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The ESER Quality Assurance Program consists of four ongoing tasks which measure:
- data completeness;
- data accuracy, using spike and laboratory control samples;
- data precision, using split samples, duplicate samples, and recounts; and
- presence of contamination in samples, using blanks.
The following discussion summarizes the results of the quality assurance program for the period from January 1 to March 31, 2003.
The Quality Assurance Project Plan (QAPP) specifies a 98 percent completeness goal for all regularly scheduled sample types (Stoller 2004). Data completeness was 100 percent during the first quarter for all sample types with the following exceptions: an air filter from Mountain View CMS on January 8 was reported lost and three other samples were invalid due to insufficient volume collected because of equipment failure (Blackfoot QA-1 on January 8, Dubois on February 19, and Blackfoot QA-1 on March 12).
During the first quarter of 2003, spikes of the following types were submitted for analyses by ESER:
The QAPP specifies a required accuracy of ±10 percent for gamma-emitting radionuclides and 131I in air and ± 10 percent for tritium in precipitation. The EAL was within the accuracy criteria for all radionuclides except for chromium-51 and cobalt-60 in LV air filters and for 131I in the charcoal cartridge spike. The gamma-emitting constituents, 51Cr and 60Co, are not typically measured in ambient air and thus do not represent a major concern. However, we will continue to track the issue. The 131I problem was determined by the EAL to be related to how the spike was prepared. The company which prepares the spikes (Analytics) appears to have spiked the wrong side of the charcoal cartridge. When the EAL reversed the cartridge, the result was accurate within the specified criterion.
The EAL also prepares internal laboratory spikes. During the first quarter of 2003, ten analyses were conducted on NIST-traceable standards for gamma-emitting radionuclides. Geometries included low-volume air filter composites and charcoal cartridges. A total of 40 analytical results were generated. All of the results within the ±20 percent range, with the exception of one result for 57Co. However, this result was within the three sigma criterion (see Data Precision section). Water samples spiked with NIST tritium standards were well within the ± 20 percent criterion, and in fact were within 5 percent of the known value. In addition, a gross beta water spike received two analyses and both were within about 10 percent of the known value.
Severn-Trent analyzes a laboratory control sample (LCS) with each batch of samples submitted by the ESER. During the first quarter these consisted only of 90Sr and actinides in air. The QAPP specifies accuracies of ± 10 percent for these analyses. All LCS results were within parameters: 90Sr was +7.6 percent, 239/240Pu was +0.5 percent, and 241Am was -1.8 percent.
Data precision is measured using duplicate samples, split samples, and recounts. The QAPP specifies that sample results should agree within ±20 percent or 3s, whichever is greater. For environmental samples at levels that are within the normal range found by the ESER, the 3s criterion is the one that applies in nearly all cases. Mathematically, the 3s criterion is expressed as:
│X-Y│ < 3 × (sqrt(sx2 + sy2)),
X is the result of the regular sample
Y is the result of the duplicate sample
sx is the uncertainty of the regular sample
sy is the uncertainty of the duplicate sample
Another measure of duplicate sample results is the relative percent difference. This value is the difference in the two results divided by the mean of the two results.
Duplicate milk samples were collected during the first quarter and were analyzed for gamma-emitting radionuclides. They were found to be within the 3s criterion for 131I and 137Cs.
Duplicate air samplers are operated at two locations adjacent to regular air samplers. In the first quarter of 2003 these samplers, designated as QA-1 and QA-2, were in operation at Mountain View and Mud Lake, respectively. Particulate filters were analyzed for gross alpha and gross beta activity. All valid QA-1 samples met the 3s criterion for gross alpha during the first quarter. Eight of 11 valid QA-1 samples met the 3s criterion for gross beta activity during the same period. Three did not meet this criterion and had relative percent differences of 25 percent, 30 percent, and 69 percent. Twelve of thirteen valid QA-2 samples met the 3s criterion for gross alpha activity and for gross beta activity during the first quarter. The relative percent difference for the ones that did not meet the criterion was 94 percent for gross alpha and 19 percent for gross beta.
Composite air samples from the two QA samplers were submitted for analysis at the end of the first quarter for gamma spectrometry at the EAL and for 90Sr at Severn-Trent. All results were within the 3s criterion.
A comparison of duplicate results can also show bias in the sampling system. For example, if one set of results is consistently lower or higher than the other one might suspect that this bias was due to a leak in the system or variations in the calibration of the flow meter. Figure 12, Figure 13, Figure 14 and Figure 15 show the ratio of results (QA duplicate sampler/main sampler) over time. A ratio of one means that the results of both samplers are exactly the same. The figure show that the bias is small (<2) and not consistent, indicating that there is no obvious bias in the duplicate sampling systems. The average bias ratios during the first quarter are 1.0, 1.0, 1.2, and 1.0 for Mountain View gross alpha, Mud Lake gross alpha, Mountain View gross beta, and Mud Lake gross beta, respectively.
The EAL splits and analyzes a number of milk, precipitation, and atmospheric moisture samples each quarter. The laboratory tests each result using both the ±20 percent criterion and the 3s criterion, although it considers the former test meaningless for analyses producing fewer than 15 total counts and questionable even where counts are on the order of 100. The latter criterion is applied in nearly all cases at the levels seen in environmental samples analyzed for the ESER program. Results of the EAL split sample analyses met the criteria for acceptance during the first quarter 2003.
The EAL also recounts a number of samples of each media type. The lab tests each recount using both 20 percent criterion and the 3s criterion, subject to the limitations described in the previous paragraph. All first quarter 2003 results were within the criteria for acceptance.
The ESER Program submits field blanks along with the regular samples to test for the introduction of contamination during the process of field collection, laboratory preparation, and laboratory analysis. The current program includes the use of two field blanks, designated as Blank A and Blank B, that each accompanies one of the air filter routes. Quarterly composites of the blanks are also submitted. After gamma spectrometry analysis, one of the blanks is analyzed for 90Sr and the other for transuranics.
The QAPP also specifies that one milk sample blank will be submitted per year (although this is now being done monthly).
The QAPP does not specify requirements for blank performance, but ideally the result should be within ±3s of zero on most analyses. The 2003 blanks submitted for analyses were, for the most part, within this range. One exception of concern is the result of (0.34 ± 0.10) pCi/composite for 90Sr in the quarterly air composite analyzed by Severn-Trent. However, the reagent blank analyzed by the laboratory at the same time had a result of (0.33 ± 0.11) pCi/sample. Therefore, the activity reported for the field blank is not due to contamination, but rather is an artifact of the laboratory analysis. All results were corrected for the activity observed in the reagent blank.
The EAL also analyzes reagent blanks to help determine if the
analysis will yield a zero result when no activity is present. Three such blanks
were analyzed for tritium in the third quarter. The results were less than the
calculated MDCs and less than three standard deviations.
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