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Landfill

Landfill


A landfill is a large area of land or an excavated site that is designed and built to receive wastes. There were 3,536 active municipal landfills in the United States in 1995 according to the U.S. Environmental Protection Agency (EPA). Today, about 55 percent of America's trash (more than 220 million tons annually) is disposed of in landfills. Municipal solid-waste landfills (MSWLFs) accept only household, commercial, and nonhazardous industrial waste. Hazardous waste generated by industrial sources must be disposed of in special landfills that have even stricter controls than MSWLFs.

In the past, garbage was collected in open dumps. Most of these small and unsanitary dumps have been replaced by large, modern facilities that are designed, operated, and monitored according to strict federal and state regulations. These facilities may be distant from urban centers, requiring the large-scale transport of waste. About 2,300 municipal solid waste landfills were operating in the United States in 2000.

A typical modern landfill is lined with a layer of clay and protective plastic to prevent the waste and leachate (liquid from the wastes) from leaking to the ground or groundwater. The lined landfill is then divided into disposal cells. Only one cell is open at a time to receive waste. After a day's activity, the waste is compacted and covered with a layer of soil to minimize odor, pests, and wind disturbances. A network of drains at the bottom of the landfill collects the leachate that flows from the decomposing waste. The leachate is usually sent to a recovery facility to be treated. Methane gas, carbon dioxide, and other gases produced by the decomposing waste are monitored and collected to reduce their effect on air quality. EPA regulations require many larger landfills to collect and burn landfill gas. EPA's Landfill Methane Outreach Program was created in 1994 to educate communities and local government
about the benefits of recovering and burning methane as an energy source. By 2002 the program had helped develop 220 projects that convert landfill gas to energy. Such projects, when analyzed in 2001, offset the release of carbon dioxide from conventional energy sources by an amount equivalent to removing 11.7 million cars from the road for one year.

Fresh Kills Landfill in Staten Island, the largest landfill in the United States, accepting approximately 27,000 tons of garbage a day in the late 1980s, closed in March 2001. Although landfills occupy only a small percentage of the total land in the United States, public concern over possible ground water contamination as well as odor from landfills makes finding new sites difficult.

see also Solid Waste; Waste, Transportation of.


internet resources

freudenrich, craig c. "how landfills work." available from http://www.howstuffworks.com/landfill.htm.

u.s. environmental protection agency office of solid waste web site. available from http://www.epa.gov/epaoswer.

Office of Solid Waste/U.S. Environmental Protection Agency

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landfill

land·fill / ˈlan(d)ˌfil/ • n. a place to dispose of refuse and other waste material by burying it and covering it over with soil, esp. as a method of filling in or extending usable land. ∎  waste material used to reclaim ground in this way. ∎  an area filled in by this process. • v. [tr.] bury in a landfill: the Florida school intends to landfill its old computers.

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landfill

landfill(sanitary landfill) A method for the hygienic disposal of bulky wastes, in which the waste is deposited in a hollow that is excavated and sealed to prevent the contamination of adjacent land or water by leaching. At intervals, usually of one day, the waste is levelled, then buried beneath soil. See also made ground.

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landfill

landfill See MADE GROUND.

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landfill

landfillbill, Brazil, brill, Camille, chill, cookchill, dill, distil (US distill), downhill, drill, Edgehill, Estoril, fill, freewill, frill, fulfil (US fulfill), Gill, goodwill, grill, grille, hill, ill, instil, kill, krill, mil, mill, nil, Phil, pill, quadrille, quill, rill, Seville, shill, shrill, sill, skill, spadille, spill, squill, still, stock-still, swill, thill, thrill, till, trill, twill, until, uphill, will •hwyl • bank bill • handbill • waxbill •playbill, waybill •cranesbill • sibyl • crossbill • sawbill •hornbill • storksbill • shoebill •spoonbill • duckbill • razorbill •gerbil • wind chill • Churchill • idyll •daffodil • back-fill • landfill • monofil •fibrefill (US fiberfill) • chlorophyll •bluegill

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Landfill

Landfill


Surface water, oceans and landfills are traditionally the main repositories for society's solid and hazardous waste . Landfills are located in excavated areas such as sand and gravel pits or in valleys that are near waste generators. They have been cited as sources of surface and groundwater contamination and are believed to pose a significant health risk to humans, domestic animals, and wildlife . Despite these adverse effects and the attendant publicity, landfills are likely to remain a major waste disposal option for the immediate future.

Among the reasons that landfills remain a popular alternative are their simplicity and versatility. For example, they are not sensitive to the shape, size, or weight of a particular waste material. Since they are constructed of soil , they are rarely affected by the chemical composition of a particular waste component or by any collective incompatibility of co-mingled wastes. By comparison, composting and incineration require uniformity in the form and chemical properties of the waste for efficient operation. Landfills also have been a relatively inexpensive disposal option, but this situation is rapidly changing. Shipping costs, rising land prices, and new landfill construction and maintenance requirements contribute to increasing costs.

