The behaviour of polynuclear aromatic hydrocarbons (phenanthrene and naphthalene) in soil and in presence of two fluids, water and supercritical CO2 has been studied experimentally and modelled. Two experimental methods were used, in a closed and an open system. The porous medium was modelled by a fixed bed of porous spherical particles; the hydrodynamic regime of water through the soil columns was determined, The experimental results obtained in aqueous and supercritical CO2 suggested the presence of adsorption sites of very different accessibility, respectively, external to the particles and intra-aggregate. The adsorption/desorption process of the studied compounds in the soil was modelled by a linear isotherm and instantaneous kinetics. The transport of molecules between the adsorbed phase and the bulk fluid was represented by an external particle-fluid transfer and by intra aggregate diffusion. The possibility of the existence of condensed phases of products was taken into account. The parameters of mass transfer were determined by calculation. The parameters obtained in the aqueous medium and supercritical CO2 were compared and completed in order to simulate the behaviour of compounds in a soil-fluid system when experimental data are not easily accessible.