Interpretation of Chemical and Isotopic Data 

From Boreholes in the Unsaturated Zone 

at Yucca Mountain, Nevada

by In C. Yangi, Gordon W. Rattray1 , and Pel Yu2

1 U.S. Geological Survey, Denver, Colorado 

2University of Colorado, Boulder, Colorado

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 96-4058

Prepared in cooperation with the 

NEVADA OPERATIONS OFFICE, 

U.S. DEPARTMENT OF ENERGY, under 

Interagency Agreement DE-AI08-78ET44802

Denver, Colorado 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL $URVEY 

Gordon P. Eaton, director

The use of trade, product,.industry, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

For additional information write to:

Chief, Earth Science Investigations

Program

Yucca Mountain Project Branch 

U.S. Geological Survey 

Box 25046, MS 421 

Denver Federal Center 

Denver, Colorado 80225

Copies of this report can be purchased from:

U.S. Geological 

Branch cf 

Box 25286 

Denver, i

Survey 

Information Services

olorado 80225
CONTENTS

Abstract...................................................^ 1

Introduction................................................................^^^ 2

Geohydrology of the Study Area........................................................................................................................................... 2

Boreholes Sampled for Chemical and Isotopic Data............................................................................................................. 4

Methods of Sample Collection and Analysis........................................................................................................................ 6

Aqueous-Phase Samples..........................................................^ 6

Extraction of Pore Water from Core Samples................................................................................................... 6

Collection of Perched and Saturated-Zone Water Samples............................................................................... 7

Analyses of Water Samples............................................................................................................................... 7

Gas Samples .................................................................................................................................................... 8

Collection from Borehole USW UZ-1.............................................................................................................. 8

Collection from Open Boreholes....................................................................................................................... 11

Analysis of Gas Samples................................................................................................................................... 11

Interpretation of Chemical and Isotopic Data........................................................................................................................ 12

Aqueous-Phase Data.................................................................................................................................................... 12

Pore-Water Chemistry....................................................................................................................................... 12

T*itium.........................................._ 25

Carbon Isotopes................................................................................................................................................. 31

Perched Water.................................................^ 34

Gaseous-Phase Data from Borehole USW UZ-1........................................................................................................ 40

Dry-Gas Composition........................................................................................................................................ 40

Carbon-Dioxide Concentrations........................................................................................................................ 40

Delta Carbon-13 Value ..................................................................................................................................... 40

Carbon-14 Data..........................................................................................................................» 45

Gaseous-Phase Data from Selected Open Boreholes.................................................................................................. 47

Model Calculations.................................................................._^ 47

Gas-Transport Model.......................................................................^ 47

Use of Tritium in Ground Water to Determine Water Mean Residence Times........................................................... 49

Piston-Flow, or Preferential-Flow, Model......................................................................................................... 49

Well-Mixed Model.................................................................................................................................... 51

Tritium Input Function...................................................................................................................................... 51

Results of Tritium Model Calculations.............................................................................................................. 52

Summary and Conclusions.................................................................................................................................................... 55

References................................................................................................................................................^ 55

FIGURES

1. Diagram showing hydrogeologic units at Yucca Mountain, Nevada....................................................................... 3

2. Maps showing locations of unsaturated-zone boreholes at Yucca Mountain, Nevada............................................ 5

3. Diagram showing gas-sampling system................................................................................................................... 9

4. Diagram showing system for separation of carbon dioxide from air for whole-gas samples.................................. 10

5. Piper diagram showing top 75 meters of USW UZ-14 pore water and saturated-zone water

compositions............................................................................................................................................................. 19

6. Piper diagram showing (A) USW NRG-6 and 7a pore-water composition, and (B) composition

of lithologic contacts and adjacent beds from USW NRG-^6,7a, and unsaturated-zone holes............................... 20

7. Piper diagram showing pore-water composition of (A) USW UZ-14 and (B) UE-25 UZ#16............................... 22

Content* III
&-11. Graphs showing:

8. Lithologic units, water content, and tritium concentrations of boreholes (A) UE-25 UZ#4

and (B) UZ#5..............................................................................^^ 26

9. Tritium and carbon-14 data from USW UZ-14 pore watcfcr and rock-gas carbon-14 data

from USW UZ-1............................................................^ 27

10. Lithologic units, tritium, and carbon-14 concentrations of boreholes: (A) USW NRG-6

and (B) USW NRG-7a............................_ 28

11. Lithologic units, tritium, and carbon-14 concentrations of borehole UE-25 UZ#16....................................... 29

12. Expanded graph of tritium, carbon-14, and carbon-13 data from figure 11, UE 25 UZ#16................................... 30

13. Expanded graph of carbon-14 and carbon-13 from USW UZ--14: (A) top 122 meters and

(B) Calico Hills Formation.....................................................j................................................................................ 33

14. Piper diagram showing perched-water composition, along wifth saturated-zone water compositions.................... 36

15-23. Graphs showing:

15. (A) Apparent carbon-14 percent modern carbon of perched waters, and (B) delta carbon-13

values of perched waters..................................................t ................................................................................ 38

16. Delta oxygen-18 compared to delta deuterium plot of saturated-zone water and perched water..................... 39

17. Sulfur hexafluoride concentration in parts per million from USW UZ-1,1984-94........................................ 41

18. Percent carbon dioxide concentration from borehole USW UZ-1: (A) 1983-87 and (B) 1988-94............... 43

19. Delta carbon-13 values in per mil from borehole USW UZ-1: (A) 1984-87 and (B) 1988-94..................... 44

20. Carbon-14 activity in carbon dioxide gas from borehole USW UZ-1: (A) 1984-87 and (B) 1988-94......... 46

21. Diffusion model calculated and observed 14(X>2 concentration relative to depth in USW UZ-1................... 50

22. Tritium input function derived from (A) annual mean va ue, and (B) highest monthly value in a 

year of tritium concentration in precipitation from four stations: Albuquerque, New Mexico; 

Flagstaff, Arizona; Menlo Park, California; and Salt Lakje City, Utah............................................................. 53

23. Calculated tritium contents of water in the unsaturated zjsne by piston-flow and well-mixed models 

using (A) annual mean value of tritium input function, aftd (B) highest monthly value of tritium 

input function...................................................................^................................................................................ 54

TABLES

1. Summary of relation of gravimetric water-content measurer] lents of composite core to geologic unit and

degree of welding for boreholes UE-25 UZ#4 and UE-25 UZ#5, Yucca Mountain, Nevada............................... 13

2. Chemical composition of pore-water and ground-water samples from boreholes UE-25 UZ#16,

UE-25 UZ-N2, and UZ-N46, Yucca Mountain, Nevada .....' ............................................................................... 14

3. Chemical composition of pore-water samples from borehole USW UZ-14, Yucca Mountain, Nevada............... 16

4. Chemical composition of pore-water and ground-water samples from borehole NRG-6/7a, Yucca Mountain,

Nevada.......................................................^ 18

5. Comparison of pore-water composition in lithologic contacts and adjacent beds, Yucca Mountain, Nevada....... 24

6. Chemical composition of perched water at Yucca Mountain, Nevada................................................................... 35

7. Isotopic composition of perched water.................................................................................................................... 37

8. USW UZ-1 dry-gas composition ..........................................j................................................................................. 42

9. Carbon-14 and delta carbon-13 data from boreholes NRG-6, NRG-7a, UZ-16, and SD-12............................... 48

IV Contents
CONVERSION FACTORS

Metric (International System) units in this report may be converted to inch-pound units by using the following 

conversion factors:

Multiply metric unit

nanometer (run)

centimeter (cm)

cubic centimeter (cm3 )

cubic meter (m3)

gram(g)

gram per cubic centimeter (g/cm3 )

kilometer squared (km2)

kilometer (km)

kilopascal (kPa)

liter (L)

liter per minute (L/min)

megapascal (MPa)

meter (m)

meter per day (m/d)

microgram per liter (ng/L)

milligram (mg)

milligram per liter (mg/L)

milliliter (mL)

millimeter (mm)

By

3.937 x 1(T8

3.937 x l(Tl

6.102 x 1(T2

6.102 x 104

2.2 x 10~3

3.6 x 10~2

1.076x 107

6.214 x 10"1

0.145

0.2642

0.2642

144.7

3.281

3.281

1

2.2 x 10"6

1

6.102 x 10~2

3.937 x 10~2

To obtain inch-pound unit

inch

inch

cubic inch

cubic inch

pound, mass

pound per cubic inch

square foot

mile

pound-force per square inch

gallon

gallon per minute

pound per square inch

foot

foot per day

part per billion

pound

part per million

cubic inch

inch

To convert degree Celsius (°C) to degree Fahrenheit (°F) use the following formula:

°F = 9/5(°C) + 32

Contents
Interpretation of Chemical and Isotopic Data 

from Boreholes in the Unsaturated Zone 

at Yucca Mountain, Nevada

By In C. Yang, Gordon W. Rattray, and Pei Yu

Abstract

Analyses of pore water from boreholes 

at Yucca Mountain indicate that unsaturatedzone pore water has significantly larger concentrations of chloride and dissolved solids than the 

saturated-zone water or perched-water bodies. 

Chemical compositions are of the calcium sulfate 

or calcium chloride types in the Paintbrush Group 

(Tiva Canyon, Yucca Mountain, Pah Canyon, and 

bedded tuffs), and sodium carbonate or bicarbonate type water in the Calico Hills Formation.

Tritium profiles from boreholes at Yucca 

Mountain indicate tritium-concentration inversions (larger tritium concentrations are located 

below the smaller tritium concentration in a 

vertical profile) occur in many places. These 

inversions indicate preferential flow through 

fractures. Large carbon-14 variations of about 

53.0 to 97.7 percent modem carbon are seen in 

UE-25 UZ# 16 bedded tuff and in the Calico Hills 

Formation. The larger value of 97.7 percent 

modern carbon and modern chlorine-36 values 

obtained from pore water and core cuttings from 

the Calico Hills Formation of UE-25 UZ#16 are 

in the same locations where large tritium concentrations are found.

The apparent carbon-14 ages of perched 

water range from 3,000 to 10,800 years. If age 

corrections are made to account for caliche dissolution, perched-water residence times all will be 

less than 7,000 years. Stable isotopic values 

of-12.1 to -13.8 parts per thousand for delta 

oxygen-18 and -87.4 to -100 per mil for delta

deuterium in perched water are not consistent 

with recharge during colder climates and therefore strongly support carbon-14 mean ages 

of less than 7,000 years. Major-ion chemistry 

of perched water indicates similar chemical 

compositions to the saturated-zone ground water 

except for USW UZ-14 perched water, which is 

typical of Topopah Spring Tuff water.

Rock-gas compositions are similar to 

that of atmospheric air except that carbon 

dioxide (CO2) concentrations are generally 

larger than those in the air. The delta carbon-13 

values of gas from USW UZ-1 are fairly constant 

from surface to 365.8 meters, indicating little 

interaction between the gas CC>2 and caliche in 

the soil. Carbon-14 data of gaseous and aqueous 

phases also show little interaction between gas 

CC>2 and caliche. With regard to gas-water 

exchange, an aqueous phase will affect a gaseous 

phase more because most carbon resides in the 

aqueous phase. The nonequilibrium condition 

observed between the two phases is likely caused 

by collecting most gas samples by pumping from 

dry fractures rather than from pore gas, which 

could have been in equilibrium with the pore 

water. Gas carbon-14 ages are significantly older 

than water carbon-14 ages in deep Topopah 

Spring Tuff and below. The observed apparent 

age differences may result from gravity-driven 

fracture flow of liquid, a process faster than the 

diffusion-controlled transport of gas.

Abstract
Model calculations indicate that the gas 

transport in the unsaturated zone at Yucca 

Mountain agrees well with the gas-diffusion 

process. Tritium-modeling results indicate that 

the high tritium value of about 100 tritium units 

in the Calico Hills Formation of UZ 16 is within 

limits of a piston-flow model with a water residence time of 32 to 35 years. The large variations 

in tritium concentrations with narrow peaks imply 

piston flow or preferential fracture flow rather 

than matrix flow. In reality, the aqueous-phase 

flow in the unsaturated zone is between piston 

and well-mixed flows but is closer to a piston 

flow.

INTRODUCTION

The unsaturated zone (UZ) at Yucca Mountain 

in Nevada is being investigated as a potential site 

for a high-level nuclear-waste repository. A thorough 

understanding of geochemical and hydrologic processes in the UZ is essential for site characterization. 

The purpose of this report is to present gas and 

liquid hydrochemical data obtained to date and 

interpretations of these data related to the flow 

mechanisms and residence times of these fluids in 

the rock mass.

Data for the gaseous phase include carbon 

dioxide concentrations and carbon isotopic concentrations [carbon-13 ( 13C) and carbon-14 ( 14C)] 

of rock gas probably from fractured tuffs. Data for 

the aqueous phase include major cation and anion 

concentrations and isotopic concentrations and compositions, which include tritium (3H), 14C, 13C, deuterium (2H), and oxygen-18 ( 18O) of pore water in cores 

obtained from boreholes in the UZ. Pore-water compositions and carbon-14 data are mostly from bedded 

and nonwelded tuffs. In addition, perched-water bodies, when detected, also were analyzed for their chemical and isotopic compositions.

Most of the UZ boreholes are drilled in the 

washes on the east side of Yucca Mountain. From 

the present chemical and isotopic data, along with 

previously published USW UZ 1 data collected

at Yucca Mountain (Yang and others, 1993), 

preliminary conceptual hydro logic-flow models 

are constructed from the data. Also, chemical 

compositions of pore water in different lithologic 

units are presented in Piper diagrams. The composition of pore water collected near the lithologic 

contacts and adjacent beds is reported and inferences to hydrologic flow are made. Finally, modeling of the gas-transport mechanism and tritium 

as altracer in ground-water residence-time 

estimation was undertaken for the UZ of Yucca 

Mountain.

This investigation was conducted by the 

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

with the U.S. Department of Energy (DOE), under 

Interagency Agreement DE-AI08-78ET44802.

GEOHYDROLOGY OF THE 

STUDY AREA

Yucca Mountain is located near the western 

boundary of the Nevada Test Site in southern 

Nye County, Nevada. Along the crest of Yucca 

Mountain, altitudes generally range from 1,465 to 

1,4^5 m (Montazer and Wilson, 1984). Yucca 

Mountain consists of a series of north-trending 

fauli;-block ridges composed of volcanic rocks that 

generally have an eastward tilt of 5° to 10° (Scott 

and Bonk, 1984). Numerous washes, generally 

underlain by alluvium, dissect the eastern side of 

the mountain. Average annual precipitation at the 

mountain is estimated to be about 150 mm, and 

nearly three-fourths of the annual precipitation falls 

from October through April (Quiring, 1983). An 

unsaturated zone that is 500-700 m thick is present 

beneath Yucca Mountain. This zone consists of ashflow tuff that is extensively fractured, densely 

welded, minimally porous but transmissive, and is 

interbedded with argillic and zeolitic bedded tuff 

and ash-flow tuff that are less fractured, nonwelded, 

porous, and transmissive (Scott and Bonk, 1984). A 

generalized section of hydrogeologic units at Yucca 

Mountain is given in figure 1.

2 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Stratigraphic 

unit

Alluvium

Group Paintbrush 

Tiva Canyon 

Tuff

Yucca Mountian 

Tuff

Bedded Tuff

Pah Canyon 

Tuff

Bedded Tuff

Topopah 

Spring 

Tuff

Calico Hills 

Formation

Q.

o 

O t «

LL

CD 

£5

O

Prow Pass Tuff

Bullfrog Tuff

Tuff 

lithology

MD

NP,B

MD

NP,B

(V) /

/ (D)

(in part 

zeolitic)

MD,NP,B 

(undifferentiated)

Hydrogeologic 

unit

Alluvium

Tiva Canyon 

welded unit

Paintbrush 

nonwelded 

unit

Topopah 

Spring 

welded 

unit

Calico Hills Jfl 

nonwelded / ~ 

unit A

r

*& a? 

*5r -^ 

rtv

Figure 1. Hydrogeologic units at Yucca Mountain, Nevada [modified from Montazer 

and Wilson (1984), table 1]. MD, moderately to densely welded; NP, nonwelded to 

partially welded; B, bedded; (V), vitric; (D), devitrified.

Geohydrology of the Study Area 3
BOREHOLES SAMPLED FOR CHEMICAL 

AND ISOTOPIC DATA

All UZ boreholes were drilled using the 

vacuum-reverse-air-circulation (VRAC) drilling 

method (Houghton, 1969). This method is intended 

to prevent the contamination of the unsaturated rocks 

with drilling fluids and thus allow the collection of 

native pore water and gas from the UZ for hydrochemical analyses. Sulfur hexafluoride (SF6) was added to 

the compressed air stream injected into the annulus 

space between the inner and outer strings. The concentration of the SF6 in the air mixture was about 

1.5 parts per million by volume (ppmv). Atmospheric 

gas that enters the formation during the drilling process can be removed later by evacuation of the borehole. Disappearance of the SF6 in the evacuated air 

assures the complete removal of the drilling air.

USW UZ-1 (fig. 2) was drilled from April 

through July of 1983 and completed to a total depth 

of 387.1 m. Coring was attempted but was unsuccessful due to the use of an inappropriate coring bit 

(Whitfield, 1985). Only two pieces of core less ' 

than 0.61 m long each were recovered. Rocks of 

Quaternary and Tertiary ages were penetrated during 

the drilling of the borehole. The stratigraphy of the 

lithologic units penetrated is described in Whitfield 

and others (1990). The top 17.4 m consists of 

alluvium, which is underlain by three units in the 

Paintbrush Group: Yucca Mountain, Pah Canyon, 

and Topopah Spring Tuffs. These are thick, ash-flow 

tuff beds separated by bedded tuff units that are each 

6 m thick. The tuff units are variously welded and 

indurated. Black glass shards were recovered during 

bailing when the borehole was 383.3 m deep, indicating the presence of friable, nonwelded tuff at the base 

of the Topopah Spring TufT (Whitfield and others, I 

1990). The borehole contained 15 instrument and 

sampling stations upon completion. Each sampling 

station has a pressure transducer, thermocouple psychrometer, and gas-sampling tubes, isolated by silica 

flour and cement grout. Details of construction were 

given by Montazer and others (1985). , UE-25 UZ#4 and UZ#5 are located in Pagany 

Wash on the north-northeast side of Yucca Mountain. 

Borehole UZ#4 is in the middle of the main wash and

is about 37.7 m north of borehole UZ#5. Borehole UZ#5 is on the southern bank of the wash and 

aboujt 3 m higher than borehole UZ#4 (fig. 2). Borehole UZ#4 drilling started September 6 and was completed October 10, 1984, to a depth of about 111.8 m. 

The top 12m of the borehole is in alluvial-colluvial 

material. Borehole UZ#5 drilling started October 11 

and was completed November 19, 1984, to a depth of 

about 111.6 m. It is totally in bedrock. Details on the 

drilling of these two boreholes are given by Loskot 

and Hammermeister (1992). The predominant rock 

type^ penetrated by the two boreholes are ash-flow and 

ash-fall tuffs. These tuffs are part of the Paintbrush 

Group and, in descending order, are the Tiva Canyon 

Tuff, Yucca Mountain Tuff, Pah Canyon Tuff, and 

upper 18 m of Topopah Spring TufT. Layers of bedded 

and reworked ruff separate each of the four tuffs. The 

tuffs show various degrees of welding, ranging from 

nonwelded to densely welded.

UE-25 UZ#16 borehole is located on the eastern side of the Yucca Mountain central block at the 

mouth of WT2 wash (fig. 2). Drilling of the borehole 

was started on May 27, 1992, and completed on 

March 11,1993, to a total depth of 513.9 m, penetrating about 15.2 m into the water table. The predominant rock types penetrated by the UE-25 UZ#16 

borehole are ash-flow and ash-fall tuffs. These tuffs 

are part of the Paintbrush Group and, in descending 

order, are the Tiva Canyon Tuff, Yucca Mountain 

Tuff, Pah Canyon Tuff, Topopah Spring Tuff, and the 

nonwelded tuffs that are interstratified with each of 

these tuffs, the Calico Hills Formation, and the Prow 

Pass Tuff. Details of the drilling of this borehole 

are given by Falah Thamir and others (U.S. Geological 

Survey, written commun., 1995).

| The USW UZ-14 borehole is located in Drill 

Hole Wash, 26.2 m from USW UZ-1. Drilling of the 

bore(iole was started on April 15, 1993, cored to a 

depth of 672.6 m by April 29, 1994, and completed to 

a total depth of 677.8 m on May 6,1994. Predominant 

rock types are similar to those of USW UZ 1 reported 

by Whitfield and others (1990). Details of the drilling 

on tin's borehole were also given by Falah Thamir 

and others (U.S. Geological Survey, written commun., 

1995).

Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
00

3 oI 

o80)

!o"

I

r

36°45' - 116°25' 116°20'

Base from U.S. Geological Survey 

1:250,000, Death Valley, California: 

Nevada, 1970

10 KILOMETERS

10 MILES

36°50'

UZ-14,

Boundary of potential repository

'uz-1

NRG-7/7a uz#4\

"""f

UZ-6S

Nevada 

Test Site 

Boundary

2 KILOMETERS

2 MILES

EXPLANATION

SD'7» BOREHOLE LOCATION AND NUMBER

Figure 2. Maps showing locations of unsaturated-zone boreholes at Yucca Mountain, Nevada.
Other deep unsaturated-zone boreholes were 

drilled in addition to the UZ boreholes. North-ramp | 

geologic boreholes NRG-6 and NRG 7a and systematic drilling geologic boreholes SD-7 and SD-9 

have been completed (fig. 2). Drilling of NRG-6 

was started on November 23, 1992, and cored to 

a total depth 335.3 m in the Topopah Spring Tuff 

on March 3, 1993. NRG-7a was drilled from 

October 21, 1993, and cored to a total depth of ! 

461.3 m in the upper Calico Hills Formation on 

May 6,1994. SD-9 was started on May 10, 1994, 

penetrating into the water table, and completed to a 

total depth of 611.6 m on September 26, 1994. SD-7 

was started on October 3, 1994, and completed to a 

total depth of 497.4 m in the Calico Hills Formation 

on July 28, 1995.

METHODS OF SAMPLE COLLECTION 

AND ANALYSIS

Dry-drilling techniques were used to obtain 

all UZ cores from boreholes. The diameter of the 

rotary core was 6.10 cm. Cores from the rock formation were obtained using a 1.52-m core barrel with 

a split inner tube. Core recovery was typically 

more than 90 percent. Three to four pieces of unfragmented solid core, approximately 15 cm long, were 

selected from most core runs for pore-water extraction. The remainder of the cores were selected for 

other hydrologic-property tests and for archiving.

Aqueous-Phase Samples

Sample-handling procedures affect the success 

of extracting uncontaminated water from core samples. Evaporation of pore water increases with sample 

exposure time in a dry climate, and strict precautions 

were taken to avoid loss of moisture or contamination 

of pore water in the cores (Striffler and Peters, 1993). 

Each core was wrapped in a thin plastic sheet, placed 

inside a lexan liner, and capped on both ends of the 

lexan liner. The lexan-contained core was then placed 

inside a thick aluminum foil bag and heat-sealed for 

moisture protection. The sealed cores were carefully 

packed into plastic coolers and transported from the 

drill site to the Sample Management Facility (SMF) 

at Jackass Flats, Nev., for log-in and storage. The 

storage temperature was kept at 6° to 9°C until the 

cores were removed for pore-water extraction.

