DOE’s current and former nuclear weapons complex includes dozens of sites nationwide containing nuclear reactors, chemical processing buildings, plants, laboratories, and maintenance facilities that manufactured thousands of nuclear warheads and together conducted more than one thousand nuclear explosion tests. The environmental legacy of nuclear weapons production includes contaminated buildings, soils, water resources, and large volumes of radioactive and hazardous wastes that require treatment, stabilization to prevent migration, and disposal. DOE estimated in 2006, that the future cost to clean up, dispose, and provide long-term oversight of all wastes will be more than $230 billion over the next 75 years. Among the sites requiring environmental cleanup are the five sites addressed in this report. The Hanford Site is located on the arid east side of Washington state near Richland and adjacent to the Columbia River. The site was established to produce plutonium for nuclear weapons during World War II and, according to DOE, subsequently produced the majority of the nation’s plutonium during the Cold War. The Idaho National Laboratory, located near Idaho Falls in the southeastern Idaho desert, was established in 1949 as the National Reactor Testing Station and was the site of the largest concentration of nuclear reactors—52—in the world. Los Alamos National Laboratory, located in a mountainous area of northern New Mexico, was established in 1943 and played a central role in researching the advanced technologies required for nuclear weapons manufacture. It is where the first atomic bomb was assembled. The Oak Ridge National Laboratory near Knoxville, Tenn., was established in 1943 to pilot the processing of uranium during World War II. The Savannah River Site, near Aiken, S.C., was built in the 1950s to produce basic materials needed in nuclear weapons manufacture, such as tritium and plutonium. DOE’s Office of Environmental Management is responsible for cleaning up contamination left behind at these sites after decades of nuclear production and research. Environmental management officials at DOE field sites plan and oversee the cleanup activities at those sites, but the work itself is carried out primarily by private firms contracted by DOE. Officials from EPA, as well as environmental agency officials from the states in which DOE sites are located, enforce federal and state environmental laws and oversee and advise DOE on its cleanup efforts. Transuranic elements, which have an atomic weight greater than uranium, are man-made radioactive elements produced in nuclear reactors. Transuranic wastes are created when materials such as clothing and tools come into contact with plutonium and other transuranic elements during processing activities and cannot be reused for other purposes. They were first generated during operations to produce and recover plutonium for nuclear weapons manufacture and are still being produced in small quantities at laboratories where nuclear research continues today. Federal law currently defines transuranic waste as waste containing more than 100 nanocuries of alpha-emitting transuranic elements (radiation) per gram and with half-lives greater than 20 years with certain exceptions. A half- life is the amount of time required for an element to decay by half, and nanocuries are a measure of radioactivity. Alpha-emitting radiation cannot pass through objects, including human skin, but is extremely dangerous if inhaled or ingested. Some buried wastes contaminated with transuranic elements may not meet the current legal definition of transuranic wastes. For ease of discussion in this report, however, we refer to these wastes as buried transuranic wastes. The cleanup agreements DOE entered into with federal and state environmental agencies require DOE to investigate and take action as necessary to clean up sites where transuranic and other wastes were buried. The legal and regulatory framework governing management and disposal of transuranic wastes has changed significantly over the past 50 years, particularly in 1970. Before 1970, there was no separate category for what is now defined as transuranic waste. Consequently, the federal government managed this waste as low-level radioactive waste, which it buried along with hazardous wastes in unlined, shallow pits and trenches, as shown in figure 1. In 1970, in response to concerns that transuranic elements remain radioactive for an extremely long time and scientific research recommending deep geologic disposal for this waste, the Atomic Energy Commission––a DOE predecessor––directed sites that generated transuranic wastes to begin segregating them from other wastes and storing them in retrievable packages for an interim period of 20 years, pending disposal in a repository. In late 1979, Congress authorized DOE to develop a deep geologic repository in New Mexico to permanently dispose of transuranic wastes, including these stored transuranic wastes. In October 1992, Congress gave DOE management responsibility for the land, and gave EPA substantial responsibility for regulating many of DOE’s activities at the repository. This repository, known as the Waste Isolation Pilot Plant (WIPP), began operating