Partial Approval and Disapproval of Air Quality Implementation Plans; Arizona; Regional Haze State Implementation Plan for the Second Implementation Period and Prong 4 (Visibility) for the 2015 Ozone and 2012 Particulate Matter Standards, 102744-102773 [2024-29508]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 89, Number 243 (Wednesday, December 18, 2024)]
[Rules and Regulations]
[Pages 102744-102773]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-29508]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2024-0005; FRL-11919-02-R9]


Partial Approval and Disapproval of Air Quality Implementation 
Plans; Arizona; Regional Haze State Implementation Plan for the Second 
Implementation Period and Prong 4 (Visibility) for the 2015 Ozone and 
2012 Particulate Matter Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is partially 
approving and partially disapproving the regional haze state 
implementation plan (SIP) revision submitted by Arizona on August 15, 
2022 (``2022 Arizona Regional Haze Plan''), under the Clean Air Act 
(CAA) and the EPA's Regional Haze Rule (RHR) for the program's second 
implementation period. Arizona's SIP submission was developed to 
address the requirement that states must periodically revise their 
long-term strategies for making reasonable progress towards the 
national goal of preventing any future, and remedying any existing, 
anthropogenic impairment of visibility, including regional haze, in 
mandatory Class I Federal areas. The SIP submission also addresses 
other applicable requirements for the second implementation period of 
the regional haze program. Within this action, the EPA is also 
disapproving the visibility transport prong of Arizona's infrastructure 
SIP submittals for the 2012 annual fine particulate matter 
(PM2.5) and 2015 ozone National Ambient Air Quality 
Standards (NAAQS). The EPA is taking this action pursuant to CAA 
sections 110 and 169A.

DATES: This rule is effective on January 17, 2025.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-R09-OAR-2024-0005. All documents in the docket are 
listed on the https://www.regulations.gov website. Although listed in 
the index, some information is not publicly

[[Page 102745]]

available, e.g., Confidential Business Information (CBI) or other 
information whose disclosure is restricted by statute. Certain other 
material, such as copyrighted material, is not placed on the internet 
and will be publicly available only in hard copy form. Publicly 
available docket materials are available through https://www.regulations.gov, or please contact the person identified in the FOR 
FURTHER INFORMATION CONTACT section for additional availability 
information. If you need assistance in a language other than English or 
if you are a person with a disability who needs a reasonable 
accommodation at no cost to you, please contact the person identified 
in the FOR FURTHER INFORMATION CONTACT section.

FOR FURTHER INFORMATION CONTACT: Michael Dorantes, Geographic 
Strategies & Modeling Section (AIR-2-2), Planning & Analysis Branch, 
Air and Radiation Division, EPA Region IX, 75 Hawthorne Street, San 
Francisco, CA 94105; phone: (415) 972-3934; email: 
[email protected].

SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us'' and 
``our'' refer to the EPA.

Table of Contents

I. Background
    A. Regional Haze Plan for the Second Implementation Period
    B. Prong 4 (Visibility) of the 2012 PM2.5 NAAQS and 
2015 Ozone NAAQS Infrastructure SIPs
II. Public Comments and EPA Responses
    A. Comment Letter From Tri-State
    B. Comment Letter From ADEQ
    C. Comment Letter From the Chamber and AMC
    D. Comment Letter From TEP
    E. Comment Letter From SRP
    F. Community Sign-On Letter
    G. Comment Letter From NPCA et al.
III. Final Action
IV. Statutory and Executive Order Reviews

I. Background

A. Regional Haze Plan for the Second Implementation Period

    On August 15, 2022,\1\ the Arizona Department of Environmental 
Quality (ADEQ) submitted the 2022 Arizona Regional Haze Plan. ADEQ 
supplemented its SIP revision on August 25, 2023, with nonpoint source 
rules (``2023 Arizona Regional Haze Rules Supplement'').\2\ ADEQ made 
these SIP submissions to address requirements of the CAA's regional 
haze program pursuant to CAA sections 169A and 169B and 40 CFR 51.308.
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    \1\ Letter dated August 15, 2022, from Daniel Czecholinski, 
Director, Arizona Department of Environmental Quality Air Quality 
Division, to Martha Guzman, Regional Administrator, EPA Region IX 
(submitted electronically August 15, 2022). On August 16, 2022, the 
EPA determined that the SIP submittal met the completeness criteria 
outlined in 40 CFR part 51, Appendix V. Letter dated August 16, 
2022, from Elizabeth Adams, Director, Air and Radiation Division, 
EPA Region IX, to Daniel Czecholinski, Director, Arizona Department 
of Environmental Quality Air Quality Division.
    \2\ Letter dated August 21, 2023, from Daniel Czecholinski, 
Director, Arizona Department of Environmental Quality Air Quality 
Division, to Martha Guzman, Regional Administrator, EPA Region IX 
(submitted electronically August 25, 2023).
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    On May 31, 2024, the EPA published a notice of proposed rulemaking 
proposing partial approval and partial disapproval of the 2022 Arizona 
Regional Haze Plan SIP submission as partially satisfying the regional 
haze requirements for the second implementation period contained in the 
CAA and 40 CFR 51.308.\3\ We did not propose to act on the 2023 Arizona 
Regional Haze Rules Supplement.
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    \3\ 89 FR 47398.
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    The EPA is now approving the elements of the 2022 Arizona Regional 
Haze Plan related to requirements contained in 40 CFR 51.308(f)(1), 
(f)(4)-(6), and (g)(1)-(5). The EPA is disapproving the elements of the 
2022 Arizona Regional Haze Plan related to requirements contained in 40 
CFR 51.308(f)(2), (f)(3), and (i)(2)-(4). Our proposed action and our 
responses to comments in section II of this document contain more 
information on the basis for this rulemaking and on our evaluation of 
the submittal.

B. Prong 4 (Visibility) of the 2012 PM2.5 NAAQS and 2015 Ozone NAAQS 
Infrastructure SIPs

    Arizona submitted its infrastructure SIP submission for the 2012 
PM2.5 NAAQS on December 11, 2015 (``2015 PM2.5 I-
SIP submittal'').\4\ Arizona also submitted its infrastructure SIP 
submission for the 2015 ozone NAAQS on September 24, 2018 (``2018 Ozone 
I-SIP submittal'').\5\
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    \4\ Letter dated December 11, 2015, from Eric Massey, Director, 
Air Quality Division, ADEQ, to Jared Blumenfeld, Regional 
Administrator, EPA Region IX.
    \5\ Letter dated September 24, 2018, from Timothy S. Franquist, 
Director, Air Quality Division, ADEQ, to Michael Stoker, Regional 
Administrator, EPA Region IX (submitted electronically September 24, 
2018).
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    Our May 31, 2024 proposed rulemaking action proposed to disapprove 
the prong 4 portions of Arizona's 2018 Ozone I-SIP submittal and 2015 
PM2.5 I-SIP submittal. The EPA is now disapproving the Prong 
4 elements of Arizona's 2018 Ozone I-SIP submittal and 2015 
PM2.5 I-SIP submittal. Our proposed action contains more 
information on the basis for this rulemaking and on our evaluation of 
the submittals.

II. Public Comments and EPA Responses

    The EPA's May 31, 2024 proposed rulemaking action provided a 30-day 
public comment period that would have ended on July 1, 2024. We 
received four comments requesting an extension of the comment period. 
On June 26, 2024,\6\ the EPA extended the comment period for the 
proposed rulemaking action by 14 days in response to requests from 
commenters. This action extended the close of the comment period to 
July 15, 2024.
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    \6\ 89 FR 53372.
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    The EPA received an additional ten unique comments, including one 
anonymous comment,\7\ two comments from private individuals,\8\ and 
comment letters from Tri-State Generation and Transmission Association, 
Inc. (``Tri-State''),\9\ ADEQ,\10\ the Arizona Chamber of Commerce and 
Industry and the Arizona Manufacturers Council (``the Chamber and 
AMC''),\11\ Tuscon Electric Power (TEP),\12\ the Salt River 
Agricultural Improvement and Power District (SRP),\13\ 12 community 
organizations (``Community Sign-on Letter''),\14\ and Earthjustice on 
behalf of the National Parks Conservation Association, Sierra Club, and 
the Coalition to Protect America's National Parks (``NPCA et 
al.'').\15\ The anonymous comment and the comments from the private 
individuals were unrelated to our proposed rulemaking. These three 
comments do not require a response. We respond to the issues raised in 
the seven remaining comment

[[Page 102746]]

letters received on our proposed rulemaking in this action.
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    \7\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0014.
    \8\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0015 and https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0019.
    \9\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0016.
    \10\ ADEQ submitted its comment letter twice. The letter is 
available at both https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0017 and https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0018.
    \11\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0020.
    \12\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0021.
    \13\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0023.
    \14\ Available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0022.
    \15\ The comment letter and all Exhibits except for Exhibits 24 
and 60 are available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0024. Exhibits 24 and 60, including an emailed copy of 
the NPCA et al.'s comment letter, are available at https://www.regulations.gov/comment/EPA-R09-OAR-2024-0005-0025.
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A. Comment Letter From Tri-State

    Sections I (``Introduction''), II (``Background Information on Tri-
State''), and III (``Tri-State Supports the Provisions of the Arizona 
Department of Environmental Quality's State Implementation Plan 
Submittal for which EPA has Proposed Approval'') of Tri-State's comment 
letter either provide background information or are supportive of the 
EPA's proposal and therefore do not require a response in our final 
action. We respond to sections IV (``The Partial Disapproval is Overly 
Vague and Should Be Reproposed with a Fulsome and Specific Explanation 
of What EPA Finds Inconsistent with the Clean Air Act and the 
Implementing Regulations''), V (``Additional Emission Reductions Are 
Inappropriate for Springerville Unit 3''), and VI (``EPA's Reliance on 
the July 8, 2021, Clarifications Memorandum Is Inappropriate Because It 
Was Issued Only Days Prior to the Regional Haze State Implementation 
Plans Being Due'') of Tri-State's comment letter below.
    Comment A.1. Tri-State comments that the proposed rule, 
specifically the partial disapproval, is overly vague and does not lend 
itself to the general public being able to adequately understand what 
the EPA finds objectionable regarding the SIP submission. Tri-State 
asserts that the EPA made broad statements about divergences from the 
Control Cost Manual and inadequacies in four-factor analyses and that 
``it [is] impossible to understand with certainty the sources to which 
these overly broad statements apply.'' The commenter also notes that 
the proposed rulemaking action only gives limited examples of what the 
EPA is referring to and asserts that the EPA needs to clearly provide 
where it has issues with the SIP revision as it was submitted not just 
examples of what it is concerned about. Specifically, Tri-State states 
that the proposed rulemaking action makes general comments about ADEQ 
conducting analyses for well-controlled sources to further reduce 
emissions but makes no reference to which sources that the EPA finds to 
be lacking in this area. Tri-State also comments that the vagueness of 
the proposal is not consistent with the cooperative nature of the CAA 
in the EPA working with states.
    Response A.1. We do not agree that the proposal was overly vague or 
that the basis for our proposed partial disapproval was unclear. The 
proposal provided a detailed summary of the 2022 Arizona Regional Haze 
Plan and the EPA's evaluation of the Plan with regard to each of the 
applicable requirements of the CAA and the RHR. With respect to the 
EPA's partial disapproval specifically, the proposal laid out multiple 
reasons for the EPA's determination that the long-term strategy did not 
fully meet the requirements of 40 CFR 51.308(f)(2), related to source 
selection, four-factor analyses (specifically, controlled emissions 
rates and deviations from the Control Cost Manual), and control 
determinations (specifically, the application of cost thresholds, the 
use of visibility as a factor to avoid controls, and the mass-based 
emissions caps at Springerville Generating Station (SGS)).\16\ In each 
instance, we provided at least one example of a unit to which this 
reason applied.\17\ We also explained why the disapproval of the long-
term strategy also necessitated disapproval of the RPG and FLM 
consultation elements.\18\
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    \16\ 89 FR 47398, 47428-47432.
    \17\ Id.
    \18\ Id. at 47432-47433 and 47435-47436.
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    We disagree with the commenter's suggestion that it was necessary 
for the EPA to specify the extent to which each of the flaws identified 
by the EPA applied to each unit considered by ADEQ. The EPA's role in 
reviewing SIPs is to determine whether they meet all of the applicable 
CAA requirements.\19\ In evaluating whether a SIP revision (or a 
portion thereof) meets all of the applicable requirements, the EPA is 
not required to separately evaluate and discuss each of the thousands 
of pieces of information, analyses and determinations comprising the 
SIP submission. Rather, the EPA may focus on those specific elements of 
the SIP revision that form the basis for our determination that certain 
applicable requirements are met and certain applicable requirements are 
not met. Therefore, in this instance, it was reasonable for the EPA to 
summarize our evaluation and cite to examples of where the State's 
documentation, analyses, and determinations did not meet CAA 
requirements, rather than separately evaluating and discussing every 
such instance throughout the SIP revision.
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    \19\ See CAA section 110(k)(3) (``the Administrator shall 
approve [a SIP] submittal as a whole if it meets all of the 
applicable requirements of [the CAA]. If a portion of the plan 
revision meets all the applicable requirements of [the CAA], the 
Administrator may approve the plan revision in part and disapprove 
the plan revision in part'').
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    For example, regarding source selection, our proposal stated that:

    ADEQ did not provide an adequate justification for screening out 
certain sources and units from conducting a four-factor analysis on 
the basis that they are `effectively controlled' as part of its 
source selection process. Specifically, in some cases, ADEQ did not 
identify the controls for each pollutant at each unit or process, 
the associated limits, or where the controls/limits currently exist 
in the Arizona SIP. In other cases, ADEQ listed the controls, but 
did not clearly explain why it is reasonable to assume, without 
conducting a four-factor analysis, that no additional controls would 
be reasonable.

    We then provided examples of specific sources to which these 
concerns applied. In addition, table 3 of the proposal listed all of 
the units that ADEQ screened out as ``effectively controlled'' and 
includes the entirety of ADEQ's rationale for each unit.\20\ This table 
clearly shows that for many of the units, ADEQ did not list controls 
for one or more of the three relevant pollutants (NOX, 
SO2, and PM). Moreover, even for those units where ADEQ did 
list this information, it did not explain why it is reasonable to 
assume, without conducting a four-factor analysis, that no additional 
controls would be reasonable. Furthermore, our proposed rulemaking 
action clearly stated that ADEQ did not adequately explain whether any 
of the existing controls for facilities evaluated within the SIP 
submittal were necessary for reasonable progress and therefore a part 
of the state's long-term strategy. Therefore, it was not necessary to 
specifically identify each source that was deficient in this respect 
because the deficiency applied to every source determined to be 
effectively controlled.
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    \20\ Consistent with their labeling in the Plan, Appendix C.1, 
Table 147, these rationales appear under the heading of 
``Comments.''
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    Finally, regarding the cooperative nature of the CAA, we note that 
the EPA worked extensively with ADEQ during SIP development. EPA and 
ADEQ staff met on a monthly basis beginning in 2019 and continuing 
through 2021 to discuss the development of the Plan. The EPA also 
provided informal written feedback on various elements of the Plan 
between 2019 and 2022. In these communications, the EPA identified many 
of the flaws that are the basis for the partial disapproval, so ADEQ 
was aware of the EPA's concerns prior to the EPA's proposal.
    In conclusion, based on the findings discussed in our proposal and 
elsewhere in this document, we find that the long-term strategy in the 
2022 Arizona Regional Haze Plan does not meet the requirements of 
51.308(f)(2) and we are disapproving the Plan with respect to this 
requirement. Therefore, pursuant to CAA section 110(c), the EPA will be 
required to develop a new

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long-term strategy as part of a FIP, unless the EPA approves a 
subsequent SIP submission that fully meets these requirements. That 
long-term strategy would necessarily include updated source selection, 
four factor analyses, and control determinations that address the 
deficiencies we identified in the Plan. We are available to work with 
ADEQ following this final action to develop a SIP revision, including 
these elements.
    Comment A.2. Tri-State asserted that additional emissions 
reductions are ``inappropriate'' for Springerville Generating Station 
(SGS) Unit 3. Tri-State made a few arguments in support of this 
contention.
    First, Tri-State noted that ADEQ evaluated the currently installed 
NOX emissions controls against technically feasible 
emissions controls and concluded that the current NOX 
emissions controls constitutes best available control technology (BACT) 
for coal-fired electric generating units (EGUs). For SO2, 
Tri-State indicated that ADEQ's analysis for SGS Unit 3 clearly 
demonstrates that Unit 3's emissions ranged from 0.069 to 0.090 lb/
MMBtu on an annual basis and has continuously complied with the Mercury 
and Air Toxics Standard (MATS) SO2 emissions standard of 
0.20 lb/MMBtu, and therefore does not warrant further emissions 
controls. Tri-State also noted language in the EPA's ``Guidance on 
Regional Haze State Implementation Plans for the Second Implementation 
Period'' (``2019 Guidance'') \21\ that describes scenarios in which the 
EPA believes it may be reasonable for a state not to select a 
particular source for further analysis for EGUs that have add-on flue 
gas desulfurization (FGD) and that meets the applicable alternative 
SO2 emissions limit of the MATS rule for power plants.
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    \21\ Guidance on Regional Haze State Implementation Plans for 
the Second Implementation Period. https://www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period. The EPA Office of Air Quality Planning and 
Standards, Research Triangle Park (August 20, 2019).
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    Second, Tri-State noted the visibility improvement at the Mount 
Baldy Wilderness Area in the first planning period, and that Arizona 
will have four additional 10-year planning periods to achieve the 1.3 
deciview improvement needed to achieve natural conditions.
    Finally, Tri-State stated that its intent is to retire SGS Unit 3 
by September 15, 2031, and requested that the EPA include in the final 
rule a provision to allow sources to work with their state regulatory 
agencies to adopt an enforceable commitment to retire a unit, such as 
through a permit condition, to allow the source to forego any further 
emissions control or reduction requirements if a unit is retiring 
within ten years of the Regional Haze SIP approval.
    Response A.2. We partially agree with this comment. First, with 
respect to NOX emissions at SGS Unit 3, ADEQ noted in the 
Plan ``[t]he current controls ([low-NOX burners (LNB), 
overfire air (OFA) with selective catalytic reduction (SCR)] represent 
the most effective NOX control technologies for coal fired 
EGUs and are estimated to achieve 85-95% removal efficiency.'' \22\ We 
agree that the existing LNB, OFA and SCR constitute effective controls 
for NOX at SGS Unit 3. As described in our proposal and in 
response B.1 of this document, existing effective controls are 
generally necessary to make reasonable progress and must be included in 
the SIP, unless the state provides a weight-of-evidence demonstration 
to justify that the existing effective controls are not necessary to 
make reasonable progress. Because the Arizona SIP does not include a 
NOX emissions limit corresponding to these controls for SGS 
Unit 3, the State should have provided such demonstration. 
Specifically, the State should have considered whether SGS Unit 3 is 
subject to an enforceable NOX emissions limit that ensures 
its NOX emissions rate will not increase. Without proper 
justification that emissions of visibility impairing pollutants will 
not increase, it is unclear how reasonable progress is being made 
within the State's long-term strategy for the second planning 
period.\23\
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    \22\ 2022 Arizona Regional Haze Plan, p. 219.
    \23\ See CAA 169A(a)(1) ``Congress hereby declares as a national 
goal the prevention of any future, and the remedying of any 
existing, impairment of visibility in [Class I areas.]'' (emphasis 
added).
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    Similarly, with respect to SO2 emissions at SGS Unit 3, 
we agree that, as described in the 2019 Guidance, an add-on FGD meeting 
the appliable alternative SO2 emissions standard under MATS 
may constitute an effective control for SO2. However, as 
noted in the previous paragraph, existing effective controls are 
generally necessary to make reasonable progress and must be included in 
the SIP, unless the state provides a weight-of-evidence demonstration 
to justify that the existing effective controls are not necessary to 
make reasonable progress. Because the Arizona SIP does not include a 
SO2 emissions limit corresponding to the existing 
SO2 controls at SGS Unit 3, the State should have provided 
such a demonstration, including consideration of whether SGS Unit 3 is 
subject to an enforceable SO2 emissions limit that ensures 
its SO2 emissions rate will not increase.
    Second, regarding the Mount Baldy Wilderness Area, although we 
commend the efforts in Arizona that contributed to the noted visibility 
improvement at the Mount Baldy Wilderness Area in the first planning 
period, previous and ongoing measures are not automatically sufficient 
to ensure ongoing reasonable progress. The regional haze requirements 
of CAA sections 169A and 169B and 40 CFR 51.308 need to be 
satisfied.\24\ In particular, the increment of progress that is 
``reasonable progress'' for a given implementation period is determined 
through the four statutory factors.\25\ While progress made in the 
first implementation period, ongoing emissions trends, and anticipated 
changes in emissions may inform a state's regional haze planning 
process, these circumstances alone do not satisfy a state's obligation 
to determine and include in its SIP the measures that are necessary to 
make reasonable progress in the second planning period. We also note 
that, while Mount Baldy is the closest Class I area to SGS and 
therefore has the highest Q/d (emissions in tons per year divided by 
distance to an affected Class I area in kilometers) value (339) with 
respect to SGS,\26\ this does not mean that Mount Baldy is the only 
Class I area affected by emissions from SGS. ADEQ did not specifically 
identify all the Class I areas that may be affected by emissions from 
each of the sources it evaluated. Nonetheless, given that SGS had a 
2018 Q of 17,044 tons per year (tpy) \27\ and is located within 300 km 
of 15 different Class I areas,\28\ it is likely to contribute to 
visibility impairment at a number of Class I areas.
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    \24\ See 64 FR 35714 (July 1, 1999), 35721-35722 for additional 
explanation as to the EPA's determination that emissions from all 
States reasonably contribute to visibility impairment and thus are 
subject to the regional haze regulations. Additionally, in the 2017 
RHR, the EPA ``reiterat[ed] that the CAA requires States to consider 
the four statutory factors . . . in each implementation period to 
determine the rate of progress towards natural visibility conditions 
that is reasonable for each Class I area.'' 82 FR 3078 (January 10, 
2017), 3080.
    \25\ 40 CFR 51.308(f)(2)(i).
    \26\ Plan Appendix C, p. 21, Table 1. Q is calculated as the 
total 2018 annual facility-wide NOX, SO2, and 
PM10 emissions in tpy, excluding processes determined by 
ADEQ to be effectively controlled.
    \27\ Id.
    \28\ 79 FR 9318, 9360, Table 50 (February 18, 2014).
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    Finally, with respect to Tri-State's request regarding enforceable 
shutdowns, we note that the EPA's role in acting on SIP submittals is 
to evaluate whether they meet applicable CAA

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requirement, not to establish new requirements. Tri-State may choose to 
work with ADEQ to establish enforceable shutdowns as part of a 
subsequent SIP revision. However, we note that even if there were an 
enforceable shutdown in 2031, this would not automatically preclude the 
unit from consideration under a four-factor analysis.\29\
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    \29\ See 2019 Guidance, pp. 20-21 (``It may be more challenging 
for a state to reasonably use a shorter remaining useful life as the 
basis for not selecting sources the further away the enforceable 
shutdown date gets from 2028'').
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    Comment A.3. Tri-State comments that it was unreasonable for the 
EPA to use the July 8, 2021 ``Clarifications Regarding Regional Haze 
State Implementation Plans for the Second Implementation Period'' 
(``2021 Clarifications Memo'') as a basis for disapproval of the 2022 
Arizona Regional Haze Plan. Tri-State indicated that although ADEQ 
submitted its plan over a year late on August 22, 2022, ADEQ was over 
three years into the process of developing the plan, working with the 
Western Regional Air Partnership, the EPA, other states, Federal Land 
Managers (FLMs) and members of the public, was nearly complete and 
ready to go through the Arizona rulemaking process when the EPA 
published the 2021 Clarifications Memo. Tri-State also noted that the 
rulemaking process can take over a year due to various tasks required.
    Response A.3. The EPA disagrees that it used the 2021 
Clarifications Memo as a basis for disapproving portions of the 2022 
Arizona Regional Haze Plan. Contrary to the commenter's suggestion, the 
EPA's guidance, including the 2021 Clarifications Memo, is not the 
basis for our disapproval. Rather, the partial disapproval is based on 
the Plan's failure to satisfy the requirements of the relevant portions 
of the RHR and CAA sections 169A and 169B. We did cite the guidance 
documents because these documents provide helpful context explaining 
the EPA's interpretations of the applicable statutory and regulatory 
requirements against which we are required to evaluate SIP submittals. 
Commenters are free to disagree and raise concerns with those 
interpretations as part of the notice and comment process on individual 
SIP actions. However, in this instance, the commenter does not appear 
to object to any of the interpretations in the 2021 Clarifications 
Memo, only to the fact that they were provided shortly before the due 
date for the plans.
    With regard to timing, we note that the 2021 Clarifications Memo 
was developed in response to issues that EPA regions and other 
stakeholders had raised regarding draft regional haze SIP revisions 
that were already under development by states.\30\ The 2021 
Clarifications Memo therefore necessarily came during the SIP 
development process and, in comparison to the SIP-specific feedback 
previously provided by the EPA prior to its issuance, was intended to 
``offer feedback more broadly to help support SIP development, 
submittal, review, and action for the second planning period.'' \31\ 
With regard to Arizona's Plan specifically, throughout the EPA's 
collaboration with ADEQ during early engagement, EPA staff advised ADEQ 
of many of the interpretations that would be expressed in the 2021 
Clarifications Memo. Therefore, we do not agree that it was improper 
for the EPA to cite to the 2021 Clarifications Memo as further 
explanation for why portions of the 2022 Arizona Regional Haze Plan did 
not comply with the applicable statutory and regulatory requirements.
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    \30\ 2021 Clarifications Memo, p. 1.
    \31\ Id.
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B. Comment Letter From ADEQ

    Sections I (``Background'') and XI (``Conclusion'') of ADEQ's 
comment letter are informational and therefore do not require a 
response. We respond to sections II-X of ADEQ's comment letter below.
    Comment B.1. ADEQ asserts that the EPA's changing guidance 
increased the burden of ADEQ's planning efforts by introducing 
uncertainty and rework. ADEQ noted delays between final publication of 
the 2017 RHR and the 2019 Guidance, as well as later changes to the 
EPA's interpretation of the RHR that came close to the plan submittal 
deadline, including the 2021 Clarifications Memo. ADEQ asserts that the 
state did not have the resources to undertake the evaluation of 
existing control measures, as noted in the 2021 Clarifications Memo, a 
process that ADEQ states was unreasonably broad-reaching and 
duplicative.
    Response B.1. We disagree with ADEQ's assertions about the EPA's 
additional guidance increasing the burden of ADEQ's planning efforts by 
introducing uncertainty and rework. First and foremost, as stated 
previously and throughout this notice, the EPA did not rely on guidance 
as the basis for its partial disapprovals. Rather, the 2019 Guidance 
and the 2021 Clarifications Memo merely provide additional context to 
the EPA's interpretations of the statutory and regulatory requirements. 
Both the 2019 Guidance and the 2021 Clarifications Memo were drafted to 
be used as tools by States in the development of their second planning 
period regional haze plans. However, neither of these documents were 
necessary for States to develop and submit their SIP revisions.
    Regarding the contents of the guidance, we do not agree that the 
EPA significantly changed its interpretations in either the 2019 
Guidance or the 2021 Clarifications Memo. The commenter has not 
provided any examples of interpretations that it believes were changed 
under the 2019 Guidance and provided only a single example from the 
2021 Clarifications Memo, relating to the section entitled, 
``Determining When Existing Measures are Necessary for Reasonable 
Progress.'' We do not agree that interpretations set forth in this 
section of the 2021 Clarifications Memo represented a significant 
change in interpretation. Rather, they were intended to clarify the 
following statement in the 2019 Guidance:

    If a state determines that an in-place emission control at a 
source is a measure that is necessary to make reasonable progress 
and there is not already an enforceable emission limit corresponding 
to that control in the SIP, the state is required to adopt emission 
limits based on those controls as part of its long-term strategy in 
the SIP via the regional haze second planning period plan 
submission.\32\
---------------------------------------------------------------------------

    \32\ 2019 Guidance, p. 423.

