This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party's use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.






Documentation of Program Change

INTRODUCTION
The U.S. Nuclear Regulatory Commission (NRC) disposal regulations, during this reporting 
period (FY 2001), are contained in 10 CFR 60.  The regulations in 10 CFR 60.21(b)(5) required 
that a repository license application must contain a description of site characterization work 
actually conducted by the U.S. Department of Energy (DOE) and an explanation of why such 
work differed from activities described in the Site Characterization Plan:  Yucca Mountain Site, 
Nevada Research and Development Area (SCP) (DOE 1988).  The Documentation of Program 
Change (DPC) is revised annually to update and document these changes.  The NRC recently 
promulgated its final rule on the Disposal of High-Level Radioactive Wastes in a Geologic 
Repository at Yucca Mountain, Nevada, as 10 CFR 63 (66 FR 55732).  This new rule (10 CFR 
63.21(b)(5)) retains the requirement that a repository license application contain a description of 
site characterization work conducted, but no longer requires a comparison with the original SCP 
(DOE 1988).  Nevertheless, the decision was made by the DOE to prepare Revision 04 of the 
DPC.  The scope of and need for future revisions of the DPC are currently being re-evaluated 
since 10 CFR 63  became effective on December 3, 2001.  Also, the DOE promulgated its final 
rule on Yucca Mountain Site Suitability Guidelines as 10 CFR 963 (66 FR 57298), and the EPA 
promulgated its final rule on the Public Health and Environmental Radiation Protection 
Standards for Yucca Mountain, Nevada, as 40 CFR 197 (66 FR 32074)1.
The SCP (DOE 1988) was developed in accordance with the Nuclear Waste Policy Act of 1982 
(NWPA), as amended, and has been the basis for the site characterization phase of the geologic 
repository program.  In 1989, the DOE assessed the progress and needs of the repository 
program and established a schedule that would result in a suitability determination for Yucca 
Mountain in fiscal year (FY) 2001, and if the site is suitable and a license granted, would result 
in start of disposal operations in FY 2010.  In parallel with the DOE assessment, the approach to 
underground characterization changed as vertical shaft and drift accesses were replaced by 
inclined ramps and drifts.  From 1989 to 1994, the DOE planned for and then conducted a 
comprehensive program of site investigations based on the SCP.
By 1994, external and internal factors had tended to broaden, rather than focus the program; 
Congress had also begun to express concern about continuing growth in the estimated cost of site 
characterization.  Furthermore, because the site characterization schedule did not call for 
definitive results until a license application was completed in 2001, progress was difficult to 
demonstrate or measure.  Thus in 1994, the DOE issued a revised Civilian Radioactive Waste 
Management Program Plan (Program Plan) (DOE 1994a) that was designed to show early 
observable progress with the financial resources likely to be available.  The program needed to 
be restructured, reorganized, and replanned in a manner that was simpler, more visible, and 
understandable to management and external oversight, and more flexible to respond to future 
changes.  Increasing scientific understanding, along with periodic total system performance 
assessment calculations, enabled focusing the ongoing site characterization program on the 
remaining uncertainties that are significant to the design, operation, and safe performance of the 
potential repository.  The previous approach to site characterization called for extensive testing 
to obtain a comprehensive understanding of the Yucca Mountain site to allow decisions to be 
made simultaneously on site suitability, licensing, and repository design issues.  Within the 
overall site technical program, the new approach distinguished among tests required to evaluate 
site suitability, to support licensing and define a cost-effective design, and to confirm the safety 
of the repository before closure.  This distinction permitted phasing of tests to achieve an earlier 
evaluation of whether Yucca Mountain appeared to be suitable and preserves the schedule for 
licensing, constructing, and operating the repository if the site were found suitable.  It also 
accommodates available resources.  As a result, a new, more flexible approach was developed, 
and site investigations were phased in such a manner that some of the original planned tests 
could be de-emphasized and others could be shifted to confirmatory status.  Previous progress 
reports have reported these changes as they affected study plans, design activities, and 
performance assessment plans.  The Civilian Radioactive Waste Management Program 
(Program) intends to continue evaluations and adjustments of work scopes as information needs 
evolve.
Congress endorsed the 1994 Program Plan (DOE 1994a) and provided a 37 percent increase in 
funding for FY 1995; subsequently, important progress was made.  However, guidance from 
Congress and a significant funding reduction in FY 1996 required another revision to the 
Program Plan, which was issued in May 1996 (DOE 1996a).  Under the funding reductions, the 
1994 Program Plan was no longer sustainable.  The Project was refocused to emphasize core 
scientific activity, which had continued to develop site characterization data and models 
throughout this period; excavation of sections of the Exploratory Studies Facility (ESF) 
necessary for scientific study; and completion of the repository and waste package conceptual 
designs.  Activities supporting the preparation and filing of a license application for the 
repository were deferred.  In FY 1997, the program was further focused on a 1998 assessment of 
the viability of geologic disposal at Yucca Mountain.  The NWPA, as amended, requires the 
Secretary of Energy to determine the suitability of the Yucca Mountain site as a nuclear waste 
repository and, if the determination is positive, forward a recommendation regarding siting of the 
potential repository to the President.
Reflecting these top-level program redirections in detailed annual and long-range plans was a 
major task during FY 1996.  With a baselined program in place at the beginning of FY 1997, 
documenting changes from the original plans presented in the SCP (DOE 1988) was a priority.  
Through the production of the 16th semiannual Site Characterization Progress Report:  Yucca 
Mountain, Nevada (DOE 1997a), progress reports provided links from the SCP to the 
requirements or planning documents that provide the basis for ongoing programs and have also 
documented changes to the site study and activity structure in the SCP.  The DPC, previously an 
appendix to the progress report and separated in 1998 as a stand-alone document, is intended to 
continue that documentation process by providing a status and rationale for changes in the design 
and performance assessment programs.  Most changes to the program will be found in the 
approaches to, amount of, and sequencing of field data collection activities.
While there have been noticeable changes to the repository and waste package design concepts 
since the Site Characterization Plan Conceptual Design Report (SNL 1987), there has not been a 
correspondingly large number of substantial changes in the technical information needed to 
design the repository and waste package.  The most significant change to the original conceptual 
design plans described in the SCP (DOE 1988) is the waste package.  That waste package was a 
thin-walled container designed to be emplaced in boreholes; current plans have shifted to a large, 
multi-barrier waste package that will be emplaced in large drifts.  A number of changes in the 
waste package design program are linked to this change.
Similarly, as additional information about the geotechnical character of the site has become 
better understood, and as system studies have examined alternative approaches to address 
10 CFR 60 requirements, the repository design concept has evolved to be responsive to this 
information.  For example, the SCP (DOE 1988) conceptual repository design (SNL 1987) was 
interfaced with the ESF design that used vertical shafts for access.  Current repository designs 
are integrated with the drift-based testing approach that has been used for the ESF.  These 
changes to the current repository design, while appearing to be substantially different from the 
conceptual design that served as the basis for the SCP, have resulted in few substantive changes 
in the definition of the technical information needed to design the repository.  While maturation 
in the understanding of constraints and design solutions has resulted in designs that are more 
responsive to 10 CFR 60 requirements, there has not been a concomitant large number of 
significant changes in the approaches embodied in the issue resolution strategies developed to 
address these regulatory requirements.
For performance assessment, changes in the regulatory framework together with new site and 
design information have increased our knowledge base so that improved approaches can be 
defined.  Many of these improved approaches have been discussed with NRC staff during 
technical interactions or summarized in previous progress reports.
This report is a continuation of documentation begun in Progress Report #15 (DOE 1997b), 
extended in Progress Report #16 (DOE 1997a), and produced separately in 1998 as 
Documentation of Program Change, Revision 00 (CRWMS M&O 1998a); in 1999 as 
Documentation of Program Change, Revision 01 (CRWMS M&O 1999f); in 2000 as 
Documentation of Program Change, Revision 02 (CRWMS M&O 2000a); and in 2001 as 
Documentation of Program Change, Revision 03 (CRWMS M&O 2001c).  The DPC provides a 
systematic review and documents the changes since the SCP (DOE 1988) was issued at a level of 
detail commensurate with the current planning basis.  Following this introduction, the changes in 
site investigations, repository design, waste package design, and performance assessment are 
discussed in turn.  The discussions first outline the background leading to the changes and then 
provide the current status for each study.
Progress Report #15 (DOE 1997b) summarized changes in the program since the issuance of the 
SCP (DOE 1988).  Additional detailed documentation of the rationale and justification for 
changes was provided in Progress Report #16 (DOE 1997a).  Revision 00 of the DPC (CRWMS 
M&O 1998a) provided an update of information for April 1, 1997, through September 30, 1997.  
Revision 01 of this document (CRWMS M&O 1999f) provided an update of information from 
October 1, 1997, through September 30, 1998.  Revision 02 of this document (CRWMS M&O 
2000a) provided an update of information from October 1, 1998, through September 30, 1999.  
Revision 03 of the DPC (CRWMS M&O 2001c) provided an update of information from 
October 1, 1999, through September 30, 2000.  This revision (Revision 04) provides an update of 
information from October 1, 2000, through September 30, 2001.
As part of the ongoing annual and long-range planning efforts, work plans are evaluated to 
ensure that the scope and schedule for activities will support the major milestones of the 
Program.
Annual updates to the DPC reports will provide rationale and justification for changes to the 
program as performance and design information matures.  Ultimately, the adequacy of the 
revised site characterization program will be judged on the basis of whether sufficient scientific 
and engineering information has been developed at each stage of the program to provide the 
technical basis necessary to support a decision on whether to continue the program.

1.	SITE PROGRAMS (SCP SECTION 8.3.1)
The Nuclear Waste Policy Act of 1982 and the high-level radioactive waste disposal regulations 
found in 10 CFR 60, specified that the DOE develop a Site Characterization Plan (SCP) 
(DOE 1988) before beginning any activities to characterize potential repository sites.  In 
addition, the disposal regulations specified that any potential license application will contain a 
description of changes to the site characterization program since the SCP was issued.  This 
requirement in 10 CFR 60.18(g) was the basis for the development of the Documentation of 
Program Change documents.  After the end of the reporting period for Revision 04 of this DPC, 
the NRC issued new disposal regulations (10 CFR 63) specific to the Yucca Mountain site 
(66 FR 55732), which no longer require a comparison with the original SCP.  
The SCP (DOE 1988) presented the initial general plan for the Yucca Mountain site and was 
based on then-available information about the site, and on then-current conceptual designs for 
the repository and the waste package.  The SCP was intended to provide the framework for all 
the site programs, but it was also intended to provide program flexibility.  The framework was to 
be augmented by study plans that were to be developed for each study and were intended to 
supply site-specific requirements for each study.  These plans were intended to describe the 
specific objectives of each study, specify the approaches and methods to be used to collect data, 
describe the accuracy and precision requirements for the data, and identify the uses for which the 
data were needed.
The SCP (DOE 1988) envisioned an extensive program of data collection designed to 
characterize the natural features and processes of the site, and reduce, or at least bound, the 
uncertainties associated with the various characterization parameters.  At the outset, the DOE 
recognized that it was initially committing to conduct a very large number of studies and that 
many of them would later be shown to be redundant or possibly unnecessary.  Thus, the SCP 
contemplated periodic revisions as the site characterization program matured.  The purpose of 
the program was originally to provide the scientific data needed to support the evaluation of site 
suitability and develop the license application for construction authorization.  As discussed in the 
introduction to this document, although the original purpose of the Project has been maintained, 
the Project was refocused to emphasize core scientific studies and excavation of those parts of 
the ESF needed for in situ scientific studies.  With completion of the ESF, the revised program 
strategy was designed to maintain momentum in scientific investigations, provide data needed to 
support the Viability Assessment, the site suitability recommendation to the President, and 
submittal of a license application to the U.S. Nuclear Regulatory Commission.
In planning the program described in the SCP (DOE 1988), the DOE adopted an approach that 
began with identifying the regulatory requirements that must be satisfied in siting and licensing 
the repository, identifying the performance and design information needed to address those 
requirements, and developing specific investigations to obtain the needed information.  This 
approach was embodied in an issue resolution strategy, which was discussed in some detail in 
Section 8.1 of the SCP.  An important part of this strategy was an issues hierarchy (discussed in 
Section 8.1.1 of the SCP and in the DOE Mission Plan (DOE 1985) that consisted of key issues, 
related issues, and information needs.  The key issues and related issues were based on the 
requirements in the disposal regulations.  The information needs defined the data and analytical 
techniques that were needed to resolve each issue.
The issues hierarchy stated questions about the performance of the disposal system and identified 
the information that would be required before a site could be selected and licensed.  The issues 
hierarchy was developed as a three-tiered framework consisting of key issues, related issues, and 
information needs.  On the highest tier were four key issues that embodied the principal 
requirements established by the regulations governing geologic disposal.  Each of the key issues 
was expanded, in the next tier, into a group of related issues that elaborated on the requirements 
stated in the parent key issue.  The lowest tier consisted of still more detailed sets of 
requirements called “information needs” that were associated with each issue.  This framework 
provided a convenient means to distinguish broad questions of overall performance and 
suitability (key issues) from more specific questions about the characteristics of the site, the 
design of the repository and the waste package, and the performance of the total geologic 
disposal system.  The framework also distinguished the key issues and related issues from the 
requirements for basic information needed to resolve the issues.
The investigations for the site characterization program have evolved based on the technical 
information obtained from laboratory and field studies, model development and data application 
activities.  Rapidly increasing scientific understanding, along with periodic total system 
performance assessment (TSPA), have enabled focusing the ongoing site characterization 
program on the remaining uncertainties that are significant to the design, operation and safe 
performance of the potential repository.  Re-evaluation and prioritization of Project needs has 
been a continuous process based on scientific judgment and resource availability, governed by 
scientific criteria to ensure that data needed for site description, performance assessment, and 
design purposes were collected and analyzed.  Data-collection that is redundant or no longer 
relevant has been eliminated.  The data-collection needs have been further analyzed and refined 
as additional knowledge has been gained through years of site characterization activities and 
analysis of site data.
In addition, major technical revisions to the repository program, including reconfiguration of the 
ESF from a shaft-and-main configuration to a ramp-and-main configuration, mechanical 
excavation of the ESF using a large diameter tunnel boring machine, and reconfiguration of the 
repository from vertical borehole emplacement to in-drift emplacement, required major revisions 
to the site programs.  The ramp-and-main configuration provided increased opportunities for 
observation of changes in stratigraphic, lithologic, and structural characteristics of the host rock.  
As a result, the strategy and methods for in situ mapping of fracture networks, faults, and 
lithostratigraphic features have changed considerably.  Most notable of these changes has been 
the acquisition of a large volume of data collected through detailed mapping of the ESF and the 
East-West Cross Drift.  Some questions about geohydrologic features and processes, inferred 
from the results of surface-based tests, could be answered by direct observation.  Because of the 
increased opportunities for direct underground observation and sampling, it was possible to 
reduce the scope of some surface-based testing activities.
Section 1 of this report is organized by individual site characterization programs.  For each 
program, background and SCP plans are summarized by study within each investigation.  
Subsequently, changes that have occurred, the basis for the changes, and the current status of 
each study are described.
1.1	GEOHYDROLOGY PROGRAM (SCP SECTION 8.3.1.2)
The geohydrology program was developed to provide an understanding of the groundwater 
environment that is essential to assessing the viability and suitability of the site.  Groundwater is 
expected to be the major transport medium of radionuclides to the accessible environment.  The 
general SCP strategy to accomplish the geohydrology program was to conduct investigations that 
would result in complete and accurate descriptions of the pertinent components of the hydrologic 
system.  The descriptions would reflect understanding of the hydrologic properties, initial and 
boundary conditions and processes, and their interrelationships.  The results of the geohydrology 
program were to be combined with the results of other site programs to produce a site model, or 
a complete description of the site.
The geohydrology program consisted of the data collection and evaluation activities that were to 
result in hydrologic models that describe two distinct regimes of the hydrologic system:  the 
unsaturated zone and the saturated zone.  Each of these regimes was to be characterized to 
provide input to the hydrologic models.  The unsaturated zone hydrologic model was to be 
developed only at the site scale, whereas the saturated zone models were to be developed at both 
site and regional scales.  The hydrologic regimes described by these models were to be those that 
significantly affect the resolution of hydrologic-related design and performance issues; these 
regimes, therefore, were to be the principal subjects of investigation in the geohydrology 
program.
The investigations included in the geohydrology program are summarized in the following 
sections.
1.1.1	Studies to Provide a Description of the Regional Hydrologic System (SCP 
Investigation 8.3.1.2.1)
Background and SCP Plans.  The objectives of this investigation were to develop a conceptual 
model of the regional hydrologic system to help assess the ability of the site to contain and 
isolate waste; and to construct a consistent, regional, numerical model of groundwater flow, so 
that reliable boundary conditions could be assigned to the more critical site area embedded 
within the regional model.  This investigation included four studies developed to accomplish the 
following:
1.	Study 8.3.1.2.1.1 (characterization of meteorology for regional hydrology):  This study 
was to: 
?	Characterize precipitation in the area surrounding Yucca Mountain and its 
relationship to surface run off, with particular emphasis on the Fortymile Wash 
drainage basin
?	Provide site-specific information on storm precipitation at and near the network 
streamflow-measurement sites as input to precipitation-run off models and to 
infiltration studies.
2.	Study 8.3.1.2.1.2 (characterization of run off and streamflow):  This study was to:
? Collect data on the characteristics, magnitudes, frequencies, and timing of 
surface-water run off at, and peripheral to, Yucca Mountain
? Develop an understanding of the relationships between specific run off events and 
the characteristics of the storms
? Provide calibration data for precipitation-run off models for the regional study 
area;
? Provide data and interpretations of surface-water run off for evaluations of the 
amounts and processes of groundwater recharge
? Document both quantitatively and qualitatively the characteristics of debris 
transported by intense surface run off and assess the potential for flood hazards 
and related fluvial-debris hazards.
3.	Study 8.3.1.2.1.3 (characterization of the regional groundwater flow system):  This 
study was to:
? Prioritize data needs for use in the regional groundwater flow description
? Determine the regional potentiometric distribution, including the cause of the 
large hydraulic gradient
? Characterize the regional hydrogeologic framework to support reliable estimates 
of groundwater flow direction and magnitude
? Use hydrologic, hydrochemical, and heat-flow data to determine the magnitude 
and direction of groundwater flow
? Determine to what extent (quantitatively, if feasible) Fortymile Wash has been a 
source of recharge to the saturated zone under present and past conditions
? Improve estimates of groundwater discharge by evapotranspiration in the 
Amargosa Desert to provide boundary-condition data for regional groundwater 
flow models.
4.	Study 8.3.1.2.1.4 (regional hydrologic system synthesis and modeling):  This study 
was to:
? Synthesize available data and identify groundwater flow system boundaries, 
hydrogeologic units, structural controls, and other hydrogeologic features 
pertaining to the regional groundwater flow system
? Update an existing two-dimensional, subregional, parameter-estimation mode
? Perform subregional, two-dimensional cross-sectional modeling to estimate 
groundwater flow direction and magnitude along a potential flow path through the 
repository block to the accessible environment and extending into the region
? Develop a comprehensive, regional, three-dimensional numerical groundwater 
flow model
? Use the regional model to test the impacts of possible future tectonic activity and 
climatic changes on the saturated hydrologic system.
Changes and Status.  The primary objectives of this investigation have not changed since the 
SCP (DOE 1988) was issued.  The SCP, however, described a more extensive program of data 
collection.  The studies for this investigation have evolved based on technical information 
obtained from laboratory and field studies, model development and data application activities of 
the site characterization program.  Rapidly increasing scientific understanding, along with 
periodic TSPA, have enabled focusing the ongoing site characterization program on the 
remaining uncertainties that are significant to the design, operation and safe performance of the 
potential repository.  Re-evaluation and prioritization of Project needs has been a continuous 
process based on scientific judgment and resource availability, governed by scientific criteria to 
ensure that data needed for site description, performance assessment, and design purposes were 
collected and analyzed.  Data-collection redundancy and overlap have been eliminated.  The data 
collection needs have been further analyzed and refined as additional knowledge has been gained 
through site characterization activities.
1.	In the meteorology study (8.3.1.2.1.1), rainfall run-off models were not developed 
because direct relationships between precipitation and both infiltration (Hudson and 
Flint 1996, p. 1; Flint et al. 1996, p. 1) and recharge (Hevesi and Flint 1995, p. 1; 
D’Agnese, Faunt et al. 1997, pp. 50–56) were developed for hydrologic models using 
methods that did not require simulation of the run off component.  Also, because run 
off occurs so infrequently, it was determined to be infeasible to maintain readiness for 
run off monitoring with available Project resources.  Instead, the emphasis of the 
meteorology study was focused on analyzing regional and synoptic-scale weather 
patterns that impact infiltration at Yucca Mountain and on statistically analyzing the 
spatial variability of average annual precipitation as it relates to estimates of 
groundwater recharge for the regional saturated zone flow model.  Meteorological data 
collection and analysis activities were focused on determining the seasonality, 
duration, intensity, and spatial variability of storms that produce net infiltration in the 
many small watersheds that compose the Yucca Mountain site area.  To accomplish 
this, a network of full weather stations and tipping-bucket precipitation gauges was 
maintained through FY 1995 and then reduced in FY 1996 (CRWMS M&O 1995a, 
pp. 6.3-4 and 6.3-36; see also (Dixon 1996).  Operation of a reduced-intensity, 
site-area, meteorological data-collection effort is continuing.  The Radiological 
Environmental Programs Department operated the network during 1997 and 1998.  
The U.S. Geological Survey (USGS) resumed operating responsibility for the tipping-
bucket precipitation-gauge portion of the network in 1999 (see Section 1.9.2, Changes 
and Status).  In FY 2000, operation of the tipping-bucket precipitation-gauge network 
was assumed by the University of Nevada Las Vegas, Harry Reid Center under 
contract to DOE.  The M&O Integrated Analysis & Management group (formerly 
Radiological & Environmental Programs Department) retained operation of four full 
meteorological stations plus a limited number of additional precipitation gauge sites.  
This arrangement continued during FY 2001.
	The DOE believes that the site-area data collection effort will be adequate to provide 
data needed for the site recommendation and license application.  Whether additional 
precipitation data are needed was addressed, at least partially, by the sensitivity 
analyses performed as part of the Total System Performance Assessment-Viability 
Assessment (TSPA-VA) (DOE 1998a, Volume 3).  The TSPA-VA did not treat 
precipitation as a separate parameter because precipitation is a major component of the 
net infiltration model, the results of which were used directly in the TSPA-VA.  In 
general, the TSPA-VA results indicate that potential increases in confidence for net 
infiltration are related more to factors other than the distribution of present-day 
precipitation.  These factors include:
? Transitions from one future climate state to another
? Mean annual temperature during future climate states
? Timing and duration of future climate states
? Development of a more quantitative basis for uncertainty in net infiltration
? Consideration of other aspects of future climates that would affect net infiltration 
(cloudiness, vegetation, surface water run off-run-on, and snow cover)
? Enhanced calibration of the net infiltration model using well-documented present-
day analogs (DOE 1998a, Volume 3, Section 6.5.1.1).
	In the TSPA for Site Recommendation (TSPA-SR) (CRWMS M&O 2000af), 
precipitation was treated the same as it was in the TSPA-VA in that it is represented in 
flow fields that consist of three infiltration cases (lower, mean, and upper) within each 
of the three climate states (present-day, monsoon, and glacial-transition) (DOE 2001a, 
Section 4.2.1.4.1).  Uncertainties in net infiltration were evaluated in the Analysis of 
Infiltration Uncertainty (CRWMS M&O 2000ai), where precipitation was one of 12 
uncertain parameters.
2.	In the run off and streamflow study (8.3.1.2.1.2), regional-run off studies and data 
collection for precipitation-run off modeling were terminated before being fully 
implemented because the data were not needed for the regional groundwater-flow 
model (D’Agnese, Faunt et al. 1997, pp. 43–56).  Regional groundwater modeling did 
not require run off data for model calibration because data describing a direct 
relationship between precipitation and groundwater recharge was used.  In recent 
years, the emphasis of the streamflow study shifted to measuring the run off 
component of the water balance in small watersheds at Yucca Mountain in support of 
the unsaturated zone infiltration study (8.3.1.2.2.1) (Progress Report #9, 
Section 2.2.1.2 (DOE 1994b); Progress Report #13, Section 3.1.2 (DOE 1996b).  
However, because the net-infiltration component is so small compared with the run off 
component and because run off occurs so infrequently, this approach was abandoned 
after instrumenting only a few watersheds (Progress Report #14, Section 3.1.2 
(DOE 1996c)).  In FY 1998, four continuous-recording stream flow gauges on Split 
Wash and Pagany Wash were reactivated in anticipation of El Niño climatic 
conditions during the winter of 1997-1998 to provide data to validate and improve the 
coupled surface run off-infiltration module of the site-scale unsaturated zone flow 
model.  El Niño produced several winter storms that produced significant run off in 
these and other washes at Yucca Mountain during February 1998.  Run off data were 
collected at several sites.  However, at the end of FY 1998, all Yucca Mountain 
streamflow measurement sites were deactivated.
	Because flooding and fluvial-debris transport were shown by the Preclosure 
Hydrology Program (8.3.1.16) to pose little or no threat to the ESF, the potential 
repository (YMP 1995a, pp. 2-6, 2-11), or surface facilities at Yucca Mountain, studies 
to document transport of debris by severe run off were terminated before being fully 
implemented.
3.	In the regional groundwater system characterization study (8.3.1.2.1.3), the drilling 
program designed to resolve uncertainties in the regional potentiometric distribution 
(including the large hydraulic gradient) has not been implemented.  In particular, a 
deep hole in the Amargosa Desert intended to establish geologic control and obtain 
potentiometric-head data for the Paleozoic carbonate aquifer was not drilled.  Instead, 
data from sources outside the Project have been relied upon almost exclusively to 
characterize the regional hydrogeologic framework and the regional potentiometric 
surface for input to the three-dimensional, regional groundwater-flow model.  Despite 
the almost exclusive use of outside data, the three-dimensional groundwater-flow 
model was successfully developed and calibrated (D’Agnese, Faunt et al. 1997, 
pp. 86–94).  Recently, however, with support from the DOE Yucca Mountain Site 
Characterization Office (YMSCO), Nye County initiated a drilling and testing 
program in the saturated zone down-gradient from Yucca Mountain in the Amargosa 
Desert.  This program, called the Nye County Early Warning Drilling Program 
(EWDP), involves drilling a series of shallow and deep boreholes to obtain aquifer 
parameters, perform hydraulic testing, and conduct long-term water-chemistry and 
water-level monitoring (Stellavato 1997).  Fifteen shallow boreholes to depths of 
1000 feet are intended to obtain aquifer parameters for the alluvial and upper tuff 
aquifers.  Six holes, as much as 4000-feet deep, are intended to obtain hydraulic 
properties, geochemical, and water level information for the deep Paleozoic carbonate 
aquifer.  The EWDP boreholes are also intended to obtain data on the long-term 
effects of repository development.  Through FY 2001, most of the Nye County EWDP 
boreholes have been drilled, stratigraphic interpretations have been made, and 
hydraulic and tracer tests have been conducted in the alluvium.
