3

Contaminant Reduction

As mentioned in Chapter 2, contaminant reduction is one of the three sets of waste-site measures embedded in the long-term institutional management approach. The focus of this chapter is the existing contamination at U.S. Department of Energy (DOE) sites and the goals, constraints, and limitations for its remediation via contaminant reduction. The role of scientific and technology research in improving contaminant reduction is also discussed.

Contamination at a site may be reduced in volume and toxicity by processes such as destruction, decontamination, processing to form a more concentrated waste stream and a less hazardous secondary waste1 product, transmutation to a less hazardous form, decay of radionuclides or of certain other hazardous substances, and removal from the site. Examples of destruction might be the incineration of certain substances or contaminated materials, biodegradation treatment, or in situ vitrification of contaminated materials, such as soil, that may destroy certain organic materials and immobilize others. These techniques require collection and handling of any hazardous residues such as gases and ashes from the destructive process. Decontamination of buildings and other structures is being conducted at many DOE sites, often resulting in a reduced amount of contaminated material, albeit more concentrated, for further management as well as some potentially useful materials and structures.

Another form of contaminant reduction includes removal of the mobile species from soil by pumping or vapor vacuum extraction and the collection of such materials for disposal or recycling for future use. Processing of high-level radioactive waste from tanks may be used to separate and concentrate the more radioactive materials for long-term management, leaving behind a lower activity waste that may have a less stringent requirement for future management. Some proposed solutions for the safe management and disposal of highly radioactive wastes containing long-lived radionuclides have focused on separating these radionuclide components of the wastes and transmuting them by neutron bombardment to form nuclides that would be either stable or radioactive with much shorter half-lives (National Research Council, 1996b). (However, development of transmutation is at such an early stage that it holds little hope for treating contamination at the sites.) Finally, the contaminants may be recovered from a site, placed in some type of acceptable waste form for transport and internment, and moved to another site, resulting in a transfer from one location to another with the expectation that the wastes will be confined in a manner that presents less risk to the public and the environment.

1  

Secondary waste is new waste produced in the course of carrying out the processing, concentration, and removal of contaminants.



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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites 3 Contaminant Reduction As mentioned in Chapter 2, contaminant reduction is one of the three sets of waste-site measures embedded in the long-term institutional management approach. The focus of this chapter is the existing contamination at U.S. Department of Energy (DOE) sites and the goals, constraints, and limitations for its remediation via contaminant reduction. The role of scientific and technology research in improving contaminant reduction is also discussed. Contamination at a site may be reduced in volume and toxicity by processes such as destruction, decontamination, processing to form a more concentrated waste stream and a less hazardous secondary waste1 product, transmutation to a less hazardous form, decay of radionuclides or of certain other hazardous substances, and removal from the site. Examples of destruction might be the incineration of certain substances or contaminated materials, biodegradation treatment, or in situ vitrification of contaminated materials, such as soil, that may destroy certain organic materials and immobilize others. These techniques require collection and handling of any hazardous residues such as gases and ashes from the destructive process. Decontamination of buildings and other structures is being conducted at many DOE sites, often resulting in a reduced amount of contaminated material, albeit more concentrated, for further management as well as some potentially useful materials and structures. Another form of contaminant reduction includes removal of the mobile species from soil by pumping or vapor vacuum extraction and the collection of such materials for disposal or recycling for future use. Processing of high-level radioactive waste from tanks may be used to separate and concentrate the more radioactive materials for long-term management, leaving behind a lower activity waste that may have a less stringent requirement for future management. Some proposed solutions for the safe management and disposal of highly radioactive wastes containing long-lived radionuclides have focused on separating these radionuclide components of the wastes and transmuting them by neutron bombardment to form nuclides that would be either stable or radioactive with much shorter half-lives (National Research Council, 1996b). (However, development of transmutation is at such an early stage that it holds little hope for treating contamination at the sites.) Finally, the contaminants may be recovered from a site, placed in some type of acceptable waste form for transport and internment, and moved to another site, resulting in a transfer from one location to another with the expectation that the wastes will be confined in a manner that presents less risk to the public and the environment. 1   Secondary waste is new waste produced in the course of carrying out the processing, concentration, and removal of contaminants.

