[Federal Register Volume 81, Number 138 (Tuesday, July 19, 2016)]
[Proposed Rules]
[Pages 46852-46865]
[FR Doc No: 2016-16959]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2016-0292; FRL-9949-06-Region 9]

Approval and Revision of Air Plans; Arizona; Regional Haze State
and Federal Implementation Plans; Reconsideration

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve a source-specific revision to the Arizona State Implementation
Plan (SIP) that addresses requirements for best available retrofit
technology (BART) at Cholla Generating Station (Cholla). The EPA
proposes to find that the SIP revision fulfills the requirements of the
Clean Air Act (CAA) and the EPA's Regional Haze Rule (RHR) for BART at
Cholla. In conjunction with this proposed approval, we propose to
withdraw those portions of the federal implementation plan (FIP) that
address BART for Cholla. We previously partially granted petitions for
reconsideration of that FIP from Cholla's owners, Arizona Public
Service Company (APS) and PacifiCorp. We are now proposing to find that
final withdrawal of the FIP, as it applies to Cholla, would constitute
our action on APS's and PacifiCorp's petitions for reconsideration of
the FIP.

DATES: Written comments must be received on or before September 2,
2016. Requests for public hearing must be received on or before August
3, 2016.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2016-0292 at http://www.regulations.gov, or via email to
<EMAIL_ADDRESS>For comments submitted at Regulations.gov, follow
the online instructions for submitting comments. Once submitted,
comments cannot be edited or removed from Regulations.gov. For either
manner of submission, the EPA may publish any comment received to its
public docket. Do not submit electronically any information you
consider to be Confidential Business Information (CBI) or other
information whose disclosure is restricted by statute. Multimedia
submissions (audio, video, etc.) must be accompanied by a written
comment. The written comment is considered the official comment and
should include discussion of all points you wish to make. The EPA will
generally not consider comments or comment contents located outside of
the primary submission (i.e. on the web, cloud, or other file sharing
system). For additional submission methods, please contact the person
identified in the For Further Information Contact section. For the full
EPA public comment policy, information about CBI or multimedia
submissions, and general guidance on making effective comments, please
visit http://www2.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Vijay Limaye, U.S. EPA, Region 9,
Planning Office, Air Division, Air-2, 75 Hawthorne Street, San
Francisco, CA 94105. Vijay Limaye can be reached at telephone number
(415) 972-3086 and via electronic mail at<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us'' and
``our'' refer to the EPA.

Table of Contents

I. General Information
II. Background
III. Summary of the Cholla SIP Revision
IV. The EPA's Evaluation of the Cholla SIP Revision
V. Proposed Action
VI. Environmental Justice Considerations
VII. Incorporation by Reference
VIII. Statutory and Executive Order Reviews

I. General Information

A. Definitions

    For the purpose of this document, we are giving meaning to certain
words or initials as follows:
     The words or initials Act or CAA mean or refer to the
Clean Air Act, unless the context indicates otherwise.
     The initials ADEQ mean or refer to the Arizona Department
of Environmental Quality.
     The initials AFUDC mean or refer to Allowance for Funds
Used During Construction.
     The initials APS mean or refer to Arizona Public Service
Company.
     The words Arizona and State mean the State of Arizona.
     The initials BART mean or refer to Best Available Retrofit
Technology.
     The term Class I area refers to a mandatory Class I
Federal area.\1\
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    \1\ Although states and tribes may designate as Class I
additional areas which they consider to have visibility as an
important value, the requirements of the visibility program set
forth in section 169A of the CAA apply only to ``mandatory Class I
Federal areas.''
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     The initials CBI mean or refer to Confidential Business
Information.
     The initials CCM mean or refer to the EPA's Control Cost
Manual.
     The words EPA, we, us or our mean or refer to the United
States Environmental Protection Agency.
     The initials FIP mean or refer to Federal Implementation
Plan.
     The initials LNB mean or refer to low-NOX
burners.
     The initials MMBtu mean or refer to million British
thermal units
     The initials NOX mean or refer to nitrogen oxides.
     The initials OFA mean or refer to over fire air.
     The initials PM10 mean or refer to particulate matter with
an aerodynamic diameter of less than 10 micrometers.
     The initials RHR mean or refer to the EPA's Regional Haze
Rule.
     The initials RP mean or refer to Reasonable Progress.
     The initials RPG or RPGs mean or refer to Reasonable
Progress Goal(s).
     The initials SCR mean or refer to Selective Catalytic
Reduction.
     The initials SIP mean or refer to State Implementation
Plan.
     The initials SNCR mean or refer to Selective Non-catalytic
Reduction
     The initials SOFA mean or refer to separated over fire
air.
     The initials SO2 mean or refer to sulfur dioxide.

B. Docket

    The EPA has established docket number EPA-R09-OAR-2016-0292 for
this action. Generally, documents in the docket for this action are
available electronically at http://www.regulations.gov or in hard copy
at EPA Region IX, 75 Hawthorne Street, San Francisco, California 94105-
3901. While all documents in the docket are listed at http://www.regulations.gov, some information may be publicly available only at
the hard copy location (e.g., copyrighted material, large maps, multi-
volume reports), and some may not be available in either location
(e.g., confidential business information (CBI)). To inspect the hard
copy materials, please schedule an appointment during normal business
hours with the contact listed in the FOR FURTHER INFORMATION CONTACT
section.

C. Public Hearings

    If anyone contacts the EPA by August 3, 2016 requesting to speak at
a public hearing, the EPA will schedule a public hearing and announce
the hearing in the Federal Register. Contact Vijay Limaye at (415) 972-
3086 or at<EMAIL_ADDRESS>to request a hearing or to determine if
a hearing will be held.

II. Background

A. Statutory and Regulatory Background

    This section provides a brief overview of the requirements of the
CAA and RHR, as they apply to this particular action. Please refer to
our previous rulemakings on the Arizona Regional Haze SIP for
additional background regarding the visibility protection provisions of
the CAA and the RHR.\2\
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    \2\ 77 FR 42834, 42837-42839 (July 20, 2012), (Arizona Regional
Haze ``Phase 1'' Rule) 77 FR 75704, 75709-75712 (December 21, 2012),
(Arizona Regional Haze ``Phase 2'' Rule).
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    In section 169A of the 1977 Amendments to the CAA, Congress created
a program for protecting visibility in the nation's national parks and
wilderness areas. This section of the CAA establishes as a national
goal the ``prevention of any future, and the remedying of any existing,
impairment of visibility in mandatory Class I Federal areas which
impairment results from manmade air pollution.'' \3\ It also directs
states to evaluate the use of retrofit controls at certain larger,
often uncontrolled, older stationary sources in order to address
visibility impacts from these sources. Specifically, section
169A(b)(2)(A) of the CAA requires states to revise their SIPs to
contain such measures as may be necessary to make reasonable progress
towards the natural visibility goal, including a requirement that
certain categories of existing major stationary sources built between
1962 and 1977 (known as ``BART-eligible'' sources) procure, install,
and operate BART. In the 1990 CAA Amendments, Congress amended the
visibility provisions in the CAA to focus attention on the problem of
regional haze, which is visibility impairment produced by a multitude
of sources and activities located across a broad geographic area.\4\
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    \3\ 42 U.S.C. 7491(a)(1).
    \4\ See CAA section 169B, 42 U.S.C. 7492.
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    In 1999, we promulgated the RHR, which requires states to develop
and implement SIPs to ensure reasonable progress toward improving
visibility in mandatory Class I Federal areas (Class I areas) \5\ by
reducing emissions that cause or contribute to regional haze.\6\ Under
the RHR, states are directed to conduct an analysis and make a BART
determination for each BART-eligible source that may be anticipated to
cause or contribute to any visibility impairment in a Class I area.\7\
In particular, under CAA section 169A(g)(2) and 40 CFR
51.308(e)(1)(ii)(A), states must analyze and consider the following
five factors as part of each source-specific BART analysis: (1) The
costs of compliance of each technically feasible control technology,
(2) the energy and non-air quality environmental impacts of compliance
of the control technologies, (3) any existing pollution control
technology in use at the source, (4) the remaining useful life of the
source, and (5) the degree of improvement in visibility which may
reasonably be anticipated to result from the use of such technology
(collectively known as the ``five-factor BART analysis'').
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    \5\ Areas designated as mandatory Class I Federal areas consist
of national parks exceeding 6000 acres, wilderness areas and
national memorial parks exceeding 5000 acres, and all international
parks that were in existence on August 7, 1977. 42 U.S.C. 7472(a).
When we use the term ``Class I area'' in this action, we mean a
``mandatory Class I Federal area.''
    \6\ See generally 40 CFR 51.308.
    \7\ 40 CFR 51.308(e).
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    In 2005, the EPA published the Guidelines for BART Determinations
under the Regional Haze Rule at Appendix Y to 40 CFR part 51 (``BART
Guidelines'') on July 6, 2005. The BART Guidelines assist states in
determining which of their sources should be subject to the BART
requirements and in determining appropriate emission limits for each
such ``subject-to-BART'' source. In making BART determinations for
fossil fuel-fired electric generating plants with a total generating
capacity in excess of 750 megawatts, states must use the approaches set
forth in the BART Guidelines. States are encouraged, but not required,
to follow the BART Guidelines in making BART determinations for other
types of sources. In lieu of requiring source-specific BART controls,
states also have the flexibility to adopt an alternative measure as
long as the alternative provides greater reasonable progress towards
natural visibility conditions than BART (i.e., the alternative must be
``better than BART'').\8\
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    \8\ 40 CFR 51.308(e)(2).
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    In addition to the visibility protection requirements of the CAA
and the RHR, SIP revisions concerning regional haze are also subject to
the general requirements of CAA section 110. In particular, they are
subject to the requirement in CAA section 110(l) that SIP revisions
must not ``interfere with any applicable requirement concerning
attainment and reasonable further progress (as defined in [CAA section
171]), or any other applicable requirement of [the CAA],'' as well as
the requirement in CAA section 110(a)(2)(A) that SIPs must include
enforceable emission limits.

B. Cholla Generating Station

    Cholla Generating Station consists of four primarily coal-fired
electricity generating units with a total plant-wide generating
capacity of 1,150 megawatts. Unit 1 is a 126 MW tangentially-fired,
dry-bottom boiler that is not BART-eligible. Units 2, 3 and 4 have
capacities of 272 MW, 272 MW and 410 MW, respectively, and are
tangentially-fired, dry-bottom boilers that are each BART-eligible.
Units 1, 2, and 3 are owned and operated by APS and Unit 4 is owned by
PacifiCorp and operated by APS.

C. Summary of State Submittals and EPA Actions

1. 2011 Arizona Regional Haze SIP
    On February 28, 2011, the Arizona Department of Environmental
Quality (ADEQ) submitted a Regional Haze SIP under Section 308 of the
RHR (``Arizona Regional Haze SIP'') to EPA. This submittal included
BART analyses and determinations for nitrogen oxides (NOX),
particulate matter with an aerodynamic diameter of less than 10
micrometers (PM10), and sulfur dioxide (SO2) at
Cholla Units 2, 3, and 4. ADEQ's BART analyses for Cholla included the
following seven steps:
     Step 1: Identify the Existing Control Technologies in Use
at the Source,
     Step 2: Identify All Available Retrofit Control Options,
     Step 3: Eliminate All Technically Infeasible Control
Options,
     Step 4: Evaluate Control Effectiveness of Remaining
Technologies,
     Step 5: Evaluate the Energy and Non-Air Quality
Environmental Impacts and Document Results,\9\
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    \9\ We note that, while ADEQ referred to its Step 5 as an
evaluation of energy and non-air quality environmental impacts, this
step also includes consideration of the costs of compliance and the
remaining useful life of the source, consistent with the BART
Guidelines, 40 CFR part 51, appendix Y, section IV.D.4.
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     Step 6: Evaluate Visibility Impacts, and
     Step 7: Select BART.\10\
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    \10\ Arizona Regional Haze SIP Revision, Appendix D, section XI.
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2. 2012 EPA Action on Arizona Regional Haze SIP and FIP
    On December 5, 2012, we issued a final rule approving in part and
disapproving in part ADEQ's BART determinations for three sources,
including Cholla.\11\ We found that ADEQ's overall approach to
conducting BART analyses and its implementation of the first four steps
of its approach were generally reasonable and consistent with the RHR
and the BART Guidelines. However, we found significant flaws in ADEQ's
implementation of the last three steps.

In particular, under step 5, we found that the costs of compliance were
not calculated in accordance with the BART Guidelines; under step 6, we
found that the visibility benefits were not appropriately evaluated and
considered; and under step 7, we found that ADEQ did not provide a
sufficient explanation and rationale for its determinations.\12\ As a
result of these flaws, we disapproved ADEQ's BART determinations for
NOX at Cholla Units 2, 3, and 4. We also found that the SIP
lacked enforceable emission limits for all units and pollutants. In the
same action, we promulgated a FIP for the disapproved portions of the
SIP, including NOX BART determinations for Units 2, 3, and
4. We determined that BART for NOX at Units 2, 3, and 4 was
an emission limit of 0.055 pounds per million British thermal units
(lb/MMBtu) determined as an average across the three units, based on a
rolling 30-boiler-operating-day average, which is achievable with the
use of low-NOX burners (LNB), overfire air (OFA) and
selective catalytic reduction (SCR). The compliance date for the
NOX BART emission limit is December 5, 2017. In addition, we
established an SO2 removal efficiency requirement of 95
percent for the scrubbers on Cholla Units 2, 3 and 4. Cholla Units 3
and 4 were required to achieve this removal efficiency by December 5,
2013, and Cholla Unit 2 was required to comply by April 1, 2016. We
also established requirements for equipment maintenance, monitoring,
recordkeeping, and reporting for all units and all pollutants.
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    \11\ 77 FR 72511.
    \12\ See 77 FR 42834, 42840-42941.
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3. 2015 APS Application for Significant Permit Revision for Cholla
Generating Station
    On January 15, 2015, APS and PacifiCorp submitted an ``Application
for Significant Permit Revision and Five-Factor BART Reassessment for
Cholla'' to ADEQ. APS and PacifiCorp requested that ADEQ conduct a
revised BART analysis and determination based on new facts (``BART
Reassessment'') and submit this BART Reassessment to the EPA as a
revision to the Arizona Regional Haze SIP. Under the Cholla BART
Reassessment, APS and PacifiCorp would commit to the following measures
in lieu of implementing the FIP requirements for the Cholla Generating
Station:
     Unit 2 would be permanently shut down by April 1, 2016;
     Unit 3 and Unit 4 would continue to operate with currently
installed LNB and separated over fire air (SOFA). In addition, by April
30, 2025, APS and PacifiCorp would permanently cease burning coal at
both units with the option to convert to pipeline-quality natural gas
by July 31, 2025, with a <=20 percent annual average capacity factor.
4. 2015 Arizona Regional Haze SIP Revision for Cholla Generating
Station
    On October 22, 2015, ADEQ submitted a revision to the Arizona
Regional Haze SIP that incorporates the Cholla BART Reassessment
(``Cholla SIP Revision''). The Cholla SIP Revision is the subject of
this proposal.

III. Summary of the Cholla SIP Revision

    The Cholla SIP Revision consists of a revised BART analysis and
determination for NOX at Cholla, an analysis under CAA
section 110(l), and a revision to Cholla's operating permit (``Cholla
Permit Revision'') \13\ to implement both the revised BART
determination for NOX and ADEQ's prior BART determinations
for SO2 and PM10 at Cholla. If fully approved by
the EPA, the Cholla SIP Revision would fill the gap in the Arizona
Regional Haze SIP that resulted from the EPA's disapproval of ADEQ's
BART determinations for NOX at Cholla Units 2, 3, and 4 and
the lack of enforceable emission limits for all units and pollutants.
Accordingly, full approval of the Cholla SIP Revision would enable the
EPA to withdraw the provisions of the Arizona Regional Haze FIP that
apply to Cholla.
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    \13\ Cholla BART SIP Revision, Appendix A Significant Permit
Revision No. 61713 to Operating Permit No. 53399 for Arizona Public
Service Company Cholla Generating Station (October 16, 2015).
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    In the Cholla SIP Revision, ADEQ determined that, if Unit 2 were
shut down by April 1, 2016, no BART determination for Unit 2 would be
necessary ``because the enforceable shutdown date is within the five-
year BART window.'' \14\ For Units 3 and 4, ADEQ performed a revised
BART analysis, taking into account the new requirements that would be
imposed as part of the Cholla BART Reassessment. This re-analysis and
the resulting BART determinations are summarized in the following
sections.
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    \14\ Cholla SIP Revision, section 2.2, page 4.
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A. BART Re-Analysis for Cholla Units 3 and 4

    ADEQ's BART re-analysis for Units 3 and 4 consists of an evaluation
of each of the five BART factors, effectively replacing step 5
(evaluation of costs of compliance, energy and non-air quality
environmental impacts, and remaining useful life) and step 6
(evaluation of visibility benefits) of ADEQ's prior BART analysis for
Cholla in the Arizona Regional Haze SIP.
1. Cost of Compliance
    ADEQ evaluated the costs of compliance for three control options:
(1) LNB and SOFA, (2) SNCR with LNB and SOFA, and (3) SCR with LNB and
SOFA. Two fuel-use scenarios were used as a comparison: (1) Twenty
years of operation on coal and (2) eight years of operation on coal
followed by twelve years of operation on natural gas (as provided for
under the BART Reassessment). The cost-effectiveness values for each
control option under each of these scenarios are shown in Tables 1 and
2. For all options, the costs associated with the BART Reassessment are
due to lower utilization periods (coal firing until 2025 instead of for
20 years) as well as significantly lower NOX emissions after
conversion to natural gas.

                           Table 1--Cost-Effectiveness of NOX Control Options at Cholla Assuming 20 Years of Operation on Coal
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                                                                              Average                                     Incremental \a\
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                                                                             Emission
          Unit                    Control option                             reduction     Average cost-    Incremental     Incremental     Incremental
                                                            Annual cost     relative to    effectiveness    annual cost      emission          cost-
                                                             ($/year)     baseline  (ton/     ($/ton)        ($/year)        reduction     effectiveness
                                                                               year)                                        (ton/year)        ($/ton)
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3.......................  LNB and SOFA..................        $483,300           1,219            $396  ..............  ..............  ..............
                          SNCR with LNB and SOFA........       3,070,443           1,911           1,607       2,587,143             691           3,742
                          SCR with LNB and SOFA.........       9,448,912           3,300           2,838       8,965,612           2,110           4,248
4.......................  LNB and SOFA..................         673,550           1,756             384  ..............  ..............  ..............

                          SNCR with LNB and SOFA........       4,086,366           2,643           1,546       3,412,816             887           3,848
                          SCR with LNB and SOFA.........      13,590,853           4,408           3,083      12,917,303           2,652           4,871
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\a\ The incremental cost effectiveness results for SNCR and SCR are based on the emission and cost differences between these technologies and the
  proposed LNB + SOFA option.

