Scientific Investigations Report 2006–5236
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5236
Shallow and deep perched ground water is present in basalt and sediments beneath several facilities at the Idaho National Laboratory (INL) resulting from low-level radioactive, chemical, and sanitary wastewater discharge to infiltration ponds since 1952. During 2001, about 293 million gallons (Mgal) was discharged to infiltration and lined evaporation ponds at the Reactor Technology Complex (RTC), and 544 Mgal was discharged to infiltration ponds at the Idaho Nuclear Technology and Engineering Center (INTEC).
During 1952–93, about 10,500 Curies (Ci) of tritium was in wastewater discharged to the RTC radioactive-waste infiltration ponds. Since 1993, tritium in wastewater has been discharged to two lined evaporation ponds, which replaced the radioactive-waste infiltration ponds. About 191 Ci of tritium was released in wastewater to the RTC lined evaporation ponds during 1999–2000. Data are not available for the total amount to tritium in wastewater discharged in 2001.
In 2001, tritium concentrations in water from seven wells completed in shallow perched ground water near the cold-waste pond at RTC were less than the reporting level. Two wells completed in shallow perched water could not be sampled in 2001 because of either a lack of water or an obstruction in the wells. During July–October 2001, tritium concentrations in water from eight wells completed in deep perched ground water at the RTC were greater than the reporting levels. Tritium concentrations ranged from 0.49±0.14 to 39.4±1.4 picocuries per milliliter (pCi/mL). During July–October 2001, reportable concentrations of tritium in water from wells completed in deep perched ground water were less than the reported concentrations measured during July–December 1998.
Several factors likely affected the distribution of tritium in perched ground water in wells at the RTC. These factors include proximity of the well to the radioactive-waste infiltration ponds, depth of water below the ponds, variations in tritium disposal rates, radioactive decay, dilution from infiltration from the cold-waste ponds, and infiltration of Big Lost River water. The replacement of the radioactive-waste infiltration ponds by lined evaporation ponds in 1993 also contributed to decreased tritium concentrations in perched ground water.
Less than 0.001 Ci of strontium-90 was discharged at the RTC during 1999; during 2000, 0.21 Ci of strontium-90/yttrium-90 was discharged at the RTC. Data are not available for the amount of strontium-90 discharged in 2001. Water from well TRA A 13 completed in shallow perched ground water, exceeded the reporting level during 1999–2001, concentrations ranged from 38±1.4 to 22.1±1.1 pCi/L (picocuries per liter). 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 October 2001, the concentration was less than the reporting level.
Concentrations of strontium-90 in water from five wells completed in deep perched ground water at the RTC exceeded reporting levels in October 2001; concentrations ranged from 2.8±0.7 to 83.8±2.1 pCi/L. The distribution of strontium-90 concentrations in water from these wells during 1999‑2001 is attributed to sorption and (or) exchange reactions between strontium-90 in solution and sediments beneath the radioactive-waste infiltration ponds.
No reportable concentrations of cesium-137 were detected in water from any wells completed in either shallow or deep perched ground water at the RTC during 1999–2001. The general absence of reportable concentrations of cesium-137 in perched ground water at the RTC probably is due to decreased cesium disposal rates, use of lined evaporation ponds instead of the radioactive-waste infiltration ponds, and sorption and (or) exchange reactions with sediments.
Chromium-51 and cobalt-60 were not detected in any water samples collected during 1999–2001. Decreased disposal and relatively short half-lives probably account for their absence.
Wastewater from RTC cooling-tower operations containing an estimated 24,000 lb of non-radioactive chromium was discharged to the radioactive-waste infiltration ponds during 1952–64. During 1964–72, chromium was discharged to a disposal well; no discharges of chromium were reported after 1972. During 1999–2001, no dissolved chromium was detected in shallow perched ground water. Dissolved chromium was detected in water from 10 wells completed in deep perched ground water at the RTC. The maximum concentration of dissolved chromium in deep perched ground water was 90 micrograms per liter (µg/L) in January 1999. This concentration decreased to 35 µg/L by October 2001. During July–October 2001, concentrations of dissolved chromium in deep perched ground water near the RTC ranged from 10 to 82 µg/L. The largest concentrations were in water from wells north and west of the radioactive-waste infiltration ponds, and the presence of dissolved chromium indicates that water from these wells contained constituents that were discharged to the radioactive-waste infiltration ponds before 1965.
About 173,000 pounds of sodium was discharged to the RTC chemical-waste pond during 1996–98. The total amount of sodium in wastewater discharged at the RTC from 1999–2001 has not been compiled. During 1999–2001, the maximum concentration of sodium in water from wells in shallow perched ground water was 23 milligrams per liter (mg/L). During July–October 2001, sodium concentrations in water from wells completed in deep perched ground water generally ranged from 7 to 20 mg/L in all wells except well USGS 68, with a concentration of 413 mg/L, a decrease from December 1998 when the concentration was 662 mg/L.
About 3,600 pounds of chloride was in wastewater discharged to the cold-waste ponds during 1996‑98. Data are not available for chloride in wastewater discharged during 1999–2001. During 1999–2001, chloride concentrations in shallow perched ground water ranged from 10 to 53 mg/L. Chloride concentrations in deep perched ground water ranged from 5 to 91 mg/L.
