Portable geophysical loggers that are specifically

designed for ground-water applications (fig. 1) are now

available. The geophysical loggers are PC-based and

have menu-driven software for the collection, real-time

display, and subsequent analysis of digital log data.

Drawworks for shallow investigations are highly

portable, and some have plastic-coated logging cables

for easy decontamination. Logging probes are available

that can be used in boreholes with a diameter as small as

5 centimeters. Many probes are capable of collecting

multiple parameters with a single logging run, thereby

greatly increasing the efficiency of the logging operation

and taking full advantage of the synergistic nature of

geophysical log data.

Figure 2. Electromagnetic-induction log delineates a leachate

plume in a sand-and-gravel aquifer downgradient of a

municipal landfill. The most highly contaminated part of the

plume is at a depth of 41 to 45 meters (Williams and others,

1993).

Advances in Borehole Geophysics for

Ground-Water Investigations

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36

34

32

30

0 20 40 60 80 100

ELECTROMAGNETIC CONDUCTIVITY,

IN MILLISIEMENS PER METER

20 40 60 80 100

GAMMA, IN COUNTS

PER SECOND

Water table

Medium

sand

Fine

sand

Sand with

cobbles,

gravel,

and clay(?)

Sand and clay

with boulders

DEPTH BELOW LAND SURFACE, IN METERS

0 1000 2000 3000

SPECIFIC CONDUCTANCE

OF GROUND WATER, IN

MICROSIEMENS PER CENTIMETER

Electromagnetic

conductivity

Specific

conductance

Detailed information on subsurface conditions is essential for the development and management of groundwater resources and the characterization and remediation of contaminated sites. Borehole geophysics provides a

highly efficient means for the collection of such information. Recent advances in methods and equipment have

greatly increased the ability of geoscientists to obtain subsurface information in ground-water investigations

through the use of borehole-geophysical techniques.

Electromagnetic-induction logging replaced normalresistivity logging in the oil industry many years ago.

Induction probes recently have been designed for smalldiameter monitoring wells. Induction logs can be

collected in water-, air-, and mud-filled holes and through

PVC casing. Major factors that affect induction-log

response in sand-and-gravel aquifers are the

concentration of dissolved solids in the ground water and

the silt and clay content of the aquifer. Induction logs,

which are commonly run in combination with gamma

logs, can be used to identify lithology and zones of

electrically conductive contamination such as landfill

leachate (fig. 2) and saltwater intrusion.

U.S. Department of the Interior Fact Sheet 002-98

U.S. Geological Survey April 1998

Figure 1. A PC-based geophysical logger with

portable drawworks and plastic-coated logging cable

in use at a contaminated ground-water site.
High-resolution flowmeters that use heat-pulse and

electromagnetic methods can measure extremely low

vertical flow rates in boreholes. Conventional impeller

flowmeters that are widely used in ground-water studies

have a lower measurement limit of about 2 meters per

minute, whereas the high-resolution flowmeters have

lower measurement limits of less than 0.03 meters per

minute. Flowmeters can be used to measure borehole

flow under ambient as well as pumped conditions.

Borehole-flow measurements made under ambient

conditions can help to delineate transmissive fractures

and other permeable zones (fig. 3) and to indicate the

direction of vertical hydraulic gradients; they also are

useful in interpreting fluid-conductivity logs and

borehole water-quality data. Borehole-flow

measurements made under pumped conditions can be

used to develop hydraulic-conductivity profiles of

aquifers.

29.2

29.3

29.4

29.5

29.6

S S WN E

DEPTH BELOW TOP OF CASING, IN METERS

NORTH

Figure 4.—"Virtual core" wrapped (left) and unwrapped (right)

images of a bedrock fracture at a depth of 29.4 meters collected

with a digital television camera. The images show that the

fracture is at the contact between pegmatite and gneiss.

Television cameras commonly are used in groundwater studies to inspect the condition of well casing and

screens; they also can be used in open bedrock wells to

directly view (1) lithologic texture, grain size, and color;

(2) water levels and cascading water; and (3) fractures.

Television logs can be obtained in clear water and above

the water level. The most sophisticated television systems

are magnetically oriented, provide a 360-degree digital

image of the borehole wall (fig. 4), and allow interactive

determination of fracture and bedding orientation.

Acoustic televiewers provide a magnetically

oriented, 360-degree, photographlike image of the

acoustic reflectivity of the borehole wall (fig. 5).

Televiewers have been used in the oil industry for many

years and are being used increasingly in ground-water

applications. Televiewer logs, which indicate acoustic

transit time and reflected amplitude, can be obtained

from water- or mud-filled holes. The newest digital

televiewer systems allow interactive determination of

fracture and bedding orientation (fig. 6).

NUMBER OF

FRACTURES

(RED INDICATES

TRANSMISSIVE)

DOWNWARD FLOW,

IN LITERS PER

MINUTE

TRANSMISSIVITY,

IN METERS

SQUARED PER DAY

DEPTH BELOW LAND SURFACE, IN METERS

0.1 1.0 10 50

10

20

30

40

50

60

70

80

90

100

110

0

0

1234 01234

Figure 3.—Heat-pulse flow measurements indicate

transmissive fracture zones in crystalline bedrock. Fracture

distribution was determined from an acoustic-televiewer log

and transmissivity was estimated from straddle-packer pump

tests (Williams and Conger, 1990).
E - W TRANSIT TIME AMPLITUDE

CALIPER

N - S

CALIPER

DEPTH BELOW TOP OF CASING, IN METERS

27

28

29

30

31

32

NE W S NE W S N

Figure 5.—Acoustic caliper, transit time, and amplitude logs

collected with a digital televiewer. The bedrock fracture at 29.4

meters is indicated by increased travel time and decreased

amplitude of the acoustic signal. The north-south and eastwest calipers calculated from the acoustic transit time show an

enlargement of the borehole at the fracture. This fracture zone

produced most of the well yield, as indicated by heat-pulse

flowmeter measurements under pumped conditions.

