emissions, the State must make this clear in the BART evaluation, as it
may have an impact on the cost analysis and the ultimate selection of
BART. Since the State did not properly document the cost of the
SO2 control options considered in the BART analysis
(including a reasonably detailed line by line breakdown of costs), we
were not able to determine if the parameters assumed in the State's
cost analysis for White Bluff Units 1 and 2 are reflective of the base
case. As explained elsewhere in this final rulemaking, we are
finalizing our proposed disapproval of SO2 BART for

Entergy White Bluff Units 1 and 2 for both the bituminous and sub-
bituminous coal firing scenarios.
    Comment: The EPA's proposed disapproval of the SO2,
NOX, and PM BART determinations for fuel oil firing for
Entergy Lake Catherine Unit 4 is correct because Entergy's BART
analyses for the fuel oil firing scenario are inadequate. Neither
Entergy nor ADEQ considered and evaluated post-combustion controls for
the fuel oil firing scenario, and Entergy improperly assumed only a 10%
capacity factor in the cost-effectiveness calculations, even though the
unit's capacity factor is not limited by any enforceable requirement.
The EPA is also correct in not allowing the unit to be exempt from BART
for the fuel oil firing scenario until the Lake Catherine permit is
revised to prohibit Unit 4 from burning fuel oil.
    Response: The EPA agrees that the State did not evaluate any
SO2 post-combustion controls and did not properly evaluate
NOX post-combustion controls for Entergy Lake Catherine Unit
4 for the fuel oil firing scenario.
    Based on comments received during the public comment period, it has
come to our attention that we made an error in our calculation of the
capacity factor for recent years for Lake Catherine Unit 4. Based on
the information provided, we agree that the source has historically
operated at less than a 10% capacity factor. The BART Guidelines
provide that for the purpose of calculating the cost of controls, the
State may calculate baseline emissions based upon continuation of past
practice.\193\ However, as explained in more detail in our response to
other comments and in our proposed rulemaking, we find that the State
did not properly document the cost analysis for NOX,
SO2, and PM controls for fuel oil firing for Entergy Lake
Catherine Unit 4 because the proper documentation necessary to allow us
to make an informed and proper evaluation of the BART analysis was not
included in the SIP, as the BART Guidelines require.
---------------------------------------------------------------------------

    \193\ Appendix Y to Part 51, section IV.4.
---------------------------------------------------------------------------

    Therefore, we are finalizing our proposed disapproval of BART for
NOX for both the natural gas and fuel oil firing scenarios,
and SO2 and PM for the fuel oil firing scenario.
    Comment: The EPA's proposed disapproval of Arkansas's BART
determinations for SO2, NOX, and PM for AECC's
Bailey Unit 1 and McClellan Unit 1 is correct. ADEQ must comply with
the requirement that once a unit is determined to be subject to BART, a
BART determination must be made for all pollutants emitted by the
source (see 40 CFR part 51, Sec.  51.301 and Appendix Y, section IV.A).
EPA must also disapprove the PM BART requirements because there was no
determination of BART for PM2.5.
    Response: While we are finalizing our proposed disapproval of the
State's BART determinations for SO2, NOX, and PM
for AECC's Bailey Unit 1 and McClellan Unit 1, we disagree that we must
disapprove the PM BART determination because the State did not make a
BART determination for PM2.5. The BART Guidelines do not
specify that States must establish a BART limit for both
PM10 and PM2.5. The BART Guidelines provide the
following:
    ``You must look at SO2, NOX, and direct
particulate matter (PM) emissions in determining whether sources cause
or contribute to visibility impairment, including both PM10
and PM2.5.'' \194\
---------------------------------------------------------------------------

    \194\ Appendix Y to Part 51, section III.A.2.
---------------------------------------------------------------------------

    This language in the BART Guidelines was intended to clarify to
States that when determining whether a source is subject to BART, the
modeling evaluation to determine the source's impact on visibility has
to account for both PM10 and PM2.5 emissions.
There are several instances in which we state in both the preamble to
the RHR, and in the BART Guidelines that PM10 may be used as
indicator for PM2.5 in determining whether a source is
subject to BART. Neither the RHR nor the BART Guidelines specify that
States must make separate BART determinations for PM10 and
PM2.5. Therefore, we disagree that we must disapprove the PM
BART determination for AECC's Bailey Unit 1 and McClellan Unit 1 on the
basis that a BART determination for PM2.5 was not made.
    Comment: The EPA's proposed disapproval of the SO2 and
NOX BART determinations for the Domtar Power Boilers No. 1
and 2 the EPA's proposed disapproval of the PM BART determination for
Domtar Power Boiler No. 2 are correct for the reasons given by EPA in
its proposed rulemaking (76 FR 64207-210).
    Response: Consistent with the comment, we are finalizing our
proposed disapproval of the State's SO2 and NOX
BART determinations for the Domtar Power Boilers No. 1 and 2 and the
State's PM BART determination for Domtar Power Boiler No. 2
    Comment: There is significant interest in the application of
appropriate BART requirements for the Flint Creek Power Plant, the
White Bluff Steam Electric Station, the AECC Carl E. Bailey Generating
Station, and the AECC John L. McClellan Generating Station. It is
critical to ensure that ratepayers are not burdened by improper and/or
unnecessary requirements. EPA's proposed rule will impose unnecessary
and/or improper costs and requirements on these and other Arkansas
facilities. ADEQ's original RH SIP submission fully met the
requirements of the CAA and its implementing regulations.
    Response: We disagree that our final action will impose unnecessary
and improper requirements on Arkansas's subject to BART sources. In
fact, for the BART determinations we are disapproving, we are not
imposing or requiring a specific BART emission limit or cost. As
explained elsewhere in our response to comments, our partial
disapproval of Arkansas's RH SIP is a proper exercise of our authority
under the CAA. Our role is to review the RH SIP submittal and determine
if the state met the applicable statutory and regulatory requirements.
When reviewing state SIPs, we must consider not only whether the State
considered the appropriate factors in making decisions but also whether
it acted reasonably in doing so. Some of Arkansas's BART determinations
for its subject to BART sources, among other portions of the RH SIP,
were not developed in accordance with the RHR and the BART Guidelines,
as discussed in our proposed rulemaking and elsewhere in this final
rulemaking. We are not imposing additional requirements beyond what the
RHR and the BART Guidelines require. Therefore, we disagree that our
proposed rulemaking, as finalized in this rulemaking, imposes
unnecessary requirements on Arkansas's subject to BART sources.
    Comment: Since limiting the sulfur content of fuel oil to 1.0% by
weight at the Bailey Unit 1 and McClellan Unit 1 is cost-effective and
post-control modeling predicted that visibility impacts to Class I
areas would be below the 0.5 dv contribution threshold, this control
option was selected as BART. It is unnecessary to perform additional
analyses for lower sulfur fuel oil for Bailey Unit 1 and McClellan Unit
1.
    Response: While we agree that limiting the sulfur content of fuel
oil to 1.0% by weight at the AECC Bailey Unit 1 and McClellan Unit 1 is
extremely cost-effective ($54.90/ton SO2 removed for Bailey
Unit 1 and $158.60/ton SO2 removed for McClellan Unit1), we
find that it is very likely that other options that would result in
greater visibility improvement may also be found to be cost effective.
According to the Arkansas RH SIP, the post-control modeling
demonstrates that with the SO2 BART controls selected by the
State for AECC Bailey Unit 1, the visibility

impact would be 0.897 dv at Caney Creek, 0.574 dv at Upper Buffalo,
0.809 dv at Hercules Glades, and 0.766 dv at Mingo.\195\ According to
the Arkansas RH SIP, the post-control modeling demonstrates that with
the SO2 BART controls selected by the State for AECC
McClellan Unit 1, the visibility impact would be 1.011 at Caney Creek
and 0.487 dv at Upper Buffalo.\196\ We note this constitutes
approximately a 50% improvement in visibility across all areas. As
such, if Arkansas conducts a proper five factor BART analysis that
considers all five statutory factors and evaluates more stringent
controls, such as a 0.5% or lower limit for the sulfur content of fuel
oil used, Arkansas may find one or more of these more stringent
controls to be cost-effective and result in even more visibility
improvement than that resulting from the control option it selected. As
explained in our proposed rulemaking, the visibility regulations define
BART as ``an emission limitation based on the degree of reduction
achievable through the application of the best system of continuous
emission reduction.'' Since recent retrofits at existing sources
provide a good indication of the current ``best system'' for
controlling emissions, these controls must be considered in the BART
analysis. The BART Guidelines provide that in identifying all options,
States must identify the most stringent option (i.e. maximum level of
control each technology is capable of achieving) as well a reasonable
set of options for analysis.\197\ The RHR states that in establishing
source specific BART emission limits, the State should identify and
consider in the BART analysis the maximum level of emission reduction
that has been achieved in other recent retrofits at existing sources in
the source category.\198\ Fuel oil with a sulfur content of 0.5% by
weight or less is being utilized in industry. In considering use of
fuel oil with low sulfur content as a control option in the BART
analysis, AECC did not identify and consider the maximum level of
control achievable from the use of low sulfur fuel oil, and therefore,
did not satisfy the RHR requirements.
---------------------------------------------------------------------------

    \195\ See Table 9.4b of the Arkansas RH SIP. Note that the pre
and post control visibility impact shown on Table 9.4b is the
modeled maximum visibility impact at each affected Class I area. As
explained in our proposed rulemaking, the original meteorological
databases generated by CENRAP did not include observations as EPA
guidance recommends. Therefore, in their evaluation to determine if
a source exceeds the 0.5 dv contribution threshold at nearby Class I
areas, states used the 1st high values (i.e. maximum value) of
modeled visibility impacts instead of the 8th high values (i.e. 98th
percentile value). The use of the 1st high modeled values was agreed
to by EPA, representatives of the Federal Land Managers, and CENRAP
stakeholders.
    \196\ See Table 9.4c of the Arkansas RH SIP. Note that that the
pre and post control visibility impact shown on Table 9.4c is the
modeled maximum visibility impact at each affected Class I area.
    \197\ Appendix Y to Part 51, section IV.
    \198\ 64 FR 35740.
---------------------------------------------------------------------------

    In addition, as pointed out in the TSD for our proposed rulemaking
on the Arkansas RH SIP, even though the State's cost analysis showed
that wet scrubbers are cost-effective ($2,108.25/ton SO2
removed and $1,658.32/ton SO2 removed), Arkansas did not
evaluate the visibility impact of this control option. As explained in
more detail elsewhere in our response to comments, the BART Guidelines
require a State to evaluate all five statutory factors before
eliminating a particular control option for BART.\199\ As articulated
in our proposed rulemaking on the Arkansas RH SIP, the State must
perform a cost analysis in which all cost estimates are properly
documented and must evaluate the visibility impacts of all technically
feasible control options considered before making a BART determination.
This was not done in Arkansas's SO2 BART analysis for the
AECC Bailey Unit 1 and McClellan Unit 1. As such, the BART analysis for
SO2 for AECC Bailey Unit 1 and McClellan Unit 1 does not
satisfy the RHR and CAA requirements.
---------------------------------------------------------------------------

    \199\ 70 FR 39130 and 39131.
---------------------------------------------------------------------------

    Therefore, we believe that it is necessary for Arkansas to perform
additional analyses to evaluate the cost and visibility impact of using
lower sulfur fuel oil at Bailey Unit 1 and McClellan Unit 1. It must
also evaluate the visibility impact of wet scrubbers and any other
control options considered in the BART analysis before making a BART
determination.
    Comment: The results of the initial BART modeling performed in
2006, which was cumulative modeling of SO2, NOX,
and PM, indicated that both the AECC Bailey Unit 1 and McClellan Unit 1
cause visibility impacts at one or more Class I areas. Pollutant-
specific modeling was then performed and the results of the pollutant-
specific modeling for NOX were all less than 0.5 dv,
demonstrating that NOX neither caused nor contributed to
visibility impacts. For this reason, a NOX engineering
analysis was unnecessary and not performed. The EPA previously had an
opportunity to comment on this issue about two years prior to ADEQ
submitting its draft SIP to EPA, when ADEQ forwarded a question to EPA
in an email dated October 19, 2006, asking whether or not five factor
analyses were required for NOX and PM since both pollutants
showed no impacts. No response to the question was ever received by
ADEQ from EPA.
    Response: While we regret any kind of miscommunication or lapse of
communication that may have occurred between us and Arkansas, we note
that it is ultimately the State's duty to make sure that its RH SIP
satisfies all the regulatory and statutory requirements and is
consistent with all applicable EPA guidance. As explained elsewhere in
our response to comments, the pollutant-specific analysis approach for
NOX and SO2 used to evaluate controls at these
AECC units does not take into consideration the chemical interaction
between these two pollutants and ammonia present in the atmosphere. A
reduction in sulfate emissions, while most likely reducing visibility
impairment overall, can result in an increase in visibility impairment
from nitrate due to the increase in ammonia available to react with
nitrate to form visibility impairing aerosol. The pre-control modeling
results indicate that nitrate is a significant contributor to
visibility impairment on some days and this contribution can increase
under conditions of decreased SO2 emissions. Therefore,
NOX and SO2 emissions should be modeled together
and emission control technologies should be evaluated for both
pollutants. We are finalizing our proposed disapproval of the State's
NOX, SO2, and PM BART determinations of the AECC
Bailey Unit 1 and McClellan Unit 1.
    Comment: We do not agree with EPA's proposed approval of no BART
determination for SO2 for the gas-firing scenario for
Entergy Lake Catherine Unit 4 (76 FR 64203-204). Once a source is
determined to be subject to BART, a BART determination must be made for
all pollutants emitted by the source (see 40 CFR part 51, Sec.  51.301
and appendix Y, section IV.A). Since the unit emits some SO2
when firing gas, it must be subject to a BART limit. EPA cannot exempt
the unit from an SO2 BART analysis when firing natural gas
just because SO2 emissions are considered to be low when
combusting such fuel. A BART analysis may show that the SO2
limit currently in the Lake Catherine Title V permit satisfies BART,
but that will not be known until a BART analysis is done.
    Response: In our review of the Arkansas RH SIP, we evaluated the
determination by ADEQ that SO2 emissions when burning
natural gas are very low and that no additional SO2 controls
are required at Entergy Lake Catherine Unit 4. Furthermore, the
modeling results submitted by Arkansas in Appendix 9.2B of the Arkansas
RH SIP indicate that under natural gas firing

