No abstract

In the management of light non–aqueous phase liquid (LNAPL)‐contaminated ground, numerical simulation is widely used to analyze LNAPL flow in the unsaturated soil (vadose) zone. Porosity effects on the hydraulic properties of unsaturated soils are highly simplified in existing mathematical models. Some important features, such as the nonlinear relation between porosity and permeability/displacement pressure, cannot be well captured. To address this problem, a new mathematical model was developed in this study, considering porosity effects on hydraulic properties of soils, including the retention behavior and permeability function of LNAPL and water. The newly developed model was implemented in MATLAB using the finite difference method and then verified by the results of a centrifuge test. Then, parametric studies were conducted to investigate the flow of LNAPL upon an active leakage at the ground surface. Based on the computed results, the influence of several factors, such as porosity magnitude, porosity distribution, and soil layering, was revealed. In particular, an increase in the porosity leads to a significant increase in the volume of LNAPL leaked into the ground, the vertical front depth, and the area of contaminated ground. This is mainly because the porosity affects not only the intrinsic permeability but also the relative permeability because (a) the intrinsic permeability of soils is larger at a higher porosity (b) when the porosity is higher, the equilibrium water saturation at a given capillary pressure is smaller. Consequently, LNAPL can achieve a larger degree of saturation and higher relative permeability.

Ground contamination by mineral oil and hydrocarbons is a serious problem worldwide. These non-aqueous phase liquid (NAPL) represents long-term contamination sources to the soil, groundwater, and ecological environment. In the existing numerical simulation models utilized in most simulation programs, the relation between porosity and the hydraulic properties of unsaturated soils is highly simplified as nonlinear. However, the nonlinear porosity effect on soil permeability and the capillary pressures cannot be well considered in this way. In this study, a new mathematical model has been developed to incorporate porosity effects into the hydraulic properties of soils, including the retention behaviour and permeability function of NAPL and water. This model has been implemented in MATLAB using the finite difference method and verified by a centrifuge test about NAPL infiltration. Then, a series of parametric studies will be carried out to investigate the multi-phase flow under a continuously leaking NAPL source. The influence of porosity magnitude and distribution will be investigated. Special attention will be paid to the influence of porosity distribution by soil consolidation on NAPL flow, which is often ignored by the existing simulations using constant porosity values.