Assessment of Consolidation-Induced Contaminant Transport for Compacted Clay Liner Systems

Abstract

This paper presents an investigation of the effect of clay consolidation on contaminant transport through compacted clay liner (CCL) and composite geomembrane liner (GML)/CCL landfill bottom liner systems. Numerical simulations were conducted using the CST2 model and consider coupled consolidation and contaminant transport with representative geometry, material properties, and applied stress conditions. Simulation results indicate that, depending on conditions, consolidation can have important effects on contaminant breakthrough time, mass flux, cumulative mass outflow, and concentration distribution within the CCL, not only during the course of the consolidation process but also long after consolidation has completed. In general, the effects of CCL consolidation increase with increasing CCL thickness, increasing magnitude of applied stress, decreasing loading time, increasing CCL organic carbon fraction, and increasing variation of effective diffusion coefficient. Traditional advective-dispersive transport analyses fail to consider transient advection and associated changes in material properties caused by CCL consolidation, and thus can lead to significantly different results. Considering the complexity of the process and the number of variables involved, case-specific analysis is recommended for the evaluation of the significance of CCL consolidation for contaminant transport through a CCL-based liner system.