Saturated Zone Flow and Transport Process Model Report Rev 00, ICN 01

TDR-NBS-HS-000001

August 2000

1. INTRODUCTION 
The U.S. Department of Energy (DOE) is investigating the possibility of using the unsaturated 
zone (UZ) at Yucca Mountain, Nevada as a permanent repository for the disposal of spent 
nuclear fuel and high-level radioactive waste. The acceptability of the potential repository is 
based on the ability of the natural geologic environment and the engineered barrier system (EBS) 
to prevent migration of radionuclides from a repository to the accessible environment in excess 
of regulatory limits. The evaluation of the potential repository must consider the potential 
transport of radionuclides from their introduction at the water table below the repository to a 
hypothetical well located 20 km (12.5 mi), or at an alternative location specified in regulations, 
downgradient from the site. CRWMS M&O (2000c) provide details regarding the location of 
the hypothetical well and the characteristics of the hypothetical receptor, who is an average 
member of the critical group of people assumed to be most at risk in the proposed U.S. Nuclear 
Regulatory Commission (NRC) standard (64 FR 8640), or is the reasonably maximally exposed 
individual in the proposed EPA standard (64 FR 46976). The DOE will also use information 
about the saturated zone to demonstrate compliance with the EPAs proposed groundwater 
standard (64 FR 46976). Under the groundwater contamination scenario, the most likely 
pathway for radionuclides to reach the accessible environment is through the uppermost 
groundwater aquifers below the potential repository. The role of these aquifers, collectively 
referred to as the saturated zone (SZ), is to delay the transport of radionuclides to the accessible 
environment and reduce the concentration of radionuclides before they reach the accessible 
environment. 
The DOE is progressing on an aggressive schedule to complete a Site Recommendation Report 
(SR) if the site is suitable. The SR will document the information considered by the Secretary of 
Energy in deciding whether to recommend the Yucca Mountain site to the President for 
development as a geologic repository for spent nuclear fuel and high-level radioactive waste. 
A series of documents that include the Yucca Mountain Site Description (YMSD) (CRWMS 
M&O 1998d), the Total System Performance Assessment (TSPA), and a set of nine Process 
Model Reports (PMRs) support the SR. The PMRs summarize the technical basis for the process 
models supporting the TSPA. The PMRs are supported by a series of lower-level Analysis 
Model Reports (AMRs). The relationships among these documents are shown schematically 
(Figure 1-1). The nine PMRs encompass the following areas: 
 Integrated Site Model 
 Unsaturated Zone Flow and Transport 
 Near Field Environment 
 EBS Degradation, Flow, and Transport 
 Waste Package Degradation 
 Waste Form Degradation 
 Saturated Zone Flow and Transport 
 Biosphere 
 Disruptive Events. 
The PMRs contain a summary and synthesis of the detailed technical information presented in 
the AMRs. This technical information consists of data, analyses, models, software, and

TDR-NBS-HS-000001 REV 00 ICN 01 1-2 August 2000 
documentation that will be used to demonstrate the applicability of each process model report 
(PMR) for its intended purpose of evaluating the postclosure performance of the potential Yucca 
Mountain repository system. The PMR process will ensure the traceability of this information 
from its source, through the AMRs, PMRs, and eventually to how that information is used in the 
TSPA. 
This document is the PMR for the SZ flow and transport model, and hereafter this report is 
referred to as the SZ PMR. The SZ PMR considers important features, events, and processes 
(FEPs) concerning flow and transport through the SZ. The SZ PMR is supported by 13 AMRs 
that cover specific aspects of SZ flow and transport (Table 1-1). Some of these AMRs are, in 
essence, data reports with limited in-depth analysis; others primarily discuss development and 
documentation of computer models; and the remainder document Performance Assessment (PA) 
abstraction of the models for subsequent use in the YMSD and TSPA. 
Many AMRs 
9 PMRs 
LA 
SR 
YMSD TSPA 
Figure 1-1. Conceptual Relationships Among the Analysis Model Reports, Process Model Reports, and 
Other Higher-Level Yucca Mountain Site Characterization Project Documents

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Table 1-1. Thirteen AMRs Directly Support the Saturated Zone Process Model Report 
AMR Title 
AMR ID 
Number Citation 
PMR 
Section 
Hydrogeologic Framework Model for the Saturated Zone Site- 
Scale Flow and Transport Model 
S0000 USGS 2000a 3.1, 3.2 
Water-Level Data Analysis for the Saturated Zone Site-Scale Flow 
and Transport Model 
S0005 USGS 2000b 3.1, 3.2, 
3.3, 3.4 
Recharge and Lateral Groundwater Flow Boundary Conditions for 
the Saturated Zone Site-Scale Flow and Transport Model 
S0010 CRWMS M&O 1999a 3.1, 3.2 
Modeling Sub Gridblock Scale Dispersion in Three-Dimensional 
Heterogeneous Fractured Media 
S0015 CRWMS M&O 2000i 3.6, 3.7 
Saturated Zone Transport Methodology and Transport 
Component Integration 
S0025 CRWMS M&O 2000j 3.3 
Probability Distribution for Flowing Interval Spacing S0030 CRWMS M&O 2000k 3.6, 3.7 
Saturated Zone Colloid-Facilitated Transport S0035 CRWMS M&O 2000l 3.6, 3.7 
Geochemical and Isotopic Constraints on Groundwater Flow 
Directions, Mixing, and Recharge at Yucca Mountain, Nevada 
S0040 CRWMS M&O 2000m 3.3, 3.4 
Calibration of the Site-Scale Saturated Zone Flow Model S0045 CRWMS M&O 2000n 3.3, 3.4 
Uncertainty Distributions for Stochastic Parameters S0050 CRWMS M&O 2000o 3.6, 3.7 
Input and Results of the Base Case Saturated Zone Flow and 
Transport Model for TSPA 
S0055 CRWMS M&O 2000p 3.6, 3.7 
Features, Events and Processes in SZ Flow and Transport S0075 CRWMS M&O 2000q 1.0 
Unsaturated Zone and Saturated Zone Transport Properties U0100 CRWMS M&O 2000r 3.1, 3.6, 
3.7 
Of the 13 supporting AMRs, three describe components, or sub-process models, of the site-scale 
SZ flow and transport model. These are the AMRs describing the hydrologic framework model 
(USGS 2000a), the SZ transport methodology (CRWMS M&O 2000j), and the calibrated SZ 
flow model (CRWMS M&O 2000n). The hydrologic framework model is a methodology to 
interpolate, extrapolate, and interpret geologic data. The result is a static, three-dimensional 
(3-D) description of the geometry of hydrostratigraphic units within the region of the site-scale 
SZ flow and transport model. The transport methodology is an approach, based on particle 
tracking, to represent advection, dispersion, diffusion, and sorption of radionuclides. Particle 
tracking is superior to finite element methods for this type of analysis because particle tracking 
does not introduce numerical dispersion or dilution of the source-term radionuclide 
concentration. For these reasons, particle tracking is used instead of a finite-element solution of 
an advection-dispersion equation. The calibrated SZ flow model is intended to provide the best 
estimate of SZ groundwater flow that is consistent with available measurements of hydraulic 
head and rock permeability. The remaining 10 PMRs are concerned mainly with data analysis, 
model abstractions, and parameter distributions. 
The basic approach of the SZ PMR is to provide a comprehensive summary of the SZ flow and 
transport issues that are discussed in the supporting AMRs. The SZ PMR documents the 
technical basis for evaluations of potential radionuclide migration in the SZ from a potential 
repository at Yucca Mountain. The SZ PMR contains a summary of relevant site 
characterization data, a summary of the hydrological setting, the conceptual model of 
groundwater flow and radionuclide transport based on those data, a description of the resulting

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process-level numerical model, and the TSPA analysis methods utilizing that numerical model. 
These five components of the SZ PMR constitute the logical progression used in the evaluation 
of the SZ system. This PMR also provides an overview of the models that use output from the 
SZ PMR. A high-level summary describes how the SZ PMR relates to technical topics presented 
in other PMRs and relevant Yucca Mountain Site Characterization Project (YMP) documents. In 
addition, references to sites around the world provide important support to views stated in the 
PMR. 
The objective of the TSPA-SR analyses is to represent flow and transport in the SZ as 
realistically as possible. However, defensibility of the assumptions, modeling approach, and 
selection of parameter values was given high priority in developing the site-scale SZ flow and 
transport model for use in TSPA-SR analyses. Consequently, the use of some model 
assumptions or parameter distributions yield model results that show more rapid radionuclide 
transport relative to alternative assumptions or parameter distributions. Conservative bounding 
of other factors was done when there was not enough information or resolution to realistically 
model these factors (Section 3.3.6.4) or when inclusion of a particular process was judged to 
seriously jeopardize the defensibility of the analysis. The resulting potential conservatism in 
simulations of radionuclide transport with the site-scale SZ flow and transport model may be 
embedded in the underlying conceptual model, the numerical implementation of the model, or in 
the uncertainty distributions for parameters used in the TSPA analyses. There is, however, no 
intent or claim that the overall results of the TSPA-SR are more conservative than the best 
estimate of expected behavior of the SZ flow and transport system. 
Conservative model assumptions are sometimes used to simplify models if more complex 
models are not defensible or are not needed. For example, sorption of radionuclides onto the 
surfaces of rock fractures is neglected (Section 3.7.1), transverse dispersion is neglected 
(Section 3.6.3.3.5), and groundwater flow is assumed to instantaneously adjust to a wetter 
climate in the future (Section 3.6.3.3.3). 
There are two ways in which the distribution of a particular parameter is potentially 
conservative. First, the mean of the distribution might be biased such that it results in poorer 
predicted repository performance. This approach is used if an unbiased selection of a mean is 
not defensible. For example, the uncertainty distribution for sorption coefficient values in 
volcanic units was selected from among the distributions defined for vitric, devitrified, and 
zeolitic rock types that constitute the lowest values. Second, the range of a parameter might be 
unrealistically large if the uncertainty for that parameter is large. Consequently, use of values 
from one of the tails of the distribution could result in unrealistically poor estimates of 
performance. Specific discharge is, for example, one parameter with a large range. Calculations 
using values from the fast tail of this distribution could result in unrealistically fast transport of 
radionuclides. 
Since 1983, under authority of the Nuclear Waste Policy Act of 1982, the DOE has been 
investigating a site at Yucca Mountain, Nevada, to determine whether it is suitable for 
development as the nations first repository for permanent geologic disposal of spent nuclear fuel 
and high-level radioactive waste. If the site is found suitable, there is an additional goal of 
licensing, constructing, operating, and closing a high-level waste disposal facility. These 
suitability investigations, referred to as site characterization, have been designed to yield

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information to support a determination of whether there is reasonable assurance that a monitored 
geologic repository constructed at Yucca Mountain would not pose an unreasonable risk to 
public health and the environment. The three main components of site characterization are 
testing, design, and PA. 
In this PMR, details of the SZ modeling efforts are provided. The SZ flow and transport process 
model (i.e., the model rather than the report) describes the movement of contaminants and 
groundwater through the SZ (i.e., in the aquifers below Yucca Mountain) to simulate the 
potential transport and release of radionuclides from a repository. This information is used in PA 
models to predict the possible dose that a receptor (e.g., a hypothetical human who is a member 
of the critical group) might be expected to receive during the postclosure period. 
The relationship among the SZ PMR and the constituent sub-process models, abstraction models, 
and analyses (as applicable) developed under administrative procedure (AP) AP-3.10Q, Analyses 
and Models, is shown schematically in Figure 1-2. As depicted, a set of models and analyses 
provide data and information to the site-scale SZ flow and transport model (a process level 
model). This model, plus additional models and analyses, provide information and data to the 
site-scale SZ flow and transport model for TSPA (the PA Abstraction). Finally, the results of 
this model, plus additional supporting information and the results of other PMRs and AMRs (not 
shown in Figure 1-2), provide data for the TSPA dose calculations, the results of which address 
dose to the accessible environment. 
The SZ PMR is organized as follows (Table 1-2): 
Chapter 1. Description of the objectives and scope of the PMR and the principal factors and 
other factors that were identified in the Repository Safety Strategy (RSS) (CRWMS 
M&O 2000a). The key hypotheses for the PMR are described as well as SZ flow and transport 
issues raised by various overseeing bodies, peer review groups, PA workshops, the NRC, and 
others. Chapter 1 concludes with the Quality Assurance (QA) status and issues regarding the 
data and software used in the supporting AMRs. 
Chapter 2. Evolution of field and laboratory testing, data collection activities, process 
modeling, and TSPA modeling of flow and transport in the SZ at Yucca Mountain. The rationale 
for the evolution of the testing program and the major advances that have been made in modeling 
of the SZ are presented in this section. 
Chapter 3. Main technical information in the SZ PMR. All of the sub-process models that are 
considered in the SZ PMR, and how they are abstracted for use in TSPA, are described and 
summarized in this section. These descriptions and summaries include the site-scale SZ flow 
and radionuclide transport model. In addition, the necessary framework for the models in terms 
of hydrogeological information, conceptual models, and numerical grids are presented in this 
section. 
Chapter 4. Key Technical Issues (KTIs) on SZ flow and transport that have been identified by 
the NRC. Each KTI is identified, and pointers are provided to the relevant sections in the SZ 
PMR where the KTIs are discussed.

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TSPA Dose Calculations 
SZ Sub-Models 
Convolution Integral 
1-D Decay Chain Transport Model 
(Sections 3.6, 3.7) 
Integrated Site Model 
Sub-Model 
Rock Properties 
(Section 1.5) 
Input and Results of the Base Case SZ Flow and Transport Model for TSPA (PA Abstractions) 
Features, Events, and 
Processes (FEPs) 
(Section 1.3) 
Hydrologic Framework Model 
(Sections 3.1, 3.2) 
Geochemical and Isotopic 
Constraints of Groundwater Flow 
Direction, Mixing and Recharge 
(Sections 3.3, 3.4) 
Water Level Data Analysis 
(Sections 3.1, 3.2, 3.3, 3.4) 
Recharge and Lateral Groundwater Flow 
Boundary Conditions 
Sub-Models 
SZ Regional Scale Model (Sections 3.1, 3.2) 
UZ Site-Scale Flow Model (Sections 3.1, 3.2) 
Focused Recharge (Sections 3.1, 3.2) 
Abstraction of Colloid Facilitated Transport 
(Sections 3.6, 3.7) 
Modeling Sub Gridblock Scale Dispersion 
(Sections 3.3, 3.6, 3.7) 
UZ and SZ Transport Properties 
(Sections 3.1, 3.6, 3.7) 
Probability Distribution for Flowing Interval 
Spacing 
(Sections 3.6, 3.7) 
Features, Events, 
and Procesess 
(FEPs) 
(Section 1.3) 
Integrated Site Model 
Sub-Model 
Geologic Framework Model 
(Section 3.0) 
Calibration of the Site-Scale SZ Flow 
and Transport Model 
(Sections 3.3, 3.4) 
SZ Transport Methodology and 
Transport Component Integration 
(Sections 3.3) 
Uncertainty Distribution for Stochastic Parameters 
(Sections 3.6, 3.7) 
Site-Scale SZ Flow and Transport Model (Process Level Model) 
(Sections 3.1, 3.2, 3.3, 3.4) 
Figure 1-2. Relationship Among Saturated Zone Models and Analyses

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Table 1-2. Roadmap for the Saturated Zone Process Model Report 
Information Report Section Cross-Referencing 
Objectives and Scope of the PMR Section 1.1 and 1.2 N/A 
Key Issues for the SZ PMR Section 1.6 Pointers to sections of the PMR for 
detailed discussions. 
Key Issues from NRC, Nuclear Waste 
Technical Review Board (NWTRB), Peer 
Review Groups, and others 
Section 1.6 Pointers to sections of the PMR 
where each issue is discussed. 
Features, Events, and Processes and their 
Screening 
Section 1.3 N/A 
Evolution of Field Testing and Model 
Development 
Section 2 N/A 
Data and Conceptual Models Section 3.1 and 3.2 N/A 
Key SZ PMR Models and Analysis Section 3.3 through 3.7 For each model, data inputs, 
relationships to other models, data 
outputs, and intended uses in TSPA 
are described. 
Alternate Views Section 3.8 N/A 
Key NRC Issues and Subissues Section 4 Pointers to sections of the PMR 
where each issue is discussed. 
Summary and Conclusions Section 5 N/A 
Chapter 5. Summary and conclusions of the SZ PMR. 
Chapter 6. References. 
Appendix A. Issues for SZ flow and transport, including source and PMR approach. 
Appendix B. NRC issue resolution status reports (IRSRs) and KTIs, including IRSR technical 
acceptance criteria. 
1.1 OBJECTIVE 
The main objectives of the SZ PMR are: 
 To synthesize all important data, analyses, model, and model abstractions of flow and 
transport within the SZ in a single document 
 To summarize the development of the site-scale SZ flow and transport model and key 
sub-process models used to analyze the various data sets from the SZ 
 To summarize the abstraction process and results for the site-scale SZ flow and transport 
model used for TSPA. 
The various AMRs supporting this PMR, and the PMR itself, are key documents that the YMP 
will rely upon and reference in the SR.

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1.2 SCOPE 
This section explains the information presented in, and the content of, the SZ PMR. It uses 
flowcharts to show the evolution of information from data to TSPA output and the evolution of 
information within the SZ PMR. The section also describes where to find relevant subject matter 
not included in the SZ PMR. References to related discussions in Chapter 2 are provided. This 
PMR is written for a readership of knowledgeable persons in technical and regulatory fields. 
1.2.1 Scope of the Saturated Zone Flow and Transport Process Model Report 
The purpose of the site-scale SZ flow and transport model is to describe the spatial and temporal 
distribution of groundwater as it moves from the water table below the potential repository, 
through the SZ, and to the point of uptake by the receptor of interest. The SZ processes that 
control the movement of groundwater and the movement of dissolved radionuclides and colloidal 
particles that might be present, and the processes that reduce radionuclide concentrations in the 
SZ, are described. 
Summary information from other PMRs (e.g., the UZ PMR and the Integrated Site Model [ISM] 
PMR), the interface between this PMR and the TSPA document, and the conclusions of this 
PMR are described. The discussion of model inputs and outputs, as implemented in the AMRs, 
is restricted to information needed for the assessment of postclosure performance of the potential 
repository. 
1.2.2 Principal Factors and Other Factors Considered 
The magnitude of the YMP, and the complexities associated with both the natural and 
engineered systems, dictate that the YMP prioritize its activities and focus on the factors most 
important to performance, hereafter named the Principal Factors. The principal factors are 
integral to the potential RSS that supports the postclosure repository safety case. The principal 
factors are those central to determining and demonstrating long-term safety of the repository 
system. In the RSS (CRWMS M&O 2000a), 7 principal factors, and 20 Other Factors of secondorder 
importance, have been identified. The selection of the principal factors was based on 
preliminary TSPA analyses and expert judgement. The 7 principal factors, the 20 other factors, 
and the PMR to which each factor belongs are listed in the RSS (CRWMS M&O 2000a, 
Table 3-1). 
The principal and other factors provided the focus of planning documents in support of the SR 
and license application (LA) decisions discussed in Volume 4 of the Viability Assessment (VA) 
(DOE 1998a). Since the VA, SR work has been underway following the planning documents. 
Four important features of the SZ were identified during the RSS (CRWMS M&O 2000a) 
analyses. For the site-scale SZ flow and transport model, two principal factors (retardation of 
radionuclide and dilution of radionuclide concentrations during migration) and two other factors 
(advective pathways and colloid-facilitated transport) were identified.

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1.2.2.1 Principal Factors 
The principal factors of the post closure case are those central to determining and demonstrating 
long-term safety of the repository system (CRWMS M&O 2000a). The two factors given below 
are the only principal factors relevant to the SZ (CRWMS M&O 2000a, Table 3-1). 
Retardation of Radionuclide MigrationThis factor describes the effect of processes that delay 
the transport of dissolved or colloidal radionuclides in groundwater moving through the volcanic 
aquifers and alluvial valley fill of the SZ. This factor focuses on radionuclides that are important 
to system performance but could experience substantially retarded migration in the SZ. In the 
current approach to the postclosure safety case: 
 The site-scale SZ flow and transport model would be used to estimate advective 
pathways below the water table; in particular, the pathways in the alluvium. 
 Retardation in the SZ would be estimated using the site-scale SZ flow and transport 
model and appropriate input parameters for the radionuclides that may be of particular 
importance to dose but may experience considerable retardation (i.e., neptunium, 
plutonium, and uranium). 
Dilution of Radionuclide Concentrations During MigrationThis factor describes the 
reduction of radionuclide concentration and spreading of the contaminant plume in groundwater 
that occur during transport in the SZ flow system. The dominant processes are dispersion of the 
contaminant plume during migration through heterogeneous media, mixing of groundwater from 
different sources, and dilution during pumping. Dilution during pumping is expected to be the 
most important of these three. The dose rate is estimated assuming a pumping volume based on 
the water use of the hypothetical community defined in applicable regulations as defined in 
proposed 10 CFR 63 (64 FR 8640). 
1.2.2.2 Other Factors 
Advective Pathways in the Saturated ZoneThis factor describes the pathways for water that 
might transport radionuclides in the SZ and includes the pathways through the volcanic aquifers 
and the valley-fill alluvium in Amargosa Valley. In general, the site-scale SZ flow and transport 
model is used to estimate the advective pathways below the water table. 
Colloid-Facilitated Transport in the Saturated ZoneThis factor describes the transport of 
radionuclides sorbed to colloids, in moving groundwater. Preliminary analyses for the VA (DOE 
1998a) indicate that colloid-facilitated transport of plutonium provided an important contribution 
to annual dose, and additional work in this area is underway by the YMP. For the postclosure 
safety case, this evaluation is conducted using simplifications in the representation of colloidfacilitated 
transport of radionuclides. 
1.3 FEATURES, EVENTS, AND PROCESSES 
An initial set of FEPs was developed for the YMP TSPA by combining lists of FEPs identified 
as relevant to the YMP (CRWMS M&O 1999b). This combined list consists of 1,261 FEP 
entries from the Nuclear Energy Agency working group, 292 FEPs from YMP literature and site

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studies, and 82 FEPs identified during YMP project staff workshops. The FEPs were identified 
by a variety of methods including expert judgment, informal elicitation, event tree analysis, 
stakeholder review, and regulatory stipulation. All potentially relevant FEPs have been included, 
regardless of origin. The compilation included the FEP entries and 151 layers, categories, and 
headings, resulting in a list of 1,786 FEPs. This approach led to considerable redundancy in the 
FEP list because the same FEPs frequently are identified by multiple sources, but it also ensures 
that a comprehensive review of narrowly defined FEPs will be performed. 
Each FEP has been classified as either primary or secondary. This classification resulted in the 
identification of 310 primary FEPs for which detailed screening arguments are developed. The 
classification and description of primary FEPs strives to capture the essence of all secondary 
FEPs that map to the primary. Secondary FEPs are either FEPs that are completely redundant or 
that can be aggregated into a single primary FEP. The primary FEPs have been assigned to 
associated PMRs. The assignments were based on the nature of the FEPs so that the analysis and 
resolution for screening decisions reside with the subject-matter experts in the relevant 
disciplines. The resolution of other than system-level FEPs are documented in AMRs prepared 
by the responsible PMR groups. In this section, a summary of the screening decisions associated 
with the FEPs for the SZ PMR group is presented. Details of the screening processes are 
documented by CRWMS M&O (2000q). 
The purpose of FEPs screening is to document and justify the treatment of the primary FEPs 
identified as potentially affecting the SZ. The FEPs that are deemed potentially important to 
repository performance are evaluated, either as components for the TSPA or as separate analyses 
in the AMR. The scope for this activity involves two tasks: 
 Identify FEPs that are considered explicitly in the TSPA (called included FEPs) and 
describe how those FEPs are included in the TSPA. 
 Identify FEPs that do not need to be included in the SZ flow and transport models and 
justify why these FEPs do not need to be included. 
Of the original list of FEPs, 46 primary FEPs were identified as potentially affecting the SZ. The 
approach used for this analysis is a combination of qualitative and quantitative screening. The 
analyses are based on the criteria provided by the NRC in the proposed 10 CFR 63 (64 FR 8640) 
and by the U.S. Environmental Protection Agency in the proposed 40 CFR 197 (64 FR 46976) to 
determine whether or not each FEP should be included in the TSPA. For FEPs that are excluded 
from the TSPA based on NRC or U.S. Environmental Protection Agency criteria, the screening 
argument includes a summary of the basis and results that indicate either low probability or low 
consequence. As appropriate, screening arguments cite work performed outside this activity, 
such as in other AMRs. 
FEPs designated as included are those directly represented in TSPA models and process-level 
models that support TSPA. Therefore, the treatment of these FEPs is described in other sections 
of this document and in the associated AMRs. Twenty-two of the primary SZ FEPs are included 
in the TSPA. Eighteen of the SZ FEPs do not need to be included in the SZ flow and transport 
model based on insignificant consequence. The six remaining FEPs are related to the thermal 
effects of the potential repository on the geosphere, and igneous and tectonic activity. Due to

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their potential impact on the waste package and UZ flow and transport, these six FEPs are 
evaluated in separate PMRs. Some of these FEPs are excluded from the TSPA on the basis of 
low probability of occurrence or insignificant consequence. Others are included in the UZ flow 
and transport models or in the analysis of disruptive events (CRWMS M&O 2000d). 
For example, the probability and potential effects of water table rise on the UZ are evaluated in 
CRWMS M&O (2000b). Because the FEPs related to water table rise are evaluated with respect 
to their effects on UZ flow and transport processes (e.g., shorter travel path through the UZ) it is 
considered appropriate that all potentially significant effects will be represented as variability in 
timing and rate of contaminant transport to the SZ. This would affect the input parameter values 
for the site-scale SZ flow and transport model but would not require alteration of the site-scale 
SZ flow and transport model. 
The primary FEPs identified as potentially affecting SZ flow and transport are listed in 
Table 1-3. This table shows the FEP number, FEP description, screening decision (include, 
exclude, or not include in SZ PMR), and basis for exclusion and non-inclusion decisions. Details 
of the screening processes and arguments and disposition of individual SZ FEPs are discussed in 
CRWMS M&O (2000q). 
Table 1-3. Screening Results for Saturated Zone Features, Events and Processes 
YMP FEP 
Database 
ID Number FEP Description TSPA Screening Decision 
1.2.02.01.00 Additional Fractures Not included in SZ PMR  low consequence 
1.2.02.02.00 Faulting Not included in SZ PMR  low consequence 
1.2.03.01.00 Seismic Activity Not included in SZ PMR  low consequence 
1.2.04.02.00 Igneous Activity Causes Changes to Rock 
Properties 
Not included in SZ PMR - low consequence 
1.2.06.00.00 Hydrothermal Activity Not included in SZ PMR  low consequence 
1.2.09.02.00 Large-Scale Dissolution Not included in SZ PMR  low consequence 
1.2.10.01.00 Hydrologic Response to Seismic Activity Not included in SZ PMR  low consequence 
1.2.10.02.00 Hydrologic Response to Igneous Activity Not included in SZ PMR - low consequence 
1.3.07.01.00 Drought/Water Table Decline Not included in SZ PMR - low consequence 
1.3.07.02.00 Water Table Rise Included changes in flux, other effects not 
included in SZ PMR - assumed low consequence 
1.4.07.01.00 Water Management Activities Included 
1.4.07.02.00 Wells Included 
2.1.09.21.00 Suspension of Particles Larger than Colloids Not included in SZ PMR - low consequence 
2.2.03.01.00 Stratigraphy Included 
2.2.03.02.00 Rock Properties of Host Rock and Other 
Units 
Included 
2.2.06.02.00 Changes in Stress Produce Change in 
Permeability of Faults 
Not included in SZ PMR - low consequence 
2.2.06.03.00 Changes in Stress Alter Perched Water 
Zones 
Not included in SZ PMR - low consequence

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Table 1-3. Screening Results for Saturated Zone Features, Events and Processes (Continued) 
YMP FEP 
Database 
ID Number FEP Description TSPA Screening Decision 
2.2.07.12.00 Saturated Groundwater Flow Included 
2.2.07.13.00 Water-Conducting Features in the Saturated 
Zone 
Included 
2.2.07.14.00 Density Effects on Groundwater Flow 
(Concentration) 
Excluded - low consequence 
2.2.07.15.00 Advection and Dispersion Included 
2.2.07.16.00 Dilution of Radionuclides in Groundwater Included 
2.2.07.17.00 Diffusion in the Saturated Zone Included 
2.2.08.01.00 Groundwater Chemistry/Composition in UZ 
and SZ 
Included 
2.2.08.02.00 Radionuclide Transport Occurs in a Carrier 
Plume in the Geosphere 
Included 
2.2.08.03.00 Geochemical Interactions in the Geosphere Included 
2.2.08.06.00 Complexation in the Geosphere Included 
2.2.08.07.00 Radionuclide Solubility Limits in the 
Geosphere 
Not included in SZ PMR - low consequence 
2.2.08.08.00 Matrix Diffusion in Geosphere Included 
2.2.08.09.00 Sorption in the UZ and SZ Included 
2.2.08.10.00 Colloid Transport in the Geosphere Included 
2.2.08.11.00 Distribution And Release of Nuclides from 
the Geosphere 
Included 
2.2.09.01.00 Microbial Activity in Geosphere Included 
2.2.10.01.00 Repository Induced Thermal Effects in the 
Geosphere 
Not included in SZ PMR - assumed low 
consequence or probability 
2.2.10.02.00 Thermal Convection Cell Develops in SZ Not included in SZ PMR - low consequence 
2.2.10.03.00 Natural Geothermal Effects Included 
2.2.10.06.00 Thermo-Chemical Alteration Included 
2.2.10.07.00 Thermo-Chemical Alteration of the Calico 
Hills Unit 
Not included in SZ PMR - assumed low 
consequence or probability 
2.2.10.08.00 Thermo-Chemical Alteration of the SZ Not included in SZ PMR - assumed low 
consequence or probability 
2.2.10.13.00 Density Driven Groundwater Flow (Thermal) Not included in SZ PMR  assumed low 
consequence 
2.2.11.01.00 Naturally-Occurring Gases in the Geosphere Not included in SZ PMR - low consequence 
2.2.12.00.00 Undetected Features Included 
2.3.02.02.00 Radionuclide Accumulation in Soils Not included in SZ PMR - low consequence 
2.3.11.04.00 Groundwater Discharge to Surface Excluded - low consequence 
3.1.01.01.00 Radioactive Decay and Ingrowth Included 
3.2.07.01.00 Isotopic Dilution Excluded - low consequence

TDR-NBS-HS-000001 REV 00 ICN 01 1-13 August 2000 
1.4 QUALITY ASSURANCE 
Pursuant to evaluations (CRWMS M&O 1999d, 1999e) performed in accordance with QAP-2-0, 
Conduct of Activities (Superceded by AP-2.21Q, Quality Determinations and Planning for 
Scientific, Engineering, and Regulatory Compliance Activities), it was determined that activities 
supporting development of the SZ PMR and its component models and their documentation are 
quality-affecting activities that are subject to the QA requirements of the Quality Assurance 
Requirements and Description (DOE 2000). 
The SZ PMR was prepared in accordance with AP-3.11Q, Technical Reports, and reviewed in 
accordance with AP-2.14Q, Review of Technical Products. The QA procedures under which the 
component AMRs were developed are identified in the respective AMRs and associated planning 
documents. The AMRs were prepared and reviewed in accordance with AP-3.10Q, Analyses 
and Models. This technical product was planned in accordance with AP-2.13Q, Technical 
Product Development Planning, under a document development plan (CRWMS M&O 2000u), 
and in accordance with AP-2.15Q, Work Package Planning Summaries, under four work 
package planning summaries (CRWMS M&O 1999c; 1999f; 1999g; and 1999h). 
This document may be affected by technical product input information that requires 
confirmation. Any changes to the document that may occur as a result of completing the 
confirmation activities will be reflected in subsequent revisions. The status of the input 
information quality may be confirmed by review of the Document Input Reference System 
(DIRS) database. 
1.4.1 Acquired and Developed Data 
The status of the acquired and developed data that support this PMR is included in the supporting 
AMRs and in the DIRS database. The data are incorporated in the Technical Data Management 
System. Data verification and qualification were carried out in accordance with procedures AP- 
3.15Q, Managing Technical Product Inputs, and AP-SIII.2Q, Qualification of Unqualified Data 
and the Documentation of Rationale for Accepted Data. 
This document and its conclusions may be affected by technical product input information that 
requires confirmation. Any changes to this document or its conclusions that may occur as a 
result of completing the confirmation activities will be reflected in subsequent revisions. The 
status of the input information quality may be confirmed by review of the DIRS database. 
1.4.2 Software 
No software codes or routines were used directly in the development of the PMR. However, all 
software codes and routines used in the analyses and models supporting this PMR, and the 
quality status of those codes, are listed in the appropriate AMRs. These codes were managed in 
accordance with AP-SI.1Q, Software Management, or used under Section 5.11 of AP-SI.1Q. 
The primary software codes used in the SZ models and analysis are: 
 FEHM (Finite Element Heat and Mass) is used to calculate hydrologic flow and the 
transport of radionuclides, the latter by a particle-tracking algorithm. This software was 
used in CRWMS M&O (2000i; 2000j; 2000n; 2000p).

TDR-NBS-HS-000001 REV 00 ICN 01 1-14 August 2000 
 LaGriT (Los Alamos Grid Toolbox) is used for generating 3-D finite element and finite 
volume meshes. This software was used in CRWMS M&O (2000n). 
 PEST (parameter estimation) is used to perform the parameter optimization for the 
hydrogeologic and feature permeabilities optimization algorithm. PEST is used in 
conjunction with FEHM to produce the calibrated site-scale SZ flow and transport 
model. This software was used in CRWMS M&O (2000n). 
 STRATAMODEL is used to perform 3-D geological modeling. This software was 
used in USGS (2000a). 
 GoldSim is used to perform probabilistic simulations of complex systems such as 
simulating the entire potential repository and natural system for TSPA. Parameter 
definitions and distributions, used as input to the site-scale SZ flow and transport model, 
are simulated using GoldSim. Radionuclide mass breakthrough curves, produced by the 
site-scale SZ flow and transport model, are provided as input to GoldSim to estimate 
radionuclide mass flux at the interface of the SZ and the biosphere. This software was 
used in CRWMS M&O (2000l; 2000o; 2000p). 
1.5 RELATIONSHIP TO OTHER PROCESS MODEL REPORTS AND KEY 
PROJECT DOCUMENTS 
The overall relationship between this SZ PMR and other key project documents is shown in 
Figure 1-1. More specifically, the SZ PMR interfaces directly with three other PMRs: the ISM 
PMR (CRWMS M&O 2000e), the UZ Flow and Transport Model PMR (CRWMS M&O 2000b), 
and the Biosphere PMR (CRWMS M&O 2000c). The SZ PMR summarizes inputs from the ISM 
and UZ PMRs, and discusses outputs of the SZ PMR to the TSPA-SR calculations. In this 
section, a summary-level statement of purpose and a description of each of these PMRs are 
given. In addition, the way in which the SZ PMR interfaces and overlaps with these three PMRs 
is discussed. 
1.5.1 Integrated Site Model Process Model Report 
The ISM PMR (CRWMS M&O 2000e) describes the overall framework for discussing the 
geologic properties (e.g., stratigraphy, structural characteristics, rock properties, and mineralogic 
properties) of the Yucca Mountain site. The ISM, which incorporates three other models, 
merges details of the Yucca Mountain geology into a single model that can be used for 
subsequent simulation (e.g., hydrologic flow and radionuclide transport models) and design of 
the potential repository. The ISM PMR summarizes the outputs that are input to the UZ flow 
and transport model, the SZ flow and transport model, the tectonic hazards analysis, and the EBS 
design. 
The three components of the ISM are the geologic framework model (GFM), the rock properties 
model (RPM), and the mineralogic model (MM). The GFM is a description of the distributions 
of rock layers and faults in the subsurface at Yucca Mountain, and it is the framework into which 
rock properties and mineralogic distributions are placed, and thus serves as the framework of the 
ISM. The GFM is a 3-D interpretation of the geology surrounding the location of the potential

TDR-NBS-HS-000001 REV 00 ICN 01 1-15 August 2000 
repository, an area of 170 km2 (66 mi2) and a volume of 771 km3 (185 mi3) (Figure 1-3). The 
boundaries of the GFM were chosen to encompass a widely distributed set of exploratory 
boreholes and the area of interest for hydrologic flow and radionuclide transport modeling 
through the UZ. The depth of the model is constrained by the estimated depth of the 
Tertiary-Paleozoic unconformity that reaches a depth of 3,962 m (13,000 ft) in the area 
considered by the model. The GFM was constructed primarily from geologic map and borehole 
data, but information from measured stratigraphy sections, gravity profiles, and seismic profiles 
were incorporated where appropriate. The GFM is incorporated into the hydrogeologic 
framework model (HFM) for the site-scale SZ flow and transport model, which encompasses a 
much larger volume than the GFM. The hydrogeologic framework development is discussed in 
the HFM AMR (USGS 2000a). The HFM provides a representation of the spatial distribution of 
hydrologic properties for the 3-D site-scale SZ flow and transport model domain. This 
representation, in turn, is founded on the underlying geologically defined stratigraphic and 
structural framework. 
The RPM is a description of the rock material properties including matrix porosity, whole-rock 
bulk density, matrix-saturated hydraulic conductivity, lithophysal porosity, and whole-rock 
thermal conductivity for most of the stratigraphic intervals described in the GFM. The RPM 
results in a spatial distribution of the rock properties based on the locations and uncertainty in 
measured values within the UZ at Yucca Mountain. Values of matrix porosity and bulk density 
from the RPM are incorporated in the site-scale SZ flow and transport model. 
The MM is a 3-D weighted, inverse distance model that enables project personnel to calculate 
mineral abundance at any position, within any region, or within any stratigraphic unit in the 
model volume to support the analyses of hydrologic properties, radionuclide transport, mineral 
health hazards, potential repository performance, and potential repository design. The MM is 
referenced to the stratigraphic framework defined in the GFM and was developed from 
mineralogic data obtained from boreholes. The MM supports the analyses of hydrologic 
properties, radionuclide transport, mineral health hazards, potential repository performance, and 
potential repository design. 
1.5.2 Unsaturated Zone Flow and Transport Process Model Report 
The UZ flow and transport PMR (CRWMS M&O 2000b) describes the processes affecting the 
amount of water entering and flowing through the UZ above the potential repository, contacting 
wastes in the potential repository, and the movement of water with dissolved radionuclides or 
colloidal particles through the UZ below the potential repository. The purpose of the model is to 
describe the spatial and temporal distribution of water flow through the UZ and the spatial and 
temporal distribution of water seepage into the underground openings of the potential repository. 
The UZ flow and transport PMR also describes inputs from other PMRs and outputs from the UZ 
flow and transport model to the SZ flow and transport model, the EBS design, and the TSPA. 
The emphasis of the discussion of model inputs and outputs is on information needed for the 
assessment of postclosure performance. The SZ flow and transport model receives inputs of 
spatial and temporal distribution of recharge and radionuclide mass from the UZ flow and 
transport model for the purpose of TSPA calculations.

TDR-NBS-HS-000001 REV 00 ICN 01 1-16 August 2000 
Figure 1-3. Domains of the Site-Scale Saturated Zone Flow and Transport Model, the Geologic 
Framework Model, and the Unsaturated-Zone Model

TDR-NBS-HS-000001 REV 00 ICN 01 1-17 August 2000 
Recharge boundary conditions for the SZ model (UZ domain) are specified based on the 
groundwater flux simulated at the base of the UZ model. Coupling of radionuclide transport 
between the UZ and the SZ is accomplished using the convolution integral method. The 
convolution integral method is used to combine the unit breakthrough curves calculated by the 
SZ flow and transport model with the time-varying radionuclide sources from the UZ. 
1.5.3 Biosphere Process Model Report 
The Biosphere PMR (CRWMS M&O 2000c) describes the processes affecting the movement of 
radionuclides after they have been released from the geosphere to the environment. The 
biosphere model describes the lifestyle and habits of individuals living in present-day Amargosa 
Valley and produces dose conversion factors that are used by TSPA to estimate the annual dose 
to which those persons might be exposed. The model considers three basic exposure pathways 
(inhalation, ingestion, and external exposure) by which radionuclides could travel from 
groundwater (via a well that is located 20 km [12.5 mi] from Yucca Mountain) to a receptor. 
Radionuclides considered are those expected to be responsible for contributing the most to 
human dose. The environmental pathways, radionuclide inventory, and unit concentrations 
(1 pCi/L) of these radionuclides are used to calculate biosphere dose conversion factors. 
Biological dose conversion factors based on unit concentrations permit researchers to calculate 
doses expected to be received from any concentration. 
1.5.4 Relationship with Other Key Yucca Mountain Project Documents 
Regulatory requirements and SR/LA design feed the allocation analysis and the RSS (CRWMS 
M&O 2000a). The RSS determines the most important factors (principal factors) that affect 
performance of the potential repository. The RSS provides input to the AMRs and the SZ PMR; 
the AMRs also feed the SZ PMR. The SZ PMR, along with eight other PMRs, provide input to 
the TSPA and the YMSD. 
1.6 ISSUES FOR SATURATED ZONE FLOW AND TRANSPORT 
1.6.1 Summary of Current Understanding of Saturated Zone Flow and Transport at 
Yucca Mountain 
The SZ PMR considers many parameters, processes, and models that describe the flow of water 
and transport of materials from under Yucca Mountain to the proposed compliance boundary in 
the Amargosa Valley. An understanding of SZ flow and transport has been gained through the 
collection of site data and the modeling of relevant processes. Hypotheses that reflect the current 
understanding of some flow and transport features and processes are summarized in Table 1-4, 
and pointers are provided from each statement to the detailed discussions in relevant sections of 
the PMR. The statements listed in the Current Understanding column of Table 1-4 are a 
mixture of observations, hypothesis, and modeling insight and only should be considered brief 
summaries of complex information.

TDR-NBS-HS-000001 REV 00 ICN 01 1-18 August 2000 
Table 1-4. Summary of Hypothesis Concerning Flow and Transport Features and Processes 
Type Current Understanding 
Addressed 
in Section 
Recharge to 
the SZ 
Recharge to the SZ is localized and focused at higher elevations and along 
major surface drainage channels. 
3.1.1.1.2, 
3.1.1.1.3, 
3.2.3.2 
Flow Through 
the Tuff 
Groundwater flow in the volcanic tuffs primarily occurs in fractures and in 
discrete flowing intervals. 
3.2.4.1 
Matrix 
Diffusion in the 
Tuffs 
Matrix diffusion occurs in the volcanic tuffs in which radionuclides can diffuse 
from the fast flowing groundwater in fractures into the stagnant water in the 
matrix. 
3.2.4.2, 
3.3.2, 
3.3.4 
Dispersion in 
the Tuffs 
Transverse dispersion in the volcanic tuffs and alluvium 3.7.2 
Large 
Hydraulic 
Gradient 
The large hydraulic gradient is caused by low-permeability material upgradient 
from Yucca Mountain. 
Alternative view: The large hydraulic gradient is a reflection of perched water 
bodies above the main groundwater system. Regardless of the cause of this 
hydraulic feature, it is represented in the SZ flow and transport model in such a 
way that it represents the measured heads. 
3.2.5.1 
3.2.2.3, 
3.2.5.1 
Role of Faults Faults may be high permeability features that provide a fast flow path. 
Alternatively, faults may have low permeability due to rock alteration or formation 
of gouge. In addition, faults alter the permeability to flow crossing the fault by 
offsetting or juxtaposing hydrostratigraphic units 
3.2.3.4, 
3.2.2.3, 
3.2.2.5 
Horizontal 
Anisotropy 
Horizontal anisotropy in permeability may be caused by the preferential 
orientation of faults and fracture zones. 
3.2.5.3 
Groundwater 
Flow in the 
Alluvium 
The alluvium behaves as a porous medium. Consequently, average flow rates 
are slower than in the tuffs, and more matrix surface area is available for 
sorption. 
3.7.2 
Alluvium in the 
Flow Path 
The flow path from the potential repository transitions from the volcanic tuffs into 
the alluvium 
3.7.2 
Sorption in 
Alluvium 
Laboratory analyses of samples from the alluvium indicate that sorption of some 
radionuclides (neptunium and iodine) is greater in the alluvium than in tuffs. 
3.1.4.1 
Upward 
Hydraulic 
Gradient 
Increasing hydraulic head with depth, which may result into upward flow from the 
Carbonate aquifer to the overlying volcanic aquifers, was documented in UE- 
25P#1 (the deep well) in the Yucca Mountain area. Other wells completed in the 
carbonate aquifer on the Nevada Test Site also have noted the increasing heads 
with depth. The site-scale SZ flow and transport model simulates an upward 
hydraulic gradient in this area. The upward flow will keep the flow paths from the 
potential repository confined to the shallow groundwater at or slightly below the 
water table. 
3.2.2.3, 
3.4.3, 
3.1.2.3 
Sorption in 
Volcanic Units 
Sorption of radionuclides may occur in the matrix of fractured tuffs. 3.2.4.3 
Climate 
Change 
In the future, wetter, glacial climate conditions will result in faster groundwater 
flow in the SZ and higher water table elevations. 
3.2.6 
The YMP has received extensive and detailed input from internal and external peers, experts, and 
oversight groups concerning the credibility and defensibility of the YMP in general and the 
TSPA prepared for the VA (DOE 1998b). Many of the issues concern how the YMP is 
addressing SZ flow and transport (Appendix A). Issues were identified, and a workshop was 
held in February 1999 (Kuzio 1999) to identify how these issues would be addressed in future 
iterations of the TSPA. The YMP also must address the KTIs that have been identified by the 
NRC as the basis for acceptance criteria for a LA. These issues, and others raised at and since

TDR-NBS-HS-000001 REV 00 ICN 01 1-19 August 2000 
the February 1999 workshop, are discussed and identified in the following sections and in 
Appendices A and B. 
1.6.2 Issues from the Total System Performance Assessment-Viability Assessment 
The data and analyses in the TSPA-VA (DOE 1998b) provide part of the information needed to 
evaluate performance of the potential repository. The analyses include an assessment of model 
enhancements and analyses that could improve future assessments of performance of the 
potential repository, including the representation of SZ flow and transport. Issues that were 
identified as having the potential to enhance confidence in the future assessments of SZ flow and 
transport, and suggestions that were made for additional work, are summarized in this section. 
Issues for SZ flow and transport that were recognized in the TSPA-VA (DOE 1998b) include: 
 Data are lacking for the SZ from approximately 10 km (6.2 miles) downgradient from 
the potential repository to 20 km (12.5 miles) downgradient. 
 There is uncertainty about where flow in the shallow SZ enters alluvium along the flow 
path, or even if flow occurs in the alluvium within 20 km (12.5 miles) of the potential 
repository. 
 There are few site-specific data on the hydraulic, mineralogic, or geochemical 
characteristics of the downgradient alluvium. 
 Additional SZ geochemical and isotopic data are needed. 
 Reliable age dating of groundwater is needed along the flow path downgradient from the 
potential repository. 
 Additional oxidation/reduction potential data from the SZ are needed. 
 Additional measurements of hydraulic and transport parameters are needed from 
locations and depths that have not yet been tested. 
 Hydrochemical data are needed from existing boreholes and new Nye County Early 
Warning Drilling Program (NCEWDP) boreholes, and these data need to be 
incorporated into the conceptual and predictive models for SZ processes. 
 Whether sorption onto colloids is reversible or irreversible needs to be evaluated. 
 A 3-D flow model for the SZ is needed. An improved, site-scale flow model should be 
consistent with all available data from the site. 
 Variability and uncertainty should be incorporated in aquifer properties and numerical 
methods for simulating solute transport with minimal numerical dispersion. 
 Uncertainty in the dilution factor for the SZ should be reduced.

TDR-NBS-HS-000001 REV 00 ICN 01 1-20 August 2000 
 SZ modeling should attempt to better reflect climate change (i.e., wetter climates) in the 
Yucca Mountain region. 
 More realistic models of colloid-facilitated transport should be implemented in the SZ 
models, and these models should be tied to site-scale observations of colloidal transport. 
 An improved definition and modeling of the interface between the geosphere and 
biosphere are needed to lend further credibility to the calculations. 
 More information is needed on how pumping from a well could mix contaminated and 
uncontaminated waters (as might storing water from multiple sources in tanks), and how 
these would dilute any contamination. 
 Transport model measurements are needed to support incorporating dispersion, chemical 
retardation, and matrix diffusion resulting from fracture-matrix interaction. 
In the TSPA-VA (DOE 1998b), it was suggested that upon resolution of these issues, the refined 
process models will be adapted for use in the TSPA-SR. The TSPA-VA identified additional 
efforts needed to develop the regional-scale flow model in cooperation with the U.S. Geological 
Survey and DOE/Nevada Operations. Hydrochemical data suggest that the groundwater flux 
beneath Yucca Mountain may be smaller than assumed for present conditions, but this possibility 
has not yet been included. Sorption behavior and chemical precipitation along transport 
pathways with reducing conditions could be quite different from those included in the model, 
and there is some evidence that such conditions exist. The conceptualization of flow in stream 
tubes may not be appropriate, and there is a lack of treatment of matrix diffusion. 
Additional modeling and characterization work was performed to address these issues. The 
site-scale model representing movement of groundwater and transport of radionuclides in the SZ 
has been updated to include the following: 
 Revised regional hydrostratigraphic data from geologic mapping south of Yucca 
Mountain. 
 Hydraulic and transport testing results from previous and planned testing of the 
Bullfrog/Upper Tram and Prow Pass units at the C-wells Complex. 
 Results from hydraulic tests in borehole USW WT-24. 
 Regional hydrochemistry and isotopic data, including apparent groundwater age, 
oxidation/reduction potential, pH, and chemical analyses. 
 Results from the model are abstracted for use in the TSPA and for evaluation of model 
sensitivity and uncertainty. 
 Information from natural and man-made analogs is used to build confidence in models 
of water movement through the SZ at site scale.

TDR-NBS-HS-000001 REV 00 ICN 01 1-21 August 2000 
The regional-scale model of water movement through the SZ is being updated to incorporate the 
following: 
 Revised regional hydrostratigraphic data from geologic mapping south of Yucca 
Mountain 
 Hydrostratigraphy results from the NCEWDP drill holes 
 Hydrostratigraphy results from boreholes at Yucca Mountain and the Nevada Test Site 
Environmental Restoration Program 
 Stratigraphic information obtained from existing geophysical survey data. 
Characterization activities include the Alluvial Test Complex established in cooperation with 
Nye County. Hydraulic and tracer tests are planned at this complex. These tests will be 
designed to evaluate aquifer and transport parameters within the alluvium. Alluvium samples 
recovered from the NCEWDP will be tested to evaluate transport properties and sorption 
coefficient (Kd) values. 
Hydraulic and tracer tests are planned at a site downgradient from the C-wells Complex where 
the water table is within the volcanic aquifer (also downgradient from the potential repository). 
These tests will be designed to evaluate aquifer parameters over a wide area along a flow path 
and obtain effective hydrologic properties averaged over a large volume of rock. Hydraulic and 
tracer tests at this site will continue to experimentally determine whether the total concentration 
of tracers is reduced. These tests will allow a direct measurement of the reduction in 
concentration due to the flow through the volcanic hydrogeological units. 
1.6.3 Issues from the Total System Performance Assessment-Viability Assessment Peer 
Review 
The YMP convened a peer review panel to provide a formal, independent evaluation and critique 
of the TSPA-VA for the potential high-level waste repository at Yucca Mountain (DOE 1998b). 
The objectives of the panel were to describe the technical strengths and weaknesses of the 
TSPA-VA and to provide suggestions for its improvement. The panel issued three interim 
reports prior to the completion of the TSPA-VA and a final report (Budnitz et al. 1999) that was 
based on the completed TSPA-VA (DOE 1998b), its supporting Technical Basis Document 
(CRWMS M&O 1998e), and on documents cited as references to the TSPA-VA. Issues 
developed by the panel regarding SZ flow and transport are tabulated in Appendix A, and the 
sections of this document and other documents that provide information to address these issues 
are identified. 
1.6.4 Issues from the Saturated Zone Flow and Transport Expert Elicitation Project 
The DOE sponsored the SZ Flow and Transport Expert Elicitation Project (CRWMS 
M&O 1998b) and asked experts to characterize the knowledge and uncertainties associated with 
certain key issues related to the SZ system in the Yucca Mountain area and the downgradient 
region. A major goal of the project was to capture the uncertainties involved in assessing the SZ 
flow processes, including uncertainty in models used to represent the physical processes

TDR-NBS-HS-000001 REV 00 ICN 01 1-22 August 2000 
controlling SZ flow and transport, and the parameter values used in the models. To capture a 
wide range of perspectives in the analyses, multiple individual judgments were elicited from 
members of an expert panel. The panel members, experts from within and outside the YMP, 
represented a range of experience and expertise. During the elicitation process, the experts 
identified a range of issues regarding the SZ. These issues are tabulated (Appendix A), and the 
sections of this document and other documents that provide information to address these issues 
are identified. 
1.6.5 Issues from the Advisory Committee on Nuclear Waste 
The NRC established the Advisory Committee on Nuclear Waste to provide independent reviews 
of, and advice on, topics that include disposal of high-level radioactive wastes in geologic 
repositories. Transcripts and summaries of transcripts from Advisory Committee on Nuclear 
Waste meetings for the period from December 1997 to December 1999 were examined to 
identify SZ flow and transport issues. These issues are tabulated in Appendix A, and the sections 
of this document and other documents that provide information to address the concerns are 
identified. 
1.6.6 Issues from the Nuclear Waste Technical Review Board 
The NWTRB was created by Congress in 1987 to review DOE scientific and technical activities 
pertaining to the management and disposal of commercial spent nuclear fuel. The activities 
reviewed include characterizing Yucca Mountain as a potential repository site as well as 
packaging and transporting commercial spent nuclear fuel and defense high-level wastes. 
The NWTRB monitors the YMP to ensure that site characterization is technically sound and 
scientifically credible. The NWTRB reports to Congress on issues involved in characterizing 
Yucca Mountain, and points out the concerns of outside parties that are of interest to the 
scientific community. Transcripts, and summaries of transcripts, from NWTRB meetings, 
NWTRB reports to Congress, and NWTRB letters to the Office of Civilian Radioactive Waste 
Management for the period from December 1997 to December 1999 were examined to identify 
SZ flow and transport issues that were developed during the meetings and provided to the Office 
of Civilian Radioactive Waste Management or Congress. These issues are tabulated in 
Appendix A, and the sections of this document and other documents that provide information to 
address the concerns are identified. 
1.6.7 Issues from the U.S. Nuclear Regulatory Commission 
The NRC has identified KTIs that are considered most important to performance of the potential 
repository. The NRC has developed IRSRs that provide criteria for evaluating each of these 
KTIs. Evaluation of the criteria in these IRSRs indicate that the following KTIs have aspects 
pertaining to SZ flow and transport: 
 Unsaturated and Saturated Flow under Isothermal Conditions 
 Radionuclide Transport 
 Total System Performance Assessment and Integration 
 Structural Deformation and Seismicity.

TDR-NBS-HS-000001 REV 00 ICN 01 1-23 August 2000 
The Issue Resolution Status Report KTI: Unsaturated and Saturated Flow Under Isothermal 
Conditions (NRC 1999a) provides direction concerning NRC expectations for many topics 
related to SZ flow and transport. A detailed listing of the applicable criteria, and pointers to 
sections of this document and other documents that provide information addressing the issues, 
are listed in Appendix B. 
In addition to the criteria in the IRSRs (discussed in detail in Section 4), the NRC provided 
comments (Paperiello 1999) to the DOE on the TSPA-VA. These comments were examined to 
identify additional SZ flow and transport issues developed by the NRC. These issues are 
tabulated in Appendix A, and the sections of this document and other documents that provide 
information to address the concerns are identified.

TDR-NBS-HS-000001 REV 00 ICN 01 1-24 August 2000 
INTENTIONALLY LEFT BLANK

TDR-NBS-HS-000001 REV 00 ICN 01 2-1 August 2000 
2. EVOLUTION OF THE SATURATED ZONE PROCESS MODEL 
In this chapter, the evolution of data-collection activities and the development of models for 
describing the characteristics, understanding the processes, assessing the viability of Yucca 
Mountain as a potential site for a nuclear waste repository, and key issues identified by 
overseeing bodies, peer review groups, and others are summarized. The Yucca Mountain Project 
has evaluated the Yucca Mountain site for over two decades. Data-collection activities have 
evolved from intensive surface-based investigations in the early 1980s to the current focus on 
underground drift tests, the Saturated Zone (SZ) Testing Complex (C-wells Complex), and the 
SZ Alluvial Test Complex. The models have evolved from early conceptual descriptions of the 
site to current site-scale SZ flow and transport model representations. 
In Section 2.1, an overview and discussion of the approach to developing the SZ Process Model 
Report (PMR) are presented. In Section 2.2, specific activities associated with geologic 
mapping, hydrologic studies, geochemical sampling, and hydraulic and tracer testing are 
described. In Section 2.3, the evolution of the SZ flow and transport modeling, and previous 
modeling at the regional, site, and sub-site scales are discussed. In Section 2.4, previous Total 
System Performance Assessment (TSPA) modeling (including previous SZ TSPA abstraction), 
coupling with other components of TSPA, a summary of the TSPA-Viability Assessment (VA) 
modeling results, and improvement to the TSPA-VA model are discussed. In Section 2.5, an 
overview of the current site-scale SZ flow and transport model is presented. 
2.1 OVERVIEW AND DEVELOPMENT APPROACH 
Each PMR describes the information used to develop a process-level model. The PMRs 
summarize the technical bases that support the TSPA model. In this role, the PMRs identify, 
document, and describe the information needed to demonstrate postclosure performance. The 
process used to develop PMRs ensures that each PMR provides transparency and traceability of 
data, information, and references that relate to the process model and support the TSPA. 
The Nuclear Waste Policy Act of 1982 was amended in 1987 to focus effort on the Yucca 
Mountain site. A site characterization plan was completed in 1988 for systematic surface-based 
investigations, underground testing, laboratory testing, and modeling activities (DOE 1988). 
The Yucca Mountain Site Description (CRWMS M&O 1998d) summarizes the results of the site 
characterization program up to 1998. The Viability Assessment of a Repository at Yucca 
Mountain (DOE 1998a) applies the available data to, and discusses the uncertainties in, a TSPA. 
This SZ PMR, together with eight other PMRs and associated analysis and model reports, is 
being developed for updating the TSPA and for supporting the Site Recommendation and 
possibly the License Application (LA) with traceable and verifiable data. The VA and the 
Repository Safety Strategy (CRWMS M&O 2000a) identify four attributes for safe disposal: 
limited water contact with waste package, long waste package life time, low rate of radionuclide 
release from breached waste package, and reduction in radionuclide concentration during 
transport. Retardation of radionuclides and dilution of radionuclide concentrations during 
migration are two principal factors evaluated by this SZ PMR for assessment of the potential 
repository performance and safety. In addition, the SZ PMR includes the SZ flow and transport

TDR-NBS-HS-000001 REV 00 ICN 01 2-2 August 2000 
processes from the water table beneath the potential repository to the accessible environment at 
the proposed compliance boundary. 
2.2 SITE CHARACTERIZATION AND DATA COLLECTION 
Prior to investigations of Yucca Mountain as a potential geologic repository, information on the 
geology and hydrology of the area was limited to surface geologic mapping and hydrologic 
investigations of localized groundwater development areas such as in the Amargosa Desert and 
Oasis Valley (Figure 2-1). The only subsurface information available was from wells J-12 and 
J13, located on the Nevada Test Site (NTS) near Fortymile Wash, that were drilled in the 1960s 
to supply water to NTS facilities in Jackass Flats (Figure 2-2). Most of the hydrologic 
information about the Yucca Mountain site has been obtained from studies conducted 
since 1978. During the first few years of these studies, the emphasis was on describing the 
hydrogeology of the SZ. As additional data became available, consideration was given to 
locating the potential repository within the unsaturated zone (UZ), which became a new focus of 
site characterization activities. 
Beginning in 1981, hydrologic test holes, some as deep as 1.8 km (1.1 mi), were drilled into the 
SZ at Yucca Mountain. The holes were logged to determine lithology and stratigraphy of the 
rocks that were penetrated, and tested to determine hydrologic parameters such as depth to water, 
total water yield, water yield as a function of stratigraphic horizon, hydraulic conductivity, 
transmissivity, water chemistry, and apparent carbon-14 ages of some of the waters. The upper 
kilometer or more of the SZ penetrated by the wells consists of extensively fractured volcanic 
tuffs that appear to derive most of their permeability from fractures rather than from the porosity 
of the matrix. 
The borehole-drilling program at Yucca Mountain originally was designed to systematically 
characterize the subsurface geology and hydrology of the potential repository site area. 
Limitations were imposed by project directives on where boreholes could be drilled and by 
accessibility to drilling equipment. Drilling within the potential repository block was limited. 
Therefore, a plan was devised that would allow for the characterization of the potential 
repository block by constructing boreholes around the periphery of the block. Subsurface 
geologic and hydrologic information from these boreholes would be used to construct cross 
sections to interpret the subsurface geology and hydrology of the potential repository site area. 
Beginning in 1978 with the drilling of borehole UE-25a#1, 33 boreholes have been drilled in the 
Yucca Mountain area that penetrate the SZ; numerous other boreholes terminate in the UZ. The 
borehole designations indicate the general area, purpose of the hole, and general sequence of 
drilling. 
All boreholes were geologically and geophysically logged. The geophysical logs are identified 
in the Yucca Mountain Site Description (CRWMS M&O 1998a, Table 5.3-11). Cores were 
taken continuously or intermittently for laboratory analysis in 20 boreholes. Cores were 
analyzed for bulk density, porosity, particle density, volumetric water content, saturation, water 
potential, and saturated hydraulic conductivity (CRWMS M&O 1998a, Table 5.3-14). 
Groundwater samples were collected from all boreholes and analyzed for major-ion content and 
isotopic content (generally deuterium, oxygen-18, tritium, carbon-13, and carbon-14).

TDR-NBS-HS-000001 REV 00 ICN 01 2-3 August 2000 
Source: Adapted from DAgnese et al. (1997) 
Figure 2-1. Boundaries of the Death Valley Regional Groundwater Flow System, the Regional-Scale 
Flow and Transport Model, the Nevada Test Site, and the Site-Scale Saturated Zone Flow 
and Transport Model 
CLARK 
SAN BERNARDINO 
KERN 
Death Valley 
Regional 
Groundwater 
Flow System 
Site-Scale 
Saturated-Zone 
Flow and 
Transport 
Model 
Regional- 
Scale 
Flow and 
Transport 
Model 
LINCOLN NYE ESMERALDA 
INYO 
35o 
38o 118o 115o 
37o 
36o 
117o 116o 
NEVADA 
TEST 
SITE 
Las Vegas 
NEVADA 
CALIFORNIA 
Universal Transverse Mercator projection, Zone 11. 
Shaded-relief base from 1:250,000-scale Digital Elevation Model; 
sun illumination from northeast at 30 degrees above horizon 
Last Chance 
Range 
Oasis 
Valley 
Yucca 
Flat 
Yucca 
Mountain 
Amargosa 
Valley 
Panamint Range 
Ash Meadows 
Pahrump 
Valley
00034DC-SZ-PMR-33.cdr 
Stonewall 
Flat 
Kawich Range 
Timpahute 
Range 
Pahranagat 
Range 
Sheep Ra 
nge 
Spring Mountains 
V a l l e y 
D e a t h 

TDR-NBS-HS-000001 REV 00 ICN 01 2-4 August 2000 
Source: DAgnese et al. (1997, Figure 2) 
Figure 2-2. Prominent Geographic Features in the Death Valley Regional Groundwater Flow System

TDR-NBS-HS-000001 REV 00 ICN 01 2-5 August 2000 
Recently the county government of Nye County, Nevada carried out additional borehole drilling 
in cooperation with the U.S. Department of Energy (DOE). This drilling program, termed the 
Nye County Early Warning Drilling Program, generally is located along Highway US 95 south 
of Yucca Mountain (Figure 2-3). Although the program still is in progress and data continue to 
be analyzed, some data have been included in Civilian Radioactive Waste Management System 
Management and Operating Contractor reports. Borehole location coordinates and water-level 
measurements are presented in USGS (2000b), chemical analyses are presented in CRWMS 
M&O (2000m), results of hydraulic tests in three boreholes are given in CRWMS M&O (2000n), 
and laboratory-derived transport properties (sorption coefficients and bulk density) are given in 
CRWMS M&O (2000r). 
2.2.1 Hydraulic Testing 
More than 150 individual hydraulic tests have been conducted on boreholes on and around 
Yucca Mountain. Almost all of these were single-borehole tests that were located in specific 
depth intervals and may have included single-well, constantdischarge pumping test; sluginjection 
(falling-head) tests; pressure-injection tests; temperature surveys; and tracer injection 
flow surveys. Multiple-well pumping tests were conducted only at the C-wells Complex 
(Luckey et al. 1996, p. 32). 
2.2.1.1 Single-Borehole Tests 
Transmissivity values were estimated from tests for the hydrogeologic units (upper volcanic 
aquifer, upper volcanic confining unit, lower volcanic aquifer, lower volcanic confining unit, and 
carbonate aquifer), and apparent hydraulic conductivity values were calculated from 
transmissivity. Apparent hydraulic conductivity values were based on reported single-borehole 
hydraulic tests and generally were calculated by dividing the reported transmissivity of the tested 
interval by the saturated thickness in the borehole. Hydraulic conductivity values for individual 
intervals in a borehole could vary by several orders of magnitude depending on whether or not 
water-bearing fractures were present. In intervals that contained no open fractures, hydraulic 
conductivity tended to be low and reflected the hydraulic conductivity of the rock matrix or of 
small fractures. In intervals that contained water-bearing fractures, the apparent hydraulic 
conductivity values may be somewhat misleading. Most, if not all, of the water produced in such 
an interval could have been produced by a few thin, highly conductive fractures in an otherwise 
thick, essentially nonproductive rock matrix (Luckey et al. 1996, p. 32). 
Flow surveys were conducted in most of the deeper boreholes at Yucca Mountain. Flow surveys 
are useful to determine the intervals of the borehole, and possibly the fractures, that produce 
water. Most of the flow surveys were conducted using a tool developed for oil-field use that 
releases small quantities of radioactive iodine-131. As the iodine moves up or down the 
borehole, it is sensed by gamma-ray detectors. Most surveys were conducted while water was 
being pumped from, or injected into, the borehole. Static tests also were conducted occasionally. 
Flow surveys are useful in determining the parts of the borehole that produce (or accept) most of 
the flow. This information is useful when subdividing a system into aquifers and confining units 
and for determining the location of, and spacing between, flowing intervals.

TDR-NBS-HS-000001 REV 00 ICN 01 2-6 August 2000 
Source: Nye County Nuclear Waste Repository Project Office (2000) 
Figure 2-3. Nye County Early Warning Drilling Program Boreholes and the C-Wells Complex

TDR-NBS-HS-000001 REV 00 ICN 01 2-7 August 2000 
2.2.1.2 Multiple-Well Tests 
C-Wells ComplexIn 1983 and 1984, three boreholes (UE-25c#1, UE-25c#2, and UE-25c#3; 
collectively called the C-wells Complex) were drilled to conduct aquifer and tracer tests. The 
C-wells Complex is located at the northern end of Bow Ridge on the west side of Midway 
Valley. This complex consists of three orthogonally spaced boreholes that are 30.4 to 76.6 m 
(99.7 to 251.3 ft) apart at the land surface, and each was drilled to a depth of 914 m (3,000 ft). 
Below the water table, which is 400 to 402 m (1,312 to 1,319 ft) deep at the site, the C-wells 
penetrate the Calico Hills Formation, and the Prow Pass, Bullfrog, and Tram Tuffs of the Crater 
Flat Group. 
In 1983 and 1984, 16 falling-head slug tests and 9 pressure-injection tests were conducted in 
UE-25c#1. A constant-head injection test was conducted in UE-25c#2 and was later converted 
into a constant-flux injection test. Two unsuccessful pumping tests were attempted in UE-25c#1. 
One pumping test was conducted in UE-25c#2, and two pumping tests were conducted in 
UE-25c#3. 
Testing resumed in 1995, and hydraulic tests were conducted in May 1995, June 1995, 
February 1996, and May 1996 to November 1997. In all of these tests, borehole UE-25c#3 was 
used as the pumping well, and boreholes UE-25c#1, UE-25c#2, ONC-1, USW H-4, 
UE-25 WT#3, and UE-25 WT#14 were used as observation wells. 
Hydraulic tests conducted at the C-wells Complex from 1995 to 1997 were designed to: 
 Confirm the results of the 1983 to 1984 tests 
 Determine hydraulic properties on a larger scale 
 Determine hydraulic properties of the six hydrogeologic intervals in the C-wells 
 Determine hydraulic properties of the composite SZ section in all geological units 
penetrated by the C-wells 
 Determine heterogeneity in the Miocene tuffaceous rocks, including the influence of 
faults, in the area encompassed by the observation wells. 
Additionally, it was hoped that monitoring UE-25p#1 would establish whether the tuffaceous 
rocks are connected hydraulically to the Paleozoic carbonate rocks, a regional aquifer 
(Section 3.2.2.1). The Paleozoic rocks are estimated to be about 455 m (1,495 ft) below the 
bottom of the C-wells. 
In hydraulic tests conducted from 1983 to 1997, the C-wells were either open or contained 
packers to isolate one or more intervals. Intervals to be packed off were determined from flow 
surveys, geophysical logs, and aquifer tests conducted between 1983 and 1995. 
Following the hydraulic test conducted in February 1996, during which quasi-steady-state 
conditions were reached, sodium iodide was injected into borehole UE-25c#2 while UE-25c#3 
continued to be pumped; this was the first conservative tracer test at the C-wells Complex.

TDR-NBS-HS-000001 REV 00 ICN 01 2-8 August 2000 
During hydraulic tests from May 1996 to November 1997, additional conservative tracer tests 
and a multi-constituent reactive-tracer test were conducted. The conservative tracer tests began 
concurrently in January 1997 and concluded when pumping stopped in November 1997. While 
UE-25c#3 was being pumped to maintain a quasi-steady-state hydraulic gradient, a benzoic acid 
tracer was injected into UE-25c#2, and pyridone was injected into UE-25c#1. 
Breakthrough curves from the conservative tracer tests were fitted to an analytical solution of the 
advection-dispersion-diffusion equation for a homogeneous, isotropic, dual-porosity medium; 
and values of porosity and longitudinal dispersivity were calculated. Two porosity values were 
calculated for each tracer test. The first, advective porosity, is attributable to a network of 
continuous and discontinuous fractures, connected by segments of matrix, that forms the flow 
pathway through which tracers move between the injection and recovery wells. The flow 
pathway has high hydraulic conductivity, but low storage attributes. The second porosity value, 
diffusive porosity (also called matrix porosity), is associated with the rock matrix surrounding 
the tracer flow pathway. 
2.2.2 Water Level Monitoring Program 
Drilling for site characterization at Yucca Mountain began in 1978, but the first hydrologic test 
well was completed in 1981. Although water levels were measured as each well was completed, 
water level monitoring, in terms of a long-term water level network, did not begin until the 
initiation of regularly scheduled periodic water level measurements during 1983. Periodic 
measuring of water levels continues through the present and generally is conducted monthly 
using calibrated steel tapes or electronic cable units. The continuous measurement of water 
levels was accomplished using pressure transducers, and water level data was collected every 
hour. Though referred to as continuous measuring of water level data, data loggers were 
programmed to receive transducer pressure hourly. This frequency of data collection is 
sufficient to document daily, monthly, and yearly water level changes and trends. However, to 
detect water level fluctuations due to seismic events, data loggers that record all transducer 
pressure changes were installed in several wells during 1992, and data were collected from these 
wells until 1996. 
Since 1981, water-level data in the Yucca Mountain area have been collected and reported from 
33 wells that monitor 41 depth intervals. Several wells monitor more than one depth interval. 
These intervals are isolated by inflatable packers or cement plugs. 
2.2.3 Data Reduction and Analysis 
Data resulting from the SZ field and laboratory testing program were reduced and analyzed, and 
the results were summarized by Luckey et al. (1996, pp. 16 to 47). These data were collected 
and analyzed to reduce the uncertainties in the conceptual model. The key uncertainties, in 
descending order, include recharge, storage properties of SZ materials, transmissive properties, 
discharge, and hydraulic head (Luckey et al. 1996, p. 53). Details of the data and model 
uncertainties are discussed in Section 3.5.

TDR-NBS-HS-000001 REV 00 ICN 01 2-9 August 2000 
2.2.4 Modeling 
Numerical models have been developed at various scales to simulate groundwater flow in the 
vicinity of Yucca Mountain. As data have been accumulated, and as modeling technology has 
advanced, the models have been refined and improved. Reviews of the principal SZ flow 
modeling efforts are presented in Luckey et al. (1996, pp. 6 to 7) and NRC (1999a, 
Section 4.5.2.14, pp. 141 to 150), and are summarized in Section 2.3. Flow and transport models 
are linked to other process models in a TSPA to construct a computer model for various aspects 
of the potential repository system and the biosphere that are important to an assessment of the 
overall performance of the potential repository system. A summary of previous TSPA modeling 
efforts is provided in Section 2.4. 
2.3 PREVIOUS SATURATED ZONE MODELING 
Yucca Mountain lies within the Death Valley regional flow system (Figure 2-1). Groundwater 
flow models that approximately encompass this entire region or that are of larger extent are here 
termed regional models, whereas groundwater flow models of a sub-region of this area are 
termed sub-regional models. Models encompassing an area of only few hundred square 
kilometers are called local or site models; and those for smaller scale are called sub-site models. 
Boundaries of the regional-scale (DAgnese et al. 1997) and site-scale SZ flow and transport 
models are shown in Figure 2-1. Regional-scale SZ models use a coarser grid to describe the 
flow system parameters and are generally less accurate in predicting the hydraulic head than subregional 
models, but are important in describing the boundary conditions for sub-regional models 
and in understanding the overall hydrological conditions of the area. Local or site models are 
important for making transport calculations because transport depend on fine scale permeability 
variations. 
An overview of regional (Table 2-1), sub-regional (Table 2-2), and site and sub-site (Table 2-3) 
scale models that were used to simulate SZ flow in the Yucca Mountain area is provided, with 
emphasis on the assumptions of each model. The technology of groundwater flow simulation 
has changed since the first flow models were applied at Yucca Mountain. Most of the models 
listed in the tables simulate the Yucca Mountain SZ flow system under present climatic and 
geologic conditions. The models are important because they improve understanding of the flow 
system and parameters of the area. Some of the models are used to investigate changes to the 
water table and hydraulic gradient due to possible climate change or disruptive geologic events. 
Changing climatic conditions may result in a change in the water table beneath Yucca Mountain. 
Possible disruptive geologic (tectonic or volcanic) conditions may result in an increase or 
decrease in the water table. An increase in the water level under Yucca Mountain is of concern 
because it will decrease the UZ barrier between the potential repository and the SZ, and it may 
increase the hydraulic gradient resulting in shorter radionuclide transport times through the SZ to 
the downgradient receptors.

TDR-NBS-HS-000001 REV 00 ICN 01 2-10 August 2000 
Table 2-1. Regional-Scale Saturated Zone Flow Models Encompassing Yucca Mountain 
Area 
Dimension/Model 
Type/Author (year) Assumptions 
Weaknesses/Effects 
Not Considered 
Strengths/Effects 
Considered 
Regional 
NTS 
2-D 
Finite Element 
Waddell (1982) 
Steady-state. 
Confined aquifer. 
Isotropic transmissivity. 
19 transmissivity zones. 
12 fluxes. 
Inaccurate heads at 
eastern Pahute Mesa 
Calibration to minimize 
head residuals. Good 
fit to head data. Fluxes 
computed. Extensive 
sensitivity analysis on 
flux, transmissivity, 
and head. 
Regional 2-D 
Finite Difference 
Rice (1984) 
Steady-state. 
Confined aquifer. 
Potential evapotranspiration 
and actual 
evapotranspiration 
estimates. 
Confined model. 
Not calibrated. 
Few transmissivity 
zones. 
Recharge data 
included. 
Recharge sensitivity 
analysis. 
Regional 
and subregional 
2-D 
Finite Difference 
Ahola and Sagar 
(1992) 
Initial steady-state. 
Free surface. 
Transient climatic changes. 
Conductivity changes due to 
volcanic or tectonic activity. 
Regional hydraulic 
conductivities and zones 
modified from Rice (1984). 
Regional model not 
calibrated (data from 
previous calibrated 
models). 
Scenario recharge 
not based on detailed 
climate analysis. 
First transient analysis. 
Unconfined aquifer 
(free surface). 
Great- 
Basin 
Regional 
Pseudo 3-D 
2-layer 
Prudic et al. (1993) 
Steady-state. 
Confined aquifer. 
97 km2 (37.5 mi2) grid. 
Carbonate aquifer only. 
No over-pumpage. 
Only large features (lakes, 
large rivers) modeled. 
Large scale of limited 
use in Yucca 
Mountain SZ 
modeling. 
May be used to 
examine boundary 
conditions in smaller 
scale models. 
Regional Pseudo-3D 
2-layer with middle 
vertical leakage 
layer 
Finite Difference 
Sinton (1987) 
Steady state. 
Confined aquifer. 
Recharge and discharge 
estimates taken from 
Waddell (1982) and 
Czarnecki and Waddell 
(1984). 
External boundary 
considered no-flow. 
Inflow modeled as 
recharge at external 
nodes. 
Calibration does not 
consider 
transmissivity, or 
recharge residuals 
Most residuals less 
that 15 m (49 ft). 
Regional 3-D 
Finite Difference 
DAgnese et al. 
(1997) 
Steady state. 
Confined aquifer. 
Calibration to head and 
spring flow. 
3 transmissivity layers. 
Temporal pump test 
data not used in 
inversion. 
Few transmissivity 
and recharge zones. 
No spatial 
transmissivity 
geostatistics. 
Use of extensive 
database (geology, 
hydrology, recharge, 
discharge, climate). 
Calibration to heads 
and stream flow. 
Compare conductivity 
to measured data. 
Regional 3-D 
Finite Difference 
DAgnese et al. 
(1999) 
As above, but future (globalwarming) 
and past (fullglacial) 
effects considered. 
As above. As above.

TDR-NBS-HS-000001 REV 00 ICN 01 2-11 August 2000 
Table 2-2. Some Sub-Regional Saturated Zone Flow Models in the Yucca Mountain Area 
Area 
Dimension/Type/ 
Author (Year) Assumptions 
Weaknesses/Effects 
Not Considered 
Strengths/Effects 
Considered 
NTS, 
Pahute 
Mesa to 
Yucca 
Flat 
Pseudo 3-D 
steady-state 
Finite Difference 
Oberlander (1979) 
Steady state. 
x-z cross section with 
correction matrix to adjust 
flow perpendicular to cross 
section 
Difficult to understand 
the results. 
No comparison to 
heads. 
Correction matrix 
concept non-physical. 
Gives general idea of 
flow and connection 
with geology over a 
cross section. 
Subregional 
Yucca 
Mountain 
2-D 
Finite Element 
Czarnecki and 
Waddell (1984) 
Steady state. 
Confined aquifer. 
X-Z cross section with 
correction matrix to adjust 
flow perpendicular to cross 
section. 
Six transmissivity zones. 
Used additional data not 
available in Waddell 
(1982). 
Calibration to head data. 
Some boundary conditions 
based on Waddell (1982). 
Inaccurate heads at 
Franklin Lake Playa 
and in the area north of 
Yucca Mountain. 
Not calibrated to 
recharge, discharge, or 
transmissivity. 
Finite Element model 
(no inactive elements). 
Model calibrated to 
heads. 
Points to data needs in 
Yucca Mountain area. 
Small head residuals. 
Subregional 
2-D 
Finite Element 
Czarnecki (1984); 
also Czarnecki 
(1990) 
As in Czarnecki and 
Waddell (1984). 
Water table simulator. 
Not calibrated to 
recharge, discharge, or 
transmissivity. 
As above. 
Subregional 
2-D 
Finite Element 
unconfined aquifer 
Haws (1990) 
X-Z cross-sectional model 
to understand vertical flow 
along a streamline. 
Intentionally left blank. Shows vertical flow up 
from carbonate aquifer 
and recharge from 
Fortymile wash needed 
to maintain heads at 
Yucca Mountain. 
Regional 
and subregional 
2-D 
Finite Difference 
saturated flow with 
free surface 
Ahola and Sagar 
(1992) 
Initial steady-state. 
Transient climatic changes. 
Conductivity changes due 
to volcanic or tectonic 
activity. 
Regional Hydraulic 
conductivities and zones 
modified from Rice (1984). 
Regional model not 
calibrated (data from 
previous calibrated 
models). 
Scenario recharge not 
based on detailed 
climate analysis. 
First transient analysis. 
Unconfined aquifer 
(free surface).

TDR-NBS-HS-000001 REV 00 ICN 01 2-12 August 2000 
Table 2-3. Site-Scale and Subsite-Scale Saturated Zone Flow Models in the Yucca Mountain Area 
Area 
Dimension/Typ 
e/Author (Year) Assumptions 
Weaknesses/Effects Not 
Considered 
Strengths/Effects 
Considered 
Local 
Yucca 
Mountain 
2-D 
Finite Element 
Barr and Miller 
(1987) 
Local model of site. 
Hand-calibration. 
Model used to investigate 
effect of catastrophic 
changes in leakage and 
hydraulic conductivity on 
flow and transport. 
Difficult to accurately 
model effects with a 2D 
model. 
Model developed before 
the development of a 
geologic framework 
model. 
Faults modeled using 
north-south high 
conductivity zones. 
Performed transport 
computations. 
Subregional 
Coupled 2-D 
Finite Element 
flow and strain 
codes 
Carrigan et al. 
(1991) 
Analysis to determine 
effects of earthquakes and 
volcanism on water table. 
Methodology described in 
a vague manner. 
Details on input 
parameters used in model 
not given. 
Model not calibrated. 
Unconfined flow model 
coupled with induced 
strain and displacement. 
Sub-sitescale 
3-D 
Integrated Finite 
Difference 
Cohen et al. 
(1997) 2-D 
Cross section 
flow simulations 
Steady flow. 
Transport simulated. 
23 vertical layers. 
Fault permeability 
assumptions tested. 
Scale analysis of 
convective heating. 
Faults have uniform 
permeability. 
Boundary conditions 
overconstrained. 
Discretization honors dip, 
thickness, and orientation 
of strata. 
Fault offsets modeled. 
Calibrated to measured 
heads and long-term 
pumping tests. 
Calibrated to water table. 
Most well residuals < 1 m 
(<3 ft) 
Sitescale 
3-D 
Finite Element 
Czarnecki et al. 
(1997) 
Steady state. 
16 zones, 1 low 
conductivity zone to 
simulate a no-flow fault. 
Only minor recharge from 
Fortymile Wash. 
Large permeability 
difference at C-wells 
Complex. 
Calibrated to water table. 
Sitescale 
2-D 
integrated Finite 
Difference 
Lehman and 
Brown (1998) 
Steady state. 
Fault controlled flow. 
Calibrated to water level 
data. 
Alternate Conceptual 
model. 
Assumes fracture 
conduits provide 
dominant flow paths. 
Large fracture volume 
assumed. 
Coarse discretization. 
2-D model. 
Few permeability zones. 
Poor agreement to 
observed temperatures 
along Solitario Canyon 
fault and Paintbrush fault. 
Data supporting wide fault 
zones not presented. 
Boundary conditions overconstrained. 
Permeabilities much 
larger than documented in 
some areas. 
Poor model 
documentation. 
Considers fault controlled 
flow. 
Heat flow modeled. 
NOTE: SZ modeling done in previous TSPA analyses not present 
Oberlander (1979) performed the first numerical modeling of the Yucca Mountain area by 
modeling a two-dimensional (2-D) cross section between Pahute Mesa and Yucca Flat. Flow in 
the unmodeled third dimension was adjusted with a correction matrix. Oberlander (1979) 
estimated the flow rate through Paleozoic rocks beneath Yucca Mountain and found an upper 
bound to the flow from Yucca Flat to Ash Meadows.

