This report provides information concerning EPA's Maximum Achievable Control Technology standards for boilers (the Boiler MACT), an EPA rule designed to reduce emissions of hazardous air pollutants, and three related rules. The related rules set standards for small boilers ("area sources") and boilers that use solid waste as fuel ("commercial and industrial solid waste incinerators"), and they identify what materials EPA considers to be solid waste. Because boilers are used as power sources throughout industry, and for power or heat by large commercial establishments and institutions, there has been widespread interest in the requirements of all four of these rules and their potential effects. On December 20, 2012, EPA finalized changes to the four rules, revising the standards that it had promulgated March 21, 2011. Owners and operators of affected boilers will have until 2016 to install equipment necessary to meet the new emission standards, with the possibility of an additional year if it is necessary. Under the March 2011 rules, major source boilers subject to the MACT rule would have faced a May 2014 deadline for compliance. On May 16, 2011, however, EPA announced that it was staying the effective dates of the Boiler MACT and one of the related rules, in order to take additional public comment and reconsider what it had promulgated, leaving in doubt both the final form of the rules and when the standards might go into effect. The federal District Court for the District of Columbia vacated the agency's stay on January 9, 2012, but the court's action had little effect, as EPA subsequently issued a "No Action Assurance Letter." The letter stated that the agency would exercise its enforcement discretion to not enforce certain notification deadlines in the March 2011 rule. The agency also proposed, in its reconsideration of the rules, to extend the effective date (and hence the required compliance date) of the Boiler MACT until three years after completion of the rules' reconsideration. In December 2012, the agency finalized that decision. Thus, when the agency publishes the reconsidered rules in the Federal Register , it will have added about two years to the deadline for emissions sources to comply. In addition, the preamble to the reconsidered rule notes that: ... the CAA allows title V permitting authorities to grant sources, on a case-by-case basis, extensions to the compliance time of up to one year if such time is needed for the installation of controls.... Permitting authorities are already familiar with, and in many cases have experience with, applying the 1-year extension authority under section 112(i)(4)(A) since the provision applies to all NESHAP [National Emission Standards for Hazardous Air Pollutants]. We believe that should the range of circumstances that commenters have cited as impeding sources' ability to install controls within three years materialize, then it is reasonable for permitting authorities to take those circumstances into consideration when evaluating a source's request for a 1-year extension, and where such applications prove to be well-founded, it is also reasonable for permitting authorities to make the 1-year extension available to applicants. Thus, the agency envisions up to a four-year compliance deadline if sources can demonstrate that extra time is needed for the installation of controls. Given the boiler rules' potential impacts, Congress has taken a strong interest in them. EPA estimates that, as finalized on December 20, 2012, the Boiler MACT will affect about 14,000 boilers and process heaters. In order to reduce emissions of a wide array of hazardous air pollutants, about 12% of the affected units would be required to install pollution control equipment. The 12% include coal-fired, biomass-fired, and liquid-fired boilers. The agency estimates the capital costs associated with the rule for existing boilers at $4.6 billion to meet the compliance deadline in 2016; annualized costs, which spread the costs of capital over the expected life of the equipment and include operating and maintenance costs as well, were estimated at $1.2 billion per year. These cost estimates are less than half the estimated cost of EPA's originally proposed version of the rule, for reasons that we will explore below. As shown in Table 2 , later in this report, most boilers—84% of those affected by the rule—are fueled by natural gas or similar gases such as refinery gas, according to EPA. These gas-powered boilers would incur capital costs averaging a little less than $6,500 per unit, according to the agency. Through fuel savings, the agency expects a reduction in operating costs to more than compensate for the capital expenditures of most gas-powered units. EPA has developed regulations addressing boiler emissions because it has found, based on emissions data, that they are major sources of hazardous air pollutants (HAPs). Section 112 of the Clean Air Act, which requires controls on major sources of HAPs, defines a major source as any facility that emits 10 tons or more of a single