Milestone      average SO2    Carbon plant
                              Year                                     (tpy)       emissions \1\   SO2 emissions
                                                                                (tpy)           (tpy)
----------------------------------------------------------------------------------------------------------------
2003............................................................         303,264         214,780           5,488
2004............................................................         303,264         223,584           5,642
2005............................................................         303,264         220,987           5,410
2006............................................................         303,264         218,499           6,779
2007............................................................         303,264         203,569           6,511
2008............................................................         269,083         186,837           5,057
2009............................................................         234,903         165,633           5,494
2010............................................................         200,722         146,808           7,462
2011............................................................         200,722         130,935           7,740
2012............................................................         200,722         115,115           8,307
2013............................................................         185,795         105,084           7,702
2014............................................................         170,868
2015............................................................         155,940
2016............................................................         155,940
2017............................................................         155,940
2018............................................................         141,849
----------------------------------------------------------------------------------------------------------------
\1\ The three-year average is based on the emissions averaged for the current and two preceding years.

    For Hunter Unit 3, Utah also explained that PacifiCorp upgraded the
LNB controls in 2008 and that the upgrade was not required under the
requirements of the CAA as of the 2002 baseline date of the SIP; the
emission reductions from the upgrade are therefore considered surplus
and creditable for the BART Alternative under 40 CFR 51.308(e)(2)(iv).
Utah noted that prior to the 2008 upgrade, the emission rate for Hunter
Unit 2 was 0.46 lb/MMBtu heat input for a 30-day rolling average as
required by Phase II of the Acid Rain Program.\76\
---------------------------------------------------------------------------

    \76\ There is a typographical error in Chapter 1, section X.C,
PacifiCorp Hunter Unit 3, p. 31. The reference to Hunter Unit 2
should be Unit 3 based on the section heading as well as confirmed
emission limits in Utah Approval Order DAQE-AN0102370012-08.
---------------------------------------------------------------------------

D. Summary of Utah's Enforceable Commitment SIP Revision

    To address potential concerns that Utah would be double counting
SO2 emissions reductions for the Carbon plant closure under
both the 40 CFR 51.308 and 309 programs, on October 7, 2015 the State
adopted an enforceable commitment into the Utah RH SIP at Chapter XX,
Section N. Utah submitted this SIP revision to EPA on October 20, 2015.
In this commitment, the State explained that it will continue to report
the historical emissions for the Carbon plant in the annual milestones
reports from 2016 through the life of the backstop trading program. In
addition, the State has committed to making revisions as necessary to
SIP Section XX.D.3.c (``Triggering the Trading Program'') and State
rule R307-150 (``Emission Inventories Program'') as well as any other
applicable provisions to implement the requirement for reporting
Carbon's historical emissions under the 309 program. The State notes it
will follow its SIP adoption process when making these SIP revisions.
The SIP will be adopted by the Governor-appointed Air Quality Board
through a rulemaking process that includes public participation. Once
approved into the SIP, the commitment will be enforceable by both EPA
and citizens under the CAA.
    The State noted that EPA has historically recognized that, under
certain circumstances, issuing full approval may be appropriate for a
SIP submission that consists of, in part, an enforceable commitment.
Utah explained that its October 2015 submission satisfies EPA's
requirements for enforceable commitments because it has adopted such a
commitment for what is a small portion of its regional haze program in
relation to its regional haze obligations as a whole. In addition,
Carbon's 8,005 tpy SO2 emissions reductions is small in
comparison to the 2018 milestone of 141,849 tpy described in Table 7.
    On the matter of timing, the State has committed to providing the
required subsequent SIP submittal by mid-March 2018.

E. Consultation With FLMs

    Utah's SIPs do not specifically discuss how it addressed the
requirements of 40 CFR 308(i)(2) for providing the FLMs with an
opportunity for consultation at least 60 days prior to holding the
public hearing for the June 2015 RH SIP. However, we are aware that
Utah consulted with the FLMs and explain those efforts here. The State
held an initial public comment period for proposed SIP amendments from
November 1 through December 22, 2014. The State provided the
opportunity for the FLMs to review the preliminary draft SIP documents
via email approximately 68 days prior to the public hearing that was
held on a December 1, 2014. Copies of the email correspondence
documenting this effort are included in the docket.
    Utah received a number of comments during the public comment period
in late 2014. After reviewing the comments and consulting with EPA,
Utah determined additional work was needed to develop a BART
alternative measure that would take credit for emission reductions from
the Carbon plant shutdown among other things. Utah held an additional
public comment period from April 1 through April 30, 2015. One of the
FLMs, the National Park Service, provided extensive public comments to
Utah during this second public comment period and Utah included
responses to these comments, along with responses to other commenters,
in the June 2015 RH SIP submittal along with other administrative
documentation.
    The October 2015 Utah RH SIP was provided for public comment August
15 through September 14, 2015, and we are not aware of any prior FLM
consultation on this SIP. The FLMs did not submit comments during this
public comment period.

V. EPA's Evaluation and Proposed Approval of Utah's Regional Haze SIP

    As explained in section II.A, EPA is soliciting comments on two
alternative proposals: A proposal to approve the State SIP in its
entirety, and a proposal to partially approve and partially

disapprove the State SIP and to issue a FIP. The co-proposals detailed
in this section and Section VI represent different conclusions
regarding Utah's NOX BART Alternative and the metrics the
State has proposed to support this alternative. As described in this
section, EPA is proposing to approve the two Utah 2015 RH SIP
revisions. Alternatively, as discussed in section VI, EPA is co-
proposing to disapprove the Utah's June 2015 and October 2015 RH SIP
revisions and promulgate a FIP.
    This document is written as two separate proposals in order to
clearly present the options and solicit comment on each. EPA intends to
finalize only one of these co-proposals; however, we also acknowledge
that additional information and comments may also lead the Agency to
adopt final SIP and/or FIP regulations that differ somewhat from the
co-proposals presented here regarding the BART Alternative, BART
control technology option or emission limits, or impact other proposed
regulatory provisions.

A. Basis for Proposed Approval

    For the reasons described later on, EPA proposes to approve the two
Utah 2015 RH SIP revisions. Our proposed action is based on an
evaluation of Utah's regional haze SIP submittals against the regional
haze requirements at 40 CFR 51.300-51.309 and CAA sections 169A and
169B. All general SIP requirements contained in CAA section 110, other
provisions of the CAA, and our regulations applicable to this action
were also evaluated. The purpose of this proposed action is to ensure
compliance with these requirements and to provide additional rationale
to support our conclusions.

B. Utah BART Alternative

1. Summary of Utah BART Alternative
    Utah has opted to establish an alternative measure (or program) for
NOX in accordance with 40 CFR 51.308(e)(2). A description of
the Utah BART Alternative is provided in section IV.B.1. The RHR
requires that a SIP revision establishing a BART alternative include
three elements as listed later. We have evaluated the Utah BART
Alternative with respect to each of these elements.
     A demonstration that the emissions trading program or
other alternative measure will achieve greater reasonable progress than
would have resulted from the installation and operation of BART at all
sources subject to BART in the State and covered by the alternative
program.\77\
---------------------------------------------------------------------------

    \77\ 40 CFR 51.308(e)(2)(i).
---------------------------------------------------------------------------

     A requirement that all necessary emissions reductions take
place during the period of the first long-term strategy for regional
haze.\78\
---------------------------------------------------------------------------

    \78\ 40 CFR 51.308(e)(2)(iii).
---------------------------------------------------------------------------

     A demonstration that the emissions reductions resulting
from the alternative measure will be surplus to those reductions
resulting from measures adopted to meet requirements of the CAA as of
the baseline date of the SIP.\79\
---------------------------------------------------------------------------

    \79\ 40 CFR 51.308(e)(2)(iv).
---------------------------------------------------------------------------

2. Demonstration of Greater Reasonable Progress for the Alternative
Program
    As discussed previously in section III.E.1, pursuant to 40 CFR
51.308(e)(2)(i), Utah must demonstrate that the alternative measure
will achieve greater reasonable progress than would have resulted from
the installation and operation of BART at all sources subject to BART
in the State and covered by the alternative program. This
demonstration, primarily included in Chapter 1 of the TSD of the Utah
RH SIP,\80\ must be based on five criteria which are addressed later.
---------------------------------------------------------------------------

    \80\ As presented in this proposal, while the majority of the
State's demonstration is contained in Chapter 1, EPA has identified
additional information regarding the demonstration and we include
references to the additional information.
---------------------------------------------------------------------------

a. A List of All BART-Eligible Sources Within the State
    As discussed previously in section IV.A.2, Utah included a list of
BART-eligible sources and noted the following sources are all covered
by the alternative program:

 PacifiCorp Hunter, Unit 1
 PacifiCorp Hunter, Unit 2
 PacifiCorp, Huntington, Unit 1
 PacifiCorp, Huntington, Unit 2

    EPA previously approved Utah's BART eligibility determinations in
our 2012 rulemaking.\81\
---------------------------------------------------------------------------

    \81\ 77 FR 74357 (Dec. 14, 2012).
---------------------------------------------------------------------------

b. A List of All BART-Eligible Sources and All BART Source Categories
Covered by the Alternative Program
    As discussed previously in section IV.A.3, the Utah BART
Alternative covers all the BART-eligible sources in the state, Hunter
Units 1 and 2 and Huntington Units 1 and 2, in addition to three non-
BART units, PacifiCorp's Hunter Unit 3 and Carbon Units 1 and 2. EPA
previously approved Utah's BART eligibility determinations in our 2012
rulemaking.\82\
---------------------------------------------------------------------------

    \82\ 77 FR 74355, 74357 (Dec. 14, 2012).
---------------------------------------------------------------------------

c. Analysis of BART and Associated Emission Reductions
    As noted in section IV.C.3, in the June 2015 Utah RH SIP, the State
compared the Utah BART Alternative to a BART Benchmark that included
the most stringent NOX BART controls, SCR plus new LNBs and
SOFA, at the four BART units. This is consistent with the streamlined
approach described in Step 1 of the BART Guidelines. The BART
Guidelines note that a comprehensive BART analysis can be avoided if a
source commits to a BART determination that consists of the most
stringent controls available.\83\
---------------------------------------------------------------------------

    \83\ 40 CFR 51, appendix Y, section IV.D.1.9.
---------------------------------------------------------------------------

    We propose to find that Utah has met the requirement for an
analysis of BART and associated emission reductions achievable at
Hunter and Huntington under 40 CFR 51.308(e)(2)(i)(C).
d. Analysis of Projected Emissions Reductions Achievable Through the
BART Alternative
    As discussed previously in section IV.C.4, a summary of Utah's
estimates of emissions for the Utah BART Alternative and the BART
Benchmark is provided in Table 3. We propose to find that Utah has met
the requirement for an analysis of the projected emissions reductions
achievable through the alternative measure under 40 CFR
51.308(e)(2)(i)(D).
e. A Determination That the Alternative Achieves Greater Reasonable
Progress Than Would Be Achieved Through the Installation and Operation
of BART
Greater Reasonable Progress Based on 40 CFR 51.308(e)(3)'s Greater
Emission Reductions Test
    EPA's evaluation of the State's demonstration based on 40 CFR
51.308(e)(3) is located in section VI.B.2.e.
Greater Reasonable Progress Based on 40 CFR 51.308(e)(2)'s Weight-of-
Evidence Test
    Although Utah found that the BART Alternative demonstrates greater
reasonable progress under 40 CFR 51.308(e)(3), it also chose to conduct
a weight-of-evidence analysis under 40 CFR 51.308(e)(2) based on a BART
Alternative involving the Hunter, Huntington, and Carbon power plants
and considered the following evidence:
i. Annual Emissions Comparison for Visibility-Impairing Pollutants
    The emissions of visibility-impairing pollutants from both the Utah
BART Alternative and the BART Benchmark, as estimated by Utah, are
summarized in Table 3 in section IV.C.4. Compared with the Utah BART
Benchmark, the State projects that the Utah BART Alternative will
result in 5,721 tpy more

NOX emissions, 8,005 tpy fewer SO2 emissions, and
573 tpy fewer PM10 emissions than the BART Benchmark. Utah
also found that the combined emissions of NOX,
SO2 and PM10 will be 2,856 tpy lower under the
BART Alternative.
    We propose to concur with Utah's finding that the BART Alternative
will achieve greater SO2 and PM10 emissions
reductions and greater aggregate emissions reductions of all
pollutants. We further propose to recognize that not all pollutants
impact visibility equally and that the total emissions reductions of
all pollutants is not necessarily a direct indicator of whether the
BART Alternative or the BART Benchmark will achieve greater reasonable
progress. However, for reasons described later in subsection vii for
our evaluation of Utah's IMPROVE monitoring metric, we propose to
concur with Utah's finding that SO2 emissions reductions
should provide visibility benefits in all seasons and that sulfate is
the largest contributor to visibility impairment at the affected Class
I areas. Furthermore, we propose to find that these observations
suggest that the BART Alternative is likely to achieve greater
reasonable progress. We note that Utah has also provided CALPUFF
modeling results for the BART Benchmark and BART Alternative scenarios
to assess the relative visibility benefits of each. These modeling
results are considered here by EPA as part of the overall weight-of-
evidence analysis.
ii. Improvement in the Number of Days With Significant Visibility
Impairment
    As discussed previously in section IV.C.5, Utah provided modeling
results to assess the improvement in the number of days with
significant visibility impairment--that is, the improvement in the
number of days with impacts that either cause (>1.0 dv) or contribute
(>0.5 dv) to visibility impairment.
    The BART Guidelines provide that, when making a BART determination,
a State may consider the number of days or hours that a threshold was
exceeded.\84\ In developing the BART Guidelines, our example modeling
analysis of a hypothetical source examined the number of days that 1.0
dv and 0.5 dv thresholds were exceeded.\85\ In addition, we have used
these metrics, and in particular the total number of days for the
meteorological years modeled, in previous regional haze rulemakings
such as for North Dakota,\86\ Montana,\87\ and Washington.\88\
---------------------------------------------------------------------------

    \84\ 40 CFR 51, appendix Y, section IV.D.5.
    \85\ 70 FR 39130 (July 6, 2005).
    \86\ 76 FR 58584 (Sept. 21, 2011).
    \87\ 77 FR 24006 (Apr. 20, 2012).
    \88\ 79 FR 33438, 33440-33441 (June 11, 2014).
---------------------------------------------------------------------------

    This metric is useful in assessing the frequency and duration of
significant visibility impacts from a source or small group of sources.
Therefore, for this reason and because these metrics are supported by
our regulations and past practice, we propose to find the State's use
of these metrics is appropriate. Moreover, we propose to find the
difference in the total number of days impacted--18 fewer days greater
than the causation threshold of 1.0 dv (775 days for the BART
Alternative vs. 793 days for the BART Benchmark), and 175 fewer days
greater than the contribution 0.5 dv threshold (1,323 days for the BART
Alternative vs. 1,498 days for the BART Benchmark)--is an indication
that the BART Alternative achieves greater reasonable progress.
iii. 98th Percentile Impact (dv)
    As discussed previously in section IV.C.5, Utah explained that the
only metric it evaluated that showed greater improvement for the BART
Benchmark in comparison to the BART Alternative was the 98th percentile
metric (when averaged across all Class I areas and meteorological years
modeled). Utah's comparison of the modeled visibility impacts on the
98th percentile day (8th highest impacted day in a given meteorological
year) for the most impacted year shows that the BART Benchmark would
result in greater visibility improvement at five of the nine Class I
areas, and is slightly better on average across all nine Class I areas
(0.11 dv difference). At the most impacted Class I areas, Canyonlands
and Capitol Reef, Utah found that the 98th percentile metric indicates
the BART Benchmark has 0.76 dv and 0.57 dv, respectively, more
improvement than the BART Alternative. At other Class I areas, Utah
found that the 98th percentile metric indicates that the BART
Alternative provides greater visibility improvement (for example, 0.44
dv at Flat Tops).
    The 98th percentile visibility impact is a key metric recommended
by the BART Guidelines \89\ when selecting BART controls. In addition,
this is one of the primary metrics that EPA has relied on in evaluating
prior regional haze actions that have included BART alternatives.\90\
In the BART Guidelines, EPA described this metric as an appropriate
measure in determining the degree of visibility improvement expected
from controls.\91\ Therefore, we propose to find that it is an
appropriate metric for assessing the relative benefits of the Utah BART
Alternative here.
---------------------------------------------------------------------------

    \89\ 40 CFR 51, appendix Y, section IV.D.5.
    \90\ See, e.g., 78 FR 79344 (Dec. 30, 2012)(proposed rule, FIP
for Tesoro Refining and Intalco Refinery BART Alternatives); 79 FR
33438 (June 11, 2014)(final rule, FIP for Tesoro Refining and
Intalco Refinery BART Alternatives); 79 FR 56322, 56328 (Sept. 19,
2014)(proposed approval of Arizona Apache BART Alternative); 80 FR
19220 (April 10, 2015)(final approval of Arizona Apache BART
Alternative); 77 FR 11827, 11837 (Feb. 28, 2012)(proposed approval
of Maryland BART Alternative); 77 FR 39938, 39940-1 (July 6,
2012)(final approval of Maryland BART Alternative).
    \91\ 70 FR at 39129.
---------------------------------------------------------------------------

    We note that when calculating visibility improvements for
individual Class I areas, Utah mixed the impacts from different
meteorological years between modeling scenarios (baseline, BART
benchmark, and BART Alternative). This may introduce some error as the
visibility improvements could be driven by year-to-year variability in
meteorological conditions, as opposed to the differences in emission
reductions between the BART Alternative and BART Benchmark. For this
reason, in addition to considering the State's numbers, EPA also
calculated the visibility improvements for each modeling scenario using
consistent meteorological years.\92\ Using this method, whether the
BART Alternative resulted in lower 98th percentile impacts depended on
both the particular Class I area and meteorological year modeled. In
some years and some Class I areas, particularly some of the most
impacted Class I areas, the BART Benchmark shows better visibility
improvement than the BART Alternative. Notably, the BART Benchmark
shows 0.93 dv greater improvement for Canyonlands in 2002 and 0.75 dv
greater improvement for Capitol Reef in 2001.\93\ By contrast, the BART
Alternative shows 0.90 dv greater improvement for Arches in 2003 and
0.43 dv greater improvement for Flat Tops in 2002.\94\ On the whole,
when using this method, the BART Benchmark is better on average across
all years and nine Class I areas (0.14 dv difference). See Table 12. We
propose to find, consistent with the State's evaluation, that this
metric favors the BART Benchmark.
---------------------------------------------------------------------------

    \92\ See EPA Calculation of 98th Percentile Improvement for Utah
Bart Alternative spreadsheet (in docket).
    \93\ Id.
    \94\ Id.

   Table 12--Summary of EPA Comparison of Utah CALPUFF 98th Percentile
      Modeling Results Based on Consistent Meteorological Years 95
------------------------------------------------------------------------
                                                            Average
                                                           visibility
                                                        improvement  of
                     Class I Area                       BART  benchmark
                                                           over BART
                                                          alternative
                                                         (delta dv)\1\
------------------------------------------------------------------------
Arches...............................................              -0.21
Black Canyon of the Gunnison.........................               0.06
Bryce Canyon.........................................               0.04
Canyonlands..........................................               0.78
Capitol Reef.........................................               0.59
Flat Tops............................................              -0.15
Grand Canyon.........................................               0.06
Mesa Verde...........................................               0.12
Zion.................................................               0.02
Class I Area Average.................................               0.14
------------------------------------------------------------------------
\1\ A negative value indicates the modeling results favor the BART
  Alternative. Results are based on the three-year average of results
  for 2001, 2002 and 2003.

iv. Annual Average Impact (dv)
    As discussed previously in section IV.C.5, Utah's modeling shows
that the average annual dv impact at all Class I areas is better under
the Utah BART Alternative at five of the nine Class I areas, and is
better on average across all the Class I areas. The average impact was
calculated by averaging all daily modeling results for each year and
then calculating a 3-year average from the annual average. Utah's
information shows that the BART Alternative is better than the BART
Benchmark by 0.009 dv on average across all nine Class I areas. While
EPA has not considered this metric in the past,\96\ since the State
includes it, we consider it here. Furthermore, the BART Guidelines
state that, ``in determining what, if any, emission controls should be
required, the State will have the opportunity to consider the
frequency, duration, and intensity of a source's predicted effect on
visibility.'' \97\ The annual average does provide an indication of the
modeled visibility impacts for the entire year while the 98th
percentile modeled results speak to a particular day (the 8th highest
impacted day). Accordingly, and while we have typically relied
primarily on the 98th percentile impacts in evaluating BART controls in
other actions, we propose to find that the annual average impact
provides additional useful information in considering Utah's weight of
evidence. However, given that the difference in this metric is small
(0.009 dv), we propose to find that it only marginally supports a
conclusion that the BART Alternative achieves greater reasonable
progress.
---------------------------------------------------------------------------

    \95\ Id.
    \96\ EPA final actions on BART alternatives that evaluated
CALPUFF modeling analysis, which did not include consideration of
annual average dv impacts include: 80 FR 19220 (April 10,
2015)(Region 9, Apache); 79 FR 33438 (June 11, 2014)(Region 10,
Tesoro Refining and Alcoa Intalco Operations); 77 FR 39938 (July 6,
2012)(Region 3, Maryland HAA).
    \97\ 70 FR 39121 (July 5, 2005).
---------------------------------------------------------------------------

v. 90th Percentile Impact (dv)
    As discussed previously in section IV.C.5, Utah's comparison of the
modeled visibility impacts at the 90th percentile (the 110th highest
day across three years) dv impact shows that the Utah BART Alternative
is better at seven of the nine Class I areas and is slightly better
averaged both across three years and across nine Class I areas (0.006
dv difference). We note that the use of the 90th percentile impacts to
evaluate alternatives has not been EPA's practice for source-specific
BART determinations; however, as discussed previously for the average
dv impact metric, the BART Guidelines allow states to consider other
visibility metrics in addition to the 98th percentile. Yet, because of
the small difference between the two scenarios (0.006 dv), we propose
to find that it only marginally supports a conclusion that the BART
Alternative achieves greater reasonable progress.
vi. Timing for the Emissions Reductions
    As discussed previously in section IV.C.5, Utah noted that
reductions under the Utah BART Alternative will occur earlier than the
BART Benchmark. The reductions under the Utah BART Alternative are
required under the State SIP by August 2015, as noted in Table 5,
providing an early and on-going visibility benefit as compared to BART.
Also notable is that combustion control upgrades at the Hunter and
Huntington facilities have been achieving significant NOX
reductions since the time of their installation between 2006 and 2014,
depending on the unit. If, as proposed in section VI.C, BART for the
four units is LNB/SOFA plus SCR, BART likely would be fully implemented
sometime between 2019 and 2021.
    Therefore, we note that the reductions from the BART Alternative
will occur before the BART Benchmark.
vii. IMPROVE Monitoring Data
    Utah's SIP presents sulfate and nitrate monitoring data at the
Canyonlands IMPROVE monitor that show that ``sulfates are the dominant
visibility impairing pollutant'' \98\ and that sulfate levels have
decreased,\99\ and references similar results at other Class I areas in
the TSD.\100\ Utah also presents data on trends in emissions from EGUs
showing substantial reductions in emissions of both SO2 and
NOX.\101\ Based on these data, Utah indicates it ``has
confidence that the SO2 reductions will achieve meaningful
visibility improvement,'' under the Utah BART Alternative, while ``the
visibility improvement during the winter months due to NOX
reductions is much more uncertain.'' \102\ Utah makes this point even
though nitrate concentrations are highest in the winter, explaining
that while there has been a reduction in NOX, the ammonium
nitrate values do not show similar improvement in the winter
months.\103\ Utah offers several possible explanations for the results,
but does not provide any definitive conclusions.\104\
---------------------------------------------------------------------------

    \98\ Utah Regional Haze State Implementation Plan, Technical
Support Document, Ch. 1, p. 12 (2015).
    \99\ Id. at p. 15.
    \100\ Id. at p.12.
    \101\ Id. at p. 14.
    \102\ Id. at p. 13.
    \103\ Id.
    \104\ Id. at pp. 16-19.
---------------------------------------------------------------------------

    Utah also presents data on the seasonality of park visitation and
monitoring data for nitrate and sulfates. The data show that the
highest measured nitrate concentrations occur in winter during the
period of lowest park visitation, and that sulfates affect visibility
throughout the year and are the dominant visibility impairing pollutant
from anthropogenic sources during the high visitation period of March
through November. Utah concludes that it has greater confidence that
reductions in SO2 will be reflected in improved visibility
for visitors to the Class I areas, while reductions in NOX
will have a more uncertain benefit for visitors to Class I areas.
    We invite comment on the information and conclusions provided by
Utah as summarized previously.
    We propose to concur with one of the State's findings. We propose
to find that visibility benefits associated with NOX
reductions are much more likely to occur in the winter months because
this is when aerosol thermodynamics favors nitrate formation.\105\ By
contrast, SO2 emissions reductions should provide

visibility benefits in all seasons.\106\ We also propose to find that,
as concluded by the GCVTC, and supported by the IMPROVE monitoring data
presented by Utah, anthropogenic visibility impairment on the Colorado
Plateau is dominated by sulfates.107 108 Therefore, we
propose to concur with Utah's statement that sulfate is the largest
contributor to visibility impairment at the affected Class I areas.
---------------------------------------------------------------------------

    \105\ Fountoukis, C. & Nenes, A. ISORROPIA II: A Computationally
Efficient Aerosol Thermodynamic Equilibrium Model for K+,
Ca2+, Mg2+,
NH4+, Na+,
SO42-, NO3-, Cl-,
H2O Aerosols, 7 Atmos. Chem. Phys., 4639-4659 (2007).
    \106\ Seinfeld, John H., Urban Air Pollution: State of the
Science, 243 Science Magazine, No. 4892, 745, 745-752 (1989).
    \107\ While natural sources of haze from wildfires or windblown
dust can be the largest contributor on some of the 20% haziest days,
the RHR defines ``impairment'' as anthropogenic impairment, and
sulfate formed from anthropogenic SO2 emissions is the
dominant contributor to anthropogenic visibility impairment on the
haziest days.
    \108\ The Grand Canyon Visibility Transport Commission
Recommendations for Improving Western Vistas, June 10, 1996, p. 32.
Available at http://www.wrapair.org/WRAP/reports/GCVTCFinal.PDF and
included in the docket.
---------------------------------------------------------------------------

    We propose to disagree with the State's findings related to park
visitation. While the BART Guidelines do mention visitation as
something that can inform a control decision,\109\ EPA is proposing to
place little weight on the State's correlation of emissions reductions
and park visitation because nothing in the CAA suggests that visitors
during busy time periods are entitled to experience better visibility
than visitors during off-peak periods. On the contrary, in the Regional
Haze provisions of the CAA, Congress declared a national goal of
remedying all manmade visibility impairment in all class I areas, which
includes both heavily-visited national parks and seldom-visited
wilderness areas. We invite comment on our evaluation and the
information and conclusions provided by Utah as summarized previously.
---------------------------------------------------------------------------

    \109\ 70 FR 39104, 39130 (July 6, 2005) (``Other ways that
visibility improvement may be assessed to inform the control
decisions would be to examine distributions of the daily impacts,
determine if the time of year is important (e.g. high impacts are
occurring during tourist season), consideration of the cost-
effectiveness of visibility improvements (i.e. the cost per change
in deciview), using the measures of deciview improvement identified
by the State, or simply compare the worst case days for the pre- and
post-control runs. States may develop other methods as well.'').
---------------------------------------------------------------------------

viii. Energy and Non-Air Quality Benefits
    As discussed previously in section IV.C.5, the State noted that the
Utah BART Alternative would avoid an annual energy penalty of
approximately $2 million due to operating four SCR units at the Hunter
and Huntington plants and presented additional non-air quality benefits
associated with the closure of the Carbon plant such as waste reduction
and decreased water usage. Because such benefits do not have direct
bearing on whether the BART Alternative achieves greater reasonable
progress, it is not material to our action whether we agree or disagree
with Utah's assessment that they reduce energy and non-air quality
impacts.
ix. Cost
    As discussed previously in section IV.C.5, the State noted that the
Utah BART Alternative would achieve greater reasonable progress at
lower cost to PacifiCorp than the BART Benchmark. Utah also noted that
cost is one of the factors listed in CAA 169A(g)(2) that should be
considered when determining BART. While we propose to find that the
described cost difference does not have a direct bearing on whether the
BART Alternative achieves greater reasonable progress, it is not
material to our action whether we agree or disagree with Utah's
conclusion that the BART Alternative would have a lower cost impact to
PacifiCorp than the BART Benchmark (i.e., costs provided by PacifiCorp
in its BART analyses of August 5, 2014, SIP TSD Chapter 2). However, we
do agree.
f. Evaluation of the Weight of Evidence
    In accordance with our regulations governing BART alternatives, we
support the use of a weight-of evidence determination as an alternative
to the methodology set forth in section 51.308(e)(3).\110\ In
evaluating Utah's weight-of-evidence demonstration, we have evaluated
all nine elements of Utah's analysis, and as discussed later, rely
primarily on the following four elements in proposing to approve the
BART Alternative: Annual emissions comparison for two pollutants;
improvement in the number of days with significant visibility
impairment; IMPROVE monitoring data regarding sulfates; and the early
timing for installation of controls. Additional elements that either
marginally support or do not support our proposed approval of Utah's
determination are also discussed later.
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    \110\ 71 FR 60622 (Oct. 13, 2006).
---------------------------------------------------------------------------

    Regarding the emissions reduction comparison, the Utah BART
Alternative will result in 8,005 tpy fewer SO2 emissions
compared to the BART Benchmark. In addition, the combined emissions of
NOX, SO2 and PM10 will be 2,856 tpy
lower under the BART Alternative.
    Regarding the improvement in the number of days with significant
visibility impairment, modeling submitted by Utah shows that the Utah
BART Alternative will result in improved visibility at all affected
Class I areas compared with baseline conditions. The units at issue
will have impacts of 1.0 dv or more at the affected Class I areas on 48
fewer days under the Utah BART Alternative as compared to BART. When
considering impacts of 0.5 dv or more, the units at issue will impact
the affected Class I areas on 154 fewer days under the BART Alternative
as compared to BART.
    Regarding the IMPROVE visibility monitoring data, we propose to
agree with the State's finding that SO2 emissions reductions
provide visibility benefits throughout the year. We also propose to
concur with Utah's statement that sulfate is the largest contributor to
visibility impairment at the affected Class I areas.
    Regarding the timing of emissions reductions, these SO2
emissions reductions were achieved in August 2015, the date in the June
2015 Utah RH SIP requiring the closure of the Carbon plant. Combustion
controls at the four BART units in addition to Hunter Unit 3 were
installed between 2006 and 2014. BART likely would otherwise have been
implemented sometime between 2019 and 2021. So the Utah BART
Alternative provides early and on-going visibility benefits as compared
to BART.
    Regarding other metrics that only marginally support or do not
support our proposed approval of Utah's BART Alternative, we propose to
find that average annual dv impact and the 90th percentile impact are
the two metrics that marginally support a conclusion that the BART
Alternative achieves greater reasonable progress.
    Regarding the 98th percentile visibility impact, we propose to find
this metric does not support our proposed approval of Utah's BART
Alternative. While the 98th percentile visibility impact is a key
metric that EPA has primarily focused on in prior actions, we propose
to conclude that by itself it is not a dispositive metric in weighing a
BART Alternative. Nonetheless, as discussed in section VI, we have
given considerable weight to this metric in previous actions where we
have evaluated BART alternatives as it captures a source's likely
greatest visibility impacts at a Class I area; as such, it is a useful
comparison point for determining whether one emission control scenario
will have a greater impact on visibility improvement than another. In
those actions, the 98th percentile visibility impact favored the BART
alternative and therefore there was less need to introduce and consider
additional evidence to determine

whether an alternative would provide greater reasonable progress. In
the case of the Utah BART Alternative, where the 98th percentile does
not favor the alternative, Utah has introduced additional evidence that
we considered in order to evaluate whether the BART Alternative, on
balance, achieves greater reasonable progress.
    Regarding the 90th percentile visibility impact, we propose to find
that consideration of this metric is appropriate in assessing the
weight of evidence associated with a BART alternative. Visibility at a
Class I area changes from day to day, and each emission control
scenario would result in visibility improvements at the affected Class
I areas that would differ from one day to another. The metrics related
to the number of days with impacts greater than 0.5 dv and 1.0 dv are
examples of the type of additional information that allows for
consideration of the frequency and duration of visibility impacts.
Similarly, the use of the 90th percentile impact metric allows for the
comparison of BART and a BART alternative at a different point in the
range of impacts. This can be useful, given the varying impacts of
different pollutants under different meteorological conditions. The
information provided by Utah for the 90th percentile shows that the
BART Alternative is better at seven of the nine Class I areas for this
metric, by amounts ranging from 0.019 to 0.140 dv, and is better when
taking into account the impacts averaged both across three years and
across nine Class I areas, but only by 0.006 dv. These values
marginally support our proposed approval of Utah's BART Alternative as
better than BART. We invite comment on this proposed assessment of how
the 90th percentile metric should be considered in the weight of
evidence determination. We also invite interested parties to submit
additional information on how the impacts of the BART Alternative under
various conditions compare to the impacts of the presumed BART
scenario, because while the 90th percentile impact provides additional
insight, it is not uniquely informative.
    Regarding the energy and non-air quality impacts, as well as cost,
we propose to find these metrics do not have direct bearing on whether
the Utah BART Alternative achieves greater reasonable progress than the
BART Benchmark; and therefore, we have not taken them into
consideration.
    Consistent with EPA's regulations governing BART alternatives,\111\
in evaluating the weight-of-evidence demonstration, we have evaluated
all of the information and data submitted by Utah, while recognizing
the relative strengths and weaknesses of that information to arrive at
our proposed decision. Based on the weight-of-evidence presented, we
propose to approve Utah's determination that the Utah BART Alternative
would achieve greater reasonable progress than BART under 40 CFR
51.308(e)(2)(i)(I).
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    \111\ 71 FR 60622 (Oct. 13, 2006).
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g. Requirement That Emission Reductions Take Place During Period of
First Long-Term Strategy
    As discussed previously in section IV.C.6, pursuant to 40 CFR
51.308(e)(2)(iii), the State must ensure that all necessary emission
reductions take place during the period of the first long-term strategy
for regional haze, i.e., by December 31, 2018. The RHR further provides
that, to meet this requirement, the State must provide a detailed
description of the alternative measure, including schedules for
implementation, the emission reductions required by the program, all
necessary administrative and technical procedures for implementing the
program, rules for accounting and monitoring emissions, and procedures
for enforcement.\112\
---------------------------------------------------------------------------

    \112\ 40 CFR 51.308(e)(2)(iii).
---------------------------------------------------------------------------

    As noted previously, the Utah SIP revision incorporates the
revisions to R307-110-17, Section IX, Control Measures for Area and
Point Sources, Part H, Emissions Limits, which includes provisions for
implementing the Utah BART Alternative. In addition to the emission
limitations for NOX and PM10, and the requirement
for shutdown of the Carbon plant listed in Table 2, the SIP includes
compliance dates, operation and maintenance requirements, and
monitoring, recordkeeping, and reporting requirements. We propose to
find that these provisions meet the requirements of 40 CFR
51.308(e)(2)(iii).
h. Demonstration That Emission Reductions From Alternative Program Will
Be Surplus
i. June 2015 Utah RH SIP
    As discussed previously in section IV.C.7, pursuant to 40 CFR
51.308(e)(2)(iv), the SIP must demonstrate that the emissions
reductions resulting from the alternative measure will be surplus to
those reductions resulting from measures adopted to meet requirements
of the CAA as of the baseline date of the SIP. The baseline date for
regional haze SIPs is 2002.\113\ As discussed in section IV.C.7, all of
the emission reductions required by the Utah BART Alternative result
from measures applicable to Hunter, Huntington and Carbon that occur
after 2002.
---------------------------------------------------------------------------

    \113\ See Memorandum from Lydia Wegman and Peter Tsirigotis,
2002 Base Year Emission Inventory SIP Planning: 8-hr Ozone,
PM2.5, and Regional Haze Programs, November 18, 2002.
http://www3.epa.gov/ttnchie1/eidocs/2002baseinven_102502new.pdf.
---------------------------------------------------------------------------

    Furthermore, the State's SIP explains that the WRAP modeling that
was done to support the Utah RH SIP included regional SO2
emissions based on the 2018 SO2 milestone and also included
NOX and PM10 emissions from the Carbon plant.
Thus, WRAP did not rely on emission reductions from the Carbon plant in
establishing the 2018 SO2 milestone.
    The State's SIP also includes SO2 trend data that
further demonstrate emission reductions from the Carbon plant do not
appear to be needed for meeting the 2018 milestone of 141,849 tpy.
Actual emissions in the three-state region are calculated each year and
compared to the milestones. As can be seen in Table 7, SO2
emissions reported for 2011 are below the 2018 milestone and the most
recent milestone report for 2013 demonstrates that SO2
emissions are currently 26 percent lower than the 2018 milestone.
Additionally, the Carbon plant was fully operational in the years 2011-
2013 when the emissions from the three-state region were below the 2018
milestone for those years. Therefore, the SO2 emission
reductions from the closure of the Carbon plant appear to be surplus to
what is needed to meet the 2018 milestone established in Utah's RH SIP.
ii. October 2015 Utah RH SIP
    As discussed previously in section IV.D, Utah submitted enforceable
commitments in its October 20, 2015 SIP to address potential concerns
that the State would be double counting SO2 emissions
reductions for the Carbon plant closure under both the 40 CFR 51.308
and 309 programs.\114\
---------------------------------------------------------------------------

    \114\ Regional Haze Section XX, N. (1).
---------------------------------------------------------------------------

    EPA has historically recognized that under certain circumstances,
it is appropriate to approve a SIP submission that consists, in part,
of an enforceable commitment. Once EPA determines that circumstances
warrant consideration of an enforceable commitment to meet section
110(a)(2)(A) of the Act (and other applicable sections as relevant),
EPA applies three factors to determine whether to approve the
enforceable commitment: (1) Whether the commitment addresses a limited
portion

of the statutorily-required program; (2) whether the state is capable
of fulfilling its commitment; and (3) whether the commitment is for a
reasonable and appropriate period of time. Once approved in a SIP, the
commitments are enforceable by both EPA and citizens under the Act.
    First, Utah's revisions address a limited portion of the
statutorily-required program. The Air Quality Board adopted revisions
to SIP Section XX, Regional Haze, and added a new subsection N,
``Enforceable Commitments for the Utah Regional Haze SIP'' that
resolves specific identified issues. In this provision of the SIP,
``[t]he State commits to resolving this double counting issue by
revising the Utah 309 plan to specifically state that the 8,005 tons of
SO2 emissions from the Carbon units will be added into the
annual milestone reports from 2016 through the life of the backstop
trading program, thereby removing any credit for that emission
reduction in meeting the levels specified in the Utah 309 plan.'' \115\
Reporting Carbon's emissions in this manner is reasonable and ensures
that these emissions reductions are only credited under the BART
Alternative.
---------------------------------------------------------------------------

    \115\ Regional Haze SIP Section XX, N. (1).
---------------------------------------------------------------------------

    The SIP indicates the Board is capable of fulfilling these
commitments by explaining that ``[a]ll required amendments to this SIP
will be done through the State's SIP adoption process'' \116\ and that
``[t]he SIP is adopted by the Governor-appointed Air Quality Board
through a rulemaking process that includes public comment periods and
an opportunity for a public hearing.'' \117\
---------------------------------------------------------------------------

    \116\ Regional Haze SIP Section XX, N. (4).
    \117\ Regional Haze SIP Section XX, N. (4).
---------------------------------------------------------------------------

    The SIP commits to resolve the identified issues (``SIP Section
XX.D.3.c and [the State's rule] R307-150 will be revised . . .''
\118\), and any other related issues, within reasonable amount of time
(``Utah will work with EPA and take appropriate action to resolve any
completeness or approvability issues that arise regarding the proposed
SIP revision by March 2018'' \119\). This will allow sufficient time
for EPA to act on the submittal before the end of the milestone
commitment.
---------------------------------------------------------------------------

    \118\ Regional Haze SIP Section XX, N. (3).
    \119\ Regional Haze SIP Section XX, N. (6), (3).
---------------------------------------------------------------------------

    We also propose to concur that Carbon's 8,005 tpy of SO2
emissions reductions is a limited portion of the overall requirements
of the 309 program and particularly in comparison to the 2018
SO2 milestone of 141,849 tpy described in Table 7.\120\
---------------------------------------------------------------------------

    \120\ Regional Haze SIP Section XX, N. (2).
---------------------------------------------------------------------------

    Based on these considerations, we propose to approve the
enforceable commitment SIP.
    Therefore, based on the information presented previously from the
State's SIP and enforceable commitment SIP, we propose to concur that
the reductions from Carbon are surplus and can be considered as part of
an alternative strategy under 40 CFR 51.308(e)(2)(iv).

