Abstract
Spatially variable refuse gas permeability and landfill gas (LFG) generation rate, cracking of the soil cover, and reduced refuse gas permeability because of liquid addition can all affect CH 4 collection efficiency when intermediate landfill covers are installed. A new gas collection system that includes a near-surface high permeability layer beneath the landfill cover was evaluated for enhancing capture of LFG and mitigating CH 4 emissions. Simulations of gas transport in two-dimensional domains demonstrated that the permeable layer reduces CH 4 emissions up to a factor of 2 for particular spatially variable gas permeability fields. When individual macrocracks formed in the cover soil and the permeable layer was absent, CH 4 emissions increased to as much as 24% of the total CH 4 generated, double the emissions when the permeable layer was installed. CH 4 oxidation in the cover soil was also much more uniform when the permeable layer was present: local percentages of CH 4 oxidized varied between 94% and 100% across the soil cover with the permeable layer, but ranged from 10% to 100% without this layer for some test cases. However, the permeable layer had a minor effect on CH 4 emissions and CH 4 oxidation in the cover soil when the ratio of the gas permeability of the cover soil to the mean refuse gas permeability ⩽0.05. The modeling approach employed in this study may be used to assess the utility of other LFG collection systems and management practices.
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