	Although possible causes of the large hydraulic gradient have been identified through 
analyzing available geologic and geophysical data (Fridrich et al. 1994; Luckey 
et al. 1996, pp. 21–25) and through hydraulic testing in well USW G-2, the cause of 
this feature remains an unresolved issue (Luckey 1996, pp. 2 and 3).  During FY 1997 
and FY 1998, additional field work and data collection were performed at borehole 
USW WT-24 in an attempt to further understand and characterize the large hydraulic 
gradient.  Drilling, water quality sampling, and testing of borehole USW WT-24, 
which is located within the large hydraulic gradient area north of the potential 
repository location, have confirmed that perched water exists on top of the Topopah 
Spring Tuff basal vitrophyre.  Further, deepening of borehole USW WT-24 into the 
Prow Pass Tuff revealed a tentative water level that seems to be consistent with the 
large hydraulic gradient.  Several alternate concepts for the large hydraulic gradient 
were considered during preliminary testing of the site-scale saturated zone flow model 
(Czarnecki et al. 1997, pp. 26–29), including:
? Faults containing low-permeability gouge
? Faults juxtaposing transmissive and non-transmissive rocks
? An extensive perched water body
? A highly permeable fault that drains water from the upper part of the aquifer.
	In early FY 2002, a revision to the saturated-zone water-level analysis/modeling report 
was prepared to incorporate data from borehole USW WT-24 and apply an alternate 
concept for development of a potentiometric-surface map for the area north of Yucca 
Mountain where the large hydraulic gradient is located (USGS 2001c, Section 1). This 
concept assumes that water levels in boreholes USW G-2 and UE-25 WT #6 represent 
perched conditions, and are not representative of the regional potentiometric surface. 
By not using the data from those two boreholes and incorporating water-level data 
from borehole USW WT-24, the large hydraulic gradient is reduced from about 0.11 to 
between 0.06 to 0.07, and the potentiometric contours are more widely spaced (USGS 
2001c, Section 6.2).  Furthermore, potentiometric contours are not offset where they 
cross faults, as would not be expected where the contours are perpendicular or nearly 
perpendicular to the fault trace
	To date, because of time constraints and technical limitations of the simulation code, 
only the low-permeability fault gouge concept has been tested with the model.
	Although reconnaissance-level studies have determined that groundwater recharge to 
the saturated zone occurs in upper Fortymile Wash (Savard 1996; Luckey 1996, pp. 3 
and 4; Savard 1998), the field studies to quantify this recharge have not been 
conducted because they were determined to be of low priority (CRWMS 
M&O 1995a).  Similarly, although evapotranspiration feasibility and prototype work 
was performed (Progress Report #11, Section 3.1.3 (DOE 1995a)), the field studies to 
improve estimates of groundwater discharge by evapotranspiration in the Amargosa 
Desert have not been conducted.  Instead, estimates of regional groundwater recharge 
and discharge were improved using a modification of the Maxey-Eakin method.  This 
method uses a geostatistically derived distribution of average annual precipitation and 
a regional distribution of recharge potential based on elevation, vegetation, 
slope-aspect, and rock and soils permeability data obtained using remote-sensing and 
Geographic Information System techniques (D’Agnese, Faunt et al. 1997, pp. 43–56).  
With this approach, the three-dimensional groundwater flow model has been 
successfully developed and calibrated.
4.	In the regional hydrologic system synthesis and modeling study (8.3.1.2.1.4), updating 
of an existing two-dimensional, subregional, parameter-estimation model, developed 
in 1984, and two-dimensional cross-sectional modeling along a potential flow path 
have not been performed as separate activities.  However, much of the work scope 
intended for these activities is being accomplished by the development and testing of 
the regional, three-dimensional groundwater flow model (Activity 8.3.1.2.1.4.4).  The 
distribution of estimated values of hydraulic conductivity from parameter-estimation 
simulations of the model are regression estimates based on field data for the region 
(D’Agnese, Faunt et al. 1997, pp. 106–111), but the model still contains uncertainty.  
This is because field values of hydraulic conductivity range over two to three orders of 
magnitude for each rock type.  Overall, the range of hydraulic conductivity values for 
the entire model is more than seven orders of magnitude.  Furthermore, there are only 
about 20 potentiometric-level control points for the lowest layer of the model where 
most of the Paleozoic carbonate aquifer is represented.  Model simulations indicate 
that the hydraulic conductivity of the Paleozoic carbonate aquifer controls important 
features of the large hydraulic gradient (D’Agnese, Faunt et al. 1997, p. 89).  Also, 
model results indicate that flow in the Paleozoic carbonate aquifer has substantial 
influence on flow in the overlying volcanic rocks.  Overall confidence in the 
simulation of the Paleozoic carbonate aquifer has been strengthened by good control 
on discharge from the aquifer through well-documented spring discharge data 
(D’Agnese, Faunt et al. 1997, p. 86).
	The overall regional saturated zone flow system in the vicinity of Yucca Mountain 
appears to be controlled by the deep Paleozoic carbonate aquifer.  From a postclosure 
performance perspective, however, the overlying tuffaceous and alluvial aquifers are 
more significant because these would contain any likely travel paths for radionuclides 
moving between the potential repository and the accessible environment.  In addition, 
any future use of groundwater in the region would likely concentrate on the shallower 
tuffaceous and alluvial aquifers rather than on the deeper, albeit more transmissive, 
carbonate aquifer.  Results of the TSPA-VA indicated substantial uncertainty in the 
overall saturated zone flow system and the potential transport of radionuclides in the 
area between 10 km and 20 km down-gradient from the potential repository 
(DOE 1998a, Volume 3, Section 6.5.1.9), particularly where flow leaves the 
tuffaceous aquifer and enters the alluvial aquifer.  Additional water level, 
hydrochemical, and hydraulic-characteristics data are needed in this area to reduce 
uncertainty with respect to groundwater flow paths and transport properties.  These 
data needs are being met by studies being conducted as parts of the EWDP and at the 
Alluvial Testing Complex (see Section 1.1.3, Changes and Status, Item 1).
	A saturated zone flow and transport model abstraction and testing workshop was held 
April 1-3, 1997, in Denver, Colorado (CRWMS M&O 1997a).  The purposes of the 
workshop were to develop a comprehensive list of issues related to key uncertainties 
about saturated zone flow and transport behavior, prioritize the list of issues based on 
impact to long-term performance of the potential repository, and develop analysis 
plans to aid in the resolution of high-priority issues and provide a basis for model 
abstraction in TSPA-VA (CRWMS M&O 1997a, Executive Summary, p. x).  The 
categories of high-priority issues include conceptual models of saturated zone flow, 
conceptual models of saturated zone geology, transport processes and parameters, and 
coupling to other components of TSPA (CRWMS M&O 1997a, Table 1-1).  Analysis 
of the high-priority issues is continuing.
	Although large-scale anisotropy has not been characterized by field tests, regional 
structural features (major faults and fault zones) have been included in the regional 
model to improve its performance (see Section 3.1.4 of Progress Report #15 
(DOE 1997b) under Activity 8.3.1.2.1.4.4).  In an effort to increase confidence in the 
regional saturated zone model, the Yucca Mountain Site Characterization Project 
(YMP) model is being integrated with other DOE-sponsored work in southern Nevada, 
including the Underground Testing Area groundwater flow model.  The expanded and 
upgraded model is referred to as the Death Valley regional flow system.  In addition, a 
new set of boreholes is being drilled by Nye County in the Amargosa Desert along 
U.S. Highway 95.  These boreholes, which constitute the first phase of Nye County’s 
EWDP, are providing additional stratigraphic, water level, and hydrochemical data to 
reduce uncertainties in the regional flow model (see description of Changes and Status 
for Study 8.3.1.2.1.3.).  Furthermore, Nye County's EWDP has additional phases that 
include constructing monitoring wells along Fortymile Wash and the Alluvial Testing 
Complex (see Figure 1-1 and description of Changes and Status for Study 8.3.1.2.3.1 
in Section 1.1.3).  More detailed information about the Nye County EWDP is available 
on the Internet at http://www.nyecounty.com.  During FY 1998, regional groundwater 
modeling focused on refining the fluxes calculated by the model for use in the site-
scale saturated zone flow model, incorporating more vertical detail in the area down-
gradient from the potential repository, and improving estimates of discharge from 
regional springs and evapotranspiration areas.  In FY 1999, Death Valley regional 
flow system modeling efforts emphasized geologic framework compilations, 
refinement of input data sets, refinement of recharge estimates based on simulated net 
infiltration, comprehensive evaluation of water-level depth-interval data, and model 
calibration and evaluation.  In FY 2000 and 2001, a new regional hydrostructural map 
and the three-dimensional hydrogeologic framework model were completed.  In 
addition, three-dimensional, steady-state, numerical-model simulations of 
predevelopment conditions in the Death Valley regional groundwater flow system 
were conducted and documented.  As of the end of FY 2001, no specific plans had 
been developed to use the Death Valley regional flow system model to simulate 
Quaternary or possible future climatic conditions.  However, such plans are under 
consideration even though Quaternary and possible future climatic conditions have 
already been adequately simulated (D’Agnese, Faunt et al. 1997).

Figure 1-1.  Map Showing Locations of Nye County Early Warning Drilling Program Wells
	Another change in the regional groundwater modeling study was the conduct of 
simulations of the hydrologic effects of possible future climatic conditions, originally 
planned under SCP (DOE 1988) Study 8.3.1.5.2.2.  The hydrologic effects of two sets 
of climatic conditions were simulated (D’Agnese, Faunt et al. 1997) using the existing 
regional groundwater flow model (D’Agnese, O’Brien et al. 1997).  One simulation 
represented climatic conditions for 21,000 years ago, when glaciation was at a 
maximum.  The other simulation represented a possible future climatic condition when 
atmospheric carbon-dioxide concentrations might be doubled.  For the 21,000-years 
ago conditions, simulated water levels beneath the potential repository block were 
60 m higher than present-day levels.  Under the conditions of doubled atmospheric 
carbon dioxide, simulated water levels beneath Yucca Mountain were less than 50 m 
higher than present-day levels.
1.1.2	Studies to Provide a Description of the Unsaturated Zone Hydrologic System at the 
Site (SCP Investigation 8.3.1.2.2)
Background and SCP Plans.  The objective of this investigation was to develop a model of the 
unsaturated zone hydrologic system at Yucca Mountain that would help assess the suitability of 
the site to contain and isolate waste.  Developing this model requires an understanding of the 
manner in which water and gases move through the unsaturated zone, including the directions, 
paths, and rates in which flow occurs.  This information was to be provided through the 
characterization of infiltration, percolation, gaseous-phase movement, and hydrochemistry.  
Flow and transport modeling designed to simulate the natural system would provide sensitivity 
analyses to help prioritize additional data collection.  This investigation includes nine studies.  Of 
these, the first seven were data-collection studies; the last two were system-modeling studies.  
These studies were developed to accomplish the following:
1.	Study 8.3.1.2.2.1 (characterization of unsaturated zone infiltration):  This study was to:
? Characterize the infiltration-related hydrologic properties and conditions of the 
surficial soils and rocks covering Yucca Mountain
? Characterize present-day, natural infiltration processes and net-infiltration rates
? Characterize the range and spatial variability of infiltration rates, flow velocities, 
and flow pathways in the near-surface unconsolidated surficial material and 
consolidated bedrock, using double-ring infiltrometer and ponding studies 
(artificial infiltration activity)
? Characterize the relationship between precipitation, soil thickness, run off, 
infiltration, evapotranspiration, and development of perched water tables in the 
near-surface unconsolidated surficial material in each representative 
hydrogeologic surficial unit, using small-plot and large-plot rainfall simulation 
tests (artificial infiltration activity)
? Estimate the future spatial distribution of infiltration rate over the repository 
block.
2.	Study 8.3.1.2.2.2 (water-movement tracer tests):  This study was to characterize the 
percolation of precipitation into the unsaturated zone at Yucca Mountain, and the 
movement of water through the unsaturated zone, using chloride and chlorine-36 
measurements.
3.	Study 8.3.1.2.2.3 (characterization of percolation in the unsaturated zone–
surface-based studies):  This study was to:
? Characterize and statistically describe the flux-related, matrix hydrologic 
properties of major unsaturated zone hydrogeologic units and structural features 
as functions of moisture content or potential through laboratory testing of 
geologic samples obtained from surface-based boreholes and from the ESF
? Determine the present vertical and lateral variation of percolation flux through the 
hydrogeologic units and structural features by measuring the potential field and 
determining the in situ bulk permeability of the unsaturated media in vertical 
boreholes throughout the site
? Evaluate the hydrogeologic significance of fracturing, brecciation, and gouge 
development within the Solitario Canyon fault zone by drilling and testing a 
horizontal borehole
? Investigate the relationships between present flux and past climatic conditions.
