SEPA
United States Environmental
Protection Agency
Office of Air and Radiation
October 2006
LANDFILL METHANE
OUTREACH PROGRAM
Frequently Asked Questions About
Landfill Gas and How It Affects Public
Health, Safety, and the Environment
Approximately 60 percent of all municipal
solid waste (MSW) generated in the United
States is currently being disposed of in
roughly 1,800 operational MSW landfills, as
referenced in EPA's Inventory of U.S. Greenhouse
Gas Emissions and Sinks: 1990-2004. Landfills are
the largest single human source of methane
emissions in the United States, accounting for 25
percent of all methane sources. Uncontrolled MSW
landfills also emit nonmethane organic compounds
(NMOC), which include volatile organic
compounds (VOC) that contribute to ozone
formation and hazardous air pollutants (HAP) that
can affect human health when exposed. However,
combustion of landfill gas significantly reduces
emissions of methane and NMOC. Nearly 400
MSW landfills in the United States recover and
combust landfill gas to generate heat or electricity,
and more than 450 other MSW landfills flare the
gas. EPA's air quality requirements and advances in
landfill gas energy technologies have encouraged the
combustion of landfill gas to benefit human health,
safety, and the environment, as well as provide
economic opportunities. The following questions
and answers are provided to inform interested parties
about compounds found in landfill gas and about
how combusting landfill gas can significantly reduce
emissions of these compounds to the atmosphere.
The answers provided in this document are not rules
nor are they binding upon the EPA in any context.
Should you have questions related to information
provided in this document, please call EPA's Landfill
Methane Outreach Program hotline toll-free at
1-888-782-7937 or visit LMOP's Web site at
How Is Landfill Gas
Generated?
Landfill gas is generated during the natural process
of bacterial decomposition of organic material
contained in MSW landfills. A number of factors
influence the quantity of gas that a MSW landfill
generates and the components of that gas. These
factors include, but are not limited to, the types and
age of the waste buried in the landfill, the quantity
and types of organic compounds in the waste, and
the moisture content and temperature of the waste.
Temperature and moisture levels are influenced by
the surrounding climate.
What Components
Make Up Landfill Gas?
By volume, landfill gas is about 50 percent methane
and 50 percent carbon dioxide and water vapor. It
also contains small amounts of nitrogen, oxygen, and
hydrogen, less than 1 percent NMOC, and trace
amounts of inorganic compounds. Some of these
compounds have strong, pungent odors (for
example, hydrogen sulfide, or H2S). Nonmethane
organic compounds consist of certain HAP and
VOC, which can react with sunlight to form
ground-level ozone (smog) if uncontrolled. Nearly
30 organic HAP have been identified in
uncontrolled landfill gas, including benzene, toluene,
ethyl benzene, and vinyl chloride. Exposure to these
HAP can lead to adverse health effects. Thermal
treatment of NMOC (including HAP and VOC)
and methane through flaring or combustion in an
engine, turbine, boiler, or other device greatly
reduces the emission of these compounds.
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How Are Nonmethane Organic
Compounds Generated in
Landfill Gas?
Nonmethane organic compounds are contained in
discarded items such as household cleaning products,
materials coated with or containing paints and
adhesives, and other items. During the waste
decomposition process, NMOC can be stripped from
the waste by methane, carbon dioxide, and other
gases and carried in landfill gas. Three different
mechanisms are responsible for the production of
NMOC and their movement into landfill gas: (1)
vaporization (the change of state from liquid or solid
to vapor) of organic compounds until the equilibrium
vapor concentration is reached, (2) chemical reaction
of materials present in the landfill, and (3) biological
decomposition of heavier organic compounds into
lighter, more volatile constituents.
At What Concentrations Are
Nonmethane Organic
Compounds Typically Found in
Uncontrolled Landfill Gas?
Concentrations of NMOC in uncontrolled landfill
gas can vary depending on several factors, including
the type of waste discarded in the landfill, the climate
surrounding the landfill, and the physical properties
of the individual organic compound. A default
concentration of 595 parts per million by volume
(ppmv) of NMOC is presented in EPA's Compilation
of Air Pollutant Emission Factors (AP-42). Of this total
NMOC, 110 ppmv are considered HAP compounds,
according to default concentrations in AP-42.
Therefore, total uncontrolled concentrations of
organic HAP at MSW landfills are typically less than
0.02 percent of the total landfill gas. The Standards of
Performance for New Stationary Sources (NSPS) and
National Emission Standards for Hazardous Air
Pollutants (NESHAP) regulations require combustion
of NMOC, a surrogate for organic HAP, at a
destruction efficiency of 98 percent, or to an outlet
concentration of 20 ppmv NMOC.
What Are the Public Health,
Safety, and Environmental
Concerns Associated with
Landfill Gas?
The public health, safety, and environmental concerns
fall into three categories: subsurface migration,
surface emissions/air pollution, and odor nuisance.
Subsurface Migration
Subsurface migration is the underground movement
of landfill gas from landfills to other areas within the
landfill property or outside the landfill property.
(Note: Most subsurface migration occurs at older,
unlined landfills because there is minimal barrier for
lateral migration. The Resource Conservation and
Recovery Act began requiring all new or expanded
landfills to be lined as of October 9, 1993. This
requirement decreases the likelihood of subsurface
migration.) Since landfill gas contains approximately
50 percent methane (a potentially explosive gas) it is
possible for landfill gas to travel underground,
accumulate in enclosed structures, and ignite. There
have been incidences of subsurface migration causing
fires and explosions on both landfill property and
private property.
Surface Emissions
Possibly the biggest health and environmental
concerns are related to the uncontrolled surface
emissions of landfill gas into the air. As previously
mentioned, landfill gas contains carbon dioxide,
methane, VOC, HAP, and odorous compounds that
can adversely affect public health and the
environment. For example, carbon dioxide and
methane are greenhouse gases that contribute to
global climate change. Methane is of particular
concern because it is 21 times more effective at
trapping heat in the atmosphere than carbon dioxide.
Emissions of VOC contribute to ground-level ozone
formation (smog). Ozone is capable of reducing or
damaging vegetation growth as well as causing
respiratory problems in humans. Finally, exposure to
HAP can cause a variety of health problems, such as
cancerous illnesses, respiratory irritation, and central
nervous system damage. Thermal treatment of
NMOC (including HAP and VOC) and methane
through flaring or combustion in an engine, turbine,
boiler, or other device greatly reduces the emission of
these compounds.
Odors
The final concern related to uncontrolled landfill gas
emissions is their unpleasant odor. Compounds found
in landfill gas are associated with strong, pungent
odors. These smells can be transmitted off-site to
nearby homes and business. Unpleasant odors can
lower the quality of life for individuals that live near
landfills and potentially reduce local property values.
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What Is EPA Doing to Protect
Public Health, Safety, and the
Environment?
The EPA promulgated Criteria for Municipal Solid
Waste Landfills (40 CFR Part 258) under the
Resource Conservation and Recovery Act (RCRA)
on October 9, 1991- The criteria contain location
restrictions, design and operating standards,
groundwater monitoring requirements, corrective
actions, financial assurance requirements, landfill gas
migration control, closure requirements, and post
closure requirements. Under the design standards
new landfills and lateral expansions that occur on or
after October 9, 1993 are required to line the
bottom and sides of the landfill prior to waste
deposition. In addition, all landfills operating after
October 9, 1991 must place a final cap over the
landfill surface. The placement of liners and caps
reduces the potential for subsurface and surface
landfill gas migration and groundwater
contamination. Recovery and combustion of landfill
gas will reduce emissions of organic compounds that
would otherwise be released from the landfill.
Because of the benefits of collecting and controlling
landfill gas, the 1996 EPA Standards of Performance
for New Stationary Sources (NSPS) and Guidelines for
Control of Existing Sources, and the 2003 National
Emission Standards for Hazardous Air Pollutants
(NESHAP) require "large" MSW landfills to collect
landfill gas and combust it to reduce NMOC by 98
percent (or to an outlet concentration of 20 ppmv).