    Many states and other stakeholders raised questions about this 
statement. In response, as part of the 2021 Clarifications Memo, the 
EPA laid out in further detail our interpretation of the CAA and RHR 
regarding how to make such a determination.
    We also disagree, on multiple grounds, with the commenter's 
assertion that the ``EPA's revised guidance requires an unreasonably 
broad-reaching review of all existing control measures that are not 
separately included in the regional haze plan to evaluate whether those 
same measures should be duplicated in the regional plan to support 
reasonable visibility progress.''
    First, the 2021 Clarifications Memo did not establish any new 
requirements. On the contrary, it clearly states that ``[t]his 
memorandum does not change or substitute for provisions or requirements 
of the CAA or RHR, nor does it create any new requirements. Rather, 
this memorandum clarifies and provides further information on the 
existing statutory and regulatory requirements.'' \33\ One of the key 
requirements of the CAA and RHR is that all measures that are necessary 
to make reasonable progress must be

[[Page 102749]]

included the SIP.\34\ However, neither the CAA, the RHR, or the 2019 
Guidance explain how to determine whether an existing measure that 
results from a four-factor analysis (or is used as the basis to avoid 
such an analysis) is necessary to make reasonable progress. Based on 
questions received on this subject during SIP development, it was clear 
that further guidance on this question would be helpful. Accordingly, 
the EPA provided this guidance in the 2021 Clarifications Memo.\35\
---------------------------------------------------------------------------

    \33\ 2021 Clarifications Memo, p. 2.
    \34\ CAA 169A(b)(2); 40 CFR 51.308(f)(2).
    \35\ 2021 Clarifications Memo, pp. 8-9.
---------------------------------------------------------------------------

    Regarding ``existing measures,'' the Memo explains:

    When the outcome of a four-factor analysis is that no new 
measures are reasonable for a source, the source's existing measures 
are generally needed to prevent future visibility impairment (i.e., 
to prevent future emission increases) and thus necessary to make 
reasonable progress. Measures that are necessary to make reasonable 
progress must be included in the SIP.
    However, there may be circumstances in which a source's existing 
measures are not necessary to make reasonable progress. 
Specifically, if a state can demonstrate that a source will continue 
to implement its existing measures and will not increase its 
emission rate, it may not be necessary to require those measures 
under the regional haze program in order to prevent future emission 
increases.

    Similarly, with regard to existing ``effective controls'' used to 
screen out sources from a four-factor analysis:

    A decision to forgo a full four-factor analysis based on a 
source's existing effective controls is equivalent to a 
determination that no new measures are necessary to make reasonable 
progress. In this scenario, existing effective controls are, 
therefore, generally necessary to make reasonable progress and thus 
must be adopted into the regulatory portion of the SIP. However, the 
state may provide a weight-of-evidence demonstration as described in 
Section 4.1 to justify that the existing effective control is not 
necessary for reasonable progress.

    Thus, the 2021 Clarifications Memo clarifies that, under the CAA 
and the RHR, there is a general presumption that existing measures 
resulting from a four-factor analysis (or relied upon to avoid such an 
analysis) are necessary to prevent future visibility impairment and 
therefore necessary to make reasonable progress. Accordingly, states 
have the option to submit all such measures into the SIP (to the extent 
they are not already approved into the SIP) without further evaluation 
of whether the measures are necessary to make reasonable progress. 
Alternatively, states may choose to provide a weight-of-evidence 
demonstration that such measures are not necessary to make reasonable 
progress. Importantly, however, such a demonstration is needed only 
where an enforceable emissions limitation corresponding to an existing 
measure has not already been approved into the SIP and is not being 
submitted for SIP approval as part of the regional haze plan. 
Therefore, we do not agree that a review of ``all existing control 
measures that are not separately included in the regional haze plan'' 
is required.
    Third, to the extent that a state chooses to undertake such a 
demonstration that existing measures are not necessary to make 
reasonable progress, we do not agree that it would be duplicative. On 
the contrary, because such a demonstration is necessary only for 
measures for which emissions limitations are not submitted into the 
SIP, the state and the EPA need to evaluate relevant evidence 
concerning whether the source will continue to implement its existing 
measures and maintain its emissions rate in the absence of SIP-approved 
requirements to do so, to ensure that visibility impairment does not 
increase.
    In sum, we disagree with ADEQ's characterization of the contents of 
the 2021 Clarifications Memo and its role in our partial approval and 
partial disapproval of the Plan.
    Comment B.2. ADEQ comments that the EPA should not issue binding 
decisions based on guidance alone where the bases for disapproval are 
not in the rule or statute. ADEQ cites to statements in the 2019 
Guidance and 2021 Clarifications Memo regarding screening out of 
effectively controlled sources and determinations of whether existing 
controls are necessary to make reasonable progress, as the examples of 
guidance. Specifically, ADEQ asserts that ``[i]t was unreasonable for 
the EPA's clarification memo to issue these additional specific 
barriers to a determination that existing measures were effective at a 
given source late in the development of second round regional haze 
plans through guidance, and without additional notice and comment.''
    Response B.2. We disagree that we issued our proposed decision 
based on guidance. Rather, the proposal action clearly indicates that 
the partial disapproval was based on failing to satisfy the 
requirements of the relevant portions of the RHR and CAA sections 169A 
and 169B, with citations to our guidance as further explanation. See 
Response A.3 for more explanation.
    We also note that ADEQ's comment appears to conflate two separate 
questions: first, whether its justification for screening out a unit 
based on existing effective emissions controls was sufficient, and 
second, whether such existing effective control measures are necessary 
to make reasonable progress. In our proposal, we discussed each of 
these issues as two separate grounds for our proposed partial 
disapproval with respect to 40 CFR 51.308(f)(2).\36\ While both 
questions apply to sources that are screened out from a four-factor 
analysis based on existing effective controls, they are distinct. The 
first issue is further addressed in Response B.3 of this document, 
while the second is addressed in Response B.1. Therefore, we do not 
agree that the 2021 Clarifications Memo created any additional barriers 
to a determination that existing measures were effective at a given 
source.
---------------------------------------------------------------------------

    \36\ See 89 FR 47398, 47428 (``ADEQ did not provide an adequate 
justification for screening out certain sources and units from 
conducting a four-factor analysis on the basis that they are 
``effectively controlled'' as part of its source selection 
process'') and 47431 (``ADEQ has not addressed whether any of the 
existing measures relied upon in its four-factor analyses or its 
`effective controls' determinations are necessary to make reasonable 
progress and thus should be a part of the State's long-term strategy 
for the second planning period.'').
---------------------------------------------------------------------------

    Comment B.3. ADEQ disagreed with the EPA's proposed determination 
that Arizona failed to provide adequate justification for deferring 
certain emissions units from consideration. ADEQ indicated that the 
state has the flexibility to reasonably select a set of sources for an 
analysis of control measures, and that it did not exclude entire 
facilities from consideration or exempt sources that had previously 
adopted BART or reasonable progress controls, but rather excluded just 
the emissions processes or units that recently installed highly 
effective controls from the calculation of the Q/d value for that 
facility. ADEQ also provided additional information regarding effective 
controls in Attachment A of its letter.
    Response B.3. We agree that states have flexibility to reasonably 
select a set of sources for analysis of controls measures. However, as 
described in our proposal, we find that ADEQ's approach to screening 
out units from conducting a four-factor analysis on the basis that they 
are ``effectively controlled'' was not adequately documented.\37\ 
Specifically, in some cases, ADEQ did not identify the controls for 
each pollutant at each unit or process, the associated limits, or where 
the controls and/or limits currently exist in the Arizona SIP. In other 
cases, ADEQ listed the controls, but did not clearly explain why it is

[[Page 102750]]

reasonable to assume, without conducting a four-factor analysis, that 
no additional controls would be reasonable.\38\ Accordingly, ADEQ 
should have identified where the existing limits are found in the SIP 
or FIP and clearly explained why no additional controls would likely be 
reasonable under a four-factor reasonable progress analysis for the 
second planning period. Without this analysis and explanation, it is 
not clear what is a part of Arizona's long-term strategy for the second 
planning period.
---------------------------------------------------------------------------

    \37\ 89 FR 47398, 47428.
    \38\ See 40 CFR 51.308(f)(2)(i) (``. . . The State must include 
in its implementation plan a description of the criteria is used to 
determine which sources or groups of sources it evaluated and how 
the four factors were taken into consideration in selecting the 
measures for inclusion in its long-term strategy''). See also 2021 
Clarifications Memo, p. 5; 2019 Guidance, p. 23.
---------------------------------------------------------------------------

    As noted in its comment, ADEQ conducted its effective controls 
screening on a unit-specific basis. However, it did not do so on a 
pollutant-specific basis. Rather, ADEQ screened out entire units from 
further evaluation for NOX, SO2, or 
PM10 if the units met ADEQ's screening criteria for any one 
of these pollutants. We find that this approach was unreasonable 
because it resulted in the screening out of entire units without 
consideration of whether the unit had effective controls for all three 
of the pollutants covered in ADEQ's long-term strategy. For example, 
ADEQ screened out AEPCO Apache Unit 3 and TEP Irvington Generating 
Station (IGS) Unit 4 from any further analysis because these units were 
converted from coal to natural gas under better-than-BART alternatives 
during the first planning period.\39\ The EPA acknowledges that fuel 
combustion units that are required to combust pipeline-quality natural 
gas are generally considered to be effectively controlled for 
SO2 and PM.\40\ However, they are not necessarily 
effectively controlled for NOX, based on burning natural gas 
alone. Therefore, we find that ADEQ has not provided adequate 
justification for screening these units out from an analysis of 
NOX controls.
---------------------------------------------------------------------------

    \39\ 2022 Arizona Regional Haze Plan, Appendix C, Table 147.
    \40\ See 2019 Guidance, p. 24.
---------------------------------------------------------------------------

    Additionally, we appreciate the documentation in Attachment A that 
ADEQ provided in its attachment letter. However, this information would 
need to be part of a SIP revision subject to review by the public and 
FLMs in order for the EPA to consider it as part of the long-term 
strategy. If ADEQ develops a new SIP revision intended to remedy the 
deficiencies discussed in our proposed and final actions on the Plan, 
it may be appropriate to include this information in that SIP revision.
    Comment B.4. ADEQ asserts that, despite indicating that flawed 
emissions rates were used for some of ADEQ's analyses, the proposed 
action identified one example of differing achievable emissions rates 
for selective catalytic reduction (SCR) and selective non-catalytic 
reduction (SNCR) controls for SGS Units 1 and 2's four factor analyses. 
In this example, ADEQ used 0.060 lb/MMBtu and 0.15 lb/MMBtu as 
reasonable estimates of the achievable rates at TEP SGS Units 1 and 2 
for SCR and SNCR, respectively.
    For SCR, ADEQ additionally states the study that the EPA cited for 
its justification that SCR has been demonstrated to achieve 0.05 lb/
MMBtu (or up to 90 percent reduction) was published in 2005 and found 
that the 20 SCR systems examined in 2003 achieved NOX 
emissions rates between 0.04 and 0.07 lb/MMBtu.\41\ In addition, ADEQ 
noted that EPA found 0.065 lb/MMBtu as a ``reasonable estimate of 
average SCR performance'' in its 2016 Regional Haze FIP action for the 
Salt River Project Coronado Generating Station Unit 1.
---------------------------------------------------------------------------

    \41\ Ravi K. Srivastava, Robert E. Hall, Sikander Khan, Kevin 
Culligan & Bruce W. Lani (2005) Nitrogen Oxides Emission Control 
Options for Coal-Fired Electric Utility Boilers, Journal of the Air 
& Waste Management Association, 55:9, 1367-1388, DOI: 10.1080/
10473289.2005.10464736. Available at: https://doi.org/10.1080/10473289.2005.10464736.
---------------------------------------------------------------------------

    For SNCR, ADEQ additionally states that the EPA did not provide a 
technical citation for disagreeing with ADEQ's use of 0.15 lb/MMBtu for 
SNCR. ADEQ noted that the proposed rule indicated that ADEQ did not 
demonstrate why source specific conditions would cause SNCR on these 
units to achieve as little as a 15 percent reduction. ADEQ noted that 
Srivastava et al. found that while smaller boilers (e.g., 76-78 MW 
units) were able to achieve greater than 60 percent NOX 
reductions, larger boilers (e.g., 500 MW units) ``may be capable of 
achieving reductions of only ~30%.'' ADEQ indicates that SGS Units 1 
and 2 units have nameplate ratings of 425 MW and would be expected to 
achieve less reductions than smaller units. ADEQ also points to the 
inlet concentration as another consideration for achievable emissions 
rates with post combustion emissions control. Citing Srivastava et al., 
ADEQ notes that the study found that ``in the absence of reliable SCR 
inlet NOX data, the SCR efficiencies are estimated using an 
inlet NOX level of 0.5 lb/10\6\ Btu.'' However, in the case 
of SGS Units 1 and 2, the NOX concentration in the exhaust 
from these units is less than 100 parts per million by volume (ppmv) 
with an assumed rate of 0.174 lb/MMBtu and 0.178 lb/MMBtu being used in 
ADEQ's four factor analysis cost calculations for Unit 1 and Unit 2, 
respectively. Given the already low NOX inlet concentration, 
an achievable emissions rate of 0.15 lb/MMBtu was determined to be 
reasonable. ADEQ further noted that additional information related to 
achievable emissions rates for SNCR for SGS Unit 1 and Unit 2 can be 
found in Appendix K, Section II(J), Comment 10 of the 2022 Arizona 
Regional Haze Plan.
    Response B.4. We acknowledge that we only highlighted a single 
example of flawed emissions rates in our proposal--for NOX 
at SGS Units 1 and 2. However, as explained in response A.1, in 
evaluating whether a SIP revision (or a portion thereof) meets each of 
these CAA requirements, the EPA is not required to separately evaluate 
and discuss each of the thousands of pieces of information, analyses 
and determinations comprising the SIP submission. Rather, the EPA may 
focus on those specific elements of the SIP revision that form the 
basis for our determination that certain applicable requirements are 
met and certain applicable requirements are not met. In this instance, 
we focused on these units because they are expected to have the highest 
NOX emissions of any units in the State (2,099 and 2,283 tpy 
respectively) by 2028, so it is important to carefully examine whether 
additional NOX reductions from these units are necessary to 
make reasonable progress. Given this context, and for the reasons 
outlined below, we do not agree with ADEQ that it has adequately 
documented the emissions rates assumed in this analysis, which are a 
critical component of a four-factor analysis.
    The emissions rate achievable by a unit equipped with SCR is 
determined by several parameters and technological limitations. There 
are periods of operation in which the SCR is not able to operate, 
particularly during periods of startup and shutdown.\42\ The SCR 
emissions rate (lb/MMBtu) achievable by a particular unit represents 
the combination of two primary elements: (1) the controlled 
NOX emissions rate during periods of normal unit operation 
when the SCR is able to operate, and (2) the uncontrolled 
NOX emissions rate

[[Page 102751]]

during periods of startup and shutdown when the SCR system cannot 
operate, and result in unit emissions higher than the SCR controlled 
emissions rate that increase the unit's overall emissions rate.
---------------------------------------------------------------------------

    \42\ Control Cost Manual, Section 4, Chapter 2 Selective 
Catalytic Reduction (June 2019), section, 2.2.1 Reduction Chemistry, 
Reagents, and Catalyst, available at https://www.epa.gov/sites/default/files/2017-12/documents/scrcostmanualchapter7thedition_2016revisions2017.pdf.
---------------------------------------------------------------------------

    With regard to the first element, the 2005 study is not the sole 
basis for our finding that an overall emissions rate of 0.050 lb/MMBtu 
is achievable with SCR on an annual average basis. There are multiple 
instances of coal-fired units installing SCR on a retrofit basis and 
achieving 0.050 lb/MMBtu in practice on an annual average basis.\43\ 
These units are typically able to achieve this overall level of control 
by being able to operate at NOX annual emissions rates at or 
below 0.050 lb/MMBtu based upon periods of normal operation. Even 
several of the units identified by ADEQ operating in the annual average 
emissions rate range of 0.055 to 0.065 lb/MMBtu are still achieving 
emissions rates of 0.050 lb/MMBtu and lower based upon periods of 
normal operation.\44\ We consider this information sufficient to 
establish that an 0.050 lb/MMBtu emissions rate warrants consideration 
as technically feasible for coal fired units generally during periods 
of normal operation, absent source specific factors affecting 
feasibility. We are not aware of assertions by either ADEQ or TEP that 
the Springerville units specifically cannot achieve 0.050 lb/MMBtu when 
operating with SCR during periods of normal operation.\45\ Therefore, 
we find that ADEQ should have considered a controlled NOX 
emissions rate of 0.050 lb/MMBtu for SGS Units 1 and 2 when operating 
with SCR during periods of normal operation.
---------------------------------------------------------------------------

    \43\ See Docket Item F-16 ``SCR Tangentially fired Coal.xlsx.''
    \44\ Id.
    \45\ TEP has indicated that vendors have been unwilling to 
provide manufacturer guarantees of 0.050 lb/MMBtu over the lifetime 
of the SCR system. Because manufacturer guarantees include 
contractual and financial considerations beyond technical 
performance of the SCR system, we do not consider an inability to 
secure a manufacturer guarantee to constitute a determination that 
an emission rate of 0.050 lb/MMBtu is not technically feasible, 
particularly with regard to periods of normal operation.
---------------------------------------------------------------------------

    The majority of analysis performed by ADEQ is relevant to the 
second element and is intended to support a position that, when the 
annual emissions rate achievable during normal operations is combined 
with emissions from the number of startup/shutdown cycles exhibited by 
SGS Units 1 and 2, an annual average emissions rate of 0.06 lb/MMBtu is 
what is reasonably achievable for these units. We consider it 
appropriate to account for the effect of startup/shutdown emissions on 
the emissions rate achievable by the unit, but disagree that the 
analysis provided by ADEQ supports an annual average emissions rate of 
0.060 lb/MMBtu. TEP's four factor analysis and ADEQ's SIP submittal did 
not include startup/shutdown history to support the assertion that 
Springerville has more startup/shutdown events than comparable 
tangentially-fired coal fired boilers. A review of Clean Air Markets 
Program Data (CAMPD) emissions and operating data over a 2021-2023 
timeframe indicate that SGS Units 1 and 2 each experienced 
approximately 9 to 14 startup events per year. While we acknowledge 
that some portion of SGS baseline emissions consist of startup/shutdown 
emissions that cannot be controlled by an SCR system, the substantial 
majority of baseline emissions are attributable to emissions during 
normal operation. We estimate that approximately 97-98% of baseline 
emissions are attributable to normal operations that could be 
controlled by SCR.\46\ Given that the majority of unit emissions can be 
controlled by SCR to 0.050 lb/MMBtu or lower and that the remaining 2-3 
percent of operations are characterized by low inlet SCR emissions 
rates, we do not consider the historical startup/shutdown operating 
profile to support deviating to an 0.06 lb/MMBtu emissions rate on an 
annual average basis.
---------------------------------------------------------------------------

    \46\ See Docket Item F-17 [SGS CAMPD 2021-23.xlsx]. To 
illustrate SCR control potential during periods of normal operation, 
this spreadsheet is based on the key assumption that emissions from 
any day a unit did not operate a full 24 hours would be attributable 
to startup/shutdown periods. An hourly analysis would provide a more 
refined and precise assessment, though we consider this assumption 
to overestimate the emissions attributable to startup/shutdown by 
including all emissions from partial operating days towards startup/
shutdown.
---------------------------------------------------------------------------

    ADEQ cites a limit of 0.065 lb/MMBtu established for SRP Coronado 
Unit 1 in a 2016 Regional Haze FIP action as support for the use of an 
annual average emissions rate of 0.060 lb/MMBtu. We wish to clarify 
that the 0.065 lb/MMBtu value was not the annual average emissions rate 
used in cost calculations, but was the emissions limit established on a 
rolling 30-boiler operating day (BOD) average, for Coronado Unit 1. We 
relied upon an 0.050 lb/MMBtu annual average emissions rate in 
developing cost calculations for SCR,\47\ which is consistent with our 
action here. In establishing a rolling 30-BOD limit for Coronado Unit 1 
in that action, we acknowledged that upward revisions to the SCR design 
rate achievable on an annual average basis would be appropriate in 
order to accommodate the effect that multiple startup/shutdown events 
would have to overall unit emissions rates on an averaging period that 
could be as short as 30 days. Based upon startup/shutdown frequency and 
projected controlled emissions rate information provided by SRP, we 
finalized 0.065 lb/MMBtu as an appropriate emissions limit and 
reasonable estimate of SCR performance over a short-term period.\48\ 
Given that the 0.065 lb/MMBtu limit reference here corresponds to a 
different, shorter averaging period, and was itself based on an 0.05 
lb/MMBtu annual average emissions rate, we do not consider it 
supportive of an 0.060 lb/MMBtu annual average emissions rate.
---------------------------------------------------------------------------

    \47\ See Docket Item EPA-R09-OAR-2012-0021-0204 for cost 
calculation details. More information related to establishing a 30 
BOD limit relative to an annual emissions rate can be found in our 
March 31, 2015 (80 FR 17010) proposed reconsideration, including 
Docket Items EPA-R09-OAR-2015-0165-0029 through -0033 for further 
details. We note that SRP identified an SCR design target during 
periods of normal operation as low as 0.03 lb/MMBtu for Coronado 
Unit 1, though we acknowledge there are source specific differences 
with the SGS units.
    \48\ It is unclear to what extent a comparable 30-BOD limit may 
be appropriate for the SGS units, but we note that the SGS units 
appear to have historically had at least as many startup/shutdown 
events as Coronado Unit 1.
---------------------------------------------------------------------------

