# United States Sugar Corp. v. Environmental Protection Agency > Court of Appeals for the D.C. Circuit · July 29, 2016 · 830 F.3d 579 URL: https://www.frixlaw.com/law-library/cases/4020089 ## Case - **Full name:** UNITED STATES SUGAR CORPORATION, Petitioner v. ENVIRONMENTAL PROTECTION AGENCY, Respondent American Chemistry Council, Et Al., Intervenors; American Forest & Paper Association, Et Al., Petitioners v. Environmental Protection Agency, Respondent American Chemistry Council, Et Al., Intervenors; American Chemistry Council, Petitioner v. Environmental Protection Agency, Respondent American Forest & Paper Association, Et Al., Intervenors - **Court:** Court of Appeals for the D.C. Circuit - **Decided:** July 29, 2016 - **Citations:** 830 F.3d 579; 424 U.S. App. D.C. 319 - **Precedential status:** Published - **Opinion:** Opinion - **Judges:** Henderson, Brown, Griffith - **Cited by:** 62 later opinions in the Frix Law Library ## Citator (automated) - No negative treatment found by the automated citator. That is not the same as a confirmation that the case is good law; read the citing cases. - Full citator and citing cases: https://www.frixlaw.com/law-library/cases/4020089 ## How later opinions describe it (automated extraction) - finding that the EPA provided a reasoned explanation for disregarding its prior factual findings because it explained that its prior findings were limited due to the fact that little research had been on the subject at the time and that the agency lacked data - describing major sources as “‘any stationary source or group of stationary sources’ that neighbor each other, share common control, and emit (or have the potential to emit) either ten tons per year or more of any single HAP or twenty-five tons per year or more of any HAP combi… - explaining that an agency's determination is arbitrary and capricious if its decision runs counter to the evidence before the agency - rejecting a proposed interpretation that would complicate EPA’s attempts to control pollutants and noting that “[n]othing in the CAA suggests that the Congress intended to so hamstring the Agency” ## Opinion text United States Court of Appeals FOR THE DISTRICT OF COLUMBIA CIRCUIT Argued December 3, 2015 Decided July 29, 2016 No. 11-1108 UNITED STATES SUGAR CORPORATION, PETITIONER v. ENVIRONMENTAL PROTECTION AGENCY, RESPONDENT AMERICAN CHEMISTRY COUNCIL, ET AL., INTERVENORS Consolidated with 11-1124, 11-1134, 11-1142, 11-1145, 11-1159, 11-1165, 11-1172, 11-1174, 11-1181, 13-1086, 13-1087, 13-1091, 13-1092, 13-1096, 13-1097, 13-1098, 13-1099, 13-1100, 13-1103 On Petitions for Review of Final Action of the United States Environmental Protection Agency William L. Wehrum Jr., David M. Friedland, and Douglas A. McWilliams argued the causes for Industry Petitioners. With them on the briefs were Allen A. Kacenjar, Katy M. Franz, Lisa Marie Jaeger, Sandra Y. Snyder, Peter H. Wyckoff, Claudia M. O=Brien, Stacey L. VanBelleghem, Eli Hopson, Jane C. Luxton, Lauren E. Freeman, Elizabeth L. Horner, William F. Lane, Alan H. McConnell, Timothy S. Bishop, Kevin G. Desharnais, Chad M. Clamage, Ronald A. Shipley, Quentin Riegel, Linda E. Kelly, and Jeffrey A. Knight. Rachel Brand, Leslie A. Hulse, Harry M. Ng, Scott J. Stone, John P. Wagner, and Lee B. Zeugin entered appearances. James S. Pew and Sanjay Narayan were on the briefs for Environmental Petitioners. Neil Gormley entered an appearance. Perry M. Rosen and Norman L. Rave, Jr., Attorneys, U.S. Department of Justice, argued the causes for respondent. With them on the brief was John C. Cruden, Assistant Attorney General, and Norman L. Rave, Jr., Attorney. Sam Hirsch and Madeline P. Fleisher, Attorneys, entered appearances. James S. Pew and Neil Gormley argued the causes for Environmental Respondent-Intervenors. With them on the briefs was Sanjay Narayan. William L. Wehrum, Quentin Riegel, Linda E. Kelly, Patrick Forrest, Douglas A. McWilliams, Peter H. Wyckoff, Jeffrey A. Knight, Claudia M. O=Brien, Stacey L. VanBelleghem, Lisa Marie Jaeger, Sandra Y. Snyder, David M. Friedland, William F. Lane, Alan H. McConnell, Ronald A. Shipley, Carol F. McCabe, Suzanne Ilene Schiller, Michael Dillon, Charles Howland Knauss, Shannon S. Broome, Timothy S. Bishop, Kevin G. Desharnais, Chad M. Clamage, Lauren E. Freeman, Elizabeth L. Horner, Larry B. Alexander, and Leslie A. Hulse were on the brief for Industry Intervenor- Respondents. Allen A. Kacenjar Jr., Rachel L. Brand, Harry M. Ng, Scott J. Stone, John P. Wagner, and Lee B. Zeugin entered appearances. No. 11-1125 AMERICAN FOREST & PAPER ASSOCIATION, ET AL., PETITIONERS v. ENVIRONMENTAL PROTECTION AGENCY, RESPONDENT AMERICAN CHEMISTRY COUNCIL, ET AL., INTERVENORS Consolidated with 11-1140, 11-1144, 11-1154, 11-1155, 11-1161, 11-1171, 11-1173, 11-1180, 11-1183, 11-1188, 13-1111, 13-1113, 13-1114, 13-1116, 13-1118, 13-1119, 13-1120, 13-1121, 13-1123, 13-1124, 13-1127 On Petitions for Review of a Final Action of the United States Environmental Protection Agency William L. Wehrum, Douglas A. McWilliams, and Jason T. Morgan argued the causes for Industry Petitioners. On the briefs were Richard G. Stoll, Leslie A. Hulse, Lisa Marie Jaeger, Sandra Y. Snyder, Peter H. Wyckoff, Jeffrey A. Knight, David M. Friedland, Jessalee Landfried, Michael B. Wigmore, Ronald A. Shipley, Chet M. Thompson, Linda E. Kelly, Quentin Riegel, William F. Lane, Alan H. McConnell, Carol F. McCabe, Suzanne Ilene Schiller, and Michael Dillon. David Y. Chung, Rachel L. Brand, Julia L. German, Jeffrey W. Leppo, and Jane C. Luxton entered appearances. Neil Gormley and James S. Pew argued the causes and filed the briefs for Environmental Petitioners. Perry M. Rosen and Norman L. Rave, Jr., Attorneys, U.S. Department of Justice, argued the causes for respondent. With them on the brief was John C. Cruden, Assistant Attorney General. Madeline P. Fleisher, Attorney, entered an appearance. James S. Pew and Neil Gormley argued the causes and filed the briefs for Environmental Respondent-Intervenors. David M. Friedland and William L. Wehrum argued the causes for Industry Intervenor-Respondents. With them on the briefs were Jessalee Landfried, Leslie A. Hulse, Richard G. Stoll, Ronald A. Shipley, William F. Lane, Alan H. McConnell, James T. Morgan, Lisa Marie Jaeger, Sandra Y. Snyder, Jeffrey A. Knight, Shannon S. Broome, Carol McCabe, Suzanne Ilene Schiller, Michael Dillon, Linda E. Kelly, Quentin Riegel, and Charles H. Knauss. Scott J. Stone, Lori A. Rubin, and Jeffrey W. Leppo entered appearances. No. 11-1141 AMERICAN CHEMISTRY COUNCIL, PETITIONER v. ENVIRONMENTAL PROTECTION AGENCY, RESPONDENT AMERICAN FOREST & PAPER ASSOCIATION, ET AL., INTERVENORS Consolidated with 11-1182, 11-1207, 11-1208, 13-1105, 13-1107 On Petitions for Review of a Final Action of the United States Environmental Protection Agency William L. Wehrum and David M. Friedland argued the causes for Industry Petitioners. On the briefs were Lisa Marie Jaeger, Sandra Y. Snyder, Jeffrey A. Knight, Quentin Riegel, and Leslie A. Hulse. Harry M. Ng, Scott J. Stone, and John P. Wagner entered appearances. Neil Gormley argued the cause for Environmental Petitioners. With him on the briefs was James S. Pew. Perry M. Rosen and Norman L. Rave, Jr., Attorneys, U.S. Department of Justice, argued the causes for respondent. With them on the brief was John C. Cruden, Assistant Attorney General. Madeline P. Fleisher, Attorney, entered an appearance. David M. Friedland and William L. Wehrum argued the causes for Industry Intervenor-Respondents. With them on the briefs were Lisa Marie Jaeger, Sandra Y. Snyder, Jeffrey A. Knight, William F. Pedersen, Pamela A. Lacey, William F. Lane, Linda E. Kelly, Quentin Riegel, James W. Conrad, Jr., and Leslie A. Hulse. Harry M. Ng, Scott J. Stone, John P. Wagner, and Nidhi J. Thakar entered appearances. James S. Pew and Neil Gormley were on the brief for Environmental Respondent-Intervenors. Before: HENDERSON, BROWN, and GRIFFITH, Circuit Judges. PER CURIAM: In these consolidated petitions for review, we address approximately thirty challenges to three regulations promulgated by the United States Environmental Protection Agency (EPA or Agency): (1) the “Major Boilers Rule,”1 (2) the “Area Boilers Rule,”2 and (3) the “Commercial/Industrial Solid Waste Incinerators (CISWI) Rule.”3 Collectively, these rules—all promulgated under the Clean Air Act (CAA or Act), 42 U.S.C. §§ 7401 et seq.—set emissions limits on certain combustion machinery known to release hazardous air pollutants (HAPs). Roughly one-half of 1 National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers and Process Heaters (2011 Major Boilers Rule), 76 Fed. Reg. 15,608 (Mar. 21, 2011), as amended, National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers and Process Heaters (2013 Major Boilers Rule), 78 Fed. Reg. 7,138 (Jan. 31, 2013). 2 National Emission Standards for Hazardous Air Pollutants for Area Sources: Industrial, Commercial, and Institutional Boilers (2011 Area Boilers Rule), 76 Fed. Reg. 15,554 (Mar. 21, 2011), as amended, National Emission Standards for Hazardous Air Pollutants for Area Sources: Industrial, Commercial, and Institutional Boilers (2013 Area Boilers Rule), 78 Fed. Reg. 7,488 (Feb. 1, 2013). 3 Standards of Performance for New Stationary Sources and Emission Guidelines for Existing Sources: Commercial and Industrial Solid Waste Incinerator Units (2011 CISWI Rule), 76 Fed. Reg. 15,704 (Mar. 21, 2011), as amended, Commercial and Industrial Solid Waste Incineration Units: Reconsideration and Final Amendments; Non-Hazardous Secondary Materials that Are Solid Waste (2013 CISWI Rule), 78 Fed. Reg. 9,112 (Feb. 7, 2013). 2 the challenges are advanced by a group of municipal-electric organizations, industrial-trade associations, oil-and-gas industry representatives, and other entities that own and operate boilers, process heaters, and incinerators (Industry Petitioners). The other one-half are pressed by organizations interested in safeguarding the environment (Environmental Petitioners). I. BACKGROUND The three rules at issue address a common phenomenon: when combustion occurs, emissions result. The emissions include numerous materials, some of which pose risks to the environment in general and to human health in particular. Because combustion is an inevitable occurrence in the machinery that helps to power modern society, the Congress has authorized the EPA to provide for a regulatory framework that minimizes the deleterious effects of the incineration industry while simultaneously allowing it to operate. In 2013, the EPA finalized its efforts to do so for discrete types of combustion machinery: boilers, process heaters, and incinerators. Two of the three rules at issue—the Major Boilers Rule and the Area Boilers Rule—govern boilers and process heaters. The former are enclosed devices that use a controlled flame to heat water and convert it into steam or hot water. 40 C.F.R. § 63.11237. The latter are also enclosed devices that use a controlled flame but, instead of generating steam, they indirectly heat a “process material,” whether liquid, gas, or solid, or a “heat transfer material” like glycol or a mixture of glycol and water. Id. For simplicity, our use of “boilers” covers both machinery types. The two boiler-specific rules further divide the machinery into three categories: industrial, commercial, and 3 institutional. See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,557. Industrial boilers are used for manufacturing, processing, mining, refining, and other similar operations. See id. Commercial boilers are used by shopping malls, laundromats, apartment complexes, restaurants, and hotels. See id. And institutional boilers include those used by, e.g., medical centers, schools, churches, prisons, and courthouses. See id. Collectively, over 200,000 boilers at over 100,000 separate facilities must comply with the standards set out in the Major Boilers Rule or the Area Boilers Rule. The third rule that we address—the CISWI Rule— governs combustion machinery known as “solid waste incineration unit[s].” 42 U.S.C. § 7429. The Act defines an incinerator as a “distinct operating unit of any facility” that burns solid waste from either commercial establishments, industrial establishments, or the general public. Id. § 7429(g)(1). An incinerator subjects “waste material” to “high temperatures until it is reduced to ash.” Incinerator, NEW OXFORD AMERICAN DICTIONARY 853 (2d ed. 2005). Incinerators fall into different subcategories and, in the past, the EPA has issued rules governing many of them, including, e.g., municipal solid-waste incinerators, medical-waste incinerators, and sewage-sludge incinerators.4 At issue in the CISWI Rule are incinerators located in commercial or industrial facilities that combust solid waste as defined in the Resource Conservation Recovery Act (RCRA), 42 U.S.C. §§ 6901 et seq. See 2011 CISWI Rule, 76 Fed. Reg. at 15,706. 4 See, e.g., 40 C.F.R. pt. 60, subpts. Cd, Ce, Eb, AAAA, BBBB, EEEE, FFFF, LLLL, MMMM. 4 A. THE CLEAN AIR ACT, 42 U.S.C. §§ 7401 ET SEQ. Enacted “to protect and enhance the quality of the Nation’s air resources so as to promote the public health and welfare and the productive capacity of its population,” 42 U.S.C. § 7401(b)(1), the Act has been amended several times since the Congress first attempted to control air pollution via legislation in 1963. In 1970, the Congress required the EPA to identify and publish a list of HAPs, which the CAA defined as substances that increase “mortality,” “serious irreversible” illness, or “incapacitating reversible” illness. Clean Air Amendments of 1970, Pub. L. No. 91-604, § 4(a), 84 Stat. 1676, 1685 (1970). The EPA had to set emission limits for every HAP based on the risk it posed to human health. See Sierra Club v. EPA (Sierra Club I), 353 F.3d 976, 979 (D.C. Cir. 2004). In other words, the EPA was to “consider[] levels of HAPs at which health effects are observed, factor[] in an ample margin of safety to protect the public health, and set emission restrictions accordingly.” Id. (quotation marks omitted). The risk-focused approach to capping HAP emissions left something to be desired. “In light of unrealistic time frames and scientific uncertain[t]y over which substances posed a threat to public health,” the EPA “only listed eight pollutants as hazardous between 1970 and 1990,” Nat. Res. Def. Council v. EPA (NRDC II), 529 F.3d 1077, 1079 (D.C. Cir. 2008), and set “emission standards for [only] seven of them,” Sierra Club I, 353 F.3d at 979; see also S. REP. NO. 101-228, at 3 (1989) (“Very little has been done since the passage of the 1970 Act to identify and control hazardous air pollutants.”). After twenty years of the risk-based approach, the Congress went back to the drawing board and, via the 1990 CAA Amendments, Pub. L. No. 101-549, 104 Stat. 2399 (1990), 5 established the technology-based approach that governs today. See Sierra Club I, 353 F.3d at 979. 1. 42 U.S.C. § 7412—“Hazardous Air Pollutants” The 1990 CAA Amendments overhauled the Act’s “Hazardous Air Pollutants” provision, codified at 42 U.S.C. § 7412. Although earlier iterations of the Act had assigned HAPs-identification responsibility to the EPA, the slow pace at which the EPA discharged its duty prompted the Congress to create a list of pollutants itself.5 See Sierra Club I, 353 F.3d at 979-80 (citing 42 U.S.C. § 7412(b)). After identifying nearly two hundred HAPs that warranted emissions restrictions, see 42 U.S.C. § 7412(b)(1), the Congress directed the EPA, first, to identify the sources of each HAP, see id. § 7412(c). The Agency then was to set emissions limits for each source that result in HAPs reduction to the greatest extent achievable by current technology. See generally Nat’l Ass’n for Surface Finishing v. EPA, 795 F.3d 1, 4 (D.C. Cir. 2015) (citing 42 U.S.C. § 7412(b)(1), (c), (d)). a. Identifying and Categorizing HAP Sources The EPA’s first task is to create HAP-source categories and subcategories. See 42 U.S.C. § 7412(c). The Act distinguishes “major” from “area” sources, defining the former as “any stationary source or group of stationary sources” that neighbor each other, share common control, and emit (or have the potential to emit) either ten tons per year or more of any single HAP or twenty-five tons per year or more 5 The EPA must keep the HAPs list current. See 42 U.S.C. § 7412(b)(2), (3). 6 of any HAP combination.6 Id. § 7412(a)(1). The latter are sources that do not emit enough HAPs to qualify as “major.” Id. § 7412(a)(2). Although the EPA must set stringent restrictions on major sources, it has discretion to set more lenient emissions caps on area sources. See id. § 7412(d)(5). Apart from the statutory distinction between major and area sources, the EPA has discretion to differentiate “among classes, types, and sizes of sources within a category or subcategory.” Id. § 7412(d)(1). Once the EPA finalizes HAPs-source categories and subcategories, the CAA mandates that it draw one final dividing line—between “new” sources and “existing” sources. See id. § 7412(d)(3). “New” sources are those “on which construction begins after EPA publishes emission standards,” Cement Kiln Recycling Coal. v. EPA, 255 F.3d 855, 858 (D.C. Cir. 2001); most of the others are “existing” sources, see 42 U.S.C. § 7412(a)(10). But if an existing source experiences either a physical change or a change in operation method and the change increases HAP emissions by more than a de minimis amount, the Act mandates that the source meet the standards set for new sources. See id. § 7412(a)(5), (g). b. Setting Emission Standards for Major Sources—the “MACT” Standard After the EPA identifies HAP-source categories and subcategories, it then sets emissions limits for each. See id. § 7412(d)(2). “[W]henever . . . feasible,” the caps must use numeric HAPs limits. Id. § 7412(h)(4). The size of the 6 The CAA defines “stationary source” as “any building, structure, facility, or installation which emits or may emit any air pollutant.” 42 U.S.C. § 7411(a)(3). 7 source—either “major” or “area”—dictates whether the EPA must set the numeric limit at the most stringent level that current technology allows or at the level set by “generally available control technologies.” Id. § 7412(d)(5). For major sources, the CAA directs the EPA to establish emissions caps that result in the “the maximum degree of reduction in emissions” that the EPA determines is “achievable.” Id. § 7412(d)(2). We refer to an emissions cap that reflects the current “maximum achievable control technology” as a “MACT” standard. See NRDC II, 529 F.3d at 1079. Setting a MACT standard is a two-step process. First, the EPA establishes a “MACT floor” for each category or subcategory. Sierra Club I, 353 F.3d at 980. The MACT floor ensures that all HAPs sources “at least clean up their emissions to the level that their best performing peers have shown can be achieved.” Id. For new sources—those built after promulgation of a HAPs limit, see 42 U.S.C. § 7412(a)(4)—the MACT floor cannot be less stringent than the emissions levels achieved by the best performing similar source. Id. § 7412(d)(3). For existing sources in categories or subcategories that have thirty or more sources, the MACT floor cannot be less stringent than the average emissions limits achieved by the best performing 12 per cent of existing sources in that category or subcategory. Id. § 7412(d)(3)(A). And for existing sources in categories or subcategories with fewer than thirty sources, the MACT floor cannot be less stringent than the average emissions achieved by the best performing five sources. Id. § 7412(d)(3)(B). When setting the MACT floor, the EPA considers only the performance of the cleanest sources in a category or subcategory; it does not take into account other factors, including the cost of putting a source in line with its better-performing counterparts. See Cement Kiln, 255 F.3d at 857-58 (citing Nat’l Lime Ass’n v. 8 EPA, 233 F.3d 625, 629 (D.C. Cir. 2000), as amended on denial of reh’g, No. 99-1325 (D.C. Cir. Feb. 14, 2001)). Second, the EPA must determine whether current technology makes it possible for a source to perform even better than the best performing similar source or sources. In other words, the CAA directs the EPA to consider whether it should set a “beyond-the-floor” MACT standard. Nat’l Lime Ass’n, 233 F.3d at 629. In determining whether a beyond-the- floor standard is “achievable,” the Agency must consider additional factors like “the cost of achieving such emission reduction,” “any non-air quality health and environmental impacts” and “energy requirements.” 42 U.S.C. § 7412(d)(2). It has broad discretion in its determination. See id.; cf. Nat’l Ass’n of Clean Water Agencies v. EPA (NACWA), 734 F.3d 1115, 1157 (D.C. Cir. 2013) (noting, in section 7429 case, that “Congress gave EPA broad discretion in considering whether to go beyond-the-floor”). c. Setting Emission Standards for Area Sources—the “GACT” Standard Although the EPA must cap HAP emissions from major sources at the “maximum degree of reduction,” see 42 U.S.C. § 7412(d)(2), it has discretion to set less stringent caps on emissions from area sources. Indeed, the EPA need not list categories of area sources at all unless: (A) it finds that the sources in that category or subcategory “present[] a threat of adverse effects” to the environment or human health, see id. § 7412(c)(1), (3); or (B) control of a particular area source category or subcategory is necessary to ensure that sources accounting for at least 90 per cent of the aggregate emissions of the thirty HAPs the EPA believes “present the greatest threat to public health in the largest number of urban areas” 9 are subject to CAA control, id. § 7412(c)(3), (k)(3)(B). If it finds that controlling emissions from a particular area source subcategory is necessary to achieve a 90 per cent reduction in the aggregate emissions of any of seven CAA-enumerated HAPs, section 7412(c)(6) requires the Agency to impose MACT caps on that subcategory. See id. § 7412(c)(6). With the exception of section 7412(c)(6)’s MACT- standard requirement, the EPA need not cap emissions from area sources at the MACT level. Instead, it may set more lenient emissions limits based on “generally available control technologies.” Id. § 7412(d)(5). We refer to these caps as GACT standards. The Act provides no guidance for setting GACT standards but the legislative history of the 1990 CAA Amendments describes GACT “as methods, practices and techniques [that] are commercially available and appropriate for application by the sources in the category considering economic impacts and the technical capabilities of the firms to operate and maintain the emissions control systems.” S. REP. NO. 101-228, at 171 (1989). According to the EPA, it can and will consider the following in setting a GACT standard:  “costs and economic impacts . . . , which [are] particularly important when developing regulations for source categories that may have many small businesses . . . ”;  “the control technologies and management practices that are generally available to the area sources in the source category”;  “the standards applicable to major sources in the analogous source category to determine if 10 the control technologies and management practices are transferable and generally available to area sources”; and  “technologies and practices at area and major sources in similar categories to determine whether such technologies and practices could be considered generally available for the area source categories at issue.” 2011 Area Boilers Rule, 76 Fed. Reg. at 15,556. And, unlike the EPA’s duty to consider a beyond-the-floor MACT standard, it need not consider a more stringent GACT standard. d. Work-Practice and Management-Practice Standards Although the CAA requires numeric emission standards where possible, the EPA can “promulgate a design, equipment, work practice, or operational standard, or combination thereof” if it determines that a numeric limit is “not feasible.” 42 U.S.C. § 7412(h)(1). In other words, the EPA can require that all sources in a given category or subcategory take a certain action (e.g., conduct a periodic tune-up) or install certain emissions-control technology (e.g., install a fabric filter). Although the EPA has discretion to impose a work-practice standard, the Act limits it by defining the operative phrase “not feasible” narrowly to mean: (A) a hazardous air pollutant or pollutants cannot be emitted through a conveyance designed and constructed to emit or capture such pollutant, or that any requirement for, or use of, such a conveyance would be inconsistent with any Federal, State or local law, or 11 (B) the application of measurement methodology to a particular class of sources is not practicable due to technological and economic limitations. Id. § 7412(h)(2). Similarly, for area sources, the EPA can impose a “management-practice standard” in lieu of a numeric GACT standard. See id. § 7412(d)(5). A management-practice GACT standard is like a work-practice MACT standard in all ways but one—the EPA need not consider feasibility when setting management-practice standards. Compare id. § 7412(d)(2), with id. § 7412(d)(5). 2. 42 U.S.C. § 7429—“Solid Waste Combustion” In addition to amending the Act’s “Hazardous Air Pollutants” provision, see id. § 7412, the 1990 CAA Amendments added to the U.S. Code section 7429, titled “Solid Waste Combustion.” Section 7429 regulates “solid waste incineration units” generally, see id. § 7429(a)(1)(A), and CISWI specifically, see id. § 7429(a)(1)(D). Although section 7412 requires the EPA to control emissions of nearly two hundred HAPs, see id. § 7412(d)(1), section 7429 mandates that the EPA control emissions from only nine specific pollutants (as well as opacity, where appropriate), none of which the Congress included on its initial section 7412 list, see id. § 7429(a)(4); see also Nat. Res. Def. Council v. EPA (NRDC I), 489 F.3d 1250, 1256 (D.C. Cir. 2007). We have held that this difference “makes promulgating . . . standards under [section 7412] and [section 7429] mutually exclusive.” NACWA, 734 F.3d at 1119. In other words, if a source (or facility) is considered a CISWI 12 and, therefore, regulated under section 7429, it cannot be regulated under section 7412. See id. Whether a source falls under section 7412 or section 7429, “the statutory directive on setting MACT standards is virtually identical.” Id.; see also Nat’l Lime Ass’n, 233 F.3d at 631. That said, regulation under one section instead of the other “has practical consequences.” NACWA, 734 F.3d at 1120. For example, section 7412 allows the EPA to impose a GACT standard for area sources only but section 7429 requires the EPA to impose MACT standards for all covered units, regardless of their size. Compare 42 U.S.C. § 7412(d)(1), (5), with id. § 7429(a)(1)(A); see also NRDC I, 489 F.3d at 1256. Moreover, section 7412 mandates that the EPA control HAP emissions from “major source[s],” which the Act defines broadly to include “group[s] of stationary sources located within a contiguous area and under common control.” 42 U.S.C. § 7412(a)(1) (emphasis added). Section 7429, in contrast, mandates that the EPA control emissions from “solid waste incineration unit[s],” which the Act defines more narrowly as “a distinct operating unit of any facility which combusts any solid waste material,” 42 U.S.C. § 7429(g)(1) (emphases added). And finally, section 7429 does not provide for work-practice standards. 3. 42 U.S.C. §§ 7661 et seq.—“Title V Permits” Finally, the 1990 CAA Amendments added a provision to Title V of the Act that requires all owners and operators of HAP sources to obtain operating permits. See id. § 7661a. Title V does no more than consolidate “existing air pollution requirements into a single document, the Title V permit, to facilitate compliance monitoring” without imposing any new substantive requirements. Sierra Club v. Leavitt, 368 F.3d 13 1300, 1302 (11th Cir. 2004). The legislative history of the 1990 CAA Amendments indicates that the Congress required the “Title V permits” so that the public might “better determine the requirements to which the source is subject, and whether the source is meeting those requirements.” S. REP. NO. 101-228, at 347. Although owners and operators of all major HAP sources must obtain Title V permits, see generally 42 U.S.C. § 7661a(a), the EPA has discretion to exempt certain area source categories if it “finds that compliance with such requirements is impracticable, infeasible, or unnecessarily burdensome,” id. B. THE MAJOR BOILERS, AREA BOILERS, AND CISWI RULES On March 21, 2011, the EPA issued the first iteration of all three rules under review. That same day, however, the EPA announced that it intended to reconsider certain aspects of each rule. Not long after, multiple parties filed the petitions for review that we now address. Earlier, the EPA had concluded its reconsideration and issued the most recent iteration of the three rules. Because of this procedural quirk, each “rule” we address is in fact two separate rules—the EPA’s “final” 2011 version and its “final” 2013 version. The EPA’s analyses remained mostly consistent from 2011 to 2013 and we indicate, where necessary, the instances in which the EPA changed course in a significant way. 1. The Major Boilers Rule The Major Boilers Rule sets HAPs emission caps for all industrial, commercial, and institutional boilers that emit a large volume of HAPs. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,611. The EPA further divided the major boiler categories into subcategories based on the primary fuel 14 combusted by the boilers in the subcategory (e.g., coal, biomass, gas, etc.) and, for some subcategories, based on the method used to “feed” the fuel into the boiler. See 2013 Major Boilers Rule, 78 Fed. Reg. at 7,144. For most of the subcategories, the EPA set a numeric MACT standard for four different HAPs: particulate matter (PM); hydrogen chloride (HCl); mercury (Hg); and carbon monoxide (CO). See id. at 7,142 tbl.3; No. 11-1108 EPA Br. 9. The EPA used some of these HAPs—particularly CO—as a surrogate (or proxy) to set emissions limits for others on the section 7412(b) HAPs list. See 2013 Major Boilers Rule, 78 Fed. Reg. at 7,144-45. For the other major boiler subcategories, the EPA set a work- practice standard (specifically, a tune-up requirement) in lieu of numeric MACT standards. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613.7 The EPA also established a tune-up work-practice standard to control for dioxin/furan emissions across all major boiler subcategories. 2013 Major Boilers Rule, 78 Fed. Reg. at 7,138. In addition to these emission standards, the Major Boilers Rule includes several other provisions relevant to the current petitions for review. a. The “Upper Prediction Limit” Several factors complicate the process of setting MACT floors. The first is the CAA itself, which mandates that all MACT floors (1) must be achievable, see 42 U.S.C. 7 The four major boiler subcategories for which the EPA established work-practice standards include “[n]ew and existing units that have a designed heat input capacity of less than 10 MMBtu/hr, and new and existing units in the Gas 1 (natural gas/refinery gas) subcategory and in the metal process furnaces subcategory.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613. 15 § 7412(d)(2); (2) must ensure continuous regulation of the covered sources, see id. § 7602(k); and (3) must be no less stringent than the emissions levels being achieved by the best- controlled sources, see id. § 7412(d)(3). The second is that no source emits any HAP at a constant level; rather, HAP emissions fluctuate over time and for many reasons, including, e.g., “operation of control technologies, variation in combustion materials and combustion conditions, variation in operation of the unit itself, and variation associated with the emission measurement techniques.” Memorandum from Stephen D. Page, EPA Director of Air Quality Planning and Standards, EPA’s Response to Remand of the Record for Commercial and Industrial Solid Waste Incineration Units (Page Mem.) (July 14, 2014), at 3 (No. 11-1125 J.A. 1316). Finally, most sources do not measure their HAP emissions at all times and under all conditions.8 Id. at 6. Instead, data are usually gathered when a source conducts a “three-run stack test.” Id. This test provides three “snapshots” of a source’s emissions in a limited set of conditions and, accordingly, it fails to demonstrate accurately a source’s emissions during all times and under all conditions. Id. To compensate for the lack of adequate emissions data, the EPA uses a statistical tool known as the “upper prediction limit” (UPL) to account for the expected variability in emissions levels. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,630. The UPL, in turn, allows the Agency to set a MACT floor that is continuously achievable. Id. We discuss the UPL mechanics at greater length below, see infra § IV.C, but, in short, the EPA: (1) ranks all sources in a given 8 As discussed below, however, the EPA does allow sources to demonstrate MACT compliance by use of “continuous monitors.” See infra § IV.I. 16 category based on their three-run stack-test data; (2) determines the HAP emissions level of the “best controlled similar source” to establish standards for new sources, 42 U.S.C. § 7412(d)(3), and determines the average HAP emissions levels of the best performing 12 per cent of sources to establish standards for existing sources, id. § 7412(d)(3)(A); and then (3) applies the UPL methodology to provide the cushion necessary to account for the expected peaks and valleys in HAP emissions not reflected in the three- run stack-test “snapshots.” See Page Mem. 4, 6. b. The “Pollutant-By-Pollutant” Approach In identifying the best performing sources in a given category, often the EPA could not identify a single source that controlled all HAPs better than all other sources. Instead, the EPA found that one source effectively controlled emissions from one HAP but was nonetheless one of the worst- performing sources at controlling emissions from a different HAP. For this reason, the EPA adopted a “pollutant-by- pollutant” approach in setting MACT floors for major boiler subcategories. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,622-23. That is, instead of identifying the one source that, on balance, best controlled all HAPs in the aggregate, the EPA used one source to set the MACT floor for, e.g., PM, and used a different source to set the MACT floor for, e.g., HCl. For at least two subcategories of major boilers—new heavy oil-fired units and existing stoker coal-fired units—the EPA’s pollutant-by-pollutant approach resulted in MACT floors that no source had achieved in toto. c. Startups, Shutdowns, and Malfunctions The EPA found it difficult to account for HAP emissions when sources start up, shut down, and malfunction. All three 17 occurrences alter HAP emissions and, historically, the EPA exempted sources from normal numeric MACT-standard compliance when these events occurred. See, e.g., Standards of Performance for New Stationary Sources, 42 Fed. Reg. 57,125 (Nov. 1, 1977). Nevertheless, concluding that the Act “require[s] that there must be continuous section [7412]- compliant standards” and observing that the exemption meant that “no section [7412] standard governs these events,” in 2008 we vacated the exemption for startups, shutdowns, and malfunctions when the issue arose in a case challenging a different rule. Sierra Club v. EPA (Sierra Club III), 551 F.3d 1019, 1027-28 (D.C. Cir. 2008) (emphasis added). In response to the Sierra Club III vacatur, the EPA established a work-practice standard in lieu of a numeric MACT standard during startup and shutdown periods (but not during malfunctions) when it promulgated the Major Boilers Rule. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613.9 It did so after determining that the “physical limitations and the short duration of startup and shutdown periods” made it technologically infeasible to conduct the requisite testing for numeric emissions limits. Id. A work-practice standard sufficed, in the EPA’s view, because “[p]eriods of startup, normal operations, and shutdown are all predictable and routine aspects of a source’s operations.” Id. 9 Specifically, the startup and shutdown work-practice standard requires a source to follow “the manufacturer’s recommended procedures for minimizing periods of startup and shutdown.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613. “If manufacturer’s recommended procedures are not available,” the Major Boilers Rule provided that “sources must follow recommended procedures for a unit of similar design for which manufacturer’s recommended procedures are available.” Id. at 15,642. 18 But because a malfunction is “sudden, infrequent, and not reasonably preventable,” id. (quoting 40 C.F.R. § 63.2), the EPA declined to treat a malfunction as a “distinct operating mode,” id. As a result, the EPA did not account for malfunctions when it set the MACT floors and it required sources to comply with all MACT floors even during periods of malfunction. Id. At the same time and recognizing that even the best equipment can fail and that such failure can spike emissions, the EPA added to the Major Boilers Rule “an affirmative defense to civil penalties for exceedances of numerical emission limits that are caused by malfunctions.” Id. In reviewing a challenge to a different EPA rule, however, we vacated a materially identical affirmative-defense provision and held that the EPA has no power under the CAA to create a defense to civil liability. See Natural Res. Def. Council v. EPA (NRDC III), 749 F.3d 1055, 1062-64 (D.C. Cir. 2014). Here, the EPA defends its decision not to address malfunctions by asserting that it will use its enforcement discretion regarding malfunctions on a case-by-case basis. d. The One-Time Energy Assessment The EPA also promulgated a “beyond-the-floor” requirement for all facilities with existing major boilers. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613. Specifically, the Major Boilers Rule mandates a “a one-time energy assessment . . . on the affected boilers and facility to identify any cost-effective energy conservation measures,” id., which assessment includes, inter alia, a review of fuel usage, energy management practices, and conservation measures, see 2013 Major Boilers Rule, 78 Fed. Reg. at 7,198-99. In some respects, the energy assessment is limited: it (1) need occur only one time, see 40 C.F.R pt. 63, subpt. DDDDD tbl.3; (2) is “based on energy use by discrete 19 segments of a facility and not by a total aggregation of all individual energy using elements of a facility,” 2013 Major Boilers Rule, 78 Fed. Reg. at 7,146; and (3) does not require an owner or operator to implement any of the energy-saving findings the assessment makes. In one respect, however, it is expansive—it requires owners and operators to assess not only the boilers themselves but also other components “located on the site of the affected boiler that use energy provided by the boiler,” including “compressed air systems” as well as “facility heating, ventilation, and air conditioning systems.” 40 C.F.R. § 63.11237. e. The Health-Based Emissions Limits for HCl Although the EPA set numeric MACT standards to control HCl emissions, see 2013 Major Boilers Rule, 78 Fed. Reg. at 7,193-98 tbls.1 & 2, in an earlier iteration of the Major Boilers Rule, the EPA did not set MACT standards for HCl. See National Emission Standards for Hazardous Air Pollutants for Industrial, Commercial, and Institutional Boilers and Process Heaters (2004 Boilers Rule), 69 Fed. Reg. 55,218, 55,227 (Sept. 13, 2004). Instead, the Agency opted for a less stringent health-based emissions limit under section 7412(d)(4). See id. The EPA changed course after concluding that HCl emissions posed health concerns the Agency had not previously considered—in particular, the EPA feared the “potential cumulative public health and environmental effects” of HCl emissions, 2011 Major Boilers Rule, 76 Fed. Reg. at 15,643-44 (emphasis added)—and after recognizing that it did not have the requisite data to weigh adequately the newly identified health risks. 20 2. The Area Boilers Rule In the Area Boilers Rule, the EPA set emissions limits for the same three boiler categories it controlled in the Major Boilers Rule, see supra § I.B.1: industrial, commercial, and institutional boilers. See 2013 Area Boilers Rule, 78 Fed. Reg. at 7,488. It further split the categories into seven subcategories, see id., and set emissions limits for three of them, see id. at 7,517-18 tbls.1 & 2.10 These include: (1) coal-fired boilers (i.e., “any boiler that burns any solid fossil fuel and no more than 15 percent biomass,” 40 C.F.R. § 63.11237); (2) oil-fired boilers (i.e., “any boiler that burns any liquid fuel and is not in either the biomass or coal subcategories,” id.); and (3) biomass-fired boilers (i.e., “any boiler that burns any” “biomass-based solid fuel that is not a solid waste” and “is not in the coal subcategory,” id.). See 2013 Area Boilers Rule, 78 Fed. Reg. at 7,517-18 tbls.1 & 2. For these subcategories, the EPA set emissions limits for three HAPs: Hg, PM, and CO, with PM functioning as a surrogate for non-Hg urban metals and CO functioning as a surrogate for polycyclic organic matter (POM). See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,586. Because Hg and POM are both listed in section 7412(c)(6), the EPA had to set MACT standards for Hg and for CO (as surrogate for POM) for any area source category that, in the EPA’s view, required 10 As noted above, see supra § I.A.1.a, the EPA has some discretion in promulgating emissions limits for area HAP sources. Exercising its discretion, the EPA had previously determined that natural gas-fired area boilers did not emit HAPs at a level necessitating regulation. See National Emission Standards for Hazardous Air Pollutants for Area Sources: Industrial, Commercial, and Institutional Boilers (2010 Proposed Area Boilers Rule), 75 Fed. Reg. 31,896, 31,900 (June 4, 2010). 21 MACT control to assure a 90 per cent reduction in the aggregate emissions of these two HAPs. See 42 U.S.C. § 7412(c)(6). The Agency complied, setting numeric MACT standards for Hg and CO emissions from large coal-fired boilers and a MACT work-practice standard (specifically, a tune-up requirement) for emissions from small coal-fired boilers. See 2013 Area Boilers Rule, 78 Fed. Reg. at 7,488, 7,517-18.11 It did not, however, set MACT standards for Hg and POM emissions from biomass or oil-fired boilers, finding it unnecessary to assure a 90 per cent reduction in aggregate emissions of those two HAPs. See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,566. Thus, with the exception of Hg and CO emissions from coal-fired boilers, the EPA had discretion to promulgate GACT standards for all other HAPs in all other source subcategories. See 42 U.S.C. § 7412(d)(5). Exercising this discretion resulted in the following standards: 11 As used in the Area Boilers Rule, the difference between “large” and “small” units depends on the heat-input capacity of the unit. See 2013 Area Boilers Rule, 78 Fed. Reg. at 7,488. It is not the same as the difference between “major” and “area” sources, which is based on the volume of HAPs a source emits. See 42 U.S.C. § 7412(a). 