Third Quarter 2007
INL Quarterly Site Environmental Report
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Air Sampling

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. Moisture in the atmosphere was sampled at four locations around the INL Site and analyzed for tritium. Air sampling activities and results for the third quarter of 2007 are discussed below. A summary of approximate minimum detectable concentrations (MDCs) for radiological analyses and DOE Derived Concentration Guide (DCG) (DOE 1993) values is provided in Appendix B.

Low-Volume Air Sampling

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 third quarter of 2007 (Figure 2). Four of these samplers are located on the INL Site, eight are situated off the INL Site near the boundary and six 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 year to a new location. One replicate sampler was placed at Mud Lake (a Boundary location) and one at the Experimental Field Station (an INL Site location) during 2007. An average of 16,148 ft3 (457 m3) of air was sampled at each location, each week, at an average flow rate of 1.60 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.

                                                                      

Figure 2.    Low-volume air sampler locations.

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. Median gross alpha concentrations in air for INL Site, Boundary, and Distant locations for the third quarter of 2007 are shown in Figure 3. Gross alpha data are tested for normality prior to statistical analyses, and generally show no consistent discernable distribution. Box and whisker plots are commonly used when there is no assumed distribution. Each data group in Figure 3 is presented as a box and whisker plot, with a median (small red square), a box enclosing values between the 25th and 75th percentiles, and whiskers representing the non-outlier range. Outliers and extreme values are identified separately from the box and whiskers. Outliers and extreme values are atypical, infrequent, data points that are far from the middle of the data distribution. For this report, outliers are defined as values that are greater than 1.5 times the height of the box, above or below the box. Extreme values are greater than 2 times the height of the box, above or below the box. Outliers and extreme values may reflect inherent variability, may be due to errors associated with transcription or measurement, or may be related to other anomalies. A careful review of the data collected during the third quarter indicates that the outlier values were not due to mistakes in collection, analysis, or reporting procedures, but rather reflect natural variability in the measurements. The outlier values lie within the range of measurements made within the past several years. Thus, rather than dismissing the outliers, they were included in the subsequent statistical analyses.

Because there is no discernable 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. The p value for each comparison is shown in Table D-1. Figure 3 graphically shows that the gross alpha measurements made at INL Site, Boundary and Distant locations are similar for the third quarter. If the INL Site were a significant source of offsite contamination, concentrations of contaminants could be statistically greater at Boundary locations than at Distant locations. However, in the third quarter the opposite case was true—gross alpha concentrations at the Distant locations were statistically greater than the Boundary locations.

Comparisons of gross alpha concentrations were made for each month of the quarter (Figures 4 – 6). Again the Kruskal-Wallis test of multiple independent groups was used to determine if statistical differences exist between INL Site, Boundary and Distant data groups.

Figure 3.    Gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations for the third quarter of 2007.

Because there is no discernable 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. The p value for each comparison is shown in Table D-1. Figure 3 graphically shows that the gross alpha measurements made at INL Site, Boundary and Distant locations are similar for the second quarter. If the INL Site were a significant source of offsite contamination, concentrations of contaminants could be statistically greater at Boundary locations than at Distant locations. However, in the second quarter the opposite case was true—gross alpha concentrations at the Distant locations were statistically greater than the Boundary locations.

Comparisons of gross alpha concentrations were made for each month of the quarter (Figures 4 – 6). Again the Kruskal-Wallis test of multiple independent groups was used to determine if statistical differences exist between INL Site, Boundary and Distant data groups.

 

 

Figure 4.   Figure 4. July gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations. Number of samples (N) = 4 at each location, except Atomic City (N = 3), Dubois (N = 2) and Main Gate (N = 3).

Figure 5.  August gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations. Number of samples (N) = 5 at each location, except Atomic City (N = 4), Blue Dome (N = 4), Dubois (N = 3), FAA Tower (N = 4) and Mud Lake (N = 4).

 

Figure 6.  September gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations. Number of samples (N) = 4 at each location, except FAA Tower (N = 2).

No statistical differences in gross alpha concentrations between groups were noted during any month of the quarter (Table D-1).