conditions, NOX contributes over 99.9% of Lake Catherine
Unit 4's total visibility impacts at all nearby Class I areas on the
most impacted days. Based on the State's modeling results, the
visibility impact of this unit from SO2 emissions alone is
so minimal such that any requirement for additional SO2
controls on this unit would have virtually no visibility benefit. It is
clear that the most effective controls to address visibility impairment
from the source during natural gas firing are those that would reduce
emissions of NOX. Therefore, in our proposed rulemaking, we
agreed that it was appropriate for the State to not establish an
SO2 BART emission limit (i.e. no additional controls) for
the natural gas firing scenario. This is consistent with the BART Rule,
which states the following:
    ``Consistent with the CAA and the implementing regulations, States
can adopt a more streamlined approach to making BART determinations
where appropriate. Although BART determinations are based on the
totality of circumstances in a given situation, such as the distance of
the source from a Class I area, the type and amount of pollutant at
issue, and the availability and cost of controls, it is clear that in
some situations, one or more factors will clearly suggest an outcome.
Thus, for example, a State need not undertake an exhaustive analysis of
a source's impact on visibility resulting from relatively minor
emissions of a pollutant where it is clear that controls would be
costly and any improvements in visibility resulting from reductions in
emissions of that pollutant would be negligible. In a scenario, for
example, where a source emits thousands of tons of SO2 but
less than one hundred tons of NOX, the State could easily
conclude that requiring expensive controls to reduce NOX
would not be appropriate.'' \200\
---------------------------------------------------------------------------

    \200\ 70 FR 39116.
---------------------------------------------------------------------------

    Based on our analysis of the data submitted by ADEQ in the Arkansas
RH SIP, and our agreement that SO2 emissions from burning
natural gas are very low, we proposed to find that it is appropriate
for the State to establish no additional control for SO2
BART. The BART Rule provides that states may determine that for a given
source no additional control satisfies the BART requirement for a
particular pollutant.\201\ In such cases, it is not necessary for a
state to establish an emission limit when no additional control is
BART. For example, in our final approval of the Kansas RH SIP, we
approved the State's determination that no additional control (and no
new BART emission limit) for PM is BART for a number of sources.\202\
In our final approval of the Oklahoma RH SIP, we also approved the
State's determination that no additional control (and no new BART
emission limit) for PM is BART for a number of sources.\203\ In the
above cases, Kansas and Oklahoma adopted no new PM emission limit for
PM BART, and we approved this based on the sources' low visibility
impact attributable to PM emissions. As such, our proposed approval of
Arkansas's determination that no additional controls for SO2
for the natural gas firing scenario satisfies SO2 BART for
Lake Catherine Unit 4 is consistent with the BART Rule and consistent
with our action on the RH SIPs of other states.
---------------------------------------------------------------------------

    \201\ 70 FR 39116.
    \202\ 76 FR 52604 and 76 FR 80754.
    \203\ 76 FR 16168 and 76 FR 81728.
---------------------------------------------------------------------------

D. Comments on the Arkansas Pollution Control and Ecology Commission
Variance for Subject to BART

    Comment: The EPA cannot approve any of the BART determinations
because each of the BART determinations is premised by Arkansas to
implement only 5 years after EPA fully approves the entire RH SIP.
Arkansas's enforceability of BART requirements are codified in Chapter
15 of Regulation No. 19 and modified in March 2010. Since EPA has not
yet proposed full approval of the Arkansas RH SIP, EPA's partial
approval of some pollutant-specific BART requirements in Regulation No.
19 for some of Arkansas's subject to BART sources will not meet the
requirements of 40 CFR 51.308(e)(iv). Also, the APCEC variance does not
account for the possibility that EPA may impose a partial FIP for RH in
Arkansas, and thus, under the variance, the backstop BART compliance
deadline will be delayed indefinitely.
    Response: We do not believe that the 2008 submitted Chapter 15 of
APCEC Regulation No. 19 and its subsequent modification submitted to us
on August 3, 2010, creates an enforceability timeframe less stringent
than that required under 40 CFR 51.308(e)(iv). We do not read that the
partial approval of Arkansas BART determination means that the
enforceability timeframe is 5 years from the full approval of the AR RH
SIP. Section 110(k)(3) of the amended Act addresses the situation in
which an entire submittal, or a separable portion of a submittal, meets
all applicable requirements of the Act. In the case where a separable
portion of the submittal meets all the applicable requirements, partial
approval may be used to approve that part of the submittal and
disapprove the remainder. Since the portions of the RH SIP submittal we
are approving are separable from the portions we are disapproving as
explained above, each approved BART determination for a particular
pollutant for a given source will have an enforceable date of 5 years
from the date of EPA's approval. If Arkansas fails to submit a revised
RH SIP that is approvable for the severable BART determinations we are
disapproving today, we will promulgate a FIP for the disapproved BART
determinations; in that case, the compliance deadline will be no later
than 5 years from the date of the FIP promulgation.
    As explained in our proposed rulemaking and as pointed out in
another comment, the APCEC variance granted to Arkansas's subject to
BART sources on March 26, 2010, will require compliance with BART
requirements ``as expeditiously as practicable but in no event later
than five (5) years after EPA approval of the Arkansas Regional Haze
SIP.'' \204\ As explained in our response to that comment, we agree
that the APCEC variance was never submitted to EPA as a revision to the
SIP. The operative rule before us is Chapter 15 of Regulation No. 19
(i.e. the State RH Rule), which requires compliance with BART either
six years after the effective date of the State's regulation or five
years after EPA approval of the Arkansas RH SIP, whichever is
first.\205\ Although we believe this timeframe is consistent with the
requirements under 40 CFR 51.308(e)(iv), because of the variance
granted to all Arkansas subject to BART sources, the State of Arkansas
no longer has the legal authority to enforce compliance within the
timeframe required by Chapter 15 of APCEC Regulation No. 19, which is
before us to act upon. Specifically, Arkansas no longer has the
authority to enforce compliance with BART within six years after the
effective date of its regulation. 40 CFR 51.230 requires that a state
must show it has the legal authority to enforce a rule that is
submitted as part of the SIP. Therefore, we are disapproving the
portion of the BART compliance provision found in the 2008 submitted
Chapter 15 of APCEC Regulation No. 19 that requires compliance with
BART requirements no later than six years after the effective date of
the State's regulation. For

purposes of our action on the RH SIP submissions, we are partially
approving and partially disapproving the portion of the BART compliance
provision in Chapter 15 of APCEC Regulation No. 19, that requires each
Arkansas subject to BART source to install and operate BART as
expeditiously as practicable, but in no event later than five years
after EPA approval of the Arkansas RH SIP, such that our disapproval is
of those portions of the regulation that correspond to portions of the
Arkansas RH SIP we are disapproving. We find that this is consistent
with the requirements under 40 CFR 51.308(e)(iv). Arkansas's inclusion
of the compliance provision that would require Arkansas subject to BART
sources to install and operate BART no later than six years after the
effective date of the State's regulation (if such date takes place
before five years from EPA approval of the Arkansas RH SIP) is not a
required element of the Regional Haze SIPs to be developed and
submitted by States pursuant to section 169 of the CAA. Therefore, we
are finalizing our approval of the BART determinations for which we
proposed approval.
---------------------------------------------------------------------------

    \204\ A copy of the March 26, 2010, APCEC Minute Order granting
all Arkansas subject to BART sources a variance from the compliance
deadline imposed by the State's RH Rule can be found in the docket
associated with this rulemaking.
    \205\ The State's BART compliance requirements are found at Reg.
19.1504(B).
---------------------------------------------------------------------------

    Comment: Arkansas has not submitted the APCEC variance to EPA as
part of the Arkansas RH SIP. The version of APCEC Regulation No. 19
that EPA is proposing to approve requires compliance with BART emission
limitations no later ``than 6 years after the effective date of
[Chapter 15 of APCEC Regulation No. 19] or five years after EPA
approval of the Arkansas Regional Haze State Implementation Plan * *
*'' (see APCEC Reg. 19.1504(B) in EPA-R06-OAR-2008-0727-0004).
Compliance with BART under the version of APCEC Reg. 19.1504(B) that
has been submitted to EPA is required by October 15, 2013, yet ADEQ
will have no authority to enforce compliance with the deadline that
will be in effect under the version of APCEC Regulation No. 19 being
proposed for approval by EPA. EPA's proposed partial approval would be
of a rule that ADEQ has no authority to enforce. Given that States are
required to have legal authority to enforce the requirements of the SIP
(see 40 CFR 51.230(b)), EPA cannot legally approve the BART compliance
deadline in APCEC Reg. 19.1504(B) until Arkansas properly revises its
SIP to address the terms of the variance and submits it to EPA for
approval. EPA seemingly ignores the fact that the variance was not
adopted by the State as a SIP revision, was not submitted to EPA as a
SIP revision, and is not being acted on by EPA in this proposed
rulemaking action. Further, the APCEC variance allows for BART
compliance deadlines less stringent than the BART compliance deadlines
of 40 CFR 51.308(e)(iv) of the Federal RH regulations because under the
variance, compliance would not be required until 5 years from EPA's
full approval of the Arkansas RH SIP. Therefore, EPA cannot approve any
of the BART determinations in the Arkansas RH SIP.
    Response: As stated in our proposal, Chapter 15 of APCEC Regulation
No. 19, was submitted by ADEQ on September 23, 2008, as part of the RH
SIP submittal. The 2008 submitted Chapter 15 of Regulation No. 19
requires each subject to BART source to install and operate BART as
expeditiously as practicable, but in no event later than six years
after the effective date of Arkansas's Chapter 15 of APCEC Regulation
No. 19 or five years after approval of the SIP or plan revision by EPA,
whichever comes first. ADEQ did revise APCEC Regulation No. 19,
including Chapter 15, and submitted these changes to EPA in 2010 but
this revised submittal did not include revisions to the provision for
BART compliance timeframe. We agree with the comment that the APCEC
variance that requires BART compliance as expeditiously as practicable
but in no event later than five years after our approval of the
Arkansas RH SIP has never been submitted to us as a revision to the
SIP. We do not believe, however, this means we cannot finalize the
approval of the BART determinations for which we proposed approval. We
agree that because of the APCEC variance, Arkansas no longer has the
authority to enforce compliance with BART within six years after the
effective date of the State's regulation. 40 CFR 51.230 requires that a
state must show it has the legal authority to enforce a rule that is
submitted as part of the SIP. Therefore we are disapproving the portion
of the BART compliance provision found in the 2008 submitted Chapter 15
of Regulation No. 19 that requires compliance with BART requirements no
later than six years after the effective date of the State's
regulation. For purposes of our action on the RH SIP submissions, we
are partially approving and partially disapproving the portion of the
BART compliance provision that requires each Arkansas subject to BART
source to install and operate BART as expeditiously as practicable, but
in no event later than five years after our approval of the Arkansas RH
SIP. We find that this is consistent with the requirements under 40 CFR
51.308(e)(iv). Arkansas's inclusion of the compliance provision that
would require Arkansas subject to BART sources to install and operate
BART no later than six years after the effective date of the State's
regulation (if such date takes place before five years from EPA
approval of the Arkansas RH SIP) is not a required element of the
Regional Haze SIPs to be developed and submitted by States pursuant to
section 169 of the CAA. We also note that with the exception of the PM
BART determination for the Domtar Ashdown Mill Power Boiler No. 1, our
partial approval of the State's BART determinations is based on a
finding that no additional control is required. Therefore the
compliance date is not relevant for RH purposes since no additional
controls would be expected for these sources.
    Our actions approving some BART determinations and disapproving
some BART determinations for Arkansas sources are severable. We can
approve some of the rules and disapprove the rest as long as the rules
that are disapproved do not affect those that are approved. This is the
case in our partial approval and partial disapproval action, in which
we are disapproving the severable BART determinations for some of the
units and approving the severable BART determinations for some of the
units in Arkansas's RH SIP. Since the portions of the RH SIP submittal
we are approving are severable from the portions we are disapproving as
explained above, each approved BART determination for a particular
pollutant for a given source will have an enforceability of 5 years
from the date of EPA's approval. If EPA cannot approve a revised RH SIP
for the severable BART determinations EPA is disapproving today before
the end of the 2 year FIP clock, EPA will promulgate a FIP for the
severable BART determinations EPA is disapproving today. In that case,
the compliance deadline will be as expeditious as practicable, but no
later than 5 years from the date of the FIP promulgation. Therefore,
EPA disagrees that compliance is required no later 5 years from EPA's
full approval of the entire Arkansas RH SIP.
    Comment: Under the Federal RH regulations, compliance with BART is
required ``as expeditiously as practicable,'' and in no event later
than five years after approval of the SIP (see 40 CFR 51.308(e)(iv),
and 42 U.S.C. 7491(b)(2)(A)). However, all parties seem to ignore this
regulatory requirement. Considering this regulatory requirement and the
significant delay in

getting an approved RH SIP or FIP in place for Arkansas, EPA must
consider tighter deadlines for BART compliance.
    Response: It is our role to determine if the State SIP submittal
meets the requirements of the CAA. Only in the context of a FIP are we
in a position to make our own determination about the appropriate
compliance deadline. It is our expectation that the State will correct
the deficiencies in the SIP and submit a revised plan that we can
approve before the expiration of the mandatory FIP clock for the
portions of the SIP we are disapproving in this final rulemaking
action. However, if this does not occur and we are forced to promulgate
a FIP, we will consider at such time what the appropriate compliance
deadline is in light of the final BART determination.