A "large" landfill is defined as having a design
capacity of at least 2.5 million metric tons and 2.5
million cubic meters and a calculated or measured
uncontrolled NMOC emission rate of at least 50
metric tons (megagrams) per year. Landfills are
meeting these gas destruction standards using flares
or energy recovery devices, including reciprocating
engines, gas turbines, and boilers. In addition to gas
destruction requirements, the NSPS and NESHAP
require that gas collection systems be well-designed
and well-operated. They require gas collection from
all areas of the landfill, monthly monitoring at each
collection well, and monitoring of surface methane
emissions to ensure that the collection system is
operating properly and to reduce fugitive emissions.
Smaller MSW landfills are not required to control
emissions by the NSPS or NESHAP but can still
greatly reduce emissions of NMOC by collecting
and combusting landfill gas for energy recovery or in
a flare.
EPA's Landfill Methane Outreach Program (LMOP)
is a voluntary assistance and partnership program
that promotes the use of landfill gas as a renewable
energy source. By preventing emissions of methane
through the development of landfill gas energy
projects, LMOP helps businesses, states, and
communities protect the environment and build a
sustainable future. LMOP helps communities and
landfill owner/operators learn more about the
benefits of using landfill gas as an alternative energy
source and helps them develop or participate in
landfill gas energy projects. In addition, LMOP
provides information, software tools, and marketing
assistance, and access to technical experts to facilitate
development of landfill gas energy projects. For
more information about LMOP, please visit the
LMOP Web site at http://www.epa.gov/lmop or call
the LMOP hotline toll-free at 1-888-782-7937.
Can Landfill Gas Combustion
Be Used as an Energy
Source?
Landfill gas can be an asset when it is used as a
source of energy to create electricity or heat. It is
classified as a medium-Btu gas with a heating value
of 350 to 600 Btu per cubic foot, approximately
one-half that of natural gas. Landfill gas can often be
used in place of conventional fossil fuels in certain
applications. It is a reliable source of energy because
it is generated 24 hours a day, 7 days a week. By
using landfill gas to produce energy, landfills can
significantly reduce their emissions of methane and
avoid the need to generate energy from fossil fuels,
thus reducing emissions of carbon dioxide, sulfur
dioxide, nitrogen oxides, and other pollutants from
fossil fuel combustion.
How Do Landfill Gas Energy
Projects Reduce Greenhouse
Gas Emissions?
Landfill gas recovery projects provide a highly
effective means of reducing overall greenhouse gas
emissions from landfills, whether the landfill gas is
combusted by flare, electricity generation
equipment, or another end use system. By using the
otherwise wasted methane contained in the collected
landfill gas to generate electricity or directly as a
fuel, fossil fuels such as oil and coal are displaced.
This displacement of fossil fuels is an environmental
benefit, the magnitude of which would depend on
the actual amount of electricity generated or landfill
gas used.
For example, if a 3 megawatt (MW) landfill gas
electricity project starts up at a landfill with
previously uncontrolled landfill gas, the project
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would have a direct methane reduction of
approximately 6,000 tons per year (125,000 tons of
carbon dioxide equivalents (C02E) per year) and a
fossil fuel displacement of approximately 18,000
tons of C02 per year. The combined emissions
reduction of 143,000 tons of C02E per year would
be equivalent to any one of the following annual
environmental benefits for 2006:
•	Removing emissions equivalent to 25,000 vehicles
•	Planting 36,000 acres of forest
•	Preventing the use of 305,000 barrels of oil
In addition, annual energy savings for a 3 MW
project equate to powering 1,900 homes.
How Do Landfill Gas Energy
Projects Reduce Emissions of
Nonmethane Organic
Compounds?
Landfill gas energy projects involve collecting and
combusting landfill gas. The process of combustion
destroys organic compounds, including methane and
NMOC. During combustion, these organic
compounds chemically react with oxygen in the
presence of heat, breaking apart to form water vapor,
carbon dioxide, and other less volatile compounds.
Combusting the gas in a reciprocating engine, gas
turbine, or boiler to generate energy also reduces
pollution associated with the extraction and use of
fossil fuels to produce the same amount of energy.
What Are Dioxins and Furans
and Are They Released from
Landfill Gas Combustion?
Dioxins and furans are a group of toxic chemical
compounds, known as persistent organic pollutants,
that share certain similar chemical structures and
biological characteristics. Dioxins/furans are released
into the air as byproducts of many combustion
processes, such as incinerating municipal waste,
burning fuels (e.g., wood, coal, or oil), and some
industrial processes such as the bleaching of pulp
and paper. Some of the conditions that are
conducive to dioxin/furan formation are the
combustion of organic material in the presence of
chlorine and particulate matter under certain
thermodynamic conditions such as low combustion
temperatures and brief combustion times. Sources of
dioxin/furan include but are not limited to: MSW
combustors (incinerators), residential and
commercial coal combustion, residential and
commercial oil combustion, backyard trash burning,
residential fireplaces, cars, cigarettes, forest and
brush fires, and the combustion of landfill gas.
However, relative to many of these combustion
sources, the characteristics of landfill gas combustion
are less conducive to dioxin/furan formation.
EPA's review of the available data indicates that
dioxins/furans can be released in small amounts
when landfill gas is combusted by flare or for
recovering energy. Based on national and
international source tests, the concentration of
dioxins from landfill gas combustion ranges from
non-detectable to 0.1 nanograms (10'9 grams) of
toxic equivalents (TEQ) per dry standard cubic
meter of exhaust, at 7 percent oxygen. Because of
the health threat from uncontrolled emissions of
other organic compounds in landfill gas, EPA found,
in developing emissions standards, that landfill gas
destruction in a proper control device (e.g., flare or
energy recovery unit) with minimal by-product
generation of dioxins/furans is preferable to the
release of uncontrolled landfill gas. In summary,
EPA believes that the potential for dioxin emissions
from the combustion of landfill gas is small.
How Does Landfill Gas
Combustion Affect Mercury
Emissions?
Mercury, although present throughout the
environment, is a health concern because it can
bioaccumulate through the food chain as methylated
mercury, an organic, more toxic form of mercury.
Sources of mercury in MSW landfills can include
batteries, fluorescent light bulbs, electrical switches,
thermometers, and paints. Once mercury enters the
waste stream, it will ultimately be released from the
landfill and is contained in uncontrolled landfill gas.
However, combustion of landfill gas reduces the
toxicity of landfill gas emissions by converting the
organic mercury compounds, including methylated
mercury, to less toxic, less hazardous, inorganic
mercury compounds. According to EPA's 1997
Mercury Study Report to Congress, MSW landfills
contributed less than 0.1 percent of the total
mercury released from all man-made sources in the
United States in 1994. When compared on an
annual basis, mercury emissions from landfill gas are
significantly less than mercury emissions generated
by small oil-fired boilers used in homes and
apartments.
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Where Can I Get Additional
Information About the Types
and Amounts of Compounds
Found in Landfill Gas?
•	Compilation of Air Pollutant Emission Factors (AP-
42), Fifth Edition, Volume I: Stationary Point and
Area Sources, Chapter 2.4. U.S. EPA, Office of Air
Quality Planning & Standards. November 1998.
AP-42 Chapter 2.4: http://www.epa.gov/ttn/chief/
ap42lch02lfinallc02s04.pdf
Background Document: http:llwww.epa.gov/ttnl
chieflap42lch02lbgdocslb02s04.pdf
This chapter of AP-42 provides typical
concentrations for individual compounds from
uncontrolled landfill gas (Tables 2.4-1 and 2.4-2);
the default concentrations are based on test data
from multiple landfill sites. The background
document provides the concentrations observed in
the individual tests. Table 2.4-3 contains control
efficiencies for several combustion devices. [It is
important to note that default concentrations and
control efficiencies in Chapter 2.4 of AP-42 are
assigned quality ratings reflecting the limited data
that were available when the chapter was
developed in 1998. Therefore, minor differences
in emission reductions for different combustion
devices should not necessarily be considered
significant. EPA collected additional test data
between 2002 and 2005 and is currently using
these data to make recommendations for changes
to the current AP-42 emission factors for MSW
landfills.]
