Understanding the Functionality of Landfills

When trash day arrives, you roll your bins to the curb, where the waste is collected by a truck and transported to a landfill. But have you ever wondered what exactly a landfill is, or where your waste ends up once it leaves your driveway?

In the United States, each person produces an astonishing 4.9 pounds (2.2 kilograms) of waste per day, which amounts to a staggering 292.4 million tons (265.3 million metric tons) annually [source: EPA]. This is roughly three times the global average, according to a 2019 report by the research firm Verisk Maplecroft [source: Smith].

What becomes of all this waste? A portion is recycled or repurposed, some is incinerated, but the bulk of it ends up in landfills. In this article, we will explore waste management, including the construction of landfills, what happens to the trash buried within them, the issues that arise from these sites, and the solutions being implemented to address these problems.

How Much Trash Does the U.S. Generate?

In 2018, the most recent year for which data is available, the U.S. generated 292.4 million tons (265.3 million metric tons) of trash. Of this, 69 million tons (62.6 million metric tons) were recycled, and 25 million tons (22.7 million metric tons) were composted.

The combined total of recycled and composted trash made up 32.1% of the overall amount. Nearly 35 million tons (31.75 million metric tons) were burned for energy recovery. However, half of the nation's waste—146 million tons (132.4 million metric tons)—was buried in landfills [source: EPA].

What Happens to Trash?

Approximately 32.1% of waste is either recycled or composted, while around 50% ends up buried in landfills [source: EPA]. The amount of waste disposed of in landfills today is roughly one-and-a-half times higher than in 1960, and the overall trash generated in the U.S. has tripled since then.

The United States ranks as the third-largest trash producer in the world, following China and India. However, despite having only 4% of the global population, the U.S. contributes a disproportionate 12% of the world's total waste [source: Smith].

What Is a Landfill?

Waste management has been an issue in the United States since its early days. Until the late 1800s, people typically discarded their household waste by tossing it into the streets, especially in cities like New York, where it was common to see piles of food scraps, broken furniture, horse manure, and even dead animals on street corners [source: Oatman-Stanford].

The Challenge

Over time, cities began to organize waste collection, but much of the trash was still taken to dumps—large, open pits in the ground—where it was often set on fire, releasing hazardous air pollution. By the 1960s, it was clear to government officials at all levels that decisive action was needed to address the escalating waste disposal problem.

The USPHS Report

In 1964, the U.S. Public Health Service (USPHS) published a concerning report predicting that the amount of solid waste generated would double in 20 years, and that urban areas would soon run out of available land for disposal. The report also highlighted the health dangers of open-burning dumps, including respiratory issues, disease risks, and groundwater contamination [source: Hickman].

The Resolution

Modern sanitary landfills—first introduced in California in 1937—offered a solution to the growing waste problem. Rather than simply dumping or burning trash, the waste was methodically buried, compacted with machinery, and then covered. In 1976, Congress enacted the Resource Conservation and Recovery Act, which established regulations for landfills to prevent them from polluting the environment [source: Zylberberg].

Present-Day Situation

Currently, there are approximately 2,600 landfills in the United States that manage municipal solid waste [source: EPA].

These facilities are designed and operated to meet federal guidelines and are primarily intended for handling household waste. Additionally, municipal solid waste landfills are permitted to accept certain types of nonhazardous industrial waste.

Design and Function

Landfills feature a composite liner above 2 feet (0.61 meters) of compacted clay at the bottom and sides, along with systems designed to capture leachate—the water that seeps through the trash—before it can contaminate the surrounding groundwater.

In addition, landfills are equipped with groundwater monitoring wells to ensure that pollution is contained. They also follow federally approved operational practices for trash handling, which include compacting and covering the waste frequently with several inches of soil. This layer helps control odors, reduce issues with insects and rodents, and prevents trash from escaping the landfill and becoming litter [source: EPA].

Getting Approval to Build a Landfill

The Approval Process

Obtaining permission to construct a landfill involves navigating a complex regulatory process. Federal regulations prohibit landfill development in certain areas, such as wetlands, floodplains, and locations with unstable soil. While landfills are not outright banned in these areas, they must meet more rigorous performance standards.

Moreover, new or expanded landfills near airports must demonstrate that they won't pose a bird hazard to aircraft, a requirement that has halted some landfill projects [source: Walsh and O'Leary].

A company seeking to build a landfill must comply with both federal and state regulations. For example, in Wisconsin, there are restrictions on placing landfills near streams, lakes, and ponds, as well as near highways and parks, unless visual barriers or landscaping are used to obstruct the view [source: Walsh and O'Leary].

Landfill Approval Procedure

Obtaining approval to build a landfill involves extensive research, as the shape of the land and the geological structures below the surface play a critical role in determining if the location is suitable for waste disposal [source: Walsh and O'Leary].

Developers must also inform the public and host a public hearing, which can lead to opposition from local residents and others who object to the idea of having a landfill nearby [source: Walsh and O'Leary].

Parts of a Landfill

Although landfill designs can vary significantly, most employ similar technologies. The exact sequence and materials may differ across locations [source: WM.com]. Some key elements commonly found in landfills, as shown in the diagram, include:

Each of these components plays a crucial role in addressing specific challenges within a landfill system.

As we go through each part of the landfill, we will explore the problems each component is designed to solve.

Bottom Liner System

The primary function of a landfill is to safely contain trash and prevent it from creating environmental hazards. A significant challenge in this process is ensuring the waste does not contaminate surrounding soil, especially groundwater. To achieve this, the bottom liner, constructed from thick plastic, acts as a barrier, keeping trash away from the soil [source: WM.com].

Cells

Heavy machinery compacts the waste into designated areas, known as cells, which typically hold the amount of refuse generated in a day. This maximizes the available space within the landfill. Once the cell is formed, it is covered with 6 inches (15 centimeters) of soil and compacted further to reduce its volume [source: Bolton].

Stormwater Drainage

To prevent rainwater from infiltrating the landfill, a stormwater management system is installed to direct runoff into drainage channels, steering it away from the buried waste. Additional components of this system include culverts—made from concrete, plastic, or metal—beneath adjacent roads, as well as stormwater basins that help reduce the amount of suspended sediment in the water, minimizing soil erosion at the landfill site [source: Uteir].

Plastic drainage pipes and storm liners gather water from various parts of the landfill and direct it towards the surrounding drainage ditches. These ditches, which may be made of concrete or gravel, then transport the water to designated collection ponds located on the landfill's perimeter.

In these collection ponds, suspended soil particles settle out of the water, and the water undergoes testing for leachate chemicals. After the particles have settled and the water passes the necessary tests, it is either pumped away or allowed to flow off the site.

Leachate Collection System

Although no water exclusion system is completely flawless, some water inevitably makes its way into the landfill. This water seeps through the waste and soil in the landfill, much like water moves through ground coffee in a drip coffee machine. As it percolates through the trash, it picks up harmful contaminants, which turn the water into leachate—a typically acidic liquid.

Leachate is gathered by perforated pipes that span the landfill. These pipes direct the leachate into a central drainage system, which then transports it to a leachate collection pond [source: Austin Community Landfill].

Methane Collection System

Bacteria break down the waste in an oxygen-deprived (anaerobic) environment due to the landfill's sealed nature. This decomposition process produces landfill gas, which consists of roughly 50% methane and 50% carbon dioxide, along with small traces of nitrogen and oxygen.

Methane is a significant concern in landfills as it is a powerful greenhouse gas, being 28 to 36 times more efficient than carbon dioxide at trapping heat in the atmosphere. Landfill gas emissions represent the third-largest source of methane emissions in the U.S., responsible for about 15% of methane that was released into the atmosphere in 2019 [source: EPA]. Additionally, methane poses a serious safety risk, as it can ignite and cause explosions [source: NY Department of Health].

Covering or Cap

Covering waste with compacted soil traps it from the air and keeps pests, such as birds, rodents, and insects, from accessing the trash. In New York's Fresh Kills Landfill, this layer of soil measures at least 2 feet (0.61 meters) thick, sloped between 4 and 33 percent to assist with stormwater drainage. Above this, additional layers of synthetic fabric and plastic are added, followed by a final layer of soil that encourages vegetation to grow on the landfill [source: Freshkills Park Alliance].

Groundwater Monitoring

Numerous groundwater monitoring stations are scattered around the landfill. These pipes are driven into the groundwater to collect and analyze samples for leachate chemicals. The temperature of the groundwater is also recorded.

As solid waste decomposes, the temperature of the groundwater increases. A rise in temperature can signal that leachate is leaking into the groundwater. Additionally, if the groundwater's pH becomes acidic, it may indicate the presence of leachate [source: EPA].

How Landfills Operate

Landfill users are generally municipalities and construction or demolition firms, although private residents may also utilize landfills. Here is a diagram of a typical landfill and its supporting infrastructure.

This description is based on a typical landfill that Mytour toured several years ago. Close to the entrance of the site, there's a recycling center (A) where local residents can drop off recyclables, such as aluminum cans, glass bottles, newspapers, mixed paper, and cardboard. This helps reduce the waste sent to the landfill. Additionally, certain items are legally prohibited from landfills because they can be recycled.

Entry and Drop-off Stations

When customers arrive at the site, they weigh their trucks at the scale house (B). A tipping fee is charged for using the facility, which helps cover bond costs and operational expenses.

Throughout the site, there are designated drop-off points for materials that are either unwanted or prohibited by landfill regulations. One such station collects tires, motor oil, lead-acid batteries, and drywall. Many of these materials can be recycled.

Additionally, a separate drop-off area is provided for household hazardous waste, including chemicals like paints and pesticides, which are not allowed in the landfill. These substances are managed by private disposal companies. Some paints may be recycled, and certain organic chemicals can be burned in incinerators or used in power plants.

Other features around the landfill include the borrow area, where soil for the landfill is sourced, as well as the runoff collection pond (N), leachate ponds (I), and the methane station (L).

Landfills are complex systems that, when designed and managed properly, fulfill an essential role in waste disposal.