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 second quarter of 2008 produced sufficient precipitation to yield 11 samples.
Tritium was measured above the 3s value in four of the eleven samples
collected during the second 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 2007). Data for all second quarter 2008
precipitation samples collected by the ESER Program were well within this
range and are listed in Table C-5
(Appendix C).