The overarching objective of this project was to demonstrate that in situ foam fractionation is a cost-effective, easily implemented, sophisticated solution requiring minimal infrastructure that efficiently removes per- and polyfluoroalkyl substance (PFAS) mass, reducing mass flux to groundwater, and lowering concentrations at downgradient receptors. Given the extensive laboratory testing previously conducted on this technology, the focus of the project was an in situ pilot test demonstration/validation (DEM/VAL), enhanced by a limited site-specific bench test, designed to identify and optimize multiple important parameters that will allow the technology to be scaled to full-scale applications. The specific technical objectives of the project were as follows: 

1. Optimize the operational parameters such as injection gas flow, pressure rates, vacuum pressure, and flow rates for the selected site. 
2. Determine the radius of influence of the wells used for fractionation. 
3. Estimate the PFAS mass removal rates from soil and groundwater. 
4. Estimate treatment cost efficiency, as measured in dollars per gram of PFAS removed and treated.

D-FAS is the commercial name given to the design approach of an in situ remediation platform technology that consists of foam fractionation, redox/geochemical manipulation, and groundwater recirculation. It is an in situ process that exploits the preference for PFAS to accumulate at air/water interfaces such as gas bubbles due to their surface-active properties. In the approach, gas bubbles are added to the base of a treatment well, and as the bubbles rise through the water column, PFAS spontaneously transfer from the dissolved phase to bubble surfaces due to their inherent partitioning properties. PFAS-laden bubbles accumulate at the top of the water column as a foam (inside the treatment well), which is then removed by a device under vacuum. The foam is condensed into a low volume, liquid concentrate which can subsequently be treated by high temperature incineration or similar methods either on- or off-site. D-FAS can remove PFAS mass in high concentration source areas and lower groundwater concentrations in downgradient areas in significantly shorter timeframes and with significant cost savings compared to conventional pump and treat approaches. This project was focused on demonstrating the effectiveness of the technology with source zone concentrations in the field and collecting engineering data to support future field applications.

The DEM/VAL met or partially met all quantitative and qualitative performance objectives. Once system optimization was complete, the system removed PFAS as designed with a minimum of on-site maintenance. The system removed 93 g of PFAS during the 15 weeks of operation and reduced perfluorooctane sulfonate and perfluorooctanoic acid in soil more than 50%. The overall mass balance assessment of the performance indicated that PFAS removal was greater than the estimate based on soil concentrations (mass in extraction tank exceeded estimated mass removal in situ) and that in situ redistribution was not the reason for the reduced soil and groundwater concentrations.

A successful implementation of the D-FAS approach is contingent upon multiple factors including the site hydrogeology, PFAS concentrations/extents, groundwater quality, site accessibility and the existing site features/operations that could impede/interfere with the treatment process. Based on the information and experience obtained from this DEM/VAL, the main cost driver to consider when evaluating implementation costs in future projects is the footprint and depth interval of the treatment zone. This is a common cost driver for most other in situ remediation technologies and is not unique to in situ foam fractionation. Given the current limitations on disposal of PFAS-containing wastes, disposal of the condensate generated from the treatment wells may be a cost driver; however, on-site treatment using emerging destructive approaches would minimize this to some degree.

Results of this demonstration bolster operational capabilities and warfighter preparedness of by mitigating the impacts of PFAS on installations. (Project Completion - 2024)