This Engineer Manual (EM) provides guidance and background for the appropriate screening and selection of in situ thermal remediation (ISTR) technologies, including steam enhanced extraction injection, electrical resistivity heating, and thermal conductive heating. This document is intended to help distinguish proper applications of the technology and identify important design, operational, and monitoring issues relevant to Government oversight personnel. It is intended for use by engineers, geologists, hydro geologists, soil scientists, chemists, project managers, and others who possess a technical education but only the broadest familiarity with ISTR technologies.