Improved model for solute transport in heterogeneous porous media

An improved model for solute transport through heterogeneous porous media, considering physical non-equilibrium and convection domination, is presented. Conventional phenomenological conceptualizations, such as the dual-porosity and capacitance models, envision the molecular diffusion as the significant mechanism in mass transfer between the stagnant liquid present in the matrix or micropores and the flowing fraction in the fractures or macropores. Because it can accurately predict the experimentally observed tailing, the new model has an advantage over the existing models by taking into account the contributions of spatial velocity variations through different scales. Consequently, it is shown that tailing is a result of the permeability contrast existing between the interacting micro- and macropore media; and the convection in low-permeability zones controls the delay in the total breakthrough. The incorporation of the matrix convection results in a system of coupled, higher-order differential equations which is solved analytically. In addition to offering an adequate description of the experimental data obtained during the investigation of the behavior of heterogeneous porous media, the new conceptualization appears to provide a more realistic insight into the physical process.