22 Boiler Hg Hg Size Age Subcategory Limit Type New Numeric MACT Large Existing Numeric MACT New Tune- MACT Coal Up Small Existing Tune- MACT Up New --- --- Large Existing --- --- Biomass New --- --- Small Existing --- --- New --- --- Large Existing --- --- Oil New --- --- Small Existing --- --- Boiler CO CO Size Age Subcategory Limit Type New Numeric MACT Large Existing Numeric MACT Coal New Tune-up MACT Small Existing Tune-up MACT New Tune-up GACT Large Existing Tune-up GACT Biomass New Tune-up GACT Small Existing Tune-up GACT New Tune-up GACT Large Existing Tune-up GACT Oil New Tune-up GACT Small Existing Tune-up GACT 23 Boiler PM PM Size Age Subcategory Limit Type New Numeric GACT Large Existing Tune-up GACT Coal New Tune-up GACT Small Existing Tune-up GACT New Numeric GACT Large Existing Tune-up GACT Biomass New Tune-up GACT Small Existing Tune-up GACT New Numeric GACT Large Existing Tune-up GACT Oil New Tune-up GACT Small Existing Tune-up GACT 2013 Area Boilers Rule, 78 Fed. Reg. at 7,488-89, 7,517-19. The Area Boilers Rule shares many of the same features as the Major Boilers Rule; for example, the Area Boilers Rule treats startups, shutdowns, and malfunctions in the same fashion as the Major Boilers Rule, see supra § I.B.1.c—i.e., the Area Boilers Rule creates work-practice (or management- practice) standards for startup and shutdown periods but does not account for malfunctions at all, save for the Agency’s commitment to consider malfunctions on a case-by-case basis. See 2013 Area Boilers Rule, 78 Fed. Reg. at 7,496; 2011 Area Boilers Rule, 76 Fed. Reg. at 15,560-61. Additionally, the Area Boilers Rule imposes the same one-time energy- assessment requirement for existing large area boilers that the Major Boilers Rule imposes for existing major boilers. See supra § I.B.1.d; see also 2013 Area Boilers Rule, 78 Fed. Reg. at 7,500; 2011 Area Boilers Rule, 76 Fed. Reg. at 24 15,560, 15,567-68. There are, however, two unique features of the Area Boilers Rule that warrant brief discussion. a. Exclusion of “Temporary Boilers” After the EPA promulgated the 2011 Area Boilers Rule but before it promulgated the 2013 version, it proposed an amendment to 40 C.F.R. § 63.11195 that added temporary boilers to the list of those boilers not regulated by section 7412. See National Emission Standards for Hazardous Air Pollutants for Area Sources: Industrial, Commercial, and Institutional Boilers (2011 Proposed Area Boilers Rule on Reconsideration), 76 Fed. Reg. 80,532, 80,535 (Dec. 23, 2011). The EPA created the exclusion because, in its view, temporary boilers are “insignificant sources[] and were not included in the EPA’s analysis of the source category.” Id. The Agency eventually defined “temporary boiler” as “any gaseous or liquid fuel boiler that is designed to, and is capable of, being carried or moved from one location to another by means of, for example, wheels, skids, carrying handles, dollies, trailers, or platforms.” See 2013 Area Boilers Rule, 78 Fed. Reg. at 7,491 (quoting 40 C.F.R. § 63.11237). b. Title V Permit Exemption for Synthetic Area Sources As noted, see supra § I.A.3, Title V of the CAA imposes a permit requirement on all owners and operators of major and area HAP sources. See 42 U.S.C. § 7661a. The EPA, however, can exempt an area source subcategory if it finds “that compliance with such requirements is impracticable, infeasible, or unnecessarily burdensome on such categories.” Id. § 7661a(a). When it proposed the Area Boilers Rule in 2010, the EPA considered exempting some area sources because, in its view, the existing restrictions on those sources 25 made Title V duplicative. See 2010 Proposed Area Boilers Rule, 75 Fed. Reg. at 31,910-13. At the time, the EPA announced that it did not intend to exempt “synthetic” area sources (i.e., area sources that, but for existing air-pollution controls, would be considered major sources). Id. at 31,913. In so doing, the EPA reasoned that synthetic area sources: (1) more closely resemble major sources than area sources, (2) are often located in populous areas, and (3) have high HAP emissions potential when uncontrolled. Id. But in the 2011 Area Boilers Rule, the EPA changed course and exempted synthetic area sources from the Title V permitting requirement. See 76 Fed. Reg. at 15,578. It reasoned that the “observations and data . . . relied upon in other rulemakings for distinguishing between sources that became synthetic area sources due to controls and other synthetic and natural area sources did not necessarily apply to this source category.” Id. In its view, it no longer had “sufficient information” to distinguish synthetic area sources from the others it exempted and, accordingly, “the rationale for exempting most area sources subject to this rule . . . is also now relevant for” synthetic area sources. Id.; see also 2013 Area Boilers Rule, 78 Fed. Reg. at 7,497. 3. The CISWI Rule In the CISWI Rule, the EPA created four CISWI subcategories: (1) incinerators (i.e., “units designed to burn [solid] waste materials for the purpose of disposal”); (2) small, remote incinerators (“SRIs”) (i.e., units that burn small waste batches); (3) energy recovery units (“ERUs”) (i.e., units that would be classified as boilers but for the fact they combust solid waste); and (4) waste-burning kilns (i.e., units that would be classified as cement kilns if they did not 26 burn solid waste). 2013 CISWI Rule, 78 Fed. Reg. at 9,118. Initially, the EPA proposed a fifth subcategory—burn-off ovens—but eliminated burn-off ovens after comments revealed that it had greatly underestimated the number of units in that subcategory (36 versus 15,000) and that it lacked the requisite data to set limits for the units. See 2011 CISWI Rule, 76 Fed. Reg. at 15,734. Of the four CISWI subcategories, the EPA further divided the ERU subcategory (for CO emissions only) into coal-fired, biomass-fired and oil/gas-fired ERUs and it further divided the waste-burning kiln subcategory (again, for CO emissions only) into long and preheater/precalcinator kilns. See 2013 CISWI Rule, 78 Fed. Reg. at 9,118 tbl.2. The EPA then set numeric MACT limits for the section 7429(a)(4) pollutants.12 See 2011 CISWI Rule, 76 Fed. Reg. at 15,709-10 tbl.1. Unlike the Major Boilers Rule and the Area Boilers Rule, the CISWI Rule contains no beyond-the- floor MACT standards. The EPA also declined to promulgate work-practice standards, concluding that it had no authority to do so because section 7429 includes no work-practice standard provision similar to that in section 7412. See id. at 15,721. The CISWI Rule shares several features with the Major Boilers Rule. In the CISWI Rule, for instance, the EPA also used the UPL, see id. at 15,722-27, as well as the pollutant- by-pollutant approach, see id. at 15,719-21, in setting MACT floors. Based in part on the differences between section 7412 12 These pollutants are (1) PM, (2) sulfur dioxide (SO2), (3) HCl, (4) nitrogen oxide (NOx), (5) CO, (6) lead (Pb), (7) cadmium (Cd), (8) Hg, (9) dioxins and dibenzofurans, and (10) opacity (where appropriate). 42 U.S.C. § 7429(a)(4). 27 and section 7429, the CISWI rule has four unique characteristics we briefly describe. a. Startups, Shutdowns, and Malfunctions As discussed, see supra § II.B.1.c, the EPA imposed a work-practice standard for major and area source boilers during periods of startup and shutdown but declined to make any regulatory modification for malfunctions. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613; 2011 Area Boilers Rule, 76 Fed. Reg. at 15,560-61. The CISWI Rule, however, makes no modification for any of these periods, mandating instead that the numeric MACT standards “apply at all times,” even when CISWI units are starting up or shutting down. 2011 CISWI Rule, 76 Fed. Reg. at 15,711, 15,737-38. The Agency concluded that it had no legal authority under section 7429 to impose anything but a numeric MACT standard on CISWI units. See id. at 15,709 tbl.1; see also id. at 15,737-38. b. The Record-Keeping Requirement Whether the EPA considers a combustion unit to be a boiler (and thus subject to section 7412) or a CISWI (and thus subject to section 7429) turns entirely on whether the unit combusts “solid waste.” See id. at 15,709. The term “solid waste” is defined in RCRA, 42 U.S.C. §§ 6901 et seq., and clarified by EPA regulation, see Identification of Non- Hazardous Secondary Materials that Are Solid Waste (NHSM Rule), 76 Fed. Reg. 15,456, 15,457 (Mar. 21, 2011). See also 2011 CISWI Rule, 76 Fed. Reg. at 15,709. If the unit combusts solid waste, it is a CISWI. Id. The source owner or operator initially decides whether the material its combustion unit burns meets the definition of 28 solid waste. See id. at 15,740. For this reason, the CISWI rule requires that the owner or operator of a combustion unit that burns materials “not clearly listed as traditional fuels” keep records explaining how the materials meet the regulatory definition of “non-solid waste.” Id.; see also 40 C.F.R. § 60.2175(v). Failure to do so means, for the purposes of the EPA, that “the operating unit is a CISWI unit.” 40 C.F.R. § 60.2265; see also 2013 CISWI Rule, 78 Fed. Reg. at 9,188. c. Emissions Averaging During the notice-and-comment period, certain industry entities urged the EPA to allow a facility containing more than one CISWI unit to demonstrate compliance with the CISWI MACT standards by averaging the HAP emissions of all units in the facility. See Commercial and Industrial Solid Waste Incineration Units: Reconsideration and Proposed Amendments; Non-Hazardous Secondary Materials that Are Solid Waste (2011 Proposed CISWI Rule on Reconsideration), 76 Fed. Reg. 80,452, 80,463 (Dec. 23, 2011). Although it allowed facility-wide averaging in the Major Boilers Rule, the Agency declined to allow it for facilities with CISWI units. See id. The EPA explained, first, that “[t]he applicability of CISWI is such that each unit is an affected facility.” Id. In response to further comments, the EPA subsequently explained that it did “not believe [it had] the legal authority to allow emissions averaging in CISWI or under section [7429] generally because each individual unit is an affected facility.” Summary of Public Comments and Responses for Commercial and Industrial Solid Waste Incineration Units (CISWI Rule—Responses to Comments), EPA-HQ-OAR-2003-0119-2638-A2 (Dec. 2012), at 195. 29 d. Treatment of Units that Begin Combusting Solid Waste Finally, in the preamble to the 2011 CISWI Rule, the EPA stated broadly that “[u]nits that begin combusting solid waste are considered existing sources under CISWI.” 76 Fed. Reg. at 15,714 (emphasis added). This categorical pronouncement drew objections from commentators who insisted that, if such units experienced an increase in HAP emissions, the units would meet the statutory definition of “modified solid waste incineration unit[s],” see 42 U.S.C. § 7429(g)(3), and would, accordingly, be subject to the MACT standards for new units, see id. § 7429(g)(2). In the subsequent proposed CISWI Rule, the EPA clarified that “[a]n existing source will not be considered a new source solely due to a combustion material switch. Assuming new source applicability is not triggered, existing sources that change fuels or materials are considered existing sources . . . .” 2011 Proposed CISWI Rule on Reconsideration, 76 Fed. Reg. at 80,459. II. STANDARD OF REVIEW For each issue, the Petitioners argue that the EPA either misinterpreted the CAA, acted arbitrarily and capriciously, or both. We review the EPA’s construction of the statute under the two-part framework established in Chevron, U.S.A., Inc. v. Nat. Res. Def. Council, Inc., 467 U.S. 837 (1984). At Chevron step 1, we ask whether the Congress “has directly spoken to the precise question at issue”; if it has, we “must give effect to [its] unambiguously expressed intent.” Id. at 842-43. In so doing, we examine the CAA’s text, structure, purpose, and legislative history to determine if the Congress has expressed its intent unambiguously. See Bell Atl. Tel. Co. v. FCC, 131 F.3d 1044, 1047 (D.C. Cir. 1997). If the statute 30 is “silent or ambiguous with respect to the specific issue,” we proceed to Chevron step 2 and defer to the EPA’s interpretation so long as it is “based on a permissible construction of the statute.” Chevron, 467 U.S. at 842-43. The CAA authorizes the Court to “reverse any [EPA] action found to be . . . arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law.” 42 U.S.C. § 7607(d)(9)(A). Our review is “narrow” and we will “not . . . substitute [our] judgment for that of the agency.” Motor Veh. Mfrs. Ass’n v. State Farm Mut. Auto. Ins. Co. (State Farm), 463 U.S. 29, 43 (1983). We “must uphold an agency’s action where [the agency] ‘has considered the relevant factors and articulated a rational connection between the facts found and the choice made,’ and has not ‘relied on [improper] factors.’” Nat’l Ass’n of Clean Air Agencies v. EPA (NACAA), 489 F.3d 1221, 1228 (D.C. Cir. 2007) (citations omitted) (quoting Allied Local & Reg’l Mfrs. Caucus v. EPA, 215 F.3d 61, 68 (D.C. Cir. 2000), and State Farm, 463 U.S. at 43). A rule is arbitrary and capricious if the agency: (1) “has relied on factors which Congress has not intended it to consider,” (2) “entirely failed to consider an important aspect of the problem,” (3) “offered an explanation for its decision that runs counter to the evidence before the agency,” or (4) “is so implausible that it could not be ascribed to a difference in view or the product of agency expertise.” State Farm, 463 U.S. at 43. We review the EPA’s factual determinations for substantial evidence. 5 U.S.C. § 706(2)(E). We also “owe[] particular deference to EPA when its rulemakings rest upon matters of scientific and statistical judgment within [its] sphere of special competence and statutory jurisdiction.” Am. Coke & Coal Chems. Inst. v. EPA, 452 F.3d 930, 941 (D.C. 31 Cir. 2006). But “[w]e are hesitant to rubber-stamp EPA’s invocation of statistics without some explanation of the underlying principles or reasons why its formulas would produce an accurate result.” NACWA, 734 F.3d at 1145. III. INDUSTRY PETITIONERS’ CHALLENGES A. STARTUPS, SHUTDOWNS, AND MALFUNCTIONS Industry Petitioners raise two sets of challenges to startup, shutdown, and malfunction periods: (1) a challenge to the EPA’s failure to take malfunctions into account in the Major Boilers and Area Boilers Rules and (2) a challenge to EPA’s failure to take into account periods of startup, shutdown, and malfunction in the CISWI Rule. For the reasons that follow, we reject all of the Industry Petitioners’ claims related to startups, shutdowns, and malfunctions. 1. Periods of Malfunction in the Major Boilers and Area Boilers Rules First, Industry Petitioners challenge the Major Boilers and Area Boilers Rules’ failure to take malfunctions into account in setting MACT floors. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613; 2011 Area Boilers Rule, 76 Fed. Reg. at 15,560-61. The EPA defends its refusal to account for malfunctions on the basis of (1) the impracticability of accounting for events that are necessarily unpredictable, and (2) the EPA’s assertion that it will use its prosecutorial discretion to determine on a case-by-case basis whether an exceedance of emission standards is attributable to an excusable malfunction or whether applicable regulatory penalties should be imposed instead. See No. 11-1108 EPA Br. 38; No. 11-1141 EPA Br. 29. 32 Both sides agree that malfunctions are inevitable in the operation of area and major boilers. According to the EPA, “even equipment that is properly designed and maintained can sometimes fail and . . . such failure can sometimes cause an exceedance of the relevant emission standard.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613; 2011 Area Boilers Rule, 76 Fed. Reg. at 15,561. Thus, the EPA defined a malfunction as a “sudden, infrequent, and not reasonably preventable failure of air pollution control and monitoring equipment, process equipment or a process to operate in a normal or usual manner.