The primary pathway by which radionuclides can move off the INL Site is through the air and for this reason the air pathway is the primary focus of monitoring on and around the INL Site.  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 Site 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 fourth quarter of 2006 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.

Low-Volume Air Sampling

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 2006 (Figure 2).  Four of these samplers are located on the INL Site, eight are situated off the INL Site near the boundary and six have been placed at locations distant to the INL Site.  Samplers are divided into INL Site, Boundary and Distant groups to determine if there is a gradient of radionuclide concentrations, increasing towards the INL Site.  Each replicate sampler is relocated every year to a new location.  One replicate sampler was placed at Mud Lake (a Boundary location) and one at the Experimental Field Station (an INL Site location) during 2006.  An average of 16,148 ft³ (457 m³) of air was sampled at each location, each week, at an average flow rate of 1.60 ft³/min (0.05 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 Site, Boundary, and Distant locations for the fourth quarter of 2006 are shown in Figure 3. Gross alpha data are tested for normality prior to statistical analyses, and generally show 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 25^th and 75^th 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 fourth 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 values lie within the range of measurements made within the past several 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 Site, Boundary and Distant locations are similar for the fourth quarter.  If the INL Site 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 Site, 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 was no statistical difference in gross alpha concentrations between location groups during the fourth quarter of 2006. 

Comparisons of gross alpha concentrations were made for each month of the quarter (Figures 4 – 6).  Again the Kruskal-Wallis test of multiple independent groups was used to determine if statistical differences exist between INL Site, Boundary and Distant data groups.

Figure 3.    Gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations for the fourth quarter of 2006.

 

Figure 4.    October gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations.  Number of samples (N) = 4 at each location. 

Figure 5. November gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations.  Number of samples (N) = 5 at each location, except at Craters, where N = 4.

Figure 6.  December gross alpha concentrations in air at ESER INL Site, Boundary and Distant locations.  Number of samples (N) = 4 at each location.

There were no statistical differences in gross alpha concentrations between Distant and Boundary locations during any month of the fourth 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 Site sample results were not included in this analysis because the onsite data, collected at only three locations, are not representative of the entire INL Site and would not aid in determining offsite impacts.  In the fourth quarter, there was one week (November 29) where a statistical difference existed between the two sample groups (Table D-2).  In this week, the gross alpha concentrations measured at Distant locations were statistically greater than those measured at Boundary locations, not indicative of an impact from the INL Site. 

Gross beta results are presented in Table C-1.  Gross beta concentrations in air for INL Site, Boundary and Distant locations for the fourth quarter of 2006 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.  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).

Figure 7.      Gross beta concentrations in air at ESER INL Site, Boundary and Distant locations for the fourth quarter 2006.

 

Monthly median gross beta concentrations in air for each sampling group are shown in Figures 8 – 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 gross beta data sets, using the Mann Whitney U test, showed statistical differences between Boundary and Distant measurements during two weeks of the fourth quarter (Table D-2).  In one of these cases, the week of November 8, the Boundary group was statistically greater than the Distant group. Examination of the data for this week indicates lower concentrations in some of the eastern valley locations (Idaho Falls, Jackson, and Rexburg) than some of the sampling locations in the northern part of the sampling area (e.g. Howe and Mud Lake).  No particular distribution was seen in the data to indicate an INL Site-related cause, and it is more likely due to random variability in the data. In the second case, the week of November 29, the Distant group was statistically higher than the Boundary group.

No ¹³¹I was detected in any of the charcoal cartridge batches collected during the fourth quarter of 2006.  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 two of the 26 measured batches of cartridges.  The analytical laboratory considers these detections a result of the materials used in the charcoal filters.

Weekly filters for the fourth quarter of 2006 were composited by location.  All samples were analyzed for gamma-emitting radionuclides, including ¹³⁷Cs (see Table C‑3, Appendix C.).  Cesium-137 was detected in one composite from Arco near the detection limit.  A recount did not find detectable ¹³⁷Cs.

Composites were also analyzed for ⁹⁰Sr, ²³⁸Pu, ^239/240Pu and ²⁴¹Am.  None of these radionuclides were detected during the fourth quarter.

Atmospheric Moisture Sampling

Fourteen atmospheric moisture samples were obtained during the fourth quarter of 2006 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. 

Eight samples exceeded the 3s uncertainty level for tritium—two from each sampling location.  All samples with detectable tritium were significantly below the DOE DCG for tritium in air of 1 ´ 10^-7 mCi/mL, ranging from (3.9 ± 1.2) x 10^-13 mCi/mL_air at Blackfoot in November/December to (14.2 ± 1.3) x 10^-13 mCi/mL_air, at Rexburg in October/November.  All results are shown in Table C-4, Appendix C.

PM₁₀ Air Sampling

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 2006]).  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 30.9 µg/m³ on October 13, 2006, at Rexburg.  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	0.0	22.4	3.5
Blackfoot, CMS	0.8	20.6	6.9
Rexburg, CMS	0.0	30.9	19.7
a.   All concentrations are in (μg/m3).