4.	Study 8.3.1.2.2.4 (characterization of percolation in the unsaturated zone–ESF 
studies):  This study was to:
? Perform ESF hydrologic tests to supplement and complement the surface-based 
hydrologic information needed to characterize the Yucca Mountain site and to 
provide information for analyzing fluid flow and the potential for radionuclide 
transport through unsaturated tuff
? Combine the integrated results from the ESF hydrologic tests with data from the 
surface-based studies to provide an overall understanding of the unsaturated zone 
hydrologic system (ESF tests were designed to provide phenomenological 
information about water flow through unsaturated, fractured tuffs, in addition to 
providing basic hydrogeologic data)
? Conduct ten sets of hydrologic tests in the ESF:
(1) Intact-fracture testing to evaluate fluid-flow and chemical-transport properties 
of single, relatively undisturbed fractures
(2) Percolation testing to determine the hydrologic conditions that control the 
occurrence of fluid flow within fractures and matrix
(3) Bulk-permeability testing to determine “representative” characteristics of 
fracture networks for model simulations at the scale at which the fractured 
host rock behaves as an equivalent porous medium
(4) Radial-borehole testing to determine rock mass hydrologic properties 
(including bulk air permeability) and to detect vertical movement of liquid 
water and/or vapor within hydrogeologic units and along contacts
(5) Excavation-effects testing to monitor changes to both the stress state and 
fractured rock permeability caused by excavating and lining the ESF and to 
calibrate a coupled hydraulic-mechanical model
(6) Testing of the Calico Hills nonwelded hydrogeologic unit to determine 
hydrologic processes, conditions, and properties under both present and 
expected future conditions
(7) Perched-water testing to detect any occurrence of perched-water zones, 
estimate hydraulic properties of the zones, and determine the implications of 
perched water on flux, flow paths, and travel times
(8) Hydrochemistry testing to understand the gas transport processes; provide 
independent evidence of flow direction, flux, and travel time of gas and water; 
and determine the extent of water-rock interaction and the geochemical 
evolution of water
(9) Multipurpose-borehole testing near the ESF to monitor potential interference 
of ESF construction with ESF tests, identify perched water, and confirm 
engineering and hydrogeologic properties of the rock before ESF construction
(10) Testing of hydrologic properties and flow conditions of major faults 
encountered in the long drifts at the main test level of the ESF.
5.	Study 8.3.1.2.2.5 (diffusion tests in the ESF):  This study was to determine in situ the 
extent to which nonsorbing tracers diffuse into the water-filled pores of the tuffs of the 
Topopah Spring welded unit and the Calico Hills nonwelded unit in the ESF.
6.	Study 8.3.1.2.2.6 (characterization of gaseous-phase movement in the unsaturated 
zone):  This study was to:
? Describe the pre-waste emplacement gas-flow field and its effect on net water-
vapor transport from the unsaturated zone
? Identify structural controls on gas-phase flow
? Determine conductive and dispersive properties of the unsaturated zone for gas 
flow to assess potential transport of gaseous radionuclides (e.g., carbon-14)
? Provide the parameters necessary for modeling gas flow
? Perform model simulations of gaseous flux of moisture affecting deep percolation 
and transport of tracers in the gas phase.
7.	Study 8.3.1.2.2.7 (characterization of the unsaturated zone hydrochemistry):  This 
study was to:
? Perform hydrochemical investigations to understand gas-transport mechanisms 
and provide evidence of gas-flow direction, flux and travel time within the 
unsaturated zone
? Design and implement methods for extracting pore fluids from the tuff
? Provide independent evidence of flow direction, flux, and travel time of water in 
the unsaturated zone
? Determine the extent of the water-rock interaction and model geochemical 
evolution of water in the unsaturated zone.
8.	Study 8.3.1.2.2.8 (fluid flow in unsaturated, fractured rock):  This study was to
? Develop and validate (through ESF testing) detailed conceptual and numerical 
models of fluid flow and transport within unsaturated, fractured rock
? Apply these models to volumes of fractured rock at or below the dimensions at 
which the rock can be replaced conceptually by an equivalent porous medium
? Use the models to help design and interpret hydrologic and pneumatic tests and 
provide information about model parameters that can be incorporated into site-
scale models (Study 8.3.1.2.2.9).
9.	Study 8.3.1.2.2.9 (site unsaturated zone modeling and synthesis):  This study was to:
? Develop appropriate conceptual models for the site unsaturated zone 
hydrogeologic system
? Select, modify, or develop numerical hydrologic models capable of simulating the 
hydrogeologic system and its component subsystems
? Construct appropriate hydrologic models for the natural site hydrogeologic 
system to simulate and investigate the present state of the system and predict 
probable future and past states of the system under changes in the environmental 
conditions;
? Evaluate the accuracy and uncertainty of the models, using stochastic modeling, 
conventional statistical analyses, and sensitivity analyses
? Integrate data and analyses to synthesize a comprehensive, qualitative, and 
quantitative description of the site unsaturated zone hydrogeologic system under 
present as well as probable, or possible, future conditions.
Changes and Status.  The primary objectives of this investigation have not changed since the 
SCP was issued.  The SCP (DOE 1988), however, described a more extensive program of data 
collection.  The studies for this investigation have evolved based on technical information 
obtained from laboratory and field studies, model development and data application activities of 
the site characterization program.  Rapidly increasing scientific understanding, along with 
periodic TSPA, have enabled focusing the ongoing site characterization program on the 
remaining uncertainties that are significant to the suitability of the potential repository site 
(DOE 1994a).  Re-evaluation and prioritization of Project needs (DOE 1994a) has been a 
continuous process based on scientific judgment and resource availability, governed by scientific 
criteria to ensure that data needed for site description, performance assessment, and design 
purposes were collected and analyzed, and to eliminate data-collection redundancy and overlap 
that would result from completion of all the studies in the SCP (DOE 1988).  The data-collection 
needs have been further analyzed and refined as additional knowledge has been gained through 
years of site characterization activities.  This process has resulted in the following changes to the 
investigation.
1.	In FY 1995, the unsaturated zone infiltration study (8.3.1.2.2.1) was reconfigured and 
accelerated (Progress Report #12, Section 3.1.5 (DOE 1995b)) in response to the site 
suitability initiative described in the Civilian Radioactive Waste Management 
Program Plan (DOE 1994a, Volume 1, pp. 18–21), which was implemented “to 
support a stepwise evaluation of the suitability or unsuitability of the Yucca Mountain 
site” (DOE 1994a, Volume 2, p. 15).  Under the Program Plan, key evaluations were 
to be accelerated (compared to the SCP schedule) to focus more effectively on site 
suitability apart from all the considerations associated with the license application 
(DOE 1994a, Volume 1, p. 20).  In support of the suitability initiative, a Technical 
Basis Report on geohydrology and transport was scheduled for completion in 
FY 1998, requiring completion of an intermediate, integrated 
geology-hydrology-geochemistry model in FY 1997 (DOE 1994a, Volume 2, 
Figure 2-3).  Because the infiltration study was to develop the upper boundary 
condition for site-scale models of unsaturated zone flow and transport, the study had to 
be accelerated and reconfigured.  As a result, the artificial-infiltration tests described 
in the SCP were deferred, even though their primary purpose was to validate the 
numerical infiltration model that has been developed.  Consequently, although the 
numerical infiltration model is technically valid, it contains uncertainty with respect to 
important rock properties and processes at the alluvium-bedrock interface.

	The primary goal of the reconfigured study was to define the spatial and temporal 
distribution of moisture flux for the upper boundary condition for site-scale models of 
unsaturated zone groundwater flow and transport.  In this context, the boundary 
condition was developed as a conceptual and numerical model using arid-land 
watershed processes.  The model has provided a dynamic link between infiltration flux 
and known climatic variability, potential climatic trends, potential changes in the 
surface environment (such as loss of vegetation), and sporadic but extreme 
meteorological events.  The integration of hydrologic-process models for the surface 
and near-surface environments with mapped surficial-material hydrologic properties 
and mapped present-day net infiltration rates (as measured in the neutron-access 
boreholes) has resulted in a stochastic-deterministic simulation of future 
upper-boundary conditions, including the probability and magnitude of potential fast 
pathways of net infiltration.
	A surficial-materials infiltration-properties map of the Yucca Mountain area showing 
the spatial distribution of eight statistically significant soil units was developed, but the 
field and laboratory measurements used to produce the map were reduced both in 
number and in scope from that envisioned in the SCP (DOE 1988) because of the 
prioritization and accelerated schedule for the infiltration study.  The effects of the 
reduction on data representativeness and utility of the properties map have not yet 
been determined.  Moisture monitoring in the network of neutron-access boreholes 
was discontinued at the end of FY 1995, after 10 years of monitoring, because 
sufficient data had been collected for this phase of the Program.  A synthesis report 
was prepared in FY 1996 (Flint et al. 1996) using existing data to assess the current 
status of the study and to provide input for the Viability Assessment.  A multiple linear 
regression model was developed to correlate annual shallow-infiltration estimates 
measured in 69 neutron-access boreholes to annual precipitation, depth to bedrock, and 
other hydrogeologic factors (Hudson and Flint 1996, p. 1), but the series of 
double-ring-infiltrometer and ponding studies intended to determine the range and 
spatial variability of infiltration rates (artificial infiltration), were not conducted.  
Similarly, although one detailed water-balance study of Split Wash was initiated to 
develop and calibrate the evapotranspiration component of the infiltration model, the 
number and scope of watershed-scale studies was reduced considerably.  Further, the 
artificial infiltration control-plot studies were not implemented.  These studies would 
have measured water-potential gradients in the shallow subsurface (<15 m) under 
ambient conditions to determine the direction of water flow and the extent to which 
barometric pumping might be removing water in the vapor phase from the system.  
Finally, although a numerical model was developed to simulate the interaction of 
processes that result in net infiltration, the small- and large-plot rainfall-simulation 
tests (artificial infiltration) were not conducted; these tests were intended to validate 
the model with respect to temporal and spatial distribution of infiltration under both 
current-climatic and wetter conditions.  Specifically, these tests would have provided 
field data on rock properties and processes of the alluvium-bedrock interface to 
replace the available data that were collected from the alluvial surface and from deeper 
within the bedrock units.  At present, the Project has no plans to collect these data on 
rock properties and processes at the alluvium-bedrock interface.
	One of the objectives of the artificial infiltration experiments described in the SCP 
(DOE 1988) was to approximate the increased infiltration that might result from 
potentially wetter climatic conditions in the future by simulating those conditions in 
the field.  Even though the artificial infiltration experiments have not been conducted, 
monitoring of moisture flux in the neutron-access boreholes over the last 10 years has 
afforded an opportunity to observe a significant range of natural infiltration events.  
The termination of the neutron-moisture monitoring at the end of FY 1995 has 
precluded measurement of the subsurface redistribution of water that infiltrated during 
the larger storm events.  Subsurface redistribution of water may require several years.  
Nonetheless, as a result of several El Niño winter storm events over the last few 
winters (especially 1992, 1993, and 1995), unusually large precipitation events have, 
in fact, occurred and have provided useful insights about the potential effects of wetter 
conditions on infiltration rates.  These El Niño events are estimated to be analogous to 
the expected precipitation during global warming (due to increases in greenhouse 
gases) and possibly wetter pluvial periods in the future.  Although monitoring the 
vertical moisture profiles immediately following these events provided direct, 
qualitative evidence of the increased infiltration, in the absence of quantitative 
information on water potentials and fracture-matrix interactions at the 
alluvium-bedrock interface, longer term direction of flow (up or down), and therefore 
net infiltration, is not known with certainty.
	In the TSPA-VA (DOE 1998a, Volume 3), uncertainties about individual components 
of the infiltration model were not analyzed.  Instead, overall uncertainty about net 
infiltration was considered by running two performance-assessment simulations:  one 
with three times and the second with one-third the distribution of infiltration used for 
the base case (DOE 1998a, Volume 3, Section 3.1.2.2).  In general, the TSPA-VA 
results indicated that potential decreases in uncertainty for net infiltration are related to 
several factors including:
? Transitions from one future climate state to another
? Mean annual temperature during future climate states
? Timing and duration of future climate states
? Development of a more quantitative basis for uncertainty in net infiltration
? Consideration of other aspects of future climates that would affect net infiltration 
(cloudiness, vegetation, surface water run off-run on, and snow cover)
? Enhanced calibration of the net infiltration model using well-documented present-
day analogs (DOE 1998a, Volume 3, Section 6.5.1.1).
	For the TSPA-SR, completed in December 2000, the infiltration model was enhanced 
(CRWMS 2000af).  For example, uncertainty in estimated infiltration rates was 
addressed by simulating mean, lower-bound and upper-bound infiltration for the 
modern and two future climate states by using present-day analog climate sites.  In 
addition, the Project is focusing on determining the resulting percolation at the 
repository level and the potential for the Paintbrush nonwelded (PTn) hydrogeologic 
unit to divert flow laterally above the repository (Progress Report #17 (DOE 1998b, 
Section 5.2).
	During FY 1997 through FY 1999, work focused on enhancing the numerical 
infiltration model to reduce the uncertainty in some of its components.  Enhancements 
include development of a coupled net infiltration-surface-flow routing module, 
improved simulation of surface evaporation and root-zone transpiration, more accurate 
simulation of effective bedrock permeability, and inclusion of the effects of 
temperature in simulation of potential future climates.  In FY 1999 and FY 2000, the 
infiltration model was revised and used to simulate present-day climate conditions and 
two possible future climate states:  monsoonal and glacial transition (USGS 2001a).  
The revised climate scenarios for future climate were simulated with the infiltration 
model in order to realistically account for climate changes that are likely to occur 
during the next 10,000 years, which is the regulatory period for the potential 
repository.  To facilitate the input of infiltration values into the TSPA model, 
uncertainties in net infiltration were evaluated further in AMR Analysis of Infiltration 
Uncertainty (CRWMS M&O 2000ai).