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites At the present time DOE legacy waste site managers are placing most attention and funding on the reduction of contamination rather than isolation or stewardship. The radioisotopes are in wastes classified as high-level, low-level, spent fuel, transuranic (TRU), or mixed (hazardous and radioactive materials together). The waste is present in tanks of varying sizes from several hundred gallons up to over 1 million gallons (3,800 m³), in burial pits from small to very large in volume, in wet and dry storage canisters, in drums and other packages, and stabilized in some forms such as glass or grout. It is also found where it has been purposefully or accidentally disposed of in the soil and the groundwater, and adhering to or contained within buildings, machines, scrap metal, concrete, protective clothing, cleanup substances, and other materials that were involved in the generation, processing, and storage of nuclear materials and the production of nuclear weapons. There are a number of non-radioactive, hazardous substances of concern at many, if not all, facilities within the DOE complex. These include both elements (especially metals) and compounds that never degrade and organic compounds that can degrade. They range from hazardous substances remaining in cleaned-up tanks to contaminants in soils and groundwater to contaminated surfaces. Hazardous substances found in remediated tanks include residual waste, lead used as shielding, and chemicals used in cleaning, plating, reprocessing, and separations operations as well as in machining and fabrication operations. The decontamination approaches for these materials are often the same as those used for radioactive materials, although the regulations governing them and the permissible ultimate disposal methods may be very different. An extensive program of contamination reduction (decontamination or destruction) of radioactively contaminated equipment, facilities, buildings, groundwater, and soil at the DOE sites is planned in connection with the long-term disposition of DOE legacy wastes (U.S. Department of Energy, 1997b, 1998a). Decontamination of a site is usually the first step in site remediation. Typically the goal of decontamination is to produce two streams: 1) a product stream—a site, facility, or piece of equipment suitable for some sort of beneficial use, or at least posing a reduced risk, and 2) a waste stream that contains the contamination. The contaminated site, facility, or equipment is treated by physical, chemical, or biological means to achieve this end. If the degree of decontamination reached is insufficient to permit the required separation and removal of the contamination, the contaminated material must be isolated from the biosphere (see Chapter 4). Examination of the table in Appendix B showing closure plans for major DOE sites reveals that almost none of the significant DOE sites will be cleaned to residential/agricultural standards in all their parts. Rather, most will be cleaned to a mixture of cleanup levels ranging from residential/agricultural to controlled access. Also, many sites will have continuing missions, with only parts of them to be made available for other than DOE uses. Uranium Mill Tailings Radiation Control Act of 1978 (UMTRCA) disposal sites form a class by themselves. A negligible number of sites revert to the original owner after cleanup; some will be turned over to state authorities. Practically all leave management responsibility of residual contamination, if any, to DOE. Approximately 19 sites from Appendix B have some degree of nongovernmental ownership. Some sites are designated to be monitored or have open-ended pump-and-treat requirements for unspecified periods of time. Management of some sites dictates both indefinite monitoring and pump-and-treat. Some observations and conclusions that may be derived from the table in Appendix B are: Many of the sites are to be released all or in part for restricted use. Some of the major sites are to be released in part for unrestricted use. Many of the major sites have ongoing DOE missions into the unspecified future. Many of the sites, major and other, are subject to open-ended pump-and-treat remediation (i.e., pump-and-treat is the method of choice for many long-term groundwater problems). Robust institutional management will probably be needed for a majority of the sites. In fact, one might reasonably argue from the information in the table that there is a need for new, imaginative, and practical follow-on or alternative groundwater cleanup or isolation methods (a science and technology focus), that there is a need for effective, long-term on-site and off-site monitoring methods, and that responsibility for those using sites after closure (e.g., federal, state, or local government agencies or the private sector) must be clearly identified and formalized.

