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Subsurface Contamination in the DOE Complex Over the last five decades, the United States has created a massive industrial complex to develop, test, manufacture, and maintain nuclear weapons for national security purposes. The U.S. Army Corps of Engi- neers, Manhattan Engineering District, started constructing the complex during the Second World War. The complex was expanded during the ensuing Cold War by the Atomic Energy Commission, the Energy Research and Development Authority, and starting in 1 977, the Depart- ment of Energy (DOE). The DOE complex, as it has come to be known, encompasses 1 34 distinct geographic sites in 31 states and one territory with a total area of over two million acres (DOE, 1 998a). The individual sites range in size from several hundred square miles to less than one square mile; these sites host a variety of defense-related activities rang- ing from uranium mining and milling to nuclear weapons testing (see Figure 2.1 ). The production and testing of nuclear weapons has created a legacy of significant environmental contamination, as described in some detail later in this chapter. In 1 989, Congress created the Office of Environ- mental Management (EM) in DOE to reduce threats to health and safety posed by the environmental contamination at DOE sites. To meet this objective, EM has undertaken a major cleanup effort, which, according to DOE, is the largest environmental cleanup in the world. This is cer- tainly true from a cost standpoint: EM is now spending about $5.8 bil- lion per year on its cleanup program and has spent over $50 billion since 1990. It expects to spend another $147 billion between 1997 and 2070 (DOE, 1 998a), but this estimate is uncertain because the magni- tude of contamination and the level of cleanup effort required at some sites are still poorly understood. In this chapter, the committee provides an overview of the subsur- face contamination problems around the DOE complex and shows by C h a p t e r 2

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~- -~ owl ~ ~ = ' I ~ -I DO \~ I ~ · ~ 1 141 _ —~ ~ · ~ FIGURE2.1 Location ofDOE example how advances in scientific and engineering knowledge can complex sites.The major improve cleanup effectiveness. The chapter is organized into three sec- sites are labeled by name on tions. The fi rst provides an overview of the DO E com p I ex and its m is- the figure. The locations of sion and describes the legacy of contamination from weapons produc- other sites are indicated by tion and re I ated activities. The second section i I I ustrates the range of closed cimles.SOURCE: DOE subsurface problems that exist across the complex today and what DOE is doing to correct them. The examples are taken from the six largest DOE sites: Hanford, Idaho, Nevada, Oak Ridge, Rocky Flats, and Savannah River (see Sidebar 2.1~. In the third section, the committee discusses how scientific and engineering research can improve the effectiveness of DOE's mission to tackle these contamination problems. S U B S U R F A C E S C ~ E N C E

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- - ~ \ · \ ~ - \ / - - ~ . ~ W:~ J ~ y J . 1 1 -in rim _ ~ / C3 / - r \ L/ This discussion will be used to support the recommendations in Chapters 5 and 6. Past Practices and Consequences Nuclear weapons production during the Cold War was a highly industrialized enterprise that involved a vast complex of mines and industrial sites across the United States. The front end of the process was focused on the production of uranium, which was then used to produce other weapons materials, particularly plutonium and tritium. C h a p t e r 2 \ /

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SIDEBAR2.1 THE DOE COMPLEX Although the DOE complex encompasses over 100 distinct sites, much of the major defense-related activities were conducted at the six largest DOE sites (see Figure 2.1) described below. The Hanford Site is located in southeastern Washington state and covers an area of about 1,450 square kilometers (560 square miles). Production of materials for nuclear weapons took place here from the 1940s until mid-1989.The site contains several production reactors,chemical separations plants,and solid and liquid waste storage sites. The Idaho National Engineering and Environmental Laboratory, first established as the Nuclear Reactor Testing Station and then the Idaho National Engineering Laboratory, occupies 2,300 square kilometers (890 square miles) in a remote desert area along the western edge of the upper Snake River plain.The site was established as a building, testing, and operating station for various types of nuclear reactors and propulsion systems, and the site also manages spent fuel from the naval reactor program. The Nevada Test Site, which occupies about 3,500 square kilometers (1,350 square miles) in southern Nevada, was the primary location for atmospheric and underground testing of the nation's nuclear weapons starting in 1951. The Oak Ridge Reservation covers an area of approximately 155 square kilometers (60 square miles) and is located about 10 kilometers (6 miles) west of Knoxville,Tennessee.The reservation has three major operating facilities: the Oak Ridge National Laboratory, the Y-12 Plant, and the K-25 Plant.The laboratory was originally constructed as a research and development facility to support plutonium production technology. The Y-12 Plant was built to produce highly enriched uranium by electromag- netic separation; and the K-25 Plant, formerly known as the Oak Ridge Gaseous Diffusion Plant, also was created to produce highly enriched uranium for nuclear weapons. The Rocky Flats Environmental Technology Site is situated on about 140 hectares (~350 acres) near Denver, Colorado, and has more than 400 manufacturing, chemical processing, laboratory, and support facilities that were used to produce nuclear weapons components. Production activities once included metalworking, fabrication and component assembly, and plutonium recovery and purification. Operations at the site ceased in 1989. The Savannah River Site, located near Aiken, South Carolina, covers an area of about 800 square kilo- meters (300 square miles).The site was established in 1950 to produce special radioactive isotopes (e.g., plutonium and tritium) for use in the production of nuclear weapons.The site contains produc- tion reactors, chemical processing plants, and solid and liquid waste storage sites. The back end was focused on the fabrication and testing of nuclear devices. The major production steps and waste byproducts are described in Sidebar 2.2. The United States is no longer produc ing plutonium and tritium1 for 1The secretary of energy has announced that DOE may produce tritium in the future to replenish current stocks of nuclear weapons. S U B S U R F A C E S C ~ E N C E 18

