection between the 

bedrock fracture system and the regolith at this location.

In an aquifer test conducted in well 13FF18, located on the 

floodplain of Redland Creek (fig. 1), the greatest drawdown 

occurred in an east-west direction from the pumped well. A 

drawdown of 1.4 ft was observed in well 13FF17, located about 

2,800 ft west of the pumped well, and a drawdown greater than 

22.5 ft was observed in well 13FF13, located about 1,900 ft east 

of the pumped well. The pumped well and these two observation wells are aligned parallel to the strike of lithologic units and 

penetrate the same lithologic units. No drawdown was observed 

in well 13FF16, located about 2,500 ft north of the pumped well 

and positioned across the strike of lithologic units.

Data collected during aquifer tests in several other highyield production wells—including 13FF23, 13FF19, and 

14FF50—indicate similar drawdown to that described above. 

In most of these tests, drawdown was greater in the direction of 

bedrock foliation and layering than perpendicular to it (see table 7 

for data from aquifer tests). As a result of this apparent preferential drawdown, pumping interferences probably will occur 

between certain wells. The largest potential interferences are 

among wells 13FF21, 13FF23, and 13FF19 (fig. 1). The interferences observed during the aquifer tests indicate that these 

particular wells, if pumped simultaneously, likely would result 

in corresponding declines in the pumping rates during long periods of time. Smaller interferences also are evident between production wells at Rhodes Jordan Wellfield (14FF10 and 14FF16) 

and wells 14FF08, 14FF50, 13FF15, 13FF16, and 14FF55.

Packer-Test Data

Packer-test data were used to determine the hydraulic 

response among individual high-yield fractures at well 14FF59. 

Using flowmeter data, six intervals (numbered 1 through 6), 

each straddling the main water-bearing fractures in the well, 

were selected for packer testing. Fracture depths, isolated borehole intervals, and the responses observed during the tests are 

listed in table 8 and illustrated on sets of hydrographs included 

on this CD–ROM. Each set of hydrographs, representing a single packer test, shows the pressure response recorded in the 

interval above the packer (top transducer), below the packer 

(bottom transducer) and in the test interval (middle transducer).

The results of packer tests at well 14FF59 indicate 

the following:

• Shut-in pressure readings (head) taken before pumping 

each of the packer intervals were above land surface and 

substantially higher than the head in shallow fractures, 

indicating that the water-bearing fractures in this well 

are confined or semiconfined.

• Pumping from test intervals 2 and 3 indicates that fractures at 267 and 282 ft are hydraulically connected as 

indicated by the drawdown response in the bottom transducer of the interval 2 test and the smaller drawdown 

response in the top transducer of the interval 3 test. Conversely, packer tests on intervals 4, 5, and 6 did not show 

a substantial response in the top and bottom transducers, 

indicating that hydraulic separation exists among these 

fractures and the shallower fractures in the well.

• Packer-test intervals 1 and 5 indicate low-permeability 

fractures are present in these intervals. Low permeability is indicated by the pressure increase on the middle 

transducer during packer inflation.

The hydrologic responses observed at well 14FF59 indicate 

that most of the water enters the borehole through foliation openings and not through joints, and confirms the high-yield nature of 

major foliation openings in the well. A small amount of water 

probably enters through joints, but this is much less than that 

derived from the major foliation openings tested. Drawdown 

responses from the packer tests also indicate a slight but noticeable vertical connection among individual high-yield foliation 

openings, which likely is attributed to steeply-dipping joints.

Water-Level Data

Ground-water levels in the study area fluctuate in response 

to seasonal variations in rainfall, stream stage, and groundwater pumping. Synoptic water-level data (table 9) were used to 

provide information on the variation of water levels across the 

study area. Continuous water-level data (table 10) were used to 

monitor seasonal water-level fluctuations in response to rainfall 

and to monitor drawdown in response to ground-water pumping. Water-level hydrographs are included on this CD–ROM for 

each well where continuous data were available (table 10).

Open-hole water levels7 in bedrock wells varied widely 

across the area ranging from about 10 ft above land surface at 

well 14FF59 to 54 ft below land surface at well 13FF15 (table 9). 