       Table 2--Cost-Effectiveness of NOX Control Options at Cholla Assuming 8 Years of Operation on Coal and 12 years of Operation on Natural Gas
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                                                                              Average                                       Incremental
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                                                                             Emission
          Unit                    Control option                             reduction     Average cost-    Incremental     Incremental     Incremental
                                                            Annual cost     relative to    effectiveness    annual cost      emission          cost-
                                                             ($/year)     baseline  (ton/     ($/ton)        ($/year)        reduction     effectiveness
                                                                               year)                                        (ton/year)        ($/ton)
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3.......................  LNB and SOFA..................        $411,300             488            $843  ..............  ..............  ..............
                          SNCR with LNB and SOFA........       2,497,743             786           3,177       2,086,443             299           6,989
                          SCR with LNB and SOFA.........       8,716,452           1,387           6,286       8,305,152             899           9,237
4.......................  LNB and SOFA..................         571,550             702             814  ..............  ..............  ..............
                          SNCR with LNB and SOFA........       3,283,930           1,085           3,027       2,712,380             383           7,091
                          SCR with LNB and SOFA.........      12,480,744           1,833           6,810      11,909,194           1,130          10,539
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2. Energy and Non-Air Environmental Impacts
    ADEQ indicated that the energy impacts of LNB, SOFA, and SNCR are
minimal and that there are no non-air quality environmental impacts
associated with LNB and SOFA. ADEQ also noted that SNCR and SCR would
result in ammonia slip and that the transport and handling of anhydrous
ammonia presents potential safety hazards.
3. Existing Air Pollution Controls
    ADEQ noted that, under the Cholla BART Reassessment, use of the
existing LNB and SOFA would be continued at Units 3 and 4. ADEQ
proposed no additional controls for these two units. Unit 2 would be
shut down in April 2016, while Unit 1 (the non-BART unit) would cease
burning coal in 2025.
4. Remaining Useful Life
    ADEQ used a 20-year amortization period in order to calculate the
costs of compliance for Units 3 and 4 because neither unit is subject
to an enforceable shutdown date.
5. Degree of Visibility Improvement
    ADEQ included the results of modeling conducted by APS and
PacifiCorp to predict the degree of visibility improvement associated
with the three BART scenarios. This modeling predicted visibility
impacts at the thirteen Class I areas within 300 km of the Cholla
facility under a baseline scenario (based on 2001-2003 emissions with
all four units operating), as well as the three BART control scenarios:
     BART Option 1: Unit 1 with 2001-2003 baseline controls
(pre-LNB), Unit 2 shut down, LNB/SOFA on Units 3 and 4;
     BART Option 2: Unit 1 with 2001-2003 baseline controls
(pre-LNB), Unit 2 shut down, LNB/SOFA and SNCR on Units 3 and 4; and
     BART Option 3: Unit 1 with 2001-2003 baseline controls
(pre-LNB), Unit 2 shut down, LNB/SOFA and SCR on Units 3 and 4.

APS and PacifiCorp used CALPUFF version 5.8 and incorporated
meteorological data for 2001-2003, an assumption of 1.0 part per
billion background concentration for ammonia, and ``Method 8b'' 20
percent best days background conditions for all cases. The results of
this modeling are shown in Tables 3 and 4.

                                      Table 3--Predicted Visibility Impacts
                                   [22nd highest delta-dv over 3-year period]
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                                                              BART Option 1     BART Option 2     BART Option 3
              Class I area                    Baseline         (LNB/SOFA)      (LNB/SOFA/SNCR)   (LNB/SOFA/SCR)
----------------------------------------------------------------------------------------------------------------
Petrified Forest NP.....................              5.31              4.33              4.05              3.55
Grand Canyon NP.........................              3.40              1.79              1.62              1.20
Capitol Reef NP.........................              2.19              1.04              0.91              0.62
Mazatzal WA.............................              2.23              0.96              0.87              0.69
Sycamore Canyon WA......................              2.27              1.00              0.88              0.67
Mount Baldy WA..........................              2.10              0.97              0.85              0.62
Gila WA.................................              1.53              0.53              0.47              0.39
Sierra Ancha WA.........................              2.28              1.05              0.97              0.81

Mesa Verde NP...........................              2.08              0.88              0.78              0.60
Galiuro WA..............................              0.96              0.34              0.31              0.27
Superstition WA.........................              2.00              1.00              0.93              0.73
Saguaro NP..............................              0.70              0.22              0.22              0.20
Pine Mountain WA........................              1.64              0.67              0.59              0.48
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                                     Table 4--Predicted Visibility Improvement over the Baseline Visibility Impacts
                                                       [22nd highest delta-dv over 3-year period]
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                                                                  BART Option 1     BART Option 2     BART Option 3     Option 2 over     Option 3 over
                         Class I area                              (LNB/SOFA)     (LNB/SOFA /SNCR)   (LNB/SOFA /SCR)      Option 1          Option 1
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Petrified Forest NP...........................................              0.98              1.26              1.77              0.28              0.79
Grand Canyon NP...............................................              1.61              1.78              2.20              0.17              0.59
Capitol Reef NP...............................................              1.15              1.28              1.57              0.13              0.42
Mazatzal WA...................................................              1.27              1.36              1.54              0.09              0.27
Sycamore Canyon WA............................................              1.27              1.39              1.60              0.12              0.33
Mount Baldy WA................................................              1.14              1.26              1.48              0.12              0.34
Gila WA.......................................................              1.00              1.06              1.14              0.06              0.14
Sierra Ancha WA...............................................              1.22              1.30              1.47              0.08              0.25
Mesa Verde NP.................................................              1.21              1.30              1.49              0.09              0.28
Galiuro WA....................................................              0.62              0.65              0.69              0.03              0.07
Superstition WA...............................................              1.00              1.07              1.28              0.07              0.28
Saguaro NP....................................................              0.48              0.49              0.50              0.01              0.02
Pine Mountain WA..............................................              0.97              1.04              1.16              0.07              0.19
Cumulative....................................................             13.92             15.24             17.89              1.32              3.97
Average.......................................................              1.07              1.17              1.38              0.10              0.31
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B. BART Determination for Cholla Units 3 and 4

    ADEQ's BART determination for Cholla Units 3 and 4 in the Cholla
SIP Revision effectively replaces step 7 (select BART) of its prior
BART analysis for NOX BART for Cholla in the Arizona
Regional Haze SIP. In making this determination, ADEQ compared the
three emission control options (LNB and SOFA, SNCR with LNB and SOFA,
SCR with LNB and SOFA). For Option 1, it found that the LNB and SOFA
controls could be installed at reasonable cost-effectiveness and would
deliver visibility improvements ranging from 0.48 to 1.61 dv over
baseline conditions across thirteen Class I areas. For Option 2, it
found the SNCR control option to be too costly in comparison to the
small additional visibility benefits it would be expected to deliver.
For Option 3, ADEQ noted that the visibility benefits of SCR (3.97 dv
cumulative incremental visibility improvement) would only last until
2025 when coal firing would cease, after which the incremental benefits
of SCR would be ``negligible.'' Based on its analysis, ADEQ found
Option 1 (LNB with SOFA) to be BART for NOX at Cholla Units
3 and 4. The rolling 30-boiler-operating-day NOX emission
limits associated with this BART determination are 0.22 lb/MMbtu
(effective until April 30, 2025), which reflects the use of coal, and
0.080 lb/MMbtu (effective May 1, 2025), which reflects the use of
natural gas.

C. 110(l) Analysis

    In addition to the BART re-analysis and determinations, the Cholla
SIP Revision also includes a demonstration of ``noninterference'' under
CAA section 110(l). In particular, ADEQ considered whether the Cholla
SIP Revision would interfere with (1) any applicable requirement
concerning attainment of any National Ambient Air Quality Standards
(NAAQS) or (2) any other applicable requirement of the CAA.
1. Demonstration of Noninterference With NAAQS Attainment
    ADEQ noted that Cholla is located in Navajo County, Arizona, which
is currently designated as attainment or unclassifiable for the
following NAAQS: Carbon monoxide (CO), lead (Pb), nitrogen dioxide
(NO2), ozone (O3) (2008 NAAQS), PM2.5
(1997 and 2006 NAAQS), PM10, and SO2 (1971
NAAQS). ADEQ also noted that it has recommended an attainment/
unclassifiable designation for this area for the 2012 PM2.5
and 2010 SO2 standards.
    ADEQ's demonstration of noninterference with attainment focused on
the NAAQS for PM10, SO2, NO2, and
O3 because ambient levels of these pollutants are affected
by emissions of PM10, SO2, and/or NOX.
Specifically, ADEQ analyzed emissions of PM10,
SO2, and NOX under the control strategies in the
Cholla BART Reassessment, as compared with the existing control
requirements in the applicable SIP and FIP. This assessment was
conducted by considering revised emissions limits included in the
Cholla SIP Revision, summarized in Table 5.

                              Table 5--Emission Limits for Cholla BART Reassessment
----------------------------------------------------------------------------------------------------------------
                                                                        Emission limit  (lb/MMbtu)
              Unit                        Dates         --------------------------------------------------------
                                                                NOX                PM10               SO2
----------------------------------------------------------------------------------------------------------------
Unit 2.........................                          Unit shut down on April 1, 2016
                                --------------------------------------------------------------------------------
Unit 3.........................  until April 30, 2025..               0.22              0.015               0.15
                                 after April 30, 2025..               0.08               0.01             0.0006
Unit 4.........................  until April 30, 2025..               0.22              0.015               0.15
                                 after April 30, 2025..               0.08               0.01             0.0006
----------------------------------------------------------------------------------------------------------------

    For its PM10 analysis, ADEQ found that the emission
control strategies in the Cholla BART Reassessment will result in
greater PM10 reductions than those in the Arizona Regional
Haze SIP beginning in 2016 and continuing into the future, as shown in
Table 6. Beginning in 2026, PM10 emissions will be further
reduced under the Cholla BART Reassessment, due to the 20 percent
capacity factor limit and the more stringent emission limits (0.01 lb/
MMBtu rather than 0.015 lb/MMBtu) that will apply after the switch to
natural gas at Units 3 and 4. Therefore, ADEQ found that the Cholla SIP
Revision will not interfere with attainment and maintenance of the
PM10 NAAQS.

