Intrinsic Backflow in Heterogeneous Aquifer During Electrokinetic Remediation: A Challenge in Field‐Scale Application

Electrokinetics is a remediation technology applying direct‐current voltage across soil to mobilize solutes. It induces electromigration whereby ions migrate toward electrodes of opposite charge, and electroosmosis whereby water flow is engendered because of surface charges in soils. As confirmed by various experiments, electroosmosis has the advantage of mobilizing non‐ionic solutes especially in low permeability clay. We argue herein that due to subsurface heterogeneity, the upscaling of electroosmosis may not be always achievable under normal conditions, mainly because of backflow in regions outside of clay. In this study, analytical solutions derived in periodic heterogeneous system demonstrate how nonuniform electroosmosis induces local hydraulic‐head gradient and backflow. Application in standard lognormal heterogeneity system produces limited backflow due to smoothly varying zeta potential, whereas discrete high absolute zeta potential lenses generate more extensive backflow. These findings highlight the importance of spatial organization (or lacunarity), especially lens size, spacing, for applications of field‐scale electrokinetic remediation.