Explanation:

 Landfill gases are the result of three processes. Evaporation of volatile organic compounds (e.g solvents), chemical reactions between waste components and microbial action , especially methanogenesis. The first two depend strongly on the nature of the waste . The dominant process in most landfills is the third process whereby anaerobic bacteria decompose organic waste to produce biogas which consists of methane and carbon dioxide together with traces of other compounds. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide.