Scientific Investigations Report 2006-5088

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5088

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Introduction

The Idaho National Laboratory (INL) is operated by the U.S. Department of Energy (DOE) and encompasses about 890 mi2 of the eastern Snake River Plain in southeastern Idaho (fig. 1). Names formerly used for this site, from earliest to most recent, were National Reactor Testing Station (NRTS, from 1949 to 1974), Idaho National Engineering Laboratory (INEL, from 1974 to 1997), and Idaho National Engineering and Environmental Laboratory (INEEL, from 1997 to 2005). The INL facilities are used in the development of peacetime atomic-energy applications, nuclear safety research, defense programs, environmental research, and advanced energy concepts. Radiochemical and chemical wastewater generated at these facilities has been discharged to either onsite infiltration ponds, evaporation ponds, disposal wells, or a combination thereof, since 1952. Wastewater disposal has resulted in detectable concentrations of several waste constituents in water from the Snake River Plain aquifer underlying the INL.

The DOE requires information about the mobility of dilute radiochemical- and chemical-waste constituents in the Snake River Plain aquifer. Waste-constituent mobility is determined, in part, by (1) the rate and direction of ground-water flow; (2) the locations, quantities, and methods of waste disposal; (3) waste-constituent chemistry; and (4) the geochemical processes taking place in the aquifer. This study was conducted by the U.S. Geological Survey (USGS) in cooperation with the DOE’s Idaho Operations Office.

Purpose and Scope

In 1949, the U.S. Atomic Energy Commission, which later became the DOE, requested that the USGS describe the water resources of the area now known as the INL. The purpose of the resulting study was to characterize these resources before the development of nuclear-reactor testing facilities. Since that time, the USGS has maintained water-quality and water-level monitoring networks at the INL to determine hydrologic trends and to delineate the movement of radiochemical and chemical wastes in the Snake River Plain aquifer.

This report presents an analysis of water-level and water-quality data collected from wells in the USGS ground-water monitoring networks during 1999–2001 as part of the continuing hydrogeologic investigations conducted by the USGS at the INL. The report describes the distribution and concentration of selected radiochemical and chemical constituents in ground water at the INL, and changes in the water-level regime since 1998.

Previous Investigations

Several reports that describe the geology and hydrology of the INL have been published; a list of references and copies of reports can be obtained at the USGS INL Project Office or on the USGS Publications Warehouse Web Site at URL http://infotrek.er.usgs.gov/pubs/.

Ground-water conditions and distribution of selected wastewater constituents in the Snake River Plain aquifer are discussed in a series of annual reports describing the NRTS. The series includes reports by Jones (1961); Olmsted (1962); Morris and others (1963, 1964, 1965); Barraclough and others (1967a); and Barraclough and others (1967b). Nace and others (1975) presented the generalized geologic framework of the NRTS. Robertson and others (1974) presented an analysis of the effects of waste disposal on the geochemistry of ground water at the NRTS. Barraclough and others (1976) gave a comprehensive discussion on the hydrology of the solid waste burial ground, now the Radioactive Waste Management Complex (RWMC). Data on hydrologic conditions at the INL have been described in a series of reports: hydrologic conditions during 1971–73 were described by Barraclough and Jensen (1976), during 1974–78 by Barraclough and others (1981), during 1979–81 by Lewis and Jensen (1985), during 1982–85 by Pittman and others (1988), during 1986–88 by Orr and Cecil (1991), during 1989–91 by Bartholomay and others (1995), during 1992–95 by Bartholomay and others (1997), and during 1996-98 by Bartholomay and others (2000).

Cecil and others (1991) discussed mechanisms responsible for formation of perched ground water at the Reactor Technology Complex (RTC) [known as the Test Reactor Area (TRA) until 2005], the Idaho Chemical Processing Plant (ICPP, now the Idaho Nuclear Technology and Engineering Center, or INTEC), and the Radioactive Waste Management Complex (RWMC) and described the distribution of chemical and radiochemical constituents in perched ground water at the RTC, ICPP, and RWMC during 1986–88. The hydrologic conditions and distribution of selected radiochemical and chemical constituents in perched ground water during 1989–91 were described by Tucker and Orr (1998), during 1992–95 by Bartholomay (1998), and during 1996–98 by Bartholomay and Tucker (2000).

