One-dimensional coupled model for landfill gas and water transport in layered unsaturated soil cover systems

Abstract

Cover systems are used to prevent water infiltration into a waste body. They also play an important role in controlling landfill gas transport from the waste body to the atmosphere. It is important to assess the flux of landfill gas at the surface of a cover system by considering the coupled effects of rainwater infiltration and gas transport in the cover soils. We have developed a 1D mathematical model for coupled transient gas and water transport in unsaturated cover soils. The coupled model was solved by the finite element method. Results obtained by the proposed model agreed well with experimental data. Based on the proposed solution, the influences of gas pressure, gas permeability, and the thickness of the cover soils on soil gas concentration profiles were investigated. The difference in soil gas concentration reached up to 31% as the thickness of cover increased from 1 to 2 m. Gas concentration at a depth of 0.2 m decreased by 6% as the amplitude of atmospheric gas pressure fluctuation increased from 20 to 100 Pa. The gas concentration increased by only 3% when gas permeability increased by a factor of 2 for a relatively long period of gas migration (e.g., 60 h) under the given conditions. Results suggest that both diffusion and advection should be considered when estimating gas transport in unsaturated cover soils. The numerical model can be used in the design of cover systems in relation to gas breakthrough time, breakthrough concentration, and flux.

Impact of Atmospheric Pressure Fluctuations on Nonequilibrium Transport of Volatile Organic Contaminants in the Vadose Zone: Experimental and Numerical Modeling

“…For example, the amplitude of fluctuation in CT concentration at 4.0 m was only 1.11% of the average concentration. Therefore, fluctuation of atmospheric pressure would influence the contaminant concentration in shallow aquifers more significantly, which is consistent with previous studies (Auer et al, 1996;Guan et al, 2016)…”

Discussão sobre abordagens de previsão de transporte, emissão e oxidação de metano em coberturas de aterros sanitários

“…Primeiramente, os trabalhos realizados com uma abordagem numérica possuem relações constitutivas da parcela advectiva (Tabela 3) dada somente pela Lei de Darcy (Metcalfe e Farquhar, 1987;El-Fadel et al, 1989;Binning et al, 2007;Guan et al, 2016;Bian et al, 2018) ou a Lei de Darcy em paralelo com a de permeabilidade relativa (Molins e Mayer, 2007;Molins et al, 2008;Garg e Achari, 2010;Ng et al, 2015;Feng et al, 2017).…”