Garbage is dirty, but it is a clean fuel

About 45 minutes north of downtown Los Angeles, a machine the size of a small truck flattens tons of food scraps, paper towels and other household trash into the side of a growing 300-foot pile.

To Waste Management, which operates the landfill, this is more than just a mountain of garbage. Pipes tunneled deep into the mound extract gas from the rotting waste and send it to a plant that turns it into electricity.

Apart from the huge-wheeled compactor driving over garbage on its surface, it looks like an ordinary hillside. And it doesn't even smell. Yet it produces enough energy to power 2,500 homes in Southern California.