Ground-Water Monitoring Networks

The USGS maintains ground-water monitoring networks at the INL to characterize the occurrence, movement, and quality of water and to delineate waste-constituent plumes in the Snake River Plain aquifer. These networks consist of wells from which periodic water-level and water-quality data are obtained. Data from these monitoring networks are on file at the USGS INL Project Office and are available on the USGS National Water Information System (NWIS) Web Site at URL http://waterdata.usgs.gov/id/nwis/nwis.

Water-Level Monitoring Network

The water-level monitoring network was designed to determine hydraulic-gradient changes that affect the rate and direction of ground-water and waste-constituent movement in the Snake River Plain aquifer, to identify sources of recharge to the aquifer, and to measure the effects of recharge. Water levels in 153 wells were monitored during 1999–2001. Water levels were measured annually in 27 wells, semiannually in 51 wells, quarterly in 60 wells, monthly in 11 wells, and continuously recorded in 4 wells. Figures 2 and 3 show the location of wells and the frequency of water-level measurements as of December 2001.

Water-Quality Monitoring Network

The radiochemical and chemical character of water in the Snake River Plain aquifer is determined from analyses of water samples collected as part of a comprehensive sampling program to identify contaminant concentrations and to define the pattern of waste migration in the aquifer. Water samples from surface-water sites at or near the INL and from wells in perched ground-water zones are analyzed to document the chemical quality of water that recharges the aquifer. Water samples are collected from wells that penetrate the aquifer to various depths and with differing well completions and are analyzed to identify trends in water quality. Numerous water samples are collected near areas of detailed study, such as the RTC, INTEC, RWMC, Test Area North (TAN), and Central Facilities Area (CFA). Water samples from the Naval Reactors Facility (NRF) are collected and analyzed as part of a separate study and results are presented in series of separate reports (Bartholomay and others, 2001a, 2001b).

The type, frequency, and depth of ground-water sampling generally depend on the information needed in a specific area. Water samples routinely are collected and analyzed for concentrations of tritium, strontium-90, cobalt-60, cesium‑137, plutonium-238, plutonium-239, -240 (undivided), americium-241, gross alpha- and beta-particle radioactivity, chromium, sodium, chloride, sulfate, nitrate, purgeable organic compounds, and measurements of specific conductance, pH, and temperature. In addition, as part of the INL ground-water monitoring program adopted in 1994 (Sehlke and Bickford, 1993), samples from several wells also are analyzed for fluoride, an extensive suite of trace elements, and total organic carbon. Water samples are analyzed for the radiochemical constituents at the Radiological and Environmental Sciences Laboratory (RESL) at the INL and for chemical constituents at the USGS National Water Quality Laboratory (NWQL) in Lakewood, CO. The location of wells in the water-quality monitoring network as of December 2001, and the frequency of sample collection are shown in figures 4 and 5, and in table 1. A sample schedule that lists the constituents analyzed at each site is given in a report by Bartholomay and others (2003, attachment 1).

