Geohydrology of Pahute Mesa-3 Test Well, 

Nye County, Nevada

By KATHRYN C. KILROY and CHARLES S. SAVARD

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 95-4239

Prepared in cooperation with the 

U.S. DEPARTMENT OF ENERGY 

(Interagency Agreement DE-AI08-86-NV10583)

Carson City, Nevada 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director

Any use of trade names in this publication is for descriptive purposes 

only and does not constitute endorsement by the U.S. Government.

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

333 West Nye Lane, Room 203 Box 25286

Carson City, NV 89706-0866 Denver, CO 80225-0046
CONTENTS

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

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

Purpose and Scope..................................................................................................................................................... 2

Location of the Study Area........................................................................................................................................ 2

Previous Work............................................................................................................................................................ 2

Aclmowledgments......................................................................................^ 2

Drilling Procedures and Test-Well Construction................................................................................................................... 2

Geology.................................................................................................................................................................................. 5

Geophysical Logging Methods.............................................................................................................................................. 6

Caliper, Acoustic, and Electric Logs.......................................................................................................................... 6

Caliper............................................................................................................................................................ 6

Acoustic ......................................................................................................................................................... 12

Resistivity....................................................................................................................................................... 12

Conductance................................................................................................................................................... 13

Spontaneous Potential..................................................................................................................................... 14

Nuclear Log^.......................................................................................................................................................^ 14

Epithennal Neutron........................................................................................................................................ 14

Density............................................................................................................................................................ 14

Spectral Gamma Ray...................................................................................................................................... 14

Gamma Ray.................................................................................................................................................... 15

Borehole Flow Survey................................................................................................................................................ 15

Temperature Prior to Tracer Survey............................................................................................................... 15

Tracer Survey.................................................................................................................................................. 16

Temperature During Pumping........................................................................................................................ 16

Discussion.................................................................................................................................................................. 16

Injection Tests........................................................................................................................................................................ 17

Analytical Methods.................................................................................................................................................^ 17

Test Conditions.................................... 18

Test Results ................................................................................................................................................................ 18

Interval A........................................................................................................................................................ 18

Interval B........................................................................................................................................................ 20

IntervalC........................................................................................................................................................ 20

Interval D........................................................................................................................................................ 20

Interval E .............................................................................................................^^ 20

MervalF......................................................^ 20

Interval G........................................................................................................................................................ 22

Discussion.................................................................................................................................................................. 22

Aquifer Test................................................................................................................................................................^ 22

Analytical Methods.................................................................................................................................................... 22

Unconfined Radial Flow................................................................................................................................. 23

Confined Radial Flow..................................................................................................................................... 24

Specific Capacity............................................................................................................................................ 25

Test Conditions...............................................................................................^^ 25

Analysis of Results..................................................................................................................................................... 26

Unconfined Conditions................................................................................................................................... 26

Confined Conditions....................................................................................................................................... 27

Discussion.................................................................................................................................................................. 27

CONTENTS III
Water Levels.......................................................................................................................................................................... 29

Water-Level Altitudes at the Test Well...................................................................................................................... 29

Ground-Water Gradient.............................................................................................................................................. 30

Ground-Water Quality........................................................................................................................................................... 32

Water Chemistry......................................................................................................................................................... 32

Relation to Regional Water Chemistry....................................................................................................................... 34

Summary................................................................................................................................................................................ 34

References Cited.................................................................................................................................................................... 36

FIGURES

1. Map showing location of Pahute Mesa-3 test well, Nye County, Nevada............................................................. 3

2. Diagram showing Pahute Mesa-3 test well hole, casing diameters, and depths, Nye County, Nevada................. 4

3-14. Graphs showing:

3. Caliper, acoustic, geologic, and electric logs from Pahute Mesa-3 test well, Nye County, Nevada.............. 9

4. Nuclear logs from Pahute Mesa-3 test well, Nye County, Nevada................................................................ 10

5. Temperature and tracer-test logs, Pahute Mesa-3 test well, Nye County, Nevada......................................... 11

6. Intervals isolated by packers during injection testing, Pahute Mesa-3 test well, Nye County, Nevada......... 18

7. Injection-test analyses for depth intervals A, B, and C for Pahute Mesa-3 test well,Nye County, Nevada... 19

8. Injection-test analyses for depth intervals D, F, and G for Pahute Mesa-3 test well, Nye County, Nevada.. 21

9. Analysis of drawdown for an unconfined aquifer under the assumption of delayed yield

during pumping and recovery at Pahute Mesa-3 test well, Nye County, Nevada....................................... 26

10. Analysis of drawdown for an unconfined aquifer under the assumption of delayed yield

and correction for well-bore storage during pumping and recovery at Pahute Mesa-3 test well,

Nye County, Nevada.................................................................................................................................... 28

11. Analysis of drawdown for a leaky confined aquifer during pumping and recovery at Pahute

Mesa-3 test well, Nye County, Nevada....................................................................................................... 29

12. Analysis of drawdown for a leaky confined aquifer under the assumption of delayed yield

and well-bore storage during pumping and recovery at Pahute Mesa-3 test well, Nye County, Nevada... 30

13. Analysis of drawdown for confined aquifer under the assumption of delayed yield and

correction for well-bore storage during pumping and recovery at Pahute Mesa-3 test well,

Nye County, Nevada.................................................................................................................................... 31

14. Water-level altitudes in Pahute Mesa-3 test well, Nye County, Nevada........................................................ 32

15. Map showing water-level-altitude contours and ground-water flow direction on Pahute Mesa,

Nye County, Nevada........................................................................................................................................... 33

16. Trilinear plots showing relative cation and anion concentrations for selected Nevada Test Site

and vicinity waters, Nye County, Nevada.......................................................................................................... 35

TABLES

1. Depth and recovery of sidewall core samples for Pahute Mesa-3 test well, Nye County, Nevada....................... 6

2. Stratigraphic and lithologic description for Pahute Mesa-3 test well, Nye County, Nevada................................. 7

3. Geophysical logs for Pahute Mesa-3 test well, Nye County, Nevada.................................................................... 8

4. Summary of porosity estimates for Pahute Mesa-3 test well, logged September 12, 1988, to

	September 20, 1988, Nye County, Nevada......................................................................................................... 13

5. Summary of injection-test analyses for Pahute Mesa-3 test well, Nye County, Nevada....................................... 23

6. Summary of aquifer-test analyses for Pahute Mesa-3 test well, Nye County, Nevada.......................................... 24

7. Water-quality data for Pahute Mesa-3 test well, Nye County, Nevada.................................................................. 34

IV Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply

foot (ft)

foot per day (ft/d)

square foot per day (f^/d)

cubic foot (ft3)

inch (in.)

mile (mi)

gallon (gal)

gallon per minute (gal/min)

part per million (ppm)

By

0.3048

0.3048

0.09290

0.0283

25.40

1.609

3.785

0.06308

1

To obtain

meter

meter per day

meter squared per day

cubic meter

millimeter

kilometer

liter

liter per second

milligram per liter

Temperature: Degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) by using the formula °F = [1.8(°C)]+32. Degrees 

Fahrenheit can be converted to degrees Celsius by using the formula °C = 0.556(°F-32).

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called "Sea-Level 

Datum of 1929"), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada.

Additional abbreviation of units used in this report:

c/s (count per second)

g/cm3 (gram per cubic centimeter)

ug/L (microgram per liter)

us/ft (microsecond per foot)

jj.S/cm (microseimen per centimeter at 25 °C)

mg/L (milligrams per liter)

mho/m (mho per meter)

mv (millivolt)

Qm (ohm meter)

CONTENTS
Geohydrology of Pahute Mesa-3 Test Well, 

Nye County, Nevada

By Kathryn C. Kilroy and Charles S. Savard 

ABSTRACT

The Pahute Mesa-3 test well is on Pahute 

Mesa about 3 miles west of the Nevada Test Site 

and 20 miles northeast of Oasis Valley near Beatty, 

Nevada. The well was drilled for the U.S. Department of Energy Radionuclide Migration Program to 

monitor conditions near the western edge of the 

Nevada Test Site. The well was drilled with conventional rotary methods and an air-foam drilling 

fluid to a depth of 3,019 feet. A10.75-inch diameter 

steel casing was installed to a depth of 1,473 feet.

The test well penetrates thick units of nonwelded to partly welded ash-flow and air-fall tuffof 

Tertiary age with several thin layers of densely 

welded tuff, rhyolite and basalt flows, and breccia. 

Geophysical logs indicate that fractures are significant in the Tiva Canyon Tuff of the Paintbrush 

Group and this was confirmed by high flow in this 

unit during a borehole-flow survey. The geophysical logs also show that the effective porosity in tuffaceous units ranges from 19 to 38 percent and 

averages 30 percent, and the total porosity ranges 

from 33 to 55 percent and averages 42 percent. The 

measured temperature gradient of 1.00 degree Celsius per 100 feet is steep, but is similar to that of 

other nearby wells, one of which penetrates a buried 

granite intrusion.

Injection tests for six intervals of the well 

yielded transmissivities that ranged from 3.1xlO"3 

to 25 feet squared per day and hydraulic conductivities that ranged from 6x10~5 to 0.12 foot per day. 

The sum of the transmissivities is 28 feet squared 

per day and the geometric mean of hydraulic 

conductivity is 1.7xlO"3 foot per day. Estimates of 

storage coefficient range from 2.1xlO"5 to 3.8xlO"3 , 

indicating that the aquifer responded to the injection tests in a confined manner.

An aquifer test produced a drawdown of 78 

feet during 31 hours of testing at 169 gallons per 

minute. Assuming that the aquifer is confined, estimates of transmissivity range from 360 to 840 feet 

squared per day and hydraulic conductivity ranges 

from 0.32 to 0.74 foot squared per day. The combined results of geophysical logging, injection tests, 

and aquifer tests indicate that most ground-water 

flow is in fractured intervals.

The water-level altitude in the test well fluctuated 6 feet, from 4,362 to 4,368 feet above sea level, 

during the 1988-90 study period.

The test well has a sodium-mixed-anion water. 

Sodium concentration is high compared to other 

water in the Pahute Mesa and Yucca Mountain area, 

but is similar to water in Oasis Valley. The water 

chemistry suggests that ground water in the vicinity 

of Pahute Mesa-3 test well may flow toward the 

south.

INTRODUCTION

The Hydrology-Radionuclide Migration Program 

(HRMP) is managed by the U.S. Department of Energy 

(USDOE) to address concerns about possible groundwater contamination from underground nuclear testing 

at the Nevada Test Site (NTS). Lawrence Livermore 

National Laboratory, Los Alamos National Laboratory, 

Desert Research Institute (DRI), and the U.S. Geological Survey work in cooperation with USDOE to 

investigate specific concerns relating to possible contamination. The overall objective of the program is to 

understand radionuclide migration and hydrologic processes in the NTS area.

The direction and rate of ground-water flow 

in and outside NTS are two hydrologic processes 

investigated by this program. The HRMP has initiated 

a drilling program to collect the data necessary to 

make interpretations of ground-water gradient, flow

ABSTRACT 1
direction, and rate. The work described in this report 

was done in cooperation with USDOE under interagency agreement DE-AI08-86-NV10583.

Purpose and Scope

The purpose of this report is to (1) present data 

collected from the drilling, testing, and monitoring of 

the Pahute Mesa-3 test well and (2) provide an initial 

geohydrologic interpretation of the data. The report 

includes discussions of the drilling, construction, and 

testing of the well. It also includes descriptions of geology, geohydrology, hydraulic properties, water level, 

and water quality for the formations penetrated by the 

test well. Data collected during drilling, borehole geophysical surveys, injection tests, an aquifer test, and 

geochemical sampling are presented and interpreted. 

Water levels are presented for the 2-year period following well completion (September 1988-January 1991).

Location of the Study Area

Pahute Mesa-3 test well, referred to as PM-3 in 

this report, is on the western slope of Pahute Mesa at an 

altitude of 5,823 ft above sea level, between the NTS 

and Oasis Valley about 25 mi northeast of Beatty, Nev. 

(fig. 1). Pahute Mesa is a volcanic plateau composed of 

ash-flow and air-fall tuffs, rhyolitic to basaltic flows, 

volcanic sediments, and flow domes erupted from 

numerous caldera complexes. The site is 3 mi west 

of the NTS boundary, 20 mi northeast of Oasis Valley, 

30 mi north of Yucca Mountain, and 150 mi northwest 

of Las Vegas. The test well is at Nevada coordinates 

N906021 E530998, which correspond to latitude 

37°14! 21" and longitude 116° 33'37". It is in the Oasis 

Valley hydrographic area of Rush (1968). It is in a flyover area for the U.S. Air Force Bombing and Gunnery 

Range.

Previous Work

Malmberg and Eakin (1962) described the flow 

system, and Malmberg and Eakin (1964) and White 

(1979) discussed the geochemistry of ground water in 

Oasis Valley. Blankennagel and Weir (1973) described 

the regional hydrogeologic and tertiary stratigraphic 

framework of the eastern part of Pahute Mesa. Winograd and Thordarson (1975) extended this framework 

throughout the NTS area. Sawyer and others (1994) 

revised the stratigraphic framework on the basis of

Argon-40/Argon-39 geochronology. Waddell and others (1984) mapped the ground-water altitudes of a large 

part of southwestern Nevada, and Claassen (1985) discussed part of the Pahute Mesa ground-water flow system in an evaluation of recharge to Amargosa Desert. 

The geology of the area around PM-3 was first 

mapped in detail by O'Connor and others (1966). Their 

work was later incorporated into geologic maps that 

included the Pahute Mesa area by Orkild and others 

(1969) and the Timber Mountain area studied by Byers 

and others (1976a) who discussed the volcanic calderas 

and lithologic suites common to the Pahute Mesa.

Acknowledgments

Personnel of the U.S. Geological Survey thank all 

individuals and agencies involved in collecting and 

analyzing the data described in this report. This report 

was funded by the U.S. Department of Energy (Interagency Agreement DE-AI08-86-NV10583). Reynolds 

Electrical and Engineering Company drilled the test 

well and provided support during the hydraulic testing 

operations. Fenix and Scisson, Inc., provided support 

for drilling, engineering, and geologic analysis. Atlas 

Wireline, Inc., did the geophysical logging and analyzed some of the logs. Baker, Inc., supplied packer and 

injection equipment and made injection tests. Desert 

Research Institute collected and analyzed water samples. The U.S. Air Force granted access to the test well 

on their bombing and gunnery range.

DRILLING PROCEDURES AND TESTWELL CONSTRUCTION

PM-3 was drilled to a depth of 3,019 ft below land 

surface in three stages (fig. 2). The objective of the first 

phase of drilling was to penetrate unconsolidated materials and regolith and set the surface casing. A 24-in. 

diameter hole was drilled in the first stage from 0 to 

124 ft on September 1,1988. A 16-in. outside-diameter 

surface casing was set in the hole from 0 to 93 ft and 

cemented from 93 ft to the surface.