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites Large amounts of radioactive metal from equipment, utilities, and structures need to be decontaminated, along with large amounts of radionuclide and chemically contaminated soil and groundwater that need to be decontaminated or dealt with in some other manner. Ideally the result of decontamination should be a site, facility, material, or equipment that is free from any restrictions on its use, and the waste stream should be small, well characterized, and economical to produce and dispose of. This ideal is difficult to achieve, however, and in general will only be reached in favorable cases. In view of the range in the levels of contamination and the sizes and number of the contaminated sites and facilities, it is expected that the levels of decontamination likely to be achieved will range from essentially complete decontamination, allowing the site to be released for unrestricted use, to levels of decontamination that require long-term institutional oversight, control, and monitoring. The possibility of additional remediation to further reduce the risk from a contaminated site will remain until contamination no longer poses a hazard. A necessary adjunct to promote success in contamination reduction is planning for contingencies. It is quite possible that, for reasons such as inadequate knowledge of the contaminated facilities or environment, or lack of appropriate and tested technology, a planned decontamination operation will fail to achieve the desired or agreed upon future state, or that future state may change. To allow for such a contingency, one or more promising alternative approaches should be identified, developed, tested, and available to ensure that the risk posed by the contamination is managed acceptably. One such alternative might be to go to isolation of the contamination, as discussed in Chapter 4. FUTURE STATES Decontamination is one of the essential aspects of site remediation that can lead to an agreed-upon future state. A future state need not necessarily be the final or end state (or condition) of the object or site being decontaminated. In essence, there may be interim states such that waste management may be phased, and that additional contamination reduction may be carried out to reduce risk in the future on sites or objects remediated to interim states. Such possibilities will continue to exist if a dynamic program of scientific and technical development is pursued toward improved scientific understanding and new methods for contamination reduction, even after a site or facility has been deactivated. Ideally, for all the necessary operations to be successfully carried out to attain the agreed-upon future state, such a state should be defined in advance of the contamination reduction operations. The future state is usually defined in consultation with and by agreements with regulatory bodies and other parties having a legitimate interest in site disposition. For interim states there should be future reevaluations, presumably at agreed-upon intervals, to determine if technological, regulatory, or institutional changes make further reductions in contamination desirable and practicable, and if so, to see that they are carried out. It is also possible that decontamination and cleanup standards or goals may have changed. This concept is elaborated in Chapter 6 of this report. The objective of the contaminant reduction operations, both in the current and interim state, is removal or destruction of the source of contamination to the extent possible, reducing reliance on containment and stewardship activities while achieving better future conditions. However, as a general rule, the greater the degree of decontamination, the greater the cost, and in some cases the greater the worker risk, the contaminant by-products, and the environmental disturbance. In practice, a balance should be sought between the degree of decontamination and the fiscal and health risks and the environmental insults associated with cleanup and the waste streams it will create. Standards for achieving sufficient decontamination are very important. There is a significant lack of clear standards for unrestricted release of decontaminated sites. The goal of decontamination may also be to move a contaminant to a location where it poses less threat to the public and the environment than it did in its pre-decontamination site. Thus, decontamination can also result in a wider range of possible future and end states for some sites. It should also be recognized that there will often be a trade-off between decontamination and containment (discussed in Chapter 4). In some cases there may be a cost-benefit advantage to containing part or all of the contamination rather than removing or destroying it. Similarly, until improved decontamination technologies are developed, containment may entail less risk to workers and the environment than contamination reduction. For example, dredging of contaminated sediments