E. Comments on BART and the Forthcoming MACT Requirements

    Comment: Flint Creek Boiler No. 1 and White Bluff Units 1 and 2
will be subject to EPA's forthcoming EGU MACT requirements, and the
BART Guidelines provide that MACT requirements should be taken into
account in determining BART (see 40 CFR part 51, appendix Y, section
IV.C). The EPA has proposed a total PM limit for existing EGUs of 0.03
lb/MMBtu, as a surrogate limit for non-mercury metal hazardous air
pollutants (HAPs) (see 76 FR 24975). EPA should not approve the lax PM
limit of 0.1 lb/MMBtu for Flint Creek Boiler No. 1 and Entergy White
Bluff Units 1 and 2 as meeting BART for PM because that emission limit
is much less stringent than the forthcoming PM MACT requirement. Recent
stack testing for White Bluff Units 1 and 2 show that the units will
not be able to meet EPA's proposed mercury MACT limit for existing
units of 1.2 lb/MMBtu. It is likely that both Flint Creek Boiler No. 1
and White Bluff Units 1 and 2 will need to install baghouses to meet
EPA's mercury MACT limit for existing EGUs. It is well known that coal-
fired boilers equipped with baghouses achieve better control of mercury
than those equipped with ESPs. Activated carbon, a sorbent which
adsorbs mercury, is typically much more effective when a baghouse is
used compared to an ESP. According to EPA, the form of mercury most
easily removed is HgCl2 and the formation of this compound
depends on how much chlorine is in the coal--the lower the chlorine
content of the coal, the less HgCl2 is formed. EGUs that
burn low chlorine coal, such as Flint Creek, often achieve better
control of mercury via existing SO2 scrubbers and PM
controls. A fabric filter baghouse provides additional opportunities
for mercury removal compared to a particle scrubber or a dry ESP.
    Response: We would like to clarify that the section of the BART
Guidelines the comment refers to was not meant to require States to
take into account MACT requirements in determining BART, but rather to
provide States with the option to streamline the BART analysis for
sources subject to the MACT standards by relying on the MACT standards
for purposes of BART.\206\ We received the originally submitted
Arkansas RH SIP on September 23, 2008 and a revision on August 3, 2010,
while EPA proposed the National Emission Standards for Hazardous Air
Pollutants from Coal- and Oil-fired Electric Utility Steam Generating
Units (EGU MACT Rule) on March 16, 2011.\207\ The EPA issued the EGU
MACT final rule on December 16, 2011.\208\ As such, it would be
unreasonable for EPA, when taking action on states' RH SIPs, to
consider EGU MACT standards proposed years after a state submitted its
RH SIP. This would potentially create an endless review loop for States
as new MACT standards are issued by EPA. In addition, the limits in the
MACT standards are established by EPA for reasons that are much
different than the reasons for the limits established in Regional Haze
SIPs. Our approval of limits on direct PM emissions in Arkansas for RH
purposes is based on minimal contribution to visibility impairment at
Class I areas and is in no way related to the reasons a lower emission
limit was established under section 112 of the Act. Therefore, EPA
disagrees that it should disapprove the PM BART limit of 0.1 lb/MMBtu
adopted by the State for Flint Creek Boiler No. 1 and White Bluff Units
1 and 2 because it is much less stringent than the PM emission limit in
the EGU MACT Rule recently promulgated by EPA or because the sources
may need to install baghouses to meet the mercury emission limit for
existing EGUs in EPA's EGU MACT Rule. EPA expects that these sources
will have to comply with these limits under the EGU MACT standard as
well.
---------------------------------------------------------------------------

    \206\ Appendix Y to Part 51, section IV.C.
    \207\ 76 FR 25091.
    \208\ See http://www.epa.gov/ttn/atw/utility/utilitypg.html for
a copy of the signed final rule.
---------------------------------------------------------------------------

    Comment: The EPA's reason for proposing to approve a limit of 0.07
lb/MMBtu and a wet ESP as PM BART for Domtar Power Boiler No. 1 is
based on an outdated 2004 Boiler MACT PM standard of 0.07 lb/MMBtu and
because according to EPA, the BART Guidelines provide that unless there
are new technologies subsequent to the MACT standards which would lead
to cost-effective increases in the level of control, sources may rely
on the MACT standards for purposes of BART (76 FR 64207). EPA's
proposed approval ignores the fact that the 2004 MACT PM standard upon
which the Domtar Power Boiler No. 1 BART determination is based was
vacated and remanded and that EPA subsequently promulgated revised
boiler MACT standards in 2011 which were more stringent. The new 2011
standards require existing solid fuel-fired boilers like Domtar's Power
Boiler No. 1 to meet a PM emission limit of 0.039 lb/MMBtu on a 30-day
rolling average, which is 44% lower than the vacated 2004 0.07 lb/MMBtu
PM MACT limit (76 FR 15608, 15689 at Table 2). Even though EPA has
delayed the effective date of the new 2011 Boiler MACT rule until
completion of reconsideration of the rule and recently reissued a
reconsideration proposal, there is no legitimate legal basis in the
applicable regulations for exempting sources from a five-factor BART
analysis based on their meeting an outdated and formally vacated PM
MACT standard as reflecting BART when that MACT standard has been
replaced with a more stringent proposed MACT standard. EPA should
disapprove the PM BART determination for Power Boiler No. 1 either
because it is less stringent than required by the MACT standards for PM
currently being proposed by EPA or because there was no five-factor
evaluation for BART for PM.
    Response: The EPA acknowledges that on June 8, 2007, the United
States Court of Appeals for the District of Columbia Circuit vacated
and remanded the national emission standards for hazardous air
pollutants for new and existing industrial/commercial/institutional
boilers and process heaters (i.e. the 2004 Boiler MACT Rule)
promulgated by EPA on September 13, 2004. However, it should be noted
that the effective date of this vacatur was July 30, 2007, which was
after the close of the public notice and comment period for Arkansas's
proposed RH Rule, which codifies all the BART determinations made by
the State. On March 21, 2011, the EPA issued a final rule to regulate
emissions of hazardous air pollutants (HAPs) from industrial,
commercial, and institutional boilers and process heaters located at
major sources of HAP emissions (i.e. the ``Major Source Boiler MACT,''
or Boiler MACT Rule). As noted in the comment, the Major Source Boiler
MACT Rule established a PM emission limit of 0.039 lb/MMBtu on a 30-day
rolling average

that applies to existing boilers designed to burn solid fuel, such as
the Domtar Ashdown Mill Power Boiler No. 1. However, EPA promulgated
the Major Source Boiler MACT Rule years after the end of the State's
public notice and comment period and years after the date of Arkansas's
submission to EPA of the RH SIP. As such, it would be unreasonable to
disapprove the State's PM BART determination for Domtar on the basis
that it is less stringent than the emission limit in the Major Source
Boiler MACT Rule issued by EPA on March 21, 2011. Furthermore, on May
18, 2011, EPA published a final rule delaying the effective date for
the Major Source Boiler MACT Rule until the proceedings for judicial
review of the rule is completed or the EPA completes its
reconsideration of the rule, whichever is earlier.\209\ And on December
2, 2011, EPA issued a proposed rule for reconsideration of the final
Major Source Boiler MACT Rule.\210\ The proposed rule for
reconsideration and the uncertainty surrounding the Major Source Boiler
MACT Rule is another reason why it is unreasonable for EPA to
disapprove the State's PM BART determination for Domtar on the basis
that it is less stringent than the emission limit in the 2011 Major
Source Boiler MACT Rule.
---------------------------------------------------------------------------

    \209\ 76 FR 28662.
    \210\ 76 FR 80598.
---------------------------------------------------------------------------

    With regard to the comment that EPA should disapprove the State's
PM BART determination for Domtar Power Boiler No. 1 because there was
no five-factor evaluation for BART for PM, EPA holds that the State did
not conduct a BART analysis for PM for Domtar Power Boiler No. 1
because at the time of the State's analysis, it was relying on the MACT
standards for purposes of BART. Furthermore, the comment disregards the
reason why the BART Guidelines provide that States could take a
streamlined BART approach for sources subject to MACT standards. The
BART Guidelines provide the following:

``Any source subject to MACT standards must meet a level that is as
stringent as the best controlled 12 percent of sources in the
industry * * * We believe that, in many cases, it will be unlikely
that States will identify emission controls more stringent than the
MACT standards without identifying control options that would cost
many thousands of dollars per ton.'' \211\
---------------------------------------------------------------------------

    \211\ Appendix Y to Part 51, section IV.C.

    Accordingly, the reason why the BART Guidelines anticipated that
states could streamline their analysis by relying on the MACT standards
for purposes of BART is because EPA believes that such controls are
among the most stringent available and that emission controls more
stringent than this are very likely not cost-effective. Notwithstanding
the court's vacatur of the 2004 Boiler MACT Rule, at the time Arkansas
performed its analysis and adopted the 0.07 lb/MMBtu emission limit for
PM BART for the Domtar Ashdown Mill Power Boiler No. 1 based on the
2004 Boiler MACT PM standard, the emissions controls reflected by that
PM standard were among the most stringent controls available at that
time and emission controls more stringent than this were at that time
likely not cost-effective for purposes of addressing visibility.
Therefore, EPA disagrees that we should disapprove the PM BART
determination for the Domtar Ashdown Mill Power Boiler No. 1.

F. Comments on Modeling

    Comment: ADEQ conducted pre-control CALPUFF modeling to show that
PM10 and PM2.5 emissions from AEP Flint Creek No.
1 Boiler have minimal visibility impacts. The EPA utilized modeling
results to exempt White Bluff Units 1 and 2 from a PM BART analysis,
while ADEQ and Entergy exempted the units from a PM BART analysis based
on their belief that most of the visibility-causing emissions from
Units 1 and 2 are due to SO2 and NOX while
PM10 emissions are well-controlled with existing
electrostatic precipitators (ESPs). The existing PM emission limit of
0.1 lbs/MMBtu, which ADEQ adopted as BART for PM, fails to reflect the
best system of continuous particulate matter reduction at the White
Bluff units, especially if Entergy is considering the installation of a
dry scrubber and baghouse at each White Bluff unit to meet BART.
    In addition, the impact threshold used in this analysis is
problematic because it is likely that ADEQ applied a 0.5 dv threshold,
although the discussion in the Arkansas RH SIP on the modeling is
limited or not present. Given the number of sources impacting
visibility at Class I areas, a 0.5 dv threshold is not appropriate for
one visibility impairing pollutant. The RHR and BART Guidelines do not
provide for exempting a source from BART for one visibility impairing
pollutant. A BART determination must be made for each pollutant and EPA
cannot exempt Flint Creek Boiler No. 1 and White Bluff Units 1 and 2
from a BART analysis for PM based on modeling that shows that PM
visibility impacts do not trip the BART impact threshold.
    Furthermore, the PM modeling used to exempt the source from a PM
BART determination utilized an emission rate much lower than the
proposed BART limit. The pre-control modeling for Flint Creek included
the 24-hr actual maximum emissions rate, which is 70% lower than the
proposed BART limit of 0.1 lbs/MMBtu. ADEQ modeled White Bluff Unit 1's
highest 24-hour actual PM10 emission rate of 15.592 grams
per second and White Bluff Unit 2's highest 24-hour actual
PM10 emission rate of 16.653 grams per second in determining
whether the plant's emissions were subject to BART, which is 85% lower
than the proposed BART limit of 0.1 lbs/MMBtu. The emission limits in
the April 2007 ENVIRON Report titled ``Cumulative Modeling of Subject
to Best Available Retrofit Technology (BART) Facilities as a
Requirement of ADEQ's BART Modeling Protocol'' (Appendix 9.2D of the
Arkansas RH SIP) are even lower than those used in the pre-control
modeling.
    Response: In our review of the Arkansas RH SIP, we evaluated the
determination by ADEQ that no additional PM controls are required for
the AEP Flint Creek Boiler No. 1 and the Entergy White Bluff Units 1
and 2. In the case of Flint Creek, ADEQ's determination was based on
the pre-control modeling performed by ADEQ and a review of AEP SWEPCO's
statement that the PM visibility modeling did not ``trip the BART
impact threshold.'' We reviewed the pre-control modeling preformed
using the 24-hr actual maximum emissions from the baseline period. The
modeling results in Appendix 9.2B of the AR RH SIP and presented in
Table 7-6 of Appendix A of the TSD,\212\ indicate that PM contributes
less than 0.5% of the total visibility impacts from Flint Creek Boiler
No. 1 at all nearby Class I areas with the exception of Upper Buffalo.
PM contributions to visibility impacts at Upper Buffalo from Flint
Creek are less than 2% of the total visibility impairment at this Class
I area. On the most impacted day at Upper Buffalo, modeling the 24-hr
actual maximum emissions, PM contributes only 0.07 dv of the total
3.781 dv modeled visibility impact from the source. Clearly, the most
effective controls to address visibility impairment from the source are
those that would reduce emissions of visibility impairing pollutants
other than direct emissions of PM.
---------------------------------------------------------------------------

