WildEarth Guardians v. EPA , 830 F.3d 529 ( 2016 )


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  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued November 6, 2015               Decided July 29, 2016
    No. 14-1145
    WILDEARTH GUARDIANS, ET AL.,
    PETITIONERS
    v.
    ENVIRONMENTAL PROTECTION AGENCY,
    RESPONDENT
    SAN JOAQUIN VALLEY UNIFIED AIR POLLUTION CONTROL
    DISTRICT AND SOUTH COAST AIR QUALITY MANAGEMENT
    DISTRICT,
    INTERVENORS
    On Petition for Review of Final Agency Action of
    the United States Environmental Protection Agency
    Paul Cort argued the cause for petitioners. With him on
    the briefs was Colin C. O'Brien.
    Brian H. Lynk, Attorney, U.S. Department of Justice,
    argued the cause for respondent. With him on the brief was
    John C. Cruden, Assistant Attorney General. Sam Hirsch,
    Attorney, entered an appearance.
    Barbara     Baird,   Lauren     Nevitt,  Annette   A.
    Ballatore-Williamson, and Jessica E. Hafer Fierro were on
    2
    the brief for respondent-intervenors San Joaquin Valley
    Unified Air Pollution Control District and South Coast Air
    Quality Management District.
    Before: SRINIVASAN, Circuit Judge, and WILLIAMS and
    GINSBURG, Senior Circuit Judges.
    Opinion for the Court filed by Circuit Judge SRINIVASAN.
    Under the Clean Air Act, the Environmental Protection
    Agency promulgates national ambient air quality standards.
    The Act sets out distinct statutory frameworks of varying
    levels of strictness for EPA to apply to air pollutants. This
    case involves the agency’s regulation under the Act of a
    specific pollutant: fine particulate matter. For some time,
    EPA subjected fine particulate matter to a relaxed statutory
    framework under the Act. In 2013, however, this court
    instructed the agency that the framework it had been applying
    to fine particulate matter was incorrect and that a more
    onerous statutory framework governed that pollutant.
    In response to our decision, EPA promulgated the
    implementation rule at issue here. During the time EPA had
    been applying the incorrect (and more relaxed) statutory
    framework to fine particulate matter, some of the stricter
    compliance deadlines that would have applied under the
    correct statutory framework had already elapsed. In its
    implementation rule, the agency made certain adjustments to
    those deadlines in an effort to avoid treating states as having
    already missed deadlines of which they were never aware.
    WildEarth Guardians challenges EPA’s authority to
    adjust the deadlines. In WildEarth’s view, after this court
    issued its decision holding that EPA had been using the wrong
    framework, the agency was required to adopt a rule grounded
    3
    in an assumption that the correct framework had been applied
    all along, even though some of the deadlines under that
    framework would have already passed.              We reject
    WildEarth’s argument.       We hold that, in the novel
    circumstances presented here, EPA reasonably acted within
    its statutory authority in adopting new deadlines aimed to
    avoid imposing retroactive burdens on states seeking to
    achieve compliance with governing air quality standards.
    I.
    A.
    The Clean Air Act, 
    42 U.S.C. §§ 7401
     et seq., requires
    EPA to publish a list of air pollutants that “may reasonably be
    anticipated to endanger public health or welfare.” 
    Id.
     §
    7408(a)(1)(A). For each pollutant, EPA must promulgate
    national ambient air quality standards (NAAQS). See id. §
    7409.
    “Once EPA establishes NAAQS for a particular
    pollutant, the standards become the centerpiece of a complex
    statutory regime aimed at reducing the pollutant’s
    atmospheric concentration.” Am. Trucking Ass’ns, Inc. v.
    EPA, 
    283 F.3d 355
    , 358-59 (D.C. Cir. 2002). EPA designates
    areas of the country as “attainment,” “nonattainment,” or
    “unclassifiable,” based on whether the region’s atmospheric
    concentration of the pollutant falls below the level permitted
    by the NAAQS—in other words, whether the region has
    “attained” compliance with the standards. 
    42 U.S.C. § 7407
    (d)(1). Each state must then devise and submit to EPA a
    state implementation plan (SIP) that explains how any
    nonattainment areas will attain the standards.          
    Id.
     §
    7410(a)(1).
    4
    EPA first regulated particulate matter in the original set
    of NAAQS promulgated in 1971. See National Primary and
    Secondary Ambient Air Quality Standards, 
    36 Fed. Reg. 8186
    (Apr. 30, 1971). Particulate matter refers to a mixture of
    liquid droplets and extremely small solids, which can be made
    up of various components including acids, chemicals, metals,
    soil, or dust. Particles can enter deep into the lungs and cause
    serious health problems. In 1987, EPA, recognizing that the
    size of particles directly affects the health risk, revised the
    particulate matter standard to include only “particles with an
    aerodynamic diameter less than or equal to a nominal 10
    micrometers.” Revisions to the NAAQS for Particulate
    Matter, 
    52 Fed. Reg. 24,634
    , 24,633-34 (July 1, 1987). Such
    particles are referred to as “PM10.”
    B.
    In 1990, Congress enacted the Clean Air Act
    Amendments. See Pub. L. No. 101-549, 
    104 Stat. 2399
    . The
    Amendments revised the procedures for implementing
    NAAQS. The new Part D established five Subparts, each of
    which sets out a different framework of deadlines and
    requirements. Whereas Subparts 2 through 5 each pertain to a
    particular pollutant, Subpart 1 serves as a catch-all category,
    establishing the requirements for all remaining pollutants.
    Subpart 4 specifically governs particulate matter. See 
    42 U.S.C. §§ 7513
    -7513b. Because PM10 was the only kind of
    particulate matter regulated by EPA at the time of the
    Amendments, Subpart 4 expressly referred to PM10. 
    Id.
    Subpart 4’s requirements are stricter than the default
    requirements set forth in Subpart 1. Compare 
    id.
     §§ 7501-
    7509a (Subpart 1), with id. §§ 7513-7513b (Subpart 4). For
    instance, Subpart 1 gives EPA greater discretion to establish
    deadlines for states to submit SIPs following a nonattainment
    5
    designation, see id. § 7502(b), whereas Subpart 4 mandates
    specific deadlines under which SIPs are due within “18
    months after the designation as nonattainment.” Id. §
    7513a(a)(2)(B).
    Additionally, Subpart 1 does not require EPA to classify
    nonattainment areas based on the severity of their air control
    problem or the length of time for which an area has failed to
    achieve attainment. See id. § 7502(a)(1). By contrast,
    Subpart 4 establishes a rigorous set of classification
    procedures. Nonattainment areas are initially classified as
    “moderate areas.” See id. § 7513(a). Such areas are expected
    to attain the requisite standards by “the end of the sixth
    calendar year after the area’s designation as nonattainment.”
    Id. § 7513(c)(1). Areas unable to achieve attainment by that
    deadline are reclassified as “serious areas” subject to
    heightened obligations. Id. § 7513(b).
    Reclassification from moderate to serious can occur
    through one of two routes. Should an area fail to attain the
    requisite standard by the moderate-area attainment date, it is
    “reclassified by operation of law as a [s]erious [a]rea.” Id. §
    7513(b)(2)(A). Alternatively, an area can be reclassified as
    serious in advance of the moderate-area attainment deadline if
    EPA determines that the area cannot achieve attainment by
    that date. Id. § 7513(b)(1). That determination often arises
    out of an area’s request to EPA for reclassification. See, e.g.,
    Intervenor Br. 7. Such voluntary reclassification must occur
    “within 18 months after the required date for the State’s
    submission of a SIP for the [m]oderate [a]rea.” 
    42 U.S.C. § 7513
    (b)(1)(B). Voluntary reclassification is advantageous
    because, if an area is reclassified as serious voluntarily rather
    than by operation of law, the state will have additional time
    (four years instead of eighteen months) to submit a SIP for
    that area. See 
    id.
     § 7513a(b)(2).
    6
    Nonattainment areas can suspend further attainment
    planning obligations altogether (such as SIP submission) upon
    obtaining a “clean data determination” from EPA. An area
    qualifies for a clean data determination if it attains the
    NAAQS for three consecutive years. After securing a clean
    data determination, an area becomes eligible to seek
    redesignation as an attainment area. See Identification of
    Nonattainment Classification and Deadlines for Submission
    of SIP Provisions for the 1997 Fine Particle (PM2.5) NAAQS
    and 2006 PM2.5 NAAQS, 
    78 Fed. Reg. 69,806
    , 69,809-10
    (proposed Nov. 21, 2013) (to be codified at 40 C.F.R. pt. 51).
    C.
    In 1997, EPA revised the particulate matter standard.
    EPA acted in response to evidence that particles with an
    aerodynamic diameter less than or equal to 2.5 micrometers
    (PM2.5) posed serious health risks even at levels permitted
    under the existing PM10 regulations. See NAAQS for
    Particulate Matter, 
    62 Fed. Reg. 38,652
    , 38,665-68 (July 18,
    1997). The agency thus established separate standards for
    two distinct types of particulate matter: fine (PM2.5) and
    coarse (PM10). 
    Id. at 38,665
    . EPA set a stricter standard for
    fine particulate matter than for coarse particulate matter.
    Since its initial adoption in 1997 of a separate standard
    for PM2.5, EPA has revised that standard twice—in 2006 and
    again in 2012. See NAAQS for Particulate Matter, 
    71 Fed. Reg. 61,144
     (Oct. 17, 2006); NAAQS for Particulate Matter,
    
    78 Fed. Reg. 3086
     (Jan. 15, 2013). This case implicates only
    the 1997 and 2006 standards. The 1997 standard took effect
    in 2005, when EPA published the initial air quality
    designations for most areas in the country. See Air Quality
    Designations and Classifications for the Fine Particles (PM2.5)
    NAAQS, 
    70 Fed. Reg. 944
     (Jan. 5, 2005). The 2006 standard
    7
    took effect in 2009 through an analogous rulemaking. See Air
    Quality Designations for the 2006 24-Hour Fine Particle
    (PM2.5) NAAQS, 
    74 Fed. Reg. 58,688
     (Nov. 13, 2009).
