The total number of confirmed releases from underground storage tanks is increasing rapidly. In addition, the treatment of contaminants in soil and groundwater at leaking underground storage tank (LUST) sites presents complex technical challenges. Most of the remedial technologies being used involve the separation of contaminants from soil or groundwater. The destruction or disposal of these separated contaminants is a tedious and expensive task. Furthermore, most of the in-situ remediation technologies are only effective for removing volatile organic compounds (VOCs) and only certain semi-volatiles from the vadose zone. Recently, new treatment methodologies have been investigated. Processes involving chemical oxidation have the potential to treat all types of organic contaminants in both vadose and saturated zones either in-situ or following excavation or, under certain conditions, to detoxify the hazardous materials that may be present in the off-gases that result from the use of vapor extraction or thermal desorption technologies. The oxidative processes can entail complete mineralization, transformation of complex substances into simple compounds, or conversion of hazardous materials to more water-soluble compounds that are typically less toxic and amenable to biodegradation.