The methods used in sampling and analyzing for selected constituents generally follow the guidelines established by the USGS (Goerlitz and Brown, 1972; Stevens and others, 1975; Wood, 1976; Claassen, 1982; W.L. Bradford, written commun., 1985; Wershaw and others, 1987; Fishman and Friedman, 1989; Faires, 1993; Fishman, 1993; and Wilde and others, 1998). Water samples analyzed by the NWQL and RESL were collected in accordance with a quality-assurance plan for water-quality activities conducted by personnel at the USGS INL Project Office. The plan was finalized in June 1989, revised in March 1992, in 1996 (Mann, 1996), and in 2003 (Bartholomay and others, 2003) and is available for inspection at the USGS INL Project Office. About 10 percent of the samples generally are collected for quality assurance. Quality-assurance samples include equipment blanks, trip blanks, splits, replicates, and spiked samples. Comparative studies to determine agreement among analytical results for water-sample pairs analyzed by laboratories involved in the USGS INL Project Office quality-assurance program were summarized by Wegner (1989), Williams (1996, 1997), and Williams and others (1998). Additional quality-assurance studies by personnel at the USGS INL Project Office include an evaluation of field-sampling and preservation methods for strontium-90 (Cecil and others, 1989), a comparison of different pump types used for sampling purgeable organic compounds (Knobel and Mann, 1993), an analysis of tritium and strontium-90 concentrations in water from wells after purging different borehole volumes (Bartholomay, 1993), an analysis of the effect of different preservation methods on nutrient concentrations (Bartholomay and Williams, 1996), and an analysis of two analytical methods for the determination of gross alpha- and beta-particle radioactivity (Bartholomay and others, 1999).

Waste-Disposal Sites at the Idaho National Laboratory

Wastewater disposal sites at INL facilities have been the principal sources of radioactive- and chemical-waste constituents in water from the Snake River Plain aquifer at and near the INL. In the past, wastewater disposal sites have included infiltration ponds and ditches, evaporation ponds, drain fields, and disposal wells. Solid and liquid wastes buried at the RWMC (fig. 1) also are sources of some constituents in ground water.

Radioactive- and chemical-waste-disposal data are collected by contractors at each INL facility. Historical radioactive-waste-disposal data presented in this report were obtained from a series of radioactive-waste-management information reports (French and others, 1997b; French and Taylor, 1998, and French and others, 1999b). Chemical-waste-disposal data were obtained from a series of nonradiological-waste-management information reports (French and others, 1997a; 1998; 1999a). Since 1999, there has been no formal program in place to compile annual amounts of constituents discharged at each facility (Richard Kauffman, U.S. Department of Energy, oral commun., 2005), however, the INEEL Site Environmental Reports (Stoller Corp., 2002a, 2002b, and 2002c) provide some radioactive waste disposal data for 1999–2001. Effluent monitoring and wastewater discharge raw data for some INL facilities were provided to the author by DOE contractor personnel (Teresa Meachum, CH2M-WG Idaho, LLC, written commun., 2005), however compilation of those data was beyond the scope of this report. Therefore, amounts and types of most radioactive- and chemical-wastes discharged at the various facilities for 1999–2001 are not presented in this report.

Reactor Technology Complex

Since 1959, low-level radioactive, chemical, and sanitary wastewater has been discharged to infiltration and lined evaporation ponds. Nonradioactive cooling-tower wastewater was discharged to radioactive-waste infiltration ponds from 1952 to 1964, to the Snake River Plain aquifer through a 1,267-ft-deep disposal well (TRA DISP, fig. 3) from 1964 until March 1982, and into two cold-waste infiltration ponds from 1982 to the present.

In 1976, the DOE contractor at the RTC began a three‑phase program to reduce radioactivity in wastewater. The first phase ran from 1976 to 1980 and the second phase ran from 1981 to 1987. The contractor finished the final phase of the program in 1993. The volume of radioactive wastewater and total number of Curies (Ci) of radioactivity discharged at the RTC decreased because of this program. During 1977–78, the average number of Curies discharged to the RTC radioactive-waste infiltration ponds was about 1,300 Ci/yr (Barraclough and others, 1981); during 1992–95, about 430 Ci of tritium was discharged to the RTC radioactive-waste infiltration ponds. During 1992–95, tritium accounted for about 96 percent of radioactivity in wastewater discharged at the RTC (Bartholomay and others, 1997). In August 1993, two lined evaporation ponds replaced the radioactive-waste infiltration ponds (B.R. Orr, U.S. Geological Survey, oral commun., 1996). The evaporation ponds may prevent radioactive wastewater from entering the aquifer.

The average annual discharge to the radioactive-waste infiltration and evaporation ponds (fig. 3) was about 116 Mgal during 1960–98. The volume of wastewater and the amount of tritium discharged to the radioactive-waste and evaporation ponds during this period are shown in figure 6. During 2000–01, effluent waste disposal to the evaporation ponds averaged about 5 Mgal (Richard Kauffman, U.S. Department of Energy, written commun., 2005), much less than the long-term average.

