Prepared in cooperation with the

U.S. DEPARTMENT OF ENERGY,

under Interagency Agreement

DE–AI08–92NV10874

Results of Hydraulic Tests in Miocene

Tuffaceous Rocks at the C-Hole Complex,

1995 to 1997, Yucca Mountain, Nye

County, Nevada

U.S. Geological Survey

Water-Resources Investigations Report 02-4141

Results of Hydraulic Tests in Miocene

Tuffaceous Rocks at the C-Hole

Complex, 1995 to 1997, Yucca

Mountain, Nye County, Nevada

By Arthur L. Geldon, Amjad M.A. Umari, Michael F. Fahy, John D. Earle, 

James M. Gemmell, and Jon Darnell

Denver, Colorado

2002

Prepared in cooperation with the

U.S. DEPARTMENT OF ENERGY,

Under Interagency Agreement

DE–AI08–92NV10874

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02–4141
District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046

For additional information write to:

Chief, Earth Science Investigations Program

Yucca Mountain Project Branch

U.S. Geological Survey

Box 25046, Mail Stop 421

Denver Federal Center

Denver, CO 80225-0046

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does 

not constitute endorsement by the U.S. Geological Survey.

Copies of this report can be purchased 

from:

U.S. Geological Survey

Information Services

Box 25286

Denver Federal Center

Denver, CO 80225
CONTENTS III

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

Introduction............................................................................................................................................................................ 2

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

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

Acknowledgments ....................................................................................................................................................... 4

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

Instrumentation ...................................................................................................................................................................... 10

Packers ......................................................................................................................................................................... 10

Transducers.................................................................................................................................................................. 10

Barometers................................................................................................................................................................... 10

Pumps .......................................................................................................................................................................... 12

Flowmeters................................................................................................................................................................... 13

Data Acquisition and Instrument Control.................................................................................................................... 14

Hydraulic Tests ...................................................................................................................................................................... 14

Analytical Methods...................................................................................................................................................... 15

Earth Tides and Barometric Effects............................................................................................................................. 15

Flow Distribution in the C-holes.................................................................................................................................. 16

Monitoring Network .................................................................................................................................................... 19

Description of Tests ..................................................................................................................................................... 21

Hydraulic Properties .............................................................................................................................................................. 33

Calico Hills Interval..................................................................................................................................................... 33

Prow Pass Interval........................................................................................................................................................ 36

Upper Bullfrog Interval ............................................................................................................................................... 36

Lower Bullfrog Interval ............................................................................................................................................... 37

Upper Tram Interval..................................................................................................................................................... 38

Miocene Tuffaceous Rocks.......................................................................................................................................... 40

Paleozoic Carbonate Rocks ......................................................................................................................................... 45

Analytical Uncertainty................................................................................................................................................. 46

Chemistry of Water Samples Collected During Hydraulic Tests........................................................................................... 51

Background Chemistry of UE-25 c #3 Water.............................................................................................................. 51

Changes in UE-25 c #3 Water Chemistry During Pumping ........................................................................................ 51

Summary and Conclusions .................................................................................................................................................... 54

References.............................................................................................................................................................................. 56

FIGURES

1. Map showing location of the C-hole complex, boreholes UE-25 c #1, UE-25 c #2, and UE-25 c #3...................... 3

2. Generalized geologic map showing the location of the C-hole complex and nearby boreholes............................... 5

3. Map showing potentiometric surface of the Miocene tuffaceous rocks in the vicinity of the C-hole complex, 

May 1995 .................................................................................................................................................................. 8

4. Section showing hydrogeologic intervals in the C-holes, May 1995 to December 1997 ......................................... 9

5. Diagram showing instrument-string assembly in UE-25 c #3, Lower Bullfrog interval, April 1996 to 

December 1997 ......................................................................................................................................................... 11

6. Diagram showing pump assembly in borehole UE-25 c #3, May 1995 to April 1996............................................. 13

7–9. Graphs showing:

7. Result of filtering out Earth tides on UE-25 c #2 Lower Bullfrog interval pressure heads, 

June 23–29, 1995............................................................................................................................................... 16

8. Difference from mean pressure head in UE-25 c #2 Lower Bullfrog interval and atmospheric pressure at 

the C-hole complex, June 23–29, 1995 ............................................................................................................. 17

9. Filtered pressure-head change in UE-25 c #2 Lower Bullfrog interval as a function of filtered atmosphericpressure change at the C-hole complex, June 23–29, 1995............................................................................... 17

10. Diagram showing flow surveys in UE-25 c #3 during the hydraulic test in June 1995 ............................................ 19

CONTENTS
IV CONTENTS

11–33. Graphs showing:

11. UE-25 c #3 discharge and drawdown, June 12–16, 1995. ................................................................................ 22

12. UE-25 c #1 drawdown, June 12–16, 1995 ........................................................................................................ 23

13. UE-25 c #2 drawdown, June 12–16, 1995 ........................................................................................................ 23

14. UE-25 c #3 discharge and drawdown, February 8–13, 1996 ............................................................................ 24

15. UE-25 c #1 drawdown, February 8–13, 1996 ................................................................................................... 25

16. UE-25 c #2 drawdown, February 8–13, 1996 ................................................................................................... 25

17. UE-25 c #3 discharge and drawdown, May 8, 1996, to November 12, 1997 ................................................... 26

18. UE-25 c #1 drawdown, May 8, 1996, to March 26, 1997................................................................................. 27

19. UE-25 c #2 drawdown, May 8, 1996, to March 26, 1997................................................................................. 28

20. Disturbance of drawdown in Lower Bullfrog interval of UE-25 c #1 and UE-25 c #2 by tracer tests in 

1996 and 1997: A, Sodium-iodide tracer test in UE-25 c #1, June 17 to July 5, 1996; B, 2,6-DFBA tracer 

test in UE-25 c #2, January 9 to 18, 1997 ......................................................................................................... 29

21. UE-25 c #1 Lower Bullfrog recovery, November 12 to December 31, 1997 ................................................... 30

22. Drawdown in UE-25 ONC-1, May 8, 1996, to November, 12, 1997................................................................ 31

23. Drawdown in UE-25 WT #3, May 8, 1996, to March 26, 1997 ....................................................................... 31

24. Drawdown in USW H-4 and UE-25 WT #14, May 8, 1996, to December 4, 1996 ......................................... 32

25. Analysis of drawdown in the Calico Hills interval of UE-25 c #2, May 8, 1996, to March 26, 1997, by 

the method of Neuman (1975) .......................................................................................................................... 36

26. Analysis of drawdown in the Prow Pass interval of UE-25 c #1, June 12–16, 1995, by the method of 

Theis (1935) ...................................................................................................................................................... 37

27. Analysis of drawdown in the Upper Bullfrog interval of UE-25 c #2, June 12–16, 1995, by the method of 

Theis (1935) ...................................................................................................................................................... 38

28. Analysis of drawdown in the Lower Bullfrog interval of UE-25 c #1, May 8, 1996, to March 26, 1997, by 

the method of Theis (1935) ............................................................................................................................... 39

29. Analysis of drawdown in the Lower Bullfrog interval of UE-25 c #1, May 8, 1996, to March 26, 1997, by 

the method of Streltsova-Adams (1978) ........................................................................................................... 39

30. Analysis of drawdown in UE-25 ONC-1, May 8, 1996 to November 12, 1997, by the method of 

Streltsova-Adams (1978)................................................................................................................................... 42

31. Analysis of drawdown in USW H-4, May 8 to June 27, 1996, by the method of Theis (1935)....................... 42

32. Analysis of drawdown in UE-25 WT #14, May 8 to June 27, 1996, by the method of Theis (1935) .............. 43

33. Analysis of drawdown in UE-25 WT #3, May 8, 1996 to March 26, 1997, by the method of Theis (1935) ... 43

34. Map showing inferred distribution of hydraulic conductivity of Miocene tuffaceous rocks in the vicinity of the 

C-holes ...................................................................................................................................................................... 45

35. Graph showing analysis of drawdown in observation wells as a function of time divided by the square of the 

distance from the pumping well 322 days after pumping started in UE-25 c #3 on May 8, 1996 ........................... 46

36. Map showing distribution of drawdown in observation wells 30,000 minutes (20.8 days) and 463,000 minutes 

(321.5 days) after pumping started in UE-25 c #3 on May 8, 1996.......................................................................... 47

37. Graphs showing analyses of drawdown in observation wells as a function of distance from the pumping well 

30,000, 200,000, 305,000, and 463,000 minutes after pumping started in UE-25 c #3 on May 8, 1996 ................. 48

38. Graph showing water-level changes in UE-25 p #1, September 3 to November 2, 1996......................................... 50

39. Diagram showing major ion chemistry of water from UE-25 c #3, Miocene tuffaceous rocks and Paleozoic 

carbonate rocks, Yucca Mountain area ..................................................................................................................... 53

TABLES

1. Approximate interborehole distance at the midpoints of hydrogeologic intervals monitored during hydraulic 

tests at the C-hole complex, August 1995 to April 1996 ........................................................................................ 6

2. Stratigraphy of Miocene tuffaceous rocks in the C-hole area................................................................................. 7

3. Location of packers emplaced in the C-holes for hydraulic tests, 1995 to 1997 .................................................... 12

4. Operative transducers in the C-holes, 1995 to 1997 ............................................................................................... 12

5. Barometric efficiency values determined for borehole intervals monitored at the C-hole complex, May 1996 

to December 1997 ................................................................................................................................................... 18
CONTENTS V

6. Interval discharges 5,800 minutes after pumping started, hydraulic tests in UE-25 c #3, June 1995 to November

1997 ........................................................................................................................................................................ 20

7. Maximum observed water-level declines related to C-holes testing, May 1996 to November 1997, in routinely 

monitored boreholes at Yucca Mountain (data from Graves, 2000)....................................................................... 33

8. Results of hydraulic tests in borehole UE-25 c #3, June 1995 to November 1997 ................................................ 34

9. Hydraulic properties computed from observation well responses to pumping in UE-25 c #3, May 1995 to 

November 1997....................................................................................................................................................... 41

10. Hydraulic properties determined from drawdown in observation wells as a function of distance from the 

pumping well, hydraulic test in UE-25 c #3, May 1996 to November 1997.......................................................... 50

11. Major ions, trace elements, and isotopes in water from UE-25 c #3, May 1995 to October 1997......................... 52

CONVERSION FACTORS, ABBREVIATIONS, AND VERTICAL DATUM

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

F=1.8 (C)+32

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929—

a geodetic datum derived from a general adjustment of the first-order level nets of the United States 

and Canada, formerly called Sea Level Datum of 1929.

The following abbreviations were used for units in both the metric and inch-pound systems:

ampere: A

hertz: Hz

kilowatt: KW

milliampere: mA

millidarcy: mD

ohm: 

volt: V

watt: W

Multiply By To obtain

cubic meter per day (m3/d) 35.31 cubic foot per day 

centimeter (cm) 0.393 inch 

kilometer (km) 0.62139 mile 

kilopascal (kPa) 0.14503 pound per square inch

liter (L) 0.26417 gallon 

liter per second m (L/s) 15.85 gallon per minute 

meter (m) 3.2808 foot

meter per day (m/d) 3.2808 foot per day

meter squared per day (m2/d) 10.76 foot squared per day

microgram per liter (g/L) 1 part per billion

milliequivalent per liter (meq/L) 1 equivalent per million

milligram (mg) 2.205106 pound

milligram per liter (mg/L) 1 part per million

square meter (m2) 10.76 square foot

square kilometer (km2) 0.3861 square mile


1

Results of Hydraulic Tests in Miocene Tuffaceous 

Rocks at the C-Hole Complex, 1995 to 1997, 

Yucca Mountain, Nye County, Nevada

By Arthur L. Geldon, Amjad M.A. Umari, Michael F. Fahy, John D. Earle, James M. Gemmel, 

and Jon Darnell

Abstract

Four hydraulic tests were conducted by the 

U.S. Geological Survey at the C-hole complex at 

Yucca Mountain, Nevada, between May 1995 and 

November 1997. These tests were conducted as 

part of ongoing investigations to determine the 

hydrologic and geologic suitability of Yucca 

Mountain as a potential site for permanent underground storage of high-level nuclear waste.

The C-hole complex consists of three 

900-meter-deep boreholes that are 30.4 to 

76.6 meters apart. The C-holes are completed in 

fractured, variably welded tuffaceous rocks of 

Miocene age. Six hydrogeologic intervals occur 

within the saturated zone in these boreholes—the 

Calico Hills, Prow Pass, Upper Bullfrog, Lower 

Bullfrog, Upper Tram, and Lower Tram intervals. 

The Lower Bullfrog and Upper Tram intervals 

contributed about 90 percent of the flow during 

hydraulic tests.

The four hydraulic tests conducted from 

1995 to 1997 lasted 4 to 553 days. Discharge from 

the pumping well, UE-25 c #3, ranged from 8.49 

to 22.5 liters per second in different tests. Two to 

seven observation wells, 30 to 3,526 meters from 

the pumping well, were used in different tests. 

Observation wells included UE-25 c #1, UE-25 

c #2, UE-25 ONC-1, USW H-4, UE-25 WT #14, 

and UE-25 WT #3 in the tuffaceous rocks and 

UE-25 p #1 in Paleozoic carbonate rocks.

In all hydraulic tests, drawdown in 

the pumping well was rapid and large (2.9–

11 meters). Attributable mostly to frictional head 

loss and borehole-skin effects, this drawdown 

could not be used to analyze hydraulic properties. 

Drawdown and recovery in intervals of UE-25 

c #1 and UE-25 c #2 and in other observation 

wells typically was less than 51 centimeters. 

These data were analyzed.

Hydrogeologic intervals in the C-holes have 

layered heterogeneity related to faults and fracture 

zones. Transmissivity, hydraulic conductivity, and 

storativity generally increase downhole. Transmissivity ranges from 4 to 1,600 meters squared 

per day; hydraulic conductivity ranges from 0.1 to 

50 meters per day; and storativity ranges from 

0.00002 to 0.002.

Transmissivity in the Miocene tuffaceous 

rocks decreases from 2,600 to 700 meters squared 

per day northwesterly across the 21-squarekilometer area affected by hydraulic tests at the 

C-hole complex. The average transmissivity of 

the tuffaceous rocks in this area, as determined 

from plots of drawdown in most or all observation 

wells as functions of time or distance from the 

pumping well, is 2,100 to 2,600 meters squared 

per day. Average storativity determined from 

these plot ranges is 0.0005 to 0.002. Hydraulic 

conductivity ranges from less than 2 to more than 

10 meters per day; it is largest where prominent 

northerly trending faults are closely spaced or 

intersected by northwesterly trending faults.

During hydraulic tests, the Miocene 

tuffaceous rocks functioned as a single aquifer. 

Drawdown occurred in all monitored intervals of 

the C-holes and other observation wells, regardless of the hydrogeologic interval being pumped. 
2 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

This hydraulic connection across geologic and 

lithostratigraphic contacts is believed to result 

from interconnected faults, fractures, and intervals with large matrix permeability. Samples of 

UE-25 c #3 water, analyzed from 1995 to 1997, 

seem to indicate that changes in the quality of the 

water pumped from that well are probably due 

solely to lateral variations in water quality within 

the tuffaceous rocks.

INTRODUCTION

Information contained in this report is presented 

as part of ongoing investigations by the U.S. Geological Survey (USGS) regarding the hydrologic and 

geologic suitability of Yucca Mountain, Nev., as a 

potential site for permanent underground storage of 

high-level nuclear waste. This investigation was 

conducted by the Yucca Mountain Project Branch 

(YMPB) of the USGS, in cooperation with the U.S. 

Department of Energy (DOE), under Interagency 

Agreement DE–AI08–92NV10874.

Purpose and Scope

This report presents information obtained from 

three cross-hole hydraulic tests conducted together 

with tracer tests in Miocene tuffaceous rocks at the 

C-hole complex at Yucca Mountain, Nev. (fig. 1), from 

June 1995 to November 1997. The report describes the 

tests that were conducted, discusses changes in water 

levels and chemistry observed in monitoring wells as a 

result of pumping, describes analyses performed on 

the test data, presents values of hydraulic properties 

determined from test analyses, and evaluates uncertainties associated with the test data, analyses, and 

quantitative results.

Previous Work

Hydrogeologic intervals discussed in this report 

were identified by Geldon (1996) on the basis of borehole geophysical logs, borehole flow surveys, crosshole seismic tomography, and aquifer tests that were 

done between 1983–84 (when the C-holes were 

drilled) and 1995. Geophysical logs that have been run 

in the C-holes include caliper, borehole-deviation, 

temperature, resistivity, gamma-gamma, acoustic, 

epithermal neutron, acoustic televiewer, and television 

logs (Geldon, 1993).

Flow surveys that have been run in the C-holes 

include tracejector, heat-pulse flowmeter, spinner, and 

oxygen activation surveys (Geldon, 1993, 1996). 

Tracejector surveys using radioactive iodide were run 

in the C-holes during hydraulic tests conducted in 

1983 and 1984. Heat-pulse flowmeter surveys were 

run in the C-holes in 1991 without the boreholes being 

pumped. Spinner and oxygen-activation surveys were 

run in borehole UE-25 c #3 during a hydraulic test in 

June 1995.

In 1993, a seismic tomogram was done between 

boreholes UE-25 c #2 and UE-25 c #3 by Lawrence 

Berkeley Laboratory (LBL) for the USGS (Ernie 

Majer, LBL, written commun., 1993). The tomogram 

showed many of the hydrogeologic details evident 

from borehole lithologic and geophysical logs and 

flow surveys.

The way in which hydrogeologic intervals in the 

C-holes transmit water and the hydraulic properties of 

these intervals were determined provisionally by 

Geldon (1996) from geophysical logs, laboratory analyses, and aquifer tests. A matrix porosity profile for 

the C-holes was developed by Geldon (1993) from a 

gamma-gamma log and nine values of core porosity 

obtained from UE-25 c #1 in 1983. A matrix permeability profile for the C-holes was developed by 

Geldon (1996) from permeameter tests on 89 core 

samples obtained from the C-holes and four nearby 

boreholes between 1980 and 1984. A hydraulicconductivity profile for the C-holes was developed by 

Geldon (1996) by analyzing falling-head and pressureinjection tests that were done in UE-25 c #1 in 1983. 

Transmissivity, hydraulic conductivity, and storativity 

of discrete intervals within the Calico Hills Formation 

and Crater Flat Group were determined by Geldon 

(1996) from analyses of a constant-flux injection test 

in UE-25 c #2 and three hydraulic tests in UE-25 c #2 

and UE-25 c #3 that were done in 1984.

From May 22 to June 12, 1995, immediately 

prior to the series of hydraulic tests discussed in this 

report, an open-hole hydraulic test was conducted in 

borehole UE-25 c #3. Simultaneous monitoring of 

water-level and atmospheric-pressure fluctuations in 

1993 established the barometric efficiency of the 

C-holes for the 1995 test (Geldon and others, 1997). 

The open-hole hydraulic test was designed to determine the transmissivity, hydraulic conductivity, and
INTRODUCTION 3

storativity of the composite saturated thickness of 

Miocene tuffaceous rocks at the C-hole complex, 

lateral variations in hydraulic properties within a 

2-mile radius of the C-hole complex, and possible 

hydraulic connection between the Miocene tuffaceous 

rocks and a regional aquifer composed of Paleozoic 

carbonate rocks. This test is described by Geldon and 

others (1998) and will be discussed in this report only 

to support analyses and interpretations presented 

herein.

Ferrill and others (1999) analyzed the data for 

the May 1996 to November 1997 hydraulic test at 

the C-hole complex. They estimated horizontal anisotropy of aquifer transmissivity on the basis of data 

from four observation wells and determined that the 

axis of the maximum transmissivity tensor is oriented 

N30E (Ferrill and others, 1999, p. 7). The estimated 

maximum transmissivity in this direction is 

5,400 m2/d, and the estimated minimum transmissivity 

(oriented perpendicular to the maximum tensor) is 

Figure 1. Location of the C-hole complex, boreholes UE-25 c #1, UE-25 c #2, and UE-25 c #3 (C-hole map is referenced to 

Nevada State, Zone 2, coordinates).

Prow

Pass

Yucca

Mountain

Yucca Wash

Fortymile Wash

Crater Flat

Armargosa Desert

Jackass

Flats

Windy Wash

NEVADA TEST SITE BOUNDARY

Fran Ridge

Bow Ridge

Busted Butte

Yucca Mountain

95

USW H-4

ONC-1 WT #14

UE-25 p #1

UE-25 c #1

UE-25 c #2

UE-25 c #3

36°

40'

36°

52'

116°30' 116°25' 116°20'

EXPLANATION

POTENTIAL REPOSITORY

 SITE

BEDROCK

Borehole

UE-25 c #2

Borehole

UE-25 c #1

SURFACE LOCATION

 OF BOREHOLE

PROJECTED TRACE

 OF BOREHOLE

 LOCATION

76.5 meters

68.3 meters

30.4 meters

N

E173,590E173,610E173,630E173,650E173,670

94 ̊

63 ̊

23 ̊

N230,780

N230,760

N230,740

N230,720

N230,700

N230,660

N230,680

Borehole

UE-25 c #3

EXPLANATION

0 5 10 KILOMETERS

0 5 10 MILES

NEVADA

CALIFORNIA

Carson City

Las Vegas

Area of

map

Solitario

Canyon

0 25 50 METERS

0 50 100 FEET
4 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

315 m2/d, although these values are poorly constrained 

(Ferrill and others, 1999, p. 7).

Acknowledgments

The authors recognize the contributions of 

several employees and contractors of the USGS who 

volunteered time and effort beyond the scope of their 

routine duties to make this study possible. The authors 

also recognize the contributions of people from the 

many organizations participating in the Yucca Mountain Project whose cooperation was essential for 

completion of this study. Russell L. Patterson (U.S. 

Department of Energy), William B. Distel and Roger 

Henning (Woodward-Clyde Federal Services), and 

Andrea Randall and Thomas Pysto (Science Applications International Corporation) coordinated activities 

among Yucca Mountain Project participants, U.S. 

Department of Energy, and State of Nevada regulatory 

agencies to enable the hydraulic tests discussed in this 

report to proceed. Personnel from Los Alamos 

National Laboratory, under the direction of Paul 

Reimus, manned the site from May to November 

1996, and shared equipment, data, and ideas.

HYDROGEOLOGIC SETTING

The C-hole complex is located in Nye County, 

Nev., at the western edge of the Nevada Test Site, 

about 145 km northwest of Las Vegas (fig. 1). The 

C-holes are in a channel of an ephemeral stream that 

cuts through Bow Ridge, a spur of Yucca Mountain 

(fig. 2). The C-hole complex is a two-tiered drill pad. 

The lower tier, in which borehole UE-25 c #1 was 

drilled, is at an altitude of about 1,130.5 m above sea 

level. The upper tier, in which boreholes UE-25 c #2 

and UE-25 c #3 were drilled, is at an altitude of about 

1,132.3 m. The C-holes are 30.4–76.5 m apart at the 

land surface (fig. 1), but interborehole distances vary 

substantially at depth because of borehole deviation 

during drilling (table 1 and fig. 1).

The C-holes are completed in Miocene 

tuffaceous rocks (table 2), that are covered by 0–24 m 

of Quaternary alluvium. The tuffaceous rocks are estimated to be 1,040–1,590 m thick in the vicinity of the 

C-holes, where they consist of nonwelded to densely 

welded ash-flow tuff with intervals of ash-fall tuff and 

volcaniclastic rocks (Geldon, 1993; Geldon and 

others, 1998). The tuffaceous rocks are pervaded by 

tectonic and cooling fractures that strike predominantly north-northeast to north-northwest and dip 

westward at angles of 50–87(Geldon, 1996, p. 4). 

Paleozoic limestone and dolomite (carbonate rocks) 

underlie the tuffaceous rocks about 455 m below the 

bottom of the C-holes (extrapolated from information 

about borehole UE-25 p #1 by Carr and others, 1986).

In the vicinity of the C-hole complex, northerly 

and northwesterly trending, high-angle faults, such as 

the Paintbrush Canyon, Midway Valley, and Bow 

Ridge Faults, have brecciated, offset, and tilted the 

Miocene tuffaceous rocks (Day and others, 1998; 

Dickerson and Drake, 1998). The dip of the tuffaceous 

rocks increases from 5o

–10o eastward at the crest of 

Yucca Mountain to about 20o

 eastward at the C-hole 

complex (Frizzell and Shulters, 1990). At the C-hole 

complex, the north-striking Midway Valley or Paintbrush Canyon Fault downfaulted Miocene tuffaceous 

rocks to the west. The Miocene tuffaceous rocks and 

the Midway Valley or Paintbrush Canyon Fault, later, 

were recast to the northeast by a northwest-striking 

fault that cuts through Bow Ridge (fig. 2).

Hydrogeologic data and numerical groundwater-flow modeling indicate that ground water 

recharged in the Yucca Mountain area discharges 

mostly to Carson Slough, Ash Meadows, Alkali Flat, 

the lower Amargosa River valley, and Death Valley 

(D'Agnese and others, 1997). Locally, ground water 

flows from mountains to valleys, mainly through 

Tertiary volcanic and tuffaceous rocks and Quaternary 

and Tertiary alluvium and lacustrine deposits. 

Controlled largely by faults and related fractures, 

ground water flows from basin to basin mainly 

through Paleozoic carbonate rocks (Faunt, 1997). 

Geldon and others (1998) concluded that a northwesttrending zone of discontinuous faults between Bow 

Ridge and Antler Wash also transmits ground water.

The potentiometric surface in the Miocene 

tuffaceous rocks at Yucca Mountain in the vicinity of 

the C-holes ranges from about 335 to 520 m below 

land surface (O’Brien and others, 1995, p. 3). In the Choles, depths to water range from 400 to 402 m. Water 

in the tuffaceous rocks generally flows southeasterly 

(Ervin and others, 1994; Tucci and Burkhardt, 1995), 

but flow patterns can be disrupted by faults acting as 

conduits or barriers to flow. Sparse water-level data in 

the vicinity of the C-holes can be interpreted to show a 

ground-water divide centered on Bow Ridge and 

Boundary Ridge that directs flow southward to Dune
HYDROGEOLOGIC SETTING 5

0

0

500 1,000

2,000 4,000 6,000 FEET

1,500 2,000 METERS

36°50'

36°48'

116°26' 116°24'

PA

NI TBRUSH

C

ANYON

FAULT

PA

NI TBRUSH

CANYON

FAULT

SPUR

MIDWAY

VALLEY

FAULT

EXILE HILL FAULT

BO

W

RIDGE

FAULT

DUNE

WASH

FAULT

MIDWAY

VALLEY

FRAN RIDGE

BOW RIDGE

BOUNDARY RIDGE

ANTLER WASH

JACKASS FLATS

DUNE WASH

WT #17

WT #3

WT #13

p #1

WT #14

J-13

H-4

C-HOLES

ONC-1

WT #1

EXPLANATION

ALLUVIUM

MIOCENE TUFFACEOUS ROCKS

BOREHOLE

GEOLOGIC CONTACT

FAULT TRACE—Fault may be partly or entirely

 concealed by alluvium; ball on downthrown side

 of normal fault; teeth on upthrown side of reverse

 fault

BOREHOLE ABBREVIATIONS

WT #1 USW WT #1

WT #3 UE-25 WT #3

WT #13 UE-25 WT #13

WT #14 UE-25 WT #14

WT #17 UE-25 WT #17

ONC-1 UE-25 ONC-1

H-4 USW H-4

p #1 UE-25 p #1

FORTYMILE

WASH

Figure 2. Generalized geologic map showing the location of the C-hole complex and nearby boreholes (Geldon and others, 

1998, p. 5).
6 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

Table 1. Approximate interborehole distance at the midpoints of hydrogeologic intervals monitored during hydraulic tests 

at the C-hole complex, August 1995 to April 1996 

[All figures in meters; north and south referenced to Nevada State, Zone 2 coordinates; depths in UE-25 c #3 and interborehole distances were changed 

slightly in April 1996, when instrumentation in UE-25 c #3 was reconfigured; c #1, UE-25 c #1; c #2, UE-25 c #2; c #3, UE-25 c #3; --, not applicable]

Physical Information UE-25 c #1 UE-25 c #2 UE-25 c #3 c #1-c #3 c #2-c#3

Calico Hills

Top depth 418 416 417 78.6 29.0

Bottom depth 547 531 540 -- --

Midpoint depth 483 474 478 -- --

North coordinate 230,771 230,691 230,703 -- --

East coordinate 173,646 173,633 173,607 -- --

Distance north/south from c #3 68.3 12.2 -- -- --

Distance east/west from c #3 39.3 26.2 -- -- --

Prow Pass

Top depth 549 533 542 81.1 28.6

Bottom depth 605 606 610 -- --

Midpoint depth 577 569 576 -- --

North coordinate 230,772 230,691 230,702 -- --

East coordinate 173,648 173,634 173,607 -- --

Distance north/south from c #3 70.4 11.0 -- -- --

Distance east/west from c #3 40.2 26.5 -- -- --

Upper Bullfrog

Top depth 607 607 612 83.2 28.6

Bottom depth 698 696 695 -- --

Midpoint depth 653 652 653 -- --

North coordinate 230,773 230,691 230,701 -- --

East coordinate 173,648 173,634 173,607 -- --

Distance north/south from c #3 72.2 9.75 -- -- --

Distance east/west from c #3 41.4 26.8 -- -- --

Lower Bullfrog

Top depth 700 698 697 85.6 29.3

Bottom depth 797 792 813 -- --

Midpoint depth 749 745 755 -- --

North coordinate 230,774 230,692 230,700 -- --

East coordinate 173,649 173,633 173,606 -- --

Distance north/south from c #3 73.8 8.84 -- -- --

Distance east/west from c #3 43.3 27.7 -- -- --

Upper Tram

Top depth 799 794 814 86.9 29.6

Bottom depth 870 870 878 -- --

Midpoint depth 834 832 846 -- --

North coordinate 230,774 230,691 230,700 -- --

East coordinate 173,648 173,632 173,604 -- --

Distance north/south from c #3 74.7 8.53 -- -- --

Distance east/west from c #3 44.2 28.3 -- -- --

Lower Tram

Top depth 872 871 879 87.2 29.9

Bottom depth 898 903 900 -- --

Midpoint depth 885 887 890 -- --

North coordinate 230,774 230,691 230,700 -- --

East coordinate 173,648 173,632 173,603 -- --

Distance north/south from c #3 74.7 8.23 -- -- --

Distance east/west from c #3 44.8 28.6 -- -- --
HYDROGEOLOGIC SETTING 7

Wash, northward to Midway Valley, and eastward to 

Fortymile Wash (fig. 3). Flow from the west into the 

area of the C-holes is inhibited by the northerly 

striking Solitario Canyon Fault (Tucci and Burkhardt, 

1995). The Solitario Canyon Fault (fig. 1) is interpreted to be a constant-head boundary, whereas 

discharge areas north, east, and south of the C-hole 

complex are interpreted to be head-dependent flux 

boundaries.

The Miocene tuffaceous rocks in the area of the 

C-hole complex comprise a single dual-permeability 

aquifer, in which the volume and direction of groundwater flow are controlled mainly by proximity to 

faults, fracture zones, and partings (Geldon and others, 

1998). Fractures in transmissive intervals have no 

preferred orientation, and the fracture density appears 

to be unrelated to the extent of welding and permeability. Matrix permeability of the Calico Hills Formation and Crater Flat Group within 5 km of the C-hole 

complex can be as much as 20 mD. On the basis of 

barometric efficiency and specific storage, the average 

effective porosity of the Calico Hills Formation near 

the water table in the C-holes was determined by 

Geldon and others (1997) to be 36 percent. The Crater 

Flat Group is much less porous than the Calico Hills 

Formation, and the average porosity of these two 

geologic units in the C-holes is 21 percent (computed 

from porosity values reported by Geldon, 1993). 

Despite the influence of fractures, rock within about 

3 km of the C-hole complex consistently responds to 

hydraulic tests as an equivalent porous medium. 

Borehole flow surveys, in combination with 

geophysical logs and aquifer tests, show that flow 

within the Miocene tuffaceous rocks at the C-hole 

complex occurs within discrete intervals (fig. 4). The 

total thickness of transmissive intervals identified in 

individual boreholes ranges from 165 to 274 m 

(Geldon, 1996). Hydraulic tests conducted in 1984 

indicated that these intervals have layered heterogeneity (Geldon, 1996, p. 69). A hydraulic test 

conducted at the C-hole complex from May 22 to 

June 12, 1995, indicated that the composite section of 

Miocene tuffaceous rocks in the vicinity of the C-holes 

has a transmissivity of 2,300 m2

/d and a storativity of 

0.003 (Geldon and others, 1998, p. 25). This same test 

indicated transmissivity values of 1,600 to 3,200 m2/d 

and storativity values of 0.001 to 0.003 for the rocks in 

individual boreholes (UE-25 c #1, UE-25 c #2, 

UE-25 ONC-1, and USW H-4).

Because only one borehole (UE-25 p #1) penetrates the Paleozoic carbonate rocks in the vicinity of 

the C-holes, little is known about hydrologic properties of these rocks in this area. An estimated transmissivity of 111 m2

/d is reported for the Paleozoic 

carbonate rocks penetrated by borehole UE-25 p #1 

(Craig and Robison, 1984, p. 22–28). The closest 

cross-hole hydraulic tests, which were conducted in 

the Amargosa Desert about 38 km southeast of the 

C-hole complex, indicated transmissivity values

Table 2. Stratigraphy of Miocene tuffaceous rocks in the C-hole area (Geldon and others, 1998, table 1, p. 6)

Geologic Unit Depth, meters below land surface

USW H-4 UE-25 c #1 UE-25 c #2 UE-25 c #3 UE-25 p #1

Timber Mountain Group

Rainier Mesa Tuff not present not present not present not present 39–55

Paintbrush Group

Tiva Canyon Tuff 0–65 0–96 21–88 24–88 55–81

Topopah Spring Tuff 65–400 96–406 88–401 88–396 81–381

Calico Hills Formation 400–496 406–516 401–510 396–496 381–436

Crater Flat Group

Prow Pass Tuff 496–693 516–656 510–652 496–644 436–558

Bullfrog Tuff 693–812 656–828 652–829 644–814 558–691

Tram Tuff 812–1,164 828–914+ 829–914+ 814–914+ 691–873

Lithic Ridge Tuff 1,164–1,219+ not reached not reached not reached 873–1,068
8 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

DUNE

WASH

FAULT

0

0

500 1,000

2,000 4,000 6,000 FEET

1,500 2,000 METERS

PAINTBRUSH

CANYON FAULT

PA NI TBRUSH CANYON

FAULT

SPUR

MIDWAY

VALLEY

FAULT

BOW

RIDGE

FAULT

MIDWAY VALLEY BOW RIDGE

YUCCA MOUNTAIN

FRAN RIDGE

BOUNDARY RIDGE

DUNE WASH

J-13

728.6

UE-25 c #3

730.3

UE-25 c #2

730.1

UE-25 c #1

730.3

UE-25 WT #14

729.7

UE-25 p #1

730.7

UE-25 ONC-1

729.8

USW H-4

730.3

FORTYMILE

36°50' WASH

36°48'

116°26' 116°24'

UE-25 WT #13

729.1

UE-25 WT #3

729.71

UE-25 WT #1

730.3

UE-25 WT #17

729.8

EXPLANATION

BOREHOLE WITH BOREHOLE NUMBER ABOVE LINE AND WATER-LEVEL ALTITUDE,

 IN METERS ABOVE NGVD OF 1929 BELOW LINE

POTENTIOMETRIC-SURFACE CONTOUR—Shows altitude above NGVD of 1929 at which

 water would have stood in tightly cased wells completed in the Miocene tuffaceous rocks in

 May 1995. Water-level altitude in UE-25 p #1 estimated from the measured hydraulic head 

 of Paleozoic carbonate rocks and the vertical head gradient between the Paleozoic carbonate

 rocks and Miocene tuffaceous rocks in the borehole. Arrow indicates approximate direction of

 ground-water flow. Contour interval is 0.2 meter

TRACE OF MAJOR FAULT

728.6

728.8

729.0

729.2

729.4

729.6

729.8

729.6

729.8

729.4

730.0

730.2

730.4

730.6

USW H-4

730.3

730.0

Figure 3. Potentiometric surface of the Miocene tuffaceous rocks in the vicinity of the C-hole complex, May 1995 (water-level 

altitudes from Graves and others, 1997; Nye County Nuclear Waste Repository Project Office, written commun., 1995).
HYDROGEOLOGIC SETTING 9

0

50 100 FEET

25 50 METERS

0

UE-25 c #3 UE-25 c #1 UE-25 c #2

BEND IN SECTION

Pt

Pt

Ch

Ch

Cp

Cp

Cb

Cb

Ct

Ct

HYDROGEOLOGIC INTERVALS

METERS BELOW

LAND SURFACE

CALICO HILLS

PROW PASS

UPPER BULLFROG

EXPLANATION

TOPOPAH SPRING TUFF

CALICO HILLS FORMATION

PROW PASS TUFF

BULLFROG TUFF

TRAM TUFF

TRANSMISSIVE INTERVAL

NONTRANSMISSIVE ROCK

TUFF BRECCIA

GEOLOGIC CONTACT

GEOLOGIC CONTACT WITH

 AN OPEN PARTING OR, IN

 BRECCIA ZONES, AN UNEVEN

 SURFACE

BOUNDARY OF TRANSMISSIVE

 INTERVAL

FAULT—Arrows indicate direction

 of movement

WATER TABLE IN JUNE 1992

LOWER TRAM

UPPER TRAM

BULLFROG-TRAM

LOWER

BULLFROG

400

500 

600 

700

800

900

Figure 4. Hydrogeologic intervals in the C-holes, May 1995 to December 1997 (modified from Geldon, 1996, fig. 7A, p. 18).
10 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

between 4,800 and 10,900 m2/d and a storativity of 

0.0005 (Leap and Belmonte, 1992, p. 89).

INSTRUMENTATION

Principal components of the equipment installed 

at the C-hole complex to conduct hydraulic tests from 

1995 to 1997 are described briefly in this report. 

Although available commercially, much of this hardware and software has not been used extensively 

because of its relatively recent development. Consequently, all of the equipment received extensive 

performance evaluation during prototype hydraulic 

tests conducted jointly with Lawrence Berkeley Laboratory (LBL) from 1992 to 1994 at a research site near 

Raymond, Calif. Modifications to system components 

and their assembly were made to address problems 

encountered during prototype testing and after the 

equipment was installed and used initially at the Chole complex. With few exceptions (discussed below), 

most system components performed remarkably well, 

despite being operated almost continuously for more 

than 2 years.

Packers

Dual-mandrel packers manufactured by TAM 

International, Inc., were installed in UE-25 c #1 and 

UE-25 c #2 throughout the tests and in UE-25 c #3 

after August 1995. The packers are about 1.83 m long 

(fig. 5) and have a diameter of about 21.6 cm when 

deflated. Suspended on 7.30-cm-diameter tubing, each 

packer contains 12 pass-through tubes to allow packerinflation lines and electrical cable to be installed in the 

borehole. The packers are inflated individually by the 

injection of argon gas through 0.64-cm, stainless steel 

tubing. Inflation pressures, which are about 1,034 kPa 

above hydrostatic pressure, range from about 2,758 to 

5,861 kPa at the depths at which packers were set in 

the C-holes from 1995 to 1997. Packer depths from 

1995 to 1997, as measured from the land surface, are 

listed in table 3.

