| Liquids that are insoluble in water and can exist as a separate fluid phase are known as non-aqueous phase liquids (NAPLs). There are two groups of NAPLs: those that are lighter than water (LNAPLs) and those with a density greater than water (DNAPLs). Most LNAPLs are hydrocarbon fuels such as gasoline and most DNAPLs are chlorinated hydrocarbons such as TCE.; The purpose of this research is to develop a numerical model to simulate the migration of non-aqueous phase liquids in the unsaturated subsurface system. A two dimensional model has been considered to describe the flow of water, NAPL, and air in a vertical cross sectional area. Mass exchange from the NAPL to the gas phase due to volatilization and to the water phase due to dissolution are taken into account. The model is verified against available analytical and experimental results.; In this thesis, the method of support-operators has been used to formulate a discrete model of the continuum physical system. Many of the standard finite difference methods and also the finite volume method are special cases of the method of support-operators. Unlike elementary finite difference methods, the method of support-operators may be used to construct finite difference schemes on grids of arbitrary structure.; Discrete methods usually give rise to a system of algebraic equations. A fully coupled Newton-Raphson technique is chosen to handle the nonlinearity and solve the equations sequentially in an iterative fashion. The nonlinearities inherent in the governing equations are the relative permeability K = , saturation, = , and gas phase density = . The equations are coupled because in all equations more than one primary variable appear concurrently.; For each grid there are (NPHASE) unknowns, where NPHASE is the number of phases considered in the simulation. The unknowns are the hydraulic head of water, , NAPL, , and air, .; The model developed here has the following characteristics and capabilities: (1) Simulating the flow of water, NAPL and air simultaneously. Also, gas phase and/or nonaqueous phase can be absent in the simulation. (2) The gas phase may be considered as a compressible or an incompressible fluid. (3) The model may be used in a heterogeneous porous media. (4) The method of support-operators allows the model to handle irregular boundaries. The method is based on an integral formulation and conservation of variable quantities is assured. (5) Extended Van Genuchten relationships are used to define the capillary pressure-saturation and the conductivity-saturation relationships. (6) A variable time step is used to increase the efficiency of solution.; Since very few experiments containing a LNAPL flow have been published and none of them was done in a heterogeneous porous medium, a laboratory experiment was conducted to provide a better understanding of the physical behavior of multi-phase flow in the unsaturated zone and verify the model against a heterogeneous case.; Two analytical solutions for water flow and one for NAPL flow were used to compare the results of the numerical solution. Solutions were also compared with several available experimental results of NAPL movement in one and two dimensional domains and also with the results from the... |