TDR-NBS-HS-000001 REV 00 ICN 01 2-13 August 2000 
Waddell (1982) used a 2-D steady-state finite element model to simulate the regional-scale NTS 
groundwater flow in the SZ. The main goals were to estimate flow fields (to be used for 
transport predictions of radionuclides) and to study the effects of model parameters uncertainty 
on these estimates. The model encompassed an area of approximately 175-km by 175-km 
(109 mi by 109 mi) with boundaries along topographic highs to the north and northeast and along 
topographic lows to the southwest. The model was calibrated by adjusting transmissivities, 
recharge, and discharge to minimize the weighted sum of the squared head residuals (observed 
head minus simulated head). Most of the absolute head residuals were less than 30 m (98 ft) in 
the final model. The model estimated recharge in most areas, but considered discharge in the 
Ash Meadows area as a known constant and modeled other areas using a constant head 
condition. The results from this model substantiated conclusions of some earlier conceptual 
models of the site. The model was not accurate in the area of Pahute Mesa, possibly due to 
vertical flow effects. The model was able to identify areas in which hydrologic properties were 
key in defining the flow direction and magnitude of adjacent regions. For example, hydrologic 
properties in the Eleana Formation had a major effect on the flow beneath Timber Mountain and 
Jackass Flats, while hydrologic properties in Fortymile Canyon and Fortymile Wash affected 
fluxes beneath Jackass Flats and Yucca Mountain. Groundwater barriers to the north of Yucca 
Mountain, recharge on Pahute Mesa, and underflow from regions north of the Pahute Mesa had a 
significant impact on the model. The model also identified areas in which Waddell (1982) felt 
that no further study was needed. 
Czarnecki and Waddell (1984) developed a sub-regional model for the area near Yucca 
Mountain that was about one-third of the size of the Waddell (1982) regional-scale model. Some 
of the boundaries coincided with the Waddell (1982) model. On other boundaries, specified 
heads or fluxes were taken from the Waddell (1982) model. The subregional model was used to 
obtain a better understanding of the groundwater flow system beneath Yucca Mountain and for 
later use in determining the change in the hydraulic head due to increased recharge under 
assumed future climatic conditions. The model provided a good match to observed hydraulic 
head data except in areas where vertical flow components were present, such as Franklin Lake 
Playa (located about 8 km (5 mi) west of Ash Meadows) and where there were steep gradients 
such as directly north of Yucca Mountain. This model showed that groundwater tends to flow 
from north to south. In the region of the potential Yucca Mountain repository, groundwater flow 
tends to be southeasterly and then southerly. 
Rice (1984) constructed a 2-D, regional-scale, steady-state model covering an area 
approximately the same as that of more recent model by DAgnese et al (1997). The objectives 
of the model were to understand the distribution of recharge, discharge, and hydraulic head 
within the model area. The hydraulic head distribution obtained from this model generally is in 
agreement with other regional-scale 2-D models. 
Czarnecki (1984) used the Czarnecki and Waddell (1984) 2-D model to assess potential effects 
of changes in future climatic conditions in the area of Yucca Mountain on the water table below 
the potential repository and the surrounding flow field. Czarnecki (1984) found that the 
simulated position of the water table rose by as much as 130 m (426 ft) in response to a 
100 percent increase in precipitation over current conditions. A 100 percent increase in 
precipitation resulted in a factor of 15 increase in the model recharge rate. Czarnecki (1984) 
further found that changes in the flow direction at Yucca Mountain would be small and that the

TDR-NBS-HS-000001 REV 00 ICN 01 2-14 August 2000 
magnitude of the groundwater flux would increase by a factor of 2 to 4 over that found in 
simulations, assuming present-day climate conditions. Czarnecki (1990) also used this model to 
examine water level changes due to pumping wells in Franklin Lake Playa. 
Sinton (1987) modeled the same area as Waddell (1982), but with a quasi-three-dimensional 
(3-D), steady-state, finite-difference model. The two-layer model included a shallow upper layer 
of volcanic, alluvial, and carbonate rock over a deep lower layer of carbonate rock. Vertical 
flow was allowed between layers through a transmissive leaky unit. A sensitivity analysis was 
performed, and the flow system was found to be particularly sensitive to transmissivity values in 
the Crater Flat and Amargosa Desert areas. 
Haws (1990) constructed a 2-D, vertical, steady-state, flow model along an assumed flow line 
extending from Timber Mountain to the north of Yucca Mountain, southward to Alkali Flat 
(Figure 2-2). An objective of this model was to examine vertical flow between the volcanic and 
carbonate aquifers. Results of the model suggest that upward leakage from the deep carbonate 
aquifer to the shallow volcanic aquifer must occur in order to maintain the water table at its 
observed elevation. 
Carrigan et al. (1991) investigated the effects of earthquakes and dike intrusions on water table 
height below Yucca Mountain using a 2-D finite element flow model coupled with a boundary 
element solver used to predict volumetric strain and displacement. The possibility of high 
vertical-permeability anisotropy, and modeling of the UZ, were considered in the model. A 
number of tectonic scenarios were considered and worst-case scenarios produced excursions in 
the water table elevation of less than 20 m (66 ft) (Carrigan et al. 1991, p. 11). The results were 
of similar magnitude to observed excursions after large earthquakes. An earlier study by Barr 
and Miller (1987) examined the effect of increases in vertical leakage (either from the surface or 
from the underlying carbonate aquifer) on flow and transport in the local area surrounding 
Yucca Mountain. 
Ahola and Sagar (1992) studied the effect of increased recharge due to climate change and 
volcanic and tectonic scenarios on the water table level below Yucca Mountain using 
regional-scale and sub-regional models. They used a regional-scale transient 2-D model in 
which the SZ was modeled as a free surface (unconfined aquifer) that covered the same area as 
that of Rice (1984). The parameters were modified to incorporate the coarser grid used by Ahola 
and Sagar (1992). Ahola and Sagar (1992, pp. 6-1, 6-2, and 6-5) found water table increases of 
about 45 m and 87 m (148 ft and 285 ft) resulted from increases in regional recharge by factors 
of 10 and 20, respectively. The transition time to change from the initial steady-state water level 
to the perturbed steady state was about 400 to 700 yrs for these simulations. This time increment 
does not consider the lag time for infiltration through the UZ, which will retard the onset of the 
climate change response and increase the transition time. An approximately linear relation 
between the water level rise and the factor increase in recharge was shown. This study did not 
consider the possibility of additional discharge (due to streams) that was produced by rises in the 
water table or the possibility of increased evaporation, and it was performed before the benefit of 
an extensive climate change analysis was available. 
Ahola and Sagar (1992) also used a sub-regional model to investigate possible changes to the 
water table due to a reduction of hydraulic conductivity produced by an intrusion of a volcanic

TDR-NBS-HS-000001 REV 00 ICN 01 2-15 August 2000 
dike downgradient from the potential repository or by an increase in hydraulic conductivity due 
to increased fracturing of the rock from tectonic activity in the postulated low conductivity 
region north and northeast of the potential repository. These simulations yielded water table 
increases from a few meters to 275 m (902 ft) (Ahola and Sagar 1992). The greatest water table 
rise resulted from a scenario where tectonic activity caused the hydraulic conductivity to increase 
by three orders of magnitude north and northeast of Yucca Mountain. 
Prudic et al. (1993) developed a two-layer, pseudo 3-D, steady-state model of the carbonate rock 
province of the Great Basin (covering much of eastern Nevada and western Utah). This model 
was used to simulate regional-scale flow in the carbonate rocks that, in the vicinity of Yucca 
Mountain, underlie Tertiary volcanic rocks. This model suggests that flow in the carbonates is 
from north to south within the domain of the site-scale SZ flow and transport model. 
DAgnese et al. (1997) developed a three-layer 3-D steady-state flow model of the SZ for the 
Death Valley region. This model incorporated large quantities of data from the Yucca Mountain 
and NTS sites compiled over the past 30 yrs. Geological data, including descriptions of 
important faults, were considered. Ten hydrogeologic units (a hydrologic unit is an area with 
distinct hydrological and geological properties and considerable lateral extent) were described 
for the area. Well logs from over 700 wells and cross sections were used to define a 3-D 
framework model of the individual hydrogeologic units, and a 3-D grid was generated taking 
into account the shape of these units. The numerical model grid consisted of 163 rows, 
153 columns, and 3 layers. The row and column grid dimension was 1,500 m (4,900 ft), and the 
depth to the bottom of each of the three layers was 500 m (1,640 ft), 1,250 m (4,100 ft), and 
2,750 m (9,020 ft), respectively from the water table surface. 
Hydraulic conductivity values were assigned to specific grid blocks in the DAgnese et al. (1997) 
model using data published by Bedinger et al. (1989), and conductivity was assumed to decrease 
with depth. Initial recharge in the area was set using a modification of the Maxey and Eakin 
(1950) method. Discharge due to evapotranspiration at the Death Valley saltpan was modeled 
using a constant head boundary at the southwest boundary. All other boundaries were set as noflow 
except for four locations in the northern part of the bottom model layer. Other sources of 
discharge include springs, wet playas, and irrigation pumpage. Discharge from these areas was 
estimated from available data. During the initial calibration process, hydraulic conductivities 
and recharge parameters were set to four classes for parameter estimation. Nonlinear regression 
was used to adjust uncertain model parameters by minimization of the squared residuals based on 
the difference between the observed and computed spring flows and heads. During calibration, 
the estimated parameter set was expanded to include layer anisotropy in hydraulic conductivity, 
the evapotranspiration rate factor, spring conductance, and groundwater pumpage. The initial 
conceptual model, permeability zone, boundaries, number of conductivity zones, boundary 
conditions, and recharge were changed in the calibration process. 
A map of residuals and weighted head residuals (weighted residuals are the residual weighted by 
the expected error at a location) showed reasonable agreement between computed and measured 
head data in the upper model layer, except in the northwest and northeast portions where data 
were sparse and of poorer quality. In the region extending from the Amargosa Valley to the 
Pahrump Valley, the simulated hydraulic gradient was somewhat higher than the observed 
hydraulic gradient. Most of the computed spring flows were less than the observed flows.

TDR-NBS-HS-000001 REV 00 ICN 01 2-16 August 2000 
However, the overall water balance was comparable to that estimated from data. A parameter 
sensitivity study indicated that flow was most sensitive to the highest recharge zone and the high 
conductivity zones prevalent in the area where wells are concentrated in the upper aquifer layer. 
More recent SZ flow modeling efforts were undertaken to evaluate the impact of long-term 
future climate forecasts on regional flow in the Yucca Mountain area. Analysis by USGS 
(2000b) forecast monsoonal and glacial-transition climates during the next 10,000 years. 
DAgnese et al. (1999) uses the model developed in DAgnese et al. (1997) to evaluate the effect 
of full-glacial and global-warming climates on the regional flow at Death Valley, which includes 
Yucca Mountain. One result of this model was that under the assumption of past (full-glacial) 
climate, the water table rises but maintains a shape similar to that found under present climate 
conditions. Assuming past full-glacial conditions, DAgnese et al. (1999, p. 2) found that 
simulated water levels rose between 60 m (197 ft) and 150 m (492 ft). Assuming future 
global-warming conditions in which atmospheric carbon dioxide doubles, the forecast recharge 
in the Yucca Mountain area was greater than present, but less than the full-glacial model. In this 
case, the simulated water level beneath Yucca Mountain was estimated to rise less than 50 m 
(165 ft). 
A recent study by Czarnecki et al. (1997) uses the 3-D code FEHM (Zyvoloski et al. 1997a) to 
model flow in the SZ at the site scale. The model incorporates 16 zones and is calibrated using 
observed water levels at wells and approximations of the flux at the boundaries. A large gradient 
area at the north of the site is modeled by assuming a barrier of very low conductivity 
perpendicular to the high gradient area. The model boundaries were set to be coincident with 
model elements of DAgnese et al. (1997). This model used a nonlinear regression to estimate 
subsets of parameters. Estimated permeability values differed from those measured values at the 
C-wells Complex, and the groundwater flux at the southern end of the boundary was twice 
(Czarnecki et al. 1997, p. 103) that found in the DAgnese et al. (1997) regional-scale model. 
A sub-site-scale SZ model was used to simulate 3-D steady flow in a 150-km2 (58-mi2) area 
including Yucca Mountain (Cohen et al. 1997). These efforts simulated the detailed geologic 
structure and included major faults as independent elements. The effects of various vertical fault 
property scenarios (for faults in the Bullfrog Tuff) were tested through the transport of a tracer. 
Minimal transverse and vertical dispersion was observed when the faults are assumed to have 
high permeability, and considerable mixing occurred when the faults were assumed to have low 
permeability. A bifurcation of the tracer was observed when the faults were assumed to be 
displacement-only. A scale analysis was performed that showed that natural heat convection in 
high permeability units in the Bullfrog Tuff would occur on the order of 20 yrs, which implies 
that heat flow modeling could be important in transport. Lehman and Brown (1998) developed 
another sub-site-scale model. This 2-D model represents an alternate conceptual view on flow 
through the SZ. The model assumes a high conductivity contrast between wide fault zones and 
matrix rock, and it also assumes that these fault zones are long in extent. As expected under 
these assumptions, water moved quickly through the SZ. 
A large number of viewpoints have been presented by a variety of researchers, agencies, and 
organizations, and many of these viewpoints are represented in the site-scale SZ flow and 
transport model. This diversity of input provided improved understanding of the hydrology of

TDR-NBS-HS-000001 REV 00 ICN 01 2-17 August 2000 
the site and the expected response of the potential repository to varying climate and disruptive 
geologic scenarios. 
2.4 PREVIOUS TOTAL SYSTEM PERFORMANCE ASSESSMENT MODELING 
In this section, a summary of the manner in which the transport of radionuclides in the SZ was 
handled in previous TSPA analyses, and some of the results of those analyses, are presented. 
Implications of the present SZ methodology relative to previous approaches are discussed. 
2.4.1 Total System Performance Assessment Modeling Before the Total System 
Performance Assessment-Viability Assessment 
Initial performance assessments of a potential repository at Yucca Mountain (e.g., Sinnock 
et al. 1984; Sinnock et al. 1986; Barnard and Dockery 1991) either completely ignored or gave 
only cursory attention to the SZ by using simple 1-D approximations to the SZ. At the time, 
estimates of radionuclide transport through the UZ typically were more than 10,000 yrs, while 
the estimates of transport through the SZ were on the order of 1,000 yrs. In addition, the EPA 
radiation protection standard that guided post-closure PA for Yucca Mountain until 1992, 
40 CFR 191 (50 FR 38066), used a metric of cumulative releases of radionuclides to the 
accessible environment over a period of 10,000 yrs. A cumulative release of a radionuclide is 
the total amount of that radionuclide that crosses a boundary over a given time period. The 
proposed boundary to the accessible environment was specified at a location that is 5 km (3 mi) 
from the potential repository, and the area within the boundary was called the controlled area. 
Because the transport time in the UZ appeared to be greater than the regulatory period, and 
because the transport time in the SZ appeared to be small compared to that in the UZ and the 
regulatory period, any need for detailed studies of the SZ were unnecessary. 
For the first TSPA, TSPA-1991 (Barnard et al. 1992, pp. 4.51 to 4.94), it was recognized that fast 
paths might exist through the UZ, and two alternative conceptual models of flow in the UZ were 
used: a model similar to the previous models that described flow predominately in the matrix, 
and a new model (the weeps model) that described flow as occurring predominately in fractures. 
This 2-D fracture-flow model was based on modeling by Czarnecki (1984) and Czarnecki and 
Waddell (1984) and encompassed the controlled area around the potential repository and the 
5-km (3-mi) distance between the potential repository and the accessible environment. 
Boundary conditions for the TSPA model were taken from the Czarnecki (1984) model. 
A particle-tracking method was implemented to determine radionuclide transport times and 
velocities from the potential repository to the accessible environment for a conservative tracer. 
Particles were placed in the footprint of the potential repository (the area in the SZ 
immediately below the potential repository) and transport times to the proposed 5-km (3-mi) 
boundary were determined. Differences in initial position and paths taken produced a 
distribution of transport times. In general, transport in the SZ was in a southeasterly direction 
with transport times varying between 900 and 1,500 yrs (velocities of 3.25 to 5.7 m/yr [10.7 to 
18.7 ft/yr]), and a mean transport of about 1,200 yrs. The results of the 2-D model were 
abstracted for the TSPA-1991 calculations into 1-D, horizontal flow tubes in a single porous 
medium. For the TSPA abstraction, dispersivities were assumed to be log-uniformly distributed 
between 50 m and 500 m (164 ft and 1,640 ft), and porosity was set to 17.5 percent. During the

TDR-NBS-HS-000001 REV 00 ICN 01 2-18 August 2000 
TSPA calculations, the 1-D model was used directly to solve the transport of radionuclides over 
the 5-km (3-mi) distance to the accessible environment. 
By the time of TSPA-1993 (Wilson et al. 1994, pp. 14-4, 14-5; CRWMS M&O 1994, pp. 3-4, 
3-6), it was apparent that an upcoming regulation for a potential repository at Yucca Mountain 
might involve a metric of radiation dose to an individual. Calculation of dose requires a method 
of accurately determining the concentration of radionuclides at the interface of the geosphere and 
biosphere where the biological environment becomes exposed to the contaminants. Cumulative 
releases can be estimated using only the transport times. A 3-D, confined-aquifer model was 
constructed for TSPA-1993 for the expressed purpose of determining whether three dimensions 
were necessary to properly define the SZ flow system. The analysts concluded that 
incorporation of 3-D geologic structures was necessary to match observed hydraulic heads 
(water-table heights) and that geologic structures, to a large degree, determined the direction and 
velocity of groundwater flow. 
For TSPA-1993 (Wilson et al. 1994), as with TSPA-1991 (Barnard et al. 1992), transport and 
velocities were determined by calculating the transport of a conservative tracer from various 
locations in each of the three geologic units that intersected the potential repository footprint to a 
location 5 km (3 mi) downgradient from the potential repository. Porosity was set to 20 percent. 
Two conceptual models were investigated: one that only allowed water to leave and enter the SZ 
domain from the sides (the non-diversionary model), and another that incorporated a drain out of 
the volcanic aquifer (the diversionary model). Results showed significant variability as 
compared to the TSPA-1991 results. Transport times in the SZ for the various conceptual 
models and transport paths ranged from 230 to 1,700 yrs (velocities of 3 to 22 m/yr [10 to 
72 ft/yr]), with averages ranging from 500 to 800 yrs (average velocities of 6 to 10 m/yr 
[20 to 33 ft/yr]). 
For TSPA-1993 (Wilson et al. 1994), the detailed outflow from the UZ transport model was used 
as input to a 1-D, single porosity model. Longitudinal dispersivity was assumed to be uniformly 
distributed between 100 m and 500 m (330 ft to 1,640 ft) to match the distribution of velocities, 
and porosity was kept at 20 percent. Dilution, and thus final concentration, was calculated from 
an estimate of the cross-sectional area of the transport plume at the proposed boundary to the 
accessible environment; the estimate was based on assumed transverse dispersivities and mixing 
depths (typically 50 m [165 ft]), and ranged between 34,000 m2 and 2,200,000 m2 (370,000 ft2 to 
24,000,000 ft2). Climate change was incorporated in TSPA-1993 as a jump from one 
steady-state condition to another. For the SZ, future climate change was approximated by an 
increase in the water table; no changes were made to flow or transport parameters resulting from 
flow through previously unsaturated areas of the formation. A water-table rise of between 50 m 
and 120 m (165 ft to 395 ft) was specified using a uniform distribution. The rise in the 
water-table elevation caused radionuclides in the UZ, but now in the SZ, to be immediately 
introduced to the SZ, resulting sometime later in a pulse of higher releases and doses at the 
accessible environment. Cumulative releases and radiation doses (drinking-water doses only) 
were considered as performance metrics in TSPA-1993 (Wilson et al. 1994). 
For TSPA-1995 (CRWMS M&O 1995), the emphasis was on a more accurate depiction of the 
EBS of the potential repository at Yucca Mountain, and no new modeling of the SZ was 
conducted. Velocities from the TSPA-1993 3-D model (Wilson et al. 1994) were used again in

TDR-NBS-HS-000001 REV 00 ICN 01 2-19 August 2000 
1-D abstractions. A constant longitudinal dispersivity of 500-m (1,640-ft) was assumed. 
Various cross-sectional areas of the contaminant plume were estimated as in TSPA-1993. From 
these cross-sectional areas and the groundwater flux, dilution factors were calculated, and the 
radionuclide concentrations from the 1-D TSPA abstracted model were reduced by these dilution 
factors. In some calculations, additional dilution was assumed for mixing with other 
groundwater basins, and for mixing with uncontaminated water during well withdrawal. As with 
TSPA-1993, water-table rise was taken from a uniform distribution, however, the rise was more 
continuous over time. 
Sensitivity studies were conducted for TSPA-1993 (Wilson et al. 1994) and TSPA-1995 
(CRWMS M&O 1995) to look at how much the uncertainty and variability in parameter 
distributions influenced the uncertainty and variability of the results. Both TSPAs found 
performance of the potential repository to be sensitive to SZ parameters. For the radiation dose 
metric in particular, results were sensitive to parameters influencing radionuclide dilution in 
groundwater. In the simplified TSPA models, these parameters were the groundwater flux and 
the cross-sectional flow area of the contaminant plume (or the dilution factor). In the actual flow 
system, these parameters correspond to groundwater flux, transverse dispersion, transport path 
lengths, and possible well-withdrawal effects. Parameters primarily affecting radionuclide 
transport times (i.e., sorption coefficients and longitudinal dispersion) were found to be of lesser 
importance. 
2.4.2 Total System Performance Assessment-Viability Assessment Modeling 
The TSPA-VA, published in 1998 (DOE 1998a), focused on calculating dose 20 km (12.5 mi) 
downgradient from the potential repository due to changes in DOE guidance that were based 
upon recommendations from the National Research Council (National Research Council 1995). 
A series of abstraction and testing workshops were conducted to compile a prioritized list of 
important technical issues related to flow and transport in the SZ (DOE 1998b, p. 3-138, 
Table 3-19). An expert elicitation also was conducted to obtain opinions from five experts on 
groundwater flow and transport regarding important issues related to the SZ (CRWMS 
M&O 1998b). The approach for conducting the TSPA-VA analysis was based upon input from 
the workshops and the expert elicitation. For the TSPA-VA, numerical simulations were 
performed for the base case, representing the most likely future evolution of the site, and 
sensitivity analyses were performed to study variations of the base case. 
The base case SZ flow and transport component of the TSPA-VA evaluated the migration of 
radionuclides from their introduction at the water table below the potential repository to the 
release point to the biosphere. A hierarchy of models was used to simulate the transport of 
radionuclides in the SZ. Explicit, 3-D modeling was not used to simulate radionuclide 
concentrations because it can generate numerical dispersion, which artificially lowers 
concentration. The TSPA 3-D SZ flow model was used only to determine flowpaths through the 
SZ (DOE 1998b, Section 4.1.12, p. 4-16). The TSPA 1-D SZ transport model (DOE 1998b, 
Section 3.7.2.1, p. 3-139) was developed based on the flowpaths from the 3-D flow modeling 
and used to determine concentration breakthrough curves at a distance of 20 km (12.5 mi) for 
unit releases of radionuclides from six streamtubes (DOE 1998b, Section 4.1.12, p. 4-16). The 
SZ transport component of the analysis was coupled to the transport calculations for the UZ that 
bring contaminants in downward percolating groundwater from the potential repository to the

TDR-NBS-HS-000001 REV 00 ICN 01 2-20 August 2000 
water table (e.g., the spatial and temporal distributions of simulated mass flux at the water table). 
The coupling was accomplished by using the convolution integral method (CRWMS 
M&O 1998e, Section 8.3.4) to combine the unit breakthrough curves calculated by the 
TSPA 1-D SZ transport model with the time-varying radionuclide sources from the UZ. 
Changes in the SZ flow and transport system in response to climatic variations were incorporated 
for the three discrete climate states (dry, long-term average, and superpluvial) considered in the 
other components of the TSPA-VA. Specific discharge and volumetric groundwater flow-rate in 
the SZ streamtubes were scaled in transport simulations to reflect climate state. The SZ transport 
results were linked to the biosphere analysis by the simulated time history, or system response as 
a function of time, of radionuclide concentration in groundwater produced from a hypothetical 
well located at the biosphere interface. The biosphere was assumed to be located 20 km 
(12.5 mi) from the potential repository. Radionuclide concentrations in the hypothetical well 
water were then used in the biosphere component to calculate doses received by the public. 
For the base case, uncertainty in the SZ system was evaluated through Monte Carlo variation in 
the input parameters (Wilson et al. 1994, pp. 3-19 to 3-21) that were used in the TSPA 1-D SZ 
transport model. Primarily, the uncertainty in radionuclide transport parameters was evaluated. 
The TSPA 1-D SZ transport model was used to calculate 101 unit breakthrough curves 
(100 Monte Carlo simulations and the expected-value case). The results of the 1-D SZ transport 
calculations were stored in a library of unit radionuclide concentration breakthrough-curves, 
and for each TSPA-VA realization, a SZ unit breakthrough curve was randomly drawn from the 
library for use in the convolution integral method. 
The convolution integral method (DOE 1998b, p. 3-141) was used in the TSPA-VA calculations 
to determine radionuclide concentrations in the SZ, 20 km (12.5 mi) downgradient of the 
potential repository, as a function of the transient radionuclide mass flux at the water table 
beneath the potential repository. This coupling method made full use of the detailed SZ flow and 
transport simulations for a given realization of the system, but without requiring complete 
numerical simulation of the SZ for the duration of each TSPA-VA realization. The two input 
functions to the convolution integral method are a unit concentration breakthrough curve (in 
response to a step-function mass flux source as simulated by the TSPA 1-D SZ transport model) 
and the radionuclide mass flux history as simulated by the UZ transport model. 
The TSPA-VA sensitivity studies were designed to examine five of the key issues related to 
assumptions about the base case SZ analysis (DOE 1998b, p. 4-2) and the importance of these 
issues with respect to performance of the potential repository. The effects of dilution in the SZ 
and vertical transverse dispersivity were investigated to address concerns from the expert 
elicitation panel. The impact of including heterogeneity and large-scale flow channelization in a 
3-D flow and transport model was studied. A 2-D dual-porosity transport model was used to 
calculate radionuclide concentrations to examine the effects of the two base case assumptions: a 
single continuum and using effective porosity as a surrogate for the matrix diffusion process. 
A study to investigate the effect of calculating a population dose, compared to the dose to an 
individual, was performed for the base case. Finally, alternative conceptual models of colloidfacilitated 
plutonium transport were developed and implemented for sensitivity analysis. 
Colloid-facilitated transport of plutonium in the SZ was simulated based on a conceptual model 
using the assumptions of equilibrium, reversible sorption of plutonium onto colloids, and the

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potential for irreversible sorption of plutonium onto some colloidal particles (DOE 1998b, 
pp. 3-92, 3-99, and 3-104). A large fraction of the plutonium mass released was simulated to 
move assuming chemical equilibrium among dissolved plutonium, plutonium sorbed onto 
colloids, and plutonium sorbed onto the aquifer material (DOE 1998b, pp. 3-140 to 3-141). 
A small fraction of the plutonium mass was simulated to be irreversibly attached onto colloids 
and transported relatively rapidly in the SZ. The relative fraction of plutonium mass that was 
subject to reversible vs. irreversible sorption onto colloids was treated as uncertain and was 
included as a stochastic parameter in the analyses. 
The three alternative climate states considered in TSPA-VA analyses (DOE 1998b, pp. 3-8 
to 3-9) were dry (present-day conditions), long-term average (corresponding to oscillating 
pluvial and glacial conditions), and superpluvial (corresponding to severe glacial conditions). 
An abstraction method for three climate states, as they affect flow and transport in the SZ, was 
developed for use with the convolution integral method. A primary simplifying assumption was 
that groundwater flow in the SZ immediately changed to a new steady state following climate 
change. Changes in the magnitude of SZ groundwater flux were represented, based on results 
from the regional-scale SZ flow model (DAgnese et al. 1997; 1999), by a scaling factor for the 
three climate states. Changes in the volumetric groundwater flow rate through each of the 1-D 
SZ streamtubes for the three climate states were based on the site-scale UZ flow model 
simulations for these climatic conditions. 
Results of the TSPA-VA model may be expressed as dose rates in millirem per year (mrem/yr) at 
a point 20 km (12.5 km) down-gradient from the potential repository (the breakthrough point) for 
the three time periods (104, 105, and 106 yrs) studied. Breakthrough is defined as the first 
appearance of a radionuclide in sufficient quantity to provide a dose of 0.001 mrem/yr. During 
the first 10,000 yrs after emplacement, the only radionuclides expected to reach the biosphere are 
technetium-99, iodine-129, and carbon-14 (DOE 1998b, p. 4-25 and Figure 4-29). The 
breakthrough of technetium-99 is calculated to occur at about 3,500 yrs, while that of iodine-129 
occurs at about 4,200 yrs. Carbon-14 provided a relatively small contribution to dose. High 
solubility and the assumption of no sorption account for the early breakthrough of these 
radionuclides compared to other radionuclides in the inventory over the first 10,000-yr period. 
From 10,000 yrs to 100,000 yrs after emplacement, technetium-99 and iodine-129 continue to 
dominate the dose to about 50,000 yrs, after which neptunium-237 begins to dominate 
(DOE 1998b, Figure 4-16). During this period, breakthrough of neptunium-237 occurs at about 
30,000 yrs. Breakthrough of uranium-234 and plutonium-239 follow at about 50,000 and 
80,000 yrs, respectively (DOE 1998b, Figure 4-16). For the time period from 100,000 to 
200,000 yrs, neptunium-237 dominates the dose (DOE 1998b, Figure 4-21). From about 
200,000 yrs to one million years, neptunium-237 and plutonium-242 dominate the dose rate. 
Notable peaks occur in the results during this last period due to assumed super-pluvial climate 
peaks and large numbers of cladding and no-drip package failures over large time steps in the 
simulations (DOE 1998b, p. 4-50). 
2.5 CURRENT SATURATED ZONE FLOW AND TRANSPORT MODEL 
The current site-scale SZ flow and transport model was developed in support of the upcoming 
TSPA-SR. The current model was built upon the model used for TSPA-VA (DOE 1998b), but 
includes a number of modifications to reflect the current understanding of the SZ flow and

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transport, address deficiencies in the TSPA-VA SZ model that were identified by reviews, and 
incorporate new data collected since TSPA-VA. Changes introduced since the TSPA-VA 
iteration include: 
 All analyses and models were developed under the quality assurance program 
(DOE 2000). 
 Use of a 3-D numerical model to simulate the flow of groundwater and the transport of 
radionuclides. 
 Use of particle tracking methodology (similar to that used in the UZ) to build the 
transport component of the model. This allowed for the elimination of numerical 
dispersion (inherent in finite elements and finite difference numerical method) and the 
solution source size dependence. 
 The site-scale SZ flow and transport model is used to simulate the mass fraction of 
radionuclides delivered to the proposed compliance boundary for TSPA-SR calculations. 
 Use of sub-grid geostatistical and heterogeneity analysis to derive values for transverse 
dispersion. 
 Use of field and laboratory tests (hydraulic and tracer) to establish and confirm the 
conceptual models for radionuclide transport and colloid-facilitated transport and to 
derive parameter values. 
 Use of the regional-scale flow and transport model, the UZ model, and the Integrated 
Site Model to provide the site-scale SZ flow and transport model with boundary 
conditions and other model parameter values. 
 Use of a 500-m (1,640-ft) grid size to simulate flow and transport. 
 Use of a deep bottom boundary (approximately 3,000 m [9,840 ft] deep) that coincides 
with that of the regional-scale model. 
 Use of new hydrogeologic data including the new geologic map and cross section 
published by the U.S. Geological Survey. 
 Use of recently collected hydraulic, geologic, geochemical, and transport data that was 
obtained from Nye County Early Warning Drilling Program Phase-I wells.

TDR-NBS-HS-000001 REV 00 ICN 01 3-1 August 2000 
3. SATURATED ZONE FLOW AND TRANSPORT MODEL AND ABSTRACTIONS 
FOR TOTAL SYSTEM PERFORMANCE ASSESSMENT FOR SITE 
RECOMMENDATION 
The U.S. Department of Energy (DOE) has conducted investigations to characterize and model 
groundwater flow and chemical transport in the vicinity of the potential Yucca Mountain 
repository because groundwater transport is expected to be the main means of radionuclide 
transport from the potential repository to the proposed compliance point. Modeling of 
groundwater flow in the saturated zone (SZ) has been carried out at regional and site scales. The 
regional-scale model (DAgnese et al. 1997), encompassing the Death Valley regional 
groundwater flow system, an area of about 50,000 km2 (19,300 mi2), and the potential repository, 
was developed to model groundwater flow. The site-scale model, encompassing an area of 
1,350 km2 (521 mi2), the potential repository, and the proposed 20 km (12.5 mi) compliance 
point (proposed 10 CFR 63.115(b)(1) [64 FR 8640]), was developed to model groundwater flow 
and chemical transport. 
In this section, the site-scale SZ flow and transport model, abstractions, analyses, uncertainties, 
and limitations of the output are discussed. Discussions are provided concerning 
characterization of SZ flow and transport (Section 3.1); the conceptual model of site-scale flow 
and transport (Section 3.2); mathematical and numerical modeling approach (Section 3.3); model 
validation activities (Section 3.4); assumptions, uses, and limits of the site-scale SZ flow and 
transport model (Section 3.5); synthesis of the site-scale SZ flow and transport model and model 
abstractions (Section 3.6); the site-scale SZ flow and transport base case (Section 3.7); and other 
views and alternative models (Section 3.8). 
3.1 SATURATED ZONE FLOW AND TRANSPORT CHARACTERIZATION 
Discussions in Section 3.1 primarily are focused on historical data collection and 
characterization of groundwater flow and radionuclide transport in the SZ. Descriptions of 
regional and site-scale physiography, climate, soil and vegetation, geology, and groundwater 
flow are provided in Section 3.1.1. Also in this section is a discussion of groundwater chemistry 
at a scale slightly larger than that of the site-scale model domain. Hydrologic data (water levels, 
well testing, and recharge) are summarized in Section 3.1.2. Hydrochemical data pertinent to 
transport (specified patterns, results of tracer test, and oxidation potential) are summarized in 
Section 3.1.3. Laboratory data from sorption, diffusion, and colloidal transport experiments are 
summarized in Section 3.1.4. 
3.1.1 Description of the Saturated Zone System 
The following subsections describe the regional and site-scale geologic setting, hydrologic 
setting, and hydrogeochemistry. The regional description, except for the discussion of 
hydrochemistry, is abstracted from DAgnese et al. (1997). The regional-scale discussion on 
hydrochemistry is based on CRWMS M&O (2000m). 
3.1.1.1 Regional Description 
PhysiographyThe Death Valley Region is situated within the southern Great Basin, a 
subprovince of the Basin and Range physiographic province. Altitudes range from 86 m (282 ft)

TDR-NBS-HS-000001 REV 00 ICN 01 3-2 August 2000 
below sea level at Badwater in Death Valley to 3,600 m (11,800 ft) above sea level at Mount 
Charleston in the Spring Mountains. The relief between valleys and adjoining mountains locally 
exceeds 1,500 m (4,920 ft). Most of the principal mountain ranges have distinct northwestsoutheast 
trends, although the trends of intermediate-scale topographic features are variable. The 
uplands occupy about 25 percent of the landscape in the region, while the remainder of the 
landscape is occupied by broad intermontane basins formed from tectonically down-dropped 
grabens. The basins are filled with alluvium and locally interbedded volcanic deposits. These 
deposits gently slope from the valley floors to the bordering mountain ranges, forming 
piedmonts. 
ClimateThe northern part of the region, including the Cactus, Kawich, and Timpahute Ranges 
(Figure 2-2), is characterized by warm, dry summers and cold, dry winters. The southern part of 
the region, including Death Valley and the Eastern Mojave Desert, is characterized by hot, dry 
summers and warm, dry winters. The central region around the Nevada Test Site (NTS) and 
Yucca Mountain has been called a transition desert, and represents a combination of the two 
climates. The upland areas receive the bulk of the annual precipitation, with mean values 
exceeding 700 mm/yr (28 in./yr) in the Spring Mountains, but the valleys receive much less, with 
a mean annual precipitation in Death Valley of only 50 mm/yr (2 in./yr). Average annual 
lake-evaporation values range from about 1,100 mm (43 in.) in the north to more than 2,000 mm 
(79 in.) in Death Valley (Grasso 1996, Table 8). 
Studies of past climates indicate that in the Death Valley region, climate oscillated between 
glacial and interglacial episodes, although glaciers were limited to colder regions of North 
America. The current climate generally is typical of interglacial periods, although paleoclimate 
records suggest that in the Yucca Mountain region, the present interglacial period is hotter and 
drier than earlier interglacial episodes (DAgnese et al. 1997). In contrast to the current climate, 
periods of more extensive glaciation dominated the climate of North America for most of the 
past 500,000 yrs. Glacial episodes (also termed pluvial episodes south of the glacier border) 
were characterized by wetter and colder conditions than at present, and they prevailed over 
approximately 80 percent of that time. 
The principal effect of a cooler, wetter climate during glacial times on the SZ hydrology was 
increased recharge. This, in turn, resulted in larger gradients of hydraulic head, more total 
groundwater flow, a rise in the water table, and increased surface discharge in the form of 
streams, springs, and wetlands. A variety of physical evidence suggest that the water table in the 
Yucca Mountain region has been up to 120 m (30 ft to 394 ft) higher than the current water table 
(CRWMS M&O 2000w, Table 9.4-1), whether due to climate change or some other cause. 
Conversely, the preponderance of field data suggest that the water table has risen no more than 
120 m (394 ft) above present levels for extended periods of time in the Yucca Mountain area 
since deposition of the volcanic units over 10 my ago (NRC 1999a, p. 30). Similarly, various 
hydrologic models that incorporate climate-induced changes predict that the water table was 
from less than 50 m to 150 m higher than the current water table (CRWMS M&O 2000w, Table 
9.4-2) during the Pleistocene glacial maximum. 
Soil and VegetationIn general, soils of the mountains and hills are shallow, coarse textured, 
and have little moisture-holding capacity. The soils of the alluvial fans on the upper slopes of 
valleys are coarse in texture, but these soils are deeper, and infiltration rates are relatively high.

TDR-NBS-HS-000001 REV 00 ICN 01 3-3 August 2000 
Infiltration rates of the alluvial basin soils are slow because the downward movement of water 
commonly is impeded by indurated calcium carbonate layers (pedogenic carbonate), fine-grained 
playa deposits, and, more commonly, by silicified hardpans that form within the soils over time. 
Vegetation often extracts most of the precipitation before it infiltrates deep enough to become 
recharge. 
3.1.1.1.1 Regional Geologic Setting 
Groundwater flow in the SZ is controlled largely by the distribution of rock types and their 
respective permeabilities and porosities. Structural features such as fractures and faults may act 
as avenues for preferential flow or as barriers to flow. Thus, an adequate understanding of the 
geologic framework is essential to effectively characterize and model groundwater flow and 
radionuclide transport. 
Geologic History and StructureThe Death Valley region primarily consists of Precambrian 
igneous and metamorphic rocks, Paleozoic-Precambrian clastic rocks, Paleozoic carbonate rocks, 
Mesozoic sedimentary and metavolcanic rocks, Tertiary-Late Jurassic granitic rocks, Tertiary 
volcanic and volcaniclastic rocks, Tertiary volcanic rocks, Quaternary-Tertiary volcanic rocks, 
Quaternary-Tertiary valley fill, and Quaternary playa deposits. 
The region has been altered by several episodes of tectonic activity. Combinations of normal, 
reverse, and strike-slip faulting and folding episodes resulted in a complex distribution of rocks. 
In contrast to earlier compressional tectonism, regional uplift, erosion, volcanism, and extension 
occurred in the Tertiary. As a result, the Death Valley region now includes numerous northsouth 
trending valleys containing alluvial, paludal, and colluvial materials that are interstratified 
with volcanic lava flows, tuffs, and tuffaceous sediments. 
HydrostratigraphyDAgnese et al. (1997, pp. 17 to 20) classified the rocks and deposits of the 
Death Valley region into 10 hydrogeologic units (Figure 3-1). These hydrogeologic units have 
considerable lateral extent and reasonably distinct hydrologic properties: 
Quaternary Playa DepositsQuaternary playa deposits are relatively homogeneous deposits 
mainly composed of sand, silt, and clay-sized particles. In some of the valleys, these deposits are 
several hundred meters thick. 
Quaternary-Tertiary Valley FillQuaternary-Tertiary valley fill is a heterogeneous mixture of 
fine-grained playa and lakebed deposits, fluvial deposits, heterogeneous debris flow and fan 
deposits, and volcanic tuffs. In many basins, the valley fill is greater than 1,300 m (4,250 ft) 
thick and may be as thick as 2,000 m (6,550 ft). Valley fill deposits form the major aquifer 
system in many valleys. 
Quaternary-Tertiary Volcanic RocksVolcanic rocks, including lava flows and 
undifferentiated volcanic rocks, underlie the valleys and crop out extensively in many of the 
mountains. The lava flows primarily are basalts, andesites, and rhyolites. Columnar jointing and 
platy fractures are common in the flows, which vary from vesicular to dense. Individual flows 
generally are less than 30 m (98 ft) thick, and some are less than 1 m (3 ft) thick; however, in 
aggregate, these deposits are as much as 1,000 m (3,300 ft) thick.

TDR-NBS-HS-000001 REV 00 ICN 01 3-4 August 2000 
Source: DAgnese et al. (1997, Figure 8) 
Figure 3-1. Hydrogeologic Units in the Death Valley Regional Groundwater Flow System Area

TDR-NBS-HS-000001 REV 00 ICN 01 3-5 August 2000 
Tertiary Volcanic RocksRhyolitic ash-flow tuffs and undifferentiated volcanic rocks underlie 
valleys and crop out extensively in northern and central portions of the Death Valley region, 
including the Yucca Mountain area where tuffs are widespread (Figure 3-1). In aggregate, these 
units are more than 4,000 m (13,000 ft) thick. 
This hydrogeologic unit includes densely welded to nonwelded, bedded, reworked, and air-fall 
tuffs. The commonly moderate to high hydraulic conductivity of welded ash-flow tuffs is largely 
a function of secondary openings along joints, bedding planes, and partings within the flows. 
Where these welded tuffs are not fractured or jointed, they tend to form confining units; thus, 
welded tuffs can only transmit large quantities of water where they are fractured. 
Nonwelded ash-flow tuffs may have a large interstitial porosity; however, they have low 
hydraulic conductivity and function as confining beds. Fractures and joints virtually are absent 
in nonwelded ash-flow tuffs. These nonwelded tuffs, however, have limited spatial extent. In 
the Yucca Mountain area, the Tertiary volcanic rocks include the Timber Mountain and the 
Paintbrush Group down to the base of the Topopah Spring Tuff. 
Tertiary Volcanic and Volcaniclastic RocksThis hydrogeologic unit is composed of tuffs and 
associated sedimentary rocks. These rocks include up to 1,500 m (4,900 ft) of a variety of 
nonwelded to welded ash-flow tuff, ash-fall tuff, tuff breccia, breccia-flow deposits, tuffaceous 
sandstone, siltstone, mudstone, freshwater limestone, and minor amounts of densely welded tuff. 
In the Yucca Mountain area, this unit includes the Calico Hills Formation, Crater Flat Group, 
Lithic Ridge Tuff, and older tuffs, lavas, and breccias. 
Tertiary-Late Jurassic Granitic RocksThis hydrogeologic unit is composed of crystalline 
granitic rocks that are widespread throughout the southern portion of the region, crop out in 
many mountain ranges (Figure 3-1), and underlie most of the southern portion of the region at 
depth. Groundwater is thought to occur in these rocks only where they are fractured, but because 
the fractures are poorly connected, these rocks mostly act as confining units. 
Mesozoic Sedimentary and Metavolcanic RocksThis hydrogeologic unit is composed of 
clastic rocks that predominantly are fluvial, lacustrine, and eolian deposits; and clastic and 
carbonate sedimentary rocks. 
Paleozoic Carbonate RocksThis hydrogeologic unit is composed of limestone, dolomite, and 
calcareous shales that underlie many valleys and crop out in some mountains (Figure 3-1). 
These carbonate rocks, which have aggregate thickness of about 8,000 m (26,000 ft), are 
generally the most permeable rocks in the area. Most of the large springs in the region are 
associated with the carbonate rocks. At the NTS, the Eleana Formation separates the carbonate 
rocks into upper and lower carbonate aquifers. The Eleana Formation, composed mostly of 
relatively impermeable argillites and shales, forms a locally important clastic confining unit. 
Paleozoic-Precambrian Clastic RocksThis hydrogeologic unit is composed of siltstone, 
quartzite, shale, sandstone, and some metamorphic rocks that form clastic confining units. 
Regionally, these rocks vary in aggregate thickness, with maximum thicknesses of about 3,500 m 
(11,500 ft).

TDR-NBS-HS-000001 REV 00 ICN 01 3-6 August 2000 
Precambrian Igneous and Metamorphic RocksThis hydrogeologic unit is composed of 
crystalline metamorphic rocks and igneous rocks that are widespread throughout the southern 
part of the region (Figure 3-1), cropping out in many mountain ranges and underlying most of 
the area at depth. 
3.1.1.1.2 Regional Hydrologic Setting 
A considerable amount of information concerning regional-scale hydrogeology was synthesized 
while conceptualizing and modeling the Death Valley regional groundwater flow system 
(DAgnese et al. 1997). A general understanding of the regional-scale system is important for 
understanding the Yucca Mountain system because the regional-scale system sets the context for 
the site-scale geologic and hydrologic systems. An important aspect of the regional 
hydrogeologic system is that the system occurs in an enclosed basin without any surface or 
subsurface points of discharge to the ocean: all water that naturally leaves the region does so 
exclusively through the processes of evaporation or evapotranspiration. 
Recharge within the Death Valley flow system occurs at high elevations where relatively larger 
amounts of snow and rainfall occur (DAgnese et al. 1997, Figure 25). In the vicinity of Yucca 
Mountain, recharge from precipitation occurs at Timber Mountain, Pahute Mesa, Rainier Mesa, 
Shoshone Mountain, and Yucca Mountain itself (Figure 2-2). Closer to Yucca Mountain, 
infiltration of runoff in Fortymile Canyon and Fortymile Wash contributes recharge to the Death 
Valley flow system (CRWMS M&O 1999a). Groundwater flows through Quaternary, Tertiary, 
and Paleozoic aquifers to discharge areas. Discharge areas for the Death Valley flow system 
include Ash Meadows, Alkali Flat (Franklin Lake Playa), Oasis Valley, and Death Valley (the 
ultimate discharge point for the regional-scale flow system). These and other areas of discharge 
within the regional groundwater system are presented by DAgnese et al. (1997, Figures 23 
to 24). Gradients of hydraulic head (represented by a potentiometric surface map, Figure 3-2) 
determine the flow paths of groundwater as it moves from areas of recharge to areas of 
discharge. Flow paths within the Death Valley regional system are presented by DAgnese 
et al. (1997, Figures 28 to 33). 
3.1.1.1.3 Regional Hydrochemistry 
The application of hydrogeochemical and isotopic chemical methods make it possible to reduce 
some of the uncertainties concerning regional groundwater flow patterns and rates of flow. They 
also provide some bounds on the magnitude and timing of recharge represented by SZ waters. 
The discussion in this section is based on CRWMS M&O (2000m) who considered flow in a 
region about 2.5 times larger than the domain of the site-scale SZ flow and transport model 
(Figure 3-3).

TDR-NBS-HS-000001 REV 00 ICN 01 3-7 August 2000 
Source: DAgnese et al. (1997, Figure 27) 
Figure 3-2. Regional-Scale Potentiometric Surface Map

TDR-NBS-HS-000001 REV 00 ICN 01 3-8 August 2000 
525000 535000 545000 555000 565000 
4030000 
4040000 
4050000 
4060000 
4070000 
4080000 
4090000 
4100000 
5 to 6 
6 to 7 
7 to 8 
8 to 9 
9 to 10 
10 to 12 
12 to 14 
14 to 16 
16 to 18 
18 to 20 
20 to 30 
30 to 50 
50 to 75 
75 to 100 
Chloride (mg/L) 
Site-Model 
Boundary 
UTM-Y (meters) 
UTM-X (meters) 
? 
? 
Path #1 
Path #2 
Path #4 
Path #3 
Path #5
Path #6 
Source: CRWMS M&O (2000m, Figure 17) 
NOTE: Thickness of the flow lines does not indicate confidence interval. 
Figure 3-3. Groundwater Flow Paths Near Yucca Mountain 
The main process that control groundwater chemistry are: 
 Precipitation (atmospheric) quantities and compositions 
 Surface-water quantities and compositions in recharge areas and along stream courses 
 Soil-zone processes in recharge areas and along flow paths between the soil and SZ 
 Rock-water interactions in the unsaturated zone (UZ) 
 Rock-water interactions in the SZ 
 Temperature and pressure effects in the UZ and SZ 
 Mixing of groundwaters from different flow systems.

TDR-NBS-HS-000001 REV 00 ICN 01 3-9 August 2000 
Groundwaters that travel along different pathways can be influenced to differing degrees by 
these various processes. As a result, these groundwaters can attain different chemical signatures 
that reflect their individual histories. Chemical constituents that show the least impact from 
interactions with water and rocks in the UZ and SZ are called conservative constituents. These 
constituents are particularly important with respect to flow path delineation because their 
concentrations primarily reflect inputs and processes that operate in recharge areas. The main 
inputs and processes in recharge areas include precipitation compositions, rates of 
evapotranspiration, and soil zone mineral dissolution and precipitation reactions. Conservative 
constituents for which analytical data are available include chloride, sulfate, fluoride, delta 
deuterium, and delta oxygen-18. None of these species is truly conservative; for example, there 
are potential mineral sources of sulfate in the map area. 
Groundwater FlowpathsSpatial distributions of chemical and isotopic data were used to 
determine (i.e., constrain) flow paths in the region. The analysis determines flow paths by 
connecting upgradient areas that have distinct chemical compositions to downgradient areas that 
have similar chemical compositions (CRWMS M&O 2000m). The map of the potentiometric 
surface was used to guide, but not to determine, the selection of which downgradient areas 
potentially could be linked by a flow path to an upgradient area. Because the flow-path analysis 
assumes that groundwater can be traced in two dimensions, it does not consider the possible 
effects of local recharge and vertical mixing between aquifers. Neglecting the effects of 
recharge and aquifer mixing in this simple two-dimensional (2-D) analysis causes the estimated 
flowpaths to be diverted away from areas where the groundwater composition changes as a result 
of these processes. In reality, recharge and vertical mixing between aquifers also could divert 
groundwater upward or downward beneath the affected areas, as well as laterally away from 
these areas. 
Flow paths can be traced using chemistry and isotopes only where compositional differences 
exist that allow some directions to be eliminated as possible flow directions. Because no single 
chemical or isotopic species varies sufficiently to determine flow paths everywhere in the study 
area, multiple chemical and isotopic species were used to infer flow paths. There are, however, 
anomalies in the chemical composition of waters along the inferred flowpaths. These are 
probably due to the wide range of sampling depths and geologic units. The flow-path analysis 
assumed that the delta deuterium, delta oxygen-18, chloride, sulfate, sodium, and calcium 
composition of groundwater along a flow path did not change because of interactions between 
rocks and the groundwater, local recharge of water with a different composition, or vertical 
mixing between aquifers. 
CRWMS M&O (2000m) used the chemical composition of groundwater to infer flow paths. 
Groundwater in the Amargosa Desert west of Bare Mountain was inferred to flow southeast 
through the corner of the site-scale model domain and into the Amargosa Valley while moving 
roughly parallel to the Amargosa River (Figure 3-3, flow path #1). Groundwater in Fortymile 
Canyon flows southward parallel to Fortymile Wash and connects with downgradient areas in 
the Amargosa Desert (Figure 3-3, flow path #2). Groundwater in the northwest corner of the 
site-scale model domain flows south-southeast through central Crater Flat and then south into the 
Amargosa Valley (Figure 3-3, flow path #3). Groundwater in central Jackass Flats flows 
southwest, roughly parallel to Fortymile Wash, into the Amargosa Valley before turning southsoutheast 
beyond the southern boundary of the site-scale model domain (Figure 3-3, flow

TDR-NBS-HS-000001 REV 00 ICN 01 3-10 August 2000 
path #4). Groundwater in northeastern Crater Flat flows south-southeast through eastern Crater 
Flat, and then after reaching the southern edge of Yucca Mountain, it flows south-southwest into 
the Amargosa Valley (Figure 3-3, flow path #5). Groundwater beneath the potential repository 
flows southeast towards Fortymile Wash, but then moves south-southwest parallel to, and west 
of, the wash until it reaches the Amargosa Valley (Figure 3-3, flow path #6). This flow path is 
constrained by (i.e., flows between) flow path #2 in Fortymile Wash and flow path #5 in eastern 
Crater Flat. The delta deuterium and delta oxygen-18 values of groundwater reflect the 
composition of the recharge water and are generally not affected by interactions between the 
water and rocks except under special conditions (e.g. boiling temperatures, gas vents) that do not 
exist at Yucca Mountain. The assumption that chloride concentrations are not altered by 
water/rock interaction is based on the absence of chloride-bearing minerals in the volcanic 
aquifer. Sulfur-bearing minerals are locally important at the base of the volcanic aquifer and in 
the Calico Hills, but generally sparse in the volcanic aquifer. Calcium and sodium concentrations 
can be altered by water/rock interactions such as rock weathering, clay precipitation, and cation 
exchange. Calcium and sodium were used only to confirm flowpath estimates based on other 
chemical or isotopic indicators, or were used where other indicators did not show compositional 
contrasts and the spatial contrasts in calcium and sodium concentrations were sufficiently large 
that departures from non-conservative behavior were acceptable. 
The regional flow paths constructed on the basis of the hydrochemical and isotopic data 
generally are consistent with flow paths that could be inferred from the potentiometric surface 
but have a stronger north-south component. The stronger north-south component could reflect 
the general north-south structural fabric of the rock, the inability of the method to account for 
chemical mixing due to recharge or upwelling from the carbonate aquifer, or simply the 
sparseness of the data in certain areas. Although it is not possible to conclusively identify the 
reason for the differences, the actual flowpaths probably are bounded by the two representations 
of the flow system, each of which relies on a different and independent set of assumptions. 
Timing of RechargeThe timing of recharge for SZ groundwaters at Yucca Mountain, as 
determined by the uncorrected carbon-14 ages of the perched water, generally is between 11,000 
and 7,000 yrs before present (CRWMS M&O 2000m). As discussed in detail by CRWMS M&O 
(2000m), the uncorrected carbon-14 ages of perched water are believed to represent the actual 
time of recharge of these waters. Corrections to the carbon-14 ages were made which consider 
plausible chemical reactions that may have produced the observed chemistry of the groundwater 
samples. The corrected carbon-14 ages were approximately one carbon-14 half-life (5,730 yrs) 
younger than the uncorrected carbon-14 ages (i.e., 6,000 to 13,000 yrs). Because of the 
assumption that all carbon contributed by carbonate dissolution had a carbon-14 activity of 
0 percent modern carbon, and because the model did not consider the increase in calcium and 
magnesium in soil water due to evaporation in the soil zone, the corrected carbon-14 ages of 
groundwater are considered lower limits for the true average age. The true carbon-14 ages 
probably are bounded by the corrected and uncorrected carbon-14 ages. 
Magnitude of RechargeEstimates of the magnitude of recharge to the SZ in the vicinity of 
Yucca Mountain were obtained using the chloride mass balance method (CRWMS M&O 
2000m). This method is simple and appears reliable based on comparisons with other techniques 
used to estimate the magnitude of recharge. Estimates of recharge range from less than 
0.5 mm/yr (0.02 in./yr) beneath washes with thick alluvial cover to a maximum of 20 mm/yr

TDR-NBS-HS-000001 REV 00 ICN 01 3-11 August 2000 
(0.8 in./yr) beneath ridge tops and side slopes. For groundwaters within the immediate vicinity 
of Yucca Mountain, chloride concentrations range from 5 to 9 mg/L, indicating local recharge 
rates of 7 to 14 mm/yr (0.3 to 0.6 in./yr). These values, based on simple methods, are consistent 
with UZ Process Model Report (PMR) values (CRWMS M&O 2000b, Section 3.5). 
3.1.1.2 Site Description 
The site-scale flow system comprises the rocks and water of the area near Yucca Mountain 
(Figures 2-1 and 3-4), extending from the water table down to a depth of 2,750 m (9,020 ft) 
below sea level. Within the site-scale model area, the physiography, climate, soils, and 
vegetation generally are similar to elsewhere in the region, as described in Section 3.1.1.1. 
However, because the altitude ranges only from about 710 m (2,330 ft) at the southern border of 
the model area to about 2,200 m (7,220 ft) at Shoshone Peak in the northeastern part of the 
model area, the climatic extremes of temperature and precipitation are less than those cited in the 
regional description. Descriptions of the site-scale geologic setting, hydrologic setting, and 
hydrochemistry are presented in Sections 3.1.1.2.1, 3.1.1.2.2, and 3.1.1.2.3, respectively. 
3.1.1.2.1 Site-Scale Geologic Setting 
Yucca Mountain consists of a group of north-south-trending block-faulted ridges (Figure 3-4) 
composed of volcanic rocks of Tertiary age that are several kilometers thick. Crater Flat, the 
basin west of Yucca Mountain (Figure 3-4), is composed of a thick sequence (about 2,000 m 
[6,500 ft]) of Tertiary volcanic rocks, Tertiary and Quaternary alluvium, and small basaltic lava 
flows of Quaternary age. The Solitario Canyon fault separates Crater Flat from Yucca Mountain. 
Fortymile Wash, a structural trough, delimits the eastern extent of Yucca Mountain. East of 
Yucca Mountain are the Calico Hills, an assemblage of Tertiary volcanic and Paleozoic rocks. 
Yucca Mountain terminates to the south in the Amargosa Desert, which consists of interbedded 
Quaternary and Tertiary alluvial, paludal, and tuffaceous sediments. At depths of about 1,800 m 
(5,900 ft) or greater at Yucca Mountain, the volcanic deposits are underlain by a thick sequence 
of early Paleozoic dolomites and limestones that form the lower carbonate aquifer. Subsequent 
to deposition, the volcanic and older rocks were faulted and tilted, resulting in a series of gently 
eastward-dipping fault blocks. 
Aspects of the site-scale geology that pertain to groundwater flow are represented in the 
site-scale hydrogeologic framework model (HFM). A detailed description of the HFM, the 
assumptions, and the methods used to develop the model are given by (USGS 2000a). 
Information from geologic maps, cross sections, borehole data, fault-trace maps, and geophysical 
data were used to construct a 3-D interpretation of the hydrostratigraphy and geologic structure 
within the domain of the HFM. Stratigraphic units within the HFM are grouped into 
hydrogeologic units that are classified by age (e.g., older volcanics) or rock type (e.g., 
carbonate). Where differentiation was possible within a unit, the unit was further divided into 
subunits having relatively high permeabilities (aquifers) or relatively low permeabilities 
(confining units). The HFM specifies the position and geometry of these hydrogeologic units. 
In addition, the HFM identifies major faults (Figure 3-4) that affect groundwater flow.

TDR-NBS-HS-000001 REV 00 ICN 01 3-12 August 2000 
535000 540000 545000 550000 555000 560000 
4050000 
4055000 
4060000 
4065000 
4070000 
4075000 
4080000 
4085000 
4090000 
UTM-Y (meters) 
UTM-X (meters) 
Highway 95 Fault 
Gravity 
Fault 
Bare 
Mountain Fault 
Crater 
Flat Fault 
Specter 
Range 
Thrust Fault 
W 
indy 
Wash 
Fault 
Paintbrush 
Canyon 
Fault 
Solitario 
Canyon Fault 
Bow 
RidgeFault 
Dune Wash 
Fault 
Ghos 
t Danc 
e 
Claim Canyon 
Caldera Boundary 
Fault 
Splay of 
Calico 
Hills 
Shoshone 
Mountain 
Fatigue Wash 
Fault 
Fortymile 
Wash 
Source: Adapted from CRWMS M&O (2000n, Figure 4) 
Figure 3-4. Structural and Tectonic Features Units within the Site-Scale Saturated Zone Model Area

TDR-NBS-HS-000001 REV 00 ICN 01 3-13 August 2000 
Ten hydrogeologic units are defined in the regional-scale flow model (Section 3.1.1.1.1); 
however, 18 hydrogeologic units are used in the site-scale HFM. Some of the regional-scale 
units are not included because they are not present in the site-scale area, and some of the 
regional-scale units are subdivided into additional units (USGS 2000a, Table 6-1). The 18 
hydrogeologic units are represented in the site-scale flow and transport model, and all are 
defined in the HFM (USGS 2000a). The following description of the eight principal aquifers and 
confining units is based on the classification in the HFM (USGS 2000a, Table 6-1). 
Basin Fill AquiferThis aquifer underlies most of the Amargosa Desert area to the east and 
south of Yucca Mountain. It is composed of alluvial fan, fanglomerate, lakebed, and mudflow 
deposits, and has a thickness of several hundred meters. This aquifer is the main water source 
for domestic and irrigation use in the Amargosa Valley. In addition, the valley-fill aquifer may 
receive lateral flow and recharge from the volcanic tuffs. 
Upper Volcanic AquiferThe Topopah Spring unit of the Paintbrush Tuff is the uppermost 
water-bearing unit of the SZ and is the upper volcanic aquifer in the Yucca Mountain area. It 
consists of variably welded ash-flow tuffs and rhyolite lavas (nonwelded tuffs). The Topopah 
Spring unit is not saturated below the potential repository, but it becomes saturated to the east 
and south of Yucca Mountain and in Crater Flat. 
Upper Volcanic Confining UnitThis confining unit consists of rhyolitic lavas, volcanic 
breccias, and nonwelded to welded tuffs, and commonly is argillaceous or zeolitic. It includes 
the lowermost part of the Topopah Spring Tuff, the Calico Hills Formation, and the uppermost 
part of the Crater Flat Group. 
Lower Volcanic AquiferThis aquifer consists of variably welded ash-flow tuffs and rhyolite 
lava. It includes most of the Prow Pass Tuff and the underlying Bullfrog and Tram tuffs of the 
Crater Flat Group. This aquifer underlies Yucca Mountain, but tends to produce less water than 
the upper volcanic aquifer. 
Lower Volcanic Confining UnitThis confining unit consists of nonwelded and commonly 
zeolitized units of the Lithic Ridge Tuff. 
Older Volcanic AquiferThis aquifer consists of variably welded ash-flow tuffs and rhyolite 
lavas below the Lithic Ridge Tuff, which corresponds to the Tub Spring member and the lava 
flow and welded tuff aquifer. It has a moderate permeability that is comparable to the 
permeability of the lower volcanic aquifer. 
Older Confining UnitIn areas where the upper carbonate aquifer is not present, such as in the 
Yucca Mountain area, the older confining unit consists of the lowermost part of the volcanic 
sequence and the uppermost part of the pre-Cenozoic sequence. The lowermost part of the 
volcanic sequence includes nonwelded and commonly zeolitized units of older volcanics at the 
lowermost interval of the volcanic sequence. The upper part of the pre-Cenozoic section is the 
Eleana Formation of Devonian or Mississippian age, which has been characterized as the upper 
clastic aquitard. In areas where the upper carbonate aquifer is present, such as western Yucca 
Flat and northern Jackass Flats, it occupies the interval between the lowermost part of the 
volcanic sequence and the Eleana Formation.

TDR-NBS-HS-000001 REV 00 ICN 01 3-14 August 2000 
Carbonate AquiferAlthough upper and lower carbonate aquifers have been identified 
regionally, the upper carbonate aquifer (a limestone aquifer) may not be present at Yucca 
Mountain. It is absent from the one borehole at Yucca Mountain that penetrates the Paleozoic 
rocks (i.e., borehole UE-25p#1). The upper carbonate aquifer is underlain by the upper clastic 
confining unit (Eleana Formation) that consists of low permeability siliceous siltstone, 
sandstone, quartzite, conglomerate, and limestone. The lower carbonate aquifer underlies the 
Eleana Formation; it consists of Paleozoic dolomite and limestone, and locally is cherty and silty. 
The lower carbonate aquifer was penetrated in borehole UE-25p#1. 
3.1.1.2.2 Site-Scale Hydrologic Setting 
The site-scale SZ hydrologic setting comprises the deposits within the site-scale model domain 
(Figure 3-4) and extends from the water table (the top of the SZ) to a depth of 2,750 m (9,020 ft) 
below the water table. As described in Section 3.1.1.2.1, the surficial and shallow rocks within 
this volume consist mainly of alluvial valley fill to the south and pyroclastic volcanic rocks to the 
north of Highway U.S. 95. These rocks are underlain throughout most of the site-scale SZ model 
area by a thick lower carbonate aquifer consisting of fractured dolomites and limestones of early 
Paleozoic age. 
Within the alluvial valley fill of the SZ, water occupies the intergranular pores of the granular 
alluvium. The matrix of the carbonate rock is dense and of low porosity, and the groundwater 
generally is limited to fractures, many of which have been enlarged by solution. In the volcanic 
rocks, intergranular porosity and fracture porosity are important. In densely welded tuffs, matrix 
porosity is low and groundwater is limited to fractures, but in ash-fall tuffs, matrix porosity is 
high and fractures are limited. A variety of rocks of intermediate porosity also occur. 
Groundwater flow in the model area is southward, from regions of high hydraulic head to regions 
of low hydraulic head (Figure 3-5). In much of the SZ model domain, the gradient of hydraulic 
head is gentle. However, large differences in measured head occur over short distances north of 
Yucca Mountain. These large differences indicate either a locally steep hydraulic gradient in the 
SZ or the presence of perched water north of Yucca Mountain. In other places, heads measured 
at locations separated by a fault differ, indicating that the fault affects groundwater flow. For 
example, heads west of the Solitario Canyon fault are more than 770 m (2,525 ft), but heads east 
of the fault are about 730 m (2,395 ft). 
Recharge to the site-scale SZ model area is limited to infiltration of precipitation and stream flow 
during infrequent episodes of runoff. Infiltration of precipitation largely is confined to the higher 
terrain in the northern part of the model area and the higher parts of Yucca Mountain 
(Section 3.2.3.2). Long-term recharge from stream flow in Fortymile Canyon and Fortymile 
Wash has been estimated by Savard (1998, Table 5). The only other sources of water to the 
model area are inflows along the northern, eastern, and western boundaries computed from the 
regional-scale site-scale flow model (DAgnese et al. 1997). These computed inflows account 
for approximately 95 percent of the total flux through the site-scale SZ model area 
(Section 3.2.3.1).

TDR-NBS-HS-000001 REV 00 ICN 01 3-15 August 2000 
Source: USGS (2000b, Figure 1-2) 
NOTE: Potentiometric contours show elevation of the potentiometric surface. Datum is sea level. 
(IIlegibility has no technical impact to the content of the record) 
Figure 3-5. Site-Scale Potentiometric Map and Structural Features

TDR-NBS-HS-000001 REV 00 ICN 01 3-16 August 2000 
Natural discharge (i.e., springs and evaporation of shallow groundwater) does not occur within 
the site-scale SZ model domain; however, substantial artificial discharge occurs from wells in the 
Amargosa Farms area in the southwestern part of the site-scale model domain (see the closely 
spaced well locations on Figure 3-5). Substantial subsurface outflow occurs across the southern 
boundary of the site-scale model domain (Section 3.4.2). 
3.1.1.2.3 Site-Scale Hydrochemistry 
Hydrochemical data provide information on several important site-scale issues including the 
existence and magnitude of local recharge, flow directions from the potential repository footprint 
to downgradient locations, and the potential for dilution of materials that could potentially be 
released from the potential repository. 
Evidence for the Existence of Local RechargeHydrochemical and isotopic data from perched 
water at Yucca Mountain compared to similar data from the regional groundwater system 
suggests that local recharge is a component of the SZ waters in volcanic aquifers beneath Yucca 
Mountain (CRWMS M&O 2000m). The data examined included uranium isotopes 
(uranium-234/uranium-238) and major anions and cations. It is possible that shallow 
groundwater is composed entirely of local recharge (CRWMS M&O 2000m). 
Likely Flow Paths from the Potential Repository AreaLikely flow paths in the Yucca 
Mountain area were determined by identifying areas that had similar concentrations of 
conservative chemical species (e.g., chloride or sulfate) and tracing paths through these 
chemically similar areas in a downgradient direction (CRWMS M&O 2000m). Of particular 
interest are paths leading from the potential repository area (Figure 3-3, flow path #6). This 
pathway starts with low chloride groundwater from the potential repository area just east of 
Yucca Mountain Crest, and passes wells along Dune Wash with similarly low chloride 
concentrations, before turning south-southwest near Fortymile Wash. Well WT#12, located 
immediately south of Dune Wash, has a higher chloride concentration, indicating that the dilute 
water beneath Dune Wash probably flows southeast along the Dune Wash fault towards 
Fortymile Wash before turning south-southwest, rather than flowing directly south under Dune 
Wash. From the intersection of Dune Wash and Fortymile Wash, the only downgradient 
borehole with a similarly low chloride concentration is borehole NCEWDP-2D (Figure 2-3). 
South of borehole NCEWDP-2D, the pathway is constrained by the presence of two areas of 
groundwater with higher chloride concentrations: (1) a western zone, composed of groundwater 
flowing south from Crater Flat and, possibly, southeast from Oasis Valley; and (2) an eastern 
zone, composed of groundwater flowing southwest from Jackass Flats and from leakage upward 
from the carbonate aquifer. The hypothesized flow path was extended south from 
NCEWDP-2D, keeping the path to the west of the axis of Fortymile Wash and east of the more 
highly concentrated water from Crater Flat and Oasis Valley. 
Importantly, the chloride data (Figure 3-3), as well as other chemical and isotopic data, suggest 
that groundwater from beneath the potential repository area may not flow along the southtrending 
faults in the southern part of the mountain. This conclusion is consistent with the 
potentiometric surface map that indicates that groundwater in this area probably flows from 
Crater Flat.

TDR-NBS-HS-000001 REV 00 ICN 01 3-17 August 2000 
3.1.2 Summary of Hydrologic Data 
As a foundation for subsequent discussions of the site-scale SZ flow and transport model, the 
following sections summarize the hydrologic data. Topics include data on water levels and 
aquifer properties obtained from hydraulic testing of wells, and information on infiltration and 
recharge available within the area covered by the site-scale SZ flow and transport model. 
3.1.2.1 Water-Level Data 
A regional-scale potentiometric surface map (Figure 3-2) was constructed using data sets 
describing water levels, boundaries of perennial marshes and ponds, topographic altitudes, 
regional spring locations, the distribution of recharge and discharge areas, and hydrogeology 
(DAgnese et al. 1997, p. 57). Supplementary data were used to help in the extrapolation of 
water levels in data-poor areas. 
In this sparsely populated, arid, and mountainous region, most water-resource extraction and 
investigation has occurred in alluvial valleys. The densest concentrations of water-level data in 
the Death Valley regional groundwater flow system occur in the two largest agricultural 
communities near Yucca Mountain: the Amargosa Farms area and Pahrump Valley (DAgnese 
et al. 1997, Figure 26). Additional water-level data are available from Oasis Valley, Sarcobatus 
Flat, and Yucca Flat. The only areas with extensive water-level data in consolidated bedrock are 
Yucca Mountain, Pahute Mesa, and Rainier Mesa (Figure 2-2). The remainder of the region 
generally is lacking in water-level data. 
An automated gridding and contouring software package was used to interpolate the water-level 
data. Numerous intermediate gridding steps were then conducted, and adjustments were made 
using hand-contouring methods. Because of the limited data from water wells, additional 
ancillary data were used to assist the potentiometric surface map construction (DAgnese 
et al. 1997). These data were used to guide interpolation of water levels in data-poor areas to 
produce a regional-scale potentiometric map with 100-m (330-ft) contour intervals (DAgnese 
et al. 1997, pp. 56 to 59): 
USGS (2000b) developed a potentiometric map for the site-scale SZ flow and transport model 
domain (Figure 3-5) that was designed to be compatible with the DAgnese et al. (1997) 
regional-scale potentiometric map (Figure 3-2). The site-scale potentiometric map (Figure 3-5) 
implies that the SZ groundwater is a hydraulically well-connected body, although locally it may 
include perched water levels where perching cannot be ruled out. The site-scale potentiometric 
map was compiled using available water-level data within the model area, including new 
information from well WT-24, information from seven wells drilled near Highway US 95 as part 
of the Nye County Early Warning Drilling Program (NCEWDP), and information from recent 
Yucca Mountain Site Characterization Project (YMP) large-scale geologic mapping. 
To some degree, most of the water levels used in compiling the site-scale potentiometric map 
(Figure 3-5) represent composite heads in more than one zone; however, it is believed that the 
surface represented probably is a close and reasonable representation of the water table.

TDR-NBS-HS-000001 REV 00 ICN 01 3-18 August 2000 
Important features of the new site-scale potentiometric surface map include: 
 Water-level data from newly drilled boreholes, including the NCEWDP wells, which 
provide control along the border between Yucca Mountain and the Amargosa Desert 
near Highway U.S. 95, an area of former water-level data deficiency. 
 Faults are assumed to have an important effect on SZ flow. 
 Contour intervals of 25 m (82 ft) represent a considerable refinement as compared to the 
100-m (328-ft) contour interval of the regional-scale potentiometric map of DAgnese 
et al. (1997, Figure 27), although the 25-m (82-ft) interval still is too coarse to 
adequately portray the small hydraulic gradient in the area between the potential 
repository and Fortymile Wash and between Fortymile Canyon and the Amargosa 
Desert. However, the large and medium hydraulic gradient area can be recognized on 
the 25-m (82-ft) contour interval map. 
 In the fault blocks to the east and west of the Solitario Canyon fault, the new map 
suggests nearly level hydraulic gradients extending about 10 km (6.2 mi) southward 
from the vicinity of the potential repository to a fault that is parallel to Highway U.S. 95. 
This interpretation suggests the existence of large areas of very small hydraulic gradient 
that are comparable to the small gradient area between Fortymile Wash and Yucca 
Mountain. 
 The time period represented by the new map is early 1990s for consistency with the 
regional-scale map of DAgnese et al. (1997, Figure 27). 
 The large hydraulic gradient is portrayed as representing the water table rather than a 
perched condition. 
Older potentiometric maps of the immediate vicinity of Yucca Mountain based on 1983 
and 1988 water-level data are described by Luckey et al. (1996, p. 21). These maps portray the 
areas of large, moderate, and low hydraulic gradients (Section 3.2.2.3), but do not portray the 
gradient near Fortymile Wash. Tucci and Burkhardt (1995) developed a potentiometric surface 
map based on 1993 water-level data (Figure 3-6); this map includes measurements to the east of 
Fortymile Wash and presents contours near Fortymile Wash. These contours indicate that 
groundwater flows toward Fortymile Wash from the east and the west, and then turns southward 
parallel to Fortymile Wash and flows toward the Amargosa Desert. The contour interval, 0.5 m 
(1.6 ft), is sufficient to portray details of the potentiometric surface in the area of small hydraulic 
gradient between Fortymile Wash and the potential repository area. While the potentiometric 
map of the site-scale model domain portrays the general southward direction of groundwater 
flow between Fortymile Canyon and the Amargosa Desert (Figure 3-5), the more detailed map 
provides the pattern of groundwater flow in the immediate vicinity of Fortymile Wash 
(Figure 3-6).

TDR-NBS-HS-000001 REV 00 ICN 01 3-19 August 2000 
Source: Tucci and Burkhardt (1995) 
Figure 3-6. Potentiometric Surface Map Developed Using Water-Level Data from 1993 
3.1.2.2 Hydraulic Well Testing 
Hydraulic conductivity and effective porosity are the most important physical properties of 
aquifers needed for calculating the transport of groundwater and contaminants. In field practice, 
transmissivity (obtained from aquifer test analyses) is divided by the tested saturated thickness to 
obtain a first approximation of hydraulic conductivity. The degree to which this approximates 
hydraulic conductivity actually is representative of the transmissive properties of fractured rock. 
It also requires subjective evaluations of the geologic setting and the results of other tests (i.e., 
flow surveys) to identify water-producing zones (i.e., flowing intervals in a well within aquifers). 
However, the actual contributing thickness of a fractured-rock aquifer probably is less than the 
tested interval, and therefore this thickness generally is unknown. Therefore, for purposes of 
comparing hydrogeologic units and discussing the overall distribution of rock-mass transmissive 
characteristics, the following discussion emphasizes transmissivity.

TDR-NBS-HS-000001 REV 00 ICN 01 3-20 August 2000 
As part of the site characterization process, more than 150 individual hydraulic tests of the SZ 
were conducted at 37 boreholes in and around Yucca Mountain (Figure 3-7). Other hydraulic 
tests have been conducted in the vicinity of Yucca Mountain for other purposes, such as the 
NCEWDP and the Environmental Restoration Program for the NTS. These tests are not 
discussed in detail in this report. Most tests at Yucca Mountain were conducted in the early 
1980s, and nearly all were single-well tests over specific depth intervals. Tests included 
constant-discharge, fluid-injection, borehole-flowmeter, and radioactive tracer tests. Multiplewell 
tests have been conducted only at the C-wells Complex, but several tests were conducted at 
the three wells at the complex. Most test results were reported as transmissivity or hydraulic 
conductivity of hydraulically isolated intervals. These values can vary by several orders of 
magnitude, depending on the presence or absence of water-producing fractures in the tested 
intervals. Storativity, or specific yields, have been reported for a few of the wells. Other 
hydraulic tests have been conducted throughout the Death Valley region, the results of which 
were summarized by Bedinger et al. (1989). 
The most recent (1995-1997) aquifer tests were conducted at boreholes USW G-2, USW WT-10, 
UE-25 WT#12, and the C-wells Complex. Single-borehole, composite-interval, constantdischarge 
tests were conducted in boreholes USW G-2 in 1996 (OBrien 1998), USW WT-10 in 
1996, and UE-25 WT#12 in 1995 (OBrien 1997). The Topopah Spring Tuff and the Calico 
Hills Formation were tested at borehole USW G-2. At borehole USW WT-10, the Topopah 
Spring Tuff was tested, and at borehole UE-25 WT#12 the Topopah Spring Tuff and the Calico 
Hills Formation were tested. 
Permeability Data from the Yucca Mountain AreaThe software used to simulate 
groundwater flow and transport at Yucca Mountain (Zyvoloski et al. 1997a) requires the use of 
permeability values rather than hydraulic conductivity or transmissivity. Permeability data from 
single-hole and cross-hole tests have been collected in the Yucca Mountain area since the early 
1980s. A statistical analysis of data collected and published prior to 1998 is presented by 
CRWMS M&O (2000n, Section 6.7.7). 
Single-Hole TestsFor the statistical analysis of the permeability data (CRWMS M&O 2000n, 
Section 6.7.7), raw data were grouped by combining permeability estimates for individual 
hydrogeologic units where possible, and by considering progressively more general groupings if 
the test interval spanned several hydrogeologic units. For instance, in cases in which the test 
interval was in the Prow Pass Tuff, with or without some portion of the adjacent bedded tuffs, 
the data were grouped with other permeability estimates for the Prow Pass Tuff. If other units 
within the lower volcanic aquifer also were present in the test interval with the Prow Pass Tuff, 
the data were considered to represent the lower volcanic aquifer. If hydrogeologic units other 
than those in the lower volcanic aquifer were present in the test interval along with the Prow Pass 
Tuff, the permeability estimate was grouped with the most general category (i.e., mixed tuffs). 
The mixed tuff category includes data that would not fit into a more restrictive category. All 
tuffs older than the Lithic Ridge Tuff are listed as Pre-Lithic Ridge Tuffs.

TDR-NBS-HS-000001 REV 00 ICN 01 3-21 August 2000 
Data Tracking Number: MO0002COV00088.001 
NOTE: This map shows some of the boreholes near Yucca Mountain in which hydraulic tests were conducted. 
Figure 3-7. Boreholes Near Yucca Mountain

TDR-NBS-HS-000001 REV 00 ICN 01 3-22 August 2000 
In instances where several kinds of hydraulic tests (injection, drawdown, or recovery) were 
conducted in the same depth interval in the same borehole, all of the permeability data that 
resulted from testing of the interval were used to calculate the summary statistics. By 
considering multiple measurements from the same test interval, the effects of measurement 
uncertainty and spatial variability were considered (CRWMS M&O 2000n, Section 6.7.7). 
Summary statistics were calculated using base-ten logarithms, but results were presented using 
the original units of measure. The analysis indicates that the deepest tuffs (the pre-Lithic Ridge 
Tuffs) and the mixed tuff group have the lowest permeabilities, and that the Topopah Spring Tuff 
and Prow Pass Tuff have the highest permeabilities. Where they could be calculated, the 
95 percent confidence limits indicate that (except for the pre-Lithic Ridge Tuffs) the mean 
permeability values are constrained within relatively narrow limits. The results also indicate that 
the Calico Hills Formation, a zeolitized tuff that functions as the upper volcanic confining unit, 
has a higher permeability than the Bullfrog Tuff and the Carbonate Aquifer. This paradoxical 
result may reflect the fact that, because it is unsaturated in the western half of Yucca Mountain, 
the Calico Hills Formation could be hydraulically tested only in the highly faulted eastern half of 
Yucca Mountain, whereas the other units also were tested in less intensely faulted areas to 
the west. 
Cross-well TestsThe C-wells Complex is a group of three boreholes (UE-25c#1, UE-25c#2, and 
UE-25c#3) located east of Yucca Mountain (Section 2.2.1.2; Figure 3-7). Aquifer tests have 
been conducted intermittently at the C-wells Complex since 1983. Preliminary pumping and 
injection tests that were conducted in 1983-1984, and heat-pulse flowmeter tests conducted 
in 1992, were re-analyzed by Geldon (1996). 
Permeability data from cross-hole tests were compiled, grouped, and analyzed in a manner 
similar to that for the single-hole tests. Whereas permeability estimates based on single- and 
cross-hole tests in the Calico Hills Formation were similar, permeability estimates based on 
single- and cross-hole tests in the Prow Pass Tuff, Bullfrog Tuff, Tram Tuff of the Crater Flat 
Group, and the Middle Volcanic Aquifer (a name used in the HFM) differed by one to several 
orders of magnitude. These differences (higher permeability based on cross-hole data) were 
attributed to the larger volume of rock affected by the cross-hole tests (which allows sampling a 
larger number of possible flowpaths, including relatively rare, high-transmissivity flow paths). 
However, some of the increase may have been due to a breccia zone associated with the Midway 
Valley fault in the Bullfrog Tuff and Tram Member. 
Permeability Data from the Nevada Test SitePermeability data and qualitative observations 
from the NTS were examined and summarized (CRWMS M&O 2000n, Section 6.7.7) to help 
constrain permeability estimates for hydrogeologic units that were not tested or which underwent 
minimal testing at Yucca Mountain. In addition, the NTS data describe the hydrogeologic 
controls on ground-water movement and provide a regional perspective for ground-water flow at 
Yucca Mountain. 
Lower Carbonate AquiferData from hydraulic tests conducted in six boreholes that penetrated 
the lower carbonate aquifer were presented in CRWMS M&O (2000n, Table 10). Permeability 
was calculated from hydraulic conductivity, but the calculation required certain assumptions

TDR-NBS-HS-000001 REV 00 ICN 01 3-23 August 2000 
(CRWMS M&O 2000n, Section 6.7.7.4), and the calculated permeabilities may overestimate 
true permeability by a factor of 2 to 3. 
In addition to providing quantitative estimates of permeability for the lower carbonate aquifer, 
CRWMS M&O (2000n, Section 6.7.7.4) also summarize qualitative observations regarding the 
distribution of permeability within the aquifer. Permeability of the carbonate aquifer showed no 
systematic decrease with depth. No major caverns were detected. Outcrop evidence indicates 
that klippen, the upper plates of low angle thrust faults and gravity slump faults, have a higher 
intensity of fracturing and brecciation than rock below the fault planes and may have above 
average porosity and permeability. Zones of above average transmissivity often may not be 
connected to each other. 
Valley-Fill AquiferPermeability of the valley-fill aquifer was estimated using published 
transmissivity estimates from four boreholes located in Emigrant Valley, Yucca Flat, and 
Frenchmen Flat (CRWMS M&O 2000n, Section 6.7.7.5, Table 11). Permeability was calculated 
from transmissivity, and the calculation required the same assumptions as those used for the 
lower carbonate aquifer (CRWMS M&O 2000n, Section 6.7.7.4). 
In addition to the quantitative estimates of the permeability of valley fill on the NTS, CRWMS 
M&O (2000n, Section 6.7.7.5) also summarize observations regarding the permeability of the 
valley fill in the Amargosa Desert. Winograd and Thordarson (1975, pp. C84 to C85) noted that 
hydraulic head contours south of Lathrop Wells (now Amargosa Valley) probably reflect the 
effects of upward leakage from the lower carbonate aquifer into poorly permeable valley fill 
along the Gravity fault and associated faults, and the drainage of this water to more permeable 
sediments farther west. Winograd and Thordarson (1975, p. C85) argued that the discharge 
across the Gravity fault near Lathrop Wells probably was small because only the lowermost part 
of the lower carbonate aquifer is present in the area and the lower clastic aquitard, which 
underlies the carbonate aquifer at shallow depths, probably would not transmit much water. 
Welded-Tuff AquiferHydraulic tests yielding permeability estimates for the welded-tuff aquifer 
were conducted in two wells in Jackass Flats (CRWMS M&O 2000n, Section 6.7.7.6). Well 
74-57 tested the Topopah Spring Tuff and well 74-61 tested the Topopah Spring Tuff and the 
Basalt of Kiwi Mesa. Permeabilities calculated from drawdown curves for these wells are 
provided by CRWMS M&O (2000n, Table 12). 
Lava-Flow AquiferRhyolitic lavas, and welded and nonwelded tuffs, fill the Silent Canyon 
caldera complex, which now lies buried beneath Pahute Mesa by younger tuffs erupted from the 
Timber Mountain caldera complex (CRWMS M&O 2000n, Section 6.7.7.7). A qualitative 
comparison of the water-producing attributes of these lavas and tuffs indicated that despite 
considerable overlap in their water-yield potential, the lavas generally were the most 
transmissive rocks tested, followed by the welded- and zeolitized nonwelded-tuffs (CRWMS 
M&O 2000n, Section 6.7.7.7). Pumping tests were conducted in boreholes at Pahute Mesa, 
including 14 boreholes in which the major water production came from rhyolitic lava flows 
(CRWMS M&O 2000n). Resistivity logs indicate that nonwelded tuffs could constitute as much 
as 73 percent of the upper 610 m (2,000 ft) of saturated rock at the boreholes listed in CRWMS 
M&O (2000n). Because most of the water pumped from the lava enters the wells from zones

TDR-NBS-HS-000001 REV 00 ICN 01 3-24 August 2000 
that constitute only 3 to 10 percent of the total saturated thickness, permeabilities in the lava may 
be locally higher than the calculated mean value. 
Inferences About Permeability From Regional ObservationsIn addition to the permeability 
values from the NTS summarized by CRWMS M&O (2000n), Winograd and Thordarson (1975) 
made numerous qualitative evaluations of the relative magnitude of permeability of different 
hydrogeologic units. These evaluations were based on the geologic setting, the magnitude of 
spring discharge in the region, the relationship between changes in hydraulic gradients and the 
underlying hydrogeologic unit, and the examination of core samples for fractures and mineral 
infilling. This section on inferences about regional permeability focuses on qualitative 
assessments of hydrogeologic units for which there are few actual test data and for which the 
qualitative evaluations become relatively more important. 
Lower Clastic AquitardCRWMS M&O (2000n, Section 6.7.7.9) summarize published 
information on the lower clastic aquitard. According to Winograd and Thordarson (1975, 
p. C43), the large-scale transmissivity of the lower clastic aquitard probably is controlled by 
interstitial permeability. Although the lower clastic aquitard is highly fractured, the fractures 
probably do not substantially augment the interstitial permeability of the unit on a regional scale 
(CRWMS M&O 2000n, Section 6.7.7.9). 
Upper Clastic AquitardThe upper clastic aquitard corresponds to the Eleana Formation, which 
consists of argillite, quartzite, conglomerate, and limestone (Winograd and Thordarson 1975, 
Table 1). The upper two-thirds of the unit consists mainly of argillite and the lower one-third of 
the unit principally is quartzite (Winograd and Thordarson 1975, p. C118). Winograd and 
Thordarson (1975, p. C43) argued that fractures were unlikely to remain open in the rock at 
depth because of the plastic deformation behavior of the rock, evidenced by tight folds and the 
fact that the formation serves as a glide plane for several thrust faults at the NTS. In the hills 
northwest of Yucca Flat, the approximately 610 m (2,000 ft) drop in hydraulic head in the 
pre-Tertiary rocks over a distance of less than 16 km (10 miles) (an apparent hydraulic gradient 
of 38 m/km [200 ft/mi]) qualitatively demonstrates the comparatively low regional permeability 
of the upper clastic aquitard. 
FaultsA summary of the possible effects of faults on groundwater movement in the Death 
Valley region is presented by CRWMS M&O (2000n, Section 6.7.7.11), and the transmissivity 
of faults in the Yucca Mountain region is discussed in relation to five factors: 
 Fault OrientationIn the vicinity of Yucca Mountain, the mean orientation of the 
minimum horizontal stress is 30611 degrees, and faults with traces oriented northnortheast 
are expected to be more open and permeable than faults with traces oriented in 
directions which place them in a shear or compressive state. 
 Fault Fill-MaterialFine-grained gouge or clay fill-material can cause faults to become 
poorly transmissive, even if their orientation relative to the stress field indicates they 
have the potential to be highly transmissive. 
 Juxtaposed FaultsDifferences in the permeabilities of hydrogeologic units juxtaposed 
by offset across a fault can affect transmissivity.