Six boreholes had water levels above land surface and four of 

these flowed when left uncapped. Most of the open-hole water 

levels were above the bottom of casing, indicating confined/

semiconfined conditions in the bedrock fracture system.

7

An open-hole water level represents a “composite” potentiometric head formed 

by differing heads of individual fractures intersecting the open section of borehole.
Table 8. Fracture depth, straddle depths, and hydraulic response observed during packer testing of well 14FF59, 

Lawrenceville, Georgia, area.

[BLS, below land surface; ft, foot; gal/min, gallons per minute; gal/min/ft, gallons per minute per foot]

Interval

Fracture 

depth 

(ft BLS)

Straddle packer 

depths 

(ft BLS)

Transducer

Hydraulic response

Shut in (pre-pumping) Pumping

1 241 236–245 Top Stops flowing, head declines 1.45 ft BLS No response

Middle* Pressure buildup due to packer inflation; 

indicates low-permeability interval 

between packers

Dewatered

Bottom Pressure buildup to 12.70 ft above land surface No response

2 267 264–273 Top Stops flowing, head declines level to land surface No response

Middle* Pressure buildup to 8.80 ft above land surface 11.20 ft drawdown at 31gal/min (2.76 gal/min/ft)

Bottom Pressure buildup to 9.20 ft above land surface 1.75 ft drawdown response due to pumping of 

middle interval

3 282 276–285 Top Stops flowing, head is.70 ft above land surface Slight but definite response indicating hydraulic 

connection to zone 2

Middle* Pressure buildup to 6.20 ft above land surface 4.37 ft drawdown at 30 gal/min (6.87 gal/min/ft)

Bottom Pressure buildup to 9.00 ft above land surface Slight inflection seen on pressure curve 

indicates small or indirect connection with 

pumped interval

4 297 294–303 Top Stops flowing, head is 1.40 ft above land surface No response

Middle* Pressure buildup to 14.00 ft above land surface 95.30 ft drawdown at 26 gal/min (0.27 gal/min/ft)

Bottom Pressure buildup to 9.70 ft above land surface No response

5 325 319–328 Top Stops flowing, head is 1.60 ft above land surface No response

Middle* Pressure buildup due to packer inflation; 

indicates low-permeability interval 

between packers

Dewatered

Bottom Pressure buildup to 9.89 ft above land surface No response

6 348 341–350 Top Stops flowing, head is 1.60 ft above land surface No response

Middle* Pressure buildup to 8.80 ft above land surface 4.00 ft drawdown at 31gal/min (7.75 gal/min/ft)

Bottom Pressure buildup; indicates low-permeability 

section of borehole below packer interval

Slight inflection seen on pressure curve 

indicates small or indirect connection with 

pumped interval

Hydrogeologic Data 27

*Middle transducer in pumped interval
28 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

do

Table 9. Water levels in wells, October 31, 2001, Lawrenceville, 

Georgia, area.

[BLS, below land surface; ft, foot; Do., ditto]

Well 

name

Land-surface 

altitude*

(ft)

Waterlevel BLS1 

(ft)

Water-level 

altitude* 

(ft)

Aquifer 

unit

13FF13 972.3 6.98 965.3 Bedrock

13FF14 987.9 -9 996.9 Do.

13FF15 1,053.2 54.05 999.2 Do.

13FF16 1,004.7 8.2 996.5 Do.

13FF17 990.9 13.34 977.6 Do.

13FF18 953.8 -6.63 960.4 Do.

13FF19 921.8 9.25 912.6 Do.

13FF20 990.1 17.05 973.1 Do.

13FF21 889.4 4.7 884.7 Do.

13FF22 929.7 -0.47 930.2 Do.

13FF23 906.2 -1.3 907.5 Do.

13FF24 889.4 3.45 886.0 Regolith

13FF25 921.6 6.08 915.5 Do.

14FF08 1,019.8 31.85 988.0 Bedrock

14FF16 994.2 243 2951.2 Do.

14FF27 1,048.3 15.1 1,033.2 Do.