    \212\ These documents can be found in the docket for our
rulemaking.
---------------------------------------------------------------------------

    For Entergy White Bluff units 1 and 2, we reviewed the data
submitted by ADEQ, including pre-control modeling in Appendix 9.2B of
the Arkansas RH SIP, to evaluate ADEQ and White Bluff's determination
that the majority of visibility-causing emissions are due to

emissions of NOX and SO2, and that no additional
PM controls are warranted. The modeling results in Appendix 9.2B of the
Arkansas RH SIP and presented in Table 7-7 of Appendix A of the TSD,
indicate that PM contributes less than 0.4% of the total visibility
impacts at all nearby Class I areas. On the most impacted day at Caney
Creek, modeling the 24-hr actual maximum emissions, PM contributes only
0.03 dv of the more than 8 dv modeled visibility impact from the White
Bluff Units 1 and 2. Clearly, the majority of visibility-causing
emissions are due to emissions of NOX and SO2 and
the most effective controls to address visibility impairment from the
units are those that would reduce emissions of NOX and
SO2 rather than direct emissions of PM. In this action, we
are finalizing our proposal to disapprove the NOX and
SO2 BART determinations for these units as ADEQ did not
properly evaluate and identify controls to address visibility
impairment from these units.
    In both cases, it is clear that the visibility impact from PM
emissions alone is so minimal such that the installation of any
additional PM controls on these units (including any upgrades to the
existing controls) could only have minimal visibility benefit and
therefore would not be justified. This is in keeping with the BART
Rule, which states the following:

    ``Consistent with the CAA and the implementing regulations,
States can adopt a more streamlined approach to making BART
determinations where appropriate. Although BART determinations are
based on the totality of circumstances in a given situation, such as
the distance of the source from a Class I area, the type and amount
of pollutant at issue, and the availability and cost of controls, it
is clear that in some situations, one or more factors will clearly
suggest an outcome. Thus, for example, a State need not undertake an
exhaustive analysis of a source's impact on visibility resulting
from relatively minor emissions of a pollutant where it is clear
that controls would be costly and any improvements in visibility
resulting from reductions in emissions of that pollutant would be
negligible. In a scenario, for example, where a source emits
thousands of tons of SO2 but less than one hundred tons
of NOX, the State could easily conclude that requiring
expensive controls to reduce NOX would not be
appropriate. In another situation, however, inexpensive
NOX controls might be available and a State might
reasonably conclude that NOX controls were justified as a
means to improve visibility despite the fact that the source emits
less than one hundred tons of the pollutant.'' \213\
---------------------------------------------------------------------------

    \213\ 70 FR 39116.

    In reviewing the State's PM BART determinations for Flint Creek
Boiler No. 1 and White Bluff Units 1 and 2, we utilized ADEQ's pre-
control screening modeling using 24-hr maximum actual emissions from
the baseline period as recommended in the BART guidelines. We did not
rely on the cumulative modeling results found in Appendix 9.2D of the
AR RH SIP in our review of ADEQ's PM BART determination for sources at
these two facilities. Based on our analysis of the data submitted by
ADEQ in the Arkansas RH SIP, we find that no additional controls are
required for PM and therefore are finalizing our proposal to find that
the existing PM emission limits are acceptable to satisfy the PM BART
requirements of Flint Creek Boiler No. 1 and White Bluff Units 1 and 2.
    Comment: Even though the modeling for Entergy's White Bluff Units 1
and 2 deviated from the standard modeling protocol in evaluating wet
and dry scrubbers, these deviations did not impact the BART analysis
and subsequent BART determination for these units. The use of the 8th
highest day rather than the maximum visibility impact did not impact
the BART determination because the units were still determined to be
subject-to-BART and the BART decision was not based upon modeling.
Therefore, ADEQ's acceptance of the modeling should be approved by EPA.
    Response: The modeling conducted for Entergy White Bluff Units 1
and 2 was not conducted appropriately for its purpose and affected the
BART analysis and subsequent BART determinations for these units. The
modeling for wet and dry scrubbers at Entergy's White Bluff units 1 and
2 evaluated both control technologies at an emission limit of 0.15 lb/
MMBtu for SO2. However, wet scrubbers and dry scrubbers are
capable of achieving a lower emission limit than was modeled by ADEQ,
and similar facilities use these controls to control SO2
emissions below the 0.15 lb/MMBtu limit included in the analysis. The
lowest emission limit achievable must be included in the BART analysis.
ADEQ evaluated the control effectiveness of the two control options of
wet and dry scrubbing, stating the wet scrubber can achieve up to 95%
control efficiency while the dry scrubber can achieve up to 92% control
efficiency. An emission limit of 0.15 lbs/MMBtu represents a control
efficiency of only approximately 80% at White Bluff Units 1 and 2.
Therefore, the visibility modeling is flawed because it did not
evaluate the level of visibility improvement reasonably achievable due
to the use of these technologies at the emission rate these
technologies are capable of achieving.
    Furthermore the original meteorological databases generated by
CENRAP did not include observations as our guidance recommends. The use
of meteorological databases that do not include observations may lead,
to less conservatism in the CALPUFF modeled visibility results compared
with modeling that uses meteorological databases with observations. To
account for this, the use of the 1st High modeling values rather than
8th high modeling values was agreed to by EPA, representatives of the
Federal Land Managers, and CENRAP stakeholders. The modeling conducted
for Entergy's White Bluff Units 1 and 2 deviated from this accepted
modeling protocol by using the 8th highest day rather than the maximum
impacted day and failed to account in any other way for the loss in
conservatism that results from using the CENRAP database that does not
include observations. In summary, an approvable visibility analysis
would follow the agreed upon modeling protocol for BART and evaluate
the visibility benefits for the lowest emission limit achievable by
each technologically feasible control as required by the RHR.
    Comment: We agree with EPA's finding that the visibility impact
analysis of the SO2 control options for Entergy White Bluff
Units 1 and 2 was not properly conducted because ADEQ's modeling for
White Bluff Units 1 and 2 considered both wet and dry scrubbers at the
same emission rate of 0.15 lb/MMBtu rather than modeling the emission
rates that these technologies are capable of achieving. In addition,
the modeling for Entergy's White Bluff Units 1 and 2 deviated from
ADEQ's modeling protocol by using the 98th percentile value of
visibility impacts rather than the highest day of impacts.
    Response: As explained elsewhere in our response to comments, we
find that the visibility impact analysis of the SO2 control
options for the White Bluff units 1 and 2 was not properly conducted
because ADEQ's modeling for White Bluff Units 1 and 2 considered both
wet and dry scrubbers at the same emission rate of 0.15 lb/MMBtu rather
than modeling the emission rates that these technologies are capable of
achieving. We find that ADEQ's modeling for Entergy's White Bluff Units
1 and 2 deviated from ADEQ's modeling protocol by using the 98th
percentile value of visibility impacts rather than the highest day of
impacts.
    Comment: ADEQ performed the BART determination modeling in
accordance with the guidance provided by EPA. ADEQ modeled
SO2 and NOX together, both pre-control and post-

control. Modeling results showed the pollutant that impacted visibility
was SO2 and not NOX. Utilizing this information
and in compliance with the EPA's BART Guidelines, ADEQ did not make
BART determination for that source or group of sources (or for certain
pollutants for those sources) when ADEQ's analysis showed that an
individual source or group of sources (or certain pollutants from those
sources) is not reasonably anticipated to cause or contribute to any
visibility impairment in a class I area.
    Response: We agree that ADEQ pre-control and post-control modeling
was performed modeling all pollutants (NOX, SO2,
and PM) together. We note that to properly evaluate the visibility
benefit from a control, NOX and SO2 emissions
should be modeled together.
    It is unclear which facility the comment is referring to regarding
ADEQ not making a BART determination for NOX based on
modeling that showed SO2 impacted visibility and not
NOX. ADEQ did make NOX BART determinations for
all but two subject-to-BART sources. Our concerns with these BART
determinations are discussed in detail in a separate response to
comment.
    For AECC Bailey Unit 1 and AECC McClellan Unit 1, ADEQ determined,
based on pollutant-specific modeling performed subsequent to the
initial pre-control screening modeling, that NOX
contributions were less than the 0.5 dv threshold and, as a result,
incorrectly determined a NOX BART determination was not
needed for these two units. ADEQ made a NOX BART
determination for all other sources they determined to be subject-to-
BART. In the case of the two AECC units, as stated in our proposal, our
evaluation of the screening modeling results for these units reveals
that on some of the most impacted days, nitrate is a significant
contributor to the visibility impairment due to these units. Post-
control modeling performed by ADEQ, applying the use of 1% sulfur fuel,
show that these units would continue to cause or contribute to
visibility impairment at a number of Class I areas, with NOX
emissions responsible for over 50% of the impairment on some days under
this control scenario. The pollutant-specific analysis approach for
NOX and SO2 used to evaluate controls at these
AECC units does not take into consideration the chemical interaction
between these two pollutants and ammonia present in the atmosphere. A
reduction in sulfate emissions can result in an increase in visibility
impairment from nitrate due to the increase in ammonia available to
react with nitrate to form visibility impairing aerosol. The pre-
control modeling results indicate that nitrate is a significant
contributor to visibility impairment on some days and this contribution
can increase under conditions of decreased SO2 emissions.
Therefore, NOX and SO2 emissions should be
modeled together and emission control technologies should be evaluated
for both pollutants. In light of the relatively high impacts due to
nitrate, a combination of NOX and SO2 controls
may prove to be cost-effective and provide for substantial visibility
improvement and must therefore be evaluated. We further discuss the
importance of evaluating all the emissions (NOX,
SO2, and PM) together from BART sources when assessing the
benefit in visibility impairment from reductions of NOX and/
or SO2 in another response to comment and also in past EPA
guidance.\214\
---------------------------------------------------------------------------

    \214\ BART Guidelines; Memo from Joseph Paisie (Geographic
Strategies Group, OAQPS) to Kay Prince (Branch Chief EPA Region 4)
on Regional Haze Regulations and Guidelines for Best Available
Retrofit Technology (BART) Determinations, July 19, 2006; EPA Q and
A--September 26, 2006.
---------------------------------------------------------------------------

