Mercury is a naturally occurring toxic metallic substance that exists as a liquid or vapor in its elemental form and can be a solid or liquid in its compound form. Elemental mercury is used in producing chlorine liquid and caustic soda, in extracting gold from ore or materials that contain gold, and in thermometers, barometers, and electrical switches. Silver-colored dental fillings (known as dental amalgam) typically contain about 50 percent metallic mercury. Mercury forms inorganic compounds when combined with elements such as chlorine, sulfur, or oxygen. Inorganic mercury compounds are used in fungicides, skin-lightening creams, topical antiseptic or disinfectant agents, antibacterials, preservatives in some prescription and over-the-counter medicines, coloring paints, and tattoo dyes. In combination with carbon, mercury forms organic compounds, the most common of which is methylmercury, which can build up in certain edible freshwater and saltwater fish and marine mammals. In recent years, mercury use has declined as the availability of nonmercury-based materials has been developed. For example, the large lamps that light parking lots used to be made with mercury, but are increasingly being made without it. Also, the Mercury-Containing and Rechargeable Battery Management Act of 1996 severely restricted the mercury content in batteries sold after the act’s enactment date of May 13, 1996. Today, the predominant uses of mercury are for the production of chlorine-related products, the amalgam used in dental fillings, and wiring devices that carry electrical current. As figure 1 shows, mercury use in the United States generally declined between 1980 and 1997, according to the U.S. Geological Survey, which compiled those data until 1997. Debris contaminated with mercury can come from various sources—often from a cleanup effort (such as a mercury spill) or demolition of a mercury-contaminated building (such as a laboratory). It can also include structural steel, glass, wooden pallets, cloth, and ruptured containers and devices. When debris contains hazardous amounts of mercury or other hazardous wastes, the hazardous waste debris must be treated to address each of the hazardous wastes. The debris definition excludes the following materials: any material for which a specific treatment standard is provided in 40 C.F.R. Part 268, Subpart D (namely lead acid batteries, cadmium batteries, and radioactive lead solids); process residuals such as smelter slag and residues from the treatment of waste, wastewater, sludges, or air emission residues; and intact containers of hazardous waste that are not ruptured and that retain at least 75 percent of their original volume. A mixture of debris and other material (such as soil or sludge) is subject to the hazardous waste debris regulations if the mixture is comprised primarily of debris, by volume, based on visual inspection. Figure 2 provides a general description of categories of waste that EPA typically classifies as debris and that could be contaminated with mercury. Mercury-contaminated debris (such as bricks, pipes, ruptured metal drums, or large chunks of concrete) may either be treated according to (a) the mercury-specific standards described above (primarily including retorting for high-mercury containing waste), or (b) encapsulated or stabilized, regardless of the mercury concentration level. If managed using the mercury-specific standards, the waste or residue from the retorting process must have their toxicity reduced to specified numerical levels before it can be land disposed. Waste managed according to the alternative treatment standards for hazardous debris does not generally have to be tested before it is land disposed because, according to EPA, obtaining a representative sample is often impractical. In addition, the leach test, which requires grinding as part of the test procedure, may not be appropriate for certain debris treatment technologies, such as encapsulation, since the grinding step would defeat the protective mechanism of the treatment technology. According to EPA officials, the agency encourages businesses that generate mercury-contaminated debris to remove the mercury contaminated material from the debris—a process referred to as source separation. Also, according to EPA and industry, there are some debris items (such as debris contaminated with mixtures of mercury and organic chemicals) that remain difficult to retort; as such, the debris regulations are needed to ensure that such debris is treated and disposed of properly. Table 1 summarizes EPA’s debris regulations and definitions of debris. In 1999, EPA issued an advance notice of proposed rulemaking to conduct a comprehensive review of the RCRA hazardous waste treatment regulations for mercury-containing wastes. EPA had identified mercury as one of the more persistent toxic chemicals regulated under RCRA. EPA stated that potential revisions, if any, would be based on the comments that it received and data obtained from ongoing studies and other sources. Among other issues, EPA requested comments on whether to (1) allow alternative treatment options to retorting for high mercury-containing waste and (2) require retorting for high mercury-containing waste that meets the definition of debris. With respect to allowing alternative treatment options to retorting for high mercury-containing waste, EPA made available data