•	 Surface geophysical methods

o Frequency-domain electromagnetics

o Time-domain electromagnetics

o Capacitively coupled electromagnetics

o Direct-current resistivity

o Magnetic resonance soundings

o Ground-penetrating radar

The geophysical workgroup actively participates and collaborates with local, State, national, and international members 

of the environmental geophysical community. In addition, it 

regularly contributes to the knowledge base through presentations and publications.

Example Applications of Geophysical Techniques

Geophysical project activities of the TXWSC have steadily 

increased over the past 10 years. All projects mentioned below 

(fig. 1) have a substantial geophysical component. Each of the 

projects listed was published during 2005–10. This is not a 

complete list of projects, but it highlights examples of several 

geophysical techniques and their applications.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3037 

May 2011

Enhancement of USGS Scientific Investigations in Texas by 

Using Geophysical Techniques, 2005–10

Printed on recycled paper

Introduction

Geophysical techniques are an increasingly important 

tool for scientific investigations, environmental planning, and 

resource management. During 2005–10 the U.S. Geological 

Survey (USGS) Texas Water Science Center (TXWSC) greatly 

expanded its capabilities of using surface and borehole geophysical techniques to gain insights into how groundwater systems 

work and the occurrence and distribution of certain contaminants. Geophysical techniques provide a relatively quick and 

inexpensive means to characterize the subsurface hydrology and 

lithology. 

Surface and borehole geophysical methods are used to 

measure the physical properties of the subsurface, such as electrical conductivity or resistivity, dielectric permittivity, magnetic 

permeability, density, and acoustic velocity. Geophysical measurements can be influenced by chemical and physical properties of soils, rocks, and pore fluids. Interpretations from these 

measurements can be used to image the distribution of physical 

properties in the subsurface. Surface and borehole geophysical 

methods and their application to groundwater and environmental investigations are described in detail in Zohdy and others 

(1974), Keys (1990), and U.S. Army Corps of Engineers (1995).

This report describes the technical capabilities and project activities of the TXWSC geophysical workgroup during 

2005–10. After a brief summary of the geophysical workgroup’s 

capabilities, the details of project activities are described. Projects are grouped by the primary techniques used and include 

overviews, project images, and Internet links to additional 

project material and related publications.

Geophysical Workgroup Skills and Capabilities 

The TXWSC geophysical workgroup consists of geophysicists and hydrologists who specialize in surface and borehole 

geophysical techniques. The workgroup collaborates with resident natural resource scientists on a diverse range of projects. 

There is emphasis on technical training to keep skills current 

with advances in software and technology. The workgroup’s 

technical capabilities include but are not limited to the

following:

•	 Borehole logging techniques

o Natural gamma

o Electromagnetic induction

o Long and short normal resistivity

o Heat pulse and electromagnetic flow meter

o Neutron density

o Acoustic and optical televiewer

o Fluid resistivity/conductivity

o Full wave sonic

In cooperation with the Barton Springs/Edwards Aquifer Conservation District

Geophysical Delineation of the Freshwater/

Saline-Water Transition Zone in the Barton 

Springs Segment of the Edwards Aquifer, 

Travis and Hays Counties, Texas, 

September 2006 

Scientific Investigations Report 2007–5244

U..S..Department of the IInteriior

U..S..GeollogiicallSurvey

In cooperation with the Texas Water Development Board 

Application of Surface Geophysical Methods, With 

Emphasis on Magnetic Resonance Soundings, to 

Characterize the Hydrostratigraphy of the Brazos River 

Alluvium Aquifer, College Station, Texas, July 2006— 

A Pilot Study 

Scientific Investigations Report 2007–5203 

U.S. Department of the Interior 

U.S. Geological Survey 

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2008–5181

In cooperation with the San Antonio Water System

An Integrated Hydrogeologic and Geophysical Investigation 

to Characterize the Hydrostratigraphy of the Edwards Aquifer 

in an Area of Northeastern Bexar County, Texas

U.S. Department of the Interior 

U.S. Geological Survey 

Scientific Investigations 

Report 2007–5143 

In cooperation with the U.S. Section, International Boundary and Water Commission 

