Modelling investigation of the sorption dynamics of per-and polyfluoroalkyl substances (PFAS) in activated carbon amended soil columns

Per- and polyfluoroalkyl substances (PFAS) have become a major environmental concern due to their widespread presence in ecosystems, even in remote and pristine areas. These substances, resulting from extensive use and improper disposal practices, pose a threat to the environment and drinking water sources. Effective remediation strategies are critical to mitigate PFAS contamination, particularly in soils. One promising technique for PFAS remediation is the stabilization of PFAS in the subsurface using colloidal activated carbon (CAC). However, a deeper understanding of this approach is essential for its optimization. Additionally, the transport behaviour of PFAS in soil and groundwater is complex due to the diverse mobility properties of individual PFAS compounds and various sorption mechanisms. This study investigates the influence of different sorption isotherms on model predictions of PFAS transport in CAC-treated soil columns, with a focus on both equilibrium and kinetic sorption processes. A one-dimensional numerical model, developed using MODFLOW and MT3DMS, simulates a column experiment to assess PFAS transport dynamics and compare model predictions to experimental observations. The results indicate that accounting for non-equilibrium sorption processes is needed to match the observed asymmetric breakthrough curves and pronounced tailing of PFAS in the leaching experiments. This suggests that kinetic sorption plays a significant role for PFAS transport in CAC-amended soil and highlights the importance of considering kinetic sorption in the modelling and remediation of PFAS contamination in soils.