An interpretative model is proposed for a series of percolation tests conducted on glauconitic sand columns. Colloidal 241Am leached from a simulated vitrified waste was used as the migrating radioisotope. The polydispersed nature of the 241 Am colloids was demonstrated, together with a sorption saturation mechanism, which was interpreted with a Langmuir isotherm. The model equations include convection, filtration, and sorption of the polydispersed colloid in solution. Good agreement was found between model and experimental results.