Precipitation samples are gathered when sufficient precipitation occurs to allow for the collection of the minimum sample volume of approximately 20 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 2008 produced sufficient precipitation to yield ten samples–three from CFA and Idaho Falls and four from the EFS.
Tritium was not measured above the 3s value in any of the samples collected during the first quarter of 2008. 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 2005, tritium measured in samples from Region 10 (which includes Idaho) ranged from -200 to 7500 pCi/L (EPA 2006). Data for all first quarter 2008 precipitation samples collected by the ESER Program are listed in Table C-5 (Appendix C).