Characteristics and Numerical Simulation of Chromium Multiphase Transportation, Migration and Transformation in Soil–Groundwater System: A Case Study at a Smelter in Guangdong Province, China

Abstract

Chromium (Cr) migration and diffusion patterns in the soil–groundwater systems  are vital for Cr contamination risk control. We selected a typical Cr-contaminated site in Guangdong Province, China, simulated complex site conditions through a three-dimensional (3D) sandbox experiment and investigated Cr migration and transformation behavior. Our study revealed that, under joint rainfall and groundwater flow action, a complex flow field favorable to 3D migration and solute diffusion was formed. The flow field characteristics were influenced by water-table depth, which in turn affected Cr behavior in the system. Moreover, downward flow field expansion in low water-table conditions led to Cr vertical migration range expansion, which caused greater contamination in the deep soil. The migration process was accompanied by Cr(VI) reduction, and approximately 75% of the total Cr was immobilized in the soil. The reactive transport model achieved a good fit for Cr retention and morphological distribution in the solid phase, and the fitting parameters were used to predict Cr long-term transport diffusion risk. The conceptualization model long-term prediction results indicated that Cr migrated and diffused from point source pollution along the groundwater flow direction under combined rainfall and groundwater effects, and diffused downstream by 15 m during the eighth year.

Keywords: chromium, contaminated site, three-dimensional sandbox experiment, soil-groundwater system, transformation