Geologic and Hydrologic 

Characterization and Evaluation 

of the Basin and Range Province 

Relative to the Disposal 

of High-level Radioactive Waste 

Part I Introduction and Guidelines ·:,.··· 

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GEOLOGICAL SURVEY CIRCULAR 904-A 

This is Part I of a series of reports being prepared 

by the U.S. Geological Survey in consultation with 

States in the Basin and Range Province. 
BASIN AND RANGE 

PROVINCE WORKING GROUP 

U.S. Geological Survey Members 

Chairman ofthe Province Working Group: 

M.S. Bedinger 

Hydrologist 

U.S. Geological Survey 

Denver, CO 

Member: 

K.A. Sargent 

Geologist 

U.S. Geological Survey 

Denver, CO 

State Members and Alternates 

ARIZONA 

Member: 

Larry Fellows 

State Geologist 

Arizona Bureau of Geology and Mineral 

Technology 

Tucson, AZ 

Alternate: 

H. Wesley Peirce 

Principal Geologist 

Arizona Bureau of Geology and Mineral 

Technology 

Tucson, AZ 

CALIFORNIA 

Member: 

Robert Streitz 

Geologist 

California Divison of Mines and Geology 

Sacramento, CA 

IDAHO 

Member: 

Frank Sherman 

Chief, Ground-Water Section 

Idaho Department of Water Resources 

Boise, ID 

Alternate: 

Darrel Clapp 

Chief, Technical Services Bureau 

Idaho Department of Water Resources 

Boise, ID 

NEVADA 

Member: 

John Schilling 

State Geologist/Director 

Nevada Bureau of Mines and Geology 

University of Nevada 

Reno, NV 

Alternate: 

Becky Weimer-McMillion 

Geologic Information Specialist 

Nevada Bureau of Mines and Geology 

University of Nevada 

Reno, NV 

Succeeded in June, 1982, by: 

Susan L. Tingley 

Deputy to the State Geologist 

Nevada Bureau of Mines and Geology 

University of Nevada 

Reno, NV 

NEW MEXICO 

Member: 

Emery Arnold 

State Geologist 

New Mexico Mining and Minerals Division 

Santa Fe, NM 

Succeeded in July, 1982, by: 

James M. Hill 

Chief, Bureau of Geology 

New Mexico Energy and Minerals Department 

Santa Fe, NM 

Alternate: 

Frank Kottlowski 

Director 

New Mexico Bureau of Mines and Mineral Resources 

Socorro, NM 

TEXAS 

Member: 

Christopher Henry 

Geologist 

Texas Bureau of Economic Geology 

University of Texas at Austin 

Austin, TX 

Alternate: 

Douglas Ratcliff 

Associate Director 

Texas Bureau of Economic Geology 

University of Texas at Austin 

Austin, TX 

UTAH 

Member: 

Genevieve Atwood 

State Geologist 

Utah Geological and Mineral Survey 

Salt Lake City, UT 
Geologic and Hydrologic 

Characterization and Evaluation 

of the Basin and Range Province 

Relative to the Disposal 

of High-level Radioactive Waste 

Part I Introduction and Guidelines 

By M.S. Bedinger, K. A. Sargent and J. E. Reed 

I 

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GEOLOGICAL SURVEY CIRCULAR 904-A 

This is Part I of a series of reports being prepared 

by the U.S. Geological Survey in consultation with 

States in the Basin and Range Province. 
United States Department of the Interior 

WILLIAM P. CLARK, Secretary 

Geological Survey 

Dallas L. Peck, Director 

Free on application to the Branch of Distribution, Eastern Region, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 

1984 
FOREWORD 

The U.S. Geological Survey is actively participating in the national program 

to identify sites suitable for permanent disposal of high-level radioactive wastes 

by conducting research and areal studies. This report introduces the U.S. 

Geological Survey's pilot effort in screening large physiographic provinces of 

the United States for favorable geohydrologic environments for isolation of 

high-level radioactive waste. As a part of the national program, the U.S. 

Geological Survey also provides advice on Earth-science aspects of the program 

to the States involved and other Federal agencies, including the U.S. Department of Energy, who has the primary responsibility for disposal of high-level 

waste, as set forth in the Nuclear Waste Policy Act of 1982. Thus the U.S. 

Geological Survey is using its extensive expertise to help find potentially suitable disposal sites, while maintaining its customary impartiality and scientific 

objectivity. 

The search for repository sites in the United States is almost 2 decades 

old and has proven to be considerably more complex, both technically and politically, than was originally conceived. Experts within the U.S. Geological Survey 

believe that past searches for sites placed too much emphasis on candidate 

host rocks for the repository and too little emphasis on hydrologic setting. 

Aside from physical exhumation by erosion, meteorite impact, or volcanic activity, ground-water flow is the only natural mechanism by which radionuclides 

could be transported to the biosphere from an underground repository. Thus, 

from the initial stages, the present study considered the pathways of ground 

water that might transport radionuclides from the repository to the accessible 

environment. Because it was not certain at the outset whether sufficient data 

would be available to successfully test this approach, the study has served 

as a pilot effort to determine the feasibility of this approach. The Basin and 

Range Province has been an ideal setting for the prototype study because 

of the diversity of its rock types and geologic and hydrologic situations. 

A unique feature of this study has been the involvement from the outset, 

of the States in the Basin and Range Province in the screening process. Technical representatives of the States have provided consultation in choosing criteria, 

assembling geohydrologic data, and assessing this information to identify environments that meet the criteria for further study. This joint effort does not 

oblige the States to accept any final choices or priorities resulting from the 

screening, but it does mean that technical representatives of the States have 

participated in the screening process from its inception, and that conclusions 

presented in this and subsequent reports in this series represent a general 

technical consensus. 

Director, 

U.S. Geological Survey 

III 

PREFACE 

This report, part I of a three-part report, provides a background and an 

introduction to a screening study to evaluate the suitability of environments 

in the Basin and Range Province for disposal of high-level radioactive waste, 

and a discussion of guidelines for geologic and hydrologic factors that will be 

used in the evaluation process. Part II is a reconnaissance-level characterization 

of the geologic and hydrologic factors to be used in the initial screening of 

the Basin and Range Province. Part III is the initial evaluation of the Province, 

using the guidelines established in Part I, and will identify regions that appear 

favorable for further study. 

Parts II and III, as summary reports, will not contain all the detailed information used in characterization and evaluation. The detailed information will 

be compiled from many published reports, files of the U.S. Geological Survey, 

and other sources. Some sets of information will be used directly from earlier 

published reports. The information compiled will be published in separate reports of the U.S. Geological Survey. Following the study of the Province, regions that appear favorable for further study will be characterized in greater 

detail and further evaluated in a later phase of the study. 

M. S. Bedinger 

K. A. Sargent 

v 

Foreword . 

Preface .. 

Summary . 

Introduction . 

Background . 

Origin of the study . 

Purpose, scope, and methods of study . 

Acknowledgments . . . . . . . . 

Guidelines for Province evaluation . 

Geologic and hydrologic factors 

Host rocks .. 

Depth ... 

Thickness. 

CONTENTS 

Page 

III 

v 

1 

2 

2 

3 

4 

5 

5 

5 

6 

6 

6 

Guidelines for Province evluation-Continued 

Geologic and hydrologic factors-Continued 

Host rocks-Continued 

Lateral extent . . . . . . . . . . . . 

Strength, mineability, and thermal 

conductivity . . . . . . . . . . . . 

Ground-water flow system . . . . . . . . 

Quaternary tectonic conditions . . . . . . . . 

Geomorphic processes and climatic change . 

Flooding ......... . 

Natural resources . . . . 

Geohydrologic environments . 

References cited . . . . . . . . . . 

ILLUSTRATIONS 

FIGURE 1. Map showing physiographic provinces in the conterminous United States . 

2. Graph showing repository nuclide inventories at various years after closure 

3-6.8ections showing geohydrologic settings in: 

3. Granite and basin-fill deposits in a region of interbasin flow . . . . . 

4. Volcanic rocks overlying Paleozoic rocks . . . . . . . . . . 

5. Granitic rocks intruding Paleozoic rocks ..... . 

6. Basin-fill deposits in a large regional flow system . . . . 

TABLE 

Page 

7 

7 

7 

9 

10 

10 

10 

10 

15 

Page 

3 

8 

12 

13 

14 

15 

Page 

TABLE 1. Values of effective porosity, hydraulic conductivity, and retardation factors used to calculate traveltimes. 11 

VII 
Multiply 

English unit 

square mi (mi2) 

foot (ft) 

mile (mi) 

inch 

CONVERSION FACTORS 

By 

cbnversion factor 

2.590 

0.3048 

1.609 

2.540 

VIII 

To obtain 

metric unit 

square kilometer (km2

) 

meter (m) 

kilometer (km) 

millimeter (mm) 
Geologic and Hydrologic Characterization and 

Evaluation of the Basin and Range Province 

Relative to the Disposal of High-Level Radioactive Waste 

PART I 

INTRODUCTION AND GUIDELINES 

By M.S. Bedinger, K.A. Sargent, and J.E. Reed 

SUMMARY 

The U.S. Geological Survey's program for geologic and hydrologic evaluation of physiographic provinces to identify areas 

potentially suitable for locating repository sites for disposal of 

high-level nuclear wastes was announced to the Governors of 

the eight States in the Basin and Range Province on May 5, 

1981. Representatives of Arizona, California, Idaho, New 

Mexico, Nevada, Oregon, Texas, and Utah, were invited to 

cooperate with the Federal Government in the evaluation process. Each Governor was requested to nominate an Earth scientist to represent the State in a province working group composed of State and U.S. Geological Survey representatives. 

This report, Part I of a three-part report, provides the 

background, introduction and scope of the study. This part also 

includes a discussion of geologic and hydrologic guidelines that 

will be used in the evaluation process and illustrates geohydrologic environments and the effect of individual factors in providing multiple natural barriers to radionuclide migration. 

Part II is a reconnaissance characterization of the geologic 

and hydrologic factors to be used in the initial screening of 

the Basin and Range Province. Part III will be the initial 

evaluation of the Province and will identify regions that appear 

suitable for further study. 

The plan for study of the Province includes a stepwise 

screening process by which successively smaller land units are 

considered in increasing detail. Each step involves characterization of the geology and hydrology and selection of subunits 

for more intensive characterization. Selection of subunits for 

further study is by evaluation of geologic and hydrologic conditions following a set of guidelines. By representation on the 

Province Working Group, the States participate in a consultation and review role in: (1) Establishing geologic and hydrologic 

guidelines, and (2) characterizing and evaluating the Province. 

The States also participate in compilation of geologic and hydrologic data used in characterizing the Province. 

The current (1983) needs for a high-level radioactive waste 

repository include: (1) Disposal in a mined repository; (2) re1 

trievability of the waste for as much as 50 years; and (3) confidence of isolation of the waste from the accessible environment. 

Isolation of the waste needs to be assured using geologic and 

hydrologic conditions that: (1) Minimize risk of inadvertent future intrusions by man; (2) minimize the possibility of disturbance by processes that would expose the waste or increase 

its mobility; and (3) provide a system of natural barriers to 

the migration of waste by ground water. The guidelines 

adopted by the Province Working Group are designed to provide a standard with which these conditions can be compared. 

The guidelines can be grouped into four principal categories: 

(1) Potential host media, (2) ground-water conditions, (3) tectonic conditions, and. (4) occurrence of natural resources. Ideally the host medium constitutes the first natural barrier to 

migration of radionculides. The host medium ideally should be 

a rock type that prevents or retards dissolution and transport 

of radionuclides. Rocks in both the saturated and unsaturated 

zones may have desirable characteristics for host media. 

Rocks-other than the host-in the ground-water flow path 

from the repository ideally should be major barriers to 

radionuclide migration. Confining beds of low permeability 

might be present to retard the rate of flow between more 

permeable beds. Additionally, sorption of radionuclides by materials such as clays and zeolites in the flow path can further 

retard the flow of radionuclides by several orders of magnitude. Tectonic conditions in an area should not present a 

probable cause for exhumation or increased mobility of radioactive waste. Natural resources are a factor for consideration 

because of the problem of future human intrusion and exposure 

to radioactivity in the quest for minerals, oil, gas, water, and 

geothermal resources. 

The ultimate evaluation of the suitability of a geohydrologic 

environment for developing a mined repository needs to assess 

all geologic and hydrologic characteristics and their interaction 

in providing confidence that a geohydrologic environment will 

effectively isolate radionuclides from human access. Several 

hypothetical settings with typical geohydrologic conditions in 

the Basin and Range Province are used to illustrate the effect 

of multiple barriers in the isolation of radionuclides. 
INTRODUCTION 

BACKGROUND 

The goal of radioactive-waste isolation in mined 

repositories is to prevent migration of radionuclides 

to the accessible environment in unacceptable 

concentrations. Accessible environment was detined in the draft rule by the U.S. Nuclear Regulatory Commission (1981) to mean "those portions 

of the environment directly in contact with or 

readily available for use by human beings." As 

used here, it includes the Earth's atmosphere, the 

land surface, surface water, and the oceans· it also . ' mcludes presently used and potentially useable 

aquifers containing potable or otherwise useable 

water and presently mined and potentially mineable natural resources. The present program of 

the U.S. Department of Energy is committed to 

pursuing a programmatic strategy that will lead 

to disposal of existing and future commercially 

generated radioactive high-level and transuranic 

wastes in mined repositories in geologic formations (U.S. Deparment of Energy, 1980). 

The search for sites suitable as radioactivewaste repositories has been underway for many 

years in several countries. Many early studies focused on a specific type of host rock. In the United 

States, early studies concentrated on salt as the 

host rock. Subsequently, basalt, tuff, granitic 

rocks, shale, and metamorphic rocks have been 

considered as potential host rocks. Although the 

host medium remains important in planning the 

engineering design of the repository and in acting 

as the iirst natural barrier to radionuclide migration, it ~s now recognized that the hydrologic, 

geochemical, and tectonic conditions of the repository and its environment are as important as the 

host rock. 

Early studies of high-level radioactive-waste 

disposal problems assumed that containment by 

the enclosing rock mass would be virtually complete. With the application of broader discipline 

studies, specifically geology and hydrology, to prospe~tive environments for waste disposal, the 

realiZation came that total isolation of the waste 

in the immediate vicinity of the repository cannot 

be assured (Bredehoeft and others, 1978). Winograd (1977) showed that many of the methods cwrrently used in the Earth sciences are not appropriate for predicting conditions or events during the 

extremely long time required for waste isolation. 

Earth processes that are of major concern during 

2 

the waste isolation storage time include: (1) Rates 

of radionuclide transport in the ground-water flow 

system, which in turn reflect chemical reactions 

of radionuclides with ground water and Earth materials; (2) climatic changes; and (3) tectonic and 

associated erosional events. To compensate for the 

limitations in our knowledge, the current rationale 

for waste isolation emphasizes the need for a 

series of independent barriers to waste migrations. Multiplicity of these barriers, both engineered and natural, will, it is hoped, compensate 

for uncertainties in predicting natural and man-induced conditions and events during the time required for waste isolation. 

The realization by the Earth-science community 

that scientific questions and limitations persisted 

prompted the U.S. Departments of Energy and 

the Interior to collaborate in assessing the magnitude of the problems. The result of this effort 

was the "Earth Science Technical Plan for the Disposal of Radioactive Waste in a Mined Repository" 

(Office of Nuclear Waste Management and U.S. 

Geological Survey, 1980). The cited report identified technical questions and established five subgroups to address problems in specific areas of 

concern. Subgroup I, scientists from the U.S. Departments of Energy and the Interior and several 

States, considered the problem of identification 

and evaluation of geologic environments potentially suitable for radioactive-waste disposal (U.S. 

Geological Survey, 1980). The other subgroups 

were concerned with waste-media interactions, 

rock mechanics, sealing repositories, and Earthscience aspects of long-term risk analysis. 

The approach proposed by Subgroup I was to 

establish a cooperative State-Federal working 

group to search for favorable geohydrologic environments containing suitable host media. The 

search would encompass the conterminous United 

States by examining the country on a physiographic province basis. The screening plan provided for considering successively smaller land 

units in each stage and ultimately recommending 

sites for characterization. Each stage would involve: (1) Characterization of the geology and hydrology; (2) identification of the most favorable 

subunits; and (3) selection of certain subunits for 

more intensive characterization. Identification of 

favorable envirnments would be based on a set 

of criteria covering the following: host-rock 

characteristics, ground-water flow-system characteristics, tectonic conditions, and occurrence of 

mineral resources. 
ORIGIN OF THE STUDY 

The U.S. Geological Survey originated the program described herein, referred to as Task I, for 

Province screening. The study will be guided by, 

but not constrained to follow the Subgroup I plan. 

As a prototype, the study of the Basin and Range 

Province will explore alternative technical 

methods and strategies for searching for environments favorable for further investigation. Because 

of the diversity of geohydrologic environments and 

100 0 100 200 300 400 500 ...._ES 

100 0 100 200 ~~ KI..Ot.ETERS 

EXPLANATION 

PHYSIOGRAPHIC PROVINCE 

the broad base of the U.S. Geological Survey's 

work in this area, the Basin and Range Province 

was selected as the prototype in this national 

screening program (fig. 1). In May, 1981, the U.S. 

Geological Survey study was introduced to the 

Governors of the eight Basin and Range StatesArizona, California, Idaho, Nevada, New Mexico, 

Oregon, Texas, and Utah, and the Indian tribes 

in those States. The States were invited to participate in the study by designating an Earth scientist 

to serve on the Province Working Group with 

U.S. Geological Survey scientists. 

1. New England- Adirondack Mountains 

2. Appalachian Highlands - Piedmont 

3. Applachian and Interior Plateaus 

4. Coastal Plain 

5. Glaciated Central Platform 

6. Western Central Platform 

7. Rocky Mountain System 

8. Colorado Plateaus 

9. Basin and Range 

10. Columbia Plateaus 

11. Pacific Mountain System 

FIGURE I.-Physiographic provinces in the contenninous United States. 

3 
The membership of the Province Working 

Group is shown in this report on the inside front 

cover. The two U.S. Geological Survey members 

of the Province Working Group are the Project 

Chief and the Associate Project Chief. The Project Chief serves as Chairman of the Province 

Working Group. Each State member of the Province Working Group is a scientist designated by 

the Governor of that State to represent the State 

on Earth-science questions. 

PURPOSE, SCOPE, AND METHODS OF STUDY 

The goals of the study are to characterize the 

geology and hydrology of the Basin and Range 

Province and identify areas prospective for 

further, more detailed study in search of potential 

high-level radioactive waste repository sites. 

Geologic and hydrologic factors are the sole basis 

for the characterization and evaluation of the Province described herein. Identification of areas for 

further study will use a set of guidelines that emphasizes isolation of high-level radioactive waste 

from the accessible environment by a system of 

multiple independent natural barriers. 

The members of the Province Working Group 

reach a general agreement on technical issues 

through participation in study and review of 

geologic and hydrologic data, preparation of 

guidelines for evaluation of the potential suitability of geologic environments for waste isolation, 

and preparation and review of reports. Although 

the division of work is not inflexible, the U.S. 

Geological Survey Task I staff members prepare 

drafts of characterization and evaluation reports. 

The State members of the Province Working 

Group provide consultation during report preparation and technical review of the reports. Both the 

U.S. Geological Survey and State members of the 

Province Working Group and their respective 

staffs participate in the compilation, review, and 

preparation for publication of geologic and hydrologic information used in characterization and 

evaluation. Participation in this cooperative study 

does not imply that the States accept the findings 

and recommendations of this study. The technical 

interpretations of an individual member of the 

Province Working Group may differ with the consensus of the group. Any group member may 

write dissenting opinions for inclusion in reports 

of the Province Working Group. 

Characterization of the Province, Part II of this 

4 

report, is based on data and information available 

in published reports and on unpublished data in 

the files of Federal agencies, State agencies, universities, and the private sector. The principal factors selected for characterizing the geology and 

hydrology for the initial screening of the Province 

consist of: 

1. Distribution of selected rocks; including granitic, argillaceous, basaltic, tuffaceous, surface and subsurface evaporitic rocks; and 

other local occurrences of potentially favorable rock types; 

2. regional ground-water flow systems and related data including hydraulic-head relations between principal water-bearing 

units, depth to water (thickness of the unsaturated zone), water use, natural areas 

of discharge by evapotranspiration, springs, 

and water quality; 

3. tectonic conditions including the occurrence of 

Quaternary faults and Quaternary volcanic 

centers, and the magnitude and historic distribution of seismic activity; 

4. metallic and nonmetallic mineral resources, 

oil, gas, and coal resources; and 

5. supplementary Province-wide data and information on geothermal heat flow, uplift and 

subsidence, occurrence of Pleistocene lakes, 

and interpretations of gravity and magnetic 

data. 

Initial evaluation of the Province, Part III of 

this report, consists of comparing the characteristics of each land unit of the Province with the 

guidelines in the context of a multiple-barrier setting. Negative and positive factors are included 

to document the evaluation. In many instances, 

no single criterion is of such overriding importance 

as to eliminate an environment for further consideration. Lack of technical information, and consequent lack of a basis for evaluation, are 

documented. The Province evaluation identifies 

parts of the Province that are prospectively favorable for further study. 

Following initial Province evaluation, subdivisions will be selected for additional study and 

more detailed information will be compiled for the 

second stage of evaluation. This will include: 

1. Stratigraphic sections, including lithologic and 

other logs of test holes; 

2. structural cross sections at selected locations; 

3. data on structural processes (folding, faulting), metamorphism, hydrothermal alteration, and other processes that enhance or 
detract from the suitability of a rock or 

area; 

4. physical, geochemical, and hydrologic properties of rocks; 

5. geochemical environment of the ground-water 

system in and downgradient from the potential host environments; 

6. data on hydrologic conditions and processes 

such as recharge rates, unsaturated sections, and interbasin flow; and 

7. information on surficial geomorphic processes 

such as potential rates of scarp retreat, denudation, and recurrence of pluvial climates. 

ACKNOWLEDGMENTS 

This report is the result of a collective effort 

reflecting the work, assistance, consultation, and 

experience of many colleagues, both in the U.S. 

Geological Survey and in State agencies. The plan 

of this study was guided and influenced by the 

work of William E. Hale, U.S. Geological Survey 

(now retired), who was the chairman of Subgroup 

I of the Earth Science Technical Plan Working 

Group. The study has been under the administrative and technical guidance of George D. DeBuchananne (now retired), John B. Robertson, 

and Eugene H. Roseboom, Jr., all of the U.S. 

Geological Survey. The State members and alternates of the Basin and Range Province Working 

Group were the principal consultants in the evolution of a plan of work and guidelines that provide 

a basis for Province screening. 

The nucleus of the guidelines for Province 

screening was drawn largely from a draft of 

geologic and hydrologic criteria prepared by 

Newell J. Trask, U.S. Geological Survey, who has 

continued in a reviewing and advisory role 

through many drafts of the guidelines. Isaac J. 

Winograd, U.S. Geological Survey, has contributed to the study from its inception, providing 

guidance in planning, constructive criticism during 

its progress, consultation with the Province Working Group on technical problems and critical review of the reports of the Province Working 

Group. Robert Schneider, U.S. Geological Survey, 

and John Hawley, New Mexico Bureau of Mines 

and Mineral Resources, have contributed greatly 

to the guidelines through review and consultation 

with the authors. 

5 

GUIDELINES FOR PROVINCE 

EVALUATION 

Site criteria developed by several groups-N ational Research Council of the National Academy 

of Science, International Atomic Energy Agency, 

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

Waste Isolation-served as a starting point for the 

Province Working Group in discussions of 

guidelines. Site criteria of these groups are briefly 

summarized in a report by the Office of Nuclear 

Waste Isolation (1981). The recently proposed rule 

for repository siting of the U.S. Nuclear Regulatory Commission (1981) also affected the design 

of guidelines used in this report. The guidelines 

adopted herein for evaluating individual geologic 

and hydrologic factors are illustrated by the use 

of hypothetical geologic settings which show the 

diverse factors that can lead to isolation of waste 

from the accessible environment and the effect of 

natural barriers in resisting radionuclide migration. 

Guidelines adopted for the Basin and Range 

Province reflect geologic and hydrologic characteristics of the Province such as aridity, faulting 

and tectonic extension, the occurrence of areas of 

high heat flow, areas subject to seismic activity, 

complex structure, widespread occurrence of a variety of potential host media, large volumes of unsaturated rock, thick non-indurated basin fills, 

zones with potable and nonpotable ground water, 

regional bedrock aquifers, and large areas of rock 

of low permeability. 

There follows a discussion of guidelines for 

geologic and hydrologic factors, such as host 

rocks, ground-water flow system, and Quaternary 

tectonic conditions; and then illustrations of how 

these individual factors are combined in the 

geohydrologic environment. 

GEOLOGIC AND HYDROLOGIC FACTORS 

The following discussion of individual factors is 

based on an arbitrary order, but provides a systematic treatment of the Earth-science factors. 

Application of the guidelines needs to be made in 

consideration of the interrelationship of the factors. 
HOST ROCKS 

The host medium constitutes the first natural 

barrier to radionuclide migration, excluding engineered barriers of the waste form and the repository. To be most effective as a barrier, host 

rocks ideally should provide an environment with 

an absence of free water (that is, zero water velocity) to prevent dissolution and transport of 

radionuclides. In the Basin and Range Province, 

these conditions are most nearly attained in unsaturated zones where recharge rates are low or 

non-existent and moisture contents are minute. 

Below the water table, host rocks ideally should 

retard ground-water movement from the repository and have the capacity to sorb radionuclides. 

The rate of ground-water movement is slow where 

rocks have a high effective porosity and a low hydraulic conductivity and where a low hydraulic 

gradient occurs. 

Buffer zones surrounding the repository need 

not be the same lithologic type as the host rock. 

However, a homogeneous rock sequence will allow 

greater confidence in calculations of nuclide transport than an inhomogeneous rock sequence with 

numerous different lithologic interbeds or zones 

with significantly different permeability. In general, the greater the thickness of the buffer zone 

between the repository and any overlying or underlying aquifer, the greater the confidence that 

the low permeability host rock can contain the 

waste for long periods. 

In the saturated zone, a host rock ideally must 

have sufficient thickness, lateral extent, and low 

permeability to provide a medium for waste disposal. In the Basin and Range Province granitic, 

intermediate and mafic intrusive rocks, argillaceous rocks, ash-flow tuffs, salt and anhydrite, volcanic mudflow (laharic) breccias, basaltic to andesitic rocks, and locally some intrusive rhyolitic 

plugs and stocks, some partly zeolitized tuff and 

some metamorphic rock such as granite gne~s, 

phyllite, and argillite have been inventoried for 

possible future examination of their host-r6ck 

properties. 

Many rock types may be potential host media 

in the unsaturated zone. The suitability of the unsaturated zone is more dependent on the mineability and hydrologic properties of the rocks and 

their geohydrologic settings than a particular 

lithology for the rock. In the unsaturated zone, 

the media ideally should be permeable to provide 

drainage, have sufficient thickness for repository 

6 

construction and buffer zones above and below the 

repository, and be in an environment with very 

little or no recharge. Downward infiltration of 

water through the repository zone would be 

minimized by a very porous and poorly permeable 

zone above the repository zone or by very slow 

recharge rate. Drainage of water which may reach 

the repository could be facilitated by diversion 

drains and drainage wells constructed in the repository chambers, and the waste could be further 

isolated from moisture by engineered capillary 

barriers (Winograd, 1981). 

DEPTH 

A deep, mined repository ideally must be located at a depth sufficient to prevent surficial processes from exposing the waste for an extremely 

long time and to limit the possibility of human intrusion. The depth of the repository ideally should 

be great enough to preclude a temperature increase at the land surface caused by the heat dissipating from the waste. If the repository is so 

engineered to impose a maximum temperature of 

100° to 150°C in the chamber, model studies show 

that a repository depth as shallow as 25 meters 

(82 ft) would cause no more than 2° or 3° C increase in near-surface temperature (D. W. Pollack, U.S. Geological Survey, oral commun., 

1983). The minimum depth requirements also need 

to be analyzed for a given geologic setting with 

consideration given to such factors as the effects 

of uplift, downcutting, stream piracy, scarp retreat, and increased rainfall. In some deeply dissected environments, depths of 300 meters (1,000 

ft) may be required; while in aggrading subsiding 

environments, depths of as little as 100 meters 

(330 ft) may suffice. 

There is no generally applicable guideline for 

maximum depth of a repository. The ambient temperature at the repository depth needs to be considered, because it can affect the heat dissipation 

and the density of waste implacement. Considerations determining the maximum depth, such as 

mining and stability problems, and costs of excavation and construction are beyond the scope of 

this study. However, 1,000 meters (3,300 ft) is 

adopted provisionally as the general guideline for 

maximum depth in screening potential host rocks. 

THICKNESS 

In the saturated zone, a minimum thickness of 

100 meters (330 ft) of host rock would provide a 

zone for repository excavations with buffer zones 
above and below. Below the water table, buffer 

zones serve as barriers to flow of water to and 

from the repository. 

For disposal above the water table, the thickness of the unsaturated zone ideally must be sufficient to include a buffer zone above the repository, 

a zone for repository excavations, and a buffer 

zone between repository and water table. The 

zone above the repository provides isolation from 

the land surface and a barrier to exhumation by 

erosion. The volume of rock between the water 

table and the repository provides a zone within 

which the water level may rise relative to the repository without saturating the repository and 

possible media for delay and sorption of radionuclides before the radionuclides reach the saturated 

zone. The probable maximum magnitude of waterlevel rise relative to the repository needs to be 

examined for each unsaturated environment being 

considered. The mechanisms by which the water 

level might rise relative to the repository include 

climatic changes, which affect the hydrologic system, and tectonic events, which could cause subsidence of the block i which the repository is located. Environments where the depth to water is 

greater than 150 me ers (500 ft) are considered 

as having potential fo further evaluation. 

The host rock ideal y should be continuous over 

the area of the rep sitory and include a lateral 

buffer zone. It is es imated that the operations 

area probably will re uire a minimum of about 8 

square kilometers (3 ·

2); the buffer zone probably 

will extend at least 2 ·lometers (1.2 miles) beyond 

all sides of the operat ons area. 

STRENGTH, MINEABILI , AND THERMAL CONDUCTIVITY 

Because of variab · · ty in the physical and engineering properties frocks, it is not possible to 

predict these propert es at depth with any degree 

of certainty. Howeve , certain rocks generally are 

believed to possess u desirable physical properties 

for mining at depth; for example, certain shales 

may deform plastic lly or thin multiple basalt 

flows may be extensi ely fractured and subject to 

caving. Furthermore, certain characteristics observed in surface e posures, such as zones of 

shearing and other tructural complications, and 

the presence of che cally altered rock, may indicate potential minin problems. Thermal conductivity of the host ro k needs to be considered in 

7 

the design of the repository to preclude adverse 

effects to the integrity of the waste form, repository, and host rock as barriers to radionuclide migration. It is generally understood that dense 

saturated rocks with little porosity, such as salt, 

dense basalt, and densely welded tuff, have greater thermal conductivities than unconsolidated or 

extensively fractured media, such as unconsolidated alluvium or brecciated lava flow. 

GROUND-WATER FLOW SYSTEM 

Major barriers to radionuclide migration ideally 

should be present in the ground-water flow path 

from the repository to the accessible environment. 

A minimum performance requirement of a groundwater flow system specified in revisions to the 

draft of a proposed rule by the U.S. Nuclear Regulatory Commission (1981) is that the waste be 

completely contained for 1, 000 years following closure and that pre-waste emplacement flow time 

from the repository to the limit of the controlled 

area be at least· 1,000 years. This time provides 

for a decrease of several orders of magnitude in 

the short-lived fission products as shown by the 

inventory of radionuclides of high-level waste 

through time (fig. 2), during which strontium-90 

and cesium-137 decay to innocuous levels. A flow 

time of water (or a conservative, non-reactive ion) 

of 10,000 years from the repository to the accessible environment as defined in this report is 

adopted as a minimum goal for this study. Sorption of radionuclides by materials in the flow path, 

or precipitation of radionuclides, particularly for 

non-oxygenated (reducing) ground water, can 

further retard rates of movement of some dissolved radionuclides by several orders of magnitude. 

Rocks composed of clays or zeolitic minerals are 

notable for their sorptive properties and are effective in retarding transport of radionuclides. In 

some environments, oxides of iron and manganese 

appear to be more sorptive for uranium and thorium than are clays and zeolites. 

A 10,000-year flow time from the repository to 

the accessible environment, plus significant sorptive capacity of the flow system will effectively 

isolate plutonium-239 and americium-243. The 

longer lived transuranic isotopes, such as uranium238, neptunium-237, and their daughters in the 

decay chain, such as radium-226, and long-lived 

isotopes such as technetium-99 and iodine-129 persist for millions of years-times that are well 
Plutoni u m-239 

lodine-129 

10 105 

TIME, IN YEARS 

FIGURE 2.-Repository nuclide inventories at various times after closure. Modified from Cloninger and others 

(1980). The inventory used in the analysis is one-fifth of the total for the spent unreprocessed fuel (no-recycle 

case) estimated to be accumulated in the United States through 2050. 

8 
beyond credible predictability for the groundwater flow system. 

Decay and sorption of technetium-99 and iodine129 are not important factors in decreasing their 

content. Though technetium-99 and iodine-129 content of the waste is reported as a relatively small 

fraction of the total curie content of the waste by 

Gera (1975) and Clo nger and others (1980), factors other than sorpt ·on will determine the hazard 

they present. These f: ctors also may be significant 

in decreasing the h ard of long-lived, sorbed 

radionuclides. The e gineered barrier system of 

the repository, and t e relative insolubility of the 

waste form and of s me of the nuclides will undoubtedly greatly · it their concentration in the 

water. Significant d creases in radionuclide concentrations can be e ected by dilution and dispersion. Dilution occurs where the flow path from a 

repository enters a arge regional aquifer or in 

some situations, a m jor stream; dilution can decrease the concentra ion of a radionuclide by as 

much as several ord rs of magnitude. Dispersion 

occurs in most flow edia, occurring to a greater 

extent in permeable rocks that are extensively 

fractured and jointed. 

For additional in£ rmation in the radionuclide 

content of high-level aste, the reader is referred 

to Gera (1975), Arne ·can Physical Society (1978), 

and Cloninger and o hers (1980); for information 

on ingestion hazard o high-level waste, the reader 

is referred to Parker 1981) and Cohen (1982). 

Downward or late al flow of water at the repository horizon wo ld eliminate the risk of upward leakage of r dionuclides through poorly 

sealed shafts or b reholes. However, upward 

movement through he repository might be acceptable if flow wa into an aquifer containing 

water of non-useable uality and having a long travel-time to the access ble environment. 

The possibility of ture intrusion of the repository by drilling woul be minimized by the following conditions: (1) Th potential host rock unit underlain by and imme · ately overlain by water of 

non-useable quality; 2) a great depth to a source 

of useable quality w ter; or (3) rocks with little 

water-yielding ability above and below the potential host rock. 

Guidelines for teet nic conditions established by 

Agency, 1977, and National Academy of Sciences, 

1978) because, under some conditions, tectonic 

events have the potential for accelerating exhumation of the repository or decreasing the transport 

time of waste to the accessible environment. In 

an extreme case, a rupture of the repository by 

volcanism could transport the waste directly to the 

accessible environment. The general approach 

suggested here is to consider the probability of 

tectonic events in an area as well as to analyze 

the consequences of tectonic events in a specific 

geohydrologic environment in a comprehensive, 

multidiscipline approach. Such an analysis provides a means to ensure that the risks are acceptably small. 

