Assessment of PFAS Vapor Intrusion Risk – Site Assessment Techniques and Strategies

Abstract: Vapor intrusion (VI) related to per- and polyfluoroalkyl substances (PFAS) is being studied because several PFAS are sufficiently volatile and/or toxic via inhalation to qualify as “vapor-forming chemicals” (EPA,2015). At least four polyfluorinated organic substances (4:2-, 6:2-, 8:2- and 10:2-fluorotelomer alcohols, FTOHs) have sufficient vapor pressure to be designated as “vapor-forming chemicals” (Lutes, 2021). Several perfluoroalkyl carboxylic acid (PFCA) compounds have been observed in soil gas using a method we have recently developed (Schumacher, 2022).
As for VI at sites impacted by in volatile organic compounds, knowledge of the site characteristics will be important. These characteristics include the water table depth, the type and permeability of vadose zone material, the presence of sewers or other utility lines potentially connecting the source to the building, the concentration of PFAS in groundwater, and the building slab conditions. However, quantifying PFAS in indoor air and determining whether the VI pathway is complete will be hindered by indoor air background sources. This is because PFAS are present in various industrial and domestic materials (e.g., water resistant clothing, cleaning products, stain resistant coating in carpets), as well as building construction materials (e.g., surface sealers for stone, tile, grout, or concrete to increase their resistance to oil, water, and stains). Thus, to evaluate the importance of PFAS-related VI, site assessors will need to rely mainly on soil, groundwater, and subslab soil vapor concentrations as main lines-of-evidence, coupled with the determination of a reliable attenuation factor or the use of PFAS vapor transport models.
There are thousands of PFAS compounds, thus refinement of a list of marker compounds with high VI potential will be necessary to evaluate the presence of PFAS VI. Potential partitioning processes of PFAS to moisture and surfaces in the building and sampling equipment will also require consideration. Given the number of background sources of PFAS present in almost any building, identification of unique tracers for PFAS that have been released to soil/groundwater based on biodegradation pathways (Evich, 2022) will be critical. Building pressure cycling tests have often been used to distinguish subsurface and indoor sources, but will require careful interpretation where PFAS have been applied to foundation materials. This presentation will summarize the current understanding of PFAS VI and offer strategies for its practical assessment in occupied structures.

References:
Evich, M. G., M. Davis, J. P. McCord, B. Acrey, J. A. Awkerman, D. Knappe, A. B. Lindstrom "Per-and polyfluoroalkyl substances in the environment." Science 375, no. 6580 (2022): eabg9065.
OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air, OSWER Publication 9200.2-154. Office of Solid Waste and Emergency Response, Washington, DC.;
Lutes, C. , G. Buckley, V. Boyd, R. Truesdale, C. Holton, H. Dawson, H. Hayes, J. Zimmerman, A. Williams and B. Schumacher “Development of Soil Gas Sampling and Analysis Methods for PFAS Compounds” Presented AWMA Annual conference 2021, June.
Schumacher, B. “Are PFAS a Concern for Vapor Intrusion” Oral presentation at AWMA Specialty Conference, “The Science of PFAS”, November, 2022.