Foams for enhanced remediation of NAPL-contaminated soils and aquifers: A review of foam formation, stability, and environmental applications

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Foam-assisted remediation is a versatile approach to improving the cleanup of NAPL-contaminated soils and aquifers by blocking highly permeable pathways, enhancing contaminant displacement, and delivering remediation amendments. Optimizing foam application requires an understanding of its physicochemical characteristics and behavior under subsurface conditions. This review synthesizes current knowledge on foam stability in bulk, behavior in porous media, and remediation applications. First, foam formulations in bulk are considered, including their physicochemical properties and the influence of experimental conditions on foam stability. Second, foam behavior in porous media is discussed, with an emphasis on hydrodynamic parameters affecting generation and propagation. Finally, applications are evaluated in the context of foam function: blocking, displacement, and delivery. While early research focused primarily on blocking and contaminant displacement, increasing attention has been given to the use of foam as a delivery medium for oxidants, reductants, nutrients, and microorganisms that enhance NAPL degradation. Recent advances and remaining challenges have been identified. This includes formulation optimization, formulation-amendment compatibility, operational windows for foam propagation, and the need to define foam function depending on the remediation method intended to assist. This review aims to support future developments in foam-assisted remediation by linking formulation design, porous media behavior, and treatment objectives.