CHARACTERIZATION OF HYDROGEOLOGIC UNITS 

USING MATRIX PROPERTIES, YUCCA MOUNTAIN, 

NEVADA 

by Lorraine E. Flint 

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 97-4243 

Prepared in cooperation with the 

NEVADA OPERATIONS OFFICE, 

U.S. DEPARTMENT OF ENERGY, under 

Interagency Agreement DE-A108-92NV10874 

Denver, Colorado 

1 998 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Thomas J. Casadevall, Acting Director 

. 

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

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

For additional information write to: Copies of this report can be purchased from: 

Chief, Earth Science Investigations Program U.S. Geological Survey 

Yucca Mountain Project Branch Information Services 

U.S. Geological Survey Box 25286 

Box 25046, Mail Stop 421 Federal Center 

Denver Federal Center Denver, CO 80225 

Denver, CO 80225-0046 
CONTENTS 

Abstract ................................................................................................................................................................................. 

Introduction ........................................................................................................................................................................... 

Site Description ..................................................................................................................................................................... 

Location and Geologic Setting .................................................................................................................................... 

Lithologic Features ..................................................................................................................................................... Hydrologic Implications of Lithologic Stratification .................................................................................................. 

Transition Zones ................................................................................................................................................ 

Capillary and Permeability Barriers .................................................................................................................. Methods ................................................................................................................................................................................. 

Sample Collection ....................................................................................................................................................... Laboratory Core Processing ......................................... .c ............................................................................................. Moisture-Retention Characterization .......................................................................................................................... Correction of Water-Content and Water-Potential Data .............................................................................................. 

Characterization of Hydrogeologic Units ............................................................................................................................ Phase 1: Porosity Profiles ........................................................................................................................................... 

Tiva Canyon Tuff .............................................................................................................................................. 

Nonwelded Paintbrush Tuff and Base of Tiva Canyon Tuff ............................................................................. Topopah Spring Tuff ......................................................................................................................................... 

Calico Hills Formation ...................................................................................................................................... Prow Pass and Bullfrog Tuffs ........................................................................................................................... Phase 2: Alteration, Microfractures, and Permeability .............................................................................................. Phase 3: Moisture Retention and Predictions of Field Water Potentials .................................................................... Phase 4: Statistical Analysis to Produce Mean Values for Modeling Parameters ..................................................... 

Spatial Distribution of Porosity ................................................................................................................................... 

Summary ............................................................................................................................................................................... References ............................................................................................................................................................................. Appendix: Frequency Distributions of Porosity for Hydrogeologic Units .......................................................................... 

FIGURES 

1 . Map of study site with locations of boreholes used to develop matrix properties data set and 

hydrogeologic units ........................................................................................................................................... 2 . Diagram of the steps used to process core samples to obtain hydrologic property measurements .......................... 3 . Porosity. saturation. particle density. and water potential with calculated no-flow conditions in 

equilibrium with the water table. with depth for borehole SD7 ........................................................................ 4 . Porosity. saturation. particle density. and water potential with calculated no-flow conditions in 

equilibrium with the water table. with depth for borehole SD9 ........................................................................ 5 . Oven-dry porosity and saturation profiles for rocks from the upper part of the Tiva Canyon Tuff 

in boreholes N36 and N27 ................................................................................................................................ 6 . Oven-dry porosity and saturation profiles for rocks between the lower part of the Tiva Canyon Tuff. 

bedded tuffs of the Paintbrush Group. Yucca Mountain and Pah Canyon Tuffs. and the upper part 

of the Topopah Spring Tuff for boreholes SD7. N54. and N55 ........................................................................ 7 . Oven-dry porosity and saturation profiles for rocks from the Paintbrush Group between the lower 

Tiva Canyon Tuff and upper Topopah Spring Tuff in boreholes N3 1 and SD9 ............................................... 8 . Oven-dry porosity and saturation profiles of rocks from the Topopah Spring Tuff in boreholes UZ14. 

UZ 16. and SD7 ................................................................................................................................................. 

1 

1 

5 

5 

7 

9 

9 

9 

11 

11 

11 

17 

18 

19 

21 

21 

21 

27 

29 

29 

32 

40 

43 

46 

54 

54 

59 

6 

16 

22 

23 

24 

25 

26 

28 

Contents Ill 
9 . Oven-dry porosity and saturation profiles of rocks from the base of the Topopah Spring Tuff; the 

pre-Topopah Spring bedded tuff; the Calico Hills Formation; and the Prow Pass. Bullfrog and 

Tram Tuffs of the Crater Flat Group from boreholes SD9. UZ16. and SD7 ................................................... 10 . Porosity determined using standard oven drying and relative humidity oven drying for core from the 

Calico Hills Formation. Prow Pass Tuff. and part of the Bullfrog Tuff in SD7 and for core from the 

lower part of the Tiva Canyon Tuff to the upper part of the Topopah Spring Tuff in borehole N3 1 ............... 

11 . Calculated particle density using water saturation versus particle density measured using helium 

pycnometry for nonwelded to densely welded tuffs that are vitric. crystallized. or zeolitized on 

samples from borehole UZ 16 ........................................................................................................................... 12 . Relation of porosity and saturated hydraulic conductivity for samples grouped (a) by various hydrogeologic 

units and (b) by vitric/crystallized. altered. and microfractured units ............................................................. 13 . Moisture-retention curves for core samples from hydrogeologic units (a) CW. (b) BT3. (c) TR. (d) TUL. 

(e) TMN. (f) PV3. (g) CHZ. and (h) PP2 ......................................................................................................... 14 . Relation of log of moisture-retention curve-fit parameter. van Genuchten alpha. to porosity ................................. 15 . Measured (squares) and estimated (circles) water potential using moisture-retention parameters 

for boreholes SD7. SD9. and UZ14 ................................................................................................................. 16 . Contour plots of the spatial distribution of p6rosity for hydrogeologic units (a) CW. using 17 boreholes. 

and (b) BT2. using 15 boreholes ...................................................................................................................... 

TABLES 

1 . 

2 . 

3 . 

4 . 

5 . 

6 . 

7 . 

8 . 

9 . 

Generalized lithostratigraphy (modified from Buesch and others. 1996b; Moyer and Geslin. 1995). 

previously used informal nomenclature (modified from Scott and Bonk. 1984). and corresponding 

major units (Montazer and Wilson. 1984) and detailed hydrogeologic units at Yucca Mountain. Nevada ..... Data tracking numbers for all data used ................................................................................................................... Borehole descriptions. locations, and drilling dates ................................................................................................. Generalized lithostratigraphy of eight deep boreholes ............................................................................................. Generalized lithostratigraphy of 23 neutron boreholes ............................................................................................ Regression equations used to predict saturated hydraulic conductivity and moisture-retention curve-fit 

parameter, a. from porosity .............................................................................................................................. Mean values and standard deviations for measured core properties compiled from all boreholes for 

each hydrogeologic unit ................................................................................................................................... Moisture-retention van Genuchten curve-fit parameters, alpha and n, for each hydrogeologic unit ....................... Mean porosity, saturation, and standard deviations for each hydrogeologic unit in each borehole ......................... 

30 

31 

34 

35 

36 

41 

42 

47 

3 

12 

13 

14 

15 

39 

44 

45 

47 

iv Characterization of Hydrogeologic Units Using Matrix Properties. Yucca Mountain. Nevada 
CONVERSION FACTORS 

Multiply BY To obtain 

micrometer (pm) 

centimeter (cm) 

centimeter squared (cm2) 

cubic centimeter (cm3) 

cubic centimeter per cubic 

centimeter (cm3/cm3) 

gram per cubic centimeter (g/cm3) 

meter (m) 

meter per second (mls) 

millimeter per year (mmlyr) 

kilometer (km) 

square kilometer (km2) 

megapascals (MPa) 

0.0394 

0.3937 

0.1550 

0.06 10 

1 .oooo 

0.036 1 

3.28 10 

3.28 10 

1x10-'~ 

Q.62 I4 

0.3861 

10.0 

inch 

inch 

inch squared 

cubic inch 

cubic inch per cubic inch 

pound per cubic inch 

feet 

feet per second 

feet per second 

mile 

square mile 

bars 

Degree Celsius (OC) may be converted to degree Fahrenheit (OF) by using the following equation: 

OF = 915 (OC) + 32. 

Degree Fahrenheit (OF) may be converted to degree Celsius (OC) by using the following equation: 

OC = 519 (OF - 32). 

Contents v 
Characterization of Hydrogeologic Units Using Matrix 

Properties, Yucca Mountain, Nevada 

By Lorraine E. Flint 

ABSTRACT 

Determination of the suitability of Yucca 

Mountain, in southern Nevada, as a geologic 

repository for high-level radioactive waste 

requires the use of numerical flow and transport 

models. Input for these models includes parameters that describe hydrologic properties and the initial and boundary conditions for all rock materials 

within the unsaturated zone, as well as some of the 

upper rocks in the saturated zone. There are 30 

hydrogeologic units in the unsaturated zone, and 

each unit is defined by limited ranges where a discrete volume of rock contains similar hydrogeologic properties. These hydrogeologic units can 

be easily located in space by using three-dimensional lithostratigraphic models based on relationships of the properties with the lithostratigraphy. 

Physical properties of bulk density, porosity, and 

particle density; flow properties of saturated 

hydraulic conductivity and moisture-retention 

characteristics; and the state variables (variables 

describing the current state of field conditions) of 

saturation and water potential were determined for 

each unit. Units were defined using (1) a data base 

developed from 4,892 rock samples collected from 

the coring of 23 shallow and 8 deep boreholes, 

(2) described lithostratigraphic boundaries and 

corresponding relations to porosity, (3) recognition of transition zones with pronounced changes 

in properties over short vertical distances, 

(4) characterization of the influence of mineral 

alteration on hydrologic properties such as permeability and moisture-retention characteristics, and 

(5) a statistical analysis to evaluate where boundaries should be adjusted to minimize the variance 

within layers. This study describes the correlation 

of hydrologic properties to porosity, a property 

that is well related to the lithostratigraphy and depositional and cooling history of the volcanic 

deposits and can, therefore, be modeled to be distributed laterally. Parameters of the hydrogeologic 

units developed in this study and the relation of 

flow properties to porosity that are described can be 

used to produce detailed and accurate representations of the core-scale hydrologic processes ongoing 

at Yucca Mountain. 

- INTRODUCTION 

Characterization of physical and hydrologic properties of subsurface materials is critical to the evaluation 

of sites for land-use practices, such as landfills, radioactive waste burial, regeneration of deforested sites, and 

agriculture. These practices all have in common the need 

to understand subsurface hydrology in terms of the water 

balance of the system and transport of chemicals through 

subsurface horizons, whether saturated or unsaturated. 

Predictions of water flow and contaminant transport 

pathways and flux rates are major issues facing many 

land managers and environmental researchers and often 

require the use of numerical models. These models generally require input of parameters describing physical 

and flow properties of the media, geometry of the modeling domain, and initial and boundary conditions. In 

addition, subsurface processes, such as perched water, 

preferential flow paths, or lateral diversion of water, 

which are influenced by features, such as faults, fractures, 

or abrupt changes in lithology, can also be understood 

through characterizing the properties of the media. 

Numerous researchers have measured hydrologic properties of the tuffs at Yucca Mountain (Anderson, 198 1 a,b, 

1984, 1991; Rush and others, 1983; Thordarson and others, 1984; Weeks and Wilson, 1984; Whitfield and others, 

1984; Whitfield and others, 1993; Peters and others, 

1984; Peters and others, 1987; Klavetter and Peters, 

1987; Flint and Flint, 1990; Kume and Hammermeister, 

1990; Nelson and others, 1 99 1 ; Rautman, 199 1 ; Loskot 

and Hammermeister, 1992; Loskot, 1993; Rautrnan and 

others, 1995; Flint and others, 1996b). This study is 

being conducted in cooperation with the U.S. Department of Energy to provide a consistent and repeatable 

framework based on samples collected and methodology 

lntroductlon 1 
performed following an approved quality-assurance 

program for the purpose of site characterization. 

The site being characterized in this study is 

Yucca Mountain, a potential location for a geologic 

repository for high-level radioactive waste. Yucca 

Mountain is located in southern Nevada within the 

southern Nevada volcanic field and is underlain by a 

thick sequence of volcanic rocks of Miocene age with 

numerous variations in lithostratigraphy and orientation of the layered Tertiary volcanic sequence (Scott 

and Bonk, 1984; Buesch and others, 1996a). The processes of eruption and deposition, including the cooling and crystallization of some deposits, and the 

postdepositional processes of alteration and tectonics 

all contribute to the distribution of volcanic rock types. 

Knowledge of these processes is critical to understanding variations in the distribution of hydrologic and 

physical properties in the unsaturated zone at this site. 

Lithostratigraphic units are based on depositional, 

welding, crystallization, alteration, and fracture characteristics (Buesch and others, 1996b; Moyer and 

Geslin, 1995), as well as variations in hydrogeologic 

properties such as bulk density, grain density, porosity, 

and permeability (Scott and others, 1983; Flint and 

Flint, 1990; Moyer and others, 1996). These properties 

correlate well in many cases with lithostratigraphic features such as welding, vitrification, and mineralogy 

(Rautman and Flint, 1992; Istok and others, 1994; Flint 

and others, 1996b; Moyer and others, 1996). 

Descriptions of lithostratigraphic units (Geslin 

and others, 1995; Geslin and Moyer, 1995; Moyer and 

Geslin, 1995; Moyer and others, 1995; Buesch and others, 1996b; Engstrom and Rautman, 1996; Rautman 

and Engstrom, 1996a, 1996b) and the properties measured during this study were used to develop distinct 

hydrogeologic units with associated mean values of 

physical properties and hydrologic parameters that can 

be used in numerical modeling. Hydrogeologic-unit 

designations have been historically confined to large 

unit divisions based primarily on degree of welding 

(Scott and others, 1983; Montazer and Wilson, 1984). 

Montazer and Wilson (1 984) grouped rocks into five 

hydrogeologic units (table 1): the Tiva Canyon 

welded, Paintbrush nonwelded, Topopah Spring 

welded, Calico Hills nonwelded, and the Crater Flat 

variably to nonwelded units. 

The purpose of this report is to provide a more 

detailed division of the rocks at Yucca Mountain. 

Being able to define most of the hydrogeologic boundaries from lithostratigraphic boundaries was a major 

consideration in order to be able to spatially distribute 

the properties for any modeling effort with the use of 

the three-dimensional lithostratigraphic framework 

model produced by the U.S. Geological Survey 

(USGS) (Buesch and others, 1996b). To provide reasonable detail and predictive ability within the magnitude and heterogeneity of the Yucca Mountain site and 

to allow for detailed process modeling as well as largescale three-dimensional modeling, the number of distinct vertical layers was limited and resulted in a total 

of 30. Relations of modeling parameters to porosity 

are also presented to provide the means by which even 

more detailed process models can be constructed; for 

example, through the scaling of parameters in transitional zones where properties change dramatically over 

short distances or in clay-altered or vapor-phase 

corroded zones. 

The Yucca Mountain site provides several challenges to understanding the distribution and modeling 

of physical properties and hydrologic parameters due 

to the depositional, cooling, and alteration history of 

the rocks. This history results in differences in porosity, connectivity and tortuosity of flow paths, waterretention character, vertical heterogeneities, and 

various scales of features that all influence the resulting 

hydrogeology at the site. These characteristics are discussed in detail in various sections of this report. There 

are 15 rock types that result from variously combining 

the type of deposition, amount of welding, and composition of grainwither glass, crystallized at high temperature (quartz, feldspar, and vapor-phase minerals), 

or diagenetically'altered (zeolites and clays). Data presented are described within the context of these 15 rock 

(lithologic) types. In several locations, horizontal 

boundaries between lithostratigraphic and hydrogeologic units are distinctly abrupt. These contacts need to 

be modeled as distinct boundaries to promote the 

appropriate modeled hydrologic responses, such as lateral diversion due to capillary banier or permeability 

barrier effects (Montazer and Wilson, 1984). In other 

locations, the transitional zones also need to be modeled appropriately so that, for example, abrupt discontinuities in modeling matrix properties do not result in 

unwarranted diversion or ponding of water where discontinuities do not actually exist (Moyer and others, 

1996), but where the change in properties is, in reality, 

gradual or smooth. Alteration of glass to clays and zeolites has occurred in several lithostratigraphic locations. These alterations are due to (1) transitions in 

lithology that have resulted in high saturations, (2) an 

2 Characterization of Hydrogeoioglc Units Using Matrix Properties, Yucca Mountain, Nevada 
Table 1. Generalized lithostratigraphy (modified from Buesch and others, 1996b; Moyer and Geslin, 1995), previously 

used informal nomenclature (modified from Scott and Bonk, l984), and corresponding major units (Montazer and Wilson, 

1984) and detailed hydrogeologic units at Yucca Mountain, Nevada 

[<, less than; > greater than; %, percentage of matrix porosity] 

Previously used Hydrogeologlc units 

Currently used formal and Informal nomenclature Informal nomenclature Detalled Major 

PAINTBRUSH GROUP 

Tiva Canyon Tuff (Tpc) 

crystal-rich member (Tpcr) 

vitnc zone (rv) 

nonlithophysal zone (m) 

subvitrophyre transition subzone (m4) 

pumice-poor subzone (m3) 

mixed pumice subzone (m2) 

Tiva 

Canyon 

Welded 

(TCw) 

vitrophyre (ccr) CCR (I 9%) 

upper chff (cuc) CUC (> 9%) 

crystal transition subzone (ml) 

lithophysal zone (rl) 

crystal-poor member (Tpcp) 

upper lithophysal zone (pul) 

middle nonlithophysal zone (pmm) 

lower lithophysal zone (pH) 

lower nonlithophysal zone (pln) 

hackly subzone (plnh) 

columnar subzone (plnc) 

argillic pumic interval (plnc2) 

vitric zone (pv) 

densely welded subzone (pv3v) 

moderately welded subzone (pv2) 

non- to partially welded subzone (pvl) 

Pre-Tiva Canyon Tuff bedded tuff (Tpbt4) 

Yucca Mountain Tuff (Tpy) 

Pre-Yucca Mountain Tuff bedded tuff (Tpbt3) 

Pah Canyon Tuff (Tpp) 

Pre-Pah Canyon Tuff bedded tuff (Tpbt2) 

Topopah Spring Tuff (Tpt) 

crystal-rich member (Tptr) 

vitric zone (rv) 

nonwelded subzone (rv3) 

moderately welded subzone (rv2) 

densely welded subzone (rvl ) 

nonlithophysal zone (m) 

dense subzone (m3) 

vapor-phase corroded subzone (m2) 

lithophysal zone (rl) 

crystal-poor member (Tptp) 

upper lithophysal zone (pul) 

middle nonlithophysal zone (pmn) 

lower lithophysal zone (pH) 

lower nonlithophysal zone (pln) 

vitric zone (pv) 

densely welded subzone (pv3) 

moderately welded subzone (pv2) 

nonwelded subzone (pvl) 

Pre-Topopah Spring Tuff bedded tuff (Tpbt 1) 

upper lithophysal (cul) CUL (<20%) 

clinkstone (cks), rounded step (crs) CW 

lower lithophysal (cll) 

hackly (ch) 

columnar (cc) 

CMW (>IS%) 

vitrophyre 

nonwelded base (ccs) CNW (>28%) 

Paintbrush 

B T4 nonwelded 

TPY (I 30%) (PTn) 

B T3 

TPP 

BT2 

vitrophyre (tc) TC (~9%) Topopah 

rounded (tr) Spring 

welded 

TR (TSw) 

TUL 

upper lithophysal (tul) 

mlddle nonl~thophysal (trnn) TMN -- . . 

lower lithophysal (tll) TLL 

mottled (tm) 

. , TM2 (u~~er . 213) a. 

TMI (lower 113) 

basal vitrophyre (tv) PV3 

nonwelded base PV2 Calico 

Hills 

nonwelded 

BTlrr (altered) (CHn) 

B TI (unaltered) 

lntroductlon 3 
Table 1. Generalized lithostratigraphy (modified from Buesch and others, 1996b; Moyer and Geslin, 1995), previously 

used informal nomenclature (modified from Scott and Bonk, 1984), and corresponding major units (Montazer and Wilsc 

1984) and detailed hydrogeologic units at Yucca Mountain, Nevada--Continued 

[<, less than; > greater than; %, percentage of matrix porosity] 

P~~VIOUSIY used Hydr~geol~gi~ units 

Currently used formal and informal nomenclature Informal nomenclature Detailed Major 

CALICO HILLS FORMATION (Tac) 

Unit 4 Pumiceous pyroclastic flow Calico Hills vitric (CHv) CHV(vitic) Calico 

Hills 

Unit 3 Lithic-rich pyroclastic flow Calico Hills zeolitized (CHz) CHZ (zeolitic) nonwelded 

Unit 2 Pumiceous pyroclastic flow (CHn) 

Unit 1 Lithic-rich pyroclastic flow 

Bedded tuff (Tacbt) BT 

Basal sandstone (Tacbs) 

CRATER FLAT GROUP 

Prow Pass 'hff (Tcp) 

Unit 4 Pyroxene rich PP4 (zeolitic) 

Unit 3 Welded pyroclastic flow PP3 (devitrified) 

PP2 (devitrified) 

Unit 2 Lithic-rich pyroclastic flow PP1 (zeolitic) 

Unit I Pumiceous pyroclastic flow 

Pre-Prow Pass bedded tuff (Tcpbt) 

Bullfrog 'hff (Tcb) BF3 (welded) Crater Flat 

Unit 4 (CF4 

Unit 3 

Unit 2 BF2 (nonwelded) 

Unit 1 

Pre-Bullfrog Tuff basal sandstone (Tcbbs) 

Tram 'hff (Tct) 

4 Characterlzatlon of Hydrogeologic Unlts Uslng Matrix Properties, Yucca Mountaln, Nevada 
ancient water table or perched water zones, (3) weathering at the surface of ash flows, or (4) local cooling in 

welded tuffs (Levy, 1984; Broxton and others, 1987; 

Bish and Aronson, 1993; Buesch and others, 1995; 

Levy and others, 1996). In the upper, crystal-rich 

zones of both of the major pyroclastic flow units, varying degrees of vapor-phase corrosion have occurred 

that also change the properties with depth. Vaporphase corrosion also occurs in the rocks of the Crater 

Flat Group and, to a lesser degree, in the Yucca Mountain and Pah Canyon Tuffs (table 1). 

When characterizing matrix properties, one 

attempts to describe the heterogeneous rocks with features of various scales. For the purpose of numerical 

modeling on all scales, the measurement of matrix .: 

properties describes small centimeter-scale features, 

but the description of hydrogeologic units is based on 

much larger scale features, such as bulk permeability. 

Scale differences are attributed mainly to the presence 

of fractures that vary from less than a micrometer to 

hundreds of micrometers in aperture and may or may 

not be stratibound (not extending across lithostratigraphic unit boundaries). This study is based on the 

measurements of rock properties from 7-centimeter 

(cm)-diameter core samples collected during the drilling of boreholes. Thus, it is limited to features and 

properties that can be captured on a relatively small 

scale. Many properties that characterize the matrix of 

the rock unit are adequately represented by analyses on 

this scale (McKenna and Rautman, 1996), but even this 

scale of core sample has heterogeneities that may be 

captured or omitted in the sampling or measurement 

phases. Alteration, microfractures, and even porosity 

occur variably within the rocks at the core scale. Some 

matrix properties are indicative of larger scale features, 

such as the increase in matrix porosity that is measured 

in lithophysal zones. On the other hand, many larger 

scale processes and features, such as the bulk properties of lithophysal cavities, fractures, and faults, will 

not be adequately represented. Based on some of the 

scale-dependent relations described herein, it is 

encouraged that modeling efforts be designed to 

acknowledge different scales of the hydrologic system 

to provide more insight into the mechanisms and processes that exist in the field. The scope of this study 

does not include characterization of the lateral distributions of rock properties, which is being much more rigorously addressed by other researchers (Rautman, 

1995). Rather, this study introduces the relation of 

hydrologic properties to porosity and provides model 

parameter values for the rock units determined to be 

hydrologically distinct. 

