Includes bibliographical references and index. Support for this project was provided by the American Petroleum Institute under contract no. 97-0000-1957, the Chemical Manufacturers' Association, Chevron, the Lawrence Livermore National Laboratory, the National Mining Association, the Nuclear Regulatory Commission under contract no. NRC-04-97-068, the U.S. Army under contract no. DACA31-97-P-1191, the U.S. Department of Energy under contract no. DE-FC01-94EW54069, the U.S. Environmental Protection Agency under contract no. R-826445-01-0, the U.S. Geological Survey under contract no. 1434-HQ-97-AG-01775, and the U.S. Navy under contract no. N62467-97-M-1009.

1. Introduction: Using Natural Processes in Groundwater Restoration. Historical Role of Natural Cleanup Processes. Limitations of Engineered Remediation Systems. Increasing Reliance on Natural Attenuation. Increasing Variety of Contaminants Considered for Natural Attenuation. Increasing Number of Natural Attenuation Protocols. Increasing Public Concerns. Focus of This Report -- 2. Community Concerns about Natural Attenuation. Specific Community Concerns. Basis for Community Concerns. Principles of Community Involvement. Mechanisms for Involving the Community -- 3. Scientific Basis for Natural Attenuation. Contaminants and Hydrogeologic Settings. Removal of Contaminant Sources. Movement of Contaminants in the Subsurface. Transformation of Contaminants in the Subsurface. Transformation by Microorganisms. Transformation by Chemical Reactions. Integration of the Mechanisms That Affect Subsurface Contaminants. Case Studies of Natural Attenuation.