The objective of the second phase of drilling 

was to reach the water table, estimated to be between 

1,200 and 1,800 ft below the land surface. A 14.75-in. 

diameter hole was drilled September 2-9, from 124 to 

1,647 ft deep. Drilling fluid became thinner at approximately 1,647 ft, indicating that the water table had 

been reached. The water table was later measured at 

1,456 ft during the first round of geophysical logging.

2 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
116°30' 116°

37°30'

37°00'

36°30'

SILENT 

CANYON 

GAllDERA

WIMBEF'MOUNTAIN CALDERA

Base prepared by U.S. Geological Survey from 

digital data, 1:100.0001979-89 

Universal Transverse Mercator projection 

Zone 11

10 MILES

10 KILOMETERS

Figure 1. Location of Pahute Mesa-3 test well, Nye County, Nevada.

DRILLING PROCEDURES AND TEST-WELL CONSTRUCTION 3
PUMP DISCHARGE 

169 GALLONS PER MINUTE

Altitude of land surface 

5,823 feet above sea level I

500 -

1,000 *

LLJ 

LLJ

LLJ 

O

Q

1

1,500

O 2,000 r

LLJ 

00

Q. 

LU 

Q

2,500 -

3,000

hole bridged or collapsed

3,0*9 feetTprlorto 

agytfer test SepterribeF 27-

3,500 

Figure 2. Pahute Mesa-3 test well hole, casing diameters, and depths, Nye County, Nevada.

4 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
A 10.75-in. outside diameter casing was set in the hole 

from 0 to 1,473 ft on September 14. The bottom 150 ft 

of the 10.75-in casing is stainless steel to meet standards for water-quality sampling. The bottom of the 

hole, between 1,473 and 1,647 ft, was filled with sand 

before the 10.75-in. casing was cemented in the hole. 

More than 150 ft3 of neat cement was used.

The objective of the third stage of drilling was 

to develop the productive segment of the test well. 

The sand was flushed from the bottom of the well at 

the beginning of drilling the third segment. A 9.875-in. 

diameter hole was drilled from 1,647 to 3,019 ft on 

September 15-19. The bottom 1,546 ft of the test well, 

from 1,473 to 3,019 ft, was left uncased to allow 

hydraulic testing of the formations in the saturated 

zone.

Borehole geophysical surveys were done after the 

second and third phases of drilling in mid-September, 

and again during the aquifer test on September 27-28. 

Injection tests were made after well completion, from 

September 23-26.

The air-foam drilling fluid was a mixture of air, 

water, soap, and minor amounts of bentonite and polymer. The fluid was circulated down the drill stem with 

compressed air, then through the drill bit and up the 

well annulus. The drilling fluid was not recirculated, 

but was disposed in a sump at the test-well location. A 

lithium bromide tracer was added to maintain the drilling fluid at a concentration of 20 mg/L. The purpose of 

the tracer is to differentiate water introduced during 

drilling from natural formation water during waterquality sampling.

Drill-bit cuttings and sidewall cores were collected to aid in definition of lithology. A bucket at the 

end of the "blooie line," the pipe carrying the drilling 

returns from the wellhead to the sump, collected part of 

the returns. Drill-bit cuttings were collected every 10 ft 

during the drilling operation. The cutting samples and 

sidewall cores were washed, examined, and stored at 

the U.S. Geological Survey Core Library in Mercury, 

Nev. Cutting samples were not collected from the following five intervals: from 60 to 70 ft; from 660 to 

670 ft; from 1,230 to 1,240 ft; from 1,240 to 1,250 ft; 

and from 1,290 to 1,300 ft.

Sidewall core samples were collected with a percussion gun during the geophysical-logging operation. 

Additional sidewall cores were collected from 1,465 

to 469 ft in an attempt to sample an anomalous gamma 

source identified by the gamma log. Sidewall core

recovery was approximately 50 percent. The depth and 

recovery length of sidewall core samples are listed in 

table 1.

A 9.875-in. drill bit was used in the test well on 

October 21,1988, to remove debris that had fallen into 

the hole during the previous month. A pump was set at 

1,655 ft on October 27 and pumped at 180 gal/min for 

24 hours to remove introduced water from the test well 

and formation. A locking wellhead cover was installed 

on October 28.

GEOLOGY

Pahute Mesa is a rolling plateau composed 

primarily of silicic volcanic rocks of Tertiary age. 

The volcanic rocks were erupted along an east trending 

belt of caldera complexes that spans the State between 

latitudes 37 and 38 degrees north. Volcanic activity 

occurred primarily between approximately 17 and 6 

million years overlapping the early phase of Basin and 

Range normal faulting that began approximately 11 

million years; therefore some of the volcanic rocks are 

highly fractured. Four calderas are mapped in the vicinity of Pahute Mesa. These are the Black Mountain, 

Claim Canyon, Silent Canyon, and Timber Mountain 

calderas (fig. 1). Deposits associated with the caldera 

complexes include: glassy and crystalline flows, 

hypabyssal intrusions, air-fall, ash-flow, lapilli, and 

reworked tuffs, and tectonic, eruptive, and flow breccias. Unit thickness and particle size decrease with distance from the caldera boundaries.

PM-3 is located between the Black Mountain, 

Silent Canyon, and Timber Mountain calderas (fig. 1). 

The Silent Canyon caldera boundary was mapped 

based on gravity studies by Healey (1968) and Healey 

and others (1987). The boundary of the Timber Mountain caldera was identified by topography, Bouguer 

gravity data, and aeromagnetic data (Byers and others, 

1976b). S.L. Drellack (Fenix and Scisson, Inc., written 

commun., 1988) determined that the test well is outside 

either caldera boundary on the basis of stratigraphy, 

lithology, and the thickness of the units penetrated. He 

also observed that the two breccia deposits, from 1,810 

to 1,835 ft and from 2,280 to 2,295 ft in depth, indicate 

that the test well is on a structural bench related to the 

Silent Canyon caldera.

A lithologic description of well PM-3 is shown 

in table 2. Approximately 85 percent of the units penetrated by the well are tuffs, 5 percent are rhyolite flows, 

5 percent are basalt flows, and 5 percent are breccias.

GEOLOGY
Table 1. Depth and recovery of sidewall core 

samples for Pahute Mesa-3 test well, Nye County, 

Nevada

Depth

(feet)

Recovery

(inches)

Depth

(feet)

Recovery

(inches)

September 13, 1988

470b

480b

490b

500b

510b

650 a

670 a

680 a

690 a

735 a

740 a

750 a

825 a

840a

845 a

880a

l,000a

1,025 a

l,160a

l,230a

l,240a

l,245 a

1,395 a

l,440a

l,460a

2.0

1.5

2.0

2.0

0.5

1.2

2.0

2.0

2.0

Trace

0.5

1.0

2.0

2.0

1.2

1.5

1.5

2.0

2.0

2.0

1.0

2.0

2.0

0.2

1.5

l,464.3a

l,464.7a

l,465.0a

l,465.3a

l,465.5a

l,466.0a

l,466.3a

l,466.7a

l,467.0a

l,467.3a

l,468.0a

l,468.7a

l,469.0a

l,469.3a

l,470a

l,490a

l,510a

l,530a

l,580a

l,600a

l,620a

1.5

1.5

1.5

0.7

1.2

1.2

0.5

1.2

0.7

1.0

0.2

1.2

.05

Trace

1.5

1.5

1.2

1.5

1.2

1.0

1.2

September 23, 1988

l,625 a

l,635 a

l,645 a

l,655 a

l,665 a

l,670a

l,675 a

l,685 a

l,700a

l,700a

l,720a

l,750a

l,815 a

l,845 a

1,920C

1,945 C

2,01 5 c

2,080C

2,110C

2,140C

1.5

1.5

1.5

1.5

1.5

1.5

1.5

0.5

1.5

1.5

1.5

1.0

0.5

1.0

1.0

1.0

1.0

2.0

1.5

1.0

2,160C

2,200C

2,230C

2,280C

2,3 10C

2,330C

2,370C

2,400C

2,420C

2,450C

2,505C

2,550C

2,600C

2,650C

2,670C

2,700C

2,730C

2,770d

2,800d

2,825d

1.0

2.0

1.0

1.0

2.0

1.0

2.0

1.5

1.5

2.0

1.5

2.0

2.0

2.0

2.0

1.0

1.5

1.5

1.5

2.0

a Timber Mountain Group

b Fortymile Canyon assemblage

Although devitrified units occur throughout the stratigraphic column, argillic alteration is primarily below 

the water table; and zeolitic alteration is found below, 

and up to 500 ft above, the water table.

GEOPHYSICAL LOGGING METHODS

Geophysical logs were used to help define the 

lithology, stratigraphy, and hydrogeology of units penetrated by PM-3. Three rounds of geophysical logging 

were completed. The first round was recorded September 9-14, 1988, after the second phase of drilling but 

prior to casing, when the well was 1,647 ft deep 

(table 3). It included caliper, epithermal neutron, 

fluid-density, gamma-gamma, gamma ray, electric, 

magnetometer, and temperature logs. Fluid-density 

logs were recorded only to determine depth to water, 

which varied between 1,455 and 1,457 ft. The second 

round of measurements was recorded September 

19-23, 1988, when the test well was drilled to its total 

depth of 3,019 ft. This included all the previously mentioned geophysical logs except the gamma ray and 

magnetometer survey. In addition, it included a borehole-compensated acoustic log and a gyroscope survey. 

The third round of measurements was recorded on September 27, 1988, during the aquifer test. It included 

temperature and tracer surveys. The geophysical logs 

are shown in figures 3,4, and 5.

The gyroscopic directional survey showed the 

test well to be nearly vertical, requiring a -0.1 ft correction to measured depths below 2,900 ft. At 2,900 ft, the 

hole is 6.5 ft north and 1.0 ft east of the surface coordinates of the test well. The directional survey log is not 

shown.

Caliper, Acoustic, and Electric Logs

The caliper, acoustic, and electric logs are shown 

in figure 3.

Caliper

Faults, friable units, and true borehole diameter 

can be identified from the caliper log (fig. 3). The caliper log also is used extensively in interpreting electric 

and nuclear logs because these methods are sensitive to 

variations in borehole diameter and a correction commonly is needed. Several caliper logs were completed 

at PM-3, including a three-pronged log, but only one is 

shown here because deviation from roundness was 

slight. The caliper had a maximum span of 31.7 in. and

Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
Table 2. Stratigraphic and lithologic description of Pahute Mesa-3 test well, Nye County, Nevada

(Geology by S.L. Drellack, Jr., Fenix and Scisson Engineering, written commun., 1988. Descriptions of color, lithic inclusions, and phenocrysts are omitted.)

Stratigraphic 

unit

Thirsty Canyon Group 

(Pliocene)

Fortymile Canyon assemblage 

(Pliocene)

Timber Mountain Group 

(Pliocene)

Paintbrush Group 

(Miocene)

Calico Hills Formation 

(Miocene)

Wahmonie Formation 

(Miocene)

Crater Flat Group (Miocene)

Belted Range Group 

(Miocene)

Pre-Grouse Canyon (Miocene)

Tuffs (Miocene)

Member

Trail Ridge Tuff 

do. 

Pahute Mesa Tuff 

do.

"middle unit" 

Intercalated tuffs 

"lower unit" 

Bedded tuffs

Ammonia Tanks Tuff 

do. 

do. 

Rainer Mesa Tuff

do. 

do. 

do. 

do.

do. 

do. 

Rhyolite of the Loop 

do.

do. 

do. 

Basalt of well U-19ac 

Breccia

Tiva Canyon Tuff 

do. 

do. 

do. 

Hornblende rhyolite

Breccia 

Topopah Spring Tuff 

do. 

do.

11 lower unit" 

do. 

Basalt of well UE-19e

Bedded tuffs 

do.

Bullfrog Tuff

Grouse Canyon Tuff

Bottom of 

depth interval 

(feet beiow 

iand surface)

80 

120 

150 

175

295 

320 

460 

505

530 

595 

620 

820

835 

835 

855 

930

1,020 

1,235 

1,308 

1,470

1,492 

1,750 

1,810 

1,835

1,885 

1,920 

2,100 

2,140 

2,280

2,295 

2,355 

2,370 

2,700

2,770 

2,810 

2,870

2,890 

2,910

2,950

2,990

3,000

3,019

Lithology

Tuff ash-flow, densely welded, devitrified 

Tuff bedded, vitric, friable 

Tuff ash-flow, densely welded, devitrified 

Tuff nonwelded or bedded, friable, vitric

Rhyolite lava, devitrified, granophyric 

Bedded tuff, intercalated between lava flows 

Rhyolite lava, devitrified 

Tuff air-fall and reworked, vitric, friable

Tuff ash-flow, nonwelded, friable, vitric 

Tuff ash-flow, partly welded, vitric 

Tuff bedded, vitric and friable, silicified 

Tuff ash-flow, partly to moderately welded, devitrified

Possible fault 

Tuff ash-flow, partly welded, devitrified 

Tuff ash-flow, nonwelded, vitric, 

Tuff ash-flow, nonwelded, friable, vitric

Tuff ash-flow(?), nonwelded, devitrified to weakly zeolitized 

Tuff ash-flow, nonwelded, zeolitized 

Tuff nonwelded or bedded, zeolitized 

Tuff ash-flow, nonwelded, zeolitized

Tuff reworked (?), zeolitized, possibly argillized 

Tuff ash-flow, nonwelded, zeolitized 

Basalt lava, zeolitized, argillized, weakly calcareous 

Breccia, densely welded tuff fragments in tuffaceous matrix

Tuff reworked, zeolitized 

Tuff ash-flow, nonwelded to partly welded, devitrified 

Tuff ash-flow, moderately welded 

Tuff ash-flow, nonwelded to partly welded 

Tuff bedded, zeolitized

Breccia or debris flow 

Tuff nonwelded massive, zeolitized 

Tuff air-fall, zeolitized 

Tuff ash-flow, nonwelded, zeolitized

Tuff bedded, zeolitized 

Tuff air-fall, zeolitized 

Basalt, devitrified

Tuff bedded, zeolitized to argillized 

Tuff ash-fall, very fine grained ash, zeolitized, argillized

Tuff ash-flow, zeolitized to argillized, partly welded

Tuff ash-flow, densely welded, flow banded, devitrified

Tuff bedded, some reworked tuff, zeolitized, argillized

Tuff flonwelded or bedded, argillized, zeolitized

GEOPHYSICAL LOGGING METHODS
Table 3. Geophysical logs for Pahute Mesa-3 test well, Nye County, Nevada

[Abbreviations: API, American Petroleum Institute; c/s, counts per second; in., inches; °F, degrees Fahrenheit; ft, foot; g/cm3 , grams per cubic 

centimeter; (as/ft, microseconds per foot; Qm, ohm meter; ppm, parts per million]

Geophysical log 

and adjustment

Acoustic (borehole compensated)

Caliper

Epithermal neutron 

(decentralized long spacing)

Fluid density

Gamma-gamma 

(borehole-compensated density log)

Gamma ray

Spectral gamma ray 

(includes potassium, uranium, thorium logs)

Gyroscope 

(50-ft stations)

Induction electrolog 

(includes spontaneous potential, conductance, 

short-normal resistivity, and inductance)

Magnetometer

Temperature

Tracer survey

Run 

No.

