Scientific Investigations Report 2006–5236
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5236
Wastewater-disposal sites at INL facilities are the principal sources of radiochemical and chemical constituents in the Snake River Plain aquifer. These sites included infiltration ponds and ditches, lined evaporation ponds, drain fields, pits, and disposal wells. During 1999–2001, wastewater was discharged to infiltration and lined-evaporation ponds. Liquid and solid waste materials buried at the RWMC (fig. 1) also are sources of some constituents in ground water.
Radiochemical and chemical constituents in wastewater migrate to the Snake River Plain aquifer through perched ground water beneath wastewater infiltration ponds at the RTC and INTEC. Perched ground water beneath the RWMC formed from infiltration of snowmelt and rain and recharge from the Big Lost River and INL spreading areas. This perched water contains constituents leached from buried radioactive and organic-chemical wastes. The extent of this perched ground water is affected by the waste-disposal practices.
Contractors at each INL facility collect radioactive‑ and chemical-waste-disposal data. 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, no formal program has been 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, b, and c) provide some radioactive waste disposal data for 1999–2001. Effluent monitoring and wastewater discharge raw data for some INL facilities were provided 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, this report does not present amounts and types of most radioactive and chemical wastes discharged at the various facilities for 1999–2001. Davis (2006) presents a more detailed description of the waste-disposal history at selected facilities.
Shallow and deep perched ground water formed at the RTC in response to wastewater disposal to radioactive-, chemical-, cold-, and sanitary-waste ponds (fig. 2). During 2001, about 293 Mgal/yr of wastewater was discharged to infiltration and lined evaporation ponds at the RTC. Selected radiochemical and inorganic chemical constituents in wastewater have been monitored in the shallow and deep perched ground water since the early 1960s.
Water samples from seven wells (CWP 1, 2, 3, 4, 5, 8, TRA A 13) (fig. 3) completed in shallow perched ground water near the RTC routinely were collected and analyzed for selected radiochemical and chemical constituents during 1999–2001. No water was present in wells CWP 6, 7, and TRA A 77 during this period. Water samples also were collected from 16 wells (PW 8 and 9, USGS 54, 55, 60 through 63, 66, 68 through 73, 78) (fig. 3) completed in deep perched ground water beneath the RTC. No samples were collected from wells USGS 53, 56, 74, and PW 7 because either the well was dry or water was below the level of the pump intake. Selection of radiochemical and chemical constituents for analyses was based on waste-disposal history at the RTC. Selected radiochemical constituents were tritium, strontium-90, cesium-137, and gamma analyses; chemical constituents were dissolved chromium, sodium, chloride, and sulfate.
Tritium has a half-life of 12.3 years (Walker and others, 1989, p. 20). During 1952–93, about 10,500 Curies (Ci) of tritium was contained in wastewater discharged to the radioactive-waste infiltration ponds at the RTC. Since August 1993, tritium in wastewater has been discharged to two lined evaporation ponds, replacing the radioactive-waste infiltration ponds (fig. 3) (Orr, 1999), which probably prevents radioactive wastewater from entering the ground. Before 1980, tritium generally accounted for less than 20 percent of the total radioactivity discharged to the ponds; 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). After 1980, tritium generally accounted for more than 90 percent of the total radioactivity. About 191 Ci of tritium was released in wastewater to the RTC lined evaporation ponds during 1999–2000 (Stoller Corp., 2002a, 2002b). Data are not available for the total amount of tritium in wastewater discharged in 2001. Figure 4 shows annual wastewater and tritium discharged to the radioactive-waste infiltration and lined evaporation ponds during 1962–2001.
Well TRA A 77 (fig. 3) is completed in shallow perched ground water in alluvium near the RTC retention basin (fig. 5), where radioactive wastewater flowed before it was discharged to the radioactive-waste infiltration ponds (figs. 3 and 5). Some wastewater reportedly leaked to the subsurface through cracks in the retention basin (U.S. Department of Energy, 1991, p. 29). To prevent discharge of radioactive wastewater to the retention basin, the retention basin was isolated in 1993 when discharge to the lined evaporation ponds began (Bartholomay and Tucker, 2000). The largest tritium concentration in water from well TRA A 77 during 1989–91 was 3,790±50 pCi/mL (Tucker and Orr, 1998, p. 15). In 1992, the largest tritium concentration increased slightly to 3,940±60 pCi/mL (Bartholomay, 1998, p. 41). In October 1995, the tritium concentration in water from well TRA A 77 had decreased to 22.4±0.9 pCi/mL (Bartholomay, 1998, p. 41) and by April 1997 to 1.0±0.15 pCi/mL (Bartholomay, 1998, table 2). Historically, tritium concentrations were variable in water from well TRA A 77. Because of the shallow depth of well TRA A 77 and its proximity to the leaking retention basin, the variability in tritium concentrations in this well could have been the result of changes in tritium disposal rates (Bartholomay, 1998, p. 10). No samples were collected from this well since April 1997 because no water was present in the well during scheduled sampling dates. The lack of water in this well may be the result of discontinued use of the retention basin for transfer of radioactive wastewater.
Maximum concentrations of tritium in water from well TRA A 13 decreased from 158±2 pCi/mL during 1982‑85 to 1.1±0.3 pCi/mL during 1986–88 (Cecil and others, 1991, p. 33); during 1989–2001, tritium concentrations in water from this well were less than the reporting level. The decrease in tritium concentrations in well TRA A 13, between the radioactive-waste infiltration ponds and the cold-waste ponds (fig. 3), likely is attributed to the large quantity of nonradioactive water discharged to the cold-waste ponds (Bartholomay and Tucker, 2000).
