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INTRODUCTION

The Committee for Yucca Mountain Peer Review: Surface Characteristics, Preclosure Hydrology, and Erosion (Appendix B) was formed by the National Research Council to provide an independent, expert peer review of the U.S. Department of Energy's (DOE's) Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion (DOE Report YMP/TBR-001, Revision 0, April 1995), hereafter referred to as the TBR. This TBR describes and synthesizes scientific data, analyses, and interpretations concerning surface characteristics at Yucca Mountain, Nevada (see Figure 1.1 at the end of this chapter), hydrology relevant to the preclosure phase of the candidate repository, and hillslope and channel erosion. This is the first of a series of planned technical basis reports on Yucca Mountain.1 These reports will be used by the DOE Yucca Mountain Site Characterization Office (YMSCO) to assess the suitability of the Yucca Mountain site as a permanent repository for the disposal of spent nuclear fuel and high-level nuclear waste.

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The Department of Energy is in the process of reorganizing its site characterization program in response to cuts in its FY1996 budget. The committee understands that the DOE may not issue the remaining technical basis reports, but may instead focus on total system performance assessment—which was to be the topic of the sixth and final technical basis report.



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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion 1 INTRODUCTION The Committee for Yucca Mountain Peer Review: Surface Characteristics, Preclosure Hydrology, and Erosion (Appendix B) was formed by the National Research Council to provide an independent, expert peer review of the U.S. Department of Energy's (DOE's) Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion (DOE Report YMP/TBR-001, Revision 0, April 1995), hereafter referred to as the TBR. This TBR describes and synthesizes scientific data, analyses, and interpretations concerning surface characteristics at Yucca Mountain, Nevada (see Figure 1.1 at the end of this chapter), hydrology relevant to the preclosure phase of the candidate repository, and hillslope and channel erosion. This is the first of a series of planned technical basis reports on Yucca Mountain.1 These reports will be used by the DOE Yucca Mountain Site Characterization Office (YMSCO) to assess the suitability of the Yucca Mountain site as a permanent repository for the disposal of spent nuclear fuel and high-level nuclear waste. 1   The Department of Energy is in the process of reorganizing its site characterization program in response to cuts in its FY1996 budget. The committee understands that the DOE may not issue the remaining technical basis reports, but may instead focus on total system performance assessment—which was to be the topic of the sixth and final technical basis report.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion The information in the TBR is organized into four chapters: Chapter 1 provides a brief discussion of the purpose and scope of the TBR and of the geologic setting and history of the Yucca Mountain site. Chapter 2 of the TBR describes the surface characteristics of the site, including drainage characteristics, drainage evolution, and the distribution and ages of surficial deposits. This chapter also assesses the potential for surface flooding that could affect the performance of an underground repository prior to closure. Chapter 3 of the TBR describes the preclosure hydrology2 of the site. It describes ground water conditions in the unsaturated zone related to the occurrence of perched water. It also assesses the potential for subsurface flooding and the availability of an adequate water supply for repository construction. Chapter 4 of the TBR addresses hillslope and channel erosion at the Yucca Mountain site. It provides descriptions of hillslope evolution and erosion processes. It discusses the Quaternary geochronologic methods that were used to date land surfaces in order to calculate long-term rates of hillslope and channel erosion. Chapter 5 provides a very brief summary of the conclusions in Chapter 2,Chapter 3, and Chapter 4 of the TBR. It is important to recognize that the topics addressed by the TBR concern different timescales. Surface flooding and hydrology are considered only during the preclosure phase of the repository, which, as noted in footnote 2, will probably last a few tens of decades. Erosion is considered during the entire period of regula- 2   The term preclosure hydrology as used in the TBR refers to ground water and perched water conditions at the site during repository construction, operation, and closure. The estimated duration of the preclosure phase of the repository is not explicitly stated in the TBR. A 50- to 100-year estimate was provided to the committee during one of its information-gathering sessions.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion tory concern for the repository. At present, the U.S. Environmental Protection Agency (USEPA) and U.S. Nuclear Regulatory Commission (USNRC) regulations set this period at 10,000 years. However, the USEPA is in the process of developing health and safety standards for high-level waste disposal at Yucca Mountain. As part of this effort, the National Research Council was asked to provide an analysis of the scientific bases for these standards. An expert committee was formed3 to provide this assessment; the committee recommended that the health and safety standards should apply to periods of peak risk to the public, which might extend beyond 10,000 years (National Research Council, 1995). REVIEW CRITERIA The committee addressed its review to the scientific and technical aspects of the TBR as prescribed by its statement of task (see Appendix C). The committee focused its efforts on assessing the validity of the data and interpretations and the adequacy of the treatment of uncertainties in describing the current state of understanding. For each of the major topics in the report (i.e., surface characteristics, preclosure hydrology, and erosion), the committee identified the major scientific or technical interpretations and conclusions. The committee examined the quality of the data and methodologies used to support these interpretations and conclusions. The committee also assessed the synthesis of analyses used to support the interpretations and conclusions. 3   Committee on Technical Bases for Yucca Mountain Standards.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion The committee did not make any judgments about the suitability of the Yucca Mountain site as a nuclear waste repository, nor did it consider regulatory compliance. That is, the committee did not consider whether the site would satisfy the qualifying or disqualifying conditions of Title 10, Part 960 of the Code of Federal Regulations4 (10 CFR 960). Short discussions of qualifying and disqualifying conditions are given at the beginning of Chapter 2,Chapter 3, and Chapter 4 in the TBR, but as specified in the task statement, they were not considered by the committee in its review. The committee relied on its collective expert judgment as informed by conventional scientific usage in applying the “validity” and “adequacy” criteria in the statement of task. The committee applied these criteria as follows: Validity of Data All data used in the analyses should be identified clearly and should be included in the report. The data should be collected and analyzed by using generally accepted scientific methods, that is, methods typically employed by other scientists on problems of a similar nature. Data collection and analysis methodologies should be explained clearly. 4   Title 10, Part 960 of the Code of Federal Regulations, General Guidelines for the Recommendation of Sites for Nuclear Waste Repositories.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion Validity of Interpretations and Conclusions The interpretations and conclusions should be stated clearly in the report. The interpretations and conclusions should be supported by available data. The interpretations and conclusions should be based on generally accepted methods of data analysis. All available relevant and technically acceptable data, including data collected by workers not associated with the site characterization program, should be considered explicitly in the analyses. All assumptions in the analyses should be stated clearly. All plausible alternative conclusions and findings should be considered against available data. Adequacy in the Treatment of Uncertainties Uncertainties in the methodologies, data, findings, and conclusions should be identified clearly and discussed. The need for additional data collection to reduce uncertainties should be discussed. These review criteria subsume questions a-d in the statement of task (Appendix C). The statement of task gives the committee flexibility to apply other criteria in its review of this TBR (see Appendix C). The committee decided also to assess the quality of presentation of