Laboratory assistance and data analysis were 

provided by Jenny Curtis, Cara Vidano, and Greg 

Mongano, all of Foothill Engineering Corp., and Mike 

Spychala of Sandia National Laboratories. Alan Flint 

is gratefully acknowledged for insight provided during 

the methods development and data interpretation, as 

well as the time and effort contributed to the collection 

and laboratory processing of core samples for this large 

data set. David Buesch provided valuable insight into 

the relations of properties to lithostratigraphy. This 

work was performed by the U.S. Geological Survey for 

the U.S. Department of Energy, Office of Civilian 

Radioactive Waste Management, Yucca Mountain Site 

Characterization Project Office under contract 

DE-AIOS92NV 10874. 

SITE DESCRIPTION 

Location and Geologic Setting 

Yucca Mountain is 145 kilometers (km) northwest of Las Vegas, Nevada (fig. I), in a climatic transitional zone between the Mojave and Great Basin 

Deserts in the Basin and Range physiographic province 

(Grayson, 1993). It is in the rain shadow of the Sierra 

Nevada, which results in an arid climate, with average 

annual precipitation of approximately 165 millimeters 

per year (mmlyr) (Flint and others, 1996). In the general vicinity of Yucca Mountain, middle Miocene sedimentary deposits are overlain by a thick sequence of 

rhyolitic lavas and pyroclastic deposits that were 

deposited from 14 to 9.5 million years ago (Ma) (Sawyer and others, 1994) and that cover an extensive area 

of about 13,000 square kilometers (km2), known as the 

southern Nevada volcanic field (Byers and others, 

1976). Many of the volcanic deposits within this field 

do not have identified source areas, but several came 

from source areas within a group of calderas known as 

the Timber Mountain-Oasis Valley caldera complex 

(Byers and others, 1976; Sawyer and others, 1994). 

Site Descrlptlon 5 
238,000 

236,000 

cn 

K 

W 

I- : 234,000 

z 

p 

I 

IK 

4 

232,000 

230,000 

170,000 172,000 174,000 

EASTING. IN METERS 

176,000 

Figure 1. Map of study site with locations of boreholes used to develop matrix properties data set and hydrogeologic units. 

6 Characterlzatlon of Hydrogeologic Unlts Using Matrlx Properties, Yucca Mountaln, Nevada 
At Yucca Mountain, which is located directly 

south of the caldera complex, geophysical evidence 

(Snyder and Carr, 1982; Nelson and others, 199 1 ; 

Nelson, 1994) and borehole investigations (Buesch and 

others, 1996a) indicate that the Tertiary volcanic 

sequence varies in thickness between 1 and 3 km with 

an unsaturated zone that is approximately 500 to 

750 meters (m) thick. The formations in the unsaturated zone at Yucca Mountain consist primarily of pyroclastic flow deposits. From youngest to oldest, they are 

the Rainier Mesa Tuff of the Timber Mountain Group; 

the Tiva Canyon, Yucca Mountain, Pah Canyon, and 

Topopah Spring Tuffs of the Paintbrush Group; the 

Calico Hills Formation; and the Prow Pass, Bullfrog, 

and Tram Tuffs of the Crater Flat Group (table 1) (Carr -' 

and others, 1986; Sawyer and others, 1994). Interstratified with the formations are bedded tuffs that consist 

primarily of fallout tephra deposits with minor amounts 

of pyroclastic flow deposits and redeposited material 

(Diehl and Chornack, 1990; Moyer and Geslin, 1995; 

Buesch and others, 1996b). The Tiva Canyon and 

Topopah Spring Tuffs contain vitric, nonwelded to 

densely welded tuff at the top and bottom and thick, 

crystallized, moderate to densely welded and fractured 

interiors. Regionally, these are compound cooling 

units, but at Yucca Mountain, they appear to be single 

cooling units (D.C. Buesch and R.W. Spengler, 

U.S. Geological Survey, written comrnun., 1996). 

Most lithostratigraphic units in the Tiva Canyon and 

Topopah Spring Tuff are laterally continuous and stratiform although a few units thin and amalgamate northward as they conform to the underlying topography of 

older rocks (Scott and Bonk, 1984; Buesch and others, 

1996b; D.C. Buesch and R.W. Spengler, U.S. Geological Survey, written commun., 1996; W.C. Day, 

U.S. Geological Survey, written commun., 1996). The 

Yucca Mountain and Pah Canyon Tuffs are relatively 

thick to the north near Yucca Wash and contain both 

nonwelded and welded intervals (Scott and Bonk,1984; 

Moyer and others, 1996). However, the welded units 

thin southward near Drill Hole Wash toward the potential repository, and only thin intervals of nonwelded 

rocks occur in the center of the potential repository 

block (D.C. Buesch and R.W. Spengler, U.S. Geological Survey, written commun., 1996; Moyer and others, 

1996). Despite the significant thickness changes from 

north to south, some units exhibit consistent physical 

and hydrologic properties from Pagany Wash south to 

Busted Butte, as shown with the moderately to nonwelded base of the Tiva Canyon Tuff by Istok and others (1 994). The Calico Hills Formation is composed of 

nonwelded pyroclastic flow and fallout deposits with 

minor amounts of redeposited material, and near the 

north end of Yucca Mountain, there are interstratified 

rhyolite lava flows (Moyer and Geslin, 1995; D.C. 

Buesch and R.W. Spengler, US. Geological Survey, 

written commun., 1996). Tuffaceous rocks have been 

zeolitized at the north end of Yucca Mountain, yet parts 

of the formation remain vitric toward the south end of 

the mountain. Only at Busted Butte are vitric tuffaceous rocks of the Calico Hills Formation exposed at 

the ground surface on or near Yucca Mountain. The 

Prow Pass Tuff consists of nonwelded to partially 

welded tuff at the top and bottom, which is typically 

zeolitized. Only in the southwestern part of Yucca 

Mountain do these rocks remain vitric, with partially to 

moderately welded, crystallized tuff in the interior. 

The Bullfrog and Tram Tuffs were only penetrated by 

one borehole used in this study; therefore, the Bullfrog 

Tuff is sparsely characterized and the Tram Tuff is not 

characterized. Throughout the text, the lithostratigraphic and hydrogeologic unit symbols (table 1) are 

used. 

Lithologic Features 

Characteristics of the pyroclastic flow deposits 

result from the sequential development of depositional 

features, zones of welding, and zones of crystallization 

although in some rocks welding can be coincident with 

deposition, and crystallization can occur synchronously with welding to inhibit development of welding 

(Riehle and others, 1995; Buesch and others, 1996b). 

Welding of a simple cooling unit typically includes 

nonwelded rocks at the top and bottom with increased 

welding toward the center of the deposit and laterally 

from it; thick deposits can have the complete range of 

welding, but thin deposits can lack the more welded 

rocks at the center of the unit (Smith, 1960a, b). Crystallization occurs in zones including high-temperature 

devitrification, vapor-phase crystallization, vaporphase corrosion, and lithophysal and fumarolic alteration and crystallization (Smith, 1960a, b; Buesch and 

others, 1996b). No fumaroles were sampled in this 

study and none are discussed. The overlap of depositional and zonal features at Yucca Mountain has 

resulted in a complex, detailed lithostratigraphy with 

zones of welding and crystallization variously developed throughout the site in the different tuffs 

Site Descrlptlon 7 
(Buesch and others, 1996b). Many rocks are vitric; 

therefore, these rocks have not undergone crystallization at high temperature to form mostly quartz and 

feldspar (also commonly referred to as devitrification) 

or alteration at low temperature to clays and zeolites. 

Alteration of glass to clays and zeolites typically 

occurs where porosity is relatively high and water is 

present for long enough periods of time to provide the 

necessary reactions. Glass that crystallized at high 

temperature forms relatively low porosity rocks in 

which the feldspars can only alter to clays, zeolites, and 

analcine under high-temperature hydrothermal conditions (Bish and Aronson, 1995). The dominant lowtemperature alteration products at Yucca Mountain are 

smectite, clinoptilolite, and mordenite, and.locally, 

opal (Bish and Chipera, 1989). The low-temperature 

alteration potential of any lithologic unit is dependent 

on (1) rock composition, (2) rock texture, (3) proximity 

to structure, and (4) water-rock interaction (Broxton 

and others, 1987; D.C. Buesch and R.W. Spengler, 

written commun., 1996). High porosity results in large 

surface area of glass shards in tuffaceous rocks or in 

highly fractured glass of lava flows. Therefore, the 

most likely candidates for alteration are high porosity, 

vitric rocks associated with faults, with perched water 

or lateral flow horizons, or within ancient or present 

saturated zones. The vitric/zeolitic boundary of the 

ancient water table at Yucca Mountain (Broxton and 

others, 1987; Buesch and others, 1995) can be a distinct 

boundary, or it can be a transitional zone, where the 

geometry appears to depend, at least in part, on the 

hydrologic and lithologic character of the rocks. Based 

on macroscopic textural and mineralogic evidence 

(D.C. Buesch and R.W. Spengler, written commun., 

1996; Rautman and Engstrom, 1996b), quantitative 

mineralogy (Smith, 1960a, b; Broxton and others, 

1987; Bish and Chipera, 1989; Bish and Aronson, 

1993), and data presented herein, it appears that a relatively abrupt boundary occurs where an ancient water 

table was confined below the Tptpv3 (table l), or it 

occurs as a gradational transition across a vertical span 

of 30-40 m in the nonwelded tuffs in the Calico Hills 

Formation, as observed from geophysical logs and core 

samples from borehole SD7. An additional alteration 

product within this zone is opal, which is present in 

many of the units below the Topopah Spring Tuff 

where ancient water tables produced zeolitic alteration. 

Textural and particle-size distribution of fallout 

tephras and bedded tuffs generally relate to several 

lithostratigraphic characteristics and hydrogeologic 

properties (Moyer and others, 1996; Flint and others, 

1996b; D.C. Buesch, written commun., 1996) that 

determine the moisture-retention character and permeability of the rocks. In some cases, however, there are 

localized regions of argillic and zeolitic alteration 

within the bedded units that contribute to their hydrologic character (Moyer and others, 1996; Flint and others, 1996b). The nonwelded zones of the flow units 

generally follow the same lithologic constraints, with 

their hydrologic character being a function of pore-size 

distribution and subsequent alteration products. 

Generally, all these features influence the hydrologic character of the rock by changing the pathways 

through which water must pass in order to flow through 

the rocks. An increase in welding results in a reduction 

of porosity and permeability. Crystallization is generally related to hydrologic features through the production of secondary porosity by vapor-phase corrosion, 

which increases the permeability, or by the deposition 

of crystals through vapor-phase processes, which can 

reduce the porosity and, therefore, the permeability. 

Typically, vapor-phase corrosion occurs in the upper, 

crystal-rich, nonlithophysal zones of both the Tiva 

Canyon and Topopah Spring Tuffs where vitric, partially to moderately welded rocks are in contact with 

crystallized, moderately to densely welded rocks 

(Buesch and others, 1996b). Vapor-phase corrosion 

also commonly occurs in the lower part of the columnar subzone and the upper part of the vitric, moderately 

welded subzone of the crystal-poor Tiva Canyon Tuff 

and is particularly well developed where the vaporphase corrosion has propagated down into the increasingly porous parts of the moderately welded rocks 

(Buesch and others, 1996b; Moyer and others, 1996). 

This secondary porosity can result in measurements 

that are anomalously high compared to those which 

would be estimated based on textures of welding 

(Buesch and others, 1996b; Moyer and others, 1996). 

Vapor-phase crystallization is typically associated with 

areas of vapor-phase corrosion and within lithophysal 

cavities and may or may not affect the porosity, 

depending on the degree of crystallization. Properties 

of lithophysal cavities, while possibly inferred, cannot 

be directly measured using core-scale analyses, but on 

a larger scale, preliminary investigations have shown 

that lithophysae may act as a mechanism to concentrate 

volumes of water. As water moves through lithophysal 

zones, the volume of rock through which the water 

passes is reduced by the occurrence of cavities, but the 

water doesn't move into the cavities under unsaturated 

8 Characterlzatlon of Hydrogeologic Units Using Matrlx Properties, Yucca Mountain, Nevada 
conditions. This results in an increase in the saturation 

within the matrix in the lithophysal rocks. 

Differences in properties that result from 

whether or not a rock has undergone devitrification are 

primarily due to the differences in grain density and 

microfracturing. Vitric rocks are lower in grain density; for rocks with the same porosity, the vitric rocks 

have a lower bulk density. The densely welded, vitric 

rocks with very little porosity and extremely low permeability also have a high density of microfractures, 

which are observable, very small fractures, that transmit water under high saturations. The dimensions of 

the micro-fractures, and whether they contain alteration products, will determine whether or not they contribute to unsaturated flow; very small fracture 

apertures, or alteration materials, may support unsaturated flow. Because the matrix permeability of these 

rocks is so low, it is common to find high saturations 

due to concentration of water flowing from higher 

porosity rocks to lower porosity rocks and permeability 

bamer effects. There are often low-temperature alteration minerals associated with these rocks, but there are 

also zones with high-temperature alteration materials 

(Levy, 1996). Devitrified, densely welded rocks have 

microfractures that are occasionally sampled in core 

and typically do not contain alteration minerals. These 

microfractures will probably not contribute to flow 

under unsaturated conditions. 

Hydrologic Implications of Lithologic 

Stratification 

Based on general volcanologic relations (Scott 

and others, 1983; Buesch and others, 1996b; Moyer 

and others, 1996) and geostatistical analyses (Rautman 

and Flint, 1992), a number of deterministic geologic 

processes, including magmatic evolution; volcanic 

eruption, transport, and emplacement; post-emplacement cooling and alteration; and late-stage (diagenetic) 

alteration, provide an important framework within 

which hydrologic characterization must take place. 

These processes can produce a relatively predictable 

vertical distribution of properties within simple cooling 

units, which simplifies the prediction of properties at 

unsampled locations. Lithologic features controlling 

the measured distribution of water have been noted 

consistently in boreholes located in the study area and 

have aided in the determination of mechanisms and 

processes ongoing in the unsaturated zone. Hydrologic 

modeling using a detailed vertical distribution of properties displays the importance of the vertical sequence 

of lithologic features (Flint and others, 1993; Flint and 

others, 1996a). Several of these distinctive lithologic 

features are critical in the characterization of water 

flow at Yucca Mountain, and the characterization of 

their physical and hydrologic properties are discussed 

in detail. 

Transition Zones 

Transition zones have a pronounced change in 

matrix properties with depth, typically caused by a 

change in porosity due to welding or vapor-phase 

Corrosion. Transition zones occur at the top and bottom 

of the Tiva Canyon and Topopah Spring Tuffs, where 

the rocks grade from nonwelded to densely welded and 

locally incorporate changes in porosity due to vaporphase corrosion. 

Corresponding to the degree of welding, the fracture density, geometry, and continuity are typically 

poorly developed in nonwelded tuffs and well developed in the welded rocks. The transition zone from 

fracture-dominated flow in welded rocks, where saturation is high, to matrix-dominated flow in nonwelded 

rocks can significantly affect flow. The rapid decrease 

or increase in porosity (that also corresponds to 

changes in the degree of fracturing) in these transition 

zones may lead to the localized concentration or depletion of water. 

Capillary and Permeability Barriers 

The concept of a natural capillary barrier is summarized by Montazer and Wilson (1 984) as a finegrained layer overlying a coarse-grained layer, where 

water cannot flow from the smaller pores into the larger 

pores until the height of water in the overlying layer 

exceeds a critical height equivalent to the difference in 

the capillary rise of the two pore sizes. At Yucca 

Mountain, the potential for this condition occurs when 

a porous medium, such as the nonwelded rocks of the 

Paintbrush Group (PTn), is bounded by double-porosity media, such as the welded and fractured rocks of the 

Tiva Canyon and Topopah Spring Tuffs (Montazer and 

Wilson, 1984). A capillary bamer could theoretically 

be present at the top of the nonwelded rocks where finegrained welded rocks overlie coarse-grained nonwelded rocks. A bamer could also be present at the 

base of the nonwelded rocks where the coarse-grained 

Site Description 9 
rocks overlie the larger aperture fractures present in the 

welded rocks. If these conditions exist in the layered, 

dipping beds at Yucca Mountain, they could potentially 

result in the lateral diversion of water. 

Theoretically, the conditions leading to lateral 

diversion of water at sloping interfaces are fairly idealized. Analytically, lateral diversion is a function of saturated hydraulic conductivity (K,), the angle of incline, 

the flux rate, and the air-entry pressure of the media 

(Ross, 1990). Ross (1990) showed there are three conditions of flow that result from changing these parameters. To create a capillary barrier with significant 

diversion capacity, fine-textured media must overlie 

coarse-textured media with a linear, sloping contact 

and a low flux rate. The barrier effect is overcome 

when the saturation is high enough in the overlying 

layer for the capillary pressure to be less than the 

underlying air-entry pressure. The barrier exists due to 

the difference in effective permeability between the 

fine layer and the coarse layer under unsaturated conditions. These conditions of flow are described in detail 

in Oldenburg and Pruess (1993). 

Ross (1990) developed an idealized, two-dimensional, tilted model that could be solved analytically to 

describe this phenomenon. The assumptions and 

approximations that define this idealized system do not 

preclude its usefulness, but need to be considered when 

it is applied to a natural system. Two of the prime 

assumptions and approximations are that all flow is 

considered steady state and that the downstream 

boundary can drain infinitely. There are several important conditions that are not considered in the idealized 

system. These include moisture gradients, which generally are present; nonlinear phenomena, such as finger 

instabilities (Hillel and Baker, 1988; Steenhuis and others, 1990); and heterogeneities at the contacts or gradational transitions between rock units as observed at 

Yucca Mountain. Heterogeneities will influence nonlinear phenomena by causing localized increases in saturation and thus reducing the diversion length. 

Gradational transitions do not provide the necessary 

contrast in properties to produce lateral diversion. Oldenburg and Pruess (1 993) did a study to test the capability of numerical models to adequately describe 

capillary diversion. The flow system analyzed, however, was chosen to conform to the idealized system 

developed by Ross (1 990). The numerical model was 

able to simulate results similar to the analytical calculations, including the prediction of significant lateral 

diversion based on the contrasting properties and low 

fluxes, but the non-idealized geometry of the natural 

system with the transitions and heterogeneities 

observed at the contacts was still not considered. 

The reverse condition, when coarse-grained 

materials overlie fine-grained materials, can also result 

in lateral diversion due to the lower layer acting as a 

permeability barrier. This condition occurs in the transition between the coarse-grained PTn and the densely 

welded, fractured, crystal-rich vitrophyre of the 

Topopah Spring Tuff (Tptrv 1) under less than saturated 

conditions. In this transition zone, both permeability 

and capillary barrier effects could be present depending 

on the degree of saturation and if the apertures of the 

fractures are larger than the overlying moderately 

welded rocks. If fractures are open and apertures are 

larger than the pore sizes of the overlying materials, 

they will act as a capillary barrier, which will cause lateral diversion. If the overlying materials become saturated enough to initiate fracture flow, then the barrier 

effects are reduced. If the fractures are filled with alteration materials, then the permeability barrier comes 

into effect. Because many of these conditions are 

likely to be concurrent in this transition location, the 

processes there can be complicated. 

Barrier effects control the hydrology by reducing 

the downward flux of water across contacts or zones 

and by either perching or laterally diverting water. 

These conditions are particularly important in vitric 

rocks. Vitric zones that maintain high saturation due to 

the capillary or permeability barrier mechanisms for 

long periods of time can alter to clays, and these clays 

can increase the contrast in properties and further 

enhance the effectiveness of the mechanisms. Vitric 

zones near transitional contacts are, therefore, particularly important to characterize properly for modeling 

purposes because of the significant control they potentially impose upon the overall hydrology of the unsaturated-zone system. Numerical hctions need to be 

developed to enable the distribution of properties with 

depth (finitely) over the transitional contacts during the 

development of numerical flow models. Furthermore, 

detailed sensitivity modeling needs to be done to determine the optimum size for grid blocks in these zones to 

properly reflect true conditions and not inappropriately 

imposq contrasts in properties that will inappropriately 

divert water laterally. 

10 Characterization of Hydrogeologlc Units Using Matrlx Properties, Yucca Mountaln, Nevada 
METHODS 

To assess the character of this large, heterogeneous, three-dimensional site, analyses of physical and 

hydrologic properties for 4,892 rock-core samples 

from 3 1 boreholes were compiled in a data base. This 

data base includes measurements of porosity, bulk density, particle density, water content, saturated hydraulic 

conductivity, and moisture-retention characteristics. 

To provide initial conditions and site calibration data, 

present-day field moisture and water-potential conditions were included, along with the associated lithostratigraphic units for all samples. 

The core samples were collected and processed 

under a full quality-assurance program (table 2). All 

samples were analyzed to determine porosity, bulk 

density, particle density, and water content. Subsets of 

samples were measured for determination of water 

potential, saturated hydraulic conductivity, particle 

density using helium pycnometry, and moistureretention measurements. The location, altitude, drilling dates, and depth for boreholes are listed in table 3 

with complete borehole designation. Following 

table 3, borehole designations will be abbreviated as 

LLN" plus the associated number for neutron boreholes 

and "UZ," "SD," and "NRG" plus associated number 

for the deep boreholes, omitting hyphens and "#" symbols. Long-term water-content measurements in the 23 

neutron boreholes 18 to 83 m in depth are described in 

detail in Flint and Flint (1995). Five boreholes (the SD 

boreholes and UZ 14 and UZ 16) were drilled from the 

surface to the water table, and three boreholes (UZ7a 

and the NRG boreholes) did not penetrate the water 

table. Deep boreholes (table 4) and neutron boreholes 

(table 5) are shown relative to a lithostratigraphic column to indicate units sampled in each borehole. Boreholes were drilled to investigate a laterally spatial 

representation of the site (fig. 1). 

Sample Collection 

Boreholes were drilled using dry-drilling technology. The neutron boreholes (prefix "N) were 

drilled using the ODEX 1 15 drilling and casing system 

(Hammermeister and others, 1985). This method uses 

simultaneous advancement of the casing with the deepening of the hole to minimize the effects of drilling 

fluids (in this case, air) on the borehole walls. Formation and core moisture conditions are minimally 

affected, and some of the cuttings produced from drilling fill the small annular spaces between the casing and 

formation, minimizing the void space. The remaining 

boreholes were drilled using reverse-circulation dualwall methodology, which also minimally affects formation and core moisture conditions. Both types of 

drilling provide continuous core sampling. Two core 

samples approximately 7 cm in diameter and 10 cm in 

length and 20 cm in length were collected approximately every 0.8 m during drilling of the boreholes. 

Intermittent depth segments occurred where core samples were not recovered due to drilling or formation 

conditions. Samples were typically placed in steel cans 

at the drill site within 5 minutes of being recovered 

'from the ground to maintain field moisture conditions. 

Laboratory Core Processing 

Cores were processed following the steps indicated in figure 2. Cores were removed from the steel 

cans and divided into approximately two equal parts. 

One part was immediately placed on a balance to 

obtain field weight for moisture content and then 

labeled with permanent ink. The other part was 

crushed and immediately sealed in a labeled, taped, 

glass jar. Crushed samples were analyzed within 

4 days for water potential by using a laboratory chilledmirror psychrometer (Water Activity Meter, Model 

CX-2, Decagon Devices, Inc., Pullman, Wash.). The 

sample chamber of the chilled-mirror psychrometer is 

4 cm in diameter and 1.5 cm in height. The chamber is 

filled with the largest chips of the crushed rock that will 

fit. Measurements of water activity, A,, are measured 

with the psychrometer simultaneously to the measurement of sample temperature using an infrared thermometer. These values are used to calculate water 

potential, yr, using the Kelvin equation, 

where T is temperature in Kelvins, and C = 4.6 18 bars 

per Kelvin (K minus 273.15 = OC). The resolution of 

the instrument introduces an error off 1 percent in A, 

over the entire range of the instrument. This is an 

error in water potential of 100 percent at 0 bars to 

11 percent at -3000 bars. Measurement error due to 

the calibration of the instrument with salt solutions is 

considered negligible. 

