What goes on inside a landfill?

Inside a landfill, garbage is slowly decomposing at varying rates, depending on the material. Initially, it decomposes in the presence of oxygen (aerobic decomposition), but as it becomes further buried under layers of other trash each day, oxygen is no longer present, so the anaerobic decomposition that occurs from that point on emits methane. Methane is a very potent greenhouse gas that is 28 to 36 times more effective than CO2 at trapping heat in the atmosphere, like an electric blanket for the planet, except scary, not cozy. According to the EPA, municipal solid waste landfills are the third-largest source of human-related methane emissions in the US (after the agriculture and energy industries), accounting for about 15% of these emissions in 2019. This is about the equivalent of the emissions from more than 21.6 million cars driven for one year!

To address this issue, the EPA has been trying to encourage landfill operators to install methane capture infrastructure to prevent these emissions and capture the methane for energy use (“landfill gas energy” infrastructure). As of March 2021, there were 550 operational landfill gas energy projects in the US. There seem to be some mixed views about the effectiveness of these installations in trapping, with the EPA estimating that a landfill gas energy project can capture 60 to 90% of methane emitted, while other reports are much less optimistic with estimates of 10–90% depending on the phase of the landfill.