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion the TBR and the process for preparing it. The criteria that the committee applied in these aspects of its review are given below: Presentation The data, analyses, and conclusions and findings should be presented in a clear and concise manner. The graphics should be informative and adequate to illustrate and support the interpretations and conclusions. Report Preparation The TBR should be prepared with the direct involvement of scientists whose data and conclusions are used in the report. The science in the TBR should be peer reviewed by the scientists whose data and conclusions are used in the report. REVIEW BASIS The committee wishes to emphasize to the reader, and particularly to DOE managers, that its evaluation of the statement of task questions related to alternative interpretations, testing, and uncertainty reduction (i.e., questions c-e in Appendix C) is based entirely on scientific judgment. The committee made no attempt to evaluate these questions in terms of DOE management decisions related to the suitability of Yucca Mountain as a high-level waste

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion repository. The committee is not properly constituted to make such judgments, and it is specifically prohibited from doing so by the statement of task. The committee recognizes, however, that the reduction of scientific uncertainty to very low levels is difficult and could require lengthy study. The committee believes that DOE scientist-managers and oversight bodies must ultimately judge how much scientific data is needed to make sound and effective policy decisions regarding the Yucca Mountain site. The committee attempted to identify weaknesses in data, methodologies, interpretations, and conclusions in the TBR. In some cases, the committee recommended that additional work be done to significantly improve scientific understanding, and—equally as important—the scientific credibility of the site characterization program. The committee made no attempt to determine whether the identified weaknesses would have a significant impact on the management decision to site a facility at Yucca Mountain. Nor has the committee determined whether the recommended work would change the management decision to site such a facility. In the committee 's view, such judgments are best left to DOE scientist-managers and appropriate oversight bodies. SOURCES OF INFORMATION USED IN REVIEW The primary source of materials for the committee's review was the TBR itself and many of the supporting materials referenced in Appendix A of the TBR. The committee requested, and DOE provided, multiple copies of all of the materials cited in Appendix A of the TBR. The committee consulted these materials frequently during the course of its review.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion The committee also held two information-gathering meetings to obtain additional information about the report from DOE and other federal agencies, the State of Nevada, and other interested organizations and individuals. Both meetings were open to the public. At the request of the committee, the YMSCO distributed advance copies of meeting notices to the organizations and individuals it had identified as “stakeholders” in the site characterization process. Prior to its first meeting, the committee asked federal, state, and local government agencies and organizations with an interest in Yucca Mountain to designate formal liaisons to the committee. A list of liaisons is given in Appendix D. These liaisons were invited to provide the committee with information they deemed relevant to its review of the TBR, either orally at the information-gathering meetings or in writing. In return, these liaisons were provided with lists of documents received by the committee, advance copies of meeting agendas, and copies of minutes of open meetings, to keep them fully informed concerning the committee's work. The committee's first information-gathering meeting was held on July 19-20, 1995, in Las Vegas, Nevada. At this meeting, the committee received formal presentations and written materials from several liaisons. The committee also obtained comments from liaisons and other members of the public in public comment sessions scheduled during each day of the meeting. The agenda for this meeting and the list of speakers can be found in Appendix E. The committee's second information-gathering meeting was held on August 27-29, 1995, and was organized around a three-day field excursion to Yucca Mountain. The committee also held a half-day meeting at the Community Center in Beatty, Nevada, on

