First Quarter 2005
INL Quarterly Site Environmental Report
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The ESER Quality Assurance Program consists of five ongoing tasks which measure:
- method uncertainty;
- data completeness;
- data accuracy, using spike and laboratory control samples;
- data precision, using split samples, duplicate samples, and recounts; and
- the 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, 2005.
The Quality Assurance Project Plan (QAPP) establishes data quality and method quality objectives for the ESER surveillance program (Stoller 2002). Since the primary concern is with detection, the lower bound for the method uncertainty is set at zero. The upper bound is defined by the ESER program as the maximum concentration in the non-outlier range of data from the past seven years. Each individual result is checked for acceptance on the basis of the result, whether it is below the lower limit (i.e., a negative value), greater than the upper limit, or between the lower and upper limit (the most common occurrence). The calculated method uncertainty is then compared to the 1s measured uncertainty. A sample is deemed acceptable when the measured 1s uncertainty is less than the calculated uncertainty. The upper bound values are currently being evaluated and revised. Preliminary results indicate that more calculated method uncertainties for detected results were acceptable.
The QAPP specifies a 98 percent completeness goal for all regularly scheduled sample types. Data completeness for sample collection and delivery was 100 percent during the first quarter for all samples types with the following exceptions. A number of precipitation samples were not collected due to the lack of precipitation. The liver was not collected from the one game animal sampled. There were three air samples that had volumes below the 7,000 ft3 or 200 m3 threshold listed in the air sampling procedure as being a valid sample. If these are not considered valid samples, the completeness of the air filter data set is 98.8 percent.
Data precision is a measure of the variability associated with a measurement
system. Precision is measured using duplicate samples, split samples, and
recounts. Data precision is measured using duplicate samples, split samples, and
recounts. The Quality Assurance Project Plan specifies that sample results
should agree within ±20 percent or 3σ, whichever is greater. For environmental
samples at levels that are within the normal range found by the ESER, the 3
standard deviation criterion is the one that applies in nearly all cases. The
standard deviation criterion is considered to be met if the values of the
duplicate samples differ by less than the root mean square of three standard
deviations of each sample result. Mathematically, this is expressed as:
│X-Y│< 3 (sqrt(σx2 + σy2)),
where:
X is the result of the regular sample
Y is the result of the duplicate sample
σx is the uncertainty of the regular sample
σy 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. The following sections of this report first check the sample results
using the 3 standard deviation criterion. If this criterion is not met, the
results are then listed for the relative percent difference.
Duplicate milk samples were collected from Rupert on March 1 and analyzed for gamma-emitting radionuclides. Duplicate milk samples were also collected from Terreton on March 1 and analyzed for gamma-emitting radionuclides. All results were within the 3σ criteria.
Duplicate air samplers are operated at two locations adjacent to regular air samplers. In the first quarter of 2005 these samplers, designated as QA-1 and QA-2, were in operation at the INL Main Gate and Howe, respectively. Particulate filters receive the standard analysis for gross alpha and gross beta; charcoal cartridges are analyzed specifically for iodine-131. All gross alpha and gross beta results for the co-located samplers met the acceptability criteria. Charcoal cartridge results are difficult to present because cartridges are counted in batches of ten.
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 analyses were within the 3s criterion with the exception of 7Be at the Howe and QA-2 stations.
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
and Figure 13
show the difference in results (Main sampler - QA duplicate sampler) over time.
The figures show that the bias is small and not consistent in one direction,
indicating that there is no obvious bias in the duplicate sampling systems in
these cases.
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 2005.
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 first quarter is presented below.
Accuracy is a measure of the degree to which a measured value agrees with the "true" value for a given parameter; accuracy includes elements of both bias and precision.
No spike samples were scheduled for analysis during the first quarter of 2005.
The Idaho State University Environmental Assessment Laboratory uses NIST standards to prepare spiked water samples and uses commercially prepared calibration standards as NIST-traceable spiked samples. ISU considers a performance to be acceptable if results pass either the ±20 percent test specified by the ESER program or the three-sigma test described in the data precision section. A variety of checks are made each quarter on different geometries.
During the first quarter of 2005, 24 analyses were conducted on NIST-traceable
standards for gamma-emitting radionuclides. Geometries tested included
low-volume air filter composites, single charcoal cartridge screening,
10-charcoal cartridge screening, 500 ml 1.0 g/cc samples, and one-liter 1.0 g/cc
samples. A total of 176 analytical results were generated. All of the results
were within the ±20 percent range.
Water samples spiked with tritium received 13 analyses during the quarterly
reporting period. All were well within the ±20 percent criterion, and in fact
all were within 6 percent of the known value with one exception. Gross beta
spikes analyzed in the first quarter were within 20 percent of the expected
values; three of five gross alpha spikes were within 20 percent and all were
within three standard deviations.
Severn-Trent analyzes a laboratory control sample (LCS) with each batch of
samples submitted by the ESER. During the first quarter this consisted only of
strontium-90 and actinides in air. The results for plutonium-239/240 and
americium-241 were within the acceptability criteria; however, the result for
strontium-90 was outside the criterion for that radionuclide (-14.1percent vs.
±10 percent).
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 Sr-90 and the other for transuranics.
The Quality Assurance Project Plan does not specify requirements for blank performance, but ideally the result should be within ±2σ of zero and preferably within ±1σ of zero on most analyses. It would be expected, based on counting statistics for a sample that was truly a blank (i.e., the true value of the analyte was zero), that 68.3 percent of analyses would fall within one standard deviation, 95.5 percent would fall within two standard deviations, and 99.7 percent would fall within three standard deviations. With a few exceptions in gross alpha and gross beta analyses, all results were within the 2σ significance level.
The Environmental Assessment Laboratory prepares and analyzes reagent blanks
to help determine if the analysis will yield a zero result when no activity is
present. ISU considers the result within specification if the concentration is
less than the minimum detectable concentration (MDC) for the analysis. One such
blank was analyzed for tritium in the first quarter for water. The blank was
below the MDC for the analysis and less than one standard deviation. A water
blank analyzed for gross alpha and gross beta was also below the MDA for the
analysis and within three standard deviations for both parameters.
Severn-Trent analyzes a blank with each set of results. First quarter blanks
were less than two standard deviations of zero for strontium-90, plutonium-238,
plutonium-239/240 and americium-241 in air.