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TABLE 2.1 Principal Dense Non-Aqueous Phase Liquic (DNAPL), Metal, anc Racionuc~ice Contaminants in the DOE Complex DNAPLs Metals Radionuclides Trichloroethylene Lead Plutonium Dichloroethylene Chromium (Vl) Strontium-90 Tetrachloroethylene Mercury Cesium-137 Perchloroethylene Zinc Uranium (various isotopes) Chloroform Beryllium Tritium Dichloromethane Arsenic Thorium Polychlorinated Biphenyls Cadmium Technetium-99 Copper Radium iodine-1 29 SOURCE: EPA (1977); INEEL (1997); Riley and Zachara (1992). nuclear weapons, and a large part of the DOE complex has been shut down or placed on standby. All of DOE's production reactors have been shut down, and only two reprocessing facilities (the F and H canyons at Savannah River) continue to operate. These are scheduled to be phased out during the next decade. The weapons design and assembly facilities also continue to operate, but their mission now includes the disassem- bly of surplus nuclear weapons. The Nevada Test Site remains open, but only subcritical nuclear tests have been conducted there since 1992. During the last decade, a large part of the DOE complex, including some of the sites d iscussed i n Sidebar 2. 1, have taken on a new m is- sion: namely, remediation of the environmental contamination resulting from weapons production. This mission is formidable, because it involves cleanup of a wide variety of hazardous chemicals and radioac- tive materials introduced into the environment during five decades of weapons production and testing (see Sidebar 2.3~. The contaminants include dense non-aqueous phase liquids (DNAPLs; see Sidebar 2.4~; toxic metals such as lead, chromium, and mercury; and radionuclides such as plutonium, cesium, strontium, and tritium (see Table 2.1~. These contaminants were introduced into the environment through a variety of pathways, including intentional disposal into the ground through injection wells, disposal pits, and settling ponds; and through accidental spills and leaks from storage tanks and waste transfer lines. In some cases, there is little information available on either the timing or magnitude of contaminant releases to the environment, or the fate of contaminants in the subsurface after release. Moreover, DOE sites are C h a p t e r 2 19

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SIDEBAR 2.2 NUCLEAR FUEL CYCLE AND NUCLEAR WEAPONS PRODUCTION The production of nuclear weapons is a technically com- plex and highly industrialized process.The major production steps and waste byproducts of this process are described below. Mining and milling. Uranium ore was mined at over 400 sites in the United States and processed in mills to produce uranium oxide.These processes produced large volumes of mine and mill tailings that contained heavy metals and radioactive radium and thori- um.This waste is being managed through the Uranium Mill Tailings Radiation Control Act program. Nuclear Weapons Production Uranium Minina and Uranium Uranium Uranium Milling Refining Enrichment Foundry Fuel and Plutonium Target Production Fabrication Reactors Uranium is mined and Uranium is processed into low- Uranium gas is Uranium metal retinediromore enrichment uranium highly convertedinto isformedinto enriched uranium, an] depleted metal fuel and target uranium elements for reactors Uranium enrichment Elaborate chemical processes were used to concentrate the fissile isotope uranium- 235 from the milled ore. Uranium enrichment facilities were built at Oak Ridge (Y-12 and K-25 Plants), Ohio (Portsmouth Plant), and Kentucky (Paducah Plant).The waste streams from the enrichment process include depleted uranium (i.e., depleted in U-235 relative to U-238), uranium-contaminated scrap metal, polychlorinated biphenyl-contaminated waste, and a variety of organic solvents. Separation of lithium isotopes at the Oak Ridge Y-12 plant also produced large amounts of mercury waste. Fuel and target fabrication. The enriched uranium was converted to metal at the Fernald Plant in Ohio and then fabricated into reactor fuel or targets for plutonium production at Hanford and Savannah River.These processes produced uranium dust and a variety of chemical wastes. Plutonium production. The United States produced about 100 metric tons of plutonium between 1944 and 1988 at 14 reactors at the Hanford and the Savannah River sites.The reactors at Savannah River also produced tritium.Thousands of tons of uranium fuel were processed through the reactors during their four decades of operation.The waste streams from these operations include solid and liquid located in a variety of climatic zones and have complex subsurface characteristics (see Table 2.2), which makes it difficult to predict the location, transport, and fate of contaminants once they are released into the environment. As discussed in some detail in other National Research Counci I reports (N RC, 1 997a, 1 999), technologies to effec- tively remediate many subsurface DNAPL, metal, and radionuclide con- tamination problems are either lacking or are unproven for large-scale site remediation. Although subsurface contamination is generally acknowledged to be a significant problem across the DOE complex, estimates of the magni- S U B S U R F A C E S C ~ E N C E 20

