Soil has approximately 30 percent to 40 percent void space. The void space between soil grains is occupied by water and vapor above the groundwater table. In some areas of the country these void spaces are teaming with methane. In the City of Los Angeles there are “Methane Zones”. These zones are typically in the area of old oil fields. The methane is constantly being burped up from deeper oil bearing zones through incompletely closed old oil wells. Other causes of high methane are nearby landfills and natural tar seeps.
The methane fills the void space of the soil in the area and has the potential to migrate up through utility lines and through foundations into buildings. High levels of methane in buildings are a fire hazard and can even cause explosions. Methane can also act as a carrier gas for other toxic chemicals.
Prior to building in a methane zone it is wise (and in some cities required) to do methane testing. The methane testing assures the future building owner that there is not methane intrusion risk or the methane testing will find high methane prior to building the foundation. High methane in soil can be safely mitigated with a soil vapor barrier and/or a passive venting system. In the City of Los Angeles, there are five different levels of methane mitigation required depending on the levels of methane measured in the soil.
Methane surveys should be conducted under the supervision of a registered civil engineer with experience in testing methane and the design of mitigation systems. Partner Engineering and Science has preformed scores of Methane Surveys across Southern California.