Modern landfills are carefully engineered facilities designed to safely contain waste, protect groundwater, manage gases, and meet strict environmental regulations. Find out how they’re built, how they operate, and what happens to waste over time.
How Do Landfills Work?
Humans have been dealing with trash for thousands of years, and today’s waste facilities play a critical role in managing it responsibly. We all know our trash has to go somewhere, but what exactly is a landfill, and how does it work?
What Exactly Are Landfills?
What Is a Landfill?
A landfill is a site designed for the controlled disposal of solid waste.
Why They Matter
Modern facilities are engineered to protect groundwater, air quality, and public health.
How They’re Regulated
They are intentionally located, designed, monitored, and operated under EPA regulations.
Difference Between a Landfill and a Dump
When people think of landfills, they often mix them up with dumps. Unlike outdated dumps, landfills are highly regulated by the government and have a liner at the bottom to catch liquid produced by the decomposing trash. This helps to protect the groundwater and reduces environmental impact.
How Landfills Used to Work
The oldest known landfill was discovered in Crete, and it dates back to about 3,000 BCE. In the United States before the mid-1900s, communities used dumps for all of their waste. These locations were usually placed on the outskirts of towns and in rural areas.
Before the modern landfill liner system, the soil surrounding dumps was often contaminated with toxins and hazardous liquids. This caused issues with the surrounding water supplies and caused harm to the health of nearby communities.
History of Landfill Regulations
The Second Industrial Revolution was followed by an increase in consumerism, and dumps could no longer contain the trash generated by the economy. In 1965, Congress passed the first legislation to address growing concerns about waste management. The Solid Waste Disposal Act gave authority to the Environmental Protection Agency (EPA) to set standards.
In the 1970s, Congress took further action to set higher standards to protect the environment. The passage of the Resource Conservation and Recovery Act (RCRA) in 1976 defined how landfills were to be built, operated, monitored, and closed.
How Modern Landfills Are Made
While landfills aren’t all built the same way, they rely on shared design principles. Most facilities include the following components:
A bottom liner to protect surrounding soil and groundwater from leachate leaks located at the bottom of the landfill.
Landfill cells, which are individual sections where trash is deposited. Landfills usually only have one cell open at a time.
A leachate collection system designed to capture and contain any liquid generated from waste.
A stormwater drainage system to control and manage stormwater runoff. These systems are separate from the layering system and keep water out of the landfill.
A groundwater monitoring system to collect groundwater data, such as water contamination levels and leachate presence in the water.
A gas collection system to collect gas generated from the decomposition of waste. Since landfill gases contribute about 14% of the total global methane emissions, the gas collection system plays a critical role in protecting the environment.
A capping system to prevent any potential contamination. Materials, such as soil or asphalt, are used to cover the landfill.
Other factors, such as placement of the landfill and its capacity, are based on an environmental risk assessment study, as recommended by UNEP.
The Four Layers of a Landfill
A landfill’s structure is built as a four-layer system designed to keep waste byproducts from entering the environment. These layers contain leachate, gases, and other harmful substances. The four layers generally include:
Layer 1: Protective Liners
A protective liner composed of thick clay, followed by a layer of 60-mil plastic. It is meant to keep out water and prevent leachate.
Layer 2: Drainage
Sits on top of the protective liners and collects leachate, which is then transported to a treatment facility before being returned to the environment. A layer of sand is placed on top of the drainage system to protect it.
Layer 3: Gas Collection
Uses a network of pipes to capture gases released during anaerobic decomposition. The gas collection system directs gases to a single location, where they are collected for energy or flared.
Layer 4: Trash
Deposited in cells and compacted using heavy equipment. Higher compaction rates make better use of landfill space. Each day, the cell is covered with dirt to prevent odors and deter wildlife.
Strict federal regulations require landfill designs to meet criteria to protect human health and the environment. All these parts work together to preserve groundwater quality and prevent air pollution. Landfill monitoring systems, such as groundwater monitoring systems and LFG monitoring systems, are essential to the facility's health.
Together, these layers work as a containment system that limits air pollution, water contamination, and long-term risk.
What Happens to Garbage in a Landfill
Most people don’t think much about what happens to trash after it’s picked up. Once waste arrives, it moves through a tightly controlled daily process:
Tipping
The dumping process is known as tipping. Each day, garbage trucks come from all over the region to one central location, hauling trash collected from dumpsters and residential trash bins. The waste is then tipped into the open cell of the landfill, called the working face. Waste management companies pay landfill tipping fees to dump their waste.
Compacting
Once the trash is tipped into the working cells of landfills, it is compacted or crushed to save space.
Daily Cover
A layer of soil known as the daily cover is used to cover the garbage in order to prevent odors, scavenging, and the spread of disease. Daily covering is required by the EPA standards outlined in the RCRA.
Monitoring
Landfills are closely monitored and daily housekeeping tasks are performed by landfill operators to ensure that dumping facilities are performing in accordance with federal regulations.
Landfill Classifications
States categorize landfills into classes or types. These categories are not designated by the EPA, and they can vary in meaning from state to state. For example, Class 1 landfills in California are designated for accepting oil field waste, while Class 1 landfills in Tennessee are for household waste.
