By the end of the 1970s, Congress had enacted several environmental laws to regulate sources of pollution in the United States, but had not yet addressed responsibility for contamination resulting from releases of pollutants into the environment. In the late 1970s, the discovery of severely contaminated sites, such as "Love Canal" in New York and Times Beach in Missouri, raised questions as to whether there should be a federal role in cleaning up environmental contamination to protect the public from potential harm. Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA; P.L. 96-510 ) to authorize the federal government to clean up contaminated sites in the United States and to make the "potentially responsible parties" connected to those sites financially liable for the cleanup costs. CERCLA created the Superfund program to carry out these authorities. The Environmental Protection Agency (EPA) administers the program. Subsequent amendments to CERCLA also authorized EPA to administer a separate grant program to support the cleanup of abandoned or idled "brownfields" properties to encourage their redevelopment. CERCLA established a broad liability scheme that holds both past and current owners and operators of contaminated facilities financially responsible for the costs of cleanup. At waste disposal sites, generators of the waste sent to the site for disposal, and transporters of the waste who selected the site for disposal, also are responsible for the cleanup costs. If these potentially responsible parties cannot be found or cannot pay for the cleanup, CERCLA authorizes the federal government to finance the cleanup to ensure the protection of human health and the environment. These costs borne by the federal government are referred to as "orphan shares." The broad liability scheme of CERCLA is intended to capture all parties that may have had some involvement in the actions that resulted in contamination of the environment, in order to minimize the burden of the costs of cleanup on the general taxpayer who had no involvement. This approach to liability is based on the principle that polluters should be required to pay for the environmental damage that they cause, often referred to as the "polluter pays principle." CERCLA established the Hazardous Substance Superfund Trust Fund to finance cleanup actions taken by the federal government at contaminated sites where the potentially responsible parties cannot pay or cannot be found. A combination of special taxes on industry and revenues from the General Fund of the U.S. Treasury initially financed the Superfund Trust Fund, but the authority to collect the industry taxes expired at the end of 1995. As the remaining revenues were expended over time, Congress increased the contribution of general Treasury revenues in an effort to make up for the shortfall from the expired industry taxes. The availability of Superfund Trust Fund monies to finance the cleanup of contaminated sites is subject to appropriations by Congress. Considering the liability of the federal government as a potentially responsible party at its own facilities, the cleanup of federal facilities is not funded with Superfund Trust Fund monies under the Superfund program, but with other federal monies appropriated for other programs administered by the agencies responsible for these facilities. The Department of Defense (DOD) and the Department of Energy (DOE) administer the cleanup of most contaminated federal facilities. EPA and the states are responsible for overseeing and enforcing the implementation of CERCLA at federal facilities to ensure that applicable requirements are met. To prioritize cleanup actions, CERCLA directed EPA to establish and maintain a National Priorities List (NPL) of the most contaminated sites in the United States which present the greatest risks to human health and the environment. The NPL includes both non-federal sites and federal facilities that are deemed to present a sufficient level of risk to warrant listing. EPA may require the potentially responsible parties to directly perform or pay for cleanup actions themselves. Alternatively, EPA may clean up a contaminated site up-front with appropriated Superfund monies and later recover those funds from the potentially responsible parties (with the exception of the cleanup of federal facilities which must be funded up-front by the administering agencies). In the event that the potentially responsible parties cannot pay or cannot be found, appropriated Superfund monies may be used to pay the orphan shares of cleanup costs at a site, under a cost-sharing agreement with the state in which the site is located. The following sections of this report summarize the major cleanup authorities of CERCLA and other relevant provisions of the act. The topics discussed herein include the overall scope and reach of these statutory authorities, the process under which cleanup actions are selected and carried out at individual sites, the financial liability of potentially responsible parties for the costs of cleanup actions, the Superfund Trust Fund that may pay for cleanup actions when the potentially responsible parties cannot pay or cannot be found, enforcement of cleanup liability against the potentially responsible parties to minimize the need for federal tax revenues to finance the cleanup of contaminated sites, the applicability of CERCLA to federal