Water bodies in the United States-including rivers, lakes, and harbors-may contain contaminated sediments that pose risks to aquatic ecosystems and human health. Contaminated sediments are toxic or hazardous substances contained in soil, sand, organic matter, or other materials accumulating on the bottom of water bodies at levels that may adversely affect human health or the environment, or both. These substances include polychlorinated biphenyls, or PCBs,1 and metals, such as mercury, many of which persist for years or decades because they do not degrade or degrade very slowly in aquatic environments. Contaminants in sediments can directly harm aquatic organisms or accumulate in their tissues, which can then be consumed by humans or wildlife. As a result, contaminated sediments are often a contributing factor to the over 4,800 fish consumption advisories issued nationwide asof 2011.2 They can also impair the navigational and recreational uses of water bodies, according to the National Research Council.3 Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in 1980, to protect human health and the environment from the effects of hazardous substances, including those in contaminated media such as groundwater, soil, or sediments.4 CERCLA established the Superfund program, which is the federal government's principal program to clean up the nation's most contaminated hazardous waste sites, and the Environmental Protection Agency (EPA) is the agency responsible for administering the program. Two basic types of cleanups, or response actions, are conducted under the Superfund program: (1) remedial actions and (2) removal actions. Remedial actions are generally long-term cleanups-consisting of one or more remedial action projects-that aim to permanently and significantly reduce contamination and that can take a considerable amount of time and money, depending on the nature of the contamination and other site-specific factors. Removal actions are usually short-term cleanups for sites that pose immediate threats to human health or the environment. The authority for selecting response actions has been delegated from the EPA Administrator to the agency's 10 Regional Administrators.