Transducers

Continuous records of pressure and temperature 

in packed-off intervals during hydraulic tests were 

obtained using absolute pressure transducers manufactured by Paroscientific, Inc. (Absolute pressure transducers record water pressure plus atmospheric 

pressure, whereas differential pressure transducers 

record only the water pressure.) The transducers used 

in the C-holes were strapped into brackets welded onto 

the 7.30-cm-diameter tubing, on which the packers 

were suspended (fig. 5).

Paroscientific transducers measure the oscillating frequency of a quartz crystal as it changes in 

response to changes in pressure. An internal sensor 

simultaneously records the temperature of the water in 

which the transducer is immersed. A digital serial 

interface board passes the pressure and temperature 

signals through a microprocessor-controlled operating 

program stored in permanent memory that calculates 

temperature-compensated pressures at user-specified 

intervals. The user communicates with the transducer 

through an RS-232 interface. Factory calibrations indicate that the transducers have an accuracy of ±7.04 cm 

of hydraulic head. Field determinations indicated a 

precision of 0.30 cm under pumping conditions and 

0.061 cm under nonpumping conditions.

 Although transducers were installed in all 

hydrogeologic intervals, several of the transducers 

failed after installation. Transducers that were operative during some or all of the hydraulic tests conducted 

from 1995 to 1997 and the locations of these transducers, as determined by subtracting recorded pressure 

heads from static water-level altitudes, are listed in 

table 4. Listed transducer altitudes have an accuracy of 

± 0.3 m.

Barometers

A nonsubmersible, temperature-compensated 

pressure transducer manufactured by Paroscientific, 

Inc., was used as a barometer during the hydraulic 

tests discussed in this report. The barometer, which 

was emplaced in a temperature-controlled office trailer 

at the C-hole complex, operates in the same way as the 

transducers installed in the C-holes to record water 

pressure. The factory-calibrated accuracy of this 

barometer is ± 0.005 percent of its full operating range 

(103 kPa). The barometer was checked periodically 

against another barometer of the same type, which was 

located at the site.
INSTRUMENTATION 11

A

B

B

C

C

D

UP

3.05 METERS 3.05 METERS

BW slotted

well screen

0.32

METER

0.84 METER 1.27 METERS 2.96 METERS

0.97 METER 1.80 METER

0.36 METER

Pup joint

extension

Packer

3

Crossover

connection

Crossover

connection

Sliding

sleeve

Transducer

bracket

Transducer

4

Pup joint

NOT TO SCALE

0.32

METER

Figure 5. Instrument-string assembly in UE-25 c #3, Lower Bullfrog interval, April 1996 to December 1997.
12 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

Pumps

A 37-stage, 25.2-L/s capacity, Centrilift 

submersible pump was used during a hydraulic test in 

June 1995. The pump, enclosed in a protective shroud, 

was suspended in borehole UE-25 c #3 on 13.9-cmdiameter tubing. The pump intake depth was 450.1 m 

(48.0 m below the water-level altitude prior to 

pumping). The pump was powered by a 250-KW 

generator, and its frequency was regulated by a variable-speed controller. Water discharged by the pump 

was transported by a 15-cm-diameter pipeline to a 

leachfield in Fortymile Wash, about 8 km from the 

C-hole complex.

The original pump was replaced in August 1995 

by a 43-stage, 12.6 L/s-capacity, Centrilift submersible 

pump. The pump, enclosed in a protective shroud, was 

offset from the main part of the 7.30-cm-diameter 

tubing on which the packers were suspended by a 

22.9-m-long "Y-block" assembly (fig. 6). The Y-block

Table 3. Location of packers emplaced in the C-holes for hydraulic tests, 1995 to 1997

[No packers in UE-25 c #3 before August 1995]

Packer

number

Packer depth

(meters below land surface)

UE-25 c #1 UE-25 c #2 UE-25 c #3

8/95–4/96 4/96–Present

1 547.4–549.3 531.3–533.1 540.4–542.2 None

2 605.3–607.2 605.6–607.5 609.9–611.7 None

3 698.3–700.1 696.5–698.3 695.0–696.8 694.6–696.5

4 797.1–798.9 791.9–793.7 812.6–814.4 812.9–814.7

5 869.9–871.7 869.6–871.4 877.5–879.4 878.1–880.0

Table 4. Operative transducers in the C-holes, 1995 to 1997

Borehole Interval

Transducer

Number Depth

(meters)

Altitude 

(meters)

UE-25 c #1 Prow Pass 2 552.09 578.51

Upper Bullfrog 3 610.03 520.57

Lower Bullfrog 1 4 703.04 427.56

UE-25 c #2 Calico Hills 1 519.83 612.36

Prow Pass 2 536.28 595.91

Upper Bullfrog 3 610.70 521.49

Lower Bullfrog 1 4 701.58 430.61

UE-25 c #3 Calico Hills 2 1 533.81 598.62

Upper Bullfrog 3 614.49 517.93

Lower Bullfrog 3 4 708.93 423.49

Upper Tram 4 5 817.68 314.75

1Monitored Lower Bullfrog and Upper Tram, combined, February to March 1996.

2

Listed transducer locations are for August 1995 to March 1996. Prior to August 1995, a single transducer was 

installed in the Calico Hills interval at a depth of 441.12 meters (altitude=691.30 meters) to monitor the composite 

geologic section in UE-25 c #3. After April 1996, a new transducer was installed at a depth of 691.31 meters 

(altitude=441.11 meters) to monitor the Calico Hills, Prow Pass, and Upper Bullfrog intervals combined. 3Operative after April 1996.

4Monitored Lower Bullfrog and Upper Tram, combined, in February and March 1996; replaced in April 1996 by 

a transducer at a depth of 819.32 meters (altitude = 313.11 meters).
INSTRUMENTATION 13

assembly was designed to allow wireline-tool access 

past the pump for opening and closing sliding sleeves 

(screens installed to allow water movement to or from 

test intervals) and for landing a plug in the tubing to 

prevent recirculation of water through the pump 

shroud.

Although the Y-block assembly facilitated operations, its placement in the instrument string created 

problems that eventually caused pump performance to 

degrade beyond an acceptable level during hydraulic 

and tracer tests conducted in February and March 

1996. Because the combined diameter of the Y-block 

assembly and main section of the instrument tubing 

(24.7 cm) was about the same as the borehole diameter 

below a depth of 463.4 m, the pump intake had to be 

set about 247 m above the top of the well screen open 

in the test interval. Frictional head losses produced by 

water flowing through small openings in the well 

screen and through the tubing from the test interval to 

the pump intake caused the pump to operate at the 

outer limit of its designed performance range. Consequently, discharge decreased from 8.77 L/s when 

pumping started on February 8, 1996, to 6.18 L/s when 

pumping terminated on March 29, 1996.

In April 1996, the pump performance problem 

was addressed by (1) discarding the Y-block; (2) 

suspending a 72-stage, 12.6-L/s-capacity Centrilift 

pump enclosed within a narrower shroud directly on 

the 7.30-cm-diameter tubing; (3) lowering the pump to 

within about 47 m of the next interval to be tested, the 

Lower Bullfrog; and (4) adding 6.1 m of slotted well 

screen in the test interval. From May 1996 to March 

1997, the reconfigured pump assembly performed 

without major problems and sustained a relatively 

constant discharge of 9.34–9.84 L/s. Problems with 

one of the generators providing power to the pump 

caused the pump to operate erratically between March 

26 and May 8, 1997, but the pump performed 

adequately again after the generator problem was 

resolved.

Flowmeters

A McCrometer turbine-type flowmeter was used 

during the hydraulic test in June 1995. Subsequently, 

the primary device used for monitoring discharge was 

a differential switched capacitor, vortex flowmeter 

manufactured by Endress and Hauser.

Figure 6. Pump assembly in borehole UE-25 c #3, May 1995 to 

April 1996. 22.9 METERS

19.2 METERS

24.7

centimeters

7.30-centimeter tubing

Shroud with

enclosed

centrilift pump

Check valve

Y block

F-nipple with

blanking plug

to prevent

recirculation

NOT TO SCALE
14 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

A vortex flowmeter measures the frequency of 

vortices produced as fluid flows past a bluff body. The 

frequency of vortex production is directly proportional 

to the flow rate and independent of fluid density. 

Signal output from the flowmeter was converted from 

milliamperes to volts by wiring the flowmeter circuit 

to a temperature-compensated, 100-ohm resistor and 

using a multimeter to measure the voltage drop across 

the resistor.

The flowmeter signal was recorded at userspecified intervals by monitoring software installed on 

a personal computer (PC) in the office trailer at the 

C-hole complex. A regression equation developed on 

the basis of the flowmeter calibration was used by the 

software program to convert the voltage signal from 

the flowmeter to a discharge rate. Periodically, 

discharge recorded by the PC was checked against 

total volume pumped (recorded at the wellhead) 

divided by the length of time of pumping. Generally 

good agreement was maintained between recorded and 

computed discharge rates.

Data Acquisition and Instrument Control

Data acquisition from, and control of, the transducers, barometer, flowmeter, and an automated water 

sampler used for tracer tests at the C-hole complex 

were accomplished with commercially available, 

graphic-language software called Labview (Johnson, 

1995), which was installed on the PC in the office 

trailer. Labview is a Windows-based application that 

makes the PC monitor screen look and act like an 

instrument panel.

In addition to the simulated instrument panel, 

Labview displays a schematic command-structure 

diagram, which is analogous to a wiring scheme. 

Instructions are passed by the user to the commandstructure diagram and on to the instrumentation, using 

buttons and text/numerical input windows on the 

simulated instrument panel. Data are passed from the 

instrumentation back to the command-structure 

diagram and displayed numerically and graphically 

within output windows on the simulated instrument 

panel.

Two separate programs were written for data 

acquisition and instrument control. One program 

communicated with the transducers, barometer, and 

flowmeter; the other program communicated with the 

automated water sampler during tracer tests. The two 

programs ran simultaneously. Small utility programs 

(called “transfer programs”) were written to transfer 

information back and forth between the two main 

programs in order to facilitate synchronization of the 

automated sampler operation with data acquisition 

from the transducers, barometer, and flowmeter.

The program communicating with the transducers, barometer, and flowmeter processes digital 

signals from these instruments through the serialcommunications port of the PC, and a digital multimeter. Signals are received through the serial-communications port of the PC as alphanumeric characters 

representing either serial numbers of the instruments, 

or pressures and temperatures sensed by the transducers and barometer. The flowmeter signal is 

processed through a Keithley multimeter and adaptor 

board before reaching the PC. Equations written into 

the schematic diagram part of the program convert 

signal output into standard engineering units. This 

information is displayed on the PC monitor screen, 

written to a text file on the PC's hard drive, and backed 

up to a disk drive at user-specified intervals.

HYDRAULIC TESTS

Hydraulic tests were conducted at the C-hole 

complex June 12–22, 1995, February 8–13, 1996, and 

May 8, 1996, to November 12, 1997. The hydraulic 

test in June 1995 involved pumping UE-25 c #3, 

without packers installed and observing drawdown 

and recovery in six hydrogeologic intervals in

UE-25 c #1 and UE-25 c #2 (shown in fig. 4) that 

were separated by packers.

From February 8 to 13, 1996, UE-25 c #3, with 

packers installed and inflated to isolate the BullfrogTram interval, was pumped to establish a steady-state 

hydraulic gradient for a tracer test in the BullfrogTram interval that continued until March 29, 1996. 

Drawdown in the Bullfrog-Tram interval and in all 

other packed-off intervals of UE-25 c #1 and UE-25 

c #2 that responded to pumping prior to the tracer test 

was analyzed.

In the third hydraulic test, UE-25 c #3, with 

packers inflated to isolate the Lower Bullfrog interval, 

was pumped for 553 days before and during a series of 

tracer tests in the Lower Bullfrog interval. Drawdown 

in the Lower Bullfrog interval and in all other intervals 

of UE-25 c #1 and UE-25 c #2 that responded to this 

pumping before mechanical problems developed on 
HYDRAULIC TESTS 15

March 26, 1997, was analyzed. Drawdown in UE-25 

ONC-1, USW H-4, UE-25 WT #14, and UE-25 

WT #3 during periods ranging from 7 to 18 months 

was analyzed to evaluate heterogeneity and scale 

effects in the Miocene tuffaceous rocks. Water levels 

in UE-25 p #1 were observed to detect a potential 

pumping response indicative of hydraulic connection 

between the Miocene tuffaceous rocks and Paleozoic 

carbonate rocks in the area of the C-holes.

Analytical Methods

Although rock at the C-hole complex is fractured pervasively, hydrogeologic intervals respond to 

pumping as an equivalent porous medium (Geldon, 

1996; Geldon and others, 1998). Because the water 

table occurs at or near the top of the Calico Hills 

interval in the vicinity of the C-hole complex, this 

interval typically responds to pumping as an anisotropic, unconfined aquifer. Pervaded by fractures that 

extend to the water table, the Prow Pass and Upper 

Bullfrog intervals can respond to pumping as either an 

unconfined, fissure-block, or confined aquifer. Isolated 

by intervals of nonfractured rock, the Lower Bullfrog 

interval typically responds to pumping as a confined 

aquifer. Recharged by flow from fractures related to 

faults (Geldon, 1993), the Upper Tram interval typically responds to pumping as a leaky, confined aquifer 

without confining-bed storage.

Analytical methods used for hydraulic tests 

discussed in this report are those of Theis (1935) and 

Cooper and Jacob (1946) for an infinite, homogeneous, isotropic, confined aquifer; Neuman (1975) for 

an infinite, homogeneous, anisotropic, unconfined 

aquifer; and Streltsova-Adams (1978) for a fissureblock aquifer. Assumptions, equations, and application 

of these analytical methods in hydraulic tests at the 

C-hole complex are discussed by Geldon (1996). 

Analysis of drawdown in this study was restricted to 

observation wells because drawdown in pumping 

wells at the C-hole complex typically is too large and 

rapid to be explained solely by hydraulic properties of 

the pumped interval (Geldon, 1996). This observation 

can be illustrated by looking at the drawdown in 

UE-25 c #3 464,000 minutes (about 323 days) after 

pumping began on May 8, 1996. This drawdown was 

599 cm. With hydraulic properties computed for the 

Lower Bullfrog interval in UE-25 c #1 and UE-25 c #2 

inserted into an approximation of the Theis (1935) 

equation given by (Lohman, 1972), the drawdown in 

UE-25 c #3 attributable to aquifer characteristics 

should have been no more than 69–72 cm after about 

323 days of pumping, or 12 percent of the recorded 

drawdown. Most of the drawdown in UE-25 c #3 probably can be attributed to frictional head loss or borehole-skin effects. Therefore, calculation of hydraulic 

properties from this drawdown is not reliable.

All of the methods used for analyzing hydraulic 

tests in this study assume that flow from observation 

wells to the pumping well is radial. However, in 

hydraulic tests of the Bullfrog-Tram interval (February 

1996) and the Lower Bullfrog interval (May 1996 to 

March 1997), drawdown was observed in the Calico 

Hills, Prow Pass, and Upper Bullfrog intervals, even 

though these intervals did not contain open screens. 

For water to reach the pumping well from the 

nonscreened intervals, a downward component of flow 

must be recognized. This downward flow was 

assumed to be much less than radial flow to the 

pumping well, in order to analyze the drawdown from 

the nonscreened intervals by the methods indicated in 

this section. Hydraulic properties calculated under this 

assumption have a high level of confidence because 

they generally are consistent with quantitative results 

of the hydraulic test in June 1995 in which flow from 

hydrogeologic intervals in UE-25 c #1 and UE-25 c #2 

to UE-25 c #3 was designed to be radial.

Earth Tides and Barometric Effects

Previous monitoring of water levels in observation wells before, during, and after hydraulic tests 

conducted in the C-holes indicated that all boreholes 

respond to Earth tides and atmospheric pressure 

changes. With frequencies of 0.9 to 2.0 cycles per day 

(Galloway and Rojstaczer, 1988), Earth tides caused 

water-level altitudes in the C-holes to fluctuate as 

much as 12 cm during a 10-day hydraulic test 

conducted at the C-hole complex from May to June 

1995 (Geldon and others, 1998). Consequently, in this 

study, Earth-tide effects were removed from simultaneously recorded water levels and atmospheric pressures before computing the barometric efficiency of 

most borehole intervals. Earth-tide effects also were 

removed from the records of observation wells in 

which drawdown caused by pumping was expected to 

be obscured by Earth tides (boreholes USW H-4, 

UE-25 WT #14, UE-25 WT #3, and UE-25 p #1). The 
16 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

boreholes requiring an Earth-tide correction to waterlevel records either are completed in the Miocene 

tuffaceous rocks more than 1,500 m from UE-25 c #3 

or are completed in a different aquifer than the C-holes 

(the Paleozoic carbonate rocks). Earth-tide effects 

were removed from records of water levels and atmospheric pressure by applying a low-pass filter with a 

cutoff frequency of 0.8 cycle/day to these records. As 

shown in figure 7, this filtering removes semidiurnal 

changes in water levels while preserving longer term 

trends.

As shown in figure 8, changes in atmospheric 

pressure in the vicinity of the C-holes typically 

produce synchronous (but opposite) changes in the 

water level in boreholes. The slope of a line fit to a plot 

of water-level change as a function of atmosphericpressure change is called the barometric efficiency. 

Determination of the barometric efficiency of the 

Lower Bullfrog interval in UE-25 c #2 is shown in 

figure 9. Barometric efficiency values of borehole 

intervals for which drawdown was computed during 

this study ranged from 0.75 to 0.99 (table 5). Barometric effects were removed from borehole records by 

subtracting atmospheric-pressure change, multiplied 

by barometric efficiency, from the change in water 

level to compute drawdown.

Flow Distribution in the C-holes

During hydraulic tests conducted in the C-holes 

in February 1996 and from May 1996 to November 

1997, all hydrogeologic intervals in the C-holes that 

were being monitored responded to pumping, regardless of the interval being pumped. Leakage around 

packers could have occurred, although the packers 

were seated in nonrugose, sparsely fractured zones, 

but it is extremely unlikely that all packers failed to 

seal properly. A more reasonable interpretation is that 

fractures beyond borehole walls are so interconnected 

that packers emplaced in the C-holes do not isolate the 

interval being pumped from other transmissive intervals within the volume of aquifer stressed by the 

pumping.

Spinner and oxygen-activation flow surveys 

(fig. 10) were run in UE-25 c #3 during the hydraulic 

test in June 1995 to determine the flow distribution in 

the C-holes under pumping conditions. However, these 

flow surveys failed to detect flow from the Prow Pass 

interval that was indicated by heat-pulse flowmeter 

surveys conducted without pumping in the C-holes in 

1991 (Geldon, 1996). Results of the 1991 and 1995 

flow surveys were combined algebraically to estimate 

a flow distribution during the hydraulic test in June 

1995 (table 6). This flow distribution was adjusted for

Figure 7. Result of filtering out Earth tides on UE-25 c #2 Lower Bullfrog interval pressure heads, 

June 23–29, 1995.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

297.40

297.41

297.42

297.43

297.44

297.45

297.46

297.47

297.48

297.49

297.50

UNFILTERED FILTERED

ELAPSED TIME, IN MINUTES

PRESSURE HEAD, IN METERS
HYDRAULIC TESTS 17

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

–5

–4

–3

–2

–1

0

1

2

3

4

5

6

7

DIFFERENCE FROM MEAN, IN CENTIMETERS

ELAPSED TIME, IN MINUTES

ATMOSPHERIC PRESSURE PRESSURE HEAD

Figure 8. Difference from mean pressure head in UE-25 c #2 Lower Bullfrog interval and 

atmospheric pressure at the C-hole complex, June 23–29, 1995.

Figure 9. Filtered pressure-head change in UE-25 c #2 Lower Bullfrog interval as a function of 

filtered atmospheric-pressure change at the C-hole complex, June 23–29, 1995.

