A joint U.S. Environmental Protection Agency (EPA) – Office of Research and Development (ORD) and Department of Defense – Strategic Environmental Research and Development Program (SERDP) emissions field test was conducted at the National Response Corporation’s (NRC’s) Moose Creek Facility soil thermal treatment facility, located in North Pole, Alaska. The purpose of this test program was to field evaluate the performance of candidate per- and polyfluoroalkyl substances (PFAS) emissions test methods in various stages of EPA development and use these tests methods to comprehensively characterize the emissions from aqueous film forming foam (AFFF) contaminated soil thermal treatment. Specifically, the quantitative performance of the EPA Method 0010 sampling train, modified for the collection and recovery of polar PFAS compounds and analyzed by isotope-dilution mass spectrometry for specific targeted PFAS compounds (e.g., EPA Method 537).
The field evaluation included the first ever use of pre-sampling surrogates (PSS), isotopically labelled PFAS compounds added to sampling media prior to sampling, and quantitatively analyzed in the identical manner as target (native) PFAS compounds to serve as quantitative indicators of overall measurement quality. A modified EPA Method 18 sampling train was used to evaluate a potential approach for measuring Total Organic Fluorine. SUMMA canisters, typically used for ambient volatile organic compound sampling, were used to collect whole air samples for volatile, nonpolar compounds. Triplicate emissions samples for each sampling approach were collected at the scrubber outlet sampling location over the course of three days while thermally treating AFFF contaminated soil. Ancillary samples, including soil samples (treated and pretreated soil), baghouse dust, and water (scrubber) were also collected for quantitative targeted PFAS compounds analysis.
This study successfully demonstrated the application of PSS to indicate overall quantitative measurement performance for targeted PFAS measurements for the modified EPA Method 0010 sampling train and associated analyses. A minimum PSS recovery of 70% and a maximum of 130% is typically required for EPA’s isotope dilution emissions measurement methods. PSS recoveries averaged 100.3% and 70.3% for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) respectively. Moreover, there was no evidence of the PSS compounds migrating from the XAD-2 to the impingers during sampling, even in an extremely high moisture environment. It is because of these results EPA is able to proceed with the preparation of a formal test method for quantitative, targeted PFAS emissions measurements. This method is now identified as DRAFT Other Test Method 45, a candidate EPA Test Method recommended for measurement of targeted PFAS compounds from stationary sources.
The modified Method 0010 sampling train combined with the associated sample train fraction analytical preparation and targeted isotope dilution analyses reporting limits (RL) and method detection limits (MDLs) were used to calculate estimated in-stack measurement method RLs and MDLs for individual PFAS compounds. These estimated in-stack measurement limits serve to indicate the excellent sensitivity of the intended method and suitability to conduct quality destruction and removal efficiency (DRE) testing determinations.
The Method 0010 sampling train nontargeted analyses were not performed at this time. As a result, the comprehensive products of incomplete combustion (PIC) characterization is also not available. The results of the nontargeted analyses, including characterization of PICs, will be the subject of a supplement to this report.
The inability to representatively characterize the PFAS levels in the AFFF contaminated soil was a complicating factor. Individual PFAS levels on the order of 1000 µg/kg had been observed by NRC and were expected. From ORD’s single, pre-treatment soil sample, the highest PFAS concentration measured for any compound was 1.46 microgram per kilogram (µg/kg) for PFOS (i.e., all the remaining that were detected were estimated concentrations between the MDL and RL). It is suspected the relatively low AFFF-contaminated feed soil levels contributed to the result that all emissions measurements were either non-detect or above MDLs, but below RLs. However, even with the relatively low AFFF-contaminated feed soil levels measured by ORD, the targeted PFAS measurements for the modified Method 0010 sampling approach were sufficiently sensitive to determine a PFOS DRE of 99.9%. The destruction and removal of PFOS or other targeted compounds is not an indication of the presence or absence of PFAS products of incomplete combustion. Regardless of the pre-treatment AFFF-contaminated feed soil PFAS levels, all post-treatment soil sample results, representing all soil treated during the study, met Alaska Department of Environmental Conservation clean-up levels for PFAS compounds.