TDR-NBS-HS-000001 REV 00 ICN 01 3-25 August 2000 
 Behavior of RockThe solubility and deformation behavior of rock adjacent to faults 
can affect transmissivity. 
 Recent Seismic HistoryOf the faults that have been mapped near the potential 
repository area, only the Solitario Canyon fault and short segments of the Bow Ridge 
fault near Exile Hill show evidence of late Quaternary (or more recent) displacement. 
The role of specific faults that act as barriers to groundwater flow has been inferred from abrupt 
discontinuities in the potentiometric surface across faults (Figure 3-5). Lower permeability in 
the direction perpendicular to the Solitario Canyon and Highway 95 faults (Figure 3-4) is 
assumed in the site-scale SZ flow model. Direct hydraulic testing of low-permeability faults in 
boreholes has not been conducted at the Yucca Mountain site. 
Nye CountyAs part of the NCEWDP, three boreholes were used for 48-hour, single-borehole, 
constant-discharge tests during January and February 1999 (Figure 2-3). The intervals tested in 
these wells include Rainier Mesa Tuff at borehole NCEWDP-01S, pre-Bullfrog bedded tuffs and 
Tram Tuff at borehole NCEWDP-03D, and Tiva Canyon Tuff at borehole NCEWDP-09S. The 
test data were analyzed by consultants for Nye County. 
Borehole JF-3Borehole JF-3 was drilled in the western part of Jackass Flats to monitor water 
levels in the volcanic rocks that provide water to boreholes J-12 and J-13. The saturated interval 
at JF-3 occurs within the Topopah Spring Tuff and the Wahmonie Formation (Plume and 
La Camera 1996, p. 7-9). 
3.1.2.3 Infiltration and Recharge 
Sources of water that enter the volcanic aquifers and confining units in the vicinity of Yucca 
Mountain include inflow from upgradient volcanic aquifers and confining units, local recharge 
from Fortymile Wash, precipitation that infiltrates the surface of Yucca Mountain (especially at 
higher altitudes at the northern end of Yucca Mountain), and upward flow from the underlying 
carbonate aquifer (Luckey et al. 1996, p. 39). The magnitudes of most of the inflows to the 
volcanic system have not been quantified. Potentiometric levels measured in holes that penetrate 
to or through the lower part of the lower volcanic confining unit indicate hydraulic connections 
between the deep volcanic and the underlying carbonate aquifer south of the large hydraulic 
gradient. Where a vertical gradient has been measured at Yucca Mountain, it generally is 
upward, indicating a potential for upward groundwater flow (Luckey et al. 1996, p. 28). 
However, no evidence of significant inflow to the volcanic rocks from the carbonates has been 
reported. 
Potentiometric data from widely spaced boreholes upgradient from Yucca Mountain indicate that 
groundwater flows south from upland recharge areas in the volcanic terrain of Pahute and 
Rainier Mesas, beneath Timber Mountain, continuing southward beneath the Yucca Mountain 
area (Luckey et al. 1996, p. 39). However, the concept of inflow from upgradient regions is 
based on limited data, particularly between Yucca Mountain and Pahute Mesa. 
Hydrochemical data (apparent, uncorrected, carbon-14 ages) indicated that water in the volcanic 
aquifer beneath Yucca Mountain and Crater Flat was recharged during wetter climatic conditions

TDR-NBS-HS-000001 REV 00 ICN 01 3-26 August 2000 
approximately 12,000 yrs (well USW H-1) to 18,500 yrs (well USW H-6) before present, and 
6,000 to 13,000 yrs before present based on corrected carbon-14 ages. However, these data do 
not preclude that some modern recharge occurs. Actual ages may be younger than apparent ages 
and the water probably is a mixture from recharge events that span a number of millennia. The 
data do not indicate whether the recharge occurred far upgradient or locally. If most of the 
groundwater beneath Yucca Mountain was recharged in the distant past, the flow system still 
may be equilibrating from an ancient recharge pulse, resulting in a gradual decline in water 
levels beneath Crater Flat and Yucca Mountain over time (Luckey et al. 1996, p. 39). 
Fortymile Wash is a major southward-draining channel located east of Yucca Mountain, 
beginning in the highlands of Pahute Mesa and ending in the Amargosa Desert. During extreme 
runoff, Fortymile Wash would be a tributary to the Amargosa River. Average recharge along the 
entire 95-km (59-mi) length of Fortymile Wash is about 4.2 x 106 m3/yr (3,400 acre-ft/yr) 
(Luckey et al. 1996, p. 40). 
Savard (1998, pp 24 to 27) used data on rising water levels in three boreholes (UE-29a#1, 
UE-29a#2, and UE-29 UZN#91) following local precipitation and runoff to suggest that recharge 
occurred in 1983, 1992, 1993, and 1995 in Fortymile Wash. Savard (1998) estimated long-term 
(1969-1995) annual recharge to groundwater from Fortymile Wash using measured and 
estimated streamflow volumes and estimated streamflow infiltration losses for four reaches of 
Fortymile Wash between its confluence with Pah Canyon and a point in the Amargosa Valley 
downstream of the Highway U.S. 95 crossing. Savard (1998, Table 5) estimated average 
recharge of 27,000 m3/yr (21.9 acre-ft/yr) for the Fortymile Canyon reach, 1,100 m3/yr 
(0.9 acre-ft/yr) for the Upper Jackass Flats reach, 16,400 m3/yr (13.3 acre-ft/yr) for the Lower 
Jackass Flats reach, and 64,300 m3/yr (52.1 acre-ft/yr) for the Amargosa Valley reach. These 
estimates total to 108,800 m3/yr (88 acre-ft/yr) for the long-term average annual groundwater 
recharge from Fortymile Wash downstream of Pah Canyon. 
As reported by Luckey et al. (1996, p. 40), tritium and carbon-14 samples were collected from 
boreholes UE-29a#1 (65.5 m [215 ft] deep) and UE-29a#2 (421.5 m [1,383 ft] deep), and it was 
found that apparently younger water was present in the shallower borehole than in the deeper 
borehole. Younger water at shallower depth with deeper older water indicated that recharge is 
occurring at or near these boreholes. In addition, the potentiometric level was about 4 m (13 ft) 
higher in the shallower borehole than in the deeper borehole, which also is consistent with 
recharge in this area. 
As reported by Luckey et al. (1996, p. 40), local infiltration from precipitation probably occurs in 
the Yucca Mountain area, but the amount of infiltration that reaches the water table may be 
inconsequential in the current climate. Near-surface infiltration ranged from 0.02 to 13.4 mm/yr 
(0.001 to 0.53 in./yr) and averaged 1.4 mm/yr (0.06 in./yr), with the higher infiltration rates 
generally occurring on the northern portion of Yucca Mountain. The amount of deep infiltration 
would be less than the amount of shallow infiltration because airflow through the mountain 
would remove some moisture, and therefore, the rate of deep infiltration may be slow enough 
under modern climatic conditions to have no substantial effect on the SZ flow system. 
In a more recent analysis, Flint et al. (1996, pp. 1 to 2) indicate that during an averageprecipitation 
year of approximately 170 mm (6.7 in.), net infiltration ranges from zero where

TDR-NBS-HS-000001 REV 00 ICN 01 3-27 August 2000 
alluvial thickness is 6 m (20 ft) or more, to more than 80 mm/yr (3.1 in./yr) where thin alluvium 
overlies highly permeable bedrock on north-facing slopes at high elevations, and that net 
infiltration averages 4.5 mm/yr (0.18 in./yr) over the Yucca Mountain study area. On a year-toyear 
basis, average net infiltration varies from zero in dry years to more than 20 mm/yr 
(0.8 in./yr) during years when precipitation exceeds 300 mm (11.8 in.). 
For areas beyond the immediate vicinity of the potential repository, estimates of recharge to the 
SZ depend generally on distributed parameter approaches using mean annual precipitation data 
weighted by altitude and other factors. An empirical precipitation-recharge relation was 
developed by Maxey and Eakin (1950) from water mass-balance estimates for basins in southern 
and eastern Nevada. They suggest that the amount of the annual precipitation, and the 
percentage of precipitation that becomes groundwater, increase with increasing altitude. Maxey 
and Eakin (1950) assumed that no recharge occurs where mean annual precipitation is less than 
about 200 mm (7.9 in.), or where altitude is lower than 1,524 m (5,000 ft). Above 1,524 m 
(5,000 ft) in altitude, they assigned an increasing percentage of precipitation that was assumed to 
become recharge to a ranked series of 305-m (1,000-ft) altitude intervals. 
The method developed by Maxey and Eakin (1950) was modified for use in the Death Valley 
regional flow model by the addition of weighting factors representing vegetation zones, slopeaspect 
ratio, and parent material types (DAgnese et al. 1997, pp. 52 to 55). This approach was 
subsequently used in developing estimates of distributed recharge for the site-scale SZ flow and 
transport model. 
Combined estimates of recharge from distributed recharge, focused recharge along Fortymile 
Wash, and recharge in the area of the UZ site-scale flow model were calculated by CRWMS 
M&O (1999a). The majority of the recharge entering the system in the area of the SZ site-scale 
flow model occurs in the northern part of the model domain. An estimated total of 
1,550,000 m3/yr (1,256 acre-ft/yr) of groundwater enters the SZ system as recharge in the SZ 
site-scale model area. Of this total, about 212,000 m3/yr (172 acre-ft/yr) of recharge occurs in 
the area of the UZ site-scale flow model, and about 95,000 m3/yr (77 acre-ft/yr) recharge occurs 
from focused recharge along Fortymile Wash. 
Recharge from Fortymile Wash is of special interest because groundwater flow along the course 
of the wash is expected to be the main avenue for contaminant transport from the potential 
repository to the compliance point near Lathrop Wells. Accordingly, CRWMS M&O (2000m, 
Section 6.5.7.1) estimate two-component mixing ratios based on uranium-234/uranium-238 
activity in the groundwater. This method uses borehole WT-3 as the end member representing 
flow from Yucca Mountain, and it uses borehole UE-29a#2 as representing Fortymile Wash 
recharge. Calculations were made of the blends represented by samples from boreholes J-12 and 
JF-3. In the sample from JF-3, it was calculated that 96 percent of the water was from Fortymile 
Wash; in the sample from J-12, it was calculated that 50 percent of the water was from Fortymile 
Wash. In both examples, Fortymile Wash was a major contributor to the blend, but at JF-3, flow 
from Yucca Mountain appeared small (4 percent).

TDR-NBS-HS-000001 REV 00 ICN 01 3-28 August 2000 
Summarizing the results reported by CRWMS M&O (2000m, Section 7), it was concluded that: 
 Flow paths based on chemical and isotopic data are in general agreement with those 
based on potentiometric gradients. 
 Local recharge was identified as a major component of recharge to groundwater at 
Yucca Mountain. 
 Chemical evidence indicates the average recharge rate at the central block of Yucca 
Mountain during the late Pleistocene to early Holocene was less than 21 mm/yr 
(0.8 in./yr). Carbon-14 data suggest that the best estimate of true age of the SZ waters at 
Yucca Mountain are about 3,700 yrs less than the uncorrected ages. 
 Hydrochemical data suggest minimal mixing between water from the lower carbonate 
aquifer and water in the overlying volcanic aquifers beneath Yucca Mountain. 
 Hydrochemical evidence suggests that groundwater at Yucca Mountain originated 
largely from local infiltration via perched water zones during late Pleistocene-early 
Holocene. Recharge beneath Fortymile Wash is estimated to be at least as great as that 
estimated by Savard (1998) and perhaps several times greater, but it is orders of 
magnitude less than estimates based on earlier flow models. 
 Hydrochemical calculations suggest that groundwater beneath Yucca Mountain makes 
up 4 percent to 50 percent of the blend of groundwater at two wells near Fortymile 
Wash. No evidence was found of modern recharge in the northern Amargosa Desert, 
where the age of the groundwaters appear to be similar to that of Yucca Mountain. 
3.1.3 Summary of Hydrochemical Data Pertinent to Transport 
Transport of radionuclides in the SZ depends on the chemistry of the groundwater, and physical 
and chemical properties of rocks along the flowpath. The following sections describe major-ion 
chemistry, results of tracer tests, and the redox state of groundwaters. 
3.1.3.1 Spatial Patterns of Groundwater Chemistry 
The hydrochemistry and isotopic hydrology of waters in the Death Valley regional groundwater 
flow system provide information on recharge and regional groundwater flow. The major-ion 
chemistry reflects the various processes that control water chemistry (Section 3.1.1.1.3), but 
provides little if any information on the timing of recharge. Isotopic chemistry provides 
independent information regarding the time and climatic regime under which groundwaters were 
recharged. 
Based on regional-scale groundwater chemistry, there are two basic types of water: a relatively 
dilute sodium-bicarbonate water of high silica content associated with volcanic rocks and 
derivative sediments, and a more concentrated calcium-magnesium-bicarbonate water of low 
silica content associated with carbonate rocks. Where these two basic rock types are mixed (as 
in alluvial valley fills), a water of calcium-magnesium-sodium-bicarbonate composition 
commonly results. In addition, some groundwaters of the valley fills reflect concentration of the

TDR-NBS-HS-000001 REV 00 ICN 01 3-29 August 2000 
chemical constituents due to evaporation, and these waters are distinguished by relatively higher 
proportions of sulfate and chloride ions. 
The isotopic chemistry data consist mainly of analyses of the deuterium and oxygen-18 content 
of water (which are sensitive to the temperature of precipitation), the radioactive tritium and 
carbon-14 content (indicators of time since recharge), and the carbon-13 content (indicative of 
the degree to which carbon-14 has been diluted through solution of non-radioactive rock carbon). 
Overall, the hydrochemical and isotopic evidence is in general agreement with the hydrogeologic 
understanding of the groundwater flow in the vicinity of Yucca Mountain. Recharge in the 
vicinity of Pahute Mesa flows via Oasis Valley and Crater Flat toward the Amargosa Desert, and 
groundwater flow along Fortymile Wash is the main contributor to recharge in the west central 
Amargosa Desert. There is some evidence of modern recharge in Fortymile Canyon and 
Fortymile Wash, but most of the groundwater at Pahute Mesa, Oasis Valley, Yucca Mountain, 
and the Amargosa Desert appears to represent late Pleistocene-early Holocene recharge, 
suggesting that groundwater throughflow has been minimal in the present climate. The Ash 
Meadows flow system is distinctly different in character, representing large-scale flow through 
solution-enlarged openings in a thick carbonate aquifer from two major recharge areas to a single 
major discharge area at Ash Meadows. 
3.1.3.2 Tracer Tests 
3.1.3.2.1 C-Wells Tracer Tests (Saturated Zone Transport in Fractured Tuffs) 
To test conceptual models of SZ transport in fractured tuffs, DOE conducted several cross-hole 
tracer and hydraulic tests at the C-wells Complex between 1995 and 1999 (CRWMS M&O 
2000r). The discussion here focuses on two tracer tests involving the injection of multiple 
tracers, as these tests provided the most rigorous and convincing testing of conceptual transport 
models for saturated, fractured tuffs (Figure 3-8). One of these tests was conducted in the lower 
Bullfrog Tuff, the most transmissive interval at the C-wells, and the other was conducted in the 
lower Prow Pass Tuff, which had relatively low transmissivity. 
Both multiple-tracer tests were conducted between wells UE-25c#2 and UE-25c#3 (a linear 
distance of approximately 30 m). Well UE-25c#3 was the production well in the Bullfrog Tuff 
test, and well UE-25c#2 was the production well in the Prow Pass Tuff test. The two tracer tests 
featured the simultaneous injection of several tracers having different physical and chemical 
characteristics: (1) nonsorbing solutes with diffusion coefficients differing by about a factor of 
3 (Bromide and pentafluorobenzoate [PFBA]), a weakly-sorbing solute (lithium), and 
carboxylate-modified latex polystyrene microspheres that served as colloidal tracers. The 
simultaneous injection of multiple tracers offers important advantages over single tracer 
injections because it allows transport processes to be better distinguished and quantified by 
comparing the responses of the different tracers.

TDR-NBS-HS-000001 REV 00 ICN 01 3-30 August 2000 
Source: Adapted from CRWMS M&O (2000r, Figure 97) 
NOTE: Tracer recoveries were 52% for PFBA, 49% for chlorine (Cl), 43% for bromide (Br), 19% for lithium (Li), 
0.3% for 640-nm spheres, and 0.1% for 280-nm spheres. 
Figure 3-8. Physical System, Conceptual Model, and Normalized Tracer Responses from the Prow 
Pass Tuff Multiple Tracer Test

TDR-NBS-HS-000001 REV 00 ICN 01 3-31 August 2000 
A series of laboratory studies were conducted in parallel with the field testing efforts to help 
support and constrain the interpretations of the field tests. These studies included batch sorption 
tests to characterize lithium sorption to C-wells tuffs, diffusion cell tests to determine matrix 
diffusion coefficients of tracers used in the field, and dynamic transport tests to study tracer 
transport in fractured and crushed tuffs under more controlled conditions than in the field. The 
batch sorption tests and dynamic transport tests provided estimates of lithium sorption 
parameters for comparison with sorption parameters derived from the field tests. Although 
lithium transport is not of direct concern for the YMP, such comparisons are important because 
they offer an indication of whether laboratory-derived radionuclide sorption parameters can be 
used defensibly in field-scale predictive calculations. CRWMS M&O (2000r) provide a 
summary discussion of the laboratory tests, and Reimus et al. (1999, Chapters 6 to 8) provide a 
more detailed discussion. 
3.1.3.2.1.1 Summary of Multiple-Tracer Field Test Results and Interpretations 
Normalized tracer responses (concentrations divided by injection masses) in the multiple-tracer 
tests in the Prow Pass Tuff (Figure 3-8) and Bullfrog Tuff (Figure 3-9) reveal an initial early 
peak concentration generally followed by a decline in concentration over time. The test 
conditions and tracer injection masses in the two tests are described in detail by Reimus et al. 
(1999, Chapter 5 [Prow Pass Tuff] and Appendix C [Bullfrog Tuff]). 
Source: CRWMS M&O (2000r, Figure 96) 
NOTE: Tracer recoveries were about 69% for PFBA, 69% for bromide, 39% for lithium, and 15% for microspheres. 
Concentrations are normalized to mass injected; both axes are log scale. 
Figure 3-9. Normalized Tracer Responses in the Bullfrog Tuff Multiple Tracer Test

TDR-NBS-HS-000001 REV 00 ICN 01 3-32 August 2000 
The most striking feature of the tracer breakthrough curves in the Bullfrog Tuff test (Figure 3-9) 
is their bimodal (double-peaked) behavior. This behavior is attributed to a relatively small 
fraction (about 13 percent) of the tracer solution exiting the injection borehole in short-residencetime 
pathways in the upper half of the injection interval, while the remaining tracer mass exited 
the borehole primarily in pathways of longer transport times deeper in the interval. These 
differences in travel times probably reflect differences in fracture or network permeability 
between the two zones, although they also could reflect differences in the length of the flow 
paths. Further discussion of this phenomenon is provided by CRWMS M&O (2000r) and 
Reimus et al. (1999, Appendix C). 
The response of PFBA and bromide in the Bullfrog Tuff and Prow Pass Tuff tests show 
qualitative evidence of matrix diffusion. The peak normalized PFBA concentrations are higher 
than the peak normalized bromide concentrations in both tests, and the second bromide peak in 
the Bullfrog Tuff test is somewhat delayed relative to the PFBA, with a tail that appears to cross 
over the PFBA at long times. These features are all consistent with greater matrix diffusion of 
the more diffusive tracer (bromide) relative to the less diffusive tracer (PFBA). Another 
qualitative indication of matrix diffusion in the Prow Pass Tuff test is the increase in solute tracer 
concentrations after each of the three flow interruptions during the tailing portion of the test, 
which indicate diffusion of tracers out of the matrix and into fractures during the interruptions. 
Thus, the two tests support the concept of dual-porosity behavior (where flow occurs primarily in 
fractures, but there is a great deal of stagnant water available for tracer or contaminant storage in 
the rock matrix) in the saturated, fractured system at the C-wells. 
The response of lithium in the two tests shows attenuation relative to the nonsorbing tracers, 
which is indicative of lithium sorption. The attenuation in the Prow Pass test and in the first 
peak of the Bullfrog Tuff test is almost exclusively a lowering of the peak concentration with 
little or no delay in delivery time. This behavior is consistent with lithium sorption in the matrix 
(after diffusion into the matrix). The attenuation in the second peak of the Bullfrog Tuff test 
involves a time delay along with a dramatic lowering of concentration. This behavior is 
consistent with sorption in the fracture flow pathways and in the matrix. 
The importance of deducing that lithium sorption occurs in the matrix cannot be overemphasized 
when considering the conceptual dual-porosity transport model. Although it is 
possible that the apparent matrix diffusion of nonsorbing tracers could be diffusion into stagnant 
free water in the system (rather than true matrix diffusion), such free-water diffusion is not 
consistent with the large attenuation of the lithium peaks. The lithium attenuation can only be 
explained by sorption onto a large surface area, which will be present only in the matrix. If the 
diffusion were only into stagnant free water with minimal surface area for sorption, the lithium 
response would fall between that of the bromide and PFBA (consistent with the fact that the 
lithium diffusion coefficient falls between that of bromide and PFBA). Thus, lithium provides 
strong evidence that the observed diffusion is due, at least in part, to true diffusion into the rock 
matrix. 
The response of the latex microspheres indicates that the microspheres were attenuated relative 
to the solute tracers, with more attenuation in the Prow Pass Tuff test. The responses in both 
tests (including both sizes of spheres in the Prow Pass test) are characterized by truncated tails 
relative to the solutes, but with measurable concentrations that persist throughout the tests. This

TDR-NBS-HS-000001 REV 00 ICN 01 3-33 August 2000 
behavior is consistent with filtration followed by slow detachment of the microspheres. It should 
be noted that while the microspheres in the Bullfrog Tuff test were injected simultaneously with 
the solute tracers (in a solution of approximately 0.2 M ionic strength), the microspheres in the 
Prow Pass Tuff test were injected in untraced groundwater two days before solutes were injected. 
Thus, while the response of the microspheres in the Bullfrog Tuff test may have been influenced 
by the destabilizing effect of the high ionic strength of the injection solution (i.e., possible 
coagulation), the microspheres in the Prow Pass Tuff test were not subjected to artificially high 
ionic strengths. Microsphere injection concentrations in both tests ranged from approximately 
2.5 x 1010/L to 5 x 1010/L. 
In both tests, the response of the tracers was interpreted by simultaneously fitting the 
breakthrough curves using a semianalytical, dual-porosity transport model (Reimus et al. 1999, 
Appendix D). The transport parameters obtained from the model fits, with the exception of 
lithium sorption parameters, are listed in Table 3-1. Further discussion of how these parameters 
were obtained and how they compare with other studies is provided by CRWMS M&O (2000r). 
Table 3-1. Transport Parameters Deduced from Bullfrog Tuff and Prow Pass Tuff Tracer Tests 
Bullfrog Tuff 
Parameter Pathway 1 Pathway 2 Prow Pass Tuff 
Mass fraction in pathway 0.12 0.59 0.75 
Residence time, linear flow 37 hr 995 hr 1230 hr 
Longitudinal dispersivity, linear flow 5.3 m 18.8 m 23.1 m c 
Residence time, radial flow 31 hr 640 hr 620 hr 
Longitudinal dispersivity, radial flow 3.6 m 10.7 m 6.3 m c 
Effective flow porosity, linear (radial)a 0.0029 (0.0025) 0.026 (0.017) 0.0068 (0.0034) 
Effective matrix diffusion mass transfer 
coefficientb 0.00158 sec-1/2 0.000458 sec-1/2 0.000968 sec-1/2 
Source: Adapted from CRWMS M&O (2000r, Tables 51 and 52) 
NOTES: Pathway 1 refers to pathways that resulted in the first tracer peak. Pathway 2 refers to pathways that 
resulted in the second peak. 
a Based on flow log information, it was assumed that 75% of the production flow contributed to the 
Pathway 1 responses and 25% of the flow contributed to the Pathway 2 responses. 
bThe value of the parameter for PFBA was assumed to be 0.577 times that for bromide. 
cLongitudinal dispersivities calculated after subtracting out apparent dispersion due to the recirculating 
flow field (Reimus et al. 1999, Chapter 5). 
Lithium sorption parameters (Table 3-2) were deduced from field and laboratory tests. Lithium 
sorption in the field was always approximately equal to or greater than the sorption measured in 
the laboratory. Details of the methods used to obtain the field lithium sorption parameters, and 
discussions of possible alternative interpretations, are provided by Reimus et al. (1999), as are 
the procedures for fitting the microsphere data. The microsphere filtration and detachment rate 
constants deduced from the Bullfrog and Prow Pass tracer tests are provided in CRWMS 
M&O (2000l).

TDR-NBS-HS-000001 REV 00 ICN 01 3-34 August 2000 
Table 3-2. Field- and Laboratory-Derived Sorption (Kd) Parameters for Lithium 
Laboratory Sorption Coefficient 
Parameter 
Field Sorption 
Coefficient Linear Fit to Data Fit at Infinite Dilutiona 
Prow Pass matrix KD assuming Central 
Prow Pass Tuff 0.66 0.13 0.26 
Prow Pass matrix KD assuming Lower 
Prow Pass Tuff 1.68 0.084 0.44 
Bullfrog matrix KD in Pathway 1 assuming 
Central Bullfrog Tuffb 0.24 0.19 0.44 
Bullfrog matrix KD in Pathway 1 assuming 
Lower Bullfrog Tuffb 0.97 0.32 1.64 
Bullfrog matrix KD in Pathway 2 assuming 
Central Bullfrog Tuffb 0.67 0.19 0.44 
Bullfrog matrix KD in Pathway 2 assuming 
Lower Bullfrog Tuffb 2.75 0.32 1.64 
Source: CRWMS M&O (2000r, Table 53) 
NOTES: Values based on linear sorption isotherms. 
a Values at infinite dilution obtained from slopes of Langmuir isotherm fits to the data (asymptotic slope 
at very low concentrations). Other values obtained from a simple linear fit to the entire range of data. 
bPathway 1 refers to pathways that resulted in the first tracer peak in the Bullfrog reactive tracer test, 
and Pathway 2 refers to pathways that resulted in the second peak in this test. KD values were 
calculated from the smallest matrix retardation factors obtained from alternative interpretations of the 
test. 
Effective matrix diffusion mass transfer coefficient for lithium was assumed to be equal to that for 
bromide (0.816). 
3.1.3.2.1.2 Conclusions from C-Wells Field and Laboratory Transport Testing 
The principal conclusions from the C-wells field and laboratory tests relevant to performance 
assessment (PA) of the potential Yucca Mountain repository are: 
 The relative responses of nonsorbing tracers in fractured tuffs are consistent with matrix 
diffusion. This result supports the use of a dual-porosity conceptual model to describe 
radionuclide transport through the saturated, fractured volcanic rocks near Yucca 
Mountain. 
 Sorption of lithium ions in the field was greater than or equal to measured sorption in the 
laboratory. Although lithium does not behave identically to any radionuclide, this result 
suggests that the use of laboratory-derived radionuclide sorption parameters in 
field-scale transport predictions is defensible and may even be conservative. 
Other transport parameters derived from the C-wells tracer tests include effective flow porosities, 
longitudinal dispersivities, matrix diffusion mass transfer coefficients, colloid filtration and 
detachment rate constants, and horizontal anisotropy ratios. Conclusions related to these 
parameters are provided by CRWMS M&O (2000r).

TDR-NBS-HS-000001 REV 00 ICN 01 3-35 August 2000 
3.1.3.2.2 Busted Butte Tracer Tests (Unsaturated Zone Transport in Tuffs) 
The Busted Butte tracer tests (CRWMS M&O 2000r, Sections 6.8.1 to 6.8.8) were conducted in 
unsaturated rock, so most of the results do not lend themselves directly to supporting the 
conceptual transport model for saturated, fractured tuffs. However, important information for 
understanding the SZ was produced. The most important points derived from the Busted Butte 
tracer tests that support the SZ conceptual transport model are that nonsorbing tracers migrated 
faster than sorbing tracers, fracture-matrix interactions were important to transport, and model 
predictions qualitatively agreed with observed results. In particular, the last point adds 
confidence to the SZ transport model. 
3.1.3.3 Oxidation and Reduction Potential 
The rate of transport of some radionuclides may be influenced by the oxidation/reduction 
potential (Eh) of the groundwater flow system (CRWMS M&O 2000r). These radionuclides can 
exist in more than one oxidation state under the conditions typical of the groundwaters in the 
vicinity of Yucca Mountain. For example, under oxidizing conditions, neptunium-237 in 
solution exists predominantly in the pentavalent oxidation state. However, under sufficiently 
reducing conditions, the pentavalent oxidation state is reduced to the tetravalent oxidation state. 
The lower oxidation state species sorb more strongly to aquifer host rocks than those of the 
higher oxidation state. For this reason, the Eh of groundwaters along potential flowpaths from 
the potential repository to the accessible environment is a parameter of considerable importance. 
Eh potentials commonly are supplemented with measurements of the concentrations of redox 
sensitive species that may be present in groundwater samples. Such species might include 
dissolved oxygen and redox couples such as ferrous/ferric iron, ammonium/nitrite/nitrate, 
sulfide/sulfate, and other couples. Analysis of the results of such measurements, when combined 
with redox potential measurements, can provide constraints on the redox state of groundwater at 
a given location. 
Measurements to define the redox state of groundwaters have been carried out on waters from a 
limited number of boreholes on Yucca Mountain (CRWMS M&O 2000r) and from the 
NCEWDP boreholes. Analyses of these data lead to the following conclusions: 
 Reducing conditions (Eh less than 200 mv) were found in the deeper portions of the 
volcanic section (i.e., Bullfrog and Tram Formations) beneath the crest of Yucca 
Mountain. 
 Reducing conditions were found close to the water table on the eastern flank of Yucca 
Mountain downgradient from the footprint of the potential repository (borehole WT-17). 
 Oxidizing conditions were found in groundwater from boreholes along Fortymile Wash. 
 Reducing conditions were found in some of the NCEWDP boreholes located along 
Highway US 95 south of Yucca Mountain. 
In summary, low-Eh barriers to radionuclide transport may be present in the deeper volcanic 
section beneath Yucca Mountain, close to the water table in volcanic rocks downgradient of the

TDR-NBS-HS-000001 REV 00 ICN 01 3-36 August 2000 
potential repository, and in the alluvium of the Amargosa Valley downgradient from the 
potential repository (CRWMS M&O 2000r). These low-Eh barriers increase the sorption 
affinity of redox sensitive elements such as neptunium and technetium. This affinity is 
quantified through sorption experiments using rock and water samples from wells located in 
zones of low-Eh potential. 
3.1.4 Summary of Laboratory Data 
This section summarizes laboratory data and interpretations that are relevant to the development 
and testing of conceptual and numerical transport models of the SZ at Yucca Mountain. The 
laboratory data obtained include sorption coefficients for various hydrologic units, diffusion 
coefficients, and parameters related to colloidal transport. The discussion in this section is 
derived from CRWMS M&O (2000r). 
The radionuclides of interest include the following elements: americium, thorium, zirconium, 
actinium, samarium, niobium, lead, radium, strontium, cesium, lead, tin, plutonium, neptunium, 
uranium, selenium, nickel, protactinium, carbon, chlorine, technetium, and iodine. Sorption 
coefficients were obtained in several types of experiments. Most of the coefficients were 
obtained in batch experiments. A limited number of experiments were carried out with crushedrock 
columns to check the results of the batch experiments in a flowing system. A small number 
of experiments were carried out with solid-rock columns to test the applicability of the results of 
crushed-rock experiments to transport in solid rock. Batch experiments also were carried out to 
evaluate the sorption of radionuclides onto colloidal-sized materials. In this set of experiments, 
the reversibility of the radionuclide sorption reactions was of particular interest. 
Effective diffusion coefficients for radionuclides were obtained in laboratory experiments with 
specially designed diffusion cells and beakers made of rock samples from the site. These 
experiments were performed with representative water and rock compositions from the site. 
A limited number of experiments were performed to evaluate the sorption and diffusion of 
radionuclides during fracture flow. 
3.1.4.1 Sorption Experiments 
Because of the nature of sorption reactions, sorption coefficients for a given element are not 
single-valued parameters. Sorption coefficients commonly are functions of water composition, 
rock composition, radionuclide concentration, temperature, and other less obvious factors such as 
the presence or absence of microbes. 
Insufficient data are available to directly obtain information on the sorption behavior of all the 
elements of interest as a function of all of these variables. To address this situation, an indirect 
approach was used based on expert elicitation. Experts who had been involved in the 
experimental determination of sorption coefficients for the YMP and who had read the available 
literature regarding the sorption behavior of the various elements of interest were asked in an 
expert elicitation to formulate probability distributions of sorption coefficients for the elements 
of interest (CRWMS M&O 2000r). These distributions were to include any information the 
experts were aware of regarding the influence of the factors listed above on the sorption behavior 
of a given element. There was an expressed intent to underestimate the limits of the distributions

TDR-NBS-HS-000001 REV 00 ICN 01 3-37 August 2000 
(i.e., smaller values for the lower and upper limits on the distributions) as an acknowledgement 
of the fact that the available database was incomplete. Distributions were formulated for 
sorption coefficients for each of the elements of interest on devitrified tuff, vitric tuff, zeolitic 
tuff, and iron oxide (as a surrogate for waste package corrosion products). This expert elicitation 
process (CRWMS M&O 2000r) was conducted in 1993, and since then, additional laboratory 
data have been obtained on selected elements and used to update the distributions. 
Sorption coefficients, obtained using waters and rock samples from the site, were obtained in 
batch experiments in which a small amount of crushed rock material is combined with water 
from the site; the water has been spiked with a known amount of a radionuclide. After a 
prescribed period of time, the water and the rock material are separated, and the concentration of 
the radionuclide in the water is measured. The sorption coefficient is calculated from the amount 
of radionuclide that was removed from solution. Although this technique is fast and 
straightforward, there are several questions that must be addressed regarding the application of 
these data in transport calculations. 
One major question is whether the static nature of the batch experiments is representative of the 
dynamic conditions under which radionuclides would be transported at Yucca Mountain. To 
address this question, experiments were carried out with columns filled with crushed rock. The 
sorption coefficients obtained in these flow experiments were compared with the results of batch 
experiments. 
Sorption coefficient distributions for radionuclides were derived from laboratory data obtained in 
experiments with waters and rock samples from the site and from data available in the literature. 
Laboratory experiments generally were performed with at least two water compositions (J-13 
and UE-25p#1) and several pH levels to evaluate the impact of these parameters on the sorption 
coefficient. Waters from wells J-13 and UE-25p#1 represent end-members in the ranges of 
major ion concentrations found in the SZ waters at Yucca Mountain (CRWMS M&O 2000b). 
Other potential influences on the sorption behavior of elements of interest (e.g., radionuclide 
concentrations, sorption kinetics, oxidation state, and temperature) also were evaluated, as were 
the potential effects of organic materials on actinide sorption. Models were developed to explain 
the sorption coefficient data in selected combinations of water, rock, and radionuclides. These 
combinations included sorbing radionuclides considered to be of greatest potential risk to the 
accessible environment based on their combination of inventory, half-life, mobility, and dose 
conversion factors. 
Because of the large numbers of experiments required to address the sorption behavior of every 
combination of water, rock, and radionuclide, some process for focusing the experimental 
program was required. The process developed has been called the minimum Kd concept 
(where Kd refers to the sorption coefficient). The essence of this concept is that a minimum Kd 
exists according to which radionuclides will not reach the accessible environment through a 
groundwater pathway over the 10,000-yr regulatory period (NRC 1998) within some adequate 
margin of error. Radionuclides that can be shown to have this minimum Kd in rock and water 
systems similar to those at Yucca Mountain would not require as much detailed investigation as 
radionuclides that do not. Those radionuclides with essentially no sorption potential are 
eliminated from further consideration and the sorption coefficient is set to zero. This allowed the

TDR-NBS-HS-000001 REV 00 ICN 01 3-38 August 2000 
experimental program to be focused on those radionuclides that could have the maximum impact 
on doses at the accessible environment over the regulatory time frame of interest. 
Sorption Coefficients for Performance AssessmentSorption coefficients for the SZ, and the 
distributions of these coefficients, are provided in Table 3-3. Details of the database used to 
derive these and other sorption coefficient distributions are presented by CRWMS M&O 
(2000r, Table 2). 
Table 3-3. Sorption-Coefficient Data and Distributions for Saturated Zone Units 
Sorption Coefficient 
Element Rock Type 
Minimum 
(mL/g) 
Maximum 
(mL/g) Mean 
Coefficient 
of Variation 
Distribution 
Type 
Devitrified 100 2000   Uniform 
Vitric 100 1000 400 0.20 Beta 
Zeolitic 100 1000   Uniform 
Americium (also 
Actinium, Niobium, 
Samarium, Thorium, 
Zirconium) Iron oxide 1000 5000   Uniform 
Devitrified 5 100 50 0.15 Beta 
Vitric 50 300 100 0.15 Beta 
Zeolitic 50 400 100 0.15 Beta 
Plutonium 
Iron oxide 1000 5000   Uniform 
Devitrified 0 5.0   Uniform 
Vitric 0 4.0   Uniform 
Zeolitic 5 20.0 7.0 0.3 Beta 
Iron oxide 100 1000   Uniform 
Uranium 
Alluvium 0 8.0   Uniform 
Devitrified 0 2.0 0.5 0.3 Beta 
Vitric 0 2.0 0.5 1.0 Beta (exp) 
Zeolitic 0 5.0 1.0 0.25 Beta 
Iron oxide 500 1000   Uniform 
Neptunium 
Alluvium 0 100 18 1.0 Beta 
Devitrified 100 500   Uniform 
Vitric 100 500   Uniform 
Zeolitic 1000 5000   Uniform 
Radium 
Iron oxide 0 1500 30 1.0 Beta (exp) 
Devitrified 20 1000   Uniform 
Vitric 10 100   Uniform 
Zeolitic 500 5000   Uniform 
Cesium 
Iron oxide 0 500 30 1.0 Beta (exp) 
Devitrified 10 200   Uniform 
Vitric 20 50   Uniform 
Zeolitic 2000 5000   Log uniform 
Strontium 
Iron oxide 0 30 10 0.25 Beta

TDR-NBS-HS-000001 REV 00 ICN 01 3-39 August 2000 
Table 3-3. Sorption-Coefficient Distributions for Saturated Zone Units (Continued) 
Sorption Coefficient 
Element Rock Type 
Minimum 
(mL/g) 
Maximum 
(mL/g) Mean 
Coefficient 
of Variation 
Distribution 
Type 
Devitrified 0 200   Uniform 
Vitric 0 50   Uniform 
Zeolitic 0 200   Uniform 
Nickel 
Iron oxide 0 1000   Uniform 
Devitrified 100 500   Uniform 
Vitric 100 500   Uniform 
Zeolitic 100 500   Uniform 
Lead 
Iron oxide 100 1000   Uniform 
Devitrified 20 200   Uniform 
Vitric 20 200   Uniform 
Zeolitic 100 300   Uniform 
Tin 
Iron oxide 0 5000   Uniform 
Devitrified 0 100   Uniform 
Vitric 0 100   Uniform 
Zeolitic 0 100   Uniform 
Protactinium 
Iron oxide 500 1000   Uniform 
Devitrified 0 1.0 0.1 1.0 Beta (exp) 
Vitric 0 1.0 0.1 1.0 Beta (exp) 
Zeolitic 0 1.0 0.2 1.0 Beta (exp) 
Selenium 
Iron oxide 0 500 30 1.0 Beta (exp) 
Carbon Iron oxide 10 100   Uniform 
Chlorine, Technetium, 
Iodine 
All tuffs 0 0    
Technetium Alluvium 0.27 0.62   Uniform 
Iodine Alluvium 0.32 0.63   Uniform 
Source: CRWMS M&O (2000r, Table 2b) 
NOTE:  means this parameter is not applicable. 
Results of Batch Sorption Coefficient ExperimentsFor most of the elements of interest, the 
batch experiments show rapid sorption kinetics and reach equilibrium in hours to several days. 
However, data on the sorption behavior of plutonium indicate that the sorption kinetics 
associated with this element are slow. It could take a year or more for plutonium sorption 
reactions to reach equilibrium in the groundwater system at Yucca Mountain. This may reflect 
the fact that plutonium can occur in several oxidation states in Yucca Mountain waters. Sorption 
experiments using plutonium in well-defined oxidation states indicate that the sorption behavior 
of plutonium depends on its oxidation state. This effect was factored into the sorption coefficient 
distributions presented in Table 3-3. The potential impacts of microbes on the results obtained in 
sorption experiments have not been evaluated (CRWMS M&O 2000r). Because plutonium can 
simultaneously exist in several oxidation states, the sorption behavior of this element may be 
affected by microbes that may be present in laboratory experiments. In deriving the sorption 
coefficient distributions for plutonium, it was assumed that any microbial influence present in 
laboratory experiments would also be present in the SZ at Yucca Mountain.

TDR-NBS-HS-000001 REV 00 ICN 01 3-40 August 2000 
Experiments with different size-fractions of crushed rock (CRWMS M&O 2000r) suggest that 
crushing the rock does not have an important affect on the sorption coefficients obtained for the 
elements tested (cesium, strontium, neptunium, and technetium). This conclusion is consistent 
with results of experiments using solid-rock wafers and solid-rock columns. However, this 
conclusion does not necessarily apply to elements not tested (e.g., plutonium). 
Batch experiments with organic molecules (model organic compounds, fulvic acid, and humic 
acid) lead to the conclusion that the potential affect of organic complexation on the sorption 
behavior of plutonium and neptunium is not significant in the rock and water systems associated 
with Yucca Mountain. The potential impact of organic molecules on the sorption behavior of 
other elements was not investigated. 
Results of Column ExperimentsExperiments with crushed-rock columns generally 
corroborated the results obtained from batch experiments. However, crushed-rock column 
experiments with plutonium indicated that an early breakthrough fraction was present in most 
experiments. This fraction decreased in magnitude as the flow rate of the column was decreased. 
The flow-rate limit at which this fraction becomes insignificant has not been determined for most 
Yucca Mountain rock and water systems. 
Solid-rock columns were studied only in relation to the transport of selenium under unsaturated 
conditions. In these studies, it was found that selenium transport rates through the columns 
could be modeled adequately with the results of batch experiments. 
3.1.4.2 Matrix Diffusion Experiments 
In addition to the C-wells field tracer tests, matrix diffusion under saturated conditions has been 
observed and quantified in the laboratory under static and dynamic (flowing) conditions. The 
laboratory experiments confirmed that matrix diffusion is a valid process affecting radionuclide 
transport, and they provided direct estimates of radionuclide and tracer diffusion coefficients in 
various volcanic tuff matrices. These experiments included: 
 Rock beaker experiments, in which radionuclide solutions are placed into thick-walled 
beakers machined out of samples of tuff materials (saturated). Diffusion coefficients 
are determined from the decline in radionuclide concentration resulting from diffusion 
into the walls of the beaker. 
 Diffusion cells, in which large concentration gradients of radionuclides or tracers are 
imposed across saturated tuff slabs. Diffusion coefficients are determined from the 
rise in concentrations of tracers in reservoirs on the initially tracer-free side of the slab. 
 Fractured tuff column experiments, in which radionuclide solutions are passed through 
saturated, fractured tuff cores, and the effects of matrix diffusion are seen as lower peak 
concentrations and longer tails for the more diffusive tracers (analogous to the C-wells 
field tracer tests). 
The results of these experiments are summarized in this section, and details are provided by 
CRWMS M&O (2000r, Sections 6.5, 6.6, 6.7, and 6.9).

TDR-NBS-HS-000001 REV 00 ICN 01 3-41 August 2000 
3.1.4.2.1 Rock Beaker Experiments 
The radionuclides tested in rock beaker experiments included tritium, technetium-95, 
neptunium-237, americium-241, strontium-85, cesium-137, and barium-133. Water from well 
J-13 was used in all experiments, and the tuff matrices studied were all devitrified. Batchsorption 
experiments with J-13 water and the tuffs studied were conducted in parallel with the 
rock beaker experiments because radionuclide uptake by the rock matrices is dependent on the 
diffusion coefficient and the sorption of the radionuclide. Typical experimental results for two 
nonsorbing radionuclides (tritium and technetium-95, as tritiated water and pertechnetate, 
respectively) and a weakly-sorbing radionuclide (neptunium-237) are presented in Figure 3-10. 
Also shown in Figure 3-10 are the results of model simulations to match the nonsorbing 
radionuclide concentration histories. Technetium-95 diffuses into the matrix more slowly than 
tritium because of its larger size and negative charge, which repels it from the negativelycharged 
rock surfaces. The neptunium-237 concentration history reflects the combined effects of 
diffusion and sorption in the matrix. Although neptunium-237 should diffuse slowly compared 
to tritium, the slow diffusion is counter-balanced by sorption onto the rock surfaces, which 
effectively lowers the neptunium-237 concentration in the pores and keeps the diffusion gradient 
high to drive additional neptunium-237 into the matrix. The other radionuclides studied all had 
much larger sorption coefficients than neptunium-237, so they were rapidly depleted from the 
rock beaker solutions. 
Source: CRWMS M&O (2000r, Figure 28) 
NOTE: Rock beaker diffusion data for tritium, technetium-95, and neptunium-237 in a devitrified tuff. 
Figure 3-10. Rock Beaker Diffusion

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Modeling of the experimental results indicated that the uptake of radionuclides into the tuff 
matrices by the combined effects of matrix diffusion and sorption was underpredicted when the 
matrix diffusion coefficient for tritiated water was used in the models in conjunction with 
radionuclide sorption parameters measured in the batch experiments. It was concluded that this 
combination of parameters should yield conservative predictions of matrix uptake of sorbing 
radionuclides in PA models. 
3.1.4.2.2 Diffusion Cell Experiments 
Diffusion cell experiments have been conducted using radionuclides and the nonradioactive, 
nonsorbing tracers that were used in the C-wells field experiments. In the latter case, the 
experiments focused on bromide and PFBA diffusion through C-wells tuff matrices. 
Radionuclide experiments have examined the diffusion of tritium, technetium-95, 
neptunium-237, plutonium-239, and natural uranium(VI) through devitrified and zeolitic tuff 
matrices. Water from well J-13 and synthetic UE-25p#1 water were used in the radionuclide 
experiments. Water from well J-13 was considered representative of groundwater from the 
volcanic aquifer beneath Yucca Mountain, and the water from well UE-25p#1 was considered 
representative of groundwater from the underlying Paleozoic carbonate aquifer. In this way, the 
diffusion cell tests included a wide range of groundwater chemistries from the SZ near Yucca 
Mountain. 
A typical set of breakthrough curves (i.e., concentrations as a function of time on the initially 
radionuclide-free side of the tuff slab) are shown in Figure 3-11 for an experiment involving 
tritium, uranium, and plutonium-239. Uranium concentrations are lower than tritium because of 
the larger size and lower diffusion coefficient of the uranium solute (probably uranyl ions) 
relative to tritium (as well as possibly some sorption of the uranium to the tuff). Plutonium-239 
does not diffuse through the slab because of the high sorption capacity of the tuff matrix for 
plutonium. In general, the relative diffusion coefficients (including the effects of sorption) of the 
radionuclides studied were tritium > technetium-95 > uranium > neptunium-237 >> plutonium- 
239. Diffusion coefficients for a given radionuclide in different tuff matrices were dependent on 
the porosity and microstructure of the tuffs, as well as on the zeolite content of the tuffs for 
radionuclides that sorb strongly to zeolites (e.g., neptunium-237). 
The C-wells diffusion cell experiments established a consistent 3:1 ratio of matrix diffusion 
coefficients for bromide and PFBA in all C-wells tuff matrices, with the smaller bromide ion 
having the higher diffusivity. This ratio was a critical constraint in the interpretation of the field 
tests. The C-wells diffusion cell experiments also established a good correlation between the log 
of the matrix diffusion coefficient and the log of the matrix permeability (which was measured 
for each diffusion cell). This correlation was better than the correlation of matrix diffusion with 
matrix porosity. This result suggests that matrix permeability may be a good predictor of matrix 
diffusion coefficients of nonsorbing radionuclides in Yucca Mountain tuffs.

TDR-NBS-HS-000001 REV 00 ICN 01 3-43 August 2000 
Source: CRWMS M&O (2000r, Figure 31) 
Figure 3-11. Diffusion of Tritium, Uranium, and Plutonium through a Devitrified Tuff 
3.1.4.2.3 Fractured Rock Column Experiments 
Matrix diffusion has been observed in many saturated fractured rock column experiments. As 
with the diffusion cells, these experiments featured the radionuclides and nonradioactive tracers 
that were used in the C-wells field experiments. Fractured rock column experiments simulate 
field conditions more realistically than rock beaker or diffusion cell experiments because they 
incorporate natural fractures with realistic geometries and mineral coatings and because they 
include the effects of flow in the observations of transport processes. Details of the experimental 
methodology for fractured rock columns are provided by CRWMS M&O (2000r, Section 6.5.3). 
Two types of fractured rock column experiments were conducted to demonstrate and quantify 
matrix diffusion. In the first type of experiment, two or more nonsorbing radionuclides or tracers 
of different diffusion coefficients are simultaneously passed through a fracture. As in the 
C-wells field experiments, the solute with the larger diffusion coefficient will have a lower peak 
concentration and a longer tail than will the solute with the smaller diffusion coefficient because 
the former loses more mass to the matrix as it passes through the fracture. For example, 
technetium-95 (as pertechnetate) passes through the fracture more rapidly than tritiated water 
because pertechnetate diffuses into the matrix more slowly than the tritiated water (Figure 3-12). 
Neptunium-237 is attenuated relative to both nonsorbing radionuclides because it sorbs to the 
fracture and matrix surfaces. Thus, these experiments also yield information on sorption 
processes and magnitudes under flowing conditions in fractures. The second type of fractured 
rock experiment yielding information on matrix diffusion actually is a series of experiments 
involving the same nonsorbing solute at two or more flow rates. At higher flow rates, there is 
less matrix diffusion of the solute because of the shorter residence time in the fracture, so the 
solute concentration will peak at a higher value and the tail will be shorter than at lower flow 
rates.

TDR-NBS-HS-000001 REV 00 ICN 01 3-44 August 2000 
Source: CRWMS M&O (2000r, Figure 25) 
NOTE: Data from borehole G4 (908.6 m [2981 ft] below surface). The earlier recovery of technetium-95 relative to 
tritium is the result of the smaller matrix diffusion coefficient of the pertechnetate ion relative to tritiated 
water. 
Figure 3-12. Cumulative Recoveries of Tritium, Technetium-95, and Neptunium-237 in a Fractured Tuff 
Column 
Both types of experiments can yield estimates of matrix diffusion mass transfer coefficients in a 
fracture flow system. In general, estimates of mass transfer rates in laboratory-scale fractures are 
greater than those deduced from the C-wells field experiments. This result may be attributable to 
(1) greater average fracture apertures in field experiments, which reduces mass transfer rates into 
the matrix, (2) an increase in matrix tortuosity (and hence a decrease in matrix diffusion 
coefficients) at increasingly greater distances into the matrix (field tests have longer time scales 
and hence larger diffusion distances into the matrix), (3) a greater diffusion resistance offered by 
fracture mineral coatings in the field, and (4) the tendency to have a higher percentage of 
diffusion into stagnant free water (with correspondingly greater effective diffusion coefficients) 
in the laboratory than in the field as a result of the shorter time scales in the laboratory. The 
mass transfer rates derived from the C-wells field experiments are more conservative, and they 
have the added benefit of being obtained over more relevant time and length scales. However, 
the laboratory experiments are useful for demonstrating the validity of matrix diffusion as an 
effective attenuation process in the SZ, and they are the only types of realistic flow experiments 
that can be conducted using radionuclides.

TDR-NBS-HS-000001 REV 00 ICN 01 3-45 August 2000 
3.1.4.3 Colloid-Facilitated Transport Experiments 
Colloids are capable of facilitating the transport of radionuclides over long distances in the SZ 
only if a large percentage of the colloids do not irreversibly attach to rock surfaces, and the 
desorption rate of radionuclides from the colloids is extremely slow (i.e., radionuclides are 
actually impregnated in the colloids or are very strongly sorbed to colloid surfaces), or if steadystate 
colloid concentrations are so high that colloid surfaces can effectively compete with 
immobile surfaces for radionuclides on the basis of surface area arguments. Analyses of colloid 
concentrations and size distributions in Yucca Mountain groundwaters have confirmed that high 
concentrations of colloids do not occur in the SZ around Yucca Mountain. Published 
correlations of colloid concentrations as a function of water chemistry, which draw upon a global 
database of measurements, also suggest that steady-state colloid concentrations are unlikely to 
ever be high enough for the latter condition to be met even under perturbed conditions 
(Triay et al. 1996). 
The YMP has addressed the attachment and detachment of colloids by using the polystyrene 
microsphere data from the C-wells field tests to obtain conservative estimates of colloid 
attachment and detachment rates in fractured tuffs, and by using published data to obtain 
estimates of attachment and detachment rates in alluvial settings (Section 3.2.4.5). The 
published correlations of colloid concentrations as a function of water chemistry also support 
indirect estimates of attachment rates, as it is widely accepted that lower concentrations occur 
under conditions where colloids are less stable and more likely to attach to surfaces. Details of 
stability-based arguments for bounding colloid concentrations and attachment rates in Yucca 
Mountain waters are provided by CRWMS M&O (2000h). 
Recent laboratory experiments addressed the magnitude and reversibility of radionuclide 
sorption onto colloids. Some of the earliest laboratory experiments involved the transport of 
cesium-137 and silica colloids in columns packed with glass beads. Cesium sorption to the silica 
was fast and reversible, and under these conditions, the ability of the colloids to facilitate 
cesium-137 transport was limited because of the large amount of competing sorptive surface area 
presented by the glass beads. Nevertheless, these experiments helped establish equilibrium- and 
kinetic-based modeling approaches for describing colloid-facilitated transport in the SZ. These 
experiments also showed that considerable colloid-facilitated transport would be an issue only 
for radionuclides that sorbed much more strongly to colloids than did cesium-137. 
Recent laboratory experiments measured the magnitude and rates of sorption and desorption of 
strongly-sorbing, long-lived radionuclides onto several different types of colloids that may be 
present in the near-field (goethite, hematite) or far-field (silica, montmorillonite clay) 
environment at Yucca Mountain (CRWMS M&O 2000f). These studies focused on 
plutonium-239 and americium-243, with the plutonium being prepared in two different forms: 
colloidal plutonium(IV) and soluble plutonium(V). Water from well J-13 and a synthetic 
sodium-bicarbonate solution were used in the experiments. Colloid concentrations were varied 
in some of the experiments to determine the effect of colloid concentration. Details of the 
experiment and summaries of the plutonium-239 sorption and desorption rates are provided by 
CRWMS M&O (2000h). These and other results can be summarized as follows:

TDR-NBS-HS-000001 REV 00 ICN 01 3-46 August 2000 
 The sorption of plutonium-239 onto hematite, goethite, and montmorillonite colloids 
was strong and rapid, but sorption onto silica colloids was slower and weaker. 
 The desorption rates of plutonium-239 from hematite colloids were too small to measure 
even after 150 days. Desorption from goethite and montmorillonite colloids also was 
slow, but not as slow as for hematite. The desorption rates of plutonium-239 from silica 
colloids was rapid relative to the other colloids studied. 
 For a given form of plutonium-239, sorption generally was stronger, faster, and less 
reversible in the synthetic sodium-bicarbonate water than in the natural water from well 
J-13. Apparently, the presence of other ions, probably calcium, in the natural water 
tended to slightly suppress the sorption of plutonium-239. 
 There was no clear trend of colloidal plutonium(IV) or soluble plutonium(V) sorbing 
more strongly to the colloids. In general, plutonium(V) sorbed slightly more to hematite 
and silica, while plutonium(IV) was sorbed slightly more to goethite and 
montmorillonite. 
 The sorption of plutonium-239 was greatest per unit mass of colloid at the lowest colloid 
concentrations (i.e., sorption was greatest when measured at low colloid concentrations). 
This result suggests that the colloid surface area at the lower colloid concentrations was 
sufficient to sorb most of the plutonium in solution, so the addition of more colloids to 
the solutions did not result in a corresponding linear increase in the amount of plutonium 
sorbed. The most conservative sorption values for PA will come from data generated at 
low colloid concentrations. 
 The sorption of americium-243 onto hematite, montmorillonite, and silica colloids 
showed the same trends as plutonium-239 sorption (i.e., hematite > montmorillonite > 
silica), and the magnitudes of sorption for the two radionuclides were similar for the 
different colloids. Results of desorption measurements for americium-243 are not yet 
available. 
There are two preliminary conclusions from this ongoing work. First, waste-form colloids such 
as hematite (resulting from degradation of waste package materials) pose the greatest risk for 
colloid-facilitated transport, although these colloids would have to travel through the UZ before 
reaching the SZ. Second, the transport of plutonium or americium in the SZ will be more 
strongly facilitated by natural clay colloids than by silica colloids. 
3.2 CONCEPTUAL MODEL OF SITE-SCALE SATURATED ZONE FLOW AND 
TRANSPORT 
The general conceptual model of SZ flow in the site-scale SZ flow and transport model area is 
that groundwater flows southerly from recharge areas of higher precipitation at higher elevations 
north of Yucca Mountain, through the Tertiary volcanic rocks of the Alkali Flat-Furnace Creek 
groundwater basin, toward the Amargosa Desert. Within the site-scale model area (Figure 3-4), 
recharge occurs from infiltration of precipitation and infiltration of flood flows from Fortymile 
Wash and its tributaries. In the southeastern part of the model area (within the Ash Meadows

TDR-NBS-HS-000001 REV 00 ICN 01 3-47 August 2000 
groundwater basin), considerable flows enter and exit the area in the lower carbonate aquifer 
system (CRWMS M&O 1999a). This aquifer system is believed to underlie much of the Alkali 
Flat-Furnace Creek groundwater basin; however, the flow patterns of groundwater in this area 
and their relationship to flow in the Ash Meadows flow system are poorly understood due to lack 
of deep-well data. 
Outflow from the site-scale SZ flow and transport model area mostly occurs across the southern 
boundary of the model and to pumpage by irrigation wells in the Amargosa Farms area. The 
following sections describe the HFM, boundary conditions of the site-scale SZ flow and 
transport flow model, and alternative conceptual models. Assumptions, uses, and limits of the 
site-scale SZ flow and transport model are discussed in Section 3.5. 
3.2.1 Hydrogeologic Framework and Hydrogeologic Units 
Building an HFM is an essential step in developing the site-scale SZ flow and transport model 
for the Yucca Mountain area. To this end, an HFM was constructed, incorporating data from the 
Death Valley Region flow model (DAgnese et al. 1997), geologic maps and cross sections, 
borehole data, geophysical data, digital elevation data, and the existing geologic framework 
model (Figure 3-4) of the 40 km2 (15 mi2) potential repository area (USGS 2000a). 
The HFM represents a 3-D version of the hydrogeology surrounding Yucca Mountain 
(Figure 3-4) and covers an area of about 1,350 km2 (521 mi2) that is 45 km long and 30 km wide 
(28.0 mi by 18.6 mi). Vertically, the model extends from an interpretation of the water table to 
the base of the regional groundwater flow model at 2,750 m (9,020 ft) below the water table 
(DAgnese et al. 1997). The model domain was selected to be: 
 Coincident with grid cells in the regional-scale groundwater flow model (DAgnese et 
al. 1997) such that the base of the site-scale SZ flow and transport model was equivalent 
to the base of the regional-scale model. 
 Sufficiently large to minimize the effects of boundary conditions on estimating 
permeability values at Yucca Mountain. 
 Sufficiently large to assess groundwater flow at distances beyond the proposed 20-km 
12.5-mi) compliance boundary downgradient from the potential repository area (a 
regulatory issue). 
 Small enough to minimize the number of computation nodes used in the model. 
 Thick enough to include part of the regional Paleozoic carbonate aquifer. 
 Large enough to include wells in the Amargosa Desert at the southern end of the 
modeled area.

TDR-NBS-HS-000001 REV 00 ICN 01 3-48 August 2000 
Assumptions used for the HFM are methodological and geological. The major assumptions are 
(USGS 2000a): 
 The HFM is an acceptable representation of the hydrogeologic units of the SZ flow 
system. Underlying this assumption is the idea that it is valid to treat the hydrologic 
properties of a hydrogeologic unit grid cell as uniform. 
 Hydrostratigraphic units influence the magnitude and direction of groundwater flow, and 
stratigraphic units can be simplified into hydrostratigraphic units. 
 Boundaries of stratigraphic units represented on maps, wells, and cross sections are 
sufficiently accurate for groundwater flow modeling purposes. 
 Interpolation algorithms using data on faults and stratigraphic unit tops from maps, 
wells, and cross sections are sufficiently accurate to characterize the top of a 
hydrogeologic unit. 
Construction of a 3-D HFM involves the following seven steps (USGS 2000a). 
 Geologic units are classified into hydrogeologic units based on hydraulic properties and 
lateral extent. 
 Digital elevation data are combined with hydrogeologic maps to provide a series of 
points in 3-D space depicting the locations of outcrops of individual hydrogeologic 
units. 
 Cross sections and lithologic logs are used to locate hydrogeologic units in the 
subsurface. 
 Maps and cross sections are used to locate faults. 
 Structure contour-maps are developed for each hydrogeologic unit by interpolating 
surface and subsurface positions with gridding software that incorporates unit offsets 
across faults. 
 An HFM is developed when the structure contour maps for the individual hydrogeologic 
units are combined, using appropriate stratigraphic principles to control their sequence, 
thickness, and lateral extent. 
 The potentiometric surface is used to truncate the top of the HFM. 
The HFM is constructed using a grid of cells. The 30-km by 45-km (18.6 by 28.0 mi) model 
domain is divided into cells that measure 125 m (410 ft) on each side, and there are 240 cells in 
the east-west dimension and 360 cells in the north-south dimension. The vertical dimension of 
each cell is not fixed; rather it is determined by the thickness of each of the 18 hydrogeologic 
units that it penetrates. The top of the model is defined as the top of the potentiometric surface

TDR-NBS-HS-000001 REV 00 ICN 01 3-49 August 2000 
(the water table), and the bottom of the model is a smoothed surface 2,750 m (9,020 ft) below the 
potentiometric surface. 
Hydrogeologic UnitsA basic principle followed in constructing the HFM is that the 
hydrogeologic units at Yucca Mountain form a series of alternating volcanic aquifers and 
confining units overlying the regional carbonate aquifer (USGS 2000a). Many of the formations 
have eroded since deposition. The volcanic rocks generally thin toward the south (away from 
their sources north of Yucca Mountain). The volcanic aquifers and confining units interfinger 
with undifferentiated valley-fill and the valley-fill aquifer to the south and southeast, while 
structural features delimit the eastern, western, and portions of the southern edges of Yucca 
Mountain. The volcanic rocks and valley-fill materials generally covered the pre-existing 
topography, so that the top of a formation may be more planar than the base. 
The geologic relationships, both actual and inferred, were simplified to accommodate computer 
mapping, framework modeling, and groundwater flow modeling limitations (USGS 2000a). The 
rocks and deposits near Yucca Mountain were classified into hydrogeologic units based on 
hydraulic properties. Where feasible, hydrogeologic units identified by previous investigators 
were retained. Many of the units are not present in the site-scale model, but are included for 
consistency with regional-scale models. In all, 18 hydrogeologic units are delineated in the sitescale 
SZ flow and transport model area. USGS (2000a, Table 6-3) summarize the hydrogeologic 
units and how they relate to the geologic units in the model area. Figure 3-13 illustrates, by way 
of a fence diagram, the complex 3-D spatial relation among these units within the site-scale 
model area. 
3.2.2 Groundwater Occurrence and Flow 
As described by Luckey et al. (1996, p. 17), the Tertiary volcanic section at Yucca Mountain 
consists of a series of ash-flow and bedded ash-fall tuffs that contain minor amounts of lava and 
flow breccia. Individual ash-flow tuffs may be several hundred meters thick, whereas bedded 
tuffs generally are less than a few tens of meters thick. Ash-flow tuffs range from nonwelded to 
densely welded, and the degree of welding varies both horizontally and vertically in a single flow 
unit. Nonwelded ash-flow tuffs, when unaltered, have moderate to low matrix permeability, but 
high porosity. Permeability is decreased by secondary alteration, and fractures are infrequent 
and often closed in the low-strength nonwelded tuffs. Consequently, these rocks generally 
constitute laterally extensive SZ confining units in the Yucca Mountain area. The properties of 
partly welded tuffs vary between those of fractured, welded tuffs and those of altered, nonwelded 
tuffs. The densely welded tuffs generally have minimal primary porosity and water-storage 
capacity, but they can be highly fractured. Where interconnected, fractures can easily transmit 
water, and highly fractured units function as aquifers. In general, the bedded tuffs have high 
primary porosity and can store large amounts of water. Their matrix permeability is moderate to 
low, depending on the degree of alteration. The bedded tuffs generally function as confining 
units, at least when compared to less porous but densely fractured ash-flow tuffs. Lavas, flow 
breccias, and other minor rock types are neither thick nor widely distributed in the Yucca 
Mountain area. Their hydraulic properties probably are as variable as the properties of the 
ash-flow tuffs, but the relatively limited spatial distribution of these minor rock types makes 
them generally unimportant to the hydrology of Yucca Mountain.

TDR-NBS-HS-000001 REV 00 ICN 01 3-50 August 2000 
Source: Modified from USGS (2000a, Figure 6-1) 
NOTE: This fence diagram illustrates the complex 3-D spatial relation among units within the site-scale model 
domain. Shading represents different hydrogeologic units. 
Figure 3-13. Fence Diagram of the Site-Scale Model Domain

TDR-NBS-HS-000001 REV 00 ICN 01 3-51 August 2000 
As described by Luckey et al. (1996, p. 17), even fractured tuffs and lavas may not easily 
transmit water because lithostatic loading keeps the fractures closed. In addition, where volcanic 
glass has been partly replaced by zeolites and clays, particularly in the originally glassy 
nonwelded tuffs, these secondary minerals substantially decrease permeability and slow 
groundwater flow through the rock. The degree of alteration can affect the water-transmitting 
characteristics of the volcanic sequence. Alteration, particularly in the Calico Hills Formation, 
increases toward the north of Yucca Mountain and probably accounts for the apparent decrease 
in hydraulic conductivity to the north. Alteration also tends to increase with depth and is 
pervasive below the Calico Hills Formation. 
Fractures vary in length, orientation, connectivity, aperture width, and amounts and types of 
coatings, all of which may affect the flow of water. The physical parameters of fractures are 
characterized by outcrop mapping, borehole logging, and mapping in the Exploratory Studies 
Facility; however, seeps of water have not been observed in outcrop mapping or in mapping in 
the Exploratory Studies Facility. 
Fractures at Yucca Mountain originated as a result of initial cooling of the volcanic deposits and 
as a result of tectonic activity. In the Tiva Canyon welded hydrologic unit, two sets of vertically 
orientated cooling fractures were observed dipping nearly vertically and striking towards the 
northwest and northeast. A third set of tectonic joints commonly abut the cooling joints, and 
these three sets of joints form an orthogonal, 3-D network. CRWMS M&O (1998c, 
Section 3.6.3) present an extensive discussion of fractures in the Yucca Mountain area. 
Fracture aperture characteristics are poorly known from direct observation, and for modeling, 
reliance is placed on indirect effects such as changes in air and water permeability. In general, 
the stress due to overburden loading across high-angle fractures will be less than across lowangle 
fractures, resulting in higher vertical than horizontal permeability. 
The volcanic rocks consist of alternating layers of welded and nonwelded ash-flow and ash-fall 
(bedded) tuff deposits. Each of the ash-flow units is underlain by an associated bedded-tuff 
layer. The ash-flow units vary in degree of welding (or recrystallization) with the maximum 
welding generally found near the center of the flow, where heat was retained the longest, and the 
degree of welding decreasing upward and downward toward the flow boundaries. 
The welded units typically have low matrix porosities and high fracture densities, whereas the 
nonwelded and bedded tuffs have relatively higher matrix porosities and lower fracture densities. 
The fracture density is correlated with the degree of welding of the volcanic rocks. 
Where glassy tuff has been saturated for long time periods (e.g., beneath the water table), the 
original glassy material generally has been altered to zeolite or clay minerals. Such alteration 
does not affect porosity greatly because it does not fill the pore spaces, but the permeability of 
the rocks is greatly reduced by alteration of the connections between the pore spaces. Alteration 
of silica to zeolites or clay minerals is not an important factor in densely welded zones because 
cooling fractures dominate permeability. 
In addition to flow within the volcanic rocks, groundwater also flows in the carbonate rocks of 
the lower carbonate aquifer. In general, it is believed that the matrix porosity of the ancient

TDR-NBS-HS-000001 REV 00 ICN 01 3-52 August 2000 
marine limestones and dolomites of the lower carbonate aquifer is negligible (Winograd and 
Thordarson 1975, p. C14) and that the large discharge from that aquifer system at Ash Meadows 
is due to flow through solution-enlarged fractures and along faults (Dudley and Larson 1976, 
pp. 5 and 9). Only one borehole, UE 25p#1, penetrates the lower carbonate aquifer near Yucca 
Mountain. Because of the lack of data on hydrologic conditions in the carbonate aquifer, the 
direction and magnitude of groundwater flow in that aquifer at Yucca Mountain is poorly 
understood. However, large groundwater flows have been modeled in the carbonate aquifer by 
DAgnese et al. (1997, Figures 46 to 47, p. 90) in the Death Valley Regional Groundwater Flow 
Model within the southern part of the site-scale flow model. These are discussed in 
Section 3.2.2.3. 
Estimates of groundwater flux in the Yucca Mountain area are based largely on indirect 
evidence. Although the potentiometric gradients generally are known, little definitive data exists 
regarding the storage properties of the rocks of the SZ, such as effective porosity and storativity 
(Luckey et al. 1996, p. 53). 
More data are available on the transmissive properties (transmissivity and hydraulic 
conductivity) of the rocks of the SZ, chiefly from aquifer tests in boreholes. However, a wide 
margin of uncertainty exists about the quantitative validity and extrapolation of such data far 
from the test sites (Luckey et al. 1996, pp. 53 to 54). Groundwater flow models have been used 
to estimate transmissivity over large areas, but these have a large uncertainty associated with 
them (Luckey et al. 1996, p. 54). 
3.2.2.1 Vertical Gradients 
Information on vertical hydraulic gradients in the SZ is concentrated near Yucca Mountain, 
although Kilroy (1991) presents some information indicating the existence of vertical gradients 
in the Amargosa Desert. The following discussion of vertical gradients primarily is extracted 
from Luckey et al. (1996, pp. 27 to 29). 
Luckey et al. (1996, pp. 27 to 29) report on potentiometric level measurements in multiple depth 
intervals in 10 boreholes at Yucca Mountain. Differences in potentiometric levels at different 
depth intervals in the same borehole ranged from as little as 0.15 m (0.5 ft) in borehole USW H-4 
to as much as 54.83 m (180 ft) in USW H-1 (Luckey et al. 1996, Table 3). The largest 
differences were between the lower carbonate aquifer or the adjoining lowermost lower volcanic 
confining unit and the overlying lower volcanic aquifer. Within the upper part of the lower 
volcanic confining unit and the lower volcanic aquifer, the differences in potentiometric levels 
generally were 1 m (3.3 ft) or less. 
Potentiometric levels generally were higher in the lower intervals of the volcanic rocks than in 
the upper intervals, indicating a potential for upward groundwater movement. However, at four 
boreholes (USW G-4, USW H-1, USW H-6, and UE-25b#1), potentiometric levels in the 
volcanic rocks were slightly higher in the uppermost intervals than in the next lower intervals. 
Overall, it appears that an upward gradient between lower and upper volcanic aquifer is 
maintained at these locations.

TDR-NBS-HS-000001 REV 00 ICN 01 3-53 August 2000 
Potentiometric levels in the Paleozoic carbonate aquifer in borehole UE-25p#1 are about 752 m 
(2,467 ft), or about 21 m (69 ft) higher than levels in the lower volcanic aquifer. A potential for 
upward groundwater movement from the Paleozoic rocks to the volcanic rocks was, therefore, 
indicated. Because of the large difference in potentiometric levels in these two aquifers, they 
seem to be hydraulically separate (Luckey et al. 1996, p. 28). Testing at the C-wells Complex in 
1984 suggested a hydraulic connection between the lower volcanic aquifer and the carbonate 
aquifer; however, testing in 1995 and 1996 using more reliable water-level measurement 
equipment did not confirm the hydraulic connection (Luckey et al. 1996, p. 28). 
In borehole UE-25p#1, the lowermost 70 m (230 ft) of the older tuffs (lower volcanic confining 
unit) had potentiometric levels similar to those in the carbonate aquifer, indicating a hydraulic 
connection between the lowermost part of the lower volcanic confining unit and the carbonate 
aquifer. Such a connection could be expected in the hanging-wall rocks adjacent to a fault, and 
such connection is supported by calcification of the basal tuffs in the borehole. The remaining 
237 m (778 ft) of the lower volcanic confining unit had a potentiometric level similar to that of 
the lower volcanic aquifer (Luckey et al. 1996, p. 28). 
No obvious spatial patterns in the distribution of vertical hydraulic gradients around Yucca 
Mountain are apparent; however, some generalizations can be made as to the distribution of 
potentiometric levels in the lower sections of the volcanic rocks. Potentiometric levels in the 
lower volcanic confining unit are relatively high (altitude greater than 750 m [2,460 ft]) in the 
western and northern parts of Yucca Mountain and are relatively low (altitude about 730 m 
[2,395 ft]) in the eastern part of Yucca Mountain. Based on potentiometric levels that were 
measured in borehole UE-25p#1, the potentiometric levels in the lower volcanic confining unit in 
boreholes USW H-1, USW H-3, USW H-5 and USW H-6 may reflect the potentiometric level in 
the carbonate aquifer. Boreholes UE-25b#1 and USW H-4 do not seem to fit the pattern 
established by the other boreholes. These two boreholes penetrated only 31 m (102 ft) and 64 m 
(210 ft), respectively, into the lower volcanic confining unit and had potentiometric levels (about 
730 m [2,395 ft]) which were similar to potentiometric levels in the lower volcanic aquifer. 
Penetration of the other four boreholes into the lower volcanic confining unit ranged from 123 m 
(403 ft) in borehole USW H-3, to 726 m (2,382 ft) in borehole USW H-1. Perhaps only in 
boreholes USW H-1, USW H-3, USW H-5, and USW H-6 are the potentiometric levels in the 
lower volcanic confining unit influenced by the potentiometric level in the carbonate aquifer 
(Luckey et al. 1996, p. 29). 
Vertical hydraulic gradients could have an important impact on the analysis of the effectiveness 
of the SZ as a barrier to radionuclide transport in that they keep the flow path for the potential 
repository in the shallow groundwater. Based on a limited data set (five boreholes), a spatially 
extensive upward gradient can be inferred between the carbonate aquifer and the volcanic 
aquifers, which may indicate that, at least for the immediate Yucca Mountain area, radionuclide 
transport would be restricted to the volcanic system (Luckey et al. 1996, p. 29). 
Kilroy (1991, pp. 11 to 16, Table 3) presents vertical gradient data for 21 nested piezometers, 
1 well cluster, and 1 river and well pair in the Amargosa Desert area. However, none of these 
locations are within the area of the site-scale SZ model, so the results are not discussed in detail 
here. Upward gradients generally were associated with freshwater limestones, carbonate rock 
outcrops, and structural features (Kilroy 1991, p. 16). The association with carbonate rocks is

TDR-NBS-HS-000001 REV 00 ICN 01 3-54 August 2000 
attributed to hydraulic connection with the carbonate aquifer regional flow system and, 
especially, to the Spotted Range-Mine Mountain fault zone, which is a conduit for flow from the 
carbonate aquifer to the basin fill. 
3.2.2.2 Flow Field 
Using the potentiometric surface map (Figure 3-5) and the assumption that hydraulic 
conductivity is isotropic, the general direction of groundwater flow within the site-scale SZ flow 
and transport model area can be deduced as being from north to south. Under this assumption, 
the direction of flow is perpendicular to the water-level contours. Under the USGS (2000a) 
interpretation of the water-level data (Figure 3-5), the water table exhibits a steep gradient 
throughout the northern part of the model area (north of the potential repository) and the 
contours curve southward to the west of Crater Flat. 
Several faults are interpreted as barriers to groundwater flow, as indicated by offsets of contours 
where they cross faults (Figure 3-5). This interpretation, however, is supported only by field 
data at the Solitario Canyon fault, west of the potential repository, which is interpreted as 
causing a differential of about 45 m (148 ft) in the potentiometric surface. In Crater Flat and on 
the southern part of Yucca Mountain, the flow direction is nearly easterly toward Fortymile 
Wash. A more detailed water-level map of the immediate vicinity of Yucca Mountain 
(Figure 3-6) indicates that flows from the west and east converge at Fortymile Wash and turn 
southward toward the Amargosa Desert. The cause of the easterly gradient in Crater Flat and 
southern Yucca Mountain is not evident, but it suggests that a groundwater barrier exists near the 
northern margin of the Amargosa Desert. In any event, the potentiometric surface upgradient of 
the 725-m (2,379 ft) contour and the Highway 95 fault appears to have little north-south flow 
over an area of about 259 km2 (100 mi2). 
As discussed in Section 3.2.2.1, the potentiometric level in well UE-25p#1, which penetrates the 
lower carbonate aquifer, is about 752 m (2,467 ft), 21 m (69 ft) higher than in nearby wells 
tapping the lower volcanic aquifer. This indicates a potential for upward flow from the lower 
carbonate aquifer; however, other lines of evidence suggest that such flow is small. The 
direction of flow and hydraulic gradient cannot be determined from a single well; however, 
regional relationships suggest that the general direction of flow in the lower carbonate aquifer 
should be southerly in the site-scale SZ flow and transport model domain (NRC 1999a, p. 109). 
Most monitoring wells in the Yucca Mountain area show little variation in water level over time 
(Luckey et al. 1996, p. 29). In contrast, water levels in the heavily pumped Amargosa Farms 
area have declined substantially since intensive irrigation development began in the 1950s. 
Kilroy (1991, p. 18) reported a water-level decline of as much as 9 m (30 ft) by 1987, and 
La Camera and Locke (1997, Figure 4) show an additional decline of about 3.4 m (11 feet) 
through 1996 at well AD-5, about 14 km (8.7 mi) southwest of Amargosa Valley. 
3.2.2.3 Large, Moderate, and Small Hydraulic Gradients 
Three distinctive hydraulic gradients of the potentiometric surface at Yucca Mountain are 
recognized: (1) a large hydraulic gradient of 0.13 between water-level altitudes of 1,030 m 
(3,380 ft) and 750 m (2,460 ft) at the north end of Yucca Mountain, (2) a moderate hydraulic

TDR-NBS-HS-000001 REV 00 ICN 01 3-55 August 2000 
gradient of 0.05 west of the crest of Yucca Mountain, and (3) a small hydraulic gradient of 
0.0001 to 0.0003 extending from Solitario Canyon to Fortymile Wash. These gradients have 
been portrayed on detailed potentiometric surface maps presented by Ervin et al. (1994), and 
Tucci and Burkhardt (1995), as well as on the maps with large contour intervals compiled by 
DAgnese et al. (1997) and by USGS (2000b). The large contour-interval maps do not portray 
the small or moderate gradients well because of limitations imposed by contour intervals; 
however the large gradient is recognizable on all of these maps. 
Luckey et al. (1996) present detailed descriptions of these gradient features and discuss 
interpretations of their causes. The large hydraulic gradient has been the subject of numerous 
theories. Summarized from Luckey et al (1996, pp. 21 to 25), the large gradient: 
 Simply is the result of flow through the upper volcanic confining unit, which is nearly 
300 m (984 ft) thick near the large gradient. 
 Represents a semi-perched system in which flow in the upper and lower aquifers is 
predominantly horizontal, whereas flow in the upper confining unit would be 
predominantly vertical. 
 Represents a drain down a buried fault from the volcanic aquifers to the lower carbonate 
aquifer. 
 Represents a spillway in which a fault marks the effective northern limit of the lower 
volcanic aquifer. 
 Results from the presence at depth of the Eleana Formation, a part of the Paleozoic 
upper confining unit, which overlies the lower carbonate aquifer in much of the Death 
Valley region. The Eleana is absent at borehole UE-25 p#1 at Yucca Mountain, which 
penetrated the lower carbonate aquifer directly beneath the lower volcanic confining 
unit. 
The cause of the moderate hydraulic gradient is less controversial than that of the large gradient, 
and Luckey et al. (1996, p. 25) suggest that the Solitario Canyon fault and its splays function as a 
barrier to flow from west to east due to the presence of poorly permeable fault gouge or to the 
juxtaposition of more permeable units against less permeable units. 
The small hydraulic gradient occupies most of the potential repository area and the downgradient 
area eastward to Fortymile Wash. Over a distance of 6 km (3.7 mi), the hydraulic gradient 
declines only about 2.5 m (8.2 ft) between the crest of Yucca Mountain and Fortymile Wash. 
The small gradient could indicate highly transmissive rocks, little groundwater flow in this area, 
or a combination of both causes (Luckey et al. 1996, p. 27). 
The latest potentiometric map (USGS 2000b), which includes head data from the recently drilled 
NCEWDP boreholes, indicates that the small hydraulic gradient extends southward to an eastwest 
fault approximately along Highway U.S. 95.

TDR-NBS-HS-000001 REV 00 ICN 01 3-56 August 2000 
3.2.2.4 Heterogeneity 
Physical and chemical heterogeneity of the rocks and water in the SZ can affect groundwater 
flow and the transport of contaminants in the SZ. The principal forms of heterogeneity in the 
site-scale SZ model area are physical and may be primary (i.e., related to the formation of the 
rocks) or secondary (i.e., related to events subsequent to their formation). 
The most obvious form of primary heterogeneity is the mode of origin (i.e., volcanic rocks, 
clastic rocks, carbonate rocks, and alluvial deposits), which is the primary basis for subdividing 
the rocks into hydrogeologic units. Within each major category, further subdivisions are 
possible. Probably the major form of primary heterogeneity affecting groundwater flow in the 
site-scale SZ model area results from the origin of the volcanic rocks (i.e., ash-flow or air-fall 
pyroclastic deposits, lava flows, and volcanic breccias). The pyroclastic rocks (termed tuffs) 
primarily are nonwelded to densely welded, vitric to devitrified ash-flow deposits separated by 
nonwelded vitric air-fall deposits. Thus, the primary heterogeneity in physical character relates 
to whether the deposits resulted from massive eruptions of hot volcanic ash from volcanic 
centers that flowed downslope as flows of fragmental material, or whether they resulted from 
explosive eruptions that injected volcanic fragments into the air to fall out as bedded tuffs. 
The thicker flow deposits, up to several hundred meters thick, were very hot, resulting in welding 
of the fragments into a dense mass. Thinner flows retained heat less effectively, resulting in 
partly welded to nonwelded ash-flow tuffs. Ash-fall tuffs, generally less than tens of meters 
thick, cooled in the atmosphere and characteristically are glassy (vitric) (Luckey et al. 1996, 
p. 17). 
The mode of origin controls the porosity and permeability of the volcanic rocks. The densely 
welded tuffs generally have minimal primary porosity and water-storage capacity, but commonly 
are highly fractured and function as aquifers (Luckey et al. 1996, p. 17). Nonwelded ash-flow 
tuffs, when unaltered, have moderate to low matrix permeability but high porosity, and 
commonly constitute confining units. Bedded tuffs have high primary porosity and moderate to 
low permeability, and they generally function as confining units. 
As the tuff deposits cooled, they were subjected to secondary processes, including formation of 
cooling fractures, recrystallization or devitrification, and alteration of the initial glassy fragments 
to zeolite minerals and clay minerals, all of which affect the hydrologic properties of the rocks. 
Beginning with deposition and throughout their subsequent history, the rocks have been 
subjected to tectonic forces resulting in further fracturing and faulting. They also have been 
subject to changes in the position of the water table, which greatly affects the degree of alteration 
of the initially glassy deposits. 
The forms of secondary heterogeneity most affecting the SZ are fracturing, faulting, and 
alteration of glassy materials to zeolites and clay minerals. Fractures, where interconnected, 
transmit water readily, which accounts for the permeable character of the welded tuffs. Cooling 
fractures, which are pervasive in welded tuffs, tend to be strata-bound, that is, confined to the 
welded portions of flows, whereas tectonic fractures tend to cut through stratigraphic units, as do 
faults.

TDR-NBS-HS-000001 REV 00 ICN 01 3-57 August 2000 
Nonwelded deposits are less subject to fracturing and more subject to alteration of the initial 
glassy deposits to zeolites and clay minerals, both of which reduce permeability. The presence 
of perched water bodies in the UZ is attributed to the ubiquitous presence of a smectite-zeolite 
interval at the base of the Topopah Spring Tuff, which, in the absence of through-going fractures, 
essentially stops the vertical movement of water (Luckey et al. 1996, p. 46). 
The heterogeneity in permeability of different types of deposits led to the subdivision of the 
Yucca Mountain geologic section into five basic SZ hydrologic units: upper volcanic aquifer, 
upper volcanic confining unit, lower volcanic aquifer, lower volcanic confining unit, and lower 
carbonate aquifer. To accommodate the more extensive area of the site-scale flow model, 
(USGS 2000a) include several additional units above and below these basic five units. 
In the vicinity of Yucca Mountain, volcanic deposits generally form laterally-extensive 
stratigraphic units; however, due to physical heterogeneity, porosity and permeability are highly 
variable both laterally and vertically. Within the site-scale model area, little specific information 
is available on the lower carbonate aquifer. However, information from nearby areas (DAgnese 
et al. 1997, p. 90, Figures 46 and 47) suggests that the lower carbonate aquifer is highly and 
uniformly permeable, and that the high permeability is attributed to pervasive solution-enlarged 
fractures. 
In the southern part of the site-scale SZ flow and transport model domain, the volcanic deposits 
thin and interfinger with valley-fill deposits. The latter are heterogeneous because of their mode 
of deposition (Walker and Eakin 1963, p. 14), but are not subject to the fracturing, faulting, and 
alteration types of heterogeneity that affect the volcanic rocks. 
3.2.2.5 Hydrologic Features 
As explained by USGS (2000a), the HFM represents faults and other hydrogeologic features, 
such as zones of hydrothermal alteration, that affect SZ flow. Information on faults includes 
fault trace maps showing where faults intersect land surface and faults shown on cross sections. 
Faults in the model area can dip at almost any angle, but most are high-angle faults. Given 
software constraints and the flow model resolution, faulting in the area is simplified and the 
faults are treated as vertical features. 
Where it was thought to be hydrologically important, thrust faults were represented by repeating 
hydrogeologic units. When geologic structural or stratigraphic surfaces are stored as arrays, they 
cannot have multiple z-values at one location. This means that thrust faults and mushroomshaped 
intrusions cannot be represented by an array. To deal with these problems, simplifying 
techniques were used. Where units were repeated by thrust faults, two different grids were 
created for the same hydrogeologic unit. A unit boundary map was then added to define an 
outline for the perimeter of the thrust sheet. Within this boundary, hydrogeologic structural 
altitude values were treated as defining unique additional hydrogeologic unit(s). Where units 
were continuous across this boundary, altitudes of surfaces are the same on each side of the 
boundary, making the boundary invisible. Because of the large number of faults in the sitescale 
SZ model area and limitations in modeling technology, only those faults and other features 
of hydrologic importance are portrayed in the HFM (USGS 2000a, Figure 6-2).