1

1

2

3

1

2

1

2 

3 

4

5

6

7

1

2

1

1

lin 

1 out

1

2

1

1

2 

3

1

2

Date

09-20-88

09-12-88 

09-20-88

09-23-88

09-13-88 

09-21-88

09-12-88

09-13-88 

09-14-88 

09-14-88

09-21-88

09-23-88 

10-10-88

09-12-88 

09-21-88

09-13-88

09-21-88

09-19-88 

09-19-88

09-12-88 

09-22-88

09-13-88

09-09-88 

09-22-88 

09-27-88

09-27-88 

09-27-88

Interval 

surveyed 

(feet below 

land surface)

1,480-2,882

40-1,624 

1,405-2,897

1,406-2,810

58-1,629 

1,419-2,812

1,399-1,476

1,352-1,410 

1,352-1,408 

1,352-1,476

1,395-1,477

1,392-1,480 

1,432-1,272

120-1,632 

1,445-2,863

0-1,629

1,000-2,845

50-2,900 

25-2,925

100-1,626 

1,458-2,832

100-1,636

13-1,633 

38-2,837 

1,398-2,825

1,600-2,900 

1,600-2,900

Calibration

Measurement 

and unit

57 ^s/fV1 

57 ^s/ftb

12,20,31.7in.a 

12, 20 in.b 

8, 16,31.4in.a 

8, 16in.b

567, 1237,3199APIunitsa 

567, 1237,3199APIunitsb 

567, 1237,3199APIunitsa 

567, 1237, 3199APIunitsb

100, 300 c/sa 

90, 290 c/sb

75, 262 c/sa 

70, 260 c/sb

1.7, 2.6 g/cm3 a 

1.7, 2.6 g/cm3 b 

1.7, 2.6 g/cm3 a 

1.7, 2.6 g/cm3 b

80, 190 c/sa 

80, 190 c/sb

5, 82, 152ppma 

5,78, 155 ppmb

not calibrated

2.064, 10, 484.5 Qma 

2.164, 10, 484.5 Qmb 

2.059, 10, 485.6 Oma 

2.045, 10. 1,488.9 Qmb

not calibrated

67, 80,95, 107, 123 °Fa 

76,79, 108, 114 °Fb

not calibrated

a Calibration prior to logging procedure. 

b Calibration after logging procedure.

8 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
CALIPER ACOUSTIC

500

1,000

1,500

2,000

2,500

3,000 i i i i

40 0 500

DIAMETER, MICROSECONDS 

IN INCHES PER FOOT

STRATIGRAPHIC 

UNIT

Thirsty

Canyon rhyolite

Group

Fortymile rhyolite 

Canyon tuffAssemblage rhyolite

tuff -

Ammonia 

Tanks Tuff

Rainer

Mesa

Tuff

tuff

_Rhyolite of 

the Loop

basalt -breccia1

Paintbrush 

Group

Tiva Canyon 

Tuff

tuff

Topopah

Spring

Tuff

Calico Hills 

Formation tuff

basalt

3ed tuff

Bull Frog

Belted Range Group

INDUCTION SPONTANEOUS 

RESISTIVITY CONDUCTANCE POTENTIAL

Induction

Short

normal

resistivity

c

5 500

LOG OHM 

METERS

MHOPER 

METER

0 0 200 

MILLIVOLTS

Figure 3. Caliper, acoustic, geologic, and electric logs from Pahute Mesa-3 test well, Nye County, Nevada.

GEOPHYSICAL LOGGING METHODS
NEUTRON DENSITY POTASSIUM URANIUM THORIUM GAMMA RAY

500

1,000

CO

5 1,500

2,000

2,500

3,000

0 10,000 0 

AMERICAN

PETROLEUM

INSTITUTE

UNITS

4 0 10 0 10 0

GRAMS PER

CUBIC 

CENTIMETER

PERCENT PARTS PER 

MILLION

PARTS PER 

MILLION

50 0 2,000

AMERICAN

PETROLEUM

INSTITUTE

UNITS

Figure 4. Nuclear logs from Pahute Mesa-3 test well, Nye County, Nevada. American Petroleum Institute units Counting rates for 

gamma-ray and neutron logs are calibrated to a section of Indiana Limestone in Texas with a porosity of 19 percent. The section, 

exposed in a pit, is arbitrarily assigned a counting rate of 1,000 API units by the American Petroleum Institute.

10 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
STATIC 

TEMPERATURE

PUMP 

DISCHARGE

TEMPERATURE TEMPERATURE 

DURING FLOW DEVIATION

FRACTURED 

INTERVALS

500

1,000

uu 

uu

LJJ

1,500

1

UU 

CO

I

Q_ 

UU 

Q

2,000

2,500

3,000

I September 9,1988

September 22,1988 

1,758

Pump 

intake

1.768 

Monitor 

line 

depth

i i i i

20 30 40 50 0 

DEGREES CELSIUS

100 0

PERCENT DEGREES 

CELSIUS

10 0 50 0 

PERMIL

Figure 5. Temperature and tracer-test logs from Pahute Mesa-3 test well, Nye County, Nevada.

830

1,250

2,380

2,810

GEOPHYSICAL LOGGING METHODS 11
was calibrated to within 0.1 in. of two endpoints before 

and after the logging. The hole was logged at a rate of 

34 ft/min.

The log (fig. 3) for the upper part of the hole, 0 to 

124 ft, which was drilled with a 24-in. bit shows the 

inside of the 16-in. surface casing. The log for the middle part of the hole, which was drilled with a 14.75-in. 

bit, shows a washout just below the surface casing from 

90 to 175 ft and soft or fractured zones at 300 and 830 

ft, and from 1,170 to 1,380 ft. The lower part of the 

hole, drilled with a 9.88-in. bit, shows a washout just 

below the casing from 1,470 to 1,640 ft (not shown) 

and soft or fractured zones at depths of 1,750 and 1,810 

ft, from 1,950 to 1,980 ft, and from 2,450 to 2,490 ft. 

The average borehole diameter of the saturated interval 

of the well below the casing is 13.6 in.

Acoustic

The acoustic, or sonic, log shows the transit time 

of an acoustic pulse between transmitter and receiver 

in the probe (fig. 3). The acoustic log can only be run 

in fluid-filled segments of the borehole and is sensitive 

to borehole diameter changes unless it is borehole 

compensated. Sonic velocities are much slower in fluids than in solid rock, so the recorded velocities are 

proportional to the amount of fluid through which the 

signal passes. The chief uses of the acoustic log are for 

the measurement of primary and secondary porosity. 

Signals that arrive at the detector approximately 30 to 

140 ^is after transmission generally are an indication of 

primary porosity, whereas signals arriving after 140 |^s 

traveled mostly through fluid and may indicate fractured media. The acoustic log for PM-3 was borehole 

compensated and calibrated to within 1 |^s/ft at one 

endpoint before and after the log was completed. The 

hole was logged at a rate of 31 ft/min.

The acoustic log (fig. 3) shows extremely slow 

transit times (greater than 140 |^s/ft) for the depth intervals from 1,480 to 1,520 ft, at 1,760 ft, from 1,810 to 

1,880 ft, from 1,950 to 2,070 ft, at 2,220 and 2,380 ft, 

and from 2,810 to 2,911 ft. The slow traveltimes in 

interval from 1,480 to 1,520 ft probably do not indicate 

a fracture, but a washout related to the lower edge of 

the casing at 1,480 ft. The others are interpreted to represent fractures or groups of fractures on the basis of 

caliper and acoustilog response. If we assume that the 

transit time in water is 190 |^s/ft and the acoustic properties of tuffs are similar to those of sandstone, 60 |^s/ft 

(Keys and MacCary, 1971, p. 90), then the effective 

porosity of the formation, ne, may be calculated by

= tt-60 

"e 190-60" ()

where,

tt is the transit time recorded on the log; 

60 |^s is the transit time in sandstone; and 

190 ^is is the transit time in water.

The results of these calculations are shown in 

table 4.

Resistivity

Resistivity-logging devices measure the electrical 

resistivity of an assumed volume of earth materials 

under the application of an alternating electric current. 

The resistivity of the rock depends on the amount and 

composition of the pore water, the shape of the pores 

or fractures, and the clay content of the rock. Fractures 

and faults may have very high resistivities if unfilled, 

or very low resistivities if filled with clay or fault 

gouge. The short-normal log (shown for the saturated 

part of the well only) gives good vertical detail, and 

records the apparent resistivity of the zone adjacent to 

the borehole invaded by drilling mud. The induction 

log records the apparent resistivity of the formation 

beyond the invaded zone. Resistivities are recorded on 

a logarithmic scale. The resistivity logs were each calibrated to within 0.01 log cycle against one endpoint 

before and after the borehole survey. The hole was 

logged at a rate of 63 ft/min. Resistivity of drilling mud 

was 11 Qm at 74°F during logging of the upper part of 

the hole, and 14 Qm at 62°F during logging of the 

lower part of the hole.

The induction logs (fig. 3) show very high resistivity at 300 ft in the tuff between the two rhyolite 

units in the Fortymile Canyon assemblage; the high 

resistivity probably indicates a washout of soft material. Both logs show low resistivity values at 460 ft, 

from 650 to 700 ft, from 810 to 850 ft, at 1,750 ft, from 

1,810 to 1,820 ft, from 2,290 to 2,300 ft, and from 

2,800 to 2,840 ft. Low values may indicate clay units or 

argillic alteration and lithologic contacts between 

softer tuffs, harder breccias, and flow units. Clay in 

fractures may be the result of the formation of fault 

gouge, and the association of clay with the tops of formations may indicate long periods of nondeposition 

when clays in soils developed. On the basis of this 

association and a lack of response on the caliper and 

acoustic logs, low values at 460 ft, from 650 to 700 ft, 

from 2,290 to 2,300 ft, and from 2,800 to 2,840 ft are

12 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
Table 4. Summary of porosity estimates for Pahute Mesa-3 test well, logged September 12,1988, to 

September 20,1988, Nye County, Nevada

[Effective porosity estimated from acoustic log. Total porosity estimated from gamma-gamma log.]

Interval 

(feet below 

land surface)

0-93

93-175

175-300

300

300-460

460-505

505-640

640-770

770

770-830

830

830-1,170

1,170-1,320

1,320-1,380

1,380-1,455

1,455

1,455-1,640

1,640-1,750

1,750

1,750-1,810

1,810-1,835

1,835-1,880

1,880-1,950

1,950-2,000

2,000-2,070

2,070

2,070-2,170

2,170-2,260

2,260-2,300

2,300-2,390

2,390-2,460

2,460-2,490

2,490-2,770

2,770-2,810

2,810-2,870

Mean

Weighted mean

Thickness 

(feet)

93

82

125

160

45

135

130

60

340

150

60

75

185

110

60

25

45

70

50

70

100

90

40

90

70

30

280

40

60

99

Effective 

porosity 

(percent)

-

~

~

~

-

~

-

-

~

35

35

~

4

«

19

~

23

23

35

31

31

38

23

35

27

-

28

30

Total 

porosity 

(percent)

~

~

12

12

55

73

55

46

55

55

~

46

46

46

~

12

~

33

-

33

33

46

33

46

46

46

46

33

27

41

42

Top of 

unit

Thirsty Canyon Group

do.

Fortymile Canyon assemblage

do.

do.

Timber Mountain Group 

Ammonia Tanks Tuff

do.

do.

do.

do.

Rainer Mesa Tuff

Rhyolite of the Loop

do.

do.

do.

do.

do.

do.

do.

Paintbrush Group

Tiva Canyon Tuff

do.

do.

do.

do.

do.

do.

do.

Topopah Spring Tuff

do.

do.

do.

Calico Hills Formation

do.

Notes

surface casing

washout

rhyolite

soft zone

rhyolite

fracture nearby ?

fracture

fracture/fault

soft zone

fractures

soft zone

water table

soft zone

fracture

basalt

fractured breccia

fractures

fractures

fracture

rhyolite

soft

fractured basalt

interpreted to be paleosols. The intervals from 810 to 

850 ft, and at 1,750 ft, are interpreted as fractures, and 

from 1,810 to 1,820 ft is a breccia.

Conductance

Conductance, a measure of the ability of the formation to conduct electricity, can be measured in either 

a wet or a dry hole. Conductance use is limited in holes 

where the contrast in electrical conductivity between 

formation water and drilling mud is large. The conductance log is the inverse of the induction log. It was

calibrated to within 1 mho/m at one endpoint at the 

beginning and end of logging. The hole was logged 

at 43 ft/min.

The conductance log (fig. 3) displays features that 

are similar to those of the short-normal resistivity and 

induction logs. Clayey units are identified at 460 ft, 

from 650 to 700 ft, from 810 to 850 ft, at 1,750 ft, 

from 1,810 to 1,820 ft, from 2,290 to 2,300 ft, and 

from 2,800 to 2,840 ft. Conductance of the rest of the 

hole are generally less than 50 mhos/m.

GEOPHYSICAL LOGGING METHODS 13
Spontaneous Potential

Spontaneous-potential (SP) logs are records of 

the natural electrical potentials developed between the 

borehole fluid and the surrounding rock formations. 

The spontaneous potential is used for geologic correlation and determination of bed thickness. The signal is 

recorded directly in millivolts. The spontaneous-potential logging instrument cannot be calibrated as other 

instruments are calibrated because the SP signal has an 

inherent component of drift. A calibration based on the 

assumption that clay or shale units yield the lowest SP 

readings can be made by drawing a straight line, the 

"shale line," through the low points and measuring 

deflections from this line. The shale line is shown on 

the graph (fig. 3). The hole was logged at 43 ft/min.

The SP log (fig. 3) has low values at 1,490 ft, 

from 1,900 to 1,920 ft, and at 2,725 ft. The low value at 

1,490 ft is because of the water table and bottom of the 

steel casing. The low SP at 1,920 ft is in the middle of 

the Tiva Canyon Tuff of the Paintbrush Group, which 

is moderately welded, but only a small amount of clay 

is indicated at this level by the other electric logs. The 

low value at 2,725 ft is in the Calico Hills Formation. 

Basalts from 1,750 to 1,800 ft and from 2,810 to 2,870 

ft are indicated by relative low values in the SP log. A 

large offset at 1,920 ft is a contact between an overlying 

nonwelded and an underlying moderately welded ashflow tuff. The largest SP readings, at depths from 1,920 

to 2,120 ft, are associated with the fractured interval of 

the Paintbrush Group.

Nuclear Logs

Epithermal Neutron

The neutron log shows the hydrogen content of 

the borehole environment. Hydrogen occurs principally as water in pores, water in fractures, clay minerals, and wide spots in the well bore. With a long-spaced 

probe, the number of neutrons measured is inversely 

proportional to the water content, so the neutron signal 

is significantly attenuated below the water table. The 

neutron probe was mounted with a decentralizing skid 

to minimize borehole effects. It was calibrated to three 

points before and after logging was completed. The 

hole was logged at a rate of approximately 29 ft/min.