Methods 11 
Table 2. Data tracking numbers for all data used. (Note: All data are qualified.) 

Core Properties 

Tracking Number Title of Technical Data Information Form 

DTN 689205083 12231.012: 

DTN GS93OlO83 1223 1.006: 

DTN GS9404083 12231 .OW: 

DTN GS9401083 1223 1.002: 

DTN GS9405083 1223 1.006: 

DTN GS9506083 12231.007: 

DTN GS9503083 1223 1 .OM: 

DTN GS9506083 1223 1 .OO5: 

DTN GS95030831223 1.003: 

DTN GSW 1 1083 1223 1 .OW: ' 

DTN GS95llO83l223I.Oll: 

DTN GS95llO83l223l.OlO: 

DTN GS95030831223 1.002: 

DTN GS9608083 1223 1 .OM: 

USW UZ-N54 and USW UZ-N55 core analysis: bulk density, porosity, particle density, and in 

situ saturation for core dried in 105OC oven. 

USW UZ-N53 core analysis: bulk density, porosity, particle density, and in situ saturation for 

core dried in 105°C oven. 

Core analysis of bulk density, porosity, particle density, and in situ saturation for three neutron 

boreholes USW UZ-N57, UZ-N61 and UZ-N62. 

Core analysis of bulk density, porosity, particle density, and in situ saturation for seventeen neutron boreholes: Data for core dried in RH oven and 105°C oven for USW UZ-N3 1, UZ-N32, 

UZ-N33, UZ-N34, UZ-N35, UZ-N38, UZ-N58, UZ-N59, UE-25 UZN#63 and USW UZ-N64; 

data for core-dried in 105OC only for USW UZ-N 11, UZ-N 15, UZ-N16, UZ-N 17, UZ-N27, UZN36, and UZ-N37. 

Core analysis of bulk density, porosity, particle density, and in situ saturation for borehole UE-25 

UZ# 1 6. 

Physical properties and water potentials of core from borehole USW NRGd 

Physical properties and water potentials of core from borehole USW SD-9 

Physical properties and water potentials of core from borehole USW UZ-14 

UE-25 UZ#16 pycnometer data 

Physical properties, water content, and water potential for borehole USW SD-7 

Physical properties, water content, and water potential for borehole USW UZ-7a 

Physical properties and water content for borehole USW NRG-717A 

Laboratory measurements of bulk density, porosity, and water content for USW SD-12 

Physical properties, water content, and water potential for lower depths in boreholes USW 

SD-12 and USW SD-7 

12 Characterization of Hydrogeologlc Units Using Metrix Properties, Yucca Mountain, Nevada 

Permeability and Moisture-Retention Measurements 

Tracking Number Title of Technical Data Information Form 

DTN GS9506083 1223 1.006: 

DTN GS96080831223 1.002: 

DTN GS9608083 1223 1.001 : 

DTN GS9506083 1223 1.008: 

DTN GS9608083 1223 1.005: 

DTN GS960808312231.003: 

Water permeability of core from SD-9 

Relative-humidity-calculated porosity measurements on samples from borehole USW SD-9 used 

for saturated hydraulic conductivity. 

Saturated hydraulic-conductivity measurements and relative-humidity-calculated porosity measurements on samples from boreholes USW UZ-N27 and UE-25 UZ#16 

Moisture retention data from boreholes USW UZ-N27 and UE-25 UZ#16. 

Water permeability and relative-humidity-calculated porosity measurements on samples from 

boreholes USW SD-7, USW SD-9, USW SD-12, and USW UZ-14 

Moisture-retention data for samples from boreholes USW SD-7, USW SD-9, USW SD-12, and 

USW UZ-14 
Table 3. Borehole descriptions, locations, and drilling dates 

Date Date Northing Easting Altitude drilling Total 

Borehole Location drilling depth deslgnatlon (meters) (meters) (meters) began completed (meters) 

UE-25 UZ # 16 172169 1220 5/27/92 

USW uz-14 

USW UZ-7a 

USW SD-7 

USW SD-9 

USW SD-12 

USW NRG-6 

USW NRG-7/7A 

US W UZ-N I I 

USW UZ-N 1 5 

USW UZ-N16 

USW UZ-N 17 

USW UZ-N27 

USW UZ-N3 1 

USW UZ-N32 

USW UZN33 

USW UZ-N34 

USW UZN35 

USW UZ-N36 

USW UZ-N37 

USW UZ-N38 

USW UZ-N53 

USW UZ-N54 

USW UZ-N55 

USW UZ-N57 

USW UZN58 

USW UZ-N59 

USW UZ-N61 

USW UZ-N62 

UE-25 UZN #63 

USW UZ-N64 

WT-2 Wash 23181 1 

Drill Hole Wash 

WT-2 Wash 

Highway Ridge 

Wren Wash 

H-5 Wash 

Drill Hole Wash 

Drill Hole Wash 

Mile High Mesa 

Bleach Bone Ridge 

Bleach Bone Ridge 

Bleach Bone Ridge 

Yucca Crest 

Split Wash 

Split Wash 

Drill Hole Wash 

Drill Hole Wash 

H-5 Wash 

Bleach Bone Ridge 

Wren Wash 

Wren Wash 

WT-2 Wash 

WT-2 Wash 

WT-2 Wash 

Abandoned Wash 

Abandoned Wash 

Abandoned Wash 

Abandoned Wash 

Yucca Crest 

Pagany Wash 

Yucca Crest 

235 155 

23 1845 

23 1328 

234083 

232244 

233758 

234355 

237919 

237 I62 

2371 80 

237203 

235 174 

232942 

232959 

2347 17 

234744 

232338 

235885 

233934 

233924 

23 1677 

231731 

231801 

230174 

230 197 

230222 

230239 

230772 

234341 

233394 

170774 

171397 

171066 

171242 

17,1178 

172008 

171598 

170390 

170643 

170574 

170687 

170344 

171527 

171541 

171051 

171069 

171392 

171780 

171820 

171707 

171979 

171987 

171983 

17094 1 

17095 1 

170959 

170960 

170171 

172568 

170516 

1350 

1290 

1363 

1302 

1 

1 

1 

1 

1 

32 1 

248 

282 

592 

557 

1560 

1563 

1481 

I266 

1267 

1320 

1318 

1295 

1415 

1257 

1265 

1236 

1233 

1241 

1276 

1274 

1274 

1275 

1489 

1202 

1460 

411 5/93 

3/22/95 

10/3/94 

5/6/94 

1 128194 

12/23/92 

10/25/93 

2/5/92 

3120192 

3/25/92 

311 7/92 

412 1 192 

9/3/92 

9/23/92 

811 3/92 

811 8/92 

1011 3/92 

2/28/92 

1/6/92 

4/8/92 

511 9/92 

11/12/92 

912319 1 

1 012 8/92 

11/5/92 

1111 8/92 

12/9/92 

3/5/93 

8/3/92 

411 6/92 

311 1/93 

5/ 1 3/94 

61 1 2/95 

1 1/9/95 

9/26/94 

8/ 1 6/95 

3/4/93 

3/4/94 

2/25/92 

3/25/92 

3130192 

31 19/92 

4130192 

9/22/92 

1019192 

811 8/92 

8/24/92 

10/26/92 

3/2/92 

1/30/92 

411 3/92 

6/ 1 2/92 

1211 0192 

11/8/91 

1 1/4/92 

11/10/92 

12/8/92 

1 21 1 7/92 

311 0193 

811 0192 

4/ 1 7/92 

514.0 

672.6 

234.7 

497.5 

677.6 

609.6 

335.3 

461.3 

25.7 

18.3 

18.3 

18.3 

61.7 

58.7 

63.2 

22.9 

25.6 

52.0 

18.2 

82.7 

27.2 

71.5 

74.6 

77.8 

36.2 

36.2 

36.2 

36.2 

18.3 

18.3 

18.3 

Methods 13 
Table 4. Generalized lithostratigraphy of eight deep boreholes. 

[Breaks in vertical lines indicate unit not present or not collected in the borehole] 

------ ------------------ 

Boreholes 

Lithostratigraphic unit 

Tiva Canyon Tuff (Tpc) 

middle nonlithophysal zone (pmn) 

lower lithophysal zone (pH) 

lower nonlithophysal zone (pln) 

hackly subzone (plnh) 

columnar subzone (plnc) 

vitric zone (pv) 

moderately welded subzone (pv2) 

non- to partially welded subzone (pvl ) 

Pre-Tiva Canyon Tuff bedded tuff (Tpbt4) 

Yucca Mountain Tuff (Tpy) 

Pre-Yucca Mountain Tuff bedded tuff (Tpbt3) 

Pah Canyon Tuff (Tpp) 

Pre-Pah Canyon Tuff bedded tuff (Tpbt2) 

Topopah Spring Tuff (Tpt) 

crystal-rich member (Tptr) 

vitric zone (rv) 

nonwelded subzon e (~3) 

moderately welded subzone (rv2) 

densely welded subzone (rvl) 

nonlithophysal zone (rn) 

dense subzone (rn3) 

vapor-phase corroded subzone (rn2) 

lithophysal zone (r I) 

crystal-poor member (Tptp) 

upper lithophysal zone (pul) 

middle nonlithophysal zone (pmn) 

lower lithohysal zone (pll) 

lower nonlithophysal zone (pln) 

vitric zone (pv) 

densely welded subzone (pv3) 

moderately welded subzone (pv2) 

nonwelded subzone (pvl ) 

Pre-Topopah Spring Tuff bedded tuff (Tpbt 1) 

CALICO HILLS FORMATION (Tac) 

Unit 4 vitric/zeolitic 

Unit 3 zeolitic 

Unit 2 zeolitic 

Unit 1 zeolitic 

Bedded tuff (Tacbt) 

Basal sandstone (Tacbs) 

Prow PassTuff (Tcp) 

Unit 4 Pyroxene rich 

Unit 3 Welded pyroclastic flow 

Unit 2 Lithic-rich pyroclastic flow 

Unit 1 Pumice~us pyroclastic flow 

Pre-Prow Pass bedded tuff (Tcpbt) 

Bullfrog Tuff (Tcb) 

Tram Tuff (Tct) 

8 

rn 

I 0 

14 Characterisatlon of Hydrogeologlc Unlts Using Matrlx Properties, Yucca Mountain, Nevada 
Table 5. Generalized lithostratigraphy of 23 neutron boreholes. 

[Breaks in vertical lines indicate unit is missing or was not collected from borehole; trans., transition; part., partially, Can, Canyon; Mtn, Mountain] 

Boreboles 

Lithostratigraphic Unit N11 N15 N16 N17 N27 N31 N32 N33 N34 N35 N36 N37 N38 N53 N54 N55 N57 N58 N59 N61 N62 N63 N64 

Tiva Canyon Tuff (Tpc) 

crystal-rich member (Tpcr) 

nonlithophysal zone (m) 

subvitrophyre trans. subzone 

pumice-poor subzone (m3) 

mixed pumice subzone (rn2) 

crystal transition subzone (m 

lithophysal zone (rl) 

crystal-poor member (Tpcp) 

upper lithophysal zone (pul) 

(m4) 

1) 

middle nonlithophysal zone (pmn) 

lower lithophysal zone (pll) 

lower nonlithophysal zone @In) 

hackly subzone (plnh) 

columnar subzone @lnc) 

vitric zone (pv) 

moderately welded subzone (pv2) 

non- to part. welded subzone (pv 1) 

Pre-Tiva Can Tuff bedded tufT (Tpbt4) 

Yucca Mountain Tuff (Tpy) 

Pah Canyon Tuff (Tpp) 

Topopah Spring Tuff (Tpt) 

crystal-rich member (Tptr) 

I 

Pre-Yucca Mtn Tuff bedded tufT (Tpbt3) 

Pre-Pah Canyon Tuff bedded tuff (Tpbt2) 

vitric zone (N) 

nonwelded subzone (~3) 

moderately welded subzone (~2) 

densely welded subzone (N 1) 

nonhthophysal zone (m) 

E dense subzone (m3) I! 

=r 

0 vapor-phase corroded subzone (m2) a 

w lithophysal zone (rl) 

I 

I I 

.. I . 

I ._ 

I I . . I 

. 

I I 

I 

I 

111. 
Borehole core, 7 cm in diameter, is divided into segments: 

- 5-10 cm long 

Preserved in 

steel can 

Sample split in half 

r7 ?7 

Subsample crushed 

and stored in sealed 

glass jar 

I 

Water 

potential of 

subsample 

measured 

Subsample 

weighed, 

saturated, 

submersed for 

volume, and dried 

in relative 

humidity and 105 

0 C ovens for 

determination of 

bulk density, 

particle density, 

porosity and 

water content. 

9 

Preserved in 

Lexan tubing 

~ubsam~le plug prepared 

2.5 cm in diameter 

x 6 cm in length 

5-cm-long plug 

saturated, 

measured for &, 

and oven-dried. 

Helium 

I I pycnometry is 

used on selected 

plugs for particle 

density. 

b---i 

u 1-cm-thick disk 

is used for 

moistureretention 

measurements 

Figure 2. Diagram of the steps used to process core samples to obtain hydrologic property measurements. 

16 Characterization of Hydrogeologic Units Using Matrix Properties, Yucca Mountain, Nevada 
After weighing the first part of the sample for 

field moisture content, core samples were saturated 

with C02 after evacuation of air under a vacuum to 

enable the saturation of small internal pores and then 

submersed in distilled, de-aired water and left overnight. Samples were removed, dried with a damp towel 

(ASTM, 1977), and weighed to determine saturated 

weight. The sample was suspended in a beaker of 

water in a wire basket to determine volume displacement, dried for 48 hours in a relative humidity oven at 

60°C and 65 percent relative humidity (RH), and 

reweighed. Relative-humidity drylng removes water 

from the pores that contribute to water flow but retains 

bound water in the crystal or mineral structure (Bush 

and Jenkins, 1970) or within very small pores or channels, providing an estimate of residual water content 

and relating pore space to that space available for water 

flow (see discussion in section on alteration, microfractures, and permeability). The samples were then dried 

at 105OC for at least 48 hours to obtain a standard dry 

weight (ASTM, 1971). Porosity [(saturated weight 

minus dry weight)/volume], bulk density (dry weight/ 

volume), and particle density Iporosityl(1 minus bulk 

density)] were calculated for both RH and 105OC ovendry weights. The error in these measurements is due to 

resolution of the balances in the weight measurements, 

which is insignificant, and in the repeatability of the 

saturated weight and volume measurement based on 

removing surface water from the rock. Errors have 

been calculated to be less than 0.5 percent for bulk 

properties. Volumetric-water content is calculated as 

[(initial weight minus dry weight)/dry weight] multiplied by bulk density, and saturation is volumetricwater content divided by porosity. The error in these 

measurements is the same as for the physical properties, but includes a calculation for evaporation during 

sample handling, which is discussed in a later section. 

Borehole core segments, 15-20 cm long, were 

collected adjacent to can samples and preserved in 

Lexan tubing for measurements of saturated hydraulic 

conductivity, particle density using helium pycnometry, and moisture retention (fig. 2). Subsamples, 2.5 cm 

in diameter and approximately 6 cm long, were prepared and subsamples, approximately 1 cm long, were 

cut off the end of these samples for determination of 

moisture-retention curves. The rest of the subsample 

was used for conductivity and helium-pycnometry 

measurements. Hydrologic flow properties were measured before conventional oven drylng (105OC) 

because structural damage may occur in certain samples with delicate clay structures or zeolites. Finally, 

the samples were dried at 105OC to obtain a standard 

dry weight. 

Saturated hydraulic conductivity (K, ) was determined on subsamples from several boreholes. Cores 

were vacuum saturated, and K, was measured using a 

steady-state permeameter that forces water through the 

core at a measured pressure while weighing the outflow 

over time. K, was calculated using Darcy's law: 

e = (AP) 

At 4 z 

where Q is the measured flow per unit time, t, in meters 

per second; A is the cross-sectional area of the sample, 

in square meters; A?' is the pressure gradient measured 

across the core sample, in meters of head; and Az is the 

length of the sample, in meters. The error in this measurement is estimated to be less than one-half an order 

of magnitude of the calculated K,. This measurement, 

differing from the typically saturated hydraulic conductivity that occurs under field conditions when rocks 

have entrapped air, provides an upper bound to the prediction of unsaturated hydraulic conductivity necessary for the numerical modeling of water flow through 

rocks. 

Helium pycnometry was performed using a 

helium pycnometer (Accupyc, Model 1330, Micromeritics Corp., Norcross, GA) on 460 samples from borehole UZ16 that had been oven-dried at 105OC 

following K, measurements. The pycnometry technique uses Boyles' gas law to measure the volume of 

the solids of a dry sample once all void spaces (pores) 

are filled with helium. The volume of the solids divided 

by the sample weight is the particle density. The error 

in this measurement is less than 0.5 percent. This technique provides information about the pore spaces 

because of the properties of helium. Helium differs 

from water because it is nonpolar and will not fill all of 

the spaces voided by water molecules, such as spaces 

within clay structures (see Characterization of Hydrogeologic Units, Phase 2). 

Moisture-Retention Characterization 

At sites where no measured unsaturated hydraulic-conductivity data are available, moisture-retention 

Methods 17 
curves are used with saturated hydraulic conductivity 

to predict unsaturated hydraulic conductivity. Moisture-retention curves were determined in the laboratory 

by using the chilled-mirror psychrometer to determine 

water potential at various saturations. Samples were 

vacuum saturated, and water-potential measurements 

were made. Following the measurement, samples were 

allowed to dry by evaporation to a new water content 

and then equilibrate in a sealed jar for approximately 

3 days. Measurement points were collected at each saturation in this manner until the final measurement point 

was determined following the drying of the sample in 

an oven set at 60°C and 65 percent relative humidity. 

The final measurement point was used to approximate 

the residual water content. For each hydrogeologic 

unit, the data sets for individual samples were compiled 

to include variability throughout the unit. These data 

sets represent the desorption process and are the upper 

bound of the moisture-retention characteristic curve, 

neglecting hysteretic behavior. For rock units in the 

shallow unsaturated zone where hysteretic behavior 

might occur due to periodic wetting and drylng and 

entrapment of air in pores, measured data from borehole samples were included with the laboratory data set 

to produce a composite data set. This was done for 

hydrogeologic units of the Tiva Canyon Tuff (with the 

exception of Tpcrn and Tpcpul, because no field waterpotential measurements were available), the PTn, and 

the upper rocks of the Topopah Spring Tuff (Tptrv and 

Tptrn). Data points from the field data that were determined to be saturated were set to -0.0 1 bars for all calculations and for curve-fitting procedures. Field data 

used in the composite-curve data sets were also 

corrected for evaporation losses using the procedure 

outlined in the following section. Composite data sets 

were developed by combining laboratory and field data 

into bins represented by equal ranges of saturation and 

determining the geometric mean of each bin. This was 

done so that the curve-fitting procedure and resulting 

curve-fit models wouldn't be biased or weighted due to 

oversampling. 

Each of the moisture-retention data sets was fitted with curve functions using RETC (van Genuchten 

and others, 199 l), a least-squares curve-fitting procedure based on van Genuchten (1980) and fitting van 

Genuchten's parameters a and n, while m = 1 -(lln). 

Water potential (y) is related to effective saturation 

(Se) by 

where effective saturation is 

(3) 

(4) 

and 8 is measured water content in meters per meter, 

8, is residual water content in meters per meter, and 8, 

is water content at saturation in meters per meter. 

Residual water content, estimated from the difference 

between 105OC oven-dry weight and RH oven-dry 

weight, was set and saturated water content was set 

to 1. (Residual water content is discussed in more 

detail in Characterization of Hydrogeologic Units, 

Phase 2). An error based on the resolution of the 

instrument was used to calculate an error in water 

potential over the range of the instrument. The 

calculated water-potential error was added to each 

measured laboratory data point, and a new curve was 

fit to the data and the standard error for the fit parameters was calculated. The error was also subtracted 

from the measured points and a curve was fit to the 

new data set. Standard errors and 95-percent confidence limits were also calculated for each of the fit 

parameters for each moisture-retention curve. Moisture-retention curve-fit parameters were then used to 

predict water potential from measured saturation using 

equation 3 and equation 4 in several boreholes for 

comparison with measured water potential. The 

water-content and water-potential values were corrected prior to the predictions by using the method 

described in the next section. 

Unsaturated hydraulic conductivity, K, (w), can 

be predicted from moisture-retention fit parameters 

using the model of van Genuchten/Mualem 

(van Genuchten, 1 980): 

with m = 1- (lln). 

Correction of Water-Content and WaterPotential Data 

Drilling and sample handling can variably 

reduce the saturation and the water potential of core 

18 Characterization of Hydrogeologic Unlts Uslng Matrix Properties, Yucca Mountain, Nevada 
samples so that they do not represent true field conditions. To more accurately represent in-situ waterpotential values, an analysis was done to correct the 

effects of drilling and sample handling on the determination of core water content and water potential. The 

degree of saturation in a core is not very sensitive to 

these influences, but water potential can be reduced 

significantly where small amounts of water are evaporated from samples of certain rock types, such as 

Tptrvl, Tptpv3, and other low-porosity rocks. The 

influence of drylng on the measurement of water potential is particularly notable at the wet or dry ends of a 

moisture-retention curve where the relation of water 

potential to water content is steep; thus, a small loss in 

water content results in a large decrease in water potenr 

tial. Loss of water will affect the water potential more 

for rocks with very small pores than for those with 

larger pores and higher porosity. 

There are three potential situations during which 

water can be lost from the sample. The first is during 

the borehole drilling when the core is exposed to drilling air. The second situation is in the trailer at the drill 

site when the inner barrel encasing the core is opened. 

The amount of time from when the core barrel is 

opened to when each sample is sealed in the steel can 

varies, but typically does not exceed 5 minutes. The 

last situation is when the can is opened at the laboratory 

for the processing of core. It takes no longer than 

30 seconds to obtain an initial weight on one subsample and crush and seal the other subsample in a glass jar 

(fig- 2). 

The analysis was done in several steps. First, an 

evaporation curve was generated for each unit. Samples of 2.5-cm-diameter core plugs representing all of 

the hydrogeologic units at Yucca Mountain were vacuum saturated and water in each sample was allowed to 

evaporate under ambient laboratory conditions on a 

top-loading balance from which weight readings were 

recorded every 10 seconds by a computer. These data 

were used to generate evaporation curves of water loss 

(in grams of water) over time for all rock types. Water 

loss was calculated as the percentage of the total volume of water within the pores that evaporated over 

time. This calculation could be used to correct water 

loss from borehole samples of various sizes and initial 

water content. Using drilling data from borehole SD9, 

which recorded the rate of penetration with depth, the 

amount of time that each rock type was exposed to 

drilling air was calculated. It was assumed that samples were exposed in the trailer at the drill site during 

packaging for an average of 5 minutes and that it took 

30 seconds to process each sample in the laboratory to 

obtain initial water content. To correct each sample for 

error due to evaporation, it was assumed that evaporation was a function of sample size (related to surface 

area and measured as total dry weight) and initial volume of water in the sample. The total volume of water 

initially in each sample was calculated, and the appropriate percentage of water evaporated was taken from 

the evaporation curve for the time that the sample depth 

was exposed to drilling air and sample handling. This 

was done for each sample to determine the amount of 

water to be added to the initial weight in order to correct the error in saturation. The moisture-retention 

function for each hydrogeologic unit was then used to 

calculate the water potential from the initial saturation 

and the corrected saturation, and the difference 

between these values was added-to the measured water 

potential. Corrected saturation and water-potential 

values were only used in this report to produce the 

composite moisture-retention curves discussed above 

and to compare with the predicted water-potential 

values. Corrected saturation and water-potential values, though only presented in this report for SD7 and 

SD9, are also available for SD12, UZ14, and UZ7a 

(table 2). 