Geophysical Analysis of the Salmon Peak Formation 

Near Amistad Reservoir Dam, Val Verde County, 

Texas, and Coahuila, Mexico, March 2006, to 

Aid in Piezometer Placement 

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2009–1017

In cooperation with the U.S. Department of Energy/National Nuclear Security Administration 

and Babcock & Wilcox Technical Services Pantex, LLC

Analysis of Vertical Flow During Ambient and Pumped 

Conditions in Four Monitoring Wells at the Pantex Plant, 

Carson County, Texas, July–September 2008

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5122

In cooperation with the San Antonio Water System

Lithologic and Physicochemical Properties and Hydraulics 

of Flow in and near the Freshwater/Saline-Water Transition 

Zone, San Antonio Segment of the Edwards Aquifer, 

South-Central Texas, Based on Water-Level and Borehole 

Geophysical Log Data, 1999–2007

500

600

700

800

900

1,000

Georgetown

Formation

Person Formation Kainer Formation

Cyclic and marine members

Leached and

collapsed members

Regional

dense member

Grainstone member

Kirschberg

evaporite member

Dolomitic member

Basal nodular member

Glen Rose

Limestone

Figure 1. Map showing the cover page of each report presented in this report. 

Lines point to approximate location of each study.
Surface Geophysical Techniques

Direct Current Resistivity

Geophysical Analysis of the Salmon Peak 

Formation near Amistad Reservoir Dam, 

Val Verde County, Texas, and Coahuila, 

Mexico, March 2006, to Aid in Piezometer 

Placement

In 1995 the Mexico Section of 

the International Boundary and Water Commission (IBWC) 

completed a study (including surface geophysics, borehole 

geophysics, and installation of piezometers) of subsurface 

conditions of the western embankment (Coahuila, Mexico) of 

Amistad Reservoir Dam. Technical advisors recommended that 

one line of similarly constructed piezometers be installed on the 

eastern embankment of the dam for comparison of water levels 

(potentiometric head) on both the western and eastern embankments of the dam. To provide technical assistance for the 

horizontal and vertical placement of piezometers on the eastern 

embankment of Amistad Reservoir Dam, the USGS, in cooperation with the U.S. Section of the IBWC, conducted a study 

along both the western and eastern embankments of Amistad 

Reservoir Dam. The study involved an integrated approach 

using surface and borehole geophysical methods. In the western 

embankment investigation, geological and geophysical characteristics that indicate relatively large water-yielding properties 

of the Salmon Peak Formation were identified. The directcurrent (DC) resistivity method was selected as the surface 

geophysical reconnaissance technique to correlate relatively 

large water-yielding properties of the Salmon Peak Formation, 

identified from analysis of borehole geophysical logs, with 

variations in subsurface resistivity. The correlation of surface 

geophysical DC resistivity, historical lithologic data, and 

general trend of documented sinkholes along the eastern end 

of the eastern embankment profile was used to justify further 

exploration (drilling of piezometers). The spatial location of the 

piezometers and screened intervals were selected to best match 

the locations of the screened intervals of the western embankment piezometers. 

•	 USGS Scientific Investigations Report 2007–5143: http://

pubs.usgs.gov/sir/2007/5143/

Capacitively Coupled Resistivity

Two-Dimensional Resistivity Investigation 

Along West Fork Trinity River, Naval Air 

Station-Joint Reserve Base Carswell 

Field, Fort Worth, Texas, October 2004

The USGS, in cooperation with 

the Naval Air Station-Joint Reserve 

Base Carswell Field (NAS–JRB) at Fort 

Worth, Tex., conducted a 2D resistivity 

investigation at a site to characterize the 

distribution of subsurface resistivity. Contaminants, primarily volatile organic compounds and metals, have entered the 

groundwater flow system through leakage from waste-disposal 

sites and manufacturing processes. The Goodland Limestone 

and the underlying Walnut Formation form a confining unit 

that underlies the alluvial aquifer. The bedrock confining unit 

is the zone of interest because of the potential for contaminated 

groundwater to enter the river through saturated bedrock. The 

study involved a capacitively coupled resistivity survey and 

inverse modeling to obtain true or actual resistivity from apparent resistivity. 