The neutron log (fig. 4) shows a large response at 

depths between 90 and 460 ft that correlates well with 

two rhyolite lavas of Ribbon Cliff and indicates their 

low content of hydrous minerals or water. Large values

in the interval from 1,220 to 1,380 ft are in Rainer Mesa 

Tuff and Rhyolite of the Loop, but also may reflect 

borehole rugosity. Large values in the depth interval 

from 1,750 to 2,100 ft are in basalt, breccia, and tuff, 

which may have lower clay content than other units. 

Low values from 460 to 510 ft, from 650 to 700 ft, from 

800 to 830 ft, from 1,800 to 1,930 ft, and at 2,100 ft correlate well with low values in the induction electrologs 

and may indicate clayey units, argillic alteration, and or 

high porosity.

Density

The density, or gamma-gamma log records the 

intensity of gamma radiation from a cesium-137 source 

backscattered by the fluid, casing, and formation. The 

main uses of gamma-gamma logs are for identification 

of lithology, computation of bulk density, and estimation of porosity. Two sensors are used to determine and 

correct for the effect of borehole rugosity. The density 

log was borehole compensated. It was calibrated to two 

endpoints, 1.7 and 2.6 g/cm3 , before and after the survey. The curve delay of the instrument was 3 in. and the 

logging rate was 29 ft/min.

The density log (fig. 4) shows unusually low densities in areas where the caliper log indicates washouts 

of the well bore from 93 to 175 ft, from 1,320 to 1,380 

ft, and suspected fractures at 830,1750, and 1810 ft, 

and from 2,810 to 2,870 ft. These low values are an 

indication of the instrument sensitivity to differences in 

borehole diameter. Bulk density is highest, approximately 2.4 to 2.5 g/cm3 , where the hole penetrates 

basalt and rhyolite flows. Assuming a grain density of 

2.65 g/cm3 and water density of 1.00 g/cm3 , the total 

porosity, nt, can be calculated from the equation:

= 2.65-p 

2.65-1.00

(2)

where p is rock density measured on the geophysical 

log.

The results of these calculations are shown in 

table 4.

Spectral Gamma Ray

The spectral gamma-ray log records natural 

gamma radiation as a function of a characteristic 

energy for each of the elements potassium, uranium, 

and thorium. The logs are helpful in distinguishing 

mafic from felsic volcanic units because all three elements are preferentially concentrated in felsic units,

14 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
and for stratigraphic correlation. The potassium log 

also may be used to determine potassium content of the 

rock. The spectral logs were calibrated to within 2 percent, 1 and 15 ppm, respectively, of one endpoint 

before and after the logging run. The hole was logged 

at a rate of approximately 6 ft/min at depths from 2,848 

to 1,000 ft and no curve delay. The upper part of the 

borehole was not logged. The segment from 1,470 to 

1,000 ft was already cased and cemented at the time of 

logging.

All three curves (fig. 4) show an offset at 1,380 ft, 

which is correlated with a transition from fractured to 

unfractured units in the caliper log and may indicate a 

more mafic interval of tuffs. Low values in all three 

logs, particularly at depths from 1,750 to 1,810 ft and 

from 2,810 to 2,848 ft, correlate with basalt flows. Uranium peaks occur at 1,300 and 1,465 ft. The peaks do 

not relate to any particular lithology, but the lower peak 

was recorded just below the water table, at 1,455 ft. 

An interval of relatively high potassium is indicated 

from 1,910 to 2,100 ft. The geologic log for this section 

indicates nonwelded to moderately welded, devitrified 

ash-flow tuff. This is the only segment of the spectral 

gamma-ray log interpreted as a devitrified unit, and it is 

roughly coincident with a zone of fractures identified 

on the acoustic and caliper logs at depths from 1,950 to 

2,000 ft. Devitrification and fractures may be related, 

possibly due to increased velocity of water.

Gamma Ray

The gamma-ray, or natural gamma log, is used 

primarily to correlate units from one borehole to 

another and to identify lithology. The gamma-ray 

log measures total radiation from natural radioactive 

isotopes of potassium, thorium, and uranium. The 

gamma-ray log was calibrated to one endpoint, 9,200 

+100 American Petroleum Institute units, before and 

after the log was completed. The hole was logged at a 

rate of approximately 6 ft/min from 2,848 to 1,000 ft.

The gamma-ray log (fig. 4) shows low values corresponding to the two basalt units at depths from 1,750 

to 1,810 ft and from 2,810 to 2,848 ft. The log also 

shows low values from 1,360 to 1,470 ft that are 

mapped as nonwelded ash-flow tuff. This interval corresponds to a zone where the borehole was larger in 

diameter and the annulus was filled with cement when 

the casing was set. Anomalous high values are found 

from 1,910 to 2,100 ft. Sidewall core samples collected 

in this interval indicate no unusual concentrations of 

radioactive material.

Borehole Flow Survey

Temperature Prior to Tracer Survey

Temperature logs were recorded about 2 weeks 

apart and show the effects of thermal equilibration of 

the well water with the aquifer following well construction. The flat geothermal gradient (note that a vertical line on the graph is a flat geothermal gradient) 

between 0 and 500 ft appears to be due to surface temperature effects in the well bore and unsaturated zone. 

Steepening of the slope of the temperature profile at a 

depth of approximately 1,456 ft is interpreted to represent the water level in the well. Temperatures between 

about 1,400 and 2,100 ft change little, so that water is 

warmer than a linear geothermal gradient would indicate. Such a flattening of the temperature profile may 

be caused by rocks with high thermal conductivity or it 

may indicate upward vertical flow of warm water in the 

well bore. A basalt flow is located approximately in the 

middle of the flat gradient; however, its thickness, 60 ft, 

is much smaller than the anomaly, which spans approximately 700 vertical ft. The other rock types in the 

interval are unwelded to moderately welded ash-flow 

tuffs, fractured ash-flow tuffs, and fractured tuff breccia. The thermal conduction properties of the basalt are 

unknown, but its small thickness and the homogeneous 

composition of the tuffs above and below the basalt 

suggest that the thermal conductivity of the rocks does 

not cause this flattening of thermal gradient. A more 

likely interpretation is that the basalt, which is shown 

by caliper and acoustic logs to be unfractured, acts as a 

confining layer to the highly fractured units below it 

and that flow of heat or water in the borehole is upward. 

An upward hydraulic gradient is not, however, indicated by differences in hydraulic head with depth. 

Temperatures below 2,100 ft approximate the average 

geothermal gradient for the entire well.

Temperature gradient of the well is the difference 

between the bottom hole temperature and the mean 

annual air temperature divided by the well depth 

expressed in degrees Celsius per 100 ft. The temperature gradient at PM-3 is high compared to other wells 

on Pahute Mesa. Using an estimated mean annual air 

temperature of 13°C, the PM-3 temperature gradient 

was calculated to be 1.00°C/100 ft. Only the temperature gradient at well PM-2,1.31°C/100 ft, is larger than 

the one at PM-3. Temperature gradient at other wells 

on Pahute Mesa range from 0.52 to 0.88°C/100 ft.

GEOPHYSICAL LOGGING METHODS 15
The high temperature gradient at PM-2 was thought by 

Blankennagel and Weir (1973) to result from remnant 

heat in granite penetrated at a depth of 8,400 ft.

Tracer Survey

A borehole-flow survey was done in the depth 

interval from 1,768 to 2,170 ft, in which fluid velocity 

and temperature within the well bore was measured 

during pumping to identify transmissive intervals of 

the aquifer. A short-lived radioactive tracer, 

iodine-131, was injected into the borehole from the 

geophysical "tracer." The iodine concentration was 

measured as it moved with the borehole fluid past a set 

of detectors. Fluid velocity was calculated from the 

time it took for the peak concentrations to move from 

detector to detector (Dresser Atlas, 1982). This method 

works best in small-diameter wells in low transmissivity aquifers. It is most sensitive to areas between the 

pump intake and the nearest highly transmissive zone. 

Such surveys generally give little information about 

segments of the well away from the pump intake. The 

first tracer survey was made with a 5-ft spacing 

between the detectors. Few iodine readings were 

obtained in this configuration. A second survey was 

made with the detectors spaced 3 ft apart. The 3-ft 

spacing increased the number of iodine peaks detected. 

Fluid velocity and hole diameter were used to compute 

aquifer discharge along the study interval. The discharge readings are expressed as a percentage of the 

average pump discharge, 169 gal/min (fig. 5). Depth 

intervals in which the percentage of pump discharge 

differs by a large amount with depth are the most transmissive.

The tracer survey indicated no vertical flow in the 

well below 2,170 ft, although flow less than a few percent over such a large interval could not be detected by 

this method. The depth interval from 2,100 to 2,170 ft 

produced less than 1 percent of the flow. The interval 

from 1,975 to 2,100 ft produced 30 percent of the 

pumping discharge, indicating a more transmissive 

unit. The interval between 1,850 and 1,975 ft produced 

only 4 percent of the flow, indicating that transmissivity is low. The interval from 1,812 to 1,850 ft produced 

18 percent of flow and is considered to be highly transmissive. The tracer survey could not be made above the 

monitor-line portal, but the remaining flow (48 percent) 

is presumed by difference to have originated from 

this interval (1,455 to 1,758 ft). This interpretation 

indicates moderate transmissivity for the interval, but

does not rule out the possibility that some high transmissivity units are interbedded with low transmissivity 

units.

Temperature During Pumping

The temperature survey made concurrently with 

the tracer survey also is shown on figure 5. For such a 

survey, flow is downward in the well bore above the 

pump intake and upward in the well bore below it during pumping. Because the tracejector and temperature 

probes were emplaced through a monitor tube with a 

portal 10 ft below the pump intake, only the well bore 

below the pump intake was monitored by the tracejector. Temperatures measured above the pump intake 

were made from inside the monitor tube adjacent to the 

pump motor and probably are not accurate. Zones in 

which the temperature is cooler than the static gradient 

indicate downward flow in the well bore and those in 

which temperature is warmer indicate upward flow.

The temperature and temperature deviation logs 

yield little information about flow to the well bore 

below 2,100 ft that cannot be attributed to the static 

gradient and measurement error, but the logs confirm 

the possibility that, in this test configuration, little 

water that reaches the pump is coming from this depth. 

Above 2,070 ft the thermal gradient flattens, indicating 

upward flow from this zone. The thermal gradient is 

relatively constant from 2,070 ft to the pump intake.

Discussion

The caliper, resistivity, neutron, and density logs 

indicate friable zones in the unsaturated zone are at 

depths of 300 and 610 ft, and that fractures or faults are 

at 830 and 1,380 ft. The spectral-gamma, and gammaray traces also indicate an accumulation of uranium at 

1,380 ft. Below the water table, the logs indicate fractured intervals from 1,810 to 1,880 ft, from 1,950 to 

2,000 ft, and from 2,810 to 2,911 ft. The two intervals 

of large hydraulic conductivity indicated by the tracer 

test, from 1,812 to 1,850 ft and from 1,990 to 2,100 ft 

coincide closely with two intervals of intense fracturing. The Tiva Canyon Tuff, which is nonwelded to 

moderately welded, appears to be an important water 

transmitter. The rhyolite flow units are not fractured, 

but the Fortymile Canyon assemblage is associated 

with washouts just above and below. The basalts are 

associated with fractures and each overlies a formation 

that may be topped by a soil or rubble zone. The basalt

16 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
of U-19ac appears to confine the Paintbrush Group so 

that flow is upward along the borehole from the Paintbrush Group to the units above.

The potassium log shows three intervals of 

increasing potassium content with depth: from 2,570 

to 2,800 ft, from 2,100 to 2,360 ft, and from 1,800 to 

2,100 ft. They are separated by zones of relatively constant potassium content. Each of the three intervals is 

bounded at the top or bottom by a flow unit. The transitions probably reflect decreasing silica saturation due 

to venting of a subcaldera magma chamber, but these 

do not coincide with specific lithologic units. The 

potassium logs may have great importance for regional 

stratigraphic correlation.

A buried granite intrusion was penetrated by 

PM-2 at 8,400 ft, only 7 mi north of PM-3. High heat 

flow may indicate buried granite at depth below PM-3 

also.

INJECTION TESTS

Analytical Methods

The injection tests were analyzed by using the 

method proposed by Cooper and others (1967). Their 

analysis was based on an assumption of radial flow 

from the injection well into the formation. This method 

was chosen because (1) it is conceptually simple, (2) 

radial flow seems probable in light of the small volumes injected and large (~ 200-ft) intervals tested, and 

(3) it is based on the same geometric and mathematical 

assumptions as the method used to interpret the aquifer-test results. The assumption of radial flow does not 

always yield satisfactory results for other NTS injection tests however, particularly in highly fractured units 

(D.L. Galloway, U.S. Geological Survey, oral commun., 1989). The assumption that transmissivity calculated by this method represents primarily the interval 

tested seems satisfactory considering the small volumes injected and large intervals tested.

The method of Cooper and others (1967) requires 

that hydraulic head and time be measured during the 

test, and radii of the well and delivery tubing be known. 

Hydraulic head in the injection conduit is measured 

with a pressure transducer and declines nonlinearly 

throughout the test. Head values may vary from a few 

feet to hundreds of feet in most injection tests. In order 

to standardize head values for the type-curve match, 

the ratio of H(t)/ HQ where, H(t), is the head in the 

injection conduit at time, t, due to the injection, and HQ

is the initial head due to injection. The ratio is plotted 

against time after the start of injection t on semilog 

graph paper. The delivery-tube radius, ra, was 0.102 ft 

for all injection tests. The well radius rw (measured 

with calipers over the total tested interval of the well) 

averaged 0.567 ft. Averages for specific intervals tested 

were used in the calculations.

Storage coefficient for the units penetrated by the 

test well is not known; however, a match to a type 

curve with a given a value may be used to make an 

order-of-magnitude estimate. A value of storage coefficient was estimated for each tested interval except 

interval D (see fig. 6). The plotted injection test data 

were matched with a type curve by superimposing the 

two plots along parallel y-axes. A matchline was chosen and the appropriate information taken from the 

type curve and the injection test plot.

Transmissivity was calculated by using the equation,

_ 1,440^

(3)

where,

T is the transmissivity, in feet squared per day; 

1,440 is a factor to convert minutes to days; 

ra is the delivery-tube radius, in feet; 

tr is the matchline from the type curve, dimensionless; and 

t is the matchline from the injection-test data, in

minutes.

Hydraulic conductivity, K, was calculated from 

the equation,

K T = b ' (4)

where b is the test interval, in feet.

Storage coefficient, S, was calculated by using the 

equation,

o o _ (5)

where,

a is a component related to storage between 10" 1

and 10'5 ; 

rw is the radius of the screened interval or uncased

well.

The specific storage for an interval was calculated 

by dividing the storage coefficient by the interval thickness.

