               FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


VINCENT HARRIS YAZZIE,                 No. 14-73100
                         Petitioner,

                v.

U.S. ENVIRONMENTAL PROTECTION
AGENCY,
                     Respondent,

GILA RIVER INDIAN COMMUNITY;
NAVAJO NATION; CENTRAL ARIZONA
WATER CONSERVATION DISTRICT;
SALT RIVER PROJECT AGRICULTURAL
IMPROVEMENT AND POWER
DISTRICT,
          Respondents-Intervenors.
2                     YAZZIE V. U.S.E.P.A.


 TO’ NIZHONI ANI; BLACK MESA                       No. 14-73101
 WATER COALITION; DINE CITIZENS
 AGAINST RUINING THE
 ENVIRONMENT,
                        Petitioners,

                     v.

 U.S. ENVIRONMENTAL PROTECTION
 AGENCY; SCOTT PRUIT,
 Administrator, * United States
 Environmental Protection Agency,
                         Respondents,

 GILA RIVER INDIAN COMMUNITY;
 NAVAJO NATION; CENTRAL ARIZONA
 WATER CONSERVATION DISTRICT;
 SALT RIVER PROJECT AGRICULTURAL
 IMPROVEMENT AND POWER
 DISTRICT,
           Respondents-Intervenors.




    *
      Scott Pruitt, Administrator of the Environmental Protection
Agency, is substituted for his predecessor, Gina McCarthy, pursuant to
Federal Rule of Appellate Procedure 43(c)(2).
                YAZZIE V. U.S.E.P.A.                    3


NATIONAL PARKS CONSERVATION              No. 14-73102
ASSOCIATION; SIERRA CLUB; GRAND
CANYON TRUST; NATURAL
RESOURCES DEFENSE COUNCIL,                 OPINION
                      Petitioners,

                v.

U.S. ENVIRONMENTAL PROTECTION
AGENCY; SCOTT PRUITT,
Administrator, United States
Environmental Protection Agency,
                       Respondents,

GILA RIVER INDIAN COMMUNITY;
NAVAJO NATION; CENTRAL ARIZONA
WATER CONSERVATION DISTRICT;
SALT RIVER PROJECT AGRICULTURAL
IMPROVEMENT AND POWER
DISTRICT,
          Respondents-Intervenors.



       On Petition for Review of an Order of the
          Environmental Protection Agency

      Argued and Submitted November 18, 2016
              San Francisco, California

                Filed March 20, 2017
4                     YAZZIE V. U.S.E.P.A.

       Before: Mary M. Schroeder, Stephen S. Trott,
            and John B. Owens, Circuit Judges.

                    Opinion by Judge Owens


                          SUMMARY **


                      Environmental Law

   The panel denied petitions for review brought by tribal
conservation organizations and non-profit environmental
organizations challenging the United States Environmental
Protection Agency’s source-specific federal implementation
plan (“FIP”) under the Clean Air Act for the Navajo
Generating Station, a coal-fired power plant on the Navajo
Nation Reservation in Arizona.

   The panel held that the federal government’s partial
ownership of the Station did not eliminate any deference to
the EPA’s interpretation of the Clean Air Act and its
implementing regulations.

   The Clean Air Act invites States to submit to the EPA a
State Implementation Plan setting forth emission limits and
other measures to improve air visibility. If a State elects not
to submit a State Implementation Plan, or the EPA rejects
the State’s plan, the EPA must generate a FIP to fill any
resulting gaps. Regional haze State Implementation Plans
must identify the “best available retrofit technology”

    **
       This summary constitutes no part of the opinion of the court. It
has been prepared by court staff for the convenience of the reader.
                   YAZZIE V. U.S.E.P.A.                    5

(“BART”) to reduce emissions from major emission
sources, like the Station. A State can bypass BART with a
“better than BART” alternative.

   In 1998, the EPA issued its Tribal Authority Rule, which
created a mechanism for tribes to develop a Tribal
Implementation Plan, similar to a State Implementation
Plan, to carry out the Clean Air Act’s requirements on tribal
land. Because tribes are not required to adopt Tribal
Implementation Plans, the Tribal Authority Rule authorizes
the EPA to promulgate a FIP to fill in any gaps.

   The panel held that the instant FIP was not subject to the
Clean Air Act’s five-year deadline to implement BART
because the FIP promulgated a “better than BART”
alternative – not BART.

   Under the Regional Haze Regulations for a BART
alternative, a State Implementation Plan must “require[] that
all necessary emission reductions take place during the
period of the first long-term strategy for regional haze.” 40
C.F.R. § 51.308(e)(2)(iii). The panel held that the EPA
reasonably concluded that the Tribal Authority Rule applied
because the Navajo Nation had not submitted a tribal
implementation plan, which gave the EPA authority to
promulgate a FIP for nitrogen oxides emissions at the
Station. The panel further held that the EPA reasonably
interpreted the Tribal Authority Rule, 40 C.F.R. §§ 49.4(e),
49.11(a), and the Regional Haze Regulations to conclude
that the emission reductions in § 51.308(e)(2)(iii) did not
apply to FIPs for regional haze that are promulgated in place
of tribal implementation plans.

   The panel held that it was reasonable for the EPA to give
the Station an emission credit when evaluating if the BART
6                  YAZZIE V. U.S.E.P.A.

alternative “results in greater emission reductions,” 40
C.F.R. § 51.308(e)(3), than BART. The panel deferred to
the EPA’s reasonable determination that the FIP alternative
was “better than BART” for nitrous oxide emissions.

  The panel held that it was a reasonable exercise of the
EPA’s discretion not to determine BART for particulate
matter for the Station.


                        COUNSEL

Brad A. Bartlett (argued), Environmental Law Clinic,
University of Denver Sturm College of Law, Denver,
Colorado; John Barth, Hygiene, Colorado; for Petitioners
To-Nizhoni Ani, Black Mesa Water Coalition, and Dine
Citizens Against Ruining our Environment.

Vincent Harris Yazzie, pro se Petitioner.

Janette K. Brimmer (argued) and Amanda W. Goodin,
Earthjustice, Seattle, Washington; Neil Levine, Staff
Attorney, Grand Canyon Trust, Denver, Colorado; for
Petitioners National Parks Conservation Association, Sierra
Club, Grand Canyon Trust, Natural Resources Defense
Council.

David A. Carson (argued), Environment & Natural
Resources Division, United States Department of Justice,
Denver, Colorado; Daniel R. Dertke, Environmental
Defense Section; John C. Cruden, Assistant Attorney
General; Environment & Natural Resources Division,
United States Department of Justice, Washington, D.C.; Ann
Lyons, Office of Regional Counsel, United States
Environmental Protection Agency, Region 9, San Francisco,
                  YAZZIE V. U.S.E.P.A.                   7

California; Lea Anderson, Office of the General Counsel,
United States Environmental Protection Agency,
Washington, D.C.; for Respondents.
Aaron M. Flynn (argued), Norman W. Fichthorn, and
William L. Wehrum, Hunton & Williams LLP, Washington,
D.C., for Respondent-Intervenor Salt River Project
Agricultural Improvement and Power District.

Colin Wittman Bradley (argued), and Katherine Belzowski,
Attorneys; Paul Spruhan, Assistant Attorney General; Ethel
B. Branch, Acting Attorney General; Navajo Nation
Department of Justice, Window Rock, Arizona; for
Respondent-Intervenor Navajo Nation.

John B. Capehart, Z.W. Julius Chen, Merrill C. Godfrey, and
Donald R. Pongrace, Akin Gump Strauss Hauer & Feld LLP,
Washington, D.C.; Thomas L. Murphy and Linus Everling,
Gila River Indian Community Office of General Counsel,
Sacaton, Arizona; for Respondents-Intervenors Gila River
Indian Community.

David L. Bernhardt and Ryan A. Smith, Brownstein Hyatt
Farber Schreck LLP, Washington, D.C., for Respondent-
Intervenor Central Arizona Water Conservation District.
8                      YAZZIE V. U.S.E.P.A.

                             OPINION

OWENS, Circuit Judge:

    Petitioners Vincent Yazzie, several tribal conservation
organizations, and certain non-profit environmental
organizations (collectively “petitioners”) 1 seek final review
of the United States Environmental Protection Agency’s
(“EPA”) source-specific Federal Implementation Plan
(“FIP”) under the Clean Air Act (“CAA”) for the Navajo
Generating Station, a coal-fired power plant on the Navajo
Nation Reservation in Arizona. 2 We have jurisdiction over
these petitions, 42 U.S.C. § 7607(b)(1), and we deny them.

I. FACTS AND PROCEDURAL HISTORY

    A. The Navajo Generating Station

    The Navajo Generating Station (“Station”) is the largest
coal-fired plant in the western United States, and emits
nitrogen oxides (“NOx”) that affect visibility at Class I
national parks and wilderness areas, including the Grand
Canyon. The Station powers a water distribution system that
meets over 20% of Arizona’s water demands. 78 Fed. Reg.
8,274, 8,275, 8,283 (Feb. 5, 2013). Coal from the Kayenta
Mine, located on both Navajo and Hopi Tribe lands, powers

    1
      These consolidated cases are related to Hopi Tribe v. EPA, No. 14-
73055, a case that was severed from the instant cases and is addressed in
a separate concurrently filed opinion.

    2
       “We apologize for the extensive use of acronyms in this opinion
and include a brief glossary at the end to aid the reader. Environmental
litigation is awash in such alphabetical shorthand, and the ‘insiders’
would not know what we meant if we used other terms.” Arizona v. EPA,
815 F.3d 519, 525 n.3 (9th Cir. 2016).
                    YAZZIE V. U.S.E.P.A.                     9

the Station and employs many tribal members, and taxes and
royalties from the coal are significant parts of the tribes’
revenues. Id. at 8,275. Under the proposed amended lease
of the land from the Navajo Nation to the owner-operators
of the Station, the Station would operate until 2044, when it
would cease conventional coal-fired generation of
electricity. 79 Fed. Reg. 46,514, 46,532 (Aug. 8, 2014);
78 Fed. Reg. 62,509, 62,514 (Oct. 22, 2013). After 2044,
the Navajo Nation has the option to continue the Station as a
“new source” that generates electricity without coal. 79 Fed.
Reg. at 46,532. Several entities, including four utilities (the
Salt River Project, Arizona Public Service Co., NV Energy,
and Tucson Electric Power), and the Department of Interior
(through the U.S. Bureau of Reclamation), co-own the
Station. Id. at 46,514. The utilities operate the Station;
terms of the lease bar the Navajo Nation from controlling or
regulating the operation of the Station. See Salt River
Project Agric. Improvement & Power Dist. v. Lee, 672 F.3d
1176, 1178 n.1 (9th Cir. 2012).

