Technical Basis Document No. 11: 
Saturated Zone Flow and Transport 
Revision 2 
By: 
Robert W. Andrews and Al A. Eddebbarh 
With Contributions By: 
Roger J. Henning, Scott C. James, August C. Matthusen, Arend Meijer, 
Hari Viswanathan, Timothy J. Vogt, Jim L. Boone, Thomas C. Booth, Mei Ding, 
Paul R. Dixon, Ernest L. Hardin, Charles Haukwa, Edward M. Kwicklis, 
Terry A. Miller, Paul W. Reimus, Richard W. Spengler, and Patrick Tucci 
Prepared for: 
U.S. Department of Energy 
Office of Civilian Radioactive Waste Management 
Office of Repository Development 
P.O. Box 364629 
North Las Vegas, Nevada 89036-8629 
Prepared by: 
Bechtel SAIC Company, LLC 
1180 Town Center Drive 
Las Vegas, Nevada 89144 
Under Contract Number 
DE-AC28-01RW12101 
QA: NA 
September 2003


1. INTRODUCTION 
This technical basis document provides a summary of the conceptual understanding of the flow 
of groundwater and the transport of radionuclides that may be potentially released to the 
saturated zone beneath and downgradient from Yucca Mountain. This document is one in a 
series of technical basis documents prepared for each component of the Yucca Mountain 
repository system important for predicting the likely postclosure performance of the repository. 
The relationship of saturated zone flow and transport to the other components is illustrated in 
Figure 1-1. 
Figure 1-1. Components of the Postclosure Technical Basis for the License Application 
This document and the associated references form an outline of the ongoing development of the 
postclosure safety analysis that will comprise the License Application. This information is also 
used to respond to open Key Technical Issue (KTI) agreements made between the U.S. Nuclear 
Regulatory Commission (NRC) and the U.S. Department of Energy (DOE). Placing the DOE 
responses to individual KTI agreements and NRC additional information needed (AIN) requests 
within the context of the overall saturated zone flow and transport process, as they relate to 
postclosure safety analyses, allows for a more direct discussion of the relevance of the 
agreement. 
September 2003 1-1 No. 11: Saturated Zone
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Appendices to this document are designed to allow for a transparent and direct response to each 
KTI agreement and AIN requests. Each appendix addresses one or more of the agreements. If 
agreements apply to similar aspects of the saturated zone subsystem, they were grouped in a 
single appendix. In some cases, appendices provide detailed discussions of data, analyses, or 
information related to the further conceptual understanding presented in this technical basis 
document. In these cases, the appendices are referenced from the appropriate section of the 
technical basis document. In other cases, the appendices provide information that is related to 
the technical basis document information but at a level of detail that relates more to the 
uncertainty in a particular data set or feature, event, or process that is less relevant to the overall 
technical basis. In these cases, the appendices reference the relevant section of the technical 
basis document to put the particular KTI agreement into context. 
This technical basis document and appendices are responsive to agreements made between the 
DOE and the NRC during Technical Exchange and Management Meetings on Radionuclide 
Transport (RT) (Reamer and Williams 2000a), Total System Performance Assessment and 
Integration (TSPAI) (Reamer 2001), and Unsaturated and Saturated Flow Under Isothermal 
Conditions (USFIC) (Reamer and Williams 2000b), and to AIN requests from the NRC to the 
DOE dated August 16, 2002 (Schlueter 2002a), August 30, 2002 (Schlueter 2002b), 
December 19, 2002 (Schlueter 2002c), and February 5, 2003 (Schlueter 2003). 
Most of the agreements were based on questions that NRC staff developed from their review of 
the site recommendation support documents and DOE presentations at the technical exchanges. 
In general, the agreements required the DOE to present additional information, conduct further 
testing, perform sensitivity or validation exercises for models, or provide justification for 
assumptions used in the Yucca Mountain Site Suitability Evaluation (DOE 2002). After those 
technical exchanges, the DOE has conducted the additional analysis and testing necessary to 
meet the agreements. The appendices present the additional information that forms the technical 
basis for addressing the intent of the KTI agreements. 
This technical basis document provides a summary-level synthesis of many relevant aspects of 
the saturated zone flow and transport modeling that is being completed to support development 
of the Yucca Mountain License Application. This includes a summary and synthesis of the 
detailed technical information presented in the analysis model reports and other technical 
products that are used as the basis for the description of the saturated zone barrier and the 
incorporation of this barrier into the postclosure performance assessment. Several analyses, 
model reports, and other technical products support this summary: 
• A Three-Dimensional Numerical Model of Predevelopment Conditions in the Death 
Valley Regional Ground-Water Flow System, Nevada and California (D’Agnese 
et al. 2002) 
• Water-Level Data Analysis for the Saturated Zone Site-Scale Flow and Transport Model 
(USGS 2001a) 
• Site-Scale Saturated Zone Transport (BSC 2003a) 
• Saturated Zone Colloid Transport (BSC 2003b) 
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• Site-Scale Saturated Zone Flow Model (BSC 2003c) 
• SZ Flow and Transport Abstraction (BSC 2003d) 
• Saturated Zone In-Situ Testing (BSC 2003e). 
• Geochemical and Isotopic Constraints on Groundwater Flow Directions and 
Magnitudes, Mixing, and Recharge at Yucca Mountain (BSC 2003f) 
• Features, Events, and Processes in SZ Flow and Transport (BSC 2003g). 
The basic approach of this document is to provide a comprehensive summary of the saturated 
zone flow and transport understanding, the details of which are presented in the supporting 
analyses, reports, and related products. 
1.1 OBJECTIVE AND SCOPE 
The objectives of this technical basis document are to: 
• Describe the processes relevant to the performance of the saturated zone flow and 
transport component of the postclosure performance assessment 
• Present data, analyses, and models used to project the behavior of the saturated zone 
flow and transport processes 
• Summarize the development of the site-scale saturated zone flow and transport models 
and key subprocess models that are used to analyze data from the saturated zone 
• Summarize the results of the flow and transport models used in the assessment of 
postclosure performance at Yucca Mountain. 
The purpose of the site-scale saturated zone flow and transport model is to describe the spatial 
and temporal distribution of groundwater as it moves from the water table below the repository, 
through the saturated zone, and to the point of uptake by a potential downgradient receptor. The 
saturated zone 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 saturated zone, are described in this document. 
The evaluation of the saturated zone in the Yucca Mountain area considers the possibility of 
radionuclide transport from their introduction at the water table beneath the repository to a 
hypothetical well located at the compliance boundary downgradient from the site. The likely 
pathway for radionuclides potentially released from the repository to reach the accessible 
environment is through groundwater aquifers below the repository. These aquifers, collectively 
referred to as the saturated zone, delay the transport of radionuclides released to the saturated 
zone and reduce the concentration of radionuclides before they reach the accessible environment. 
A simplified conceptualization of the saturated zone flow and transport for Yucca Mountain and 
its relationship to transport in the unsaturated zone and biosphere is provided in Figure 1-2. 
Radionuclides released into seepage water contacting breached waste packages in the repository 
September 2003 1-3 No. 11: Saturated Zone
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would migrate downward through the unsaturated zone for approximately 210 to 390 m to the 
water table. At that point, radionuclides would enter the saturated zone and migrate 
downgradient within the tuff and alluvial aquifers to the accessible environment. At a distance 
of 15 to 22 km along the flow path from the repository, groundwater flow enters the alluvial 
aquifer and remains in the alluvium for an additional 1 to 10 km until it is subject to uptake into 
the accessible environment. 
Figure 1-2. Conceptual Representation of Radionuclide Transport Pathways from the Repository to the 
Biosphere 
1.2 DESCRIPTION OF PROCESSES AFFECTING THE PERFORMANCE OF THE 
SATURATED ZONE 
The saturated zone is a barrier to the migration of dissolved and colloidal radionuclides that may 
be released from the repository. This barrier delays the transport of radionuclides and increases 
the time until they are potentially withdrawn from a well used by a hypothetical person (the 
reasonably maximally exposed individual). 
Radionuclides that enter the saturated zone are expected to do so over a spatial and temporal 
scale that depends on the degradation modes and degradation rates of the engineered barriers and 
the transport processes from the degraded engineered barriers, through the unsaturated zone, to 
the saturated zone. For example, it is possible that the engineered barriers will fail over a broad 
temporal scale (ranging from thousands to hundreds of thousands of years) due to natural 
degradation processes, or they may fail over a relatively short time due to a low probability 
disruptive event (e.g., a large seismic or volcanic event). The spatial scale over which 
radionuclides enter the saturated zone may be confined to an area on the order of 100 m2 for each 
degraded waste package (for cases where the flow is predominantly vertical through the 
unsaturated zone), concentrated at locations where most of the unsaturated groundwater flow 
intersects the water table, or dispersed over a large fraction of the repository footprint (i.e., 
several square kilometers). The timing and spatial extent of radionuclides that enter the saturated 
zone and reach the accessible environment are considered in the performance assessment using a 
range of spatial locations, a range of transport times within the saturated zone, and a range of 
No. 11: Saturated Zone September 2003 1-4
Revision 2 
times when radionuclides are predicted to reach the saturated zone, as described in the SZ Flow 
and Transport Abstraction (BSC 2003d). 
The processes that affect the performance of the saturated zone barrier include both groundwater 
flow and radionuclide transport processes. The groundwater flow processes determine the rate of 
water movement within the saturated zone and the flow paths through which the water is likely 
to travel. These flow paths extend from where the radionuclides may possibly enter the saturated 
zone to where they exit at the point of compliance. These flow paths define the different 
geologic materials through which potentially released radionuclides are likely to be transported. 
Radionuclide transport processes include those that determine the advective velocity of dissolved 
radionuclides within the saturated fractures or pores of the geologic media and processes that 
relate to interactions between the dissolved or colloidal radionuclides and the rock or alluvium 
materials with which they come in contact. Advective transport is determined by the rate of 
groundwater flow and the effective porosity of the media through which the flow occurs. Lower 
effective porosities yield higher groundwater velocities and shorter transport times. Dispersive 
processes are affected by small scale velocity heterogeneity that allows some dissolved 
constituents to travel faster or slower than the average advective transport time. Dispersive 
processes also spread the radionuclide mass concentration, although the reduced concentration is 
not important for postclosure performance because of the mixing that occurs when the 
radionuclide mass flux is mixed with the annual water demand of 3.7 million m3 
(3,000 acre-feet). 
Dissolved radionuclides diffuse from fractures in the volcanic tuff (in which they are advectively 
transported) into the matrix, which has little advective flux and tends to slow the transport time 
of these species. The effectiveness of this process depends on the diffusive properties of the 
matrix and the degree of spacing between the flowing fracture zones. Larger diffusion 
coefficients or smaller spacings between flowing fracture zones result in slower transport times 
within the fractured rock. 
Many radionuclides potentially important to repository performance are sorbed within the matrix 
of the rock mass. Although these radionuclides may be sorbed on fracture surfaces, this 
retardation mechanism has not been considered in the performance assessment. The degree of 
sorption depends on the individual radionuclide. Some radionuclides (e.g., technetium, iodine 
and carbon) are not sorbed, and are transported considering only advection, dispersion, and 
matrix diffusion processes. Other radionuclides (e.g., neptunium, uranium, and plutonium) are 
sorbed in the matrix or pores of the fractured tuffs and alluvium. The stronger the sorption, the 
longer the radionuclide transport time compared with advective-dispersive transport times. 
These saturated zone flow and transport processes are represented by conceptual and numerical 
models to predict the expected behavior of the saturated zone barrier as it relates to performance 
of the Yucca Mountain repository. These include regional and site-scale models of groundwater 
flow and models of radionuclide transport. The bases of these models are derived from sitespecific 
in situ observations, field tests, and laboratory tests to determine relevant parameter 
values. This technical basis document presents a summary of the bases for the models and 
parameters, plus a discussion of the uncertainty associated with the models, the parameters, and 
the predicted results (i.e., radionuclide transport times) relevant to postclosure performance. 
September 2003 1-5 No. 11: Saturated Zone
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1.3 SUMMARY OF CURRENT UNDERSTANDING 
An understanding of saturated zone flow and transport in the vicinity of Yucca Mountain has 
been gained through the collection of regional and site data and through the incorporation of 
these data into models that describe processes affecting the behavior of the saturated zone 
barrier. Hydrogeologic data have been collected from boreholes that penetrate the saturated zone 
and from nonintrusive field investigations (i.e., geophysical surveys). These data were used to 
develop a scientific understanding of the subsurface hydrogeology and to assemble the database 
necessary to evaluate the expected performance characteristics of the saturated zone. 
In general, the rate and direction of groundwater flow within the saturated zone is controlled by 
the spatial configuration of the potentiometric surface, plus the hydrologic properties and 
characteristics of the materials that constitute the saturated zone. Based on the potentiometric 
surface in the Yucca Mountain area, groundwater within the saturated zone beneath the 
repository is inferred to move from upland areas of recharge (located north of Yucca Mountain) 
towards areas of natural discharge (springs and playas south of Yucca Mountain). This flow 
direction is supported by hydrochemistry and isotopic data. 
Groundwater flow in the saturated zone below and directly downgradient from the repository 
occurs in fractured, porous volcanic tuffs relatively close to the water table and in fractured 
carbonate rocks of Paleozoic age (limestones and dolomites) at much greater depths. At 
distances of about 15 to 18 km downgradient from the repository, where the volcanic rocks thin 
out beneath valley fill materials, the water table transitions from volcanic rocks to valley-fill 
(alluvial) material. 
The most likely pathway for radionuclides to reach the accessible environment is through the 
uppermost groundwater aquifers below the repository. These aquifers (i.e., the saturated zone) 
delay the transport of radionuclides and reduce the radionuclide concentration before they reach 
the accessible environment. Delay in the release of radionuclides to the accessible environment 
allows radioactive decay to further diminish the mass of radionuclides that are ultimately 
released. Dilution of radionuclide concentrations in the groundwater used by the potential 
receptor occurs during transport and in the process of extracting more groundwater from wells 
than water containing radionuclides released from the repository. The key processes that affect 
the performance of the saturated zone barrier are summarized in the following text. 
To determine the characteristics of the saturated zone, flow and transport processes need to be 
considered. Pertinent data for characterizing groundwater flow in the saturated zone includes 
measurements of water levels in boreholes and wells (which define the configuration of the water 
table and potentiometric surface) and hydraulic testing to determine hydraulic properties (e.g., 
hydraulic conductivity, permeability, and storage coefficient) of the rock and alluvial materials. 
Data on hydraulic properties have been obtained from more than 150 hydraulic tests conducted 
in boreholes and wells in the Yucca Mountain area. These hydraulic tests include 
constant-discharge pumping tests, slug injection (falling head) tests, pressure injection tests, and 
fluid logging techniques (e.g., temperature measurement and tracer injection surveys). 