    Comment: The EPA is inconsistent in its approach to the
contribution threshold to visibility impairment. The EPA initially
approved ADEQ's selection of a threshold of 0.5 dv in the Arkansas RH
SIP. However, the EPA later on states that a lower threshold value is
needed in evaluating pollutant-specific modeling for sources that emit
more than one visibility impairing pollutant. Arkansas properly modeled
the visibility impacts of NOX and SO2 emissions
separately from one another. Arkansas's application of the 0.5 dv
threshold in considering the impacts of NOX, SO2,
and PM on a per-pollutant basis is consistent with the BART Guidelines.
The EPA argues that the 0.5 dv threshold in the BART Guidelines applies
to all three visibility impairing pollutants combined, and requires the
state to lower the threshold value in evaluating pollutant-specific
modeling for sources that emit more than one visibility impairing
pollutant. This is unsupported as a legal, factual, and policy matter,
and it is unclear what EPA actually expects states to do on this issue.
    The EPA's proposed rule does not provide any guidance on EPA's
views as to how Arkansas and other states should modify the 0.5 dv
threshold to account for separate modeling of PM, on the one hand, and
NOX and SO2, on the other hand. The EPA cannot
reasonably purport to require the state to apply a new, untested, and
previously unarticulated standard in its BART analyses if it does not
provide guidance on how it should do so. Consistent with the 2006 EPA
memorandum cited by EPA in its proposal, it is believed that numerous
BART contribution analyses separating PM from NOX and
SO2 have been performed without revising the 0.5 dv
contribution threshold on this basis alone. EPA has not previously
stated or suggested that any such revision is necessary and there is no
basis for any suggestion that such a revision is necessary. EPA should
recognize that states may use the default 0.5 dv contribution threshold
and allow the application of this threshold regardless of how
pollutants are modeled. EPA's proposed new approach needlessly
complicates the analysis, is inappropriate and unsupported, and should
be withdrawn. ADEQ's selection of a threshold of 0.5 dv is reasonable
and appropriate, and should be approved by EPA.
    Response: We reviewed ADEQ's methodology to initially identify
which sources were subject-to-BART. This methodology included modeling
all pollutants together and applying a contribution threshold of 0.5
dv. As discussed in our proposed rule, we agree with ADEQ's selection
of the 0.5 dv threshold as it applies to the initial screening modeling
performed by ADEQ when all three pollutants, NOX,
SO2 and PM are considered together.
    We disagree with the characterization of the 0.5 dv threshold as a
default value. The BART Guidelines state that ``the appropriate
threshold for determining whether a source contributes to visibility
impairment' may reasonably differ across states,'' but, ``[a]s a
general matter, any threshold that you use for determining whether a
source `contributes' to visibility impairment should not be higher than
0.5 deciviews.'' 70 FR 39104, 39161. The 0.5 dv threshold is not set as
a default value but rather a ceiling to what may be determined to be
appropriate in any situation. Further, in setting a contribution
threshold, the BART Guidelines say that states should ``consider the
number of emissions sources affecting the Class I areas at issue and
the magnitude of the individual sources' impacts.'' 70 FR 39104, 39161.
The BART Guidelines affirm that states are free to use a lower
threshold if they conclude that the location of a large number of BART-
eligible sources in proximity of a Class I area justifies this
approach.
    The pollutant-specific approach is acceptable only for PM BART
contribution analyses. Furthermore, as

stated in the 2006 EPA memorandum\215\ referenced in the comment, using
CALPUFF on a pollutant-specific basis for PM is only appropriate in
certain situations, such as if a State chooses to adopt the Clean Air
Interstate Rule (CAlR) program/CSAPR to address emissions of
SO2 and NOX from EGUs. In such an instance, the
CAIR/CSAPR may satisfy the requirements for BART for these pollutants
from these sources. However, the State must determine whether its BART-
eligible EGUs are subject to review under BART for direct emissions of
PM.
---------------------------------------------------------------------------

    \215\ Memo from Joseph Paisie (Geographic Strategies Group,
OAQPS) to Kay Prince (Branch Chief EPA Region 4) on Regional Haze
Regulations and Guidelines for Best Available Retrofit Technology
(BART) Determinations, July 19, 2006.
---------------------------------------------------------------------------

    Arkansas did not rely on CAIR to address emissions of
SO2 and NOX. Therefore, pollutant specific
analysis is not appropriate for a single source analysis. For non-CAIR
situations, it is necessary to model the source's total emissions
(NOX and SO2) in any CALPUFF modeling to estimate
visibility impairment or change in visibility impairment from the
potential installation of controls or no controls. Separate pollutant-
specific analyses for NOX and SO2 do not take
into consideration the chemical interaction in the atmosphere. Such
modeling does not take into account the competition/balance of these
two pollutants chemical reactions with ammonia present in the
atmosphere. A reduction in sulfate emissions can result in an increase
in visibility impairment due to nitrate due to the increase in ammonia
available to react with nitrate to form visibility impairing aerosol.
Therefore, NOX and SO2 emissions should be
modeled together and emission control technologies should be evaluated
for both pollutants.\216\
---------------------------------------------------------------------------

    \216\ BART Guidelines; Memo from Joseph Paisie (Geographic
Strategies Group, OAQPS) to Kay Prince (Branch Chief EPA Region 4)
on Regional Haze Regulations and Guidelines for Best Available
Retrofit Technology (BART) Determinations, July 19, 2006; EPA Q and
A--September 26, 2006
---------------------------------------------------------------------------

    ADEQ's approach to modeling a single source on a pollutant specific
basis could allow for a BART applicable source to model below 0.5 for
each of the pollutants individually (NOX, SO2,
and PM), which could lead to a potential cumulative impact of up to
1.47 dv (3 x 0.49 dv) and yet the source would not be evaluated for
controls. This process would allow a determination to be made in this
maximum hypothetical case that a 1.47 dv impact from a subject to BART
source, which is above the 1.0 dv impact that would result in the
source causing a significant visibility impairment, would ``screen''
out of a full BART analysis using ADEQ's approach. This is not
appropriate and is inconsistent with our BART Guidelines and guidance.
In evaluation of pollutant-specific impacts from a source (i.e.
visibility impacts from PM emissions), consideration of the amount of
visibility impairment contribution from a source's PM emissions can be
evaluated against the visibility impairment contribution from the
source's combined NOX and SO2 emissions.\217\
---------------------------------------------------------------------------

    \217\ Ibid.
---------------------------------------------------------------------------

    EPA also disagrees that we have developed or implemented any new
guidance in our proposal. EPA's approach is based on the 2005 BART
guidelines, and additional guidance provided in 2006.
    Comment: Although the use of daily maximum emissions for BART
modeling purposes meets the modeling protocol, this protocol should be
revisited due to the fact that using daily maximum emissions is
completely unrealistic and overly conservative in most cases, as it
assumes that such an emission rate occurs every day for three years.
This is especially overly conservative for Unit 1 of the Carl E. Bailey
Generating Station and Unit 1 of the John L. McClellan Generation
Station, as these units primarily fire natural gas and have rarely
fired fuel oil over the past few years. With upcoming EPA environmental
regulations such as the Utility MACT Rule being promulgated, these
units are likely to continue the trend of low capacity factors of fuel
use. Any controls required to be implemented on these units will only
be used 5% or less of the time, and it is certainly not cost-effective.
Logic and practicality dictate that the minimal use of fuel oil at
these two units requires an accommodation in this instance.
    Response: We agree that the modeling protocol and the BART
Guidelines state that the daily maximum emissions should be used for
modeling visibility impacts during the baseline period. We note that
the BART Guidelines do allow for consideration of limited operation of
a source or fuel type. Given that there are no permit requirements in
place that would limit the time of operation of the AECC units when
burning fuel oil, the facilities can legally be operated well above the
5% capacity factor that AECC assumes it will be operating under in the
future. It is likely that if the fuel oil burning capacity of these
units is significantly limited, installation of controls to address the
emissions during fuel oil burning would prove to be not cost-effective
on a dollar per ton removed basis. A federally enforceable limit must
be in place that can be relied upon to limit the emissions of the
source during fuel oil burning scenarios. We are disapproving the
SO2 BART analysis for these two units because ADEQ did not
consider the option of burning fuel oils with sulfur content less than
1.0%. As articulated in our proposal, the use of fuel oil with a 0.5%
sulfur content or lower is technically feasible and ADEQ should have
evaluated its cost effectiveness and visibility impact for the AECC
Bailey Unit 1 and the AECC McClellan Unit 1. Alternatively, an
operating air permit restriction to use only natural gas as the fuel
source for the two units or significantly restricting fuel oil burning
may be acceptable.
    At this time, it is speculation to assume that the future amended
MACT rule will lower the capacity factors of fuel use for sources. When
evaluating a state's BART determination, the EPA looks at existing
requirements and cannot rely on potential future actions in its
decision to approve or disapprove a state SIP. ADEQ cannot rely on a
future MACT Rule to limit the capacity factor of fuel oil use.
    Comment: All post-control CALPUFF modeling completed in Domtar's
analysis was cumulative-type modeling, taking into account all
pollutants--NOX, SO2, and PM10 in each
analysis. The EPA needs to list in detail any concerns about the
methods used to complete modeling analysis of Domtar's facility.
    Response: We agree with the commenter that post-control modeling
for the Domtar facility was performed modeling all visibility impairing
pollutants together (SO2, NOX and PM). As
discussed in the proposed action, we are finding the chosen model and
the general modeling methodology used by ADEQ to be acceptable. Because
Domtar's visibility modeling was performed following the ADEQ modeling
protocol, we also find that the modeling methodology followed by Domtar
is acceptable. However, the BART determinations made for the subject-
to-BART units at the Domtar facility were performed without evaluating
the visibility improvement anticipated due to the use of all
technically feasible control options. Visibility modeling was performed
only after a control technology was selected as BART. This approach is
unacceptable and does not allow for a comparison of the effectiveness
of available controls in reducing visibility impacts to be considered
as part of the BART determination. ADEQ's and Domtar's BART
determinations were flawed

because the modeling did not evaluate all technically feasible control
options or evaluate the control technology at the control efficiencies
they are capable of achieving to inform the BART determination. We
note, that to properly evaluate the visibility benefit from each
control, NOX and SO2 emissions must be modeled
together for each control scenario examined, similar to the modeling
performed in the post-and pre-control modeling scenarios.
    Comment: The EPA cannot rely on post-control modeling to justify
the requirement to evaluate post-combustion controls for NOX
in the agency's disapproval of the BART determinations for Entergy's
White Bluff facility. While EPA states that post-control modeling shows
continued post-control modeled visibility impairment due to
NOX emissions, the models, including CALPUFF, significantly
overstate nitrate-caused RH, and reliance on those models is not a
credible approach. Even EPA acknowledges that the CALPUFF model tends
to magnify the actual visibility effects of an individual source and
the CALPUFF model is less advanced than some of the recent atmospheric
chemistry simulations. A more recent version of CALPUFF tends to reduce
the nitrate over prediction using more advanced chemistry modules
borrowed from regional models such as CAMx and CMAQ, but this version
has not been yet approved by EPA. Because there is not a credible
version of CALPUFF with adequate chemistry to assess the visibility
impact of Arkansas NOX emissions in an unbiased manner, it
is helpful to look at actual monitoring data taken at IMPROVE sites and
to keep in mind that the nitrate chemistry and the IMPROVE monitoring
data indicate that NO3 particulate formation tends to occur
on the coldest days, while on warmer days, invisible HNO3
vapor formation is preferred, which has no visibility impact. The
Arkansas sources that affect the class I areas subject to this rule are
south and east of the areas, which are generally not associated with
the coldest conditions when the worst nitrate haze is observed to
actually occur.
    Response: We disagree that we relied on post-control modeling to
justify the requirement to evaluate post-combustion controls. The post-
control model results indicate that even after application of the
State's selected combustion controls to reduce NOX
emissions, a significant visibility impact due to NOX
emissions from White Bluff Units 1 and 2 remains. This demonstrates
that post-combustion controls that result in larger reductions of
NOX may prove to be cost-effective and result in significant
visibility improvement. We note that the modeling of changes in
visibility impacts is only one of five factors that are evaluated in a
BART analysis. In performing a BART analysis, the State must take into
consideration all technologically feasible and available control
technologies, the costs of compliance, the energy and non-air quality
environmental impacts of compliance, any pollution control equipment in
use at the source, the remaining useful life of the source, and the
degree of improvement in visibility which may reasonably be anticipated
to result from the use of such technology.\218\ As articulated in more
detail in our proposal and in our response to previous comments, when
evaluating NOX controls for White Bluff Units 1 and 2, the
State considered only combustion controls that would achieve the
presumptive NOX emission limit even though there are
technically feasible and available control technologies (including
post-combustion controls) that are currently being used at similar
facilities to meet an emission limit much more stringent than the 0.15
lb/MMBtu presumptive limit for NOX. The BART Guidelines
provide that in identifying control options for evaluation in a BART
analysis, states must identify the most stringent option and a
reasonable set of options for analysis that reflects a comprehensive
list of available technologies.\219\ In addition, the RHR requires that
in establishing source specific BART emission limits, a state's BART
analysis must identify and consider the maximum level of emission
reduction that has been achieved in other recent retrofits at existing
sources in the source category.\220\ Therefore, as explained in more
detail in our response to previous comments, in its NOX BART
analysis for White Bluff Units 1 and 2, the State must evaluate
NOX post-combustion controls at the most stringent emission
limit capable of being achieved by these controls.
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    \218\ See 40 CFR 51.308(e)(1)(ii)(A) and 42 U.S.C. 7491(g)(2).
    \219\ Appendix Y to Part 41, section IV.D.
    \220\ 64 FR 35740.
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    We disagree with the comment's characterization that the CALPUFF
model approved for regulatory actions is not a credible model to assess
visibility impacts of NOX emissions from Arkansas sources.
For the specific purposes of the RHR's BART provisions, we concluded
that CALPUFF (versions that EPA has approved) is sufficiently reliable
to inform the decision making process in determining if a full BART
analysis is required and in estimating the degree of visibility
improvement that may reasonably be expected from controlling a single
source in order to inform the BART determination.\221\ When we
developed the BART Guidelines and determined the acceptability of using
CALPUFF in estimating visibility impacts from BART sources (BART
eligible or subject to BART sources), EPA was aware that EPA had not
approved the regulatory version of CALPUFF for doing full chemistry as
a Guideline on Air Quality Models (GAQM) preferred model. The final
BART Guidelines recommend that CALPUFF's 98th percentile modeling
results be used to estimate the visibility impairment. This is in
contrast to the approach in our BART Guidelines proposal to use the
highest daily impact value. We acknowledged that the chemistry modules
in the CALPUFF model are simplified and likely to provide conservative
(higher) results for peak impacts. To address the concerns which are
now being raised by the comment, we made the decision to consider the
less conservative 98th percentile to account for this potential
bias.\222\
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    \221\ Regulatory version that had been approved by EPA for
assessing Long Range Transport of primary pollutants. Final BART
guidelines published July 6, 2005. (70 FR 39104-39172).
    \222\ ``Most important, the simplified chemistry in the model
tends to magnify the actual visibility effects of that source.
Because of these features and the uncertainties associated with the
model, we believe it is appropriate to use the 98th percentile--a
more robust approach that does not give undue weight to the extreme
tail of the distribution.'' 70 FR 39104, 39121.
---------------------------------------------------------------------------

    The BART modeling protocol, developed by the CENRAP for use by all
CENRAP states and reviewed by EPA and the FLM including the use of
CALPUFF, was adopted by ADEQ. In general, this protocol was followed by
ADEQ in determining which sources were subject-to-BART and in modeling
visibility impacts from controls in evaluating BART.\223\ In
development of the CENRAP BART modeling protocol, we were concerned
that CENRAP had not included meteorological observation data in
development of the

meteorological data sets for the BART CALPUFF modeling. We were
concerned that this approach, that did not follow our guidelines, would
lead to some underestimation of impacts. As a result, EPA, FLM
representatives, states, and stakeholders agreed that they would either
use the maximum model predicted values (instead of the 98th percentile)
or develop a modeling protocol to generate the meteorological datasets
with meteorological observations, which we would then allow the use of
the 98th percentile. We note that the CALPUFF modeling in ADEQ's SIP
that was provided by Entergy White Bluff's contractors did not use the
maximum value but did use the CENRAP meteorological dataset and used
the 98th percentile, which creates a concern that visibility impairment
will be underestimated. We noted this concern in our proposal and also
a concern that Entergy had utilized a higher emission rate than is
likely achievable by the selected control technology and both of these
issues would lead to underestimations in the visibility benefit
anticipated from the use of additional controls.\224\ These issues will
need to be addressed when a revised BART analysis is completed.
---------------------------------------------------------------------------

    \223\ As discussed in detail in a separate response to comment,
because the CENRAP meteorological databases used in the CALPUFF
modeling analyses do not include observations, the use of the
maximum impact rather than the 98th percentile was agreed upon. The
use of meteorological databases that do not include observations may
lead, in some applications, to potentially less conservatism in the
CALPUFF modeled visibility results compared with modeling that uses
meteorological databases with observations. The use of the 1st High
modeling values was agreed to by EPA, representatives of the Federal
Land Managers, and CENRAP stakeholders to account for this.
    \224\ See 76 FR 64205-64207.
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    The comment suggests that CALPUFF version 6.4 has been updated with
an allegedly more robust chemistry and purportedly performs better
according to the comment than the current version of the model approved
for regulatory actions (currently CALPUFF version 5.8). The comment
claims that CALPUFF version 6.4 was shared with EPA in December 2010.
We wish to clarify that EPA had a meeting with API representatives and
others in February 2011. At this meeting, a PowerPoint was shared about
CALPUFF version 6.4, but the full model code, explanations and
documentation of the code, model evaluations, etc., have not been
provided to EPA as of February 2012. We have a detailed procedure for
evaluation of new models that includes documentation, peer review,
evaluation, performance analysis, etc. Furthermore, significant changes
in models (such as a significant upgrade in the chemistry module) are
often required to go through a formal rulemaking process for adoption.
As noted by the comment, we previously received comments about the
CALPUFF version 6.4 model in another action and provided a response
that a proper review analysis and evaluation have not been
conducted.\225\ As noted by the comment, the more recently developed
model version (version 6.4) has not gone through the appropriate review
to assess if it is founded in appropriate science and performs
adequately and reliably and is an improvement to the current version
that is acceptable for regulatory actions. If the revised versions of
CALPUFF can be shown to be reliable and acceptable to EPA through the
appropriate process, it would likely be appropriate to the use Highest
Daily impact (1st High instead of the 8th High) based on the
presumption that the updated chemistry of the CALPUFF model would
result in less conservative results than EPA approved CALPUFF versions
5.8 or 5.711. In past agreements in using the CAMx photochemical model,
which has a robust chemistry module, Region 6 has required the use of
the 1st High value when sources are screened out of a full BART
analysis based on the CAMx results.
---------------------------------------------------------------------------

    \225\ See 76 FR 52431--52434 and the Response to comments
document (pg. 124-133) for a full agency discussion on why CALPUFF
version 6.4 (and other non-EPA approved versions) are not acceptable
at this time for regulatory analyses (EPA Docket ID No. EPA-R06-OAR-
2010-0846).
---------------------------------------------------------------------------

    With regard to the comment's observation that the monitoring data
indicates visibility impacts due to nitrate formation occur on colder
days and that these days are not when winds are generally from the
south or east, EPA notes that monitoring data is only collected every
three days at each IMPROVE monitor and there is only one monitor in a
Class I area. Modeling provides for an analysis of visibility
conditions during every day of the baseline period at a number of
receptor locations at each Class I area, and is not limited by the
number of days data is collected. Modeling also allows for receptors to
be placed throughout the Class I area and not limited to one monitor
location for estimating visibility impairment throughout the Class I
areas. Thus, the comment's observation is overly generalized that the
winds do not generally come from the south and east during the colder
periods when nitrates are a concern at the Class I areas of concern.
This overly broad-brushed statement about wind patterns is not
supported by a more detailed analysis of wind patterns nor transport
phenomena as wind directions change. We included a more sophisticated
approach for source-receptor analysis in our BART Guidelines that takes
into account meteorological transport patterns on every day of the
year. Since transport of pollutants to the Class I area is not always a
direct route as wind patterns change, the more sophisticated approach
discussed in the BART guidelines is to use a full meteorological
modeling analysis using prognostic meteorological data that has wind
speed and direction throughout many atmospheric layers from the surface
to the upper atmosphere. CALPUFF visibility modeling was performed
using three years (2001-2003) of prognostic meteorological data and 24-
hr actual maximum emissions, following the methods in the BART
Guidelines. Pre-control and post-control modeling show significant
visibility impacts due to the Entergy White Bluff's NOX
emissions, with some of the highest impacted days occurring during the
fall and winter months. This analysis did not include an evaluation
based on the most effective emission limit that can be achieved. So it
is likely that there are underestimates in the visibility improvement
that could potentially be achieved from installation of BART. The use
of CALPUFF and prognostic meteorological data that is generated with
the same meteorological models as weather forecasting, with the many
layers of wind speed and direction, is a much more appropriate and
sophisticated approach to analyzing visibility impairment than the
comment's assessment of potential impacts from Arkansas sources
indicated. Therefore, we disagree with the statement that the source
would not be affecting the Class I areas because the winds are not
generally from the south or east when the coldest conditions occur that
are associated with the worst nitrate haze.

G. Comments on Legal Issues

1. Comments on Regional Haze
    Comment: The EPA does not have the authority under the CAA to
partially disapprove portions of Arkansas's RH SIP including BART
determinations that did not address all the BART factors, BART
determinations that adopted presumptive limits, Arkansas's LTS, and
Arkansas's RPGs. The EPA's proposal improperly encroaches on the
state's authority and discretion in developing a RH SIP. Arkansas has
properly exercised its statutory authority under the CAA. The EPA must
defer to Arkansas determinations in their RH SIP since EPA lacks the
authority to substitute its own judgment or policy preferences for the
state's determination. The EPA's role in implementing the visibility
program under the RH SIP is one of support and cooperation in
implementation.
    Response: The EPA's proposed partial disapproval of Arkansas's RH
SIP is a proper exercise of EPA's authority under the Clean Air Act.
Congress crafted the CAA to provide for states to

take the lead in developing implementation plans, but balanced that
decision by requiring EPA to review the plans to determine whether a
SIP meets the requirements of the CAA. The EPA's review of SIPs is not
limited to support and cooperation in implementation of a state SIP,
nor is it to simply rubber-stamp state decisions. When reviewing state
SIPs, EPA must consider not only whether the state considered the
appropriate factors in making decisions, but acted reasonably in doing
so. In undertaking such a review, EPA does not usurp the state's
authority but ensures that such authority is reasonably exercised.
    In taking action on the Arkansas RH SIP submittals, EPA is
disapproving a portion but approving as much of the Arkansas RH SIP as
possible. Our action today is consistent with the statute. In
finalizing our proposed determinations, we are approving the following:
Arkansas's identification of affected Class I areas; the establishment
of baseline and natural visibility conditions; the determination of
URP; Arkansas's RPG consultation; the RH monitoring strategy and other
SIP requirements under Sec.  51.308(d)(4); Arkansas's commitment to
submit periodic RH SIP revisions and periodic progress reports
describing progress towards the RPGs; Arkansas's commitment to make a
determination of the adequacy of the existing SIP at the time a
progress report is submitted; and Arkansas's consultation with FLMs. We
are also largely approving those portions of the SIP addressing
Arkansas's identification of those sources that are BART-eligible
sources and those subject to BART sources; some of the State's BART
determinations for five units; Arkansas's RH Rule; and the LTS.
    We are, however, disapproving some of the State's BART
determinations for nine units. As explained in the proposal and the
previous response to comments, some of the State's BART determinations
for the nine units are not approvable because Arkansas did not follow
the requirements of section 40 CFR 51.308(e). 76 FR at 64186, at 64187.
As a result of EPA's disapproval of the BART determinations, we are
also partially disapproving that portion of the LTS affected by this
disapproval. Similarly, EPA's disapproval of Arkansas's RPGs is based
on the state's failure to follow the requirements of 40 CFR
51.308(d)(i)(A). See also CAA Sec.  169A(g). In concluding that
Arkansas did not adhere to the requirements of the RHR, EPA is not
substituting its policy judgment for that of Arkansas but rather
exercising its authority to ensure that the state's decisions are
reasonable ones that meet statutory and regulatory requirements.
    Comment: The CAA gives primacy to the states in devising the LTS
for making reasonable progress toward the national visibility goal and
in making BART determinations and limited authority to EPA. In
accordance with section 169A(a)(4), EPA promulgates regulations to
assure progress towards the national goal of preventing future and
remedying existing visibility impairment in Federal class I areas while
the states are required to submit SIP which meets these measures. In
1999 and 2005, EPA promulgated and subsequently amended the RHR which
gives guidance to the states on how to develop a visibility program
that meets the national visibility goal for their state. Section
169(A)(b)(2) requires States to direct sources subject to BART to
comply with a BART determination. In accordance with section 169B,
states, acting together through visibility transport commissions, are
primarily responsible for formulating a coordinated response to
interstate transport of visibility. With respect to the RHR and the
BART Guidelines, the CAA only requires that states take measures
necessary to make reasonable progress toward the national goal by
engaging in the process of weighing statutory factors. Regarding EPA's
role, section 169A(g)(2) (as defined in Train v. Natural Res. Def.
Council, 421 U.S. 60, 79 (1975)) provides that EPA may disapprove a SIP
only where a state's SIP fails to meet the minimum CAA requirements.
    Response: We agree that the states are assigned statutory and
regulatory authority to draft and implement the visibility program as
well as to make BART determinations for sources within their state.
Although the states generally have the freedom to determine the weight
and significance of the statutory factors in making BART determinations
\226\, they have an overriding obligation to come to a conclusion that
is based on reasoned analysis. Similarly, states are given flexibility
in determining reasonable progress, but in making that determination,
they are required by the CAA to consider certain factors. Whether one
characterizes EPA's role as limited or not limited in reviewing RH
SIPs, EPA must determine if the state's SIP meets the applicable
statutory and regulatory requirements. The state's BART determinations
for some sources, its LTS, and RPGs were flawed for reasons discussed
elsewhere in this notice and the proposed rulemaking. While states have
the authority to exercise different choices in determining BART or
setting RPGs, such decisions must be reasonable and consistent with
statutory and regulatory requirements. Arkansas's errors were
significant enough that we cannot conclude that the state's decision
met this standard. Our disapproval of portions of the RH SIP has an
appropriate basis in our CAA authority.
---------------------------------------------------------------------------

    \226\ States must follow the BART Guidelines in making BART
determinations for EGUs at power plants with a total generating
capacity greater than 750 MW. 40 CFR 51.308(e)(1)(ii)(B). In
establishing presumptive limits for these sources, EPA undertook a
partial weighing of the statutory factors that apply to BART
determinations.
---------------------------------------------------------------------------

