Experimental study of gas breakthrough and emission in an unsaturated clay landfill cover

Decomposition of municipal solid waste (MSW) generates a large amount of landfill gases (LFG) which can pose a high risk to the health of nearby residents and significantly promote global warming when they are released to the atmosphere. A commonly used method to control LFG emission is to place an engineering cover with a gas collection system over MSW. LFG pressure increases in landfill covers when the efficiency of gas collection systems is low, resulting in large gas emissions from cover surface. Compacted clay has been commonly used in landfill cover systems as a hydraulic barrier. However, the effectiveness of compacted clay as a gas barrier, especially resisting gas breakthrough and reducing emission rate under controlled conditions is not fully understood. In this paper, gas breakthrough pressure and emission rate were determined through a one-dimensional (1D) column over a wide range of landfill gas pressures under various degrees of saturation, thicknesses and degrees of compaction. Experiment results show that under a gas pressure of 10 kPa, a minimum of 0.4 m thick clay layer is able to prevent gas breakthrough at degree of saturation of about 60% (in humid regions). The reduction of gas emission rate by increasing degree of compaction is most prominent in the range of intermediate degree of saturation.