Landfills are areas where solid garbage is buried. The construction, use, and maintenance of landfills can impact aquifers and groundwater that lie underneath and around the landfill.

Groundwater is fresh water in the rock and soil layers beneath Earth’s land surface; aquifers are a type of groundwater source that yields water suitable for drinking. The material inside a landfill can contain harmful chemicals and microorganisms.

As some of the material in a landfill decomposes (breaks down), other harmful chemicals can be created and released. One wellknown example is methane gas; another is leachate, the acidic liquid that contains water and contaminants from the products of decomposition.

Landfills are a necessary part of life in highly developed countries such as the United States. The United States has over 3,000 landfills that are being filled with trash and over 10,000 landfills that have already been filled, according to the U.S. Environmental Protection Agency.

The need for all this garbage storage is because the amount of garbage produced every day in the United States averages four pounds for each American. That’s over 200 million tons every year, more than twice the trash produced in many other countries.

Some of it can be recycled or burned but most, about 150 tons per year in the United States, is left over. While some of these leftovers will break down over time into the basic chemicals that make up the material, without a landfill, the result can be a stinky mess that lies in the open air.

What is a landfill?

A landfill is a carefully designed structure that is built into the ground or as a pile above the ground. The garbage that is added to the landfill does not contact the surrounding soil and rock. Rather, a layer of pounded-down clay or a film of plastic or other material is used to line the outside of the landfill.

The purpose of this liner is to prevent what is inside the landfill from escaping into the nearby soil. A landfill can be thought of as a vault in which trash is locked away forever.

Some landfills have only the clay zone barrier. These are known as sanitary landfills. Other landfills use the plastic barrier, and these are called municipal solid waste landfills. There are some landfills that use both barriers, although this process is more expensive.

Ideally, the break down of material in a landfill should hardly occur as the inside of the landfill is supposed to be dry, although small amounts of moisture within the garbage itself contributes to the breakdown of some materials, resulting in an acidic solution of water and dissolved chemicals called leachate. Leachate is drained into a collection pond and is eventually treated similar to sewage or other wastewater.

When landfills work properly they are an efficient means to hide trash. They can even be put to some use. In the Canadian city of Toronto, Ontario, one landfill has been turned into a small ski resort that is locally known as “Garbage Hill.”

However, a badly designed or malfunctioning landfill can result in the escape or runoff (water that flows on the surface) of contaminated material, and can pollute nearby water sources.

Construction of a landfill

Construction of a landfill
Construction of a landfill

In most areas of the world careful planning and safety rules are in place to spell out how a landfill is constructed. In the United States, before a landfill can be built a survey must demonstrate that the landfill will not disturb the environment in an unacceptable manner (environmental impact study).

Some things that an environmental impact study examines include the proposed location for the landfill, nearby animal habitats, the location of nearby surface water sources, the direction in which material escaping the landfill would flow, and how close to the surface any underground water supply lies.

A properly constructed landfill will include the liner, collection areas to trap any liquid that escapes, and a method of releasing gases such as methane that build up inside the landfill.

Efficient landfills are constructed in small sections (cells) that are filled up with trash that is compressed by bulldozers and other equipment, which drive back and forth over it.

One cell is sealed off before another cell is filled. Ultimately, a landfill is completely sealed with a plastic layer, and at least 6 inches (15 centimeters) of soil and grass is planted over it.

Landfill monitoring

It is important to make sure that a landfill is not disturbing the environment, both during its construction, as it is filled, and in the years after the site is closed.

Pipes are usually placed into the ground at many sites throughout a landfill and these pipes are connected to a water source for regular testing. If the water temperature is higher than normal, it may indicate that decomposing material is leaking into the water.

Additionally, chemical tests are conducted to ensure that harmful chemicals are not leaking into the groundwater. Careful records of landfill sites are also maintained in order to determine which landfill sites can be reused.