alternative, latitude exists to consider special circumstances
pertinent to the specific source under review, or regarding the prior
application of the control alternative'', (70 FR 39166) and that ``[t]o
complete the BART process, you must establish enforceable emission
limits that reflect the BART requirements . . .'' (70 FR 39172). The
five-factor BART analysis described in the Guidelines is a case-by-case
analysis that considers site specific factors in assessing the best
technology for continuous emission controls. After a technology is
determined as BART, the BART Guidelines require establishment of an
emission limit that reflects the BART requirements, but does not
specify that the emission limit must represent the maximum level of
control achieved by the technology selected as BART. For these reasons,
EPA is not using the lower limit recommended by the commenter in
setting the BART Benchmark.
    Comment: BART limit for NGS should be in the range of 0.07-0.08 lb/
MMBtu.
    Several commenters asserted that the NOX emission limit
EPA proposed for NGS is unachievable. One commenter noted that the
averaging period for the proposed limit of 0.055 lb/MMBtu includes
periods when the SCR is unable to operate such as startup, shutdown,
and periods of load-cycling. The commenter made the following
arguments: (1) The S&L analysis submitted by the commenter shows that
the proposed emission limit is unachievable on a continuous basis; (2)
the NOX emissions achieved in other SCR retrofit situations
do not justify the proposed emission limit.
    Response: EPA disagrees with the commenter that the limit used in
setting the BART Benchmark for NGS should be higher than our proposed
limit of 0.055 lb/MMBtu, in the range of 0.07 to 0.08 lb/MMBtu.\93\
---------------------------------------------------------------------------

    \93\ The response included in this Final Rule is abbreviated and
excludes the graphs and tables EPA generated to support our
response. For additional detail, please see the RTC.
---------------------------------------------------------------------------

    The S&L report generally argues that because the emission limit is
established based on a 30-BOD average basis, the proposed emission
limit of 0.055 lb/MMBtu is not consistently achievable at NGS. The S&L
analysis is based on a design target of 0.03 lb/MMBtu and suggests an
emission limit in the range of 0.07-0.08 lb/MMBtu would be required to
accommodate periods of load-cycling operation, startups, and shutdowns.
S&L is recommending a limit that is 2.3 to 2.7 times higher than the
design target, or a compliance margin of 133 to 167 percent.
    The S&L report discusses the temperature limitations associated
with SCR and explains that at temperatures below a specific minimum
operating temperature, a component of the SCR system (i.e., ammonia
injection) must cease to prevent ammonium salt formation on the
catalyst. S&L asserts that a minimum operating temperature of
580[emsp14][deg]F is typical for retrofit SCR control systems installed
on coal-fired electric generating units with similar coal sulfur
content and states that this temperature corresponds with a gross load
of approximately 650 MW (650 gross MW, or MWg). S&L further assumes
that SRP will likely modify the units to increase flue gas temperatures
at lower operating loads by installing one of several options for low
load temperature control. In their analysis, S&L assumes the low load
temperature control would be achieved with a water-side bypass (to
allow water to bypass the economizer tube bundles during low-load
operation). The S&L report

states ``[b]ased on a preliminary review of the available systems, a
water-side bypass system should be capable of increasing the
temperature of the bulk flue gas by approximately 25[emsp14][deg]F to
65[emsp14][deg]F during low-load operation. For this evaluation, a low-
load temperature control system capable of achieving a temperature
increase of 65[emsp14][deg]F during low-load operations was assumed for
modeling purposes.'' S&L further estimates that this would correspond
to a minimum gross load of 450 MWg for the SCR to operate, or operation
at 55 percent capacity.
    Using the assumption that the SCR would not operate at loads below
450 MWg, S&L used 2012 operations data at NGS to estimate emission
rates at NGS assuming a design target of 0.03 lb/MMBtu with actual
steady-state operations achieving 0.04 lb/MMBtu. S&L modeled eighteen
different operating scenarios and identified seven scenarios, which
included periods of low load cycling along with unit startup and
shutdowns, that resulted in the maximum 30-BOD average for each unit
and facility-wide, that exceeded 0.055 lb/MMBtu. The highest 30-BOD
average S&L modeled was 0.077 lb/MMBtu for Unit 2, achieved under 3
different operating scenarios involving low-load cycling.
    SRP and S&L did not provide the underlying data used in the S&L
analysis. Therefore, EPA evaluated the S&L report by reviewing
emissions data from the EPA Air Markets Program Data (AMPD) for
multiple years, as well as emissions data from other facilities that
were constructed or retrofit with SCR. EPA sought to understand 2012
operations at NGS within the context of longer term operational trends
at the facility, as well as understand the minimum operating load
assumed by S&L for NGS within the context of minimum operating loads at
other facilities with SCR.
    EPA evaluated the reported hourly gross load operating data for
Units 1-3 at NGS for the years 2001, 2003, 2010, 2011, 2012, and
2013.\94\ Emission data from AMPD show that NGS, and in particular,
Unit 2, spent a higher percentage of operating hours at gross loads
below 450 MWg in 2012 compared to other years. The 2012 gross load
profiles for Unit 2 (as well as Units 1 and 3) are characteristic of
load-cycling units, with significant periods of time below the
purported SCR minimum operating load of 450 MWg, particularly in the
spring. Please see the RTC for more detail. In 2010, Unit 2 also
operated for significant periods of time at loads below 450 MWg.
However, these periods in 2010 occurred following the major outage on
Unit 2 (following installation of LNB/SOFA on that unit). Although
Units 1-3 at NGS did appear to operate as load-cycling units and
operated below 450 MWg for significant periods of time in 2012, this
type of operation does not appear to be characteristic of typical
operation at NGS, based on our evaluation of previous years, as well as
2013.
---------------------------------------------------------------------------

    \94\ See RTC and references therein.
---------------------------------------------------------------------------

    Based on the gross load operating profiles for six years, EPA
estimated the rolling 30-BOD averages for each BOD to determine whether
the operating profiles (which included actual startup, shutdown, and
load-cycling in each year) would result in 30-BOD averages that would
exceed 0.055 lb/MMBtu. Based on our analysis, EPA projected the highest
30-BOD average to be 0.079 lb/MMBtu (Unit 2 in 2010). Using 2012 data,
representative of load-cycling operation, EPA projected the highest 30-
BOD average to also occur on Unit 2 (0.075 lb/MMBtu). Similarly, S&L
projected the highest 30-BOD average in 2012 was from Unit 2, at 0.077
lb/MMBtu. Therefore, although the scenarios modeled by S&L and EPA were
not identical, the highest 30-BOD averages projected by EPA and S&L,
using similar starting assumptions, were comparable. Our analysis, of
projected SCR performance, which included emission and operating
profiles of actual startup and shutdown events, and load-cycling in
various years, showed that Unit 3 was not projected to exceed 0.055 lb/
MMBtu in any of the evaluated years, and that there were several years
within these six selected years that Units 1 and 2 would also not
exceed 0.055 lb/MMBtu.
    The analysis of projected 30-BOD average emission rates assumes
that S&L's value of 450 MWg (or 55 percent capacity) for the minimum
operating load to operate SCR at NGS is correct. EPA notes that 450 MWg
was a value that S&L assumed based on preliminary analysis of available
low load temperature control systems. SRP submitted a similar S&L
analysis to EPA for Units 1 and 3 at Coronado Generating Station
(CGS).\95\ Units 1 and 2 at CGS are 430 MWg Riley-Turbo units that
typically operate as load-cycling units. CGS burns low-sulfur coal from
the Powder River Basin (PRB coal). With the application of low-load
temperature controls on these units, S&L's analysis suggests that the
minimum operation load for SCR on Units 1 and 2 at CGS would be 138 MWg
(or 32 percent capacity). This is significantly lower than the 55
percent capacity S&L assumed for NGS. S&L stated that the coal sulfur
content will affect the minimum operating load for SCR. NGS does not
burn PRB coal; however, NGS does burn low-sulfur coal from the Kayenta
Mine. AECOM, SRP's consultant for visibility modeling, reported the
maximum sulfur content of the coal as 0.593 percent based on daily data
for the 2001-2003 period. For comparison, various sources reference PRB
coal as generally low-sulfur coal with a sulfur content of less than 1
percent, or a mean of 0.5 percent.\96\ In contrast, high sulfur coal is
typically above 3 percent.\97\
---------------------------------------------------------------------------

    \95\ See RTC and references therein.
    \96\ See, for example, publication from the U.S. Geological
Survey, figure PQ-4 and Table PQ-1, available at http://pubs.usgs.gov/pp/p1625a/Chapters/PQ.pdf.
    \97\ Id.
---------------------------------------------------------------------------

    EPA evaluated emission data of eight well-performing units burning
PRB coal and generated empirical estimates for minimum operating loads
and capacity requirements for SCR operation at those facilities. Based
on this analysis (see RTC for further detail), EPA estimated capacity
requirements for SCR operation that ranged from 35 percent to 46
percent, with an average value of 40 percent. Using the average (40
percent) and the maximum (46 percent) capacity requirement to operate
SCR, EPA projected that NGS would meet a limit of 0.055 lb/MMBtu (on a
30-BOD average) for all but 3 cases (i.e., Units 1 and 2 in 2012, and
Unit 2 in 2010) under the 46 percent capacity requirement. Under the 40
percent capacity requirement to run SCR, Units 1 and 2 in 2012 would
remain below 0.055 lb/MMBtu and for Unit 2 in 2012 the highest 30-BOD
average was projected to be exactly 0.055 lb/MMBtu. Operation of Unit 2
in 2010 was not typical of normal operation. Please see RTC for more
detail on this analysis.
    The S&L report concludes that even with a design target for SCR of
0.03 lb/MMBtu, a limit of 0.07-0.08 lb/MMBtu is required to accommodate
periods of startup, shutdown, and load-cycling operation. EPA agrees
that load-cycling operation appears to be an important factor; however,
EPA concludes that the critical S&L assumption, that the units at NGS
must operate at approximately 55 percent capacity in order for the SCR
to operate, was not sufficiently supported and was acknowledged by S&L
to be an assumption based on a preliminary review of available low-load
temperature control systems. EPA also notes that in the S&L revised
2013 cost analysis, S&L included costs for hot water recirculation
systems which

``maintains SCR in operation at all plant operating loads'' (emphasis
added).\98\
---------------------------------------------------------------------------

    \98\ See page 1-2 of the Sargent and Lundy report prepared for
SRP, dated January 2, 2014, included as Appendix U to the SRP
comment letter in the docket for this rulemaking.
---------------------------------------------------------------------------

    In summary, EPA is finalizing a BART Benchmark based on an emission
limit for NGS of 0.055 lb/MMBtu on a rolling 30-BOD basis. In
determining the achievability of this limit, EPA has conducted an
analysis that considers actual periods of startup, shutdown, and low-
load cycling. Based on the understanding that S&L would design the SCR
system at NGS to a design target of 0.03 lb/MMBtu, the BART limit of
0.055 lb/MMBtu represents an adequate compliance margin to accommodate
periods of startup, shutdown, and load-cycling operation.
    Comment: Presumptive Limit for NOX.
    Several commenters noted that with existing LNB/SOFA controls, NGS
emits NOX at rates below the presumptive limit of 0.28 lb/
MMBtu established by the EPA in the BART Guidelines. A commenter stated
that to properly justify departure from the presumptive BART limit, EPA
must evaluate the impacts of the presumptive BART limit in its five-
factor analysis.
    Response: EPA disagrees with the comment that installation of LNB/
SOFA at NGS should satisfy BART simply because it meets the presumptive
limit for NOX of 0.28 lb/MMBtu in the BART Guidelines for
tangential-fired boilers burning bituminous coal. Presumptive BART
limits, and the corresponding technology upon which those limits are
based, do not preclude states or EPA from setting limits that differ
from those presumptions based on case-specific consideration of the
relevant BART factors. The presumptive limits generally represent a
minimum level of control for BART for various types of power plants,
based on EPA's assessment of the typical costs of controls and likely
visibility benefits.\99\ EPA further disagrees with the assertion that
we did not evaluate the impacts of the presumptive BART limit in our
five-factor analysis. The presumptive BART limit of 0.28 lb/MMBtu is
based on the installation and operation of modern combustion controls.
EPA evaluated LNB/SOFA (at a limit of 0.24 lb/MMBtu, which is each
unit's existing permitted NOX limit for operation with LNB/
SOFA) in the five-factor analysis on which our proposed rule was based.
Please see our RTC for a detailed discussion.
---------------------------------------------------------------------------

    \99\ See 77 FR 14604, 14608-14610 (March 12, 2012) for a
detailed discussion of the presumptive limits.
---------------------------------------------------------------------------

    Comment: Install SCR within 3.5 years.
    One commenter stated that the CAA requirement for BART to be
installed ``as expeditiously as practicable'' requires installation and
full implementation of SCR on all three units at NGS within 3.5 years
rather than five years. The commenter stated that EPA provided no site-
specific factors at NGS that would require a longer-than-average
installation time for SCR (particularly in light of the fact that it
appears contractors in the region will not be overwhelmed).
    Response: EPA disagrees with the commenter that a 3.5-year
compliance deadline for the installation of SCR would be practicable
for NGS. EPA agrees that there are numerous sources of information,
including EPA's response to comments on its BART determination for
SJGS, to suggest that on average, the time required to design and
construct an SCR system can range from 37 to 43 months. The commenter
also cites EPA documents suggesting that it generally takes 21 months
to design, install, and test one SCR unit, and 35 months for SCR
installation at power plants with multiple SCR units, and another
publication that suggests that SCR can be installed in less than five
years (i.e., document from The Brattle Group). Our RTC contains a
detailed discussion of our conclusion that the Brattle Group estimate
of 47 months (nearly 4 years) applies to one unit, not multiple units
at one facility.\100\
---------------------------------------------------------------------------