in the late 1990s and, in 1999, received its first shipment of transuranic wastes generated after the 1970 directive to segregate and store such wastes. The Atomic Energy Commission’s 1970 directive did not apply to transuranic wastes buried prior to 1970, and DOE considered these wastes permanently disposed. However, the sites where these wastes are buried have since become subject to CERCLA and other environmental laws. In particular, section 120 of CERCLA requires EPA to evaluate federal waste sites for possible inclusion on the National Priorities List. In 1989, EPA included on this list, the waste sites that contain most of DOE’s buried transuranic wastes—Hanford, Idaho, Oak Ridge, and Savannah River. With this designation, CERCLA requires DOE to evaluate the nature and extent of contamination at these sites and determine what cleanup actions, if any, are necessary to protect human health and the environment. The buried transuranic waste sites at Los Alamos were evaluated but were not placed on the list. Cleanup of Los Alamos is being carried out under other authorities. At Los Alamos, the cleanup is being conducted under agreements with New Mexico—implementing the Resource Conservation and Recovery Act of 1976, as amended (RCRA) and state law—and under DOE’s Atomic Energy Act authority. The provisions of the Los Alamos cleanup agreements are similar to those under CERCLA requirements, including a schedule for conducting the cleanup. Los Alamos has multiple waste sites that contain buried transuranic wastes, and DOE’s agreements with the state of New Mexico address each waste area separately. To carry out the cleanup of its National Priorities List sites under CERLCA, DOE must follow a process that includes extensive consultation between DOE, EPA, and state environmental agencies, as well as opportunities for public participation, to reach a decision on how DOE should clean up the respective site. The process begins with DOE consulting EPA and state environmental agencies and investigating the nature and extent of contamination at each site and undertaking a feasibility study to identify and evaluate possible approaches for cleaning up each site. After evaluating the approaches, DOE selects a “preferred alternative” that meets CERCLA requirements and presents, for public comment, a proposed plan explaining its preferred approach for cleaning up the wastes. DOE considers the public’s comments and consults with EPA and the state environmental agency to determine a cleanup approach. Once the parties have reached agreement, the approach and the rationale for selecting it are published in a legally binding Record of Decision. In addition, DOE must enter into an interagency agreement with EPA that includes, among other things, a schedule for completing cleanup of the site. The environmental agency in the affected state is also a party to the agreements for Hanford, Idaho, Oak Ridge, and Savannah River. If the selected cleanup approach will involve leaving hazardous substances at the site, DOE must monitor the effectiveness of the approach and review the action every 5 years to determine whether any additional actions are necessary to protect human health and the environment. The provisions of the agreements, including the milestones, are legally enforceable and can be revised, as necessary, to incorporate new information and address changing conditions. As shown in table 1, DOE is currently scheduled to complete cleanup actions at all five sites by 2025. DOE has made cleanup decisions and is addressing transuranic wastes at Oak Ridge and Savannah River, but the department is still investigating cleanup options at the other three locations where most of DOE’s transuranic wastes are buried. DOE plans to leave transuranic wastes buried at Oak Ridge and Savannah River in place under an engineered barrier and take additional measures to prevent intrusions that could expose humans and the environment to the buried contaminants. In contrast, DOE is still evaluating cleanup options at the Idaho National Laboratory, Hanford Site and Los Alamos National Laboratory, where about 90 percent of its buried transuranic wastes are located. The extent to which DOE will be required to retrieve buried wastes or will be allowed to manage these wastes in place is currently unknown, and cleanup decisions for the majority of these wastes are several years away. However, DOE has agreed to retrieve some of the wastes buried at Hanford and Idaho, because the wastes may threaten nearby surface waters and groundwater. In accordance with CERCLA’s requirements, DOE evaluated a number of approaches for addressing transuranic wastes buried at Oak Ridge and Savannah River. At both sites, DOE had originally disposed of the wastes in near-surface burial pits and trenches, often with other radioactive or hazardous wastes, including cesium, strontium, and volatile organic compounds. The two sites contain about 10 percent of the estimated 127,000 cubic meters of transuranic wastes buried across the five DOE sites. DOE officials at both sites considered several cleanup options, ranging from managing the wastes in place to removing them from the ground and disposing of any exhumed transuranic wastes at WIPP.