The environmental impact of PFAS (Per- and Polyfluoroalkyl substances) is highly concerned because of their toxicity and persistence incurring in aquifer system. Significant attention is now being focused on PFAS behaviors in the vadose zone underneath a waste management unit. Using model to evaluate transport and fate of the contaminants leaching from the source area is specifically useful for environmental management and risk assessment of PFAS impacted subsurface system.   

In a source area, PFAS typically exist as complex chemical mixtures. Some species of PFAS, like Perfluorooctanoate (PFOA) and Perfluorooctanesulfonate (PFOS) are typical surfactants, which may be dissolved in groundwater and significantly alter the interfacial characteristics of air-water and mobility of the subsurface fluids. While some may appear as NAPL (Non-Aqueous Phase Liquid) under the subsurface conditions, like FTOH (Fluorotelomer alcohols), which behaves a separate phase causing more complex multi-phase flow processes. Contaminants breakthough retardation in the vadose zone can occur because of a combination of retention mechanisms, including non-equilibrium/non-linear adsorption onto the soil surface and the interface of fluid phases. In addition, the alteration of the interface characteristics also influences the mobility of air, water and NAPLs. At many groundwater sites that are associated with the PFAS source zone, remediation is driven by the ability to adequately characterize complex subsurface processes.

The work is to develop numerical model to simulate the fate and transport of PFAS mixtures (involving long-chain and short-chain PFAS) in subsurface formations. The numerical model will consider multi-phase and multi-component processes in the saturated/saturated aquifer system. The numerical modeling will focus on four primary aspects: 1) flow and transport for gas/water/NAPLs system; 2) Gibbs adsorption isotherm; 3) physical/chemical status of PFAS mixtures, 3) validation of the numerical model.  The innovative numerical model may provide site managers with a tool for characterizing the fate and transport of PFAS mixtures, revealing the spatial and temporal features of the PFAS contaminants in the vadose zone/water table aquifer system.