Numerical Modeling Of NAPLs Transport In Soils

Leaking of non-aqueous phase liquids (NAPLs) will result in soil and groundwater pollution, which poses a serious threat to public health and welfare, and may cause the environment damage. It is an important task to investigate the transport behavior of NAPLs.The transport mechanism of NAPLs in unsaturated soil and groundwater system is explained where the soil is assumed as a porous medium, and the concept model for NAPLs transport is establish by combining the models of multi-phase flow and contaminant transport. The NAPL transport occurs in a multi-phase system where NAPLs, air and water can flow at the same time. Also there is mass exchange between the phases, including dissolution, volatilization and adsorption, and NAPLs have different phases such as dissolved, volatized, absorbed and free phase. Dissolved and volatized NAPL will transport in the water by advection and dispersion.The transport of NAPLs in soil system is a complicated process. The transport of free NAPLs in a multi-phase system is governed by the Darcy's Law. The multi-phase flow model in porous media relating permeability coefficient ~ saturation ~ capillary pressure is summarized and mathematical models are listed. Based on the above a conceptual model is selected to characterize the transport of NAPLs in soils. The transport of dissolved and volatized NAPL can be described by advection-dispersion equations. With its mathematical representation, a numerical model is derived by transforming the mathematical model.The selected S~P model parameters such as density of NAPL, permeability of the soil, interfacial tension, residual saturation, and viscosity and of solubility of NAPL in the water are tested by numerical simulation. The transport of NAPLs is computed by the numerical software to investigate the tempo-spatial distribution of NAPLs, and the impacts of soil types, leaked NAPL volumes, leaking duration, groundwater velocity are further investigated.The simulation results from this study demonstrate that the numerical analysis is an effective method to study the transport of NAPLs in soils.