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites from streambeds may cause an unacceptable increase in exposure to workers as well as to the public and the environment. Different interim and end states may be possible in the future due to (a) development of new technologies and more economical cleanup to lower levels of residual contamination; (b) availability of additional resources; (c) changes in the values of the interested and affected public and regulators; or (d) failure of the remediation approach used or of stewardship measures. A phased approach (one that proceeds toward a goal in stages while important information and technology gaps are filled) to contaminant reduction and final disposition of a still-contaminated facility or site will allow for future resolution of current unknowns and uncertainties and for new technologies and methodologies (National Research Council, 1996d). A large number of decontamination technologies is available today, as discussed in recent reports of the National Research Council (1994c, 1996e, 1997b, 1998b, 1999c,e). The preferred ones are likely to be those that produce the least amount of secondary waste, are the most economical to use, and provide the lowest risks to the workers, the surrounding community, and the environment during the decontamination operations. The many regulations governing acceptable levels of decontamination for various purposes are discussed in Appendix E. A significant problem in these regulations is the absence of volumetric standards. Waste Storage Tanks Underground waste tanks at the Hanford Site in Washington, the Savannah River Site in South Carolina, the Oak Ridge Reservation in Tennessee, and the Idaho National Engineering and Environmental Laboratory were used for storage of liquid waste from the processing of irradiated fuel elements. In general, sites with underground tanks formerly used for high-level radioactive waste will not be released for public use in any foreseeable time frame. The degree of decontamination achievable is not known, and will doubtless differ from one tank to another. It is not clear what the trade-offs will be between contaminant reduction and containment. Also, from what the committee has learned, it is not clear what the final criteria will be for tank cleanup and closure. Closure measures required for waste tanks at the major DOE weapons sites are typically viewed as a matter that should involve the interested and affected public, DOE, the states, the U.S. Environmental Protection Agency (EPA), and Native American tribes. The public is broadly viewed as including local residents, health organizations and environmental activist groups, and others not directly associated with the site. However, the type and degree of decontamination required for tanks are not entirely matters of agreements, cost, and risk. Very definite limitations are imposed by the physical nature and condition of the tanks and by the state of the art of tank decontamination technology. For example, most tanks were built without consideration of their final disposition, and many have been in use beyond their planned lifetimes. They often have dozens of internal structures for purposes such as transfer of contents, monitoring systems, structural reinforcement, venting, cooling, and sampling. These features are significant impediments to removal of sludges and solids that lie in many, if not most, of the large tanks (especially those at the Hanford Site). They not only present a significant problem in carbon steel tanks containing neutralized waste, but they also can inhibit extraction of acid wastes from stainless steel tanks. The appropriate degree of waste extraction from tanks has been the subject of extensive discussion between DOE and the U.S. Nuclear Regulatory Commission (USNRC) for the past 10 years. Early discussions concentrated on identifying whether wastes could be sufficiently identified as high-level by identifying their source. This led to efforts to change the definition of high-level waste to cover a greater amount of wastes. In denying a petition to change the definition of high-level waste, the USNRC gave three criteria to be used to determine whether high-level waste has been extracted and waste incidental to reprocessing remains (Bernero, 1993). Those criteria are: “[the waste] (1) has been processed (or will be further processed) to remove key radionuclides to the maximum extent that is technically and economically practical; (2) will be incorporated in a solid physical form at a concentration that does not exceed the applicable concentration limits for Class C low-level waste as set out in 10 CFR Part 61; and (3) will be managed, pursuant to the Atomic Energy Act, so that safety requirements comparable to the performance objectives set out in 10 CFR Part 61 are satisfied.” These criteria offered DOE a reasonable basis to judge when the bulk of the high-level waste has been extracted and the residues, still in the tanks or from