Extraction of Pore Water from 

Core Samples

Pore water was extracted from the cores by 

using a high-pressure one-dimensional (uniaxial) 

compression procedure (Mower and others, 1991, 

1994; J.D. Higgins and others, Colorado School of 

Mines, written commun., 1995). Briefly, compression 

operations start with applying pressure to the first 

stress level of 103.4 MPa at a rate of 69 kPa/s. 

Loading continues in eight increments of 103.4 MPa 

(at the same loading rate) until the final stress level of 

827 MPa is reached. Additional pore water can be 

extracted by injecting dry nitrogen gas (greater than 

99.99 percent pure) into the pore space and by forcing 

out pore water at the end of compression. Water and 

gas s.amples are taken when adequate volumes are collected in the syringes. The extracted water was filtered through Nucleopore filters (0.45 nm) into 

suitable bottles. Samples for major ions were stored in 

polyethylene bottles, and samples for stable isotopes 

and 14C were stored in glass bottles.

The densely welded Topopah Spring Tuff, 

which generally has less than a 5-percent moisture 

content by weight, cannot yield water by compression. 

Therefore, the vacuum distillation method (Stewart, 

1972; Walker and others, 1991) was used in this study. 

Cores which had undergone high-pressure compression were also distilled in a vacuum for the remaining

1 1 ft water. That water can only be analyzed for H, O, 

and?H.

I In vacuum distillation, water from cores is 

distilled by heat in a vacuum system and captured 

in a cold trap at -78°C. A temperature of 150°C was 

maintained at the heating mantle, resulting in a core 

temperature of about 110°C. Vacuum-distilled water 

samples were stored in glass bottles for analysis of tritium. In samples with high zeolite contents (such as 

samples from the Calico Hills Formation), water may 

be fractionated and become more depleted in the 

heavy 18O isotope when it reacts with zeolites in cavities or channels. Therefore, pore-water samples for 

stable isotopic analyses (5D and 6 18O) should be processed by vacuum distillation on a nonzeolitic core 

sample, while compressed water which represents percolating water should be used for zeolite samples. 

Further investigations on the extent of isotopic fractionation by the zeolite minerals are in progress using 

isotope-tagged (known stable isotopic values) water 

imbibed into dry core from the Calico Hills Formation 

and the bedded tuff.

6 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Collection of Perched and Saturated-Zone Water 

Samples

Perched-water samples were collected from 

USW UZ-1, UZ-14, NRG-7a, SD-7, and SD-9. 

In addition, water samples were collected from the 

saturated zone immediately below the water table in 

J-13, ONC#1 (Office of Nye County), USW G-2, and 

UE^-25 UZ#16. All water samples were collected 

using plastic bailers or stainless-steel bailers. Samples 

were stored inside an ice cooler after collection and 

transferred to the SMF at the end of the day for longterm storage in a 6-9°C cold room. Water-quality 

parameters, such as pH, specific conductance, 

and temperature (and occasionally bicarbonate concentration), were measured in the field laboratory. 

USW UZ-14 and USW SD-7 boreholes produced 

sufficient perched waters for hydraulic pumping 

tests. Consequently, only one complete set of 

perched-water samples was collected from each 

borehole except UZ-14 and SD-7, which were 

collected during pumping tests.

While drilling USW UZ-1 to a depth of 

387.1 m, a body of perched-water was penetrated. 

During a 495-minute period, 491 L of water was 

removed by bailing (Whitfield and others, 1990). 

One sample was collected on July 7, 1983, using a 

plastic bailer. The other water sample was collected 

on July 11, 1983, using the same bailer. Prior to 

initiation of drilling operations, the unsaturated 

section had been estimated to be about 470 m thick 

at the USW UZ-1 location. During the drilling of 

USW CM in 1980, located 305 m to the southeast of 

USW UZ-1, operational difficulties were experienced 

at a depth of 303.9 m (Spengler and others, 1981). At 

this point, a portion of the drill rods and several types 

of retrieval tools were lost into the borehole. The 

borehole was reamed to a larger diameter and 

cemented from 239.3 to 308.8 m. The cement plug 

was then drilled through to a depth of 309.7 m. A total 

of 9,250 m3 of drilling fluids was lost to the formation 

during reaming and cementing operations.

On July 30,1993, wet cores from UZ-14 were 

observed from 383.0 to 383.6 m (Falah Thamir and 

others, U.S. Geological Survey, written commun., 

1995). A fracture was observed at 383.7 m. Core 

was dry below this fracture. A plastic bailer was 

left at the bottom of the borehole (384.6 m) over the 

weekend. On Monday morning (August 2, 1993), 

the bailer was full of water when it was pulled up. 

A whole set of hydrochemical samples was collected.

A supplemental set was collected on the same day 

using a plastic bailer. The third set was collected on 

August 2,1993, using a stainless-steel bailer. About 

20 L of water was collected. All water samples were 

stored in a refrigerator at the SMF.

On August 3,1993, the borehole was drilled 

from 386.1 to 387.7 m and wet cores were recovered. 

A plastic bailer was lowered down the borehole and 

17 bailers of water samples were collected. On 

August 4,1993, the borehole was drilled from 387.7 to 

389.2 m and cores were wet throughout. Coring 

continued from 389.2 to 390.8 m. All cores were wet. 

Lithologically, the lower 1.3 m of this interval was 

composed of basal vitrophyre. On the morning of 

August 5,1993, the water level was at 381.3 m. Eight 

bailers of water samples were collected.

Hydraulic drawdown and recovery tests were 

conducted on August 17, 1993, to estimate the size 

of the perched-water body. A Moyno pump was 

placed at the bottom of the borehole, and pump tests 

were concluded on August 27, 1993. Four sets of 

hydrochemical samples were collected during the 

tests, and a final set of hydrochemical samples was 

collected on August 31, 1993.

Pumping tests for USW SD-7 were conducted 

for 1 week, from March 16 through 21,1995, at a rate 

of 11 L/min. Perched-water samples for hydrochemical analysis were collected on March 8, 1995, when 

perched water at USW SD-7 was first reached, then 

collected twice a day during the pumping tests.

One sample of all other perched water 

(NRG--7A, SD-9) was collected from each borehole by using a plastic bailer.

Analyses of Water Samples

The tritium was analyzed at the UZ hydrochemistry laboratory in building 56 of the Denver Federal 

Center using procedures published by Thatcher 

and others (1977). Tritium values were calculated 

by regressing back to the date of sample collection 

so that tritium decay was considered between sample 

collection and dates of analysis. Tritium errors 

were approximately ±4 tritium units [1 tritium unit 

(1 TU) = 1 3H atom per 10 18 *H atoms]. Cation concentrations were measured using inductively coupled 

plasma emission spectroscopy, and anion concentrations were measured using ion chromatography at 

Huffman Laboratories, Inc., in Golden, Colo. Because 

only a small volume (3 to 30 mL) of pore water was 

obtained for each sample, complete measurements of

Methods of Sample Collection and Analysis 7
water composition were not possible for individual 

samples. The analytical error is ±5 percent for all 

major ions except sulfate, for which the error is 

±10 percent. Charge balance is calculated by. subtracting total milliequivalent anions from total milliequivalent cations divided by the total milliequivalents of 

cation and anion multiplied by 100. However, silica 

concentration is not considered in the charge balance 

because of difficulty in assessing charge on silicate 

species. Analysis by Tandem Accelerator Mass 

Spectrometer (TAMS) for 14C and 5 13C required 

about 30 to 60 mL of water. Samples were sent to 

Beta Analytic, Inc., in Miami, Fla., for analyses. 

Bicarbonate in water was converted to carbonate and 

then precipitated as strontium carbonate. Carbonate 

samples were acidified to yield carbon dioxide and 

subsequently converted to graphite for determination 

by TAMS. Uncertainty in 8 13C values was ±0.2 part 

per thousand (%o), and for 14C was ±0.7 percent modern carbon (pmc). Stable isotopes of oxygen and 

hydrogen were analyzed by mass spectrometer at the 

U.S. Geological Survey Research Laboratory in 

Reston, Va., and at the Stable Isotope Laboratory, 

Institute of Arctic and Alpine Research, University of 

Colorado, Boulder, Colo. Precision for the measurements was ±0.2%o for 5 18O and ±1.0%o for 5D. All 

uncertainties quoted are one standard deviation.

Gas Samples

Gas samples were collected using a peristaltic 

pump connected through short silicone tubing to the 

downhole gas-sampling tubes. Gas-sampling tubes 

were pumped overnight before sample collection to 

purge the tubes of any atmospheric air that might 

have been introduced while connecting the pumps 

to the system. Generally, four types of gas samples 

were collected: gas composition, CO2 concentration, 

8 13C, and 14C. Gas-sampling devices used were 

500 cm3-per-minute peristaltic pumps connected 

through 0.95-cm-diameter Teflon tubes to the pumping 

ports.

Collection from Borehole USW UZ-1

Rock-gas samples were collected using a 

syringe inserted into a three-way stopcock in the 

gas-sampling line of borehole USW UZ-1 (fig. 3), 

which is permanently instrumented for gas sampling. 

Gas-sampling lines were pumped overnight (20 hours)

before gas samples were taken. The syringe was 

flushed with sample gas at least three times before 

collection of a sample. Gas was then drawn into the 

syringe, the syringe was transported to the laboratory, 

and gas was injected into a gas chromatograph for 

composition analysis. Each probe was sampled daily 

during a gas-sampling trip more frequently when 

abnormal gas compositions were observed.

I Two gas-sampling methods were used for deter11 mination of 8 C ratio in carbon dioxide samples. In 

the first, the molecular-sieve (MS) method, the gas 

stream was initially passed continuously through a 

silica-gel tower to remove moisture (fig. 3), then 

through a 300-mL stainless-steel cylinder containing 

a 50-nanometer (50-nm), anhydrous (dehydrated 

under a vacuum at 350°C) molecular sieve to trap the 

CO2 gas. The 50-nm molecular sieve strongly traps 

CO2, which may be later recovered in the laboratory 

by heating to 350°C the stainless-steel cylinder (containing the molecular-sieve pellets) under a vacuum. 

This collection method was used from 1984 to 1991. 

In 1991, it was replaced by the whole-gas method 

described below.

The second method, the whole-gas (WG) 

method, was used for batch sampling. A gas stream 

was allowed to flow through a 500-mL glass container 

(or into a Mylar balloon) to purge the container several 

times before sampling (this "glass container" replaced 

the "gas sampler" in fig. 3). When the gas stream had 

attained a steady flow (indicated by flow meter), stopcocks at both ends were closed and the glass container 

removed from the flow line. The collection time was 

less than 5 minutes. This has become a preferred 

method and has been used continuously. Whole-gas 

samples collected in 500-mL glass containers are 

brought back to the laboratory for processing. About 

99 percent of the gas collected is air. Separation of 

CO2 from air required a specially designed, W-shaped 

glass! coil trap (fig. 4). The gas sample from the field 

collection was allowed to flow slowly through an H2O 

trap cooled with a dry-ice alcohol slurry to trap the 

water vapor, then through the W-shaped trap, cooled 

with liquid nitrogen to trap the CO2 . Noncondensable 

gases exited through the vacuum pump. The process 

was completed in 5 hours for 3 L of gas and 3 hours 

for 500 mL of gas.

8 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
 o

oo o

Io

I

PERISTALTIC 

PUMP

SOIL

GAS

PROBE

SILICAGEL 

TOWER

STOPCOCK

t

OR

\

nun

a

THREE-WAY 

VALVE

STOPCOCK

\J

GLASS

VACUUM

TRAP

ONE-WAY 

VALVE

GAS 

SAMPLER

SYRINGE

DoQi

FLOW 

METER

(O

Figure 3. Gas-sampling system.
I

CD "c"

N

i

0)oi

VACUUM 

GAGE

VACUUM

AND

PRESSURE 

GAGE

FLOW-THROUGH

GLASS 

CONTAINER

OR

MYLAR 

BALLOON

r

TO

VACUUM 

PUMP

DeltaC-13 

SAMPLE

CO2 W-SHAPED TRAP

\J

CO2

STORAGE 

CYLINDER

Figure 4. System for separation of carbon dioxide from air for whole-gas samples.
The method for 14C-sample collection was similar to the MS method used for 5 13C samples except 

that the collection time is 5-10 days depending on the 

C02 concentration of the gas. The C02 gas trapped in 

the MS was degassed in the laboratory, and heated in 

the vacuum line system to 350°C to release the trapped 

CC>2. Released carbon dioxide was collected in the 

cold trap, volume measured, and transferred to the 

storage cylinders. In the earliest stages of this study, 

some of the 14C samples were collected by sorption in 

concentrated KOH solution as described in Haas and 

others (1983) and Yang and others (1985).

Collection from Open Boreholes

After a borehole was drilled, the atmospheric air 

that entered the formation during the drilling process 

was removed by evacuation from the surface with a 

large-capacity pump. The tracer (SF6) concentration 

in the evacuated air was continuously monitored. 

Disappearance of the SF6 (concentration less than 

0.1 ppm) assures the complete removal of the drilling 

air. Prototype tests for gas sampling from open boreholes was conducted by the U.S. Geological Survey 

near Superior, Ariz., in 1990, and results were reported 

by Peters and others (1991).

For UE^-25 UZ#4 and UZ#5 boreholes, casing 

was retained inside the borehole for 6 years. Therefore, gas sampling was not conducted. Packers were 

installed inside the open boreholes in NRG-6, SD-12, 

and UZ#16 for gas-sample collections. Two intervals 

were packed in NRG-6 (one at the Tiva Canyon 

Tuff and one at the Topopah Spring Tuff), five intervals were packed in UZ#16 (one between the 

Tiva Canyon Tuff and Topopah Spring Tuff; two 

within the Topopah Spring Tuff, one between the 

Topopah Spring Tuff and Prow Pass Tuff, and one 

at the bottom of the borehole in the Prow Pass Tuff), 

and two intervals were packed in SD-12 (both within 

the Topopah Spring Tuff). In addition, a simple gassampling technique using clusters of nylon tubes 

hanging down the borehole at different depths was 

conducted at NRG-6, NRG-7a, and UZ#16.

Gas-composition samples were collected using 

a syringe inserted into a three-way stopcock in the 

gas-sampling line in the same way as described above. 

Each probe was sampled daily during a gas-sampling 

trip, more frequently when abnormal CC>2 concentrations were observed (usually rock-gas contains higher

C02 concentration than atmospheric C02, which is 

about 350 ppmv).

For the 5 13C samples, a 3-L Mylar balloon was 

used to collect a rock-gas sample. A deflated balloon 

was connected to the outlet of the pump and inflated 

with the sample gas.

Carbon-14 samples were collected the same as 

for the instrumented borehole. The gas stream was 

initially passed continuously through a silica-gel tower 

to remove moisture (fig. 3), then through a 300-mL 

stainless-steel cylinder containing a 50-nm, anhydrous 

(dehydrated under a vacuum at 350°C) molecular 

sieve to trap the C02 gas. The 50-nm molecular sieve 

strongly traps C02, which may be later recovered in 

the laboratory by heating the stainless-steel cylinder to 

350°C (containing the molecular-sieve pellets) under a 

vacuum. The collection time is 5 10 days depending 

on the C02 concentration of the gas.

Analysis of Gas Samples

Gas chromatography was used for composition 

analyses. Sulfur hexafluoride (SF6) was measured 

using an electron-capture detector with pure nitrogen 

gas as a carrier gas. Carbon dioxide was measured 

using a flame-ionization detector and pure nitrogen 

gas as a carrier gas. Nitrogen (N2), oxygen (02), 

and argon (Ar) were measured using a thermalconductivity detector and pure helium gas as a 

carrier gas. Nitrogen, oxygen, and argon were analyzed at a U.S. Geological Survey laboratory in 

Reston, Va. Analytical errors are about ±0.004 ppm 

for SF6 in a concentration range of 0.5 to 1.5 ppm, 

±0.003 percent for C02 in a concentration range of 

0.01 to 0.10 percent by volume, 0.1 percent for N2 

and 02, and ±0.02 percent for Ar at atmospheric 

concentrations.

Samples for 5 13C were analyzed by mass 

spectrometry in the U.S. Geological Survey laboratory in Denver. The precision of 5 13C analysis was 

about ±0.2%o. Carbon-14 samples were sent to 

Geochron Laboratories (Krueger Enterprises, Inc.), 

Cambridge, Mass., for 14C determination by gas 

counting in a gas-proportional counter. Uncertainty 

in the 14C measurement was ±0.7 pmc. Conventional 

14C determination (proportional counting, or liquid 

scintillation counting) requires about 1 2 L of pure 

C02 gas at one atmosphere and 25°C. Analysis by 

TAMS method requires only 10-20 mL of C02 gas

Methods of Sample Collection and Analysis 11
at the same pressure and temperature; however, the 

cost of analysis is twice as great by TAMS than by 

the conventional method. Only a few samples from 

UZ 1 have been run by TAMS. Small 14C samples 

were sent to the University of Arizona in Tucson for 

analysis by TAMS. Uncertainty in the 14C measurement was ±1.5 pmc.

INTERPRETATION OF CHEMICAL AND 

ISOTOPIC DATA

Understanding the unsaturated-zone gas 

and water transport and flow mechanism at Yucca 

Mountain is essential to the site-characterization 

program. Chemical composition of pore water (which 

reflects the extent of water-rock interactions between 

the recharge water and the matrix rock), tritium, and 

14C ages, provide insight on the nature of flow mechanisms and residence times of the unsaturated-zone 

water. Carbon-14 concentration measurement in the 

gaseous phase can provide information relevant to the 

residence time of CC>2 in the unsaturated zone. Delta 

carbon-13 isotopic data can help to identify carbon 

sources, a necessary step in 14C age estimation. Also, 

a depth profile of gas carbon isotopic data can provide 

information on gas-flow mechanisms through the 

unsaturated zone as well as interactions with aqueous 

phase and calcite mineral. From the present chemical 

and isotopic data, along with previously published 

USW UZ-1 data collected at Yucca Mountain (Yang 

and others, 1993), preliminary conceptual hydrologicflow models are described.

Aqueous-Phase Data

Samples for aqueous-phase chemical data can 

only be acquired from drill cores where water contents 

are greater than 7.7% by weight (Mower and others, 

1994). The water contents of cores vary according to 

geologic unit and to degree of welding. As indicated 

in table 1 (Loskot and Hammermeister, 1992), the 

densely welded units sampled in UE-25 UZ#4 and 

UZ#5 have the smallest water contents, ranging 

from 2.4% to 6.4% (gram weight of f^O per gram of 

dry rock times 100) in the Tiva Canyon Tuff and 

ranging from 0.7% to 3.5% in the Topopah Spring 

Tuff. The nonwelded part of the Tiva Canyon Tuff 

had the largest water content of the nonwelded units 

sampled, with a maximum average water content of

36.3% in borehole UZ#4. Unnamed bedded tuff units 

generally have average water contents of about 16.7%. 

The Calico Hills Formation in USW UZ-14 has average water content of about 17.5%.

Pore-Water Chemistry

Water for chemical analyses was extracted 

from cores obtained from bedded tuff below the 

Pah Canyon Tuff in UE-25 UZ#4 at depths ranging 

from about 91 to about 100 m and from cores obtained 

near the top of the Topopah Spring Tuff in UZ#5 at 

depths ranging from about 103 to about 105 m. 

Thes^ data have been published previously (Yang 

and others, 1988; Yang, 1992). All other UZ-hole 

and NRG-hole pore-water compositions were obtained 

from nonwelded tuffs, bedded tuff, or the Calico Hills 

Formation because of higher moisture content in these 

units These data are presented in tables 2, 3, and 4 

for UEr-25 UZ#16, USW UZ-14, and USW NRG-6 

and NRG 7a, respectively. Also, precipitation 

(rainwater) near the neutron-access boreholes 

(UE-25 UZN#2) and ground water inside the neutronaccess boreholes (UEr-25 UZN#2 and USW UZN-46) 

were collected whenever water was detected at the 

bottom of the neutron-access boreholes (water was 

detected during the spring snowmelts or after the summer rainstorms). However, water inside the neutronaccess boreholes usually remained there only for a 

couple of days and then seeped into depth. Results of 

these chemical analyses are also presented in table 2 

for references.

Chemical changes induced by compression 

appear to be minor, as evidenced from results of compression and centrifugation-extraction procedures 

(Yang and others, 1990). Peters and others (1992) 

reported pore-water chemistry changes under greater 

compression loads. Complete analyses of major- and 

trace-element concentrations on individual samples 

were not possible because of limited volumes of water 

( 14C analysis requires about 70-80 mL of water for

each sample); only major ions were selected for the

chemical analyses.

A Piper diagram is a convenient graphical 

method for displaying the chemical composition of 

water. For example, in figure 5 it can be seen that 

major cations (sodium, calcium, and magnesium 

concentrations in percent milliequivalent) of one 

water sample are represented by one symbol in the 

lower left-hand side of the triangle, and major anions 

(chloride, sulfate, and bicarbonate plus carbonate in

12 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Table 1. Summary of relation of gravimetric water-content measurements of composite core to geologic unit and degree of 

welding for boreholes UE-25 UZ#4 and UE-25 UZ#5 1 , Yucca Mountain, Nevada

[All water-content data in gram per gram; .indicates no data]

Lithologic

unit

Tiva Canyon

Yucca Mountain

Pah Canyon

Bedded tuff

Topopah Spring

Water content, 

gram/gram

UE-25 UZ#4

Data range

0.036-0.0642

0.061-0.063

0.253-0.521

0.101-0.210

0.092-0.182

0.069-0.391

--

0.007-0.035

Average

0.039

0.062

0.363

0.157

0.134

0.167

--

0.020

UE-25 UZ#5

Data range

0.024-0.036

--

0.145-0.290

0.059-0.143

0.084-0.221

0.078-0.365

0.221-0.279

0.011-0.015

Average

0.030

--

0.202

0.110

0.122

0.176

0.248

0.013

Degree of

welding

Densely welded

Moderately welded

Partly to nonwelded

Partly to nonwelded

Partly to nonwelded

Nonwelded

Densely welded

'From Loskot and Hammermeister (1992).

percent milliequivalent per liter) of the same sample 

are also represented by the same symbol in the 

lower right-hand side of the triangle. When these two 

major cation and anion locations are projected upward 

parallel to their respective grids, they intersect at 

one point in the upper diamond diagram and are represented by the same symbol for both major cation and 

anion compositions of that sample. The locations in 

the diamond diagram represent the type of water 

composition for each sample. Calcium chloride or 

sulfate type water formed from recharging water interacting with near-surface or shallow-depth soils will be 

located near the top part of the diamond. The ground 

water that has interacted with deep Calico Hills 

Formation rocks will result in sodium carbonatebicarbonate type water located near the lower part 

of the diamond. The middle part of the diamond will 

represent intermediate chemical compositions for 

ground water in the Topopah Spring Tuff. Dissolved 

solids in pore water expressed in parts per million are 

represented by the circle size with the scale shown in 

figures.

Figures 5, 6A and 6B, and 7A and 7B are Piper 

diagrams for (1) the top 75 m (245 ft) of USW UZ-14 

and saturated-zone chemical data; (2) USW NRG-6 

and NRG-7a and lithologic contacts and adjacent 

beds; and (3) USW UZ-14 and UE-25 UZ#16. 

