Simulation of Final Cover Systems in Mitigating Landfill Gas Migration

Abstract

Landfill cover systems have to serve as a hydraulic barrier as well as a gas barrier. The ability of multilayered cover systems to mitigate landfill gas migration was assessed. A finite element model, SEEP/W®, was used to simulate the landfill cover system. It was found that gas advective flux through the single GCL barrier was highly dependent on the differential gas pressure across the cover system and the conditions of soils above the barrier layer. The change from wet to dry condition resulted in the increase of gas flux up to 3000 times. Gas flux variations were much lower for the case of a single CCL. The use of a geomembrane on top of a CCL or a GCL significantly increased the effectiveness of the barrier layer in mitigating gas migration, particularly in a dry climatic condition. Furthermore, the change of the cover conditions had less effect on gas flux through a composite cover system than gas flux through a single barrier cover system. For the effective control of landfill gas migration, the cover system must be maintained at the high moisture content conditions.