Third 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 third 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 third 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 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. 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, Boundary, and Distant locations for the third quarter of 2005 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 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 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.
Figure 3 graphically shows that the gross alpha measurements made at INL, Boundary, and Distant locations are similar for the third quarter. If the INL 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 INL, 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 third quarter 2005.
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 results between groups for any month during the third 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 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. 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).
Gross beta results are presented in
Table C-1.
Gross beta concentrations in air for INL, Boundary, and Distant locations for
the third 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, only showed a statistical difference between Boundary and Distant measurements during the week of August 10 (Table D-2). During this week, the Distant locations were statistically higher than the Boundary locations. Because the Distant locations were higher, an INL-related cause for the statistical difference is not indicated and it is more likely due to random variability in the data.
No 131I was detected in any of the charcoal cartridge batches collected during the third quarter of 2005. 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 36 of the 234 measured cartridges.
Weekly filters for the third quarter of 2005 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. All results for composite filter samples are shown in Table C 3, Appendix C.
No manmade gamma-emitting radionuclides or isotopes of plutonium were detected. Two composites, Arco and Atomic City, had 90Sr concentrations that were above the 3s level but below the laboratory’s minimum detectable concentration.
The composite from Van Buren Gate had a detectable concentration of 241Am at (8.52 ± 0.59) x 10-17 mCi/mL. Americium-241 has consistently been detected in the past at both onsite and offsite locations, but the concentration measured this quarter is outside the range normally detected. The origin of this radionuclide on the filter is unknown at this time. Windblown soil from the nearby Radioactive Waste Management Complex is unlikely since this soil also contains plutonium isotopes, and the amount of dust measured on the filter is too light. Laboratory contamination is not indicated by either the field blank or laboratory blank. Further investigation is needed to identify a possible cause. The detected value is 0.43 percent of the DOE Derived Concentration Guide for 241Am.
Twenty-two atmospheric moisture samples were obtained during the third quarter of 2005 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.
Three samples exceeded the 3s uncertainty level for tritium—two from
Blackfoot and one from Rexburg. All samples with detectable tritium were well
below the DOE DCG for tritium in air of 1 x 10-7 mCi/mL (3.7 x 10-3
Bq/mL), ranging from (5.8 ± 1.2) x 10-13 mCi/mLair
([21.3 ± 4.6] x 10-9 Bq/mL) at Blackfoot in August to (7.6 ± 2.0) x
10-13 mCi/mLair
([28.1 ± 7.3] x 10-9 Bq/mL), also in Blackfoot. All results 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 [CFR 2005]). 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 52.47 µg/m3
on August 7, 2005, at Atomic City. 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.
Table 1. Summary of 24-hour PM10 values.
|
|
Concentrationa |
||
|
Location |
Minimum |
Maximum |
Average |
|
Atomic City |
10.38 |
52.47 |
20.90 |
|
Blackfoot, CMS |
4.81 |
42.42 |
24.08 |
|
Rexburg, CMS |
3.89 |
44.84 |
24.16 |
|
a. All concentrations are in (μg/m3). |
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