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Weapons Design Testing Nonnuclear Components Reprocessing to Separate Plutonium Nuclear Components fin_ I_ Assembly and dismantlement Department —~~\\~—\ of Defense Warhead Triggers/ neutron generators, and other electrical and mechanical components are assembled into complete warheads Uranium slugs are irradiated to create plutonium metal and chemical separation is used to extract it Uranium and plutonium are further processed for warhead triggers Figure Source: DOE radioactive waste, acids, and solvents.The cooling water from the reactors contained some radionu- clides, most notably tritium. Plutonium Separation. Plutonium and other special isotopes were separated from the irradiated fuel by a variety of chemical processes. Chemical separations plants were located at the Hanford, Savannah River, and Idaho sites. Operation of the separations plants produced significant volumes of highly radioactive and hazardous chemical waste and water containing low levels of radionuclides and haz- ardous chemicals. Weapons design, fabrication, and assembly. Weapons design was the responsibility of the Los Alamos and Lawrence Livermore National Laboratories.Weapons components were produced at several sites in the United States, and final assembly took place at the Pantex Plant in Texas.The fabrication process produced several waste streams, including scrap uranium and plutonium metal and solvents. Weapons testing. The United States has conducted more than a thousand nuclear weapons tests in the atmosphere, under water, and underground, and most have occurred at the Nevada Test Site. This test- ing resulted in the contamination of surface and subsurface sites with radioactive materials, including tritium, plutonium, and fission products. tude of the problem vary considerably, as shown in Table 2.3. Accord- ing to recent DOE estimates (DOE, 1 998a) there are about 6.4 hi l l ion cubic meters (226 billion cubic feet) of contaminated soil, groundwater, and related environmental media at its sites.2 Most of this contamina- 2The subsurface contamination estimates provided in this chapter are compiled from various DOE documents. The committee cannot evaluate the accuracy of any of these estimates, but believes based on the briefings and documents it received during the course of this study that the estimates are likely to have very large uncertainties. C h a p t e r 2 21

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tion is at two sites, the Hanford Site in eastern Washington and the Idaho National Engineering and Environmental Laboratory in south- central Idaho (see Figure 2.1~. At these two sites alone, EM cleanup is not expected to be completed before 2050, and after cleanup is "com- plete" EM does not know how much contamination will remain in the ground to be managed through surveillance and containment. EM's current cleanup plans, which also are given in the Paths to Closure report (DOE, 1 998a), anticipate expenditures on the order of $57 hi I I ion between 1 997 and 2006 to complete cleanup at al I but 1 0 TABLE 2.2 Geologic anc C~imato~ogic Variability Across the DOE Weapons Complex DOE Site Climate Geology and Hydrogeology Surface Waters Depth to Groundwater (m) Savannah River Humid, subtropical Atlantic Coastal Plain with clay soils. Savannah River 0-38a Site The strata are deeply dissected by creeks, and most groundwater eventually seeps into and is diluted by the creeks. Hanford Site Arid,cool;mild Alluvial plain of bedded sediments Columbia River 60-90b winters and warm with sands and gravels. Groundwater summers;average flows toward the Columbia River. annual rainfall 16 cm (6.3 in.) Oak Ridge Humid,typical of Valley and ridge province bordering Clinch River 6-37' Reservation the southern the Cumberland Plateau. Primary Appalachian region; porosity is low, but fracture porosity average annual is present. High clay content. precipitation Shallow water table. 138 cm (54.4 in.) Rocky Flats Temperate, semiarid, Colorado Piedmont section of the Several streams 0-93 Environmental and continental Plains physiographic province. occur on or near Technology temperatures; average Alluvial deposits cover the site. the facility Site annual rainfall just under 40 cm (1 5 in.) Idaho National Semiarid with Near the northern margin of the Big Lost River and 60-240 Engineering and sagebrush-steppe Eastern Snake River plain, a low-lying other ephemeral Environmental characteristics located area of late Tertiary and Quaternary streams Laboratory in a belt of prevailing volcanism and sedimentation. western winds; Basalt covers three-quarters of its average annual rainfall surface. 22 cm (8.5 in.) Michelle Ewart, SRS, personal communication, 2000. bGephart and Lundgren (1998). 'Grover Chamberlain, DOE-HQ, personal communication, 2000. Christine Gel les, DOE-HQ, personal communication, 2000. SOURCE: Adapted from Sandia National Laboratories (1996),except where noted. S U B S U R F A C E S C I E N C E 22

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of its sites, including the major sites shown in Table 2.3. DOE expects an additional expenditure of $79 billion to clean up those remaining 10 sites between 2007 and 2070. About $14 billion will be incurred for SIDEBAR 2.3 A PRIMER ON RADIOACTIVE WASTE Radioactive wastes are the unwanted byproducts of the nuclear fuel cycle (see Sidebar 2.2) and may contain both radioactive isotopes and hazardous chemicals. In the United States, radioactive waste is classified and managed by its source of production rather than by its physical, chemical, or radioactive properties. Consequently, different classes of waste can contain many of the same radioactive isotopes, and even"low-level"waste can contain certain long-lived radioactive isotopes. In general, nuclear fuel cycle wastes are grouped into the following broad classes for purposes of man- agement and disposal: · Mill tailings are wastes resulting from the processing of ore to extract uranium and thorium. · Spent nuclear fuel is fuel that has been irradiated in a nuclear reactor, and for the purposes of dis- posal may include cladding and other structural components. · High-level waste is the primary waste produced from chemical processing of spent nuclear fuel.This waste is usually liquid in form and contains a wide range of radioactive and chemical constituents. Spent nuclear fuel is often referred to as high-level waste in nuclear waste management terminolo- gy although it is defined differently in the regulations. · Transuranic waste excludes high-level waste as defined above and includes waste that contains alpha-emitting transuranium (i.e., atomic number greater than 92) isotopes with half lives greater than 20 years and concentrations greater than 100 nanocuries per gram. DOE also includes U-233 in its definition of transuranic waste.This waste usually consists of contaminated materials like clothing and tools resulting from the manufacture of nuclear weapons. · Low-level waste is radioactive waste that does not meet one of the definitions given previously. There are two other classes of materials that DOE sometimes manages as waste: · Nuclear materials, such as plutonium and special-use isotopes, that may be declared as surplus and disposed of as waste. · Contaminated environmental media, such as contaminated soil and groundwater, that may fall under the Environmental Protection Agency's Comprehensive Environmental Response, Compensation and Liability Act.The cleanup of this contamination may generate additional radioactive and chemical waste streams that must be treated and managed. In the United States, the federal government regulates the management and disposal of most types of radioactive waste. Federal regulations seek to reduce to reasonably achievable levels the exposure of workers and other members of the public to this waste.The guiding philosophy for waste management is sequestration, that is, to isolate the waste from human populations and the environment, either through long-term storage or disposal in an underground facility until it no longer poses a hazard. C h a p t e r 2 23

