Analytical solutions for organic contaminant diffusion in triple-layer composite liner system considering the effect of degradation

Abstract

This paper presents analytical solutions for predicting one-dimensional diffusion of an organic contaminant through a triple-layer composite liner system comprising a geomembrane (GM), a geosynthetic clay liner (GCL), and a compacted clay liner (CCL). We consider two different bottom boundary conditions, i.e., fixed-concentration bottom boundary and semi-infinite bottom boundary, for which the methods of separation of variables and Laplace transform, respectively, are used to obtain the analytical solutions. The proposed analytical solutions are then verified against the CST3 numerical model and an analytical solution available in the literature. Using the verified analytical solutions, a series of parametric studies is conducted to investigate the effect of several relevant parameters on contaminant transport through the GM/GCL/CCL liner system. The results indicate that the CCL thickness, the CCL distribution coefficient, and the effective diffusion coefficient of CCL have significant impact on contaminant diffusion in the GM/GCL/CCL liner system, whereas the effective diffusion coefficient of the GCL, the diffusion coefficient of the GM, and the partition coefficient of the GM have negligible effect on contaminant diffusion in the GM/GCL/CCL liner system. The analytical solutions presented herein can be used to aid the design of a triple-layer composite liner system and the verification of other numerical models.