Figure 2. Low-volume air sampler locations.
The primary pathway by which radionuclides can move off the INEEL is through the air and for this reason the air pathway is the primary focus of monitoring on and around the INEEL. Samples for particulates and iodine-131 (131I) gas in air were collected weekly at 16 locations using low-volume air samplers for the duration of the quarter. Moisture in the atmosphere was sampled at four locations around the INEEL and analyzed for tritium. Concentrations of airborne particulates less than 10 micrometers in diameter (PM10) were measured for comparison with EPA standards at three locations. Air sampling activities and results for the second quarter, 2004 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.
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 second quarter of 2004 (Figure 2). Three of these samplers are located on the INEEL, eight samplers (including one replicate samplers at Mud Lake) are situated off the INEEL near the boundary, and seven samplers (including one replicate at Blackfoot) have been placed at locations distant to the INEEL. Each replicate sampler is relocated every year to a new location. Samplers are divided into INEEL, Boundary, and Distant groups to determine if there is a gradient of radionuclide concentrations, increasing towards the INEEL. An average of 15,624 ft3 (442 m3) of air was sampled at each location, each week, at an average flow rate of 1.6 ft3/min (0.045 m3/min). Particulates in air were collected on glass fiber 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. More information concerning gross alpha and beta radioactivity can be found in Gross versus Specific Analyses under Helpful Information.
The weekly particulate filters collected during the quarter for each location were composited and analyzed for gamma-emitting radionuclides. Composites were also analyzed by location for 90Sr, or 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 INEEL, Boundary, and Distant locations for the second quarter of 2004 are shown in Figure 3. The data were tested for normality prior to statistical analyses. The data showed 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. Note that outliers and extreme values are identified separately from the box and whiskers. Outliers (open red circles) and extreme values (open red triangles) 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 second 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 and extreme values lie within the range of measurements made within the past five years. Thus, rather than dismissing the outliers, they were included in the subsequent statistical analyses. Further discussion of box plots may be found in Determining Statistical Differences under Helpful Information.
Figure 3 graphically shows that the gross alpha measurements made at INEEL, Boundary, and Distant locations are similar for the second quarter. If the INEEL were a significant source of offsite contamination, concentrations of contaminants could be statistically greater at Boundary locations than at Distant locations. 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 INEEL, 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. There were no statistical differences in gross alpha concentrations between location groups during the second quarter 2004.
Comparisons of gross alpha concentrations were made for each month of the quarter (Figure 4, Figure 5, and Figure 6). Again the Kruskal-Wallis test of multiple independent groups was used to determine if statistical differences exist between INEEL, Boundary, and Distant data groups.
There were no statistical differences in gross alpha results between groups for any month during the second 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. INEEL sample results were not included in this analysis because the onsite data, collected at only three locations, are not representative of the entire INEEL and would not aid in determining offsite impacts. The gross alpha concentrations measured at Boundary locations were not statistically greater than those measured at Distant locations in any of the thirteen weeks of data evaluated (Table D-2). More detail on the statistical tests used can be found in Determining Statistical Differences under Helpful Information.
Gross beta results are presented in Table C-1. Gross beta concentrations in air for INEEL, Boundary, and Distant locations for the second quarter of 2004 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. As in the case of alpha activity, 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).
Monthly median gross beta concentrations in air for each sampling group are shown in Figure 8, Figure 9 and Figure 10. Statistical data are presented in Table D-1. Again as in the case of alpha activity, the monthly data for each group during the second quarter 2004 appear to be similar and were determined using the Kruskal-Wallace test to be statistically the same (Table D-1). Comparison of weekly Boundary and Distant data sets, using the Mann Whitney U test, also showed no statistical difference between Boundary and Distant measurements.
No 131I was detected in any of the charcoal cartridge batches collected during the second quarter of 2004. 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 in 43 of the 235 measured cartridges.
Weekly filters for the second quarter of 2004 were composited by location. All samples were analyzed for gamma-emitting radionuclides, including 137Cs. Composites were also analyzed for 90Sr, 238Pu, 239/240Pu, and 241Am. Only 241Am (two samples) and 239/240Pu (one sample) were detected in any quarterly composited sample. Americium-241 was detected in the composite samples from FAA Tower and the Rexburg CMS. Plutonium-239/240 was also detected in the Rexburg CMS sample. It is not uncommon to detect these compounds, especially at the CMS stations as agricultural activities in the area resuspend particles associated with historic above ground weapons testing. The maximum concentration of 241Am was from FAA Tower of (5.63 ± 1.70) x 10-18 μCi/mL ([2.08 ± 0.63] x 10-13 Bq/mL) is below the DOE DCG for 241Am of 2 x 10-14 μCi/mL (7.4 x 10-10 Bq/mL). The 239/240Pu concentration of (2.12 ± 0.38) x 10-17 μCi/mL ([7.84 ± 1.41] x 10-13 Bq/mL) was also below the DCG value of 2 x 10-14 μCi/mL (7.4 x 10-10 Bq/mL). All results for composite filter samples are shown in Table C 3, Appendix C.
Atmospheric moisture is collected by pulling air through a column of absorbent material (i.e., silica gel or 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. Sixteen atmospheric moisture samples were obtained during the second quarter of 2004 from Atomic City, Blackfoot CMS, Idaho Falls, and Rexburg CMS.
Four samples exceeded the 3s uncertainty level for tritium (one silica gel and three molecular sieve). Samples from the Blackfoot CMS, Idaho Falls and the Rexburg CMS were all collected around mid May. Another sample from Idaho Falls was collected at the beginning of April. The maximum concentration of (6.7 ± 1.8) x 10-13 mCi/mLair ([2.48 ± 0.67] x 10-9 Bq/mL) from Idaho Falls in May is well below the DOE DCG for tritium in air of 1 x 10-7 mCi/mL (3.7 x 10-3 Bq/mL). All three results from May were within the same range. All results are shown in Table C-4.
The EPA began using a standard for concentrations of airborne particulate matter (PM) less than 10 micrometers in diameter (PM10) in 1987 (40 CFR 50.6 [CFR 1996]). Particles of this size can be inhaled deep into the lungs and are considered to be responsible for most of the adverse health effects associated with airborne particulate pollution. The air quality standards for these particulates are an annual average of 50 µg/m3, with a maximum 24-hour concentration of 150 µg/m3.
The ESER Program operates three PM10 particulate samplers, one each at the Rexburg CMS and Blackfoot CMS, and one in Atomic City. Sampling of PM10 is informational only as no chemical analyses are conducted for contaminants. A twenty-four hour sampling period is scheduled to run once every six days. The maximum 24-hour particulate concentration was 45.98 µg/m3 on May 8, 2004, at the Rexburg CMS. The average, maximum, and minimum results of the 24-hour samples are shown are shown in Table 1. Results for all PM10 samples are listed in Table C-5, Appendix C.
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|
Concentrationa |
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Location |
Minimum |
Maximum |
Average |
|
Atomic City |
0.00 |
26.54 |
13.05 |
|
Blackfoot, CMS |
1.47 |
39.32 |
17.58 |
|
Rexburg, CMS |
6.69 |
45.98 |
|
|
a. All concentrations are in (μCi/m3). |
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