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remedial action, which is defined by DOE as the characterization and cleanup of sites where contaminants or contaminated materials were released into the environment. The cleanup of these sites will involve the recovery and treatment of abandoned materials; remediation of soil, grou ndwater and su rface water; and man itori ng where contam i nation cannot be cleaned up to unrestricted release standards. According to EM, site cleanup will be considered "complete" when, among other things, releases to the environment have been cleaned up in accordance with agreed standards and groundwater contamination TABLE 2.3 Projectec Magnituce,Timing, anc Cost of DOE Cleanup Activities DOE Site Projected Completion Soil, Pre-2006 Post-2006 Residual Residual End State(s)a Date of Groundwater, Life-Cycle Life-Cycle Conta- Conta- Planned end Other Costs Costs minants minants Cleanup Media Requiring (1998 $B) (1998 $B)b in Soil in Water Projects Remedial Action (1 o6 ma) u u vie ~ ,,, — ~ ~ ~ a Hanford IM, other TBD 2046 1,400 13 37.4 Idaho UR, RR, IM 2050 4,700 5.1 11.3 Nevada RR, IM, 2014 3.1 d 0.92 1.3 Test Site otherTBD & Other Associated Sites' Oak Ridge & UR, RR, IM 2013 31 5.4 7.7 Associated Sitese Rocky Flats UR, RR, IM 2006-2010 0.79 5.3 0.96 Savannah IM, other TBD 2038 1 72 1 2 1 7.7 River Other Sites UR, RR, IM, 1999-2038 120 7.8 2.8 other TBD Totals 6,400 50 79 aUR = unrestricted release; RR = restricted release; IM = long-term institutional management;TBD = to be determined. bPost-2006 cost estimates include some but not all costs for long-term institutional management. 'Includes the Nevada Test Site and eight off-site locations in five states (Alaska, Colorado, Mississippi, Nevada, and New Mexico) where under- ground nuclear tests were conducted. Estimate does not include groundwater contaminated by nuclear testing. elncludes the Oak Ridge Reservation, the Paducah and Portsmith Gaseous Diffusion Plants in Kentucky and Ohio, respectively, and the Weldon Spring Site in Missouri. SOURCE: Compiled from DOE (1 998a, 1999). S U B S U R F A C E S C I E N C E

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has been contained or long-term treatment or monitoring has been put in place (DOE, 1 998a, p. 1-7~. In other words, even after EM has com- pleted its cleanup projects there will still be contaminants left in the subsurface and in surface land-disposal facilities that will require long- term management and possibly future actions to prevent further spread. Examples of Subsurface Contamination Problems at Ma jor DOE Sites The committee received several briefings on soil and groundwater contamination problems and remediation activities at five of the six major DOE sites (see Sidebar 2.1~: Idaho, Hanford, Nevada, Oak Ridge, SIDEBAR 2.4 NON-AQUEOUS PHASE LIQUIDS IN HETEROGENEOUS FORMATIONS Non-aqueous phase liquids (NAPLs) are a common class of subsurface contaminants at many DOE sites. Dense non-aqueous phase liquids (or DNAPLs) are organic chemicals such as trichloroethylene, tetrachloroethylene, and polychlorinated biphenyls that have densities greater than water (i.e., ~ 1.0 gram per cubic centimeter) at standard temperature and pressure and have low solubilities.Their rela- tively high density causes them to migrate downward through soils and groundwater under the influ- ence of gravity.When they encounter a low-permeability layer, they may pool or move laterally. Because of their low solubilities, NAPLs remain as a separate phase and may provide a long-term source of groundwater contamination. The detection, characterization, and remediation of DNAPL contamination is generally difficult for a number of reasons, including geological heterogeneity; complex physical, chemical, and biological interactions; lack of efficient and cost effective field characterization techniques; and limitations and unavailability of properly validated modeling tools for the design and evaluation of remediation tech- niques. Experimental studies (e.g.,Schwille, 1988; Keeper and Fried, 1991; lilangasekare and others, 1995) have shown that geologic heterogeneity can cause lateral spreading, preferential flow, and DNAPL pooling. In fact, such heterogeneities may be the major factor in controlling the entrapment distribution of DNAPLs in the subsurface.The DNAPL may exist as discontinuous, stable pore-scale masses trapped in soils under capillary forces, but it may also exist as an immobile continuous phase trapped by various heterogeneity features. Researchers (e.g., Pfannkuch, 1984; Schwille, 1988) have identified two geometries associated with subsurface DNAPL contamination: (1 ) cylinders or fingers, and (2) pools on impermeable layers or bedrock.The experimental work by Illangasekare and others (1995) and the conceptual studies by Hunt and others (1 986a,b) demonstrate that other geometries are possible as well, including zones of high saturation trapped in coarse lenses below the water table; thin pools trapped in coarse sand lay- ers; and suspended pools trapped on top of fine sand or clay layers. C h a p t e r 2 25

