BART,'' \184\ and proposes replacing reliance on CAIR with reliance on
the trading programs of CSAPR as an alternative to SO2 and
NOX BART for Texas EGUs.\185\ Not only is EPA requiring
Arkansas EGUs covered by CSAPR to control emissions under BART in the
FIP proposal, but EPA has not even considered CSAPR as an option for
making reasonable progress. Even if EPA ultimately rejected CSAPR as a
means to meet the reasonable progress requirements under the Regional
Haze Rule, EPA is required to cogently explain why it has exercised its
discretion in a given manner. EPA's failure to consider CSAPR is
arbitrary and capricious in light of its treatment of other states. EPA
should withdraw the FIP proposal and remove the source-specific
NOX BART requirements for Arkansas EGUs that are covered by
CSAPR in any subsequently proposed plan.
---------------------------------------------------------------------------

    \180\ 40 CFR 51.308(e); 77 FR 33642.
    \181\ 76 FR 48208.
    \182\ 77 FR 33642 (June 7, 2012).
    \183\ Approval and Promulgation of Implementation Plans; Texas
and Oklahoma; Regional Haze State Implementation Plans; Interstate
Transport State Implementation Plan To Address Pollution Affecting
Visibility and Regional Haze; Federal Implementation Plan for
Regional Haze and Interstate Transport of Pollution Affecting
Visibility, 79 FR 74818.
    \184\ 79 FR 74818, 74851.
    \185\ 79 FR 74818, 74853.
---------------------------------------------------------------------------

    Response: Arkansas EGUs are subject to CSAPR for ozone season
NOX, and we acknowledge that a state in the CSAPR region
whose EGUs are subject to the requirements of the CSAPR trading program
for ozone season NOX may rely on CSAPR to satisfy the
NOX BART requirement for its EGUs. However, when standing in
the shoes of a state and promulgating a FIP, EPA has the same
discretion as the state to choose to either conduct source-specific
BART determinations or to rely on EPA's 2012 finding that CSAPR is
better than BART. Our decision to make source-specific NOX
BART determinations for Arkansas is reasonable for multiple reasons: It
is the approach Congress chose in the statute itself; \186\ it is
consistent with Arkansas' earlier decision to conduct

source-specific NOX BART determinations in lieu of relying
on CAIR to meet the BART requirements; and at the time of our proposed
action, it properly accounted for uncertainty in the CSAPR better-than-
BART regulation created by ongoing litigation regarding the CSAPR
program. Further explanation of these reasons is given below.
---------------------------------------------------------------------------

    \186\ See CAA section 169A(g)(2) in which Congress defined the
five factor analysis for determining BART but did not expressly
provide for an alternative to source by source BART.
---------------------------------------------------------------------------

    The Regional Haze regulations provide generally that ``[a] State
may opt'' to rely on an emissions trading program rather than to
require source-specific BART controls.\187\ More specifically, in 2005
EPA revised the Regional Haze regulations to provide that a state
subject to CAIR ``need not require affected BART-eligible EGUs to
install, operate, and maintain BART.'' \188\ Following the D.C.
Circuit's vacatur and remand of CAIR,\189\ EPA issued CSAPR as a
replacement rule. EPA revised its regulations in 2012 to allow states
to rely on CSAPR in lieu of source-specific BART.\190\
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    \187\ 40 CFR 51.308(e)(2).
    \188\ 70 FR 39104, 39156 (July 6, 2005).
    \189\ North Carolina v. EPA, 531 F.3d 896 (D.C. Cir. 2008).
    \190\ 77 FR 33642.
---------------------------------------------------------------------------

    In its 2008 regional haze SIP submittal, Arkansas decided to not
rely on CAIR to satisfy the NOX BART requirement for its
EGUs.\191\ In our Regional Haze FIP proposal for Arkansas, we did not
rely on CSAPR (the follow up rule to CAIR) to satisfy the
NOX BART requirement for EGUs because we chose to follow the
same source-specific approach to NOX BART that Arkansas
selected in its Regional Haze SIP submittal. In addition, litigation
surrounding CSAPR was ongoing at the time that we issued our proposed
Arkansas Regional Haze FIP. CSAPR was issued in 2011, but on December
30, 2011, the D.C. Circuit stayed the rule prior to implementation. The
D.C. Circuit subsequently vacated CSAPR, an action later reversed by
the Supreme Court in 2014. The case was then remanded to the D.C.
Circuit. Then, after our April 2015 Regional Haze FIP proposal, the
D.C. Circuit issued a July 2015 decision in EME Homer City Generation
v. EPA \192\ upholding CSAPR but remanding without vacatur a number of
the Rule's state NOX and SO2 emissions budgets.
Arkansas' ozone season NOX budget is not itself affected by
the remand. However, the Court's remand of the affected states'
emissions budgets has implications for CSAPR better-than BART, since
the demonstration underlying that rulemaking relied on the emission
budgets of all states subject to CSAPR, including those that the D.C.
Circuit remanded, to establish that CSAPR provides for greater
reasonable progress than BART. As of the time EPA is taking this action
to finalize Arkansas' Regional Haze FIP, we are in the process of
acting on the Court's remand consistent with the planned response we
outlined in a June 2016 memorandum.\193\
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    \191\ As Arkansas did not rely on CAIR to satisfy requirements
in the regional haze SIP, Arkansas is not included in the EPA's
limited disapproval of regional haze SIPs that relied on CAIR to
satisfy certain regional haze requirements. See 77 FR 33642, at
33654. In that same rulemaking, the EPA promulgated FIPs to replace
reliance on CAIR with reliance on CSAPR in many of those regional
haze SIPs; however, Arkansas was likewise not included in that FIP
action.
    \192\ 795 F.3d 118 (DC Cir 2015).
    \193\ https://www3.epa.gov/airtransport/CSAPR/pdfs/CSAPR_SO2_Remand_Memo.pdf.
---------------------------------------------------------------------------

    Our final action on the Arkansas Regional Haze FIP is consistent
with our final action on the Texas Regional Haze FIP. Although we
proposed to rely on CSAPR to address the NOX BART
requirements for EGUs in Texas, we did not finalize that portion of our
proposed Texas FIP given the uncertainty arising from the remand of the
CSAPR budgets for Texas and other states.\194\ In light of the above,
the comments that we are treating Arkansas differently than other
states where EPA relied on CSAPR to meet the BART requirements are no
longer applicable.
---------------------------------------------------------------------------

    \194\ 81 FR 296, 302.
---------------------------------------------------------------------------

    As we have noted throughout this document, we are willing to work
with ADEQ to develop a SIP revision that could replace our FIP. Such a
SIP revision will need to meet the CAA and EPA's Regional Haze
regulations. In its SIP revision, ADEQ may elect to rely on CSAPR to
satisfy the NOX BART requirements for Arkansas' EGUs instead
of doing source-specific NOX BART determinations. Such an
approach could be appropriate if, as we expect, the uncertainty created
by the D.C. Circuit's remand of the affected states' emission budgets
will shortly be resolved.
    With regard to the comment that we should not require EGUs that are
covered under CSAPR to also install additional emissions controls under
reasonable progress analysis, we disagree. In our 2012 finding that
CSAPR is better than BART, we stated that states with EGUs covered
under CSAPR may rely on CSAPR to satisfy the BART requirement. However,
controls under reasonable progress are a separate requirement from
BART, and we disagree that states can rely on CSAPR to satisfy the
reasonable progress requirements under Sec.  51.308(d)(1). As explained
in the 2005 rulemaking addressing reliance on CAIR, our determination
that a trading program provides for greater reasonable progress than
BART is not a determination that the trading program satisfies all
reasonable progress requirements.\195\
---------------------------------------------------------------------------

    \195\ 70 FR 39104, 39143; see also 77 FR 33642, 33653.
---------------------------------------------------------------------------

I. Cost

    We received numerous comments related to the cost analyses we
proposed. These comments were received from both industry and
environmental groups, and covered all aspects of our cost analyses.
    We received comments from industry concerning our proposed scrubber
cost analyses that objected to our use of the IPM cost algorithms that
Sargent and Lundy (S&L) developed under contract to us. As we discuss
in our TSD, we programmed the Spray Dryer Absorber (SDA--a type of dry
scrubber), and wet FGD cost algorithms, as employed in version 5.13 of
our IPM model, into spreadsheets in our analysis of various aspects of
the Entergy White Bluff and Independence scrubber cost analyses.\196\
Industry stated these cost algorithms were not accurate enough to
warrant their use in individual unit-by-unit cost analyses, do not
consider site-specific costs, and that our use of them violated our
Control Cost Manual. Environmental groups supported our use of the IPM
cost algorithms, and employed them as well in costing scrubber and SCR
control costs to support their own comments. In response, we conclude
that the IPM cost algorithms provide reliable, study-level, unit-
specific costs for regulatory cost analysis such as required for BART
and reasonable progress.\197\
---------------------------------------------------------------------------

    \196\ See discussion beginning on pages 9 and 20 of our TSD
Appendix A.
    \197\ We believe that the IPM cost algorithms provide study
level accuracy. See pdf page 17 of our Control Cost Manual:
``[a]``study'' level estimate [has] a nominal accuracy of  30% percent. According to Perry's Chemical Engineer's
Handbook, a study estimate is `. . . used to estimate the economic
feasibility of a project before expending significant funds for
piloting, marketing, land surveys, and acquisition . . . [However]
it can be prepared at relatively low cost with minimum data.'''
---------------------------------------------------------------------------

    We received comments relating to our critique of Entergy's White
Bluff dry scrubber cost analysis. These primarily involved claims that
we (1) improperly escalated Entergy's own cost analyses, (2) improperly
excluded costs, (3) under-estimated O&M costs, (4) improperly
calculated the SO2 baseline, (5) improperly excluded
``Allowance for Funds Used During Construction''

