Radioactivity associated with airborne particulates was monitored continuously by 18 ESER Program air samplers at 16 locations during the third quarter of 2001 (Figure 1).  Three of these samplers are located on the INEEL, seven are located off the INEEL near the boundary, and six are at locations distant the INEEL.  These locations allow samplers to be divided into INEEL, Boundary and Distant groups to determine if there is a gradient of radionuclide

FIGURE 1. Continuous air sampling locations.

Filters and charcoal cartridges were changed weekly at each station during the quarter.  Each filter was screened 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.  See the Gross versus Specific Analyses portion of the Helpful Information section of this report for more information concerning gross alpha and beta radioactivity.   Charcoal cartridges were analyzed for gamma-emitting radionuclides, specifically ¹³¹I.   Iodine-131 is of great 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 any ¹³¹I that is detected would be from a recent release of fission products.  Finally, the 13 weekly filters for each location collected during the quarter are composited and analyzed for gamma-emitting radionuclides.  Composites are also analyzed by location for strontium-90 (⁹⁰Sr), or plutonium-238 (²³⁸Pu), plutonium-239/240 (^239/240Pu), and americium-241 (²⁴¹Am) as determined by a schedule that rotates quarterly.   

Weekly gross alpha concentrations in air for INEEL, Boundary, and Distant locations are shown in Figure 2. The data were tested for normality prior to statistical analyses and were not found to be normally or lognormally distributed.  Box and whiskers plots are commonly used when there is no assumed distribution. Each data group is presented as a box and whiskers plot, with a median, a box representing 25^th and 75^th percentiles, and whiskers representing the minimum and maximum values. Note that outliers and extreme values are plotted separately from the box and whiskers. Outliers and extreme values are atypical, infrequent observations; data points which are far from the middle of the distribution of data. Outliers are defined mathematically as values that are equal to 1.5 times the height of the box, above or below the box. Extreme values are equal to 2 times the height of the box, above or below the box. Outliers and extreme values may reflect inherent variability, or may be due to errors associated with transcription or measurement or other anomalies. A careful review of the data 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 the Determining Statistical Differences portion of the Helpful Information.

The graphs in Figure 2 visually show that the gross alpha measurements made at INEEL, Boundary, and Distant locations are similar and tend to demonstrate comparable patterns over time (i.e., increases or decreases in one set of data are tracked by increases or decreases in the other two sets of data).  There do not appear to be any differences in the data sets. This hypothesis was tested statistically.

If the INEEL were a significant source of offsite contamination, concentrations of contaminants would be statistically greater at Boundary locations than at Distant locations. Because the data were determined not to be normally or lognormally distributed, nonparametric (distribution-free) tests of significance were used to compare data collected at Boundary with data collected at Distant locations. The use of nonparametric tests gives less weight to outliers and extreme values thus allowing a more appropriate comparison of data groups.  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 would not aid in determining offsite impacts.  The INEEL air monitoring stations were established in the past primarily to assess concentrations in the predominant wind directions downwind from the INTEC facility. At that time the INTEC facility was the primary source of radionuclide releases at the INEEL. This is no longer the case, since radionuclide releases are now more evenly distributed between the major facilities. As such, the three onsite locations do not adequately represent the near field impact of facility releases.

The comparisons between Boundary and Distant locations were made on a weekly basis. 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.  See the Determining Statistical Differences portion of the Helpful Information for more detail on the statistical tests used.

Weekly median gross beta concentrations in air for INEEL, Boundary, and Distant locations are shown in Figure 3. Box and whiskers plots were used because the data are not normally or lognormally distributed. 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 data for each group appear to be similar and to track each other over time. Comparison of weekly Boundary and Distant data sets, using the Mann Whitney U test, indicates no differences between the two location groups. The INEEL data were not included in the analysis for the reasons presented in the previous discussion on gross alpha measurements. 

Monthly median gross alpha and beta concentrations in air at each sampling location are shown in Figures 4 – 9.  The graphs show similar results between locations and over time.

• Figure 4. Monthly median gross alpha concentrations in air at INEEL locations.
• Figure 5. Monthly median gross alpha concentrations in air at Boundary locations.
• Figure 6. Monthly median gross alpha concentrations in air at Distant locations,
• Figure 7. Monthly median gross beta concentrations in air at INEEL locations.
• Figure 8. Monthly median gross beta concentrations in air at Boundary locations.
• Figure 9. Monthly median beta gross beta concentrations in air at Distant locations.

A summary of approximate minimum detectable concentrations (MDC) for radiological analyses and DOE Derived Concentration Guide (DCG) values is provided in Appendix B, while gross alpha and beta results for individual filters are listed in Table C-1 of Appendix C.

No ¹³¹I was detected in any of the weekly charcoal cartridges during the third quarter.   Weekly ¹³¹I results for each location are listed in Table C-2 of Appendix C.  

Weekly filters for the third quarter of 2001 were composited by location.  All samples were analyzed for gamma emitting radionuclides including ¹³⁷Cs.  Composites are also analyzed by location for ⁹⁰Sr, or ²³⁸Pu, ^239/240Pu, and ²⁴¹Am as determined by a schedule that rotates quarterly.  Cesium-137 was not detected in any of the third quarter composite samples.  Several human-made radionuclides were detected including ⁹⁰Sr, ²³⁸Pu, ^239/240Pu, and ²⁴¹Am.  

Strontium-90 was detected in the Mud Lake, Atomic City, Arco, Dubois, and Arco Q/A-1 samples.  Plutonium-238 was detected in all of the locations except Idaho Falls, EFS, and Howe Q/A-2.  Plutonium-239/240 was detected in only the Idaho Falls, Howe, and FAA Tower locations.  Americium-241 was detected only in the EFS sample.  Samples with detected radionuclides are shown in Figure 10.

Levels of ⁹⁰Sr were significantly lower than the associated DCG value.  Levels of ^239/240Pu were much lower than the associated DCG value.  Levels of ²³⁸Pu were well below the associated DCG value.  The level of ²⁴¹Am detected was many times lower than its associated DCG value. 

Strontium-90, ²³⁸Pu, ^239/240Pu, and ²⁴¹Am were deposited around the world from atmospheric nuclear weapons testing, so the measurements of these radionuclides do not necessarily indicate releases from the INEEL.  Concentrations are within the range of values reported in past quarterly reports (Table B-1), and within the range of values reported throughout the world (EPA, 2002).  Results for all composite filter samples are shown in Table C-3 of Appendix C.

Back