A novel two-dimensional model for colloid transport in physically and geochemically heterogeneous porous media

A two-dimensional model for colloid transport in geochemically and physical ly heterogeneous porous media is presented. The model considers patchwise g eochemical heterogeneity, which is suitable to describe the chemical variab ility of many surficial aquifers with ferric oxyhydroxide-coated porous mat rix, as well as spatial variability of hydraulic conductivity, which result s in heterogeneous flow field. The model is comprised of a transient fluid flow equation, a transient colloid transport equation, and an equation for the dynamics of colloid deposition and release. Numerical simulations were carried out with the model to investigate the colloid transport behavior in layered and randomly heterogeneous porous media. Results demonstrate that physical and geochemical heterogeneities markedly affect the colloid transp ort behavior. Layered physical or geochemical heterogeneity can result in d istinct preferential flow paths of colloidal particles. Furthermore, the co mbined effect of layered physical and geochemical heterogeneity may result in enhanced or reduced preferential flow of colloids. Random distribution o f physical heterogeneity (hydraulic conductivity) results in a random flow field and an irregularly distributed colloid concentration profile in the p orous medium. Contrary to random physical heterogeneity, the effect of rand om patchwise geochemical heterogeneity on colloid transport behavior is not significant. It is mostly the mean value of geochemical heterogeneity rath er than its distribution that governs the colloid transport behavior. (C) 2 001 Elsevier Science B.V. All rights reserved.