A Finite Difference Model for Heavy Metal Contaminant Transport in a Sand-Bentonite Cutoff Wall

Soil and groundwater contamination from landfill leakage, industrial discharges, chemical storage tanks failures, and mining activities have emerged as a growing global concern. Vertical cutoff walls are widely implemented as geoenvironmental barriers to mitigate contaminant transport. This study employs a finite difference approach to simulate the heavy metal contaminant transport through the buffer zone-cutoff wall-aquifer system. The model also accounts for the consolidation of the sand-bentonite cutoff wall, which occurs due to arching and lateral squeezing from surrounding soils. The present study investigates the effects of uniform and nonuniform contaminant distributions, inflow concentrations, soil types in buffer and aquifer zones, and the partial distribution coefficient (Kd) on the breakthrough time (tb). For the considered heavy metal contaminants (cadmium, chromium, lead, and zinc), increasing Kd enhances the tb by 1.69–2.88 times, while low-permeability soils in the buffer and aquifer zones increase the tb by 6.5–11.27 times. Conversely, higher inflow concentrations reduce the tb, ranging from 1.33 to 2.26 times. Design charts are developed to evaluate the thickness and location of the cutoff wall from the contaminant source. The proposed model serves as a valuable tool in optimizing the thickness and location of the cutoff wall by incorporating key parameters such as contaminant distribution, inflow concentration, soil type in the buffer and aquifer zones, and partial distribution coefficient of the cutoff wall.