2.	The water movement test study (8.3.1.2.2.2) was expanded considerably in scope and 
complexity from that outlined in the SCP (DOE 1988, pp. 8.3.1.2-179–8.3.1.2-181).  
The expanded scope was intended to provide corroboration of borehole data, which 
were initially interpreted as indicating that pore waters were on the order of hundreds 
of thousands of years old.  Corroboration, if provided, was expected to support 
low-flux arguments.  The SCP indicated that sampling of tuffs for chlorine-36 would 
focus primarily on obtaining a profile in what was then planned to be a vertical shaft 
ESF.  Additional chlorine-36 measurements were to be performed on samples 
collected after a survey of Yucca Mountain to determine areas of active percolation.  
Since that time, the set of targets for sampling has expanded to include:
? Soil samples within the “perimeter-drift boundary” and from pits in Midway 
Valley
? Drill cuttings from the last set of neutron-access holes and deep systematic 
drilling, unsaturated zone and north ramp geologic boreholes
? Pore water extracted from cores of deep unsaturated zone and geologic boreholes 
in the ESF, East-West Cross Drift and Busted Butte Field Transport Facility
? Rain water and water from the bottom of neutron holes
? Perched water from several deep boreholes near the ESF
? Water samples from several deep saturated zone holes
? Water from springs and shallow wells in the Amargosa Valley and Death Valley
? Packrat middens (Progress Reports #6 through #15 (DOE 1992a, 1992b, 1993, 
1994b, 1994c, 1995a, 1995b, 1996b, 1996c, and 1997b)).
	With reconfiguration of the ESF into the ramp and drift configuration, the number of 
samples from the ESF and Cross Drift has increased substantially through systematic 
sampling along these tunnels and their niches and alcoves, and sampling of exposed 
discrete structural features that are potential fast-transport paths (Fabryka-Martin 
et al. 1997, Section 6.4).  The most significant aspect of this expanded sampling was 
finding elevated levels of chlorine-36 at several locations in the ESF and Cross Drift.  
These were attributed to the transport of bomb-pulse chlorine-36 to the sampled depths 
in less than 50 years.  The locations at which these elevated signals occurred appeared 
to be associated with faults.  The complexity of the study consequently increased by 
using the chlorine-36 method to investigate the spatial frequency of fracture flow, 
residence times of infiltrating water, and groundwater travel times.  In addition, the 
chlorine-36 results have been used in connection with the site-scale unsaturated zone 
transport model to estimate percolation flux at the repository horizon, to establish 
bounds on the ranges of hydrologic parameter values used in the site-scale model, and 
to develop and evaluate alternative conceptual models of flow and transport at the site.  
The study has also given increasing attention to the implications of pore water chloride 
concentrations as a surrogate measure of infiltration rates and as another 
environmental tracer useful for calibrating numerical flow models of the unsaturated 
zone.  For these reasons many of the samples selected for chlorine-36 analysis have 
also been analyzed for chloride contents.
	During FY 2000 and FY 2001, a chlorine-36 validation study was initiated and 
conducted because of concerns about possible contamination, representativeness of 
samples, lack of bomb-pulse chlorine-36 in the southern part of the ESF, and 
difficulties with replicating earlier analyses (DOE 2001c, Section 1.2.2).  As a part of 
the validation study, additional samples have been collected from the ESF and 
analyzed for chlorine-36 and tritium.  The validation study is expected to be completed 
during FY 2002.
3.	The percolation in the unsaturated zone surface-based study (8.3.1.2.2.3) has been 
reduced in scope in accordance with the priorities and planning assumptions for site 
investigations implemented for FY 1996 (CRWMS M&O 1995a, Volume 1, p. 6.3-1).  
The SCP (DOE 1988) indicated that 17 vertical boreholes would be drilled, tested, and 
instrumented in support of this study, 9 holes would penetrate to just above the 
potential repository horizon, and 8 holes would penetrate the unsaturated zone below 
the potential repository horizon.  Monitoring of pneumatic pressure, temperature, and 
water potential was to be performed in each hole for a minimum of 3 to 5 years.  
Although 16 holes have been drilled and used by this study, four of these were drilled 
along the alignment of the north ramp of the ESF rather than in the feature-based 
locations originally planned.  Of the 16 holes drilled, 8 terminated above the repository 
horizon and 7 penetrated to below the repository horizon.  However, no deep borehole 
has been drilled, or excavation made, to characterize the Ghost Dance fault in the 
Calico Hills Formation below the repository horizon.  No additional surface-based 
drilling is scheduled in this area in the Long-Range Plan (CRWMS M&O 1996a, 
p. A-6), except that which could be a part of confirmatory testing.  Perched water was 
detected in 7 of the 16 boreholes (CRWMS M&O 2000c, Section 8.5.2).
	Of the 16 holes drilled, 7 have been instrumented as planned to monitor pneumatic 
pressure, temperature, and water potential, while 2 holes were instrumented for 
pressure and temperature (Nye County), 2 for pressure only (flexible borehole liners), 
and 1 for vertical seismic profiling.  A significant change in the study has been the 
increased emphasis on the effects of ESF construction on the natural gas-phase system.  
This occurred because of commitments made to the NRC to perform “pneumatic 
instrumentation and data collection in the vicinity of the ESF, prior to the passage of 
the tunnel boring machine, to characterize the pneumatic pathways of the mountain 
before the ESF cuts across possible pneumatic barriers” (CRWMS M&O 1995a, 
Volume 1, p. 6.3-1).  Air-injection tests to determine gas-phase permeability have 
been conducted in 4 of the holes, only one of which penetrated below the repository 
horizon.  Air-permeability testing in surface-based boreholes was suspended because 
sufficient data have been collected to support this phase of the Civilian Radioactive 
Waste Management Program.  Further, no cross-hole pneumatic or gas-tracer tests 
have been conducted, and no additional pneumatic tests are planned.  Contrary to the 
SCP (DOE 1988), no boreholes have been drilled and tested on opposite sides of the 
Solitario Canyon fault or at the southern end of Yucca Mountain.  In FY 1999, 
borehole USW SD-6 was drilled from the crest of Yucca Mountain to obtain 
information about rock properties of the repository horizon and hydrologic data on the 
saturated zone.  The hole was drilled to a depth of 2,808 ft (855.9 m).  There are no 
plans to instrument this or other surface-based boreholes at the crest for hydrologic 
monitoring in the unsaturated zone or for vertical seismic profiling.
	Pneumatic and aqueous tracer tests in instrumented boreholes associated with the 
Solitario Canyon study have been deleted from the testing program, consistent with the 
revised program strategy described in the Program Plan (DOE 1994a, Volume 1, 
Appendix A, p. A-4).  However, many of the objectives of the Solitario Canyon fault 
horizontal borehole study are expected to be met by planned hydrologic testing in the 
cross drift being constructed as part of the Enhanced Characterization of the 
Repository Block (ECRB), also known as the East-West Cross Drift.  However, testing 
has yet to be implemented.  For more information on the ECRB cross drift, see the 
description of study 8.3.1.2.2.4 below.
	Although there are no additional surface-based boreholes planned to intersect the 
Ghost Dance fault, two test alcoves off the main ESF tunnel have been constructed, 
and horizontal boreholes drilled from these alcoves intersected the Ghost Dance fault.  
Much of the hydrogeologic testing planned for these boreholes has been completed 
(see Progress Report #17 (DOE 1998b, Section 5.2)).  Data from these tests were used 
to characterize hydrologic conditions in the vicinity of the fault at the repository 
horizon.  These hydrologic conditions have been used to constrain the unsaturated 
zone flow and transport models (Bodvarsson et al. 1997, pp. 7-27 through 7-33).
	From FY 1995 through FY 1998, monitoring of pneumatic pressure, temperature, and 
water potential continued in all seven instrumented boreholes.  During late FY 1998 
and early FY 1999, three boreholes were removed from the active monitoring network 
to reduce costs.  Monitoring in the other four boreholes continued through FY 2000 
and FY 2001.  After performing a detailed decision analysis in late FY 2001, the DOE 
decided to deactivate the remaining boreholes because no additional data were needed 
from them to support the site recommendation or the license application.  Following 
final equipment calibration and other close-out activities, the remaining four boreholes 
are expected to be deactivated by the end of the first quarter of FY 2002.
4.	In the percolation in the unsaturated zone ESF study (8.3.1.2.2.4), a number of 
changes in testing strategy resulted from reconfiguration of ESF from vertical shafts to 
ramps and drifts.  The multipurpose-borehole testing was deleted because of its 
association with vertical shafts and was replaced by the series of north ramp geologic 
holes and other boreholes.  The intact-fracture and excavation-effects tests have been 
terminated consistent with the strategy described in the Program Plan (DOE 1994a, 
Volume 1, Appendix A, p. A-4) because they would not lead to reduction in residual 
uncertainty in hydrologic parameters at the site scale.  The in situ testing for the 
bulk-permeability test has been combined with the radial-boreholes and major-faults 
tests, both of which are ongoing, consistent with the work-consolidation efforts 
implemented as part of FY 1996 planning (CRWMS M&O 1995a, pp. 6.3-51 and 
6.3-52).  The modeling part of the bulk-permeability test is being accomplished under 
Study 8.3.1.2.2.8 (fluid flow in unsaturated fractured rock).  Although the percolation 
tests on blocks of intact rock were deleted from the testing program, a reconfigured 
series of in situ field tests have been implemented.  These tests are continuing to 
estimate hydrologic properties of the faulted and unfaulted rock mass and the flux of 
water moving downward through the repository horizon in the ESF under present-day 
conditions.  These tests include the Ghost Dance Fault hydrologic testing, niche 
seepage studies, cross drift niche test, cross drift systematic hydrological 
characterization, Alcove 8/Niche 3 test, and the cross drift bulkhead and 
moisture-monitoring studies.  Testing of the hydrologic properties of the Ghost Dance 
Fault in the ESF is documented in LeCain et al. (2000).  In the niche seepage studies, a 
series of seepage-rate threshold tests were conducted at three niches along the ESF 
main drift during FY 2000.  The data were used for the development, calibration, and 
validation of the Seepage Calibration Model (CRWMS M&O 2001a) as it applies to 
the TSw middle nonlithophysal unit.  The cross drift niche test is being conducted to 
measure seepage and seepage thresholds in the TSw lower nonlithophysal unit.  The 
cross drift systematic hydrological characterization effort, started in May 2000, is 
utilizing slanted boreholes drilled into the crown of the cross drift at an interval of one 
borehole every 30 m.  The boreholes are used for determination of spatial 
heterogeneity of seepage potential and to measure effective porosity.  The Alcove 
8/Niche 3 test is evaluating seepage potential in a fault zone and the Cross Drift 
bulkhead and moisture-monitoring study is investigating the source of moisture 
(seepage or condensation) observed in sections of the cross drift that have been 
isolated from ventilation.  Progress in these studies is described in Progress Report 23 
(DOE 2001c) and in Section 3.3. of Progress Report 24 (in progress).
	Because perched water was never encountered in the ESF, the perched-water test was 
never implemented.  However, perched-water testing was conducted in surface-based 
boreholes under Studies 8.3.1.2.2.3 (Section 1.1.2) and 8.3.1.2.3.1 (Section 1.1.3).
	Extensive studies of secondary minerals deposited in the unsaturated zone and fluid 
inclusions within the minerals have been conducted and are continuing in the ESF and 
cross drift.  These studies are intended to determine the age of the deposits, source of 
the deposition water, temperature of the water, percolation flux associated with 
mineral deposition, distribution of flux in fractures and fault zones, and the overall 
response of the unsaturated zone to past climate changes.  These studies are 
summarized and statused in Section 1.4.2, Changes and Status, item 1.
	A test not anticipated in the SCP (DOE 1988) involving moisture monitoring in the 
ESF is under way.  This test is intended to develop a water mass balance for the ESF 
and to determine how much naturally occurring water is being removed from the ESF 
by the ventilation system.  In addition, two drift-scale seepage tests have been 
implemented in alcoves off the ESF main drift and north ramp.  The seepage test in the 
Southern Ghost Dance Fault Alcove (Alcove 7) is being conducted under close to 
natural conditions, in that the alcove was sealed from the rest of the ESF in 
December 1997 with a bulkhead to inhibit drying of the alcove by the ESF ventilation 
system.  A drip-detection system was installed in the Southern Ghost Dance Fault 
Alcove to monitor natural seepage into the alcove, which is located at the repository 
horizon about 200 m (650 ft) below land surface.  This seepage test was implemented 
just prior to a period of increased surface infiltration caused by above-normal 
precipitation because of El Niño climatic conditions.  The other drift-scale seepage test 
is being conducted under artificial conditions in the Upper Tiva Canyon Alcove 
(Alcove 1), which is only 35 m (115 ft) below land surface.  In this seepage test, water 
was applied artificially to the land surface using a drip-irrigation system to simulate 
wetter-than-normal climatic conditions.  This test was conducted to observe how a 
moisture front moves through fractured rock and how the drift itself influences 
percolation through the fracture network.  Results of the Alcove 1 seepage test are 
described in Progress Report 22 (DOE 2000a).