14FF42 1,082.2 29.46 998.7 Do.

14FF46 1,022.9 0.65 1,022.3 Do.

14FF47 1,004.2 5.86 998.3 Do.

14FF49 1,041.7 36.3 1,005.4 Do.

14FF50 1,019.3 22.21 997.1 Do.

14FF52 1,082.3 18.4 1,063.9 Do.

14FF53 967.7 49.61 918.1 Do.

14FF55 969.6 0.47 969.1 Do.

14FF56 936.3 7.29 929.0 Do.

14FF57 954.1 6.03 948.1 Do.

14FF58 1,030.2 -1.96 1,032.2 Do.

14FF59 952.1 -9.7 961.8 Do.

14FF60 952.8 3.43 949.4 Regolith

14FF61 970.6 5.62 965.0 Do.

*NGVD 29

 

1

A negative number indicates water level above land surface.

2

Water level during pumping.

Seasonal ground-water level fluctuations varied from 

about 1 to 3 ft for the longer periods of record and varied from 

0.25 to 0.5 foot during shorter periods (see hydrographs for 

wells 13FF13 and 14FF47, CD–ROM) in response to variations 

in rainfall. In these wells, ground-water levels generally 

increased during wet periods in response to recharge from infiltrating precipitation and decreased during dry periods in 

response to ground-water discharge to streams and evapotranspiration. The magnitude of seasonal water-level fluctuations 

observed in these wells is similar to longer trends observed in 

other parts of the Piedmont region (Coffin and others, 2003). 

Note that a large fluctuation of about 9 ft was observed in well 

14FF42 from June–November 1996; however, this magnitude 

of fluctuation seems to be atypical for the Lawrenceville area.

Variations in stream stage also may influence the water 

level in at least one well. The water level in well 13FF22 

increased approximately 1 ft in response to a rise in stream stage 

(see hydrograph, CD–ROM).

Water levels in about one-half of the wells used in this study 

fluctuate in response to pumping at the Rhodes Jordan Well 

Field (table 10). Some of the responses observed are summarized as follows:

• In the immediate vicinity around the wellfield (wells 

14FF17, 14FF18, 14FF26, and 14FF39) drawdown in 

response to pumping ranges between 75 and 135 feet, 

depending on the rate and duration of pumping. Lowering the water level in the vicinity of Rhodes Jordan 

Wellfield dewaters the shallow water-bearing fractures. 

Pumping does not, however, lower the water level in a 

nearby regolith observation wells (well 14FF36), indicating poor hydraulic connection between the bedrock 

and regolith at this location.

• Away from the wellfield, drawdown in the bedrock is 

extensive and observed in wells as far away as 7,000 ft 

from the center of pumping. Some of these wells are 

located across a major topographic divide (Chapman, 

1999, p. 29; Tharpe and others, 1997), indicating that 

bedrock fracture system supplying the wellfield is not 

bounded by topographic basin divides. Well 13FF14, 

the well farthest from Rhodes Jordan Wellfield that is 

influenced by pumping, shows a drawdown in the range 

from 0.5 ft to about 6 ft during longer periods of time.

• Drawdown in bedrock wells varies with the duration, 

rate of pumping, distance, and direction from the 

Rhodes Jordan Wellfield. In well 14FF08, located about 

4,700 ft west of Rhodes Jordan Wellfield (fig. 1), the 

water-level drawdown in response to cyclic weekly 

pumping ranges from about 1 to 2 ft (fig. 8), with a longterm estimated drawdown8 from 4 to 5 ft. Other wells 

responding to pumping at the Rhodes Jordan Wellfield 

are listed in table 10.

• The direction and magnitude of drawdown generally is 

greater in the east-west direction parallel to bedrock 

foliation and layering than in the north-south direction, 

which is similar to the responses observed during aquifer tests described above. The preferential east-west 

drawdown indicates that recharge and ground-water 

flow probably is greatest along bedrock foliation planes 

and compositional layering toward the pumped wells.

8

Long-term drawdown was estimated using a period of increased pumping from 

July 9–26, 1996, and a period of decreased pumping from February 5–17 1997
Summary and Conclusions 29

.

