Ex Situ Soil Washing to Remove PFAS Adsorbed to Soils from Source Zones
Joseph Quinnan | Arcadis U.S., Inc.
The objective of this project is to demonstrate and validate soil washing as a cost-effective mass removal technology that can be applied to treat soil in source zones impacted by per- and polyfluoroalkyl substances (PFAS). Consistent with the objectives of the Defense Environmental Restoration Program, this project seeks to protect Defense’s groundwater resources by preventing the vertical migration of PFAS from soil into groundwater. Ex situ soil washing will be demonstrated at field scale by conducting a treatment trial at a suitable Department of Defense (DoD) facility using a mobile-scale soil washing plant. The technology will be validated using advanced analytical techniques, such as the Total Oxidizable Precursor (TOP) assay, and other analytical methods including the United States Environmental Protection Agency (USEPA) Method 537/DoD QSM 5.1 for the DoD target analyte list. Incorporation of lessons learned from a recent Australian soil washing trial will be critical to the success of this project and will aid in the optimization of the treatment processes to ensure that the system is capable of achieving U.S. remediation standards. Success will be measured by the mass removal efficiencies achieved for each size fraction treated, reliability and scalability of the treatment process, ability to achieve the target U.S. remediation and groundwater protection standards, and treatment cost per ton of soil. Successful demonstration of the ex situ soil washing system will enable the commercialization and application of the technology at multiple sites, provide a cost-effective alternative to destruction technologies, and facilitate the beneficial reuse of treated soils.
The technology used for this project is a closed-circuit ex situ soil washing system. Soil washing is a physico-chemical treatment process that uses physical separation and chemical desorption techniques to remove PFAS from soil. Water soluble PFAS removed from soil are transferred into the aqueous phase, where they can be readily treated using granular activated carbon (GAC) and ion-exchange resins. Treatment is highly effective for coarse grained and sandy soils. Fine soil (clay and silt) and organic fractions typically require secondary treatment following soil washing. By removing the mass of PFAS in source zones, soil washing represents a cost-effective alternative to destructive technologies and will provide DoD with a lower-risk alternative to adsorption, stabilization, and capping technologies, which do not remove PFAS from soil.
The demonstration will provide the DoD with a cost-effective soil treatment technology that can be applied to remove PFAS from soils in source zones at a lower cost than thermal treatment. This project will apply the lessons learned from the Australian trials to optimize the treatment process. Successful application of our soil washing technique will prevent the infiltration of PFAS from soil into groundwater and maximize the potential for beneficial reuse of treated materials. At an estimated treatment cost of $180 to $210/ton, soil washing is approximately 40 to 50 percent more cost-effective than thermal treatment at approximately $350/ton. Even with stabilization or thermal treatment of the fines and organics, soil washing is expected to be significantly cheaper than thermal treatment alone.