About 57% of the solid waste generated in the United States still is dumped in landfills. In a sanitary landfill, refuse is compacted each day and covered with a layer of dirt. This procedure minimizes odor and litter, and discourages insect and rodent populations that may spread disease. Although this method does help control some of the pollution generated by the landfill, the fill dirt also occupies up to 20 percent of the landfill space, reducing its waste-holding capacity. Sanitary landfills traditionally have not been enclosed in a waterproof lining to prevent leaching of chemicals into groundwater, and many cases of groundwater pollution have been traced to landfills.

Historically landfills were placed in a particular location more for convenience of access than for any environmental or geological reason. Now more care is taken in the siting of new landfills. For example, sites located on faulted or highly permeable rock are passed over in favor of sites with a less-permeable foundation. Rivers, lakes, floodplains, and groundwater recharge zones are also avoided. It is believed that the care taken in the initial siting of a landfill will reduce the necessity for future clean-up and site rehabilitation . Due to these and other factors, it is becoming increasingly difficult to find suitable locations for new landfills. Easily accessible open space is becoming scarce and many communities are unwilling to accept the siting of a landfill within their boundaries. Many major cities have already exhausted their landfill capacity and must export their trash, at significant expense, to other communities or even to other states and countries.

Although a number of significant environmental issues are associated with the disposal of solid waste in landfills, the disposal of hazardous waste in landfills raises even greater environmental concerns. A number of urban areas contain hazardous waste landfills. Love Canal is, perhaps, the most notorious example of the hazards associated with these landfills. This Niagara Falls, New York neighborhood was built over a dump containing 20,000 metric tons of toxic chemical waste. Increased levels of cancer , miscarriages, and birth defects among those living in Love Canal led to the eventual evacuation of many residents. The events at Love Canal were also a major impetus behind the passage of the Comprehensive Environmental Response, Compensation and Liability Act in 1980, designed to clean up such sites. The U.S. Environmental Protection Agency estimates that there may be as many as 2,000 hazardous waste disposal sites in this country that pose a significant threat to human health or the environment .

Love Canal is only one example of the environmental consequences that can result from disposing of hazardous waste in landfills. However, techniques now exist to create secure landfills that are an acceptable disposal option for hazardous waste in many cases. The bottom and sides of a secure landfill contain a cushion of recompacted clay that is flexible and resistant to cracking if the ground shifts. This clay layer is impermeable to groundwater and safely contains the waste. A layer of gravel containing a grid of perforated drain pipes is laid over the clay. These pipes collect any seepage that escapes from the waste stored in the landfill. Over the gravel bed a thick polyethylene liner is positioned. A layer of soil or sand covers and cushions this plastic liner, and the wastes, packed in drums, are placed on top of this layer.

When the secure landfill reaches capacity it is capped by a cover of clay, plastic and soil, much like the bottom layers. Vegetation in planted to stabilize the surface and make the site more attractive. Sump pumps collect any fluids that filter through the landfill either from rainwater or from waste leakage. This liquid is purified before it is released. Monitoring wells around the site ensure that the groundwater does not become contaminated. In some areas where the water table is particularly high, above-ground storage may be constructed using similar techniques. Although such facilities are more conspicuous, they have the advantage of being easier to monitor for leakage.

Although technical solutions have been found to many of the problems associated with secure landfills, several nontechnical issues remain. One of these issues concerns the transportation of hazardous waste to the site. Some states do not allow hazardous waste to be shipped across their territory because they are worried about the possibility of accidental spills. If hazardous waste disposal is concentrated in only a few sites, then a few major transportation routes will carry large volumes of this material. Citizen opposition to hazardous waste landfills is another issue. Given the past record of corporate and governmental irresponsibility in dealing with hazardous waste, it is not surprising that community residents greet proposals for new landfills with the NIMBY (Not In My BackYard ) response. However, the waste must go somewhere. These and other issues must be resolved if secure landfills are to be a viable long-term solution to hazardous waste disposal.

See also Groundwater monitoring; International trade in toxic waste; Storage and transportation of hazardous materials

[George M. Fell and Christine B. Jeryan ]


RESOURCES

BOOKS


Bagchi, A. Design, Construction and Monitoring of Landfills. 2nd ed. New York: Wiley, 1994.

Neal, H. A. Solid Waste Management and the Environment: The Mounting Garbage and Trash Crisis. Englewood Cliffs, NJ: Prentice-Hall, 1987.

Noble, G. Siting Landfills and Other LULUs. Lancaster, PA: Technomic Publishing, 1992.

Requirements for Hazardous Waste Landfill Design, Construction and Closure. Cincinnati: U.S. Environmental Protection Agency, 1989.