    \100\ See May 2012 Brattle Group document, page 12 and page 17,
in the docket for this rule.
---------------------------------------------------------------------------

    In addition, although EPA cited one facility where the retrofit of
seven units required 35 months, EPA also stated ``ideally, longer than
35 months would allow for all the retrofits to occur over a period of
several years so that facility owners can properly plan outages and
suppliers can properly plan for resource availability.'' \101\
---------------------------------------------------------------------------

    \101\ See EPA 2002 Multipollutant Strategies document, page 22,
in the docket for this rule.
---------------------------------------------------------------------------

    The commenter also states that ``it appears contractors in the
region will not be overwhelmed'' to justify why installation time for
SCR should not be longer than average.\102\ We note that ``installation
time'' is one part of compliance, and that EPA must also consider time
for design, procurement, and permitting. We also note that the
commenter did not provide any support for its statement that
contractors in the region will not be overwhelmed. We note that several
EGUs in the southwest have compliance dates for the installation of SCR
around 2018.\103\ Therefore, EPA anticipates that leading up to 2018,
numerous coal-fired EGUs in the region will be retrofited with post-
combustion controls.
---------------------------------------------------------------------------

    \102\ See page 17 of the EarthJustice comment letter, in the
docket for this rule.
    \103\ See Final BART FIP for Four Corners Power Plant an
compliance dates under the BART Alternative at 77 FR 51620 at 51648
(August 24, 2012) and Final Regional Haze FIP for Arizona (phase 1)
at 77 FR 72512 at 72578 (December 5, 2012).
---------------------------------------------------------------------------

    In taking action to finalize a BART Benchmark, EPA is retaining the
five year compliance period as proposed. Because BART compliance at NGS
involves the design, procurement, and installation of SCR on three
units and upcoming ownership changes at NGS as discussed in our
proposed rule, EPA is determining that a five-year BART compliance
timeframe at NGS is as expeditious as practicable. This is within the
range cited by the commenters and the facility operator (i.e., average
of 21 to 47 months per unit, or 35 months to 67 months for multiple
units at one facility) and is consistent with the CAA which requires
BART compliance as expeditiously as practicable but no later than five
years following the effective date of the final rule.\104\
---------------------------------------------------------------------------

    \104\ See section 169A of the CAA (sections 169A(b)(2)(A) and
(g)(4)).
---------------------------------------------------------------------------

G. Comments on BART for PM

    Comment: Support/opposition for finding not to establish PM BART.
    Several commenters supported EPA's statement in the Proposed Rule
that ``[b]ecause emissions of PM are well controlled at NGS through
federally enforceable limits, EPA is not proposing that it is
``necessary or appropriate'' under the TAR to determine BART for PM
emissions at NGS.''
    Some commenters noted that implementation of the Mercury and Air
Toxics Standards (MATS) in the near future will establish an additional
federally enforceable limit for PM of 0.03 lb/MMBtu. The commenters
added that the BART Guidelines provide that one can generally rely on
MACT standards for purposes of BART.
    In contrast, two commenters asserted that EPA was incorrect to
determine that it need not evaluate BART for control of PM at NGS. The
commenter asserts that the existing PM limit of 0.06 lb/MMBtu was not
based on a BART analysis and does not reflect a well-controlled PM
emission rate for a coal-fired EGU.
    One commenter asserted that the electrostatic precipitators (ESPs)
at NGS do not represent the best system of control for PM. The
commenter believes that EPA's determination is inconsistent with recent
BART and BACT

determinations for coal-fired utility boilers that set emissions limits
for PM of 0.015 lb/MMBtu or lower based on the use of fabric filter
baghouses. The commenter concluded that EPA should revise its
determination and complete a BART analysis for PM that includes
evaluation of fabric filter baghouses.
    Response: EPA agrees with the comment that it is not necessary or
appropriate to require BART for PM emissions from NGS at this time. As
we stated in our proposed rule: ``Emissions of PM and SO2
are controlled by hot-side electrostatic precipitators (HS-ESPs) and
wet scrubbers, respectively.'' \105\ Because NGS will be required to
comply with the PM emissions limits in the MATS rule, EPA continues to
find that it is not necessary or appropriate at this time to promulgate
a BART emission limit for PM from NGS. EPA is not determining that the
existing PM emission limit for NGS is BART. Instead, it is EPA's
position that it is not necessary or appropriate under our
discretionary authority under the TAR, promulgated at 40 CFR 49.11, to
conduct a BART determination for PM emissions because they are
currently well-controlled and will be further reduced by compliance
with the 0.03 lb/MMBtu emission limit in the MATS rule.
---------------------------------------------------------------------------

    \105\ 78 FR 8279 (February 5, 2013).
---------------------------------------------------------------------------

    One commenter asserted that EPA should require fabric filter
baghouses as BART for PM. EPA cannot agree or disagree that baghouses
would be required as BART for PM because, as described above, we have
determined that it is not necessary or appropriate at this time to
conduct a BART determination for PM at NGS.

H. Comments on BART for SO2

    Comment: Support for finding that Reasonable Progress is met for
SO2.
    Several commenters noted that EPA recognized in the Proposed Rule
that the emission limits EPA established for SO2 in 1991
were determined to achieve greater reasonable progress than would BART.
Several commenters agreed that no additional emission limits or
controls should be required as a result of BART for SO2
emissions. One commenter noted that the existing SO2 limit
at NGS is more stringent than the BART Guidelines' presumptive
SO2 limit.
    Response: EPA agrees with these comments. As EPA stated in our
proposal in February 2013, the SO2 emissions limit
established in EPA's 1991 SO2 FIP was determined to be
better than BART under the visibility regulations addressing reasonably
attributable visibility impairment. Specifically, EPA determined that
promulgating a SO2 emission limit of 0.10 lb/MMBtu on an
annual average basis would result in greater cumulative SO2
emissions reductions and visibility improvement over time than would
the SO2 BART limit that EPA had proposed for NGS. NGS
installed a wet flue gas desulfurization system to reduce
SO2 emissions on each of its boilers in 1997-1999.\106\
---------------------------------------------------------------------------

    \106\ EPA initially codified the requirements for NGS to meet an
SO2 emission limit in an existing FIP for the State of
Arizona. See 40 CFR 52.145. After promulgation of the TAR, EPA moved
the NGS SO2 FIP to 40 CFR 49.5513
---------------------------------------------------------------------------

I. Comments on EPA's BART Alternative

    Comment: Support for EPA's authority for ``better than BART.''
    Several commenters discussed and supported EPA's policy and legal
rationale for its discretion to approve ``better than BART''
alternatives and to provide an extended period for implementation of
such an alternative at NGS. One commenter also opined that the
5[hyphen]year compliance period for BART that is defined in section
169A(g)(4) of the CAA applies by its terms only to: (1) SIPs, by
providing that the BART compliance date shall be no later than ``five
years after the date of approval of a plan revision under this
section''; and (2) FIPs promulgated under CAA section 110(c), by
providing that the BART compliance date under any such FIP shall be no
later than ``five years after . . . the date of promulgation of such a
plan revision in the case of action by the Administrator under section
110(c).'' The commenter concluded that because the FIP for NGS is not
promulgated under section 110(c) of the CAA, the 5-year timeframe for
BART does not apply to NGS.
    Response: EPA agrees with the comment in support of our action to
find that the TWG Alternative meets the framework established in our
Proposed Rule. EPA agrees that we have the legal authority under the
CAA and RHR to implement a ``better than BART'' alternative.\107\ EPA
agrees that we have the authority under the CAA and the TAR to extend
the compliance date that will apply to the ``better than BART''
alternative pursuant to CAA Section 301(d)(4) and 40 CFR 49.11(a), as
discussed in detail below.
---------------------------------------------------------------------------

    \107\ See 40 CFR 51.308(e)(2); CAWCD v. EPA, 990 F.2d 1531 (9th
Cir. 1993); CEED v. EPA, 398 F.3d 653 (D.C. Cir. 2005); UARG v. EPA,
471 F.3d 1333 (D.C. Cir. 2006).
---------------------------------------------------------------------------

    We also note that regardless of whether the commenter is correct
that the CAA does not require compliance with the BART requirements
within five years for sources subject to a FIP in Indian country, we
consider five years to be a reasonable timeframe for the installation
and operation of SCR at NGS. To the extent the commenter is correct
that the timing provisions of section 169A(g)(4) are outside the scope
of EPA's action to implement a FIP in Indian country under section 301
and the TAR, this further supports EPA's determination that extending
the compliance deadline beyond 2018 for a BART alternative at NGS is
appropriate.
    EPA also agrees with the comment that approving the TWG Alternative
for NGS will not compromise the ultimate goal of the RHR based on
progress toward eliminating human[hyphen]caused visibility impairment
in Class I areas by 2064.\108\ The TWG Agreement provides that NGS will
cease conventional coal-fired generation in 2044. Because the TWG
Agreement included this provision, we are including a provision in the
Final Rule that requires the operator of NGS to cease conventional
coal-fired generation by December 22, 2044.\109\ The TWG Agreement
further states that the Navajo Nation may elect to operate NGS after
December 22, 2044 consistent with EPA approval. EPA is not including
this provision in the regulatory requirements at Sec.
49.5513(j)(3)(iii); however, EPA expects that NGS would be
substantially modified if the Navajo Nation were to elect to continue
operation of the facility after NGS ceases conventional coal-fired
generation in 2044, and that NGS would then need to meet all applicable
regulatory and permitting requirements in existence at that time. In
addition, any power generating units that may be built to replace NGS
would also be subject to environmental review and air permitting
requirements.
---------------------------------------------------------------------------

    \108\ See CAA section 169A(1)(a).
    \109\ See 79 FR 12944, 12950 (March 7, 2014). ``While it is true
that the Regional Haze Rule and BART Guidelines do not contemplate
unit retirements as a potential BART option, neither rule prohibits
states or EPA from considering a shutdown as part of a BART
determination if the strategy is proposed by the owner of a BART-
eligible source.''
---------------------------------------------------------------------------

    Comment: General opposition to EPA's ``better than BART''
determinations.
    One commenter stated that EPA may approve an alternative to BART
only under certain limited circumstances, with the fundamental legal
requirement being a demonstration that the alternative will ``achieve
greater reasonable progress toward natural visibility conditions'' as
supported by the clear weight of evidence. The commenter indicated that
there are two ways EPA can make such a

demonstration: (1) Showing that the distribution of emissions is
substantially similar under BART and the alternative measure, and that
the alternative measure provides greater emissions reductions; or (2)
performing modeling to demonstrate that visibility does not decline in
any affected Class I area and there is an overall improvement in
visibility. The commenter stated that the EPA may not use the first
prong of the above test because the TWG Alternative distributes
emissions over time differently than BART. Because the TWG Alternative
also results in reductions of SO2 and PM, the commenter
states that the pollutants reduced are also distributed differently.
The commenter added that a BART alternative must ensure that all
necessary emission reductions occur in the first planning period, which
ends in 2018, and that any emission reductions resulting from the
alternative measure must be surplus to reductions required under other
provisions of the CAA.
    Response: EPA disagrees with the commenter's statement that the TWG
Alternative fails to demonstrate that it will ``achieve greater
reasonable progress toward natural visibility conditions.'' As
explained below, we disagree with the various comments underlying the
argument that our framework for analyzing the TWG Alternative is
flawed.
    EPA appropriately focused on a comparison of the emissions
reductions from BART and the TWG Alternative, rather than using
visibility modeling to compare the two approaches. As the commenter
noted, EPA's regulations provide a specific two-pronged test that may
be used to demonstrate that a BART alternative achieves greater
reasonable progress. In this rulemaking, EPA has applied the first
prong of that test to demonstrate that the TWG Alternative provides for
greater reasonable progress. The first prong of the test, set out in 40
CFR 51.308(e), states that if the distribution of emissions is not
substantially different under BART and the alternative, and ``the
alternative measure results in greater emission reductions,'' the
alternative may be deemed to achieve greater reasonable progress.
Because both BART and the TWG Alternative apply to the same source the
geographic distribution of emissions is similar.\110\ EPA therefore
applied this test to determine whether the TWG Alternative provided for
greater reasonable progress, taking into account total NOX
emissions over the 2009 to 2044 period from both BART and the TWG
Alternative.
---------------------------------------------------------------------------

    \110\ In providing states with the flexibility to adopt
alternative measures in lieu of BART, EPA assumed that under the
BART alternative provisions, states would most likely adopt a
trading program rather source specific BART controls. See, e.g., 40
CFR 308(e) (a regional haze SIP must contain BART limits unless the
State demonstrates that ``an emissions trading program or other
alternative will achieve greater reasonable progress. . .''). The
geographic distribution of emissions under a trading program is
unlikely to be similar to that under source-specific BART. In
contrast, the geographic distribution of emissions under a ``better
than BART'' alternative that applies only to the BART source in
question would be similar.
---------------------------------------------------------------------------

