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 2010 produced sufficient precipitation to yield ten samples.
Tritium was measured above the 3s value in four of the ten
samples collected during the first quarter of 2010. 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 in the range of this value
(averaging 95 pCi/L) and are listed in
Table C-5 (Appendix C).