During the course of nuclear weapons production, the Department of Energy (Department) and its predecessor agencies constructed over 20,000 facilities, ranging from temporary trailer-type buildings and office space to state-of-the-art nuclear reactors and laboratories. As the Department's mission has evolved, many of these structures are no longer needed and, as such, have been identified as excess facilities. Currently, the Department has nearly 1,200 excess facilities totaling almost 16 million square feet. Costs associated with these facilities, primarily for surveillance and maintenance, exceed about $70 million annually. Over time, these costs are expected to increase, as will the health and safety risks that these buildings pose to workers and the environment.