The geologic evidence of faults, volcanism, uplift, and tectonic extension during the Quaternary 

Period (about 2 million years to present) is considered the most useful means to assessing the 

probability of activity of these factors in the future 

(U.S. Nuclear Regulatory Commission, 1981). 

Tectonic activity in the Basin and Range Province 

is further indicated by historic seismicity and by 

heat flow. 

Seismicity and faulting .-Operational considerations and engineering and construction costs would 

favor locating a repository away from areas of 

major seismic activity. However, engineering design can compensate for potential damage to structures by a certain degree of seismic activity. A 

fault or earthquake near a repository cannot be 

treated as a "failure" of the system and it need 

not result in a degradation of the isolation system 

(Trask, 1982). In some ground-water regimes, 

such movement may have no effect on the existing 

ground-water flow system (Davis, 1980). In other 

ground-water regimes, ruptures may change 

ground-water flow patterns by creating permeable 

zones that result in new flow paths. 

Most repository-breaching and risk-assessment 

alternatives considered in the literature (see for 

example Nuclear Energy Agency, 1980) are for 

repositories in the zone of saturation. If the repository were in the unsaturated zone, where 

drainage from the repository is desirable, a rupture near or in the repository after closure might 

be of minimal significance. A geohydrologic setting 

in the unsaturated zone in which nearby faulting 

and associated subsidence and alluviation enhance 

waste isolation is described by Winograd (1981). 

other groups general y emphasize tectonic stabil- Quaternary volcanism.-U nacceptable risk of volity (see for example, nternational Atomic Energy canic activity at the repository and in the ground9 
water flow paths from the repository to the discharge area need to be avoided. A useful example 

of assessment of volcanic risk was made by Crowe 

and Carr (1980) for a site in southern Nevada on 

the basis of studies characterizing the geology, 

chronology, and tectonic setting of Pliocene and 

Quaternary volcanism in the region. 

Heat flow.-Areas of greater than normal heat 

flow and the occurrence of thermal springs need 

to be evaluated for their significance as indicators 

of relatively shallow igneous activity, upwelling 

from deep ground-water flow sytems, ambient 

temperatures at repository depth, and with regard 

to the effects of heat transfer from waste to host 

rock. Another consideration is that areas with significant heat flow may be subject to subsurface 

exploration for geothermal energy, thereby providing a potential for human intrusion into the repository area. 

GEOMORPHIC PROCESSES AND CLIMATIC CHANGE 

Geomorphic processes and climatic changes are 

important factors where relatively shallow repository environments (150 to 300 meters or 500 to 

1,000 ft) are to be evaluated. Geomorphic processes are of concern because of the potential for 

exhumation of waste by erosion and, conversely, 

the possible benefit of increased burial depth by 

aggradation. Factors such as tectonic stability and 

rates of scarp retreat (Cole and Mayer, 1982), and 

denudation (Schumm, 1963) or aggradation need 

to be considered in evaluation of repository environments. 

Climatic change is a factor to be considered in 

evaluating future geomorphic change and in 

evaluating possible changes in hydrologic conditions that might affect a site. Climatic and associated hydrologic changes extending back to the 

beginning of the Pleistocene Epoch (about 2 million years before present) will be used as a guide 

in evaluating future climatic changes. Therefore, 

the effect of a pluvial climatic cycle (similar to 

those that occurred during the Pleistocene Epoch) 

on surface-water and ground-water levels, length 

of flow paths, and flow times from the reposit~ry 

to the accessible environment need to be colllsidered in evaluating potential repository settings. 

FLOODING 

Flooding as a factor in repository siting includes 

the hazard of flooding of the surface-engineering 

facilities by natural surface runoff and by failure 

of man-made or natural impoundments. This factor 

is site-specific and will not be considered in Province evaluation. Flooding as related to recurrence 

of pluvial lakes, as existed in the Pleistocene 

Epoch, was considered in the previous section. 

NATURAL RESOURCES 

Guidelines discussed heretofore primarily were 

concerned with natural conditions relating to containment and isolation of high-level radioactive 

waste. Non-geologic factors are not addressed, as 

such, in this study. However, the problem of 

human intrusion in the quest for metallic and nonmetallic minerals, hydrocarbon resources, geothermal resources, and water supplies overlaps 

the areas of geohydrologic and nongeohydrologic 

factors. Exploration for resources could result in 

inadvertent human intrusion into the waste repository or into flow paths from the waste (see 

Cameron, 1981). Society can attempt to prevent 

intrusion by institutional control of the affected 

area. Beyond institutional control, documentation 

of the repository for the benefit of future societies 

is considered necessary (Kaplan, 1982). Assessments of natural resources need to be made to 

provide society with the knowledge necessary to 

make decisions about whether or not to dedicate 

a volume of earth, and the contained mineral and 

water resources, to the permanent isolation of 

waste. 

GEOHYDROLOGIC ENVIRONMENTS 

Guidelines discussed in the preceding sections 

consider individual factors as separate entities, 

yet, they are interrelated. To complement the discussion of individual factors, this section illustrates the interaction of the various factors in the 

total geohydrologic environment and their effect 

in providing multiple barriers. The settings are 

hypothetical, but are similar to combinations of 

geologic and hydrologic conditions that exist in the 

Basin and Range Province. For each setting, calculations are made of time of flow from repository 

to discharge area. The calculations include traveltimes through the unsaturated zone, confining 

beds, and aquifers, and consider retardation of 

selected radionuclides by sorption. Because these 

are hypothetical examples, specific aspects are 

highlighted in each setting. The settings were 

selected to illustrate favorable flow times from the 

repository to the discharge area. No attempt is 

10 
TABLE 1.-Values of effective porosity, hydraulic conductivity, and retardation factors used in 

calculating traveltimes. 

[Tc, technetium-99; Sr, strontium-90; Am, americium-243; Pu, plutonium-239] 

Hydraulic Retardation factors 

Water conductivity 

Lithology content (meter per year) 

Tc Sr Am Pu 

Unsaturated zone 

Granite 

Zeolitized tuff 

Densely-welded tuff 

Sandstone 

Basin-fill sediments 

0.005 

.075 

.025 

.005 

.06 

1x10-2 1 

6Xl0-4 1 

6xl0-4 1 

6Xl0-4 1 

1x10-a 1 

1 2 10 

10 lo2 lOS 

2 10 lo2 

2 10 lo2 

2 10 lo2 

Saturated zone 

Granite 

Zeolitized tuff 

Sand, silt, and clay 

Clay and silt 

Dolomite 

Shale 

Shaley limestone 

Quaternary sediments 

Granodiorite 

Sandstone 

Basin-fill sediments 

Ash-flow tuff 

Paleozoic carbonate rocks 

.01 

.15 

.3 

.3 

.01 

.01 

.01 

.3 

.01 

.01 

.3 

.05 

.01 

made to systematically discuss and evaluate all 

other factors in the settings. 

Calculations of traveltime and retardation are 

very conservative; that is, values selected for retardation coefficients are one to two orders of 

magnitude smaller than values commonly reported 

as average; values selected for hydraulic conductivity are larger than values commonly reported 

as average. Consequently, calculated traveltimes 

of a nonreactive chemical constituent, and 

radionuclide traveltimes are much shorter than 

probably exist in the Basin and Range Province. 