•	 USGS Data Series Report 178–06: http://pubs.usgs.gov/

ds/ds178/

Magnetic Resonance Soundings

Application of Surface Geophysical 

Methods, With Emphasis on Magnetic 

Resonance Soundings, to Characterize 

the Hydrostratigraphy of the Brazos River 

Alluvium Aquifer, College Station, Texas, 

July 2006—A Pilot Study

The USGS, in cooperation with the 

Texas Water Development Board, used 

surface geophysical methods in a pilot study to characterize the 

hydrostratigraphic properties of the Brazos River alluvium aquifer at the Texas A&M University Brazos River Hydrologic Field 

Research Site near College Station, Texas, and determine the 

effectiveness of the methods to aid in generating an improved 

groundwater-availability model. Three noninvasive surface 

geophysical methods were used to characterize the electrical 

stratigraphy and hydraulic properties and to interpret the hydrostratigraphy of the Brazos River alluvium aquifer. Two methods, 

time-domain electromagnetic (TDEM) soundings and twodimensional direct-current (2D–DC) resistivity imaging, were 

used to define the lateral and vertical extent of the near-surface 

hydrogeologic zones. Magnetic resonance sounding (MRS), a 

recently developed geophysical method, was used to derive estimates of the hydrologic properties including percentage water 

content and hydraulic conductivity. Results from the geophysics 

study demonstrated the usefulness of combined TDEM, 2D–DC 

resistivity, and MRS methods to reduce the need for additional 

boreholes in areas with data gaps and to provide more accurate 

information for groundwater availability models.

•	 USGS Scientific Investigations Report 2007–5203: http://

pubs.usgs.gov/sir/2007/5203/

Time-Domain Electromagnetics

Geophysical Delineation of the Freshwater/

Saline-Water Transition Zone in the Barton 

Springs Segment of the Edwards Aquifer, 

Travis and Hays Counties, Texas, September 

2006

The USGS, in cooperation with 

the Barton Springs/Edwards Aquifer 

Conservation District, conducted a pilot 

geophysical study to use TDEM soundLake Worth

West Fork Tri nity River

and 3 

ea

0 0.25 0.5 MILE

EXPLANATION

NAS–JRB boundary

Boundary of resistivity

investigation site

Concentration of TCE, in micrograms per liter

5 to 50

50.1 to 500

500.1 to 1,000

1,000.1 to 5,000

5,000.1 to 15,000

More than 15,000.1

Base map USGS Digital Orthophoto Quarter Quadrangle - 2002 

State Plane Coordinate System, North Central Zone, NAD 83

32o46'

97o25'

32o47'

97o24'

