The overarching goal of this work is to develop an effective in situ remedial technology for removal of a wide range of per- and poly-fluoroalkyl substances (PFAS) from groundwater in impacted sand and gravel aquifers. The aims of this one-year, proof-of-concept study are: (1) to conduct bench-scale experiments that will assess the hydrodynamic, charge, transport and adhesion behavior of high-PFAS affinity cationic colloidal polymers in saturated sands, and (2) to measure their capacity for removal of PFAS from solution under simulated aquifer conditions. The injectable high-affinity polymers (IHAP) to be employed have been synthesized by the team (under separate SERDP funding) using a cross-linking approach that results in colloidal, high specific-surface-area adsorbents that exhibit a very high affinity for PFAS removal from solution. This study would provide a foundation for further detailed column and mesocosm experiments that could be supported with two additional years of SERDP support. These would be intended to, in turn, provide data needed to transition to field deployment of the technology.

The project team will provide a proof-of-concept test of the capability of the synthetic colloidal polymers to serve as injectable adsorbents in saturated sand and gravel aquifer systems impacted with PFAS. The following tasks will be conducted.

• Task 1 is to conduct a detailed characterization of polymer colloid chemistry, focusing on hydrodynamic size and surface charge properties, using dynamic and static light scattering methods.
• Task 2 will involve a series of saturated column experiments subjected to polymer colloid injection under a range of aqueous geochemical conditions (pH, ionic strength, and ionic composition) to quantify the transport and adhesion behavior of the IHAPs in quartz and Al-hydroxidecoated quartz sands.
• Task 3 involves experiments focused on quantifying the uptake of 25 PFAS species onto polymer-coated sands.
• In Task 4, the team will examine the column-scale removal of PFAS species from an impacted groundwater sample deriving from the Central Tucson PFAS Project, which is impacted by PFAS from the Davis Monthan Air Force Base.

The team has previously shown that the polymers can be synthesized as nanoparticles, and that they can control their surface charge and hydrodynamic properties by changing aqueous chemistry. The work will be conducted in collaboration with the Arizona Department of Environmental Quality and Tucson Water; both have indicated their interest in this project's in situ technology for the effective removal of PFAS from impacted Arizona groundwater.

The PFAS family of compounds are emerging as high priority groundwater chemicals of concern that are prevalent in aquifers underlying Department of Defense (DoD) facilities where aqueous film forming foams have been applied. The current common remedial approach is "pump & treat", where impacted groundwater is pumped to the surface, treated to remove PFAS, commonly by adsorption to granular activated carbon, and then discharged either back into the aquifer or to surface water. This is expensive and energy intensive. Therefore, the team seeks to address the urgent need for in situ remediation of groundwater impacted by PFAS.

In prior DoD-funded work, the team synthesized cationic polymers with hydrophobic moieties that were shown to exhibit very high affinity for PFAS sequestration. Here, the team plans to develop these polymers into a colloidal form that is suitable for injection into impacted aquifers as stable aqueous suspensions. Bench-scale testing is an essential component of technology development for eventual transition to field-scale deployment. By developing an effective method for the remediation of groundwater impacted by PFAS, this project will address a major environmental challenge faced by the DoD. (Anticipated Project Completion - 2023)