First Quarter 2005
INL Quarterly Site Environmental Report
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The primary pathway by which radionuclides can move off the INL is through the air and for this reason the air pathway is the primary focus of monitoring on and around the INL. 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 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 first quarter, 2005 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 first quarter of 2005 (Figure 2). Four of these samplers are located on the INL, eight are situated off the INL near the boundary, and six have been placed at locations distant to the INL. Samplers are divided into INL, Boundary, and Distant groups to determine if there is a gradient of radionuclide concentrations, increasing towards the INL. Each replicate sampler is relocated every year to a new location. One replicate sampler was placed at Howe (Boundary location) and one at the INL Main Gate (onsite location) during 2005. An average of 14,643 ft3 (415 m3) of air was sampled at each location, each week, at an average flow rate of 1.45 ft3/min (0.04 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 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, Boundary, and Distant locations for the first quarter of 2005 are shown in Figure 3. The data were tested for normality prior to statistical analyses. For the most part the data showed no 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, 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 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 first quarter indicates that the outliers and extreme values were not due to mistakes in collection, analysis, or reporting procedures, but rather reflect natural variability in the measurements. The outliers 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 INL, Boundary, and Distant locations are similar for the first quarter. If the INL were a significant source of offsite contamination, concentrations of contaminants should 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 INL, Boundary, and Distant locations. The use of nonparametric tests, such as Kruskal-Wallis, gives less weight to outliers 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 groups for the first quarter.
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 INL, Boundary, and Distant data groups. There were no statistical differences in gross alpha between groups for February or March (Table D-1). However, there was a statistical difference between groups for January. The major difference exists between the INL group results (median = 1.56 × 10-15 mCi/mL) and the Boundary group results (median = 0.89 × 10-15 mCi/mL). It is suspected that the result is a function of statistical variability in the results and small sample size for the INL (three locations) and does not implicate any INL release during January.
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 sample results were not included in this analysis because the onsite data, collected at only three locations, are not representative of the entire INL and would not aid in determining offsite impacts. Gross alpha concentrations measured at Distant locations were not statistically greater than those measured at Boundary locations for any week of the quarter (Table D-2). . Analysis for each week by Boundary location group and Distant location group showed no statistical difference between stations. In other words, no one or group of stations appeared to be significantly higher or lower than the other stations. Thus, it is interpreted that the statistical difference is a result of natural variability More detail on the statistical tests used can be found in Determining Statistical Differences under Helpful Information.
Gross beta results are also presented in Table C-1. Gross beta concentrations in air for INL, Boundary, and Distant locations for the first quarter of 2005 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. There were no statistical differences in gross beta between groups for any month during the quarter (Table D-1).
Comparison of weekly Boundary and Distant data sets, using the Mann Whitney U test, indicates no statistical differences between the two location groups during the first quarter (Table D-2).
No 131I was measured above the 3s value in any of the charcoal cartridge batches during the quarter. Weekly 131I results for each location are listed in Table C-2 of Appendix C.
Weekly filters for the first quarter of 2005 were composited by location and analyzed for gamma-emitting radionuclides, including cesium-137 (137Cs). Selected composites were also analyzed for 90Sr, 238Pu, 239/240Pu, and 241Am. The concentrations measured during this quarter are consistent with those recorded in the past. All results were far less than their respective DCGs. None of the radionuclides were detected above the associated 3s uncertainty values. All results for composite filter samples are shown in Table C-3, Appendix C.
Eighteen atmospheric moisture samples were collected using molecular sieve and silica gel material during the first quarter of 2005. Samples were grouped as follows: five each from Atomic City, Idaho Falls, and Blackfoot, and three from Rexburg. Atmospheric moisture is collected by pulling air through a column of absorbent material (i.e., molecular sieve or silica gel) 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.
Four of the samples exceeded their respective 3s values (one each from Blackfoot and Rexburg, and two from Atomic City). All sample results were well below the DOE DCG for tritium in air of 1 x 10-7 mCi/mL (3.7 x 10-3 Bq/mL). The maximum value was (6.44 ± 0.95) x 10-13 mCi/mL of air ([23.82 ± 3.51] x 10-9 Bq/mL of air). All results for atmospheric moisture samples are shown in Table C-4, Appendix C.
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, 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 samplers, one each at the
Rexburg CMS and Blackfoot CMS, and 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.
Equipment problems nullified one sample from the Atomic City location on
February 2, 2005. In addition, the result collected from Atomic City on January
5 was not used as it represented a 2-week sample. The maximum 24-hour
concentration was 33.11 µg/m3 on February 26, 2005, at Rexburg. The
minimum, maximum, and average results of the 24-hour samples are summarized in
Table 1. None of the results exceeds the maximum 24-hour air quality standard
established by EPA of 150 µg/m3. Results for all PM10 samples are
listed in Table C-5, Appendix C.
Table 1. Summary of 24-hour PM10 values.
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|
Concentrationa |
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|
Location |
Minimum |
Maximum |
Average |
|
Atomic City |
0.14 |
10.12 |
3.79 |
|
Blackfoot, CMS |
0.27 |
25.39 |
12.32 |
|
Rexburg, CMS |
0.00 |
33.11 |
15.46 |
|
a. All concentrations are in (mg/m3). |
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