Abstract: Composite cutoff walls are commonly used in projects aimed at preventing pollution and permeation in contaminated areas. For a composite cutoff wall made of geomembrane and soil-bentonite, a theoretical model is developed to analyze the two-dimensional transport of organic contaminants in a buffer layer-composite cutoff wall-aquifer system. This model takes into account the presence of a buffer layer and the non-uniform distribution of organic contaminant concentrations at different depths in the source zone. The model is solved using the finite difference method. Subsequently, the rationality of the proposed theoretical model is confirmed through comparison with experimental data, calculations from an existing analytical model, and simulations using COMSOL software. The study investigates the transport characteristics of an organic contaminant in a composite cutoff wall. Results show that the organic contaminant concentration in the wall is lower under the two-dimensional transport model compared to the one-dimensional model, attributed to horizontal transport slowing due to vertical diffusion. The presence of a buffer layer slows down transport in the wall, with a thicker buffer layer leading to a longer breakthrough time to and lower total transport flux at the wall exit. Increasing the geomembrane permeability coefficient from 0.5×10⁻¹² m/s to 5.0×10⁻¹² m/s reduces t_b from 172.8 years to 28.2 years. Greater cutoff wall thickness and linear adsorption coefficient enhance barrier effectiveness, allowing selection of wall thickness based on adsorption performance.

Key words: organic contaminant, composite cutoff wall, two-dimensional transport, theoretical model, buffer layer, breakthrough time