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 23 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.
Odors
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.
EPA Protections
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.
Reducing 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 (125,000 tons of carbon dioxide equivalent per year) and a fossil fuel displacement of approximately 16,000 tons of carbon dioxide per year. The combined emissions reduction of 141,000 tons of carbon dioxide equivalent per year would be equivalent to any one of the following annual environmental benefits for 2008:
- Annual greenhouse gas emissions from 23,000 passenger vehicles
- Carbon sequestered annually by 29,000 acres of pine or fir forests
- Carbon dioxide emissions from 299,000 barrels of oil consumed
In addition, annual energy savings for a 3–megawatt project equate to powering 1,900 homes.
Reducing Nonmethane Organic Compounds Emissions
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.
Dioxins and Furans
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.
Landfill Gas Combustion
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.
— www.epa.gov/lmop/faq/public.html