Science and Technology for DOE Site Cleanup: Workshop Summary (2010)

The National Research Council (NRC) has a long record of advising the federal government on the management and cleanup of wastes resulting from nuclear weapons production.¹ The NRC appointed its first study committee on radioactive waste management and disposal practices in 1955 to advise the Atomic Energy Commission (AEC). In its first two decades of operation, this NRC committee published eight technical reports (NRC, 1956, 1957, 1966, 1970a, 1970b, 1972, 1974, 1975) and one individual paper (NRC, 1958) that examined research and development (R&D) activities and waste management and disposal practices at the large AEC sites.²

Starting in 1976, NRC committees began a more intensive examination of disposal practices at these sites, which were then being managed by the Energy Research and Development Administration³ (ERDA) and later by the Department of Energy (DOE). A 1976 report focused on the shallow land burial of wastes at ERDA sites (NRC, 1976; see also NRC, 1993). Later reports provided reviews of waste management programs, plans, and practices at Hanford (NRC, 1978b, 1985a, 1992c), Idaho (NRC, 1991b, 1994a), Savannah River (NRC, 1981, 1998a) and Oak Ridge (NRC, 1985b). In 1987, the NRC published reports on the management of buried low-level and transuranic waste and contaminated soil (NRC, 1987b) and on management of uranium mill tailings (NRC, 1987c).

During that same time period, other NRC committees were established to advise DOE on the development of what was to become the Waste Isolation Pilot Plant (NRC, 1979c, 1979d, 1980, 1983, 1984a, 1987a, 1988a, 1988b, 1989b, 1991a, 1992b, 1996e, 2000c, 2001e, 2001h, 2002b, 2004). WIPP is now being used to dispose of defense transuranic waste that originated within DOE and its predecessor agencies.

With the creation of DOE-EM in 1989, the focus of NRC work expanded to include environmental cleanup. The first NRC report focusing almost exclusively on environmental cleanup was published in 1989 (NRC, 1989a). That report provided a review of a draft DOE environmental restoration and waste management plan. Also in 1989 the NRC provided a review of a draft DOE plan for applied research, development, demonstration, and testing to support the cleanup program (NRC, 1989c).

In 1994 the NRC established a Committee on Environmental Management Technologies to advise EM on technology development and use. This committee and its successor committees produced a series of reports addressing technology development in five “focus areas” identified by EM: contaminant plumes, landfills, high-level wastes, mixed wastes, and decontamination and decommissioning (NRC, 1995b, 1996a, 1998e, 1999b, 1999c, 1999d, 1999g). During that same period, another NRC committee published a series of reports advising EM on the management of buried and tank wastes and other related issues (NRC, 1994a, 1994b, 1995a, 1996b, 1996c, 1996d, 1997b, 1998b, 2000d).

In 1995 then-Assistant Secretary Grumbly requested that the NRC establish a committee to evaluate the science, engineering, and health basis for EM’s Environmental Management Program. The report from that activity, Improving the Environment (NRC, 1995c), included an extensive discussion on the utilization of science, engineering, and technology in the cleanup program. Subsequent NRC reports addressed technology development and selection decision making (NRC, 1998c, 1999e), R&D portfolio development and funding (NRC, 2001g), and the use of peer review in technology development programs (NRC, 1997d, 1999a). The 1999 peer review report was cited by the Office of Management and Budget in its standards for agency peer reviews.

In 1995 Congress created the Environmental Management Science Program (EMSP) to develop new knowledge and tools for the cleanup effort. The program was housed within EM but was jointly managed with the DOE Office of Science. At the request of EM, the NRC undertook a series of studies beginning in 1996 to advise on the implementation of this program. The first three reports focused on the structure and management of the EMSP (NRC, 1996g, 1996h, 1997c). Later reports identified knowledge gaps and research needs on the following topics:

• Contaminated soil and groundwater (NRC, 1998d, 2000a)

• High-level waste (NRC, 2000f, 2001d)

• Deactivation and decommissioning (NRC, 2000g, 2001c)

• Transuranic and mixed waste (NRC, 2002c)

• Excess nuclear materials and spent fuel (NRC, 2003a)

The recommendations in these reports were used by EM and the Office of Science to develop the annual research solicitations for the EMSP. The EMSP was transferred to the Office of Science in fiscal year 2003 and now primarily focuses on soil- and groundwater-related research.

