Keep America Beautiful

landfill

 

 

 

 

 

 

 

 

Landfilling

After source reduction, recycling, and composting, a large portion of municipal solid waste must still be placed in landfills. In 2003, 55.4% of municipal solid waste was landfilled or about 2.46 pounds per person per day. This is down from 56.2% in 2000.

A landfill is where garbage is deposited and then buried. Properly managed landfills are an environmentally safe means of disposal, and are closely monitored for their environmental impact by the U.S. EPA as well as state and local authorities.

Over the past several years, the number of landfills has decreased from almost 8,000 in 1988 to 1,767 in 2002. Many landfills closed because they could not meet federal environmental standards. The size of the average landfill, however, has increased. Current landfill capacity is stable, although some communities may face shortages.

 

Landfill Standards

Municipal solid waste landfills are regulated under Subtitle D of the Resource Conservation and Recovery Act passed by Congress in 1976.  In 1991, the U.S. EPA published a supplemental set of Landfill Rules which now serve as the basis for state regulatory and permitting requirement.  New landfills may also collect potentially harmful landfill gas emissions, such as methane, and convert them into energy.

Because today's landfills need to operate with unquestioned safety and efficiency, it often can take five or more years from the time a site is selected until design, permit application, and public hearings are completed and the facility is built. 

How a Landfill Operates

A typical landfill is divided into a series of sections called "cells."  Solid waste is placed on what is called a "working face," which is a portion of a landfill cell that is currently available to accept this material.  Only limited sites in a landfill are exposed at any given time to minimize exposure of the landfill's contents to environmental elements like wind and rain.  Because a landfill is filled so systematically, landfill operators may be able to pinpoint where a specific load of garbage was deposited days, weeks, or even months afterward. 

Landfill schematic smallAt the conclusion of each day's activity in a cell, a layer of earth (sometimes ash or compost), called "daily cover," is spread across the compacted waste to minimize odor, prevent windblown litter, and deter insect and vermin.  The daily cover may also consist of a layer of foam or sheets of synthetic materials.  The landfill operator moves from working face to work face, and from cell to cell as the landfill gradually reaches its capacity over periods of many years, even decades. 


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Environmental Safeguards

Rain, snow, and liquids created by the compaction and decomposition of solid waste, which can seep through a landfill cell, is called "leachate."  Leachate is a potential pollutant of surface waters (lakes, rivers, streams, or oceans) or groundwater, which is the source of most drinking water. 

A protective liner is used to prevent filtration of liquid from the landfill.  Liners may be made of compacted clay or impermeable materials such as plastic.  When clay is used, the layer may be as much as ten feet thick. This site preparation is done so that any liquid entering the landfill can be controlled and treated externally, or retained inside the landfill, rather than being permitted to pass through. 

Beyond protective liners, modern landfills  include multiple safeguards to contain leachate and other waste and waste byproducts and isolate them from surrounding water and soil.  To prevent leachate contamination, a network of drains is installed at the bottom of the landfill to collect the liquid that has percolated through the solid waste.  Leachate is then pumped to waste water recovery points for treatment. 

Groundwater monitoring wells are also installed around the perimeter of the landfill to ensure that surrounding groundwater is not contaminated with leachate.  Should a liner system fail by breaking or deteriorating, leak detectors installed under the liners signal the presence of leachate, allowing corrective action to prevent any movement of leachate from the landfill toward nearby ground or surface waters.

Landfills and Gas Emissions

Gases emanating from the landfill are also closely monitored and controlled.  As the organic portion of waste (e.g. food and yard wastes) decomposes, large amounts of methane gas and carbon dioxide are produced.  Under the Resource Conservation and Recovery Act and the Clean Air Act, landfill operators are required to monitor gas both on the surface and around the boundaries of landfills. 

As cells to the landfill are sealed off, venting systems are installed to prevent methane from diffusing under ground, and to collect any gas released and burn it off.  In many cases, energy is recovered from the combustion of the gases to be used on site or sold to local homes or businesses.

Closing a Landfill

When a landfill has reached its capacity, it is required to close consistent with U.S. EPA "final cap" environmental requirements.  A final layer of clay and dirt "cap" the landfill.  It is then is re-landscaped according to closure plans drawn up in accordance with the community.  This process is planned many years in advance. 

To be granted a license to operate, a landfill operator must have a complete plan for the site's eventual closure.  The operator is also required to set aside the financial resources which will be necessary for all closure, post-closure, and corrective activity which may be needed over the lifetime of the landfill.

Once a landfill is capped, operators are obligated to monitor the site for gas and leachate for up to 30 years after the closure date.  They are often involved in the ongoing efforts to reclaim the land for other uses.  Landfills can end up as open space for communities to use as parks, or other recreational facilities.  Building any permanent structure on landfills is less common because, as solid waste decomposes in the landfill, the entire landscape can settle.