	Another major study in the ESF involved the East-West Cross Drift.  The cross drift 
was constructed from the ESF north ramp to the southwest about 2.8 km (1.6 mile) 
(CRWMS M&O 1997b).  The cross drift crosses over the main loop of the ESF, 
traverses the repository block from northeast to southwest, and then penetrates the 
Solitario Canyon fault system.  A series of five studies will be conducted in the cross 
drift:
? Geologic mapping of stratigraphy and structure
? Analysis of geotechnical and hydrologic rock properties
? Mineralogical analysis to estimate past percolation flux and flow paths
? Hydrological studies to assess the moisture conditions, identify preferential and/or 
fast flow paths, and assess effects of variable surface infiltration
? Predictive analyses.
	The predictive analyses involved preparation of a series of reports on the geology, 
hydrology, and geochemistry along the cross drift before excavation in order to help 
confirm and validate the general understanding of the repository block.  As noted 
above, extensive moisture monitoring is being conducted in the cross drift bulkhead 
and moisture-monitoring study.
	Discrete testing of the Calico Hills nonwelded (CHn) hydrogeologic unit in the ESF 
was deleted from the study plan in Revision 9 of the Yucca Mountain Site 
Characterization Program Baseline (YMP 1992).  However, testing in the CHn may 
be conducted as part of future testing activities in the cross drift.  To obtain early 
information on the CHn, a large-scale unsaturated zone transport test was started 
during FY 1998 within the Busted Butte facility about 6 km (3.6 mi) from the south 
portal of the ESF.  This two-phase test is providing information crucial to 
understanding radionuclide retardation and colloid migration in the Calico Hills 
Formation (Bussod et al. 1997, pp. 5-31, 5-39).  The test results also will help resolve 
scaling issues associated with the use of laboratory data to validate transport-model 
input for the Total System Performance Assessment.
5.	No diffusion tests have been conducted in the ESF (Study 8.3.1.2.2.5), and plans to 
conduct such tests have been suspended indefinitely.  Natural radioisotopes have been 
encountered in samples collected at several locations from the ESF and surface-based 
boreholes.  The occurrence of these naturally occurring (albeit possibly 
anthropogenically enhanced) tracers will continue to be used in conjunction with 
laboratory testing of matrix diffusion processes and parameters to define the role of 
matrix diffusion in the unsaturated zone radionuclide transport model.  In addition, 
tracer testing in the saturated zone at the C-hole complex has provided information, at 
the scale of several tens of meters, about the role of matrix diffusion in the tuffaceous 
rocks at Yucca Mountain.  Preliminary results of C-hole tracer tests completed in the 
Prow Pass Tuff (the uppermost unit in the saturated zone) indicate that matrix 
diffusion occurs, flow rates and hydraulic conductivity are very low, lithium sorption 
is greater than predicted by laboratory tests, and microsphere transport is reduced, 
indicating low hydraulic conductivity (Progress Report 20, Section 3.4 (DOE 1999b).
6.	Although the gas-phase movement study (8.3.1.2.2.6) has collected and used data from 
about a dozen more boreholes than was expected, the scope of work planned for key 
locations and boreholes has been reduced because not as many surface-based 
boreholes were drilled as anticipated by the SCP (DOE 1988), and because of a 
judgment that sufficient data have been collected to support this phase of the Program.  
Accordingly, the study investigators were requested to produce a synthesis report in 
FY 1996 (CRWMS M&O 1995a, p. 6.3-2) using existing data to assess the status of 
the study and provide input to the Viability Assessment.  The results of this study 
provide input to evaluation of the potential for transport of significant amounts of heat 
energy and water vapor from the rock mass into the atmosphere under both natural 
conditions and the thermal load associated with emplaced nuclear waste (Bodvarsson 
and Bandurraga 1996, Section 12.4; Patterson et al. 1996, p. 3).  Gas and water-vapor 
flow through the unsaturated zone are driven by changes in barometric pressure, 
temperature-induced density differences, and wind effects.  Preliminary evaluations of 
these mechanisms are described in Patterson et al. (1996, pp. 67–75), Bodvarsson and 
Bandurraga (1996, Section 2.3.1), and Weeks (1993).
	Examples of reduced technical scope include the fact that neither the two vertical 
boreholes planned to straddle the Solitario Canyon fault nor the horizontal borehole to 
penetrate it were drilled.  Also, the cross-hole tracer tests planned for the USW UZ-9 
borehole complex have not been conducted because this cluster of boreholes has been 
deleted from the testing program.  Further, the extensive sampling of boreholes for 
chlorofluorocarbons to determine residence time of gas in the Tiva Canyon welded 
(TCw) hydrogeologic unit and to investigate possible breaches in PTn hydrogeologic 
unit was not conducted.
	A significant change from the original study strategy has been the use of the effects of 
ESF construction on the gas-phase system to estimate pneumatic properties of the 
unsaturated zone.  This occurred because of commitments made to the NRC to 
perform “pneumatic instrumentation and data collection in the vicinity of the ESF, 
prior to the passage of the tunnel boring machine, to characterize the pneumatic 
pathways of the mountain before the ESF cuts across possible pneumatic barriers” 
(CRWMS M&O 1995a, Volume 1, p. 6.3-1).  This was new work, identified since the 
SCP (DOE 1988) was issued.  The work was done to take advantage of the 
opportunity to use barometric responses to estimate large-scale pneumatic diffusivity 
in the ESF.  Specifically, a numerical gas-flow model of the ESF north ramp was 
constructed to simulate the progressive effects of excavating the north ramp as 
detected in nearby surface-based boreholes (Patterson et al. 1996, pp. 50–67).  
A parameter-estimation technique was used to determine horizontal and vertical 
permeabilities of the Topopah Spring Tuff.  Although this preliminary, 
three-dimensional gas-phase modeling of the ESF north ramp area was done for this 
study, all remaining site-scale, gas-phase modeling will be done under 
Study 8.3.1.2.2.9.
7.	In the unsaturated zone hydrochemistry study (8.3.1.2.2.7), pore water has been 
extracted for hydrochemical and isotopic analysis from the cores of 9 of the 
15 boreholes drilled to support deep unsaturated zone studies (see item 3 above).  The 
scope of the hydrochemistry study was reduced because sufficient data have been 
collected to support this phase of the Program.  Accordingly, a synthesis report was 
produced in FY 1996 using existing data to provide input for the Viability Assessment 
(CRWMS M&O 1995a, p. 6.3-2).  Detailed, time-series gas-composition and 
isotopic-content data has been collected from borehole USW UZ-1, which is north of 
the repository.  Gas samples have been collected from 8 other boreholes, but in two 
instances the sampling was very limited (Yang, Rattray et al. 1996, pp. 40–47).  
Further, gas samples have been collected from below the repository horizon in the 
Calico Hills Formation in one borehole (Yang, Yu et al. 1998, p. 4).  Overall, although 
inferences and conclusions regarding fluid movement have had to be based on fewer 
data from fewer locations in the vicinity of Yucca Mountain, the data collected are 
sufficient to meet the basic objectives and strategy for this study.
	Significant additional information on naturally occurring radioisotopes has been 
collected from the ESF.  These data have increased confidence in the unsaturated zone 
flow and transport models.  These data from the ESF combined with the borehole 
hydrochemical and isotopic data have been used to constrain these models.
8.	Because of significant changes in the ESF testing strategy (see item 4 above), the flow 
in unsaturated fractured rock study (8.3.1.2.2.8) has de-emphasized development of 
conceptual and numerical models solely for design and interpretation of small-scale 
ESF tests.  Instead, the study has concentrated on using all data available from the ESF 
to construct representative fracture-flow models at about the drift scale.  These 
models, particularly of the Topopah Spring welded (TSw) hydrogeologic unit, have 
provided a basis for calculation of the spatial distribution and magnitude of fracture 
flow that could seep into drifts of the potential repository (Tsang et al. 1997; CRWMS 
M&O 2000aj).  Evaluation of the fracture-network models is complete; it has been 
determined that one of the most appropriate models is the dual-permeability model, 
including both fracture and matrix continua.  This model has now been used as one of 
the main models for TSPA for both the drift-scale seepage model and the site-scale 
model.  In addition, as part of model development, a series of modeling approaches for 
small-scale flow phenomena have been applied directly to the unsaturated zone site-
scale model (Bodvarsson et al. 1997, Chapters 7, 21, and 24).  These include fracture-
matrix interaction modules, a hysteresis model, and an equivalent for unsaturated 
fracture models.  These approaches and models provide the theoretical and applied 
basis for evaluating various complex processes within the site-scale model.
9.	The site-scale unsaturated zone modeling and synthesis study (8.3.1.2.2.9) has 
exceeded expectations for simulation of the site-scale unsaturated zone system.  This 
has occurred, in part, because of significant advances in the numerical code and 
computer technology used in the modeling effort (Section 3.1.13, 
Activity 8.3.1.2.2.9.2 of Progress Report #15 (DOE 1997b); Progress Reports #7, #8, 
and #9, Section 2.2.1.13, Activity 8.3.1.2.2.9.2 (DOE 1992b, 1993, and 1994b)).  In 
addition, construction of the ESF ramp-and-drift configuration, during the time that the 
site-scale model was being developed, afforded an unexpected opportunity to calibrate 
the gas-phase part of the model.  Although it has been necessary to develop and 
calibrate the model with data from fewer surface-based boreholes than originally 
expected, data from instrumented boreholes documenting atmospheric-pressure 
fluctuations from ESF construction on the gas-phase system has made possible 
enhanced, large-scale, transient-state modeling of gas-pressure propagation through 
the mountain (Ahlers et al. 1995, Section 4).  These data have led not only to enhanced 
simulation of the gaseous phase but also to improved understanding and representation 
of fracture and fault diffusivities and permeabilities in the site-scale model.  Further, 
using temperature-gradient and heat-flow data for the unsaturated zone has led to 
enhancement of the ability of the model to simulate and predict moisture flow 
(Progress Report #15, Section 3.1.13, Activity 8.3.1.2.2.9.3 (DOE 1997b); Bodvarsson 
and Bandurraga 1996, Chapters 6, 8, and 9).  The model calibration has been further 
refined by using a variety of site information, including pneumatic pressures, 
saturations, updated data on the geologic framework, hydrologic properties, fracture 
and fault properties, vertical temperature variations, and perched water data.  
Hydrochemistry and isotopic ratios have also been considered.  Conceptual models for 
fracture-matrix interaction have also been incorporated.  The Unsaturated Zone Model 
utilized this calibrated hydrologic property set with a three-dimensional, steady-state, 
isothermal, dual-permeability modeling approach, including both fracture and matrix 
continua, to generate 39 flow fields for use by TSPA.  Enhancements are currently 
planned or underway, including—but not limited to—the use of multi-dimensional 
inversions, continued updating of the hydrologic properties with new site data, and 
further development of the fracture-matrix interaction model.  During FY 1998 
through FY 2000, development of the unsaturated zone flow and transport model for 
TSPA-SR was completed, including coupled-processes and drift-seepage components.  
Complete descriptions of model development and results of simulations are 
documented in Unsaturated Zone Flow and Transport Model Process Model Report 
(CRWMS M&O 2000aq).  During FY 2001, components of the unsaturated-zone 
model were updated, including flow, transport, coupled processes, and drift seepage.  
Descriptions of the updated model components and results of recent simulations are 
described in the FY 01 Supplemental Science and Performance Analyses, Volume 1:  
Scientific Bases and Analyses (SSPA Vol. 1) (BSC 2001k).
	A major technical issue that has emerged since the SCP (DOE 1988) was written 
concerns the relation between site-scale percolation flux and the quantity of water that 
might seep into an individual drift in the potential repository.  Consequently, modeling 
of gas and water movement in the vicinity of a drift is receiving considerable emphasis 
(Tsang et al. 1997) (see also Progress Report #19, Section 2.3 (DOE 1999a); Progress 
Report #20, Section 3.3 (DOE 1999b); and appropriate sections of more recent 
progress reports).  Drift-scale modeling has been conducted and is continuing to:
? Incorporate results from various ESF hydrologic tests into the model for 
calculating the temporal and spatial distribution of fluxes near a drift
? Study the sensitivity of the model results to parameters not well established from 
measurements
? Calibrate modeling results against observations in the ESF and, in particular, 
recent niche experiments
? Estimate seepage locations and seepage flow rates at each location and for each 
realization of the drift model
? Incorporate the effects of near-field thermal and chemical alterations (i.e., calcite 
and/or silica precipitation cap)
? Simulate drift seepage for a number of alternative drift geometries, including 
rectangular and moderate step-like geometries.
	The results of recent drift-scale seepage and coupled-processes models are 
documented in Seepage Calibration Model and Seepage Testing Data (CRWMS 
M&O 2001a), Seepage Model for PA Including Drift Collapse (CRWMS M&O 
2000aj), and Drift-Scale Coupled Processes (DST and THC Seepage) Models (BSC 
2001i).
1.1.3	Studies to Provide a Description of the Saturated Zone Hydrologic System at the 
Site (SCP Investigation 8.3.1.2.3)
Background and SCP Plans.  The objective of this investigation was to develop a model of the 
saturated zone hydrologic system of Yucca Mountain that will help assess the suitability of the 
site to contain and isolate waste.  Developing this model requires an understanding of 
groundwater flow.  This understanding will be provided through studies focusing on the 
determination of boundary conditions imposed by structure, recharge, and discharge; hydraulic 
gradients in three dimensions; and bulk aquifer properties of units.  Modeling activities will use 
the resulting information to calculate groundwater flow paths, fluxes, and velocities within the 
saturated zone.  This investigation included three studies developed to accomplish the following:
1.	Study 8.3.1.2.3.1 (characterization of the site saturated zone groundwater flow 
system):  This study was to:
? Determine the hydrogeologic nature of the Solitario Canyon fault in the saturated 
zone
? Refine the spatial and temporal distribution of the potentiometric surface at the 
site to determine hydraulic gradients and groundwater flow magnitudes and 
directions
? Analyze water-level fluctuations to determine their causes and to estimate 
formation properties
? Analyze previously completed single- and multiple-well hydraulic-stress tests 
conducted in the C-holes to determine types of flow, hydraulic boundaries, and 
bulk hydraulic properties
? Conduct multiple-well interference testing in the C-holes to determine hydraulic 
properties, the appropriateness of anisotropic porous-media or fracture-network 
models, and the appropriateness of single-well or multiple-well tests
? Conduct single- and multiple-well conservative tracers tests at the C-holes and 
throughout the site to determine transport properties
? Conduct reactive tracer tests in the C-holes and throughout the site to determine 
properties of the geologic media that will affect retardation of radionuclides in the 
saturated zone.