PERIODICALS

"Experimental Landfills Offer Safe Disposal Options." Journal of Environmental Health 51 (March-April 1989): 21718.

Loupe, D. E. "To Rot or Not; Landfill Designers Argue the Benefits of Burying Garbage Wet vs. Dry." Science News 138 (October 6, 1990): 21819+.

Wingerter, E. J., et al. "Are Landfills and Incinerators Part of the Answer? Three Viewpoints." EPA Journal 15 (March-April 1989): 2226.

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Landfill

Landfill

Sanitary landfill

Method types

Decomposition

Operating principles

Alternatives to landfills

Recycling

Composting

Resources

The term sanitary landfill was first used in the 1930s to refer to the compacting of solid waste materials. Initially adopted by New York City and Fresno, California, the sanitary landfill used heavy earth-moving equipment to compress waste materials and then cover them with soil. The practice of covering solid waste was evident in Greek civilization over 2,000 years ago, but the Greeks did it without compacting. Approximately 20,000 landfills were used in the United States in 1978. Ten years later, only 5,498 were reported in use by the U.S. Environmental Protection Agency. As of 2004, fewer than 1,700 active landfills exist in the United States. By the year 2008, the EPA predicts only 1,234 landfills will be available. (Although the number of landfills has decreased, the size of the average landfill has increased. Overall, the total capacity of landfills in the United States has gone up.)

As of 2005, the United States annually produces about 409 million tons of post-consumer (non-hazardous) waste, according to the Environmental Protection Agency. About 65 to 75% of the solid waste garbage generated in the United States still is dumped in landfills. This is generally broken down as paper and cardboard (40%), yard waste (18%), metals (9%), plastics (8%), and other products (25%). U.S. industries produces over twenty-five times that much waste in the form of pre-consumer waste, about 11.7 billion tons of waste each year.

Today, the sanitary landfill is the major method of disposing waste materials in North America and other developed countries, even though considerable efforts are being made to find alternative methods, such as recycling, incineration, and composting. Among the reasons that landfills remain a popular alternative are their simplicity and versatility. For example, they are not sensitive to the shape, size, or weight of a particular waste material. Since they are constructed of soil, they are rarely affected by the chemical composition of a particular waste component or by any collective incompatibility of co-mingled wastes. By comparison,

composting and incineration require uniformity in the form and chemical properties of the waste for efficient operation. In an average year in the 2000s, about 67% of the solid waste generated in the United States is still dumped in landfills. This corresponds to several tons of waste per landfill daily, considering 4.5 lb (2 kg) of solid waste is generated each day per person in the United States. The many tons of solid waste dumped in a landfill today will not decompose for (on average) 30 years. In order to create environmentally friendly landfills, new sites are being engineered to recover the methane gas that is generated during decomposition, and some older landfills are being mined for useful products.

About 70% of materials that are routinely disposed of in landfills could be recycled instead. More than 30% of bulk municipal garbage collections consist of paper that could be remanufactured into other paper products. Other materials like plastic, metal, and glass can also be reused in manufacturing, which can greatly reduce the amount of waste materials disposed in landfills, as well as preserving sources of nonrenewable raw materials.

Sanitary landfill

Sanitary landfills involve well-designed engineering methods to protect the environment from contamination by solid or liquid wastes. A necessary condition in designing a sanitary landfill is the availability of vacant land that is accessible to the community being served and has the capacity to handle several years of waste material. In addition, cover soil must be available. Of course, the location must also be acceptable to the local community. Historically, landfills were placed in a particular location more for convenience of access than for any environmental or geological reason. Now more care is taken in determining the location of new landfills. For example, sites located on faulted or highly permeable rock are passed over in favor of sites with a less-permeable foundation. Rivers, lakes, floodplains, and groundwater recharge zones are also avoided. It is believed that the care taken in the initial location of a landfill will reduce the necessity for future clean-up and site rehabilitation. Locations near airports are avoided because the landfill usually attracts birds that can interfere with aircraft. Due to these and other factors, it is becoming increasingly difficult to find suitable locations for new landfills. Easily accessible open space is becoming scarce and many communities are unwilling to accept the building of a landfill within their boundaries. Since 1978, over 14,000 landfills have been filled up and shut down. Many major cities have already exhausted their landfill capacity and must export their trash, at significant expense, to other communities or even to other states and countries.

The three basic procedures that are carried out in sanitary landfills are: spreading the solid waste materials in layers; compacting the wastes as much as possible; and covering the material with dirt at the end of each day. This method reduces the breeding of rats and insects at the landfill, reduces the threat of spontaneous fires, prevents uncontrolled settling of the materials, and uses the available land efficiently. Although this method does help control some of the pollution generated by the landfill, the fill dirt also occupies up to 20% of the landfill space, reducing its waste-holding capacity. Another important consideration for landfill design is the use of the site after it is filled. Some sites have become parks, housing projects, or sites for agriculture. Under pressure from the government, environmentalists, and the public, and with diminishing natural and financial resources available to them, municipalities are now planning their landfills carefully to avoid some of the later costs of cleanup or containment.

