Desiccation of Mineral Liners Below Landfills with Heat Generation

Abstract

In the case of landfills with heat generation, the long-term efficiency of composite liners at the landfill base is imperiled by desiccation and subsequent cracking of the mineral liner below the geomembrane. Downward vapor diffusion due to temperature gradients leads to desiccation unless it can be balanced by capillary rise. A numerical model (SUMMIT) of coupled transport of water, vapor, and heat in unsaturated porous media was developed to assess the landfill-specific desiccation risk of mineral liners (in terms of matric potentials). Water retention and unsaturated hydraulic conductivity of mineral liner and subsurface materials were measured. Simulations of nonisothermal lab and field experiments show that nonisothermal vapor diffusion can be up to five times higher than is physically explainable. Matric potentials in the mineral liner decrease (and thus the risk of cracking increases) with decreasing unsaturated hydraulic conductivity and water capacity, and increasing air porosity and distance to ground water. Desiccation simulations for typical landfill conditions show that the drainage layer directly beneath the mineral liner will most probably lead to cracking.