DATA

REGRESSION LINE

ATMOSPHERIC-PRESSURE CHANGE, IN CENTIMETERS

–0.10

–0.10

–0.08

–0.06

–0.04

–0.02

0

0.02

0.04

0.06

0.08

0.10

–0.08 –0.06 –0.04 –0.02 0 0.02 0.04 0.06 0.08 0.10 0.12

PRESSURE-HEAD CHANGE, IN CENTIMETERS
18 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

the hydraulic tests conducted in February 1996 and 

May 1996 to November 1997 (table 6) by inserting 

discharge and drawdown values recorded at the same 

elapsed time in the three hydraulic tests into the 

following equation:

(1)

where 

P1 = the proportion of flow determined for a hydrogeologic interval during the hydraulic test 

in June 1995;

P2 = the proportion of flow determined for a hydrogeologic interval during a hydraulic test in 

either February 1996 or May 1996 to 

November 1997;

Q1 = the average discharge during the hydraulic test 

in June 1995;

Q2 = the average discharge during a hydraulic test in 

February 1996 or May 1996 to November 

1997;

S1 = the drawdown in a hydrogeologic interval 

during the hydraulic test in June 1995; and

S2 = the drawdown in a hydrogeologic interval 

during a hydraulic test in either February 

1996 or May 1996 to November 1997.

In the three hydraulic tests discussed in this 

report, the Lower Bullfrog interval consistently 

contributed about 70 percent of the flow from observation wells to the pumping well at the C-hole complex; 

the Upper Tram interval consistently contributed about 

20 percent of this flow; and all other intervals 

combined contributed about 10 percent of the total 

flow. To analyze the drawdown in any hydrogeologic 

interval, the total discharge from UE-25 c #3 was first 

multiplied by the percentage of flow contributed by 

the interval being analyzed, to avoid calculating erroneously large values of transmissivity and storativity 

(both of which are directly proportional to discharge).

P2

Q1 P1 S1 

Q2 S1  = ------------------------------

Table 5. Barometric efficiency values determined for borehole intervals monitored at the C-hole complex, May 1996 to 

December 1997

Borehole Interval Barometer 

location

Period of

record

Barometric

efficiency 

Regression 

coefficient

UE-25 c #1 Prow Pass C-holes June 23–29, 1995 0.96 0.98

Upper Bullfrog C-holes June 24–29, 1995 .99 .97

Lower Bullfrog 1 C-holes June 23–29, 1995 .97 .98

UE-25 c #2 Calico Hills C-holes June 23–29, 1995 .93 .94

Prow Pass C-holes June 23–29, 1995 .93 .97

Upper Bullfrog C-holes June 23–29, 1995 .93 .97

Lower Bullfrog1 C-holes June 23–29, 1995 .91 .96

UE-25 c #3 Calico Hills 2 C-holes February 7–8, 1996 .83 .89

Lower Bullfrog C-holes May 9–13, 1996 .87 .92

Bullfrog-Tram C-holes Not applicable .94 3 Not applicable

UE-25 ONC-1 Prow Pass ONC-1 July 1–September 13, 1995 .99 .90

USW H-4 Prow Pass to Lithic Ridge ONC-1 June 8–12, 1995 .91 .87

UE-25 WT #14 Calico Hills C-holes June 4–12, 1995 .89 .94

UE-25 WT #3 Lower Bullfrog C-holes June 4–12, 1995 .91 .82

UE-25 p #1 Paleozoic carbonates C-holes January 1–June 20, 1986 .75 Not applicable

1Barometric efficiency of Lower Bullfrog also used for Bullfrog-Tram in hydraulic test February 8–13, 1996. 2Barometric efficiency of Calico Hills also used for Calico Hills-Upper Bullfrog in hydraulic test February 8–13, 1996. 3

Barometric efficiency estimated from values for Bullfrog-Tram in UE-25 c #1 and UE-25 c #2.
HYDRAULIC TESTS 19

Monitoring Network

Borehole UE-25 c #3 was selected as the 

pumping well for all hydraulic tests conducted from 

1995 to 1997, based on evaluation of two hydraulic 

tests conducted in 1984. Boreholes UE-25 c #1 and 

UE-25 c #2 were used as observation wells for the 

hydraulic tests conducted in June 1995 and February 

1996. Boreholes UE-25 c #1, UE-25 c #2, UE-25 

ONC-1, USW H-4, UE-25 WT #14, UE-25 WT #3, 

and UE-25 p #1 were used as observation wells for the 

hydraulic test conducted from May 1996 to November 

1997. Recording barometers were located at the 

C-hole complex during all hydraulic tests; a barometer 

located at borehole UE-25 ONC-1 also was used 

during the third hydraulic test.

Borehole UE-25 c #3 is 900.4 m deep. The borehole is cased and grouted to a depth of 417.0 m. 

During the hydraulic test in June 1995, UE-25 c #3 did 

not contain packers and was open from the Calico 

Hills to the Lower Tram interval. After packers were 

emplaced in August 1995, manipulation of the 

packers, well screens, and slotted casing allowed 

hydraulic communication with the Lower Bullfrog and 

Upper Tram intervals during hydraulic and tracer tests 

in February and March 1996 and with the Lower Bullfrog interval from May 1996 to December 1997.

Figure 10. Flow surveys in UE-25 c #3 during the hydraulic test in June 1995.

EXPLANATION

SPINNER SURVEY

OXYGEN-ACTIVATION SURVEY

FLOW ZONE—Percentage of total

 discharge rate from UE-25 c #3

 during flow surveys indicated

UPPER

TRAM

LOWER

BULLFROG

UPPER

BULLFROG

PROW PASS

CALICO

HILLS

8.6 Percent

3.8 Percent

61.9 Percent

6.4 Percent

21.3 Percent 850

800

750

700

650

600

550

500

DEPTH, IN METERS
20 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

Borehole UE-25 c #2 is 30.4 m from UE-25 c #3 

at the land surface and 910.1 m deep. It is cased and 

grouted to a depth of 416.0 m. Five dual-mandrel 

packers, suspended on 7.30-cm-diameter tubing, were 

emplaced in the borehole to isolate hydrogeologic 

intervals throughout the period of testing discussed in 

this report. Manipulation of packers and well screens 

allowed hydraulic communication with all six hydrogeologic intervals shown in figure 4 in June 1995, with 

the Lower Bullfrog and Upper Tram intervals in 

February and March 1996, and with the Lower Bullfrog interval from May 1996 to December 1997.

Borehole UE-25 c #1 is 68.4 m from UE-25 c #3 

at the land surface and is 897.6 m deep. It is cased and 

grouted to a depth of 417.9 m. Five dual-mandrel 

packers, suspended on 7.30-cm-diameter tubing, were 

emplaced in the borehole to isolate hydrogeologic 

intervals throughout the period of testing discussed in 

this report. Manipulation of packers and well screens 

allowed hydraulic communication with the Calico 

Hills, Prow Pass, Upper Bullfrog, and Lower Bullfrog 

intervals in June 1995, with the Lower Bullfrog and 

Upper Tram intervals in February and March 1996, 

and with the Lower Bullfrog interval from May 1996 

to December 1997.

Borehole UE-25 ONC-1 (Nye County Nuclear 

Waste Repository Project Office, written commun., 

1995) is 842.8 m from borehole UE-25 c #3 at the land 

surface and is 469.4 m deep (about 36.3 m below the 

water level in the borehole). The borehole is telescoped downward and has a diameter of about 13 cm 

in the saturated zone. Seven packers inflated between 

the bottom of casing and a depth of 410 m separate the 

unsaturated and saturated zones; another packer 

emplaced at a depth of 452 m divides the saturated 

zone into two intervals. The upper of the saturatedzone intervals is open in the Calico Hills Formation 

and Prow Pass Tuff; the lower of these intervals is 

open in the Prow Pass Tuff. Absolute transducers, 

installed in all packed-off intervals, transmitted total 

(atmospheric and hydraulic) pressures to a data logger 

every 15 to 20 minutes during this study. Data from the 

lowermost transducer, which is at a depth of 458 m, 

were converted to pressure heads for analysis.

Borehole USW H-4, which is 2,245 m from 

borehole UE-25 c #3 at the land surface, is 1,219 m 

Table 6. Interval discharges 5,800 minutes after pumping started, hydraulic tests in UE-25 c #3, June 1995 to November 1997 

[Flow proportion for the Bullfrog-Tram interval shown in June 1995 is the sum of values for the Lower Bullfrog and Upper Tram intervals; L/s, liters per 

second; cm, centimeters; %, percentage; E, estimated; N/A, not applicable]

Hydrogeologic

unit

June 1995 February 1996 May 1996 to November 1997

Discharge

(L/s)

Drawdown

(cm)

Flow

%

Discharge

(L/s)

Drawdown

(cm)

Flow

%

Discharge

(L/s)

Drawdown

(cm)

Flow

%

UE-25 c #1

Calico Hills 22.5 No data 3.8 8.45 No data 0.5E 9.72 No data 1.1E

Prow Pass 22.5 43.0 2.9 8.45 14.0 2.5 9.72 14.9 2.3

Upper Bullfrog 22.5 52.1 3.9 8.45 21.6 4.3 9.72 19.2 3.3

Lower Bullfrog 22.5 49.7 68.3 8.45 No data No data 9.72 21.0 66.8

Bullfrog-Tram 22.5 No data 89.4 8.45 19.5 92.7 9.72 N/A N/A

Upper Tram 22.5 No data 21.1 8.45 No data No data 9.72 No data 26.5

Lower Tram 22.5 No data trace 8.45 No data trace 9.72 No data trace

UE-25 c #2

Calico Hills 22.5 351.7 3.8 8.45 16.4 0.5 9.72 43.0 1.1

Prow Pass 22.5 75.6 2.9 8.45 14.6 1.5 9.72 22.2 2.0

Upper Bullfrog 22.5 62.2 3.9 8.45 25.0 4.2 9.72 26.5 3.8

Lower Bullfrog 22.5 49.4 68.3 8.45 No data No data 9.72 21.9 70.2

Bullfrog-Tram 22.5 No data 89.4 8.45 21.0 93.8 9.72 N/A N/A

Upper Tram 22.5 283.2 21.1 8.45 No data No data 9.72 No data 22.9

Lower Tram 22.5 239.6 trace 8.45 No data trace 9.72 No data trace
HYDRAULIC TESTS 21

deep (Graves and others, 1997). The borehole diameter is 37.5 cm to a depth of 564 m and 22.2 cm below 

564 m. Casing extends to a depth of 561 m; it is perforated below the water level, which was at an average 

depth of 518.3 m from 1985 to 1995. A packer 

emplaced at a depth of 1,181 m separates the Prow 

Pass, Bullfrog, and Tram Tuffs and the upper part of 

the Lithic Ridge Tuff from the lower part of the Lithic 

Ridge Tuff in the borehole. A 48-mm-diameter 

piezometer tube is installed in the upper part of the 

borehole, and a 62-mm-diameter piezometer tube is 

installed in the lower part of the borehole. Differential 

transducers emplaced in the two monitored intervals 

transmitted hydraulic pressures to a data logger every 

15 minutes during this study. Only the data from the 

upper interval were used.

Borehole UE-25 WT #14, which is 2,249 m 

from borehole UE-25 c #3 at the land surface, is 399 m 

deep (Graves and others, 1997). The borehole has a 

diameter of 22.2 cm below the water table, which was 

at an average depth of 346.4 m from 1985 to 1995. The 

borehole is cased to a depth of 37 m and is open in the 

Topopah Spring Tuff and Calico Hills Formation. A 

62-mm-diameter piezometer tube is installed in the 

borehole. A differential transducer emplaced in the 

piezometer tube transmitted hydraulic pressures to a 

data logger every 15 minutes during this study.

Borehole UE-25 WT #3, which is 3,526 m from 

borehole UE-25 c #3 at the land surface, is 348 m deep 

(Graves and others, 1997). The borehole has a diameter of 22.2 cm below the water table, which was at an 

average depth of 300.5 m from 1985 to 1995. The 

borehole is cased to a depth of 12 m and is open in the 

Bullfrog Tuff. A 62-mm-diameter piezometer tube is 

installed in the borehole. A differential transducer 

emplaced in the piezometer tube transmitted hydraulic 

pressures to a data logger every 15 minutes during this 

study.

Borehole UE-25 p #1, which is 630 m from 

borehole UE-25 c #3 at the land surface, is 1,805 m 

deep (Graves and others, 1997). The borehole diameter decreases from 37.5 to 15.6 cm with depth. Casing 

and cement emplaced to a depth of 1,297 m isolate 

Miocene tuffaceous rocks in the upper part of the borehole from Paleozoic carbonate rocks in the lower part 

of the borehole. The water-level altitude for the Paleozoic carbonate rocks in UE-25 p #1 is monitored 

through a 38-mm-diameter piezometer tube. The 

average depth to water in the piezometer tube was 

361.8 m from 1985 to 1995. A differential transducer 

emplaced in the piezometer tube transmitted hydraulic 

pressures to a data logger every 60 minutes during this 

study.

Other boreholes beyond the immediate vicinity 

of the C-holes, which are part of a larger monitoring 

network for Yucca Mountain (Graves and others, 

1997), were monitored periodically (generally 

monthly) during the hydraulic and tracer tests.

Description of Tests

A hydraulic test was conducted in June 1995 to 

determine hydraulic properties of the six hydrogeologic intervals at the C-hole complex that are shown in 

figure 4. The six intervals were isolated by packers in 

boreholes UE-25 c #1 and UE-25 c #2. Well screens 

opened in the packed-off intervals of the observation 

wells allowed hydraulic communication with the 

pumping well, UE-25 c #3, which was uncased and 

contained no packers to isolate intervals. Because of 

malfunctioning transducers, analyzable data were 

obtained only from the Prow Pass, Upper Bullfrog, 

and Lower Bullfrog intervals of UE-25 c #1 and the 

Calico Hills, Prow Pass, Upper Bullfrog, and Lower 

Bullfrog intervals of UE-25 c #2.

The hydraulic test started on June 12 at 14:23:59 

and ended after 5,803 minutes (4.03 days) on June 16 

at 15:06:53. Recovery was monitored until June 29, by 

which time it appeared to be complete in all intervals. 

At an average discharge rate of 22.5 L/s, drawdown in 

UE-25 c #3 rapidly increased to more than 10 m and 

reached a maximum of 10.9 m (fig. 11). The pumping 

in UE-25 c #3 produced drawdown ranging from 43.0 

to 52.1 cm in intervals of UE-25 c #1 (fig. 12) and 

from 49.4 to 352 cm in intervals of UE-25 c #2 

(fig. 13).

The most permeable interval identified in the 

hydraulic test conducted in June 1995, the Lower Bullfrog interval, was chosen for subsequently planned 

tracer tests at the C-hole complex to increase the 

chance of successful transport of tracers between the 

injection and recovery wells. Because the transducer in 

the Lower Bullfrog interval of UE-25 c #3 was not 

working, the packers between the Lower Bullfrog and 

Upper Tram intervals in all three of the C-holes were 

deflated, and the combined Lower Bullfrog and Upper 

Tram intervals (shown in figure 4 as the Bullfrog-Tram 

interval) became the test interval for the next series of 

tests.
22 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

After testing pump performance in January 

1996 and allowing water levels in the C-holes to 

recover, pumping to establish a steep, quasi-steadystate hydraulic gradient between UE-25 c #2 (the 

injection well) and UE-25 c #3 (the recovery well) for 

a conservative tracer test began on February 8, 1996, at 

13:54:45. Tracer injection occurred on February 13 at 

10:18:22. The tracer injection disturbed the hydraulic 

pressure in the injection interval for 750 minutes and 

effectively terminated the analyzable drawdown 

record. The 6,984 minutes of drawdown recorded 

between the start of pumping and the injection of 

tracer were analyzed as a hydraulic test.

During the hydraulic test in February 1996, 

operation of the pump outside of its optimal performance range caused the discharge to decrease steadily, 

despite an adjustment of the pump speed on February 

12, 5,640 minutes after pumping started. Prior to this 

adjustment, discharge decreased from 8.78 to 8.21 L/s. 

Adjusting the pump speed restored the discharge to 

8.75 L/s, but it immediately began to decrease and was 

8.57 L/s when the tracer test started on February 13 

(fig. 14). Although average discharge after adjusting 

the pump speed was 0.10 L/s larger than before this 

adjustment, deviation from the average discharge of 

8.49 L/s was just 3 percent of the mean for the entire 

period of pumping.

Figure 11. UE-25 c #3 discharge and drawdown, June 12–16, 1995.

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000

22.1

22.2

22.3

22.4

22.5

22.6

22.7

6

7

8

9

10

11

12

DISCHARGE

DRAWDOWN

DISCHARGE, IN LITERS PER SECOND

TIME SINCE PUMPING STARTED, IN MINUTES

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN METERS
HYDRAULIC TESTS 23

As shown in figure 14, the pumping produced as 

much as 2.86 m of drawdown in the Bullfrog-Tram 

interval of UE-25 c #3 (96 percent of which occurred 

in the first 10 minutes). Adjustment of the pump speed 

caused a steplike increase of 0.19 m in UE-25 c #3 

drawdown, but it had no discernible effect on drawdown in the other C-holes. Although oscillatory, drawdown in UE-25 c #1 steadily increased and ranged 

from 14.3 to 22.1 cm in the Prow Pass, Upper Bullfrog, and Bullfrog-Tram intervals (fig. 15). Although 

oscillatory, drawdown in UE-25 c #2 steadily 

increased and ranged from 14.9 to 25.3 cm in the 

Calico Hills, Prow Pass, Upper Bullfrog, and BullfrogTram intervals (fig. 16). Steady increases in observation-well drawdown, together with small deviation 

from the average discharge, enabled the observationFigure 12. UE-25 c #1 drawdown, June 12–16, 1995.

0 1,000 2,000 3,000 4,000 5,000 6,000

0

5

10

15

20

25

30

35

40

45

50

55

60

PROW PASS

UPPER BULLFROG

LOWER BULLFROG

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000

0

8

16

24

32

40

48

56

64

72

80

0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2

3.6

4.0

CALICO HILLS

PROW PASS

UPPER BULLFROG

LOWER BULLFROG

CALICO HILLS DRAWDOWN, IN METERS

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

Figure 13. UE-25 c #2 drawdown, June 12–16, 1995.
24 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

well drawdown to be considered a single-cycle 

response to pumping for the entire period before tracer 

injection.

After the tracer test in the Bullfrog-Tram 

interval ended in March 1996, a new transducer was 

installed in the Lower Bullfrog interval of UE-25 c #3, 

and packers in the borehole were reconfigured. Subsequently, it was possible to conduct hydraulic and tracer 

tests in just the Lower Bullfrog interval. With nearly 

continuous pumping, a series of tracer tests was 

conducted in this interval by the USGS and Los 

Alamos National Laboratory from May 1996 to 

November 1997.

Pumping in UE-25 c #3 to establish a steep, 

quasi-steady-state hydraulic gradient for tracer tests in 

the Lower Bullfrog interval began May 8, 1996, at 

11:16:57. From May 24, 1996, to March 26, 1997, the 

pump shut off 11 times because of problems with the 

generators that provided power to the pump. On March 

26, 1997, at about 17:52, the pump shut off because of 

generator problems, which were not resolved until 

May 8, 1997. Problems with the power supply caused

Figure 14. UE-25 c #3 discharge and drawdown, February 8–13, 1996.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

8.0

8.1

8.2

8.3

8.4

8.5

8.6

8.7

8.8

8.9

9.0

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

2.5

2.6

2.7

2.8

2.9

3.0

DISCHARGE

DRAWDOWN

TIME SINCE PUMPING STARTED, IN MINUTES

TIME SINCE PUMPING STARTED, IN MINUTES

DISCHARGE, IN LITERS PER SECOND DRAWDOWN, IN METERS
HYDRAULIC TESTS 25

Figure 15. UE-25 c #1 drawdown, February 8–13, 1996.

Figure 16. UE-25 c #2 drawdown, February 8–13, 1996.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

0

2

4

6

8

10

12

14

16

18

20

22

24

PROW PASS

UPPER BULLFROG

BULLFROG-TRAM

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

0

2

4

6

8

10

12

14

16

18

20

22

24

26

CALICO HILLS

PROW PASS

UPPER BULLFROG

BULLFROG-TRAM

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS

the pump to shut off for 30 seconds seven times 

between May 30 and September 29, 1997 and at least 

once a day between October 15 and November 12, 

1997. Pumping was terminated on November 12, 

1997, at 15:59:50, 553.24 days after pumping started, 

and recovery was monitored until December 31, 1997.

Discharge between May 8, 1996 and March 

26,1997 initially oscillated between 9.6 and 9.8 L/s, 

eventually stabilized at about 9.4 L/s, and averaged 

9.53 L/s (fig. 17). After the generators were restored to 

service on May 8,1997, discharge decreased steadily 

from 9.3 to 8.9 L/s and averaged 9.01 L/s. The volume 

of water withdrawn between May 8, 1996 and 

November 12, 1997 was 440.2 million L, which is 

equivalent to an average discharge of 9.21 L/s.

As in previous hydraulic tests, drawdown in the 

pumped well was large and reached steady-state 

rapidly (fig. 17). Drawdown in the Lower Bullfrog
26 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

interval of UE-25 c #3 reached 4.8 m in 60 minutes 

and remained at 4.85–5.0 m until October 16, 1996, 

232,000 minutes after pumping started. For unknown 

reasons, drawdown began increasing steadily after 

232,000 minutes of pumping and was 5.98 m on 

March 26, 1997, 464,000 minutes after pumping 

started. After March 26, the frequent pump shutoffs 

kept drawdown below 5.9 m, except during the process 

of restarting the pump. Pump shutoffs typically caused 

rapid and complete or nearly complete recovery in 

UE-25 c #3, but these effects were reversed just as 

rapidly when the pump was restarted. Tracer test operations affected drawdown in the pumped well minimally. Recovery from pumping on December 12, 

1997, 42,965 minutes after pumping stopped, was 99 

percent of antecedent drawdown.

The prolonged period of unsteady pump 

discharge after March 26, 1997, effectively ended the 

drawdown record that could be analyzed as a hydraulic 

test for all observation wells except UE-25 ONC-1. 

The analyzable drawdown record from May 8, 1996, 

to March 26, 1997, is 464,134 minutes (322.32 days) 

Figure 17. UE-25 c #3 discharge and drawdown, May 8, 1996, to November 12, 1997.

0 80,000 160,000 240,000 320,000 400,000 480,000 560,000 640,000 720,000 800,000

8.0

8.2

8.4

8.6

8.8

9.0

9.2

9.4

9.6

9.8

10.0

3.6

4.0

4.4

4.8

5.2

5.6

6.0

6.4

6.8

PUMP OFF 11/12/97, 15:59:50

DISCHARGE

DRAWDOWN

DISCHARGE, IN LITERS PER SECOND DRAWDOWN, IN FEET

TIME SINCE PUMPING STARTED, IN MINUTES

0 80,000 160,000 240,000 320,000 400,000 480,000 560,000 640,000 720,000 800,000

TIME SINCE PUMPING STARTED, IN MINUTES
HYDRAULIC TESTS 27

long. With 11 downtimes ranging from 2 to 185 

minutes, the pump was off for 649 minutes (about 0.1 

percent of the time) during this period. 

Drawdown in response to pumping the Lower 

Bullfrog interval of UE-25 c #3 is known to have 

occurred in the Prow Pass, Upper Bullfrog, and Lower 

Bullfrog intervals of UE-25 c #1 and in the Calico 

Hills, Prow Pass, Upper Bullfrog, and Lower Bullfrog 

intervals of UE-25 c #2. Drawdown in all intervals of 

these boreholes generally increased steadily but was 

very oscillatory. Peak drawdown by March 26, 1997, 

ranged from about 36 to 42 cm in intervals of UE-25 

c #1 (fig. 18) and from about 35 to 51 cm in intervals 

of UE-25 c #2 (fig. 19).

Disruptions of drawdown in the Lower Bullfrog 

and other intervals of UE-25 c #1 and UE-25 c #2 

occurred from pump shutoffs 11 times between May 

1996 and March 1997. Pump shutoffs (most of the 

unlabeled downward spikes in figures 18 and 19) 

generally resulted in 20–50 percent recovery of water 

levels. However, these effects dissipated 50 to 

Figure 18. UE-25 c #1 drawdown, May 8, 1996, to March 26, 1997.

0

5

10

15

20

25

30

35

40

45

50

PROW PASS

UPPER BULLFROG

DRAWDOWN, IN CENTIMETERS DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000 360,000 400,000 440,000 480,000

TIME SINCE PUMPING STARTED, IN MINUTES

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000 360,000 400,000 440,000 480,000

–30

–20

–10

0

10

20

30

40

50

60

LOWER BULLFROG

Partial recirculation (see figure 20A)

Pyridone tracer injected

Iodide tracer injected
28 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

500 minutes after the pump was restarted and did not 

affect analysis of the drawdown.

Recirculation of water during tracer tests 

conducted between May and November 1996 generally caused small decreases in drawdown in the Lower 

Bullfrog interval of UE-25 c #1 or decreases followed 

by increases in drawdown in the Lower Bullfrog 

interval of UE-25 c #2 at the start and end of recirculation, that generally lasted 70 to 560 minutes. However, 

recirculation of water in UE-25 c #1 from June 17 to 

July 3, 1996, to facilitate transport of the sodium 

iodide tracer between the injection and recovery wells 

caused drawdown in the Lower Bullfrog interval of 

UE-25 c #1 to decrease in steps for 23,350 minutes 

(figs. 18 and 20A). Pumping water into UE-25 c #1 

faster than it could drain probably caused the drawdown to decrease. Periodic increases in the injection 

pump rate caused this decrease to occur in steps.

Figure 19. UE-25 c #2 drawdown, May 8, 1996, to March 26, 1997. 

CALICO HILLS

PROW PASS

UPPER BULLFROG

0

5

10

15

20

25

30

35

40

45

60

55

50

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000 360,000 400,000 440,000 480,000

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

LOWER BULLFROG

DFBA Tracer injected

DFBA/bromide tracer injected (see figure 20B)

DFBA tracer injected

TIME SINCE PUMPING STARTED, IN MINUTES

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000 360,000 400,000 440,000 480,000

DRAWDOWN, IN CENTIMETERS
HYDRAULIC TESTS 29

Tracer injection during four tests that were 

conducted between May 1996 and November 1997 

caused increased drawdown in the Lower Bullfrog 

interval of UE-25 c #1 or UE-25 c #2, that generally 

lasted 180 to 750 minutes. However, following injection of 2,6 difluorobenzoic acid tracer into UE-25 c #2 

on January 10, 1997, drawdown in the Lower Bullfrog 

interval of UE-25 c #2 remained high for 8,360 

minutes (figs. 19 and 20B). Increased drawdown could 

have resulted from opening fractures within an 

unknown (probably small) radius of the injection well 

because enlarged fractures would have allowed water 

to drain from the well faster. Lowered hydraulic heads 

associated with the dense injectate as it slowly drained 

Figure 20. Disturbance of drawdown in Lower Bullfrog interval of UE-25 c #1 and UE-25 c #2 by 

tracer tests in 1996 and 1997: A, Sodium-iodide tracer test in UE-25 c #1, June 17 to July 5, 1996; 

B, 2,6-DFBA tracer test in UE-25 c #2, January 9 to 18, 1997 (2,6-DFBA, 2,6-difluorobenzoic acid).

A

B

Tracer injected

Tracer injected

Injection

tubing

filled

Recirculation starts

Fractures opened (?) 

Fractures closed (?) 

Recirculation ends

TIME SINCE PUMPING STARTED, IN MINUTES

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS DRAWDOWN, IN CENTIMETERS

57,000

354,000 356,000 358,000 360,000 362,000 364,000 366,000 368,000

59,000 61,000 63,000 65,000 67,000 69,000 71,000 73,000 75,000 77,000 79,000 81,000 83,000

60

50

40

30

20

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

60

10

–10

0

–20

–30
30 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

from UE-25 c #2 also could have produced the 

observed water-level changes in UE-25 c #2.

Hypotheses regarding disturbances from tracertest operations are not testable and, therefore, are 

presented only for consideration. It is important to 

note that (1) tracer-test operations conducted in one 

borehole generally did not affect drawdown in other 

boreholes; and (2) disturbances from tracer-test operations did not affect analyses of drawdown in UE-25 

c #1 and UE-25 c #2.

Events of unknown origin caused hydraulic 

heads in the Lower Bullfrog interval of UE-25 c #1 

and UE-25 c #2 to rise 5 to 8 cm from June 1 to 11, 

1996 (a period of 14,800 minutes), and from 

November 6 to 14, 1996 (a period of 11,900 minutes). 

Because six observation wells within 3.5 km of UE-25 

c #3 showed similar rises in hydraulic head, the events 

that produced these disturbances were not local in 

scale. No earthquakes were recorded in the vicinity of 

the Nevada Test Site at the time of these disturbances 

(U.S. Geological Survey National Earthquake Information Center, oral commun., 1997). Whatever the 

origin, the unknown events did not affect analyses of 

drawdown data.

Shutting off the pump in UE-25 c #3 on 

November 12, 1997, caused erratic responses in the 

Lower Bullfrog intervals of UE-25 c #2 and UE-25 

c #1 that are not analyzable. Recovery in the Lower 

Bullfrog interval of UE-25 c #1 reached a plateau from 

8,000 to 38,500 minutes after pumping stopped, after 

which it began increasing cyclically. On December 29, 

1997, 67,000 minutes after pumping stopped, recovery 

in the Lower Bullfrog interval of UE-25 c #1 was 

about 95 percent of the antecedent drawdown 

(fig. 21). The transducer in the Lower Bullfrog interval 

of UE-25 c #2 was removed on December 9, 1997, at a 

time when readings from the transducer were erratic, 

and recovery was only about 70 percent of the antecedent drawdown. 

Pumping in the Lower Bullfrog interval of 

UE-25 c #3 from May 1996 to March 1997 caused 

drawdown in all four of the observation wells beyond 

the C-hole complex that are completed in Miocene 

tuffaceous rocks. As in UE-25 c #1 and UE-25 c #2, 

drawdown in the four outlying observation wells was 

very oscillatory. Drawdown in these wells was not 

affected by pump shutoffs or tracer test operations.

Drawdown in UE-25 ONC-1, the nearest observation well to the C-holes, was detected 200 minutes 

after pumping started and increased steadily thereafter 

(fig. 22). Peak drawdown by March 26, 1997, was 

about 28 to 30 cm. Peak drawdown when pumping 

ended on November 12, 1997, was about 36 to 37 cm. 

Recovery in UE-25 ONC-1 followed a pattern similar 

to the Lower Bullfrog interval in UE-25 c #1 (fig. 21). 

On December 29, 1997, 67,500 minutes after pumping 

stopped, recovery in UE-25 ONC-1 was about 

76 percent of the antecedent drawdown.

Figure 21. UE-25 c #1 Lower Bullfrog recovery, November 12 to December 31, 1997.

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000 55,000 60,000 65,000 70,000

0

5

10

15

20

25

30

35

40

45

50

Pump off 11/12/97, 15:59:50 Pacific Standard Time

CALCULATED

RECOVERY, IN CENTIMETERS

ANTECEDENT

TIME SINCE PUMPING STOPPED, IN MINUTES
HYDRAULIC TESTS 31

Borehole UE-25 WT #3, the farthest observation 

well from the C-holes, responded similarly to the 

C-holes and UE-25 ONC-1 to the pumping in UE-25 

c #3 that began on May 8, 1996. Drawdown in UE-25 

WT #3 was detected 9,130 minutes after pumping 

started (fig. 23). Peak drawdown by March 26, 1997, 

was about 14 to 16 cm. Drawdown in UE-25 WT #3 

was more oscillatory than in the other observation 

wells after 240,000 minutes of pumping, possibly 

because (1) UE-25 WT #3 was much farther from the 

pumping well than the other observation wells and 

affected by environmental stresses that did not extend 

to the other wells; and (2) pumping-related water-level 

changes in UE-25 WT #3 were much smaller than in

Figure 22. Drawdown in UE-25 ONC-1, May 8, 1996, to November 12, 1997.

Figure 23. Drawdown in UE-25 WT #3, May 8, 1996 to March 26, 1997.

0 80,000 160,000 240,000 320,000 400,000 480,000 560,000 640,000 720,000 800,000

0

4

8

12

16

20

24

28

32

36

40

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000 360,000 400,000 440,000 480,000

–2

0

2

4

6

8

1 0

1 2

1 4

1 6

1 8

2 0

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS
32 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

the other observation wells and, therefore, harder to 

separate from barometric and Earth-tide effects.

Unlike other observation wells monitored 

during the hydraulic test that began in May 1996, 

USW H-4 and UE-25 WT #14 exhibited steady-state 

drawdown as pumping progressed (fig. 24). Drawdown in both boreholes was delayed for about 

5,000 minutes after pumping started, although very 

small, oscillatory water-level changes, possibly caused 

by borehole-storage release, occurred during this time. 

Between 5,000 and 72,000 minutes after pumping 

started, drawdown increased steadily in response to 

pumping. Drawdown in USW H-4 peaked at about 

22 cm; drawdown in UE-25 WT #14 peaked at about 

15 cm. After about 72,000 minutes of pumping, fluxes 

from recharge boundaries prevented further drawdown. As in a hydraulic test of the Tram interval in 

UE-25 c #1 conducted in 1984 (Geldon, 1996), 

recharge boundaries affecting USW H-4 and UE-25 

WT #14 are inferred to be faults present near the

Figure 24. Drawdown in USW H-4 and UE-25 WT #14, May 8, 1996, to December 4, 1996.

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000

–2

0

2

4

6

8

10

12

14

16

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS

UE-25 WT#14, MAY 8 TO DECEMBER 3,1996

0 40,000 80,000 120,000 160,000 200,000 240,000 280,000 320,000

0

2

4

6

8

10

12

14

16

18

20

22

24

TIME SINCE PUMPING STARTED, IN MINUTES

DRAWDOWN, IN CENTIMETERS

USW H-4, MAY 8 TO DECEMBER 4, 1996
HYDRAULIC PROPERTIES 33

observation wells. Numerous faults are located near 

USW H-4 (Day and others, 1998), and several 

segments of the Paintbrush Canyon Fault are located 

near UE-25 WT #14 (Dickerson and Drake, 1998). 

Conversely, there are no known changes in stratigraphy or lithology between the C-holes and either 

USW H-4 or UE-25 WT #14 that might be interpreted 

to create a hydraulic boundary.

Water-level declines observed in several other 

routinely monitored boreholes at Yucca Mountain 

from May 1996 to November 1997 are believed to be 

related to pumping at the C-hole complex (Graves, 

2000). In boreholes in which declines were observed, 

the maximum declines ranged from 0.1 to 0.4 m 

(table 7). Water-level declines of about 0.2 m were 

observed in a borehole (USW WT-11) more than 8 km 

from the C-hole complex. Water levels in all of the 

boreholes returned to prepumping levels after 

pumping at the C-holes ceased.

HYDRAULIC PROPERTIES

Hydraulic tests conducted at the C-hole complex 

from 1995 to 1997 revealed much about the ability of 

hydrogeologic intervals in the C-holes and the 

Miocene tuffaceous rocks in the vicinity to store and 

transmit water. However, it must be emphasized that 

hydraulic properties computed from these tests pertain 

only to the structural setting in which the tests were 

conducted. The Lower Bullfrog interval is the most 

permeable interval in the C-holes because it is located 

in these boreholes where two intersecting faults have 

caused intense fracturing. The Calico Hills interval is 

the least permeable interval in the C-holes because it is 

the farthest interval vertically from faults that intersect 

these boreholes. In a different structural setting, the 

Lower Bullfrog, Calico Hills, and other intervals of the 

Miocene tuffaceous rocks could have different 

hydraulic properties than indicated at the C-hole 

complex. For example, the Bullfrog Tuff yielded very 

little of the water produced from the Miocene 

tuffaceous rocks during a tracejector flow survey of 

UE-25 p #1 (Craig and Robison, 1984), and the Calico 

Hills Formation yielded 32 percent of the water 

produced from the Miocene tuffaceous rocks during a 

tracejector flow survey of UE-25 b #1 (Lahoud and 

others, 1984). Cross-hole hydraulic tests at several 

sites on Yucca Mountain would enable extrapolation 

of hydraulic properties of the Miocene tuffaceous 

rocks beyond the immediate vicinity of the C-hole 

complex.

Calico Hills Interval

The Calico Hills interval responded in most 

hydraulic tests, including one conducted from May to 

June 1984 (Geldon, 1996), as an unconfined aquifer. 

In four tests conducted from 1984 to 1997, the Calico 

Hills interval consistently was determined to be the 

least permeable interval in the C-holes (table 8). The 

hydraulic test in May and June 1984 indicated that the 

Calico Hills interval in UE-25 c #1 has transmissivity

Table 7. Maximum observed water-level declines related to C-holes testing, May 1996 to November 1997, in routinely monitored boreholes at Yucca Mountain (data from Graves, 2000)

Borehole Geologic unit

Maximum 

water-level 

decline 

(meters)

USW WT-1 Calico Hills Formation, Bullfrog Tuff 0.3

USW WT-2 Prow Pass Tuff 0.4

UE-25 WT #4 Calico Hills Formation 0.2

USW WT-11 Topopah Springs Tuff, Calico Hills Formation 0.2

UE-25 WT #14 Topopah Springs Tuff, Calico Hills Formation 0.2

UE-25 WT #16 Calico Hills Formation 0.1

UE-25 b #1 upper interval Calico Hills Formation, Prow Pass Tuff, Bullfrog Tuff, upper Tram Tuff 0.3

USW H-1 uppermost interval Prow Pass Tuff 0.4

USW H-4 upper interval Calico Hills Formation, Prow Pass Tuff, Bullfrog Tuff, Tram Tuff, upper Lithic Ridge 

Tuff

0.3
34 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

Table 8. Results of hydraulic tests in borehole UE-25 c #3, June 1995 to November 1997[nd, no data; na, not applicable; est, estimated to be the same as values obtained from a hydraulic test in May 1984]

Starting date 06/12/95 02/08/96 02/08/96 05/08/96 05/08/96 06/12/95 02/08/96 05/08/96 05/08/96 UE-25 c #1 UE-25 c #2

Calico Hills

 Analyzed data None None na None na Drawdown Drawdown Drawdown na Period of record (minutes) na na na na na 5,800 7,000 464,100 na Aquifer type Unconfined Unconfined na Unconfined na Unconfined Confined Unconfined na Transmissive thickness (meters) 60.4 60.4 na 60.4 na 45.4 45.4 45.4 na Distance from pumping well (meters) 78.3 78.3 na 78.3 na 29.0 29.0 29.0 na Average discharge (liters per second) 0.85 0.042 na 0.10 na 0.85 0.042 0.10 na Transmissivity (meters squared per day) 9(est) 9(est) na 9(est) na 6 10 4 na Horizontal hydraulic conductivity (meters per day) 0.2(est) 0.2(est) na 0.2(est) na 0.1 0.2 0.08 na Vertical hydraulic conductivity (meters per day) 0.3(est) 0.3(est) na 0.3(est) na nd nd 0.01 na Storativity (dimensionless) nd nd na nd na 0.0002 0.0006 0.0003 na Specific yield (dimensionless) 0.003(est) 0.003(est) na 0.003(est) na nd nd 0.4 na

Prow Pass

 Analyzed data Drawdown Drawdown Drawdown Drawdown na Drawdown Drawdown Drawdown na Period of record (minutes) 5,800 7,000 7,000 464,100 na 5,800 7,000 464,100 na Aquifer type Confined Unconfined Confined Confined na Confined Confined Confined na Transmissive thickness (meters) 18.9 18.9 18.9 18.9 na 23.8 23.8 23.8 na Distance from pumping well (meters) 81.1 81.1 81.1 81.1 na 28.6 28.6 28.6 na Average discharge (liters per second) 0.65 0.21 0.21 0.22 na 0.65 0.13 0.19 na Transmissivity (meters squared per day) 60 50 60 50 na 40 30 30 na Horizontal hydraulic conductivity (meters per day) 3 3 3 3 na 2 1 1 na Vertical hydraulic conductivity (meters per day) nd 0.0001 nd nd na nd nd nd na Storativity (dimensionless) 0.0003 0.0003 0.0004 0.0002 na 0.0004 0.003 0.0008 na Specific yield (dimensionless) nd nd nd nd na nd nd nd na