Table 10. Range of dates where continuous water-level data are 

available and influence from pumping, Lawrenceville, Georgia, area.

[RJWF, Rhodes Jordan Well Field; Do., ditto; ft, foot; <, less than; —, no data]

Well 

name Well type Range of dates1

Influenced by 

pumping at RJWF

Drawdown 

range2

13FF12 Bedrock 10/1998–12/1999 Yes 0.5 to 2 ft

13FF13 Do. 7/1998 – 4/1999 No None observed

13FF14 Do. 7/1998– 1/2000 Yes 0.5 to 6 ft

13FF17 Do. 8/2001– 11/2001 No None observed

13FF19 Do. Do. No Do.

13FF20 Do. Do. No Do.

13FF21 Do. Do. No Do.

13FF22 Do. Do. No Do.

14FF08 Do. 2/1996–1/2000 Yes 0.8 to 1.3 ft

14FF16 Do. 7/1995– 2/1996

7/1996 – 8/1997

Yes < 135

14FF17 Do. 2/1995 – 3/1997 Yes < 135

14FF18 Do. 2/1995 – 7/1996 Yes < 135

14FF26 Do. 8/1995 – 12/1995

5/1998 – 11/1999 Yes < 144

14FF27 Do. 11/1995 – 4/1999 No None observed

14FF36 Regolith 4/1996 – 12/1996 No Do.

14FF38 Bedrock 12/1995 – 11/1999 Yes 0.5 to 1 ft

14FF39 Do. 3/1996 – 6/1996

9/1997 – 5/1998

Yes < 112

14FF42 Do. 6/1996 – 4/1999 No None observed

14FF46 Do. 5/1998 – 12/1999 Yes 0.5 to 1 ft

14FF47 Do. 8/1998 – 4/1999 No None observed

14FF49 Do. 9/1998 – 4/1999 No 0.25 to 0.50

14FF50 Do. 9/1998 – 10/1998 Yes —

14FF55 Do. 8/2001 – 11/2001 Yes 1.5 to 3 ft

14FF56 Do. Do. No None observed

14FF57 Do. Do. No Do.

14FF59 Do. 8/2001 – 10/2001 No Do.

1Approximate range of dates where continuous water-level data are available.

2

Approximate range of drawdown in feet caused by pumping at RJWF.

Summary and Conclusions

Large ground-water supplies needed for municipal and industrial use have been developed from igneous and metamorphic 

crystalline rocks in many parts of the Piedmont and Blue Ridge 

physiographic provinces. Little information generally is available, however, to assess the potential of developing additional 

ground-water supplies from these complex aquifer systems. The 

U.S. Geological Survey, in cooperation with the City of 

Lawrenceville, conducted this study to determine what geologic 

structures, if any, contribute to the development of increased permeability and high ground-water yield in the area.

Thirty-two wells, ranging in depth from 180 to 630 feet (ft), 

were used to evaluate the bedrock lithology, fracture, and water 

yielding characteristics in the Lawrenceville area. The depth and 

nature of the fractures were determined by directly observing 

them in 32 open boreholes of wells with a borehole camera and 

by using borehole-imaging and geophysical techniques. Yield 

from individual water-bearing fractures was estimated by correlating increases in yield recorded during drilling to the measured 

depths of these zones. Individual yield of water-bearing zones 

was confirmed in 12 wells using flowmeter surveys. Ten aquifer 

tests were conducted to determine longer-term yield from the 

wells, which is the yield of all water-bearing fractures contributing water to the borehole, and to determine the direction and magnitude of drawdown resulting from pumping. Packer tests were 

conducted in one well to determine the hydraulic response among 

discrete water-bearing fractures. Continuous water-level data 

were collected from 26 wells to monitor the effects of rainfall, 

stream stage, and pumping on water levels in the study area.

Using borehole imaging data and correlating these to individual fracture yield, two main systems of water-bearing zones were 

identified: (1) joints, open joints, and zones of joint concentration 

consisting mostly of steeply-dipping low-yielding fractures; and 

(2) small and large openings along foliation planes and layering 

consisting of discontinuous but high-yield fractures, which are 

defined in this report as “foliation parallel-parting systems.” 