INJECTION TESTS 17
Test Conditions

Injection tests were made to determine the 

hydraulic properties of six depth intervals in the test 

well. The depth intervals were selected on the basis of 

results of the borehole-flow survey. Three intervals, A, 

B, and C, from 1,473 to 1,667 ft; 1,665 to 1,865 ft; and 

1,886 to 1,933 ft, respectively, were tested with 

a straddle-packer assembly (fig. 6). The packer assembly became lodged in the test well after the third injection test. After several days the assembly was 

dislodged, but was damaged and required factory 

repair. The D and F intervals, from 1,934 to 2,134 ft 

and from 2,390 to 2,550 ft respectively, were tested 

with a bridge plug and single packer. The bridge plug 

and single packer allowed more flexibility in selecting 

test intervals, but required more operating time than the 

straddle packer assembly. Interval E was not tested. 

The last interval, G, was tested with only a single 

packer set at 2,550 ft and although the hole originally 

extended to 3,019 ft, the well had collapsed to 2,605 ft 

at the time of the test.

Pressure data were recorded on site by a contractor, who provided the packers. The pressure data were 

collected from above, between, and below the straddle 

packer assembly with crystal transducers during the

first three tests, and from above and between the packers on the last three tests. Pressure data were recorded 

at small time intervals of several seconds at the beginning of each test and at longer intervals as the test went 

on. The instantaneous maximum at the beginning of 

each injection test was determined by extrapolation. 

Injection tests were terminated when pressure reached 

equilibrium with pre-injection conditions, when a plot 

of pressure against elapsed time reached an inflection 

point, or when the test had extended beyond the time 

estimated to be necessary from preliminary calculations. The vertical hydraulic-head gradient, indicated 

by the difference in head at two depth intervals of the 

well, could not be defined because only one injection 

test reached equilibrium.

Water samples were collected from intervals B 

and C; however, the samples were muddy and a large 

amount of formation debris accumulated above the 

lower packer after each sample. Presumably the suction placed on the wall of the well by the sampler was 

greater than the formation material could withstand. 

Sampling was discontinued after the straddle packer 

assembly became lodged in interval C.

Test Results

ULJ 

ULJ

1,400

1,600

1,800

B

September 9^ 1988

1,473 teli 

(straddle packer)

1(886 to t,933Jeet

uu

< 2,000 

cc

w

§ 2,200

3 

£

O 2,400

uu

CO

I

t 2,600

uu

Q

2,800

Figure 6. Intervals isolated by packers during injection 

testing, Pahute Mesa-3 test well, Nye County, Nevada.

(no test) 

2,39Qto;2»59Pfeet

£55&to 2,605: feet

Interval A

Interval A, from 1,473 to 1,667 ft, is near the top 

of the thermal anomaly recorded on the temperature 

logs. Lithology in this interval consists of nonwelded, 

zeolitized ash-flow and reworked tuffs of the Rhyolite 

of the Loop member of the Timber Mountain Group. 

Fractures were detected in the upper part of this interval. The top packer was set in the bottom of the casing 

to prevent overinflation and to provide a tight fit; however, this meant that the top of the interval was only 18 

ft below the static water level. Water was added to raise 

the hydraulic head in the delivery tubing 253 ft above 

the formation water level of 1,455 ft. Three attempts to 

do the test produced poor results. During the first two 

tests, the time steps used were too large to adequately 

document the rapid water-level declines observed. 

The third test was made with an adequate time step; 

however, the pressure transducer had been placed too 

high in the access port and was left dry after only 19 

minutes, and water level did not drop smoothly as it did 

in other tests. Results of the third injection test are 

shown in figure 7.

18 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
LLI

I

C/D 

C/D 

LLI

o

C/D 

LLI

O

I

1.0

0.8

0.6

0.4

0.2

0 

0.1

Interval A, from 1,473 to 1,667 feet

H0=253 feet

rw=0.707 foot

ra=0.102foot

a=10-3

T=[1,440(tr)ra2]/t 

=[1,440(1.0)(0.102)2]/5 

=3.0 feet squared per day

S=a ra2/rw2 

=2.1x10-5

10 100 1,000

Q

a

w

C/D 

LLI

O 

C/D

LLI

O

1.0

0.8

0.6

0.4

0.2

Interval B, from 1,665 to 1,865 feet

Hrj=74 feet

rw=0.613foot

ra=0.102 foot

a=10'1

T=[1,440(tr)ra2]/t 

=[1,440(0.1)(0.102)2]/130 

=1.2x10'2 feet squared per day

S=a ra2/rw2 

=2.8x10'3

0.1 10 100 1,000

i_i

S

C/D C/D

LLI

C/D

O

1.0

0.8

0.6

0.4

0.2

0.1

Interval C, from 1,886 to 1,933 feet

Hrj=155feet

rw=0.553 foot

ra=0.102 foot

a=10-1

T=[1,440(tr)ra2]/t 

=[1,440(0.1 )(0.102)2]/480 

=3.1x10-3 feet squared per day

S=a ra2/rw2 

=3.4x10-3

Matchline 

ti- e

1 10 100 

TIME AFTER INJECTION STARTED, IN MINUTES

1,000

Figure 7. Injection-test analyses for depth intervals A, B, and C for Pahute Mesa-3 test well, Nye County, 

Nevada. Abbreviations: T, transmissivity; S, storage coefficient; H(t), head in the well above initial head at the 

time since injection; H0, head in the well above initial head at the instant of injection; rw, radius of open interval 

of well; ra, delivery tube radius; a, alpha; tr, matchline from type curve; t, time.

INJECTION TESTS 19
The data matched the type curve for a=10~3 . 

The matchline was at t=5 minutes and fr the dimensionless time factor from the type curve, was 1.0. 

Transmissivity for rocks in this interval is a moderately 

large 3 ft2/d and hydraulic conductivity is 1.5xlO"2 ft/d. 

Storage coefficient is 2.1xlO"5 and specific storage is 

(l.lxlO~7)/ft. The small storage coefficient shows that 

this uppermost interval responds as a confined unit.

Interval B

Interval B, from 1,665 to 1,865 ft, was selected 

because it is near the middle of the interval in which 

a thermal anomaly was detected by the temperature 

survey. The 200-ft interval consists of nonwelded, 

zeolitized reworked tuffs, ash-flow tuffs, basalt, and 

tuff breccia of the Rhyolite of the Loop member of 

Timber Mountain Group and the upper part of the Tiva 

Canyon Tuff of the Paintbrush Group. The breccia and 

units below appear to be fractured. Results of the injection test are shown on figure 7. Water was added to 

raise the hydraulic head in the delivery tubing 74 ft 

above the estimated formation water level of 1,456 ft. 

The test was 233 minutes, but this was not long enough 

to reach equilibrium. No data were recorded between 

12 and 188 minutes because of communication problems between the pressure transducers and the recording instruments.

The data best matched the type curve for a=10" 1 , 

although an inflection point was never reached. The 

matchline was f=130 minutes for the injection test data 

and tr =0.1. Transmissivity for rocks in this interval 

was calculated to be 1.2xlO"2 ft2/d and hydraulic conductivity was 6.0x10"5ft/d. Storage coefficient was 

estimated to be 2.8xlO~3 and specific storage was 

(1.4xlO-5)/ftInterval C

Interval C from 1,886 to 1,933 ft, was selected to 

determine the hydraulic properties associated with the 

lower part of a thermal anomaly on the temperature 

log. The 47-ft interval is composed entirely of nonwelded to partly welded ash-flow tuffs of the Tiva Canyon Tuff of the Paintbrush Group. No fractures were 

intersected in this interval. Water was added to raise the 

hydraulic head in the delivery tubing 155 ft above the 

estimated formation water level of 1,455 ft. The injection test was 100 minutes (fig. 7). The test was not continued to equilibrium or to the inflection point because 

the estimated time was too long.

The injection-test data for this interval matched 

the type curve for a=10" 1 . The matchline was at t =480 

minutes and tr=0. 1. Transmissivity was calculated to be 

3.1x10 ft/d and hydraulic conductivity was 6.6xlO"5 

ft/d. Storage coefficient was estimated to be 3.4xlO"3 

and specific storage was (7.2x10"5)/ft.

Interval D

Interval D, from 1,934 to 2,134 ft, was selected to 

determine the hydraulic properties for the source of 

inflow indicated by the temperature log between 1,900 

and 2,100 ft. The interval consists of the Tiva Canyon 

Tuff of the Paintbrush Group, a nonwelded to densely 

welded ash-flow tuff. Fractures were mapped from 

1,915 to 2,000 ft and at 2,070 ft. Water was added to 

raise hydraulic head in the delivery tubing 122.5 ft 

above the estimated formation water level of 1,455 ft 

(fig. 8). The injection test was run for 18 minutes, at 

which time the injection water reached equilibrium 

with the formation water.

The data did not match any of the type curves for 

radial flow, but matched a curve for a line source by 

Cooper and others (1967). The matchline was at £=0.6 

minutes and tr=l .0. Transmissivity was calculated to be 

25 fP/d and hydraulic conductivity was 1.2xlO-1 ft/d. 

Storage coefficient and specific storage were not calculated.

Interval E

Interval E, from 2,134 to 2,390 ft, was not tested 

because no inflow or outflow was indicated by the constant temperature gradient. It includes the hornblende 

rhyolite and breccia in the Calico Hills Formation. No 

fractures were identified in this interval.

Interval F

Interval F, from 2,390 to 2,550 ft, was selected to 

determine the hydraulic properties of the units above a 

small change in the temperature gradient at 2,550 ft. 

The 160-ft interval is composed of the Topopah Spring 

Tuff of the Paintbrush Group, a zeolitized nonwelded 

ash-flow tuff. Fractures were not found in this interval. 

Water was added to raise the hydraulic head in the 

delivery tubing 535 ft above the estimated formation 

water level of 1,455 ft (fig. 8). The injection test was 

run for almost 430 minutes. The test was not continued 

to equilibrium because the time was too long, but an 

inflection point was reached.

20 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
Q

S

w 

w

LU_l 

2

o

w

LU

O

I

111

I

W 

W 

111

_l

O

LII

o

1,000

Interval D, from 1,934 to 2,134 feet

Ho=122.5 feet

rw=0.495 foot

ra=0.102 foot

a=10-3

T=[1,440(tr)ra2]/t 

=[1,440(1.0)(0.102)2]/0.6 

=25 feet squared per day

S not estimated

Interval F, from 2,390 to 2,550 feet

Hrj=535 feet

rw=0.586 foot

ra=0.102foot

a=10-2

T=[1,440(tr)ra2]/t 

=[1,440(1.0)(0.102)2]/82 

=0.18 feet squared per day

S=a ra 

=3.0x10-4

100 1,000

Q

$> Hi

o

I

1.0

0.8

0.6

0.4

0.2

0.1

Interval G, from 2,550 to 2,605 feet

H0=187feet

rw=0.520 feet

ra=0.102 feet

a=10'1

T=[1,440(tr)ra2]/t 

=[1,440(1.0)(0.102)2]/102 

=O.T5 feet squared per day

S=ara2/rw2

=3.8x10-3

1 10 100 

TIME AFTER INJECTION STARTED, IN MINUTES

1,000

Figure 8. Injection-test analyses for depth intervals D, F, and G for Pahute Mesa-3 test well, Nye County, 

Nevada. Abbreviations: T, transmissivity; S, storage coefficient; H(t), head in the well above the initial head at 

the time since injection; H0, head in the well above initial head at the instant of injection; rw, radius of screened 

interval; ra, delivery tube radius; a, alpha; tr, matchline from type curve; t, time

INJECTION TESTS 21
The test data matched the type curve for o=10~2 . 

The matchline was f=82 minutes and tr=l.Q. Transmissivity was calculated to be 0.18 ft2/d and hydraulic conductivity was LlxlO"3 ft/d. Storage coefficient was 

estimated to be 3x10~4 and specific storage was 

(1.9xlO-6)/ft

Interval G

Interval G, from 2,550 to 2,605 ft, was tested with 

a single packer set at 2,550 ft. Although the well had 

been drilled to 3,019 ft, collapse of material into the 

well bore during previous injection tests resulted in 

a shorter interval for the test. The 5 5-ft interval was 

selected to determine the hydraulic properties of 

the units below a small change in the temperature gradient at 2,550 ft. The interval penetrates nonwelded 

to densely welded air-fall and ash-flow tuffs of the 

Topopah Spring Tuff of the Paintbrush Group. Water 

was added to raise the hydraulic head in the delivery 

tubing 187 ft above the estimated formation water level 

of 1,455 ft (fig. 8). The injection test was run for 250 

minutes. The test was not continued to equilibrium 

because the time was too long, but an inflection point 

was reached.

The test data matched the type curve for a=10" 1 . 

The matchline was t=lQ2 minutes and fr=1.0. Transmissivity was calculated to be 0.15 ft2/d and hydraulic 

conductivity was 2.7x10" 3 ft/d. Storage coefficient was 

estimated to be 3.8xlO"3 and specific storage was 

(6.9xlQ-5)/ft.

Discussion

The results of the injection tests are shown in 

table 5. For the six tested intervals, A, B, C, D, F, and 

G, transmissivity varied more than four orders of magnitude, from 3.1xlO"3 to 25 ft2/d, and hydraulic conductivity varied from 6.0xlO'5 to 1.2X10' 1 ft/d. These 

values are small compared with the range of hydraulic 

conductivity for fractured igneous rocks reported by 

Freeze and Cherry (1979, p. 29) of 10'2 to 102 ft/d. 

Only intervals A and D are within this range and only 

intervals A, B, and D intersect significant zones of fractures. Intervals A, B, and D also were identified by the 

tracer survey as being most productive. Interval B, 

from 1,665 to 1,865 ft, had a low hydraulic conductivity, 6.0x10'5ft/d. It includes the interval from 1,810 to 

1,8 80 ft that was fractured and also showed flow during 

the tracer test. The reason for its low hydraulic conductivity is not known. Intervals C, F, and G had no fractures, and relatively low to moderate hydraulic 

conductivity.

Lohman (1972, p. 8) reported a range in specific 

yield of 0.1 to 0.3 for most unconfined aquifers and a 

range in storage coefficient of 10"5 to 10 , which is 

about 10 per ft of aquifer thickness, for most confined 

aquifers. All the estimates for storage coefficient from 

the injection tests are small enough to suggest that the 

aquifer is confined below 1,473 ft.

AQUIFER TEST

An aquifer test was made to determine properties 

farther from the well bore than the area affected by the 

injection tests. The aquifer test, September 27-28, 

1988, followed completion of the injection tests. 

During the injection tests, the bottom part of the well 

(below 2,605 ft) was bridged or filled with debris that 

was not removed prior to the pumping test. The thickness of the test interval was 1,132 ft (from the bottom 

of the casing at 1,473 ft to the top of the bridge at 2,605 

ft). The well was pumped at a rate of 169 gal/min for 

31 hours. Drawdown was 78 ft. The pump and well 

during the test are shown in figure 2. Results of the 

aquifer-test analyses are shown in table 6.

Analytical Methods

Estimates of storage coefficient from the injection 

tests range from 2.1xlO"5 to 3.8xlO"3 and are in the 

range for confined aquifers. Also, the largest transmissivity from the injection tests, 25 ft2/d, was from interval D, from 1,934 to 2,134 ft, and indicates drawdown 

during pumping would be controlled by such a layer. 