Figure 5 shows saturated-zone water chemistry 

(Benson and McKinley, 1985) compared to the 

composition of unsaturated-zone pore water in the 

top 75 m of USW UZ-14, between the Tiva Canyon

Tuff and pre-Pah Canyon bedded tuff. It is evident 

from the plot that dissolved solids are, in most cases, 

significantly higher in the unsaturated-zone pore water 

than in the saturated-zone ground water except in 

some saturated-zone carbonate aquifers, where both 

are about the same. This comparison is based on 

saturated-zone chemical-composition data that were 

collected prior to implementation of the approved 

U.S. Geological Survey Yucca Mountain Project 

quality-assurance program and, therefore, the data 

are not qualified. Furthermore, pore water in the 

Tiva Canyon, bedded tuff, and Pah Canyon tuffs are 

all grouped near the top of the diamond in the Piper 

diagram (that is, calcium sulfate or chloride type 

water), whereas saturated-zone ground waters are 

grouped near the bottom of the diamond (that is, 

sodium bicarbonate or carbonate type water). The 

composition of pore water from NRG-6 and NRG-7a 

boreholes is given in figure 6A; pore-water composition of lithologic contacts and adjacent beds is given in 

table 5 and in figure 6B. In figure 6A, sample G represents core obtained from borehole NRG-6 at a depth 

of 256 feet. The location of this core is in the upper 

Topopah Spring Tuff and contains about 3,500 mg/L 

in dissolved solids. It is too deep in the borehole to be 

explained as a result of surface evaporation. Rather, 

such a large value of dissolved solids probably 

resulted from prolonged contact of percolating water 

with the less permeable silicate rocks without replacement by fresher, younger water.

Interpretation of Chemical and Isotopic Data 13
Table 2. Chemical composition of pore-water and ground-water samples from boreholes UE-25 UZ#16, UE-25 UZ N2, and 

UZ N46, Yucca Mountain, Nevada

[|u,S/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -, data not available; 0, values below detection limit; <, less than; 

*, contamination with sodium chloride during water-level measurement (accidentally dropped the measuring tape coated with sodium chloride); charge 

balance, (rnilliequivalent cation - milliequivalent anion)/(milliequivalent cation + milliequivalent anion) times 100]

Sample 

Identification

UZ-N2 Precip

UZ-N2 Water

UZ-^2 Water

UZHN2 Water

UZ-N2 Water

UZ-^46 Water

UZ 16 Pore water

UZ-16/163.5-163.9

UZ-1 6/1 80.9-1 8 1.3

UZ-1 6/1 166.19-1 166.47

UZ-1 6/1 227.4-1 227.7

UZ-1 6/1 235. 1-1 235.41

UZ-1 6/1 269.6-1 269.9

UZ-1 6/1 280.4-1 280.8

UZ-1 6/1 296.8-1 297.06

UZ-1 6/1317.9-1318.2

UZ-1 6/1 343.7-1 344.0

UZ-1 6/1 358.0-1 358.4

UZ-16/1379.6-1379.9

UZ-1 6/1 389.3-1 389.6

UZ-1 6/1395.5-1395.9

UZ-1 6/1 397.7-1 398.0

UZ-1 6/1 398.5-1 398.7

UZ-1 6/1408.2-1408.6

UZ-1 6/1412.9-1413.2

UZ-1 6/1428. 1-1428.4

UZ-1 6/1434.2-1 434.6

UZ-1 6/1442.8-1 443.2

UZ-1 6/1 486.9-1 487.3

UZ-1 6/1 601. 1-1 601. 5

UZ-1 6/1 607.7-1 608.1

UZ-1 6/1 643.4-1 647.2

UZ-1 6/1 65 1.6-1 65 1.7

UZ 16 ground water #1

(1609.0-1614.0)

UZ 1 6 ground water #2

(1609.0-1614.0)

UZ 1 6 ground water #3

(1609.0-1614.0)

Symbol 

in Piper 

diagram 

(fig. 7B)

...

...

...

...

...

1

2

3

4

5

6

7

8

9

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

R

...

...

Average 

depth 

(meters)

0

15.8

15.8

15.8

15.8

30.1

49.90

55.20

367.74

374.17

376.52

387.04

390.33

395.33

401.76

409.62

413.98

420.56

423.52

425.41

426.08

426.29

429.28

430.71

435.35

437.21

439.83

453.27

488.08

490.09

501.49

503.44

491.19

491.19

491.19

Date

03-31-92

08-18-89

02-14-92

03-16-92

03-31-92

02-14-92

12-02-92

11-16-92

09-27-94

08-09-93

08-1 1-93

08-04-93

09-02-93

09-23-93

09-09-93

07-01-93

05-06-93

06-29-93

05-18-93

03-31-94

07-07-93

04-05-94

07-28-93

09-16-93

09-14-93

07-13-93

06-17-93

09-21-93

12-30-93

01-24-94

03-01-94

03-15-94

02-24-93

02-25-93

02-25-93

PH

...

7.7

...

...

7.6

7.5

8.7

8.1

8.2

8.5

8.3

7.4

7.3

8.4

7.5

8.6

7.0

7.8

8.7

8.0

9.2

8.7

8.8

8.5

7.6

9.2

8.9

9.0

9.0

8.4

...

...

Specific Calcium 

:onductance Ca

(nS/cm) (mg/L)

...

308

...

...

...

425

430

710

430

480

430

530

930

420

530

550

490

530

710

550

710

580

450

570

550

550

360

570

660

490

420

...

...

...

0.7

14

1.4

14.4

25

0.8

42.5

55

28.9

26.5

33.5

14.1

20.5

32.4

20.6

17

3.4

4.4

3.6

5.4

5

5

3.3

1.2

1.9

3.2

1.7

6.3

10

25

91

17.3

11.4

19.2

30.1

Magnesium Sodium 

Mg Na

(mg/L) (mg/L)

0.5

2.3

0.5

3.9

4.7

0.5

13.4

11

13.7

6.2

7.9

2.4

3.7

19.7

5.1

2.4

0.3

0.6

0.9

0.3

0.5

0.4

0.3

0.1

0.1

0.6

0.8

0.8

0.3

0.3

12

0.3

1.6

2.1

2.9

0.8

51

1.7

25

16

1

21

20

1

2

6

5

83.6

47.9

51.3

67 5

92.0

98 2

60.1

99

76.7

95

114.6

155

124

145

104

101

134

113

79.9

79.5

100

108

34

66

79.2

175 1*

360.5*

Silica 

SiO2 

(mg/L)

0.9

18

0

5.8

11.8

0.2

77.5

83

57.1

62.2

52.9

57.1

71.8

46.7

131.6

62.1

47.9

66.3

62.5

88.0

79.2

123

68.5

75.9

80.5

109.1

68.9

233.3

36

34

70

47.4

36.2

25.5

27.2

14 Interpretation of Chemical and Isotopic Data From Boreholes in tho Unsaturated Zone at Yucca Mountain, Nevada
Table 2. Chemical composition of pore-water and ground-water samples from boreholes UE-25 UZ#16, UE-25 UZ-N2, and 

UZ N46, Yucca Mountain, Nevada Continued

[|LiS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -, data not available; 0, values below detection limit; <, less than; 

*, contamination with sodium chloride during water-level measurement (accidentally dropped the measuring tape coated with sodium chloride); charge 

balance, (milliequivalent cation - milliequivalent anion)/(milliequivalent cation + milliequivalent anion) times 100]

Sample 

identification

UZr-16 ground water #1 

(1649.3-1659.2) 

UZ 16 ground water #2 

(1649.3-1659.2) 

UZ 16 ground water

(1649.3-1686.2)

Sampie 

identification

UZ-N2 Precip

UZ-N2 Water

UZ-N2 Water

UZ-^Sf2 Water

UZ-N2 Water

UZ-N46 Water

UZ 1 6 Pore water

UZ-1 6/1 63.5-1 63.9

UZ-1 6/1 80.9-1 8 1.3

UZ-1 6/1 166. 19-1 166.47

UZ-1 6/1 227.4-1 227.7

UZ-16/1235.1-1235.41

UZ-1 6/1 269.6-1 269.9

UZ-1 6/1 280.4-1 280.8

UZ-1 6/1 296.8-1 297 .06

UZ-16/1317.9-1318.2

UZ-16/1343.7-1344.0

UZ-16/1358.0-1358.4

UZ-1 6/1 379.6-1 379.9

UZ-1 6/1 389.3-1 389.6

UZ-16/1395.5-1395.9

UZ-1 6/1397.7-1 398.0

UZ-16/1398.5-1398.7

UZ-1 6/1408.2-1408.6

UZ-1 6/14 12.9-14 13.2

UZ-1 6/1428. 1-1428.4

UZ-1 6/1434.2-1434.6

UZ-1 6/1442.8-1443 .2

UZ-1 6/1486.9-1487.3

UZ-16/1601. 1-1601.5

UZ-1 6/1 607.7-1 608.1

UZ-1 6/1 643 .4-1 647.2

Symbol in Piper ****£* 

diagram , *? * x Date "H <fig7B) <meters)

Specific Calcium Magnesium Sodium Silica 

conductance Ca Mg Na SIO2 

(nS/cm) (mg/L) (mg/L) (mg/L) (mg/L)

504.22 03-08-93 

504.22 03-09-93

508.33 03-15-93

Aluminum Al"

(mg/L)

0

...

0

0.0

0

0.0

0.5

0.1

0

0.3

0

0

1.5

0

1.1

1.7

1.1

2.6

2.0

3.9

4.7

7.8

3.4

1.0

3.4

6.1

1.2

26.2

0.7

1.0

3

Bicarbonate 

HC03 

(mg/L)

23.3

112

11.7

58.2

127.6

23.3

114.7

120

196

137.0

154

139

192.0

324

171

47.6

140.3

72

122

216.0

131.8

237.0

72

165.0

160.0

72

18.3

137.0

181.0

170.0

162.0

Carbonate 

C03

(mg/L)

0

0

0

0

0

0

45.0

0.0

0

0

0

13

0

12

0

58.8

0

46.8

36.0

24.0

35.4

31.0

70.8

0

43.0

70.8

87.6

0

0

0

0

Chiorine 

Cl

(mg/L)

2.4

10

12.2

10

5.8

3.3

32.4

38

82

24

52

27

28

50

32

56

22.8

21

23.5

17

45

14

20

26

23

23

18.9

38

53

71

70

10.3 

8.6

8.4

Bromine 

Br

(mg/L)

0

0.54

0

1.7

0.9

0

0.0

<1

0

0

0

0

0

0

0

0.0

0.0

0.0

0.0

0

0.0

0

0.0

0

0

0.0

0.0

0

0

0

0

1.8 

0.7

1.3

Nitrate 

N03

(mg/L)

2

...

8.2

27.3

19.7

1.6

23.1

33

17

23

26

18

19

19

20

18

16.1

18

18.5

16

25

16

14

24

19

16

11.3

6

13

10

8

76.1 

65.4

87.2

Sulfate 

SO4

(mg/L)

4.1

29

7.8

21

15.6

4.7

72.3

38

28

26

29

14

19

18

18

23

18.7

25

23.8

22

45

20

16

30

23

19

13.7

11

27

33

28

170.6 

18.4

16.5

Charge 

balance

-0.5

0.4

-0.6

0.0

-0.6

-0.5

-2.0

0.2

-1.4

1.2

-4.7

-2.7

6.9

-1.9

^.0

6.5

-0.1

0.3

0.6

11.9

-0.3

4.8

0.1

0.1

3.9

0.3

-0.6

2.7

-3.6

2.8

13.6

Interpretation of Chemical and Isotopic Data 15
Table 2. Chemical composition of pore-water and ground-water samples from boreholes UE-25 UZ#16, UE-25 UZ-N2, and 

UZ-N46, Yucca Mountain, Nevada Continued

[US/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -, data not available; 0, values below detection limit; <, less than; 

*, contamination with sodium chloride during water-level measurement (accidentally dropped the measuring tape coated with sodium chloride); charge 

balance, (milliequivalent cation - milliequivalent anion)/(milliequivalent cation + milliequivalent anion) times 100]

Sample 

Identification

UZ-16/165 1.6-1 651.7 

UZ-16 ground water #1 

(1609.0-1614.0) 

UZ-1 6 ground water #2 

(1609.0-1614.0) 

UZ- 1 6 ground water #3 

(1609.0-1614.0) 

UZ-16 ground water #1 

(1649.3-1659.2) 

UZ-16 ground water #2 

(1649.3-1659.2) 

UZ-16 ground water 

(1649.3-1686.2)

Aluminum 

Al** 

(mg/L)

0.7 

1.2 

0 

0.2 

19.9 

0 

0.1

Bicarbonate 

HC03 

(mg/L)

87.0 

210.6 

196.7 

200.0 

164.2 

151.6 

197.3

Carbonate 

C03 

(mg/L)

19.0 

0 

0 

0 

0 

0 

0

Chlorine 

Cl 

(mg/L)

27 

10.6 

188.0* 

488* 

13.4 

10.6

8.6 i.., 

Bromine 

Br 

(mg/L)

0 

0.6 

0.6 

0.7 

0 

0 

1

Nitrate

NOg

(mg/L)

6 

0.2 

0 

0.5 

0.3 

0 

0

Sulfate 

SO4 

(mg/L)

20 

29.1 

31.8 

34.6

27.7 

25.5 

27.7

Charge 

balance

6.1 

-0.2 

-0.4 

-0.3 

0.3 

0.0 

0.3

Table 3. Chemical composition of pore-water samples from borehole USW UZ 14, Yucca Mountain, Nevada

[US/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -, data not available; 0, values below detection limit; <, less than; 

N/S, not sampled; N/A, not analyzed; upl, uniaxial pressure stage #1; charge balance, (milliequivalent cation - milliequivalent anion)/(milliequivalent 

cation + milliequivalent anion) times 100]

Sample 

Identification

UZ-14/45.(M5.4/upl 

UZ-14/85.2-85.6/upl

UZ-14/91.0-91.3/upl

UZ-14/95.5-95.9/upl

UZ-14/96.2-96.6/upl

UZ-14/1 00.4-1 00.8/upl

UZ-14/114.8-115.0/upl

UZ-l4/135.5-135.8/upl

UZ-14/144.8-145.2/upl

UZ-14/147.7-148.1/upl,2

UZ-14/1 77.6-1 77.9/upl

UZ-14/1 78. 1-1 78.4/upl

UZ-14/215.7-216.1/up2

UZ-14/225.9-226.2/upl

UZ-14/235.1-235.4/upl

UZ-14/240.8-241.1/upl

UZ-14/245.5-245.8/upl

UZ-14/ 1 258.5-1 258.8/up Ivb

UZ-14/ 1 277.4-1 277 .7/up 1

UZ-1 4/ 1 277.7-1 278.0/up 1

UZ-14/ 1409.4-1409.8/up 1

f*LM Average '" Plper depth 

diagram . r v <fig%B) (meters)

1 

2

3

4

5

6

7

8

9

A

B

C

D

E

F

G

H

I

J

K

L

13.78 

26.03

27.80

29.17

29.38

30.66

35.02

41.36

44.20

45.08

54.19

54.35

65.81

68.92

71.72

73.46

74.89

383.65

389.41

389.50

429.65

Date

09-19-94 

03-24-94

03-17-94

04-21-94

05-03-94

03-22-94

09-01-94

04-12-94

08-11-94

04-14-94

09-12-94

04-19-94

04-21-94

10-31-94

03-02-94

03-02-94

02-07-94

01-14-94

01-14-94

01-14-94

01-30-95

pH

8.6 

6.9

7.6

7.2

6.9

7.0

6.6

6.9

7.7

6.9

6.5

6.8

6.9

7.9

7.1

7.6

6.8

...

N/A

N/A

7.8

Specific Calcium 

conductance Ca 

(nS/cm) (mg/L)

1,320 

630

530

600

550

600

540

690

650

640

730

740

710

640

630

810

580

...

N/A

N/A

720

19.6 

49.9

40.7

53.3

46.9

51.1

49.0

68.5

65.5

54.8

67.8

64.0

65.5

58.6

67

32

65

43

62

74

30.0

Magnesium 

Mg 

(mg/L)

6.1 

13.2

10.1

13.2

12.7

13.8

10.5

14.3

12.0

11.5

11.3

10.6

10.7

10.4

10.5

1

12

3.7

4.5

5.1

0.7

Sodium 

Na 

(mg/L)

249.3

43.5

37.1

38.1

33.6

41.3

35.9

56.2

48.2

51.6

48.7

49.1

39.4

48.4

29

103

9

67

49

45

88.0

Silica 

SIO2 

(mg/L)

59.5 

89.8

80.6

81 .5

79.6

91 .8

93.9

92.0

81 .5

77.3

77

93

.5

.1

97.8

91

63

61

46

35

44

38

.2

57.0

I

16 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Table 3. Chemical composition of pore-water samples from borehole USW UZ-14, Yucca Mountain, Nevada Continued

I^S/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -. data not available; 0, values below detection limit; <, less than; 

N/S, not sampled; N/A. not analyzed; up], uniaxial pressure stage #1; charge balance, (milliequivalent cation - milliequivalent anion)/(milliequivalent 

cation + milliequivalent anion) times 100]

Sample 

Identification

UZ-1 4/14 19.5-14 19.8/upl

UZ-1 4/1 46 1.9-1 462.1 /up 1

UZ-14/1495.8-1496.0/upl

UZ-1 4/1 524.55-1 524.75/up 1

UZ-1 4/1 542.3-1 542.8/up 1 ,2,3

UZ-14/1563.6-1563.8/upl,2,3

UZ-1 4/1 564.6-1 564.8/up 1 ,2,3

UZ- 14/1 564.9-1 565.0/upl

UZ-1 4/1 585.0-1 585.2/upl

UZ-14/1585.3-1585.6/upl,5

UZ-14/1605.9-1606.1/upl

UZ-14/1 644.3-1 644.5/up 1

UZ-14/1674.8-1675.1/upl

UZ-1 4/ 1 695 .4-1 695 .6/up 1

UZ-14/1715.0-1715.3/upl

UZ-1 4/1 734.5-1 734.7/upl

UZ-1 4/2 104.05/well bottom

Sample 

Identification

UZ-1 4/45. 0-45.4/upl

UZ-14/85.2-85.6/upl

UZ-1 4/91. 0-9 1.3/upl

UZ-1 4/95. 5-95.9/upl

UZ-14/96.2-96.6/upl

UZ-14/100.4-100.8/upl

UZ-14/1 14.8-1 15.0/upl

UZ-14/135.5-135.8/upl

UZ-14/144.8-145.2/upl

UZ-14/147.7-148.1/upl,2

UZ-14/177.6-177.9/upl

UZ-14/178.1-l78.4/upl

UZ-14/215.7-216.1/up2

UZ-1 4/225. 9-226.2/upl

UZ-14/235.1-235.4/upl

UZ-1 4/240.8-24 1.1 /up 1

UZ-14/245.5-245.8/upl

UZ-1 4/1 258.5-1 258.8/up 1 vb

UZ-14/1 277.4-1 277.7/upl

UZ-1 4/ 1 277.7-1 278.0/up 1

UZ-1 4/ 1 409.4-1 409. 8/up 1

UZ-14/1419.5-1419.8/upl

UZ-14/1461.9-1462.1/upl

UZ-14/1495.8-1496.0/upl

Symbol 

in Piper 

diagram 

(fig.7B)

M

N

0

P

R

S

T

U

V

w

X

Y

Z

$

&

*

+

Average 

depth Date 

(meters)

432.72 12-22-94

445.62 04-04-95

455.95 04-11-95

464.73 04-14-95

470.18 07-25-94

476.62 08-30-94

476.92 08-23-94

477.01 08-17-94

483.14 09-14-94

483.23 10-03-94

489.51 10-07-94

501.21 01-19-95

510.54 10-24-94

516.79 12-29-94

522.79 03-28-95

528.71 05-02-95

641.33 04-22-94

pH

8.3

7.6

8.4

7.7

8.6

8.7

9.0

8.3

8.9

9.3

8.9

8.8

7.2

7.9

7.3

8.7

9.4

Aluminum Bicarbonate Carbonate 

Al* HCO3 C03 

(mg/L) (mg/L) (mg/L)

1

0.3

0.0

0

0

0.0

0

0

0

0

0

0

0

0

0.0

3

0

0.0

0.0

0.0

0.1

1.4

1.2

0.3

245

131

87

73

79

128

67

105

118

79

49

62

55

55

96

162

66

170

170

170

160

166

265

228

18

0

0

0

0

0

0

0

0

0

0

0

0

0

N/S

N/S

N/S

N/S

N/S

N/S

0

0

0

0

Specific 

conductance

(nS/cm)

410

570

500

560

760

660

590

690

460

400

470

420

N/S

N/A

390

750

...

Calcium 

Ca 

(mg/L)

20.0

9.2

2.1

1.1

3.6

1.2

1.3

1.7

0.9

1.2

1.0

2.2

1.8

1.4

0.2

2.0

2.1

Chlorine Bromine 

Cl Br 

(mg/L) (mg/L)

245

60

47

79

59

44

61

83

77

83

100

97

85

93

84

99

77

88

87

130

75

24

24.2

28.0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0.0

0.0

0

0

Magnesium Sodium 

Mg Na 

(mg/L) (mg/L)

0.6

0.1

0.0

0.1

0.5

0.2

0.2

0.5

0.3

0.5

0.3

0.7

0.6

1.1

0.0

0.3

0.7

Nitrate 

N03

(mg/L)

35

22

26

29

26

23

25

23

22

22

23

21

14

16

15

17

12

16

17

15

5

6

6.2

10.8

68.0

128

122

137

207

155.0

129

169.0

106.8

85.0

87.8

110.0

58.0

115.8

88

184

143

Sulfate 

SO4

(mg/L)

33

66

81

83

75

83

90

96

102

102

130

120

130

116

94

100

79

19

45

38

106

21

37.3

14.3

Silica 

SI02 

(mg/L)

60.0

68.7

56.7

54.8

143.0

72.0

140.4

54.0

74.5

75.0

67.2

74

64.6

55.9

52.9

50.7

352

Charge 

balance

-1.8

-0.9

^.1

-1.9

-0.9

0.5

-2.1

4.6

-1.7

-1.5

-2.0

-3.0

-3.0

-2.6

-5.7

-11.7

-4.7

-4.9

-7.1

-10.3

-13.2

1.0

1.1

3.9

Interpretation of Chemical and Isotopic Data 17
Table 3. Chemical composition of pore-water samples from borehole USW UZ 14, Yucca Mountain, Nevada Continued

[|j.S/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -, data not available; 0, values below detection limit; <, less than; 

N/S, not sampled; N/A, not analyzed; upl, uniaxial pressure stage #1; charge balance, (milliequivalent cation - milliequivalent anion)/(milliequivalent 

cation + milliequivalent anion) times 100]

Sample 

Identification

UZ-14/1524.55-1524.75/upl 

UZ-14/1 542.3-1 542.8/up 1 ,2,3 

UZ-14/1563.6-1563.8/upl,2,3 

UZ-14/1 564.6-1 564.8/up 1 ,2,3

UZ-14/1 564.9-1 565.0/up 1

UZ-14/1 585.0-1 585 2/upl

UZ-14/1 585.3-1 585.6/up 1,5

UZ-14/1605.9-1606 1/upl

UZ-14/ 1 644.3-1 644.5/up 1

UZ-14/1674.8-1675 1/upl

UZ-14/1 695.4-1 695.6/up 1

UZ-14/1715.0-1715.3/upl

UZ-14/1734.5-1734.7/upl

UZ-14/2104.05/well bottom

Aluminum Al* 

(mg/L)

1.1 

13.8 

13.9 

9.4

15.5

5

16.3

6

30.9

18

10

0.6

0.1

38

Bicarbonate 

HC03 

(mg/L)

232 

384 

160 

61

376

98

148

178

74.0

104

203

168

211

229

Carbonate 

C03 

(mg/L)

0 

46

97 

113

0

67

18

0

79

0

18

0

79

19

Chlorine 

Cl 

(mg/L)

26.2 

20 

16 

16

23

14

11

18

14

10

21

11.9

39.4

10

Bromine 

Br 

(mg/L)

0 

0 

0.0 

0

0.0

0

0.0

0

0.0

0

0

0

0

0

Nitrate 

N03 

(mg/L)

12.5 

4 

4 

4

1

7

6

6

0

4

5

3.1

5.6

4

Sulfate 

SO4 

(mg/L)

22.3 

28 

14 

17

30

10

9

9

9

9

26

16.0

17.5

23

Charge 

balance

7.2 

1.0 

1.2 

0.4

0.1

1.6

2.4

2.4

5.5

8.6

0.6

5.1

2.9

10.1

*0.45-|^m filter paper was used; hence, particulate aluminum is likely included in these values.

