The Environmental Protection Agency (EPA) estimates that one in four Americans lives within 3 miles of a hazardous waste site. To clean up these highly contaminated sites, the Congress established the Superfund program under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in 1980. EPA, the principal agency responsible for administering the Superfund program, has since identified more than 47,000 hazardous waste sites potentially requiring cleanup actions and has placed some of the most seriously contaminated sites on its National Priorities List (NPL). Through the end of fiscal year 2007, EPA had classified 1,569 sites as NPL sites. Cleanup efforts at NPL sites are typically expensive and can take many years. There are two basic types of cleanup actions: (1) removal actions--generally short-term or emergency cleanups to mitigate threats--and (2) remedial actions--generally long-term cleanup activities. Among other efforts, EPA may respond to and provide technical support for emergency actions, collect and analyze site data, and design and construct remedies, or oversee the work of others. However, the parties responsible for contributing to the contamination of a hazardous waste site are also primarily responsible for conducting or paying for the cleanup of the site. Responsible parties include current or former owners or operators of a site or the generators and transporters of the hazardous substances. CERCLA authorizes EPA to compel the responsible parties to clean up contaminated sites and also allows EPA to conduct cleanups and then seek reimbursement from the responsible parties. One of EPA's goals is ensuring that, to the extent possible, parties who are responsible for the contamination perform or pay for cleanup actions. In some cases, however, parties cannot be identified or may be unwilling or financially unable to perform the cleanup; we previously found that the number of NPL sites without viable responsible parties may be increasing. In these cases, EPA can assume responsibility for site cleanup and seek reimbursement from any responsible parties that can be identified. The states may also play a significant role in cleaning up hazardous waste sites. Most states have established programs to help address hazardous waste sites, although many states have limited capacity to address costly and complex sites. To fund program activities, CERCLA established a trust fund that was financed primarily by taxes on crude oil and certain chemicals, as well as an environmental tax assessed on corporations based upon their taxable income. Although the authority for these taxes expired in 1995, some tax revenues have continued to accrue to the fund as audits of past years' tax returns have led to the recovery of Superfund taxes previously owed by companies. In addition, the trust fund continued to receive revenue--also referred to as receipts--from various other sources, including appropriations from the general fund. EPA receives annual appropriations from the trust fund for program activities; since 1981, Superfund appropriations have totaled over $32 billion in nominal dollars, or about $1.2 billion annually. CERCLA authorizes EPA to use its Superfund appropriation to conduct cleanup actions, and the agency's Office of Solid Waste and Emergency Response (OSWER) is accountable for achieving Superfund's cleanup goals. In this context, Congress asked us to examine the (1) sources of funding for the Superfund trust fund and (2) allocation of these resources to Superfund program activities, particularly enforcement and administration.