Over the past decade, the NRC has published several reports focused on specific site cleanup problems. These include groundwater cleanup at Hanford (NRC, 2001f) and the Los Alamos National Laboratory (NRC, 2006b); high-level waste processing at Idaho, Hanford, and Savannah River (NRC, 1999f, 1999h, 2000e, 2001a, 2001b, 2005d, 2006a); remediation of the Moab, Utah mill tailings site (NRC, 2002a); and long-term institutional management of early-closure sites (NRC, 2003b). The NRC has also undertaken broader-based examinations of technology development and technology use in soil and groundwater cleanup (NRC, 1994d, 1997e, 2000b). Other recent NRC reports have examined the use of risk analysis in cleanup decision making (NRC, 2005b) and opportunities for accelerating DOE’s cleanup efforts (NRC, 2005c).

As illustrated by this summary, NRC studies have examined and reported on a remarkable range of waste management, cleanup, and disposal issues over the past half century. The thousands of pages of information, analyses, and discussions contained in these reports continue to be a valuable resource for DOE managers, technical staff at DOE sites, national laboratory staff, and Congress.

Although some of the older reports are outdated, they still provide an important historical record of the federal government’s efforts to manage the environmental legacy of the nation’s nuclear weapons production and testing programs. Many and perhaps most of these reports still contain relevant information and advice that can help inform future cleanup efforts.

This section provides a high-level synthesis of science and technology gaps derived from previous NRC reports. Interested readers are encouraged to read the original reports to obtain more details. Most of the reports published since 1994 can be read online (Web addresses for these reports are provided in Appendix A).

NRC reports identify science and technology gaps using a variety of labels: for example, research needs, technology needs, cleanup challenges, and knowledge gaps. These reports were also written for different audiences—basic researchers, technology program

managers, EM management, and Congress—and consequently these needs, challenges, and gaps are written in different styles with different levels of supporting detail. In developing this synthesis, these needs, challenges, and gaps have been combined, reordered, and in some cases reworded to remove specialized jargon and provide a consistent level of supporting detail.

The science and technology gaps were derived primarily from NRC reports on cleanup challenges at the large DOE sites and therefore tend to be biased toward those sites’ research and development needs. Some of the identified gaps will require basic research, whereas others will require a combination of applied research and technology development. Some of the gaps can probably be addressed in short time frames (1 to 5 years), whereas others will require medium- (5 to 10 years) and longer-term (>10 years) efforts.

Science and technology gaps have been organized as follows:

• High-level waste and tank cleanup

• Facility⁴ cleanup

• Groundwater and soil cleanup

• Waste and contamination containment

• Containment monitoring

These gaps were not prioritized in previous NRC reports, and no attempt has been made to prioritize them here. The comments from workshop panelists in Chapter 3 will serve to update and extend these identified gaps.

To keep this chapter to a reasonable length, no effort was made to include science and technology gaps from NRC reports published before DOE-EM was established. Also, there is no discussion of research gaps for transuranic and mixed waste, nuclear materials, and spent nuclear fuel. These tend to be site- and waste-stream specific needs that are less important in terms of cost and schedule than the other cleanup problems. Additional information on research gaps for these excluded wastes and materials can be found in NRC (2002c, 2003a).

There are about 400 million liters (about 105 million gallons) of high-level radioactive waste stored in 225 large underground tanks at the Hanford and Savannah River sites and about 4400 cubic meters

(160,000 cubic feet) of calcined high-level waste stored in bins at the Idaho site.^5,6 The Hanford Site is also storing over 1900 stainless steel capsules containing about 130 million curies of cesium and strontium separated from high-level waste. Most of the tank waste is a multiphase mixture of solids and liquids containing a variety of radionuclides and hazardous chemicals. The tanks themselves are between about 40 and 65 years old, and some have developed leaks. In 2000, DOE estimated that it would cost over $50 billion to complete high-level waste and tank cleanup at its sites.⁷

Figure 3 provides a graphical illustration of DOE’s process for high-level waste cleanup at the Savannah River Site.⁸ DOE plans to retrieve waste from the underground tanks at the site for treatment, immobilization, and disposal. The sludge waste (a precipitate of metal oxides and hydroxides) will be processed and immobilized in glass for eventual disposal in a geological repository. The salt waste (a mixture of highly alkaline liquid and crystallized waste) will be processed to remove cesium, strontium, and actinides, which will be immobilized in glass. The remaining low-activity salt will be immobilized in grout and disposed of onsite. The tanks, including any residual waste, will be disposed of in place.

