In situ gas sparging for concentration and removal of per‐ and polyfluoroalkyl substances (PFAS) from groundwater

Abstract

AbstractPer‐ and polyfluoroalkyl substances (PFAS) have unique chemical properties that require new remediation technologies or innovative applications/combinations of existing remediation technologies. Due to their surfactant properties, we propose the application of a well‐established remediation technology for volatile organic compounds, air sparging directly in aquifers (or trenches filled with porous media), that can be used to drive PFAS from the saturated zone to the top of an impacted aquifer. As shown in a small‐scale laboratory experiment, when a sparge gas is introduced in a groundwater treatment zone, PFAS will collect at the air‐groundwater interfaces and be drawn upwards by the buoyancy of the sparged gas. The sparging results in lower PFAS concentrations in the deeper portions of the sparged zone, remediating this portion of the aquifer. The sparging will also create higher PFAS concentrations and a PFAS foam/buoyant material comprised of a mixture of air, water, and PFAS that is less dense than water (and therefore buoyant in the subsurface). This buoyant material migrates to near the top of the aquifer, sometimes through channels formed by the material and/or through pressure. This migration makes it easier to remove the PFAS by skimming the low volume of groundwater containing higher concentrations of PFAS and/or by direct removal of any foam/buoyant material near the water table. This in situ concentration of PFAS in groundwater would provide the following benefits as it would: (i) reduce the volume of the contaminated plume; (ii) reduce the amount of extracted groundwater that needs to be treated; (iii) facilitate the removal of PFAS from the subsurface; and (iv) reduce PFAS‐impacted waste generation. Alternatively, the concentrated PFAS could be left in place as the retention of perfluoroalkyl acids in unsaturated soils is strong due to air/water partitioning. We propose that this process can be applied to PFAS sites where conventional air‐sparging can be re‐purposed to manage PFAS groundwater plumes.