Analytical model of contaminant advection, diffusion and degradation in capped sediments and sensitivity to flow and sediment properties

Abstract

An analytical model is developed for contaminant advection-diffusion-degradation in a contaminant containment system of multiple layers of porous media such as a clean substrate or cap placed above contaminated sediment. Typically, sediment cap is modeled as a stratified system consisting of a biologically active zone (BAZ), cap protection layer (CPL), sorbent or chemical isolation layer (CIL), and contaminated sediment layer (CS). Diffusion, advection, linear equilibrium sorption, and first-order biodegradation processes are all included in this model. The proposed analytical solution is concise and easy to implement by introducing an innovative solution methodology combining the separation of variables and the transfer matrix method. The analytical solution is verified against existing analytical and numerical solutions. A comparative analysis of the two scenarios of treating the source as a constant concentration boundary and a finite initial concentration distribution is conducted. The solutions can be used for the design of a multi-layer containment system, verification of numerical models, and evaluation of experimental data. An analytical model can easily be used to understand the effects of key model parameters and the effects of the mass transfer coefficient at the benthic boundary layer, the biodegradation in BAZ, and the absorption capacity of CIL are investigated for diffusion-dominated and advection-diffusion scenarios. Results show that advection, adsorption and biodegradation significantly affect contaminant transport while mass transfer in the benthic boundary layer is important only under some circumstances.