MWC3-4 MWB2-4 MWA2-4

45

50

55

60

65

70

35

40

45

50

55

60

65

70

25

30

35

40

45

50

55

60

65

70

50 100 150 200 250 300 350 400 450 500 550

DISTANCE, IN METERS

BRA09

BRA100

BRA160 BRA110

BRA170

BRA180

BRA60

BRA70 BRA80 BRA90

BRA01

BRA05

BRA40

BRA50

DC resistivity profile

MWB2-4 MWA2-4

MWC3-4

746,700 746,800 746,900 747,000 747,100 747,200

3,382,800

3,382,900

EASTING, IN METERS

NORTHING, IN METERS

BRA05 BRA09

BRA100

BRA160 BRA110

BRA170

BRA40

BRA50

BRA60

BRA70

BRA80

BRA90 BRA180

BRA01

less

than 10 20 32 54 89 greater

than 175

Direct-current resistivity,

Clay in ohm-meters Sand and gravel

Water level

Direct-current resistivity profile

Time-domain electromagnetic sounding

and identifier

EXPLANATION

Time-domain electromagnetic

layered-earth model sounding

BRA170

MWC3-4

Lithology

Monitoring well and identifier Shale

)B( )C( )D(

ALTITUDE, IN METERS ABOVE NAVD 88

APPROXIMATE LAND SURFACE

500 ft

200

500 ft

240

500 ft

245

500 ft

247

500 ft

250

500 ft

260

ALLTITUDE, IN FEET ABOVE NGVD 29

A

B

-100

0

100

200

300

400

500

600

700

0

50100

150200

250

0

50100

0

50050100

050

0

50

EXPLANATION

Taylor Group

Austin Group

Eagle Ford Group

Buda Limestone

Del Rio Clay

Georgetown Formation

Edwards Group

Regional dense member TDEM apparent resistivity,

in ohm-meters

Edwards aquifer

Upper confining unit

TDEM sounding

and identifier

1,000 0 1,000 FEET

-100

0

100

200

300

400

500

600

700

Top of Edwards aquifer

Approximate land-surface elevation

ALTITUDE, IN FEET ABOVE NGVD 29

200

240

245

247

250

260

C

6 20 43 66 89 113 145

Resistivity, in ohm-meters

200

0 46 325 641 925 1,202 1,583 2,081

Dissolved solids concentration,

in milligrams per liter

200

240 245

250

260

247

DC resistivity profile

Spring 2

Spring 3

GG15

GG17

200 m

200 m

W E A70E A70W

A72E A72W

A74E A74W

A76E A76W

A80E A80W

LA-6

LA-7

LA-8L

LA-10

LA-11

LA-12L

LA-14

LA-15

LA-16L

Profile 1

Profile 2

240

250

260

270

280

290

300

310

320

330

340

DISTANCE, IN METERS

ELEVATION, IN METERS

ABOVE NAVD 88

less than

75 166 256

greater than

365

RESISTIVITY,

IN OHM-METERS

0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400

Base from U.S. Department of Agriculture National Agricultural Imagery Digital Ortho Photo Image

Universal Transverse Mercator projection, Zone 14

North American Datum of 1983

Direct-current resistivity profile

Top of zone of weathered features in limestone

Top of limestone

Argillaceous fossiliferous zone

Section trace line

EXPLANATION

Selected core hole and identifier

Piezometer and identifier—Underlined 

identifier indicates logged well

Spring and identifier

Sinkhole and identifier

.

A

B
feet or meter F

Z

other3serv

M latitude 29 40 58.4

deltat matrix 44

mud temp NA

res mud filtrate

elev kb NA log meas from LSD

sys version 3.59T

temp gradient 0 mud res NA

file type id

township NA

time circ stopped NA

eng units or cps E

recorded by THOMAS

field office TWSC - AUSTIN

depth driller 320

field CSSA

range NA

mean surface temp

casing type STEEL

casing bottom 45

tool serial num

deltat fluid

longitude -098 38 18.8

fluid viscosity

SERVICE COMPANY USGS

bit size 6.125

01. t ni el p mas gol U noit ceri d gol

elect cutoff 9999

elev perm datum1179

county BEXAR

truck cal num .599 

mud sample source NA

temp mud cake

LOCATION

casing diameter 10.

drl meas from NA

permanent datum LSD

Name Prn AP

UNIQUE WELL ID

neutron matrix DOLOMITE

fluid type H2O

fluid ph

company CSSA - U.S. GEOLOGICAL SURVEY

elev df NA

state TX

PROVINCE

temp mud filtrate

file type ORIGINAL 

sys serial 1

remarks1 AMBIENT

other1serv

ZE

log bottom 328.60

time 12:13:

section NA

density matrix 2.85

logging unit 302

remarks2 WL = 156.46

casing thick 0

elev gl 1179

log top 2.90

well I10-4

DATE 02/17/11

Z

other2serv

I

mag declination 0

res mud cake NA

fluid density

Depth

1ft:120ft

GAM(NAT)

0 CPS 150

RES(FL)

0 OHM-M 35

SP

75 MV 175

RES(16N)

1 OHM-M 1000

RES(64N)

1 OHM-M 1000

TEMP

68 DEG F 73

LATERAL

1 OHM-M 1000

DEL TEMP

-1 DEG F 1

CALIPER

0 INCH 10

CCL

60000 CPS 63000

IND. Res

1 OHM-M 1000

AP-COND

0 MMHO/M 150

SP COND

300 US/CM 350

Tool.Image-NM

0° 90° 180° 270° 0°

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250

260

270

280

290

300

310

320

Depth

1ft:120ft

GAM(NAT)

0 CPS 150

RES(FL)