During 1974–79, about 10 percent of the radio­activity in wastewater discharged was attributed to tritium; most of the rest consisted of radionuclides with half-lives on the order of several weeks, as well as small amounts of strontium-90, cesium-137, and cobalt-60 (Barraclough and others, 1981). In 1980, about 50 percent was attributed to tritium; and during 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 RTC has been attributed to tritium (fig. 6).

A chemical-waste infiltration pond was used for disposal of chemical wastewater from an ion-exchange system at the RTC (fig. 3) from 1962 to 1999. The average annual discharge to this pond was about 17.5 Mgal for the period 1962–98 (Bartholomay and others, 2000). The average annual discharge for 1996–98 was 5.8 Mgal, 33 percent of the long-term average (Bartholomay and others, 2000). Sulfate and sodium hydrate were the predominant constituents in the chemical wastewater. The sodium hydrate consists of a 50 percent sodium hydroxide solution (Bartholomay and others, 2000). During 1996–98, average annual amounts of about 210,280 lb of sulfate and 98,800 lb of sodium hydrate were discharged to the chemical-waste infiltration pond. Additionally, about 11,100 lb of sodium ion was discharged in October 1996 (French and others, 1997a). Average annual concentrations of sulfate and sodium hydrate in the wastewater were about 4,300 and 2,000 mg/L, respectively (Bartholomay and others, 2000). In 1999, the chemical-waste infiltration pond was closed and covered with a protective cap (Stoller Corp., 2002a).

The TRA disposal well, which currently is used as an observation well, was used from 1964 to March 1982 to inject nonradioactive wastewater from cooling-tower operations at the RTC into the Snake River Plain aquifer. Since March 1982, this wastewater has been discharged to two cold-waste infiltration ponds (fig. 3). 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 (Bartholomay and others, 2000). This wastewater contained an average annual amount of about 402,000 lb of sulfate and 94,000 lb of other chemicals during 1996–98 (Bartholomay and others, 2000).

Sewage effluent discharged to sanitary-waste infiltration ponds (fig. 3) at the RTC was about 28 Mgal/yr during 1996–98 (Bartholomay and others, 2000), about 17 Mgal in 2000, and about 52 Mgal in 2001 (Richard Kauffman, U.S. Department of Energy, written commun., 2005). In 1989, the sewage effluent contained about 1,070 lb of chloride and 1,550 lb of hypochlorite. Chloride and hypochlorite were not reported as part of the sewage effluent after February 1990 (Bartholomay and others, 2000).

Idaho Nuclear Technology and Engineering Center

From 1952 to February 1984, the INTEC discharged most of its low-level radioactive, chemical, and sanitary wastewater into the Snake River Plain aquifer through a 600‑ft‑deep disposal well (fig. 5). The average annual discharge of wastewater to the well was about 363 Mgal (Pittman and others, 1988, p. 24). Two infiltration ponds were used for wastewater disposal during 1999–2001 (fig. 3). The first pond was completed in February 1984 and the second pond was completed in October 1985. The annual discharge to the disposal well and ponds ranged from 260 Mgal in 1963 to 665 Mgal in 1993. The discharge to the ponds during 2001 was about 544 Mgal (Stoller Corp., 2002c, p 5-9); data for 1999 and 2000 are not available. The volume of wastewater discharged to the disposal well and infiltration ponds during 1962–2001 is shown in figure 7.

Most of the radioactivity in wastewater discharged to the infiltration ponds at the INTEC is attributed to tritium. Tritium has accounted for more than 90 percent of the radioactivity in wastewater discharged at the INTEC since 1970 (fig. 7). During 1986–88, a total of 556 Ci of tritium was discharged at the INTEC and the average annual amount was 185 Ci (Orr and Cecil, 1991, p. 20). During 1990–91, only 2.7 Ci of tritium was discharged; during 1992 and 1995 only about 0.3 Ci was discharged; no tritium was discharged during 1989, 1993, 1994, and 1996–99; and 0.03 Ci was discharged during 2000 (fig. 7). No data are available for the amount of tritium discharged during 2001.

