Polymer injection for soil and groundwater remediation: Mechanisms, applications, and lessons learned

This review examines the use of polymer solutions for in-situ subsurface remediation, with a focus on their rheological behavior and implications for contaminant removal. The in-situ remediation of subsurface contamination is often constrained by aquifer heterogeneity, preferential flow, and limited reagent contact with trapped contaminants. Polymer solutions, particularly shear-thinning biopolymers such as xanthan gum (XG), have emerged as promising tools to overcome these challenges. Originally adapted from enhanced oil recovery applications, their unique rheological properties allow high injectivity near the well while promoting mobility control farther into the formation. This enables more stable displacement fronts, suppression of viscous fingering, and enhanced crossflow into low-permeability zones, thereby improving Non-Aqueous Phase Liquids (NAPLs) recovery while also enhancing contaminant removal and amendment delivery in low-permeability regions of heterogeneous media. Beyond direct displacement, polymers may act as carriers for a wide range of remedial amendments, including oxidants, reducers, electron donors, surfactants, and nanoparticles, improving their placement, persistence, and effectiveness. Yield-stress and densified formulations further expand applications by blocking preferential pathways or counteracting buoyancy forces in gravity-dominated systems. Field demonstrations confirm these benefits: Polymer-amended oxidants and electron donors have produced larger swept volumes, more homogeneous propagation, and longer remanence than water-based solutions, with electrical resistivity tomography and coring providing direct evidence of improved distribution and contact. Industrial-scale applications have also shown that formulation and injectivity must be carefully balanced to avoid excessive pressures, fracturing, or reagent incompatibility. Continued integration of laboratory rheology, numerical models, and field validation will be essential to fully realize polymers as multifunctional technologies for contaminant displacement, amendment delivery, and unwanted flow blocking. With growing field evidence, polymer solutions are poised to become central to the design of predictable, durable, and site-specific remediation strategies.