Surface and/or drinking water are sampled twice each year in the second and fourth quarters at 19 locations around the INEEL (see Appendix A).  Monthly composite precipitation samples are collected from Idaho Falls and the Central Facilities Area (CFA) on the INEEL. Weekly precipitation samples are collected from the Experimental Field Station (EFS) on the INEEL. This section discusses precipitation samples collected during the third quarter of 2001.

When adequate precipitation occurred, samples were taken of a monthly composite from Idaho Falls and CFA, and weekly from the EFS.  A minimum sample volume of approximately 20 mL of precipitation is needed for a single sample.  Precipitation samples are analyzed for tritium.  For the third quarter of 2001, there was enough precipitation for a total of seven samples – three from Idaho Falls, three from CFA, and one from EFS.             

Tritium was detected in three samples, one from Idaho Falls for August and two from CFA (August and September).  While there is no regulatory restriction on tritium in precipitation, the DOE DCG and maximum contaminant level (MCL) set by EPA for tritium in drinking water can be used as a measure.  The highest value was the September CFA sample with a value of 125.2 ± 63.7 pCi/L (4.64 ± 2.36 Bq/L).  This value is many times below the DOE DCG and 160 times lower than the EPA MCL.  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 Environmental Radiation Ambient Monitoring System (ERAMS), measured tritium from –2.00 x 10² to 7.38 x 10⁶ pCi/L (-7.4 to 2.7 x 10⁵ Bq/L) in precipitation samples across the United States (EPA, 2002).  Data for all precipitation samples for the third quarter 2001 are listed in Table C-6 (Appendix C).

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