    For SNCR, we appreciate the additional analysis provided in the 
comment and citation to Appendix K summarizing ADEQ's responses to 
public comments. We acknowledge that low inlet NOX 
concentrations are a general consideration in evaluating NOX 
controls that can negatively impact control efficiencies and achievable 
controlled emissions rates. Therefore, in order to further evaluate 
whether a rate lower than 0.15 lb/MMBtu may be achievable with SNCR at 
SGS Units 1 and 2 on an annual basis, we examined CAMPD emissions data 
over a 2019-2023 time period for SNCR-equipped units comparable to SGS 
Units 1 and 2, specifically filtering for tangentially-fired coal units 
operating with SNCR on a retrofit basis.\49\ We identified four 
currently operating SNCR-equipped units achieving NOX 
emissions rates below 0.15 lb/MMBtu, ranging between 0.10 to 0.12 lb/
MMBtu.\50\ These values represent the highest performing SNCR-equipped 
units, with the next best performing units operating at emissions rates 
of 0.15 lb/MMBtu and higher. At least one of the four units we 
identified has the capability to use natural gas,

[[Page 102752]]

which could have the effect of lowering emissions rates relative to 
units that do not have this capability, such as SGS Units 1 and 2.\51\ 
Based on the three remaining units, each unit had relatively low pre-
SNCR emissions rates that are comparable to SGS Unit 1 and 2, and each 
unit is able to achieve SNCR emissions rates below 0.15 lb/MMBtu and 
control efficiencies better than 15 percent. Neither ADEQ or TEP has 
provided documentation to support a claim that SGS Units 1 and 2 
specifically cannot achieve an annual emissions rate lower than 0.15 
lb/MMBtu with SNCR. Therefore, we find that ADEQ should have considered 
a NOX emissions rate of lower than 0.15 lb/MMBtu for SNCR at 
SGS Units 1 and 2.
---------------------------------------------------------------------------

    \49\ See Docket Item F-21, ``SNCR Tangential Coal Units.xlsx.''
    \50\ See Docket Item F-21. These units include Boswell Energy 
Center (MN) Unit 4, Will County (IL) Unit 4, and Jeffrey Energy 
Center (KS) Units 2 and 3.
    \51\ Based on reported natural gas fuel usage, the Boswell 
Energy Center appears to use natural gas primarily as a startup 
fuel, but does periodically use quantities of natural gas that 
suggest co-firing with coal for electricity generation purposes.
---------------------------------------------------------------------------

    We also note that this was one of multiple flaws that formed the 
basis of our determination that the State's long-term strategy did not 
satisfy the requirements of 40 CFR 51.308(f)(2), including reasons 
related to source selection and control determinations, as detailed in 
our proposal and elsewhere in this document. Therefore, even assuming 
that a control efficiency of 15 percent for SNCR at SGS Units 1 and 2 
was reasonable, it would not have changed our determination that the 
2022 Arizona Regional Haze Plan did not satisfy the requirements of 40 
CFR 51.308(f)(2).
    Comment B.5. ADEQ disagrees with the EPA's determination that 
Arizona deviated from the Control Cost Manual without documentation as 
part of its four factor analyses with regards to remaining useful life 
calculations for the El Paso Natural Gas (EPNG) Williams facility and 
the use of source specific interest rates without providing adequate 
documentation in the control measure analyses for the EPNG Williams and 
Willcox facilities.
    ADEQ indicates that the EPA Control Cost Manual Section 4, Chapter 
2, states that ``. . . a representative value of the equipment life for 
SCR at power plants can be considered as 30 years . . . [f]or other 
sources, the equipment life can be between 20 and 30 years.'' ADEQ 
noted that while it erroneously omitted this citation from the EPNG 
Williams Turbine analysis, the Control Cost Manual citation and 
justification for use of 25 years is the midpoint between the 20-30 
year range for non-EGU SCR systems and was included in the EPNG Willcox 
SCR analysis for Turbines 1 and 2.\52\ ADEQ also noted that it received 
cost calculation spreadsheets utilizing a 25-year useful life for SCR 
for the EPNG Williams Turbine 1 from the US Forest Service.\53\
---------------------------------------------------------------------------

    \52\ 2022 Arizona Regional Haze Plan, Appendix C, Section 
C3.8.5.2, Page 146.
    \53\ 2022 Arizona Regional Haze Plan, Appendix L, Section 4.2.4, 
Comment 14.
---------------------------------------------------------------------------

    ADEQ also explains that in its analysis of remaining useful life 
for compressor engines at the EPNG Williams facility, ADEQ documented 
the assumptions and basis for using 20 years to amortize NOX 
controls in Appendix C, Section C3.7.6.5, which includes citations to 
the Control Cost Manual and the EPA's 2016 technical support document 
for the Cross State Air Pollution Rule for the 2008 Ozone NAAQS.
    Response B.5. We appreciate the clarification regarding ADEQ's 
reasoning for use of a 25-year remaining useful life for the EPNG 
Williams turbines and 20 years for the EPNG Williams engines. While 
there are instances of combustion turbines with operating lifetimes 
beyond 25 years (with or without retrofit controls), we acknowledge 
that EPA guidance such as the Control Cost Manual has not recommended a 
value beyond the 20-30 year range. ADEQ's use of a 25-year useful life 
represents the midpoint of Control Cost Manual recommendations, and 
therefore we agree that it is consistent with the Control Cost Manual. 
However, we note that the lack of documentation of remaining useful 
life for the units at Williams Compressor Station was one of the many 
flaws that we identified in the state's long-term strategy including 
reasons related to source selection and control determinations, as 
detailed in our proposal and elsewhere in this document. Therefore, 
this clarification does not change our determination that the 2022 
Arizona Regional Haze Plan did not satisfy the requirements of 40 CFR 
51.308(f)(2).
    Comment B.6. ADEQ disagrees with the EPA's determination that ADEQ 
did not reasonably weigh the statutory factors in reaching its control 
determinations with regards to application of cost thresholds. ADEQ 
disagrees that Arizona's consideration of incremental cost 
effectiveness in its four factor analyses were done in an unreasonable 
manner. ADEQ cites to its explanation that the incremental cost of 
requiring low-emission combustion 2 (LEC 2) as opposed to Air-Fuel 
ratio adjustments is $5,034/ton, which ADEQ considered reasonable, and 
therefore ADEQ found that LEC 2 is a more appropriate control for 
Williams Reciprocating Engine 1 (RECIP-1).\54\
---------------------------------------------------------------------------

    \54\ 2022 Arizona Regional Haze Plan, Appendix C, Section 
C3.7.6.2, page 129.
---------------------------------------------------------------------------

    ADEQ also asserts that it also analyzed other determinations from 
the regional haze first implementation period besides the incremental 
cost effectiveness value for the Nelson Lime Plant action, and ADEQ 
provides this information in Table 1 of its comment letter.
    Response B.6. We appreciate ADEQ's explanation about LEC 2 on 
RECIP-1, but we note that ADEQ also rejected LEC 3 on Williams RECIP-1, 
on the grounds that the incremental costs of these controls, relative 
to less stringent controls, were excessive. In addition, ADEQ did not 
provide or consider incremental cost effectiveness values for the same 
controls for the other units at the same source (RECIP-2 or RECIP-5). 
Although states may choose to consider incremental costs in a 
reasonable manner,\55\ we find it was unreasonable for ADEQ to do so 
only for specific units and controls, rather than in a consistent 
manner across all units and controls. Such inconsistent treatment of 
sources without explanation is the ``the hallmark of arbitrary 
action.'' \56\
---------------------------------------------------------------------------

    \55\ See, e.g., 2019 Guidance, p. 40.
    \56\ Nat'l Parks Conservation Ass'n v. EPA, 788 F.3d 1134, 1145 
(9th Cir. 2015).
---------------------------------------------------------------------------

    We also appreciate the addition of Table 1 identifying other first 
implementation period incremental cost effectiveness decisions. 
However, this information was not included in the Plan and therefore 
not subject to review by the public or FLMs. Accordingly, it cannot be 
relied upon to meet the requirement of 40 CFR 51.308(f)(2)(iii) for 
States to document the technical basis for their long-term strategy. 
Moreover, even if the information had been included in the Plan, it 
would not have justified ADEQ's inconsistent consideration of 
incremental cost effectiveness, for the reasons described in our 
proposal and the preceding paragraph.
    Comment B.7. ADEQ states that, contrary to the EPA's contention, 
ADEQ did not rely upon visibility benefits for its control 
determinations, but rather visibility impacts were reported for some 
sources to give reference to the reader as to the relative impact of 
these sources or controls on visibility. ADEQ also asserts that nothing 
in the CAA, RHR, or 2019 Guidance prevents the department from 
considering visibility benefits as part of its analysis and stated that 
``the ADEQ's labeling of the visibility benefits associated with 
specific control scenarios as `small'

[[Page 102753]]

comports with similar language used by the EPA in their regional haze 
actions.'' \57\
---------------------------------------------------------------------------

    \57\ Citing e.g., ``relatively small visibility benefits'' in 79 
FR 52419, 52439 (September 3, 2014).
---------------------------------------------------------------------------

    Response B.7. We agree with ADEQ that in its Response to Comments, 
ADEQ stated that ``[v]isibility impacts were reported for some sources 
to give reference to the reader as to the relative impact of these 
sources or controls considered on visibility. However, this information 
was not considered in the Department's emissions control measure 
determinations.'' \58\ However, this assertion is contradicted by the 
language of some of the control determinations in the Plan. For 
example, in the NOX four-factor analysis for SGS, ADEQ 
stated that:
---------------------------------------------------------------------------

    \58\ Id., Appendix K, p. 9.

    ADEQ does find visibility impacts a useful consideration given 
the goal of the regional haze program is to improve visibility in 
Class I areas. As such, ADEQ reports modeled visibility impacts in 
this documentation. The small modeled visibility benefits associated 
with the modeled hypothetical NOX emission reduction 
supports the determination that no additional NOX 
controls are necessary to make reasonable progress towards natural 
visibility at Class I areas during this implementation period.\59\
---------------------------------------------------------------------------

    \59\ Plan, Appendix C, p. 221 (emphases added).

    Similar language appears following the SO2 four factor 
analysis for SGS \60\ and in the summary of ADEQ's NOX 
reasonable progress determination for IGS Unit 3.\61\ This language 
indicates that ADEQ did consider visibility for these units, and 
specifically, that it weighed the ``small modeled benefits'' of 
controls in determining that no additional NOX controls were 
warranted at SGS Units 1 and 2 and IGS Unit 3, and no more stringent 
SO2 controls were warranted at SGS Units 1 and 2.
---------------------------------------------------------------------------

    \60\ Id. at 234 (``The small visibility benefits associated with 
the modeled SO2 controls supports the determination that 
CDS and wet FGD control options are not necessary to make reasonable 
progress towards natural visibility at Class I areas during this 
implementation period.'').
    \61\ Id. at 197 (``The small modeled visibility benefits 
associated with additional controls support the determination that 
no additional controls are necessary to make reasonable progress 
towards natural visibility at Class I areas during this 
implementation period.'').
---------------------------------------------------------------------------

    While states have the option to consider visibility benefits, along 
with the four statutory factors, in making control determinations, if 
they choose to do so, they must do so ``in a reasonable way that does 
not undermine or nullify the role of the four statutory factors in 
determining what controls are necessary to make reasonable progress.'' 
\62\ In this case, we find it was not reasonable for ADEQ to consider 
visibility benefits only for specific sources and without any 
explanation of what would constitute a significant visibility benefit.
---------------------------------------------------------------------------

    \62\ 2021 Clarifications Memo, p. 12 (quoting Response to 
Comments on Protection of Visibility: Amendments to Requirements for 
State Plans; Proposed Rule at 186).
---------------------------------------------------------------------------

    In the action cited by ADEQ where the EPA considered ``relatively 
small visibility benefits,'' \63\ we were comparing the relatively 
small benefits of a control at one source to the relatively larger 
visibility benefits expected to result from controls at other 
sources.\64\ In contrast, in the 2022 Arizona Regional Haze Plan, ADEQ 
did not find any visibility benefits at any source to be anything other 
than small. Thus, as explained in our proposal regarding SGS Units 1 
and 2, ``[i]n the absence of any opportunities for larger emissions 
reductions and corresponding visibility benefits, we find that ADEQ's 
reliance on `small' visibility benefits as an additional justification 
for not adopting more stringent controls at these units is not 
persuasive.'' \65\
---------------------------------------------------------------------------

    \63\ 79 FR 52420, 52439.
    \64\ See, e.g., id. at 52442 (referring to ``large visibility 
benefits) and 52458 (``we consider this visibility benefit 
sufficient to support installation of controls.'').
    \65\ 89 FR 47398, 47430.
---------------------------------------------------------------------------

    Finally, we note that, even assuming that ADEQ did not consider 
visibility benefits as part of its control determinations for SGS Units 
1 and 2, we would still conclude that the determinations were flawed 
for other reasons. In particular, for NOX, ADEQ did not 
adequately justify the control efficiency used for SCR and SNCR, as 
discussed in the proposal and response B.4.\66\ For SO2, 
ADEQ unreasonably rejected wet FGD on the basis of incremental cost, 
and set mass-based caps that will not ensure implementation of the 
emissions reduction measures that are necessary to make reasonable 
progress at these units, as discussed in the proposal and response B.8. 
Furthermore, the lack of clarity in the Plan regarding whether or not 
ADEQ considered visibility benefits in making its control 
determinations for SGS Units 3 and 4 and IGS Unit 3, indicates a lack 
of reasoned decision making that also supports our disapproval of the 
Plan's long-term strategy.
---------------------------------------------------------------------------

    \66\ 89 FR 47398, 47428 (May 31, 2024).
---------------------------------------------------------------------------

    Comment B.8. ADEQ disagrees with the EPA's determination that ADEQ 
did not reasonably weigh the statutory factors in reaching its control 
determinations with regards to three issues noted in the proposed rule 
concerning the mass-based emissions caps at SGS and IGS.
    First, ADEQ asserts that the EPA's rationale is arbitrary and 
capricious in regard to the rejection of wet FGD for SGS Units 1 and 2. 
ADEQ states that the use of emissions limits in lieu of codifying 
specific control technologies is a flexibility that the EPA itself used 
in its reasonable progress determination for Phoenix Cement Clarkdale 
(PCC).\67\ ADEQ asserts that the EPA established an emissions limit for 
PCC that did not require the installation of a particular control 
technology but rather compliance through other means of meeting the 
limit.
---------------------------------------------------------------------------

    \67\ 79 FR 52420, 52460.
---------------------------------------------------------------------------

    Second, regarding the EPA's contention that spray dry absorber 
(SDA) upgrades may still be cost effective after the establishment of 
the mass-based emissions caps, ADEQ comments that this manner of 
analysis is not contemplated in the four-factor analysis as outlined in 
the RHR or the 2019 Guidance. ADEQ asserts that the EPA has never 
applied this standard whereby after the establishment of an emissions 
limit based on the reductions achievable from a considered control 
technology that a State must revisit and update the baseline emissions 
of its four-factor analysis to reflect the new emissions limit. ADEQ 
claims that for its analysis of SGS, ADEQ did not select a control 
scenario in its four-factor analysis that included the imposition of 
both emissions limits and the installation of SDA upgrades, and 
therefore, the EPA should not substitute its judgment for ADEQ's 
selection of SDA upgrades as the evaluated control measure for SGS 
Units 1 and 2 or reject ADEQ's determination based on an arbitrary and 
circular four factor analysis standard.
    Third, ADEQ further disagrees with the EPA's assertion that the 
mass-based emissions caps at SGS and IGS would not meaningfully 
constrain the emissions from one unit during periods when the other 
unit is not operating and argues that the rationale is arbitrary and 
capricious. ADEQ notes that the EPA referenced TEP's 2023 Integrated 
Resources Plan (IRP) and highlighted TEP's plans to retire SGS Unit 1 
in 2027, but states that as the operating scenarios outlined in the IRP 
are not federally enforceable conditions, ADEQ has no basis for the 
consideration of these future scenarios as part of its control measure 
analysis and the establishment of the mass-based emissions limits. ADEQ 
states that the EPA should not rely upon unenforceable and hypothetical 
operating scenarios to reject ADEQ's reasonable progress 
determinations.
    Lastly, ADEQ disagrees with the EPA's rationale that IGS Unit 3's 
mass-

[[Page 102754]]

based emissions limits are not yet enforceable and therefore are not an 
appropriate basis for modifying the baseline control scenario for a 
four-factor analysis. ADEQ cites that for the EPA's BART determination 
for Arizona Public Service (APS) Cholla generating station, the EPA 
accepted a source specific permit revision for APS Cholla Unit 2 that 
included a trigger that was conditional on the EPA's approval of the 
SIP revision that altered the remaining useful life of the unit in 
ADEQ's four factor analysis.\68\ Therefore, ADEQ concludes that the EPA 
should approve ADEQ's reasonable progress determination for IGS Unit 3.
---------------------------------------------------------------------------

    \68\ 81 FR 46852, 46860 (July 19, 2016).
---------------------------------------------------------------------------

    Response B.8. We disagree with ADEQ's comments arguing that the 
EPA's justification for disapproving the reasonable progress 
determinations for SGS and IGS as it relates to the mass-based 
emissions caps at SGS and IGS was improper.
    First, we wish to clarify that we do not object to the use of 
numeric emissions limitations as a means to implement control 
determinations. Indeed, CAA section 169A(b)(2) specifically requires 
the long-term strategy to include ``enforceable emissions limitations, 
compliance schedules, and other measures that are necessary to make 
reasonable progress.'' As explained in our proposal:

    The amount of progress that is ``reasonable progress'' is based 
on applying the four statutory factors in CAA section 169A(g)(1) in 
an evaluation of potential control options for sources of visibility 
impairing pollutants, which is referred to as a ``four-factor'' 
analysis. The outcome of that analysis is the emissions reduction 
measures that a particular source or group of sources needs to 
implement to make reasonable progress towards the national 
visibility goal. . . . Such measures must be represented by 
``enforceable emissions limitations, compliance schedules, and other 
measures'' (i.e., any additional compliance tools) in a state's 
long-term strategy in its SIP.\69\
---------------------------------------------------------------------------

    \69\ 89 FR 47398, 47402-47403.

    We find that the mass-based emissions caps set for SGS do not 
represent the emissions reduction measures that were the outcome of the 
state's four-factor analysis for the reasons described in our proposal 
\70\ and herein. Therefore, these caps do not meet the requirements of 
169A(b)(2) and (g)(1), or the corresponding provisions of the RHR.
---------------------------------------------------------------------------

    \70\ 89 FR 47398, 47430.
---------------------------------------------------------------------------

    Regarding PCC, we agree that in the EPA's reasonable progress 
determination for PCC in the first implementation period, the EPA 
established a mass-based emissions limitation for NOX. 
However, the circumstances between PCC and SGS Units 1 and 2 differ in 
important ways. The limit for PCC was set pursuant to 40 CFR 
51.308(d)(3), which required the long-term strategy for the first 
implementation period to ``include enforceable emissions limitations, 
compliance schedules, and other measures as necessary to achieve the 
reasonable progress goals established by States having mandatory Class 
I Federal areas.'' \71\ In this instance, the Class I areas primarily 
affected by emissions from PCC were in Arizona,\72\ and the emissions 
reductions from PCC were reflected in the applicable RPGs for these 
areas by scaling of visibility extinction components in proportion to 
changes in total annual emissions.\73\ Under these circumstances, an 
annual mass-based emissions limit corresponding to the level of annual 
emissions reductions assumed in the RPG calculations was sufficient to 
meet the applicable requirement for an emissions limit ``as necessary 
to achieve'' the relevant RPGs.
---------------------------------------------------------------------------

    \71\ 40 CFR 51.308(d)(3) (emphasis added).
    \72\ See 79 FR 9318, 9354 Table 41 (showing impacts on Arizona I 
class I areas).
    \73\ 79 FR 52420, 52468-52469; FIP_RPG_estimates.xlsx.
---------------------------------------------------------------------------

    In contrast, for the second planning period, the EPA clarified in 
40 CFR 51.308(f)(2) that ``the long-term strategy must include the 
enforceable emissions limitations, compliance schedules, and other 
measures that are necessary to make reasonable progress, as determined 
pursuant to (f)(2)(i) through (iv).'' 40 CFR 51.308(f)(i) in turn 
requires the state to ``evaluate and determine the emission reduction 
measures that are necessary to make reasonable progress by 
considering'' the four statutory factors. Thus, the revised rule 
clarifies that the long-term strategy must include emissions 
limitations, compliance schedules, and other measures representing the 
emissions reduction measures that the state determined to be necessary 
to make reasonable progress, considering the four statutory factors.
    The EPA provided recommendations on the appropriate form of such 
emissions limitations and other measures in the 2019 Guidance and the 
Clarifications Memo. Specifically, the 2019 Guidance recommends the use 
of throughput-based limits, rather than mass-based limits (i.e., 
``caps'') for emissions limitations to implement measures necessary for 
reasonable progress in most instances.\74\ The Guidance notes that 
mass-based limits are allowed under the RHR, but explains that, ``[i]f 
the state has determined, independent of the forecasted operating 
level, that operation of the emission control equipment . . . is 
necessary to make reasonable progress, a mass-based emission limit may 
not be appropriate.'' \75\ The Clarifications Memo also reaffirms that 
``whether for new or existing measures . . . an emission limit . . . 
should be in the form of the emission rate achieved when implementing 
those measures (e.g., pounds per million British thermal units or lbs/
MMBtu, pounds per hour or lbs/hr, or pounds per ton or lbs/ton of 
produced material).'' \76\
---------------------------------------------------------------------------

    \74\ 2019 Guidance p. 44.
    \75\ Id. pp. 44-45.
    \76\ 2021 Clarifications Memo, p. 11.
---------------------------------------------------------------------------

    With regard to SGS 1 and 2, ADEQ concluded, based on a four-factor 
analysis that, ``it is reasonable to require TEP to upgrade the current 
SDA systems'' \77\ and did not indicate that this determination was 
conditioned on a particular level of operation. Therefore, ADEQ should 
have set limits in the form of the emissions rates achieved when 
implementing SDA upgrades, e.g., lb/MMBtu limits, or should have 
provided a rationale for why the mass-based limits, which could be met 
without any control upgrades, nonetheless represent SDA upgrades.
---------------------------------------------------------------------------

    \77\ Plan Appendix C, p. 232.
---------------------------------------------------------------------------

    We also note that the mass-based limit at PCC was for a single 
unit, meaning that it necessarily constrained the emissions from that 
unit on an annual basis. In contrast, the mass-based limit at SGS Units 
1 and 2 were set across two units. Accordingly, if one unit ceases to 
operate, the limits would not meaningfully constrain emissions from the 
other unit. In addition, ADEQ rejected more stringent controls at SGS 
Units 1 and 2 based on its ``determination that another viable 
reasonable control exists to reduce SO2 emissions from Units 
1 & 2 (upgraded SDA).'' In contrast, the EPA did not reject any more 
stringent controls for PCC based on incremental cost effectiveness. 
Furthermore, the cap at PCC was intended, in part, to address concerns 
raised during consultation with the facility's owner, the Salt River 
Pima Maricopa Indian Community (SRPMIC).\78\ No similar considerations 
exist with respect to SGS Units 1 and 2. Therefore, we find that the 
circumstances concerning the PCC

[[Page 102755]]

mass-based cap are distinguishable from those concerning SGS Units 1 
and 2.
---------------------------------------------------------------------------

    \78\ 79 FR 9318, 9366 (``An annual cap would allow SRPMIC to 
delay installation of controls until the Plant's production returns 
to pre-recession levels and would thus help to address the 
Community's concerns about the budgetary impacts of control 
requirements.'')
---------------------------------------------------------------------------

    Second, regarding our finding that SDA upgrades would be cost 
effective after the establishment of the mass-based emissions caps, we 
disagree that we substituted our judgment for ADEQ's by arbitrarily 
rejecting ADEQ's determination based on a circular four-factor analysis 
standard. Contrary to ADEQ's suggestion, we did not state that ADEQ was 
required to revisit and update the baseline emissions of its four-
factor analysis to reflect the new emissions limitation. However, we 
note that ADEQ did use this approach for IGS Unit 3 and determined that 
with the emissions reductions associated with the new Unit 3 emissions 
caps, no additional controls are necessary to make reasonable progress. 
ADEQ did not provide any rationale for why it used this approach for 
IGS Unit 3, but not for SGS Units 1 and 2.
    Furthermore, the fact that the SDA upgrades would still be cost 
effective following implementation of the mass-based caps at SGS Units 
1 and 2 is relevant to whether the use of caps (in lieu of throughput-
based limits) is reasonable and appropriate in this particular case. 
The fact that throughput-based (e.g., lb/MMBtu) limits equivalent to 
SDA would still be cost-effective following implementation of the caps 
(i.e., if TEP complies with the caps by lowering its operating level) 
indicates that throughput limits based on the emissions rates 
achievable with SDA upgrades may be necessary to make reasonable 
progress, regardless of the future operating level. As previously 
noted, the 2019 Guidance explains that, under such circumstances, mass-
based caps are generally not appropriate. Therefore, we believe this 
consideration is relevant to the evaluation of whether mass-based caps 
were reasonable and consistent with the requirements of the RHR in this 
case.
    Third, we agree with ADEQ's statement that the operating scenarios 
outlined in the IRP are not federally enforceable conditions. However, 
ADEQ's statement in its comment letter that it has ``no basis for the 
consideration of these future scenarios as part of its control measure 
analysis and the establishment of the mass-based emission limits'' is 
inconsistent with its stated rationale in the Plan for establishing 
caps instead of mass-based limits. Specifically, ADEQ stated that:

    As discussed in TEP's 2020 IRP, Units 1 will transition to 
seasonal operation in 2023 and Unit 2 in 2024. TEP is planning to 
retire Unit 1 in 2027 and Unit 2 in 2032. TEP will be very likely to 
manage its operating level strategically instead of completing the 
upgrades to the SDA systems for meeting the RP requirements. 
Therefore, ADEQ determines that a mass-based emission limit is 
reasonable.\79\
---------------------------------------------------------------------------

    \79\ 2022 Arizona Regional Haze Plan, Appendix C, p. 236.

