PFAS sources persist decades after releases occur in soils. The combination of complex vadose zone leaching behavior, stringent part-per-trillion (PPT) maximum contaminant levels (MCLs), and near ubiquitous anthropogenic background make it difficult for stakeholders to select practical remedial goals and strategies. PFAS retention is influenced by familiar dual-domain storage in low permeability zones and hydrophobic interactions, but also by electronegative interactions with clays and adsorption metal oxides and oxyhydroxides. In addition, partitioning of long-chain PFAS to the air-water interface increases retention in the vadose zone significantly.
 
The key to pragmatic, cost-effective strategies is to evaluate vadose zone source loading compared to aquifer retention capacity and treat the source to achieve a balance and create stable plumes that protect receptors. In this session, we will discuss retention in the vadose zone and how to estimate the vadose zone source loading to develop practical remediation targets including aquifer retention goals.
 
This webinar provides a roadmap for understanding PFAS behavior in vadose zone, based on the authors’ involvement in DoD-funded research, site assessments and remediation, and existing regulations and regulatory frameworks. We review key site characteristics that influence leaching and transport; provide a summary of the state-of-the-practice, balancing the science with practical approaches; lessons learned; and finally provide a more practical framework for establishing defensible site-specific leaching standards at your sites.