Water-bearing zones also are formed from the dissolution of preexisting crosscutting mineralized joints; these create irregular 

openings that cut across foliation and layering. Chemical dissolution along joints, foliation planes, and contacts between compositional layers was apparent in several of the boreholes studied.

Joints generally are complex “crisscross” fractures that break 

up the rock into blocks and slabs of differing dimensions. In boreholes, joints are differentiated from other fractures by their occurrence in sets, common planar geometry, and their orientation cutting across rock foliation and layering. Most joints observed in 

boreholes appeared as tight “hairline” fractures and typically did 

not form significant water-bearing zones. Small to moderate 

amounts of water—generally in the range from 1 to 5 gallons per 

minute (gal/min)—were produced from open, steeply-dipping 

joints and zones of joint concentration.
30 Methods and Hydrogeologic Data in Lawrenceville, Georgia, Area

Foliation partings and major foliation openings, which are 

fractures formed nearly parallel to foliation and layering, 

yielded large quantities of water to open boreholes in the 

Lawrenceville area. Foliation partings, which are small openings typically less than 0.5-inch wide, yielded 1 to 15 gal/min, 

with a maximum value of about 63 gal/min. In some boreholes, 

groups of foliation partings formed substantial water-bearing 

zones and yielded as much as 50 gal/min. Major foliation openings, which are large openings typically 1 to 8 inches wide, 

yielded substantially more water than the smaller foliation partings. A range in yield from 50 to 100 gal/min is typical for these 

larger fracture openings, making these the primary water-bearing features responsible for high-yield wells in the 

Lawrenceville area. All the high-yield wells in the area penetrate at least one major foliation opening.

Dissolution openings along mineral infilled joints or veins 

were observed in a few wells with air-lift yields of up to 

35 gal/min. This amount exceeds the typical range in yield for 

open joints and zones of joint concentration, indicating the 

importance of dissolution features in the bedrock. Dissolution 

features may be more common than would be indicated by the 

data collected because their identification requires a clear, highquality image that shows remnants of the mineral infilling 

around the edges of the joint or vein. These types of high-quality images were not available in most of the wells studied.

Flowmeter surveys confirmed the depth and yield contribution from various types of water-bearing fractures in selected 

wells, specifically the high-yielding nature of foliation partings 

and major foliation openings. In several wells, flowmeter surveys helped to identify confined/semiconfined water-bearing 

zones. Water from the confined/semiconfined zones flowed 

from the fracture, up the borehole, and typically exited from the 

borehole through shallower fractures. From these data, ground 

water under ambient and pumping conditions appears to be 

derived from discrete fractures intersecting the boreholes, 

rather than being distributed evenly along the open interval. 

Most of the inflow typically was concentrated within two to 

three intervals, corresponding to the depth of water-bearing 

fractures identified through other geophysical methods.

Aquifer tests confirmed that production wells could sustain 

large pumping rates for the period of the tests. Yields from aquifer tests ranged from 75 to 600 gal/min. In several wells, the 

aquifer-test yield was substantially less than the reported air-lift 

yield; whereas in other wells, the aquifer-test yield was greater 

than the reported air-lift yield. The recovery of water levels following pumping varied from slow, indicating a small recharge 

rate to the fracture(s) supplying the well, to fast, indicating a 

Figure 8. Partial record of water-level hydrograph for well 14FF08 showing effect of pumping at the 

Rhodes Jordan Wellfield, Lawrenceville, Georgia.

16

16.5

17

17.5

18

18.5

19

19.5

20

WATER LEVEL BELOW LAND SURFACE, IN FEET

Pump off

Pump on

Rhodes Jordan Wellfield 

off/on pumping cycle

DECEMBER 1998 JANUARY 1999

11 21 26 31 5 9 16
References Cited 31

large recharge rate to the fracture(s) supplying the well. Drawdown during the tests varied depending on the distance and 

direction from the pumped well. In most of the aquifer tests, the 

magnitude of drawdown was greater in the direction parallel to 

bedrock foliation and layering than perpendicular to it. Aquifer 

test results also indicated a strong potential for interferences 

between certain wells. If pumped simultaneously, interferences 

between wells likely would result in corresponding declines in 

the pumping rates during long periods of time.