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion August 27, 1995, where it questioned scientists on the topics of perched water, water supply, and probable maximum flooding. The public was also given an opportunity to provide comments and information at this session. A copy of the agenda for this meeting appears in Appendix E. The purpose of the field excursion was to examine evidence in the field and to discuss data, analyses, and conclusions in the TBR with scientists who are working at the Yucca Mountain site. The excursion was organized by the committee with the assistance of staff from YMSCO and the Nevada Nuclear Waste Project Office. Field trip stops were selected by committee members to address their specific questions and concerns about the interpretations and conclusions in the TBR. At the committee's request, YMSCO and the Nevada Nuclear Waste Project Office designated scientists to make brief presentations or respond to the committee's questions at each stop. An agenda for the field excursion also appears in Appendix E, and the locations of the field trip stops are shown in Figure 1.1 and Figure 1.2. The committee found the open sessions and the field excursion to be very helpful in its review of this TBR. These sessions helped the committee to understand the process used by YMSCO to produce the TBR and also provided the committee with additional relevant scientific and technical information that was not referenced in the TBR. Some of this additional material was published after the release of the TBR. Other material was available prior to release of the TBR, but presumably was not deemed to be of direct relevance by those responsible for preparing the report. Although the TBR was reviewed on its own merits, this additional information was helpful to the committee in clarifying its thinking about the need for additional work and analyses. The committee did attempt to identify and obtain all materials

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion deemed relevant to its review. The review of the literature, however, was not exhaustive, due mainly to limitations of time. Additionally, there may be relevant literature that the committee was unable to identify or obtain. The exchanges that occurred during the open meetings and field excursion among the scientists who work for the many organizations concerned with Yucca Mountain were also very helpful to the committee in its review. These exchanges helped the committee to understand points of disagreement among scientists working in the Yucca Mountain area and the nature of uncertainties in the data, analyses, interpretations, and conclusions presented in the TBR. These exchanges also provided the committee with an enlightening view of science management at Yucca Mountain. The committee held three executive sessions during the course of its review of this TBR. Executive sessions were held after the two information-gathering meetings (discussed above), and a third executive session was held at the National Academy of Sciences' Beckman Center in Irvine, California, in October 1995. Executive sessions were held to conduct the following business: (1) the conflict-of-interest discussion, which is required by the National Research Council of all committees; (2) discussion of the statement of task; (3) discussion of information provided during the open sessions; (4) development of recommendations; and (5) drafting of the report. Following established practices of the Board on Radioactive Waste Management, the parent board to this committee, these executive sessions were closed to all but National Research Council committee and staff members. Although the minutes of these executive sessions were not distributed to the

