Contaminant transport through the heterogeneous GCL/SL composite liner: Experimental and analytical studies

Abstract

This paper proposes an analytical solution of two-dimensional mobile-immobile model (MIM) for contaminant transport through a composite liner including a geosynthetic clay liner (GCL) and a soil liner (SL). The effects of the soil heterogeneity and non-uniform contaminant distribution in the leachate on contaminant transport are taken into consideration. A cylindrical tank experiment and a numerical approach are conducted to verify the accuracy of the solution. The effects of the contaminant source distribution, flow conditions, composite liner properties and mass exchange on contaminant transport are illustrated. The results show that the mass exchange between the mobile and immobile regions and the contaminant distribution can significantly influence the contaminant transport in the composite liner. Additionally, the performance of the composite liner can be improved with the decrease of the volumetric water content of mobile region (θ_m) when θ_m ≤ 0.3. This is mainly because the contaminant transport will be slowed down as the hydraulic conductivity of the SL decreases with the decrease of the θ_m. Moreover, the variations of θ_m and standard deviation of contaminant distribution pose the relatively more significant effect on the contaminant transport compared with other parameters in the early time (t < 13.5 years) and later time (t > 15 years), respectively. The proposed analytical solution can provide a more accurate prediction for the performance of the composite liner and offer advice for the design of the landfill barrier system.