Theoretical Study and Experimental Validation of Transport Coefficients for Hydrocarbon Pollutants in Aquifers

Recent work has been done in order to better understand the transport of hydrocarbons in the saturated zone. Phenomenological correlarions were proposed for the mass transfer coefficient. Unfortunately there is little agreement between those correlations as the mass transfer coefficient varies over several orders of magnitude. In this paper, a new method is proposed to estimate this transport coefficient in a binary system. Dissolution and transport experiments of trapped residual non aqueous phase liquids (NAPLs) in water saturated homogeneous porous media were carried in a laboratory column. Saturation fields were measured by the gamma ray attenuation technique and pollutant concentration was measured by gas chromatography. A macroscopic model based on the averaged pore-scale mass balance equations was used to simulate experiments. The model takes into account convection, dispersion and interfacial mass transfer. The mass transfer coefficient was calculated in pore-scale periodic unit cells containing the solid phase, an immobile phase (NAPL), and a flowing phase (water) by the means of averaging theory results. Confrontation of experimental and numerical results shows that the model predicts well the total dissolution time and the shape of the dissolution front. An estimate of the mass transfer coefficient, and the construction of a representative (of the geometry of trapped NAPL blobs) unit cell are therefore possible.