C. PM10 BART Determinations

    As discussed previously in section IV.B.2, Utah determined that the
PM10 BART emission limit for Hunter Units 1 and 2 and
Huntington Units 1 and 2 was 0.015 lb/MMBtu based on a three-run test
average. Utah noted that because the most stringent technology is in
place at these units and that the PM10 emission limits have
been made enforceable in the SIP, no further analysis was required.
    EPA has reviewed Utah's PM10 BART streamlined five-
factor analysis and PM10 BART determinations for Hunter
Units 1 and 2 and Huntington Units 1 and 2 and proposes to find that
these determinations meet the requirements of 40 CFR 51.309(d)(4)(vii).
The fabric filter baghouses installed at these BART units are
considered the most stringent technology available. The emission limit
of 0.015 lb/MMBtu at these units represents the most stringent emission
limit for PM10. Utah's use of a streamlined approach to the
five-factor analysis is reasonable as the BART Guidelines provide that
a comprehensive BART analysis can be avoided if a source commits to a
BART determination that consists of the most stringent controls
available.\121\
---------------------------------------------------------------------------

    \121\ 40 CFR 51, appendix Y, section IV.D.1.9.
---------------------------------------------------------------------------

    Utah's regulatory text provides, ``[e]missions of particulate (PM)
shall not exceed 0.015 lb/MMBtu heat input from each boiler based on a
3-run test average.'' It further states that ``[s]tack testing for the
emission limitation shall be performed each year on each boiler.''
\122\ We note that BART limits must apply at all times. See CAA section
302(k), 40 CFR part 51, appendix Y, section V. Furthermore, EPA's
credible evidence rule requires that a state's plan must not preclude
the use of any credible evidence or information, which can include
evidence and information other than the test method specified in the
plan, that would indicate whether a source was in compliance with
applicable requirements.\123\
---------------------------------------------------------------------------

    \122\ June 2015 Utah RH SIP, Sections IX.H.22.a.i.A-B,
IX.H.22.b.i.A-B.
    \123\ 40 CFR 51.212(c).
---------------------------------------------------------------------------

    Consistent with these requirements, we propose to interpret Utah's
regulatory text as imposing a PM limit of 0.015 lb/MMBtu that applies
at all times and does not preclude the use, including the exclusive
use, of any credible evidence or information, relevant to whether a
source is in compliance with the limit.

D. Monitoring, Recordkeeping, and Reporting

    EPA has reviewed Utah's monitoring, recordkeeping and reporting
measures in its June 4, 2015 SIP Section IX, Part H for the BART
Alternative and the PM10 BART determinations and proposes to
approve these measures as meeting the requirements of section 110(a)(2)
of the CAA and 40 CFR 51, subpart K, Source Surveillance, with the
exception of reporting requirements for violations of PM10
emissions limitations. For PM10 reporting, we are proposing
to conditionally approve this element in accordance with CAA section
110(k)(4) based on Utah's commitment to submit specific measures to
address the reporting requirement.\124\ Utah's letter commits to adopt
and submit rule language that would require sources to report any
deviation from the requirements of the RH SIP provisions, which would
include the PM10 emission limitations. The specific language
is detailed in Utah's commitment letter.
---------------------------------------------------------------------------

    \124\ Letter from Department of Environmental Quality, State of
Utah to EPA, DAQP-120-15 (Dec. 10, 2015).
---------------------------------------------------------------------------

    Otherwise, the SIP includes adequate measures that pertain to
operation of Hunter and Huntington and the closure of Carbon. EPA
previously approved state rule provisions that Utah has also cross
referenced in these new regional haze measures, including terms,
conditions and definitions in R307-101-1, R307-101-2 and R307-170-4 as
well as other continuous emission monitoring system (CEMS) requirements
referenced in R307-107. These measures are consistent with similar
monitoring, recordkeeping, and reporting requirements that EPA has
approved in other states or that we have adopted in federal plans,\125\
and in particular contain the requirements that were missing from
Utah's prior regional haze submittals.\126\ As described previously in
section IV.A.3, Utah has provided the emission limitations, work
practice standards, monitoring, recordkeeping, and reporting

requirements for all the units that are part of Utah's BART Alternative
for the Hunter, Huntington, and Carbon plants.
---------------------------------------------------------------------------

    \125\ 77 FR 57864; 79 FR 5032.
    \126\ 77 FR 74365-74366 (Dec. 14, 2012).
---------------------------------------------------------------------------

    If we finalize our proposed approval, the regulatory text contained
in our final rule for 40 CFR part 52 subpart TT will be consistent with
the relevant provisions of Utah's regional haze submittals for making
the emission limits and other requirements enforceable. If EPA
finalizes the conditional approval of Utah's PM10 reporting
provision, the State has one year from the date of EPA's final action
on the June 4, 2015 SIP to submit the necessary SIP revisions. If the
State fails to meet its commitment within the one-year period, the
approval is treated as a disapproval. EPA proposes to find that the
necessary SIP revisions meet EPA's criteria for conditional approvals
\127\ as the revisions appear to involve a limited amount of technical
work, are anticipated to be non-controversial, and can reasonably be
accomplished within the length of time for the State's adoption
process.
---------------------------------------------------------------------------

    \127\ See Memorandum from John Calcagni to EPA Regional
Directors. ``Processing of State Implementation Plan (SIP)
Submittals'' (July 1992), available at http://www3.epa.gov/ttn/oarpg/t1/memoranda/siproc.pdf.
---------------------------------------------------------------------------

E. Consultation with FLMs

    As discussed previously in section IV.G, Utah conducted FLM
consultation during late 2014, providing over 60 days prior to the
December 1, 2014 public hearing. Subsequently, the National Park
Service provided extensive comments in response to a second public
comment period in April 2015. Based on these considerations, we propose
to find that Utah has met the requirements of 40 CFR 308(i)(2).

VI. EPA's Evaluation and Proposed Partial Approval and Partial
Disapproval of Utah's Regional Haze SIP

    In this section, we present the second of two alternative proposed
actions on which EPA is soliciting comment. As explained previously in
sections II.A and V, EPA is soliciting comments on two alternative
proposals: a proposal to approve the State SIP in its entirety, and a
proposal to partially approve and partially disapprove the State SIP
and to issue a FIP. The co-proposals detailed in this section and
Section V represent different conclusions regarding Utah's
NOX BART Alternative and the metrics the State has proposed
to support this alternative.
    As described in this section, EPA is proposing to partially approve
and partially disapprove Utah's June 2015 and October 2015 RH SIP
revisions and propose a FIP. Alternatively, as discussed in section V,
EPA is co-proposing in the alternative to approve Utah's June 2015 and
October 2015 RH SIP revisions.
    This document is written as two separate proposals in order to
clearly present the options and solicit comment on each. EPA intends to
finalize only one of these co-proposals; however, we also acknowledge
that additional information and comments may also lead the Agency to
adopt final SIP and/or FIP regulations that differ somewhat from the
co-proposals presented here regarding the BART Alternative, BART
control technology option or emission limits, or impact other proposed
regulatory provisions.

A. Basis for Proposed Partial Disapproval and Partial Approval

    For the reasons described later, EPA proposes to partially approve
and partially disapprove the two Utah 2015 RH SIP revisions. Our
proposed action is based on an evaluation of Utah's regional haze SIP
submittals against the regional haze requirements at 40 CFR 51.300-
51.309 and CAA sections 169A and 169B, as well as the supplemental
information EPA developed, such as EPA's calculations of the visibility
improvements for each modeling scenario using consistent meteorological
years in evaluating the 98th percentile modeling and referencing the
topographical maps in evaluating whether distribution of emissions
would be substantially different under the Utah BART Alternative. All
general SIP requirements contained in CAA section 110, other provisions
of the CAA, and our regulations applicable to this action were also
evaluated. The purpose of this action is to ensure compliance with
these requirements. As discussed in section V, EPA is also co-proposing
to approve the Utah's June 2015 and October 2015 RH SIP revisions.

B. Utah BART Alternative

1. Summary of Utah BART Alternative
    Utah has opted to establish an alternative measure (or program) for
NOX in accordance with 40 CFR 51.308(e)(2). A description of
the Utah BART Alternative is provided in section IV.C. The RHR requires
that a SIP revision establishing a BART alternative include three
elements as listed later. We have evaluated the Utah BART Alternative
with respect to each of these elements.
     A demonstration that the emissions trading program or
other alternative measure will achieve greater reasonable progress than
would have resulted from the installation and operation of BART at all
sources subject to BART in the State and covered by the alternative
program.\128\
---------------------------------------------------------------------------

    \128\ 40 CFR 51.308(e)(2)(i).
---------------------------------------------------------------------------

     A requirement that all necessary emissions reductions take
place during the period of the first long-term strategy for regional
haze.\129\
---------------------------------------------------------------------------

    \129\ 40 CFR 51.308(e)(2)(iii).
---------------------------------------------------------------------------

     A demonstration that the emissions reductions resulting
from the alternative measure will be surplus to those reductions
resulting from measures adopted to meet requirements of the CAA as of
the baseline date of the SIP.\130\
---------------------------------------------------------------------------

    \130\ 40 CFR 51.308(e)(2)(iv).
---------------------------------------------------------------------------

2. Demonstration of Greater Reasonable Progress for Alternative Program
    As discussed previously in section III.E.1, pursuant to 40 CFR
51.308(e)(2)(i), Utah must demonstrate that the alternative measure
will achieve greater reasonable progress than would have resulted from
the installation and operation of BART at all sources subject to BART
in the State and covered by the alternative program. This
demonstration, primarily included in Chapter 1 of the TSD of the Utah
RH SIP,\131\ must be based on five criteria presented below.
---------------------------------------------------------------------------

    \131\ As presented in this proposal, while the majority of the
State's demonstration is contained in Chapter 1, EPA has identified
additional information regarding the demonstration and we include
references to the additional information.
---------------------------------------------------------------------------

a. A List of All BART-Eligible Sources Within the State
    As discussed previously in section IV.C.1, Utah included a list of
BART-eligible sources and noted the following sources are all covered
by the alternative program:
     PacifiCorp Hunter, Unit 1,
     PacifiCorp Hunter, Unit 2,
     PacifiCorp, Huntington, Unit 1, and
     PacifiCorp, Huntington, Unit 2.
    EPA approved Utah's BART eligibility determinations in our 2012
rulemaking.\132\
---------------------------------------------------------------------------

    \132\ 77 FR 74357 (Dec. 14, 2012).
---------------------------------------------------------------------------

b. A List of All BART-Eligible Sources and All BART Source Categories
Covered by the Alternative Program
    As discussed previously in section IV.A.3, the Utah BART
Alternative covers all the BART-eligible sources in the state, Hunter
Units 1 and 2 and Huntington Units 1 and 2, in addition to three non-
BART units, PacifiCorp's Hunter Unit 3 and Carbon Units 1 and 2. EPA
previously approved Utah's

BART eligibility determinations in our 2012 rulemaking.\133\
---------------------------------------------------------------------------

    \133\ 77 FR 74357 (Dec. 14, 2012).
---------------------------------------------------------------------------

c. Analysis of BART and Associated Emission Reductions Achievable
    As noted previously in section IV.C.3, in the June 2015 Utah RH
SIP, Utah compared the Utah BART Alternative to a BART Benchmark which
included the most stringent NOX BART controls, SCR plus new
LNBs and SOFA, at the four BART units. This is consistent with the
streamlined approach described in Step 1 of the BART Guidelines. The
BART Guidelines note that a comprehensive BART analysis can be avoided
if a source commits to a BART determination that consists of the most
stringent controls available.\134\
---------------------------------------------------------------------------