Table 4. Chemical composition of pore-water and ground-water samp as from borehole NRG-6/7a, Yucca Mountain, Nevada

microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; } - -, data not available; 0, values below detection limit; upl, uniaxial 

pressure stage #1; charge balance, (milliequivalent cation -milliequivalent anion)/( milliequivalent cation + milliequivalent anion) times 100]

Sample 

Identification

NRG-6/158.2-158.6/upl 

NRG-6/160.8-161.2/upl

NRG-6/171.0-171.3/upl

NRG-6/175.6-176.0/upl

NRG-6/2 1 9.9-220.2/up 1

NRG-6/244.6-245.0/UP 1

NRG-6/255.9-256. 1/upl

NRG-7a/1492.7-1493. I/up 1

NRG-7/1498.6-1498.9/upl

Sample 

Identification

NRG-6/158.2-158.6/upl

NRG-6/1 60.8-1 6 1.2/upl

NRG-6/171.0-171.3/upl

NRG-6/1 75.6-1 76.0/upl

NRG-6/2 1 9.9-220.2/up 1

NRG-6/244.6-245.0/UP 1

NRG-6/255.9-256. 1/upl

NRG-7a/1492.7-1493. 1/upl

NRG-7/1498.6-1498.9/upl

Symbol 

in Piper 

diagram 

(fig.7B)

A 

B

C

D

E

F

G

H

I

Silica 

SiOz 

(mg/L)

97.4

84.0

79.4

78.1

61.4

51.0

68.0

71.5

83.0

Average 

depth 

(meters)

48.28 

49.07

52.18

53.58

67.09

74.62

78.03

455.04

456.83

Aluminum 

Al 

(mg/L)

0

1.6

0

0

1

0.6

0.9

0.0

1

Date p

07-06-94 6 

01-17-95 7

07-21-94 7

08-01-94 6

Specific 

H conductance

(pS/cm)

4 

0

0

6

11-30-94 7JO

01-10-95 6J6

01-12-95 6,7

05-26-94

06-28-94 7,5

Bicarbonate Carbonate 

HCCv, [CO, 

(mg/L) (ta/L)

34 0

55 0

48 13

60 0

92 0

61 0

61 ; 0

104

156

34

0

1070 

860

620

520

660

630

1920

...

500

Chlorine 

Cl 

(mg/L)

185

148

58

47

77

49

115

39

50

Calcium Magnesium 

Ca Mg 

(mg/L) (mg/L)

122 

104

70.5

49.2

24.3

33

176

30.6

28.7

Bromine 

Br 

(mg/L)

1

0.9

0

0

0

0.1

0.0

0

0

23.3 

18

11.5

8.6

4.2

4.9

19

0.3

0.5

Nitrate 

N03 

(mg/L)

32

35

43

42

47

40

35

18

17

Sodium 

Na 

(mg/L)

35.6 

35.0

29.2

29.4

99.3

72.0

215.0

74.7

73.2

Sulfate 

S04

(mg/L)

159

139

94

64

77

115

840

23

18

18 Interpretation of Chemical and Isotopic Data From Boreholes in the) Unsaturated Zone at Yucca Mountain, Nevada
0 1000 2000 3000 4000 5000

I I I I I I CIRCLE DIAMETER =TOTAL DISSOLVED

SOLIDS, IN PARTS PER MILLION

60 -< 40 

Calcium (Ca)

20 Na+K HC03+C03 20

PERCENTAGE OF MILLIEQUIVALENTS PER LITER

40 >- 60 

Chlorine (Cl)

80 Cl

I J12 

J J13

K UE-25B#1 

L UE-25C#1 

M UE-25P1

UE-29A2 

USW-G-4 

USW-H-1 

USW-H-3 

USW-H4

EXPLANATION

T USW-H5 

u USW-H6 

v USW-VH-1

1 UZ-14 (45.2 feet)

2 UZ-14 (85.4 feet)

3 UZ-14 (91.2 feet)

4 UZ-14 (95.7 feet)

5 UZ-14 (96.4 feet)

6 UZ-14 (100.6 feet)

7 UZ-14 (114.9 feet)

8 UZ9 UZ

A UZB UZ

c UZD UZE UZ

F UZG UZH UZ14 (135, 

14 (145, 

14 (147, 

14(177, 

14 (178, 

14 (215, 

14 (226, 

14 (235, 

14 (241, 

14 (245,

7 feet) 

0 feet) 

9 feet) 

8 feet) 

3 feet) 

9 feet) 

0 feet) 

3 feet) 

Ofeet) 

7 feet)

Figure 5. Piper diagram showing top 75 meters of USW UZ-14 pore water (1-9, and A-tH) and saturated-zone 

water compositions (I-V).

Interpretation of Chemical and Isotopic Data 19
A.

0 1000 2000 3000 4000 5000

I I I I I I CIRCLE DIAMETER =TOTAL DISSOLVED

SOLIDS, IN PARTS PER MILLION

60 -< 40 

Calcium (Ca)

40 >- 60 

Chlorine (CD

PERCENTAGE OF MILLIEQUIVAljNTS PER LITER

EXPLANATION

A NRG-6 (158.2-158.6 feet)

B NRG-6 (160.8-161.2 feet)

c NRG-6 (171.0-171.3 feet)

D NRG-6 (175.6-176.0 feet)

E NRG-6 (219.9-220.2 feet)

F NRG-6 (244.6-245.0 f.jet)

G NRG-6 (255.9-256.1 faet)

H NRG-7a (1492.7-1493.1 feet)

i NRG-7a (1498.6-1498.9 feet)

Figure 6. Piper diagram showing (A) USW NRG-6 and 7a pore-water composition, and (B) composition of 

lithologic contacts and adjacent beds from USW NRG-6, 7a, and unsaturated-zone boreholes.

i 20 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
0 1000 2000 3000 4000 5000

I I I I I I CIRCLE DIAMETER =TOTAL DISSOLVED

SOLIDS, IN PARTS PER MILLION

Ca 80 60 -< 40 

Calcium (Ca)

40 >- 60 

Chlorine (CD

20 Na+K HCO3+CO3 20 80

PERCENTAGE OF MILLIEQUIVALENTS PER LITER

EXPLANATION

1 NRG-6 (158.2-158.6 feet) [SHARDY/BED]

2 NRG-6 (171.0-171.3 feet) [BED]

3 NRG-6 (175.6-176.0 feet) [PAH]

4 UZ-14 (235.1-235.4 feet) [PAH]

5 UZ-14 (240.8-241.1 feet) [PAH-BED]

6 UZ-14 (245.5-245.8 feet) [BED]

7 UZ-16 (1434.2-1434.6 feet) [CH]

s UZ-16 (1442.8-1443.2 feet) [CH]

A UZ-16 (1486.9-1487.3 feet) [CH-PROW]

B UZ-16 (1604.1-1605.1 feet) [PROW]

Figure 6. Piper diagram showing (A) USW NRG-6 and 7a pore-water composition, and (B) composition of 

lithologic contacts and adjacent beds from USW NRG-6, 7a, and unsaturated-zone boreholes Continued.

ci

Interpretation of Chemical and Isotoplc Data 21
©

0 1000 2000 3000 4000 5000

I I I I I I CIRCLE DIAMETER =TOTAL DISSOLVED 

SOLIDS, IN PARTS PER MILLION

Ca 80 60 -< 40 

Calcium (Ca)

20 Na+K HCOs+CQs20 40 >- 60

Chlorine (Cl)

PERCENTAGE OF MILLIEQUIVALENTS PER LITER

80 Cl

	EXPLANATION

E UZ-14 (226.1 feet)

F UZ-14 (235.3 feet)

G UZ-14 (241.0 feet)

H UZ-14 (245.7 feet)

i UZ-14 (1258.7 feet)

J UZ-14 (1277.6 feet)

K UZ-14 (1277.9 feet)

L UZ-14 (1409.6 Feet)

M UZ-14 (1419.7 Feet)

N UZ-14 (1462.0 Feet)

o UZ-14 (1495.9 Feet)

P UZ-14 (1524.7 Feet)

R UZ-14 (1542.6 feet)

Figure 7. Piper diagram showing pore-water composition of (A) USW UZ 14 and (B) UE-25 UZ#16.

1

2

3

4

5

6

7

8

9

A

B

C

D

UZ-14 (45.2 feet)

UZ-1 4 (85.4 feet)

UZ-14 (91. 2 feet)

UZ-14 (95.7 feet)

UZ-14 (96.4 feet)

UZ-14 (100.6 feet)

UZ-1 4 (11 4.9 feet)

UZ-14 (135.7 feet)

UZ-14 (145.0 feet)

UZ-14 (147.9 feet)

UZ-14 (177.8 feet)

UZ-14 (178.3 feet)

UZ-14 (215.9 feet)

s

T 

U 

V

w

X 

Y

z 

$ 

&

+

UZ-14 (1563.7 feet) 

UZ-14 (1564.7 feet) 

UZ-14 (1565.0 feet) 

UZ-14 (1585.1 feet) 

UZ-14 (1585.5 feet) 

UZ-14 (1606.0 feet) 

UZ-14 (1644.4 feet) 

UZ-14 (1675.0 feet) 

UZ-14 (1695.5 feet) 

UZ-14 (1715.2 feet) 

UZ-14 (1734.6 feet) 

UZ-14 (2104.1 feet)

22 Interpretation of Chemical and Isotopic Data From Boreholes In th< Unsaturated Zone at Yucca Mountain, Nevada
0

1000

I

2000

I

3000 4000

I

5000

CIRCLE DIAMETER =TOTAL DISSOLVED 

SOLIDS, IN PARTS PER MILLION

Ca 80 60 -< 40 

Calcium (Ca)

20 Na+K HCOs+COs 20 

PERCENTAGE OF MILLIEQUIVALENTS PER LITER

40 >~ 60 

Chlorine (CD

EXPLANATION

UZ#16 (163.7 feet) E

UZ#16 (181.1 feet) F

UZ#16 (1166.3 feet) G

UZ#16 (1227.6 feet) H

UZ#16 (1235.3 feet) i

UZ#16 (1269.8 feet) J

UZ#16 (1280.6 feet) K

UZ#16 (1296.9 feet) L

UZ#16 (1318.1 feet) M

UZ#16 (1343.9 feet) N

UZ#16 (1358.2 feet) o

UZ#16 (1379.8 feet) P

UZ#16 (1389.5 feet) R

UZ#16 (1395.7 feet) 

UZ#16 (1397.9 feet) 

UZ#16 (1398.6 feet) 

UZ#16 (1408.4 feet) 

UZ#16 (1413.1 feet) 

UZ#16 (1428.3 feet) 

UZ#16 (1434.4 feet) 

UZ#16 (1443.0 feet) 

UZ#16 (1487.1 feet) 

UZ#16(1601.3feet) 

UZ#16 (1607.9 feet) 

UZ#16 (1645.3 feet) 

UZ#16(1651.7feet)

Figure 7. Piper diagram showing pore-water composition of (A) USW UZ-14 and (B) UE-25 UZ#16 Continued.

Interpretation of Chemical and Isotopic Data 23
Table 5. Comparison of pore-water composition in lithologic contacts arid adjacent beds, Yucca Mountain, Nevada

[m, meters; mg/L, milligrams per liter]

Sample 

identification

NRG-6/1 58.2-1 58.6 (Shardy base/bedded)

NRG-6/ 1 7 1 .0-1 7 1 .3 (Bedded)

NRG-6/1 75.6-176.0 (Pah Canyon)

UZ- 14/235. 1-235.4 (Pah Canyon)

UZ- 14/240.8-24 1 . 1 (Pah Canyon/Bedded)

UZ- 14/245.5-245.8 (Bedded)

UZ- 16/1 434.2-1 434.6 (Calico Hills)

UZ-1 6/1442.8-1443.2 (Calico Hills)

UZ- 16/1486.9-1487.3 (Calico Hills/Prow Pass)

UZ- 1 6/ 1 60 1 . 1-1 60 1 .5 (Prow Pass)

Sample 

identification

NRG-6/1 58.2-1 58.6 (Shardy base/bedded)

NRG-6/ 1 7 1 .0-1 7 1 .3 (Bedded)

NRG-6/175.6-176.0 (Pah Canyon)

UZ- 1 4/235 . 1-235 .4 (Pah Canyon)

UZ- 14/240.8-24 1 . 1 (Pah Canyon/Bedded)

UZ-1 4/245 .5-245. 8 (Bedded)

UZ-1 6/1 434.2-1434.6 (Calico Hills)

UZ-16/1442.8-1443.2 (Calico Hills)

UZ-1 6/1486.9-1487 .3 (Calico Hills/Prow Pass)

UZ- 1 6/ 1 60 1 . 1-1 60 1 .5 (Prow Pass)

Symbol 

in Piper 

diagram 

(fig. 6B)

1

2

3

4

5

6

7

8

A

B

Average Aluminum Calcium 

Depth Al* Ca 

(m) (mg/L) (mg/L)

48.28

52.18

53.58

71.72

73.46

74.89

437.21

439.83

0 122

0 70.5

0 49.2

0.0 67

3 32

0 65

6.1 3.2

1.2 1.7

453.27 26.2 6.3

488.08 0.7 10

Carbonate Chloride Bromine 

CO3 Cl Br 

(mg/L) (mg/L) (mg/L)

0

13

0

N/S

N/S

N/S

118

146

0

0

185

58

47

84

99

77

23

18.9

38

53

*0.45-|im filter paper was used, hence, participate aluminum is likely included in tl

1

0

0

0

0

0

0

0

0

0

lese values.

Magnesium Sodium 

Mg Na 

(mg/L) (mg/L)

23.3

11.5

8.6

10.5

1

12

0.6

0.8

0.8

0.3

Nitrate 

N03 

(mg/L)

32

43

42

15

17

12

16

11.3

6

13

35.6

29.2

29.4

29

103

9

113

79.9

79.5

100

Sulfate 

SO4 

(mg/L)

159

94

64

94

100

79

19

13.7

11

27

Bicarbonate 

HC03 

(mg/L)

34

48

60

96

162

66

59

15

137

181

Silica 

SiO2 

(mg/L)

97.4

79.4

78.1

63

61

46

109.1

68.9

233.3

36

For pore water extracted from lithologic 

contacts and adjacent beds, the pore-water compositions are shown in figure 6B. A shardy base/bedded 

tuff contact in the NRG 6 borehole is shown by 

symbol 1 and a Pah Canyon/bedded tuff contact in 

the USW UZ 14 borehole is shown by symbol 5. 

Both of these pore waters have larger dissolved-solids 

values (about 1,200 mg/L) than the adjacent bed pore 

waters represented by symbols 4 and 6 in figure 6B. 

This is likely due to the fact that more water is flowing 

through the adjacent beds than along contacts. 

More water flow will cause pore water to be dilute. 

A water from a lithologic contact of the Calico Hills 

Formation/Prow Pass in the UE 25 UZ# 16 borehole is 

shown by A in figure 6B, which does not show a larger 

value of dissolved solids. However, this pore water

is veiV high in aluminum (Al, 26.2 mg/L) and silica 

(SiOj, 233.3 mg/L) concentrations (table 5). In most 

pore waters from bedded tuff and the Calico Hills 

Formation, aluminum (Al) concentrations are from 

zero to 2 mg/L, and silica (Si02) concentrations are 

from 50 to 100 mg/L. These pore-water compositions 

and total dissolved solids in the lithologic contacts and 

adjacent beds are interesting observations. Although 

more data are needed to substantiate these observations,} they may imply that percolating water is 

rerouted above the lithologic contacts and flows laterally through tilted porous tuffs (such as bedded tuff or 

Calico Hills Formation).

Finally, figures 7A and 7B present the compositions of pore water from USW UZ 14 and 

UE-25 UZ#16 boreholes. In general, the trends are

24 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
consistent in that ground waters are calcium bicarbonate, 

sulfate, or chloride type of shallow depths (top of diamond in the Piper diagram) and sodium bicarbonate 

or carbonate types (near the bottom of diamond) in the 

Calico Hills Formation. The composition of the porewater sample from 13.8 m (45.2 ft) in USW UZ-14 is 

an exception to this trend shown by point 1 in figure 7A. 

This core sample is in the Yucca Mountain Tuff, and 

the pore water has very high concentrations of dissolved 

solids. The chemical composition is not the calcium 

chloride or sulfate type typical of the shallow-depth 

pore water, but it is similar to the Topopah Spring Tuff 

pore water, which has an intermediate composition on 

the diagram (points G and L). Repeated concentration 

of pore water by evaporation and/or extended water-rock 

interactions might result in the observed larger dissolvedsolids concentration.

Compositions of pore water from the upper 

Calico Hills Formation of UE-25 UZ#16 are shown by 

symbols 4 and 5 in figure 7B. These waters have less 

water-rock interactions in the Calico Hills Formation and 

are similar to the water type of a Topopah Spring Tuff. 

Also, a core at 501.5 m (1,645 ft) deep in the Prow Pass 

Tuff of UZ#16 is shown by symbol P in figure 7B, which 

shows a chemical composition similar to symbol 1 at a 

shallow depth of only 49.8 m (164 ft) in the same borehole (fig. 7B). This suggests that young waters are 

rapidly transported through fractures with little waterrock interaction and are present in the upper Calico Hills 

Formation or Prow Pass Tuff of UE^-25 UZ#16. This is 

chemical evidence that preferential flow occurred around 

UE-25 UZ#16. The faults and fault zones and Sundance 

fault near this borehole may contribute to fast-flow paths 

(Spengler and others, 1994).

Tritium

The tritium concentration in precipitation before 

the atmospheric nuclear tests (pre-1952) was about 

10 TU (Davis and Bentley, 1982). However, between 

1952 and 1963, the United States and the Union of 

Soviet Socialist Republics conducted a series of 

atmospheric nuclear tests in the northern hemisphere 

that produced significant amounts of tritium in the Earth's 

atmosphere. As a result, the tritium concentration in 

precipitation increased rapidly from 1952 and peaked in 

the early 1960's. Michael (1989) reported a yearly 

tritium-concentration average of 2,700 TU in precipitation collected in 1963 at a Salt Lake City, Utah, station. 

A nuclear-test ban in 1963 stopped further tests in the

atmosphere, and the tritium concentration gradually 

decreased to the present level of about 10 to 40 TU 

measured in precipitation at the Nevada Test Site 

(Milne and others, 1987).

Water content and tritium data for pore water 

extracted from cores from UE-25 UZ#4 and UZ#5 are 

shown in figures 8A and 8B. The tritium concentrations range from zero to 45 TU in UZ#4, and the peak 

concentration is at about 46-49 m (fig. 8A). In UZ#5, 

the peak concentration of 75 TU is at about 32 m 

(fig. 8B). The larger tritium concentrations at these 

depths relative to the tritium concentrations of 30 to 

40 TU in precipitation during the 1980's are likely 

the result of water infiltrated in the early 1960's. No 

tritium data were obtained from the surface to a depth 

of 25 m in borehole UZ#5 because the cores were not 

available for pore-water extraction. Similarly, no tritium data are available between 50 and 95 m in UZ#4 

and between 47 and 67 m in UZ#5. (Tritium data for 

UZ#4 and UZ#5 were collected prior to implementation of the approved U.S. Geological Survey Yucca 

Mountain Project quality-assurance program and, 

therefore, the data are not qualified.)

USW UZ-14 tritium-concentration profiles 

from pore waters are shown in figure 9. They do 

not show any significantly large concentrations. 

However, there are several peaks at 18 to 30 TU 

in the Pah Canyon Tuff that likely are from the 

postbomb era.

Only small intervals of the NRCM> and 

NRG-7a cores were analyzed for pore-water 

tritium and 14C. The data are shown in 

figures 10A and 10B. High tritium concentrations of about 30 to 150 TU in a broad peak are 

observed in NRG-6 boreholes (fig. 10A) from 

53.3 m to 74.7 m in the Pah Canyon Tuff, and 

near the top of Topopah Spring Tuff.

Tritium concentrations from UE-25 UZ#16 are 

plotted in figure 11. An extremely high concentration 

of about 150 TU is observed at a depth of 48 m just 

above the bedded tuff unit, which is similar in location 

to the high tritium values in UZ#4, UZ#5, and NRG-6 

near the bedded and Pah Canyon Tuffs. In addition, 

several postbomb peaks are observed in the Topopah 

Spring Tuff at depths of 80 m, 204 m, and 317m 

to 357 m in UE-25 UZ#16. Other large peaks, in 

figure 12, are seen in the Calico Hills Formation at 

depths of 426 m (44 TU) and 437 m (103 TU).

interpretation of Chemical and isotopic Data 25
B

i

a

o

3 

ra

S

I

N

20

40

0)

DC

LU 

LU

60

LU 

Q

80

100

120

Alluvium

Tiva 

" Canyon

Bedded 

Tuff

. Yucca 

Mtn.

Bedded 

Tuff

Pah 

Canyon

-

Bedded 

Tuff

Topopah 

Spring

Op\Q ' 1 ' I ' I ' 1 '

J@ CUTTINGS 

/ o CORE 

J

V°° o °

9," "

0 o

0° 0

o 

o

8

i

o° o

Q Q ° LOW CONDUCTIVITY 

° O C-1 4 AGE = 1 ,000 YRS

, I , I , I , I , I ,

I

I I J II I [ I II II II

:

;

^ DETECTION 

"^ LIMIT = 4 TU

, , I , , , I , , , I , , ,

50

100

150

LU

LU

200

250

300

350

0 10 20 30 40 50 0 20 40 60 80 

WATER CONTENT, IN WEIGHT PERCENT TRITIUM UNITS (TU)

u

20

40

en

DC

LU

LU

I

LU

Q

80

100

19O

Tiva

Canyon

' Bedded

Tuff

: J

Yucca

" Mtn.

Bedded

 Tuff

- Pah 

Canyon

Bedded

- Tuff

.

