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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 this quarter (Figure 2). 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 Blackfoot (Distant location) and one at Mud Lake (Boundary location) during 2004. An average of 17,469 ft³ (495 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 glass fiber particulate filters (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.

Figure 2. Low-volume air sampler locations.

LABORATORY ANALYSES

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.

Charcoal cartridges were placed in batches of ten or less and 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. If ¹³¹I is detected in any batch of cartridges, the laboratory analyzes each individual cartridge in that batch to determine the source(s) of the detected ¹³¹I.

The weekly particulate filters collected during the quarter for each location were composited and analyzed for gamma-emitting radionuclides. Composites were also radiochemically analyzed by location for ⁹⁰Sr, or ²³⁸Pu, ^239/240Pu, and ²⁴¹Am as determined by a rotating quarterly schedule.
 

STATISTICAL ANALYSES AND DATA PRESENTATION

Quarterly gross alpha and gross beta data typically show no discernable distribution (e.g., normal or lognormal) and are thus analyzed using nonparametric statistics. Box and whisker plots are routinely used to present the descriptive statistics of nonparametric data. Each data group is presented in this quarterly report 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. 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. All outliers and extreme values were investigated further to identify any irregularities in collection, analysis, or reporting. If no anomaly was identified, the data were compared with historical measurements to determine if the values lie within the range of natural variation (see Historical Measurements under Helpful Information). If this was the case, the outliers and extreme values were included in the subsequent statistical analyses.

If the INEEL were a significant source of offsite contamination, concentrations of contaminants should be statistically greater at Boundary locations than at Distant locations. The nonparametric Kruskal-Wallis test of multiple independent groups was used to test for statistical differences between quarterly median gross alpha and gross beta values grouped by INEEL, Boundary, and Distant locations. This test was also used to test for statistical differences between monthly gross alpha and gross beta medians calculated for 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.

As an additional check, comparisons between gross alpha and gross beta 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. A ‘p’ value greater than 0.05 signifies no statistical difference between weekly data groups.

More detail on the statistics used for data analyses can be found in Determining Statistical Differences under Helpful Information.

RESULTS

Gross alpha activity. All gross alpha results are reported in Table C-1. The data were tested for normality prior to statistical analyses and found to be neither normally nor log-normally distributed. A careful review of the data collected during the first 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, as indicated by comparison with historic measurements.

Median gross alpha concentrations in air for INEEL, Boundary, and Distant locations during the first quarter of 2004 are shown in Figure 3 . Figure 3 graphically shows that the gross alpha measurements made at INEEL, Boundary, and Distant locations are similar for the first quarter. There were no statistical differences in gross alpha concentrations between location groups for the first quarter of 2004, as determined by the Kruskal-Wallis test of multiple independent groups (Table D-1).

Median gross alpha concentrations for each month of the quarter are shown by location in Figure 4, Figure 5, and Figure 6. Using the Kruskal-Wallis test, no statistical differences were determined between median gross alpha results grouped by location for any month of the first quarter (Table D-1).

Comparison of weekly Boundary and Distant location gross alpha data sets, using the Mann Whitney U test, show no statistical differences between and Boundary and Distant data sets during any week of the first quarter (Table D-2).

Gross beta activity. Gross beta results are presented in Table C-1. The data were tested and found to be neither normally nor log-normally distributed. Outliers and extreme values were retained in subsequent statistical analyses because they are within the range of measurements made historically, and because these values could not be attributed to mistakes in collection, analysis, or reporting procedures.

Gross beta concentrations in air for Boundary, Distant, and INEEL locations for the first quarter of 2004 are shown in Figure 7. As in the case of gross alpha activity, the quarterly gross beta data for each group appear to be similar and were determined using the Kruskal-Wallis test to be statistically the same ( Figure 6 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. There was no statistical difference between median gross beta concentrations grouped by location for any month during the quarter (Table D-1).

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 week ending on February 4, 2004 (Table D-2). The Boundary group was statistically greater than the Distant group. The highest concentration was measured at the Arco location during this period. When the Arco result was removed from the data set, there was no statistical difference between Boundary and Distant location groups. The Arco result was well within historic measurements and was attributed to natural variations.

Iodine 131. No ¹³¹I was detected at a level greater than the associated 3s value in any of the batches of charcoal cartridges. Weekly ¹³¹I results for each location, including individual recount data, are listed in Table C-2 of Appendix C.

Gamma-emitting radionuclides. Weekly filters for the first quarter of 2004 were composited by location and analyzed for gamma-emitting radionuclides, including ¹³⁷Cs. Composites were also analyzed for ⁹⁰Sr, ²³⁸Pu, ^239/240Pu, and ²⁴¹Am. No man-made radionuclides were detected above the 3s value during the quarter. All results were far less than their respective DCGs. All results for composite filter samples are shown in Table C-3, Appendix C.

ATMOSPHERIC MOISTURE SAMPLING

Atmospheric moisture is collected by pulling air through a column of absorbent material (i.e., silica gel) 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. Starting in 2004 the ESER program began an evaluation of a molecular sieve material as an absorbent material. As a result the locations with two samples yielded one sample of each material (silica gel and molecular sieve).

Seven atmospheric moisture samples were obtained during the first quarter of 2004; two each from Blackfoot, Idaho Falls, Atomic City, and one from Rexburg. Results are presented in Table C-4, Appendix C. Both samples collected at Atomic City exceeded their 3s values. The maximum sample result of (4.4 ± 1.3) x 10^-13 μCi/mL_air ([1.6 ± 0.5] x 10^-8 Bq/mL_air), was well below the DOE DCG for tritium in air of 1 x 10^-7 mCi/mL (3.7 x 10^-3 Bq/mL) and consistent with historical measurements.

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. Measurement problems nullified only two of samples from Atomic City during the quarter. The maximum 24-hour particulate concentration was 47.6 µg/m³ on March 9, 2004, at Rexburg. 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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