By infiltration of water-insoluble substances NAPL (Non-Aqueous Phase Liquid) in an aquifer a multiphase flow system is formed.

The spreading of a NAPL as a cohesive phase in the aquifer, with characteristics different from the surrounding water, cannot be described physically by a conventional one-phase transport model.

In order to assess distribution and spreading of such substances in soil as well as the effect of decontamination procedures, modelling with a multiphase flow model is required.