Hydrodynamic behavior of a water-drainage layer below a landfill bottom

A risk analysis was performed to analyze the effect of a water-drainage layer placed in a landfill below an artificial impermeable barrier. A model based on the finite-element method (Feflow®) was implemented for the solution of the unsaturated flow and transport problem in a porous medium under unsteady-state conditions. Simulations were conducted under the same head boundary conditions for two different landfill settings, one including the water-drainage layer and the other without it. Results show that the water-drainage layer at the landfill bottom, when present, quickly reaches the saturated state under the influence of the hydraulic head within the landfill body, thus determining a greater risk of leachate spread due to accidental or structural spillage from the bottom impermeable barrier. The results confirm the validity of the provision included in the Italian regulations concerning landfills, specifically the law D.Lgs 36/2003, which forbids the adoption of water-drainage layers below landfills due to environmental protection reasons.