    From 1997 onward, EPA implemented all of the PM2.5
    standards pursuant to the more relaxed provisions of Subpart
    1, rather than the more prescriptive and onerous requirements
    of Subpart 4. See NAAQS for Particulate Matter, 62 Fed.
    Reg. at 38,695. The agency maintained that, under the plain
    terms of the statute, Subpart 4 referred specifically to PM10.
    See id.
    In Natural Resources Defense Council v. EPA, 
    706 F.3d 428
     (D.C. Cir. 2013) (NRDC), we rejected EPA’s approach of
    enforcing PM2.5 standards under Subpart 1 rather than Subpart
    4. By definition, we concluded, PM2.5 is PM10. 
    Id. at 435
    .
    And under the statute, the agency was required to “implement
    all standards applicable to PM10—including its PM2.5
    standards—pursuant to Subpart 4.” 
    Id. at 436
    . We therefore
    “remand[ed] to EPA to re-promulgate the[] [implementation]
    rules” for fine particulate matter under the correct framework.
    
    Id. at 437
    .
    D.
    In an effort to shift its implementation of PM2.5 standards
    to Subpart 4 per our direction in NRDC, the agency
    promulgated the Implementation Rule at issue here. The Rule
    set forth new nonattainment designations and revised
    deadlines for states to submit SIPs for nonattainment areas.
    Identification of Nonattainment Classification and Deadlines
    for Submission of SIP Provisions for the 1997 Fine Particle
    (PM2.5) NAAQS and 2006 PM2.5 NAAQS, 
    79 Fed. Reg. 31,566
     (June 2, 2014) (to be codified at 40 C.F.R. ch. I). In
    fashioning the Rule, EPA sought to account for the fact that,
    8
    had it applied Subpart 4 to PM2.5 from the outset, some of the
    original Subpart 4 deadlines would have already passed by the
    time of the Rule (and of our decision in NRDC).
    One set of those deadlines pertains to the submission of
    SIPs. For the 1997 standard, EPA issued nonattainment area
    designations in 2005, with an effective date of April 5 of that
    year. See Air Quality Designations and Classifications for the
    Fine Particles (PM2.5) NAAQS, 70 Fed. Reg. at 944. Under
    the Subpart 1 framework applied to PM2.5 at the time, EPA
    had discretion to establish the deadline for submission of SIPs
    for those areas. See 
    42 U.S.C. § 7502
    (b). But if Subpart 4
    had been applied, states would have been statutorily required
    to submit SIPs within eighteen months of the nonattainment
    designation, see 
    id.
     § 7513a(a)(2)(B), or by October 5, 2006.
    For the 2006 standard, correspondingly, the deadline for the
    submission of SIPs for nonattainment areas would have been
    June 14, 2011, because nonattainment designations under that
    standard became effective on December 14, 2009. See Air
    Quality Designations for the 2006 24-Hour Fine Particle
    (PM2.5) NAAQS, 74 Fed. Reg. at 58,688. A failure to submit
    SIPs by the deadline results in a renewed requirement to
    submit plans and the possibility of penalties. See 
    42 U.S.C. § 7509
    .
    Another set of affected deadlines pertains to
    reclassification of nonattainment areas. In particular, if the
    Subpart 4 framework had applied all along, moderate
    nonattainment areas for the 1997 standard would have already
    been reclassified as serious. That is because, under the April
    5, 2005, effective date for EPA’s nonattainment designations
    for the 1997 standard, the deadline for moderate areas to
    achieve attainment would have been December 31, 2011. See
    
    id.
     § 7513(c)(1). And if EPA did not find that an area
    achieved attainment within six months of that deadline, or by
    9
    June 30, 2012, Subpart 4 would have called for
    reclassification of the area to serious by operation of law as of
    that date. See id. § 7513(b)(2)(A). Affected states then would
    have been subject to the accelerated deadline for submission
    of SIPs for serious areas, under which the SIPs would have
    been due within eighteen months, or by December 31, 2013.
    See id. § 7513a(b)(2).
    In its Implementation Rule, EPA declined to impose
    deadlines on states that rested on a counterfactual assumption
    that Subpart 4 had been applied to fine particulate matter from
    the outset. Such an approach, in EPA’s view, would have
    carried unfair, retroactive implications for states that had been
    operating under the Subpart 1 framework (erroneously)
    applied by EPA.
    EPA instead adopted an approach in which it made two
    adjustments to offset the fact that some Subpart 4 deadlines
    would have already passed had that framework been used all
    along. First, rather than find that states had already missed
    SIP submission deadlines for moderate areas, EPA established
    a deadline of December 31, 2014, for states to submit plans in
    accordance with Subpart 4.            See Identification of
    Nonattainment Classification and Deadlines for Submission
    of SIP Provisions for the 1997 Fine Particle (PM2.5) NAAQS
    and 2006 PM2.5 NAAQS, 79 Fed. Reg. at 31,570. That
    revised deadline superseded all deadlines previously set under
    the Subpart 1 framework (as well as any deadlines that would
    have applied under the Subpart 4 framework). Second, rather
    than treat certain nonattainment areas as if they had already
    been reclassified as serious by operation of law, EPA
    classified all nonattainment areas under both the 1997 and
    2006 standards as moderate. See id. at 31,567-70.
