Landfills

Introduction

A landfill is an area that is used to dispose of solid waste material. It can be dug into the ground, with the waste gradually filling up the hole, or the waste can be piled up in an organized way and buried. Liquid waste needs to be disposed of in other ways than in a landfill, to avoid the risk of leaching of the wastewater into the ground.

Landfills are the oldest form of disposal of waste that is not reused or destroyed in other ways, as for example by burning. Landfills may also be used as a temporary place for the storage of waste that, as one example, needs to be sorted and allocated for various recycling routes.

In the United States in 2006, about 251 million tons (228 million metric tons) of municipal solid waste (waste other than industrial, hazardous, and construction waste) were generated, according to figures from the U.S. Environmental Protection Agency (EPA), representing almost four times the amount produced in 1960. As well, the amount of garbage produced by each person (per capita generation) has increased from 2.7 lb (1.2 kg) per day in 1960 to 4.6 lb (2.1 kg) per day in 2006. According to the EPA, in 2006 about 32.5% of this waste was recycled or composted and 12.5% was burned at high temperatures in specially designed facilities (incineration). The remaining 55%, representing at least 138 million tons (125 million metric tons), was disposed of in 1,754 approved landfills.

Although the number of landfills in the United States has declined from nearly 8,000 in 1988, landfills have steadily increased in size.

When designed properly, a landfill is a safe means of containing solid waste. For example, a properly designed landfill will be equipped with vents to allow methane gas (CH₄) produced during decomposition of some of the waste to be released from underground. However, land-fills can experience problems that include degradation of breakage of the plastic lining of landfills (older landfills may not have a liner, increasing the chance of leakage of fluid produced during decomposition into the surrounding soil), clogging of pipes that collect generated liquid, improper capping of a landfill, and illegal construction and use of landfills in environmentally sensitive regions.

Historical Background and Scientific Foundations

A Brief History and Examples

Landfills have existed for over 5,000 years. Archaeological evidence of landfills dates back to 3000 BC in Crete, where waste was deposited in pits that were subsequently covered up with earth when full. A municipal landfill operated on the outskirts of Athens at least 2,500 years ago; residents were required to transport waste to the site, which was outside of the city gates, sparing the walled city from the stench of the open-air system.

By the beginning of the twentieth century in the United States, a regular system of garbage collection was in use in a majority of cities. By the 1920s, wetlands began to be used to dispose of garbage. An example is the Back Bay area of Boston. Now a prestigious residential area, Back Bay was once a wetland that was pressed into use as a landfill.

In 1937, a landfill that opened in Fresno, California, first utilized compacting of waste and daily application of a covering layer of soil. This more sanitary disposal of garbage, as opposed to the open-air and haphazard dumping of trash in dumps, became even more publicly acceptable during World War II (1939–1945), with images of troops burying their garbage. By the end of the war, more than 100 cities in the United States had established “sanitary landfills.”

In 1948, the Fresh Kills landfill was opened on New York’s Staten Island. Before it was closed due to environmental concerns in 2001, the landfill grew to occupy 2,200 acres (890 hectares); at one time it was the largest landfill in the world. At the site’s peak, five barges transported almost 3,300 tons (3,000 metric tons) of garbage to the site every day. By 2001, the mound of garbage that had been produced was higher than the Statue of Liberty.

Neighboring wetlands in surrounding regions of New Jersey were indiscriminately used as landfill sites beginning in the nineteenth century. By the late 1960s, problems with odor, contamination of tidal marshes, and hazards to aircraft due to the huge bird populations that scavenged at the open-air sites had become serious. Then, legislation was passed that resulted in the closure of many of the region’s landfills, although illegal disposal of garbage remains a problem in 2008.

By the mid-1950s, the booming U.S. economy had increased the allure for disposable goods, as a demonstration of people’s affluence. As a result, the amount of solid waste, and so the need for disposal sites, increased markedly. From 1958 to 1976, the amount of disposal packaging used in the United States increased almost 70%.

By the late 1950s, management of landfills was becoming more regulated. For example, the American Society for Civil Engineers published a guide to sanitary landfilling in 1959. The guide specified that garbage be compacted prior to addition to a landfill to reduce its volume and so increase the usable lifetime of the facility, and that each day’s addition of trash be covered with a layer of soil to minimize odor and attraction of pests such as rodents. In 1965, the federal Solid Waste Disposal Act was passed. Following its creation in 1970 by President Richard M. Nixon, the EPA assumed responsibility for the regulation of existing landfills and approval of new facilities. In 1979, open landfills were banned in the United States by the EPA, and legally enforceable standards for landfill construction and operation were enacted.