         Table 6--Comparison of Annual PM10 Emissions for 2011 Arizona SIP vs. Cholla BART Reassessment
----------------------------------------------------------------------------------------------------------------
                                                                              Annual PM10 (tons per year (tpy))
                                                                           -------------------------------------
                Time period                             Unit No.                                   Cholla SIP
                                                                               2011 AZ SIP          revision
----------------------------------------------------------------------------------------------------------------
2016.......................................  Unit 1.......................                 84                 84
                                             Unit 2.......................            \a\ 214             \b\ 78
                                             Unit 3.......................                197                197
                                             Unit 4.......................                269                269
                                            --------------------------------------------------------------------
                                                Total.....................                764                628
----------------------------------------------------------------------------------------------------------------
2017-2025..................................  Unit 1.......................                 84                 84
                                             Unit 2.......................                181                  0
                                             Unit 3.......................                197                197
                                             Unit 4.......................                269                269
                                            --------------------------------------------------------------------
                                                Total.....................                731                550
----------------------------------------------------------------------------------------------------------------
2026 forward...............................  Unit 1.......................                 84                 13
                                             Unit 2.......................                181                  0
                                             Unit 3.......................                197                 30
                                             Unit 4.......................                269                 39
                                            --------------------------------------------------------------------
                                                Total.....................                731                 82
----------------------------------------------------------------------------------------------------------------
\a\ Based on compliance date of April 1, 2016 for emissions limit of 0.015 lb/MMBtu.
\b\ Based on operation of Unit 2 until April 1, 2016.

    ADEQ also compared SO2 emission control strategies in
the 2011 SIP with those in the Cholla BART Reassessment. As shown in
Table 7, the control strategies in the Cholla BART Reassessment will
result in greater SO2 reductions than those in the 2011 SIP
beginning in 2016 and continuing into the future. Therefore, ADEQ found
that the emissions reductions achieved by the control strategy outlined
in the Cholla SIP Revision will not interfere with attainment and
maintenance of the SO2 NAAQS.

          Table 7--Comparison of Annual SO2 Emissions for 2011 Arizona SIP vs. Cholla BART Reassessment
----------------------------------------------------------------------------------------------------------------
                                                                                Annual SO2  (tpy)
                                                                                -------------------------------
                  Time period                               Unit No.                                Cholla SIP
                                                                                2011 AZ SIP      revision
----------------------------------------------------------------------------------------------------------------
2016..........................................  Unit 1..........................             844             844
                                                Unit 2..........................           1,614         \a\ 452
                                                Unit 3..........................           1,966           1,966
                                                Unit 4..........................           2,688           2,688
                                               -----------------------------------------------------------------

                                                   Total........................           7,112           5,950
----------------------------------------------------------------------------------------------------------------
2017-2025.....................................  Unit 1..........................             844             844
                                                Unit 2..........................           1,614               0
                                                Unit 3..........................           1,966           1,966
                                                Unit 4..........................           2,688           2,688
                                               -----------------------------------------------------------------
                                                   Total........................           7,112           5,498
----------------------------------------------------------------------------------------------------------------
2026 forward..................................  Unit 1..........................             844               1
                                                Unit 2..........................           1,614               0
                                                Unit 3..........................           1,966               2
                                                Unit 4..........................           2,688               2
                                               -----------------------------------------------------------------
                                                   Total........................           7,112               5
----------------------------------------------------------------------------------------------------------------
\a\ Based on operation of Unit 2 until April 1, 2016.

    ADEQ also analyzed the emission control strategies for
NOX in the Cholla BART Reassessment (Unit 2 shutdown and
LNB/SOFA controls at Units 3 and 4 until conversion to natural gas by
2025 with a <=20 percent annual average capacity factor) in comparison
to the FIP, which requires the installation of SCR with LNB and SOFA at
all units by December 5, 2017. As shown in Table 8, while the shutdown
of Unit 2 results in lower NOX emissions than the FIP for
2016, the Reassessment will allow for 4,161 tpy more NOX
emissions than the FIP between 2018 and 2025. However, after 2025, due
to the conversion to natural gas, the Cholla BART Reassessment will
result in greater annual NOX emission reductions than the
FIP. ADEQ found that, because there are no nonattainment or maintenance
SIPs that rely on emission reductions at Cholla to ensure continued
attainment of the NO2 NAAQS and the Cholla BART Reassessment
will result in NOX emission reductions relative to the
existing operating conditions of the facility, it will not interfere
with attainment or maintenance of the current NO2 NAAQS.

                Table 8--Comparison of NOX Annual Emissions for FIP vs. Cholla BART Reassessment
----------------------------------------------------------------------------------------------------------------
                                                                            Annual NOX  (tpy)
                                                        --------------------------------------------------------
                                                                                Annual emission
           Time period                   Unit No.                                                change (Cholla
                                                              EPA FIP          Cholla BART            BART
                                                                               reassessment     reassessment  to
                                                                                EPA FIP)
----------------------------------------------------------------------------------------------------------------
2016.............................  Unit 1..............              1,131              1,131                  0
                                   Unit 2..............              3,601            \a\ 900             -2,701
                                   Unit 3..............              2,766              2,766                  0
                                   Unit 4..............              3,548              3,548                  0
                                  ------------------------------------------------------------------------------
                                      Total............             11,046              8,345             -2,701
----------------------------------------------------------------------------------------------------------------
2017.............................  Unit 1..............              1,131              1,131                  0
                                   Unit 2..............              3,601                  0             -3,601
                                   Unit 3..............              2,766              2,766                  0
                                   Unit 4..............              3,548              3,548                  0
                                  ------------------------------------------------------------------------------
                                      Total............             11,046              7,445             -3,601
----------------------------------------------------------------------------------------------------------------
2018-2025........................  Unit 1..............              1,131              1,131                  0
                                   Unit 2..............                602                  0               -602
                                   Unit 3..............                655              2,766              2,111
                                   Unit 4..............                896              3,548              2,652
                                  ------------------------------------------------------------------------------
                                      Total............              3,284              7,445              4,161
----------------------------------------------------------------------------------------------------------------
2026 forward.....................  Unit 1..............              1,131                105             -1,026
                                   Unit 2..............                602                  0               -602
                                   Unit 3..............                655                244               -411
                                   Unit 4..............                896                308               -588
                                  ------------------------------------------------------------------------------

                                      Total............              3,284                657             -2,627
----------------------------------------------------------------------------------------------------------------
\a\ Based on operation of Unit 2 until April 1, 2016.

    Similarly, with regard to ozone, for which NOX emissions
are a precursor, ADEQ noted that there are no nonattainment or
maintenance SIPs that rely on emission reductions at Cholla to ensure
continued attainment of the NAAQS and that the Cholla BART Reassessment
will result in greater long-term NOX emission reductions
than the existing FIP. Accordingly, ADEQ concluded that the Cholla BART
Reassessment will not interfere with the attainment or maintenance of
the 2008 ozone NAAQS.
2. Demonstration of Noninterference With Other CAA Requirements
    With regards to the other applicable CAA requirements, ADEQ
considered whether the Cholla BART Reassessment would interfere with
(1) the requirements of the Regional Haze program or (2) the CAA's air
toxics requirements.
    In evaluating potential interference with the RHR, ADEQ relied
primarily on the results of air quality modeling (using CALPUFF)
performed by APS and PacifiCorp to assess the visibility impacts of
Cholla under the Cholla SIP Revision compared to the existing SIP and
FIP requirements.\15\ These results, summarized in Table 9, show that,
compared with the existing SIP and FIP requirements, the Cholla SIP
Revision would result in less visibility improvement at all affected
Class I areas between 2018 and 2025, but would result in greater
improvement starting in 2026. Based on these results and taking into
consideration the long-term goal of the Regional Haze Rule to achieve
natural visibility conditions, ADEQ found that the BART Reassessment
will not interfere with the requirements of the regional haze program.
---------------------------------------------------------------------------

    \15\ Id.

                                  Table 9--Modeled Visibility Impacts of Cholla
----------------------------------------------------------------------------------------------------------------
                                                            EPA FIP and     SIP Revision BART  SIP Revision BART
                                                            existing SIP       (2018-2025)       (2026 forward)
                      Class I Area                      --------------------------------------------------------
                                                             Visibility         Visibility         Visibility
                                                            impacts (dv)       impacts (dv)       impacts (dv)
----------------------------------------------------------------------------------------------------------------
Petrified Forest NP....................................               2.64               3.75               1.45
Grand Canyon NP........................................               1.11               1.48               0.45
Capitol Reef NP........................................               0.62               0.92               0.29
Mazatzal WA............................................               0.75               0.83               0.30
Sycamore Canyon WA.....................................               0.73               0.94               0.29
Mount Baldy WA.........................................               0.69               0.87               0.28
Gila WA................................................               0.46               0.47               0.17
Sierra Ancha WA........................................               0.82               0.94               0.36
Mesa Verde NP..........................................               0.63               0.84               0.30
Galiuro WA.............................................               0.29               0.30               0.09
Superstition WA........................................               0.73               0.88               0.30
Saguaro NP.............................................               0.20               0.19               0.05
Pine Mountain WA.......................................               0.51               0.58               0.17
Cumulative impacts.....................................              10.18              12.99               4.50
----------------------------------------------------------------------------------------------------------------

    Concerning air toxics, ADEQ noted that in addition to ceasing
operation of Unit 2, the Cholla facility proposes to implement sorbent
injection at Units 1, 3, and 4 by March 2016 to reduce air toxics and
achieve compliance with the EPA's Mercury and Air Toxics (MATS) rule.
Therefore, ADEQ concluded that the Cholla BART Reassessment will not
interfere with any air toxics requirements of the CAA.