Method types

Trench and area methods, along with combinations of both, are used in the operation of landfills. Both methods operate on the principle of a cell, which in landfills comprises the compacted waste and soil covering for each day. The trench method is good in areas where there is relatively little waste, low groundwater, and the soil is over 6 ft (1.8 m) deep. The area method is usually used to dispose of large amounts of solid waste.

In the trench method, a channel with a typical depth of 15 ft (4.6 m) is dug, and the excavated soil is later used as a cover over the waste. Grading in the trench method must accommodate the drain-off of rainwater. Another consideration is the type of subsurface soil that exists under the topsoil. Clay is a good source of soil because it is nonporous. Weather and the amount of time the landfill will be in use are additional considerations.

In the area method, the solid wastes and cover materials are compacted on top of the ground. This method can be used on flat ground, in abandoned strip mines, gullies, ravines, valleys, or any other suitable land. This method is useful when it is not possible to create a landfill below ground.

A combination method is called the progressive slope or ramp method, where the depositing, covering, and compacting are performed on a slope. The covering soil is excavated in front of the daily cell. Where there is no cover material at the site, it is then brought in from outside sources.

Decomposition

A landfill has three stages of decomposition. The first one is an aerobic phase. The solid wastes that are biodegradable react with the oxygen in the landfill and begin to form carbon dioxide and water. Temperature during this stage of decomposition in the landfill rises about 30°F (16.7°C) higher than the surrounding air. A weak acid forms within the water and some of the minerals are then dissolved. The next stage is anaerobic, in which microorganisms that do not need oxygen break down the wastes into hydrogen, ammonia, carbon dioxide, and inorganic acids.

In the third stage of decomposition in a landfill, methane gas is produced. Sufficient amounts of water and warm temperature shave to be present in the landfill for the microorganisms to form the gas. About half of the gas produced during this stage will be carbon dioxide, but the other half will be methane. Systems of controlling the production of methane gas are either passive or active. In a passive system, the gas is vented into the atmosphere naturally, and may include venting trenches, cutoff walls, or gas vents to direct the gas. An active system employs a mechanical method to remove the methane gas and can include recovery wells, gas collection lines, a gas burner, or a burner stack. Both active and passive systems have monitoring devices to prevent explosions or fires.

Operating principles

While landfills may outwardly appear simple, they need to operate carefully and follow specific guidelines that include where to start filling, wind direction, the type of equipment used, method of filling, roadways to and within the landfill, the angle of slope of each daily cell, controlling contact of the waste with groundwater, and the handling of equipment at the landfill site.

Considerations have to be made regarding the soil that is used as a daily cover, which is usually 6 in (15.2 cm) thick, an intermediate cover of 1 ft (30.5 cm), and a final cover of 2 ft (61 cm). The compacting of the solid waste and soil has to be considered as well, so that the biological processes of decomposition can take place properly.

Shredding of solid wastes is one method of saving space at landfills. Another method is baling of wastes. The advantages to shredding are twofold. The material can be compacted to a greater density, thereby extending the life of the landfill, and it can be compacted more quickly as well. Less cover is required and there is also less danger of spontaneous fire. Landfills using shredded materials produce more organic decomposition than those disposing of unshredded solid wastes. The advantages of baling are an increase in landfill life because of an increase in waste density. Hauling times are reduced, as are litter, dust, odor, fires, traffic, noise, earth moving, and land settling. Less heavy equipment is needed for the cover operation and the amount of time it takes for the land to stabilize is reduced. Using biodegradable materials also helps save space in landfills because microorganisms can break down these materials more quickly. Trash bags made of biodegradable materials are of particular use because microorganisms cause holes to form in the bags, allowing the material inside to break down more quickly as well.

When the secure landfill reaches capacity, it is capped by a cover of clay, plastic, and soil, much like the bottom layers. Vegetation is planted to stabilize the surface and make the site more attractive. Sump pumps collect any fluids that filter through the landfill either from rainwater or from waste leakage. This liquid is purified before it is released. Monitoring wells around the site ensure that the groundwater does not become contaminated. In some areas where the water table is particularly high, above-ground storage may be constructed using similar techniques. Although such facilities are more conspicuous, they have the advantage of being easier to monitor for leakage.

The uses to which closed landfills have been put are varied. Efforts to limit what goes into the landfill reflect particular concerns of different communities across the country. They include industrial parks, airport runways, recreational parks, ski slopes, ball fields, golf courses, playgrounds, and many others. When it has been determined that the bearing capacity of the landfill surface is adequate, buildings can also be erected. The antiquated view of landfills as garbage dumps has given way to a science to engineer the establishment, maintenance, closure, and re-use of the area for the community.

Alternatives to landfills

The United States Environmental Protection Agency (EPA) requires all new landfills to include a leachate collection system. Recirculation of leachate accelerates the decomposition of solid waste. Another alternative use of landfills is to capture the methane gas produced during decomposition to generate electricity. For example, in Yolo County, California, a landfill releases 1.4 million cubic feet of gas a day used to generate electricity.

Landfill mining is another process that is used to reclaim the materials of the landfill for other purposes. More than 65% of the product from a landfill is usable soil. Small percentages of other materials, such as rock, metal, wood, aluminum, glass, plastic, polystyrene, and other items, can also be extracted from a landfill that is ready to be closed. The soil can be used as daily cover at other landfills and for grading roads and other construction projects. This process can only take place in landfills that are free of toxic wastes. Other landfill mining projects use the material to turn waste into energy.

Another alternative to landfill disposal for many areas has been the incineration of solid wastes. This method is often criticized because it has the potential of polluting the air, and the residual ash still has to be buried in a secure landfill. Dumping in the ocean has also come under attack by environmentalists who cite pollution of marine ecosystems and destruction of recreational beaches as reasons against ocean dumping.

Recycling

As a method of reducing the costs of solid waste disposal in landfills and of solving the problem of finding suitable landfill sites, many communities have initiated recycling programs. Some programs are carried out by segregating and collecting the recyclables separately from the materials destined for the landfill. There are also many drop-off programs for specific items such as glass bottles, plastics, aluminum (and other metal) cans, and newspapers.

Some communities require individual households to separate glass, plastic, and paper, while other programs have installed systems to separate the items at a plant and then sell them to manufacturers. The special collection of hazardous chemical wastes has also been initiated in communities that either recycle them or dispose of them more safely than in a landfill. Several things, besides saving space in landfills, are then accomplished with recycling programs. One is a cost benefit to the municipality and another is a decrease in the exploitation of natural resources, such as trees, metals, and petroleum.

Composting

The composting of organic materials for reuse in gardening and in agriculture can help alleviate the problem of using land to dispose of waste material. Plant and food substances are biodegradable, which means they are capable of decomposing through the agency of bacteria, fungi, and other living organisms. Temperature and sunlight play a role in the decomposition of biodegradable substances as well. When

KEY TERMS

Aerobic Requiring or in the presence of oxygen.

Anaerobic Describes biological processes that take place in the absence of oxygen.

Baling Compacting solid waste under heavy pressure to form a compressed bundle.

Biodegradable Able to decompose naturally through the agency of bacteria, fungi, and other micro-organisms.

Biodigester A landfill that uses methods to hasten the decomposition of its solid waste materials.

Compacting The practice of compressing solid waste to take up less space.

Composting The process by which organic waste, such as yard waste, food waste, and paper, is broken down by microorganisms and turned into a useful product for improving soil.

Density The amount of mass of a substance per unit volume.

Fault A fracture in the Earths crust accompanied by a displacement of one side relative to the other.

Floodplain The flat, low-lying area adjacent to a river or stream that becomes covered with water during flooding; flood waters deposit sand, silt and clay on this surface.

Groundwater Water within the Earth that supplies wells and springs.

Humus Organic material made up of well-decomposed, high molecular-weight compounds.

Incineration The burning of solid waste as a disposal method.

Inorganic solids Solids composed of compounds lacking carbon.

Leachate Excess rainwater draining from a landfill.

Organic solids Solids composed of compounds containing carbon.

Permeable Having small openings that allow liquids and gases to pass through.

Recycling The use of disused (or waste) materials, also known as secondary materials or recyclables, to produce new products.

Shredding The milling of solid wastes before disposal in the landfill.

Water table The upper limit of the portion of the ground wholly saturated with water.

substances are not biodegradable, they may remain in the environment and may be capable of polluting the soil and water of an area if they are toxic. Some biodegradable pollutants may also be capable of causing harm to the environment.

Substances that in the past were freely disposed of by dumping are now being considered by many municipalities for recycling as compost, such as weeds, leaves, and cut grass. Many communities throughout the country encourage people to compost plant material and use it as humus in their gardens. Since plant material is biodegradable this is a significant way to reduce solid waste problems for towns and cities. Other significant efforts involve the use of composted sewage sludge for soil application on farms, yards, and golf courses.

See also Hazardous wastes; Leaching; Waste management.

Resources

BOOKS

Boone, Christopher G. City and Environment. Philadelphia, PA: Temple University Press, 2006.

Miller, Donald, and Gert de Roo, eds. Urban Environmental Planning: Policies, Instruments, and Methods in an International Perspective. Aldershot, UK, and Burlington, VT: Ashgate, 2005.

