Landfills

For centuries, humans have found it convenient to dump unwanted wastes into ravines, swamps, and pits. With increased emphasis on sanitation, open dumps have been replaced with landfills, where wastes are placed into excavations and covered with soil. Landfilling is the most common method of solid waste management.

Hazardous versus Nonhazardous Wastes

Almost all human activity produces unwanted by-products called waste. For individual residences, these unwanted wastes are household garbage. Commercial businesses also create large amounts of waste materials. These can be classified as either hazardous or nonhazardous. Hazardous wastes contain chemical compounds that can endanger public health or the environment. Nonhazardous wastes may contain small amounts of toxic or hazardous ingredients but present no threat to human communities if disposed of correctly.

Most landfills separate these types of materials, with typical facilities handling only nonhazardous waste. Because of the severe environmental restrictions and legal liabilities associated with burying hazardous materials in the ground, recycling and incineration have become the principal disposal options for hazardous wastes. Sites at which toxic wastes are buried are tightly controlled and carefully monitored, to ensure that no leakage occurs that could pollute groundwater.

Land Disposal

One of the primary methods for getting rid of waste is land disposal. Land disposal may take the form of placing the unwanted material directly on the land surface, especially in low, swampy areas, ravines, and old gravel, or other mined-out pits. These types of land disposal are known as "dumps," or "open dumps," because the unwanted wastes are haphazardly dumped at the site, and the waste piles often are not covered until some other use is made of the surface. The term “landfill,” although sometimes used to describe dumps, refers to the land disposal of wastes in which the disposal site is designed and operated to a specific plan. Modern landfills are designed to receive a certain amount of refuse over a specified period of time, such as twenty years. At the end of that period, the site is reclaimed and converted for a different land use.

When the earth’s population was small, waste products were discarded on the ground surface or thrown into streams near campsites. The amount of waste generated and disposed of was small enough that there was no significant pollution or adverse effects on the environment. As the population grew and more people began to live concentrated in towns, garbage was often thrown in ravines and low, swampy areas as a means of disposal. This also served to fill in the land and create a more usable area. This practice of open dumping has continued globally into the twenty-first century. The chief advantages of this method of waste disposal are its ease of use and low cost.

By 2023, the global population had reached 8 billion people. In the same year, the number of people living in the United States had increased to over 330 million. The population concentration has shifted from rural to urban areas. To supply the demands of the public, industries developed and produced a wide variety of materials and chemicals, such as plastics used in packaging, that end up as waste products after use. Millions of metric tons of solid waste are generated each year in the United States: by 2018, municipal rubbish and garbage alone—that is, nonindustrial, household trash—made up 292.4 million tons, the equivalent of 4.9 pounds per person per day, based on Environmental Protection Agency (EPA) data. About 69 million tons of that municipal solid waste was recycled and 25 million composted industrially. Nearly 22 percent of that solid waste was food matter in 2018; the following year. In 2015, the EPA and the US Department of Agriculture devised a joint plan to reduce food waste by half by 2030, but based on data gathered in 2018, this number was only increasing.

As the amount of municipal wastes increased over time, more space was needed for open dumps. Many serious problems arose as the use of dumps conflicted with land use, sanitation, and aesthetics in the surrounding communities. The pollution of rivers and groundwater was directly traced to uncontrolled dumping of toxic wastes in dumps and pits. In response, the federal government enacted a series of laws to protect the environment and especially the surface and groundwaters from pollution. The result of the legislation was to define and separate wastes that were hazardous to humans from the municipal wastes in land disposal. Special restrictions were placed on the disposal of hazardous wastes. At first, no special restrictions were placed on the land disposal of municipal wastes. Nonetheless, the need to protect rivers and groundwater from pollution required states to establish a permit process that set limits on where dumps and landfills could be located. Thus, the cost increased for the disposal of municipal and industrial wastes.

Landfill Facilities and Features

There are thousands of active and inactive nonhazardous waste landfills of various types in the United States. Specialized industrial landfills handle construction and demolition debris, coal combustion by-products, and materials containing polychlorinated biphenyl (PCB). Modern landfills cover many acres. Some are more than 100 acres in size.

Although the actual size and shape of each landfill depend upon the site geology and the amount of waste, landfill facilities generally are excavated into the ground to form a pit. The depth of excavation to form the pit will depend upon the thickness of low-permeability clay soils over a buried water-bearing deposit, called an aquifer, which supplies drinking water to households and towns. Enough clay soil must be left to prevent the seepage of any leachate that may escape from the landfill and pollute the aquifer. (Leachate is rainwater that has seeped through the landfill refuse and has become polluted.) Monitoring wells are placed around the landfill into the aquifer to ensure that no pollution occurs. After the excavation has been dug to its intended depth, a protective liner is placed over the bottom and sides of the pit. The liner may be of clay compacted by a construction roller, or it may be a plastic sheet called a geomembrane.

Waste material that is brought to the landfill daily is placed in specified layers called cells. At the close of each day, the exposed waste is covered with soil to prevent odors, blowing debris, and infestation by vectors. “Vector” is a term used to refer to any disease-carrying insects or animals, such as rats, flies, and birds, that would infest the waste material. The daily cells are stacked one on top of another until the final height is reached. Once the design height is reached, a final soil cover is added, and the ground surface is reclaimed to form a moundlike hill. Leachate and gas collection pipes are installed throughout the landfill to collect and dispose of dangerous gases and liquids. These perforated pipes are covered with a layer of gravel through which the leachate can easily flow from the landfill waste to the collection network. In some landfills, the gas generated by decomposing waste (methane), is captured and used to generate energy.

Site Evaluation

Before a landfill can be constructed and operated at a proposed location, the site must be evaluated to ensure that it satisfies all local, state, and federal regulations relating to protecting the environment and the health and welfare of the citizens. The landfill operator must collect and assess much information before applying to a state pollution control board or similar governing commission for a permit. The information must verify that the landfill will present no danger to the public or to the environment. A large number of factors must be evaluated and presented to the permit board.

By far the most important factor for determining whether a site is satisfactory for a landfill is the geology. The local geology must contain thick and continuous clay soils or their rock equivalent, shale. These deposits do not allow water or contaminated water from landfills (leachate) to flow rapidly through them; their low permeability will prevent any leachate that may escape from the pit from flowing into surface streams or underlying aquifers, which supply water to the surrounding communities. Generally, additional lines of defense are installed, such as impermeable plastic barriers and clay liners. It is very important to protect these aquifers; once they become polluted, it is extremely difficult (and costly) to clean them up for public use in a short period of time. Compared to water in surface streams, groundwater in porous aquifers moves quite slowly. Also, because the aquifer is hidden beneath the surface, it is difficult to trace and clean up the polluted water flow. To evaluate the subsurface geology of the site and the surrounding region, the company proposing the landfill will drill holes around the area and take soil samples so that a geologist can identify the different soils and rocks and construct a cross-section illustrating the thicknesses, types, and relationships of the different materials.

Besides the geology, other major factors that must be assessed are climate and weather, flooding, ecology, historical landmarks, nearness to airports, traffic, and land-use and zoning restrictions. The climate and weather describe the rainfall and winds to be expected. All landfills must be above the 100-year flood height or have suitable flood protection. Special emphasis is placed on the ecology: A landfill cannot be built in protected wetlands or compromise the habitat of endangered species of plants and animals. Also, landfills are not allowed to destroy historical landmarks and archaeological sites. Municipal landfills attract birds; therefore, landfills must be more than a mile away from airports. Information on the road system and traffic volumes must be gathered to assess the impact of waste trucks, which add both more traffic and greater loads to the roads. Landfills are not the most desirable form of land use and, therefore, such developments must prove compatible with the surrounding land use. Many communities have zoning restrictions. Thus, evaluating a proposed site for a landfill is a complex and time-consuming job.

Landfill Design

A company must supply to the state permit board data and plans outlining the overall design, construction, operation, and reclamation of the land when the landfill is closed—in addition to information and assessment on the suitability of the proposed site. The design information must include drawings showing the depth and size of the pit area. The plans must give details on how the leachate is prevented from escaping from the pit, and where monitoring wells will be drilled around the site to detect any leakage that may occur. Landfills that contain garbage and other organics will generate gas that must be collected and either flared into the atmosphere or piped away for fuel. Some landfills use the gas at the site for commercial and light-industrial energy.

The final aspect in a landfill design is closing the operation and "remediation" of the site for a different land use. A final soil cover is placed over all the waste to isolate it from the public. Five to ten feet in thickness, this layer of soil controls vectors, prevents odors, and beautifies the landfill’s surface. Periodic checks are made by the owner after the landfill has been reclaimed to sample the monitoring wells and to repair any erosion features. A decommissioned landfill may later be used as a site for another facility after it is monitored for an extended time and deemed safe; in the United States this reclamation takes place in three stages. Category 1 reuse treats the landfill as an open space suitable for light recreation or agriculture. Category 2 allows the installation of some structures, pavement, and utilities, such as for a golf course. Category 3 development allows major construction, with examples ranging from a football stadium to a shopping center.

Public Policy

The US federal government, the states, and communities have had to reevaluate their policies of uncontrolled dumping of municipal and industrial wastes because of serious pollution to the water supplies. With the enactment of laws to protect the environment and prevent pollution, such as the Solid Waste Disposal Act, land disposal of wastes is now controlled and monitored. Hazardous wastes are a severe threat to the health and welfare of communities. As a result, with few exceptions, land disposal of these wastes is no longer the primary disposal option.

Land disposal remains the primary method of disposing of nonhazardous wastes. Liquid nonhazardous wastes usually are disposed of in lagoons. Solid wastes, such as garbage and trash, are placed in landfills. For cities and other urban areas, large acreage of open land is scarce, and citizens generally object to having a landfill constructed nearby. Thus, cities and adjacent communities have often been forced to cooperate on large regional landfills. It is therefore necessary for companies wanting to site new landfills to hunt for undeveloped land of a hundred acres or more where the geology can prevent pollution of the public water supplies. Even though municipal landfills, often called sanitary landfills, are considered nonhazardous, they generally contain from 5 to 10 percent toxic material. If the landfill is small, such as in rural communities, the amount of hazardous leachate that may escape from the pit site is small and thus will pose no appreciable detrimental effects on the environment and public health. The large landfills that serve cities, however, do pose a threat to the public welfare and health if major amounts of leachate escape from the site. It is extremely difficult and costly to purify groundwater used for public water supplies if an aquifer becomes polluted. When households and communities lose their groundwater supply to pollution, the hardships to the citizens are both severe and costly. Some communities have had to transport water from other areas and impose tight controls on how the water is used.

Waste disposal is a very important part of the lifestyle of modern society; with the quest for more and more conveniences and services, the unwanted by-products of civilization continue to increase and must be disposed of in some way. In addition, the natural environment has deteriorated to a point of serious concern. Therefore, landfilling must be done with the utmost care and planning in order to guard against pollution. The amount of material sent to landfills may be reduced through waste reduction methods and recycling. Alternatives to landfills include incineration, mechanical biological treatment, anaerobic digestion, and composting.

Principal Terms

aquifer: a porous, water-bearing zone beneath the surface of the earth that can be pumped for drinking water

clay: a term with three meanings—a particle size (less than 2 microns), a mineral type (including kaolin and illite), and a fine-grained soil that is like putty when damp

geomembrane: a synthetic sheet (plastic) with very low permeability used as a liner in landfills to prevent leakage from the excavation

groundwater: water found below the land surface

leachate: water that has seeped down through the landfill refuse and has become polluted

permeability: the ability of a soil or rock to allow water to flow through it; sands and other materials with large pores have high permeabilities, whereas clays have very low permeabilities

pollution: a condition of air, soil, or water in which substances therein make it hazardous for human use

saturated zone: that zone beneath the land surface where all the pores in the soil or rock are filled with water rather than air

vector: a term used in waste disposal when referring to rats, flies, mosquitoes, and other disease-carrying insects and animals that infest dumps

water table: the upper surface of the saturated zone; above the water table, the pores in the soil and rock containing both air and water

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