Full opinion text
Opinion for the Court filed PER CURIAM. PER CURIAM. TABLE OF CONTENTS I. BACKGROUND.1036 A. Statutory Framework.1037 B. The NOx SIP Call.1037 C. The Original Section 126 Rule-Conditional Findings.1038 D. Revised Section 126 Rule-Final Findings.1039 II. COMMON AND GENERAL ISSUES. 1040 A. Scrivener’s Error.'... 1040 B. The NOx SIP Call and § 126 . 1044 C. Significant Contribution.1048 D. Emission Limitation Determinations.1051 1. Standard of Review.1051 2. The Integrated Planning Model.1052 3. EGU Growth Factors.1053 4. Non-EGU Budget Determinations.1055 5. Local Regulation and Permit Trading.1055 E. Regulation of “Future” Sources.1056 F. The Dorris Report.1058 III. NON-ELECTRIC GENERATING UNIT ISSUES.1060 A. Alleged Budget Allocation Errors.1060 B. Treatment of Cogenerators.1061 C. Source-Specific Issues.1063 1. AK Steel Corporation.1063 2. New Boston Coke Corporation.1064 IV. FACILITY-SPECIFIC ISSUES .1064 A. Midland Cogeneration Venture .1065 B. Indiana Municipal Power Agency .1065 V. PITTSBURGH.1066 VI. CONCLUSION.1067 In response to petitions from several northeastern states that alleged that nitrogen oxide emitted in neighboring states was harming their local air quality, the Environmental Protection Agency promulgated a rule that requires many NOx-emitting facilities in several midwestern and southeastern states to conform to emission limits set by the EPA and to participate in an emissions trading program. Numerous petitioners challenge the rule as inconsistent with the Clean Air Act, arbitrary and capricious, and technically deficient. We uphold most aspects of the rule but remand several particulars to the Agency for reconsideration. I. BACKGROUND On January 18, 2000, the Environmental Protection Agency (“EPA”) issued its final rule to control emissions of nitrogen oxide (“NOx”) under section 126 of the Clean Air Act (“CAA”). 42 U.S.C. § 7426. Under certain conditions, NOx combines with hydrocarbons in the atmosphere to create ozone, commonly known as “smog.” In the January rule, the EPA made final its findings that stationary sources of NOx emissions in twelve upwind states and the District of Columbia contribute significantly to ozone nonattainment in northeastern states. This finding triggers direct federal regulation of stationary sources of NOx in the upwind states. The rule further established a “cap and trade” system for NOx emissions within each upwind jurisdiction. Covered sources must obtain NOx emission allowances to cover their emissions, adopt ' additional emission controls, or cease operations. Numerous petitions for review challenge various aspects of the rule. A. Statutory Framework Under the Clean Air Act, the EPA promulgates national ambient air quality standards (“NAAQS”) for criteria air pollutants, including tropospheric ozone. See 42 U.S.C. § 7409. The EPA then designates those areas of the United States that fail to meet the various NAAQS. 42 U.S.C. § 7407(d). States, in turn, are required to adopt state implementation plans (“SIPs”) providing for the attainment of the NAAQS. 42 U.S.C. § 7410. The SIPs are submitted to the EPA for approval, and may be revised at the EPA’s insistence if found to be inadequate to ensure maintenance of the NAAQS or public health. States that fail to comply with these requirements are subject to various sanctions and the imposition of a Federal Implementation Plan (“FIP”). 42 U.S.C. § 7509. Much air pollution is a local or regional problem. Some pollution, however; is caused or augmented by emissions from other states. Emissions from “upwind” regions may pollute “downwind” regions. Several provisions of the CAA are designed to address such transboundary air pollution. In particular, section 110(a)(2)(D)(i)(I) of the Act requires states to prohibit emissions within the state in amounts that will “contribute significantly to nonattainment in, or interfere with maintenance by, any other State” of the NAAQS. 42 U.S.C. § 7410(a)(2)(D)(i)(I). CAA section 126 provides a mechanism whereby downwind states may petition the EPA to directly regulate upwind sources of pollution. Under section 126(b), 42 U.S.C. § 7426(b), a downwind state “may petition the Administrator for a finding that any major source or group of stationary sources emits or would emit any air pollutant in violation” of CAA section 110(a)(2)(D). Once the EPA makes a section 126(b) finding, section 126(c) provides that: it shall be a violation of this section and the applicable implementation plan in such State — • (1) for any major proposed new (or modified) source with respect to which a finding has been made under subsection (b) of this section to be constructed or to operate in violation [of this section or section 110], or (2) for any major existing source to operate more than three months after such finding has been made with respect to it. 42 U.S.C. § 7426(c). The Administrator may allow the continued operation of existing sources beyond three months provided such sources comply with emission limitations and compliance schedules provided by the Administrator which “bring about compliance ... as expeditiously as practicable, but in no case later than three years after the date of such finding.” Id. At issue in this case is the extent of the EPA’s authority to make findings and directly regulate sources in upwind states under section 126, and whether the EPA’s section 126 rule was arbitrary and capricious or contrary to law. B. The NOx SIP Call In October 1998, the EPA issued a final rule calling upon twenty two states and the District of Columbia to revise their ozone SIPs to address interstate air pollution (aka “interstate transport”). See Finding of Significant Contribution and Rulemaking for Certain States in the Ozone Transport Assessment Group Region for Purposes of Reducing Regional Transport of Ozone, 63 Fed. Reg. 57,356 (1998) (“NOx SIP Call”). Concluding that upwind states contribute significantly to ozone nonattainment problems in downwind states, the EPA required each jurisdiction to promulgate a new SIP to reduce NOx emissions. This “NOx SIP call” required states to reduce NOx emissions by the amount that could be accomplished by emission controls capable of reducing emissions at a cost of $2,000 or less per ton. Under the rule, revised SIPs were due by September 30,1999, and SIP provisions covering stationary sources had to be implemented by May 1, 2003. Failure to submit an adequate NOx SIP by the deadline would result in implementation of a FIP by the EPA. In other words, if the states do not submit a plan for meeting their CAA obligations, the EPA will impose one of its own. C. The Original Section 126 Rule-Conditional Findings In August 1997, eight states submitted petitions requesting that the EPA find that stationary sources in upwind states contribute significantly to downwind air pollution. Specifically, the petitioning states sought findings pursuant to CAA section 126(b), 42 U.S.C. § 7426(b), that specified sources or categories thereof are the source of NOx emissions that contribute significantly to ozone nonattainment in the petitioning states in violation of CAA section 110(a)(2)(D). 