Wells CWP 1 through CWP 9 monitor shallow perched ground water around the cold-waste ponds at the RTC. During 1982–2001, tritium was less than the reporting level in water from wells CWP 1 through CWP 7. A tritium concentration of 0.8±0.2 pCi/mL was measured in water from well CWP 8 in November 1988, and since then, concentrations have been less than the reporting level. Tritium concentrations in water from well CWP 9 (fig. 2) decreased from 6.3±0.2 pCi/mL during 1982–85 to 1.1±0.2 pCi/mL during 1986–88 (Cecil and others, 1991, p. 35). No samples have been collected at CWP 9 since 1988. Discharge of cooling-tower wastewater to the TRA disposal well ceased in 1982 and this water subsequently was discharged to the cold-waste ponds. The absence of detectable tritium concentrations in most CWP wells was attributed to the large quantity of nonradioactive wastewater discharged to the cold-waste ponds since 1982, which has diluted any residual radioactive-waste infiltration pond water (Bartholomay and Tucker, 2000).
Tritium concentrations in water from nine wells completed in deep perched ground water (PW 8, PW 9, USGS 54, 55, 61, 66, 70, 71, and 73) generally were greater than the reporting levels during 1999–2001. Concentrations decreased in some wells and varied randomly in other wells (table 2), and all reportable concentrations were less than the 1998 concentrations. Tritium concentrations in water from four wells (USGS 60, 68, 69, and 78) were less than the reporting level during 1999–2001 (table 2). Tritium concentrations varied between reportable and nonreportable concentrations in water from two wells, USGS 62 and 63, during 1999‑2001. Tritium concentrations in water from well USGS 62 were greater than the reporting level in October 1999 and April 2000, but the concentration decreased to less than the reporting level by October 2001. Concentrations in water from well USGS 63 were greater than the reporting level in October 2000, however, the concentration decreased to less than the reporting level by October 2001 (table 2). An obstruction in well USGS 53 in 1996 prevented water-level measurement or water-quality sampling. The water level in well USGS 56 decreased below the pump intake in 1997 and no samples have been collected at this well since January 1997 due to lack of water. No samples were collected at wells USGS 74 and PW 7 because they have been dry since 1993 and 1994, respectively. The decreases in concentration and lack of water in wells USGS 53 and 56 may be attributed to discontinuing wastewater disposal to the radioactive-waste infiltration ponds. Variations in tritium concentrations in water from these wells likely are attributed to fluctuations in disposal rates and to mixing of water from the radioactive- and cold-waste ponds (Bartholomay and Tucker, 2000).
During July–October 2001, the most recent tritium concentrations in water from eight wells completed in deep perched ground water at the RTC exceeded the reporting levels (fig. 5; table 2). Tritium concentrations ranged from 0.49±0.14 pCi/mL (well PW 8) to 39.4±1.4 pCi/mL (well PW 9). During July–October 2001, reportable tritium concentrations in water from wells completed in deep perched ground water (fig. 5) were less than concentrations measured during July–December 1998 (Bartholomay and Tucker, 2000, fig. 5).
Water samples collected in October 2001 from wells USGS 73 and PW 9 contained tritium concentrations of 9.3±0.5 and 39.4±1.4 pCi/mL, respectively. These concentrations represent generally steady decreases since 1993 when the radioactive-waste infiltration ponds were taken out of service. Water in well USGS 74 contained 93.1±1.7 pCi/mL in April 1992; however, no samples have been collected since 1992 because the well has been dry. The well was removed from the sampling schedule in October 2001. These three wells are more than 1,500 ft west of the radioactive-waste infiltration ponds (fig. 5). Historically large tritium concentrations in water from these wells indicate that the chemistry of perched ground water west of the RTC was affected by radioactive-waste infiltration pond disposals. Discontinuation of wastewater discharge to the radioactive-waste infiltration ponds and subsequent use of lined evaporation ponds, together with the radioactive decay process, may account for the decreased tritium concentrations in this area and could indicate an eastward migration of the extent of deep perched water relative to well USGS 74.
Water-level hydrographs for wells USGS 60 and 73 (fig. 6) indicate that wastewater disposal to the cold-waste ponds since 1982 has hydraulically affected perched ground water flow to the west and east. Disposal to the cold-waste ponds affected water levels much less in wells USGS 54 and 70, to the north and northeast of the cold-waste ponds (fig. 6). Water levels in all four wells decreased significantly in 1992 (fig. 6), when wastewater discharge to the cold-waste ponds was much less than during other years (Bartholomay and Tucker, 2000). Because of the effect of disposal to the cold-waste ponds on water levels and the removal of the radioactive-waste infiltration ponds as a water source, tritium concentrations in perched ground water at the RTC likely decreased as nonradioactive wastewater from the cold-waste ponds mixed with water derived from earlier radioactive-waste infiltration pond disposal (Bartholomay and Tucker, 2000).
Bartholomay (1998) determined that increases in tritium concentrations in water from wells USGS 53, 56, and 70 corresponded partly to tritium disposal rates. The hydraulic connection between the radioactive-waste infiltration ponds and wells USGS 53 and 56 is also demonstrated by the fact that well USGS 53 dried up and the water level in well USGS 56 declined below the pump intake subsequent to cessation of wastewater disposal to the ponds.
Bartholomay (1998) noted that increases and decreases in tritium concentrations in water from well USGS 73 lagged from 3 to 13 months behind increases and decreases in well USGS 56. This time lag indicated that tritium in ground water moved from the radioactive-waste infiltration ponds to well USGS 73 during that period. Bartholomay (1998) also determined that changes in tritium concentrations in water from well USGS 54 did not correspond directly to monthly changes in tritium disposal. The lack of correspondence indicated that other factors, including hydraulic effects and dilution from the cold-waste ponds, affected tritium concentrations in water from that well.
Several factors have affected the distribution of tritium in perched ground water at the RTC. These factors include proximity of the wells to the radioactive-waste infiltration ponds, depth of the water below the ponds, variations in the tritium disposal rate, and radioactive decay. Since 1982, tritium concentrations also have been affected by dilution from the cold-waste ponds. Replacement of the radioactive-waste infiltration ponds with the lined evaporation ponds in 1993 contributed to decreases in tritium concentrations in perched ground water and decreases in the amount of perched water in some wells. Infiltration from the Big Lost River during 1999 and early 2000 may have contributed to diluted tritium concentrations in perched ground water southeast of the RTC . Tritium concentrations in wells USGS 62, 66, and 71 decreased slightly during 1999–2001.
Strontium-90 has a half-life of 29.1 years (Walker and others, 1989, p. 29). During 1952–93, about 93 Ci of strontium-90 was in wastewater discharged to the radioactive-waste infiltration ponds at the RTC, an average of 2.3 Ci/yr (Bartholomay and Tucker, 2000). During 1996–98, about 0.03 Ci was discharged to the lined evaporation ponds (Bartholomay and Tucker, 2000). During 1999, less than 0.001 Ci of strontium-90 was discharged at the RTC (Stoller Corp., 2002a, table 7-2); during 2000, 0.21 Ci of strontium‑90/yttrium-90 was discharged at the RTC (Stoller Corp., 2002b, table 6-2). Data are not available for the amount of strontium‑90 discharged in 2001.
During 1996–98, strontium-90 concentrations in water from wells TRA A 77 and TRA A 13, completed in shallow perched ground water, were above the reporting levels (Bartholomay and Tucker, 2000, table 2). Concentrations in water from well TRA A 77 ranged from 4,710±140 pCi/L in October 1996 to 6,800±200 pCi/L in April 1997. Well TRA A 77 was not sampled during 1999–2001 because of well access problems or lack of water in the well. In October 1998, the concentration of strontium-90 in water from well TRA A 13 was 23.5±1.2 pCi/L. Water from well TRA A 13 exceeded the reporting level during 1999–2001 and in April 2001 the concentration was 22.1±1.1 pCi/L (table 2), consistent with the October 1998 concentration. The well was not sampled in October 2001 because of an obstruction in the well. Well CWP 1, also completed in shallow perched ground water, exceeded the reporting level in June 1999 with a concentration of 3.1±0.7 pCi/L, however, by July 2001, the concentration was less than the reporting level.
In October 2001, concentrations of strontium-90 in water from wells PW 8, USGS 54, 55, 63, and 70, completed in deep perched ground water at the RTC were greater than reporting levels (table 2 and fig. 7); concentrations ranged from 2.8±0.7 pCi/L in well USGS 63 to 83.8±2.1 pCi/L in well USGS 54. The distribution of strontium-90 concentrations in water from these wells during 1999–2001 is attributed to exchange reactions between strontium-90 in solution and sediments beneath the radioactive-waste infiltration ponds. Strontium‑90 was not detected in water from the Snake River Plain aquifer beneath the RTC (Bartholomay and others, 1997, p. 30); the absence of detectable concentrations indicates that strontium‑90 in solution is removed possibly by sorption and (or) exchange reactions in the unsaturated zone. Study of strontium distribution coefficients for samples of surficial sediment, sedimentary interbeds, and sediment-filled fractures in basalts (Liszewski and others, 1997, 1998; Pace and others, 1999) at the INL support this theory.
Water in wells PW 9 and USGS 62 contained strontium‑90 at concentrations less than reporting levels in some samples collected during 1999–2001, but greater than reporting levels in other samples (table 2). Because 2001 strontium-90 disposal data were not available, fluctuations could not be correlated with disposal during 1999–2001. In addition, lined evaporation ponds were in use, which probably prevented contaminated water from percolating into the ground.
Cesium-137 has a half-life of 30.17 years (Walker and others, 1989, p. 34). About 138 Ci of cesium-137 was in wastewater discharged to the radioactive-waste infiltration ponds at the RTC during 1952–93. The average disposal rate decreased from 2.0 Ci/yr during 1979–81 (Lewis and Jensen, 1985) to 0.65 Ci/yr during 1982–85 (Pittman and others, 1988, p. 35). The average disposal rate of cesium-137 during 1986–88 was 0.23 Ci/yr (Cecil and others, 1991, p. 36). The rate decreased during 1989–91 to 0.02 Ci/yr (Tucker and Orr, 1998, p. 17), and averaged 0.7 Ci/yr during 1992–93 (Bartholomay, 1998, p. 16). After 1993, wastewater was discharged to lined evaporation ponds, which probably prevents any cesium-137 from percolating into the ground.
During 1999–2001, no reportable concentrations of cesium-137 were detected in water from any wells completed in either shallow or deep perched ground water. The general absence of reportable concentrations of cesium-137 in perched ground water at the RTC probably is due to decreasing cesium-137 disposal rates, change from using the radioactive-waste infiltration ponds to lined evaporation ponds, and sorption and (or) exchange of cesium-137 to minerals in sediments. During 1996–97, cesium-137 concentrations in water from shallow well TRA A 77 exceeded the reporting level and ranged from 42,300±1,800 pCi/L in April 1996 to 1,200±110 pCi/L in April 1997. No samples were collected from well TRA A 77 during 1998–2001 because the well was dry. The intermittent presence of cesium-137 in water from well TRA A 77 may have been due to the proximity of the well to the retention basin and to the amount of suspended sediment in water samples collected onto which cesium-137 may have sorbed.
Chromium-51 has a half-life of 27.7 days (Walker and others, 1989, p. 24). About 2,390 Ci of chromium-51 was in wastewater discharged to the radioactive-waste infiltration and lined evaporation ponds during 1979–98. Data are not available for the amount of chromium-51 discharged during 1999–2001. The average disposal rate of chromium-51 during 1979–81 was 766 Ci/yr (Pittman and others, 1988, p. 35). A total of 25.7 Ci of chromium-51 was discharged during 1986‑88, an average of 8.6 Ci/yr (Cecil and others, 1991, p. 35). During 1989–91,11.6 Ci was discharged for an average of 3.9 Ci/yr (Tucker and Orr, 1998, p. 17). During 1992–95, 10 Ci was discharged, an average of 2.5 Ci/yr (Bartholomay, 1998, p. 16). During 1996–98, 6.2 Ci was discharged, an average of 2.1 Ci/yr (Bartholomay and Tucker, 2000).
