Scientific Investigations Report 2006–5236
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5236
Radiochemical and chemical wastes generated at facilities at the Idaho National Laboratory (INL) were discharged since 1952 to infiltration ponds at the Reactor Technology Complex (RTC) (known as the Test Reactor Area [TRA] until 2005), and the Idaho Nuclear Technology and Engineering Center (INTEC) and buried at the Radioactive Waste Management Complex (RWMC). Disposal of wastewater to infiltration ponds and infiltration of surface water at waste burial sites resulted in formation of perched ground water in basalts and in sedimentary interbeds above the Snake River Plain aquifer. Perched ground water is an integral part of the pathway for waste-constituent migration to the aquifer.
The U.S. Geological Survey (USGS), in cooperation with the U.S. Department of Energy, maintains ground-water monitoring networks at the INL to determine hydrologic trends, and to monitor the movement of radiochemical and chemical constituents in wastewater discharged from facilities to both perched ground water and the aquifer. This report presents an analysis of water-quality and water-level data collected from wells completed in perched ground water at the INL during 1999–2001, and summarizes historical disposal data and water-level-and water-quality trends.
At the RTC, tritium, strontium-90, cesium-137, dissolved chromium, chloride, sodium, and sulfate were monitored in shallow and deep perched ground water. In shallow perched ground water, no tritium was detected above the reporting level. In deep perched ground water, tritium concentrations generally decreased or varied randomly during 1999–2001. During October 2001, tritium concentrations ranged from less than the reporting level to 39.4±1.4 picocuries per milliliter (pCi/mL). Reportable concentrations of tritium during July‑October 2001 were smaller than the reported concentrations measured during July–December 1998. Tritium concentrations in water from wells at the RTC were likely affected by: well’s distance from the radioactive‑waste infiltration ponds (commonly referred to as the warm‑waste ponds); water depth below the ponds; the amount of tritium discharged to radioactive-waste infiltration ponds in the past; discontinued use of radioactive-waste infiltration ponds; radioactive decay; and dilution from disposal of nonradioactive water.
During 1999–2001, the strontium-90 concentrations in two wells completed in shallow perched water near the RTC exceeded the reporting level. Strontium-90 concentrations in water from wells completed in deep perched ground water at the RTC varied randomly with time. During October 2001, concentrations in water from five wells exceeded the reporting level and ranged from 2.8±0.7 picocuries per liter (pCi/L) in well USGS 63 to 83.8±2.1 pCi/L in well USGS 54. No reportable concentrations of cesium-137, chromium-51, or cobalt-60 were present in water samples from any of the shallow or deep wells at the RTC during 1999–2001.
Dissolved chromium was not detected in shallow perched ground water at the RTC during 1999–2001. Concentrations of dissolved chromium during July–October 2001 in deep perched ground water near the RTC ranged from 10 micrograms per liter (µg/L) in well USGS 61 to 82 µg/L in well USGS 55. The largest concentrations were in water from wells north and west of the radioactive-waste infiltration ponds. During July–October 2001, dissolved sodium concentrations ranged from 7 milligrams per liter (mg/L) in well USGS 78 to 20 mg/L in all wells except well USGS 68 (413 mg/L). 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 during 1999–2001. 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. The maximum dissolved sulfate concentration in shallow perched ground water was 419 mg/L in well CWP 1 during July 2000. 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 in July–October 2001. The maximum concentration of dissolved sulfate in water during July–October 2001 was 1,409 mg/L in well USGS 68 west of the chemical-waste pond.
At the INTEC, tritium, strontium-90, cesium-137, dissolved sodium, chloride, sulfate, and nitrite plus nitrate (as nitrogen) were monitored in shallow and deep perched ground water. No reportable concentrations of tritium were measured in shallow perched ground water 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 in wells PW 1 and PW 5 to 9.7±0.5 pCi/mL in well PW 6 during 1999–2001. The strontium-90 concentration in water from well SWP 8, completed in shallow perched ground water, was 2.1±0.7 pCi/L in July 2001. 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.
Dissolved sodium, chloride, and sulfate concentrations in shallow and deep perched ground water at the INTEC infiltration ponds during 1999–2001 were similar to or less than the average annual effluent monitoring data.
At the RWMC, tritium, strontium-90, cesium-137, plutonium-238, plutonium-239, -240 (undivided), americium-241, dissolved chloride, and a suite of volatile organic compounds were monitored in deep perched ground water at well USGS 92. Radiochemical constituents in all water samples from well USGS 92 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 slightly above the reporting level at 0.45±0.14 pCi/mL in October 2001. Samples contained concentrations greater than the minimum reporting levels of 15 volatile organic compounds.
U.S.
Department of the Interior | U.S. Geological
Survey
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