In the anaerobic underlayers of a mixed solid waste landfill, subsurface chemical reactions are common and expected.
These reactions, facilitated by microbes that break down the waste, produce gas that can be used to create bioenergy. Collection systems, usually consisting of plastic piping through the landfill, collect the gases. While gas temperatures of 80 to 100 degrees Fahrenheit are typical, Bryan Staley, president of the North Carolina-based Environmental Research and Education Foundation (EREF), notes that temperatures in excess of 160 degrees suggest the potential for an abnormal situation. Temperatures can even get high enough, Staley says, that plastic gas collection pipes begin to melt, and the normal microbial process at work in the landfill could be disrupted.
Extreme subsurface temperatures can be caused by exothermic reactions created by interaction among landfill materials, such as secondary aluminum waste, which reacts with water and can release substantial heat. But Staley says there are other reactions that the industry knows little about.