Stratified migration and distribution of the constituents of coal tar in the stratum

Abstract

Coal tar (CT) is widely used in the rubber industry to produce a reinforcing substance known as carbon black. Due to the complexity constituents of CT, the migratory dynamics of its constituents have not been characterized, resulting in contamination of soil and groundwater. To understand the migration and distribution characteristics of different nature components of CT in the study site, the distribution and migration patterns of total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs), and Dense Non-Aqueous Phase Liquids (DNAPLs, ρ≫1 g/cm³) in soil and groundwater in a rubber enterprise were characterized and analyzed. We found that: the different components in CT settle at different points in the soil as they migrate, exhibiting stratification. Specifically, TPHs in soil and groundwater are mainly concentrated in the shallow layer near the tank area, and the maximum concentration is 113,000 mg/kg; PAHs are more migratory than TPHs, and the maximum concentration of PAHs is 7408 mg/kg. Most PAHs are concentrated in the middle layer and above; DNAPLs tend to be transported to deeper stratum, penetrating deeper into the terrain and aggregating into pools (depth＞13 m). In addition, the inherently slow flow of groundwater slower groundwater flow does not significantly impact the further migration of pooled DNAPLs, but it does influence the orientation of their pollution plume. This study provides a more accurate characterization of the dynamics of pollutants associated with rubber enterprises; these results bring forth a theoretical basis for the remediation and management of pollution linked with CT.