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites the high-level waste concentration process, can fairly be classified as waste incidental to reprocessing. The DOE has promulgated its overall criteria for the management of radioactive wastes in DOE Order 435.1 and its supporting documents. Recent experience with waste retrieval from tanks is revealing problems that have implications for the long-term institutional management of the tanks once wastes are removed. Historical records are used to estimate the initial load of waste in the tank because an assay of the residue can be extremely difficult. Some of the residue is sludge or solids trapped in difficult-to-reach locations of the structures; some is caught on or in the corroded carbon steel surface of the tank interior. Thorough, direct sampling and characterization are not really possible in a practical sense. Current tank cleaning and extraction are being done with water-based hydraulic methods. There are questions about the in-tank residue and whether it can meet Class C limits through a concentration-averaging approach. More aggressive techniques, such as using acid flushes, may not turn out to be technically or economically practical and may even cause leaks in the tanks in the attempts to remove the wastes. It is apparent that many of the tanks' physical structures will be left in place following removal of most of the waste. The current state of the art leaves two evident options for the tank closure process. If the USNRC criteria for high-level waste removal are used to judge what is acceptable, residual wastes in the tanks would be acceptable if they do not exceed Class C waste performance standards. If this type of in situ disposal is accepted, this option leads to a final stabilization solution (end state) that involves filling and surrounding the tanks with a grout or with concrete engineered barriers (see Chapter 4). Site monitoring would still be required. In contrast, an interim tank closure might be selected in anticipation of development of more effective treatment technologies for the tank and its residues at a future time. In this approach, the tanks and their contents would be stabilized in a reversible way (e.g., by filling the tanks with gravel or “poor grout” [grout that is removable] and establishing a pump-and-treat system to recover any wastes that might escape). Most of the tank wastes contain currently hazardous fission product radionuclides having half-lives of about 30 years or less (e.g., strontium, cesium, and tritium); these radionuclides will decay by a factor of at least 1,000 over about 300 years. An incentive for adopting the interim closure option with its greater burden of institutional management would be, where warranted, the flexibility it provides for more complete tank decontamination at some future date if improved or new decontamination processes are developed. Buried Waste A certain amount of long-lived radioactive waste currently buried will probably be removed for further processing and transfer to another storage site or to a repository. Such waste includes TRU wastes buried in trenches and pits in the Radioactive Waste Management Complex at the Idaho National Engineering and Environmental Laboratory (INEEL). Some residual contamination will remain in place and in the soils after remediation, possibly requiring some form of contaminant isolation for the duration of the health and environmental risk. Table 2 gives a cursory summary of solid wastes across the DOE complex. It is difficult to acquire site-specific information, but R.E. Gephart (Pacific Northwest National Laboratory, 2000, personal communication) provided some information concerning the Hanford Site. “The Hanford Site contains about 700,000 cubic meters of solid waste buried in 75 landfills—containing 6 million curies of radioactivity (decayed to 1998) and 70,000 tons (6.3 × 107 kilograms) of chemicals. Materials include 0.4 tons (400 kilograms) of plutonium and 650 tons (5.9 × 105 kilograms) of uranium. A small percentage (about 3 percent) was stored in above-ground facilities. Sixty percent of Hanford's solid waste was buried before 1970.” As another example, highly radioactive residues separated during the processing of very rich uranium ores from the former Belgian Congo (now Zaire) are presently stored at the Niagara Falls Storage Site in Lewiston, New York, buried under an interim cap to inhibit influx of moisture from precipitation and to decrease outflux of radon gas. A study by the National Research Council (1995a) recommended that these highly radioactive residues be removed, treated, and disposed off site to reduce the potential long-term risk to the public, rather than be covered with a “permanent” cap. No matter how well the cleanup is conducted at sites such as these, a certain amount of residual contamination will remain behind that may well require long-term monitoring and barrier maintenance.

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites TABLE 2 Summary of Solid Waste Across the DOE Complex (from Linking Legacies[U.S. Department of Energy, 1997b, pp. 39, 47, 53, 54]) Waste Category Volume (m³) Curies Low-Level Wastea 3.3 × 106 50 × 106 Low-Level Mixed Wasteb 0.15 × 106 2.4 × 106 Transuranic Wastec 0.22 × 106 3.8 × 106 Total 3.67 × 106 56.2 × 106 a Low-level waste (LLW) includes all radioactive waste that is not classified as high-level waste, spent nuclear fuel, transuranic (TRU) waste, uranium and thorium mill tailings, or waste from processed ore. In volume, most low-level waste consists of large amounts of waste materials contaminated with small amounts of radionuclides, such as contaminated equipment (e.g., gloveboxes, ventilation ducts, shielding, and laboratory equipment), protective clothing, paper, rags, packing material, and solidified sludges. However, some low-level waste can be quite high in radioactivity. b Low-level mixed waste (LLMW) contains both hazardous and low-level radioactive components. The hazardous components are subject to the Resource Conservation and Recovery Act of 1976, as amended (RCRA), whereas the radioactive components are subject to provisions in the Atomic Energy Act. LLMW results from a variety of activities, including the processing of nuclear materials used in nuclear weapons production and energy research and development activities. c Transuranic (TRU) waste is waste containing more than 100 nanocuries of alpha-emitting transuranic isotopes per gram of waste, with half-lives greater than 20 years, except for (a) high-level waste, (b) waste that DOE has determined, with the concurrence of the EPA, does not need the degree of isolation required by 40 CFR 191, or (c) waste that the U.S. Nuclear Regulatory Commission (USNRC) has approved for disposal on a case-by-case basis in accordance with 10 CFR 61. TRU waste is generated during research, development, nuclear weapons production, and spent nuclear fuel reprocessing. Soil Contaminated soil is present at the major DOE weapons sites, especially at Hanford, Savannah River, Idaho Falls, Rocky Flats, the Nevada Test Site, and Oak Ridge, where large, diverse, and highly radioactive operations were carried out. There is also substantial soil contamination at sites such as Fernald, the gaseous diffusion plants, and the uranium mill tailings sites. Because surface soil contamination has a tendency to spread, it can increase the volume of the contaminated subsurface zones albeit at reduced concentrations of contaminants. Reduction of the contamination in soil may be achieved by chemical and/or physical means (National Research Council, 1999e). Radioactive contaminants in soil are generally removed to an on-site or remote burial ground; rarely is soil treated in situ. When the contaminants are organic compounds the soil may be decontaminated to regulatory limits by a number of means, such as “stripping” by passing a stream of air through it, thermal destruction by heating the soil batch-wise, or microbial action. In some cases, the soil volume and nature of contamination is such that selective leaching or other segregation of the contaminant may be feasible to reduce the soil contamination to the desired end state. The Nevada Test Site (NTS) presents an example of soil contaminated by nuclear testing. The area contaminated is extensive, and it is not contained by any sort of engineered barrier. However, because decontamination of the site would be prohibitively costly using currently available technologies, at present no subsurface contamination reduction program is planned. Part of the site is used currently for disposal of low-level radioactive waste. DOE has not formally announced the end state for future land use at NTS other than to maintain a mission objective of possible resumption of weapons testing. Currently there are no set standards for soil decontamination. The National Council on Radiation Protection and Measurements (NCRP) (1999) published screening limits for radionuclides in soil that relate an effective dose to a critical group to a corresponding soil contamination level. The screening levels are consistent with the NCRP recommendation that the maximally exposed individual should not exceed 0.25 mSv per year (25 mrem per year)