CHARACTERIZATION OF 

HYDROGEOLOGIC UNITS 

The determination of distinct hydrogeologic 

units for the purpose of numerical flow modeling 

required a large, spatially distributed data set of hydrologic properties and corresponding lithostratigraphic 

descriptions. The intent of developing hydrogeologic 

units as discrete layers with associated parameters and 

properties for flow models was twofold: (I) that the 

layers could be related spatially to existing threedimensional lithostratigraphic or porosity models; and 

(2) that they would be distinct enough, with minimal 

vertical and lateral heterogeneity, that, when used in a 

numerical model, they would reasonably'predict measured field conditions in a vertical borehole at any location on the mountain, while not being so detailed as to 

be numerically cumbersome or limiting. With these 

criteria in mind, the following procedure was implemented: 

Characterization of Hydrogeologic Units 19 
Phase 1: Preliminary layer boundaries were chosen 

based on lithostratigraphic boundaries and porosity 

profiles. Layers were refined in the transition zones at 

the top and bottom of the PTn to minimize the range in 

porosity. 

Phase 2: Layer properties were evaluated based on 

the relationship of K, to porosity, and unique zones 

were refined where altered materials influence flow, 

such as at the base of the Tiva Canyon Tuff and in the 

zeolitized rocks below the Topopah Spring Tuff. 

Phase 3: Moisture-retention characteristics of layers 

were evaluated. Moisture-retention curves are measured on fewer samples than any other measurement 

and need to represent a spectrum of field measurements. Field measurements were incorporated into 

laboratory measurements to help represent hysteretic 

conditions in the shallow layers of the Tiva Canyon 

Tuff and the PTn. Predicted water potentials were 

compared with measured water-potential profiles in 

selected boreholes. If there were moisture-retention 

characteristics that differed appreciably within layers, 

then adjustments of layers were made accordingly. 

Phase 4: Means and standard deviations were calculated for all properties for each hydrogeologic unit. 

Arithmetic mean calculations are used for normally 

distributed properties such as porosity, bulk density, 

particle density, and water content. Geometric means 

are used for saturated hydraulic conductivity and 

water potential. K, is averaged using a geometric 

mean 

L i=1 J 

and a power-law average 

(7) 

where N is the number of samples and w is an empirical coefficient. Arithmetic means used to describe the 

distribution of K, of hydrogeologic units are inappropriate, except for flow parallel to layering in a layered 

system (McKenna and Rautman, 1996). A vertical 

distribution of K, in a vertically heterogeneous system 

is best described by the geometric mean. The major 

problem with using the geometric mean as an estimate 

of the effective K, for any given hydrogeologic unit is 

that the calculated value of the geometric mean can be 

dominated by a small number of low-value outliers in 

the data, whereas the actual effective K, may be virtually independent of the low-valued outliers, especially 

in three-dimensional domains (Jensen, 199 1). The 

flow process is primarily driven by the highconductivity values. 

The calculation for the power-law average is 

essentially the same as the geometric mean if w = 0 

(McKenna and Rautman, 1996). If the property distribution is described by an arithmetic mean, then w = 1. 

A distribution described by a harmonic mean uses 

w = -1. This is best used when flow is perpendicular to 

the stratification within the system. This calculation is 

used extensively in the oil industry to estimate the 

effective hydraulic conductivity of simulated grid 

blocks from core-scale measurements (Journel and 

others, 1986; Deutsch, 1989). A series of numerical 

experiments simulating flow through a cross-sectional 

model of Yucca Mountain indicates a power coefficient 

of -0.4 is appropriate for the tuffs at this site due to the 

dips of the units (McKenna and Rautman, 1996), and 

this value was used for the calculations in this report. 

If significant variances existed within hydrogeologic units that could be reduced by the adjustment of 

layer boundaries, then the appropriate adjustments 

were made, particularly where porosity was the factor 

determining the location of the boundary. A final 

consideration was that of the spatial distribution of the 

mean porosity for those hydrogeologic units penetrated 

by a large number of boreholes. It was considered 

useful to assess horizontal trends or outliers for incorporation into the layer development. 

As outlined above, division of the rocks into 

hydrogeologic units is an iterative process. Hydrogeologic unit divisions were initially made based on lithostratigraphic unit boundaries, refined based on changes 

in porosity and other properties such as moisture-retention characteristics, evaluated as to statistical similarity, and examined in the context of lithostratigraphic 

features. This section describes the nomenclature and 

character of the hydrogeologic units and is followed by 

details and rationale behind the influences of the various features, alteration and permeability, and moistureretention character. Hydrogeologic-unit nomenclature 

is associated with lithostratigraphic units in table 1. 

Nomenclature abbreviations are maintained at a maximum of three letters for the ease of creating numerical 

20 Characterlzatlon of Hydrogeoioglc Units Using Matrix Properties, Yucca Mountain, Nevada 
model input files and generally are related to nomen- Tiva Canyon Tuff 

clature abbreviations from Scott and Bonk (1984). 

Porosity, saturation, and particle density are generally good indicators of lithostratigraphic boundaries 

(table 1) and are shown, along with lithostratigraphic 

units, for samples from two deep boreholes, SD7 and 

SD9 (figs. 3 and 4). These figures exemplify the vertically stratified nature of the unsaturated zone at Yucca 

Mountain. The shading represents the formations Tpc, 

Tpt, and Tcp (table 1). Corrected saturation and water 

potential are shown for each borehole with a line indicating water potential calculated for no-flow conditions 

in equilibrium with the water table. Many of the waterpotential measurements lie to the right of this calcu- .' 

lated no-flow line, which suggests (though highly 

unlikely) that there is a mechanism contributing to the 

drying out of the formation at great depths. Most 

likely, the values outside the no-flow line are located in 

rocks that are subject to drilling or sample-handling 

effects that were not or could not be accounted for in 

the error analysis and corrections. In general, porosity 

is high and saturation is low in the nonwelded rocks, 

except for those close to the water table, and porosity is 

low and saturation is high in the welded rocks (table 1 ; 

figs. 3,4). Particle density is generally high in the 

devitrified rocks and low in the vitric rocks (table 1). 

The details of the individual units are discussed below. 

Phase 1 : Porosity Profiles 

A usekl first step in developing layers for hydrologic flow models uses lithology and its corresponding 

relationship with porosity. Porosity has been shown to 

be a reasonable surrogate for flow properties when 

relationships are developed according to the lithologic 

and alteration character of the rocks (Flint and others, 

1996b; Istok and others, 1994; Schenker and others, 

1994). Keeping in mind that all layer divisions have to 

reflect the vertical distribution of rock units (that is, 

units with similar properties, if separated in space vertically, need to be separate layers), the first separation 

is by lithostratigraphic unit. In zones where vaporphase corrosion is prevalent, such as in Tpcrn, Tpcplnc, 

and Tptrn, porosity is used as the determinant for layer 

boundaries. 

The Tiva Canyon welded hydrogeologic unit 

(Tpc) is described by Montazer id Wilson3 984) as 

the densely to moderately welded uppermost stratigraphic layer that underlies much of Yucca Mountain. 

It dips 5O to 1 O0 eastward, is absent in some washes, and 

is about 150 m thick beneath Yucca Crest. 

The transition through the uppermost rocks of 

the Tiva Canyon Tuff is shown in boreholes N36 and 

N27 (fig. 5). The upper part of Tpcrn4 is densely 

welded, and the lower part of Tpcrn4 and the underlying Tpcrn3 are increasingly vapor-phase corroded 

(table 1). Tpcrn2 and Tpcrnl have lower porosity and 

less vapor-phase corrosion than the overlying units, but 

higher porosity and vapor-phase corrosion than 

Tpcpul. Boundaries of the hydrogeologic units are 

selected on the basis of porosity. The boundary 

between CCR and CUC is located at the depth that the 

porosity increases to greater than 9 percent, and the 

boundary between CUC and CUL is located at the 

depth at which the porosity decreases to less than 

20 percent. The CUL has somewhat higher porosity 

than the underlying densely welded rocks of the Tiva 

Canyon Tuff, and the lower boundary of CUL is at the 

lithostratigraphic contact. 

The middle and lower parts in the crystallized 

rocks of the Tiva Canyon Tuff include the Tpcpmn, 

Tpcpll, and Tpcpln (table 1). As shown in boreholes 

SD7, N54, N55, and N3 1, these lithostratigraphic units 

have low variability in porosity, and, together, comprise CW (figs. 6 and 7). The base of the lower nonlithophysal columnar subzone (Tpcplnc) is higher in 

porosity due to an increased amount of vapor-phase 

corrosion, as well as being the initial part of the transition from welded to nonwelded in the vitric rocks 

below (Buesch and others, 1996b) (figs. 6 and 7). The 

base of the CW is where the porosity increases in the 

vapor-phase corroded rocks to 15 percent or greater. 

Nonwelded Paintbrush Tuff and Base of Tiva 

Canyon Tuff 

The Paintbrush nonwelded hydrogeologic unit of 

Montazer and Wilson (1984) is described as consisting 

of the nonwelded and partially welded base of the Tiva 

Canyon Tuff, the Yucca Mountain and Pah Canyon 

Tuffs, the upper nonwelded and partially welded upper 

part of the Topopah Spring Tuff, and the associated 

bedded tuffs. It consists of thin, nonwelded ash-flow 

Characterization of Hydrogeologlc Units 21 
I , t 

St1313W NI 'Hld3Q 

Flgure 3. Porosity, saturation, particle density, and water porential with calculaled no-flow conditions in equilibrium with the 

water table, with depth for borehole SD7. 

22 Characterizatlon of Hydrogeologlc Unlts Using Matrix Properties, Yucca Mountain, Nevada 
0 8 3 8 8 8 Q 7 N -5 u> 8 

SUX3W NI 'Hld30 

Figure 4. Porosity, saturation, particle density, and water potential with calculated no-llow conditions in equilibrium with 

water table, with depth for borehole SD9. 

the 

Characterizalion of Hydrogeologlc Units 23 
N 36 N27 

0 

5 

0 

Qf 

E 

z 

i 

a 

W 

0 

15 

20 

0.2 0.4 0.6 0.8 1 

POROSITY, SATURATION 

- 

CCR 

- 

CUC 

0. T~crn3 

10 

20 

0 

% 

30 

2 

z 

40 

W 

a 

50 

60 

Tpcpll 

Porosity Saturation 

• 9 

," 

0 0.2 0.4 0.6 0.8 

POROSITY, SATURATION 

CUC 

CUL 

CW 

Figure 5. Oven-dry porosity and saturation profiles for rocks from the upper part of the Twa Canyon Tuff in boreholes N36 and 

N27. 

24 Characterlzatlon of Hydrogwlogk Unlts Uslng Matrix Properties, Yucca Mountain, Nevada 
SD7 

OrlPOROSITV, SATURATION 

0 

20 

40 

60 

80 

N54 

0.2 0.4 0.6 0.8 1 

POROSITY, SATURATION 

0 

20 

40 

60 

1 

0.2 0.4 0.6 0.8 1 

POROSITY. SATURATION 

Figurn 6. Oven-dry porosity and saturation profiles for rocks between the lower part of the Tiva Canyon Tuff, bedded tuffs of 

the Paintbrush Group, Yucca Mountain and Pah Canyon Tuffs, and the upper part of the Topopah Spring Tuff for boreholes 

SD7, N54, and N55. 

Characterization of Hydrogeologic Units 25 
0 

10 

20 

a 

LT 

W 

kJ 

5 

Z - 30 

1- 

Ii 

W 

13 

40 

50 

N 31 

Porosity Saturation I 

" CW 

I.I,I,I, 

0.2 0.4 0.6 0.8 1 

POROSITY, SATURATION 

SD9 

Or 

20 

40 

60 

80 

100 

Tpcplnc 

TP~P? 

I I t Tpp 

0 0.2 0.4 0.6 0.8 

POROSITY, SATURATION 

CNW 

B T4 

7PP 

B T3 

TPP 

BT2 

TC 

TR 

Figure 7. Oven-dry porosity and saturation profiles for rocks from the Paintbrush Group between the lower Tiva Canyon Tuff 

and upper Topopah Spring Tuff in boreholes N31 and SD9. 

26 Characterlzatlon of Hydrogeologic Units Uslng Matrix Properties, Yucca Mountain, Nevada 
sheets and bedded tuffs that thin to the southeast from 

a maximum thickness of 100 m to a minimum of about 

20 m. This unit crops out in several locations, particularly along Solitario Canyon and Yucca Wash. 

To define the detailed character of these rocks for 

this study, they are separated into several hydrogeologic units. The rocks near the base of the Tiva Canyon 

Tuff are characterized by a transition in porosity and 

also in mineral alteration and are divided into the CMW 

and CNW hydrogeologic units. The CMW hydrogeologic unit consists of moderately welded rocks near the 

base of the Tpcplnc and usually most of Tpcpv2 and 

ranges from greater than 15 percent porosity at the top 

of the unit to greater than 28 percent porosity at the bottom of the unit (figs. 6 and 7). The CNW consists of .. nonwelded to partially welded rocks in Tpcpvl and 

locally includes the base of Tpcpv2 (figs. 6 and 7). 

The lithostratigraphic units of the PTn commonly are thin, but distinct enough in properties to 

delineate as separate hydrogeologic units. A numerical 

modeling exercise was done by Flint and others 

(1996a) to assess the hydrologic impact of these individual units and whether the properties were different 

enough to maintain the individual layers as separate 

units. It was determined that abrupt and linear contacts, along with the contrasts in properties, were 

instrumental in creating lateral diversion along the 

sloping contacts. As an exercise, this indicated that the 

property contrasts were different enough in most cases 

to maintain separate units. However, in reality, this 

exercise simplified the linear character of the contacts. 

These contacts are only locally linear and are less likely 

to divert water laterally due to heterogeneities that 

cause increases in saturation and local instabilities that 

result in penetration across the boundary. The Yucca 

Mountain Tuff (Tpy) has properties very similar to the 

Tpbt4 and Tpbt3 to the south of Drill Hole Wash (fig. 

6, boreholes N54 and N55), but has lower porosity and 

becomes moderately welded to the north (fig. 7, see 

borehole SD9). In the modeling exercise (Flint and 

others, 1996a; Moyer and others, 1996), this unit was 

represented by the properties of the lower porosity 

rocks, and it diverted water laterally. As a result, TPY 

represents rocks of less than or equal to 30 percent 

porosity. In boreholes where the TPY is greater than 30 

percent porosity, the properties of BT4 are used to represent the TPY. If no BT4 exists in the borehole, properties from the unit Tpbt3 are used. Typically to the 

south of Drill Hole Wash, the hydrogeologic unit BT3 

represents both Yucca Mountain Tuff and Tpbt3. The 

Pah Canyon Tuff is welded far to the north in Yucca 

Wash, but no boreholes sampled in that unit contained 

welded or even moderately welded rocks; therefore, 

the nonwelded to partially welded Pah Canyon Tuff is 

hydrogeologic unit TPP. The Tpbt2 and the nonwelded 

top of the Topopah Spring Tuff, Tptrv3, were not different enough in properties to maintain as separate 

units (Flint and others, 1996a; Moyer and others, 1996) 

and are represented by hydrogeologic unit BT2. 

Tptrv2 is a thin unit that transitions sharply from nonwelded to densely welded rock such that the sample 

spacing of 0.8 m was not enough to characterize the 

transition, and it is included as the lower part of BT2. 

Topopah Spring Tuff 

The Topopah Spring welded unit (Montazer and 

Wilson, 1984) consists of a very thin upper vitrophyre; 

a thick central zone consisting of several densely 

welded, devitrified ash-flow sheets; and a thin lower 

vitrophyre. The unit contains several lithophysal 

cavity zones of varying thickness, and the rocks are 

intensely fractured. This unit is the thickest and most 

extensive of the Paintbrush Group and contains the 

central and lower densely welded and devitrified zones 

being considered for the potential repository. 

The vitric, densely welded (Tptrvl) subzone, 

which contains the vitrophyre, is typically less than 

0.5 m thick, but varies from 0 to 2 m thick across Yucca 

Mountain (D.C. Buesch and R.W. Spengler, U.S. Geological Survey, written commun., 1996) (fig. 8). The 

Tptrvl typically has porosity less than 5 percent. It has 

highly contrasting properties to the rocks overlying it. 

The underlying dense subzone of the crystal-rich nonlithophysal zone (Tptrn3) also has very low porosity 

(less than 9 percent) and can be combined with the 

Tptrvl as the hydrogeologic unit TC. Tptrn3 is typically thicker to the north and very thin in the southern 

parts of the study area. 

Most of the crystallized, moderately to densely 

welded Topopah Spring Tuff is divided into five hydrogeologic units that closely correspond to lithostratigraphic units. The vapor-phase corroded and crystaltransition subzones of the crystal-rich nonlithophysal 

zone (Tptrn2) (fig. 8) have porosity similar to the 

underlying lithophysal zone, but moisture-retention 

characteristics differ (discussed below). Therefore, 

Tptm2 is represented by TR and has greater than 9 percent porosity. The lithophysal (Tptrl, Tptpul, and Tptpll) and nonlithophysal (Tptprnn, Tptpln) zones differ 

Cherecterlzatlon of Hydrogeologlc Unlts 27 
UZ14 UZ16 SD7 

POROSITY, SATURATION POROSITY, SATURATION 

0.2 0.4 0.6 0.8 1 

POROSIPI, SATURATION 

TUL 

- 

TMN 

- 

TLL 

- 

TM2 

TM1 

Figure 8. Oven-dry porosity and saturation profiles of rocks from the Topopah Spring Tuff in boreholes UZ14, UZ16, and 

SD7. 

28 Characterization of Hydrogeologic Unlts Uslng Matrix Properties, Yucca Mountaln, Nevada 
in porosity with the lithophysal zones being approximately 14 percent porosity and the nonlithophysal 

zones approximately 11 percent (figs. 3,4, and 8). 

They differ particularly in moisture-retention characteristics; therefore, each zone is represented by individual hydrogeologic units: TUL, the upper lithophysal 

zone; TMN, the middle nonlithophysal zone; TLL, the 

lower lithophysal zone; and TM2 and TMl, comprising the lower nonlithophysal zone. The lower nonlithophysal zone of the Topopah Spring Tuff transitions 

into lower porosity (approximately 9 percent) and 

locally vitric rocks at the base that have different moisture-retention characteristics due to a downward 

increase in the amount of smectite (Bish and Chipera, 

1989) and is, therefore, divided into two hydrogeologic. 

units (discussed below). 

Vitric rocks at the base of the Topopah Spring 

Tuff are highly contrasting in porosity (fig. 9) with 

rocks above and below them. The very low-porosity 

densely welded subzone (Tptpv3), which contains the 

vitrophyre, is a discrete hydrogeologic unit, PV3. The 

moderately welded subzone (Tptpv2) is PV2. The nonwelded base of the Topopah Spring Tuff, Tptpvl, is 

similar in properties to the underlying bedded tuff, 

Tpbtl, and they are combined in hydrogeologic unit 

BTI. 

Calico Hllls Formation 

The Calico Hills nonwelded hydrogeologic unit 

of Montazer and Wilson (1 984) includes the nonwelded to partially welded vitric zone, which is locally 

zeolitic, that is the lowermost part of the Topopah 

Spring Tuff. It also includes the pre-Topopah Spring 

Tuff bedded tuff; the beds of the Calico Hills Formation; a bedded tuff; a bedded sandstone; the Prow Pass 

Tuff, which is nonwelded to welded; the pre-Prow Pass 

bedded tuff; and the upper part of the Bullfrog Tuff, 

where it is above the water table. The Prow Pass Tuff 

and the Bullfrog Tuff are actually within the Crater Flat 

Group. Within the unsaturated zone, the thickness of 

this hydrogeologic unit ranges from 0 to more than 

500 m. 

The Calico Hills Formation examined as part of 

this study consists of nonwelded pyroclastic flow and 

thin fallout deposits, and locally there is a basal bedded 

sandstone. These rocks are either vitric or zeolitic, and 

this difference strongly controls the flow of water 

through the rocks. The part of the formation that is primarily pyroclastic flow deposits, which includes units 

1 to 4, is divided into hydrogeologic units CHV and 

CHZ, depending on whether or not it is vitric or 

zeolitic, respectively. The vitric-zeolitic boundary, 

rather than using lithologic descriptions which typically include estimates of mineral percentages, is 

based on the degree of hydrologic response. It is 

defined in this case as a 5-percent difference in the 

porosities measured using elevated relative humidity 

(RH) drylng and standard 105OC oven drying at ambient relative humidity (generally less than 20 percent) 

(see section in Phase 2 below for more detailed discussion of alteration influences on properties). This value 

was chosen on the basis of associated abrupt changes 

in saturation (see SD7, figs. 9 and 10). The bedded 

tuff near the base of the Calico Hills Formation 

(Tacbt) is relatively high in porosity, but is partially 

silicified and contains opal, and this strongly affects 

the moisture-retention characteristics and permeability. Tacbt, along with the thin basal sandstone, Tacbs, 

which is similar in properties to the bedded tuff, comprise the hydrogeologic unit, BT. 

Prow Pass and Bullfrog Tuffs 

The Prow Pass Tuff is only sampled in four deep 

boreholes used in this study (table 4) and is variable 

among these boreholes. It is composed of four pyroclastic units and an underlying interval of bedded tuff 

(fig. 9). Lithostratigraphic units Tcp4, Tcp2, and Tcp 1 

are sequences of nonwelded to partially welded pyroclastic flow deposits, and Tcp3 is a partially to moderately welded pyroclastic flow deposit that displays a 

compound cooling history. The alteration of the initially vitric rocks to zeolites is pervasive throughout the 

Prow Pass Tuff, with the exception of Tcp3 that is 

devitrified and vapor-phase crystallized where the 

welding increases. As a result, the Prow Pass Tuff is 

hydrogeologically divided based primarily on lithostratigraphic unit boundaries and secondarily on the differential porosity based on the separation of RH and 

105OC calculations. In this case, the mechanism is not 

always as clear and remains basically empirical with 

the 5-percent differential in porosity relating well to 

saturation profiles and moisture-retention characteristics. The hydrogeologic units are PP4, which is equivalent to lithostratigraphic unit Tcp4 and is altered to 

zeolites and high in porosity; PP3, which is the upper 

part of Tcp3, is high in porosity, and has no zeolites, but 

is high in vapor-phase minerals that appear to influence 

the 5-percent differential porosity; PP2, which is the 

Characterization of Hydrogeologic Units 29 
SD9 UZ16 

450 

500 

V) 

IY 

W 

550 

z 

z 

1- 

In 

W 

0 

600 

650 

700 

0 

=T 

0.2 0.4 0.6 0 .a 1 

POROSITY, SATURATION 

P v3 

- 

BT1 

CHZ 

- 

BT 

- 

PP4 

- 

PP3 

PP2 

PPl 

35C 

40C 

45C 

5M; 

55C 

500 

m I 

PomsilySaturation 

. O 

0.2 0.4 0.6 0.8 1 

POROSITY. SATURATION 

I Tct I 

0 0.2 0.4 0.6 0.8 1 

POROSITY, SATURATION 

Figure 9. Oven-dry porosity and saturation profiles of rocks from the base of the Topopah Spring Tuff; the pre-Topopah 

Spring bedded tuff; the Calico Hills Formation; and the Prow Pass, Bullfrog and Tram Tuffs of the Crater Flat Group from 

boreholes SD9, UZ16, and SD7. 

