It can be challenging to develop a robust conceptual site model (CSM) for federal sites with per- and polyfluoroalkyl substances (PFAS).
There are multiple aspects to PFAS sites that differ from more often encountered contaminants, which may substantially increase the effort and associated cost to achieve a robust CSM that supports site-management decision making. This presentation will focus on three PFAS site characterization challenges and approaches to overcoming these challenges. Challenges include: a) source identification; b) estimating total PFAS mass and type; and, c) unsaturated zone mass.
The first challenge is identifying the source(s) of PFAS present at a site, and distinguishing site-related PFAS from potential external sources. PFAS have become widely distributed in the environment, and not all PFAS at a site may originate from releases or activities at the site. For example, identifying other potential sources is particularly important when PFAS are found either in surface water bodies or near landfills, airports, agricultural areas with biosolids application, or large industrial facilities.
The second challenge is quantifying the total mass and types of PFAS present. Over 3,000 PFAS have been commercially produced; therefore potentially many and varied PFAS may be present at a site. Accurately assessing PFAS types and total PFAS mass is critical for developing the CSM, site management strategy, evaluation of potential pathways and associated risks, and identifying and designing a remedial strategy. For example, not all PFAS may be effectively or equally treated by a given technology, including common methods such as sorption to granular activated carbon in pump and treat systems.
The third challenge is assessing the mass of PFAS in the unsaturated zone. Many PFAS releases result in a considerable portion of mass being present in the unsaturated zone, which over time infiltrates with successive precipitation and infiltration events. Characterizing the unsaturated zone mass is important for predicting future groundwater plume footprints and concentrations. Additionally, PFAS-specific infiltration dynamics need to be considered, for example transport of some PFAS are retarded by surfactant interactions in the unsaturated zone.
This presentation will discuss approaches to address these challenges including techniques such as PFAS forensics, specialized analytical capabilities, and robust site media characterization.