The values of hydrologic and retardation factors 

used in calculating water-particle and radionuclide 

traveltime are given in table 1. 

Traveltimes estimated in the settings refers to 

the traveltime of a water molecule or a nonreactive chemical constituent. The following equation 

relates traveltime of water (tw) to effective porosity($), length of flow path (L), hydraulic conductivity (K), and hydraulic gradient (/): 

11 

1 

30 

2x10S 

lxlo2 

lxlOS 

1 

10 

lxlOS 

1 

lxlOS 

1Xl03 

1x10S 

lxlOS 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 2 

10 lo2 

2 10 

10 lo2 

1 2 

10 lo2 

2 10 

2 10 

1 2 

1 2 

2 10 

1 2 

1 2 

cJ>A 

t =--· 

w KI 

10 

lOS 

lo2 

lOS 

10 

lOS . 

lo2 

lo2 

10 

10 

lo2 

10 

10 

(1) 

Retardation refers to the sorption of radionuclides by natural Earth materials in the flow path 

from repository to discharge area. The radionuclides technetium-99, strontium-90, americium243, and plutonium-239 were selected to illustrate 

the retardation effects of sorption radionuclides 

having half-lives from 29 years to 24,000 years. 

Calculations of retardation of these radionuclides 

in the discharge area are based on radionuclide 

half-life, retardation factors for the radionuclides 

of the flow-system media, and water-particle 

traveltime. The retardation factor (K1) is the ratio 

of water velocity to nuclide velocity (Cloninger 

and others, 1980): 

(2) 
where r is the ratio of bulk-rock density to effective porosity, and Kd is the ion-exchange distribution coefficient as defined by: 

Kd =quantity of nuclide in solid phase/mass of solid 

quantity of nuiclide in liqmd phase/volume of liquid 

The traveltime of the radionuclide (tn) is the product of the traveltime of the water and the retardation factor, or: 

Ground water in the playa area is nonpotable; 

granite characteristically yields little water to 

wells or excavations. Assuming conservative values of permeability for materials in the flow path, 

the time of travel from repository A, in the saturated zone in the granite, to the discharge area 

would be about 30,000 years. Sorption of strontium-90, americium-243, and plutonium-239 by minerals in the flow path, principally in the zeolitized 

tuff and clay may effect a traveltime for these 

radionuclides of one to three orders of magnitude 

greater than water-particle traveltime. For repository B, in the unsaturated zone in the granite, 

(3) assuming a recharge rate of 1 millimeter per year 

In the settings described below, the short- to 

intermediate-duration (half-life less than 25,000 

years), sorbed radionuclides strontium-90, 

americium-243, and plutonium-239 decay to very 

small or insignificant concentrations before reaching the discharge area. Technetium-99, which is 

not sorbed and with a very long half-life does not 

decrease significantly in the settings. 

The geohydrologic environment shown in figure 

3 includes a granite cropping out in a range block 

and extending underneath zeolitized-bedded tuff 

and clastic basin fill. The hydraulic gradient is 

2 x 10-2

(about 30 meters per kilometer or 100 ft/mi) 

in the granite outcrop area, and 1 x 10-4 (about 2 

meters per kilometer or 5 ft/mi) in the basin fill. 

SCALE 

METERS FEET 

1000 

7000 

2000 

1000 

5000 1500 

40<10 SAND, SILT 

AND CLAY 

1000 5000 

zooo 

500 

1000 

0 0 

(less than 0.4 in./yr) or less, leach rate of the 

waste would be a very small fraction of the rate 

under saturated conditions, whereas traveltimes 

would be practically the same as from repository 

A. 

Evaluation of repositories in this and other settings would involve consideration of such factors 

as: (1) Possibility of exhumation of the repository 

by slope retreat and denudation, (2) effects of a 

change in length of flow path and a rise in groundwater level on hyraulic gradient, and consequently 

on traveltime, (3) seismic hazard of the site, ( 4) 

possibility of human intrusion into the repository 

and into the flow path from the repository in 

search of mineral resources and water supplies, 

and (5) possibility of disruption of the repository 

or the ground-water flow path by faulting or a 

ARROW(-) INDICATES DIRECTION OF FLOW OF WATER 

0 10 

Altitude above arbitrary datum 

Vertical exaggeration about x5 

15 KILOMETERS 

FIGURE 3.-Section showing geohydrologic setting in granite and basin-fill deposits in a region of interbasin flow. 

12 
volcanic eruption. The retreat from the fault scarp 

indicates that the main fault displacement is not 

recent. However, the trace of the fault needs to 

be investigated for recent movement. 

A setting in a mesa overlying a folded and 

faulted sequence of carbonates, shales, and sandstones of Paleozoic age is shown in figure 4. Depth 

to water is about 700 meters (2,300 ft) below the 

surface of the mesa. A repository in the unsaturated zone could be in a fractured or jointed basalt 

or densely welded tuff, or in a well-sorted sand 

that would provide drainage from the repository 

if recharge from the surface reached the repository. Drainage could be enhanced, if necessary, 

by wells constructed to drain the repository. Isolation of the waste from contact with the water 

could be further aided by capillary barriers 

(Winograd, 1981) constructed around the waste 

package. 

In an arid environment, in which precipitation 

is greatly exceeded by potential evapotranspiration, recharge rates can be expected to be extremely slow or nil. Leaching of the waste 

package, if it occurs, would presumably be at a 

SCAL.E 

METERS FEET 

0000 

7000 

2000 

6000 

5000 1000 

4000 

1000 3000 

zooo 

500 

1000 

0 0 

TUFFACEOUS 

FLL 

DENSELY 

WELDED TUFF 

ZEOLITIZED 

TUFF 

CALCAREOUS 

SANDSTONE 

INSET SHOWING ALTERNATIVE 

TOPOGRAPHIC SETTING IN SIMILAR ROCKS 

significantly slower rate than in the saturated 

zone. However, assuming leaching of the waste 

occurs, a regional flow system in the Paleozoic 

rocks, discharging 75 kilometers (47 mi) away 

from the mesa under an average gradient of 6x 

10-4, would provide a conservatively estimated 

traveltime in the saturated zone of about 20,000 

years from mesa to discharge area. Transport 

time of sorbed radionuclides will be one to three 

orders of magnitude greater because of sorption 

by zeolitized tuff, clayey siltstone, or a lacustrine 

sequence that might overlie the Paleozoic rocks. 

Dilution of the radionuclide concentration would 

be effected by the greater flow volume and dispersion in Paleozoic rocks. As in the previous example, attendant risks of releasing unacceptable concentrations of radionuclides by tectonic hazards, 

climatic change, and human intrusion need to be 

considered. 

A setting in which granite has intruded a folded 

and thrust-faulted sequence of Paleozoic shale, 

sandstone, limestone, siltstone, and gypsum is 

shown in figure 5. The hydraulic gradient is 4 x 

10 -a for the 29 kilometers (18 mi) from the granite 

REPOSITORY 

10 15 KILOMETERS 

IOMILES 

Altitude above arbitrary datum 

Vertical exaggeration about x5 

FIGURE 4.--Section showing geohydrologic setting in volcanic rocks overlying Paleozoic rocks. 