(AFUDC) and owner's costs, and (6) improperly extended our White Bluff
scrubber cost analyses to the Independence facility. In response to
these comments, we have made some minor adjustments to our White Bluff
scrubber cost analyses, but those changes do not change our proposal
that scrubbers remain cost-effective for the White Bluff facility, and
by extension to the Independence facility.
    We received comments from environmental groups concerning the White
Bluff, Independence, and Flint Creek facilities that (1) generally
supported our proposed control suite, (2) criticized us in some cases
for not proposing stricter control levels, (3) criticized our control
cost analyses for being too conservative in some cases and/or
containing errors, and (4) criticized us in some cases for not
requiring earlier compliance. These groups also generally opposed our
BART determination for Lake Catherine Unit 4.
    Below we present a summary of our responses to the more significant
comments we received that relate to our proposed cost analyses.
    Comment: S&L states we significantly under-estimated the direct
Operating and Maintenance (``O&M'') costs projected for the scrubbers
by using its Integrated Planning Model (``IPM'') Spray Dryer Absorber
(``SDA'') cost model to scale the O&M costs rather than estimating
these costs using current utility pricing information. S&L stated that
our use of the IPM cost algorithms was not in keeping with our Control
Cost Manual and because of the limited number of site-specific inputs,
the IPM cost algorithms provide order-of-magnitude control system cost
estimates, but do not provide case-by-case project-specific cost
estimates meeting the requirements of the BART Guidelines, nor do the
IPM equations incorporate the cost estimating methodology described in
the Control Cost Manual.
    Response: We disagree with S&L. As we discuss in our TSD,\198\ we
needed to adjust Entergy's O&M costs for its White Bluff SDA model
because of a mismatch between Entergy's SO2 emission
baseline and the SO2 inlet it assumed in the design of its
scrubber (discussed in our response to another comment). Entergy costed
a scrubber capable of treating a SO2 level of 2.0 lbs/MMBtu,
when it historically burned coal that averaged less than 0.6 lbs/MMBtu
from 2009-2013. This had the effect of worsening the cost effectiveness
(increasing the $/ton) over what it would have been had Entergy
designed it to treat the coal it historically burned. We could not
directly adjust Entergy's O&M costs because Entergy's O&M cost
estimates were based on an S&L economic model from May 2008, which it
did not supply.\199\ These issues, which we discuss in our responses to
comments elsewhere, dictated a revision to Entergy's cost estimate. We
were left with no choice but to seek an alternative means of estimating
Entergy's O&M costs, in order to address the mismatch described above.
We utilized the IPM SDA cost model that Entergy's own contractor
designed for us.
---------------------------------------------------------------------------

    \198\ See Section 3.1 in Appendix A of our TSD.
    \199\ See Section 2.7 in Appendix A of our TSD.
---------------------------------------------------------------------------

    We disagree that our cost estimates were not in keeping with the
Control Cost Manual. As we stated in our TSD Appendix A, we relied on
the methods and principles contained within the Control Cost Manual,
namely the use of the overnight costing method. In fact, the Control
Cost Manual does not include any method for estimating the costs
specific to any of the SO2 control equipment evaluated in
this action. We note our technique of relying on a publicly available
control cost tool is similar to the strategy the states themselves
employed in the development of their SIPs. For instance, as explained
in the Texas SIP, the ADEQ used the control strategy analysis completed
by the CENRAP, which depended on the EPA AirControlNET tool \200\ to
develop cost per ton estimates. We have used IPM cost models to
estimate BART costs in other similar rulemakings including our Arizona
Regional Haze FIPs,\201\ the Wyoming Regional Haze FIP,\202\ and to
supplement our analysis in the Oklahoma FIP.\203\ S&L used real world
cost data to construct its cost algorithms and confirm their validity.
These cost models have been updated and maintained since their
introduction in 2010 and we have been continuously using them since
that time. These control costs are based on databases of actual control
project costs and account for project specifics such as unit size, coal
type, gross heat rate, and retrofit factor. The costs further require
unit specific inputs such as reagent cost, waste disposal cost,
auxiliary power cost, labor cost, gross load, and emission information.
We believe that the IPM cost models provide reliable study-level, unit-
specific costs for regulatory cost analysis such as required for BART
and reasonable progress. We are confident enough in the basic
methodology behind the S&L cost algorithms that in our recent update of
the SCR chapter of the Control Cost Manual \204\ we presented an
example costing methodology that is based on the IPM S&L SCR
algorithms, which were developed using a similar methodology to the wet
FGD, SDA, and DSI cost algorithms discussed herein. Lastly, we note
that Entergy used a number of general approximations when estimating
the wet scrubbing costs for White Bluff, as we describe in our
TSD.\205\ We conclude that our approach is in keeping with the Control
Cost Manual and is sufficiently accurate for its intended purpose.
---------------------------------------------------------------------------

    \200\ Our AirControlNET tool is out of date and no longer
supported.
    \201\ 77 FR 42852 (July 20, 2012).
    \202\ Memorandum from Jim Staudt to Doug Grano, EPA, Re: Review
of Estimated Compliance Costs for Wyoming Electricity Generating
Units (EGUs)--Revision of Previous Memo, February 7, 2013, EPA-R08-
OAR-2012-0026-0086_Feb 7, 2013.
    \203\ 76 FR 81728 (December 28, 2011).
    \204\ https://www3.epa.gov/ttn/ecas/cost_manual.html.
    \205\ See discussion beginning on page 19 of Appendix A to our
TSD.
---------------------------------------------------------------------------

    Comment: Entergy disagreed with our approach for escalating a 2013
scrubber cost analysis for its White Bluff facility to 2015, rather
than obtaining a revised cost estimate. Entergy claims this caused us
to underestimate our scrubber cost estimate by $36,322,881 (total for
both units). Entergy also disagreed with our application of the
Chemical Engineering Plant Cost Index (CEPCI) indices in several
instances from 2008 that de-escalated costs, resulting in lower costs
in 2013 as compared to 2008. Entergy states that our cost calculations
ignored the updated 2012 direct annual costs it provided, and instead
included the 2008 costs. In a subsequent comment, Entergy calculates an
escalation rate of 4.7%, based on a comparison of a revised 2013 quote
to a 2009 quote, and applies that escalation rate along with other
corrections to various cost line items in concluding that we
underestimated the cost of installing scrubbers at the White Bluff
facility by $42,607,547 per unit.
    Response: For our proposal, we used Entergy's revised BART analysis
for the White Bluff facility, as submitted by it on October 14, 2013,
because at the time it was the latest information available to us.\206\
In our proposal, our control cost analysis used the same basic
information that Entergy previously presented to us in 2013. As we
describe in Appendix A of our TSD, Entergy stated that it received two
different SDA cost estimates for White Bluff: An early 2009 Sargent and
Lundy (S&L) estimate with a total contractor cost of $291,930,000, and
a December 2009

estimate from Alstom of $247,856,184. Entergy stated that unlike the
S&L quote, the Alstom estimate was not itemized and only included a
total price. Entergy used the 2009 Alstom price quote as the basis for
its BART cost analysis for White Bluff by increasing it by 10%, and
scaling the S&L itemized cost to match the 110% adjusted Alstom total
price. As we describe in our RTC, we critiqued certain aspects of
Entergy's use of this information. For example, Entergy mistakenly
included certain NOX controls in its 2013 cost analysis. It
also failed to document certain BOP costs that we had no choice but to
exclude. However, between the 2009 S&L and the 2009 Alstom quotes, and
with these corrections, we were able to construct a reasonable control
cost estimate. In so doing, we used the same 2009 Alstom total, and the
Alstom payment schedule for its quote, as the actual Alstom quote was
not supplied and no better information was presented by Entergy.
Because Entergy's 2013 cost estimate used 2009 Alstom pricing, we had
no choice but to escalate it to 2013--more recent information was not
available.
---------------------------------------------------------------------------

    \206\ See section 2.1 of Appendix A to our TSD.
---------------------------------------------------------------------------

    Entergy did not provide its updated 2015 cost estimate, which it
references in its comment, until after our proposal. Entergy's 2015
report uses updated 2013 pricing from Alstom as its basis. As we
discuss in our RTC, we reviewed this 2015 cost analysis and found that
it presents problems that prevent us from using it, primarily because
it is undocumented.
    In this comment, Entergy attempts to use its newly submitted 2015
cost analysis to discredit the escalation technique we employed to
adjust its previous 2013 cost analysis. It does so without even
presenting the 2013 Alstom quote on which it states the 2015 cost
estimate relies. Thus, we have no basis to conclude that the costs
Entergy presents in its first table above even cover the same scope of
work. This is an important consideration and a different scope can
cause a significant difference in cost. Entergy itself noted this when
it used a revised BOP estimate to adjust its 2009 Alstom quote because
the scope had changed. Even different cost estimates received in the
same year can result in significantly different totals. For instance,
as we also note in our TSD, Entergy stated that it received two
different SDA cost estimates for White Bluff: An early 2009 S&L
estimate with a total contractor cost of $291,930,000, and a December
2009 estimate from Alstom of $247,856,184.\207\ We note that the
difference between these two quotes is $44,073,816, which is more than
Entergy calculates in its first table above is the difference between
our escalated 2013 quote ($261,581,119) and its revised 2015 cost
estimate, based on the its 2013 Alstom quote ($297,904,000).
---------------------------------------------------------------------------

    \207\ See section 2.1 of Appendix A to our TSD.
---------------------------------------------------------------------------

    Escalation from one year's cost basis to another \208\ is not only
allowed by the Control Cost Manual, it is a required procedure in order
to allow an apples-to-apples comparison between control cost analyses.
Our use of the Chemical Engineering Plant Cost Index (CEPCI) is a
standard method of escalating costs,\209\ and one that power companies
have also used on numerous occasions. Entergy itself has used the CEPCI
in an attempt to escalate its costs. Unfortunately, as we explain in
our TSD, Entergy did so incorrectly and we corrected that error.\210\
We certainly prefer revised vendor quotations to escalating older cost
estimates. However, when revised vendor quotes are not available as in
this case, we have no choice but to escalate older cost estimates in
order to bring the cost basis to the present.
---------------------------------------------------------------------------