Multiple-well pumping and tracer tests have been conducted in the three C-Wells, a complex of 
boreholes located about 3 km east of the repository. Multiple-well hydraulic tests and 
September 2003 1-6 No. 11: Saturated Zone
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single-well hydraulic and tracer tests have been conducted in cooperation with Nye County at the 
Alluvial Testing Complex, a complex of wells located near U.S. Highway 95. 
Hydrochemical data (e.g., chloride and sulfate concentrations) and isotopic data (e.g., 234U/238U 
ratios, and strontium, oxygen, deuterium, and carbon isotope ratios) also have been collected 
from a number of boreholes and wells. These data were used to independently define likely 
groundwater flow paths from the repository area. 
Processes important to the transport of radionuclides in the saturated zone include advection, 
sorption, diffusion (especially matrix diffusion), hydrodynamic dispersion, decay and ingrowth, 
and colloid transport. These characteristics have been evaluated through a range of in situ tests 
(such as at the C-Wells and Alluvial Testing complexes) and laboratory tests. In situ tests 
generally are used to evaluate properties such as effective porosity and longitudinal dispersivity, 
while laboratory tests are used to evaluate sorption characteristics. Sorption coefficients (Kds) 
have been measured in the laboratory for a number of important radionuclides based on crushedrock 
and alluvium samples using batch and column tests that used borehole core samples from 
selected saturated zone rock units at Yucca Mountain. Estimates of Kds have been developed for 
various radionuclides (e.g., americium, thorium, uranium, protactinium, neptunium, and 
plutonium). 
Estimates of colloid filtration in saturated, fractured volcanic rocks have been obtained from 
tracer tests conducted at the C-Wells complex using polystyrene microspheres as surrogate 
colloids. Physical data applicable to the attachment, detachment, and transport of radionuclides 
on natural colloidal substrates (e.g., silica and clay minerals) have been obtained for selected 
radionuclides (e.g., 239Pu and 243Am) through laboratory experiments and testing. 
Analyses conducted using the saturated zone transport model indicate that the saturated zone is a 
barrier to the transport of radionuclides released from the repository to the accessible 
environment within the 10,000-year period of regulatory concern. The saturated zone is 
expected to delay the transport of sorbing radionuclides and radionuclides associated with 
colloids for many thousands of years, even under wetter climatic conditions in the future. 
Nonsorbing radionuclides are expected to be delayed for hundreds of years during transport in 
the saturated zone. 
1.4 ORGANIZATION OF THIS REPORT 
The report is organized as: 
Section 1. Introduction–Objectives and scope of this document and a discussion of the 
saturated zone as a barrier. 
Section 2. Saturated Zone Flow–Descriptions of regional and site-scale field and laboratory 
testing, data collection activities, and modeling of groundwater flow processes. 
Section 3. Saturated Zone Radionuclide Transport–Site-scale field and laboratory testing, 
data collection activities, and modeling of radionuclide transport processes. 
September 2003 1-7 No. 11: Saturated Zone
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Section 4. Summary–Results of the saturated zone flow and transport processes as they relate 
to postclosure performance projections of the repository. 
Section 5. References–Sources of information used in this document. 
Appendices–Thirteen appendices (Table 1-1) address specific KTI agreement items and AIN 
requests. 
Appendix 
A 
14C Residence Time 
B
C
D
E
F
G Uncertainty in Flow Path Lengths in Tuff and 
Alluvium 
Transport Properties H
I
J
K
L 
Hydrochemistry 
M 
Table 1-1. List of Appendices and the KTI Agreements that are Addressed 
Appendix Title 
The Hydrogeologic Framework 
Model/Geologic Framework Model Interface 
Hydrostratigraphic Cross Sections 
Potentiometric Surface and Vertical Gradients 
Regional Model and Confidence Building 
Horizontal Anisotropy 
Key Technical Issues Addressed 
USFIC 5.10 
RT 2.09 AIN-1 AND USFIC 5.05 AIN-1 
USFIC 5.08 AIN-1 
USFIC 5.02, USFIC 5.12, AND USFIC 5.11 AIN-1 
USFIC 5.01 
USFIC 5.06 
RT 2.08, RT 3.08, and USFIC 5.04 
RT 1.05, RT 2.01, RT 2.10, GEN 1.01 (#28 and 
#34), AND RT 2.03 AIN-1 
RT 2.02, TSPAI 3.32 and TSPAI 4.02. 
RT 1.04. 
RT 2.06, RT 2.07, and GEN 1.01 (#41 and #102) 
TSPAI 3.31 
RT 3.08 AIN-1 and GEN 1.01 (#43 and #45) 
September 2003 
Transport—Spatial Variability of Parameters 
Determination of Whether Kinetic Effects 
Should be Included in the Transport Model 
Transport—Kds in Alluvium 
Transport—Temporal Changes in 
1-8 
Microspheres as Analogs 
1.5 NOTE REGARDING THE STATUS OF SUPPORTING TECHNICAL 
INFORMATION 
This document was prepared using the most current information available. This technical basis 
document and the appendices provide KTI agreement responses (Table 1-1) that were prepared 
using preliminary or draft information reflecting the status of the Yucca Mountain Project 
scientific and design bases at the time of submittal. In some cases, this involved using draft 
analysis, model reports, and other references, the contents of which may change with time. 
Information that changes through revisions of the reports and references will be reflected in the 
License Application as the approved analyses of record at the time of License Application 
submittal. Consequently, this technical basis document and the KTI agreement appendices will 
not routinely be updated to reflect changes in the supporting references prior to submittal of the 
License Application. 
No. 11: Saturated Zone
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2. SATURATED ZONE GROUNDWATER FLOW 
2.1 INTRODUCTION 
The following sections summarize the understanding of saturated zone flow processes, models, 
and parameters. This understanding is important to describing the likely groundwater flow paths 
and flow rates, as well as the geologic units through which groundwater is likely to flow in the 
vicinity of Yucca Mountain. This summary includes discussions of the regional and site-scale 
geologic setting, hydrogeologic setting, hydrogeochemistry, and groundwater flow modeling. 
The hydrogeologic setting in the Death Valley region in general, and in the vicinity of Yucca 
Mountain in particular, has been the focus of data collection, interpretation, and analysis over the 
last several decades. This focus has, in part, been due to Federal government interest in 
understanding the groundwater flow system at the Nevada Test Site and in the region around 
Death Valley National Park, as well as State of Nevada and Nye County interest in 
understanding the available groundwater resources in the area. Early work by Maxey and Eakin 
(1950) provided a quantitative basis for estimating groundwater recharge as a function of 
precipitation in the arid southwest, and Winograd and Thordarson (1975) established the likely 
groundwater flow paths controlling the discharge of groundwater to springs in and around Death 
Valley. Since these early investigations, studies of groundwater flow in the Death Valley region 
have benefited from additional geologic and hydrologic characterization conducted via drilling 
and testing at numerous boreholes and wells in the area. 
A general understanding of regional-scale groundwater flow is important for understanding the 
Yucca Mountain groundwater flow system because the regional-scale system sets the context for 
the site-scale system. An important aspect of the regional hydrogeologic system is that it occurs 
in an enclosed basin without any surface or subsurface discharge to the ocean (i.e., all water that 
naturally leaves the region does so exclusively through evaporation or evapotranspiration). This 
regional basin, which includes natural discharge at springs in the Death Valley area, is referred to 
as the Death Valley regional flow system. 
The site-scale conceptual model is a synthesis of what is known about flow and transport 
processes at the scale required for postclosure performance assessment analyses, that is, at a 
scale relevant to assessing potential radionuclide transport from beneath Yucca Mountain to a 
point about 18 km south of Yucca Mountain where the reasonably maximally exposed individual 
may extract groundwater from the aquifer. This knowledge builds on, and is consistent with, 
knowledge that has accumulated at the regional scale, but it is more detailed because a higher 
density of data is available at the site-scale level. 
2.2 REGIONAL GROUNDWATER FLOW SYSTEM 
The Death Valley regional flow system encompasses an area of about 70,000 km2 in southern 
California and southern Nevada, between latitudes 35º and 38º 15' north and longitudes 115° and 
118° 45' west. The region varies topographically and geologically, and these features tend to 
control the groundwater flow system. The highest elevations are in the Spring Mountains 
(greater than 3,600 m) and in the Sheep Range (greater than 2,900 m). The lowest elevations 
September 2003 2-1 No. 11: Saturated Zone
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occur in Death Valley (-86 m) and along the major tributaries to the Amargosa River. The major 
physiographic features within the regional flow system are illustrated in Figure 2-1. 
Groundwater in the Death Valley region flows through a variety of rock types ranging from 
Paleozoic carbonate to Tertiary volcanic rocks (such as those in the Yucca Mountain area) to 
alluvial aquifers (such as those from which water is extracted for irrigation and other domestic 
purposes in the Amargosa Farms area). Within the Death Valley region, the presence of 
hydrostratigraphic discontinuities due to tectonic features, such as faults, has caused many of the 
aquifers to be heterogeneous. Faults, which disrupt the hydrostratigraphic continuity, divert 
water in regional circulation to subregional and local discharge. 
The following discussion summarizes regional recharge and discharge areas and amounts, 
hydraulic potentials, hydrogeologic characteristics, and hydrochemistry observations and 
inferences that are used to constrain the groundwater flow system in the vicinity of Yucca 
Mountain. 
2.2.1 Regional Groundwater Recharge and Discharge 
One of the first steps in developing a consistent representation of the groundwater flow regime in 
a groundwater basin is to identify the major recharge and discharge locations, types, and 
amounts. By comparing these distributions, an overall understanding of the water budget within 
the basin can be developed. Differences between the annual average recharge and discharge 
amounts are indicative of conditions when water is added to (or taken from) the total water in 
storage within the aquifers of the basin. 
Groundwater recharge in the Death Valley region principally is from water that directly 
infiltrates the soil horizon due to precipitation (rainfall and snowmelt) and that is not lost from 
the soil horizon due to evaporation or transpiration. Although some recharge occurs along 
intermittent rivers and streams in the area, most notably the Amargosa River and tributaries, the 
areal and temporal extent of this recharge is negligible from the perspective of the overall water 
budget (although local geochemistry and isotopic variations have, in part, been attributed to local 
intermittent recharge; Hevesi et al. 2002, p. 12). Although this intermittent recharge was not 
explicitly incorporated in the regional flow model, its effect on the site-scale flow model has 
been included (see Section 2.3.2). Net infiltration in the region is controlled by variability in 
precipitation and other factors, including the timing of precipitation, elevation, slope, soil or rock 
type, and vegetation. Net infiltration usually is episodic and generally occurs after periods of 
winter precipitation when evapotranspiration is low (Hevesi et al. 2002, p. 10). 
September 2003 2-2 No. 11: Saturated Zone
Source: Belcher et al. 2002, Figure 1. 
NOTE: The different model boundaries reflect different regional model studies that are discussed and referenced in 
the source. 
Figure 2-1. Major Physiographic Features in the Death Valley Regional Flow System 
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September 2003 2-3
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Estimates of net infiltration are based on a number of approaches. A traditional approach has 
been to empirically correlate net infiltration to average annual precipitation. This approach was 
originally postulated by Maxey and Eakin (1950). A more process-based approach was recently 
developed by the U.S. Geological Survey (USGS), in which the estimated recharge is a function 
of precipitation, soil depth, evapotranspiration, soil and rock permeability, and other factors. The 
application of this approach resulted in an estimate of net infiltration in the Yucca Mountain 
region (Figure 2-2 and Table 2-1). Although there is uncertainty (about a factor of three) in the 
range of estimates of average annual net infiltration over the Death Valley region, the results 
generally confirm that most of the recharge occurs at higher elevations in the Spring Mountains 
and in the Sheep Range, and at other locations above about 1,500 m elevation. 
Naturally occurring discharge from aquifers in the Death Valley region generally occurs due to 
evapotranspiration from the shallow water table beneath playas or at springs. Locations of 
surface features where regional discharge is expected are described by D’Agnese et al. (2002). 
The current understanding of discharge locations and rates are summarized in Figure 2-3 and 
Table 2-2. These estimates have been compiled from estimates of evapotranspiration rates and 
observations of spring discharge in the area. 
September 2003 2-4 No. 11: Saturated Zone
Source: D’Agnese et al. 2002, Figure 21. 
Figure 2-2. Location of Principal Recharge Areas and Amounts in the Death Valley Regional Flow 
System 
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September 2003 2-5
Table 2-1. 
Precipitation 
Model 
1980 to 1995 
Modeled 
Precipitation 
1920 to 1993 
Cokriged 
Precipitation 
Original Maxey-Eakin 
estimated recharge 
Source: Based on Hevesi et al. 2002, Table 2. 
NOTE: Volumetric flows rounded to the nearest 10 million m3/year. 
No. 11: Saturated Zone 
Summary of Precipitation, Modeled Net Infiltration, and Estimated Recharge Using 
Maxey-Eakin Methods for the Area of the Death Valley Regional Groundwater Flow Model. 
Revision 2 
Model Type 
Model net infiltration 
Model net infiltration of 
areas with 
>200 mm/year 
precipitation 
Modified Maxey-Eakin 
estimated recharge 
Modified Maxey-Eakin 
of areas with 
>200 mm/year 
precipitation 
Original Maxey-Eakin 
estimated recharge 
Modified Maxey-Eakin 
estimated recharge 
Average Value for 
Area of Death Valley 
Groundwater Flow 
Model (mm/year) 
202 
7.8 
4.8 
6.3 
2.6 
4.8 
188 
5.1 
3.7 
2-6 
Net Infiltration 
or Recharge as 
a Percentage of 
Precipitation 
.
3.9 
6.2 
3.1 
5.1 
2.4 
.
2.7 
2.0 
Total Area 
Volume 
(million m3/year) 
7,980 
310 
190 
250 
110 
190 
7,430 
200 
150 
September 2003
Source: Based on D’Agnese et al. 2002, Figure 18. 
NOTE: Location codes are defined in Table 2-2. 