Because of the decreased amount of chromium-51 discharged and the relatively short half-life, this radionuclide was not detected in water from wells completed in deep perched ground water during 1986–88 (Cecil and others, 1991, p. 35). Chromium-51 was not detected in shallow perched ground water from wells TRA A 13 and CWP 1 through CWP 9 during 1982–88. During 1989–91, chromium-51 was detected in water from wells TRA A 77, USGS 53, and USGS 56 (Tucker and Orr, 1998, p. 17). During 1992–95, chromium‑51 was detected only in shallow well TRA A 77; concentrations ranged from 2,700±500 to 24,500±1,300 pCi/L (Bartholomay, 1998, p. 16). Chromium-51 was not detected in any wells during 1996–2001.
Cobalt-60 has a half-life of 5.27 years (Walker and others, 1989, p. 25). About 442 Ci of cobalt‑60 was in wastewater discharged to the radioactive-waste infiltration ponds at the RTC during 1952–88. The average cobalt-60 disposal rate decreased from 2.3 Ci/yr during 1979–81 to 1 Ci/yr during 1982–85 (Pittman and others, 1988). The average disposal rate was 2.2 Ci/yr during 1986–88, 0.15 Ci/yr during 1989–91, 0.8 Ci/yr during 1992–95 (Bartholomay, 1998, p. 16) and about 0.3 Ci/yr during 1996–98.
During 1996–98, cobalt-60 concentrations in water from wells TRA A 77 and USGS 56 exceeded the reporting level. Concentrations of cobalt-60 in water from well TRA A 77 ranged from 7,700±260 to 44,000±1,400 pCi/L. The concentration in water from well USGS 56 was 220±30 pCi/L (Bartholomay and Tucker, 2000). The presence of cobalt-60 in these wells probably is due to their proximity to the ponds and retention basin. During 1999–2001, no samples were collected from these two wells because well TRA A 77 was dry and water was below the pump intake level in well USGS 56. Cobalt-60 was not detected in any other water samples analyzed during 1999–2001.
An estimated 24,000 lb of nonradioactive chromium in wastewater from RTC cooling-tower operations was discharged to the radioactive-waste infiltration ponds during 1952–64 (Mann and Knobel, 1988, p. 7–10). During 1964–72, a disposal well at the RTC was used to dispose chromium directly to the Snake River Plain aquifer. In October 1972, chromium was replaced by polyphosphate as a corrosion inhibitor in cooling-tower operations. No disposal of chromium to the subsurface was reported after 1972.
During 1996–98, dissolved chromium concentrations in shallow perched ground water ranged from less than 5 µg/L in several wells to 26 µg/L in well TRA A 77 (Bartholomay and Tucker, 2000). During 1999–2001, wells TRA A 77, CWP 6, and CWP 7 could not be sampled because the wells were dry. During 1999–2001, dissolved chromium was not detected in shallow perched ground water (table 3).
The LRL for dissolved chromium varied from 14 µg/L in October 1998 to 0.8 µg/L in October 2001; consequently, concentrations within that range were designated according to those LRLs as detections or nondetections during 1999–2001. Estimated concentrations (table 3) less than the LRLs are treated as nondetected concentrations for consistency with treatment in previous publications, and because an estimated concentration is considered a “qualitatively detected analyte” (Childress and others, 1999, p. 7).
Dissolved chromium was detected in water from 10 wells (PW 8, 9, USGS 54, 55, 61, 63, 68, 70, 71, and 73) completed in deep perched ground water at the RTC during 1999–2001 (table 3). During 1996–98, the maximum concentration of dissolved chromium was 200 µg/L in well USGS 56 in April 1996; this well was not sampled during 1999–2001 because the water level was below the pump intake. During 1999–2001, the maximum concentration of dissolved chromium in deep perched ground water was 90 µg/L in well PW 9 in January 1999. This concentration decreased to 35 µg/L by October 2001. During July–October 2001, the most recent concentrations of dissolved chromium in wells completed in deep perched ground water near the RTC ranged from 10 µg/L in well USGS 61 to 82 µg/L in well USGS 55 (table 3 and fig. 8). The largest concentrations were in water from wells north and west of the radioactive-waste infiltration ponds (PW 9 and USGS 55, 68). The presence of dissolved chromium in water from wells completed in perched water indicates that water from these wells contains chromium and other constituents that were discharged to the radioactive-waste infiltration ponds before 1965, when disposal practices changed to injection of cooling-tower blowdown water to the disposal well.
During 1962–70, wastewater containing about 500 tons/yr of sodium hydroxide and 50 tons/yr of sodium chloride were discharged to the chemical-waste pond (Robertson and others, 1974). Average annual sodium disposal was 188,000 lb during 1971–73 (Barraclough and Jensen (1976); 117,600 lb during 1974–78 (Barraclough and others, 1981); 101,000 lbs during 1979–81 (Lewis and Jensen, 1985); 85,000 lb during 1982–85 (Pittman and others, 1988); 183,000 lbs during 1986–88 (Cecil and others, 1991); 171,000 lb during 1989–91 (Tucker and Orr, 1998); and 168,000 lbs during 1992–95 (Bartholomay, 1998). An estimated 173,000 lb of sodium was contained in wastewater discharged to the chemical-waste pond during 1996–98. Average dissolved sodium concentration in wastewater discharged to the chemical-waste pond was about 2,000 mg/L (Bartholomay and Tucker, 2000). Total sodium discharged at the RTC is the amount of sodium ion estimated from the discharged sodium hydrate solution (Bartholomay and Tucker, 2000). The total amount of sodium in wastewater discharged at the RTC from 1999 to 2001 has not been compiled.
During 1999–2001, only one analysis was made for dissolved sodium concentrations (23 mg/L) in shallow perched ground water from well TRA A 13. Concentrations of dissolved sodium in other wells completed in shallow perched ground water were not available because (1) wells were dry during 1999–2001, (2) wells could not be sampled because of access problems, or (3) analyses for dissolved sodium were not requested from the laboratory (table 3). Dissolved sodium concentrations in water from 16 wells completed in deep perched ground water also were determined. During July–October 2001, dissolved sodium concentrations ranged from 7 to 20 mg/L in all wells except well USGS 68, with a concentration of 413 mg/L (table 3), a decrease from December 1998 when the concentration was 662 mg/L (Bartholomay and Tucker, 2000, table 3). The decreased concentration of dissolved sodium in water from well USGS 68 may be attributed to the closure of the chemical-waste pond in 1999.