listed HAP or 25 tons of any combination of HAPs annually. The HAPs themselves (187 substances) were listed by Congress in the 1990 Clean Air Act Amendments. Boilers emit at least 20 of the listed HAPs, including mercury, arsenic, chromium, cadmium, selenium, nickel, lead, manganese, phosphorous, antimony, beryllium, polycyclic organic matter, benzene, formaldehyde, acetaldehyde, dioxins, furans, hydrogen chloride, hydrogen cyanide, and hydrogen fluoride. Six of these 20 are classified as known or probable human carcinogens. Others affect the lungs, skin, central nervous system (including adverse developmental effects), and/or kidneys. By controlling boiler emissions, EPA expects to avoid 3,100 to 7,900 premature deaths annually, as well as many other health effects, including 5,000 nonfatal heart attacks annually. The Boiler MACT will replace a rule promulgated on September 13, 2004, and subsequently vacated and remanded to EPA by the D.C. Circuit Court of Appeals. The court vacated that rule in 2007, saying EPA had wrongly excluded many industrial boilers from the definition of solid waste incinerators, which have more stringent emissions requirements under the Clean Air Act. EPA was under a court order to finalize replacement rules by February 21, 2011. Meanwhile, boiler emissions have been subject to state standards, which are generally not as stringent as what EPA has proposed. In early December 2010, the agency petitioned the District Court for the District of Columbia for up to 15 months of additional time to complete the rulemaking. The agency argued that in light of the extensive comments it received on the proposed rules, "EPA believes that the overall public interest is best served by allowing EPA to re-propose the rules so that [it] will be able to issue emission standards that are based upon a thorough consideration of all available data and reduce potential litigation risks." The court had issued a summary judgment against the agency in 2006 for failure to discharge fully its duty to promulgate standards for emissions of hazardous air pollutants. On March 31, 2006, the court imposed a schedule under which EPA was to have discharged all of the statutory duties at issue by June 15, 2009. That deadline was subsequently extended by more than a year and a half. On January 20, 2011, the court denied EPA's request for a further 15-month extension, concluding that EPA had engaged in discretionary delay in the face of a congressional directive (i.e., the 1990 Clean Air Act Amendments, under which the rules were to have been promulgated by November 2000); the court gave the agency one month to issue final rules. Having been denied the extension it sought, the agency issued a statement saying, "The standards will be significantly different than what EPA proposed…. The agency believes these changes still deserve further public review and comment and expects to solicit further comment through a reconsideration of the rules." True to its word, the agency issued a Notice of Reconsideration at the same time that it promulgated the final rule in March 2011. The notice listed 14 provisions for which the agency thought additional opportunity for public review and comment should be obtained, and it stated that the agency might seek public comment on other aspects of the rules. The 14 provisions included such basic elements as the subcategories used to set standards in the boiler rule, the emission standards themselves, and the monitoring requirements. This left numerous questions concerning not only the substance of the rule, but the schedule for implementation. Following promulgation, existing facilities would normally have three years to comply with the standards, but since the agency was reconsidering key aspects of the rules, one was left to wonder how regulated entities should determine what standards they would ultimately be required to comply with, and on what schedule. By staying the effective date of the standards on May 16, 2011, the agency addressed this uncertainty, effectively giving itself and regulated entities an extension of time that the court had denied them. In the end, the agency added almost two years to its deliberation process before finalizing the reconsidered rules in December 2012. In order to understand the standards that EPA finalized in December 2012 and the controversy surrounding them, it helps to begin with the agency's June 4, 2010, proposal (which we refer to, generally, in this report as the standards EPA "originally" proposed). In that proposal, EPA divided boilers into 11 subcategories, with separate emission limits for new and existing units in 9 of the 11. The nine subcategories included three types of coal-fired boilers and four types of biomass-fired boilers. The proposed emission limits covered five substances (or groups of substances): mercury; dioxins/furans; particulate matter (as a surrogate for non-mercury metals); hydrogen chloride (as a surrogate for all acid gases); and carbon monoxide (as a surrogate for non-dioxin organic air toxics, including formaldehyde).