Unsaturated contaminant transport through holed wrinkles of composite liners

The contaminant transport of chloride through a single composite liner facility comprised of a geomembrane (GMB) with holed wrinkles over a compacted clay liner (CCL) and an aquitard underlain by an aquifer is examined. A two-dimensional finite element (2D FE) model (HYDRUS-2D) was employed for simulating variably saturated contaminant transport. Parametric analyses under saturated and unsaturated conditions explored the effects of geometric parameters, including aquitard and CCL thicknesses, the number of holed wrinkles per hectare, and wrinkle spacing, on peak chloride concentrations at the aquifer’s outlet. Results showed that while CCL thickness plays an important role in controlling contaminant transport, thicker aquitards are more effective, through creating unsaturated conditions, which decreases hydraulic conductivity of the layer. Increasing holes from 1 to 5 per hectare raised peak aquifer concentrations from 10.8 mg/L to 29.4 mg/L. Closer spacing between two holed wrinkles increased aquifer contaminant levels from 16 mg/L to 30 mg/L by enhancing saturation level and hydraulic conductivity. Unsaturated conditions created by thicker aquitards showed greater sensitivity to increased flow caused by GMB failure, as peak aquifer concentrations increased from 16.2 mg/L (no GMB rupture) to 31.4 mg/L (GMB rupture at 150 years), compared to saturated conditions.