Upper Bullfrog

 Analyzed data Recovery Drawdown na Drawdown na Drawdown Drawdown Drawdown na Period of record (minutes) 5,700 7,000 na 464,100 na 5,800 7,000 464,100 na Aquifer type Confined Unconfined na Fissure-block na Confined Confined Confined na Transmissive thickness (meters) 46.0 46.0 na 46.0 na 24.1 24.1 24.1 na Distance from pumping well (meters) 83.2 83.2 na 82.3 na 28.6 28.6 28.6 na Average discharge (liters per second) 0.88 0.37 na 0.32 na 0.88 0.36 0.36 na Transmissivity (meters squared per day) 90 40 na 50 na 100 100 80 na Horizontal hydraulic conductivity (meters per day) 2 0.8 na 1/.00002* na 4 4 3 na Vertical hydraulic conductivity (meters per day) nd 0.5 na nd na nd nd nd na Storativity (dimensionless) 0.00006 0.0009 na 0.0001/.0009* na 0.00003 0.00002 0.00002 na Specific yield (dimensionless) nd 0.002 na nd na nd nd nd na
HYDRAULIC PROPERTIES 35

Starting date 06/12/95 02/08/96 02/08/96 05/08/96 05/08/96 06/12/95 02/08/96 05/08/96 05/08/96 UE-25 c #1 UE-25 c #2

Bullfrog-Tram

 Analyzed data na Drawdown na na na na Drawdown na na Period of record (minutes) na 7,000 na na na na 7,000 na na Aquifer type na Confined na na na na Confined na na Transmissive thickness (meters) na 112 na na na na 51.2 na na Distance from pumping well (meters) na 86.3 na na na na 29 na na Average discharge (liters per second) na 7.84 na na na na 7.93 na na Transmissivity (meters squared per day) na 2,500 na na na na 2,500 na na Horizontal hydraulic conductivity (meters per day) na 20 na na na na 50 na na Vertical hydraulic conductivity (meters per day) na nd na na na na nd na na Storativity (dimensionless) na 0.0003 na na na na 0.002 na na Specific yield (dimensionless) na nd na na na na nd na na

Lower Bullfrog

 Analyzed data Recovery None na Drawdown Drawdown Drawdown None Drawdown Drawdown Period of record (minutes) 6,300 na na 464,100 464,100 5,800 na 464,100 464,100 Aquifer type Confined Confined na Confined Fissure-block Confined Confined Confined Fissure-block Transmissive thickness (meters) 62.8 62.8 na 62.8 62.8 29.9 29.9 29.9 29.9 Distance from pumping well (meters) 85.6 85.6 na 85.6 85.6 29.3 29.3 29.3 29.3 Average discharge (liters per second) 15.3 nd na 6.37 6.37 15.3 nd 6.69 6.69 Transmissivity (meters squared per day) 1,800 nd na 1,600 1,300 1,900 nd 1,600 1,300 Horizontal hydraulic conductivity (meters per day) 30 nd na 30 20/.0004* 60 nd 50 40/.001* Vertical hydraulic conductivity (meters per day) nd nd na nd nd nd nd nd nd Storativity (dimensionless) 0.0004 nd na 0.0002 0.0002/.002* 0.003 nd 0.001 0.002/.02* Specific yield (dimensionless) nd nd na nd nd nd nd nd nd

Upper Tram

 Analyzed data None None na None na None None None na Period of record (minutes) na na na na na na na na na Aquifer type Leaky Leaky na Leaky na Leaky Leaky Leaky na Transmissive thickness (meters) 49.7 49.7 na 49.7 na 21.3 21.3 21.3 na Distance from pumping well (meters) 86.9 86.9 na 86.9 na 29.6 29.6 29.6 na Average discharge (liters per second) 4.74 nd na 2.52 na 4.74 nd 2.18 na Transmissivity (meters squared per day) nd nd na 800 na nd nd 900 na Horizontal hydraulic conductivity (meters per day) nd nd na 20 na nd nd 40 na Vertical hydraulic conductivity (meters per day) nd nd na nd na nd nd nd na Storativity (dimensionless) nd nd na 0.0001 na nd nd 0.001 na Specific yield (dimensionless) nd nd na nd na nd nd nd na

* First number is for fractures; second, for matrix

Table 8. Results of hydraulic tests in borehole UE-25 c #3, June 1995 to November 1997—Continued[nd, no data; na, not applicable; est, estimated to be the same as values obtained from a hydraulic test in May 1984]
36 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

of 9 m2/d, horizontal hydraulic conductivity of 

0.2 m/d, vertical hydraulic conductivity of 0.3 m/d, 

and a specific yield of 0.003 (Geldon, 1996). The 

hydraulic test in June 1995 indicated that the Calico 

Hills interval in UE-25 c #2 has transmissivity of 6 

m2

/d, horizontal hydraulic conductivity of 0.1 m/d, 

and storativity of 0.0002. Hydraulic tests conducted in 

February 1996 and from May 1996 to November 1997 

generally supported the previous analyses. A representative plot indicating a match between the data and one 

of the type curves of Neuman (1975) for an unconfined, anisotropic aquifer is shown in figure 25.

Prow Pass Interval

The Prow Pass interval generally responded to 

hydraulic tests as a confined aquifer (table 8). The 

hydraulic test in June 1995 indicated that the Prow 

Pass interval in UE-25 c #1 has transmissivity of 

60 m2/d, hydraulic conductivity of 3 m/d, and storativity of 0.0003. The same hydraulic test indicated that 

the Prow Pass interval in UE-25 c #2 has transmissivity of 40 m2

/d, hydraulic conductivity of 2 m/d, and 

storativity of 0.0004. Hydraulic tests conducted in 

February 1996 and from May 1996 to March 1997 

generally supported the previous analyses. A representative plot indicating a match between the data and the 

type curve of Theis (1935) for a confined aquifer is 

shown in figure 26.

Upper Bullfrog Interval

The Upper Bullfrog interval in UE-25 c #2 

responded to all hydraulic tests as a confined aquifer 

(table 8). These tests consistently indicated transmissivity of 80 to 100 m2

/d, hydraulic conductivity of 3 to 

4 m/d, and storativity of 0.00002 to 0.00003. A representative plot indicating a match between the data and 

the type curve of Theis (1935) for a confined aquifer is 

shown in figure 27.

The hydraulic test in June 1995 produced results 

for the Upper Bullfrog interval in UE-25 c #1 that 

were consistent with results for this interval in 

UE-25 c #2 (table 8). During longer tests conducted in

Figure 25. Analysis of drawdown in the Calico Hills interval of UE-25 c #2, May 8, 1996, to 

March 26, 1997 by the method of Neuman (1975).

0.1

1 10 100 1,000 10,000 100,000 1,000,000

1.0

10.0

100.0

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE

DATA
HYDRAULIC PROPERTIES 37

February 1996 and May 1996, sufficient time elapsed 

to reveal the effects of fractures on flow between the 

Upper Bullfrog interval in UE-25 c #1 and screened 

intervals in the pumping well. Analyses of drawdown 

complicated by downward flow through fractures indicated smaller values of transmissivity and hydraulic 

conductivity and larger values of storativity than analyses of drawdown in which the effects of fractures 

were not evident (table 8). Hydraulic properties determined from hydraulic tests conducted in 1996 and 

1997 are considered less reliable than properties determined from the hydraulic test in June 1995 because 

the later tests were influenced substantially by screen 

placement in the observation and pumping wells.

Lower Bullfrog Interval

The undisturbed drawdown in the Lower Bullfrog interval of UE-25 c #1 and UE-25 c #2 during the 

hydraulic test conducted from May 1996 to November 

1997 can be interpreted in several ways that were not 

evident from previous hydraulic tests of much shorter 

duration. Although previous tests indicated a confinedaquifer response, the test beginning in May 1996 

progressed long enough for a double-humped drawdown curve characteristic of a fissure-block aquifer to 

develop. From 158,000 minutes after pumping started 

in May 1996 to the end of the analyzed record 

(464,100 minutes after pumping started), drawdown in 

UE-25 c #1 and UE-25 c #2 was more than could be 

anticipated on the basis of the earlier drawdown for 

long periods [using the equation of Theis (1935) to 

extrapolate drawdown]. The oscillatory pattern of 

drawdown in the C-holes after 158,000 minutes of 

pumping can be interpreted to indicate that the 

spreading cone of depression encompassed volumes of 

the Lower Bullfrog that alternately were less transmissive or as transmissive as the Lower Bullfrog in the 

C-holes.

Values of transmissivity computed for the 

Lower Bullfrog interval are significantly different 

depending on whether the interval is considered a 

confined aquifer or a fissure-block aquifer (table 8). In 

UE-25 c #1 and UE-25 c #2, transmissivity is 

1,600 m2/d if the Lower Bullfrog is analyzed as a 

confined aquifer (fig. 28) and 1,300 m2/d if the Lower

Figure 26. Analysis of drawdown in the Prow Pass interval of UE-25 c #1, June 12–16, 1995, by the 

method of Theis (1935).

TYPE CURVE

DATA

0.01

1 10 100 1,000 10,000

0.10

1.00

10.00

100.00

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES
38 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

Bullfrog is analyzed as a fissure-block aquifer 

(fig. 29). Although the two analytical solutions 

produced equally plausible results, the fissure-block 

aquifer solution is consistent with a tracer test 

conducted from February to March 1996 that indicated 

dual porosity in the Bullfrog-Tram interval (Fahy, 

1997). Also, the longer pumping required for the 

fissure-block aquifer response to develop, and the 

lower transmissivity value determined from this 

response, can be interpreted to confirm that less transmissive rocks were reached as the cone of depression 

spread to increasingly distant areas during the 

hydraulic test that began in May 1996.

Values of hydraulic conductivity and storativity 

are considerably larger in the rock mass between 

UE-25 c #2 and UE-25 c #3 than in the rock mass 

between UE-25 c #1 and UE-25 c #3. The hydraulic 

conductivity of the Lower Bullfrog interval is 50 m/d 

in UE-25 c #2 and 30 m/d in UE-25 c #1. The storativity of the Lower Bullfrog interval is 0.001 in 

UE-25 c #2 and 0.0002 in UE-25 c #1 (The hydraulic 

conductivity and storativity of the interval in both 

boreholes are about the same as that of the fractures in 

the interval in both boreholes).

Upper Tram Interval

The Upper Tram interval was known from 

hydraulic tests conducted in 1984 to respond to 

pumping as a leaky aquifer without confining-bed 

storage because of recharge from faults that intersect 

the C-holes in this interval (Geldon, 1996). Although 

hydraulic properties of the Upper Tram (UT) interval 

could not be determined directly from hydraulic tests 

conducted during this study (because of transducer 

malfunction), they could be calculated by subtracting 

values of hydraulic properties determined for the 

Lower Bullfrog (LB) interval from those determined 

for the Bullfrog-Tram (BT) interval. The following 

equations were used:

(2)

(3)

(4)

TUT TBT TLB –=

SUT SBT SLB –=

KUT KBT bBT KLB bLB   – bUT = 

Figure 27. Analysis of drawdown in the Upper Bullfrog interval of UE-25 c #2, June 12–16, 

1995, by the method of Theis (1935).

1

1 10 100 1,000 10,000

10

100

1,000

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE

DATA
HYDRAULIC PROPERTIES 39

0.1

1 10 100 1,000 10,000 100,000 1,000,000

1.0

10.0

100.0

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE

DATA

Figure 28. Analysis of drawdown in the Lower Bullfrog interval of UE-25 c #1, May 8, 1996, to 

March 26, 1997, by the method of Theis (1935).

Figure 29. Analysis of drawdown in the Lower Bullfrog interval of UE-25 c #1, May 8, 1996, to 

March 26, 1997, by the method of Streltsova-Adams (1978).

0.01

1 10 100 1,000 10,000 100,000 1,000,000

0.10

1.0

10.0

100.0

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE, r/B=0.05

DATA
40 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

where: 

T = transmissivity (m2/d);

S = storativity (dimensionless);

K= hydraulic conductivity (m/d); and

b = thickness (m).

Only hydraulic properties of the LB interval 

determined by the Theis (1935) solution were used in 

these calculations because hydraulic properties of the 

BT interval (which includes the Lower Bullfrog) were 

determined by this method. These calculations indicated transmissivity of 800 m2

/d, hydraulic conductivity of 20 m/d, and storativity of 0.0001 for the 

Upper Tram interval in UE-25 c #1 and transmissivity 

of 900 m2

/d, hydraulic conductivity of 40 m/d, and 

storativity of 0.001 for the Upper Tram interval in 

UE-25 c #2 (table 8).

Miocene Tuffaceous Rocks

Indicative of hydraulic connection through a 

highly developed fracture network, diverse intervals of 

the Miocene tuffaceous rocks in six observation wells 

responded to the pumping in UE-25 c #3 from May 

1995 to November 1997 (table 9). The C-holes, UE-25 

ONC-1, and USW H-4 appear to be connected hydraulically through a northwest-trending zone of discontinuous faults that extends from Bow Ridge to Antler 

Wash (Geldon and others, 1998). The Paintbrush 

Canyon and related faults that intersect UE-25 

WT #14 and the C-holes probably enhance hydraulic 

connection between these boreholes. Hydraulic 

connection between the C-holes and UE-25 WT #3 

probably is enabled both stratigraphically and structurally because these boreholes were open during 

hydraulic tests in the same geologic unit (the Bullfrog 

Tuff) and are cut by the same faults (the Paintbrush 

Canyon and related faults).

Analyses of the drawdown in individual observation wells (figs. 30–33) indicate hydraulic properties 

of the rock mass at the scale of the distance between 

these boreholes and UE-25 c #3 (table 9). Analyses of 

drawdown in multiple observation wells, either as a 

function of time (normalized by dividing by the square 

of the distance between the observation and pumping 

wells) or as a function of distance at a specified time, 

indicate hydraulic properties of the rock mass in which 

all of the included observation wells are located.

Despite being 843 m from UE-25 c #3, UE-25 

ONC-1 responded to pumping after only 200 minutes, 

because it is in the same structural block as the 

C-holes (between the Bow Ridge and Paintbrush 

Canyon Faults) and is well connected by fractures 

related to northwest-trending faults. This fracture 

connection is reflected in a characteristic fissure-block 

aquifer response. From 200 to 2,000 minutes, flow 

from fractures caused drawdown to increase as a function of log time. From 2,000 to 6,000 minutes, as flow 

from the rock matrix into fractures occurred, drawdown remained relatively constant. After 6,000 

minutes, drawdown increased again as a function of 

log time as flow from both the fractures and matrix 

occurred. Drawdown conformed to the type curve of 

Streltsova-Adams (1978) for  = 10 and r/B = 1.0 

(fig. 30). Transmissivity computed from the typecurve match equals 1,000 m2/d. If the transmissive 

thickness between the C-hole complex and UE-25 

ONC-1 is assumed to vary linearly between known 

thicknesses in UE-25 c #2 and USW H-4, then it can 

be estimated to be about 193 m in UE-25 ONC-1. 

Dividing transmissivity by the estimated transmissive 

thickness indicates a fracture hydraulic conductivity of 

5 m/d. In comparison, the hydraulic conductivity of 

the matrix (table 9) is insignificant. Computed storativity for the fractures in UE-25 ONC-1 is 0.001, which 

is one-tenth of the computed storativity of the matrix.

Located 2,245 m from UE-25 c #3, borehole 

USW H-4 took 5,000 minutes to respond to pumping. 

From 5,000 to 72,000 minutes after pumping started, 

drawdown in USW H-4 conformed to the type curve 

of Theis (1935) for a confined aquifer (fig. 31). After 

72,000 minutes, drawdown became relatively constant 

in response to the recharge effect of nearby fault 

boundary. The preboundary drawdown indicated transmissivity of 700 m2/d and storativity of 0.002 (table 

9). Dividing transmissivity by the transmissive thickness obtained from a flow survey (Whitfield and 

others, 1984) indicated a hydraulic conductivity value 

of 2 m/d. The location of the recharge boundary could 

not be ascertained because only USW H-4 was 

affected by this boundary, and the analytical solution 

to determine the location of a boundary (Lohman, 

1972) requires that at least two wells be affected by the 

same boundary. 

Located 2,249 m from UE-25 c #3, borehole 

UE-25 WT #14 took 5,250 minutes to respond to 

pumping. From 5,250 to 9,000 minutes, a transition 

from borehole-storage release to release of water from 

the aquifer occurred. From 9,000 to 72,000 minutes
HYDRAULIC PROPERTIES 41

after pumping started, drawdown in UE-25 WT #14 

conformed to the type curve of Theis (1935) for a 

confined aquifer (fig. 32). After 72,000 minutes, drawdown became very oscillatory, but broad oscillations 

in the data deviated about a relatively constant value. 

The late-time data are interpreted to be a less-thanideal response to a recharge boundary. The 

preboundary drawdown indicates transmissivity of 

1,300 m2

/d and storativity of 0.002 (table 9). 

Hydraulic conductivity and the location of the 

boundary could not be determined because of insufficient data.

Located 3,526 m from UE-25 c #3, borehole 

UE-25 WT #3 took 9,130 minutes to respond to 

pumping. Thereafter, drawdown in UE-25 WT #3 was 

very oscillatory, but it could be fit to the type curve of 

Theis (1935) for a confined aquifer (fig. 33). This 

solution indicated transmissivity of 2,600 m2/d and

Table 9. Hydraulic properties computed from observation well responses to pumping in UE-25 c #3, May 1995 to November 

1997

[est, estimated]

Borehole UE-25 c #2 UE-25 c #2 UE-25 c #1 UE-25 c #1

Starting date of hydraulic test 05/22/95 05/08/96 05/22/95 05/08/96

Period of record (minutes) 14,400 464,100 11,400 464,100

Analyzed data Drawdown Drawdown Recovery Drawdown

Geologic units in monitored interval Calico Hills to Tram Calico Hills to Tram Calico Hills to 

Tram

Calico Hills to 

Tram

Aquifer type Unconfined Variable Unconfined Variable

Transmissive thickness (meters) 165 144 252 238

Distance from pumping well (meters) 29.0 29.0 82.6 82.9

Average discharge (liters per second) 17.9 9.53 17.9 9.53

Transmissivity (meters squared per day) 2,100 2,400–2,600 1,800 2,200–2,600

Horizontal hydraulic conductivity (meters per 

day)

13 16–18 7 9–11

Vertical hydraulic conductivity (meters per day) 1.7 Unknown 0.3 Unknown

Storativity (dimensionless) 0.003 0.003–.004 0.001 0.002

Specific yield (dimensionless) 0.2 Unknown 0.01 Unknown

Borehole UE-25 ONC-1 USW H-4 UE-25 WT #14 UE-25 WT #3

Starting date of hydraulic test 05/08/96 05/08/96 05/08/96 05/08/96

Period of record (minutes) 796,700 72,000 72,000 463,500

Analyzed data Drawdown Drawdown Drawdown Drawdown

Geologic units in monitored interval Prow Pass Prow Pass to Lithic 

Ridge

Topopah Spring 

and Calico 

Hills

Bullfrog

Aquifer type Fissure-block Confined Confined Confined

Transmissive thickness (meters) 193 (est) 276 Unknown 47.5 (est)

Distance from pumping well (meters) 843 2,245 2,249 3,526

Average discharge (liters per second) 9.21 9.72 9.72 9.59

Transmissivity (meters squared per day) 1,000 700 1,300 2,600

Horizontal hydraulic conductivity (meters per 

day)

5/.002* 2 Unknown 56

Storativity (dimensionless) 0.001/.01* 0.002 0.002 0.002

* First number is for fractures; second, for matrix (Values of transmissivity and hydraulic conductivity listed for UE-25 ONC-1 and USW H-4 differ 

from those obtained from a hydraulic test conducted from May 22 to June 1, 1995, but the values determined from the longer test beginning in May 1996 are 

considered more reliable).
42 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

0.001

1 10 100 1,000 10,000

0.010

0.100

10.000

1.000

100.000

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE, r/B=1.0

DATA

Figure 30. Analysis of drawdown in UE-25 ONC-1, May 8, 1996, to November 12, 1997, by the method 

of Streltsova-Adams (1978).

