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 2011 produced sufficient precipitation to yield nine samples.

Tritium was measured above the 3s values in all of the nine samples. 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 third quarter precipitation samples collected by the ESER Program were within the range of this value (averaging about 124 pCi/L) and are listed in Table C-5 (Appendix C).

WATER SAMPLING

Samples were collected from the Big Lost River on the INL Site near the beginning of its period of flow and near the end of its period of flow. Samples were collected on June 30 at the public rest area on US Highway 20/26, on Lincoln Boulevard near the Idaho Nuclear Technology and Engineering Center (INTEC), at the Experimental Field Station, at Lincoln Boulevard north of the Naval Reactors Facility, and at the Big Lost River Sinks near Howe. A control sample was also collected from the Birch Creek outflow at the northern INL Site boundary. These areas were sampled again on July 14, except for the INTEC location, which was completely dry. Samples were analyzed for gross alpha, gross beta, and tritium. Results are listed in Table C-6 of Appendix C.

Gross alpha and gross beta activity was detected in all samples. Concentrations were generally similar to previous results from surface water sampling. A couple of the gross alpha results were somewhat above last year’s values, but well within the historical range. Tritium was also detected in all of the samples. Concentrations were similar to those found in atmospheric moisture and precipitation samples and were consistent with previous years.