Model-Based Evaluation of PFAS Transport in Colloidal Activated Carbon Permeable Reactive Barriers based on Laboratory Column Studies

Firefighting training sites constitute common hotspots for per- and polyfluoroalkyl substances (PFAS) originating form aqueous film forming foams (AFFF) in Europe and worldwide. An example is  Örnsköldsvik airport (OER) in northern Sweden,  with groundwater concentrations downstream the hotspot exceeding 100,000 ng/L. To investigate how PFAS migration from these sites can be reduced, a pilot-scale colloidal activated carbon (CAC) barrier was injected at OER within a governmental assignment to the Swedish Geotechnical Institute and Swedish Geological Survey. Two years of monitoring shows that the barrier successfully has  slowed PFAS migration,however, the long-term performance still  remains uncertain, as PFAS breakthrough under field conditions can take decades. This study focuses on numerical modelling of PFAS transport in laboratory-scale soil columns representing CAC-embedded barrier sections from the Örnsköldsvik site, aiming to predict long-term barrier performance. A one-dimensional model was developed using MODFLOW and MT3DMS to simulate PFAS transport, incorporating both equilibrium and kinetic sorption processes. Different sorption models were tested to predict CAC adsorption behaviour and model calibration against experimental breakthrough curves. The simulation will quantify adsorption and retardation for individual PFAS compounds, assessing the influence of CAC content and sorption mechanisms on transport dynamics. By linking laboratory data to predictive modelling, this study provides a robust framework for evaluating CAC barrier efficiency, optimising in situ remediation strategies, and improving predictions of long-term PFAS behaviour in contaminated soils and groundwater.