Solute transport in porous media; An experimental pore-scale study using physical micromodels

Abstract

Groundwater contamination is a worldwide problem and is predominantly caused by soluble contaminant compounds in the aqueous phase. Therefore, it is essential to understand transport of contaminants in groundwater bodies. For that reason, dispersion of solutes in saturated porous media has been the subject of many studies. However, saturated porous media lacks experimental data to provide more insight in the porosity and flow rate dependency of hydrodynamic dispersion. This study aims to research the effects of porosity and flow rate on dispersion in single-phase flow and transport in porous media. By injecting an ink solution in micromodels with varying porosity (n = 0.435, 0.494, and 0.551) and under various flowrates (Q = 0.05, 0.1, and 0.2 ml hr -1 ) solute transport was recorded real-time using an optic visualization setup. By determining the relation between the image grayscale intensity and ink concentration value in the micromodel, solute breakthrough curves (BTCs) were obtained. Next, the BTCs were analysed using the analytical solutions to obtain estimates of longitudinal dispersivity (α L ). An increase in porosity was found to decrease dispersion and therefore decrease the longitudinal dispersivity. An increase in flow rate was found to increase mixing of the solute in the saturated micromodel, leading to an increase in α L . One two-phase flow experiment was carried out, which proves that similar mechanisms can be researched under two-phase conditions with the fabricated heterogeneous porous network and visualization setup.