During 1996–98, chloride, fluoride, nitrate, sodium, and sulfate were the predominant chem­ical constituents in wastewater discharged to the INTEC infiltration ponds. Average annual amounts of about 1,166,000 lb of chloride; 1,070 lb of fluo­ride; 86,700 lb of nitrate; 708,000 lb of sodium, and 146,000 lb of sulfate were in wastewater discharged at the INTEC. Data for predominant constituents and amounts in wastewater discharged during 1999–2001 have not been compiled.

Radioactive Waste Management Complex

Solid and liquid radioactive and chemical wastes have been buried in trenches and pits at the Subsurface Disposal Area (SDA) at the RWMC (fig.  3) since 1952. These constituents include transuranic wastes, other radiochemical and inorganic chemical constituents, and organic compounds. The transuranic wastes were buried in trenches until 1970, and stored above ground at the RWMC after 1970. Only low‑level mixed waste has been buried at the RWMC since 1970. Before 1970, little or no sediment was retained between the excavation bottoms and the underlying basalt. Since 1970, a layer of sediment has been retained in excavations to inhibit downward migration of waste constituents.

About 17,100 Ci of plutonium-238, 64,900 Ci of plutonium-239, 17,100 Ci of plutonium-240, and 183,000 Ci of americium-241 were buried in the SDA during 1952-99 (Holdren and others, 2002, 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.

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 (TAN Disposal Well, fig. 4). In 1972, the disposal well was replaced by a 35‑acre infiltration pond. No records are available as to the amount of radioactivity in wastewater that was discharged at TAN before 1959. During 1959–93, a total of about 61 Ci of radioactivity in wastewater was 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 liquid waste (Energy Research and Development Admin­istration, 1977, p. II–110, II–111). No radioactive wastewater has been discharged since 1993 (Bartholomay and others, 2000).

An average of about 6.6 Mgal/yr of chemical wastewater was discharged to the infiltration pond at the Technical Support Facility during 1996–98 (Bartholomay and others, 2000). The predominant constituents were chloride and sodium. Average annual amounts of 6,900 lb of chloride and 4,500 lb of sodium were discharged. The average annual amount of all other chemical constituents in the wastewater was about 760 lb (Bartholomay and others, 2000). During 1999–2001, about 28.5 Mgal of wastewater was discharged (Teresa Meachum, CH2M-WG Idaho, LLC, written commun., 2005). Data for total amounts of individual constituents disposed in wastewater for 1999–2001 are unavailable.

Central Facilities Area

A total of about 65 Ci of radio­activity in about 1,500 Mgal of wastewater was discharged to the sewage-plant tile drain field at the CFA (fig. 1) during 1952–93. Most of the radioactive wastes discharged to this drain field were from aquifer water pumped from well CFA 1 (fig. 4), which obtains water from within the INTEC contaminant plume in the Snake River Plain aquifer. Most of the radioactivity in waste­water discharged at the CFA is attributed to tritium. During 1993–98, no radioactivity was recorded in wastewater discharged at the CFA (Bartholomay and others, 2000).

An average of about 42.1 Mgal/yr of wastewater was discharged to a pond at CFA and a computerized central pivot system discharged about 13.6 Mgal/yr to native desert rangeland during 1999–2001 (Stoller Corp., 2002c; Teresa Meachum, CH2M-WG Idaho, LLC, written commun., 2005). Chloride and sodium were the predominant chemical constituents in the waste­water during 1996–98. Average annual amounts of about 7,800 lb of chloride and 5,300 lb of sodium were discharged during 1996–98. The average annual amount of all other constituents in the wastewater was about 6,300 lb; about 5,400 lb was from disposal of janitorial supplies (Bartholomay and others, 2000). Data for total amounts of individual constituents disposed in wastewater for 1999–2001 are unavailable.

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