    The commenter argues, however, that the emissions must be
temporally similar in order for this test to apply. When EPA added
Sec.  51.308(e)(3) to the regional haze regulations in 2005, however,
we made clear that EPA intended this test to apply where the geographic
distribution of emissions between the BART and an alternative were
similar.\111\ This approach is reasonable, as visibility modeling is
not needed to demonstrate that a greater reduction in emissions from a
source will result in greater visibility benefits than a lesser
reduction in emissions from the same source. Accordingly, to the extent
that the regulations are not clear that the test applies where the
geographic distribution of emissions is similar, our interpretation is
a reasonable one. In concluding that this test is the appropriate one
to apply, EPA is not ignoring the commenter's argument that the TWG
Alternative distributes emissions over time very differently than would
BART, and that in the near term, visibility would improve more rapidly
if EPA were to require the installation of BART controls sooner. It is
not necessary to model the visibility impacts of the TWG Alternative
and BART, however, to reach that conclusion.\112\
---------------------------------------------------------------------------

    \111\ 70 FR 39136.
    \112\ Although the commenter argues that visibility modeling is
required to demonstrate that the TWG Alternative makes greater
reasonable progress, the commenter notes only in passing the second
test set out in the regulations at 40 CFR 51.308(e)(3) governing
situations where BART and a BART alternative will result in
dissimilar distributions of emissions. In such situations, greater
reasonable progress may be shown if visibility modeling shows that
(i) visibility does not decline in any Class I area, and (ii) there
is an overall improvement in visibility by comparing the average
differences between BART and the alternative over all affected Class
I areas. Even absent visibility modeling, it seems clear that the
TWG Alternative, which requires NGS to reduce emissions from current
levels, will not cause visibility to decline in any Class I area.
Visibility modeling done by EPA in response to comments regarding
the limited benefits of SO2 and PM reductions suggests
that the TWG Alternative also passes the second half of this test.
As explained in the RTC, EPA modeled the visibility impacts of TWG
Alternatives A1, A2, and A3 (the operating scenarios that include
reductions in alternative pollutants). See RTC for further
discussion. This modeling shows that the cumulative visibility
benefits of the TWG Alternative outweigh those associated with BART.
Although we have not modeled the visibility impacts of Alternative
B, compliance with the 2009-2044 and 2009-2029 NOX Caps
will require NGS to achieve emission reductions similar to those
required under Alternative A1 because the 2009-2029 NOX
Cap is based on emissions that would be expected to occur under
Alternative A1 (closure of one unit in 2019) and the 2009-2044
NOX Cap applies to all alternatives under the TWG
Alternative.
---------------------------------------------------------------------------

    EPA is accordingly determining that the provisions for retiring
capacity and installing SCR under the TWG Alternative achieve a similar
geographic distribution of emissions and that the appropriate test to
apply is whether the alternative provides for greater emissions
reductions than BART. In applying that test, EPA considers it
reasonable to consider the cumulative emissions under BART and the BART
alternative, rather than to simply compare annual emissions in some
future year under the two scenarios. This approach provides a
reasonable mechanism to give credit to NGS for its early reduction in
NOX emissions from the installation of combustion controls.
    The commenter also objects to EPA's decision to approve a BART
alternative that will not be fully implemented by 2018. EPA agrees that
the regional haze rule requires BART alternatives to be fully
implemented by states by 2018, the end of the first planning period for
states that were required to submit regional haze plans.\113\ As noted
in the Proposed Rule, given the deadline for the submittal of regional
haze SIPs, EPA's regulations accordingly built in an additional five
years beyond the BART compliance date for the implementation of BART
alternatives.\114\
---------------------------------------------------------------------------

    \113\ 40 CFR 51.308(e)(2)(iii).
    \114\ 78 FR 8288.
---------------------------------------------------------------------------

    We note that in this action, although the TWG Alternative will not
be fully implemented until 2044, NOX emissions from NGS have
already declined from historical levels, and significant additional
declines in emissions are expected in 2019 and again in 2030.
Nonetheless, we acknowledge that we are looking forward to 2044 for
full implementation of the TWG alternative, well beyond the 2018 date
in the RHR. We explained the basis for our proposed decision to set the
compliance period for the TWG Alternative in the Supplemental Proposal.
EPA's reasoning on this issue is grounded in CAA section 301 and the
TAR. The TAR generally exempted Tribes from the CAA submittal deadlines
that applied to States. EPA interprets the requirement in 40 CFR
51.308(e)(2)(iii) to constitute a reasonably severable RHR submittal
deadline that applies to States but not

to Tribes. If the alternative measure is promulgated by the State, it
must ``submit[s] an implementation plan containing the following plan
elements and include[s] documentation for all required analyses: . . .
(iii) A requirement that all necessary emission reductions take place
during the period of the first long-term strategy for regional haze.''
Therefore, it is a required ``plan element'' for a State-only required
implementation plan submittal. See 40 CFR 51.308(b)(3) (requirements
for States to submit long-term strategies). Because it is not mandatory
for the Tribe to submit a long-term strategy, there is no mandatory
requirement for the Tribe to ensure that all emissions reductions from
a better than BART alternative occur within some deadline.
    This result is equitable as well as reasonable. States were
required to submit SIPs in 2007, allowing 11 years for a ``better than
BART'' alternative to be achieved in 2018. Because this is a FIP for a
source in Indian country, and we are only now implementing the
requirement in 2014, it is equitable to extend the compliance time as
well. Please see the RTC for a more detailed discussion.
    In summary, EPA is determining that the TWG Alternative is ``better
than BART'' based on achieving greater NOX emissions
reductions over a similar geographic distribution, within the date of
the goal specified in the RHR of achieving natural conditions in 2064.
Given the requirement to cease conventional coal-fired generation at
NGS in 2044, and with cumulative emissions over 2009 to 2044 being less
than the BART Benchmark, the TWG Alternative satisfies the requirements
of the RHR with respect to NOX BART as applied to Navajo
Nation based on the TAR.
    Comment: EPA overestimated the BART Benchmark.
    Aside from its assertions that an approach using a BART Benchmark
based on total emissions is not lawful under the CAA, one commenter (an
organization representing itself and several other non-governmental
organizations) stated that EPA's assumptions in calculating a numerical
value for the BART Benchmark included errors and improper credits.
Specifically, the commenter asserted that: (1) EPA's credit for the
early installation of LNB/SOFA runs counter to the Regional Haze Rule,
EPA's longstanding policies, and EPA's specific statements regarding
the haze determination for NGS, (2) EPA's proposal to delay BART due to
the LNB/SOFA credit creates a dangerous precedent that threatens to
significantly undermine the regional haze program, (3) EPA made a
number of errors in its calculations that all have the effect of
artificially inflating the BART Benchmark. The specific errors
purported by the commenter are outlined in more detail in the RTC. The
commenter asserts that in total, assuming a final rule by July 1, 2014,
their recommended revisions to the BART Benchmark would reduce the
estimated emissions under BART during EPA's chosen timeframe (2009-
2044) by nearly 100,000 tons, a reduction of approximately 26 percent.
The commenter asserted that if EPA persists in using the emission cap
framework, EPA must correct the NOX cap to prevent
alternatives from being compared to an artificially inflated estimate
of total NOX emissions.
    Response: EPA disagrees with the assertion that we are delaying
BART. As stated elsewhere in the RTC, as well as in our Proposed Rule
and Supplemental Proposal, EPA did not propose to ``delay BART.'' EPA
proposed to provide additional flexibility in the compliance timeframe
for alternatives to BART.\115\
---------------------------------------------------------------------------

    \115\ See 78 FR 8288, column 1, describing our proposed BART
determination. See also 78 FR 8289, section titled ``Legal Rationale
for Extending Compliance Schedule for Alternative Measures for
NGS.''
---------------------------------------------------------------------------

    The commenter alleges that ``EPA's claimed reliance on ``early''
LNB/SOFA as an excuse to avoid or delay what is legally required is
misplaced and without foundation in the facts or law.'' \116\ The
commenter cites three sources to support its assertion that the LNB/
SOFA credit runs counter to the RHR and EPA's long-standing policies:
(1) Page 18 of a report written by Victoria Stamper (Stamper Report),
which was commissioned by the commenter and submitted as part of its
comments,\117\ (2) page 35728 of the July 1, 1999 Regional Haze Rule,
and (3) section IV.D.4.d of the BART Guidelines.\118\ EPA disagrees
with these assertions.
---------------------------------------------------------------------------

    \116\ See page 22 of the EarthJustice comment letter dated
January 3, 2014 (document 0367 in the docket for this rule).
    \117\ See document number 0372 in the docket for this rule.
    \118\ Id. page 21.
---------------------------------------------------------------------------

    First, the commenter's use of quotation marks around the word
``early'' implies that the LNB/SOFA modifications were not, as a
factual matter, installed early. However, EPA notes that in 2008, when
the operator of NGS began discussions with EPA regarding the permitting
requirements associated with the significant increase in carbon
monoxide (CO) emissions that would result from the installation of LNB/
SOFA, EPA had already begun our process for evaluating BART for NGS,
but had not yet proposed a BART determination or put forth our ANPR.
Therefore, no requirement existed that mandated the installation of
LNB/SOFA at NGS. In addition, the operator of NGS was aware that a BART
determination, that would likely involve but may not be limited to LNB/
SOFA, was forthcoming. As noted in our Proposed Rule, the operator of
NGS could have waited until the compliance date for BART to initiate
any reductions in NOX emissions; however, the operator
elected in 2008 to seek the necessary permit to install LNB/SOFA on one
unit per year over 2009-2011.\119\ Thus, because the LNB/SOFA
modifications were made in 2009-2011, NOX emissions from NGS
declined from a high of over 35,000 tons in 2002 to less than 20,000
tons after 2011.\120\ Although some of the decline in total
NOX emissions can be attributed to a decrease in capacity
utilization (i.e., decline in heat input of approximately 13 percent
when comparing 2002 to 2013), the dominant contributor to the decline
in NOX emissions from NGS was from the installation of LNB/
SOFA over 2009-2011. EPA considers these emission reductions to be real
reductions that were not required (i.e., voluntary and surplus) and
were achieved in advance of any actual requirement to reduce emissions
(i.e., early).
---------------------------------------------------------------------------

    \119\ See Proposed Rule at 78 FR 8289 (February 5, 2013).
    \120\ See RTC and references therein. In 2011, NGS emitted
19,900 tons of NOX, in 2012, NGS emitted nearly 16,500
tons of NOX and in 2013, nearly 17,500 tons of
NOX.
---------------------------------------------------------------------------

    In addition, each of the three citations provided by the commenter
does not support its assertions that our proposal to credit NGS for the
early installation of LNB/SOFA runs counter to the Regional Haze Rule
or EPA's long-standing policies. These three citations merely address
the appropriate baseline period to use in the five-factor BART
analysis. Page 18 of the Stamper Report supports our use of 2001-2003
as the baseline period for our BART determination for NGS and cites to
64 FR 35728 of the July 1, 1999 Regional Haze Rule that discusses EPA's
determination that the most appropriate baseline period would be over
the 2001 to 2004 timeframe. The baseline period is used for evaluating
the costs and visibility benefits of controls. The Stamper Report also
cites Section IV.D.4.d of the BART Guidelines at 40 CFR Part 51
Appendix Y, that states baseline emissions should generally

represent a realistic depiction of anticipated emissions for the source
based on actual emissions from a baseline period.
    The commenter also cited the discussion in our Proposed Rule under
Factor 3, where we described, in 2008, how the early installation of
LNB/SOFA would not prejudice the implementation of more effective
controls for BART. As stated previously, we did not use the LNB/SOFA
credit to justify a less stringent determination of BART for NGS. The
commenter characterizes the credit as a shift in course from the
agreements and understandings established in 2008 during the PSD permit
process for the installation of LNB/SOFA. EPA disagrees. As stated in
our Proposed Rule, citing the Ambient Air Quality Impact Report from
the 2008 Proposed PSD Permit, EPA stated that the early installation of
LNB/SOFA systems would not affect the baselines for cost or visibility
improvements, and therefore will not influence EPA's determination of
the NOX reductions required for BART.\121\ EPA's BART
analysis for NGS was consistent with this statement. As previously
noted, EPA used the 2001-2003 period as the baseline for determining
cost-effectiveness and visibility benefits of controls, and determined,
based on our analysis of all five factors, that SCR+LNB/SOFA is an
appropriate BART Benchmark for NGS.
---------------------------------------------------------------------------

    \121\ See 78 FR 8284 (February 5, 2013).
---------------------------------------------------------------------------

    The commenter relies on EPA's statements about the appropriate
baseline period to support an assertion that in a BART analysis, EPA
should not give consideration or credit for controls installed after
the baseline period. As stated in section 5.0 of the RTC (section 5.0),
although we appropriately acknowledged the installation of LNB/SOFA
after the baseline period at NGS under Factor 3 (existing controls at
the facility), our analysis of cost-effectiveness and anticipated
visibility benefits appropriately compared SCR+LNB/SOFA against the
2001-2003 baseline period.\122\
---------------------------------------------------------------------------

    \122\ We note that in State of North Dakota v. EPA, the U.S.
Court of Appeals for the Eighth Circuit vacated and remanded EPA's
promulgation of a FIP for Coal Creek Station because EPA did not
consider the existing pollution control technologies in use at Coal
Creek Station that were voluntarily installed after the baseline
period. This document is included in the docket for this rule.
---------------------------------------------------------------------------

    EPA's proposed credit for early installation of LNB/SOFA was not
associated with our five-factor analysis or BART determination for NGS.
Rather, EPA discussed the LNB/SOFA credit in our framework for
evaluating alternatives to BART. Specifically, in discussing our
framework for BART Alternatives, EPA calculated the cumulative
NOX reductions achieved early because the operator of NGS
elected to install LNB/SOFA on one unit per year over 2009-2011,
instead of waiting for the compliance period for BART. In our Proposed
Rule and Supplemental Proposal we used this value, the LNB/SOFA credit,
when comparing BART Alternatives to BART. As discussed elsewhere in the
RTC, EPA's proposal to allow BART Alternatives to take credit for the
early installation of LNB/SOFA at NGS is a reasonable use of our
discretion under the TAR.\123\
---------------------------------------------------------------------------

    \123\ See 78 FR 62511 (October 22, 2013).
---------------------------------------------------------------------------

    EPA disagrees with the assertion that this credit creates a
dangerous precedent that threatens to significantly undermine the
regional haze program. EPA notes that part of our rationale for the
better than BART framework for NGS (including the credit for the early
installation of LNB/SOFA and the adjusted compliance timeframe for BART
Alternatives) was the potential impacts to numerous tribes that rely on
NGS and/or CAP, as well as EPA's regulations specifying that SIP
submittal deadlines that apply to states do not apply to Tribes (or to
EPA when implementing FIPs in Indian country). Further, EPA notes that
the relationship between NGS and CAP is unique, the only other BART-
eligible source in Indian country is the Four Corners Power Plant, and
EPA has already completed the BART determination and FIP for this
facility.\124\
---------------------------------------------------------------------------

    \124\ See 77 FR 51620 (August 24, 2012).
---------------------------------------------------------------------------

    EPA also disagrees with the assertion that we overestimated the
BART Benchmark and NOX Cap. The commenter argues that SCR
can meet a lower emission limit than proposed by EPA and that EPA
should have set a compliance date within 3.5 years. As discussed in
Section 8.1 of the RTC, EPA disagrees that the BART Benchmark should be
based on an emission limit of 0.040 lb/MMBtu and that compliance should
be required in 3.5 years. EPA is finalizing a BART Benchmark based on
our determination requiring NGS to meet a limit of 0.055 lb/MMBtu
within five years of the effective date of the Final Rule. Therefore,
EPA is not revising the BART Benchmark or NOX Cap to assume
a limit of 0.040 lb/MMBtu or a shorter compliance time for BART.
    In addition, the commenter recommends that EPA use average heat
input over the baseline period (i.e., over 2001-2003) rather than the
average over the pre-LNB/SOFA time period (i.e., average over 2001-
2008) to calculate future emissions. The commenter notes that our
calculations for cost-effectiveness use baseline heat input over 2001-
2003 to calculate pre- and post-control emissions (approximately 5,264
tons per year). The commenter asserts that this inconsistency is
arbitrary. The commenter correctly notes that EPA used the average heat
input over 2001-2008 (the pre-LNB/SOFA time period) to estimate
emissions over 2009-2019 that would have occurred if the operator of
NGS had not installed LNB/SOFA early, and emissions over 2019 to 2044
under BART (5,345 tons per year). The average heat input over the
baseline period of 2001-2003 was 191,505,266 MMBtu, while the average
heat input over 2001-2008 was 194,373,910 MMBtu. This is a difference
of about 1.5 percent. EPA agrees that use of the same 2001-2003
baseline heat input value for estimating pre- and post-control emission
rates is appropriate and consistent with the RHR and BART Guidelines,
particularly in light of the goal of understanding the effect of a
given control technology on emissions (i.e., assume identical values
for baseline and future heat input to isolate the impact of control
technologies). However, this approach does not mean that an average
from the three-year baseline period (2001-2003) is most appropriate for
estimating future emissions in determining the BART Benchmark. EPA
notes that the use of average heat input for 2001-2008 includes the
baseline period recommended by the commenters and provides a larger
data set, and therefore a more robust average value for estimating
future emissions. EPA considers the use of an average value based on
three years to be less robust than an average value based on eight
years of data for representing potential future operation; therefore,
EPA is retaining our use of the average heat input over 2001-2008 for
estimating emissions over 2009-2044. EPA further notes that emission
caps in permit requirements are typically established based on the
facility's potential to emit (PTE) and would thus be calculated using
maximum heat input values. The highest observed annual heat input value
was 199,398,687 MMBtu and, if used in the NOX cap, would
result in a significantly higher BART Benchmark.
    The commenter also argues that in calculating the NOX
cap, EPA should use a value that reflects an annual average for post-
control emission rates rather than a rate based on a 30-day average
limit of 0.055 lb/MMBtu. The commenter reviewed daily data from

2000 to 2013 and calculated the ratio of the maximum 30-day average
rate to the annual rate for each year and determined an average ratio
of 1.135. Based on this ratio, the commenter recommended that the BART
emission limit of 0.055 lb/MMBtu (on a rolling average of 30 boiler
operating days) be reduced by a factor of 1.135 as an estimate of what
the annual average post-control emission rate would be at NGS (i.e.,
0.048 lb/MMBtu). EPA agrees that generally, emission rates averaged
over an annual basis are lower than emission rates averaged over a 30-
day basis. However, EPA did not propose setting a BART limit for NGS on
an annual average basis and EPA did not receive any comments suggesting
that we do so. Without an enforceable annual limit, EPA considers it
inappropriate to assume a lower emission rate in our calculation of the
NOX Cap. We note that the BART Guidelines require that BART
limits for EGUs be set on a rolling average of 30 boiler operating
days. Therefore, although the BART Guidelines would not preclude
establishing multiple emission limits over different averaging periods,
the BART Guidelines do not require it.
    Separately, the commenter also asserts that EPA overestimated the
2009-2044 NOX Cap. The commenter represents EPA's
NOX Cap as the scenario it calls ``CAP-1'' with a value of
494,899 tons. This value is consistent with the 2009-2044
NOX Cap EPA proposed in our Supplemental Proposal.\125\ The
commenter asserts that this value is overestimated because (1) actual
heat input data should be used to calculate the NOX Cap; and
(2) the LNB/SOFA could be installed in two years.\126\ EPA disagrees
with these assertions.
---------------------------------------------------------------------------

    \125\ See Table 3 of our Supplemental Proposal at 78 FR 62516
(October 22, 2013).
    \126\ See Table 3 of the report written by Nathan Miller and
Raijit Sahu (Miller/Sahu Report) commissioned by the commenter and
submitted with its comments. See document number 0370 in the docket
for this rule.
---------------------------------------------------------------------------

    The commenter argues that for the period of 2009-2013, actual heat
input data should be used to calculate the NOX Cap instead
of the average heat input value over 2001-2008. EPA acknowledges that
actual heat input data is available for the 2009-2013 period; however,
EPA considers using the average value to be appropriate, recognizing
that years of lower than average capacity utilization will be balanced
with years of higher than average capacity utilization at NGS.
    The commenter also asserts that LNB/SOFA could have been required
in two years, on a separate compliance timeframe than installation of
SCR and that this should have been incorporated in our calculation of
the NOX Cap. EPA is not aware of any BART determination that
required combustion controls on a different schedule than post-
combustion controls. Although the commenter correctly notes that LNB/
SOFA was installed in three years (on one unit per year over 2009-
2011), EPA notes that the operator began the permitting process in 2008
and installed the LNB/SOFA during periods of major outage for each
unit, which occurs at NGS every six years for each unit.\127\ EPA
expects that it would not have been practicable to require installation
of LNB/SOFA within two years following the final rule because, in order
to accommodate one year for permitting, it would have required major
outages on all three units in the same year. Therefore, EPA does not
consider it practicable to assume the LNB/SOFA would or could have been
installed on a separate track from the SCR.
---------------------------------------------------------------------------

    \127\ See tab titled ``Outage Cycle'' in the document titled
``EPA Analysis of BART Alternatives'' in document number 0004 in the
docket for this rule.
---------------------------------------------------------------------------

    Although the commenter makes assertions related to purported
overestimations of the BART Benchmark and the 2009-2044 NOX
Cap separately, the commenter combines all of the assertions together
to argue that the 2009-2044 NOX Cap should be 373,029 tons
(121,870 tons, or 25 percent, lower than EPA's proposed 2009-2044
NOX Cap of 494,899 tons). As outlined above, EPA disagrees
than any of the purported corrections suggested by the commenter are
necessary or appropriate for projecting annual emissions to calculate
the 2009-2044 NOX Cap.
    Comment: EPA double-counted the benefits of LNB/SOFA.
    One commenter asserted that EPA double-counted the benefits of the
early installation of LNB/SOFA, stating that EPA calculated cumulative
emissions for the BART alternatives including the benefits of early
reductions, then subsequently applied a LNB/SOFA credit again to BART
alternatives.
    Response: EPA disagrees with the assertion that we double-counted
emission reductions associated with the early installation of LNB/SOFA.
    In our February 5, 2013 proposed rule, EPA calculated the value of
the LNB/SOFA credit based on the difference between total emissions
under the BART scenario where LNB/SOFA is installed concurrently with
SCR and the actual scenario when LNB/SOFA was installed early. The
value of this credit was then applied to total emissions over 2009-2044
under Alternative 1.\128\ Although our calculation of emissions under
Alternative 1 did account for actual emissions with early installation
of LNB/SOFA, and thus applying the LNB/SOFA credit to the BART
Alternative may appear to be double counting, it is not double-counting
because the BART Alternatives were compared against a BART Benchmark
that also accounted for actual emissions with early installation of
LNB/SOFA. Thus, both the BART Benchmark and Alternative 1 were
calculated the same way (actual emissions accounting for early LNB/SOFA
installation), and the LNB/SOFA credit was only applied to Alternative
1. An example of double-counting would have been if EPA had applied the
LNB/SOFA credit to cumulative emissions over 2009-2044 under
Alternative 1 and then compared that value to total emissions over the
same period under BART assuming LNB/SOFA and SCR were installed
concurrently.
---------------------------------------------------------------------------

    \128\ See document titled ``EPA Analysis of BART
Alternative.xlsx'' in document 0004 in the docket for the rule.
---------------------------------------------------------------------------

    In our October 22, 2013 Supplemental Proposal, EPA approached the
calculation from a different but equivalent perspective. The new
calculation approach was used because it was more intuitive to apply
and understand in the context of an enforceable cap on NOX
emissions. In the Supplemental Proposal, the BART Benchmark was
established as the total emissions over 2009-2044 that would have
occurred if LNB/SOFA and SCR were installed concurrently, five years
following the effective date of the final rule. Total emissions under
BART Alternatives were then calculated using actual emissions beginning
in 2009 (i.e., accounting for the early installation of LNB/SOFA) and
projections for future emissions. Thus, in the methodology used in the
Supplemental Proposal, the LNB/SOFA credit was applied to the BART
Benchmark and NOX Cap, rather than to the TWG Alternative.
This method is equivalent to the one used in the Proposed Rule but does
not give the appearance of double-counting. In our Supplemental
Proposal and supporting documents, EPA included calculations to show
that these two methods are equivalent.\129\ The two methods are
equivalent because what matters in the ``better than BART'' context is
the difference between total emissions under BART and total emissions
under

the BART Alternative. Whether the LNB/SOFA credit is applied to BART or
BART Alternatives will affect the absolute value of a total (e.g.,
using the numbers in Table 2 of the Supplemental Proposal, the LNB/SOFA
credit represents a difference of 377,008 tons or 480,489 tons), but it
does not affect the difference between BART and BART Alternatives. The
method used in the Supplemental Proposal is more intuitive because BART
and the BART Benchmark reflect total emissions over 2009-2044 that
would have occurred if LNB/SOFA were installed concurrently with SCR,
and the BART Alternatives reflect actual emissions without further
credit or modification. Because no credits or modifications are made to
actual emissions under the BART Alternatives, this method is the more
logical accounting methodology for determining compliance with the
2009-2044 NOX Cap.
---------------------------------------------------------------------------

    \129\ See Table 2 of the Supplemental Proposal (78 FR 62515,
October 22, 2013) and document number 0191 titled ``Supplemental
Better than BART Alterntives.xlsx'' in the docket for this rule.
---------------------------------------------------------------------------

    Comment: BART Alternatives would interfere with reasonable progress
goals in other states.
    One commenter stated delaying the compliance date for BART will
allow NGS to continue emitting pollutants in excess of the levels
modeled by the WRAP and will interfere with the ability of Arizona,
Utah, and Colorado to meet their reasonable progress goals for 2018.
    Response: The issue raised by the commenter is outside the scope of
our rulemaking addressing the NOX BART requirements for NGS.
Although 40 CFR 51.308(d)(3) requires states to submit long-term
strategies that are sufficient to ensure that the state has included
all measures needed to achieve its share of emission reductions agreed
to through the regional planning process, the Navajo Nation has not yet
submitted a long-term regional haze strategy. In addition, EPA has not
yet found it necessary or appropriate to address these requirements
through a FIP. If EPA determines it is necessary or appropriate to do
so, we will take appropriate action.
    Meanwhile, we note that for NGS, the WRAP assumed that
NOX emissions in 2018 would equal 10,611 tons per year.
NOX emissions under the TWG Alternative, in turn, will range
from approximately 13,000 to 15,000 tons per year following the closure
of one unit (or equivalent curtailment) at the end of 2019. We also
note that the closure of one unit (or equivalent curtailment) by the
end of 2019 would reduce not only NOX, but also emissions of
SO2. Given the overall changes in emissions from the various
regional haze actions since the WRAP made its projections, we will be
better able to assess the need, if any, for further action once
Arizona, Utah, and Colorado have prepared regional haze SIPs for the
second planning period.