0 OHM-M 35

SP

75 MV 175

RES(16N)

1 OHM-M 1000

RES(64N)

1 OHM-M 1000

TEMP

68 DEG F 73

LATERAL

1 OHM-M 1000

DEL TEMP

-1 DEG F 1

CALIPER

0 INCH 10

CCL

60000 CPS 63000

IND. Res

1 OHM-M 1000

AP-COND

0 MMHO/M 150

SP COND

300 US/CM 350

Tool.Image-NM

0° 90° 180° 270° 0°

NORTH SOUTH

N

27 103 206 308 411 513 616 718 821 923

RESISTIVITY, IN OHM-METERS

EXPLANATION

Time-domain electromagnetic 

sounding site and identier

Site–12

Fault projection (Stein and Ozuna, 1995)

Interpreted fault location from

geophysical data

Indicates change in location of fault, based

on interpretation of geophysical data

Interpreted karst feature from

geophysical data

K

Kkd (VII) Geologic unit (hydrostratigraphic zone) (table 1)

Site–12 Site–13

Kkd (VII)

Kkd (VII)

Bat Cave fault

(Stein and Ozuna, 1995)

Kkd (VII)

Bat Cave fault

interpreted from

surface geophysics

Kplc (III)

Kplc (III) Kprd (IV)

Bat Cave fault

(Stein and Ozuna, 1995)

Bat Cave fault

interpreted from

surface geophysics

K K

ALTITUDE, IN METERS

ABOVE NAVD 88

245

255

265

275

285

295

305

315

325

CAPACITIVELY

COUPLED

SURVEY

Site–13

Site–12

LINE

Bat Cave fault

(George, 1952; Stein and Ozuna, 1995)

Unnamed fault

Geologic units, hydrostratigraphic zones, and fault locations interpreted

from geophysical data and hydrogeologic mapping for this report 125 0 125 METERS

Vertical scale greatly exaggerated

Altitude of log datum (ft above NAVDof 1988) 3539.11

Casing depth (ft) 613

Log datum LSD

Well name PTX06–1044

County Carson

Borehole bit size (in) 7.865

Borehole depth (ft) 622

Casing diam. (in) 4

Latitude N 35 deg. 19' 44"

Date of log 7/25,8/11,9/24/08

Owner Pantex Site ID 351944101324201

State Texas

Longitude W 101 deg. 32' 42"

Depth EMFM Amb Before Construction

-5 Gal/Min 5

Neutron

0 CPS 50

Natural Gamma

0 CPS 150

RES(FL) Amb Before

15 OHM-M 20

EMFM Pu Before

-5 Gal/Min 5

WL Depth Before

54 0Ft005

WL Depth After

54 0Ft005

Trans. Before

0.5 Ft^2/D 500

TEMP Amb. Before

63 DEG F 73

TEMP Pu Before

63 DEG F 73

RES(FL) Pu Before

15 OHM-M 20

EMFM Amb After

-5 Gal/Min 5

Trans. After

0.5 Ft^2/D 500

Static WL

0 1

EMFM Pu After

-5 gpm 5

TEMP Amb After

63 DEG F 73

RES(FL) Amb. After

15 OHM-M 20

RES(FL) Pu After

15 OHM-M 20

400

450

500

550

600

473

482

481

481

481

473

9/24/08

34 Lithologic and Physicochemical Properties and Hydraulics of Flow, Freshwater/Saline-Water Transiti on Zone

Estimated ow less than

0.1 gallon per minute (gpm)

1

Corrected owstation 05/19/2005

Corrected owstation 06/20/2006

Corrected owstation 09/14/2006

gpm

gpm

gpm

Zone of inow or outow

Depth1 inch:100 feet

Acoustic televiewer

0° 180°90° 270° 0°

0 cps 100

GAM(NAT)

2 inch 12

CALIPER

-1

-1 1

-1 1

Corrected owstation 11/06/2007

-1 gpm 1

Stratigraphic unit

24.2 29.2

COND 05/19/2005

TEMP 06/20/2006

TEMP 09/13/2006

23 28

COND 09/13/2006

10000 35000

COND 11/06/2007

7000 32000

TEMP 11/06/2007

25 30

deg C

deg C

deg C

deg C

10000 μS/cm 35000

μS/cm

μS/cm

Generalized caliper prole

Conductance (COND), in

microsiemens

per centimeter (μS/cm)

