Formation Of perched leachate zones in MSW landfill

Abstract

The paper presents a 1D mathematical model for the simulation of the percolation fluxes throughout a landfill for municipal solid waste (MSW). Specifically, the model is based on mass balance equations, that enable one to simulate the formation of perched leachate zones in a landfill for MSW. The model considers the landfill divided in several layers evaluating the in and out flow throughout each layer as well as the continuous moisture distribution. The infiltration flow is evaluated by means of the Darcy’s law for an unsaturated porous medium, while the moisture distribution evaluation has been carried out on the basis of the theory of the vertically distributed unsaturated flow. The solution of the model has been obtained by means of the finite difference scheme. The model has been applied to a semi-idealized landfill located in Palermo landfill (Bellolampo). Specifically, field measurements enable us to assess a relationship between porosity variation and applied vertical strain. Such relationship has been applied in order to relate vertical strain to waste porosity. The inflow rate was simulated by considering a synthetic hyetograph whose characteristics have been assessed throughout an hydrologic study previously developed. Three cases have been considered in the model application characterized by different initial moisture contents. The model results showed a different response of the landfill in terms both of flow rates throughout the landfill and moisture profile. Indeed, the initial moisture content drastically influence not only the formation of perched leachate zones but also their extension. The model can be a useful tool in design and management optimization of landfill.