Figure 2-3. Location of Principal Naturally Occurring Discharge Areas in the Death Valley Regional 
Flow System 
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September 2003 2-7
Table 2-2. Inferred Naturally Occurring Discharge Amounts in the Death Valley Regional Flow System 
Location 
Ash Meadows, Amargosa Flat 
Ash Meadows, Carson Slough 
Ash Meadows, central area 
Ash Meadows, upper drainage 
Ash Meadows, northern area 
Ash Meadows, southern area 
Chicago Valley 
Corn Creek Springs 
Death Valley, Badwater basin area 
Death Valley, Confidence Hills area 
Death Valley, Cottonball basin area 
Death Valley, Furnace Creek alluvial fan 
Death Valley, Mesquite Flat area 
Death Valley, Middle basin 
Death Valley, Mormon Point area 
Death Valley, Nevares Springs 
Death Valley, Saratoga Springs area 
Death Valley, Texas Spring 
Death Valley, Travertine Springs 
Death Valley, western alluvial fans 
Franklin Well area 
Franklin Lake, eastern area 
Franklin Lake, northern area 
Franklin Lake, southern area 
Grapevine Springs, Scotty's Castle area 
Grapevine Springs, spring area 
Indian Springs and Cactus Springs 
Oasis Valley, Beatty area 
Oasis Valley, Coffer's Ranch area 
Oasis Valley, middle Oasis Valley area 
Oasis Valley, Springdale area 
Pahrump Valley, Bennett Spring area 
Pahrump Valley, Manse Spring area 
Penoyer Valley area 
Sarcobatus Flat, Coyote Hills area 
Sarcobatus Flat, northeastern area 
Sarcobatus Flat, southwestern area 
Shoshone basin, northern area 
Shoshone basin, southern area 
Stewart Valley, predominantly playa area 
Stewart Valley, predominantly vegetation area 
Tecopa basin, Amargosa Canyon area 
Tecopa basin, China Ranch area 
Tecopa basin, Resting Spring area 
Tecopa basin, Sperry Hills area 
Tecopa basin, central area 
Source: Based on D’Agnese et al. 2002. 
No. 11: Saturated Zone 
Location Code 
G-AM-AMFLT 
G-AM-CARSL 
G-AM-CENTR 
G-AM-UPDRN 
G-AM-NORTH 
G-AM-SOUTH 
G-CHICAGOV 
G-CORNCREK 
G-DV-BADWT 
G-DV-CONFI 
G-DV-COTTN 
G-DV-FRNFN 
G-DV-MESQU 
G-DV-MIDDL 
G-DV-MORMN 
G-DV-NEVAR 
G-DV-SARAT 
G-DV-TEXAS 
G-DV-TRVRT 
G-DV-WESTF 
G-FRANKWEL 
G-FRNKLK-E 
G-FRNKLK-N 
G-FRNKLK-S 
G-GRAPE-SC 
G-GRAPE-SP 
G-INDIANSP 
G-OV-BEATY 
G-OV-COFFR 
G-OV-OASIS 
G-OV-SPRDL 
G-PAH-BENT 
G-PAH-MANS 
G-PENOYERV 
G-SARCO-CH 
G-SARCO-NE 
G-SARCO-SW 
G-SHOSH-N 
G-SHOSH-S 
G-STEWRT-P 
G-STEWRT-V 
G-TC-AMCAN 
G-TC-CHRNC 
G-TC-RESTS 
G-TC-SPERY 
G-TC-TECOP 
TOTAL 105,776,270 m3 per year 
2-8 
Revision 2 
Observed Discharge (m3/day) 
6,019 
498 
21,444 
3,219 
19,499 
10,085 
1,452 
676 
5,019 
6,651 
3,547 
10,185 
29,075 
2,587 
7,225 
1,884 
6,535 
1,220 
4,633 
13,637 
1,182 
411 
2,254 
711 
1,035 
2,450 
2,240 
2,774 
5,343 
3,157 
8,113 
16,753 
5,375 
12,833 
1,503 
30,421 
11,960 
2,259 
4,831 
995 
2,381 
3,394 
1,784 
2,537 
1,341 
12,221 
September 2003
Revision 2 
In addition to natural discharge, groundwater has been withdrawn from the aquifers in the Death 
Valley regional groundwater basin for various domestic, agricultural, industrial, and government 
purposes over the last several decades. Locations and estimates of groundwater extraction are 
summarized in Figure 2-4. Although these discharges from the regional aquifers are small in 
comparison to natural discharge, they potentially affect the flow paths and flow rates in the 
vicinity of the pumping centers. 
In comparing areas of recharge and discharge, it is apparent that most of the recharge occurs at 
higher elevations, while most discharge occurs at lower elevations. The total volumetric annual 
recharge and discharge rates in the basin should be similar assuming there is no net water gain or 
loss from the aquifers within the basin. The differences between Tables 2-1, 2-2, and Figure 2-4 
might result from several factors. For example, they may reflect the degree of temporal 
averaging in different techniques or in the estimation method used to determine the net 
infiltration (Hevesi et al. 2002). Alternatively, the differences may indicate that there is a 
nonsteady component of the regional flow system and that recharge and discharge are not in 
equilibrium. However, it is more likely that the estimates of recharge and discharge are 
essentially equivalent, and the differences simply represent the precision of the estimation 
method. Therefore, given the vastness of the groundwater basin, it is not surprising that the 
regional estimates of recharge and discharge only agree to within a factor of about three, as the 
regional recharge estimates range from about 110 to 310 million m3/year, and the regional 
discharge estimate is about 106 million m3/year. Uncertainty in the estimate of the overall water 
budget was considered in the estimate of the aquifer characteristics that affect the local flow 
system around Yucca Mountain. 
2.2.2 Regional Potentiometric Surface 
D’Agnese et al. (1997) constructed a regional-scale potentiometric map for the Death Valley 
regional flow system (Figure 2-5). This regional-scale map was constructed using data 
describing water levels from monitoring wells, boundaries of perennial marshes and ponds, 
spring locations, general inferences based on the distribution of recharge and discharge areas, 
and a general understanding of the regional hydrogeology. The regional potentiometric surface 
corresponds to the major recharge and discharge areas identified above. The major recharge 
areas are represented by potential highs in the Spring Mountains, the Sheep Range, and other 
areas with elevations greater than 1,500 m. Discharge is represented by areas with a very low 
potential gradient or in areas with elevations less than 500 m. 
September 2003 2-9 No. 11: Saturated Zone
Revision 2 
Source: Fenelon and Moreo 2002, Figure 11. 
NOTE: To convert total withdrawals over the reported period to annual water withdrawals, divide by 12 to convert to 
acre-feet/year, or multiply by about 100 to convert to m3/year (there are 1,233 m3 in 1 acre-foot). Therefore, 
the largest pumping center in the Amargosa Valley during this period was discharging 1 to 2 million m3/year, 
on average. 
Figure 2-4. Location of Principal Anthropogenic Groundwater Discharge Areas in the Death Valley 
Regional Flow System 
September 2003 2-10 No. 11: Saturated Zone
Source: Based on D’Agnese et al. 1997, Figure 27. 
NOTE: The regional flow system model boundary indicated on this figure reflects the boundaries used by D’Agnese 
et al. (1997), which have been revised in the more recent interpretations described by D’Agnese et al. 
(2002) and presented in Figures 2-1 to 2-3. 
Figure 2-5. Regional-Scale Potentiometric Surface Map 
2-11 No. 11: Saturated Zone 
Revision 2 
September 2003
Revision 2 
Using only the potentiometric information and knowledge of major recharge and discharge areas, 
D’Agnese et al. (2002) inferred the general regional groundwater flow directions in the central 
Death Valley subregion of the Death Valley regional flow system (Figure 2-6), which generally 
is southerly in the vicinity of Yucca Mountain. Although these interpreted flow directions are 
useful indicators of general trends, they do not directly quantify uncertainty in the flow paths, 
and they primarily are used to confirm the flow directions developed at the scale of the site 
model. 
2.2.3 Death Valley Regional Hydrogeology 
Hydrogeology in the Death Valley region is characterized by rocks of differing lithology and 
hydraulic characteristics depending in part on the location and proximity to major tectonic 
features. Faults can also affect the flow system, ranging from acting as barriers to groundwater 
flow when flow is perpendicular to the fault strike to providing preferential flow paths 
(horizontally and vertically) when flow is parallel to the fault strike. 
The major hydrogeologic units from oldest to youngest are: the Lower Clastic Confining Unit, 
the Lower Carbonate Aquifer, the Upper Clastic (Eleana) Confining Unit, the Upper Carbonate 
Aquifer, the Volcanic Aquifers, the Volcanic Confining Units, and the Alluvial Aquifer. The 
Lower Clastic Confining Unit forms the basement and generally is present beneath the other 
units except in caldera complexes. The Lower Carbonate Aquifer is the most extensive and 
transmissive unit in the region, and it is the source of regional discharge in the springs of Death 
Valley National Park. The Upper Clastic Confining Unit is present in the north-central part of 
the Nevada Test Site. It typically impedes flow between the overlying Upper Carbonate Aquifer 
and the underlying Lower Carbonate Aquifer, and is associated with many of the large hydraulic 
gradients in and around the Nevada Test Site. The Volcanic Aquifers and Volcanic Confining 
Units form a stacked series of alternating aquifers and confining units in and around the Nevada 
Test Site. The Volcanic Aquifers are moderately transmissive and are saturated in western 
sections of the Nevada Test Site. The Alluvial Aquifer forms a discontinuous aquifer in the 
region. Regional outcrops of these hydrogeologic units are depicted in Figure 2-7, and 
representative cross sections through the region, depicting the correlation of these different units, 
are presented in Figure 2-8. 
September 2003 2-12 No. 11: Saturated Zone
Revision 2 
Source: Based on D’Agnese et al. 2002, Figure 11. 
NOTE: The Central Death Valley Subregion is one of three subregions identified in the Death Valley Regional Flow 
Model. 
Figure 2-6. Inferred Groundwater Flow Paths in the Central Death Valley Subregion 
September 2003 2-13 No. 11: Saturated Zone
Revision 2 
Source: Belcher et al. 2002, Figure 4. 
Figure 2-7. Outcrops of Major Hydrogeologic Units in the Death Valley Region 
September 2003 2-14 No. 11: Saturated Zone
Source: Belcher et al. 2002, Figure 35. 
Figure 2-8. Representative Hydrogeologic Cross Sections through the Death Valley Region 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-15
Revision 2 
Understanding the regional groundwater flow requires evaluating the water-transmitting 
capability of the major lithologic units. Belcher and Elliot (2001) compiled estimates of 
transmissivity, hydraulic conductivity, storage coefficients, and anisotropy ratios for major 
hydrogeologic units within the Death Valley region. Belcher et al. (2002) used a compilation of 
930 hydraulic conductivity measurements to derive estimates of the hydraulic characteristics for 
several of the hydrogeologic units. Regional variability in aquifer characteristics is summarized 
in Figure 2-9. Although this figure illustrates an apparent depth dependency of hydraulic 
conductivity, the objective of presenting the information in this format primarily is to depict 
variability in hydraulic conductivity as a function of rock type. The depth dependency, which 
presumably is related to confining stress, has not been directly incorporated in the regional 
hydrogeologic models. Although the information is presented as a function of rock type, it is 
also probable that the range of variation within a particular rock type is largely affected by the 
degree of fracturing of the rock in the vicinity of the borehole that was tested (i.e., they reflect 
local heterogeneity of the rock mass). Uncertainty and variability in hydraulic conductivity were 
evaluated during construction of the regional and site-scale hydrogeologic models. Uncertainty 
in hydraulic conductivity does not greatly constrain the flow models. 
Source: Belcher and Elliot 2001, Figure 4. 
Figure 2-9. Depth Dependency of Regional Hydraulic Conductivity Estimates 
September 2003 2-16 No. 11: Saturated Zone
Revision 2 
2.2.4 Regional Geochemistry 
In addition to hydraulic observations, an understanding of regional flow systems can be 
ascertained from interpretations of the regional hydrogeochemistry. The application of 
hydrogeochemical and isotopic methods make it possible to reduce some uncertainties 
concerning regional groundwater flow patterns and flow rates. They also provide some bounds 
on the magnitude and timing of recharge of saturated zone groundwater. 
The main processes that control groundwater chemistry are: 
• Precipitation (atmospheric) quantities and compositions 
• Soil-zone processes in recharge areas 
• Rock-water interactions in the unsaturated zone between the zone of infiltration and the 
water table 
• Rock-water interactions in the saturated zone along the flow path from the recharge 
location to the point where the water is sampled 
• Mixing of groundwater from different flow systems. 
Groundwater is influenced to differing degrees by these processes, and as a result, groundwater 
extracted from different places (and therefore traveling by different pathways) can attain 
different chemical signatures that reflect individual pathway histories. The first three of the main 
processes do not affect the composition of groundwater after it enters the aquifer. However, 
input compositions differ in the recharge area because of evapotranspiration (which affects ion 
concentrations), recharge temperatures (which affect ä-deuterium and ä18O), precipitation 
compositions, soil-zone mineral dissolution, and precipitation reactions. 
After entering an aquifer, chemical characteristics can be affected by interactions between the 
groundwater and the rocks. Conservative geochemical constituents (i.e., those that show the 
least effects of interactions with water and rocks) are particularly important for delineating flow 
paths because these concentrations primarily reflect inputs and processes that operate in recharge 
areas. Generally, conservative constituents, for which analytical data are available, include 
chloride, sulfate, ä-deuterium, and ä18O. Where a lack of downgradient continuity in chemical 
and isotopic compositions was observed, the possibility of groundwater mixing was evaluated 
and quantified with inverse geochemical mixing and reaction models. 
Areal distribution maps of groundwater solutes and isotopes were used in Geochemical and 
Isotopic Constraints on Groundwater Flow Directions and Magnitudes, Mixing, and Recharge at 
Yucca Mountain (BSC 2003f) to obtain initial estimates of groundwater flow paths. Water type 
locations and the corresponding observation points used to evaluate geochemical signatures are 
depicted in Figure 2-10. Figure 2-11 illustrates the same information while showing chloride 
concentrations in the identified boreholes. Table 2-3 summarizes the basis for the flow paths 
illustrated on Figure 2-11. Similar plots for sulfate and ä-deuterium were also used in 
interpreting these flow paths (Figures 2-12 and 2-13, respectively). 
September 2003 2-17 No. 11: Saturated Zone
Revision 2 
Source: BSC 2003f, Figure 62. 
NOTE: The termination of flow paths implies that the flow paths could not be traced from geochemical information 
downgradient from these areas because of mixing or dilution by more actively flowing groundwater; flow 
path terminations do not imply that groundwater flow has stopped. 
Figure 2-10. Location of Geochemical Groundwater Types and Regional Flow Paths Inferred from 
Hydrochemical and Isotopic Data 
September 2003 2-18 No. 11: Saturated Zone
Revision 2 
Source: Based on BSC 2003f; chloride from Figure 15; flow paths from Figure 62. 
NOTE: The termination of flow paths implies that the flow paths could not be traced from geochemical information 
downgradient from these areas because of mixing or dilution by more actively flowing groundwater; flow 
path terminations do not imply that groundwater flow has stopped. 
Figure 2-11. Regional Groundwater Chloride Concentrations and Inferred Regional Flow Paths 
September 2003 2-19 No. 11: Saturated Zone
Table 2-3. Summary of Bases for Regional Flow Paths and Mixing Zones Derived from Geochemistry 
Flow Path or 
Mixing Zone 
(Figure 2-10) 
1
2
3
4
5 
No. 11: Saturated Zone 
Observations 
Geochemical Flow Path or 
Mixing Zone Description 
Oasis Valley through the 
Amargosa Desert along the axis 
of the Amargosa River to the 
confluence with Fortymile Wash 
Fortymile Canyon area 
southward along the axis of 
Fortymile Wash into the 
Amargosa Desert 
Jackass Flats in the vicinity of 
well UE-25 J-11 southward 
along the western edge of the 
Lathrop Wells area and 
southward through boreholes in 
the FMW-E area 
Lower Beatty Wash area into 
northwestern Crater Flat. This 
groundwater flows 
predominantly southward in 
Crater Flat past borehole USW 
VH-1 and NC-EWDP-3D. 