Temperature (TEMP), in

Natural gamma (GAM(NAT)), in degrees Celsius (deg C)

counts per second (cps)

TEMP 05/19/2005

μS/cm 23.8 28.8

COND 06/20/2006

10000 35000

23.7 28.7

COND 11/08/2002

25000 μS/cm 50000 deg C

TEMP 11/08/2002

600

700

800

900

Note: “Corrected” indicates that EM owmeter data sets were corrected by zeroing out values measured in intervals

where no ow was expected, such as in the casing, and by subtracting those values from owmeter measurements made

in open borehole; this adjustment allowed for more consistent owmeter data sets and well hydraulic interpretations.

Georgetown

Formation

Person Formation Kainer Formation

Cyclic and marine members

Leached and

collapsed

members

Regional

dense member

Grainstone

member

Kirschberg

evaporite

member

Dolomitic

member

Basal nodular member

570

575

580

585

590

595

600

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEP

OCT

NOV

DEC

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEP

OCT

NOV

DEC

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEP

OCT

NOV

DEC

5002 6002 7002

ALTITUDE, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988

EXPLANATION

Geophysical data collected 

May 2005

Geophysical data collected 

June 2006

Geophysical data collected 

September 2006

Geophysical data collected 

November 2007

Daily mean equivalent 

freshwater head, in feet 

above North American

Vertical Datum of 1988.

Water-level data provided

by the San Antonio Water

System

DATE

Figure 8. Daily mean equivalent freshwater head and borehole geophysical data in Kyle 4 well (LR–67–02–105), San Antonio segment 

of the Edwards aquifer, south-central Texas, 2005–07. 

ing to delineate the freshwater/saline-water transition zone of 

the Edwards aquifer in Travis and Hays Counties, Tex.. There 

was uncertainty regarding the application of TDEM sounding 

for this purpose because of the depth of the aquifer (200–500 

feet to the top of the aquifer) and the relatively low-resistivity 

clayey units in the upper confining unit. Twenty-five TDEM 

soundings were made along four 2- to 3-mile-long profiles in a 

study area overlying the transition zone. The soundings yielded 

measurements of subsurface electrical resistivity, the variations 

in which were correlated with hydrogeologic and stratigraphic 

units, and then with dissolved-solids concentrations in the 

aquifer. On the basis of reasonably close matches between the 

inferred locations of the freshwater/saline-water transition zone 

from resistivities and from dissolved-solids concentrations in 

three of the four profiles, TDEM sounding appears to be a suitable tool for delineating the transition zone.

•	 USGS Scientific Investigations Report 2007–5244: http://

pubs.usgs.gov/sir/2007/5244/

Frequency-Domain Electromagnetic Profiling

An Integrated Hydrogeologic 

and Geophysical Investigation 

to Characterize the 

Hydrostratigraphy of the 

Edwards Aquifer in an Area of 

Northeastern Bexar County, 

Texas

The USGS, in cooperation 

with the San Antonio Water System, did a hydrogeologic and 

geophysical investigation to characterize the hydrostratigraphy 

(hydrostratigraphic zones) and karst features (features such as 

sinkholes and caves) of the Edwards aquifer in a 6.2-squaremile area undergoing urban development. Existing hydrostratigraphic information, enhanced by local-scale geologic mapping 

in the area, and surface geophysics were used to associate 

ranges of electrical resistivities, obtained from capacitively 

coupled resistivity surveys, frequency-domain electromagnetic 

(FDEM) surveys, TDEM soundings, and 2D-DC resistivity 

surveys, with each of seven hydrostratigraphic zones of the 

Edwards aquifer. The principal finding of this investigation 

is the relation between electrical resistivity and the contacts 

between the hydrostratigraphic zones of the Edwards aquifer 

and the underlying Trinity aquifer in the area. 

