The overall objective of this project is to reduce the flux of per- and polyfluoroalkyl substances (PFAS) from an aqueous film forming foam (AFFF)-impacted Department of Defense (DoD) installation to an adjacent surface water by deploying a permeable absorptive barrier (PAB) in the saturated zone of the subsurface near the boundary with the lake. Specific tasks include:
- 1-Dimension (D) column and 2-D aquifer cell test to optimize delivery and dosage,
- initial site monitoring and conceptual site model development, and
- design, construction, and performance monitoring of the PAB.
The research team has developed a method for the in situ sequestration of PFAS in groundwater by introducing material that dramatically increases the sorption of PFAS. Specifically, polydiallyldimethylamine chloride (polyDADMAC), a drinking water coagulant, has been identified as an excellent sorption enhancer for the six PFAS on the Unregulated Contaminant Monitoring Rule 3 (UCMR3) list. Furthermore, the addition of powdered activated carbon (PAC) greatly increases the retention of PFAS in sandy soil. PFAS form complexes with the polyDADMAC that associate with the solid matrix when sufficient organic carbon and clay material are present in the soil. These complexes and their adsorption appears to be irreversible and resistant to microbial degradation. In the laboratory, polyDADMAC addition to columns of soil from a PFAS impacted facility increased the retention of PFAS 5 to 20-fold. For soils with low organic carbon and clay content, PAC can be added to serve as a strong sorbent for PFAS. The polyDADMAC is an aqueous solution, and therefore can be directly injected into a groundwater system. For PAC, a slurry of polyDADMAC and PAC has been shown to remain in suspension despite centrifugation at high speed, allowing the suspension to be injected into and uniformly deposited in the subsurface. When testing the method on Ottawa sand in the laboratory, the polyDADMAC/PAC was shown to create a retentive barrier that required approximately 4100 pore volumes of PFAS at 100 micrograms per liter (µg/L) prior to expected breakthrough.
Current technology for treating groundwater impacted with PFAS from AFFF use, spills and leakage is to either excavate or pump and treat the water. The research team anticipate this new method to be lower cost in terms of installation, to require less person-hours to operate, and to be a system where it is not necessary to dispose of a waste product. The team's primary performance objective of remediation effectiveness will be at least an 80% reduction in mass flux of PFAS leaving the treated plume for the first year of deployment of the PAB.