Soil remediation is also known as soil washing. This term refers to multiple processes designed to remove pollutants and contaminants such as heavy metals, hydrocarbons, pesticides, herbicides and volatile chemicals from soil, both for commercial cultivation as well as to benefit wild flora and fauna. This is part of the larger environmental remediation initiative in which efforts are made to clean up and maintain higher standards for the quality of air, soil and water.
Bioremediation involves the use of bacteria, both aerobic and anaerobic species, specifically targeted to ingest and break down hydrocarbons and heavy metals in soil. This process works most effectively in soil that maintains a temperature of 70 degrees F with intermittent rain for optimum moisture. Soils in colder climates must be covered and insulated for bioremediation to be effective. Still, this process can take years to complete and the involved dangers of humans exposed to bioremediator microbes are not entirely known.
Air sparging is the process by which pressurized air is injected into the soil to force pockets of organic vapors to the surface. From there, these vapors are broken down with carbon filters. According to Terra Resources, Ltd., this procedure costs approximately $128 (as of 2007) for every ton of soil remediated, though this can fluctuate dependent on factors such as soil pH, soil permeability and depth and degree of contamination.
Encapsulation does not filter or wash out pollutants from soil so much as it quarantines them. This can be completed in several ways. Contaminated soil is mixed with lime, concrete and cement, thereby stopping the pollutants from spreading to clean soil, though this and all other methods preclude using said soil for cultivation. Contaminated soil can be turned into glass, locking in pollutants by inserting electrodes into the ground and heating the soil to the point of vitrification.
Contaminated soil is placed in a specially designed vessel which is heated by diesel or natural gas to approximately 800 degrees F. In doing so, all hydrocarbons, volatiles, pesticides and herbicides are burned away. However, heavy metals do remain. Given that this method consumes 200 gallons of fuel per hour, creating both significant costs and air pollution, thermal remediation is rarely used on a large-scale.