Register, Richard. Ecocities: Rebuilding Cities in Balance with Nature. Gabriola, Canada: New Society Publishers, 2006.

Robinson, William D. The Solid Waste Handbook. New York: John Wiley & Sons, 1986.

Scragg, Alan H. Environmental Biotechnology. Oxford, UK: Oxford University Press, 2005.

Vita Richman

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Landfill

Landfill

The term "sanitary landfill" was first used in the 1930s to refer to the compacting of solid waste materials. Initially adopted by New York City and Fresno, California, the sanitary landfill used heavy earth-moving equipment to compress waste materials and then cover them with soil . The practice of covering solid waste was evident in Greek civilization over 2,000 years ago, but the Greeks did it without compacting.

Today, the sanitary landfill is the major method of disposing waste materials in North America and other developed countries, even though considerable efforts are being made to find alternative methods, such as recycling , incineration , and composting . Among the reasons that landfills remain a popular alternative are their simplicity and versatility. For example, they are not sensitive to the shape, size, or weight of a particular waste material. Since they are constructed of soil, they are rarely affected by the chemical composition of a particular waste component or by any collective incompatibility of co-mingled wastes. By comparison, composting and incineration require uniformity in the form and chemical properties of the waste for efficient operation. About 67% of the solid waste generated in the United States is still dumped in landfills. This corresponds to several tons of waste per landfill daily, considering 4.5 lb (2 kg) of solid waste is generated each day per person in this country. Americans will have created approximately 220 million tons of solid waste in the year 2000. The many tons of solid waste dumped in a landfill today will not decompose until 30 years from now. In order to create environmentally friendly landfills, new sites are being engineered to recover the methane gas that is generated during decomposition , and some older landfills are being mined for useful products.

About 70% of materials that are routinely disposed of in landfills could be recycled instead. More than 30% of bulk municipal garbage collections consist of paper that could be remanufactured into other paper products. Other materials like plastic, metal , and glass can also be reused in manufacturing, which can greatly reduce the amount of waste materials disposed in landfills, as well as preserving sources of nonrenewable raw materials.


Sanitary landfill

Sanitary landfills involve well-designed engineering methods to protect the environment from contamination by solid or liquid wastes. A necessary condition in designing a sanitary landfill is the availability of vacant land that is accessible to the community being served and has the capacity to handle several years of waste material. In addition, cover soil must be available. Of course, the location must also be acceptable to the local community. Historically, landfills were placed in a particular location more for convenience of access than for any environmental or geological reason. Now more care is taken in determining the location of new landfills. For example, sites located on faulted or highly permeable rock are passed over in favor of sites with a less-permeable foundation. Rivers , lakes, floodplains, and groundwater recharge zones are also avoided. It is believed that the care taken in the initial location of a landfill will reduce the necessity for future clean-up and site rehabilitation . Locations near airports are avoided because the landfill usually attracts birds that can interfere with aircraft . Due to these and other factors, it is becoming increasingly difficult to find suitable locations for new landfills. Easily accessible open space is becoming scarce and many communities are unwilling to accept the building of a landfill within their boundaries. Since 1978, over 14,000 landfills have been filled up and shut down. Many major cities have already exhausted their landfill capacity and must export their trash, at significant expense, to other communities or even to other states and countries.

The three basic procedures that are carried out in sanitary landfills are: spreading the solid waste materials in layers; compacting the wastes as much as possible; and covering the material with dirt at the end of each day. This method reduces the breeding of rats and insects at the landfill, reduces the threat of spontaneous fires, prevents uncontrolled settling of the materials, and uses the available land efficiently. Although this method does help control some of the pollution generated by the landfill, the fill dirt also occupies up to 20% of the landfill space, reducing its waste-holding capacity. Another important consideration for landfill design is the use of the site after it is filled. Some sites have become parks, housing projects, or sites for agriculture. Under pressure from the government, environmentalists, and the public, and with diminishing natural and financial resources available to them, municipalities are now planning their landfills carefully to avoid some of the later costs of clean-up or containment.

Method types

Trench and area methods, along with combinations of both, are used in the operation of landfills. Both methods operate on the principle of a "cell," which in landfills comprises the compacted waste and soil covering for each day. The trench method is good in areas where there is relatively little waste, low groundwater, and the soil is over 6 ft (1.8 m) deep. The area method is usually used to dispose of large amounts of solid waste.

In the trench method, a channel with a typical depth of 15 ft (4.6 m) is dug, and the excavated soil is later used as a cover over the waste. Grading in the trench method must accommodate the drain-off of rainwater. Another consideration is the type of subsurface soil that exists under the topsoil. Clay is a good source of soil because it is nonporous. Weather and the amount of time the landfill will be in use are additional considerations.

In the area method, the solid wastes and cover materials are compacted on top of the ground. This method can be used on flat ground, in abandoned strip mines, gullies, ravines, valleys, or any other suitable land. This method is useful when it is not possible to create a landfill below ground.

