PFAS MIGRATION IN UNSATURATED ZONE AT A LANDFILL AND A FIREFIGHTING FACILITY

In recent years excessive exposure to toxic micro-pollutants show long-term health effects of which per and polyfluoroalkyl substances (PFAS) are a group of emerging organic contaminants with significant chemical stability and low degradability. Understanding the transport mechanism of PFAS from the surface to the aquifer is of utmost importance in order to protect the groundwater and related surface water bodies from pollution. In this study, we present PFAS presence in the unsaturated zone of two typical sources: (1) landfill and (2) zones exposed to PFAS containing fire-fighting chemicals. A Vadose zone Monitoring System (VMS) which enables continuous tracking of water flow and solute transport in the unsaturated zone was installed in representing sites: (a) municipal landfill (Rishon Letzion, Israel) and (b) fire-fighting training facility (Korsor, Denmark). Water samples obtained from multiple depths across the unsaturated zone along with real-time variations in the profile moisture enable tracking of PFAS transport and transformation across the unsaturated zone, from land surface to the aquifer.

PFAS distribution profile from pore water samples in the unsaturated zone at the landfill shows high concentrations of long chain PFAS (PFOA) in the waste layers and higher occurrences of short chain PFAS (PFBA) in the underlying sandy unsaturated zone. PFBA release into the sand layers beneath the waste body reflects preferential release and transport of short chain PFAS which is hydrophilic and mobile. Moreover, PFBA is often a breakdown product of long chain PFOA accounting for its higher presence at deeper depths. The unsaturated zone under the firefighting training site, composed of laminated meltwater sand/clay sandy till, exhibits elevated concentrations of PFAS across the entire profile from the land surface to the water table. In general, short chain PFAS like PFBA, PFBS and PFPeA are found in higher concentrations while the longer chains like PFOA and PFHxA are present in much lower concentrations. A relatively higher concentration of all compounds was found in the fine sand layers. Time series of variations in PFAS concentration across the unsaturated zone with respect to the infiltration as reflected from variation in the profile water content enables tracking of the migration pattern and potential groundwater pollution from the unsaturated zone.