Visualizing Environmental Science

Solid Waste 401

Compacted trash covered

daily with soil to keep out

vermin and reduce odor.

Trash

unloaded.

Trash pushed into place

and compacted by bulldozers.

Portable fences used to

catch windblown debris.

Original ground

Pipes sunk

through compacted

layers collect

methane gas and

either burn it

off or convert

it to energy.

Layers of compacted clay

and high-density plastic

liners protect groundwater.

Final layer of soil

seeded and planted.

Earth cover obtained

by excavation.

.

30 cm (1 ft)

Intermediate cover

Gravel

Part of drainage grid:

Perforated drains collect

leachate for treatment.

61 cm (2 ft)
Thomas Kitchin & Victoria Hurst/All Canada Photos/Getty Images final earth cover.

a. A bulldozer compacts trash at a sanitary

landfill in California. To the average person,

a sanitary landfill is just a “dump.”

b. Environmental engineers know that

sanitary landfills constructed today require

protective liners of compacted clay and

high-density plastic, and sophisticated

leachate collection systems that minimize

environmental problems such as

groundwater contamination. Solid waste

is spread in a thin layer, compacted into

small sections called cells, and covered

with soil.

WHAT A SCIENTIST SEES

Sanitary Landfills

The special problem of plastic The amount of plastic in

our solid waste, more than half of it from packaging, is

growing faster than any other component of municipal

solid waste. Most plastics are chemically stable and do not

readily decompose. This characteristic, although essential

in the packaging of products such as food and medicine,

causes long-term problems: Most plastic debris disposed

of in sanitary landfills will probably last for centuries. In

response to concerns about the volume of plastic waste,

some areas have banned the use of certain types of plastic,

such as the polyvinyl chloride employed in packaging.

Special plastics that have the ability to degrade or

disintegrate have been developed. Some of these are

photodegradable—that is, they break down after being

exposed to sunlight—which means they will not break

down if buried in a sanitary landfill. Other plastics are

biodegradable—they are decomposed by microorganisms

such as bacteria. Whether biodegradable plastics actually

break down under the conditions found in a sanitary land-

fill is not yet clear, although preliminary studies indicate

that they probably do not. (Other waste management

options for plastic are discussed later in this chapter.)