Precipitation Sampling
Of
the precipitation samples collected, two EFS samples (collected on April
4 and April 18) yielded tritium results greater than the 2s
uncertainty. The sample
collected on April 4 did not exceed the MDC, while the sample collected
on April 18 did exceed the MDC (see table B-1 for MDC values).
Tritium was also detected above the 2s level in the Idaho Falls
sample in May and the duplicate sample from Idaho Falls in June.
However, neither of these samples exceeded their associated MDC,
indicating false positives. While
there are no specific limits on the amount of tritium in precipitation,
the SDWA limits tritium in drinking water to 2
x 104 pCi/L (Appendix B-1).
The level of tritium detected in the
sample from EFS that was above its associated 2s and MDC
value was 140 times lower than the SDWA limit. Although
tritium was detected (above its associated 2s and MDC) in precipitation
from EFS and an INEEL source cannot be completely discounted for
contributing to this, the measured level was within the range of
background tritium that exists throughout the world.
Low levels of
tritium exist in the environment at all times.
The major natural source of tritium
is cosmic ray reactions in the upper atmosphere.
From 1978 to 2001 the EPA, as part of its ERAMS, measured tritium
from –2.00 x 102 to 7.38 x 106 pCi/L in
precipitation samples across the United States (EPA, 2002).
Data for all precipitation samples
collected by the ESER Program during the second quarter of 2001, are
listed in Table C-6 (Appendix C). |
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When
adequate precipitation occurred, samples were taken on a monthly
interval from Idaho Falls and CFA, and on a weekly interval from the EFS.