D. Cholla Permit Revision

    The Cholla Permit Revision, which is incorporated as Appendix A to
the Cholla SIP Revision, was issued by ADEQ on October 16, 2015. The
Permit Revision incorporates emission limits and compliance dates as
well as monitoring, recordkeeping, and reporting requirements to
implement both the Cholla BART Reassessment and ADEQ's prior BART
determinations for SO2 and PM10 at Cholla.

IV. The EPA's Evaluation of the Cholla SIP Revision

    We have evaluated the Cholla SIP Revision for compliance with the
requirements of the CAA, the RHR, and the BART Guidelines.\16\ Our
evaluation of each of the major components of the

Cholla SIP Revision is summarized in the following sections.
---------------------------------------------------------------------------

    \16\ CAA section 169A(b)(2) and 40 CFR 51.308(e)(1)(ii)(B)
require that BART for each fossil-fuel fired generating power plant
having a total generating capacity in excess of 750 megawatts be
determined pursuant to the BART Guidelines. Cholla has a total
generating capacity in excess of 750 megawatts, so the BART
Guidelines are mandatory for the Cholla BART analysis and
determination.
---------------------------------------------------------------------------

A. The EPA's Evaluation of the Enforceable Retirement Provision for
Cholla Unit 2

    The Cholla Permit Revision requires Unit 2 to be permanently
retired by no later than April 1, 2016.\17\ This date coincides with
the compliance deadlines for SO2 and PM10 in the
Arizona Regional Haze FIP and precedes the deadline for NOX
by over a year.\18\ In fact, the unit was shut down on October 1,
2015.\19\ If Unit 2 were not retired, APS would have been required to
install additional controls to meet the SO2 and
PM10 limits in the SIP, as well as the NOX limit
in the FIP, which is achievable with SCR. The requirement for permanent
retirement will become effective and federally enforceable when the
Cholla SIP Revision is approved into the SIP and the FIP provisions
applicable to Cholla are withdrawn.\20\ Accordingly, we agree with ADEQ
that no further analysis is required for Cholla Unit 2, and we propose
to approve the requirement for permanent retirement as satisfying the
requirements of the CAA and RHR for Cholla Unit 2.
---------------------------------------------------------------------------

    \17\ Cholla Permit Revision section I.C.1.
    \18\ See 40 CFR 51.145(f)(4).
    \19\ Letter from Edward Seal, APS, to Kathleen Johnson, EPA, and
Eric Massey, ADEQ (October 28, 2015).
    \20\ Cholla Permit Revision section I.A.
---------------------------------------------------------------------------

B. The EPA's Evaluation of ADEQ's BART Analysis for Cholla Units 3 and
4

    We find that ADEQ's BART analysis for Cholla Units 3 and 4 is
consistent with the requirements of the CAA, RHR, and the BART
Guidelines. In particular, we find that ADEQ's BART re-analysis
addresses the flaws that were the basis for our disapproval of ADEQ's
prior BART analysis for Cholla.\21\
---------------------------------------------------------------------------

    \21\ See 77 FR 42840-42941 and 42849, 77 FR 72565-72566.
---------------------------------------------------------------------------

    With regard to the cost of compliance, in its previous BART
analysis for Cholla, ADEQ included certain line item costs not allowed
by the EPA Control Cost Manual (CCM),\22\ such as owner's costs,
surcharge, and Allowance for Funds Used During Construction
(AFUDC).\23\ This approach did not comply with BART Guidelines'
direction that cost estimates should be based on the CCM. In the Cholla
SIP revision, by contrast, ADEQ used the cost estimates that the EPA
developed as part of the Regional Haze FIP,\24\ which were calculated
using the CCM methodology.\25\
---------------------------------------------------------------------------

    \22\ EPA Air Pollution Control Cost Manual, available at https://www3.epa.gov/ttn/ecas/cost_manual.html.
    \23\ See 77 FR 42849.
    \24\ See, e.g., Cholla SIP Revision, Appendix B, Table B-1,
footnote (a).
    \25\ See 77 FR 42852.
---------------------------------------------------------------------------

    We note that in May 2016, EPA revised the CCM chapter that concerns
SCR systems.\26\ The revised CCM recommends use of a 30-year equipment
life for SCR systems,\27\ whereas the previous version recommended a
20-year life.\28\ As noted above, ADEQ used a 20-year remaining useful
life in its cost calculations in the Cholla SIP Revision, which was
consistent with the current CCM recommendation at the time of SIP
submittal in October 2015. Given that the majority of other BART
analyses, including the EPA's analysis for Cholla in the Arizona
Regional Haze FIP,\29\ have used a 20-year remaining useful life for
SCR, we believe that this remains an appropriate assumption in this
instance in order to ensure a consistent comparison with the cost
estimates for SCR in other BART determinations. Nonetheless, we have
also conducted an additional analysis to evaluate how use of a 30-year
remaining useful life would affect the cost-effectiveness values for
SCR at Cholla Units 3 and 4. We found that use of a 30-year remaining
useful life would increase the average cost-effectiveness of SCR at
Unit 3 from $6,286/ton to $7,864/ton and the ``incremental'' cost-
effectiveness (as compared with LNB+SOFA) from $9,237/ton to $11,295/
ton.\30\ The average and ``incremental'' (as compared with LNB+SOFA)
cost-effectiveness of SCR at Unit 4 would be increased from $6,810/ton
to $8,401/ton and from $10,539 to $12,674, respectively.\31\ Thus, if
ADEQ had calculated the average and incremental cost-effectiveness of
SCR based on a 30-year remaining useful life, it would have provided
further support for ADEQ's determination that the incremental costs of
compliance for SCR are not warranted by the incremental benefits.
---------------------------------------------------------------------------

    \26\ CCM (7th Edition), Section 4, Chapter 2--Selective
Catalytic Reduction (May 2016), available at https://www3.epa.gov/ttn/ecas/docs/SCRCostManualchapter7thEdition_2016.pdf.
    \27\ See id. at 2-78 (``broadly speaking, a representative value
of the equipment life for SCR at power plants can be considered as
30 years.'')
    \28\ CCM (6th edition), Section 4.2, Chapter 2--Selective
Catalytic Reduction (October 2000), available at https://www3.epa.gov/ttn/ecas/docs/cs4-2ch2.pdf, at 2-48 (``An economic
lifetime of 20 years is assumed for the SCR system.'')
    \29\ See 77 FR 42854.
    \30\ See Cholla_SCR_costs (30 yr life).xlsx.
    \31\ Id.
---------------------------------------------------------------------------

    With regard to visibility modeling, in its previous BART analysis
for Cholla, ADEQ considered the benefits from controls on only one
emitting unit at a time and overlooked significant benefits at multiple
Class I areas, thereby understating the full visibility benefits of the
candidate controls.\32\ By contrast, in the Cholla SIP revision, ADEQ
looked at the visibility impacts and potential improvements from all
three BART-eligible units together and also considered impacts and
potential improvements at all 13 Class I areas within 300 km of Cholla,
based on modeling performed by APS and PacifiCorp.\33\
---------------------------------------------------------------------------

    \32\ See 77 FR 42849.
    \33\ See, e.g., Cholla SIP Revision, Table 4 and 5.
---------------------------------------------------------------------------

    In considering the results of this modeling, it should be noted
that the baseline scenario included emissions from Unit 2, but the
control scenarios did not include any emissions from Unit 2. As a
result, the total visibility improvement anticipated under each of the
control scenarios represents not only the visibility benefits of
controls on Units 3 and 4, but also the visibility benefits of the
closure of Unit 2. We consider this to be a reasonable approach because
it is consistent with the requirement of the BART Guidelines for states
to consider the visibility improvement from controls applied to the
entire BART-eligible source.\34\ However, given that ADEQ is not making
a BART determination for Unit 2 in this instance, we believe it is
appropriate to also consider the visibility improvement expected to
result from controls on Units 3 and 4 only. ADEQ's evaluation of the
``incremental'' visibility benefits of SNCR (``Option 2 over Option 1''
in Table 4) and SCR (``Option 3 over Option 1'' in Table 4) effectively
excludes the benefits of the Unit 2 shutdown because Options 1, 2, and
3 all exclude emissions from Unit 2. Given that ADEQ relied heavily on
these ``incremental'' visibility benefits in reaching its ultimate BART
determination,\35\ we find that ADEQ appropriately considered the
visibility

benefits of controls on Units 3 and 4 only, as well as the benefits of
the Cholla BART Reassessment as a whole.
---------------------------------------------------------------------------

    \34\ In particular, the BART Guidelines explain that, ``[i]f the
emissions from the list of emissions units at a stationary source
exceed a potential to emit of 250 tons per year for any visibility-
impairing pollutant, then that collection of emissions units is a
BART-eligible source.'' 40 CFR part 51, appendix Y, section II.A.4.
In other words, the BART-eligible source (the list of BART emissions
units at a source) is the collection of units for which one must
make a BART determination. The BART Guidelines also state ``you must
conduct a visibility improvement determination for the source(s) as
part of the BART determination.'' Id, section IV.D.5. This requires
consideration of the visibility improvement from BART applied to the
BART-eligible source as a whole.
    \35\ See Cholla SIP Revision section 2.3.
---------------------------------------------------------------------------

