Numerical evaluation of effectiveness of different soil amendments to stabilise PFAS in shallow soil

Starting in the 1970s, PFAS-containing aqueous film-forming foams (AFFFs) have been used globally for fighting fires and accidentally created a tremendous environmental legacy for society as a whole. Over the last decade, environmental monitoring and increasing research efforts have progressed towards understanding the scale of the problem and the technical and financial efforts that it will take to mitigate the problems.
Recent investigations, including those performed at Australian DoD sites, have indicated notable retention of PFAS in the vadose zone below discrete AFFF source zones. This has led to the identification of the unsaturated zone as a long-term source for sustained PFAS contamination of groundwater and a target for management. Technologies that mitigate the release of PFAS from shallow source zones include excavation, soil washing, thermal desorption, and stabilization/ solidification (S/S). Stabilization uses a chemical amendment to reduce and/or eliminate contaminant leaching.
In this study, we developed a process-based numerical vadose zone transport model that quantifies the changes in the physico-chemical soil characteristics following the application of selected stabilisation technologies. The effect on the velocity and residence time of water and the retention characteristics of PFAS in the vadose zone as well as the long-term effectiveness of soil amendments are evaluated. Simulated reductions in PFAS leaching over time are compared to laboratory, pilot, and field-scale evaluations.