    \134\ 40 CFR 51, appendix Y, section IV.D.1.9.
---------------------------------------------------------------------------

    We propose to find that Utah has met the requirement for an
analysis of BART and associated emission reductions achievable at
Hunter and Huntington under 40 CFR 51.308(e)(2)(i)(C).
    d. Analysis of Projected Emissions Reductions Achievable Through
the BART Alternative
    As discussed previously in section IV.C.4, a summary of Utah's
estimates of emissions for the Utah BART Alternative and the BART
Benchmark is provided in Table 3. We propose to find that Utah has met
the requirement for an analysis of the projected emissions reductions
achievable through the alternative measure under 40 CFR
51.308(e)(2)(i)(D).
e. A Determination That the Alternative Achieves Greater Reasonable
Progress Than Would Be Achieved Through the Installation and Operation
of BART
Greater Reasonable Progress Based on 40 CFR 51.308(e)(3)'s Greater
Emission Reductions Test
    As discussed previously in section III.E.1, 40 CFR 51.308(e)(3)
allows a state to satisfy the final step of the better-than-BART
demonstration by showing that that ``distribution of emissions is not
substantially different than under BART'' and that ``the alternative
measure results in greater emission reductions.'' EPA has explained
that when the BART alternative ``achieves greater emission reductions
than each of the individual BART determinations'' \135\ for each of the
pollutants, ``as well as in the aggregate,'' \136\ ``visibility
modeling is not required to support a better-than-BART determination. .
. .'' \137\ However, as EPA explained in responding to comments in the
final rule for the BART Alternative for the Apache Generating Station
in Arizona's SIP, ``where BART and the BART Alternative result in
reduced emissions of one pollutant but increased emissions of another,
it is not appropriate to use the `greater emission reductions' test.''
Instead, the proper approach is to employ a clear weight-of-evidence
approach under 40 CFR 51.308(e)(2) in order to demonstrate that the
alternative achieves greater reasonable progress than BART.'' \138\ We
have not considered a total emissions profile that combines emissions
of multiple pollutants to determine whether BART or the alternative is
``better,'' except where every visibility impairing pollutant is
reduced by a greater amount under the BART alternative.\139\ A
comparison of mass emissions from multiple pollutants (such as
NOX and SO2) is not generally informative,
particularly in assessing whether the alternative approach provides for
greater reasonable progress towards improving visibility. Instead, when
emissions of one or more pollutants increases under an alternative, EPA
has ``given the most weight to the visibility impacts based on air
quality modeling'' \140\ and used modeling to determine whether or not
a ``BART Alternative measure that relies on interpollutant trading
results in greater reasonable progress.'' \141\
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    \135\ 79 FR 9318, 9335 (Feb. 18, 2014).
    \136\ 79 FR 9318, 9335 (Feb. 18, 2014). See, e.g., 77 FR 11827,
11837 (Feb. 28, 2012) (proposed approval of Maryland BART
Alternative, which shows greater SO2 and NOX
reductions from the Alternative than application of BART, the two
pollutants covered by the Alternative); 77 FR 39938, 39940-1 (July
6, 2012) (final approval of Maryland BART Alternative, explaining in
responding to comments that because the emission reductions are
greater for the Alternative than BART and the distribution of
emissions is not substantially different, the Alternative was found
to meet 40 CFR 51.308(e)(2) and visibility dispersion modeling was
not needed).
    \137\ 79 FR 9318, 9335 (Feb. 18, 2014) (proposed approval of
Arizona BART Alternative for Sundt Unit 4). See also, 79 FR 52420
(Sept. 3, 2014) (final approval of Arizona BART Alternative for
Sundt Unit 4); 77 FR 18052, 18073-18075 (Mar. 26, 2012) (proposed
approval of Colorado BART Alternative, no modeling required where
the 40 CFR 51.308(e)(3) test was met); 77 FR 76871 (Dec. 31, 2012)
(final approval of Colorado BART Alternative).
    \138\ 80 FR 19220, 19221 (Apr. 10, 2015). See, e.g., 79 FR
56322, 56327-28 (Sept. 19, 2014); 77 FR 18052, 18075 (Mar. 26.
2012).
    \139\ 77 FR 18052, 18075 (Mar. 26, 2012).
    \140\ 79 FR 56322, 56328 (Sept. 19, 2014) (proposed approval of
Arizona Apache BART Alternative); 80 FR 19220 (Apr. 10, 2015) (final
approval of Arizona Apache BART Alternative).
    \141\ 79 FR 33438, 33441 (June 11, 2014) (final rule, FIP for
Tesoro Refining BART Alternative); See, e.g., 79 FR 56322, 56328
(Sept. 19, 2014) (proposed approval of Arizona Apache BART
Alternative); 80 FR 19220 (Apr. 10, 2015) (final approval of Arizona
Apache BART Alternative); 77 FR 11827, 11837 (Feb. 28, 2012)
(proposed approval of Maryland BART Alternative); 77 FR 39938,
39940-1 (July 6, 2012) (final approval of Maryland BART
Alternative).
---------------------------------------------------------------------------

    The State's demonstration appears to satisfy the first part of the
test under 40 CFR 51.308(e)(3) (the distribution of emissions may not
be substantially different than under BART) since the Hunter,
Huntington and Carbon plants are all located within close proximity of
each other in central Utah, as discussed previously in section IV.C.5.
EPA's interpretation of the requirement under 40 CFR 51.308(e)(3) that
the alternative measure ``results in greater emission reductions'' has
been that the emission reduction comparisons are pollutant specific. We
have not looked at a total emissions profile that combines emissions of
multiple pollutants to determine whether a BART benchmark or a BART
alternative is ``better,'' except where every visibility impairing
pollutant is reduced by a greater amount under the BART
alternative.\142\ Therefore, we propose to find that the State's
demonstration does not meet the second part of the test. While in the
aggregate there are fewer SO2 and PM10 emissions
for the BART Alternative, the total NOX emissions are
greater under the BART Alternative than the BART Benchmark. Therefore,
we propose to disapprove Section XX.D.6.c of the Utah SIP under the
test in 40 CFR 51.308(e)(3).
---------------------------------------------------------------------------

    \142\ 79 FR 9318, 9335 (Feb. 18, 2014)(proposed approval of
Arizona BART Alternative for Sundt Unit 4). 79 FR 52420 (Sept. 3,
2014) (final approval of Arizona BART Alternative for Sundt Unit 4);
77 FR 18052, 18073-18075 (Mar. 26, 2012) (proposed approval of
Colorado BART Alternative, no modeling required where the 40 CFR
51.308(e)(3) test was met); 77 FR 76871 (Dec. 31, 2012) (final
approval of Colorado BART Alternative).
---------------------------------------------------------------------------

Greater Reasonable Progress Based on 40 CFR 51.308(e)(2)'s Weight-of-
Evidence Test
    Utah also chose to conduct a weight-of-evidence analysis under 40
CFR 51.308(e)(2) based on a BART Alternative involving certain units at
the Hunter, Huntington, and Carbon power plants, which included the
following nine categories of evidence.
i. Annual Emissions Comparison of all Visibility-Impairing Pollutants
    The emissions of visibility-impairing pollutants from both the Utah
BART Alternative and the BART Benchmark, as estimated by Utah, are
summarized in Table 3 in section IV.C.4. Compared with the Utah BART
Benchmark, the State projects that the Utah BART Alternative will
result in 5,721 tpy more NOX emissions, 8,005 tpy fewer
SO2 emissions and 573 tpy fewer PM10 emissions
than the BART Benchmark. As discussed previously, Utah also

noted that the combined emissions of NOX, SO2 and
PM10 will be 2,856 tpy lower under the BART Alternative than
the BART Benchmark.
    While the total emission reductions under the Utah BART Alternative
are less than those under the BART Benchmark, a comparison of emissions
of multiple pollutant species of emissions is generally not
informative, particularly when the Agency is assessing whether an
approach provides for greater reasonable progress towards improving
visibility. As explained in section VI.B.e, our interpretation of the
language in 40 CFR 51.308(e)(3) (``results in greater emission
reductions . . . may be deemed to achieve greater reasonable
progress'') has been pollutant specific. EPA has not relied on a total
emissions profile that combines emissions of multiple pollutants
together to determine that either BART or a BART alternative is
``better,'' because visibility modeling is the most appropriate method
to assess the overall improvements in visibility impacts from control
scenarios where reductions of multiple pollutants are considered,
except where every visibility impairing pollutant is reduced by a
greater amount under the alternative.\143\ As we have explained,
``[e]ach of the five pollutants which cause or contribute to visibility
impairment has a different impact on light extinction for a given
particle mass, making it therefore extremely difficult to judge the
equivalence of interpollutant trades in a manner that would be
technically credible, yet convenient to implement in the timeframe
needed for transactions to be efficient. This analysis is further
complicated by the fact that the visibility impact that each pollutant
can have varies with humidity, so that control of different pollutants
can have markedly different effects on visibility in different
geographic areas and at different times of the year.'' \144\ As other
Agency actions on BART alternatives have explained, modeling assesses
``both pollutants' chemical aerosol formation mechanisms and impacts on
visibility,'' \145\ which allows evaluation of the ``relative
visibility impacts from the atmospheric formation of visibility
impairing aerosols of sulfate and nitrate.'' \146\ Since we find that
Utah's BART Alternative provides greater emission reductions for two
pollutants (SO2 and PM10), but find that
NOX emissions would be greater under the BART Alternative,
we propose to find that it is not appropriate to combine all three
pollutants in the annual emissions comparison test to support the BART
Alternative as the State has done. While we acknowledge that two of the
pollutants are less under the BART Alternative, one of the pollutants
is greater, therefore we further propose to find that the annual
emissions comparison of all three pollutants does not show that the
BART Alternative is better than the BART Benchmark.
---------------------------------------------------------------------------

    \143\ 79 FR 9318, 9335 (Feb. 18, 2014) (proposed approval of
Arizona BART Alternative for Sundt Unit 4). 79 FR 52420 (Sept. 3,
2014) (final approval of Arizona BART Alternative for Sundt Unit 4);
77 FR 18052, 18073-18075 (Mar. 26, 2012) (proposed approval of
Colorado BART Alternative, no modeling required where the 40 CFR
51.308(e)(3) test was met); 77 FR 76871 (Dec. 31, 2012) (final
approval of Colorado BART Alternative).
    \144\ 64 FR 35714, 35743 (July 1, 1999).
    \145\ 78 FR 79344, 79355 (Dec. 30, 2013).
    \146\ 79 FR 33438, 33440 (June 11, 2014).
---------------------------------------------------------------------------

ii. Improvement in the Number of Days With Significant Visibility
Impairment
    As discussed previously in section IV.C.5, Utah provided modeling
results to assess the improvement in the number of days with
significant visibility impairment--that is, the improvement in the
number of days with impacts that either cause (>1.0 dv) or contribute
(0.5 dv) to visibility impairment.
    The BART Guidelines provide that, when making a BART determination,
a State may consider the number of days or hours that a threshold was
exceeded.\147\ In developing the BART Guidelines, our example modeling
analysis of a hypothetical source examined the number of days that 1.0
dv and 0.5 dv thresholds were exceeded.\148\ As detailed in section
IV.C.5.b, we note the difference in the total number of days impacted--
18 fewer days greater than the causation threshold of 1.0 dv (775 days
for the BART Alternative vs. 793 days for the BART Benchmark), and 175
fewer days greater than the contribution 0.5 dv threshold (1,323 days
for the BART Alternative vs. 1,498 days for the BART Benchmark. Utah's
results show that there are fewer days with impacts over 0.5 dv for the
BART Alternative, which indicates greater improvement in visibility.
Therefore, the results for the 0.5 dv threshold favor the BART
Alternative.
---------------------------------------------------------------------------

    \147\ 40 CFR 51, appendix Y, section IV.D.5.
    \148\ 70 FR 39130 (July 6, 2005).
---------------------------------------------------------------------------