TDR-NBS-HS-000001 REV 00 ICN 01 3-58 August 2000 
As discussed by CRWMS M&O (2000n, Section 6.3), some hydrogeologic features of the HFM 
were accorded special treatment in constructing the site-scale SZ flow and transport model. 
These features include 15 from the HFM, an alluvial uncertainty zone, and a zone representing 
Fortymile Wash (Figure 3-14). The hydrological features included in the site-scale SZ flow and 
transport model primarily represent faults, fault zones, and areas of chemical alteration. The 
features essentially are vertical, some being linear in the horizontal extent, and some being of 
areal extent. These features are distinct from the subhorizontal geological formations that form 
zones with distinct geometry and material properties and are described in Section 3.2.1. Each of 
these features includes multiple geologic formations and represents zones of altered permeability 
within the individual formations: some features have enhanced permeability, some have reduced 
permeability, and others have anisotropic permeability. Each of them has an important impact 
on the site-scale SZ flow and transport model. The geometric definition, description, nature of 
permeability alteration, and impact on the model for each of these features are described by 
CRWMS M&O (2000n, Table 6). 
Certain hydrogeologic features of the HFM overlap (e.g., the entire Northern Zone embraces the 
Claim Canyon Caldera, Shoshone Mountain altered zone, and the Calico Hills altered zone). As 
explained by CRWMS M&O (2000n, Table 6), the rationale for segregating these smaller units 
within the larger northern zone is that a different permeability reduction is applied to these 
smaller units (CRWMS M&O 2000n, Table 12). 
Where appropriate, several features are subdivided geographically (Figure 3-14). For example, 
Fortymile Wash, north and south; and Claim Canyon, east and west, are subdivided. As 
indicated by CRWMS M&O (2000n), the same parameter adjustment values were used in the 
model calibration process throughout each of the 17 special features. 
Most of the special features were defined as extending from the top of the carbonate aquifer to 
the top of the model (water table). Exceptions to this generalization are the Spotted Range-Mine 
Mountain zone, which extends from the top of the model to the bottom; the Alluvial uncertainty 
zone, which extends from the top of the model down through the undifferentiated valley fill, and 
the Imbricate fault zone, which extends from the top of the model to the top of the 
undifferentiated valley fill (CRWMS M&O 2000n, Table 6). 
3.2.3 Boundary Conditions 
The site-scale SZ flow and transport model is designed to be compatible with the regional-scale 
SZ model (DAgnese et al. 1997), to use the HFM (USGS 2000a), and to use available data on 
recharge within the site-scale model area (CRWMS M&O 1999a). Recharge data for the 
site-scale SZ flow and transport model domain includes input from the site-scale UZ flow model, 
estimates of recharge along Fortymile Wash (Savard 1998), and recharge estimated from the 
regional-scale SZ flow model (CRWMS M&O 2000n, Figure 2).

TDR-NBS-HS-000001 REV 00 ICN 01 3-59 August 2000 
535000 540000 545000 550000 555000 560000 
81 
82 
57,58
59 
61,62 63,64 
65,66 
69-72 
74
75 
76 
77 
78
79 
80 
90 
83 
84 
88 
91 
45 
UTM-X (meters) 
56 
Source: CRWMS M&O (2000n, Figure 4) 
NOTE: Numbers, or ranges of numbers, identify the following regions: 45Lower Fortymile Wash zone; 56East- 
West Barrier zone; 57 and 58Fortymile Wash zones; 59-Spotted Range-Mine Mountain zone; 61 and 
62Claim Canyon Caldera zones; 63 and 64Shoshone Mountain altered zones; 65 and 66Calico Hills 
altered zones; 69, 70, 71, and 72Crater Flat fault zones; 74, 83, and 84-Solitario Canyon fault zones; 
75 and 76Solitario Canyon fault zones (east branch); 77 and 78-Solitario Canyon fault zones (west 
branch); 79Highway 95 fault zone; 80 and 90Bare Mountain fault zones; 81Northern zone; 82Northern 
Crater Flat zone; 88Alluvial Uncertainty zone (expected case); 91Imbricate fault zone. 
Figure 3-14. Geological Features Represented in the Site-Scale Flow and Transport Model

TDR-NBS-HS-000001 REV 00 ICN 01 3-60 August 2000 
3.2.3.1 Lateral Boundaries 
Most of the inflows to, and outflow from, the site-scale SZ flow and transport model occurs as 
groundwater flows across the lateral boundaries. The best estimates of flow rates are the 
cell-by-cell fluxes calculated by the regional-scale model. These fluxes are compiled in four 
tables (CRWMS M&O 1999a, Tables 7.2-1, 7.2-2, 7.2-3, and 7.2-4) corresponding to the 
rectangular boundaries of the site-scale flow model. The flows are compiled by the three depth 
layers (0 to 500 m [0 to 1,640 ft], 500 to 1,250 m [1,640 to 4,100 ft], and 1,250 to 2,750 m 
[4,100 to 9,020 ft] below the water table) of the regional-scale flow model (DAgnese et al. 
1997, p. 75). 
3.2.3.2 Recharge 
The three recharge components (site-scale UZ model, regional-scale SZ model, and Fortymile 
Wash) take different forms and must be combined into a single result. Recharge from the 
site-scale UZ model is taken as the flow through the base of that model, the domain of which 
includes approximately 50 km2 (19.3 mi2). The UZ flow model uses dual permeability; 
accordingly, the output includes fluxes for fracture and matrix flow. These data are combined 
into a total volumetric flow rate and an average percolation flux (CRWMS M&O 1999a, 
Figure 6.1.3-2). 
Estimates of recharge from the infiltration of surface flows in Fortymile Wash are given by 
linear reaches along the wash. Recharge estimates were interpolated to a 500-m (1,640-ft) wide 
recharge zone for most of the wash and a broader area of distributary channels in the Amargosa 
Desert (CRWMS M&O 1999a, Table 6.1.3-1, Figure 6.1.3-2). 
The distributed recharge, limited to the northernmost portion of the site-scale model area, was 
extracted from the regional-scale SZ flow model (DAgnese et al. 1997). No recharge within the 
UZ model area was included. A plot of distributed recharge is provided by CRWMS M&O 
(1999a, Figure 6.1.1-1). 
Estimated recharge from all three sources is displayed by CRWMS M&O (1999a, 
Figure 6.1.3-2). Total recharge was about 1,550,000 m3/yr (1,256 acre-ft/yr). Of this total, about 
212,000 m3/yr (172 acre-ft/yr) was attributed to flux from the UZ model area and about 
95,000 m3/yr (77 acre-ft/yr) was attributed to infiltration along Fortymile Wash, leaving a 
remainder of about 1,240,000 m3/yr (1,007 acre-ft/yr) from distributed recharge. 
Groundwater inflows along the eastern, northern, and western boundaries of the site-scale SZ 
flow and transport model total 17.8 x 106 m3/yr (14,430 acre-ft/yr), 6.21 x 106 m3/yr 
(5,034 acre-ft/yr), and 3.74 m3/yr (3,032 acre-ft/yr), respectively (CRWMS M&O 1999a). These 
inflows, totaling 27.75 x 106 m3/yr (22,500 acre-ft/yr), represent nearly 18 times the estimated 
recharge from the surface in the model area. Of the total inflow for the eastern boundary, 
17.6 x 106 m3/yr (14,273 acre-ft/yr), or 99 percent, occurs in the Amargosa Desert sector 
(CRWMS M&O 1999a), and nearly all of that occurs in layers 2 and 3 of the regional-scale flow 
model (CRWMS M&O 1999a, Table 7.2-2) and represents flows in the lower carbonate aquifer 
(DAgnese et al. 1997, p. 90, Figures 46 to 47).

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3.2.3.3 Discharge 
There is no natural discharge (i.e., springs or evapotranspiration) from the SZ within the sitescale 
model domain; therefore, natural discharge to the surface was not represented in the 
simulations. 
3.2.3.4 Role of Faults 
Faults, fault zones, and zones of chemical alteration are hydrogeologic features that require 
special treatment in the site-scale SZ flow and transport model. Faulting and fracturing are 
pervasive at Yucca Mountain, and they greatly affect groundwater flow patterns because they 
may act as preferred conduits or barriers to groundwater flow. The role that faults play in 
facilitating or inhibiting groundwater flow depends on the nature of the fault (i.e., whether the 
faults are in tension, compression, or shear) and other factors such as the juxtaposition of varying 
geologic units along the fault plane, the rock types involved, fault zone materials, and depth 
below land surface. 
Faunt (1997) investigated the effect of faulting on groundwater movement in the Death Valley 
region and developed a map of fault traces (Faunt 1997, Figure 10) and rose diagrams 
(Faunt 1997, Figure 11) showing the orientation of faults within the principal structural 
provinces of region. Faunt (1997, p. 38) grouped the faults into three categories depending on 
their orientations relative to the present-day stress field (i.e., those in relative tension, 
compression, or shear). 
Faults in relative tension are more likely to be preferential conduits for groundwater, and faults 
in shear or compression are more likely to deflect or block groundwater movements. Within the 
site-scale model area, faults assumed to have the most evident effects on groundwater 
movement, such as effects on potentiometric contours (Figure 3-5), include the Solitario Canyon, 
Stagecoach Road, Highway 95, Crater Flat, and Bare Mountain faults, all of which appear to act 
as barriers to groundwater flow. Faults within the site-scale model area of hydrologic 
importance include the Spotted Range-Mine Mountain shear zone, which Faunt (1997, p. 34) 
describes as a major high-permeability zone in the lower carbonate aquifer, and the following 
features to which CRWMS M&O (2000n) accords special treatment in the site-scale SZ flow and 
transport flow model: Crater Flat fault, Solitario Canyon fault, Highway 95 fault, Bare Mountain 
fault, Imbricate fault zone (between the Ghost Dance and Paintbrush Canyon faults at Yucca 
Mountain), Fortymile Wash zone (which may not be a fault), and the East-West barrier (which 
appears to cause the large hydraulic gradient north of Yucca Mountain). These features fall into 
two categories depending on their hydrologic impacts: (1) zones of permeability enhancement 
parallel to faults and zones of permeability reduction perpendicular to faults (Crater Flat, 
Solitario Canyon, and Highway 95 faults), and (2) zones of permeability enhancement (Bare 
Mountain fault, Imbricate fault zone, Fortymile Wash zones, Spotted Range-Mine 
Mountain zone. 
3.2.4 Solute Transport Processes 
The site-scale SZ flow and transport modeling performed by the YMP focused on the key 
controlling factors that influence the measured head distributions at the site. A summary of these

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conceptual models and numerical implementations of these models is presented in 
Sections 3.2.1, 3.2.2, 3.2.3, and 3.3. The focus of this section is on the transport of radionuclides 
in the SZ, which in addition to flow issues, requires consideration of processes specific to the 
migration of solutes. The flow path from the potential repository to the proposed compliance 
boundary begins in the volcanic tuffs, but ends in the alluvium, and different transport processes 
operate in the volcanic tuffs and the alluvium (Figure 3-15). The conceptual models for transport 
in the volcanic tuffs and in the alluvium are different: matrix diffusion occurs only in the 
volcanic tuffs, and sorption in the volcanic tuffs only occurs after radionuclides diffuse into the 
matrix. The mathematical formulation of the conceptual model and the numerical 
implementation of dispersion are the same for both media, but numerical implementation for 
sorption is different because sorption in the volcanic tuffs is linked to matrix diffusion. A 
conceptual model for transport processes in the two media (i.e., fractured porous media and the 
alluvium) is presented. The conceptual model for the fractured porous media includes 
dispersion, diffusion of radionuclides into the porous rock matrix, and sorption. The conceptual 
model for transport in the alluvium includes dispersion and sorption. 
Figure 3-15. Conceptual Model of Transport Processes in the Volcanic Tuffs and the Alluvium

TDR-NBS-HS-000001 REV 00 ICN 01 3-63 August 2000 
This description of solute transport is organized in two parts. First, the relevant small-scale flow 
processes that influence transport are reviewed, with focus placed on flow processes likely to 
influence radionuclide movement. Then a simplified matrix-diffusion model, the mathematics of 
the model, and simulations designed to assess the amount of matrix diffusion likely to be present 
in SZ transport under natural conditions are presented. 
3.2.4.1 Advection 
3.2.4.1.1 Advection in the Fractured Porous Media 
Current hydrologic evidence supports the model of fluid flow within fractures in the moderately 
to densely welded tuffs of the SZ (e.g., Waddell et al. 1984). Hydraulic conductivities measured 
for core samples in the laboratory are orders of magnitude higher when the sample is fractured 
(Peters et al. 1984). Also, there generally is a positive correlation between fractures, identified 
using acoustic televiewer or borehole television tools, and zones of high transmissivity (Erickson 
and Waddell 1985, Figure 3). 
Because the role of fractures is so important to the hydrology in the SZ, the permeability 
distribution and principal flow directions depend strongly on the spatial distribution and 
orientations of fractures. Erickson and Waddells (1985) televiewer log data show that 83.1 
percent of the fractures have a strike direction between N 10 W and N 55 E, with most 
fractures steeply dipping at angles greater than 60. Karasaki and Galloway (1990) point out that 
fractures oriented perpendicular to the least principal stress direction of N 6065 W should be 
more open and more permeable. Karasaki et al. (1990) tentatively conclude that the regions of 
high transmissivity in the C-wells correlate with fractures of this general orientation, with the 
steeply dipping fractures contributing most to the transmissivity. 
In the natural groundwater flow state, all fractures, regardless of orientation, will have effective 
pressures between 71 to 163 bar. In this range, the laboratory tests of Peters et al. (1984) show a 
relatively minor effect of effective pressure on hydraulic aperture, at least compared with other 
uncertainties. Thus, it appears that the spatial distribution of fractures (densities and 
interconnectivities) is more important in determining the hydraulic conductivity ellipsoid than 
the effect of the stress field on the apertures of individual joints. However, pressure testing that 
greatly lowers the effective pressure in a joint will result in increased hydraulic apertures and 
erroneous estimates of the transmissivity. Stock et al. (1984) point out that, in some wells drilled 
with mud, the weight of the fluid column exceeded the minimum horizontal stress, probably 
resulting in induced hydraulic fracturing during drilling or the opening of favorably oriented 
preexisting joints. This possibility may also be true of some slug tests. 
Even though the simplifying assumption is made that, from a hydrologic standpoint, all joints are 
under similar effective stresses, the role of in situ stress nonetheless is an important controlling 
factor governing the nature of fluid flow within a fracture. For transport, the result is a 
propensity of fluid and solute to travel preferentially along channels in which the apertures are 
largest. Thus, for flow within fractures in the SZ, a channel-flow model or a fracture-flow model 
recognizing and accounting for flow channels is necessary.

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Radionuclide Transport Conceptual Model DevelopmentGiven the complex geohydrologic 
setting, the most appropriate approach is to construct a plausible conceptual transport model that 
describes the relevant processes in the SZ. This model, along with its mathematical 
representation, allows identification of areas of uncertainty that are necessary to explore and 
incorporate into the site-scale model. The radionuclide transport times could be several orders of 
magnitude larger than the transport times computed assuming the fluid velocity within the 
fractures is the effective radionuclide migration velocity. This implies that the SZ could be an 
important barrier to radionuclide migration. Therefore, field tests such as those at the C-wells 
have been designed and carried out to validate the model (Robinson 1994). 
Summary of Conceptual ModelSummarizing the discussion of fluid flow behavior given 
above, the SZ fluid-flow model, into which transport submodels are built, is outlined below: 
 Radionuclides enter the SZ via fluids percolating through the unsaturated rock above the 
water table. The exact nature of this transport is not expected to exert a great effect on 
the subsequent site-scale SZ flow and transport model, and thus, the SZ transport 
component of the site-scale SZ model can be developed independently from a transport 
model for the UZ (which acts as a source term for the site-scale SZ model). 
 Flow occurs within the highly fractured portions of the tuffs near the water table. There 
probably is not a continuous zone of high permeability to the alluvium in Amargosa 
Valley. Assuming there is not, then the low-permeability regions effectively will act as 
large-scale heterogeneities that give rise to large-scale macroscopic dispersion due to the 
tortuous nature of flow over the scale of hundreds of meters to kilometers. 
 Although the vertical matrix permeability is assumed to be small over the scale of 
several hundreds of meters, the vertical fractured-region permeabilities should be as 
large as the horizontal permeabilities. Thus, radionuclides will spread vertically and be 
present throughout the entire thickness of a fractured zone. The thicknesses of these 
fractured zones are difficult to estimate from the present data. However, the extent of 
fracturing correlates reasonably well with the degree of welding, and the degree of 
welding is one of the criteria used to define the submembers within a lithologic unit. 
Therefore, it is reasonable to assume that the heights of the fracture zones are on the 
order of the thicknesses of the individual lithologic members (i.e., 100 m to 200 m 
[328 ft to 656 ft]). This possibility is in contrast to flow zones detected in individual 
boreholes, where measurements reflect the intersection of specific fractures with the 
well. Nevertheless, these data should be useful in estimating the effective distance 
between flowing fractures, a parameter that may be important in quantitative 
assessments of radionuclide transport behavior. 
 Fluid flow occurs within the fractures, while stagnant fluid resides in the rock matrix. 
All fractures have large contact areas due to the in situ stresses exerted on them at these 
depths. The conductivity of an individual fracture probably is not a strong function of 
its orientation because all are on the flat portion of the aperture versus effective-pressure 
curves. Therefore, the magnitude and direction of the components of the hydraulic 
conductivity tensor should be controlled by the distribution of joints of various

TDR-NBS-HS-000001 REV 00 ICN 01 3-65 August 2000 
orientations. Fractures detected from geophysical logs generally are oriented in a northsouth 
direction and are within 30 of vertical. 
 Fluid and solute tend to travel preferentially along channels in which the apertures are 
largest. The fluid travels preferentially within regions of large apertures with large 
sections of the fracture surface containing stagnant fluid or no fluid where the faces are 
in contact. 
 Matrix materials conduct no fluid under natural groundwater flow conditions, but are 
physically connected to the fracture fluid through the pore network. Fluid is stored in 
this pore space and is important to radionuclide migration (see below). The matrix 
porosities of interest are those of the rock within the fractured regions. Fractures 
generally are found within the moderately to densely welded tuffs, so the range of matrix 
porosities of these tuffs (0.06 to 0.09 for densely welded and 0.11 to 0.28 for moderately 
welded) more accurately reflect the fluid storage of interest rather than the generally 
wider ranges of values found within a specific lithologic member. 
3.2.4.1.2 Advection in the Alluvium 
Fluid flow in the alluvium is likely to be well represented using a porous continuum conceptual 
model. This is due to the more porous, less fractured nature of the alluvial material. However, 
this assumption does not mean that the medium is homogeneous. On the contrary, flow is likely 
to occur through the relatively more permeable regions within the medium, with the lowpermeability 
regions acting as flow barriers that groundwater flows around rather than through. 
Data to quantify this portion of the flow path are sparse, and hydrologic parameters used in 
numerical models are based on regional-scale, rather than site-scale data (CRWMS M&O 2000o, 
Section 6.3.1), and should be considered to represent large uncertainty. Discussions of the 
hydraulic characteristics of the alluvium are presented by CRWMS M&O (2000n) and CRWMS 
M&O (2000o). 
3.2.4.2 Matrix Diffusion 
Instead of simply traveling at the flow rate of the fluid in the SZ, radionuclides potentially will 
undergo physical and chemical interactions that must be characterized to predict large-scale 
transport behavior. These interactions include molecular diffusion into the rock matrix, sorption 
on the minerals along the fractures or within the rock matrix, and transport in colloidal form. 
When a dissolved species travels with the fluid within a fracture, it may migrate by molecular 
diffusion into the stagnant fluid in the rock matrix. When a molecule enters the matrix, its 
velocity effectively goes to zero until Brownian motion carries it back into a fracture. The result 
is a delay of the delivery of the solute to a downgradient location from what would be predicted 
if the solute had remained in the fracture. In hydrologic tests not involving tracers, the pore 
water velocity often can be estimated given assumptions about the fracture porosity. For 
interpreting hydrologic tests, the fracture porosity usually is the correct porosity value because 
pump testing is controlled by fracture flow. However, the groundwater travel time often is 
computed by dividing the flow path length by this velocity. This estimate potentially is a severe 
underestimate of the time required for a water molecule to migrate along the flow path. A more

TDR-NBS-HS-000001 REV 00 ICN 01 3-66 August 2000 
accurate definition of travel time for predicting transport behavior takes into account matrix 
diffusion. 
Several theoretical, laboratory, and field studies have demonstrated the validity of the matrixdiffusion 
model. As reviewed by CRWMS M&O (2000j), mathematical models were first used 
to demonstrate the likely effect of matrix diffusion and flow in fractured media. In these studies, 
transport was idealized as plug flow in the fracture with diffusion into the surrounding rock 
matrix. Experiments were performed of transport in natural fissures in granite, and it was 
concluded that matrix diffusion was necessary to model conservative tracer data. As reviewed 
by CRWMS M&O (2000j), the concept of matrix diffusion was extended to examine the 
coupling between matrix diffusion and channel flow usually thought to occur within natural 
fractures. 
Transport models incorporating matrix-diffusion concepts also have been proposed to explain the 
often-conflicting groundwater ages obtained from carbon-14 data compared to ages predicted 
from flow data. Sudicky and Frind (1981) developed a model of flow in an aquifer with 
diffusion into a surrounding aquitard to show that the movement of carbon-14 can be much 
slower than predicted if only movement with the flowing water is considered. Maloszewski and 
Zuber (1985) reached a similar conclusion with a model for carbon-14 transport that consists of 
uniform flow through a network of equally spaced fractures with diffusion into the surrounding 
rock matrix between the joints. Their model also includes the effect of chemical exchange 
reactions in the matrix, which further slows the migration velocity. Maloszewski and Zuber 
(1985) also present analyses of several interwell tracer experiments that show that their matrixdiffusion 
model can be used to provide simulations of these tests that are consistent with the 
values of matrix porosity obtained in the laboratory and aperture values estimated from hydraulic 
tests. In all cases, the results are superior to previous analyses that did not include matrix 
diffusion effects. Finally, of greatest relevance to the SZ beneath Yucca Mountain is the C-wells 
reactive tracer test (Section 3.1.3.2), which demonstrated that models that incorporate matrix 
diffusion provide more reasonable fits to the tracer-experiment data than those that assume a 
single continuum. Maloszewski and Zuber (1985) demonstrated that a suite of tracers with 
different transport characteristics (e.g., different diffusion coefficients or sorption coefficients) 
produced breakthrough curves that can be explained using a diffusion model that assumes 
diffusion of tracers into stagnant or near-stagnant water. 
Data from naturally occurring isotopes, such as carbon-14, provide valuable clues into the 
processes controlling transport in the SZ. However, these data sets are best used in the 
development of conceptual models rather than as observations used directly in formal calibration 
exercises. The reasons for this approach are twofold. First, there is considerable uncertainty in 
the conceptual model of SZ flow that gives rise to the data set. Waddell et al. (1984) observe 
that the hydrologic conditions that describe modern-day conditions, with recharge presumed to 
occur at higher elevations, probably is not correct for the climatic conditions during the 
Pleistocene Epoch. Yet many of the water ages in the SZ imply an origin of these fluids during 
the Pleistocene. Given that the chemical signature of the recharge fluid probably was different 
during the Pleistocene, and that more widespread recharge and discharge areas were present, the 
application of steady-state models to simulate the data may not be adequate.

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Instead of using carbon-14 data as a calibration measurement, the ages are taken into account at 
the level of conceptual model development. The ages of SZ fluids are on the order of several 
thousand years or more. These old ages imply either that transport of carbon is slowed by matrix 
diffusion, or that advective porosity is much larger than is expected for a fractured media. This 
argument is consistent with the conceptual model of interchange of solutes between the fractures 
and matrix found in the matrix-diffusion model. 
The fact that matrix diffusion appears to be consistent with the conceptual model does not imply 
that the fracture and matrix fluids must therefore be in chemical equilibrium at all locations in 
the SZ. The model is consistent with different chemical compositions in the fracture and matrix 
fluid. This situation would occur if the fracture spacing were sufficiently large that a solute 
traveling through fractures has insufficient time to diffuse fully within the matrix block between 
fractures. In reality, a spectrum of different transport regimes probably is present in the SZ, from 
fracture-dominated transport at some locations to complete equilibration between fracture and 
matrix fluids at other locations. The carbon-14 data constrain this possibly wide range of 
behavior by establishing that considerable communication between fractures and matrix is likely. 
3.2.4.3 Sorption 
Sorption reactions are chemical reactions that involve the distribution of chemical constituents 
between water and solid surfaces. Although these reactions can be complex in detail, they 
typically are represented in transport calculations by a constant called the sorption coefficient. 
Accurate prediction of the rate of transport of chemical constituents in a well-characterized flow 
system requires that three conditions are met concerning the sorption reactions: the reactions 
must be in equilibrium, instantaneous, and reversible. 
In the case of the Yucca Mountain flow system, an important goal is the prediction of the 
maximum rate of transport of the mean concentrations of radionuclides. This allows the three 
conditions to be relaxed. For example, sorption reactions that are not fully reversible result in 
rates of transport that are slower than would be the case for fully reversible reactions. Therefore, 
for radionuclides that sorb nonreversibly, using a sorption coefficient would result in 
conservative predictions of transport rates. 
If sorption reactions are not instantaneous for a given radionuclide, the possibility exists that the 
radionuclide could be transported at a faster rate than would be predicted by the use of a sorption 
coefficient in the transport calculations. The term instantaneous does not necessarily refer to an 
absolute rate but rather to a rate referenced to the flow rate. If the flow rate is slow relative to the 
sorption reaction rate, noninstantaneous sorption reactions need not be a problem. However, if 
the sorption reaction rate is slow relative to the flow rate, there could be a problem in prediction 
of the minimum breakthrough time. To address this possibility, the sorption coefficient 
distributions used in transport calculations have been biased downward for the radionuclides of 
interest that appear to have slow sorption kinetics (i.e., this assumes less sorption). In effect, the 
results of short-term experiments with these radionuclides were included in the distributions. 
The issue of equilibrium in sorption reactions relates to reversibility and the rate of sorption 
reactions. Equilibrium can be considered in terms of the rates of the forward and backward 
reactions in an overall chemical reaction. At equilibrium, the forward and backward rates are

TDR-NBS-HS-000001 REV 00 ICN 01 3-68 August 2000 
equal and the reaction is, by definition, reversible. A common occurrence in sorption reactions is 
the situation in which the forward reaction is relatively fast compared to the backward reaction. 
In this case, the reaction is not entirely reversible. Use of an equilibrium-based sorption 
coefficient in this case would lead to conservative predictions of transport rates. The case in 
which the forward reaction is slow and the backward reaction is fast also is possible. In this 
case, use of equilibrium-based sorption coefficients tends to predict rates of transport that are 
higher than expected. For the elements that show this sort of behavior, sorption coefficients 
based on short-term experiments, relative to the rate of flow in the aquifers, would have to be 
used. The database compiled by the YMP (CRWMS M&O 2000r, Table 2b) does not indicate 
any elements of interest with this type of behavior. 
Sorption in Fractured Porous MediaSorption of radionuclides on rock surfaces is a 
mechanism that will result in retardation. Radionuclide-rock interactions potentially can occur 
on the surfaces of fractures and within the rock matrix. This distinction is important because the 
surface-area to fluid-volume ratio and the mineral distributions probably are different in the 
fractures as compared to the matrix. Sorption on fracture surfaces is not included in total system 
performance assessment (TSPA) simulations of radionuclide transport. The lithium tracer in the 
C-wells reactive tracer experiment was modeled using a matrix-diffusion model with the sorption 
coefficient as an additional adjustable parameter (Section 3.1.3.2). The matrix sorption 
coefficient that fit the data agreed quite well with the value determined in laboratory sorption 
tests, thus providing an additional degree of confidence in the matrix-diffusion model. The fact 
that the early lithium response had the same timing as that of the nonsorbing tracers, but with a 
lower normalized peak concentration, is consistent with matrix diffusion coupled with sorption 
in the matrix. 
Sorption in the AlluviumIn contrast to the fractured tuffs, there are no field-scale tracer 
transport tests in the alluvium south of Yucca Mountain to confirm the validity of the sorption 
coefficient data. However, the transport of sorbing solutes in porous media that is not controlled 
by fractures has been well studied (e.g., Freeze and Cherry 1979). Sorption coefficients onto 
alluvium from the Nye County wells have been measured for a few key radionuclides 
(CRWMS M&O 2000r). For the remaining radionuclides, sorption coefficients have been 
estimated based on the corresponding values measured for crushed tuff (CRWMS M&O 2000r). 
3.2.4.4 Hydrodynamic Dispersion 
Dispersion is caused by heterogeneities at all scales, from the scale of individual pore spaces to 
the scale of the thickness of individual strata and the length of structural features such as faults. 
The spreading and dilution of radionuclides that result from these heterogeneities could be 
important to performance of the potential repository. The largest heterogeneities are represented 
explicitly in the site-scale SZ flow and transport model, and other features are included in the 
HFM on which the model is built. For dispersion at smaller scales, it is assumed that the 
convective-dispersion model applies with dispersion characterized using an anisotropic 
dispersion coefficient tensor consisting of longitudinal, horizontal-transverse, and 
vertical-transverse dispersivities.

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Field studies of transport and dispersion have been conducted at a variety of length scales (from 
meters to kilometers) to address the issue of dispersion (Figure 3-16). The results show a trend 
toward larger apparent dispersion coefficients for transport over longer distances. Solutes 
encounter larger-scale heterogeneities at larger scales, and thus, spreading is more pronounced. 
Also shown in Figure 3-16 is a black diamond representing the dispersivity determined for the 
C-wells reactive tracer experiment (Section 3.1.3.2). There is uncertainty in this estimate due to 
uncertainty in the exact flow paths taken by a tracer during the test. Nevertheless, the estimate 
falls within the range of values from other sites, suggesting that transport in the fractured tuffs 
exhibits similar dispersive characteristics. The values used in the simulations of radionuclide 
transport are somewhat higher than those estimated from the C-wells because of the larger scale 
that is relevant for radionuclide migration to the accessible environment. Little experimental 
information exists for assigning transverse dispersivity values. 
An important caveat on the validity of dispersive transport models must be recognized when 
interpreting the results. When attempting to capture all dispersion mechanisms at scales smaller 
than the size of a typical grid cell with a simple dispersion model, certain features likely to be 
present are simulated as averages. For example, suppose the physical system has a localized, 
high-permeability pathway within the domain defined by a grid cell. This region may have high 
concentration within the pathway and lower concentrations in the rest of the domain. A 
continuum model averages these differences, and a single value of concentration is defined for 
the block. Concentration differences at scales smaller than the grid cell, if present, are not 
resolved. 
Whether this distinction is important depends on specific performance criteria and scenarios for 
exposure to humans or plants. Because the site-scale SZ flow and transport model is used to 
predict concentrations under a well-withdrawal scenario, the potentially complex distribution of 
radionuclides within a grid block will be averaged in the process of extracting water from the 
aquifer. 
3.2.4.5 Colloid Facilitated Transport 
The conceptual model of colloid-facilitated transport of radionuclides in the SZ consists of two 
modes of transport (Figure 3-17). The first mode involves radionuclides that are irreversibly 
(permanently in the time frame of groundwater transport) sorbed onto or embedded in colloids. 
The second mode deals with radionuclides that are reversibly attached to colloids, such that at 
any time, radionuclides are partitioned between the aqueous and colloid phases.

TDR-NBS-HS-000001 REV 00 ICN 01 3-70 August 2000 
Source: CRWMS M&O (2000r, Figure 100) 
NOTE: The black diamond represents the dispersivity determined for the C-wells reactive tracer experiment. 
Figure 3-16. Estimated Dispersivity as a Function of Length Scale 
10 5 
10 4 
10 3 
10 2 
10
1 
10 -1 
10 -2 
10 -3 
10 3 10 -4
10 -2 10 -1 1 10 10 -2 10 -3 10 -4 10 -5

TDR-NBS-HS-000001 REV 00 ICN 01 3-71 August 2000 
Figure 3-17. Conceptual Model of Colloid-Facilitated Transport of Radionuclides 
3.2.4.5.1 Radionuclides Reversibly Sorbed to Colloids 
Radionuclides that are reversibly sorbed onto colloids reside in the aqueous phase and on the 
surfaces of colloids. Thus, the transport behavior of these radionuclides is governed by a 
combination of the transport characteristics of aqueous solutes and colloids. The conceptual 
model for this mode of colloid facilitated transport assumes equilibrium sorption of radionuclides 
on the colloids, and equilibrium sorption of the aqueous form of the radionuclide on the 
immobile rock surface. The colloids that form the substrate for the reversible sorption can be of 
any type, for example, natural colloids (typically clay or silica), waste form colloids resulting 
from degradation of spent fuel or glass, and iron oxyhydroxide colloids resulting from 
degradation of the waste container.

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For TSPA-Site Recommendation (TSPA-SR), radionuclides that are reversibly sorbed onto 
colloids are modeled using a distribution coefficient that represents the equilibrium partitioning 
of radionuclides between the aqueous phase and the colloidal phase (CRWMS M&O 1997, 
Equation 8-10, p. 8-35). The distribution coefficient is assumed to be a function of radionuclide 
sorption properties, colloid substrate properties, aqueous chemistry, and colloid concentration, 
and not any properties of the immobile media through which transport occurs; thus, to a first 
approximation, the same distribution coefficient applies to transport of a radionuclide in the 
volcanic units and the alluvium. 
In theory, a unique distribution coefficient probably exists for each radionuclide sorbing onto the 
colloidal material. However, except for a few radionuclides, these data are unavailable. 
Therefore, for TSPA-SR, the sorption coefficient for americium onto waste form colloids 
(CRWMS M&O 2000f) is assumed to represent a conservative bound on colloid transport for all 
radionuclides transported via this mechanism. Selecting a strongly sorbing radionuclide should 
lead to shorter transport times than if actual sorption coefficients were available. CRWMS 
M&O (2000o) present the cumulative probability density function used in the SZ site scale flow 
and transport TSPA-SR calculations. 
3.2.4.5.2 Colloid Attachment and Detachment in Fractured Tuffs 
As discussed in Section 3.1.4.3, it generally is accepted that colloids are capable of facilitating 
radionuclide transport over long distances in the SZ only if two conditions are met. First, a large 
percentage of the colloids must not irreversibly mechanically-filter or attach to rock surfaces; 
and second, the desorption rate of radionuclides from the colloids must be slow (i.e., 
radionuclides are actually impregnated in the colloids or are strongly sorbed to colloid surfaces). 
The first condition was addressed using polystyrene microspheres in the C-wells tracer tests. 
The second condition has been addressed by conducting laboratory sorption experiments to 
determine magnitudes and rates of sorption and desorption of long-lived radionuclides on 
different types of colloids that may be present in the near-field or the far-field environments at 
Yucca Mountain. These experiments have shown that plutonium-239 desorption rates from 
hematite colloids (near-field) are so slow that it is not possible to measure them, and desorption 
rates from goethite and montmorillonite colloids also are slow. Because of these observations, 
and the fact that there are large uncertainties due to the sparseness of the experimental data, the 
YMP has adopted the conservative position of assuming that a fraction of the mass of long-lived 
radionuclides (most notably plutonium-239 and americium) will be irreversibly sorbed to 
colloids. Consequently, the current conceptual model for colloid-facilitated transport in the SZ 
focuses on colloid attachment and detachment processes as the primary mechanisms for 
attenuating the transport of radionuclides irreversibly sorbed to colloids. 
The conceptual model for colloid-facilitated transport of irreversibly attached radionuclides in 
saturated fractured tuffs includes two key elements: 
 Colloids will move exclusively through fractures with negligible matrix diffusion 
because of their large size and low diffusivity relative to solutes. 
 Colloid attachment and detachment to fracture surfaces can be described by first-order 
rate expressions.

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Mathematically, the conceptual model is summarized by two equations (CRWMS M&O 2000l). 
These equations were used to fit the microsphere responses in the C-wells tracer tests, thus 
providing estimates of colloid attachment and detachment rate constants. In the fitting 
procedure, it was assumed that the spheres had the same mean residence times and dispersion 
coefficients as the solute tracers that were injected with them, so the rate constants were the only 
adjustable parameters. Details of the procedure for obtaining the rate constants are presented by 
CRWMS M&O (2000l). 
Based on the estimated rate constants and the range of transport times being considered for 
transport through saturated fractured tuffs, it was shown (CRWMS M&O 2000l) that the local 
equilibrium assumption is valid for all but the shortest transport times, and it is conservative for 
the shortest transport times. Thus, transport is sufficiently long that assuming local equilibrium 
between mobile and attached colloids yields the same results as assuming that colloid attachment 
and detachment are kinetic processes. 
The distribution, defined by the cumulative probability density function, will be sampled 
randomly to obtain retardation factors to be used in PA calculations of colloid transport in the 
SZ. The retardation factor will be one of many parameters that are sampled randomly for a large 
number of simulations that collectively will yield probability distributions for radionuclide 
transport through the SZ. Because radionuclides are assumed to be irreversibly sorbed to 
colloids, colloid-facilitated radionuclide transport in these simulations effectively will be the 
product of colloid transport and the mass loading of radionuclides assumed to be associated with 
the colloids. 
3.2.4.5.3 Colloid Attachment and Detachment in the Alluvium 
The conceptual model for colloid-facilitated transport in the alluvium is essentially the same as 
in fractured tuffs in that colloids are assumed to transport only in advective water (no diffusion 
into stagnant water or into grains), and colloid attachment and detachment onto alluvial surfaces 
are described by first-order rate expressions. Because no site-specific data for colloid transport 
in the alluvium are available, filtration theory and literature data are used to obtain distributions 
or bounds for attachment and detachment rate constants. Details of the analyses and references 
to the original data are presented by CRWMS M&O (2000l). 
As in the case of colloid transport in fractured tuffs, it was shown (CRWMS M&O 2000l) that, 
for the distributions of alluvium rate constants, the local equilibrium assumption will be valid for 
all but the shortest transport times, and it will be conservative for the shortest transport times. 
A probability density function for the retardation factor in the alluvium was constructed by 
randomly sampling the assumed distributions of parameters to generate a large number of 
potential retardation values.

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3.2.5 Alternative Conceptual Models 
Luckey et al. (1996, p. 52) reviewed the major conceptual uncertainties relating to the SZ flow 
system at Yucca Mountain. They identified the following major areas of uncertainty: 
 Whether the flow system can be simulated as a porous medium or if discrete features 
needs to be simulated 
 Uncertainty about the behavior of the flow system in the areas of the large hydraulic 
gradient and the moderate hydraulic gradient (Section 3.2.4.1) 
 Uncertainty about recharge and the time-scale at which it comes into equilibrium with 
climate (Section 3.2.4.2) 
 How best to translate data from field sampling and borehole testing to the scale of the 
flow models. 
The issue of whether the flow system can be simulated as an effective continuum model is 
addressed in CRWMS M&O (2000n), which notes that the site-scale SZ flow and transport 
model uses the effective continuum representation of fracture permeability. While it is 
recognized that the alternative discrete fractures approach retains the discrete nature of the 
fractures observed in the resulting model, the present data relating to the hydrologic properties 
of discrete fractures are limited and are not sufficient for a viable modeling effort. Additionally, 
the scale of this SZ flow and transport model is discussed in Section 3.5.1. 
Although the site-scale SZ flow and transport model is an effective continuum model, special 
hydrologic features, including selected major faults, fault zones, and zones of chemical 
alteration, are treated in the model as zones of enhanced or reduced permeability (CRWMS 
M&O 2000n, Table 6). 
The issue of translation of data from field sampling scale to flow-model scale remains 
problematic. Extensive hydraulic testing at the C-wells Complex indicates that much higher 
permeabilities were obtained from multi-well testing than from earlier single-hole testing at the 
same wells (Luckey et al. 1996, pp. 36 to 37). This casts doubt on the quantitative importance of 
the single-hole test results (Luckey et al. 1996, pp. 53 to 54); however, most of the data on 
permeability at Yucca Mountain are from single-hole tests. Chemical tracer tests 
(Section 3.1.3.2) augment the data from the C-wells Complex and Busted Butte 
(Section 3.1.3.2.2), but additional data on the hydraulic properties of the SZ are needed, 
particularly in the area between Yucca Mountain and Amargosa Valley (CRWMS M&O 1998b, 
Table 3-2). 
3.2.5.1 Large Hydraulic Gradient 
Luckey et al. (1996) present detailed descriptions of the gradient features and discuss 
interpretations of their causes (Section 3.2.2.3). The large hydraulic gradient particularly has 
been the subject of numerous theories.

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An expert elicitation panel on SZ flow and transport convened by DOE addressed the issue of the 
cause of the large hydraulic gradient and other issues (CRWMS M&O 1998b, pp. 3-5 to 3-6). 
The panel narrowed the theories to the two most credible hypotheses: the large hydraulic 
gradient is caused by flow through the upper volcanic confining unit or it is semi-perched water. 
The consensus of the panel slightly favored semi-perched water. The experts were in agreement 
that the issue was mainly one of technical credibility, that the probability of any large transient 
change in the configuration of the large gradient is low, and that long-term transient readjustment 
of gradients was of low probability (CRWMS M&O 1998b, p. 4-3). 
The only important new results pertaining to the cause of the large gradient include the drilling 
of borehole WT-24 in the area of the large gradient and the analysis of hydrochemical data by 
CRWMS M&O (2000m). 
Borehole WT-24 reportedly encountered a perched-water zone at 987-m (3,240-ft) elevation, 
then encountered unsaturated conditions to about 734-m (2,410-ft) elevation, where a waterbearing 
fracture was encountered. At that point, water levels in the borehole rose to an elevation 
of about 840 m (2,760 ft) and remained at about that level as the borehole was deepened to an 
elevation of 630 m (2,070 ft). The 840-m (2,760-ft) elevation, therefore, represents the 
potentiometric level for the fracture encountered at 734 m (2,410 ft), not another perched zone, 
because unsaturated conditions were present from 987 m (3,240 ft) to 734 m (2,410 ft). The 
borehole currently is not deep enough to test conclusively whether the small hydraulic gradient 
extends that far north (CRWMS M&O 2000w). 
With respect to the cause of the large hydraulic gradient, the drilling of borehole WT-24 
demonstrated that the previous portrayal of the large gradient (Tucci and Burkhardt 1995, 
Figure 4) probably included perched water; however, the question of whether perching of water 
is the cause of the large gradient was not fully resolved. 
CRWMS M&O (2000n, Table 6) treats the large hydraulic gradient area as a linear east-west 
barrier or zone of reduced permeability in the site-scale SZ flow and transport model. In plots of 
predicted particle flow paths (CRWMS M&O 2000n, Figures 10 to 12), particles are shown 
detouring around the barrier to the east and west. 
3.2.5.2 Perched Water 
Hydrochemical information on the ratio of uranium-234 to uranium-238 presented by CRWMS 
M&O (2000m, Section 6.5.3) suggests that local recharge, as represented by perched water, is a 
major component in the groundwater at Yucca Mountain. The best estimate of the time of 
recharge (based on carbon-14 ages of groundwater in the SZ at Yucca Mountain) range of about 
14,000 to 8,000 yrs, that is, during late Pleistocene to early Holocene time. The best estimate for 
the age of the perched water (based on carbon-14 data that are uncorrected for potential 
interaction between groundwater and carbonate minerals) suggest recharge between 7,000 and 
11,000 yrs, although dates as young as 3,300 yrs were noted in a sample from borehole NRG-7a, 
and in one of several samples from borehole UZ-14 (CRWMS M&O 2000m, Section 6.5). 
Taken together, these data suggest that the SZ water at Yucca Mountain originated mainly from 
local recharge via perched water zones during late Pleistocene-early Holocene time, and that 
throughflow under the current climate is minimal. The proportion of recharge that arrives at the

TDR-NBS-HS-000001 REV 00 ICN 01 3-76 August 2000 
water table via faults and fractures versus that which arrives via flow through the matrix beneath 
the perched zones has not been quantified, but the chemical resemblance of SZ water to perched 
water suggests that matrix flow is minimal. The weight of the hydrochemical evidence suggests 
that throughflows from the large hydraulic gradient to the north of Yucca Mountain, and that 
from the moderate hydraulic gradient to the west toward the area of the small hydraulic gradient 
extending from Yucca Mountain to Fortymile Wash, are minimal under the current climatic 
regime. 
Perched water was encountered in six boreholes near the potential repository (CRWMS M&O 
1998a, p. 5.3-162). The contact zone between the Topopah Spring welded and Calico Hills 
nonwelded hydrogeologic units is characterized by a basal vitrophyre stratum in the Topopah 
Spring welded hydrogeologic unit above a zone of zeolitic altered tuffs in the Calico Hills 
nonwelded hydrogeologic unit. For a perched zone to exist, the vertical permeability of the 
perching units would have to be low (less than 1 microdarcy) and fracture permeability would 
have to be negligible. 
The perched water bodies that have been encountered were below the potential repository 
horizon (CRWMS M&O 1998a, p. 5.3-162). Perched water has been encountered at the base of 
the Topopah Spring welded hydrogeologic unit or in the top of the underlying nonwelded to 
partially welded tuffs of the Calico Hills nonwelded hydrogeologic unit in several dry-drilled 
boreholes that penetrated the contact zone between the Topopah Spring welded and the Calico 
Hills nonwelded hydrogeologic units. The occurrence and modeling of perched water is 
discussed in CRWMS M&O (2000b, Section 3.7). 
The chemical character of the perched water encountered in the six boreholes is distinctly 
different from matrix pore waters from the same depth interval, and the isotopic character 
distinguishes the perched water from the deeper groundwater of the SZ. Generally, the perched 
waters have moderate concentrations of sodium bicarbonate, and are similar to the SZ waters. 
The pore waters typically have higher concentrations of sodium bicarbonate, and also are higher 
in chloride content than the perched waters. 
The age of the perched water has been dated by carbon-14 analysis. Recharge is estimated to 
have occurred between about 7,000 and 11,000 yrs before present, which is younger than could 
be accounted for by matrix flow. The stable isotope composition (deuterium and oxygen-18) is 
consistent with little or no evaporation and post-Pleistocene ages. The deuterium/oxygen-18 
composition of the perched water is at the heavy (i.e., less negative values) end of the range of 
values found in SZ waters. This suggests SZ waters in the Yucca Mountain region infiltrated 
under somewhat colder conditions than the perched waters within Yucca Mountain. If SZ 
groundwaters and perched waters infiltrated over approximately the same time interval, the 
difference in oxygen-18 and deuterium ratios could reflect upgradient recharge of SZ 
groundwaters at elevations that were higher than the surface of Yucca Mountain. Alternatively, 
the carbon-14 ages for SZ groundwaters may have been overcorrected and these groundwaters 
actually are older than the perched waters. The deuterium and oxygen-18 data could be 
explained if the SZ groundwaters were only a few thousand years older than the perched waters 
(i.e., latest Pleistocene in age).

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Analysis of tritium in perched waters indicates that, if present, tritium in most groundwater 
samples is below the detection level of 4 tritium units, which indicates that if water affected by a 
nuclear bomb test has reached the perched water bodies, the amount is statistically insignificant 
in these samples. Only one perched-water sample contained tritium (10 TU) above the detection 
level (Yang et al. 1996, p. 34). This sample may have a component of post-bomb infiltration. 
The importance of perched water bodies with regard to their implications for the movement of 
water within the UZ is discussed by CRWMS M&O (2000b). However, on the basis of 
chlorine-36 and oxygen-18 data, CRWMS M&O (2000m) tentatively conclude that uncorrected 
carbon-14 ages approximate the true carbon-14 ages, that is, they generally are between 7,000 
and 11,000 yrs before present (CRWMS M&O 2000m, Section 6.5.4.2.2). In either case, these 
dates suggest that recharge episodes occurred several thousand years ago and that there is no 
evidence of a large amount of recharge under current climatic conditions. 
3.2.5.3 Horizontal Anisotropy 
Anisotropic conditions exist if the permeability of media varies as a function of direction. 
Because groundwater primarily flows in fractures within the volcanic units downgradient of 
Yucca Mountain, and because fractures and faults occur in preferred orientations, it is possible 
that anisotropic conditions of horizontal permeability exist along the pathway of potential 
radionuclide migration in the SZ. Performance of the potential repository could be affected by 
horizontal anisotropy because the flow could be diverted to the south, causing transported solutes 
to remain in the fractured volcanic tuff for longer distances before moving into the valley fill 
alluvial aquifer. A reduction in the length of the flow path in the alluvium would decrease the 
amount of radionuclide retardation that could occur for those radionuclides with greater sorption 
coefficients in alluvium than in fractured volcanic rock matrix. In addition, potentially limited 
matrix diffusion in the fractured volcanic units could lead to shorter transport in the volcanic 
units relative to the alluvium. 
A conceptual model of horizontal anisotropy in the tuff aquifer is reasonable, given that flow in 
the tuff aquifer is believed to occur in a fracture network that exhibits a preferential north-south 
strike azimuth (CRWMS M&O 2000i). Major faults near Yucca Mountain that have been 
mapped at the surface also have a similar preferential orientation (Figure 3-4). In addition, north 
to north-northeast striking structural features are optimally oriented perpendicular to the 
direction of least principal horizontal compressive stress, suggesting a tendency toward dilation 
and potentially higher permeability (Ferrill et al. 1999, p. 5). 
Evaluation of the long-term pumping tests at the C-wells Complex supports the conclusion that 
large-scale horizontal anisotropy of aquifer permeability may occur in the SZ (Ferrill et al. 1999, 
p. 7). Results of this hydrologic evaluation generally are consistent with the structural analysis 
of potential anisotropy. However, there are important uncertainties, including differences in 
pumping test analysis methods, the fact that only a minimum number of observation wells were 
used, and the additional uncertainty regarding the validity of assuming a homogenous effective 
continuum over the scale of the test (Winterle and La Femina 1999, p. 4-29). 
Taken together, these observations and inferences support an alternative conceptual model in 
which large-scale horizontal anisotropy of permeability, with higher permeability in a north

TDR-NBS-HS-000001 REV 00 ICN 01 3-78 August 2000 
northeasterly direction, occurs in the volcanic units of the SZ to the southeast of the potential 
repository. Sufficient uncertainty exists in this interpretation to warrant retention of the simpler, 
horizontal isotropic model of permeability as the nominal conceptual model. Anisotropy is used 
in the TSPA calculations. 
3.2.6 Changes in the Saturated Zone Flow System 
In this section, factors that change the fluid flow path, flux magnitude, or water table position are 
considered. Changes in the SZ flow system may be brought about by climate changes, changes 
in the permeability field due to tectonic or volcanic events, or changes in the water table and 
hydraulic gradient due to increased pumpage. Changes to the SZ flow system due to climate 
change are likely in the next 10,000-yr period, and climate change is included in the base case 
model for the TSPA-VA. Large changes in the permeability field or changes in the water table 
and gradient due to tectonic and seismic events are considered in the features, events, and 
processes (FEPs) and uncertainty modeling. It is assumed that pumpage does not cause a 
significant change in the water table and does not change the hydraulic gradient. 
Future climate is likely to change the SZ flow conditions (USGS 2000c). In particular, the 
amount of precipitation is important because it largely determines the amount of infiltration. 
Forecasting future climate (i.e., using future climate scenarios), rather than modeling future 
climate, was used because climate modeling, among many complications, requires knowledge of 
the future climate boundary conditions (e.g., wind speed, water vapor flux, and heat flux) for 
input to a model. These boundary conditions cannot accurately be predicted at present. 
Forecasts of future climates for the next 10,000 yrs are described in USGS (2000c). Some 
discussion is presented here on climate forecasts to about 400,000 yrs. The principle 
assumptions concerning future climate change are: 
 Climate is cyclical, so past climates provide insight into potential future climates. 
 A relationship exists between the timing of long-term past climate change (glacial and 
interglacial cycles) and the timing of changes in certain earth-orbital parameters. This 
relation establishes a millennial-scale climate-change clock that provides a way to 
predict the timing of future climate changes. 
 A relationship exists between the characteristics of past climates and the sequence of 
those climates in the long earth-orbital cycle (approximately 400,000 yrs in length). The 
characteristics of past glacial and interglacial climates within the long earth-orbital cycle 
differ from each other, but they appear to differ systematically. This climate-sequence 
relation provides a defensible criterion for the selection of a particular past climate as an 
analog for a future climate. 
 Long-term earth-based climate-forcing functions, primarily tectonics, that operate on the 
million-year time scale have remained relatively unchanged during the last long earth 
climate cycle and will remain relatively unchanged during the next 10,000 yrs. If 
changes due to the climate-forcing functions are ignored, then climate may be forecasted 
as cyclical with a period of approximately 400,000 yrs. The potential impact of long

TDR-NBS-HS-000001 REV 00 ICN 01 3-79 August 2000 
term earth-based forcing functions on climate may need to be considered for 
understanding climate change to one million years. 
Climate proxies, or the physical remains of substances that carry the imprint of past climates, 
indicate that the climate in the Yucca Mountain region is not static. In the Yucca Mountain area, 
climate proxies are provided by the delta oxygen-18 isotopic composition of groundwater and by 
the Owens Lake climate record. The delta oxygen-18 isotopic composition of groundwater near 
Yucca Mountain is linked to the delta oxygen-18 isotopic composition and temperature at its 
source (i.e., the Pacific Ocean), the path taken from the source to the recharge area, precipitation 
losses, and the temperature at which the precipitation forms. 
Climate changes may be inferred from the ancient delta oxygen-18 isotopic composition of 
groundwater as recorded in calcite deposits in Devils Hole, a spring located approximately 
40 km (25 mi) southeast of Yucca Mountain near Ash Meadows. Devils Hole provides a record 
of climate change over the past 425,000 yrs. The record shows continual variation, often with 
rapid jumps, between cold glacial climates and warm interglacial climates that are similar to 
present conditions. The fluctuations average about 100,000 yrs in length. The relationship 
between variations in the delta oxygen-18 isotopic composition of groundwater and the 
precession (in degrees) of the earth is presented by USGS (2000c). A 100,000-yr component is 
evident in both data sets. 
The Owens Lake climate record is used to describe climate conditions at Yucca Mountain based 
on inferences from plant and animal fossils. Sediments deposited in Owens Lake, north of Death 
Valley and west of Yucca Mountain, hold remains of ostracode and diatom species that now 
occur in Canada. The presence (cool and wet) or absence (warm and dry) of these species 
implies climate changes during the past 400,000 yrs. Uncertainty in the rate of sediment 
deposition in Owens Lake requires calibration of the time record. The reconstruction of past 
climate from this lake was calibrated from modern climatological data and plant macrofossils 
obtained from packrat middens (deposits consisting of plant macrofossils cemented by packrat 
urine that can be dated by radiocarbon methods). 
The four assumptions above, plus the Devils Hole delta oxygen-18 isotopic record and the 
Owens Lake fossil deposits, establish a defensible means for assuming periodicity in climate 
forecasting. 
The climate in the Yucca Mountain region during the last 10,000 yrs generally has been warming 
and drying, and presently it is warm and semiarid, with a mean annual temperature of 16C 
(61F) and mean annual precipitation of about 170 mm/yr (6.7 in./yr). Climate forecasts for the 
next 10,000 yrs at Yucca Mountain suggest that the modern-day climate should persist for 400 to 
600 yrs, followed by a warmer and wetter monsoon climate for the next 900 to 1,400 yrs, 
followed by a cooler and wetter glacial-transition climate for the next 8,000 to 8,700 yrs. The 
range of ages represents uncertainty in the sediment accumulation rates in Owens Lake. The 
upper and lower bounds for each climate are described from what are believed to be 
meteorological stations representative of the forecasted climates. For sites potentially 
representing the average upper bound of the monsoonal climate, Nogales (south-central Arizona) 
and Hobbs (southeast New Mexico) were chosen. For the average lower bound of the 
monsoonal climate, Yucca Mountain was chosen. Three sites in eastern Washington were

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chosen as sites potentially representing the average upper bound of the glacial climate, while the 
average lower bound was represented by Beowawe (north-central Nevada) and Delta 
(central Utah). 
USGS (2000c) did not forecast climate farther than 10,000 yrs into the future, however, they did 
present Owens Lake data for the previous 400,000 yrs, and these data can be used to make 
forecasts longer than 10,000 yrs. USGS (2000c) also did not include the potential effects of 
anthropogenically-induced global climate change. This was because in a forecast taking into 
account a doubling of carbon dioxide from anthropogenic sources, DAgnese et al. (1999) found 
that groundwater recharge was reduced relative to the USGS (2000c) model. Therefore, models 
that considered the effects of anthropogenically-induced global climate change would be less 
conservative than the present forecasts (USGS 2000c). 
3.2.6.1 Changes in Water Table Elevation 
Climate changes induce changes in the water table, groundwater flux, and recharge and 
discharge. An increase in the elevation of the water table under Yucca mountain is important 
because it decreases the UZ barrier between the potential repository and the SZ, and also because 
it may increase the hydraulic gradient resulting in shorter radionuclide transport in the SZ. An 
increase in the water table also may change the direction of the transport flow path, although 
change in the flow path direction is unlikely (DAgnese et al. 1999). 
A higher water table is expected to result from future climate changes (USGS 2000c). Regionalscale 
flow modeling, considering the full glacial climate forecast (DAgnese et al. 1999), 
predicted a rise in the water table of 100 to 200 m (328 to 656 ft), depending on the assumed 
drain conductance of springs in the area. Geochemical studies (CRWMS M&O 1998e) provide 
evidence based on analysis of strontium isotopes in the UZ that the water table was about 60 m 
to 85 m (197 to 279 ft) higher in the past than at present. This higher water table appears 
associated with wetter climate conditions. Based on a mineralogic analysis of the distribution of 
vitric and zeolitized tuffs and the structural history of the site, CRWMS M&O (1998e) 
concluded that the water level has not risen more than 60 m (197 ft) above its present position. 
Based on the DAgnese et al. (1999) analysis, changes in the water table elevation due to future 
climate changes are modeled as an increase in fluid flux along the transport path. 
Other factors may cause water table changes at Yucca Mountain. Possible disruptive geologic 
(tectonic or volcanic) conditions may result in an increase or a decrease in the water table 
beneath Yucca Mountain. Transient fluctuations on the order of a few decimeters have been 
observed in response to barometric variations and earth tides and changes on the order of a few 
decimeters to a few meters have been observed following earthquakes (CRWMS M&O 1998e). 
Most modeling scenarios involving earthquakes or volcanic intrusions (Section 2.3) show that 
the maximum increase in the elevation of the water table resulting from these events is expected 
to be on the order of a few decimeters to perhaps 20 m (66 ft). A scenario (Ahola and 
Sagar 1992) involving a three-order of magnitude increase in hydraulic conductivity in the area 
north and northeast of Yucca Mountain (where a large hydraulic gradient exists), resulted in 
increases (up to 275 m [902 ft]) in the water table below Yucca Mountain. However, modeling 
of this scenario was not performed to show under what tectonic or volcanic conditions such an 
increase in conductivity could occur.

TDR-NBS-HS-000001 REV 00 ICN 01 3-81 August 2000 
Not all investigators are in agreement concerning the hypothesis of continuous unsaturated 
conditions at Yucca Mountain during past epochs. Szymanski (1989) postulated and modeled 
possible rises in the water table due to tectonic activity. A study of fluid inclusions in 
calcite/opal deposits located at and near faults at Yucca Mountain by Hill et al. (1995) showed 
evidence of past ingress of hypogene waters of elevated temperature into the potential repository 
horizon. Hill et al. (1995) suggest that upwelling of waters below the potential repository as a 
possible source of the inclusions. Stuckless et al. (1998), however, point out a number of errors 
and cite other sources of evidence to arrive at the contrary conclusion that the source of waters in 
the inclusions was more likely infiltration through overlying soil and rock. The National 
Academy of Sciences also reviewed this issue and concluded that none of the evidence cited as 
proof of ground-water upwelling in and around Yucca Mountain could reasonably be attributed 
to that process (National Research Council 1992, p. 3). Possible scenarios in which the water 
table rises to saturate the potential repository have been excluded from consideration in TSPA 
analyses as indicated in Section 1.3, but they are discussed further in Section 3.8.1. 
The 3-D site-scale SZ flow simulator assumes confined conditions within the SZ. Changes in 
water level are modeled by increasing the hydraulic gradient and reducing the thickness of the 
UZ (Section 3.3.5). 
3.2.6.2 Changes in Groundwater Flux 
Climate change in the TSPA-VA is modeled by increasing the groundwater flux along the 
transport flow path (Section 3.6.3.3.3), and an increase in solute flux is computed analytically 
from the increased groundwater flux. The effects of climate change on the transport of 
radionuclides in the SZ are incorporated in TSPA calculations by scaling the radionuclide mass 
breakthrough curves simulated for present climatic conditions and assumes a proportional 
scaling of groundwater flux in the entire SZ system in response to future wetter climatic 
conditions. 
3.2.6.3 Changes in Recharge and Discharge 
Regional discharge estimates under present and glacial-transition climate conditions have been 
computed by DAgnese et al. (1997, 1999). Flow during glacial-transition climate conditions 
reversed at some areas such as the boundary near Pahranagat Lakes. The playa region of Death 
Valley becomes a lake (i.e., Lake Manly reappears) under glacial-transition climate conditions. 
In many low-lying areas of the central Death Valley subregion, water was shown to discharge 
because the simulated water table exceeded the land surface elevation. Potential discharge areas 
close to Yucca Mountain were examined. Drains located in the northern portion of Fortymile 
Wash did not discharge, however water did discharge from drains in the southern portion of 
Fortymile Wash where it flowed into the Amargosa River. Drains at the southern end of Crater 
Flat did not discharge; however, the water table was close to the land surface in this area. 
DAgnese et al. (1997) assumed no well pumpage in these simulations because they were 
comparing future conditions to past glacial-transition climate conditions.

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3.3 MATHEMATICAL AND NUMERICAL MODELING APPROACH 
The mathematical and numerical modeling approach used to implement the conceptual model of 
flow and transport (Section 3.2) is presented below. In the first part of the section, the 
development of the mathematical models is presented, and this is followed by a discussion of the 
numerical methods used to implement these mathematical models. Then a discussion of the 
development of the site-scale SZ flow and transport model, the calibration of the model, and a 
summary of the calibration results is presented. Finally, a discussion of the sensitivity of the 
flow model is provided. Assumptions, uses, and limits of the site-scale SZ flow and transport 
model are discussed in Section 3.5. 
3.3.1 Mathematical Model of Groundwater Flow 
An effective continuum approach is adopted for simulating groundwater flow through the 
fractured rock and alluvial materials within the domain of the site-scale SZ flow and transport 
model (Figure 2-1). Based on this conceptualization, the equations governing groundwater flow 
can be derived by combining the equations describing the conservation of mass and Darcys 
Law. The conservation of mass is described by 
0 mass 
mass mass 
A 
f q 
t 
 
 
+ѷ + = 
v 
, (Eq. 3-1) 
where Amass is the fluid mass per unit volume given by Amass = fr, 
v 
f mass is the fluid mass flux 
given by 
v 
f mass = rv v , f is the porosity in the system [dimensionless], r is the fluid density [M/L3], 
vv is the fluid velocity [L/T], t is the time [T], and qmass is the fluid mass source. 
The velocity of the fluid can be expressed by Darcys Law: 
v v = - 
k
m
 P - rg ( ), (Eq. 3-2) 
where P is pressure [MT2/L2], m is the dynamic viscosity of the fluid [M/LT], k is the 
permeability [L/T], and g is the acceleration resulting from gravity [L/T2]. 
Equations 3-1 and 3-2 can be combined to yield: 
( ) 0 mass 
mass 
A k 
P g q 
t 
 r 
r 
 
  
-ѷ  - + =   m   
, (Eq. 3-3) 
which is the fundamental equation describing groundwater flow. Groundwater flow is simulated 
in the site-scale SZ flow and transport model by obtaining a numerical solution to this equation. 
A more detailed discussion of the mathematical model used for describing groundwater flow is 
provided by CRWMS M&O (2000n, Section 6.5).

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3.3.2 Mathematical Model of Radionuclide Transport 
During development of the SZ conceptual model, a number of processes that affect solute 
transport were identified (Section 3.2.4). These processes include advection, dispersion, matrix 
diffusion, sorption, and colloid-facilitated transport. The mathematical models developed for 
describing these processes are presented below. 
3.3.2.1 Advective-Dispersion Equation 
As described by CRWMS M&O (2000j), the fundamental mass transport equation for transport 
of a nonreactive, dilute species in a saturated porous medium (with no sources or sinks) has the 
form 
0 ) ( ) ( =    -   + C D C v 
t 
C v 
 
 
(Eq. 3-4) 
where C denotes the solute concentration in units of moles per liter, v
r 
designates the solute 
average pore-water velocity vector [L/T], and D denotes the dispersion tensor [L2 /T]. 
For an isotropic medium, dispersion has the form 
ij 
j i 
T L ij T ij D 
v
v v 
v D d a a d a 0 ) ( + - + = (Eq. 3-5) 
where L a and T a denote the longitudinal and transverse dispersivities [L], respectively, D0 
represents the molecular diffusion constant [L2/T], and n is equivalent to v
r 
, the magnitude of 
the velocity vector [L/T]. 
Using a Cartesian coordinate system, the dispersion tensor given in Equation 3-5 can be written 
as a nine element (3 by 3) numerical matrix. However, in an anisotropic system, the expression 
for the dispersion tensor is more complex, involving as many as 36 independent parameters. 
However, a simplified form is adopted for simulating solute transport in the site-scale SZ flow 
and transport model. This representation of the dispersion tensor uses three parameters: 
longitudinal ( L a ), transverse horizontal ( H 
T a ), and transverse vertical ( V
T a ) dispersivities. This 
formulation of the dispersion tensor was chosen because of its relative simplicity and 
correspondence to the primary terms normally estimated in field studies. 
This formulation of the dispersion tensor can be written as a nine element (3 by 3) numerical 
matrix. The off-diagonal terms of the dispersion tensor are important because they ensure proper 
treatment of dispersion parallel and perpendicular to the direction of flow when flow is not 
parallel to any of the coordinate axes. A detailed discussion of the mathematical formulation of 
the advective-dispersion equation, including the formulation of the dispersion tensor, is provided 
by CRWMS M&O (2000j, Section 6.1).

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3.3.2.2 Matrix Diffusion 
As described by CRWMS M&O (2000j), the conceptual model developed for simulating 
transport in the site-scale SZ flow and transport model includes the diffusion of radionuclides 
into the matrix of fractured rocks (Section 3.2.4.2). An analytical solution is used to incorporate 
the effect of matrix diffusion into the site-scale SZ flow and transport model. This analytical 
solution describes transient contaminant transport in equally spaced parallel fractures. The 
model upon which the solution is based takes into account advective transport in the fractures, 
molecular diffusion from the fracture to the porous matrix, adsorption on the fracture face, and 
adsorption within the matrix. Although the analytical solution provides for incorporating 
adsorption on the fracture face, this option is not used in the model due to the lack of conclusive 
information on this process and the anticipated small impact of this option on the radionuclide 
transport simulations. The model uses a no-flux condition at the mid-point of the rock matrix 
between fractures. The analytical solution requires the definition of a number of specific 
parameters, including fracture aperture, mean fracture spacing, linear groundwater velocity 
within the fracture, porosity of the rock matrix, retardation factors in the rock matrix and in the 
fracture, and the effective matrix diffusion coefficient. Based on the values specified for these 
parameters, this analytical solution can be used to identify the distribution of contaminants along 
the fracture at any point in time. A detailed discussion of the analytical solution used to 
incorporate matrix diffusion into the transport model is provided in CRWMS M&O (2000j, 
Section 6.2). 
3.3.2.3 Sorption 
Sorption is incorporated into the site-scale SZ flow and transport model using a linear isotherm 
model (Section 3.2.4.3). Based on the linear isotherm model, the distribution coefficient, Kd, is 
defined as the ratio of the mass of solute on the solid phase per unit mass of solid phase to the 
concentration of solute in solution. Using the distribution coefficient, the effect of sorption may 
be incorporated into the advection-dispersion equation (Equation 3-4) to obtain 
0 ) ( = 
 
 
+    + 
 
 
t 
C 
K 
n 
C D 
t 
C 
d 
b r 
(Eq. 3-6) 
where rb is the bulk mass density [M/L3] and n is the matrix porosity [dimensionless]. 
Equation 3-6 maybe rearranged into a more familiar form by defining a retardation factor, 
R = 1 + (rb/n)(Kd), to obtain 
0 ) ( ) ( =    -   + 
 
 
C D C 
t 
C 
R n . (Eq. 3-7) 
Based on Equation 3-7, the retardation coefficient may be applied to the velocity and dispersion 
terms to effectively account for the effects of sorption on the advective and dispersive fluxes. 
The application of the retardation factor within the numerical solution of the transport equation is 
discussed in Section 3.3.4.2. A detailed discussion of the mathematical treatment of sorption is 
provided by CRWMS M&O (2000r).

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3.3.2.4 Colloid-Facilitated Transport 
The conceptual model for colloid-facilitated transport focuses on colloid attachment and 
detachment processes (Section 3.2.4.5). It is assumed that in saturated fractured tuffs, colloids 
will move exclusively through fractures with negligible matrix diffusion and that colloid 
attachment and detachment to fracture surfaces can be described by first-order rate expressions. 
An assumption of local equilibrium has been adopted to describe these processes. Using these 
assumptions, and in a manner similar to the case of sorption (Section 3.3.2.3), the mathematical 
model for colloid-facilitated transport in fractured tuffs can be written as 
( ) ( ) 0, c 
c c c 
C 
R vC D C 
t 

 
+ -  = v (Eq. 3-8) 
where 
res 
filt 
C bk 
k 
R 1 + = is the effective retardation factor for colloid transport, Cc is the colloid 
concentration in solution, kfilt is the filtration rate constant, kres is the detachment rate constant, 
and b is the fracture half aperture. 
The conceptual model for colloid-facilitated transport in the alluvium essentially is the same. 
Consequently, the mathematical model for colloid facilitated transport in alluvium is identical to 
that for fractured tuffs with the exception that Rc is defined as 
1 ,f a 
C 
r 
k 
R 
n k 
r 
= + (Eq. 3-9) 
where ra denotes the density of the alluvial material [M/L3], n is the matrix porosity 
[dimensionless], f k is the attachment rate [#/M-T], and kr is the detachment rate constant 
[#/L3-T]. 
A detailed discussion of the mathematical model for colloid-facilitated transport is provided by 
CRWMS M&O (2000l). 
3.3.3 Numerical Solution of the Groundwater Flow Equation 
The FEHM code (Zyvoloski et al. 1997a) is used in site-scale SZ modeling to obtain a numerical 
solution to the mathematical equation describing groundwater flow (Equation 3-4). FEHM is a 
nonisothermal, multiphase flow and transport code that simulates the flow of water and air, and 
the transport of heat and solutes, in 2-D and 3-D saturated or partially saturated heterogeneous 
porous media. The code includes comprehensive reactive geochemistry and transport modules 
and a particle tracking capability. Fractured media can be simulated using an equivalent 
continuum, discrete fracture, dual porosity, or dual permeability approach.

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As described by CRWMS M&O (2000n, Section 6.5), the control-volume finite element method 
is used in FEHM to obtain a numerical solution to the groundwater flow equation over the model 
domain. Finite-element methods are based on the assumption that a continuum may be modeled 
as a series of discrete elements. For each element, equations based on a discretized form of the 
groundwater flow equation are written that describe the interaction of that element with its 
neighbors. This discretization leads to a set of equations that must be solved to obtain the values 
of groundwater pressure at each node throughout the model domain. 
3.3.4 Numerical Solution of Transport Equation 
The numerical approach implemented in FEHM to obtain a solution for the transport equation 
was selected based on a number of important requirements. The transport model needs to be 
based on a 3-D process-level flow model. The transport model also needs to be able to handle 
extremes of the advective-dispersive transport that include a wide range of dispersivity values. 
The model must be able to handle cases of low transverse dispersivity (including no transverse 
dispersivity) throughout the entire travel path or higher dispersivity in the fractured volcanic 
rocks transitioning abruptly to low dispersivity in the alluvium. Capturing this low level of 
dispersion transverse to the mean trajectory of a solute plume is extremely difficult using typical 
finite-element or finite-volume transport models unless an extraordinarily fine grid discretization 
is employed. 
It may be necessary for the model to simulate the transport of plumes that have smaller 
dimensions than the grid block size of the flow model. Finite element simulations of transport 
cannot capture the details of radionuclide spreading if the plumes have characteristic dimensions 
that are of the same order or smaller than the grid block size of the flow simulation. Numerical 
dispersion effects arising from such an approach can be misinterpreted as dilution. A numerical 
method that retains the accuracy of the local concentration for small plumes is required for the 
solution of the transport equation. 
The numerical approach used to solve the transport equation also must include a method for 
introducing the radionuclide source term into the model that is flexible enough to handle small 
and large source regions at the water table. Spreading of radionuclide mass (computed from the 
UZ flow and transport model) over large areas would only be valid if the source at the potential 
repository is due to many waste packages leaking simultaneously and if there is sufficient 
transverse dispersion within the UZ to smear the source within the percolating UZ fluid. 
Although smearing the radionuclide mass may be a good assumption under some circumstances, 
releases from a small number of waste packages cannot be handled with such a model. 
Radionuclide mass releases from a small number of waste packages, if distributed over large 
areas, would introduce large and artificial dilution factors at the interface of the UZ and SZ. 
The site-scale SZ flow and transport model must be able to capture the important 
physicochemical processes known or suspected to occur in fractured porous rock. To properly 
account for transport through the fractured tuff, the transport model must include a dual-porosity 
transport formulation. This dual-porosity transport formulation must include the effects of 
sorption within the rock matrix that come into play only if considerable diffusion into the matrix 
pores occurs as radionuclides travel through the system. The effects of sorption in the alluvial 
aquifer system must also be included in the transport formulation.

TDR-NBS-HS-000001 REV 00 ICN 01 3-87 August 2000 
Finally, it must be possible to abstract the results of the process-level site-scale SZ flow and 
transport model for use in TSPA-SR calculations. The main purpose of the site-scale SZ flow 
and transport model is to predict the concentration of radionuclides in the aquifer and at a 
hypothetical pumping well. Because these abstractions are employed in TSPA-SR, the transport 
model must predict breakthrough curves at a compliance point. 
To meet these requirements, a particle tracking method has been implemented in FEHM to 
provide a solution to the advection-dispersion transport equation. In this approach, transport is 
decomposed into three interrelated components: advective, dispersive, and physiochemical. For 
the advective component, a particle tracking method is used. A random walk algorithm was 
combined with the particle tracking approach to account for the dispersive component of the 
advection-dispersion transport equation. To incorporate the dual-porosity transport and sorption 
components of transport equation, special modules were incorporated into the FEHM code. 
These approaches to the solution of the components of the advection-dispersion transport 
equation are discussed below. 
3.3.4.1 Particle Tracking and Random Walk Algorithm 
As described by CRWMS M&O (2000j), particle-tracking methods provide an efficient 
numerical algorithm for modeling the large-scale transport of solutes in heterogeneous porous 
media. By contrast, continuum approaches involving finite difference or finite element solution 
methods generally suffer from numerical dispersion, primarily because of the large grid blocks 
required to model large-scale systems. Furthermore, when using particle tracking, plumes can be 
simulated at scales smaller than the grid block size, and source regions can be smaller than the 
grid spacing. Particle tracking methods are particularly effective for handling advectiondominated 
transport. Consequently, a particle tracking method is used in FEHM to solve the 
transport equation in the site-scale SZ flow and transport model. 
The particle-tracking method incorporated into FEHM is based on placing particles at specific 
points in the flow field to represent a specified mass of solute. These particles can be placed 
throughout the model domain to represent existing solute concentrations and can be introduced 
as necessary over time at specific source locations to represent radionuclide migration from the 
UZ. The particle-tracking method assumes a Lagrangian point of view, in which these particles 
move with the prevailing flow velocity. Based on a velocity field derived from the flow model, 
the trajectories for each particle are computed one at a time. Through a series of time steps, the 
particles are moved according to these computed trajectories. 
The dispersive component of the transport is calculated using the random-walk method CRWMS 
M&O (2000j). This approach is based on the analogy between the mass transport equation and 
the Fokker-Plank equation of statistical physics. The dispersive displacement of each particle is 
computed using uniform random numbers, based on the dispersivity tensor and the porous flow 
velocity field at the particle location. In this model, the proper terms in the random-walk 
algorithm are derived from an anisotropic version of the dispersion coefficient tensor 
(Section 3.3.2.1). During each time step, the trajectory of each particle is computed using the 
advective component of transport that is modified through a series of displacements due to the 
dispersion calculated for each particle.

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The method requires the development of a flow velocity field. The velocity field is developed by 
computing the velocities at the finite volume cell faces surrounding each node using Darcys 
Law and the hydraulic heads computed in the flow solution at each node of the computational 
mesh. These velocities are then interpolated within the cell using the velocity interpolation in 
which a semianalytical solution to the particle tracks is obtained by interpolating the flow 
velocities linearly within each computational cell, permitting the flow lines to be computed in an 
efficient manner (CRWMS M&O 2000j). 
For this method to work properly, the time step must be selected such that, on average, a particle 
spends several time steps within each cell. In a system with large variations in pore-water 
velocity due to permeability and porosity differences from cell to cell, the appropriate time step 
can vary greatly throughout the domain. In FEHM, this factor is accounted for by dynamically 
determining the time step. In a given cell, the magnitude of the velocity in the cell is used to 
scale the time step. The time required to traverse the cell completely in each of the three 
coordinate directions is computed, and the minimum is determined. Then, a user-defined 
parameter is multiplied by this minimum time to obtain the time step for the particle within the 
cell. This approach ensures that several steps are taken by a particle within a cell but minimizes 
computational time by tailoring the time step to the characteristic velocity within each cell. 
Two options have been incorporated into FEHM to report the results of the particle tracking 
simulations. The model options can be used to predict the delivery time and concentrations of 
radionuclides at a particular boundary (e.g., a compliance boundary). This can be accomplished 
by defining a set of finite element grid points that corresponds to the desired boundary. The code 
determines the first arrival of each particle at any node along this boundary and subsequently 
reports the cumulative arrival time distribution for all particles. This arrival time distribution is 
then converted to the pumping well concentration, and the resulting curves can be used as input 
to the convolution portion of PA analysis (Section 3.6.3.3). Alternatively, the concentrations of 
particles at any cell in the finite element domain can be reported as a number of particles residing 
in the cell divided by the fluid mass in the cell. A detailed discussion of the particle tracking and 
random walk algorithms used to simulate advective and dispersive transport in the site-scale SZ 
flow and transport model is provided in CRWMS M&O (2000j, Section 6.1). 
3.3.4.2 Matrix Diffusion and Sorption 
As described by CRWMS M&O (2000j), to incorporate the influence of matrix diffusion and 
sorption, the residence time transfer function particle-tracking method has been adapted to the 
particle-tracking algorithm. In this method, adjustments to the travel time of a particle are made 
to account for the influence of physicochemical processes such as sorption and matrix diffusion. 
During its path along a streamline, the particle travel time is governed by a transfer function 
describing the probability of the particle spending a given length of time on that portion of its 
path. For a cumulative probability distribution function of particle residence times, the travel 
time of a particle along this portion of its path is computed by generating a random number 
between 0 and 1 and determining the corresponding residence time. On average, if a large 
number of particles travel through this portion of the model domain, the cumulative residence 
time distribution of particles will reproduce the shape of the transfer function.

TDR-NBS-HS-000001 REV 00 ICN 01 3-89 August 2000 
The form of the transfer function is derived from an analytical or numerical solution to capture 
the appropriate processes being considered. The analytical solution identified in Section 3.3.2.2, 
and the retardation coefficients developed in Section 3.3.2.3, are used by the model in 
developing the transfer function and determining the value of the delayed travel time along a 
pathline for each particle resulting from the effects of matrix diffusion and sorption. 
As described by CRWMS M&O (2000j), the final step of the model development is to integrate 
the matrix diffusion model with the random-walk transport model. Specifically, the time 
intervals over which the time delays are applied must be set in a manner that allows for obtaining 
computationally efficient and accurate solutions. In this model, the time delay is applied to a 
particle at the time at which it exits a cell, after having determined the cumulative time the 
particle spent in advective transport through the cell. Within a cell, the transport properties of 
diffusion and sorption are, by definition, uniform, so a unique set of transport dimensionless 
parameters can be defined. To apply the time delay, the particle is held at that location until the 
time of the simulation run catches up to the time of that particle, after which the particle is 
allowed to resume its transport. 
Finally, for sorption without matrix diffusion, the time delay is computed deterministically by 
computing a retardation factor based on the sorption coefficient; otherwise, the method is 
identical to the matrix-diffusion method. A detailed discussion of the methods (and alternative 
conceptual methods) used to incorporate the influence of matrix diffusion and sorption into the 
transport model for the site-scale SZ flow and transport model is provided by CRWMS M&O 
(2000j, Section 6.2). 
3.3.5 Flow Model Development 
As described by CRWMS M&O (2000n), development of the site-scale SZ flow and transport 
model requires the generation of a computational grid, the identification of the hydrogeologic 
unit at each node on the grid, the specification of boundary conditions, the specification of 
recharge values, and the assignment of nodal hydrogeologic properties. Each of these elements 
of model development is discussed in this section. 
3.3.5.1 Grid Generation 
As described by CRWMS M&O (2000n, Section 6.2), the computational grid developed for the 
site-scale SZ flow and transport model was formulated so that the horizontal grid is coincident 
with the grid cells in the regional-scale SZ flow model. The depth of the computational grid is 
approximately the same as depth of the regional-scale SZ flow model. The top of the 
computational grid begins at the water table surface and extends to a depth of 2,750 m (9,020 ft) 
below sea level. 
Previous models of SZ flow and transport at Yucca Mountain used unstructured meshes and 
structured grids. However, to use the streamline particle tracking capability of FEHM, an 
orthogonal grid was required. Consequently, a structured grid using orthogonal hexahedral 
elements was developed for the site-scale SZ flow and transport model. 
Although structured grids are not as flexible as unstructured meshes in fitting complex geometry, 
studies have shown that they provide accurate solutions as long as there is adequate resolution.

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The grid must contain sufficient resolution to represent adequately the geometry of the different 
materials in each hydrogeologic layer. Moreover, there must be adequate resolution to 
adequately account for any large gradients present in the flow or transport model. 
The accuracy of the flow solution and the transport solution was a principal concern during the 
process of formulating a grid for the site-scale SZ flow and transport model. A study was 
performed on ten grids to determine the appropriate resolution for representing flow and 
transport in the Yucca Mountain groundwater flow system (CRWMS M&O 2000n, Section 6). 
Although the study was based on an earlier HFM, the results show that a 500-m (1,640-ft) 
horizontal grid spacing is adequate for use in the site-scale SZ flow and transport model, and 
consequently, a 500-m (1,640-ft) horizontal grid spacing was adopted. The grid resolution in the 
vertical dimension also is important for adequately representing groundwater flow and transport 
in the SZ. Each layer in the model grid is horizontal, but the layering of the physical 
hydrogeologic units is subhorizontal. Therefore, a finer grid resolution was used in the vertical 
dimension than in the horizontal dimension, and this was sufficient to represent adequately the 
approximately 7 percent dip to the east of the hydrogeologic units. 
The vertical grid spacing was established to provide the resolution necessary for accurately 
representing flow and transport along critical flow and transport pathways in the SZ. A finer 
grid spacing was adopted for shallower portions of the model, while a progressively coarser grid 
was adopted for deeper portions of the aquifer. The vertical grid spacing ranged from 10 m 
(33 ft) near the water table to 550 m (1,805 ft) at the bottom of the model domain. The vertical 
dimension of the model domain was divided into 11 zones, and constant vertical grid spacing 
was adopted in each of these eleven zones. The structure of the vertical layering used in the sitescale 
SZ flow and transport model grid is summarized in Table 3-4. In total, 38 layers were 
included in the vertical dimension. 
Table 3-4. Vertical Grid Spacing Used in the Site-Scale Saturated Zone Flow and Transport Model 
Node Elevation Zone Boundaries (m) 
Upper Lower Grid Spacing (m) Zone Width (m) 
Grid Lines 
per Zone 
1200 1000 50 200 4 
1000 840 40 160 4 
840 760 20 80 4 
760 700 10 60 6 
700 640 20 60 3 
640 600 40 40 1 
600 300 50 300 6 
300 0 100 300 3 
0 -600 200 600 3 
-600 -2200 400 1600 4 
-2200 -2750 550 550 1 
Total: 39 
Source: CRWMS M&O (2000n, Table 4) 
NOTE: Of the 39 grid lines, one defined the lower boundary of the model, and thus was not considered in the 
model, therefore, there were only 38 grid lines in the model.

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A 3-D representation of the computational grid is provided in Figure 3-18. Not all model layers 
extend throughout the entire horizontal extent of the model domain. Because the model domain 
is truncated at the water table, and because the water table exhibits considerable variation in 
altitude over the model domain, those layers in the higher water table areas (i.e., to the north of 
the model domain) are truncated as the water table decreases in altitude toward the south. To 
maintain an approximately constant thickness of the model domain, several of the model layers 
at the bottom of the model were not extended throughout the model domain. 
Source: Adapted from CRWMS M&O (2000n, Figure 3) 
NOTE: This representation of the computation grid illustrates the complex 3-D spatial relation among units within 
the site-scale model area. Shading represents different hydrogeologic features included in the model. 
Figure 3-18. Three-Dimensional Representation of the Computation Grid 
3.3.5.2 Hydrogeologic Framework Model 
After establishing the grid, the physical hydrogeologic unit present at each node in the site-scale 
SZ flow and transport model grid was identified using the HFM (Section 3.2.1; USGS 2000a). 
Using the 3-D geometry of the hydrogeologic units represented in the HFM, the LaGriT code 
(Version 2.0) was used to assign a hydrogeologic unit designation to each node of the 
computation grid used. This resulted in assigning 13 to 27,097 (average of 7,518) nodes per 
hydrogeologic unit to the valley-fill confining unit and the lower carbonate aquifer, respectively 
(Table 3-5). The assignment of hydrogeologic units to grid cells is shown in the 3-D 
representation of the grid depicted in Figure 3-18.

