As a result of human activity, soil can accumulate so many harmful substances that it can cause harm or danger to the environment or to human health. Hazardous substances may get into the soil as a result of individual accidents, damage or long-term gradual emissions. Substances can migrate to groundwater and waterways or spread to surrounding areas. Environmental degradation may be observed after decades when operations have already ended.
Soil contamination is the most commonly investigated when the use or ownership of a suspected area of activity has changed, is being built on or the activities in the area are terminated. Remediation of contaminated soil is necessary whenever a risk assessment indicates that harmful substances pose significant environmental or health hazards. In addition, areas may be remediated, for example, when ownership of an area changes along with the change in responsibility for its remediation. As urban construction becomes more concentrated, former industrial and commercial sites are being used for residential use, often requiring soil remediation.