Landfills containing organic wastes produce biogas consisting of methane (CH4) and biogenic carbon dioxide (CO2). Landfills are significant sources of CH4 that contribute to climate change. In the US, as well as in Europe, waste disposal represents the second largest source of anthropogenic CH4 emission, comprising approximately 22% of the total anthropogenic CH4 emission (European Environment Agency, 2008 and USEPA, 2010). Landfill gas (LFG) extraction and utilization plants have been made mandatory at new waste disposal sites in many countries. A low-cost alternative approach to reduce LFG emissions from existing landfills where gas collection systems have not been implemented and/or are not economically feasible is to establish biocovers optimized for biological oxidation of CH4 (Scheutz et al., 2009a). A biocover is a landfill cover system that has been designed to optimize environmental conditions for biological CH4 consumption so that the system functions as a vast biofilter. The cover typically consists of a gas distribution layer with high gas permeability to homogenize LFG fluxes (e.g. gravel, crushed construction waste, shredder waste, etc.), and an overlying oxidation layer designed to support the methanotrophic populations that will consume the CH4 for carbon and energy. Alternatively to a biocover system, the CH4 oxidation might take place in a biowindow system.