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613 (citing 40 C.F.R. § 63.2); 2011 Area Boilers Rule, 76 Fed. Reg. at 15,560 (same). In attempting to write rules to account for emissions, however, the EPA faced an intractable problem: how to account for a malfunction which is, by definition, unpredictable in terms of timing, duration, magnitude, and effect. While the existence of malfunctions is entirely predictable, the nature of those malfunctions is not, and it is the malfunction’s nature that affects emissions and thus is relevant to the application of emission limits. At first glance, the EPA’s chosen approach to malfunctions may seem counterintuitive, as the Agency appears to have several reasonable alternatives: it could exempt periods of malfunction entirely from the application of the emission standards; or it could apply the standards to malfunctions while giving boiler owners the opportunity to defend against a penalty by demonstrating they were not at fault for the malfunction. But the EPA has previously been stymied in its attempts to implement either of these solutions, as this court has concluded neither approach is consistent with the Agency’s enabling statutes. For instance, in Sierra Club III, the EPA attempted to exempt major sources from complying with emission standards during start up, shut 33 down, and malfunction. See 551 F.3d at 1027-28. This court rejected that approach because the Congress “required that there must be continuous section 112-compliant standards” and so the EPA lacked discretion to exempt certain periods from compliance, regardless of their unpredictability. Id. at 1027. In NRDC III, this court considered a challenge to the affirmative defense provision the EPA adopted for persons defending against civil suits under 42 U.S.C. § 7604(a), which allows “any person” to “commence a civil action on his own behalf” against any entity alleged to be in violation of an emission standard or limitation. The affirmative defense provision was meant to shield alleged violators from liability for certain emissions violations caused by “unavoidable” malfunctions; under the provision, therefore, “the district court [could] assess penalties only if violators fail[ed] to meet [their] burden of proving all of the requirements in the affirmative defense.” NRDC III, 749 F.3d at 1062 (internal quotation omitted). The court rejected this provision as an impermissible intrusion on the judiciary’s role. See id. at 1063 (“[U]nder this statute, deciding whether penalties are ‘appropriate’ in a given private civil suit is a job for the courts, not for EPA.”). Faced with an obvious dilemma, the EPA arrived at the approach it defends today. Malfunctions receive no special treatment and the EPA instead exercises “its enforcement discretion to address exceedances of emission limits that may be caused by such uncertain, unpredictable events, on a case- by-case basis.” No. 11-1108 EPA Br. 38; see also No. 11- 1141 EPA Br. 29. The EPA’s current treatment of malfunctions thus differs from its invalid affirmative defense provision because the Agency is exercising its own regulatory enforcement power on an ad hoc basis outside the context of citizen suits. When an exceedance occurs during a 34 malfunction, the EPA determines what enforcement action— if any—it should take by considering “the good faith efforts of the source to minimize emissions during malfunction periods, including preventative and corrective actions, as well as root cause analyses to ascertain and rectify excess emissions.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613; see also 2011 Area Boilers Rule, 76 Fed. Reg. at 15,561 (same). The EPA also considers whether the exceedance was in fact “not reasonably preventable” or whether it was “caused in part by poor maintenance or careless operation.” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613 (citing 40 C.F.R. § 63.2); see also 2011 Area Boilers Rule, 76 Fed. Reg. at 15,561 (same). For our purposes, we need not (indeed, must not) evaluate the policy implications of the EPA’s regulatory choice because our review is confined to determining whether the EPA’s regulation reflects a permissible reading of the applicable statute under Chevron. Here, we conclude that it does. The relevant statute requires only that the EPA set “achievable” standards, 42 U.S.C. § 7412(d)(2), and it defines achievability to be no less “than the emission control that is achieved in practice by the best controlled similar source,” 42 U.S.C. § 7412(d)(3). The “best controlled similar source,” however, is unlikely to be a malfunctioning source, and the EPA is bound to enact a standard in keeping with emission limits achieved by that “best controlled similar source.” If anything, then, the statutory language on its face prevents the EPA from taking into account the effect of potential malfunctions when setting MACT emission standards. At the very least, the language permits the EPA to ignore malfunctions in its standard-setting and account for them instead through its regulatory discretion. Our Sierra Club III decision confirms this. See 551 F.3d at 1027-28. Because the 35 EPA had no option to exclude these unpredictable periods, its approach is reasonable. We therefore reject Industry Petitioners’ argument that the EPA either misinterpreted the CAA or acted arbitrarily and capriciously in failing to account for malfunctions when setting MACT floors in the Major and Area Boilers Rules. Nor do we agree with the Industry Petitioners’ secondary argument that the EPA acted arbitrarily and capriciously by failing to set a work-practice or a GACT management- practice standard for malfunction periods. First, the statute makes clear that these kinds of standards are to be set at the discretion of the EPA, so it would be difficult to interpret the statute consistently with its text while holding that the text’s permissive language in fact sets out a requirement that the Agency set work-practice or GACT management-practice standards. As to work-practice standards, “[t]he Administrator may, in lieu [of a numeric standard], promulgate a design, equipment, work practice, or operational standard, or combination thereof,” and any such standard set must “in the Administrator’s judgment [be] consistent with the provisions of subsection (d).” 42 U.S.C. § 7412(h)(1). As to GACT management-practice standards, “the Administrator may . . . elect to promulgate” such standards with respect to certain “categories and subcategories of area sources.” Id. § 7412(d)(5). It should go without saying that “may means may.” McCreary v. Offner, 172 F.3d 76, 83 (D.C. Cir. 1999) (internal quotations omitted). Second, the Petitioners have not demonstrated and the EPA does not concede that setting work-practice or GACT management-practice standards would even be feasible for periods of malfunction. As for work-practice standards, the EPA would have to conceive of a standard that could apply 36 equally to the wide range of possible boiler malfunctions, ranging from an explosion to minor mechanical defects. Any possible standard is likely to be hopelessly generic to govern such a wide array of circumstances. Similar problems exist for setting GACT management practices. These management practices would also need to apply to the wide range of possible malfunctions, and the EPA would need to determine that the standard would “reduce emissions of hazardous air pollutants,” an evidence-based standard that is difficult (perhaps impossible) to apply to the unpredictable circumstances of malfunctions. 42 U.S.C. § 7412(d)(5). Thus, we reject the Industry Petitioners’ argument that the EPA was required to set a work-practice or GACT management-practice standard for malfunction periods. In doing so, we are mindful that the EPA is not the only entity able to bring enforcement actions under the CAA, but that private citizens are also empowered to enforce emission standards by filing suit in district court. 42 U.S.C. § 7604(a). Assurances that the EPA will use its prosecutorial discretion to account for malfunctions would mean little if private citizens could seek strict enforcement of those same standards. But as we stated in NRDC III, “the Judiciary, not any executive agency, determines ‘the scope’—including the available remedies—‘of judicial power vested by’ statutes establishing private rights of action.” 749 F.3d at 1063 (quoting City of Arlington v. FCC, 133 S. Ct. 1863, 1871 (2013)). Accordingly, in citizen suits under the CAA, “the courts determine, on a case-by-case basis, whether civil penalties are ‘appropriate.’” Id. Boiler operators can argue that penalties should not be assessed because of an unavoidable malfunction, and they can support that argument with other relevant facts, “such as the defendant’s ‘full 37 compliance history and good faith efforts to comply.’” Id. (quoting 42 U.S.C. § 7413(e)(1)). The EPA can also provide supporting argumentation as intervenor or amicus. Id. Courts should not hesitate to exercise their judicial authority to craft appropriate civil remedies in the case of emissions exceedances caused by unavoidable malfunctions. 2. Periods of Startup, Shutdown, and Malfunction in the CISWI Rule In the CISWI Rule, the EPA made no modification for periods of startup, shutdown, or malfunction. The Industry Petitioners argue that failing to account for these periods violated the EPA’s statutory instruction to set “achievable” standards. Additionally, the Industry Petitioners claim it was arbitrary and capricious for the EPA to set work-practice standards for startup and shutdown periods under the Major Boilers Rule but not under the CISWI Rule. Both arguments are without merit. First, the EPA’s emission standards for small incinerators do take into account periods of shutdown and startup. The EPA based its standards for these machines on “short term stack tests for pollutants,” in which incinerators are monitored during the course of normal operation, which includes daily startup and shutdown periods. See 2011 CISWI Rule, 76 Fed. Reg. at 15,738. Thus, startup and shutdown times are already incorporated into the standards the EPA set, and what is more, nearly all pollutants are present in smaller numbers during startup and shutdown anyway, when incinerators are burning fuels alone rather than fuels and solid waste. See Standards of Performance for New Stationary Sources and Emission Guidelines for Existing Sources: Commercial and Industrial Solid Waste Incineration Units (2010 Proposed CISWI Rule), 38 75 Fed. Reg. 31,938, 31,964 (June 4, 2010). Given this reality, the CISWI Rule satisfies the statutory standard of “achievability” and is not arbitrary and capricious. Second, as to periods of malfunctions, the same analysis applies to the CISWI Rule as applies to the Boilers Rules. The EPA adopted a reasonable interpretation of the CAA when it excluded periods of malfunction from its calculations of achievability given that malfunction periods are by their very nature unpredictable in terms of their effect on emissions. The EPA’s decision to account for malfunctions in its discretion is likewise a reasonable interpretation of 42 U.S.C. § 7412(d)(2) and (3). For these reasons, we reject the Industry Petitioners’ challenges to the EPA’s regulatory choices with regard to periods of startup, shutdown, and malfunction. B. THE POLLUTANT-BY-POLLUTANT APPROACH The EPA must look to the performance of the best major boilers and CISWI incinerators when setting MACT floors for a pollutant. As described above, for new units, the EPA must set floors at the level achieved by the best similar unit in each subcategory. For existing units, the Agency must set floors at the level achieved by the best 12 per cent of similar units in each subcategory. 42 U.S.C. §§ 7412(d)(3)(A), 7429(a)(2). As a result, the EPA had to identify the best performing units in each subcategory when setting the MACT floors for the Major Boilers and CISWI Rules. But the EPA often could not identify a single unit or set of units that controlled all HAPs better than the other units in the subcategory. Instead, the EPA sometimes found that a unit might rank among the best 39 in its subcategory at controlling emissions of one HAP, but among the worst at controlling emissions of a different HAP. To address this problem, the EPA adopted a “pollutant- by-pollutant” approach in setting the MACT floors: instead of identifying the unit or units that best controlled all HAPs in the aggregate, the EPA used one unit or set of units to set the MACT floor for, e.g., PM, and used a different unit or set of units to set the MACT floor for, e.g., HCl. See 2011 Major Boilers Rule, 76 Fed. Reg. at 15,621-23; 2011 CISWI Rule, 76 Fed. Reg. at 15,720-21. For at least two subcategories of major boilers—new heavy oil-fired units and existing stoker coal-fired units—the EPA’s pollutant-by-pollutant approach resulted in MACT floors that no unit in the subcategory had achieved in toto. Similarly, for small, remote incinerators (SRIs), the approach resulted in standards for existing units that only two of the 28 SRI units had met in toto, and standards for new units that no existing SRI had met in toto. The Industry Petitioners challenge the EPA’s use of the pollutant-by-pollutant approach. According to the Industry Petitioners, the CAA’s plain language requires the Agency to identify the best overall unit or set of units—not the best unit or set of units for a particular pollutant—in each subcategory when setting MACT floors. They further claim the EPA’s pollutant-by-pollutant approach was unreasonable with regard to SRIs because it resulted in a set of emission standards that no single unit in the subcategory had achieved in practice. We disagree, and conclude that the EPA’s pollutant-by- pollutant approach is a reasonable interpretation and application of the statute. For the purposes of this challenge, the MACT floor provisions for major boilers and CISWI units are identical. 40 Under both provisions, the EPA must set emission standards for new units based on “the emissions control that is achieved in practice by the best controlled similar unit, as determined by the Administrator.” 42 U.S.C. § 7429(a)(2) (CISWI); see also id. § 7412(d)(3) (major boilers). For existing units, the MACT floor is based on “the average emissions limitation achieved by the best performing 12 percent of units in the category.” Id. § 7429(a)(2) (CISWI); see also id. § 7412(d)(3)(A) (major boilers). The Industry Petitioners claim this language unambiguously forecloses the EPA’s pollutant-by-pollutant approach. For new units, they assert, the statute requires the EPA to find the single unit that performs best overall and use this unit—and only this unit—to set standards for all regulated pollutants. For example, if Incinerator 3 were deemed the best overall performer in a subcategory, then the EPA would use Incinerator 3’s emissions levels to set standards for PM, CO, and each of the other regulated pollutants. This would be true even if Incinerator 1 in the same subcategory had lower CO emissions and Incinerator 2 had lower PM emissions. The Industry Petitioners also make this argument for existing sources. For these units, under their interpretation, the mandate to identify the “best performing 12 percent of units” required the EPA to use data from the 12 per cent of sources with the lowest overall emissions in the subcategory. In short, the Industry Petitioners argue that the best “unit” referred to by the provision cannot be a “hypothetical composite” of multiple units that result in standards for new units that no actual unit has met in practice with regard to every pollutant, or standards for existing units that 12 per cent of actual units have not met with regard to every pollutant. 