    In other words, ADEQ elected to establish caps specifically because 
it anticipated that TEP could comply with these caps by reducing its 
operating level consistent with its then-current IRP. Therefore, we do 
not agree that it was inappropriate for the EPA to consider information 
contained in TEP's most recent (2023) IRP in evaluating whether the 
mass-based caps were reasonable and consistent with the RHR.
    Lastly, we agree that for APS Cholla Unit 2, the EPA accepted a 
source-specific permit revision that included a trigger that was 
conditional on the EPA's approval of the SIP revision that altered the 
remaining useful life of the unit in ADEQ's four factor analysis. 
However, the APS Cholla scenario was distinguishable because, as 
explained in the proposed rule,\80\ the SIP revision for APS Cholla 
replaced the FIP that was applicable to these units.\81\ Therefore, it 
would not have been reasonable to subject them to two inconsistent 
requirements, one State and one Federal, under the RHR at the same 
time. Thus, under these circumstances it was appropriate for ADEQ to 
make the effectiveness of the permit conditions contingent on EPA SIP 
approval. In the current case, there is no existing FIP in place 
applicable to IGS Unit 3, so no similar rationale exists for making the 
cap contingent upon approval by the EPA.
---------------------------------------------------------------------------

    \80\ 89 FR 47398, 47407, Table 1.
    \81\ 77 FR 72511 (December 5, 2012).
---------------------------------------------------------------------------

    Comment B.9. ADEQ asserts that the EPA should approve ADEQ's 
reasonable progress goal (RPG) for the Sycamore Canyon Wilderness Area. 
The state indicates that it provided the required ``robust 
demonstration'' by including a detailed analysis of visibility data at 
the Sycamore site to demonstrate that its slower rate of progress 
results from significant increases in light extinction from coarse 
mass.
    Response B.9. As ADEQ notes in its comment, its analysis regarding 
Sycamore Canyon focused on the substantial increase in coarse mass and 
soil impairment at the Sycamore Canyon site. However, as explained in 
our proposal, the rule requires a state with a Class I area whose RPG 
is above the glidepath to demonstrate, based on the source selection 
and four factor analyses required under 40 CFR 51.308(f)(2)(i), that 
there are no additional emissions reduction measures for sources that 
may reasonably be anticipated to contribute to visibility impairment in 
the Class I area that would be reasonable to include in the long-term 
strategy.\82\ Although ADEQ provided a detailed analysis of monitoring 
data concerning Sycamore Canyon, it did not provide ``a robust 
demonstration, including documenting the criteria used to determine 
which sources or groups or sources were evaluated and how the four 
factors required by paragraph (f)(2)(i) were taken into consideration 
in selecting the measures for inclusion in its long-term strategy.'' 
\83\ Instead, it relied solely on monitoring data and the source 
selection and four-factor analyses contained elsewhere in the Plan.\84\ 
For the reasons described in our proposal and elsewhere in this 
document, we find that these analyses were inadequate to meet the 
requirements of 40 CFR 51.308(f)(2). Therefore, the Plan also did not 
meet the requirements of 40 CFR 51.308(f)(3)(ii)(A) with respect to 
Sycamore Canyon.
---------------------------------------------------------------------------

    \82\ 89 FR 47398, 47433.
    \83\ 40 CFR 51.308(f)(ii)(A).
    \84\ See Plan p. 106, footnote 112 (citing Plan Section 8 and 
Appendix C).
---------------------------------------------------------------------------

    Comment B.10. ADEQ indicates that the State intends to coordinate 
with EPNG to provide supporting documentation for the interest rate. 
ADEQ indicates that it intends to provide the interest rate 
documentation as confidential business information (CBI) to the EPA for 
review prior to publication of the final rule and requests that the EPA 
approve the cost calculation for EPNG Willcox and Williams based on the 
site-specific interest rate and supporting documentation.
    Response B.10. Although ADEQ referenced the existence of 
documentation and the possibility of sharing it with the EPA in its 
response to comments in the Plan,\85\ no supporting documentation for 
the interest rate was submitted as part of the Plan or prior to the 
close the public comment period on the EPA's proposed partial approval 
and partial disapproval. Therefore, the EPA is unable consider the 
interest rate information as part of this action.
---------------------------------------------------------------------------

    \85\ 2022 Arizona Regional Haze Plan, Appendix K.
---------------------------------------------------------------------------

    Additionally, we note that the lack of documentation of EPNG's 
firm-specific interest rate was one of several flaws that we identified 
in the state's long-term strategy. Therefore, even if the appropriate 
documentation had been submitted and within the proper time frame, that 
alone would not have changed our determination that the

[[Page 102756]]

2022 Arizona Regional Haze Plan did not satisfy the long-term strategy 
requirements of 40 CFR 51.308(f)(2).
    Comment B.11. ADEQ voiced procedural concerns with the lack of 
specificity in the EPA's proposed disapproval of the 2022 Arizona 
Regional Haze Plan. ADEQ cites CAA 307(d)(3) as requiring a detailed 
notice of rulemaking and cites Small Ref. Lead Phase-Down Task Force v. 
EPA, 705 F.2d 506, 518-19 (D.C. Cir. 1983), for the proposition that 
the notice provided in the proposal may be too general to be adequate 
and that ``[a]gency notice must describe the range of alternatives 
being considered with reasonable specificity.'' The commenter asserts 
that the EPA's proposed rule does not provide ``detailed notice'' of 
certain specific issues that form the basis for disapproval of entire 
sections of the 2022 Arizona Regional Haze Plan, denying ADEQ the 
opportunity to specifically address those bases for disapproval during 
the comment period.
    Response B.11. We disagree that the EPA's proposal provided 
inadequate notice. The EPA's action on the 2022 Arizona Regional Haze 
Plan is not subject to the requirements of CAA section 307(d). Those 
requirements apply only to specific enumerated types of actions under 
the CAA and to ``such other actions as the Administrator may 
determine.'' \86\ Actions on SIPs are not one of the enumerated 
actions, and the Administrator had not determined that this action is 
subject to 307(d) pursuant to Section 307(d)(1)(V). Therefore, this 
action is subject to the procedural requirements of the Administrative 
Procedure Act (APA).
---------------------------------------------------------------------------

    \86\ CAA Section 307(d)(1).
---------------------------------------------------------------------------

    Accordingly, pursuant to 5 U.S.C. 553(b)(2) and (3), the EPA's 
notice of proposed rulemaking regarding the Plan was required to 
include ``reference to the legal authority under which the rule is 
proposed'' and ``either the terms or substance of the proposed rule or 
a description of the subjects and issues involved.'' The proposal 
clearly met these requirements, as it stated the applicable legal 
authorities and provided the EPA's review of the Plan in relation to 
those requirements. The comment provides no basis to conclude that the 
proposal failed to meet these requirements. Indeed, the opinion cited 
by the commenter contrasts these more general APA requirements to the 
more exacting requirements of CAA section 307(d) concerning the 
contents of proposed rulemaking.\87\ While we agree with the commenter 
that ``[a]gency notice must describe the range of alternatives being 
considered with reasonable specificity,'' \88\ we find that our 
proposal met this requirement, as it plainly stated that the EPA was 
considering partially approving and partially disapproving the 2022 
Arizona Regional Haze Plan and detailed the reason for this proposed 
action. Please also see Responses A.1.
---------------------------------------------------------------------------

    \87\ Small Ref. Lead Phase-Down Task Force v. EPA, 705 F.2d 506, 
518-19 (D.C. Cir. 1983),
    \88\ Id. at 549.
---------------------------------------------------------------------------

    Comment B.12. ADEQ acknowledges that further FLM consultation is 
required for a plan revision that will correct the deficiencies 
identified in the proposed rulemaking action, but contends that the 
inclusion of the nonpoint source selection analysis and selected 
controls for nonpoint sources in the FLM review draft of the plan 
provided FLMs adequate notice and review of Arizona's nonpoint source 
rules that were codified after plan submission and submitted in the 
2023 Arizona Regional Haze Rules Supplement.\89\
---------------------------------------------------------------------------

    \89\ ADEQ SIP Revision: Nonpoint Rules to Supplement Arizona's 
2022 Regional Haze SIP, ``2023 Arizona Regional Haze Rule 
Supplement,'' August 22, 2023.
---------------------------------------------------------------------------

    Response B.12.The EPA disagrees with ADEQ's contention that it 
provided the FLMs with adequate notice and review of Arizona's nonpoint 
source rules. The information about FLM consultation regarding the 
rules specifically is not detailed in either the 2023 Arizona Regional 
Haze Rules Supplement, or the 2022 Arizona Regional Haze Plan. The 2023 
Arizona Regional Haze Rules Supplement indicated that further 
information on how this SIP revision complied with 40 CFR 51.308(i) 
requirements for federal land manager consultation is section 2.4 of 
the 2022 Arizona Regional Haze Plan.\90\ However, section 2.4 of the 
plan only describes the FLM review of the 2022 Arizona Regional Haze 
Plan, and does not specify if ADEQ provided a draft of the three 
nonpoint source rules to the FLMs for review. The rules were not 
included in the 2022 Arizona Regional Haze Plan. Should Arizona choose 
to submit a SIP revision, clarification of the FLM review process of 
the nonpoint source rules that are listed in Table 1-1 of the 2023 
Arizona Regional Haze Rules Supplement would be helpful for EPA review.
---------------------------------------------------------------------------

    \90\ Id, at Chapter 4.
---------------------------------------------------------------------------

C. Comment Letter From the Chamber and AMC

    Parts I (``The Chamber and AMC are supportive of the goals of the 
Regional Haze Rule'') and III (``Conclusion'') of the Chamber and AMC's 
comment letter are informational and therefore do not require a 
response. We respond to part II, sections A-E of the Chamber and AMC's 
comment letter below.
    Comment C.1. The Chamber and AMC note that the EPA's delayed action 
and partial disapproval of Arizona's Regional Haze Plan is an example 
of erosion of cooperative federalism. The commenter contends that the 
timeline of events leading up to the EPA's partial disapproval of 
Arizona's Regional Haze Plan is problematic and that the EPA seems to 
routinely miss statutory deadlines, only to get sued by third-party 
entities for failure to act, resulting in agreements to deadline 
extensions that delay action for years. In the meantime, the resources 
and analysis invested by states depreciate in value, often requiring 
states to reinvest in efforts to update an analysis with new 
information. The commenter also asserted that ``[r]egularly, an even 
worse scenario plays out in which EPA denies a SIP because the 
information submitted in good faith by a state has since become dated 
and stale.''
    Response C.1. We do not agree that either the timing or substance 
of the EPA's partial disapproval of Arizona's Regional Haze Plan is an 
example of the erosion of cooperative federalism. We acknowledge that 
the EPA did not act on the 2022 Arizona Regional Haze Plan within the 
statutory deadline under CAA section 110(k)(3), and that we were 
subsequently sued for failing to meet that deadline. This resulted in a 
court-ordered deadline for the EPA to take action on the Plan by March 
30, 2025.\91\ However, we do not agree that this resulted in a 
``deadline extension'' of any sort, or an erosion of cooperative 
federalism. On the contrary, in issuing a partial approval and partial 
disapproval of the Plan, the EPA is fulfilling our statutorily-mandated 
role to review SIPs for compliance with the requirements of the CAA and 
the RHR, as further described in Response D.3.
---------------------------------------------------------------------------

    \91\ Sierra Club v. EPA (D.D.C. Case No. 1:23-cv-01744-JDB), 
Consent Decree entered July 12, 2024.
---------------------------------------------------------------------------

    We also disagree with the suggestion that the EPA is disapproving 
the 2022 Arizona Regional Haze Plan, partially or entirely because 
information became ``dated or stale.'' The comment did not provide 
examples of information becoming dated, resulting in disapproval; thus, 
we cannot comment on any specific concerns the commenter has with the 
information within the 2022 Arizona Regional Haze Plan.
    Further, as explained in Responses A.1 EPA staff also discussed 
with ADEQ many of the concerns that became bases for our disapproval 
during the SIP development process.

[[Page 102757]]

    Comment C.2. The Chamber and AMC state that guidance should not be 
cited as grounds to disapprove the 2022 Arizona Regional Haze Plan. The 
commenter asserts that guidance should be viewed only as a reference 
and not a legal requirement to be used to approve or disapprove a 
state's plan. The Chamber and AMC also claim that the EPA published 
final guidance for Regional Haze Plans three weeks before the plans 
were due, making compliance with the guidance practically impossible 
before the deadline. The commenter concludes that relying on the 
guidance to partially disapprove the Plan was therefore arbitrary and 
capricious, and the EPA should withdraw all of the proposed 
disapprovals based upon the 2021 Clarifications Memo.
    Response C.2. The EPA disagrees that it relied on guidance, 
including the 2021 Clarifications Memo, as the basis for our partial 
disapproval. See responses A.5, B.1, and B.2.
    Comment C.3. The Chamber and AMC assert that Arizona's source 
selection methodology was reasonable and that the EPA should give 
deference to the State on this matter. The commenter indicates that 
sources that applied controls in the first round of Regional Haze had 
recently made significant investments in the design, engineering, 
procurement, construction and operation of those air pollution control 
devices. They note that forcing facilities to consider improvement or 
replacement of these air pollution control devices long before they 
have depreciated is an unnecessary economic burden for the source and 
the State. The Chamber and AMC note that ADEQ chose not to force 
additional analysis from these sources and reasonably relied upon 
reductions from other emissions sources for visibility improvement, a 
method that resulted in all but one of Arizona's Class I areas either 
meeting or exceeding the uniform rate of progress (URP) toward natural 
conditions.
    Response C.3. We disagree that it was reasonable for Arizona to 
screen out sources solely because they applied controls during the 
first planning period, for the reasons described in section IV.E.2.a. 
of our proposal and in response B.3 of this document.
    We also disagree that our disapproval will automatically force 
sources to consider improving or replacing any recently installed air 
pollution devices. Rather, ADEQ has the option to provide additional 
documentation and justification for its effective control 
determinations in a responsive SIP revision. We anticipate that for 
many units that recently installed controls, ADEQ will be able to 
provide an adequate demonstration of effective controls on a unit-
specific and pollutant-specific basis, if it chooses to do so, which 
would preclude the need for a four-factor analysis for those units and 
pollutants. Any affected units and pollutants for which ADEQ is unable 
to make such demonstration would be subject to the four-factor analysis 
requirement as required by 40 CFR 51.308(f)(2).
    Finally, we note that all states are subject to the requirements at 
40 CFR 51.308(f)(2) and (3) regardless of whether the 2028 RPGs for 
Class I Areas they affect are above or below URP.
    Comment C.4. The Chamber and AMC assert that the EPA should give 
deference to Arizona's deviation from the EPA Control Cost Manual in 
developing cost estimates. The commenter notes that the Cost Control 
Manual is not accurate for all sources and cites examples such as 
variable interest and emissions rates. They conclude that the use of 
different interest rates and different control efficiencies for 
different projects should be viewed as reasonable.
    Response C.4. We do not agree that we should have deferred to 
Arizona's deviation from the EPA Control Cost Manual in the absence of 
adequate justification. As discussed in Response D.3, Congress charged 
the EPA with independently evaluating and reviewing SIP submissions for 
compliance with the applicable requirements under the CAA. 40 CFR 
51.308(f)(2)(iii) requires states to ``document the technical basis, 
including modeling, monitoring, cost, engineering, and emissions 
information, on which the State is relying to determine the emission 
reduction measures that are necessary to make reasonable progress in 
each mandatory Class I Federal area it affects.'' The technical 
documentation must include the modeling, monitoring, cost, engineering, 
and emissions information on which the state relied to determine the 
measures necessary to make reasonable progress. For the reasons noted 
in section IV.E.2.b.ii (``Deviations from Cost Control Manual'') of our 
proposed rule, we found that Arizona failed to adequately document the 
technical basis that it relied upon to determine emissions reduction 
measures, as required by 40 CFR 51.308(f)(2)(iii). Specifically, as 
explained in our proposal, it is important to use consistent methods in 
order to allow for reasoned comparisons between different sources 
within a state, and cost analyses in other states.\92\ Therefore, while 
our regulations allow for flexibility among various methodologies, 
where a state deviates from these methods, it should explain how its 
alternative approach is reasonable, appropriate, and consistent with 
the regulations and the statutory requirement to make reasonable 
progress towards the national goal. Arizona did not do so. We therefore 
disagree that the EPA should give deference to Arizona's approach in 
the Plan.
---------------------------------------------------------------------------

    \92\ 89 FR 47398, 47428-47429.
---------------------------------------------------------------------------

    Comment C.5. The Chamber and AMC indicate that Arizona's plan 
should be viewed in the context that it results in all but one monitor 
having an RPG that provides for a greater rate of visibility 
improvement than the adjusted URP. The commenter asserts that Arizona 
has created a plan that meets or exceeds the URP at all monitors except 
for Sycamore Canyon, which was moved to an intersection of two dirt 
roads in 2014. The commenter concludes that the fact that visibility at 
Arizona's Class I areas is improving at a pace to reach natural 
conditions prior to the RHR goal of 2064 is important context in 
evaluating the source selection methodology and other decisions made by 
Arizona.
    Response C.5. We do not agree with the commenter's characterization 
of the role of the URP. As explained in our proposal:

    The URP is a planning metric used to gauge the amount of 
progress made thus far and the amount left before reaching natural 
visibility conditions. However, the URP is not based on 
consideration of the four statutory factors and therefore cannot 
answer the question of whether the amount of progress being made in 
any particular implementation period is ``reasonable progress.'' 
\93\
---------------------------------------------------------------------------

    \93\ 89 FR 47398, 47406.

    Moreover, being on or below the URP does not exempt a state from 
any of the requirements of the CAA or the Regional Haze Rule.\94\
---------------------------------------------------------------------------

    \94\ See 82 FR 3078,3093 and 3099-3100.
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    It should also be noted that the URP represents the amount of 
visibility improvement that would need to be achieved during each 
implementation period to achieve natural visibility conditions by the 
end of 2064. However, the 2064 date is used solely to calculate the URP 
as a tracking metric. The CAA and RHR do not contain any end dates for 
the regional haze program and do not have a ``goal'' or requirement to 
achieve natural conditions by 2064 specifically.
    Please also see Response B.9 for more information on the robust

[[Page 102758]]

demonstration required for Sycamore Canyon under 40 CFR 
51.308(f)(3)(ii), which is missing from Arizona's submission.

D. Comment Letter From TEP

    The ``Background'' section of TEP's comment letter is informational 
and therefore does not require a response. We respond to the ``Comments 
of Proposed Disapproval'' section of TEP's comment letter below.
    Comment D.1. TEP claims that ADEQ's source selection methodology 
was reasonable and the EPA should approve the determination. First, TEP 
cites to the 2019 Guidance and 2021 Clarifications Memo as providing 
states discretion for source selection and notes that ADEQ applied a Q/
d screening threshold of 10 for each process at a source. TEP further 
describes ADEQ's screening out processes where the facility recently 
adopted ``effective controls,'' which the Agency defined as controls 
installed to meet the requirements of the PSD program (BACT), the first 
regional haze planning period (BART), or other NAAQS requirements. 
Second, TEP further suggests that the EPA is proposing to approve 
``many aspects of ADEQ's source selection process,'' including ADEQ's 
choice of screening threshold and focus on NOX, 
SO2, and PM10 in evaluating visibility impacts, 
but simultaneously proposing to find that the State did not adequately 
justify its determination of effective emissions reduction measures.
    Response D.1. First, we disagree with the commenter that ADEQ 
applied a Q/d screening threshold of 10 for each process at a source. 
As noted in the 2022 Arizona Regional Haze Plan, the Q value was 
calculated from facility-wide PM10, NOX, and 
SO2 annual emissions, not process-specific emissions.\95\
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    \95\ 2022 Arizona Regional Haze Plan, Appendix C2.2, p. 26.
---------------------------------------------------------------------------

    Second, we clarify that the EPA did not propose to approve ``many 
aspects of ADEQ's source selection process.'' We found that ADEQ 
reasonably and adequately explained and documented many aspects of its 
source selection process, such as its focus on sulfate, nitrate, and 
coarse mass and its use of a Q/d value of 10 for point sources. 
However, we are not separately approving or disapproving specific 
elements of ADEQ's long-term strategy, including any elements of the 
source-selection process. Rather, we are disapproving the long-term 
strategy as a whole under 40 CFR 51.308(f)(2), for the reasons 
described in our proposal and in this document.
    Comment D.2. TEP asserts that ADEQ reasonably evaluated existing 
controls at IGS Unit 4 and SGS Units 3 and 4.
    First, the commenter states that ADEQ did not determine that 
sources were effectively controlled based on BART controls alone, but 
also evaluated additional emissions reduction measures at several units 
that were controlled during the first regional haze planning period, 
citing Table 8-2 in the 2022 Arizona Regional Haze Plan. For IGS Unit 4 
specifically, the commenter states that ADEQ evaluated existing 
emissions reduction measures at IGS Unit 4 from a source-specific 
perspective, and determined that further analysis would be futile. TEP 
cites to statements regarding post-combustion controls in the 2019 
Guidance and states that, in a recent FIP action for Arizona, the EPA 
determined that eliminating coal combustion at Unit 4 would control 
emissions beyond the best available NOX and SO2 
controls.\96\ TEP concludes that these emissions reduction measures 
remain the best available controls at this unit in the second planning 
period. TEP further notes that ADEQ's determination that IGS Unit 4 is 
well-controlled is also consistent with recent decreasing emissions 
trends across BART-eligible EGUs, including IGS Unit 4, and between 
2014 and 2019. TEP points to the recent proposed rule for Georgia's 
Regional Haze SIP,\97\ and comments that the EPA cited to similar 
visibility-impairing emissions trends as support for Georgia's source-
selection methodology. Citing to the 2021 Clarifications Memo,\98\ TEP 
also indicates that ADEQ was not required to consider emissions trends 
and that the State has discretion to emphasize other considerations, 
such as the EPA's prior FIP evaluation.
---------------------------------------------------------------------------

    \96\ 79 FR 52420, 52422.
    \97\ 89 FR 47481 (June 3, 2024).
    \98\ Specifically, TEP quotes page 3 of the 2021 Clarifications 
Memo (``[t]he [Regional Haze Rule] does not explicitly list factors 
that states must or may not consider when selecting sources for 
analysis,'') and cites page 5 of the 2021 Clarifications Memo as 
supporting its assertion that ``EPA has recommended that states 
consider projected and actual emissions in evaluating existing 
emission reduction measures.''
---------------------------------------------------------------------------

    Second, TEP states that the EPA's proposed disapproval fails to 
engage with ADEQ's analysis for SGS Unit 3 and 4. TEP notes that ADEQ 
considered potential additional control measures that could be used to 
achieve emissions reductions at SGS Units 3 and 4 based on an initial 
control analysis submitted by TEP.\99\ In this analysis, TEP provided 
information on technically feasible control measures, as well as the 
actual and projected emissions rates at each unit.
---------------------------------------------------------------------------

    \99\ TEP, Identification and Evaluation of Emission Control 
Measures for Units 3 and 4 at the Springerville Generating Station 
for Purposes of the Regional Haze Second Planning Period Under 40 
CFR 51.308(f)(2) (Mar. 2020), available at https://static.azdeq.gov/aqd/haze/tep_spr_4fa_u34.pdf.
---------------------------------------------------------------------------

    Response D.2. We disagree that ADEQ's evaluations regarding 
effective controls at IGS Unit 4 and SGS Units 3 and 4 were reasonable 
and justified. Contrary to TEP's claim, ADEQ did not evaluate 
additional emissions reduction measures at several units that were 
controlled during the first regional haze planning period. Table 8-2 
cited by TEP to support its claim that ADEQ evaluated additional 
emissions reduction measures at units that were controlled during the 
first regional haze planning period only depicts annual, source-level 
total emissions of NOX, SO2 and PM10 
and does not include any information regarding unit-specific or 
pollutant specific emissions rates or controls. The commenter also 
provides no citation for its assertion that ADEQ evaluated existing 
emissions reduction measures at IGS Unit 4 from a source-specific 
perspective. Therefore, based on the contents of the 2022 Arizona 
Regional Haze Plan, it was reasonable for the EPA to determine that 
ADEQ did not evaluate additional emissions reduction measures at units 
that were controlled during the first regional haze planning period.
    Similarly, the commenter's citation to the discussion of post-
combustion controls in the 2019 Guidance is misleading because no such 
controls were installed at IGS Unit 4. Rather, the unit was converted 
from coal to gas as part of a ``better-than-BART'' determination 
pursuant to 40 CFR 51.308(e)(2).\100\ Therefore, the actual relevant 
effective controls discussion in the 2019 Guidance is the discussion of 
fuel combustion units that are required to burn pipeline quality 
natural gas. Such units are generally considered to be effectively 
controlled for SO2 and PM.\101\ However, they are not 
necessarily effectively controlled for NOX. Therefore, we 
disagree with the commenter that, given TEP's recent conversion of IGS 
Unit 4 from coal to natural gas, ADEQ's conclusion that further 
analysis was not required was reasonable. As stated in the proposed 
rule,\102\ ADEQ should have explained why it is reasonable to assume, 
without conducting a four-factor analysis, that no additional 
NOX controls would be reasonable.\103\
---------------------------------------------------------------------------

    \100\ See 40 CFR 52.145(j)(4).
    \101\ See 2019 Guidance, p. 24.
    \102\ 89 FR 47398, 47428.
    \103\ See 40 CFR 51.308(f)(2)(i) (``. . .The State must include 
in its implementation plan a description of the criteria is used to 
determine which sources or groups of sources it evaluated and how 
the four factors were taken into consideration in selecting the 
measures for inclusion in its long-term strategy.''). See also 2021 
Clarifications Memo, p. 5; 2019 Guidance, p. 23.

