What is methane and why is it a safety concern?
Methane (a gas composed of carbon and hydrogen) is produced two ways. The first is through biologic decomposition of organic matter at shallow depths. Swamps, landfills, and even shallow bedrock are some settings where this occurs. Methane can also be derived over millions of years by high pressure and high temperature processes that produce fossil fuels deep underground. Examples include coal deposits and oil and natural gas accumulations.
Under the right conditions, methane gas can migrate into water wells along with the groundwater. High concentrations of methane in water wells can accumulate in confined spaces and act as an asphyxiant or become flammable. These dangers can be mitigated through enhanced venting of the well casing or venting confined spaces (like basements) and removing any ignition sources.