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SIDEBAR 2.7 EFFECTS OF SUBSURFACE HETEROGENEITY ON FATE AND TRANSPORT MODELING AND REM EDIATI ON Lawrence Livermore National Laboratory, a DOE facility in California, overlies groundwater contami- nated with volatile organic chemicals originating from land disposal of chemicals when the site was used as a naval airfield in the 1940s.There are multiple contamination zones corresponding to differ- ent disposal locations, consisting primarily of dissolved trichloroethylene and perchloroethylene groundwater contaminant plumes.The western-most plume stretches for over a mile and is of concern because it is migrating slowly toward municipal water supply wells in the city of Livermore. For over 10 years the site has been subject to intensive hydrogeologic investigation and remedial action (Thorpe and others, 1990). As a result, hundreds of monitoring wells have been installed to provide for geologic characterization of the site, monitor the composition and flow of groundwater, and support the design and implementation of remediation technologies. To more clearly understand the role and effects of geologic heterogeneity on remediation,Tompson and others (1998) used hydraulic conductivity data from 240 of these monitoring wells to construct a statistical distribution depicting the heterogeneous aquifer beneath the site. For a given realization of this distribution, together with various boundary conditions used to reflect remedial (associated with a remedial pumping well) or ambient conditions, groundwater flow paths can be produced using a finite difference flow model. To illustrate the effects of the fine-scale heterogeneity on contaminant transport and remedial recov- ery, hypothetical contaminant pulses were released in each model realization to evaluate plausible migration scenarios over 40 years of ambient conditions and then over 200 additional years of remedi- al pumping from a well located 1,000 meters from the original source. Model runs indicated a wide range of possible outcomes from one realization to the next.When the total pumping time was allowed to run for 200 years, in some cases most of the contaminant mass was recovered from the model domain,whereas in other realizations as little as one-third of the input mass was recovered.This indicates the drastic effect that spatial variability of aquifer materials the exact distribution of which is never known in precise detail can have on predictions of contaminant transport.The variation in the results is indicative of the real uncertainty that would be expected for the behavior of a natural system. Significant uncertainties in understanding of the inventory, distribu- tion, and movement of contaminants in the unsaturated zone exist at Hanford. Further, attempts to model contaminant fate and transport there have met with mixed success. Inaccurate models can have disas- trous consequences when they mislead treatment or containment strate- gies. Therefore, improved models for predicting contaminant migration are needed to evaluate the impact of such releases into the environ- ment. These models must be based on a good understanding of the sub- surface features that control contaminant fate and transport (e.g., see Sidebar 2.7), as well as important transport processes. S U B S U R F A C E S C ~ E N C E 36

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Metal and Radionuclide Contamination at Idaho An important mission at the Idaho site was chemical processing of spent fuel from research and naval reactor programs. After chemical processing, the high-level liquid waste was stored in underground tanks. Idaho managers recognized early on that tank storage space wou Id be insufficient, so the site developed a faci I ity to convert the waste into a powdered ceramic, or calcine, that could be more safely handled and stored. Consequently, Idaho was able to avoid the inten- tional discharge of high-level liquid wastes into the subsurface. There have nevertheless been several releases of radionuclides and metals from the single tank farm that supported the site's chemical pro- cessing facility. An underground waste transfer line was accidentally ruptured by drilling, and up to 13,700 liters (~3,600 gallons) of high- level waste with a total activity of over 32,000 curies was released into the unsaturated zone between 1956 and 1974. In 1972, another leak in the tank farm released about 52,900 1 iters (~1 4,000 gal ions) with a total activity of about 28,000 curies. The major contaminants include chromium, mercury, cesium, strontium, plutonium, and iodine. Some of this waste is located in a perched water zone beneath the tank farm, but the extent of waste migration is poorly known. The Idaho site is characterized by a thick unsaturated zone (see Table 2.2), but this zone overlies one of the largest aquifers in the west- ern United States, the Snake River aquifer, which covers an area of about 26,000 square kilometers (10,000 square miles). This aquifer sup- plies water to most of central Idaho and provides a major source of recharge to the Snake River. Protection of the aquifer and the river is a high priority at the Idaho site and is driving many of the site's remedia- tion decisions. Decisions about remediation of the radionuclide conta- mination beneath the tank farms is hampered by a lack of information about the distribution of contamination, as well as the physical and chemical characteristics of the unsaturated zone.6 Contamination in the Saturated Zone The saturated zone is defined as that part of the subsurface where pore spaces are filled with water. In unconfined aquifers, the top of the saturated zone defines the groundwater table. The principal saturated zone contamination problem across the DOE complex are contaminated groundwater plumes (i.e., large volumes of groundwater contaminated with dissolved and complexed chemicals, metals, and radionuclides). 6The committee was told that the least expensive remediation alternative would cost about $600 million and would involve removal of the perched water zone and pump-and-treat remediation of the underlying aquifer. C h a p t e r 2 37