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. In the third quarter, there were two weeks (July 25 and August 29) where a statistical difference existed between the two sample groups (Table D-2). In both cases, the gross alpha concentrations measured at Boundary locations were statistically greater than those measured at Distant locations. In the other two cases, the Distant locations had statistically higher gross alpha concentrations. When comparing weekly values, one or two results can have a significant impact on the group averages. For example, during the week of July 25 the gross alpha concentration at Monteview was somewhat higher than the other locations, resulting in a higher average for the Boundary group. During the week of August 29, an elevated value at Blue dome impacted the Boundary group mean. No particular distribution was seen in the data to indicate an INL site-related cause, and it is more likely due to random variability in the data.

Gross beta results are presented in Table C-1. Gross beta concentrations in air for INL Site, Boundary and Distant locations for the third quarter of 2007 are shown in Figure 7. The data were tested and found to be neither normally nor log-normally distributed. Box and whiskers plots were used for presentation of the data. 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. The quarterly data for each group appear to be similar and were determined using the Kruskal-Wallace test to be statistically the same (Table D-1).

Figure 7. Gross beta concentrations in air at ESER INL Site, Boundary and Distant locations for the third quarter 2007.

Monthly median gross beta concentrations in air for each sampling group are shown in Figures 8 – 10. Statistical data are presented in Table D-1. There were no statistical differences in gross beta between groups for any month during the quarter.

Comparison of weekly Boundary and Distant gross beta data sets, using the Mann Whitney U test, showed statistical differences between Boundary and Distant measurements during one week in the third quarter, the week of September 5 (Table D-2). In this case, the Distant group was statistically greater than the Boundary group. During that week higher measurements at Idaho Falls and Rexburg appeared to impact the group mean.

No 131I was detected in any of the charcoal cartridge batches collected during the third quarter of 2007. Weekly 131I results for each location are listed in Table C-2 of Appendix C. Gamma spectrographic analysis is also done with the 131I analysis. Cesium-137 was detected near the detection limit in 13 of the 26 measured batches of cartridges. The analytical laboratory considers these detections a result of the materials used in the charcoal filters.

Weekly filters for the third quarter of 2007 were composited by location. All samples were analyzed for gamma-emitting radionuclides, including 137Cs (see Table C 3, Appendix C). Cesium-137 was not detected in any third quarter composites.

Composites were also analyzed for 90Sr, 238Pu, 239/240Pu and 241Am (see Table C 3, Appendix C.) One composite, from the INL Main Gate, had detectable 90Sr. The respective measured concentration of (43.9 ± 14.3) x 10-18 mCi/mL is within historical measurements and substantially below the Derived Concentration Guide of 9,000,000 x 10-18 mCi/mL.
 

Figure 8. July gross beta concentrations in air at ESER INL Site, Boundary and Distant locations. Number of samples (N) = 4 at each location, except Atomic City (N = 3), Dubois (N = 2) and Main Gate (N = 3).

Figure 9. August gross beta concentrations in air at ESER INL Site, Boundary and Distant locations. Number of samples (N) = 5 at each location, except Atomic City (N = 4), Blue Dome (N = 4), Dubois (N = 3), FAA Tower (N = 4) and Mud Lake (N = 4).

Figure 10. September gross beta concentrations in air at ESER INL Site, Boundary and Distant locations. Number of samples (N) = 4 at each location, except FAA Tower (N = 2).

Atmospheric Moisture Sampling

Twenty-four atmospheric moisture samples were obtained during the third quarter of 2007 from Atomic City, Blackfoot CMS, Idaho Falls and Rexburg CMS. 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.

Twenty-one of the 24 samples exceeded the 3s uncertainty level for tritium. All samples with detectable tritium were significantly below the DOE DCG for tritium in air of 1 x 10-7 mCi/mLair, and ranged from (7.2 ± 1.1) x 10-13 mCi/mLair at Rexburg collected in late September to (17.3 ± 2.8) x 10-13 mCi/mLair at Idaho Falls in a sample collected early in August. All results are shown in Table C-4, Appendix C.
 

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Third Quarter 2007
INL Quarterly Site Environmental Report
Return to Index