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 first quarter, 2003 are discussed below. A summary of approximate minimum detectable concentrations (MDCs) for radiological analyses and DOE Derived Concentration Guide (DCG) values (DOE 1993) 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 2003 (Figure 2). Three of these samplers are located on the INEEL, nine (7 samplers plus two replicates) are situated off the INEEL near the boundary, and six have been placed at locations distant to the INEEL. Samplers are divided into INEEL, Boundary, and Distant groups to determine if there is a gradient of radionuclide concentrations, increasing towards the INEEL. Each replicate sampler is relocated every year to a new location. One replicate sampler was placed at Blackfoot (Distant location) and one at Mud Lake (Boundary location) during 2003. An average volume of 16,877 ft3 (478 m3) of air was sampled at each location, each week, at an average flow rate of approximately1.3 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.
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 first quarter of 2003 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 value, 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 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 outlier values shown in Figure 3 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 first quarter. If the INEEL
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 INEEL, 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
). 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 between groups for
any month (Table D-1).
As a further 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 Distant locations were statistically greater than those measured at Boundary locations for only the week ending April 2, 2003 (Table D-2). ). In general, this appeared to be a function of filter loading (i.e., there tended to be higher concentrations of particulate matter on filters collected at distant locations). 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 Boundary, Distant, and INEEL locations for the first quarter of 2003 are shown in Figure 7 . The data showed no discernable distribution. 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 (Figure 7 and 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 was no statistical difference, using the Kruskal-Wallace test, between monthly median gross beta concentrations of the different groups for any month during the quarter.
Comparison of weekly Boundary and Distant data sets, using the Mann Whitney U test, indicated a statistical difference between the two location groups for the weeks ending January 22, and February 12, 2003 (Table D-2). The Boundary group was statistically greater than the Distant group for both weeks. The results were all well within historical measurements made at the INEEL for all locations. They are also within recent historical measurements made by EPA in EPA Region 10 (Alaska, Idaho, Oregon, and Washington). The EPA’s ERAMS program collects air samples from across the United States. From 1996 through 2002, tritium measured in Region 10 samples ranged from (0.06 ± .01) x 10-14 to (10.7 ± .08) x 10-14 pCi/mL (from [0.2 ± 0.7] x10-10 to [39.6 ± 2.8] x 10-10 Bq/mL) (EPA 2004). The INEEL results thus do not implicate any release from the INEEL.
Iodine-131 was not detected (at a level greater than the associated 3s value) in any batch of charcoal cartridges. Each batch contained eight charcoal cartridges. Weekly 131I results for each location are listed in Table C-2 of Appendix C.
Weekly filters for the first quarter of 2003 were composited by location and analyzed for gamma-emitting radionuclides, including 137Cs. Composites were also analyzed for 90Sr, 238Pu, 239/240Pu, and 241Am. Plutonium-239/240 was detected in one of the quarterly composites, at a concentration of (8.3 ± 1.8) x 10-18 µCi/mL ([ 3.1 ± 0.7] x 10-13 Bq/mL) collected at Rexburg CMS. Strontium-90, cesium-137, and 238Pu were not detected in any sample. Occasional detection of human-made radionuclides is not unusual and represents natural variations in concentrations of radionuclides introduced by historical nuclear weapons testing. The 239/240 Pu concentration measured during this quarter is consistent with those recorded in the past and is far less than the DCG (2 x 10-14 µCI/mL). All results for composite filter samples are shown in Table C-3, Appendix C.
Seven atmospheric moisture samples and three duplicate samples were obtained during the first quarter of 2003: two samples and two duplicate samples from Blackfoot, two samples and a duplicate sample from Idaho Falls, two samples from Rexburg, and one sample from Atomic City. Atmospheric moisture is collected by pulling air through a column of absorbent material (i.e., 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
Two samples, one collected at Idaho Falls in January and one collected at Rexburg in March, exceeded their respective 3s values. All seven sample results were well below the DOE DCG for tritium in air of 1 x 10-7 µCi/mL (3.7 x 10-3 Bq/mL). The maximum value (collected at Rexburg in March) was (5.5 ± 1.6) x 10-13 µCi/mL of air ([2.1 ± 0.6] x 10-8 Bq/mL of air). 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 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. Measurement problems nullified only two of samples from Atomic City during the quarter. The maximum 24-hour concentration was 37.9 µg/m3 on January 8, 2003, at Rexburg. The average, maximum, and minimum 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. Results for all PM10 samples are listed in Table C-5, Appendix C.
|
|
Concentrationa |
||
|
Location |
Minimum |
Maximum |
Average |
|
Atomic City |
0.0b |
6.9 |
1.7 |
|
Blackfoot, CMS |
1.3 |
13.1 |
5.6 |
|
Rexburg, CMS |
0.4 |
37.9 |
10.8 |
|
a. All concentrations are in (µg/m3). b. Result less than 0. |
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