SW Crater Flat Group 
Revision 2 
Geochemical Evidence of Flow Path or 
Mixing Zone 
Areal plots of chloride and scatterplots of SO4 versus Cl. Groundwater 
along this flow path becomes more dilute to the south as it becomes 
increasingly mixed with groundwater near Fortymile Wash. Upstream 
of this mixing zone, high groundwater 14C activities and variable äD 
and ä18O compositions indicate the presence of relatively young 
recharge in the groundwater due to runoff or irrigation in the area 
Similar anion and cation concentrations along the flow line and 
dissimilarities compared to regions to the east and west. Groundwater 
along the northern part of this flow path is distinguished from 
groundwater at Yucca Mountain by äD and ä18O compositions that are 
heavier or more offset from the Yucca Mountain meteoric water line 
than the groundwater found under Yucca Mountain. Based on the 
observation that 14C activities do not decrease systematically 
southward in the northern or southern segments of the wash, some 
part of the groundwater along Fortymile Wash may also be derived 
from recharge due to runoff or irrigation in the area. 
High SO4 and low ä34S characteristics of groundwater from well UE-25 
J-11 distinguish it from the high SO4 and high ä34S groundwater 
characteristic of the Gravity fault and the low SO4 and low ä34S 
groundwater of the Fortymile Wash. A scatterplot of ä34S versus 
1/SO4 indicates a mixing trend involving well UE-25 J-11 as an end 
member, with wells in the Lathrop Wells and FMW-E groups having up 
to 20 percent of a UE-25 J-11-like groundwater. These mixing 
relations were confirmed with PHREEQC inverse models involving 
selected boreholes in these groups. 
Scatterplots and PHREEQC inverse models show that a mixture of 
groundwater is required to account for the Cl, äD, and ä18O 
compositions characteristic of this flow path. East of Flow Path 4, the 
extremely light ä13C and high ä87Sr of groundwater in northern Yucca 
Mountain compared to Timber Mountain groundwater, indicates that 
groundwater from the Timber Mountain and Beatty Wash areas is not 
the dominant component of groundwater at Yucca Mountain north of 
Drill Hole Wash. 
Chemically and isotopically distinct from groundwater that 
characterizes Flow Path 4, with higher concentrations of most major 
ions (but lower concentrations of F and SiO2), and relatively high ä18O 
and äD. Groundwater in Oasis Valley has some of the lightest oxygen 
and hydrogen isotopic compositions in the Yucca Mountain area, 
eliminating flow from Oasis Valley under Bare Mountain as a possible 
source of groundwater in southwest Crater Flat. A more likely source 
for groundwater along this flow path is local recharge at Bare 
Mountain, a source suggested by the similarly heavy äD and ä18O 
compositions of perched water emanating from a spring at Bare 
Mountain (Specie Spring) and groundwater in southwest Crater Flat. 
This similarity indicates that local recharge and runoff from Bare 
Mountain may be the source of groundwater along this flow path, as 
schematically indicated by the dashed nature of the beginning of this 
flow path in Figure 2-10. 
September 2003 2-20
Table 2-3. Summary of Bases for Regional Flow Paths and Mixing Zones Derived from Geochemistry 
Observations (Continued) 
Flow Path or 
Mixing Zone 
(Figure 2-10) 
6
7
8
9 
Mix A 
No. 11: Saturated Zone 
Geochemical Flow Path or 
Mixing Zone Description 
From borehole USW WT-10 
southward toward borehole 
NC-EWDP-15P 
From northern Yucca Mountain 
southeastward toward YM-SE 
boreholes in the Dune Wash 
area, then southwestward along 
the western edge of Fortymile 
Wash 
Leakage of groundwater from 
the carbonate aquifer across 
the Gravity fault 
Deep underflow of groundwater 
from the carbonate beneath the 
Amargosa Desert and Funeral 
Mountains to discharge points 
in Death Valley 
Samples from the Nye County 
and SW Crater Flat boreholes 
along U.S. Highway 95 
Revision 2 
Geochemical Evidence of Flow Path or 
Mixing Zone 
This flow path is identified from PHREEQC models that indicate that 
groundwater from borehole NC-EWDP-15P is formed from subequal 
amounts of groundwater from boreholes USW WT-10 and USW VH-1, 
and a small percentage (less than 5 percent) of groundwater from the 
carbonate aquifer. Although the predominant direction of flow from the 
Solitario Canyon area is southward along the Solitario Canyon fault, 
evidence for the leakage of small amounts of groundwater eastward 
across the fault is provided by similarities in the concentrations of 
many ions and isotopes between boreholes in the Solitario Canyon 
Wash and Yucca Mountain Crest areas. This chemical and isotopic 
similarity indicates that groundwater as far east as borehole USW H-4 
may have some component of groundwater from the Solitario Canyon 
Wash area and possibly NC-EWDP-19D. The short southeastoriented 
dashed lines from boreholes in the Solitario Canyon Group 
schematically illustrate this leakage. 
The upper segment of this flow path is motivated by the high 
groundwater 234U/238U activity ratios found in the northern Yucca 
Mountain and Dune Wash areas. High 234U/238U activity ratios (greater 
than 7) typify perched water and groundwater along and north of Drill 
Hole Wash but not groundwater along Yucca Crest at borehole USW 
SD-6 or perched water at borehole USW SD-7. Based on the 
conceptual model for the evolution of 234U/238U activity ratios, 
congruent dissolution of thick vitric tuffs that underlie the Topopah 
Spring welded tuff along Yucca Crest south of Drill Hole Wash would 
be expected to decrease the 234U/238U activity ratios of deep 
unsaturated-zone percolation south of the wash. High 234U/238U 
activity ratios are expected only where these vitric tuffs are absent, as 
in northern Yucca Mountain. 
Hydrogeologists and geochemists have recognized leakage across the 
fault (Winograd and Thordarson 1975; Claassen 1985). The 
carbonate aquifer component in this groundwater is recognized by 
many of the same chemical and isotopic characteristics that typify 
groundwater discharging from the carbonate aquifer at Ash Meadows. 
These characteristics include high concentrations Ca and Mg, low 
SiO2, heavy ä13C values, low 14C activity, and ä18O and äD values 
comparable to Ash Meadows groundwater. 
The similarity in the chemical and isotopic characteristics of 
groundwater found in the Gravity fault area and groundwater that 
discharges from Nevares and Travertine springs support this 
interpretation. The dissimilarity in Cl, Mg, and SiO2 concentrations in 
these springs compared to the groundwater from the alluvial aquifer 
along the Amargosa River suggests that this alluvial groundwater is 
not the predominant source of the spring discharge in Death Valley. 
The zone is demonstrated by groundwater compositions of samples 
that are intermediate between the compositionally distinct groundwater 
of the carbonate aquifer and dilute groundwater of the volcanic aquifer 
that is interpreted to have originated in the Yucca Mountain area (see 
discussion of flow paths 6 and 7). 
September 2003 2-21
Table 2-3. Summary of Bases for Regional Flow Paths and Mixing Zones Derived from Geochemistry 
Observations (Continued) 
Flow Path or 
Mixing Zone 
(Figure 2-10) 
Mix B 
Mix C 
Source: BSC 2003f. 
No. 11: Saturated Zone 
Geochemical Flow Path or 
Mixing Zone Description 
Samples from the FMW-W and 
AR/FMW groups, plus a few 
samples from the FMW-S group 
All samples from the Lathrop 
Wells and FMW-E groups, a 
few of the more westerly 
samples form the Gravity fault 
group, and at least one sample 
(#141) from the FMW-S group 
Revision 2 
Geochemical Evidence of Flow Path or 
Mixing Zone 
The zone highlights groundwater with compositions that are 
intermediate between the distinct and consistent groundwater 
compositions of the Amargosa River Group and the dilute groundwater 
of the FMW-S group. 
Characterized by small percentages of the distinctively high SO4 
groundwater from Well UE-25 J-11. Groundwater with this distinctive 
signature is mixed to variable degrees with dilute water from the 
FMW-S group to the west or with groundwater from the carbonate 
aquifer (Gravity fault group) to the east. 
September 2003 2-22
Source: BSC 2003f, Figure 16. 
Figure 2-12. Areal Distribution of Sulfate in Groundwater 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-23
Revision 2 
Source: Based on BSC 2003f, Figure 24. 
Figure 2-13. Regional Groundwater ä-Deuterium 
Flow paths were interpreted based on a number of approaches, including examination of areal 
distribution plots for spatial trends (e.g., Figures 2-11, 2-12, and 2-13), examination of 
scatterplots between chemical or isotopic variables that indicate relationships (including mixing) 
between groundwater from the different geographic areas (identified in Figure 2-10), and inverse 
geochemical models used to estimate the mixing fractions of various upgradient groundwaters 
present in a downgradient groundwater, recognizing that groundwater composition can be a 
result of mixing and water-rock interactions (BSC 2003f). The first two approaches focus on 
patterns and relationships displayed among relatively nonreactive species (e.g., chloride, sulfate, 
and ä-deuterium). The potential groundwater sources and mixing relationships suggested by the 
first two approaches were examined quantitatively by inverse mixing and reaction models that 
also considered the evolution of more reactive species through water-rock interaction. The first 
approach is essentially two dimensional, but the second and third approaches incorporate the 
effects of three-dimensional mixing with local recharge or with groundwater upwelled from the 
deep carbonate aquifer. 
2-24 September 2003 No. 11: Saturated Zone
Revision 2 
The regional flow paths and mixing zones, identified based on the groundwater geochemical 
signatures, are consistent with the general flow directions and recharge-discharge relationships 
discussed in Section 2.2.2. For example, the southwesterly flow in the deep carbonate aquifer 
across the Amargosa Desert is consistent with recharge in the Spring Mountains and Sheep 
Range and with discharge in the springs around Death Valley. Similarly, the relatively shallow 
southerly flow through tuff and alluvium from recharge in the Rainer Mesa area along the 
Fortymile Canyon and under Fortymile Wash discharges in the wells in Amargosa Valley or at 
natural discharge areas such as Franklin Lake Playa. All of these figures illustrate a general 
southerly flow of regional groundwater in the vicinity of Yucca Mountain and a mixing of 
different groundwater types in the alluvial aquifer underlying the Amargosa Valley. 
2.2.5 Groundwater Flow Model and Results 
Several models have been constructed over the past decade to describe the hydrogeology in the 
Death Valley region. The current three-dimensional digital hydrogeologic framework model 
developed for the Death Valley regional flow system contains elements from both of the 
hydrogeologic framework models used in previous investigations: the 1997 Death Valley 
regional flow system model (D’Agnese et al. 1997) and the Under Ground Test Area regional 
model (DOE 1997). 
The Death Valley regional flow system has been analyzed by the USGS using a threedimensional 
steady-state model. The required model parameter values were supplied by 
discretization of the three-dimensional hydrogeologic framework model and digital 
representations of the remaining conceptual model components. The three-dimensional 
simulation and corresponding sensitivity analysis supported the hypothesis of interactions 
between a relatively shallow local and subregional flow system and a deeper dominant regional 
system controlled by the carbonate aquifer. 
Model calibration was completed to estimate hydraulic parameters that best fit observed 
hydraulic data and evaluate alternative conceptual models of the flow system. The results of the 
model are illustrated in Figure 2-14, where the residual difference between the simulated and 
observed heads is plotted. Acceptable matches to observed hydraulic heads generally occur in 
areas of low hydraulic gradients. Poorer fits generally occur in areas with a steep hydraulic 
gradient. Although some of the observed and simulated heads differ by more than 100 m, the 
general flow directions and recharge and discharge relationships are preserved. 
Figure 2-14 indicates that in some parts of the regional flow model, the data are too sparse to 
sufficiently constrain the model. That is, the model attempts to reduce the hydraulic head 
residual with equal weight applied to all observations. In areas where more boreholes exist to 
constrain the predicted hydraulic heads, the residuals generally are lower. This is the case in the 
Amargosa Farms area, Yucca Flat, Oasis Valley, and in the vicinity of Yucca Mountain. In areas 
with less hydraulic constraint, such as north of Indian Springs and along the Eleana Range, the 
residuals generally are greater. 
Although considerable uncertainty exists in the observed and predicted hydraulic heads in the 
regional flow model, the general trends indicate major recharge and discharge areas that are 
consistent with the observed areas presented in Figures 2-2 and 2-3. 
September 2003 2-25 No. 11: Saturated Zone
Source: Based on D’Agnese et al. 2002, Figure 40. 
Figure 2-14. Comparison of Predicted and Observed Hydraulic Heads in the Death Valley Regional 
Groundwater Flow Model 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-26
Revision 2 
Comparison of modeled and inferred discharge is presented in Figure 2-15. Given the large 
uncertainty in the hydraulic characteristics and the sparseness of the observations, the match is 
acceptable for understanding the overall flow system and estimating the flow rates in the vicinity 
of Yucca Mountain. 
Uncertainties in the regional flow model can be attributed to uncertainties in the hydrogeology 
represented in the framework model, water levels being represented as static rather than perched, 
and resolution of detailed hydrostratigraphy in the coarse grid of the regional model. 
Considering these constraints, the regional representation of groundwater flow is sufficiently 
characterized to define a general southerly flow direction in the vicinity of Yucca Mountain. 
Figure 2-15. Simulated and Observed Groundwater Discharge for Major Discharge Areas 
Source: D’Agnese et al. 2002, Figure 43. 
2.3 SITE-SCALE GROUNDWATER FLOW SYSTEM 
To better represent the groundwater flow system at the scale of interest for the repository, it is 
necessary to develop a more refined estimate of the groundwater regime than is possible using 
only the regional characterization. The regional groundwater flow characterization provides the 
context of the site-scale representation by constraining the likely groundwater flow paths 
(through regional understanding of recharge, discharge, hydraulic potentials, and geochemistry) 
and the average volumetric flow rates (through regional understanding of the hydraulic 
characteristics and the regional water budget). The regional representation is not suitable for 
evaluating the details of the groundwater flow rates (e.g., specific discharge) or the distribution 
of flow rates along the paths of likely radionuclide migration from Yucca Mountain to the 
compliance point specified in regulations. 
No. 11: Saturated Zone September 2003 2-27
Revision 2 
Figure 2-1 depicts the location and scale of the site-scale groundwater flow representation. This 
model encompasses an area of 30 by 45 km and extends from the top of the water table to the 
lower clastic confining unit. Although the site-scale model resides within the regional-scale 
representation and must be consistent with the regional characterization, details of the flow paths 
and hydrogeology at the scale of hundreds of meters to kilometers necessitates a finer resolution 
of understanding than the scale of kilometers to tens of kilometers used in the regional model. 