A combination method is called the progressive slope or ramp method, where the depositing, covering, and compacting are performed on a slope. The covering soil is excavated in front of the daily cell. Where there is no cover material at the site, it is then brought in from outside sources.


Decomposition

A landfill has three stages of decomposition. The first one is an aerobic phase. The solid wastes that are biodegradable react with the oxygen in the landfill and begin to form carbon dioxide and water . Temperature during this stage of decomposition in the landfill rises about 30°F (16.7°C) higher than the surrounding air. A weak acid forms within the water and some of the minerals are then dissolved. The next stage is anaerobic , in which microorganisms that do not need oxygen break down the wastes into hydrogen , ammonia , carbon dioxide, and inorganic acids.

In the third stage of decomposition in a landfill, methane gas is produced. Sufficient amounts of water and warm temperatures have to be present in the landfill for the microorganisms to form the gas. About half of the gas produced during this stage will be carbon dioxide, but the other half will be methane. Systems of controlling the production of methane gas are either passive or active. In a passive system the gas is vented into the atmosphere naturally, and may include venting trenches, cutoff walls, or gas vents to direct the gas. An active system employs a mechanical method to remove the methane gas and can include recovery wells, gas collection lines, a gas burner, or a burner stack. Both active and passive systems have monitoring devices to prevent explosions or fires.


Operating principles

While landfills may outwardly appear simple, they need to operate carefully and follow specific guidelines that include where to start filling, wind direction, the type of equipment used, method of filling, roadways to and within the landfill, the angle of slope of each daily cell, controlling contact of the waste with groundwater, and the handling of equipment at the landfill site.

Considerations have to be made regarding the soil that is used as a daily cover, which is usually 6 in (15.2 cm) thick, an intermediate cover of 1 ft (30.5 cm), and a final cover of 2 ft (61 cm). The compacting of the solid waste and soil has to be considered as well, so that the biological processes of decomposition can take place properly.

Shredding of solid wastes is one method of saving space at landfills. Another method is baling of wastes. The advantages to shredding are twofold. The material can be compacted to a greater density , thereby extending the life of the landfill, and it can be compacted more quickly as well. Less cover is required and there is also less danger of spontaneous fire. Landfills using shredded materials produce more organic decomposition than those disposing of unshredded solid wastes. The advantages of baling are an increase in landfill life because of an increase in waste density. Hauling times are reduced, as are litter, dust, odor, fires, traffic, noise, earth moving, and land settling. Less heavy equipment is needed for the cover operation and the amount of time it takes for the land to stabilize is reduced. Using biodegradable materials also helps save space in landfills because microorganisms can break down these materials more quickly. Trash bags made of biodegradable materials are of particular use because microorganisms cause holes to form in the bags, allowing the material inside to break down more quickly as well.

When the secure landfill reaches capacity, it is capped by a cover of clay, plastic, and soil, much like the bottom layers. Vegetation is planted to stabilize the surface and make the site more attractive. Sump pumps collect any fluids that filter through the landfill either from rainwater or from waste leakage. This liquid is purified before it is released. Monitoring wells around the site ensure that the groundwater does not become contaminated. In some areas where the water table is particularly high, above-ground storage may be constructed using similar techniques. Although such facilities are more conspicuous, they have the advantage of being easier to monitor for leakage.

The uses to which closed landfills have been put are varied. Efforts to limit what goes into the landfill reflect particular concerns of different communities across the country. They include industrial parks, airport runways, recreational parks, ski slopes, ball fields, golf courses, playgrounds, and many others. When it has been determined that the bearing capacity of the landfill surface is adequate, buildings can also be erected. The antiquated view of landfills as "garbage dumps" has given way to a science to engineer the establishment, maintenance, closure, and re-use of the area for the community.

Alternatives to landfills

The United States Environmental Protection Agency (EPA) requires all new landfills to include a leachate collection system. Recirculation of leachate accelerates the decomposition of solid waste. Another alternative use of landfills is to capture the methane gas produced during decomposition to generate electricity . For example, in Yolo County, California, a landfill releases 1.4 million cubic feet of gas a day used to generate electricity.

Landfill mining is another process that is used to reclaim the materials of the landfill for other purposes. More than 65% of the product from a landfill is usable soil. Small percentages of other materials, such as rock, metal, wood , aluminum , glass, plastic, polystyrene, and other items, can also be extracted from a landfill that is ready to be closed. The soil can be used as daily cover at other landfills and for grading roads and other construction projects. This process can only take place in landfills that are free of toxic wastes. Other landfill mining projects use the material to turn waste into energy .