J. Comments on the TWG Alternative and EPA's Supplemental Proposal

    Comment: Opposition to TWG Alternative because it is premised on
SCR as BART.
    One commenter argued that the 2009-2044 NOX Cap used for
the TWG Alternative is unduly and arbitrarily stringent because it is
based on a limit of 0.055 lb/MMBtu, which the commenter believes is too
stringent because (1) EPA should not have determined that SCR is BART
and (2) even if SCR were the appropriate basis for BART, 0.055 lb/MMBtu
is not achievable. The commenter stated that because Arizona
agricultural users will phase out their use of CAP Ag Pool water by
December 2030 pursuant to the 2004 Arizona Water Settlement Act (AWSA),
capital costs that are collected in advance of SCR operation will be
imposed on NIA users in exchange for no benefit. The commenter asserted
that if EPA finalizes either of the ``better than BART'' alternatives
without modification, it would be arbitrarily and capriciously
apportioning compliance costs to NIA water users for which they are not
responsible. Given EPA's acknowledgment of the compliance flexibility
that exists with respect to the TAR, the commenter believes that the
failure to consider potential ``better than BART'' alternatives that
would afford compliance flexibility to all NGS stakeholders on an
evenhanded basis constitutes an abuse of discretion on the part of EPA.
    Response: EPA disagrees with the assertion that the TWG Alternative
is unduly and arbitrarily stringent because it is based on a BART limit
of 0.055 lb/MMBtu. We consider the limit of 0.055 lb/MMBtu to
appropriate for establishing the BART Benchmark for NGS. EPA addressed
specific comments related to the BART limit in section 8.1 of the RTC.
We also note that the TWG Alternative was developed as an agreement
between diverse stakeholders, including SRP, the operator of NGS on
behalf of itself and other co-owners, and the CAWCD. Although both
entities submitted comments in opposition to the proposed BART limit of
0.055 lb/MMBtu, both parties signed the TWG Agreement that establishes
the NOX Cap based on the proposed BART limit of 0.055 lb/
MMBtu.
    The commenters indicate that their access to CAP Ag Pool water is
expected to end in 2030, and assert that the timeframes for compliance
with the limit of 0.07 lb/MMBtu in 2030 would necessitate water rate
increases prior to 2030. The commenter asserts that it is arbitrary and
capricious for NIA water users to pay a few years of higher CAP water
rates for controls that will not be operational until after their
access to the CAP Ag Pool expires. EPA notes that the direct impact of
compliance with the limit of 0.07 lb/MMBtu in 2030 under the TWG
Agreement, presumably with installation and operation of SCR, would be
on the cost of electricity generation. Increasing water rates are
indirect impacts that result from the relationship between NGS and CAP.
EPA does not set or determine water rates charged by CAWCD to the CAP
Ag Pool or any other classes of CAP customers. EPA's proposed and final
approval of requirements consistent with the TWG Agreement as a
``better than BART'' alternative is based on our review of the
anticipated emission reductions associated with the TWG Alternative
compared to BART. Although EPA, DOI, and DOE have committed to work
together on many issues related to NGS, including funding for the
federal portion of capital improvements at NGS, EPA does not determine
how controls would be financed and how and when electricity or water
rates would be adjusted to recover costs.
    Comment: TWG Alternative does not fully meet EPA's obligations to
the Gila River Indian Community.
    The Gila River Indian Community said that even though it fully
supports the TWG Alternative, it is concerned that EPA has not met its
obligations to the Community because of the significant costs on NGS
and associated impacts on the Community. Rather, the commenter views
the TWG Alternative as the first step in a process that will limit the
impacts on the Community because only under the TWG Alternative will
key U.S. commitments contained in the TWG Agreement be realized.
Specifically, under the TWG Agreement, and as outlined by the
commenter, DOI will work with the Community and other tribes in the
area around NGS, to evaluate the actual impacts the regulatory
requirements will have on NGS over time. The commenter specifically
referred to the U.S. commitment to allocate $10 million annually for 10
years starting in 2020, from the Reclamation Water Settlements Fund to
reduce impacts to the Development Fund.
    Response: EPA acknowledges the comment and is aware that costs
associated with implementing the TWG Alternative will have implications
for numerous Tribes, including the Gila

River Indian Community. EPA is committed to continuing to work with the
Department of the Interior and the Department of Energy in the
Interagency Working Group on NGS, as laid out in the Joint Statement
signed in January 2013 by the heads of the three agencies, to work with
tribes to address long-term issues related to NGS. The provisions in
the TWG Agreement that are not related to EPA's authority to evaluate
BART or a ``better than BART'' alternative, however, are beyond the
scope of this rulemaking.
    Comment: TWG Alternative is vague and unenforceable.
    One commenter stated that a BART determination must include clear
requirements for emissions reductions and a clear timeline for those
reductions, to ensure continuing visibility improvements in Class I
areas. The commenter indicated that without specific emission limits
and/or commitments to retire specific amounts of capacity from specific
units, as of a date certain, it is impossible to calculate the
visibility improvements that will result from the TWG Alternative,
particularly TWG Alternatives A3 and B, and it will be impossible for
individuals or EPA to assess whether NGS is on track to meet the
emission reductions necessary to ensure reasonable progress toward
natural visibility in affected Class I areas.
    Response: EPA disagrees with the assertion that the TWG Alternative
is vague and unenforceable. EPA acknowledges that the TWG Alternative
provides flexibility in a manner that appears complex. This complexity
is a result of the role future ownership outcomes will have in
determining the most reasonable compliance options in the future. Once
the ownership issues are resolved, the scope of options under the TWG
Alternative narrows. Although some flexibility still remains in the TWG
Alternative, particularly under TWG Alternative B, the options for
future operation of NGS are bounded by the limitations provided by the
2009-2044 and 2009-2029 NOX Caps.
    Contrary to the assertions by commenters, EPA included proposed
regulatory language in our Supplemental Proposal that provided specific
and enforceable timelines for achieving emission reductions under the
TWG Alternative. The proposed language under 40 CFR 49.5513(j)(3)(i),
``Operating Scenarios to Comply with 2009-2044 NOX Cap,''
defines the timeframes and requirements under TWG Alternatives A1, A2,
A3, and B, all of which must be implemented in a manner that ensures
total NOX emissions over 2009-2044 remain below the 2009-
2044 NOX Cap. Specifically, Sec.  49.5513(j)(3)(i)(A)
defines Alternative A1, and specifies the following requirements: (1)
By December 31, 2019, the owner/operator shall permanently cease
operation of one coal-fired unit and (2) by December 31, 2030, the
owner/operator shall comply with a NOX emission limit of
0.07 lb/MMBtu on each of the two remaining coal-fired units.
Alternative A1 is the simplest of the possible operating scenarios
under the TWG Alternative and Sec.  49.5513(j)(3)(ii)(A) specifies that
Alternative A1 applies under three potential future ownership
possibilities.
    TWG Alternative A2 is defined in Sec.  49.5513(j)(3)(i)(B) and
requires (1) by December 31, 2019, the owner/operator shall permanently
cease operation of one coal-fired unit, and (2) by December 31, 2019,
the owner/operator may elect to increase net generating capacity of the
remaining two coal-fired units by a combined total of no more than 189
MW. The actual increase in net generating capacity shall be limited to
the sum of 19 MW and the ownership interest, in net MW capacity of up
to 170 MW, purchased by the Navajo Nation by December 31, 2019. The
owner/operator shall ensure that any increase in the net generating
capacity is in compliance with all pre-construction permitting
requirements, as applicable, and (3) by December 31, 2030, the owner/
operator shall comply with a NOX emission limit of 0.07 lb/
MMBtu on each of the two remaining coal-fired units. The future
ownership possibilities that would trigger Alternative A2 are defined
in Sec.  49.5513(j)(3)(ii)(B).
    TWG Alternative A3 is defined in Sec.  49.5513(j)(3)(i)(C) and
requires (1) by December 31, 2019, the owner/operator shall reduce net
generating capacity of NGS by no less than 561 MW. The actual reduction
in net generating capacity of NGS shall be determined by the difference
between 731 MW and the ownership interest, in net MW capacity of up to
170 MW, purchased by the Navajo Nation by December 31, 2019, and (2) by
December 31, 2030, the owner/operator shall comply with a
NOX emission limit of 0.07 lb/MMBtu on two units. The future
ownership possibilities that would trigger Alternative A2 are defined
in Sec.  49.5513(j)(3)(ii)(C).
    TWG Alternative B is defined in Sec.  49.5513(j)(3)(i)(D) and
requires that in addition to the 2009-2044 NOX Cap, the
owner/operator shall ensure compliance with the 2009-2029
NOX Cap. The 2009-2044 NOX Cap is defined in
Sec.  49.5513(j)(2)(ii) as no more than 494,899 tons of NOX,
and the 2009-2029 NOX Cap is defined in Sec.
49.5513(j)(2)(i) as no more than 416,865 tons of NOX. The
2009-2029 NOX Cap is based on closure of one unit by
December 31, 2019 and the 2009-2044 NOX Cap is based on
compliance with the BART emission limit of 0.055 lb/MMBtu by July 1,
2019. The future ownership possibilities that would trigger Alternative
B are defined in Sec.  49.5513(j)(3)(ii)(D). As described in Sec.
49.5513(j)(4)(iv), if TWG Alternative B is triggered, the owner/
operator must submit annual Emission Reduction Plans that contain the
anticipated year-by-year emissions to ensure compliance with the 2009-
2029 and 2009-2044 NOX Caps.
    The commenter asserts that under the scenario of reduced capacity
(three units remain open, i.e., TWG Alternative A3), EPA ignored other
possible outcomes and simplistically assumed that two units would
continue to operate at full capacity with SCR and the unit whose
operation is curtailed would operate only with LNB/SOFA. The commenter
asserts that there is no guarantee that the operator will choose to
comply with TWG Alternative A3 in this manner. Although this specific
arrangement under TWG Alternative A3 is not required, EPA disagrees
that nothing compels the operator to comply with this operating
scenario in a manner that reduces emissions comparably with the
assumption that two units would operate at full capacity with SCR and
the unit that is curtailed would operate with LNB/SOFA. EPA notes that
under TWG Alternative A3, as well as all other TWG Alternatives, the
owner/operator must operate the units at NGS so that total emissions
remain below the 2009-2044 NOX Cap (as well as the 2009-2029
NOX Cap under Alternative B). For example, under TWG
Alternative A3, if the operator chose to curtail all three units by a
total of 561 MW equally and comply with a limit of 0.07 lb/MMBtu on two
units and 0.24 lb/MMBtu on one unit, total emissions over 2009-2044 are
not likely to comply with the 2009-2044 NOX Cap.\130\ Thus,
the operator would be prohibited from operating in this manner and
would need to, for example, significantly curtail operations to reduce
emissions further, or risk violating the FIP.
---------------------------------------------------------------------------

    \130\ See RTC and references therein.
---------------------------------------------------------------------------

    As noted in our Supplemental Proposal, EPA estimated total
NOX emissions over 2009-2044 for TWG Alternatives A1, A2,
and A3 to provide assurance that the owner/operator could reasonably
meet the 2009-2044 NOX Cap under the specific terms of those
alternatives. EPA does not need to

determine that all operating possibilities that are consistent with the
requirements of TWG Alternative A1, A2, and A3 would also meet the
2009-2044 NOX Cap. The regulatory requirements EPA is
finalizing for the TWG Alternative provide specific dates on which the
owner/operator must close a unit, curtail operations, and meet emission
limits. While there is some flexibility in how emissions might be
curtailed under TWG Alternative A3, the 2009-2044 NOX Cap
ensures that the operator does not implement a strategy that results in
substantially more emissions than would be achieved by installing SCR
on the two units that are operated at full capacity and curtailing
operations on the unit that was not retrofit with SCR.
    The commenter asserts that there are an infinite number of ways the
operator could comply with the 2009-2029 and 2009-2044 NOX
Caps under TWG Alternative B. The commenter further states that the two
possibilities EPA considered in our Supplemental Proposal are not
likely to be the outcomes under TWG Alternative B. EPA agrees that TWG
Alternative B provides more flexibility than TWG Alternative A.
However, EPA disagrees that TWG Alternative B is so open-ended that it
would not be enforceable or result in emission reductions at NGS. We
note that the 2009-2029 NOX Cap was calculated based on the
closure of one unit with no additional increase in capacity (i.e.,
equivalent to emissions under TWG Alternative A1). Thus, the operator
cannot maintain the status quo (operation of all three units at full
capacity at a limit of 0.24 lb/MMBtu) and meet the 2009-2029
NOX Cap. We recognize that several commenters are concerned
about the flexibility under TWG Alternative B. However, as discussed
further in the RTC, we note that the range of possible operating
choices for TWG Alternative B is substantially constrained by the
requirement to comply with the 2009-2029 and 2009-2044 NOX
Caps.
    Although we disagree with commenters that the TWG Alternative is
vague and unenforceable, in response to the concerns expressed by these
commenters, to provide additional assurance that cumulative emissions
of NOX from NGS under the TWG Alternative will not exceed
the BART Benchmark, EPA is adding the following provisions to the Final
Rule. Under all Alternatives, if cumulative emissions of NOX
from NGS exceed the 2009-2044 NOX Cap prior to 2044, the
operator of NGS must permanently cease operation of NGS. In addition,
under Alternative B, if cumulative emissions of NOX exceed
the 2009-2029 NOX Cap prior to 2029, the operator of NGS
must temporarily cease operation of all units at NGS.\131\
---------------------------------------------------------------------------