2.3.1 Site Characterization and Data Collection 
Drilling to evaluate the Yucca Mountain site began in 1978, and the first hydrologic test borehole 
was completed in 1981. Detailed site characterization commenced in 1986. Water levels were 
measured as each borehole was completed, and long-term water-level monitoring commenced in 
1983. Periodic measuring of water levels continues through the present. The network of 
monitoring boreholes has evolved over the years and continues to increase as boreholes are 
installed as part of the ongoing Nye County Early Warning Drilling Program. The boreholes 
provide measurements at various depths, and a number of boreholes monitor more than one 
depth interval. 
The location of monitoring boreholes used to characterize the groundwater flow system in the 
vicinity of Yucca Mountain are illustrated in Figure 2-16. This figure includes boreholes drilled 
and tested by the DOE in support of the Yucca Mountain Site Characterization Project and those 
drilled and tested by Nye County as part of the Nye County Early Warning Drilling Program. 
2.3.2 Site-Scale Recharge and Discharge 
Within the scale of the site model of saturated zone groundwater flow, the bulk of the recharge 
and discharge occurs along the lateral boundaries with the regional model (Figure 2-17a). Inflow 
generally occurs along the northern and eastern boundaries, and discharge generally is along the 
southern boundary (Table 2-4). Figure 2-17a shows the segments of the north, east, and west 
boundaries listed in Table 2-4. Inflow from the north generally is the result of regional recharge 
that occurs at Timber Mountain, Pahute Mesa, and Rainer Mesa. Inflow from the east is 
generally the result of regional underflow in the carbonate aquifers that were recharged in the 
Specter Range. Outflow to the south is the result of carbonate underflow and flow in the alluvial 
aquifers that ultimately discharges to wells in Amargosa Valley or naturally at Ash Meadows. 
Table 2-4 shows the site-scale base-case flow model and the 1997 Death Valley regional flow 
system model. Appendix D also compares the 2001 Death Valley regional flow system model. 
Local recharge due to infiltration along Yucca Mountain and, to a lesser extent, along Fortymile 
Wash is also considered. The distributions of vertical recharge in the site-scale model are 
depicted in Figure 2-17b. 
September 2003 2-28 No. 11: Saturated Zone
CRWMS M&O 2000a, Figure 3-7. DTNs: MO0105GSC01040.000, MO0106GSC01043.000, 
MO0203GSC02034.000, and MO0206GSC02074.000. 
Source: 
Figure 2-16. Location of Boreholes used to Characterize the Site-Scale Groundwater Flow System 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-29
Of the total volumetric recharge and discharge in the regional flow basin (on the order of 100 to 
300 million m3/year), about 10 to 30 percent (depending on the assumed regional flow balance) 
flows through the site-scale model boundaries. The bulk of the flow is within the carbonate 
aquifers that are recharged to the east and north of the site model area. Groundwater flows into 
and across the site model boundaries, and it ultimately discharges to the south of the site model. 
Table 2-4 compares the regional and site-scale model fluxes for an evaluation of consistency. 
Based on the discussion of uncertainty in the regional potentiometric surface, the uncertainty and 
variability in regional aquifer characteristics, and the uncertainty in regional recharge and 
discharge amounts and distribution, the uncertainty in the boundary fluxes (which is not 
quantified on this table) is considerable. All three types of information (hydraulic heads, 
hydraulic conductivity, and recharge-discharge amounts) are integrated into the site-scale model 
to develop an integrated and self-consistent representation of the overall flow system. Although 
uncertainty exists in each type of information, the integrated representation appropriately reflects 
all three observations.
Table 2-4. Comparison of Regional and Site-Scale Fluxes 
Boundary Zone Regional Flux (million m3/year) 
-3.2 
-0.5 
-1.7 
-0.6 
-6.1 
0.1 
-2.2 
-0.2 
0.1 
-1.5 
-3.7 
-17.5 
-0.2 
0.1 
-0.1 
-17.7 
28.9 
Site-Scale Flux (million m3/year) 
-1.9 
-1.1 
-1.0 
-1.4 
-5.4 
0.1 
<<0.1 
<<0.1 
<<0.1 
-0.2 
-0.1 
-17.5 
0.1 
0.5 
0.5 
-16.4 
22.8 
N1 
N2 
N3 
N4 
Subtotal of North Boundary Fluxes 
W1 
W2 
W3 
W4 
W5 
Subtotal of West Boundary Fluxes 
E1 
E2 
E3 
E4 
Subtotal of East Boundary Fluxes 
S
Source: Based on BSC 2001a, Table 14. 
NOTES: Negative values indicate flow into the model. Values were converted from mass flux to volumetric 
flux and rounded to the nearest 0.1 million m3/yr. 
2-30 No. 11: Saturated Zone September 2003 
Revision 2
Revision 2 
Source: BSC 2001a, Figure 16. 
NOTE: Locations indicate discrete places where boundary fluxes from the regional model are applied to the sitescale 
flow model. The southern boundary is not coded S because it is one segment. 
Figure 2-17a. Flux Zones used for Comparing Regional and Site-Scale Flux
September 2003 2-31 No. 11: Saturated Zone
Source: BSC 2001b, Figure 6.1.3-2. 
Figure 2-17b. Recharge to the Saturated Zone Site-Scale Flow Model 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-32
Revision 2 
2.3.3 Site-Scale Potentiometric Surface 
Figure 2-18 depicts the results of an analysis of water-level data prepared by the USGS to 
provide the potentiometric surface within the site-scale model domain and target water-level data 
for model calibration (USGS 2001b). During this analysis, the water-level data were used to 
generate a single representative potentiometric surface for the saturated zone site-scale model 
domain. When developing the potentiometric surface, water-level altitudes representing the 
uppermost aquifer system, typically the volcanic or alluvial system, were used. Water-level 
altitudes in some boreholes represent composite heads from multiple hydrogeologic units and 
fracture zones. Generally, water levels in the uppermost saturated zone appear to represent a 
laterally continuous, well-connected aquifer system. However, locally, it is possible that the 
observed uppermost potential represents a perched or semiconfined interval, or that a more 
transmissive unit deeper in the borehole controls the local potential. The faults depicted in 
Figure 2-18 are described in Site-Scale Saturated Zone Flow Model (BSC 2003c) and 
Water-Level Data Analysis for the Saturated Zone Site-Scale Flow and Transport Model 
(USGS 2001b). 
The USGS (2001a) provided an updated analysis of water-level data (Figure 2-19). This analysis 
included water-level data collected through December 2000, including water-level data obtained 
from the expanded Nye County Early Warning Drilling Program and data from borehole USW 
WT-24. In addition to the inclusion of new water-level data, the primary difference in the 
approach taken to generate the revised potentiometric surface was the assumption that water 
levels in the northern portion of the model domain (boreholes USW G-2 and UE-25 WT #6) 
represent perched conditions and are not representative of the regional potentiometric surface. 
As a result, the revised potentiometric surface map represents an alternate concept for the large 
hydraulic gradient area north of Yucca Mountain. 
Comparison of Figures 2-18 and 2-19 indicates that the potentiometric surface maps are similar. 
Although differences can be noted in these two conceptualizations, both potentiometric surfaces 
indicate a predominately southerly component of groundwater flow in this area. 
Based on the potentiometric surface map, three distinct hydraulic gradient areas in the vicinity of 
Yucca Mountain have been identified: a large hydraulic gradient between water-level altitudes of 
1,030 m and 750 m at the northern end of Yucca Mountain, a moderate hydraulic gradient west 
of the crest of Yucca Mountain, and a small hydraulic gradient extending from Solitario Canyon 
to Fortymile Wash. 
September 2003 2-33 No. 11: Saturated Zone
Source: USGS 2001b, Figure 1-2. 
NOTE: Black lines indicate major faults, which are identified in the source document. 
Figure 2-18. Nominal Site-Scale Potentiometric Surface 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-34
Revision 2 
Figure 2-19. Alternative Site-Scale Potentiometric Surface 
Source: USGS 2001a, Figure 6-1. 
September 2003 2-35 No. 11: Saturated Zone
Revision 2 
A number of explanations have been proposed to explain the presence of the large hydraulic 
gradient at the north end of Yucca Mountain (Czarnecki and Waddell 1984; Ervin et al. 1994). 
Explanations proposed for the large hydraulic gradient include: 
• Faults that contain nontransmissive fault gouge 
• Faults that juxtapose transmissive tuff against nontransmissive tuff 
• The presence of a less fractured lithologic unit 
• A change in the direction of the regional stress field and a resultant change in the 
intensity, interconnectedness, and orientation of open fractures on either side of the area 
with the large hydraulic gradient 
• A disconnected, perched or semi-perched water body (i.e., the high water-level altitudes 
are caused by local hydraulic conditions and are not part of the regional saturated zone 
flow system). 
The cause of the moderate hydraulic gradient generally is believed to be the result of the 
Solitario Canyon fault and its splays functioning as a barrier to flow from west to east due to the 
presence of low-permeability fault gouge or to the juxtaposition of more permeable units against 
less permeable units (Luckey et al. 1996, p. 25). 
The small hydraulic gradient occupies most of the repository area and the downgradient area 
eastward to Fortymile Wash. Over a distance of 6 km, the hydraulic gradient declines only about 
2.5 m 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 
(Luckey et al. 1996, p. 27). 
In addition to an understanding of the areal hydraulic potential gradient distribution, local 
vertical potential gradients have been observed in individual boreholes that have isolated test 
intervals. The results of these individual head observations are tabulated in Table 2-5. 
Depending on the location of the borehole, small vertical potential differences are probably not 
indicative of vertical flow but, instead, represent the degree of horizontal heterogeneity within 
the aquifer that is tested. However, large vertical potential differences, such as those between the 
carbonate aquifer and the overlying tuff or alluvial aquifers, are generally representative of more 
extensive flow field differences. 
The vertical hydraulic gradients in the vicinity of Yucca Mountain are generally oriented upward 
(i.e., they are positive values in Table 2-5). These upward gradients effectively limit the 
downward potential for migration of water within the tuff aquifers or between the tuff aquifers 
and the underlying carbonate aquifer. Although locally downward hydraulic gradients are 
possible, these have been attributed to the presence of local recharge conditions and low 
permeability confining units. Additional details on observed vertical gradients in the vicinity of 
Yucca Mountain are presented in Appendix B. 
September 2003 2-36 No. 11: Saturated Zone
Table 2-5. Summary of Vertical Head Observations at Boreholes in the Vicinity of Yucca Mountain 
Revision 2 
Head Difference deepest to shallowest 
intervals (m) Borehole 
USW H-1 tube 4 
USW H-1 tube 3 
USW H-1 tube 2 
USW H-1 tube 1 
USW H-3 upper 
USW H-3 lower 
USW H-4 upper 
USW H-4 lower 
USW H-5 upper 
USW H-5 lower 
USW H-6 upper 
USW H-6 lower 
USW H-6 
UE-25 b #1 upper 
UE-25 b #1 lower 
UE-25 p #1 (volcanic) 
UE-25 p #1 (carbonate) 
UE-25 c #3 
UE-25 c #3 
USW G-4 
USW G-4 
UE-25 J-13 upper 
UE-25 J-13 
UE-25 J-13 
UE-25 J-13 
NC-EWDP-1DX (shallow) 
NC-EWDP-1DX (deep) 
NC-EWDP-2D (volcanic) 
NC-EWDP-2DB (carbonate) 
NC-EWDP-3S probe 2 
NC-EWDP-3S probe 3 
NC-EWDP-3D 
NC-EWDP-4PA 
NC-EWDP-4PB 
NC-EWDP-7SC probe 1 
NC-EWDP-7SC probe 2 
NC-EWDP-7SC probe 3 
NC-EWDP-7SC probe 4 
NC-EWDP-9SX probe 1 
NC-EWDP-9SX probe 2 
NC-EWDP-9SX probe 4 
NC-EWDP-12PA 
NC-EWDP-12PB 
NC-EWDP-12PC 
NC-EWDP-19P 
NC-EWDP-19D 
Source: Based on USGS 2001a, Table 6-1. 
Negative values indicate downward gradient. NOTE: 
No. 11: Saturated Zone 
Open Interval (m below 
land surface) 
573-673 
716-765 
1097-1123 
1783-1814 
762-1114 
1114-1219 
525-1188 
1188-1219 
708-1091 
1091-1219 
533-752 
752-1220 
1193-1220 
488-1199 
1199-1220 
384-500 
1297-1805 
692-753 
753-914 
615-747 
747-915 
282-451 
471-502 
585-646 
820-1063 
WT-419 
658-683 
WT-493 
820-937 
103-129 
145-168 
WT-762 
124-148 
225-256 
24-27 
55-64 
82-113 
131-137 
27-37 
43-49 
101-104 
99-117 
99-117 
52-70 
109-140 
106-433 
Potentiometric Level 
(m above sea level) 
730.94 
730.75 
736.06 
785.58 
731.19 
760.07 
730.49 
730.56 
775.43 
775.65 
775.99 
775.91 
778.18 
730.71 
729.69 
729.90 
751.26 
730.22 
730.64 
730.3 
729.8 
728.8 
728.9 
728.9 
728.0 
786.8 
748.8 
706.1 
713.7 
719.8 
719.4 
718.3 
717.9 
723.6 
818.1 
786.4 
756.6 
740.2 
766.7 
767.3 
766.8 
722.9 
723.0 
720.7 
707.5 
712.8 
2-37 
54.7 
28.9 
0.1 
0.2 
2.2 
-1.0 
21.4 
0.4 
-0.5 
-0.8 
-38.0 
7.6 
-1.5 
5.7 
-77.9 
0.1 
2.2 
5.3
September 2003
Revision 2 
Only two boreholes, UE-25 p #1 and NC-EWDP-2D/2DB, provide information on vertical 
gradients between volcanic rocks and the underlying Paleozoic carbonate rocks. At borehole 
UE-25 p #1, water levels currently are monitored only in the carbonate aquifer; however, waterlevel 
data were obtained from within the volcanic rocks as the borehole was drilled and tested. 
At this borehole, water levels in the Paleozoic carbonate rocks are about 20 m higher than those 
in the overlying volcanic rocks. Borehole NC-EWDP-2DB penetrated Paleozoic carbonate rocks 
toward the bottom of the borehole (Spengler 2001a). Water levels measured within that deep 
part of the borehole are about 8 m higher than levels measured in volcanic rocks penetrated by 
borehole NC-EWDP-2D. 
Water levels monitored in the lower part of the volcanic-rock sequence at Yucca Mountain also 
generally are higher than levels monitored in the upper part of the volcanics. For example, 
boreholes USW H-1 (tube 1) and USW H-3 (lower interval) both monitor water levels in the 
lower part of the volcanic rock sequence, and upward gradients are observed with head 
differences of 55 and 29 m, respectively. The gradient at USW H-3 is not completely 
characterized because the water levels in the lower interval had been continuously rising before 
the packer that separates the upper and lower intervals failed in 1996. 