•	 USGS Scientific Investigations Report 2008–5181: http://

pubs.usgs.gov/sir/2008/5181/

Borehole Geophysical Techniques

Analysis of Vertical Flow During Ambient 

and Pumped Conditions in Four Monitoring 

Wells at the Pantex Plant, Carson County, 

Texas, July–September 2008

The USGS, in cooperation with 

B&W Pantex, made a series of flowmeter measurements and collected other 

borehole geophysical logs during July–

September 2008 to analyze vertical flow 

in screened intervals of four selected monitoring wells at the 

Pantex Plant. Hydraulic properties (transmissivity values) of 

the section of the High Plains (Ogallala) aquifer penetrated by 

the wells also were computed. Geophysical data were collected under ambient and pumped flow conditions in the four 

monitoring wells. Unusually large drawdowns occurred at two 

monitoring wells while the wells were pumped at relatively 

low rates. A decision was made to redevelop those wells, and 

logs were run again after redevelopment in the two monitoring 

wells. 

•	 USGS Open-File Report 2009–1017: http://pubs.usgs.

gov/of/2009/1017/

Lithologic and Physicochemical Properties 

and Hydraulics of Flow in and near the 

Freshwater/Saline-Water Transition Zone, 

San Antonio Segment of the Edwards 

Aquifer, South-Central Texas, Based on 

Water Level and Borehole Geophysical Log 

Data, 1999–2007

The freshwater zone of the Edwards 

aquifer in south-central Texas is bounded 

to the south and southeast by a zone of transition from freshwater to saline water (hereinafter, the transition zone). The 

boundary between the two zones is the freshwater/saline-water 

interface (hereinafter, the interface), defined as 1,000-milligrams per liter of dissolved solids. This report presents the 

findings of a study, done by the USGS in cooperation with 

the San Antonio Water System, to obtain lithologic properties 

and physicochemical properties and to analyze the hydraulics 

of flow in and near the transition zone of the Edwards aquifer 

on the basis of water level and borehole geophysical log data 

collected from 15 monitoring wells in four transects during 

1999–2007. A hydraulic connection between the transition zone 

and the freshwater zone is indicated by similar patterns in the 

hydrographs of the 15 transect monitoring wells in and near 

the transition zone and three county index wells in the freshwater zone during 1999–2007. The data for this report support, 

in part, a conceptualization of regional flow in and near the 

transition zone in which water enters the transition zone from 

the freshwater zone in the western part of the Edwards aquifer, 

flows toward the northeast, and discharges to the freshwater 

zone in the eastern part of the aquifer. The data for this report 

support the hypothesis that the interface is likely to remain 

laterally and vertically stable over time. 

•	 USGS Scientific Investigations Report 2010–5122: http://

pubs.usgs.gov/sir/2010/5122
References Cited

Keys, W.S., 1990, Borehole geophysics applied to ground water 

investigations: U.S. Geological Survey Techniques of WaterResources Investigations, book 2, chap. E2, 150 p.

U.S. Army Corps of Engineers, 1995, Geophysical exploration 

for engineering and environmental investigations: Engineering Manual 1110-1-1802, chap. 4, 57 p.

Zohdy, A.A.R., Eaton, G.P., and Mabey, D.R., 1974, Application 

of surface geophysics to ground-water investigations: U.S. 

Geological Survey Techniques of Water-Resources Investigations, book 2, chap. D1, 116 p.

Geophysical Workgroup Contact Information

Gregory P. Stanton Jason D. Payne

Groundwater Specialist Geophysicist

1505 Ferguson Lane 944 Arroyo Street

Austin, Tx 78754 San Angelo, Tx 76903

512-927-3558 325-944-4600 x-28

Andrew P. Teeple Jonathan V. Thomas

Hydrologist Geophysicist

944 Arroyo Street 2775 Alta Mesa Blvd.

San Angelo, Tx 76903 Fort Worth, Tx 76133

325-944-4600 x-17 817-263-9545 x-228

Publishing support provided by

Lafayette Publishing Service Center

For additional information, contact 

Director

USGS Texas Water Science Center

http://tx.usgs.gov/

gs-w-txpublic-info@usgs.gov 

Time-domain electromagnetic sounding layout and operation

Transmitter loop

Protem-47 transmitter

Eddy currents

Receiver loop

Receiver