DOE is currently retrieving waste from tanks at Hanford and Savannah River, and the sludge waste at Savannah River is currently being immobilized in glass. Several reports (NRC, 1999h, 2001d, 2003c, 2005d, 2006a) have identified opportunities to improve the technical effectiveness and reduce the costs of high-level waste cleanup, as described below.

FIGURE 3 Simplified flow sheet for management of tank wastes at the Savannah River Site. Low-level waste (LLW) will be disposed of onsite; high-level waste (HLW) will be stored onsite and eventually disposed of in a geological repository; a disposition pathway for failed melters from the Defense Waste Processing Facility has not yet been established; TRU = transuranic isotopes. SOURCE: NRC (2001d).

The high-level waste tanks at Hanford and Savannah River generally have small access ports, and some tanks contain debris and (at Savannah River) cooling coils that further inhibit access and waste retrieval. Many single-containment (also known as “single-shell”) tanks at Hanford have leaked waste into the environment, some double-containment (“double-shell”) tanks at Savannah River have leaked waste into the annulus between the tank walls, and buried waste transfer lines and ancillary equipment (e.g., smaller tanks, valves, and pumps) may also contain waste. Many tanks also contain insoluble residual waste (referred to as “heels”) that is difficult, time consuming, and costly to remove.

Residual waste retrieval from tanks and ancillary pipelines has been identified as an important technology gap in three NRC reports (2001d, 2005d, 2006a; see also NRC, 2003c). These reports recommended the development of physical and chemical cleaning technologies to improve the effectiveness of residual waste removal in tanks, tank annuli, and pipelines, especially technologies that reduce the risks of leakage of wastes to the environment during the removal operations (e.g., by using little or no water to retrieve

wastes). Opportunities for expanding the use of robotics technologies for waste retrieval and tank cleaning are discussed in NRC (2005d, 2006a).

The calcine waste at the Idaho Site is a powdered ceramic solid of various sizes and compositions. It was transferred pneumatically to the bins for storage. DOE plans to retrieve the calcine using the same process. However, pneumatic retrieval could be difficult if calcine caking has occurred (e.g., from the addition of moisture to the bins or by particle sintering). A previous NRC report (1999h, p. 22) noted that there will probably be problems in retrieving the calcine waste but that they could be handled. NRC (2006a) reached the same conclusion.

High-level waste must be characterized prior to and at several points during processing. Current processing approaches are generally expensive and labor and time intensive. NRC (2001d) recommended that DOE develop innovative methods to achieve real-time and, when practical, in situ physical, chemical, and radiological characterization of high-level waste streams at all phases of processing.

Finding reliable and robust high-throughput methods to separate cesium, strontium, and actinides from salt wastes at Savannah River has been a significant science and technology gap. Such separations processes will also be required at the Hanford Site and possibly at the Idaho Site. Several NRC reports have recommended that DOE carry out research to address this gap (NRC, 1999h, 2000e, 2001d).

DOE’s baseline approach for immobilizing the high-activity portion of its waste is vitrification in borosilicate glass. While borosilicate glass can probably be used to immobilize all of DOE’s high-level waste, there are opportunities to reduce waste volumes and costs through the development of alternate waste forms that allow for higher waste loadings and have less sensitivity to waste stream compositional variations (NRC, 2001d; see also NRC, 1996f). NRC (1999h) recommended that DOE examine a range of technical options for immobilizing high-level waste calcine at the Idaho Site. NRC (2003a) recommended research on the cesium and strontium capsules at Hanford to help ensure their continued safe storage, to identify methods to convert the isotopes to stable glass or ceramic

forms, and to understand the long-term hazards of disposition options.

DOE considers it impractical to dismantle and remove tanks after they have been emptied because of costs and worker risks. Instead, DOE plans to characterize and stabilize the residual waste in the tanks. NRC (2001d) identified methods for tank waste heel characterization, especially to estimate radionuclide concentrations, as an important science and technology gap.