42 U.S.C. § 7410(a)(2)(D). Each petition further sought to have the EPA implement direct federal regulation of stationary sources in upwind states, primarily electric generating facilities and fossil-füel fired industrial boilers and turbines. Because the section 126 petitions raised many of the same issues as the NOx SIP call, and would require comparable emission reductions, the EPA coordinated its response to the section 126 petitions with the NOx SIP call rulemaking. In a final rule published on May 25, 1999, the EPA determined that NOx emissions in twelve states and the District of Columbia contribute significantly to nonat-tainment of the one-hour ozone NAAQS in Connecticut, Massachusetts, New York, and Pennsylvania. Findings of Significant Contribution and Rulemaking on Section 126 Petitions for Purposes of Reducing Interstate Ozone Transport, 64 Fed. Reg. 28,250 (May 25, 1999) (“May 1999 Rule”). The twelve states are Delaware, Indiana, Kentucky, Maryland, Michigan, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Virginia, and West Virginia. Rather than make section 126 findings at that time, however, the EPA determined that it was appropriate to postpone such findings pending the resolution of the NOx SIP call process. Accordingly, the EPA issued a rule providing that the findings would automatically be deemed made with regard to sources from a given state should that state fail to comply with a NOx SIP- call deadline. The EPA based this decision on the judgment that full compliance with the NOx SIP call would obviate the need for section 126 findings. Once made, the section 126 findings would require covered sources to come into compliance no later than May 1, 2003. Sources that failed to comply by that date would be required to cease operations. D. Revised Section 126 Rule-Final Findings Subsequent to the completion of the section 126 rulemaking, this court issued two orders which caused the EPA to change course. First, on May 14, 1999 this court remanded the EPA’s proposed revisions to the ozone NAAQS. American Trucking Ass’ns v. EPA, 175 F.3d 1027, reh’g granted in part and denied in part, 195 F.3d 4 (D.C.Cir.1999), rev’d in part sub nom. Whitman v. American Trucking Ass’ns, 531 U.S. 457, 121 S.Ct. 903, 149 L.Ed.2d 1 (2001). Second, this court issued an order staying the NOx SIP call deadline. Michigan v. EPA, No. 98-1497 (D.C.Cir. May 25, 1999) (order granting stay in part). In response to these orders, the EPA revised the section 126 rule. Findings of Significant Contribution and Rulemaking on Section 126 Petitions for Purposes of Reducing Interstate "Ozone Transport, 65 Fed. Reg. 2674 (Jan. 18, 2000) (“Jan. 2000 Rule”). In particular, the EPA made the requested findings of significant contributions, granting the relevant portions of the section 126 petitions and delinking the section 126 findings from compliance with the NOx SIP call. The EPA explained that it was “implementing the requirements of section 126 of the CAA in the absence of any currently effective requirement for upwind States to address the interstate pollution transport problems themselves.” Id. at 2683. Instead, the EPA’s new rule contained a provision to withdraw the relevant findings upon approval of a NOx SIP in accordance with the October 1998 NOx SIP call. As with the NOx SIP call, the EPA considered both NOx emissions and the cost of control in determining which sources contribute significantly to downwind ozone nonattainment. Based upon its analysis of the cost of emissions controls, the EPA concluded that measures which can reduce NOx emissions for $2,000 or less per ton are highly cosNeffective. May 1999 Rule, 64 Fed. Reg. at 28,299. The EPA then divided NOx emission sources into various categories and determined the level of emission reduction that would be highly cost-effective for each category. Id. at 28,300-01. The section 126 rule also established an emission allowance “cap and trade” program, known as the Federal NOx Budget Trading Program. Under this program, originally outlined in the May 1999 rule, regulated sources are allocated tradeable NOx emission allowances and are prohibited from emitting more NOx than the amount of allowances held. If a facility emits more than its initial allowance allocation, it must purchase additional allowances from another facility, reduce its emissions, or cease operations. Jan. 2000 Rule, 65 Fed. Reg. at 2733. To determine the initial allocations, the EPA established a NOx emission cap for each upwind state. Each state’s cap is based upon expected emission reductions from highly cost-effective controls in that state as of 2007. Id. at 2698. Ninety-five percent of each state’s cap is allocated proportionally among existing sources based upon each facility’s heat input. Five percent of the cap is set aside for future, as-yet-unproposed sources. Id. at 2698-99. These initial allocations will apply for the 2003-07 time period. Id. at 2700. The EPA will issue revised allocations for the 2008-12 time period, and every five years thereafter. Id. Since the issuance of the final section 126 rule, this Court has ruled on various challenges to the EPA’s NOx SIP call. In Michigan v. EPA, 213 F.3d 663 (D.C.Cir.2000), we upheld the SIP call in most respects, remanding portions of the rule to the EPA. Of greatest relevance to these proceedings, we upheld the EPA’s analy-ses of interstate transport of NOx emissions and its use of cost-effectiveness criteria in determining which upwind sources “contribute significantly” to nonattainment in downwind states. Subsequently, we entered an order amending the deadline for full implementation of NOx SIP revisions from May 1, 2003 to May 31, 2004. Michigan v. EPA, No. 98-1497, 2000 WL 1341477 (D.C.Cir. Aug. 30, 2000) (order denying motion to stay mandate pending petition for certiorari). After the EPA published the final section 126 rule in January 2000, numerous groups petitioned this Court for review. Among the petitioners are a group of upwind states from the midwestern and southeastern United States (“MW & SE State Petitioners”); utilities and other operators of electric generating facilities (“Non-State Petitioners”); companies that operate non-electric generating/industrial facilities (“Non-EGU Petitioners”); and several individual companies that have facility-specific concerns (“Facility — Specific Petitioners”). A group of northeastern states (“NE State Petitioners”) also petitioned for review alleging that the EPA’s rule did not go far enough in controlling upwind NOx emissions. The northeastern states otherwise intervened in support of the EPA, as did a group of environmental organizations. The various petitions for review were consolidated into this case. II. COMMON AND GENERAL ISSUES A. Scrivener’s Error The Clean Air Act Amendments of 1990 eliminated a subsection of § 110 of the Clean Air Act (“CAA”), causing § 110(a)(2)(E) to be renumbered as § 110(a)(2)(D). See Clean Air Act, Pub.L. No. 101-549, sec. 101(b), § 110(a)(2)(D), 104 Stat. 2399, 2404 (1990) (codified at 42 U.S.C. § 7410(a)(2)(D)). The Amendments correspondingly updated several references to § 110(a)(2)(E)(i) that had appeared in § 126 of the Clean Air Act, but changed them to read “section 110(a)(2)(D)(ii).” See Clean Air Act, Pub.L. No. 101-549, sec. 109(a), § 126(b)-(c), 104 Stat. at 2469-70 (codified at 42 U.S.C. § 7426). The 1990 Amendments thus not only substituted “(D)” for “(E)” in § 126, as necessitated by the renumbering, but also substituted “(ii)” for “(i).” The EPA, which contends that the Congress amended § 126 only in order to update the cross-references so as to preserve the status quo ante, claims that this substitution of “(ii)” for “(i)” was “inadvertent[].” May 1999 Rule, 64 Fed. Reg. at 28,267/3. The agency therefore construes § 126 as if this “inadvertence” had not occurred, i.e., as if that section referred to § 110(a)(2)(D)(i). See id. The Non-State Petitioners, by contrast, argue that § 126 should be read as written, that is, to refer to § 110(a)(2)(D)(ii). Section 126 gives a state the right to petition the EPA to find “that any major source or group of stationary sources [in another state] emits or would emit any air pollutant in violation of the prohibition of’ a subsection of § 110(a)(2)(D), the subsection here at issue. 42 U.S.C. § 7426(b). As we have noted, the ability of such a source or group of sources to operate is severely constrained once such a finding is made. 42 U.S.C. § 7426(c). The constraints in § 126(c) are triggered by the “prohibition” in whichever subsection of § 110(a)(2)(D) it is that § 126 cross-references. Section 110(a)(2)(D) provides that a state implementation plan (“SIP”), which' describes how a state plans to comply with the National Ambient Air Quality Standards (“NAAQS”), must (D) contain adequate provisions— (i) prohibiting ... any source or other type of emissions activity within the State from emitting any air pollutant in amounts which will' — ■ (I) contribute significantly to nonat-tainment in, or interfere with maintenance by, any other State with respect [to the NAAQS] or (II) interfere with [various other] measures. (ii) insuring compliance with the applicable requirements of sections 7426 [CAA § 126] and 7415 [CAA § 115] of this title (relating to interstate and international pollution abatement). 42 U.S.C. § 7410(a)(2)(D). Thus, prior to the 1990 Amendments, § 126 provided an avenue by which a state could compel the EPA to enforce emissions limitations upon a neighboring state the emissions from which contributed to its own nonattainment of the NAAQS. The EPA argues that § 126 should still be read to have this effect, notwithstanding the substitution of “(ii)” for “(i)” therein. Reading a statute contrary to its seemingly clear meaning is permissible “[i]f ‘the literal application of a statute will produce a result demonstrably at odds with the intentions of its drafters.’ ” Mova Pharm. Corp. v. Shalala, 140 F.3d 1060, 1068 (D.C.Cir.1998) (quoting United States v. Ron Pair Enterprises, 489 U.S. 235, 242, 109 S.Ct. 1026, 103 L.Ed.2d 290 (1989)). We will not, however, invoke this rule to ratify an interpretation that abrogates the enacted statutory text absent an extraordinarily convincing justification: [T]he court’s role is not to “correct” the text so that it better serves the statute’s purposes, for it is the function of the political branches not only to define the goals but also to choose the means for reaching them.... Therefore, for the EPA to avoid a literal interpretation at Chevron step one, it must show either that, as a matter of historical fact, Congress did not mean what it appears to have said, or that, as a matter of logic and statutory structure, it almost surely could not have meant it. Engine Mfrs. Ass’n v. EPA, 88 F.3d 1075, 1089 (D.C.Cir.1996). The EPA’s reading of the reference in § 126 to § 110(a)(2)(D)(ii) to mean § 110(a)(2)(D)(i) meets this test. The cross-references to § 110(a)(2)(D)(ii) that appear in § 126 clearly do not reflect the intent of the Congress. Although the cross-references as written “point[] in one direction, all the other evidence from the statute points the other way,” United States Nat’l Bank of Oregon v. Independent Ins. Agents of America, Inc., 508 U.S. 439, 455, 113 S.Ct. 2173, 124 L.Ed.2d 402 (1993). See Thomas W. Merrill, Golden Rules for Transboundary Pollution, 46 Duke L.J. 931, 955 n.124 (1997) (“[S]ection 126(b) contains what appears to be a typographical error which, if read literally, would render the EPA’s obligation to make [a § 126] finding meaningless”). For example, although § 126 twice refers to the “prohibition of section 7410(a)(2)(D)(ii) [CAA § 110(a)(2)(D)(ii)],” there is no literal “prohibition” in that section — whereas there is in § 110(a)(2)(D)(i) (“prohibiting ... any source”). The petitioners dismiss this point, arguing that “prohibition” is not a term of art and that it easily embraces the directive of § 110(a)(2)(D)(ii) to “insur[e] compliance with the applicable requirements of sections 7426 [CAA § 126] and 7415 [CAA § 115].” For support, the petitioners note that the third and final reference to § 110 in § 126 refers to the “requirements contained in section 7410(a)(2)(D)(ii) [CAA § 110(a)(2)(D)(ii)].” 42 U.S.C. § 7426(c). Although the “requirements” of these sections certainly in-elude some “prohibitions,” the petitioners’ argument that the two terms are “interchangeably]” stretches the ordinary meaning of the term “prohibition.” It does not, however, stretch that meaning beyond recognition. Taken alone, therefore, the usage is insufficient to prove the agency’s claim of scrivener’s error; in conjunction with the other evidence described below, however, it lends credence to the view that such an error indeed was made. A similar analysis applies to the observation that § 126 as written creates a circular cross-reference: both § 126(b) and § 126(c) refer to the “prohibition” or “requirements” of § 110(a)(2)(d)(ii), which in turn mandates compliance with “the applicable requirements of [CAA § 126].” Although a fully circular cross-reference would be absurd, the petitioners note that § 110(a)(2)(d)(ii) refers to § 126 in its entirety, rather than to §§ 126(b) and (c) alone; it thus includes the requirement of § 126(a) that a state’s SIP provide for notifying its neighbors of any major proposed new source that might affect their air quality adversely, see 42 U.S.C. § 7426(a). This reading is not unreasonable. Cf. Connecticut v. EPA, 656 F.2d 902, 907 (2d Cir.1981) (“When [CAA § 110(a)(2)(D)(ii)] requires an SIP to insure compliance with § 126, it clearly refers to subsection (a) [of § 126] only and not to the petition procedure set forth in subsection (b)”). A statute that incorporates a cross-reference that is only partially circular is not for that reason absurd, although — as in this case — such a reference may make the statute sufficiently convoluted to warrant searching for a less infelicitous construction. It is impossible to accept, however, that the Congress intended simultaneously to repeal the regulatory regime that had existed before the 1990 Amendments and to replace it with the one that the petitioners describe. See Nat’l Bank of Oregon, 508 U.S. at 454, 113 S.Ct. 2173 (eschewing “purported plain-meaning analysis” of statute as written when scrivener’s error has “distort[ed] a statute’s tiue meaning”); id. at 461 n. 10, 113 S.Ct. 2173 (holding theory of scrivener’s error constituted “best reading” of statute notwithstanding that statute as written could be coherently explained). Before the 1990 Amendments— and still today, under the EPA’s reading— § 126 provided a mechanism by which a state could compel the EPA to control emissions from sources in a neighboring state that contributed to the complaining state’s nonattainment of the NAAQS. See 42 U.S.C. § 7426(b)-(c). The petitioners argue that, by substituting “(ii)” for “(i)” in the cross-references of § 126, the Congress intended to withdraw the state’s right to force the hand of the EPA when emissions from a neighboring state contributed to its own violation of the NAAQS, and simultaneously to create a right by which a state may compel such enforcement when a neighboring state fails to meet “the requirements of [42 U.S.C. §§] 7426 and 7415 of this title [CAA §§ 126 and 115] (relating to interstate and international pollution abatement).” 42 U.S.C. § 7410(a)(2)(D)(ii). This reading makes no sense of either § 126 or § 115. As we have noted, in order to avoid circularity, the petitioners suggest that the reference to § 126 in § 110(a)(2)(d)(ii) refers only to the notification requirements of § 126(a). According to the petitioners’ reading, the 1990 amendment of §§ 126(b) and (c) gave each state the right to compel enforcement against another state that fails to provide notice of new sources and took away their right to compel enforcement against a state that actually pollutes the complaining state’s air. Even were we to assume that such a counterintuitive switch from substantive to procedural compliance could plausibly reflect congressional policy, the petitioners’ reading would still be flawed. Section 126(b) permits a state to petition the EPA to find that “any major source or group of stationary sources emits or would emit any air pollutant in violation of the prohibition of section 7410(a)(2)(D)(ii) [CAA § 110(a)(2)(D)(ii)].” 42 U.S.C. § 7426(b). The notice requirement of § 126(a), to which the’ petitioners claim this reference ultimately points, binds states only to warn their neighbors of proposed new and modified sources; it does not restrict the behavior of sources or groups of sources, whose “violation” of § 110(a)(2)(D) is the predicate for a § 126(b) finding. See id. § 7426(a). For § 126 to incorporate the reference of § 110(a)(2)(d)(ii) to § 115 is similarly anomalous. Section 115 allows a foreign nation affected by a state’s emissions to complain to the EPA, which can then require the state to revise its SIP. 42 U.S.C. § 7415. According to the petitioners, the 1990 Amendments created a new right whereby a state may compel enforcement against a neighboring state polluting a foreign country, while simultaneously abrogating that state’s preexisting right to compel enforcement against a neighboring state polluting the complaining state. That any state would be empowered to trump the EPA’s discretion in an international dispute to which it is not a party— even as it lost the power to address another state’s pollution of its own air — cannot be taken to express congressional intent if there is any plausible alternative reading of the statute. The petitioners’ suggestion that the enactment of §§ 176A and 184, 42 U.S.C. §§ 7506a, 7511c, as part of the 1990 Amendments somehow mitigates these problems is without foundation. Those sections authorize the EPA to designate a multistate “transport region” in a case where one state’s emissions affect another state’s attainment of the NAAQS; for each such region, the EPA must convene a “transport commission,” including officials from each state within the region, to advise the EPA Administrator. Id. The petitioners correctly describe these new sections as establishing, at least in part, a new approach to interstate air pollution. Because the Congress did not repeal § 126, however, this new- approach was clearly not meant to be exclusive; and neither § 176A nor § 184 renders the change in § 126 from “(i)” to “(ii)” any less linguistically or substantively anomalous. Even if the Congress had simultaneously enacted §§ 176A, 184 and 126 as written, we might not embrace the petitioners’ reading. See Environmental Defense Fund, Inc. v. EPA, 82 F.3d 451, 468 (D.C.Cir.1996) (refusing to construe a statute literally in order to avoid “absurd and futile results”). This case, however, is much clearer: the EPA has demonstrated not only that § 126 as written is at odds with congressional intent; it also offers a convincing account of how it came to be enacted nevertheless. We find it quite plausible that the Congress substituted “(ii)” for “(i)” in § 126 inadvertently in the course of a routine renumbering of statutory cross-references. Cf. In re Chateaugay Corp., 89 F.3d 942, 953-54 (2d Cir.1996) (accord regarding a post-amendment renumbering of the bankruptcy code). Because the EPA has established that the “seemingly clear statutory language does not reflect the ‘unambiguously expressed intent of Congress,’ ” Mova, 140 F.3d at 1068 (quoting Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 842, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984)), we proceed under Chevron step two to consider whether the EPA’s construction of § 126 is reasonable. Lest it “obtain a license to rewrite the statute,” id., however, we do not give an agency alleging a scrivener’s error the benefit of Chevron step two deference, by which the court credits any reasonable construction of an ambiguous statute. Rather, the agency “may deviate no further from the statute than is needed to protect congressional intent.” Id. By reading § 126 to refer to § 110(a)(2)(D)(i) — thus restoring it to the meaning it had before the 1990 Amendments, as the Congress almost certainly intended — the EPA in no way overreaches; we therefore accept its reading. B. The NOx SIP Call and § 126 The Administrator of the EPA must require a state to revise its SIP “as necessary” whenever she finds such a plan “substantially inadequate to ... comply” with various requirements of the Act, including the requirement that the plan “contain adequate provisions” to prevent sources within a state from contributing significantly to any other state’s nonattainment or nonmaintenanee of the NAAQS. Id. §§ 7410(a)(2)(D)(i)(I), 7410(k)(5). Pursuant to this authority, in October 1998 the EPA issued a request for SIP revisions, or a “SIP call,” that required 22 states and the District of Columbia to revise their SIPs in order to mitigate the interstate transport of ozone. Michigan v. EPA, 213 F.3d 663, 669 (D.C.Cir.2000) (explicating NOx SIP Call, 63 Fed. Reg. at 57,358-59). This court upheld the essential elements of the NOx SIP call in March 2000, although we remanded the rule for further proceedings with regard to three states and to certain types of sources. Id. at 695. In August 1997, during the preparation of the NOx SIP call, eight states petitioned the EPA to find, pursuant to CAA § 126(b), that “major-stationary sources or groups of sources” in specified states were contributing to the petitioning states’ failure to meet the NAAQS for ozone. 42 U.S.C. § 7426(b). In the first of the two rules challenged here, the EPA announced that because it was “operating on basically the same set of facts” in making determinations under § 126 as it had when it issued the NOx SIP call — that is, facts showing that upwind sources contributed to downwind nonattainment of the NAAQS — it would eschew making formal findings under § 126. May 1999 Rule, 64 Fed. Reg. at 28,274/3, 28,275/2. Instead, the agency made the “affirmative technical determination” that sources in upwind states were contributing to nonattainment in downwind states, and provided that a formal finding to that effect under § 126 would be deemed to be made for such sources in a state if by May 1, 2000, EPA has not either (a) approved a state’s SIP revision to comply with the NOx SIP call or (b) promulgated implementation plan provisions meeting the [CAA] section 110(a)(2)(D)(i) requirements. Id. at 28,275/2. The EPA used this “automatic trigger mechanism,” Jan. 2000 Rule, 65 Fed. Reg. at 2679/1, as part of a “coordinated approach” to the SIP call and the § 126 petitions, May 1999 Rule, 64 Fed. Reg. at 28,275/3: § 126 findings would be withheld until the conclusion of the SIP call, but would be entered automatically should a state’s response to the SIP call be either unsatisfactory or untimely. May 1, 2000 was chosen as the date for triggering the § 126 finding because § 126(c) allows the EPA to permit sources found to contribute to another state’s nonattainment to continue to operate for no more than three years after the date of such a finding. 42 U.S.C. § 7426(c). For findings made on May 1, 2000, the three-year clock would expire on May 1, 2003 — the same date by which states were required to have implemented controls over sources of interstate ozone under the original NOx SIP call. See NOx SIP Call, 63 Fed. Reg. at 57,308/1. The congruence between the two schedules was disrupted by an order of this court staying the EPA’s original SIP call deadline. See Michigan v. EPA, No. 98-1497 (D.C.Cir. May 25, 1000); see also Michigan v. EPA, No. 08-1407, 2000 WL 1341477 (D.C.Cir. Aug. 30; 2000) (ordering new deadline of May 31, 2004 for implementation of SIPs that are revised pursuant to the SIP call). The extended timetable for the SIP call led the EPA to determine that “the circumstances under which the linkage between action on the section 126 petitions and the NOx SIP call was appropriate are no longer present.” Jan. 2000 Rule, 65 Fed. Reg. at 2680/1; see also id. at 2676/2. The EPA therefore abandoned the automatic trigger mechanism and instead simply made the § 126 findings. See id. at 2679/1. The EPA maintains that its approach is necessitated by the “language and purposes of section 126” and that it is consistent with “the language of section 110, the cooperative federalism structure of title I of the CAA, [and this] court’s decision to stay the deadlines for States to submit SIP revisions under the NOx SIP call.” Id. at 2680/1. The MW & SE State and Non-State Petitioners disagree. They argue that §§ 110 and 126 require the agency to refrain from making any § 126 findings while the NOx SIP call is ongoing, and that a similar constraint is imposed by the doctrine of “cooperative federalism” that this court has recognized as being embodied in the Act. Once the “prohibition” to which § 126 refers is understood as the “functional prohibition” upon emissions of pollutants that subsequently cross state lines, the petitioners can find little support for their position by parsing §§ 110 and 126. The Non-State Petitioners argue that [a]t a time when the relevant States were under a legal obligation to adopt “adequate [SIP] provisions” to control NOx emissions found by EPA to significantly contribute to ozone nonattainment — and at a time when States had not defaulted on that obligation — EPA lacked the authority to determine that those same States’ NOx emission sources were “in violation” of that same prohibition. Non-State Petitioners Br. at 29. This statement lacks a logical basis. It is entirely reasonable for the EPA to regard a state that is under a legal obligation to revise its plan as being, in the meantime, in violation of a functional prohibition. The petitioners’ primary argument, therefore, is that Title I of the Clean Air Act is animated by a commitment to “cooperative federalism” under which the EPA is to determine what level of air quality is required but must defer in the first instance to the judgments of the states regarding how to achieve that level. This principle, according to the petitioners, requires that a SIP call inviting states to respond to the problem of interstate transport be the preferred remedy, while direct federal regulation of sources, as authorized by § 126, must be a last resort reserved for cases in which states cannot or do not meet their SIP obligation. In Michigan this court assessed the legality of the emissions budgets that the EPA assigned to each state as. part of the NOx SIP call with respect to what we called the “Train-Virginia federalism bar.” 213 F.3d at 687. We referred there to our holding in Virginia v. EPA, 108 F.3d 1397, 1408, modified on other grounds, 116 F.3d 499 (1997), that under § 110 each state retains the power, in its SIP, to determine how it will achieve the NAAQS, and that the EPA may not dictate to a state a particular “source-specific means” to that end, a proposition for which we relied. upon Train v. Natural Resources Defense Council, Inc., 421 U.S. 60, 79, 95 S.Ct. 1470, 43 L.Ed.2d 731 (1975). This principle, of course, cannot be absolute in the face of § 126, which contemplates that in at least some circumstances the EPA will directly regulate sources within a state. See 42 U.S.C. § 7426(c). Neither Train and Virginia nor Michigan considered the interaction of their holdings with § 126, but in its 1999 rule the EPA noticed the tension between § 126 and the Train-Virginia line of cases, and properly sought to accommodate the two: Section 126 is somewhat unusual in Title I [of the CAA] in that it authorizes EPA to control sources directly, rather than providing a means for EPA to encourage states to control those sources. In that sense, it is similar to the provisions for federal implementation plans in section 110(c). With both of these provisions, Congress provided tools for direct federal action to address serious failures of state action. Nevertheless, Congress’ clear preference throughout Title I is that states are to decide and plan how they will control their sources of air pollution. May 1999 Rule, 64 Fed. Reg. at 28,273/2. This analysis led the EPA to adopt the automatic trigger approach during the pendency of the NOx SIP call. The petitioners contend that the delay in the NOx SIP call deadline, because it did not affect the “Congress’ clear preference” for state implementation decisions, should not have altered the EPA’s determination that the SIP call takes precedence over § 126. The EPA, however, is obligated not only to give to § 110 a meaning that is consistent with Train and Virginia, but also reasonably to construe § 126. The EPA, which considers the two provisions to be “independent statutory tools to address the problem of interstate pollution transport” that the EPA may deploy either singly or in tandem, Jan. 2000 Rule, 65 Fed. Reg. at 2680/1, reasonably construes both provisions. The EPA’s view accords with the position of the Second Circuit which, in Connecticut v. EPA, was presented with the converse of the question before us: Do §§ 110 and 126 require the EPA to postpone its approval of SIP revisions pending its final action upon petitions for findings under § 126(b)? 656 F.2d at 906-08. Although the Connecticut court suggested that “§ 126(b) appears to have been primarily designed as a means for resolving interstate pollution disputes in situations where an SIP is not being revised,” id. at 907 — a dictum in some tension with the EPA’s view that § 126 is “independent” of the SIP revision process- — the Second Circuit’s point was only that the EPA need not, upon receipt of a § 126 petition, suspend the SIP revision process. The court therefore concluded, properly we think, that “[a]s the substantive inquiry for decision is the same in both [§ 110 and § 126] proceedings, an argument that one proceeding must be completed as a prerequisite to a final decision in the other makes no sense.” Id. at 907; see also id. at 908 n. 4 (quoting statement of H.R. Rep. No. 95-249, at 331, reprinted in 4 A Legislative History of the Clean Air Act Amendments of 1977, at 2798 (1978), that “the § 126(b) process is designed to provide an ‘entirely alternative method and basis for preventing and abating interstate pollution’ ”) (emphasis omitted). By contrast, three critical provisions of § 126 would lose their force if, as the petitioners suggest, the lengthened timetable of the NOx SIP call were to suspend the § 126 process. First, § 126 emphatically requires that any source found to contribute to downwind nonattainment may in no event be permitted to operate for more than three years after such finding. See 42 U.S.C. § 7426(c). Second, under § 126 “[rjelief does not depend upon any action by the upwind states, as is necessary for a SIP revision.” May 1999 Rule, 64 Fed. Reg. at 28,264/2. Third, relief under § 126 is independent also of the discretionary policy preferences of the EPA; the agency must act upon a request for a § 126 finding within 60 days. See 42 U.S.C. § 7426(b). Under the EPA’s approach, of course, § 126 retains each of these features. See, e.g., Jan. 2000 Rule, 65 Fed. Reg. at 2681/1 (“Congress provided section 126 to downwind states as a critical remedy to address pollution problems ... otherwise beyond their control, and EPA has no authority to refuse to act under this section”). The petitioners argue, however, that the EPA’s construction deprives § 110 of its force because it constrains the development of the SIP: sources subject to a § 126 finding will be bound by emissions limitations set by the agency, see 42 U.S.C. § 7426(c), and by the emissions trading program, see Part II.D below, even if the state in which they are located prefers to regulate different sources or to use different methods to mitigate downwind nonat-tainment. The petitioners argue that such constraints violate § 110 as interpreted in Virginia, but they plainly do not. In Virginia, this court disapproved the EPA’s plan to reject SIPs that did not incorporate particular limits upon emissions from new cars; we held that the EPA may not, as part of the “section 110 process,” intervene in a state’s choice of how to reach the NAAQS. 108 F.3d at 1410; cf. id. at 1406 (question is what is permissible “under section 110”). We did not suggest that under § 110 states may develop their plans free of extrinsic legal constraints. Indeed, SIP development, like any environmental planning process, commonly involves decisionmaking subject to various legal constraints. That § 126 imposes one such limitation — and it is surely not the only independent provision of federal law to do so — does not affect a state’s discretion under § 110. The MW & SE State Petitioners argue in the alternative that, if §§ 110 and 126 are independent, then the EPA may select either one but cannot impose § 126 findings and a SIP call simultaneously. Neither the statute nor the states’ brief offers support for this suggestion, and the states’ suggestion that the EPA embraced it in the preamble to its second rule is without foundation. Because it is reasonable, and because the “Congress provided both [§§ 110 and 126] without indicating any preference for one over the other,” Jan. 2000 Rule, 65 Fed. Reg. at 2680/1, the EPA’s conclusion that these two provisions operate independently merits our deference under Chevron step two. See Chevron, 467 U.S. at 843, 104 S.Ct. 2778. Finally, we note that the MW & SE State Petitioners object to the EPA’s construction of 40 C.F.R. § 52.34(i), which provides that § 126 findings will be withdrawn if the EPA takes “final action” to approve a SIP or impose a FIP that will control NOx emissions that contribute to downwind nonattainment. See 40 C.F.R. § 52.34(f) (2000), promulgated at 65 Fed. Reg. at 2727. Although the rule contains no date, the agency avers that it will apply the rule only to SIPs or FIPs adopted before May 1, 2003, the § 126 deadline. The Supreme Court recently held that we should not defer to an agency’s interpretation imputing a limiting provision to a rule that is silent on the subject, lest we “permit the agency, under the guise of interpreting a regulation, to create de facto a new regulation.” Christensen v. Harris County, 529 U.S. 576, 588, 120 S.Ct. 1655, 146 L.Ed.2d 621 (2000). The Court, however, carefully limited this principle to cases in which the agency’s interpretation postdated its adoption of the rule and was not itself “subject to the rigors of ... notice and comment.” Id. (citing Reno v. Koray, 515 U.S. 50, 61, 115 S.Ct. 2021, 132 L.Ed.2d 46 (1995)). We therefore continue to grant “a high degree of deference” to an interpretation that the agency promulgates contemporaneously with its own regulation, affirming it “unless it is plainly erroneous or inconsistent with the regulation.” Jersey Shore Broad. Corp. v. FCC, 37 F.3d 1531, 1536 (D.C.Cir.1994). Here the agency contends that it imputed a date to § 52.34(f) not post hoc but “[throughout the Section 126 rulemaking.” Although the date might better have been made explicit in the preamble to the rule, the agency did clearly, albeit implicitly, assume that § 52.34(i) would apply only to SIPs promulgated before the § 126 deadline. This is evident from the agency’s express reservation for another rulemak-ing of the question whether it would “automatically withdraw the section 126 findings upon EPA approval of a later SIP revision.” Jan. 2000 Rule, 65 Fed. Reg. at 2683/2. A contrary interpretation, moreover, would apparently create a conflict between § 52.34(i) and the § 126 deadlines, the sanctity of which the EPA emphasized throughout its rulemaking. Because the EPA appears ever since the rule was promulgated to have interpreted § 52.34(f) to apply only to SIPs approved before May 1, 2003, and because this interpretation is not “plainly erroneous or inconsistent with the regulation,” Jersey Shore, 37 F.3d at 1536, we defer to the agency’s view. C. Significant Contribution Non-State Petitioners challenge the methodology by which EPA reached its findings of “significant contribution” to nonattainment of the “1-hour” ozone rule under § 126, 42 U.S.C. § 7426. EPA started with the two-step method that it had used in issuing the SIP call and that we upheld in Michigan v. EPA, 213 F.3d 663, 674-80 (D.C.Cir.2000). As we explained there, EPA first performed computer modeling to determine whether a state’s manmade NOx emissions perceptibly hindered a downwind state’s attainment. Id. at 675. For any state exceeding EPA’s threshold criteria, EPA then defined as “significant” those emissions that could be eliminated through application of “highly cost-effective” controls, namely measures costing no more' than $2,000 per ton of NOx removed. Id. Similarly, EPA relied here on the statewide threshold findings made in the SIP call and then applied the same cost-effectiveness criterion to determine which sources to include. See Findings of Significant Contribution and Rulemaking on Section 126 Petitions for Purposes of Reducing Interstate Ozone Transport, 63 Fed. Reg. 56,292, 56,301/3 (proposed Oct. 21, 1998) (“Oct. 1998 Rule”). As discussed above, see supra Part II.B, both the SIP call and the § 126 rulemak-ing are directly linked to the requirement under § 110(a)(2)(D)(i) that SIPs contain provisions prohibiting “any source or other type of emissions activity within the State from emitting any air pollutant in amounts which will ... contribute significantly to nonattainment....” § 110(a)(2)(D)(i), 42 U.S.C. § 7410(a)(2)(D)(i). But the necessary determinations are different in at least two material respects. First, whereas the SIP call exercise yielded a total amount of NOx cutback for each state, which the state was then free to achieve however it might, see Michigan, 213 F.3d at 687-88, here the mandate applies directly to sources. Second, whereas § 110(a)(2)(D)’s broad reference to “any source or other type of emissions activity” supported SIP call findings based on aggregate emissions from within each regulated state, § 126 demands that the significant contribution come from a “major source or group of stationary sources.” 42 U.S.C. § 7426(b) (emphasis added). The Non-State Petitioners argue that this latter distinction renders EPA’s reliance on the SIP call findings inadequate; the findings based on all emissions can’t determine whether stationary source emissions are sufficient. Instead of using those findings, petitioners argue, EPA needed first to make the more rigorous finding that the specified stationary sources within a given state independently met its threshold test for effect on 'downwind nonattainment. Petitioners find support for their view of the statute in Michigan, where we said that the first step in EPA’s § 110(a)(2)(D)(i) finding must show a “measurable contribution” to downwind nonattainment. 213 F.3d at 683-84. Here, EPA did not purport to satisfy such a standard on the basis of the covered stationary sources alone. Rather, it conceded, “[i]t is conceivable that modeling only the emissions from the section 126 sources would result in smaller ambient impacts downwind [compared to total man-made emissions], and.... those smaller impacts, if analyzed on the basis of the metrics and thresholds developed for State-wide [total man-made] emissions, may not exceed those thresholds.” May 1999 Rule, 64 Fed. Reg. at 28,283/1. EPA defended its approach both as a recognition of the fact that the ozone problem is due to the accumulation of emissions and as a sensible reconciliation of § 110(a)(2)(D)(i) and § 126. See id. at 28,-282-83. On the need for some aggregation, of course, there can be no quarrel. Congress’s use of the phrase “group of ... sources” plainly reflected a decision to act against sources whose emissions, while harmless individually, could become harmful when combined with others. And, given the relevant statutory provisions, it was reasonable for EPA to link its stationary source findings to the significance of a state’s total NOx emissions. By speaking of stationary sources that emit pollutants “in violation of the prohibition of [§ 110(a)(2)(D)(i)],” Congress clearly hinged the meaning of § 126 on that of § 110(a)(2)(D)(i). EPA reasoned that if it treated any state’s entire manmade emissions as the controlling aggregate for both purposes and found a “significant contribution,” “then the State’s section 126 sources may be subject to SIP controls.” Id. at 28,282/3 (emphasis added). In other words, a source can be subject to § 126 controls only if it is at least at risk of being subject to SIP controls. The effect, of course, is to displace the discretion the state would enjoy in the SIP process under § 110(a)(2)(D)(i). But this displacement of state power seems not materially greater than is inherent in EPA’s interpretation of § 126, which we uphold vis-á-vis the objections petitioners raised in their initial briefs. See supra Part II.B. EPA’s current reading, to be sure, may not be the only possible or even the most compelling view of § 126. Perhaps the EPA could reasonably read it as petitioners would, and require that stationary sources as a whole independently satisfy some “meaningful contribution” test before they may be subject to § 126 findings. But given § 126’s silence on what it means for a stationary source to violate § 110(a)(2)(D)(i), EPA’s approach is at least reasonable, and therefore entitled to deference under Chevron. Petitioners point to language we used in Michigan striking down part of what EPA had done there. For certain states EPA had analyzed emissions data only from a portion of the state closest to the affected downwind areas, and, finding that portion to have made contributions exceeding the threshold, had made “contribution” findings for the entire state. We held this extension to the whole state invalid because EPA might well have included areas that were “wholly innocent of material contributions.” Michigan, 213 F.3d at 681-85. In that context, we said that a significant contribution finding required evidence of a “measurable contribution” and that “^Interstate contributions cannot be assumed out of thin air.” Id. at 684. In the present case Non-State Petitioners do not dispute that emissions from affected § 126 sources actually contribute to total manmade NOx emissions that, at the statewide aggregate level, meet the EPA criteria upheld in Michigan. The process here does not involve sweeping up individual sources that might well not be part of the problem at all. The concern that drove our discussion in Michigan is inapplicable. Non-EGU Petitioners, by contrast, suggest a point that might conceivably implicate Michigan’s “measurable contribution” concern. They argue that because EPA failed to model the contribution of each particular source individually, its findings ignore the effects of industrial sources’ having lower smoke stacks than utility sources. If in fact NOxemissions from stationary sources with low smoke stacks do not reach other states as easily as emissions from other sources, these petitioners might have a point as to the scope of what Michigan allows. But the petitioners’ vague claim that lower stack height “affects the downwind impact” in no way quantifies the effect, much less makes out a claim that cex-tain sources do not measurably contribute to downwind nonattainment. In Michigan we left “EPA free to select states as a unit of measurement,” saying that “[i]n turn, states (or the areas of states that believed themselves innocent of material contributions, or sources located therein), might respond by offering finer-grained computations.” 213 F.3d at 684. So, too, the low-stack sources might have come forward with such numbers, but they have not. Or they might have shown that EPA’s modeling bore “no rational relationship to the reality it purport[ed] to represent,” Sierra Club v. EPA, 167 F.3d 658, 662 (D.C.Cir.1999), thereby throwing the burden back on EPA, but they have not. A final challenge to the “contribution” findings is the Non-State Petitioners’ argument that for four states (Indiana, Kentucky, Michigan and New York) EPA used siaie-based aggregations to find the contribution but then applied controls to sources in only part of each state. This is a reverse of what we struck down in Michigan-. there extension from part to the whole, here, contraction from the whole to a part. EPA’s explanation was that while the modeling was statewide, § 126 empowered it only to address sources named in the downwind states’ petitions (which here they did by area). See Jan. 2000 Rule, 65 Fed. Reg. at 2685/1. Petitioners do not contest EPA’s legal assumption, but simply say that the process invalidates the finding. EPA questions whether this objection was raised with reasonable specificity, which under 42 U.S.C. § 7607(d)(7)(B) is a precondition for judicial review. But in the rulemaking itself EPA plainly acknowledged a claim that it was wrong to rely on all manmade emissions from an entire state where the petitions sought relief “from sources located in only a portion of the upwind State.” May 1999 Rule, 64 Fed. Reg. at 28,292/3. Nonetheless, petitioners’ claim leaves out a critical point. Extension of a finding from an area responsible for pollution problems to another area, where the two are linked only by falling within state boundaries, raises obvious risks of burdening the innocent with the guilty. That risk is far lower in moving from the whole to a part, at least in the absence of some reason to doubt that the part in question shared in the state’s “con-tribut[ory]” role or that it had been rationally selected on the basis of relevant criteria. Accordingly, the principle that we accepted above in the context of the broad claim (based on § 126’s exclusive focus on stationary sources) — namely, that EPA may subject to § 126 controls any source that might have been subject to SIP controls properly adopted under § 110(a)(2)(D)(i), see id. at 28,282/3 — appears to cover this issue equally well — at least in the absence of any contention that the petitioning states were arbitrary or discriminatory in their designation of sources (whether they identified them by geographic category, as here, or otherwise). D. Emission Limitation Determinations In order to allocate NOx emission allowances to individual sources, the EPA made state-by-state emission projections for 2007. The EPA based each state’s NOx emission budget on projected 2007 heat input (or “utilization”) for electric generating units (“EGUs”) and projected 2007 emissions for non-electric generating, industrial facilities (“non-EGUs”). The projections were developed with computer models working off of “baseline” emissions and heat input data from 1995 and 1996. Various petitioners challenge the EPA’s budget allocations as arbitrary and capricious. While we generally uphold the EPA’s authority to make emission projections and set emission limitations accordingly, we do so only where the EPA adequately responded to comments and explained the basis for its decisions. Thus, although we uphold the EPA’s use of the Integrated Planning Model (“IPM”) as against the specific challenges forwarded by MW & SE Petitioners, we conclude that at least one application of the model is sufficiently unexplained that we must remand the EPA’s IPM-derived growth factors for further explanation. 1. Standard of Review Agency determinations based upon highly complex and .technical matters are “entitled to great deference.” Public Citizen Health Research Group v. Brock, 823 F.2d 626, 628 (D.C.Cir.1987); see also Huls Am., Inc. v. Browner, 83 F.3d 445, 452 (D.C.Cir.1996) (“[W]e will give an extreme degree of deference to the agency when it ‘is evaluating scientific data within its technical expertise.’” (citation omitted)). In a prior case named Appalachian Power Co. v. EPA, 135 F.3d 791, 802 (D.C.Cir.1998), we described statistical analysis as “perhaps the prime example” of an area of technical wilderness into which judicial expeditions are best limited to ascertaining the lay of the land. Although computer models are “a useful and often essential tool for performing the Herculean labors Congress imposed on EPA in the Clean Air Act,” their scientific nature does not easily lend itself to judicial review.... [I]t is only when the model bears no rational relationship to the characteristics of the data to which it is applied that we will hold that the use of the model was arbitrary and capricious. Id at 802 (citation omitted). Under this standard, the EPA has “undoubted power to use predictive models” so long as it “explain[s] the assumptions and methodology used in preparing the model” and “provide[s] a complete analytic defense” should the model be challenged. Small Refiner Lead Phase-Down Task Force v. EPA, 705 F.2d 506, 535 (D.C.Cir.1983) (“SRLPTF”) (citations and internal quotation marks omitted). That a model is limited or imperfect is not, in itself, a reason to remand agency decisions based upon it. Ultimately, ... we must defer to the agency’s decision on how to balance the cost and complexity of a more elaborate model against the oversimplification of a simpler model. We can reverse only if the model is so oversimplified that the agency’s conclusions from it are unreasonable. Id. 2. The Integrated Planning Model The MW & SE Petitioners contend that the EPA’s emissions growth projections were arbitrary and capricious because they relied upon a computer model — the “IPM” — that underestimated growth rates for electric power generation in some upwind states. Several states, including North Carolina, submitted comments to the EPA arguing that they projected significantly greater growth in electric power generation than that predicted by the IPM. Rather than address the specific complaints of each commenting state, the EPA defended its reliance upon the IPM on three broad grounds. First, all state NOx budget growth rates should be based upon the same methodology to ensure consistency in the NOx cap’s application. Responses to Significant Comments on the Proposed Findings of Significant Contribution and Rulemaking on Section 126 Petitions for Pwposes of Reducing Interstate Ozone Transport at 111 (April 1999) (‘April 1999 RTC’). Second, the IPM “has received extensive comment, review, and revision over the past several years” during the NOx SIP call and other proceedings. Id; see also Appalachian Power, 135 F.3d at 814-15 (upholding the EPA’s use of the IPM). Third, the IPM “provides a reasonable forecast of State growth rates because it carefully takes into account the most important determinants of electricity generation growth that are facing the power industry today.” April 1999 RTC at 112. Given the highly deferential standard of review applied to such question's, and the EPA’s clear authority to rely upon computer models in place of inconsistent, incomplete, or unreliable empirical data, the Agency’s decision to rely upon the IPM, rather than the projections offered by individual states, was not arbitrary and capricious. See Texas Mun. Power Agency v. EPA, 89 F.3d 858, 870 (D.C.Cir.1996). In the EPA’s judgment, the IPM offered a more comprehensive and consistent means of allocating emission allowances than sorting through the various state-specific projections. That the EPA’s projections depend, in large part, on economic projections, rather than environmental factors, makes little difference. “[I]t is within the scope of the agency’s expertise to make such a prediction about the market it regulates, and a reasonable prediction deserves our deference notwithstanding that there might also be another reasonable view.” Environmental Action, Inc. v. FERC, 939 F.2d 1057, 1064 (D.C.Cir.1991). MW & SE State Petitioners may believe their projections are superior to the EPA’s — and they may even be correct— but they have not proved their case. 3. EGU Growth Factors Accepting the EPA’s general reliance upon the IPM, Non-State Petitioners object to the EPA’s use of growth rates generated by the IPM for 2001-2010 to estimate facility utilization growth for the period 1996-2007. According to petitioners, this yielded estimates for facility utilization in 2007 that not only fail to reflect the best information available to the Agency but that are flatly inconsistent with observed growth rates through 1998. Such apparently anomalous estimates, petitioners claim, are arbitrary and capricious, at least absent any explanation from the agency as to why they are appropriate. As a result, Non-State Petitioners claim, at least some E