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites from any single set of sources. Different screening levels are derived for various land uses from farming to commercial use. However, these limits are stated not to be used as cleanup standards on the grounds that they apply to the maximally exposed person and are conservative. A cleanup standard for plutonium in surface soil of 200 pCi/g (7400 Bq/kg) is in use as a de facto standard at NTS. This concentration is estimated to give an exposure of 100 mrem per year for a full time resident. The USNRC has promulgated cleanup standards for radioactive contamination in soil that are applicable to decommissioning of USNRC-licensed sites. The USNRC ground cleanup standard is based on individual radiation exposures of no more than 25 mrem/year to an average member of the critical group (10 CFR 20.1402). However, the EPA objects to this standard and recommends a limit of 15 mrem/year from all pathways, with no more than 4 mrem/year through the drinking water pathway for decommissioned sites. The appropriate contaminated soil remediation action is determined by the details of the particular situation, both with respect to the degree of health and environmental threats, the availability of practicable remediation technologies, and the financial resources to implement the technologies. It should be noted that all of these potential standards for soil contamination are for calculated doses, derived by using various models to predict the radiation doses resulting from the contamination. These radiation doses are all very low when compared with typical background radiation doses and variations in background radiation, making the contamination doses extremely difficult to measure. Although the federal agencies involved (DOE, USNRC, EPA, and Department of Defense) have not agreed on standards for soil contamination, they have collaborated on guidance for radiological surveys conducted to demonstrate compliance with such a standard in the report Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) (U.S. Department of Defense, U.S. Department of Energy, U.S. Environmental Protection Agency, and U.S. Nuclear Regulatory Commission, 1997). Groundwater Many soil contamination problems become water contamination problems through solubilization or suspension of the contaminant(s). The magnitude and severity of the water contamination problem is strongly influenced by the nature of the site, especially the composition and structure of the local geological formations and the climate. An essentially dry climate such as prevails at the Nevada Test Site, the Idaho National Engineering and Environmental Laboratory, and the Hanford Site poses very different problems from those regions having a wet climate such as found at the Oak Ridge Reservation and the Savannah River Site. It is also important to consider the rate at which the contaminants move and the likelihood of contaminated water being used for agriculture, by wildlife, or for domestic residential purposes. If these events are likely, the cleanup problem takes on a greater urgency. The Columbia River is important in this regard at the Hanford Site, as is the Savannah River at the Savannah River Site and the aquifer underlying INEEL. At other sites, such as the Fernald and Mound sites, a major aquifer is at risk. Pump-and-treat systems, which involve installing wells at strategic locations to pump contaminated groundwater to the surface for treatment, are by far the most commonly used and proposed decontamination treatment for contaminated groundwater. Studies indicate, however, that pump-and-treat systems may be unable in most cases to remove enough contamination to restore groundwater to drinking water standards, or that removal may require a very long time—in some cases centuries (National Research Council, 1994c). In the cases where the contaminant is a relatively short-lived radionuclide (e.g., tritium), it is possible to conceive of a situation where pumping and treating the contaminated groundwater to storage or to recycle it repetitively might provide enough time for radioactive decay to reduce the contaminants to acceptable levels (for example, the “pump and reinject” system used at the Savannah River Site to deal with tritium). Radioactive decay in this case is a form of “natural attenuation”2 (National Research Council, 2000a). Although pump-and-treat is apparently intended for use at 2   Natural attenuation usually means that no action is taken to treat the contamination and that radioactive decay or natural destruction of an organic pollutant alone takes care of the problem. However, it may be interpreted more broadly to include natural flushing (and dilution) of contamination by the movement of water across the contaminated zone or object.