    Comment: U.S. courts agree that EPA's role in reviewing visibility
programs and determining BART is limited. According to American Corn
Growers Ass'n v. EPA, 291 F.3d 1 (DC Circuit 2002), states play the
lead role in designing and implementing RH programs. American Corn
Growers outlined the legislative history, including the Conference
Report on the 1977 amendments, when the Court invalidated past
regulatory provisions regarding BART for constraining state authority.
The Court stated that the Conference report confirmed that Congress
intended states to decide which sources impair visibility and what BART
controls apply to those sources.
    Response: We agree that the CAA places the requirements for
developing RH plans and determining BART for BART-eligible sources on
states. As discussed above, EPA's role is to review the RH SIP
submittal including the BART determinations and determine if the state
met the applicable statutory and regulatory requirements. While the
court in American Corn Growers found that EPA had impermissibly
constrained state authority, it did so because it found that EPA forced
states to require BART controls without first assessing a source's
particular contribution to visibility impairment. This is not the case
with our action. We are not forcing Arkansas to adopt a particular
measure or to weigh the statutory factors in a particular way. Rather,
we are disapproving portions of Arkansas's RH SIP that address BART,
LTS, and RPGs because the state omitted critical analyses and made
flawed assumptions that compromise any decisions.
    Comment: The Supreme Court has ruled that states have primary
authority in issues relating to the CAA. In Train v. Natural Res. Def.
Council, 421 U.S. 60 (1975), the court ruled that EPA had no authority
to question the wisdom of a state's choices of emissions limitations if
they are part of a plan which satisfies the standards of the CAA. The
EPA may

devise and promulgate a specific plan of its own only if a state fails
to submit an implementation plan which satisfies those standards.
    Response: Our action does not contradict the Supreme Court's
decision in Train. States have significant responsibilities in
implementation of the CAA and meeting the requirements of the RHR. We
recognize that states have the primary responsibility of drafting an
implementation plan to address the requirements of the CAA Visibility
Program. We also recognize that we have the responsibility of ensuring
that the state plans, including RH SIPs, conform to the CAA
requirements. We cannot approve a RH SIP that fails to address BART,
LTS, and RPGs with a reasoned consideration of the statutory and
regulatory requirements of the CAA and the RHR.
    Comment: Because visibility impairment is primarily aesthetic and
does not rise to the same level of public policy concern as dangers to
the public health, Congress made the national visibility goal
discretionary. Accordingly, unlike other provisions of the CAA, the
national visibility goal is not considered to be a non-discretionary
duty of the Administrator under section 169A(f). Likewise, the court in
American Corn Growers has recognized that the natural visibility goal
is not a mandate but a goal. In addition, the CAA does not mandate a
particular timeframe to meet the national goal of natural visibility,
only that states make reasonable progress. The amount of progress that
is reasonable is not defined according to objective criteria but
instead involves balancing of public interest.
    Response: We do not agree that the CAA or RHR prescribes a
different degree of authority to states based on the program having the
goal of improving visibility as opposed to preventing adverse human
health effects. Among other things, the CAA requires states to submit
plans that satisfy NAAQS standards set to protect both public health
and welfare. Nothing in the terms of the CAA or its implementation
history directs that SIP submittals addressing visibility are subject
to a different standard of evaluation than SIP submittals that directly
address public health issues associated with air pollutants. The
distinction is not relevant to state authority to develop RH SIPs and
does not diminish our responsibility and authority to require that they
conform to the RHR and the Act.
    More generally, we agree that the CAA does not mandate a particular
timeframe to meet the national visibility goal. The comment is not
relevant, however, as our action to partially disapprove Arkansas's RH
SIP is not based on a finding by EPA that Arkansas's RH SIP fails to
achieve the national goal. Similarly, EPA is not disapproving
Arkansas's RH SIP because we disagree per se with the State's
conclusions as to what constitutes reasonable progress for this time
period. Our disapproval of the Arkansas RH SIP is based on the fact
that critical analyses were omitted and that these omissions compromise
Arkansas's determinations as to the measures necessary to make
reasonable progress.
    Comment: Although EPA can set national goals and guidelines for the
RH program, individual states have the authority to select BART for
specific sources of emissions and design the specific plans that are
appropriate for respective populations. The RHR does not require a
definitive dv or percent improvement in visibility. The only thing the
RHR requires of each state is to demonstrate an improvement in
visibility. The Arkansas RH SIP meets EPA's national goals and
guidelines. The Arkansas RH SIP establishes a firm foundation to meet
the required RPGs and meets and in some cases even exceeds the
requirements of the RHR.
    Response: We do not agree that the only thing that the RHR requires
is for each state to demonstrate an improvement in visibility. The RHR
outlines a process by which states are to evaluate and develop RH SIPs,
including the process for making BART determinations. The EPA is
disapproving portions of Arkansas's RH SIP that address BART, LTS, and
RPGs because the state omitted critical analyses in accordance with the
requirements of the CAA and the RHR.
    Comment: The preamble to the RHR recognized that States are the
primary decision makers in determining how to make BART determinations
and determining which sources are subject to BART. In analyzing the
applicability of certain executive orders to the proposed RHR, EPA
states that states will ultimately determine the sources subject to
BART and the appropriate level of control for such sources, and that
states accordingly exercise substantial intervening discretion in
implementing the final rule (70 FR 39155).
    Response: We agree that states are assigned statutory authority to
determine BART and that EPA has made statements confirming the state's
authority in this regard. States have the flexibility to determine the
weight and significance of the statutory factors. However, states must
make a reasoned determination consistent with the requirements of the
RHR. As detailed in our proposal and the supporting TSD, Arkansas's
BART determination for nine units, Arkansas's LTS, and RPGs did not
provide reasoned determinations conforming to the requirements of the
RHR.
    Comment: The EPA partially disapproved Arkansas's RH SIP because
the EPA disagreed with the State's conclusions. The EPA failed to defer
to the State's lawful exercise of its discretion pursuant to the CAA's
provisions for visibility protection.
    Response: Our partial disapproval of Arkansas's RH SIP is not based
on the resulting Arkansas conclusions. Rather our decision to
disapprove Arkansas's BART determinations for nine units, LTS, and RPGs
is because the state omitted critical analyses and made flawed
assumptions that compromise the resulting determinations. The State
could submit and EPA would approve RH SIP revisions that reached
identical determinations as the current SIP submittal if Arkansas's
analysis in reaching those determinations meets the RHR and the Act.
    Comment: The EPA has overstepped its authority in proposing to
reject the state's BART determinations on the basis of EPA's view that
the state's consideration of certain statutory factors was not
``adequate.'' The state, as the determining authority, has the power to
decide how each of the BART factors should be taken into account and
weighed. As long as a state considers a given factor, it has met its
obligations in regards to that factor. Once the state has made its
decision, EPA has no authority to ``second-guess'' the conclusions that
the state has reached.
    Response: As explained earlier, the states have the responsibility
to draft the RH SIP and the EPA has the responsibility of ensuring
State plans, including RH SIPs, conform to the CAA. As the drafter of
the RH SIP, the state generally has the authority to decide how each of
the BART factors are taken into account and weighed. EPA is not
disapproving Arkansas's BART determinations because it disagrees with
how Arkansas weighed the relevant factors, such as the cost of controls
or the degree of visibility improvement resulting from the use of
controls. The EPA is disapproving certain Arkansas's BART
determinations because they did not consider these factors in their
BART determinations in accordance with the RHR and the Act.
    Comment: All of the BART determinations made by Arkansas RH SIP
should be disapproved because

Arkansas did not do its own BART analysis in making its BART
determinations. Instead, Arkansas RH SIP adopted the companies' BART
analysis as part of the RH SIP and promulgated them into State
regulation. Given that Arkansas has not made any of its own BART
determinations, there are no BART determinations for EPA to act on.
    Response: Arkansas submitted a RH SIP which provided BART
determinations for sources that are subject to BART. Arkansas requested
that sources subject to BART submit material including a BART analysis.
Arkansas then reviewed the analysis and data provided by the sources
and adopted its BART determinations. The EPA reviews RH SIP submittals
from states that rely upon source-generated data and information to
evaluate whether the State's decisions meet the Act and EPA rules. In
Arkansas's case, after their review of the sources' provided
information, they reached the same BART determinations as was provided
by the source.
    Comment: Arkansas improperly planned to make its BART
determinations during the permitting process, not in the SIP submittal.
In 2009, ADEQ proposed a Title V permit amendment for Entergy's White
Bluff power plant to, among other things, incorporate BART emission
limits and requirements, in which ADEQ proposed different pollution
controls as BART than what was in the company's BART analysis in
Appendix 9.3 of the Arkansas RH SIP submitted to EPA.
    Response: We disagree that Arkansas planned to make its BART
determinations during the permitting process, be it through the New
Source Review preconstruction permitting SIP process or the Title V
operating permit program. The State adopted its BART determinations
through rulemaking and they are found in Chapter 15 of APCEC Regulation
No. 19, as contained in the RH SIP submissions. Each of the BART
determinations approved by EPA today becomes effective under Federal
law. It also becomes an applicable requirement that must be included in
a Title V permit. Any source subject to the BART determinations
approved today must at a minimum meet these requirements, as expressed
in 40 CFR 51.308(e). If Arkansas issues a Title V permit that has less
stringent requirements than the EPA-approved BART determination, then
the source is subject to Federal enforcement action. It is incumbent
upon the source to ensure that its Title V permit application meets all
the applicable Federal requirements. It also is incumbent upon the
source to ensure that it meets the most stringent applicable Federal
requirement. If the State wishes to impose BART emission limitations in
a Title V permit that are different from what EPA is approving today as
BART, then Arkansas must adopt and submit a revised RH SIP and submit
it to EPA for approval as a SIP revision.
    Comment: The EPA should not act on any of the company's BART
analyses, unless it conducts its own analysis of a company's submittal
in the context of a FIP.
    Response: Under the CAA, we must, within 24 months following a
final disapproval, either approve a SIP or promulgate a FIP.\227\ As
stated elsewhere in this final rulemaking, we will consider, and would
prefer, approving a SIP if the State submits a revised plan that we can
approve before the expiration of the mandatory FIP clock for the
portions of the SIP we are disapproving in this rulemaking action. In
light of this, we are choosing at this time not to perform any BART
analyses and not to develop and propose a FIP for the BART
determinations we are disapproving.
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    \227\ CAA section 110(c)(1).
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    Comment: The EPA has no reason to disapprove a State BART
determination that meets the presumptive BART level. The DC Circuit
Court of Appeals held in American Corn Growers Association v. EPA, that
there is nothing in the CAA that would require a State to adopt
provisions more stringent than the Federal requirement.
    Response: In disapproving BART determinations for certain subject-
to-BART sources that adopted the presumptive limits, EPA is not
requiring Arkansas to establish BART limits that are more stringent
than Federal requirements. Under the RHR, presumptive limits were
established to provide a path for States to follow when analyzing BART
for particular EGUs. The RHR has presumptive limits that act as a
starting point for the establishment of BART emission limits unless the
state's analysis indicates that an emission limit more or less
stringent than the presumptive limit is required. The EPA's BART Rule
and the BART Guidelines make clear that in developing the presumptive
emission limits, EPA made many design and technological assumptions,
and that the presumptive limits may not be BART in every case. As such,
the presumption in the BART Rule is that the controls reflected by the
presumptive limits are cost-effective, not that the presumptive limits
will be BART in every case.
    Thus, EPA's proposed rulemaking on the Arkansas RH SIP did not
propose to require Arkansas's subject to BART sources to achieve an
emission rate more stringent than the presumptive emission limits.
Rather, EPA's proposed rulemaking proposed to disapprove the BART
emission limits for subject to BART sources where the State adopted
presumptive emission limits without conducting a proper BART five-
factor analysis. Only after the State conducts a proper evaluation of
the five statutory factors, as required by 40 CFR 51.308(e)(1)(ii)(A)
and section 169A(g) of the CAA, or EPA conducts one in the context of a
FIP, will it be demonstrated whether any of Arkansas's subject to BART
sources must achieve an emission rate more (or less) stringent than the
presumptive limits.
    Comment: Because the State of Arkansas adopted EPA's presumptive
emission limits by default, the State of Arkansas did not fulfill its
statutory duty under 169A of the CAA and under Arkansas law to
determine BART. In addition, the State of Arkansas failed to determine,
using the five factors required under section 169A of the CAA whether
the actual costs of the proposed control technology justified the
State's determination of BART for those facilities.
    Response: As explained above, presumptive limits are the starting
point in a BART determination unless the state determines that the
general assumptions underlying EPA's analysis in the RHR are not
applicable to a particular case. Section 169A outlines the analysis
that is required in order to make a BART determination. We are finding
that the State's BART determinations for certain subject-to-BART
sources do not comply with the CAA requirements by adopting the
presumptive emissions limit without conducting a proper BART five
factor analysis. Only after the State conducts a proper evaluation of
the five statutory factors, as required by 40 CFR 51.308(e)(1)(ii)(A)
and section 169A(g) of the CAA, or EPA conducts one in the context of a
FIP, will it be demonstrated whether any of Arkansas's subject to BART
sources must achieve an emission rate more (or less) stringent than the
presumptive limits.
    Comment: The portion of the Arkansas RH SIP that EPA has proposed
to approve is not separable from the overall Arkansas RH SIP. The EPA
should fully disapprove the Arkansas RH SIP because it fails to meet
the requirements for RH SIPs.
    Response: The Arkansas BART determinations for some of the units,
LTS, and RPGs are separable portions of

