Landfill gas production results from chemical reactions and microbes acting upon the waste as the putrescible materials begins to break down in the landfill. The rate of production is affected by waste composition and landfill geometry, which in turn influence the microbial populations within it, chemical make-up of waste, thermal range of physical conditions, and the biological ecosystems co-existing simultaneously within most sites. This heterogeneity, together with the frequently unclear nature of the contents, makes landfill gas production more difficult to predict and control than standard industrial bioreactors for sewage treatment.
Due to the continual production of landfill gas, the increase in pressure within the landfill (together with differential diffusion) causes the gases release into the atmosphere. Such emissions lead to important environmental, hygiene and security problems in the landfill.
Several accidents have occurred, for example at Loscoe, England in 1986, where migrating landfill gas, which was allowed to build up, partially destroyed the property. An accident causing two deaths occurred from an explosion in a house adjacent to Skellingsted Landfill in Denmark in 1991. Due to the risk presented by landfill gas there is a clear need to monitor gas produced by landfills. In addition to the risk of fire and explosion, gas migration in the subsurface can result in contact of landfill gas with groundwater. This, in turn, can result in contamination of groundwater by organic compounds present in nearly all landfill gas.
Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Landfill gas also contains varying amounts of nitrogen and oxygen gas, water vapour, hydrogen sulphide, and other contaminants.
General options for managing landfill gas are: venting to atmosphere, flaring, boiler (makes heat), internal combustion engine (makes electricity), gas turbine (makes electricity), convert the methane to methyl alcohol, clean it enough to pipe it to other industries or into natural gas lines.
Geoinvestigate provide a full Landfill Gas Monitoring service compliant with Environment Agency and Local Planning Authority requirements from the installation of Gas wells to measurement of gas flow under varying atmospheric pressure.