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These plumes have been formed by the injection or migration of waste into moving groundwater and have length scales on the order of kilo- meters to tens of kilometers, depending on the nature of the source and the rate and direction of groundwater movement. All of the major DOE sites contain contaminated groundwater plumes, and in some cases these plumes have migrated off site or are discharging into surface waters. The following examples from the Savannah River, Nevada, Hanford, and Idaho sites are illustrative of plume-related problems across the DOE complex. DNAPt Plumes at Savannah River The Savannah River Site contains dozens of groundwater plumes containing DNAPLs, metals, and radionuclides, but the DNAPL plume in the Administrative and Materials Manufacturing Area is perhaps most interesting because of its size and location. That area comprises about 140 hectares (350 acres) in the northern portion of the Savannah River Site and is located less than a mile from the site boundary. Currently a research and development center, the area was first established for the manufacture of production reactor components, including target assem- blies and fuel rods (Westinghouse Savannah River Co., 1995~. From the 1 950s through the early 1 980s, contaminated wastewater from fuel and target manufacturing was pumped through an under- ground line into a settling basin, which had a capacity of about 30 mil- lion liters (8 million gallons). The basin overflowed periodically into a natural seepage area and a shallow depression known as Lost Lake and released approximately 1.6 million kilograms (3.5 million pounds) of solvents (principally trichloroethylene and tetrachloroethylene) and heavy metals to the environment. DOE believes that most of the heavy metals were trapped in the soil and about half of the solvents evaporat- ed, while the remainder migrated downward from the seepage areas into the groundwater (Westinghouse Savannah River Co., 1995~. In this part of the site the groundwater moves at rates ranging from a few cen- timeters to about 90 meters per year. DOE has instal led some 400 monitoring wel Is since 1 981 to track the spread of contamination, and based on these monitoring data and model ing studies, scientists at the Savannah River Technology Center have created a three-dimensional representation of the plume. DOE has installed a pump-and-treat system at the downstream toe of the plume to halt its further spread. DOE has been unable to locate or remove the DNAPL sources that are feeding this plume or to apply effective reme- diation technologies to the plume itself; it therefore faces the prospect of long-term institutional management of this contamination, including pump-and-treat remediation. S U B S U R F A C E S C ~ E N C E

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. Radionuclide Contamination at the Nevada Test Site Over 925 nuclear tests were conducted at the Nevada Test Site between 1 951 and 1 992 and resu Ited i n the emplacement i nto the sub- surface of several hundred million curies of radioactivity, including significant quantities of tritium, plutonium, and fission products (see Table 2.4~. Many of these tests were conducted at or below the ground- water table. Nevada officials contend that the site contains more conta- minated media than any other site in the DOE complex (Walker and Liebendorfer, 1 998~. DOE notes in Paths to Closure (DOE, 1 998a, p. E-56) that it has no plans to remediate the subsurface in and around the underground tests because "cost-effective remediation technologies have not yet been demonstrated." TABLE 2.4 Isotope Inventories from Uncergrounc Testing at the Nevaca Test Site Location Isotope Inventory (1 o6 curies) (Numbers are rounded) Pahute Mesaa Tritium 69.9 Cesium-1 37 1.95 Strontium-90 1.56 Krypton-85 0.13 Plutonium-241 0.09 Samarium-1 51 0.07 Europium-1 52 0.03 Plutonium-239 0.02 Europium-1 54 0.02 Others (34 isotopes) 0.05 Total Pahute Mesa 73.8 Non-Pahute Mesa Tritium 30.7 Potassium-40 24.7 Cesium-1 37 1.48 Strontium-90 1.19 Plutonium-241 0.10 Krypton-85 0.09 Europium-1 52 0.06 Samarium-1 51 0.05 Europium-1 54 0.05 Plutonium-238 0.03 Plutonium-239 0.01 Others (32 isotopes) 0.04 Total Non-Pahute Mesa 58.5 aSee Figure 2.5 for locations. SOURCE: Presentation to the committee by Robert Bangerter, DOE-Nevada Operations Office, December 15, 1998. C h a p t e r 2 39