    \208\ Note that escalation during the construction period is
disallowed, however, because that is not a part of the overnight
method.
    \209\ Vatavuk, William, M., ``Updating the CE Plant Cost
Index,'' Chemical Engineering, January 2002.
    \210\ See section 2.6 of Appendix A to our TSD.
---------------------------------------------------------------------------

    Entergy also apparently objects to any escalation technique that
results in a reduction in a future year's cost basis, holding it up as
evidence of our error.\211\ This is a fundamental misunderstanding of
escalation. For instance, although the Composite CE index usually
increases from year to year, it does occasionally decrease, due to
various broad economic factors, such as it did from 2008 to 2009, and
again from 2011 to 2013. This is mainly due to broad economic factors
that influence the cost of raw materials, supply and demand, vendor
profit, etc. Thus, Entergy's objection over the ``de-escalation'' of
cost from 2008 to 2013 is entirely misplaced. In other words,
escalation is escalation: Most of the time it is positive but sometimes
it is negative. We therefore do not agree with Entergy's objections to
our escalation technique. We take up the issue of Entergy's 2015 cost
estimate in our response to another comment.
---------------------------------------------------------------------------

    \211\ Entergy's reference to de-escalated costs.
---------------------------------------------------------------------------

    Entergy states that our cost calculations ignored the updated 2012
direct annual costs provided by Entergy, and instead included the 2008
costs. As noted in the first sentence of our response to this comment,
we were constrained to use Entergy's revised BART analysis for the
White Bluff facility, as submitted by Entergy on October 14, 2013
(hereafter referred to as the ``2013 SDA Cost Analysis''). These costs
employed a 2008 vintage total direct annual cost, as we indicate in
Appendix A of our TSD.\212\ Regarding its direct annual costs, Entergy
further states, ``The cost estimates were scaled to reflect 2012
dollars.'' \213\ We therefore agree that Entergy did provide what it
stated was 2012 vintage direct annual costs. We did not use those costs
because Entergy incorrectly escalated them from 2008, as we discuss
above. For instance, Entergy presented its 2008 direct annual cost as
$7,901,369. It then ``scaled'' them to 2012 using a 2008 CEPCI index of
530.7 and a 2012 CEPCI index of 593.6, resulting in a 2012 value of
$8,837,861. As we discuss in Appendix A of our TSD, Entergy appears to
have incorrectly used the January monthly CEPCI value for each year
instead of the annual CEPCI value. Entergy should have used a 2008
CEPCI index of 575.4 and a 2012 CEPCI index of 584.6, resulting in a
2012 escalated direct annual cost of $8,027,703 ($7,901,369 x 584.6/
575.4). As we also discuss in our TSD, because we were conducting our
analysis later, we escalated Entergy's 2008 direct annual cost to 2013,
resulting in a value of $7,790,140 ($7,901,369 x 567.3/575.4). These
facts appear to have been ignored by Entergy in its comment. We
therefore have no choice but to disagree with Entergy's comment
concerning our not using its 2012 direct annual cost.
---------------------------------------------------------------------------

    \212\ See section 2.7 of Appendix A to our TSD.
    \213\ Revised Bart Five Factor Analysis, White Bluff Steam
Electric Station, Redfield, Arkansas (AFIN 35-00110). Appendix A,
SDA cost analysis, June 2013, Appendix A.
---------------------------------------------------------------------------

    Comment: Entergy and Nucor stated that we improperly excluded AFUDC
and owner's costs from our White Bluff control cost analysis. Entergy
also objects to our disallowance of certain BOP costs.
    Response: As we have noted in a number of our FIPs, AFUDC and
Owner's Costs are not valid costs under our Control Cost Manual
methodology. We invite the commenters to examine our response to
similar comments we received in response to those actions.\214\
---------------------------------------------------------------------------

    \214\ See, e.g., ``Response to Technical Comments for Sections E
through H of the Federal Register Notice for the Oklahoma Regional
Haze and Visibility Transport Federal Implementation Plan,'' Docket
No. EPA-R06-OAR-2010-0190, 12/13/2011.
---------------------------------------------------------------------------

    In Appendix A to our TSD, we noted that Entergy used BOP costs from
a 2008 S&L quote to supplement its adjusted 2009 Alstom quote in its
2013 SDA cost analysis for the White Bluff BART determination. However,
due to a lack of documentation, it appeared that a number of items were
either not appropriate for a SO2 scrubber, or were

already covered as part of the Alstom quote. As discussed in detail in
our RTC document, we removed those items from our proposed SDA cost
analysis and invited Entergy to supply additional documentation to
verify these costs. S&L now points to an S&L Report #012831, which
contains a 2015 White Bluff SDA cost estimate, for that documentation.
First, Entergy states that its 2015 SDA cost estimate is based on a
2013 Alstom quote. As with the 2009 Alstom quote it used to support its
2013 SDA cost analysis, Entergy did not provide this Alstom quote.
Consequently, we have no way of verifying Entergy's 2015 cost
calculations or to conclude that their scopes are the same. Therefore,
we have no choice but to conclude that Entergy has not demonstrated
that our removal of costs associated with the reagent preparation
enclosure and reagent handling system and ductwork was incorrect.
Similarly, we continue to find that Entergy has not documented certain
BOP indirect costs, miscellaneous contract labor, Entergy internal
costs, and capital suspense.
    We do agree that Entergy has provided documentation for other
costs, including demonstrating that recalibration of the CEMS and
painting of the chimney are justified, and we have adjusted our White
Bluff scrubber cost analysis accordingly. Other costs that were
calculated as percentages of the equipment, material, and labor costs
were similarly adjusted. We have revised our cost analysis to include
these adjustments, and have determined that dry scrubbers are estimated
to cost $2,565/SO2 ton removed at Unit 1 and $2,421/
SO2 ton removed at Unit 2.\215\ Revising these costs did not
change our final determination that dry scrubbers are cost-effective
for the White Bluff facility.
---------------------------------------------------------------------------

    \215\ See the file, ``White Bluff_R6 cost revisions2-
revised.xlsx'' in our docket.
---------------------------------------------------------------------------

    Comment: S&L objects to our approach of calculating an
SO2 baseline for the White Bluff and Independence
facilities, in which we eliminated the high and low annual emission
values from 2009 to 2013, and averaged the remaining values. S&L
presents four alternative approaches in which a straight five year
average from 2009 to 2013, and different three year averages from 2009
to 2013 are examined for White Bluff Units 1 and 2 and Independence
Units 1 and 2, and concludes that in all cases, at least one of the
alternative approaches would have resulted in lower baseline
SO2 emissions for one of the units.
    Response: We disagree with S&L that we erred in the procedure we
used in estimating baseline emissions for our BART and reasonable
progress scrubber upgrade cost analyses. We calculated our baseline
SO2 emissions by first acquiring the 2009 to 2013 emissions
as reported to us by the facilities in question.\216\ We reasonably
eliminated the high and low values from the 2009-2013 emissions to
better address potential yearly variations in in coal sulfur data,
capacity usage, etc., and to make the baseline more representative of
plant operations and thereby provide the basis for a more accurate
estimate of the cost effectiveness of controls. The fact that S&L can
construct alternative approaches to our baseline calculation that
result in lower emissions estimates does not invalidate our BART and
reasonable progress approaches. As can be seen from an examination of
S&L's own data, regardless of whether a 3-year average or a 5-year
average of a particular set of years is employed, the resulting
emissions baselines are all similar. In fact, for three out of four
units, one of S&L's alternative approaches would have produced higher
SO2 emissions baselines, which if used would have resulted
in the cost analyses we performed being even more cost-effective. We
believe that the procedure we used is in compliance with the BART
Guidelines, which states:
---------------------------------------------------------------------------

    \216\ http://ampd.epa.gov/ampd/

    How do I calculate baseline emissions?
    1. The baseline emissions rate should represent a realistic
depiction of anticipated annual emissions for the source. In
general, for the existing sources subject to BART, you will estimate
the anticipated annual emissions based upon actual emissions from a
baseline period.
    2. When you project that future operating parameters (e.g.,
limited hours of operation or capacity utilization, type of fuel,
raw materials or product mix or type) will differ from past
practice, and if this projection has a deciding effect in the BART
determination, then you must make these parameters or assumptions
into enforceable limitations. In the absence of enforceable
limitations, you calculate baseline emissions based upon
continuation of past practice.\217\
---------------------------------------------------------------------------

    \217\ 70 FR 39104, 39167.