30 Characterlzatlon of Hydrogeologlc Unlts Uslng Matrlx Properties, Yucca Mountain, Nevada 
0 0.2 0.4 

POROSITY 

-- 

1 

1 

45,14 

62 

60 

14 

21 

49,68 

49 

53 

46 

50 

55 

54 

46 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

-- 

35 

29 

42 

53 

60 

54 

82 

68 

56 

61 

49 

53 

39 

53 

60 

52 

34 

N31 

0 1 2 5% 

I I Porosity Porosity 'OSC RH 

8 

Tpcpll 

Tpcplnh 

&3J 

CW 

ZMW 

- 

>NW 

BT3 

40 - 

50 - 

TPP 

- 

I I I I 

0.2 0.4 0.6 

POROSITY 

RESIDUAL WATER CONTENT (HGU) 5% OR GREATER 

Figure 10. Porosity determined using standard oven drying and relative humidity oven drying for core from the Calico Hills 

Formation, Prow Pass Tuff, and part of the Bullfrog Tuff in SD7 and for core from the lower part of the Tiva Canyon Tuff to the 

upper part of the Topopah Spring Tuff in borehole N31. 

Cherecterlzatlon of Hydrogeologic Units 31 
lower one-half of unit 3 and is welded, devitrified, 

unaltered, and lower in porosity; and PPl, which is 

composed of Tcp2 and Tcp 1, both of which are zeolitized. The boundary between PP3 and PP2 varies 

among the four boreholes penetrating Tcp3, but the 

direct approach of dividing the unit in two halves 

seems to adequately minimize the variance. 

The Bullfrog and Tram Tuffs were only penetrated by SD7 and have been divided only on the basis 

of alteration character. The hydrogeologic units are 

BF3, which is the unaltered units 4 and 3 of the Bullfrog Tuff, and BF2, which is the slightly altered units 2 

and 1 of the Bullfrog Tuff, the underlying basal sandstone, and the altered samples of the Tram Tuff. 

Phase 2: Alteration, Microfractures, and 

Permeability 

Water is stored in, and flows through, the interconnected pores of the rock matrix; therefore, porosity 

is useful for characterizing the hydrologic character of 

the various rock types. In general, the porosity can be 

related primarily to the depositional features and 

amount of welding of a rock, with the lowest porosity 

in the most densely welded rocks and the highest 

porosity in the nonwelded and bedded rocks. For many 

rocks, the porosity is also related to alteration history 

because clays, zeolites, opal, and calcite form in place 

or are deposited in pore channels and throats and, 

therefore, may decrease porosity. Occurrence of clay 

or zeolite zones only slightly reduces the measured 

porosity because water can be stored in clay and zeolite 

mineral structures rather than occupy space within the 

pores (which would reduce the measured porosity). 

This is true unless water is held in smectites that swell 

with the incorporation of water to as much as 300 times 

their original size, thus reducing the porosity. Clays 

and zeolites do influence the pore-size distribution and, 

thus, the character of the moisture-retention curve and 

the permeability. Rocks containing clay or zeolites can 

maintain a relatively large volume of water, but by 

holding it tightly within clay structures, small pores, or 

pore throats, the permeability is reduced. Zones with 

clay or zeolites may be an important factor contributing 

to perched water. Borehole SD7 has a saturation profile (fig. 9) in the rocks below the Topopah Spring Tuff 

(Tpt) that strongly indicates, by high saturations, the 

presence of alteration minerals and their ability to store 

water and influence its downward transmission. In 

zones where there is little or no alteration, such as in the 

vitric rocks of the Calico Hills Formation (Tac, CHV) 

and some of the devitrified and vapor-phase corroded 

rocks of the Prow Pass Tuff (Tcp, PP3), the saturations 

are extremely low because the pores are larger and 

drain more easily. In the crystallized and minimally 

vapor-phase-corroded Prow Pass Tuff (PP4, PP2, and 

PPl), the saturation is high because the rocks are 

welded with small pores. There is also some evidence 

that indicates an influence of some of the high-temperature alteration products, such as the vapor-phase crystallization minerals tridymite and cristobalite, on the 

retention of water in this zone. 

Residual water content is defined as that water 

content for which the gradient (deldy; where 8 is water 

content and y is water potential) becomes zero (van 

Genuchten, 1980). It has alternatively been suggested 

as that point in saturation where liquid flow stops due 

to discontinuous columns of water, and vapor flow 

begins. This value is generally used as the dry-end fit 

parameter for moisture-retention curves and its magnitude will greatly influence the prediction of unsaturated 

hydraulic conductivity at low water contents. The 

water left in a rock at very low saturation will be in the 

smallest pores or channels or within mineral structures 

such as clays or zeolites. The volume of water remaining will then be indicative of either the quantity of very 

small pores or channels or the presence of waterabsorbing minerals such as clays or zeolites. Bush and 

Jenkins (1 970) determined that drylng rock samples in 

an oven at a temperature of 60°C and 40 percent relative humidity maintained water within the clay structures, as well as 1-2 molecular layers of water adsorbed 

to their surface, while removing it from the pore channels. Studies done on soils indicate that residual water 

content can be defined by the amount of water left in 

the pores after equilibrating in an environment of 

approximately -700 bars water potential, or about 

65 percent relative humidity (Jackson, 1963; Rose, 

1963). The influence of alteration, whether it be clays, 

zeolites, or vapor-phase minerals, on pore structure and 

water-holding capacity can be examined more closely 

by varying the relative humidity and temperature ofthe 

drying oven during the processing of the samples for 

the determination of porosity. 

Rock samples were dried at 60°C and 65 percent 

relative humidity and at 105OC and ambient relative 

humidity (<20 percent), and porosity was calculated 

using both dry weights (fig. 10). The altered rocks, 

32 Characterization of Hydrogeologic Units Using Matrix Properties, Yucca Mountain, Nevada 
such as Tacbt, Tacbs, Tcp4, and Tcpl, have porosity 

calculated from relative-humidity-dried rocks that is 

much lower, presumably because the water was held in 

the altered minerals. Values of the percentages of measured zeolite (in the form of clinoptilolite) (Chipera 

and others, 1996) are indicated (fig. 10). In locations in 

SD7 where there are no measured zeolites (indicated 

by "--"), yet there is a 5-percent differential porosity 

(indicated by the black bar), there are elevated quantities of vapor-phase minerals tridymite and cristobalite 

(Chipera and others, 1996). Cristobalite is present 

from depths 502.3 m to 569.4 m (2 to 35 percent), and 

tridymite is present from 502.3 m to 538.4 m (1 to 

6 percent). The 5-percent differential porosity typically occurs in rocks where zeolites were measured. It, 

does not occur in the rocks where zeolites were not 

measured but where only cristobalite was present 

(538.4 m to 569.4 m), but it did occur in the rocks 

located at the depths where there were both tridymite 

and cristobalite, indicating a possible influence of certain vapor-phase minerals, possibly tridymite or the 

combination of both, on the structure or geometry of 

the pore spaces and increasing the moisture-retention 

capacity of these rocks at low saturations. The increase 

in tortuosity of the flow channels due to the presence of 

clay, zeolites, or vapor-phase minerals also reduces the 

permeability, which is discussed below. [There is evidence that very high percentages of Opal-CT, which is 

a disordered silica phase containing both cristobaliteand tridymite-like structural units (Bish and Chipera, 

1989), which are often found in the pre-Calico Hills 

bedded tuff (Tacbt), may influence the hydrologic character of rocks by reducing the permeability even more 

than the presence of zeolites.] The method of determining porosity from RH drylng and comparing it to 

porosity determined from standard oven drylng has 

been shown to be useful in classifjmg rocks into zones 

that have similar properties, such as permeability and 

moisture-retention characteristics, for the development 

of distinct model layers. It also may provide parameters useful in modeling as the measurements of all the 

physical properties using RH drying better reflect field 

conditions and are suggested for use in the interpretation of geophysical logs. 

Hydrogeologic properties similar to those in SD7 

that result in the 5 -percent differential porosity, are 

apparent in rocks near the base of the Tiva Canyon 

Tuff, Tpcpv, and are exemplified in N3 1 (fig. 10). This 

zone of differential porosity, which, based on quantitative mineralogy from similar stratigraphic position, 

contains up to 35 percent smectite, is pervasive across 

the site, although to varying degrees (Bish and Chipera, 

1989). The extent ofthe alteration appears to be related 

to the topographic location of the borehole; for example, boreholes situated in narrow up-wash channels 

may receive more frequent runoff and, therefore, can 

maintain higher water contents for longer periods of 

time (Flint and Flint, 1995). This zone of differentia 

porosity at the base of the Tiva Canyon Tuff, which 

occurs within the CMW unit, is an important hydrologic feature because it may accentuate the capillary 

barrier effect caused by small pores situated above 

large pores at this transition into the nonwelded tuffs 

.1 

The differential porosity appears through the base of 

the BT3 hydrogeologic unit, but the combination of 

very large porosities and the particular pore-size distributions of the units below the CMW, despite the presence of clay, results in the drainage and relatively low 

saturation of these units. 

Another measurement method that gives insights 

into the structure or sizes of pores and the influence of 

clays and zeolites is the determination of particle density using helium pycnometry. A selection of various 

lithologic types from UZ16 was analyzed using water 

saturation to calculate particle density from bulk density and porosity and helium pycnometry to directly 

measure the volume of the solid particles of the rock to 

calculate particle density (fig. 11). These samples 

included vitric bedded tuff, zeolitized bedded tuff and 

nonwelded to moderately welded rocks, vitric densely 

welded rocks, and crystallized moderately to densely 

welded rocks. The moderately to densely welded, 

devitrified rocks (welded crystallized in fig. 11) lie 

close to the 1: 1 line and have particle densities of 

approximately 2.55 to 2.6 g/cm3, and rocks with abundant vapor-phase minerals will be closer to 2.5 because 

those minerals are approximately 2.3 g/cm3 (fig. 1 1). 

The welded devitrified rocks do not respond differently 

to water or helium, so there is a 1 : 1 relation. Densely 

welded, vitric rocks, which include Tptpv3, are 

approximately 2.38 g/cm3 (supported by Scott and 

others, 1983) when calculated using water saturation. 

The porosity in these rocks is extremely small, as are 

the pores (inferred by the moisture-retention curve, 

fig. 13f) and the occupation of these pores by helium, 

when voided of water for the pycnometry measurement, may be limited by the nonpolarity of the helium 

molecule. In addition, vitric rocks typically contain as 

much as 5 percent water @.C. Buesch, U.S. GeologiCharacterization of Hydrogeologic Unlts 33 
Nonwelded 

Zeditic 

Densely Welded 

Vitric 

Z, 

0 

4 77 I I I 

9 2.2 2.3 24 2.5 2.6 2.7 

MEASURED PARTICLE DENSITY, IN GRAMS PER CUBIC CENTIMETER 

Figure 11. Calculated particle density using water saturation versus particle density measured using helium pycnometry for 

nonwelded to densely welded tuffs that are vitric, crystallized, or zeolitized on samples from borehole UZ16. 

34 Characterlzatlon of Hydrogeologlc Units Using Matrix Properties, Yucca Mountain, Nevada 
1 E-4 

1 E-5 s 

c 1 E-6 I 

I2 

0 1E-7 z 

S 

0 2 1 E-8 

3 

4 

a: 

0 5 1E-9 

S 

I- 2 1E-10 

3 

'z 

(I) 1E-11 

3 

0 

13 

TPC, Tpt 

crystallized 

CMW 

X 

all PTn units 

0 

TC PV3 iBT1 

0 

CHV * 

CHZ 

BT, PP4 PP3, PP1 X 

PP2, BF3, BF2 + 

1E-12 

0.2 0.4 0.6 0.8 

POROSITY 

1 E-4 

'"1 7 

1 E-7 

0 2 1 E-8 

a 

a: 

0 5 1 E-9 

0 

W 

~"80wg'w' 00 

0 Vitridcrystallized 

0 

I- 2 1E-10 

3 

5 1 E-1 1 

1 E-12 

0.2 

w 

, 

Altered 

0 -- 2' Microfractured + 

I 

0.4 

POROSITY 

0.6 0.8 

Figure 12. Relation of porosity and saturated hydraulic conductivity for samples grouped (a) by various hydrogeologic units 

and (b) by vitric/crystallized, altered, and microfractured units. 

Characterization of Hydrogeologic Units 35 
a), 0,000 

p l,OOO 

a 

4 

g 100 

blo,ooo 

g 1,000 

a * 

z_ I00 

2 

5 10 

W 

Ig 

P! I 

W 

I w 1 

0.01 

0 

1 

0.2 0.4 0:6 0.8 I 

SATURATION 

i' 

2 

z 10 

W 

L 

0 

n 

P! I 

W 

0. 

0.0 

0 0.2 0.4 0.6 0.8 I 

SATURATION 

1,000 

100 

10 

1 

0.1 

I 

--i--------_=1 g 

0.01 11 4 

0 0.2 0.4 0.6 0.8 1 

SATURATION 

1,000 

100 

10 

I 

I -...I 

I - -.-...- 

0.01 I I I I 

0 0.2 0.4 0.6 0.8 I 

SATURATION 

Figure 13. Moisture-retention curves for core samples from hydrogeologic units (a) CW, (b) BT3, (c) TR, (d) TUL, (e) TMN, 

(f) PV3, (g) CHZ, and (h) PP2. All units have laboratory measurements of core whereas units CW, BT3, and TR have field 

measurements included. 

36 Characterlutlon of Hydrogeologlc Unlts Using Matrlx Properties, Yucca Mountain, Nevada 
e) 10,000 ~10,000 

p 1,000 1,000 

a 

V) 

a 

a 

4 

Z 100 z 100 - 

J 

9 

IZ 

W 

A 

9 

10 

W 

L 

0 I U 

0. Lab data Data sets Model +Error -Error 

0.0 

I I - V.V I 

0 0.2 0.4 0.6 0.8 1 

SATURATION 

0 0.2 0.4 0.6 0.8 1 

SATURATION 

g)10,000 

1,000 

100 

10 

1 

h~o.ooo I 

p 1,000 

5 

Z 100 

I- 

: 

a 1 

.w 

- .- - - 

Lab Data Model +Error -Error 

- - . . . . -

0.01 

0 0.2 0.4 0.6 0.8 1 

SATURATION 

I 

0.1 Lab Data data sets Model +Error -Error 

I - 

0.01 1 ' I I I 1.1 

0 0.2 0.4 0.6 0.8 1 

SATURATION 

Figure 13. Moisture-retention curves from laboratory measurements of core for hydrogeologic units (e) TMN, (f) PV3, (g) 

CHZ, and (h) PP2.4ontinued 

Characterization of Hydrogeologic Units 37 
cal Survey, written commun., 1996), which would be 

dehydrated prior to the pycnometry measurement and 

not replaced by the helium due to the nonpolarity, thus 

underestimating the particle density. Particle densities 

for the densely welded vitric rock samples are approximately 0.045 g/cm3 lower using the helium pycnometry method. The nonwelded vitric and zeolitic samples 

have a larger range of particle densities, incorporating 

zeolites (particle density of 2.16 g/cm3 for clinoptilolite), and in the vitric samples, smectites (particle density of 2.5 g/cm3). These two minerals result in varying 

responses of the samples to the different measurement 

techniques due to their structural character. Zeolitic 

samples are approximately 0.08 g/cm3 lower in particle 

density when measured using pycnometry, and the 

nonwelded vitric samples, which contain from 0 to 

18 percent smectite (mostly in the form of montmorillonite) (Chipera and others, 1994), are an average of 

0.06 g/cm3 higher. Zeolites contain 1.5 to 3 times the 

water of glass in a high relative humidity environment, 

yet do not exhibit significant swelling. This adsorbed 

water (due to ion-dipole interactions) and zeolite water 

(in-filling channels and cages in the crystal-lattice 

framework) can be removed at temperatures of 70 to 

300°C (Martin and others, 1991). [Bound water (covalent and hydrogen bonds within the crystal structure) is 

removed at temperatures of greater than 260 - 600°C.] 

Montmorillonite has adsorbed and interstitial water 

that can increase the interlamellar spacing of the mineral from 10 to 19 angstroms (Deer and others, 1966), 

resulting in volume changes up to 300 times the dehydrated size of the mineral. Based on measurements of 

standard thermal dehydration curves of montmorillonite (Nutting, 1943), Gardner (1 965) suggests temperatures of 165 - 175°C be used to remove adsorbed and 

interstitial water from clays, and Bush and Jenkins 

(1 970) suggest it requires 180°C to remove all unbound 

water. During water saturation measurements, 

adsorbed and interstitial water occupies space within 

the zeolite and clays, as well as within the pore spaces. 

The samples were dried at a temperature of 105°C and 

some, but not all, water was removed from the zeolites, 

clays, and pore spaces. Because helium sorbs to neither zeolite nor clay (Martin and others, 1991) when 

added to the samples during the pycnometry measurement, it occupies the pore spaces, but does not occupy 

the spaces within the zeolite and clay minerals. This 

results in a lower measured particle density for the 

samples with zeolites. The nonwelded, vitric samples 

with clays, however, respond differently because of the 

large swelling capacity of the montmorillonite (Iwata 

and others, 1988; Deer and others, 1966). When dried, 

the removal of water results in a collapse of the clays 

(Bish, 1989), reducing the clay volume to a greater 

degree than the actual volume of water removed (Iwata 

and others, 1988). Therefore, the weight of the sample 

is reduced less than the corresponding increase in volume, which is filled by helium, and the calculation of 

particle density for the clay samples is higher for the 

helium pycnometry measurement than for the water 

saturation method. 

The effects of alteration materials on the hydrologic character of the rocks were evaluated by comparing the porosity with the measured K, for 593 samples 

from all lithostratigraphic units (fig. 12). The upper 

figure shows the relation of the log of K, to porosity for 

samples grouped by hydrogeologic unit. The most 

obvious outliers are those from the zeolitized rocks in 

the Calico Hills Tuff (CHZ) that have a relatively high 

porosity but a very low conductivity. Samples from the 

crystal-rich and crystal-poor vitrophyres of the 

Topopah Spring Tuff (Tptrv 1, TC and Tptpv3, PV3) 

have very low matrix porosities yet have several samples with high conductivities resulting from microfractures. It is possible that some of these samples with low 

values of K, had microfractures, but they were filled 

with alteration materials. Three crystallized and 

welded samples from Tptrn, Tptpul, and Tptpln, with 

fairly low porosity yet with high conductivity, contained visible microfractures. The correlation between 

lithostratigraphic features and properties such as porosity and conductivity is exemplified by simply plotting 

the data as vitric/crystallized, altered, and microfractured (fig. 12). The microfractured category includes 

TC and PV3, plus the three welded samples with the 

visible microfractures that do not represent the matrix 

permeability. The "altered" category includes all 

lithostratigraphic units below the vitric/zeolitic boundary (BTla, CHZ, BT, PP4, PP3, PP2, PP1, BF3, and 

BF2), plus the CMW, and the vitric/crystallized category includes all remaining hydrogeologic units. The 

"altered" category is crudely defined, because there are 

crystallized and unaltered zones within this category, 

but was selected for simplicity to aid in the application 

of predictive equations. Relations between these simplified, lithostratigraphic, feature-based categories, 

porosity, and conductivity can be represented by 

regression models developed using all measured 

38 Characterization of Hydrogeoioglc Units Using Matrix Properties, Yucca Mountain, Nevada 
samples (table 6; fig. 12). (There is not enough spatial 

representation for all of the units included in the 

"altered" grouping for these units to be divided accurately into unique hydrogeologic units represented by 

alteration alone, and for appropriate characterization, 

they need to be better sampled.) Regression models 

were used to estimate Ks on the remaining 4,300 

unmeasured samples, some of which included samples 

with conductivities too low to measure (less than 5 x 

10-l2 mls) with the current laboratory technique. The 

estimates provide a representation of Ks of the densely 

welded tuffs, as well as providing estimates of matrix 

permeability on samples with microfractures for prediction of unsaturated hydraulic conductivity. These ..- 

microfractured samples are likely to only have high 

conductivities when saturated and, after the fractures 

drain, they have relatively no flow. 

The hydrogeologic units at the vitriclzeolitic 

boundary vary spatially over the mountain. In the 

southern part of the site where the boundary is as much 

as 140 m below the Tptpv3, the upper parts of the Calico Hills Tuff, Tpbt l, Tptpv l, and Tptpv2 are unaltered. This condition exists in only two boreholes 

sampled, SD7 and SD 12. Remaining boreholes are in 

locations to the north and east where the vitriclzeolitic 

boundary is typically defined at the base of Tptpv3, 

with zeolitization along the fractures in that unit. Properties for the BTl hydrogeologic unit, which includes 

Tptpvl and Tpbtl, have been characterized for both 

altered and unaltered samples, BTla and BTl, respectively. 

Table 6. Regression equations used to predict saturated hydraulic conductivity and moisture-retention 

curve-fit parameter, a, from porosity 

Altered (CMW, BTl, CHZ, BT, PP4, PP3, PP2, PPl, BF3, and BF2) 

log (saturated hydraulic conductivity) = - 13.1 + 13.8 (porosity) 

Standard error of y estimate 1 .25 

? 0.28 

number of observations 

log (a) = -2.9 + 8.2 (porosity) 

Standard error of y estimate 

? 

206 

0.65 

0.32 

number of observations 10 

Microfractures flC, PV3) 

log (saturated hydraulic conductivity) = -1 0.8 + 45.1 (porosity) 

Standard error of y estimate 1.40 

? 0.66 

number of observations 17 

Remaining vitric and crystallized(CCR, CUC, CUL, CW, CNW, BT4, TPY, BT3, TPP, 

BT2, TR, TUL, TMN, TLL, TM2, TM 1, PV2, BT I, CHV) 

log (saturated hydraulic conductivity) = -14.2 + 69.0 (porosity) - 63.3 (p~rosity)'.~ 

Standard error of y estimate 1.00 

? 0.80 

number of observations 371 

log (a) = -2.0 + 28.6 (porosity) -28.6 (por~sity)',~ 

Standard error of y estimate 0.48 

? 0.74 

number of observations 2 1 

Characterization of Hydrogeologic Units 39 
Phase 3: Moisture Retention and Predictions 

of Field Water Potentials 

Moisture-retention curves are represented for 

eight hydrogeologic units in figure 13a-h. The first 

three units (fig. 13a-c) represent both laboratory desorption curves and composite curves combining laboratory data and all field data that was measured from 

each hydrogeologic unit. Standard errors of the curvefit parameters, a and n, were used to include the 

66-percent confidence intervals about the curve-fit 

models. These intervals were used for graphical purposes because the lower limits of the 95-percent intervals were undefined for a number of the hydrogeologic 

units. Two models were developed: one model is associated with the laboratory desorption data (thick &did 

line in fig. 13a, b, and c) and the second model is associated with the composite data set (thinner solid line). 

In all three units, the composite model was lower as a 

result of including field data that had lower water contents for given water potentials than the desorption 

data. This results in slightly wetter air-entry values 

(lower a), which increases modeled fluxes for the same 

matrix saturation. 

The remaining five hydrogeologic units 

(fig. 13d-h) are data sets from laboratory desorption 

measurements only and include the error incorporated 

into the laboratory measurement due to the instrument 

resolution. This analysis was conducted on data from 

the first three curves (fig. 13a-c), but not incorporated 

into those figures for purposes of graphical clarity. The 

values are included in table 8. The curves representing 

the instrument error are included on the remaining figures (fig. 13d-h) and represent an upper and lower 

bound. Various hydrogeologic units are represented by 

different numbers of individual samples on which measurements were made to produce individual curves, so 

the relative degree of scatter in the points may be somewhat misleading. Several ofthe curves not shown only 

had one sample; therefore, the resulting error in the fit 

parameters is very low. On the other hand, for example, the difference between the CHZ and PP2 is a function of the relative vertical heterogeneity in the unit, 

which is low in the CHZ and high in the PP2. In an 

effort to represent an entire unit with one curve, all 

samples are included and the curve-fitting process 

smoothes out the extremes, which are then expressed 

by the standard errors. 

