An analytical solution to organic contaminant diffusion through composite liners considering the effect of degradation

An analytical solution is developed to predict the performance of composite liners consisting of a geomembrane (GM) and a compacted clay liner (CCL) or a GM and a geosynthetic clay liner (GCL). Organic contaminant diffusion through the geomembrane is assumed to be a steady-state process. The degradation effect of the organic contaminants in the soil liner beneath the GM is considered. The results obtained by the proposed analytical solution are in good agreement with those obtained from the finite-layer method for both GM/CCL and GM/GCL composite liners. For a GM/CCL, the 100-year base concentration of benzene for the contaminant half-life of 10 years can be 1.1 orders of magnitude less than that assuming no degradation. As the half-life of benzene decreases from 50 years to 10 years, the 100-year base contaminant flux of GM/CCL decreases by a factor of about 3.5. The relative sensitivity of the bottom concentration of the composite liners to the half-life, diffusion coefficient of GM and the distribution coefficient of the soil liner were also investigated. The proposed analytical solutions can only be used to calculate the diffusion of organic contaminant through two-layered composite liners (e.g., a GM/CCL or a GM/GCL). The solutions are relatively simple, and can be used for preliminary design of landfill composite liners, verification of complicated numerical methods and evaluation of the experimental data.