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1 Introduction and Task The Hanford Site was established by the federal government in 1943 as part of the secret wartime effort to produce plutonium for nuclear weapons. The site operated for about four decades and produced roughly two thirds of the 100 metric tons of plutonium in the U.S. inventory. Millions of cubic meters of radioactive and chemically hazardous wastes, the by-product of plutonium production, were stored in tanks and ancillary facilities at the site or disposed or discharged to the subsurface, the atmosphere, or the Columbia River. In the late 1 980s, the primary mission of the Hanford Site changed from plutonium production to environmental restoration. The federal government, through the U.S. Department of Energy (DOE), began to invest human and financial resources to stabilize and, where possible, remediate the legacy of environmental contamination created by the defense mission. During the past few years, this financial investment has exceeded $1 billion annually. DOE, which is responsible for cleanup of the entire weapons complex, estimates that the cleanup program at Hanford will last until at least 2046 and will cost U.S. taxpayers on the order of $85 billion (DOE, 1 998e).4 Although the "final" condition of the site (i.e., the condition of the site when the cleanup program is complete) has not yet been agreed upon by DOE, its regulators, and other interested parties, work is in progress to stabilize waste and restore the environment so that parts of the site can be released for other uses. After DOE cleanup is completed, however, large areas of subsurface contamination will still remain at the site, including groundwater contamination, and there will be large burial grounds that contain waste from both the defense and the cleanup missions. The cost and duration of the cleanup effort cited above do not account for the long-term investments that will be required to manage these contaminated areas until they no longer pose a hazard to humans or the environment.2 One of the most difficult cleanup problems at the Hanford Site involves remediation of the underground high-level waste storage tanks Life-cycle cost estimate fully escalated to year of expenditure. The estimated life-czycle cost in constant fiscal year 1998 dollars is about $51 billion. The report Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites (National Research Council, 2000c) discusses these long-term management challenges. See also From Cleanup to Stewardship (DOE, 1 999f) and A Report to Congress on Long-Term Stewardship (DOE, 2001~. 6

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Introduction and Task and the underlying soil and grounclwater in the 200 Area (see Chapter 2~. There are 177 underground storage tanks at the site, which collectively contain about 54 million gallons of high-level waste generated from plutonium separation processes. According to DOE, 67 of these tanks are known or suspected to have leaked high-level waste into the subsurface, and it is now recognized that some of this leaked material has reached groundwater. Part of the motivation for this National Research Council (NRC) study grew out of suggestions that the subsurface migration of radionuclides that leaked from these tanks was more extensive than had been predicted (see DOE [1997b] for details). It had been predicted that most radionuclides from these tank leaks would be effectively sorbed onto minerals contained in the subsurface sediments, thereby retarding their migration to groundwater. This assessment appeared to be supported by numerical models developed to predict radionuclide transport beneath the tanks. Such predictions were called into question, however, by actual measurements of radionuclide (cesium-137) distributions in boreholes around and beneath the tanks in the SX Tank Farm beginning in 1994 (DOE, 1996~. These measurements suggested that cesium-137 had migrated greater than 38 meters (125 feet) beneath the SX Tank Farm (DOE, 1 998a, pp. 4.50-4.52~.3 Although the actual extent of deep radionuclide migration and the mechanisms for such migration remain unclear (DOE, 1 997b), such observations have fueled public concerns and drawn attention to Hanford vadose zone issues in high levels of government (GAO, 1998~. Indeed, this discovery received a great deal of attention by the media and prompted congressional inquiries and a General Accounting Office investigation (GAO, 1998~. In response, and with the strong encouragement of DOE Headquarters, Hanford Site management established the Groundwater/\/adose Zone Integration Project in 1997 to coordinate and provide scientific and technical support for waste management and cleanup efforts under way at the site. The Integration Project was created through a memorandum of understanding among three preexisting organizations at the Hanford Site (see Chapter 3) and is being led by Bechtel Hanford, Inc., with oversight from DOE. The project was established with the following five objectives (DOE, 1 998d, p. 1 .1 ):4 3Subsequently, technetium-99 was detected in the groundwater beneath these and other tank farms in the 200 East Area (PNNL, 1999, p. 6.38; DOE, 1998, p. 4-50~. 4The objectives given here are direct quotes from DOE (1 998d). These objectives have been reworded in a subsequent document (DOE, 2000a).

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8 Science and Technology for Environmental Cleanup 1. Integrate all Hanford Site GWNZ [groundwater/vaclose zone] related work scope. 2. Predict current and future impacts resulting from contaminants that have been (or are predicted to be) released to the soil column at the Hanford Site. 3. Provide a sound science and technology (S&T) basis for site decisions and actions. 4. Promote open and honest involvement of Tribal Nations, regulators, and stakeholders so that project outcomes reflect expressed interests and values. 5. Establish an independent technical peer review. As discussed in more detail in Chapter 3, the Integration Project is responsible for developing and conducting assessments to determine the effects of chemical and radioactive contaminants on groundwater, the Columbia River, and users of the river's resources. The project is not directly responsible for waste management or cleanup activities at the site. These tasks are the responsibility of the three Hanford Site organizations that signed the memorandum of understanding that gave rise to the Integration Project. At the request of DOE Headquarters, two technical teams were established to provide peer review of Integration Project activities as called for in the fifth program objective: The Integration Project Expert Panel (IPEP)5 was created in 1998 to provide advice and recommendations on key programmatic, technical, and administrative issues affecting the success of the Integration Project. This group has been meeting quarterly and has issued several reports that address various aspects of the integration effort at the site.6 In addition, the Assistant Secretary for Environmental Management requested that the National Research Council review the science and technology S&T program established under the auspices of the Integration Project as called for by the third program objective. That request led to the current study, the results of which are summarized in this report. 51PEP consists of eight technical experts: Edgar Berkey, chair, and members Randy Bassett, John Conaway, James Karr, Michael Kavanaugh, John Matuszek, Ralph Patt, and Peter Wierenga. 6The expert panel's reports are available on-line at http://www.bhi-erc.com/ projects/vadose/peer/ipep.htm.

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Introduction and Task 9 SCOPE OF THIS STUDY The NRC was asked to review the S&T program and to provide recommendations to improve its technical merit and relevance to DOE's remediation decisions, with particular attention to the following issues: the technical merit of the S&T work to be carried out under the program, including its likely contribution to advancing the state of scientific knowledge; . the relevance and timeliness of the planned S&T work to DOE remediation decisions at the Hanford Site; and the potential applicability of S&T results to contamination problems at other DOE sites. The chair of the National Research Council appointed a committee of 14 experts (Appendix A) to undertake this study. The committee met six times to gather information, deliberate on the issues, and develop this report. Three meetings were held in Richland, Washington, near the Hanford Site, so that the committee could receive briefings from DOE staff and site contractors, obtain comments from interested stakeholders, and tour the Hanford Site to see first-hand the cleanup activities and ongoing scientific work. A list of briefings received by the committee at its meetings is provided in Appendix B. REPORT CONTENT AND ORGANIZATION The committee's review of the Integration Project's S&T program is organized as follows: Chapters 2 and 3 provide background information on the Hanford Site and the Integration Project. Chapter 4 provides a discussion of the System Assessment Capability, an Integration Project- developed risk assessment tool to estimate quantitative effects of contaminant releases. Chapters 5 through 9 provide reviews of the technical elements of the science and technology program, and Chapter 10 provides programmatic-level recommendations. The S&T program is at an early stage of development the draft program plan (DOE, 1998d) was completed in fiscal year 1998, and funding for scientific work was provided beginning in fiscal year 1999. As a result, many aspects of the program exist only on paper, and there is relatively little scientific output on which to judge program effectiveness. In fact, as noted repeatedly in subsequent chapters, detailed written plans in

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10 Science and Technology for Environmental Cleanup individual S&T projects do not exist for many elements of the program, although there are a few notable exceptions.7 Consequently, the reviews of the S&T program elements that are provided in this report are based primarily on committee members' general knowledge and understanding of relevant scientific and engineering disciplines and Hanford Site problems. Except as noted explicitly in the following chapters, none of the committee's comments should be construed as an endorsement of specific individual projects. Rather, the committee's comments address general directions of the SOT program and the apparent appropriateness of program priorities. The committee has adopted a long-term perspective in its review of this program In recognition of the fact that the DOE clean up program is likely to last for several decades. Even then, there will be a need for continuing management of residual contamination. Consequently, there will be a need for S&T beyond that required to meet near-term milestones and regulatory requirements. Indeed, the S&T work is likely to continue for many years and, if done well, could substantially and positively impact cleanup decisions at the site. J 7Primarily the S&T work under the auspices of the Vadose Zone Technical Element, for which detailed planning documents are available (see Chapter 6~.