Abstract
Per- and Polyfluoroalkyl substances (PFAS) are a category of synthetic chemicals that possess surfactant properties desirable across many industries. The use of these compounds has been integrated into products worldwide and human contact with them is almost unavoidable. Until relatively recent years, the health repercussions these chemicals can have on humans were unknown. Because of the health risks associated with PFAS, they have become a topic of study and their transport mechanisms and pathways needed to be widely analyzed. Particularly, in groundwater, the implementation of 3D modeling has been used in order to assess the factors that influence sorption and transport of these chemicals.
The research and simulation created in this thesis project aim to replicate site-specific aquifer properties in order to assess the movement of PFAS through an aquifer. Through the Model Muse graphical interface, MODFLOW and MT3D-USGS software was used to simulate a real-world occurrence of PFAS contamination. The town of Killingworth, Connecticut was selected for modeling due to the documentation of PFAS materials found in the area. Official state investigation, initiated by the Connecticut Department of Energy and Environmental Protection (CDEEP), reported that the detection of PFAS compounds in the town was directly correlative to historical use of Aqueous Film Forming Foams (AFFFs) due to Firefighting Training Activities (FTAs) near the Killingworth Town Hall. For the purpose of study, the described project will analyze the movement of Perfluorooctane sulfonic acid (PFOS), a derivative from the family of PFAS compounds, due to its heavy use in FTAs.
The findings of this report document a validated 3D model that simulates a contaminant plume dispersion caused by a PFOS source. Model calibration was determined through regression modeling techniques that incorporate root mean square error (RMSE) calculations between recorded data and simulated values. The objective of simulating the spread of PFOS was to determine whether the Killingworth Reservoir, located southeast of the PFAS source, was at risk of contamination. Model results predicted that there is not a threat of contamination to the body of water in future years. Research was furthered by determining the effects of increased and decreased recharge into the aquifer, simulating changes in climactic conditions on the site. It was found that increased recharge enhanced the transport of the plume. Alternatively, a lower rate of recharge into the aquifer was characterized by slower transport of PFOS concentrations. Overall, the simulated model served as a tool that predicted how changes in the hydrogeological setting would affect a PFOS concentration plume.