Robertson and others (1974, pg. 92) estimated that chloride (in the form of sodium chloride) was discharged to the chemical-waste pond at a rate of about 50 tons/yr during 1962–70. Negligible chloride concentrations were discharged in wastewater during 1974–78 (Barraclough and Jensen, 1976). Average annual disposal of chloride to the chemical-waste pond was 1,540 lb during 1979–81 and 2,000 lb during 1982–85 (Pittman and others, 1988). About 1,975 lb/yr of chloride were discharged to the chemical- and sanitary-waste ponds during 1986–88 (Cecil and others, 1991). About 1,215 lb/yr of chloride were discharged to the chemical-waste pond during 1989–91; discharge of chloride to the sanitary-waste pond was curtailed after 1989 (Tucker and Orr, 1998). About 4,430 lb of chloride contained in wastewater was discharged to the cold-waste ponds during 1992–95 (Bartholomay, 1998). During 1996–98, about 3,600 lb of chloride was in wastewater discharged to the cold-waste ponds. Data are not available for chloride in wastewater discharged during 1999–2001.
During 1999–2001, dissolved chloride concentrations in shallow perched ground water ranged from 10 mg/L in wells CWP 1, 3, and 4 to 53 mg/L in well TRA A 13. Dissolved chloride concentrations in deep perched ground water ranged from 5 mg/L in well USGS 78 to 91 mg/L in well USGS 73 (table 3).
Compiled data are not available for sulfate in wastewater discharged during 1999–2001. During 1996–98, about 833,000 lb of sulfate was in wastewater discharged to the chemical- and cold-waste ponds at RTC, an average of 278,000 lb/yr (Bartholomay and Tucker, 2000). This represents a decrease from the sulfate discharge of 920,000 lb/yr during 1989–1991 (Tucker and Orr, 1998) and 595,500 lb/yr discharged during 1992–95 (Bartholomay, 1998).
The maximum dissolved sulfate concentration in shallow perched ground water was 419 mg/L in well CWP 1 in July 2000. This concentration is attributed to sulfate disposal to nearby cold-waste ponds. The dissolved sulfate concentration in well CWP 1 decreased to 31 mg/L by July 2001. The most recent detected concentrations of dissolved sulfate in water from wells USGS 54, 60, 63, 69, and PW 8, completed in deep perched ground water near the cold-waste ponds, ranged from 115 to 285 mg/L during July–October 2001 (fig. 9). These large concentrations indicate that water in the wells also was affected by discharge into the cold-waste ponds. Monitoring data for dissolved sulfate concentrations in wastewater discharged to the cold-waste pond for 1999–2001 are summarized in Stoller Corp. (2002a, 2002b, 2002c).
During July–October 2001, the maximum concentration of dissolved sulfate in deep perched ground water was 1,409 mg/L in well USGS 68 (table 3), west of the chemical-waste pond (fig. 9). This dissolved sulfate concentration had decreased from 2,278 mg/L in December 1998 (Bartholomay and Tucker, 2000, table 3), which in part may be the result of the chemical-waste pond closure in 1999 (fig. 9) or a decrease in disposal rates.
Two wastewater-infiltration ponds were constructed south of the INTEC in 1984 and 1985 to replace the INTEC disposal well (fig. 3). Wastewater infiltrating from these ponds formed perched ground water in the basalt and sedimentary interbeds above the eastern Snake River Plain aquifer. The volumes of wastewater discharged to the well and infiltration ponds during 1962–2001 are shown in figure 10.
Annual discharge to the disposal well and ponds ranged from 260 Mgal in 1963 to 665 Mgal in 1993 and averaged about 442 Mgal (Bartholomay and Tucker, 2000). The average annual discharge during 1996–98 to the ponds was about 570 Mgal. Discharge to the ponds during 2001 was about 544 Mgal (Stoller Corp., 2002c, p 5–9); data for 1999 and 2000 are not available. This report focuses on perched water derived from the INTEC infiltration ponds, however, perched ground water also has been identified in other areas beneath the INTEC and may be attributed to other infiltration ponds, leaking wastewater lines, leach fields, ruptured casing in the upper part of the INTEC disposal well, and landscape irrigation (Tucker and Orr, 1998).
Many auger holes were drilled in 1983 to obtain geohydrologic and engineering data at the site of the planned INTEC infiltration ponds. Two holes (SWP 8 and 13 [fig. 3]) subsequently were used as monitoring wells to sample and measure water levels in shallow perched ground water in surficial sediment at the ponds. Attempts were made to sample wells SWP 8 and 13 annually during 1999–2001, however in some years, the wells were dry. Wells PW 1, 2, 3, 4, 5, and 6 were completed in 1986 to monitor deep perched ground-water levels and water-quality changes under the INTEC infiltration ponds (fig. 3). Well USGS 50 was used to monitor deep perched ground water near the INTEC disposal well. All these wells were sampled quarterly or semiannually during 1999–2001 (table 1). The following sections summarize concentrations of selected constituents in water from these wells and auger holes used to monitor water-quality changes related to infiltration of water from the INTEC infiltration ponds.
Overall, most radioactivity in wastewater discharged to the infiltration ponds at the INTEC has been from tritium. About 960 Ci of tritium in wastewater was discharged to the INTEC infiltration ponds during 1984–88. During 1986–88, the average rate of tritium disposal was 185 Ci/yr (Cecil and others, 1991). During 1989–91, 2.7 Ci of tritium was discharged to the ponds and during 1992–95, 0.3 Ci was discharged (Bartholomay, 1998). There was no discharge during 1996–99; however, during 2000, 0.03 Ci of tritium was discharged (Stoller Corp., 2002a, 2002b) (fig. 10). Data are not available for the total tritium discharged in 2001.
