On the surface, landfills might not seem all that complicated: Find a spot that’s not near any housing or surface water, and dump all of your trash there. Simple, right? However, there is so much more that goes into the preparation and management of a modern, sanitary landfill. Here’s the science behind how a landfill works.

Find a spot

Aerial view of large landfill area being prepared and cleared
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Finding the proper location for a landfill is a highly scientific matter. It’s much more involved than just finding a spot that’s away from any homes or water; this idea is closer to what dumps are like. Dumps, specifically, are more open and less regulated, which often allows for vermin and birds to mill about. A landfill, on the other hand, takes years and years worth of planning and building, and decades more to properly fill and maintain the site.

Obviously, there are extensive environmental impact evaluations to determine every possible repercussion of building a landfill on the site. Is it close to ponds, rivers, or wetlands? How will the landfill impact the ground soil or surrounding plants and animals? Once the environmental impact is determined, it’s time to see how the new dump will affect the nearby towns.

Researchers perform traffic impact studies to see if trucks coming and going from the landfill will affect local streets and commutes. They also determine the impact on local businesses and homes in the vicinity. This process alone can be time consuming and take months or even years to complete.

Prepare the site

Once a site is determined to be acceptable, it’s time to prepare the land. The first step toward building a landfill is digging a giant hole. The bigger the city, the deeper the hole. Some landfills in major cities like Los Angeles can reach depths of up to 500 feet.

When the pit is finished, it’s lined with clay. The clay is compacted to the point that even liquids can’t pass through it. A high-density plastic liner is installed on top of the clay for added protection. Similar to the trashcan in your kitchen, landfills have liners to prevent hazardous materials from leaking into the soil below.


Aerial view of large bulldozer moving huge piles of plastic bottles in a landfill
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Solids are easy to contain. It’s liquids that are the problem. The bottom of the landfill is lined to prevent any liquids, either from rain or from waste, from seeping into the ground. Liquid that drains from a landfill is called leachate. Without drainage, the entire pit would become a trash-filled pond, and nobody wants that!

Perforated pipes are installed at the bottom of the landfill pit. Small holes in the pipes allow liquids to pass through but keep out solids. The leachate collection pipes drain into a collection pond where liquid can be tested for chemicals and allowed to settle for some time. Some landfills drain the leachate straight into water treatment plants where it can be treated and safely released back into the environment.

Also, to make sure that the groundwater is always safe, deep sensors are drilled all around the landfill. If these sensors detect any traces of harmful toxins or chemicals being released beyond the layers of lining, the sensors send an emergency signal to the landfill's operators who can then begin containment procedures.

Methane collection

Nearly every day waste is placed in the landfill, compacted, and then covered with soil. Once covered, the soil creates an airtight seal on top of the waste. When waste decomposes, it creates what’s known as "landfill gas," which is about equal parts carbon dioxide and methane. It’s important to have a plan for this gas; methane is highly flammable, and large underground pockets of it has the potential to explode.

Before the landfill is operational, a methane collection system is installed. Typically, this system is a series of vertical pipes that reach to the bottom of the pit. Since methane can also be used as a fuel, most modern landfills extract the methane and use it to create energy. Some landfills can create enough energy through methane extraction to power tens of thousands of nearby homes.


Big crane moves large piles of garbage in crowded landfill
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Now that the landfill has been equipped with a liner, drainage system, methane collection system, and a groundwater monitoring system, it’s time to open the landfill. Waste that is brought to the landfill is examined for liquid content and sorted before it can enter the pit. At least every day, the waste in the pit is compacted and covered with a few feet of soil. The process continues until the landfill is full; landfills can generally operate for 30-50 years before reaching capacity.

Once full, the mound is covered with another liner, similar to the one that lines the bottom of the pit, and topped with several feet of soil. The area is continually monitored for the next 30 years to make sure that no chemicals or toxins escape. After some time, the land can be used once again for industrial or commercial use. Retired landfills can even be used as greenspace and turned into beautiful parks and community gathering spaces—essentially making one generation's trash another one's pleasure.