Interval D is considered to be confined because it lies 

below a basalt layer that appears to be a confining unit 

on the basis of temperature logs and the tracer test. 

However, the uppermost section of the open part of the 

well is approximately 18 ft below the water table. During pumping, the water level in the well dropped 60 ft 

below the cased interval of the well, so that the upper 

part of the aquifer was dewatered, not just depressured. 

Thus, the response to pumping indicates a combination 

of confined and unconfined systems.

The shape of the time-drawdown curve may 

be interpreted as either a response to delayed yield 

(unconfined aquifer), or a response to a leaky confining 

unit (confined aquifer). The pumping-test data were 

analyzed for both confined and unconfined conditions

22 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
Table 5. Summary of injection-test analyses for Pahute Mesa-3 test well, Nye County, Nevada

TransDepth Jss^w THICK- HyHdra"iict

(feet (It** nessp««s conaucilv °!!du?tivlt"

^eei ness .f

squared (feet) l "7 *

per day) day)

Hydraulic Specific

"* ~ * 

1,473-1,667

1,665-1,865

1,886-1,933

1,934-2,134

2,134-2,390

2,390-2,550

2,550-2,605

Geometric mean

Sum

A

B

C

D

E

F

G

3.0

1.2xlO'2

3.1x10°

25

not tested

0.18

0.15

28

194

200

47

200

256

160

55

1,112

1.5xlO-2

6.0xlO'5

6.6x1 0'5

1.2X10' 1

1.1x10°

2.7x10°

1.7x10°

2.1xlO'5

2.7x10°

3.4x10°

3.0xlO'4

3.8x10°

7.4x1 0'4

l.lxlO'7

1.4xlO'5

7.2xlO'5

1.9xlO'6

6.9xlO'5

6.8xlO'6

Timber Mountain Group, Rhyolite of the Loop

nonwelded reworked ash-flow tuff

Timber Mountain Group, Rhyolite of the Loop

ash-flow tuff, basalt of well U-19ac, breccia

Paintbrush Group, Tiva Canyon Tuff nonwelded to partly welded ash-flow tuff

Paintbrush Group, Tiva Canyon Tuff moderately welded ash-flow tuff

Paintbrush Group, Tiva Canyon Tuff and

Topopah Spring Tuff, zeolitized nonwelded

bedded tuff, breccia, and hornblende rhyolite

Paintbrush Group, Topopah Spring Tuff, zeolitized nonwelded ash-flow tuff

Paintbrush Group, Topopah Spring Tuff, nonwelded to densely welded air-fall and ash-fall

tuffs

during pumping and recovery to determine hydraulic 

properties. In addition, bore-hole storage effects were 

considered because the well bore has a large diameter 

(17 in.) just below the casing due to fluid-flow effects 

during the construction of the well.

Unconfined Radial Flow

Analysis of the data, assuming that the aquifer is 

unconfined and flow is radial towards the test well, is 

based on the theoretical work of Boulton (1963) for 

delayed yield. The data are plotted on logarithmic 

paper as drawdown, s, against time, t. The graphs are 

matched against plots of W(u), the well function, and 

1/u for different values of r/B, 

where,

r is the well radius in the producing zone, in feet; 

B is a coefficient that relates well-bore storage to 

aquifer storage.

W(u) is defined,

(6)

The function u (dimensionless) is defined,

u =

47Y (7)

where,

t is the time elapsed since pumping began, in minutes, and

S is storage coefficient, dimensionless.

Transmissivity is then computed from the data at 

the matchpoint from,

4ns (8)

where,

Tis the transmissivity, in square feet per day; 

s is the drawdown, in feet; and 

Q is the pump discharge, in cubic feet per day.

and hydraulic conductivity, K, is computed as in equation (4).

To accommodate well-bore storage, the data are 

plotted on logarithmic paper as s/Q where Q is the discharge derived only from the aquifer and not from 

well-bore storage, against t/r2 where r is the well radius 

and may vary for each increment of pumping time and 

drawdown measured. The above equations are used in 

computations of transmissivity and hydraulic conductivity.

Type curves for delayed yield can be matched 

to either the early part of the time-drawdown data, the 

late part, or preferably both, and the difference used to 

estimate vertical hydraulic conductivity. For such an

AQUIFER TEST 23
Table 6. Summary of aquifer-test analyses for Pahute Mesa-3 test well, Nye County, Nevada

Analysis

Depth 

interval Thickness 

(feet) (feet)

Hydraulic 

Transmissivity conductivity 

(feet squared (feet per 

per day) day)

Unconfined Aquifer

Pumping1

Recovery1

Pumping, well-bore storage effects removed1

Recovery, well-bore storage effects removed1

Pumping2

Recovery2

Pumping well-bore storage effects removed3

Recover, well-bore storage effects removed3

Pumping, well-bore storage effects removed4 

Recovery, well-bore storage effects removed4

Specific capacity5

1,473-2,605

do.

do.

do.

Confined Aquifer

do.

do.

do.

do.

do. 

do.

do.

1,132

do.

do.

do.

do.

do.

do.

do.

do. 

do.

do.

70

55

51

38

76

52

370

360

410 

840

640

6.2x1 0'2

4.9xlO'2

4.5xlO'2

3.4xlO'2

6.7xlO'2

4.6xlO'2

0.33

0.32

0.36 

0.74

0.57

1 Boulton, 1963, and Neuman, 1975

2 Hantush and Jacob, 1955

3 Papadopulos and Cooper, 1967

4 Cooper and Jacob, 1946

5 Lohman, 1972

analysis, Neuman (1975, eqn. 23) shows that a new 

term, P, is included. P may be calculated from r/B of 

Boulton (1963) as:

= 3.063-0.567 log P (9)

where P is a proportionality constant between hydraulic conductivity and the part of the aquifer affected by 

pumping. The type curves of Neuman (1975) are in 

other respects similar to those of Boulton, although the 

theories differ in their treatment of the phreatic surface. The data collected during this test did not indicate late drawdown that would allow such an 

interpretation, and so vertical hydraulic conductivity is 

not discussed here.

Analysis of aquifer recovery following pumping 

is a good check on the aquifer response during the aquifer test, particularly if the pumping rate varied during 

the test, or if flow in the well bore was turbulent during 

pumping (Todd, 1976, p. 132). If the well-aquifer system achieved a steady-state condition during pumping, 

the Houpert-Pouchan assumption may be invoked 

(de Marsily, 1986, p. 177). When this condition is met, 

the recovery curve is plotted as residual drawdown and 

interpreted as a drawdown curve. The test results from 

PM-3 meet this Houpert-Pouchan assumption, as drawdown changed little between the 2d and 31st (final) 

hour of pumping.

Confined Radial Flow

Analysis of the data assuming that the aquifer is 

confined and flow is radial was based on the theoretical 

work of several authors. Hantush and Jacob (1955) 

derived an analysis for leaky confined aquifers. The 

data are plotted on logarithmic paper as drawdown, s, 

against time, t. The graphs are matched against plots of 

L(u,v), the well function, against 1/u for different values of v on a logarithmic graph. L(u, v) (dimensionless) 

is defined in the equation:

L(u,v) =

4nTs

Q

(10)

where v is a coefficient relating horizontal to vertical 

hydraulic conductivity. The function u (dimensionless) 

is defined as in equation (7).

Transmissivity is then computed from the matchpoint from,

r= L(u,v)Q

4ns

Hydraulic conductivity, K, is computed as in 

equation (4).

An analysis to accommodate well-bore storage 

was proposed by Papadopulos and Cooper (1967) for 

confined aquifers. The analysis assumes two-dimensional radial flow from the formation into the test well. 

The data are plotted on logarithmic paper as drawdown, s, against time, t. Type curves are generated by

24 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
plotting F(u,a), the well function, against 1/u for different values of a on a logarithmic graph. F(U,OL) is 

defined,

F(u,a) = (12)

where the function u is defined as in equation (7) and 

the value of a (dimensionless) is defined,

a = (13)

where rc is the well radius where the water level is 

drawing down and rw is the well radius within the 

aquifer. Values for F(u,a) are presented by Papadopulos and Cooper (1967) for different combinations of u 

and a.

Transmissivity is calculated from,

, (14) 4ns

and hydraulic conductivity is calculated as in 

equation (4).

Aquifer recovery after pumping ceased may 

also be analyzed by these two methods following the 

assumptions of Houpert-Pouchan (de Marsily, 1986, 

p. 1 77). The recovery curve is plotted as residual drawdown and interpreted as a drawdown curve.

The straight-line method of Cooper and Jacob 

(1946) also may be used to estimate well-bore effects 

in a confined aquifer and, in addition, yield insight into 

barriers and changes in conditions at some distance 

from the well. The method is not valid for short tests, 

when u < 0.01, but is generally valid for later periods. 

For well-bore storage, data are plotted on semilog 

paper as s/Q against t/r2. Transmissivity is computed 

from:

_

1)]

(15)

where A(t/r) is usually taken as one log cycle so that 

log A^/r2) equals 1.

For analysis of recovery using the Cooper and 

Jacob (1946) straight-line method and including wellbore storage effects, the Houpert-Pouchan assumption

is not used. Instead, the data are plotted as s/Q against 

t/t'(r), where t is time since pumping began and t' is 

time since pumping stopped.

47iA ^

(16)

Specific Capacity

Specific-capacity tests are less accurate than aquifer tests because they utilize only the endpoint data. 

They are based on the assumption of two-dimensional 

radial flow in a confined aquifer where pumping has 

continued long enough that steady-state drawdown 

is reached. Specific capacity is calculated according to 

the asymptotic method of Cooper and Jacob (1946) as 

shown in Lohman (1972, p. 52). The specific-capacity 

analysis is included because it is a common method, 

and other data with which the results of this test will be 

compared generally are available only from specificcapacity tests.

Specific capacity is calculated from successive 

iterations of the equation:

T = (-@-}ln2.25

\4nsJ \r*s

IL2

(17)

where Ton the right side of the equation is initially 

estimated as some likely value (1,000 ft^/d) and then 

replaced by the calculated value of T for three or four 

iterations until both T's match. An order of magnitude 

estimate of specific storage also is required for the successful use of this method. AT is calculated as shown 

above (eqn. 4).

Test Conditions

The aquifer test was made about 2 weeks after 

the test well had been completed. A submersible pump 

with a 180 gal/min discharge capacity was installed 

with a 2.875 in. pump column at a depth of 1,758 ft. 

A 2.375-in. diameter open-ended monitor line was 

attached to the pump column. The orifice was 10 ft 

below the pump intake to allow access to the lower part 

of the test well during pumping. The well was developed with two pumping and recovery periods prior to 

the aquifer test.

The aquifer test began at 1600 hours on September 26 and ended at 2300 hours on September 27. Water 

levels were measured during the first 18 hours of the 

test by means of a pressure transducer set at 1,740 ft.

AQUIFER TEST 25
Recording and printing equipment at the surface provided continuous drawdown data. After 18 hours, 

the transducer was removed from the well and the 

temperature and tracejector probes emplaced for the 

borehole-flow survey. After the borehole-flow survey, 

the transducer was returned to the well at a depth of 

1,700 ft and allowed to stabilize to the ambient water 

temperature. Water-level recovery was measured for 

9 l/2 hours after the pump was turned off, until the water 

level returned to the prepumping level of 1,455 ft. 

Pump discharge was monitored during the test by manual observations of a totalizing flow meter set in the 

pump discharge line. Discharge volumes for brief periods were recorded throughout the test and compared to 

totalized volumes for longer periods. The average 

pump discharge was 169 gal/min for the duration of the 

test, with a total volume of 314,000 gal pumped.

Analysis of Results

Figure 9 shows time-drawdown plots of representative data for the aquifer test. Drawdown was 78 ft at 

the completion of the 1,860-minute aquifer test and 

drawdown recovered to prepumping levels within 100 

minutes after the pump was turned off. The shape of the 

recovery curve was similar to that of the drawdown 

curve.

Unconfined Conditions

Comparison of the aquifer-test drawdown data to 

curves for unconfined flow with delayed yield (fig. 9) 

(Boulton, 1963; Neuman, 1975) yielded a matchpoint 

of 1/u equal to 10, W(u) equal to 1.0, t equal to 16 minutes, and s equal to 37 ft for r/B of 0.4 ({3=0.04). Transmissivity was calculated to be 70 f^/d and hydraulic 

conductivity was 6.2x10 ft/d. The recovery curve

100

LLJ 

, LU

Ss

LU .

O

cc

Q

10

Matchpoint

W(u)=1.0

1/u=10

t=16 minutes

s=37 feet

* Matchpoint

Type curve for

r/B=0.4

p=0.04

0=169 gallons per minute 

T=70 feet squared per day 

K=6.2x10'2 foot per day

10 100 

TIME, IN MINUTES SINCE PUMPING STARTED

1,000

100

LU 

LLJ 

LL

CO

LU

CC 

Q

10

a

Matchpoint

W(u)=1.0

1/u=10

t=12 minutes

s=47 feet

0=169 gallons per minute 

T=55 feet squared per day 

K=4.9x10"2 foot per day

Type curve for

r/B=0.6

p=0.10

10 100 1,000

TIME, IN MINUTES SINCE PUMPING STOPPED

Figure 9. Analysis of drawdown for an unconfined aquifer under the assumption of delayed yield during A, pumping 

and B, recovery at Pahute Mesa-3 test well, Nye County, Nevada. Abbreviations: W(u), the well function of u; u, the 

argument of the well function; t, time; s, drawdown in the well; Q, pump discharge; T, transmissivity; K, hydraulic 

conductivity; r, radius of the well; B, leakage factor.

26 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
(fig. 9B) yielded a matchpoint of 1/u of 10, W(u) equal 

to 1.0, t equal to 12 minutes, and s equal to 47 ft for r/B 

equal to 0.6 (P=0.10). Transmissivity was calculated to 

be 55 ft2/d and hydraulic conductivity was 4.9x10"2 

ft/d.

Analysis of the aquifer-test data with well-bore 

storage taken into account is shown in figure 10. The 

pumping data yielded a matchpoint of 1/u equal to 1.0, 

W(u) equal to 1.0, t/r2 equal to 2.4 mm/ft2, and s/Q 

equal to 0.3 ft/gal/min for r/B of 0.6 ((3=0.1). Transmissivity was calculated to be 51 fi^/d and hydraulic conductivity was 4.5x10"2 ft/d. The recovery curve (fig. 

10B) yielded a matchpoint of 1/u of 1, W(u) equal to 1, 

t/r2 equal to 6.5 min/fr, and s/Q equal to 0.4 ft/gal/min 

for r/B equal to 0.8 (p=0.18). Transmissivity was calculated to be 38 fi^/d and hydraulic conductivity was 

3.4xlO'2 ft/d.