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites many of the DOE sites (see table in Appendix B), it may be effective for some purposes such as control of migration, but not for others such as complete removal of the contaminated fluids. In the many instances where long-term pump-and-treat methods are proposed, there is a need for equipment maintenance, monitoring, and all the operations involved in packaging the removed contaminant, transporting it to an acceptable disposal area, and disposing of it. In some cases, for example, organic contaminants, further treatment such as destruction by incineration might be required. Management of these operations will probably have to be carried out at a large number of sites, sometimes for decades or centuries. In addition, it should be borne in mind that in situ methods such as pump-and-treat are limited in the degree to which they can remove contaminants. In some cases the number of cycles necessary to reach the desired level of contamination will be impracticably large. Nuclear Weapons Test Sites Somewhat unusual in terms of contamination are sites where nuclear weapons have been tested underground, on the surface, or in the air. The committee visited the Nevada Test Site (NTS) at the request of DOE and because it is representative of a large DOE site where substantial amounts of radioactive and hazardous materials exist and are likely to remain. The NTS at once epitomizes the activities (e.g., ongoing operations, reindustrialization, cleanup, and the need for long-term stewardship) that are required at many of the DOE sites. Thus, a short description of the NTS situation as it relates to stewardship is given in Appendix F to give the reader a better appreciation of how the integrated set of activities at an actual site relate to the concepts presented in this report. The committee was unable to identify any specific commitment or process that would result in future re-examination of the major features of site remediation decisions being made today for the NTS, although decisions will be made on specific details (e.g., cleanup levels for specific locations) on a continuing basis. There appears to be little driving force for such reconsideration at present. Thus, the destiny of the NTS appears to be a limited number of remedial actions consistent with reindustrialization in selected portions of the site, followed by an indefinite period of institutional control in anticipation of possible future resumption of testing. Surface Structures and Equipment A very large number of contaminated structures exist on DOE sites, some of which are destined to be dismantled and disposed, while others are intended to be made available for use by industry. There are many firms devoted to decontaminating structures, and federal guidance for decontamination is evolving (U.S. Atomic Energy Commission, 1974; U.S. Nuclear Regulatory Commission, 1998 and in review; Federal Register Notice 63FR64132, 1998; U.S. Department of Energy, 1995b). However, the decontamination process may produce airborne particulates and/or liquid waste and contamination. In the abstract, the “best” decontamination treatment depends on the likely future use of the materials being decontaminated (National Research Council, 1998b), but future uses are often difficult or impossible to predict. CONSTRAINTS AND LIMITATIONS Technologies that will achieve a desired future state may be very expensive and produce unacceptably large volumes of secondary waste or their application may be necessary for impracticably long periods of time. In such cases it may not be practicable to achieve the desired level of decontamination. This puts greater requirements on contaminant isolation and stewardship activities. Therefore, a reasoned judgement is required of the technical, fiscal, safety, and regulatory aspects of the available technologies prior to deciding which one to deploy. The cost, risk, and systems analyses of such technologies should not proceed sequentially, but simultaneously, with strong interactions among them. It is important to recognize that although a risk assessment strives for an accurate and quantitative evaluation of risk, risk assessment is inherently a subjective process that is based on assumptions determined by the policy preferences of the assessor. Furthermore, the uncertainty associated with the resulting calculations may be very large due to a number of factors, including incomplete characterization of the site or contaminants, limitations on the ability to validate models of physical, chemical, and biological processes during