Figure 31. Analysis of drawdown in USW H-4, May 8 to June 27, 1996, by the method of Theis 

(1935).

1

1,000 10,000 100,000 1,000,000

10

100

1,000

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE

DATA
HYDRAULIC PROPERTIES 43

0.1

1,000 10,000 100,000 1,000,000

1.0

10.0

100.0

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE

DATA

Figure 32. Analysis of drawdown in UE-25 WT #14, May 8 to June 27, 1996, by the method of 

Theis (1935).

Figure 33. Analysis of drawdown in UE-25 WT #3, May 8, 1996, to March 26, 1997, by the 

method of Theis (1935).

0.1

1,000 10,000 100,000 1,000,000

1.0

10.0

100.0

DRAWDOWN, IN CENTIMETERS

TIME SINCE PUMPING STARTED, IN MINUTES

TYPE CURVE

DATA
44 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

storativity of 0.002 (table 9). Dividing transmissivity 

by the length of the open interval in UE-25 WT #3, 

47.5 m, indicated a hydraulic conductivity value of 

56 m/d. Actual hydraulic conductivity probably is 

smaller than the calculated value because the thickness 

of transmissive rock between the C-hole complex and 

UE-25 WT #3 probably exceeds the length of the open 

interval.

The transmissivity of the Miocene tuffaceous 

rocks appears to decrease northwestward in the area 

containing the observation wells used in the hydraulic 

test that began in May 1996. Depending on the analytical solutions used, transmissivity could be interpreted 

to decrease from 2,600 m2/d in the vicinity of UE-25 

WT #3 to about 2,000 m2/d in the vicinity of the 

C-holes. The transmissivity of the Miocene tuffaceous 

rocks is 1,300 m2/d in the vicinity of UE-25 WT #14, 

1,000 m2/d in the vicinity of UE-25 ONC-1, and 

700 m2/d in the vicinity of USW H-4.

The hydraulic conductivity distribution of the 

Miocene tuffaceous rocks in the vicinity of the C-holes 

is believed to be structurally controlled. Hydraulic 

conductivity in UE-25 c #2 decreases from 20–60 m/d 

in the Upper Tram and Lower Bullfrog intervals to 

0.08–0.2 m/d in the Calico Hills interval as the vertical 

distance from faults that intersect the borehole 

increases (table 8). The average hydraulic conductivity 

of the Miocene tuffaceous rocks in UE-25 c #2 is twice 

that in UE-25 c #1 (table 9), possibly because UE-25 

c #2 is located nearer to the subsurface intersection of 

the northerly trending Paintbrush Canyon or Midway 

Valley Fault and a northwest-trending fault (shown in 

figure 2) that underlies the gap through the northern 

part of Bow Ridge. If spatial relations between faults 

and hydraulic conductivity at the C-hole complex are 

combined with values of hydraulic conductivity determined from analyses of drawdown in UE-25 ONC-1, 

UE-25 WT #3, and USW H-4 (table 9), then a general 

distribution of hydraulic conductivity for the Miocene 

tuffaceous rocks in the vicinity of the C-holes can be 

inferred. This inferred general distribution is shown in 

figure 34.

In the 21-km2 area encompassed by observation 

wells used in hydraulic tests at the C-hole complex 

from 1995 to 1997, the storativity of Miocene 

tuffaceous rocks in these observation wells uniformly 

is 0.001 to 0.003 (table 9). Analysis of the drawdown 

in observation wells not affected by boundaries as a 

function of the time divided by the square of the 

distance from the pumping well (fig. 35) indicates that 

the average storativity of the Miocene tuffaceous rocks 

in the area encompassed by the observation wells is 

0.002. This same analysis indicates that the average 

transmissivity of the Miocene tuffaceous rocks in this 

area is 2,200 m2

/d. Being able to derive a single 

analytical solution for UE-25 c #1, UE-25 c #2, UE-25 

ONC-1, and UE-25 WT #3 confirms that the Miocene 

tuffaceous rocks in the structural block delimited by 

the Paintbrush Canyon, Bow Ridge, and Dune Wash 

Faults, at least as far north as lower Midway Valley, 

are a single aquifer in which flow is influenced by the 

same structural, stratigraphic, and climatic factors.

Plots of drawdown in observation wells as a 

function of distance 30,000, 100,000, 200,000, 

305,000, and 463,000 minutes after pumping started in 

May 1996 (drawdown at 30,000 and 463,000 minutes 

shown in figure 36) confirm the ovoid pattern of drawdown aligned with faults extending from Bow Ridge to 

Antler Wash that was detected during the hydraulic 

test conducted from May 22 to June 1, 1995 (Geldon 

and others, 1998). Analyzed by the method of Cooper 

and Jacob (1946), plots of drawdown as a function of 

distance (fig. 37) indicate values of transmissivity 

ranging from 2,100 to 2,600 m2

/d and values of storativity ranging from 0.0005 to 0.002 (table 10). In 

comparison, analysis of drawdown in observation 

wells as a function of distance 14,000 minutes after 

pumping started in May 1995 indicated transmissivity 

of 2,300 m2

/d and storativity of 0.003 (Geldon and 

others, 1998). Distance-drawdown and time-drawdown analyses discussed in this section converge on 

the same solutions.

During the four hydraulic tests conducted at the 

C-hole complex from 1995 to 1997, drawdown 

occurred in all monitored intervals of the C-holes and 

other observation wells, regardless of the geologic 

interval being pumped. This hydraulic connection 

across geologic and lithostratigraphic contacts is 

believed to result from interconnected faults, fractures, 

and intervals with large matrix permeability. The 

Miocene tuffaceous rocks appear to respond to 

pumping as a single aquifer in the Yucca Mountain 

area. This conclusion is supported by being able to use 

the drawdown from observation wells completed in 

different Miocene geologic units in single analytical 

solutions of drawdown as a function of time or 

distance, and the widespread observed water-level 

declines related to pumping. The Paintbrush Canyon
HYDRAULIC PROPERTIES 45

Fault appears to be an effective recharge boundary 

within the aquifer because the effects of pumping were 

minimal or not observed east of this feature. Designation of separate aquifers and confining units within the 

Miocene tuffaceous rocks, therefore, may not be 

appropriate in this area.

Paleozoic Carbonate Rocks

Borehole UE-25 p #1 was monitored during 

hydraulic tests in 1995 and 1996 to evaluate hydraulic 

connection between the Miocene tuffaceous rocks 

and Paleozoic carbonate rocks in the vicinity of the 

C-holes, which previously had been indicated by 

hydraulic head measurements in UE-25 p #1 and borehole flow surveys in the C-holes. Measurements as 

UE-25 p #1 was being drilled in 1983 indicated a 22-m 

difference in hydraulic heads for the Paleozoic 

carbonate rocks and Miocene tuffaceous rocks in 

UE-25 p #1 (Craig and Robison, 1984), which indicated a potential for water to flow from the lower to 

the upper hydrogeologic unit. Flow surveys conducted 

in the C-holes in 1991 indicated upward flow in the

Figure 34. Inferred distribution of hydraulic conductivity of Miocene tuffaceous rocks in the vicinity of the C-holes.

Boundary

Bow

Midway

Paintbrush

Canyon

Fault

Zone

Valley

Fault

Ridge

Fault

Ridge

Fault

Zone

Map referenced to Nevada coordinate system,

zone 2

230,113

0

0 1/2 1 MILE

0.5 1 KILOMETER

231,637

172,204 175,251

NORTHING, IN METERS 

EASTING, IN METERS

5

EXPLANATION

More than 10

5 to 10

2 to 5

Less than 2

HYDRAULIC CONDUCTIVITY,

 IN METERS PER DAY

FAULT TRACE

LINE OF EQUAL INFERRED HYDRAULIC

 CONDUCTIVITY—Interval, in meters

 per day, is variable

OBSERVATION WELL—Numbers indicate

 the following boreholes:

 1. USW H-4

 2. UE-25 WT #14

 3. UE-25 ONC-1

 4. UE-25 c #1

 5. UE-25 c #3

 6. UE-25 c #2

 7. UE-25 p #1

5

5

5

5

2

2

5

5

5

10

5

10

5

10

10

10

2

1

3

4

4

6

7

2

5
46 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

lower parts of these boreholes (Geldon, 1996), which 

most likely originated in the Paleozoic carbonate rocks 

because the intervening tuffaceous rocks generally are 

considered a confining unit (Luckey and others, 1996).

Although UE-25 p #1 was monitored for 

14,400 minutes after pumping started in May 1995 

(Geldon and others, 1998) and 256,200 minutes after 

pumping started in May 1996 (fig. 38), drawdown in 

the Paleozoic carbonate rocks was not detected. This 

lack of drawdown could indicate that the water being 

pumped was drawn laterally from the Miocene 

tuffaceous rocks. Alternatively, the water could have 

been drawn upward from the Paleozoic carbonate 

rocks without causing drawdown in the underlying 

aquifer if the Paleozoic rocks have a large storage 

capacity. Hydraulic connection between the Miocene 

tuffaceous rocks and Paleozoic carbonate rocks could 

not be confirmed or refuted by monitoring water levels 

in UE-25 p #1 during this study.

Analytical Uncertainty

Analytical methods used in this study to determine hydraulic properties rely on assumptions about 

the type of aquifer, some of which are violated in 

nearly all applications. These violations are tolerated 

to simplify the flow system being analyzed, but they 

create unquantifiable uncertainty in computed 

hydraulic properties. For example, all methods assume 

that the aquifer is a porous medium. However, the 

influence of fractures is fundamental to conceptualizing the flow of water in Miocene tuffaceous rocks at 

and near the C-hole complex. The solution to this 

conundrum is to consider fractures to be so interconnected that the Miocene tuffaceous rocks respond to

Figure 35. Analysis of drawdown in observation wells as a function of time divided by the square of the distance from the pumping 

well 322 days after pumping started in UE-25 c #3 on May 8, 1996.

TYPE CURVE 

UE-25 C #1

UE-25 C #2

UE-25 ONC-1

UE-25 WT #3

0.0001 0.0010 0.0100 0.1000 1.0000 10.0000 100.0000 1,000.0000

TIME SINCE PUMPING STARTED, DIVIDED BY THE SQUARE OF DISTANCE

FROM PUMPING TO OBSERVATION WELL, IN MINUTES/(METERS SQUARED)

0.1

1.0

10.0

100.0

DRAWDOWN, IN CENTIMETERS
HYDRAULIC PROPERTIES 47

EXPLANATION

OBSERVATION WELL—Well number to left

 of slash; drawdown, in centimeters, to right

 of slash; not applicable if drawdown affected

 by a recharge boundary 

LINE OF EQUAL DRAWDOWN—Interval

 5 centimeters

OBSERVATION WELL NUMBERS

 1. UE-25 WT #14

 2. USW H-4

 3. UE-25 ONC-1

 4. UE-25 c #1

 5. UE-25 c #2

 6. UE-25 c #3

 7. UE-25 WT #3

5

3/14

30,000 minutes

463,000 minutes

36°50'

36°48'

116°26' 116°24'

36°50'

36°48'

116°26' 116°24'

0

0

1,000

3,000 6,000 FEET

2,000 METERS

20

25

30

25

20

15

35

40

10

15

10

5

20

25

30

2/14

1/11

7/4

3/26

4/37

7/11

5/41

3/14

4/29

5/31

6/(?)

6/(?)

1/Not

 applicable

2/Not

 applicable

Figure 36. Distribution of drawdown in observation wells 30,000 minutes (20.8 days) and 463,000 minutes (321.5 days) 

after pumping started in UE-25 c #3 on May 8, 1996.
48 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

1 0 100 1,000 10,000

0

5

10

15

20

25

30

35

30,000 MINUTES

DATA

REGRESSION LINE

Y=11.976 x LOG X + 50.102

R squared = 0.94

DISTANCE FROM UE-25 c #3, IN METERS

DRAWDOWN, IN CENTIMETERS

10 100 1,000 10,000

0

5

10

15

20

25

30

35

40

45

200,000 MINUTES

DATA

REGRESSION LINE

Y=14.371 x LOG X + 61.452

R squared = 0.98

DISTANCE FROM UE-25 c #3, IN METERS

DRAWDOWN, IN CENTIMETERS

Figure 37. Analyses of drawdown in observation wells as a function of distance from the pumping 

well 30,000, 200,000, 305,000, and 463,000 minutes after pumping started in UE-25 c #3 on 

May 8, 1996.
HYDRAULIC PROPERTIES 49

10 100 1,000 10,000

0

5

10

15

20

25

30

35

40

45

305,000 MINUTES

DATA

REGRESSION LINE

Y=13.447 x LOG X + 60.620

R squared = 0.96

DISTANCE FROM UE-25 c #3, IN METERS

DRAWDOWN, IN CENTIMETERS

10 100 1,000 10,000

0

5

10

15

20

25

30

35

40

45

50

463,000 MINUTES

DATA

REGRESSION LINE

Y=13.807 x LOG X + 62.803

R squared = 0.96

DISTANCE FROM UE-25 c #3, IN METERS

DRAWDOWN, IN CENTIMETERS

Figure 37. Analyses of drawdown in observation wells as a function of distance from the pumping 

well 30,000, 200,000, 305,000, and 463,000 minutes after pumping started in UE-25 c #3 on 

May 8, 1996—Continued.
50 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

pumping as “an equivalent porous medium.” This 

rationalization seems to be justified by the way in 

which plots of drawdown or recovery of water levels in 

wells successfully conform to type curves derived for 

porous media.

Another fundamental assumption that 

commonly is violated is that flow to the pumping well 

is derived from an aquifer of infinite extent. The many 

faults in the area of the C-holes functioning as either 

recharge or barrier boundaries make the concept of an 

infinite aquifer unsupportable. Generally constraining 

observation wells between faults bounding the block 

in which the C-holes are located minimized boundary 

effects but did not eliminate them. Drawdown in USW 

Table 10. Hydraulic properties determined from 

drawdown in observation wells as a function of 

distance from the pumping well, hydraulic test in 

UE-25 c #3, May 1996 to November 1997

Time since 

pumping

started, 

in minutes

Transmissivity,

in meters

squared per day

Storativity

30,000 2,600 0.0005

100,000 2,500 0.0009

200,000 2,100 0.002

305,000 2,300 0.001

402,000 2,200 0.001

463,000 2,200 0.001

Figure 38. Water-level changes in UE-25 p #1, September 3 to November 2, 1996.

170,000 180,000 190,000 200,000 210,000 220,000 230,000 240,000 250,000 260,000

–10

–8

–6

–4

–2

0

2

4

6

8

10

TIME SINCE PUMPING STARTED, IN MINUTES

WATER-LEVEL CHANGE, IN CENTIMETERS

H-4 and UE-25 WT #14 obviously was affected by 

recharge boundaries during the hydraulic test that 

began in May 1996.

All of the analytical methods used in this study 

assume radial flow to the pumping well. The flow 

from intervals other than the one being pumped that 

was detected during hydraulic tests in February 1996 

and May 1996 to November 1997 indicates that flow 

during these tests actually was three-dimensional or 

spherical. Ignoring the vertical component of flow 

seems to have been justified by the generally good 

agreement between results of the hydraulic test in June 

1995, in which flow between observation and pumping 

wells was radial, and results for most intervals monitored in subsequent tests. Nevertheless, there is some 

inaccuracy involved in analyzing the flow from 

unscreened intervals above or below the pumped 

interval by techniques developed only for analyzing 

flow from the pumped interval.

The most commonly applied analytical method 

in this study, that of Theis (1935), assumes flow from 

an infinite, homogeneous, isotropic, confined aquifer. 

Transected by numerous faults and variably welded, 

the Miocene tuffaceous rocks in the vicinity of the 

C-holes are neither homogeneous nor isotropic. As a 

result, hydraulic gradients toward the pumping well 

vary directionally, a situation that is ignored by the 

mathematics of the Theis (1935) solution. Disregarding a nonuniform hydraulic gradient seemingly
CHEMISTRY OF WATER SAMPLES COLLECTED DURING HYDRAULIC TESTS 51

would result in inaccurate computations of hydraulic 

properties. Consistent calculations of hydraulic properties for individual intervals and the composite 

section of Miocene tuffaceous rocks from test to test, 

from well to well, or when multiple observation wells 

are used in a time-drawdown or distance-drawdown 

analysis indicates that either errors are being made 

consistently, or calculated values approximate actual 

values of hydraulic properties, despite simplification 

of structural and lithologic complexities.

All of the analytical techniques used in this 

study required input parameters that had to be determined or approximated for hydrogeologic intervals or 

boreholes in which drawdown was monitored. 

Included in these parameters are the distance of the 

interval or borehole from the pumping well, the transmissive thickness of the interval or borehole, the barometric efficiency of the interval or borehole, the 

proportion of flow from a hydrogeologic interval, and 

the fracture spacing within a hydrogeologic interval. 

Errors in deriving any of these input parameters could 

have changed calculated hydraulic properties considerably.

Values of transmissivity and storativity determined in this study are believed to be accurate to one 

significant figure, but reported values of hydraulic 

conductivity are more uncertain. Hydraulic conductivity can be calculated from the known thickness of 

transmissive intervals within a test interval, the entire 

thickness of the test interval, or an assumed thickness 

of transmissive rock between the observation and 

pumping wells. Because the transmissive thickness 

was unknown, it was impossible to determine 

hydraulic conductivity in many analyses. Even where 

hydraulic conductivity could be determined, it was 

done without much confidence. For example, it is 

impossible to know whether the hydraulic conductivity of the Lower Bullfrog interval in UE-25 c #1 

really is about half that in UE-25 c #2 or whether these 

calculated hydraulic conductivity values result solely 

from about the same transmissivity value in each borehole being divided by an assumed transmissive thickness that is twice as large in UE-25 c #1 than in UE-25 

c #2.

Analytical uncertainty can be decreased with 

additional study of the Miocene tuffaceous rocks at 

Yucca Mountain. Hydraulic tests are needed in the 

Prow Pass or Upper Bullfrog interval of the C-holes to 

determine with more confidence hydraulic properties 

of poorly transmissive rocks. A hydraulic test in the 

Upper Tram interval of the C-holes would assess 

directly the influence of faults on ground-water flow. 

Cross-hole hydraulic tests, preceded by extensive 

hydrogeologic characterization, at several sites in the 

Yucca Mountain area would help determine lateral 

variations in hydraulic properties as a result of lithologically and structurally caused heterogeneity. 

CHEMISTRY OF WATER SAMPLES 

COLLECTED DURING HYDRAULIC TESTS

Sampling of water from UE-25 c #3 was done 

periodically during the hydraulic and tracer tests 

conducted from May 1995 to November 1997 to 

monitor chemical and isotopic changes that may occur 

with long-term pumpage. Background chemistry of 

UE-25 c #3 water and changes in the water as a function of the volume pumped (average discharge multiplied by the time since pumping started) between May 

1995 and October 1997 (table 11) are discussed briefly 

in this section. More extensive interpretation and 

discussion of this water chemistry are beyond the 

scope of this study.

Background Chemistry of UE-25 c #3 

Water

Water pumped from UE-25 c #3 is a sodiumbicarbonate type, which except for large concentrations of lithium, bromide, and strontium is typical of 

water from the Miocene tuffaceous rocks (fig. 39). In 

contrast, water from the Paleozoic carbonate rocks is a 

calcium-magnesium-bicarbonate type (fig. 39).