•	Landfill Gas Emissions Model (LandGEM) and
User's Manual, Version 3.02. U.S. EPA, Office of
Research and Development and Clean Air Tech-
nology Center. EPA/600/R-05-047- May 12, 2005-
http://www. epa.gov/ttn/catc/products. html#sofiware
This software model can be used to estimate
emissions of total landfill gas, methane, NMOC,
and several other compounds from individual
MSW landfills based on the default
concentrations in AP-42.
•	Emission Reduction Benefits of Landfill Gas
Combustion, Final Report. Prepared for
Environment Canada, National Office of
Pollution Prevention, by Cheminfo Services Inc.
February 2002.
This report interprets the Environment Canada
test results for the emissions of 19 selected
compounds measured at four landfill sites. The
study summarizes the pollutant emissions before
and after the landfill gas combustion process.
•	A Review of the Literature Regarding Non-
Methane and Volatile Organic Compounds in
Municipal Solid Waste Landfill Gas. H. Soltani-
Ahmadi, University of Delaware, Department of
Civil and Environmental Engineering. Featured in
the September/October 2002 issue of MSW
Management (Forester Communications, Inc.).
http://www.forester.net/nmocvoc.pdf
This paper reviews and compiles information
from the current literature regarding
concentrations of NMOC and VOC from landfill
gas. Various potential techniques for VOC
treatment with their advantages and disadvantages
are described. In addition, a critical review of
sample source, concentration, and flux
measurement techniques is presented.
Where Can I Get Additional
Information About the
Potential Health Effects of
Landfill Gas?
•	Landfill Gas Primer: An Overview for
Environmental Health Professionals. U.S.
Department of Health and Human Services,
Agency for Toxic Substances and Disease Registry.
November 2001.
http://www. atsdr. cdc.gov/HAC/landfll/html/toc. html
This primer was designed to provide environ-
mental health professionals with a general
understanding of landfill gases and to help them
respond to community concerns that may be
related to landfill gas issues. It provides basic
information about the composition, formation,
and movement of landfill gas. The primer also
discusses health and safety issues related to landfill
gas, and it provides information about landfill gas
monitoring methods and control measures.
Where Can I Get Additional
Information About Standards
for MSW Landfills?
•	Standards of Performance for New Stationary
Sources (NSPS) and Guidelines for Control of
Existing Sources: Municipal Solid Waste
Landfills. U.S. EPA, Office of Air Quality
Planning & Standards. 61 FR 9905. March 12,
1996.
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As required under the Clean Air Act (CAA), this
document contains the final emission standards
for new MSW landfills and the final emission
guidelines for existing MSW landfills. These
standards and guidelines require certain MSW
landfills to control NMOC emissions using flares
or other combustion devices. Minor amendments
have been made since 1996, and the latest
versions of the standards and guidelines are
contained in the Code of Federal Regulations at
40 CFR part 60, subparts Cc and WWW
(.http://www.access.gpo.gov/nara/cfr/waisidx_05/40cfr
60_05.html).
•	National Emission Standards for Hazardous Air
Pollutants (NESHAP): Municipal Solid Waste
Landfills, Final Rule. U.S. EPA, Office of Air
Quality Planning & Standards. 68 FR 2227.
January 16, 2003.
http:lla257.gakamaitech.net/7l257l2422ll4mar20
010800ledocket.access.gpo.govl2003lpdfl03-88.pdf
This final rule outlines the emission standards for
reducing HAP from MSW landfills. These
standards contain the same requirements as the
NSPS and Guidelines for Control of Existing
Sources for MSW landfills with added
requirements for bioreactor landfills.
