The soil and water of the earth have long been considered convenient respositories for solid and liquid wastes. Humans have been burying soild wastes for thousands of years, but the process has escalated in the past 50 years. Every year, about 300 metric tons of pollutants, industrial wastes, and garbage are deposited into the natural environment. Often, this dumping is done with the mistaken idea that naturally occurring microbes will eventually biodegrade ( break down ) waste material.