    Regarding the baseline used in our Independence reasonable progress
analysis, our 2007 Reasonable Progress Guidance notes the similarity
between some of the reasonable progress factors and the BART factors
contained in Sec.  51.308(e)(1)((ii)(A), and suggests that the BART
Guidelines be consulted regarding cost, energy and nonair quality
environmental impacts, and remaining useful life.\218\ We are therefore
relying on our BART Guidelines for assistance in interpreting those
reasonable progress factors, as applicable. One of these areas is in
the calculation of the baseline emissions in determining cost
effectiveness.
---------------------------------------------------------------------------

    \218\ ``Guidance for Setting Reasonable Progress Goals Under the
Regional Haze Program,'' at 5-1.
---------------------------------------------------------------------------

    The difference between our baseline calculations and any of the
alternative procedures S&L outlines is small and would not change our
conclusions for the White Bluff BART determinations and the
Independence reasonable progress determinations.
    Comment: S&L objects to our extending our White Bluff scrubber cost
analysis to the Independence facility on the basis of the similarity of
the two facilities. S&L states that our use of EIA information,
satellite photographs and other points of comparison are inadequate to
account for potential site-specific differences between the two
facilities, such as operating data, O&M practices, underground utility
interferences, geotechnical differences, and seismic differences.
    Response: While there are likely differences between the two
facilities that would have some minor impact on the scrubber cost
analyses, we reasonably concluded based on the information available to
us that there were enough similarities between the facilities to make
our approach appropriate. As we discuss in our TSD:

    The White Bluff and Independence facilities are sister
facilities. According to EIA,\219\ the boilers were manufactured by
Combustion Engineering with in-service dates of 1980 and 1981 for
White Bluff, and 1983 and 1985 for Independence. All four units are
tangentially firing boilers having nameplate capacities of 900 MW
and similar gross ratings. As we indicate above, all four units burn
coal from the Powder River Basin of Wyoming with similar
characteristics. All four units employ cold side electrostatic
precipitators for particulate collection. Other pertinent
characteristics are similar.\220\
---------------------------------------------------------------------------

    \219\ See ``EIA Consolidated Data_WB and IND_Y2012.xlsx.''
    \220\ See document titled ``AR RH FIP TSD Appendix A--White
Bluff and Independence SO2 Cost Analysis,'' found in the
docket for this rulemaking.

    We further presented satellite photographs to demonstrate that the
layout of these facilities are extremely similar. We consequently
expect that the differences Entergy describes in its comments result in
minor differences in the cost to install and operate scrubbers. As we
have discussed in our response to another comment, the Control Cost
Manual explains that the sole input required for making an ``order of
magnitude'' estimate is the control

system's capacity (often measured by the maximum volumetric flow rate
of the gas passing through the system). Such an estimate, for example,
could be obtained from the cost reported in dollars per megawatt ($/MW)
or dollars per million BTUs fired ($/MMBtu), metrics that are widely
reported in the literature. The Control Cost Manual indicates that
``the costs and estimating methodology in this Manual are directed
toward the `study' estimate with a nominal accuracy of +/-30%
percent.'' This is the long-standing rule of thumb for cost estimate
accuracy used by the EPA for regulatory cost effectiveness analyses. We
see nothing in Entergy's comments that would suggest that the
differences between these two facilities are so significant they would
impact this required level of accuracy. Indeed, Entergy does not
attempt to estimate the capital costs of these differences or otherwise
provide a cost estimate specific to the Independence facility in
support of its argument that it was inappropriate for us to extend our
White Bluff scrubber cost analysis to the Independence facility.
    Comment: Entergy objects to our correction to its White Bluff
scrubber control cost analysis to adjust the cost for a scrubber
designed to treat a 2.0 lb/MMBtu coal to 0.68 lbs/MMBtu to account for
the lower sulfur coal it has historically burned. Entergy states that
we correctly assumed that the 2.0 lb/MMBtu design basis for the White
Bluff scrubber was to preserve fuel flexibility, but our conclusions
that, ``either (1) this higher cost be balanced against its greater
SO2 reduction potential, or (2) that the scrubber system's
capability and cost be adjusted down to match the facility's historical
emissions'' are without basis and inconsistent with the BART
guidelines. Entergy also concludes that its assumption that a 2.0 lb/
MMBtu scrubber inlet was in error and a 1.2 lb/MMBtu inlet assumption
is now appropriate. Entergy presents SO2 emission data in
support of its position that our 0.68 lbs/MMBtu coal assumption was
incorrect and recalculates its O&M and capital costs. Lastly, Entergy
states that in correcting its scrubber control cost analysis to account
for a 0.68 lbs/MMBtu coal, we misapplied a correction factor to our
total direct and indirect costs.
    Response: As we noted in our TSD, ``either (1) this higher cost be
balanced against its greater SO2 reduction potential, or (2)
that the scrubber system's capability and cost be adjusted down to
match the facility's historical emissions.'' Entergy chose to do
neither and costed a scrubber capable of treating a coal far in excess
of what it historically burned, but continued to base the capabilities
of the scrubber on its historical SO2 baseline. Thus, either
Entergy's annualized cost (the ``$'') or its tons reduced (the
``tons'') in the $/ton cost effectiveness calculation are
misrepresented. Our approach was to recalculate Entergy's scrubber cost
to bring its scrubber design in line with the coal it has historically
burned. Entergy could have taken the alternative approach of
calculating a new baseline on the basis of its higher sulfur design
coal, but it chose not to do so. We see nothing in Entergy's comments
that would cause us to conclude our reasoning was in error. With regard
to Entergy's concerns with the 0.68 lbs/MMBtu baseline that we use, it
appears the SO2 emission data Entergy presented was hourly
data, which should not be used to design a scrubber that would have to
meet a 30-BOD average. Our analysis indicates the individual hourly
data fluctuations Entergy presents are inconsequential. Further, an
examination of the running 30-BOD average indicates that our decision
to fix the mismatch between Entergy's scrubber costs and its historical
SO2 baseline on the basis of a SO2 inlet of 0.68
lbs/MMBtu is reasonable.
    In apparent agreement with our basic approach, Entergy recalculates
its variable and fixed O&M costs on the basis of 0.68 lb/MMBtu fuel
sulfur levels. We note that our own variable and fixed O&M costs are
actually greater, adding to the conservativeness of our calculation. To
illustrate the small difference in capital costs associated with the
revised design basis (1.2 lb/MMBtu versus 0.68 lb/MMBtu), Entergy then
performs a sensitivity analysis and concedes there is a ``small
difference in capital costs associated with the revised design basis
(1.2 lb/MMBtu versus 0.68 lb/MMBtu). . . .'' This conclusion is borne
out by our own figures, which indicate there is a small difference in
capital costs to even the 2.0 lbs/MMBtu case; the capital, engineering
and construction costs, which cover the fundamental design parameter of
a scrubber--gas flow rate--were only changed by less than 5%. In sum,
Entergy's assertion that our cost analysis improperly designed the
White Bluff scrubber system is without merit and would make an
insignificant difference in the final outcome.
    Lastly, we agree with Entergy that we misapplied a correction
factor to our total direct and indirect costs. We incorporate that
correction in our final SDA cost analysis for the White Bluff and
Independence facilities, which we discuss in more detail in our
response to other comments. This correction has a relatively minor
impact on the overall cost analysis.
    Comment: The Sierra Club supported our proposal regarding
SO2 for the White Bluff and Independence facilities, but
concluded that our proposed SO2 emission rate of 0.06 lbs/
MMBtu on a 30-BOD average should have been stricter at 0.04 lbs/MMBtu,
based on wet scrubbing. The Sierra Club also agrees with our assessment
that Entergy included undocumented costs in its White Bluff scrubber
cost estimate.
    The Sierra Club's consultant performed a cost analysis of dry and
wet scrubber systems, including Alstom's NID circulating dry scrubber,
and concluded that our White Bluff scrubber cost analysis was
conservative, that scrubbers are cost effective compared to controls
required pursuant to other BART determinations, and that we should have
required compliance in 3 years instead of 5 years.
    Response: We confirm that we intended to construct conservative
cost estimates. With some minor disagreements with the Sierra Club, we
generally agree that an independent cost analysis such as it presents
does support our basic position that scrubbers are cost effective at
both the White Bluff and Independence facilities. However, as we
discuss in our RTC document, we disagree that in this specific instance
wet scrubbers are more cost effective than dry scrubbers. Our scrubber
cost analyses was built off of the analyses supplied by Entergy, and we
determined that wet scrubbers were significantly less cost effective--
again, in the specific cases of the White Bluff and Independence
facilities for BART and reasonable progress respectively. We disagree
with the SO2 baseline Sierra Club uses in its cost analysis,
rendering its scrubber cost analysis and ours not directly comparable.
Consequently, we disagree that an SO2 emission rate of 0.04
lbs/MMBtu averaged over a 30-boiler-operating-day period, based on a
wet scrubber cost analysis, is appropriate for either the White Bluff
or Independence facilities. We agree that in some cases scrubbers can
be installed in less than the 5 years that we proposed. However, this
is site-specific and, in this case, we have found that installation
within 5 years is as expeditious as practicably possible.
    We agree that the Alstom NID circulating dry scrubber is a
promising SO2 control option. We reviewed NID in our
preliminary work but ultimately decided not to evaluate it as a control
because we had no relevant operating data and no method to estimate
costs.

    After addressing all comments from Entergy and the Sierra Club
concerning our White Bluff and Independence scrubber cost analyses, we
made several minor corrections.\221\ Below we summarize those
corrections:
---------------------------------------------------------------------------

    \221\ Those corrections are contained in the file, ``White
Bluff_R6 cost revisions2-revised.xlsx,'' which appears in our
docket.

Table 18--Corrections to Our Cost-Effectiveness Calculations for Dry FGD
                    for White Bluff and Independence
------------------------------------------------------------------------
                                          Proposed cost-    Final cost-
                  Unit                     effectiveness   effectiveness
                                              ($/ton)         ($/ton)
------------------------------------------------------------------------
White Bluff Unit 1......................          $2,227          $2,565
White Bluff Unit 2......................           2,101           2,421
Independence Unit 1.....................           2,477           2,853
Independence Unit 2.....................           2,286           2,634
------------------------------------------------------------------------

    We find that these revised cost-effectiveness calculations do not
change our proposed findings for BART and reasonable progress for these
units.
    In addition, we have examined the effect of adding back in a number
of the BOP and other costs we excluded (based on these costs being
either disallowed by the Control Cost Manual, or having lacked
documentation from Entergy). This exercise also appears in the file
``White Bluff_R6 cost revisions2-revised.xlsx.'' These costs include:
     BOP Costs associated with the reagent prep enclosure and
the reagent handling system, totaling $21,229,000.
     BOP Costs associated with the flue gas system ductwork,
totaling $1,754,000.
     BOP indirect costs of $8,474,666 (escalated to 2013).
     Miscellaneous contract labor costs of $4,448,074
(escalated to 2013).
     Entergy internal costs of $19,482,518 (escalated to 2013).
     Capital suspense costs of $8,101,226 (escalated to 2013).

