Research Needs in Subsurface Science (2000) / Chapter Skim
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2 Subsurface Contamination in the DOE Complex
2 Subsurface Contamination in the DOE Complex
Pages 15-46
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In this chapter, the committee provides an overview of the subsurface contamination problems around the DOE complex and shows by C h a p t e r 2
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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~.
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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.
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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.
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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.
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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.
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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.
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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.
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· 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 terminology although it is defined differently in the regulations.
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'Includes the Nevada Test Site and eight off-site locations in five states (Alaska, Colorado, Mississippi, Nevada, and New Mexico) where underground nuclear tests were conducted.
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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.
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To highlight this fact, the committee has organized the discussion around different contaminant settings: waste burial ground contamination, soil contamination, unsaturated zone contamination, and saturated zone contamination. These are illustrated schematically in Figure 2.2.
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Radioactive Waste Management Complex at Idaho The Radioactive Waste Management Complex was established in 1952 for disposal of solid low-level radioactive waste generated on site. Waste from other DOE sites was also buried here, including transuranic waste from Rocky Flats.
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Remediation efforts currently SIDEBAR 2.5 HISTORICAL WASTE MANAGEMENT PRACTICES IN THE DOE COMPLEX This April 1962 photograph was taken a few days after rapid melting and rain caused flooding of a pit in what is now the Radioactive Waste Management Complex at the Idaho site. Barrels and boxes containing mixed (radioactive and hazardous)
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One of the guiding philosophies of waste management throughout the DOE complex, especially prior to the 1 980s, can perhaps best be characterized as "out of sight, out of mind." Such radioactive and chemical wastes as tritium, chromium, mercury, lubricating oils, solvents, and raw sewage were discharged directly into surface waters, surface drainage basins, or directly into aquifers through injection wells. Solid and liquid radioactive and chemical wastes were also buried in shallow pits and trenches, which are now known by the somewhat euphemistic term "burial grounds." Some of these trenches filled with water during periods of high rainfall, which promoted migration of chemicals and radionuclides into the subsurface.
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Travel time from the complex to the underlying Snake River plain aquifer has been the subject of intense debate spanning several decades. Because of site aridity, it was initially assumed that the thick unsaturated zone beneath the complex afforded a high degree of contaminant retardation, but even 40 years ago concerns were raised about the assumption of a long travel time.
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Soil4 Contamination Contamination of surface and near-surface environments is a pervasive problem at all of the major DOE sites. This contamination includes metals, radionuclides, and hazardous chemicals and is the result of poor waste management practices, such as those illustrated below.
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. Mercury and Cesium Contamination at Oak Ridge Because of poor operational and waste management practices, the streams and rivers on part of the Oak Ridge site have been extensively contaminated with mercury and radioactive cesium.
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The unsaturated zone exists at all of the major DOE sites, but as shown in Table 2.2 its thickness varies significantly among sites. The unsaturated zone tends to be the thickest at the arid western sites at Hanford, for example, the unsaturated zone is up to about 90 meters (~300 feet)
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The waste disposal facilities include surface settling basins and underground drainage cribs constructed for disposal of low-activity liquid wastes as well as solid waste burial pits and trenches. The waste storage facilities include 18 tank farms that contain 177 underground storage tanks containing about 200 million liters (54 million gallons)
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This discovery came as a surprise to DOE, because cesium and strontium were assumed to be immobile in the unsaturated zone, and DOE's models of the unsaturated zone predicted that these radionuclides would not migrate significantly. This finding has prompted a reorganization of the cleanup work and a greater effort to integrate science into cleanup activities at Hanford.5 5As a result of this discovery and at the prompting of Congress, DOE created a new organization (Office of River Protection)
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Significant uncertainties in understanding of the inventory, distribution, 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.
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Protection of the aquifer and the river is a high priority at the Idaho site and is driving many of the site's remediation decisions. Decisions about remediation of the radionuclide contamination 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.
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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.
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Many of these tests were conducted at or below the groundwater table. Nevada officials contend that the site contains more contaminated media than any other site in the DOE complex (Walker and Liebendorfer, 1 998~.
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The primary source of the contaminated 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.
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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)
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, but additional work will be needed to improve the knowledge of the extent and magnitude of subsurface contamination at the Hanford site. Improvements in understanding and modeling fate and transport processes in the subsurface is also needed to provide long-term predictive capabilities.
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~ ~ ~~ ~i. 4 ~ Is; ~ ~ is ~:~ ~ ~ off FIGURE 2.7 Plan view showing the fast spread of tritium plumes from the 200 East Area at the Hanford Site to the Columbia River.
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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)
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The report of the NRC Committee on Building an Effective Environmental Management Science Program (NRC, 1 997b, p.
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