The Superfund program had its 25 th anniversary in 2005. Although Superfund debate has lessened, as compared with past years, particular aspects of the program continue to generate debate. Policymakers are faced with broad programmatic concerns, as well as more specific issues concerning program implementation. This report discusses some of these questions: Who should pay to clean up the nation's most contaminated sites if responsible parties cannot be found? Is the program receiving enough funding to meet its current and future obligations? How does the statute interact with abandoned hardrock mining sites and animal feeding operations? To supply the context for these issues, this report first provides a background and overview of the Superfund program. On December 11, 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, P.L. 96-510 ) to create the hazardous substance cleanup program. The program became known as "Superfund" in reference to the trust fund established by the law. The fund was originally supported by taxes levied on specific petroleum products and chemicals, and a corporate environmental income tax. Until recent years, the Superfund taxes provided the majority of the funding for the needs of the program. At the time of CERCLA's enactment, other federal environmental statutes provided federal agencies with only limited authority to address contamination at abandoned sites. CERCLA gave the federal government the authority to take direct action to respond to instances involving uncontrolled releases of hazardous substances (or pollutants and contaminants) that may endanger public health or the environment. CERCLA also enables the Environmental Protection Agency (EPA) to compel the persons responsible to clean up their contaminated sites. If the potentially responsible parties (PRPs) cannot be located, or they are unable (generally for financial reasons) to perform cleanup, EPA is authorized to use monies from the Superfund Trust Fund to clean up the site. CERCLA was expanded and reauthorized by the Superfund Amendments and Reauthorization Act of 1986 (SARA, P.L. 99-499 ). Amendments after SARA have been narrowly focused. In 1992 and 1996, Congress enacted legislation allowing for easier transfer of military bases with contaminated areas to local entities. In 1996 and 1999, Congress provided conditional liability exemptions for financial institutions and recycling facilities. In 2002, Congress enacted the Small Business Liability Relief and Brownfields Revitalization Act ( P.L. 108-118 ), which added further liability relief and authorized the Brownfields Program. Table 1 lists the various CERCLA amendments. The National Oil and Hazardous Substances Pollution Contingency Plan (NCP) contains the procedures and regulations for implementing the Superfund program. Generally, EPA leads the response to releases on land and in inland waters, whereas the Coast Guard leads the response in coastal waters of the United States. Actions under the Superfund program are triggered by a release (or threat of release) of a hazardous substance into the environment. The CERCLA "environment" includes all media: water (surface and groundwater), soil, and air. CERCLA defines "hazardous substance" to include all the materials identified as hazardous under the Resource Conservation Recovery Act (RCRA), the Clean Water Act (CWA), the Clean Air Act (CAA), and the Toxic Substances Control Act (TSCA). CERCLA also authorizes EPA to respond to releases of "pollutants or contaminants," which are broadly defined to include virtually anything that can threaten the health of "any organism." Petroleum is specifically excluded from the definition of hazardous substance and pollutant or contaminant. This means that neither CERCLA authority nor trust fund monies may be used to respond to releases of petroleum. However, the 2002 Brownfields law authorizes the cleanup of some petroleum-contaminated sites. The Superfund cleanup process starts either with a site discovery or with a notification to EPA of a potential hazardous substance release. Sites of concern can be discovered by various parties: citizens, state agencies, or EPA Regional offices. CERCLA § 103 requires release notification. Facilities must notify the National Response Center if there has been a release of a hazardous substance above a certain threshold, termed a reportable quantity (RQ). Since the inception of the Superfund program, EPA has catalogued more than 47,000 potentially contaminated sites in the agency's database: the Comprehensive Environmental Response, Compensation, and Liability Information System (CERCLIS) . After a site has been identified, EPA or a state agency performs a preliminary assessment to judge the site's potential hazards. After further screening, EPA uses the Hazard Ranking System (HRS) to score the site's contamination and its risk of exposure to surrounding communities. Sites that score high enough on the HRS are eligible for the National Priorities List (NPL), which is generally considered the official list of the most hazardous sites in