The use of plastic concrete barriers to prevent pollutant migration is a common technical approach. By integrating soil–water characteristic curve parameters and retardation factors obtained from experiments. This study thoroughly examines the influences of convection, dispersion, diffusion, and adsorption on pollutant transport. The impact of different permeability coefficients of plastic concrete barriers on the retardation of pollutants is evaluated. A two-dimensional simulation model integrating groundwater flow and pollutant movement was developed for a chemically contaminated site using HYDRUS-2D software. Numerical methods were applied to explore how pollutants migrate through groundwater and to evaluate how effectively the separation wall controls this movement. The results indicate that for an isolation barrier with an initial 5000 mg/L Ba2⁺ concentration, a depth of 48 m, and with a 1 m thickness, the failure criterion is based on the Ba2⁺ pollution levels outlined in the “Environmental Quality Standard for Groundwater”: With a permeability coefficient of 1 × 10−7 cm/s, the barrier fails after 4284 days (11.73 years). In contrast, with a permeability coefficient of 1 × 10–8 cm/s, the failure time increases to 53,848 days (147.53 years).