An upward gradient is also observed between the alluvial deposits monitored in borehole 
NC-EWDP-19P and underlying volcanic rocks monitored in borehole NC-EWDP-19D. The 
vertical head difference at this site is 5.3 m; however, levels reported for NC-EWDP-19D 
represent a composite water level for the alluvium and volcanics, so that the true head difference 
between those units is not completely known. 
Several downward gradients have also been observed within the saturated zone site-scale flow 
and transport model area (Table 2-5). The largest downward gradient is observed between the 
deep and shallow monitored intervals at borehole NC-EWDP-1DX (head difference of 38 m) and 
NC-EWDP-7S (head difference of about 78 m). The depth to water at both of these locations is 
anomalously shallow and probably represents either locally perched conditions or the presence of 
a low permeability confining unit close to the surface that effectively impedes the downward 
migration of water to the more contiguous tuff and alluvium aquifers at greater depths. 
2.3.4 Site-Scale Hydrogeologic Framework 
The site-scale hydrogeologic framework represents site hydrostratigraphy at a scale 
commensurate with the scale of the flow system and sufficient to define the hydrogeologic units 
through which water may move from the repository block to a compliance point about 18 km 
south of Yucca Mountain. Understanding the various lithologic units through which water 
migrates is important due to the transport characteristics of the different lithologies in the vicinity 
of Yucca Mountain. In particular, the transport characteristics of fractured and porous welded 
tuffs are different from fractured nonwelded tuffs, which are both different from porous 
alluvium. Of particular interest to the behavior of the saturated zone barrier at Yucca Mountain 
are the effective porosity and retardation characteristics of the different lithologies, as well as the 
length of the flow path in the alluvial aquifer. 
September 2003 2-38 No. 11: Saturated Zone
Revision 2 
The hydrogeologic framework sets the lithologic constraints through which water is likely to 
flow. This framework is based on direct outcrop observations (Figure 2-20), geologic 
observations from boreholes in the area, interpolation from the regional hydrogeology, 
geophysical logs (especially resistivity and seismic surveys), and geologic inferences of 
lithologic unit thicknesses from regional facies variations. Representative cross sections of the 
site-scale hydrogeologic framework model are presented in Figure 2-21. 
Aspects of the site-scale geology important to groundwater flow are represented in the site-scale 
hydrogeologic framework model. A detailed description of the hydrogeologic framework model, 
assumptions, and methods used to develop the model are given in Hydrogeologic Framework 
Model for the Saturated-Zone Site-Scale Flow and Transport Model (USGS 2001c). A 
comparison of the revised hydrogeologic framework model with the geologic framework model 
used to evaluate the detailed site geology is presented in Appendix A. 
Since development of the hydrogeologic framework model used in the total system performance 
assessment license application base-case model, the Yucca Mountain hydrogeologic framework 
model has been reinterpreted incorporating data recently obtained from the Nye County Early 
Warning Drilling Program and through the reinterpretation of existing data from other areas 
(including geophysical data in the northern area of the site). The major changes in the revised 
hydrogeologic framework model are in the southern part of the model and include new 
information on the depths and extent of the alluvial layers. 
As a result of reinterpreting the hydrogeologic framework model, the number and distribution of 
hydrogeologic units has been modified in the 2002 hydrogeologic framework model, and it now 
corresponds to the units in the regional hydrogeologic framework model. A comparison of the 
hydrogeologic units identified in the hydrogeologic framework models used in the base-case and 
2002 models is provided in Table 2-6. The table indicates that there were 19 hydrogeologic units 
in the base-case hydrogeologic framework model and 27 hydrogeologic units in the 2002 
hydrogeologic framework model. Four of the 27 units present in the regional model are not 
found within the boundary of the site-scale hydrogeologic framework model because they are 
pinched out by adjacent units. The hydrogeologic framework model revision has the same units 
and is consistent with the Death Valley regional flow system model (D’Agnese et al. 2002). 
The development of the 2002 site-scale hydrogeologic framework model revision was influenced 
primarily by geologic observations made from Nye County boreholes drilled since the earlier 
version of the model. Although these boreholes serve multiple geologic and hydrogeologic 
purposes, an important use has been to better characterize the thickness and lateral extent of the 
alluvial aquifer north of U.S. Highway 95. The location of these Nye County boreholes and 
cross-section lines are illustrated in Figure 2-22. 
Figure 2-23 shows the cross-sections for these Nye County boreholes. Figures 2-24 and 2-25 
depict the total alluvial thickness and saturated alluvial thickness derived from borehole 
observations and geophysical logging completed in the area between Yucca Mountain and 
U.S. Highway 95. 
September 2003 2-39 No. 11: Saturated Zone
Source: USGS 2001c, Figure 4-2. 
NOTE: The lines of section correspond to the cross sections shown on Figure 2-21. 
Figure 2-20. Outcrop Geology of the Site-Scale Hydrogeologic Framework Model 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-40
Source: USGS 2001c, Figure 6-1. 
Note: 
Figure 2-21. Representative Cross-Sections through the Site-Scale Hydrogeologic Framework Model 
No. 11: Saturated Zone 
“D’Agnese & others, 1997” refers to D’Agnese et al. (1997). 
2-41 
Revision 2 
September 2003
Models 
Abbreviation 
Base 
ICU 
XCU 
LCCU 
LCA 
UCCU 
UCA 
LCCU_T1 
LCA_T1 
SCU 
VSU Lower 
OVU 
BRU 
CFTA 
CFBCU 
CFPPA 
WVU 
CHVU 
PVA 
TMVA 
VSU 
YVU 
LFU 
LA 
OACU 
OAA 
YACU 
YAA 
Source: BSC 2003h, Table 7.5-2. 
Table 2-6. Correspondence between Units of the Revised- and Base-Case Hydrogeologic Framework 
NOTE: These units do not have a one-to-one correlation. This table approximately relates the new hydrogeologic 
units to the base-case version. Four units that do not occur in the site-scale hydrogeologic framework 
model (OACU, YVU, BRU, and SCU) are included here to maintain the relationship to the regional model. 
Revision 2 
Base-Case Hydrogeologic Framework Model 
Upper Clastic Confining Unit, Upper Clastic 
Confining Unit—thrust 2 (uccu, uccut2) 
Lower Clastic Confining Unit—thrust 1 (lccut1) 
Lower Carbonate Aquifer thrusts 1 and 2 (lcat1, 
lcat2) 
NA 
9, 10, 11 Older Volcanic Confining Unit, Older Volcanic 
Aquifer, Lower Volcanic Confining Unit (lvcu, lva, 
mvcu) 
NA 
Lower Volcanic Aquifer—Tram Tuff (tct) 
Lower Volcanic Aquifer—Bullfrog Tuff (tcb) 
Lower Volcanic Aquifer—Prow Pass Tuff (tcp) 
Upper Volcanic Confining Unit (uvcu) 
Upper Volcanic Confining Unit (uvcu) 
Upper Volcanic Aquifer (uva) 
Upper Volcanic Aquifer (uva) 
Undifferentiated valley-fill (leaky) 
NA 
Valley-fill Aquifer (alluvium), Undifferentiated 
valley-fill (leaky) 
Valley-fill Confining Unit (playas) 
Valley-fill Aquifer (alluvium) 
No. 11: Saturated Zone 
Revised (Site and Regional Transient 
Model in Preparation) 
Hydrogeologic Name Unit 
Base (-4000 m) 
Intrusive Confining Unit 
Crystalline Confining Unit 
Lower Clastic Confining Unit 
Lower Carbonate Aquifer 
Upper Clastic Confining Unit 
1
2
3
4
5
6 
Upper Carbonate Aquifer 
Lower Clastic Confining Unit— thrust 
Lower Carbonate Aquifer—thrust 
7
8
9 
NA 
11 
Sedimentary Confining Unit (none in 
site area) 
Lower Volcanic and Sedimentary 
Units 
Older Volcanic Units 12 
Belted Range Unit (none in site area) 
Crater Flat - Tram Aquifer 
Crater Flat - Bullfrog Confining Unit 
Crater Flat - Prow Pass Aquifer 
Wahmonie Volcanic Unit 
Calico Hills Volcanic Unit 
Paintbrush Volcanic Aquifer 
Timber Mountain Volcanic Aquifer 
Volcanic and Sedimentary Units 
NA 
14 
15 
16 
17 
18 
19 
20 
21 
NA 
23 
24 
NA 
Young Volcanic Units (none in site 
area) 
Lavaflow Unit 
Limestone Aquifer 
Older Alluvial Confining Unit (none in 
site area) 
Older Alluvial Aquifer 26 
Young Alluvial Confining Unit 
Young Alluvial Aquifer 
27 
28 
2-42 
Hydrogeologic Name Unit 
Base (bottom of regional flow model) 
Granitic confining unit (granites) 
Lower Clastic Confining Unit (lccu) 
Lower Clastic Confining Unit (lccu) 
Lower Carbonate Aquifer (lca) 
1
2
3
3
4
5 
NA NA 
NA 
6 
NA 
Undifferentiated valley-fill (leaky) 8 
NA 
12 
13 
14 
15 
15 
16 
16 
8 
NA 
Lava-flow Aquifer (basalts) 17 
Limestone Aquifer (amarls) 18 
NA NA 
20 
19 
20 
September 2003
Revision 2 
Source: Nye County Department of Natural Resources and Federal Facilities 2003, Figure 4.5-3. 
NOTE: The cross sections A–A’ and B–B’ are shown in Figure 2-23. 
Figure 2-22. Locations of Nye County Alluvium Cross Sections 
September 2003 2-43 No. 11: Saturated Zone
Revision 2 
Source: Nye County Department of Natural Resources and Federal Facilities 2003, Figure 4.5-4. 
Figure 2-23. Nye County Alluvium Cross Sections 
September 2003 2-44 No. 11: Saturated Zone
Revision 2 
Source: DTN: GS021008312332.002. 
Figure 2-24. Alluvial Zone Total Thickness in the Vicinity of Yucca Mountain
September 2003 2-45 No. 11: Saturated Zone
Revision 2 
Figure 2-25. Alluvial Zone Saturated Thickness in the Vicinity of Yucca Mountain 
Source: DTN: GS021008312332.002. 
2.3.5 Site-Scale Hydrogeology 
Site-Scale Hydrogeologic Characteristics 2.3.5.1 
The permeability of rock units in the vicinity of Yucca Mountain has been determined by single 
and cross-hole hydraulic testing. These data have been used as starting points to support the 
calibration of the site-scale flow model (Section 2.3.7). 
Tuff Hydrogeologic Characteristics Derived from Testing at the C-Wells 2.3.5.2 
The C-Wells complex comprises three boreholes drilled and packed off in the Crater Flat Group. 
This complex is located about 700 m southeast of the South Portal of the Exploratory Study 
Facility (Figure 2-26), and it has been used to test the hydraulic and transport characteristics of 
the tuff aquifers along the likely travel path of groundwater from Yucca Mountain. Figure 2-27 
summarizes the borehole construction and identifies the major flowing intervals observed in 
these three boreholes. 
No. 11: Saturated Zone September 2003 2-46
Revision 2 
Source: Based on BSC 2003e, Figure 6.1-1. 
Figure 2-26. Location of the C-Wells and the Alluvial Testing Complex 
September 2003 2-47 No. 11: Saturated Zone
Revision 2 
Source. BSC 2003e, Figure 6.1-2. 
NOTE: Packer locations indicate intervals in which tracer tests were conducted (tracer tests conducted between 
UE-25 c#2 and UE-25 c#3). The two borehole logs represent matrix porosity (dimensionless) and fracture 
density (number of fractures per meter), from left to right, respectively. 
Figure 2-27. Stratigraphy, Lithology, Matrix Porosity, Fracture Density, and Inflow from Open-Hole 
Surveys at the C-Wells 
September 2003 2-48 No. 11: Saturated Zone
Revision 2 
In addition to the single- and cross-hole testing performed at the C-Wells, a large-scale pump test 
was performed in this complex. This test was conducted for more than a year and resulted in 
discernible drawdowns in boreholes located several kilometers away (Figures 2-28 and 2-29). 
These drawdowns indicate the lateral continuity of the saturated zone aquifer in these tuff rock 
units as well as similarities in transmissivities and average hydraulic characteristics. 
Source: BSC 2003e, Figure 6.2-36. 
Figure 2-28. Distribution of Drawdown in Observation Boreholes at Two Times After Pumping Started in 
September 2003 2-49 
UE-25 c#3 
No. 11: Saturated Zone
Revision 2 
Source: BSC 2003e, Figure 6.2-39. 
Figure 2-29. Drawdowns Observed in Boreholes Adjacent to the C-Wells Complex During the Long 
2.3.5.3 
September 2003 2-50 
Term Pumping Test 
Site-Scale Permeability 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 potential pathway of 
radionuclide migration in the saturated zone (BSC 2003e, Section 6.2.6). Performance of the 
repository could be affected by horizontal anisotropy if the permeability tensor is oriented in a 
north-south direction because the groundwater flow could be diverted to the south, causing any 
transported solutes to remain in the fractured volcanic tuff for longer distances before moving 
into the valley-fill alluvial aquifer (Figures 2-24 and 2-25). More southerly oriented flow 
directions would, therefore, reduce the length of the travel path through the alluvium to the 
compliance point. A reduction in the length of the flow path in the alluvium would decrease the 
amount of radionuclide retardation that could occur for radionuclides with greater sorption 
capacity in the alluvium than in fractured volcanic rock matrix. In addition, potentially limited 
matrix diffusion in the fractured volcanic units could lead to shorter transport times in the 
volcanic units relative to the alluvium. 
A conceptual model incorporating horizontal anisotropy in the tuff aquifer is acceptable, given 
that flow in the tuff aquifer generally occurs in a fracture network that exhibits a preferential 
north-south strike azimuth. Major faults near Yucca Mountain that have been mapped at the 
surface and that have been included in the site-scale hydrogeologic framework model also have a 
similar preferential orientation (Figure 2-20). In addition, north to north-northeast striking 
structural features are optimally oriented perpendicular to the direction of least principal 
No. 11: Saturated Zone
Revision 2 
horizontal compressive stress, thus promoting flow in that direction, suggesting a tendency 
toward dilation and potentially higher permeability (Ferrill et al. 1999, pp. 5 to 6). 
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 saturated zone. 
Results of this hydrologic evaluation (Appendix E) generally are consistent with the structural 
analysis of potential anisotropy and indicate anisotropy that is oriented in a north-northeast to 
south-southwest direction, assuming the response in borehole USW H-4 is not considered. The 
response in borehole USW H-4 is consistent with the effect of the Antler Wash fault being 
superimposed on this uniform anisotropy, resulting in a northwest to southeast anisotropy. 
