Landfill Methane Outreach Program
Public Health, Safety, and the Environment
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- What are the public health, safety, and environmental concerns associated with landfill gas?
- What is EPA doing to protect public health, safety, and the environment?
- How do landfill gas energy projects reduce greenhouse gas emissions?
- How do landfill gas energy projects reduce emissions of nonmethane organic compounds?
- What are dioxins and furans and are they released from landfill gas combustion?
- How does landfill gas combustion affect mercury emissions?
- Where can I get additional information about:
The answers provided in this document are not rules, nor are they binding upon EPA in any context. Should you have questions related to information provided in this document, please contact LMOP.
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 (LFG) from landfills to other areas within the landfill property or outside the landfill property. (Most subsurface migration occurs at older, unlined landfills because there is minimal barrier for lateral migration. The Resource Conservation and Recovery Act (RCRA) began requiring all new or expanded landfills to be lined as of October 9, 1993. This requirement decreases the likelihood of subsurface migration.) Since LFG contains approximately 50 percent methane (a potentially explosive gas), it is possible for LFG to travel underground, accumulate in enclosed structures, and ignite. Incidences of subsurface migration have caused 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 LFG into the air. LFG contains carbon dioxide, methane, volatile organic compounds (VOCs), hazardous air pollutants (HAPs), 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 25 times more effective at trapping heat in the atmosphere than carbon dioxide. Emissions of VOCs contribute to ground-level ozone formation (smog). Ozone can reduce or damage vegetation growth and cause 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 nonmethane organic compounds (or NMOCs—a category that includes HAPs and VOCs) and methane through flaring or combustion in an engine, turbine, boiler, or other device greatly reduces the emission of these compounds.
The final concern related to uncontrolled LFG emissions is their unpleasant odor. Compounds found in LFG 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 people who live near landfills and reduce local property values.
What is EPA doing to protect public health, safety, and the environment?
EPA promulgated Criteria for Municipal Solid Waste Landfills (40 CFR Part 258) under RCRA on October 9, 1991. The criteria contain location restrictions, design and operating standards, ground water monitoring requirements, corrective actions, financial assurance requirements, LFG migration controls, closure requirements, and post–closure requirements. Under the design standards, new landfills and lateral expansions that occur on or after October 9, 1993, must be lined on the bottom and sides before waste is deposited. In addition, all landfills operating after October 9, 1991 must place a final cap over the surface. The placement of liners and caps reduces the potential for subsurface and surface LFG migration and ground water contamination.
Recovery and combustion of LFG will reduce emissions of organic compounds that would otherwise be released from the landfill. Because of the benefits of collecting and controlling LFG, the 1996 EPA Standards of Performance for New Stationary Sources (NSPS) and Guidelines for Control of Existing Sources, as well as the 2003 National Emission Standards for Hazardous Air Pollutants (NESHAP), require "large" municipal solid waste (MSW) landfills to collect LFG and combust it to reduce NMOC by 98 percent (or to an outlet concentration of 20 parts per million by volume). 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 LFG for energy recovery or in a flare.
How do landfill gas energy projects reduce greenhouse gas emissions?
LFG recovery projects are a highly effective way to reduce overall greenhouse gas emissions from landfills, whether the LFG is combusted by flare, electricity generation equipment or another end use system. By using the otherwise wasted methane contained in the collected LFG 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 LFG used.
For example, if a 3–megawatt LFG electricity project starts up at a landfill with previously uncontrolled LFG, the project would have a direct methane reduction of approximately 6,000 tons per year (150,000 tons of carbon dioxide equivalents per year) and a fossil fuel displacement of approximately 13,000 tons of carbon dioxide per year. The combined emissions reduction of 163,000 tons of carbon dioxide equivalents per year would be equal to any one of the following annual environmental benefits for 2014:
- Carbon sequestered by nearly 121,000 acres of U.S. forests in one year
- CO2 emissions from about 800 railcars' worth of coal burned
- CO2 emissions from about 16.6 million gallons of gasoline consumed
How do landfill gas energy projects reduce emissions of nonmethane organic compounds?
LFG energy projects involve collecting and combusting LFG. 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 dioxins/furans 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 LFG. Relative to many of these combustion sources, the characteristics of LFG 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 LFG is combusted by flare or for recovering energy. Based on national and international source tests, the concentration of dioxins from LFG combustion ranges from non–detectable to 0.1 nanograms (10–9 grams) of toxic equivalents per dry standard cubic meter of exhaust, at 7 percent oxygen. Because of the health threat from uncontrolled emissions of other organic compounds in LFG, EPA found, in developing emissions standards, that LFG destruction in a proper control device (e.g., flare or energy recovery unit) with minimal byproduct generation of dioxins/furans is preferable to the release of uncontrolled LFG. In summary, EPA believes that the potential for dioxin emissions from the combustion of LFG is small.
How does landfill gas combustion affect mercury emissions?
Although it is present throughout the environment, mercury 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 LFG. However, combustion of LFG reduces the toxicity of LFG 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 artificial sources in the United States in 1994. When compared on an annual basis, mercury emissions from LFG are significantly less than mercury emissions generated by small, oil-fired boilers used in homes and apartments.
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 (PDF) (19 pp, 134K). U.S. EPA, Office of Air Quality Planning & Standards. November 1998. Chapter 2.4. Background Document (PDF) (125 pp, 663K).
This chapter of AP–42 provides typical concentrations for individual compounds from uncontrolled LFG (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. (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 Technology Center. EPA/600/R–05/047. May 12, 2005.
This software model can be used to estimate emissions of total LFG, methane, NMOCs, 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 LFG 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.).
This paper reviews and compiles information from the current literature regarding concentrations of NMOCs and VOCs from LFG. 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.
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.
As required under the Clean Air Act, 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.
- National Emission Standards for Hazardous Air Pollutants (NESHAP): Municipal Solid Waste Landfills, Final Rule (PDF) (16 pp, 97K). U.S. EPA, Office of Air Quality Planning & Standards. 68 FR 2227. January 16, 2003.
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.
As required under 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.
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.
This database serves as a repository for dioxin/furan 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 (PDF) (23 pp, 172K). U.S. EPA, National Center for Environmental Assessment. EPA/600/P–00/001Bb. September 2000.
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 scientific reassessment (begun in 1991) of the health risks resulting from exposure to 2,3,7,8–tetrachlorodibenzo–p–dioxin 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 and 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.
This memorandum summarizes readily available information on the byproduct production of dioxin from the combustion of LFG.
Where can I get additional information about national greenhouse gas emissions?
- Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2012. U.S. EPA, Office of Atmospheric Programs. EPA 430-R-14-003. April 2014.
This report presents estimates by the U.S. government of U.S. human-related greenhouse gas emissions and sinks for the years 1990 through 2012. 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.
Where can I find more information about the Greenhouse Gas Reporting Rule?
- In October 2009, EPA issued a rule that requires the reporting of greenhouse gases (40 CFR Part 98). The rule requires reporting of greenhouse gas emissions from large sources and suppliers in the United States, and is intended to collect accurate and timely emissions data to inform future policy decisions. More information on the rule may be found on the Greenhouse Gas Reporting Program page.