Pollution characteristics and vertical cutoff wall optimization at an industrial contaminated site in China

Vertical cutoff walls have been widely used in the remediation of contaminated sites. However, determining the best method for evaluating the long-term barrier performance of vertical cutoff walls presents a major difficulty in actual projects. Here, a case study is presented for a typical electroplating, medical, and chemical industrial park in China. Based on the analysis of groundwater pollution characteristics at the site, pollutants included metals (Ni, Al), ammonia nitrogen, and 1,2-dichloroethane. Finite element model simulations of Ni transport at the site showed that a vertical cutoff wall with a thickness of 60 cm and a hydraulic conductivity of 1.0 × 10^-8 cm/s could significantly attenuate pollutant transport in the horizontal direction. Compared with other methods such as reducing the hydraulic conductivity or increasing the adsorption retardation factor of the vertical cutoff wall, increasing the thickness was more effective in controlling pollutant transport at the study site. Doubling the thickness would cause the Ni leakage concentration to decrease by more than 98% and the breakthrough time to increase by more than 47 years. It is recommended that the thickness of cutoff walls be maximized to optimize their effects on pollutant transport.