Even though classification varies at the state level, all states are regulated by the EPA under the umbrella of the RCRA. Here is the most common categorization of non-hazardous waste landfills:
Class 1: Household Waste
Class 2: Industrial and Commercial Waste
Class 3: Organic Waste
Class 4: Construction and Demolition Waste
Different Types of Landfills
Under the RCRA, all waste is categorized as either municipal solid waste, industrial waste, or hazardous waste.
Municipal Solid Waste Landfills
Solid household waste is disposed of in Municipal Solid Waste Landfills (MSWLFs) that are governed by local and state municipalities. These are designed to handle nonhazardous household waste.
Bioreactor landfills
A subcategory of MSWLFs designed for handling organic waste that degrades quickly. About 20% of all waste that goes into landfills is organic, including all plant or animal-based materials. Unless organic waste ends up in a bioreactor landfill, it doesn’t decompose properly.
Industrial Waste Landfills
American industries produce billions of tons of waste each year, but it’s hard to track and measure. Some industrial waste is recycled, and it’s even sold as a commodity to other countries, like China. Industrial food waste is often composted or made into biodiesel fuels.
The two types of industrial waste landfills with exclusive designations include:
Construction and Demolition (C&D) Debris Landfills designed to accept waste from all types of construction and demolition projects.
Coal Combustion Residual (CCR) Landfills designed to dispose of coal ash.
Waste that is toxic to humans and the environment is considered hazardous, and it requires special handling at a hazardous waste landfill. Hazardous waste can be liquids, solids, or contained gases, and must be disposed of carefully.
Do Landfills Ever Get Full?
Landfills have a capacity for how much trash they can take in. Once a facility gets full, there is a capping process that prevents air and water pollution from occurring. A final layer of heavy plastic is used to cover the landfill and prevent water from seeping into it. Soil is then placed on top of the cover, and vegetation is planted to stabilize the ground and prevent runoff.
Once a facility is closed, it may be repurposed into building sites or used as solar and wind farms. In some cases, cities are built on top of capped landfills, like parts of Manhattan.
What is Landfill Mining?
Landfill mining is becoming more popular as a way to free up space and improve waste management sustainability practices. Mining involves excavating old or closed landfills in order to recover and recycle materials, such as metals, plastics, glass, and soil, while also removing hazardous material.
The lifespan of a landfill is about 30 to 50 years.
Landfill and Garbage Statistics
The average American produces 4.6 pounds of waste each day for a total of about 290 million tons of garbage annually in the United States. The lifespan of a landfill is about 30 to 50 years, and waste experts predict that landfill space could be used up by 2050. Many states are quickly running out of landfill space: New York City, which pays $1 million per day to other states to handle its waste, ran out of space years ago.
It makes sense that we are running out of landfill space given the rate we produce trash and the size of the average landfill, which is 600 acres. The biggest landfill in the United States is the Apex Regional Landfill, located near Las Vegas. With a capacity of over 1 billion tons of waste, it has twice the capacity of the next largest landfill, located in Utah. Even with large landfills like these, the United States faces serious waste management problems.
Can Landfills Be Sustainable?
Landfills present a range of environmental challenges, and their long-term sustainability remains a topic of ongoing discussion. A landfill can take roughly 450 to 600 years to fully break down and continues to produce gases, leachate, and other harmful byproducts during that time. Plastic comprises almost 20% of municipal solid waste and never decomposes. Even though it has only been produced abundantly since the 1950s, plastics are quickly filling up landfills.
Another sustainability issue is landfill gases, which are the third largest contributor to greenhouse gases in the United States. Gases like methane, carbon dioxide, and hydrogen sulfide, also known as sewer gas, contribute to climate change and have an impact on public health.
While landfills remain necessary, their environmental impact highlights the importance of reducing waste, improving recovery, and investing in alternatives.
Landfill Alternatives
As space for our trash runs out, alternatives become more critical. When city governments focus on prevention, recycling, and recovery, they can reduce solid waste disposal.
Waste incineration is an option for some municipalities, and many states operate waste-to-energy plants. However, waste incineration delivers toxins into the air and requires strict regulations.
Organic landfills are not required by the EPA, but they are becoming more commonplace as communities look for eco-forward solutions like composting. Green landfills provide a place for people to take organic waste and save valuable space in MSWLFs, which prevent food and organic waste from decomposing because of the layering system.
Additionally, many communities are focusing on zero-waste management practices that change the way resources are used. By allowing for more recycling and recovery of materials through practices like composting and using biodegradable packaging, municipalities can reduce the need for landfills.
Landfill Terms and Definitions
Leachate: A liquid that forms from waste decomposition and contains harmful contaminants.
Cell: A section of a landfill designated for waste disposal, separated from adjacent cells by a liner system.
Groundwater: Water located beneath the earth's surface that can become contaminated by pollutants.
Anaerobic decomposition: The breakdown of organic matter by microorganisms without oxygen, producing landfill gas.
Greenhouse gases: Gases that trap heat in the Earth's atmosphere, including those produced by landfill decomposition.
Flaring: Burning of landfill gas emissions to convert methane into less harmful carbon dioxide and water vapor.
EPA: The Environmental Protection Agency, a federal agency in the United States that sets waste management standards and regulates landfills.