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SIDEBAR 2.8 PLUTONIUM MIGRATION AT NEVADA TEST SITE? A potentially significant example of the deficiency in understanding subsurface radionuclide transport processes was provided by Karsting and others (1999), who reported that they had detected plutoni- um in groundwater at the Nevada Test Site. The plutonium was detected in water collected from moni- toring wells on Pahute Mesa, near the northwestern border of the test site (Figure 2.5).The plutonium was apparently being carried on colloids.The origin of the colloids and the plutonium geochemistry is still uncertain. Karsting and others were able to trace the plutonium to the Benham Test, which was detonated in 1968 in zeolitized bedded tuft at a depth below the surface of about 1,400 meters.This test is located about 1.3 km laterally and up to 600 meters below the monitoring wells.The origin of the plutonium was identified from its 240Pu/239Pu isotopic ratio,which is distinctive for each underground test.The pluto- nium ratio is recorded in the melt-glass collected from the underground test cavities. No evidence was found for migration of plutonium from other nearby tests. The suggested transport of plutonium at the test site has potentially significant implications for DOE's plans to passively manage contaminants there, especially if plutonium transport proves to be more pervasive than is currently recognized.This discovery also has potentially significant implications for the underground disposal of nuclear waste. Conventional wisdom suggests that plutonium is relatively immobile in oxidizing subsurface environments like at the test site and has strong sorbing tendencies. Indeed, underground tests at the test site were believed to demonstrate the effective fixation of pluto- nium in subsurface environments.The work by Karsting and others has demonstrated that the concep- tual models for plutonium migration are incomplete; it also suggests that additional basic research on the geochemical behavior of plutonium is required. Tritium is very mobile in groundwater, and large plumes of tritium have been detected from many of the underground tests. It has long been argued that most other radionuclides, and especially plutonium, are relatively immobile due to their low solubilities in groundwater and strong sorption onto mineral surfaces. As discussed in Sidebar 2.8, how- ever, recently published work challenges this conventional view. Mixed Contaminant Plumes at Test Area North Test Area North at the Idaho N ational Engi neeri ng and Envi ran mental Laboratory covers about 50 hectares (125 acres) in the northern part of the site and was used to support the Aircraft Nuclear Propulsion Program between 1954 and 1961. From 1960 through the 1 970s, the area housed the Loss-of-Fluid Test Facility, which was used for reactor safety testing and behavior studies. The primary source of the contami- nated groundwater plume is the Technical Support Faci I ity injection wel 1, which was used from 1 953 to 1 972 to inject I iquid wastes directly into the Snake River plain aquifer. The contaminants included raw sewage, trichloroethylene, tritium, strontium-90, and cesium-137. S U B S U R F A C E S C ~ E N C E 40

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Although the source area for this plume the injection wel I is known, the source term is not. Moreover, the subsurface in this region consists of highly fractured rock, which makes it difficult to locate and characterize the contamination. Characterization of the extent of conta- mination began in 1988, and recent data suggest that most of the con- tamination probably occurred as entrained sludge in two major fracture zones (see Figure 2.6~. Contaminant Plumes at the Hanford Site DOE estimates that groundwater under more than 220 square kilo- meters (85 square miles) of the Hanford Site is contaminated above cur- rent standards, mostly from operations in the 100 and 200 Areas (Plate 3~. The 100 Area is located on about 6,900 hectares (17,000 acres) in the northern section of the Hanford site and contains nine production reactors and several waste burial sites (DOE, 1996~. The main sources of subsurface contamination in the 100 Area are from radionuclide (mainly tritium) contaminated reactor cooling water and metal and DNAPL contaminants from operations and disposal. Contamination in the 200 Area was discussed in the section on the unsaturated zone ear- lier in this chapter. Disposal of supernatant liquids into the ground and leaks from the high-level waste tanks have produced significant contamination of the saturated zone in the 200 Area (Gephart and Lundgren, 1998~. Groundwater plumes of the following contaminants exist at levels exceeding current drinking water standards at the 200 Area: tritium, strontium-90, technetium-99, iodine-1 29, carbon tetrachloride, chromi um, and uranium. The plumes are flowing northeast toward the Columbia River at several tens of meters per year (see Figure 2.7~. Nevada \ Test Site Repute Mesh \L . ~ .' ." ~- I Nevada ~ ,i~ ~ 1\ 1\ .~ . . _ ~ _ Nevada\t Test Site · = Underground I nuclear test ~ 1 ~ l l l 0 15km C h a p t e r 2 \ Benham to Molbo \ ~ \O Tybo l XER-20-5 \ ~ Belmont 1 ~ 1 0 1200 2400 m , _ 1~ ~ ID 1 In 103 FIGURE 2.5 Plan view of Pabute Mesa with location of the Benham Test and groundwater collection well cluster ER-20-5. SOURCE: Karsting and others (1999).

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FIGURE2.6 Conceptual model for subsurface conta- mination at TestArea North at the Idaho Site. Dense non-aqueous phase liquids (DNAPLs) may be entrained in fractures and perched on dense basalt flows and sedi- mentary interbeds. SOURCE: Idaho Engineering and Environmental Laboratory. Not to Scale 1 ...... ~.2 ~ ......... . in. ~ TSF-05 injection well s 'A ~2su'd'-c'ie'l so- !_ & ~ ~ I Inlerlayereu casalt Claw ~1 1 1 ~~- ~ 1- P-Q Inlerbed _ ! ~ — inter, !!~ _1 ~ _ _ _ =t of I OW! ·:- l. i..~ .. .... · .- · · ·: . ... .... . . . .. _ . . ;' , s .. _. ~ . ~ 11 ~ ~1~ It - ~ Possible pooled DNAPL on _ _ 7`inlerbed moving info fractures | _ ~ 1~- _ ~ t rlPt~llnclwntpr Girl - rlir~r'lir~n _ J .. . _ . : ~ - | i; ~ ga~ TCE p bole ; ~ ., 1 .. I -: ;1 .::;.. 1 Possible DNAPL Pooled Din fract~,,: fractured and fissured flow margins ~ dense central portion of basalt fInw Q-R Inierbed DOE has established an extensive network of monitoring wells to track the movement of the groundwater plumes, but very little remedia- tion work is being done at present. DOE has established a groundwater extraction well network to intercept a chromium plume in the 100 Area. The ch rom i u m is extracted usi ng ion exchange and the treated water is returned to the aquifer. Pump-and-treat systems also have been established in the 200 Area to contain the highest concentrations of a uranium and technetium-99 plume and a carbon tetrachloride plume (DOE, 1 998b). DOE has a very poor understanding of the source areas, amounts, and timing of contaminant discharges into the subsurface at Hanford. ~ ~ . . . . UL)t IS beginning to support "forensic" investigations of past waste releases to the subsurface (e.g., Agnew and others, 1997), but additional work will be needed to improve the knowledge of the extent and mag- nitude of subsurface contamination at the Hanford site. Improvements in understanding and modeling fate and transport processes in the sub- surface is also needed to provide long-term predictive capabilities. S U B S U R F A C E S C ~ E N C E