Notable differences in the moisture-retention 

curves (fig. 13) are chiefly a function of the pore-size 

distributions of the rock types. These different distributions are primarily due to degree of welding and are 

exemplified by comparing the curve for the bedded tuff 

(BT3) to those of the welded tuffs, CW, TUL, TMN, 

and PV3 (fig. 13). These welded tuff units all have 

high air-entry pressures, approximately equivalent to 

lla, and describe the water potential at which the pores 

initially drain, and thus are the largest pores. Rocks in 

the hydrogeologic unit TR are vapor-phase corroded, 

which increases the size of the pores and results in pore 

structures that drain at lower water potential than in 

other noncorroded welded rocks. Another notable feature is the residual saturation, which is approximately 

represented by the saturation at which the dry end of 

the curves becomes asymptotic. It is related to the 

abundance of very small pores that retain water at 

approximately 60-percent relative humidity or 

-700 bars. Altered rocks, such as CHZ, or vitrophyres, 

such as PV3, have the largest residual saturations. 

There are also observable differences between the 

lithophysal and nonlithophysal units, TUL and TMN, 

with the nonlithophysal unit having a greater abundance of small pores. 

The log of a is well correlated to porosity for the 

unaltered vitric, crystallized, and microfractured samples (fig. 14). The correlation is not as good for the 

altered samples. Regression models were done for the 

prediction of log of a that was determined for all 

hydrogeologic units (table 6) for the purposes of estimating parameters from porosity. This is useful for the 

development of more gradual transition zones in 

numerical models (Glass and others, 1994) to eliminate 

the lateral diversion of water due to model artifacts that 

are a result of model layers that are unrealistically contrasting in flow properties (Flint and others, 1996a; 

Moyer and others, 1996). The form of the model equation for the relation of log of a to porosity is the same 

as for K, for both altered and unaltered hydrogeologic 

units. 

For core samples from boreholes SD7, UZ14, 

and SD9, water potential was estimated from saturation 

data using equations 3 and 4 for each hydrogeologic 

unit and compared to measured water-potential values 

(fig. 15). Water-potential and saturation values corrected for water loss due to evaporation were used. 

Matches are relatively good for most zones, with the 

exception of the Calico Hills (Tac) in UZ 14 and SD9 

and the lower part of the Prow Pass Tuff (Tcp) in SD7. 

The moisture-retention curves for the Calico Hills were 

40 Characterizatlon of Hydrogeologic Unlts Uslng Matrix Properties, Yucca Mountaln, Nevada 
1 E+l 

cn 

a: 

3 Y 

aI 1E+O 

9 

Z 

W 

F 

I 2 1E-1 

Z 

W 

0 

Z 

s 

1 E-2 

t 

0 Oo 0 

0.1 0.2 0.3 0.4 0.5 

POROSITY 

Figure 14. Relation of log of moisture-retention curve-fit parameter, van Genuchten alpha, to porosity. 

Characterization of Hydrogeologlc Units 41 
800 PI - . . , , , , , , , . .d 

0.1 1 10 100 

WATER POTENTIAL. IN -BARS 

, "" 

0.1 1 10 100 

WATER POTENTIAL, IN -BARS 

500 

$,  

) 

Fl m - -0 - - 

WATER POTENTIAL, IN -BARS 

Figure 15. Measured (squares) and estimated (circles) water potential using moisture-retention parameters for boreholes 

SD7, SD9, and UZ14. 

42 Characterlzatlon of Hydrogeologlc Units Using Matrix Propeflfes, Yucca Mountain, Nevada 
measured on samples from UZ 16, which does not well 

represent the two boreholes farthest away (SD9 and 

UZ14), but matches the data from SD7 better. The 

curves for the lower part of the Prow Pass Tuff (Tcp) 

were determined from samples from SD9, which does 

not match the measurements in SD7. These discrepancies are probably due to the inability to adequately represent the lateral heterogeneity of these units on the 

basis of measurements from one borehole and support 

the contention that there is lateral variability in the Calico Hills Formation and in the Prow Pass Tuff, which is 

difficult to substantiate with physical properties 

because few boreholes penetrated these units. In all 

deep boreholes, it was noted that a division was necessary in the Topopah Spring Tuff lower nonlithophysal 

unit, TM. The unit was divided into an upper twothirds, TM2, and a lower one-third, TM 1, primarily on 

the basis of moisture-retention characteristics and 

partly on differences in K,. This division and development of an additional moisture-retention curve for the 

lower one-third of the unit aided in matching the waterpotential measurements for all the deep boreholes. 

This was not the case for the Prow Pass Tuff. Although 

litho-stratigraphic contacts did not provide hydrogeologic units that had consistent properties among all five 

measured boreholes, there were no additional divisions, aside from the one in PP3, which was made 

based on degree of vapor-phase alteration, that could 

be made that would reduce the variance in properties 

for all boreholes. 

Phase 4: -Statistical Analysis to Produce 

Mean Values for Modeling Parameters 

Once all the measured data were compiled, along 

with the estimated K, from the regression analysis, 

mean values and standard deviations were calculated 

for each property for each hydrogeologic unit (table 7). 

Minor adjustments were made in boundaries on the 

basis of porosity, such as the upper units and near the 

base of the Tiva Canyon Tuff. In general, the variation 

in porosity within each hydrogeologic unit was relatively small, with the exception of BT4, BT2, and PV2. 

BT4 is very thin, and few samples were collected. The 

relatively variable properties in BT2 result from being 

composed of four units in Tpbt.2 and Tptrv3 (Moyer 

and others, 1996) that vary in the amount of argillization and include Tptrv2 that grades rapidly into low 

porosity rocks; thus, few low-porosity samples are represented. The same mixture of properties is true for 

PV2 that grades relatively sharply from very low to relatively high porosity. 

Several trends emerge from comparing the mean 

values of porosity for the hydrogeologic units. In the 

Tiva Canyon Tuff, the lithophysal CUL is twice as high 

in mean porosity (16 percent) as the mostly nonlithophysal CW (8 percent). The Topopah Spring Tuff (Tpt) 

does not differ as much with the upper (TUL) and 

lower (TLL) lithophysal units having mean porosities 

of 15 percent and 13 percent respectively, whereas the 

upper and lower nonlithophysal units (TMN, TM2 and 

TMl) are 11 percent, 1 1 percent, and 9 percent, respectively. The vitric bedded tuffs and nonwelded ignimbrites in the PTn, included in CNW, BT4, BT3, and 

BT2, vary in mean porosity from 39 percent to 

49 percent. These porosities are significantly higher 

than similarly deposited vitric tuffaceous rocks in BT1 

and CHV that have mean porosities of 27 percent and 

34 percent, respectively. All units below the Topopah 

Spring Tuff have moderate to high mean porosity 

(26 percent to 35 percent), except for BF3, which is 

12 percent. Frequency distributions of porosity are 

shown for each hydrogeologic unit in Appendix I and 

indicate normal distributions for most units. 

Mean water content, saturation, and water potential have been calculated (table 7), but several factors 

must be considered to help explain these values. Spatial averaging of water content, saturation, and water 

potential is not realistic based on consideration of the 

spatial distribution of infiltration that results from the 

distribution of precipitation, the varying thickness of 

alluvial cover, the topographic positions of boreholes, 

and the variable thickness of shallow rock units with 

different properties (Flint and Flint, 1994; Flint and 

Flint, 1996). 

Variances are also a function of spatial distribution of alteration features or sampling of microfractures. Large variances are noted in the hydrogeologic 

unit CMW, as the argillic alteration is likely to be variable among samples vertically and laterally between 

boreholes, and in TC due to the random sampling of 

microfractures. Means of K, calculated using the 

power law with w equal to -0.4 are generally slightly 

lower than those calculated using a geometric mean. 

Geometric means calculated for KT estimated from 

regression analyses are frequently lower than those calculated using measured values. This is particularly true 

for samples with microfractures because the conductivCharacterlzatlon of Hydrogeologlc Unlts 43 
TaMe7. Mean values and standard deviations for measured core properties compikd from all boreholes for each hydrogeobic unit. 

IN, number of samples; vlv, dimemionless volume; g/cm3, gms per cubic centimeter; mls, meters per second; SD, standard deviation; geom., geometric; -, no samples] 

n 

: 

B 

8 

a .* 0 

3 

Estimated 

Relative Volumetric Saturated Saturated saturated 

Hydro- humidity Bulk Particle water Water hydraulic hydraulic hydraulic 

gwlogic porosity N danslty Porosity density N conknt Saturation N potential N conductivity conductivity N conductivity N 

unit (~1'4 (glcd) (vlv) (glcma) (~1'4 (hars) - ---- -- (nw (nw - - (nw 

hn SD Msrn SD Wmn SD Mean SD ban SD Mean SD Geom. SD Geom. SD Power SD Geom. SD 

mean mean law memn 

mean 

2 

E - 

C BT4 

TPY 

q BT3 

!I 4 f TR 

8 TU 

8 Tw 

= TU 3 mo 3 ,-M 

PV3 3 PV2 I) BT1 a 

BT1 

CHV 

wz 

BT 

PP4 

PP3 

PP2 

PP1 

ff3 

ff2 

- - 

0.235 0.025 

0.128 0.038 

0.066 0.026 

0.140 0.w 

0.300 0.068 

0.389 0.120 

0.234 0.082 

0.353 0.079 

0.- 0.m 

0.464 0.093 

0.042 0.m 

0.146 0.034 

0.136 0.032 

0.089 0.021 

0.115 0.032 

0.092 0.m 

0.071 0.019 

0.020 0.018 

0.123 0.079 

0.193 0.077 

0.265 0.065 

0.321 0.037 

0.240 0.049 

0.169 0.050 

0.238 0.056 

0.274 0.053 

0.217 0.060 

0.197 0.055 

0.102 0.m 

0.213 0.083 

0 

17 

31 

405 

61 

58 

24 

37 

60 

132 

118 

50 

435 

455 

266 

453 

225 

102 

89 

39 

36 

43 

69 

293 

69 

47 

1 66 

140 

245 

86 

65 

2.39 0.07 0.062 0.020 

1.91 0.13 0.253 0.080 

2.10 0.14 0.164 0.082 

2.30 0.08 0.082 0.m 

1.97 0.14 0.203 0.054 

1.46 0.17 0.387 0.070 

1.31 0.29 0.- 0.123 

1.79 0.23 0.254 0.062 

1.39 0.18 0.411 0.079 

1.13 0.09 0.499 0.041 

1.20 0.28 0.489 0.106 

2.38 0.10 0.054 0.m 

2.15 0.08 0.157 0.03 

2.13 0.08 0.154 0.031 

2.25 0.05 0.110 0.020 

2.21 0.17 0.'130 0.031 

2.27 0.08 0.112 0.031 

2.30 0.06 0.094 0.019 

2.27 0.26 0.m 0.- 

1.96 0.25 0.173 0.108 

1.66 0.16 0.288 0.072 

1.66 0.14 0.273 0.067 

1.47 0.06 0.345 0.034 

1.57 0.10 0.331 0.- 

1.79 0.13 0.266 0.041 

1.62 0.09 0.325 0.045 

1.79 0.12 0.303 0.w 

1.85 0.21 0.263 0.072 

1.74 0.15 0.280 0.053 

2.28 0.09 0.115 0.040 

1.79 0.21 0.259 0.084 

2.55 0.04 

2.56 0.09 

2.52 0.03 

2.51 0.05 

2.47 0.06 

2.38 0.10 

2.34 0.14 

2.40 0.11 

2.37 0.10 

2.28 0.09 

2.37 0.23 

2.51 0.04 

2.55 0.03 

2.51 0.02 

2.53 0.03 

2.54 0.17 

2.56 0.03 

2.54 0.03 

2.36 0.25 

2.37 0.03 

2.34 0.05 

2.28 0.07 

2.24 0.10 

2.36 0.05 

2.44 0.08 

2.41 0.04 

2.58 0.05 

2.51 0.08 

2.42 0.07 

2.57 0.03 

2.41 0.05 

9 0.048 0.015 0.75 

101 0.098 0.048 0.40 

98 0.094 0.021 0.61 

589 0.w 0.026 0.80 

90 0.185 0.062 0.90 

101 0.258 0.081 0.69 

33 0.220 0.097 0.51 

43 0.163 0.046 0.68 

85 0.216 0.065 0.54 

164 0.178 0.w 0.36 

171 0.185 0.089 0.39 

66 0.034 0.024 0.62 

439 0.078 0.019 0.51 

455 0.108 0.022 0.72 

266 0.093 0.019 0.85 

453 0.101 0.024 0.78 

225 0.095 0.026 0.85 

102 0.081 0.016 0.87 

89 0.034 0.- 0.88 

39 0.148 0.107 0.84 

36 0.267 0.076 0.93 

43 0.083 0.020 0.32 

69 0.168 0.078 0.50 

293 0.320 0.041 0.97 

69 0.265 0.040 1.00 

47 0.308 0.051 0.94 

166 0.165 0.092 0.55 

140 0.248 0.081 0.93 

245 0.269 0.051 0.98 

86 0.112 0.- 0.98 

65 0.281 0.089 1.00 

0.13 9 

0.17 101 

0.15 98 

0.14 589 

0.13 90 

0.24 101 

0.19, 33 

0.20 43 

0.16 85 

0.13 156 

0.15 171 

0.17 66 

0.13 439 

0.15 455 

0.12 266 

0.14 453 

0.10 225 

0.09 102 

0.14 87 

0.16 39 

0.16 36 

0.10 43 

0.24 69 

0.07 293 

0.03 69 

0.08 47 

0.29 166 

0.10 140 

0.08 245 

0.07 86 

0.08 65 

- - 0 - - - - 0 1.E-12 2.lE-12 9 

- - 0 3.8Ea 2.2Ea 3.3Ea 5.9Ea 3 3.E- 1.4E47 101 

- - 0 1.2Ea - 1.2Ea - 1 5.7E-10 1.2E47 98 

8.8 8.9 183 5.4E-115.2E-12 4.6E-1ll.OE-10 6 3.8E-124.lE.09589 

0.9 16.0 13 5.OE-10 5.E- 1.6E-10 4.7Ea 4 8.8E-12 l.E-11 90 

0.2 0.5 25 3.1Ea 4.1E-06 7.6E-10 4.8E47 8 2.6E47 2.2E-06 101 

0.1 0.0 5 1.6E472.4Ea 2.6E.096.5Ea 3 4.1E471.8EG 33 

0.1 0.0 9 3.3Ea2.OE47 1.2Ea2.5E47 2 1.7Ea7.4E47 43 

0.1 0.1 34 5.4E471.2E-06 1.7E472.3E-06 17 7.8E471.1E-06 85 

0.1 0.1 64, 8.8E47 4.2E47 7.3E47 6.7E47 10 3.6E-06 1.2E-06 164 

0.3 0.7 41 3.2E-06 5.6E-06 8.8E47 9.6E-06 19 l.7Ea 2.E-06 171 

9.4 186.7 

1.2 4.5 

1.4 4.7 

8.6 10.1 

1.3 3.6 

3.0 9.2 

12.8 12.8 

4.9 66.2 

3.3 15.9 

0.3 1.6 

0.1 0.4 

0.2 0.2 

0.5 1.8 

0.2 2.3 

0.3 10.9 

0.6 0.8 

0.4 1.7 

0.6 5.5 

0.6 4.5 

0.1 3.4 

21 7.6E-10 7.5E.09 1.E-10 1.3Ea 

159 1.7E.09 1.6E47 8.6E-10 1.4E-06 

246 2.OE-10 3.Ea 9.7E-11 2.5E47 

176 4.M-11 4.3E-11 2.2E-11 4.4E-10 

253 2.3E-10 2.2E.09 8.7E-11 9.3E.09 

157 9.6E-10 8.8E47 1.9E-10 2.4E-06 

70 7.5E-11 4.E-12 6.5E-11 8.2E-11 

70 5.OE-11 2.7E-10 2.6E-11 8.5E-10 

30 7.3E-10 3.5Ea 1.E-10 2.4Ea 

29 5.4E.091.6Ea 1.4E.094.3Ea 

43 1.6EG - 1.6EG - 

62 5.5E47 2.9E-06 1 .OE47 3.2E-06 

206 4.5E-11 6.5E-10 3.2E-11 9.9Ea 

58 8.4E-11 8.5E-12 7.4E-11 l.OE47 

43 7.5E-11 3.4E-11 5.9E-11 l.OE47 

141 1.9Ea 2.9Ea 3.2E.09 7.0Ea 

124 2.8E-10 1.2E.09 1.4E-109.9Ea 

226 9.4E-11 1.6E-10 5.5E-11 1.OE47 

86 8.7E-11 - 8.7E-11 - 

61 8.8E-10 5.4E-10 5.3E-10 9.8Ea 

3 6.2E-13 7.1E-10 66 

45 3.9E-10 1.OE.09 439 

33 2.3E-10 5.2E-10 455 

11 1.5E-11 2.3E-11 266 

43 7.M-11 4.E-10 453 

15 1.8E-11 2.1E.09 225 

2 4.8E-12 5.8E-12 102 

7 1.5E-13 2.lE-12 89 

4 7.4E-11 2.OE47 39 

4 6.OE-11 8.E-10 36 

1 6.1Ea 3.2E47 43 

6 2.1 E47 5.E47 69 

69 l.lE-10 1.3E-10 293 

3 1.4E-11 2.1E-11 69 

5 9.6E-11 1.4E-10 47 

29 2.E-10 4.OE-10 166 

25 5.6E-11 1.lE-10 140 

21 3.1E-11 5.6E-11 245 

1 2.lE-12 2.4E-12 86 

2 5.OE-11 7.OE-10 65 
Table 8. Moisture-retention van Genuchten curve-fit parameters, alpha and n, for each hy drogeologic unl. 

[SE, standard error; vlv, dimensionless volume; undef., undefined values of less than or equal to zero on a log scale; N, number of data sets; m, 1-(1111); paramete 

unl CCR are from unit TC; parameters for units BT1 and CHV are from unit BT2] 

__ ________________-________________________________________-- ------------------------------------------------------------------------------------------------------------------------------------------------------------- ----. 

Laboratory Desorption Curves van Genuchten parameters Composite Curves van Genuchten parameters 

___ --------------------- -- ____--___-_-__-------------- -------------------- ---------- -- 

Hydro- 95-percent 95-percent 95-percent 95-percent Residual 

geologic alpha SE confidence limits n SE confidencelimits m alpha SE confidencelimits n SE confidence limits m Saturation 

Unit N (llbars) upper lower upper lower (1 I bars) upper lower upper lower (V lv ) 

------ ___--____---- -----------------------------------------------------------------------------------------------------------------

CCR 

CUC 

CUL 

CW 

chw 

CNW 

BT4 

TPY 

BT3 

TPP 

BT2 

TC 

TR 

TUL 

Tw 

TLL 

lM2 

7-M 

PV3 

PV2 

BTla 

BTI 

CHV 

CHZ 

BT 

PP4 

PP3 

PP2 

PP1 

BF3 

BF2 

3 

3 

7 

2 

4 

5 

2 

3 

1 

2 

2 

3 

4 

3 

3 

1 

1 

3 

1 

3 

4 

1 

1 

3 

3 

2 

1 

1 

0.335 

0.827 

1.404 

0.115 

0.023 

7.522 

3.652 

0.756 

2.590 

3.412 

9.800 

0.335 

2.037 

0.657 

0.064 

0.273 

0.047 

0.022 

0.010 

1.255 

0.01 9 

9.800 

9.800 

0.394 

0.015 

0.01 0 

1.817 

0.072 

0.179 

0.036 

0.01 2 

0.140 

0.227 

0.462 

0.029 

0.008 

6.465 

1.930 

0.296 

1.500 

2.145 

8.695 

0.140 

0.754 

0.150 

0.01 3 

0.105 

0.005 

0.002 

0.003 

0.652 

0.008 

8.695 

8.695 

0.125 

0.001 

0.001 

0.599 

0.01 2 

0.060 

0.010 

0.001 

1.290 0.364 

2.344 0.463 

0.173 0.056 

0.039 0.007 

20.61 0 undef . 

7.516 undef. 

1.380 0.131 

5.659 undef. 

8.265 undef. 

27.939 undef. 

0.632 0.039 

3.576 0.499 

0.958 0.355 

0.091 0.038 

0.485 0.060 

0.060 0.034 

0.026 0.017 

0.016 0.004 

2.797 undef. 

0.035 0.003 

27.939 undef. 

27.939 undef. 

0.647 0.142 

0.018 0.012 

0.009 0.007 

3.032 0.601 

0.097 0.046 

0.305 0.054 

0.063 0.009 

0.014 0.010 

1.254 

1.840 

1.529 

1.300 

1.776 

1.203 

1.285 

1.953 

1.310 

1.427 

1.294 

1.254 

1.335 

1.331 

1.470 

1.294 

1.713 

2.141 

1.582 

1.310 

1.561 

1.294 

1.294 

1.290 

1.909 

3.035 

1.455 

1.603 

1.454 

1.680 

2.477 

0.037 

0.221 

0.110 

0.041 

0.309 

0.047 

0.052 

0.377 

0.067 

0.129 

0.072 

0.037 

0.051 

0.032 

0.076 

0.051 

0.078 

0.267 

0.127 

0.075 

0.180 

0.072 

0.072 

0.037 

0.1 11 

0.404 

0.071 

0.081 

0.078 

0.202 

0.275 

2.291 

1.752 

1.383 

2.41 7 

1.299 

1.389 

2.747 

1.443 

1.719 

1.445 

1.332 

1.439 

1.396 

1.624 

1.398 

1.897 

2.727 

1 ,845 

1.488 

1.931 

1.445 

1.445 

1.365 

2.151 

3.967 

1.599 

1.768 

1.616 

2.240 

3.353 

1.388 

1.306 

1.219 

1.135 

1.107 

1.181 

1.158 

1.168 

1.136 

1.144 

1.175 

1.231 

1.267 

1.316 

1.189 

1.530 

1.554 

1.319 

1.133 

1.191 

1.144 

1.144 

1.215 

1.667 

2.104 

1.31 1 

1.439 

1.292 

1.119 

1.602 

0.203 

0.457 

0.346 

0.231 0.124 0.024 

0.437 0.028 0.011 

0.169 2.420 1.647 

0.222 17.889, 11.110 

0.488 2.638 1.812 

0.237 41.540 19.147 

0.299 40.016 15.204 

0.227 52.638 41.468 

0.203 0.885 0.418 

0.251 3.776 2.399 

0.249 

0.320 

0.227 

0.41 6 

0.533 

0.368 

0.237 

0.359 

0.227 

0.227 

0.225 

0.476 

0.671 

0.31 3 

0.376 

0.31 2 

0.405 

0.596 

0.176 0.072 

0.054 0.002 

6.197 undef . 

43.509 undef. 

7.296 undef. 

85.691 undef . 

77.217 2,915 

148.261 undef . 

1.907 undef. 

9.151 undef. 

1.690 

1.890 

1.380 

1.233 

1.507 

1.234 

1.494 

1.278 

1.249 

1.317 

0.171 

0.337 

0.124 

0.049 

0.171 

0.044 

0.140 

0.076 

0.043 

0.106 

2.068 

2.692 

1.666 

1.346 

1.947 

1.336 

1.837 

1.454 

1.354 

1.553 

1.321 

1.098 

1.095 

1.120 

1.067 

1.133 

1.151 

1.103 

1.145 

1.081 

0.408 

0.471 

0.275 

0.189 

0.336 

0.190 

0.331 

0.21 8 

0.199 

0.241 

0.20 

0.04 

0.06 

0.1 3 

0.33 

0.10 

0.10 

0.14 

0.17 

0.10 

0.1 0 

0.1 1 

0.04 

0.06 

0.18 

0.08 

0.18 

0.32 

0.50 

0.12 

0.36 

0.04 

0.06 

0.20 

0.33 

0.25 

0.07 

0.10 

0.18 

0.09 

0.19 
ity was estimated using the regression equation for the 

matrix only and is 3 orders of magnitude lower for TC 

and 2 orders of magnitude lower for PV3. There are 

also mismatches in the units below the Topopah Spring 

Tuff, which have variable degrees of alteration and 

crystallization and were all estimated using the equation for the altered rocks. 

