Landfill gas (LFG) is typically about 50 percent methane, making it the chief component present in emissions. This gas can be monitored and used to determine how much LFG a site is emitting, both directly as methane and as a surrogate for total emissions.
Methane can be monitored above the surface of the landfill as a gauge of potential emissions or can be directly measured using techniques that test for the rate or flux of emissions. The above-surface monitoring techniques for gauging potential emissions include surface emission monitoring. Surface emission monitoring (SEM) is a technique that involves using a portable methane detector near the landfill’s surface to measure concentrations while traversing the site.