Solid Waste Management Program fact sheet
Division of Environmental Quality Director: Ed Galbraith

What is landfill gas?
Landfill gas is generated in a landfill from the decomposition of organic material. The most significant gases generated in a landfill are methane and carbon dioxide. Nitrogen is also produced, initially at high levels, but then drops rapidly until it stabilizes at low levels. Gases called trace gases are produced in much smaller amounts. Hydrogen sulfide is a trace gas that helps give landfill gas its characteristic odor. Depending on the composition of the waste, other trace gases may also be produced.

Does landfill gas pose an immediate threat?
Methane is the primary constituent of concern in landfill gas. Methane is colorless and odorless, and highly explosive when present in air between 5 and 15 percent of the total air volume.

Methane becomes potentially dangerous when it migrates into confined spaces in these concentrations. Confined spaces can range from trenches or cavities in the soil to buildings and structures. In addition to the risk of explosion, higher concentrations of methane in confined spaces can displace the oxygen and may lead to suffocation.

What requirements are in place to protect public safety?
Most modern landfills have gas monitoring wells in place near the property boundary of their facility. They are required to test these wells and report their findings to the Department of Natural Resources. Regulations enforced by the department prohibit methane gas concentrations, as measured in wells, from exceeding 2.5 percent by volume in soil at the landfill property boundary. Since methane is explosive at 5 percent by volume, this limit provides an extra level of protection to ensure public safety. In the event methane concentrations measured in these gas wells exceed 2.5 percent at the property boundary, the department requires the landfill owner to determine the extent of the methane migrating off of the property, contact adjacent property owners and take corrective actions to control methane gas in the soil to within allowable safe levels.

Most older landfills, however, are not required to have gas monitoring wells in place. In the case of these older landfills without gas wells, department staff look for any signs of methane migration during routine inspections, (e.g., dead or distressed vegetation off the fill boundary, gas bubbles in standing puddles of water, odors). If homes are nearby and there is a concern that methane may be leaving the site, the department may require the landfill to install gas monitoring wells and investigate for potential gas problems. Protecting Missouri citizens is the department’s highest priority.

How do I protect myself from methane gas?
An individual can take a number of steps to minimize the risk associated with methane migrating from a landfill. Some of these steps may include: