Bioremediation is a treatment process that uses the metabolic activity of microorganisms (bacteria and fungi) to naturally degrade organic contaminants in the soil. The process can be conducted in the ground at the site of contamination (in-situ) or at land-farms, bio-piles or bioreactors specially set up to receive and treat the soil (ex situ) either on or off-site.

Treatment can be enhanced and its efficiency accelerated by the addition of nutrients, oxygen and water to the soil, by manipulating the temperature and pH of the soil, or by combining the process with a soil vapor extraction system.

Bioremediation is particularly effective in treating petroleum hydrocarbons, volatile organic compounds, and in some cases, even chlorinated solvents.