Stabilization of this residual waste will be accomplished by filling the tanks with grout. The grout serves several purposes: It encapsulates and stabilizes the residual waste, provides structural support for the tank walls and roof, and acts as a barrier to water infiltration and intruders. NRC (2006a) recommended focused research to improve the fundamental understanding of tank fill materials and also to improve DOE’s ability to tailor grout formulations to specific tanks or groups of tanks.

Over 20,000 facilities were constructed to support nuclear weapons production, testing, and related activities, and DOE has identified over 5000 of these as surplus.⁹ Additional facilities may be declared as surplus in the future. These surplus facilities include production and test reactors, fuel and target fabrication facilities, chemical processing facilities, and gaseous diffusion plants. Some of these facilities are the most massive reinforced concrete structures ever built and are filled with heavily contaminated process equipment. It could take decades for DOE to complete the cleanup of these facilities.¹⁰

DOE is following a two-phase strategy for facility cleanup: The first is to deactivate the facility to reduce worker risks and maintenance costs. This includes shutting off nonessential safety and security systems, flushing process lines and equipment, and removing dangerous materials. The second is to decommission the facility. This includes decontamination of the facility and equipment (i.e., removal of radioactive and hazardous chemical contamination) and possibly dismantlement; the decommissioning end state will be

determined separately for each facility. DOE’s most recent low-end estimate of its deactivation and decommissioning costs is about $10 billion.¹¹

Facility cleanup will be technically challenging and expensive for several reasons (NRC, 2001c, p. 24):

• Personnel hazards in these facilities—penetrating radiation, airborne contamination, and chemical and industrial hazards.

• Number and size of facilities and bulk of concrete shielding walls.

• Complex, crowded, and often retrofitted equipment arrangements.

• Lack of knowledge concerning the history of operations and contamination.

• Difficulty in identifying and quantifying many of the radioactive and chemical contaminants.

• Lack of decisions on the end states for many facilities.

NRC (2001c) concluded that the following DOE facilities will pose the most difficult cleanup challenges:

• Radiochemical separation facilities at Hanford and Savannah River and the Chemical Processing Plant at Idaho.

• Gaseous diffusion plants at Oak Ridge, Paducah, and Portsmouth (see NRC [1996i] for descriptions of these facilities).

• Plutonium processing plants and Hanford, Savannah River, and Los Alamos.¹²

• Tritium processing facilities at Savannah River.

NRC (2001c) identified specific science and technology gaps; these are described in the following sections.

Characterization describes the processes used to estimate the types and quantities of contamination present in facilities and equipment that are undergoing deactivation and decommissioning. Characterization is used to make the initial assessment of radioactive and chemical contaminants to guide decommissioning planning. It is

also used to monitor progress in removing contamination during the decontamination process. When decontamination is complete, characterization is again used to assess the effectiveness of decontamination and determine the disposition pathways for wastes, surplus equipment, and possibly the facility itself.

Hundreds of thousands of individual measurements might be required during the decontamination of a facility. Characterization as presently practiced requires workers to enter facilities to collect samples and make measurements. This labor-intensive process exposes workers to radiation and other hazards and is costly. In 2000, DOE estimated that characterization consumed an estimated 15 to 25 percent of facility cleanup budgets (NRC, 2001c, p. 50).

NRC (2001c) identified contaminant characterization for decommissioning as an important science and technology gap. That report recommended that research be undertaken to support development of the following:

• Devices for rapid characterization of low-levels of contamination (radionuclides and Environmental Protection Agency-listed substances) on surfaces of construction materials and equipment, including devices that can detect very-low-energy beta emitters (e.g., tritium) and low-energy photon emitters (iodine-125).

• Minimally invasive methods to characterize contaminant concentrations as a function of depth in construction materials, especially concrete.

• Instruments for remote mapping of radionuclide contamination at low levels that can differentiate specific radionuclides, including beta and alpha emitters.

Like characterization, decontamination is carried out at many stages of the decommissioning process. Initially, it might be used to lower radiation levels to allow workers to access a facility. It might also be used before equipment is disassembled or a facility is dismantled to prevent the spread of contamination. The primary objective of decontamination is to reduce the volume of contaminated waste that requires special handling and to allow the bulk of waste material to be recycled or disposed of without special precautions.

