Rubbish, trash, garbage, municipal solid waste—whatever we call it, we throw away a lot of stuff. Except there’s no such place as away. We recycle or compost some of it. Some areas use waste-to-energy incinerators. In the US, however, most of it goes to the landfill. It’s important for us to know what a landfill is and how landfills work.

It’s not the same as a garbage dump. We don’t have those in the US anymore. A garbage dump was a trash-filled area with mice, rats, gulls, insects, and other vermin having a feast. No one covered it with dirt. It stank. Rainwater flowed through and from it, picking up pollutants and eventually making its way to a river or lake.

In contrast, a landfill is carefully designed to isolate trash from animals, water, and in general, the rest of the environment. A sanitary landfill uses a clay liner for that purpose. A municipal solid waste landfill uses a plastic liner.

Modern waste management in the US

The modern American sanitary landfill originated in Fresno, California at the end of the 1930s. The federal government stepped in with national standards with the passage of the Solid Waste Disposal Act of 1965. The Resource Conservation and Recovery Act of 1976 specifically regulated the design and siting of landfills.

Instead of simply dumping trash in a pit, a sanitary landfill layers solid wastes and dirt in a trench and then compacts it. At the end of each day, the filled areas are covered with dirt. That has solved the vermin and odor problems but caused some new ones.

For one thing, municipal solid waste has long included batteries and all kinds of hazardous substances. Rainwater percolating through the buried trash dissolves some of these substances and creates leachate. Contrary to the experts’ early expectations of how sanitary landfills would work, the leachate eventually travels to pollute groundwater.

Deciding where to put a landfill

Siting a landfill requires an environmental impact statement. It looks at five factors:

• how much land the landfill will need
• the composition of the soil and bedrock
• how water flows over the surface
• how the proposed landfill will affect wildlife and other environmental considerations
• the archeological or historical value of the site

How much land is needed for a landfill? The North Wake County Landfill near Raleigh, North Carolina occupies 230 acres. The sanitary landfill there closed in 1997, but it still has an active municipal solid waste landfill.

The two of them occupy only 70 acres of the site. The rest of it comprises collection ponds for runoff and leachate, drop-off stations, areas that provide soil for the daily covering, and buffer areas.

Once the proposed landfill has gotten all the necessary permits, it is necessary to build access roads and then excavate. The North Wake County Landfill required digging 10 feet below the level of the roads.

Construction of a landfill

Construction of a landfill begins with excavating a hole that can occupy up to 20 acres. Next comes the liner, which comprises a compacted layer of clay two feet deep, a plastic liner, a nonporous geotextile membrane, and a layer of granular material. The whole design funnels eventual leachate into the leachate collection system.

It still requires a layer of up to two feet of soil before it is ready to receive trash. And the first layer of trash typically comprises materials such as old mattresses that will protect the liner.

Landfill design also requires planning for dealing with landfill gas.

The operation of a landfill

Landfills are divided into cells that contain only one day’s trash. Trucks dump trash into the cell. Compacting tractors run over it periodically to reduce its volume as much as possible. At the end of the day, everything must be completely covered to deter vermin, limit rainwater runoff, control odors, and prevent fires.

Daily cover usually means six inches of soil. That much soil requires a lot of space. Some landfills have started to experiment with spraying paper or cement/paper emulsions. These substances work as well as the soil but are only a quarter of an inch thick. Using materials such as geotextile cloth, ash, or old tires also reduce the need for that much soil.

Leachate collection uses perforated pipes install on top of the liner. These pipes drain into another pipe that carries leachate outside the landfill and into a collection pond. Some landfills pump the leachate there. Others rely on gravity. From the collection ponds, the leachate goes to the wastewater treatment plant and from there to a river or lake.

Sometimes leachate can seep through to the surface of the landfill. When that happens, a crew must immediately repair the seepage by excavating around it, filling it with soil, and compacting the soil to force the leachate to flow back into the landfill.

Throughout the life of the landfill and beyond, it is necessary to monitor groundwater conditions and take whatever steps are necessary when any contamination is discovered.

Oh, and landfill gas, too.

What organic waste does in a landfill

Organic matter decayed quickly in an old-fashioned dump. Not so with modern landfill disposal. All that dirt keeps air out of the filled cells, but not perfectly. It doesn’t allow either aerobic bacteria or anerobic bacteria to operate at peak efficiency.

So the waste decays slowly. It releases methane, a greenhouse gas. Periodically, it is necessary to install trenches and wells to collect and channel the gas emissions. Landfill gas, which accounts for the landfill’s largest environmental impact, comprises roughly half methane and half carbon dioxide.

In principle, it should be possible to collect this gas and use it for fuel. Most landfills simply burn it, which is a shame. Burning it releases less greenhouse gas than simply letting it escape into the air, however. But it can be refined into natural gas instead and become a source of renewable energy. Economic and technological problems can discourage this practice.

End of life for a landfill

When a cell is full, it gets a cap comparable to the bottom liner, topped with soil. It will be a long time before the land is fit for any kind of reuse. In the meantime, the landfill crew plants some kind of vegetation. Eventually, the landfill will reach capacity. Or political pressure may close a landfill before that time.

The vegetation that covers the cap over a completed section of landfill—or a closed landfill––does not include trees or anything else with deep penetrating roots. Those would damage the cap. Most of the vegetation consists of grasses or other spreading plants with shallow roots.

Landfill disposal doesn’t resemble a composting operation. Nothing decomposes very fast. When old landfills have been excavated, 40-year old newspapers are still legible. Food waste is about the same color as it had been when discarded.

Still, organic matter decomposes enough to make the land unstable for 30 years after a landfill closes. During that time, it is still necessary to monitor groundwater and landfill gases. Eventually, an old landfill becomes suitable for certain other uses.

The current landfill crisis in the US

Americans generated more than four and a half pounds of trash per person every day in 2006. It added up to 251 million tons of trash. Somewhat less than a third of it was recycled or composted. About half the garbage Americans generate winds up in a landfill. Since the Chinese recycling ban, too much of what gets collected for recycling makes its way there, too.

Much of what goes to landfills could have been recycled or composted. Most other major countries generate half the trash we do or less.

Despite constant improvement in techniques of compacting waste, eventually all landfills will reach capacity and have to be closed. Finding places for new ones faces two very different kinds of problems.

The first is geological as described earlier. The second is social. After all, no one wants a new landfill close by. Many existing landfills have been built in poor neighborhoods mostly occupied by people of color. And they are no longer willing to be pushed around.

Running a landfill is a complicated task. Many things can go wrong, even in the best run of landfills. So there is probably no such thing as a good landfill and probably not much room for improvement over the system we have.

It’s past time for us as a society to commit to reducing the amount of trash we produce. That means we can’t leave it up to governments and big businesses. Individual households must take steps not to be inundated by trash. I hope knowing how landfills work will provide some inspiration.

Related posts:

Attractive new life for ugly closed landfills
The cost of convenience in trash collection
How the pandemic has affected trash collection services
Keeping food waste out of landfills
Keeping stuff out of landfills
Municipal solid waste disposal methods and why they don’t work
The past, present, and future of solid waste disposal
What happens when an old landfill closes?

Sources:

How landfills work / Craig Freudenrich, How Stuff Works. October 16, 2000, revised no later than August 2008. Link no longer works as of April 5, 2023
How sanitary landfills work / Gemma Alexander, Earth911. January 6, 2022