13 
outcrop to the playa where discharge occurs. 

Water in the system is not potable because of excessive concentration of dissolved sulfate derived 

from the gypsum. The traveltime of a water particle from repository A in the shale, or repository 

B in the granite to the playa would be about 

10,000 or 16,000 years respectively. Traveltime of 

strontium-90, americium-243, and plutonium-239 

will be one to three orders of magnitude greater 

than water-particle traveltime because of sorption 

in shale beds along the flow path. Thrust faults 

that cross the ground-water flow path may be 

ground-water conduits or ground-water barriers. 

If the faults have significant permeability, the hydraulic gradient will cause water to move downward along the fault planes. If the faults have little permeability, these faults will impede movement of water to the discharge area. 

As in the previous examples, the factors of 

climatic change, tectonic activity, and human intrusion need to be considered. Human intrusion 

resulting from a search for water supplies is greatly mitigated by the nonpotable quality of the 

water. The suitability of the shale as a host rock 

and the feasibility of constructing a mine in the 

shale is questionable; tests would be needed to determine its homogeneity, permeability, thermal 

conductivity, chemical properties, lithologic continuity and mining properties. 

A setting with repositories in unsaturated basin 

fill (A) and zeolitized tuff (B) is shown in figure 

SCALE 

METERS FEET 

0000 

1000 

2000 

11000 

5000 1000 

SHALEY 4000 LIMESTONE 

KlOO 5000 SANDSTONE 

2000 

•oo 1000 

0 0 

6. Repository A is at a depth of 150 meters (500 

ft) below land surface and about 300 meters (1,000 

ft) above the water table. The region is actively 

undergoing tectonic extension and the basin is aggrading. Seismic activity is greater than normal, 

and there is a Quaternary fault within 1.6 kilometers (1 mi) of the repository. Paleozoic rocks including a regional carbonate aquifer underlie the 

basin fill. Distance from the repository to the discharge area of the carbonate-rock aquifer is 65 

kilometers (40 mi), and the gradient is 6x 104 . In 

the arid climate, the recharge rate is very slow 

to nonexistent. If recharge occurs and the waste 

were leached, a conservative estimate of traveltime of a water particle to the discharge area 

would be about 15,000 years. Time of travel of 

strontium-90, americium-243, and plutonium-239 is 

one to three orders of magnitude greater than 

water-particle traveltime, because of sorption in 

the zeolitized tuff underlying the repository. Also, 

radionuclide concentrations would be decreased 

significantly because of dilution and dispersion in 

the carbonate-rock aquifer. 

The great depth to water and the absence of 

economically mineable resources greatly decrease 

the possibility of human intrusion. Seismic activity 

at the repositories is a concern; however, engineering design of site facilities could mitigate the 

operational problems. Following decommissioning, 

a breach of the repositories by faulting would not 

be unacceptable because it would not significantly 

ARROW(-) INDICATES DIRECTION OF FLOW OF WATER 

10 15 KILOMETERS 

Altitude above arbitrary datum 

Vertical exaggeration about x5 

IOMILES 

FIGURE 5.-Section showing geohydrologic setting in granitic rocks intruding Paleozoic rocks. 

14 
affect radionuclide traveltime to the discharge 

area. The repositories are located in fault blocks 

that will subside during active movement along 

the fault planes. The buffer zones of 200 to 300 

meters (660 to 1,000 ft) will adequately protect 

the repositories from ground-water saturation due 

to possible rise in water level during a pluvial 

cycle and subsidence of the basin block. In a similar geohydrologic setting, based on altitude of 

spring orifices, length of flow path, and transmissivity of the aquifer, and liberal estimates of recharge during the Pleistocene, Winograd and Doty 

(1980) estimated that the rise of water level in 

future pluvials would not likely exceed 30 meters 

(100 ft). Based on rates of movement on faults 

in the Basin and Range Province given by Trask 

(1982), subsidence during 1 million years probably 

would not exceed 100 meters (330ft). 

REFERENCES CITED 

American Physical Society, 1978, Report to the American 

Physical Society by the study group on nuclear fuel cycles 

and waste management: Reviews of Modem Physics, v. 

50, no. 1, pt. II, 184 p. 

SCALE 

METERS FEET 

8000 

7000 

2000 

6000 

•ooo 1000 

4000 WATER 

TABLE 

1000 3000 

2000 

•oo 1000 

0 0 

0 

Bredehoeft, J. D., England, A. W., Stewart, D. B., Trask, 

N.J., and Winograd, I. J., 1978, Geologic disposal of highlevel radioactive wastes- Earth-science perspectives: U. 

S. Geological Survey Circular 779, 15 p. 

Cameron, F. X., 1981, Human intrusion into geologic repositories for high-level radioactive waste-Potential and 

prevention: Radioactive Waste Management, v. 2, no. 2, 

p. 179-187. 

Cloninger, M. 0., Cole, C. R., and Washburn, J. F., 1980, 

An analysis on the use of engineered barriers for geologic 

isolation of spent fuel in a reference salt site repository: 

Richland, Wash., Battelle Memorial Institute, Pacific 

Northwest Laboratory, PNL--3356, 46 p. 

Cohen, B. L., 1982, Effects of ICRP publication 30 and the 

1980 BEIR report on hazard assessments of high-level 

waste: Health Physics, v. 42, no. 2, p. 133-143. 

Cole, K. L., and Mayer, Larry, 1982, Use of packrat middens 

to determine rates of cliff retreat in the eastern Grand 

Canyon, Arizona: Geology, v. 10, no. 11, p. 597--599. 

Crowe, B. M., and Carr, W. J. , 1980, Preliminary assessment 

of the risk of volcanism at a proposed nuclear waste repository in the southern Great Basin: U. S. Geological Survey Open-File Report 80-357, 15 p. 

Davis, S. N., 1980, Hydrogeologic effects of natural disruptive 

events on nuclear repositories: Richland, Wash., Battelle 

Memorial Institute, Pacific Northwest Laboratory, PNL--

2858, 33 p. 

Fenneman, N. M., 1928, Physiographic divisions of the United 

States (3d ed.): Annals of the Association of American 

Geographers, v. 18, no. 4, p. 261-'!53. 

ui 15 KILOMETERS 

IOMILES 

Altitude above arbitrary datum 

Vertical exaggeration about x5 

FIGURE 6.-Section showing geohydrologic setting in basin-fill deposits in a large regional flow system. 

15 
Gera, Ferrucio, 1975, Geochemical behavior of long-lived 

radioactive wastes: Oak Ridge National Laboratory Report ORNL-TM-4481, 95 p. 

Heckman, R. A., Towse, D. F., Isherwood, Dana, Harvey, 

Ted, and Holdsworth, Thomas, 1979, High-level waste repository site suitability study-status report: Lawrence 

Livermore Laboratory, NUREG/CR-0578, UCRL-52633, 

290p. 

International Atomic Energy Agency, 1977, Site selection factors for repositories of solid high-level and alpha-bearing 

wastes in geological formations: Technical Report Series 

no. 177, 64 p. 

Kaplan, M. F., 1982, Archaeological data as a basis for repository marker design: U. S. Department of Energy, Office 

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16 

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i" U.S. GOVERNMENT PRINTING OFFICE1 1984 0-461-431/10077