Well SWP 13 (fig. 3), completed in shallow perched ground water, was not sampled in 1999 and 2000 because the well was dry. In 2001, the tritium concentration in well SWP 13 was less than the reporting level (table 4). Well SWP 8 (fig. 3) was dry during 1999. During 2000–01, the tritium concentrations in well SWP 8 were less than the reporting level. During 1999–2001, tritium concentrations in water from wells completed in deep perched ground water beneath the infiltration ponds ranged from less than the reporting level in wells PW 1 and PW 5 to 9.7±0.5 pCi/mL in well PW 6 (table 4), the same concentration as in October 1998. Tritium concentrations in water from well PW 6 varied during 1999–2000 and remained similar to concentrations reported during 1996–98 (Bartholomay and Tucker, 2000). No water was in well PW 6 in from July 2000 through October 2001. Tritium concentrations in water from wells near the infiltration ponds had decreased significantly from concentrations during 1986–88, when disposal of tritium was about 185 Ci/yr (Orr and Cecil, 1991). During 1999–2001, tritium concentrations in perched ground water in the wells closest to the ponds (PW 1 through 5, and SWP 8) decreased or remained less than 1 pCi/mL (table 4). These concentration decreases likely are due to decreased tritium disposal to the ponds and radioactive decay. During 1999–2001, tritium concentrations in water from well USGS 50 (fig. 11), near the disposal well, decreased slightly from 37.5±1.4 pCi/mL in April 1999 to 31.7±1.2 pCi/mL in October 2001 (table 4; fig. 11). The large tritium concentrations in water from well USGS 50 may be due to leakage of wastewater from ruptures in the upper part of the disposal well casing or to leakage from wastewater lines at the INTEC (Tucker and Orr, 1998). The slight decrease in tritium concentrations can be attributed mostly to radioactive decay or dilution of well water from a nonradioactive source such as landscape irrigation. Figure 11 shows concentrations of tritium in wells near the INTEC as of October 2001. Many wells were dry or were not sampled because of well access problems.
About 0.3 Ci of strontium-90 was in wastewater discharged to the INTEC infiltration ponds during 1984–95 and about 0.03 Ci was discharged during 1996–98 (Bartholomay and Tucker, 2000). During 1999–2000, less than 0.001 Ci/yr of strontium-90 was discharged at the INTEC (Stoller Corp., 2002a, table 7-2, footnote b; 2002b, table 6-2, footnote b); data are not available for the amount of strontium-90 discharged in 2001. Additional sources of strontium-90 in perched ground water at the INTEC include more than 33 Ci of strontium-90 reportedly discharged to a shallow pit (fig. 12) in 1962–63 (Robertson and others, 1974, p. 119).
A strontium-90 concentration of 2.1±0.7 pCi/L in July 2001 in water from well SWP 8 (fig. 3) completed in shallow perched ground water continued the steady decrease in strontium-90 concentrations in water from this well since 1991. During 1999–2001, concentrations of strontium-90 varied in water from all wells completed in deep perched ground water beneath the INTEC infiltration ponds. In October 2001, strontium-90 concentrations in deep perched ground water in wells closest to the ponds were less than the reporting level, not sampled because of access problems, or the wells were dry (fig. 12).
The largest concentrations of strontium-90 in perched ground water at the INTEC were in well USGS 50 near the INTEC disposal well. During 1999–2001, strontium-90 concentrations in water from well USGS 50 were variable and ranged from 204±5 pCi/L in October 1999 to 134±3 pCi/L in October 2001 (table 4), indicating an overall decrease in strontium-90 concentrations since the mid–1980s. Strontium‑90 concentrations in water from well USGS 50 may be due to leakage of wastewater from ruptures in the disposal well casing or leakage from wastewater pipelines at the INTEC.
Wastewater discharged to the INTEC infiltration ponds during 1984–95 contained about 0.5 Ci of cesium-137. During 1996, wastewater discharged to the ponds contained about 0.0006 Ci of cesium‑137; no cesium-137 was discharged during 1997–98. During 1999–2000, less than 0.001 Ci/yr of cesium-137 was discharged to the INTEC infiltration ponds (Stoller Corp., 2002a, table 7-2, footnote b; 2002b, table 6-2, footnote b). Data are not available for cesium-137 discharged during 2001.
During 1999–2001, concentrations of cesium-137 did not exceed the reporting level in shallow or deep perched ground water in wells closest to the infiltration ponds or in well USGS 50. The absence of reportable concentrations of cesium-137 in perched ground water at the INTEC probably is due to decreased disposal and to sorption and (or) exchange of cesium-137 to minerals in sediments.
Robertson and others (1974, pg. 121) stated that the quantity of wastes disposed at the INTEC were not routinely monitored during 1952–70; however, the most abundant waste product discharged to the INTEC disposal well was sodium chloride. Barraclough and Jensen (1976) reported that 254,000 lb/yr of sodium were discharged to the INTEC disposal well during 1971–73. During 1974–78, about 310,000 lb/yr of sodium were discharged to the disposal well (Barraclough and others, 1981); and 397,000 lb/yr were discharged during 1979–81 (Lewis and Jensen, 1984). About 324,000 lb/yr of sodium were discharged at the INTEC during 1982–85; however, in 1984 the new INTEC infiltration ponds were put in use. About 72 percent of the sodium was discharged to the infiltration ponds and about 28 percent was discharged to the disposal well (Pittman and others, 1988). In 1985, nearly all sodium was discharged to the INTEC infiltration ponds (Pittman and others, 1988). During 1986–88, an estimated 22 million lb of sodium was discharged to the INTEC infiltration ponds (Cecil and others, 1991); during 1989–91, no sodium discharge data were available, however chloride discharge records were used to estimate that about 23 million lb of sodium may have been discharged to the INTEC infiltration ponds (Tucker and Orr, 1998); and during 1992–95 about 3 million lb of sodium was discharged to the infiltration ponds (Bartholomay, 1998). About 708,000 lb of sodium was discharged to the INTEC infiltration ponds during 1996–98 (Bartholomay and Tucker, 2000). No compilation was made of the total amount of sodium discharged to the INTEC infiltration ponds during 1999–2001. The concentration of sodium in wastewater decreased from an average of 127 mg/L in 1999 to 111 mg/L in 2001 (Stoller Corp., 2002a, table 7-3; 2002b, table 6-3; 2002c, table 5-6).