facilities, and federal assistance for the cleanup of brownfields properties. A briefer summary of these topics is presented in CRS Report RL30798, Environmental Laws: Summaries of Major Statutes Administered by the Environmental Protection Agency . It should be emphasized that how and to what degree a specific contaminant at an individual site must be cleaned up under CERCLA are not specified in the law itself. The specific actions that are required to clean up contaminants at individual sites are determined on a site-by-site basis. Although CERCLA established a general process for making cleanup decisions, more specific direction is provided in EPA regulation and agency guidance. Other federal agencies that administer the cleanup of federal facilities under CERCLA have developed additional guidance documents that apply to their own respective facilities. Although the statutory authorities upon which federal agencies have based their cleanup regulations and guidance are discussed in this report, the content of these regulations and guidance is not examined here. As such, this report summarizes selected statutory provisions of CERLCA, but does not discuss agency regulations and guidance that may provide more detailed direction for carrying out cleanup actions at individual sites. Congress has amended CERCLA on numerous occasions to clarify the applicability of the cleanup authorities of the statute, and to provide relief from liability for certain categories of parties who may not have been involved in actions that led to contamination, or who may have contributed only certain quantities or types of waste to a site. Congress also has amended the statute to authorize federal assistance for the cleanup of abandoned or idled "brownfields" properties to encourage their redevelopment. Further, certain amendments have addressed unique cleanup challenges at federal facilities, such as the cleanup of unexploded ordnance on decommissioned military training ranges in the United States, and responsibility for the cleanup of contaminated federal property when it is transferred out of federal ownership. The Superfund Amendments and Reauthorization Act of 1986 (SARA; P.L. 99-499 ) clarified that federal facilities are subject to the cleanup requirements of CERCLA to the same extent as non-federal entities, and amended various response, liability, and enforcement provisions of the law. The 1986 amendments also renewed the authorization of appropriations for EPA's Superfund program through FY1991, and established a separate Defense Environmental Restoration Program within the Department of Defense (DOD) to address contamination at active and decommissioned military facilities in the United States. Title VI of the Omnibus Budget Reconciliation Act of 1990 ( P.L. 101-508 ) extended the authorization of appropriations for EPA's Superfund program through FY1994, and Title XI of that statute extended the authority to collect the special Superfund taxes on industry through December 31, 1995. Although reauthorizing legislation has been introduced in various Congresses, the taxing authority for the Superfund Trust Fund has not been renewed to date, nor has the authorization of appropriations for EPA's Superfund program been extended. Instead, Congress has continued to fund the Superfund program primarily with general Treasury revenues through the annual appropriations process. Congress has annually authorized and appropriated funding for the Defense Environmental Restoration Program each year since its establishment. Most of this funding is supported with general Treasury revenues, with the exception of some revenues generated from the sale or lease of closed military bases which help fund their cleanup. In 1992, the Community Environmental Response Facilitation Act ( P.L. 102-426 ) amended the federal facility provisions of CERCLA to facilitate the transfer of uncontaminated parcels of surplus federal property on which hazardous substances or petroleum products were not released. Section 334 of the National Defense Authorization Act for FY1997 ( P.L. 104-201 ) further amended CERCLA to allow the transfer of contaminated surplus federal property before cleanup is complete, if assurances are provided to guarantee that the property will be cleaned up to a level that would be suitable for its intended use after transfer. Other amendments have attempted to address the fairness of the liability scheme of CERCLA, either by limiting or eliminating the liability of certain categories of parties. In 1996, the Asset Conservation, Lender Liability, and Deposit Insurance Protection Act (Subtitle E, Title II, Division A of P.L. 104-208 ) amended CERCLA to protect certain fiduciaries and financial lenders from liability. In 1999, the Superfund Recycling Equity Act (Title VI, Appendix I of P.L. 106-113 ) exempted generators and transporters of recyclable scrap materials from cleanup liability under CERCLA, if the person who received the materials disposed of them instead and the disposal resulted in contamination. There had been some concern that the potential liability of generators and transporters under CERCLA could be a deterrent to recycling. In 2002, the Small Business Liability Relief and Brownfields Revitalization Act ( P.L. 107-118 ) provided relief from cleanup liability for (1) persons who contributed very small quantities of waste or only municipal solid (i.e.