Final covers, especially when supplemented with gas collection, are highly engineered systems to prevent landfill methane release into the atmosphere. However, some methane production begins even before open cells are covered and often well before final capping, representing an unaddressed source of methane release. A number of biotic cover designs, such as biofilters, biocovers, and bio-"windows", have been proposed as supplements to gas collection or as top covers on older landfills lacking gas collection systems. These systems employ media that promote the growth of bacteria which are able to oxidize methane to carbon dioxide and water. The purpose of this investigation is to explore the potential use of the methane oxidation capacity of methanotrophs embedded in a "biotarp" to mitigate methane release from open, active landfill cells. If successful, the biotarp could serve as an alternative daily cover during routine landfill operation. A mixed methanotroph cell population was enriched and isolated from landfill cover soil. Three cell immobilization techniques were evaluated, including cell entrapment in alginate beads and in liquid-core gel capsules. Adsorption to a synthetic geotextile was found to be most feasible and yield the best methane oxidation rates (2.0 g CH4/day). Evaluation of nine geotextiles produced two that would likely be suitable biotarp components. Pilot tarp prototypes were tested in continuous flow systems simulating landfill gas conditions. Multilayered biotarp prototypes consisting of alternating layers of the two geotextiles were found to remove 16% of the methane flowing through the biotarp. The addition of landfill cover soil, compost, or shale as amendments to the biotarp increased the methane removal to over 30%. With successful methane removal in a laboratory bioreactor system, prototypes were evaluated at a local landfill using flux chambers installed atop a landfill section with an intermediate cover layer. The 4-layered biotarp and amended biotarp configurations were all found to decrease landfill methane flux; however negative controls were also observed to reduce methane flux equally well. Spatial and chronological variations in methane flux were also noted.