- Topopah 

Spring

0' I ' I ' I ' I ' I 

0 CUTTINGS

° o CORE

o

,

".

"" @ o

° ^ 0°

°o ° o

O o

°$

°0

& n

0 °

n 0

* £>

O ,-, &

/

&

0%>

^

1

O 0

o°o 0

0 °

u 0

° ^CH

°n°

0

Q) ° C-1 4 AGE = 4,900 YR

?

, I , I , I , I , I 

0 10 20 30 40 50 

WATER CONTENT, IN WEIGHT PERCE

Figure 8. Lithologic units, water content, and tritium concentrations of boreholes (A) UE 25 UZ#4 and (B) UZ#5.
200

C/3

o:

LLJ 

LJJ

D_ 

LJJ 

Q

300

400

500

600

O

o

o 

o

 TU(UZ-14)

 14C(water)(UZ-14)

O 14C(gas)(UZ-1)

Alluvium 

Yucca Mtn

B«Med Tuff 

Pah Canyon

Topopah 

Spring ~

Calico 

Hill

Prow 

Pass

400

800

LJJ 

LJJ 

U.

1,200

1,600

2,000

20 40 60 80 100 120 

3H IN TRITIUM UNITS (TU) AND 14C, IN PERCENT MODERN

140

Figure 9. Tritium and carbon-14 data from USW UZ 14 pore water and rock-gas carbon-14 data from 

USW UZ-1.

Interpretation of Chemical and Isotoplc Data 27
B

u

1

i

a 

o

2, 20

o

i

8

B

 40

I

« Xi

? S5 * H

 LU

§ z 60

00 -r-~

i H

O LU

8 Q

3

a 80

C

££ 

1

N 100

o

i

C

B

o 120

-

_

..

9

-

 

o

4

^

_

 3H

0 14C

I I I , I

-

Tiva

Canyon

-

Bedded 

Tuff

rdl 1 Canyon -

-

Topopah

Spring

-

.

_

 * °

_

I , I , I 

| 0 50 100 150 200 0 20 40 60 

? 3H IN TRITIUM UNITS (TU) AND 14C, IN PERCENT MODERN 3H IN TRITIUM UNITS (TU) AND 14C, I

o

B Figure 10. Lithologic units, tritium, and carbon-14 (water) concentrations of boreholes: (A) USW NRG-6 and (B) US

B
100

200

CO 

QC111

tn

400

500

-14.0

C-13(water)

-9.3 145TU

>-9.0 

-9.4

0-16.5

-14.7

C-13(gas)

Detection limit = 4 TU

3H (water) 

14C (water) 

14C(gas)

Alluvium

Tiva 

Canyon

Bedded Tuff

Topopah - 

Spring

Calico 

Hills

Prow 

Pass

200

400

600

800 uj 

LJU

LJ_

1,000

1,200

1,400

1,600

0 40 80 120 

CONCENTRATION IN TRITIUM UNITS (TU) AND 14C, IN PERCENT MODERN

Figure 11. Lithologic units, tritium, and carbon-14 (gas and water) concentrations of borehole UE 25 UZ#16. Lines through gas data indicate zone of sample collection.

1,800

Interpretation of Chemical and Isotoplc Data 29
375 -;

400 -

DC LU

LJJ

LU 

Q

425

450 -

475 -

3H (water) 

 14C (water) 

0 14C(gas)

0 40 80 120 

CONCENTRATION IN TRITIUM UNITS (TU) AND

Figure 12. Expanded graph of tritium, carbon-14, and carbon-13 data from

i i

Calico 

Hills

Prow 

Pass

1,200

1,300

LII LII LL

1,400 -_

a.

LII 

Q

1,500

1,600

14C, IN PERCENT MODERN

figure 11,UE-25UZ#16.

30 Interpretation of Chemical and Isotopfc Data From Boreholes In the Unsaturated Zone at Yucca Mountain, Nevada
Postbomb tritium concentrations down to the depth 

of 60 m were observed in the past (Yang, 1992). However, the large postbomb tritium concentrations found 

in the Calico Hills Formation of UZ#16 were unexpected. 

Possible laboratory contaminations were initially 

suspected, and much effort was devoted to identifying 

possible sources of contamination. Measurements were 

made on the laboratory air and storage room (cold room) 

air in Denver for tritium concentrations, which were 

about 60 to 100 TU. If contamination occurred, it should 

affect all samples, not just a few. If radon contamination 

was present, then the high activity should disappear 

after a month due to a short half-life of radon gas 

(3.5 days). A recount of the same sample after a 

month still showed the high activity. Therefore, radon 

contamination was ruled out. Possible Pb-210 contamination was considered but was unlikely because water 

samples for tritium measurements were distilled from 

cores. Inorganic lead (Pb) compounds are nonvolatile 

at these temperatures.

From the tritium data observed in the boreholes 

mentioned above, tritium-concentration inversions 

(larger tritium concentrations located below the smaller 

tritium concentration in a vertical profile) occurred in 

many places. These inversions indicate that vertical 

water percolation through the matrix is not a normal 

flow mechanism at Yucca Mountain. Postbomb tritium 

concentrations were observed down to bedded tuff or 

Pah Canyon Tuff in many boreholes. The occurrence of 

postbomb tritium waters (recent water) below old water 

in a vertical profile is strong evidence of fracture flows 

occurring at Yucca Mountain. With regard to postbomb 

tritium concentrations observed at the Calico Hills 

Formation of UZ#16, we believe these postbomb tritium 

peaks are real unless they can be proven otherwise. However, the flux is very small because the tritium-peak shape 

is so narrow. A large flux should result in a broader peak.

Supporting evidence of the above conclusions 

can be seen from the 14C and 36C1 data. Liu and 

others (1995) reported modern 36C1 values in the 

Calico Hills Formation of UZ#16. The 14C values 

obtained from pore water of UZ#16 in the Calico Hills 

Formation also showed young ages near the locations 

where the high tritium concentrations were found. 

It has been reported by Spengler and others (1994) 

that the Sundance fault, trending from northwest to

southeast at Yucca Mountain, crosses near the 

UE-25 UZ#16 borehole. Only fracture flow can 

explain the observed rapid percolation.

Field observations have shown that: (1) several 

neutron-access boreholes in washes accumulated 30 

to 60 cm of water at the bottom of the boreholes after 

storms or periods of spring snowmelt and disappeared 

the next day (Alan Flint, U.S. Geological Survey, oral 

commun., 1993); and (2) in boreholes USW SD-9 

and UE-25 UZ#4, water was dripping down from a 

borehole wall near fractures (SD-9 and UZ#4 from 

field log books). Also, many fractures (although 

not all) are coated with calcite minerals, as reported 

by Whelan and others (1992, 1994). These calcite 

deposits indicate that water has flowed through the 

fractures, depositing the minerals as they became 

saturated. These fractures are possible conduits for 

the rapid flow of young water to significant depths.

Carbon Isotopes (513C and 14C)

Only one carbon-isotope value was obtained for 

each borehole of UE-25 UZ#4 and UZ#5 because of 

the large amounts of time involved in compressing 

50 to 90 mL of pore water from cores for each 14C 

age determination. For other deeper boreholes, such 

as UE-25 UZ#16 and USW UZ-14, core compression 

was conducted mostly on the high-moisture-content 

intervals (or units) (bedded tuff and Calico Hills 

Formation). Therefore, 14C data from pore waters 

are mainly available from these intervals. The 14C 

residence time of 1,000 years is indicated for water 

at a depth of 96.0 to 100.6 m (bedded unit above 

Topopah Spring Tuff) at UE-25 UZ#4. The water 

14C residence time of 4,900 years at a depth of 103.5 

to 105.2 m (in upper Topopah Spring Tuff) in borehole UE-25 UZ#5 is older than water from the corresponding depth in UZ#4 by nearly a factor of five 

(Yang, 1992). These abrupt changes in 14C residence 

times support a rapid flow of younger water through 

fractures to the location where younger 14C ages are 

observed (Yang, 1992).

For borehole USW UZ-1, there was no core 

recovered. Therefore, pore-water isotopic data are not 

available. However, because borehole USW UZ-14 

is about 26.2 m (86 ft) away from USW UZ-1, 

pore-water isotopic data from USW UZ-14 and

Interpretation of Chemical and Isotopic Data 31
UZ 1 should be representative of both boreholes. 

Carbon-14 data of pore water compressed from borehole USW UZ 14 cores are shown in figure 9 along 

with gaseous 14C data from USW UZ-1. Water 14C 

values (uncorrected) from the top 91 m (300 ft) ranging from 70 to 95 pmc and are similar to values for 

the Calico Hills Formation pore-water 14C values, 

which are between 70 and 96 pmc (uncorrected) 

between depths of 426.7 and 522.4 m. It was 

unexpected to see 14C values in the Calico Hills 

Formation of USW UZ-14 between 80 and 96 pmc 

even at a depth below 500 m. This is quite different 

from borehole UE-25 UZ#16 where seven 14C values 

in the Calico Hills Formation of UE-25 UZ#16 ranged 

from 53 to 98 pmc, with three of the values between 

53 and 61 pmc (see fig. 11 and discussion below). 

The apparent young 14C or high 14C pmc values could 

be related to: (1) young 14CO2 in the gaseous phase 

possibly exchanging with the bicarbonate species 

in the pore water; and/or (2) the large amounts of 

cement used below a perched-water zone at 383.1 m 

(1,257 ft) in order to seal off a borehole wall and 

prevent perched-water leakage (portland cement 

contains a small amount of Ca(OH)2, which will 

absorb atmospheric C02 during mixing with water 

and release the C02 during exothermic curation).

Figures 13A and 13B are expanded versions of 

the top 91 m 14C data and the Calico Hills Formation 

14C data, respectively, for borehole UZ 14. From 

figure 13 A, gas 14C values are different from water 

14C values. This indicates that a nonequilibrium 

condition may exist between gaseous and aqueous 

phases. 13C from gaseous and aqueous phases, 

and the C02(g)-H2C03 (liq.)-HC03 (liq.) 

system also shows a nonequilibrium condition 

(this will be explained in detail later in the section 

on 6 13C Isotopic Ratio in Gaseous-Phase Chemistry 

of USW UZ 1). There are no gaseous-phase data 

in the Calico Hills Formation at present (1995). 

When borehole UZ-14 is instrumented, gaseousphase chemical and isotopic data will be collected 

and studied. If the gaseous-phase 14C age from the 

Calico Hills Formation is significantly older than the 

aqueous-phase 14C values, the apparent young 

14C ages in the aqueous phase will not be the result 

of gas C02 and liquid bicarbonate exchange. The 

existence of cement in the borehole could release

C02 g^s during cement curation. If enough C02 gas 

was released, potential contamination to pore water 

14C age could be significant.

Delta carbon-13 values of pore water are shown 

in parenthesis in figures 13 A and 13B near the respecdata. It is unexpected to see 6 13C data so 

spread (-10.3 to -25%o) compared to perched

14

values 

in the

live

widel)

water or saturated-zone waters. Soil C02 6 13C

have been measured at the Nevada Test Site 

ast 3 years by E.A. McConnaughey (Science

Applic ations International Corp., Denver, Colorado, 

written commun., 1995). Their measured 6 13C values 

vary from year to year depending on the vegetation 

growth (-10 to -25%o), which in turn depends on the 

amount of precipitation. Therefore, 14C ages of pore 

waters! will be more variable if these changes exist. 

Furthermore, due to wide variations in 14C ages of 

caliche that dissolved partially or totally into subsurface water, the uncertainty will be larger. It would 

be difficult to make a good age correction. However, a 

possible range of ages with some uncertainty can be 

assigned in the future when more data become available. At present, apparent ages will be used to make 

preliminary interpretations.

Carbon-14 and 6 13C data from UE^-25 UZ#16 

are plotted in figures 11 and 12. Pore-water 14C data 

(uncoirected) from depths between 45.7 and 76.2 m 

(150-250 ft) are all close to 88 pmc, and 8 13C values 

range from -9.0 to -9.4%o, indicating dissolution of 

calicht. The deeper 14C data (uncorrected) in the 

Calico Hills Formation have a wider range of 

14C values (53 to 97 pmc): three in the range of 53 

to 61 pmc, three in the range of 72 to 87 pmc, and one 

at 97 pmc. This wide scatter of 14C values indicates 

preferential flow rather than a well-mixed unsaturatedzone \|/ater. The flux of the fast-flowing water is small 

judging from the narrow shape of the tritium peaks. 

One iilnportant consideration is the mixing of young 

14C age water with the old 14C age water. As calculated by Liu and others (1995), for 99% volume of 

pore water (matrix water) having an age of 5,000 years 

mixed with a 1% volume of bomb-pulse component 

from the fracture fluid, the effect to the matrix 14C age 

woulc be negligible. This mixing effect would not be 

significant until matrix water ages are more than 

35,000 years.

i 

32 Interpretation of Chemical and isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
B

u

20

40

CO

DC

LU 

LLI

| 60

I

Q.

LU 

Q

80

 3

1

§

a

o 100

i

0

e.

§

a

I

% 120

3H data

/

y-/ 1 3C data (water) +~ (-17.1) 

d~~^ (-15.0).

- m^^m o

ms==^^M (-13.0).

*<^~

f

i

A 1 4C data (gas) ^- o 

\ (-25.0).

C (-10.5).

\ (-21.2)*o \

\ 14C data (water)

\

" \

S

i

~ i l i l i l i l i l 

Alluvium

Yucca

Mtn

Bedded 

Tuff

Pah

Canyon

-

Bedded - 

Tuff

Topopah

Spring -

,

u

400

100

450

CO

. QC

h- LU 

L1J HLLJ UJ

200 ? z 

CL ^ 500

S g

300 550

600

400

(~

v^^

/ 1

/ 14C data (wa

r^> \ 

> (-11-1)1 

"^^-P

/ 

~ /

/ 

v^ (-15.8

S 

V (-14.

f (-1

\ 

\ 

. \ 

F/V

^v

- 3H data

>

.

^^

_

N, i , i , i , 

80 100 120 140 

3H IN TRITIUM UNITS (TU) AND 14C, IN PERCENT MODERN 3H IN TRITIUM UNITS (TU) AND 

Figure 13. Expanded graph of carbon-14 and carbon-13 from USW UZ-14 (fig. 9): (A) top 122 meters and (B) Calico Hills 
The other consideration is the exchange of 

younger 14CO2 gas with the pore-water bicarbonate, 

resulting in younger pore water. Due to limited data at 

present, further confirmation from other boreholes is 

needed. The gaseous-phase 14C data shown in 

figure 11 are not conclusive because the measured 

5 C data are between -14%o and -16.5%o, whereas 

the USW UZ-1 stemmed-borehole gas data are -18 

to -20%o. A possible air leak in the inflated packer 

system and the borehole wall or incomplete removal 

of air-contaminated rock gas can cause the shift in 

6 13C to the measured heavier values. However, one 

value in the Prow Pass from a depth of 477-481 m 

(1,565-1,578 ft) using a commercially constructed 

packer system has a 14CO2 gas value of 25.8 pmc 

and 613C of -18.4%o, similar to the USW UZ-1 value 

at depth.

Perched Water

Perched-water compositions from boreholes USW UZ^14, USW NRG-7a, USW SD-9, 

and SD-7 are presented in table 6. The data are 

plotted in a Piper diagram in figure 14 along with 

ONC#1 and USW G-2 samples collected from the 

saturated zone. Most of these perched-water zones 

were in the upper Calico Hills Formation, with the 

exception of UZ-14, which is in the Topopah Spring 

Tuff. As can be seen from table 6, major cation and 

anion concentrations were fairly constant throughout 

the pumping tests for USW UZ-14 and USW SD-7. 

Chloride concentration, which is hydrologically conservative, is fairly small ranging from about 4 to 

8 mg/L except one at 15 mg/L.

The composition of perched water located near 

or in the upper part of the Calico Hills Formation is, 

in general, closer to the pore-water composition of 

the Calico Hills Formation from UEr-25 UZ#16 and 

USW UZ-14 and also similar to saturated-zone water. 

But the chloride concentrations in all pore water are 

significantly larger than in the perched water. For 

example, perched waters collected from USW UZ-14 

all have chloride concentration between 6 and 

15 mg/L (represented by symbols C through J in 

fig. 14). In contrast, the chloride concentration of pore 

water compressed from USW UZ-14 cores obtained 

from perched-water zone (represented by symbols I 

and J in fig. 7A) are about 87.5 mg/L. If matrix pore 

water contributes significantly to the perched-water 

body, then the chloride concentration of perched water

should be similar to that of the pore water. This was 

not observed. The smaller concentration of chloride in 

perched water means that there is less interaction of 

fluid with rock, and that the source of the perched 

water flows through fractures. This is another point 

of evidence that fracture flows are the principal source 

of peiched-water bodies at Yucca Mountain. In addition, ihe large chloride difference also indicates nonequilibrium conditions between the perched water 

and plore water. Furthermore, the compositions of 

the perched water are also different from pore water. 

Analyses of a USW UZ-14 perched-water sample 

collected before the pumping test (sample UZ 14C) 

indicated that the perched water contained a polymer 

that was used in the drilling of USW G-l (Whitfield 

and others, 1990). If the polymer-contaminated 

perch ed water had a different chemical composition 

than the noncontaminated pore water, the chemical 

compositions between the two phases should be equilibrate^ after 10 years (USW UZ-1, which is only 

26.2 :m away from USW UZ-14, was drilled in 1985). 

It could be that trapped air in the porous medium 

prevents perched water from equilibrating with the 

pore water.

Perched-water isotopic-composition data are 

given in table 7. All perched waters contain background tritium concentration. If postbomb fracture 

waters are mixed in these perched waters, they 

are small in volume and subsequently are diluted 

by the large quantity of perched water, resulting in 

an undetectable tritium concentration.

Carbon-14 and 613C values are plotted in 

figures 15A and 15B. As can be seen from the 

figures, the 14C values range from 66.9 to 27.2 pmc, 

corresponding to apparent 14C residence times 

of about 3,500 years to 11,000 years. Water 

14C ages are affected by the dissolution of older 

caliche by the infiltrating water. This dissolution 

can tj>e identified by the 8 13C isotopic values since 

caliche has 6 13C values in the range of-3 to -9%o 

(Szapo and Kyser, 1985; Whelan and Stuckless, 

1992), while biogenic CO2 has 6 13C values of-18 

to -i3%o (UZ-1 data in this report). The heavier 6 13C 

values in the water will indicate the dissolution of 

caliche in the ground water. Carbon-14 ages of caliche at Yucca Mountain have been dated and range 

fronj 20,000 to several hundred thousands of years 

(WhLlan and others, 1994; Szabo and Kyser, 1985).

34 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Table 6. Chemical composition of perched water at Yucca Mountain, Nevada

[fjS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; - - -, data not available; 0, values below detection limit; charge 

balance, (milliequivalent cation - milliequivalent anion)/(milliequivalent cation + milliequivalent anion) times 100]

Sample Jplper A^e Date 

identification diagram {J^

NRG-7a

SD-9/TS

UZ-14A

UZ-14 A2

UZ-14B

UZ-14 C

UZ-14PT-1

UZ-14PT-2

UZ-14 PTM

UZ-14 D

ONC#1

USWG-2

SD-7(3/8)

SD-7(3/16)

SD-7(3/17)

SD-7(3/20)

SD-7(3/21)

Sample 

identification

NRG-7a

SD-9/TS

UZ-14 A

UZ-14 A2

UZ-14 B

UZ-14 C

UZ-14 PT-1

UZ-14 PT-2

UZ-14 PT^»

UZ-14 D

ONC#1

USWG-2

SD-7(3/8)

SD-7(3/16)

SD-7(3/17)

SD-7(3/20)

SD-7(3/21)

A

B

C

D

E

F

G

H

I

J

L

M

X

X

X

X

X

460.25

453.85

384.60

384.60

387.68

390.75

390.75

390.75

390.75

390.75

432.97

649.22

479.76

488.29

488.29

488.29

488.29

Sodium 

Na 

(mg/L)

42

98

39

38

40

88

40

35

34

35

50.6

46

45.5

45.3

45.8

45.5

44.6

03-07-94

07-17-94

08-02-93

08-02-93

08-03-93

08-05-93

08-17-93

08-19-93

08-27-93

08-31-93

12-15-94

02-08-95

03-08-95

03-16-95

03-17-95

03-20-95

03-21-95

Temperature Specific 

(degree pH conductance 

Celsius) (nS/cm)

...

27.0

27.1

27.1

23.8

24.2

...

...

...

...

...

...

...

21.8

22.6

23.3

23.2

Silica _. . . 

... Bicarbonate 

&IU2 urn 

(mg/L) HC°3

9

64.2

34.2

36.4

51.4

7.7

21.4

25.7

32.1

40.7

26.5

51

62.3

57.4

50.9

55

55.9

114

197

150

148.8

147.6

106.1

144.0

144.0

141.5

146.4

115

116

112

128

130

127

128

8.7

8.6

7.6

7.8

8.1

8.3

...

...

...

7.8

8.7

7.7

...

8.1

8.2

8.0

8.2

Carbonate 

C03 

(mg/L)

...

10

0

0

0

0

0

0

0

0.

8.8

...

0

0

0

0

0

224

445

312

308

335

518

...

...

...

...

302

259

...

239

285

265

259

Chlorine 

CL 

(mg/L)

7

5.6

7.9

9.1

8.3

15.5

7.2

7.0

6.7

7.0

7.1

6.5

4.4

4.1

4.1

4.1

4.1

Aluminum 

Al 

(mg/L)

0.0

2.1

0.7

1.0

6.1

0.0

0.0

0.0

0.0

0.0

11

...

0.28

0.44

0

0

0

Bromine 

Br 

(mg/L)

0

0

0.2

0.1

0.4

0.4

0.1

0.1

0.1

0.1

0

0.1

0

0

0

0

0

Calcium Magnesium 

Ca Mg 

(mg/L) (mg/L)

3

2.9

23

24

31

45

37

30

27

31

13.3

7.9

14.2

13.3

12.8

12.9

13.5

Nitrate 

N03 

(mg/L)

1

3.3

8.6

12.5

16.9

0

12.7

15.4

14.5

17.1

5.2

...

33.8

33.8

22.8

13.4

13.2

0

0.2

1.8

1.8

2.7

4.1

3.1

2.4

2.1

2.5

1.1

0.5

0.13

0.13

0.08

0.07

0.08

Sulfate 

SO4 

(mg/L)

4

27.6

14.3

13.8

16.3

223

57.3

22.9

14.1

24.2

23.6

13

9.1

9.1

8.6

8.5

10.3

Potassium 

K 

(mg/L)

6.8

9.8

5.6

3.9

4.4

5.8

6.3

3.3

1.8

4.1

3.6

5.2

5.3

5.3

5.5

5.4

5.5

Charge 

balance

-1.9

-6.6

-0.1

-0.2

0.2

-0.4

-0.1

-0.1

0.1

-0.3

8.4

6.9

-6.1

-4.6

-2.4

0.6

-1.0

Interpretation of Chemical and isotopic Data 35
0 1000 2000 3000 4000 5000

I I I I I I CIRCLE DIAMETER =TOTAL DISSOLVED

SOLIDS, IN PARTS PER MILLION

Ca 80 60 -< 40 

Calcium (Ca)

20 Na+K HC03+C<}3 20

PERCENTAGE OF MILLIEQUIVAJ.ENTS PER LITER

40 >- 60 

Chlorine (CD

80 Cl

EXPLANATION

A NRG-7a (1510.0 feet) 

B SD-9/TS (1489.0 feet) 

c UZ-14A(1261.8feet) 

D UZ-14A2(1261.8feet) 

E UZ-14B (1271.9 feet) 

F UZ-14C (1282.0 feet) 

G UZ-14PT-1 (1282.0 feet) 

H UZ-14PT-2 (1282.0 feet) 

i UZ-14PT-4 (1282.0 feet)

J UZ-14D (1282.0 feet) 

L ONC#1 (SZ) (1420.5 feet) 

M USW-G-2 (SZ) (2292.6 feet) 

x SE>-7 (3/8) (1574.0 feet) 

x SE>-7 (3/16) (1602.0 feet) 

x SE»-7 (3/17) (1602.0 feet) 

x SE>-7 (3/20) (1602.0 feet) 

x SE>-7 (3/21) (1602.0 feet)

Figure 14. Piper diagram showing perched-water composition, along with saturated-zone water compositions 

(ONC#1, L, and USW G-2, M).

