Sonolysis-Based In Situ PFAS Treatment Within an HRX Well
Craig Divine | Arcadis US Inc.
Recently, the Horizontal Reactive Media Treatment Well (HRX Well®) technology was successfully field demonstrated through ESTCP project ER-201631. In short, this project confirmed the hydraulic, contaminant treatment, and long-term mass discharge control features of the HRX Well. The HRX well concept is particularly well-suited for sites where long-term mass discharge control is a primary performance objective. Recently, Clarkson University (Clarkson) developed a compact sonolytic reactor, termed the in situ reactor technology (InSRT), specifically designed to treat per- and polyfluoroalkyl substances (PFAS) within an HRX Well. This project will demonstrate the InSRT reactor for destructive PFAS treatment within an existing HRX Well.
The HRX Well, either passively (applied in low-permeability settings) or actively (applied in higher-permeability settings via pumping), captures and focuses flow from a wide zone upgradient of a horizontal well installed parallel to groundwater flow. This captured groundwater then flows through a segment of the well where treatment occurs through contact with an emplaced granular treatment media or via some other treatment process. The treated water then flows back into the aquifer through a down-gradient screen section. By eliminating pumping groundwater to the surface for ex situ treatment, continuous operational costs are significantly reduced.
InSRT consists of a cylindrical sonolysis reactor that is specifically designed to be placed within an HRX Well. It contains a flow controller and a series of transducers to deliver ultrasound waves to PFAS-impacted groundwater passively flowing through the reactor. It is connected to an aboveground power supply and ultrasound generator via cables that run through the well casing to the surface. This design allows multiple reactors to be placed in line and the flow rate through the reactor can be controlled by incorporating a low-energy pump within the HRX Well.
This project will demonstrate InSRT for destructive PFAS treatment within an HRX Well that will be installed at Peterson Air Force Base to control mass discharge. The actual hydraulic capture, PFAS treatment efficiency, and mass discharge reduction will be measured and compared to model predicted performance. The overall technical and sustainability performance of the use of InSRT technology will be assessed and an existing user-friendly HRX Well design tool and guidance, that addresses technology applicability and limitations, anticipated performance, design and installation considerations, and lifecycle costs will be updated and further developed.
For many of the DoD’s sites, it is increasingly recognized that chemical mass flux and discharge reduction will be a primary objective of PFAS plume treatment, especially for source zones. Therefore, remedial objectives and treatment technologies focusing primarily on long-term mass discharge reduction will be increasingly favored. The HRX Well technology offers several potential technical, implementation, operation and maintenance, and cost-related advantages over conventional pump and treat approaches. It provides a reliable method for controlling contaminant migration and mass discharge that requires little long-term maintenance, can be applied in complex geological settings, reduces impact on surface operations, and/or translates to significantly reduced lifecycle costs over currently available alternatives. By incorporating in situ sonolytic reactors to destroy PFAS, pumping groundwater to the surface for ex situ treatment is eliminated and long-term operational costs and energy requirements may be significantly reduced. Furthermore, the destructive treatment process eliminates the need for disposal of PFAS-laden spent sorbent media. (Anticipated project completion: December 2023)