Landfill Construction and Operation

A new landfill must be built to meet a variety of specifications. The site needs to be near road and/or rail routes to allow for the convenient, safe, and economical transport of the garbage. Even though the base of the site will be lined, the geology of the underlying region needs to be acceptable. For example, a site with a subsurface that readily absorbs water or that consists of rock containing cracks is unacceptable, since liquid can be transferred down into the ground, perhaps even to groundwater. Additionally, moisture-laden porous soil may sag downward under the increasing weight of the landfill. As well, the water table (the upper limit where the subsurface is completely saturated with water) must not be close to

WORDS TO KNOW

ANAEROBIC: The absence of oxygen.

COMBUSTION: The process of burning a material.

COMPOSTING: Breakdown of organic material by microorganisms.

REMEDIATION: A remedy. In the case of the environment, remediation seeks to restore an area to its unpolluted condition, or at least to remove the contaminants from the soil and/or water.

the surface, which would increase the chance of groundwater contamination. The proposed site must not have any known archeological value and its development should have a minimal impact on local and migrating wildlife. As a final example, the site must be an acceptable distance from surface waters to minimize their contamination.

In contrast to massively large landfills such as Fresh Kills, newly constructed landfills tend to be confined to areas that are as small as possible for the intended lifetime of the facilities. To increase the lifetime, garbage is compacted to as small a volume as possible prior to being added to the landfill. The dense packing of trash in a landfill reduces the oxygen (O) level. As a result, materials in the landfill that can be decomposed by microorganisms will be broken down very slowly. This is an advantage, since it reduces the production of gases such as methane inside the landfill. An efficient and widely used recycling program helps to reduce the amount of decomposable material that ends up in a landfill. Still, in 2006, organic materials (which are decomposable) continued to make up the largest proportion of materials in landfills, according to data from the EPA.

Typically, vehicles that arrive at a landfill are inspected to help detect unacceptable waste such as potentially hazardous medical and industrial wastes, and the garbage is weighed. Once the load is tipped into the landfill at a specified location, compactors and bulldozers distribute the garbage over a wider area and compact it. Exiting vehicles are usually cleaned to minimize the chance that they will carry material off the site that could contaminate the environment.

At the end of each day’s operation, the newly added trash is covered up. This can be done by spreading soil or wood chips over the compacted garbage. The addition of garbage to a landfill proceeds in a predetermined pattern, which helps to increase the efficiency of the operation, extend the lifetime of the facility, and provide more of a safety control.

A landfill is lined with a clay and/or plastic liner that provides a barrier between the trash and the surrounding land. A liner is intended to prevent contamination of groundwater, keep the interior of the landfill dry, and restrict air from passing from the ground into the land-Keeping the garbage dry and oxygen-free reduces decomposition, which is mainly done by bacteria that require oxygen for their survival and activity.

In the United States, a municipal solid waste landfill is required to be constructed in a certain way, whether construction involves a pit dug into the ground or whether the garbage is to be piled up into a mound. The bottom-most layer can be compacted clay, on which rests a puncture-resistant plastic liner, or just the liner may be present. The material is typically polyethylene or polyvinylchloride, which are both very durable and resistant (but not totally) to decomposition. In some landfills, the liner is sandwiched between a fabric mat known as a geotextile mat, which helps protect the liner from being torn or punctured by rocks and gravel.

A pipeline positioned near the bottom of the landfill collects liquid (leachate) that percolates down through the garbage. The leachate is pumped out to a neighboring holding pond. This water cannot be directly released to the environment, since it could contain potentially toxic compounds. Tests are done to determine the presence and concentrations of various target compounds that are indicators of compromised water quality. Once the water quality has been assured and its release approved, the water can be released from the holding pond into a watercourse. The watercourse will be monitored during the release, so that the process can be stopped if necessary.

Similarly, precipitation can be collected in a drainage system composed of storm pipes. The water drains into a concrete or gravel drainage ditch that runs around the base of the landfill and empties into a collection pond. This pond is separate from the holding pond, since the water may not be toxic. Once particles in the collected water have settled out and tests have verified that the water quality is acceptable for release into the environment, the collected water can be allowed to drain off onto adjacent land or into a watercourse.

Each day’s garbage is put in a predetermined area of the landfill. At the end of the day, that area is covered with a layer of soil or wood chips to protect the fresh garbage from scavaging by rodents, birds, and insects. A new area is used the following day. Because the soil layer, which is typically up to 6 in (15 cm) thick, represents space that could otherwise be used for trash, some landfills have begun to substitute a layer of material or a spray of a paper and cement mixture that hardens into a protective shell. Either covering is only about 0.25 in (0.6 cm) thick.

Each daily section of a landfill is termed a cell. By dividing the available area in a landfill into cells, the process of garbage addition is streamlined, and the amount of space available for the garbage is maximized. In a typical landfill, a cell will be approximately 50 ft (15.2 m) long, 50 ft (15.2 m) wide, and 14 ft (4.2 m) high.

As sections of a landfill are completed and sealed off, precautions must be put into place to vent any methane gas that can form as a byproduct of microbial breakdown of organic material in the landfill. If this is not done, the gas that is produced occupies volume in the landfill, which could cause the total volume to increase. Methane can ignite, which poses a risk. Additionally, release of methane to the air can be dangerous for both wildlife and workers in the immediate area. A series of pipes placed throughout the landfill collects the methane, which can then be ignited and destroyed.

More recently, some landfills have begun to use the methane as an energy source. The gas can be collected for use as fuel. Not only does this remove a potential environmental problem from the landfill, but the sale of the gas brings additional revenue to the facility.

Completed sections of a landfill are permanently sealed using a polyethylene covering. This material is almost inert, and so will withstand environmental fluctuations and extremes for decades. The polyethylene “cap” is then covered by up to 2 ft (0.6 m) of compacted soil. Planting of grass stabilizes the soil, minimizing the chances of erosion, and increases the aesthetic beauty of the space. Tress or shrubs are not planted, since their roots could puncture the protective cap. Over time,

however, such vegetation may develop, as the landfill becomes more natural in character.

This is not to imply that landfills are not monitored when their productive lifetime is up. Periodic monitoring is done to ensure that leachate is not leaking from an unstable area of the landfill where, for example, the cap may have punctured. As well, pipes that were previously sunk into the groundwater in regions immediately surrounding the landfill are used to recover groundwater samples for monitoring. The finding of unacceptably polluted water can be an indication that the landfill is failing to contain the garbage. Remediation must then be done.

Monitoring is a long-term commitment, because the decomposition that does occur takes decades. For example, studies that have sampled the interior of landfills have recovered 40-year-old newspaper that is barely affected. EPA requires monitoring data for 30 years following the decommissioning of a landfill.

Impacts and Issues

The present-day regulations concerning the construction and operation of landfills, as well as the monitoring that is required during the use of a landfill and following its closure, reflects the great impact that the huge concentration of garbage can have on the environment. As well, the environmental vigilance has come from the bad experiences of the past, in which the uncontrolled and inappropriate use of landfills has contaminated air and water.

Although most developed countries have stringent landfill approval and operation regulations, the same is still not true of many developing and underdeveloped countries. For example, electronic waste (“e-waste”) including used computer monitors are routinely exported from countries like the United States to developing countries such as India, China, and the African continent. This continues in mainland China despite a government-imposed ban on the practice in 2000.

In India, tens of thousands of workers are employed at scrap yards that process up to 22,000 tons (20,000 metric tons) of e-waste annually. In such facilities, e-waste is incinerated, often under uncontrolled and unsafe conditions, which releases heavy metals such as lead (Pb), mercury (Hg), and cadmium (Cd) into the air. If workers are not properly protected with high-quality inhalation masks, they are at risk. As well, if the metals end up in water or sediment, they bio accumulate in the food chain. Human consumption of fish and other foods can be unhealthy.

Much of the e-waste that remains in the United States ends up in landfills. The EPA estimates that in the year 2000, almost 5.5 million tons (5 million metric tons) of e-waste was sent to landfills.

Even in developed countries, the use of landfills can be contentious. For example, under a 2003 provision of the North American Free Trade Agreement, the cross-border disposal of wastes that contribute to greenhouse-gas emissions was permitted. The city of Toronto, Ontario, Canada, currently ships in excess of 10,000 tons (9,000 metric tons) of garbage each day to landfills in Michigan. In return, Michigan is allowed to export hazardous waste (including radioactive waste) to landfills in Ontario. Public opposition by local residents on both sides of the border to these landfill policies has been vigorous.

The recovery or burning of landfill-emitted methane also benefits the atmosphere from the standpoint of global warming, since methane is a greenhouse gas. It is about 20 times more potent than carbon dioxide (CO₂). Accumulation of methane in the atmosphere has been linked to the increasing retention of heat in the region of the atmosphere called the troposphere. Similar to a greenhouse, the result is the warming of the air above Earth’s surface.

According to Environment Canada, the methane produced by landfills in Canada is sufficient to heat 600,000 homes a year. Recovery is limited as of 2008, but is expanding. This energy source will likely become more as fossil fuels become scarcer and more expensive to process.

See Also Groundwater Quality; Land Use

BIBLIOGRAPHY

Books

Newman, William, and Wilfred E. Houlton. Boston’s Back Bay: The Story of America’s Greatest Nineteenth-Century Landfill Project. Holliston, MA: Northeastern, 2007.

Rodgers, Heather. Gone Tomorrow: The Hidden Life of Garbage. New York: The New Press, 2006.

Royte, Elizabeth. Garbage Land: On the Secret Trail of Trash. Boston: Back Bay Books, 2006.

Web Sites

Environment Canada. “Mounting Concerns over Electronic Waste.” June 26, 2003. http://www.ec.gc.ca/envirozine/english/issues/33/feature1_e.cfm (accessed April 20, 2008).

Brian D. Hoyle