Environmental Engineering Reference
In-Depth Information
A secure landfi ll is a carefully engineered depression in the ground
into which wastes are put. The aim is to avoid any water-related con-
nection between the wastes and the environment. Ideally, a landfi ll
should be located on impermeable (waterproof) rock and have strict
construction requirements. The base of the landfi ll should be sloped, and
it should have a plastic liner at its base. Today's landfi ll liners are made
of a tough plastic fi lm one-tenth of an inch thick. But the liners do not
last forever; most are guaranteed for only fi fty years or less. Landfi ll
operators are liable for landfi ll problems for thirty years after closure of
the facility. After that, the public must pay to rectify problems.
Overlying the liner is a system of pipes and sealed pumps to collect
leachate, the liquid that drains through the wastes. Garbage commonly
contains hazardous liquids such as drain cleaners, bug sprays, turpentine,
weed killer, and many other materials that must be prevented from
mixing with our water supply. Each year every American household
sends an average of 1.5 quarts of hazardous liquid to landfi lls, and there
are more than 100 million households in the United States.
Many of these household chemicals can degrade the plastic liner and
cause it to leak. Eighty-two percent of landfi lls leak.
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Studies show that
a ten-acre landfi ll will leak up to 10 gallons per day.
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However, if the
rock beneath it is impermeable, the leachate (contaminated water that
drips through the waste) will not be able to move downward and con-
taminate groundwater. Collecting pipes funnel leachate to a wastewater
treatment plant. But experience has revealed that leachate collection
systems can become clogged in less than ten years by mud, microorgan-
isms growing in the pipes, or chemical reactions that cause the precipita-
tion of minerals in the pipes. The pipes may also become weakened by
chemical attack by acids, solvents, oxidizing agents, or corrosion and
may then be crushed by the tons of garbage piled on them.
Each day's waste should have an impermeable cover of clay or other
material to serve as an umbrella over the landfi ll to keep water out and
keep leachate to a minimum.
Landfi ll problems result not only from liner and pipe failures. More
important are problems with older landfi lls that were not built to today's
standards. Many are built on permeable soil and rock, others have no
liner at their base or no pipes to collect leachate, and others were located
too close to streams or lakes. The average landfi ll does not meet current
mandated standards, but even the best-designed and best-built landfi ll is
likely to leak eventually. Sharp objects in the garbage may puncture the
plastic liner. Vermin burrowing through the waste pile in search of food
