Environmental remediation is the removal of contaminants from soil, water, air or sediment, typically after a spill or other industrial accident. Remediation removes the toxic materials, allowing the affected area to become habitable and safe again. For instance, a nuclear accident may leave small radioactive particles mixed in with soil and water that can threaten health and life if not filtered out and removed.
Environmental remediation is used for situations where the toxins released into the environment are too dangerous to allow the natural effects of wind and rain to wash them away. Substances that could present a threat to groundwater or contaminate animal and plant life are of particular concern, as they can easily spread to a wider region if not contained.
Typically, remediation projects are divided into two groups, in-situ and ex-situ. In-situ projects deal with the contaminants on-site, while ex-situ projects remove the contaminated media to an off-site location. For instance, a contaminated reservoir could be treated in-situ with chemical additives designed to bond with contaminants for later collection, or the water could be pumped out ex-situ and taken to a filtration facility for cleaning and later restoration.
In some cases, toxic substances can be too hazardous or too prevalent for environmental remediation. The area around the Chernobyl reactor is considered too hazardous for human habitation, and the government simply established an exclusion zone around the disaster site rather than attempt an extremely expensive and long-term cleanup project.