Numerical Simulation and Estimation of the Transvers Macrodispersivity Coefficient of Aqueous Phase (Miscible) Contaminants of Salt Water in a Heterogeneous and Homogeneous Porous Media

Deterioration of groundwater resources in coastal regions due to the progression of saline water in aquifers in these regions is currently one of the important issues in providing water needs in these areas. In coastal regions, saline water enters the aquifer from below in shape of wedge. Due to the difference in the density between fresh and salty water, an interface zone forms between two fluids. In order to better understanding the importance of this issue, experiments and numerical investigations of density-depended flow and transport through a tank filled with a variety of sand, are great help in achieving this. In this research, the real sand tank was simulated using SUTRA model. This simulation includes configuration, discretization, property assignment and boundary conditions determination. Finally, the transverse macro-dispersivity coefficient was estimated for different scenarios of the solute transport in this tank. The purpose of this research is to analyze of the solute dispersion, in mixing salt and fresh water, and the effect of seepage velocity, concentration of pollutant source and heterogeneity of porous media on the flow dispersivity property. In this research, after studying the effect of different boundary conditions in SUTRA model on the development of the salt water plume, simulation of the model of heterogeneous sand tank and comparing its results with laboratory model and homogeneous model were performed. As a practical result of this research, the diagram of changes in the coefficient of transverse dispersivity against the source concentration and seepage flow velocity was plotted. In numerical simulation of heterogeneous Porous media, for all concentrations, with the exception of the concentration C0= 35000, with increasing flow velocity, the values of the transverse dispersivity coefficient AT calculated by SUTRA decreased. Also AT for all seepage velocities, with the exception of seepage velocity u=4 m/day, increased with increasing source concentration. Also, the values obtained AT from the SUTRA model were more than the values of AT obtained from experiments. In numerical simulation of the homogeneous porous media, for all velocities, as the concentration source C0 increases, the transvers macro dispersivity coefficient AT increases. According to the applied results, suitable solutions can be found to improve the quality of groundwater and prevent the mixing of fresh and saltwater resources.