    However, Utah's results for the total number of days with impacts
over 1.0 dv on a Class I area-by-area basis are not as clear in
supporting the BART Alternative. The modeling results for the total
number of days with impacts greater than 1.0 dv show that the BART
Alternative would have more days with impacts greater than 1.0 dv at
seven of the nine Class I areas, and that only two of the Class I
areas, would have fewer days with impacts greater than 1.0 dv compared
to the BART Benchmark. Therefore, the Class I area-by-area results do
not show that the BART Alternative is better than the BART Benchmark.
Similarly, the results for the average number of days with impacts over
1.0 dv show that most of the Class I areas have the same result under
both the BART Alternative and Benchmark, or are within one day of
having the same result. In this context, a difference of one day is not
particularly significant. We therefore propose to find that these
results do not show the BART Alternative is better.
    Utah's results in applying the number of days with impacts greater
than 1.0 dv show the BART Alternative is better ``on average'' across
all nine Class I areas. We agree that use of average visibility impacts
could be acceptable as part of assessing the multiple-area impacts and
improvements. However, in this case the visibility results for the
individual Class I areas do not consistently support or undermine the
BART Alternative; there is variation by Class I area. Here, averaging
the visibility results has the effect of obscuring the impacts on the
individual Class I areas. Additionally, we propose to not the give the
difference in days significant weight because by itself it does not
indicate whether benefits on those days were large or small. Therefore,
while we note that the BART Alternative shows fewer days with impacts
greater than 1.0 dv when looking at the average over all nine areas, we
propose to find that averaging the number of days with impacts greater
than 1.0 dv across all affected Class I areas is not a relevant metric
under these circumstances. We therefore further propose to find that
this metric does not show the BART Alternative is better.
iii. 98th Percentile Impact (dv)
    As discussed previously in section IV.C.5, Utah asserted that the
only metric it evaluated that showed greater improvement for the BART
Benchmark in comparison to the BART Alternative was the 98th percentile
metric when averaged across all Class I areas and meteorological years
modeled. Utah's comparison of the modeled visibility impacts on the
98th percentile day (8th highest impacted day in a given meteorological
year) for the most impacted year shows that the BART Benchmark would
result in greater visibility improvement at five of the nine Class I
areas, and is better on average across all nine Class I areas (0.11 dv
difference). At the most

impacted Class I areas, Canyonlands and Capitol Reef, Utah found that
the 98th percentile metric indicates the BART Benchmark has 0.76 dv and
0.57 dv, respectively, more improvement than the BART Alternative. At
other Class I areas, such as Arches, Utah found that the 98th
percentile metric indicates that the BART Alternative provides greater
visibility improvement (for example, 0.44 dv at Flat Tops).
    The 98th percentile visibility impact is a key metric recommended
by the BART Guidelines when selecting BART controls.\149\ As noted
previously, we described this metric as an appropriate measure for
determining the degree of visibility improvement to be expected from
controls.\150\ In addition, this is one of the primary metrics that EPA
has relied on in evaluating prior regional haze actions that have
included BART alternatives.\151\
---------------------------------------------------------------------------

    \149\ 40 CFR 51, appendix Y, section IV.D.5.
    \150\ 70 FR at 39129.
    \151\ See, e.g., 78 FR 79344 (Dec. 30, 2012)(proposed rule, FIP
for Tesoro Refining and Intalco Refinery BART Alternatives); 79 FR
33438 (June 11, 2014)(final rule, FIP for Tesoro Refining and
Intalco Refinery BART Alternatives); 79 FR 56322, 56328 (Sept. 19,
2014)(proposed approval of Arizona Apache BART Alternative); 80 FR
19220 (Apr. 10, 2015)(final approval of Arizona Apache BART
Alternative); 77 FR 11827, 11837 (Feb. 28, 2012)(proposed approval
of Maryland BART Alternative); 77 FR 39938, 39940-1 (July 6,
2012)(final approval of Maryland BART Alternative).
---------------------------------------------------------------------------

    We note that when calculating visibility improvements for
individual Class I areas, Utah mixed the impacts from different
meteorological years between modeling scenarios (baseline, BART
benchmark, and BART Alternative). As discussed in section V.B.2.e, the
State's use of different meteorological years may introduce some error
as the visibility improvements could be driven by year-to-year
variability in meteorological conditions, as opposed to the differences
in emission reductions between the BART Alternative and BART Benchmark.
For this reason, in addition to the information from the State, EPA has
also calculated the visibility improvements for each modeling scenario
using paired-in-time meteorological and emissions data.\152\ Using this
method, whether the BART Alternative resulted in lower 98th percentile
impacts depends on both the particular Class I area and meteorological
year modeled. In some years and some Class I areas, particularly some
of the most impacted Class I areas, the BART Benchmark shows better
visibility improvement than the BART Alternative (for example, 0.93 dv
greater improvement for Canyonlands and 0.75 in 2002 dv greater
improvement for Capitol Reef in 2001).\153\ At other Class I areas, the
98th percentile metric indicates that the BART Alternative provides
greater visibility improvement (for example, by 0.90 dv at Arches in
2003 and 0.43 dv at Flat Tops in 2002).\154\ On the whole, when using
this method, the BART Benchmark is slightly better on average across
all years and nine Class I areas (0.14 dv difference).\155\ We propose
to find, consistent with the State's evaluation, that this metric
favors the BART Benchmark.
---------------------------------------------------------------------------

    \152\ See EPA Calculation of 98th Percentile Improvement for
Utah Bart Alternative spreadsheet (in docket).
    \153\ Id.
    \154\ Id.
    \155\ Id.
---------------------------------------------------------------------------

iv. Annual Average Impact (dv)
    As discussed previously in section IV.C.5, Utah's modeling shows
that the average annual dv impact at all Class I areas is better under
the Utah BART Alternative at five of the nine Class I areas, and is
better on average across all the Class I areas. The average impact was
calculated by averaging all daily modeling results for each year and
then calculating a three-year average from the annual average. Utah's
information shows that the BART Alternative is better than the BART
Benchmark by 0.009 dv on average across all nine Class I areas. While
EPA has not considered this metric in the past,\156\ since the State
includes it,\157\ we consider it here. Furthermore, the BART Guidelines
state that, ``in determining what, if any, emission controls should be
required, the State will have the opportunity to consider the
frequency, duration, and intensity of a source's predicted effect on
visibility.'' \158\ We note that the difference in the annual average
metric of 0.009 dv only marginally supports the BART Alternative and
that this metric shows less or equal visibility improvement at four of
the nine Class I areas. Because the annual average metric averages over
all days, it does not represent the benefits of the BART Alternative on
the maximum impact days. In previous evaluations of BART alternatives
we have relied on either the 98th percentile metric or the average
improvement for the worst 20% IMPROVE monitoring days to evaluate
greater reasonable progress. Therefore, we propose to find that the
information from the annual average metric does not support a
conclusion that the BART Alternative achieves greater reasonable
progress than the BART Benchmark.
---------------------------------------------------------------------------

    \156\ EPA final actions on BART Alternatives that evaluated
CALPUFF modeling analysis, which did not include consideration of
annual average dv impacts include: 80 FR 19220 (Apr. 10,
2015)(Region 9, Apache); 79 FR 33438 (June 11, 2014)(Region 10,
Tesoro Refining and Alcoa Intalco Operations); 77 FR 39938 (July 6,
2012)(Region 3, Maryland HAA).
    \157\ See Utah Regional Haze State Implementation Plan,
Technical Support Document, Ch. 1, p. 23 (2015).
    \158\ 70 FR 39121 (July 5, 2005).
---------------------------------------------------------------------------

v. 90th Percentile Impact (dv)
    As discussed previously in section IV.C.5, Utah's comparison of the
modeled visibility impacts at the 90th percentile (the 110th highest
day in a year) dv impact shows that the Utah BART Alternative is better
at seven of the nine Class I areas and is slightly better averaged both
across three years and across nine Class I areas (0.006 dv difference).
We note that the use of the 90th percentile impacts to evaluate
alternatives has not been EPA's practice for source-specific BART
determinations; however, as discussed previously for the average dv
impact metric, the BART Guidelines allow states to consider other
visibility metrics in addition to the 98th percentile. Yet, because of
the small difference between the two scenarios (0.006 dv), we propose
to find that it is questionable whether the 90th percentile supports a
conclusion that the BART Alternative achieves greater reasonable
progress.

vi. Timing for the Emissions Reductions

    As discussed previously in section IV.C.5, assuming the four BART
units receive five years to come into compliance, Utah noted that
reductions under the Utah BART Alternative will occur earlier than the
BART Benchmark. The reductions under the Utah BART Alternative are
required under the State SIP by August 2015, as noted in Table 5, and
would provide an early and on-going visibility benefit as compared to
BART. Also notable is that combustion control upgrades at the Hunter
and Huntington facilities have been achieving significant
NOX reductions since the time of their installation between
2006 and 2014, depending on the unit.\159\ Finally, if, as proposed in
section VI.C, BART for the four units is LNB/SOFA plus SCR, BART likely
would be fully implemented sometime between 2019 and 2021.
---------------------------------------------------------------------------

    \159\ Copies of Administrative Orders DAQE-AN0102370012-08 and
DAQE-AN0102380021-10 are included in the docket, and include
information regarding the schedule for installation of combustion
controls at Hunter and Huntington.
---------------------------------------------------------------------------

    Therefore, we recognize that the reductions from the BART
Alternative would occur before the BART Benchmark.

vii. IMPROVE Monitoring Data
    Utah's SIP presents sulfate and nitrate monitoring data at the
Canyonlands IMPROVE monitor that show that ``sulfates are the dominant
visibility impairing pollutant'' \160\ and that sulfate levels have
decreased,\161\ and references similar results at other Class I areas
in the TSD.\162\ Utah also presents data on trends in emissions from
EGUs showing substantial reductions in emissions of both SO2
and NOX.\163\ Based on these data, Utah indicates it ``has
confidence that the SO2 reductions will achieve meaningful
visibility improvement'', under the Utah BART Alternative,\164\ while
``the visibility improvement during the winter months due to
NOX reductions is much more uncertain,'' \165\ Utah makes
this point even though nitrate concentrations are highest in the
winter, explaining that while there has been a reduction in
NOX, the ammonium nitrate values do not show similar
improvement in the winter months. Utah offers several possible
explanations for the results, but does not provide any definitive
conclusions.\166\
---------------------------------------------------------------------------

    \160\ Utah Regional Haze State Implementation Plan, Technical
Support Document, Ch. 1, p. 12 (2015).
    \161\ Id. at p. 15.
    \162\ Id. at p. 12.
    \163\ Id. at p. 14.
    \164\ Id. at p. 13.
    \165\ Id.
    \166\ Id. at pp. 16-19.
---------------------------------------------------------------------------

    Utah also presents data on the seasonality of park visitation and
monitoring data for nitrate and sulfates. These data show the highest
measured nitrate concentrations occur in winter during the period of
lowest park visitation, and that sulfates affect visibility throughout
the year and are the dominant visibility impairing pollutant from
anthropogenic sources during the high visitation period of March
through November. Utah concludes that it has greater confidence that
reductions in SO2 will be reflected in improved visibility
for visitors to the Class I areas, while reductions in NOX
will have a more uncertain benefit for visitors to Class I areas. We
invite comment on the information and conclusions provided by Utah as
summarized earlier.
    We propose to concur with one of the State's findings. We propose
to find that visibility benefits associated with NOX
reductions are much more likely to occur in the winter months because
this is when aerosol thermodynamics favors nitrate formation.\167\ By
contrast, SO2 emissions reductions should provide visibility
benefits in all seasons.\168\ We also propose to find that, as
concluded by the GCVTC, and supported by the IMPROVE monitoring data
presented by Utah, anthropogenic visibility impairment on the Colorado
Plateau is dominated by sulfates. Therefore, we propose to concur with
Utah's statement that sulfate is the largest contributor to visibility
impairment at the affected Class I areas.
---------------------------------------------------------------------------

    \167\ Fountoukis, C. & Nenes, A., ISORROPIA II: A
Computationally Efficient Aerosol Thermodynamic Equilibrium Model
for K+, Ca2+,
Mg2+, NH4+,
Na+, SO42-,
NO3-, Cl-, H2O Aerosols,
7 Atmos. Chem. Phys., 4639-4659 (2007).
    \168\ Seinfeld, John H., Urban Air Pollution: State of the
Science, 243 Science Magazine, no. 4892, 745, 750 (1989).
---------------------------------------------------------------------------

    We propose to disagree with the State's findings related to park
visitation. While the BART Guidelines do mention visitation as
something that can inform a control decision,\169\ EPA is proposing to
place little weight on the State's correlation of emissions reductions
and park visitation because nothing in the CAA suggests that visitors
during busy time periods are entitled to experience better visibility
than visitors during off-peak periods. On the contrary, in the Regional
Haze provisions of the CAA, Congress declared a national goal of
remedying all manmade visibility impairment in all class I areas, which
includes both heavily-visited national parks and seldom-visited
wilderness areas. We invite comment on our evaluation and the
information and conclusions provided by Utah as summarized previously.
---------------------------------------------------------------------------

    \169\ 70 FR 39104, 39130 (July 6, 2005) (``Other ways that
visibility improvement may be assessed to inform the control
decisions would be to examine distributions of the daily impacts,
determine if the time of year is important (e.g., high impacts are
occurring during tourist season), consideration of the cost-
effectiveness of visibility improvements (i.e., the cost per change
in deciview), using the measures of deciview improvement identified
by the State, or simply compare the worst case days for the pre- and
post-control runs. States may develop other methods as well.'').
---------------------------------------------------------------------------

viii. Energy and Non-Air Quality Benefits
    EPA's evaluation of the State's information on energy and non-air
quality benefits is located earlier in section V.B.2.e.viii.
ix. Cost
    EPA's evaluation of the Utah's cost information is located in
section V.B.2.e.ix.
f. Evaluation of the Weight of Evidence
    In this section we evaluate Utah's SIP under 40 CFR 51.308(e)(2),
to determine whether the State met the final step of the better-than-
BART analysis ``based on the clear weight of evidence that the trading
program or other alternative measure achieves greater reasonable
progress than would be achieved through the installation and operation
of BART at the covered sources.'' 40 CFR 51.308(e)(2)(i)(E).
    As discussed previously, we evaluated Utah's demonstration and all
available information and data presented by the State, as well as
additional information and data EPA developed and presented in this
notice. We propose to find that this information and data do not meet
the requirements of 40 CFR 51.308(e)(2)(i)(E). Specifically, we propose
that Utah's demonstration does not show by the ``clear weight of
evidence'' that the BART alternative ``measure achieves greater
reasonable progress than would be achieved through the installation and
operation of BART at the covered sources.'' 40 CFR 51.308(e)(2)(i)(E).
We have evaluated the relative strengths and weakness of the
information and propose to find that the State's analysis and
conclusions do not clearly show that the BART Alternative results in
greater reasonable progress than the BART Benchmark for the following
reasons: (1) The key metric EPA has used in evaluating alternatives
(98th percentile) on average across all the Class I areas favors the
BART Benchmark by 0.14 dv and not the BART Alternative; (2) the
majority of information and data that the State asserts favor the BART
Alternative over BART show small differences; (3) the comparison of net
emissions reductions across three pollutants, which the State relies on
significantly is not appropriate because not all pollutants are reduced
under the BART Alternative and each pollutant may have different
effects on visibility; and (4) while some information may show the
Alternative is better than BART, the information is not adequate to
meet the ``clear weight of evidence'' test.
    First, consistent with the Agency's practice, we have considered
all information, but have given most weight to the visibility impacts
based on air quality modeling.\170\ Here, the 98th percentile impacts
from the State's CALPUFF modeling show that the