2.3.5.4 Hydrogeologic Characteristics of the Alluvium Derived from Nye County 
Testing 
Hydraulic testing of the alluvium has been performed at the Alluvial Testing Complex 
(Figure 2-26). Figure 2-30 presents a summary of the lithology in the boreholes at the Alluvial 
Testing Complex. 
One of the most important results from the Alluvial Testing Complex was the interpretation of 
the “huff-puff” injection-withdrawal tracer test. In this test, a tracer was added to the wellbore 
and briefly injected into the aquifer. After a period of time (ranging from 0.5 days to 30 days), 
the tracer was pumped back. The migration of the tracer during the intervening time is 
controlled by the natural groundwater flux. The results of this test are illustrated in Figure 2-31. 
Although uncertainty exists in the interpretation of such tests, using reasonable ranges of 
effective porosity (ranging between 5 and 30 percent), a range of specific discharges in the 
vicinity of the borehole can be determined. Table 2-7 presents the results of this analysis and 
indicates a specific discharge in the range of 1.2 to 9.4 m/year. 
September 2003 2-51 No. 11: Saturated Zone
Source: Location of screened intervals from Questa Engineering Corporation 2002. Lithostratigraphic logs from 
Spengler 2001b; Spengler 2003a; Spengler 2003b. Borehole names refer to Nye County EWDP 
boreholes.
Figure 2-30. Summary of Lithology at the Alluvial Testing Complex 
No. 11: Saturated Zone 2-52 
Revision 2 
September 2003
Table 2-7. Specific Discharges and Seepage Velocities Estimated from the Different Drift Analysis 
Methods as a Function of Assumed Flow Porosity 
Assumed Flow Porosity a 
Peak Arrival Analysis 
Late Arrival Analysis b 
Mean Arrival Analysis c 
Mean Arrival Analysis d 
Linked Analytical Solutions 
Source: BSC 2003e, Table 6.5-7. 
NOTE: aThe three values are approximately the lowest, expected, and highest values, respectively, of 
the alluvium flow porosity used in Yucca Mountain performance assessments (BSC 2001c). 
bTime/Volume associated with approximately 86.4 percent recovery in each test (the final 
recovery in the 0.5-hr rest period test, which had the lowest final recovery of any test). 
c Mean arrival time calculated by truncating all tracer response curves at approximately 
86.4 percent recovery in each test. 
d Alternative mean arrival time calculated by extrapolating the tracer response curves in the 
0.5-hr rest period test to 91.3 percent and truncating the response curves in the two-day rest 
period test to 91.3 percent recovery (the final recovery in the 30-day rest period test). 
No. 11: Saturated Zone 
Specific Discharge (m/year) / Seepage Velocity (m/year) 
0.18 0.05 
2.4 / 13.1 1.2 / 24.5 
7.3 / 40.4 3.9 / 77.1 
3.8 / 20.9 2.0 / 40.3 
4.6 / 25.8 2.5 / 49.1 
1.5 / 15 with a flow porosity of 0.10 and a longitudinal dispersivity of 5 m. 
2-53 
Revision 2 
0.3 
3.0 / 9.9 
9.4 / 31.3 
4.9 / 16.4 
6.0 / 20.2 
September 2003
Revision 2 
Source: BSC 2003e, Figure 6.5-26. 
NOTE: The plots are fits of three injection-pumpback tracer tests with theoretical curves resulting from three 
solutions to the advection-dispersion equation for the three phases of injection, drift, and pumpback. “Plot 0” 
is the model fit and “Plot 1” is the data curve. The parameters used in the calculations are: flow porosity = 
0.1; matrix porosity = 0.0; longitudinal dispersivity = 5.05 m; transverse dispersivity = 1.00 m; test interval 
thickness = 32.0 ft; tracer volume injected = 2,800 gal; chase volume injected = 22,000 gal; injection rate = 
15.0 gpm; mass injected = 5.0 kg; natural gradient = 0.002 m/m; T for gradient = 20.0 m2/day; specific 
discharge = 1.5 m/year. The Q values for the 0-, 2-, and 30-day tests are 13.41, 11.00, and 13.50, 
respectively. 
Figure 2-31. Fitting the Injection-Pumpback Tracer Tests in Screen #1 of NC-EWDP-19D1 Using the 
September 2003 2-54 
Linked-Analytical Solutions Method 
2.3.6 Site-Scale Geochemistry: Analyses of Water Types and Mixing 
Hydrochemical data provide information on several important site-scale issues, including the 
existence and magnitude of local recharge, flow directions from the repository to downgradient 
locations, and the potential for mixing and dilution of groundwater that could be released from 
the repository. 
A comparison of hydrochemical and isotopic data from perched water at Yucca Mountain to data 
from the regional groundwater system suggests that local recharge is a component of the 
saturated zone waters in volcanic aquifers beneath Yucca Mountain. The data examined 
included uranium isotopes (234U/238U) (Figure 2-32) and major anions and cations. It is possible 
that shallow groundwater beneath Yucca Mountain is composed entirely of local recharge. For 
example, by comparing the isotopic signature of perched waters in boreholes USW UZ-14 and 
USW WT-24 with saturated zone groundwater obtained from boreholes to the southeast, it is 
apparent that these waters have a similar origin, predominately from vertical recharge through 
the unsaturated tuff units in the vicinity of Yucca Mountain (BSC 2003f, Section 6.7.6.6). 
No. 11: Saturated Zone
Source: Paces et al. 2002, Figure 5. 
Figure 2-32. Groundwater Uranium and 234U/238U Ratios in the Vicinity of Yucca Mountain 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-55
Revision 2 
The chloride concentrations of the groundwater identified from uranium isotopes as having 
originated from Yucca Mountain have been used to estimate the recharge flux through Yucca 
Mountain (BSC 2003f, Section 6.7.6.6). Based on the chloride data, and assuming that the 
chloride flux from precipitation was between one and two times its estimated present-day value, 
past infiltration rates ranged between 6.5 and 16.5 mm/year. These groundwaters probably 
infiltrated during the late Pleistocene when the climate was cooler and wetter, so the relatively 
high infiltration rates should be interpreted as reflecting past, rather than present-day, conditions. 
Despite the sometimes large distances between boreholes, differences in regional groundwater 
chemical and isotopic compositions are often large enough that groundwater flow paths at a 
regional scale can be identified with some confidence (Figure 2-10). In contrast, despite the 
closer borehole spacing, the compositions of groundwaters in the immediate vicinity of Yucca 
Mountain are often too similar to allow detailed flow paths from the repository to be identified 
with certainty. However, because flow paths do not cross in plan view, possible flow directions 
from the repository area are constrained by regional Flow Paths 6 and 2 to be dominantly south 
or southeastward from the repository area. Geochemical inverse models (BSC 2003f, 
Section 6.7.8) for borehole NC-EWDP-19D indicated that groundwater at this borehole could 
have originated from the area of borehole UE-25 WT#3 at the mouth of Dune Wash (as depicted 
by Flow Path 7), or as a result of the mixing of groundwater flowing from the vicinity of 
borehole USW WT-10 and local Yucca Mountain recharge (indicated schematically by small 
eastward-pointing arrows on Flow Path 6; Figure 2-10). An origin for NC-EWDP-19D 
groundwater from the Solitario Canyon area would imply groundwater from the repository area 
should be forced to flow southeastward toward Fortymile Wash; conversely, an origin for 
borehole NC-EWDP-19D groundwater from the Dune Wash area near borehole UE-25 WT#3 
implies that groundwater from the repository area flows along a more southerly trajectory. 
2.3.7 Site Scale Groundwater Flow Model and Results 
Site-Scale Groundwater Flow Model Development 2.3.7.1 
Development of the site-scale groundwater flow 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. 
The computational grid developed for the site-scale saturated zone flow and transport model was 
formulated so that the horizontal grid is coincident with the grid cells in the regional-scale flow 
model. The depth of the computational grid is approximately the same as the depth of the 
regional-scale saturated zone flow model. The computational grid begins at the water table 
surface and extends to a depth of 2,750 m below sea level. 
The vertical grid spacing was established to provide the resolution necessary to represent flow 
and transport along critical flow and transport pathways in the saturated zone. 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 near the 
water table to 550 m at the bottom of the model domain. The vertical dimension of the model 
September 2003 2-56 No. 11: Saturated Zone
Revision 2 
domain was divided into 11 zones, and constant vertical grid spacing was adopted in each of 
these 11 zones. In total, 38 model layers were included in the vertical dimension. 
A three-dimensional representation of the base-case computational grid is provided in 
Figure 2-33. The grid is truncated at the water table surface, which is at 1,200 m in the north and 
700 m in the south. The grid extends from Universal Transverse Mercator coordinates (Zone 11, 
North American Datum 1927) 533340E to 563340E in the east-west direction, and from 
4046780N to 4091780N north-south direction. This representation of the computation grid 
illustrates the complex three-dimensional spatial relation among units within the site-scale model 
area. 
Source: BSC 2003c, Figure 6.5-2. 
correspond to the units shown in Figure 2-21. 
NOTE: Shading represents hydrogeologic features included in the model. View (500 m, 3x elevation) shows node 
points colored by hydrogeologic unit values from the hydrogeologic framework model. The units shown here 
September 2003 
Figure 2-33. Three-Dimensional Representation of the Computation Grid 
2-57 No. 11: Saturated Zone
Revision 2 
Site-Scale Groundwater Flow Model Comparisons to Observations 2.3.7.2 
The results of the calibrated site-scale saturated zone flow and transport model have been 
compared to direct and indirect indicators of groundwater flow processes. These analyses 
include a comparison between: (1) the observed and predicted water-level data, (2) calibrated 
and observed permeability data, (3) boundary fluxes predicted by the regional-scale flow model 
and the calibrated site-scale saturated zone flow model, (4) the observed and predicted gradients 
between the carbonate aquifer and overlying volcanic aquifers, (5) hydrochemical data and 
particle pathways predicted by the model, and (6) thermal data. 
Predicted and Observed Water-Level Elevations–Predicted and observed heads from the 
site-scale groundwater flow model are illustrated in Figure 2-34. As in the case of the regional 
model, the comparison is favorable in areas of low hydraulic gradient, but becomes more 
uncertain in areas of steep gradients. In the areas downgradient from Yucca Mountain, the 
match is acceptable. 
Since the site-scale flow model was calibrated, a number of boreholes have been installed as part 
of the Nye County Early Warning Drilling Program. These new boreholes include those 
installed at new locations and those completed at depths different from those previously 
available at existing locations. Comparison of water levels observed in the new Nye County 
Early Warning Drilling Program boreholes with water levels predicted by the calibrated 
site-scale flow model at these new locations and depths offered an opportunity to validate the 
site-scale flow model using new data not used for developing and calibrating the flow model. 
Predicted and observed water levels are provided in Table 2-8. 
Examination of the residuals (Table 2-8) indicates that uncertainty associated with the predicted 
water levels depends on the location of the borehole within the site-scale model domain. 
Residuals generally are higher in the western portion of the Nye County Early Warning Drilling 
Program area. The gradients are steeper in this area, and the calibrated model generally is less 
capable of predicting these steeper gradients. 
The observed residuals tend to improve at boreholes located further to the east. For example, 
residuals in the general area of NC-Washburn-1X, NC-EWDP-4, and NC-EWDP-5 are low. 
These boreholes are in the flow path inferred by hydrochemical data, and therefore these 
additional water-level data support the capability of the site-scale flow model to predict water 
levels in this portion of the flow path. 
September 2003 2-58 No. 11: Saturated Zone
Source: Based on BSC 2003c, Figures 6.4-5 and 6.4-6. 
NOTE: Upper figure represents observed hydraulic heads; lower figure represents predicted hydraulic heads and 
head residuals (predicted minus observed heads). 
Figure 2-34. Comparison of Observed and Predicted Hydraulic Heads in the Site-Scale Groundwater 
Flow Model 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-59
Table 2-8. Comparison of Observed and Predicted Water Levels at Nye County Early Warning Drilling 
Program Boreholes 
Site Name 
NC-EWDP-1DX, deep 
NC-EWDP-1DX, shallow 
NC-EWDP-1S, P1 
NC-EWDP-1S, P2 
NC-EWDP-2DB 
NC-EWDP-2D 
NC-EWDP-3D 
NC-EWDP-3S, P2 
NC-EWDP-3S, P3 
NC-EWDP-5SB 
NC-EWDP-9SX, P1 
NC-EWDP-9SX, P2 
NC-EWDP-9SX, P4 
NC-Washburn-1X 
NC-EWDP-4PA 
NC-EWDP-4PB 
NC-EWDP-7S — Zone 1 
NC-EWDP-7S — Zone 2 
NC-EWDP-7S — Zone 3 
NC-EWDP-7S — Zone 4 
NC-EWDP-12PA 
NC-EWDP-12PB 
NC-EWDP-12PC 
NC-EWDP-15P 
NC-EWDP-19P 
NC-EWDP-19D 
NC-EWDP-16P 
NC-EWDP-27P 
NC-EWDP-28P 
Source: BSC 2003c, Table 7.1-2. 
Permeability–For model validation, the permeabilities estimated during calibration of the sitescale 
saturated zone flow and transport model were compared to permeabilities determined from 
aquifer test data from the Yucca Mountain area and elsewhere at the Nevada Test Site 
(BSC 2003c, Section 7). The logarithms of permeability estimated during calibration of the 
model were compared to the mean logarithms of permeability determined from aquifer test data 
from Yucca Mountain (Figure 2-35) and to data from elsewhere at the Nevada Test Site 
(Figure 2-36). For most geologic units, calibrated permeabilities were within the 95 percent 
confidence limits of the mean permeabilities estimated from the data. Given the available data, 
the agreement between the model-calibrated value and the estimated site permeability value for 
the carbonate aquifer is considered to provide an adequate basis for confidence in the validity 
and representativeness of the site-scale flow model. 
No. 11: Saturated Zone 
x (m) 
536768 
536768 
536771 
536771 
547800 
547744 
541273 
541269 
541269 
555676 
539039 
539039 
539039 
551465 
553167 
553167 
539638 
539638 
539638 
539638 
536951 
536951 
536951 
544848 
549329 
549317 
545648 
544936 
545723 
y (m) Observed 
Head (m) 
748.8 4062502 
786.8 4062502 
787.1 4062498 
786.8 4062498 
713.7 4057195 
706.1 4057164 
718.3 4059444 
719.8 4059445 
719.4 4059445 
723.6 4058229 
766.7 4061004 
767.3 4061004 
766.8 4061004 
714.6 4057563 
717.9 4056766 
723.6 4056766 
818.1 4064323 
786.4 4064323 
756.6 4064323 
740.2 4064323 
722.9 4060814 
723.0 4060814 
720.7 4060814 
722.5 4058158 
707.5 4058292 
712.8 4058270 
730.9 4064247 
730.3 4065266 
729.7 4062372 
2-60 
Revision 2 
Residual 
Error (m) 
Modeled 
Head (m) 
13.9 762.7 
-30.1 756.7 
-19.8 767.3 
-19.5 767.3 
4.3 717.0 
3.3 709.2 
-14.6 703.7 
-17.3 702.5 
-16.8 702.6 
-6.6 718.0 
-35.0 731.7 
-35.6 731.7 
-35.1 731.7 
-0.1 714.5 
-2.4 715.5 
-8.1 715.5 
-48.5 769.6 
-16.8 769.6 
13.0 769.6 
29.4 769.6 
-17.6 705.3 
-17.7 705.3 
-16.4 704.3 
-11.5 711.0 
5.7 713.2 
0.4 713.2 
-19.9 711.0 
-17.1 713.2 
-16.5 713.2 
September 2003
Revision 2 
Source: Based on BSC 2001a, Figure 14. 