the nation. Only a small percentage of the sites assessed are placed on the NPL. Over Superfund's history, EPA has placed 1,569 sites on the NPL (as of October 1, 2007). Of these sites, 321 have met cleanup goals and have been subsequently removed (deleted) from the NPL. At an additional 1,030 sites all physical construction activities have been performed, and operation and maintenance (such as treatment of contaminated groundwater) is ongoing. These sites are referred to as "construction complete." The NPL has been described as the centerpiece of the Superfund program, and thus it has been a focal point for Superfund criticism. As noted in a comprehensive report prepared by Resources for the Future (RFF) (hereafter referred to as the RFF Report): The expense and pace of cleaning up NPL sites has been, and continues to be, a contentious topic among followers of the Superfund program.... [E]ven though more than half of all NPL sites have been deemed "construction complete"—meaning that all physical remedies are in place and immediate risks posed by the site have been addressed—there remain hundreds of sites placed on the NPL during the early years of the program where cleanup remedies have still not been fully implemented. Some interest groups have questioned the listing process itself and the slow pace of cleanup at NPL sites. The decision to list a site on the NPL is ultimately at EPA's discretion. Many factors, other than the HRS score, influence whether a site is proposed for listing—for example, state support, community concerns, and Superfund budgetary issues. EPA has stated that The NPL is only of limited significance, however, as it does not assign liability to any party or to the owner of any specific property. Neither does placing a site on the NPL mean that any remedial or removal action necessarily need be taken. There are two categories of response activity in the Superfund program: (1) short-term removal action and (2) long-term remedial action. The trust fund can support removal action at NPL or non-NPL sites. However, trust fund monies can be used for remedial activity only if the site is on the NPL. The removal program grew out of the recognition that certain hazardous substance releases would necessitate a quick response. Removal action seeks to stabilize a site, and in some cases this minimizes the need for further cleanup. Removal action can be undertaken at sites regardless of their NPL status, and historically, most removal actions occur at non-NPL sites. CERCLA limits removal action to a one-year effort and expenditures of not more than $2 million. This limit applies only to efforts led by EPA and funded by trust fund dollars, not at sites where the responsible party is performing cleanup. Not all actions under the removal program are considered equally urgent. EPA groups removal actions into the following three categories: (1) Classic emergencies. Those actions where the release requires that on-site activities be initiated within minutes or hours of the determination that a removal action is appropriate. (2) Time-Critical Actions. Those actions where, based on an evaluation of the site, EPA determines that less than six months is available before site activities must be initiated. (3) Non-Time-Critical Actions. Those actions where, based on an evaluation of the site, EPA determines that more than six months is available before on-site activities must begin. Removal actions may include, but are not limited to: repairing a hazardous waste storage unit (e.g., landfill cover), transporting leaking drums to an appropriate disposal facility, and erecting a security fence to reduce opportunity of exposure. In recent years, the removal program has consistently received about one-third of the amount appropriated to the remedial program (see Figure 1 ). The remedial program is the core of the Superfund program. In contrast to removal actions, remedial actions, in general, take more time, cost more money, and represent a more permanent solution. Congress consistently apportions about half of the annual Superfund appropriation to the remedial program (see Figure 1 ). The remedial program consists of multiple process steps, each with its own term of art. Although the remedial process does not typically follow a linear, step-by-step progression, a simplified version of events is discussed below, highlighting the main milestones. The remedial program first involves a comprehensive investigation of the site and analysis of cleanup alternatives or remedies. This examination process (the Remedial Investigation/Feasibility Study, or RI/FS) can take months, or even years. Following completion of the RI/FS, EPA selects a remedy to address the site's contamination. EPA must solicit public comment when determining the remedy for the site, and states typically play an active role in the remedy selection process. CERCLA directs EPA to select a permanent remedy or treatment whenever possible. The less-preferred option is to leave the waste in place and reduce human exposure (e.g., soil cover or security fence).