Figure 7.—Borehole radar detects fracture zones in granite.

The radar reflector indicated by the arrow corresponds to a

fracture zone that intersects the borehole at a depth of 75

meters. The fracture zone reportedly yielded more than 1,000

liters per minute (Lane and others, 1994).

Borehole radar provides a method to detect fracture

zones at distances as far as 30 meters or more from the

borehole in electrically resistive rocks (fig. 7). Fracture

zones with electrical properties that differ from the

surrounding nonfractured rock are excellent radar

reflectors. Borehole radar has been successfully applied

in granite, gneiss, and other crystalline rocks as well as

in limestone and dolomite. Radar measurements can be

made in a single borehole (transmitter and receiver in

same borehole) or by cross-hole tomography

(transmitter and receiver in separate boreholes). Singlehole, directional radar can be used to identify the

location and orientation of fracture zones (fig. 6). Crosshole tomography including radar velocity and

attenuation can be used to delineate fracture zones

between boreholes. The movement of a saline tracer

through fracture zones can also be monitored by

borehole radar (fig. 8).

Acoustic Televiewer Borehole Radar

Figure 6.—Fracture orientation in limestone as determined from

acoustic televiewer and borehole radar. Lower hemisphere

equal-area projections of fracture poles reveal a conjugate set

of northwest and southeast dipping fractures. Blue denotes that

the fracture zone is transmissive, as indicated by heat-pulse

flowmeter measurements (Lane and others, 1996).

 0.00 0.10 0.20 0.30 0.40 0.50

 20

 25

 30

 35

 40

 45

 50

 55

 60

 65

TRAVEL TIME, IN MICROSECONDS

DEPTH BELOW LAND SURFACE, IN METERS

0 10 20 30

RADIAL DISTANCE FROM BOREHOLE, IN METERS
References

Johnson, C.D., 1994, Use of a borehole color video

camera to identify lithologies, fractures, and borehole

conditions in bedrock wells in the Mirror Lake Area,

Grafton County, New Hampshire, in U.S. Geological

Survey Toxic Substance Hydrology Program—

Proceedings of the Technical Meeting, Colorado

Springs, Colorado, September 20-24, 1993: U.S.

Geological Survey Water-Resources Investigations

Report 94-4015, p. 89-93.

Lane, J.W., Haeni, F.P., and Williams, J.H., 1994, Detection of bedrock fractures and lithologic changes using

borehole radar at selected sites, in Proceedings of the

Fifth International Conference on Ground Penetrating

Radar, Kitchener, Ontario, Canada, June 12-16, 1994:

Waterloo, Ontario, Waterloo Centre for Groundwater

Research, p. 557-592.

Lane, J.W., Haeni, F.P., Placzek, G., and Wright, D.L.,

1996, Use of borehole-radar methods to detect a saline

tracer in fractured crystalline bedrock, Mirror Lake,

Grafton County, New Hampshire, in Proceedings of

the 6th Annual International Conference on Ground

Penetrating Radar, Sendai, Japan, September 30-

October 3, 1996, p. 185-190.

Lane, J.W., Haeni, F.P., Soloyanis, S., Placzek, G.,

Williams, J.H., and others, 1996, Geophysical characterization of a fractured-bedrock aquifer and blastfractured contaminant-recovery trench, in Proceedings

of the Symposium on the Application of Geophysics

to Engineering and Environmental Problems, Keystone, Colorado, April 28-May 2, 1996: Wheat Ridge,

Colo., Environmental and Engineering Geophysical

Society, p. 429-442.

Paillet, F.L., Crowder, R.E., and Hess, A.E., 1996, Highresolution flowmeter logging applications with the

heat-pulse flowmeter: Journal of Environmental

Engineering Geophysics, v. 1, no. 1, p. 1-11.

Williams, J.H. and Conger, R.W., 1990, Preliminary

delineation of contaminated water-bearing fractures

intersected by open-hole bedrock wells: Ground Water

Monitoring Review, v. 10, no. 3, p. 118-126.

Williams, J.H., Lapham, W.W., and Barringer, T.H.,

1993, Application of electromagnetic logging to

contamination investigations in glacial sand-andgravel aquifers: Ground Water Monitoring and

Remediation Review, v. 13, no. 3, p. 129-138.

Young, S.C. and Pearson, H.S., 1995, The electromagnetic borehole flowmeter - description and application:

Ground Water Monitoring and Remediation Review,

v. 15, no. 4, p. 138-147.

0 15 5 10

0 0.2 0.1

60

50

40

30

0 15 5 10

0 0.2 0.1

RADIAL DISTANCE FROM BOREHOLE, IN METERS

TRAVEL TIME, IN MICROSECONDS

DEPTH BELOW TOP OF

CASING, IN METERS

Figure 8.—Borehole radar before (left) and after (right) injection

of saline tracer in crystalline bedrock. Fracture zones that

intersect the well at 39 and 44 meters (indicated by arrows) are

major pathways for movement of the saline tracer (Lane and

others, 1996).

For further information, contact:

John W. Lane

U.S. Geological Survey

11 Sherman Place, U-5015

Storrs, Connecticut 06269

(860) 487-7402

email: jwlane@usgs.gov

World Wide Web:

http://wwwrvares.er.usgs.gov/ogw/bgas

John H. Williams and John W. Lane

John H. Williams

U.S. Geological Survey

425 Jordan Road

Troy, New York 12180-8349

(518) 285-5670

email: jhwillia@usgs.gov

World Wide Web:

http://ny.usgs.gov