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 fourth quarter of 2010 produced sufficient precipitation to yield 14; results were available for 12 of the samples.
Tritium was measured above
the 3s values in 6 of the 12 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 fourth quarter
precipitation samples collected by the ESER Program were just about at this
value (averaging 115 pCi/L) and are listed in
Table C-5 (Appendix C).