    10
    The areas primarily affected by the new Rule are those
    that were previously designated as nonattainment under the
    Subpart 1 regime and that had not yet submitted a SIP to the
    agency or received a clean data determination suspending
    attainment planning obligations altogether. Such areas, rather
    than being treated as having already missed the submission
    deadline for SIPs or as having been already reclassified as
    serious by operation of law, were classified as moderate areas
    and given until December 31, 2014, to submit SIPs. Three
    nonattainment areas fell into that category for the 1997
    standard. Five areas did so for the 2006 standard.
    II.
    WildEarth filed a petition for review in this court in
    which it challenges EPA’s approach in the Implementation
    Rule as inconsistent with Subpart 4’s statutory deadlines.
    Before addressing the merits of WildEarth’s claim, we must
    resolve the threshold question of whether we have
    jurisdiction. This court generally has jurisdiction to review
    final actions taken by EPA under the Clean Air Act. See 
    42 U.S.C. § 7607
    (b)(1). EPA argues, however, that WildEarth
    lacks Article III standing to bring this challenge or, in the
    alternative, that intervening events have rendered the case
    moot. We disagree and conclude that WildEarth has standing
    to bring this petition for review and that the case is not moot
    with respect to WildEarth’s challenge to the 2006 standard.
    First, with regard to the question of standing, WildEarth,
    as the party filing suit, bears the burden of establishing its
    standing. See Kokkonen v. Guardian Life Ins. Co., 
    511 U.S. 375
    , 377 (1994). To do so, WildEarth must demonstrate it
    has suffered an “injury in fact” that is “fairly traceable” to the
    defendant’s action and that can likely be “redressed by a
    favorable decision.” Lujan v. Defs. of Wildlife, 
    504 U.S. 555
    ,
    11
    560-61 (1992) (quotations, internal alterations, and quotation
    marks omitted). The health and economic costs of increased
    PM2.5 pollution for individuals in nonattainment areas
    constitute injuries in fact that are fairly traceable to the EPA’s
    challenged rule, satisfying the first two standing requirements.
    The dispute here is primarily about the last prong,
    redressability.
    EPA argues that a ruling in favor of WildEarth would not
    redress WildEarth’s injury, because, while a favorable ruling
    would invalidate EPA’s Implementation Rule, it would then
    have the effect of reinstating the preexisting (and more
    relaxed) Subpart 1 rules. That argument is unpersuasive. The
    necessary consequence of vacating the Implementation Rule
    on the ground that it failed adequately to adhere to Subpart 4
    would be some kind of corrective EPA action strictly
    implementing that Subpart, e.g., immediate findings
    reclassifying nonattainment areas as serious (rather than
    moderate). And even if EPA were to fail to initiate that sort
    of remedial response, WildEarth could then file a mandamus
    petition to compel agency action.          WildEarth’s injury
    therefore could be redressed if it were to prevail in this
    challenge.
    This brings us to the question of mootness. “[I]f an event
    occurs while a case is pending on appeal that makes it
    impossible for the court to grant any effectual relief whatever
    to a prevailing party, the appeal must be dismissed.” Church
    of Scientology of Cal. v. United States, 
    506 U.S. 9
    , 12 (1992)
    (quotation and internal quotation marks omitted). EPA
    asserts that intervening events have rendered this case moot.
    Although we agree with EPA as to the 1997 PM2.5 standard,
    we conclude that WildEarth continues to have a legally
    cognizable interest in the outcome of the case with respect to
    the 2006 standard.
    12
    Understanding why the case is moot with regard to the
    1997 standard, but not moot with regard to the 2006 standard,
    requires a highly technical review of the effect of WildEarth’s
    prevailing in this case on the nonattainment areas affected by
    the Implementation Rule. For the 1997 standard, the Rule, as
    previously noted, affected three nonattainment areas. (All
    other areas that had been classified as nonattainment had
    already obtained a clean data determination by the time of the
    Rule’s promulgation and accordingly had no ongoing
    planning obligations.) The three affected nonattainment areas
    were: Libby, Montana; Los Angeles-South Coast Air Basin,
    California; and San Joaquin Valley, California.            See
    Identification of Nonattainment Classification and Deadlines
    for Submission of SIP Provisions for the 1997 Fine Particle
    (PM2.5) NAAQS and 2006 PM2.5 NAAQS, 78 Fed. Reg. at
    69,809.      Due to developments following the Rule’s
    promulgation, the challenged aspects of the Rule no longer
    have any effect on those three areas.
    San Joaquin Valley has since been reclassified as serious
    and has submitted its serious-area SIP. See Designation of
    Areas for Air Quality Planning Purposes, 
    80 Fed. Reg. 18,528
    (Apr. 7, 2015) (to be codified at 40 C.F.R. pts. 52, 81). San
    Joaquin thus would be unaffected by a decision in
    WildEarth’s favor—i.e., a decision vacating the
    Implementation Rule on the ground that EPA lacked authority
    to set a revised deadline for submission of SIPs of December
    31, 2014. Because the extended timeline for submission of
    serious-area SIPs is the only consequential result of that
    revision, vacatur of the Rule’s December 31, 2014, deadline
    would have no effect on an area (like San Joaquin) that has
    already submitted its plan. Even if EPA were to reject San
    Joaquin’s plan, that rejection, regardless of the outcome in
    this case, would result in the imposition of a twelve-month
    period within which to submit plan revisions because of San
    13
    Joaquin’s failure to achieve the 1997 standard by the serious-
    area attainment date of December 31, 2015. See 42 U.S.C. §
    7513a(d). WildEarth’s sole response is that EPA conceivably
    could do more than merely reject San Joaquin’s plan, in that
    EPA might separately revoke the 1997 standard altogether
    and end any unmet planning obligations under that standard.
    That possibility is highly (and unduly) speculative, too much
    so to resuscitate an otherwise-moot controversy as to San
    Joaquin.
    There is also no remaining practical effect for the other
    two affected areas—Libby and South Coast—under the 1997
    NAAQS. Since the Rule’s promulgation, Libby and South
    Coast have both received clean data determinations
    suspending all planning obligations under that standard. See
    Determinations of Attainment of the 1997 Annual Fine
    Particulate Matter Standard for the Libby, Montana
    Nonattainment Area, 
    80 Fed. Reg. 40,911
     (July 14, 2015) (to
    be codified at 40 C.F.R. pt. 52); Clean Data Determination for
    1997 PM2.5 Standards; California-South Coast (signed July 8,
    2016) (to be codified at 40 C.F.R. pt. 52). WildEarth
    responds that, if it were to prevail in this challenge, Libby and
    South Coast would be subject to the stricter requirements
    applicable to serious areas, and those additional restrictions
    would remain in effect notwithstanding a clean data
    determination. See 42 U.S.C. § 7513a(b). At this point,
    however, Libby and South Coast no longer face the possibility
    of reclassification as serious: it is clear from the clean data
    determinations for those areas that they, as of today, have
    attained the 1997 standard, precluding their reclassification as
    serious. For Libby and South Coast, then—as with San
    Joaquin—there is no continuing controversy as to the 1997
    standard.
    14
    WildEarth’s challenge is not moot, however, with regard
    to the 2006 standard. That standard took effect on December
    14, 2009. See Air Quality Designations for the 2006 24-Hour
    Fine Particle (PM2.5) NAAQS, 74 Fed. Reg. at 58,688. At the
    time, five areas were designated as nonattainment. Had the
    Act been implemented correctly from the outset, i.e., under
    Subpart 4, moderate-area SIPs for those areas would have
    been due on June 14, 2011. See 42 U.S.C. § 7513a(a)(2)(B).
    WildEarth thus contends that, as relief, we should compel
    EPA to make an immediate finding under section
    7410(k)(1)(B) that the states failed to submit their plans. See
    WildEarth Opening Br. 21. EPA claims the issue is now
    moot, because, under its approach in the Rule, such failure-to-
    submit findings have been ongoing in any event: the Rule
    called for states to submit moderate-area plans in compliance
    with Subpart 4 no later than December 31, 2014. Based on
    the statutory framework, EPA then had until June 30, 2015, to
    determine whether any state had failed to submit. See 
    42 U.S.C. § 7410
    (k)(1)(B). Were we now to compel EPA to
    make failure-to-submit findings based on the Rule’s supposed
    departure from Subpart 4, the agency contends, it would
    merely delay the time of its failure-to-submit findings.
    Even assuming that to be true, however, the schedule
    pursuant to which the failure-to-submit findings are
    conducted and imposed—i.e., the timeline under Subpart 4
    versus the modified schedule under the Rule—would have a
    significant effect: it would determine whether areas can elect
    voluntary reclassification as serious. Under the statutory
    scheme, EPA can voluntarily reclassify an area only if (i) the
    moderate-area attainment deadline has yet to pass, and (ii)
    reclassification occurs within eighteen months of the deadline
    for submitting a SIP. See 
    id.
     § 7513(b)(1). According to
    WildEarth, because moderate-area SIPs would have been due
    15
    by June 14, 2011, had Subpart 4 been applied all along,
    EPA’s ability to grant voluntary reclassification expired
    eighteen months later, on December 14, 2012. The Rule, by
    contrast, set a new plan submission deadline of December 31,
    2014, which had the effect of triggering a new window for
    voluntary reclassification. As a result, EPA was able to grant
    requests for voluntary reclassification until the December 31,
    2015, moderate-area attainment deadline (which was
    unchanged by the Rule).
