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 third quarter of 2010 produced sufficient precipitation to yield only eight samples; results were available for six of the samples.
Tritium was
measured above the 3s values in two of the six 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 third quarter precipitation samples collected by the ESER Program
were below this value (averaging 79 pCi/L) and are listed in
Table C-5 (Appendix C).