36 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Table 7. Isotopic composition of perched water

[m, meter; %o, parts per thousand; pmc, percent modem carbon; - - -, data not available; PDB, Pee Dee Belemnite standard; SMOW, Standard Mean Ocean 

Water]

Sample 

identification

SD-7(3/8)

SD-7(3/16)

SD-7(3/17)

SD-7(3/20)

SD-7(3/21)

SD-9/TS

UZ-14A

UZ-14 A2

UZ-14B

UZ-14 C

UZ-14 PT-1

UZ-14 PT-2

UZ-14 PT-^t

UZ-14D

NRG-7a

Depth 

(m)

479.76

488.29

488.29

488.29

488.29

453.85

384.60

384.60

387.68

390.75

390.75

390.75

390.75

390.75

460.25

Date

03-08-95

03-16-95

03-17-95

03-20-95

03-21-95

07-17-94

08-02-93

08-02-93

08-03-93

08-05-93

08-17-93

08-19-93

08-27-93

08-31-93

03-07-94

Carbon-13

13C

(%., PDB)

-10.4

-9.4

-9.5

-9.5

-9.5

-14.4

-10.2

-10.1

-9.5

-9.2

-9.8

...

-9.6

-11.3

-16.6

Carbon-14 

14C 

(pmc)

34.4

28.6

28.4

27.9

28.4

41.8

41.7

40.6

36.6

66.8

32.3

28.9

27.2

29.2

66.9

Tritium 

"H 

(tritium units)

6.2

...

...

...

...

0.0

0.3

3.1

0.0

0.4

1.8

3.1

0.0

0.0

10.4

Deuterium 

D 

(%., SMOW)

-99.8

-99.7

-99.6

-99.6

-99.6

-97.8

-98.6

-97.5

-97.1

-87.4

-97.8

-97.9

-97.3

-97.6

-93.9

Oxygen-18

18Q

(3^, SMOW)

-13.4

-13.3

-13.4

-13.4

-13.3

-13.3

-13.8

-13.5

-13.4

-12.1

-13.3

-13.4

-13.4

-13.1

-12.8

Perched-water 5 13C values range from -9.2 to -14.4%o 

(except NRG-7a, which is -16.6%o), which indicates 

older caliche was dissolved into the ground water, 

making water ages look older than their actual 

ages. For NRG 7a perched water, because the 

13C value is -16.6%o, it implies that gas-liquid 

exchange might have occurred after caliche dissolution, causing the apparent age to look younger than 

its real age. If age corrections are applied to account 

for dilution by the older caliche and gas-liquid 

exchange after caliche dissolution, the implied 

perched-water residence times will probably be in 

the range of 2,000 to 7,000 years. Further investigations for 14C-age corrections will be made using 

geochemical model "NETPATH" in the near future. 

Since 5 13C values for perched waters are very consistent, and their large water volumes were presumably 

little affected by the gas-water exchanges, relative 

1 C residence times within the perched-water samples 

can be compared without correction.

Stable isotopic data (oxygen-18 and deuterium) are plotted as 5 18O relative to 5D in figure 16. 

Perched-water values are slightly heavier than 

the saturated-zone values and generally are closer 

to the Yucca Mountain precipitation line, indicating 

little evaporation before infiltration (Craig, 1961; 

Dansgaard, 1964). Moreover, it can be seen that 

518O and 5D values in table 7 for USW SD-7 

pumping tests (from March 16 through 21) are 

fairly constant. If mixing of older waters (more than 

10,000 years old, last ice age) is involved, stable

1 fi 5 O and 5D isotopic values will be significantly 

more negative than -15%o for 518O and -105%o 

for 8D [last ice age 5 18O value is about -15 to -20%o, 

and between -115 to -120%o for 5D (I.C. Yang, 

U.S. Geological Survey, unpub. data, 1996)]. All 

perched-water stable-isotopic values shown in 

table 7 are between -12.8 and -13.8%o for 5 18O 

and -94 and -99.8%o for 5D. These values are consistent with a 14C residence time of less than 7,000 years 

for the perched waters.

interpretation of Chemical and Isotopic Data 37
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14C, IN PERCENT MODERN 813C, IN PER MIL

Figure 15. (A) Apparent carbon-14 percent modern carbon of perched waters, and (B) delta carbon-13 values of perched 
-80

 3 

3

o 

1

sr

-90

-100

DC 

m 

a.

-110

-120

-130

-18

YUCCA MOUNTAIN 

PRECIPITATION LINE

WORLD METEORI

WATER LINE

-16 -14 -12 

6 18O, IN PER MIL

Figure 16. Delta oxygen-18 compared to delta deuterium plot of saturated-zone water and perched water. Saturated-

from: UE-25 b#1, c#3, p#1, a#2, and USW G^l, H-1, -3, -4, -5, -6, VH-1.

r
Gaseous-Phase Data from 

Borehole USW UZ-1

Gas sampling at USW UZ-1 is ongoing 

(1995). The data in this report are those collected 

from 1983 through 1994. Data from 1983 through 

mid-1985 and from 1988 to 1991 were published by 

Yang and others (1985, 1993). From 1983 through 

1987, gas samples from each probe were collected 

twice a year. It was several years before sample 

composition stabilized in the borehole. Once stabilized, sample collections were reduced to once a 

year (since 1988). (Gaseous-phase chemical and 

isotopic data for 1983-88 were collected prior to 

implementation of the approved U.S. Geological 

Survey Yucca Mountain Project quality-assurance 

program and, therefore, the data are not qualified. 

However, the data collected from 1989-94 are 

qualified.)

Dry-Gas Composition

When USW UZ-1 drilling was completed, 

the borehole was evacuated for a few hours before 

stemming and instrumentation. No SF6 concentration check was undertaken at that time. During 

all subsequent sampling, each probe was pumped 

at a rate of 250 to 500 mL per minute continuously 

for about 10 days. As shown in figure 17, SF6 

concentrations measured in 1984 were generally 

about 0.15 ppmv except for large values near the 

surface and small values of about 0.09 and 0.1 ppmv 

at 189 m and 228 m. The probes above 45 m have 

concentrations of 0.3 to 0.45 ppmv. Since 1988, the 

SF6 concentration has decreased steadily to less 

than 0.15 ppmv in all but the 1989 measurements. 

The reason for the large values in 1989 is unknown. 

In general, the drilling air appears to have been 

removed by 1986-87, and data collected since 

that time should be representative of the rock-gas 

composition.

Results of gas chromatographic analysis 

on gas composition (April 1984, September 1986, 

and July 1994) of USW UZ-1 samples are shown 

in table 8. The gas composition is similar to atmospheric air, with slightly more C02.

Carbon-Dioxide (COj*) Concentrations

As shown in figures 18A and 18B, CC>2 concentrations are rather large (greater than 0.15 percent) 

at shallow depths (probes 1,2,3, and 4) and near the 

bottom (probe #15) relative to others in the profiles 

(less than 0.15 percent). The larger concentrations 

at the! shallow depths (more than 0.3 percent by volume) 

are also larger than other environments near and 

around Yucca Mountain (Thorstenson and others, 

1990). This is attributed to the biologically produced 

CC>2 from burial of vegetation during construction of 

the USW UZ-1 drilling pad. The larger C02 concentrations at the bottom probe may be attributed to the breakdown of organic polymers from the drilling-fluid 

contamination. The C02-concentration profiles as a 

function of time (fig. ISA) indicate that low C02 concentr^tions were measured in 1983 and that, except for 

probe 13, concentrations steadily increased until 1987. 

The atmospheric CO2 concentration (0.034 percent) is 

significantly lower than most of the soil C02 concentration foi USW UZ-1. Thus, the early C02 samples, 

diluted by drilling air in the borehole, showed relatively 

low (p02 concentrations. As the semiannual gassampling process proceeded, more drilling air was 

remojved from the borehole and the pristine rock-gas 

composition was revealed. From 1988 through 1994, 

the C02 concentration from 100 to 360 m showed little 

change (fig. 18B). The invariant C02 concentrations 

at probe 13 are puzzling. This probe yielded the lowest 

amoijmt of C02 gas for 10 days of pumping.

Delta Carbon-13 Value

Delta carbon-13 values, relative to depth 

(fig. 19A) showed large variations in 1984 and 1985. 

As was explained previously concerning the C02 concentration, the 1984 shift was the result of the drillingair contamination in the borehole. The 8 13C value 

of thfe atmospheric CO2 at Yucca Mountain is about 

-8.5%o (Thorstenson and others, 1990, 1995). The 

presence of atmospheric air in collected samples would 

thus lead to larger 5 13C values. Between 1986 and 1987 

(fig. 19A), and 1988 through 1994 (fig. 19B), all 5 13C 

values were fairly constant, ranging from -18 to -23%o 

except for probes 9 and 10 in 1992 and near the bottom 

of thje borehole (probes 13 and 14), where occasional 

departures from the average value were observed.

40 Interpretation of Chemical and Isotopic Data From Boreholes in tho Unsaturated Zone at Yucca Mountain, Nevada
o

I

I o

0

8

D

a

o

N

100 ±r

150 

111

111

DL 

ID

a

Pro

No

200 

250 

300 -

350

0.3

- 1984

-O 1986-87

-- - - 1988

+- 1989

-# 1990

H 1991

-0 1992

--j 1993

-X 1994

7

8

9

10

11

12

13

14

15

0.6 0.9 

SF6 CONCENTRATION, IN PPM

Figure 17. Sulfur hexafluoride concentration in parts per million from USW UZ-1,1984-84.

1.2
Table 8. USW UZ 1 dry-gas composition (percent by volume)

[- - -, data not available]

Probe 

no.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Probe 

no.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

April 1984

Depth Carbon 

(meters) NIIJJfl«" Oxy9en Ar9on dioxide

12.8 79.6

18.9 79.7

28.3 79.2

39.9 79.1

61.3 78.5

81.1 78.4

106.1 78.4

128.3 78.4

152.7 78.4

189.3 78.6

227.7 78.7

265.5 78.5

304.2 78.5

335.3

367.9

September 1986

r*ovtwi 

Nitrogen Oxygen Argon .. .

KI si * dlOXIC N2 O2 Ar __

78.4 19.4 0.97 1.30

79.0 19.7 0.98 0.39

79.1 19.9 0.99 0.05

-

-

-

... ... ...

... ... ...

... ... ...

78.4 20.6 0.97 0.10

-

-

-

-

-

... ... ...

... ... ...

... ... ...

... ... ...

... ...

78.5 20.6 0.96 0.02

78.6 20.4 0.97 0.07

80.3 18.5 0.99 0.26

18.5 0.99 0.83

19.3 1.01 0.02

19.8 1.01 0.03

20.1 0.90 0.03

20.3 0.92 0.24

20.5 0.98 0.08

20.6 0.95 0.07

20.5 1.01 0.09

20.6 0.96 0.05

20.4 0.96 0.04

20.3 0.96 0.03

20.6 0.98 0.01

20.5 1.02 0.01

... ... ...

...

July 1994

n ..,.»_ n Carbon 

e Nlt 9en Oxygen djoxide

"* °* C02

78.2 20.8 0.79

77.8 20.6 0.53

77.1 20.4 0.22

77.1 20.4 0.41

77.7 20.4 0.23

78.5 20.8 0.20

78.1 20.8 0.11

77.9 20.8 0.10

78.0 20.8 0.08

77.7 20.6 0.08

77.4 20.4 0.11

76.7 20.5 0.11

76.9 20.5 0.05

78.1 20.9 0.13

78.1 20.6 0.36

The 5 13C value of about -20%o at shallow depths is 

representative of biogenic C02 (C02 gas respired 

from plant roots). The average 5 13C value of near

-20%o at all depths indicates that the C02 gas in the 

UZ has not exchanged with or is in equilibrium with 

in-situ calcite or caliche because the solid fracturefilling carbonates have a 8 13C value generally between

-9 and -3%o in the UZ (Szabo and Kyser, 1985;

Whelan and Stuckless, 1992). If exchange had 

occurred, the C02 gas 8 13C values would have 

become larger, which was not observed (fig. 19B). 

Also, the C age of the C02 gas would be older 

than its real age because of the old 14C age of calcite 

and caliche [greater than 20,000 years to as much as 

several hundred thousand years (Szabo and Kyser, 

1985t Whelan and others, 1994)].

42 interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
I

CD 

O

I

N

100

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UJ

2

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Alluvium

Yucca Mtn. 

Bedded Tuff

Pah 

Canyon

Topopah 

Spring

10

11

12

13

14

15

Lithologic Probe 

Unit No.

0.1 0.2 0.3 

CO2, IN PERCENT

0.4

300

600

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UJ 

Q

900

0.5

1,200

100 -

CO

oc

UJ 

H 

UJ

UJ 

Q

200 -

300 -

Lithologic Probe 0 

Unit No.

0

CO2, IN P

Figure 18. Percent carbon dioxide concentration from borehole USW UZ-1: (A) 1983-87 and (B) 1988-84.
Probe 

No.

Lithologic 

Unit B

Ii

o

2. 

o

o

3

CD

O

c

N

sO 

0

I

I

50

100

8 150

LU 

LU

H 200

Q. 

LU 

Q

250

300

350 

-35

1984

 0-1985

 - -1986

 # 1987

10

11

12

13

14

15

Alluvium

Yucca Mtn.

Bedded Tuff

Pah 

Canyon

Bedded Tuff

Topopah 

Spring

-30 -25 -20 -15 -10 

513C, IN PER MIL

-5 -35

-30 -25 -20 

513C, IN PE

Figure 19. Delta carbon-13 values in per mil from borehole USW UZ-1: (A) 1984-87 and (B) 1988-94.
On the other hand, the extent of interactions 

between the gaseous-phase CO2 and the pore-water 

bicarbonate can be seen from the following data analysis. 

The concentration of dissolved CO2, as bicarbonate, 

analyzed from pore water of UZ boreholes has values 

ranging from 30 mg/L at shallow depth to about 

250 mg/L at a depth of about 500 m with some exceptions. These bicarbonate concentrations are equivalent 

to 0.5-AO millimoles per liter (mmol/L). Volumetrically, 

the pore-water volume to the pore-air volume can be estimated as follows. According to Montazer and Wilson 

(1984), saturation in the Yucca Mountain cores ranges 

from 60 percent in the Paintbrush Tuff to 90 percent in the 

Calico Hills Formation. Therefore, the volume ratio of 

pore water to pore air will range from (60/40=) 1.5 to 

(90/10=) 9. The concentration of CO2 in pore air is 

about 0.1 percent (fig. 18B). Thus, the amount of CO2 

in a liter of pore air at 25°C and one atmosphere is 

(11) x (0.001)/(24 I/mole) = 0.00004 mol or 0.04 mmol. 

Since pore-water volume is about 1.5 to 9 times greater 

than the pore air, the amount of carbon in an aqueousphase reservoir relative to carbon in the CO2 gaseousphase reservoir is about |[(0.5+4.0)/2] x 1.5/0.04} = 84 

to |[(0.5+4.0)/2] x 9/0.04 =} 506 times greater. Therefore, most carbon present in the underground UZ is in the 

aqueous phase. Consequently, an aqueous phase will 

dominate the gaseous phase if any exchange occurs. 

Preliminary 5*3C values for pore water from UZ cores 

ranged from -10 to -25%o (this report). If CO2 gas is in 

equilibrium with the pore-water bicarbonate, the equilibrium ftactionation factor (Friedman and others, 1977) for 

the CO2(g)-HCO3(aq.) system predicts a 5 I3C value 

about -8.5%o lighter for CO2(g) relative to the 5 13C value 

of bicarbonate in an aqueous phase. If so, 5 13C values 

of CO2 gas in the borehole would be between -18.5%o 

and -33.5%o, which is not always the case in figure 19B. 

The CO2-gas 14C values are also not in equilibrium 

with the aqueous-phase 14C values, as mentioned previously (figs. 11 and 13A). Drilling air in the borehole of 

USW UZ-1 in 1984 through 1987 may have an effect 

on this disequilibrium between gaseous and pore-water 

phases. Furthermore, many open boreholes are known 

to inhale or exhale throughout the year. This could also 

affect the disequilibrium. However, the fact that the 

I4C values of rock gas are decreasing steadily with 

depth infers little effect by inhalation or exhalation (if 

topographic effect is significant, I4C values will scatter 

instead of steadily decreasing). The nonequilibrium 

condition in a CO2(g)-HCO3(aq.) system could be due to 

the fact that gas samples were collected mainly from dry

fractures with little contribution from pore gas, which 

is in equilibrium with pore water. Thus, interactions 

between pore gas and pore water are not detected. 

Thorstenson and others (1990) also observed that 

approximately 2 x 106 m3 of gas was exhausted by 

USW UZ-6s borehole without compositional changes 

in rock gas. If the gas CO2 was interacting with a 

large aqueous-phase carbon reservoir, a gas-phase 

CO2 concentration would be modified, which was not 

observed. It is conceivable that such nonequilibrium 

conditions exist between gaseous and aqueous phases 

in many parts of Yucca Mountain. Due to insufficient 

gaseous-phase data and knowledge of the fractured 

system at the mountain, this statement is preliminary.

Carbon-14 Data

The I4C data plotted in figure 20A also 

indicate large variations in 1984 and 1985. The 

values tend to lie on the right-hand side of the 1986 

values (that is, higher I4C activity values). This 

is consistent with the previous explanation of the 

drilling-air contamination in the borehole. Presentday 14C activity in the atmospheric air is about 

120 pmc, which would cause the I4C activity of soil 

CO2 gas to shift toward higher values. After pumping 

for 2 years, the I4C data are very consistent for the last 

7 years (fig. 20B), with a gradual decrease in I4C 

activity with depth to about 23 pmc at 368 m.

The 14C profile in figure 20B shows that there 

is an abrupt change in the slope at probe 5. The 

transport velocity ( 14C concentration gradient over 

distance) between probes 1 and 5 is smaller than 

the transport velocity between probes 5 and 15. 

The smaller transport velocity may be due to higher 

porosity and moisture content in this zone. An estimate of the traveltime in the Topopah Spring Tuff 

(between probes 5 and 15) based on the apparent 

14C ages and the distance yields gas movement of 

3.26 cm/yr. This is a minimum value because the 

distance used for the calculation is simply depth in 

the borehole.

A gas-diffusion effect would cause 12CO2 

to diffuse downward faster than the heavier 14CO2 

molecules and would result in an older 14C age at 

a greater depth than if the I4C decay alone were 

considered. However, the effect is small and can 

be neglected.

Gaseous-Phase Data from Borehole USW UZ-1 46
i

a

O

I

5

00

O

g

S 

3

I

N

O

i

1984 

-1985

 G 1986

-$£-1987

20 40 60 

- 300

100

600

LLI 

LLI 

U_

LLI 

Q

CO

<r

LLI 

LLI

Q. 

LLI 

Q

200

- 900

300

1,200 

LithucJ|°9icPr°Je 20 40 60 80 100 120 140

Pah 

Canyon

Topopah 

Spring

10

11

12

13

14

15

LithologicProbe 

Unit No.

i i i i 

14C ACTIVITY, IN PERCENT MODERN 

Figure 20. Carbon-14 activity in carbon dioxide gas from borehole USW UZ-1: (A) 1984-87 and (B) 1988-94.

40 60 

14C ACTIVITY, IN PE
Gaseous-Phase Data from Selected Open 

Boreholes

Dry-gas composition was measured in the instrumented borehole of UZ-1. Since the gas composition 

was essentially the same as the atmospheric air composition, no attempt was made to repeat the measurement 

Carbon dioxide and carbon isotopic data were measured 

in selected open boreholes (NRG-6, NRG-7a, UZ#16, 

and SD-12J and are given in table 9. As can be seen from 

the table, 5 C values are heavier, in many cases, than the 

values for UZ-1. Also, 14C values do not show a steady 

decrease with depths, as seen in UZ-1. The reason for the 

heavier 5 13C values and younger 14C values at depths 

could be due to contamination with atmospheric air as a 

result of a leaking packer or incomplete removal of drilling air. It has been observed in many locations at Yucca 

Mountain that topographic effects cause the gas to inhale 

or exhale through the open boreholes. This will also 

result in possible contamination of formation gas by air. 

In one case at the Prow Pass zone in UE-25 UZ#16 where 

the air-K test packer system was used, the rock-gas 

14C age is about 10,000 years, similar to the gas age 

obtained from the deepest probe in USW UZ 1, an instrumented borehole. This could be due to the packer used in 

this zone having a tight seal, or alternatively gas inhalation or exhalation in the borehole does not reach to this 

depth. The 5 13C value of -18.4%o strongly supports this 

argument We have not collected any gas data from 

NRG-6 and NRG-7a boreholes because instrument tests 

are still in progress. The long-term carbon isotopic data 

(more than 10 years' data) from USW UZ-1, which show 

steady decrease in 14C ages as a function of depth with 

consistent 5 13C values, are the only dependable rock-gas 

data so far in the Topopah Spring unit and below.

MODEL CALCULATIONS

A gas-diffusion and two aqueous-flow models were 

applied to explain the observed gaseous 14C distributions 

in USW UZ-1 and tritium concentrations in pore-water 

samples of UE^-25 UZ#16.

The gas-diffusion model: A steady-state diffusion 

of 14C02 from a constant source at the surface with firstorder radioactive decay was considered. In this case, the 

finite depth of the UZ must be taken into account because 

of the length of times possibly available for diffusion. 

The equation for steady-state diffusion and first-order 

homogeneous reaction in a finite layer is taken from Bird 

and others (1960, p. 533, eq. 17.4-7). The equation

assumes that the reactant and product species are 

present in very small concentrations and that the net 

gas flux is zero. Thus, multicomponent effects 

(Thorstenson and others, 1989) and advective transport due to local topographic effects (Weeks, 1987) are 

not considered.

The aqueous-flow model: Piston-flow and wellmixed models were used to determine if observed 

tritium concentrations are feasible, given estimated 

tritium input functions for the Yucca Mountain site. 

