Development and Laboratory Validation of Mathematical Modeling Tools for Prediction of PFAS Transformation, Transport, and Retention in AFFF Source Areas

This integrated experimental and modeling research was designed to address data gaps associated with PFAS transport and transformation in natural subsurface environments and to develop models and decision tools that could aid site managers in the assessment of PFAS mobility and persistence in complex AFFF source areas. A matrix of experiments of increasing scale and complexity was undertaken with individual PFAS and mixtures, employing reference media and natural aquifer materials collected from PFAS-impacted sites. Experiments encompassed air-water and nonaqueous phase liquid (NAPL)-water interfacial tension and soil sorption measurements, biotransformation microcosm experiments for selected PFAS precursors, and single and multiphase column transport experiments. Mathematical models based upon research findings were used to explore potential PFAS transport and fate under representative field conditions. Research findings revealed that PFAS migration and retention are greatly influenced by interfacial processes. Under conditions consistent with AFFF releases, competitive sorption effects were found to be pronounced, and spill conditions were shown to have a strong influence on PFAS mobility and mass fluxes at the water table. Experimental observations improved our understanding of the potential for biotransformation of fluorotelomerization (FT)- and electrochemical fluorination (ECF)-based precursors in AFFF-impacted soils under various environmental conditions. Results provide insight into the structure-relevant stability of PFAS and a starting point for screening microbes and functional genes engaged in PFAS biotransformation. Field-scale model applications led to development of a meta-analysis table for use by practitioners that depicts the extent of correlation of important transport metrics with AFFF release parameters and site conditions.