

Landfill Gas Primer - An Overview for Environmental Health Professionals

Landfill Gas Primer - An Overview for Environmental Health Professionals

Historical Document


ATSDR Landfill Gas-Fact Sheet

Municipal solid waste (MSW) landfills emit gas that may reach surrounding neighborhoods. This fact sheet contains general information about the sources of landfill gas, where it goes, and the possible health and safety concerns that may be associated with it.

Where does landfill gas come from?

Bacterial activity causes the wastes in landfills to decompose over time. As these wastes decompose, gas is produced. The amount of gas created varies and depends on factors such as: the amount and type of waste; moisture content of the landfill; amount of oxygen present; landfill size and characteristics; and temperature. Also, certain chemical reactions and the evaporation of some chemicals produce landfill gas.

Most landfill gas is created within a few years after waste is dumped, when the rate of decomposition is highest. Almost all gas is produced within 20 years after waste is dumped.

Where does landfill gas go?

Gas is created under the landfill surface and generally moves away from the landfill, either by rising up through the landfill surface or migrating underground to surrounding areas. Three factors influence where gas goes:

  1. Permeability. Gas flows through areas of least resistance. If one side of the landfill is very permeable, then gas will likely leave the landfill from that area. Artificial channels such as drains and trenches can act as pipelines for gas movement.
  2. Diffusion. Gas moves to areas with lower gas concentrations. Gas concentrations are generally lower in areas surrounding the landfill.
  3. Pressure. Gas moves to areas of lower pressure. This means that the pressure of the surrounding areas (e. g., changing weather conditions) will affect gas movement from the landfill.

Gas that is released into the air is carried by wind. While wind dilutes the gas with fresh air, it can also move gas into neighboring communities. Wind speed and direction determine how much gas reaches nearby residents, so the degree of the problem varies greatly from day to day. At locations near the landfill, the worst time of the day is often early morning because winds tend to be gentle, providing the least dilution of the gas.

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What types of gas are produced?

Landfill gas is typically about 50 % methane and 50 % carbon dioxide, and less than 1 % sulfides (e.g., hydrogen sulfide, dimethyl sulfide, mercaptans) and non-methane organic compounds (NMOCs) (e.g., trichloroethylene, benzene, and vinyl chloride). The amount of sulfides and NMOCs varies from landfill to landfill and depends on whether the landfill receives wastes containing these chemicals and whether chemical reactions are occurring which create or remove them.

What causes the odor?

Sulfides are the source of the "rotting" smell often noticed near landfills and can cause this unpleasant odor even at very low concentrations. Some NMOCs also have recognizable odors. Methane and carbon dioxide are odorless. Odors can be destroyed by collecting and flaring the landfill gas or by venting it through special filters. Also, certain chemicals can be used to mask landfill gas odors.

In addition to landfill gas, there are three other common sources of landfill odor:

  • New waste being dumped
  • Special wastes with strong odors such as manures and fermented grains
  • Leachate (liquid within the landfill) coming to the surface

Odors from the dumping of new and special wastes do not tend to last long and are usually not noticeable beyond a few hundred feet of the dump site.

Note: Although certain types of gas cause odors, odor is not a good indicator of whether gas is present in surrounding areas because: (1) many gases do not have strong or distinctive odors, and (2) people get used to odors quickly so that they stop noticing them. Periodic monitoring is necessary to determine the nature and extent of landfill gas emissions.

What health and safety hazards are associated with landfill gas?

Health Concerns. Landfill gas generally represents more of an odor nuisance than a community health hazard; however, there are some potential health concerns you should be aware of: Some people may experience slight nausea or headache when they smell a bad odor. Although this is highly undesirable, the effects usually reverse when the odor goes away and do not require medical attention.

There is some concern that hydrogen sulfide might precipitate asthmatic attacks in highly sensitive people. However, a controlled study of asthmatics found that exposure to levels of hydrogen sulfide higher than those found at most landfills did not trigger an asthmatic attack or alter respiratory function.

Certain NMOCs are known carcinogens (e. g., vinyl chloride, benzene, and chloroform), and some NMOCs may have adverse effects on organ systems such as the kidney, liver, pulmonary, reproductive, and central nervous systems. However, the levels of NMOCs likely to reach surrounding communities are far below levels known to cause any ill effects. In most cases, landfills do not emit enough NMOCs to increase their concentration above the background levels commonly found in the community. Current research efforts are looking into the potential cumulative effects of being exposed to low levels of the types of NMOCs emitted from landfills.

Methane Gas Explosions. The accumulation of methane gas in structures both within and beyond the landfill (e. g., basements, crawl spaces, utility ducts) has resulted in explosions and fires which have caused personal injury and death. Accumulation is often the result of underground gas migration. EPA regulations require large landfills to monitor and control methane emissions.

How Can Explosion Risks and Odors be Reduced?

Passive vents and active gas pumping systems can be used to control the migration of methane gas. Passive systems use natural pressure gradients and trenches or pipes to vent landfill gas to the atmosphere. These vents can be equipped with flares to burn off gas (Note: this control can also be used to destroy odorous gases). If there is a high risk of methane accumulating in nearby structures, active gas collection systems are used to literally pump gas out of the landfill and recover it. A growing trend at landfills across the country is to use the recovered methane gas as an energy source. Collecting methane gas for energy use greatly reduces the risk of explosions, provides financial benefits for the community, and conserves other energy resources.

Missouri Department of Natural Resources Landfill Gas Facts What is Landfill Gas?

Landfill gas is generated during the decomposition of trash. The major gases generated in a landfill are methane and carbon dioxide. Nitrogen is produced, initially at high levels, then drops rapidly until it stabilizes at low levels.

Additional gases, called trace gases, are produced in much smaller amounts. Hydrogen sulfide is a trace gas that gives landfill gas its characteristic odor. Other trace gases may also be produced, depending on the composition of the waste.

Does Landfill Gas Pose an Immediate Threat?

Methane gas is the constituent of concern in landfill gas. It is a by-product of landfill decomposition and is colorless and odorless. Methane is highly explosive at certain concentrations in air (between 5% and 15% of the total air volume). Methane can become dangerous when it migrates into confined spaces in these concentrations. Confined spaces can range from trenches or holes in the soil to buildings and structures. Additionally, higher concentrations of methane in confined spaces can displace the oxygen and may lead to suffocation.

How Do I Protect Myself From Methane Gas?

An individual can take a number of steps in order to minimize the risk associated with gases migrating from a landfill.

Step 1: Properly ventilate all confined spaces. Some examples are removing some of the skirting from around a mobile home or opening basement and garage windows.

Step 2: Remove all potential ignition sources (portable heaters, open flames, etc.) in confined spaces which cannot be properly ventilated.

Step 3: Install a methane gas detector with an alarm set at or close to 1% methane gas by volume [20% of the Lower Explosive Limit (LEL)] in buildings or structures.

Information Sources

For more information contact these agencies:
Missouri Department of Natural Resources
Solid Waste Management Program
P.O. Box 176
Jefferson City, Missouri 65102
Phone: (573) 751-5401

Missouri Department of Natural Resources
Environmental Services Program/
Environmental Emergency Response
P. O. Box 176
Jefferson City, Missouri 65102
Phone: (573) 526-3315
Emergency: (573) 634-2436

U. S. Environmental Protection Agency
Region VII Office
726 Minnesota Avenue
Kansas City, Kansas 66101
Phone: (913) 236-3884

You can also contact your local fire department or Emergency Planning Commission.

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