Methane is the largest component of natural gas. In its natural form, methane gas is colorless, odorless, and tasteless. One natural source of methane is the decomposition of plant and animal waste. Methane gas may enter groundwater through natural or industrial processes. Other sources of methane gas include coal mines, wastewater treatment, landfills, natural gas and petroleum systems, and certain agricultural and industrial processes. Before being used as a fuel, methane gas is mixed with an odorant, as a safety measure to help detect leaks.