In the beginning, man dumped his garbage over the edge: into a ravine, a swamp, a river. When swamps grew scarce and man grew civilized (sort of), man dug holes and filled them with waste, sometimes burning it first to reduce its mass. The result could be successful new real estate (an airport runway, perhaps), but more often it was an odoriferous nightmare (slums atop oozing mounds).

In 1937, after traveling the dumps of the United States, Jean Vincenz built in his hometown of Fresno, CA, the country's first "sanitary landfill" (England had a sanitary landfill, too, but it never accepted household waste). Every day, Vincenz, Fresno's commissioner of public works, carefully positioned and compacted the city's waste. Then, to keep down vermin, birds, odors, and dust, he buried it with soil that he'd dug out to make room for the next day's haul. The sanitary-landfill idea began to catch on during World War II, when the U.S. military adopted Vincenz's methods. By 1945, a hundred cities had jumped on the bandwagon, and by the '50s the sanitary method was in full flower.

America's trash heaps now looked cleaner, but their subterranean aspects were anything but. A blanket of dirt over the garbage (or an equivalent blanket of foam or shredded paper or glass) didn't protect groundwater from the contaminated moisture, called leachate, that seeped through the garbage, and it didn't control or capture leaking landfill gases, many of which are toxic. It wasn't until the 1980s and '90s that the Environmental Protection Agency (EPA), through its Resource Conservation and Recovery Act, began to protect human health and the environment against these discharges by requiring bottom liners and leachate collection systems and, for larger dumps, gas collection systems. In 1991, the agency gave landfills six years to modernize or close. But complicated liner systems are expensive: Dumps that couldn't or wouldn't come up to code shut down. In 1988, there were nearly 8,000 landfills across the country; in 1999, there were 2,314; and by 2005, there were only 1,654.

Is there a shortage of landfill space?
Not in most of the country. These modern landfills are huge-hundreds if not thousands of square acres in size-and they accept trash from other communities, states, and even countries. Dumps in Michigan take Toronto's trash, for example, and New Brunswick, Canada, takes Maine's. In 2003, 32 states exported waste and 24 imported waste; obviously, some did both. (Why would a community welcome another's garbage? Money. Landfill owners pay hefty fees to cash-starved "host" communities, and often provide free dumping as well.)

But just because there's room out there for our trash doesn't mean it's a good idea to continue generating and burying waste. (In 2005, American residents, businesses, and institutions generated more than 245 million tons of trash, which works out to 4.5 pounds per person per day.) It costs a lot of money to haul waste around the country, and garbage trucks pollute the air, congest our roadways, and inevitably leak and litter.

What happens to our stuff once it's buried in a landfill?
If it's kept dry, not that much, it turns out. "Dry tomb" landfills, which are designed to keep moisture away from garbage, can be more like mummifiers than composters. Digging deep inside old dumps in arid regions, archeology students working with the University of Arizona's Garbage Project extracted 70-year-old newspapers that could still be read and 40-year-old hot dogs that looked nearly edible. Once garbage is compacted and deeply buried, the students discovered, degradation grinds nearly to a halt. Below roughly the top eight feet of a landfill, few organisms that require oxygen-which means precious few of the variety that most greedily chew up waste-can survive. Aerobic biodegradation works best when organic material is chopped up, kept moist and warm, and exposed to oxygen with regular turning. This is exactly the opposite of what happens when our sealed plastic bags are compressed in a landfill.

Are landfills safe?
In a word, no. When moisture reach biodegradable materials-whether they're food scraps, grass clippings, paper, or wood-they'll decompose and generate two serious forms of pollution. The first is methane, a powerful greenhouse gas. Landfills are the largest man-made source of methane (CH4) in this country. Some landfill operators collect methane and other gases, mostly to keep it from migrating and bursting into flame (not uncommon). They either flare the gas or use it to generate electricity. But these collection systems vacuum up, at best, only 75 percent of gases, and that percentage rapidly declines as pipes get clogged and crushed. Some experts put the collection rate even lower-in the 20 percent range.

The other kind of pollution generated by landfills is the leachate mentioned earlier, which forms when rain filters through all the junk we've pitched into our trash bins, picking up traces of metals and chemicals and settling into a toxic soup at the bottom of the landfill. Leachate contains heavy metals, acids, solvents, pesticides, motor oil, and flame retardants. (Not everything thrown into a dump is bagged.) Yes, modern landfills have complicated liners made of gravel, clay, and geotextile membranes (thin plastic, that is), but even the best landfill liner will ultimately fail-and it will fail long before the contents of the landfill cease to threaten water and soil. How long does a landfill pose a threat to the environment? For as long as the landfill exists. The dumps of the Roman empire, more than 2,000 years old, are still leaching heavy metals today. Landfills become more dangerous over time, not less.

Is there a better way to deal with household waste?
Some engineers are experimenting with "bioreactors," in which leachate is collected and then, instead of being treated and discharged into nearby waterways, is repeatedly injected back into the dump. All this moisture accelerates decomposition, so that bacteria feeding off waste produce more gas more quickly. After the fermentation of waste has stopped, the dump contents are rinsed with freshwater, and the toxic runoff is collected and treated before final discharge. Because the garbage shrinks while it decomposes, the landfill settles and stabilizes faster than with the dry tomb method-while monitors are still keeping an eye on things, it is to be hoped. (The EPA requires landfill owners to monitor and maintain their properties for only 30 years after they've been filled up, covered, capped, and planted. After that, liability shifts back to taxpayers.) It's too soon to say whether wet landfills are any safer than dry: None has yet been closed.

Of course, we'd all be better off if most of this stuff was never dumped into a landfill in the first place (or into an incinerator, which poses its own set of environmental hazards). Recycling keeps valuable materials out of dumps. (For more on this topic, click here.) Making new goods from old goods saves enormous amounts of energy; it also cuts down on air and water pollution. Composting organic material-food scraps, yard waste, wood-avoids the generation of methane and leachate. According to the EPA, more than 60 percent of the contents of our municipal landfills is potentially compostable.

Even better than diverting waste for other uses is reducing consumption: refusing to buy over-packaged goods, using both sides of each sheet of paper, printing in ink-saving "draft" mode instead of higher-quality "normal" whenever possible, and reusing what's already out there (reupholstering a couch, buying goods through Craigslist). Even further up the hierarchy is redesign. If brand owners or manufacturers designed goods with nontoxic materials that lasted longer and were easier to take apart and either fix or reuse, we wouldn't be arguing over dry tomb versus bioreactor landfills. We'd have little use for either.

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