Three-Dimensional Modeling of Contaminant Transport in Subsurface Soil Media Using UFV Approach

In this study, an upwind finite-volume (UFV) scheme was used to solve a three-dimensional contaminant transport model in order to investigate contaminant movement within a clay deposit beneath and around 10-year operation of an uncontrolled municipal solid waste (MSW) landfill site in Hamedan, Iran. Concentrations of Cl-, Na+, K+, and total organic carbon (TOC) in pore water soil samples collected up to a 5-m depth were analyzed. The governing equation describing the fate and transport of a dissolved contaminant included advection, dispersion, and diffusion processes, as well as geochemical reaction and first-order decay of chemicals. A special domain decomposition method for solving the transport equation in porous media was implemented to efficiently reduce the computational time of the simulation. The field profiles for Cl-, Na+, and K+ were compared with the simulated profiles generated using the proposed methodology. After calibration of the developed model, values for advective velocities, dispersivity, effective diffusion coefficient, and retardation factor of the ionic species for these till deposits were obtained. The results showed that after a 10-year period of operation, Cl- percolated to a depth greater than 4 m below the ground level. Advection and mechanical dispersion are the dominant transport mechanisms for shallow depths of the till.