  Table 19--Alternate Cost-Effective Calculations for Dry FGD on White
                         Bluff and Independence
                       [Include disallowed costs]
------------------------------------------------------------------------
                                                          Alternate cost-
                          Unit                             effectiveness
                                                              ($/ton)
------------------------------------------------------------------------
White Bluff Unit 1......................................          $3,013
White Bluff Unit 2......................................           2,843
Independence Unit 1.....................................           3,351
Independence Unit 2.....................................           3,093
------------------------------------------------------------------------

    We continue to believe that these costs are either disallowed by
the Control Cost Manual, or are properly disallowed because they lack
documentation from Entergy. We have presented this information to
indicate that these disallowed costs have a relatively minor effect on
the final cost effectiveness. Although our final decision regarding
BART and reasonable progress for the White Bluff and Independence units
does not rest upon these cost-effectiveness calculations that include
the disallowed costs, had our final decision rested on these cost-
effectiveness calculations, we would have reached the same conclusions
regarding BART and reasonable progress for these units.
    Comment: The Sierra Club stated that the NOX emission
limit of 0.15 lbs/MMBtu based on LNB/SOFA we proposed for White Bluff
Units 1 and 2 does not satisfy BART. The Sierra Club asserted that
NOX BART for these units should have been based on SCR. The
Sierra Club's consultant concluded that we overestimated the costs of
SCR and underestimated the visibility benefits of SNCR and SCR. The
consultant's conclusions are based on cost-effectiveness calculations
developed by the consultant, which rely on the S&L IPM SCR Cost Module
and assume an achievable NOX emission rate of 0.04 lb/MMBtu
for LNB/SOFA plus SCR. The Sierra Club stated that LNB/SOFA can be
installed in much shorter timeframe than the 3 years we proposed. The
Sierra Club also stated that we should have evaluated SNCR and SCR for
the Independence facility.
    Response: We have a number of disagreements with the Sierra Club's
consultant concerning the SCR cost analysis provided, including the
NOX baseline and the emission limit, which are outlined in
detail in our RTC document. After addressing those issues, we do not
believe that the cost effectiveness of SCR or SNCR fall within a range
that justifies the relatively small incremental visibility improvement
(over our NOX BART determination based on LNB/SOFA) that
would result from the installation of SNCR or SCR at the White Bluff
facility. As we discussed in our proposal,\222\ our modeling indicated
that the visibility improvement at several Class I areas from the
installation of LNB/SOFA at the Independence facility was of a similar
magnitude as the same controls at the White Bluff facility, and
cumulatively (i.e., at all Class I areas combined) the visibility
improvement of the controls at Independence was lower than at White
Bluff. Therefore, we reasoned that since White Bluff and Independence
are sister facilities with near identical units, the cost effectiveness
of SCR or SNCR at Independence would likely not fall within a range
that justifies the relatively small incremental visibility improvement
(over LNB/SOFA) that would result from installation of these controls.
Therefore, we did not evaluate SCR or SNCR controls for Independence.
As we discuss in a separate response, after carefully considering the
comments we have received, we are finalizing an 18-month compliance
date for the NOX emission limits we are establishing for
White Bluff Units 1 sand 2 under BART and Independence Units 1 and 2
under reasonable progress.
---------------------------------------------------------------------------

    \222\ See our supplemental NOX modeling results for
the Independence facility in 80 FR 24872 vs. our NOX
modeling results for the White Bluff facility in 80 FR at 18974.
---------------------------------------------------------------------------

    Comment: The Sierra Club and others stated that the costs of both a
wet and a dry scrubber are reasonable at the two Independence units.
The Sierra noted our proposed costs are reasonable in other reasonable
progress determinations that it summarizes. The Sierra Club's
consultant independently calculated the costs of scrubbers at
Independence Units 1 and 2 and concluded that those calculations
confirm that a scrubber is cost-effective. The consultant also noted
that the significant visibility improvement from a scrubber at
Independence Units 1 and 2 would equal or exceed the visibility
improvement from other reasonable

progress controls we have previously approved. The Sierra Club's
consultant also incorporated comments for the White Bluff facility
regarding time for installation and control level.
    Response: We take no position on the separate cost analysis that
the Sierra Club's consultant has conducted for dry and wet scrubbers
and that uses to conclude that our cost analyses are reasonable. We
agree that our finding that the control costs are reasonable, given the
visibility improvements achieved, is consistent with other EPA actions.
We refer the Sierra Club's consultant to our responses to other similar
comments regarding the White Bluff facility scrubber concerning control
level and installation time.
    Comment: The Sierra Club and others stated that our proposal that
SO2 BART for AEP Flint Creek is a NID dry scrubber is
appropriate, but argued that a NID dry scrubber is even more cost-
effective than what AEP and EPA have estimated. The Sierra Club's
consultant presented cost analyses for wet and NID scrubbing for Flint
Creek, based on the IPM cost algorithms we used in our recent Texas-
Oklahoma FIP. In so doing, the consultant applied the SDA cost
algorithm to NID, citing to documentation that indicates that NID may
be 1-2% lower in cost to an SDA system. The Sierra Club's consultant
argues that both wet and dry scrubbers are capable of even greater
levels of control than what we assumed.
    Response: As we discuss in our TSD,\223\ we noted a number of
issues with AEP's NID and wet scrubber cost analyses that if corrected
would have resulted in more favorable (lower $/ton) cost-effectiveness
values. Nevertheless, even disregarding those errors, we concluded that
NID was cost-effective and worth the visibility benefit that will
result from its installation. We also determined that wet scrubbing
would remain less cost-effective than NID, and was not worth the small
additional visibility that would result from its installation in this
particular instance.
---------------------------------------------------------------------------

    \223\ See page 65 of our TSD: ``[W]e believe that AEP's
escalation of the cost of controls to 2016 dollars has likely
resulted in the over estimation of the average cost-effectiveness
values. Therefore, we believe a wet scrubber and NID are more cost-
effective (i.e., less dollars per ton of SO2 removed)
than estimated by AEP (see table above). However, we did not adjust
the cost numbers and cost-effectiveness values because we do not
believe that doing so would change our proposed BART determination.
We believe that the average cost-effectiveness of both control
options was likely over-estimated and the costs associated with a
wet scrubber would continue to be higher than the costs associated
with NID if the estimates were adjusted, yet the installation and
operation of a wet scrubber is projected to result in minimal
incremental visibility improvement over NID.
---------------------------------------------------------------------------

    We extensively analyzed the performance potential of wet scrubbers
in our recent Texas-Oklahoma FIP.\224\ We concluded that a control
level of 98%, not to go below an emission rate of 0.04 lbs/MMBtu on a
30-BOD average, was a reasonable lower level of control. We applied the
same reasoning to our Arkansas proposal. As we discuss in our response
to another comment, although we regard NID as a promising technology
that may in fact be capable of greater levels of control than what we
have assumed, there is no real long-term monitoring data to
substantiate such a conclusion. Therefore, because we have concluded
that in this instance the cost-effectiveness of wet scrubbers is not
justified by their relatively small additional visibility benefit, we
disagree that SO2 BART for Flint Creek Unit 1 should be
0.04, based on the performance of a wet scrubber.
---------------------------------------------------------------------------

    \224\ See response to comment beginning on page 310 of our
Response to Comments for the Federal Register Notice for the Texas
and Oklahoma Regional Haze State Implementation Plans; Interstate
Visibility Transport State Implementation Plan to Address Pollution
Affecting Visibility and Regional Haze; and Federal Implementation
Plan for Regional Haze, Docket No. EPA-R06-OAR-2014-0754, 12/9/2015.
---------------------------------------------------------------------------

    Comment: The Sierra Club and others stated that the LNB/OFA
proposal for Flint Creek does not satisfy NOX BART, which
should have been based on SCR. The Sierra Club stated that we and AEP
used very conservative assumptions that inflated the cost of the SCRs
and SNCRs as NOX BART options for Flint Creek. The Sierra
Club's consultant stated that the 20-year life assumed in AEP's SCR
cost analysis should have been 30 years, and that the assumed level of
control should have been 0.04 lbs/MMBtu. The consultant then performed
an SCR control cost analysis and concluded that the cost effectiveness
was within a range we have previously found to be acceptable in other
BART determinations. The Sierra Club's consultant also stated that AEP
overestimated the cost of SNCR because it based it on a reduction of
from 0.31 lbs/MMBtu to 0.2 lbs/MMBtu, when in fact, the first-in-line
LNB/OFA controls would have already reduced the NOX to 0.23
lbs/MMBtu, resulting in a lesser loading to the SNCR system and
reducing its operating costs.
    Response: We note that we provided comments to ADEQ,\225\ which
included a recommendation that 30 years should be used as an equipment
life for SNCR. AEP did not adopt this recommendation in its September
2013 BART analysis for the Flint Creek facility. We agree with the
Sierra Club's consultant that AEP overestimated the cost of SNCR
because its calculation based it on a reduction of from 0.31 lbs/MMBtu
to 0.2 lbs/MMBtu. We have corrected this error, and the error in AEP
SWEPCO's assumed 20-year equipment life, and recalculated the SNCR cost
effectiveness for Flint Creek. We calculated that SNCR + LNB/OFA has a
revised cost-effectiveness of $1,346/ton, as opposed to cost
effectiveness of $1,258/ton for LNB/OFA alone. Also, we calculated that
the incremental cost effectiveness of SNCR + LNB/OFA over LNB/OFA alone
is $1,581/ton. We then re-applied the BART five factors, with emphasis
on cost and visibility improvement. The incremental visibility
improvement of SNCR + LNB/OFA over LNB/OFA alone is 0.033 dv at Caney
Creek and ranges from 0.005 to 0.01 dv at each of the other affected
Class I areas. As discussed in our proposal, we consider the
incremental visibility improvement of SNCR + LNB/OFA to be relatively
small at Caney Creek and to be very small in the remaining three
affected Class I areas. We conclude that despite the improvement in the
cost-effectiveness of SNCR + LNB/OFA over LNB/OFA alone, under these
circumstances the resulting relatively small incremental visibility
improvement is still not worth the additional cost of the more
stringent controls.
---------------------------------------------------------------------------