---------------------------------------------------------------------------

[[Page 102759]]

    The commenter's discussion of emissions trends is also misleading 
on several grounds. First, the commenter mischaracterizes the EPA's 
review of Georgia's regional haze source selection methodology. In the 
section of the Georgia proposal cited by TEP, the EPA considered trends 
in total measured visibility impairment at three Class I areas affected 
by Georgia's sources as supporting the reasonableness of the state's 
overall source selection methodology.\104\ The EPA did not, however, 
consider trends in emissions from specific sources and did not indicate 
that such trends would be relevant either to the reasonableness of a 
state's overall source selection methodology or especially to the 
question of a whether a particular source may be screened out on the 
grounds that it is ``effectively controlled.'' Furthermore, the trends 
cited by the commenter were for multiple BART-eligible EGUs, not just 
IGS. Therefore, we do not agree that decreasing SO2 and 
NOX emissions at BART-eligible EGUs in Arizona between 2014 
and 2019 are relevant to whether IGS Unit 4 is effectively controlled.
---------------------------------------------------------------------------

    \104\ 89 FR 47481, 47497-47498.
---------------------------------------------------------------------------

    Second, the commenter mischaracterizes the contents of the 2021 
Clarifications Memo as it relates to how to determine whether a source 
is effectively controlled. The first section cited by the commenter, 
regarding ``Factors to Consider for Source Selection'' \105\ relates to 
a State's overall source selection methodology, which is generally 
considered to be the first step of determining what measures are 
necessary for reasonable progress.\106\ Whether and how to screen out 
particular sources on the grounds that they are effectively controlled 
is a subsequent step. As previously noted, we found that many aspects 
of ADEQ's source selection process were reasonable and adequately 
explained and documented,\107\ consistent with the statement in the 
Clarifications Memo that, ``whatever choices states make should be 
reasonably explained and produce a reasonable outcome.'' \108\ However, 
once the sources were initially selected for evaluation of additional 
control measures, we found that ADEQ did not provide an adequate 
justification for subsequently screening out certain sources and units 
from ultimately conducting a four-factor analysis on the basis that 
they are effectively controlled.
---------------------------------------------------------------------------

    \105\ 2021 Clarifications Memo, p. 3.
    \106\ Id. (``Source selection is a critical step in states' 
analytical processes. All subsequent determinations of what 
constitutes reasonable progress flow from states' initial decisions 
regarding the universe of pollutants and sources they will consider 
for the second planning period.'')
    \107\ 89 FR 47428.
    \108\ 2021 Clarifications Memo, p. 3.
---------------------------------------------------------------------------

    The second section of the 2021 Clarifications Memo mischaracterized 
by the commenter, ``Sources that are Not Selected Based on Existing 
Effective Controls,'' does address the screening out of particular 
sources on the grounds that they are effectively controlled. In 
particular, this section recommends that, ``States should first assess 
whether the source in question already operates an `effective control' 
as described in the August 2019 Guidance. They should further consider 
information specific to the source, including recent actual and 
projected emission rates, to determine if the source could reasonably 
attain a lower rate.'' \109\ For the reasons detailed in our proposal 
and elsewhere in this document, we find that ADEQ did not reasonably 
explain and support its determination at the first step that IGS Unit 4 
already operates effective controls, particularly for NOX. 
Moreover, even if IGS Unit 4 does have effective controls, ADEQ should 
have considered recent actual and projected emissions rates for this 
particular unit, not for all BART-eligible units as a group, in order 
to determine whether these controls are necessary to make reasonable 
progress.
---------------------------------------------------------------------------

    \109\ Id., p. 5 (emphasis added).
---------------------------------------------------------------------------

    Finally, we disagree that our proposed disapproval fails to engage 
with ADEQ's analysis for SGS Unit 3 and 4. Contrary to the commenter's 
suggestion, ADEQ did not screen out SGS Units 3 and 4 at the source 
selection stage,\110\ but instead conducted four-factor analyses for 
these units.\111\ We summarized these analyses on pages 47422-47423 of 
our proposal. We did not note any particular flaws in these analyses or 
the resulting determinations that no additional controls were necessary 
to make reasonable progress in our proposal. However, we found that 
ADEQ had not addressed whether any of the existing measures relied upon 
in these four-factor analyses were necessary to make reasonable 
progress and thus should be a part of the State's long-term strategy 
for the second planning period.\112\ We also noted that, as part of its 
analysis of whether these existing measures are necessary to make 
reasonable progress, the State should have considered whether the 
relevant sources are subject to enforceable emissions limits that 
ensure their emissions rates will not increase. Without this 
information, it is not clear what measures are in the State's long-term 
strategy for the second planning period and how controls on these units 
result in each of the affected Class I areas making reasonable progress 
towards the national goal.
---------------------------------------------------------------------------

    \110\ 2022 Arizona Regional Haze Plan, Appendix C, Exhibit CI.
    \111\ Id., Chapter C3.13.
    \112\ 89 FR 47431.
---------------------------------------------------------------------------

    Comment D.3. TEP asserts that ADEQ reasonably evaluated additional 
control measures using a four-factor analysis for SGS Units 1 and 2. 
Citing Oklahoma v. EPA, 723 F.3d 1201, 1209 (10th Cir. 2013), the 
commenter asserts that while the statute identifies the factors that 
must be considered, Congress left to states the determination as to how 
these factors should be weighed.
    Response D.3. While we agree that states have significant 
discretion in how they consider and apply the four statutory factors as 
part of a Regional Haze SIP, they do not have unlimited discretion. On 
the contrary, the EPA has a crucial role in reviewing such SIP 
submissions for compliance with the requirements of the CAA and the 
RHR. Pursuant to CAA section 110, states must submit SIP revisions to 
the EPA for review and the EPA must evaluate whether each SIP 
submission meets all of the applicable requirements of the Act.\113\ 
The EPA must disapprove any SIP revision that ``would interfere with 
any applicable requirement'' of the Act.\114\ CAA section 110(a)(2)(J) 
specifically requires that SIPs ``meet the applicable requirements'' of 
Part C of Title I of the CAA including the requirements for visibility 
protection set forth in sections 169A and 169B.\115\ Pursuant to 
section 169A(b), the EPA is required to promulgate visibility 
protection regulations that apply to ``each applicable implementation 
plan'' (i.e., each SIP or FIP) \116\ for each State containing one or 
more Class I areas and each State ``emissions from which may reasonably 
be anticipated to cause or contribute to any impairment of

[[Page 102760]]

visibility in any [Class I area].'' The CAA specifies that these 
regulations (including the RHR) must require each such SIP or FIP to 
``contain such emission limits, schedules of compliance and other 
measures as may be necessary to make reasonable progress toward meeting 
the national goal.'' \117\ Thus, the statute provides the EPA a key 
oversight role in reviewing SIPs, including regional haze SIPs, and the 
``EPA has substantive authority to assure that a state's proposals 
comply with the Act, not simply the ministerial authority to assure 
that the state has made some determination.'' \118\
---------------------------------------------------------------------------

    \113\ CAA section 110(a)(1), (k)(3), 42 U.S.C. 7410(a)(1) and 
(k)(3).
    \114\ CAA section 110(l), 42 U.S.C. 7410(l).
    \115\ CAA sections 110(a)(2)(J), 169A and 169B 42 U.S.C. 
7410(a)(2)(J), 7491 and 7492.
    \116\ Under the CAA, ``applicable implementation plan'' is 
defined as ``the portion (or portions) of the implementation plan, 
or most recent revision thereof, which has been approved under [CAA 
section 110], or promulgated under [CAA section 110](c) . . . and 
which implements the relevant requirements of [the CAA].'' CAA 
section 302(q), 42 U.S.C. 7602(q). In other words, an ``applicable 
implementation plan'' is an EPA-approved SIP or Tribal 
Implementation Plan, or an EPA-promulgated FIP.
    \117\ 42 U.S.C. 7491(b)(2).
    \118\ Arizona ex. rel. Darwin v. EPA, 815 F.3d 519, 531 (9th 
Cir. 2016).
---------------------------------------------------------------------------

    Nothing in the Oklahoma case cited by the commenter undermines this 
authority. On the contrary, the Oklahoma court upheld the EPA's 
disapproval of BART determinations that were part of a regional haze 
SIP, noting BART ``does not differ from other parts of the CAA--states 
have the ability to create SIPs, but they are subject to EPA review.'' 
\119\ Likewise, all regional haze SIPs are subject to EPA review, as 
described in the preceding paragraph.
---------------------------------------------------------------------------

    \119\ Oklahoma v. EPA, 723 F.3d 1201, 1209 (10th Cir. 2013).
---------------------------------------------------------------------------

    In our action on the Plan, we are exercising our substantive 
authority to review the state's submittal for compliance with the 
applicable requirements of the CAA and RHR. Based on our review of the 
Plan, we find, among other things, that ADEQ had not reasonably 
evaluated and weighed the four statutory factors for SGS Units 1 and 2 
for the reasons noted in section IV.E.2 of our proposal and responses 
B.4., B.6, B.7 and B.8 of this document.
    Comment D.4. TEP states that ADEQ's choice of cost-effectiveness 
threshold was reasonable, and that the EPA's proposed rule did not 
afford appropriate deference to ADEQ's assessment of reasonable cost-
effectiveness values. TEP also cites a previous EPA action stating that 
``Congress did not provide any direction as to how states should 
consider `the costs of compliance' when determining reasonable 
progress.'' \120\ TEP also provides the following reasons for why it 
believes ADEQ's choice of cost-effectiveness threshold was reasonable.
---------------------------------------------------------------------------

    \120\ 81 FR 296, 310 (January 5, 2016).
---------------------------------------------------------------------------

    First, TEP states that ADEQ selected a threshold based on the 
State's evaluation of the highest cost controls during the first 
planning period. TEP notes that this threshold is nearly $1,000/ton 
higher than the 98th percentile value for EGU boilers during the first 
planning period and $1,500/ton higher than costs rejected by Georgia in 
evaluating additional emissions reduction measures in its SIP 
submission.\121\
---------------------------------------------------------------------------

    \121\ 89 FR 47494.
---------------------------------------------------------------------------

    Second, TEP claims that ADEQ's bright-line approach to analyzing 
available controls above its cost-effectiveness threshold was also 
reasonable. TEP disagrees with the EPA's concern about the average cost 
of installing SNCR at SGS Unit 2 being $269/ton above ADEQ's $6,500/ton 
threshold.\122\ TEP states that the 2019 Guidance emphasized that the 
RHR does not prevent states from implementing ``bright line'' cost-
effectiveness thresholds when considering additional control measures, 
consistent with the Ninth Circuit's decision in NPCA v. EPA.\123\ TEP 
asserts that this threshold sets an amount above which a state would 
reject control options as too expensive, and that for controls falling 
below this threshold, it is reasonable for ADEQ to evaluate additional 
factors, such as incremental costs, visibility impacts, and the other 
statutory factors, in determining whether these controls are necessary 
for reasonable progress.
---------------------------------------------------------------------------

    \122\ 89 FR 47429.
    \123\ 2019 Guidance at 38 (citing NPCA v. EPA, 788 F.3d 1134, 
1142-43 (9th Cir. 2015)).
---------------------------------------------------------------------------

    Response D.4. As TEP describes, the EPA noted in prior rulemakings 
that ``Congress did not provide any direction as to how states should 
consider `the costs of compliance' when determining reasonable 
progress.'' However, consistent with our prescribed statutory role, as 
described in Response D.3, the EPA is required to evaluate whether each 
State exercised its flexibility and conducted the required analyses in 
a reasonable way and in accordance with the applicable requirements. As 
described throughout our proposal and this final action, we determined 
that Arizona did not do so.
    For example, contrary to TEP's claim, the EPA did not find that 
ADEQ's average cost-effectiveness thresholds of $6,500/ton for point 
sources and $5,000/ton for nonpoint sources were unreasonable. Rather, 
as explained in our proposal, we found that the State inconsistently 
and unreasonably applied these cost thresholds to the control 
determinations.\124\
---------------------------------------------------------------------------

    \124\ 89 FR 47398, 47429.
---------------------------------------------------------------------------

    In particular, we found that ADEQ incorrectly characterized its 
average cost effectiveness threshold for points sources as a bright-
line threshold,\125\ given that ADEQ, in fact, rejected controls that 
were below this threshold. In these instances, ADEQ relied on 
incremental cost effectiveness as a basis to find the cost of control 
excessive, but, again, did not do so consistently, as described in 
Response B.6 of this document. Thus, ADEQ did not consistently apply 
either its chosen average cost effectiveness threshold or any defined 
incremental cost effectiveness threshold as a basis to choose whether 
to adopt or reject control measures, nor did it explain its reasoning 
for these inconsistencies. The EPA finds this to be unreasonable. Based 
on this and other flaws in the long-term strategy described in the 
proposal and elsewhere in this document, we find that the long-term 
strategy in the Plan did not meet the requirements of 40 CFR 
51.308(f)(2).
---------------------------------------------------------------------------

    \125\ See 2022 Arizona Regional Plan, Appendix K, p. 7.
---------------------------------------------------------------------------

    We also note that, while our proposed rule recommended that ADEQ 
revisit control determinations with controls that were slightly above 
the cost thresholds, given the flaws in the cost-effectiveness 
analyses, we did not indicate that, in the absence of such flaws, use 
of a bright line threshold would have been improper, as long it was 
appropriately justified and consistently applied. Finally, we note that 
the fact that other states have applied lower or similar thresholds 
does not automatically make Arizona's threshold reasonable.
    Comment D.5. TEP states that ADEQ's evaluation of control costs is 
conservative and results in projected costs that are lower than what 
TEP would incur. TEP asserts that ADEQ selected baseline assumptions 
consistent with the EPA's Control Cost Manual. In particular, TEP 
indicates that ADEQ calculated control costs using an assumed interest 
rate of 4.75 percent and a maximum equipment life of 30 years, but that 
these assumptions resulted in unrealistically low control cost 
estimates. TEP noted that the EPA previously used 20-year equipment 
life and 7 percent interest rate for both NOX and 
SO2 candidate emissions reduction measures for IGS as part 
of a previous regional haze FIP,\126\ and that these assumed values of 
7 percent and 20 years better reflect actual control costs.
---------------------------------------------------------------------------

    \126\ 79 FR 9318.
---------------------------------------------------------------------------

    TEP also asserted that ADEQ is not required to treat the guidance 
provided by the Control Cost Manual as dispositive, and, citing Wyoming 
v. EPA, 78 F.4th 1171, 1180 (10th Cir. 2023), TEP asserted that the EPA 
cannot treat nonbinding guidelines as mandatory in evaluating a SIP 
submission.\88\

[[Page 102761]]

    Response D.5 We do not agree that ADEQ's evaluation of costs was 
conservative and results in projected costs that are lower than what 
TEP would incur. Regarding the EPA's previous analyses for IGS, first, 
we note that the EPA has revised several chapters of the Control Cost 
Manual, since the 2014 regional haze FIP cited by TEP in the comment 
letter. In particular, the chapter concerning SCR was updated in 
2019.\127\ As part of that update, the remaining useful life for SCR 
was revised from 20 years to 30 years.\128\ Consistent with this 
change, ADEQ used a remaining useful life of 30 years for SCR, but used 
20 years for SNCR.\129\
---------------------------------------------------------------------------

    \127\ Control Cost Manual, Section 4, Chapter 2 Selective 
Catalytic Reduction (June 2019), section, 2.4.2 Total Annual Costs, 
Indirect costs, available at https://www.epa.gov/sites/default/files/2017-12/documents/scrcostmanualchapter7thedition_2016revisions2017.pdf.
    \128\ Id. at page 87 of 107 (PDF document pagination), (``a 
representative value of the equipment life for SCR at power plants 
can be considered as 30 years'').
    \129\ Id., Appendix C, p. 219 (``The estimated life for SCR and 
SNCR were set at 30 and 20 years respectively to match current EPA 
guidance for these control technologies on utility boilers.'') The 
commenter's citation to page 146 of the Plan appears to be in error, 
as there is no such page in the main body of the Plan, and page 146 
of Appendix C discusses the Willcox compressor station.
---------------------------------------------------------------------------

    Second, as explained in the Control Cost Manual,\130\ interest 
rates change with time due to changes in prices over time for all 
relevant goods and services such as capital equipment, engineering 
services, other materials and reagents used in the construction and 
operation of control equipment. In the absence of source-specific 
information, ADEQ relied on a 4.75 percent interest rate developed by 
analyzing and averaging historical bank prime rate data. ADEQ looked at 
3-year average bank prime rates for the periods of 2017-2019 (4.83 
percent) and April 2018-March 2020 (4.78 percent). These dates were 
chosen as they were the most recent data at the time of the 
analysis.\131\ In contrast, ADEQ also explained in its SIP submittal 
that the 7 percent interest rate from the first planning period FIP 
cited by TEP was the 3-year average bank prime rate during 2005-
2007.\132\ Therefore, the 7 percent rate used by the EPA in our 
previous FIP was not appropriate for the cost analysis for the Plan, 
which was developed in 2020-2022.
---------------------------------------------------------------------------

    \130\ Control Cost Manual, Section 4, Chapters 1 and 2, 
available at https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/cost-reports-and-guidance-air-pollution.
    \131\ 2022 Arizona Regional Haze Plan, Chapter 8.3.2.
    \132\ Id.
---------------------------------------------------------------------------

    Finally, we disagree with the commenter's suggestion that we 
treated the Control Cost Manual, or any other guidance, as binding. As 
discussed in Responses A.3 and C.4, the EPA's citations to guidance 
documents were intended to provide further context on what is generally 
considered to be a reasonable approach to fulfill the statutory and 
regulatory requirements. We acknowledge that the suggestions in those 
guidance documents are not binding, but are generally assumed to be 
reasonable. States can deviate from the suggestions within EPA guidance 
documents. However, they must do so in a reasonable way, accompanied by 
sufficient justification. The Plan did not do so for the reasons 
described in our proposal and elsewhere in this document.
    Comment D.6. TEP asserts that ADEQ's analysis of SCR and SNCR 
reasonably approximated emissions limits achievable at SGS Units 1 and 
2. TEP explains that the emissions rate used in the analysis was unit-
specific, and that ADEQ considered baseline NOX emissions, 
inlet concentrations, and the frequency of startup/shutdown cycles at 
SGS Units 1 and 2. TEP reiterates that ADEQ explained that a higher 
number of startup/shutdown cycles results in higher average 
NOX emissions rates with SCR, and that SGS Units 1 and 2 
experience a higher frequency of startup/shutdown cycles than average 
EGUs.
    TEP further disagrees that SGS Units 1 and 2 are able to achieve an 
emissions rate of 0.05 lb/MMBtu. TEP notes that ADEQ further explained 
in its response to public comments that it was inappropriate to use an 
annual emissions limit of 0.05 lb/MMBtu because the CAMPD database only 
contains three comparable units, out of fifty-eight units, which are 
operating below this emissions limit in 2019-2021. The CAMPD database 
shows that approximately 20% of the units achieved emissions below 0.06 
lb/MMBtu in 2019-2021, which ADEQ believed was a reasonable estimate of 
the rate achievable with SCR for SGS Units 1 and 2. TEP also notes that 
based on their extensive industry experience, vendors will not 
guarantee a rate of 0.05 lb/MMBtu due to concerns about degradation 
over time.
    TEP also states that even if ADEQ adopted the EPA's preferred 
emissions rate of 0.05 lb/MMBtu, ADEQ's analysis of control measures 
for SGS Units 1 and 2 would remain substantially the same. Table 3 of 
TEP's comment letter provides the updated cost-effectiveness value 
using a 0.05 lb/MMBtu rate for SGS Units 1 and 2, assuming a 4.75 
percent interest rate and a remaining useful life of 30 years.
    Response D.6. We do not agree that ADEQ's analysis of SCR and SNCR 
reasonably approximated emissions limits achievable at SGS Units 1 and 
2. Our proposed rule acknowledged the startup/shutdown considerations 
noted by ADEQ.\133\ However, the proposed rule also explains that ADEQ 
has not demonstrated why these startup/shutdown considerations would be 
significant enough at SGS Units 1 and 2 on an annual average basis, 
which is the averaging period used to calculate ton/year emissions 
reductions for cost effectiveness calculations, to preclude them from 
achieving this emissions reduction level with SCR. As discussed in more 
detail in Response B.4, we would consider it appropriate for an 
emissions limitation established on a shorter averaging period to have 
a higher value to account for startup/shutdown emissions, which have a 
greater effect on overall unit emissions rates over shorter averaging 
periods.
---------------------------------------------------------------------------

    \133\ 89 FR 47398, 47428.
---------------------------------------------------------------------------

    We also disagree with TEP that ADEQ's review of emissions rates for 
other tangentially fired coal units in CAMPD should be determinative of 
the SCR emissions rate achievable for the SGS units. We do not 
necessarily consider the inventory of unit emissions data in CAMPD to 
be representative of what is achievable with SCR technology because 
units whose emissions are included in CAMPD have been required to 
install SCR as a result of a variety of regulatory programs. Not all of 
these programs may have fully considered technological factors in 
establishing emissions requirements or allowable emissions limits, 
which would have the effect of elevating reported emissions rates. For 
example, several units in the eastern U.S. have installed SCR but have 
not been required to operate in a manner that fully accounts for 
periods of startup operations,\134\ while other units may only operate 
their SCR systems seasonally.\135\ Other SCR systems may have been 
required by a Consent Decree, which involves a

[[Page 102762]]

negotiated settlement in which allowable emissions limits may be 
established as part of injunctive relief, and may not necessarily be 
representative of SCR technical capabilities. Therefore, we find that 
ADEQ's analysis of other tangentially fired coal units in CAMPD is not 
determinative of the SCR emissions rate achievable for the SGS units.
---------------------------------------------------------------------------

    \134\ 87 FR 31798 (May 25, 2022) and Docket Item EPA-R03-OAR-
2022-0347-0059 for further details.
    \135\ Docket Items EPA-HQ-OAR-2021-0668-0115 and EPA-HQ-OAR-
2021-0668-0096 examine ozone season data from several mid-atlantic 
states and identifies best performing months for several units. An 
examination of operating data on a monthly or daily basis over the 
course of a calendar year indicates that several units, such as 
Pleasants Power Station 1 and 2 (WV), Conemaugh 2 (PA), and DB 
Wilson W1 (KY) operate at much lower NOX emission rates 
during ozone season months.
---------------------------------------------------------------------------

    Finally, though we appreciate the summary provided in Table 3 of 
the comment letter, the analysis is new information not included in the 
Plan. This information would need to be part of a SIP revision subject 
to review by the public and FLMs in order for the EPA to consider it as 
part of the long-term strategy.
    Comment D.7. TEP asserts that ADEQ reasonably determined that 
SO2 emissions limits were an appropriate and equivalent 
control measure compared to SDA upgrades. TEP notes that while the EPA 
suggests that TEP should also be required to install the SDA upgrades 
in addition to the mass-based limits, the EPA does not explain why SDA 
upgrades would achieve emissions reductions beyond the mass-based 
limits adopted by TEP, which are equivalent to SDA upgrades.
    Further, TEP states that the selection of emissions limits is 
consistent with the CAA and is entitled to deference. First, TEP 
reasons that the CAA does not require the installation of specific 
control technologies, and that the EPA has recognized in the 2019 
Guidance that mass-based limits may be a reasonable alternative to 
specific control technologies, particularly where fixed capital costs 
are high, so long as such limits do not enable a source to cease 
operating an existing control technology. Second, TEP asserts that the 
emissions limits are equally or more protective than control 
technologies because the total SO2 emitted cannot exceed the 
caps, and whether one or both units is operating is irrelevant, and 
because it provides the flexibility for greater total emissions 
reductions to occur, should TEP ultimately retire SGS Unit 1 in 2027. 
The commenter specifies that if TEP elects to achieve compliance with 
the proposed caps by shutting down Unit 1, it is projected to reduce 
SO2 emissions by 2,982 tpy and achieve significant 
reductions in NOX and PM emissions, whereas the installation 
of SDA upgrades at both units is projected to reduce SO2 
emissions by 2,122 tpy. Third, TEP asserts that the emissions limits 
are consistent with EPA precedent. TEP listed previous examples of EPA-
approved mass-based emissions limits, such as the Hawaii Regional Haze 
FIP for three Hawaiian Electric facilities \136\ and the Regional Haze 
FIP for PCC.\137\
---------------------------------------------------------------------------

    \136\ 77 FR 61478 (October 9, 2012).
    \137\ 79 FR 52420.
---------------------------------------------------------------------------

    Response D.7. We disagree with TEP's assertions that the selection 
of mass-based SO2 emissions limits for SGS Units 1 and 2 was 
reasonable for the reasons described in Section IV.E.2.c.iii of our 
proposal,\138\ and Response B.8 of this document.
---------------------------------------------------------------------------

    \138\ 89 FR 47398, 47430-47431.
---------------------------------------------------------------------------

    We also disagree with TEP's assertion that the EPA did not explain 
why SDA upgrades would achieve emissions reductions beyond the mass-
based limits adopted by ADEQ. As stated in the proposed rule,\139\ 
because the limits are set across two units and the ton per day (tpd) 
limit is based on a 30-calendar-day average (rather than a 30-day-
boiler-operating day average),\140\ they would not meaningfully 
constrain the emissions from one unit during periods when the other 
unit is not operating. In particular, the annual SO2 cap of 
3,739 tpy is significantly higher than ADEQ's projected 2028 
SO2 emissions for either Unit 1 or Unit 2 (2,869 and 2,982 
tpy, respectively) \141\ and nearly double each unit's recent emissions 
(1,980 and 1,988 tpy respectively on average 2021-2023).\142\ 
Accordingly, if TEP shuts down SGS Unit 1 by 2028, as it has stated it 
intends to do,\143\ Unit 2 would be able to emit 3,739 tpy 
SO2 in 2028, nearly double what it emitted on average in 
2021-2023 and significantly more than the 2,982 tpy it is projected to 
emit in the absence of a cap and closure of Unit 1. In contrast, a lb/
MMBtu limit representing SDA upgrades on each unit would ensure 
emissions from Unit 2 would be reduced by approximately \1/3\ from 
recent emissions levels (i.e., a reduction of roughly 663 tpy) even if 
Unit 1 ceases operation. Therefore, under the scenario projected by TEP 
to occur in 2028 (i.e., closure of SGS Unit 1), implementation of SDA 
upgrades at Unit 2 would achieve significant emissions reductions 
beyond the mass-based limits adopted by ADEQ.
---------------------------------------------------------------------------

    \139\ Id.
    \140\ A limit based on boiler operating days would effectively 
exclude days with zero emissions from the calculation of the 30-day 
average whereas a limit based on calendar days does not.
    \141\ Plan, appendix C, p. 213, Table 83.
    \142\ Emissions information can be publicly accessed through the 
EPA Clean Air Markets Program data, available at https://campd.epa.gov/.
    \143\ As part of its preferred alternative in its 2023 
Integrated Resources Plan, p. 56, TEP states that ``Initially, the 
units will alternate idling between spring and fall (both seasons 
include the adjacent winter months). TEP plans to transition Unit 1 
to summer-only operations prior to full retirement at the end of 
2027.''
---------------------------------------------------------------------------

    We also note that, if SGS Unit 1 does not close and both units 
continue operation at roughly the same level as 2021-2023, a lb/MMBtu 
limit representing SDA upgrades on each unit would ensure emissions 
from both Unit 1 and Unit 2 would be reduced by approximately \1/3\ 
(i.e., a reduction of roughly 1,323 tpy based on 2021-2023 emissions), 
whereas ADEQ's annual cap of 3,739 tpy would only ensure reductions of 
229 tpy (i.e., compared to total 2021-2023 annual average emissions of 
3,968). Therefore, we expect that lb/MMBtu limits representing SDA 
upgrades on each unit would achieve significantly greater emissions 
reductions than the two-unit mass-based limits adopted by ADEQ.
    For similar reasons, we also do not agree with TEP's statements 
that ``the proposed form of the limit is potentially more 
environmentally protective than the installation of controls because it 
provides the flexibility for greater total emission reductions to 
occur, should TEP ultimately retire SGS Unit 1 in 2027'' and that 
``[r]equiring the use of air pollution control technology at each unit 
individually would foreclose a more environmentally beneficial 
compliance option.'' Specifically, TEP incorrectly cites Table 83 as 
supporting its assertion that if it ``elects to achieve compliance with 
the proposed caps by shutting down Unit 1, it is projected to reduce 
SO2 emissions by 2,982 tpy and also to achieve significant 
reductions in NOX and PM emissions.'' This mischaracterizes 
the content of Table 83, which reflects ADEQ's baseline projection of 
emissions at the TEP units, based on emissions and throughput data for 
2016, 2018 and 2019.\144\ These values were the starting point for 
ADEQ's four-factor analysis and do not represent the projected 
emissions of these units following implementation of the emissions caps 
and/or the closure of Unit 1. No such projection is included in the 
Plan. However, as noted in the preceding paragraph, if TEP shuts down 
SGS Unit 1 by 2028, as it has stated it intends to do, Unit 2 could 
emit as much as 3,739 tpy SO2 in 2028, nearly double what it 
emitted on average in 2021-2023 and significantly more than the 2,982 
tpy it is projected to emit in the absence of a cap and closure of Unit 
1.
---------------------------------------------------------------------------

    \144\ Plan, Appendix C, pp. 212.
---------------------------------------------------------------------------

    Third, in response to TEP's claim about EPA precedent, both FIP 
actions cited by TEP apply to first planning period requirements and 
thus preceded the 2017 revisions to the RHR, which added 40 CFR 
51.308(f). Please see Response B.8 for more information

[[Page 102763]]

about PCC. The other precedent cited by ADEQ, a cap on the Hawaiian 
Electric sources, was not based solely on a determination that a 
particular control measure was necessary to make reasonable progress 
under the four statutory factors. Rather, the cap was intended 
primarily to ensure that no degradation in visibility conditions would 
occur at the affected Class I area during the first or subsequent 
planning periods, as required under the RHR.\145\ This was based on 
circumstances that were specific to Hawaii in the first planning 
period, namely, that no photochemical modeling had been performed for 
Hawaii's Class I areas and the EPA set the RPGs for these areas based 
on island-specific emissions inventories.\146\ None of these 
circumstances apply to Arizona generally, or to SGS Units 1 and 2 
specifically, in the second regional haze planning period and thus are 
inappropriate to rely upon.
---------------------------------------------------------------------------

    \145\ 77 FR 31692, 31712 (May 29, 2012) (``without further 
control, emissions of SO2 on the Big Island are projected 
to increase by nearly 4% between 2005 and 2018. Therefore, 
additional, federally enforceable SO2 reductions are 
needed on the Big Island to ensure reasonable progress.'')
    \146\ Id. at 31708.
---------------------------------------------------------------------------

    Comment D.8. TEP comments that ADEQ reasonably rejected additional 
control measures based on the four factors. For remaining useful life 
specifically, TEP indicates that a 20-year remaining useful life is 
more appropriate for SGS Units 1 and 2 because the shutdowns are 
publicly documented in the 2023 IRP. TEP cites the 2021 Clarifications 
Memo as stating, ``reasonable bases for projecting that future 
emissions will be significantly different than past emissions are 
enforceable requirements and energy efficiency, renewable energy, or 
other similar programs, where there is a documented commitment to 
participate and a verifiable basis for quantifying changes in future 
emissions.'' \147\ TEP noted that consistent with this guidance, TEP's 
planned retirement of these units significantly shortens the remaining 
useful life of any controls and projected emissions reductions, and a 
20-year remaining useful life is a reasonable, conservative basis to 
analyze cost-effectiveness of additional controls.
---------------------------------------------------------------------------

    \147\ 2021 Clarifications Memo, p. 12.
---------------------------------------------------------------------------

    Response D.8. We disagree that 20 years is a reasonable remaining 
useful life for SGS Units 1 and 2. The portion of the 2021 
Clarifications Memo cited by TEP concerns setting emissions limits for 
control measures found necessary to make reasonable progress, not 
remaining useful life. Therefore, this citation does not support TEP's 
assertion. Additionally, the 2019 Guidance and Clarifications Memo 
clearly indicate that, under the RHR, where a shutdown date is used to 
shorten a source's remaining useful life as part of a reasonable 
progress determination, an enforceable requirement to shutdown must be 
included in the SIP and/or be federally enforceable.\148\ The potential 
shutdowns of SGS Units 1 and 2 are not federally enforceable. 
Therefore, they cannot be relied upon to shorten the remaining useful 
life of these units. In the absence of an enforceable requirement for 
SGS Units 1 and 2 to retire, we do not agree that a 20-year remaining 
useful life is reasonable.
---------------------------------------------------------------------------

    \148\ 2019 Guidance, p. 34 (citing 40 CFR 51.308(f)(2)); 
Clarifications Memo, p. 10.
---------------------------------------------------------------------------

    Comment D.9. TEP comments that ADEQ reasonably rejected additional 
control measures in part by considering incremental costs. TEP noted 
that ADEQ determined incremental costs for additional controls would 
range from $9,400-13,500/ton, and that even the low end of this range 
exceeded similar incremental costs that the EPA determined to be 
excessive for sources in Arizona as part of the 2014 BART FIP.\149\
---------------------------------------------------------------------------

    \149\ 79 FR 9318, 9341, Table 24 (rejecting DSI based on 
incremental costs of $8,576/ton compared to lower sulfur fuel 
blend).
---------------------------------------------------------------------------

    TEP further states that ADEQ reasonably considered incremental 
cost-effectiveness where the cost impacts were not clear due to 
uncertainty in the remaining useful life of the additional controls. 
Citing American Corn Growers Association vs. EPA, TEP states that it is 
reasonable for a state to consider incremental visibility improvements 
and other incremental metrics to inform its assessment of whether a 
particular control is ``too costly . . . for a particular source.'' 
\150\ TEP notes that such an assessment does not give ``controlling 
weight'' to the cost factor, but rather considers whether, on balance, 
it would be unreasonable to require installation of a control, 
consistent with the language of CAA section 169A.
---------------------------------------------------------------------------

    \150\ American Corn Growers Association v. EPA, 291 F.3d 1, 6-7 
(D.C. Cir. 2002).
---------------------------------------------------------------------------

    Lastly, TEP asserts that ADEQ reasonably compared the costs of and 
emissions reductions achievable with wet FGD and circulating dry 
scrubbers (CDS) to the costs of and emissions reductions achievable 
with SDA upgrades, even where such upgrades were not required to be 
installed. The commenter argues that ADEQ reasonably used SDA upgrades 
as a proxy for its mass-based emissions limits, since these limits were 
developed based on equivalence with SDA upgrades and the EPA's approach 
for Hawaiian Electric.
    Response D.9. We disagree that ADEQ's use of incremental cost 
effectiveness was reasonable for the reasons explained in Section 
IV.E.2.C.IX of our proposal \151\ and Response B.6 of this document. We 
also note that, while the commenter refers to ``similar incremental 
costs that the EPA determined to be excessive for sources in Arizona as 
part of the 2014 BART FIP,'' the accompanying citation refers to only 
to a single source, i.e., Nelson Lime Kiln, which is the same source 
cited by ADEQ in the Plan.
---------------------------------------------------------------------------

    \151\ 89 FR 47398, 47429.
---------------------------------------------------------------------------

    We also find that the commenter's citation to American Corn Growers 
is inapposite. That decision concerned the EPA's interpretation of the 
BART provisions of the CAA and turned on the fact that the CAA includes 
the ``the degree in improvement in visibility that would be expected at 
each Class I area as a result of imposing BART'' as one of five factors 
to be considered in BART determinations.\152\ In contrast, the Act does 
not mandate visibility improvement as one of the four factors to be 
considered in determining reasonable progress.\153\ As discussed in 
Response B.7, ADEQ indicated in its Response to Comments that it did 
not consider this factor in its determinations.\154\ Furthermore, even 
if ADEQ did consider visibility improvement in making control 
determinations for SO2 at SGS Units 1 and 2,\155\ it is 
evident that ADEQ did not consider incremental visibility improvement 
associated with Wet FGD compared to SDA upgrades. Rather, ADEQ 
considered only ``a hypothetical SO2 emission reduction of 
3,236 tpy, which is approximately equivalent to 0.08 lb/MMBtu for SGS 
Units 1 and 2.'' \156\ This level of reductions does not correspond 
either to SDA upgrades or wet FGD, so ADEQ could not possibly have 
considered the incremental visibility benefit between the levels of 
control. Accordingly, American Corn Growers has no bearing on our 
assessment of whether ADEQ's approach to its four factor analyses and

[[Page 102764]]

determinations for SGS Units 1 and 2 were reasonable.
---------------------------------------------------------------------------

    \152\ Id. (interpreting CAA section 169A(g)(2)).
    \153\ CAA 169A(g)(1).
    \154\ 2022 Arizona Regional Haze Plan, Appendix K, p. 9.
    \155\ See 2022 Arizona Regional Haze Plan, Appendix C, p. 234 
(``small visibility benefits associated with the modeled 
SO2 controls supports the determination that CDS and wet 
FGD control options are not necessary to make reasonable progress 
towards natural visibility at Class I areas during this 
implementation period'').
    \156\ Id.
---------------------------------------------------------------------------

    In addition, we also disagree that there is uncertainty in the 
remaining useful life of SGS Units 1 and 2, because the potential 
shutdowns at these units are not federally enforceable. See Response 
D.8.
    Finally, we disagree that ADEQ reasonably used SDA upgrades as a 
proxy for its mass-based emissions limits. See Responses B.8 and D.7.
    Comment D.10. TEP states that the EPA incorrectly implies that ADEQ 
based its control determinations on visibility benefits, when ADEQ 
stated otherwise in its SIP submission.\157\
---------------------------------------------------------------------------

    \157\ 2022 Arizona Regional Haze Plan, Appendix K at 9 
(explaining that visibility information ``was not considered in the 
Department's emission control measure determination'').
---------------------------------------------------------------------------

    Second, TEP notes that any consideration of visibility would be 
consistent with recent EPA actions on regional haze and the text of the 
statute. Citing the EPA's recent proposed action on the Georgia 
Regional Haze SIP, TEP states that the EPA emphasized incremental 
visibility improvements and that ``Georgia is also not contributing to 
visibility impairment at any Class I areas above the URP.'' \158\ TEP 
claims that because Arizona has similarly de minimis contributions to 
visibility impairment at Class I areas,\159\ the EPA cannot apply 
inconsistent criteria to its review of SIP submissions by different 
states. Finally, citing Loper Bright Enterprises v. Raimondo, 144 S. 
Ct. 2244, 2263 (2024), TEP argues that ``EPA's suggestion that 
visibility should play little-to-no role in a state's assessment of 
reasonable progress is unreasonable and counter to the text of the 
statute.''
---------------------------------------------------------------------------

    \158\ Citing 89 FR 47481, 47498.
    \159\ 89 FR 47398, 47432, Table 21.
---------------------------------------------------------------------------

    Response D.10. Regarding whether ADEQ considered visibility 
benefits, in its control determinations, please see Response B.7.
    We disagree that the EPA is applying inconsistent criteria to 
review of SIP submissions by different states. As explained in Response 
D.2, in the section of the Georgia action cited by the commenter, the 
EPA considered overall trends in visibility impairment in evaluating 
the reasonableness of Georgia's source selection methodology. This is 
entirely different from weighing the potential visibility benefits of 
specific controls at specific units, which is what the commenter 
appears to be advocating for. Additionally, the quoted section of the 
Georgia proposal simply states as a fact that Georgia is not 
contributing to visibility impairment at any Class I areas above the 
URP. That information is not used and should not be used as a ``safe 
harbor'' argument to exclude contributing sources from a four-factor 
analysis and potentially including cost-effective controls in the long-
term strategy.
    Moreover, we do not agree that Arizona has de minimis contributions 
to visibility impairment at Class I areas. In support of this 
assertion, TEP cites Table 21 on page 47432 of the proposal. This table 
shows Baseline Conditions, Adjusted URP and 2028 RPGs at Arizona's 
Class I areas. However, the table provides no indication of which 
sources contribute to visibility impairment at these Class I areas, or 
whether these sources are located in Arizona or elsewhere. This table 
also does not address any Class I areas outside of Arizona. 
Furthermore, there is no other information in the Plan that suggests 
that emissions from Arizona have de minimis contributions to visibility 
impairment at all potentially affected Class I areas. Therefore, we do 
not agree that the EPA is applying inconsistent criteria to review of 
SIP submissions by different states.
    Finally, we disagree that we suggested that ``visibility should 
play little-to-no role in a state's assessment of reasonable 
progress.'' Rather, we stated that ``[w]hether a particular visibility 
impact is meaningful should be assessed in context and cannot be used 
to undermine the four statutory factors that are to be analyzed in 
order to determine what measures are necessary for reasonable 
progress.'' \160\ Applying these considerations to ADEQ's discussion of 
visibility benefits at SGS Units 1 and 2, we found that ``[i]n the 
absence of any opportunities for larger emissions reductions and 
corresponding visibility benefits, we find that ADEQ's reliance on 
`small' visibility benefits as an additional justification for not 
adopting more stringent controls at these units is not persuasive.'' 
\161\ Therefore, we do not agree with the commenter's characterization 
of our proposal.
---------------------------------------------------------------------------

    \160\ 89 FR 47398, 47430 (citing 40 CFR 51.308(f)(2)(i)).
    \161\ Id.
---------------------------------------------------------------------------

    Comment D.11. TEP asserts that ADEQ appropriately incorporated 
``on-the-way'' measures in assessing baseline conditions at IGS Unit 3. 
TEP cites the 2021 Clarifications Memo and states that the EPA has 
explicitly recognized ``on-the-way'' measures that ``have not yet been 
implemented and the associated emissions reductions have not yet 
occurred as of the SIP submission date,'' and that the EPA indicated 
that these measures may impact a state's choice of baseline for a four-
factor analysis at a particular source (``reasonable bases for 
projecting that future emissions will be significantly different than 
past emissions are enforceable requirements and energy efficiency, 
renewable energy, or other similar programs, where there is a 
documented commitment to participate and a verifiable basis for 
quantifying changes in future emissions'').\162\ TEP claims that the 
operational conditions at IGS Unit 3 have been incorporated in an 
enforceable permit, and will become effective upon approval of 
Arizona's SIP submission. TEP also claims that it has a documented 
commitment to complying with these limits by requesting these permit 
limits.
---------------------------------------------------------------------------

    \162\ 2021 Clarifications Memo, pp. 10, 12.
---------------------------------------------------------------------------

    Response D.11. TEP mischaracterizes the contents of the 2021 
Clarifications Memo. The first section of the memo cited by the 
commenter, entitled ``On-the-Way'' Measures and Shutdowns, states that 
``on-the-way measures . . . are necessary to make reasonable progress 
and must be included in a SIP.'' \163\ In this case, because the IGS 
Unit 3 limits have not taken effect under State law, their inclusion as 
part of the SIP revision is not meaningful, and they are not an 
appropriate basis for modifying the baseline control scenario for a 
four-factor analysis.
---------------------------------------------------------------------------

    \163\ Id. p. 10.
---------------------------------------------------------------------------

    The second portion of the 2021 Clarifications Memo cited by TEP 
concerns setting emissions limits for control measures that have been 
found necessary to make reasonable progress. It is not relevant to the 
question of the extent to which existing measures may be considered as 
part of the baseline for a control analysis. Regarding this latter 
question, the 2019 Guidance states that:

    Enforceable requirements are one reasonable basis for projecting 
a change in operating parameters and thus emissions; energy 
efficiency, renewable energy, or other such programs where there is 
a documented commitment to participate and a verifiable basis for 
quantifying any change in future emissions due to operational 
changes may be another. A state considering using assumptions about 
future operating parameters that are significantly different than 
historical operating parameters should consult with its EPA Regional 
office.\164\
---------------------------------------------------------------------------

    \164\ 2019 Guidance p. 29 (emphases added).

    Again, the emissions limits at IGS Unit 3 are not enforceable by 
the State or the EPA unless and until the resulting reasonable progress 
determination is approved into the SIP. Moreover, the permit conditions 
that would implement the caps were adopted specifically to meet 
regional

[[Page 102765]]

haze requirements and were not part of ``energy efficiency, renewable 
energy, or other such programs.'' \165\ Therefore, we find that they 
are not a reasonable basis for projecting a change in operating 
parameters.
---------------------------------------------------------------------------

    \165\ See, e.g., 2022 Arizona Regional Haze Plan, Appendix C, p. 
197 (describing TEP's submittal of permit application for 
NOX caps in response to ADEQ's initial regional haze 
control determination); Appendix G, p. 58 (``The purpose of the 
proposed SIP and significant permit revision is to support ADEQ's 
forthcoming periodic comprehensive regional haze SIP submittal to 
EPA.'').
---------------------------------------------------------------------------

    Comment D.12. TEP asserts that ADEQ reasonably evaluated additional 
control measures using a four-factor analysis for IGS Unit 3 based on 
excessive costs. TEP explains that each of the NOX controls 
available for IGS Unit 3 exceed Arizona's cost threshold of $6,500/ton, 
and ADEQ therefore determined that no additional controls were 
reasonable for the second planning period. TEP also noted that while 
the average cost of installing combustion control retrofits at IGS Unit 
3 was only $230/ton above ADEQ's $6,500/ton threshold, the RHR does not 
prevent states from implementing ``bright line'' cost-effectiveness 
thresholds when considering additional control measures.
    Response D.12. We partly agree with this comment. We agree that the 
NOX controls analyzed for IGS Unit 3 exceed the cost 
threshold of $6,500, when the emissions limits in the permit (which are 
not yet in effect) are considered as part of the baseline control 
scenario. However, as described in section IV.E.2.c.iii of our 
proposal, and Response D.11, we do not agree that these limits are an 
appropriate basis for modifying the baseline control scenario for a 
four-factor analysis. We also agree the RHR does not prevent states 
from implementing ``bright line'' cost-effectiveness thresholds, but we 
find that ADEQ did not do so in a reasonable or consistent manner in 
the Plan, as discussed in Response D.4.

E. Comment Letter From SRP

    Sections I (``Introduction''), II (``Background''), III (``SRP 
Facilities Subject to the Proposed Rule'') and IV (``EPA Has 
Appropriately Proposed Approval of Several Aspects of Arizona's 
Regional Haze SIP'') of SRP's comment letter either provide background 
information or are supportive and therefore do not require a response. 
We respond to sections V-XI of SRP's comment letter below.
    Comment E.1. SRP comments that the proposed rule is vague and 
deprives the public of an adequate opportunity for comment. Citing 
American Iron & Steel Institute v. EPA, SRP notes that the EPA is 
obligated to provide the public with information sufficient to 
facilitate public comment on the proposal, and that it is not clear 
which grounds for the proposed partial disapproval of the SIP 
submission apply to which sources. SRP provides a few examples of 
allegedly vague language in the proposed rule, for example, noting 
``some'' of Arizona's four-factor analyses were affected in a few 
instances. SRP asserts that because it is not clear which aspects of 
the EPA's analysis apply to which facilities, the public cannot 
reasonably evaluate the grounds for the proposed disapproval actions, 
and therefore the EPA needs to issue a new proposed rule that provides 
additional necessary detail in support of the proposed actions.
    Response E.1. We disagree with this comment. In American Iron & 
Steel Institute,\166\ the court denied, in part, review of an EPA 
interim final rule due to a lack of proper notice. However, as 
described in Response A.1, we do not agree that the proposed rule 
deprives the public of an adequate opportunity for comment.
---------------------------------------------------------------------------

    \166\ See 568 F.2d 284 (3d Cir.1977), cert. denied, 435 U.S. 
914, 98 S.Ct. 1467, 55 L.Ed.2d 505 (1978).
---------------------------------------------------------------------------

    We also note that, in acting on the 2022 Arizona Regional Haze 
Plan, the EPA is not issuing new requirements applicable to any 
emissions sources. Rather, this final partial disapproval establishes a 
two-year deadline for the EPA to promulgate a FIP to address the 
relevant requirements under CAA section 110(c), unless the EPA approves 
a subsequent SIP submission that meets these requirements. Accordingly, 
Arizona can develop and submit a SIP revision addressing the 
disapproved elements of the Plan. Both the state's adoption of that SIP 
revision and the EPA's subsequent action on that SIP revision would be 
subject to public notice and comment requirements.\167\ Similarly, if 
the EPA does not fully approve a SIP submission addressing the 
disapproved elements of the Plan, any FIP promulgated by the EPA would 
be subject to public notice and comment. Accordingly, there will be 
ample additional opportunities for the public, including potentially 
regulated entities, to engage in the rulemaking process before any 
additional requirements take effect.
---------------------------------------------------------------------------

    \167\ See CAA section 110(l), 40 CFR 40 CFR 51.102, and 5 U.S.C. 
553.
---------------------------------------------------------------------------

    Comment E.2. SRP asserts that the EPA should approve Arizona's 
determination that Coronado Generating Station and SGS Unit 4 are 
effectively controlled because they are consistent with the law and EPA 
guidance. SRP states that the 2019 Guidance indicates that sources that 
have recently installed effective controls are the prime example of 
sources that do not require evaluation during the current planning 
period. Specifically, SRP notes that the 2019 Guidance states that 
BART-eligible units that installed and began operating controls to meet 
BART emissions limits for the first implementation period, including 
sources that installed controls to comply with a better-than-BART 
alternative, may be considered to be effectively controlled.
    For Coronado, SRP states that the source is subject to a better-
then-BART alternative that the EPA approved in October 2017, and that 
there have been no intervening changes in technology since that time. 
SRP states that Coronado will also install new controls (SCR) to comply 
with the BART alternative by January 2026.\168\ SRP noted that the 
first planning period regional haze SIP submission for Coronado also 
includes two additional requirements for SO2: an 
SO2 emissions limit of 0.060 lb/MMBtu, calculated on a 30-
boiler-operating-day rolling average and an annual plant-wide 
SO2 emissions cap of 1,970 tons per year.
---------------------------------------------------------------------------

    \168\ SRP cited in the comment letter, but we note that the 
correct citation is 82 FR 46903 (October 10, 2017).
---------------------------------------------------------------------------

    SRP further asserts that SGS Unit 4 is similarly well-controlled. 
ADEQ determined that Unit 4's existing controls of combustion controls 
(LNB+OFA) and SCR is the most effective control technology available 
for NOX for coal fired EGUs, and thus, no further analysis 
for other control technologies was needed. For SO2, Unit 4 
is equipped with SDA systems subject to the MATS rule and has been 
achieving an SO2 emissions rate over the most recent five 
years ranging from 0.076 to 0.10 lb/MMBtu on an annual basis. For PM, 
Unit 4 is equipped with a baghouse, which ADEQ found to have the 
highest PM control efficiency of any PM control considered for Unit 4.
    Response E.2. Regarding Coronado Generating Station, we agree that 
the source was subject to a better-than BART alternative. However, we 
note that the commenter mischaracterizes the contents of the 2019 
Guidance regarding effective control determinations for BART-eligible 
sources. The relevant portion of the Guidance includes as an example of 
potentially effective controls, ``BART-eligible units that installed 
and began operating controls to meet BART emission limits for the first 
implementation period, on a

[[Page 102766]]

pollutant-specific basis.'' \169\ The Guidance further explains that:
---------------------------------------------------------------------------

    \169\ See 2019 Guidance, p. 25 (emphasis added).
---------------------------------------------------------------------------

    Although the Regional Haze Rule anticipates the re-assessment of 
BART-eligible sources under the reasonable progress Rule provisions, if 
a source installed and is currently operating controls to meet BART 
emission limits, it may be unlikely that there will be further 
available reasonable controls for such sources. However, states may not 
categorically exclude all BART-eligible sources, or all sources that 
installed BART controls, as candidates for selection for analysis of 
control measures.
    The associated footnote clarifies that this consideration is not 
applicable to BART-subject units for which the BART requirement was met 
in whole or in part by emissions reductions at other units as part of a 
better-than-BART alternative or trading program.\170\
---------------------------------------------------------------------------

    \170\ Id., n. 54.
---------------------------------------------------------------------------

    As discussed in our proposal and Response B.3 of this document, 
ADEQ excluded all units that installed BART (or better-than-BART) 
controls between 2014 and 2028 for any pollutant. We therefore disagree 
that Arizona followed the 2019 Guidance in evaluating effective 
controls because it categorically excluded all such units without 
considering whether the unit in question installed effective controls 
for NOX, SO2 and PM10, or whether the 
BART requirement was met in part by reductions at other units as part 
of a better-than-BART alternative.
    Regarding SGS Unit 4, see Response D.2.
    Comment E.3. SRP states that the EPA's assumed emissions rate for 
SCR controls of 0.05 lb/MMBtu is not feasible at coal-fired EGUs. SRP 
asserts that the EPA cannot assume all coal-fired units are capable of 
the same efficiencies following pollution control installation or that 
these controls incur the same costs for each unit nationwide, 
irrespective of the local conditions and operations impacting 
individual units. SRP further notes that the EPA's conclusion that all 
SCR retrofitted units can uniformly meet a NOX emissions 
limit of 0.05 lb/MMBtu without proper evaluation and consideration of 
individual units is arbitrary and capricious and may unlawfully impose 
limits on EGUs that are unachievable. SRP further points out that the 
cited Srivastava et al. study notes units that achieved NOX 
emissions rates between 0.04 and 0.07 lb/10\6\ Btu, and that this range 
illustrates the variability associated with SCR-controlled coal-fired 
unit NOX emissions rates and the importance of considering 
unit-specific factors when identifying a controlled emissions rate.
    Citing Appendix K of the Plan, SRP further asserts that ADEQ 
specifically addressed unit-specific considerations when setting the 
SGS Unit 1 and 2 NOX emissions rates by reviewing CAMPD 
data. By assuming an SCR controlled NOX emissions rate of 
0.06 lb/MMBtu, ADEQ is assuming that SGS Units 1 and 2 will achieve a 
controlled emissions rate within the top 21 percent of tangentially-
fired EGUs. SRP indicates that without acknowledging ADEQ's evaluation, 
the EPA states that ADEQ did not provide adequate justification and 
unreasonably assumes an emissions rate within the top 5 percent of SCR 
controlled tangentially-fired EGUs is appropriate for the SGS Unit 1 
and 2. SRP concludes that while the state made reasonable conclusions 
as to the emissions rates achievable by SCR at specific facilities, the 
EPA has not.
    Response E.3. We disagree that the EPA has assumed that all coal-
fired units are capable of the same efficiencies following pollution 
control installation or that these controls incur the same costs for 
each unit. As described in Responses B.4 and D.6, we have considered 
unit-specific factors in evaluating the emissions rates achievable with 
SCR at SGS Units 1 and 2, and we are not aware of any assertions that 
SGS specifically cannot achieve 0.050 lb/MMBtu when operating with SCR 
during periods of normal operation. Therefore, we find that ADEQ should 
have considered a controlled NOX emissions rate of 0.050 lb/
MMBtu for SGS Units 1 and 2 when operating with SCR during periods of 
normal operation. As further explained in Response B.4, this does not 
mean that 0.050 lb/MMBtu would be an appropriate 30-BOD limit for these 
units, but rather that it should be considered as annual emissions rate 
for purposes of the control cost analysis.
    Comment E.4. SRP comments that it is not necessary to include 
control requirements for Coronado Generating Station in Arizona's 
Regional Haze SIP. SRP states that under CAA section 169A, a state (or 
the EPA) may only require a long-term strategy to include those control 
measures that are found to be necessary to make reasonable progress 
through the evaluation of the four statutory reasonable progress 
factors. SRP claims that the EPA's position that in the absence of a 
four-factor analysis supporting new controls, existing controls should 
generally be deemed necessary to make reasonable progress and be 
included in the regional haze SIP is not a valid reading of the CAA's 
visibility provisions. Further, SRP claims that the CAA framework ties 
reasonable progress controls to the four-factor analysis, and does not 
leave room for the EPA's presumption that existing controls must be 
included in a SIP even whenever a four-factor analysis failed to 
identify new controls that should be implemented. Such existing 
controls may only be deemed necessary components of a regional haze SIP 
if a four-factor analysis independently identifies such controls as 
necessary for reasonable progress.
    SRP further cites both the 2021 Clarifications Memo (``There may be 
other cases where, after having conducted robust source selection and 
rigorous analysis of the four factors, states have not identified any 
new measures that are reasonable to require for a source. In such 
cases, states will have to address whether the source's existing 
measures are necessary to make reasonable progress'') and 2019 
Guidance: (``[i]f a state determines that an in-place emission control 
at a source is a measure that is necessary to make reasonable progress 
and there is not already an enforceable emission limit corresponding to 
that control in the SIP, the state is required to adopt emission limits 
based on those controls as part of its long-term strategy in the SIP 
via the regional haze second planning period plan submission''). SRP 
claims that the EPA therefore acknowledged that there should be no 
presumption that existing measures are needed for reasonable progress.
    Lastly, SRP states that Coronado Generating Station is already 
subject to a source-specific SIP revision that was designed to 
implement the better-than-BART alternative during the first planning 
period of the regional haze program. SRP asserts that because these 
requirements are already binding and enforceable, there is no need for 
any additional action to address Coronado.
    Response E.4. First, we disagree that existing controls being 
necessary for reasonable progress does not have a basis in the statute 
for two reasons. First, under CAA 169A(a)(1), the national visibility 
goal is generally seperated into two parts: (1) the prevention of any 
future, and (2) the remedying of any existing anthropogenic visibility 
impairment. As noted in the proposed rule,\171\ and in response B.1, 
continued implementation of the source's existing measures is generally 
necessary to prevent future emissions increases and thus necessary

[[Page 102767]]

to make reasonable progress towards the national goal.
---------------------------------------------------------------------------

    \171\ 89 FR 47398, 47404.
---------------------------------------------------------------------------

    Second, control measures used to fulfill a CAA requirement must be 
in the SIP.\172\ In this instance, in order to make reasonable progress 
toward the national goal, the CAA requires every regional haze SIP to 
contain ``such emission limits, schedules of compliance, and other 
measures as may be necessary for reasonable progress.'' \173\ The CAA 
also requires each regional haze SIP submission to include a long-term 
strategy ``for making reasonable progress toward meeting the national 
goal.'' \174\ Finally, reasonable progress is defined in the CAA as a 
consideration of the four factors outlined in CAA 169A(g)(1). If the 
State opts to avoid conducting the required consideration of the four 
statutory factors on a source or group of sources based solely on the 
source's existing measures, then, in order to fulfill its long-term 
strategy requirements, those existing measures must also be in the SIP, 
or else the state must demonstrate that the existing measures are not 
necessary to make reasonable progress. This ensures that this source's 
contribution to visibility impairment will not increase, and also 
ensures that all measures being relied upon to fulfill the regional 
haze requirements are in the SIP. Therefore, if Arizona is relying on 
existing measures to avoid the statutorily required four factor 
analysis, then those existing measures must be in the SIP and thus a 
part of its long-term strategy for the second planning period, unless 
the State demonstrates that they are not necessary to make reasonable 
progress.
---------------------------------------------------------------------------

    \172\ See Committee for a Better Arvin v. EPA, 786 F.3d 1169, 
1175-77 (9th Cir. 2015).
    \173\ CAA 169A(b)(2).
    \174\ CAA 169A(b)(2)(B).
---------------------------------------------------------------------------

    Additionally, we disagree that the EPA's guidance documents 
acknowledged that there should be no presumption that existing measures 
are needed for reasonable progress. The 2021 Clarifications Memo is 
clear that, under the CAA and the RHR, ``when the outcome of a four-
factor analysis is that no new measures are reasonable for a source, 
the source's existing measures are generally needed to prevent future 
visibility impairment (i.e., to prevent future emission increases) and 
thus necessary to make reasonable progress.'' \175\ ADEQ did not 
provide this analysis of whether existing measures are necessary to 
make reasonable progress.
---------------------------------------------------------------------------

    \175\ 2021 Clarifications Memo, pp. 8-9 (emphasis added).
---------------------------------------------------------------------------

    Finally, while we agree that Coronado Generating Station is already 
subject to a source-specific SIP that was designed to implement a 
better-than-BART alternative for the first implementation period, we do 
not agree that this automatically means, without further justification, 
that there is no need for any additional action to Coronado in the 
second implementation period for the reasons described in E.2.
    Comment E.5. SRP asserts that the EPA should approve Arizona's 
control determinations and four-factor analyses with respect to cost-
effectiveness thresholds, incremental costs, compliance with the 
Control Cost Manual, and consideration of visibility.
    First, regarding cost-effectiveness thresholds, SRP indicates that 
Arizona's cost-effectiveness threshold of $6,500/ton is reasonable and 
should be approved, along with the control determinations the state 
made in reliance on that threshold. SRP noted other examples of cost-
effectiveness thresholds in other states (Georgia and Arkansas) that 
are lower than the values Arizona adopted. SRP also cites the EPA's 
recent proposal for Missouri that cites a $6,060 to $7,600/ton 
threshold from the Central Regional Air Planning Association and Texas 
BART FIP threshold range of $5,300/ton to $6,500/ton that is consistent 
with the $6,500/ton threshold adopted by Arizona. Therefore, SRP 
concludes that ADEQ's threshold is reasonable and represents a 
conservatively high threshold from a historical perspective.
    Second, regarding incremental costs, SRP asserts that the EPA 
provided no rationale for finding ADEQ's approach unreasonable, and 
that it was appropriate to only consider incremental costs if a simple 
dollar-per-ton analysis suggests a control might be cost-effective in 
the absence of more nuanced information. SRP notes that suggesting that 
states cannot reasonably take incremental costs into account to reject 
control requirements far exceeds the EPA's statutory authority, citing 
the court decision in American Corn Growers Association vs. EPA as 
stating that ``[t]he Haze Rule calls for states to play the lead role 
in designing and implementing regional haze program to clear the air in 
national parks and wilderness areas.'' SRP further states that the EPA 
states that Arizona considered only a single BART determination in 
finding that incremental costs of $9,400-13,500/ton were excessive, but 
this value is in line with past EPA actions finding incremental costs 
excessive.\176\
---------------------------------------------------------------------------

    \176\ See, e.g., 79 FR 9318, 9342 (rejecting controls based on 
incremental costs of $8,803 and $8,576/ton); 76 FR 80754, 80756 
(December 27, 2011) (rejecting controls based on incremental costs 
of $5,367/ton).
---------------------------------------------------------------------------

    Third, regarding compliance with the Control Cost Manual, SRP 
states that the EPA did not provide enough information for the public 
to tell what it considers to be the full range of the deviations from 
the Cost Control Manual, except for some of the State's remaining 
useful life values. SRP asserts that the EPA's rules specifically allow 
for deviations from the Manual's methodology and sample calculations 
and values whenever site-specific information is more accurate.
    Lastly, regarding consideration of visibility, SRP asserts that the 
EPA appears to place inappropriate limits on Arizona's consideration of 
visibility impacts as part of its assessment of reasonable progress, 
and that the State took visibility into account as additional 
confirmation that controls were not reasonable. SRP also states that 
the EPA has provided no context or analysis for stating that visibility 
impacts must be assessed in context to determine if they are truly 
meaningful and justify expensive control requirements. SRP points out 
that Table 10-5 of the 2022 Arizona Regional Haze Plan shows that 
natural visibility is projected to occur at all statewide sites between 
2028 and 2056, well ahead 2064 natural conditions. SRP concludes that 
Arizona appropriately determined that controls were not reasonable for 
SGS when visibility is rapidly improving, costs are over or very near a 
reasonable cost threshold, and where visibility improvements from 
potential controls would be relatively small.
    Response E.5. The EPA disagrees with this comment for a number of 
reasons. First, with respect to cost-effectiveness thresholds, the EPA 
clarifies that we are not disapproving Arizona's average cost-
effectiveness threshold specifically, but rather, finds that the State 
inconsistently applied the threshold and did not adequately justify how 
this approach resulted in a reasonable set of control measures in the 
long-term strategy for the second planning period. We also note that 
the fact that other states have applied lower or similar thresholds 
does not automatically make Arizona's threshold reasonable. For further 
explanation on this point, see Response D.4.
    Second, with respect to incremental costs, contrary to the 
commenter's assertion, our proposed rule did not suggest that Arizona 
cannot consider incremental costs. However, we reiterate that, if a 
state chooses to consider incremental costs, it must do so in a 
reasonable and consistent manner and

[[Page 102768]]

that Arizona did not do so in the Plan. See Responses B.6, B.8, and 
D.9.
    Third, with respect to compliance with the Control Cost Manual, we 
note that, in addition to discussing remaining useful life values, we 
cited an example of where the State used an interest rate that was 
above the then-current prime rate without adequate documentation.\177\ 
While we agree with the commenter that States can deviate from the Cost 
Control Manual's methodology and sample calculations and values 
whenever site-specific information is more accurate, ADEQ did not 
provide such relevant site-specific documentation. In situations where 
an enforceable shutdown date does not exist, the remaining useful life 
of a control under consideration should be the full period of the 
useful life of that control as recommended by the EPA's Control Cost 
Manual.\178\ See Responses A.1 and C.4.
---------------------------------------------------------------------------

    \177\ 89 FR 47398, 47429.
    \178\ 2019 Guidance, pp. 33-34. See also 40 CFR 
51.308(f)(2)(iii) (``The State must document the technical basis, 
including modeling, monitoring, cost, engineering, and emissions 
information, on which the State is relying to determine the emission 
reduction measures that are necessary to make reasonable progress in 
each mandatory Class I Federal area it affects'').
---------------------------------------------------------------------------

    With respect to consideration of visibility, we disagree that the 
EPA has provided no context or analysis for stating that visibility 
impacts must be assessed in context. On the contrary, in our proposed 
notice, we explained why the evaluation and control of smaller and 
better-controlled sources in Arizona may be necessary to achieve the 
national goal.\179\ However, we also noted that SGS specifically is by 
far the largest emissions source analyzed by ADEQ in the 2022 Arizona 
Regional Haze Plan and ADEQ found that Units 3 and 4, as well as Units 
1 and 2 for PM10, were effectively controlled, leaving only 
NOX and SO2 at Units 1 and 2 as providing an 
opportunity for further control at this source.\180\ In addition, we 
cited to portions of the 2019 Guidance and Clarifications Memo that 
provide additional recommendations to states that visibility 
improvements could reasonably be considered in conjunction with a four-
factor analysis. To the extent that the commenter is arguing that the 
EPA should have provided our own analysis of visibility impacts, we 
disagree. The EPA's role in reviewing SIP submittals is to assess their 
compliance with applicable requirements, not to address those 
requirements ourselves, as we would be obligated to do in a FIP.
---------------------------------------------------------------------------

    \179\ 89 FR 47398, 47430.
    \180\ Id.
---------------------------------------------------------------------------

    Regarding Table 10-5, we note that this table is based on Arizona's 
RPGs, and that contrary to SRP's suggestion, ADEQ did not cite or 
discuss this table or otherwise reference its RPGs in making its 
control determinations. Furthermore, as explained in our proposal 
``[b]ecause RPGs are the modeled result of the measures in states' 
long-term strategies (as well as other measures required under the 
CAA), they cannot be determined before states have conducted their 
four-factor analyses and determined the control measures that are 
necessary to make reasonable progress.'' \181\ Accordingly, we do not 
agree that Arizona did or should have considered the information in 
Table 10-5 in making its control determinations. We also note that the 
commenter mischaracterizes the contents of this table, insofar as the 
``projected date of natural visibility for SYCA'' is 2089, which is 
well after 2064. See also response C.5.
---------------------------------------------------------------------------

    \181\ Id. at 47405.
---------------------------------------------------------------------------

    In sum, we disagree that Arizona appropriately determined that 
controls were not reasonable for SGS for the reasons described in this 
response, elsewhere in this document and in our proposal.
    Comment E.6. SRP claims that the EPA improperly asserts that 
Arizona's SIP must require installation of specific control 
technologies, specifically with regards to SDA upgrades at SGS Units 1 
and 2. SRP states that the regional haze program has not been used to 
impose requirements to install and operate specific technologies, and 
that some states have made use of emissions caps rather than emissions 
rates and other creative tools to address regional haze requirements, 
including Coronado Generating Station during the first planning period.
    Response E.6. We agree with the commenter that ADEQ was not 
obligated to require installation of a particular control. However, the 
State is obligated to set emissions limitations or establish other 
measures corresponding to the controls that it determined to be 
necessary to make reasonable progress.\182\ See also Response B.8 where 
we note issues with ADEQ's provided rationale in justifying the mass-
based emissions caps at SGS and IGS. Finally, we note that the example 
of Coronado Generating Station was under the better-than-BART 
provisions of 40 CFR 51.308(e)(2), rather than the provisions of 40 CFR 
51.308(f), which govern regional haze plans for the second 
implementation period.
---------------------------------------------------------------------------

    \182\ CAA 169A(b)(2) (``. . . each applicable implementation 
plan for a State . . . which may reasonably be anticipated to cause 
or contribute to any impairment of visibility . . . [must] contain 
such emissions limits, schedules of compliance and other measures as 
may be necessary to make reasonable progress[.]''); 40 CFR 
51.308(f)(2) (``Each State must submit a long-term strategy that 
addresses regional haze visibility impairment . . . the long-term 
strategy must include the enforceable emissions limitations . . . 
that are necessary to make reasonable progress.''); see also 2021 
Clarifications Memo, pp. 8-9.
---------------------------------------------------------------------------

    Comment E.7. SRP comments that the EPA's disapproval of 40 CFR 
51.308(f)(3)(ii) for the Sycamore Canyon monitor fails to acknowledge 
or address critical monitoring deficiencies. SRP noted that ADEQ's 
determination that monitor irregularities should preclude the site from 
40 CFR 51.308(f)(3)(ii)(A) requirements, and that the EPA cannot ignore 
the issues. SRP states that ADEQ has shown that the site would have 
experienced drastic visibility improvements if not for the impact of 
PM, and that the increases of coarse mass and soil that occurred after 
the monitor was relocated in 2015 shows that the increasing trends of 
dust at the monitor originate from local sources. SRP further notes 
that the current monitor location is not within the Class I area, so it 
is unreasonable to assume the local dust impacts experienced at the 
monitor result in visibility degradation within the Class I area. SRP 
asserts that the EPA's current disapproval deprives the public of an 
adequate opportunity to comment as the EPA fails to discuss the 
monitoring irregularities at the monitor. SRP claims that the EPA's 
disapproval of 40 CFR 51.308(f)(3)(ii) is arbitrary and capricious 
because the action ignores the facts presented by ADEQ, ADEQ's 
recommendation that the SYCA monitor should not be used for long-term 
progress analysis, and instead relies on questionable monitoring data 
without any discussion of its merits.
    Response E.7. Please see Response B.9.
    Further, we do not agree that we ignored ADEQ's monitoring 
analysis. On the contrary, we specifically acknowledged this analysis 
in our proposal.\183\ However, we found this analysis was insufficient 
to meet the requirements of 40 CFR 51.308(f)(3)(ii)(A), given the flaws 
in ADEQ's long-term strategy.
---------------------------------------------------------------------------

    \183\ See 89 FR 47398, 47433 (``ADEQ provided a discussion in 
its submission that explains how the monitor was relocated in 2015 
and experienced increases in soil and coarse mass extinction.'')
---------------------------------------------------------------------------

    We also disagree with the commenter's assertion that ADEQ 
determined that monitor irregularities should preclude the site from 40 
CFR 51.308(f)(3)(ii)(A) requirements. Rather, ADEQ asserted that the 
Plan complied

[[Page 102769]]

with these requirements.\184\ We do not agree with this assertion for 
the reasons stated in our proposal and Response B.9 of this document. 
ADEQ also noted that it will continue to monitor and investigate the 
source of coarse mass impacts at the monitor site during subsequent 
progress reports and periodic comprehensive Regional Haze SIP 
revisions.\185\ We will work with ADEQ and other stakeholders on the 
consideration of this issue in the development of future SIP revisions.
---------------------------------------------------------------------------

    \184\ Plan p. 106 (``In accordance with 40 CFR 
51.308(f)(3)(ii)(A), Arizona has provided robust documentation in 
support of the state's source selection criteria and reasonable 
progress determinations for selecting measures for inclusion in its 
long-term strategy.'')
---------------------------------------------------------------------------

F. Community Sign-On Letter

    The Community Sign-On Letter is supportive with three suggestions 
for improvement. The supportive portions of the letter do not require a 
response.
    Comment F.1. The commenter requests that the EPA confirm the 
polluting facilities that ADEQ improperly excluded from analysis in the 
state's plan.
    Response F.1. Please see Response A.1, which describes the EPA's 
approach to reviewing the Plan generally and source selection 
specifically.
    Comment F.2. The commenter requests that the EPA confirm the 
specific errors in each of the selected source's review of pollution 
controls.
    Response F.2. We have explained the bases for our partial 
disapproval with respect to 40 CFR 51.308(f)(2) in our proposal and 
elsewhere in this document. Therefore, the EPA's disapproval of 
51.308(f)(2) is justified.
    Comment F.3. The commenter requests that the EPA consider the 
equity and environmental justice impacts of the state's plan and 
maximize the environmental justice co-benefits of haze pollution 
reduction opportunities.
    Response F.3. The regional haze statutory provisions do not 
explicitly address considerations of environmental justice, and neither 
do the regulatory requirements of the second planning period in 40 CFR 
51.308(f), (g), and (i). As explained in ``EPA Legal Tools to Advance 
Environmental Justice,'' \186\ the CAA provides states with the 
discretion to consider environmental justice in developing rules and 
measures related to regional haze. While a State may consider 
environmental justice under the reasonable progress factors, neither 
the statute nor the RHR requires states to conduct an environmental 
justice analysis for the EPA to approve a SIP submission. Furthermore, 
the CAA and applicable implementing regulations neither prohibit nor 
require such an evaluation of environmental justice with regard to a 
regional haze SIP submission. The EPA is not identifying environmental 
justice as a basis for its decision to partially approve and partially 
disapprove Arizona's SIP revision.
---------------------------------------------------------------------------

    \186\ See EPA Legal Tools to Advance Environmental Justice, May 
2022, available at www.epa.gov/system/files/documents/2022-05/EJ%20Legal%20Tools%20May%202022%20FINAL.pdf at 35-36.
---------------------------------------------------------------------------

G. Comment Letter From NPCA et al.

    Sections I (``Background'') and II (``EPA's Proposed Rule Correctly 
Disapproves ADEQ's Approach To Source Selection, Four-Factor Analyses, 
Control Determinations, and Reasonable Progress Goals'') of the NPCA et 
al.'s comment letter either provide background information or are 
supportive and therefore do not require a response. We respond to 
sections III-VI of the NPCA et al.'s comment letter below.
    Comment G.1. NPCA et al. request the EPA to be more specific about 
the point sources of concern. First, the commenter states that in the 
final rule, the EPA should list the sources that ADEQ improperly 
screened out and failed to conduct a four-factor reasonable progress 
analysis for, namely Apache Unit 3. Cholla Units 1, 3-4, Coronado, 
ASARCO Hayden Smelter, Lhoist-Nelson Lime Plant, Apache Nitrogen, 
Freeport-McMoRan Miami Smelter.
    Second, the commenter states that the EPA should list each point 
source for which the EPA is disapproving ADEQ's control determinations, 
namely SGS Units 1 and 2 NOX and SO2 analyses, 
SGS 3 and 4 SO2 analyses, IGS 3 and 4 NOX 
analyses, Williams Compressor Station NOX analysis, Wilcox 
Compressor Station NOX analysis, Drake Cement Plant 
NOX and SO2 analyses, and Phoenix Cement-
Clarkdale Plant, NOX and PM10 analyses.
    Response G.1. See Response A.1. The EPA is disapproving long-term 
strategy as a whole. Any subsequent SIP revision developed by the 
State, or FIP developed by EPA, will need to establish a long-term 
strategy in accordance with the regulatory requirements. 40 CFR 
51.308(f)(2).
    Comment G.2. NPCA et al. comment that the EPA must consider the 
equity and environmental justice impacts of its action on Arizona's 
Regional Haze SIP. The commenter indicates that the EPA guidance 
documents direct states to consider the broader environmental 
implications of their regional haze plans, by requiring an analysis of 
the ``non-air quality environmental impacts of compliance,'' including 
environmental justice, and that meaningful outreach and engagement to 
environmental justice communities is crucial. NPCA et al. request ADEQ 
and the EPA to conduct meaningful outreach, substantively incorporate 
equity and environmental justice into the SIP revision and the 
supporting technical documents, such as preparing maps that detail the 
location of environmental justice communities in Arizona and the 
location of nearby visibility-impairing sources. The commenters specify 
that a number of visibility-impairing sources in Arizona are located 
near vulnerable communities, yet ADEQ did not conduct a four-factor 
analysis for many of these sources.
    Response G.2. See Response F.3. NPCA et al. provided additional 
demographic information for communities near several sources in 
Arizona. Without agreeing with the particular relevance or accuracy of 
this information, the EPA acknowledges the demographic information 
provided as part of the comment. As discussed in our proposal and in 
this document, the EPA has evaluated Arizona's SIP submission against 
the statutory and regulatory regional haze requirements and determined 
that it has not satisfied certain minimum requirements.
    Comment G.3. NPCA et al. note that the EPA must disapprove ADEQ's 
adjustments to the URP glidepath for each Class I area. The commenter 
asserts that the EPA can only approve these URP glidepath adjustments 
if it determines ADEQ used ``scientifically valid data and methods'' 
per 40 CFR 51.308(f)(1)(vi)(B), and they request the EPA to disapprove 
ADEQ's URP glidepath adjustments for two reasons.
    First, NPCA et al. state that the EPA incorrectly suggests that 
ADEQ's adjustments were de minimis and had no effect on whether the 
RPGs for each Class I area are above or below the URP glidepath. 
However, ADEQ's decision to adjust the default URP glidepaths 
significantly affected whether the RPG for several Class I areas are 
above or below the glidepath, such as Chiricahua Wilderness, Saguaro 
National Park, and Superstition Wilderness.
    Second, NPCA et al. state that the EPA's determination that ADEQ's 
glidepath adjustments used scientifically valid data and methods is 
unsound given that the EPA previously expressed concerns with these 
data and methods. The commenter further states that the EPA highlighted 
substantial problems in its 2019 Modeling

[[Page 102770]]

Technical Support Document (TSD) \187\ with available data and methods 
for adjusting Class I glidepaths based on both international and 
prescribed wildland fire emissions, including international emissions 
data from just a single year,\188\ and uncertainty in many of the 
calculations and modeling and ambient data.\189\
---------------------------------------------------------------------------

    \187\ Memorandum from Richard A. Wayland, Director, Air Quality 
Assessment Division, EPA, to Regional Air Division Directors, 
Subject: ``Availability of Modeling Data and Associated Technical 
Support Document for the EPA's Updated 2028 Visibility Air Quality 
Modeling,'' September 19, 2019, available at https://www.epa.gov/visibility/technical-support-document-epas-updated-2028-regional-haze-modeling.
    \188\ 2019 Modeling TSD, p. 37.
    \189\ 2019 Modeling TSD, p. 67.
---------------------------------------------------------------------------

    Response G.3. As noted in our proposal and in our response to 
Comment C.5, being on or below the URP does not relieve a state from 
considering the four statutory factors to determine what level of 
control is needed to achieve reasonable progress.\190\ The URP is used 
in later steps of the reasonable progress analysis for informational 
purposes and to provide a non-enforceable benchmark against which to 
assess a Class I area's rate of visibility improvement. Achieving the 
URP does not mean that a Class I area is making ``reasonable progress'' 
and does not relieve a state from using the four statutory factors to 
determine what level of control is needed to achieve such 
progress.\191\
---------------------------------------------------------------------------

    \190\ 89 FR 47398, 47402, n. 52.
    \191\ See, e.g., 82 FR 3078, 3093 and 89 FR 47398, 47402, n. 52.
---------------------------------------------------------------------------

    We also find that the specific points raised by NPCA are 
overstated, and we therefore disagree that we should disapprove ADEQ's 
glidepath adjustments. First, the EPA's proposal stated, ``[t]he choice 
of adjustment option made no difference in whether the RPG for each 
area was above or below its URP glidepath,'' \192\ not that an 
adjustment, in general, made no difference. That is, the glidepath 
adjustment results were nearly the same between the option that 
adjusted for international anthropogenic impacts alone, and the option 
that adjusted for international impacts together with wildland 
prescribed fire impacts. The commenter is correct that for several 
Class I areas, the adjustment itself does make a difference in the 
assessment of whether projected visibility impacts are above or below 
the glidepath. Our assessment of the URP and RPGs took that into 
account, as noted in our proposal.\193\ If the adjustment were rejected 
altogether, that would strengthen the case for the need for the State 
to make a ``robust demonstration'' that there are no reasonable 
additional emissions reduction measures, although in this case that 
need is already established because Sycamore Canyon Wilderness impacts 
are above its glidepath with or without adjustment.\194\
---------------------------------------------------------------------------

    \192\ 89 FR 47398, 47411 (emphasis added).
    \193\ 89 FR 47398, 47432-47433.
    \194\ 2022 Arizona Regional Haze Plan, p. D-24 and Figure D-39.
---------------------------------------------------------------------------

    Second, the EPA disagrees that the glidepath adjustments were not 
based on scientifically valid data and methods. The 2019 Modeling TSD 
acknowledges various limitations and uncertainties in various model 
inputs and calculation approaches, which is always the case in 
modeling. That acknowledgement was not intended as an assertion by the 
EPA that its own data and methods were scientifically invalid. 
Similarly, it was not intended that a glidepath adjustment made using 
the same or similar methods would not be based on scientifically valid 
data and methods. Rather, the data and methods used were the best 
available to the EPA at the time of the modeling in that TSD, and 
presented as a reasonable and valid approach for glidepath adjustment 
that states could consider in developing their SIPs, without precluding 
the use of better data and methods that a state might develop. The 
EPA's specific statement about ``uncertainty in many of the 
calculations and modeling and ambient data'' was in the context of 
alternative approaches to adjusting the glidepath, for which the 2019 
Modeling TSD provided five,\195\ including the default. Those 
approaches differed in whether international impacts and prescribed 
fire should be combined with the baseline model run on an absolute or 
relative basis (i.e., simply added in or applied as a percent 
difference), and whether natural conditions should be estimated from 
monitored data or from modeling. There is not one clearly best approach 
that would be most appropriate for all Class I areas in the country, 
but the EPA chose one as the default and provided a range of adjustment 
results. For Arizona Class I areas, the glidepath adjustment in the 
default approach was nearly the same as the maximum among the 
approaches examined, except for the Grand Canyon and Sycamore Canyon 
Wilderness, where it gave closer to the minimum adjustment among the 
approaches considered.\196\ As noted in the EPA's proposal, the WRAP 
results used by ADEQ were fairly close to default approach values 
estimated by the EPA and were determined to be based on scientifically 
valid data and methods.\197\ The EPA does not find any reason, and the 
commenters do not provide any additional reasons to determine 
otherwise.
---------------------------------------------------------------------------

    \195\ 2019 modeling TSD, p. 55.
    \196\ 2019 modeling TSD, p. 56, Table 5-2.
    \197\ 89 FR 47398, 47411.
---------------------------------------------------------------------------

    Comment G.4. NPCA et al. indicate that the EPA must disapprove 
additional aspects of ADEQ's source selection process, noting that 
ADEQ's Q/d threshold of 10 is arbitrarily high, ADEQ should not have 
eliminated the totality of ``effectively-controlled'' process emissions 
from its Q/d analysis, and ADEQ's ``de minimis point source process 
determination'' is arbitrary and capricious.
    Response G.4. As explained in our proposal and the 2021 
Clarifications Memo, the RHR does not require states to consider 
controls for all sources, all source categories, or any or all sources 
in a particular source category.\198\ Rather, the states have 
discretion to choose any source selection methodology or threshold that 
is reasonable, but the choices they make must be explained and should 
be designed to result in a set of sources which capture a meaningful 
portion of the state's total contribution to visibility impairment. To 
this end, 40 CFR 51.308(f)(2)(i) requires that a state's SIP submission 
must include ``a description of the criteria it used to determine which 
sources or groups of sources it evaluated.'' The technical basis for 
source selection, which may include methods for quantifying potential 
visibility impacts such as emissions divided by distance metrics, 
trajectory analyses, residence time analyses, and/or photochemical 
modeling, must also be appropriately documented, as required by 40 CFR 
51.308(f)(2)(iii).
---------------------------------------------------------------------------

    \198\ 89 FR 47398, 47403; 2021 Clarifications Memo, Sections 2 
and 2.1.
---------------------------------------------------------------------------

    Overall, in this particular instance, the EPA finds that that many 
aspects of ADEQ's source selection process, such as its focus on 
sulfate, nitrate, and coarse mass and its use of a Q/d value of 10 for 
point sources, were reasonable and adequately explained and documented. 
However, we also find that ADEQ did not provide an adequate 
justification for screening out certain sources and units from 
conducting a four-factor analysis on the basis that they are 
``effectively controlled'' as part of its source selection 
process.\199\ As the

[[Page 102771]]

EPA has previously stated, ``[s]ource selection is a critical step in 
states' analytical processes. All subsequent determinations of what 
constitutes reasonable progress flow from states' initial decisions 
regarding the universe of pollutants and sources they will consider for 
the second planning period.'' \200\ Therefore, Arizona's source 
selection methodology, including unjustified effectively controlled 
determinations, supports the EPA's determination that Arizona's long-
term strategy did not include all measures necessary to make reasonable 
progress. Therefore, EPA's disapproval of 40 CFR 51.308(f)(2), as a 
whole, is reasonable.
---------------------------------------------------------------------------

    \199\ See 40 CFR 51.308(f)(2)(i) (``. . . The State must include 
in its implementation plan a description of the criteria is used to 
determine which sources or groups of sources it evaluated and how 
the four factors were taken into consideration in selecting the 
measures for inclusion in its long-term strategy'').
    \200\ 2021 Clarifications Memo, p. 3.
---------------------------------------------------------------------------

    Comment G.5. NPCA et al. state that ADEQ's average cost-
effectiveness threshold is too low, and requests the EPA to further 
clarify that ADEQ's $6,500 per ton cost threshold is too low and 
unreasonably excludes cost-effective control measures.
    Response G.5. While the EPA is not disapproving ADEQ's cost 
threshold, we nonetheless find that the State did not apply this 
threshold in a consistent and reasonable manner, as described in our 
proposal \201\ and Response D.4 of this document.
---------------------------------------------------------------------------

    \201\ 89 FR 47398, 47429.
---------------------------------------------------------------------------

    Comment G.6. NPCA et al. comment that the EPA must promptly issue a 
Regional Haze FIP for Arizona. The commenter recommends that to provide 
sufficient time for sources to implement control measures before the 
second implementation period ends in 2028, the EPA should issue a 
proposed FIP in 2024 and finalize the FIP by the end of 2025.
    Response G.6. Disapproving a SIP submission establishes a two-year 
deadline for the EPA to promulgate a FIP to address the relevant 
requirements under CAA section 110(c), unless the EPA approves a 
subsequent SIP submission that meets these requirements. The EPA is not 
proposing a FIP for the disapproved requirements of the 2022 Arizona 
Regional Haze Plan at this time.

III. Final Action

    Under CAA section 110(k)(3), and based on the evaluation and 
rationale presented in the proposed rule and this final rule, the EPA 
is partially approving and partially disapproving the 2022 Arizona 
Regional Haze Plan. Specifically, the EPA is approving the elements of 
the 2022 Arizona Regional Haze Plan related to requirements contained 
in 40 CFR 51.308(f)(1), (f)(4)-(6), and (g)(1)-(5). The EPA is 
disapproving the elements of the 2022 Arizona Regional Haze Plan 
related to requirements contained in 40 CFR 51.308(f)(2), (f)(3), and 
(i)(2)-(4). Further, the EPA is disapproving the interstate transport 
requirements of CAA section 110(a)(2)(D)(i)(II) prong 4 (visibility) 
for the 2018 Ozone I-SIP submittal and 2015 PM2.5 I-SIP 
submittal.
    Under section 179(a) of the CAA, final disapproval of a submittal 
that addresses a requirement of part D, title I of the CAA or is 
required in response to a finding of substantial inadequacy as 
described in CAA section 110(k)(5) starts a sanctions clock. Arizona's 
2022 Regional Haze Plan, 2018 Ozone I-SIP submittal, and 2015 
PM2.5 I-SIP submittal were not submitted to meet any of 
these requirements. Therefore, the disapprovals noted in section III.B 
will not trigger any offset or highway sanctions clocks. Disapproving a 
SIP submission also establishes a two-year deadline for the EPA to 
promulgate a FIP to address the relevant requirements under CAA section 
110(c), unless the EPA approves a subsequent SIP submission that meets 
these requirements. We anticipate that any SIP or FIP that remedies the 
disapprovals with respect to Regional Haze requirements, would also, in 
conjunction with the existing Arizona Regional Haze FIP, remedy the 
disapproval for the interstate transport visibility requirement of CAA 
section 110(a)(2)(D)(i)(II) for the 2018 Ozone I-SIP submittal and 2015 
PM2.5 I-SIP submittal.

IV. Statutory and Executive Order Reviews

    Under the CAA, the Administrator is required to approve a SIP 
submission that complies with the provisions of the Act and applicable 
federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in 
reviewing SIP submissions, the EPA's role is to review state choices, 
and approve those choices if they meet the minimum criteria of the Act. 
Accordingly, this final action partially approves and partially 
disapproves state law as meeting federal requirements and does not 
impose additional requirements beyond those imposed by state law.
    Additional information about these statutes and Executive orders 
can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    This action is not a significant regulatory action and was 
therefore not submitted to the Office of Management and Budget (OMB) 
for review.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA because this action does not impose additional requirements 
beyond those imposed by state law.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities beyond those 
imposed by state law.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in 
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect 
small governments. This action does not impose additional requirements 
beyond those imposed by state law. Accordingly, no additional costs to 
State, local, or Tribal governments, or to the private sector, will 
result from this action.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the states, on the relationship between 
the national government and the states, or on the distribution of power 
and responsibilities among the various levels of government.

F. Executive Order 13175: Coordination With Indian Tribal Governments

    This action does not have Tribal implications, as specified in 
Executive Order 13175, because the SIP is not approved to apply on any 
Indian reservation land or in any other area where the EPA or an Indian 
Tribe has demonstrated that a Tribe has jurisdiction, and will not 
impose substantial direct costs on Tribal governments or preempt Tribal 
law. Thus, Executive Order 13175 does not apply to this action.

G. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

    The EPA interprets Executive Order 13045 as applying only to those

[[Page 102772]]

regulatory actions that concern environmental health or safety risks 
that the EPA has reason to believe may disproportionately affect 
children, per the definition of ``covered regulatory action'' in 
section 2-202 of the Executive Order. Therefore, this action is not 
subject to Executive Order 13045 because it merely partially approves 
and partially disapproves state law as meeting federal requirements. 
Furthermore, the EPA's Policy on Children's Health does not apply to 
this action.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution, or Use

    This action is not subject to Executive Order 13211, because it is 
not a significant regulatory action under Executive Order 12866.

I. National Technology Transfer and Advancement Act (NTTAA)

    Section 12(d) of the NTTAA directs the EPA to use voluntary 
consensus standards in its regulatory activities unless to do so would 
be inconsistent with applicable law or otherwise impractical. The EPA 
believes that this action is not subject to the requirements of section 
12(d) of the NTTAA because application of those requirements would be 
inconsistent with the CAA.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    Executive Order 12898 (Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations, 59 FR 7629, 
Feb. 16, 1994) directs Federal agencies to identify and address 
``disproportionately high and adverse human health or environmental 
effects'' of their actions on communities with environmental justice 
(EJ) concerns to the greatest extent practicable and permitted by law. 
Executive Order 14096 (Revitalizing Our Nation's Commitment to 
Environmental Justice for All, 88 FR 25251, April 26, 2023) builds on 
and supplements E.O. 12898 and defines EJ as, among other things, ``the 
just treatment and meaningful involvement of all people, regardless of 
income, race, color, national origin, or Tribal affiliation, or 
disability in agency decision-making and other Federal activities that 
affect human health and the environment.''
    The State did not evaluate EJ considerations as part of its SIP 
submittal; the CAA and applicable implementing regulations neither 
prohibit nor require such an evaluation. EPA did not perform an EJ 
analysis and did not consider EJ in this action. Due to the nature of 
the action being taken here, this action is expected to have a neutral 
to positive impact on the air quality of the affected area. 
Consideration of EJ is not required as part of this action, and there 
is no information in the record inconsistent with the stated goal of 
E.O. 12898/14096 of achieving EJ for communities with EJ concerns.

K. Congressional Review Act (CRA)

    This action is subject to the CRA, and the EPA will submit a rule 
report to each House of the Congress and to the Comptroller General of 
the United States. This action is not a ``major rule'' as defined by 5 
U.S.C. 804(2).

L. Petitions for Judicial Review

    Under section 307(b)(1) of the CAA, petitions for judicial review 
of this action must be filed in the United States Court of Appeals for 
the appropriate circuit by February 18, 2025. Filing a petition for 
reconsideration by the Administrator of this final rule does not affect 
the finality of this rule for the purposes of judicial review nor does 
it extend the time within which a petition for judicial review may be 
filed, and shall not postpone the effectiveness of such rule or action. 
This action may not be challenged later in proceedings to enforce its 
requirements (see section 307(b)(2)).

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Intergovernmental relations, Nitrogen oxides, Ozone, 
Particulate matter, Reporting and recordkeeping requirements, Sulfur 
Oxides, Volatile organic compounds.

    Dated: December 10, 2024.
Martha Guzman Aceves,
Regional Administrator, Region IX.

    For the reasons stated in the preamble, the EPA amends chapter I, 
title 40 of the Code of Federal Regulations as follows:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

Subpart D--Arizona

0
2. In Sec.  52.120(e), amend Table 1 by adding an entry for ``State 
Implementation Plan Revision: Regional Haze Program (2018-2028)'' 
before the entry for ``Arizona State Implementation Plan Revision under 
Clean Air Act Section 110(a)(1) and (2); Implementation of the 2008 
Lead National Ambient Air Quality Standards, excluding the 
appendices.''
    The addition reads as follows:


Sec.  52.120  Identification of plan.

* * * * *
    (e) * * *

                                           Table 1--EPA-Approved Non-Regulatory and Quasi-Regulatory Measures
                           [Excluding certain resolutions and statutes, which are listed in tables 2 and 3, respectively] \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       Applicable geographic
        Name of SIP provision          or nonattainment area         State submittal date              EPA approval date               Explanation
                                          or title/subject
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                             The State of Arizona Air Pollution Control Implementation Plan
                        Clean Air Act Section 110(a)(2) State Implementation Plan Elements (Excluding Part D Elements and Plans)
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
State Implementation Plan Revision:   State-wide.............  August 15, 2022................  January 17, 2025...............
 Regional Haze Program (2018-2028),
 excluding Chapters 2, 6.1, 6.2,
 6.3, 7, 8, 9, and 10 and Appendices
 B, C, D, E, F, G, H, I, J, and L.
 

[[Page 102773]]

 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Table 1 is divided into three parts: Clean Air Act Section 110(a)(2) State Implementation Plan Elements (excluding Part D Elements and Plans), Part
  D Elements and Plans (other than for the Metropolitan Phoenix or Tucson Areas), and Part D Elements and Plans for the Metropolitan Phoenix and Tucson
  Areas.

* * * * *

0
3. Section 52.145 is amended by adding paragraph (o) to read as 
follows:


Sec.  52.145  Visibility protection.

* * * * *
    (o) Disapproval. On August 15, 2022, the Arizona Department of 
Environmental Quality submitted the ``State Implementation Plan 
Revision: Regional Haze Program (2018-2028).''
    (1) The following portions of the ``State Implementation Plan 
Revision: Regional Haze Program (2018-2028)'' are disapproved because 
they do not meet the applicable requirements of Clean Air Act sections 
169A and 169B and the Regional Haze Rule in 40 CFR 51.301 through 
51.308.
    (i) Chapters 2, 6.1, 6.2, 6.3, 7, 8, 9, and 10;
    (ii) Appendices B, C, D, E, F, G, H, I, J, and L.

0
4. Section 52.147 is amended by adding paragraph (f) to read as 
follows:


Sec.  52.147  Interstate transport.

* * * * *
    (f) Disapproval. The SIPs submitted on December 11, 2015 and 
September 24, 2018 do not meet the requirements of Clean Air Act 
section 110(a)(2)(D)(i)(II) (interfere with measures in any other state 
to protect visibility, only) for the 2012 PM2.5 NAAQS and 
the 2015 ozone NAAQS, respectively.

[FR Doc. 2024-29508 Filed 12-17-24; 8:45 am]
BILLING CODE 6560-50-P