Modelling of contaminant transport in heterogeneous vertical barrier

Vertical barrier technique is an ideal candidate for site contamination control. In practical application, the characteristic of vertical cut-off wall is heterogeneous with permeability decreases with depth due to the increasing geostatic stress. In this study, a numerical model was established considering the coupling effect of groundwater flow and contaminant transport considering depth dependent permeability. The results showed that a heterogeneous barrier with variable permeability can reduce the breakthrough time by 63.7% compared to a fixed permeability barrier. The contaminant concentration inside the wall was up to 10 times higher than outside. Shallow leakage occurs where the horizontal migration is dominated by advection. The distribution of pore-water pressure in the system after the installation of high-density polyethylene (HDPE) membranes significantly reduced the shallow convective effect by reducing up to 90% pore-water pressure. Reinforcing the vertical barrier wall using HDPE membrane can effectively prevent the shallow leakage caused by the heterogeneity.

Automated summary

The vertical barrier technique is an ideal option for controlling site contamination. A numerical model was used to investigate the groundwater flow and contaminant transport coupling effect in a vertical cut-off wall with depth-dependent permeability. The results showed that a variable permeability barrier can significantly reduce breakthrough time compared to a fixed permeability barrier. The presence of the barrier increased the contaminant concentration inside the wall and shallow leakage occurred where horizontal migration was dominated by advection. Installing high-density polyethylene (HDPE) membranes reduced the shallow convective effect by up to 90% due to a decrease in pore-water pressure. Reinforcing the vertical barrier with HDPE membranes effectively prevents shallow leakage caused by heterogeneity.