    \225\ See email from Dayana Medina to Mary Pettyjohn on 8/21/13.
---------------------------------------------------------------------------

    Regarding the Sierra Club's consultant's SCR control cost analysis,
we do not believe that a NOX emission limit of 0.04 lbs/
MMBtu has been maintained on a 30 boiler-operating-day average at other
similar facilities. We conclude that, as we did in our New Mexico FIP,
a 30 boiler-operating-day NOX average of 0.05 lbs/MMBtu is
an appropriate assumption for SCR installation at the Flint Creek
facility. We also note that the maximum visibility improvement due to
SCR at Flint Creek based on the modeled rate of 0.067 lb/MMBtu was
0.245 dv, which occurred at Caney Creek. If we make reasonable,
conservative adjustments to the anticipated visibility benefit, based
on a control level of 0.055 lbs/MMBtu rather than the modeled rate of
0.067 lbs/MMBtu,\226\ we estimate that the resulting visibility
improvement at Caney Creek would be no higher than

0.26 dv.\227\ Based on this adjustment, the incremental visibility
improvement of SCR + LNB/OFA over SNCR + LNB/OFA is 0.146 dv. Even
accepting the Sierra Club's consultant's SCR cost analysis of $3,511/
ton (which would be higher were it revised using a controlled
NOX rate of 0.05 lbs/MMBtu) and taking into consideration
the adjustments we have made to the cost analysis for SNCR + LNB/OFA,
the incremental cost effectiveness of SCR + LNB/OFA over SNCR + LNB/OFA
is $4,969/ton. In the context of this BART determination, we do not
consider the relatively small incremental visibility improvement to be
worth the incremental cost of the SCR installation.
---------------------------------------------------------------------------

    \226\ Modeled emission rates were based on a maximum heat input
of 6,324 MMBtu/hr multiplied by the anticipated control rate (e.g.
0.067 lb/MMBtu) Baseline emissions determined from 2001-2003 CAMD
data were 1,945 lb/hr, approximately 0.308 lb/MMbtu.
    \227\ Modeled visibility benefit at CACR over baseline from SCR
at 0.067lb/MMbtu was 0.245 dv. SCR at 0.055 lb/MMBtu would result in
an additional reduction in emissions from baseline of only 4%.
Assuming a linear relationship between emission and visibility
impacts, this would also result in an increase in visibility benefit
of only 4%.
---------------------------------------------------------------------------

    Comment: The Sierra Club and others stated that the Lake Catherine
Unit 4 BART analysis failed to accurately consider compliance costs,
non-environmental impacts, and the degree of visibility improvement.
The Sierra Club further stated we underestimated the cost of BOOS and
overestimated the costs of low NOX burners, over-fired air,
SNCR, and SCR. The Sierra Club's consultant also alleges that the
documentation to support the Lake Catherine NOX BART
analysis is incomplete. Lastly, the Sierra Club stated that our cost-
effectiveness analysis should be based on a capacity calculation that
depends on time of operation, and our proposal to use a 10% capacity is
unenforceable. Had we used a higher capacity factor, the Sierra Club
reasons that the increase in NOX emissions removed by the
various pollution control equipment would have improved their cost-
effectiveness (lower $/ton), making them more attractive.
    Response: The Sierra Club's consultant raises a number of issues
pertaining to missing documentation or errors in Entergy's
NOX BART analysis for Lake Catherine Unit 4, on which we
relied on in making our BART decision. We reviewed the issues raised by
the Sierra Club's consultant in detail in our RTC document and conclude
they are unfounded or lack documentation. We conducted an analysis of
Lake Catherine's data on heat input, operational time, and
NOX emissions to investigate the correlation between heat
input and operational time to NOX emissions, and further
conclude that capacity calculations for the Lake Catherine Unit 4
should be based on heat input and not operational time. Lastly, we
calculate the historical capacity for the Lake Catherine Unit 4 as
follows:

           Table 20--Lake Catherine Unit 4 Historical Capacity
------------------------------------------------------------------------
                                                             Capacity
                          Year                              factor  (%)
------------------------------------------------------------------------
2001....................................................            28.2
2002....................................................            24.2
2003....................................................            11.3
2004....................................................             3.7
2005....................................................             4.7
2006....................................................             0.6
2007....................................................             0.8
2008....................................................             2.3
2009....................................................             2.8
2010....................................................             3.5
2011....................................................             2.9
2012....................................................            14.3
2013....................................................            11.1
2014....................................................             2.0
2015....................................................             3.9
------------------------------------------------------------------------

    We agree that the Lake Catherine Unit 4 historical capacity has
sometimes exceeded the 10% capacity Entergy has assumed in its control
cost analyses. However, the average from the last ten years of data
(2006 to 2015) has been 4.4%. Typically, we place the most emphasis on
the last five years of data, and our recent practice has been to
discard the high and low values and average the remaining three
years.\228\ Applying that procedure to the Lake Catherine Unit 4
capacity factor results in a value of 6.0%. Alternatively, calculating
a straight average of the last five years results in a value of 6.8%.
Thus, we disagree that we erred in accepting Entergy's assumption of a
10% capacity factor in its control cost analysis. We note that in its
response to us, Entergy stated, ``If future capacity factors change,
ADEQ and EPA may impose further NOX emission reductions on
Unit 4, if necessary, in later planning periods to show reasonable
progress.'' We believe that is an appropriate strategy and we will re-
examine Lake Catherine's historical capacity in our review of Arkansas'
next regional haze SIP.
---------------------------------------------------------------------------

    \228\ This was our approach in calculating the SO2
baselines used in our recent TX-OK FIP.
---------------------------------------------------------------------------

    Comment: We received comments from Nucor, Entergy and Conway
Corporation stating that we should have used the dollar per deciview
($/dv) metric to weigh the cost versus the visibility benefit of
controls for the White Bluff and Independence facilities. The Sierra
Club supported our position that we are not required to use this
metric.
    Response: The BART Guidelines require that cost effectiveness be
calculated in terms of annualized dollars per ton of pollutant removed,
or $/ton.\229\ The BART Guidelines list the $/deciview metric as an
optional cost effectiveness measure that can be employed along with the
required $/ton metric for use in a BART evaluation. The metric can be
useful in comparing control strategies or as additional information in
the BART determination process; however, due to the complexity of the
technical issues surrounding regional haze, we have never recommended
the use of this metric as a cutpoint or threshold in making BART
determinations or reasonable progress determinations. We note that to
use the $/deciview metric as the main determining factor would most
likely require the development of thresholds of acceptable costs per
deciview of improvement for BART and reasonable progress determinations
for both single and multiple Class I analyses. We have not developed
such thresholds for use in BART or reasonable progress determinations.
Generally speaking, while the $/deciview metric can be useful if
thoughtfully applied, we view the use of this metric as suggesting a
level of precision in the calculation of visibility impacts that is not
justified in many cases. While we did not use a $/deciview metric in
the BART and reasonable progress determinations we make in this FIP, we
did, however, consider the visibility benefits and costs of control
together, as noted above by weighing the costs in light of the
predicted visibility improvement. We have addressed this issue in a
number of our previous actions since we first discussed this issue in
our Oklahoma FIP,\230\ and our position with regard to the $/deciview
metric was reviewed and upheld in Oklahoma v. EPA, 723 F.3d 1201 by the
Tenth Circuit which ruled:
---------------------------------------------------------------------------

    \229\ 70 FR at 39167.
    \230\ Response to Technical Comments for Sections E. through H.
of the Federal Register Notice for the Oklahoma Regional Haze and
Visibility Transport Federal Implementation Plan, Docket No. EPA-
R06-OAR-2010-0190, 12/13/2011, pdf 116.

    Oklahoma first suggests EPA should not have rejected the
visibility analysis it conducted in the SIP, which used the dollar-
per-deciview method. This argument is misguided. The EPA rejected
the SIP because of the flawed cost estimates. When promulgating its
own implementation plan, it did not need to use the same metric as
Oklahoma. The guidelines merely permit the BART-determining
authority to use dollar per deciview as an optional method of
evaluating cost effectiveness. See 40 CFR pt. 51 app.
Y(IV)(E)(1).\231\ And in the final rule, the EPA

explained why it did not use the dollar-per-deciview metric used by
Oklahoma. ``Generally speaking, while the metric can be useful if
thoughtfully applied, we view the use of the $/deciview metric as
suggesting a level of precision in the calculation of visibility
impacts that is not justified in many cases.'' 76 Fed. Reg. at
81,747. The EPA has never mandated the use of this metric, and has
not developed ``thresholds of acceptable costs per deciview
improvement.'' Id. While the federal land managers have developed
thresholds, these thresholds were apparently developed without input
from the EPA and without notice-and-comment review. EPA Br. at 54 n.
13. In light of this, we do not find it arbitrary or capricious that
the EPA chose not to use the dollar-per-deciview metric in
evaluating BART options in creating the FIP. We therefore also
conclude that any argument by the petitioners that the dollar-per-
deciview measurement proves the scrubbers are not cost effective
lacks merit. See Pet. Reply Br. at 16.
---------------------------------------------------------------------------

    \231\ We note, however, that in both its final rule and in its
brief the EPA asserts that the guidelines require the use of the
dollar-per-ton metric in evaluating cost effectiveness. The
guidelines themselves are a bit unclear. In the section on cost
effectiveness, the guidelines mention only the dollar-per-ton
metric. 40 CFR pt. 51 app. Y(IV)(D)(4)(c). However, the guidelines
later state that in evaluating alternatives, ``we recommend you
develop a chart (or charts) displaying for each of the
alternatives'' that includes, among other factors, the cost of
compliance defined as ``compliance--total annualized costs ($), cost
effectiveness ($/ton), and incremental cost effectiveness ($/ton),
and/or any other cost-effectiveness measures (such as $/deciview).''
Id. app.Y(IV)(E)(1) (emphasis added).

