Steady-state analytical model for vapour-phase volatile organic compound (VOC) diffusion in layered landfill composite cover systems

Abstract

An analytical model for the diffusion of one-dimensional vapour-phase volatile organic compounds (VOCs) through a four-layer landfill composite cover system consisting of a protective layer, drainage layer, geomembrane (GMB), and compacted clay liner (CCL) is developed. Effects of degree of water saturation (Sr), adsorption, and degradation on vapour-phase VOC diffusion in a cover system are then analyzed. The vapour-phase benzene concentration profile increases with increase of Sr in the drainage and protective layers. When Sr1 = Sr2 = 0.5 (where Sr1 and Sr2 are degree of water saturation of the protective and drainage layers, respectively), surface flux for the case with the degree of water saturation of the CCL layer Sr4 = 0.3 is 1.3 and 1560 times larger than that with Sr4 = 0.7 and = 0.9, respectively. The effect of adsorption of the VOCs in the CCL on performance of the cover system is more important than that in the drainage and protective layers. Surface flux and concentration of benzene tends to be zero when CCL is amended with 0.5% biochar due to an increase of the retardation factor. The effect of degradation rate on benzene concentration increases with increase of degree of water saturation. The influence of half-life of VOCs in the soil layer, t1/2, on vapour-phase VOC concentration can be neglected when Sr ≤ 0.3.