SIMULATION AND EXPERIMENTAL STUDY ON SOLUTE TRANSPORT IN SOIL COLUMNS

Abstract

In this work, an attempt is made to investigate the solute transport behavior through mobile immobile region created in the soil column experiment under steady water flow condition. For this, immobile and mobile domains have been created with clay (immobile) and fine sand (mobile) for analyzing the behavior of solute transport through it. Both Chloride and Fluoride are used as conservative and reactive tracer respectively. Continuous flow type boundary condition is used during experiment. It is also known that mobile-immobile model divides the liquid phase of the porous medium into mobile and immobile domains. It is assumed that advective dispersive transport equation is used for mobile domain, and solute exchange between two liquid domains is described as a first-order process. However, present experimental setup behaves as preferential flow, it means advection is only allowed in the fine sand (mobile) and advection is zero in the clay (immobile). It is assumed that first order mass transfer coefficient is considered for accounting the transfer of solute mass from mobile to immobile region. Afterwards, numerical model is developed for mobile-immobile advective dispersion transport equation including equilibrium sorption and first order degradation. Present numerical model has been used to simulate observed experimental data of chloride and fluoride through heterogeneous soil column using constant dispersion, linear and exponential distance dependent dispersion models. It has been found that exponential distance dependent dispersion model simulates better as compared to constant dispersion and Linear distance dependent dispersion model. iii