In situ remediation of groundwater impacted with per- and polyfluoroalkyl substances (PFAS) is particularly challenging due to the recalcitrant nature of these compounds and the need to achieve drinking water target levels at low concentrations (ng/L). As part of a previous SERDP project, the project team developed a novel suspension of ground, stabilized ion exchange resin (IXR) that can be directly injected into porous media to form adsorptive barriers to remove PFAS from groundwater. The stable suspension is prepared with a water soluble, low toxicity surfactant (Pluronic® F-127) and a commercially available IXR (Amberlite® IRA 910) that exhibits favorable adsorption for a range of PFAS. Previous experiments demonstrated the uniform distribution of S-IXR in quartz sand columns, with removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) increasing by five orders-of-magnitude in S-IXR treated columns compared to untreated control columns. 

The overall objective of this demonstration project is to achieve reductions in the concentration and mass flux of PFAS in groundwater using an in situ permeable adsorptive barrier (PAB) created by injecting this polymer-stabilized ion exchange resin (S-IXR) through a line (i.e., transect) of wells oriented perpendicular to groundwater flow. The field demonstration will be conducted at a PFAS-impacted Department of Defense facility. The primary site is one with a shallow sandy aquifer that is well-suited for particle injection and monitoring.

Laboratory-scale column experiments and aquifer cell studies will be conducted to verify PFAS removal with site-specific materials (i.e., soil and groundwater), to evaluate the potential for in situ regeneration of the resin and assess long-term performance. The treatability tests will serve to provide the design parameters of the field-scale demonstration with the S-IXR PAB (e.g., well spacing, injection volume). Performance of the PAB will be assessed based on measured concentrations of PFAS in soil and groundwater samples collected up-gradient and down-gradient from the PAB before and after installation. Additionally, the flow field will be monitored during operations to assess the potential for flow by-passing to occur. Criteria for success include (a) a 90% reduction in PFAS concentrations and (b) concentrations below 70 ng/L (ppt) for PFOA + PFOS in the treated zone.

There are currently no technologies available that can achieve complete PFAS destruction during in situ treatment, and therefore, most remediation approaches rely on groundwater extraction and ex situ treatment (i.e., pump and treat). Although colloidal activated carbons (CACs) are commercially available and have undergone limited field testing, the project team anticipates that the S-IXR will provide lower cost per mass of PFAS adsorbed than CAC, allow for treatment of groundwater to lower concentrations than either CAC or S-PAC, and exhibit improved performance for shorter chain length PFAS. Additionally, injectable resins offer better potential for in situ regeneration. (Anticipated Project Completion - 2026)