Pollution prediction for heavy metals in soil-groundwater systems at smelting sites

The spread of heavy metal contaminations originating from polluted industrial sites pose major environmental risks to surrounding areas. However, the migration of heavy metals in the subsurface is a very complex process that requires the coupling of geological, hydrological, solute transport and geochemical data to better understand and predict contaminant flow paths, plume movement in space and time. In this study, a three-dimensional (3D) variable saturated solute transport numerical model of soil-groundwater was developed to understand pollution risks in a large lead–zinc (Pb-Zn) smelting site. Using the calibrated numerical model, risk trends of heavy metal pollution were predicted, and the design and evaluation of a pollution control technology were proposed. The results showed that the risk of heavy metal spillover was extremely high. It could break through the geographical boundary of the site after 60 days and affect the downstream river on the 712th day. By using a permeable reactive barrier (PRB) based on zero-valent iron (ZVI) and bentonite, the time for the Cd pollution plume to reach the river could be effectively delayed by 225 days, and its diffusion range reduced to 10.2%. However, 31–42% of the contaminants continued to spread outwards through lateral flow pathways even with a PRB. Based on these results, a better remediation strategy for the smelting site is to first remove, passivate or solidify the existing pollution sources, and then use PRB technology to block the pollution transmission pathways. The research results have expanded the application of numerical simulation in the study of industrial pollution sites, providing guidance methods and technical support for pollution prevention and control and space utilization at polluted non-ferrous smelting sites.