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 for sample collection and delivery was 100 percent during the second quarter for all sample types with one exception: a number of precipitation samples were not collected due to lack of precipitation.
Two air samples were determined to invalid due to insufficient volume collected because of equipment failure (Dubois on April 25 and Monteview on May 28). The completeness of air filter data is thus considered to be 99.2 percent
During the second quarter of 2003, spikes of the following types were obtained and submitted:
The Quality Assurance Project Plan specifies a required accuracy of ± 20 percent for 131I in milk, gross alpha and gross beta in air, ± 10 percent for tritium in water, and 25 percent for 90Sr in air. A comparison is also provided using the 3 sigma standard described in the Data Precision section.
The EAL was within the accuracy criteria for all radionuclides except for cobalt-60 in milk, gross alpha activity in LV air filters, and 90Sr in the water. The gamma-emitting radionuclide, 60Co, is not typically measured in milk and thus does not represent a major concern. Gross alpha activity is difficult to measure accurately since the analyst must calibrate the spectrometer to specific radionuclides, which may or may not represent the major source of alpha activity in the sample. Alpha and beta measurements are at best screening tools which can indicate higher or lower concentrations of radionuclides in air. The 90Sr concentration measured in the spiked water sample was 11.7 percent below the actual concentrations. The activity was within the 3s criterion. Because the measurement was close to the ± 10% criterion and within the 3s criterion (see Data Precision section), the result was judged to be reasonably accurate. However, we will continue to track the issue.
The EAL also prepares internal laboratory spikes. During the second quarter of 2003, 32 analyses were conducted on NIST-traceable standards for gamma-emitting radionuclides. Geometries included low-volume air filter composites and charcoal cartridges. A total of 207 analytical results were generated. All of the results within the ± 20 percent range, with the exception of one result for 88Y. However, this result was within the three sigma criterion (see Data Precision section). Water samples were spiked with NIST tritium standards. Ten analyses were conducted and all results were well within the ± 20 percent criterion, and in fact were within 4 percent of the known value. In addition, a tritium milk spike analysis was also within 20 percent of the known value.
Severn-Trent analyzes a laboratory control sample (LCS) with each batch of samples submitted by the ESER. During the second quarter these consisted of 90Sr and actinides in air, 90Sr in milk, and 90Sr, actinides, and 137Cs in marmots. The QAPP specifies accuracies of ± 10 pecent for radionuclides in air, ± 25 percent for 90Sr in milk, and ± 20 percent for 90Sr, actinides, and 137Cs in marmots. All LCS results were within parameters.
Both EAL and Severn-Trent participate in the DOE Environmental Measurements
Laboratory (EML) Quality Assessment Program QAP-58 reported in June 2003. Air
filter, water, soil, and vegetation samples were spiked by the EML with specific
alpha, beta, and gamma emitters. All of the EAL analytical results were
acceptable within EML QAP limits. Some Severn-Trent results were not within the
acceptable limits (a value less than the 5th percentile and greater than the
98th percentile.) These included 90Sr in an air filter and 239Pu
in vegetation. The 90Sr measurement made by the laboratory was 33.4
percent of the EML value. The 239Pu measurement made by Severn-Trent
was 7.2 percent of the spike concentration. Severn-Trent has been made aware of
the results and is investigating.
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)),
where:
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 second 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 second 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 analyzed by the EAL met the 3s criterion for gross alpha and gross beta during the second quarter.
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 15, Figure 16, Figure 17, and Figure 18 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 figures 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 second 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 second quarter 2003 results were within the criteria for acceptance.
The ISU EAL recounts a number of samples of each media type. The lab tests each recount using both the 20 percent criterion and the 3σ criterion, subject to the limitations described in the previous section.
A summary of the recount results for the second quarter is presented below.
41 low-volume air filters were recounted for alpha activity; one was recounted twice. All were within the 3σ criterion.
41 low-volume air filters were recounted for beta activity; one was recounted twice. All were within the 3σ criterion.
22 milk samples were recounted for iodine-131. All were within the 3σ criterion.
11 groups of charcoal cartridges were recounted for iodine-131. All were within the 3σ criterion.
21 tissue samples were recounted for cesium-137. All were within the 3σ criterion.
Three precipitation samples were recounted for tritium. Two were outside the 3σ criterion, but within the 20 percent criterion.
One water sample was recounted for tritium. The result was within the 3σ criterion.
Two milk samples were recounted for tritium. One result was not within the 3σ criterion, but was within 20 percent.
13 atmospheric moisture samples were recounted for tritium.
All were within the 3σ criterion.
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 ± 3σ 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 (1.71 ± 0.33) × 10-10 pCi/mL for 90Sr in the quarterly air composite analyzed by Severn-Trent. However, the reagent blank analyzed by the laboratory at the same time was also between 4-5 standard deviations. In addition, the reagent blank for marmots was between five and six standard deviations for 90Sr. All results were corrected for the activity observed in the reagent blank. The case narrative for wheat samples in the third quarter said that the laboratory had a high strontium-90 sample come through the lab so they cleaned everything and re-did the wheat sample. So the lab may have been contaminated during the second quarter as well. We will continue to follow this issue.
The EAL also analyzes reagent blanks to help determine if the analysis will yield a zero result when no activity is present. Two such blanks were analyzed for tritium in the second quarter. The results were less than the calculated MDCs and less than three standard deviations. Reagent blanks for gross alpha and gross beta were less than one standard deviation of zero.
There were no significant QA problems noted for the second
quarter. A new HPGe detector was installed during the quarter. No samples were
analyzed on this system as control chart data was being collected
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