to the public in 2003 on two studies that assessed the feasibility of land disposal for elemental mercury and for difficult-to-treat high mercury-containing waste that had been treated by stabilization. From these studies, EPA concluded that treatment by stabilization may not result in a waste that is stable under some hazardous waste landfill conditions. According to EPA officials, the agency was concerned about using stabilization for elemental mercury in certain landfill conditions where leaching was more likely to occur. EPA did not change the existing hazardous waste regulations for mercury-containing waste. With respect to requiring that high mercury-containing waste that meets the definition of debris be retorted, all of the comments that EPA received, except one, expressed the view that EPA should not modify the alternative treatment standards for debris to require the retorting of debris with high concentration levels of mercury because debris is not always amenable to retorting and because the alternative treatment standards for debris provide needed flexibility to manage difficult-to-treat wastes. EPA did not modify the debris regulations. In 2003, EPA collaborated with the Association of State and Territorial Solid Waste Management Officials and the Northeast Waste Management Officials’ Association to discuss potential mismanagement of mercury-contaminated debris. Based on those discussions, EPA issued a debris memorandum in October 2003 to state waste managers that provided guidance for managing mercury-contaminated debris. In that guidance memorandum, EPA sought to clarify the types of waste that are eligible for treatment under the alternative treatment standards for debris, provide information on the improved capabilities of mercury “retorters” to accept and recover mercury from debris-like waste, and describe how to meet the performance standards for several debris treatment technologies. In a May 2004 follow-up letter, the Administrator of EPA stated that EPA had not found any evidence that there is a significant environmental problem associated with the management of mercury-contaminated debris under EPA’s current rules. Figure 3 shows that mercury-containing waste comes from industrial and nonindustrial sources. EPA requires the collection of data on hazardous waste activities from industrial sources, but not from nonindustrial sources. Nonindustrial sources generate mercury-containing waste, such as household thermometers and dental amalgam, which may, if not recycled, be generally disposed of in municipal solid waste landfills. Under RCRA, hazardous waste landfills and businesses that retort mercury-contaminated debris must meet federal standards designed to protect public health and the environment. Among other standards, hazardous waste landfills must meet minimum technological requirements, including double composite liners, a leachate collection and removal system, and a leak detection system, as well as provide for groundwater monitoring. In addition, hazardous waste landfills may not operate without a RCRA permit. Landfills must also meet other more stringent state requirements, if any, which often include on-site state inspectors and additional groundwater monitoring wells. According to EPA’s RCRAInfo data, there are 19 commercial hazardous waste landfills in the United States, most of which accept mercury-containing waste. Facilities that retort mercury-contaminated debris may only retort wastes below specified organic concentration limits or above specified heating values. In addition, the facilities must comply with waste sampling and analysis requirements. As of 2005, four companies reported that they operate seven facilities that retort mercury-contaminated debris. Figure 4 show the locations of the 19 commercial hazardous waste landfills and seven retorting facilities in the United States. Every 2 years, EPA compiles and summarizes data on the amount of hazardous waste generated, treated, and disposed of. For this biennial report, EPA requires businesses to submit information to the states on each waste generated, treated, and/or disposed of. Among other things, businesses report on the type of hazardous constituent(s) present in the waste, the process (such as chlorine production) or activity (such as demolition) that generated the hazardous waste, and the treatment or disposal method used in managing the hazardous waste. EPA also requests, but does not require, that businesses submit certain additional information about the waste, including the portion of the waste that is debris. EPA maintains the data in its RCRAInfo database. The states conduct data reliability assessments (such as checking for missing values, out-of-range values in each field, and inconsistencies and errors in the data) before entering the information into RCRAInfo; EPA also conducts data reliability assessments of RCRAInfo data. EPA uses its RCRAInfo database, which began in 1999, to maintain data on hazardous waste submitted by states. According to EPA officials, RCRAInfo was designed specifically to track national trends of hazardous waste generation, treatment, and disposal. In 1991, EPA began producing its biennial reports, and it began collecting data on debris as a separate category of physical form in 2001. EPA’s most recent biennial hazardous waste report, for the 2003 reporting cycle, was released in April 2005.