•	Criteria for Municipal Solid Waste Landfills. U.S.
EPA, Office of Solid Waste. 40 CFR Part 258.
October 9, 1991. http:llwww.access.gpo.gov/naral
cfr/waisidx_05/40cfr258_05- html
As required under the Resource Conservation and
Recovery Act (RCRA), the purpose of this
regulation is to establish minimum national
criteria for all MSW landfill units. The criteria
contain location restrictions, design and operating
standards, groundwater monitoring requirements,
corrective actions, financial assurance
requirements, migration control, closure
requirements, and post closure requirements.
Where Can I Get Additional
Information About Releases of
Mercury Compounds or
Dioxins/Furans?
•	Mercury Study Report to Congress, Volume II:
An Inventory of Anthropogenic Mercury
Emissions in the United States. U.S. EPA, Office
of Air Quality Planning & Standards and Office
of Research and Development. EPA/452/R-97-
004. December 1997.
http://www. epa.gov/mercury/report, htm
This report provides an assessment of the
magnitude of U.S. mercury emissions by source,
the health and environmental implications of
those emissions, and the availability and cost of
control technologies.
•	Database of Sources of Environmental Releases of
Dioxin-like Compounds in the United States:
Version 3-0 for Reference Years 1987 and 1995-
U.S. EPA, Office of Research and Development,
National Center for Environmental Assessment.
EPA/600/C-01-012. March 2001.
http://www. epa.gov/NCEAJdioxindb. htm
This database serves as a repository for
dioxins/furans emissions data from all known
sources in the United States. The information
contained in the database is associated with two
reference years — 1987 and 1995. This database
provides the technical basis for the derivation of
emission factors used to estimate dioxin/furan
releases by source in the draft final report below.
•	Exposure and Human Health Reassessment of
2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD)
and Related Compounds. Part I: Estimating
Exposure to Dioxin-Like Compounds. Volume 2:
Sources of Dioxin-Like Compounds in the U.S.,
Draft Final Report. U.S. EPA, National Center
for Environmental Assessment. EPA/600/P-
OO/OOlBb. September 2000. http:/lwww.epa.gov/
ncealpdfsldioxinlpartllvolume2lvolume2.pdf
This document is the ultimate reference for
sources of dioxin-like compounds (including
furans) in the United States. This report is part of
EPA's Dioxin Reassessment effort, which began in
1991, to conduct a scientific reassessment of the
health risks resulting from exposure to 2,3,7,8-
tetrachlorodibenzo-p-dioxin (TCDD) and
chemically similar compounds collectively known
as dioxins/furans.
•	Summary of Readily Available Information and
Conclusions Drawn Regarding the By-product
Production of Dioxin from the Combustion of
Landfill Gas. U.S. EPA. Memorandum from M.
Laur, Office of Air Quality Planning & Standards,
to the Air and Radiation Docket and Information
Center. Publicly available in Docket No. A-98-28,
Item No. II-B-23. March 20, 2000.
http://www. regulations.gov/
(Search for All Documents and ID
EPA-HQ-OAR-2002-0047-0025)
This memorandum summarizes readily available
information on the by-product production of
dioxin from the combustion of landfill gas.
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Where Can I Get Additional
Information About National
Greenhouse Gas Emissions?
• Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2004. U.S. EPA, Office of Atmo-
spheric Programs. EPA/430/R-06-002. April 15,
2006. http:llyosemite.epa.govloarlglobalwarming. nsfl
conten t/Reso urce Cen terPublica tio ns GHGEm issio ns
USEmissionsInventory2006.html
This report presents estimates by the United
States government of U.S. human-related
greenhouse gas emissions and sinks for the years
1990 through 2004. The information provided in
this inventory is presented in accordance with the
Revised 1996 Intergovernmental Panel on
Climate Change (IPCC) Guidelines for National
Greenhouse Gas Inventories.

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