Figure 2-35. Comparison of Calibrated and Observed Permeabilities from Yucca Mountain Pump Test 
Data in the Site-Scale Groundwater Flow Model 
Source: BSC 2001a, Figure 15. 
Figure 2-36. Comparison of Calibrated and Observed Permeabilities from Nevada Test Site Pump Test 
Data in the Site-Scale Groundwater Flow Model 
September 2003 2-61 No. 11: Saturated Zone
Revision 2 
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 Nevada Test Site. A discrepancy exists between the calibrated permeability 
for the Tram Tuff and the mean permeability derived from the cross-hole tests. However, 
permeabilities measured for the Tram Tuff of the Crater Flat Group may have been enhanced by 
the presence of a breccia zone in the unit at boreholes UE-25 c#2 and UE-25 c#3 (Geldon et al. 
1997, Figure 3; BSC 2003e). 
The permeability data obtained from single-hole and cross-hole testing at the Alluvial Testing 
Complex also compare acceptably with the permeabilities predicted in the site-scale flow model. 
Single-well hydraulic testing of the saturated alluvium in borehole NC-EWDP-19D1 was 
conducted between July 2000 and November 2000. During this testing, a single-well test of the 
alluvial aquifer to a depth of 247.5 m below land surface at the NC-EWDP-19D1 resulted in a 
permeability measurement of 2.7 × 10-13 m2 (BSC 2003c; Table 7.2-1). A cross-hole hydraulic 
test was also conducted at the Alluvial Testing Complex in January 2002. During this test, 
borehole NC-EWDP-19D1 was pumped in the open-alluvium section, while water-level 
measurements were made in the two adjacent boreholes. The intrinsic permeability measured in 
this test for the tested interval is 2.7 × 10-12 m2. The calibrated permeability for the Alluvial 
Uncertainty Zone was 3.2 × 10-12 m2. Because the cross-hole tests intercepted a larger volume of 
rock, they are considered to be more representative of the water-transmitting capability at this 
location, and therefore they are more appropriate for comparison with the calibrated permeability 
values. 
Boundary Fluxes–A comparison of fluxes at the boundary of the site-scale model domain 
predicted by the regional-scale model and the calibrated site-scale saturated zone flow and 
transport model was used to further validate the site-scale model (CRWMS M&O 2000a, 
Section 3.4.2). Volumetric fluxes computed along the boundary by the two models match 
acceptably well (Table 2-4). The total fluxes across the northern boundary computed by the 
regional and site-scale models were 6.0 × 106 m3/year and 5.3 × 106 m3/year, respectively. The 
boundary fluxes computed along the east side of the site-scale saturated zone flow model domain 
also indicate a good match. The total fluxes across the eastern boundary computed by the 
regional and site-scale models were 1.8 × 107 and 1.6 × 107 m3/year, respectively. The match is 
particularly good along the lower thrust area where both models predict large fluxes across the 
boundary. Both models also predicted small fluxes across the remainder of the eastern boundary. 
The effect of the small differences between the two flux predictions on the specific discharge is 
within the uncertainty range used. The southern boundary flux is simply a sum of the other 
boundary fluxes plus recharge. Fluxes across the southern boundary computed by the two 
models indicate a relatively good match. The difference in the fluxes computed by the regional 
and site-scale models across the southern boundary is approximately 2.9 × 107 and 
2.3 × 107 m3/year, respectively (Table 2-4). 
Upward Hydraulic Gradient–An upward hydraulic gradient between the lower carbonate 
aquifer and the overlying volcanic rocks has been observed in the vicinity of Yucca Mountain. 
Principal evidence for this upward gradient is provided by data from boreholes drilled into the 
upper part of the carbonate aquifer (UE-25 p#1 and NC-EWDP-2DB). Hydraulic head 
measurements in borehole UE-25 p#1 indicate that the head in the carbonate aquifer is about 
752 m, which is about 21 m higher than the head measured in this borehole in the overlying 
September 2003 2-62 No. 11: Saturated Zone
Revision 2 
volcanic rocks. The head in the carbonate aquifer at this borehole was estimated as part of the 
model calibration process. The increasing head with depth was preserved during model 
calibration, although the head difference was only 12.73 m (BSC 2003c, Table 16). The 
difference in predicted and observed upward hydraulic gradient values at this location results, in 
part, because the constant vertical head boundary conditions imposed on the lateral boundaries of 
the model domain constrained the vertical groundwater flow and gradients within the model 
interior (CRWMS M&O 2000a, Sections 6.7.11 and 6.1.2). 
Hydrochemical Data Trends–To provide further validation of the site-scale saturated zone flow 
and transport model, flow paths (Figure 2-37) predicted by the calibrated model were compared 
with those estimated using groundwater chemical and isotopic data (Figure 2-10). Flow paths 
predicted by the calibrated site-scale saturated zone flow model were generated using the 
particle-tracking capability of the Finite Element Heat and Mass Transfer Code (Zyvoloski et al. 
1997) by placing particles at different locations beneath the repository and running the model to 
trace the paths of these particles across a range of horizontal anisotropies. 
Comparison of the flow paths indicate that most of the particles travel between Flow Paths 2 
and 6, and they roughly follow the trajectory of Flow Path 2 through the alluvium along the west 
side of Fortymile Wash. These particle trajectories are permitted by the constraints provided by 
the groundwater geochemical and isotopic data. 
Thermal Modeling–Temperature measurements can be used as an indirect indicator of 
groundwater flow. Although uncertainty exists in the interpretation of the thermal anomalies in 
that they could result from thermal properties (notably thermal conductivity), heat flux, or 
overburden variability, and not the result of areal or vertical groundwater flux, an acceptable 
comparison of observed and simulated temperatures for the site-scale flow model has been 
obtained. The temperature data used in the thermal modeling are taken from temperature 
profiles measured within the model domain. The temperature data were extracted at 200-m 
intervals from these temperature profiles, and a total of 94 observations from 35 boreholes were 
obtained. 
Coupled thermal modeling and conduction-only modeling have been completed to evaluate the 
consistency of the saturated zone flow model with the thermal observations. The details related 
to this thermal modeling are presented in Appendix D. Given the uncertainties associated with 
interpreting the thermal anomalies, the results presented in Appendix D provide a reasonable 
comparison. 
September 2003 2-63 No. 11: Saturated Zone
Source: BSC 2003c, Figure 7.3-1b. 
NOTE: Black lines are predicted flow paths; red lines with arrowhead are flow paths inferred from geochemical data 
(Figure 2-11) 
Figure 2-37. Predicted Groundwater Flow Path Trajectories and Flow Paths Inferred from Geochemistry 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-64
Revision 2 
Model Results 2.3.7.3 
Using the calibrated flow model, specific discharge was estimated for a nominal fluid path 
leaving the repository area and traveling 0 to 5 km, 5 to 20 km, and 20 to 30 km. The specific 
discharge simulated by the flow model for each segment of the flow path was determined using 
the median travel time for a group of particles released beneath the repository. Specific 
discharge values of 0.67, 2.3, and 2.5 m/year were obtained for the three flow path segments, 
respectively. The first segment reflects flow in the tuff aquifers, and the last segment reflects 
flow in the alluvial aquifer. An expert elicitation panel was convened prior to the site 
recommendation (CRWMS M&O 1998, Figure 3-2e), and it estimated a specific discharge of 
0.71 m/year for the 0-to-5-km segment. Thus, the specific discharge values predicted by the 
model and the expert elicitation panel were similar. In addition, the lower end of the range of 
inferred specific discharges from the single-well tracer-injection test conducted in the alluvial 
aquifer (1.2 and 9.4 m/year) acceptably reproduces the median-modeled specific discharge at this 
location (about 2.3 m/year). 
The particle-tracking capability of the Finite Element Heat and Mass Transfer Code (Zyvoloski 
et al. 1997) was used to illustrate flow paths predicted by the calibrated site-scale saturated zone 
flow and transport model. One hundred particles were distributed uniformly over the area of the 
repository and allowed to migrate until they reached the model boundary (Figure 2-38). The 
pathways leave the repository and generally travel south-southeasterly to the 18-km compliance 
boundary. 
The flow paths from the water table beneath the repository to the accessible environment directly 
affect breakthrough curves and associated radionuclide travel times. Because the flow paths and 
water table transition from volcanic tuffs to alluvium, flow path uncertainty directly affects the 
length of flow in the volcanic tuffs and in the alluvium. Uncertainty in flow paths is affected by 
permeability anisotropy of the volcanic tuffs. Large-scale anisotropy and heterogeneity were 
implemented in the saturated zone site-scale flow model through direct incorporation of known 
hydraulic features, faults, and fractures. Detailed discussion of the uncertainty in flow path 
lengths in the tuff aquifers prior to intersecting the alluvial aquifers is presented in Appendix G. 
September 2003 2-65 No. 11: Saturated Zone
Source: Based on BSC 2003c, Figure 6.6-3. 
Figure 2-38. Predicted Saturated Zone Particle Trajectories from Yucca Mountain 
No. 11: Saturated Zone 
Revision 2 
September 2003 2-66
Revision 2 
2.4 SUMMARY 
The regional and site-scale groundwater flow representations indicate that groundwater in the 
shallow tuff aquifers flows south-southeasterly from the repository and parallels Fortymile Wash 
to the point where it discharges from the shallow tuff aquifers and mixes with other groundwater 
in the alluvium of the Amargosa Desert. The flow paths are acceptably constrained by the 
available hydrogeologic and geochemical information, and the location of the tuff-alluvium 
contact is also acceptably constrained by recent drilling and geophysics conducted by Nye 
County. The exact location where groundwater at the water-table enters the alluvium is 
uncertain. This uncertainty is due, in part, to uncertainty in the flow paths, which is due to 
uncertainty in anisotropy and in the tuff-alluvium contact. The uncertainty in the tuff-alluvium 
contact is included in the uncertainty of radionuclide transport times along the likely paths of 
radionuclide migration in the saturated zone. 
The average flow rate in the alluvium, as defined by the specific discharge distribution in the 
alluvium, has been independently evaluated to be about 2.5 m/year, with a range of about 
1.2 to 9.4 m/year. To account for uncertainty in the hydraulic properties and specific discharge, 
a range of specific discharge values was used in the assessment of repository performance. The 
values ranged from a factor of one-third to a factor of three times the median specific discharge. 
The regional and site-scale groundwater flow models have been calibrated with potentiometric, 
recharge, discharge, and hydraulic characteristic observations. In addition, these flow models 
have been independently corroborated with geochemical observations (conservative tracers and 
stable isotopes), thermal observations, and tracer test determinations of specific discharge. 
September 2003 2-67 No. 11: Saturated Zone
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September 2003
Revision 2 
3. SATURATED ZONE RADIONUCLIDE TRANSPORT 
If radionuclides are released in the aqueous phase from the repository and migrate through the 
unsaturated zone as dissolved species or sorbed onto colloids, they will enter the groundwater 
flow regime in the saturated zone. Released radionuclides would be expected to travel along the 
groundwater flow paths described in Section 2 (Figure 2-38). The rate of radionuclide transport 
is a function of key radionuclide transport processes and parameters such as effective porosity, 
matrix diffusion, hydrodynamic dispersion, and radionuclide sorption (i.e., retardation). The 
transport of radionuclides as solute is affected by advection, diffusion, and dispersion, and for 
reactive constituents, sorption. The transport of radionuclides sorbed onto colloids is affected by 
filtering (where colloids with diameters greater than the pore openings are filtered by the 
medium) and by attachment-detachment processes. Mixing and dilution of radionuclides in the 
groundwater affects the concentration of radionuclides released to the environment. This section 
presents observations and test data that provide the conceptual basis and understanding of 
radionuclide transport through the saturated zone. 
3.1 INTRODUCTION 
Processes relevant to the performance of the saturated zone barrier at Yucca Mountain are 
described conceptually in Figure 3-1. Advection, matrix diffusion, dispersion, and sorption 
processes occur at different scales within the saturated zone. The effect and importance of these 
processes differ in the fractured tuff units and the porous alluvium. 
In fractured tuffs, advective transport occurs within fractures; therefore, the effective fracture 
spacing and porosity are important for describing the advective velocity of dissolved 
constituents. Major flowing fracture zones (termed flowing intervals) are generally spaced on 
the order of meters to tens of meters apart, while fractures themselves may be more closely 
spaced and have sub-millimeter apertures. Radionuclides that are transported through the 
fractures may diffuse into the surrounding matrix or sorb onto the fracture surfaces. If the 
radionuclides diffuse into the matrix, they may also be sorbed within the matrix of the rock. 
In the alluvium, advective transport occurs through the porous matrix. Because the effective 
porosity of the alluvium is considerably greater than that of the fractured tuff, the transport 
velocity in the alluvium is greatly reduced in comparison to that of the tuff (even though the 
specific discharge in the alluvium is about a factor of three greater than that of the tuff; see 
Section 2.3.7). Radionuclides transported through the porous alluvium can also sorb onto 
minerals within the alluvium. 
September 2003 3-1 No. 11: Saturated Zone
Revision 2 
Figure 3-1. Conceptual Model of Radionuclide Transport Processes in the Saturated Zone 
In addition to the advective, diffusive, and retardation mechanisms, small-scale heterogeneities 
in aquifer characteristics, which result in a small-scale variability in advective velocities, can 
effectively disperse the radionuclides as they migrate through the saturated zone. This dispersive 
phenomenon tends to allow some radionuclides released at a particular point to migrate either 
faster than or slower than the average velocity along the groundwater flow trajectory. 
Finally, although it is possible for groundwater beneath Yucca Mountain to mix with other 
groundwater as they flow southward towards Amargosa Valley, it is apparent that the likely flow 
paths remain constrained over an aquifer width of a few kilometers. At the compliance point, 
located about 18 km south of Yucca Mountain, the reasonably maximally exposed individual 
uses well water that is extracted from the aquifer at a rate of 3.7 × 106 m3/year (3,000 acreft/
year). The hypothetical well is located in the center of the groundwater flow trajectories to 
maximize the concentration of any dissolved radionuclides that may be contained within the 
groundwater. The pumping discharge is likely to extract all of the radionuclides in the 
groundwater at the well location, plus mix with other groundwater that does not contain any 
radionuclides. Th