Numerous studies of surface- and ground-water ages 

and mixing rates have been conducted over the years 

with the use of tritium (Carmi and Gat, 1973; Pearson 

and Truesdell, 1978; Simpson and Carmi, 1983; 

Egboka and others, 1983; Knott and Olimpio, 1986; 

Vuataz and Goff, 1986; and Shevenell, 1991). Discussions of piston-flow compared to well-mixed flow 

behavior have been abundant in these and other studies. Simpson and Carmi (1983) focused on a simple 

exponential model of piston flow while studies by Nir 

(1964) discussed the concepts of well-mixed and 

piston-flow reservoirs, utilizing hydrodynamic dispersion coefficients in describing the well-mixed endmember. Carmi and others (1973) simulated wellmixed behavior with the use of an age function that 

incorporates a recharge weighting function to determine ages from the combination of tritium input over 

a given number of years. Pearson and Truesdell 

(1978) and Shevenell (1991) applied this model to 

the geothermal systems.

Gas-Transport Model

To a first approximation, the 5 13C data suggest 

that there is no systematic C02 reaction with solid carbonate in the USW UZ-1 borehole. Thus, the possibility must be considered that the gas in the borehole is 

stagnant and that the decrease of ^C with depth is due 

to radioactive decay and that the 14C data thus imply 

substantial "ages" of the C02 at depth.

The C02 concentrations in the upper few probes 

(probes 1 through 4, figs. ISA and 18B) are anomalously high relative to concentrations observed in 

other environments at the NTS (Thorstenson and others, 1990). The UZ-1 data also suggest that these high 

concentrations are migrating downward with time 

(fig. 18). It is likely that construction of the UZ-1 drill 

pad caused some effects on these C02 concentrations, 

for example, through burial of vegetation during construction. Consequently, gas 14C data from the upper 

few probes will not be considered here.

Model Calculations 47
Table 9. Carbon-14 (14C) and delta carbon-13 (gas) data from boreholes NRG-6, NRG-7a, UZ-16, and SD-12

[- - -, data not analyzed; pmc, percent modem carbon; %o, parts per thousand; PDB, Pee Dee Belemnite standard]

Borehole

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-6

NRG-7a

NRG-7a

NRG-7a

NRG-7a

NRG-7a

NRG-7a

NRG-7a

NRG-7a

NRG-7a

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

Depth 

(meters)

6.1

6.1

6.1

24.4

24.4

26.8-38.1

26.8-38.1

26.8-38.1

26.8-38.1

26.8-38.1

26.8-38.1

26.8-38.1

61.0

61.0

61.0

83.8

83.8

107

183

183

221

221

233-238

233-238

282

282

305

305

42.7

42.7

149

149

149

271

271

271

370

45.7

45.7

45.7

14.3-74.1

14.3-74.1

73.1

73.1

Uthoiogic 2* 

Unlt (CG

Tiva Canyon 0.0

Tiva Canyon

Tiva Canyon

Tiva Canyon 0. 1

Tiva Canyon

On 14c 13C/12c

* (pmc) (%* PDB)

7 - - - -12.83

-15

-15

.18

.15

L -14.25

92.1 -15.2

Tiva Canyon 0.07 --- -14.60

Tiva Canyon

Tiva Canyon

Tiva Canyon

Tiva Canyon

Tiva Canyon

Tiva Canyon

61.0 -13.9

-14.62

-14.61

-14.63

-14.99

-15.02

Pah Canyon 0.10 --- -14

Pah Canyon

Pah Canyon

.14

-14.24

91.0 -14.9

Topopah Spring 0.05 --- -15.05

Topopah Spring

Topopah Spring

-15.05

-17.24

Topopah Spring 0.10 83.2 -15.5

Topopah Spring -14.06

Topopah Spring 0.07 --- -14.69

Topopah Spring

Topopah Spring

Topopah Spring

-14.69

-10.14

-10.31

Topopah Spring 0.11 94.2 -16

Topopah Spring

.1

-14.14

Topopah Spring O.o| --- -14.43

Topopah Spring -14.34

Yucca Mountain 0.1$ 108.0 -16.8

Yucca Mountain -17.24

Topopah Spring 0.19 --- -17.69

Topopah Spring

Topopah Spring

-17.68

111.7 -18.2

Topopah Spring 0.15 111.0 -19.0

Topopah Spring

Topopah Spring

Topopah Spring 0.1'

Tiva Canyon

Tiva Canyon

Tiva Canyon

Tiva to Topopah

Tiva to Topopah

Topopah Spring

Topopah Spring

-17.75

-17.73

) --- -17.61

73.2 -15.5

-13.82

-13.72

72.7 -14.0

-12.32

-13

-13

.19

.14

Isotopic 

analytical 

laboratory

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

48 interpretation of Chemical and Isotopic Data From Boreholes in the! Unsaturated Zone at Yucca Mountain, Nevada
Table 9. Carbon-14 ( 14C) and delta carbon-13 (gas) data from boreholes NRG-6, NRG-7a, UZ-16, and SD-12 Continued

[- - -, data not analyzed; pmc, percent modern carbon; %o, parts per thousand; PDB, Pee Dee Belemnite standard]

Borehole

UZ-16

UZ-16

UZ-16

UZ 16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

UZ-16

SD-1 2

SD-1 2

Depth 

(meters)

82.3

82.3

74.1-148

74.1-148

74.1-148

74.1-148

148-163

148-163

163-512

163-512

477^81

477-481

477^81

477^81

477-481

216-220

342-347

 in. i i Carbon Lithoioglc diox|de

unlt (co2)

Topopah Spring

Topopah Spring

Topopah Spring

Topopah Spring

Topopah Spring

Topopah Spring

Topopah Spring

Topopah Spring

Topopah Spring to Prow Pass

Topopah Spring to Prow Pass

Prow Pass

Prow Pass

Prow Pass

Prow Pass

Prow Pass

Topopah Spring

Topopah Spring

14C 

(pmc)

...

...

87.0

...

...

...

81.6

...

89.2

...

...

25.8

...

...

...

74.33

60.17

13C/12c 

(%., PDB)

-12.97

-12.94

-16.5

-19.71

-20.07

-20.86

-14.7

-18.31

-17.0

-15.63

-17.60

-18.4

-16.32

-16.26

-15.51

-11.6

-16.1

Isotoplc 

analytical 

laboratory

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

Geochron

USGS stable isotope

USGS stable isotope

USGS stable isotope

Geochron

Geochron

Surface 14CO2 concentration is calculated with 

CO2 = 0.125% and a 14CO2 = 100 pmc. The steadystate diffusion of 14CO2 from a constant source at the 

surface with first-order radioactive decay was considered 

by Thorstenson and others (U.S. Geological Survey 

administrative report, 1995). Calculations were made 

with a depth of 500 m for values of diffusivity ranging 

from 10~6 to 10~7 m2/s. A good visual fit is obtained 

with D = lO'6'7 m2/s (D = 2.0 x 10~7 m2/s).

The calculated and observed concentrations of 

14CO2 are plotted in figure 21. The calculations do 

not explicitly take into account solubility or reactions. 

While simple Fickian diffusion may not be the only 

process that is operative, it appears that it can account 

for the observed depth distribution of 14CO2 in the 

fractured Topopah Spring. (This conclusion is supportable using solely the data that were collected in compliance with the approved U.S. Geological Survey Yucca 

Mountain Project quality-assurance program.) This 

is in marked contrast to the observations in the open 

boreholes at the Yucca Mountain crest, where it appears 

impossible to account for observations without major 

advection in the system (Weeks, 1987; Thorstenson 

and others, 1990).

Use of Tritium in Ground Water to 

Determine Water Mean Residence Times

Tritium generally behaves conservatively in the 

ground-water system. Therefore, its concentration in 

water is a reliable indicator of mixing and relative 

ground-water ages. The flow type is assumed to be 

either piston flow, well-mixed flow, or some combination of the two. The piston flow (no mixing between 

fluids of different ages) provides an upper limit, and 

the well-mixed model (complete mixing of fluids of 

different ages) provides the lower limit on mean residence times of ground water in the system.

Piston-Flow, or Preferential-Flow, Model

This flow model does not take into account 

hydrodynamic-dispersive mixing within the 

unsaturated-zone reservoir system, nor from other 

sources of water. Output tritium concentrations 

depend only on the input concentration at recharge 

and the elapsed time since the recharge. The relationship between input and output concentration is simply 

a standard decay equation:

Model Calculations 49
s

3

s.

o

8 

zl

i5"

I

 n 

3

DO

8

I

ff

I

N

i

3

I

C/} 

(T 

LJJ

LU

LU 

Q

50

100

150

200

250

300

350

400

Alluvium

Yucca Mtn. 

Bedded Tuff

Pah 

Canyon

Bedded Tuff

Topopah 

Spring

8

9

10

12

13

14

15

Lithologic Unit Probe o 

No.

0.5

effective diffusivity = 2.2 X10~7 meter 

1.0 1.5 2.0 2.5 3

CARBON-14 IN 10'13 MOLES PER SQUARE METER

Figure 21. Diffusion model calculated and observed 14CO2 concentratbn relative to depth in USW UZ-1.
where

Cout(t) = output tritium concentration at time /, expressed 

in calendar year 19xx (not number of years); 

Cin(t) = tritium concentration of fluid recharging the

system;

T = residence time; and 

A, = tritium decay constant (5.576 x 10~2/yr).

This equation can be solved by the analytical method for 

tritium concentrations relative to residence times with 

known tritium input function.

Well-Mixed Model

On the other hand, the well-mixed model assumes 

that all sources of water input to the reservoir are completely mixed with the water already in the reservoir. For 

such a reservoir, it is assumed that volume does not 

change with time and input rate equals the output rate 

(QirrQout)- The mass-balance equation presented by 

Pearson and Truesdell (1978) is given as follows:

-A,C(0

where

Cft) = the tritium level in the reservoir, and at the

	discharge point, at time /; 

Cin(t) = input tritium concentration; 

Qin = recharge flow rate, Qin = Qout; 

Qout = discharge flow rate;

V - volume of reservoir, constant;

/ = residence time, V/Q\ and

X = decay constant of tritium (5.576 x 10~2/yr).

This differential equation can easily be solved by 

the numerical method with a known tritium input 

function.

Tritium Input Function

In order to evaluate the end-member models, the 

tritium concentration of recharge water before and after 

nuclear testing must be estimated in the study area. Prior 

to 1952, little tritium data were reported. A few measurements were made on lake water, ground water, and wines 

from Chicago and New York areas. These measurements 

indicate that the average natural background tritium value 

for the interior of North America is about 6 TU, depending on the latitude and altitude (Craig and Lal, 1961; 

Kaufman and Libby, 1954). Also, tritium values in precipitation were reported by Payne (1972) to be between 2

and 25 TU prior to the 1950's. Tritium 

data in precipitation at Yucca Mountain were reported 

by Milne and others (1987) from November 1983 to 

June 1985 only. Other reported data, not from Yucca 

Mountain but from States neighboring Nevada, are 

available from stations set up by the International 

Atomic Energy Agency (IAEA) in Menlo Park, Calif., 

Albuquerque, N. Mex., Flagstaff, Ariz., and Salt Lake 

City, Utah. The averaged data from these four stations 

were taken to represent the Yucca Mountain area even 

though there are differences in latitude, altitude, and 

local climatic conditions between these four stations 

and Yucca Mountain. The average monthly tritium 

concentration in precipitation has been reported by 

IAEA for these four stations since 1963 (International 

Atomic Energy Agency, 1969-1986). However, no 

data were reported from 1953 to 1962. To estimate the 

pre-1963 tritium concentrations for the four stations, 

the IAEA data from Ottawa in Canada, which has a 

complete record of tritium values in precipitation since 

1953, were used to formulate the tritium input data. 

This same method was also used by Pearson and 

Truesdell (1978), Campana and Mahin (1985), Knott 

and Olimpio (1986), and Shevenell (1991).

The IAEA tritium data, reported as a monthly 

average, increases in concentration during the spring 

and summer. The long-term precipitation records of 

Las Vegas, Nev., also show increases in tritium concentrations in spring and summer (Cayan and others, 

1991). Annual average value and maximum monthly 

value of each year from IAEA were used as input 

functions for these models.

To estimate the missing tritium data at these 

stations between 1953 and 1962, trends of tritium concentration at these stations are assumed to be similar to 

the tritium concentrations in the Ottawa station. The 

best-fit linear regression equations for four stations 

and their correlation coefficient (R2) are shown below. 

Using annual average:

Y, = 0.960393 Xj - 0.07485 R2 = 0.9015

(estimated linear equation at Flagstaff) 

Y2 = 1.168409 Xj- 0.36611 R2 = 0.9622

(estimated linear equation at Salt Lake

City) 

Y3 = 1.080147 X{ - 0.37512 R2 = 0.944

(estimated linear equation at Albuquerque) 

Y4 = 0.745824 X! -0.36611 R2 = 0.799

(estimated linear equation at Albuquerque)

Model Calculations 51
where

Y^log (annual 3H concentration at Flagstaff), 

Xi=log (annual 3H concentration at Ottawa) 

Y2=log (annual 3H concentration at Salt Lake City) 

Y3=log (annual 3H concentration at Albuquerque) 

Y4=log (annual 3H concentration at Menlo Park) 

Similarly, using maximum monthly value of each 

year:

Y^l.099583 X! - 0.36034 R2 = 0.904

(estimated linear equation at Flagstaff) 

Y2=l.195766 X! - 0.45923 R2 = 0.908

(estimated linear equation at Salt Lake

City) 

Y3=l.129000 Xj-0.44896 R2 = 0.887

(estimated linear equation at Albuquerque) 

Y4=0.905918 Xj -0.29431 R2 = 0.790

(estimated linear equation at Albuquerque) 

where 

Yi=log (maximum monthly value of 3H concentration

at Flagstaff), 

Y2=log (maximum monthly value of 3H concentration

at Salt Lake City) 

Y3=log (maximum monthly value of 3H concentration

at Albuquerque) 

Y4=log (maximum monthly value of 3H concentration

at Menlo Park)

The average of the tritium concentration at the 

four stations is assumed to represent the concentration 

at Yucca Mountain (figs. 22A and 22B). The most 

notable feature of the concentration profile is that the 

maximum tritium concentrations in precipitation, 

approximately 250 times above background levels, 

occurred in 1963. The estimated annual average 

tritium concentration of 1984 is 23.0 TU, which is 

close to the measured tritium concentration (19.7 TU) 

in precipitation at Yucca Mountain (Milne and others, 

1987).

Results of Tritium Model Calculations

Pre-1952 tritium concentrations in precipitation 

ranging from 5 to 20 TU are used as an initial concentrations for input into the well-mixed model sensitivity 

analyses. The results indicate that the output tritium 

concentrations change insignificantly. Therefore, a 

pre-1952 tritium concentration of 6 TU was adopted 

for the annual average value, and 12 TU was adopted 

for the maximum monthly average value.

Figures 23A and 23B show the calculated 

tritium concentrations relative to mean residence 

times for the two end-member cases for the samples

collected in 1993 at Yucca Mountain (a) using an 

annual mean value, and (b) using the highest monthly 

tritium value in a year in precipitation as input functions. The curve for the piston-flow model indicates 

several peak concentrations of tritium, reflecting the 

various nuclear-test series begun in 1953. On the 

other hand, mixed-reservoir curves show smooth 

increases in the tritium content of a reservoir caused 

by high tritium inputs from the mid-1950's to 1963, 

followed by a decrease to the present (1995) level. 

It is important to note that the piston-flow model using 

the highest monthly value in figure 23B gives the 

highest tritium concentrations of up to 700 TU, in 

1993 with residence time of 30 years, from 1963 

nuclear-test fallout. The highest tritium concentration 

in 4e well-mixed reservoir is only about 55 TU. 

Usifag the annual mean value from the closest four 

stations for tritium concentration in precipitation, the 

piston-flow model gives 350 TU as a maximum, and 

the well-mixed model gives 25 TU as a maximum in 

ground water in 1993. The piston-flow model with 

either type of input function can account for the 

observed tritium peaks of more than 100 TU in the 

Calico Hills Formation of UE-25 UZ#16. However, 

the well-mixed model cannot account for the observed 

values.

In reality, no hydrologic system should be 

expected to exhibit pure piston-flow or pure wellmixed flow behavior. The results of piston-flow and 

well-mixed flow models only give the lower and upper 

limits of peak tritium concentrations for various residence times. Although tritium, with its short half-life, 

cannot be used rigorously to obtain an accurate mean 

residence time of an older water, this study demonstrates that it can be used to obtain an order of magnitude estimate of a residence time.

Extremely variable tritium values in the 

USW UZ-14 and U&-25 UZ#16 profiles indicate 

unsaturated-zone waters are not well mixed (as 

seen from tritium model calculation) but are transported in large part by piston flow (between piston and 

we] 1-mixed flows, but closer to a piston flow). Therefore, preferential flow through fractures is the dominant mechanism. Other evidence of fracture flow is 

supported by the presence of many calcite and silica 

deposits in fractures, boreholes, and the Exploratory 

Study Facilities. Also, water was observed to seep out 

from the fractures in several boreholes. Large tritium 

concentrations in borehole UZ#16 in the Calico Hills 

Foimation are within limits of piston-flow-model 

calculation (about 30 years' residence time).

52 Interpretation of Chemical and Isotopic Data From Boreholes in tie Unsaturated Zone at Yucca Mountain, Nevada
10,000

1,000

CO

ocI100

10

10,000

i i i i i i r i i i i i r i i i i i i

ANNUAL MEAN

J

1950 1960 1970 1980 1990

1,000

CO

cc

100

10

B

I

MONTHLY MAXIMUM

1950 1960 1970 

YEARS

1980 1990

Figure 22. Tritium input function derived from (A) annual mean value, and (B) highest monthly value in a 

year of tritium concentration in precipitation from four stations: Albuquerque, New Mexico; Flagstaff, Arizona; 

Menlo Park, California; and Salt Lake City, Utah.

Model Calculations 53
1,000

DC 

HI

Z 

Hi"

P 

HI 

O

HI 

Q

C/) 

HI 

DC

Z 

HI

PISTON-FLOW MODEL

5 10 20 i 50 100 200 

TRITIUM UNITS (TU)

500 1,000

PISTON-FLOW MODEL

10 20 50 100 

TRITIUM UNITS (TU)

200 500 1,000

Figure 23. Calculated tritium contents of water in the uns aturated 

models using (A) annual mean value of tritium input function 

tritium input function (fig. 22B).

54 Interpretation of Chemical and Isotopic Data From Boreholes In line Unsaturated Zone at Yucca Mountain, Nevada

zone by piston-flow and well-mixed 

(fig. 22A), and (B) highest monthly value of
SUMMARY AND CONCLUSIONS

Unsaturated-zone pore water generally has significantly larger concentrations of dissolved solids than either 

the saturated-zone water or perched water. Pore-water 

composition plotted on Piper diagrams define groups 

related to lithologic units. Pore waters in the Tiva 

Canyon, Yucca Mountain, Pah Canyon, and bedded 

tuffs are calcium sulfate or calcium chloride types that 

group together near the top of the diamond on the Piper 

diagram. Calico Hills Formation waters are sodium 

carbonate or bicarbonate type and plot near the bottom 

of the diamond. Pore waters in the Topopah Spring Tuff 

are at the middle of the diamond.

Tritium profiles show inversions occurred in 

several places. These inversions indicate that vertical 

water percolation through the matrix is not the normal 

flow mechanism at Yucca Mountain. Rather, fracture 

flow is the dominant fluid-flow mechanism. The postbomb tritium concentrations observed in the Calico Hills 

Formation of UE 25 UZ#16 are also supported by the 

young 14C ages and modern 36C1 signals found in the 

same locations. However, total water flux to the Calico 

Hills Formation is small.

Large 14C variations of about 53 to 97.7 pmc 

are seen in UE 25 UZ#16 bedded tuff and in the 

Calico Hills Formation. Three values ranging from 

53 to 61 pmc values in the Calico Hills Formation 

are in agreement with observed values in perched 

water. Many of the 14C values in the Calico Hills 

Formation of USW UZ-14 are between 80 and 

95 pmc (equivalent to apparent 14C ages of about 

1,800 and 400 years), although one value is 70 pmc. 

Further investigations are in progress to confirm 

these apparent young 14C ages.

Chemical and isotopic compositions of the perched 

water indicated that (1) the apparent 14C ages of perched 

water are similar to apparent 14C ages of the Calico 

Hills Formation pore water in UE-25 UZ#16, ranging 

from 3,000 to 7,000 years; (2) stable isotopic values 

of-12.1 to -13.8%o for 8 18O and -87.4 to -100%o 

for 8D in perched water strongly support the postglacial 

14C ages; (3) the hydrogen and oxygen isotopic compositions of perched-water samples indicate that perched 

water rapidly infiltrated into fractures; (4) chloride 

concentrations of the perched water indicate that 

perched waters were recharged mainly from fracture 

waters with little contribution from matrix water; and 

(5) major-ion chemistry indicates that most perched 

waters have similar chemical compositions to the

saturated-zone ground water except the perched water 

in USW UZ-14, which is typical of Topopah Spring 

Tuff water.

Rock-gas compositions are similar to the 

atmospheric air except that CO2 concentrations are 

generally larger than in air. The 8 13C (gas) values 

of USW UZ-1 are fairly constant from the surface to 

365.8 m, indicating little interaction between the gas 

CO2 and caliche in the soil. With regard to gas-water 

exchange, most of the carbon is in the aqueous phase. 

Consequently, an aqueous-phase 14C age will affect a 

gaseous-phase 14C age more than the converse. The 

reason for the nonequilibrium condition observed 

between the two phases is probably due to the fact that 

most of the gas was collected from fractures rather 

than from pores where equilibrium conditions may 

exist. Carbon-14 ages in the gaseous phase are significantly older than the water l C ages in the deep 

Topopah Spring Tuff and subadjacent units. The 

observed apparent age differences may result from 

liquid-gravity fracture flow, a process faster than 

gas-diffusion flow.

Model calculations indicate that gas transport in 

the unsaturated zone of Yucca Mountain agrees well 

with the steady-state diffusion and decay process, 

based on the 14C data from USW UZ-1. Tritiummodeling results indicate that the high tritium value of 

about 100 TU in the Calico Hills Formation of UZ#16 

is within limits of a piston-flow model with residence 

time of about 30 years. The large variations in tritium 

values with narrow peaks suggest an aqueous-phase 

flow in the unsaturated zone that is closer to a piston or 

preferential fracture flow than to a matrix flow.

REFERENCES

Benson, L.V., and McKinley, P.W., 1985, Chemical composition of ground water in the Yucca Mountain area, 

Nevada, 1971-84: U.S. Geological Survey Open-File 

Report 85-484,10 p.

Bird, R.B., Stewart, W.E., and Lightfoot, E.N., 1960, Transport phenomena: New York, John Wiley, 780 p.

Campana, M.E., and Mahin, D.A., 1985, Model-derived 

estimates of groundwater mean ages, recharge rates, 

effective porosities and storage in a limestone aquifer: 

Journal of Hydrology, v. 76, no. 3-4, p. 247-264.

Carmi, I., and Gat, J.R., 1973, Tritium in precipitation and 

freshwater sources in Israel: Israeli Journal of Earth 

Sciences, v. 22, no. 2, p. 71-92.

Summary and Conclusions 55
Cayan, D.R., McLain, D.R., Nichols, W.D., and

DiLeo-Stevens, J.S., 1991, Monthly climatic time 

series data the Pacific Ocean and western Americas: 

U.S. Geological Survey Open-File Report 91-92, 

380 p.

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waters: Science, v. 133, no. 3465, p. 1702-1703.

Craig, Harmon, and Lal, D., 1961, The production rate 

of nature tritium: Tellus, v. 13, p. 85-105.