Confined Conditions

Analysis of the aquifer-test data assuming leaky 

confined conditions (Hantush and Jacob, 1955) yielded 

a matchpoint withL(u,v) equal to 1.0, 1/u equal to 10, t 

equal to 13 min, and s equal to 34 ft, for a v of 0.2 

(fig. 1L4). Transmissivity was calculated to be 76 ff/d 

and hydraulic conductivity was 6.7x10" ft/d. The 

recovery curve (fig. 1 IB) yielded a matchpoint with 

L(u, v) equal to 1, 1/u equal to 10, t equal to 14 min, and 

s equal to 50 ft, for a v of 0.3. Transmissivity was calculated to be 52 ft2/d and hydraulic conductivity was 

4.6xlO'2 ft/d.

Analysis of the aquifer-test data for well-bore 

storage assuming confined conditions (Papadopulos 

and Cooper, 1967) yielded a matchpoint with F(u,a) 

equal to 10, 1/u equal to 10,000, t equal to 8.5 minutes, 

and s equal to 70 ft, for an a of 10'3 (fig. \2A). Transmissivity was calculated to be 370 ft2/d, hydraulic conductivity was calculated to be 0.33 ft/d. The recovery 

curve (fig. 125) yielded a matchpoint of 1/u equal to 

10,000, F(u,a) equal to 10, t equal to 5 minutes, and s 

equal to 72 ft, for an a of 10"3 . Transmissivity was calculated to be 360 ft2/d and hydraulic conductivity was 

0.32 ft/d.

The straight-line analysis of pumping (Cooper 

and Jacob, 1946) yielded As/Q equal to 0.085 

ft/gal/min/log cycle of t/r2 (fig. 13A). Radial transmissivity was calculated to be 410 ft2/d and hydraulic 

conductivity was 0.36 ft/d. The recovery analysis 

(fig. 135) yielded As/0 of 0.042 ft/gal/min/log cycle 

oft/t'r2 . Transmissivity was 840 fi^/d and hydraulic 

conductivity was 0.74 ft/d. Because the plots do not

conform well to the theoretical analysis, these estimates of transmissivity and hydraulic conductivity are 

considered less accurate than the above tests.

The specific capacity test yielded an estimate of j. j. _ / /

transmissivity of 640 ft/d and a hydraulic conductivity 

of 0.57 ft/d, assuming a storage coefficient of 0.0007 

(geometric mean of injection test results). The analysis 

of specific capacity is based on only the endpoint measurement and, therefore, is the least accurate of the 

three pumping-test analyses.

Discussion

The pumping-test results do not lead to a singular 

conclusion about aquifer properties. Transmissivities 

calculated using the assumption that the aquifer is 

unconfined with delayed yield ranges from 38 to 70 

fr/d. These are slightly larger than the sum of the 

injection tests, 28 ft^d. Hydraulic conductivity ranges 

from 3.4xlO"2 to 6.2x10"2 ft/d, whereas the geometric 

mean of the injection tests is 1.7xlO"3 . Corrections for 

well-bore storage do not significantly affect the transmissivity, and hydraulic-conductivity estimates under 

the assumption of unconfined conditions.

Transmissivity calculated under the assumption 

that the aquifer is confined by a leaky layer yields estimates from 52 to 840 ff/d. The correction for wellbore storage has a significant effect. The range of transmissivity for data corrected for well-bore storage is 

from 360 to 840 ff/d, approximately an order of 

magnitude larger than the sum of the injection-test 

estimates. Hydraulic conductivity is 0.32 to 0.74 ft/d, 

approximately two orders of magnitude larger than the 

geometric mean of the injection-test estimates.

Several possible reasons why the injection test 

results do not agree with the aquifer test results include: 

(1) Injection tests were made shortly after completion 

of the well, prior to development, and may have been 

affected by the presence of drilling fluids. The larger 

density and viscosity of drilling fluids would reduce the 

rate of inflow of injected water and lead to lower estimates of transmissivity. The aquifer test was run about 

2 weeks later, following a period of development.

(2) The injection tests measure a much smaller volume 

of aquifer than the aquifer test. In a fractured medium, 

some fractures that are near the well bore, but do not 

intersect it, will only affect tests that include a large 

volume surrounding the well. Hence, the longer aquifer 

test may produce a larger estimate of transmissivity.

(3) Sidewall coring was done in the well after the 

injection tests but before the aquifer test. The affect on

AQUIFER TEST 27
LU

DC 

LU 

D_

CO

o

O 

DC 

LU 

D_

LU 

LU

O

0.1

0.01

A

Matchpoint 

W(u)=1.0 

1/u=1

t/i-^2.4 min/ft2 

s/Q=0.3 ft/gal/min

* Matchpoint

Type curve for

r/B=0.6

p=0.1

Q=169 gallons per minute 

T=51 feet squared per day 

K=0.045 foot per day

10 100 

t/r2 , IN MINUTES SINCE PUMPING STARTED PER AREA

1,000

LU

DC 

LU 

D_

CO

DC 

LU 

D_

IDLU

Q

CO 

LU 

DC

0.1

0.01

a

Matchpoint 

W(u)=1.0

1/U-1

t/r*=6.5 min/ft2 

s/Q=0.4 ft/gal/min Matchpoint

Q=169 gallons per minute 

T=38 feet squared per day 

K=0.034 foot per day

Type curve for

r/B=0.8

p=0.18

10 100 

t/r2 , IN MINUTES SINCE PUMPING STOPPED PER AREA

1,000

28

Figure 10. Analysis of drawdown for an unconfined aquifer under the assumption of delayed yield and correction for well-bore storage during A, pumping and B, recovery at Pahute Mesa-3 test well, Nye County, 

Nevada. Abbreviations: W(u), the well function of u; u, the argument of the well function; t, time; s, drawdown in the well; Q, pump discharge; T, transmissivity; K, hydraulic conductivity; r, radius of the well; B, 

leakage factor.

Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
100

Ill

ill

10

Matchpoint

L(u,v)=1.0

1/u=10

t=13 minutes

s=34 feet

* Matchpoint

Type curve for 

v=0.2

Q=169 gallons per minute 

T=76 feet squared per day 

K=6.7x10'2 foot per day

10 100 

TIME, IN MINUTES SINCE PUMPING STARTED

1,000

100

in in

LL

ES

10

B

Matchpoint 

L(u,v)=1.0 

1/u=10 

t=14 minutes 

s=50 feet

* Matchpoint

Q=169 gallons per minute 

T=52 feet squared per day 

K=4.6x10'2 foot per day

Type curve for 

v=0.3

10 100 1,000

TIME, IN MINUTES SINCE PUMPING STOPPED

Figure 11. Analysis of drawdown for a leaky confined aquifer during A, pumping and B, recovery at Pahute Mesa-3 

test well, Nye County, Nevada. Abbreviations: L(u,v), the well function of u for a leaky confined aquifer; u, the argument of the well function; v, the coefficient relating horizontal to vertical hydraulic conductivity; t, time; s, drawdown in 

the well; Q, pump discharge; T, transmissivity; K, hydraulic conductivity.

hydraulic conductivity of setting off numerous small 

charges in the well, and removal of small cores is 

unknown. Such procedures do increase the surface area 

of the well bore, could increase fractures, and may lead 

to increased hydraulic conductivity.

The response of the unconfined part of the aquifer 

cannot be separated from the response of the confined 

part of the aquifer in the analysis of drawdown. The 

most transmissive section of the aquifer, interval D, 

however, probably is the major control on drawdown 

during the aquifer test. Interval D remained confined 

throughout the aquifer test. On the basis of this 

assumption, the average transmissivity estimated using 

the leaky confined theory with well-bore storage 

effects removed, 360 fr/d, is the best estimate for the

depth interval from 1,473 to 2,605 ft under the conditions of this test, and the best estimate of hydraulic conductivity is 0.32 ft/d.

WATER LEVELS

Water-Level Altitudes at the Test Well

Water levels at PM-3 for September 1988 to June 

1990 are shown in fig. 14. Water-level altitude was 

computed by subtracting the depth to water from the 

altitude of the measuring point, which is 5,823 ft above 

sea level. The measuring point is the rim of the casing 

at land surface. A contractor measured water levels 

from September 9 to October 10, 1988, using a fluidWATER LEVELS 29
100

ID

111

oc

Q

10

Matchpoint 

F(u,a)=10 

1/u=10,000 

t=8.5 minutes 

s=70 feet

Type curve for 

a=1o"

Q=169 gallons per minute 

T=370 feet squared per day 

K=0.33 foot per day

10 100 

TIME, IN MINUTES SINCE PUMPING STARTED

1,000

Matchpoint 

F(u,a)=10 

1/u-10,000 

t=5 minutes 

s=72 feet

0=169 gallons per minute 

T=360 feet squared per day 

K=0.32 foot per day

Type curve for a=10'3

10 100 

TIME, IN MINUTES SINCE PUMPING STOPPED

1,000

Figure 12. Analysis of drawdown for a leaky confined aquifer under the assumption of delayed yield and well-bore 

storage during A, pumping and B, recovery at Pahute Mesa-3 test well, Nye County, Nevada. Abbreviations: F(u,a), 

the well function of u for a leaky confined aquifer with delayed yield; u, the argument of the well function; a, the coefficient relating horizontal to vertical hydraulic conductivity; t, time; s, drawdown in the well; Q, pump discharge; T, 

transmissivity; K, hydraulic conductivity.

density geophysical instrument or other geophysical 

logs. The USGS measured water levels from December 

1988 to June 1990 with an electric tape mounted on a 

truck hoist unit. Water-level measurements made during the aquifer and injection tests are not shown on 

figure 14.

Water-levels changed slightly when the test well 

was deepened from 1,647 to 3,019 ft in 1988. During 

the first geophysical logging phase, when the test well 

was 1,647 ft deep, water-level altitudes ranged from 

4,367 to 4,368 ft. During the second logging phase, 

when the test well was 3,019 ft deep, water-level altitudes ranged from 4,366 to 4,367 ft.

Water-level altitudes during the 2-year period 

from November 1988 to June 1990, after drilling and 

testing was completed, ranged from 4,362 to 4,366 ft.

The water-level-altitude range is typical. Robison and 

others (1988) measured 4-ft water-level fluctuations 

during several months in the Yucca Mountain area, 

30 mi to the south. Water levels were lowest in December 1988 and September 1989, suggesting a seasonal 

effect.

Ground-Water Gradient

Blankennagel and Weir (1973, pi. 1) mapped 

water-level altitudes in and near Silent Canyon caldera 

to the north and east of PM-3. Their work shows that 

water levels in the area of PM-3 outside of the caldera 

slope to the southeast and that water levels within the 

caldera slope to the southwest (fig. 15). Blankennagel 

and Weir inferred that a hydraulic barrier to flow is

30 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
HI 

CC

I 

O 

CO 

Q 

0.

IHJ

25 

^ z

E- S 

LU cc

 5 HI

§9

DC 

LU

I

0.6

0.5

0.4

cc 0.3

Q ~ 0.2 _i

HI 

HI

0.1

A s/Q=0.085 ft/gal/min/log cycle 

Q=169 gallons per minute 

T=410 feet squared per day 

K=0.36 foot per day

10 100 1,000 

t/r2, IN MINUTES PER SQUARE FOOT

10,000

LU

O

CO 

Q 

Q.

-

Q Q]

HI

LU 

_l

DC 

HI

I

0.6

0.5

0.4

0.3

~ 0.2

B

A s/Q=0.042 ft/gal/min/log cycle 

Q=169 gallons per minute 

T=840 feet squared per day 

K=0.74 feet per day

0.1

10,000 1,000 100

t/t'r2 , IN (SQUARE FEET) ~ 1

10

Figure 13. Analysis of drawdown for a confined aquifer under the assumption of delayed yield and correction for well-bore storage during A, pumping and B, recovery at Pahute Mesa-3 test well, Nye County, 

Nevada. Abbreviations: As, the change in drawdown since the last time step; Q, pump discharge; T, 

Transmissivity; and K, hydraulic conductivity.

WATER LEVELS 31
4,370

u

LJ UJ 

< 03 

-I LU 

LU > 

> O

cc iLU LU 

h- LU

4,365

4,360 LJ-J-1-1

1988 1989 1990 1991

YEAR

Figure 14. Water-level altitudes in Pahute Mesa-3 test well, Nye County, Nevada

located approximately along the western boundary of 

the caldera between areas of southeastward and southwestward gradients. The Silent Canyon caldera boundary fault juxtaposes intracaldera rocks with moderate 

permeabilities against precaldera rocks having lower 

permeabilities, hence it is not so much a barrier as a 

boundary that functions as a conduit to transmit fluid.

Contours west of the caldera boundary were 

based on water levels in only three wells. The water 

level in PM-3 does not contradict the interpretation of 

Blankennagel and Weir (1973); however, it does show 

that inferred positions of the 4,500 and 4,600-ft contours should be a little closer together to allow for a 

4,400-ft contour.

GROUND-WATER QUALITY

Water Chemistry

Water-quality parameters analyzed for samples 

from PM-3 to document water chemistry at the site 

(table 7). A water sample was collected on October 28 

when the test well was pumped to remove fluids introduced during cleaning of the test well on October 21. 

The pump intake was set at a depth of 1,655 ft and the 

test well was pumped for approximately 24 hrs before 

the sample was collected. Four methods were used by 

DRI personnel to ascertain that formation water, and 

not introduced water, was being sampled: (1) intermittent field measurements of temperature, pH, and specific conductance indicated the characteristics of water 

being discharged had stabilized; (2) bromide, which 

was used as a tracer at 20 mg/L in fluids introduced into 

the test well, was 0.54 mg/L; (3) field measurements 

of detergent concentration were much lower than in

drilling fluid samples; and (4) major cation and anions 

collected after the aquifer test yielded values similar to 

those collected after the injection tests.

The water sample was analyzed for dissolved 

constituents by the USGS water-quality laboratory 

(table 7). Temperature, pH, and specific conductance 

were measured in the field by USGS personnel and the 

results, within the limits of analytical uncertainty, were 

similar to those collected by DRI personnel. Samples 

collected for laboratory analysis of major ions by the 

USGS also yielded results similar to those for samples 

collected by DRI personnel. DRI personnel also analyzed for stable and unstable isotopes. Water samples 

collected prior to the injection tests contained too much 

drilling fluid and formation material to be representative of formation water. A bailed sample taken during 

the first period of geophysical logging and an air-lifted 

sample taken from the test well after a weekend shutdown in drilling also contained excessive drilling fluid 

and were not representative of formation water.

Water from PM-3 is a sodium mixed-anion water. 

Sodium had the highest concentration, 130 mg/L, and 

the highest percentage in milliequivalents per liter, 

73 percent, of the major cations. Calcium, potassium, 

and magnesium had concentrations of 36,10, and 

1.5 mg/L respectively (23, 3, and 1 percent of the 

milliequivalents per liter). Bicarbonate had the highest 

concentration, 150 mg/L, of the major anions. Sulfate, 

chloride, and fluoride concentrations were 130,98, and 

2.4 mg/L, respectively. Bicarbonate, sulfate, chloride, 

and fluoride were 31, 34, 35, and 0.006 percent in 

milliequivalents per liter, respectively.

