The Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) grants the President the authority to respond to releases of hazardous chemical substances that imminently and substantially threaten public health or welfare, or the environment. The Act, which establishes a $1.6 billion Superfund to finance response actions, and which charges the Environmental Protection Agency with administering critical portions of the response program was designed to build on the existing environmental response authority given to EPA under Section 311 of the Clean Water Act During an emergency response to a release of a hazardous substance, the On-Scene Coordinator will require scientific information for the decision-making process. This manual provides guidance in establishing and maintaining scientific support for responses to such releases. The manual delineates the methods and technical aspects of scientific support required during implementation of Superfund removal activities, regardless of the government unit (state, local or Federal) that may be performing the implementation. Although comprehensive in coverage, the primary emphasis is on environmental effects on inland areas. Pre-response activities are emphasized. Consultantants, scientific literature, computer data bases, records and analytical capabilities must be identified and appropriate contracts or other agreements must be arranged before an emergency response. Region-specific resources must be identified.