Visualization and simulation of non-aqueous phase liquids solubilization in pore networks

The design of in-situ remediation of contaminated soils is mostly based on a description at the macroscopic scale using averaged quantities. These cannot address issues at the pore and pore network scales. In this paper, visualization experiments and numerical simulations in pore networks are carried out to understand basic aspects of mass transfer during the solubilization of residual non-aqueous phase liquids (NAPL). The experiments are carried out in 2-D etched-glass micromodels with randomly distributed pore sizes. The evolution of the configuration of the residual phase, the pressure drop across the micromodel and the concentration of the effluent are continuously recorded under various displacement conditions. A pore network numerical model, based on the convection–diffusion equation using appropriate modifications for the local mass transfer coefficients, is developed to simulate mass transfer during the solubilization of a residual phase. The pore network simulator is found to match well the experimental results, provided that the local mass transfer coefficients are properly modeled. Under the assumption of spatially uniform local mass transfer coefficients, an asymptotic power-law scaling between the effluent concentration and the Peclet number is obtained, the exponent of which is related to the local mass transfer expression.