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites contaminant transport and uptake, uncertainty and variability in the values of the parameters required by the models, and uncertainty in the quantitative estimates of health effects to human populations (Harley, 2000). Because of these factors there should also be consideration of contingency scenarios that would reflect different policy preferences and accommodate uncertainties in technologies, risks, and funding levels, as noted above. In addition to the above considerations, any specific decontamination technology would need to meet regulatory requirements, and may be subject to non-technical constraints. Treatment of groundwater is a major concern because of the pervasiveness of groundwater contamination and the difficulty of effectively dealing with the contamination problem. Many of the major DOE sites have groundwater contamination problems that can affect rivers, lakes, and aquifers. Pump-and-treat cannot be relied on as a universally applicable technology for the indefinite future, and it is not clear what the follow-on treatments should be. The EPA and states have set groundwater concentrations of radionuclides for “safe” drinking. New standards are in the process of being promulgated for such elements as uranium and radon. As research on radiation carcinogenesis provides better quantitative data on the health effects of very low-level radiation exposures, risk guidelines may change (Jaworowski, 19993 ). Similarly, successful decontamination of structures and materials is complicated by several limiting factors. The state of present technologies is the most pressing limitation, but physical structures and regulatory standards also present problems. FUTURE DIRECTIONS FOR IMPROVEMENTS It is likely that improvements in methods for characterization of contaminants will lead to changes in the selection and priorities of sites and facilities for cleanup. In this connection there is a need for new and improved methods of chemical speciation of contaminants. Cost reduction of characterization is highly desirable, as is increased sensitivity and speed. For example, new and improved methods for decontamination that reduce the amounts and risks of secondary wastes and reduce costs are needed, as are methods for rapidly, efficiently, and economically measuring the amounts of residual contaminants. Similarly, groundwater cleanup by methods other than pump-and-treat is highly desirable. Passive treatment systems and subsurface treatment walls show some promise for containment of some health and environmental threats. The amount of contamination persisting at a site for long-term management (some for hundreds or even thousands of years) will be determined by the level of remediation that has been accomplished (based on such factors as budget, risk to the public and the environment, technical capability, regulations, and planned future land use) and the natural lifetime of remaining constituents (by such processes as natural attenuation, decomposition, biodegradation, or radioactive decay). As a consequence, decisions will be made at some time between the cost and risk of remediation and of long-term control and management. Such decisions will have to be revisited over time, based on new understanding of the contaminated environment and the new technology achieved from a continuing commitment to support of science and technology development directed toward environmental management and better understanding of the risk implications of social changes. At most DOE facilities visited by the committee, a concern about the lack of appropriate and adequate data on the waste for modeling its migration into the environment was expressed. It is axiomatic that trustworthy decisions should be made based on sufficient, high-quality data. To solve the data deficiency, specifically for radioactive waste, requires qualified scientific and technical measurement groups and equipment that can assist in the characterization of the contamination across sites. Such a group, having expertise in radiation detection and measurement, could develop detailed knowledge of each site and identify similarities in types of contaminants and in physical properties of the environment. This would avoid duplication of effort among sites, provide a pathway for new generic instrument development and modeling, and augment sharing of novel equipment. Collaboration across sites produces an important gain in efficiency in site characterization measurements such as types of contaminants and environmental properties, as opposed to ad hoc individual site effort. 3   This article elicited many comments in the Letters section of subsequent issues of Physics Today (e.g., April and May 2000).

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Long-Term Institutional Management of U.S. Department of Energy Legacy Waste Sites The criteria for dealing with residues in liquid waste tanks should be amplified and refined, working with the USNRC, EPA, and the states. The changes should be based on consideration of the difficulties in characterizing the residues and their distribution. Consideration should be given to postponement of some tank closures to develop more effective residue characterization and extraction methods. Different sites use different contractor laboratories or in-house measurement procedures for quality control. In order to have trust in any data collected, there should continue to be a long-term data comparison program among laboratories. In addition, experts are needed to undertake a quantitative and realistic evaluation of the potential health risks at each site, taking into account the natural background at that site. To accomplish this requires establishing a relationship with the regulatory organizations. Discussions, studies, and actions should take place for the purpose of reviewing existing compliance guidelines and determining any appropriate research necessary to quantify the risk of cancer and other health problems from low level exposures to be used to guide decontamination operations.