BART Alternative is not better than the BART Benchmark because the BART
Benchmark would provide a 0.14 dv greater average improvement than the
BART Alternative. In addition, Table 12 lists a comparison of 2001-2003
three-year average 98th percentile visibility improvement for each of
the nine Class I areas; and the results for seven of the Class I areas
favor BART over the Alternative (Black Canyon of the Gunnison (0.06
dv), Bryce Canyon (0.04 dv), Canyonlands (0.78 dv), Capitol Reef (0.59
dv), Grand Canyon (0.06 dv), Mesa Verde (0.12 dv), and Zion (0.02 dv)).
---------------------------------------------------------------------------

    \170\ See, e.g., 78 FR 79344 (Dec. 30, 2012) (proposed rule, FIP
for Tesoro Refining BART Alternative); 79 FR 33438, 33441 (June 11,
2014) (final rule, FIP for Tesoro Refining BART Alternative); 79 FR
56322, 56328 (Sept. 19, 2014) (proposed approval of Arizona Apache
BART Alternative); 80 FR 19220 (Apr. 10, 2015) (final approval of
Arizona Apache BART Alternative); 77 FR 11827, 11837 (Feb. 28, 2012)
(proposed approval of Maryland BART Alternative); 77 FR 39938,
39940-1 (July 6, 2012) (final approval of Maryland BART
Alternative).
---------------------------------------------------------------------------

    Second, several metrics that the State suggests favor the BART
Alternative over BART show only small improvements as compared to BART.
We propose to find that the slight comparative benefits in the annual
average impacts are not compelling evidence that the BART Alternative
will provide for greater reasonable progress than BART. Additionally,
we propose to find that it is questionable whether the 90th percentile
supports a conclusion that the BART Alternative will provide for
greater reasonable progress than BART.
    Third, regarding the energy and non-air quality impacts, as well as
cost, for the reasons presented previously, we propose to find that
because these metrics do not have a direct bearing on whether the Utah
BART Alternative achieves greater reasonable progress, it is not
material to our action whether we agree or disagree with Utah's
assessment that they reduce energy and non-air quality impact.
    As explained previously in this section, in the aggregate the
SO2 and PM10 emissions are lower for the BART
Alternative. However, the NOX emissions are greater under
the BART Alternative. Additionally, while Utah's results show that some
of the metrics support the Alternative (e.g., there are fewer days with
impacts over 0.5 dv for the Alternative indicating greater improvement
in visibility under the BART Alternative; emission reductions would
occur earlier under the Alternative; the Alternative will result in
8,005 tpy lower SO2 emissions and 573 tpy lower
PM10 emissions compared to the BART Benchmark; sulfate is
the largest contributor to visibility impairment at the affected Class
I areas), we propose to find that these metrics are not enough by
themselves to meet the ``clear weight of evidence'' test.
    Thus, we propose to find that the BART Alternative does not meet
the requirements in the RHR because it does not show the BART
Alternative would achieve greater reasonable progress than the BART
Benchmark, and therefore, we are proposing to disapprove the resultant
BART Alternative SIP.
g. Evaluation That Emission Reductions Take Place During Period of
First Long-Term Strategy
    EPA's evaluation of Utah's information regarding the timing of
implementation of controls is located in section V.B.2.g.
h. Demonstration That Emission Reductions From Alternative Program Will
Be Surplus
    EPA's evaluation of Utah's information regarding whether the
emission reductions are surplus is located in section V.B.2.h.

C. Monitoring, Recordkeeping and Reporting for Utah's BART Alternative

    As discussed previously in section IV.B.3, Utah's June 2015 RH SIP
includes enforceable measures and monitoring, recordkeeping and
reporting requirements for the Utah BART Alternative and the State's
PM10 BART determinations. Because in this co-proposal we are
proposing to disapprove Utah's BART Alternative, we are also proposing
to disapprove (in other words, to not make federally enforceable as
part of the SIP) the monitoring, recordkeeping and reporting
requirements located in SIP Sections IX.H.22 associated with the BART
Alternative. This includes SIP Section IX.H.22, subsections a.ii,
a.iii, b.ii, and c.i.
    Concurrently, as described earlier in section V.C, we are proposing
to approve the remainder of the monitoring, recordkeeping and reporting
requirements associated with Utah's PM10 BART
determinations. This includes SIP Section IX.H.21 in its entirety and
Section IX.H.22, subsections a.i and b.i.

D. Proposed Federal Implementation Plan

    The following explanation details the support for EPA's FIP
proposed in conjunction with the proposed partial approval and partial
disapproval of Utah's SIP. This FIP constitutes EPA's proposed
determination of NOX BART for Utah's four subject-to-BART
sources.
1. BART Evaluations
    In determining BART, the state, or EPA if promulgating a FIP, must
consider the five statutory factors in section 169A(g)(2) of the CAA:
(1) The costs of compliance; (2) the energy and non-air quality
environmental impacts of compliance; (3) any existing pollution control
technology in use at the source; (4) the remaining useful life of the
source; and (5) the degree of improvement in visibility which may
reasonably be anticipated to result from the use of such technology.
See also 40 CFR 51.308(e)(1)(ii)(A). Our evaluation of BART for Hunter
and Huntington follows the Guidelines for BART Determinations Under the
Regional Haze Rule.
    Following the identification of subject-to-BART sources as
described in section IV.A.3, the next step of a BART evaluation is to
perform the BART analysis. The BART Guidelines describe the BART
analysis as consisting of the following five steps: \171\
---------------------------------------------------------------------------

    \171\ 40 CFR 51, appendix Y, section IV.D.
---------------------------------------------------------------------------

     Step 1: Identify All Available Retrofit Control
Technologies;
     Step 2: Eliminate Technically Infeasible Options;
     Step 3: Evaluate Control Effectiveness of Remaining
Control Technologies;
     Step 4: Evaluate Impacts and Document the Results; and
     Step 5: Evaluate Visibility Impacts.
    The results of this five step analysis are then used to select
BART, taking into consideration the five factors listed earlier.\172\
---------------------------------------------------------------------------

    \172\ See id. section IV.E.
---------------------------------------------------------------------------

    Immediately following this, we provide background information that
is common to our cost of compliance analysis (under Step 4) and
visibility impacts analysis (step 5) for all BART sources. This is
followed by the five step analysis and proposed selection of BART
specific to each BART source.
a. Costs of Compliance
    In accordance with the BART Guidelines, we have estimated the costs
of compliance consistent with the EPA Air Pollution Control Cost Manual
(CCM).\173\ In addition, we have utilized portions of the draft 2015
revisions to the CCM chapters for the post-combustion NOX
control technologies, selective non-catalytic reduction (SNCR) and
selective catalytic reduction (SCR).\174\ In addition, we rely on the

cost of compliance estimates supplied to EPA by Andover Technology
Partners (ATP).\175\ These estimates in turn rely on the cost estimates
that PacifiCorp submitted to Utah in 2012 and 2014, but with those cost
estimates adjusted in a number of cases for reasons described in the
ATP report. All costs are presented in 2014 dollars. Refer to the ATP
report and associated spread sheets for details on how the costs of
compliance are calculated.
---------------------------------------------------------------------------

    \173\ EPA's CCM Sixth Edition, January 2002, EPA 452/B-02-001.
    \174\ Chapter 1, Selective Noncatalytic Reduction, --6/5/2015--
Draft for Public Comment (``the 2015 SNCR CCM''); Chapter 2
Selective Catalytic Reduction, --6/5/2015--Draft for Public Comment
(``the 2015 SCR CCM''). The draft CCM SNCR and SCR revisions were
made available for public comment in a Notice of Data Availability
(NODA) on June 12, 2015, 80 FR 33515, and on July 17, 2015, 80 FR
42491, the public comment period was extended to September 10, 2015.
In this co-proposal for Utah's regional haze SIP, we are not taking
comment on the revisions to the CCM. We are only taking comment on
the application of those revisions of the CCM to the particular
facts and circumstances for the two subject-to-BART sources, Hunter
and Huntington, at issue in this action.
    \175\ Cost of NOX BART Controls on Utah EGUs, from
Andover Technology Partners, to EC/R, Inc., October 22, 2015 (ATP
report). Andover Technology Partners is a subcontractor to EC/R
Incorporated.
---------------------------------------------------------------------------

b. Visibility Impact Modeling
    The BART Guidelines provide that states may use the CALPUFF
modeling system or another appropriate model to determine the
visibility improvement expected at affected Class I areas from
potential BART control technologies. The BART Guidelines also recommend
that states develop a modeling protocol for modeling visibility
improvement, and suggest that states may want to consult with EPA and
their RPO to address any issues prior to modeling. In consultation with
EPA, Utah developed a CALPUFF modeling protocol titled ``Air Quality
Modeling Protocol: Utah Regional Haze State Implementation Plan'',
February 13, 2015, to support its BART Alternative analysis (see
Chapter 6 of the State's TSD). The Utah protocol follows
recommendations for long-range transport described in appendix W to 40
CFR part 51, Guideline on Air Quality Models, and in the federal
Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary
Report and Recommendations for Modeling Long Range Transport Impacts,
as recommended by the BART Guidelines (40 CFR part 51, appendix Y,
section III.D.5). Utah's protocol also follows Federal Land Managers'
Air Quality Related Values Workgroup--Phase I Report (revised 2010). In
section VI.B.e, we evaluate the State's modeling approach in
consideration of the purpose for which it is intended (i.e., analyzing
the BART Alternative). However, because Utah's modeling is not meant to
support analysis of control options for individual BART sources under a
five factor analysis, EPA developed separate CALPUFF modeling for this
purpose. While the Utah modeling assesses the combined impacts of all
of the BART and non-BART sources included in the BART Alternative--
Carbon, Hunter, and Huntington--our modeling assesses the impacts of
the individual BART sources. In addition, our modeling assesses the
visibility impacts of all of the NOX BART control
technologies found to be technologically feasible in Step 2: LNB and
OFA, LNB and OFA with SNCR, and LNB and OFA with SCR. Beyond assessing
impacts from individual BART sources and evaluating all technologically
feasible control options, our modeling methodology is otherwise very
similar to that employed by Utah. Our modeling protocol, and visibility
impact results, can be found in the docket.\176\ Also, the visibility
impacts for each BART source are provided later in the respective five
factor analyses.
---------------------------------------------------------------------------

    \176\ Air Quality Modeling Protocol: Utah Regional Haze Federal
Implementation Plan, EPA Region 8, November 2015.
---------------------------------------------------------------------------

    EPA notes that, in considering the visibility improvements
reflected in our revised modeling, EPA interprets the BART Guidelines
to require consideration of the visibility improvement from BART
applied to the entire BART-eligible source. The BART Guidelines explain
that, ``[i]f the emissions from the list of emissions units at a
stationary source exceed a potential to emit of 250 tons per year for
any visibility-impairing pollutant, then that collection of emissions
units is a BART-eligible source.'' In other words, the BART-eligible
source (the list of BART emissions units at a source) is the collection
of units for which one must make a BART determination. The BART
Guidelines state ``you must conduct a visibility improvement
determination for the source(s) as part of the BART determination.''
This requires consideration of the visibility improvement from BART
applied to the subject-to-BART source as a whole.
    We note, however, that while our regulations require states and EPA
to assess visibility improvement on a source-wide basis, they provide
flexibility to also consider unit-specific visibility improvement in
order to more fully inform the reasonableness of a BART determination,
but that does not replace the consideration of visibility benefit from
the source (facility) as a whole. In making the BART determinations in
this final action we have considered visibility improvements at the
source, and then also at the units that comprise the source.
2. Hunter Power Plant
    As described previously in section IV.A, Hunter Units 1 and 2 were
determined to be subject to BART, while Unit 3 is not subject to BART.
Hunter Units 1 and 2 have a nameplate generating capacity of 488.3 MW
each.\177\ The boilers are tangentially fired pulverized coal boilers,
burning bituminous coal from the Deer Creek Mine in Utah.
---------------------------------------------------------------------------

    \177\ U.S. Energy Information Administration, Electric
Generating Capacity for 2011 taken from Form EIA-860. See spread
sheet titled ``EIA existing generating units 2011.xls'' in the
docket.
---------------------------------------------------------------------------

