When trash day comes we all perform the ritual of hauling garbage out to the curb. The next morning, it's gone. We all know that garbage trucks come early in the morning to take the trash away. But where do they take it?

To a landfill, where the trucks dump our garbage into a big hole in the ground, which is then covered with dirt. Simple, right? Wrong. Landfills are complex trash storage systems that perform a variety of functions.

Most landfills built today are called municipal solid waste landfills, and use a plastic liner and layer of clay to isolate trash from the environment. Placed along the bottom of a landfill, these safeguards prevent contaminants from touching the outside soil, and especially from polluting groundwater.

Keeping trash dry and away from water is a landfill's most important function. To that end, drainage pipes and ditches siphon off rainwater that falls on the site. The water that does manage to penetrate a landfill filters through the trash, picking up chemical contaminants much like water dripping through a coffee maker. Pipes on top of the plastic liner run along the bottom of a landfill, collecting this contaminated water and draining it into collection ponds.

Some landfills perform other valuable functions, such as producing usable energy in the form of methane gas. The main problem with landfills, however, is that they require a lot of space near places that produce a lot of trash. Since Americans produce 210 million tons of trash every year, landfill space is at a premium. However well landfills work, eventually we'll have to adopt an alternative trash disposal solution.