The primary pathway by which radionuclides can move off the INL Site is through the air and for this reason the air pathway is the primary focus of monitoring on and around the INL Site. Samples for particulates and iodine-131 (131I) gas in air were collected weekly for the duration of the quarter at 16 locations using low-volume air samplers. The sampler in Jackson resumed operation at the end of 2016 following completion of the construction at a new sampling location. Moisture in the atmosphere was sampled at four locations around the INL Site and analyzed for tritium. Air sampling activities and results for the first quarter of 2017 are discussed below. A summary of approximate minimum detectable concentrations (MDCs) for radiological analyses and DOE Derived Concentration Standard (DCS) (DOE 2011b) values is provided in Appendix B.
Radioactivity associated with airborne particulates was monitored continuously by 18 low-volume air samplers (two of which are used as replicate samplers) at 16 locations during the first quarter of 2017 (Figure 2). Three of these samplers are located on the INL Site, seven are situated off the INL Site near the boundary, and eight have been placed at locations distant to the INL Site. Samplers are divided into INL Site, Boundary, and Distant groups to determine if there is a gradient of radionuclide concentrations, increasing towards the INL Site. Each replicate sampler is relocated every other year to a new location. At the start of 2016, one replicate sampler was moved to Sugar City (a Distant location) and one was moved to Blackfoot (also a Distant location). An average of 19,251 ft3 (545 m3) of air was sampled at each location, each week, at an average flow rate of 1.91 ft3/min (0.05 m3/min). Particulates in air were collected on membrane particulate filters (1.2-µm pore size). Gases passing through the filter were collected with an activated charcoal cartridge.
Filters and charcoal cartridges were changed weekly at each station during the quarter. Each particulate filter was analyzed for gross alpha and gross beta radioactivity using thin-window gas flow proportional counting systems after waiting about four days for naturally-occurring daughter products of radon and thorium to decay.
The weekly particulate filters collected during the quarter for each location were composited and analyzed for gamma-emitting radionuclides. Selected composites were also analyzed by location for 90Sr, 238Pu, 239/240Pu, and 241Am as determined by a rotating quarterly schedule.
Charcoal cartridges were analyzed for gamma-emitting radionuclides, specifically for iodine-131 (131I). Iodine-131 is of particular interest because it is produced in relatively large quantities by nuclear fission, is readily accumulated in human and animal thyroids, and has a half-life of eight days. This means that any elevated level of 131I in the environment could be from a recent release of fission products.
Gross alpha results are reported in Table C-1 and shown in Figures 3 through 6. Gross alpha data are tested for normality prior to statistical analyses, and generally show no consistent discernible distribution. Because there is no discernible distribution of the data, the nonparametric Kruskal-Wallis test of multiple independent groups was used to test for statistical differences between INL Site, Boundary, and Distant locations. The use of nonparametric tests, such as Kruskal-Wallis, gives less weight to outlier and extreme values thus allowing a more appropriate comparison of data groups. A statistically significant difference exists between data groups if the (p) value is less than 0.05. Values greater than 0.05 translate into a 95 percent confidence that the medians are statistically the same. Comparisons of gross alpha concentrations were made for the quarter and for each month of the quarter using this methodology. The p-value for each comparison is shown in Table D-1. In the first quarter, there was a statistical difference for the quarter as a whole and for the month of March. In both cases, the Boundary group showed the highest concentration, followed by the Distant group. The INL Site group was actually the group with the lowest gross alpha concentrations. The differences between the groups was very small, however, as shown in Figure 3.
As an additional check, comparisons between gross alpha concentrations measured at Boundary and Distant locations were made on a weekly basis. The Mann-Whitney U test was used to compare the Boundary and Distant data because it is the most powerful nonparametric alternative to the t-test for independent samples. INL Site sample results were not included in this analysis because the onsite data, collected at only three locations, are not representative of the entire INL Site and would not aid in determining offsite impacts. There were two weeks where a statistical difference existed between the two sample groups (Table D-2). These were the weeks of January 11 and February 1. Nothing unusual was noted in the data when individual locations were compared, with Sugar City being somewhat low on January 11 and Arco on the higher end on February 1.
Gross beta results are presented in Table C-1 and displayed in Figures 7 through 10. The data are tested quarterly and generally are found to be neither normally nor log-normally distributed. Outliers and extreme values were retained in subsequent statistical analyses because they are within the range of measurements made in the past five years, and because these values could not be attributed to mistakes in collection, analysis, or reporting procedures. A statistical difference was noted in the quarterly data and during January (Table D-1). As with the gross alpha data, the difference between groups was fairly small. During the winter months, gross beta concentrations tend to be more variable than during other seasons. This is due to variations in weather conditions between individual sampling locations, such as when inversion conditions are persistent at some locations.
Weekly comparisons were also made using the same method as for the gross alpha data and statistical differences were found during two weeks of the quarter (Table D-2). These were the first two weeks of the quarter (January 4 and January 11). In both cases, the Boundary locations were higher than the Distant locations. No particular pattern was found when looking at individual location concentrations.
Iodine-131 was not detected in any of the 26 sets of charcoal cartridges measured during the first quarter. Weekly 131I results for each location are listed in Table C-2 of Appendix C.
No 137Cs or other human-made gamma-emitting radionuclides were found in quarterly composites. No 90Sr or 239/240Pu were found either. Plutonium-238 was detected just above the 3s uncertainty level in the composite from the duplicate sampler at Blackfoot (but not in the composite from the regular sampler in Blackfoot). In comparison to the Derived Concentration Standard, the 239/240Pu result was 0.004 percent of the DCS. Amercium-241 was also reported in composites from Idaho Falls and Jackson, also just above the detection limit. The higher of these two values was 0.005 percent of the DCS. A lower detection limit achieved by the current laboratory performing these analyses has resulted in a few results near the detection limit in 2016 and 2017. Results for these analyses are found in Table C-3 of Appendix C.
Atmospheric moisture is collected by pulling air through a column of absorbent material (molecular sieve material) to absorb water vapor. The water is then extracted from the absorbent material by heat distillation. The resulting water samples are then analyzed for tritium using liquid scintillation.
Results were available for eight atmospheric moisture samples collected during the first quarter of 2017. Seven of the eight results exceeded the 3s uncertainty level for tritium, with similar results to those reported previously. Results also remain similar between the four sampling locations. All samples were significantly below the DOE DCS for tritium in air of 1.4 x 10-8 mCi/mLair with a maximum reported value of 6.77 x 10-13 mCi/mLair at Sugar City. Results are shown in
Table C-4, Appendix C.
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