Current decontamination processes are labor intensive and costly. These processes also generate large volumes of secondary wastes and often leave behind unwanted residual contamination. Because of its cost and hazards, cleanup contractors often choose to dispose of

contaminated equipment and construction materials rather than decontaminate and recycle them.

NRC (2001c) identified decontamination as an important science and technology gap and recommended specific areas of research needed to improve decontamination technologies, including:

• Research on the chemical and physical interactions between contaminants and construction materials (e.g., steel and concrete) to gain a better understanding of how contaminants bind to and penetrate these materials.

• Research to support the development of biologically based decontamination processes, such as bioleaching agents, biosurfactants, and biocatalysts.

DOE can probably complete its decommissioning program using current approaches, which typically involve direct hands-on work in contaminated facilities. However, this approach is costly and potentially hazardous to workers. The utilization of robotics and intelligent machines in decommissioning could reduce worker exposures and might also reduce project costs (NRC, 1996i).

DOE is making limited use of some robotic technology, for example, as part of the Glovebox Excavator Method used to demonstrate retrieval of some buried transuranic waste at the Idaho Site (NRC, 2005c, p. 43). NRC (2003a) recommended that DOE develop such robotic technologies for retrieval and repackaging of buried waste. Such technologies could potentially be applied to some facility cleanups.

NRC (2001c) recommended research to develop intelligent and adaptable robotic systems that can be used for facility decommissioning. The specific need is to develop actuators (the power component of robotic systems) that can provide real-time information on position, velocity, and force of the robotic tool, as well as software that gives these systems a more humanlike ability to adapt to the variety of tasks likely to be encountered in actual decommissioning projects. NRC (1996i) recommended that DOE undertake focused demonstration of robotic decontamination technologies.

NRC (2001c) noted that DOE must determine the final end state of a facility before the decommissioning process can be completed. Possible end states range from complete dismantlement of the facility to unrestricted release of an intact building for other uses. The end state is usually established through a decision-making process that is informed by risk assessment and frequently involves negotiations with local parties. The general lack of understanding of the long-term behavior of contaminants in construction materials like steel and concrete may further limit end-state choices. NRC (2001c) identified long-term contaminant behavior as an important science and technology gap. The report recommended research to provide an improved understanding of long-term contaminant behavior in building construction materials. This includes understanding how the physical and chemical forms of contaminants evolve with time and how they are affected by decontamination activities. This research will help improve knowledge of how such changes might affect the eventual release of contaminants from building materials.

Chemicals, metals, and radionuclides have been introduced into the environment at DOE sites through accidental spills and leaks from storage tanks and waste transfer lines and also through intentional disposal via injection wells, disposal pits, and settling ponds. Releases into the environment generally were not closely tracked, and many release sites were unmarked and forgotten. Some of these sites are being rediscovered as DOE proceeds with its cleanup program.

This environmental contamination occurs in two distinct settings:

• Waste burial grounds. Waste was disposed of in pits, trenches, and auger holes at all major DOE sites. These were unlined and frequently unmarked after closure. There are major burial grounds at Hanford, Idaho, Oak Ridge, and Savannah River, and some of these are leaking contaminants to surface water and groundwater.

• Surface and subsurface contamination. Contamination of surface soils with metals, radionuclides, and hazardous chemicals is a pervasive problem at DOE sites. There is also extensive contamination of the subsurface with chemicals, metals, and radionuclides at all of the major DOE sites.

Groundwater and soil are contaminated with dense nonaqueous-phase liquids, toxic metals, and radionuclides. DOE estimates that its sites contain some 6.4 billion cubic meters (230 billion cubic feet) of contaminated groundwater and 40 million cubic meters (1.4 billion cubic feet) of contaminated soils and debris. The majority of this contamination exists at the Hanford Site (1.4 billion cubic meters [50 billion cubic feet]) and Idaho National Laboratory (4.7 billion cubic meters [170 billion cubic feet]) (see NRC 2000a, Table 2.3), where liquid and solid wastes were dumped or buried or pumped underground through injection wells. DOE’s most recent low-end estimate for environmental restoration activities at its sites exceeds $10 billion.¹³ The following science and technology gaps for soil and groundwater cleanup have been identified in previous NRC reports.