Moisture-retention curve-fit parameters have 

been calculated for all the hydrogeologic units with 

corresponding standard error and 95-percent confidence limits as are the parameters for composite curves 

(table 8). Units CUC and CUL, although penetrated by 

boreholes, did not have samples that were measured for 

field water potential, so no composite curves were 

obtained for those units and parameters are fromJaboratory measurements only. The number of data sets, N, 

on which laboratory measurements for moisture retention were made is noted for each unit. Several of the 

units, CCR, TPP, BT2, TC, and CHV, posed measurement challenges as samples disintegrated due to fiequent sample handling and, therefore, are represented 

by only a few samples. It is not believed that the 

parameters for units TPP, BT2, or TC were unrepresentative or were compromised due to the low number of 

samples. Parameters for CCR are represented by 

hydrogeologic unit TC, and this approximation is supported by the general similarities in lithostratigraphic 

features and context of the units @.C. Buesch and 

R.W. Spengler, U.S. Geological Survey, written commun., 1996). Data obtained for CHV could only be 

obtained on coherent samples and was very biased 

toward unrepresentative lower porosity inclusions. 

Parameters from these samples, therefore, did not represent the saturations measured in boreholes SD7 and 

SD 12. The saturation profiles were better represented 

by the parameters calculated for unit BT2 that had the 

highest a of all units. Both the CHV and BT2 are vitric, are high in porosity and conductivity, and have 

slight and variable alteration. No moisture-retention 

data were available for the unaltered BTl , and this unit 

is also represented by the BT2 parameters. Residual 

saturation values used in the curve-fitting process are 

included in table 8. 

Spatial Distribution of Porosity 

Representation of hydrologic properties of a spatially heterogeneous site, based on core-scale-sized 

samples from one-dimensional boreholes sparsely distributed over the study area has uncertainty. Vertical 

variability of matrix properties within hydrogeologic 

units can be reasonably described for most of the units. 

Problematic units are very thin or layered units or are 

those with features that are larger than core-size samples that might dominate the flow of water in numerical 

models. The lateral distribution of core-scale properties might adequately be represented for large-scale 

models by the correlation of properties with surrogates, 

such as porosity, that can be modeled using lithostratigraphic distributions and that has been shown to be 

related to flow properties in this report and others (Istok 

and others, 1994; Rautman and others, 1995; Flint and 

others, 1996b; Rautman, 1995). The correlation of 

porosity with lithology provides a much larger data 

base with which to calculate spatial distributions. 

Few of the hydrogeologic units described in this 

report were penetrated by enough boreholes that spatial 

trends in porosity, if present, could be visualized. A 

data set was compiled for all boreholes sampled that 

includes means and standard deviations for porosity 

and saturation for all hydrogeologic units (table 9). 

Table 9 helps illustrate two important limitations of 

these data for representing the spatial variability of 

properties such as porosity. Of the 30 hydrogeologic 

units, there are 17 units that occur in 6 or fewer boreholes. These units are typically above CW and below 

TLL. Of the 203 entries in table 9, where each entry 

represents at least 1 sample of a unit in a borehole, 

57 units have 5 or fewer samples per unit, and a total of 

107 units have 10 or fewer samples per unit. With 

about 53 percent of all available means calculated on 

10 or fewer samples per unit, the statistical significance 

of these data must be kept in perspective. Many of the 

units were extremely variable; for example, the thin, 

infrequently sampled hydrogeologic unit, BT4, ranges 

from a mean porosity of 26 percent in N3 1 to 62 percent in SD9. The thicker and more frequently sampled 

unit, TPP, on the other hand, only ranges from 47 percent to 52 percent porosity. Porosity ranges from 7 percent to 12 percent for unit CW, with a general trend of 

increasing porosity to the northwest (fig. 16). This 

trend is consistent with descriptions of lithostratigraphic units exposed at the surface (Scott and Bonk, 

1984; W. C. Day, U.S. Geological Survey, written commun., 1996) and in core from boreholes (Buesch and 

others, 1996b). More spatially variable is hydrogeologic unit BT2 (fig. 16), with a range of 44 percent to 

53 percent porosity, except for one low value of 35 percent in the south in SD7. Rocks in the PTn are likely 

46 Characterlzatlon of Hydrogeologlc Unlts Uslng Matrlx Properties, Yucca Mountaln, Nevada 
A B 

m 

a: 

W 

IW 

I 

z 

(5 

z - 

I 

Ia: 

0 

z 

237000 

236000 

235000 

234000 

233000 

232000 

235000 

234000 

0 

- 

233000 

232000 

23 1 000 

170500 171 500 172500 170750 171 750 

EASTING, IN METERS EASTING, IN METERS 

Figure 16. Contour plots of the spatial distribution of porosity for hydrogeologic units (a) CW, using 17 boreholes, and (b) 

BT2, using 15 boreholes. 

Characterlzatlon of Hydrogeologlc Units 47 
Table 9. Mean porosity and saturation, and standard deviations for each hydrogeologic unit in for each 

borehole 

[Por, porosity, SD, standard deviation; Sat, saturation; N. number of samples] 

Unit NRGd NRG-7 SD12 SD7 SD9 UZ 14 UZ 16 UZ 27r N-11 N-15 N-16 N-17 N-27 N-31 N-32 

CCR Meanpor 0.05 0.08 

SD Por 

Mean Sat 

SD Sat 

N 

0.00 

0.87 

0.00 

I 

0.01 

0.64 

0.02 

2 

CUC Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

0.24 

0.06 

0.5 1 

0.12 

22 

0.25 0.26 

0.05 0.06 

0.52 0.24 

0.1 1 0.08 

26 24 

CUL Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

0.13 0.14 

0.04 0.02 

0.59 0.62 

0.11 0.11 

9 43 

CW Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

0.09 0.09 0.09 0.09 0.07 0.07 0.12 

0.03 0.02 0.03 0.02 0.02 0.02 0.00 

0.75 0.85 0.79 0.77 0.96 

0.15 0.10 0.17 0.12 0.04 

38 16 64 80 34 40 2 

0.10 0.08 

0.01 0.02 

0.66 0.87 

0.12 0.03 

7 24 

0.07 

0.02 

0.82 

0.07 

32 

0.18 

0.02 

0.90 

0.10 

6 

0.36 

0.05 

0.88 

0.07 

5 

0.55 

0.12 

0.71 

0.05 

2 

CM W Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

0.18 0.18 0.17 0.20 0.30 0.27 0.21 

0.03 0.02 0.01 0.03 0.08 0.10 0.03 

0.88 0.97 0.96 0.91 0.71 

0.07 0.03 0.05 0.10 0.26 

10634 6 4 2 

0.20 

0.03 

0.96 

0.03 

8 

CNW Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

0.39 0.36 0.34 0.43 0.36 0.42 0.37 0.47 

0.03 0.03 0.03 0.00 0.04 0.00 0.07 0.09 

0.78 0.39 0.68 0.59 0.78 0.44 

0.18 0.02 0.17 0.09 0.18 0.24 

49526 2 8 10 

0.38 

0.06 

0.99 

0.01 

6 

BT4 Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

0.38 0.41 0.61 0.56 0.62 0.52 0.35 0.51 

0.00 0.08 0.00 0.00 0.00 0.00 0.01 0.07 

0.64 0.53 0.60 0.62 0.57 0.34 

0.00 0.00 0.00 0.00 0.02 0.07 

1 5 1 1 1 12 6 

0.26 

0.1 1 

0.77 

0.12 

4 

TPY Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

BT3 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

0.29 0.18 0.23 

0.0 1 0.02 0.03 

0.94 0.54 

0.08 0.18 

3 7 6 

0.40 0.36 0.42 0.34 0.36 0.41 0.44 0.39 

0.02 0.08 0.06 0.02 0.06 0.07 0.08 0.03 

0.55 0.57 0.53 0.77 0.41 0.68 

0.07 0.07 0.13 0.20 0.09 0.03 

5 10 3 3 16 11 7 3 

0.42 0.51 

0.12 0.06 

0.55 0.59 

0.08 0.09 

4 5 

TPP Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

0.51 0.49 0.47 0.47 0.49 0.48 

0.03 0.03 0.02 0.03 0.04 0.00 

0.50 0.33 0.50 0.54 

0.05 0.04 0.06 0.00 

22 27 4 13 46 1 

0.50 0.50 

0.04 0.03 

0.49 0.44 

0.09 0.08 

9 10 

BT2 Meanpor 

SD POI 

Mean Sat 

SD Sat 

N 

0.50 0.50 0.50 0.35 0.49 0.53 0.53 0.49 

0.10 0.04 0.09 0.09 0.07 0.05 0.10 0.05 

0.47 0.52 0.35 0.33 0.29 0.41 

0.14 0.14 0.12 0.05 0.08 0.13 

22 9 9 411 813 8 

0.50 0.53 

0.08 0.07 

0.51 0.51 

0.11 0.12 

16 16 

48 Characterlzatlon of Hydrogeologic Unlts Uslng Matrlx Properties, Yucca Mountaln, Nevada 
Table 9. Mean porosity and saturation, and standard deviations for each hydrogeologic unit in for each 

borehole 

[Por, porosity. SD, standard deviation; Sat, saturation; N, number of samples] 

Unlt K33 N-34 N-35 N-36 N-37 N-38 N-53 N-54 N-55 N-57 K58 N-59 N-61 N-SZ N-63 N44 

SD PO; 

Mean Sat 

SD Sat 

N 

CUC MeanPor 

SD Por 

Mean Sat 

SD Sat 

N 

CUL MeanPor 

SD Por 

Mean Sat 

SD Sat 

N 

CW Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

CMW Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

CNW Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

BT4 Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

TPY Mean Por 

SD Por 

Mean Sat 

SD Sat 

N 

BT3 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TPP Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

BT2 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

0.19 

0.06 

0.97 

0.01 

6 

0.4 1 

0.07 

0.75 

0.14 

8 

0.42 0.39 

0.08 0.07 

0.61 0.70 

0.16 0.06 

7 3 

0.22 0.23 

0.07 0.05 

0.65 0.76 

0.16 0.16 

6 11 

0.02 

0.76 

0.14 

6 

0.18 

0.00 

0.47 

0.00 

1 

0.29 

0.05 

0.45 

0.08 

15 

0.08 0.09 0.09 0.08 0.07 0.08 

0.03 0.04 0.02 0.06 0.02 0.02 

0.81 0.85 0.88 0.85 0.82 0.80 

0.12 0.11 0.05 0.06 0.09 0.13 

38 21 17 54 43 67 

0.20 0.20 0.26 0.19 0.20 

0.03 0.04 0.05 0.02 0.04 

0.84 1.02 0.92 0.82 0.94 

0.13 0.13 0.13 0.05 0.05 

8 11 5 3 11 

0.45 0.41 0.37 0.34 

0.04 0.03 0.05 0.04 

0.65 0.69 0.71 0.67 

0.25 0.19 0.24 0.18 

8 7 11 6 

0.46 

0.08 

0.42 

0.00 

2 

0.52 

0.04 

0.27 

0.07 

32 

0.48 

0.09 

0.38 

0.12 

12 

0.39 0.46 

0.10 0.04 

0.54 0.50 

0.13 0.06 

9 9 

0.44 0.50 

0.14 0.09 

0.38 0.44 

0.15 0.15 

16 15 

0.42 

0.05 

0.4 1 

0.09 

7 

0.46 

0.07 

0.46 

0.08 

9 

0.49 

0.01 

0.34 

0.02 

2 

0.24 0.24 

0.01 0.03 

0.32 0.26 

0.04 0.15 

5 12 

0.13 0.16 

0.03 0.02 

0.73 0.62 

0.16 0.16 

20 11 

0.08 

0.03 

0.82 

0.13 

22 

Characterizatlon of Hydrogeologlc Units 49 
Table 9. Mean porosity and saturation, and standard deviations for each hydrogeologic unit in for each 

borehole--Continued 

[Por. porosity, SD, standard deviation; Sat, saturation; N, number of samples] 

~nlt NRGd NRG-7 SD12 SD7 SD9 UZ 14 UZ 16 UZ 278 N-11 N-15 N-16 N-17 N-27 N-31 N-32 

TC Mean por 0.04 0.06 0.03 0.05 0.03 0.04 0.07 

SD Por 0.02 0.02 0.00 0.02 0.01 0.01 0.02 

Mean Sat 0.74 0.74 0.65 0.80 0.60 

SD Sat 0.00 0.08 0.16 0.19 0.18 

N 841 7932 

TR Meanpor 0.15 0.15 0.16 0.17 0.14 0.16 0.16 0.16 

SDPor 0.04 0.03 0.02 0.03 0.03 0.04 0.02 0.02 

Mean Sat 0.49 0.49 0.65 0.53 0.45 0.60 

SD Sat 0.09 0.06 0.13 0.16 0.10 0.14 

N 62 49 31 30 34 37 29 31 

TUL Meanpor 0.17 0.16 0.15 0.13 0.16 Q.15 0.14 0.14 

SD Por 0.03 0.03 0.03 0.03 0.03 .0.03 0.03 0.04 

Mean Sat 0.75 0.79 0.80 0.85 0.70 0.86 

SD Sat 0.13 0.11 0.09 0.08 0.09 0.08 

N 75 74 49 57 61 66 40 13 

TMN Meanpor 0.10 0.12 0.10 0.11 0.12 0.12 0.10 0.10 

SD Por 0.01 0.02 0.01 0.02 0.02 0.03 0.02 0.02 

Mean Sat 0.86 0.94 0.92 0.88 0.90 0.82 

SD Sat 0.05 0.03 0.05 0.08 0.05 0.09 

N 26 27 37 39 -27 35 37 38 

TLL Meanpor 0.14 0.13 0.12 0.13 0.13 0.14 0.14 0.12 

SD Por 0.03 0.02 0.03 0.03 0.02 0.03 0.04 0.02 

Mean Sat 0.87 0.89 0.85 0.82 0.78 0.78 

SD Sat 0.05 0.05 0.07 0.09 0.12 0.08 

N 73 63 40 59 72 44 61 39 

TM2 Meanpor 0.11 0.10 0.10 0.11 0.12 0.11 

SD Por 0.03 0.02 0.04 0.02 0.03 0.04 

Mean Sat 0.82 0.91 0.88 0.89 0.88 

SD Sat 0.10 0.04 0.05 0.07 0.07 

N 27 40 41 31 45 41 

TMI Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

PV3 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

PV2 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

0.10 0.08 0.08 0.10 0.10 

0.02 0.01 0.01 0.02 0.02 

0.89 0.91 0.92 0.91 

0.05 0.03 0.08 0.07 

15 20 18 13 19 

0.02 0.07 0.03 0.02 0.04 

0.02 0.1 1 0.01 0.01 0.02 

0.89 0.89 0.85 0.96 

0.06 0.07 0.07 0.12 

8 7 26 18 18 

0.07 0.15 0.09 0.18 0.26 

0.02 0.07 0.03 0.00 0.12 

0.66 0.78 0.70 0.97 

0.17 0.09 0.00 0.02 

4 10 7 1 12 

BTI Mean por 0.26 0.33 0.22 0.29 0.31 

SD Por 0.04 0.03 0.05 0.09 0.04 

Mean Sat 0.27 0.36 0.84 1.07 

SD Sat 0.06 0.10 0.16 0.08 

N 7 21 22 18 11 

0.10 

0.02 

0.85 

0.06 

17 

0.06 

0.03 

0.92 

0.06 

I I 

0.2 1 

0.06 

0.93 

0.03 

5 

0.04 0.05 

0.01 0.02 

0.78 0.64 

0.22 0.23 

2 4 

50 Charaderlzatlon of Hydrogeologlc Unlts Using Matrlx Properties, Yucca Mountain, Nevada 
Table 9. Mean porosity and saturation, and standard deviations for each hydrogeologic unit in for each 

borehole--Continued 

[POT, porosity, SD, standard deviation; Sat, saturation; N, number of samples] 

unit N-33 N-34 N-35 N-36 N-37 N-38 N-53 N-54 N-55 N-57 N58 N59 N6l N62 N63 N44 

TC Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TR Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TUL Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TMN Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TLL Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TM2 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

TMI Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

PV3 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

PV2 Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

BTI Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

0.03 

0.01 

0.62 

0.10 

7 

0.05 0.05 

0.01 0.00 

0.66 0.67 

0.07 0.00 

2 1 

0.14 

0.01 

0.42 

0.15 

4 

0.06 0.06 0.06 

0.02 0.00 0.03 

0.70 0.47 0.64 

0.17 0.07 0.1 2 

7 2 7 

0.17 0.16 0.16 0.17 

0.03 0.02 0.03 0.02 

0.53 0.51 0.50 0.48 

0.08 0.09 0.12 0.10 

41 30 36 30 

0.16 0.17 0.18 0.18 

0.01 0.02 0.01 0.02 

0.60 0.48 0.60 0.58 

0.04 0.13 0.03 0.10 

3935 

Characterlzatlon of Hydrogeologlc Unlts 51 
Table 9. Mean porosity and saturation, and standard deviations for each hydrogeologic unit in for each 

borehole--Continued 

[Por, porosity, SD, standard deviation; Sat, saturation; N, number of samples] 

unit NRG-6 NRG-7 SD-12 SD-7 SD-B UZ 14 UZ 16 UZ 270 N-11 N-15 N-16 N-17 N-27 N-31 N-32 

CHV Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

CHZ Meanpor 

SD Por 

Mean Sat 

SD Sat 

N 

BT Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

PP4 Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

PP3 Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

PP2 Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

PPI Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

BF3 Mevlpor 

SD Por 

Mean Sat 

SD Sat 

N 

BF2 Meanpor 

SD Por 

Mean Sat 

SD Sat N 

0.35 0.34 

0.04 0.03 

0.45 0.45 

0.23 0.19 

30 31 

0.31 0.37 0.35 0.34 0.32 0.32 

0.02 0.03 0.03 0.03 0.04 0.04 

0.92 0.92 0.96 1.00 0.97 

0.12 0.1 1 0.04 0.08 0.03 

4 34 21 91 68 83 

0.26 0.29 0.26 -9.27 0.25 

0.04 0.05 0.03 0.03 0.03 

1.03 0.99 1.00 0.98 0.98 

0.05 0.03 0.01 0.01 0.03 

12 19 17 11 10 

0.28 0.33 0.31 0.34 0.33 

0.01 0.06 0.03 0.02 0.07 

0.97 0.90 0.97 0.95 0.91 

0.02 0.16 . 0.01 0.02 0.05 

2 10 15 16 4 

0.32 0.33 0.33 0.35 0.30 

0.03 0.02 0.03 0.02 0.04 

0.44 0.3 1 0.95 0.78 0.42 

0.27 0.16 0.04 0.18 0.08 

34 30 22 11 21 

0.24 0.20 0.27 0.3 1 0.21 

0.05 0.06 0.02 0.02 0.04 

0.65 0.63 0.99 0.96 0.86 

0.24 0.22 0.02 0.02 0.14 

33 31 25 12 20 

0.30 0.28 0.30 0.20 

0.04 0.06 0.02 0.07 

1.02 0.90 0.99 0.96 

0.05 0.10 0.01 0.03 

98 126 69 19 

0.12 

0.04 

0.98 

0.07 

86 

0.27 

0.07 

1.02 

0.04 

61 

52 Characterlutlon of Hydrogeologic Units Using Matrlx Properties, Yucca Mountaln, Nevada 
Table 9. Mean porosity and saturation, and standard deviations for each hydrogeologic unit in for each 

borehole-Continued 

[Por, porosity, SD, standard deviation; Sat, saturation; N, number of samples] 

Unlt N-33 N-34 N-35 N-36 N-37 N-38 N-53 N-54 N-55 N-57 N-58 N-59 N-61 N-62 N-63 N44 

CHV 

CHZ 

BT 

PP4 

PP3 

PP2 

PPI 

BF3 

BF2 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Pa 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Mean por 

SD Por 

Mean Sat 

SD Sat 

N 

Characterization of Hydrogeologic Units 53 
to show different trends based on depositional mechanisms (pyroclastic flow or fallout deposits, for example), but a study near the base of the Tiva Canyon Tuff, 

which examined the Tpcplnc (moderately welded), 

Tpcpv2, Tpcpv 1, and Tpbt4 units along an exposure 

over 1 krn long, showed little evidence of lateral trends 

in properties at any stratigraphic position within these 

four units (Istok and others, 1994; Rautman and others, 

1995), at least on the scale of the study, from Yucca 

Wash to Busted Butte. The Yucca Mountain and Pah 

Canyon Tuffs do not vary significantly across the 

potential repository location, but become increasingly 

welded to the north where the samples are very limited. 

The zeolitized rocks of the Calico Hills Formation also 

do not vary substantially in hydrologic properties over 

lateral distances up to 3 km (Rautman, 1991). Saturation is far more spatially variable and is included for 

information only and in table 8 as initial conditions. 

SUMMARY 

water. The close spatial sampling through many units 

helped define two types of boundaries between units: 

transition zones where properties change dramatically 

but smoothly over short vertical distances, such as at 

the top of the PTn, and abrupt changes in properties, 

such as at the bottom of the PTn. These two types of 

boundaries are of particular interest because of the possibility of capillary or permeability barriers. Zones of 

variably developed vapor-phase corrosion are characterized individually on the basis of changes in porosity. 

To develop functions that could be used to further discretize models in zones where properties change across 

short distances, the relation of porosity to saturated 

hydraulic conductivity and a was analyzed. As a 

result, hydrologic properties specific to the volcanic 

rocks at Yucca Mountain were characterized to provide 

modeling parameters representing all significant 

hydrogeologic units in the unsaturated zone. 

Measured values of rock core porosity, saturated 

hydraulic conductivity, moisture-retention characteristics, and saturation, along with lithostratigraphic 

descriptions, were used to divide the unsaturated zone 

at Yucca Mountain into 30 discrete hydrogeologic units 

that can be related to the existing three-dimensional 

lithostratigraphic models. These units, with some 

exceptions in the Prow Pass and Bullfrog Tuffs, are 

intended to be hydrologically similar and distinct 

enough to be used successfully to design large- and 

small-scale numerical models to describe water flow at 

Yucca Mountain. Mean values and standard deviations 

of bulk density, porosity, particle density, saturation, 

water potential, and saturated hydraulic conductivity 

are provided for each hydrogeologic unit, as well as 

representative values of van Genuchten moistureretention curve-fit parameters, a and n, and residual 

saturation. 

Porosity was the most useful property in characterizing individual hydrogeologic units because it was 

measured on the most samples, and it is well correlated 

to saturated hydraulic conductivity and the moistureretention curve-fit parameter, a. Several additional 

features played an important part in the hydrogeologicunit development. Zones of mineral alteration, especially at the base of the Tiva Canyon Tuff and the zeolitized rocks below the Topopah Spring Tuff, have a 

substantial influence on the storage and transmission of 

American Society of Testing Materials, 1977, Adsorption 

and bulk specific gravity of natural building stone: 

American Society of Testing Materials, ANSVASTM 

R97-47, Annual Book of ASTM Standards, Part 19, 

472 p. 

Anderson, L.A., 198 1 a, Rock property analysis of core samples from the Calico Hills UE25a-3 borehole, Nevada 

Test Site, Nevada: U.S. Geological Survey Open-File 

Report 81-1337,30 p. 

Anderson, L.A., 198 1 b, Rock property analysis of core sarnples from the Yucca Mountain UE25a-1 borehole, 

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

Open-File Report 8 1-1338,3 1 p. 

