Investigating the Role of Soil in PFAS Contamination from AFFF: A Case Study of US Military Bases

Abstract:

Aqueous film forming foam (AFFF) is a class B fire suppressant foam that contains the emerging contaminants, per and polyfluoroalkyl substances (PFAS). AFFF that contain PFAS was widely used regularly on US military bases from the early 1970s up to early 2000. There is a need to better understand PFAS transport in various soils in order to develop and utilize a targeted remediation strategy. Data was gathered from site inspection military reports created by the Department of Defense (DOD) and provided by the Social Science Environmental Health Research Institute (SSEHRI). Four military bases were chosen randomly from different regions of the US to ensure a range of different soil profiles and factors. This study explored contamination trends using boring logs, soil profile models, PFAS measurements of soil and groundwater, and historical analysis available from the collected reports. There was a limitation in investigating mobility patterns so long after usage has stopped, however, PFAS long retention in the soil profiles still allowed for analysis.

Many samples followed expected trend established by Brusseau et al. (2020), with decreasing concentrations correlated with decreasing depth seen in most locations at McGhee Tyson Air National Guard Base in Tennessee (Case Study 1) for compounds other than PFOA. However, some locations showed the opposite trend with increasing concentrations at depth, such as the PFOA concentrations in Case Study 1 and at the Phoenix Air National Guard Base in Arizona (Case Study 2). There are multiple factors to rationalize the inconsistent contamination trends per depth such as the different soil profiles influencing the mobility of the PFAS in the foam through interactions between the functional groups of the PFAS molecules with the clay charges in the soil, porosity of the soil, and interactions with the groundwater table, which could create a smear zone in the lower portion of the soil profile. This exploration reveals the need for further studies that focus on the molecular scale interactions between PFAS and the soil minerals.