Visualizing Environmental Science

400 CHAPTER 16 Solid and Hazardous Waste

lessens the danger of fires, and decreases the amount of

odor. If a sanitary landfill is operated in accordance with

solid waste management–approved guidelines, it does not

pollute local surface water and groundwater. Layers of com-

pacted clay and plastic sheets at the bottom of the landfill

prevent liquid waste from seeping into groundwater.

Newer landfill construction incorporates a double

liner system (plastic, clay, plastic, clay) and uses sophisti-

cated systems to collect leachate (liquid that seeps through

the solid waste) and gases that form during decomposition.

The choice of where to locate a sanitary landfill is

based on a variety of factors, including the geology of

the area, soil drainage properties, and the proximity of

nearby bodies of water, wetlands, and groundwater. A

landfill should be far enough away from centers of dense

human population so it is inoffensive but close enough

so as not to require high transportation costs.

Although the operation of sanitary landfills has

improved over the years with the passage of stricter and

stricter guidelines, few landfills are ideal. Most sanitary

landfills in operation today do not meet current legal stan-

dards for new landfills and encounter a variety of problems:

sMethane gas, produced by microorganisms that de-

compose organic material anaerobically (in the ab-

sence of oxygen), may seep through the solid waste

and accumulate in underground pockets, creating

the possibility of an explosion—even in basements

of nearby homes. Landfill operators typically collect

and burn off methane, but a growing number use

the methane for gas-to-energy projects. About 550

landfills in the United States currently use methane

gas to generate electricity.

sLeachate that seeps from unlined landfills or

through cracks in the lining of lined landfills can

potentially contaminate surface water and ground-

water. Because even household trash contains toxic

chemicals such as heavy metals, pesticides, and or-

ganic compounds, the leachate must be collected

and treated to neutralize its negative effects.

sLandfills, by their nature, fill up. They are not a long-

term remedy for waste disposal. From 1988 to 2007,

the number of U.S. landfills in operation decreased

from 8000 to 1754; many reached their capacity, and

others did not meet state or federal environmental

standards. Fewer new sanitary landfills are being

opened; many desirable sites are already taken, and

people are usually adamantly opposed to the con-

struction of a landfill near their homes.

Disposal of Solid Waste

Solid waste has traditionally been regarded as material

that is no longer useful and should be disposed of. We can

get rid of solid waste in four ways: dump it, bury it, burn it,

or recover it by recycling or composting (Figure 16.4).

Open Dumps The old method of solid waste disposal

was dumping. Open dumps, which are now illegal, were

unsanitary, malodorous places where disease-carrying

vermin such as rats and flies proliferated. Methane gas

was released into the surrounding air as microorganisms

decomposed the solid waste, and fires polluted the air with

acrid smoke. Liquid oozed and seeped through the heaps

of solid waste, often leaching hazardous materials that

then contaminated soil, surface water, and groundwater.

Sanitary Landfills Open dumps have been replaced

by sanitary landfills, which in 2010 received 54.2 percent

of the municipal solid waste gen-

erated in the United States today.

Sanitary landfills differ from open

dumps in that the solid waste is

placed in a hole, compacted, and

covered with a thin layer of soil

every day (see What a Scientist Sees).

This process reduces the number

of rats and other vermin usually associated with solid waste,

sanitary landfill

The most common

disposal site for

solid waste, where

waste is compacted

and buried under a

shallow layer of soil.

Discarded in

sanitary landfills

54.2%

Recovery

34.1%

Incineration

with energy

recovery

11.7%

Based on data from United States Environmental Protection Agency(EPA),

Solid Waste Facts

, 2010.

U.S. disposal of municipal solid waste
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In 2050, do you think these percentages will

be the same or different? Why?

Think Critically