The Office of Site Operations (OSO) is responsible for implementing long-term surveillance and maintenance (LTS&M) at more than 100 sites in over 30 states and with 25 tribes that have been transferred to the Office of Legacy Management (LM). Site managers oversee the cleanup remedies to assure they continue to protect communities from exposure to hazardous wastes. LM is also preparing for the transition of 20 sites over the next five years at which LM will also conduct LTS&M. Important activities that OSO performs at transition sites prior to them formally becoming the responsibility of LM include developing LTS&M plans and identifying other regulatory requirements that LM will have for the sites, including cultural, historical, and natural resources. The OSO also runs the safety and health, quality assurance, and environmental compliance programs. It is important to engage other federal agencies, the environmental community, universities, national laboratories, and the international scientific community, and incorporate advances in science and technology to improve stewardship capabilities, cost effectiveness, sustainability, and protectiveness of environmental remedies at LM sites. In addition, the OSO leads interagency work on Defense-Related Uranium Mines and manages the Uranium Leasing Program in western Colorado.