Fate and Transport of PFAS in Unsaturated Porous Media across Scales: Interfacial Partitioning, Thin Water Films, and Upscaling

Per- and polyfluoroalkyl substances (PFAS) are contaminants that have accumulated extensively in soils, which can act as long-term sources of groundwater contamination. Quantifying soil PFAS leaching is therefore critical for risk assessment, remediation, and regulatory decision-making. However, PFAS transport differs fundamentally from that of conventional contaminants because many PFAS are surfactants that adsorb at air??"water and solid??"water interfaces, leading to complex retention behavior and flow??"transport coupling under variably saturated conditions.

I present a cross-scale framework for understanding and modeling PFAS fate and transport in soils and groundwater. I discuss the dominant processes controlling PFAS retention and migration, introduce a mechanistic mathematical model that incorporates PFAS-specific interfacial processes, and show how thin water films can uniquely control PFAS transport in unsaturated soils. This is followed by a multi-continuum, semi-analytical framework as a potential route for upscaling these processes and incorporating them into practical modeling tools. The goal is to connect interfacial physics across scales to improve predictions of long-term PFAS retention, leaching, and mass discharge to groundwater.

Speaker: Bo Guo, University of Arizona