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Table 3-5. Number of Nodes Assigned to Hydrogeologic Units in the Site-Scale Saturated-Zone Flow 
and Transport Model 
Geologic Units Number of Nodes 
Alluvium (Valley-Fill Aquifer) 6,188 
Valley-Fill Confining Unit 13 
Limestones 227 
Lava Flows 891 
Upper Volcanic Aquifer 13,831 
Upper Volcanic Confining Unit 7,845 
Crater Flat - Prow Pass 5,666 
Crater Flat - Bullfrog 6,472 
Crater Flat - Tram 11,676 
Lower Volcanic Confining Unit 9,142 
Older Volcanic Aquifer 210 
Older Volcanic Confining Unit 11,012 
Undifferentiated Valley Fill 21,578 
Upper Carbonate Aquifer 23 
Lower Carbonate Aquifer Thrust 1,192 
Upper Clastic Confining Unit 5,923 
Lower Carbonate Aquifer 27,097 
Lower Clastic Confining Unit 13,259 
Granites 608 
Base 0 
Total Number of Nodes 142,853 
Source: CRWMS M&O (2000n, Table 5) 
3.3.5.3 Boundary Conditions 
As described by CRWMS M&O (2000n, Section 6.1.2), data from the potentiometric map 
(Figure 3-5) were used to set boundary conditions for head values around the periphery of the 
computational grid. A uniform, constant head was applied through each layer of the model that 
was based on the water level at the top of the model at that location. While this boundary 
condition may not correspond with actual conditions and tends to limit vertical flow in the 
exterior portions of the model, sufficient data are not available to establish vertical gradients for 
boundary conditions along the boundaries of the computational grid. However, vertical gradients 
still are simulated internally in the model domain in response to geohydrologic conditions, and 
the calibrated model is capable of representing the upward vertical gradients observed between 
the carbonate aquifer and overlying volcanic aquifers (Section 3.4.3). 
Historically, groundwater has been extracted from wells in the Amargosa Valley south of the 
site-scale model domain. Draindown from the wells is represented in the potentiometric surface 
map that was used to establish boundary head conditions. Consequently, the affect of pumping 
on flow within the model domain is accounted for by the head values specified along the 
southern boundary. A small amount of pumping also has occurred from the southern portion of 
the site-scale model. This pumping was included in the regional-scale model, but not the sitescale 
model. Ignoring this pumping is assumed to have very little effect on the calculated flow 
paths and flow times to compliance boundaries.

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A no-flow boundary was established for each node located along the bottom of the 
computational grid. While flow conditions in the deeper portions of the model domain are not 
well established, the depth of the bottom boundary is such that it is not likely to exert an 
important influence on flow in the more shallow areas where groundwater flow and transport is 
of greater interest to PA. 
The top surface of the computational grid also is represented by no-flow boundary conditions. 
A no-flow boundary at the top of the model was assumed to facilitate the adoption of a confinedaquifer 
solution approach for the site-scale SZ flow and transport model. This approach assumes 
no UZ and, therefore, solves a simplified and computationally more efficient numerical model. 
The assumption of no-flow conditions at the top of the model does not preclude the addition of 
spatially varying source terms to model recharge. 
3.3.5.4 Recharge 
Recharge is applied to the top surface of the computational grid as a flux boundary condition. 
Spatial distribution of recharge developed for application to the site-scale SZ flow and transport 
model is discussed in Section 3.2.3.2 and is described in detail in CRWMS M&O (1999a). 
Using the recharge map developed in CRWMS M&O (1999a), recharge amounts were 
interpolated onto the computational grid for the site-scale SZ flow and transport model. Based 
on this interpolation, a value for mass flux of recharge is assigned to each surface node as a 
boundary condition. However, with the exception of the zone directly beneath the UZ model, the 
recharge map was developed for recharge directly to land surface. As a result, there are nodes at 
the top of the model (i.e., at the water table surface) where the permeability is too small to accept 
the recharge developed for the land surface at that location. To rectify this problem, the 
permeability of the top nodes at these locations was increased so that the recharge could be more 
easily redistributed to neighboring areas of higher permeability. 
3.3.5.5 Assignment of Nodal Hydrogeologic Properties 
As described by CRWMS M&O (2000n), hydrogeologic properties are specified for each node 
in the computational grid. For flow modeling, the hydrologic properties include permeability, 
porosity, and viscosity. Permeability is used as a calibration parameter, and the assignment of 
this value to each node is discussed in Section 3.3.6.3. Because steady-state flow is simulated in 
the site-scale SZ flow and transport model, the value assigned to specific storage at each node 
does not influence the water levels predicted by the model. 
The parameter values for viscosity depend on the temperature at each node, and a uniform 
temperature gradient is assumed. Borehole temperature data (Sass et al. 1988) indicate that there 
is variability in the temperature gradient at different locations and within individual wells, 
presumably due to advective redistribution of heat from infiltration and vertical groundwater 
flow. However, these data also indicate that temperature gradients generally become more linear 
with increasing depth below the water table. It is important to note that the viscosity of water 
only changes by a factor of about 3.5 over the temperature range of 20C to 100C ([68F to 
212F] Streeter and Wylie 1979) expected within the range of depths in the site-scale SZ flow 
and transport model domain. Thus, assuming a constant temperature gradient when calculating

TDR-NBS-HS-000001 REV 00 ICN 01 3-94 August 2000 
nodal viscosity values should not introduce significant error in the site-scale SZ flow and 
transport model. 
The approach taken to incorporating groundwater temperature in the site-scale SZ flow and 
transport model is to evaluate the average temperature gradient (using temperature measurements 
in boreholes) and to use that temperature gradient to specify temperatures at grid nodes in the 
model. As implemented, temperatures remain fixed at the specified value, and heat-transport 
equations are not solved in the simulation. Thus, in the model, the specified values of 
temperatures are used to calculate the local groundwater viscosity, but temperature variations do 
not result in any variable-density flow processes because at the temperatures involved, the 
density of water changes by less than 1 percent. 
Temperatures presented by Sass et al. (1988) were used to estimate an approximate average 
temperature gradient and a representative surface temperature for the site. There is considerable 
variability, about 15C/km to 60C/km (51F/mi to 205F/mi), in the temperature gradients 
observed in the wells. However, among wells, the average value of the temperature gradient is 
approximately 25C/km (85F/mi), and the average surface temperature is about 19C (66F). 
By using these values for the average temperature gradient and surface temperature, along with 
the water table and topographic surface evaluations, estimated temperature at the water table is 
calculated (Figure 3-19). Lower temperatures correspond to areas of relatively thin unsaturated 
thickness, and the higher temperatures correspond to a thick UZ (Figure 3-19). CRWMS M&O 
(2000n, Section 6.6) provide further details of the development and application of temperature 
profiles for establishing nodal values of viscosity. 
3.3.6 Model Calibration 
As described by CRWMS M&O (2000n, Section 6.4), calibration is the process by which values 
of important model parameters are estimated and optimized to produce the best fit between the 
model output and the observed data. Calibration generally is accomplished by adjusting model 
input parameters (e.g., permeability) to minimize the difference between observed and simulated 
conditions (in this case, comparing predicted and observed head values and lateral boundary 
fluxes). The process of selecting an optimal set of parameters (based on, for example, 
minimizing the difference between observed and simulated conditions) frequently is referred to 
as inverse modeling or model inversion. Model calibration may be performed through manual 
methods or through automated optimization procedures. Automated optimization procedures 
generally employ a carefully prescribed mathematical process that selects the optimal set of 
parameters based on minimizing an objective function describing the difference between 
observed and simulated conditions. These procedures generally provide the most structured and 
thorough means of calibrating a model, and frequently they provide useful additional information 
regarding model sensitivity to parameters and other useful statistical measures. Consequently, an 
automated optimization procedure has been used to calibrate the site-scale SZ flow and transport 
model. However, manual adjustments to the calibration also were performed to ensure an 
accurate model.

TDR-NBS-HS-000001 REV 00 ICN 01 3-95 August 2000 
535000 540000 545000 550000 555000 560000 
UTM Easting (m) 
4050000 
4055000 
4060000 
4065000 
4070000 
4075000 
4080000 
4085000 
4090000 
UTM Northing (m) 
15 
20 
25 
30 
35 
40 
Temperature 
( C ) 
Source: CRWMS M&O (2000n, Figure 5) 
NOTE: Data were calculated assuming a temperature gradient of 25C/km (85F/mi) and a surface temperature of 
19C (66F). 
Figure 3-19. Modeled Temperature at the Water Table for the Site-Scale Model Domain 
The calibration process (including the parameter estimation software, the formulation of the 
objective function used to optimize parameters, the parameters that were optimized during model 
calibration, and the manual adjustments to calibration) is discussed below. 
3.3.6.1 Parameter Estimation Software 
Parameter estimation was achieved through the use of the model independent parameter 
estimation software, PEST, from Watermark Computing. PEST was selected because of the 
ability to couple it with FEHM without changing the FEHM code. PEST is designed to be used 
with virtually any model, and it previously was coupled with FEHM by Czarnecki et al. (1997) 
to calibrate a preliminary SZ flow model. 
PEST uses nonlinear least squares regression to estimate parameters. The benefits of using 
nonlinear regression include an expedited determination of best-fit parameter values,

TDR-NBS-HS-000001 REV 00 ICN 01 3-96 August 2000 
quantification of the quality of the calibration estimates, estimates of the confidence limits on 
parameter estimates, and identification of correlation among parameters. PEST accomplishes 
parameter optimization using a LevenbergMarquardt-based algorithm, an algorithm that is well 
established, robust, and widely applicable. 
The parameter optimization process using the coupled FEHM-PEST code is begun by specifying 
an initial estimate for each unknown parameter. FEHM then computes head values using the 
initial parameter estimates and passes the computed head values to PEST. Through a series of 
PEST-directed FEHM simulations with perturbations in the parameters, PEST subsequently 
computes the derivative of the objective function with respect to each of the parameters. Based 
on information derived from these derivatives, PEST determines the amount of change in the 
current value of parameter and uses this information to improve the fit to the data during the next 
iteration to further minimize the objective function. This process is repeated until the fit is 
within a prescribed tolerance or until no further improvement is possible. 
To enable the PEST-FEHM code to search for the global minimum of the objective function, a 
procedure is attached to the code that carries out a simulated annealing process. This process 
allows the PEST-FEHM code to move from one local minimum to another, better, local 
minimum. This process is repeated until no further improvement occurs and it is assumed that 
the global minimum has been found. Thus, the PEST-FEHM code is capable of searching for the 
minima of a multidimensional objective function. Further details regarding the parameter 
estimation code and algorithm are available in CRWMS M&O (2000n, Section 6.4) 
3.3.6.2 Objective Function 
The objective function used during the parameter optimization was the sum of the squared 
differences between observed hydraulic conditions and those simulated by the site-scale SZ flow 
and transport model. Hydraulic conditions included water levels (hydraulic heads) at selected 
locations and lateral fluxes at selected model boundaries. In the calibration process, the specific 
water levels and boundary fluxes are referred to as calibration targets. 
3.3.6.2.1 Water Levels 
For calibration targets, 115 water level and head measurements were used (CRWMS M&O 
2000n, Section 6.7). To correspond with hydraulic conditions simulated in the regional-scale 
flow model, target water level data were selected to represent hydraulic conditions in the 
early 1990s. 
Most of the water levels are composite levels from one or more water-producing zones. For 
modeling purposes, it is assumed that the midpoint of the open interval, or applicable packed-off 
interval, is representative of the measurement location. In open holes, it is assumed that the 
midpoint can be calculated from the depth of the hole and the water-level altitude. When 
comparing simulated water levels to target water levels, the model represents water levels at the 
target locations by linearly interpolating the head from the eight nodes surrounding the target 
location. 
During the calibration process, emphasis is given to minimizing the difference between observed 
and simulated water levels for selected calibration targets (i.e., at selected target locations). This

TDR-NBS-HS-000001 REV 00 ICN 01 3-97 August 2000 
is accomplished by multiplying the squared differences at that location by a weighting factor. 
A weighting factor of 1.0 (i.e., no particular importance) normally is applied to calibration 
targets. However, a preferential weighting factor (20) is applied to approximately 30 calibration 
targets in the low-gradient region to the south and east of Yucca Mountain. These calibration 
targets are given high weighting because they are in the likely pathway of fluid leaving the 
potential repository site and because small changes in head in this area could produce a large 
effect on the flow direction. Calibration targets north of Yucca Mountain are given a low 
weighting (0.05; i.e., little importance). The five wells in this category are given low weights 
primarily because of the possibility of perching and the attendant uncertainty in water-level 
measurements in this region. The one head measurement in the carbonate aquifer is given a 
preferential weighting factor (20) because of the importance of this calibration target for 
reproducing an upward gradient in the calibrated model. The inclusion of an upward gradient 
within the calibrated site-scale SZ flow and transport model is considered important for 
generating a realistic model because an upward gradient tends to force flow along shallower 
pathlines as indicated by geochemical data. A complete listing of all target water level values, 
target locations, and the weighting applied to each target is provided by CRWMS M&O 
(2000n, Table 7). 
3.3.6.2.2 Boundary Fluxes 
The fluxes in and out of the site-scale model domain were estimated using the regional-scale and 
site-scale models. The differences between the two estimates were used in the objective function 
during parameter optimization. The computation of these fluxes is discussed in Section 3.2.3.1 
and is described in detail in CRWMS M&O (1999a). 
Fluxes from all of the boundary segments on the eastern and northern boundaries of the site-scale 
SZ flow and transport model domain were included in the objective function during parameter 
optimization. Fluxes from the five western boundary segments were not included in the 
objective function. Preliminary calibration runs indicated that it was difficult to match the fluxes 
along these segments predicted by the site-scale model with those predicted by the regional-scale 
model. This difficulty largely was a result of the different HFMs used in the site-scale and 
regional-scale models. It was decided that the goal of ensuring that the total flux through the 
site-scale model domain is similar to that predicted by the regional-scale model was best 
achieved by not forcing a close match along those boundary segments for which the rock types 
were different in the two models. 
3.3.6.3 Calibration Parameters 
As described by CRWMS M&O (2000n), permeability was optimized during calibration of the 
site-scale SZ flow and transport model. The model formulation and FEHM code allows for the 
specification of a permeability value at each node. However, there is not sufficient water level 
and permeability data to warrant identifying a specific value of permeability for each individual 
node during calibration. Consequently, sets of nodes were grouped into specific permeability 
zones based on similar permeability characteristics. A single permeability value was assigned to 
each zone. These zonal values of permeability served as the parameters that were optimized 
during model calibration.

TDR-NBS-HS-000001 REV 00 ICN 01 3-98 August 2000 
There is a large uncertainty in recharge. Consequently, it is a candidate for use as a calibration 
parameter. However, the sensitivity of the calibration to recharge values is decreased by the fact 
that recharge applied on the upper boundary of the site-scale flow model accounts for only a 
small portion of the total groundwater flow through the model domain. 
Permeability zones were created for hydrogeologic units identified in the HFM and for specific 
hydrogeologic features. With the exception of the basal unit that served as a lower boundary for 
the model, a permeability zone was established for each hydrogeologic unit. All of the nodes 
within a specific hydrogeologic unit were assigned to that permeability zone unless they were 
included in one of permeability zones established for specific hydrogeologic features. 
For permeability, vertical anisotropy was assigned a value of 10:1 (horizontal to vertical) in the 
volcanic and valley-fill units in the site-scale SZ flow and transport model. Relatively lower 
permeability in the vertical direction may occur in stratified media, and the ratio of 10:1 is in the 
generally accepted range (CRWMS M&O 1998b, Table 3-2). Furthermore, the relatively high 
vertical gradient observed in well UE-25p#1 suggests that vertical permeability is lower than 
horizontal permeability. 
Specific hydrogeologic features that were thought to potentially impact groundwater flow were 
classified as permeability zones. The permeability variable used for a specific feature was 
assigned to all of the nodes within that feature. The hydrogeologic features for which special 
permeability zones were established were primarily faults, fault zones, and areas of chemical 
alteration (Section 3.2.2.5). These features are distinct from the subhorizontal hydrogeologic 
units identified in the HFM. Each of the identified hydrogeologic features includes multiple 
geologic formations and represents zones of altered permeability within the individual 
formations. One permeability zone, the east-west barrier, is noteworthy in that it does not 
represent a feature of the HFM. Instead, it was added to the model specifically to reproduce the 
combination of the steep hydraulic gradient and the relatively flat gradient located north of the 
steep gradient. The necessity of using this model approach to match head observations reflects 
uncertainty in the geology and hydrology of this region of the model domain. These features are 
discussed in CRWMS M&O (2000n, Section 6.3). 
As described by CRWMS M&O (2000n), 27 permeability zones were established for model 
calibration. In addition, permeability multipliers were assigned to four zones that contained 
geologic features that penetrated a number of hydrogeologic units. The permeability multipliers 
were used to modify the permeability values assigned to the hydrogeologic units in the area of 
the geologic features. While the permeability parameter or multiplier values for most zones were 
optimized during calibration, permeability for the upper carbonate aquifer was assigned a 
constant value because sensitivity analyses indicated that the model was not sensitive to this 
parameter value. 
The parameters used in the calibration of the SZ flow and transport model were a combination of 
permeabilities of hydrogeologic units, permeabilities of faults and other features, and 
permeability multipliers of faults and features. Permeabilities of the 18 hydrogeologic units were 
chosen as calibration parameters because of the importance of the parameter in the flow system 
and the fact that each of the units was identified in the HFM. The parameters that represent these 
features were added because they were identified as important structural features (e.g., the

TDR-NBS-HS-000001 REV 00 ICN 01 3-99 August 2000 
Solitario Canyon fault), they were in the regional-scale model (e.g., the Spotted Range-Mine 
Mountain zone), or they were necessary for some conceptual feature such as the high head 
gradient north of Yucca Mountain (east-west barrier). The number of parameters represent a 
computationally tractable set. 
Upper and lower bounds were placed on each permeability variable during parameter 
optimization. The upper and lower bounds for the permeabilities and permeability multipliers 
were chosen to reflect maximum and minimum field values (permeability) or a reasonably 
realistic range of values (permeability multipliers). For example, when the multiplier 
represented flow in the plane of a fault, the multiplier was allowed to take on values between 
1 and 100; when the multiplier represented geochemical alteration, the multiplier was allowed to 
take values between 0.00001 and 0.50000. The final calibrated values of the parameters were 
not sensitive to initial parameter values within the range specified. 
A list of permeability zones, including the parameter type assigned to each zone, the upper and 
low bounds specified for the parameter, and an identification of the parameters optimized during 
calibration, are provided in Table 3-6 (CRWMS M&O 2000n, Table 8). 
3.3.6.4 Manual Adjustments to Calibration 
Proper calibration of the site-scale SZ flow and transport model requires consideration of the full 
range of available data. The available data include field data for water levels and hydraulic 
heads, permeability data from field and laboratory tests, locations of known faults and other 
geologic data, and hydrochemical data. Opinions expressed during the expert elicitation process 
(CRWMS M&O 1998b) also must be considered. The goal during development of site-scale SZ 
flow and transport model was to deliver to PA a model that is realistic where data exists and is 
conservative where data is lacking. Thus, when field data and interpretations produce conflicting 
trends in calibration, the data that produced a more conservative model are used. 
A number of techniques were employed during parameter optimization using PEST to ensure a 
representative but conservative model. As previously discussed, these include the incorporation 
of important hydrogeologic features into the model and the placement of upper and lower bounds 
on the allowable permeability values. However, it was necessary to make several adjustments to 
the model in addition to the PEST parameter optimization. These adjustments were made to 
improve the model in ways that were not possible during the PEST optimization. The most 
important of these adjustments were made to insure that the specific discharge within 5 km 
(3 mi.) of the potential repository was approximately equal to the median estimate given by the 
SZ expert elicitation (CRWMS M&O 1998b). Because the specific discharge was calculated 
with the particle-tracking feature of FEHM after the flow calculations were performed, this 
adjustment could not easily be incorporated in the PEST optimization. The specific discharge 
was adjusted by changing the permeability of the Bullfrog unit. Because the Bullfrog unit is 
highly permeable, specific discharge could be manipulated by changing the Bullfrog unit 
permeability value without adversely affecting the heads in the low gradient area near Yucca 
Mountain. Adjustments also were made to the permeability in the lower Fortymile Wash area so 
that water levels in the 2-D and Washburn wells would be more consistent with those in the 
upper Fortymile Wash area, thus preserving the observed head gradient. Adjustments to the 
permeability of the alluvial uncertainty zone and the valley fill aquifer also were made to better 
match the fluxes estimated from the regional-scale flow model for the eastern boundary of the 
site scale model.

TDR-NBS-HS-000001 REV 00 ICN 01 3-100 August 2000 
Table 3-6. Permeability Zones Established in Site-Scale Saturated Zone Flow and Transport Model with 
Upper and Lower Bounds Applied During Calibration 
Geologic Unit 
Calibrated 
Valuea 
Parameter 
Typeb 
Minimum 
Valuea 
Maximum 
Valuea 
Granites 1.96x10-16 P 1.00x10-17 1.00x10-14 
Lower Clastic Confining Unit 1.00x10-16 P 1.00x10-16 1.00x10-14 
Lower Carbonate Aquifer 5.00x10-14 P 5.00x10-14 1.00x10-12 
Upper Clastic Confining Unit 1.00x10-16 P 1.00x10-16 1.00x10-14 
Lower carbonate Aquifer Thrust 1.00x10-14 P 1.00x10-14 1.00x10-12 
Upper carbonate Aquifer 4.08x10-14 P (fixed) 4.08x10-14 4.08x10-14 
Undifferentiated Valley Fill 5.00x10-15 P 5.00x10-15 1.00x10-12 
Older Volcanic Confining Unit 2.00x10-16 P 2.00x10-16 1.00x10-11 
Older Volcanic Aquifer 5.00x10-16 P 3.00x10-16 1.00x10-12 
Lower Volcanic Confining Unit 2.00x10-15 P 1.00x10-15 1.00x10-11 
Crater Flat-Tram 2.36x10-13 P 1.00x10-13 1.00x10-11 
Crater Flat-Bullfrog 1.54x10-11 P 1.00x10-13 8.00x10-11 
Crater Flat-Prow Pass 8.00x10-12 P 1.00x10-13 5.00x10-11 
Upper Volcanic Confining Unit 5.00x10-14 P 4.00x10-14 1.00x10-12 
Upper Volcanic Aquifer 8.00x10-14 P 8.00x10-14 1.00x10-11 
Lava Flow Aquifer 1.00x10-12 P 1.00x10-16 2.00x10-12 
Limestone Aquifer 1.00x10-12 P 1.00x10-15 1.00x10-11 
Valley Fill Aquifer 5.00x10-12 P 1.00x10-13 8.00x10-12 
East-West Barrier 1.05x10-18 P 1.00x10-18 1.00x10-15 
Solitario Canyon Fault 1.00x10-18 P 1.00x10-18 1.00x10-15 
Fortymile Wash Fault 10 M 2 100 
Spotted Range Thrust 11.7789 M 1 70 
Northern Low Perm Zone 7.11x10-02 M 1.00x10-05 0.5 
Imbricate Fault Zone 1 M 1 100 
Crater Flat Fault 5.00x10-14 P 1.00x10-15 5.00x10-13 
Alluvial Uncertainty Zone 3.20x10-12 P 1.00x10-13 1.00x10-11 
Lower Fortymile Wash Zone 5.00x10-12 P 1.00x10-14 8.00x10-12 
Source: CRWMS M&O (2000n, Table 8) 
NOTES: aMeasurement units for permeabilities are m2; multipliers are dimensionless. 
bP=Permeability; M=Multiplier 
Values estimated for recharge and inflow to the SZ are not independent of permeability. This is 
because an increase in the recharge and inflow estimate causes a corresponding increase in the 
permeability estimate to produce the same hydraulic head field. Inflow into the site-scale model 
across lateral boundaries is estimated from regional-scale models (DAgnese et al. 1997, 1999). 
Estimates of recharge are made by modeling infiltration through the UZ, taking into account past 
and future climates (USGS 2000c). Similarly, estimates from pumping tests provide a range of 
hydraulic conductivity for each hydrologic unit, some of which are fairly restrictive. These 
estimates serve to restrict the domain of possible recharge, inflow, and permeability model 
parameters. Uncertainty exists in these parameter estimates, and this uncertainty is addressed in 
the TSPA-SR.

TDR-NBS-HS-000001 REV 00 ICN 01 3-101 August 2000 
3.3.7 Calibration Results 
In this section, results of the model calibration with respect to water levels, predicted flow paths, 
and specific discharge at selected distances from the potential repository area are discussed. 
Details are presented by CRWMS M&O (2000n). 
3.3.7.1 Water Levels 
Model calibration resulted in a weighted residual sum of squares of about 27,600 m2, which is 
equivalent to an average weighted residual of 16 m (52 ft) at each target measurement. Without 
weighting, the sum-squared residual was about 90,000 m2, which corresponds to an 
approximately 30-m (98-ft) average residual for each observation. The potentiometric surface 
predicted by the calibrated site-scale SZ flow and transport model (Figure 3-20) is shown with 
residual heads at the location of each target observation. The largest head residuals (about 
100-m [330-ft]) are in the northern part of the model in the high head gradient area near the eastwest 
barrier. These head residuals are largely the result of the low weighting (0.05) assigned to 
these calibration targets and of the uncertainty in these measurements due to the perched 
conditions that may exist in this area. The next highest group of head residuals borders the eastwest 
barrier and Solitario Canyon fault. These residuals (about 50) most likely result from a grid 
resolution insufficient to resolve the 780-m to 730-m (2,560-ft to 2,395-ft) drop in head that 
occurs over a short distance in this area. 
3.3.7.2 Predicted Flow Paths 
The particle tracking capability of FEHM was utilized to demonstrate flow paths predicted by the 
calibrated site-scale SZ flow and transport model. One hundred particles were distributed 
uniformly over the area of the potential repository and allowed to migrate until they reached the 
model boundary (Figure 3-21). The pathways generally leave the potential repository and travel 
in a south-southeasterly direction to the potential 20-km (12.5-mi) compliance boundary 
(NRC 1998). From the 20-km (12.5-mi) boundary to the end of the model, the flow paths trend 
to the south-southwest and generally follow Fortymile Wash. Most of the pathways pass through 
the designated Imbricate Zone (Zone 91 of Figure 3-14). Some of the pathways follow fault 
zones along Fortymile Wash (Zones 57 and 58 of Figure 3-14). 
3.3.7.3 Specific Discharge 
Using the calibrated flow model, specific discharge was estimated for a nominal fluid path 
leaving the potential repository area and traveling 0 to 5-, 5 to 20-, and 20 to 30-km (0, 3, 12.5, 
and 18.6 mi.). The specific discharge simulated by the flow model for each segment of the 
flowpath from the repository was determined using the median travel time for a group of 
particles released beneath the repository. Values for specific discharge of 0.67 m/yr., 2.3 m/yr., 
and 2.5 m/yr. (2.2, 7.5, and 8.2 ft/yr.) were obtained, respectively, for the three segments of the 
flowpath. The expert elicitation panel (CRWMS M&O 1998b, Figure 3-2e) estimated a specific 
discharge of 0.71 m/yr. (2.3 ft/yr.) for the 5-km (3-mi) distance. Thus, good agreement is found 
between the specific discharge predicted by the calibrated model and that estimated by the expert 
elicitation panel for the 5-km (3-mi) distance. The expert elicitation committee did not consider 
other travel distances.

TDR-NBS-HS-000001 REV 00 ICN 01 3-102 August 2000 
Source: Adapted from CRWMS M&O (2000n, Figure 7) 
Figure 3-20. Simulated Potentiometric Surface and Calibration Residuals 
-89.26 to -50.00 
-50.00 to -30.00 
-30.00 to -20.00 
-20.00 to -10.00 
-10.00 to -5.00 
-5.00 to -1.00 
-1.00 to 1.00 
1.00 to 5.00 
5.00 to 10.00 
10.00 to 20.00 
20.00 to 30.00 
30.00 to 40.00 
40.00 to 50.70 
535000 540000 545000 550000 555000 560000 
UTM-X (meters) 
Residual Head 
(m)

TDR-NBS-HS-000001 REV 00 ICN 01 3-103 August 2000 
535000.00 545000.00 555000.00 
4050000.00 
4055000.00 
4060000.00 
4065000.00 
4070000.00 
4075000.00 
4080000.00 
4085000.00 
4090000.00 
UTM-Y (meters) 
UTM-X (meters) 
Source: Adapted from CRWMS M&O (2000n, Figure 8) 
Figure 3-21. Flow Paths Predicted by Site-Scale Saturated Zone Flow and Transport Model

TDR-NBS-HS-000001 REV 00 ICN 01 3-104 August 2000 
3.3.7.4 Summary of Calibration Results 
The calibrated site-scale SZ flow and transport model provides a reasonable representation of the 
SZ groundwater flow system that matches key data from the Yucca Mountain site. The model 
reasonably simulates the observed water levels and hydraulic gradients, particularly in the area 
along the flowpath from beneath the potential repository. The flowpaths simulated by the 
site-scale SZ flow model generally agree with interpretations from the hydrochemical data. 
There is good agreement between the calibrated value of specific discharge and the value 
estimated by an expert panel. However, there is uncertainty in the groundwater fluxes simulated 
by the regional-scale SZ flow model. There is an important relationship between recharge and 
rock permeability in groundwater basins in which flow is at steady state. This is because the rate 
of groundwater flow must equal recharge at the basin scale. One implication of this relationship 
for flow modeling is that different combinations of permeability and recharge result in the same 
calculated head distribution. The domain of the site scale model, however, is only a portion of a 
groundwater basin. Therefore, recharge, permeability, and groundwater flow across lateral 
boundaries are related. Different combinations of values for these parameters result in the same 
calculated head distribution. The uncertainty introduced by this non-uniqueness is addressed 
directly in TSPA-SR calculations in that multiple flow fields are calculated by multiplying 
values of recharge, permeability, and boundary flux by the same factor. It is noted that recharge 
applied on the upper boundary of the site-scale flow model accounts for only a small portion 
(perhaps 5 percent) of the total groundwater flow through the model domain. 
3.3.8 Sensitivity Analysis 
The sensitivity of the estimated parameter values and the distribution of weighted residuals were 
evaluated using a sensitivity analysis (CRWMS M&O 2000n, Section 6.9). Results indicate that 
there is a wide range in composite scaled sensitivities, and it appears that the model is most 
sensitive to observations located close to Yucca Mountain. The model is most sensitive to the 
permeability of the Claim Canyon, Calico Hills, and Shoshone Mountain fault zones, and 
decreasingly sensitive to the lower-carbonate aquifer, Bullfrog unit, lower Fortymile Wash 
channel, and Tram unit permeabilities. The model is relatively insensitive to the remaining 
parameters, as reflected in their wide confidence intervals (CRWMS M&O 2000n, Table 16). 
The large range in parameter sensitivities indicates that the most sensitive parameters can be 
divided into multiple parameter zones and that the least sensitive parameters should be grouped 
into fewer parameters. The correlation between the permeability of the lower-carbonate aquifer 
and the permeability of the Spotted Range-Mine Mountain fault zone has a value of 1.0, 
indicating that the two parameters cannot be estimated uniquely and that one should be set at a 
fixed value. 
The sensitivity of recharge and boundary conditions were not considered in the analysis. 
However, uncertainty in these parameters is considered in the TSPA-SR. These parameters are 
varied over a realistic range in the TSPA. 
Analysis of the distribution of weighted residuals (CRWMS M&O 2000n, Section 6.9.2) in the 
low hydraulic gradient region between Yucca Mountain and Fortymile Wash (Figure 3-20) 
reveals that most of these residuals are small negative values, indicating that the model predicts 
slightly more water in this area than actually is present. Because most of the residuals are

TDR-NBS-HS-000001 REV 00 ICN 01 3-105 August 2000 
negative (rather than a sampling of positive and negative values), some aspect of the real system 
apparently has not been captured in the site-scale SZ flow and transport model. While predicted 
heads along flow paths from the potential repository area are too high (by less than 1 m [3.3 ft]), 
the observed gradients of head along these paths are well represented by the model. 
3.4 MODEL VALIDATION 
Model validation is the process of testing the validity of the conceptual, mathematical, and 
numeric representation of the system being modeled. For this model, validation consists of a set 
of confidence-building exercises. There are three components of the site-scale SZ flow and 
transport model: the HFM, the transport methodology, and the calibrated flow model. 
Validation issues concerning the three components are described in detail in three analysis model 
reports (AMRs) (USGS 2000a, CRWMS M&O 2000j, 2000n; respectively). The HFM is 
empirical, and consequently, is not amenable for validation by comparison to independent data. 
It was validated instead by checking to assure that input data are consistent with a model grid 
representing the top of a hydrogeologic unit. Because the calibrated flow model incorporates the 
HFM, additional validation of the HFM was achieved as part of the validation of calibrated flow 
model as discussed below. The transport methodology was validated by comparing calculation 
results to analytical solutions to various hypothetical transport problems that include the 
processes of dispersion, sorption, and diffusion. The conceptualization of the transport processes 
also was validated through field and laboratory testing. This aspect of model validation has 
previously been discussed in Sections 3.1 and 3.2. The validation exercises provide sufficient 
confidence that the HFM and the transport methodology are adequate for use as components of 
the site-scale flow and transport model. 
For two reasons, this section focuses mainly on validation of the calibrated flow model. First, 
the calibrated flow model incorporates the HFM, and therefore, validation of the flow model also 
adds confidence in the HFM. Second, the calibrated flow model was validated in the exact 
configuration that is used for TSPA-SR calculations. The transport methodology, in contrast, 
was validated for hypothetical problems. Validation of the transport model by comparison to 
field observations is not practical because such a calibration would require field tests of 
extremely long distance and time scales. 
The ability of the calibrated site-scale SZ flow model to reproduce the potentiometric surface at 
Yucca Mountain is an initial indication of the validity of the flow model. The validity of the 
calibrated site-scale SZ flow and transport model has been further evaluated by comparing the 
results of the calibrated flow model to various elements of the ground-water flow system at 
Yucca Mountain. This further evaluation of the validity of the calibrated site-scale SZ flow 
model includes a comparison of the calibrated permeability values with observed permeability 
data (Section 3.4.1), a comparison between boundary fluxes predicted by the regional-scale flow 
model and the calibrated site-scale SZ flow and transport model (Section 3.4.2), a comparison 
between observed and predicted gradients between the carbonate aquifer and overlying volcanic 
aquifers (Section 3.4.3), and a comparison between hydrochemical data trends and particle 
pathways predicted by the model (Section 3.4.4).

TDR-NBS-HS-000001 REV 00 ICN 01 3-106 August 2000 
Comparisons performed for model validation indicate that flowpaths predicted by the model 
generally agree with those interpreted from hydrochemical data. The boundary conditions 
calculated by the site-scale model are close to those calculated by the regional-scale model. It is 
noted, however, that some of the boundary fluxes were also used as part of the model calibration 
target. The calculated vertical direction of flow (upward) matches the direction indicated by 
head measurements in the single well (UE-25p#1) that penetrates the carbonate aquifer. 
However, the magnitude of the calculated gradient is about half of the observed gradient. The 
combined results of the validation comparisons provide sufficient confidence that the calibrated 
site-scale flow model is adequate for use in the TSPA calculations. 
3.4.1 Comparison of Permeability Data to Calibrated Permeability Values 
As described by CRWMS M&O (2000n, Sections 6.7.7 and 6.7.8), permeabilities estimated 
during calibration of the site-scale SZ flow and transport model were compared to permeabilities 
determined from pump-test data from the Yucca Mountain area (Figure 3-22) and elsewhere at 
the NTS (Figure 3-23). Data from reports pertaining to the NTS were included in the 
comparison to help constrain permeability estimates for hydrogeologic units that were not tested 
or that underwent minimal testing at Yucca Mountain. For most of the geologic units, the 
calibrated permeabilities are within the 95 percent confidence limits of the mean permeabilities 
estimated from the data (Figures 3-22 and 3-23). 
The mean-measured permeability of the carbonate aquifer is higher elsewhere at the NTS than 
either the mean-measured permeability at Yucca Mountain or the calibrated permeability for the 
carbonate aquifer (Figures 3-22 and 3-23). The calibrated permeability for the Upper Volcanic 
Aquifer is about two orders of magnitude less than the mean-measured permeability of this unit. 
With the exception of the calibrated values for the upper volcanic aquifer, the calibrated 
permeabilities generally are consistent with most of the permeability data from Yucca Mountain 
and elsewhere at the NTS. Of particular importance are the permeabilities of the Bullfrog and 
Prow Pass units because they carry most of the flow in the region 5 km (3 mi.) down-gradient 
from the potential repository. Data from the cross-hole tests at the C-wells Complex is of high 
quality and has a small range (less than one order of magnitude). A good match was achieved 
for these units, which are important to TSPA calculations. A discrepancy exists between the 
calibrated permeability for the Tram Tuff and the mean permeability derived from the cross-hole 
tests; however, these permeabilities may have been enhanced by a breccia zone in boreholes 
UE-25c#2 and UE-25c#3 (Geldon et al. 1997, Figure 3).

TDR-NBS-HS-000001 REV 00 ICN 01 3-107 August 2000 
Source: CRWMS M&O (2000n, Figure 14) 
NOTE: Estimated permeabilities calculated from site-scale SZ flow and transport model. Observed permeabilities 
calculated from pump-test data. Bars indicate 95% confidence intervals; diamonds indicate the mean value. 
Figure 3-22. Estimated and Observed Permeabilities for Nine Stratigraphic Units at Yucca Mountain

TDR-NBS-HS-000001 REV 00 ICN 01 3-108 August 2000 
Source: CRWMS M&O (2000n, Figure 15) 
NOTE: Estimated permeabilities calculated from site-scale SZ flow and transport model. Observed permeabilities 
calculated from pump-test data. Bars indicate 95% confidence intervals; diamonds indicate the mean value. 
Figure 3-23. Estimated and Observed Permeabilities for Four Aquifers at the Nevada Test Site 
3.4.2 Comparison of Fluxes Derived from Regional Model with the Boundary Fluxes 
Calculated by Calibrated Model 
The site-scale SZ flow model domain includes only a small part of the Death Valley regional 
groundwater flow system and the boundaries of the site-scale model domain were not established 
along hydrologic boundaries. However, the domain of the regional-scale model encompasses a 
generally closed system and contains data from spring discharges to help fix the groundwater 
flux through the system (DAgnese et al. 1997, p. 59). Consequently, a comparison of predicted 
mass fluxes at the boundaries of the site-scale model domain with mass fluxes predicted by the 
regional-scale model should provide an indication of the validity of the calibrated site-scale SZ 
flow model. The expert elicitation panel (CRWMS M&O 1998b) suggested a comparison 
between these two fluxes as a means of validating the site-scale SZ flow model.

TDR-NBS-HS-000001 REV 00 ICN 01 3-109 August 2000 
There is uncertainty associated with the groundwater fluxes simulated by the regional-scale SZ 
flow model. The source of this uncertainty includes limited characterization of the total 
groundwater budget through the regional flow system, uncertainty in the spatial distribution of 
recharge, and limited vertical resolution of the model (i.e., only three layers). Matching the 
values of simulated groundwater fluxes at the lateral boundaries of the site-scale SZ flow model 
implies the propagation of the uncertainties in the regional-scale flow model to the site-scale 
flow model. However, a relatively large degree of uncertainty in groundwater fluxes is 
incorporated into the stochastic realizations of radionuclide transport used in the TSPA-SR 
(Section 3.7.2). 
As discussed in Section 3.3.6.2.2, the differences between the mass fluxes computed by the sitescale 
SZ flow and transport model and by the regional-scale flow model along certain segments 
of the site-scale SZ flow model boundary were included in the objective function used during 
parameter optimization. For this purpose, the north, east, and west boundary of the site-scale SZ 
flow model were divided into thirteen segments (Figure 3-24). The southern boundary was 
designated as a fourteenth boundary segment. As discussed in Section 3.3.5.3, constant head 
boundary conditions were established along the boundary of the site-scale SZ flow model. The 
mass flux computed by the site-scale model at the boundaries is determined by the head 
gradients and the permeability distribution along the boundaries. 
A comparison of the boundary fluxes predicted by the calibrated site-scale SZ flow model and 
the regional-scale flow model is presented in Table 3-7. The mass fluxes of the two models 
match reasonably well. The total fluxes across the northern boundary computed by the regionalscale 
and site-scale models were 6.2 x 106 m3/yr (5,040 acre-ft/yr.) and 5.4 x 106 m3/yr 
(4,343 acre-ft/yr.), respectively, a difference of only 14 percent based on the regional-scale 
value. The fluxes computed for individual segments along the northern boundary by the two 
models are distributed somewhat differently; however, this difference is expected because the 
regional-scale and site-scale HFM models are different. 
A comparison of the boundary fluxes computed along the east side of the site-scale SZ flow 
model domain indicates a good match. The match is particularly good along the lower thrust 
area where both models predict large fluxes across the model boundary. Both models also 
predicted small fluxes across the other boundary zones along the eastern boundary. 
Fluxes across the western boundary computed by the regional-scale model and the site-scale SZ 
flow model do not match as well as those along the northern and eastern boundaries. The 
regional-scale model predicts a greater inflow along the western boundary than does the 
site-scale SZ flow model. The discrepancy in fluxes computed along the western boundary by 
the two models largely is the result of the different HFMs upon which the two models are based. 
For example, the newer HFM used as the basis for the site-scale SZ flow model includes a large 
amount of low permeability clastic rock along the W5 boundary segment that was not included 
in the regional-scale HFM. This zone of low permeability rock would not support the large flux 
predicted by the regional-scale model across this portion of the western boundary. As previously 
indicated (Section 3.3.6.2.2), the fluxes across western boundary segments were not included in 
the objective function used during calibration.

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535000 540000 545000 550000 555000 560000 
4050000 
4055000 
4060000 
4065000 
4070000 
4075000 
4080000 
4085000 
4090000 
UTM-X (meters) 
UTM-Y (meters) 
W5 
W4 
W3 
W2 
W1
N1 N2 N3 N4 
E1 
E2 
E3 
E4 
Source: CRWMS M&O (2000n, Figure 16) 
Figure 3-24. Zones Used for Comparing Groundwater Fluxes between the Regional- and Site-Scale

TDR-NBS-HS-000001 REV 00 ICN 01 3-111 August 2000 
Table 3-7. Groundwater Fluxes Computed from the Regional-Scale and Site-Scale Groundwater Flow 
Models 
Boundary Zone Regional Flux (kg/s) Site-Scale Flux (kg/s) Calibration Target 
N1 -101.24 -60.009275 Yes 
N2 -16.48 -33.442643 Yes 
N3 -53.05282 -30.557419 Yes 
N4 -18.41 -44.807523 Yes 
W1 3.45 4.1663 No 
W2 -71 -0.0071871 No 
W3 -6.9 -0.0000078 No 
W4 2.73 -0.0000223 No 
W5 -46.99 -6.8542863 No 
E1 -555.45 -553.85002 Yes 
E2 -5.46 3.5334027 Yes 
E3 2.65 16.4956192 Yes 
E4 -3.07 16.8224586 Yes 
S 918 724 No 
Source: CRWMS M&O (2000n, Table 14) 
NOTE: Negative values indicate flow into the site-scale model. 
The southern boundary flux is the sum of the other boundary fluxes plus recharge. A 
comparison of the fluxes across the southern boundary computed by the regional-scale model 
and the site-scale SZ flow model indicates a relatively good match. The difference in the fluxes 
computed by the two models across the southern boundary is approximately 21 percent. 
There are several differences between the regional-scale flow model and site-scale SZ flow 
model that influence the match between the boundary fluxes. The HFM used in the regionalscale 
model is older than the one used in the site-scale model. These differences appear to be 
responsible, at least in part, for the discrepancies in fluxes on the northern and western 
boundaries. The vertical resolution of the computation grid used in the site-scale SZ model is 
finer than that used in the regional-scale model: the site-scale SZ model uses 39 model layers, 
while the regional-scale model included only 3 model layers (Sections 2.3 and 3.3.5.1). As a 
result, the fluxes predicted by the site-scale model might depend more strongly on a few units 
than does the regional-scale model. This is important because many of the hydrogeologic unit 
permeabilities in the site-scale SZ model were constrained during calibration by field data 
(Section 3.3.6.3). The flux distribution predicted by the regional-scale model also is influenced 
by the use of permeability classes. Based on this approach, permeabilities associated with 
specific units were not assigned to individual nodes. Rather, the permeabilities are grouped into 
larger classes, which are then assigned to individual grid blocks.

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3.4.3 Comparison of Measured Upward Hydraulic Gradient with Predicted Upward 
Hydraulic Gradient 
An upward gradient between the lower carbonate aquifer and overlying volcanic aquifers has 
been observed in the vicinity of Yucca Mountain (Section 3.1.1.2). Evidence of this upward 
gradient is obtained from the head measurement in well UE-25p#1, the only well that penetrates 
the carbonate aquifer. The measured head in the carbonate aquifer at this point is 751 m 
(2,467 ft). The measured heads in the overlying volcanic aquifers in the same area are 
approximately 730 meters. The site-scale SZ flow model predicts a head at well UE-25p#1 of 
740 m (2,430 ft) (CRWMS M&O 2000n, Section 6.7.11). Thus, the upward gradient in this area 
is partially represented in the calibrated site-scale SZ flow and transport model. 
The failure to fully represent the upward vertical gradient can be attributed, at least in part, to the 
constant head conditions established on boundaries of the model. As discussed previously 
(Section 3.3.5.3), a uniform, constant head was applied to each layer of the model at each 
boundary node. This specification does not allow vertical flow at the boundaries. However, 
vertical gradients may develop internally in the model domain in response to geohydrologic 
conditions. Although the upward gradient produced by the model is not as large as that indicated 
by field measurements, it nevertheless is sufficient to keep the simulated fluid pathlines 
downgradient from the potential repository in the shallow volcanic aquifers, a condition 
corroborated with geochemical data. 
3.4.4 Comparison of Hydrochemical Data Trends with Calculated Particle Pathways 
To provide further validation of the site-scale SZ flow and transport model, the flow paths 
predicted by the calibrated site-scale SZ flow and transport model (Section 3.3.7.2; Figure 3-21) 
were compared with those estimated using groundwater chemical and isotopic data 
(Section 3.1.1.1.3; Figure 3-3). 
The particle tracking capability of the FEHM code was used to generate the flow paths predicted 
by the calibrated site-scale SZ flow and transport model. A detailed discussion of the 
development of these flow paths is presented by CRWMS M&O (2000n, Section 6.7). The flow 
paths were generated by placing particles along the western, northern, and eastern boundaries of 
the model at intervals of 5,000 m (16,400 ft) and tracing their downgradient movement. At each 
location along the boundaries, particles were placed at 600 m, 0 m, -600 m, and -1,200 m, 
(1970, 0, -1970, and -3940 ft, respectively) relative to sea level. The model was run to trace the 
path of these particles over one million years. The paths of particle movement for a starting 
elevation of 600 m (1970 ft) are shown in Figure 3-25.

TDR-NBS-HS-000001 REV 00 ICN 01 3-113 August 2000 
535000.00 545000.00 555000.00 
4050000.00 
4055000.00 
4060000.00 
4065000.00 
4070000.00 
4075000.00 
4080000.00 
4085000.00 
4090000.00 
UTM-X (meters) 
UTM-Y (meters) 
Source: CRWMS M&O (2000n, Figure 10) 
Figure 3-25. Paths of Particle Starting at 600 Meters Elevation 
Particles follow a variety of flow paths depending on their initial location and the depths at 
which they originated (Figure 3-25; CRWMS M&O 2000n). Many of the particles exit the flow 
system at the nearest boundary, and some exit at locations not previously shown to have net 
outflows (Section 3.2.3). This occurs because the boundary zones included some individual cells 
that exhibit an outward flux at the model boundary. Some particle trajectories appear to 
terminate within the flow system, but these particles had not yet moved through the system 
within the one million years over which the particle paths were traced. The failure of these 
particles to exit the flow system after one million years suggests that stagnant conditions exist 
locally within these portions of the modeled flow system. Many particles exhibit complex 
trajectories in both map view and in three dimensions. These trajectories include an apparent 
crossing of some flow paths. A 3-D analysis of the particle paths indicates that the apparent 
crossing of flow paths in map view is a result of the different depths of the particle paths.

TDR-NBS-HS-000001 REV 00 ICN 01 3-114 August 2000 
Most of the particles that originate along the boundaries in the northeastern part of the model 
domain exit through the eastern boundary (Figure 3-25). Only the particles that begin along the 
southern one-third of the eastern boundary near the Skeleton Hills exit the southern boundary. 
The particle trajectories also indicate that groundwater near the town of Amargosa Valley 
originates predominantly from flow entering from the east, rather than flow from the northeast as 
shown by path #4 on Figure 3-3. However, a particle originating east of Fortymile Canyon at the 
-1,200 m (-3940 ft) elevation also passes beneath Amargosa Valley (CRWMS M&O 2000n, 
Figure 13). 
Particles along the northern boundary that do not immediately exit the flow system bifurcate 
around the east-west barrier in northern Yucca Mountain, which was used to simulate the large 
hydraulic gradient in that area. Particles originating immediately to the west of Fortymile 
Canyon flow around the western edge of the barrier and then eastward across Solitario Canyon 
and beneath Yucca Mountain before turning southwest in the Fortymile Wash area. Particles 
originating immediately to the east of Fortymile Canyon flow around the eastern edge of the 
barrier and, depending on the original elevation of the particle, either exit along the eastern 
boundary, terminate in southwestern Jackass Flats, or flow toward the southern boundary 
beneath Amargosa Valley (CRWMS M&O 2000n, Figures 10, 11, and 12, respectively). The 
particles originating toward the western end of the northern boundary flow beneath Crater Flat 
and southern Yucca Mountain along a somewhat more eastward trajectory than is indicated by 
paths #3 and #5 in Figure 3-3. 
Some of the particles originating along the western boundary of the model (between coordinates 
4,067,500 and 4,077,500 m) flow east-southeast beneath the southernmost portion of Yucca 
Mountain before turning southwest. The trajectory of these particles is more strongly eastward 
than the direction of flow indicated by paths #3 and #5 in Figure 3-3. The movement of the 
particles originating at 600 m (1,970 ft) (Figure 3-25) and 0 m (0 ft) elevation (CRWMS 
M&O 2000n, Figure 10) along the western boundary (at coordinate 4,062,500 m) agree with the 
direction of groundwater movement indicated by path #1 in Figure 3-3. 
The trajectories of particles originating at the potential repository (Figure 3-25) can be compared 
to path #6 in Figure 3-3. Path #6 follows Dune Wash before turning southwestward near the 
intersection of Dune Wash and Fortymile Wash, whereas the particle trajectories shown in 
Figure 3-25 flow south across Dune Wash before turning southwestward. Nonetheless, the 
general direction of groundwater movement from the potential repository area predicted by the 
numerical model is in agreement with the flow direction determined from the hydrochemical and 
isotopic data. 
In summary, some differences exist between the flow directions determined by the site-scale SZ 
flow and transport model and flow directions determined from an analysis of the hydrochemical 
and isotopic data. The most prominent difference is the stronger eastward component of flow in 
Crater Flat in the flow model compared to the flow directions determined in the hydrochemical 
analysis. The differences in the flow directions for Crater Flat could be due to the inability of the 
simple hydrochemical analysis to account for vertical mixing due to recharge or mixing between 
aquifers, the assumption in the numerical model that the rock in Crater Flat is isotropic with 
respect to permeability, or a combination of these factors. However, the most important flow

TDR-NBS-HS-000001 REV 00 ICN 01 3-115 August 2000 
paths determined by the numerical model (i.e., the flow paths from the potential repository area) 
are similar to those estimated from the hydrochemical data. 
3.4.5 Natural Analogues 
The fourth of five elements comprising the postclosure safety case (YMP 1999) calls for an 
assessment of insights gained from the study of natural analogues. Relevant information about 
the possible system performance of the site can be gleaned from analysis of natural processes 
that share characteristics with the potential repository system. These data may provide a degree 
of independent validation of the reasonableness of selected aspects of the assessments of 
repository performance (YMP 1999). An understanding of the principal factors upon which the 
safety case is based can be strengthened through confidence-building using natural analogues. 
Three factors were identified as important to the postclosure safety case for the SZ (Table 3-8) 
based in part on process model and TSPA sensitivity analyses. These factors serve as an 
organizing framework for discussing natural analogues that relate to each factor and for 
prioritizing the processes that need to be further bounded and quantified. 
Table 3-8. Saturated Zone Factors Important to Repository Safety and Corresponding Natural 
Analogues 
Factors Important to 
SZ Performance 
Processes Included in the 
SZ Flow and Transport Model Natural Analogues 
Advective pathways 
Dispersion 
SZ flow and transport 
Transverse dispersion 
Longitudinal dispersion 
DOE sites (e.g., NTS, Hanford) 
Alligator Rivers 
Sorption diffusion 
Matrix diffusion 
Sorption coefficient in alluvium 
Sorption onto fracture coatings 
Matrix diffusion 
NTS 
Palmottu 
Poos de Caldas 
Oklo 
Colloid-facilitated transport Colloidal transport in SZ NTS 
Cigar Lake 
Poos de Caldas 
3.4.5.1 Confidence-Building Using Natural Analogues 
Because natural analogues can be used to test conceptual and numerical models over large 
distances and long time scales not possible with laboratory or field experiments, they are 
uniquely suited to building confidence in process-level models and are used as a means of model 
validation. Because no single analogue site is a perfect match for all of the processes at Yucca 
Mountain, sites with specific analogous processes are examined. An ideal analogue site for 
Yucca Mountain should satisfy as many of the following conditions as possible (DOE 1995): a 
known source term, a set of radionuclides similar to those important for safety considerations at 
Yucca Mountain, well-characterized site-specific data, geologic conditions similar to Yucca 
Mountain, identifiable boundaries of the system, and involving processes relevant to 
understanding performance of the potential repository at Yucca Mountain. 
In addition to using natural analogues for building confidence in long-term model predictions, 
anthropogenic analogues may be used for testing models at shorter time scales. Anthropogenic

TDR-NBS-HS-000001 REV 00 ICN 01 3-116 August 2000 
analogues, such as Hanford, Washington; the Idaho National Engineering and Environmental 
Laboratory (INEEL); and the NTS; provide possibilities for investigating physicochemical 
processes such as fracture and matrix interactions, sorption, and colloidal transport. 
3.4.5.2 Natural Analogues to SZ Flow and Transport 
Several analogue studies that have been conducted in saturated environments are reviewed in this 
section. These sites occur around the world (Figure 3-26), and all involve uranium ore and rareearth 
(lanthanide) deposits in different types of host rock. Characteristic of these sites are the 
presence of redox fronts (e.g., Poos de Caldas, Oklo, and Palmottu) or weathering and periodic 
influx of oxidizing water (e.g., Alligator Rivers and Poos de Caldas). Although Cigar Lake 
involves reducing groundwater (which is not relevant to conditions at Yucca Mountain), 
localized oxidation may have resulted from radiolysis effects that could be useful. 
Anthropogenic analogues for SZ transport are discussed in Section 3.4.5.3. 
Figure 3-26. Natural Analogue Sites Used for Comparison with Yucca Mountain 
3.4.5.2.1 Alligator Rivers, Australia 
The Alligator Rivers Analogue Project was an investigation of radionuclide migration from the 
Koongarra secondary enriched-uranium deposit in the Northern Territory of Australia 
(Figure 3-26). The Koongarra ore body lies in two distinct parts composed of uraninite and 
pitchblende-bearing veins within a zone of steeply dipping, sheared quartz-chlorite schists and a 
fault that brings the ore body in contact with the Kombolgie sandstone. Leaching of the primary 
ore has resulted in the formation of four distinct zones: the unaltered primary ore consisting of 
uraninite and pitchblende, a uranium silicate zone formed by in situ alteration of the primary ore, 
a zone of secondary uranyl phosphate minerals that currently are being leached by groundwater, 
and a shallow dispersed uranium zone with the uranium in association with clays and iron 
oxyhydroxides (Isobe et al. 1992). Dissolved uranium is transported roughly from the uranium 
oxide zone at depth to the silicate zone, also at depth, then upward to the phosphate zone. The 
uranyl phosphate zone exists in the most oxidized weathered zone near the surface 
(Snelling 1980).

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A dispersion fan has developed in the weathering zone where uranium has been mobilized. 
Secondary minerals are found as far as 50 m (164 ft) downstream from the ore body, with 
detectable concentrations of uranium-series nuclides for about 300 m (984 ft) downstream in the 
dispersion fan. The age of the dispersion fan is estimated to be 0.5 to 3.0 million years 
(Golian and Lever 1992). 
The uppermost of the four mineral zones (above about 20 m [66 ft]) is the most weathered. 
Chlorite has been altered to kaolinite, minor smectite, hematite, and various iron oxyhydroxides. 
A transitional zone (20 to 25 m [66 to 82 ft] deep) of less weathered rock consists predominantly 
of vermiculite derived from primary chlorite (present below about 24 m [79 ft]) which is altered 
to kaolinite and iron oxides. Weathering of the quartz-chlorite schist produces different mineral 
assemblages according to degree of alteration. The migration behavior of nuclides at each depth 
is thought to be related to the chlorite alteration mineral assemblage (Ohnuki et al. 1990). The 
zone of lowest uranium concentration corresponds to the chlorite-rich zone; that of intermediate 
uranium concentration to the vermiculate-rich zone, and that of greatest uranium concentration to 
the kaolinite-rich zone. The highest uranium concentrations in the dispersion fan are associated 
with the lower part of the kaolinite-weathered zone (Ohnuki et al. 1990; Isobe et al. 1992). 
Isobe et al. (1992) describe uranium redistribution associated with weathering. Uranium activity 
closely follows oxidation fronts in the slightly weathered zone and advances most readily along 
cracks and fissures in which percolation of oxidizing groundwater is most enhanced. 
Considerable flow occurs as fracture flow rather than as porous media flow. Uranium 
distribution in the most strongly weathered rocks depends only on the mineralogy present and is 
not controlled by the presence of fissures, as is the case for the more moderately weathered 
rocks. In the dispersion fan, processes that control the amount of radionuclides that are removed 
from the groundwater include equilibrium sorption; chemical incorporation into iron oxides, 
uranium minerals, or other crystalline phases; and recoil transfer of daughter products caused by 
alpha-particle decay. 
Groundwaters are slightly acidic to neutral, oxidizing, relatively dilute, and the major ion 
chemistry is dominated by magnesium and bicarbonate. Waters from the weathered zone are not 
fully saturated with respect to a number of uranium-bearing minerals, consistent with the idea 
that the present groundwaters may be dissolving and dispersing uranium in the phosphate zone of 
the deposit. 
Groundwater samples taken from boreholes at Koongarra were studied with respect to their 
colloidal contents. Boreholes closest to faults have the greatest variety of colloids. The colloids 
identified included particles of iron, kaolinite, chlorite, silica, lead, uranium, and titanium. All 
colloid samples were dominated by iron-rich particles, and uranium was only found in iron-rich 
species (Ivanovich et al. 1987). Low colloid concentrations (about 106 particles/L or less) and 
the absence of radionuclides in colloids outside the center of the ore body indicated that colloidal 
transport of radionuclides is minor at Koongarra (Payne et al. 1992). 
In summary, Koongarra may represent a worst-case scenario for transport because of the 
near-surface exposure to oxidizing weathering conditions and monsoonal climate. The 
dissolution and reprecipitation of uranium in the dispersion fan is especially notable. Data

TDR-NBS-HS-000001 REV 00 ICN 01 3-118 August 2000 
associated with the rate of migration and pattern of dispersion in the Koongarra dispersion fan 
could be used to test models of SZ plume dispersion at Yucca Mountain. 
3.4.5.2.2 Poos de Caldas, Brazil 
The Poos de Caldas caldera in Brazil (Figure 3-26) was the focus of a natural analogue study 
involving the Osamu Utsumi mine, which is a uranium ore body with subsidiary thorium, 
zirconium, and rare-earth element (REE; i.e., lanthanide) enrichment; and Morro do Ferro, which 
is a thorium and REE ore body with subsidiary uranium. The Osamu Utsumi uranium mine is 
known for its well-developed redox front within the uranium ore. 
Osamu Utsumi is an open pit mine that consists of an upper weathered zone (laterite soil, top 
40 m [130 ft]) that is completely argillized, depleted in silicon and potassium, and enriched in 
alumina. The underlying oxidized zone is approximately 150 m (500 ft) thick and consists of 
alternating areas of oxidized and reduced bedrock. The reduced zone consists of essentially 
altered phonolites (62 percent potassium-feldspar, 37 percent clay minerals with accessory 
pyrite, fluorite, and barite). The primary mineralogical difference between the oxidized and 
reduced rocks is the presence of pyrite in the reduced rocks (Smellie et al. 1989). 
Primary mineralization mostly is low-grade and dispersed throughout the rock. The redox front 
generally is sharp, but irregular in profile as it follows the dips of faults and fractures along 
which oxidizing waters have penetrated. At the redox front, uranium mineralization occurs in 
the form of pitchblende nodules several centimeters across. The mine has been excavated to the 
level of the redox front. 
Morro do Ferro is a hill that stands about 140 m (460 ft) above the surrounding plateau, and is 
5 km north of the Osamu Utsumi mine. It has been weathered (to a greater degree than Osamu 
Utsumi) to a depth of at least 100 m (330 ft), and now the hill is composed of gibbsite, kaolinite, 
and illite, with additional veins of magnetite and manganese hydroxides that tend to form distinct 
layers. The thorium-REE ore occurs as elongated mineralized lenses that extend down the hill 
slope. Thorium and REE mineralization is very enriched, with up to 3 weight-percent thorium 
dioxide and up to 20 weight-percent total REE in some soils and weathered rocks (Waber 1991). 
No uranium mineralization is known at Morro do Ferro. 
Groundwaters in the Poos de Caldas area typically have low concentrations (less than 1 mg/L) 
of colloids (Miekeley et al. 1989). Most of the colloids are composed of iron and organic 
species. Only minor amounts of uranium are associated with colloids, but thorium and REEs are 
transported by the colloids. The suspended particle concentration is 5 to 10 times greater at 
Morro do Ferro than at Osamu Utsumi, but there appears to be little thorium transport at Morro 
do Ferro, either by colloids or in solution. Groundwater at Morro do Ferro is lower in most 
major- and trace-element concentrations than groundwater at Osamu Utsumi (Miekeley 
et al. 1989). However, high concentrations of manganese in groundwaters are an exception and 
result from the presence of nodular manganese-oxides. 
The groundwaters at Osamu Utsumi have high concentrations of uranium (up to 10 mg/L), 
whereas those from Morro do Ferro are lower (Miekeley et al. 1991). Thorium-232

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concentrations are low in groundwaters from both sites (less than 0.1 mg/L) but occasionally are 
higher (up to 100 times) in surficial waters with abundant humic compounds or sulfate. 
The groundwaters in the Poos de Caldas area have a potassium-iron-sulfate composition 
because of the weathering of the altered, mineralized, potassium-rich rocks (Nordstrom et al. 
1990). Also, relatively high concentrations of barium and sulfate detected in the groundwater 
from Osamu Utsumi may be important because microcrystalline barite can act as a scavenger for 
radionuclides. The groundwater flow at Osamu Utsumi is upward from depth, except for the 
upper 10 to 15 m (33 to 50 ft) where lateral surface flow predominates. 
West et al. (1989) suggest that microbial activity may encourage immobilization of uranium 
instead of forming mobile colloids or dissolved uranium complexes. Microbial activity is 
important for the oxidation of pyrite and may be responsible for the mobilization and 
reprecipitation of uraninite at the redox front. At Poos de Caldas, microbes were found in all 
samples of core and groundwater, independent of depth (West et al. 1989). West et al. (1989) 
reported that microbes enhance the supply of oxidants from the rock mass and thereby accelerate 
the rate at which the redox front advances. This could explain the observation that the redox 
front is moving faster than would be expected simply on the basis of dissolved oxygen 
concentration. 
The natural plutonium concentration in a centimeter-sized nodule was measured, and the 
plutonium/uranium ratio was consistent with a state of secular equilibrium with the matrix 
phonolite. Based on the plutonium/uranium ratio in the nodule, it appears that the two elements 
have resided (unfractionated and in the most highly uraniferous rock in the deposit) for the last 
100,000 yr. Even if alteration has occurred more recently, the processes did not significantly 
fractionate plutonium from uranium (Chapman et al. 1991, pp. 37, 39). 
The results of the colloid study suggest that the transport of radionuclides and other trace 
elements by particulate material in deep groundwaters does not play an important role in the 
geochemical processes of weathering, dissolution, and erosion of these ore deposits. The reason 
for this is assumed to be filtration of particulate material, which, even in the highly fractured and 
porous rocks of the Poos de Caldas plateau, seems to be an efficient process (Smellie 
et al. 1989). 
Redox front morphology provides direct evidence of flow channeling in fractures and solute 
transport in the rock matrix as the key controls on the shape and movement of these fronts. A 
consistent picture emerged of slow front movement and solute transport over the front dominated 
by diffusion. The front plays an important role in retarding a wide spectrum of redox-sensitive 
trace elements. Lichtner (1996) demonstrated that the zonation of the redox front, characterized 
by a narrow gap (or leached zone) separating precipitation of iron oxide on the oxidized side of 
the front and uraninite nodules in the reduced zone, could be explained by oxidation of pyrite 
and diffusive transport across the front. 
3.4.5.2.3 Oklo, Gabon 
The Oklo uranium mine, located in southeastern Gabon (Figure 3-26), contains the only known 
examples of natural fission reactors. Fourteen reactor zones have been identified among three

TDR-NBS-HS-000001 REV 00 ICN 01 3-120 August 2000 
uranium deposits in the Franceville Basin (Gauthier-Lafaye et al. 1989). The uranium deposits 
containing the natural fission reactors are located at the top of the basal sandstone-conglomerate 
unit (Gauthier-Lafaye et al. 1989). 
Two grades of ore, associated with two different occurrences of uranium as pitchblende with rare 
coffinite, can be distinguished in the Franceville Basin. Low-grade ore contains 0.1 to 
1.0 percent uranium oxide, and high-grade ore (greater than 1.0 percent) contains up to 
10 percent uranium oxide (Gauthier-Lafaye et al. 1989). Low-grade ore is primary and more 
common. High-grade ore is secondary and occurs within the secondary porosity of fractured 
sandstones (Gauthier-Lafaye et al. 1989). The formation of the high grade ore is attributed to the 
remobilization of low-grade ore by oxidizing hydrothermal fluids, which transported the uranium 
along the faults, followed by precipitation within the fracture zones under reducing conditions. 
In places, the uranium ore in the secondary deposit is extremely enriched (up to 70 percent 
uranium oxide), and at the time of formation, a critical mass of uranium-235 formed and initiated 
natural fission reactions. Because of the high uranium-235/uranium-238 ratio (3.5 percent) that 
was present 2 billion years ago (a concentration similar to uranium-235 enrichment for modern 
nuclear fuel), and the presence of an appropriate moderator (probably groundwater), a selfsustaining 
nuclear reaction was possible (Cowan 1976). Criticality was reached about 
1,968 + 50 million years ago and lasted intermittently for 0.1 to 0.8 million years, with reactions 
lasting for thousands of years (Holliger 1993). 
Some of the fission products are the same radionuclides that might be emplaced in the potential 
radioactive waste repository (e.g., technetium, neptunium, plutonium, and americium). The 
fission products originally collected in the crystalline uraninite of the reactor zones as the nuclear 
reaction proceeded. Although little alteration of uraninite occurred subsequent to its formation, 
some of the fission products have escaped from the uraninite, probably by solid-state diffusion 
(Curtis et al. 1981), and some transport of radionuclides has occurred subsequent to their release 
from the uraninite. 
Curtis (1986) postulated that increased temperatures and greater oxidizing conditions in the 
reactors led to the dissolution of technetium in hydrothermal fluids and to the migration of 
technetium to the surrounding rocks where it precipitated in response to declining temperature 
and more reducing conditions. Curtis et al. (1989) suggested that a portion of the fissionproduced 
tellurium, ruthenium, palladium, technetium, cadmium, and molybdenum was retained 
essentially at the site of production and that the portion that escaped the uraninite crystals was 
completely removed from the reactor zone. Curtis et al. (1989) present evidence that 
neodymium and tin were removed from the site of production, but that they were retained within 
the reactor zone. 
Because the reactions ended nearly two billion years ago, the short-lived radionuclides have 
decayed to more stable daughter radionuclides. According to Brookins (1978), plutonium, 
neptunium, and americium likely were retained within the reactor. Most geochemical 
observations at Oklo support these predictions to varying degrees. Curtis et al. (1989) conclude 
that the retention of fission products is related to their partitioning into uraninite or secondary 
mineral assemblages. Those fission products that partitioned into the secondary mineral 
assemblages were largely lost over time, pointing to the importance of small uraninite grains in 
controlling the chemical microenvironment.

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3.4.5.2.4 Palmottu, Finland 
The Palmottu natural analogue study is based on a small uranium-thorium deposit located in 
southwestern Finland (Figure 3-26). The deposit at Palmottu is hosted by Precambrian gneisses 
and migmatites whose protoliths were arkoses and graywackes. The deposit is up to 15 m (50 ft) 
thick, 400 m (1,300 ft) long, and extends to depths of 300 m (1,000 ft), but it is discontinuous in 
the form of uraniferous pegmatites and veins. The principal ore mineral is disseminated grains 
of uraninite, thinly coated with coffinite. The uranium is thought to have been derived during the 
latest stages of metamorphism, 1,700 to 1,800 million years ago, from late-stage granitic fluids 
of the nearby Perni granite. 
The ongoing natural analogue study has concentrated on processes, such as colloids and matrix 
diffusion, which may affect radionuclide migration and retardation in fractured crystalline rocks 
under groundwater-saturated conditions. A major focus has been on understanding the redox 
control of the system and propagation of redox fronts. The groundwaters, measured in open 
boreholes, show a distinct layered zonation: the upper waters are oxidizing and the lower waters 
are slightly saline and reducing. The change in water composition and the redox front both occur 
at a depth of about 125 m (410 ft). The pH increases from 7.4 close to the surface, to 
approximately 9.0 at the bottom (195 m [640 ft]) of the borehole (Jaakkola et al. 1989). Tritium 
values also decreased with depth to below detectable limits, indicating a lack of meteoric water 
infiltration at depth. Uranium is contained in primary uraninite, coffinite, and monazite 
(thorium-bearing), and is associated with iron oxides and clay minerals in the more altered areas 
and as fracture coatings. Coffinite precipitated along fractures short distances (less than 1 m 
[3.3 ft]) from uraninite grains. Considerable dissolution of uraninite has occurred at all depths, 
regardless of the modern, measured oxidation potential. Jaakkola et al. (1989) suggest that the 
oxidation potential at depth was higher in the past, perhaps because of infiltration of meteoric 
waters to greater depths. 
The concentration of uranium is higher in the oxidizing upper waters than in the lower, more 
reducing waters, even though the uranium concentration in the rock is greatest at depth 
(Valkiainen 1989). The opposite trend is observed with uranium in particulate matter. Most 
particulate matter in the upper 100 m (330 ft) contains little or no uranium, whereas uranium at 
depth is associated predominantly with particulate matter. 
Sorption onto fracture coatings, particularly calcite, efficiently retards uranium transport in 
fractures, and high concentrations of uranium have been measured in calcite. Long retention 
time of uranium in calcite, determined by uranium-series disequilibrium measurements, has been 
recognized. The uranium-234/uranium-238 ratio in the dissolved fraction increases with depth 
from a value of nearly 1.0, whereas uranium-234/uranium-238 in the particulate fraction shows a 
slight (though less significant) decrease with depth. The uranium-234/uranium-238 ratios of 
extracted phases suggest limited mixing of groundwaters in the study area 
(Blomqvist et al. 1995). 
3.4.5.2.5 Cigar Lake 
The Cigar Lake uranium deposit in northern Canada (Figure 3-26) was studied as an analogue 
for a potential radioactive waste disposal repository under water-saturated, reducing conditions

TDR-NBS-HS-000001 REV 00 ICN 01 3-122 August 2000 
located deep beneath the water table. However, radiolysis effects may have produced localized 
oxidizing conditions that would apply to oxidation of spent fuel at Yucca Mountain. This 
analogue also may be useful for understanding colloidal transport of uranium. The broad aims of 
this natural analogue project were to investigate the stability of uraninite as a natural analogue 
for spent fuel and to investigate the mechanisms that caused the retention of the radionuclides in 
the ore body, particularly the effect of colloids. The primary mineralization occurred 
1,300 million years ago (Cramer and Smellie 1994). 
Several major fractures cut the ore body and the clay envelope that surrounds the ore. These 
originally were features of the basement rocks but were reactivated after deposition of sandstone 
and formation of the ore. The uranium apparently was transported upward to the base of the 
unconformity along the fracture zone by hydrothermal solutions and deposited as uraninite at the 
unconformity when these solutions came into contact with groundwater in the sandstone. These 
hydrothermal solutions are responsible for the alteration of the sandstone surrounding the 
ore body. 
According to Curtis et al. (1999), naturally produced plutonium and technetium migrated short 
distances, but they remained within the deposit. Only one event seems to have disturbed the 
system since its formation (Cramer 1995). Small, isolated pockets of remobilized uranium have 
been found in some of the steeply dipping fractures above and in the shield rocks directly 
beneath the main ore body. The age of this younger event has been estimated at between 320 
and 293 million years, and most likely represents the temporary opening of fractures and faults in 
association with tectonic movement of the North American plate that allowed groundwaters to 
mobilize some of the uranium (Cramer 1995). 
Migration of radionuclides from the deposit into the surrounding rocks has been limited by a 
combination of hydrogeological, mineralogical, and geochemical factors (Cramer 1986). First, 
the deposit is in a basal sandstone unit, which is the main local aquifer, and this unit has a much 
higher groundwater flux than the deposit itself. Second, the present fluids are reducing; Eh is 
estimated at 0.2 to +0.2 volts (Sunder et al. 1988). Consequently, there is little dissolution of 
the uraninite or of the daughter radionuclides. Third, the clay-rich zones surrounding the ore 
have relatively low hydraulic conductivities compared with the sandstone of the overlying 
aquifer (Cramer and Sargent 1994). This effectively seals the ore zone from bulk groundwater 
flow and filters out colloids during mass transport from the ore zone. In addition, the clay-rich 
rocks and hydrothermally altered sandstones are enriched in pyrite and marcasite, providing 
effective redox buffering in the undisturbed system (Sunder et al. 1988). Fourth, any 
radionuclides that dissolve and migrate away from the ore zone encounter a naturally sorptive 
mineralogical barrier in the form of the clay alteration zone (Cramer 1986). 
Vilks et al. (1988) studied particulate and colloid matter in groundwater and showed that half or 
more of the uranium in the water is carried in suspension associated with particulate matter. 
Radiolysis of the groundwater within the ore zone may be the cause of locally oxidizing 
conditions causing formation of the iron-oxyhyroxides (e.g., goethite) at the top of the ore body, 
as well as the uranyl minerals reported by Fayek et al. (1997). Perhaps because of absorption 
onto amorphous iron-silicon-hydroxides at the interface of the ore and clay, uranium 
concentrations in the surrounding sandstone are depleted with respect to the ore body water.

TDR-NBS-HS-000001 REV 00 ICN 01 3-123 August 2000 
Also, the filtration of particulate matter by clay minerals probably plays a role in reducing 
groundwater uranium concentration (Vilks et al. 1988). 
3.4.5.3 Anthropogenic Analogues of Saturated Zone Flow and Transport 
The purpose of investigating anthropogenic analogues is to obtain a better understanding of 
migration over shorter time scales than is amenable to study by natural analogues. In this 
section, radionuclide transport at INEEL, Hanford, and the NTS is discussed, as is the potential 
applicability of future investigations of selected radionuclide plumes in Russia as anthropogenic 
analogues. 
3.4.5.3.1 Idaho National Engineering and Environmental Laboratory 
One of the facilities at the INEEL that can provide a potential anthropogenic analogue site is the 
Idaho Chemical Processing Plant (ICPP). The ICPP was designed principally to recover highly 
enriched uranium (> 93 percent uranium-235) from different fuel types used in naval propulsion, 
research, and test reactors. From 1952 until 1984, low-level radioactive waste was discharged 
from the ICPP directly to the Snake River Plain by means of an injection well and seepage 
ponds. Over time, a suite of radionuclides has been measured in the aquifer, including 
hydrogen-3, chlorine-36, strontium-90, cesium-137, iodine-129 and isotopes of plutonium. 
Beasley et al. (1998) reported the first measurement of long-lived radionuclides (technetium-99, 
uranium-236, and neptunium-237) in the aquifer and downgradient changes in concentration 
during water transport through fractured basalt. Their study showed that chlorine-36 and 
technetium-99 behave conservatively during transport, while iodine-129, uranium-236, and 
neptunium-237 were retarded. The mobility of technetium-99 is sensitive to the redox state of 
groundwater. 
The ICPP is located east of the Big Lost River, in the south-central part of the INEEL. Beasley 
et al. (1998, p. 3875) reported that water in the Snake River Plain aquifer is unconfined, with the 
highly fractured tops of basalt flows leading to high hydraulic conductivities. Beasley et al. 
(1998, p. 3876) further state that the calculated residence time of water in the Snake River Plain 
is 55 to 82 yr., although water travel times within different parts of the aquifer, from recharge to 
discharge points, are estimated between 12 and 350 yr.. Groundwater flow is from the northeast 
to the southwest, and depth to groundwater varies from about 60 m (200 ft) at the northern site 
boundary to about 275 m (900 ft) at the southern site boundary. Beasley et al. (1998, p. 3876) 
report that the average hydraulic gradient across the INEEL is about 2 m/km (11 ft/mi.), and 
water travel times between the ICPP and the southern site boundary have been estimated at 
2 m/day (6.6 ft/day).

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Radionuclides were sampled from 8 to 23 groundwater monitoring wells at INEEL, located 0 km 
(0 mi.) to 12 km (7 mi.) from the ICPP, in 1991, 1992, and 1994. Activity concentrations were 
measured for chlorine-36, technetium-99, uranium-236, iodine-129, and neptunium-237. To 
determine the relative mobility of these radionuclides, individual radionuclide activities in wells 
near the ICPP were normalized to those at a distance (Figure 3-27). The similarity between 
chlorine-36 and technetium-99 suggests that these radionuclides behave conservatively in the 
fractured basalt and that the decrease in concentration occurs as a result of dilution or dispersion 
(Beasley et al. 1998, p. 3880). Iodine-129 is attenuated, and neptunium-237 and uranium-236 
are even more attenuated. Because none of these radionuclides were routinely monitored in lowlevel 
waste streams discharged from the ICPP, the possibility cannot be excluded that the 
relationships (Figure 3-27) could have arisen from variable discharge rates over time. However, 
Beasley et al. (1998) point out that even though the absolute amounts of radioactivity probably 
varied over time, the ratios of radionuclides in the discharges probably were consistent in order 
not to affect the composition of radioactivity in the waste streams. 
Source: Adapted from Beasley et al. (1998, p. 3879) 
NOTE: For chlorine-36, technetium-99, and iodine-129, the values are normalized to their concentrations in well-57, 
whereas uranium-236 and neptunium-237 concentrations are normalized to well-123. 
Figure 3-27. Decrease in Relative Concentrations of Radionuclides in the Snake River Plain Aquifer with 
Distance from the Idaho Chemical Processing Plant

TDR-NBS-HS-000001 REV 00 ICN 01 3-125 August 2000 
The INEEL site provides an anthopogenic analogue for testing models describing flow and 
reactive transport through fractured rock, as well as the interaction between fractured and 
nonfractured stratigraphic layers. Both of these features are important for modeling the potential 
Yucca Mountain repository. Characteristic features such as fracture flow and ponding on 
stratigraphic layers of low permeability are present at INEEL and Yucca Mountain. However, 
the fractured basalt at INEEL has distinctly different properties compared to fractured tuff at 
Yucca Mountain. For example, the basaltic flows at INEEL are interbedded with sedimentary 
deposits several meters thick. As such, characteristics of transport through fractured basalt at 
INEEL may be different than those at Yucca Mountain. However, the INEEL site provides a 
useful test area for predictive models such as those needed to evaluate the potential repository at 
Yucca Mountain. 
3.4.5.3.2 Hanford Effluent Treatment Facility 
The Hanford Effluent Treatment Facility (ETF) was selected as an anthropogenic analogue for 
modeling studies of radionuclide migration in the SZ at Yucca Mountain. The ETF is a 
combined treatment plant and disposal facility where waste streams resulting from various 
cleanup activities are treated and discharged into the UZ. The treated effluent migrates through 
the soil to the water table. The first detection of tritium in groundwater monitoring wells 
occurred in July 1996, roughly one year after operations commenced at the site. The plume 
emanating from the ETF site is well characterized and provides an opportunity for studying the 
transport of nonreactive and reactive groundwater constituents (Barnett et al. 1997). Migration 
of the tritium plume has been modeled using the CFEST computer code (Barnett et al. 1997), 
enabling a comparison between this model and the FEHM code (Zyvoloski et al. 1997a) that was 
used for modeling flow and transport in the SZ at Yucca Mountain. 
3.4.5.3.3 Nevada Test Site 
The 0.75-kiloton Cambric underground nuclear test was conducted in 1965 in tuffaceous 
alluvium 73 m (220 ft) below the water table (Hoffman and Daniels 1981). Data from a field 
experiment initiated in 1974 at the Cambric site provide information on the inferred radionuclide 
transport rates through alluvium. Tests began after the cavity and chimney were predicted to be 
filled with groundwater to the predetonation static water level. It was assumed that tritium, 
plutonium, and uranium fission products would be present in the cavity and in the groundwater 
within the cavity, and that these could be used to study possible migration from the cavity 
(Hoffman and Daniels 1981). 
The field study began with the completion of a well (RNM-2S) that was 91 m (300 ft) from the 
Cambric cavity, followed by drilling of a well (RNM-1) into the cavity itself. Solid and liquid 
samples were taken from well RNM-1 to determine the distribution of radionuclides between the 
solid material and the groundwater. Water was then pumped from the satellite well to induce an 
artificial gradient sufficient to draw water from the Cambric cavity through the surrounding 
rocks. 
Approximately two years after pumping began, large amounts of tritiated water were found in 
water from well RNM-2S, signaling the arrival of water from the Cambric cavity region. After 
almost six years of pumping, the tritium concentration in the pumped water reached a maximum

TDR-NBS-HS-000001 REV 00 ICN 01 3-126 August 2000 
(Hoffman et al. 1977). By the end of September 1984, about 60 percent of the initial tritium 
inventory had been pumped out through well RNM-2S. 
Other radionuclides also have been measured in water from well RNM-2S, including 
chlorine-36, krypton-85, ruthenium-106, and iodine-129. Strontium-90 and cesium-137 were not 
detected in water from well RNM-2S during the 10-yr experiment (Thompson 1986). A 
chlorine-36 pulse preceded the tritium pulse in well RNM-2S. Krypton was shown to be 
correlated with tritium but more strongly sorbed onto alluvium than tritium (Thompson 1986). 
Ruthenium-106 was detected in well RNM-2S water and is unretarded in the alluvium. 
Iodine-129 arrived at well RNM-2S sooner than tritium. 
The Cheshire event took place in 1976. Detonation occurred at a depth of 1,167 m (3,829 ft), 
approximately 544 m (1,785 ft) below the water table in fractured rhyolitic lavas of Pahute Mesa. 
Water was obtained from two wells, one inside the Cheshire experimental site and the other 
300-m (985-ft) away. Tritium, krypton, strontium, cesium, antimony, cobalt, cerium, and 
europium were detected in the pumped water, and all of the cobalt, cerium, and europium were 
associated with colloids in samples from both locations. Buddemeier and Hunt (1988) 
maintained that the presence of colloidal radionuclides outside the cavity indicates radionuclide 
transport on colloids. 
The Benham test was detonated in 1968 at a depth of 1,402 m (4,600 ft) below the water table. 
In a recent field test, plutonium was measured in groundwater at the NTS ER-20-5 wells at a 
maximum activity concentration of 0.63 pCi/L (Kersting et al. 1999). The ratio of 
plutonium-240 to plutonium-239 indicates that the plutonium originated at the site of the 
Benham test, a distance of 1.3 km (0.81 mi.) from the wells. Therefore, the inferred minimum 
rate for plutonium migration at the NTS is 1.3 km (0.81 mi.) in 28 yr. (46 m/yr. [151 ft/yr.]). 
The plutonium was associated with colloidal material consisting mainly of clays, zeolites, and 
silica (Kersting et al. 1999). It is not likely that the plutonium was transported by prompt 
injection or that the soluble fraction migrated along fast flow paths. Colloidal transport is a 
possible mechanism for plutonium migration because colloidal transport of radionuclides was 
observed at the Cheshire site. However, stability arguments limit the amount of colloids in 
suspension. The association of plutonium in colloidal form at the NTS indicates the need to 
incorporate the colloidal transport mechanisms into transport process models and PA 
calculations for radionuclide releases at Yucca Mountain. 
3.4.5.3.4 Russian Sites 
Deep injection of liquid radioactive waste into confined geologic units was a frequent disposal 
methodology in Russia. Leakage from the confining unit has taken place at the deep injection 
site of Krasnoyarsk-26. The disposal setting at Krasnoyarsk provides an opportunity to 
investigate plume dispersion in fractured biotite gneiss. It also provides an opportunity to 
observe the effects of short-term (decades) of radioactivity-caused thermal effects on mineralogy 
in the injected medium.

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3.4.5.4 Relationship of Analogue Studies to the Yucca Mountain Conceptual Model 
The natural and anthropogenic analogue studies reviewed here have been confined to qualitative 
or semi-qualitative analysis, rather than detailed numerical studies. They may be used to place 
bounding conditions on the importance of various processes under different environmental 
conditions. A number of the analogue studies, either directly or indirectly, support confidence in 
modeling these processes over the long time spans required for the TSPA for the potential Yucca 
Mountain repository. The conceptual model for transport of radionuclides at Yucca Mountain 
involves processes such as advection through fractured tuff and alluvium, dispersion, colloid 
transport, and sorption, all of which have been studied in analogous sites. 
Overall, these sites contribute to understanding migration processes at a detailed scale, in a 
variety of settings, and over long periods of time. They also allow placement of broad bounds on 
processes such as colloid transport and confirm the importance of fracture flow and sorption onto 
fracture-coating minerals such as calcite and hematite. 
Underground nuclear tests have provided anthropogenic analogues for transport of radionuclides 
through fractures and alluvium, and by colloids. The INEEL analogue involves transport of 
radionuclides through fractured basalt and can aid in testing fracture models. The Hanford ETF 
analogue site provides the opportunity to test the YMP FEHM code (Zyvoloski et al. 1997a) 
against other codes. 
3.4.5.5 Summary and Conclusions 
The following conclusions can be drawn from the natural and anthropogenic analogue studies: 
 At Oklo, under criticality conditions far more extreme than those anticipated at Yucca 
Mountain, only several percent of the uranium was estimated to have been mobilized. 
Technetium migrated short distances, whereas plutonium, neptunium, and americium 
were retained in the natural reactors. At Oklo, subsequent transport has been controlled 
by reducing conditions, sequestration within small uranium grains, and by hydrologic 
barriers. 
 At Poos de Caldas, Chapman et al. (1991) showed that plutonium and uranium have 
reached secular equilibrium in a pitchblende nodule and that the two elements have 
resided, unfractionated, in a system closed to them, but not closed to groundwater 
circulation, for the last 100,000 yr. within the phonolite matrix. The implication from 
this observation (i.e. that plutonium and uranium may remain unfractionated in spent 
fuel of a repository) needs to be examined more completely. 
 Colloidal transport of uranium was shown to be minimal at Koongarra, Cigar Lake, and 
Poos de Caldas, where filtration of colloids appears to be effective. The observation of 
rapid transport of colloids at the NTS must be tempered by knowledge that the natural 
system at the NTS has been disturbed by nuclear testing and by pumping.

TDR-NBS-HS-000001 REV 00 ICN 01 3-128 August 2000 
 Fractures act as transport pathways and places of retardation at a number of the analogue 
sites. At Poos de Caldas, uranium has been transported small distances along fractures, 
and is sorbed onto iron oxide and calcite. Even at Palmottu, where migration of uranium 
has been extensive, sorption onto fracture coatings in the SZ has been identified as an 
important retardation mechanism. Advective transport along fractures has been 
identified as a more important transport mechanism than matrix diffusion in all of the SZ 
analogue sites, although matrix diffusion is a mechanism attributed to lead-loss in 
uraninites at Oklo and Cigar Lake (Janeczek and Ewing 1992), and plays a role in 
retarding uranium migration. In the YMP TSPA, transport models are not sensitive to 
fracture sorption, but the natural analogues suggest that fracture sorption enhances 
radionuclide retardation. 
 Although the initial conditions and geologic medium are different at INEEL compared 
to Yucca Mountain, Beasley et al. (1998) provide a degree of confirmation of the 
conservative or retarding nature of a number of the same radionuclides as would be 
present in a Yucca Mountain repository (e.g., chlorine-36, technetium-99, uranium-236, 
iodine-129, and neptunium-237). 
Taken in total, information from the analogue systems provides a qualitative validation of the 
conceptual model of radionuclide transport in the site-scale SZ flow and transport model. 
Differences in geochemical and hydrologic conditions between analogue sites and the Yucca 
Mountain system, as well as uncertainties in radionuclide source terms for analogue systems, 
generally preclude quantitative validation of the conceptual model of transport that has been 
developed for the SZ at Yucca Mountain. Differential migration of radionuclides resulting from 
sorption process at analogue sites provides an important confirmation that this aspect of the 
conceptual model operates at the field scale. Observations of colloid-facilitated transport of 
actinides in analogue systems validates the conceptual model for the site-scale SZ model that 
some small fraction of strongly sorbing radionuclides may be subject to transport by this 
mechanism. Evidence of dispersive and diffusive processes at analogue sites also provide 
general confirmation that the conceptual model of transport in the SZ at Yucca Mountain 
correctly incorporates these processes. 
3.5 ASSUMPTIONS, USES, LIMITS OF THE SATURATED ZONE SITE-SCALE 
FLOW AND TRANSPORT MODEL 
In any numerical simulation of a physical process using a mathematical model, assumptions are 
made and limitations apply. In the following sections, some of the assumptions and limitations 
of the site-scale SZ flow and transport model, as well as the parameters that are used as input in 
this model, are discussed. The list of assumptions presented here is not exhaustive. Many of the 
parameters used in the site-scale SZ flow and transport model are estimated using simple 
mathematical models. Other parameters may be estimated from data using methods that are 
biased and require extrapolation or corrections that carry assumptions. Assumptions used in 
estimating individual parameter values are not included in this section, but may be obtained from 
the AMRs. For example, stochastic parameters and their associated uncertainty distribution are 
presented by CRWMS M&O (2000o).

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Taken in total, these data provide an appropriate and adequate basis for the conceptual model and 
numerical model of the site-scale SZ flow and transport system. The site-characterization 
information, along with inferences based on that information, support a conceptual model in 
which groundwater flow is controlled by the spatial distribution of geologic units and structural 
features. Site-specific data, together with regional-scale studies, suggest that a large fraction of 
groundwater flowing in the SZ enters the Yucca Mountain site area as lateral flow from the north 
with a small fraction contributed by recharge near Yucca Mountain. The conceptual model of 
radionuclide transport in fractured rocks includes the processes of advection, dispersion, matrix 
diffusion, sorption, and colloid-facilitated transport, as supported by site data. These 
components of the conceptual model are implemented numerically in the site-scale SZ flow and 
transport model, which represents the processes relevant to radionuclide migration from Yucca 
Mountain to the biosphere. 
3.5.1 Groundwater Flow Processes 
Assumptions used in modeling the groundwater flow process include those of the regional-scale 
models and the site-scale SZ flow and transport model, and those made in estimating parameters 
that are used as input to these models. For the following reasons, the effective continuum 
representation of fracture permeability is used: 
 On the scale represented by the site-scale SZ flow and transport model, the site is wellrepresented 
by a continuum flow model. Pumping tests show evidence of fracture flow 
near Yucca Mountain (Geldon et al. 1997). Numerical modeling of fracture properties is 
done in one of two ways: discrete fracture models or effective continuum models. 
Discrete fracture models represent each fracture as a distinct object within the modeling 
domain. While a discrete fracture model might reproduce the flow system more 
accurately, flow modeling is conducted using a continuum model for the following 
reasons: 
- The exact characterization of hydraulic and geometric properties of fractures 
necessary to construct an accurate discrete fracture model does not exist for Yucca 
Mountain. A methodology for obtaining accurate fracture porosity in situ has not 
been developed, although some information may be obtained from well flow-meter 
surveys. 
- At Yucca Mountain, studies of the density and spacing of flowing intervals generally 
indicate that flow occurs through fracture zones (CRWMS M&O 2000k, Figure 15). 
The fractures or fracture zones are located in various geological units, and in most 
cases, no single zone dominates the flow through a well. Geochemical studies 
(CRWMS M&O 2000m) independently confirm a south-southeasterly trace of the 
particle flow path. For the limited set of wells (Luckey et al. 1996, Figure 11), flow 
appears to be carried through fracture zones separated by a few tens of meters rather 
than by a few individual fractures. 
- Part of the flow system is an alluvium unit for which flow and transport is 
appropriately modeled using a continuum model.

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- The drawdown response to pumping at wells surrounding the C-wells Complex in 
multi-well pump tests indicates a well-connected fracture network in the Miocene 
tuffaceous rocks in this area (Geldon et al. 1998, p. 31). 
- While the discrete fracture approach retains the discrete nature of the observed 
fractures within the model, the computational burden of calculating a flow solution 
using a discrete fracture model becomes extremely large even for relatively simple 
fracture models. 
The following assumptions also apply to the TSPA-SR continuum modeling approach (CRWMS 
M&O 2000p): 
 Estimates of discharge from the volcanic aquifer, elicited from the SZ expert elicitation 
panel, are applicable to the entire flowpath from the potential repository to the accessible 
environment. The estimates of specific discharge from the SZ expert elicitation 
primarily were based on data from hydraulic testing in wells in volcanic units and the 
hydraulic gradient inferred from water level measurements (CRWMS M&O 1998b, p. 3- 
8). The relative values of groundwater flux in the volcanic aquifer and along the 
flowpath farther to the south are constrained by the calibration of the site-scale SZ 
model. It is reasonable to extrapolate the degree of uncertainty in the absolute value of 
groundwater flux from the volcanic aquifer to the flowpath farther to the south. 
 Horizontal anisotropy in permeability is adequately represented by a permeability tensor 
that is oriented in the north-south and east-west directions. For the purposes of the 
TSPA nominal case, horizontal isotropy and anisotropy are considered for radionuclide 
transport. The numerical grid of the site-scale SZ flow and transport model is aligned 
north-south and east-west, and values of permeability may be specified only in 
directions parallel to the grid. Analysis of the probable direction of horizontal 
anisotropy shows that the direction of maximum transmissivity is N 33 E (Winterle and 
La Femina 1999, p. iii), indicating that the anisotropy applied on the site-scale SZ model 
grid is within approximately 30 of the inferred anisotropy. Horizontal isotropy was 
assumed in the calibrated flow model. Inclusion of a 5:1 (north-south to east-west) 
horizontal anisotropy in the calibrated flow model resulted in head residuals that were 
less than the calibrated isotropic model along the transport path (CRWMS M&O 2000p, 
Figures 7 to 8). 
 Horizontal anisotropy in permeability applies to the fractured and faulted volcanic units 
of the SZ system along the groundwater flowpaths that run from the potential repository 
to points south and east of Yucca Mountain. The inferred flowpath from beneath the 
potential repository extends to the south and east. This is the area in which potential 
anisotropy could have an important impact on radionuclide transport in the SZ. Given 
the conceptual basis for the anisotropy model, it is appropriate to apply anisotropy only 
to those hydrogeologic units that are dominated by groundwater flow in fractures.

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 Anisotropy in permeability represents an alternative conceptual model of groundwater 
flow at the Yucca Mountain site. Sufficient uncertainty in the analysis of horizontal 
anisotropy exists to warrant consideration of two possible conceptual models: one with 
anisotropy and one without anisotropy (i.e., isotropic permeability). 
 Current groundwater flow conditions in the SZ system are at steady state. A steady-state 
model of the flow conditions is used to reflect the assumption that a steady-state 
representation of the SZ system is accurate. Studies by Luckey et al. (1996, pp. 29 to 
32) indicate that there are no long-term consistent trends in the data from wells at Yucca 
Mountain. Some individual wells show a positive trend in potentiometric level, but the 
nature of the hydrographs for these wells indicate that the rise in potentiometric levels is 
likely due to recovery from the drilling process which pumped the wells dry (Luckey 
et al. 1996, pp. 20 to 32). These conclusions are based on data collected over a period of 
a few years. There exists the possibility of slowly increasing potentiometric levels, not 
noticeable over a time period of a few decades, but large over hundreds or thousands of 
years. Such a trend would require a forcing physical effect such as an increase in 
precipitation or a geophysical mechanism. No such mechanisms have been identified 
(USGS 2000c). The convolution integral method has been extended to incorporate 
multiple steady-state flow conditions for alternative climate states (CRWMS 
M&O 2000p, Section 6.4.1). 
 Changes in the water table elevation (due to future climate changes) will have negligible 
effect on the direction of the groundwater flow near Yucca Mountain. This assumption 
has been studied in regional-scale (DAgnese et al. 1999) and subregional-scale 
(Czarnecki 1984) flow models. These studies found that the flow direction did not 
change significantly under increased recharge scenarios. The studies were based on 2-D 
confined aquifer models that did not take into account the free surface boundary at the 
water table or the saturation of geological units that currently are in the UZ overlying the 
present-day SZ. These UZ tuffs generally have a lower permeability than those in the 
SZ, and as such, UZ units are not likely to introduce faster flow paths. 
 Future water supply wells that might be drilled near Yucca Mountain (including outside 
the proposed regulatory boundary) will have a negligible effect on the hydraulic 
gradient. This assumption, however, is not appropriate for water levels at the southern 
boundary of the site-scale SZ flow and transport model (in the Amargosa valley) that 
currently show the effect of well pumpage (Luckey et al. 1996, p. 41). It is assumed that 
future pumpage will not cause further alteration of the water table. 
 Possible effects due to temperature gradients and heat transport are assumed to be 
negligible. Heat transport can affect flow modeling through the temperature dependence 
of fluid viscosity and density. 
3.5.2 Radionuclide Transport Properties 
Radionuclide transport is modeled using a particle tracking methodology (CRWMS 
M&O 2000j). The 3-D particle tracking model assumes transport along streamlines and takes 
into account advection, dispersion, sorption, and matrix diffusion. The particle tracking model is

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semianalytical in nature and has been developed to include anisotropic structures. Modeling 
transport using particle tracking has some advantages over numerical solutions of an advectiondispersion 
equation. Two of these advantages include less numerical dispersion and the ability 
to model plumes on a sub-grid block scale. Disadvantages are that computations of 
concentration may require a large number of particles and that particles may diffuse into zones of 
low advection requiring a very long time to exit. Assumptions of the transport model are: 
 On the scale represented by the site-scale SZ flow and transport model, the site is wellrepresented 
by a continuous flow and transport model. In particular, the specific 
discharge field computed by the FEHM flow model (Zyvoloski et al. 1997a) represents 
the specific discharge averaged over grid cells that are 500 m (1,640 ft) long. The 
specific discharge field is determined by the grid discretization and the scale of spatial 
heterogeneity of the underlying permeability field. Possible long (more than 500 m 
[1,640 ft]) high-permeability conduits would not be represented accurately by the 
present transport model because the computed discharge in the present model is based 
on blocks of 500 m (1,640 ft). The possible existence of relatively long, highpermeability 
structural features with a north-south orientation is explicitly incorporated 
in the site-scale SZ flow and transport model through the inclusion of horizontal 
anisotropy. Within the Yucca Mountain flow system, it is recognized that most 
groundwater flow occurs in fracture zones. This fact is recognized in transport modeling 
by assuming that all flow occurs through flowing intervals that occupy a small subvolume 
of each grid block. Spatially varying transport velocities, used in the particle 
tracking model, are computed using the flowing interval porosity in fractured units. In 
the valley-fill alluvial aquifer, transport velocities were computed using the effective 
porosity, consistent with a porous media conceptualization for this area. 
 The convolution integral method is appropriate for scaling transport to account for 
increasing mass flux in response to changes in the future climate. An assumption 
inherent to the convolution integral method is that the system being simulated exhibits a 
linear response to the input function. In the case of solute transport in the SZ system, 
this assumption implies, for example, that a doubling of the input mass flux results in a 
doubling of the output mass flux. This assumption is valid for the site-scale SZ flow and 
transport model because the underlying transport processes (e.g., advection and sorption) 
are linear with respect to solute mass. The method of scaling solute mass breakthrough 
curves for climate change is not an exact representation of the matrix diffusion process, 
but it does provide a reasonable approximation within the context of the ranges of 
uncertainty for underlying stochastic parameters. 
 Fractures are equally spaced, smooth, and have constant aperture. The numerical 
representation of matrix diffusion assumes equally spaced, smooth, constant aperture 
fractures. An important question is whether matrix diffusion is modeled adequately by a 
parallel fracture model. Radionuclide transport depends on the fracture (flowing 
interval) porosity, the flowing interval spacing, and the effective diffusion coefficient, 
and values of these parameters were estimated from flow-meter data taken from wells 
near Yucca Mountain (CRWMS M&O 2000k) and laboratory data. Fluid velocity in a 
single fracture may be computed from fracture porosity measurements and the specific 
discharge found in the site-scale SZ flow model, under the assumption that a flowing

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interval is represented by a single fracture and that no flow occurs in the matrix. The 
assumption that the fracture aperture width is equal to that of a flowing interval tends to 
underestimate fluid velocity, while the assumption that no flow occurs in the matrix 
tends to overestimate the fluid velocity in the fracture. 
 Fluid in the matrix of volcanic rocks is stagnant. This assumption is conservative from 
the perspective of the performance of the potential repository because if mass flows in 
the matrix, then the mass available for faster transport and flow velocities in the flowing 
intervals (fractures) is reduced. The assumption will not greatly affect concentration and 
integrated discharge computations when the matrix permeability is an order of 
magnitude or more below that of the fractures because radionuclide transport to the site 
boundary through the fracture network (flowing intervals) occurs much earlier than 
transport through the matrix. A difference of an order of magnitude or more in the 
permeability of volcanic rocks is supported by CRWMS M&O (1998a, Section 5.2). 
 Linear sorption at equilibrium. The mathematical representation assumes linear sorption 
due to the large temporal and spatial scales involved in radionuclide transport. 
Furthermore, the low relative concentrations of radionuclides support this assumption 
(CRWMS M&O 2000r). 
3.5.3 Use of the Site-Scale Model in Site Characterization Activities 
Important processes that affect radionuclide transport in the SZ are advection, dispersion, matrix 
diffusion, and sorption. In addition to its use for TSPA, the site-scale SZ flow and transport 
model is used to integrate all available data and to guide additional site characterization. The 
model was used to estimate a band-width for potential travel paths from the potential repository 
to the proposed compliance boundary. The travel path estimate was used together with other 
data to locate the Alluvial Test Complex and other NCEWDP wells to characterize the alluvium 
along the flow path from the potential repository to the proposed compliance boundary, confirm 
the conceptual model for flow and transport in the alluvium, and to obtain flow and transport 
parameter values. 
3.5.4 Modeling Limitations 
The site-scale SZ flow and transport model is adequate for its intended purpose, which is to 
model groundwater flow and radionuclide transport from the potential Yucca Mountain 
repository to the site-scale model boundary under present day and potential future climate 
conditions. Here, adequate means that the transport model is an internally consistent 
representation of the SZ that is subject to considerable uncertainty due to assumptions and 
simplification inherent in groundwater flow and transport modeling. The important processes, 
and the sub-process models that address them, have been identified. Many processes are 
inherently uncertain and this uncertainty is handled through the use of stochastic realizations. 
The site-scale SZ flow and transport model is not appropriate for: 
 Computing transport over short distances. Over short distances (less than 1 km 
[0.6 mi.]), transport likely is dominated by discrete fractures or fracture zones.

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 Computing scenarios involving heavy well pumpage near Yucca Mountain. These 
scenarios violate the assumption of a steady state groundwater system and they might 
involve large changes to the water table. 
 Computing short-term transient hydrologic conditions. The site-scale SZ flow and 
transport model is not appropriate for computing short-term transient hydrologic 
conditions because it has not been calibrated using transient pumping tests. 
 Performing analyses of disruptive events. Disruptive events may have several effects on 
the hydrogeologic environment at Yucca Mountain, including altering the permeability 
field or causing transient changes to the water table. The analysis of disruptive events 
may require modifying the HFM, regridding, or modifying other sub-process models and 
parameters to account for transient changes to the water table. 
3.5.5 Process Model Uncertainty 
The site-scale SZ flow and transport model and its components are comprehensive and complex. 
The model was used by TSPA-SR to characterize flow and transport processes that operate in the 
SZ below Yucca Mountain (from the potential repository to the proposed compliance boundary). 
Limitations and uncertainties associated with the model and its components should be 
recognized. The accuracy and reliability of predictions from the site-scale SZ flow and transport 
model are critically dependent on the accuracy of estimated model properties to which the model 
is sensitive, other types of input data, and conceptual models of the hydrology and geology. 
These models are limited mainly by the current characterization of the SZ system (including the 
geological and conceptual models), the continuum modeling approach, steady state flow, and the 
available field and laboratory data. 
Investigations have indicated that a large amount of variability exists in the flow and transport 
parameters over the spatial scale of the SZ flow and transport model domain. Even though 
considerable progress has been made in this area, the major remaining uncertainties in model 
parameters are: 
 Transport properties including effective porosity in the alluvium 
 Sorption coefficients for different elements in the alluvial and volcanic units 
 Matrix molecular diffusion in different hydrogeological units for different radionuclides 
 Dispersivities in volcanic and alluvial units 
 Location of the transition zone where the flow path from the potential repository to the 
proposed compliance boundary transitions from volcanic to alluvial hydrogeological 
units. 
All of these uncertainties have been addressed in this report. The stochastic parameter 
uncertainty distributions are developed from limited field and laboratory data, expert elicitation,

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and literature surveys. These uncertainties are addressed in Section 3.7.1, Section 3.7.2, and 
CRWMS M&O (2000o). 
3.6 SYNTHESIS OF SATURATED ZONE MODEL AND MODEL ABSTRACTIONS 
In this section, the synthesis of SZ flow and transport data and process models for abstraction in 
TSPA analyses is described. The incorporation of additional information relevant to 
radionuclide migration into the site-scale SZ flow and transport model for TSPA simulations is 
discussed. This section also is used to document modifications to the site-scale SZ flow and 
transport model for the purpose of incorporating uncertainty in SZ groundwater flux and 
horizontal anisotropy in permeability. Abstraction methods for conducting TSPA simulations, 
including the convolution integral method, alternative climate states, dilution in the water supply 
of the critical group, and radionuclide decay chains are described. 
3.6.1 Introduction 
The site-scale SZ flow and transport model represents a synthesis of available data on the 
groundwater flow system at the Yucca Mountain site, as well as information from regional-scale 
studies of the SZ. Key information utilized in the construction of the site-scale SZ flow model 
includes a 3-D representation of the geology of the system (USGS 2000a), water level 
measurements in wells (USGS 2000b), pumping tests of the volcanic units (CRWMS M&O 
2000n), hydrochemical data (CRWMS M&O 2000m), and simulations of groundwater flux from 
the SZ regional-scale flow model (CRWMS M&O 1999a). The calibration process for the sitescale 
SZ flow model provides an internally consistent representation of the SZ flow system that 
reproduces the key observations about the system. 
Additional information on the characteristics of the SZ system relevant to contaminant transport 
is incorporated into the site-scale SZ flow and transport model for simulating radionuclide 
migration. Key information incorporated into the transport model includes sorption coefficients 
for sorbing radionuclides, flowing interval spacing and porosity, and matrix porosity in fractured 
volcanic units, effective porosity in alluvial units, dispersivity, and effective diffusion coefficient 
(CRWMS M&O 2000o). Additional data and inferences regarding colloid-facilitated transport 
of radionuclides are used in the site-scale SZ flow and transport model to simulate this process 
(CRWMS M&O 2000l, 2000o). 
3.6.2 Results of Synthesis 
The primary result of this synthesis is the site-scale SZ flow and transport model used for 
simulations of radionuclide transport in TSPA analyses. This model includes modification of the 
final calibrated flow model to accommodate variable parameter values for stochastic 
radionuclide transport parameters and consists of six alternative groundwater flow fields that 
incorporate uncertainty in groundwater flux and horizontal anisotropy. The site-scale SZ flow 
and transport model for TSPA also produces simulation results in the appropriate format for 
coupling the radionuclide transport results with other components of the TSPA analyses.

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3.6.3 Analysis Approach to Saturated Zone Flow and Transport for Total Systems 
Performance Assessment Analyses 
It is desirable to integrate detailed process-level modeling into TSPA analyses to incorporate 
site-specific information about the system represented by the process-level model. This may be 
accomplished by explicitly coupling the process-level computational model into the TSPA 
simulator or by abstracting the process-level model results for incorporation into the TSPA 
analyses. An abstraction approach is chosen for the implementation of SZ flow and transport in 
the TSPA-SR analyses, primarily because of the size and complexity of the site-scale SZ flow 
and transport model. In addition, an abstraction approach that largely captures the information 
that is provided by the site-scale SZ flow and transport model about system behavior is possible. 
The site-scale SZ flow and transport model results are abstracted by performing radionuclide 
transport simulations that assume a constant, unitary radionuclide mass flux at the upstream 
end of the SZ. The resulting radionuclide mass breakthrough curves at the downstream end of 
the SZ basically contain all of the information about the model behavior for those source and 
receptor locations, assuming steady groundwater flow. These results are obtained by running the 
site-scale SZ flow and transport model for each stochastic realization and saving the results for 
later use by the TSPA simulator. 
3.6.3.1 General Approach 
The TSPA site-scale SZ flow and transport model is used to simulate unit breakthrough curves 
for radionuclides at the interface between the SZ and the biosphere. Radionuclide concentration 
is then calculated as the average concentration in the water supply that is defined for the 
hypothetical farming community in the biosphere. 
Using the streamline particle tracking algorithm of the FEHM software code (Zyvoloski 
et al. 1997a), radionuclide transport is simulated directly for those radionuclides that are not the 
product of radioactive decay and ingrowth. The convolution integral method is used to simulate 
the time-varying radionuclide flux to the biosphere, based on these model runs and the UZ flow 
and transport model results. Transport of radionuclides that occur as the daughter products of 
radioactive ingrowth is directly simulated with the 1-D SZ transport model implemented in the 
TSPA simulator. Radioactive ingrowth is the generation of radionuclide mass from the decay of 
a parent radionuclide. 
The approach used for SZ radionuclide transport in the TSPA-SR differs from the approach used 
in the TSPA-VA (DOE 1998b) in several ways. For the TSPA-SR, the SZ flow and transport 
model is used to simulate the unit breakthrough curves for radionuclide mass at the interface 
between the SZ and the biosphere. Radionuclide concentration is calculated as the average 
concentration in the water supply for the hypothetical farming community in the biosphere. For 
TSPA-SR, the 3-D site-scale SZ flow and transport model is used to simulate radionuclide 
transport directly for those radionuclides that are not the product of radioactive decay and 
ingrowth using the FEHM streamline particle tracking algorithm. In contrast, for TSPA-VA 
(DOE 1998b), the breakthrough curves of radionuclide concentration in the SZ were simulated 
directly with the SZ flow and transport model. For TSPA-VA, an abstracted 1-D SZ flow and 
transport model was used to simulate transport of all radionuclides to generate breakthrough

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curves at the accessible environment. Use of the convolution integral method to simulate the 
time-varying radionuclide flux to the biosphere remains the same in the approach for TSPA-SR. 
3.6.3.2 Total System Performance Assessment Three-Dimensional Flow and Transport 
Model 
The calibrated site-scale SZ flow and transport model (CRWMS M&O 2000n) lays the 
foundation for the site-scale SZ flow and transport model for TSPA. As described in 
Section 3.4, the base case SZ model is a single calibrated steady-state flow model that assumes 
horizontally isotropic permeability within units and present-day climatic conditions. Other than 
particle tracking for the purpose of flowpath delineation, the base case model does not consider 
relevant transport parameters or phenomena. 
As described by CRWMS M&O (2000p), the calibrated site-scale SZ flow model input files are 
modified for use in radionuclide transport simulations to include relevant radionuclide transport 
parameters and to perform simulations of radionuclide transport. Input files for radionuclide 
transport include incorporation of values for stochastic parameters that have been generated for 
100 random realizations of the SZ system. The simulated water table and particle tracking 
pathways for the TSPA site-scale SZ flow and transport model with isotropic horizontal 
permeability are shown in Figure 3-21. 
In addition to the relatively high degree of uncertainty in the radionuclide transport 
characteristics of the SZ system, there is uncertainty in the groundwater flow in the system. 
Uncertainties exist in the SZ groundwater flux and in the direction of groundwater flow 
downgradient from the potential repository. To evaluate the uncertainty in groundwater flux, 
three discrete cases were examined. These consist of the mean case (corresponding to the mean 
flux of the calibrated site-scale SZ flow model), the low case (mean flux times 0.1), and the high 
case (mean flux times 10). The flux multipliers and the corresponding probabilities for these 
cases are quantified based on the uncertainty distribution for specific discharge in the volcanic 
aquifer from the SZ expert elicitation (CRWMS M&O 1998b, Section 3.7.2). The analysis is 
provided in CRWMS M&O (2000p, Section 6.2.5). Uncertainty in the direction of groundwater 
flow along the flowpath from the potential repository is incorporated as alternative groundwater 
flow fields, with and without horizontal anisotropy in permeability (CRWMS M&O 2000o). 
The result of considering both types of uncertainty is six alternative groundwater flow fields 
(three flux-cases times two anisotropy-cases). 
Implementation of the alternative groundwater flow fields is accomplished by establishing a 
steady-state solution of groundwater flow in the site-scale SZ model for each of the six cases. 
Small variations in the simulated heads exist among the six steady-state flow solutions (generally 
variations of less than 1 m [3.3 ft]). All six flow fields represent acceptable matches to measured 
water levels. The steady-state conditions for each of these cases are imposed as the initial 
conditions for the appropriate TSPA realizations of radionuclide transport. In addition, a 
separate set of input files for the site-scale SZ flow and transport model that incorporate 
modifications to the boundary conditions and values of permeability for each case are 
constructed. Each realization is assigned to the appropriate flow field based on the values of the 
stochastic parameters that represent uncertainty in groundwater flux and horizontal anisotropy 
(CRWMS M&O 2000p).

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3.6.3.3 Abstraction of Radionuclide Transport 
Several types of abstraction for TSPA analyses are discussed in this section. The convolution 
integral method is described with regard to incorporating results of the site-scale SZ flow and 
transport model in TSPA calculations (Section 3.6.3.3.1). An abstraction method for including 
the effects of climate change is described (Section 3.6.3.3.2). Assumptions used in the 
abstraction of radionuclide transport are discussed in Section 3.6.3.3.3. The approach for 
calculating the average radionuclide concentrations in the water supply of the hypothetical 
farming community containing the critical group (NRC 1998) is discussed in Section 3.6.3.3.4. 
A simplified 1-D abstraction of radionuclide transport for decay chains is described in 
Section 3.6.3.3.5. 
3.6.3.3.1 Convolution Integral Method 
As discussed in CRWMS M&O (2000p, Section 6.4.1), the convolution integral method is used 
in the TSPA-SR calculations to determine the radionuclide mass flux at the assumed interface of 
the SZ and the biosphere, 20 km (12.5 mi.) downgradient from the potential repository. This 
computationally efficient method combines information about the response of the system, as 
simulated by the site-scale SZ flow and transport modeling, with the radionuclide source history 
from the UZ to calculate transient system behavior. The most important assumptions of the 
convolution method are linear system behavior and steady-state flow conditions in the SZ. 
The convolution integral method provides an approximation of the transient radionuclide mass 
flux at a particular distance downgradient in the SZ. This response is a function of the transient 
radionuclide mass flux from the UZ. This coupling method makes full use of detailed SZ flow 
and transport simulations for a given realization of the system, without requiring complete 
numerical simulation of the SZ for the duration of each TSPA realization. The two input 
functions to the convolution integral method are a unit radionuclide mass breakthrough curve in 
response to a step-function mass flux source as simulated by the SZ flow and transport model, 
and the radionuclide mass flux history as simulated by the UZ transport model. The output 
function is the radionuclide mass flux history downgradient in the SZ. 
Radioactive decay is applied to radionuclide mass flux calculated with the convolution integral 
software code. The convolution integral method consists of numerical integration that accounts 
for the contributions to the outlet radionuclide mass flux from a series of time intervals. Because 
the travel time for each contribution to radionuclide mass flux is known, the loss of radionuclide 
mass (and consequent decrease in mass flux) during transport is calculated by first-order decay 
for that time interval. 
3.6.3.3.2 Alternative Climate States 
The effects of climate change on the transport of radionuclides in the SZ is incorporated in TSPA 
calculations by scaling the radionuclide mass breakthrough curves simulated for present climatic 
conditions (CRWMS M&O 2000p, Section 6.4.2). The scaling procedure is performed as part of 
the convolution integral method and assumes a proportional scaling of groundwater flux in the 
entire SZ system in response to wetter climatic conditions. This method treats the shift in 
climatic conditions as an instantaneous change from one steady-state groundwater flow condition

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in the SZ to another steady-state, in a manner consistent with other components of the TSPA 
simulations. 
Estimates of the scaling factors for groundwater flux in the SZ under alternative climatic 
conditions are based on simulations using the regional-scale SZ flow model (DAgnese et al. 
1999) and on results from the site-scale UZ flow model (CRWMS M&O (2000b). Simulations 
using the regional-scale SZ flow model were conducted for the past-climate state that likely 
existed about 21,000 yr. ago. This climatic state approximately corresponds to the glacialtransition 
state, as defined for TSPA-SR calculations. An evaluation of the change in 
groundwater flux in the SZ near Yucca Mountain under past-climate conditions using the 
regional-scale SZ model indicates an increase in flux of approximately 3.9 relative to present-day 
climate condition simulations. The ratio of glacial-transition infiltration in the UZ model to the 
present-day infiltration is the same value as the estimate of increased SZ groundwater flux from 
the regional-scale SZ flow model (i.e., 3.9). This correspondence suggests that the UZ 
infiltration ratio provides a reasonable estimate of the flux ratio for the SZ. For monsoonal 
climatic conditions, the ratio of UZ infiltration to the infiltration for present-day conditions 
is 2.7. This value is applied to the SZ flux as well (CRWMS M&O (2000p, Section 6.4.2). The 
effect of changes in groundwater flux is incorporated into the convolution method by scaling the 
timing of radionuclide mass breakthrough curves proportionally to the change in SZ specific 
discharge. 
3.6.3.3.3 Assumptions of the Abstraction of Radionuclide Transport 
There are several important assumptions in the use of the convolution integral method (CRWMS 
M&O 2000p, Section 5). Groundwater flow in the SZ is assumed to be in steady state. The 
site-scale SZ flow model is a steady-state model of the flow conditions (CRWMS M&O 2000n), 
reflecting the conclusion that a steady-state representation of the SZ system is accurate. This 
conclusion is supported by the lack of consistent, large-magnitude variations in water levels 
observed in wells near Yucca Mountain (Luckey et al. 1996, pp. 29 to 32). The transport 
processes in the SZ are assumed to be linear with respect to the solute source term (i.e., a 
doubling of the solute mass source results in a doubling of mass flux). This assumption is valid 
for the site-scale SZ flow and transport model because the underlying transport processes (i.e., 
advection, dispersion, diffusion, and sorption) are linear with respect to solute mass. In addition, 
the flow and transport processes in the UZ and the SZ are assumed to be independent. 
It is assumed that the change in groundwater flow in the SZ from one climatic state to another 
occurs rapidly and is approximated by an instantaneous shift from one steady-state flow 
condition to another steady-state flow condition. In reality, even an extremely rapid shift in 
climatic conditions would result in a transient response of the SZ flow system because of 
changes in groundwater storage associated with water table rise or fall and because of the 
response time in the UZ flow system. The assumption of instantaneous shifts to new steady-state 
conditions would tend to be conservative with regard to radionuclide transport in the TSPA 
calculations. The progression of climate states in the 10,000 yr. following closure of the 
potential repository is from drier to wetter climatic conditions, and thus, from slower to more 
rapid groundwater flow in the SZ. By assuming an instantaneous shift to higher groundwater 
flux in the SZ, the simulations tend to overestimate the radionuclide transport flow rates during 
the period of transition from drier conditions to wetter conditions.

TDR-NBS-HS-000001 REV 00 ICN 01 3-140 August 2000 
Groundwater flow pathways in the SZ from beneath the potential repository to the accessible 
environment are assumed not to be altered appreciably for wetter climatic states. Scaling of 
present-day groundwater flux and radionuclide mass breakthrough curves by a proportionality 
factor implies that only the groundwater flow rates are changed in the SZ system in response to 
climate change. This assumption is supported by the observation that the shape of the simulated 
potentiometric surface downgradient from Yucca Mountain remains basically the same under 
glacial climatic conditions in simulations using the SZ regional-scale flow model (DAgnese 
et al. 1999, p. 30). Wetter climatic conditions and a rise in the water table directly beneath the 
potential repository would tend to place volcanic units that presently are higher in the 
stratigraphic sequence, at or just below the water table. These higher volcanic units (Prow Pass 
Tuff and Calico Hills Formation) have lower values of permeability than the underlying Bullfrog 
Tuff. Disregarding changes in groundwater pathways, which would be redirected into these 
lower-permeability units with a rise in the water table, generally is conservative from the 
perspective of radionuclide transport. 
It is assumed that the entire mass of radionuclides crossing the 20-km (12.5-mi) fence in the SZ 
is captured by wells of the hypothetical farming community. This assumption implies that the 
total volumetric groundwater usage by the hypothetical community is large relative to the 
volumetric flow in the plume of contaminated groundwater in the SZ and that the flow path of 
the contaminant plume is close to the pumping wells. This assumption is justified on the basis of 
conservatism with respect to the analysis of performance of the potential repository. The total 
mass of radionuclides released to the biosphere for a given time period cannot be larger than the 
amount of radionuclide mass delivered by groundwater flow (for the nominal case). 
3.6.3.3.4 Dilution in Water Supply 
The hypothetical release of radionuclides from the SZ to the biosphere occurs by pumping of 
groundwater as the water supply for a future farming community in the nominal case of the 
TSPA-SR (CRWMS M&O 2000p, Section 6.2.4). Based on the proposed rule 10 CFR Part 63 
(64 FR 8640), this hypothetical community is located along the groundwater flowpath in 
Amargosa Valley at a distance of 20 km (12.5 mi.) from the potential repository. Radionuclide 
concentrations in the water supply of the hypothetical farming community are calculated by 
assuming that all radionuclide mass is captured by pumping wells and that this mass is uniformly 
distributed in the total volume of groundwater used by the community. Complete capture of the 
radionuclide plume by groundwater pumping is a reasonable assumption, given the relatively 
large volumetric groundwater use of the hypothetical community. The assumption of complete 
capture also is a bounding, conservative approach. Although it reasonably may be expected that 
variations in radionuclide concentration would exist among the pumping wells in the community, 
redistribution of radionuclides by multiple pathways of radionuclide migration in the biosphere 
would tend to homogenize the dose among the critical group. 
A detailed analysis of the groundwater use by the hypothetical farming community is presented 
by CRWMS M&O (2000c). The analysis is based on present-day groundwater use and 
agricultural practices of the residents in Amargosa Valley. The analysis does, however, consider 
potential differences between the characteristics of the present population of Amargosa Valley 
and the characteristics of the hypothetical future farming community. The assessment of 
groundwater use includes uncertainty in this parameter and presents an uncertainty distribution

TDR-NBS-HS-000001 REV 00 ICN 01 3-141 August 2000 
for use in the stochastic realizations of the system for TSPA. The results of the analysis indicate 
a range of 1.79 to 2.99 x 106 m3/yr (1,454 to 2,423 acre-ft/yr.) (CRWMS M&O 2000c, p. 5-5) for 
the expected value of total estimated annual groundwater use by the hypothetical farming 
community. Comparison with the total simulated groundwater flow across the southern 
boundary of the site-scale SZ flow model (approximately 23.5 x 106 m3/yr [19,000 acre-ft/yr.] 
[CRWMS M&O 2000n]) indicates that the quantity of groundwater assumed to be used by the 
hypothetical community would be available in the SZ flow system. 
3.6.3.3.5 One-Dimensional Transport Model 
The 1-D radionuclide transport model for TSPA-SR is used for simulating radioactive decay and 
ingrowth for four decay chains (CRWMS M&O 2000p, Section 6.5). This simplified model is 
required because the radionuclide transport methodology used in the 3-D site-scale SZ flow and 
transport model is not capable of simulating ingrowth by radioactive decay. Although it is not 
anticipated that the decay products from these radioactive decay chains are large contributors to 
the total radiological dose, regulations concerning groundwater protection may require explicit 
analysis of their concentrations in the water supply of the critical group. The results of 
1-D transport modeling are used only for the daughter radionuclides. Although transport of the 
parent radionuclides also is included in the 1-D transport model, the results from the 3-D sitescale 
SZ flow and transport model are used for the parent radionuclides in the TSPA-SR 
simulations. The 1-D radionuclide transport model for TSPA differs from the site-scale SZ flow 
and transport model in that it is implemented directly in the TSPA model. The four simplified 
decay chains include the following: 
1) Actinium series: 
Ac Pa U Pu Am 227 231 235 239 243     
2) Neptunium Series: 
Th U Np Am 229 233 237 241    
3) Thorium Series: 
Ra Th U Pu 228 232 236 240    
4) Uranium Series: 
 
   
  
Pu 
Pb Ra Th U 
U Pu 
238 
210 226 230 234 
238 242 
The 1-D radionuclide transport model is implemented in the TSPA simulator as a series of 
pipe segments, in which the transport of all radionuclides in the decay chains occurs. Except 
for transverse dispersion, the same radionuclide transport processes that are simulated in the 
3-D site-scale SZ flow and transport model (e.g., sorption, matrix diffusion in fractured units, 
and colloid-facilitated transport) are analyzed in the pipe segments. Neglecting the process of 
transverse dispersion is a conservative approximation, from the perspective of radionuclide 
dilution. Although strict consistency between the 1-D transport model and the 3-D site-scale SZ 
model is not possible, average groundwater flow and transport characteristics of the site-scale SZ 
model are used to define flow and transport properties within the pipe segments of the 
1-D model. Average specific discharge along different segments of the flowpath is estimated

TDR-NBS-HS-000001 REV 00 ICN 01 3-142 August 2000 
using the 3-D site-scale SZ flow model. The resulting values of average specific discharge are 
applied to the individual pipe segments in the 1-D transport model. 
3.6.3.4 Coupling of Saturated Zone Flow and Transport with Other Components of 
Total System Performance Assessment Analyses 
Coupling of the SZ flow and transport models with the upstream and downstream components to 
the natural system in the TSPA analyses is accomplished through the mass of radionuclides 
entering and leaving the SZ system. The mass of radionuclides leaving the UZ transport model 
at the water table during a time step in the TSPA analysis is transferred to the convolution 
integral abstraction of the site-scale SZ flow and transport model and to the 1-D SZ transport 
model. The radionuclide mass leaving the SZ flow and transport models during a time step is 
converted to a value of radionuclide concentration based on groundwater use in the biosphere 
component of the TSPA analysis. This process is discussed by CRWMS M&O (2000p, 
Section 6.2 and 6.3). 
3.6.3.4.1 Unsaturated Zone Flow and Transport 
The source of radionuclide contamination entering the site-scale SZ flow and transport model is 
specified as a point within each of four source regions beneath the potential repository. The 
point source is located at an elevation of 725 m (2,380 ft) in the nominal case, which is 
approximately 5 m (16 ft) below the water table over most of the area beneath the potential 
repository. The horizontal location of the point source in each of the four source regions varies 
stochastically from realization to realization, reflecting uncertainty in the location of leaking 
waste packages and transport pathways in the UZ. Radionuclide transport simulations with the 
site-scale SZ flow and transport model are performed using 1,000 particles, which are released at 
each of the four point source locations at the beginning of the simulation. Each particle 
represents an equal mass of radionuclide. 
The radionuclide mass that reaches the water table from the UZ in the TSPA simulator is 
assigned to one of the four source regions. This radionuclide mass represents the source term 
used in the convolution integral method for that source region for a given time step. A point 
source of radionuclide mass from an entire quadrant of the UZ transport model is physically 
realistic for the situation in which contamination is coming from a single leaking waste package 
or in which a high degree of groundwater flow focusing occurs in the UZ flow system. 
Combining the radionuclide mass from a quadrant of the UZ transport model at later times, when 
multiple leaking waste packages contribute contamination, may not be physically realistic, but 
represents a conservative approximation from the perspective of performance of the potential 
repository. 
The timing and hydrologic impacts of climate change are applied with the TSPA simulator in a 
consistent manner in the SZ and UZ. When the climatic state of the system shifts, the 
appropriate UZ flow field is applied to radionuclide transport in the UZ, and the lower boundary 
of the UZ (i.e., the water table) is changed (to higher levels for wetter climatic conditions). 
Simultaneously, the groundwater flux in the SZ is implicitly scaled to match the prevailing 
climatic state by scaling the radionuclide mass breakthrough curves for the present climatic state.

TDR-NBS-HS-000001 REV 00 ICN 01 3-143 August 2000 
Climate change is imposed as an instantaneous change to the new steady-state groundwater flow 
conditions in the SZ and the UZ. 
3.6.3.4.2 Biosphere 
The breakthrough curves for the mass fraction of radionuclides delivered to the 20-km (12.5-mi) 
distance are simulated with the site-scale SZ flow and transport model by obtaining travel times 
from the FEHM code when particles cross a fence of nodes in the model grid. Three fences of 
nodes (corresponding to distances of 5 km, 20 km, and 30 km [3 mi., 12.5 mi., and 18.6 mi.]) are 
specified for the breakthrough curves. These fences of grid nodes are located at the prescribed 
distance from the southern corner of the outline of the potential repository and extend from the 
upper surface to the lower surface of the site-scale SZ model domain. The SZ groundwater flow 
pathway from beneath the potential repository extends in a generally southerly direction and all 
particles are counted as they cross the intervening fences of grid nodes. The model setup of 
the 1-D SZ transport model provides output of radionuclide mass at the exit of each pipe 
segment, and these segments are constructed to end at 5-km, 20-km, and 30-km (3-m, 12.5-m, 
and 18.6-mi) distances. 
The contributions of radionuclide mass flux at the 20-km (12.5-mi) fence from the four source 
regions in the site-scale SZ flow and transport model are summed to obtain the total radionuclide 
mass flux for a time step in the TSPA simulator. Summing the values of radionuclide mass flux 
occurs following the convolution integral calculation. The mass flux of the daughter 
radionuclides from the 1-D SZ transport model is also included in the calculation at this point. 
Radionuclide concentrations in groundwater are used in the TSPA analysis along with the 
biosphere dose conversion factors to calculate annual dose. The concentrations of radionuclides 
are calculated by dividing the radionuclide mass delivered to the biosphere per year for that time 
step by the total groundwater use per year of the hypothetical farming community. 
3.6.3.4.3 Implementation with the GoldSim Software Code 
Simulation of the entire potential repository and natural system is performed in the TSPA model 
with the GoldSim software code. The results of the site-scale SZ flow and transport model 
simulations consist of a library of unit radionuclide mass breakthrough curves. These 
breakthrough curves are contained in a set of files, each one of which includes the radionuclide 
mass breakthrough curves from all 100 realizations for a particular radionuclide and from a 
particular source region. The 100 realizations of SZ flow and transport correspond to the 
100 realizations with the TSPA simulator. The parameter uncertainty definitions and 
distributions used to create the 100 SZ model realizations are included in the GoldSim input file 
for the TSPA simulator, guaranteeing consistency in parameter values with other components of 
the TSPA for each realization. 
At each time step within the GoldSim simulation, the current climate state, and the radionuclide 
mass flux at the water table from the UZ for each of the radionuclides, at each of the four sourceregions, 
are passed to the convolution integral software code. The convolution integral 
subroutine calculates the radionuclide mass flux for each of the four source regions at the 20-km 
(12.5-mi) distance for that time step based on the unit radionuclide breakthrough curves for that

TDR-NBS-HS-000001 REV 00 ICN 01 3-144 August 2000 
realization (Figure 3-28). The radionuclide mass flux at the 20-km (12.5-mi) distance is then 
summed for the four source regions in the SZ for each radionuclide at that time step in the 
GoldSim simulation. The radionuclide mass flux of decay chain daughter products is taken from 
the 1-D SZ transport model, which is simulated directly in the GoldSim simulation. 
Figure 3-28. The Convolution Integral Method Used in Saturated Zone Flow and Transport Calculations 
for TSPA-SR

TDR-NBS-HS-000001 REV 00 ICN 01 3-145 August 2000 
Calculation of radionuclide concentrations is performed with the GoldSim software code by 
dividing the total radionuclide mass flux by the volumetric groundwater usage of the farming 
community for each radionuclide. The groundwater usage of the farming community is a 
stochastic parameter that varies from realization to realization, but is constant through time for a 
given realization. The calculation of radionuclide concentrations is performed for each time step 
in the TSPA simulation. 
3.7 SATURATED ZONE SITE-SCALE FLOW AND TRANSPORT NOMINAL CASE 
For the nominal case of TSPA-SR, analyses of SZ flow and transport incorporate uncertainty in 
the SZ groundwater flow system and in the parameters relevant to the transport of radionuclides 
through the system. Uncertainty in groundwater flow is incorporated through the use of six 
discrete flow fields that consider uncertainty in the magnitude of groundwater flux and 
uncertainty in horizontal anisotropy in permeability. Multiple realizations of the SZ transport 
model are constructed using continuous uncertainty distributions for the parameters that define 
the transport characteristics of the SZ system. 
3.7.1 Description of the Nominal Case 
The nominal case of SZ flow and transport for the TSPA-SR explicitly incorporates many FEPs 
of the SZ system and includes others in an implicit fashion. Those FEPs that implicitly are 
incorporated primarily are captured in the range of uncertainty assigned to parameters varied in 
the stochastic analyses. 
The most important features of the SZ system that explicitly are represented in the simulations 
are the geometry and variability in properties among hydrogeologic units in the subsurface. Of 
particular importance is the distinction between units consisting of fractured volcanic rock media 
and those that consist of porous alluvial media. In addition, numerous hydrologic features 
corresponding to faults and geologic zones are explicitly incorporated into the site-scale SZ flow 
and transport model as part of the calibration process (Section 3.3.6.3). The presence of faults 
and fracture zones that are not explicitly represented in the site-scale SZ flow and transport 
model and their potential impact on groundwater flow is implicitly included in the nominal case 
through consideration of horizontal anisotropy in permeability in the fractured volcanic units 
downgradient of the potential repository. The features of the nominal case are considered 
permanent, but uncertain, characteristics of the system that are not altered by the potential 
repository or by future events. 
Release of radionuclides from the SZ to the biosphere through groundwater pumping by a 
hypothetical, future farming community is the event leading to the exposure of the critical group 
in the nominal case. The presence of the hypothetical farming community is permanent, and the 
community is located at a distance of 20 km (12.5 mi.) from the potential repository. The 
discharge of contaminated groundwater explicitly is included in the nominal case analyses to the 
extent that all radionuclide mass reaching the 20-km (12.5-mi) distance is captured in the 
groundwater supply of the farming community. Pumping by the hypothetical farming 
community is implicitly included because actual groundwater withdrawal is not simulated in the 
site-scale SZ model.

TDR-NBS-HS-000001 REV 00 ICN 01 3-146 August 2000 
Climate change explicitly is included in the nominal case of SZ flow and transport for TSPA-SR. 
Increases in SZ groundwater flux for the monsoonal and glacial-transition climate states are 
included in the analyses. The impact of a rising water table on groundwater flowpaths in the SZ 
is not explicitly included in the SZ flow and transport model for the nominal case. The 
assumption that the transport pathways simulated by the TSPA model will not be significantly 
altered by a rising water table is based on the results of the regional-scale groundwater flow 
model. This assumption requires justification through sensitivity analysis of the TSPA model. 
The release of radionuclides from the UZ to the SZ in the nominal case is by the downward 
percolation of groundwater containing radionuclides. The radionuclides may be aqueous or 
attached to colloids. Migration of radionuclides from the UZ to the SZ is assumed to occur by 
undisturbed, natural movement of recharge at the water table in the nominal case. 
Important processes relevant to radionuclide transport in the SZ that are explicitly included in the 
TSPA-SR analyses are advection in groundwater, dispersion, matrix diffusion in fractured media, 
sorption of radionuclides, colloid-facilitated transport, and radioactive decay and ingrowth. 
Advection is the natural movement of groundwater through fractured or porous media in 
response to gradients in groundwater potential. In the site-scale SZ flow and transport model, 
dispersion is explicitly simulated as a random-walk process that occurs in the longitudinal and 
transverse directions; only longitudinal dispersion is simulated in the one-1-D SZ transport 
model. Diffusion of radionuclides from fractures into the immobile groundwater of the matrix is 
simulated to occur in fractured volcanic units using an analytical solution for mass transfer in an 
idealized fracture network. Sorption of radionuclides is simulated to occur in the matrix of 
volcanic units, but is conservatively disregarded in fractures of the SZ. Colloid-facilitated 
transport is included in the transport simulations as occurring in two modes: as irreversible 
attachment of radionuclides to colloids originating from the waste, and as equilibrium attachment 
of radionuclides to colloids. Radioactive decay is simulated to occur for all radionuclides, and 
ingrowth is simulated for the daughter radionuclides in four key decay chains in the one-1-D SZ 
transport model. 
The nominal case of site-scale SZ flow and transport for the TSPA-SR includes uncertainty in 
key model parameters and conceptual models. The probabilistic analysis of uncertainty is 
implemented through Monte Carlo realizations of the SZ in a manner consistent with the TSPA 
simulations implemented with the GoldSim software code. A summary of the analysis forming 
the basis for parameter uncertainty is presented in Section 3.7.2. Alternative models of 
groundwater flux and horizontal anisotropy are included as uncertainty among six SZ 
groundwater flow fields. Uncertainty in the location of the contact between volcanic units and 
the alluvium is incorporated as geometric variability in the alluvium zone. Alternative models of 
colloid-facilitated transport are considered in the uncertainty analysis by using two coexisting 
modes of colloid-facilitated transport. 
3.7.2 Parameter Uncertainty Distributions 
In this section, the stochastic parameters and the constant-value parameters that are used in the 
site-scale SZ flow and transport model for nominal case TSPA are discussed. All of the 
parameters used, details of the basis of these parameters, and the associated assumptions are 
presented by CRWMS M&O (2000o, Section 6).

TDR-NBS-HS-000001 REV 00 ICN 01 3-147 August 2000 
In general, parameters to which the model results are sensitive, due to the importance of the 
parameter in the model and the uncertainty in the parameter value, are represented stochastically. 
Conversely, it is determined appropriate that parameters to which the model results are not 
sensitive, are sufficiently represented by constant values. This is considered appropriate because 
the results are not significantly altered by variation in those parameters. 
Groundwater Specific Discharge (Stochastic)Considerable uncertainty exists in the 
groundwater flux in the SZ along the flowpath to the hypothetical point of release to the 
biosphere. This uncertainty was quantified as a distribution of specific discharge in the volcanic 
aquifer near Yucca Mountain by the SZ expert elicitation project (CRWMS M&O 1998b). The 
results of the SZ expert elicitation are used as a quantitative basis for assigning probabilities to 
three discrete cases of groundwater flux in the SZ (low-, mean-, and high-flux). The calibrated 
site-scale SZ flow model corresponds to the mean-flux case. The low-flux case is constructed by 
downwardly scaling the values of permeability and the boundary fluxes in the site-scale SZ flow 
model by a constant factor of 10 (i.e., the value times 10). The high-flux case is constructed in a 
similar manner by scaling the values of permeability and boundary fluxes upward by a factor 
of 10. Proportional scaling of permeability values and boundary fluxes in the site-scale SZ flow 
model preserves the calibration of the model to head measurements in wells among the three flux 
cases. 
Uncertainty of Alluvium Boundary (Stochastic)Uncertainty in the geology below the water 
table exists along the inferred flowpath from the potential repository at distances of 
approximately 10 km to 20 km (6.2 to 12.5 mi.) down gradient of the potential repository. The 
location at which groundwater flow moves from fractured volcanic rocks to alluvium is of 
particular importance from the perspective of assessing the performance of the potential 
repository. This is because of differences between the fractured volcanic units and the alluvium 
in terms of groundwater flow (i.e., fracture-dominated flow versus porous-medium flow) and in 
terms of sorptive properties of the media for some radionuclides. 
The uncertainty in the location of the northern boundary of the alluvium is represented in the 
site-scale SZ flow and transport model as a polygonal region (Figure 3-29) that is assigned 
radionuclide transport properties representative of the valley-fill aquifer hydrogeologic unit. The 
alluvial uncertainty region is approximately bounded by wells on the north and south and by 
surface outcrops of volcanic units on the west. In the site-scale SZ flow and transport 
simulations for TSPA, the boundaries of the polygonal region are varied stochastically. The 
northern boundary of the uncertainty zone is varied from its most northerly position 
(Figure 3-29) to the southern boundary of the uncertainty zone. The western boundary of the 
uncertainty zone is varied from the western boundary (Figure 3-29) to the eastern-most dashed 
line. 
Future lithologic data from NCEWDP boreholes will provide constraints on the uncertainty in 
the location of the contact zone between the volcanic tuffs and the alluvium at the water table. 
Data from these additional boreholes will be evaluated and appropriately incorporated into the 
HFM and, if necessary, into the assessment of uncertainty in the stochastic analyses for TSPA.

TDR-NBS-HS-000001 REV 00 ICN 01 3-148 August 2000 
535000 540000 545000 550000 555000 560000 
UTM Easting (m) 
4050000 
4055000 
4060000 
4065000 
4070000 
4075000 
4080000 
4085000 
4090000 
UTM Northing (m) 
Source: CRWMS M&0 (2000o, Figure 2) 
NOTE: Alluvial uncertainty zone. The solid outline indicates the largest extent of the alluvial uncertainty zone. The 
dashed straight lines indicate the most easterly and the median locations of the western boundary of the 
uncertainty zone. The northern boundary of the uncertainty zone is varied from the most northerly to the 
most southerly line. The curved dashed line indicates a distance of 20-km (12.5 mi.) from the potential 
repository. Crosses represent borehole locations. 
Figure 3-29. Alluvial Uncertainty Zone

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Effective Porosity in the Alluvium (Stochastic) and Volcanic (Constant)Average linear 
groundwater velocities are used in the simulation of radionuclide transport in the site-scale SZ 
model. They are customarily calculated by dividing the volumetric flux rate of water through a 
model grid cell by the porosity. Average linear velocities are rendered more accurate when 
dead-end pores are eliminated from consideration (because they do not transmit water), resulting 
in effective porosity. Effective porosity is less than or equal to total porosity. 
Currently there are no site-specific data available for effective porosity in the alluvium. 
However, data from different sources have applicability and relevance, and some of these 
sources provide data from areas close to Fortymile Wash. The most useful data comes from a 
study of hydraulic characteristics of alluvium within the Basin and Range Province (Bedinger 
et al. 1989). This study appears relevant to the local valley-fill conditions and provides values 
for effective porosity. Additional information on the effective porosity value of the alluvium is 
provided by CRWMS M&O (1998b). 
Matrix porosity is treated as a constant parameter for 9 of the 19 SZ model hydrogeologic units 
(matrix porosity varies from one unit to another, but given a particular unit, the porosity is 
constant for all realizations). Matrix porosity is only one of several parameters involved in the 
dual-porosity simulations employed for these units. In this formulation, advection does not 
occur in the matrix. Therefore, the dual-porosity transport simulations are far more sensitive to 
other parameters, including flowing interval spacing and effective diffusion coefficient, than 
they are to matrix porosity. 
Flowing Interval SpacingThe flowing-interval parameter is a key parameter in the 
dual-porosity component of the site-scale SZ flow and transport model. A flowing interval is 
defined as a fractured zone that transmits flow, as identified through borehole flow-meter 
surveys. The analysis uses the term flowing interval spacing as opposed to fracture spacing, 
which typically is used in the literature. The term fracture spacing was not used because the data 
used identified a zone (or a flowing interval) that contains fluid-conducting fractures but does not 
distinguish how many or which fractures comprise the flowing interval. The flowing interval 
spacing is measured between the midpoints of each flowing interval. This parameter is 
documented by CRWMS M&O (2000k). 
Flowing Interval PorosityThe flowing interval porosity is defined as the volume of pore space 
in the active flow field relative to the total saturated volume of rock in fractured media. There 
are no direct measurements of the flowing interval porosity. It is considered appropriate that the 
fracture system can be represented as a series of parallel plates or intersecting parallel plates for 
theoretical estimates of flowing interval porosity for tuff deposits in the Yucca Mountain region. 
If this porosity is equivalent to the flowing interval porosity, it implies that only the fractures 
associated with flow are measured and that no flow is occurring in the matrix. 
There is uncertainty in the flowing interval porosity. Estimates of this parameter value, based on 
theoretical models, pumping tests, and tracer data, range over four orders of magnitude. The 
parallel plate model is used to estimate the lower bound of the range, and the upper bound is 
based on interpretations of pumping tests and tracer data.

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Effective Diffusion CoefficientsThe effective diffusion coefficient is variable and uncertain. 
The effective diffusion coefficient is a function of the molecular diffusion and the tortuosity of 
the material. Variability in the effective diffusion coefficient is caused by differences in 
molecular diffusion for individual contaminants. The variability in molecular diffusion occurs 
primarily due to differences in the size (atom, ion, or molecule) and charge of individual 
contaminants. The effective diffusion coefficients also vary over time and space due to 
variability (spatial) and changes (temporal) in the temperature of pore fluids, geochemical 
conditions, and tortuosity. There is additional uncertainty in the effective diffusion coefficient 
on a field scale due to the limitations of the laboratory measurements such as: limited number of 
measurements made under limited geochemical conditions, potential effects of fracture coatings 
on effective diffusion coefficient, and temperature uncertainty and variability along the transport 
pathway. A brief analysis shows that tortuosity has the greatest impact on the diffusion 
coefficient. Using the range in tortuosity and molecular diffusion coefficients, a range of 
effective diffusion coefficients is calculated. Details are provided by CRWMS M&O (2000o). 
Bulk DensityBulk density is treated as a constant parameter for all hydrogeologic units. 
Constant, in this sense, means that bulk density will vary from one unit to another, but, given a 
particular unit, the bulk density is constant for all realizations. Bulk density is only one of 
several parameters involved in the dual-porosity simulations. The dual-porosity transport 
simulations are more sensitive to flowing interval spacing and effective diffusion coefficient than 
they are to bulk density. Bulk density is used to calculate the retardation of solutes due to 
chemical adsorption in the FEHM computer code (Zyvoloski et al. 1997b). 
Sorption Coefficients (Stochastic and Constant)Sorption is the process by which dissolved 
radionuclides adhere to substrates along a transport path. Sorption occurs because of the electrochemical 
affinity between the dissolved species and the substrate. Sorption is important because 
it results in the retardation of radionuclide movement because the radionuclides spend time 
attached to immobile surfaces. 
Sorption is a function of water chemistry and the mineralogy of the rock matrix, both of which 
vary spatially, and it cannot be defined for all points in space with certainty. Not only are these 
characteristics of the system variable, but the exact path that a radionuclide takes through the 
system is uncertain. Uncertainties regarding mineralogy and chemistry implicitly are included in 
the sorption coefficient uncertainty distributions. Additionally, alternative models for sorption 
(Section 3.1.4.1) include deviations from the assumption of a linear sorption model, and these 
deviations also are represented in the uncertainty distributions. The sorption coefficient 
parameter is highly uncertain, and the probability distributions span several orders of magnitude. 
The most recent summary of data on sorption in the alluvium for neptunium, technetium, and 
iodine is presented by CRWMS M&O (2000r). Sorption coefficients for the volcanic units were 
determined for neptunium and uranium, and these values were based on sorption coefficients in 
CRWMS M&O (2000o). For the volcanic units, iodine, technetium, and carbon were classified 
as constant parameters and given sorption values of 0, indicating no retardation in the volcanic 
units. The selection of radionuclides included in the analysis is described by CRWMS M&O 
(2000o).

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Longitudinal DispersivityLongitudinal dispersion is the mixing of a solute with water that 
occurs in the direction of the flowpath. This mixing is a function of many factors, including the 
relative concentrations of the solute, the velocity pattern within the flow field, and properties of 
the host rock. An important component of dispersion is the dispersivity, a coarse measure of 
solute (mechanical) spreading properties of the rock. The dispersion process causes spreading of 
the solute in directions transverse to the flow path as well as in the longitudinal flow direction. 
Longitudinal dispersivity will be important only at the leading edge of an advancing plume, 
while transverse dispersivity is the strongest control on plume spreading and possible dilution 
(CRWMS M&O 1998b, p. LG-12). 
The dispersivities (longitudinal, vertical transverse, and horizontal transverse) are used in the 
advection-dispersion equation governing solute transport and are implemented in the site-scale 
SZ model as a stochastic parameter. In the site-scale SZ flow and transport model, longitudinal 
dispersivity is sampled in log-space for 100 realizations, and transverse dispersivities are 
calculated according to the relationship recommended by the SZ expert elicitation (CRWMS 
M&O 1998b). 
Horizontal AnisotropyThere is uncertainty in the potential for horizontal anisotropy in 
permeability over the scale of the transport path length. Winterle and La Femina (1999) 
estimated values for anisotropic transmissivity using data from the pumping tests at the C-well 
Complex. These estimates are poorly constrained and may not be representative of the 
anisotropy on the scale of the transport model. The uncertainties include differences in pumping 
test analysis methods, the fact that only a minimum number of observation wells were used, and 
uncertainty regarding the validity of assuming a homogenous effective continuum over the scale 
of the test (Winterle and La Femina 1999, p. 4-29). Given the uncertainty in anisotropy, and to 
simplify the model, the potential effects of anisotropy are bounded by setting the anisotropy ratio 
to 1 (isotropic) or 5 (anisotropic), values that are based on the C-wells data. 
Source Region DefinitionsVariations in SZ transport pathways and radionuclide transport 
times from various locations beneath the potential repository are considered by defining four 
radionuclide source regions at the water table. For any particular TSPA realization, a point at the 
water table is defined randomly within each of the four regions, and this point is used as the 
source region for simulation of radionuclide transport in the site-scale SZ flow and transport 
model. A point source of radionuclides in the SZ is appropriate for a single leaking waste 
package or for highly focused groundwater flow along a fault or fracture in the UZ. Whereas a 
more diffuse source of radionuclides at the water table may be more realistic for later times when 
numerous leaking waste packages occur, use of a point source in the SZ is a conservative 
approach that can be applied for all situations. 
Retardation of Radionuclides Irreversibly Sorbed on ColloidsRadionuclides that are 
irreversibly sorbed onto colloids are conceptualized as embedded in the colloids and are part of 
the colloidal structure. Thus, these radionuclides are unavailable for dissolution and their 
transport characteristics are the same as the transport characteristics of the colloids. The most 
important radionuclides transported by this mechanism are americium and plutonium. The 
fraction of colloids that are irreversibly sorbed is determined in the engineered barrier system 
component of TSPA-SR.

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Modeling advective and dispersive processes is handled as if colloids were solute. Matrix 
exclusion in the volcanic units is invoked because of the large size and small diffusivities of the 
colloids compared to the solute, plus the possibility of similar electrostatic charge of the colloids 
and the tuff matrix. CRWMS M&O (2000l) derived colloid transport parameters from tracer 
tests conducted in fractured tuffs at the C-wells Complex. Based on these parameters, the 
discrete cumulative probability density function for microsphere retardation factors in the 
fractured tuff is used for colloid filtration in the volcanic units (CRWMS M&O 2000o, Figure 5 
and Table 13). 
The discrete cumulative probability density function for microsphere retardation factors in the Cwells 
tracer tests was randomly sampled to obtain retardation factors for PA calculations of 
colloid transport for the volcanic units. The retardation factor is one of many parameters that are 
randomly sampled for a large number of simulations that will collectively yield probability 
distributions for radionuclide transport through the SZ. Because radionuclides are irreversibly 
sorbed to colloids, colloid-facilitated radionuclide transport in these simulations effectively is the 
product of colloid transport and the mass loading of radionuclides associated with the colloids. 
As with radionuclides that are irreversibly sorbed onto colloids in the volcanic units, filtration in 
the alluvium is modeled by applying a retardation factor to the transport parameter. CRWMS 
M&O (2000l) developed the statistical distribution of retardation in the alluvium, and this 
distribution was used for input into the site-scale SZ model for TSPA-SR (CRWMS M&O 
2000o, Figure 6 and Table 14). This distribution is sampled and used in the same manner in PA 
calculations as for colloid-facilitated transport in fractured tuffs (described in Section 3.2.4.5). 
Retardation of Radionuclides Reversibly Sorbed on ColloidsRadionuclides that are 
reversibly sorbed onto colloids are temporarily attached to the surface of colloids. Thus, these 
radionuclides are available for dissolution and their transport characteristics are a combination of 
the transport characteristics of solute and colloids. 
For TSPA-SR, radionuclides that are reversibly sorbed onto colloids are modeled using the 
reversible distribution coefficient, Kc concept (CRWMS M&O 1997, Equation 8-10, p. 8-35). 
The Kc is a distribution coefficient defined as Kc = (Kdcol)(Ccol) that represents the equilibrium 
partitioning of radionuclides between the aqueous and colloidal phases, where Kdcol is the 
sorption coefficient on colloids and Ccol is the concentration of colloids in the groundwater. The 
Kc is a function of only radionuclide sorption properties, colloid substrate properties, and colloid 
concentration; but not any properties of the immobile media through which transport occurs. 
Thus, the same Kc applies to transport of a radionuclide in the volcanic units and the alluvium. 
For TSPA-SR, the Kdcol parameter is based on the Kdcol for americium onto waste-form colloids 
(CRWMS M&O 2000f). The Ccol parameter was taken directly from CRWMS M&O (2000f) 
and is considered the maximum colloid concentration. The product of Kdcol and Ccol is a simple 
linear transformation of the Kdcol distribution from CRWMS M&O (2000f). 
3.7.3 Probabilistic Analyses 
A series of radionuclide transport simulations are performed using the site-scale SZ flow and 
transport model for TSPA. A separate model run is conducted for each realization, for each

TDR-NBS-HS-000001 REV 00 ICN 01 3-153 August 2000 
radionuclide (or class of radionuclides), and for each of the four source regions. Parameter 
vectors for stochastic parameters are generated for all 100 realizations prior to the model runs 
using the parameter-sampling algorithm in the GoldSim software code. Results of the site-scale 
SZ flow and transport model runs are archived in files for use by the convolution integral 
subroutine of the TSPA simulator (see Section 3.6.3.3.1 for a discussion of inputs to the 
convolution integral method). 
The Monte Carlo realizations of the 1-D radionuclide transport model for decay chains are 
conducted directly in the TSPA simulator with the GoldSim software code. The mass flux for 
daughter radionuclides to the biosphere is used to calculate the contribution to total radiological 
dose from each of these daughter radionuclides in a manner similar to that used for radionuclides 
in the 3-D site-scale SZ flow and transport model. 
3.7.4 Results 
The results of radionuclide transport simulations using the site-scale SZ flow and transport 
model consist of the radionuclide mass breakthrough curves for eight species or classes of 
species (CRWMS M&O 2000p, Section 6.3). Results are obtained for 100 stochastic realizations 
of the SZ system (the nominal case) and for one additional case utilizing the expected value (i.e., 
the median) for all stochastic parameters (expected-value case). These results constitute the 
library of SZ flow and transport simulations that are provided to the convolution integral 
software code in the TSPA-SR simulations. More detailed presentation of the results is given by 
CRWMS M&O (2000p, Section 6). 
Radionuclide mass breakthrough curves for the expected-value realization of the site-scale SZ 
flow and transport model were generated (Figure 3-30). The distribution of transport times in the 
SZ (from beneath the potential repository to a distance of 20 km [12.5 mi.]) for the non-sorbing 
species (e.g., carbon) generally is less than 1,000 yr.. Iodine and technetium are subject to minor 
sorption in the alluvium and have transport times of 1,000 to 2,000 yr.. For radionuclides that 
irreversibly attach to colloids (all actinides), the transport times in the SZ are somewhat less than 
10,000 yr.. Species that are subject to moderate to high sorption have simulated transport times 
of greater than 10,000 yr.. These species are categorized into three categories: moderately 
sorbing species (technetium and iodine in the alluvium, neptunium, and uranium), moderatelystrongly 
sorbing species (cesium, strontium, and palladium), and strongly sorbing species 
(americium, thorium, and plutonium). The results (Figure 3-30) are for transport from Source 
Region 1 under the northern portion of the potential repository. Results vary somewhat among 
source regions, having generally longer transport times from the northern and eastern source 
regions. The radionuclide mass breakthrough curves shown in Figure 3-30 and subsequent 
figures do not include radioactive decay, which is implemented in the convolution integral 
portion of the TSPA analyses.

TDR-NBS-HS-000001 REV 00 ICN 01 3-154 August 2000 
10 100 1000 10000 100000 1000000 
Time (years) 
0 
0.2 
0.4 
0.6 
0.8
1 
Relative Mass Flux 
C
I
Kc (actinides) 
Np 
Tc 
U
Irreversibly Sorbed, Colloid-Facilitated 
Kc (fission products) 
Source: CRWMS M&0 (2000p, Figure 11) 
NOTE: Results are shown for 20-km (12.5 mi.) distance from source Region 1. 
Figure 3-30. Simulated Unit Breakthrough Curves of Radionuclide Mass Flux for the Expected-Value 
Case

TDR-NBS-HS-000001 REV 00 ICN 01 3-155 August 2000 
The simulated radionuclide mass breakthrough curves from 100 stochastic realizations for 
carbon, technetium, neptunium, and the Kc model (Section 3.7.2) of highly sorbing radionuclides 
are shown in Figures 3-31, 3-32, 3-33, and 3-34, respectively. These results illustrate the 
variability in radionuclide transport among individual realizations and among species. Results 
for carbon indicate relatively short transport times of less than 1,000 yr. for most realizations, but 
significantly longer distributions of transport times for some realizations. Technetium is 
subjected to slight retardation in alluvium, and the resulting breakthrough curves (Figure 3-32) 
indicate somewhat longer transport times for the faster breakthrough curves relative to carbon. 
The results for neptunium (Figure 3-33) indicate that transport times are significantly longer than 
are those for carbon or technetium. Neptunium is subject to relatively minor sorption in the 
volcanic units, and to moderate sorption in alluvium. Results for colloid-facilitated transport of 
strongly sorbing radionuclides (the Kc equilibrium model) show a large degree of retardation 
relative to the other species modeled (Figure 3-34). For many realizations, the majority of the 
retardation in radionuclide migration is attributable to the alluvium. This is because of the 
relatively higher sorption and effective porosity in the alluvium in comparison to that of the 
fractured tuff. 
3.7.5 Interpretations 
These SZ flow and transport modeling results can be interpreted, in a general sense, regarding 
their importance to performance of the potential repository. Detailed and quantitative 
assessments of the importance of simulated flow and transport behavior in the SZ requires 
coupling of these results with other components of the TSPA-SR analyses and formal sensitivity 
analyses. Interpretation of the results presented here is further complicated by the fact that the 
breakthrough curves presented do not indicate the impact of radioactive decay, which is 
incorporated in the TSPA simulation by the convolution integral algorithm. Considerable 
decrease in concentration of radionuclide mass may occur for the radionuclides with half-lives 
that are short relative to their potential transport times in the SZ (e.g., carbon-14, plutonium-239, 
plutonium-240, americium-241, and americium-243). The results and interpretations for the 
1-D radionuclide transport model for radionuclide daughter products are not presented in this 
report because these simulations occur within the TSPA simulator. 
Radionuclide migration through the SZ affects total system performance in two ways. First, the 
SZ functions as a mechanism to delay the release of radionuclides to the biosphere. This delay 
potentially allows radioactive decay to reduce the release of radionuclides to the biosphere. 
Second, there may be considerable dilution of radionuclides during transport in the SZ. 
Although the dispersive processes that lead to dilution are incorporated in the site-scale SZ flow 
and transport model, a simplified approach is mandated by proposed 10 CFR 63 (64 FR 8640). 
The simplified approach is used to calculate concentrations in the water supply of the 
hypothetical farming community and negates the need to analyze in situ radionuclide 
concentrations in the SZ.

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2000 4000 6000 8000 10000 
Time (years) 
0 
0.2 
0.4 
0.6 
0.8
1 
Relative Mass Flux 
10 100 1000 10000 100000 1000000 
Median Travel Time (years) 
0
5 
10 
15 
20 
Frequency 
Source: Adapted from CRWMS M&O (2000p, Figure 12) 
NOTE: Results are shown for 20-km (12.5 mi.) from the source. 
These breakthrough curves are based on a model that is appropriately conservative for TSPA analyses and 
consequently should not be used to evaluate the expected breakthrough of radionuclides at the compliance 
boundary. 
Figure 3-31. Simulated Unit Breakthrough Curves and Histogram of Median Transport Times of Mass 
Flux for Carbon

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2000 4000 6000 8000 10000 
Time (years) 
0 
0.2 
0.4 
0.6 
0.8
1 
Relative Mass Flux 
10 100 1000 10000 100000 1000000 
Median Travel Time (years) 
0
5 
10 
15 
20 
Frequency 
Source: Adapted from CRWMS M&O (2000p, Figure 18) 
NOTE: Results are shown for 20-km (12.5 mi.) from the source. 
These breakthrough curves are based on a model that is appropriately conservative for TSPA analyses and 
consequently should not be used to evaluate the expected breakthrough of radionuclides at the compliance 
boundary. 
Figure 3-32. Simulated Unit Breakthrough Curves and Histogram of Median Transport Times of Mass 
Flux for Technetium

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20000 40000 60000 80000 100000 
Time (years) 
0 
0.2 
0.4 
0.6 
0.8
1 
Relative Mass Flux 
10 100 1000 10000 100000 1000000 
Median Travel Time (years) 
0
5 
10 
15 
20 
Frequency 
Source: Adapted from CRWMS M&O (2000p, Figure 16) 
NOTE: Results are shown for 20-km (12.5 mi.) from the source. 
These breakthrough curves are based on a model that is appropriately conservative for TSPA analyses and 
consequently should not be used to evaluate the expected breakthrough of radionuclides at the compliance 
boundary. 
Figure 3-33. Simulated Unit Breakthrough Curves and Histogram of Median Transport Times of Mass 
Flux for Neptunium

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200000 400000 600000 800000 1000000 
Time (years) 
0 
0.2 
0.4 
0.6 
0.8
1 
Relative Mass Flux 
10 100 1000 10000 100000 1000000 
Median Travel Time (years) 
0
5 
10 
15 
20 
Frequency 
Source: Adapted from CRWMS M&O (2000p, Figure 14) 
NOTE: Results are shown for 20-km (12.5 mi.) from the source. 
These breakthrough curves are based on a model that is appropriately conservative for TSPA analyses and 
consequently should not be used to evaluate the expected breakthrough of radionuclides at the compliance 
boundary. 
Figure 3-34. Simulated Unit Breakthrough Curves of Mass Flux and Histogram of Median Transport 
Times for the Kc Model of Colloid-Facilitated Transport for Highly Sorbing Radionuclides

TDR-NBS-HS-000001 REV 00 ICN 01 3-160 August 2000 
Delays in the release of radionuclides due to processes in the SZ potentially are important to 
performance of the potential repository if transport is long compared to the half-life or if 
transport is long relative to regulatory time limits. This situation applies to some of the later 
breakthrough curves for carbon-14 (half-life of 5,730 yr.; Figure 3-31). As a more extreme 
example, plutonium-240 (half-life of 6,540 yr.) that is subject to SZ transport via the Kc model 
would experience considerable attenuation due to long travel times for most of the realizations 
shown in Figure 3-34. However, several of the radionuclides that may be important contributors 
to doses (i.e., neptunium-237, iodine-129, and technetium-99), would not experience a large 
amount of decay during transport in the SZ. 
Delays in the release of radionuclides from the SZ are highly variable among the radionuclides 
that were considered. Transport times through the SZ for carbon-14, technetium-99, and 
iodine-129 primarily are less than 10,000 yr., with many realizations having transport times of 
less than 1,000 yr.. The sorption of technetium-99 and iodine-129 in the alluvial units results in 
somewhat longer transport for these radionuclides. Thus, in the context of a 10,000-yr 
regulatory standard, carbon-14, technetium-99, and iodine-129 are of concern for any early 
releases from the potential repository and UZ. Transport times for plutonium and americium 
(which are subject to transport by irreversible attachment to colloids) and uranium are near 
10,000 yr. for the expected-value realization (Figure 3-30). Neptunium-237, and other 
radionuclides that are subject to reversible attachment to colloids, have transport times in the 
range of 20,000 to 100,000 yr. in the SZ for the expected value realization, indicating that they 
are of lesser importance in the context of a 10,000-yr regulatory standard. 
For particular radionuclides, variability among realizations for SZ transport indicates a high 
degree of compound uncertainty in the SZ transport processes. Variations in the mean delivery 
times for different realizations primarily reflect the influences of sorption in the volcanic and 
alluvium units, the groundwater flux case, matrix diffusion in fractured units, effective porosity 
in the alluvium units, and fraction of the flowpath in alluvium. The impacts of uncertainty in the 
SZ transport processes, other than sorption, are visible in the breakthrough curves for carbon-14 
(Figure 3-31). Variations among realizations for sorbing radionuclides are even greater 
(Figure 3-33). 
Variations in the shapes of the radionuclide mass breakthrough curves are a function of the 
matrix diffusion process, dispersion, and to a lesser extent, the variations in the flowpath through 
the system. Relatively steep breakthrough curves with early first arrival are indicative of limited 
matrix diffusion due to large flowing interval spacing and small effective diffusion coefficient 
for the matrix. Breakthrough curves with later arrival and a plateau at relative mass flux 
near 1.0 indicate a greater degree of matrix diffusion. Realizations in which an intermediate 
degree of matrix diffusion occurs are characterized by less steep breakthrough curves with longer 
tails at the upper end of the travel time distribution. 
The radionuclide mass breakthrough curves from the stochastic realizations of SZ flow and 
transport reflect the impacts of uncertainty and conservatism in the stochastic parameters and in 
the site-scale SZ flow and transport model. As discussed in Section 1, these impacts may take 
the form of a consistent bias or may be reflected in the breadth of the simulated results. 
Certain modeling assumptions and simplifications, such as neglecting sorption on fracture walls, 
introduce a conservative bias to the simulation results. The results of this bias shifts the

TDR-NBS-HS-000001 REV 00 ICN 01 3-161 August 2000 
radionuclide mass breakthrough curves from the stochastic realizations toward shorter travel 
times relative to the alternative assumptions and more complex modeling approaches. Although 
it is difficult to quantify the integrated effects of such biases on the radionuclide transport results, 
it is believed that the overall effect on the stochastic results is not large. Consequently, the 
median behavior among the 100 stochastic realizations of radionuclide transport constitutes a 
somewhat conservative, but reasonably realistic representation of SZ system behavior. 
Conversely, the cumulative effect of stochastic parameters with broad uncertainty distributions 
results in a few simulations with much shorter radionuclide travel times through the SZ, for 
which the conservative end of uncertainty distributions have been simultaneously sampled for 
multiple parameters. Thus the realizations of radionuclide transport in the SZ that represent the 
worst system performance (i.e., shortest travel times) result from the relatively wide uncertainty 
in some stochastic parameters and not from systematic conservative bias in the site-scale SZ flow 
and transport model. 
Several stochastic parameters in the site-scale SZ flow and transport model have relatively broad 
uncertainty distributions and affect the more conservative realizations of radionuclide transport. 
The most influential of these is the parameter that determines if the low, medium, or high 
groundwater flux case is used for specific discharge in the SZ. The high groundwater flux case 
results in significantly shorter travel times. The relatively broad uncertainty in this parameter is 
primarily a reflection of the fact that multi-well pump test data are available from only one 
location (the C-wells Complex) along the SZ flowpath. Additional multi-well pump testing is 
planned at the Alluvial Tracer Complex, which will provide information on hydraulic 
conductivity (and indirectly on groundwater flux) at another location in the SZ flow system. It is 
anticipated that these additional data will narrow the uncertainty in specific discharge along the 
flowpath from the repository. Uncertainty in the transition from groundwater flow in fractured 
tuff to flow in alluvium also results in some of the shorter radionuclide travel times shown in the 
results. Lithologic data from additional boreholes being drilled under the NCEWDP will reduce 
the breadth of the alluvial uncertainty zone that is utilized in the stochastic realizations of SZ 
flow and transport. Stochastic parameters related to matrix diffusion, such as flowing interval 
spacing, effective diffusion coefficient, and fracture porosity, also have relatively broad 
uncertainty distributions that contribute to the more conservative realizations of radionuclide 
transport. In summary, the stochastic realizations of radionuclide transport that exhibit 
apparently overly conservative, short travel times are the result of very broad uncertainty 
distributions for key underlying stochastic parameters. Additional data or reinterpretation of data 
that narrows the uncertainty distributions for these key parameters may reduce the probability of 
obtaining these conservative results. 
3.8 SUMMARY OF OTHER VIEWS AND ALTERNATIVE MODELS 
The main alternative models dealing with the SZ flow and transport system pertain to postulated 
rises in the water table due to seismic, hydrothermal, or a combination of both processes 
(Section 3.8.1), and to alternate views of SZ flow in the immediate vicinity of the potential 
repository (Section 3.8.2).

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3.8.1 Disruptive Events and Rises in the Water Table 
Field observations at Yucca Mountain have been made of surficial and fault-filling calcite and 
opaline-silica. The commonly accepted view of the origin of these deposits, which are known as 
caliche or calcrete and are ubiquitous in the desert Southwest, is that they formed by pedogenic 
(soil-forming) processes from downward-flowing water. However, an alternative interpretation, 
the upwelling water model, has been proposed. Based on interpretations of the calcite and 
opaline-silica mineral deposits, it was proposed that changes in stress in the crust of the earth 
(caused by earthquakes or recurring hydrothermal activity) had repeatedly forced groundwater 
up to the land surface such that the water table intermittently and repeatedly rose to, and above, 
the elevation of the potential repository horizon. This upwelled groundwater, then, is thought to 
have left the mineral deposits. Discussions of this issue and its history are provided in CRWMS 
M&O (1998e, Section 3.4.3.4), DOE (1998c, Section 2.2.1.3), and NRC (1999a, 
Section 4.5.2.13). 
The upwelling water model has been evaluated by the following reviewers who are external to 
the DOE program: 
 A five-member peer review panel composed of outside reviewers convened by the YMP 
(Powers et al. 1991; Archambeau and Price 1991). 
 A U.S. Geological Survey (USGS) reviewer at the request of one of the members of the 
five-member panel (Evernden 1992). 
 A 17-member panel established by the National Academy of Sciences National 
Research Council (NAS-NRC) at the request of the DOE (National Research 
Council 1992). 
 U.S. Nuclear Regulatory Commission contractors at the Center for Nuclear Waste 
Regulatory Analyses (CNWRA) (Leslie 1994). 
 An expert elicitation panel convened by the DOE to consider SZ flow and transport and 
the topic of disruptive events and a rise in the water table (CRWMS M&O 1998b, 
Section 3.2.9.3). One member of the panel, Tsang, is associated with the Yucca 
Mountain Project. 
 The U.S. Nuclear Waste Technical Review Board (NWTRB) and a panel convened by 
the NWTRB to review documents submitted to the NWTRB in 1997 in support of the 
upwelling water model (Cohon 1998a). 
Brief discussions of these reviews are provided below. Additionally, scientists associated with 
the YMP have reviewed reports that support the alternative model. Stuckless et al. (1998) 
provided comments on a document included in the 1997 submission to the NWTRB, and 
Hill et al. (1995) and Whelan (1998) provided comments on a recent draft report by 
Dublyansky (1998).

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3.8.1.1 Five-Member Peer Review 
A five-member external panel was formed by the DOE to review unpublished reports regarding 
the upwelling water model. Two panel members (Archambeau and Price) were chosen by the 
author of the reports, and three members (Powers, Rudnicki, and Smith) were selected by the 
DOE. Differing opinions developed within the panel, leading to the preparation of minority 
(Archambeau and Price 1991) and majority (Powers et al. 1991) reports. 
3.8.1.1.1 Majority Report 
The majority conclusions included (Powers et al. 1991, pp. S-1 to S-3): 
 The proposal develops neither an adequate theoretical basis for the mechanisms and 
consequences, nor a body of evidence that is sufficiently supportive, to require further 
investigations of the proposed concepts. 
 The essential concept (i.e., faults suddenly open, fill with water, close, and force the 
water to the surface) has not been established, and it is not supported by experience or 
other evidence. 
 The database supporting the stress distribution is very weak. 
 Calculations presented in the report are inadequate to support claims about the 
magnitudes and volumes of fluid movement that could lead to a tectonically-induced rise 
of the water table. 
 There is no convincing evidence to support the claim that the lithostratigraphic 
framework can be relegated to a role of minor or no importance in influencing rates and 
patterns of groundwater flow or when interpreting field data. 
 Surficial deposits cited as evidence of upwelling fluids are consistent in isotopic and 
physical character with surficial, pedogenic processes. Isotopically, these deposits are 
not consistent with known groundwater in the Yucca Mountain area. The majority sees 
no reason to reject surficial sources of calcite and silica to account for these deposits. 
 A major flaw in the reports is that the proposals have not been cast in any testable forms. 
The panel majority also had concerns with fundamental elements of the proposed model that 
purport to explain the linkage between the tectonic and hydrologic systems. 
3.8.1.1.2 Minority Report 
The minority state that the upwelling water model appears to be a good working model for 
processes at Yucca Mountain, including water flow and mineral deposition, and the model 
cannot be rejected as incompatible with current observations or theory (Archambeau and 
Price 1991).

