This Guide contains the regulatory and policy requirements governing remediation of ground water contaminated with hazardous waste [including radioactive mixed waste (RMW)], hazardous substances, or pollutants/contaminants that present (or may present) an imminent and substantial danger. It was prepared by the Office of Environmental Policy and Assistance, RCRA/CERCLA Division (EH-413), to assist Environmental Program Managers (ERPMs) who often encounter contaminated ground water during the performance of either response actions under CERCLA or corrective actions under Subtitle C of RCRA. The Guide begins with coverage of the regulatory and technical issues that are encountered by ERPM`s after a CERCLA Preliminary Assessment/Site Investigation (PA/SI) or the RCRA Facility Assessment (RFA) have been completed and releases into the environment have been confirmed. It is based on the assumption that ground water contamination is present at the site, operable unit, solid waste management unit, or facility. The Guide`s scope concludes with completion of the final RAs/corrective measures and a determination by the appropriate regulatory agencies that no further response action is necessary.