Three NRC reports (1994d, 1997e, 1999c) have examined the feasibility of active remediation, such as pump-and-treat, for soil and groundwater cleanup. The overall conclusion of these reports is that these remediation approaches have limited effectiveness. One of these reports (1997e) recommended that additional work be undertaken to assess the effectiveness of active remediation technologies, but these reports generally have not recommended further R&D on remediation technologies themselves.

Four NRC reports (1994d, 1997e, 1999c, 2000b) also have examined passive remediation technologies—for example, monitored natural attenuation. Three reports (NRC 1994d, 1997e, 1999c) have recommended that additional work be undertaken on passive remediation technologies, including reactive barriers and in situ bioremediation.

The challenges of locating subsurface contamination are magnified by the wide range of contaminant types (e.g., mixtures of organic solvents, metals, and radionuclides) in the subsurface at many DOE sites; the wide variety of geological and hydrological conditions at these sites; and the wide range of spatial resolutions at which this contamination must be located and characterized, from widely dispersed contamination in groundwater plumes to small isolated hot spots in waste burial grounds. Three NRC reports

(2000a, 2001f, 2002c) have identified characterization as an important science and technology gap. In particular, these reports recommended that DOE support research to develop new or improved capabilities to:

• Characterize the physical, chemical, and biological properties, including heterogeneity, of the subsurface, especially the unsaturated zone.

• Measure contaminant migration in the subsurface.

• Characterize buried waste in the subsurface, including waste container conditions.

Quantitative, or predictive, models are being increasingly utilized to estimate the long-term fate of contaminants in the subsurface and to investigate the potential effectiveness of potential remediation actions. Building such models requires a good knowledge of subsurface characteristics and behavior of natural processes that control contaminant transport. This assembled knowledge is referred to as a conceptual model of the subsurface. NRC (2000a) noted that existing conceptual and predictive models have often proven ineffective for predicting contaminant movement, especially at sites that have thick unsaturated zones or complex subsurface characteristics (e.g., the Hanford and Idaho sites and the Nevada Test Site).

NRC (2000a) also identified conceptual model development as an important science and technology gap. This report recommended basic research focused on the following topics to improve model development capabilities:

• New approaches for conceptual model development for complex subsurface environments.

• New approaches for incorporating subsurface heterogeneity into conceptual model formulations at scales that dominate contaminant flow and transport behavior.

• Development of coupled-process models that account for the physical, chemical, and biological processes that govern contaminant fate and transport behavior.

• Methods to integrate process knowledge from tests and observations into conceptual model formulations, and methods for establishing bounds on the accuracy of parameters and conceptual model estimates from field and experimental data.

When DOE’s cleanup program is completed, many sites will still contain substantial surface and near-surface contamination. These include waste burial sites, both historical sites from weapons production activities and new sites developed specifically for onsite disposal of waste from cleanup activities, stabilized underground tanks, abandoned facilities, and other near-surface release sites.

DOE plans to stabilize¹⁴ and cover many of these waste sites with surface barriers, or caps, to limit contact of the waste with surface water. The potential need for such barriers is enormous: There are potentially hundreds of near-surface sites (burial grounds, closed underground tanks, and liquid discharge sites) that will need to be covered with barriers to limit surface water infiltration. These sites occur in both arid and humid environments. The barriers installed on these sites must function for many generations.

The current emphasis in barrier deployment at DOE sites is on low-permeability engineered caps that are constructed of multiple layers of engineered and natural materials for stability, for intrusion prevention (especially by animals), and to limit infiltration. Subsurface barriers are not yet in wide use at DOE sites (except in engineered landfill facilities) but may receive increased attention in the future as DOE completes cleanup of tanks, burial sites, and other waste sites. These could include horizontal or vertical layers of clay, grout, or frozen or fused soil. DOE has experimented with reactive barriers to treat or retard contaminants in contaminated groundwater. Some of these could in principle also be used for waste containment.