    We see no reason to deviate from our view of the $/deciview metric
here.

J. Modeling

1. Cumulative Visibility Impairment
    Comment: Several commenters opposed the use of a ``cumulative
deciviews'' or ``total'' visibility improvement metric and claim the
``cumulative deciviews'' metric has no basis in the CAA and EPA's
regulations. It also allegedly mischaracterizes visibility improvements
in Class I areas. Determinations instead should be based on the
predicted visibility improvements at individual Class I areas.
Furthermore, the cumulative metric is deceptive and provides no
information that could be used to assess whether any single Class I
area would experience perceivable visibility improvements as a result
of BART or reasonable progress controls, and may mask the fact that no
individual Class I area would experience any discernible visibility
improvement from control of emissions at any particular source. The
cumulative metric represents an illusory visibility benefit; it is an
improvement that cannot be perceived and therefore provides no
indication of whether the proposed controls will contribute to the goal
of the regional haze program: To reduce human perception of visibility
impairment in Class I areas. The only purpose of the cumulative
visibility improvement indicator is to imply that facilities are having
a large impact across numerous Class I areas, but this indicator can be
deceptive if it includes imperceptible visibility improvements for some
Class I areas.
    The commenters also suggest that the use of a ``total dv'' metric
is inconsistent with BART guidelines (40 CFR part 51 Appendix Y,
IV.D.5) that state it is appropriate to model impacts at the nearest
Class I area as well as other nearby Class I areas to determine where
the impacts are greatest. Modeling at other Class I areas may be
unwarranted if the highest modeled effects are observed at the nearest
Class I area. The commenters claim the analysis should be focused on
the visibility impacts at the most impacted area, not all areas. Other
commenters supported the use of the cumulative visibility metric,
stating that it is appropriate and lawful, and within the spirit of the
statutory mandate and expressly permissible within the regulation to
consider cumulative impacts.
    Response: We agree with the comments supporting the consideration
of cumulative visibility impacts and benefits. We disagree with the
other commenters that cumulative improvement over multiple areas is an
inappropriate metric, or that examining a single Class I area is
sufficient. The cumulative improvement metric (i.e., the simple sum of
impacts or improvements over all the affected Class I areas) is not
intended to correspond to a single human's perception at a given time
and place. The approach is simply one way of assessing improvements at
multiple areas, for consideration along with other visibility metrics.
Another approach would be to simply list visibility improvements at the
various areas, and qualitatively weigh the number of areas and the
magnitudes of the improvements. The cumulative sum is simply an easily
understood and objective way of weighing cumulative visibility
improvement, as part of the overall control evaluation along with the
visibility improvement at each impacted Class I area. As noted by some
comments, we have calculated cumulative visibility in a number of
Regional Haze actions evaluating the benefits of controls under BART
and when visibility is considered in the reasonable progress analysis.
Furthermore, the FLMs have provided comments in support of the use of
this metric in past actions.\232\
---------------------------------------------------------------------------

    \232\ For example, see 76 FR 52388, 52429 (August 22, 2011).
---------------------------------------------------------------------------

    The comment opposing cumulative modeling does not provide the full
context when citing to the BART guidelines. The portion referred to by
the commenter discusses the development of a modeling protocol and
establishing the receptors to model. The full portion of the BART
Guidelines that the commenter referenced states:

    The receptors that you use should be located in the nearest
Class I area with sufficient density to identify the likely
visibility effects of the source. For other Class I areas in
relatively close proximity to a BART-eligible source, you may model
a few strategic receptors to determine whether effects at those
areas may be greater than at the nearest Class I area. For example,
you might chose to locate receptors at these areas at the closest
point to the source, at the highest and lowest elevation in the
Class I area, at the IMPROVE monitor, and at the approximate
expected plume release height. If the highest modeled effects are
observed at the nearest Class I area, you may choose not to analyze
the other Class I areas any further as additional analyses might be
unwarranted.\233\
---------------------------------------------------------------------------

    \233\ 40 CFR 51 Appendix Y, IV.D.5.

    This section of the BART Guidelines addresses how to determine
visibility impacts as part of the BART determination. Several
paragraphs later in the BART Guidelines it states: ``You have
flexibility to assess visibility improvements due to BART controls by
one or more methods. You may consider the frequency, magnitude, and
duration components of impairment,'' emphasizing the flexibility in
method and metrics that exists in assessing the net visibility
improvement.
    In fully considering the visibility benefits anticipated from the
use of an available control technology as one of the factors in
selection of BART, it is appropriate to account for visibility benefits
across all affected Class I areas and the BART guidelines provide the
flexibility to do so. One approach as noted above is to qualitatively
consider, for example, the frequency, magnitude, and duration of
impairment at each and all affected Class I areas. Where a source
significantly impacts more than one Class I areas, the cumulative
visibility metric is one way to take magnitude of the impacts of the
source into account.
    With respect to our analysis of controls under reasonable progress,
we rely on our Reasonable Progress Guidance.\234\ Our Reasonable
Progress Guidance notes the similarity between some of the reasonable
progress factors and the BART factors contained in Sec.
51.308(e)(1)((ii)(A), and suggests that

the BART Guidelines be consulted regarding cost, energy and nonair
quality environmental impacts, and remaining useful life. We are
therefore relying on our BART Guidelines for assistance in interpreting
those reasonable progress factors, as applicable.
---------------------------------------------------------------------------

    \234\ ``Guidance for Setting Reasonable Progress Goals Under the
Regional Haze Program,'' June 1, 2007.
---------------------------------------------------------------------------

    Also, similar to a BART analysis, we are also considering the
projected visibility benefit in our analysis following the BART
guidelines and the use of CALPUFF.\235\ We rely on the BART Guidelines
here and in other actions evaluating reasonable progress controls
because they provide a reasonable and consistent approach regarding
visibility modeling. This includes the flexibility in metrics that
exists in assessing the net visibility improvement, and the use of
cumulative visibility, along with visibility impacts at individual
Class I areas, as one way to take magnitude of the impacts of the
source into account where a source evaluated under reasonable progress
significantly impacts more than one Class I area.
---------------------------------------------------------------------------

    \235\ As we explain in our proposed action (80 FR at 18993):
``While visibility is not an explicitly listed factor to consider
when determining whether additional controls are reasonable under
the reasonable progress requirements, the purpose of the four-factor
analysis is to determine what degree of progress toward natural
visibility conditions is reasonable. Therefore, it is appropriate to
consider the projected visibility benefit of the controls when
determining if the controls are needed to make reasonable
progress''. See 79 FR at 74838, 74840, and 74874.
---------------------------------------------------------------------------

    For each subject-to-BART source and the source evaluated for
reasonable progress controls, we evaluated the visibility impacts from
the source and benefits of controls at four separate Class I areas. In
addition to providing the visibility impacts and potential benefits at
each Class I area in the proposal, we also summed the impact and
improvement across the four Class I areas. The results show that some
sources significantly impact visibility at more than one Class I area,
emission reductions result in visibility benefits at all impacted class
I areas, and in some situations, the largest visibility benefits from
controls can occur at Class I areas other than the most impacted.
    Therefore, consistent with the BART Guidelines, and based upon
these facts, we determined additional analyses were not only warranted
but necessary. The BART Guidelines only indicate that additional
analyses may be unwarranted at other Class I areas, and in no way
exclude such analyses, as the commenter suggests. We concluded that a
quantitative analysis of visibility impacts and benefits at only the
most impacted area would not be sufficient to fully assess the impacts
and benefits of controlling emissions from the sources evaluated for
BART and reasonable progress.
    Nothing in the Regional Haze Rule suggests that a state (or EPA in
issuing a FIP) should ignore the full extent of the visibility impacts
and improvements from controls at multiple Class I areas. Given that
the national goal of the program is to improve visibility at all Class
I areas, it would be short-sighted to limit the evaluation of the
visibility benefits of a control to only the most impacted Class I
area. We believe such information is useful in quantifying the overall
benefit of controls. As discussed in our proposal, we evaluated the
statutory factor, visibility benefits anticipated due to controls, at
each Class I area in making BART determinations and considered the
visibility benefits in consideration of controls for reasonable
progress.
2. Imperceptible Visibility Improvement
    Comment: EPA must withdraw the proposed FIP because the FIP would
only achieve visibility improvements below one deciview, which is not
discernible to the naked eye. Commenters state that the CAA only
provides EPA with the authority to regulate the ``impairment of
visibility.'' \236\ Visibility extends only to things that humans can
see with their naked eyes.\237\ By extension, EPA only has authority to
regulate the impairments of visibility that are perceptible to the
human eye. Under both the plain language and dictionary definitions of
``visibility,'' the statute does not provide EPA with the authority to
regulate haze below a single deciview, which would be invisible to the
naked eye. Since the Proposed FIP will only achieve visibility
improvements smaller than one deciview, the EPA lacks authority to
revise the RPGs suggested by Arkansas, and it should withdraw the
Proposed FIP.
---------------------------------------------------------------------------

    \236\ CAA section 169A (``Congress hereby declares as a national
goal the prevention of any future, and the remedying of any
existing, impairment of visibility in mandatory class I Federal
areas which impairment results from manmade air pollution.)
(emphasis added).
    \237\ E.g. Webster's Third New International Dictionary 2557
(1981) (``visible'' means ``capable of being seen''; ``visibility''
means ``the degree or extent to which something is visible . . .
[by] the observer's eye unaided by special optical devices'').
---------------------------------------------------------------------------

    Commenters also state that the EPA may not require a source ``to
spend millions of dollars for new technology that will have no
appreciable effect on haze in any Class I area.'' Am. Corn Growers
Ass'n. v. EPA \238\ (vacating EPA's BART determinations because EPA
left open the possibility that it could require a source to install
technologies even when those technologies had no appreciable effect on
visibility). Yet the EPA requires certain stationary sources of immense
value to the State of Arkansas and its citizens to install controls
that will cost billions of dollars in order to achieve imperceptible
visibility improvements.
---------------------------------------------------------------------------

    \238\ Am. Corn Growers Ass'n v. EPA, 291 F.3d 1, 7 (D.C. Cir.
2002).
---------------------------------------------------------------------------

    Response: We disagree with commenters that the Regional Haze Rule
requires that controls on a source or group of sources result in
perceptible visibility improvement.\239\ We believe, for reasons we
have outlined in our proposal and elsewhere in our response to
comments, that the controls we proposed under our FIP will result in
significant improvements in visibility at a number of Class I areas. In
a situation where the installation of BART may not result in a
perceptible improvement in visibility, the visibility benefit may still
be significant, as explained by the Regional Haze Rule:
---------------------------------------------------------------------------

    \239\ It is generally recognized that a change in visibility of
1.0 deciview is humanly perceptible.

