Scientific Investigations Report 2006-5122
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5122
Wastewater-disposal sites at Test Area North (TAN), the Test Reactor Area (TRA), and the Idaho Nuclear Technology and Engineering Center (INTEC) were the principal sources of radioactive- and chemical-waste constituents in water in the Snake River Plain aquifer. In the past, wastewater-disposal sites have included lined evaporation ponds, unlined infiltration ponds and ditches, drain fields, and disposal wells. Waste materials buried at the Radioactive Waste Management Complex (RWMC) also are sources of some constituents in ground water. A brief history of wastewater-disposal practices at various facilities on the INL is provided below. Most of this historical information is documented in a report by Bartholomay and others (2000).
Test Area North—From 1953 to 1972, low-level radioactive, chemical, and sanitary wastewater was discharged at TAN (fig. 1) into the Snake River Plain aquifer through a 310‑ft‑deep disposal well. In 1972, the disposal well was replaced by a 35‑acre infiltration pond. No records are available on the amount of radioactivity in wastewater discharged at TAN before 1959. During 1959–93, about 61 Ci of radioactivity was in wastewater discharged to the disposal well and infiltration pond. Of this amount, about 20 Ci was discharged to the disposal well in 1968 and 1969 in response to problems with an evaporator used to reduce the volume of wastewater. No radioactive wastewater was discharged to TAN disposal sites since 1993.
Test Reactor Area—Since 1952, wastewater containing low-level radioactive contaminants was discharged to infiltration and evaporation ponds at the TRA. The wastewater was discharged to a series of infiltration ponds until 1993, when two lined evaporation ponds replaced the infiltration ponds to prevent the wastewater from entering the aquifer. The average annual discharge to the infiltration and evaporation ponds was about 116 Mgal during 1960–98 (Bartholomay and others, 2000, p. 10). Radioactive constituents in the wastewater discharged to the ponds included tritium (about 10,000 Ci), strontium-90 (about 93 Ci), cesium-137 (about 138 Ci), and cobalt-60 (about 438 Ci). During 1974–79, about 10 percent of the radioactivity in wastewater discharged to the subsurface was attributed to tritium; in 1980, about 50 percent was attributed to tritium; and in 1981–85, about 90 percent was attributed to tritium (Pittman and others, 1988, p. 22). Since 1986, about 97 percent of the radioactivity in wastewater discharged at the TRA was attributed to tritium.
The radioactive-waste infiltration ponds also were used for disposal of wastewater containing nonradioactive chemical wastes until 1962, when a chemical-waste infiltration pond was constructed. This infiltration pond was used principally for disposal of chemical wastewater from an ion-exchange system at the TRA. The average annual discharge to this pond was about 17.5 Mgal for the period 1962–98. Sulfate and sodium hydrate were the predominant constituents in the wastewater.
Nonradioactive cooling-tower wastewater was discharged to the radioactive-waste infiltration ponds from 1952 to 1964, to the Snake River Plain aquifer through a 1,267‑ft‑deep disposal well from 1964 until 1982, and into two cold‑waste infiltration ponds from 1982 to present. Until 1972, cooling-tower wastewater contained concentrations of dissolved chromium used as a rust inhibitor. The average annual discharge to the well and the infiltration ponds was about 226 Mgal during 1964–95 and about 181 Mgal during 1996–98.
Idaho Nuclear Technology and Engineering Center—From 1952 to February 1984, most of the low-level radioactive, chemical, and sanitary wastewater at the INTEC (fig. 1) was discharged to the Snake River Plain aquifer through a 600‑ft‑deep disposal well. The average annual discharge of wastewater to the well was about 363 Mgal (Pittman and others, 1988, p. 24). Beginning in 1984, two infiltration ponds were used for wastewater disposal. An average of 442 Mgal of wastewater was discharged annually to the well and infiltration ponds during 1962–98. The annual discharge to the well and ponds ranged from a low of 260 Mgal in 1963 to a high of 665 Mgal in 1993.
Tritium has accounted for more than 90 percent of the radioactivity in wastewater discharged at the INTEC since 1970. More than 20,000 Ci of tritium in wastewater was discharged to the disposal well and infiltration ponds at the INTEC.
Radioactive Waste Management Complex—Solid and liquid radioactive and chemical wastes were buried in trenches and pits at the Subsurface Disposal Area (SDA) at the RWMC (fig. 1) since 1952. These constituents include transuranic wastes (buried in trenches until 1970), other radiochemical and inorganic chemical constituents, and organic compounds. Before 1970, little or no sediment was retained between the excavation bottoms and the underlying basalt. Since 1970, a layer of sediment was retained in excavations to inhibit downward migration of waste constituents.
About 9,600 Ci of plutonium-238, 160,000 Ci of plutonium-239, 38,000 Ci of plutonium-240, 960,000 Ci of plutonium-241, and 365,000 Ci of americium-241 were buried in the SDA during 1952–70 (Becker and others, 1998, table 4-1). An estimated 88,400 gal of organic waste was buried before 1970 (Mann and Knobel, 1987, p. 1). These buried wastes included about 24,400 gal of carbon tetrachloride; 39,000 gal of lubricating oil; and about 25,000 gal of other organic compounds, including trichloroethane, trichloroethylene, perchloroethylene, toluene, and benzene.
Regional-, subregional-, and local-scale models require different levels of descriptive information (table B1). For example, all three models require information about the distribution of the major rock types that compose the aquifer. In the eastern Snake River Plain, basalt is the most abundant rock type and has many different forms. For a regional-scale model (Garabedian, 1992) it may not be necessary to account explicitly for these different forms of basalt. However, for a subregional-scale model, it is meaningful to describe the general distribution of fractured, massive, and altered basalt. For a local- or facility-scale model, it may be necessary to describe the distribution of the many different forms of basalt and associated volcanic deposits that are present at any one place (Anderson and others, 1999).
U.S.
Department of the Interior | U.S. Geological
Survey
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