The influence of water percolation on flow of light non aqueous phase liquids in soil

Keywords ,: multi-phase flow, entrapment, numerical modeling, similarity solution, horizontal migration, percolation theory, relative permeability.In this thesis the physical behavior of Light Non-Aqueous Phase Liquids (LNAPL) at the capillary fringe, is studied with multiphase flow models. Phenomena like a fluctuating water table or percolation of (infiltration) water have a large impact on this behavior. Both the geometry and the mobility of the LNAPL lens are affected. These two physical phenomena mentioned imply downwards and upwards water flow through the LNAPL lens. Different techniques were used in this investigation. Numerical calculations show that fluctuations of the phreatic groundwater level result in retardation of the horizontal migration of the LNAPL lens over the groundwater level. An expression is derived which quantifies the part of the simulated time during which the LNAPL can actually flow. This expression is implemented in an existing analytical solution that describes horizontal LNAPL migration, to enable that the effect of a fluctuating water level can be calculated analytically. Laboratory experiments are performed which verify these results. The effect of water flow through an LNAPL lens also affects the mobility of LNAPL. Numerical results show that both for upwards and for downwards water invasion of a lens, the mobility of the LNAPL has increased significantly. To obtain more qualitative insight on the pore scale, percolation theory is used. Percolation theory is applied to this problem and the appropriate series of drainage and imbibition processes are calculated to simulate the water percolation. The accompanying relative permeabilities show that the mobility increases after water percolation. Qualitative insight on the pore scale shows that the LNAPL is displaced to a larger amount of pore radii which advances the mobility of the LNAPL. This observation is in agreement with the numerical results