    \131\ The combination of the 2009-2044 and 2009-2029
NOX Caps under TWG Alternative B means that if NGS
exceeds the 2009-2029 NOX Cap prior to 2029 it must cease
operation, but the operator may re-start operation after 2030 as
long as cumulative emissions have not yet exceeded the 2009-2044
NOX Cap.
---------------------------------------------------------------------------

    One commenter asserted that EPA was incorrect to claim that the TWG
Alternative would absolve NGS of obligations related to a Reasonably
Attributable Visibility Impairment (RAVI) finding that may be made for
NGS.\132\ EPA disagrees that we claimed that the TWG Alternative would
absolve NGS of obligations related to RAVI. The commenter cited to
footnote 21 in our Supplemental Proposal.\133\ In that footnote, we
acknowledged that the TWG had intended their alternative to satisfy
both the ``better than BART'' requirements of the RHR as well as any
requirements of the RAVI program. Our footnote merely noted that there
was no outstanding petition to certify impairment from NGS at any Class
I area and outlined the process and requirements for triggering a BART
determination under RAVI. Although we stated that a BART determination
under RAVI would likely be the same as a BART determination under
regional haze (i.e., an analysis of the five factors listed in the
CAA), EPA did not make any conclusions or absolve NGS of any
obligations related to RAVI because there is currently no action before
EPA to make an attribution finding related to NGS.
---------------------------------------------------------------------------

    \132\ See EarthJustice letter, page 10, footnote 25.
    \133\ See Supplemental Proposal, 78 FR 62513, footnote 21
(October 22, 2013).
---------------------------------------------------------------------------

    EPA is finalizing the requirements of the TWG Alternative,
consistent with Appendix B of the TWG Agreement, which require, among
other things, emission reductions in 2019 and 2030. EPA is also adding
as an enforceable requirement, the commitment from the TWG Agreement to
cease conventional coal-fired electricity generation at NGS by 2044.
EPA considers these timeframes to be consistent with the stated goal of
section 169A of the CAA. EPA has addressed comments regarding
consistency with EPA's regulations, including the RHR and the TAR, in
section 8.5 of the RTC.
    Comment: Additional concerns with TWG Alternative.
    The Hopi Tribe indicated that it has serious concerns with the
proposed TWG Alternative for several reasons, including because the TWG
Alternative does not specify the technology, i.e., either SCR or an
equivalent that will be used to achieve the same level of
NOX reductions as the BART proposal. The commenter states
the TWG Alternative is ambiguous because both scenarios are vague and
do not include the same level of assurance that the NOX
reductions will be the same as under the BART proposal. Also, because
the time NGS would be permitted to operate without SCR (or equivalent
alternative) would be adjusted under the TWG Alternative, the commenter
believes the TWG Alternative jeopardizes the goal of the CAA and the
purpose of this regulation.
    Response: Our proposed BART determination did not specify what
technology must be used because BART is defined as an emission limit
that represents the level of control representing BART, not a
particular technology. Thus, our Proposed Rule and the Supplemental
Proposal both imposed emission limits for NOX. The limits
for BART (0.055 lb/MMBtu) and the TWG Alternative (0.07 lb/MMBtu) are
based on what is achievable using a specific technology. Both limits
are achievable with SCR, but the operator may consider using newer
technologies, if available, as long as each unit complies with its
applicable emission limit by its compliance date. The commenter also
noted that the extended period for compliance under the TWG Alternative
may jeopardize the goal of the CAA and the purpose of the RHR. Under
section 169A of the CAA and the RHR, the goal of restoring visibility
in Class I areas to natural conditions is set for 2064.\134\
---------------------------------------------------------------------------

    \134\ 40 CFR 51.308(d).
---------------------------------------------------------------------------

    Comment: ``Arbitrary'' 2044 end date.
    One commenter stated that the 2009-2044 period analyzed for the TWG
Alternative is arbitrary because it is quite likely that one or more
NGS units will operate beyond that time frame. The commenter asserted
that if NGS units continue to operate for even 3 additional years,
until 2047, the TWG Alternative permits outcomes that will result in
greater total NOX emissions than the 2009-2044
NOX Cap.
    Response: EPA disagrees with the comment that the 2044 end date for
the NOX Cap is arbitrary. EPA used 2044 as the end date in
our calculations of the BART Benchmark. We selected 2009-2044 as most
appropriate because it includes the early installation dates for LNB/
SOFA and extends until the anticipated 2044 termination date of the
renewed site lease that was approved by the Navajo Nation.\135\ Under
the TWG

Agreement signed by six entities including the Navajo Nation and SRP,
the NGS Co-Tenants shall cease their operation of conventional coal-
fired generating at NGS no later than December 22, 2044. At its
election, consistent with the Lease Amendment, the Navajo Nation may
continue plant operations at NGS after December 22, 2044 consistent
with EPA approval.\136\ Thus, the Navajo Nation may seek to operate NGS
after 2044, however, EPA expects that operation of NGS after the owners
cease conventional coal-fired generation would involve substantial
modification to NGS and NGS would be required to meet all applicable
regulatory and permitting requirements in existence at that time. To
make this end date federally-enforceable, EPA is adding it as a
requirement to the regulatory language in today's final action. EPA is
adding the regulatory language in the Final Rule under 40 CFR
49.5513(j)(3)(iii) stating that by December 22, 2044, the owner/
operator shall permanently cease operation of all coal-fired units at
NGS. At its election, the Navajo Nation may continue plant operation at
NGS after December 22, 2044, consistent with EPA approval under the New
Source Review program.
---------------------------------------------------------------------------

    \135\ See Footnote 60 in the Proposed Rule, 78 FR 8290 (February
5, 2013).
    \136\ See Section VII.F of the TWG Agreement (page 14).
---------------------------------------------------------------------------

    Comment: Emissions under the TWG Alternative.
    One commenter stated that neither EPA nor TWG have provided a
comprehensive technical analysis of the emissions that are possible
under the TWG Alternative. The commenter asserted that it is EPA's
responsibility to provide an administrative record that contains
comprehensive modeling and analysis for any BART proposal, but EPA left
this critical component of the alternatives analysis undone.
    The commenter provided its own calculations of emissions under TWG
Alternative A and B and compared those estimates with its own
calculation of a NOX Cap and BART Benchmark, and concluded
that cumulative emissions from possible scenarios under the TWG
Alternative are not lower than its NOX Cap or BART
Benchmark.
    Response: EPA disagrees with the comment that we have failed to
provide a comprehensive technical analysis of the TWG Alternative. We
also disagree with the assertion that our administrative record for
this rulemaking is incomplete. As stated elsewhere in the RTC, EPA's
analysis of the TWG Alternative is consistent with the required
analyses for alternatives to BART outlined in the RHR.
    The comment relies on a report prepared by Nathan Miller and
Ranijit Sahu (Miller/Sahu) for the commenter contending that EPA's
evaluation of the TWG Alternative is incorrect. But the report changes
the central inputs underlying our calculations for BART and the TWG
Alternative. The specific technical reasons that we disagree with the
inputs that Miller/Sahu changed (e.g., NOX emissions limit
achievable with SCR, heat input values from baseline period, annual vs.
30-day emission rates) are explained in detail in section 8.5 of the
RTC.
    Table 2 in the Miller/Sahu report depicts BART-1 as ``EPA BART (No
Corrections),'' showing a value of 379,152 tons of cumulative
NOX emissions over 2009-2044 that is nowhere traceable to
EPA's documents.\137\ The Miller/Sahu report then makes several
``corrections'' to reach a value of 280,554 tons of NOX
emissions. EPA has explained in detail why we disagree with each of the
Miller/Sahu ``corrections'' in section 8.5 of the RTC and references
therein. For the reasons set forth in section 8.5, we also continue to
disagree that our calculation of the BART Benchmark or the
NOX Cap has relied on any incorrect inputs.
---------------------------------------------------------------------------

    \137\ Miller/Sahu Report, Table 2 at p. 7.
---------------------------------------------------------------------------

    Because we disagree with the ``corrections'' and the values
presented in the Miller/Sahu report, we also disagree with the
conclusions of Miller/Sahu that the TWG Alternative fails to satisfy
our requirements for demonstrating an alternative is ``better than
BART''. The commenter cannot change the fact that its alternative
preferences on the inputs for calculating BART are just preferences by
simply calling them ``corrections.''
    Comment: Visibility modeling under the TWG Alternative.
    One commenter stated that the TWG Alternative distributes emissions
over time very differently than BART: While BART would require
NOX reductions within 5 years, the bulk of the reductions in
the TWG Alternative might not come until the end of the 2009-2044
period. The commenter stated that the additional analysis and modeling
it conducted reveals that the TWG Alternative is likely substantially
worse than BART.
    Response: As discussed elsewhere in this document, because emission
reductions achieved under the TWG Alternative will have the same
geographic distribution as emission reductions under BART, EPA
disagrees that visibility modeling is required for our evaluation of
the TWG Alternative. We note that the commenter provided its own
visibility modeling and EPA disagrees with methodologies used and
conclusions drawn by the commenter.
    The Miller/Sahu Report compared anticipated visibility impacts from
the TWG Alternative against the anticipated visibility impacts based on
its own preferences for the NOX Cap and BART Benchmark.
Although the commenter asserts that its analysis shows that visibility
under the TWG Alternative is substantially worse than under its
preferences for the BART Benchmark and NOX Cap, their
analysis also shows that when the TWG Alternative is compared to the
BART Benchmark and NOX Cap as proposed by EPA, the TWG
Alternative scenarios it explored that meet the 2009-2044 and 2009-2029
NOX Caps (as applicable) generally result in lower or
comparable visibility impacts as BART.\138\
---------------------------------------------------------------------------

    \138\ See Exhibit 2 to the Miller/Sahu report and RTC and
references therein.
---------------------------------------------------------------------------

    EPA conducted visibility modeling to compare TWG Alternatives A1,
A2, and A3 in 2019 and 2030 against the BART Benchmark.\139\ As
indicated by commenters, other possibilities exist beyond the scenarios
for the TWG Alternatives we considered explicitly in our Supplemental
Proposal. EPA has stated elsewhere that we need not consider potential
emissions under all possible scenarios in setting the NOX
Cap, but must verify that NGS can reasonably be expected to comply with
2009-2044 NOX Cap under the various constraints imposed
under the TWG Alternatives (i.e., closure, curtailment, and a secondary
2009-2029 NOX cap). However, EPA explored two other
possibilities under TWG Alternative A3 that included reducing capacity
on all three units equally or reducing capacity on two units and
installing SCR on the two units that operate at reduced capacity.\140\
EPA did not include those two additional possibilities under TWG
Alternative A3 in our visibility modeling analysis because those
scenarios do not reduce emissions sufficiently to meet the 2009-2044
NOX Cap.
---------------------------------------------------------------------------

    \139\ See RTC and references therein.
    \140\ Id.
---------------------------------------------------------------------------

    Our visibility modeling of the TWG Alternatives compared to our
proposed BART determination shows that, as expected, during the
approximate 10-year period between 2019 and 2030, the visibility
impacts of NGS under the TWG Alternatives are higher than the
visibility impacts of NGS under BART. After 2030, when NGS achieves
additional emission reductions through compliance with a limit of 0.07
lb/

MMBtu on two units, our modeling indicates that the visibility impacts
under the TWG Alternatives are comparable to or lower than visibility
impacts under BART (see RTC for further detail). These results are not
surprising and mirror the comparative reduction in NOX
emissions under the TWG Alternatives and the BART Benchmark over time,
showing greater overall visibility improvement under the TWG
Alternative than under the BART Benchmark.
    As noted elsewhere in the RTC, EPA is including as part of the TWG
Alternative, in the regulatory language in the Final Rule, a provision
consistent with the TWG Agreement that the operator of NGS permanently
cease conventional coal-fired generation by the end of 2044. Thus,
under the TWG Alternative, the visibility impact of NGS is likely to be
zero or near zero in 2045 and thereafter.\141\ Under BART, there would
be no commitment or enforceable requirement to close after 2044,
therefore, visibility impacts of NGS at all 11 Class I areas would be
expected to continue in 2045 and thereafter.
---------------------------------------------------------------------------

    \141\ EPA expects that if the Navajo Nation elects to operate
NGS after the owners have ceased conventional coal-fired generation,
this would likely involve substantial modifications to NGS and NGS
would be subject to all applicable regulatory and permitting
requirements in existence at that time.
---------------------------------------------------------------------------

    Comment: Economic Impacts of the TWG Alternative.
    The Hopi Tribe expressed concern that EPA did not assess the
potential economic impacts of the TWG Alternative to the Hopi Tribe.
The commenter opined that EPA recognized the significance of NGS to the
Hopi Tribe in its analysis under Factor 2. Because the TWG Alternative
includes closure of at least one unit in 2019, and EPA did not address
the potential economic impacts of partial closure of NGS on the Hopi
Tribe, the commenter contended that the Agency has not complied with
the RHR and BART Guidelines. The Hopi Tribe noted that in the event
capacity is reduced at NGS under the Supplemental Proposal, the amount
of coal and water purchases from the Tribe would decrease leading to a
decrease in income to the tribe from the sale of these. The commenter
also stated that the Supplemental Proposal is not as effective in
improving air quality and visibility for the Hopi Reservation.
Extending the timeframe during which NGS can continue to operate
without SCR or an equivalent technology would cause a continued air
quality burden on the Hopi Tribe.
    Response: EPA recognizes that the TWG Alternative, which includes
closure of one unit at NGS or equivalent curtailment of operation, may
change the royalties and other payments related to coal and water that
are paid to the Hopi Tribe. Although EPA evaluated cost-effectiveness
and affordability of the options in our analysis of BART controls, we
disagree that we must also conduct an economic impact analysis for
alternatives to BART. The BART Guidelines provide little guidance on
the evaluation of alternatives to BART and the RHR does not require an
analysis of economic impacts of BART Alternatives. EPA's evaluation of
potential impacts to tribes in our analysis of BART controls was used
to inform our government-to-government consultation with tribes and is
consistent with BART. In addition, we have held numerous government-to-
government consultation meetings with tribes to discuss NGS during this
rulemaking. EPA continues to recognize the issues and concerns of
tribes located in Arizona regarding NGS and is committed to continuing
to work with our federal partners and the tribes through the Joint
Federal Agency Work Group on NGS to help address these issues.
    The Hopi Tribe also expressed concern that the TWG Alternative is
less effective than BART at improving air quality and visibility on the
Hopi Reservation. EPA notes that the purpose of the RHR is to reduce
visibility impairment at Class I areas; however, EPA disagrees that the
TWG Alternative is less effective than BART. Although the timeframe for
implementation of the TWG Alternative (new reductions in 2019 and 2030)
is longer than the timeframe for BART (in 2019), we note that BART
would only reduce emissions of NOX, whereas the TWG
Alternative, in 2019, would also reduce emissions of SO2,
PM, CO2, and hazardous air pollutants as a result of the
closure of one unit (or equivalent curtailment).
    Comment: Support for some changes EPA made to the TWG Agreement in
the Supplemental Proposal.
    The TWG noted that there were several differences between Appendix
B to the TWG Agreement and EPA's Supplemental Proposal of the TWG
Alternative. The commenters expressed support for some of the
differences, and expressed concern with others. One commenter agreed
with the methodology that EPA used to calculate the 2009-2044
NOX Cap of 494,899 tons.
    The commenter supported the additional requirement to report annual
heat input, although this information is already reported through the
Acid Rain Program. However, the commenters requested that additional
time be provided to ensure that the data submitted in the annual report
are consistent with the data that the NGS operator submits to the Clean
Air Markets Database (CAMD), in the annual emission inventory, and in
the greenhouse gas (GHG) report required by 40 CFR part 98, which are
not due until March 31st.
    Response: EPA recognizes that the TWG supports some of the changes
EPA made to Appendix B to the TWG Agreement, including EPA's revisions
to the 2009-2044 NOX Cap and the requirement to report
annual heat input. EPA agrees that it is reasonable to require the
timeframe for the reporting requirements under BART to generally be
more consistent with other reporting requirements. Therefore, EPA is
revising the regulatory language accordingly.
    Comment: Suggested addition to Sec. Sec.  49.5513(j)(4)(iv)(A) and
(B).
    The TWG requested that EPA clarify the scope and content of the
title V permit revision that is necessary to incorporate elements of
the BART alternative by adding the language from Appendix B of the TWG
Agreement to the requirements of the TWG Alternative.
    Response: EPA did not include the language from the TWG Agreement
related to the title V (part 71) operating permit in the regulatory
language in our Supplemental Proposal because the title V (part 71)
regulations require that the operating permits include all applicable
requirements, which for NGS would include the permit limits that exist
in its PSD permit (i.e., the limit of 0.24 lb/MMBtu when operating with
LNB/SOFA) as well as the final requirements in this FIP (e.g., the
limit of 0.07 lb/MMBtu on two units in 2030). Therefore, a specific
requirement in the FIP that directs the operating permit to incorporate
applicable requirements is not necessary. However, to the extent the
TWG requests consistency with the language in the TWG Agreement,
although EPA considers it unnecessary, EPA will amend Sec.
49.5513(j)(4)(iii) as suggested by the commenter.
    We further note that in the proposed regulatory language in our
Supplemental Proposal, EPA inadvertently did not specify an averaging
period for the emission limits under the TWG Alternative Operating
Scenarios (Sec.  49.5513(j)(3)). Therefore, EPA is adding to the
regulatory language that emission limits apply over a rolling average
of 30 boiler operating days, to 40 CFR Sec.  49.5513(j)(3),
(j)(3)(i)(A)(2), (j)(3)(i)(B)(3), and (j)(3)(i)(C)(2).
    Comment: Another suggested addition to Sec. Sec.
49.5513(j)(4)(iv)(A) and (B).

    The TWG stated that the Supplemental Proposal specified a
short[hyphen]term NOX limit of 0.07 lb/MMBtu for TWG
Alternative A, but not for Alternative B as was included in the TWG
Agreement.
    Response: EPA agrees that if the owners of NGS elect to install SCR
in order to comply with the applicable NOX Caps under TWG
Alternative B, then it is useful to specify the emission limit that
would apply. Although the limit of 0.07 lb/MMBtu (on a rolling average
basis of 30 boiler operating days) would apply under TWG Alternatives
A1, A2, A3, or B, EPA notes that the operator of NGS may need to
operate SCR at an emission rate that is lower than 0.07 lb/MMBtu
depending on their compliance with the NOX Cap, but the
addition of this provision would prohibit emissions of NOX,
when operating with SCR, to exceed 0.07 lb/MMBtu (on a rolling average
basis of 30 boiler operating days). EPA will amend the regulatory text
accordingly.
    Comment: Omitted ownership outcome.
    The TWG stated that the EPA described the NGS ownership outcomes in
a manner that is different from the scenarios outlined in the TWG
Agreement. The commenter indicated that the ownership outcomes appear
to be consistent, except that one potential outcome was omitted--the
scenario in which one or more of the existing NGS Participants (LADWP
or NV Energy) remain in NGS, which would trigger Alternative B.
    Response: EPA agrees that we inadvertently omitted from Sec.
49.5513(j)(3)(ii)(D) the potential scenario where one or both of the
Departing Participants (i.e., LADWP or NV Energy) do not exit NGS as
expected. EPA is updating the language to incorporate the omitted
ownership possibility.
    Comment: Describe details of TWG Agreement more fully in the
preamble to the Final Rule.
    The TWG expressed concern that EPA only briefly described the
elements of the TWG Agreement in the Supplemental Proposal. One member
of the TWG asserted that the limited discussion does not accurately
present the provisions of the Agreement as it relates to clean energy
economic development for affected Tribes, the rigorous development and
consideration of clean energy alternatives to NGS, mitigation of
CO2 emissions, and Local Benefit Fund to address concerns of
the public in the vicinity of NGS and the Kayenta-Black Mesa Mine
Complex. Should EPA proceed with this alternative in the Final Rule,
the commenter requested that the Agency fully describe the key elements
in the preamble to the Final Rule.
    Response: EPA acknowledges that the TWG Agreement contains
additional provisions that will be beneficial to the tribes in the area
and to the environment. However, EPA does not consider it appropriate
to provide a detailed discussion of these additional provisions of the
TWG Agreement in our Final Rule. EPA was not a signatory to the TWG
Agreement and did not participate in the TWG Stakeholder group. The TWG
Agreement speaks for itself and the participants and signatories are
the appropriate entities to interpret the provisions of the TWG
Agreement. EPA is finding that it is necessary or appropriate to
regulate NOX emissions from NGS to reduce visibility
impairment at the GCNP and 10 other Class I areas. The other measures
described by the commenter are outside the scope of our authority for
this action. Therefore, EPA is declining to provide any further
discussion of the provisions in the TWG Agreement that go beyond
addressing regional haze concerns associated with NOX
emissions from NGS.
    The comment also requests EPA to add certain language to the Final
Rule. Specifically, the comment asks EPA to add: ``Nothing in this
final rule shall preclude the NGS Participants from seeking to obtain
greenhouse gas emission reduction credits, or similar commodities
associated with activities committed to in the TWG Agreement, under any
Federal or State law or policy to the extent permitted under such
applicable law or policy.''
    EPA is also declining to add the requested language to our Final
Rule. EPA is not exercising any authority in this action other than
implementing the BART provisions in CAA section 169A and the RHR,
through our discretion in the TAR. It would be inappropriate in this
action to take any position on the future use or regulation of GHG
emission reductions or ``similar commodities.''
    Comment: TWG Alternative meets Reasonable Progress requirements.
    One member of the TWG stated that the TWG Alternative was intended
to meet not only BART requirements, but also reasonable progress
requirements applicable to NGS through 2044. The commenter requested
that EPA acknowledge, in the preamble to the Final Rule, that the TWG
Alternative satisfies both the BART and reasonable progress
requirements of the CAA through 2044.
    Response: Today's final rule addresses the NOX BART
requirements of the RHR for NGS. We have not considered whether the TWG
Alternative meets the reasonable progress requirements for NGS. We note
that EPA has not made any finding pursuant to 40 CFR 49.11(a) that it
is necessary or appropriate at this time to promulgate a FIP to meet
the reasonable progress or other requirements under the RHR. The
requirement for states to develop reasonable progress goals and long-
term strategies to achieve those goals is set out in CAA section 169A
and 40 CFR 51.308(d). There is no requirement that EPA address these
requirements for sources on the Navajo Nation unless EPA makes a
determination that it is necessary or appropriate for EPA to do so.
    Comment: Delete requirement to keep records of maintenance.
    One member of the TWG requested that EPA delete the requirement
that the NGS operator keep records of all major maintenance activities
that occur at NGS. According to the commenter, the existing title V
permit, which requires that the operator maintain and operate emission
control equipment in a manner that is consistent with good engineering
practices to keep emissions at or below applicable emissions
limitations, provides sufficient assurance that emission control
equipment will be operated and maintained in accordance with best
practices.
    Response: EPA is deleting the requirement proposed under Sec.
49.5513(j)(7)(vi) to require the operator of NGS to keep records of all
major maintenance activities at NGS because records of major
maintenance activities are not needed for demonstrating compliance with
the 2009-2044 or 2009-2029 NOX Caps or other provisions of
the TWG Alternative.
    Comment: Require recordkeeping for the life of the plant.
    One commenter indicated that the requirement to maintain records
for 5 years is insufficient and inappropriate for the compliance
schedule associated with NGS and recommended that records be maintained
from 2009 through the remaining operating life of the plant.
    Response: EPA agrees that because the operator of NGS must ensure
compliance with the 2009-2044 NOX Cap, the operator of NGS
should also maintain records for the life of the facility to
demonstrate compliance with the TWG Alternative. In the regulatory
language in our Final Rule, EPA is amending Sec.  49.5513(j)(7) to
require the owner or operator of each unit to maintain records, as
required under Sec.  49.5513(j)(7)(i) to (vi), until the earlier of
December 22, 2044 or the date that

the owners cease conventional coal-fired operation of all units at NGS.
    Comment: Concern that affected parties were excluded from TWG.
    Numerous commenters expressed frustration that all affected parties
were not included in the development of the TWG Alternative. The Hopi
Tribe noted that they have a Generating Performance Agreement with SRP
that should have mandated their involvement. The White Mountain Apache
Tribe also noted that it was not party to the TWG Agreement. Another
commenter noted that Executive Order (EO) 13175 requires that all
tribal nations be consulted on these types of regulations, and asserted
that EPA and DOI violated this EO. Another commenter argued that the
TWG did not include grassroots organizations and discouraged their
participation in TWG public forums.
    One commenter stated that the EPA did not give the public enough
time to comment on the TWG Alternative before proposing approval of it
and, on that basis, demanded that the EPA withdraw its proposed
approval. The commenter added that the TWG Agreement assumes that the
Hopi will support the Kayenta Mine Lease extension when it expires in
2025, but the Hopi have yet to discuss the extension with the 12 Hopi
independent villages, which is a requirement in the Hopi Constitution.
Furthermore, the commenter noted that the TWG Agreement ignores the
requirement of completing an EIS and ROD before the NGS site lease with
the Navajo Nation expires in 2019. The commenter argued that DOI's
signing of the TWG Agreement, without the fulfillment of these
requirements, violates NEPA. The commenter added that in 1989, the Hopi
Tribe rejected the Draft Kayenta Mine-Black Mesa Mine EIS in its
entirety, and implied that the decision to accept the TWG proposal
could compromise EPA's final decision.
    Response: EPA recognizes that there are affected tribes and other
stakeholders that were not invited to participate in the Technical Work
Group. EPA was not involved in the formation of the TWG and not
involved in any meetings or discussions of the TWG.\142\ As discussed
in section 10.0 of the Response to Comments document, consistent with
Executive Order 13175: Consultation and Coordination with Indian Tribal
Governments, EPA consulted with tribes early and regularly during the
development of this rulemaking for NGS. We note that the Regional
Administrator for Region 9 spoke with Chairman of the Hopi Tribe, LeRoy
Shingoitewa, on September 13, 2013 about the TWG Alternative and
notified elected leaders or legal counsel for five tribes when EPA
signed the Supplemental Proposal. EPA also held individual and joint
consultation meetings with tribal leaders in Phoenix, Arizona on
December 9 and 10, 2013.
---------------------------------------------------------------------------

    \142\ At the request of the TWG, at their kick-off meeting, EPA
presented a summary of our Proposed Rule and framework for BART
Alternatives. The presentation at the TWG kick-off meeting was
generally the same presentation EPA provided to other stakeholders.
See document 0033 in the docket for the rule.
---------------------------------------------------------------------------

