How Landfills Work

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].

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, and the overall trash production in the United States has tripled since then.

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].

Solid waste management has been a problem in the United States since the country's inception. Up until the late 1800s, people often simply tossed their household garbage 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].

The Problem

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 waste disposal.

The USPHS Report

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].

The Solution

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, the waste 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].

Current State

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 industrial waste.

Design and Operation

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].

Regulatory Process

Getting permission to build a landfill requires going through a complicated regulatory process. Federal regulations restrict development of landfill sites in some places, including wetlands, flood zones and areas with unstable soil. While landfills aren't necessarily banned from those places, they must 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].

Approval Process

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:

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

Heavy equipment compacts trash 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. Other parts of the system include 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 [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 landfill gas emissions 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 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 (e.g., 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.

Entry and Drop-off Stations

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.