Radioactivity associated with airborne particulates was monitored continuously by 18 ESER Program air samplers at 16 locations during the fourth quarter of 2001 (Figure 1).  Three of these samplers were located on the INEEL, nine were located off the INEEL near the boundary, and six were 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.  One replicate sampler was placed at an Arco (Boundary location) and one at Howe (Boundary location) during 2001.  An average of 13,168 ft³ (373 m³) of air was sampled at each location, each week, at an average flow rate of 1.3 ft³/min (0.04 m³/min).  Particulates in air were collected on filters (1.2-µm pore size), while gases were pulled through activated charcoal cartridges. 

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.   

Low-volume air sampler locations.

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 Idaho Nuclear Technology and Engineering Center (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 using the Mann-Whitney U test.  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 discussed previously.

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 gross beta concentrations in air at Distant locations.

A summary of approximate minimum detectable concentrations (MDCs) 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.

Initial laboratory analysis of one batch containing ten charcoal cartridges collected on 12/5/01 detected ¹³¹I greater than the associated 2s and MDC values.  Immediate reanalysis of each individual cartridge yielded results below both the MDC and 2s values.  Because initial counting is done as a batch sample it appears that the cumulative activity for these ten cartridges was above the 2s/MDC value, but was not attributable to any single location (cartridge).  Weekly ¹³¹I results for each location, including individual recount data, are listed in Table C-2 of Appendix C.

Weekly filters for the fourth quarter of 2001 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.  Five samples collected from air monitoring stations (Arco, Blackfoot CMS, Blue Dome, Howe Q/A-2, and Van Buren) showed at least one human-made radionuclide greater than its related 2s value (Figure 10).  All results were far less than their respective DCGs.  In addition, ²⁴¹Am was detected in one blank sample.  Because blank samples should have no detectable radioactivity and the result was between 2-3s, the result is questionable and most likely not valid.  All results for composite filter samples are shown in Table C-3, Appendix C.