Although there has been an increasing emphasis on and acceptance of waste containment and stabilization as “final” corrective actions at DOE sites, both by DOE management and regulatory agencies, there is relatively little understanding of the long-term performance of containment and stabilization systems. Moreover, there is a general absence of robust and cost-effective methods to validate that such systems are installed properly or that they can provide effective long-term protection.

Several NRC studies have called for research to develop improved containment and stabilization systems and to assess their effectiveness (NRC, 1996c, 1999c, 2000a, 2001f; see also NRC, 1997b, 2000d, 2005c). The specific science and technology gaps that

underpin the development of these improved technologies include the following (NRC, 2000a):

• Better understanding of the mechanisms and kinetics of chemically and biologically mediated reactions that can be exploited in containment systems. For example, better understanding of reactions that can extend the use of reactive barriers to a greater range of contaminant types found at DOE sites or that can be used to understand the long-term reversibility of chemical and biological stabilization methods.

• The physical, chemical, and biological reactions that occur among contaminants, soils, and barrier components so that more compatible and durable materials for containment and stabilization systems can be developed.

• The fluid transport behavior in conventional barrier systems to support the design of more effective infiltration barrier systems.

• The development of methods for assessing the long-term durability of containment systems.

Monitoring, defined broadly, refers to methods used to plan for and demonstrate the effectiveness of any remedial action, including waste containment. For example, monitoring is used to collect information to support the development of conceptual and predictive models of subsurface and contaminant behavior. It is also used to demonstrate the effectiveness of efforts to remove, treat, or especially to contain contamination or to gain regulatory approval for such actions.

Monitoring will be especially important to assess the long-term performance of the containment systems that will likely be installed across DOE sites. Such monitoring could in principle be used to assess the performance of containment barriers and provide an early warning of contaminant releases. NRC (2006a, pp. 84-90) identified the characteristics of a good monitoring system; the report also noted that DOE sites have not yet developed plans for postclosure monitoring of underground waste tank closures. The report recommended that DOE begin to plan now for postclosure monitoring so that provisions can be built into closure plans and designs.

Many of DOE’s sites will not be cleaned up sufficiently for unrestricted release after the cleanup program is completed (see NRC, 2000d). Those sites (or portions of sites) that cannot be released will be transferred to DOE’s Office of Legacy Management

once cleanup activities have ended; this office will be responsible for long-term site monitoring and maintenance. DOE’s low-end estimate for conducting these long-term stewardship activities is almost $10 billion through 2070.¹⁵

Two NRC reports have identified postclosure monitoring as an important science and technology gap for tank closure (NRC, 2001d, 2006a). NRC (2001d) recommended the development of in situ and noninvasive methods to monitor the near-field environment within and surrounding the tanks to detect early degradation of barriers or movement of contaminants.

More generally, some NRC reports (e.g., 2000a, 2001f, 2002c, 2005c) have recommended research to develop the following:

• Monitoring methods that can provide measurements of current conditions and detect changes in system behaviors, especially in the unsaturated zone and within and beneath caps and barriers.

• Methods to monitor fluid and gaseous fluxes through the unsaturated zone and within and beneath caps and barriers and for differentiating diurnal and seasonal changes from longer-term changes.

• Validation processes for modeling of containment systems, including determination of the key measurements that are required to validate models, the spatial and temporal resolutions at which such measurements must be obtained, and the extent to which surrogate data (e.g., data from lab-scale testing facilities) can be used in model validation efforts.

• Remote sensing technology to replace point-to-point practices for sampling and analyzing groundwater.

Such monitoring methods have potentially important application to engineered waste disposal facilities like WIPP to help validate their long-term performance (see NRC, 2000c, 2002c).

A recurring theme from many NRC reports published since the Environmental Management Program was created in 1989 is the importance of science and technology development for DOE’s site cleanup mission. This is perhaps best expressed in NRC (1995c, p. 114):

The identification of science and technology as a core continuing need in the cleanup program was identified in the first NRC review of DOE’s plans for waste management and environmental restoration (NRC, 1989a, p. 2):

Other NRC reports have highlighted the importance of science and technology development for improving cleanup capabilities, understanding and reducing cleanup risks, and reducing cleanup costs and schedules. These reports have generally taken a long-term (decadal or longer) view of science and technology development and have encouraged DOE not to ignore longer-term needs in the rush to meet short-term schedules. The following excerpts illustrate many of these points: