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Bottom liner system - separates trash and subsequent leachate from groundwater

Cells (old and new) - where the trash is stored within the landfill

Storm water drainage system - collects rain water that falls on the landfill

Leachate collection system - collects water that has percolated through the landfill itself and contains contaminating substances (leachate)

Methane collection system - collects methane gas that is formed during the breakdown of trash

Covering or cap - seals off the top of the landfill

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The basic parts of a landfill, as shown in Figure 3, are:

Bottom liner system - separates trash and subsequent leachate from groundwater

Cells (old and new) - where the trash is stored within the landfill

Storm water drainage system - collects rain water that falls on the landfill

Leachate collection system - collects water that has percolated through the landfill itself and contains contaminating substances (leachate)

Methane collection system - collects methane gas that is formed during the breakdown of trash

Covering or cap - seals off the top of the landfill

Each of these parts is designed to address specific problems that are encountered in a landfill. So, as we discuss each part of the landfill, we'll explain what problem is solved.

Bottom Liner System

A landfill's major purpose and one of its biggest challenges is to contain the trash so that the trash doesn't cause problems in the environment. The bottom liner prevents the trash from coming in contact with the outside soil, particularly the groundwater. In MSW landfills, the liner is usually some type of durable, puncture-resistant synthetic plastic (polyethylene, high-density polyethylene, polyvinylchloride). It is usually 30-100 mils thick. The plastic liner may be also be combined with compacted clay soils as an additional liner. The plastic liner may also be surrounded on either side by a fabric mat ( geotextile mat) that will help to keep the plastic liner from tearing or puncturing from the nearby rock and gravel layers.

Cells (Old and New)

Perhaps, the most precious commodity and overriding problem in a landfill is air space. The amount of space is directly related to the capacity and usable life of the landfill. If you can increase the air space, then you can extend the usable life of the landfill. To do this, trash is compacted into areas, called cells, that contain only one day's trash. In the North Wake County Landfill, a cell is approximately 50 feet long by 50 feet wide by 14 feet high (15.25m x 15.25m x 4.26m). The amount of trash within the cell is 2,500 tons and is compressed at 1,500 pounds per cubic yard! This compression is done by heavy equipment (tractors, bulldozers, rollers and graders) that go over the mound of trash several times). Once the cell is made, it is covered with six inches of soil and compacted further. Cells are arranged in rows and layers of adjoining cells ( lifts).

In addition to compressing the trash into cells, space is conserved by excluding bulky materials, such as carpets, mattresses, foam and yard waste, from the landfill.

Storm Water Drainage

It is important to keep the landfill as dry as possible to reduce the amount of leachate. This can be done in two ways:

Exclude liquids from the solid waste. Solid waste must be tested for liquids before entering the landfill. This is done by passing samples of the waste through standard paint filters. If no liquid comes through the sample after 10 minutes, then the trash is accepted into the landfill.

Keep rainwater out of the landfill. To exclude rainwater, the landfill has a storm drainage system. Plastic drainage pipes and storm liners collect water from areas of the landfill and channel it to drainage ditches surrounding the landfill's base.

The ditches are either concrete or gravel-lined and carry water to collection ponds to the side of the landfill. In the collection ponds, suspended soil particles are allowed to settle and the water is tested for leachate chemicals. Once settling has occurred and the water has passed tests, it is then pumped or allowed to flow off-site.

Leachate Collection System

No system to exclude water from the landfill is perfect and water does get into the landfill. The water percolates through the cells and soil in the landfill much as water percolates through ground coffee in a drip coffee maker. As the water percolates through the trash, it picks up contaminants (organic and inorganic chemicals, metals, biological waste products of decomposition) just as water picks up coffee in the coffee maker. This water with the dissolved contaminants is called leachate and is typically acidic.

To collect leachate, perforated pipes run throughout the landfill (Figure 3). These pipes then drain into a leachate pipe, which carries leachate to a leachate collection pond. Leachate can be pumped to the collection pond or flow to it by gravity, as it does in the North Wake County Landfill.

The leachate in the pond is tested for acceptable levels of various chemicals (biological and chemical oxygen demands, organic chemicals, pH, calcium, magnesium, iron, sulfate and chloride) and allowed to settle. After testing, the leachate must be treated like any other sewage/wastewater; the treatment may occur on-site or off-site. At the North Wake County Landfill, leachate is released to the wastewater treatment plant in Raleigh, where it is treated and released into the Neuse River. Some landfills recirculate the leachate and later treat it. This method reduces the volume of leachate from the landfill, but increases the concentrations of contaminants in the leachate.

Methane Collection System

Bacteria in the landfill break down the trash in the absence of oxygen (anaerobic) because the landfill is airtight. A byproduct of this anaerobic breakdown is landfill gas, which contains approximately 50 percent methane and 50 percent carbon dioxide with small amounts of nitrogen and oxygen. This presents a hazard because the methane can explode and/or burn. So, the landfill gas must be removed. To do this, a series of pipes are embedded within the landfill to collect the gas. In some landfills, this gas is vented or burned.

More recently, it has been recognized that this landfill gas represents a usable energy source. The methane can be extracted from the gas and used as fuel. In the North Wake County Landfill, a company collects the landfill gas, extracts the methane, and sells it to a nearby chemical company to power its boilers. The extraction system is a split system, meaning that methane gas can go to the boilers and/or the methane flares that burn the gas. The reason for the split system is that the landfill will increase its gas production over time (from 300 cubic feet per minute to 1,250 cubic feet per minute) and exceed the capacity of the boilers at the chemical company. Therefore, the excess gas will have to be burned. It is not cost-effective to compress the excess gas to liquid and sell it.

Covering or Cap

As mentioned above, each cell is covered daily with six inches of compacted soil. This covering seals the compacted trash from the air and prevents pests (birds, rats, mice, flying insects, etc.) from getting into the trash. This soil takes up quite a bit of space. Because space is a precious commodity, many landfills are experimenting with tarps or spray coverings of paper or cement/paper emulsions. These emulsions can effectively cover the trash, but take up only a quarter of an inch instead of 6 inches!

When a section of the landfill is finished, it is covered permanently with a polyethylene cap (40 mil). The cap is then covered with a 2-foot layer of compacted soil. The soil is then planted with vegetation to prevent erosion of the soil by rainfall and wind. The vegetation consists of grass and kudzu. No trees, shrubs or plants with deep penetrating roots are used so that the plant roots do not contact the underlying trash and allow leachate out of the landfill.

Occasionally, leachate may seep through weak point in the covering and come out on to the surface. It appears black and bubbly. Later, it will stain the ground red. Leachate seepages are promptly repaired by excavating the area around the seepage and filling it with well-compacted soil to divert the flow of leachate back into the landfill.

Groundwater Monitoring

At many points surrounding the landfill are groundwater monitoring stations. These are pipes that are sunk into the groundwater so water can be sampled and tested for the presence of leachate chemicals. The temperature of the groundwater is measured. Because the temperature rises when solid waste decomposes, an increase in groundwater temperature could indicate that leachate is seeping into the groundwater. Also, if the pH of the groundwater becomes acidic, that could indicate seeping leachate.

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The basic parts of a landfill, as shown in Figure 3, are: Bottom liner system - separates trash and subsequent leachate from groundwater Cells (old and new) - where the trash is stored within the landfill Storm water drainage system - collects rain water that falls on the landfill Leachate

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First, access roads to the landfill site must be built if they do not already exist. These roads will be used by construction equipment, sanitation services and the general public. After roads have been built, then the landfill can be excavated. In the North Wake County Landfill, the landfill began 10 feet below the road surface.

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What happens to all of that trash the dump truck picks up every week? It doesn't just disappear into a parallel universe: Each day, we all contribute to the local landfill, and the waste disposal system is pretty involved.

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For a landfill to be built, the operators have to make sure that they follow certain steps:
1. First, it must be determined if there is sufficient land for the landfill.
2.Second, the composition of the underlying soil and bedrock must be determined.
3.Third, the flow of water over the area must be studied.
4.Fourth, you need to determine the potential effects of the landfill and possible contamination on local wildlife.
5.Finally, if the site contains any historical or archeological artifacts, you would not want to build a landfill there.

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Craig Freudenrich, Ph.D., Patrick J. Kiger

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What happens to all of that trash you put on the curb every week? It doesn’t just disappear into a parallel universe. Much of it probably goes to the local landfill, and how it gets handled there is a very involved system.

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1. What purpose does this landfill have?

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1. What purpose does this landfill have?

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The purpose of a landfill is to bury the trash in such a way that it will be isolated from groundwater, will be kept dry and will not be in contact with air. Under these conditions, trash will not decompose much. A landfill is not like a compost pile, where the purpose is to bury trash in such a way that it will decompose quickly.

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You have just finished your meal at a fast food restaurant, and you throw your uneaten food, food wrappers, drink cups, utensils and napkins into the trash can. You don't think about the trash again. On trash pickup day in your neighborhood, you drag your trashcans to the curb, and workers dump the contents into a big truck and haul it away. You don't have to think about that trash again, either.

But maybe you have wondered, as you watch the trash truck pull away, just where that garbage ends up?

Americans generate trash at an astonishing rate of 4.9 pounds (2.2 kilograms) per person each day, which collectively amounts to 292.4 million tons (265.3 million metric tons) per year [source: EPA]. Americans produce roughly three times the global average for garbage, according to a 2019 report by research firm Verisk Maplecroft [source: Smith].

What happens to this trash? Some gets recycled or recovered, and some is burned, but the majority is buried in landfills. In this article, we will examine how landfills are built, what happens to the trash in landfills, what problems are associated with landfills and how these problems are solved.

Of the 292.4 million tons (265.3 million metric tons) per year of trash that the U.S. generated in 2018, the most recent year for which data is available, 69 million tons (62.6 million metric tons) were recycled, and another 25 million tons (22.7 million metric tons) were composted. The recycled and composted trash amounted to 32.1 percent of the total. Another nearly 35 million tons (31.75 million metric tons) were combusted for energy recovery. But half of the nation's trash - 146 million tons (132.4 million metric tons - ended up being buried in landfills [source: EPA].

The trash production in the United States has tripled since 1960. This trash is managed in various ways. About 32.1 percent of the trash is recycled or composted, and just about 50 percent is buried in landfills [source: EPA]. The amount of trash buried in landfills is about one-and-a-half times the amount put in landfills in 1960. The U.S. is the third biggest producer of trash after China and India, but the U.S. creates a disproportionate 12 percent of the world's garbage, considering that it only has 4 percent of the world's population [source: Smith].

What to do with trash has always been a problem in America. Up until the late 1800s, people often simply tossed their refuse into the gutter in cities such as New York, where it was common to see knee-high piles of food waste, broken furniture, horse manure and even dead animals on street corners [source: Oatman-Stanford].

Eventually, cities began to collect trash, but often garbage was hauled to dumps - open holes in the ground - where it often was burned, creating air pollution that was a hazard to human health. By the 1960s, though, it was obvious to local, state and federal government officials that something had to be done about trash.

In 1964, the U.S. Public Health Service (USPHS) issued a disturbing report, in which it predicted that solid waste generation would double in 20 years' time, and that urban areas would run out of nearby land for garbage disposal. Additionally, the USPHS found that open-burning dumps were causing respiratory harm and posed disease threats, and polluted groundwater as well [source: Hickman].

Modern sanitary landfills - the first of which was created in California back in 1937 - became the solution to this problem. Instead of just dumping or burning trash, it was systematically buried, compacted with heavy equipment, and then covered. In 1976, Congress passed the Resource Conservation and Recovery Act, which imposed requirements on landfills to prevent them from polluting the environment [source: Zylberberg].

Today, there are about 2,600 landfills that handle municipal solid waste across the U.S. [source: EPA.]

These facilities, which are designed and operated to conform to federal regulations, primarily are for the purpose of handling household trash. In addition, municipal solid waste landfills also are allowed to take some other types of nonhazardous waste from businesses and industry.

They have a composite liner on top of 2 feet (0.61 meters) of compacted clay soil on the bottom and sides, as well as systems to capture leachate, the water that percolates down through the trash, before it can contaminate groundwater.

Additionally, landfills are equipped with groundwater testing wells to make sure that pollution isn't escaping. Landfills also must use federally approved operating practices for handling the trash, which include compacting and covering it frequently with several inches of soil. That layer of soil helps reduce the odor and problems with insects and rodents, and also prevents trash from getting out of the landfill and turning into litter [source: EPA].

In the sections that follow, we'll go into more detail about how landfills are designed and built, and how they work.

Getting permission to build a landfill requires going through a complicated regulatory process. Federal regulations restrict landfill development in some places, including wetlands, flood zones and areas with unstable soil. While landfills aren't necessarily banned from those places, they're required to meet more stringent performance standards.

Additionally, new or expanded landfills located near airports have to show that they won't create a bird hazard for aircraft, a restriction that's prevented some landfill projects from being built [source: Walsh and O'Leary].

A company that wants to build a landfill must meet federal regulations, as well as those in the state where the site is located. In Wisconsin, for example, there are rules against putting landfills close to streams, lakes and ponds, and barring them close to highways and parks, unless there are barriers or landscaping to block the view [source: Walsh and O'Leary].

Getting a landfill approved requires a lot of careful research, since things such as the land's contours and the geological formations under the ground can affect whether a site is suitable for burying trash [source: Walsh and O'Leary].

Landfill developers also must notify the public and hold a public hearing, and they may have to contend with opposition from neighbors and members of the public who don't want trash to be buried nearby [source: Walsh and O'Leary].

Modern landfills aren't all identical in design, but most utilize similar technologies, though the exact sequence and type of materials used may different from site to site [source: WM.com]. Some basic parts of a landfill, as shown in the image above, include:

plastic liners (C): separate trash and subsequent leachate from groundwater

cells (I and J): where the trash is stored within the landfill

stormwater drainage systems (G): collect rainwater that falls on the landfill

leachate collection systems (D and K): collect water that has percolated through the landfill itself and contains contaminating substances (leachate)

methane collection systems: collect methane gas that is formed during the breakdown of trash

covering or caps: seal off the top of the landfill

Each of these parts is designed to address specific problems in a landfill.

So, as we discuss each part of the landfill, we'll explain what problem is solved.

Bottom Liner System

A landfill's major purpose and one of its biggest challenges is to contain the trash so that the trash doesn't cause problems in the environment. The bottom liner, made of thick plastic, prevents the trash from coming in contact with the outside soil, particularly the groundwater [source: WM.com].

Cells

Trash is compacted by heavy equipment into areas, called cells, which typically contain a day's worth of refuse to get the most use of the volume of space in the landfill. Once the cell is made, it is covered with 6 inches (15 centimeters) of soil and compacted further [source: Bolton].

Stormwater Drainage

To keep rainwater out, a landfill has a storm drainage system to route the runoff into drainage ditches and away from the buried trash. Concrete, plastic or metal culverts underneath nearby roads and stormwater basins, which can reduce the suspended sediment in the water to minimize soil loss from the landfill, are other parts of the system [source: Uteir].

Plastic drainage pipes and storm liners collect water from areas of the landfill and channel it to drainage ditches surrounding the landfill's base. The ditches are either concrete or gravel-lined and carry water to collection ponds to the side of the landfill. In the collection ponds, suspended soil particles are allowed to settle and the water is tested for leachate chemicals. Once settling has occurred and the water has passed tests, it is then pumped or allowed to flow off-site.

Leachate Collection System

No system to exclude water from the landfill is perfect and water does get into the landfill. The water percolates through the cells and soil in the landfill similar to how water percolates through ground coffee in a drip coffee maker. As the water trickles through the trash, it picks up contaminants. This water with contaminants is called leachate and is typically acidic.

To collect leachate, perforated pipes run throughout the landfill. These pipes then drain into a leachate pipe, which carries leachate to a leachate collection pond [source: Austin Community Landfill].

Methane Collection System

Bacteria break down the trash in the absence of oxygen (anaerobic) because the landfill is airtight. A byproduct of this anaerobic breakdown is landfill gas, which contains approximately 50 percent methane and 50 percent carbon dioxide with small amounts of nitrogen and oxygen.

Methane is a serious issue for landfills because it's a potent greenhouse gas, some 28 to 36 times more effective than carbon dioxide at trapping heat in the atmosphere. And landfills are the third-largest source of methane emissions in the U.S., accounting for about 15 percent of the gas that escaped into the atmosphere in 2019 [source: EPA]. Methane also is a potential safety hazard, since methane can explode and burn [source: NY Department of Health].

Covering or Cap

Putting down a covering of compacted soil seals the trash from the air and prevents pests (birds, rats, mice, flying insects, etc.) from getting into the trash. At New York's Fresh Kills Landfill, trash is covered with at least 2 feet (0.61 meters) of soil, graded between 4 and 33 percent to help with stormwater drainage. That layer is topped by additional layers of synthetic fabric and plastic and a layer of soil to allow vegetation to grow atop the landfill [source: Freshkills Park Alliance].

Groundwater Monitoring

At many points surrounding the landfill are groundwater monitoring stations. These are pipes that are sunk into the groundwater so water can be sampled and tested for the presence of leachate chemicals. The temperature of the groundwater is also measured. Because the temperature rises when solid waste decomposes, an increase in groundwater temperature could indicate that leachate is seeping into the groundwater. Also, if the pH of the groundwater becomes acidic, that could indicate seeping leachate [source: EPA].

Landfill customers are typically municipalities and construction/demolition companies, although residents may also use a landfill as well. A layout of a typical landfill with supporting structures is shown here.

This description is of a typical landfill that HowStuffWorks visited years ago. Near the entrance of the site is a recycling center ( A) where residents can drop off recyclable materials (aluminum cans, glass bottles, newspapers, blend paper, corrugated cardboard). This helps to reduce the amount of material in the landfill. Some of these materials are banned from landfills by law because they can be recycled.

As customers enter the site, their trucks are weighed at the scale house ( B). Customers are charged tipping fees for using the site. These fees are used to pay for bonds or operation costs.

Along the site, there are drop-off stations for materials that are not wanted or legally banned by the landfill. A multi-material drop-off station is used for tires, motor oil, lead-acid batteries and drywall. Some of these materials can be recycled.

In addition, there is a household hazardous waste drop-off station for chemicals (paints, pesticides, etc.) that are banned from the landfill. These chemicals are disposed by private companies. Some paints can be recycled and some organic chemicals can be burned in incinerators or power plants.

Other structures alongside the landfill include the borrowed area that supplies the soil for the landfill, the runoff collection pond ( N), leachate collection ponds ( I) and methane station ( L).

Landfills are complicated structures that, when properly designed and managed, serve an important purpose.

Originally Published: Oct 16, 2000

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What happens to all of that trash you put on the curb every week? It doesn't just disappear into a parallel universe. Much of it probably goes to the local landfill, and how it gets handled there is a very involved system.