Numerical Analysis of Vertical Migration of Dense Nonaqueous-phase Liquids in Saturated Clay

Abstract:

An analytical module based on the COMSOL Multiphysics software was developed to consider the effects of two-phase flow and convective dispersion. Using chlorobenzen as the material and choosing typical parameter values, the numerical analysis of vertical migration of DNAPL in homogeneous saturated clay was conducted. The convective diffusion analysis shows that the migration speed of the dissolved DNAPL by molecular diffusion is very slow，only about several centimeter per year. The DNAPL - water two-phase flow coupled convective diffusion analysis indicates that for saturated cohesive soil with a larger permeability coefficient (k=1×10-6 cm?s-1), The DNAPL migration velocity caused by the two-phase flow is large, about tens of centimeters per year. The dissolution of liquid DNAPL leads to the concentration of dissolved DNAPL in pore-liquid quickly and achieves solubility. These results suggest that two - phase flow is likely to be the main mechanism for the deep migration of DNAPL in saturated clay observed in some sites.