    The opportunity to obtain voluntary reclassification in
    turn affects the deadline for a state’s submission of a serious-
    area SIP: whereas voluntarily reclassified areas receive four
    years to submit a plan, areas reclassified by operation of law
    receive only eighteen months. See id. § 7513a(b)(2). If, as
    WildEarth suggests, areas can no longer obtain voluntary
    reclassification with respect to the 2006 standard, those areas
    would have to submit serious-area plans within eighteen
    months of their reclassification by operation of law—i.e., by
    December 31, 2017 (assuming, as WildEarth submits,
    reclassification occurred by operation of law within six
    months of the December 31, 2015, moderate-area attainment
    deadline). See id. § 7513(b)(2). By contrast, under EPA’s
    approach, states with voluntarily-reclassified areas would
    have four years from the date of reclassification within which
    to submit serious-area plans—i.e., until December 31, 2019.
    The difference between SIP submission deadlines of
    December 2017 and December 2019 would affect areas for
    which EPA has issued Proposed Rules granting voluntary
    reclassification as serious with regard to the 2006 standard.
    See Approval and Promulgation of Implementation Plans, 
    80 Fed. Reg. 1816
     (proposed Jan. 13, 2015) (to be codified at 40
    C.F.R. pts. 52, 81) (San Joaquin Valley); Approval and
    Promulgation of Implementation Plans, 
    80 Fed. Reg. 69172
    16
    (proposed Nov. 9, 2015) (to be codified at 40 C.F.R. pt. 52)
    (Logan, Utah/Franklin County, Idaho). Because of the Rule’s
    impact on the serious-area SIP deadline for those areas, the
    case presents a live controversy as to the 2006 standard.
    At oral argument, EPA counsel contended that the case
    nonetheless was moot even with respect to the 2006 standard.
    That contention was based on an EPA regulation promulgated
    long ago (and apparently since dormant) under which,
    according to counsel, the agency has leeway to disregard
    section 7513(b)(1)(B)’s requirement that voluntary
    reclassification be sought “within 18 months after the required
    date for the State’s submission of a SIP for the Moderate
    Area.” 
    42 U.S.C. § 7513
    (b)(1)(B); see State Implementation
    Plans for Serious PM-10 Nonattainment Areas, and
    Attainment Date Waivers for PM-10 Nonattainment Areas
    Generally, 
    59 Fed. Reg. 41,998
     (Aug. 16, 1994). As a result
    of that regulation, EPA counsel contended at argument,
    voluntary reclassification of the affected three areas is
    permissible regardless of the outcome of WildEarth’s
    challenge. We are unpersuaded.
    Initially, it is unclear from the text of the regulation
    whether it necessarily even provides support for the
    interpretation suggested at oral argument. The regulation
    appears to reserve some discretion for EPA in allowing
    voluntary reclassification by clarifying that the statutory
    “directive does not restrict EPA’s general authority”; but it
    otherwise affirms the statute’s mandate that “[a]ppropriate
    areas are . . . reclassified as serious within 18 months after the
    required date for the State’s submission of a moderate area
    PM-10 SIP.” 
    Id. at 41
    ,999 & n.4. Moreover, we are unaware
    of any indication that the agency has previously invoked the
    authority purportedly established by the regulation to
    overcome the statute’s eighteen-month timeframe, much less
    17
    of any judicial interpretation of that supposed authority.
    Lastly, the agency failed to note the regulation, even while
    arguing mootness, at any prior point in the proceedings. In
    these circumstances, the government has failed to carry its
    “heavy” burden to demonstrate mootness based on the
    regulation (or otherwise). Cty. of L.A. v. Davis, 
    440 U.S. 625
    ,
    631 (1979) (quotation omitted).
    III.
    Having concluded that WildEarth has established its
    standing to challenge the Rule and that EPA has failed to
    demonstrate mootness with regard to the 2006 standard, we
    turn to the merits of WildEarth’s challenge to EPA’s
    implementation of that standard. (In light of our conclusion
    that WildEarth’s challenge concerning the 1997 standard is
    moot, we have no occasion to consider WildEarth’s argument
    that EPA lacked authority to classify all nonattainment areas
    under the 1997 standard as moderate.) With respect to the
    2006 standard, WildEarth argues that the plan submission
    deadline established by the Implementation Rule is
    incompatible with Subpart 4. We conclude that, in the unique
    circumstances presented here, the Rule constitutes a
    reasonable exercise of EPA’s rulemaking authority.
    A.
    The Act grants the EPA Administrator general authority
    “to prescribe such regulations as are necessary to carry out his
    functions under this chapter.” 
    42 U.S.C. § 7601
    (a)(1). Of
    course, “EPA cannot rely on its gap-filling authority to
    supplement the Clean Air Act’s provisions when Congress
    has not left the agency a gap to fill”—i.e., “when there is
    statutory language on point.” Nat. Res. Def. Council v. EPA,
    
    749 F.3d 1055
    , 1063-64 (D.C. Cir. 2014). Here, in response
    18
    to our remand in NRDC, see 706 F.3d at 437, EPA relied on
    its gap-filling authority to issue the Implementation Rule in an
    effort to bring its enforcement of the PM2.5 standards into
    alignment with the Subpart 4 framework. In doing so,
    WildEarth argues, EPA exceeded its authority by overriding
    specific statutory requirements prescribed by Subpart 4.
    WildEarth’s argument is grounded in the understanding
    that, once EPA has established a particulate matter standard
    and identified nonattainment areas, Subpart 4 constrains the
    agency’s discretion over implementation of the standard in
    certain ways. See generally Whitman v. Am. Trucking Ass’ns,
    
    531 U.S. 457
    , 484-85 (2001); Nat. Res. Def. Council v. EPA,
    
    777 F.3d 456
    , 464 (D.C. Cir. 2014).            For instance,
    classification of an area as moderate occurs “by operation of
    law”—without any further action by EPA—“at the time of [an
    area’s] designation” as nonattainment. 
    42 U.S.C. § 7513
    (a).
    Moreover, the statute sets the moderate-area plan submission
    deadline, again without any action by EPA, as eighteen
    months after the date of nonattainment designation. See 42
    U.S.C. § 7513a(a)(2)(B). And while a failure-to-submit
    finding by EPA is necessary to trigger sanctions for a state’s
    failure to meet the plan submission deadline, see id. §
    7509(a), the statute limits EPA’s control over the timing of
    that finding, calling for the agency to make the finding “no
    later than 6 months after” the (statutorily mandated)
    submission deadline. Id. § 7410(k)(1)(B).
    Under the language of those provisions, WildEarth
    argues, EPA was required to issue immediate, failure-to-
    submit findings for any state that had yet to submit a
    moderate-area plan for the 2006 standard. WildEarth reasons
    as follows: because Subpart 4 prescribes the date of
    moderate-area classification and the resulting deadlines for
    moderate-area plan submission and failure-to-submit findings,
    19
    and because all of those dates would have long lapsed had
    Subpart 4 been correctly applied to PM2.5 from the outset, see
    supra p. 8, EPA was obligated to issue immediate, failure-to-
    submit findings to comply with the terms of Subpart 4.
    Instead of doing so, EPA adopted a Rule giving states the
    opportunity to submit moderate-area SIPs by a new deadline
    of December 31, 2014. That approach, WildEarth contends,
    is foreclosed by the statute.
    We find that EPA acted within its authority under the
    statute. It is true that Subpart 4 sets the schedule for plan
    submission and failure-to-submit findings once the agency
    issues nonattainment designations, and that the agency
    generally lacks discretion to modify that schedule. But the
    statute does not address what should happen if, as in the novel
    circumstances of this case, all affected parties have been long
    acting on the mistaken assumption that a different
    framework—and hence a different schedule—controls. Of
    particular significance, the statute is silent about the
    appropriate course when, as here, issuing immediate, failure-
    to-submit findings (as WildEarth urges) in a purported effort
    to adhere to Subpart 4’s plan submission schedule would have
    the effect of nullifying another feature of Subpart 4.
    That is because, if EPA had found that states had already
    failed to submit moderate-area plans by the applicable
    deadline (WildEarth’s approach) rather than establish a
    modified deadline for the submission of moderate-area plans
    (the Rule’s approach), the agency would have eliminated a
    state’s ability to request voluntary reclassification of a
    moderate area as serious. Ordinarily, states can receive
    voluntary reclassification within eighteen months of the plan
    submission deadline. See 
    42 U.S.C. § 7513
    (b)(1)(B). By
    pursuing that course, states gain an additional 2.5 years to
    submit a SIP for the area. See 
    id.
     § 7513a(b)(2). Under
    20
    WildEarth’s approach, however, the moderate-area plan
    submission deadline would have passed without states’
    awareness on June 14, 2011, such that states would have
    (unknowingly) lost the opportunity to seek voluntary
    reclassification within eighteen months of that (unknown)
    deadline. That result would effectively read out of the statute
    the voluntary-reclassification option afforded by Subpart 4,
    which presumably exists to encourage states to be proactive
    about meeting their obligations under the Act. EPA’s
    approach in the Rule avoids that consequence.
    In addition, the Rule thereby avoids a situation in which
    the agency’s action would impose retroactive consequences
    on states, a result we have sought to avoid in our decisions.
    In Sierra Club v. Whitman, 
    285 F.3d 63
     (D.C. Cir. 2002)
    (Sierra Club I), for instance, we ordered EPA to make a
    mandatory ozone NAAQS determination for the St. Louis
    area, which, under the statute, the agency should have done
    several years earlier. We refused, however, to order EPA to
    backdate its determination “to the date the statute envisioned,
    rather than the actual date of EPA’s action.” 
    Id. at 68
    . We
    saw no basis for concluding that “Congress intended to give
    EPA the unusual ability to implement rules retroactively.” 
    Id.
    “Although EPA failed to make the nonattainment
    determination within the statutory time frame,” we explained,
    “Sierra Club’s proposed solution [would] only make[] the
    situation worse” because states “would face fines and suits”
    for not having timely implemented plans “even though they
    were not on notice at the time” of the various requirements
    and deadlines. 
    Id.
    Similar considerations animated our decision in Sierra
    Club v. EPA, 
    356 F.3d 296
     (D.C. Cir. 2004) (Sierra Club II).
    In that case, EPA reclassified the District of Columbia from
    “serious” to “severe” nonattainment (a classification not at
    21
    issue here). The agency established a new deadline for the
    District’s submission of a severe-area nonattainment plan
    because the original statutory deadline for such plans had long
    since passed. We rejected Sierra Club’s argument that the
    original statutory deadline should govern, reasoning that such
    a result “would give the reclassification retroactive effect by
    holding the States in default of their submission obligations
    before the events necessary to trigger that obligation
    (reclassification) occurred.” 
    Id. at 309
     (quotation and
    alteration omitted).
    Those cases differ from this one in certain respects, as
    WildEarth emphasizes. The petitioners in Sierra Club I
    requested backdated findings, for instance, whereas
    WildEarth urges present findings of noncompliance. And in
    Sierra Club II, EPA had specific authority under Subpart 2 to
    “adjust any applicable deadlines (other than attainment dates)
    to the extent such adjustment is necessary or appropriate to
    assure consistency among the required submissions.” 42
    U.S.C. § 7511a(i). Subpart 4 includes no such specific
    authority to adjust deadlines.
    At a more fundamental level, though, invalidating the
    Rule before us on the rationale that EPA should have
    immediately found that states had already missed the plan
    submission deadline would impose retroactive consequences
    of the kind that raised concerns in Sierra Club I and Sierra
    Club II. States would be held to long-passed deadlines of
    which they were unaware, with meaningful legal
    consequences. EPA emphasized those sorts of concerns in its
    rulemaking: “Because of the complexity of the [Act]’s SIP
    provisions and the interrelationship between federal and state
    action,” EPA explained, “it is inappropriate to impose
    retroactive effect on decisions in a manner that would create
    deadlines that have long passed.”           Identification of
    22
    Nonattainment Classification and Deadlines for Submission
    of SIP Provisions for the 1997 Fine Particle (PM2.5) NAAQS
    and 2006 PM2.5 NAAQS, 79 Fed. Reg. at 31,568.
    For those reasons, we reject WildEarth’s argument that
    the Rule’s establishment of a new plan submission date under
    the 2006 standard is foreclosed by Subpart 4. In the novel
    circumstances confronting EPA here, we conclude that EPA
    did not exceed its statutory authority under section 7601 in
    promulgating the Rule.
    B.
    We also find that the Rule was a reasonable exercise of
    EPA’s gap-filling authority. In devising the new plan
    submission deadline, the agency took into account the
    “amount of time that ha[d] passed since the NRDC decision,
    when this rulemaking will be finalized, and the amount of
    time remaining before the 2006 PM2.5 NAAQS attainment
    deadline under [S]ubpart 4 for most areas of December 31,
    2015.” Id. at 31,569. EPA sought to ensure that “all states
    with PM2.5 nonattainment areas have a reasonable amount of
    time to develop any additional SIP elements that may be
    required under [S]ubpart 4 in response to the NRDC
    decision.” Id. at 31,570.
    Viewed in light of those understandable considerations,
    the Rule constitutes a reasonable effort to implement the
    Subpart 4 requirements in a timely fashion. Significantly, the
    agency retained the attainment deadline of December 31,
    2015, for the 2006 standard, even though that date was fast
    approaching by the time of the Rule’s promulgation in June
    2014. Moderate areas thus received no additional time within
    which to achieve attainment with the 2006 NAAQS.
    Moreover, the agency’s plan submission deadline of
    23
    December 31, 2014, was less than two years after the NRDC
    decision and some six months after the Rule. That short
    timeframe suggests a reasonable effort to expedite compliance
    with the Subpart 4 framework without imposing unfair
    obligations on states.
    Additionally, in our decision in NRDC, we specifically
    declined NRDC’s request to set a deadline for EPA to re-
    promulgate the rules governing PM2.5 plans. See NRDC, 706
    F.3d at 437 n.10. And rather than vacate the preexisting
    implementation rules, we chose to remand them, presumably
    in an effort to avoid “substantial disruption” and “at least
    temporarily preserve the environmental values covered by
    [the existing rules] until [they] could be replaced by a rule
    consistent with [the court’s] opinion.” EME Homer City
    Generation, L.P. v. EPA, 
    795 F.3d 118
    , 132, 134 (D.C. Cir.
    2015) (quotation and internal quotation marks omitted).
    EPA’s approach in the Rule is in keeping with those concerns.
    The Rule, in short, is a reasonable exercise of EPA’s general
    rulemaking authority to bring its enforcement of PM2.5
    standards into alignment with the Subpart 4 framework.
    *   *   *    *   *
    For the foregoing reasons, we dismiss the petition for
    review insofar as it concerns the 1997 standard, and we
    otherwise deny the petition.
    So ordered.