Remediation of per- and poly-fluorinated substance (PFAS) groundwater plumes can be particularly challenging because of the unique chemical, transport, and toxicological properties of PFAS. Sorbent permeable reactive barriers (PRBs) are an emerging technology, but as commonly implemented, have several limitations, such as 1) the relatively low adsorption capacity provided by currently available and commonly used adsorbents like granulated activated carbon (GAC), and 2) the non-destructive nature of the removal by PRB with sorption and the potential for breakthrough and release of sorbed PFAS. To overcome these limitations, this project will integrate two existing technologies to develop a novel, synergistic, flexible, robust, and renewable in situ treatment system for PFAS groundwater plumes: engineered nanoscale sorbents combined with an in situ vessel PRB (ISV-PRB).

The ISV-PRB combines two key elements: 1) a novel sorbent designed for PFAS removal, “NanoSPEI”, and 2) a classic in situ treatment technology, funnel-and-gate. NanoSPEI is a type of engineered nanoscale composite material consisting of nanoscale iron oxides (Fe₃O₄, 10-30 nm) as the functional core, which supports various polyethyleneimine (PEI) coatings, and have been developed under SERDP Project ER-2714. This class of sorbent is now ready for field-scale testing. The NanoSPEI sorbent has exhibited PFAS sorption capacity two orders of magnitude higher than GAC. The classic funnel-and-gate design will be reimaged and adapted to the removal of PFAS in groundwater by the replaceable NanoSPEI.

As illustrated, the ISV-PRB consists of a permeable trench to collect impacted groundwater, an in situ “reactive vessel” (or vessels) containing the sorbent, and a downgradient redistribution trench to discharge treated groundwater. For some sites, an in between optional vertical barrier wall (e.g., slurry wall) can increase performance and reliability. Similar PRB designs have been used extensively in Europe, and at least one site in the U.S. (the Marzone Superfund Site in Georgia). The Marzone PRB, which uses GAC as the sorbent, has been operated successfully since 1998.

Diagram of the in situ vessel permeable reactive barrier (ISV-PRB)

With the successful demonstration of NanoSPEI sorbents combined with ISV-PRB, this project will demonstrate a powerful, reliable, and also sustainable new technology to control PFAS plumes and remove PFAS from the subsurface. More importantly, the technology has the potential to expand the number of viable PFAS plume control options beyond pump-and-treat and particulate injection that only sequesters PFAS in the subsurface. Successfull completion of this project will ultimately fortify the Department of Defense's operational capabilities and secure warfighter preparedness. (Anticipated Project Completion - 2027)