TDR-NBS-HS-000001 REV 00 ICN 01 3-164 August 2000 
The views of the minority are outlined below, however, it should be noted that the minority 
report has an Appendix titled A Consensus Statement of the Review Panel Evaluation of Key 
Physical Properties in the Szymanski Model and Recommendation for Additional Investigative 
Studies (Archambeau and Price 1991, Appendix 1). Multiple places in the minority report also 
refer to this consensus statement. Section IX of the minority report, Evaluation of the 
Szymanski CHT Model: September 1990 Consensus Statements of the Entire Panel contains 
excerpted statements from the text of Appendix 1, and the claim is made that these statements 
represent the shared view of all the members (Archambeau and Price 1991, p. 121). However, 
in a letter dated 12/9/1991, the Chairman of the panel wrote: The appendix in the minority 
report is not, and should not be taken as, any statement of consensus for the panel about our 
assessment of the validity of the ideas presented by Szymanski (Powers 1991). Given this 
statement by the Chairman, only the Minority Group evaluation from Section X (Archambeau 
and Price 1991, pp. 125 to 128) is presented and quoted here: 
The physical and geologic field evidence relating to observed calcretes and 
calcite-opal veins at the surface and at depth, such as relationships to faulting and 
hydrothermal alterations, support the interpretation of deposition by up-welling 
water from considerable depth. This finding is consistent with the Cyclic 
Hydro-Tectonic model proposed by Szymanski. The geologic observations are 
not, in several particulars, consistent with a pedogenic, descending water origin 
for most of these mineral deposits. 
The physical processes and mechanisms incorporated in Szymanski's model for 
an interactive hydro-tectonic system at Yucca Mountain are meaningful and 
appear appropriate; and can provide a basis for prediction. The dynamical 
interactions are, however, highly non-linear and quantitative predictions based on 
analytical formulations and numerical modeling are very approximate and 
incomplete, in that only some of the phenomena inherent in the model can 
presently be incorporated in a computational program. Nevertheless, in principle 
Szymanski's model can be described in terms of a set of coupled integraldifferential 
equations that analytically express the dynamics of such a system. In 
this regard, a preliminary computation, designed to simulate a short time history 
of seismic pumping in a fractured medium following an earthquake, did predict 
significant water and gas flows that could be indicative of those to be expected at 
Yucca Mountain. However, no other quantitative aspects of the model, such as 
long term convection and chemical deposition, could be evaluated. Nevertheless, 
while only preliminary, the quantitative analysis so far accomplished does support 
at least one aspect of the Szymanski model; that is the possibility of pressure 
driven water and gas flows, from upper to mid-crustal depths, following a large 
earthquake. 
Field observations as well as modeling calculations indicate that gas-assisted 
(CO2) flows of high energy may occur in some circumstances. In particular, it is 
concluded that such flows have occurred at Yucca Mountain in the past and that 
there is a reasonably high probability that they could also occur in the future. 
This inference is beyond those drawn by Szymanski and specifically incorporated 
in his model, but nevertheless is compatible with it.

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The isotopic and mineralogic characteristics of the calcite-opal vein deposits at 
the surface and at depth are similar and imply a common origin of deposition. 
Owing to sealing and near surface erosional infill, pervasive pedogenic 
descending-water deposition at depth is highly unlikely. Consequently, the 
numerous veins at depth are almost certainly due to up-welling water from the 
Precambrian and the Paleozoic limestone formations beneath Yucca Mountain 
and, by inference based on isotopic similarity, those exposed at the surface should 
also have this origin as well. 
The isotopic characteristics of the calcite-opal veins at the surface at Yucca 
Mountain, in particular those at Trench 14, appear to be consistent with upwelling 
water from depth, from 2 to 5 km or deeper, mixed with the shallower 
water from the tuff formations. If the calcite encrustations on cobbles and soil 
calcretes used as a pedogenic standard are indeed rain water evaporation deposits, 
as assumed in the study by Quade and Cerling, then the oxygen-carbon isotopic 
data for Trench 14 also appears to be consistent with a descending-water 
pedogenic origin. However, if the latter assumption is not true, then a 
pedogenic model origin is doubtful and deep up-welling water deposition is 
preferred. If the assumption is true, then both origins can apparently be in 
agreement with the data and cannot be differentiated on the basis of C-O isotopic 
data alone. 
The isotopic characteristics of the vein calcites at Trench 14 appear consistent 
with a source of deep up-welling water as inferred by Szymanski through his 
demonstration of the correlation with the water from current up-welling source 
regions' in the area of the Nevada Test Site. The lack of correlation between 
calcite isotopes at Trench 14 and those from the shallow water currently beneath 
Yucca Mountain, as inferred by Stuckless et. al., can only enforce the conclusion 
that young meteoric water from shallow depths was not involved, or was only a 
minor constituent of the water depositing these vein calcites. This conclusion 
clearly does not negate the possibility of the source being from up-welling water 
from great depth. 
Stuckless et al. assumed a pedogenic model origin for a number of calcite deposits 
that they use as a standard. If these are wholly or partly of up-welling origin, then 
their comparison of these deposits with Trench 14 vein carbonates could force 
them to a different conclusion; namely that up-welling water from large depths 
could be responsible for the Trench 14 vein carbonates. 
An up-welling, deep source for the water that deposited vein calcites and silica at 
Yucca Mountain is quite possible based on Szymanski's isotope correlations and 
is permissible on the basis of the Stuckless et al. study. This possibility is also 
supported by the inference, by Whelan and Stuckless, of large water table 
elevation changes at Yucca Mountain in the past; to as much as 500 m above and 
300 m below the present level.

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Age dates for the deposition of calcretes and calcite-opal veins at Yucca Mountain 
are somewhat uncertain, so that a highly confident assessment of when the most 
recent up-welling has occurred, and how frequently it has occurred in the past, is 
not possible at present. Indirect lines of evidence and inference lead us to believe, 
however, that the young ages obtained for some veins and calcretes are probably 
representative of true depositional ages, but we cannot absolutely rule out 
different, possibly older, ages. 
Based on all lines of assessment, the model proposed by Szymanski appears to be 
a good working model for interactive dynamical processes at Yucca Mountain, 
including water flow and mineral deposition, and certainly is not one that can be 
rejected as incompatible with current observations or theory. Indeed, it is the only 
model that is self consistent and compatible with the field observations. 
3.8.1.2 Evernden Review 
C.D. Archambeau (a member of the five member panel and co-author of the minority report 
[Archambeau and Price 1991]) requested to have J.F. Evernden (USGS) evaluate the credibility 
of the minority report. Evernden evaluated the report based on available data and field 
excursions, and compared his conclusions to those of the minority report. In his introduction, 
Evernden (1992, p. 2) stated that he disagreed with almost everything in the minority report. 
Regarding the Minority Report and the proposed upwelling model, Evernden (1992) concludes: 
I find little that I can accept in the interpretations of extant data given in the 
Minority Report and even less in their proposed model of past or potential future 
events (Evernden 1992, p. 60). 
The minority Report asserts that several lines of evidence refute the idea of a 
pedogenic source for the Trench 14 calcretes. I have shown that, in every case, 
they are in error in their interpretations and conclusions. Their errors appear to 
arise out of an inadequate background in the requisite geologic disciplines 
(Evernden 1992, p. 60). 
Their appeals to such exotic processes as seismic pumping associated with 
repetitive major earthquakes along the faulted west side of Yucca Mountain and 
convection of hot groundwater induced by abnormal rates of heat flow under 
Yucca Mountain and environs are appeals unsupported by data, in fact denied by 
data (Evernden 1992, p. 60). 
Contrary to their assertion, their model is not a model at all, simply a set of 
unsupported and unsupportable assertions (Evernden 1992, p. 60). 
3.8.1.3 National Research Council Evaluation 
Detailed discussions of the evidence relating to the issue of groundwater upwelling in the Yucca 
Mountain area are presented a report by National Research Council (1992). The panel 
concluded:

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The panels overall conclusion was that none of the evidence cited as proof of 
ground-water upwelling in and around Yucca Mountain could reasonably be 
attributed to that process. The preponderance of features ascribed to ascending 
water clearly: (1) were related to the much older (13-10 million years old [Ma]) 
volcanic eruptive process that produced the rocks (ash-flow tuffs) in which the 
features appear, (2) contained contradictions or inconsistencies that made an 
upwelling ground-water origin geologically impossible or unreasonable, or (3) 
were classic examples of arid soil characteristics recognized world-wide (National 
Research Council 1992, p. 3). 
3.8.1.4 Saturated Zone Flow and Transport Expert Elicitation Panel 
The panel members were asked for their judgments regarding the potential magnitude of water 
table changes that might accompany disruptive events such as earthquakes, as well as the 
potential for long-lived or permanent changes in water table (CRWMS M&O 1998b). All of the 
experts addressing this issue concluded that changes to the water table associated with 
earthquakes will not be important and will not be long-lived. Freeze and others note that 
earthquakes can perturb the stress field and can produce short-lived spikes of increased fluid 
pressure in confined aquifers. Because these events do not cause a large transfer of water, Freeze 
reasons, they are not likely to lead to large or long-lived changes in water table elevation. 
Neuman notes that fluctuations from earthquakes tend to be rapid, short lived, and on the order 
of centimeters to meters; and Tsang concludes that the expected changes will be transitory in the 
time-frame of the potential repository (CRWMS M&O 1998b, Section 3.2.9.3). It should be 
noted that Tsang was and is associated with the Yucca Mountain Project. 
3.8.1.5 Center for Nuclear Waste Regulatory Analyses Evaluation 
The CNWRA completed a systematic analysis of the logic used to conclude that at Yucca 
Mountain hydrothermal and auxiliary gas-assisted processes pose an important hazard for time 
spans measured in 10,000 yr. (Leslie 1994). The CNWRA evaluated the validity of the 
argument, the premises used to support the conclusions of the arguments, and the geological 
evidence supporting each individual premise. Leslie (1994) identified several flawed premises 
that were key components to the overall argument presented by Szymanski (1992). Critical 
evaluation of the site data and the logic used in Szymanski (1992) indicates that there is 
inadequate documentation to support the assertions (Leslie 1994). 
3.8.1.6 Nuclear Waste Technical Review Board Review 
The NWTRB and its consultants reviewed recent reports supporting the upwelling water model 
and reached three conclusions (Cohon 1998a, pp. 2 to 3 of transmittal letter), which are quoted 
below: 
The material reviewed by the Board does not make a credible case for the 
assertion that there has been ongoing, intermittent hydrothermal activity at Yucca 
Mountain or that large earthquake-induced changes in the water table are likely at 
Yucca Mountain. This material does not significantly affect the conclusions of 
the 1992 NAS report (National Research Council 1992).

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There are several areas where additional research could be used to further 
evaluate the hypotheses of ongoing, intermittent hydrothermal activity and large 
earthquake-induced changes in the water table at Yucca Mountain. However, 
because of the lack of any substantive evidence supporting either of these 
hypotheses, the Board views additional research on these issues, if not already 
carried out, as generally having a lower priority than more important issues in the 
evaluation of repository performance. 
However, some fluid inclusions found in mineral deposits at Yucca Mountain do 
provide direct evidence of the past presence of fluids at elevated temperatures (at 
least 72C) in the vicinity of the proposed repository. This could be an indicator 
of some degree of past hydrothermal activity. The critical question is, At what 
time in the past were such fluids present? If fluids at elevated temperatures were 
present less than 100,000 yr. ago, as some of the reviewed reports claim, this 
could lend credence to the hypothesis of ongoing hydrothermal activity at Yucca 
Mountain. On the other hand, if these fluids were present around 10,000,000 yr. 
ago or earlier, they could be associated with volcanic events related to the original 
formation of Yucca Mountain and would have no bearing on the hypotheses of 
ongoing hydrothermal activity. The Board believes that the ages of fluid 
inclusions should be determined. A joint program between federal and State of 
Nevada scientists for collecting, dating, and analyzing fluid inclusions would be 
one way to help eliminate some of the past disagreements associated with sample 
collection and handling. 
In addition to these conclusions, the NWTRB evaluated the quality of the data. Based on these 
evaluations, the NWTRB noted that (Cohon 1998a, pp. 2 to 3): 
Although the data generally appear to be of good quality, often there is poor or 
insufficient documentation of important details. Examples of this deficiency 
include the lack of detailed information on the location of the study of Stagecoach 
Road fault stable isotopes; the lack of clear information on the locations of the 
fluid-inclusion sample sites in the underground ESF; the lack of adequate 
description of a proposed hydrothermal eruption breccia; and the lack of a clear 
and persuasive description of how the critically important ages of fluid inclusions 
were determined. 
Far more serious are the problems associated with the interpretation of the data, 
which is the critical part of many scientific analyses. Examples include the very 
tenuous fits of lines to scattered small data sets showing presumed stable-isotope 
changes with depth and with distance; photographs allegedly demonstrating the 
hydrothermal origin of zircon that do not show the zircons growing on vein walls 
or fractures, the sort of evidence that would be required if this interpretation were 
true; the implication that relatively unimportant differences in chemical analyses 
of rocks imply large-scale alteration by hydrothermal processes (metasomatism); 
and the assumption that all fluid inclusions at depth were formed at the same time, 
permitting the determination of a paleogeothermal gradient although their own 
very limited data show otherwise.

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The NWTRB also evaluated how much credence the data lend to the hypothesis of ongoing, 
intermittent hydrothermal activity at Yucca Mountain. Based on these evaluations, the NWTRB 
(Cohon 1998a) noted that: 
Little credence is lent by the data to the hypothesis of ongoing, intermittent 
hydrothermal activity at Yucca Mountain. With the possible exception of the 
fluid inclusions (discussed below), the data presented do not pose a serious 
challenge either to findings reached in the 1992 NAS report or to the reasoning 
behind those findings. Above all, the reports can be criticized because of the 
pervasive presence of unsubstantiated interpretations, examples of which are 
given above). This is the primary reason for the criticism by the Boards 
consultants of the quality of the reports they were asked to review. The 
consultants cited the  apparent selective use of information  with nonsupporting 
data being ignored. (insert ellipse); documents that are  frustrating 
and confusing to review and that rely heavily on unpublished documents, 
which are difficult to obtain and which are loosely interpreted, sometimes with a 
misleading effect. Important dissenting information  is not mentioned or 
discussed. In many instances, these documents make conclusions that are so 
strong as to seem divorced from the preceding data and discussion. (insert 
ellipse); reports that are  full of unsubstantiated conclusions, errors of fact and 
ex cathedra statements not supported by any, or dubious, evidence. (insert 
ellipse); and  full of non-sequiturs, special pleadings, reliance on dubious 
conclusions reported in the earlier reports and assertions presented as proofs. 
3.8.1.7 Conclusions 
The upwelling water model (Szymanski 1992) has been repeatedly reviewed by independent 
external panels. With the exception of the of the authors of the minority report (Archambeau and 
Price 1991), who were chosen for the review by the proponent of the upwelling water model, 
multiple reviewers and review panels have found little or no basis to support it. Evernden (1992, 
p. 60) noted that the reports in support of the upwelling model include errors in their 
interpretations and conclusions. Leslie (1994) found that the reports provide inadequate 
documentation of supporting assertions and that key components of the model are based on 
flawed premises. The NWTRB states that the reports supporting the upwelling model contain 
unsubstantiated conclusions; errors of fact and statements supported by, at best, dubious 
evidence; non-sequiturs; special pleadings; and assertions presented as proofs; and that newer 
reports rely on dubious conclusions presented in earlier reports (Cohon 1998a, p. 3). 
In response to the NWTRB recommendation, a DOE-funded investigation of fluid inclusions has 
been initiated and is ongoing at the University of Nevada-Las Vegas under the oversight of DOE 
and the State of Nevada. 
3.8.2 Saturated Zone Flow at Yucca Mountain 
Lehman and Brown (1996, pp. 24 to 36) use water-table temperature data from the USGS (Sass 
et al. 1988), together with USGS data on the response of SZ water levels to earthquakes, to 
develop an alternative conceptual model of the SZ that has the following main features:

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 Considerable groundwater flows from west to east across the Solitario Canyon fault. 
 Fault and fracture zones act as major flow paths in the SZ. 
 A redrawn SZ potentiometric contour map is used as the foundation for the emphasis on 
fault and fracture flow. 
 The hydrologic system may change unpredictably due to local earthquakes that affect 
fault and fracture permeability. 
Using the above features, the model is used to simulate groundwater flows and temperature 
distributions at the water table. Taking each of the features separately, the positions of the YMP 
and Lehman and Brown are compared in the following sections. 
3.8.2.1 Relationship of the Solitario Canyon Fault Zone to Saturated Zone Flow System 
The position of the YMP with respect to the Solitario Canyon fault zone is described by Luckey 
et al. (1996, p. 25). The Solitario Canyon fault is described as the eastern boundary of a distinct 
flow domain. In this respect, Lehman and Brown (1996) and Luckey et al. (1996) are in 
agreement. Luckey et al. (1996, p. 26) and Lehman and Brown (1996) also agree regarding 
upwelling of warm water along the fault from deeper aquifers. The only important area of 
disagreement involves groundwater flow across the fault. Lehman and Brown (1996, Figure 17) 
hypothesize a large groundwater flux across the Solitario Canyon fault, while Luckey et al. 
(1996, p. 25) indicate that the fault generally acts as a barrier to groundwater flow, although 
some flow undoubtedly crosses the fault because of the large difference of hydraulic potential 
(45 m [148 ft]) across it. Luckey et al. (1996, p. 25) further suggest that most of the groundwater 
west of the fault flows to the south, either along the fault or through an aquifer in Crater Flat. 
3.8.2.2 Faults and Fractures as Major Saturated Zone Flow Paths 
Lehman and Brown (1996, p. 28) present a model where recharge is focused along fault and 
fracture zones in the SZ and UZ. This alternative differs from early conceptual models 
(Montazer and Wilson 1984) in which most recharge was via matrix flow in the UZ. 
The conceptual model currently used for UZ and SZ flow and transport modeling (DOE 1998a) 
proposes that groundwater flow occurs in the UZ almost entirely within well-connected fractures 
in welded tuff, and that flow occurs only partly in the matrix of the bedded tuffs (i.e., a model 
that is based on fracture flow data available from the ESF). In this respect the models of Lehman 
and Brown (1996, p. 28, 30) and DOE (1998a) are in agreement. 
3.8.2.3 Revised Potentiometric Surface Map 
Lehman and Brown (1996, Figure 16) present a revised potentiometric surface map based on 
data from Ervin et al. (1994), but which differs from the potentiometric map presented by Ervin 
et al. (1994, Figure 1) with respect to the 730 m (2,395 ft) contour in the area east of the Solitario 
Canyon fault (the small hydraulic gradient area). Ervin et al. (1994, Figure 1) show a smooth 
730 m (2,395 ft) contour trending generally north to south, more or less parallel to adjacent 
contours, with a 0.25 m (0.8 ft) interval. Lehman and Brown (1996, Figure 16) indicate a series

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of embayments or potentiometric lows in the 730 m (2,395 ft) contour that are coincident with 
northwest trending shear zones along the eastern flank of the Yucca Mountain. 
3.8.2.4 Effects of Earthquakes on Saturated Zone Flow Systems 
Lehman and Brown (1996, pp. 26 to 30) present a brief description of the Landers (California), 
Big Bear (California), and Little Skull Mountain (Nevada) earthquakes of June 28-29, 1992, and 
discuss water-level changes related to these earthquakes as reported by OBrien (1993). Some 
wells near Yucca Mountain showed increases in water levels in response to the earthquakes, 
while water levels in other wells decreased. Lehman and Brown interpret these responses to 
possibly indicate that some regions experienced compressive strain, while other areas 
experienced tensile strain. They also offer an alternative interpretation involving changes in 
fracture aperture. 
3.8.2.5 Simulation of Groundwater Flow and Temperature Distribution at the Water 
Table 
Lehman and Brown (1996, p. 32) present a brief description of a preliminary 2-D numerical 
model of the SZ flow system at Yucca Mountain. The model consists of 396 elements in a 
rectangular grid, and the system is divided into 10 domains to which specific values are assigned 
for porosity, permeability, and element volume (Lehman and Brown 1996, Table 4, Figure 18). 
Lehman and Brown (1996) used a computer code to model their scenario, calibrated it against 
water-level measurements via adjustments in permeability values, and obtained good agreement 
between observed water levels and the model solutions. Lehman and Brown (1996) state that the 
model poorly predicted temperature patterns in the groundwater. Lehman and Brown conclude 
that the future use of a 3-D model which includes a representation of vertical heat flow along 
fractures is warranted. 
3.8.2.6 Conclusions 
The conceptual model proposed by Lehman and Brown (1996) has much in common with the 
conceptual models represented by the site-scale SZ flow and transport model. Each of the 
conceptual models recognize that flow in volcanic rocks occurs primarily in fractures and that 
structural features have a strong influence on groundwater flow. Lehman and Browns 
conceptual model indicates a flow path away from the potential repository that does not pass 
through valley-fill deposits in the Amargosa Valley. The TSPA-SR model considers such a flow 
path as being feasible, but considers a path through the fill deposits to be much more likely. This 
difference is important because transport of radionuclides through the valley-fill deposits will be 
much slower than transport through fractured volcanic rocks. The conceptual model of Lehman 
and Brown also holds that future earthquakes might cause adjustments in the hydrologic system 
including rapid changes in the water table elevation, altered flow patterns, and adjustments in 
flow velocities. In short, Lehman and Brown (1996) criticize the treatment of the SZ in past 
TSPA models for not considering a broad enough range of conceptual models, and for not 
accounting for a sufficient level of complexity in the natural system. This latter concern has 
been addressed in the current SZ flow and transport model developed for the TSPA-SR by 
including additional geologic features in the model.

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4. RELATIONSHIP TO U.S. NUCLEAR REGULATORY COMMISSION ISSUE 
RESOLUTION STATUS REPORTS 
4.1 SUMMARY OF THE KEY TECHNICAL ISSUES 
As part of the review of site characterization activities, the U.S. Nuclear Regulatory Commission 
(NRC) has undertaken an ongoing review of information on Yucca Mountain site 
characterization activities to allow early identification and resolution of potential licensing 
issues. The principal means of achieving this goal is through informal, prelicensing consultation 
with the U.S. Department of Energy (DOE). By obtaining input and striving for consensus from 
the technical community, interested parties, and other groups on such issues, this approach 
reduces the number of, and better defines, issues that may be in dispute during the NRC licensing 
review. 
The NRC has focused prelicensing issue resolution on topics most critical to the postclosure 
performance of the potential geologic repository. These topics are called Key Technical Issues 
(KTIs) and each KTI is subdivided into a number of subissues. The KTIs are: 
 Activities Related to Development of the Environmental Protection Agency Standard 
 Container Lifetime and Source Term 
 Evolution of the Near-field Environment 
 Igneous Activity 
 Radionuclide Transport 
 Repository Design and Thermal Mechanical Effects 
 Structural Deformation and Seismicity 
 Thermal Effects on Flow 
 Total System Performance Assessment (TSPA) and Integration 
 Unsaturated and Saturated Flow under Isothermal Conditions. 
Identifying KTIs, integrating their activities into a risk informed approach, and evaluating their 
importance for postclosure performance helps ensure that the NRC is focused on technical 
uncertainties that will have the greatest affect on the assessment of repository safety. 
Early feedback among all parties is essential to define what is known, what is not known, and 
where additional information is likely to make an important difference in the understanding of 
future repository safety. The Issue Resolution Status Reports (IRSRs) are the primary 
mechanism used by the NRC to provide feedback to the DOE on the status of the KTI subissues. 
IRSRs focus on NRC acceptance criteria for issue resolution and the status of issue resolution, 
including areas of agreement, comments, and questions. Open meetings and technical exchanges 
between the NRC and the DOE provide additional opportunities to discuss issue resolution, 
identify areas of agreement and disagreement, and develop plans to resolve disagreements. 
KTIs are subdivided into a number of subissues. For most subissues, the NRC staff has 
identified technical acceptance criteria that the NRC may use to evaluate the adequacy of 
information related to the KTIs. The NRC also has identified two cross-cutting programmatic 
criteria that apply to all IRSRs related to the implementation of the Quality Assurance (QA) 
Program and the expert elicitation. The following sections provide a summary level discussion

TDR-NBS-HS-000001 REV 00 ICN 01 4-2 August 2000 
of the KTIs by subissue (Section 4.2) and a discussion of the specific NRC acceptance criteria 
(Section 4.3). Details of the IRSR technical acceptance criteria, and how and where they are 
addressed in this Process Model Report (PMR), are presented in Appendix B. 
4.2 RELATIONSHIP OF THE SATURATED ZONE FLOW AND TRANSPORT 
PROCESS MODEL REPORT TO THE KEY TECHNICAL ISSUES 
The saturated zone (SZ) PMR provides technical analyses that relate to four of the KTIs and their 
associated IRSRs. These four KTIs and their subissues are presented in Table 4-1. The KTIs 
and subissues that relate directly to the SZ PMR are discussed in the following sections. 
Table 4-1. Issue Resolution Status Report and Key Technical Issues Related to the Saturated Zone 
Process Model Report 
NRC Key Technical Issues Subissues 
Radionuclide Transport 
Radionuclide transport through porous rock 
Radionuclide transport through alluviuma 
Radionuclide transport through fractured rocka 
Nuclear criticality in the far-fielda 
Structural Deformation and Seismicity 
Faulting 
Seismicity 
Fracturing and structural framework of the geologic settinga 
Tectonic framework of the geologic setting 
Total System Performance Assessment 
(TSPA) and Integration 
System description and demonstration of multiple barriersa 
Model abstractiona 
Scenario Analysisa 
Demonstration of overall performance objective 
Unsaturated and Saturated Flow Under 
Isothermal Conditions 
Climatic Change 
Hydrological effects of climate changea 
Present-day shallow groundwater infiltration 
Deep percolation (present and future) 
Saturated zone ambient flow conditions and dilution processesa 
Matrix diffusiona 
NOTES: Programmatic criteria (QA and use of expert elicitations) apply to all subissues. 
a These subissues directly relate to the SZ PMR. 
4.2.1 Radionuclide Transport 
The primary objective of the Radionuclide Transport KTI is to evaluate the processes that may 
affect the transport of radionuclides from the potential repository to the biosphere (NRC 1999b). 
The key elements of this KTI are retardation of radionuclides in the fractures and matrix of the 
unsaturated zone (UZ), and retardation in the fractured rock and alluvium of the SZ (NRC 
1999b, p. 5). The IRSR focuses on sorption and other chemical processes that affect transport 
and colloid-facilitated transport. Two mechanisms that can reduce radionuclide concentrations 
along flow paths (matrix diffusion and dilution) are evaluated separately in the IRSR/KTI for 
Unsaturated and Saturated Flow under Isothermal Conditions (Section 4.2.4). Resolution of the 
KTI for radionuclide transport requires adequate characterization of the physical and chemical 
processes that affect radionuclide transport (NRC 1999b, p. 3).

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Three of the subissues for this KTI relate to the SZ PMR, as described in the following 
subsections. The UZ PMR (CRWMS M&O 2000b) also provides information relevant to 
radionuclide transport. 
4.2.1.1 Radionuclide Transport Through Alluvium 
This subissue focuses on consideration of the flow paths through the alluvium, the alluvial 
materials encountered by radionuclides transported from the site through fractured rock into the 
alluvium, and the processes affecting transport (NRC 1999b, p. 3). 
Few data are available for this subissue and considerable information will be provided from the 
Nye County Early Warning Drilling Program (NRC 1999b, pp. 93 to 94). NRC indicates 
resolution of this issue will await the collection of data from the Nye County drilling program. 
Fluid flow in the alluvium is likely to be well represented using a porous continuum conceptual 
model. Data to quantify the alluvial portion of the flow path are sparse, and hydrologic 
parameters used in numerical models should be considered to be bounding (Section 3.2.4.1.2). 
Transport of sorbing solutes in porous media not controlled by fractures is a subject that has been 
well studied. Sorption coefficients for alluvium from the Nye County Drilling Program have 
been measured for a few key radionuclides; for the remaining radionuclides, sorption coefficients 
have been estimated based on the corresponding values measured for crushed tuff. 
The conceptual model for colloid-facilitated transport in the alluvium is essentially the same as 
in fractured tuffs in that colloid transport is assumed to occur only in advective water 
(no diffusion into stagnant water or into grains) and colloid attachment and detachment onto 
alluvial surfaces are described by first-order rate expressions (Section 3.2.4.5.3). Because no 
site-specific data for colloid transport in the alluvium are available, filtration theory and literature 
data are used to obtain distributions or bounds for attachment and detachment rate constants. 
4.2.1.2 Radionuclide Transport Through Fractured Rock 
This subissue evaluates radionuclide transport in fractured rock where there is a potential for 
preferential pathways for transport and limited radionuclide-rock interactions (NRC 1999b, p. 3). 
The transport characteristics of the Yucca Mountain site must be adequately estimated and 
radionuclide transport through fractured rocks must be appropriately considered in assessments 
of performance of the potential repository. 
The site-scale SZ flow and transport model is a three-dimensional, site-scale numerical model 
that simulates groundwater flow and radionuclide transport from the water table beneath the 
potential repository to the accessible environment using an equivalent continuum formulation 
and implicit fault and fracture representation to capture flow through fracture and matrix. 
Numerous hydrologic features corresponding to faults and geologic zones are explicitly 
incorporated into the site-scale SZ flow and transport model as part of the model building 
process (Section 3.2.1). The presence of faults and fracture zones that are not explicitly 
represented in the site-scale SZ flow and transport model, and their potential impact on 
groundwater flow, is implicitly included through consideration of horizontal anisotropy in

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permeability in the fractured volcanic units along the SZ flow path from Yucca Mountain. These 
features are considered to be permanent, but uncertain, characteristics of the system that are not 
altered by the potential repository or by future events. 
Important processes relevant to radionuclide transport in the SZ that are explicitly included in the 
TSPA-SR analyses are advection in groundwater, dispersion, matrix diffusion in fractured media, 
sorption of radionuclides, colloid-facilitated transport, and radioactive decay and ingrowth. 
Advection is the natural movement of groundwater through fractured or porous media in 
response to gradients in groundwater potential. Dispersion is explicitly simulated as a randomwalk 
process in the site-scale SZ flow and transport model that occurs in the longitudinal and 
transverse directions. Only longitudinal dispersion is simulated in the one-dimensional SZ 
transport model. Diffusion of radionuclides from fractures into the immobile groundwater of the 
matrix is simulated to occur in the fractured volcanic units of the SZ system using an analytical 
solution for mass transfer in an idealized fracture network. Sorption of radionuclides is 
simulated to occur in the rock matrix of volcanic units, but is conservatively disregarded in 
fractures of the SZ. Colloid-facilitated transport is included in the transport simulations as 
occurring in two modes: as irreversible attachment of radionuclides to colloids originating from 
the waste, and as equilibrium attachment of radionuclides to colloids. Radioactive decay is 
simulated to occur for all radionuclides, and ingrowth is simulated for the daughter radionuclides 
in four key decay chains in the one-dimensional SZ transport model. 
4.2.1.3 Nuclear Criticality in the Far Field 
This subissue focuses on mechanisms and conditions that could concentrate fissile material into a 
critical configuration in the geologic environment removed from the thermally perturbed area. 
The DOE plans to evaluate criticality using the method in the criticality analysis methodology 
topical report (YMP 1998) and its supporting documents. Features, events, and processes (FEPs) 
screening considers criticality events in the far field to be low probability. Preliminary analyses 
show no significant effect on calculated performance in the first 10,000 yr. even if waste 
packages are breached. 
4.2.2 Structural Deformation and Seismicity 
The objective of this KTI is to evaluate the tectonic FEPs that may affect performance of the 
potential repository (NRC 1999c). Two of the acceptance criteria for one of the subissues for this 
KTI relate to the SZ PMR. The Disruptive Events PMR (CRWMS M&O 2000d) provides 
information relevant to the remaining subissues. 
4.2.2.1 Fracturing and Structural Framework of the Geologic Setting 
The NRC will evaluate alternative modeling approaches for distribution and properties of 
fractures that are consistent with current data and geologic understanding. They will review 
representations of fracture data and properties in the SZ flow and transport models and their 
abstractions to evaluate the degree to which data on fracture variability are honored, the 
justification for excluding data, and the degree to which fracture data are adequately integrated 
into the SZ flow and transport models (NRC 1999c, p. 51).

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The NRC indicates that the assumptions in the TSPA-Viability Assessment (VA) (DOE 1998b) 
of homogeneous and isotropic material properties lack a technical basis and are not conservative. 
The NRC was concerned that these assumptions do not capture anisotropy due to fault and 
fracture orientations that could influence groundwater flow paths (NRC 1999c, p. 119). 
Numerous hydrologic features corresponding to faults and geologic zones are explicitly 
incorporated into the site-scale SZ flow and transport model (Section 3.2.2.5). The presence of 
faults and fracture zones that are not explicitly represented in the site-scale SZ flow and transport 
model and their potential impact on groundwater flow is implicitly included in the nominal case 
through consideration of horizontal anisotropy in permeability in the fractured volcanic units 
downgradient of the potential repository. Given the uncertainty in anisotropy, and to simplify 
the model, the potential effects of anisotropy are bounded in the model. Anisotropy and 
incorporation of the effects of anisotropy in the model are discussed in Sections 3.5.1 and 3.7.2, 
respectively. 
4.2.3 Total System Performance Assessment and Integration 
The objective of this KTI is to describe an acceptable methodology for conducting assessments 
of the performance of the potential repository, and using these assessments to demonstrate 
compliance with the overall performance objective and requirements for multiple barriers 
(NRC 2000). 
Three of the subissues for this KTI relate to the SZ PMR, as described in the following 
subsections. 
4.2.3.1 System Description and Demonstration of Multiple Barriers 
The system description and demonstration of multiple barriers subissue focuses on the 
demonstration of multiple barriers and includes: identification of design features of the 
engineered barrier system and natural features of the geologic setting that are considered barriers 
important to waste isolation; descriptions of the capability of barriers to isolate waste; and 
identification of degradation, deterioration, or alteration processes of engineered barriers that 
would adversely affect the performance of natural barriers. In addition, it addresses NRC 
expectations of the contents of the TSPA and the supporting documents. Specifically, it focuses 
on those aspects of the TSPA that will allow for an independent analysis of the results 
(NRC 2000, p. 4). 
4.2.3.2 Model Abstraction 
The model abstraction subissue focuses on the information and technical needs related to the 
development of abstracted models for TSPA. Specifically, the following aspects of model 
abstraction are addressed under this subissue: data used in development of conceptual 
approaches or process-level models that are the basis for abstraction in a TSPA, resulting 
abstracted models used to perform the TSPA, and overall performance of the repository system 
as estimated in a TSPA. In particular, this subissue addresses the need to incorporate numerous 
FEPs into the PA and the integration of those factors to ensure a comprehensive analysis of the 
total system (NRC 2000, p. 4). For the site-scale SZ flow and transport model, this KTI focuses 
on two elements of the abstraction process: groundwater flow paths (NRC 2000, p. 98) and

TDR-NBS-HS-000001 REV 00 ICN 01 4-6 August 2000 
radionuclides transport in the SZ (NRC 2000, p. 106). The acceptance criteria for each subissue 
address five general principles of the TSPA model for the Yucca Mountain site (NRC 2000, 
p. 32):
 Data and model justification 
 Data uncertainty and verification 
 Model uncertainty 
 Model verification 
 Integration. 
These two elements of the abstraction process relate to the subissues discussed in Section 4.2.4 
(Unsaturated and Saturated Flow and Transport under Isothermal Conditions) and Section 4.2.1 
(Radionuclide Transport). For each of these elements, this PMR addresses the five general NRC 
principles that are listed in Section 4.2.3. The PMR summarizes: 1) data available to support the 
conceptual basis of the process models and abstractions, 2) the basis for bounding assumptions 
and representations of uncertainties and parameter variabilities, 3) model uncertainty and 
alternative conceptual models, 4) abstractions based on, and consistent with, the underlying 
process models, and 5) incorporation of design features, physical phenomena, couplings, and use 
of consistent assumptions throughout the abstraction process. To address consistency in the 
assumptions, the analysis model reports (AMRs) that document assumptions have been subjected 
to interdisciplinary review to help ensure that assumptions are applied consistently to the extent 
practicable. In addition, the PMRs have been reviewed by a single team whose main objective 
was to identify inconsistencies among the PMRs. These measures provide confidence that 
consistent assumptions are used in the abstraction process, as appropriate. 
4.2.3.3 Scenario Analysis 
The scenario analysis subissue considers the process of identifying possible processes and events 
that could affect repository performance, assigning probabilities to categories of events and 
processes, and the exclusion of processes and events from PA (NRC 2000, p. 4). The scenario 
analysis process is a key factor in ensuring the completeness of the TSPA. 
A systematic method was applied to identify and screen FEPs for SZ flow and transport 
phenomena. One hundred and fifteen FEPs have been identified and grouped into two broad 
categories of primary and secondary FEPs. The primary FEPs capture the issues associated with 
the secondary FEPs. The FEPs are further divided into included and excluded FEPs. 
Included FEPs are those directly represented in TSPA models and process models that support 
the TSPA. Analyses have focused on the identification and screening of FEPs; this work 
partially addresses this subissue (Section 1.3). 
4.2.4 Unsaturated and Saturated Flow under Isothermal Conditions 
The main objective of this KTI is to evaluate all aspects of the ambient hydrological regime at 
Yucca Mountain that may adversely affect the performance of a potential repository 
(NRC 1999a). Another objective is to assess the adequacy of the characterization of key

TDR-NBS-HS-000001 REV 00 ICN 01 4-7 August 2000 
hydrological processes and features at the site and in the region that may adversely affect 
performance. 
Three of the subissues for this KTI relate to the SZ PMR, as described in the following 
subsections. The UZ PMR (CRWMS M&O 2000b) provides additional information on this 
subissue. 
4.2.4.1 Hydrological Effects of Climate Change 
The NRC considers all acceptance criteria for this subissue (NRC 1999a, pp. 172 to 174) closed 
with the exception of the programmatic criterion on adequacy of the QA program. This PMR 
includes revisions to the evaluation of climate effects since the VA (DOE 1998a). The effect of 
climate change is calculated with the site-scale SZ flow and transport model using the modern, 
monsoon, and glacial transition climate states (Section 3.2.6). 
4.2.4.2 Saturated Zone Ambient Flow Conditions and Dilution Processes 
The NRC considers that characterization of the ambient flow conditions and dilution processes in 
the SZ at Yucca Mountain is important for the performance of the potential repository. Ambient 
flow conditions can be affected by subsurface geology; areal recharge patterns; inter-basin, interaquifer 
mixing, and transfer of groundwaters; and long-term climate cycles. Reliable estimates 
of groundwater flowpaths, flux, and aquifer hydrologic and transport properties are needed to 
estimate radionuclide concentrations and delivery at receptor locations, should a release occur 
(NRC 1999a, p. 182). 
The SZ PMR presents a model that has been revised from the TSPA-VA and that includes new 
data (Section 3.7.2). Uncertainty in travel distances through aquifers of differing properties is 
stochastically bounded in the model by varying the amount of alluvium along the flow path. 
A dual porosity approach is incorporated explicitly into the transport methodology for volcanic 
units to simulate matrix diffusion. Potential effects of horizontal anisotropy are bounded by 
setting the anisotropy ratio stochastically to either 1 (isotropic) or 5 (based on the C-wells data) 
by making permeability values for the volcanic units 5 times greater in the north-south direction 
than in the east-west direction. Uncertainty in groundwater flux is incorporated by considering 
three discrete cases of low, mean, and high flux by scaling the values of permeability and the 
boundary fluxes of the mean-flux case downward or upward by a constant factor of 10. 
Proportional scaling preserves the calibration of the model to head measurements among the 
three cases. Potentiometric levels in the carbonate aquifer at UE-25p#1 are about 21 m (69 ft) 
higher than levels in the overlying rocks. This indicates a potential for upward flow and suggests 
that water will not flow from the tuffs into the carbonates. 
4.2.4.3 Matrix Diffusion 
If the DOE takes credit for matrix diffusion in the SZ, then the NRC will expect rock matrix and 
solute diffusion parameters to be based on a SZ transport model that reasonably matches the 
results of the field tracer-tests that are conducted over different distance scales and flow rates 
with multiple tracers of different diffusive properties, and is consistent with laboratory data 
(NRC 1999a, p. 192).

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Diffusion of radionuclides from fractures into the immobile groundwater of the matrix occurs in 
the fractured volcanic units of the SZ and slows the rate of travel of radionuclides. The 
conceptual models for transport in the volcanic tuffs and the alluvium are different in that matrix 
diffusion occurs only in the volcanic tuffs, and sorption in the volcanic tuffs occurs only after 
radionuclides diffuse into the matrix. Diffusion of radionuclides from fractures into the 
immobile groundwater of the matrix is simulated to occur in the fractured volcanic units of the 
SZ system using an analytical solution for mass transfer in an idealized fracture network. 
The C-wells reactive tracer test (Section 3.1.3.2) demonstrated that models that incorporate 
matrix diffusion provide more reasonable fits to the tracer-experiment data than do models that 
use a single continuum. The matrix sorption coefficient that fit the data for the lithium tracer in 
the C-wells reactive tracer experiment was similar to values determined in laboratory sorption 
tests. This provides confidence that the matrix-diffusion model is appropriate. The fact that the 
early lithium response had the same timing as that of the nonsorbing tracers, but with a lower 
normalized peak concentration, is consistent with matrix diffusion coupled with sorption in the 
matrix (Figure 3-9). 
4.3 U.S. NUCLEAR REGULATORY COMMISSION ACCEPTANCE CRITERIA 
Specific technical acceptance criteria for each of the subissues that relate to this PMR are 
summarized in Table 4-1. Details of the approach to addressing the criteria, and the sections of 
the PMR where these approaches and details are discussed, are provided in Appendix B. 
The SZ PMR also addresses NRC programmatic criteria for QA and the use of expert elicitation. 
These programmatic criteria apply to all subissues and are not repeated under each subissue in 
Table 4-1. 
The acceptance criteria for QA address the implementation of an adequate QA program by the 
DOE. The SZ PMR was developed in accordance with project procedures for documenting data, 
analyses, models, computer codes, and preparing and reviewing technical reports (Section 1.4). 
The programmatic criterion for expert elicitation specifies that expert elicitation should be 
conducted in accordance with NUREG-1563 (Kotra et al. 1996) or other acceptable approaches. 
The statements for the programmatic criterion relating to expert elicitations vary among IRSRs, 
but the overall requirements are similar in all the IRSRs: expert elicitations are to be conducted 
and documented using the guidance in the Branch Technical Position on Expert Elicitation 
(Kotra et al. 1996) or other acceptable approaches. 
A SZ flow and transport expert elicitation (CRWMS M&O 1998b) was sponsored by the DOE to 
characterize the knowledge and uncertainties associated with certain key issues related to the SZ 
system in the Yucca Mountain area and the downgradient region. The procedures and 
approaches for eliciting expert judgments were developed through conducting many studies and 
have been formalized in guidance documents prepared by the DOE, NRC, and a study sponsored 
by the NRC, the DOE, and the Electrical Power Research Institute (CRWMS M&O 1998b, 
p. 2-2). The process followed in the expert elicitation was consistent with these guidance 
documents and studies. The NRC (1999a, p. 190) indicates that the expert elicitation on SZ flow 
and transport (CRWMS M&O 1998b) was conducted and documented in an acceptable way.

TDR-NBS-HS-000001 REV 00 ICN 01 4-9 August 2000 
Even though the NRC indicates that the expert elicitation was conducted and documented in an 
acceptable way, NRC 1999a (Attachment D) cautions that the NRC is not bound by the 
conclusions of an elicitation based solely on adherence to guidance provided by the staff.

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5. SUMMARY AND CONCLUSIONS 
This document summarizes the development of the site-scale saturated-zone (SZ) flow and 
transport model, the results of which will be used in calculations presented in the Total System 
Performance Assessment (TSPA)-Site Recommendation (SR) report. The site-scale SZ flow and 
transport model was developed in several stages. First, the hydrogeology of a region around 
Yucca Mountain was characterized. Many aspects of this characterization were synthesized 
while conceptualizing and numerically simulating a regional-scale groundwater flow system 
(referred to as the Death Valley regional groundwater flow system). Second, a detailed 
conceptual model of flow and transport processes was developed for a smaller region (i.e., the 
site-scale region) that is appropriate for TSPA-SR calculations. Third, a numerical model of 
groundwater flow and radionuclide transport was developed (i.e., the site-scale SZ flow and 
transport model). Finally, results of the numerical model (i.e., those that describe the transport of 
radionuclides and the associated uncertainty in the SZ) were abstracted for use in the TSPA-SR 
calculations. 
The organization of this section follows that of Chapter 3 of this document. Sections 5.1 and 5.2 
refer to characterization of site-scale SZ flow and transport (Section 3.1) and the conceptual 
model of site-scale SZ flow and transport (Section 3.2), respectively. Material presented in 
Sections 3.3 and 3.4 regarding the mathematical model and numerical approach are summarized 
in Section 5.3. Section 5.4 summarizes the SZ model abstraction for TSPA discussed in 
Sections 3.6 and 3.7. Conclusions are presented in Section 5.5. 
5.1 SATURATED ZONE FLOW AND TRANSPORT CHARACTERIZATION 
A large amount of information about the regional-scale hydrogeology is known from activities of 
the Yucca Mountain Site Characterization Project (YMP), as well as from numerous additional 
hydrogeologic studies that have been conducted in the vicinity of the Nevada Test Site (NTS). 
Specifically, sufficient information is available to describe the stratigraphy, structure, and 
hydraulic properties of rocks in this region, recharge and discharge regions, and groundwater 
flow paths. 
The climate in the Yucca Mountain area is arid and the SZ generally is far below the land 
surface. Natural recharge to the SZ is from precipitation that infiltrates at the land surface and 
percolates through the unsaturated zone. Recharge occurs primarily in mountainous areas where 
relatively larger amounts of snow and rainfall occur. Areas of recharge include Yucca Mountain 
and other regions of higher elevation to the north and northeast, and the Spring Mountains 50 km 
(31 mi.) southeast of Yucca Mountain. Estimates of recharge rates at the regional scale are based 
on empirical relationships. Confidence in these estimates comes from numerical models which 
ensure that, at a regional scale, recharge to and discharge from the SZ are equal. Natural 
discharge from the Death Valley flow system is from evapotranspiration and springs at low 
elevations, mainly in Death Valley and Ash Meadows. Groundwater flows from regions of 
recharge to regions of discharge. Flow paths in the SZ are well characterized at the regional 
scale because a large number of measurements of water levels in boreholes are available. Taken 
together, information about recharge and discharge and measured water levels provide a sound 
understanding of groundwater flow paths in the SZ in the Death Valley regional groundwater 
flow system.

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In the area near Yucca Mountain, water level measurements, hydraulic testing in wells, and 
geochemical analyses provide more detailed information on groundwater flow in the SZ. Water 
level measurements indicate considerable differences in the magnitude of the hydraulic gradient 
to the north (apparent large hydraulic gradient), west (moderate hydraulic gradient), and 
southeast (low hydraulic gradient) of Yucca Mountain. The hydraulic gradient results in the 
flow of groundwater away from the potential repository to the southeast and south. A vertical, 
upward hydraulic gradient from the underlying carbonate aquifer and the deeper volcanic units is 
observed at one location immediately downgradient of Yucca Mountain. Hydraulic testing in 
wells provides estimates of the variability in permeability for tuffs and information on the 
distribution of groundwater flow in fractured volcanic units. Data on groundwater chemistry 
indicate significant spatial variability in geochemical and isotopic composition that results from 
differences in flow paths, recharge locations, and groundwater age. 
Due to the long period of time over which the performance of the potential Yucca Mountain 
repository must be evaluated, the possible impact of a future wetter climate must be considered. 
Modeling studies suggest that greater and more widespread recharge would result in a higher 
water table and steeper hydraulic gradients. Field mapping of the occurrence of zeolites and 
paleospring deposits has confirmed that a higher water table existed during past wetter climates 
and provides confidence in numerical simulations of the possible impacts of climate change. 
The general locations of areas of recharge and discharge depend mainly on the topography of the 
land surface. Consequently, wetter climates in the future are expected to result in faster 
groundwater flow rates along essentially present-day flow paths. 
As groundwater in the Death Valley system moves from recharge to discharge areas, flow rates 
and paths depend largely on the hydraulic properties of the rocks and materials along the flow 
paths. Geologic studies have resulted in a sufficient understanding to identify the important rock 
types and their spatial distribution. The rock types that play the largest role in regional 
hydrogeology are Paleozoic carbonates, Quaternary-Tertiary volcanic rocks, and Quaternary- 
Tertiary sediments and volcanic tuffs that fill structural depressions (referred to as valley-fill 
material in portions of this report). The valley fill primarily is alluvium. Relatively shallow flow 
occurs in the volcanic rocks and valley fill. Deeper flow occurs in the regionally extensive 
carbonate aquifer. Along the inferred shallow flow path in the SZ from Yucca Mountain, 
groundwater flow occurs in volcanic rocks near the potential repository site and in younger 
valley-fill deposits at greater distances. 
The permeability of the volcanic rocks in the vicinity of Yucca Mountain typically is increased 
by the presence of fractures. An extensive suite of field observations, interpretations of borehole 
logs, hydrologic tests in boreholes, lab-scale tests, and field tracer tests (C-wells Complex) 
confirm that fractures enhance groundwater flow in the volcanic rocks. However, flow in the 
alluvium occurs through the primary porosity of these sediments. 
Tracer testing between wells in fractured volcanic units and laboratory measurements have 
provided information on the processes controlling the transport of potential radionuclide 
contamination, including matrix diffusion, sorption, dispersion, and colloid-facilitated transport. 
Field-scale tests and laboratory experiments have demonstrated the occurrence of solutes 
diffusing from fractures into the immobile groundwater in the rock matrix. Data on the sorption 
of radionuclides onto volcanic rocks and alluvium have been obtained in laboratory experiments.

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Tracer testing using an analog sorbing species has demonstrated reasonable agreement with 
laboratory-scale measurements of sorption for the same species. Values of longitudinal 
dispersivity, derived from tracer tests in fractured tuffs, generally agree with measurements made 
at other sites. Field-scale tests and laboratory experiments provide information on the transport 
of colloids in fractured media from the site. 
5.2 CONCEPTUAL MODEL OF SITE SCALE FLOW AND TRANSPORT 
The site-scale conceptual model is a synthesis of what is known about flow and transport 
processes at the scale required for TSPA-SR calculations. This knowledge builds on, and is 
consistent with, knowledge that has accumulated at the regional scale, but is more detailed 
because a higher density of data is available for the site-scale level. 
Information from geologic maps and cross sections, borehole data, fault-trace maps, and 
geophysical data were used to construct a three-dimensional (3-D) interpretation (hydrogeologic 
framework model) of the hydrostratigraphy and geologic structure within the domain of the sitescale 
model. Rock stratigraphic units within the framework model are grouped into 
18 hydrogeologic units that are classified as having relatively large permeability (aquifers), or 
relatively small permeability (confining units). The framework model specifies the position and 
geometry of these hydrogeologic units. In addition, the framework model identifies major faults 
that affect groundwater flow. 
The source of most of the groundwater flow through the site-scale model is lateral flow across 
the western, northern, and eastern boundaries. A small portion (approximately 5 percent) of the 
total flux through the site-scale model is from recharge of precipitation falling within the model 
domain and surface runoff infiltrating along Fortymile Wash. Outflow from the site-scale region 
mainly is by groundwater flow across its southern boundary. A small amount of water is 
removed by pumping wells located in the Amargosa Valley near the southern boundary of the 
model domain. 
As groundwater moves away from the area beneath the potential repository, it first flows through 
a series of welded and nonwelded volcanic tuffs. These flow paths pass into alluvium after 
traveling approximately 15 km (9 mi.). The distance to the contact between the tuffs and the 
alluvium is uncertain. 
The conceptual model of radionuclide transport in the SZ includes the processes of advection, 
dispersion, matrix diffusion in fractured volcanic units, sorption, and colloid-facilitated transport. 
Advection is the process by which groundwater flow moves contaminants along the flow path in 
the SZ. The process of dispersion spreads solute in the longitudinal and transverse directions due 
to small-scale variations in groundwater flow velocity. Matrix diffusion is the process by which 
solute moves between the relatively rapidly moving groundwater in fractures to the immobile 
groundwater in the low-permeability rock matrix by the process of molecular diffusion. As 
noted above, groundwater flow in tuffs primarily is in fractures, and flow in the alluvium is in 
the primary porosity. The extent to which flow occurs in fracture porosity, primary porosity, or 
both, plays an important role in the transport and retardation of radionuclides. Sorption is the 
process in which solute may be attached to the surface of solid grains in the aquifer. The 
conceptual model of the sorption process includes potential sorption of radionuclides onto the

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rock matrix in fractured volcanic units and onto the granular medium of the alluvium. Sorption 
onto the walls of fractures in the volcanic units is conservatively neglected in the current 
conceptual model, requiring matrix diffusion to allow access of radionuclides to the sorptive 
capacity of the matrix in fractured units. Colloid-facilitated transport of radionuclides is 
conceptualized to occur by two possible modes. Radionuclides may be irreversibly attached to 
some colloids that form during degradation of the waste. The colloids with irreversibly attached 
radionuclides are subject to filtration and resuspension as they move through the fractured 
volcanic units and alluvium. The second mode of colloid-facilitated transport is a conceptual 
model in which radionuclides are reversibly attached to colloids in the SZ flow system. In this 
mode, equilibrium exists among the radionuclide concentration on colloids, the aqueous-phase 
concentration of the radionuclide, and the concentration of the radionuclide sorbed on the 
mineral grains of the aquifer. 
5.3 MATHEMATICAL MODEL AND NUMERICAL APPROACH 
The mathematical basis of the site-scale SZ flow and transport model, and the associated 
numerical approaches, are designed to assist in quantifying the uncertainty in the permeability of 
rocks in the geologic framework model and to accurately represent the flow and transport 
processes included in the site-scale conceptual model. A description of the methodology used to 
simulate transport processes is given in Section 3.3.4. An inverse approach was used to estimate 
the distribution of rock permeability that resulted in calculated values of hydraulic head that best 
matched measured values, and calculated rates of lateral flow across model boundaries that are 
compatible with results of the regional-scale model. 
Calculations of groundwater flow (specific-discharge field) assume the flow field does not 
change with time and that flow occurs in a continuous porous media. The approach of not 
explicitly representing fractures in the volcanic rocks is valid at the scale required for TSPA-SR 
(tens of kilometers) but is not accurate at length scales shorter than the dimensions of model grid 
blocks (tens to hundreds of meters). The transport processes considered include advection and 
dispersion of solutes and colloids by moving groundwater, diffusion of solutes, and equilibrium 
sorption of radionuclides on mineral surfaces, and reversible and irreversible sorption of 
radionuclides onto colloid particles. A particle tracking approach is used to simulate advection 
and dispersion of solutes to minimize numerical dispersion. A semi-analytic method is used to 
calculate the retardation of radionuclide transport due to diffusion into the matrix of the fractured 
tuffs. 
Confidence in the results of the mathematical model was obtained by comparing calculated to 
observed hydraulic heads, estimated to measured permeabilities, and lateral flow rates calculated 
by the site-scale SZ flow and transport model to those calculated by the regional-scale model. In 
addition, it was confirmed that the flowpaths leaving the region of the potential repository are 
consistent with those inferred from gradients of measured head and those inferred independently 
from water chemistry data.

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5.4 SUMMARY OF SATURATED ZONE MODEL ABSTRACTION FOR TOTAL 
SYSTEM PERFORMANCE ASSESSMENT-SITE RECOMMENDATION 
The objective of the analysis implemented using the site-scale SZ flow and transport model is to 
simulate unit breakthrough curves for radionuclide mass at the interface between the SZ and the 
biosphere. These breakthrough curves contain information on the radionuclide transport through 
the SZ that is used in the TSPA calculations to determine the mass fraction of radionuclides 
delivered to the biosphere. 
The starting point for the analysis of the site-scale SZ flow and transport is the calibrated 
site-scale SZ groundwater flow model. Input files for the site-scale SZ flow model are modified 
to include relevant radionuclide transport parameters and to produce the output needed for 
breakthrough curves of radionuclide mass. The simulation of radionuclide decay chains and 
radioactive ingrowth in the SZ is performed using the simplified one-dimensional (1-D) 
radionuclide transport model and are conducted directly in the TSPA simulator. 
Uncertainties are explicitly incorporated into the SZ TSPA site-scale flow and transport 
abstractions through key parameters and conceptual models. The probabilistic analysis of 
uncertainty is implemented through Monte Carlo realizations of the site-scale SZ flow and 
transport system, in a manner consistent with the TSPA simulations implemented with the 
GoldSim software code. Alternative models of groundwater flux and horizontal anisotropy are 
included as uncertainty among six SZ groundwater flow fields. Uncertainty in the location of the 
contact between volcanic units and the alluvium is incorporated as geometric variability in the 
alluvium zone in the site-scale SZ flow and transport model. Alternative models of colloidfacilitated 
transport of radionuclides are considered in the uncertainty analysis through the use of 
two coexisting modes of colloid-facilitated transport. The nominal case of SZ flow and transport 
for the TSPA-SR explicitly incorporates many features, events, and processes of the SZ system 
and implicitly includes others. 
Abstraction methods for conducting TSPA simulations include the convolution integral method, 
alternative climate states, dilution of radionuclides in the water supply of the critical group, and 
radionuclide decay chains. The convolution integral method is used in TSPA-SR analyses to 
calculate the radionuclide mass flux at the interface of the SZ and the biosphere, based on the 
transient radionuclide mass flux at the water table beneath the potential repository and the 
appropriate unit breakthrough curve simulated by the site-scale SZ flow and transport model. 
This computationally efficient method combines information about the unit response of the SZ 
system with the radionuclide source history from the UZ to calculate transient system behavior. 
The effects of climate change on radionuclide transport in the SZ are incorporated in the 
TSPA-SR analyses by scaling the radionuclide mass breakthrough curves to reflect the greater 
groundwater specific discharge under wetter climatic conditions. The hypothetical release of 
radionuclides from groundwater to the biosphere occurs by the pumping of groundwater to 
supply water for a future farming community in the nominal case for TSPA-SR. Radionuclide 
concentrations in the water supply of the hypothetical farming community are calculated by 
assuming that all of the radionuclide mass is captured by the pumping wells and that this mass is 
uniformly distributed in the total volume of groundwater used by the community. The 1-D 
radionuclide transport model for TSPA-SR is used for simulating radioactive decay and 
radionuclide ingrowth in the SZ for four decay chains. The 1-D radionuclide transport model,

TDR-NBS-HS-000001 REV 00 ICN 01 5-6 August 2000 
while based on results of the 3-D site-scale SZ flow and transport model, represents a 
simplification or abstraction of the site-scale SZ flow and transport model. 
5.5 CONCLUSIONS 
Site characterization activities in the SZ at Yucca Mountain have provided a basic understanding 
of the SZ system in terms of groundwater flow and potential radionuclide transport. This 
understanding includes the general flow pathway from beneath Yucca Mountain to areas of 
potential groundwater discharge to the biosphere by future pumping. Subsurface data also 
provide information on the geologic media present in the SZ, water levels, and the groundwater 
flow characteristics in fractured volcanic rocks. Field-scale and laboratory-scale studies of 
transport characteristics in the SZ establish an understanding of the processes relevant to the 
potential migration of radionuclides. Regional-scale studies of the groundwater flow system in 
the SZ constitute an important framework of understanding into which the Yucca Mountain sitescale 
SZ system is placed. 
Taken in total, these data provide an appropriate and adequate basis for the conceptual model and 
numerical modeling of the site-scale SZ flow and transport system. The site-characterization 
information, along with inferences based on that information, support a conceptual model in 
which groundwater flow is controlled by the spatial distribution of geologic units and structural 
features. Site-specific data, together with regional-scale studies, suggest that a large fraction of 
groundwater flowing in the SZ enters the Yucca Mountain site area as lateral flow from the north 
with a small fraction contributed by recharge near Yucca Mountain. The conceptual model of 
radionuclide transport in fractured rocks includes the processes of advection, dispersion, matrix 
diffusion, sorption, and colloid-facilitated transport, as supported by site data. These 
components of the conceptual model are implemented numerically in the site-scale SZ flow and 
transport model, which represents the processes relevant to radionuclide migration from a 
potential repository at Yucca Mountain to the biosphere. 
The site-scale SZ flow and transport model forms the basis for analyses of performance of the 
potential repository in the TSPA-SR. The site-scale SZ flow and transport model constitutes a 
reasonable and adequate representation of the SZ system for the purposes of TSPA, particularly 
when considered in the context of the uncertainty of key model parameters incorporated in the 
Monte Carlo analyses performed for TSPA-SR. Abstraction methods used to incorporate SZ 
modeling results into the TSPA simulations are appropriate numerical simplifications that retain 
information embodied in the results of the underlying site-scale SZ model. 
Radionuclide migration through the SZ could affect total system performance in two ways. First, 
the SZ functions as a mechanism to delay the release of radionuclides to the biosphere. This 
delay potentially allows radioactive decay to reduce the release of radionuclides to the biosphere. 
Second, the radionuclide concentrations may be diluted during the transport in the SZ. Although 
the dispersive processes that lead to dilution are incorporated in the site-scale SZ flow and 
transport modeling, the simplified approach used to calculate concentrations in the water supply 
of the critical group negates the need to analyze in situ radionuclide concentrations in the SZ. 
These two factors are of primary importance to performance of the potential repository. The 
transport time of contaminants in the SZ allows for considerable radioactive decay of some 
radionuclides and may delay the release of some radionuclides beyond the limits of regulatory

TDR-NBS-HS-000001 REV 00 ICN 01 5-7 August 2000 
concern. The calculated dose in TSPA analyses is directly proportional to the concentration of 
radionuclides in the groundwater supply of the receptors of interest. 
The site-scale SZ flow and transport model, as used in TSPA-SR analyses, contains aspects that 
are potentially conservative from the perspective of assessing performance of the potential 
repository. The defensibility of assumptions, modeling approach, and parameter values was 
given high priority in the model development, analysis process, and TSPA abstractions. 
Consequently, the models and results may be more conservative than the best estimate of 
expected behavior of the site-scale SZ flow and transport system. The resulting potential 
conservatism in simulations of radionuclide transport with the site-scale SZ model is embedded 
in the underlying conceptual model, the numerical implementation of the model, or in the 
uncertainty distributions for parameters used in the TSPA analyses.

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TDR-NBS-HS-000001 REV 00 ICN 01 6-1 August 2000 
6. REFERENCES 
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310. Munich, Germany: R. Oldenbourg Verlag. TIC: 247532. 
Waber, N. 1991. Mineralogy, Petrology and Geochemistry of the Poos de Caldas Analogue 
Study Sites, Minas Gerais, Brazil II: Morro do Ferro. SKB Technical Report 90-12. Stockholm, 
Sweden: Swedish Nuclear Fuel and Waste Management Company. TIC: 206350. 
Waddell, R.K. 1982. Two-Dimensional, Steady-State Model of Ground-Water Flow, Nevada Test 
Site and Vicinity, Nevada-California. Water-Resources Investigations Report 82-4085. Denver, 
Colorado: U.S. Geological Survey. ACC: NNA.19870518.0055. 
Waddell, R.K.; Robison, J.H.; and Blankennagel, R.K. 1984. Hydrology of Yucca Mountain and 
Vicinity, Nevada-California--Investigative Results through Mid-1983. Water-Resources 
Investigations Report 84-4267. Denver, Colorado: U.S. Geological Survey. 
ACC: NNA.19870406.0343. 
Walker, G.E. and Eakin, T.E. 1963. Geology and Ground Water of Amargosa Desert, Nevada 
California. Ground-Water Resources  Reconnaissance Series Report 14. Carson City, Nevada: 
State of Nevada, Department of Conservation and Natural Resources. TIC: 208665. 
West, J.M.; McKinley, I.G.; and Vialta, A. 1989. The Influence of Microbial Activity on the 
Movement of Uranium at OSAMU UTSUMI Mine, Poos de Caldas, Brazil. Scientific Basis for 
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Lutze, W. and Ewing, R.C., eds. 127, 771-777. Pittsburgh, Pennsylvania: Materials Research 
Society. TIC: 236107. 
Whelan, J. 1998. Review of Yuri Dublyansky's Reports Entitled Fluid Inclusion Studies of 
Samples from the Exploratory Studies Facility, Yucca Mountain, Nevada and an Attachment 
Entitled Fluid Inclusions in Calcite Samples from the ESF, Nevada Test Site, Nevada. 
Memorandum from J. Whelan (USGS) to D. Williams (DOE), November 9, 1998, with enclosure. 
ACC: MOL.19981209.0014. 
Wilson, M.L.; Gauthier, J.H.; Barnard, R.W.; Barr, G.E.; Dockery, H.A.; Dunn, E.; Eaton, R.R.; 
Guerin, D.C.; Lu, N.; Martinez, M.J.; Nilson, R.; Rautman, C.A.; Robey, T.H.; Ross, B.; Ryder, 
E.E.; Schenker, A.R.; Shannon, S.A.; Skinner, L.H.; Halsey, W.G.; Gansemer, J.D.; Lewis, L.C.; 
Lamont, A.D.; Triay, I.R.; Meijer, A.; and Morris, D.E. 1994. Total-System Performance 
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Central Great Basin, Nevada-California, with Special Reference to the Nevada Test Site. 
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TDR-NBS-HS-000001 REV 00 ICN 01 6-19 August 2000 
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at the C-Holes Complex Near Yucca Mountain, Nevada. San Antonio, Texas: Center for Nuclear 
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Boreholes in the Unsaturated Zone at Yucca Mountain, Nevada. Water-Resources Investigations 
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Methods for the FEHM Application - A Finite Element Heat- and Mass-Transfer Code. 
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6.2 CODES, STANDARDS, REGULATIONS, AND PROCEDURES 
50 FR 38066. Protection of Environment: Environmental Standards for the Management and 
Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes; Final Rule. 
Readily available. 
64 FR 8640. Disposal of High-Level Radioactive Wastes in a Proposed Geologic Repository at 
Yucca Mountain, Nevada. Proposed rule 10 CFR 63. Readily available. 
64 FR 46976. Environmental Radiation Protection Standards for Yucca Mountain, Nevada; 
Proposed rule 40 CFR 197. Readily available. 
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Department of Energy, Office of Civilian Radioactive Waste Management. 
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of Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.19990701.0616. 
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Department of Energy, Office of Civilian Radioactive Waste Management. 
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Regulatory Compliance Activities. Washington, D.C.: U.S. Department of Energy, Office of 
Civilian Radioactive Waste Management. ACC: MOL.20000802.0003. 
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Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.19990702.0314. 
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Office of Civilian Radioactive Waste Management. ACC: MOL.19990701.0620. 
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Department of Energy, Office of Civilian Radioactive Waste Management. 
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Energy, Office of Civilian Radioactive Waste Management. ACC: MOL.20000223.0508. 
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Rationale for Accepted Data. Washington, D.C.: U.S. Department of Energy, Office of Civilian 
Radioactive Waste Management. ACC: MOL.19991214.0625. 
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QAP-2-0, Rev. 5. Conduct of Activities. Las Vegas, Nevada: CRWMS M&O. 
ACC: MOL.19980826.0209. 
6.3 SOURCE DATA, LISTED BY DATA TRACKING NUMBER 
MO0002COV00088.001. Coverage: BORESQ2. Submittal date: 02/24/2000.

TDR-NBS-HS-000001 REV 00 ICN 01 August 2000 
APPENDIX A 
ISSUES FOR SATURATED ZONE FLOW AND TRANSPORT

TDR-NBS-HS-000001 REV 00 ICN 01 August 2000

TDR-NBS-HS-000001 REV 00 ICN 01 A-1 August 2000 
APPENDIX A 
ISSUES FOR SATURATED ZONE FLOW AND TRANSPORT 
Table A-1. Issues for Saturated Zone Flow and Transport 
Issue Source PMR Approach 
The saturated-zone (SZ) needs additional 
characterization: 
 Between the repository and the accessible 
environment 20 to 30 km (12.5 to 18.6 mi.) away. 
 Information about long-range colloid transport, 
 The Nye County Early Warning Drilling Program 
(NCEWDP) should provide valuable information 
on the part of the SZ downgradient of Yucca 
Mountain. However, the wells may not provide 
sufficient data, and additional testing may be 
needed at other sites closer to Yucca Mountain. 
Paperiello 1999; 
NWTRB 1999a; 
NWTRB 1999b; 
Budnitz et al. 
1999 
 NCEWDP was started, in part, to 
characterize areas between the 
potential repository and areas 30 km 
18.6 mi.) down gradient. The program 
is continuing. Hydrologic data 
discussed in Section 3.1.2. 
 Laboratory colloid experiments 
discussed in Section 3.1.4.3; C-wells 
hydraulic testing with microspheres 
discussed in Section 3.1.3.2. 
 Next phases of NCEWDP testing are 
ongoing and are closer to Yucca 
Mountain. 
Evaluate, integrate, and incorporate alternate 
models (such as those developed by State of 
Nevada hydrologists) into coherent SZ model. 
Cohon 1998b; 
Cohon 1999b 
Alternative conceptual models, including 
the models presented by State of 
Nevada hydrologists, are evaluated. 
Discussion in Section 3.8. 
Borehole WT-24 drilling was stopped too soon to 
evaluate the large hydraulic gradient. 
Much work was planned to characterize the large 
hydraulic gradient, but was not done. People will 
ask why. 
Cohon 1999a; 
NWTRB 1998a 
Borehole WT-24 provides sufficient 
information to determine that the large 
hydraulic gradient is due in part to 
perching. The large hydraulic gradient is 
discussed in Sections 3.2.2.3 and 
3.2.5.1. 
Warm water in some NCEWDP wells needs 
investigation. 
Cohon 1999a; 
NRC 1999c 
Warm water is not anomalous compared 
to other wells in region (e.g., Sass et al. 
1988). NCEWDP and U.S. Department 
of Energy (DOE) investigations are 
ongoing. 
Characterizing effects of molecular diffusion, 
hydrodynamic dispersion, and sorption on dilution 
in the SZ will be difficult and may be impractical 
because it could take many years for the tracers to 
travel from Yucca Mountain to the monitoring wells. 
Some data may be obtained from long term tracer 
test at proposed second SZ well complex. 
Cohon 1998b Tracer tests have been done using 
multiple tracers to identify effects. 
Characterization discussed in 
Section 3.1; hydraulic well tests in 
Section 3.1.2.2; tracer tests in 
Section 3.1.3.2; laboratory data in 
Section 3.1.4. 
Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3.

TDR-NBS-HS-000001 REV 00 ICN 01 A-2 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
SZ modeling needs more model integration and 
reality checking using data from the site. 
Cohon 1998b Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
Current estimates of SZ dilution eventually may 
prove to be conservative, but supporting a larger 
dilution factor will be difficult unless new data are 
obtained. 
NWTRB 1999b More data have been obtained from multiwell, 
multi-tracer tests, and work 
continues to collect more data. 
Characterization discussed in Section 3.1; 
hydraulic well tests in 3.1.2.2; tracer tests 
in 3.1.3.2; laboratory data in 3.1.4. 
Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3. 
Presentation reported Gamma spike in 
geophysical logs in borehole NCEWDP-3D in 
conjunction with high uranium content. 
NWTRB 1999c; 
NRC 1999d 
[Nye County 
Presentation] 
NCEWDP investigations and DOE work 
are ongoing. 
Presentation indicated that drillers log for old 
Washburn Well (approximately north of Town of 
Amargosa Valley) predicted about 91 m (300 ft) to 
water; however, it went to 248 m (815 ft) and did 
not hit water. NCEWDP to investigate this 
anomaly. 
NWTRB 1998c 
[Nye County 
Presentation] 
NCEWDP could not reenter original 
Washburn hole (caved too much and 
liability concerns). NC-Washburn-1X was 
sited about 400 m (0.25 mi.) from the 
original Washburn Well site, drilled to a 
depth of 200 m (658 ft), and the static 
water level in the well after completion 
was 107.8 m (353.8 ft) below land 
surface. (Hole elevation: 823.5 m [2701.7 
ft] above mean sea level determined by 
Global Positioning System). Water table 
altitude about 716 m (2,350 ft) at NCWashburn-
1X is consistent with regional 
trends (Nye County Nuclear Waste 
Repository Project Office 1999). No water 
table anomaly noted in new hole. 
Possible anomaly does not appear to 
have regional significance. No further 
Nye County investigations indicated at this 
location. 
Concerns expressed regarding transparency of 
stream tubes model of SZ flow and transport 
model. 
NWTRB 1998b New three-dimensional (3-D) finite 
element site model developed; evolution 
of model discussed in Section 2; 
improvements to old model discussed in 
Section 2.4.6.

TDR-NBS-HS-000001 REV 00 ICN 01 A-3 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Transport in the SZ adopted a streamtube-based 
approach. This is less desirable than a more 
detailed treatment of dispersion but it is appropriate 
given the limitations in the data concerning the SZ. 
Budnitz et al. 
1999 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6. Transport and 
transport processes discussed in Sections 
3.2.4, 3.3.2, 3.3.4, 3.5.2, and 3.6.3. 
Current SZ flow and transport at Yucca Mountain 
has three main weaknesses 
1. Lack of data for some important parameters 
2. Incomplete nature of site characterization 
3. Continuing questions regarding the adequacy 
of the numerical models. 
Budnitz et al. 
1999 
More data have been, and continue to be, 
gathered. Parameters have been 
bounded or treated stochastically where 
appropriate. 
This is discussed in CRWMS M&O 
(2000o) and Section 3.5. Saturated zone 
flow and transport model revised from the 
Total System Performance Assessment 
for the Viability Assessment (TSPA-VA) 
model. Characterization discussed in 
Section 3.1; hydraulic well tests in Section 
3.1.2.2; tracer tests in Section 3.1.3.2; 
laboratory data in Section 3.1.4. 
Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3. 
Mathematical and numerical modeling 
approach discussed in Section 3.3; 
validation and calibration activities 
discussed in Section 3.4. 
Lack of site data results in: 
 An apparent difficulty in estimating vertical flow in 
the SZ 
 Establishing location of the lower boundary 
 Lack of account for anisotropy and heterogeneity. 
Budnitz et al. 
1999 
More data have been, and continue to be, 
gathered. Saturated zone flow and 
transport model revised from TSPA-VA 
model. Anisotropy and heterogeneity 
explicitly considered in model. SZ flow 
system discussed in Section 3.1.1; 
conceptual model and hydrologic 
framework discussed in Section 3.2.1; 
vertical gradient discussed in Section 
3.2.2.1; relationship of SZ PMR to 
Integrated Site Model (ISM) PMR 
(CRWMS M&O 2000e) discussed in 
Section 1.5.1; heterogeneity discussed in 
Section 3.2.2.4; anisotropy included in 
model, discussed in Sections 3.2.5.3 
and 3.5.1. 
Evaluating the effects of retardation on radionuclide 
transport is an inherent problem with two aspects: 
1. The division of flow between the matrix and 
fractures in the SZ zone 
2. The magnitude of the sorption values to be 
used. 
Budnitz et al. 
1999 
Multi-well, multi-tracer tracer tests have 
been done and provide more confidence 
in representativeness of sorption values. 
Laboratory data on sorption, matrix 
diffusion, and colloid transport discussed 
in Section 3.1.4; hydraulic well tests 
discussed in Section 3.1.2.2, tracer tests 
discussed in Section 3.1.3.2.

TDR-NBS-HS-000001 REV 00 ICN 01 A-4 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Sorption values cannot be used without knowing 
how representative they are of field conditions. 
Budnitz et al. 
1999; 
CRWMS M&O 
1998b 
Multi-well, multi-tracer tracer tests have 
been done and provide more confidence 
in representativeness of sorption values. 
Laboratory data on sorption, matrix 
diffusion, and colloid transport discussed 
in Section 3.1.4; hydraulic well tests 
discussed in Section 3.1.2.2, tracer tests 
discussed in Section 3.1.3.2. 
Estimating the permeability field currently is based 
on the calibration of pressure heads. Data are 
lacking over a substantial region of the SZ. It is 
acknowledged that pressure data inversion does 
not guarantee uniqueness in parameter estimates. 
Thus, potential fast paths in the SZ (such as 
permeability channels) may be underestimated. 
Budnitz et al. 
1999 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
Three vertical layers are used to represent the 
large-scale hydrology and a typical grid has a linear 
size of the order of 1,500 m (4,920 ft) in regional 
model. Intra-grid heterogeneity is seriously 
misrepresented. This also applies to the site-scale 
model, with a grid resolution of 200 m (655 ft). As 
permeability spans 7 orders of magnitude, this 
limited resolution raises the issue of the relevance 
of numerical predictions regarding the postulated 
flow fields. 
Budnitz et al. 
1999 
A more detailed regional-scale model 
(DAgnese et al. 1997) was used than the 
one used in TSPA-VA. Comparison of 
regional- and site-scale models discussed 
in Section 3.4.2. New 3-D finite element 
site model developed; evolution of model 
discussed in Section 2; improvements to 
old model discussed in Section 2.4.6. 
Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3. 
Streamtubes are assumed not to vary with time, 
regardless of the changes in climate. This 
assumption is not consistent with the change in the 
ratio of the water flux through the unsaturated zone 
(UZ) and the SZ. 
Budnitz et al. 
1999 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; climate change in conceptual 
model discussed in Section 3.2.6; 
alternative climate states in the 
abstraction of radionuclide transport 
discussed in Section 3.6.3.3.2. 
Recharge on top of the projected flow path would 
alter the streamlines resulting in a substantial layer 
of clean water above the contaminated water that 
could be 100 to 150 m (325 to 500 ft) thick. This 
would call into doubt the basic biosphere model, in 
which a farm family is assumed to pump 
contaminated water from the plume. 
Budnitz et al. 
1999; 
Gelhar 1998 
Saturated zone flow and transport flow 
path model revised. Assumptions 
regarding biosphere model and pumping 
are governed by regulation. Relationship 
to Biosphere PMR (CRWMS M&O 2000c) 
discussed in Section 1.5.3.

TDR-NBS-HS-000001 REV 00 ICN 01 A-5 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
A numerical approach to the modeling of dispersion 
and dilution based on a streamtube formalism, 
well-resolved near the plume and with a correct 
representation of dispersion and retardation, is 
feasible (provided that a good description of the 
heterogeneity from field data is available). 
Development of such an approach would permit 
sensitivity studies to be conducted of the effects of 
various factors, including geostatistics, and would 
circumvent the necessity to rely solely on estimates 
from the expert Panel and/or empirical corrections. 
Budnitz et al. 
1999 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6; Transport and 
transport processes discussed in Sections 
3.2.4, 3.3.2, 3.3.4, 3.5.2, and 3.6.3. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
In the TSPA-VA model, flow is assumed to occur 
only through the fractures. The problem with this 
representation is that the degree of fracture-matrix 
interaction is fixed a priori, rather than being a timedependent 
process as it is in reality. Given that 
retardation is associated with the matrix, this 
assumption will affect the transport predictions. 
Budnitz et al. 
1999 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6. Transport and 
transport processes discussed in Sections 
3.2.4, 3.3.2, 3.3.4, 3.5.2, and 3.6.3. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
Averaging the source concentrations over six areas 
at the interface between the UZ and the SZ. 
Introduces an artificial spreading which will lead to 
non-conservative estimates, particularly at early 
times (e.g., within the first 10,000 yr.) when 
leakage of radionuclides from waste packages is 
associated with isolated failures. [Note: refers to 
streamtube model]. 
Budnitz et al. 
1999 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6. 
Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3. 
Coupling of SZ flow and transport with UZ 
discussed in Section 3.6.3.4.1. 
The project conducted a sensitivity analysis (Arnold 
and Kuzio 1998) of the effect of the source size on 
the dilution factor at the 20-km (12.5-mi) point. The 
TSPA-VA underestimates the dose rates, for the 
base case parameter values, by a factor of 3. A 
correction was not introduced in the TSPA-VA, 
however. The Panel recommends that the current 
TSPA-VA treatment be modified to correct the 
existing deficiency. 
Budnitz et al. 
1999 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6. 
Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3.

TDR-NBS-HS-000001 REV 00 ICN 01 A-6 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
One critical aspect of the TSPA-VA is the degree to 
which an appropriate conceptual model and 
approach were applied to the behavior of the 
radionuclides in the UZ and SZ environments that 
involve complex coupled processes or dataintensive 
analyses of a large heterogeneous site. 
The difficulty stems from the heterogeneity of the 
site and the large distances over which the 
transport of radionuclides is to be assessed. It is 
not feasible to know the structure of the flow paths 
in sufficient depth to model these phenomena in 
detail. 
Budnitz et al. 
1999 
Conceptual model and mathematical 
model have been revised since TSPA-VA 
to account for heterogeneity more 
explicitly. Conceptual model of SZ flow 
and transport discussed in Section 3.2, 
heterogeneity addressed in 
Section 3.2.2.4. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
The merits of the two different approaches taken 
for modeling transport in the UZ and the SZ, 
namely the use of particle-tracking vs. the use of 
an overall dilution factor, need to be compared. It 
is the Panels position that a uniform approach 
should be adopted for both cases. 
Budnitz et al. 
1999 
Particle tracking method adopted in SZ 
modeling; discussed in Section 3.3.4. 
The four performance factors most affected by 
climate change appear to be: 
1. The fraction of waste packages that experience 
liquid drips 
2. The transport time for water through the UZ 
3. Subsequent transport time in SZ 
4. Dilution in the SZ. 
Budnitz et al. 
1999 
1. Discussed in Waste Package PMR 
(CRWMS M&O 2000s). 
2. Discussed in UZ PMR (CRWMS M&O 
2000b). 
3. Transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 
3.3.4, 3.5.2, and 3.6.3. 
4. Transport and transport processes 
discussed in Sections 3.2.4, 3.3.4, 
3.5.2, and 3.6.3. 
The large hydraulic gradient is a manifestation of 
the local flow system controlled by interactions 
between topography, geology, and recharge. It is 
not a cause for alarm. 
The large hydraulic gradient is not considered a 
crucial issue. 
CRWMS M&O 
1998b 
[summaries, 
Freeze and 
Gelhar] 
The large hydraulic gradient is discussed 
in Sections 3.2.2.3 and 3.2.5.1. 
The horizontal flux vector in the uppermost part of 
the SZ beneath Yucca Mountain is needed for the 
TSPA both for current conditions and for climate 
change or repository heating scenarios. 
CRWMS M&O 
1998b 
[summaries, 
Freeze] 
Groundwater flow discussed in 
Section 3.2.2; conceptual model of 
changes in SZ flow system due to climate 
change discussed in Section 3.2.6. 
There will also be mixing in the wellbore of watersupply 
wells in the Amargosa Desert. If future 
groundwater exploitation were to increase 
substantially, and if such pumping rates were 
spatially and temporally erratic, then there might 
also be considerable mixing in the capture zones of 
those wells due to the pumping transients. 
CRWMS M&O 
1998b 
[summaries, 
Freeze] 
Dilution in water supply discussed in 
Section 3.6.3.3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-7 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Recommendations For Reducing Uncertainty: 
1. Careful construction of flow nets in the vicinity 
of the large hydraulic gradient, using all 
available head data in a 3-D context, would aid 
in settling the large hydraulic gradient 
controversy. Uncertainties with respect to the 
large hydraulic gradient could be further laid to 
rest by two or three well-placed boreholes. 
However, ordinary drilling protocols will not 
suffice. It is difficult to determine whether lowpermeability 
rocks are fully saturated (or just 
nearly so), and special protocols would be 
needed to obtain the necessary downhole 
information on saturation. 
CRWMS M&O 
1998b 
[summaries, 
Freeze] 
Borehole WT-24 drilled to investigate the 
large hydraulic gradient and indicates that 
some perching was involved in previous 
mapping of the large hydraulic gradient. 
The large hydraulic gradient is discussed 
in Sections 3.2.2.3 and 3.2.5.1. 
2. Fault zone hydraulic uncertainties properties 
measured in the UZ probably can be 
meaningfully projected into the SZ. Hydraulic 
tests in the vicinity of a known fault might also 
clarify fault properties, as might further 
simulation and calibration of the new site-scale 
model. 
CRWMS M&O 
1998b 
[summaries, 
Freeze] 
New site-scale model developed. Role of 
faults discussed in Section 3.2.3.4. 
3. Further well-controlled field tracer tests may 
help clarify the nature of dispersion, matrix 
diffusion, and sorption in the fractured volcanic 
rocks. Laboratory Kd values should be 
confirmed in situ. 
CRWMS M&O 
1998b 
[summaries, 
Freeze] 
Multi-well, multi-tracer tracer tests have 
been done to clarify the nature of 
dispersion, matrix diffusion, and sorption. 
Tracer tests discussed in Section 3.1.3.2; 
laboratory data discussed in 
Section 3.1.4. 
4. Underground testing is still needed to clarify 
thermohydrologic processes associated with 
repository heating. Continued 
thermohydrologic modeling should be carried 
out to identify more fully the possible impacts 
on the SZ. 
CRWMS M&O 
1998b 
[summaries, 
Freeze] 
Underground testing ongoing, discussed 
in Near Field Environment PMR (CRWMS 
M&O 2000t). 
Perhaps a variety of models should be considered, 
ranging from a homogeneous continuum model to 
a highly channelized model, and the importance of 
their differences evaluated. In the flow system 
downgradient from the repository, it is difficult to 
see hydraulic evidence for channelization. 
Experience elsewhere has shown that large-scale 
lateral persistence of geologic features may not 
imply lateral persistence of hydraulics properties. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
Assumptions, uses, and limitations of the 
site-scale SZ flow and transport model 
discussed in Section 3.5. 
Other views and alternative conceptual 
models discussed in Section 3.8.

TDR-NBS-HS-000001 REV 00 ICN 01 A-8 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Large-scale (kilometer-scale) tracer tests are 
needed to examine the large-scale interconnected 
nature of the flow system. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
No kilometer-scale tracer tests have been 
done, however multi-well, multi-tracer 
tracer tests have been done at the Cwells. 
These data have been integrated 
with the hydrologic framework model. 
Tracer tests discussed in Section 3.1.3.2. 
Integration of the hydrologic framework 
model with the conceptual model 
discussed in Section 3.2. 
In evaluating recharge and discharge in the 
regional model, there are considerable 
uncertainties that will be difficult to reduce. In 
addition to the amounts of recharge and discharge, 
we dont know the internal distribution of 
permeability throughout the regional system. To 
evaluate whether the regional system is steady 
state, I would look at the response times and 
transmissivities. The regional model is most 
important as a tool for evaluating the effect of 
climate change on the flow system. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Regional flow system discussed in 
Section 3.1.1.1; boundary conditions of 
site-scale model discussed in Section 
3.2.3; response of conceptual model to 
climate change discussed in 
Section 3.2.6. 
The plume from the repository is not likely to move 
down deep into the aquifer system. There may be 
some tendency for the plumes movement to have 
a stronger downward component in the confining 
units in the volcanics, but in general the plume will 
stay shallow. At distances of 20 to 30 km (12.5 to 
18.6 mi.), the plume likely will be depressed 
somewhat below the water table because of the 
recharge occurring along the path of the plume. 
A continuum model for the alluvium probably is 
sufficient. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
As currently modeled, plume stays 
shallow. Particle tracking method for new 
SZ model discussed in Section 3.3.4. 
The large hydraulic gradient and the evidence for 
perching beneath Yucca Mountain confirm the 
presence of low-permeability zones. During 
climate change, the potential for increased perched 
water beneath the repository is a greater concern 
than the potential for a change in the large 
hydraulic gradient. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
The large hydraulic gradient is discussed 
in Sections 3.2.2.3 and 3.2.5.1. 
Climate change discussed in 
Section 3.2.6.

TDR-NBS-HS-000001 REV 00 ICN 01 A-9 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Some of the sources of uncertainty and limitations 
to the site-scale model include the following: 
 The representation of the geology in the model 
may not be adequate. 
 The spatial distribution of units occurring at the 
water table shows major inconsistencies with 
Fridrich et al. (1994, Figure 5). 
 The scheme used for assigning head boundary 
conditions is not defensible. 
 Using the PEST code for only one parameter at a 
time will not provide meaningful estimates of 
uncertainties. 
 No site-specific hydraulic conductivity data. 
 The estimated hydraulic conductivity values of 
0.1 m/day (0.3 ft/day) for basin fill and 
0.026 m/day (0.09 ft/day) for the middle volcanic 
aquifer seem low in comparison with the site data 
and with experience with similar formations. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Uncertainty of new model discussed in 
several Sections: 
 Hydrogeologic framework discussed in 
3.2.1; new representation based on ISM 
PMR (CRWMS M&O 2000e) has been 
developed, and relationship of SZ PMR 
to ISM PMR discussed in Section 1.5.1. 
 Hydrogeologic framework model 
discussed in Sections 3.2.1 and 3.3.5.2. 
 Boundary conditions discussed in 
Section 3.2.3. 
 Parameter uncertainty discussed in 
Section 3.7.2. 
 Hydrologic data summarized in 
Section 3.1.2; hydraulic well tests in 
Section 3.1.2.2. 
 Validation of new model by various 
methods discussed in Section 3.4. 
This effect of concentration variability around the 
mean represents an additional source of 
uncertainty that is not accounted for in the classical 
advection-dispersion models being used to 
simulate contaminant transport for Yucca 
Mountain. The degree of dilution ultimately is 
controlled by local dispersion and molecular 
diffusion, but is strongly influenced by the finescale 
variations in the flow field. Very small-scale 
variations in flow create large concentration 
gradients and large surface areas over which local 
dispersion can act to more effectively decrease 
concentration differences. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
New model developed that includes 
diffusion and dispersion due to 
heterogeneities. Mathematical model of 
radionuclide transport discussed in 
Section 3.3.2. 
Particle tracking method for new SZ 
model discussed in Section 3.3.4. 
During wetter climates there will be more 
fluctuations in hydraulic gradients, which will likely 
lead to greater dispersion. I would expect 
increases of factors of 2 to 3 times in transverse 
dispersivity during wetter periods and no change in 
longitudinal dispersivity. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Response of model to climate change 
discussed in Sections 3.2.6 and 3.6.3.3.2. 
Recommendations For Reducing Uncertainty: 
1. Large-Scale Hydraulic and Tracer Tests: 
Probably the most important activity that would 
contribute to significant reduction of uncertainty 
would be additional large-scale, multi-hole 
hydraulic and tracer testing. These tests 
should be conducted in the area south-southeast 
of the site (south of the C-wells) to gain 
information along the flowpaths from the 
repository. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
No kilometer-scale tracer tests have been 
done, however multi-well, multi-tracer 
tracer tests have been done at the Cwells. 
Testing in another well complex not 
accomplished to date, but is planned. 
Alluvial Tracer Complex is currently being 
drilled and will be tested during fiscal year 
2000; second complex in tuffs planned for 
fiscal year 2001.

TDR-NBS-HS-000001 REV 00 ICN 01 A-10 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
2. Re-evaluation of Single-Borehole Tests: The 
existing single-borehole data should be reanalyzed 
using the latest techniques, possibly 
including 3-D numerical simulation with discrete 
fracture effects, to see whether a quantitative 
explanation can be found for the apparent bias 
in the original interpretations. If an appropriate 
correction can be devised, the single-borehole 
data would be very useful in defining the spatial 
distribution of hydraulic properties at the site. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Task has not been done. Multi-well 
testing at C-wells provides hydraulic data 
capable of providing bounding 
parameters. 
3. Improvements of the Site-Scale Model: The grid 
used in the model should be refined to 
adequately represent the known hydrogeologic 
units and to resolve the expected plume 
structure (with small transverse dispersivities). 
The model grid should also be designed to 
simulate the C-wells aquifer test and any future 
multi-well hydraulic testing at the site; the flux 
imposed by these tests would be the primary 
basis for calibrating the site-scale model. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
New 3-D finite element site model 
developed; evolution of model discussed 
in Section 2; improvements to old model 
discussed in Section 2.4.6; grid discussed 
in Section 3.3.5.1; hydrogeologic 
framework model discussed in Section 
3.3.5.2; relationship of SZ PMR to ISM 
PMR (CRWMS M&O 2000e) discussed in 
1.5.1; transport and transport processes 
discussed in Sections 3.2.4, 3.3.2, 3.3.4, 
3.5.2, and 3.6.3. Calibration discussed in 
Sections 3.3.6 and 3.3.7. Model 
validation now includes comparisons of: 
permeability data to calibrated 
permeability values, fluxes from regional 
models with fluxes from calibrated model, 
measured upward gradient with predicted 
upward gradient, hydrochemical data with 
calculated particle pathways, and natural 
analogs. These activities and process 
model uncertainties are discussed 
in Section 3.4. 
4. Field Measurements of Ambient Matrix 
Diffusion Effects: Sampling and water analyses 
similar to those reported by Rousseau et al. 
(1996, p. 187) for the perched water at UZ-14 
should be done. If similar differences in water 
chemistry between fracture and matrix are seen 
at several locations, this would call into 
question the effectiveness of matrix diffusion 
under natural flow conditions. Diffusion cell lab 
tests on natural fracture surfaces also are 
suggested. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Suggested tests not done on perched 
zones. Laboratory matrix diffusion 
experiments discussed in Section 3.1.4.2. 
Multi-well tracer tests at C-wells with 
multiple tracers provides evidence for 
effectiveness of matrix diffusion. Tracer 
tests discussed in Section 3.1.3. 
5. Improved Interpretation and Documentation of 
the C-Wells Multi-Tracer Test: Many important 
details of experimental and interpretative 
methodology  must be provided. For 
example, explicit experimental evidence is 
needed to demonstrate that the two nonsorbing 
tracers behave ideally for the geochemical 
conditions corresponding to the field. The 
interpretative analyses implicitly neglect any 
effects of transverse mixing, but this process 
likely will come into play with a model that 
contains multiple paths having different 
advective transport rates 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Referenced document not published, to 
date.

TDR-NBS-HS-000001 REV 00 ICN 01 A-11 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
6. Improvements to the Report on the Los Alamos 
National Laboratory Sorption/Diffusion Testing: 
Although the draft report (Triay et al. 1997) 
contains many specifics about experimental 
equipment and procedures, it lacks crucial 
details about the overall experimental design 
and the justification in terms of field 
applicability. From the material presented, the 
reader is unable to determine where samples 
were collected, particularly in relation to the in 
situ hydrologic characteristics of the SZ. 
CRWMS M&O 
1998b 
[summaries, 
Gelhar] 
Comment was not incorporated into 
subject document as the document was 
published prior to final SZ Expert 
Elicitation report (CRWMS M&O 1998b). 
Groundwater levels downgradient vary so slowly 
that any error in their measurement translates into 
a large error in the estimation of hydraulic 
gradients. Groundwater elevation data in this area 
are sufficiently ambiguous to allow some 
hydrogeologists to contour them by means of 
smooth curves unaffected by faults, while allowing 
others to contour them to delineate embayments 
around faults. The available data are insufficient to 
compute ambient fluxes underneath Yucca 
Mountain with any reasonable degree of certainty. 
It is important to base calculations of groundwater 
flux in the Yucca Mountain area not only on site 
hydraulic data, but also on regional recharge and 
discharge data in a manner that renders all such 
calculations fully compatible and consistent with 
each other. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Water level data discussed in 
Section 3.1.2.1. Model validation now 
includes comparisons of: permeability 
data to calibrated permeability values, 
fluxes from regional models with fluxes 
from calibrated model, measured upward 
gradient with predicted upward gradient, 
and hydrochemical data with calculated 
particle pathways, as well as natural 
analogs. These activities and process 
model uncertainties are discussed in 
Section 3.4. Alternative models of SZ 
discussed in Section 3.8. 
Bomb-pulse isotopes at depth within the UZ attest 
to the occurrence of intermittent fast flow through 
both welded and nonwelded volcanic units. Major 
springs associated with the Paleozoic carbonate 
aquifer constitute evidence for highly localized flow 
in parts of the Death Valley basin. It is safe to 
assume that focused flow is ubiquitous throughout 
both the UZ and SZ in the basin on many scales. 
I therefore propose that corresponding narrow 
channels of elevated permeability be included in 
high-resolution conditional simulations of flow and 
transport in and around the Yucca Mountain area. 
The low potential for dilution associated with such 
potentially fast-flow channels should (in my view) 
be weighted against the probability (which could be 
high for detectable features such as major faults) 
that they may be intercepted by water supply wells. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Anisotropy included in the model, 
discussed in Sections 3.2.5.3 and 3.5.1. 
Heterogeneity and hydrologic features of 
the Hydrologic framework discussed in 
Section 3.2.2.4 and 3.2.2.5. Role of faults 
as internal boundaries discussed in 
Section 3.2.3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-12 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Site-scale and regional flow models developed for 
the SZ to date are consistent neither with each 
other nor with site measurements of rock hydraulic 
properties. The models differ in their hydrogeologic 
and gridding structures; in their prescribed or 
computed parameters; in conditions computed or 
prescribed along their interfaces; and in conditions 
computed or prescribed along their overlapping 
upper surfaces. The regional model consists of 
three layers that represent not hydrogeologic units 
but perceived (not clear how established) shallow, 
intermediate, and deep flow systems. The 
permeabilities ascribed to hydrologic units in both 
models, including calibrated values, are orders of 
magnitude lower than values determined in field 
tests, most notably pumping tests conducted in the 
C-wells. 
Because the site-scale and regional flow models 
incorporate at most a few discrete faults explicitly 
within their respective grids, it would have been 
logical for them to incorporate the effect of all other 
faults implicitly by rendering all hydrogeologic units 
anisotropic in the horizontal and vertical directions, 
yet this was not done. 
The site-scale model was calibrated in a manner 
that fails to guarantee unique or meaningful results; 
calibration of the regional model has led to 
reliability estimates that seem to be unduly 
optimistic and hence of questionable validity. This 
is especially true when considering that uncertainty 
of the input data into these models has not been 
fully and convincingly quantified. Additionally, the 
models are too crude to provide reliable qualitative 
insight into, or quantitative information about, 3-D 
flow at the site or within the basin. 
In their present form, the site-scale and regional 
flow models are of very limited value. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
A more detailed regional-scale model, 
developed by DAgnese et al. (1997), was 
used than the one used in TSPA-VA. 
Comparison of regional- and site-scale 
models is discussed in Section 3.4.2. 
New 3-D finite element site flow and 
transport model developed; evolution of 
model discussed in Section 2; 
improvements to old model discussed in 
Section 2.4.6. Relationship of SZ PMR to 
ISM PMR (CRWMS M&O 2000e) 
discussed in Section 1.5.1. Transport and 
transport processes discussed in Sections 
3.2.4, 3.3.2, 3.3.4, 3.5.2, and 3.6.3. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
Heterogeneity and hydrologic features of 
the hydrogeologic framework discussed in 
Section 3.2.2.4 and 3.2.2.5. 
Role of faults as internal boundaries 
discussed in Section 3.2.2. 
The only mechanisms by which dilution can take 
place in the absence of groundwater withdrawal for 
sampling or use are molecular diffusion, advective 
dispersion caused by space-time meandering of 
pathlines and variations in velocity along as well as 
among stream tubes, and turbulent eddies that are 
unlikely to occur in the vicinity of Yucca Mountain. 
Otherwise, dilution can occur when water is drawn 
into samplers or wells from multiple horizons and/or 
directions, and when waters in samplers or wells 
mix by diffusion and turbulence caused by shaking, 
stirring, or rapid flow. Density effects due to spacetime 
variations in solution chemistry, temperature, 
and pressure may either enhance or prevent 
mixing (as in buoyant or gravity segregation of 
fluids having different densities). Another factor 
that may contribute to mixing is instability of fluid 
interfaces and resultant fingering; this does not 
appear to play a role in the SZ of Yucca Mountain. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Dilution in water supply discussed in 
Section 3.6.3.3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-13 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
The stirred tank model, in which contaminated 
waters from the UZ mix rapidly with pristine waters 
in the SZ down to some specified mixing depth 
does not appear credible. 
Buoyancy of warmer waters from the repository 
area, and small vertical dispersivity will probably 
keep the incoming plume of radionuclides at 
shallow depth except where it is intercepted by 
major vertical fractures or faults within which there 
is significant downward flow. 
The scientific basis for the notion that waters from 
neighboring subbasins mix naturally along a flow 
path is also questionable; only where flow paths 
from the two subbasins converge will their waters 
mix by dispersion under natural conditions. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Site-scale SZ flow and transport model 
does not incorporate stirred tank. 
Previous modeling discussed in 
Sections 2.3 and 2.4; conceptual model 
transport processes discussed in 
Section 3.2.4; mathematical modeling of 
transport discussed in Section 3.3.2; 
particle tracking for radionuclide transport 
discussed in Section 3.3.4. 
Mixing by dispersion may occur, but it is important 
to recognize that dispersion cannot be interpreted 
as dilution except in special cases. 
On the laboratory scale, dispersion coefficients 
compensate for our inability to resolve the 
intricacies of advective transport and diffusion in 
the pore space, about which we have no direct 
information. On the field scale, dispersion 
coefficients compensate additionally for our inability 
to resolve the intricacies of advective transport and 
local-scale dispersion in a heterogeneous porous 
or fractured rock, about which we have only partial 
information. 
Clearly, lack of resolution does not necessarily 
imply mixing and dilution; only if we sample on a 
scale comparable to that of unresolved 
heterogeneities should we expect dispersion to 
imply mixing and dilution. Hence, confusing 
dispersion with mixing and dilution is inappropriate 
except in special circumstances. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Site-scale SZ flow and transport model is 
being used. Previous modeling discussed 
in Sections 2.3 and 2.4; conceptual model 
transport processes discussed in Section 
3.2.4; mathematical modeling of transport 
discussed in Section 3.3.2, particle 
tracking for radionuclide transport 
discussed in Section 3.3.4. 
Recommendations For Reducing Uncertainty: 
1. Investigate the hydrogeology of the Timber 
Mountain area between Pahute Mesa and 
Yucca Mountain, which may hold the key to a 
reliable estimation of fluxes under and 
downstream of a repository at the site. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Borehole USW WT-24 drilled north of the 
site. New regional model developed and 
integrated with site model. Model 
validation now includes comparisons of: 
permeability data to calibrated 
permeability values, fluxes from regional 
models with fluxes from calibrated model, 
measured upward gradient with predicted 
upward gradient, hydrochemical data with 
calculated particle pathways, and natural 
analogs. These activities and process 
model uncertainties are discussed in 
Section 3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-14 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
2. Conduct field tests to help determine hydraulic 
properties of faults and fault zones in Yucca 
Mountain area. Likewise, utilize available 
information about the pneumatic properties of 
faults in the unsaturated Topopah Spring unit 
when analyzing flow and transport in the 
saturated part of this unit. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Characterization discussed in Section 3.1. 
Hydraulic well tests discussed in Section 
3.1.2; tracer tests discussed in Section 
3.1.3. 
3. Base calculations of groundwater flux in the 
Yucca Mountain area not only on site hydraulic 
data, but also on regional recharge and 
discharge data in a manner that renders all 
such calculations fully compatible and 
consistent with each other. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
New regional-scale model developed and 
integrated with site model. Infiltration and 
recharge discussed in Section 3.1.2.3. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
Fluxes from regional-scale model 
compared with fluxes from calibrated 
model discussed in Section 3.4.2. 
Use of boundary flux in model calibration 
discussed in Section 3.3.6.2.2. 
4. Where faults are not incorporated explicitly into 
flow models, account for them implicitly by 
rendering all hydrogeologic units anisotropic in 
horizontal and vertical directions parallel to 
dominant fault planes. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Heterogeneity and hydrologic features of 
the hydrogeologic framework discussed in 
Sections 3.2.2.4 and 3.2.2.5. Role of 
faults as internal boundaries discussed in 
Section 3.2.3.4. 
5. Plan and conduct several additional tests 
similar to the C-wells, using existing boreholes, 
to better characterize the hydraulic properties of 
hydrogeologic units at the site; identify the 
hydraulic influence and properties of faults in 
the test area; and provide data against which it 
may be possible to calibrate a comprehensive, 
high-resolution groundwater flow model. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Alluvial Tracer Complex is currently being 
drilled and will be tested in Fiscal Year 
2000. Additional test complex in tuffs 
scheduled for Fiscal Year 2001. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-15 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
6. Develop a comprehensive, high-resolution 
groundwater flow model and render it 
compatible with all relevant site and basin-wide 
hydrologic and hydrogeologic data. Make the 
horizontal and vertical spatial resolutions of this 
model much greater than those of present site 
and regional flow models, especially in and 
downstream of the Yucca Mountain area, and 
coordinate its development with that of a 
similar-scale model recently constructed for 
environmental management of the Nevada Test 
Site. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Site-scale SZ flow and transport 3-D finite 
element model developed; evolution of 
model discussed in Section 2; 
improvements to TSPA-VA model 
discussed in Section 2.4.6. Model 
validation now includes comparisons of: 
permeability data to calibrated 
permeability values, fluxes from regional 
model with fluxes from calibrated model, 
measured upward gradient with predicted 
upward gradient, hydrochemical data with 
calculated particle pathways, and natural 
analogs. These activities and process 
model uncertainties are discussed in 
Section 3.4. 
7. Quantify the uncertainty of all input data into the 
above model and include reliable prior 
information, especially that concerning 
hydraulic parameters from large-scale pumping 
tests, formally in its calibration. A model that 
encompasses the entire basin has betterdefined 
boundary inflows and outflows than 
does a site model that has artificial boundaries, 
and is therefore better suited for calculation and 
calibration of water balance. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional model with fluxes from calibrated 
model, measured upward gradient with 
predicted upward gradient, hydrochemical 
data with calculated particle pathways, 
and natural analogs. These activities and 
process model uncertainties are 
discussed in Section 3.4. 
8. To further improve the prospects of 
constructing and calibrating a meaningful 
regional flow model, strengthen the isotope 
hydrology program of the Yucca Mountain 
Project to obtain more extensive and reliable 
information about groundwater ages and 
directions of flow throughout the basin. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Geochemistry Analysis and Model Report 
(CRWMS M&O 2000m) discusses 
hydrochemistry in detail and provides 
evaluation of groundwater ages and 
confirmation of flow paths; Section 3.1.3.1 
discusses spatial patterns of groundwater 
chemistry. Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional model with fluxes from calibrated 
model, measured upward gradient with 
predicted upward gradient, hydrochemical 
data with calculated particle pathways, 
and natural analogs. These activities and 
process model uncertainties are 
discussed in Section 3.4. 
9. Drill an additional borehole strategically into the 
large hydraulic gradient area, then log and 
sample it thoroughly enough to confirm or deny 
that the large hydraulic gradient is an artifact of 
perched conditions, as some propose. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Borehole WT-24 drilled in large hydraulic 
gradient area and indicates that the large 
hydraulic gradient is, in part, due to 
perching. The large hydraulic gradient is 
discussed in Sections 3.2.2.3 and 3.2.5.1.

TDR-NBS-HS-000001 REV 00 ICN 01 A-16 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
10. To investigate mixing and dilution, conduct 
high-resolution, statistically based conditional 
flow and transport simulations in the manner 
described within the text. Even a small number 
of conditional Monte Carlo simulations, 
conducted in this manner, may be more telling 
with regard to dilution and mixing than would 
deterministic or stochastic simulations that do 
not achieve a comparable degree of resolution. 
They may also provide meaningful, if not fully 
accurate, insight into the uncertainty associated 
with such simulations. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Calibration discussed in Sections 3.3.6 
and 3.3.7. 
Validation activities discussed in 
Section 3.4. 
11. Include narrow channels of elevated 
permeability in high-resolution conditional 
simulations to allow for focused flow and 
transport. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
Horizontal anisotropy included in model, 
discussed in Sections 3.2.5.3 and 3.5.1. 
Heterogeneity and hydrologic features 
included in model, discussed in 
Sections 3.2.2.4 and 3.2.2.5. Role of 
faults as internal boundaries discussed in 
Section 3.2.3.4. 
12. Conduct large-scale, long-term tracer 
experiments in and around the C-holes to 
obtain meaningful parameters (kinematic 
porosities, dispersivities, slow/fast path transfer 
coefficients, and retardation factors) for 
transport simulations. 
CRWMS M&O 
1998b 
[summaries, 
Neuman] 
No kilometer-scale tracer tests have been 
done, however multi-well, multi-tracer 
tracer tests have been done at the Cwells. 
Multi-well, multi-tracer tests 
conducted, tracer tests discussed in 
Section 3.1.3.2. 
A comparison of average d18O, dD, Na, Ca, Cl, and 
SO4 concentrations in groundwaters under Yucca 
Mountain, with their concentrations in the 
presumed groundwater flow direction in wells J-13 
and J-12 along Fortymile Wash, suggests that 
groundwater under Yucca Mountain contributes a 
negligible fraction of flow to the groundwaters in 
Fortymile Wash. The data also tentatively suggest 
that significant surface runoff (snowmelt runoff?) 
infiltrates to groundwater east of Yucca Mountain in 
Fortymile Wash. Such infiltration could significantly 
dilute radionuclide concentrations introduced from 
a Yucca Mountain repository. Groundwater from 
beneath Yucca Mountain can be thought of as 
being titrated into the relatively large Fortymile 
Wash groundwater system. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
CRWMS M&O (2000m) discusses 
hydrochemistry; Section 3.1.3.1 discusses 
spatial patterns of groundwater chemistry. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4. 
A key issue for radionuclide transport is whether or 
not, and to what degree, flowpaths from the 
repository enter the carbonate aquifer at distances 
of 5 to 30 km (3.1 to 18.6 mi.). The regional 
hydrologic model suggests that groundwater flow 
paths enter the carbonate aquifer about 10 km 
(6.2 mi.) south of the site and, farther south, come 
back up into the alluvial aquifer. If flow in the 
carbonates occurs, important Np(V) adsorption by 
calcite could be expected. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
No indication of flow in carbonates to 
date. Characterization discussed in 
Section 3.1; geologic setting of regional 
flow system discussed in 
Section 3.1.1.1.1; geologic setting of site 
flow system discussed in 
Section 3.1.1.2.1; relationship of SZ PMR 
to ISM PMR (CRWMS M&O 2000e) 
discussed in Section 1.5.1; hydrogeologic 
framework discussed in Sections 3.2.1 
and 3.3.5.2.

TDR-NBS-HS-000001 REV 00 ICN 01 A-17 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
The DOE approach to defining amounts of 
radionuclides that could be released from the 
buried waste and transported to the accessible 
environment through the UZ and SZ is in general 
highly conservative. The possible benefits of 
sorption, solubility, and redox reactions on reducing 
the maximum possible concentrations of 
radionuclides in groundwater have not been 
sufficiently emphasized. An analysis of transport 
processes and parameters that considers only 
sorption reactions as the geochemical control on 
maximum radionuclide concentrations is 
inadequate. Sorption only delays the peak release 
of long-lived radionuclides such as neptunium-237 
to the environment. Solubility, if applicable, can 
greatly reduce or eliminate releases. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Solute transport processes in conceptual 
model discussed in Section 3.2.4; in 
mathematical model in Section 3.3.2; 
particle tracking discussed in Section 
3.3.4; assumptions, uses, and limitations 
of radionuclide transport processes 
discussed in Section 3.5.2; abstraction of 
transport for TSPA discussed in 
Section 3.6.3.3. 
Some of the assumptions in TSPA-95 (CRWMS 
M&O 1995) that may be unnecessarily 
conservative are: 
1. The assumed solubility of U(VI) in Yucca 
Mountain groundwater probably is about 102 
too high. 
2. he assumed solubility of neptunium(V) in Yucca 
Mountain groundwater probably is at least 
about 101 too high. 
3. Reduction of neptunium(V) to neptunium(IV) by 
Iron(II)-containing minerals in the matrix of the 
volcanic rocks seems likely during groundwater 
flow. Reduction could lower the solubility of 
neptunium by about 103 times 
4. Adsorption of Np(V) by trace or minor minerals 
in the tuff, which are relatively ubiquitous and 
include Mn oxides, Iron(II)-containing silicates, 
and calcite, could reduce neptunium 
concentrations in the rock matrix by orders of 
magnitude. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Assumptions, uses, and limitations of 
radionuclide transport processes 
discussed in Section 3.5.2; abstraction of 
transport for TSPA discussed in 
Section 3.6.3.3. 
The potential effect of the thermal pulse on the SZ 
beneath the site will be a function of whether the 
flow occurs in the fractures or in the matrix (which 
includes tight fractures). If there is fracture flow 
only, then effects will occur at greater distances 
from the repository. If there is significant matrix 
flow, I would expect the increased temperatures to 
cause silica in the volcanic rocks to dissolve, to 
move to cooler locations, and then to precipitate 
and possibly clog the system. If calcite is saturated 
in the water, because of its retrograde solubility, it 
will precipitate and may clog the matrix and fine 
fractures adjacent to the hot waste. The clogging 
may lead to additional residence time for 
radionuclides in the matrix. Refluxing of 
condensed water may cause similar effects to 
occur at the water table beneath the site. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
UZ PMR (CRWMS M&O 2000b). 
Relationship of SZ to UZ discussed in 
Section 1.5.2; coupling of SZ with UZ 
discussed in Section 3.6.3.4.1.

TDR-NBS-HS-000001 REV 00 ICN 01 A-18 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
The likely fate of colloids will be the following: 
 Many will be filtered out by crushed tuff backfill or 
tuff invert under unsaturated conditions. 
 Degradation colloids (such as Pu oxides) and 
radiocolloids will be undersaturated with respect 
to the groundwater as soon as they move away 
from the waste. They will therefore tend to 
dissolve in the groundwater and, once in 
solution, tend to be adsorbed by rock surfaces in 
fractures and especially in the matrix. 
 Actinides on the surfaces of geocolloids will tend 
to desorb with groundwater flow. They will be 
readsorbed by surrounding rock surfaces that 
have the same surface bond strengths toward 
the actinides but have unoccupied surface sites 
and orders of magnitude more reactive surface 
area. The colloidal microspheres tracer test in 
the C-wells showed that the peak arrival 
preceded the conservative tracers (20 hrs versus 
30 hrs). About 85% of the microspheres were 
lost. This suggests that colloids can move in the 
SZ, but radionuclides/colloidal particles must 
travel first through the UZ, and losses are 
expected in the SZ. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
 This is discussed in the Engineered 
Barrier System PMR (CRWMS M&O 
2000g) and UZ PMR (CRWMS M&O 
2000b). 
 This is discussed in the Engineered 
Barrier System PMR (CRWMS M&O 
2000g) and UZ PMR (CRWMS M&O 
2000b). 
 Tracer tests discussed in Section 
3.1.3.2. Colloid lab experiments 
discussed in Section 3.1.4.3; modeling 
of colloid-facilitated transport discussed 
in Sections 3.2.4.5 and 3.3.2.4. 
The key radionuclide of concern in colloidal 
transport is Pu. Pu transport has been 
documented in a shallow aquifer in Mortland 
Canyon, Los Alamos National Laboratory. Pu 
movement was at the surface in alluvial sediments 
and was washed downward on sediments to the 
shallow groundwater table. This scenario is not 
analogous to possible Pu migration in the SZ 
beneath Yucca Mountain. In a second study, Pu 
from underground nuclear tests at the Nevada Test 
Site moved in the groundwater several kilometers 
from an underground test. The Pu was probably 
within melted tuff particles that were transported by 
explosive injection. This is obviously not an 
analogue for Yucca Mountain. Bomb pulse 
chlorine-36-aged water found deep in the UZ under 
Yucca Mountain indicates the existence of fast 
paths that may extend to the SZ. It is possible that 
colloidal radionuclides could take the same 
pathways. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Colloid-facilitated transport is now 
explicitly modeled. Tracer tests discussed 
in Section 3.1.3.2. Colloid laboratory 
experiments discussed in Section 3.1.4.3; 
modeling of colloid-facilitated transport 
discussed in Sections 3.2.4.5 and 3.3.2.4. 
Recommendations For Reducing Uncertainty: 
1. C-wells tests should be run for longer times to 
evaluate the relative importance of matrix vs. 
fracture flow in the Tertiary volcanic rocks. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Multi-well, multi-tracer testing at C-wells 
has been done. Hydraulic well testing 
discussed in Section 3.1.2.2, tracer tests 
discussed in Section 3.1.3.2.

TDR-NBS-HS-000001 REV 00 ICN 01 A-19 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
2. Available groundwater chemistry and isotopic 
data for the whole Yucca Mountain-Fortymile 
Wash flow system to its discharge area in the 
Amargosa Desert should be mapped in detail. 
The southern end of this system was last 
examined by Claassen (1983). This task might 
lead to conclusions regarding amounts of 
possible mixing of volcanic, carbonate, and 
alluvial groundwaters in southern Fortymile 
Wash. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Maps have been done. CRWMS M&O 
(2000m) and Section 3.1.3 discuss 
hydrochemical data and provide detailed 
maps. Section 3.1.1.1.3 discusses the 
hydrochemistry of regional system. 
Section 3.1.1.2.3 discusses the 
hydrochemistry of site system. 
Section 3.4.4 discusses comparison of 
hydrochemical data with calculated flow 
pathways. 
3. Delta carbon-14 groundwater data from the 
literature should be corrected using the 
NETPATH code approach presented to us by 
Kwicklis in a SZ Expert Elicitation Workshop 
(CRWMS M&O 1998b). This would provide an 
internally consistent delta carbon-14 data set 
for the general area, including the complete 
Yucca Mountain groundwater flow system. 
Such data might be useful for computing 
groundwater travel times and matrix versus 
fracture flow. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
CRWMS M&O (2000m, Table 8) 
document results of the NETPATH code 
corrections to groundwater carbon-14 
ages; Section 3.1.3 discuss 
hydrochemical data; Section 3.1.1.1.3 
discusses the hydrochemistry of regional 
system; Section 3.1.1.2.3 discusses the 
hydrochemistry of site system. Section 
3.4.2 discusses calibration of model to 
hydrochemical observations. 
4. Interpreting and modeling the groundwater 
geochemical data in the vicinity of Yucca 
Mountain in the context of the geology and 
groundwater hydrology should be emphasized. 
Groundwater chemistry should be related to 
sampling depths, water levels and 
transmissivity, fracture zones, specific 
formations and their mineralogy, and rock 
matrix versus fracture flow properties. Such an 
analysis could help explain much of the water 
chemistry information, which in turn should help 
us resolve ambiguous interpretations of the 
groundwater hydrology. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Extensive interpretation of groundwater 
geochemical data done and documented 
in CRWMS M&O (2000m). Section 3.1.3 
discuss hydrochemical data. 
Section 3.1.1.1.3 discusses the 
hydrochemistry of regional system. 
Section 3.1.1.2.3 discusses the hydrochemistry 
of site system. 
Section 3.4.4 discusses comparison of 
hydrochemical data with calculated flow 
pathways. 
5. Geochemical and hydrologic data and models 
should be used to evaluate the relative 
contributions of infiltrating surface runoff and 
groundwater from under Yucca Mountain to the 
volume of groundwater flow in Fortymile Wash 
east and southeast of Yucca Mountain. Runoff 
infiltration in Fortymile Wash may be the chief 
dilutent for radionuclides released from the 
repository. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Section 3.1.3 discusses hydrochemical 
data; Section 3.1.1.1.3 discusses the 
hydrochemistry of regional system; 
Section 3.1.1.2.3 discusses the hydrochemistry 
of site system; Section 3.4.4 
discusses comparison of hydrochemical 
data with calculated flow pathways.

TDR-NBS-HS-000001 REV 00 ICN 01 A-20 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
6. Pump tests of shallow wells in the Tertiary 
volcanics under Yucca Mountain probably will 
sample fracture flow which is likely to be 
oxidizing with an Eh above 300 mv. The only 
way to determine if matrix flow will lead to Eh 
values low enough to cause reduction of Np(V) 
to insoluble Np(IV) is theoretically, or preferably 
experimentally, in the laboratory. My 
predictions of percentile of CDF values for 
Np(V) adsorption were based on theory. Lab 
experiments could be performed in closed 
vessels using rock fragments or an 
ultracentrifuge and rock cores to speed up flow, 
with measurements being made of dissolved 
oxygen levels and Eh as a function of time. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Oxidation potential discussed in 3.1.3.3. 
Laboratory sorption discussed in 
Section 3.1.4.1. 
7. The prediction that maximum uranium 
concentrations in Yucca Mountain groundwater 
are limited by the solubility of uranophane is 
based on computer modeling. Experiments 
should be performed on the solubility of 
uranophane in simulated groundwater in the 
presence of volcanic tuff materials to confirm 
model calculations. 
CRWMS M&O 
1998b 
[summaries, 
Langmuir] 
Tests not done to date. UZ model 
provides input to SZ model on 
concentrations of radionuclides. 
It is possible to analyze the tracer breakthrough 
curves to obtain information and parameters 
associated with the small-scale heterogeneities 
that control flow channeling. A more direct way is 
to obtain permeability values from packed-off 
intervals in the many boreholes at the site. This 
can also be done by flow-meter testing without 
packers. In this case, a conventional spinner flow 
meter may not be accurate enough. One may 
need to use a heat-pulse flow meter or the fluid 
logging method. C-hole data already indicate that 
strong variations in permeability occur at Yucca 
Mountain. Flows into C#1, C#2, and C#3 are 
dominated by three, three, and four specific vertical 
intervals, respectively, with one interval in each 
case carrying more than 50 percent of the flow into 
the well. This is consistent with the current 
knowledge that roughly 10 to 20 percent of the 
fractures contribute to flow, with only 1 to 
10 percent contributing significantly. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Multi-well, multi-tracer tests done at 
C-wells. Characterization discussed in 
Section 3.1; hydraulic well tests in Section 
3.1.2.2; tracer tests in Section 3.1.3.2; 
laboratory data in Section 3.1.4. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional models with fluxes from 
calibrated model, measured upward 
gradient with predicted upward gradient, 
hydrochemical data with calculated 
particle pathways, and natural analogs. 
These activities and process model 
uncertainties are discussed in Section 3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-21 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
We need to know the source term at the 
unsaturated-saturated zone interface, where 
channelized flow from the unsaturated region 
enters the saturated region, and where flow is 
expected to be channeled. The source term must 
be studied carefully and its characteristics 
evaluated. 
Two potentially important issues need to be 
considered: 
1. Under steady flow conditions in the UZ, flow is 
expected to be channeled along relatively small 
pores (corresponding perhaps to smaller local 
permeabilities), because the large pores will be 
occupied by air, while the main flow in the SZ 
will be channeled along higher-permeability 
regions. The switch-over from lowerpermeability 
areas to higher-permeability areas 
of the heterogeneous field needs to be 
evaluated in terms of possible dilution process. 
2. The water table cuts through a number of 
hydrogeologic units, whose permeabilities differ 
by several orders of magnitude. The particular 
units in which leakage from the potential 
repository reaches the SZ may each provide 
different source term characteristics. These 
two issues are in addition to the usual concern 
of solute transport through the capillary fringe 
and effects of changes in the water table. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
UZ model (CRWMS M&O 2000b) 
provides input to SZ model on 
concentrations of radionuclides. Coupling 
of SZ flow and transport with UZ flow and 
transport discussed in Section 3.6.3.4.1. 
Beyond the source region at the water table, flow 
will follow hydrogeologic units, probably primarily 
the Bullfrog unit. Here, flow will be according to 
stream lines, and dilution will be minor. As it 
encounters offsets due to faults cutting through the 
hydrogeologic unit, it will digress, bifurcate, or 
spread out depending on the fault permeability and 
local conditions. It is not clear whether there will be 
significant dilution at such locations, but careful 
analysis can, and should, be made to answer this 
question. Solutes along the stream lines are 
subjected to local dispersion or molecular diffusion 
and can spread to neighboring stream lines. The 
dilution resulting from this process would be much 
smaller than that commonly assumed for 
dispersion. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Site-scale SZ flow and transport model 
developed. Roles of faults discussed in 
Section 3.2.3.4. 
Heterogeneity discussed in 
Section 3.2.2.4. 
Particle tracking method for radionuclide 
transport discussed in Section 3.3.4. 
After a tortuous journey, flow arrives at the users' 
area and is collected from a so-called capture 
zone. If a fault or special feature occurs near this 
area, it may provide a focusing effect near the 
location where the regulatory criteria are to be 
applied. Such features must be included in the 
model. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Dilution in water supply discussed in 
Section 3.6.3.3.4. 
Relationship to Biosphere PMR (CRWMS 
M&O 2000c) discussed in Section 1.5.3. 
Coupling with biosphere model discussed 
in Section 3.6.3.4.2.

TDR-NBS-HS-000001 REV 00 ICN 01 A-22 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
The mixing depth concept is not realistic. Rather, 
we need to consider the three stages of tracer 
transport to address this issue. First, one must 
consider the source term to the SZ. It is likely that 
there will be channeled flow in the UZ, and that 
these channeled flow paths will then enter the SZ. 
Thus the source term is not a smeared-out plume, 
but a number of localized, higher-concentration 
"point sources. Second, once the solutes enter 
the SZ, they will again follow certain stream tubes, 
or flow channels, with only minor dispersion within 
each stream tube. The degree of such 
channelization depends on the degree of 
heterogeneity (standard deviation of the hydraulic 
conductivity values), and the spacing of these 
channels depends on the spatial correlation 
structure of heterogeneities in permeability. Then, 
thirdly, the different flow paths will come to the 
observational "fence" area and to an extraction 
well, where they will be captured and pumped for 
various uses. At this point, a dosage limit is to be 
imposed. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
UZ model (CRWMS M&O 2000b) 
provides input to SZ model on 
concentrations of radionuclides. 
Relationship of SZ to UZ discussed in 
Section 1.5.2. 
Coupling of UZ flow and transport model 
with SZ flow and transport discussed in 
Section 3.6.3.4.1. 
Large dilution of the solute concentration between 
the source zone at the unsaturated-saturated zone 
interface and the capture zone of the users wells is 
not expected. Molecular diffusion will occur within 
the flow channels, but there will likely be only a 
small longitudinal dispersion. Dilution is expected 
to be only about a factor of 2 to 10 over even 
kilometers of distance. This is because longitudinal 
dispersion occurs from Taylor dispersion, which 
has a characteristic length that is on the order of 
the width of the channel. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Site-scale SZ flow and transport model 
developed that addresses dispersion 
better. Conceptual model diffusion, 
sorption, and dispersion discussed in 
Sections 3.2.4.2, 3.2.4.3, and 3.2.4.4; 
mathematical model diffusion, sorption, 
and dispersion discussed in 
Sections 3.3.2.2, 3.3.2.3, and 3.3.2.4; 
transport processes assumptions, uses, 
and limitations discussed in Section 3.5.2. 
There are two places where significant dilution may 
occur. The first is at the interface between the 
unsaturated and the saturated zones, especially if 
the interface (i.e., the water table) fluctuates. If 
flow channels go from a low-permeability area in 
the UZ to a high-permeability area in the SZ, 
spreading may also occur. Unfortunately, this has 
not been carefully studied. Research is underway; 
we hope to have some results and know their 
implications in the near future. The other dilution 
step is at the production well. The production well 
creates what is called a capture zone, inside of 
which all the stream lines are captured and mixed 
in the production wells. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Coupling of UZ flow and transport model 
with SZ flow and transport discussed in 
Section 3.6.3.4.1. 
Dilution in water supply discussed in 
Section 3.6.3.3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-23 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
A dilution factor can be assessed by using a 
"bundle-of-particle-lines" model. Consider the 
source term at the SZ-UZ interface to be 
represented by a number of localized "point 
sources" that correspond to channeled flow in the 
UZ. Then, from each point source, particles are 
traced along stream lines through the 
hydrogeologic units, allowing for flow around faultrelated 
offsets and across or around faults. Along 
the way one can account for molecular diffusion 
and local dispersion by allowing particles to jump to 
neighboring stream lines. These particle lines are 
traced to the capture zone of the users wells, 
where these lines and flow lines without 
contamination are collected. Thus, dilution can be 
calculated. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Site-scale SZ flow and transport model 
developed. Coupling of UZ flow and 
transport model with SZ flow and transport 
discussed in Section 3.6.3.4.1. 
Particle tracking method for radionuclide 
transport discussed in Section 3.3.4. 
Dilution in water supply discussed in 
Section 3.6.3.3.4. 
If the data are carefully considered, it should be 
possible to use the laboratory Kd derived for Yucca 
Mountain rocks. A migration experiment done at 
the Grimsel site found good agreement between 
laboratory and field measurements of Kd and 
demonstrated that matrix diffusion exists in the field 
by examining the tails of the breakthrough curves. 
To obtain consistency, the flow model must be 
conceptualized correctly based on a careful 
analysis of field hydraulic data. Under such a 
strong prerequisite, results from column 
experiments probably are consistent and useful for 
estimating field data. It is somewhat troubling that 
there is a ten-fold discrepancy between the C-wells 
data and laboratory data. It is likely that the flow 
field was not properly modeled 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Multi-well, multi-tracer tests done at 
C-wells. Laboratory data on sorption, 
matrix diffusion, and colloid transport 
discussed in Section 3.1.4; hydraulic well 
tests discussed in Section 3.1.2.2; tracer 
tests discussed in Section 3.1.3.2. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional model with fluxes from calibrated 
model, measured upward gradient with 
predicted upward gradient, hydrochemical 
data with calculated particle pathways, 
and natural analogs. These activities and 
process model uncertainties are 
discussed in Section 3.4. 
Kd use is open to some questions. It would be 
useful to consider real chemistry and perform 
chemical modeling, accounting for detailed 
chemical reactions to assess the range and limit of 
this approach. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Laboratory data on sorption, matrix 
diffusion, and colloid transport discussed 
in Section 3.1.4; hydraulic well tests 
discussed in Section 3.1.2.2; tracer tests 
discussed in Section 3.1.3.2.

TDR-NBS-HS-000001 REV 00 ICN 01 A-24 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
Recommendations For Reducing Uncertainty: 
1. Perform long-term interference tests with 
pumping in a C-well (or another well) and 
monitoring as many observation wells as 
possible over a wide area. These tests will help 
determine the horizontal distribution of 
hydraulic conductivity and the hydraulic 
parameters associated with major faults. 
Analysis using a multi-parameter fit of a 
numerical model will be needed. Associated 
with this effort, a long-term tracer test should 
also be performed. Careful design studies with 
numerical model are needed. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Multi-well, multi-tracer tests done at 
C-wells. 
Characterization discussed in Section 3.1; 
hydraulic well tests in Section 3.1.2.2; 
tracer tests in Section 3.1.3.2; laboratory 
data in Section 3.1.4. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional model with fluxes from calibrated 
model, measured upward gradient with 
predicted upward gradient, hydrochemical 
data with calculated particle pathways, 
and natural analogs. These activities and 
process model uncertainties are 
discussed in Section 3.4. 
Uses of the SZ model in site 
characterization activities discussed in 
Section 3.5.3. 
2. Re-drill borehole G-2 and emplace packers to 
study relative changes in packed intervals to 
reduce the uncertainty concerning the causes 
for the large hydraulic gradient. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
The large hydraulic gradient is discussed 
in Sections 3.2.2.3 and 3.2.5.1. 
Borehole WT-24 drilled to investigate the 
large hydraulic gradient indicates that the 
large hydraulic gradient is partially due to 
perching. 
3. Use temperature log data in a calibration of a 
3-D site- or subsite-scale model, especially to 
address the question of upward flow into the 
volcanic aquifer. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
Temperature-log data not used in 
calibration as most temperature data were 
not collected in a manner that would allow 
their use for this purpose (i.e., cased 
boreholes or temperature measured 
without allowing hole to equilibrate). 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional model with fluxes from calibrated 
model, measured upward gradient with 
predicted upward gradient, hydrochemical 
data with calculated particle pathways, 
and natural analogs. These activities and 
process model uncertainties are 
discussed in Section 3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-25 August 2000 
Table A-1. Issues for Saturated Zone Flow and Transport (Continued) 
Issue Source PMR Approach 
4. Recalibrate site-scale model, allowing for a 
more careful and definite coupling with the 
regional model. For example, the fluxes into 
and out of the site-scale area in the regional 
model must be consistent with the imposed 
boundary conditions on the site-scale model, so 
that total fluxes at the boundaries are 
conserved. This eventually would yield more 
convincing results from the site model. 
CRWMS M&O 
1998b 
[summaries, 
Tsang] 
New site and regional models developed; 
groundwater flux relationship between 
models discussed in Section 3.4.2. 
Model validation now includes 
comparisons of: permeability data to 
calibrated permeability values, fluxes from 
regional model with fluxes from calibrated 
model, measured upward gradient with 
predicted upward gradient, hydrochemical 
data with calculated particle pathways, 
and natural analogs. These activities and 
process model uncertainties are 
discussed in Section 3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 A-26 August 2000 
INTENTIONALLY LEFT BLANK

TDR-NBS-HS-000001 REV 00 ICN 01 August 2000 
APPENDIX B 
U.S. NUCLEAR REGULATORY COMMISSION ISSUE RESOLUTION 
STATUS REPORTS AND KEY TECHNICAL ISSUES

TDR-NBS-HS-000001 REV 00 ICN 01 August 2000

TDR-NBS-HS-000001 REV 00 ICN 01 B-1 August 2000 
APPENDIX B 
U.S. NUCLEAR REGULATORY COMMISSION ISSUE RESOLUTION STATUS 
REPORTS AND KEY TECHNICAL ISSUES 
Table B-1. Issue Resolution Status Report Technical Acceptance Criteria 
Key Technical Issue: Radionuclide Transport 
Subissue 2 
Radionuclide Transport Through Alluvium PMR Approach 
1a. For the estimation of radionuclide transport through 
alluvium, the Department of Energy (DOE) has 
determined, through performance assessment (PA) 
calculations, whether radionuclide attenuation 
processes such as sorption, precipitation, radioactive 
decay, and colloidal filtration are important to 
performance. 
PA calculations indicate these processes are important. 
Laboratory data on sorption, matrix diffusion and colloids 
discussed in Section 3.1.4; conceptual models of solute 
transport, Section 3.2.4; mathematical models of 
radionuclide transport, Section 3.3.1; sorption and matrix 
diffusion sub-model, Section 3.3.4.2; assumptions and 
limitations associated with radionuclide transport 
processes, Section 3.5.2; abstraction of radionuclide 
transport in Total System PA, Section 3.6.3. 
1b. For the estimation of radionuclide transport through 
alluvium, DOE has (i) assumed the sorption 
coefficient is zero and radionuclides travel at the rate 
of groundwater flow, if it has been found that 
radionuclide attenuation is unimportant to 
performance and it can be demonstrated that this 
assumption is conservative, in which case Criteria 2 
and 3 do not have to be met or (ii) demonstrated that 
Criterion 2 or 3 has been met, if radionuclide 
attenuation in alluvium is important to performance or 
if an assumption that the sorption coefficient is zero in 
alluvium is not conservative. 
For radionuclides with essentially no sorption potential 
(e.g., carbon, chlorine, iodine), the sorption coefficient (Kd) 
is assumed to be zero in alluvium. Laboratory data on 
sorption, matrix diffusion, and colloids discussed in 
Section 3.1.4; tracer tests, Section 3.1.3.2; conceptual 
models of solute transport, Section 3.2.4; mathematical 
models of radionuclide transport, Section 3.3.1; sorption 
and matrix diffusion sub-model, Section 3.3.4.2; 
assumptions and limitations associated with radionuclide 
transport processes, Section 3.5.2; abstraction of 
radionuclide transport in Total System Performance 
Assessment (TSPA), Section 3.6.3.3. 
2a. For the valid application of the Kd approach, using 
equation (1) Rf = 1+ rbKd/n, DOE has demonstrated 
that the flow path acts as a single continuum porous 
medium. If the flow cannot be shown to be a single 
continuum porous medium, then the acceptance 
criteria for radionuclide transport in fractured rock 
apply. 
Fluid flow in the alluvium is likely to be well represented 
using a porous continuum conceptual model. Data to 
quantify the alluvial portion of the flow path are sparse, 
and hydrologic parameters used in numerical models 
should be considered to be bounding (Section 3.2.4.1.2). 
2b. For the valid application of the Kd approach, using 
equation (1) Rf = 1+ rbKd/n, DOE has demonstrated 
that appropriate values for the parameters, Kd, n or t, 
and rb have been adequately considered (e.g., 
experimentally determined or measured). 
Transport of sorbing solutes in porous media is a subject 
that has been well studied. Sorption coefficients onto 
alluvium from the Nye County Early Warning Drilling 
Program (NCEWDP) wells have been measured for a few 
key radionuclides; for the remaining radionuclides, 
sorption coefficients have been estimated based on the 
corresponding values measured for crushed tuff. Recent 
evaluations for the sorption of neptunium, technetium, and 
iodine have been accomplished for alluvium. Laboratory 
data on sorption, matrix diffusion, and colloids are 
discussed in Section 3.1.4. In the alluvium, n is modeled 
stochastically and rb is modeled as a constant.

TDR-NBS-HS-000001 REV 00 ICN 01 B-2 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 2 
Radionuclide Transport Through Alluvium 
(Continued) PMR Approach 
2c. For the valid application of the Kd approach, using 
equation (1) Rf = 1+ rbKd/n, DOE has demonstrated 
that the following assumptions (i.e., linear isotherm, 
fast reversible sorption reaction, and constant bulk 
chemistry) are valid. 
Sorption is incorporated into the site-scale saturated-zone 
(SZ) flow and transport model using a linear isotherm 
model (Sections 3.2.4.3 and 3.3.2.3). Laboratory data on 
sorption, matrix diffusion, and colloids are discussed in 
Section 3.1.4; tracer tests, Section 3.1.3.2; conceptual 
models of solute transport, Section 3.2.4. 
3a. For the valid application of process models such as 
surface complexation, ion exchange, 
precipitation/dissolution, and processes involving 
colloidal material, DOE has demonstrated that the 
flow path acts as a single continuum porous medium 
(see USFIC IRSR [NRC 1999a], deep percolation on 
subissue describing methods of estimating matrix 
properties as parameters). 
Fluid flow in the alluvium is likely to be well represented 
using a porous continuum conceptual model. Data to 
quantify the alluvial portion of the flow path are sparse, 
and hydrologic parameters used in numerical models 
should be considered to be bounding (Section 3.2.4.1.2). 
Conceptual model of SZ flow and transport discussed in 
Section 3.2, heterogeneity in Section 3.2.2.4. Model 
validation now includes comparisons of: permeability data 
to calibrated permeability values, fluxes from regional 
model with fluxes from calibrated model, measured 
upward gradient with predicted upward gradient, and 
hydrochemical data with calculated particle pathways; as 
well as natural analogs. These activities and process 
model uncertainties are discussed in Section 3.4. (Note: 
criterion refers to deep percolation in USFIC IRSR (NRC 
1999a), which is an unsaturated zone [UZ] subissue.) 
3b. For the valid application of process models such as 
surface complexation, ion exchange, 
precipitation/dissolution, and processes involving 
colloidal material, DOE has demonstrated that 
appropriate values are used in process models. 
Characterization discussed in Section 3.1; laboratory data, 
Section 3.1.4; hydraulic well tests, Section 3.1.2.2; tracer 
tests, Section 3.1.3.2. Model validation now includes 
comparisons of: permeability data to calibrated 
permeability values, fluxes from regional model with fluxes 
from calibrated model, measured upward gradient with 
predicted upward gradient, hydrochemical data with 
calculated particle pathways, and natural analogs. These 
activities and process model uncertainties are discussed 
in Section 3.4. 
3c. For the valid application of process models such as 
surface complexation, ion exchange, 
precipitation/dissolution, and processes involving 
colloidal material, DOE has demonstrated that the 
three implicit assumptions (as in 2c) are valid, if 
process models are intended to yield a constant Kd 
for use in equation (1); otherwise determined 
transport in a dynamic reactive transport system 
model (e.g., PHREEQC, MULTIFLO, 
HYDROGEOCHEM, etc.) 
Laboratory data on sorption, matrix diffusion, and colloids 
discussed in Section 3.1.4; tracer tests, Section, 3.1.3.2; 
conceptual models of solute transport, Section 3.2.4. 
Model validation now includes comparisons of: 
permeability data to calibrated permeability values, fluxes 
from regional model with fluxes from calibrated model, 
measured upward gradient with predicted upward 
gradient, hydrochemical data with calculated particle 
pathways, and natural analogs. These activities and 
process model uncertainties are discussed in Section 3.4.

TDR-NBS-HS-000001 REV 00 ICN 01 B-3 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
KTI: Radionuclide Transport 
Subissue 3 
Radionuclide Transport Through Fractured Rock PMR Approach 
1a. For the estimation of radionuclide transport through 
fractured rock, DOE has determined, through PA 
calculations, whether radionuclide attenuation 
processes such as sorption, precipitation, radioactive 
decay, and colloidal filtration are important to 
performance. 
PA calculations have determined that such processes are 
important. Abstraction of radionuclide transport in TSPA 
is discussed in Section 3.6.3.3; laboratory data on 
sorption, matrix diffusion, and colloids, Section 3.1.4; 
conceptual models of solute transport, Section 3.2.4; 
mathematical models of radionuclide transport, Section 
3.3.1; sorption and matrix diffusion sub-model, Section 
3.3.4.2; assumptions and limitations associated with 
radionuclide transport, Section 3.5.2; heterogeneity, 
Section 3.2.2.4. 
1b. For the estimation of radionuclide transport through 
fractured rock, DOE has assumed Kd (or KA) is zero 
and radionuclides travel at the rate of groundwater 
flow through fractures, if it has been found that 
radionuclide attenuation in fractures is unimportant to 
performance and it can be demonstrated that this 
assumption is conservative. In this case, Acceptance 
Criterion 2 does not have to be met. 
For radionuclides with essentially no sorption potential 
(e.g., carbon, chlorine), the sorption coefficient (Kd) is 
assumed to be zero. Laboratory data on sorption, matrix 
diffusion, and colloids discussed in Section 3.1.4; tracer 
tests, Section, 3.1.3.2; heterogeneity, Section 3.2.2.4; 
conceptual models of solute transport, Section 3.2.4; 
mathematical models of radionuclide transport, Section 
3.3.1; sorption and matrix diffusion sub-model, Section 
3.3.4.2; assumptions and limitations associated with 
radionuclide transport processes, Section 3.5.2; 
abstraction of radionuclide transport in TSPA, Section 
3.6.3.3. 
1c. For the estimation of radionuclide transport through 
fractured rock, DOE has justified the length of the 
flowpath to which these fracture transport conditions 
apply. 
Chloride data (Figure 3-3), as well as other chemical and 
isotopic data (CRWMS M&O 2000m and Section 
3.1.1.2.3) and the potentiometric surface map 
(Figure 3-5), have been used to constrain flowpaths. 
Particle tracking methodology is discussed in Section 
3.3.4; validation in Section 3.4; assumptions, uses, and 
limitations of flow model, Section 3.5. 
2a. If credit is to be taken for radionuclide attenuation in 
fractured rock, DOE has demonstrated the capability 
to predict breakthrough curves of reactive, 
nonreactive, and colloidal tracers in field tests. 
Model of fracture flow and matrix diffusion consistent with 
data. Sorbing tracer (lithium) breakthrough consistent 
with combined matrix diffusion/sorption model. 
Microspheres break through slightly earlier than solutes, 
but are attenuated. Tracer tests discussed in Section 
3.1.3.2. Calibration to pump tests in C-wells discussed in 
Section 3.4.3. 
2b. If credit is to be taken for radionuclide attenuation in 
fractured rock, DOE has demonstrated 
nonradioactive tracers used in field tests are 
appropriate homologues for radioelements. 
Model of fracture flow and matrix diffusion consistent with 
data. Sorbing tracer (lithium) breakthrough consistent 
with combined matrix diffusion/sorption model. 
Microspheres break through slightly earlier than solutes, 
but are attenuated Tracer tests discussed in Section 
3.1.3.2. Calibration to pump tests in C-wells discussed in 
Section 3.4.3. 
2c. If credit is to be taken for radionuclide attenuation in 
fractured rock, DOE has justified the length of the 
flowpath to which these fracture transport conditions 
apply. 
Chloride data (Figure 3-3), as well as other chemical and 
isotopic data (CRWMS M&O 2000m and Section 
3.1.1.2.3) and the potentiometric surface map 
(Figure 3-5), have been used to constrain flowpaths. 
Particle tracking methodology discussed in Section 3.3.4; 
validation, Section 3.4; Assumptions, uses, and limitations 
of flow model, Section 3.5.

TDR-NBS-HS-000001 REV 00 ICN 01 B-4 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 4 
Nuclear Criticality in the Far Field PMR Approach 
1. DOE has determined the probabilities of scenarios 
that lead to the accumulation of a critical mass of 
fissile material into a critical configuration within 
10,000 years in the far-field using appropriate site 
characteristics. 
The DOE plans to evaluate criticality using the method in 
the criticality analysis methodology topical report (YMP 
1998) and its supporting documents. Features, events, 
and processes (FEPs) screening considers criticality event 
in far field to be low probability. Preliminary analyses 
show no significant effect on calculated performance in 
first 10,000 yr., even if waste packages are breached. 
FEPs are discussed in Section 1.3. 
2. For those scenarios that have probabilities greater 
than 10-7, the DOE has determined their effects on 
performance. 
The DOE plans to evaluate criticality using the method in 
the criticality analysis methodology topical report (YMP 
1998) and its supporting documents. FEPs screening 
considers criticality event in far field to be low probability. 
Preliminary analyses show no significant effect on 
calculated performance in first 10,000 yr., even if waste 
packages are breached. FEPs are discussed in Sections 
1.3. 
Key Technical Issue: Structural Deformation and Seismicity 
Subissue 3 
Fracturing and Structural Framework 
of the Geologic Setting PMR Approach 
Criterion 3Alternative modeling approaches for fracture 
distribution and properties of fractures consistent with 
available data and current geologic understanding are 
investigated, and results and limitations are appropriately 
considered in process, TSPA, or both models of ambient 
and perturbed repository conditions. (Review method [p. 
51 in IRSR] indicates that staff will examine the fracture 
data and properties that DOE has abstracted into its 
process level models and SZ groundwater flow models to 
ensure adequate integration.) 
Heterogeneity and hydrologic features of the 
hydrogeologic framework are discussed in Sections 
3.2.2.4 and 3.2.2.5. Role of faults as internal boundaries 
is discussed in Section 3.2.3.4. Numerous hydrologic 
features corresponding to faults and geologic zones are 
explicitly incorporated into the site-scale SZ flow and 
transport model as part of the calibration process 
(Section 3.2.2.5). The presence of faults and fracture 
zones that are not explicitly represented in the site-scale 
model, and their potential impact on groundwater flow, is 
implicitly included in the nominal case through 
consideration of horizontal anisotropy in permeability in 
the fractured volcanic units downgradient of the 
repository. Given the uncertainty in anisotropy, and to 
simplify the model, the potential effects of anisotropy are 
bounded in the model. Anisotropy and incorporation of 
effects in the model are discussed in Sections 3.5.1 and 
3.7.2. Horizontal anisotropy discussed in Section 3.2.5.3. 
Criterion 5Integration results of abstractions of fracture 
data are consistent with physical and geological 
phenomena and coupled processes. (Review method [p. 
52 in IRSR] indicates that staff will examine input of 
fracture models to SZ flow modules to ensure adequate 
integration.) 
Heterogeneity and hydrologic features of the 
hydrogeologic framework are discussed in Sections 
3.2.2.4 and 3.2.2.5; role of faults as internal boundaries, 
Section 3.2.3.4

TDR-NBS-HS-000001 REV 00 ICN 01 B-5 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Key Technical Issue: Total System Performance Assessment and Integration 
System Description and Demonstration 
of Multiple Barriers PMR Approach 
Element 1 - Transparency and Traceability of the 
Analysis 
T1. Documents and reports are complete, clear, and 
consistent. 
The SZ PMR was carefully structured to be complete, 
clear, and consistent. Reviews of the draft document 
included checks for completeness, clarity, and 
consistency. 
T2. Information is amply cross referenced. The SZ PMR contains ample references to data sources, 
codes, assumptions, and conclusions. 
Element 2 - Features, Events, and Processes 
Identification and Screening 
T1. The screening process by which FEPs were included 
or excluded from the TSPA is fully described. 
Excluded and included FEPs, including the rationale for 
these decisions, are summarized in Section 1.3. 
T2. Relationships between relevant FEPs are fully 
described. 
Relationship between primary and secondary FEPs 
described in Section 1.3. Additional documentation 
including the TSPA disposition of FEPs, IRSR issues 
relevant to specific FEPs, and analysis and discussion on 
specific FEPs are provided in the SZ FEPs AMR (CRWMS 
M&O 2000q). 
Element 3 - Abstraction Methodology 
T1. The levels and method(s) of abstraction are described 
starting from assumptions defining the scope of the 
assessment down to assumptions concerning specific 
processes and the validity of given data. 
For each submodel in the SZ PMR, descriptions are 
provided of process models and, if the models are 
abstracted, descriptions of the abstractions of the models. 
The description includes a summary of data and 
assumptions used to construct models. The AMRs 
describing the models and the abstracted models provide 
additional details regarding data and assumptions. 
T2. A mapping (e.g., a road map diagram, a traceability 
matrix, a cross-reference matrix) is provided to show what 
conceptual features (e.g., patterns of volcanic events) 
and processes are represented in the abstracted models, 
and by what algorithms. 
The SZ PMR and supporting AMRs provide descriptions of 
the basis for the decisions and assumptions that were 
made during the abstraction process. 
T3. An explicit discussion of uncertainty is provided to 
identify which issues and factors are of most concern or 
are key sources of disagreement among experts. 
The SZ PMR provides a discussion of uncertainties and 
limitations for the major process models included in the 
report. The AMRs describing the abstracted models 
provide additional details regarding uncertainties and 
limitations. 
Element 4 - Data Use and Validity 
T1. The pedigree of data from laboratory tests, natural 
analogs, and the site is clearly identified. 
The quality assurance status of the data and software 
used in the component models is summarized in 
Section 1.4. 
T2. Input parameter development and basis for their 
selection is described. 
Input parameter development and the basis for using the 
parameters are discussed in the SZ PMR. The AMRs 
describing the models provide additional details regarding 
input parameter development and the basis for input 
selection.

TDR-NBS-HS-000001 REV 00 ICN 01 B-6 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
System Description and Demonstration 
of Multiple Barriers (Continued) PMR Approach 
T3. A thorough description of the method used to identify 
performance confirmation program parameters 
The Performance Confirmation Plan (CRWMS M&O 
2000v) specifically addresses the methodology for 
identifying and selecting parameters that are important to 
performance based upon TSPA sensitivity analyses and 
the repository safety strategy. Methods used to collect 
information for each parameter will be described by the 
performance confirmation plan or relevant supporting 
documents to support the license application. 
Performance confirmation test selection and rationale is 
described in the plan based upon the importance of the 
parameter being measured, and the ability of the test to 
distinguish construction, emplacement, or time dependent 
changes in the parameter important to performance. 
Element 5- Assessment Results 
T1. PA results (i.e., the peak expected annual dose 
within the compliance period) can be traced back to 
applicable analyses that identify the FEPs, assumptions, 
input parameters, and models in the PA. 
Features, processes, conceptual models, and their 
implementation into the TSPA are summarized in the 
TSPA-SR. This discussion will be based in part on 
information provided by the SZ PMR. 
T2. The PA results include a presentation of intermediate 
results that provide insight into the assessment (e.g., 
results of intermediate calculations of the behavior of 
individual barriers). 
TSPA-SR provides performance analysis results for the 
total system and will include intermediate results for the 
components of the system. 
Element 6 - Code Design and Data Flow 
T1. The flow of information (input and output) between 
the various modules is clearly described. 
A description of information flow between component 
models including couplings between information and data, 
conceptual and process-level models, and abstracted 
models are provided in the TSPA-SR. 
T2. Supporting documentation (e.g., user's manuals, 
design documents) clearly describes code structure and 
relationships between modules. 
The TSPA code and supporting documentation (i.e., the 
users guide) are described or referenced in the 
TSPA-SR. 
Subissue 3 
Model Abstraction PMR Approach 
Element 8  Flow Paths in the Saturated Zone 
T1. Sufficient hydrogeologic data (field, laboratory, 
and/or natural analog data) are available to adequately 
define relevant parameters and conceptual models 
necessary for developing the flow paths in the SZ 
abstraction in TSPA. Where adequate data do not exist, 
other information sources such as expert elicitation have 
been appropriately incorporated into TSPA. 
Characterization and site data discussed in Section 3.1; 
conceptual models, Section 3.2; abstraction of 
radionuclide transport, Section 3.6.3.3; synthesis of SZ 
model and model abstractions, Section 3.6. 
T2. Parameter values, assumed ranges, probability 
distributions, and/or bounding assumptions used in the 
flow paths in the SZ abstraction, such as the effect of 
climate change on the SZ fluxes and water table level 
and well pumping practices, are technically defensible 
and reasonably account for uncertainties and variability. 
Synthesis of SZ model and model abstractions discussed 
in Section 3.6; parameter uncertainty distributions, 
Section 3.7.2; probabilistic analyses, Section 3.7.3. 
T3. Alternative modeling approaches consistent with 
available data and current scientific understanding are 
investigated, and results and limitations appropriately 
factored into the flow paths in the SZ. 
Synthesis of SZ model and model abstractions discussed 
in Section 3.6; assumptions, uses, and limitations of 
model, Section 3.5.

TDR-NBS-HS-000001 REV 00 ICN 01 B-7 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 3 
Model Abstraction (Continued) 
PMR Approach 
T4. Flow paths in the SZ abstraction output are verified 
through comparison to output of detailed process 
models, and/or empirical observations (laboratory tests 
or natural analogs, or both). 
Synthesis of SZ model and model abstractions discussed 
in Section 3.6; validation, Section 3.4. 
T5. Important site (geologic and hydraulic) features, 
physical phenomena and couplings, and consistent and 
appropriate assumptions are incorporated into the flow 
paths in the SZ abstraction. 
Synthesis of SZ model and model abstractions discussed 
in Section 3.6; assumptions, uses, and limitations of 
model, Section 3.5. 
Element 9 - Radionuclide Transport in the 
Saturated Zone 
T1. Sufficient data (field, laboratory, and/or natural 
analog data) are available to adequately define relevant 
parameters and conceptual models necessary for 
developing the radionuclide transport in the saturated 
zone abstraction in TSPA. Where adequate data do not 
exist, other information sources such as expert elicitation 
have been appropriately incorporated into TSPA. 
SZ characterization and data discussed in Section 3.1; 
laboratory data, Section 3.1.4;. Synthesis of SZ model 
and model abstractions, Section 3.6. 
T2. Parameter values, assumed ranges, probability 
distributions, and/or bounding assumptions used in the 
radionuclide transport in the saturated zone abstraction, 
such as sorption on fracture surfaces and Kd for matrix, 
are technically defensible and reasonably account for 
uncertainties and variability. 
SZ characterization and data discussed in Section 3.1; 
laboratory data, Section 3.1.4. parameter uncertainty 
distributions, Section 3.7.2; probabilistic analyses, Section 
3.7.3; synthesis of SZ model and model abstractions, 
Section 3.6. 
T3. Alternative modeling approaches consistent with 
available data and current scientific understanding are 
investigated, and results and limitations appropriately 
factored into radionuclide transport in the saturated zone 
abstraction. 
Assumptions, uses, and limitations of model, Section 3.5; 
synthesis of SZ model and model abstractions, 
Section 3.6. 
T4. Radionuclide transport in the saturated zone 
abstraction output is verified through comparison to 
output of detailed process models, and/or empirical 
observations (laboratory tests or natural analogs, or both. 
Validation is discussed in Section 3.4; synthesis of SZ 
model and model abstractions, Section 3.6. 
T5. Important site (geologic and hydrologic) features, 
physical phenomena and couplings, and consistent and 
appropriate assumptions are incorporated into the 
radionuclide transport in the saturated zone abstraction. 
Assumptions, uses, and limitations of model, Section 3.5; 
synthesis of SZ model and model abstractions, 
Section 3.6. 
Element 12 - Dilution of radionuclides Due to Well 
Pumping 
T1. Sufficient data (field, laboratory, and/or natural 
analog data) are available to adequately define relevant 
parameters and conceptual models necessary for 
developing the dilution of radionuclides due to wellpumping 
abstraction in the TSPA. Where adequate data 
do not exist, other information sources such as expert 
elicitation have been appropriately incorporated into 
TSPA. 
No credit for dilution specifically due to well pumping is 
taken in TSPA. A detailed analysis of the groundwater 
use by the hypothetical farming community is presented in 
CRWMS M&O (2000c). Concentration in water supply in 
abstraction of radionuclide transport discussed in Section 
3.6.3; synthesis of SZ model and model abstractions, 
Section 3.6.

TDR-NBS-HS-000001 REV 00 ICN 01 B-8 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 3 
Model Abstraction (Continued) 
PMR Approach 
T2. Parameter values, assumed ranges, probability 
distributions, and/or bounding assumptions used in the 
dilution of radionuclides in groundwater due to well 
pumping abstraction, such as the pumping well 
characteristics and water usage by the receptor groups, 
are technically defensible and account for uncertainties 
and variability. 
No credit for dilution specifically due to well pumping is 
taken in TSPA. A detailed analysis of the groundwater 
use by the hypothetical farming community is presented in 
CRWMS M&O (2000c). Concentration in water supply in 
abstraction of radionuclide transport discussed in Section 
3.6.3; parameter uncertainty distributions, Section 3.7.2; 
probabilistic analyses, Section 3.7.3; synthesis of SZ 
model and model abstractions, Section 3.6. 
T3. Alternative modeling approaches consistent with 
available data and current scientific understanding are 
investigated, and results and limitations appropriately 
factored into the dilution of radionuclides in groundwater 
due to well pumping abstraction. 
No credit for dilution specifically due to well pumping is 
taken in TSPA. A detailed analysis of the groundwater 
use by the hypothetical farming community is presented in 
CRWMS M&O (2000c). Concentration in water supply in 
abstraction of radionuclide transport discussed in Section 
3.6.3; assumptions, uses, and limitations of model, 
Section 3.5; synthesis of SZ model and model 
abstractions, Section 3.6. 
T4. Dilution of radionuclides in groundwater due to well 
pumping abstraction output is verified through 
comparison to outputs of detailed process models or 
empirical observations (laboratory tests). 
No credit for dilution specifically due to well pumping is 
taken in TSPA. A detailed analysis of the groundwater 
use by the hypothetical farming community is presented in 
CRWMS M&O (2000c). Concentration in water supply in 
abstraction of radionuclide transport discussed in Section 
3.6.3; validation, Section 3.4; synthesis of SZ model and 
model abstractions, Section 3.6. 
T5. PA analyses incorporate important hydrogeologic 
features, physical phenomena and couplings, and 
consistent and appropriate assumptions are incorporated 
into the dilution of radionuclides due to well pumping 
abstraction. 
No credit for dilution specifically due to well pumping is 
taken in TSPA. A detailed analysis of the groundwater 
use by the hypothetical farming community is presented in 
CRWMS M&O (2000c). Concentration in water supply in 
abstraction of radionuclide transport discussed in Section 
3.6.3; assumptions, uses, and limitations of model, 
Section 3.5; synthesis of SZ model and model 
abstractions, Section 3.6. 
Scenario Analysis PMR Approach 
Element 1 - Identification of initial FEPs 
T1. DOE has identified a comprehensive list of 
processes and events that: (1) are present or might 
occur in the Yucca Mountain region and (2) include those 
processes and events that have the potential to influence 
repository performance. 
Relevant FEPs for SZ flow and transport are discussed in 
Section 1.3. Included FEPs are directly represented in the 
process models and abstractions that support TSPA, and 
discussed in sections of the PMR corresponding to the 
specific models. 
Element 2 - Classification of Processes and Events 
T1. DOE has provided adequate documentation 
identifying how its initial list of processes and events has 
been grouped into categories. 
Identification and categories of relevant FEPs for SZ flow 
and transport are discussed in Section 1.3. 
T2. Categorization of processes and events is 
compatible with the use of categories during the 
screening of processes and events. 
Categories of relevant FEPs for SZ flow and transport and 
their use are discussed in Section 1.3. 
Element 3 - Screening of processes and events 
T1. Categories of processes and events that are not 
credible for the Yucca Mountain repository because of 
waste characteristics, repository design, or site 
characteristics are identified and sufficient justification is 
provided for DOE's conclusions. 
Excluded FEPs and the rationale for exclusion are 
discussed in Section 1.3. The exclusion of FEPs from 
TSPA is based on arguments of low probability or low 
consequence.

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Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Scenario Analysis (Continued) PMR Approach 
T2. The probability assigned to each category of 
processes and events not screened based on criterion 
T1 or T2 is consistent with site information, well 
documented, and appropriately considers uncertainty. 
Rationale for excluding FEPs is discussed in Section 1.3. 
T3. DOE has demonstrated that processes and events 
screened from the PA on the basis of their probability of 
occurrence, have a probability of less than one chance in 
10,000 of occurring over 10,000 years. 
Rationale for excluding FEPs is discussed in Section 1.3. 
T4. DOE has demonstrated that categories of processes 
and events omitted from the PA on the basis that their 
omission would not significantly change the calculated 
expected annual dose, do not significantly change the 
calculated expected annual dose. 
Excluded FEPs and the rationale for their exclusion are 
discussed in Section 1.3. 
Element 4 - Formation of scenarios 
T1. DOE has provided adequate documentation 
identifying (1) whether processes and events have been 
addressed through consequence model abstraction or 
scenario analysis and (2) how the remaining categories 
of processes and events have been combined into 
scenario classes. 
Information on FEPs that are directly or indirectly included 
in the analysis of UZ flow and transport are discussed in 
Section 1.3. 
T2. The set of scenario classes is mutually exclusive and 
complete. 
Information on FEPs that are directly or indirectly included 
in the analysis of UZ flow and transport are discussed in 
Section 1.3. 
Element 5 - Screening of scenario classes 
T1. Scenario classes that are not credible for the Yucca 
Mountain repository because of waste characteristics, 
repository design, or site characteristics--individually or in 
combination--are identified and sufficient justification is 
provided for DOE's conclusions. 
FEPs screening database has been assembled, SZ FEPs 
AMR has been written (CRWMS M&O 2000q); FEPs 
discussed in Section 1.3. 
T2. The probability assigned to each scenario class is 
consistent with site information and well documented and 
appropriately considers uncertainty. 
FEPs screening database has been assembled, SZ FEPs 
AMR has been written (CRWMS M&O 2000q); FEPs 
discussed in Section 1.3. 
T3. Scenario classes that combine categories of 
processes and events may be screened from the PA on 
the basis of their probability of occurrence, provided (1) 
the probability used for screening the scenario class is 
defined from combinations of initiating processes and 
events and (2) DOE has demonstrated that they have a 
probability of less than one chance in 10,000 of occurring 
over 10,000 years. 
FEPs screening database has been assembled, SZ FEPs 
AMR has been written (CRWMS M&O 2000q); FEPs 
discussed in Section 1.3. 
T4. Scenario classes may be omitted from the PA on the 
basis that their omission would not significantly change 
the calculated expected annual dose, provided DOE has 
demonstrated that excluded categories of processes and 
events would not significantly change the calculated 
expected annual dose. 
FEPs screening database has been assembled, SZ FEPs 
AMR has been written (CRWMS M&O 2000q); FEPs 
discussed in Section 1.3.

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Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Key Technical Issue: Unsaturated and Saturated Flow Under Isothermal Conditions 
Subissue 2 
Hydrologic Effects of Climate Change PMR Approach 
Criterion 1If bounding analyses are used to predict 
climate-induced effects (e.g., water table rise), the 
analyses are based on a reasonably complete search of 
paleoclimate data pertinent to water table rise and other 
effects (e.g., changes in precipitation and geochemistry), 
including, at a minimum, information contained in Paces 
et al. (1996), Szabo et al. (1994), and Forester et al. 
(1996). 
A comprehensive literature search of the paleoclimate 
data has been completed and documented in the Yucca 
Mountain Site Description (CRWMS M&O 1998d). This 
description references Paces et al. (1996) in Section 5 
(Hydrologic System). Szabo et al. (1994) and Forester et 
al. (1996) are referenced in Section 4 (Climatology and 
Meteorology). 
Response of conceptual model to climate change 
discussed in Section 3.2.6; alternative climate states 
abstraction of radionuclide transport, Section 3.6.3.3.2. 
Criterion 2Regional and sub-regional models for the SZ 
that are used to predict climate-induced consequences 
are calibrated with the paleohydrology data and are 
consistent with evidence that the water-table rise during 
the late Pleistocene was up to 120 m (394 ft). 
Climate change, response of conceptual model to climate 
change discussed in Section 3.2.6; alternative climate 
states abstraction of radionuclide transport, Section 
3.6.3.3.2. (NOTE: Newest USFIC IRSR [NRC 1999a] 
provides evidence that water table rise in Pleistocene was 
not up to 120 m [394 ft].) 
Criterion 3DOE has incorporated future climate 
changes and associated effects in its PAs. For example, 
available information does not support an assumption 
that present-day climate will persist unchanged for 
10,000 yr. or more. 
Alternative climate states abstraction of radionuclide 
transport discussed in Section 3.6.3.3. 
Effects of Climate Change on SZ Flux: Incorporated in 
TSPA by increases in flux by a factor of about 3.9 for 
glacial-transition state and about 2.7 for monsoonal, the 
increases are modeled as an instantaneous change 
(Section 3.6.3.3.2). By assuming an instantaneous shift to 
the increased flux, the simulations tend to overestimate 
radionuclide transport velocities. 
Effects of Climate Change on Water Table Rise: Flow 
paths assumed to be similar to those at present; water 
table rise beneath the repository would place presently 
unsaturated, less permeable volcanic units at or just 
below the water table; disregarding rises in groundwater, 
which would be redirected into lower-permeability units 
generally is conservative with regard to radionuclide 
transport. 
Subissue 5 
Saturated Zone Ambient Flow Conditions and 
Dilution Processes PMR Approach 
Criterion 1DOE has considered conceptual flow and 
data uncertainties. Uncertainties due to sparse data or 
low confidence in the data interpretations have been 
considered by analyzing reasonable conceptual flow 
models supported by site data or by demonstrating 
through sensitivity studies that the uncertainties have 
little impact on repository performance. 
Model validation now includes comparisons of: 
permeability data to calibrated permeability values, fluxes 
from regional model with fluxes from calibrated model, 
measured upward gradient with predicted upward 
gradient, hydrochemical data with calculated particle 
pathways, and natural analogs. These activities and 
process model uncertainties are discussed in Section 3.4; 
assumptions, uses, and limitations, Section 3.5; SZ base 
case, uncertainty, parameter uncertainty distribution, and 
probabilistic analysis discussed in Section 3.7.

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Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 5 
Saturated Zone Ambient Flow Conditions and 
Dilution Processes (Continued) PMR Approach 
Criterion 2DOE has reasonably delineated possible flow 
paths from beneath the repository to potential receptor 
locations based on data that is sufficient to elucidate (i) 
the relative travel distances through aquifers of differing 
hydrologic and geochemical properties; (ii) in fracturedrock 
aquifers, the portions of flow through rock matrix 
and fractures; (iii) flow directions with respect to the 
hydraulic gradient, considering the potential effects of 
horizontal anisotropy; (iv) approximate volume fluxes and 
pore velocities; and (v) vertical hydraulic gradients, 
including the potential for flow between the Paleozoic 
carbonate aquifer and the volcanic tuff aquifer. A 
sufficient number of wells and exploratory holes should 
be drilled, and an adequate number of tests conducted, 
to reasonably bound the hydraulic and transport 
properties of the units downgradient from the proposed 
repository. 
Uncertainty in travel distances through aquifers of differing 
properties stochastically bounded in model by varying 
amount of alluvium along the flow path. Dual porosity 
approach is incorporated explicitly into the transport 
methodology for volcanic units to simulate matrix diffusion. 
Potential effects of horizontal anisotropy are bounded by 
setting the anisotropy ratio stochastically to either 1 
(isotropic) or 5 (based on the C-wells data) by making 
permeability values for the volcanic units 5 times greater 
in the north-south direction than in the east-west direction. 
Uncertainty in groundwater flux is incorporated by 
considering three discrete cases of low-, mean-, and highflux 
by scaling the values of permeability and the 
boundary fluxes of the mean-flux case downward or 
upward by a constant factor of 10. Proportional scaling 
preserves the calibration of the model to head 
measurements among the three cases. Potentiometric 
levels in the carbonate aquifer at well UE-25p#1 are about 
21 m (69 ft) higher than levels in the overlying rocks. This 
indicates a potential for upward flow and suggests that 
water will not flow from the tuffs into the carbonates. 
Regional-scale flow system discussed in Section 3.1.1.1; 
site-scale flow system, Section 3.1.1.2; conceptual model 
of hydrogeologic framework, Section 3.2.1. Uncertainty 
discussed in CRWMS M&O (2000o). SZ base case, 
uncertainty, parameter uncertainty distribution, and 
probabilistic analysis discussed in Section 3.7. Horizontal 
anisotropy discussed in Section 3.2.5.3. 
Criterion 3DOE has provided an hydrologic assessment 
to describe likely causes of the "moderate hydraulic 
gradient" and the "large hydraulic gradients." 
Relationship of moderate and large hydraulic gradients to 
hydrogeologic framework discussed in Section 3.2.2.3; 
large hydraulic gradient alternative models, 
Section 3.2.5.1. 
Criterion 4DOE has provided maps of approximate 
potentiometric contours of the regional uppermost aquifer 
for an area that, at a minimum, includes wells J-11 on the 
east, VH-1, VH-2, and the GEXA Well on the west, UE- 
29a#2 to the north, and domestic and irrigation wells 
south of Amargosa Valley (aka Lathrop Wells). Maps of 
regional and site-scale recharge and discharge should 
be provided, along with site-scale hydrostratigraphic 
cross sections constructed along the paths to the 
accessible environment, and site-scale flow-net analysis 
of the SZ. 
New maps of approximate potentiometric contours 
(Figure 3-5) based on new data provided. Regional-scale 
flow system discussed in Section 3.1.1.1; hydrologic data, 
Section 3.1.2; water level data, Section 3.1.2.1; recharge, 
Section 3.2.3.2; discharge, Section 3.2.3.3.

TDR-NBS-HS-000001 REV 00 ICN 01 B-12 August 2000 
Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 5 
Saturated Zone Ambient Flow Conditions and 
Dilution Processes (Continued) PMR Approach 
Criterion 5DOE estimates of key hydrologic parameters 
are described in the form of either probability 
distributions or deterministic bounding values that are 
reasonably consistent with site data. These parameters 
should include transmissivity, hydraulic gradient, 
effective flow porosity, effective immobile porosity, and 
effective aquifer thickness. 
Estimates of key hydrologic parameters are described in 
the form of either probability distributions or deterministic 
bounding values that are reasonably consistent with site 
data. The descriptions are as follows: matrix porosity 
description is deterministic bounding; hydraulic gradient 
description is deterministic bounding; flow porosity 
description is probabilistic. Transmissivity and effective 
aquifer thickness are not pertinent parameters. However, 
for permeability related to transmissivity and thickness, 
description is probabilistic. 
Uncertainty discussed in CRWMS M&O (2000o). Section 
3.7 discusses SZ base case, uncertainty, parameter 
uncertainty distribution, and probabilistic analysis. Model 
validation now includes comparisons of: permeability data 
to calibrated permeability values, fluxes from regional 
model with fluxes from calibrated model, measured 
upward gradient with predicted upward gradient, 
hydrochemical data with calculated particle pathways, and 
natural analogs. These activities and process model 
uncertainties are discussed in Section 3.4. 
Criterion 6DOE has used mathematical groundwater 
model(s) that incorporate site-specific climatic and 
subsurface information. The models were reasonably 
calibrated and reasonably represent the physical system. 
Fitted aquifer parameters compare reasonably well with 
observed site data. Implicitly- or explicitly-simulated 
fracturing and faulting are consistent with the data in the 
3D geologic model. Abstractions are based on initial and 
boundary conditions consistent with site-scale modeling 
and the regional models of the Death Valley groundwater 
flow system. Abstractions of the groundwater models for 
use in PA simulations should use appropriate spatialand 
temporal-averaging techniques. 
The 3-D site-scale SZ flow and transport numerical model 
simulates groundwater flow and radionuclide transport 
from the water table beneath the potential repository to 
the accessible environment using an equivalent 
continuum formulation and implicit fault and fracture 
representation to capture flow through fracture and matrix. 
The site-scale SZ flow and transport model is generated 
based on data from the hydrogeologic framework, 
integrated site, rock properties, and mineralogy models. It 
is calibrated and tested against relevant data that include 
water level, permeability, temperature, and ambient 
hydrochemistry data. The conceptual model of the SZ 
model is also validated using natural analogues. 
Model validation includes comparisons of: permeability 
data to calibrated permeability values, fluxes from regional 
model with fluxes from calibrated model, measured 
upward gradient with predicted upward gradient, 
hydrochemical data with calculated particle pathways, and 
natural analogs. These activities and process model 
uncertainties are discussed in Section 3.4. 
Criterion 7If credit for wellbore dilution is taken, a 
demonstration has been provided that reasonable 
assumptions have been made about well design, aquifer 
characteristics, plume geometry, withdrawal rates, and 
capture zone analysis for the receptor location. 
Dilution in water supply is discussed in Section 3.6.3.3.4. 
Criterion 8If credit is taken for dilution due to either 
dispersion, groundwater mixing below the repository 
footprint, or mixing of the Yucca Mountain water with 
water from the north in Fortymile Wash, reasonable 
assumptions have been made about spatial and 
temporal variations of aquifer properties and 
groundwater volumetric fluxes. 
Assumptions, uses, and limitations of site-scale flow and 
transport model are in Section 3.5.

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Table B-1. Issue Resolution Status Report (IRSR) Technical Acceptance Criteria (Continued) 
Subissue 5 
Saturated Zone Ambient Flow Conditions and 
Dilution Processes (Continued) 
PMR Approach 
Criterion 9DOE has incorporated key conclusions 
regarding potential geothermal and seismic effects on 
the ambient SZ flow system (e.g., National Research 
Council 1992; NWTRB 1998d; Craig 1997). 
Other views, alternative conceptual models, and 
incorporation of key conclusions are discussed in 
Section 3.8. 
Subissue 6 
Matrix Diffusion PMR Approach 
Criterion 2If credit for matrix diffusion in the SZ is taken, 
rock matrix and solute diffusion parameters must be 
(i) based on an SZ transport model that reasonably 
matches the results of the field tracer tests that are 
conducted over different distance scales and flow rates 
with multiple tracers of different diffusive properties and 
(ii) consistent with laboratory data. 
The C-wells reactive tracer test (Section 3.1.3.2) 
demonstrated that models that incorporate matrix diffusion 
provide more reasonable fits to the tracer-experiment data 
than those that assume a single continuum. The matrix 
sorption coefficient that fit the data for the lithium tracer in 
the C-wells reactive tracer experiment agreed well with the 
value determined in laboratory sorption tests. This 
provides confidence that the matrix-diffusion model is 
appropriate. The fact that the early lithium response had 
the same timing as that of the nonsorbing tracers, but with 
a lower normalized peak concentration, is consistent with 
matrix diffusion coupled with sorption in the matrix (see 
Figure 3-9). Matrix diffusion laboratory tests are 
discussed in Section 3.1.4.2; tracer tests, Section 3.1.3.2; 
matrix diffusion in conceptual model, Section 3.2.4.2; 
matrix diffusion in mathematical model, Section 3.3.2.2; 
matrix diffusion sub-model in particle tracking 
methodology, Section 3.3.4.2; validation, Section 3.4.

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