   B. The Clean Air Act’s Visibility Protections

    The 1990 amendments to the CAA expanded the CAA’s
focus to include regional haze, which is “visibility
impairment that is caused by the emission of air pollutants
from numerous sources located over a wide geographic
area.” 40 C.F.R. § 51.301; see also 42 U.S.C. § 7492.
Emissions of fine particles (such as sulfates, nitrates, and
other particulate matter) and their precursors (e.g., SO2,
NOx) produce regional haze. 64 Fed. Reg. 35,714, 35,715
(July 1, 1999). In 1999 and again in 2005, the EPA issued
Regional Haze Regulations, and guidelines. 40 C.F.R.
§ 51.300-09; 70 Fed. Reg. 39,104, 39,156–72 (July 6, 2005).
The Regulations set a goal of achieving natural visibility by
2064. 40 C.F.R. § 51.308(d).
10                     YAZZIE V. U.S.E.P.A.

    The CAA “invites each State to submit to EPA a ‘State
Implementation Plan’ (“SIP”) setting forth emission limits
and other measures necessary to make reasonable progress
toward the national visibility goal.”            Nat’l Parks
Conservation Ass’n v. EPA, 788 F.3d 1134, 1138 (9th Cir.
2015) (citing 42 U.S.C. §§ 7410(a), 7491(b)(2)). If a State
elects not to submit a SIP, or if the EPA rejects a SIP in part
or in whole, the EPA must generate a Federal
Implementation Plan (“FIP”) to fill any resulting gaps. Id.
at 1138–39 (citing 42 U.S.C. § 7410(c)(1)(A)).

    Regional haze SIPs must identify the “best available
retrofit technology” (“BART”) to reduce emissions from
certain major emission sources, like the Station. 42 U.S.C.
§ 7491(b)(2). BART is “an emission limitation based on the
degree of reduction achievable through the application of the
best system of continuous emission reduction for each
pollutant which is emitted by an existing stationary facility.”
40 C.F.R. § 51.301. Five factors dictate BART for a
particular source of regional haze. 3 Any source subject to
BART must install and operate the appropriate technology
“as expeditiously as practicable but in no event later than
five years” after approval of a SIP or issuance of a FIP.
42 U.S.C. § 7491(g)(4).

    A State can bypass BART with a “better than BART”
alternative. See Arizona, 815 F.3d at 526; see also 40 C.F.R.
§ 51.308(e)(2). For a state to adopt a BART alternative, its
SIP must “require[] that all necessary emission reductions
     3
       These factors are: (1) the costs of compliance; (2) the energy and
nonair quality environmental impacts of compliance; (3) any existing
pollution control technology in use at the source; (4) the remaining useful
life of the source; and (5) the degree of improvement in visibility which
may reasonably be anticipated to result from the use of such technology.
42 U.S.C. § 7491(g)(2).
                   YAZZIE V. U.S.E.P.A.                    11

take place during the period of the first long-term strategy
for regional haze.” 40 C.F.R. § 51.308(e)(2)(iii). In one of
three ways, a State can demonstrate “better-than-BART”
through “greater reasonable progress: (1) “[i]f the
distribution of emissions is not substantially different than
under BART, and the alternative measure results in greater
emission reductions”; (2) “[i]f the distribution of emissions
is significantly different,” then a State must conduct
“dispersion modeling,” which focuses on visibility rather
than emissions; or (3) the catch-all “otherwise based on the
clear weight of the evidence.”                   40 C.F.R.
§ 51.308(e)(2)(i)(E), (e)(3).

   C. Tribal Authority Rule

    The 1990 CAA Amendments authorized the EPA “to
treat Indian Tribes as States” if certain conditions were met,
and to issue regulations outlining when that treatment should
occur. 42 U.S.C. § 7601(d)(1)(A). The Amendments also
permitted the EPA to directly administer haze reduction
efforts on tribal lands if it “determine[d] that the treatment
of Indian tribes as identical to States is inappropriate or
administratively infeasible[.]” Id. § 7601(d)(4).

    In 1998, the EPA issued its “Tribal Authority Rule”
(“TAR”), which created a mechanism for tribes to develop a
“Tribal Implementation Plan” (“TIP”), similar to a SIP, to
carry out the CAA’s requirements on tribal land. 40 C.F.R.
§§ 49.1–11; 63 Fed. Reg. 7,254 (Feb. 12, 1998). The TAR
treats eligible tribes “in the same manner as States with
respect to all provisions of the Clean Air Act and
implementing regulations,” except for mandatory plan
submittal deadlines. 40 C.F.R. § 49.3; see also id. § 49.4.
“Tribes may choose, but are not required, to adopt [TIPs] for
their reservations. Because tribes are not required to adopt
[TIPs], the TAR authorizes EPA to promulgate [FIPs] to fill
12                 YAZZIE V. U.S.E.P.A.

in any gaps.” Ariz. Pub. Serv. Co. v. EPA, 562 F.3d 1116,
1119 (10th Cir. 2009) (APS). When a Tribe chooses not to
issue a TIP, the EPA must “promulgate without
unreasonable delay such Federal implementation plan
provisions as are necessary or appropriate to protect air
quality.” 40 C.F.R. § 49.11(a).

    The TAR also exempted tribes from certain CAA
requirements because States were farther along in
“developing air planning and implementation expertise.”
63 Fed. Reg. at 7,265. For example, the TAR permits the
EPA more time to promulgate a FIP for a tribe than for a
State, and exempts tribes from “specific visibility
implementation plan submittal deadlines established under
section 169A of the Act,” 42 U.S.C. § 7491. 40 C.F.R.
§ 49.4(e).

     D. The Station and its FIP

        1. The EPA’s Initial Proposal

    The Navajo Nation did not issue a TIP for the Station, so
in February 2013 the EPA issued a proposed FIP under the
TAR. Relevant here, the FIP proposed both a BART
determination and a BART alternative. Under the BART
determination, the Station would reduce its NOx emissions
by nearly 80% within five years after the effective date of a
final FIP, largely through the installation of both catalytic
reduction and low NOx burners/separated over-fired air
technologies. 78 Fed. Reg. at 8,287–88. Under its BART
alternative determination, the FIP extended the deadlines for
achieving NOx emission reductions to 2023. Id. at 8,289. It
also gave an emission “credit” for the Station’s early and
voluntary 2009–11 installation of the low NOx
burners/separated over-fired air technology. Id.
                      YAZZIE V. U.S.E.P.A.                          13

    The EPA proposed these alternatives so that the Station
had “options for flexibility in achieving emissions
reductions required” under the proposed BART
determination. Id. at 8,288. Flexibility was necessary, the
EPA concluded, because of the important economic and
water issues tied to the future of the Station. Id. at 8,289.

        2. The EPA’s Supplemental Proposal

    After receiving feedback from the Technical Work
Group (“TWG”) 4 during the comment period, the EPA
issued its supplemental proposal in October 2013. 78 Fed.
Reg. at 62,509. Under this revised plan, the Station would
cease conventional coal-fired power generation by the end
of 2044. Id. at 62,521. The plan would impose a “lifetime
cap” on total NOx emissions from 2009 to 2044, reduce
power generation at the Station, and would incorporate an
emission credit for the Station’s early installation of the low
NOx burners/separated over-fired air technology. Id. at
62,513–14, 62,521. The EPA concluded that this revised
plan qualified as a better than BART alternative. Id. at
62,514–17.

        3. The EPA’s Final Rule and Challenges

    In August 2014, the EPA issued its final rule, which
tracked its October 2013 supplemental proposal. 79 Fed.
Reg. at 46,514. It finalized the longer deadline for emission
reductions, as well as the emission credit. Id. at 46,518,
46,547. The EPA reiterated that a “more flexible, extended
    4
     The TWG consisted of the U.S. Department of the Interior, the
Navajo Nation, the Gila River Indian Community, the Salt River Project,
the Central Arizona Water Conservation District, the Environmental
Defense Fund and Western Resource Advocates. 78 Fed. Reg. at 62,512.
14                    YAZZIE V. U.S.E.P.A.

compliance schedule” was warranted due to (1) the Station’s
“unusual and significant challenges”; and (2) the EPA’s
discretion under the TAR. 5 Id. at 46,515–16. Petitions
challenging this final rule were filed timely, and
consolidated.

II. STANDARD OF REVIEW

     Under the Administrative Procedures Act (“APA”), we
uphold a final agency action unless it is “arbitrary,
capricious, an abuse of discretion or otherwise not in
accordance with law.” 5 U.S.C. § 706(2). 6 The standard is
“highly deferential, presuming the agency action to be valid
and affirming the agency action if a reasonable basis exists
for its decision.” Bahr v. EPA, 836 F.3d 1218, 1229 (9th Cir.
2016) (citation and internal quotation marks omitted).

    Further, agency interpretations of statutes and
regulations may be entitled to deference. An agency’s
interpretation of a statute it administers is governed under
the two-step framework established in Chevron, U.S.A., Inc.
v. Natural Resources Defense Council, 467 U.S. 837, 842–
45 (1984). The first step investigates whether Congress has
addressed “the precise question at issue. If the intent of
Congress is clear, that is the end of the matter; for the court,

     5
       The EPA also finalized that under the TAR, it was not “necessary
or appropriate” to conduct a BART determination for particulate matter
(“PM”) emissions because they were “well controlled,” and because the
Station would be required to further reduce PM emissions pursuant to
the Mercury and Air Toxics Standards (“MATS”) rule. 79 Fed. Reg. at
46,531-32.

    6
      The EPA’s final action is reviewed under the APA rather than
under the CAA, 42 U.S.C. § 7607(d)(9). See APS, 562 F.3d at 1122 n.4.
The parties agree that the standards are equivalent.
                    YAZZIE V. U.S.E.P.A.                    15

as well as the agency, must give effect to the unambiguously
expressed intent of Congress.” Id. at 842–43 (citation
omitted). Under the second step, “if the statute is silent or
ambiguous with respect to the specific issue, the question for
the court is whether the agency’s answer is based on a
permissible construction of the statute.” Id. at 843.

    In addition, an agency’s interpretation of its own
regulation is “controlling unless plainly erroneous or
inconsistent with the regulation.” Auer v. Robbins, 519 U.S.
452, 461 (1997). When faced with ambiguous regulatory
language, “we defer to the EPA’s interpretation if it is
reasonable, i.e., if it ‘sensibly conforms to the purpose and
wording of the regulations.’” El Comite Para el Bienestar
de Earlimart v. EPA, 786 F.3d 688, 696 (9th Cir. 2015)
(citation omitted).

    Petitioners argue that the EPA’s interpretation of the
CAA and its implementing regulations should not be
afforded deference here because: (1) the U.S. Government
has a financial interest in the Station via the U.S. Department
of the Interior’s nearly 25% ownership stake in the Station;
and (2) the EPA along with the U.S. Department of Interior
and the U.S. Department of Energy issued a joint statement
in January 2013 in which petitioners contend the EPA
essentially agreed to minimize negative impacts on U.S.
government ownership interests. We disagree.

    The federal government’s partial ownership of the
Station does not weigh against affording deference to the
EPA’s interpretation of the CAA and its implementing
regulations. Importantly, here the EPA does not have any
self-serving or financial interest in the Station’s continued
operation. Cf. Amalgamated Sugar Co. LLC v. Vilsack,
563 F.3d 822, 834 (9th Cir. 2009) (holding that Chevron
deference was inappropriate where the agency itself, rather
16                 YAZZIE V. U.S.E.P.A.

than the U.S. government in general, had a financial interest
in a particular statutory interpretation).

    Further, the joint statement does not demonstrate that the
EPA’s interpretation was intended to protect the U.S.
government’s ownership interest in the Station. Rather,
petitioners take phrases from the joint statement out of
context, and overlook that the statement also provided that it
“does not alter the[] authorities and responsibilities” of the
various federal agencies overseeing the Station, including
the EPA’s “Clean Air Act regulatory role relating to air
quality and visibility in the region, which includes
promulgating Best Available Retrofit Technology (BART)
requirements for [the Station].”

    Accordingly, the federal government’s partial ownership
of the Station does not eliminate any deference to the EPA’s
interpretation of the CAA and its implementing regulations.

III. DISCUSSION

     A. Applicability of Emission Reduction Deadlines to
        Instant FIP

        1. Statutory Deadline to Implement BART

    Under the CAA, BART must be implemented “as
expeditiously as practicable but in no event later than five
years” after a SIP’s approval or the promulgation of a FIP.
42 U.S.C. § 7491(b)(2)(A), (g)(4). Petitioners contend that
the EPA failed to comply with this statutory deadline.

    However, the CAA’s five-year deadline does not apply
here. By its terms, this statutory deadline only applies to
BART, and here, the FIP promulgated a “better than BART”
alternative – not BART. Therefore, the instant FIP is not
                      YAZZIE V. U.S.E.P.A.                          17

subject to the CAA’s five-year deadline to implement
BART.

        2. Regulatory Deadline to Implement BART
           Alternative

    Under the Regional Haze Regulations, for a BART
alternative, a SIP must “require[] that all necessary emission
reductions take place during the period of the first long-term
strategy for regional haze.” 40 C.F.R. § 51.308(e)(2)(iii).
The parties dispute whether this regulatory deadline applies
to the instant FIP promulgated in place of a Tribal
Implementation Plan under the TAR, rather than under a
State Implementation Plan.

             a. Applicability of TAR to the Station

    As a preliminary matter, petitioners contend that              the
EPA could not issue the FIP under the TAR because                  the
Navajo Nation contracted away its right to regulate                the
Station and, therefore, it was not a tribe eligible                for
“treatment as a State” and could not issue a TIP. 7

    The CAA authorizes the EPA “to treat Indian tribes as
States.” 42 U.S.C. § 7601(d)(1)(A). But the EPA may treat
Indian tribes as States only if the tribe meets certain
requirements, including “if the Indian tribe is reasonably
expected to be capable, in the judgment of [the EPA], of
carrying out the functions to be exercised in a manner
consistent with the terms and purposes of this chapter and all
applicable regulations.” Id. § 7601(d)(2)(C); see also
40 C.F.R. § 49.6(d). Further, “[i]n any case in which [the

    7
      Contrary to the EPA’s contentions, petitioners’ argument is not
waived because Yazzie sufficiently raised it during the comment period.
18                  YAZZIE V. U.S.E.P.A.

EPA] determines that the treatment of Indian tribes as
identical to States is inappropriate or administratively
infeasible, [the EPA] may provide, by regulation, other
means by which [the EPA] will directly administer such
provisions so as to achieve the appropriate purpose.”
42 U.S.C. § 7601(d)(4).

    Pursuant to this statutory authority, the EPA issued the
TAR, 40 C.F.R. § 49.11(a). This section provides that the
EPA shall promulgate “such Federal implementation plan
provisions as are necessary or appropriate to protect air
quality . . . if a tribe does not submit a tribal implementation
plan meeting the completeness criteria . . . or does not
receive EPA approval of a submitted tribal implementation
plan.” 40 C.F.R. § 49.11(a).

    Petitioners argue that § 49.11(a) only applies when a
tribe “eligible” for treatment as a State fails to submit an
approved TIP, and here the Navajo Nation was not “eligible”
for treatment as a State because it had contracted away its
power to regulate the Station.

    However, § 49.11(a) by its plain terms is not limited to
“eligible” tribes who can be treated as a State. Rather, it
applies so long as “a tribe” does not submit an approved TIP;
it mentions nothing about a tribe’s eligibility. 40 C.F.R.
§ 49.11(a). Moreover, the CAA, 42 U.S.C. § 7601(d)(4),
authorizes the EPA to adopt a FIP when a tribe is not treated
as a State (i.e., “[i]n any case in which [the EPA] determines
that the Treatment of Indian tribes as identical to States is
inappropriate or administratively infeasible”). Thus, the
EPA’s authority to promulgate a FIP for tribal areas under
the TAR is not dependent on a tribe’s eligibility for treatment
as a State.
                      YAZZIE V. U.S.E.P.A.                         19

    In sum, the EPA reasonably concluded that the TAR
applied because the Navajo Nation had not submitted a TIP,
which under § 49.11(a), gave the EPA authority to
promulgate a FIP for NOx emissions at the Station. See
Auer, 519 U.S. at 461 (an agency’s interpretation of its own
regulation is “controlling unless plainly erroneous or
inconsistent with the regulation”); see also Chevron,
467 U.S. at 842–45 (setting forth standard for deferring to
agency statutory interpretation).

             b. Applicability of Section 51.308(e)(2)(iii) to
                the FIP

    Under § 51.308(e)(2)(iii), if a State implements a BART
alternative, its SIP must “require[] that all necessary
emission reductions take place during the period of the first
long-term strategy for regional haze.”             40 C.F.R.
§ 51.308(e)(2)(iii). The parties dispute whether the FIP for
the Station is subject to this deadline. 8 We conclude that the
EPA reasonably determined that it is not.

    The EPA contends that § 51.308(e)(2)(iii)’s deadline
only applies when a State adopts a BART alternative. It
reasons that the deadline is explicitly tied to “the period of
the first long-term strategy for regional haze,” for which
States were required to submit a plan by December 2007, but
which tribes were not subject to under the TAR. See
40 C.F.R. § 49.4(e) (exempting tribes from “[s]pecific
visibility implementation plan submittal deadlines
established under section 169A of the Act”). We cannot say

    8
       The parties also dispute whether the end of the first long-term
strategy period under § 51.308(e)(2)(iii) is December 31, 2017, or
December 31, 2018. The exact deadline is irrelevant because the key
issue is whether the deadline in § 51.308(e)(2)(iii) applies at all.
20                  YAZZIE V. U.S.E.P.A.

that the EPA’s interpretation of its own regulation – that
§ 51.308(e)(2)(iii) does not apply to tribes because tribes are
not subject to the underlying deadline for long-term
strategies – is “plainly erroneous or inconsistent with the
regulation.” Auer, 519 U.S. at 461.

    The EPA contends that the TAR entitled it to establish
different “necessary or appropriate” deadlines for the FIP.
40 C.F.R. § 49.11(a) (providing that the EPA shall
promulgate “such Federal implementation plan provisions as
are necessary or appropriate to protect air quality” where a
tribe fails to submit an approved TIP); see also 79 Fed. Reg.
at 46,533–34; 79 Fed. Reg. at 8,289.

     Petitioners argue that the EPA’s interpretation is
contrary to the plain language and purpose of the CAA and
its implementing regulations. They assert that any flexibility
under the TAR applies only to “procedural,” not
“substantive,” requirements of the CAA, or that it only
applies to “submission deadlines, not compliance
deadlines.” See 40 C.F.R. § 49.4(e) (exempting tribes from
“[s]pecific visibility implementation plan submittal
deadlines established under section 169A of the Act”
(emphasis added)); 70 Fed. Reg. at 39,158 (“Tribes are not
subject to the deadlines for submitting visibility
implementation plans and may use a modular approach to
CAA implementation.” (emphasis added)). Accordingly,
petitioners contend that the TAR does not exempt tribal
sources from meeting the substantive pollution reduction
requirements for a BART alternative under the CAA, which
purportedly includes § 51.308(e)(2)(iii)’s compliance
deadline.

   The Tenth Circuit’s decision in APS is instructive. In
APS, the court rejected the environmentalists’ argument that
a FIP promulgated in place of a TIP for the Four Corners
                         YAZZIE V. U.S.E.P.A.                          21

Power Plant on the Navajo Nation reservation in New
Mexico was arbitrary and capricious because the FIP did not
satisfy the SIP “completeness criteria.” 562 F.3d at 1119–
21. The court reasoned that the TAR “provides the EPA
discretion to determine what rulemaking is necessary or
appropriate to protect air quality and requires the EPA to
promulgate such rulemaking. Nothing in § 49.11(a) requires
the EPA – as opposed to a tribe – to submit a plan meeting
the completeness criteria[.]” Id. at 1125. The court thus
deferred to the EPA’s interpretation of the TAR because it
was not “plainly erroneous or inconsistent with the
regulation,” and denied the environmentalists’ petition. Id.
(citation omitted).

    Importantly, APS did not hold that the TAR only excused
tribes from meeting procedural requirements. Rather, the
court also rejected the environmentalists’ more substantive
argument that “the TAR requires the EPA to implement a
more stringent federal plan[.]”9 Id. at 1124 (emphasis in
original).

    As recognized by APS, the TAR grants the EPA wide
discretion to determine what rulemaking is required to
protect air quality on tribal lands. Nothing in the TAR
requires the FIP to comply with the regional haze deadline
applicable to a SIP under § 51.308(e)(2)(iii).

   Petitioners also argue that the instant FIP is inconsistent
with a Four Corners FIP that, like here, concerned regional
haze and NOx emissions. 10 The Four Corners FIP BART
    9
      Further, contrary to petitioners’ argument, APS did not suggest that
a FIP must be stricter than a SIP (or a proposed FIP). See 562 F.3d at
1125.

    10
         This Four Corners FIP differs from the one at issue in APS.
22                 YAZZIE V. U.S.E.P.A.

alternative complied with § 51.308(e)(2)(iii)’s requirement
that “all necessary emission reductions take place during the
period of the first long-term strategy for regional haze.”
77 Fed. Reg. 51,620, 51,641 (August 24, 2012). However,
the fact that the Four Corners FIP complied with the
regulatory deadline does not establish that the TAR as a rule
requires a FIP to comply with this deadline. Given that the
Four Corners FIP had a longer timeframe to comply with the
regulatory deadline (it was promulgated in 2012 rather than
in 2014 like the instant FIP) the EPA could have simply
exercised its discretion to determine that it was not
“necessary or appropriate” to consider whether the Four
Corners BART alternative required an extended deadline
under § 49.11(a).

    In sum, the EPA reasonably interpreted the TAR
(40 C.F.R. §§ 49.4(e), 49.11(a)) and the Regional Haze
Regulations (40 C.F.R. § 51.308(e)(2)(iii)) to conclude that
the emission reductions deadline in § 51.308(e)(2)(iii) does
not apply to FIPs for regional haze that are promulgated in
place of TIPs. We must defer to this interpretation because
it is not “plainly erroneous or inconsistent with the
regulation.” Auer, 519 U.S. at 461.

     B. EPA’s Determination that the FIP Alternative is
        “Better than BART” for NOx Emissions

    Petitioners next challenge the EPA’s determination that
the FIP alternative is “better than BART,” i.e., that it “will
achieve greater reasonable progress than would have
resulted from the installation and operation of BART.”
40 C.F.R. § 51.308(e)(2)(i). Under the Regional Haze
Regulations, there are three different methods to show that
an alternative will result in “greater reasonable progress”:
(1) “[i]f the distribution of emissions is not substantially
different than under BART, and the alternative measure
                    YAZZIE V. U.S.E.P.A.                     23

results in greater emission reductions,” id. § 51.308(e)(3);
(2) if the distribution of emissions is significantly different,
“dispersion modeling” must be conducted, which focuses on
visibility rather than emissions, id.; or (3) “otherwise based
on the clear weight of the evidence,” id. § 51.308(e)(2)(i)(E).

    Here, EPA relied on the first method: that (1) the
“distribution of emissions” is not substantially different
under BART and the alternative; and (2) the alternative
“results in greater emission reductions.” Id. § 51.308(e)(3);
see also 79 Fed. Reg. at 46,533.

        1. “Clear Weight of the Evidence” Standard
           Inapplicable Here

    As a preliminary matter, petitioners argue that the EPA
failed to show “by the clear weight of the evidence” that its
alternative achieves “greater reasonable progress” than
BART. Petitioners also fault the EPA for not conducting
visibility modeling for its BART alternative.

    As described above, there are three separate methods to
establish that an alternative is “better than BART.” See
71 Fed. Reg. 60,612, 60,622 (Oct. 13, 2006) (2006 revision
to BART Guidelines stating that the “weight of evidence”
approach is “an alternative to the methodology set forth in
section 51.308(e)(3)” (emphasis added)); WildEarth
Guardians v. EPA, 770 F.3d 919, 934 (10th Cir. 2014)
(concluding that a “state can use the two quantitative
methods stated in § 51.308(e)(3) or apply a qualitative
standard (the clear weight of evidence)” (emphasis added)).
The “clear weight of the evidence” standard only applies to
the third method. 40 C.F.R. § 51.308(e)(2)(i). Here, the
EPA chose the first method, which does not incorporate the
“clear weight of the evidence” standard. Id. § 51.308(e)(3).
Similarly, the EPA was not required to conduct visibility
24                  YAZZIE V. U.S.E.P.A.

modeling, as that is only required under the second method.
Id.

    Therefore, under its chosen method, the EPA was only
required to show that (1) the “distribution of emissions” is
not substantially different under BART; and (2) the
alternative “results in greater emission reductions.” Id.

       2. EPA Interpretation          of   “Distribution    of
          Emissions”

    Petitioners contend that the FIP did not meet the initial
prong of the first method of demonstrating greater
reasonable progress – showing that the “distribution of
emissions” is not substantially different under BART and the
FIP. The EPA concluded that the distribution of emissions
is not substantially different between BART and the FIP’s
BART alternative because the “geographic distribution of
emissions is similar” as both “apply to the same source” (i.e.,
the Station). 79 Fed. Reg. at 46,533 (emphasis added). As
such, the EPA interpreted the phrase “distribution of
emissions” under § 51.308(e)(3) to refer only to the
geographic distribution of emissions (i.e., locations/sources
of the emissions). Petitioners insist that “distribution of
emissions” should also include the temporal distribution of
emissions (i.e., the timing of the emissions).

    The plain language of the regulation – “distribution of
emissions” – does not indicate whether the distribution is
geographic, temporal, or both. However, the EPA has
consistently interpreted this phrase to refer to geographic
distribution. See, e.g., 77 Fed. Reg. 18,052, 18,075 (March
26, 2012); 70 Fed. Reg. at 39,137. The consistency of the
EPA’s interpretation weighs in its favor. See Nat. Res. Def.
Council v. EPA, 526 F.3d 591, 602 (9th Cir. 2008) (“As a
component of whether an agency’s interpretation is
                       YAZZIE V. U.S.E.P.A.                            25

permissible, we will take into account the consistency of the
agency’s position over time.”); see also Bassiri v. Xerox
Corp., 463 F.3d 927, 933 (9th Cir. 2006) (special deference
due to Department of Labor’s consistent interpretation of its
own regulation).

    Moreover, as the EPA notes, this interpretation is
reasonable because where, as here, there is only one source
being regulated, “if emissions are reduced . . . visibility in
the impacted area is necessarily improved.”

    Further, while the EPA acknowledges that the timing of
emissions reductions is important under the CAA and its
implementing regulations, the key inquiry here is whether
§ 51.308(e)(3) requires the EPA to consider timing in
evaluating the “distribution of emissions” prong. 11 As
explained above, the BART statutory deadline does not
apply to a BART alternative. Nor does the BART alternative
regulatory deadline apply to this FIP promulgated under the
TAR. Petitioners have not shown that the EPA was required
to incorporate timing in this comparison, or that the EPA’s
consistent interpretation of “distribution of emissions” (as
referring to geographic distribution, not temporal
distribution) is “plainly erroneous or inconsistent with the

    11
         It is of note that the instant FIP contains timing requirements,
albeit not as expeditious as petitioners would like. The BART alternative
has a lifetime cap on total NOx emissions from 2009 to 2044. 79 Fed.
Reg. at 46,518. In addition, conventional coal-fired power generation at
the Station must cease by 2044. Id. Further, the Regional Haze
Regulations set a goal of achieving natural visibility at all Class I areas
by 2064. 40 C.F.R. § 51.308(d); see also 79 Fed. Reg. at 46,534 (“EPA
. . . determin[ed] that the TWG Alternative is ‘better than BART’ based
on achieving greater NOx emissions reductions over a similar
geographic distribution, within the date of the goal specified in the
[Regional Haze Regulations] of achieving natural conditions in 2064.”).
26                   YAZZIE V. U.S.E.P.A.

regulation.” Auer, 519 U.S. at 461. As such, we must defer
to the EPA’s interpretation.

        3. The FIP’s Inclusion of Emission Credit in
           Comparison of Emission Reductions

    Putting aside the timing of emission reductions,
petitioners also argue that the FIP’s BART alternative does
not actually “result[] in greater emission reductions” than
BART, 40 C.F.R. § 51.308(e)(3), and therefore does not
meet the second prong of the first method for demonstrating
greater reasonable progress.        The BART alternative
incorporated an emission credit for the Station’s voluntary
2009–11 installation of the low NOx burners/separated over-
fired air technology. 78 Fed. Reg. at 62,513–14, 62,521.
The EPA concedes that absent this credit, the BART
alternative would not achieve greater NOx reductions than
BART. The key issue is thus whether it was reasonable for
the EPA to give the Station an emission credit when
evaluating if the BART alternative “results in greater
emission reductions” than BART under 40 C.F.R.
§ 51.308(e)(3).

    Petitioners argue that the EPA’s incorporation of the
credit into its BART alternative calculation is unreasonable
because it is inconsistent with the EPA’s prior statements
regarding BART for the Station. In particular, when the
Station applied for a permit to install the low NOx
burners/separated over-fired air technology, the EPA
represented that the “early installation . . . will not affect the
baselines for cost or visibility improvements in the BART
determination, and therefore will not influence EPA’s
determination of the proper NOx reductions required to be
achieved from BART.” 78 Fed. Reg. at 8,284.
                    YAZZIE V. U.S.E.P.A.                     27

    The EPA’s BART determination was consistent with this
prior statement. For its BART analysis, the EPA used a
baseline period of NOx emission from 2001–03, prior to the
installation of the low NOx burners/separated over-fired air
technology. 79 Fed. Reg. at 46,535; 78 Fed. Reg. at 8,285.
As such, the EPA did not consider the emission credit in its
“five-factor analysis or BART determination for” the
Station. 79 Fed. Reg. at 46, 535. Rather, the EPA only used
the emission credit for “evaluating alternatives to BART.”
Id. Therefore, the EPA’s incorporation of the credit into its
BART alternative was not inconsistent with its prior
statement.

    Petitioners also argue that the EPA was inconsistent in
factoring in the emissions credit when computing the
emissions reductions under the BART alternative, but not
when calculating reductions that would be attributable to
BART. The credit, however, reflects the fact that the
technology was installed years before it would have been
required to be installed under BART. This is because the
Station could have waited until it was required to implement
BART before installing any emissions reduction technology.
The credit thus reflects the reductions achieved years prior
to the time they would have been required.

    Moreover, as the EPA noted in its FIP, the TAR gave it
discretion to allow a credit for the BART alternative. 79 Fed.
Reg. at 46,535. As discussed above, the TAR grants the
EPA wide latitude to determine what “Federal
implementation plan provisions . . . are necessary or
appropriate to protect air quality” for a source on tribal lands
when there is no TIP. 40 C.F.R. § 49.11. Here, it was not
unreasonable for the EPA to reward the Station through a
credit for its early and voluntary installation of the low NOx
28                 YAZZIE V. U.S.E.P.A.

burners/separated over-fired air technology, which resulted
in real and early emission reductions.

    In sum, it was reasonable for the EPA to give the Station
an emission credit when evaluating if the BART alternative
“results in greater emission reductions,” 40 C.F.R.
§ 51.308(e)(3), than BART. See Auer, 519 U.S. at 461; see
also Chevron, 467 U.S. at 842–45. Accordingly, we defer to
the EPA’s reasonable determination that the FIP alternative
was “better than BART,” i.e., that it “will achieve greater
reasonable progress than would have resulted from the
installation and operation of BART.”             40 C.F.R.
§ 51.308(e)(2)(i).

     C. EPA Decision not to Determine BART for
        Particulate Matter

    Finally, petitioners contend that the EPA unlawfully
failed to conduct a BART analysis or include any BART
emission limits for PM for the Station. The EPA determined
that it was not “necessary or appropriate” under TAR to
conduct a BART determination for PM emissions because
they were already “well controlled” and the Station would
be required to further reduce PM emissions pursuant to the
MATS rule. 79 Fed. Reg. at 46,531–32; 78 Fed. Reg. at
8,279. This was a reasonable exercise of the EPA’s
discretion under the TAR.

IV. CONCLUSION

    In light of the discretion that the EPA enjoys, we cannot
conclude that, under these unique circumstances, the EPA
acted arbitrarily and capriciously. We thus deny the
petitions.
       YAZZIE V. U.S.E.P.A.                    29

       Glossary of Acronyms

BART      best available retrofit technology

CAA       Clean Air Act (also, the “Act”)

EPA       U.S. Environmental Protection
          Agency

FIP       Federal Implementation Plan

MATS      Mercury and Air Toxics Standards

NOx       nitrogen oxides

PM        particulate matter

SIP       State Implementation Plan

TAR       Tribal Authority Rule

TIP       Tribal Implementation Plan

TWG       Technical Work Group