Packer tests conducted in one well indicated that most of the 

water enters the borehole through foliation openings and not 

through joints, and confirms the high-yield nature of foliation 

openings. A small amount of water probably enters through 

joints, but this is much less than derived from the foliation openings tested. Drawdown responses from the packer tests also 

indicated a slight but noticeable vertical connection among 

individual high-yield foliation openings, likely resulting from 

steeply-dipping joints.

Ground-water levels in the study area fluctuate in response 

to seasonal variations in rainfall, stream stage, and groundwater pumping. Open-hole water levels rise mostly above the 

bottom of casing. Water levels measured in open boreholes represent a composite potentiometric head of all the water-bearing 

fractures. Six boreholes had water levels above land surface and 

four of these flowed when left uncapped. Seasonal groundwater level fluctuations varied from about 1 to 3 ft in response 

to variation in rainfall. Ground-water levels generally increased 

during wet periods in response to recharge from infiltrating precipitation and decreased during dry periods in response to 

ground-water discharge to streams and evapotranspiration. 

Variations in stream stage also may influence the water level in 

at least one well. The water level in this well increased approximately 1 ft in response to the rise in stream stage.

Water levels in about half of the wells used in this study 

fluctuate in response to pumping at the Rhodes Jordan Wellfield. In the immediate vicinity around the wellfield, drawdown 

varies between 75 and 135 ft, depending on the rate and duration of pumping. Lowering of the water level in the vicinity of 

Rhodes Jordan Wellfield dewaters shallow water-bearing fractures but does not lower the water level in a nearby regolith 

observation well, indicating poor hydraulic connection between 

the bedrock and regolith at this location. Away from the wellfield, drawdown in the bedrock was observed as far away as 

7,000 ft in wells located across a major topographic divide, indicating the bedrock fracture system supplying the wellfield is not 

bounded by topographic basin divides. Drawdown is from 

about 4 to 5 ft in one well, located 4,700 ft west of Rhodes 

Jordan Wellfield. The magnitude and direction of drawdown 

around the wellfield, is greater in the east-west direction, parallel to bedrock foliation and layering, than in the north-south 

direction. The east-west drawdown indicates that recharge and 

ground-water flow probably is concentrated along bedrock foliation planes and layering toward the pumped wells.

Collectively, the data from this study indicate that foliation 

parallel-parting systems, consisting of discontinuous zones of 

foliation partings and major foliation openings, strongly influence the yields of wells in the Lawrenceville area. Wells tapping these systems are capable of sustaining large ground-water 

withdrawals for extended periods of time, as indicated from the 

continuous operation of the Rhodes Jordan Wellfield since 

1995. Open-hole water levels, flowmeter surveys, and 

preferential drawdown parallel to foliation and compositional 

layering indicate a general hydraulic confinement of foliation 

parallel-parting systems and indicate strong lithologic and 

structural control on the development of these water-bearing 

fracture systems.

Foliation parallel-parting systems are easily identified in 

boreholes using geophysical methods described in this report. 

The yield potential of foliation parallel-parting systems within 

an individual topographic basin or several topographic basins 

can be large, depending on the areal extent of the waterbearing zones and the interconnectivity of these zones with 

sources of recharge.

References Cited

Atkins, R.L., and Higgins, M.W., 1980, Superimposed folding 

and its bearing on geologic history of the Atlanta, Georgia, 

area in Frey, R.W., ed., Excursions in Southeastern Geology: 

The American Geological Institute, Washington, D.C., v. 1, 

p. 19–40.

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Prepared by U.S. Geological Survey, Water Resources 

Discipline, Georgia District, Atlanta, Georgia.

Figure design and production by Caryl J. Wipperfurth and 

Bonnie J. Turcott .

Editing and page layout by Patricia L. Nobles.