Effect of the loam inter-layer on the migration and breakthrough of benzene under constant flow in the unsaturated zone: column experiments

The reliable prediction of transport and attenuation of dissolved-phase contamination in the unsaturated zone is a complex and multi-process problem. Based on the adsorption properties of soil samples to solutes, the soil column test and laboratory analysis were carried out in this study. The effects of the loam inter-layer on the migration and breakthrough of the characteristic pollutant benzene and non-absorbent Br− were studied. The results showed that the relatively high clay content of the inter-layer significantly changed the BTC (breakthrough curve). It not only delayed the migration time of benzene into the aquifer but also to some extent produced an attenuation effect, effectively reducing the content of the characteristic pollutants through the unsaturated zone. The dispersion coefficient was obtained through the measured Br−. The theoretical values were calculated and compared with the experimental data by using a one-dimensional unsaturated solute transport equation. The result was basically consistent, which proved the validity and reliability of the model. Through the BTC of benzene, the retardation factor was obtained and used to describe the influence of the loam inter-layer on the migration and breakthrough, which could provide the basis for the accurate modeling of groundwater remediation projects.