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 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 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 third quarter, 2003 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 fourth quarter of 2003 (Figure 2). Three of these samplers are located on the INEEL, eight (7 samplers plus a replicate) are situated off the INEEL near the boundary, and seven (6 samplers plus a replicate) have been placed at locations distant to the INEEL. Samplers are divided into INEEL, Boundary, and Distant groups for statistical purposes 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 16,145 ft3 (457 m3) of air was sampled at each location, each week, at an average flow rate of approximately 1.6 ft3/min (0.05 m3/min). Particulates in air were collected on glass fiber particulate filters with a 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.
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 must 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 fourth 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 (the 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 (open red circles) are defined as values that are greater than 1.5 times the height of the box, above or below the box. Extreme values (open red triangles) 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 fourth 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. 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 fourth quarter. If the INEEL was 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, allows for the inclusion of outliers and extreme values bit gives them less weight, 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. A p-value of 1.00 indicates the values are identical. 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 fourth 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) during the quarter.
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 standard 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 statistically greater than those measured at Distant locations only for the week ending December 3, 2003 (Table D-2). Evaluation by station for the week in question showed that the concentrations from Jackson, Rexburg, and Craters of the Moon appeared to be much lower than the other stations. All these sites are in close proximity to the surrounding mountain ranges and may not have been affected as much by atmospheric conditions out on the Snake River Plain. 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 fourth 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 November 12, and December 3 and 10, 2003 (Table D-2). The Boundary group was statistically greater than the Distant group in each case. Throughout the quarter the Boundary group stations tended to track higher than the Distant group. Evaluation for each week by station revealed a wide scatter for each station and no clear pattern in the difference for the weeks of November 12 or December 3. The week of December 10 revealed the western Boundary stations (Arco, Atomic City and Blue Dome) were unusually low compared to other stations.
All results were well within historical measurements made at the INEEL for all locations. 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 fourth 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. Americium-241 was detected above the 3s uncertainty value at the Blackfoot Community Monitoring Station (CMS). The concentration was (8.5 ± 1.5) x 10-18 mCi/mL ([3.2 ± 0.6] x 10-13 Bq/mL). Occasional detection of human-made radionuclides is not unusual and represents natural variations in concentrations of radionuclides introduced into the environment by historical nuclear weapons testing. The 241Am concentration measured during this quarter was consistent with those recorded in the past and far less than its DCG value of 2 x 10-14 mCI/mL. All results for composite filter samples are shown in Table C-3, Appendix C.
Twenty six atmospheric moisture samples were obtained during the fourth quarter of 2003: one sample from Blackfoot, six samples from Rexburg, six samples and a duplicate sample from Idaho Falls, and twelve samples from Atomic City. Atmospheric moisture is collected by pulling air through a column of absorbent material (i.e., silica gel or molecular sieve) 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 samples were detected above their 3s values. Two samples came from Idaho Falls, and one each from Atomic City and Rexburg. Concentrations ranged from (3.4 ± 1.1) x 10-13 mCi/mL of air (1.3 ± 0.4) x 10-8 Bq/mL) at Idaho Falls to (6.8 ± 2.1) x 10-13 mCi/mL of air (2.5 ± 0.8) x 10-8 Bq/mL) at Atomic City. All were silica gel absorbent, but there was no common date. All seven sample results were well below the DOE DCG for tritium in air of 1 x 10-7 mCi/mL. All results are shown on Table C-4 of 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. All measurements were acceptable during the quarter. The maximum 24-hour concentration was 173.7 µg/m3 on October 23, 2003, at Blackfoot. The average, maximum, and minimum results of the 24-hour samples are summarized in Table 1. One sample each from Rexburg and Blackfoot exceeded the maximum 24 hour air quality standard established by EPA. Since both exceedances were on the same date it is likely the high particulate load is related to agricultural activities (e.g., potato harvest) in the areas of the samplers. Results for all PM10 samples are listed in Table C-5, Appendix C.
|
|
Concentrationa |
||
|
Location |
Minimum |
Maximum |
Average |
|
Atomic City |
1.3 |
50.5 |
11.3 |
|
Blackfoot, CMS |
2.5 |
173.7 |
21.8 |
|
Rexburg, CMS |
1.2 |
153.9 |
22.6 |
|
a. All concentrations are in (γg/m3). |
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