the RH SIP submittal. The EPA can approve some of the SIP submittal and
disapprove the remainder as long as the portions that are disapproved
do not affect those that are approved. This is the case in our action
partially disapproving Arkansas's RH SIP for its BART determinations
for some of the units, LTS, and RPGs and approving the remainder of the
RH SIP.
2. Comments on Interstate Transport and Visibility
    Comment: Arkansas's April 2008 Interstate Transport SIP was in
accordance with the 2006 Guidance, and virtually identical to those
submitted by Arizona, Iowa, Kansas, Minnesota, Nebraska, Nevada, South
Dakota, Utah, and Wyoming. The EPA approved those states' Interstate
Transport SIPs in a timely fashion because they were consistent with
EPA's 2006 Guidance, yet ignored Arkansas's Interstate Transport SIP
until after EPA's statutory deadline to act; when it evaluated the SIP,
it was not by the criteria established in the 2006 Guidance. In an
August 2011 rulemaking to promulgate a Federal implementation plan
(FIP) for visibility improvement in New Mexico, EPA for the first time
claimed its 2006 Guidance interpreting the Good Neighbor Provision of
the CAA- on which Arkansas had based its 2008 Interstate Transport SIP-
had been published ``in error'' (76 FR 52418). In the same rulemaking,
EPA put forth a new framework for interpreting the requirements
pursuant to the visibility component of the Good Neighbor Provision.
Inconsistent with the 2006 Guidance, EPA now holds that it is possible
to determine whether a state is violating the Good Neighbor Provision,
based on what the state ``should'' have in its Regional Haze SIP. EPA's
new criteria for evaluating Interstate Transport SIP submissions is
based on the air quality modeling performed by regional planning
organizations, and on whether there are differences between emissions
reductions in a state's RH SIP and emissions reductions assumptions
derived from the air modeling performed by regional planning
organizations. Although EPA has not issued a new guidance document to
reflect what states ``should'' have in their SIPs ``at this point in
time,'' EPA has approved the visibility component of several Interstate
Transport SIPs using criteria other than the 2006 Guidance. The EPA has
not explained this regulatory inconsistency between its treatment of
Arkansas's Interstate Transport SIP versus Arizona, Iowa, Kansas,
Minnesota, Nebraska, Nevada, South Dakota, Utah, and Wyoming's
Interstate Transport SIPs. The EPA cannot hold different states to
different requirements pursuant to the visibility component of the
CAA's Good Neighbor Provision.
    Response: Section 110(a)(2)(D)(i)(II) does not explicitly define
what is required in SIPs to prevent the prohibited impact on visibility
in other states nor does it explicitly define how to determine if an
action by a state is interfering with another state's specific
visibility measure. A RH SIP that provides for emissions reductions
consistent with the assumptions used in the modeling of other CENRAP
states is an appropriate way to meet a state's obligations to the other
regional planning states with regards to non-interference with another
state's visibility measures is consistent with the CAA.
    On March 28, 2008, Arkansas submitted revisions to its section
110(a)(2)(D)(i) Interstate Transport SIP. In its March 28, 2008 SIP
submission, Arkansas stated it is meeting the requirements for
protection of visibility in section 110(a)(2)(D)(i)(II) by the adoption
in 2007 of Chapter 15 of APCEC Regulation No. 19, which established
Arkansas's RH program requirements. Arkansas also stated in the March
28, 2008, SIP submission, that it was not possible at that time to
assess whether there is interference with measures in the applicable
SIP for another state until the Arkansas RH SIP is submitted and
approved by EPA. Arkansas also submitted Chapter 15, Regulation 19 in
its September 9, 2008 RH SIP submittal. The Arkansas RH regulation
established a compliance timeframe of October 15, 2013, six years after
the adoption of the state regulation or within five years of the date
of the approval of the RH SIP by EPA, whichever date comes first.
Chapter 15, Regulation 19 outlined the BART determinations for sources
within Arkansas including some sources that do not require a mandatory
BART determination under the RHR. The emission reductions resulting
from the State BART determinations codified in Chapter 15, Regulation
19 are identical to the emissions reductions promised by Arkansas to
the other CENRAP member states and included in the CENRAP 2018
emissions inventory modeling to represent Arkansas's share of emission
reductions for the region. The CENRAP member states are basing their
RPGs and RH programs from this anticipated CENRAP 2018 emissions
inventory modeling. On September 23, 2008, Arkansas submitted its RH
SIP including Chapter 15, Regulation 19 to EPA for approval.
    The EPA could have approved Arkansas's 110(a)(2)(D)(i) Interstate
Transport SIP in 2008 when Arkansas originally submitted the SIP.
Chapter 15, Regulation 19 originally established a compliance timeframe
of October 15, 2013, six years after the adoption of the state
regulation or within five years of the date of the approval of the RH
SIP by EPA, whichever date comes first. This provided the necessary
emission limits and enforceable mechanisms to ensure Arkansas's
apportionment of emissions reductions used in the CENRAP modeling.
However, on March 17, 2010, Arkansas granted a variance from the
October 15, 2013 deadline imposed by Regulation 19.1504(B) for sources
subject to BART listed at Regulation 19.1504(A). Instead, sources
subject-to-BART are required to comply with BART only within five years
after EPA approves Arkansas's RH SIP. This variance was never submitted
to EPA as a SIP revision. As explained in an earlier response to
comments, we are disapproving the portion of the BART compliance
provision found in the 2008 submitted Chapter 15 of Regulation No. 19
that requires compliance with BART requirements no later than six years
after the effective date of the State's regulation since Arkansas no
longer has the legal authority to enforce this provision. We are
partially approving and partially disapproving the portion of the BART
compliance provision that requires each Arkansas subject-to-BART source
to install and operate BART as expeditiously as practicable, but in no
event later than five years after EPA approval of the Arkansas RH SIP
consistent with the requirements under 40 CFR Sec.  51.308(e)(iv).
Because of our disapproval of the six year compliance timeframe in
Arkansas's 2008 submitted Chapter 15 of Regulation 19, as well as
disapproval of certain BART determinations, all of Arkansas's promised
enforceable emission reductions factored into CENRAP's 2018 emissions
inventory modeling and relied upon by fellow CENRAP member states in
developing their RPGs and RH SIPs will not be met. Thus, the
requirements for section 110(a)(2)(D)(i)(II) will not be met.
    If we had acted upon the Arkansas RH SIP earlier than 2010, it
would not change EPA's determination that Arkansas's emissions are
interfering with other states' visibility programs because Arkansas's
subsequent adoption of the BART variance removing the guaranteed six
year compliance requirement would have rendered the hypothetically-
approved section

110(a)(2)(D)(i)(II) SIP provisions unenforceable. To address this, we
would be required to issue a SIP Call now and Arkansas would be
required to revise its SIP to correct the inadequacies by a given due
date or face sanctions for failure to timely submit a complete SIP
revision. The BART determinations we would have disapproved in our
earlier hypothetical action would no longer be required to occur by
October 2013 under the State's law regardless of EPA's disapproval
action, and therefore Arkansas emissions would continue to interfere
with other states' visibility programs. The emissions reductions
resulting from those BART determinations would not be required to
happen at all since the variance conditions BART compliance upon EPA
approval of the Arkansas RH SIP.
    The EPA's partial disapproval of Arkansas's SIP addressing section
110(a)(2)(D)(i)(II) is consistent with EPA's actions on the SIPs of
Arizona, Iowa, Kansas, Minnesota, Nebraska, Nevada, South Dakota, Utah,
and Wyoming. Section 110(a)(2)(D)(i)(II) does not explicitly define
what is required in SIPs to prevent the prohibited impact on visibility
in other states. However, because the RH program requires measures that
must be included in SIPs specifically to protect visibility, EPA's 2006
Guidance recommended that RH SIP submissions meeting the requirements
of CAA section 110(a)(2)(D)(i)(II) with respect to visibility would be
sufficient. We approved the SIPs of Arizona, Iowa, Kansas, Minnesota,
Nebraska, Nevada, South Dakota, Utah and Wyoming in accordance with the
2006 Guidance in 2007 and 2008. However, our 2006 Guidance reflected
our recommendations for how states could potentially meet the section
110(a)(2)(D)(i)(II) requirement at that point in time. As of August
2006, we stated our belief that it was ``currently'' premature for
states to make a more substantive SIP submission for this element,
because of the anticipated imminent RH SIP submissions. We explicitly
stated that ``at this point in time'' in August of 2006, it was not
possible to assess whether emissions from sources in the state would
interfere with measures in the SIPs of other states. As subsequent
events have demonstrated, we were mistaken as to the assumption that
all states would submit RH SIPs in December of 2007 and mistaken as to
the assumption that all such submissions would meet applicable RH
program requirements and therefore be approved shortly thereafter.
Thus, the premise of the 2006 Guidance that it would be appropriate to
await submission and approval of such RH SIPs before evaluating SIPs
for compliance with section 110(a)(2)(D)(i)(II) was in error. Our 2006
Guidance was clearly intended to make recommendations that were
relevant at that point in time, and subsequent events have rendered it
inappropriate in this specific action.
    Because of the need to act immediately on section 110(a)(2)(D)(i),
when some states did not make the RH SIP submission in whole or in
part, or did not make an approvable RH SIP submission, we have
evaluated whether states could comply with section 110(a)(2)(D)(i)(II)
by other means. Thus, we have elsewhere determined that states may also
be able to satisfy the requirements of CAA section 110(a)(2)(D)(i)(II)
with something less than an approved RH SIP, see e.g. Colorado (76 FR
22036 (April 20, 2011)), Idaho (76 FR 36329 (June 22, 2011)), and New
Mexico (76 FR 52388 (August, 22, 2011)). In other words, an approved RH
SIP is not the only possible means to satisfy the requirements of CAA
section 110(a)(2)(D)(i)(II) with respect to visibility; however such a
SIP could be sufficient.
    As stated earlier, Arkansas submitted revisions to its section
110(a)(2)(D)(i) Interstate Transport SIP that addressed the
requirements for protection of Visibility in section
110(a)(2)(D)(i)(II) by enacting the Arkansas Pollution Control and
Ecology Commission regulation Chapter 15, Regulation 19 that
established Arkansas's RH program requirements and stating that it was
not possible at this time to assess whether there is interference with
measures in the applicable SIP for another state until Arkansas's RH
SIP is submitted and approved by EPA. Since EPA was no longer waiting
for the approval of a RH SIP to determine interference with another
state's visibility program, we looked at BART determinations cited in
Chapter 15, Regulation 19 and submitted in their Interstate Transport
SIP. The emission reductions resulting from the BART determinations in
Chapter 15, Regulation 19 are identical to the emissions reductions
promised by Arkansas to the other CENRAP member states and included in
the 2018 CENRAP modeling to represent Arkansas's share of emission
reductions for the region. The CENRAP member states are basing their
RPGs and RH programs on this CENRAP modeling.
    As in New Mexico, we have determined that the analysis conducted by
a RPO such as CENRAP provides an appropriate means to ensure that
emissions from sources within the state are not interfering with the
visibility programs of other states, as contemplated in section
110(a)(2)(D)(i)(II). In developing their visibility projections using
photochemical grid modeling, CENRAP states assumed a certain level of
emissions from sources within Arkansas. Although we have not yet
received all RH SIPs, we understand that the CENRAP states used the
visibility projection modeling to establish their own respective RPGs.
Thus, we believe that an implementation plan that provides for
emissions reductions consistent with the assumptions used in the CENRAP
modeling will ensure that emissions from Arkansas sources do not
interfere with the measures designed to protect visibility in other
states.
    For Arkansas, the EPA is disapproving certain BART determinations.
This means that some sources within Arkansas do not have an enforceable
emission reduction requirement to meet the emissions reductions
promised by Arkansas to CENRAP member states and modeled by CENRAP in
their anticipated 2018 emissions inventory because, as explained
earlier, Arkansas's enactment of a variance that conditions the BART
determinations in Chapter 15, Regulation 19 upon EPA's approval of
Arkansas RH SIP. Since Arkansas no longer has an enforceable
requirement for certain Arkansas BART determinations that EPA is
disapproving, their promised emissions reductions included in CENRAP's
modeling and the resulting 2018 emissions inventory will not be
realized even though other CENRAP member states are relying upon them
in the promulgation of their RPGs and RH SIPs. Thus, our disapproval of
some of Arkansas's BART determination means that we have to disapprove
a portion of the section 110(a)(2)(D)(i)(II) SIP submittal.
    Comment: The EPA cannot at this time make a determination of
whether Arkansas RH SIP interferes with measures in another state's RH
SIP for purposes of protecting visibility since EPA has not yet
approved any other RH SIP for a state with a class area that may be
affected by Arkansas sources.
    Response: We disagree that we cannot make a determination of
whether the Arkansas RH SIP interferes with measures in another state's
RH SIP for purposes of protecting visibility without approving other
states' RH SIPs that have a class I area that may be affected by
Arkansas sources. The comment is inconsistent with the objectives of
the statute to protect visibility programs in

other states if a state never submits an approvable RH SIP. Second,
this approach is inconsistent with the time requirements of section
110(a)(1) which specifies that SIP submissions to address section
110(a)(2)(D)(i), including the visibility prong of that section, must
be made within three years after the promulgation of a new or revised
NAAQS. While there have been delays with both RH SIP submissions by
states and our actions on those RH SIP submissions, those delays do not
support a reading of the statute that overrides the timing requirements
of the statute. At this point in time, states are required to have
submitted RH plans to EPA that establish RPGs for class I areas. This
requirement applies whether or not states have, in fact, submitted such
plans. We believe that there are means available now to evaluate
whether a state's section 110(a)(2)(D)(i)(II) SIP submission meets the
substantive requirement that it contain provisions to prohibit
interference with the visibility programs of other states, and
therefore that further delay, until all RH SIPs are submitted and fully
approved, is unwarranted and inconsistent with the key objective to
protect visibility.
    Comment: There is nothing in the record to demonstrate that
Arkansas RH SIP interferes with any measure included in any other
state's SIP for the purpose of protecting visibility. Missouri is the