Wastewater that contained about 833,000 pounds of sulfate was discharged to the chemical- and cold-waste ponds at RTC during 1996–98. Compiled data are not available for the amount of sulfate in wastewater discharged during 1999–2001. During July–October 2001, concentrations of dissolved sulfate in water from wells completed in deep perched ground water ranged from 115 to 1,409 mg/L. The maximum concentration of dissolved sulfate in deep perched ground water was from water from well USGS 68, west of the chemical-waste pond.
Two infiltration ponds were constructed south of the INTEC in 1984 and 1985 to replace the INTEC disposal well. Wastewater from these ponds formed perched ground water in the basalt and sedimentary interbeds above the Snake River Plain aquifer. The discharge to the ponds during 2001 was about 544 Mgal; data for 1999 and 2000 are not available. Perched ground water 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.
Tritium discharged to the ponds decreased over the years from 960 Ci during 1984–88 to 0.03 Ci in 2000. Data are not available for tritium discharged in 2001. In 2001, tritium concentrations in water from wells completed in shallow perched ground water were less than the reporting level. During 1999–2001, the tritium concentration in water from wells completed in deep perched ground water beneath the infiltration ponds ranged from less than the reporting level to 9.7±0.5 pCi/mL. Tritium concentrations have decreased in shallow and deep perched ground water near the INTEC since 1986–88.
During 1999–2000, less than 0.001 Curie per year (Ci/yr) of strontium-90 was discharged at the INTEC; data are not available for strontium-90 discharged in 2001. A concentration of 2.1±0.7 pCi/L was detected in July 2001 in one well completed in shallow perched ground water. During 1999–2001, concentrations of strontium-90 were variable in water from all wells completed in the 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. Overall, concentrations of strontium-90 have been decreasing in wells near the INTEC.
During 1999–2000, less than 0.001 Ci/yr of cesium‑137 was discharged to the INTEC infiltration ponds. Data are not available for cesium-137 discharged during 2001. Concentrations of cesium-137 did not exceed the reporting level in perched ground water. The absence of reportable cesium-137 concentrations 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.
Estimates of sodium discharged at the INTEC are not available for 1999–2001. Sodium concentrations in water from two wells completed in shallow perched ground water ranged from 92 to 102 mg/L in July 2001, which was similar to the average wastewater concentration. During 1999–2001, dissolved sodium concentrations in deep perched ground water in wells closest to the infiltration ponds ranged from 109 mg/L in October 2001 to 164 mg/L in October 1999. 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.
Estimates of chloride discharged at the INTEC are not available for 1999–2001. In July 2001, dissolved chloride concentrations in two wells completed in shallow perched ground water ranged from 153 to 157 mg/L. During 1999‑2001, dissolved chloride concentrations in deep perched ground water in wells closest to the infiltration ponds ranged from 79 to 348 mg/L. In October 2001, some wells were dry, some were not sampled because of well access problems, and water in two wells contained dissolved chloride concentrations of 167 mg/L and 175 mg/L. 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. 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. Dissolved chloride concentrations in water from this well steadily decreased since sampling began in 1959.
Estimates of sulfate discharged during 1999–2001 are not available. Dissolved sulfate concentrations in water from two wells completed in shallow perched ground water ranged from 30 to 34 mg/L in July 2001. Dissolved sulfate concentrations in water from wells completed in the deep perched ground water closest to the INTEC infiltration ponds ranged from 28 to 30 mg/L in 2001. Historically, dissolved sulfate concentrations in these wells have fluctuated between about 22 and 41 mg/L. Concentrations of dissolved sulfate in samples from well USGS 50 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. These concentrations are consistent with the average concentration of dissolved sulfate in wastewater.
Estimates of dissolved nitrite plus nitrate (as nitrogen) discharged during 1999–2001 are not available. In July 2001, the concentration of dissolved nitrite plus nitrate (as nitrogen) in wells completed in shallow perched ground water ranged from 0.6 to 1.3 mg/L. Dissolved nitrite plus nitrate (as nitrogen) concentrations in deep perched ground water near the INTEC disposal well ranged from 58.4 mg/L in 1999 to 4.7 mg/L in 2001.
Perched ground water beneath the Radioactive Waste Management Complex (RWMC) is in sedimentary interbeds in basalts and can be attributed primarily to infiltration of snowmelt and rainfall and to recharge from the Big Lost River and the INL spreading areas and, therefore, may contain waste constituents leached from liquid and solid radiochemical and organic chemical wastes buried at the RWMC. During 1999–2001, radiochemical constituents in all water samples from well USGS 92 were less than the reporting level with the exception of two samples analyzed for tritium. The tritium concentration in water from well USGS 92 was at the reporting level at 0.3±.0.1 pCi/mL in April 2000 and near the reporting level at 0.45±14 pCi/mL in October 2001. Tritium concentrations in water from well USGS 92 have been variable through time.
Dissolved chloride concentrations in water from four samples collected from well USGS 92 at the RWMC ranged from 78.0 to 81.2 mg/L during 1999–2001. These dissolved chloride concentrations are consistent with concentrations measured historically.
During 1999–2001, samples from well USGS 92 contained concentrations greater than the reporting levels of 15 volatile organic compounds (VOCs). Water from well USGS 92 was analyzed for the same VOCs as in previous years. Mostly the same VOCs detected during 1996–98 were detected during 1999–2001, except that toluene was not detected and benzene and chloroethane were detected. Most VOCs have fluctuated through time and showed no distinct trend.
U.S.
Department of the Interior | U.S. Geological
Survey
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