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Air Sampling

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.

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 third quarter of 2003 (Figure 1). Three of these samplers are located on the INEEL, nine 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 the Blackfoot Community Monitoring Station (CMS) (Distant location) and one at Mud Lake (Boundary location) during 2003. An average of 14,412 ft³ (408 m³) of air was sampled at each location, each week, at an average flow rate of 1.44 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.

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. 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 third 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, a box enclosing values between the 25th and 75th percentiles, and whiskers representing the non-outlier range. Note that 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 third quarter indicates that the outliers and extreme values were not due to mistakes in collection, analysis, or reporting procedures, but 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  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 third 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 third quarter.

Comparisons of gross alpha concentrations were made for each month of the quarter (Figure 4, Figure 5, and Figure 6). Again 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 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. 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 different than those measured at Distant locations for the week of September 10, 2003 (Table D-2). Additional analysis of results for that week showed no statistical difference between Boundary locations or between Distant locations. Review of the box and whisker plot reveals that the Distant location group is higher than the Boundary location group. For this reason it is believed that the values reflect natural variability and not a potential release from the INEEL. More detail on the statistical tests used can be found in Determining Statistical Differences under Helpful Information.

Gross beta results are also presented in Table C-1. Gross beta concentrations in air for INEEL, Boundary, and Distant locations for the third quarter of 2003 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. 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 (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 were no statistical differences in gross beta between groups for any month during the quarter (Table D-1).

Comparison of weekly Boundary and Distant data sets, using the Mann Whitney U test, indicates a difference between the two location groups for the weeks of July 16 and September 17, 2003 (Table D-2). As with gross alpha the Distant group was statistically greater than the Boundary group for the week of July 16. Analysis for that week showed a statistical difference between stations of the Boundary location group. Review showed the Mud Lake average was significantly less than the remaining stations. As no specific cause could be ascertained for this, it is attributed to natural variability. The week of September 17 showed the Boundary location group to be higher than the Distant location group. No statistical difference was found between stations of either the Boundary or Distant location groups. Thus, this also is interpreted as natural variability.

No ¹³¹I was measured above the 3s value in any of the charcoal cartridge batches during the quarter. Two ten-cartridge batches had questionably detected ¹³¹I. However, recounts of individual cartridges showed no evidence of ¹³¹I in the weekly samples. Weekly ¹³¹I results for each location are listed in Table C-2 of Appendix C.

Weekly filters for the third quarter of 2003 were composited by location and analyzed for gamma-emitting radionuclides, including cesium-137 (¹³⁷Cs). Selected composites were also analyzed for ⁹⁰Sr, ²³⁸Pu, ^239/240Pu, and ²⁴¹Am.

Plutonium-238 was detected in one of the quarterly composites, at a concentration of (9.1 ± 2.8) x 10^-18 Ci/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 CI/mL). variations in concentrations of radionuclides introduced by historical nuclear weapons testing. The concentrations measured during this quarter are consistent with those recorded in the past. All results were far less than their respective DCGs. Only the Howe composite had ²³⁸Pu measured above the 3s value. Figure 11 shows the ²⁴¹Am and ²³⁸Pu, composite results that were greater than their 3s values. A large ^239/240Pu result was measured in the Howe composite. Further investigation of this result revealed that it was close to the value of the QA spiked sample, and likely represents laboratory contamination rather than an actual detection. Figure 12 shows the same for the ⁹⁰Sr results. All results for composite filter samples are shown in Table C-3, Appendix C.

ATMOSPHERIC MOISTURE SAMPLING

Twenty-four atmospheric moisture samples were collected using silica gel and nine samples using molecular sieve material during the third quarter of 2003. Samples were divided as follows: twenty four samples from Atomic City, and nine samples from Idaho Falls. Atmospheric moisture is collected by pulling air through a column of absorbent material (i.e., silica gel or molecular seive) 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.

Eleven of the samples exceeded their respective 3s values (seven from Atomic City, four from Idaho Falls). All sample results were well below the DOE DCG for tritium in air of 1  10^-7 Ci/mL (3.7  10^-3 Bq/mL). The maximum value was (4.91 ± 0.51)  10^-12 Ci/mL of air (1.82 ± 0.19  10^-7 Bq/mL of air).  (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, 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. Equipment problems nullified one sample from the Rexburg location. The maximum 24-hour concentration was 60.2 µg/m³ on August 18, 2003, in Rexburg. This sample corresponds to the end of wheat harvest. 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.

Table 1.   Summary of 24-hour PM₁₀ values.

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