With the enactment of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in 1980, the Congress created the Superfund program to clean up the nation’s most severely contaminated hazardous waste sites. The Congress extended the program in 1986 and 1990 and is now considering another reauthorization. Under CERCLA, EPA investigates contaminated areas and places the most highly contaminated sites on the National Priorities List (NPL) for study and cleanup. As of December 1996, there were 1,210 sites on the NPL. After a site is placed on the NPL, EPA extensively studies and evaluates the site to determine the appropriate cleanup remedy for it. The remedy selected depends upon the site’s characteristics, such as the types and levels of contamination, the risks posed to human health and the environment, and the applicable cleanup standards. The site’s cleanup can be conducted by EPA or the party responsible for the contamination, with oversight by EPA or the state. Through fiscal year 1995, the latest period for which EPA has data, EPA had selected incineration as a Superfund cleanup remedy 43 times, or in about 6 percent of the decisions on remedies it had reached through that date.At the time of our review, three incinerators were operating at Superfund sites—the Bayou Bonfouca site in Louisiana, the Times Beach site in Missouri, and the Baird and McGuire site in Massachusetts. As of October 1996, EPA planned to use incineration at four additional sites. Incineration is the burning of substances by a controlled flame in an enclosed area that is referred to as a kiln. Incineration involves four basic steps: (1) wastes, such as contaminated soil, are prepared and fed into the incinerator; (2) the wastes are burned, converting contamination into residual products in the form of ash and gases; (3) the ash is collected, cooled, and removed from the incinerator; and, (4) the gases are cooled, remaining contaminants are filtered out, and the cleaned gases are released to the atmosphere through the incinerator’s stack. (See fig. 1.) Incinerators may be fixed facilities that accept waste from a variety of sources, or they may be transportable or mobile systems. Fixed facility hazardous waste incinerators are required by the Resource Conservation and Recovery Act of 1976 (RCRA) to obtain an operating permit from EPA. RCRA regulates all facets of the generation, transportation, treatment, storage, and disposal of hazardous wastes in the United States. RCRA requires that fixed facility hazardous waste incinerators be operated according to EPA’s regulations and be inspected by EPA every 2 years. Incinerators used to clean Superfund sites are generally “transportable,” that is, they are transported to the site in pieces, assembled, and removed when the cleanup is complete. These incinerators are constructed and operated by contractors. CERCLA exempts any portion of a cleanup action conducted entirely on-site, including incineration, from the need to obtain any permit. However, CERCLA requires EPA to apply legally applicable or relevant and appropriate environmental standards from other federal laws, including RCRA, to Superfund cleanups. Accordingly, EPA requires incinerators at Superfund sites to meet RCRA’s substantive requirements, such as the act’s standards for emissions. EPA relies on four principal methods to ensure the safe operation of incinerators used to clean up Superfund sites. These methods are (1) setting site-specific standards for emissions and operations, (2) incorporating safety features into an incinerator’s emergency systems, (3) monitoring emissions at the incinerator’s stack and along the site’s perimeter, and (4) providing 24-hour on-site oversight. (See app. I for more details on the safeguards at the three incinerators in operation at the time of our review.) EPA establishes specific cleanup standards for each incinerator used at a Superfund site. These standards are based on studies of the site’s characteristics (e.g., the type and concentration of contamination present) conducted during the incinerator’s design and construction. Standards can be adopted from other environmental programs or laws, such as RCRA or the Toxic Substances Control Act. Typically, RCRA’s standards for fixed facility hazardous waste incinerators are applied. RCRA’s standards govern the extent to which an incinerator must destroy and remove contaminants and set limits on emissions from the incinerator. EPA establishes the operating parameters needed for the incinerator to achieve the emissions standards and tests the parameters through a “trial burn” required under RCRA. The operating parameters can include the temperature of the kiln, the minimum oxygen levels needed to break down contaminants in the kiln, and the maximum carbon monoxide levels that may be produced. Although not required by EPA’s regulations, a trial burn plan was reviewed by a RCRA expert at all the sites we visited to determine whether the proper operating conditions were being tested. According to EPA officials, if the incinerator operates within the parameters established at the trial burn, the incinerator will be operating safely. Besides establishing standards for emissions and operations, EPA requires engineering controls to prevent the standards from being exceeded. In addition, incinerators at the three sites we visited had built-in safety features unique to each model to prevent excessive emissions of contaminants in the event of an emergency shutdown. RCRA’s regulations, which EPA applies at Superfund sites, require that incinerators have devices, called automatic waste feed cutoffs, that will stop contaminated waste from being fed into an incinerator when the operating conditions deviate from the required operating parameters. The waste feed would be cut off, for example, when a change in pressure or a drop in temperature occurred that could compromise the kiln’s effective incineration of the contaminants. These cutoffs are set with a “cushion” so that the waste feed shuts down before the incinerator operates outside the established parameters. The number and type of waste feed cutoffs will depend on the requirements for each site. According to EPA officials, some cutoffs are routine, to be expected during the normal course of an incinerator’s operations, and a sign that the safety mechanisms are working properly. For example, cutoffs can be triggered by expected changes in pressure within the kiln brought on by variations in the waste input stream. However, other cutoffs, especially repeated cutoffs, can be signs of problems. At the three sites we visited, all of the incinerators had some additional safety measures, not required by regulation, in the event that a critical part of the incinerator failed. At the Times Beach and the Bayou Bonfouca sites, the incinerators have emergency systems that fully shut down the incinerator and decontaminate the gases remaining in the system at the time of the shutdown. These systems seal off the gases and expose them to a high-temperature flame to destroy any residual contamination. At the Baird and McGuire site, the emergency system ensures that metals and particulates are removed before gases are emitted from the kiln. The most common reason for activating the emergency systems at the three sites was a shutdown caused by a power outage. EPA continuously monitors the air in the vicinity of an incinerator to ensure that emissions from the stack and from areas where soil is being excavated before being put into the incinerator do not exceed the maximum permitted levels. Air monitoring at the sites involves measuring conditions in real time and performing detailed laboratory analyses of samples that are collected over a longer period of time. For example, at the Baird and McGuire site, stack emissions are monitored continuously to measure key indicators of combustion, such as the oxygen levels in exhaust gases, to ensure that the incinerator is operating properly. For organic contamination, a more detailed laboratory analysis is carried out during the trial burn to provide additional assurance that dioxin, a cancer-causing substance produced by the burning of organic substances, is not excessively emitted. The Baird and McGuire site also has nine air monitors at its perimeter, each of which is hooked up to alarms that sound if emission levels approach the established parameters. These monitors, which are intended primarily to detect possible emissions from the on-site excavation of contaminated soil, monitor and record data every minute. According to the incineration contractor’s project manager at the Baird and McGuire site, the air monitors picked up elevated levels only once during an excavation, when a drum of chemicals was removed. In a situation such as this, the excavation is slowed to bring emissions down to required levels. According to EPA’s reports for the three sites we visited, emissions from the incinerators’ stacks never exceeded the permitted levels. Although 24-hour oversight is not required by regulations or formal EPA policy, Corps of Engineers or state officials continuously observed the operations of the incinerator at each of the sites we visited. For the two cleanups that EPA managed (at the Baird and McGuire and Bayou Bonfouca sites), EPA had contracted with the U.S. Army Corps of Engineers for on-site oversight, while at Times Beach, where a responsible party was conducting the cleanup, a Missouri state agency provided oversight. At the time of our visit, these sites had staff to cover operations 24 hours a day. For example, at Baird and McGuire, 12 Corps of Engineers staff were assigned to monitor the incinerator’s operations. On-site observation involves visual inspections and record reviews to ensure that the incineration companies are meeting the operating conditions specified by EPA.