Precipitation samples are gathered when sufficient precipitation occurs to allow for the collection of the minimum sample volume of approximately 50 mL. Samples are taken of monthly composites from Idaho Falls and CFA, and weekly from the EFS. Precipitation samples are analyzed for tritium. Storm events in the first quarter of 2011 produced sufficient precipitation to yield 13; results were available for 11 of the samples.
Tritium was measured above the 3s values in 2 of the 11 samples for which results were available. Low levels of tritium exist in the environment at all times as a result of cosmic ray reactions with water molecules in the upper atmosphere. The EPA’s RadNet program collects precipitation samples from across the United States. From 1980 to 2008, tritium measured in samples from Region 10 (which includes Idaho) averaged 117 pCi/L (EPA 2009). Data for all first quarter precipitation samples collected by the ESER Program were below this value (averaging about 65 pCi/L) and are listed in Table C-5 (Appendix C).
Two non-routine precipitation samples were collected from the Idaho Falls location to monitor for fallout from Japan’s Fukushima nuclear accident. The first samples covered a period from March 14 to March 22 and the second covered the period from March 22 to March 28. Iodine-31 was measured in the first samples at 74 pCi/L and in the second at 275 pCi/L. In addition, cesium-137 was detected in both samples at 17 pCi/L and 72 pCi/L, respectively. These values are consistent with those reported by EPA’s RadNet across the western United States.
WATER SAMPLING
Results were available for drinking and surface water samples collected during the fourth quarter of 2010 in conjunction with the state of Idaho’s INL Oversight Program. Drinking water was collected at Minidoka, Mud Lake and Shoshone (plus a duplicate); surface water was collected from springs near Twin Falls, Buhl, and Hagerman. All samples were analyzed for gross alpha, gross beta, and tritium. Results are listed in Table C-6 of Appendix C.
Tritium was not detected in any sample. Gross alpha was detected in all of the samples and gross beta was detected in two of the drinking water samples and two of the surface water samples. Gross beta activity was found in all of the samples. It is not unusual to detect these constituents in water of the Snake River Plain, related to natural production from the basalts that make up the aquifer. In 2006, the last year in which the ESER Program sampled these locations, gross alpha concentrations ranged up to 3.77 pCi/L and gross beta concentrations ranged up to 8.82 pCi/L, similar to those values found in the fourth quarter of 2010.