The U.S. Environmental Protection Agency (EPA) Engineering Issues are a new series of technology transfer documents that summarize the latest available information on selected treatment and site remediation technologies and related issues. They are designed to help remedial project managers (RPMs), on-scene coordinators (OSCs), contractors, and other site managers understand the type of data and site characteristics needed to evaluate a technology for potential applicability to their specific sites. Each Engineering Issue document is developed in conjunction with a small group of scientists inside the EPA and with outside consultants, and relies on peer-reviewed literature, EPA reports, Internet sources, current research, and other pertinent information. The purpose of this document is to present the state of the science regarding management and treatment of hard-rock mines. Internet links are provided for readers interested in additional information; these Internet links, verified as accurate at the time of publication, are subject to change.