Water from well SWP 8, completed in shallow perched ground water, contained a maximum concentration of 133 mg/L of dissolved sodium in July 2000. This concentration decreased to 102 mg/L in July 2001. Water from well SWP 13, also completed in shallow perched ground water, contained a dissolved sodium concentration of 92 mg/L in July 2001. This well was not sampled in 1999 or 2000 because the well was dry (table 5). During 1999–2001, dissolved sodium concentrations in deep perched ground water in wells closest to the infiltration ponds (PW 1 through 5) ranged from 109 mg/L in well PW 2 in October 2001 to 164 mg/L in well PW 5 in October 1999 (table 5). By October 2001, most wells could not be sampled due to lack of water in the well or well access problems. Dissolved sodium concentrations in shallow and deep perched ground water at the INTEC infiltration ponds during 1999–2001 were similar to or less than those in wastewater (Stoller Corp., 2002a, table 7-3; 2002b, table 6-3; 2002c, table 5-6).
Dissolved sodium concentrations in two water samples from well USGS 50 were nearly constant during 1999–2000. The concentration in October 2000 was 60 mg/L (table 5), nearly the same as concentrations reported in Bartholomay and Tucker (2000, table 5) for 1996–98. Analysis for dissolved sodium in water from well USGS 50 was not requested in 2001. These dissolved sodium concentrations may be due to leakage of wastewater from pipelines or infiltration of landscape irrigation at the INTEC.
Robertson and others (1974, pg. 121) stated that the quantity of wastes disposed at the INTEC were not routinely monitored during 1952–1970, however, the most abundant waste product discharged to the INTEC disposal well was sodium chloride. Barraclough and Jensen (1976) reported that 386,000 lb/yr of chloride were discharged to the INTEC disposal well during 1971–73. During 1974–78, about 548,000 lb/yr of chloride were discharged (Barraclough and others, 1981); about 875,000 lb/yr during 1979–81 (Lewis and Jensen, 1984); and about 735,000 lb/yr during 1982–85; however, in 1984, waste discharge ceased to the INTEC disposal well, and wastes were discharged to the INTEC infiltration ponds. About 35 million lb of chloride was discharged to the INTEC infiltration ponds during 1986–88 (Cecil and others, 1991); 36 million lb was discharged during 1989–91 (Tucker and Orr, 1998); 49 million lb was discharged during 1992–95 (Bartholomay, 1998); and 35 million lb was discharged during 1996–98 (Bartholomay and Tucker, 2000). The total chloride discharged to the infiltration ponds at the INTEC was not compiled for 1999–2001; however, the concentration of dissolved chloride in wastewater decreased from an average of 193 mg/L in 1999 to 153 mg/L in 2001 (Stoller Corp., 2002a, table 7-3; 2002b, table 6-3; 2002c, table 5-6).
During 1999, well SWP 8 (fig. 3) was not sampled because the well was dry. The dissolved chloride concentration in well SWP 8 decreased from 241 mg/L in July 2000 to 153 mg/L in July 2001. No samples were collected from well SWP 13 during 1999–2000 because the well was dry; the dissolved chloride concentration in July 2001 was 157 mg/L. During 1999–2001, dissolved chloride concentrations in deep perched ground water in wells closest to the infiltration ponds (PW 1 through 5) ranged from 79 mg/L in well PW 4 to 348 mg/L in well PW 5 (table 5). In October 2001, wells PW 1 and 6 were dry and wells PW 4 and 5 were not sampled because of well access problems. Dissolved chloride concentrations in water from wells PW 2 and 3 were 167 and 175 mg/L, respectively (table 5; fig. 13). When water was present, lower concentrations were measured in water from well PW 6 than wells PW 1 through 5 (table 5). Dissolved chloride concentrations in shallow and deep perched ground water at the INTEC infiltration ponds were similar to or less than the dissolved chloride concentrations in wastewater (Stoller Corp., 2002a, table 7-3; 2002b, table 6-3; 2002c, table 5-6).
During 1999–2001, dissolved chloride concentrations in water from well USGS 50 were consistent, ranging from 59 mg/L in April 1999 to 55 mg/L in April 2001 (table 5). The dissolved chloride concentrations may be due to leakage of wastewater from ruptures in the disposal well casing or leakage from wastewater pipelines at the INTEC. Dissolved chloride concentrations in water from this well steadily decreased since sampling began in 1959.
The quantity of wastes disposed at the INTEC was not routinely monitored during 1952–1970; however, high values of sulfate near the center of the INL may be associated with waste disposal (Robertson and others, 1974, p. 70, 121). The estimated average wastewater dissolved sulfate concentration was about 25 mg/L (Robertson and others, 1974, p. 124). About 73,000 lb/yr of sulfate were discharged to the INTEC disposal well during 1971–73 (Barraclough and Jensen, 1976), 103,000 lb/yr during 1974–78, except during 1976 when no sulfate disposal was reported (Barraclough and others, 1981), and 146,000 lb/yr during 1979–81. During 1982–85, 575,000 lb/yr were discharged to the disposal well and INTEC infiltration ponds (Pittman and others, 1988). About 227,000 lb/yr of sulfate were discharged to the infiltration ponds during 1986–88 (Cecil and others, 1991) and 575,000 lb/yr during 1989–91 (Tucker and Orr, 1998). During 1992–95, about 166,000 lb/yr of sulfate were discharged to the INTEC infiltration ponds (Bartholomay, 1998) and during 1996–98, about 146,000 lb/yr was discharged (Bartholomay and Tucker, 2000). Total sulfate discharged to the infiltration ponds at the INTEC has not been compiled for 1999–2001. The average concentrations of dissolved sulfate in wastewater were about 34 mg/L in 1999, 30 mg/L in 2000, and 34 mg/L in 2001 (Stoller Corp., 2002a, table 7-3; 2002b, table 6-3; 2002c, table 5-16).