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion sponsor, liaisons, or other members of the public, the minutes of all other sessions were made public. ORGANIZATION OF THIS REPORT The committee's detailed review of Chapter 2,Chapter 3, and Chapter 4 of the TBR is provided in Chapter 2 and Chapter 3 of this report.5 The committee's review of surficial characteristics and erosion is presented in Chapter 2 of this report. The review of preclosure hydrology is presented in Chapter 3. Chapter 4 of this report provides some general observations about the TBR and the processes used to produce it. This chapter also offers some constructive suggestions for improvements. This report is organized to group related topics and differs somewhat from the organization of the TBR. Table 1.1 provides a roadmap between the sections of the TBR and the review of those sections in this report. The committee chose this alternative organization scheme to reduce redundancy in its review, to provide better flow to the text, and to allow for a more logical development of ideas. Each major section in Chapter 2 and Chapter 3 of this review (indicated in the left-hand column in Table 1.1) is structured to provide an explicit discussion of each of the questions in the statement of task (Appendix C). The headings for these subsections and the corresponding statement-of-task questions (in italics) are shown below: 5   Chapters 1 and 5 of the TBR contain background and summary materials only. They were read but not reviewed by the committee.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion TABLE 1.1 Organization of the Review of the TBR Section of This Report Section in the TBR Chapter 1: Introduction — Chapter 2: Surface Characteristics and Erosion Potential 2.1 Review of Surficial Geology 2.2, 2.3, 2.4 Review of Erosion Potential of Alluvial Deposits 2.3, 2.4, 2.5, 4.4.3 Review of Quaternary Geochronology 4.3 Review of Erosion Rates 4.1, 4.2, 4.4, 4.6,a 4.7 Chapter 3: Preclosure Hydrology 3.1 Review of Surface Flooding 2.6 Review of Subsurface Flooding 3.2b Review of Water Resource Potential 3.3 Chapter 4: Concluding Comments — a The TBR has no Section 4.5. bPage 3-5 is miscollated, separating two parts of Section 3.2.2. Adequacy of Data Collection and Analysis. Have the data been collected and analyzed in a technically acceptable manner? Support for Technical Interpretations. Do the data, given the associated error and analytical and technical uncertainties, support the technical interpretations and conclusions made within the technical basis report?

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion Credible Alternative Interpretations. Are there credible alternative interpretations that would significantly alter the conclusions reached? Testing to Discriminate Among Alternative Interpretations. What testing, if any, would discriminate among alternative technical interpretations? If such testing is recommended, how effective would it be at reducing significant uncertainties? To aid the reader of this review, the committee has produced several figures for this report from materials obtained from DOE and its contractors. These figures are collated for the reader's convenience in this introductory chapter. Figure 1.1, which is modified from Figure 1.3-2 in the TBR, is a location map for the Yucca Mountain area showing major features and the locations of the field trip stops. Figure 1.2, which is modified from Figure 2.3-1 of the TBR, shows topography of Yucca Mountain and the location of the North Portal Site, South Portal Site, Shaft Site No. 2, and a few field trip stops. Figure 1.3 and Figure 1.4 are north-south and east-west cross sections, respectively, through Yucca Mountain. They show elevations, the location of the proposed repository, geology and structure, the position of the water table, and locations of selected wells. The committee has provided references as needed throughout this report to support the discussions and conclusions of its review. In certain parts of the review, it is useful for the reader to know which of the references were cited in the TBR and which are from other sources. In order to make this distinction clear, the committee has adopted the convention of boldfacing all of the references cited in the TBR.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion The committee recognizes that there is likely to be broad interest in this review of the TBR. Therefore, the committee has endeavored to write its report to be understandable to the educated lay person. The committee has avoided the use of unnecessary jargon and has used footnotes throughout this report to define specialized terms and explain complicated principles. It has also provided a list of acronyms and symbols in Appendix A.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion FIGURE 1.1 Generalized location map of the Yucca Mountain, Nevada, region (after TBR Figure 1.3-2). The numbered circles indicate the locations of the field trip stops. The numbers are keyed to the field trip agenda in Appendix E.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion FIGURE 1.2 Topography of Yucca Mountain and vicinity, showing the locations of the North Portal Site, South Portal Site, Shaft Site No. 2, and selected drillhole locations (after TBR Figure 2.3-1). The numbered circles indicate the locations of the field trip stops (see Appendix E). The Fortymile Wash Drainage Basin, which is partially shown in the figure, includes Yucca Wash, Sever Wash, Drillhole Wash, and Coyote Wash. The approximate position of Fortymile Wash is indicated by the dashed line.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion FIGURE 1.3 North-south cross section (A-A') through Yucca Mountain showing the elevation of the land surface, geologic units, major faults, and selected wells. The location of the proposed repository is projected onto the cross section. The figure is based on materials received from the DOE and its contractors during the committee's information-gathering sessions.

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Review of U.S. Department of Energy Technical Basis Report for Surface Characteristics, Preclosure Hydrology, and Erosion FIGURE 1.4 East-west (B'-B) cross section through Yucca Mountain showing the elevation of the land surface, geologic units, major faults, selected wells, and the location of the proposed repository. The figure is based on materials received from the DOE and its contractors during the committee's information-gathering sessions.