Application of Multisorbent Traps to Characterization and Quantification of Workplace Exposure Source Terms Page: 3 of 8
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Multisorbent traps are currently being used to sample the headspace of underground storage tanks
at the Department of Energy's Hanford site, in Richland, Washington. The Hanford reservation, which is 560
square-miles, is located about 120 miles south of Spokane, Washington. After approximately 40 years of
nuclear weapons production at the site, 60 million gallons of mixed radioactive waste have accumulated in
177 underground storage tanks (3). The tank capacities vary from 0.5 to 1 million gallons, although most are
not filled to capacity. The general methodology for analyzing tank headspace samples by thermal
desorption/gas chromatography/mass spectrometry (TD/GC/MS) was presented at 1994 EPA/AWMA
Measurement of Toxic and Related Air Pollutants Symposium. The purpose of this discussion is to describe
some of the results that have been obtained and the quality assurance controls that have been implemented
to improve the methodology.
DISCUSSION
Westinghouse Hanford Company (WHC) is characterizing the waste tank headspace vapors for
primarily three reasons (4). First, there are worker health and safety issues. The tanks are workplace source
terms. Thus, WHC needs to adequately characterize the tanks since there exists a potential hazard to tank
farm workers. A second significant issue is headspace flammability. Although combustible gas meters are
used to monitor tank headspace flammability, some headspace composition issues may not be addressed by
these meters. Lastly, WHC would like to identify, based on headspace organic concentrations, those tanks
which could potentially have pools of organic liquids.
Ten cases of worker exposure to vapors from tank 241-C-103 prompted the establishment of the
Tank Vapor Issue Resolution Program (4). Consequently, tank 241-C-103 was the first tank to be
comprehensively studied by the program. Based on the results from initial scoping experiments with 241-C-
103, a list of target analytes was generated by a panel of Pacific Northwest Laboratory experts in various
areas of toxicology. The target organic analytes listed in Table 1 include C6 to C13 alkanes, alkyl nitriles, alkyl
ketones, dibutyl butyl phosphonate and tributyl phosphate. Target analyte concentrations are quantified
against calibration standards for each tank. Therefore, these analytes serve as way of integrating the data for
tank to tank comparisons. TD/GC/MS methodology validation studies were performed using these target
analytes, including measurements of pre-analytical holding times.
A holding time study was performed on a representative subset of the target analytes using a method
developed at ORNL(5). The Practical Reporting Time, or PRT, is defined as the time (in days) when there
is a 15% risk that the concentration will be below the critical (initial) value. The method depends on
approximating models to represent the degradation of analyte concentrations with time. For this study, either
zero-order (linear) kinetic model, log-term model, or inverse-term model was applied to the data. The
majority (84%) of the data was fitted to the linear model. One attribute of this method is that it allows for
judgement beyond the last experimental data points. Therefore, a prediction can be made to assess the
probability of being below the critical value during any time period. A total of 56 triple sorbent traps were
spiked with vapor phase organic analytes (nominal 400 ng/trap) for the PRT study. The experiments were
divided into two disciplines according to how the traps were stored: refrigerated (2*C) and ambient (22*C).
Each day's analyses consisted of three standards and four PRT "samples", which were analyzed by thermal
desorption/gas chromatography/flame ionization detection (TD/GC/FID). Just prior to analysis, each TST
was spiked with three vapor phase internal standards, namely hexafluorobenzene, di-ethylbenzene, and d,6-
dodecane. PRT samples were analyzed on 0, 7, 14, 21, 28, 63, and 84 days of storage at both ambient and
refrigerated temperatures. Data from only one analyses was discarded due to experimental error. Therefore,
the conclusions are based on 55 data points. The PRT results are presented in Table 2 (6). Eleven of the
sixteen analytes (i.e, acetone, butanal, 1-butanol, pentanenitrile, and 2-pentanone were the exceptions) stored
at refrigerated temperatures showed no significant decreases during 84 days. The PRTs for these eleven
analytes under refrigerated conditions are at least 84 days. Also, nine of the sixteen analytes (i.e, acetone,
1-butanol, butanal, 2-octanone, pentanenitrile, propanenitrile, and 2-pentanone were the exceptions) stored
at ambient temperatures showed no significant decreases during 84 days. The ketones that were stable under
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Dindal, A. B.; Ma, Cheng-Yu; Jenkins, R. A.; Higgins, C. E.; Skeen, J. T. & Bayne, C. K. Application of Multisorbent Traps to Characterization and Quantification of Workplace Exposure Source Terms, article, August 1, 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc621279/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.