Anderson, L.A., 1984, Rock property measurements on 

large-volume core samples from Yucca Mountain USW 

GU-3lG-3 and USW G4 boreholes, Nevada Test Site, 

Nevada: U.S. Geological Survey Open-File 

Report 84-552,39 p. 

Anderson, L.A., 199 1, Results of rock property measurements made on core samples from Yucca Mountain 

boreholes, Nevada Test Site, NevadePart 1, Boreholes UE25A-4, -5, -6, and 7; part 2, Borehole 

UE25p#1: U.S. Geological Survey Open-File Report 

90474,47 p. 

Bish, D.L., 1989, Evaluation of past and future alterations in 

tuff at Yucca Mountain, Nevada, based on the clay mineralogy of drill cores USW G-1, G-2, and G-3: Los 

Alamos National Laboratory Report LA-10677-MS, 

40 p. 

54 Characterlzatlon of Hydrogeologic Unlts Uslng Matrlx Properties, Yucca Mountaln, Nevada 
Bish, D.L., and Aronson, J.L., 1993, Paleogeothermal and 

paleohydrologic conditions in silicic tuff from Yucca 

Mountain: Clays and Clay Minerals, v. 41, no. 2, 

p. 14-161. 

Bish, D.L., and Chipera, S.J., 1989, Revised mineralogic 

summary of Yucca Mountain, Nevada: Los Alamos 

National Laboratory Report LA-1 1497-MS, 68 p. 

Broxton, D.E., Bish, D.L., and Warren, R.G., 1987, Distribution and chemistry of diagenetic minerals at Yucca 

Mountain, Nye County, Nevada: Clays and Clay 

Minerals,~. 35,no.2,p. 89-110. 

Buesch, D.C., Nelson, J.E., Dickerson, R.P., Drake, R.M., 

Spengler, R.W., Geslin, J.K., Moyer, R.C., and San 

Juan, C.A., 1996% Distribution of lithostratigraphic 

units within the central block of Yucca Mountain, . 

Nevade A three-dimensional computer-based model, 

version YMP.R2.0: U.S. Geological Survey Open-File 

Report 95-124,6 1 p. 

Buesch, D.C., Spengler, R.W., Moyer, T.C., and Geslin, J.K., 

1996b, Proposed stratigraphic nomenclature and macroscopic identification of lithostratigraphic units of the 

Paintbrush Group exposed at Yucca Mountain, Nevada: 

U.S. Geological Survey Open-File Report 94-469, 

47 p. 

Buesch, D.C., Spengler, R.W., Nelson, P.H., Vaniman, D.R., 

Chipera, S.J., and Bish, D.L., 1995, Geometry of the 

vitric-zeolitic transition in tuffs and the relation to fault 

zones at Yucca Mountain Nevada [abs.]: International 

Union of Geodesy and Geophysics, XXI General 

Assembly, Boulder, Colo., Abstracts Week A, p. A426. 

Bush, D.C., and Jenkins, R.E., 1970, Proper hydration of 

clays for rock property determinations: Journal of 

Petroleum Technology, v. 22, no. 7, p. 800404. 

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

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

cauldrons of the Timber Mountain-Oasis Valley 

Caldera Complex, southern Nevada: U.S. Geological 

Survey Professional Paper 9 l9,7O p. 

Carr, W.J., Byers, F.M., Jr., and Orkild, P.P., 1986, Stratigraphic and volcano-tectonic relations of the Crater Flat 

Tuff and some older volcanic units, Nye County, 

Nevada: U.S. Geological Survey Professional Paper 

1323,28 p. 

Chipera, S.J., Vaniman, D.T., Carlos, B.A., and Bish, D.L., 

1994, Mineralogic variation in drill core UE-26 UZ 

#16, Yucca Mountain, Nevada: Los Alamos National 

Laboratory Report LA-1287%MS, 40 p. 

Deer, W.A., Howie, R.A., and Zussman, J., 1966, An Introduction to the rock-forming minerals: New York, 

Wiley, p. 264-269. 

Deutsch, C.V., 1989, Calculating effective absolute permeability in sandstonelshale sequences: SPE Formation 

Evaluation, v. 4, p. 343-348. 

Diehl, S.F., and Chornack, M.P., 1990, Stratigraphic correlation and petrography of the bedded tuffs, Yucca Mountain, Nye County, Nevada: U.S. Geological Survey 

Open-File Report 89-3, 152 p. 

Engstrom, D.A., and Rautman, C.A., 1996, Geology of the 

USW SD-9 drill hole, Yucca Mountain, Nevada: 

Albuquerque, N. Mex., Sandia National Laboratories 

Yucca Mountain Project Report SLTR96-0002, 148 p. 

Flint, A.L., and Flint, L.E., 1994, Spatial distribution of 

potential near surface moisture flux at Yucca Mountain: 

International High-Level Radioactive Waste Conference, Las Vegas, Nev., May 2-26, 1994, Proceedings, 

7 PFlint, A.L., Flint, L.E., and Hevesi, J.A., 1993, Influence of 

long term climate change on net infiltration at Yucca 

Mountain, Nevada: Intemational High-Level Radioactive Waste Conference, Las Vegas, Nev., April 25-30, 

1993, Proceedings, 12 p. 

Flint, L.E., and Flint, A.L., 1990, Preliminary permeability 

and moisture retention of nonwelded and bedded tuffs 

at Yucca Mountain, Nevada: U.S. Geological Survey 

Open-File Report 90-569,57 p. 

Flint, L.E., and Flint, A.L., 1995, Shallow infiltration processes at Yucca Mountain, Nevada-Neutron logging 

data 1984-93: U.S. Geological Survey WaterResources Investigations Report 95-4035,46 p. 

Flint, L.E., Flint, A.L., Moyer, T.C., and Geslin, J.K., 1996a, 

Lateral diversion of water in the Paintbrush Tuff nonwelded hydrologic unit, Yucca Mountain, Nevada: 

EOS, American Geophysical Union Proceedings, Fall 

meetings, 1996. 

Flint, L.E., Flint, A.L., Rautman, C.A., and Istok, J.D., 

1996b, Physical and hydrologic properties of rock outcrop samples at Yucca Mountain, Nevada: U.S. Geological Survey Open-File Report 95-280,70 p. 

Gardner, W.H., 1965, Water content, in Black, C.A., ed., 

Methods of soil analysis, part I,: Madison, Wis., American Society of Agronomy, Inc., p. 82-127. 

Geslin, J.K., and Moyer, T.C., 1995, Summary of lithologic 

logging of new and existing boreholes at Yucca Mountain, Nevada, March 1994 to June 1994: U.S. Geological Survey Open-File Report 94-45 1, 16 p. 

Geslin, J.K., Moyer, T.C., and Buesch, D.C., 1995, Summary 

of lithologic logging of new and existing boreholes at 

Yucca Mountain, Nevada, August 1993 to February 

1994: U.S. Geological Survey Open-File 

Report 94-342,39 p. 

References 55 
Glass, R.J., Flint, A.L., Tidwell, V.C., Peplinski, W., and 

Castro, Y., 1994, Fracture-matrix interaction in 

Topopah Spring tuff-Experiment and numerical simulation: International High-Level Radioactive Waste 

Conference, Las Vegas, Nev., May 22-26, 1994, 

Proceedings, 9 p. 

Grayson, D.K., 1993, The desert's past-A natural prehistory of the Great Basin: Washington D.C., Smithsonian 

Institution Press, 356 p. 

Hammermeister, D.P., Blout, D.O., and McDaniel, J.C., 

1985, Drilling and coring methods that minimize the 

disturbance of cuttings, core and rock formation in the 

unsaturated zone, Yucca Mountain, Nevada: National 

Water Well Association, Proceedings of the National 

Water Well Association Conference on Characterization and Monitoring of the Vadose (UnsaturatedFZone, 

p. 507-54 1. 

Hillel, D., and Baker, R.S., 1988, A descriptive theory offingering during infiltration into layered soils: Soil 

Science, v. 146, p. 51-56. 

Istok, J.D., Rautman, C.A., Flint, L.E., andFlint, A.L., 1994, 

Spatial variability in hydrologic properties of a volcanic 

tuff: Ground Water, v. 32, no. 5, p. 75 1-760. 

Iwata, S., Tabuchi, T., and Warkentin, B.P., 1988, Soil-water 

interactions: New York, MarceI Dekker, Inc., 

p. 155-164. 

Jackson, R.D., 1964, Water vapor diffusion in relatively dry 

soil-111, Steady-state experiments: Soil Science 

Society of America Proceedings, v. 28, p. 467-470. 

Jensen, J.L., 199 1, Use of the geometric average for effective 

permeability estimation: Mathematical Geology, v. 23, 

p. 833440. 

Journel, A.G., Deutsch, C.V., and Desbarats, A.J., 1986, 

Power averaging for block effective permeability: 

Richardson, Tex., Society of Petroleum Engineers, 

54th California Regional Meeting, Oakland, Calif, 

SPE Paper 15 128, p. 329-334. 

Klavetter, E.A., and Peters, R.R., 1987, An evaluation of the 

use of mercury porosimetry in calculating hydrologic 

properties of tuffs from Yucca Mountain, Nevada: 

Albuquerque, N. Mex., Sandia National Laboratories 

Report SAND864286,74 p. 

Kume, Jack, and Hammermeister, D.P., 1990, Geohydrologic data from test hole USW UZ-7, Yucca Mountain 

area, Nye County, Nevada: U.S. Geological Survey 

Open-File Report 88-465,46 p. 

Levy, S.S., 1984, Studies of altered vitrophyre for the prediction of nuclear waste repository-induced thermal alteration at Yucca Mountain, Nevada, in McVay, G.L., ed., 

Scientific basis for nuclear waste management: 

Elsevier, New York, Proceedings of the 7th Material 

Research Society Symposium, p. 959-966. 

Levy, S.S., Norman, D.I., and Chipera, S.J., 1996, Alteration 

history studies in the Exploratory Studies Facility, 

Yucca Mountain, Nevada, USA, in Murphy, W., and 

Knecht, D., eds., Scientific Basis for Nuclear Waste 

Management XIX: Pittsburgh, Pa., Materials 

Research Society, p. 543-548. 

Loskot, C.L., 1993, Geohydrologic data from test hole USW 

UZ4s, Yucca Mountain, Nye County, Nevada: 

U.S. Geological Survey Open-File Report 93-60,25 p. 

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, Nevada: 

U.S. Geological Survey Open-File Report 9&369, 

56 p. 

Martin, J.W., Felice, C. W., DeVan, R.T., and Green, S.J., 

1991, Grain density measurements on zeolitized tuff: 

Symposium on Containment of Underground Nuclear 

Explosions, 6th University of Nevada, Reno, Nev., 

Sept. 24-27, 1991, Proceedings, 12 p. 

McKe~a, S.A., and Rautman, C.A., 1996, Scaling of properties for Yucca Mountai- Literature review and 

numerical experiments on saturated hydraulic conductivity: Albuquerque, N. Mex., Sandia National 

Laboratories Report SAND95-2338, 11 7 p. 

Montazer, Parviz, and Wilson, W.E., 1984, Conceptual 

hydrologic model of flow in the unsaturated zone, 

Yucca Mountain, Nevada: U.S. Geological Survey 

Water-Resources Investigation Report 844345, 55 p. 

Moyer, T.C., and Geslin, J.K., 1995, Lithostratigraphy of the 

Calico Hills Formation and Prow Pass Tuff(Crater Flat 

Group) at Yucca Mountain, Nevada: U.S. Geological 

Survey Open-File Report 94460,59 p. 

Moyer, T.C., Geslin, J.K., and Buesch, D.C.,1995, Summary 

of lithologic logging of new and existing boreholes at 

Yucca Mountain, Nevada, July 1994 to November 

1994: U.S. Geological Survey Open-File Report 

9445 1,22 p. 

Moyer, T.C., Geslin, J.K., and Flint, L.E., 1996, Stratigraphic relations and hydrologic properties of the Paintbrush Tuffnonwelded (PTn) hydrologic unit, Yucca 

Mountain, Nevada: U.S. Geological Survey Open-File 

Report 95-397, 15 1 p. 

Nelson, P.H., 1994, Saturation levels and trends in the unsaturated zone, Yucca Mountain, Nevada: American 

Nuclear Society, Proceedings, International High-Level 

Radioactive Waste Management Conference, v. 1, 

p. 949-954. 

Nelson, P.H., Muller, D.C., Schimschal, U., and Kilber, J.E., 

1991, Geophysical logs and core measurements from 

forty boreholes at Yucca Mountain, Nevada: 

U.S. Geological Survey Geophysical Investigations 

Map GP-1001,64 p. 

56 Characterizatlon of Hydrogeologic Unlts Uslng Matrix Properties, Yucca Mountain, Nevada 
Nutting, P.G., 1943, Some standard thermal dehydration 

curves of minerals: U.S. Geological Survey 

Professional Paper 197-E, 28 p. 

Oldenburg, C.M., and Pruess, K., 1993, On numerical modeling of capillary barriers: Water Resources Research, 

v. 29, no. 4, p. 1045-1056. 

Peters, R.R., Klavetter, E.A., George, J.R., and Gauthier, 

J.H., 1987, Measuring and modeling water imbibition 

into tuff, in Evans, D.D., and Nicholson, R.H., eds., 

Flow and transport through unsaturated fractured rock: 

Washington, D.C., American Geophysical Union, 

Geophysical Monograph 42, p. 99-106. 

Peters, R.R., Klavetter, E.A., Hall, I.J., Blair, S.C., Heller, 

P.R., and Gee, G.W., 1984, Fracture and matrix hydrogeologic characteristics of tuffaceous materials fromYucca Mountain, Nye County, Nevada: Albuquerque, 

N. Mex., Sandia National Laboratories Report 

SAND84-1471, 108 p. 

Rautman, C.A., 1991, Estimates of spatial correlation in volcanic tuff, Yucca Mountain, Nevada: Albuquerque, 

N. Mex., Sandia National Laboratory Report 

SAND8s2270, 1 17 p. 

Rautman, C.A., 1995, Preliminary geostatistical modeling 

of thermal conductivity for a cross section of Yucca 

Mountain, Nevada: Albuquerque, N. Mex., 

Sandia National Laboratories Report SAND95-2283, 

50 p. 

Rautman, C.A., and Engstrom, D.A., 1996% Geology of the 

USW SD-7 drill hole, Yucca Mountain, Nevada: 

Albuquerque, N. Mex., Sandia National Laboratories 

Yucca Mountain Project Report SAND96-1474, 164 p. 

Rautman, C.A., and Engstrom, D.A., 1996b, Geology of the 

USW SD-12 drill hole, Yucca Mountain, Nevada: 

Albuquerque, N. Mex., Sandia National Laboratories 

Yucca Mountain Project Report SAND96-1368, 132 p. 

Rautman, C.A., and Flint, A.L., 1992, Deterministic processes and stochastic modeling, in Proceedings, 2nd 

Annual International High-Level Radioactive-Waste 

Management Conference; La Grande Park, Ill., 

American Nuclear Society, v. 2, p. 16 17-1 624. 

Rautman, C.A., Flint, L.E., Flint, A.L., and Istok, J.D., 1995, 

Physical and hydrologic properties of outcrop samples 

from a nonwelded to welded tuff transition, Yucca 

Mountain, Nevada: U.S. Geological Survey Open-File 

Report 95-406 1,28 p. 

Riehle, J.R., Miller, R.F., and Bailey, R.A., 1995, Cooling, 

degassing and compaction of rhyolitic ash flow tuffA computational model: Bulletin of Volcanology, v. 57, 

no. 5, p. 3 ls336. 

Rose, D.A., 1963, Water movement in porous materials 

Part 2, The separation of the components of water 

movement: British Journal Applied Physics, v. 14, p. 

49 1496. 

Ross, Benjamin., 1990, The diversion capacity of capillary 

barriers: Water Resources Research, v. 26, no. 10, 

p. 2625-2629. 

Rush, F.E., Thordarson, William, and Bruckheimer, L., 

1983, Geohydrologic and drill-hole data for test well 

USW H-1, adjacent to the Nevada Test Site, Nye 

County, Nevada: U.S. Geological Survey Open-File 

Report 8>141,68 p. 

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

and Broxton, D.E., 1994, Episodic volcanism in the 

Miocene southwest Nevada volcanic field- Stratigraphic revisions, 40 geochronologic framework, and implications for magmatic evolution: 

Geological Society of America Bulletin, v. 106, no. 10, 

p. 1304-1318. 

Schenker, A.R., Guerin, D.C., Robey, T.H., Rautman, C.A., 

and Barnard, R.W., 1995, Stochastic hydrogeologic 

units and hydrogeologic properties development for 

total-system performance assessments: Albuquerque, 

N. Mex., Sandia National Laboratories Report 

SAND94-0244, 165 p. 

Scott, R.B., and Bonk, Jerry, 1984, Preliminary geologic 

map of Yucca Mountain with geologic sections, Nye 

County, Nevada: U.S. Geological Survey Open-File 

Report 84494, scale 1 : 12,000. 

Scott, R.B., Spengler, R.W., Diehl, S., Lappin, A.R., and 

Chomack, M.P., 1983, Geologic character of tuffs in the 

unsaturated zone at Yucca Mountain, southem Nevada, 

in Mercer, J.W., Rao, P. S.C., and Marine, I. W., eds., 

Role of the unsaturated zone in radioactive and hazardous waste disposal: Ann Arbor, Mich., Ann Arbor Science, p. 289-335. 

Smith, R.L., 1960a, Ash flows: Geological Society of 

America Bulletin, v. 7 1, p. 795-4342. 

Smith, R.L., 1960b, Zones and zonal variations in welded 

tuffs: U.S. Geological Survey Professional 

Paper 354F, p. 14s159. 

Snyder, D.B., and Carr, W.J., 1982, Preliminary results of 

gravity investigations at Yucca Mountain and vicinity, 

southern Nye County, Nevada: U.S. Geological Survey 

Open-File Report 82-701,36 p. 

Steenhuis, T.S., Kung, K.-J.S., Parlange, J.-Y., Selker, J.S. 

and Chen, X.-X., 1990, Flow regimes in sandy soils 

with inclined layers: Annual Hydrology Days, American Geophysical Union, 1 Oth, Fort Collins, Colo., 

April 10-1 2, 1990, Proceedings, 10 p. 

References 57 
Thordarson, William, Rush, F.E., Spengler, R.W., and 

Wadell, S.J., 1984, Geohydrologic and drill-hole data 

for test well USW H-3, Yucca Mountain Nye County, 

Nevada: U.S. Geological Survey Open-File 

Report 84149,2 1 p. 

TRW, 1995, Total system performance assessment - 1995- 

An evaluation of the potential Yucca Mountain Repository: Las Vegas, Nev., TRW Environmental Safety 

Systems, B00000000417 17-2200401 36. 

van Genuchten, M.Th., 1980, A closed-form equation for 

predicting the hydraulic conductivity of unsaturated 

soils: Soil Science Society of America Journal, v. 44, 

p. 892-898. 

van Genuchten, M.Th., Leij, F.J., and Yates, S.R., 199 1, The 

RETC code for quantifying hydraulic functions of 

unsaturated soils: U.S. Environmental Protection -' 

Agency Report EPAl60012-91/065,93 p. 

Weeks, E.P., and Wilson, W.E., 1984, Preliminary evaluation 

of hydrologic properties of cores of unsaturated tuff, 

test well USW H-1, Yucca Mountain, Nevada: 

U.S. Geological Survey Water-Resources 

Investigations Report 84-4 193.30 p. 

Whitfield, M.S., Jr., Cope, C.M., and Loskot, C.L., 1993, 

Borehole and geohydrologic data for test hole USW 

UZ-6, Yucca Mountain area, Nye County, Nevada: 

U.S. Geological Survey Open-File Report 92-28,4 1 p. 

Whitfield, M.S., Jr., Thordarson, William, and Eshom, E.P., 

1984, Geohydrologic and drill-hole data for test well 

USW H4, Yucca Mountain, Nye County, Nevada: 

U.S. Geological Survey Open-File Report 84-449, 

20 p. 

Wittwer, C.S., Bodvarsson, G.S., Chornack, M.P., Flint, 

A.L., Flint, L.E., Lewis, B.D., Spengler, R.W., and 

Rautman, C.A., 1992, Design of a three-dimensional 

site-scale model for the unsaturated zone at Yucca 

Mountain, Nevada: International High-Level Radioactive Waste Conference, Las Vegas, Nev., April 12-16, 

1992, Proceedings, p. 263-27 1. 

58 Characterlzatlon of Hydrogeologic Units Uslng Matrlx Properties, Yucca Mountain, Nevada 
APPENDIX: FREQUENCY DISTRIBUTIONS OF 

POROSITY FOR HYDROLGEOLOGIC UNITS 

APPENDIX: FREQUENCY DISTRIBUTIONS OF POROSITY FOR HYDROLGEOLOGIC UNITS 59 
4 CCR 

111111111111111111111111111111111111 

CUC 

" 

0 .08 .I6 .24 .32 .4 .48 .56 .64 

POROSITY 

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0 .08 .I6 .24 .32 .4 .48 .56 .64 

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POROSITY 

30 

CMW 

IIIIIIIIIIIIIIIIIIIIIIIIIIIII 

25 

0 .08 .16 24 .32 .4 .48 .56 .64 

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5 

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n 

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5 

w 2 10 

LC ul m 

Z 

3 

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POROSITY 

60 Characterization of Hydrogeologic Units Using Matrix Properties, Yucca Mountain, Nevada 
6 

V) W 

J P4 

I 

s 

8 

a: W m 

3 2 Z 

0 

15 

0 

5 10 

% V) 

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APPENDIX: FREQUENCY DISTRIBUTIONS OF POROSITY FOR HYDROLGEOLOGIC UNITS 61 
z lo z 

POROSITY POROSITY 

150 

V) 

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100 

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3 

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62 Characterization of Hydrogeologic Units Using Matrix Properties, Yucca Mountain, Nevada 

V) 

60 - 

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!k 

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CHZ 

lrn 

0 .08 .16 .24 .32 .4 .48 .56 .64 

POROSITY 

POROSITY 

8 - CHV 

1111111111111111111IIIIIIIIIIIIIIII 

0 .08 .16 .24 .32 .4 .48 .56 .64 

POROSITY 

20 

BT 

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 

15 - 

rn 

!? 

P 

9 

rn 

& 10- 

B 

m 

3 

Z 

5- 

n IIIIIIIII IIIIIIIIIIIII

0 .J8 .16 .24 .32 .4 .48 .56 .64 

POROSITY 

APPENDIX: FREQUENCY DISTRIBUTIONS OF POROSITY FOR HYDROLGEOLOGIC UNITS 63 
10 

8 

0) W 

$ 6 

;f 

B 

E 4 m 

5 

Z 

2 

C 

z - 

- 

- 

- 

11111111111111, 0 .08 .16 .24 .32 .4 .48 .56 .64 

POROSITY 

PP2 30 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII~ 

25 IPOROSITY 

25 

BF3 

IIIIIIIIIIIIIIIIIII111111111111111 

POROSITY 

40 PP3 

111111111111111111111111111111111111 

80 

60 0) 

! 

4 

$ & 40 

u W m 

3 

Z 

20 

0 

10 

8 

rn 

Y 3 

B 

u 

u m 4 

3 

Z 

2 

0 

0 .08 .16 24 32 .4 .48 .56 .64 

POROSITY 

PP1 

IIIIIIIIIIIIIIIIIII111111111111111111 

IIIIA AIIIIIIIIIIIIII 0 .08 .16 .24 32 .4 .48 .56 .64 

POROSITY 

BF2 

1111111111111111111IIIIIIIIIIIIIIIII 

0 .08 .16 24 .32 .4 .48 .56 .64 

POROSITY 

64 Characterization of Hydrogeologic Units Using Matrix Properties, Yucca Mountain, Nevada 

7!7 U.S. GOVERNMENT PRINTING OFFICE: 1998 - 673-083 / 20013 REGION NO. 8