Performance Evaluation of Contaminant Transport in a Cutoff Wall with Stratified Buffer and Aquifer Zones

Vertical cutoff walls are among the most effective in situ barrier systems employed to regulate the horizontal transport of contaminants into the soil and groundwater. This study presents a two-dimensional finite-difference model to simulate contaminant transport through a cutoff wall system incorporating layered buffer and aquifer zones. The buffer and aquifer zones are each assumed to comprise three distinct soil layers, characterized by low-, medium-, and high-permeability soils. Six scenarios, representing different configurations of these layers, are analyzed to assess their influence on the cutoff wall performance. The investigation further considers the effects of uniform and nonuniform contaminant concentration distributions with depth, temporal variations, and contaminant biodegradation within the cutoff wall. The results indicate that the performance of the cutoff wall is significantly influenced by the characteristics of the layered buffer and aquifer zones, as well as the distribution and biodegradation of the contaminant. The earliest contaminant breakthrough occurs when the uppermost soil layer exhibits high permeability, resulting in breakthrough times of 63 years for uniform contaminant distribution and 76 years for nonuniform contaminant distribution. Moreover, biodegradation effects become critical for accurate performance evaluation when the contaminant half-life is less than 200 years. Overall, the proposed model provides a realistic and comprehensive framework for analyzing contaminant transport behavior in layered cutoff wall systems.