    We also note that ADEQ did not quantify the expected visibility
benefits of SCR and SNCR on Units 3 and 4 after these units are
converted to gas in 2025, but characterized these benefits as
``negligible.'' In order to evaluate ADEQ's characterization, we scaled
the modeled visibility benefits of SCR under the coal-fired scenario to
roughly estimate what the benefits would be under the gas-fired
scenario. The results of this scaling indicate that, under the gas-
fired scenario, the approximate benefits of SNCR would be 0.07 dv at
the most-improved Class I area and 0.31 dv cumulatively over all
affected Class I areas, while the approximate benefits of SCR would be
0.15 dv at the most-improved Class I area and 0.77 dv cumulatively over
all affected Class I areas.\36\ Thus, the benefits of SNCR or SCR under
the gas-fired scenario would be significantly less than under the coal-
fired scenario, for which the expected ``incremental'' benefits over
LNB+SOFA are 0.28 dv at the most-improved area and 1.32 dv cumulative
for SNCR and 0.79 dv at the most-improved Class I area and 3.97 dv
cumulative for SCR.
---------------------------------------------------------------------------

    \36\ See Cholla_SCR_vs_NG rev2.xlsx.
---------------------------------------------------------------------------

    In the Cholla SIP Revision, ADEQ also appropriately accounted for
the requirements that will apply to Units 3 and 4 as of 2025, i.e., the
permanent cessation of coal burning by April 30, 2025, with the option
to convert to pipeline-quality natural gas and comply with a 20 percent
annual average capacity factor limit by July 31, 2025. These new
requirements significantly decrease the emission reductions achievable
by SCR or SNCR beginning in 2025 and thus increase the average $/ton of
both SCR and SNCR over the remaining useful life of the units, as shown
in Tables 1 and 2 above. Similarly, these requirements limit the
timeframe in which significant visibility benefits would result from
either SCR or SNCR to less than eight years.
    We note that ADEQ did diverge slightly from the BART Guidelines in
its calculation of the incremental cost-effectiveness of SCR. In
particular, ADEQ calculated the incremental cost, as well as
incremental visibility benefits, based on a comparison between SCR with
LNB+SOFA and LNB+SOFA only. This differs from the approach to
calculating incremental cost-effectiveness that is set forth in the
BART Guidelines, under which incremental cost-effectiveness is
calculated by comparing ``the costs and performance level of a control
option to those of the next most stringent option . . . .'' \37\ In
this case, SNCR with LNB+SOFA is the next most stringent option
compared to SCR with LNB+SOFA. Had ADEQ compared SCR with LNB+SOFA to
SNCR with LNB+SOFA, the incremental cost-effectiveness using a 20-year
remaining useful life would have been $10,347/ton for Unit 3 and
$12,295/ton for Unit 4,\38\ rather than $9,237/ton for Unit 3 and
$10,539/ton for Unit 4. Similarly, had ADEQ calculated the incremental
visibility benefits of SCR with LNB+SOFA based on a comparison to SNCR
with LNB+SOFA, the per area incremental benefits would have ranged from
0.01 dv to 0.51 dv, rather than 0.07 dv to 0.79 dv, and the cumulative
incremental benefit would have been 2.65 dv rather than 3.97 dv.\39\
Thus, if ADEQ had calculated the incremental costs and benefits of SCR
in accordance with the BART Guidelines, it would have resulted in
higher incremental cost-effectiveness values and lower incremental
visibility benefits compared with the figures provided in the Cholla
SIP Revision, which would provide further support for ADEQ's
determination that the incremental costs of compliance for SCR are not
warranted by the incremental benefits. Accordingly, in reviewing the
reasonableness of ADEQ's re-analysis of BART for these units, we find
that ADEQ's diversion from the BART Guidelines in this regard was of no
consequence.
---------------------------------------------------------------------------

    \37\ 40 CFR part 51 appendix Y, section IV.D.4.e (emphasis
added). The BART Guidelines do not specify a method for calculating
incremental visibility benefits. We consider it appropriate to
calculate these benefits in the same manner as incremental costs,
i.e. by comparing the expected benefits of a control option to those
of the next most stringent option.
    \38\ Cholla Units 3 and 4 Incremental Costs and Benefits.xlsx.
    \39\ Id.
---------------------------------------------------------------------------

    Based on our findings that the Cholla SIP Revision addresses the
flaws that were the basis for our disapproval of ADEQ's prior BART
analysis for Cholla and otherwise meets the requirements of the CAA,
RHR, and the BART Guidelines, we propose to approve ADEQ's BART re-
analysis for Cholla Units 3 and 4.

C. The EPA's Evaluation of ADEQ's BART Determination for Cholla Units 3
and 4

    We also find that ADEQ's BART determination for NOX at
Cholla Units 3 and 4 is consistent with the requirements of the CAA,
RHR, and the BART Guidelines. In particular, we find that ADEQ
appropriately considered and weighed the five BART factors in relation
to the available control options and reached a reasonable BART
determination based on its consideration of the factors.
    With regard to SCR, we find that it was reasonable for ADEQ to
conclude that the costs of SCR were not warranted by the visibility
benefits in this instance. In particular, with regard to costs, we are
not aware of any instance in which the EPA has determined SCR to be
BART where the average cost-effectiveness of SCR was greater than
$6,000/ton and the incremental cost-effectiveness (calculated in
accordance with the BART Guidelines) was greater than $10,000/ton, as
is the case with Cholla Units 3 and 4. Similarly, we are not aware of
any instance in which the EPA has disapproved a state's BART
determination that rejected SCR as BART based on similar cost-
effectiveness values. Furthermore, while the total visibility benefits
of the SCR-based control scenario (``BART Option 3'') are large (2.20
dv at the most improved area and 17.89 dv cumulative across all
affected areas), as noted in the previous section, these benefits
include not only the effect of SCR installation on Units 3 and 4, but
also the retirement of Unit 2. Thus, we believe it was appropriate for
ADEQ to focus primarily on what it characterized as the ``incremental''
visibility benefits, i.e., the relative degree of visibility
improvement expected under Option 3 (Unit 2 retired and SCR with
LNB+SOFA on Units 3 and 4) compared with Option 1 (Unit 2 retired and
LNB+SOFA on Units 3 and 4), which were 0.07 dv to 0.79 dv per area and
3.97 dv cumulative.\40\ While these benefits are significant, we
believe it was reasonable for ADEQ to determine that the benefits were
not warranted in light of the high costs of SCR and the fact that
benefits of this magnitude would only last for approximately eight
years, after which the benefits of SCR would be far less (roughly 0.15
dv at the most-improved Class I area and 0.77 dv cumulatively over all
affected Class I areas).
---------------------------------------------------------------------------

    \40\ As described in the previous section, if ADEQ had
calculated the incremental benefits of SCR in accordance with the
BART Guidelines, the per area incremental benefits would have ranged
from 0.01 dv to 0.51 dv, and the cumulative incremental benefit
would have been 2.65 dv.
---------------------------------------------------------------------------

    With regard to SNCR, we find that it was reasonable for ADEQ to
conclude that the costs of SNCR were not warranted by the visibility
benefits. In particular, with regard to costs, we are not aware of any
instance in which the EPA has determined SNCR to be BART where the
average cost-effectiveness of SNCR was greater than $3,000/ton and

the incremental cost-effectiveness was roughly $7,000/ton, as is the
case with Cholla Units 3 and 4. Similarly, we are not aware of any
instance in which the EPA has disapproved a state's BART determination
that rejected SNCR as BART based on similar cost-effectiveness values.
Furthermore, while the total visibility benefits of the SNCR-based
control scenario (``BART Option 2'') are large (1.78 dv at the most
improved area and 15.24 dv cumulative across all affected areas), as
noted above, these benefits include not only the effect of SNCR
installation on Units 3 and 4, but also the retirement of Unit 2. Thus,
we believe it was appropriate for ADEQ to focus primarily on
incremental visibility benefits, i.e., the relative degree of
visibility improvement expected under Option 2 (Unit 2 retired and SNCR
with LNB+SOFA on Units 3 and 4) compared with Option 1 (Unit 2 retired
and LNB+SOFA on Units 3 and 4), which were 0.01 dv to 0.28 dv per area
and 1.32 dv cumulative. While these benefits are not insignificant, we
believe it was reasonable for ADEQ to determine that the benefits were
not warranted in light of the relatively high costs of SNCR and the
fact that benefits of this magnitude would only last for approximately
eight years, after which the benefits of SNCR would be far less
(roughly 0.07 dv at the most-improved Class I area and 0.31 dv
cumulatively over all affected Class I areas).
    Therefore, we propose to approve ADEQ's determination that BART for
NOX at Cholla Units 3 and 4 consists of LNB+SOFA with
associated emission limits of 0.22 lb/MMbtu (rolling 30-boiler-
operating-day average) for each unit. As explained above, these
emission limits will remain in effect until April 30, 2025, at which
point both units will be permanently retired or converted to natural
gas with NOX emission limits of 0.08 lb/MMBtu (rolling 30-
boiler-operating-day average).