2.	Study 8.3.1.2.3.2 (characterization of the saturated zone hydrochemistry):  This study 
was to:
? Describe the spatial variations in chemical composition of saturated zone 
groundwaters in the regional and site areas through analysis of representative 
water samples collected from wells and springs
? Describe the chemical and isotopic composition of the upper part of the saturated 
zone through analysis of representative water samples collected from the upper 
100 m of the saturated zone
? Conduct geochemical modeling to identify chemical and physical processes that 
influence groundwater chemistry
? Aid in the identification and quantification of groundwater travel times, climatic 
conditions during periods of recharge, and fluxes to and from the saturated zone 
by analyzing the chemical and isotopic compositions of interstitial-water and gas 
samples collected from immediately above the water table.
3.	Study 8.3.1.2.3.3 (saturated zone hydrologic system synthesis and modeling):  This 
study was to:
? Synthesize available data into a conceptual model and make a qualitative analysis 
of how the site saturated zone hydrogeologic system was functioning
? Develop fracture-network models for simulating groundwater flow and 
conservative solute transport and relate results of hydraulic and conservative-
tracer tests in wells to fracture-network characteristics
? Develop a comprehensive site-scale model of groundwater flow and transport to 
simulate groundwater flow direction and magnitude for input into travel-time 
calculations and evaluate the appropriateness of the porous-media and 
fracture-network concepts.
Changes and Status.  The primary objectives of this investigation have not changed since the 
SCP (DOE 1988) was issued.  The SCP, however, described a more extensive program of data 
collection.  The studies for this investigation have evolved based on technical information 
obtained from laboratory and field studies, model development and data application activities of 
the site characterization program.  Rapidly increasing scientific understanding, along with 
periodic TSPA, have enabled focusing the ongoing site characterization program on the 
remaining uncertainties that are significant to the suitability of the potential repository site 
(DOE 1994a).  Reevaluation and prioritization of Project needs (DOE 1994a) has been a 
continuous process based on scientific judgment and resource availability, governed by scientific 
criteria to ensure that data needed for site description, performance assessment, and design 
purposes were collected and analyzed; and to eliminate data-collection redundancy and overlap 
that would result from completion of all the studies in the SCP (DOE 1988).  The data collection 
needs have been further analyzed and refined as additional knowledge has been gained through 
site characterization activities.  This process has resulted in the following changes to the 
investigation:
1.	In the site-scale saturated zone groundwater flow system study (8.3.1.2.3.1), the study 
of the Solitario Canyon fault in the saturated zone has not been conducted and is not 
included in the long-range plan.  This is a result of the judgment (CRWMS 
M&O 1996a, p. A-6) that Solitario Canyon fault is not considered as crucial to 
predicting movement of radionuclides in the saturated zone as are hydrogeologic 
features and conditions down-gradient from the repository area.  Although 14 of the 
planned 22 water table boreholes were drilled in the early 1980s, only one of the 
additional 8 water table holes described in the SCP (DOE 1988) has been drilled 
(USW WT-24).  Water table boreholes that have not been drilled include two for the 
Solitario Canyon fault study and a second to investigate the large hydraulic gradient.  
Some hydraulic tests have been conducted in borehole USW G-2, but these tests 
resulted in no new major understanding, and the nature and cause of the large 
hydraulic gradient remain unresolved.  Two possible hydrogeologic models for the 
large hydraulic gradient have been described by Fridrich et al. (1994).  As a result, 
estimates of saturated zone flux, flow velocities, and dilution beneath the site may 
differ considerably for different explanations of the cause of the large hydraulic 
gradient (Luckey 1996, p. 2).  During FY 2000 and FY 2001, a comprehensive 
analysis of site saturated-zone water levels was performed to provide the saturated-
zone, site-scale flow and transport model with the configuration of the potentiometric 
surface and to target water-level data for model calibration (USGS 2001b).  At the end 
of FY 2001, responsibility for maintaining the site water-level monitoring network 
was assumed by the University of Nevada Las Vegas Harry Reid Center.
	The Project has recognized the need for additional drilling to investigate the nature of 
the large hydraulic gradient.  Consequently borehole USW WT-24 was drilled and 
partially tested in an attempt to reduce the uncertainty associated with the existence of 
the large hydraulic gradient north of the potential repository site and to determine 
whether or not perched water exists in the area.  Water-quality sampling and hydraulic 
testing have confirmed that perched water exists on top of the Topopah Spring Tuff 
basal vitrophyre at the location of USW WT-24.  Further, deepening of borehole 
USW WT-24 into the Prow Pass Tuff revealed an apparent water level that seems to 
be consistent with the large hydraulic gradient.  (Note:  USW WT-24 was completed at 
a depth of about 2834 feet (864 m) on May 14, 1998.  For information on drilling 
progress, see CRWMS M&O 1998o.)
	Although the C-holes multiple-well interference and tracer tests have been conducted 
mostly as planned, not as many of the high-producing flow zones have been tested as 
originally planned, and testing at the low-producing zone will probably be limited 
(Progress Report #16, Section 3.1.14 (DOE 1997a).  To date, cross-hole hydraulic and 
tracer tests at the C-holes have been conducted in the lower part of the Bullfrog Tuff 
and the Prow Pass Tuff.  The Prow Pass tests were completed in February 1999 and 
data were submitted to the Project technical database.  In FY 2000 and FY 2001, final 
calibrations were obtained for equipment used in the C-holes tests (transducers and 
flow meters) and data packages were modified.  In addition, data, analyses, and 
interpretations from the C-holes hydraulic and tracer tests were compiled as input to 
the saturated-zone in situ-testing AMR, which is in preparation.
	C-holes testing was reduced in scope in accordance with the priorities and planning 
assumptions for site investigations implemented for FY 1996 (CRWMS M&O 1995a, 
Volume 1, p. 6.3-62).  In addition, the sequencing of testing has been modified so that 
hydraulic, conservative-tracer, and reactive-tracer tests are being conducted 
sequentially in a single flow zone before conducting any tests in the next flow zone.  
Although single-well hydraulic tests have been conducted in two water table holes 
(USW WT-10 and UE-25 WT#12), the results are of limited value (O’Brien 1997, 
p. 35) because storativity data were not obtainable from the tests, and well-bore losses 
imparted additional uncertainties to the test results.  Therefore, no other single-well 
hydraulic or tracer tests are planned.  Instead, a second multiple-well test site has been 
drilled along a flow path south of the repository site, and the complex is now being 
called the Alluvial Testing Complex (ATC).  The multiple-well test site being 
considered is near the proposed 20-km compliance boundary (probably near 
U.S. Highway 95) and will be implemented cooperatively with the Nye County 
EWDP.  This test site offers the opportunity for hydraulic and tracer testing in the 
alluvium.  A few widely spaced wells were drilled in FY 1999 by Nye County, and 
one of these (NC-EWDP-19D1) was chosen for the ATC.  Additional wells were 
drilled in FY 2000 to obtain a closely spaced well cluster that allows hydraulic and 
tracer testing over reasonable time frames.  Hydraulic and tracer tests were conducted 
at the ATC during FY 2000 and FY 2001 to determine hydrologic properties and to 
measure the reduction in the concentration of solutes as they move through the 
saturated zone.  Results from the Nye County EWDP and the Alluvial Testing 
Complex are summarized in Section 3.4 of Progress Report 24 (in progress).
2.	In the saturated zone hydrochemistry study (8.3.1.2.3.2), the SCP (DOE 1988) called 
for intensive water and gas sampling from discrete intervals in 22 water table holes, 
14 existing and 8 new holes.  Hydrochemical testing was to include the clean out of all 
existing water table holes, extraction and analysis of interstitial water from cores of the 
new holes, and multi-element geochemical analyses of selected samples.  Although a 
few mixed-interval samples have been collected from two water table holes, the 
C-holes, and USW G-2, the site saturated zone hydrochemistry study remains only 
partially implemented.  Subsequent to the SCP, a plan was devised for in situ 
determinations of pH, Eh, and temperature in all 22 water table holes using a 
sophisticated downhole hydrochemical tool.  However, this plan was abandoned 
because of the high cost of the tool, uncertain potential for increasing knowledge, and 
the need to support critical saturated zone modeling efforts.  Although a limited 
number of water samples have been collected for chemical and isotopic analyses from 
springs during the regional study near Death Valley, the regional hydrochemistry 
study also remains only partially implemented.
	The saturated zone hydrochemistry study has not been implemented as planned 
because of the programmatic judgment (CRWMS M&O 1995a, Volume l, p. 6.3-66) 
that saturated zone hydrochemistry studies would have less impact on site suitability 
determinations than other studies and were therefore assigned a lower priority.  This is 
consistent with the strategy described in the Program Plan (DOE 1994a, Volume 1, 
Appendix A, p. A-4) that not all studies in the SCP (DOE 1988) would be completed 
before the suitability of Yucca Mountain is evaluated.  It should be kept in mind that 
the primary purpose of the saturated zone hydrochemistry study was to use 
hydrochemical and isotopic data to corroborate purely hydrogeologic evidence of 
regional and site-scale groundwater sources, recharge, fluxes, flow paths, and travel 
times.  Hydrochemical corroboration for regional flow paths has been adequately 
accomplished, as described below.  However, a similar evaluation at site scale may not 
be possible at present because of a lack of hydrochemical data from existing boreholes 
in the immediate vicinity of Yucca Mountain.  The importance of the hydrochemical 
corroboration at the site scale is debatable and does not currently have a high priority.
	In FY 1998, because the NRC announced its intention to issue new disposal 
regulations specific to Yucca Mountain (which ultimately became 10 CFR Part 63) 
that would be dose based, the Project re-evaluated the need for hydrochemical 
investigations in the saturated zone and implemented systematic hydrochemical 
sampling of wells down-gradient from Yucca Mountain.  The focus of this testing has 
shifted to the Nye County wells along U.S. Highway 95 and in the northern Amargosa 
Desert because of their proximity to the proposed compliance boundary.  
Consequently, hydrochemical and isotopic sampling of wells down-gradient from 
Yucca Mountain continued during FY 1999, FY 2000, and FY 2001 to help determine 
flow paths in the saturated zone.
	Regional hydrogeochemical information has been collected by other programs along 
the likely paths of regional groundwater flow.  The regional data, combined with the 
limited data collected under this study, have been used to enhance confidence in the 
regional groundwater flow model.  The geochemical “signatures” of greatest interest 
are distributions of major dissolved ions and stable isotope ratios that occur over large 
scales and are indicative of general mixing and geochemical evolution along regional 
flow paths.  Accordingly, following calibration of the regional groundwater flow 
model, general flow-path maps were generated from model output and superimposed 
over a series of maps depicting regional hydrochemical data.  Apparent hydrochemical 
evolution along major flow paths was evaluated qualitatively to corroborate the 
possibility or likelihood of the flow path generated by the model.  These evaluations 
were performed along general flow paths from major recharge areas (i.e., Spring 
Mountains, Pahute Mesa, Sheep Range) to major discharge areas (i.e., Ash Meadows, 
Oasis Valley, Furnace Creek Ranch).  Even though the hydrochemical-data sets along 
these major flow paths are somewhat incomplete and discontinuous, in general, the 
hydrochemical evaluation corroborated the flow paths generated by the flow model.
	To continue this analysis, a new activity was implemented in FY 1999 titled “Isotopic 
and Hydrochemical Saturated Zone Studies” with the principal objective of delineating 
saturated zone flow paths and establishing travel times down-gradient from the 
potential repository using hydrochemical and isotopic data.  The results of the initial 
phase of this activity are summarized in Progress Report 23 (DOE 2001c).  The results 
are being used to constrain and validate the regional groundwater flow model in terms 
of testing the credibility of model flow paths with regard to the chemical and isotopic 
parameters along these suggested pathways.  This effort continued in FY 2000 and FY 
2001 and is expected to continue for several more years.
3.	In the site saturated zone hydrologic system synthesis and modeling study 
(8.3.1.2.3.3), construction and calibration of a site-scale, porous-media-equivalent 
flow model is proceeding generally as planned, and a preliminary model has been 
completed (Czarnecki et al. 1997).  However, because of the application of 
sophisticated geographic information system and geologic-modeling techniques, the 
geologic framework model on which the flow model is based may be more rigorous 
and detailed than was envisioned when the SCP (DOE 1988) was issued.
	Although not completely calibrated, the final saturated zone, site-scale model will 
contain uncertainty for several reasons:
? Limited field tests have been completed to characterize the large-scale anisotropy 
because of a sparseness of hydraulic-test locations to serve as control points for 
model calibration
? Uncertainty persists about the cause of the large hydraulic gradient
? Uncertainty persists about fluxes at the northern model boundary because no 
potentiometric data are available in the Timber Mountain area to calibrate the 
regional model from which boundary fluxes are derived for the site-scale model
? Sparse hard data are available on the geometry and hydraulic properties of the 
Paleozoic carbonate aquifer underlying Yucca Mountain
? High quality chemical and isotopic data from the saturated zone are not sufficient 
to corroborate flow patterns.
