Third Quarter 2006
INL Quarterly Site Environmental Report
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The ESER Quality Assurance Program consists of five ongoing tasks which measure:
The following discussion briefly summarizes the results of the quality assurance program for the period from July 1 to September 30, 2006.
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 for the range of data over the past ten years, excepting those values determined to be extremes using box plots generated by a statistical data program. 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 were recently re-evaluated and revised. Preliminary results indicate that more calculated method uncertainties for detected results were acceptable.
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 third quarter for all sample types with these exceptions: a number of precipitation samples were not collected due to lack of precipitation and one of the lettuce samples failed to grow in the portable lettuce gardens.
Three air samples were determined to invalid due to insufficient volume collected because of equipment failure or electrical work (two from Arco and one from Blue Dome). In addition, one air sample was invalidated because the gooseneck assembly holding the sampler head was broken and found on the ground at sample collection time. Another filter was lost when the pump malfunctioned and blew the paper filter out of the head. The completeness of air filter data is thus considered to be 98.1 percent.
No samples were lost in analysis during the third quarter.
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.
Spike Samples Submitted with Field Samples
During the third quarter of 2006, spikes (samples prepared with known amounts of radionuclides) of the following types were obtained and submitted:
Tritium in milk and plutonium-238 in air were within specifications. Although the Americium-241 result for the air filter spike was within about 6 percent of the known value, the result was considered out of specification because of a low yield and a high uncertainty value.
Internal Laboratory Spikes
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 third quarter of 2006, seven 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 and 500 ml 0.8 g/cc samples. A total of 28 analytical results were generated. All of the results were within the ±20 percent range, with the exception of one result for Cobalt-57. This radionuclide had decayed for approximately 10 half-lives, which may have contributed to the result outside the ±20 percent range. The sample was within the three-sigma test criterion.
Water samples spiked with tritium received six analyses during the quarterly reporting period. All were well within the ±20 percent criterion, generally -4 percent to -5 percent. Gross beta spikes analyzed in the third quarter were within 20 percent of the expected values; three of four gross alpha spikes were within 20 percent; the one sample outside this range was within the 3s criterion.
Severn-Trent analyzed a laboratory control sample (LCS) with each batch of samples submitted by the ESER. During the third quarter this consisted of strontium-90 in wheat.
|
Media |
Analyte |
QAPP Accuracy |
LCS Result |
Within Criterion? |
|
Air |
Strontium-90 |
±10 percent |
+4.1 percent |
Yes |
|
Air |
Americium-241 |
±10 percent |
-42.4 percent |
No |
|
Air |
Plutonium-239/240 |
±10 percent |
-12.9 percent |
No |
|
Wheat |
Strontium-90 |
±20 percent |
+14.3 percent |
Yes |
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.
Figure 12. Difference in QA-1/Main Gate gross alpha and gross beta activities.
Figure 13. Difference in QA-2/Howe gross alpha and gross beta activities.
Lab Split Samples
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 third quarter 2006.
Sample Recounts
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. For the third quarter reporting period, all 143 recounts met the criteria for acceptance.
Field blanks
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. Blanks are also submitted for milk and some other sample types.
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. In the third quarter, all results were within the 3σ significance level except for two gross alpha blanks and one gross beta blank.
Reagent Blanks
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 third quarter for milk. The blank was below the MDC for the analysis and between two and three standard deviations.
Severn-Trent analyzes a blank with each set of results. The third quarter blank
was less than three standard deviations of zero for strontium-90 in wheat.
Teledyne Brown also analyzes a blank with each set of results. All blanks for
third quarter samples met Teledyne Brown’s acceptance limits.