The in-situ and on-site assessment and remediation of contaminated sites, together with risk-based management and control of hazardous substances, are potentially less expensive than other assessment and remediationapproaches, while maintaining accuracy and effectiveness. Cost-effective remedial and management approaches that are also effective in minimizing exposure and risk to human health and the environment are a critical needthroughout the world, especially in Eastern Europe and the former Soviet Union, where resources that can be devoted to chemical cleanup are especially limited. Although much of the focus of the book is on natural processesand how they might be enhanced for the management of contaminated sites, there is also a recognition that a portion of sites may require more invasive approaches, which are especially useful in managing source areas thatcontribute to the migration of contaminants in groundwater and other media. Among the more invasive approaches discussed are solvent extraction, direct bioremediation of PCBs, source areas and munitions, and chemicaloxidation.