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Conclusions The examples provided in this chapter illustrate that subsurface con- tamination is an enormously difficult cleanup problem as well as a sig- nificant challenge to science. Much of the subsurface contamination at DOE sites is poorly characterized and widely dispersed in the environ- ment, making it very expensive or technically impractical to treat effec- `,3 2; so ~ ~ i:-i3s3sss¢~$ ?~ ~ ~~ ~i. 4 ~ Is; ~ ~ is ~:~- ~ ~ off FIGURE 2.7 Plan view show- ing the fast spread of tritium plumes from the 200 East Area at the Hanford Site to the Columbia River. SOURCE: Richland Operations Office. sow- z ~:03~Li~:d B~333,3t fi3Xz~= Liz' ''I. otiose ~~#tS~ C;33 .,.. ~~ o~.~ 2 4 ~ ~ kzinm~s.~: ~'~1 ~ ~ ~N ~ $ 2 4 ~ zoom ~ ~ - ` ~$ ~ C h a p t e r 2 ), ~ SSS 3: A_ :~x §~3is33sis - ~ it; 3.\J~ ~

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tively with current technologies. Moreover, the contamination that can- not be removed or effectively isolated from the environment will require long-term management, which represents a potentially large future mortgage for the nation. · ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ .. SIDEBAR 2.9 BASIC SCIENCE CAN IMPROVE ENVIRONMENTAL MANAGEMENT Basic scientific research can provide several benefits to waste management efforts if it is properly focused on difficult cleanup problems (see Chapter 6). Basic research can produce new scientific knowl- edge and engineering tools to improve the effectiveness of cleanup efforts, lower cleanup costs, reduce risks to worker and public health, and improve environmental quality. Equally important, basic research can help improve current waste management practices and thereby reduce the likelihood of future environmental insults. Scientific studies in the 200 Area at Hanford provide a simple yet com- pelling illustration of the potential benefits for environmental management. The 200 Area is comprised of two major operating zones (200 East and 200 West) that contain a variety of waste disposal and waste storage facilities (see Plate 3).These facilities,which include drainage cribs, settling basins, and underground tanks, are major contributors to the site's groundwater contam- ination. As discussed elsewhere in this chapter, groundwater contaminant plumes have formed beneath both areas, but the plumes originating from the 200 East Area are significantly larger in size, extending some 15 kilometers (9 miles) to the Columbia River (see Figure 2.7). Basic geological research conducted at Hanford (see Reidel and others [1992] and DOE [1998b] for a summary of the Hanford geology) suggests that plume size is controlled to a large extent by the physi- cal and chemical properties of the geological formations underlying the 200 Area.The 200 East Area is underlain by the Hanford Formation, which is comprised of permeable sands and gravels that provide relatively direct pathways to the groundwater some 100 meters below the surface. The 200 West Area, on the other hand, is underlain by the Ringold Formation, which consists of less permeable sands, grav- els, and clays that provide a barrier to widespread contaminant migration. These findings provide a compelling demonstration that~geology counts" in waste management and site remediation, and that locating disposal facilities must take account of subsurface properties as part of a defense-in-depth waste containment strategy.' DOE is constructing and operating several facilities in the 200 Area to dispose of a variety of cleanup and defense wastes. It recently sited a large land disposal facility (the Environmental Restoration Disposal Facility) in 200 West to manage certain types of chemically and radioactively hazardous cleanup wastes from other parts of the Hanford Site. At least two other disposal facilities have been constructed or are planned for the 200 East Area: the Naval Reactor Disposal Facility, which contains nuclear reactors from decommissioned U.S. Navy sub- marines, and the planned Immobilized Low-Activity Waste Disposal Facility,which will take low-activity waste generated during processing of high-level waste from the Hanford tanks. If the past is a guide to the future, the disposal facilities in the 200 East Area may create new site contamination problems that will require additional remediation efforts. HA defense-in-depth waste containment strategy uses multiple artificial or natural barriers to improve the long-term performance of the containment system. S U B S U R F A C E S C ~ E N C E 44

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The committee believes that this future mortgage could be reduced significantly through the development of new and improved technolo- gies to locate, remove or contain, and monitor subsurface contamina- tion at DOE sites. However, the development of such technologies will require advances in basic understanding of the complex natural systems at DOE sites and also in understanding the nature of contaminant "insults" to those systems. The report of the NRC Committee on Building an Effective Environmental Management Science Program (NRC, 1 997b, p. 22) concluded that "new technologies are required to deal with EM's most difficult problems, and new technologies require new science." The present committee agrees with this statement and notes that, given the long-term nature of the cleanup mission and its projected cost (see Chapter 1), DOE has necessary cause and time to do the required basic research to support the development of these needed technologies (see Sidebar 2.9~. C h a p t e r 2 45

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S U B S U R F A C E S C I E N C E 46