    EPA disagrees that we did not provide the public enough time to
review the TWG Alternative. EPA posted the TWG Alternative to the
public docket on July 26, 2013, the same day it was submitted to
EPA.\143\ EPA reviewed the TWG Alternative and on September 25, 2013,
signed a Supplemental Proposal that put forth the TWG Alternative as an
additional better than BART alternative for public comment. On October
22, 2013, the Supplemental Proposal was published in the Federal
Register.\144\ The public had nearly six months to review the TWG
Agreement and Alternative as submitted to EPA and approximately three
months to review and comment on EPA's Supplemental Proposal. EPA also
notes that EPA's rulemaking is not subject to NEPA.
---------------------------------------------------------------------------

    \143\ See document number 0122 in the docket for this rule.
    \144\ See document number 0182 and 0186 in the docket for this
rule.
---------------------------------------------------------------------------

    Comment: EPA's relationship to the TWG is confusing.
    The White Mountain Apache Tribe stated that although EPA stated it
was not involved in the Technical Work Group, EPA was a signatory of
the ``Joint Federal Agency Statement Regarding Navajo Generating
Station,'' the scope of which includes numerous elements that reference
EPA's commitments, along with the Departments of the Interior and
Energy, in relation to NGS. The commenter suggests that EPA was
involved in a legal triangulation with the TWG signatories and that
such action is an extra-jurisdictional exercise by EPA, to which the
Tribe does not consent. The commenter concludes that the Tribe cannot
consider the TWG Alternative unless its published form is changed by
EPA to fully disentangle the proposal from the signatory group and all
non-BART Agreement terms, and additional public comment is thereafter
allowed.
    Response: We disagree that the Joint Federal Agency Statement
Regarding Navajo Generating Station indicates that EPA was involved in
the TWG. The Joint Federal Agency Statement was signed by the
Administrator of EPA and the Secretaries of the Interior and Energy on
January 4, 2013. Among other things, that document acknowledged that
each of the three federal agencies has an interest in the operation of
NGS and set forth the goals of the agencies with respect to NGS and
energy production in the region served by NGS.
    Although EPA clearly has an interest in reducing the visibility
impacts of NGS, EPA was not part of the TWG. EPA did not participate in
any of the substantive discussions and negotiations of the TWG. Two
representatives of EPA attended the beginning of the first meeting of
the TWG but only to present a summary of EPA's February 5, 2013
Proposed Rule.\145\ After the initial meeting, EPA was not involved
with the TWG until the TWG Agreement was completed. As such, EPA
disagrees with the commenter that EPA is ``entangled'' with the TWG.
---------------------------------------------------------------------------

    \145\ At the request of the TWG, at their kick-off meeting, EPA
presented a summary of our Proposed Rule and framework for BART
Alternatives. The presentation at the TWG kick-off meeting was
generally the same presentation EPA provided to other stakeholders.
See document 0033 in the docket for the rule.
---------------------------------------------------------------------------

    The TWG was not primarily composed of federal agencies. The TWG had
two Tribes (Gila River Indian Community and the Navajo Nation), two
environmental organizations (Environmental Defense Fund and Western
Resource Advocates), two Arizona utilities (CAWCD and SRP) and DOI.
Appendix B of the TWG Agreement contains provisions relating to BART
but there were several other provisions of the TWG Agreement that are
beyond the scope of BART and are not part of EPA's rulemaking in this
action.
    For all the above reasons, EPA does not agree with the assumption
underlying the comment that the White Mountain Apache Tribe ``cannot
consider the TWG Alternative unless its published form is changed by
EPA to fully disentangle the proposal from the signatory group and all
non-BART Agreement terms.'' EPA does not agree that any further public
comment is warranted.

K. Other BART Alternatives

    Comment: Suggested BART Alternative from EarthJustice.
    Despite its objections to the proposed BART alternatives, one
commenter suggested an alternative that includes (1) an enforceable
requirement that one NGS unit shut down by 2020 and (2) an enforceable
requirement that the remaining two units install SCR and meet a
NOX emission limit of 0.065 lb/MMBtu by the beginning of
2020. The

commenter recognized that other alternatives may exist, but asserted
that for any alternative to comply with the minimum legal requirements,
it must produce better visibility outcomes in Class I areas than BART
and demonstrate that it does so through the use of visibility modeling.
    Response: Neither the BART requirements nor the provisions in the
RHR governing alternatives to BART requires that BART sources cease
operation. As such, EPA does not consider it appropriate for the Agency
to require the shutdown of one unit of NGS by 2020 absent the consent
of the owners. Regardless of whether the suggested alternative would
provide for earlier and greater visibility improvement, it is not an
option at this time. As explained in this rulemaking, the TWG
Alternative does comply with the legal requirements for BART
alternatives.
    Comment: Suggested BART Alternative from CAP NIA Users: New
controls should not be required until after 2030.
    One commenter presented a table purporting to show EPA's
calculations of the NOX caps that would apply for a range of
potential BART emission limits: 0.055, 0.06, 0.07, and 0.15 lb/MMBtu.
According to the commenter, the NOX cap that would apply
under limits of 0.06 and 0.07 lb/MMBtu would exceed the proposed 2009-
2044 NOX CAP by 2.5 and 7.5 percent, respectively. The
commenter asserted that these differences would have imperceptible
impacts on visibility and that, therefore, the use of the
NOX cap based on a limit of 0.055 lb/MMBtu unduly
constrained TWG Alternative A and resulted in an unwarranted
requirement to install SCR on two NGS units by 2030, which would impose
inequitable compliance costs on agricultural water users. The commenter
stated that a NOX cap based on a BART limit of 0.06 or 0.07
lb/MMBtu would be very similar to the proposed 2009-2044 NOX
Cap, but would provide enough of an incremental increase to add 3 years
of additional compliance flexibility for the installation of SCR on two
units.
    The same commenter also stated that based on the 2009-2044
NOX Cap as proposed in the Supplemental Proposal, TWG
Alternative A contains unused ``headroom'' that renders the operation
of SCR by 2030 unnecessary. According to the commenter, TWG Alternative
A has the effect of forcing NOX emissions to a level that is
at least 33,000 tons below the NOX cap, which the commenter
believes makes the requirement to install and operate SCR by 2030
artificially stringent and unnecessary, and therefore arbitrary and
capricious. The commenter indicated that the headroom under TWG
Alternative A1 would yield more than 6 years of additional compliance
flexibility for the operation of SCR, and TWG Alternatives A2 and A3
would yield more than 3 years. The commenter concluded that EPA should
revise the TWG Alternatives to provide the maximum amount of compliance
flexibility for installation of SCR on NGS so as to not unnecessarily
impose costs on NIA water users.
    Response: EPA disagrees with the assertion that new controls should
not be required until after 2030. As stated previously, the TWG
Agreement was a negotiated agreement, submitted to EPA, representing
diverse interests. EPA evaluated the TWG Alternative to determine
whether it was consistent with our framework for better than BART
alternatives. Thus, although a few commenters may believe that the
timeframes for compliance in the TWG Alternative are too stringent, the
TWG Alternative is consistent with our proposed framework and it is
consistent with the level of control in Appendix B to the TWG
Agreement, which the operator and owners of NGS, as well as CAP, two
tribes and two environmental organizations, have determined is
acceptable.
    As stated elsewhere in the RTC, we disagree with the assertion that
BART for NGS is an emission limit associated with SNCR (0.15 lb/MMBtu)
or a less stringent limit associated with SCR (0.06 or 0.07 lb/MMBtu).
Therefore, the additional time for compliance suggested by the
commenters using higher BART Benchmarks or NOX Caps is not
appropriate. The commenters further assert that NGS could comply with a
limit of 0.07 lb/MMBtu in 2032 and 2033 and still maintain total
emissions below the 2009-2044 NOX Cap. EPA disagrees with
commenters that the ``unused headroom'' warrants additional time to
comply with the limit of 0.07 lb/MMBtu. The emission estimates that EPA
presented in our Supplemental Proposal for the TWG Alternative involved
projecting future emissions to 2044 based on average heat input at NGS
over 2001-2008. Heat input in the future is expected to be variable and
could possibly remain higher than average over an extended period of
time, significantly affecting the total flexibility or compliance
margin. EPA's analysis was provided simply to assess whether operation
consistent with the requirements under each TWG Alternative (A1-A3)
could reasonably be determined to maintain emissions below the 2009-
2044 NOX Cap and were not intended to represent actual year-
by-year emissions in the future. Thus, the ``unused headroom'' is
theoretical and could be smaller or larger than cited by the
commenters.

L. Other Comments

    Comment: Disproportionate impacts to tribes.
    The Tonto Apache Tribe and the San Carlos Apache Tribe commented
that both the original BART proposal and the proposed TWG Alternative
are contrary to the obligations of the United States and its trust
responsibilities to Indian Tribes under CAP. The commenters stated that
both regulatory programs would have disproportionate impacts on tribes
with CAP contracts. The commenters noted that environmental quality is
of utmost importance to the tribes, but that clean air is the
responsibility of all citizens. Therefore, the commenters assert that
because the United States owns 24.3 percent of NGS, the costs of
compliance for that 24.3 percent share should be shared among all
American people, who will benefit from cleaner air. The commenters
urged EPA to develop an alternative regulation that does not place
additional burden on Indian Tribes.
    Response: EPA agrees that our proposed BART determination and the
TWG Alternative will impact tribes with CAP water contracts. We note
that the Joint Federal Agency Statement on NGS reflects the U.S.
Government's recognition of its responsibilities related to NGS and
trust responsibility to Indian tribes affected by NGS.
    Although EPA is finalizing a BART Benchmark for NGS, the regulatory
requirements of this Final Rule will include only the requirements and
compliance timeframes for the TWG Alternative as proposed in our
Supplemental Proposal. Under the TWG Alternative, emission reductions
at NGS would be achieved in phases, including closure of one unit or
the equivalent in 2019, and compliance with an emission limit
achievable with SCR in 2030. We note that the closure of one unit was
possible because of the planned divestment of LADWP and NV Energy from
NGS by 2019. Because LADWP and NV Energy are unrelated to CAP, EPA does
not expect substantial compliance costs to be borne by Reclamation (and
thus, tribes or other CAP water users) due to the first phase of
emission reductions at NGS in 2019. EPA further notes that the 2030
compliance date for meeting an emission limit achievable with SCR on
two units at NGS is approximately 16 years from the present day. As
stated elsewhere in the RTC, the requirements

under BART and the TWG Alternative include emission limits, rather than
technology requirements. Thus, 16 years from now, although SCR will be
capable of meeting the emission limit, other technologies or options
may become available for the operator of NGS to more cost-effectively
meet the NOX emission limit of 0.07 lb/MMBtu.
    EPA recognized the potential impacts to tribes of our proposed BART
determination and sought ways to provide flexibility and a framework
for affected stakeholders to develop alternative approaches to BART.
EPA has determined that the TWG Alternative achieves greater emission
reductions than would otherwise be achieved under our BART
determination, while providing additional time for compliance. This
additional time allows the DOI, DOE, and EPA time to work with tribal
stakeholders to identify and implement strategies for achieving the
goals outlined in the Joint Federal Agency Statement on NGS.
    Comment: EPA lacks authority to regulate NGS
    Several commenters indicated that EPA overstepped its authority and
stated that EPA's proposal hinders the state's ability to deal with
environmental issues on a local level. One commenter stated that EPA's
regulations are an attack on free enterprise, and believes that the
agenda of the current administration is to ban all coal-fired power
plants regardless of the economic effect.
    Response: EPA disagrees that it has overstepped its regulatory
authority and disagrees that any State has authority to regulate air
pollution from sources located on the Navajo reservation. EPA's
authority to regulate NGS is established in sections 301(a) and
301(d)(4) of the CAA and the TAR. Section 301(d)(4) authorizes EPA to
directly administer provisions of the CAA in Indian country under
certain circumstances. The State of Arizona lacks authority to regulate
air pollution sources located on the Navajo reservation.
    EPA disagrees that the regulations promulgated in this action,
which are requirements consistent with the TWG Agreement, constitutes
an attack on free enterprise. The TWG Alternative was submitted to EPA
by a stakeholder group that had determined it was a more cost-effective
approach to continuing to operate NGS than a prior proposal by EPA. EPA
considered the direct costs of compliance in our five-factor BART
analysis, and although not specifically required in the BART
Guidelines, EPA also considered numerous indirect impacts and costs in
our analysis of Factor 2. The comment provides no information other
than conclusory statements that EPA failed to adequately consider the
cost of compliance. EPA also disagrees that there is any agenda or
effort to ban coal burning electricity generation. The TWG Agreement,
as agreed upon by the members of the TWG, includes a provision that
specifies continued operation of NGS as a conventional coal-fired power
plant until 2044 when its lease with the Navajo Nation expires.
Therefore, this rulemaking does not constitute a ban on burning coal.
    Comment: Lack of Consultation with Tribes.
    The Navajo Nation commented that EPA should improve communication
at the start of any rulemakings to ensure that the Navajo Nation can
provide meaningful information. The commenter said that even when the
Agency develops supporting rule information like the RIA the Navajo
Nation would like to be involved as it could impact the Nation. The
commenter pointed out that EPA has known for decades that the Navajo
Nation would be impacted by regulation of NGS and FCPP. The commenter
quoted excerpts from Executive Order 13175--Consultation and
Coordination with Indian Tribal Governments and said that the standard
for determining if a regulation has tribal implication is not whether
it ``impose[s] substantial direct compliance costs on tribal
governments,'' but rather a regulation has ``substantial direct effects
on one or more Indian tribes.''