41 The Industry Petitioners read too much into the statutory language. It is true that the statute requires the EPA to base MACT standards on what is “achieved” by the best “unit” or “12 percent of units.” But, as the EPA argues, the statute says nothing about how the Agency should determine which units are the best. Cf. Sierra Club v. EPA, 167 F.3d 658, 661 (D.C. Cir. 1999) (noting that section 7429(a) “on its own says nothing about how the performance of the best units is to be calculated”). Both the industry-favored method of choosing the best overall unit and the EPA’s method of choosing the best unit as to each particular pollutant facially comport with the statute’s mandate to determine which units are best. Because the statute is ambiguous as to how the EPA should identify those units, we must defer to the Agency’s choice so long as it is reasonable. See Sierra Club I, 353 F.3d at 990. Here, the EPA’s choice is reasonable. The statute provides that emission standards shall reflect “the maximum degree of reduction in emissions of [regulated pollutants] that the Administrator . . . determines is achievable for new or existing units in each category.” 42 U.S.C. § 7429(a)(2); see also id. § 7412(d)(2). It then provides that the “degree of reduction in emissions that is deemed achievable for new units in a category shall not be less stringent than the emissions control that is achieved in practice by the best controlled similar unit, as determined by the Administrator.” Id. § 7429(a)(2); see also id. § 7412(d)(3). Reading these provisions together, they support a pollutant-by-pollutant approach. The “best controlled similar unit” language does not exist in a vacuum; rather, it exists to measure the “degree of reduction in emissions that is deemed achievable.” Id. § 7429(a)(2); see also id. § 7412(d)(3). That “reduction in emissions” is the reduction in emissions of each pollutant listed in sections 7429(a)(4) and 7412(b)(1). The EPA’s 42 approach to setting standards on a pollutant-by-pollutant basis thus comfortably fits within this statutory scheme. Moreover, the Industry Petitioners have not explained how their preferred approach would better comport with the statute. Were the EPA required to determine which units perform best “overall,” we see at least two possibilities for how it could do so: First, the EPA could calculate a unit’s average emissions for each pollutant in consistent units of measurement, add these emissions together, and then choose the unit with the smallest overall sum in each subcategory. But this approach could produce arbitrary results, because the “best performing” overall unit might emit unusually low quantities of some pollutants and unusually high quantities of others. This would mean the emission standards for some pollutants would be lenient while others would be stringent, with no principled reason for the difference. Alternatively, the Agency could identify which source is best overall based on which emits the lowest level of the riskiest pollutants. But this approach would require the Agency to rank pollutants’ relative risks without any congressional guidance on how to do so. This approach would also contravene our previous understanding of the congressional intent behind the MACT floor provisions. As we have explained, the MACT floors “are to be based not on an assessment of the risks posed by [pollutants], but instead on the maximum achievable control technology (MACT) for sources in each category.” Sierra Club I, 353 F.3d at 980. The Industry Petitioners nevertheless argue that the CAA’s legislative history supports their preferred approach. In particular, they point to the floor comments of Senator Durenberger discussing the potential impact on MACT floors of mutually incompatible control technologies. 136 Cong. 43 Rec. S17,238 (daily ed. Oct. 26, 1990) (statement of Senator Durenberger). Mutually incompatible control technologies cannot be used at the same time and therefore present regulators with a dilemma. For example, say Technology 1 and Technology 2 cannot be used together. If Technology 1 is better at reducing PM than Technology 2, and Technology 2 is better at reducing CO than Technology 1, the EPA would have to choose which of the two technologies to factor into emission standards. In such situations, Senator Durenberger anticipated that the “EPA should judge MACT to be the technology which best benefits human health and the environment on the whole.” Id. The Industry Petitioners argue this statement demonstrates that Congress intended the EPA to make an overall determination of which units are the best performing “on the whole.” Senator Durenberger’s statement does not support this broad principle. The statement merely explains that, where two technologies cannot be used together, the EPA should base MACT standards on the technology it considers best overall. Here, the Industry Petitioners do not identify any relevant control technologies that are mutually incompatible. Indeed, the EPA found in the CISWI Rule that “there is no technical reason why [the] air pollution control systems cannot be combined.” 2011 CISWI Rule, 76 Fed. Reg. at 15,721; see also 2011 Major Boilers Rule, 76 Fed. Reg. at 15,623 (“All available data for boilers and process heaters indicate that there is no technical problem achieving the floor levels contained in this final rule for each HAP simultaneously, using the MACT floor technology.”). There is thus no reason to believe that the EPA’s current MACT floor standards cannot be achieved. Instead, the Industry Petitioners merely insist that no units currently meet the EPA’s new unit standards with regard to every regulated 44 pollutant in certain subcategories, and only a few sources meet all of the standards for existing units in the same subcategories. But, if the statute permits the EPA to determine which units are best on a pollutant-by-pollutant basis—and it does—then the EPA’s choice to adopt that approach does not become unlawful merely because few or no units have achieved those standards for all pollutants. Finally, the Industry Petitioners argue that even if the pollutant-by-pollutant approach is reasonable in some circumstances, it is arbitrary and capricious as applied to certain SRIs because it exacerbates certain problems posed by the “batch” nature of SRIs. As explained at infra § III.E, SRIs burn waste in small batches. According to the Petitioners, this means that the SRIs that the EPA identified as best performing were, in reality, burning cleaner waste at the time emissions testing was done; they were not actually better than other units at removing or destroying waste. The pollutant-by-pollutant approach, the Industry Petitioners argue, “simply captures the results from units that happened to be burning wastes with low levels of that particular pollutant during testing,” and this reality makes it harder for SRI units to meet emission standards for all pollutants at the same time. No. 11-1125 Indus. Pet’rs’ Reply Br. 8 (emphasis omitted). This argument fails because the Industry Petitioners have not demonstrated that the Agency considered impermissible factors, failed “to consider important aspect[s] of the problem,” or offered an unreasonable explanation for its decision when setting the MACT floors for SRIs. See State Farm, 463 U.S. at 43. Rather, their argument is a back-door attempt to challenge the Agency’s alleged failure to consider waste inputs, which we reject below at infra § III.E. 45 Petitioners have also not shown that it is infeasible for the SRI units to meet the MACT floor standards or that any individual pollutant standard was not achieved in practice by an existing SRI unit. They merely assert, without evidence, that no existing unit burning high sulfur garbage can match the SO2 performance achieved by the unit the EPA used to set SO2 standards because that latter unit was burning low sulfur waste at the time of the emissions testing. But MACT floors are not unreasonable simply because they are difficult to achieve in practice. As such, we find the EPA’s pollutant-by- pollutant approach to be a reasonable interpretation and application of the statute, and deny the Industry Petitioners’ challenge to the EPA’s use of this approach. C. THE ENERGY-ASSESSMENT REQUIREMENT The Major Boilers Rule and the Area Boilers Rule generally require sources with existing boilers to perform a one-time energy assessment. In the assessment, facilities must “identify energy conservation measures”—such as “process changes or other modifications to the facility”— “that can be implemented to reduce the facility energy demand,” thereby “reduc[ing] fuel use.” 2011 Area Boilers Rule, 76 Fed. Reg. at 15,573; see also 2011 Major Boilers Rule, 76 Fed. Reg. at 15,632. While facilities must conduct the assessment, they need not implement its conclusions. See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,573; 2011 Major Boilers Rule, 76 Fed. Reg. at 15,632. The logic behind the assessment is straightforward. Boilers produce HAP emissions when fuel is combusted. Less combustion means fewer emissions. The EPA primarily justified the assessment as a beyond-the-floor MACT requirement under section 7412(d)(2). See 2011 Area Boilers 46 Rule, 76 Fed. Reg. at 15,573; 2011 Major Boilers Rule, 76 Fed. Reg. at 15,632. With respect to certain biomass and oil- fired boilers located at area sources, the assessment was justified as a GACT management practice under section 7412(d)(5). See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,567. Industry Petitioners raise three principal challenges to the energy-assessment requirement, none of which have purchase. The first challenge claims that the energy assessment regulates aspects of facilities that are off limits to the EPA— namely, the energy needs supplied by regulated boilers. Petitioners point to the language of the CAA, which requires the EPA to “list . . . categories and subcategories of major sources and area sources” of enumerated air pollutants. 42 U.S.C. § 7412(c)(1). “For the categories and subcategories the Administrator lists, the Administrator” must set “emissions standards under” section 7412(d). Id. § 7412(c)(2). As relevant here, the EPA defined the source categories to include “industrial boilers and commercial and institutional boilers.” 2011 Area Boilers Rule, 76 Fed. Reg. at 15,557; 2011 Major Boilers Rule, 76 Fed. Reg. at 15,608. To the extent the assessment concerns parts of the facility other than the boiler itself, the Industry Petitioners claim it exceeds the EPA’s authority. The Industry Petitioners misapprehend both the scope of the assessment and the CAA. The assessment requires facilities to evaluate energy systems “located on the site of the affected boiler,” including “[p]rocess heating[,] compressed air systems[,] . . . facility heating, ventilation, and air conditioning systems,” and “[o]ther systems that use steam, hot water, process heat, or electricity, provided by the affected boiler.” 40 C.F.R. § 63.11237; see id. § 63.7575. Based on 47 that evaluation, facilities must compile a “comprehensive report detailing the ways to improve efficiency, the cost of specific improvements, [anticipated] benefits, and the time frame for recouping those investments.” 40 C.F.R. pt. 63, subpt. JJJJJJ tbl.2; id. pt. 63, subpt. DDDDD tbl.3. Contrary to the Industry Petitioners’ argument, the EPA has not “regulate[d] virtually every piece of equipment at all affected facilities.” No. 11-1141 Indus. Pet’rs’ Br. 19. Only “energy use systems” that “us[e] energy clearly produced by affected boilers” must be evaluated; facilities need not review the “total aggregation of all individual energy using segments of a facility.” 2013 Area Boilers Rule, 78 Fed. Reg. at 7,493 (emphasis added); see also 2013 Major Boilers Rule, 78 Fed. Reg. at 7,188. The assessment focuses on “discrete segments of a facility,” such as “production area[s] or building[s]” associated with a particular boiler. 2013 Area Boilers Rule, 78 Fed. Reg. at 7,493; see 2013 Major Boilers Rule, 78 Fed. Reg. at 7,188. Energy requirements satisfied by other sources—not by a HAP-emitting boiler—fall outside of that mandate. See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,573 (limiting the assessment to “specific portions of the source that directly affect emissions from the affected boiler”). And regulated facilities are under no obligation to implement the results they reach. In essence, rather than setting inflexible and generally applicable beyond-the-floor numeric limits, the EPA required facilities to take stock of the actual energy demands placed on their boilers. By reducing energy demands and associated fuel consumption, facilities could reduce HAP emissions. That requirement is more measured than the Industry Petitioners contend. And that measured requirement falls within the EPA’s statutory authority. The CAA authorizes the EPA to regulate 48 “major sources and area sources” of HAPs, and to subdivide those sources into categories and subcategories. 42 U.S.C. § 7412(c)(1), (c)(2). To Industry Petitioners, the authority to subdivide sources means the EPA may only regulate the narrowest applicable categorization—in this instance, commercial and industrial boilers. But the statute does not require so rigid a reading. While the EPA is permitted to subdivide sources, each subdivision remains a component of either a major or area “source.” Dividing sources into categories and subcategories does not make them any less of a “source” subject to the EPA’s regulation. For that reason, the EPA explained that the Rules reach, respectively, “[a]ny area source facility using a boiler,” 2011 Area Boilers Rule, 76 Fed. Reg. at 15,555 (emphasis added), and “major source facilities having affected boilers or process heaters,” 2011 Major Boilers Rule, 76 Fed. Reg. at 15,613 (emphasis added). Likewise, the regulations implementing the energy assessment requirement apply to those who “own or operate an existing affected boiler,” not merely to the boiler itself. 40 C.F.R. § 63.11214(c); see id. § 63.7485. Going further, the relevant part of the CFR applies, by its own terms, to the “owner or operator of any stationary source.” Id. § 63.1(b)(1). The Congress’s definition of the terms major and area source supports this reading. At bottom, both terms refer to a “stationary source.” See 42 U.S.C. § 7412(a)(1), (a)(2). Stationary source, in turn, means “any building, structure, facility, or installation which emits or may emit any air pollutant.” Id. § 7411(a)(3). Against that backdrop, the Rules apply to any “building, structure, facility, or installation” that contains a boiler emitting the specified HAPs. The EPA’s 49 regulatory authority reaches the relevant stationary source, of which the boiler is part. That the EPA may regulate stationary sources does not mean it may regulate every nook and cranny of those sources. The CAA directs its authority to the establishment of emission standards; it does not provide some general power to superintend the business processes of plants and manufacturing facilities. In this case, however, we have no occasion to parse the precise parameters of the EPA’s authority to regulate aspects of area sources. It is enough to conclude that the challenged energy assessment—which applies only to systems that “us[e] energy clearly produced by affected boilers”—falls within the EPA’s authority under the CAA. 2013 Area Boilers Rule, 78 Fed. Reg. at 7,493; 2013 Major Boilers Rule, 78 Fed. Reg. at 7,188. In the remaining two challenges, the Industry Petitioners take issue with the EPA’s justification of the energy assessment as a beyond-the-floor MACT standard and a GACT management-practice standard. We reject both challenges. The assessment represents a valid beyond-the-floor MACT standard.13 As discussed, after the Agency sets the MACT floor, it must determine “whether stricter standards are ‘achievable,’” Nat’l Lime Ass’n, 233 F.3d at 629 (quoting 42 U.S.C. § 7412(d)(2)), considering costs, “any non-air 13 In addition to challenging the assessment as a beyond-the- floor measure, the Industry Petitioners claim the assessment represents an invalid work-practice standard. But “[t]he energy assessment is not . . . a work practice standard, and EPA makes no claim that it is.” No. 11-1141 EPA Br. 47 n.9. Therefore, we decline to address that contention. 50 quality health and environmental impacts and energy requirements,” 42 US.C. § 7412(d)(2). These “measures, processes, methods, systems or techniques includ[e], but [are] not limited to, measures which— (A) reduce the volume of, or eliminate emissions of, such pollutants through process changes, substitution of materials or other modifications, . . . (D) are design, equipment, work practice, or operational standards . . . or (E) are a combination of the above. Id. The EPA primarily justified the energy assessment as a beyond-the-floor measure designed to identify “process changes or other modifications to the facility” that would reduce fuel use and thereby reduce hazardous emissions. 2011 Area Boilers Rule, 76 Fed. Reg. at 15,573; 2011 Major Boilers Rule, 76 Fed. Reg. at 15,632. The Industry Petitioners argue that the EPA skipped a step, imposing the energy assessment as a beyond-the-floor measure without first setting a relevant MACT floor. That is incorrect. The EPA first set a numeric MACT emissions limit for the categories and subcategories of sources subject to the energy assessment. See 40 C.F.R. pt. 63, subpt. JJJJJ tbl.1; id. pt. 63, subpt. DDDDD tbl.2. The energy assessment represents a step beyond that—a measure designed to discover energy efficiencies that, once implemented, could decrease emissions below the floor level. Before setting a beyond-the-floor measure, the EPA must consider whether it is “achievable” based on a number of 51 factors, among them cost, “non-air quality health and environmental impacts and energy requirements.” 42 US.C. § 7412(d)(2). The EPA did so here. To begin, the EPA adequately considered costs. In the EPA’s estimation, “[t]he one-time cost of an energy assessment ranges from $2500 to $55,000 depending on the size of the facility.” 2010 Proposed Area Boilers Rule, 75 Fed. Reg. at 31,907; National Emission Standards for Hazardous Air Pollutants for Major Sources: Industrial, Commercial, and Institutional Boilers and Process Heaters (2010 Proposed Major Boilers Rule), 75 Fed. Reg. 32,006, 32,026 (June 4, 2010). Because saving fuel saves money, common sense suggested that sources would often find the energy assessment “cost-effective” to implement. 2011 Area Boilers Rule, 76 Fed. Reg. at 15,568 (“By definition, any emission reduction [achieved as a result of the energy assessment] would be cost effective or else it would not be implemented.”); see also 2011 Major Boilers Rule, 76 Fed. Reg. at 15,633. In addition to costs, the EPA considered non-air quality health and environmental impacts in general terms, concluding that “improving energy efficiency reduces negative impacts on the environment.” 2010 Proposed Area Boilers Rule, 75 Fed. Reg. at 31,907; 2010 Proposed Major Boilers Rule, 75 Fed. Reg. at 32,026. Given the nature of the assessment, the EPA’s somewhat terse analysis of health and environmental impacts suffices. Performing the assessment involves rudimentary tasks—examining the boiler and associated energy systems and drafting a report—that do not impose meaningful health or environmental impacts. The same holds for the EPA’s consideration of energy use requirements. Facilities would expend very little energy in conducting the one-time assessment, and could conserve 52 energy by implementing the results. The assessment therefore represents a lawful beyond-the-floor measure. We also find that the assessment is a valid GACT management practice. With respect to area sources, the EPA has discretion to require the use of “generally available control technologies or management practices . . . to reduce emissions of hazardous air pollutants.” 42 U.S.C. § 7412(d)(5). The EPA justified the energy assessment as a GACT management practice for oil- and biomass-fired boilers. See 2011 Area Boilers Rule, 76 Fed. Reg. at 15,567. The Industry Petitioners challenge that justification, claiming the energy assessment—which does not require implementation—cannot “reduce emissions of hazardous air pollutants.” 42 U.S.C. § 7412(d)(5). We disagree. The EPA did not need to make implementation mandatory to make the assessment lawful. Under the CAA, the EPA may sometimes act with a soft touch, rather than a firm hand. Here, the EPA selected a soft touch, requiring an assessment but not implementation. It was not unreasonable for the EPA to conclude, “after considering the structure of the requirement, the incentives it presents, and the likely behavior of sources, . . . that sources will find it cost-effective to implement the conservation measures identified in the energy assessment.” 2011 Area Boilers Rule, 76 Fed. Reg. at 15,573. If the results were implemented, HAP emissions would be reduced. For present purposes, that is enough. For those reasons, we reject the Industry Petitioners’ challenges to the energy-assessment requirement. 53 D. RECORDKEEPING REQUIREMENT FOR CISWI UNITS Section 7429 regulates combustion units that burn solid waste; units that do not burn solid waste will generally be regulated under section 7412. RCRA defines the term “solid waste” to mean (in part) “discarded material . . . resulting from industrial [or] commercial . . . operations.” 42 U.S.C. § 6903(27); see id. § 7429(g)(6) (directing that “solid waste” carry “the meanings established by the Administrator pursuant to” RCRA). On the same day the EPA issued a rule setting emission standards for CISWI, it issued a separate rule fleshing out the meaning of solid waste in the context of combustion units. See NHSM Rule, 76 Fed. Reg. at 15,456. The NHSM Rule generally provides that “non-hazardous secondary materials that are combusted are solid wastes,”14 subject to several exceptions and exemptions. 40 C.F.R. § 241.3(a). Among the exceptions, non-hazardous secondary materials that meet certain “legitimacy” criteria do not qualify as solid waste. See id. § 241.3(b), (d). Source owners and operators may also seek a finding from the EPA that particular materials do not constitute solid waste when combusted by a third party. Id. § 241.3(c). And the rule exempts altogether a variety of materials from the definition of solid waste, including “traditional fuels.” Id. § 241.2. The NHSM Rule is self-implementing: each source owner or operator must determine whether combusted materials meet the definition of solid waste. See 2011 CISWI Rule, 76 Fed. Reg. at 15,740. To ensure that owners and 14 The NHSM Rule defines non-hazardous secondary material to “mean[] a secondary material that, when discarded, would not be identified as a hazardous waste.” 40 C.F.R. § 241.2. 54 operators “review and apply” the NHSM Rule and its exceptions, the EPA issued strict recordkeeping requirements. Id. Owners and operators who determine the secondary materials they combust are not solid waste must “keep a record” justifying that decision. 40 C.F.R. § 60.2175(v). Failing to file records carries consequences. For units combusting discarded material other than traditional fuels, the failure to “keep and produce records” results in the determination that “the operating unit is a CISWI unit.” Id. §§ 60.2265, 60.2875 (containing an identical provision). Industry Petitioners challenge this last provision of the CISWI Rule.15 They argue that the EPA cannot automatically treat units that fail to keep certain paperwork as CISWI units. Section 7429 permits regulation of “solid waste incineration units”—not units whose owners fail to file paperwork. As a result, the Industry Petitioners ask this court to invalidate the regulatory provision as exceeding the EPA’s statutory authority.16 We decline the invitation. At Chevron’s first step, we find that “Congress did not speak directly, let alone clearly, to 15 In their reply brief, the Industry Petitioners clarify that they do not challenge the EPA’s authority to require sources to keep records. 16 The Industry Petitioners also argue the EPA arbitrarily failed to provide sufficient notice of the recordkeeping presumption. We disagree. The Industry Petitioners had sufficient notice of the CISWI Rule, which was promulgated after notice and comment and “give[s] fair warning of the conduct it prohibits.” Gen. Elec. Co. v. EPA, 53 F.3d 1324, 1328 (D.C. Cir. 1995) (quoting Gates & Fox Co. v. OSHRC, 790 F.2d 154, 156 (D.C. Cir. 1986)). 55 this issue.” Am. Chem. Council v. EPA, 337 F.3d 1060, 1064 (D.C. Cir. 2003). Section 7429 regulates “solid waste incineration units,” a phrase that Congress defined “plainly and broadly to include ‘a distinct operating unit of any facility which combusts any solid waste material from commercial or industrial establishments or the general public.’” NRDC I, 489 F.3d at 1257 (emphasis omitted) (quoting 42 U.S.C. § 7429(g)(1)). In NRDC I, we vacated an earlier iteration of the CISWI Rule that narrowed the scope of that definition beyond what its language would bear. See id. at 1257-58. When the Congress commanded the EPA to regulate units that burn “any” solid waste, the Congress meant what it said. See id. In this case, the EPA included within the revised CISWI Rule a presumption designed to enforce the Congress’s command. Section 7429 nowhere addresses whether the EPA may establish presumptions to ensure its regulations reach all sources burning solid waste. At the same time, the Congress plainly intended the EPA to regulate sources burning “any” solid waste, a goal presumably advanced by the recordkeeping presumption. See id. Against that backdrop, we cannot conclude that the presumption offends the text or purpose of section 7429. Moving to Chevron’s second step, we conclude the recordkeeping presumption is reasonable. In American Chemistry Council, we upheld a regulation issued under RCRA defining hazardous waste to include any mixture or derivative of hazardous substances. See 337 F.3d at 1064-65. “[B]ecause many mixtures of and derivatives from hazardous wastes are themselves hazardous, it [was] reasonable for the EPA to assume that all such mixtures and derivatives are hazardous until shown otherwise.” Id. at 1065. In that 56 context, it made good sense for the EPA to “[p]lac[e] the burden upon the regulated entity” to show that a given substance lacked “hazardous characteristic[s].” Id. Similar reasoning applies here. The EPA crafted the presumption to reach sources likely to be burning solid waste, namely, those burning discarded materials other than traditional fuels. See 42 U.S.C. § 6903(27) (defining “solid waste” to include, among other things, “discarded material”); 40 C.F.R. § 241.2 (exempting traditional fuels, defined as “materials that are produced as fuels . . . that have not been discarded,” from the definition of solid waste). Such sources are subject to strict recordkeeping requirements. See 40 C.F.R. § 60.2175(v). Within those confines, placing the burden on unit operators who have the mandatory obligation and the information to establish their non-regulable status is reasonable. Cf. Am. Chem. Council, 337 F.3d at 1065. There is, however, a difference between the presumption in this case and the one we upheld in American Chemistry Council. The CISWI recordkeeping presumption appears to turn on the failure to file paperwork, rather than the presence of a regulated substance. However broadly the Congress defined “solid waste incineration unit” in section 7429, the Congress did not allow for the regulation of non-waste burning sources—even when those sources fail to file paperwork. Indeed, had the EPA attempted to regulate sources based purely on a failure to file paperwork, we may well have reached a different conclusion. But the CISWI presumption does not stretch so far. As explained, the presumption depends on factors beyond the mere failure to keep records. Sources subject to the presumption burn materials likely to qualify as solid waste, 57 and must satisfy demanding recordkeeping requirements. The EPA acted reasonably when it presumed such sources were burning solid waste. Despite the provision’s narrow reach, the Industry Petitioners fear it will sweep up sources not burning solid waste. To the extent that possibility exists, sources wrongfully regulated as CISWI have multiple forms of recourse. Most obviously, sources can prepare and file the records they were already required to make under 40 C.F.R. § 60.2175(v). They can also avail themselves of procedures designed to identify non-waste materials in 40 C.F.R. § 241.3. The existence of these safety valves calms concerns that the presumption will regulate non-waste burning sources. We therefore reject the Industry Petitioners’ challenges to the recordkeeping presumption.17 E. WASTE-STREAM VARIANCE FOR SRI UNITS The EPA regulated SRIs as a subcategory in the CISWI Rule. See Memorandum from Eastern Research Group, Inc., to Toni Jones, U.S. Environmental Protection Agency, CISWI Emission Limit Calculations for Existing and New Sources for the Reconsideration Final Rule (Jones Mem.) (Nov. 16, 2012) (No. 11-1125 J.A. 1159, 1162). There are 28 SRI units, 17 The Industry Petitioners also contend that the CISWI Rule functions as a form of injunctive relief in violation of 42 U.S.C. § 7413(a). That is incorrect. The provision is neither styled nor operated as a form of injunctive relief. Cf. 42 U.S.C. § 7413(a) (permitting the Administrator to issue, among other forms of relief, “an administrative penalty order” or “an order requiring [a person in violation of EPA regulations] to comply with such requirement or prohibition”). 