	The degree to which these uncertainties in the saturated zone flow model might affect 
its use in TSPA was ascertained during the saturated zone flow and transport model 
abstraction and testing workshop, held April 1-3, 1997 in Denver, Colorado (CRWMS 
M&O 1997a).  The workshop identified and prioritized key uncertainties about 
saturated zone flow and developed analysis plans to aid in the resolution of 
high-priority issues.
	Alternative representations of the large hydraulic gradient north of the site were not 
addressed by an analysis plan (CRWMS M&O 1997a, pp. 1-12).  This is because it 
was the consensus of the workshop participants that these alternative representations 
would have little or no impact on the predicted concentrations of radionuclides 30 km 
down-gradient from the potential repository.  However, alternative representations of 
the large hydraulic gradient have been tested as part of the ongoing development and 
refinement of the site-scale saturated zone flow model.  If the potential impacts to 
onsite performance appear to be large from these alternative flow models, the 
alternative representations can be incorporated into the abstraction process at a later 
date (CRWMS M&O 1997a, pp. 1-12).  Abstractions are developed using a conceptual 
model that has a large hydraulic gradient.
	The Project also conducted a saturated zone flow and transport expert elicitation 
(CRWMS M&O 1998b).  The experts generally agreed that groundwater in the 
saturated zone flows from beneath the repository to the southeast and south primarily 
through fractured volcanic tuffs of the middle volcanic aquifer and the valley fill 
alluvium (DOE 1998a, Volume 3, Section 3.7.1.4).  Some panel members suggested 
that sorptive characteristics of the alluvium could significantly contribute to 
retardation of some radionuclides.  They expected faults and fracture zones to have 
important impacts on flow in the volcanic units.  The panel members offered 
alternative hypotheses for the large hydraulic gradient north of Yucca Mountain, and 
there was disagreement regarding the importance of this feature to repository 
performance.  The panel members did agree that any major transient change in the 
large hydraulic gradient is unlikely.  The panel members also generally concurred with 
interpretations of geochemical and paleospring data indicating water table rises of 80 
to 120 m (260 to 395 ft) beneath the repository in response to past climatic variations.
	For transport of contaminants in the saturated zone, the experts emphasized the 
limitations of processes that would cause dilution of contaminant concentrations.  The 
experts believe that transport would be by movement in vertically thin plumes through 
flow tubes beneath the repository.  Dilution of contaminants would occur by vertical 
transverse dispersion and transient fluctuations in the direction of the hydraulic 
gradient.  The experts generally rejected a mixed tank model in which contaminated 
flow from the unsaturated zone would mix on a large scale with uncontaminated 
groundwater in the saturated zone.  Consequently, the flow model, developed by 
Czarnecki et al. (1997), was not used for the TSPA-VA flow and transport 
calculations.  Instead, simulations of radionuclide transport in the saturated zone for 
the TSPA calculations were performed with six one-dimensional flow tubes using the 
FEHM code (V2.0 STN:  10031-2.0-00), which simulates heat and mass transfer for 
finite elements (DOE 1998a, Volume 3, Section 3.7.2).  Streamtubes are taken from a 
concept in classical fluid dynamics that is used to visualize and estimate the behavior 
of the elements of a flow system.  Each of the six streamtubes is a continuation of a 
groundwater flow path from the repository in the unsaturated zone.
	For TSPA-SR, the updated saturated zone flow and transport model (CRWMS M&O 
2000ak) was used to evaluate the migration of radionuclides from their introduction at 
the water table below the potential repository to the release point to the biosphere, 
which was assumed to be a hypothetical well down-gradient from the site (DOE 
2001a, Section 4.2.9.4).  This component of the analysis was coupled with the 
transport calculations for the unsaturated zone, which describe the movement of 
contaminants in downward percolating groundwater from the potential repository to 
the water table.  The input to the saturated zone flow-and-transport calculations is the 
spatial and temporal distribution of simulated mass flux at the water table that has 
been transported through the unsaturated zone.
	Although “generic” fracture-network-modeling techniques have been developed, a 
fracture-network model of the C-hole complex has not yet been developed because the 
extensive data that would have been required exceeded the data that could be 
collected.  Fracture-network models require intensive fracture mapping and 
characterization in order to develop a simulated fracture network that is statistically 
similar to the “real” network.  The level of detail required for the fracture data is on 
the order of that obtained in the ESF.  That degree of fracture characterization is not 
possible in vertical boreholes (even at the scale of the three C-holes) because of 
limited access to the rock mass and because of the bias introduced by boreholes 
intersecting subvertical fractures.  Although an exhaustive series of tracer tests might 
be possible to isolate and map individual fractures from one C-hole to another, such 
tests would be extremely time-consuming and very costly.  Moreover, fracture-
network modeling has been abandoned in general because analysis of field data and 
reasonable conceptual models of saturated zone flow at scales of interest (drawdown 
transients in the C-holes and in neighboring wells as far as 3.5 km) fit continuum 
analytic models.  Furthermore, dispersivities derived from tracer tests at the C-holes 
exhibit both continuum and non-continuum.
1.2	GEOCHEMISTRY PROGRAM (SCP SECTION 8.3.1.3)
The geochemistry program was intended to characterize site geochemical conditions and 
evaluate the effectiveness of the geochemical “barriers” that are expected to inhibit the transport 
of radionuclides away from the potential repository.  The program of geochemical testing 
described in the SCP (DOE 1988) concerned characterizing those areas of the site that lie beyond 
the “altered zone” (see Section 1.15 of this document).  The major purpose of the geochemistry 
program was to quantify the radionuclide retardation factor.  This factor was expected to be 
greater than one, and values greater than one were expected to provide added confidence to the 
calculations of transport to the accessible environment based on advective and dispersive 
transport calculations.
1.2.1	Studies to Provide Information on Water Chemistry within the Potential 
Emplacement Horizon and Along Potential Flow Paths (SCP 
Investigation 8.3.1.3.1)
Background and SCP Plans.  The objectives of this investigation were to provide a 
groundwater chemistry model that would explain the present groundwater composition as a 
result of interactions of the groundwater with minerals and be able to predict future variations in 
groundwater chemistry (under anticipated and unanticipated conditions) that could alter 
radionuclide flux through the saturated and unsaturated zone.  This investigation included one 
study developed to accomplish the following:
Study 8.3.1.3.1.1 (groundwater chemistry modeling):  This study was to develop pre- and 
post-emplacement groundwater chemistry models that would integrate the unsaturated and 
saturated zone data with the processes of water infiltration, water flow, and mineralogic changes 
to develop a mechanistic description of the current and future groundwater chemistry.  The study 
was also intended to consider changes in infiltration as influenced by climatic conditions; 
long-term mineralogic changes, particularly those influenced by the thermal pulse from 
emplaced waste; and changes in the material properties caused by the emplaced waste, or 
possible igneous activity.  These models have been integrated with several investigations in the 
geochemistry program.
Changes and Status.  The primary objectives of this investigation have not changed since the 
SCP was issued.  The SCP (DOE 1988), however, described a more extensive program of data 
collection.  The studies for this investigation have evolved based on technical information 
obtained from laboratory and field studies, model development and data application activities of 
the site characterization program.  Rapidly increasing scientific understanding, along with 
periodic TSPA, have enabled focusing the ongoing site characterization program on the 
remaining uncertainties that are significant to the design, operation and safe performance of the 
potential repository (DOE 1994a).  Reevaluation and prioritization of Project needs 
(DOE 1994a) has been a continuous process based on scientific judgment and resource 
availability, governed by scientific criteria to ensure that data needed for site description, 
performance assessment, and design purposes were collected and analyzed.  Data-collection 
redundancy and overlap have been eliminated.  The data-collection needs have been further 
analyzed and refined as additional knowledge has been gained through years of site 
characterization activities.  This process has resulted in changes to the investigation.
In the groundwater chemistry modeling study (8.3.1.3.1.1), the number of laboratory 
experiments on water-rock interaction has been decreased, resulting in remaining uncertainty 
about the quantitative models of the processes that control water chemistry in the saturated and 
unsaturated zones.  To address a majority of these uncertainties, saturated zone hydrochemistry 
testing is under way both at Yucca Mountain and in the new Nye County EWDP wells.  This 
testing provides information about spatial variability in water chemistry, oxidation-reduction 
potential (Eh), pH, colloid content, and groundwater flow using both chemical and isotopic 
tracers.  The oxidation-reduction chemistry of the saturated zone may play a major role in the 
retardation of the very soluble radionuclides Np and Tc (see Section 1.2.4, Study 8.3.1.3.4.3).  
Uncertainties also involve the rate and manner in which volcanic glass is altered when it comes 
in contact with different water compositions.  Alteration of glass can strongly influence pH and 
the concentrations of other constituents in solution.
Information has been provided to studies of radionuclide retardation and transport.  Additional 
information on the solid phases involved in the alteration of volcanic glass would be needed to 
develop detailed deterministic models of groundwater chemistry.  The solid phases buffer the 
dissolved concentrations of major solutes which, in turn, influence the distribution of dissolved 
radionuclides.  A range of possible water and rock compositions, which may change with time, 
are expected to be encountered along the likely paths of radionuclide transport in the unsaturated 
and saturated zones.  Some of the compositional variation will likely result from 
repository-induced effects (e.g., temperature increases).  To the extent that these variations are 
known or predictable, they will be included in the hydrochemical model.  However, significant 
uncertainty regarding the identity of secondary phases and reaction kinetics involving these 
phases will remain.  The extent to which these variabilities and uncertainties affect radionuclide 
transport will be bounded in future TSPAs.  In FY 2000 and FY 2001, comprehensive reports on 
the geochemistry of the unsaturated and saturated zones were developed as input to TSPA-SR 
(BSC 2001j; CRWMS M&O 2001b).
1.2.2	Studies to Provide Information on Mineralogy, Petrology, and Rock Chemistry 
within the Potential Emplacement Horizon and Along Potential Flow Paths 
(SCP Investigation 8.3.1.3.2)
Background and SCP Plans.  The purpose of this investigation is to provide the baseline set of 
data and a basic understanding of the natural environment in which geochemical and other 
processes interact.  The objectives of this investigation are to determine the three-dimensional 
distribution of mineral types, compositions, and abundances in rocks beyond the host rock that 
provide pathways to the accessible environment; determine the timing, temperatures, and 
hydrologic conditions of past alteration at Yucca Mountain; study experimentally the

dehydration of smectite, zeolite, and glass; and use the results to develop descriptive and 
predictive models of mineral distributions along potential pathways to the accessible 
environment.  This investigation includes two studies developed to accomplish the following:
1.	Study 8.3.1.3.2.1 (mineralogy, petrology, and chemistry of transport pathways):  This 
study was to
? Determine the petrologic variability within the devitrified Topopah Spring Tuff at 
Yucca Mountain and define the stratigraphic distribution of variability
? Determine the three-dimensional distribution chemistry and total abundance of all 
major rock-matrix minerals between the host rock and the accessible environment
? Determine the distributions of minerals within fractures at Yucca Mountain.
2.	Study 8.3.1.3.2.2 (history of mineralogy and geochemical alteration at Yucca 
Mountain):  This study was to:
? Determine past temperatures from alteration mineral assemblages as a means to 
estimate the long-term thermal stabilities of important sorptive phases, such as 
clinoptilolite, and of the silica polymorphs that can influence water composition, 
precipitation, and the stabilities of other silicate minerals
? Investigate correlations between alteration mineralogy and rock hydrologic 
properties so that patterns of alteration can provide technical justification for 
choices of bounding and extrapolated property values used in numerical 
simulations
? Coordinate mineralogic and textural analysis with isotopic studies of groundwater 
percolation to promote understanding of fault, fracture, and matrix flow paths
? Determine how minerals and glasses in the rocks at Yucca Mountain will 
dehydrate and transform under expected thermal loads and investigate the ability 
of zeolites and smectites to rehydrate after the peak in temperature.
Changes and Status.  The primary objectives of this investigation have not changed since the 
SCP was issued.  The SCP (DOE 1988, pp. 8.3.1.3-43 to -48), however, described a more 
extensive program of data collection.  The studies for this investigation have evolved based on 
technical information obtained from laboratory and field studies (Vaniman et al. 1996, 
pp. 641-646; Levy et al. 1996, pp. 785–789), model development and data application activities 
of the site characterization program.  Rapidly increasing scientific understanding, along with 
periodic TSPA, have enabled focusing the ongoing site characterization program on the major 
uncertainties that are significant to the design, operation and safe performance of the potential 
repository (DOE 1994a).  Reevaluation and prioritization of Project needs (DOE 1994a) has been 
a continuous process based on scientific judgment and resource availability, governed by 
scientific criteria to ensure that data needed for site description, performance assessment, and 
design purposes are collected and analyzed.  Data-collection redundancy and overlap have been 
eliminated.  The data-collection needs have been further analyzed and refined as additional 
knowledge has been gained through years of site characterization activities (Vaniman et al. 1996, 
pp. 641-646; Levy et al. 1996, pp. 785-789).  In addition, resource constraints as Site 
Recommendation and license application approach, has led to termination of some mineralogic 
and petrologic work or deferral to the outyears.  This process has resulted in the following 
changes to the investigation:
1.	In the mineralogy, petrology, and chemistry of transport path