Dansgaard, W., 1964, Stable isotopes in precipitation: 

Tellus, v. 16, no. 4, p. 436-468.

Davis, S.N., and Bentley, H.W., 1982, Dating groundwater in nuclear and chemical dating techniques, 

in Currie, L.A., ed., Interpreting the environmental 

record: Washington, D.C., American Chemical 

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Egboka, B.C.E., Cherry, J.A., Farrolden, R.N., and 

Frind, E.O., 1983, Migration of contaminants in 

groundwater at a landfill A case study 3, Tritium 

as an indicator of dispersion and recharge: Journal 

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Friedman, Irving, and O'Neil, J.R., 1977, Compilation of 

stable isotope fractionation factors of geochemical 

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Paper 440-KK.

Haas, H.H., Fisher, D.W., Thorstenson, D.C., and 

Weeks, E.P., 1983, 13CO2 and 14CO2 measurements on soil atmosphere sampled in the subsurface 

unsaturated zone in the western Great Plains of the 

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226, and 264, IAEA, Vienna, 1969, 1971, 1973, 1975, 

1979,1983, and 1986.

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p. 1337-1344.

Knott, J.F., and Olimpio, J.C., 1986, Estimation of recharge 

rates to the sand and gravel aquifer using environmental tritium, Nantucket Island, Massachusetts: 

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26 p.

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and Sharma, P., 1995, Significance of apparent 

discrepancies in water ages derived from atmospheric radionuclides at Yucca Mountain, Nevada, in 

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Moore, I.E., eds., Water resources at risk, a selection 

of the papers presented at the conference held in 

Denver, Colo., May 14 18, 1995: American 

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Loskot, C.L., and Hammermeister, D.P., 1992, Geohydrologic data from test holes UE 25 UZ#4 and 

UE 25 UZ#5, Yucca Mountain area, Nye County, 

I Nevada: U.S. Geological Survey Open-File 

; Report 90-369,56 p.

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Water-Resources Investigations Report 89 4072, 

46 p.

Millie, W.K., Benson, L.V., and McKinley, P.W., 1987, 

Isotope content and temperature of precipitation in 

southern Nevada, August 1983 August 1986: 

U.S. Geological Survey Open-File Report 87-463, 

32 p.

Mofttazer, Parviz, Weeks, E.P., Thamir, Falah, Yard, S.N., 

1 and Hofrichter, P.B., 1985, Monitoring the vadose zone 

I in fractured tuff, Yucca Mountain, Nevada, in National 

I Water Well Association Conference on Characterization and Monitoring of the Vadose (Unsaturated) Zone, 

Denver, Colo., November 19 21,1985, Proceedings: 

Denver, Colo., National Water Well Association, 

p. 439-469.

Montazer, Parviz, and Wilson, W.E., 1984, Conceptual 

hydrologic model of flow in the unsaturated zone, 

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55 p.

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triaxial and one-dimensional compression methods, 

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i Advances in hydroscience, v. 8: New York, Academic 

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Pearson, F.J., and Truesdell, A.H., 1978, Tritium in the 

water of Yellowstone National Park, in Zartman, R.E., 

ed., Short papers of the 4th international conference, 

geochronology, cosmochronology, isotope geology, 

August 20 25,1978, Snowmass-at-Aspen, Colo.: 

U.S. Geological Survey Open-File Report 78-701, 

p. 327-329.

56 Interpretation of Chemical and Isotopic Data From Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada
Peters, C.A., Striffler, P.S., Yang, I.C., Ferarese, J.S., 1991, 

Field testing the effectiveness of pumping to remove 

sulfur hexafluoride traced drilling air from a prototype 

borehole near Superior, Arizona, in Proceedings, 

Workshop 5 Flow and transport through unsaturated 

fractured-rock-related to high-level radioactive waste 

disposal: Tucson, Arizona, January 7 10, 1991, 

p. 79-83. (NUREG/CP-0040)

Peters, C.A., Yang, I.C., Higgins, J.D., and Burger, P.A., 

1992, A preliminary study of the chemistry of pore 

water extracted from tuff by one-dimensional compression: Proceedings, International Symposium on 

Water-Rock Interaction, 7th (WRI-7), Park City, Utah, 

July 13-18, 1992, p. 741-745.

Quiring, R.F., 1983, Precipitation climatology of the Nevada 

Test Sites: U.S. National Weather Service Report 

WSNSO 351-38,34 p. (NNA.870406.0324)

Scott, R.B., and Bonk, Jerry, 1984, Preliminary geologic map of 

Yucca Mountain, Nye County, Nevada, with geologic sections: U.S. Geological Survey Open-File Report 84-494, 

10 p., scale 1:12,000.

Shevenell, Lisa, 1991, Tritium in the thermal water discharging 

in Loowit Canyon, Mount St. Helens, Washington, U.S.A: 

Chemical geology; Isotope-Geoscience Section, v. 94, 

no. 2, p. 123-135.

Simpson, B., and Carmi, I., 1983, The hydrology of the

Jordan tributaries (Israel) Hydrolographic and isotopic 

investigation: Journal of Hydrology, v. 62, no. 1 4, 

p. 225-242.

Spengler, R.W., Braun, C.A., Martin, L.G., and Weisenberg, 

C.W., 1994, The Sundance Fault A newly recognized 

shear zone at Yucca Mountain, Nevada: U.S. Geological 

Survey Open-File Report 94-49, 11 p.

Spengler, R.W., Byers, P.M., Jr., and Warner, J.B., 1981, 

Stratigraphy and structure of volcanic rocks in 

drill hole USW G-l, Yucca Mountain, Nye 

County, Nevada: U.S. Geological Survey OpenFile Report 81-1349, 50 p.

Stewart, C.L., 1972, Clay-water interaction, the behaviour

t *)

of H and H in absorbed water, and the isotope effect: 

Proceedings, Soil Science Society of America, v. 36, 

no. 3, p. 421^26.

Striffler, P.S., and Peters, C.A., 1993, Effects of core sealing 

methods on the preservation of pore water: Proceedings 

of the Fourth Annual International Conference on HighLevel Radioactive Waste Management, Las Vegas, 

Nevada, April 26-30,1993, p. 960-966.

Szabo, B.J., and Kyser, T.K., 1985, Uranium, thorium 

isotopic analyses and uranium-series ages of calcite 

and opal, and stable isotopic compositions of calcite 

from drill cores UE-25a #1, USW G-2, and 

USW G-3/GU-3, Yucca Mountain, Nevada: 

U.S. Geological Survey Open-File Report 85-224, 

30 p.

Thatcher, L.L., Janzer, V.J., and Edwards, K.W., 1977, 

Methods for determination of radioactive substances in 

water and fluvial sediments: Book 5, chapter A5 of 

Techniques of water-resources investigations of the 

United States Geological Survey, 243 p.

Thorstenson, D.C., Haas, Herbert, Peters, C.A., and

Yang, I.C., 1995, The reactions and transport of CO2 

and its C-isotopes in the unsaturated zone at the crest 

of Yucca Mountain, Nevada: U.S. Geological Survey 

Administrative Report.

Thorstenson, D.C., and Pollock, D.W., 1989, Gas transport 

in unsaturated zones Multicomponent systems and 

the adequacy of Pick's laws: Water Resources 

Research, v. 25, no. 3, p. 477-507.

Thorstenson, D.C., Weeks, E.P., Haas, H.H., and Fisher, 

D.W., 1983, Distribution of gaseous 12CO2, 13CO2 , 

and 14CO2 in the subsoil unsaturated zone of the western U.S. Great Plains: Radiocarbon, v. 25, no. 2, 

p. 315-346.

Thorstenson, D.C., Weeks, E.P., Haas, H.H., and 

Woodward, J.C., 1990, Physical and chemical 

characteristics of topographically affected airflow 

in an open borehole at Yucca Mountain, Nevada, 

in Nuclear waste isolation in the unsaturated zone, 

Focus '89, Sept. 17-21,1990, Las Vegas, Nev., 

Proceedings: Las Vegas, Nev., p. 256 270.

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of thermal and nonthermal water in the Valles caldera, 

Jemez Mountains, northern New Mexico: Journal of 

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stable isotope composition of soil water: International 

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p. 509-517.

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unsaturated fractured rock, in Evans, D.D., and 

Nicholson, T.J., eds., Geophysical Monograph 42: 

American Geophysical Union, p. 165 170.

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implications of the stable isotopic composition of 

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of Yucca Mountain, Nevada, in High-level radioactive 

waste management, international conference, 3d, 

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Las Vegas, Nev., p. 1572-1581.

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international conference, 5th, Las Vegas, Nev., 

May 22-26,1994, Proceedings: Las Vegas, Nev., 

p. 2738-2745.

References 57
Whitfield, M.S., 1985, Vacuum drilling of unsaturated 

tuffs at a potential radioactive-waste repository, 

Yucca Mountain, Nevada, in National Water Well 

Association conference on characterization and monitoring of the vadose (unsaturated) zone, Denver, Colo., 

November 19 21, 1985, Proceedings: Denver, Colo., 

National Water Well Association, p. 413-423.

Whitfield, M.S., Thordarson, William, and Hammermeister, 

D.P., 1990, Drilling and geohydrologic data for 

test hole USW UZ 1, Yucca Mountain, Nye 

County, Nevada: U.S. Geological Survey OpenFile Report 90-354,40 p.

Yang, I.C., 1992, Flow and transport through unsaturated 

rock Data from two test holes, Yucca Mountain, 

Nevada, in High-level radioactive waste management, international conference, 3d, Las Vegas, Nev., 

April 12 16, 1992, Proceedings: Las Vegas, Nev., 

p. 732-737.

Yang, I.C., Davis, G.S., and Sayer, T.M., 1990, Comparison of pore-water extraction by triaxial compression and high-speed centrifugation method,

in Zaporozec, Alexander, ed., Minimizing risk to 

the hydrologic environment: Dubuque, Iowa, 

Kendall/Hunt Publishing Company, p. 250-259.

Yang, I.C., Herbert, H.H., Weeks, E.P., and Thorstenson, 

jD.C., 1985, Analysis of gaseous-phase stable 

and radioactive isotopes in the unsaturated zone, 

Yucca Mountain, Nevada, in National Water Well 

Association conference on characterization and moni- 

[toring of the vadose (unsaturated) zone, Denver, Colo., 

|November 19 21,1985, Proceedings: Denver, Colo., 

National Water Well Association, p. 488 506.

Yang, I.C., Peters, C.A., and Thorstenson, D.C., 1993, 

Carbon isotopic data from test hole USW UZ 1, 

Yucca Mountain, Nevada, in High-level radioactive 

waste management, international conference, 4th, 

Las Vegas, Nev., April 26 30,1993, Proceedings: 

Las Vegas, Nev., p. 401-406.

YangL I.C., Turner, A.K., Sayre, T.M., and Montazer, Parviz, 

i!988, Triaxial-compression extraction of pore water 

from unsaturated tuff, Yucca Mountain, Nevada: 

U.S. Geological Survey Water-Resources Investigations Report 88-4189,68 p.

58 Interpretation of Chemical and Isotopic Data From Boreholes In the Unsaturated Zone at Yucca Mountain. Nevada

* U.S. GOVERNMENT PRINTING OFFICE 1996-0-774-216/40007
Corrected Table 5, WRIR 96-4058. Comparison of pore-water composition in lithologic contacts and adjacent beds, Y

[m, meters; mg/L, milligrams per liter] Revisions in the outlined cells below have been checked and accepted by:

I. C. Yan

Cells with changes are outlined

Sample 

Identification

Compression stage codes have been added 

to the sample Identification

NRG-6/1 58.2-1 58.6/up1 Shardy base/bedded 

NRG-6/171.0-171.3/up1 Bedded 

NRG-6/1 75.6-1 76.0/up1 Pah Canyon

UZ-1 4/235. 1 -235.4up1 Pah Canyon 

UZ-1 4/240.8-241 .1 /up1 Pah Canyon/ Bedded 

UZ-14/245.5-245.6/up1 Bedded

UZ-1 6/1 434.2-1 434.6/up1 Calico Hills 

UZ-1 6/1 442.8-1 443.2/up1 Calico Hills 

UZ-1 6/1 486.9-1 487.3/up1 Calico Hills/Prow Pass 

UZ-1 6/1 601 . 1 -1 601 .5/up1 Prow Pass

Footnotes:

Symbol 

in Piper Average 

diagram Depth 

(fig.6B) (m)

1 48.28 

2 52.18 

3 53.58

4 71.72 

5 73.46 

6 74.89

7 437.21 

8 439.83 

A 453.27 

B 488.08

Aluminum* 

Al 

(mg/L)

0 

0 

0

0 

3 

0

6.1 

1.2 

26.2 

0.7

Calcium 

Ca 

(mg/L)

122 

70.5 

49.2

67 

32 

65

3.2 

1.7 

6.3 

10

Magnesium Sodium 

Mg Na 

(mg/L) (mg/L)

23.3 35.6 

11.5 29.2 

8.6 29.4

10.5 29 

1 103 

12 9

0.6 113 

0.8 79.9 

0.8 79.5 

0.3 100

Bicarbonate 

HCO3 

(mg/L)

34 

48 

60

96 

162 

66

72 [a] 

18.3 [a]

137 

181

Carbonate 

CO3 

(mg/L)

0 

13 

0

na 

na 

na

70.8 [a] 

87.6 [a]

0 

0

Chloride 

CL 

(mg/L) 

185 

58 

47

84 

99 

77

23 

18.9 

38 

53

[a] - Values reported by the laboratory for these samples were for CaCO3 equivalent. The table values posted here have been mathematica

bicarbonate and carbonate concencentration. Compression code; /up1 indicates first-stage uniaxial compression.

*0.45 urn filter paper was used, hence, particulate aluminum is likely included in these values.
Corrected Table 2, WRIR 96-4058. Chemical composition of pore-water and ground-water samples from boreholes UE-25 UZ#16, UE-25 

Cells with changes are outlined

Sample Identification

UZ-N2-Area Precipitation 

UZ-N2-Water 

UZ-N2-Water 

UZ-N2-Water 

UZ-N2-Water 

UZ-N46-Water

H| Revisions in the outlined cells below have been checked and accepted by. ^^^ ~^^~*-'^^~*~/ l rty/ff

Symbol 

in Piper 

diagram 

(fi8-7B)

Average 

Depth 

(meters)

0 

15.8 

15.6 

15.8 

15.8 

30.1

Specific Calcium Magnesium 

Date pH Conductance Ca Mg 

(nS/cm) (mg/L) (mg/L)

03/31/92 --- --- 0.7 0.5 

08/1 8/89 7.7 308 14 2.3 

02/14/92 --- --- 1.4 0.5 

03/16/92 --- --- 14.4 3.9 

03/31/92 --- --- 25 4.7 

02/14/92 --- --- 0.8 0.5

I. C. Yang

Sodium Silica 

Na Si02 

(mg/L) (mg/L)

0.8 0.9 

51 18 

1.7 0 

25.1 5.8 

16.2 11.8 

1.6 0.2

( Date

Aluminum Bicarbonate 

Al HC03 

(mg/L) (mg/L)

0 23.3 

112 

0 11.7 

0 58.2 

0 127.6 

0 23.3

Carb

C

(m

UZ 16 Pore Water - Compression stage codes have been added to the sample Identification for UZ-16 samples. |

UZ-18/1 63.5-163.9/up1 

UZ-1 6/1 80.9-1 81 .3/up4 

UZ-18/1 166.19-1 166.47/up1 

UZ-18/1 227.4-1 227.7/up1 

UZ-18/1 235.1-1235.41/up1 

UZ-1 6/1 269.6-1 269.9/up1 

UZ-1 6/1 280.4-1 280.8/up3 

UZ-16/1 296.8-1297 .06 /up1 

UZ-18/1317.9-1318.2/up1 

UZ-18/1343.7-1344.07up1 

UZ-18/1358.0-1358.4/up1 

UZ-16/1379.6-1379.9/up1 

UZ-1 6/1 389.3-1 389.6/up3 

UZ-1 8/1 395.5-1 395.9/up1 

UZ-1 6/1 397.7-1 398.0/up1 

UZ-18/1398.5-1398.7/up1 

UZ-16/1 408.2-1 408.6/up1 

UZ-16/1412.9-1413.2Aip1 

UZ-16/1428.1-1428.4/up1 

UZ-16/1 434.2-1434.8/up1 

UZ-16/1 442.9-1 443.2/up6 

UZ-16/1486.9-1487.3/up1 

UZ-18/1 601. 1-1601 .5/up1 

UZ-18/1607.7-1608.1/up1 

UZ-18/l'643.4-1647.2/up1 

UZ-16/1651.6-1651.7/up1

UZ-16 ground water #1 

(1609.0-1614.0) 

UZ-16 ground water #2 

(1609.0-1614.0) 

UZ-16 ground water #3 

(1609.0-1614.0) 

UZ-16 ground water #1 

(1649.3-1659.2) 

UZ-16 ground water #2 

(1649.3r1 659.2) 

UZ-16 ground water 

(1649.3-1686.2)

1 

2 

3 

4 

5 

6 

7 

8 

9 

A 

B 

C 

D 

E 

F 

G 

H 

I 

J

L 

M 

N 

0 

P 

R

49.90 

55.20 

| 355 48 | 

374.17 

376.52 

387.04 

390.33 

395.33 

401.76 

409.62 

413.98 

420.56 

423.52 

425.41 

426.08 

426.29 

429.28 

430.71 

435.35 

437.21 

439.83 

453.27 

488.08 

490.09 

501.49 

503.44

491.19 

491.19 

491.19 

504.22 

504.22 

508.33

12/02/92 7.6 425 

11/16/92 7.5 430 

09/27/94 8.7 710 

08/09/93 8.1 430 

08/11/93 8.2 480 

08/04/93 8.5 430 

09/02/93 8.3 530 

09/23/93 7.4 930 

09/09/93 7.3 420 

07/01/93 8.4 530 

05/06/93 7.5 550 

06/29/93 8.6 490 

05/18/93 7.0 530 

03/31/94 7.8 710 

07/07/93 8.7 550 

04/05/94 8.0 710 

07/28/93 9.2 580 

09/16/93 8.7 450 

09/14/93 8.8 570 

07/13/93 8.5 550 

06/17/93 7.6 550 

09/21/93 9.2 360 

12/30/93 8.9 570 

01/24/94 9.0 660 

03/01/94 9.0 490 

03/15/94 8.4 420

02/24/93 

02/25/93 

02/25/93 

03/08/93 

03/09/93 

03/15/93 --- 

42.5 13.4 

55 11 

28.9 13.7 

26.5 6.2 

33.5 7.9 

14.1 2.4 

20.5 3.7 

32.4 19.7 

20.6 5.1 

17 2.4 

3.4 0.3 

4.4 0.6 

3.6 0.9 

5.4 0.3 

5 0.5 

5 0.4 

3.3 0.3 

1.2 0.1 

1.9 0.1 

3.2 0.6 

1.7 0.8 

6.3 0.8 

10 0.3 

25 0.3 

91 12 

17.3 0.3

11.4 1.6 

19.2 2.1 

30.1 2.9 

10.3 1.8 

8.6 0.7 

8.4 1.3

21.5 77.5 

20 83 

83.6 57.1 

47.9 62.2 

51 .3 52.9 

67.5 57.1 

92.0 71.8 

98.2 46.7 

60.1 131.6 

99 62.1 

76.7 47.9 

95 66.3 

114.8 62.5 

155 88 

124 79.2 

145 123 

104 66.5 

101 75.9 

134 80.5 

113 109.1 

79.9 68.9 

79.5 233.3 

100 36 

108 34 

34 70 

66 47.4

79.2 38.2 

175.1* 25.5 

360.5* 27.2 

76.1 170.6 

65.4 18.4 

87.2 16.5

0.5 

0.1 

0 

0.3 

0 

0 

1.5 

0 

1.1 

1.7 

1.1 

2.6 

2.0 

3.9 

4.7 

7.8 

3.4 

1 

3.4 

6.1 

1.2 

26.2 

0.7 

1.0 

0 

0.7

1.2 

0 

0.2 

19.9 

0 

0.1

11 4.7 [a] 

146.4 [a]

196 

137 

154 

139 

192 

324 

171 

47.6

140.3 [a]

72

122 [a]

216 

131.8 

237

72 [a]

165 

160

72 [a]

18.3 [a]

137 

181 

170 

162 

87

210.3 |

196.7 

200 

164.2 

151.6 

197.3

45.

<0.

5

0

4

36.

2

3

3

70.

4

70.

87.

[a] Values reported by the laboratory for these samples were for CaCO, equivalent The table values posted here have been mathematically converted to bicarbonate 

stag* codes; /up Indicate* sampto was extracted by unlaxlal compression; /up1 , /up2, /up3, etc. Indicates tint, second, third stage compression and so forth.

The published footnotes for the table have not changed and still apply. Charge balance values have not changed and the column has been intentionally omitted from this revised t
Corrected Table 1, WRIR 96-4058. Summary of relation of gravimetric water-content measurements of composite 

core to geologic unit and degree of welding for boreholes UE-25 UZ#4 and UE-25 UZ#51 , Yucca Mountain, Nevada

| Cells with changes are outlined _____ | [All water-content data in gram per gram; - -, indicated no data]

The revision in the outlined cell below has been checked and accepted by: ^Xu_ ve^^CT *^~^~^/ . v/tjP/f

Lithologic 

Unit

Tiva Canyon 

Tiva Canyon 

Tiva Canyon 

Yucca Mountain 

Pah Canyon 

Bedded Tuff 

Topopah Spring 

Topopah Spring

UE-25 UZ#4

Data Range

| 0.036-0.042 |

0.061-0.063 

0.253-0.521 

0.101-0.210 

0.092-0.182 

0.069-0.391

0.007-0.035

Water Content, 

gram/gram

Average

0.039 

0.062 

0.363 

0.157 

0.134 

0.167

0.020

UE-25 UZ#5

Data Range

0.024-0.036

0.145-0.290 

0.059-0.143 

0.084-0.221 

0.078-0.365 

0.221-0.279 

0.011-0.015

I. C. Yang '

Average

0.030

0.202 

0.110 

0.122 

0.176 

0.248 

0.013

^ / Date

Degree of 

Welding

Densely welded 

Moderately welded 

Partly to nonwelded 

Partly to nonwelded 

Partly to nonwelded

Nonwelded 

Densely welded

1 From Loskot and Hammermeister (1992)
United States Department of the Interior

U. S. GEOLOGICAL SURVEY 

Box 25046 M.S. 421

IN REPLY REFER TO:

Denver Federal Center 

Denver, Colorado 80225

MEMORANDUM

Date: August 31, 2000

To: Distribution

From: T. Brady, USGS, WRD, YMPB, Denver, CO

Subject: Publications ~ Errata for USGS Water-Resources Investigations Report 96-4058 

"Interpretation of Chemical and Isotopic Data from Boreholes in the Unsaturated Zone at Yucca 

Mountain, Nevada

This errata sheet corrects Tables 1, 2, and 5 of this report. 

Please enclose this errata sheet with the distribution of this report.

Thank you for your cooperation with this request. If you have any questions that pertain to this 

matter, please contact Tim Brady at (303)236-5050, ext 249.

For

Tim Brady, Reports Specialist 

Bob Craig, Chief, YMPB

BTM/mm 

Enclosure