The water from UE-25 c #3 is fresh, slightly 

alkaline, and warm. The water has a dissolved solids 

concentration of 219–234 mg/L and a specific conductance of 272–340 S/cm. The pH of this water ranges 

from 7.7 to 7.9. The concentration of dissolved oxygen 

in water from a depth of 697 to 813 m was 3.5 mg/L 

on May 13, 1997 (Kenneth Covay, U.S. Geological 

Survey, written commun., 1997). 

Changes in UE-25 c #3 Water Chemistry 

During Pumping

As the volume of water pumped from UE-25 

c #3 increased during hydraulic and tracer tests
52 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

Table 11. Major ions, trace elements, and isotopes in water from UE-25 c #3, May 1995 to October 1997 

[L/s, liters per second, C, degrees Celsius; mg/L, milligrams per liter; ND, not detected]

Date Time

Average 

discharge

(L/s)

Time since

pump on

(minutes)

Volume

pumped

(kiloliters)

Field pH

(Standard 

units)

Temperature

(C)

05/18/95 09:45:00 23.1 1,332 1,846 7.7 ND

05/22/95 16:00:00 17.8 62 66 7.7 41.4

05/23/95 11:30:00 17.7 1,232 1,310 7.7 41.4

05/31/95 17:00:00 17.9 13,082 14,050 7.7 40.3

12/04/96 13:00:00 9.59 302,563 174,100 7.8 38.3

02/19/97 10:00:00 9.55 413,263 236,800 7.8 40.2

06/12/97 09:25:00 9.29 575,948 321,000 7.9 40.0

10/21/97 09:30:00 9.22 764,593 423,000 7.8 39.8

Date Time Ca

(mg/L)

Mg

(mg/L)

Na

(mg/L)

K

(mg/L)

SiO2

(mg/L)

05/18/95 09:45:00 11 0.31 55 1.9 55

05/22/95 16:00:00 11 0.30 58 1.9 60

05/23/95 11:30:00 11 0.30 57 1.9 58

05/31/95 17:00:00 11 0.30 56 1.9 57

12/04/96 13:00:00 12 0.32 51 1.9 52

02/19/97 10:00:00 12 0.31 54 2.0 53

06/12/97 09:25:00 12 0.30 53 2.1 52

10/21/97 09:30:00 12 0.32 54 2.0 52

Date Time HCO3

(mg/L)

SO4

(mg/L)

Cl

(mg/L)

F

(mg/L)

NO2+NO3 

(mg/L)

05/18/95 09:45:00 140 20 6.7 2.2 1.2

05/22/95 16:00:00 140 19 6.4 2.2 ND

05/23/95 11:30:00 141 19 6.5 2.2 ND

05/31/95 17:00:00 1751 19 6.4 2.2 1.2

12/04/96 13:00:00 135 21 6.9 1.9 ND

02/19/97 10:00:00 135 20 6.3 2.1 ND

06/12/97 09:25:00 135 19 6.3 2.1 1.2

10/21/97 09:30:00 133 20 6.6 2.1 ND

Date Time Sr 

(mg/L)

Li 

(mg/L)

Al 

(mg/L)

Fe 

(mg/L)

Br 

(mg/L)

05/18/95 09:45:00 ND ND 0.0070 0.100 0.060

05/22/95 16:00:00 0.042 0.100 ND 0.070 0.060

05/23/95 11:30:00 0.043 0.090 ND 0.030 0.060

05/31/95 17:00:00 0.044 0.080 ND 0.020 0.060

12/04/96 13:00:00 0.049 0.084 0.0065 0.010 0.64

02/19/97 10:00:00 0.048 0.082 <0.005 0.012 0.24

06/12/97 09:25:00 0.048 0.079 0.0036 0.0040 0.13

10/21/97 09:30:00 0.049 0.072 <0.005 0.0034 0.10

Date Time 2H

(per mil)

18O

(per mil)

13C

(per mil)

87Sr

(per mil)

Dissolved 

solids

(mg/L)

05/18/95 09:45:00 –100 –13.4 ND ND 220

05/22/95 16:00:00 –99.3 –13.4 –6.5 0.96 227

05/23/95 11:30:00 –99.7 –13.4 –6.2 0.86 221

05/31/95 17:00:00 –99.8 –13.4 –6.5 0.83 226

12/04/96 13:00:00 –99.8 –13.4 –6.4 0.72 ND

02/19/97 10:00:00 –99.7 –13.4 –7.5 0.78 219

06/12/97 09:25:00 –99.6 –13.5 –7.6 ND 222

10/21/97 09:30:00 ND ND ND 0.78 234

Isotopic notation: Deuterium, oxygen, carbon, and strontium isotopic ratios are reported using the delta () notation in units of parts per thousand. 

The delta notation is calculated as  = [(Rsample/Rstandard)–1)]*1,000 where Rsample can be 2H/1H, 18O/16O, 13C/12C, or 87Sr/86Sr, and Rstandard, the appropriate isotope ratios of the reference standards. The standards are Vienna Standard Mean Ocean Water (VSMOW) for 2H and 18O, Vienna PeeDee 

belemnite (VPDB) for 13C, and the mean ocean water value for 87Sr. 1Analyzed value probably is incorrect because it is much larger than values determined for other samples obtained from 1995 to 1997. 
CHEMISTRY OF WATER SAMPLES COLLECTED DURING HYDRAULIC TESTS 53

conducted from 1995 to 1997, small changes occurred 

in some of the dissolved ion concentrations and in the 

isotope ratios. Calcium increased slightly from 11 to 

12 mg/L whereas magnesium remained constant 

within analytical error. Concurrently, sodium 

decreased erratically and potassium increased. The net 

effect of these very slight variations is that the ratio of 

calcium plus magnesium to sodium plus potassium in 

the water increased slightly with increased pumpage. 

More significantly, the isotope parameters, 2H and 

Figure 39. Major ion chemistry of water from UE-25 c #3, Miocene tuffaceous rocks, and Paleozoic carbonate rocks, 

Yucca Mountain area (Data from McKinley and others, 1991; Perfect and others, 1995; U.S. Geological Survey, 

unpublished data). 

EXPLANATION

MIOCENE TUFFACEOUS ROCKS

UE-25 c #3

PALEOZOIC CARBONATE ROCKS

PERCENT MILLIEQUIVALENTS

 PER LITER

SODIUM + POTASSIUM

CALCIUM

MAGNESIUM

CHLORIDE + FLUORIDE

SULFATE

BICARBONATE + CARBONATE

Na+K

Ca

Mg

Cl 

SO 4

HCO + CO 3 3

% meq/l 
54 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

18O, remained constant whereas 13C increased 

slightly and 87Sr decreased considerably. These 

chemical and isotopic changes may indicate a change 

in the source of water with increased pumpage. The 

isotopic data are not supportive of an increasing 

component of water from carbonate rocks. The 13C 

ratio of carbonate water from UE-25 p #1 is –2.3 per 

mil (Stuckless and others, 1991) and the 87Sr ratio is 

+3.6 per mil (Zell Peterman, U.S. Geological Survey, 

written commun., 2002). These values cannot provide 

an end member for the trends shown in table 11 

because the effects would be opposite of what is 

observed. Further, the 2

H value for water from the 

carbonate rocks at UE-25 p #1 is –106 per mil, which 

is much smaller than the nearly constant and larger 

values for the UE-25 c #3 water (table 11). More 

likely, the small dissolved ion and isotopic variations 

simply reflect lateral variations in these parameters in 

the volcanic aquifer that are being sampled with 

increasing pumpage at UE-25 c #3. The variability in 

dissolved ions in the volcanic aquifer shown in 

figure 39 is more than sufficient to account for the 

small variability in dissolved ions in UE-25 c #3 with 

pumpage.

SUMMARY AND CONCLUSIONS

Four hydraulic tests were conducted by the U.S. 

Geological Survey in Miocene tuffaceous rocks at the 

C-hole complex at Yucca Mountain, Nevada, between 

May 1995 and November 1997. The C-hole complex 

consists of three orthogonally spaced boreholes that 

are 30.4 to 76.6 m apart at the land surface and about 

900 m deep. The C-holes are located at the northern 

end of Bow Ridge, on the west side of Midway Valley. 

Below the water table, which is 400 to 402 m deep at 

the site, the C-holes penetrate the Calico Hills Formation, and the Prow Pass, Bullfrog, and Tram Tuffs of 

the Crater Flat Group. A northerly trending fault, 

believed to be either the Paintbrush Canyon or 

Midway Valley Fault, and an offsetting northwesterly 

trending fault intersect the C-holes at the bottom of the 

Bullfrog and top of the Tram Tuffs.

Borehole flow surveys, geophysical logs, and 

aquifer tests done between 1983 and 1995 identified 

six hydrogeologic intervals in the C-holes—the Calico 

Hills, Prow Pass, Upper Bullfrog, Lower Bullfrog, 

Upper Tram, and Lower Tram intervals. Flow within 

these intervals comes from diversely oriented fractures 

and the interstices of variably welded ash-flow, ashfall, and reworked tuff. During hydraulic tests, the 

Lower Bullfrog interval contributed about 70 percent 

of the flow, the Upper Tram interval contributed about 

20 percent of the flow, and all other intervals 

combined contributed about 10 percent of the flow. 

Because these hydrogeologic intervals are defined by 

spatially related faults and fracture zones, their existence and hydraulic properties cannot be extended 

beyond the immediate vicinity of the C-holes.

Hydraulic tests were conducted at the C-hole 

complex in May 1995, June 1995, February 1996, and 

May 1996 to November 1997. In all of these tests, 

borehole UE-25 c #3 was used as the pumping well, 

and boreholes UE-25 c #1 and UE-25 c #2 were used 

as observation wells.

During the first and last hydraulic tests, boreholes UE-25 ONC-1, USW H-4, UE-25 WT #14, 

UE-25 WT #3, and UE-25 p #1 also were used as 

observation wells. Borehole UE-25 ONC-1, which is 

842.8 m from UE-25 c #3, is completed in the Prow 

Pass Tuff. Borehole USW H-4, which is 2,245 m from 

UE-25 c #3, is completed in the Prow Pass, Bullfrog, 

Tram, and Lithic Ridge Tuffs. Borehole UE-25 WT 

#14, which is 2,249 m from UE-25 c #3, is completed 

in the Topopah Spring Tuff and Calico Hills Formation. Borehole UE-25 WT #3, which is 3,526 m from 

UE-25 c #3, is completed in the Bullfrog Tuff. Borehole UE-25 p #1, which is 630 m from UE-25 c #3, is 

completed in Paleozoic carbonate rocks.

Hydraulic tests conducted at the C-hole complex 

from 1995 to 1997 were designed sequentially to 

determine: (1) hydraulic properties of the composite 

saturated-zone section in the C-holes; (2) hydraulic 

properties of the six hydrogeologic intervals in the 

C-holes; and (3) heterogeneity in the Miocene 

tuffaceous rocks, including the influence of faults, in 

the area encompassed by observation wells. Additionally, it was hoped that monitoring UE-25 p #1 might 

establish whether the tuffaceous rocks are connected 

hydraulically to the Paleozoic carbonate rocks, a 

regional aquifer. The Paleozoic rocks are estimated to 

be about 455 m below the C-holes.

The hydraulic test conducted in May 1995 is 

discussed briefly in this report and in more detail by 

Geldon and others (1998). During the test, which 

lasted 10.0 days, all of the C-holes were open from the 

bottom of casing to the bottom of the borehole. UE-25 

c #3 was pumped at an average rate of 17.9 L/s. Drawdown in the pumping well was 7.76 m; drawdown in 

observation wells ranged from 0 to 42 cm.
 SUMMARY AND CONCLUSIONS 55

 The hydraulic test in June 1995 lasted 4.0 days. 

During the test, UE-25 c #3 was open from the bottom 

of casing to the bottom of the borehole. The six hydrogeologic intervals in UE-25 c #1 and UE-25 c #2 were 

isolated by packers and screened open to flow. UE-25 

c #3 was pumped at an average rate of 22.5 L/s. Drawdown in the pumping well was 10.9 m; drawdown in 

intervals of UE-25 c #1 and UE-25 c #2 ranged from 

43 to 352 cm.

The hydraulic test in February 1996 lasted 

4.9 days. The six hydrogeologic intervals in the 

C-holes were isolated by packers. Well screens in 

these boreholes were opened in the Lower Bullfrog 

and Upper Tram intervals. However, all monitored 

intervals responded to pumping. UE-25 c #3 was 

pumped at an average rate of 8.49 L/s. Drawdown in 

the pumping well was 2.86 m; drawdown in intervals 

of UE-25 c #1 and UE-25 c #2 ranged from 14 to 

25 cm.

The hydraulic test conducted from May 1996 to 

November 1997 lasted 553.2 days. The Lower Bullfrog interval was isolated by packers in the pumping 

well. Packers remained in place from the previous test 

in UE-25 c #1 and UE-25 c #2. Only the Lower Bullfrog interval was screened open in the C-holes, but all 

monitored intervals in these boreholes responded to 

pumping. UE-25 c #3 was pumped at an average rate 

of 9.21 L/s. Drawdown in the pumping well reached 

5.98 m by March 26, 1997, but was kept below 5.9 m 

during the remainder of the test by frequent pump 

shutoffs caused by problems with generators used to 

supply power to the pump. Drawdown in all observation wells was very oscillatory. Peak drawdown by 

March 26, 1997, ranged from 35 to 51 cm in intervals 

of UE-25 c #1 and UE-25 c #2. Drawdown in UE-25 

ONC-1 began 200 minutes after pumping started and 

reached 37 cm when pumping ended. Drawdown in 

UE-25 WT #3 began 9,130 minutes after pumping 

started and reached 16 cm when generator problems 

developed on March 26, 1997. Drawdown attributable 

to aquifer stress was detected in USW H-4 5,000 

minutes after pumping started, peaked at 22 cm 

67,000 minutes later, and became steady-state for the 

remainder of the test. Drawdown attributable to 

aquifer stress was detected in UE-25 WT #14 

5,250 minutes after pumping started, peaked at 15 cm 

67,000 minutes later, and became steady-state for the 

remainder of the test. Water-level declines, believed to 

be related to the C-hole pumping, were observed in 

other boreholes in the area. These declines were 

observed in boreholes that were more than 8 km from 

the C-hole complex. No drawdown was observed in 

UE-25 p #1.

In all hydraulic tests, large, rapid drawdown 

(and recovery) in the pumping well far exceeded what 

could have been predicted from hydraulic properties 

calculated from observation-well drawdown in the 

same tests. Most of this pumping-well drawdown 

probably can be attributed to frictional head loss or 

borehole-skin effects. Because the pumping-well 

drawdown largely is independent of aquifer properties, 

analyses of this drawdown result in misleadingly small 

values of transmissivity and hydraulic conductivity. 

Consequently, only drawdown and recovery in observation wells were used for analyses of hydraulic tests 

discussed in this report. Hydraulic tests at the C-hole 

complex imply that analyses of pumping-well drawdown throughout the Yucca Mountain area are not 

reliable.

Hydrogeologic intervals in the C-holes have 

layered heterogeneity. The Calico Hills interval is 

unconfined, the Prow Pass and Upper Bullfrog intervals are confined, the Lower Bullfrog interval is a 

fissure-block aquifer, and the Upper Tram interval 

receives flow from crosscutting faults in response to 

pumping. Transmissivity increases downhole from 

4–10 m2/d in the Calico Hills interval to 1,300–

1,600 m2/d in the Lower Bullfrog interval, although 

this trend is reversed near the bottom of the C-holes. In 

the Upper Tram interval, transmissivity is 800–

900 m2/d. Hydraulic conductivity increases downhole 

from 0.1–0.2 m/d in the Calico Hills interval to 20–

50 m/d in the Lower Bullfrog and Upper Tram intervals. Storativity in UE-25 c #2 generally increases 

downhole from 0.0002–0.0004 in the Calico Hills and 

Prow Pass intervals to 0.001–0.002 in the Lower Bullfrog and Upper Tram intervals, although the storativity 

of the Upper Bullfrog interval is an order of magnitude 

smaller than in other intervals above the Lower Bullfrog. Storativity in the Prow Pass and Upper Bullfrog 

intervals in UE-25 c #1 is similar to that in UE-25 

c #2, but the storativity of the Lower Bullfrog and 

Upper Tram intervals in UE-25 c #1 is about a tenth of 

that in UE-25 c #2. Vertical distributions of hydraulic 

properties in the C-holes are believed to represent the 

increasing influence of faults and related fractures 

toward the bottom of the boreholes.

Distributions of drawdown in the hydraulic tests 

conducted in May 1995 and from May 1996 to 

November 1997 were influenced strongly by north-
56 Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, 

Nevada

westerly and northerly trending faults. Drawdown in 

UE-25 ONC-1 in the latter test showed a fissure-block 

aquifer response, possibly because of fractures related 

to a northwesterly trending zone of discontinuous 

faults that extends between Bow Ridge and Antler 

Wash. Drawdown in UE-24 WT #14 and USW H-4 

during the same test reached steady-state after 

72,000 minutes of pumping because of recharge from 

the Paintbrush Canyon Fault and a zone of northerly 

trending faults that transects Boundary Ridge.

Drawdown data from four wells monitored 

during the hydraulic test conducted from May 1996 to 

November 1997 matched to the type curve for a 

confined aquifer indicated transmissivity of 

2,200 m2/d and storativity of 0.002 for the Miocene 

tuffaceous rocks within a 21-km2 area surrounding the 

C-holes. Plots of drawdown in observation wells as a 

function of their distance from the pumping well at 

various times during the same test indicated transmissivity of 2,100–2,600 m2/d and storativity of 0.0005–

0.002. Analyses of drawdown in the composite saturated-zone section of the C-holes in May 1995 and in 

outlying observation wells from May 1996 to 

November 1997 indicated that the transmissivity of the 

tuffaceous rocks decreases northwesterly from 

2,600 m2/d in UE-25 WT #3, to about 2,000 m2/d in 

the C-holes, to 700 m2

/d in USW H-4.

The hydraulic conductivity of the Miocene 

tuffaceous rocks areally ranges from less than 2 to 

more than 10 m/d. It is largest where prominent, northerly trending faults are closely spaced or intersected by 

northwesterly trending faults. Relatively large 

hydraulic conductivity occurs beneath Fran Ridge, 

Bow Ridge, and Boundary Ridge. Hydraulic conductivity is smallest toward the crest of Yucca Mountain 

and Jackass Flats.

During the four hydraulic tests conducted at the 

C-hole complex from 1995 to 1997, drawdown 

occurred in all monitored intervals of the C-holes and 

other observation wells, regardless of the geologic 

interval being pumped. This hydraulic connection 

across geologic and lithostratigraphic contacts is 

believed to result from interconnected faults, fractures, 

and intervals with large matrix permeability. The 

Miocene tuffaceous rocks appear to respond to 

pumping as a single aquifer in the Yucca Mountain 

area. This conclusion is supported by being able to use 

the drawdown from observation wells completed in 

different Miocene geologic units in single analytical 

solutions of drawdown as a function of time or 

distance, and the widespread observed water-level 

declines related to pumping. The Paintbrush Canyon 

Fault appears to be an effective boundary within the 

aquifer because the effects of pumping were minimal 

or not observed east of this feature. Designation of 

separate aquifers and confining units within the 

Miocene tuffaceous rocks, therefore, may not be 

appropriate in this area.

Water pumped from UE-25 c #3 is a sodiumbicarbonate type, which except for large concentrations of lithium, bromide, and strontium is typical of 

water from the Miocene tuffaceous rocks. In contrast, 

water from the Paleozoic carbonate rocks is a calciummagnesium-bicarbonate type. Samples of UE-25 c #3 

water, analyzed from 1995 to 1997, seem to indicate 

that changes in the quality of the water pumped from 

that well are probably due solely to lateral variations in 

water quality within the tuffaceous rocks. The isotopic 

data are not supportive of an increasing component of 

carbonate aquifer water.

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