D. The EPA's Evaluation Under CAA Section 110(l)

    CAA section 110(l) requires that any revision to an implementation
plan shall not be approved by the EPA Administrator if the revision
would interfere with any applicable requirement concerning attainment
and reasonable further progress (RFP) or any other applicable
requirement of the Act.\41\ In evaluating whether the Cholla SIP
Revision would interfere with any CAA requirements, we note that
overall, the Cholla SIP Revision will result in reduced emissions of
both SO2 and PM10 compared to the existing SIP
and FIP requirements beginning in 2016 (see Tables 6 and 7 above) due
to the retirement of Unit 2. While the Cholla SIP Revision will require
fewer NOX reductions than the FIP between 2018 and 2025, it
will ensure that NOX emissions remain at or below current
levels (i.e., levels consistent with non-operation of Unit 2 \42\ and
operation of LNB and SOFA on Units 1, 3 and 4) until 2025, after which
it will require a substantial reduction in NOX emissions
compared to both current levels and the FIP (see Table 8 above).
---------------------------------------------------------------------------

    \41\ CAA Section 110(l), 42 U.S.C. 7410(l).
    \42\ As shown in Table 8, ADEQ projected that total
NOX emissions at Cholla Unit 2 would be 900 tpy in 2016,
based on a Unit 2 shutdown date of April 1, 2016. Because Unit 2 was
retired in October 2015, 2016 emissions from Unit 2 will actually be
zero, so we anticipate the total NOX emissions from the
facility will be roughly 7,445 tpy for all years between 2016 and
2025.
---------------------------------------------------------------------------

    With regard to applicable requirements concerning attainment and
RFP, as explained by ADEQ, Cholla is located in north central Navajo
County, Arizona, which is designated as unclassifiable/attainment for
all of the NAAQS for which the EPA has issued designations.\43\ ADEQ
also indicated that it has recommended an attainment/unclassifiable
designation for this area for the 2012 PM2.5 and 2010
SO2 standards. With regard to the 2012 PM2.5
standard, the EPA has finalized a designation of unclassifiable/
attainment for Navajo County.\44\ With regard to the 2010
SO2 standard, we note that, under the EPA's Data
Requirements Rule,\45\ ADEQ is required to develop and submit air
quality data characterizing ambient concentrations of SO2 in
the area around Cholla.\46\ The EPA will take these data into
consideration in finalizing a designation for the area. Finally, we
note that, on October 1, 2015, the EPA promulgated revised primary and
secondary ozone NAAQS.\47\ State designation recommendations for the
2015 ozone NAAQS are due to the EPA by October 1, 2016.\48\
---------------------------------------------------------------------------

    \43\ Cholla SIP Revision, pages 12-13, Table 7.
    \44\ See 40 CFR 81.303.
    \45\ 40 CFR part 51, subpart BB.
    \46\ See Letter from Eric Massey, ADEQ, to Doris Lo, EPA
(January 13, 2016).
    \47\ 80 FR 65292 (October 26, 2015).
    \48\ Id. at 65438.
---------------------------------------------------------------------------

    In summary, Cholla is located in area that is designated
unclassifiable/attainment or has not yet been designated for each of
the current NAAQS. Thus, the Arizona SIP does not currently rely on
emission limitations at Cholla to satisfy any attainment or RFP
requirements. Given that the Cholla SIP Revision will result in
equivalent or lower emissions of NOX, PM10 and
SO2 for all future years, compared to current emission
levels, in an area that is designated unclassifiable/attainment or has
not yet been designated for all NAAQS, we propose to find that the
Cholla SIP Revision would not interfere with any applicable
requirements concerning attainment or RFP.
    The other requirements of the CAA that apply to Cholla are:
     Standards of Performance for New Stationary Sources
(NSPS), 40 CFR part 60, subpart D;
     National Emission Standards for Hazardous Air Pollutants
(NESHAP), 40 CFR part 63, subpart UUUUU (also known as MATS);
     Compliance Assurance Monitoring (CAM), 40 CFR part 64; and
     BART and other visibility protection requirements under
CAA section 169A and the RHR.
    The Cholla SIP Revision would not affect the applicable NESHAP,
NSPS and CAM requirements. Therefore, we propose to find that the
Cholla SIP Revision would not interfere with the applicable NESHAP,
NSPS and CAM requirements.
    We also propose to find that Cholla SIP Revision would not
interfere with the visibility protection requirements of the CAA and
the RHR. Our proposed approval of the BART Reassessment is based on our
determination that, taking into consideration the differences in the
facts underlying the EPA's prior BART analysis for NOX in
Arizona Regional Haze FIP and the Cholla BART Reassessment, ADEQ's
revised BART analysis and determination for Cholla meet the BART
requirements of the CAA and RHR. Furthermore, the Cholla SIP Revision
would result in greater visibility improvement than the existing SIP
and FIP requirements beginning in 2026, which is consistent with the
long-term national goal of restoring natural visibility conditions at
Class I areas. Thus, we propose to find that the Cholla SIP Revision
would not interfere with the visibility protection requirements of the
CAA.

E. The EPA's Evaluation of Enforceable Emission Limits

    CAA section 110(a)(2)(A) requires SIPs to include enforceable
emission limitations as necessary or appropriate to meet the applicable
requirements of the Act. In addition, SIPs must contain regulatory
requirements related to monitoring, recordkeeping, and reporting for
applicable emission limitations.\49\ The Cholla Permit Revision
includes such enforceable

emission limits, as well as associated monitoring, recordkeeping, and
reporting requirements, for all units and pollutants. These
requirements will become effective and federally enforceable when the
Cholla SIP Revision is approved into the SIP and the FIP provisions
applicable to Cholla are withdrawn.\50\ Therefore, we propose to find
that the Cholla SIP Revision meets the requirements of the CAA and the
EPA's implementing regulations for enforceable emission limitations.
---------------------------------------------------------------------------

    \49\ See, e.g., CAA section 110(a)(2)(F) and 40 CFR 51.212(c).
    \50\ Cholla Permit Revision section I.A.
---------------------------------------------------------------------------

V. Proposed Action

    For the reasons described above, the EPA proposes to approve the
Cholla SIP Revision. Because this approval would fill the gap in the
Arizona Regional Haze SIP left by the EPA's prior partial disapproval
with respect to Cholla, we propose to withdraw the provisions of the
Arizona Regional Haze FIP that apply to Cholla. We also propose to find
that withdrawal of the FIP would constitute our action on APS's and
PacifiCorp's petitions for reconsideration of the Arizona Regional Haze
FIP.

VI. Environmental Justice Considerations

    As shown in Tables 6 and 7, the Cholla SIP Revision will result in
reduced emissions of both SO2 and PM10 compared
to the existing SIP and FIP requirements beginning in 2016. As shown in
Table 8, while the Cholla SIP Revision will result in fewer
NOX reductions than the FIP between 2018 and 2025, it will
ensure that NOX emissions remain at or below current levels
until 2025, after which it will require a substantial reduction in
NOX emissions compared to both current levels and to the
existing Arizona Regional Haze FIP. Therefore, the EPA believes that
this action will not have potential disproportionately high and adverse
human health or environmental effects on minority, low-income, or
indigenous populations.

VII. Incorporation by Reference

    In this rule, the EPA is proposing to include in a final EPA rule,
regulatory text that includes incorporation by reference. In accordance
with requirements of 1 CFR 51.5, the EPA is proposing to incorporate by
reference ``Significant Permit Revision No. 61713 to Operating Permit
No. 53399'' issued by ADEQ on October 16, 2015. The EPA has made, and
will continue to make, this document available electronically through
www.regulations.gov and in hard copy at U.S. Environmental Protection
Agency Region IX, Air-2, 75 Hawthorne Street, San Francisco, CA, 94105-
3901.

VIII. Statutory and Executive Order Reviews

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. This rule applies to only one facility and is therefore not
a rule of general applicability.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under
the PRA. This rule applies to only one facility. Therefore, its
recordkeeping and reporting provisions do not constitute a ``collection
of information'' as defined under 44 U.S.C. 3502(3) and 5 CFR
1320.3(c).

 C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic
impact on a substantial number of small entities. This action will not
impose any requirements on small entities. Firms primarily engaged in
the generation, transmission, and/or distribution of electric energy
for sale are small if, including affiliates, the total electric output
for the preceding fiscal year did not exceed 4 million megawatt hours.
Both owners of Cholla, APS and PacifiCorp, exceed this threshold.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain an unfunded mandate of $100 million or
more as described in UMRA, 2 U.S.C. 1531-1538, and does not
significantly or uniquely affect small governments.

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: Consultation and Coordination With Indian
Tribal Governments

    This action does not have tribal implications, as specified in
Executive Order 13175. It will not have substantial direct effects on
any Indian tribes, on the relationship between the Federal Government
and Indian tribes, or on the distribution of power and responsibilities
between the Federal Government and Indian tribes. 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 EO 13045 as applying only to those regulatory
actions that concern 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.
This action is not subject to Executive Order 13045 because it does not
concern an environmental health risk or safety risk.

H. Executive Order 13211: Actions Concerning Regulations 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

    This rulemaking does not involve technical standards. The EPA is
not revising any technical standards or imposing any new technical
standards in this action.

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

    The EPA believes the human health or environmental risk addressed
by this action will not have potential disproportionately high and
adverse human health or environmental effects on minority, low-income,
or indigenous populations. The results of this evaluation are contained
in section VI above.

K. Determination Under Section 307(d)

    Pursuant to CAA section 307(d)(1)(B), the EPA proposes to determine
that this action is subject to the provisions of section 307(d).
Section 307(d) establishes procedural requirements specific to certain
rulemaking actions under the CAA. Pursuant to CAA section 307(d)(1)(B),
the withdrawal of the provisions of the Arizona Regional Haze FIP that
apply to Cholla is subject to the requirements of CAA section 307(d),
as it constitutes a revision to a FIP under CAA section 110(c).
Furthermore, CAA section 307(d)(1)(V) provides that the provisions of
section

307(d) apply to ``such other actions as the Administrator may
determine.'' The EPA proposes that the provisions of 307(d) apply to
the EPA's action on the Cholla SIP revision.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Nitrogen dioxide, Particulate
matter, Reporting and recordkeeping requirements, Sulfur dioxide,
Visibility.

