Modeling of groundwater flow and transport of pollutants caused by a difference in groundwater densities (on the example of the valley of Vulche dere creek, downstream of Eleshnitsa tailings pond)

Abstract

An attempt is made to model numerically the transport of dissolved substances caused by a difference in groundwater densities. It is supposed that initially at the surface of the aquifer a sector exists with high concentration of а pollutant (sulphates) while it is zero elsewhere in it. As a result, there is a higher water density near the surface. Due to this difference, a density driven flow arises and starts slow upwelling and downwelling movement of the water. The pollution located initially at the surface moves down and after a period of time reaches the bottom of the aquifer. Unsteady Darcy equation for creeping subsurface flow and mass transfer equation in a porous media were solved simultaneously in 2D area by the finite element method. The geometry of the area used in the calculations follows approximately the real contour of the aquifer. The aim of this study is to predict time needed for given amount of pollution coming from surface water into Quaternary aquifer to reach the lower Neogene aquifer. Plots representing the streamlines of the flow and concentration spreading for different times are shown.