Research Needs in Subsurface Science provides an overview of the subsurface contamination problems across the DOE complex and shows by examples from the six largest DOE sites (Hanford Site, Idaho Engineering and Environmental Laboratory, Nevada Test Site, Oak Ridge Reservation, Rocky Flats Environmental Technology Site, and Savannah River Site) how advances in scientific and engineering knowledge can improve the effectiveness of the cleanup effort. This report analyzes the current Environmental Management (EM) Science Program portfolio of subsurface research projects to assess the extent to which the program is focused on DOE's contamination problems. This analysis employs an organizing scheme that provides a direct linkage between basic research in the EM Science Program and applied technology development in DOE's Subsurface Contaminants Focus Area. Research Needs in Subsurface Science also reviews related research programs in other DOE offices and other federal agencies (see Chapter 4) to determine the extent to which they are focused on DOE's subsurface contamination problems. On the basis of these analyses, this report singles out the highly significant subsurface contamination knowledge gaps and research needs that the EM Science Program must address if the DOE cleanup program is to succeed.