Abstract: In order to understand the one-dimensional transient transport process of organic contaminants in a triple-layer composite liner composed of geomembrane (GMB), geosynthetic clay liner (GCL) and compacted clay liner (CCL) under the non-isothermal distribution condition, the factors such as advection, diffusion, mechanical dispersion, adsorption, degradation and thermal diffusion are considered, and the corresponding mathematical model is established, in which the variations of parameters such as diffusion coefficient and permeability coefficient with temperature are incorporated. The numerical solution for the proposed model is obtained by using the finite difference method. The correctness of the established model is verified by comparing the calculation results of the model with the experimental data, the calculation results of the existing analytical model and the numerical results of COMSOL software. Based on the defined breakthrough time t_b, toluene is adopted as a representative organic contaminant to analyze and discuss the influences of different factors on the transport behaviors. The results show that: (1) The non-isothermal distribution condition changes the parameters such as the permeability coefficient, the diffusion coefficient and the linear adsorption coefficient. The variations of the permeability coefficient and the diffusion coefficient accelerate the transport process, especially for the diffusion coefficient, while the variation of the linear adsorption coefficient slows down the transport rate. (2) The increase of the temperature difference ΔT between the upper and bottom of the composite liner reduces the breakthrough time t_b and increases the bottom transport flux Jb. When ΔT values are 0, 10, 20, 30 and 40 K, the corresponding tb values are 65.7, 58.5, 54.3, 52.0 and 51.2 years, respectively. (3) When the diffusion coefficient D_m,R of GMB changes from 3.0×10⁻¹⁴ m2/s to 3.0×10⁻¹³ m2/s, the effect of Dm,R on t_b is obvious. It is found that the existence of GCL has a little effect on the transport behaviors by comparing t_b in the two cases.

Key words: non-isothermal distribution condition, triple-layer composite liner, organic contaminants, transient transport, breakthrough time