32 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
116°30'

37°22'30" -

37°07130" ~

Base prepared by U.S. Geological Survey from 

digital data, 1:100,000 1979-89 

Universal Transverse Mercator projection 

Zone 11

EXPLANATION

 4200 Water-level contour-Shows altitude of water level. Interval 100 feet. 

Datum is sea level. Modified from Blankennagel and Weir (1973, plate 1)

Approximate position of Inferred hydraulic boundary-Modified from 

Blankennagel and Weir (1973, plate 1)

Caldera boundary-Modified from David A. Sawyer (U.S. Geological Survey 

written commun., 1991)

General direction of ground-water flow

'UE-20H 

4441

Well-Well identifier, and water-level altitude, in feet above sea level 

Figure 15. Water-level-altitude contours and ground-water flow direction on Pahute Mesa, Nye County, Nevada.

GROUND-WATER QUALITY 33
Table 7. Water-quality data for Pahute Mesa-3 test well, Nye County, Nevada

[All values are for dissolved concentrations. Abbreviations: N, nitrogen; P, phosphorus; <, less than; ng/L, micrograms per liter; us/cm, microsiemens per 

centimeter; mg/L, milligrams per liter; °C, degrees Celsius]

Date 

sampled

10-28-88

Calcium 

(mg/L)

36

Alumium 

(ug/L)

<10

Lithium 

(ug/L)

130

Time

1030

Magnesium 

(mg/L)

1.5

Arsenic 

(ug/L)

4

Manganese 

(ug/L)

14

Temperature 

(°C) pH

35.5

Sodium 

(mg/L)

130

Barium 

(ug/L)

2

Mercury 

(Mg/L)

<0.1

7.60

Potassium 

(mg/L)

10

Beryllium 

(Mg/L)

<0.5

Molybdenum 

(ug/L)

<10

Specific 

conductance 

(|as/cm 

at25°C)

833

Bicarbonate 

(mg/L)

150

Cadmium 

(ug/L)

<1

Nickel 

(ug/L)

5

Dissolved 

solids 

(residue 

at 180°C)

550

Chloride 

(mg/L)

98

Choride 

(ug/L)

2

Selenium 

(ug/L)

<1

Carbon- 13 

(Permil) 1

-116

Sulfate 

(mg/L)

130

Cobalt 

(ug/L)

<3

Silver 

(ug/L)

<1.0

Deuterium 

(Permil) 1

-15.0

Fluoride 

(mg/L)

2.4

Copper 

(ug/L)

<1

Strontium 

(ug/L)

81

Oxygen- 18 

(Permil) 1

-6.7

Bromide 

(mg/L)

0.54

Iron 

(Mg/L)

60

Vanadium 

(ug/L)

<6

Nitrate 

plus 

nitrite Phosphorus 

as N as P 

(mg/L) (mg/L)

0.390 0.010

Silicon 

(mg/L)

63

Lead 

(ug/L)

<5

Zinc 

(ug/L)

7

1 Isotopic analyses by Desert Research Institute, written communication, 1988.

Relation to Regional Water Chemistry

Water from PM-3 does not fit into the sodium 

potassium bicarbonate facies of other Pahute Mesa 

waters as defined by Winograd and Thordarson (1975) 

because calcium, chloride, and sulfate concentrations 

are higher in the PM-3 water (fig. 16; Blankennagel 

and Weir, 1973, table 10). An exception is water from 

well UE-20J. Well UE-20J is about 1 mi north of PM-3 

and also is west of an inferred hydraulic boundary. The 

chemistry of water at this site is similar to that of PM-3. 

The differences in concentration between water west of 

the caldera and water within the Silent Canyon caldera 

indicate that water from west of the hydraulic boundary 

represents a different ground-water source than water 

east of it.

Magnesium, bicarbonate, and fluoride concentrations in the PM-3 water are in the range of concentrations from Yucca Mountain area waters, but calcium, 

sodium, potassium, chloride, and sulfate concentrations exceed those of water from Yucca Mountain 

(Benson and others, 1983, table 1). These differences 

suggest PM-3 water may not flow toward the Yucca 

Mountain area. Major ion concentrations in PM-3 

water are similar to Oasis Valley water, except sulfate, 

which is higher at PM-3 (Malmberg and Eakin, 1962, 

table 3). These similarities in chemistry, and a southsloping gradient suggest that PM-3 water may flow 

toward the Oasis Valley discharge area.

SUMMARY

PM-3, a 3,019-ft test well, was drilled to collect 

ground-water data on Pahute Mesa between the 

Nevada Test Site and Oasis Valley discharge area. The 

test well was rotary drilled from September 1 to 19, 

1988, with air-foam using conventional circulation. 

The test well was cased with 10.75-in. diameter casing 

to a depth of 1,473 ft. A 9.875-in. diameter hole was 

drilled below the casing to 3,019 ft.

Volcanic rocks of Tertiary age were penetrated 

the entire depth of the test well. Lithologic samples, 

drill-bit cuttings, and sidewall cores were collected and 

are stored in the USGS core library at Mercury, Nev. 

Core samples and geophysical logs helped determine 

the test-well lithology and hydrostratigraphy. Geophysical logs indicate that the tuffs are fractured in 

places, and that some of the fractures control the hydrologic response of the well. A moderately welded ashflow tuff, the Tiva Canyon Tuff of the Paintbrush 

Group was the most conductive unit penetrated by the 

test well. Effective porosity ranged from 19 to 38 percent in the tuffs and rhyolites, and was 4 percent in 

basalt. Total porosity ranged from 33 to 55 percent in 

the tuffs and from 12 to 27 percent in basalt and 12 to 

46 percent in rhyolite. The 1.00°C/100 ft temperature 

gradient was high compared with that in other Pahute

34 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
MAGNESIUM

NOTE: TR

INDICATE 

BASIS OF 

PER LITE

EXPLANATION

 Pahute Mesa Well From 

Blankennegal and Weir, 1973

O PM-3orUE-20j 

© UE-20J

Oasis Valley well or spring From 

Malmberg and Eakin, 1962

Yucca Mountain well From Benson 

and others, 1983

BICARBONATE

3J

Figure 16. Relative cation and anion concentrations for selected Nevada Test Site and vicinity waters, Nye County, Nevada.

CJ 

OI
Mesa wells, possibly resulting from a buried heat 

source, which may be the southward extension of a 

granitic body north of PM-3.

Six injection tests were made on the packed intervals of the well. The time-hydraulic head data were 

matched to type curves for radial-confined flow. The 

tests indicate transmissivities range from 3.1xlO"3 to 

25 ft2/d. The sum of transmissivities is 28 ft/d. Estimates of hydraulic conductivity range from 6.0xlO"5 to 

0.12 ft/d. The geometric mean of hydraulic conductivity is 1.7xlO"3 ft/d. The storage coefficient was estimated to be between 2.1x10 and 3.8xlO"3 , which is 

typical of a confined aquifer. Estimates of specific storage ranged from (l.lx!0'7)/ft to (7.2xlO'5)/ft and averaged (6.8xlO-6)/ft.

An aquifer test was run for 31 hours with an average pump discharge of 169 gal/min and a maximum 

water-level drawdown of 78 ft. Well-bore storage 

affected test results for the first hour of pumping. Timedrawdown data were matched to radial-flow type 

curves for unconfined and confined conditions. Assuming unconfined conditions, estimates of transmissivity 

ranged from 38 to 70 r^/d and hydraulic conductivity 

ranged from 3.4xlO"2 to 6.2xlO'5 ft/d. Estimates of 

storage determined from the injection tests, however, 

show that even the uppermost interval of the well 

responds as if it were confined. Assuming confined 

conditions, with well-bore storage taken into account, 

transmissivity estimates ranged from 360 to 840 ft^/d. 

Hydraulic conductivity estimates ranged from 0.32 to 

0.74 ft/d.

The response of the unconfined part of the aquifer 

cannot explicitly be separated from the response of the 

confined part of the aquifer. However, the most transmissive section of the aquifer, interval D, probably was 

the major control of drawdown during the pumping 

test; interval D remained confined throughout the test. 

On the basis of this assumption, the best estimate of 

transmissivity from leaky confined theory is 360 ft^/d 

for the interval from 1,473 to 2,605 ft under the conditions of this test and the best estimate of hydraulic conductivity is 0.32 ft/d.

Water-level altitude fluctuated from 4,362 to 

4,368 ft, in the test well during October 1988 to June 

1990.

Analyses of formation water sampled during 

pumping indicate that the PM-3 water is a sodium 

mixed-anion water. Sodium is the predominant cation 

and bicarbonate, sulfate, and chloride are the major 

anions. The calcium, chloride, and sulfate concentrations are high compared to other Pahute Mesa waters, 

except for water from a nearby well, UE-20J. The water 

chemistry indicates that flow may be to the south, 

toward Oasis Valley.

REFERENCES CITED

Benson, L.V., Robison, J.H., Blankennagel, R.K., and 

Ogard, A.E., 1983, Chemical composition of ground 

water and the locations of permeable zones in the Yucca 

Mountain area, Nevada: U.S. Geological Survey OpenFile Report 83-854, 19 p.

Blankennagel, R.K., and Weir, I.E., Jr., 1973, Geohydrology 

of the eastern part of Pahute Mesa, Nevada Test Site, 

Nye County, Nevada: U.S. Geological Survey Professional Paper 712-B, 35 p.

Boulton, N.S., 1963, Analysis of data from non-equilibrium 

pumping tests allowing for delayed yield from storage: 

London, Institute of Civil Engineers Proceedings, v. 26, 

p. 469-482.

Byers, P.M., Jr., Carr, W.J., Christiansen, R.L., Lipman, 

P.W., Orkild, P.P., and Quinlivan, W.D., 1976a, Geologic map of the Timber Mountain caldera area, Nye 

County, Nevada: U.S. Geological Survey Miscellaneous Investigations Series Map 1-891.

Byers, P.M., Jr., Carr, W.J., Orkild, P.P., Quinlivan, W.D., 

and Sargent, K.A., 1976b, Volcanic suites and related 

caldrons of Timber Mountain-Oasis Valley caldera 

complex, southern Nevada: U.S. Geological Survey 

Professional Paper 919, 70 p.

Claassen, H.C., 1985, Sources and mechanisms of recharge 

for ground water in the west-central Amargosa Desert, 

Nevada A geochemical interpretation: U.S. Geological Survey Professional Paper 712-F, 31 p.

Cooper, H.H., Jr., and Jacob, C.E., 1946, A generalized 

graphical method for evaluating formation constants 

and summarizing well-field history: American Geophysical Union Transactions, v. 27, no. 4, p. 526-534.

Cooper, H.H., Jr., Bredehoeft, J.D., and Papadopulos, I.S., 

1967, Response of a finite diameter well to an instantaneous charge of water: Water Resources Research, v. 3, 

no. 1, p. 263-269.

de Marsily, Ghislain, 1986, Quantitative hydrogeology 

Groundwater hydrology for engineers: New York, 

Academic Press, Inc., 440 p.

Dresser Atlas, 1982, Interpretive methods for production 

well logs: Houston, Dresser Industries, Inc., 159 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, N.J., Prentice-Hall, Inc., 604 p.

Hantush, M.S., and Jacob, C.E., 1955, Nonsteady radial flow 

in an infinite leaky aquifer: American Geophysical 

Union Transactions, v. 36, no. 1, p. 95-100.

36 Geohydrology of Pahute Mesa-3 Test Well, Nye County, Nevada
Healey, D.L., 1968, Application of gravity data to geologic 

problems at Nevada Test Site, in Eckel, E.B., ed., 

Nevada Test Site: Geologic Society of America Memoir 110, p. 147-156.

Healey, D.L., Hams, R.N., Ponce, D.A., and Oliver, H.W., 

1987, Complete Bouguer gravity map of the Nevada 

Test Site and vicinity, Nevada: U.S. Geological Survey 

Open-File Report 87-506.

Keys, W.S., and MacCary, L.M., 1971, Application of borehole geophysics to water-resources investigations: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 2, chap. El, 126 p.

Lohman, S.W., 1972, Ground-water hydraulics: U.S. Geological Survey Professional Paper 708, 70 p.

Malmberg, G.T., and Eakin, T.E., 1962, Ground-water 

appraisal of Sarcobatus Flat and Oasis Valley, Nye and 

Esmeralda Counties, Nevada: Nevada Department of 

Conservation and Natural Resources, Ground-water 

Resources Reconnaissance Series Report 10, 39 p.

 1964, Relation of fluoride content to recharge and 

movement of ground water in Oasis Valley, southern 

Nevada: U.S. Geological Survey Professional Paper 

475-D, p. 189-191.

Neuman, S.P., 1975, Analysis of pumping test data from 

anisotropic unconfined aquifers considering delayed 

gravity response: Water Resources Research, v. 11, 

no. 2, p. 329-342.

O'Connor, J.T., Anderson, R.E., and Lipman, P.W, 1966, 

Geologic map of the Thirsty Canyon quadrangle, Nye 

County, Nevada: U.S. Geologic Survey Geologic 

Quadrangle Map GQ-524, scale 1:24,000.

Orkild, P.P., Sargent, K.A., and Snyder, R.P., 1969, Geologic 

map of Pahute Mesa, Nevada Test Site and vicinity, Nye 

County, Nevada: U.S. Geologic Survey Miscellaneous 

Geologic Investigations Map 1-567.

Papadopulos, I.S., and Cooper, H.H., Jr., 1967, Drawdown in 

a well of large diameter: Water Resources Research, 

v.3,no. I, p. 241-244.

Robison, J.H., Stephens, D.M., Luckey, R.R., and Baldwin, 

D. A., 1988, Water levels in periodically measured wells 

in the Yucca Mountain area, Nevada, 1981-87: U.S. 

Geological Survey Open-File Report 88-468,132 p.

Rush, F.E., 1968, Index of hydrographic areas Nevada: 

Nevada Division of Water Resources, Information 

Report 6, 38 p.

Sawyer, D.A., Fleck, R.J., Lanphere, M.A., Warren, R.G., 

Broxton, D.E., and Hudson, M.R., 1994, Episodic 

caldera volcanism in the Miocene southwestern Nevada 

volcanic field Revised stratigraphic framework, 

40Ar/39Ar geochronology, and implications for magmatism and extension: Geological Society of America 

Bulletin, v. 106, p. 1304-1318

Todd, O.K., 1976, Ground-water hydrology (2d edition): 

New York, John-Wiley, 535 p.

Waddell, R.K., Robison, J.H., and Blankennagel, R.K., 

1984, Hydrology of Yucca Mountain and vicinity, 

Nevada-California Investigative results through 

mid-1983: U.S. Geological Survey Water-Resources 

Investigations Report 84-4267, 72 p.

White, A.F., 1979, Geochemistry of ground water associated 

with tuffaceous rocks, Oasis Valley, Nevada: U.S. Geological Survey Professional Paper 712-E, 25 p.

Winograd, I.J., and Thordarson, William, 1975, Hydrogeologic and hydrochemical framework, south-central 

Great Basin, Nevada-California, with special reference 

to the Nevada Test Site: U.S. Geological Survey 

Professional Paper 712-C, 126 p.

REFERENCES CITED 37