Another alternative to landfill disposal for many areas has been the incineration of solid wastes. This method is often criticized because it has the potential of polluting the air, and the residual ash still has to be buried in a secure landfill. Dumping in the ocean has also come under attack by environmentalists who cite pollution of marine ecosystems and destruction of recreational beaches as reasons against ocean dumping.


Recycling

As a method of reducing the costs of solid waste disposal in landfills and of solving the problem of finding suitable landfill sites, many communities have initiated recycling programs. Some programs are carried out by segregating and collecting the recyclables separately from the materials destined for the landfill. There are also many drop-off programs for specific items such as bottles, plastics , cans, and newspapers.

Some communities require individual households to separate glass, plastic, and paper, while other programs have installed systems to separate the items at a plant and then sell them to manufacturers. The special collection of hazardous chemical wastes has also been initiated in communities that either recycle them or dispose of them more safely than in a landfill. Several things, besides saving space in landfills, are then accomplished with recycling programs. One is a cost benefit to the municipality and another is a decrease in the exploitation of natural resources , such as trees, metals, and petroleum .


Composting

The composting of organic materials for reuse in gardening and in agriculture can help alleviate the problem of using land to dispose of waste material. Plant and food substances are biodegradable, which means they are capable of decomposing through the agency of bacteria , fungi , and other living organisms. Temperature and sunlight play a role in the decomposition of biodegradable substances as well. When substances are not biodegradable, they may remain in the environment and may be capable of polluting the soil and water of an area if they are toxic. Some biodegradable pollutants may also be capable of causing harm to the environment.

Substances that in the past were freely disposed of by dumping are now being considered by many municipalities for recycling as compost, such as weeds, leaves, and cut grass. Many communities throughout the country encourage people to compost plant material and use it as humus in their gardens. Since plant material is biodegradable this is a significant way to reduce solid waste problems for towns and cities. Other significant efforts involve the use of composted sewage sludge for soil application on farms, yards, and golf courses.

See also Hazardous wastes; Leaching; Waste management.


Resources

books

Beatley, Thomas. Green Urbanism. Washington DC: Island Press, 2000.

Forster, Christopher F. Environmental Biotechnology. New York: John Wiley & Sons, 1987.

McConnell, Robert, and Daniel Abel. Environmental Issues:Measuring, Analyzing, Evaluating. 2nd ed. Englewood Cliffs, NJ: Prentice Hall, 2002.

Robinson, William D. The Solid Waste Handbook. New York: John Wiley & Sons, 1986.

periodicals

"Composting: Nature's Recycling Program." Consumer Reports February 1994: 112.

Ladesich, Jim. "Composting Comes of Age." American City &County July 1993: 1012.

Magnuson, Anne. "Garbage: Gold at the End of the Rainbow." American City & County July 1993: 48.

"Managing Land Use And Land-Cover Change: The New Jersey Pinelands." Annals of The Association of American Geographers 89, no. 2 (1999): 220.

"Solid Waste Management." American City & County July 1993: 3, 13.


Vita Richman

KEY TERMS


Aerobic

—Requiring or in the presence of oxygen.

Anaerobic

—Describes biological processes that take place in the absence of oxygen.

Baling

—Compacting solid waste under heavy pressure to form a compressed bundle.

Biodegradable

—Able to decompose naturally through the agency of bacteria, fungi, and other microorganisms.

Biodigester

—A landfill that uses methods to hasten the decomposition of its solid waste materials.

Compacting

—The practice of compressing solid waste to take up less space.

Composting

—The process by which organic waste, such as yard waste, food waste, and paper, is broken down by microorganisms and turned into a useful product for improving soil.

Density

—The amount of mass of a substance per unit volume.

Fault

—A fracture in the earth's crust accompanied by a displacement of one side relative to the other.

Floodplain

—The flat, low-lying area adjacent to a river or stream that becomes covered with water during flooding; flood waters deposit sand, silt and clay on this surface.

Groundwater

—Water within the earth that supplies wells and springs.

Humus

—Organic material made up of well-decomposed, high molecular-weight compounds. Humus contributes to soil tilth, and is a kind of organic fertilizer.

Incineration

—The burning of solid waste as a disposal method.

Inorganic solids

—Solids composed of compounds lacking carbon.

Leachate

—Excess rainwater draining from a landfill.

Organic solids

—Solids composed of compounds containing carbon.

Permeable

—Having small openings that allow liquids and gases to pass through.

Recycling

—The use of disused (or waste) materials, also known as secondary materials or recyclables, to produce new products.

Shredding

—The milling of solid wastes before disposal in the landfill.

Water table

—The upper limit of the portion of the ground wholly saturated with water.

Cite this article
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"Landfill." The Gale Encyclopedia of Science. . Encyclopedia.com. 15 Nov. 2018 <https://www.encyclopedia.com>.

"Landfill." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 15, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/landfill-0

"Landfill." The Gale Encyclopedia of Science. . Retrieved November 15, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/landfill-0

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Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

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