58 all of which are located in Alaska, and the EPA had emissions data for nine of them. Id. As explained supra § I.B.3, the EPA used the pollutant-by-pollutant approach to establish MACT emission standards for these units. For new-unit standards, the EPA determined which of the nine units had the lowest emissions for a particular pollutant and set the MACT floor for that pollutant at the level achieved by the identified unit. See 42 U.S.C. § 7429(a)(2) (explaining that MACT floors for new units must be set at “the emissions control that is achieved in practice by the best controlled similar unit”). When setting MACT floors for existing units, the EPA had to calculate the average level of emissions achieved by the best performing 12 per cent of units. See id. It therefore determined which four sources had the lowest emissions for a given pollutant and set the emissions standard for that pollutant at the average level achieved by those four units. The Industry Petitioners argue that the EPA’s approach was unlawful because it failed to account for the unique role that waste inputs play in emissions from SRIs. Unlike larger incinerators, SRIs burn small batches of waste at a time. Some batches include cleaner waste, such as wood and cardboard, while others include waste, such as sewage, that generates large quantities of SO2 and other pollutants. Moreover, existing SRIs cannot use certain “end-of-stack” control technologies like wet scrubbers due to the Alaskan climate. The Industry Petitioners thus contend that emissions from SRIs are more closely tied to waste input than are emissions from other types of incinerators. This difference, they assert, required the EPA to take into account, when determining which SRI units were best performing for MACT floor purposes, the kind of waste an SRI unit was burning at the time of testing. Because the Agency did not do so, the 59 Industry Petitioners contend the MACT standards for SRIs are arbitrary and capricious. We disagree. To support their challenge, the Industry Petitioners advance two arguments, neither of which has merit. Petitioners first point to section 7429(a)(3), which directs the EPA to base emission standards on “methods and technologies for removal or destruction of pollutants before, during, or after combustion.” 42 U.S.C. § 7429(a)(3). According to the Industry Petitioners, this language requires the EPA to identify best performing units for MACT purposes by considering which units are best at removing or destroying pollutants. The Industry Petitioners assert that the Agency did not do this. Instead, they contend, the EPA set standards without regard to whether that unit happened to be burning cleaner waste. And, according to the Industry Petitioners, remote incinerators in Alaska cannot control their waste inputs because the core purpose of SRIs is to burn waste that is impracticably far from municipal landfills. The fact that emissions levels varied dramatically during test runs for the SRI units, they claim, is thus the result of random variance in the type of waste the unit was combusting, rather than any “method” or “technology” aimed at “removing” or “destroying” pollutants. The EPA responds that the approach it adopted for SRIs complies with section 7429(a)(3) because “waste segregation”—that is, diverting dirtier waste to landfills and burning only cleaner waste—is a “method . . . for removal . . . of pollutants before . . . combustion.” See 42 U.S.C. § 7429(a)(3). In fact, during notice and comment, the EPA estimated that many SRIs would choose to comply with the MACT standards by segregating their waste instead of by installing expensive control technologies. See Jones Mem. 60 The Agency also determined that waste segregation was possible for SRIs because their waste often contained materials that could be recycled. Id. Finally, the Agency factored in any additional variance in emissions from these units by calculating the MACT floors according to the UPL formula described at supra §§ I.B.1.a, IV.C. For these reasons, the Agency contends, it did not need to consider further any variation in emissions that might be caused by differences in waste inputs for SRIs. The EPA has the better argument, based on both text and precedent. Textually, waste segregation plainly can be a “method[]” for “removal” of pollutants “before” combustion. See 42 U.S.C. § 7429(a)(3). Accordingly, the EPA, when setting MACT floors, could not have looked solely to technologies used to reduce emissions during combustion. Accord Sierra Club v. EPA (Sierra Club II), 479 F.3d 875, 883 (D.C. Cir. 2007) (per curiam). Instead, the plain language of section 7429(a)(3) requires the Agency to consider whether emission reductions can be achieved by non-combustion-related controls such as using cleaner fuels or waste inputs. Accord id. The statute supports the approach that the Agency took here. Our holding in Sierra Club II confirms that our conclusion is correct. In that case, the EPA had acknowledged that kilns emitted lower levels of pollutants when burning cleaner clay but nevertheless based MACT standards only on the emission reductions achieved by control technology during the combustion process. Id. at 882. The Agency explained that clean clay existed only in certain areas and that transportation of the clay over long distances was impractical. Id. The EPA therefore considered only those emission reductions that were attributable to “deliberate steps 61 kiln operators [took] to reduce emissions rather than to the ‘happenstance’ of being located near cleaner clay.” Id. at 883. But we rejected that approach, finding that “the Clean Air Act requires neither an intentional action nor a deliberate strategy to reduce emissions.” Id. Instead, where “non- technology factors” affect emission levels, we held the EPA must consider those effects when setting MACT floors. Id. Applying that same reasoning, the EPA acted reasonably when it decided to consider the emissions reduction that could be achieved by waste segregation in SRI units before combustion. This is true even if an element of “happenstance” plays into an SRI unit’s ability to segregate its waste. And, had the EPA instead determined that the best performers were those SRI units that most effectively reduced pollutants only during combustion, as the Industry Petitioners suggest, the resulting MACT standards may have run afoul of our holding in Sierra Club II. We cannot, as a result, find the Agency’s choice to avoid that outcome unreasonable. The Industry Petitioners’ second argument also comes up short. According to Petitioners, the EPA selected the best performers for SRIs merely because those units happened to be burning batches of cleaner waste at the time of the emissions test. They claim this happenstance resulted in test data that did not reasonably estimate the typical performance of the units, and thus misidentified the best performers. See Cement Kiln, 255 F.3d at 862 (finding that although the EPA has authority to estimate which units perform best, its methodology must “provide[] an accurate picture of the relevant sources’ actual performance”). Petitioners further argue that the Agency’s use of the UPL method to account for variability did not fix this problem because the EPA applies that method only after identifying the best performers. 62 If the record supported this argument, it might well be persuasive; in NACWA, we accepted a similar contention that the EPA’s dataset for determining MACT floors must fairly represent a unit’s typical performance. See 734 F.3d at 1146. But the record here does not support the Industry Petitioners’ position. None of the evidence on which Petitioners rely can bear the weight they would have us place on it. First, Petitioners cite evidence indicating that XTO Energy, which operates the incinerator that the EPA deemed the best performer for SO2, was burning low-sulfur “waste wood, cardboard, and oily waste” during the relevant test runs. See ConocoPhillips Co., Comment on EPA’s Proposed National Emission Standards for Hazardous Air Pollutants, EPA-HQ-OAR-2003-0119 (Feb. 12, 2012) (No. 11-1125 J.A. 1036). But the record does not show that the resulting test data were unrepresentative of XTO’s typical performance because the record says nothing about what XTO typically burns. Id. Second, Petitioners note that Drift River, the unit the EPA deemed the worst performer for SO2, had emissions results similar to XTO Energy’s when burning low-sulfur waste, but results over 1,000 times higher when burning high- sulfur waste. See id. (No. 11-1125 J.A. 1032-33). But again, the record does not say anything about the type of waste Drift River typically burns or its sulfur content; it merely demonstrates that the unit’s test results varied greatly from one run to the next. See id. Third, Petitioners point to additional test data they provided for the Kuparuk unit, a source that met the EPA’s MACT standards for NOx. See id. (No. 11-1125 J.A. 1017, 1027-28). They claim this data shows that the Kuparuk unit 63 “consistently” emits NOx levels exceeding that standard when burning sewage sludge. Id. This claim is both factually untrue—as the data reveals exceedances on only one day— and says nothing about whether the test data that the EPA used was representative of Kuparuk’s typical performance. Id. Instead, the record supports the EPA’s assertion that it gave Petitioners “multiple opportunities” to present data on the variability of waste streams for SRIs, but Petitioners never provided a reasonable empirical basis upon which the Agency could adjust the MACT standards due to this variability. The Industry Petitioners have thus not met their burden to show that the EPA’s test data was unrepresentative of SRI units’ actual or typical performance. In sum, no record evidence suggests that the current SRI emission standards are not achievable. The Industry Petitioners instead offer only general statements about the “small batch” nature of SRIs and the difficulty of using waste segregation or other controls in remote locations. These factors alone do not call into question the EPA’s assertion that controls such as waste segregation and technology upgrades are a feasible means of achieving compliance with the MACT floors that it established. See 2011 CISWI Rule, 76 Fed. Reg. at 15,730 (explaining that the MACT floors will require SRIs to employ “the best demonstrated technologies that are technologically feasible at these facilities,” such as afterburners and waste segregation, and noting that such controls “are sufficient to meet the MACT floor limits”). As a result, the EPA’s action here was reasonable; the Agency did not need to account further for waste stream variance in setting MACT floor standards for these SRI units. 64 F. CARBON MONOXIDE AS A SURROGATE In setting MACT standards for major boilers, the EPA used carbon monoxide (CO) as a surrogate for several of the HAPs that the Agency was required to regulate. A surrogate is another chemical that stands in as a proxy for the regulated HAP when the EPA sets numeric emission standards. The EPA regulates the surrogate in order to regulate the HAP, sometimes because the HAP itself is too difficult to measure. We have previously approved the use of surrogates where the EPA’s choice of a surrogate for the HAP is “reasonable.” See, e.g., Nat’l Lime Ass’n, 233 F.3d at 637. Here, the Industry Petitioners claim the EPA’s use of CO as a surrogate was not reasonable for a particular type of emissions— organic HAP emissions from coal-fired boilers—for two reasons. First, the EPA based the MACT standards on datasets that contained numerous “non-detects” for these organic HAPs. Second, the Agency failed to explain why it used CO as a surrogate for major boilers, but used work- practice standards to regulate similar emissions from other types of boilers in another rule. We find no merit in either argument and, accordingly, deny this challenge. The Industry Petitioners base their first argument on a deficiency in the EPA’s dataset for coal-fired boilers’ emissions—i.e., the dataset contained numerous “non-detects” for organic HAP emissions. A test result is considered a “non-detect” when emissions testing returns a value below that which the test methods are capable of detecting. According to the Industry Petitioners, multiple non-detects in a dataset demonstrate that it is “not feasible” to set a numeric emission standard for the affected HAP. As a result, they argue, the EPA should have set work-practice standards for 65 these HAPs under section 7412(h)(2), which permits the EPA to set such standards when it is “not feasible” to set a numeric emission standard. See 42 U.S.C. § 7412(h)(2). This argument fails because Petitioners have not explained how the non-detects here made setting numeric emissions “not feasible,” as that term is defined in the CAA. The CAA expresses a clear preference for MACT emission standards and limits the EPA’s ability to fashion more flexible work-practice standards. Compare id. § 7412(d)(3) (providing that emission standards “shall not be less stringent” than the MACT floor), with id. § 7412(h)(1) (permitting work-practice standards only if MACT standards are “not feasible”). To set a work-practice standard for these emissions, in fact, the EPA would need to find that it is infeasible to set a numeric standard for a particular HAP. Id. § 7412(h)(1). And, as relevant here, the statute defines setting a numeric standard as “not feasible” where “the application of measurement methodology to a particular class of sources is not practicable due to technological and economic limitations.” Id. § 7412(h)(2)(B). This is a high bar and Petitioners have not demonstrated that the non-detects they have identified meet it. During notice and comment, the Agency reasonably explained that non-detects are present in many of its datasets because they are inherent to the imprecision associated with measuring boiler emissions. See, e.g., 2011 Major Boilers Rule, 76 Fed. Reg. at 15,623. The EPA’s scientific conclusion that its data was nevertheless sufficient to set numeric standards receives an “extreme degree of deference.” Kennecott Greens Creek Mining Co. v. Mine Safety & Health Admin., 476 F.3d 946, 954-55 (D.C. Cir. 2007) (quotations omitted). And the Industry Petitioners never explain here why the particular 66 level of non-detects found in this dataset nevertheless made a numeric standard infeasible. Although the Industry Petitioners point to several comments asserting that no coal- fired boiler could meet the current numeric standards in all HAP categories, these general comments say nothing about the relevant question under the statute: whether it was feasible to establish numeric standards for organic HAP emissions in light of the non-detects in the coal-fired boiler datasets. We also reject the Industry Petitioners’ second argument that the EPA needed to explain why it established work- practice standards for other types of boilers in the unrelated “Utility MATS” rule. We take an “every tub on its own bottom” approach to the EPA’s setting of emission standards pursuant to the CAA. Sierra Club I, 353 F.3d at 986. The adequacy of the underlying justification offered by the Agency is what matters in an arbitrary-and-capricious review—not what the Agency did on a different record concerning a different industry. Id. As a result, we cannot find that it was unreasonable for the EPA to use CO as a surrogate in setting numeric standards for coal-fired boilers on this basis. Nor can we find that the EPA was required on reconsideration to explain the discrepancy between its approach to organic HAP emissions in these two rules, as Petitioners assert. See id. at 987 (“EPA could have noted where the bases for its decision in this case differed from those with respect to other decisions in other cases, as was done in the EPA’s brief to this court . . . but such explanations are not required given the different contexts of the v [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/cases/4020089. Public record. Not legal advice.