An analytical model for contaminant transport in cut-off wall and aquifer system

Abstract

The vertical cut-off wall is a practical means of site contamination control. It is of great importance to predict the service time of a vertical cut-off wall. Previous analytical models on simulation of a cut-off wall neglected the existence of the aquifer, which can lead to simulation errors. An analytical model was developed for contaminant transport in a vertical cut-off wall and an aquifer system. Three cases were considered – that is, advection and diffusion of contaminant towards the same direction, advection and diffusion towards the opposite direction and the pure diffusion case. The analytical solution is obtained by using Laplace transform and binomial theorem. Increasing the scale of the aquifer can extend the breakthrough time. With a fixed hydraulic gradient of 0·5, as the dispersivity of the aquifer increases from 1 to 10 m, the breakthrough time for chloride (Cl−) increased by a factor of 1·7. The breakthrough behaviour of chloride is more sensitive to the scale of the aquifer than the breakthrough behaviour of lead is. The breakthrough time of lead obtained by the single-layer model is always longer than that of the proposed model due to overestimation of retardation.