This paper presents an experimental and numerical investigation of the electrokinetic propagation of acid or base fronts through clayey soil. The experimental study included measuring the electric current, the mass of water extracted, and the advance of the acid and base fronts in synthetic sediment composed of 25% kaolinite and 75% silt. The results show that the flux rate remains constant over time and that the medium acidifies with time. The numerical model is based on the transport equations and, by considering adsorption and auto-ionization of water, it describes the temporal evolution of pH in the specimen. The experimental evaluation of the adsorption isotherms allows us to calculate the retardation factor, which is 69 and 19.5 for the hydronium and hydroxyl ions, respectively. Given these retardation factors, the results of the numerical model are consistent with experimental results and show how the acid and base fronts evolve in a saturated porous medium. Numerical model results show that electromigration is the major contributor to the migration of ions in the porous medium during electrokinetic treatment.