Impact of diffuse layer processes on contaminant forward and back diffusion in heterogeneous sandy-clayey domains

Low-permeability aquitards can significantly affect the transport, distribution, and persistence of contaminant plumes in subsurface systems. Although such low-permeability materials are often charged, key role charge-induced electrostatic processes during transport has not been extensively studied. This work presents a detailed investigation exploring coupled effects heterogeneous distribution physical, chemical properties on reactive field-scale groundwater systems including spatially distributed clay zones. We performed an extensive series numerical experiments three distinct sandy-clayey domains with different levels complexity. The flow simulations were by explicitly resolving complex velocity fields, small-scale processes, compound-specific diffusive/dispersive fluxes utilizing multi-continua based code (MMIT-Clay). In each particular domain, focusing both forward back diffusion through interfaces. results illuminate control microscopic mechanisms macroscopic mass transfer. Coulombic interactions clay's diffuse layer accelerate or retard species depending its charge. Furthermore, heterogeneity plays major storage release transport. Neglecting lead to substantial over- underestimation overall behavior, which underlines need for integrated approaches accurately describe transfer inclusions.