Analysis of groundwater pollution characteristics and pollutant migration law of a decommissioned chemical plant site in Southwest China

Taking a decommissioned chemical site as the research object, in view of the organically polluted groundwater aquifer in it, the groundwater pollution characteristics were investigated. The risk assessment model and DRASTIC model were applied to evaluate the human health risk and groundwater vulnerability in the study area, respectively, and the groundwater migration and diffusion model of typical pollutants was constructed to further analyze the influencing factors and dynamic modes of the migration and diffusion of typical pollutants. The results showed that the groundwater in the study area was polluted by 1,2-dichloroethane, benzene and trichloromethane. The total carcinogenic risk of 1,2-dichloroethane was 4.00×10⁻⁶, exceeding the acceptable level of human health risk, which was mainly caused by inhaling gaseous pollutants from groundwater in indoor air. The groundwater vulnerability index of the study area ranged from 4.912 to 5.305, which was at the medium vulnerability level as a whole. The groundwater system had a strong ability to resist pollution. The groundwater depth, net recharge and aquifer thickness were the main factors affecting groundwater vulnerability. The migration and diffusion of 1,2-dichloroethane were jointly affected by the convection of groundwater, the adsorption and retardation of aqueous media, and biochemical effects. Groundwater convection was the main driving force for its migration and diffusion. Moreover, the adsorption and retardation of aqueous media and biochemical effects had significant effects on the distribution range of 1,2-dichloroethane.