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 second quarter of 2010 produced sufficient precipitation to yield 16 samples; results were available for 13 of the samples.

Tritium was measured above the 3s values in 5 of the 13 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 second quarter precipitation samples collected by the ESER Program were in the range of this value (averaging 84 pCi/L) and are listed in Table C-5 (Appendix C).
 

SURFACE WATER SAMPLING

The Big Lost River contained water on the INL Site for a short period during the second quarter of 2010. Samples were collected at four locations and analyzed for gross alpha activity, gross beta activity, and tritium. Collection locations included the public rest area on US Highway 20/26, on Lincoln Boulevard near the Idaho Nuclear Technology and Engineering Center, at EFS (plus a duplicate sample), and on Lincoln Boulevard near the Naval Reactors Facility.

Gross alpha was detected in all of the samples and gross beta was detected in four of the five samples analyzed. 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 offsite surface water, gross alpha concentrations ranged up to 3.77 pCi/L and gross beta concentrations ranged up to 8.82 pCi/L. All results from the Big Lost River sampling were well within these ranges (see Appendix C, Table C-6).

Tritium was detected in four of the five samples. As described in the Precipitation section above, an average of 117 pCi/L was detected in water taken across the region. The samples from the Big Lost River averaged 116 pCi/L, or nearly exactly the same as the background results (Appendix C, Table C-6).