    Our evaluation of BART for Hunter Units 1 and 2 follows the BART
Guidelines. For Hunter Units 1 and 2, the BART Guidelines are mandatory
because the combined capacity for all three units at the Hunter
facility is greater than 750 MW. See 40 CFR 51.302(e)(1)(ii)(B) (``The
determination of BART for fossil-fuel fired power plants having a total
generating capacity greater than 750 megawatts must be made pursuant to
the guidelines in appendix Y of this part''). Under the Guidelines,
cost estimates for control technologies should be based on the CCM,
where possible.
    The BART Guidelines establish presumptive NOX limits for
coal-fired EGUs greater than 200 MW located at greater than 750 MW
power plants that are operating without post-combustion controls. For
the tangential-fired boilers burning bituminous coal at Hunter, that
presumptive limit is 0.28 lb/MMBtu.\178\ The BART Guidelines provide
that the five factor analysis may result in a limit that is different
than the presumptive limit, and the presumptive limits do not obviate
the need to determine BART on a case-by-case basis considering the five
factors.\179\
---------------------------------------------------------------------------

    \178\ 40 CFR part 51, appendix Y, IV.E.5, Table. 1.
    \179\ See 40 CFR 51.301 (definition of BART); 40 CFR 51.308(e).
---------------------------------------------------------------------------

    PacifiCorp provided BART analyses for Hunter Unit 1 to Utah in 2012
and 2014 which we utilize in our proposed BART evaluation here.\180\
Although we are using some information provided by Utah and PacifiCorp,
we are independently evaluating all five statutory BART factors, as is
appropriate for this co-proposed FIP.
---------------------------------------------------------------------------

    \180\ PacifiCorp BART Analysis for Hunter Units 1 (July 2,
2012); PacifiCorp BART Analysis for Hunter Unit 2 (June 7, 2012);
Utah's Regional Haze BART Submittal, Chapter 2 of the Technical
Support Document (2015); PacifiCorp's BART Analysis Update for
Hunter Units 1 and 2 and Huntington Units 1 and 2 (Aug. 5, 2014).
---------------------------------------------------------------------------

a. Hunter Unit 1
    The Hunter Unit 1 boiler is of tangential-fired design with newer
generation low-NOX burners and separated overfire air which
were installed in 2014. Unit 1 currently achieves an annual emission
rate of approximately 0.21 lb/MMBtu with these combustion controls.
Under Utah's submitted regional haze SIP, Unit 1 is subject to a state-
law NOX emission

limit of 0.26 lb/MMBtu on a 30-day rolling average. Prior to the
installation of LNB and SOFA the unit operated with an actual annual
emission rate of about 0.40 lb/MMBtu.
Step 1: Identify All Available NOX Control Technologies
    In its 2012 BART analysis for Hunter Unit 1, PacifiCorp identified
several NOX control technologies, both for combustion
controls and post-combustion controls.\181\ The combustion controls
identified by PacifiCorp include: low-NOX burners and
separated overfire air (LNB and SOFA; already installed), rotating
overfire air, neural network optimization system, flue gas
recirculation, gas reburn, fuel lean gas reburn, coal switching, water
injection, and others. Post-combustion control options identified by
PacifiCorp include: SNCR, rich reagent injection (RRI), SCR, and
others.
---------------------------------------------------------------------------

    \181\ 2012 PacifiCorp BART analysis for Hunter Unit 1, page 2.a-
106.
---------------------------------------------------------------------------

    We note that the combustion controls, LNB and SOFA, have already
been installed on Hunter Unit 1, and so we consider them here as ``any
existing controls'' under the third statutory BART factor. In addition,
the BART Guidelines recognize that ``[c]ombinations of inherently
lower-emitting processes and add-on controls'' are a category of
retrofit controls which can be considered.\182\ Accordingly, the
inherently lower-emitting combustion controls, LNB and SOFA, are
evaluated in combination with the add-on controls, SNCR and SCR.
---------------------------------------------------------------------------

    \182\ BART Guidelines, IV.D.1.
---------------------------------------------------------------------------

    We have reviewed PacifiCorp's review of NOX control
technologies and find it to be comprehensive. We propose to adopt it to
satisfy Step 1 and we refer the reader to the 2012 PacifiCorp BART
analysis for details on the available NOX control
technologies.
Step 2: Eliminate Technically Infeasible Options
    In its 2012 BART analysis,\183\ PacifiCorp eliminated available
NOX control technologies that PacifiCorp evaluated as
technologically infeasible for Hunter Unit 1. The remaining
technologically feasible control technologies are the combustion
controls, LNB and SOFA, and the post-combustion controls, SNCR and SCR.
---------------------------------------------------------------------------

    \183\ 2012 PacifiCorp BART analysis for Hunter Unit 1, pages
2.a-106 through 2.a-123.
---------------------------------------------------------------------------

    We agree with PacifiCorp's evaluation of technologically available
controls for Hunter Unit 1 and propose to adopt it for Step 2.
Step 3: Evaluate Control Effectiveness of Remaining Control
Technologies
    As noted previously, Hunter Unit 1 is currently achieving an actual
annual emission rate of approximately 0.21 lb/MMBtu with LNB and SOFA.
This represents a 48.4 percent reduction from the baseline emission
rate of 0.40 lb/MMBtu.
    The post-combustion control technologies, SNCR and SCR, have been
evaluated in combination with combustion controls. That is, the inlet
concentration to the post-combustion controls is assumed to be 0.21 lb/
MMBtu (annual). This allows the equipment and operating and maintenance
costs of the post-combustion controls to be minimized based on the
lower inlet NOX concentration.
    Typically, SNCR reduces NOX an additional 20 to 30
percent above combustion controls without excessive NH3
slip.\184\ For this analysis, the control efficiency of SNCR has been
calculated based on the formula in the 2015 draft CCM SNCR
chapter,\185\ which for Hunter Unit 1 yields an additional reduction of
21.4 percent after combustion controls. When combined with LNB and
SOFA, SNCR is anticipated to achieve an annual emission rate of 0.16
lb/MMBtu, corresponding to an overall control efficiency of 59.4
percent.
---------------------------------------------------------------------------

    \184\ White Paper, SNCR for Controlling NOX
Emissions, Institute of Clean Air Companies, pp. 4 and 9, February
2008.
    \185\ 2015 SNCR CCM, Figure 1.1c: SNCR NOX Reduction
Efficiency Versus Baseline NOX Levels for Coal-fired
Utility Boilers.
---------------------------------------------------------------------------

    SCR can achieve performance emission rates as low as 0.04 to 0.07
lb/MMBtu on an annual basis.\186\ For this analysis, consistent with
our actions elsewhere, as well with PacifiCorp's analysis, we use an
annual emission rate of 0.05 lb/MMBtu for SCR, which when combined with
LNB and SOFA achieves an overall control efficiency of 87.5 percent.
---------------------------------------------------------------------------

    \186\ Srivastava, R., Hall, R., Khan, S., Lani, B., & Culligan,
K., Nitrogen Oxides Emission Control Options for Coal-Fired Utility
Boilers, 55 J. Air & Waste Mgmt. Assoc. 1367, 1367-88 (2005).
---------------------------------------------------------------------------

    A summary of emissions projections for the control options
evaluated is provided in Table 13.

                  Table 13--Summary of NOX BART Analysis Control Technologies for Hunter Unit 1
----------------------------------------------------------------------------------------------------------------
                                               Control
             Control option                 effectiveness   Annual  emission      Emissions         Remaining
                                                 (%)         rate (lb/MMBtu)   reduction (tpy)   emissions (tpy)
----------------------------------------------------------------------------------------------------------------
LNB/SOFA +SCR...........................              87.5              0.05             5,500               784
LNB/SOFA +SNCR..........................              59.4              0.16             3,735             2,549
LNB/SOFA................................              48.4              0.21             3,042             3,242
Baseline\1\.............................  ................              0.40  ................             6,284
----------------------------------------------------------------------------------------------------------------
\1\ Baseline emissions were determined by averaging the annual emissions from 2001 to 2003 as reported to EPA
  Air Markets Program Data, available at http://ampd.epa.gov/ampd/. The annual emissions data is presented in
  Chapter 4.a of Utah's June 2015 submittal.

Step 4: Evaluate Impacts and Document Results
    Under Step 4, the Guidelines list impact analyses in four parts:
costs of compliance, energy impacts, non-air quality environmental
impacts, and remaining useful life. For convenience, we combine energy
and non-air quality environmental impacts later on.
Part 1--Costs of Compliance
    We obtained capital costs for LNB and SOFA from the 2014 PacifiCorp
BART analysis. PacifiCorp did not report any operating and maintenance
costs for LNB and SOFA. Similarly, we obtained capital cost estimates
for LNB and SOFA with SNCR from the 2014 PacifiCorp BART analysis.
However, for operating and maintenance costs we propose to rely on the
draft 2015 draft SNCR chapter of the CCM. Refer to the ATP report for
details. Capital costs for LNB and SOFA with SCR were also obtained
from the 2014 PacifiCorp BART analysis. However, PacifiCorp's capital
costs were adjusted to account for items that were double-counted or
should not be allowed under the CCM, such as an allowance for funds
used during construction (AFUDC).\187\ In

addition, the capital costs were adjusted to account for a significant
overestimation of the catalyst volume and related costs. These
adjustments are documented in the ATP report and associated spread
sheet. A discussion of operating and maintenance costs of SCR is also
included in the ATP report. For the reasons given in the report, we
propose to adopt the cost estimates contained in it.
---------------------------------------------------------------------------

    \187\ See 79 FR 5032, 5133 (Jan. 30, 2014) (discussing reasons
for rejecting use of AFUDC).
---------------------------------------------------------------------------

    A summary of our proposed cost estimates for all control options is
presented in Table 14.

                                                  Table 14--Summary of NOX BART Costs on Hunter Unit 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Average cost
               Control option                   Total capital    Indirect annual    Direct annual     Total annual        Emissions     effectiveness ($/
                                                 investment           costs             costs             cost        reductions (tpy)        ton)
--------------------------------------------------------------------------------------------------------------------------------------------------------
LNB/SOFA....................................            $11.6M             $1.2M               $0M             $1.2M             3,042              $382
LNB/SOFA/SNCR...............................             19.0M              1.9M              1.9M              3.8M             3,735             1,016
LNB/SOFA/SCR................................            110.3M             10.5M              2.5M             13.1M             5,500             2,380
--------------------------------------------------------------------------------------------------------------------------------------------------------

Parts 2 and 3--Energy and Non-Air Quality Environmental Impacts of
Compliance
    SNCR slightly reduces the thermal efficiency of a boiler as the
reduction reaction uses thermal energy from the boiler, decreasing the
energy available for power generation.\188\ Using the CCM, we have
calculated the electrical power consumption of SNCR to be 326,000 kW-hr
per year for Hunter Unit 1.
---------------------------------------------------------------------------

    \188\ EPA Air Pollution Control Cost Manual p. 1-21 (6th ed.
2002), available at http://www3.epa.gov/ttncatc1/dir1/c_allchs.pdf.
---------------------------------------------------------------------------

    For SCR, the thermal efficiency is much more reduced because the
new ductwork and the reactor's catalyst layers decrease the flue gas
pressure. As a result, additional fan power is necessary to maintain
the flue gas flow rate through the ductwork and reactor. Using the CCM,
we have calculated the electrical power consumption of SCR to be
approximately 18,541,000 kW-hr per year for Hunter Unit 1.
    Both SCR and SNCR also require some minimal electricity to service
pretreatment and injection equipment, pumps, compressors, and control
systems. The energy requirements described earlier are not significant
enough to warrant elimination of either SNCR or SCR as BART. In
addition, the cost of the additional energy requirements has been
included in our cost effectiveness calculations.
    SNCR and SCR will slightly increase the quantity of ash that will
need to be disposed. In addition, transportation and storage of
chemical reagents may result in spills or releases. However, these non-
air quality environmental impacts do not warrant elimination of either
SNCR or SCR as BART.
    There are no additional energy requirements associated with the new
LNB and SOFA, and no significant non-air quality environmental impacts.
    In summary, we propose to determine that we have adequately
considered these impacts by including cost of additional energy in cost
effectiveness and assessing non-air quality environmental impacts as
insufficient to eliminate or weigh against any of the BART options.
Part 4--Remaining Useful Life
    PacifiCorp assumes a remaining useful life of at least 20 years for
Hunter Unit 1 in its BART analysis, and has not indicated any intention
to retire, or curtail generation from, Hunter Unit 1. Therefore, this
factor does not preclude any of the control options considered. In
addition, this factor is consistent with our BART calculation of cost
effectiveness because annualized costs have been calculated over a 20
year period for each of the control options considered. We propose that
this gives adequate consideration to this factor.
Step 5: Evaluate Visibility Impacts
    Table 15 presents the highest of the 98th percentile visibility
improvements at the affected Class I areas for the three meteorological
years modeled, 2001 through 2003. Tables 16 and 17 present the number
of days (summed across three years) with impacts greater than the
contribution and causation thresholds--0.5 dv and 1.0 dv, respectively.

                                Table 15--Hunter Unit 1--Visibility Improvements
----------------------------------------------------------------------------------------------------------------
                                                           LNB with SOFA    LNB with SOFA and  LNB with SOFA and