DESICCATION OF MINERAL LINERS BELOW LANDFILLS WITH HEAT-GENERATION

In the case of landfills with heat generation, the long-term efficienc y of composite liners at the landfill base is imperiled by desiccation and subsequent cracking of the mineral liner below the geomembrane. D ownward vapor diffusion due to temperature gradients leads to desiccat ion unless it can be balanced by capillary rise. A numerical model (SU MMIT) of coupled transport of water, vapor, and heat in unsaturated po rous media was developed to assess the landfill-specific desiccation r isk of mineral liners (in terms of matric potentials). Water retention and unsaturated hydraulic conductivity of mineral liner and subsurfac e 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 simu lations for typical landfill conditions show that the drainage layer d irectly beneath the mineral liner will most probably lead to cracking.