Dissolved sulfate concentrations in shallow perched ground water from wells SWP 8 and 13 were 34 and 30 mg/L, respectively, in July 2001 (table 5), which were similar to the average wastewater concentration. Dissolved sulfate concentrations in water from wells completed in the deep perched ground water closest to the INTEC infiltration ponds (PW 1 through 5) ranged from 28 to 30 mg/L in 2001 (table 5). These concentrations also were consistent with the average concentration in the wastewater. Historically, dissolved sulfate concentrations in these wells have fluctuated between about 22 and 41 mg/L. The dissolved sulfate concentration in water from well PW 6 was 18 mg/L in 1999; this well was dry during 2000–01. Concentrations of dissolved sulfate in water from well PW 6 have historically fluctuated between 13 and 24 mg/L.
Concentrations of dissolved sulfate in samples from well USGS 50 (table 5) ranged from 39 to 41 mg/L during 1999–2001. Historically, dissolved sulfate concentrations in water from well USGS 50 have fluctuated slightly around these values. The dissolved sulfate concentrations in water from this well are attributed to leakage from wastewater pipelines at the INTEC.
Robertson and others (1974, p. 121) reported that insignificant amounts of nitrate probably were discharged to the INTEC disposal well during 1952–70. In 1973, about 101,000 lb of nitrate was discharged (Barraclough and Jensen, 1976. During 1974–78, about 131,000 lb/yr was discharged to the disposal well (Barraclough and others, 1981) and 288,000 lb/yr during 1979–81 (Lewis and Jensen, 1984). During 1982–85, 274,000 lb/yr were discharged at the INTEC and after February 1984, most wastewater was disposed to the new INTEC infiltration ponds (Pittman and others, 1988). During 1986‑88, 160,400 lb/yr of nitrate were discharged to the infiltration ponds (Cecil and others, 1991); 56,000 lb/yr during 1989–91; and 41,000 lb/yr during 1992–95 (Bartholomay and others, 1997). Wastewater discharged to the INTEC infiltration ponds during 1996–98 contained about 260,000 lb of nitrate; of that amount, about 221,000 lb was discharged in February 1996. Annual discharge amounts of nitrate for 1999–2001 have not been compiled. The concentration of nitrate (as nitrogen) in wastewater was nearly constant with an average of 0.92 mg/L in 1999 to 0.91 mg/L in 2001 (Stoller Corp., 2002a, 2002b, 2002c).
Dissolved nitrite plus nitrate (as nitrogen) analyses are done annually on water from shallow perched ground water wells at the infiltration ponds and on water from well USGS 50. Nitrite analyses indicated that almost all dissolved nitrite plus nitrate concentration is from nitrate. Well SWP 8, completed in shallow perched ground water, was not sampled in 1999 because the well was dry. The dissolved nitrite plus nitrate (as nitrogen) concentration in water from SWP 8 was 0.7 mg/L in July 2000 and 1.3 mg/L in July 2001. Well SWP 13 was not sampled in 1999 or 2000 because the well was dry; the dissolved nitrite plus nitrate (as nitrogen) concentration in July 2001 was 0.6 mg/L. During 1999–2001, dissolved nitrite plus nitrate (as nitrogen) concentrations in water from well USGS 50 ranged from 58.4 mg/L in October 1999 to 4.7 mg/L in October 2001 (table 5), a fluctuating but overall decreasing trend since sampling began in 1988. The nitrate concentrations may be due to leakage from wastewater pipelines at the INTEC.
Solid and liquid radioactive and chemical wastes have been buried in trenches and pits at the Subsurface Disposal Area (SDA) at the RWMC (figs. 1, 3) since 1952. These 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.
Perched ground water beneath the RWMC is in sedimentary interbeds in basalts and can be attributed primarily to local snowmelt and rain infiltration and recharge from the Big Lost River and the INL spreading areas.
Well USGS 92 (fig. 3) is in the SDA at the RWMC and is completed in a sedimentary interbed (Anderson and Lewis, 1989, p. 29) 214 ft below land surface. Perched water in this well has moved through overlying sediments and basalt and may contain waste constituents leached from radiochemical and organic chemical wastes buried in the SDA. Small amounts of water in well USGS 92 frequently preclude collection of an adequate sample for all requested analyses. Adequate samples for requested analyses were collected during October 1999 and in the spring of 1996–98. The sample collected in October 2000 yielded only enough water for tritium, strontium-90, and cesium-137 analyses; part of the October 2001 sample was lost prior to analysis (table 6).
During 1999–2001, radiochemical constituents in all water samples from well USGS 92 (table 6) were less than the reporting level with the exception of the April 2000 and October 2001 samples analyzed for tritium. The tritium concentration was at the reporting level at 0.3±.0.1 pCi/mL in April 2000, and near the reporting level at .45±.14 pCi/mL in October 2001 (table 6). Tritium concentrations in water from well USGS 92 have been variable through time.
Historically, the concentration of americium-241 was above the reporting level in October 1992, and the concentration of plutonium-238 was above the reporting level in November 1994 (Bartholomay, 1998).
Dissolved chloride concentrations in water from four samples collected from well USGS 92 ranged from 78.0 to 81.2 mg/L during 1999–2001 (table 6). These dissolved chloride concentrations are consistent with concentrations measured historically.
In 1987, 9 VOCs were detected in water from well USGS 92 (Mann and Knobel, 1987, p. 16–17); in January 1990, 6 VOCs were detected (Tucker and Orr, 1998); and in April 1992, water samples contained concentrations of 18 VOCs (Bartholomay, 1998, p. 28; Greene and Tucker, 1998). During 1996–98, 14 VOCs were detected (Bartholomay and Tucker, 2000). During 1999–2001, water from well USGS 92 was analyzed for the same VOCs as in previous years. Most of the same VOCs detected during 1996–98 were detected during 1999–2001, except toluene was not detected and benzene and chloroethane were detected. Table 7 lists the concentrations of 15 VOCs detected in 1999–2001 as well as VOCs detected during 1996–98. Most VOCs fluctuated through time and show no distinct trend. The MRL for some VOCs was changed from 0.2 to 0.1 µg/L during 1998–2001, a change that could result in detections of smaller concentrations and (or) different VOCs than detected in previous years.
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