Simulation of the migration law of Cr(VI) in groundwater using a fully coupled numerical model

Abstract

Coupled numerical model is widely used for the investigation of heavy metal migration in groundwater. This study selected a chromium slag stacking site in Henan Province, China, and its surrounding area as the research object to investigate the effective prevention of the pollution of soil and groundwater by hexavalent chromium (Cr(VI)), a by-product of chromium salt production. To this end, a three-dimensional numerical model of the water flow and solute transport, fully coupled with convective dispersion, was constructed. The model was employed to examine the migration patterns of Cr(VI) in soil and groundwater, while considering the influence of phreatic surface fluctuations caused by rainfall infiltration and soil matrix adsorption. The simulation results demonstrated that compared to the absence of rainfall, rainfall enhanced the convection and dispersion of groundwater flow. Consequently, this promoted the migration of Cr(VI)in the groundwater of the saturated zone, resulting in a decrease in the concentration of Cr(VI)in the soil center of the vadose zone from 568 to 224 mg/kg within five years, and a decrease in the concentration of Cr(VI)in the groundwater of the saturated zone from 271 to 159 mg/kg. The investigation of soil adsorption revealed that the adsorption of the soil matrix can expand the range of variation in Cr(VI) concentration, while reducing the overall migration quantity compared to the absence of rainfall.