Analytical model for methane migration through fractured unsaturated landfill cover soil

Migration of gas in the fractured porous media plays an important role in geoenvironmental engineering issues. Compacted clay liners (CCLs) are extensively used as engineering barriers for groundwater and soil pollution induced by landfill contaminant transport. Analytical model and semi-analytical model were developed for methane transport in fractured CCL by using Laplace transformation and Laplace inversion using Stehfest method. Methane diffusion and oxidation in the matrix of CCL and gas advection-diffusion in the fracture were considered. Dimensionless analysis shows that advection plays a more important role than diffusion for methane transport through the fracture. Diffusion and oxidation of methane in the matrix of CCL have relatively less influences on methane transport in the fracture. The steady-state methane surface flux for the case with D-m = 3.14 x 10(-9) m(2)/s is 1.02 and 1.5 times greater than that with D m = 3.14 x 10(-8) m(2)/s when the fracture width 2b = 5 mm and 2b = 3 mm, respectively. Methane oxidation rate in the matrix of CCL (lambda(1) ) plays a more important role on methane transport in fracture than methane oxidation rate in the fracture (lambda(2)). When lambda(1) and lambda(2) increase by one order of magnitude, the steady-state surface fluxes decrease by factors of 1.05 and 1.53, respectively. Transport of methane can be greatly restrained by the compost-amended CCL due to the increase of methane oxidation rate. The proposed semi-analytical and analytical model can be used in the design and assessment of cover system for landfill and mining facilities with different soil moisture contents.