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

    Dated: June 30, 2016.
Deborah Jordan,
Acting Regional Administrator, EPA Region IX.

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.  52.145, revise paragraphs (f)(1), (2), (3), (4), (5), and
(10) to read as follows:

Sec.  52.145  Visibility protection.

* * * * *
    (f) * * *
    (1) Applicability. This paragraph (f) applies to each owner/
operator of the following coal-fired electricity generating units
(EGUs) in the state of Arizona: Coronado Generating Station, Units 1
and 2. The provisions of this paragraph (f) are severable, and if any
provision of this paragraph (f), or the application of any provision of
this paragraph (f) to any owner/operator or circumstance, is held
invalid, the application of such provision to other owner/operators and
other circumstances, and the remainder of this paragraph (f), shall not
be affected thereby.
    (2) Definitions. Terms not defined below shall have the meaning
given to them in the Clean Air Act or EPA's regulations implementing
the Clean Air Act. For purposes of this paragraph (f):
    ADEQ means the Arizona Department of Environmental Quality.
    Boiler-operating day means a 24-hour period between 12 midnight and
the following midnight during which any fuel is combusted at any time
in the unit.
    Coal-fired unit means any of the EGUs identified in paragraph
(f)(1) of this section.
    Continuous emission monitoring system or CEMS means the equipment
required by 40 CFR part 75 and this paragraph (f).
    Emissions limitation or emissions limit means any of the Federal
Emission Limitations required by this paragraph (f) or any of the
applicable PM10 and SO2 emissions limits for
Coronado Generating Station submitted to EPA as part of the Arizona
Regional Haze SIP in a letter dated February 28, 2011, and approved
into the Arizona State Implementation Plan on December 5, 2012.
    Flue Gas Desulfurization System or FGD means a pollution control
device that employs flue gas desulfurization technology, including an
absorber utilizing lime, fly ash, or limestone slurry, for the
reduction of sulfur dioxide emissions.
    lb means pound(s).
    NOX means nitrogen oxides expressed as nitrogen dioxide
(NO2).
    Owner(s)/operator(s) means any person(s) who own(s) or who
operate(s), control(s), or supervise(s) one or more of the units
identified in paragraph (f)(1) of this section.
    MMBtu means million British thermal unit(s).
    Operating hour means any hour that fossil fuel is fired in the
unit.
    PM10 means filterable total particulate matter less than
10 microns and the condensable material in the impingers as measured by
Methods 201A and 202 in 40 CFR part 51, appendix M.
    Regional Administrator means the Regional Administrator of EPA
Region IX or his/her authorized representative.
    SO2 means sulfur dioxide.
    SO2 removal efficiency means the quantity of
SO2 removed as calculated by the procedure in paragraph
(f)(5)(iii)(B) of this section.
    Unit means any of the EGUs identified in paragraph (f)(1) of this
section.
    Valid data means data recorded when the CEMS is not out-of-control
as defined by 40 CFR part 75.
    (3) Federal emission limitations--(i) NOX emission
limitations. The owner/operator of each coal-fired unit subject to this
paragraph (f) shall not emit or cause to be emitted NOX in
excess of the following limitations, in pounds per million British
thermal units (lb/MMBtu) from any coal-fired unit or group of coal-
fired units. Each emission limit shall be based on a rolling 30-boiler-
operating-day average, unless otherwise indicated in specific
paragraphs.

------------------------------------------------------------------------
                                                               Federal
        Coal fired unit or group of coal-fired units           emission
                                                              limitation
------------------------------------------------------------------------
Coronado Generating Station Unit 1.........................        0.065
Coronado Generating Station Unit 2.........................        0.080
------------------------------------------------------------------------

    (ii) [Reserved]
    (4) Compliance dates. (i) The owners/operators of each unit subject
to this paragraph (f) shall comply with the NOX emissions
limitations and other NOX-related requirements of this
paragraph (f) no later than December 5, 2017.
    (ii) The owners/operators of each unit subject to this paragraph
(f) shall comply with the applicable PM10 and SO2
emissions limits submitted to EPA as part of the Arizona Regional Haze
SIP in a letter dated February 28, 2011, and approved into the Arizona
State Implementation Plan on December 5, 2012, as well as the related
compliance, recordkeeping and reporting of this paragraph (f) no later
than June 3, 2013.
    (5) Compliance determinations for NOX and SO2--(i) Continuous
emission monitoring system.
    (A) At all times after the compliance date specified in paragraph
(f)(4) of this section, the owner/operator of each coal-fired unit
shall maintain, calibrate, and operate a CEMS, in full compliance with
the requirements found at 40 CFR part 75, to accurately measure
SO2, NOX, diluent, and stack gas volumetric flow
rate from each unit. In addition, the owner/operator of Cholla Units 2,
3, and 4 shall calibrate, maintain, and operate a CEMS, in full
compliance with the requirements found at 40 CFR part 75, to accurately
measure SO2 emissions and diluent at the inlet of the sulfur
dioxide control device. All valid CEMS hourly data shall be used to
determine compliance with the emission limitations for NOX
and SO2 in paragraph (f)(3) of this section for each unit.
When the CEMS is out-of-control as defined by 40 CFR part 75, that CEMs
data shall be treated as missing data, and not used to calculate the
emission average. Each required CEMS must obtain valid data for at
least 90 percent of the unit operating hours, on an annual basis.
    (B) The owner/operator of each unit shall comply with the quality
assurance procedures for CEMS found in 40 CFR part 75. In addition to
these 40 CFR part 75 requirements, relative accuracy test audits shall
be calculated for both the NOX and SO2 pounds per
hour measurement and the heat input measurement. The CEMs monitoring
data shall not be bias adjusted. The inlet SO2 and diluent
monitors required by this rule shall also meet the Quality Assurance/
Quality Control (QA/QC)

requirements of 40 CFR part 75. The testing and evaluation of the inlet
monitors and the calculations of relative accuracy for lb/hr of
NOX, SO2 and heat input shall be performed each
time the 40 CFR part 75 CEMS undergo relative accuracy testing.
    (ii) Compliance determinations for NOX.
    (A) [Reserved]
    (B) Coronado Generating Station. Compliance with the NOX
emission limits for Coronado Unit 1 and Coronado Unit 2 in paragraph
(f)(3)(i) of this section shall be determined on a rolling 30 boiler-
operating-day basis. The 30-boiler-operating-day rolling NOX
emission rate for each unit shall be calculated in accordance with the
following procedure: Step one, sum the total pounds of NOX
emitted from the unit during the current boiler operating day and the
previous twenty-nine (29) boiler operating days; Step two, sum the
total heat input to the unit in MMBtu during the current boiler
operating day and the previous twenty-nine (29) boiler operating days;
Step three, divide the total number of pounds of NOX emitted
from that unit during the thirty (30) boiler operating days by the
total heat input to the unit during the thirty (30) boiler operating
days. A new 30-boiler-operating-day rolling average NOX
emission rate shall be calculated for each new boiler operating day.
Each 30-boiler-operating-day average NOX emission rate shall
include all emissions that occur during all periods within any boiler
operating day, including emissions from startup, shutdown, and
malfunction.
    (C) If a valid NOX pounds per hour or heat input is not
available for any hour for a unit, that heat input and NOX
pounds per hour shall not be used in the calculation of the 30-day
rolling average.
    (iii) Compliance determinations for SO2. (A) The 30-day rolling
average SO2 emission rate for each coal-fired unit shall be
calculated in accordance with the following procedure: Step one, sum
the total pounds of SO2 emitted from the unit during the
current boiler-operating day and the previous twenty-nine (29) boiler-
operating days; step two, sum the total heat input to the unit in MMBtu
during the current boiler-operating day and the previous twenty-nine
(29) boiler-operating day; and step three, divide the total number of
pounds of SO2 emitted during the thirty (30) boiler-
operating days by the total heat input during the thirty (30) boiler-
operating days. A new 30-day rolling average SO2 emission
rate shall be calculated for each new boiler-operating day. Each 30-day
rolling average SO2 emission rate shall include all
emissions and all heat input that occur during all periods within any
boiler-operating day, including emissions from startup, shutdown, and
malfunction.
    (B) [Reserved]
    (C) If a valid SO2 pounds per hour at the outlet of the
FGD system or heat input is not available for any hour for a unit, that
heat input and SO2 pounds per hour shall not be used in the
calculation of the 30-day rolling average.
    (D) If both a valid inlet and outlet SO2 lb/MMBtu and an
outlet value of lb/hr of SO2 are not available for any hour,
that hour shall not be included in the efficiency calculation.
* * * * *
    (10) Equipment operations.
    (i) [Reserved]
    (ii) Coronado Generating Station. At all times, including periods
of startup, shutdown, and malfunction, the owner or operator of
Coronado Generating Station Unit 1 and Unit 2 shall, to the extent
practicable, maintain and operate each unit in a manner consistent with
good air pollution control practices for minimizing emissions. The
owner or operator shall continuously operate pollution control
equipment at all times the unit it serves is in operation, and operate
pollution control equipment in a manner consistent with technological
limitations, manufacturer's specifications, and good engineering and
good air pollution control practices for minimizing emissions.
Determination of whether acceptable operating and maintenance
procedures are being used will be based on information available to the
Regional Administrator which may include, but is not limited to,
monitoring results, review of operating and maintenance procedures, and
inspection of each unit.
* * * * *
[FR Doc. 2016-16959 Filed 7-18-16; 8:45 am]
 BILLING CODE 6560-50-P