    Even though the visibility improvement from an individual source
may not be perceptible, it should still be considered in setting
BART because the contribution to haze may be significant relative to
other source contributions in the Class I area. Thus, we disagree
that the degree of improvement should be contingent upon
perceptibility. Failing to consider less-than-perceptible
contributions to visibility impairment would ignore the CAA's intent
to have BART requirements apply to sources that contribute to, as
well as cause, such impairment.\240\
---------------------------------------------------------------------------

    \240\ 70 FR 39104, 39129.

    Section 169A of the CAA requires that certain major sources that
emit any pollutant which may reasonably be anticipated to cause or
contribute to visibility impairment in Class I Areas install BART. The
following factors must be taken into account in determining BART: The
costs of compliance, the energy and nonair quality environmental
impacts of compliance, any existing pollution control technology 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.\241\
---------------------------------------------------------------------------

    \241\ CAA section 169A(g)(2).
---------------------------------------------------------------------------

    The CAA also requires that in determining reasonable progress there
shall be taken into consideration the costs of compliance, the time
necessary for compliance, the energy and nonair

quality environmental impacts of compliance, and the remaining useful
life of any existing source subject to such requirements. Our 2007
Reasonable Progress Guidance \242\ notes the similarity between some of
the reasonable progress factors and the BART factors contained in Sec.
51.308(e)(1)(ii)(A), and suggests that the BART Guidelines be consulted
regarding cost, energy and nonair quality environmental impacts, and
remaining useful life. We are therefore relying on our BART Guidelines
for assistance in interpreting those reasonable progress factors, as
applicable, including visibility improvement even though it may not be
perceptible from an individual source. Also, similar to a BART
analysis, we are also considering the projected visibility benefit in
our analysis of reasonable progress controls following the BART
guidelines.\243\ We rely on the BART Guidelines here and in other
actions evaluating reasonable progress controls because they provide a
reasonable and consistent approach regarding visibility modeling.
---------------------------------------------------------------------------

    \242\ ``Guidance for Setting Reasonable Progress Goals Under the
Regional Haze Program,'' June 1, 2007.
    \243\ As we explain in our proposed action (80 FR at 18993):
``While visibility is not an explicitly listed factor to consider
when determining whether additional controls are reasonable under
the reasonable progress requirements, the purpose of the four-factor
analysis is to determine what degree of progress toward natural
visibility conditions is reasonable. Therefore, it is appropriate to
consider the projected visibility benefit of the controls when
determining if the controls are needed to make reasonable
progress''. See also 79 FR at 74838, 74840, and 74874.
---------------------------------------------------------------------------

    We accordingly disagree that selection of control measures under
BART or for reasonable progress should be contingent upon perceptible
visibility improvement. As we stated in our previous rulemaking
addressing the BART determinations in Oklahoma:

    Given that sources are subject to BART based on a contribution
threshold of no greater than 0.5 deciviews, it would be inconsistent
to automatically rule out additional controls where the improvement
in visibility may be less than 1.0 deciview or even 0.5 deciviews. A
perceptible visibility improvement is not a requirement of the BART
determination because visibility improvements that are not
perceptible may still be determined to be significant.\244\
---------------------------------------------------------------------------

    \244\ 76 FR 81728, 81739.

    The Regional Haze Rule provides that BART-eligible sources with a
0.5 dv impact at a Class I area ``contribute'' to visibility impairment
and must be analyzed for BART controls. BART determining authorities,
however, are free to establish thresholds less than 0.5 dv.
Consequently, even though the visibility improvement from controlling
an individual source may not be perceptible, it should still be
considered because the contribution to haze may be significant when the
aggregate contribution of other sources in the Class I area is taken
into account and because the contribution to haze from the source may
be significant relative to other source contributions in the Class I
area. Thus, in our visibility improvement analysis for BART sources and
in consideration of visibility benefits from controls under our
reasonable progress analysis, we have not considered perceptibility as
a threshold criterion for considering improvements in visibility to be
meaningful.
    We have considered visibility improvement in a holistic manner,
taking into account all reasonably anticipated improvements in
visibility, and the fact that, in the aggregate, improvements from
controls on multiple sources (either under BART or reasonable progress)
will contribute to visibility progress towards the goal of natural
visibility conditions. Visibility impacts below the thresholds of
perceptibility cannot be ignored because regional haze is produced by a
multitude of sources and activities which are located across a broad
geographic area. In this action, we found that the required cost-
effective controls reduce visibility impairment from those BART sources
that contribute or cause visibility impairment at nearby Class I areas
and result in meaningful visibility benefits towards the goal of
natural visibility conditions. Similarly, we also found that the
required cost-effective controls at the Entergy Independence facility
reduce visibility impairment from the source with the largest potential
visibility impacts (among all Non-BART sources) and result in
meaningful visibility benefits towards the goal of natural visibility
conditions.
    The commenter mischaracterizes a statement made by the D.C. Circuit
Court of Appeals in Am. Corn Growers Ass'n. v. EPA. The statement made
by the Court is as follows: ``[U]nder EPA's take on the statute, it is
therefore entirely possible that a source may be forced to spend
millions of dollars for new technology that will have no appreciable
effect on the haze in any Class I area.'' \245\ The Court made this
statement in reviewing EPA's approach to the BART requirements in the
Regional Haze Rule promulgated in 1999 which did not require the
source-specific assessment of a BART eligible source's visibility
impacts at any step of the BART process.\246\
---------------------------------------------------------------------------

    \245\ Am. Corn Growers Ass'n v. EPA, 291 F.3d 1, 7 (D.C. Cir.
2002).
    \246\ Id.
---------------------------------------------------------------------------

    The Court disagreed with the approach used by EPA to determine what
BART eligible sources are reasonably anticipated to cause or contribute
to regional haze and therefore subject to BART.\247\ The approach in
the Regional Haze Rule required a State to analyze ``the degree of
visibility improvement that would be achieved in each mandatory Class I
Federal area as a result of the emission reductions achievable from all
sources subject to BART located within the region that contributes to
visibility impairment in the Class I area.'' \248\ The Court held that
the Rule's treatment of ``the degree of improvement in visibility which
may reasonably be anticipated to result from the use of such
technology'' factor infringed on states' authority with respect to BART
determinations under the Act.\249\ The Court noted that the Act does
not assign a specific weight with which to consider each factor, it
solely mandates that all the factors be considered in making a BART
determination.\250\ The Court's issue was not with the weight, or lack
thereof, placed on this factor by EPA. It found issue with what it
considered to be ``dramatically'' different treatment of the visibility
factor by EPA. Id. While the court in American Corn Growers Ass'n. v.
EPA found that we had impermissibly constrained State authority, it did
so because it found that we 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 in
Arkansas. In response to this court decision and to address these
concerns we finalized revised Regional Haze Regulations and Guidelines
for Best Available Retrofit Technology (BART) Determinations.\251\
---------------------------------------------------------------------------

    \247\ Id. at 7-8.
    \248\ 40 CFR 51.308(e)(1)(ii)(B).
    \249\ Id.
    \250\ 291 F.3d at 6.
    \251\ 70 FR 39104.
---------------------------------------------------------------------------

    Our analysis does not give greater weight to one factor over
another; rather, we considered all five BART factors fully, revealing
that the cost and visibility factors were the two most important
factors in our decisions. In American Corn Growers Ass'n. v. EPA, the
D.C. Circuit Court faulted how EPA assessed the statutory fifth factor
of visibility improvement in a BART determination by using a regional,
multi-source, group approach to assessing the visibility improvement
factor, while assessing the other four

statutory BART factors on a source-specific basis. Here, we did not
give greater weight to our consideration of visibility improvement or
consider the visibility in a different fashion from the other factors.
All BART factors were evaluated on a source-specific basis.
    The Court also noted that it is the State's and not EPA's duty to
determine what BART is (provided that the State's determination
complies with the Act and EPA guidelines.\252\). When EPA promulgates a
FIP, it is acting in the place of the State, and thus has the same
authority a state has when the state promulgates a SIP. It is therefore
our duty to determine what BART is since we are proposing a FIP for
Arkansas. We must also consider the same factors that the State is
mandated to consider by the CAA. The ``degree of improvement in
visibility which may reasonably be anticipated to result from the use
of such [best available retrofit] technology'' is just one of several
factors the State, or EPA in the case of a FIP, must consider in
determining what BART is for a specific source.
---------------------------------------------------------------------------

    \252\ 291 F. 3d at 8-9.
---------------------------------------------------------------------------

    We also disagree with commenter's statement that we required
emissions reductions just for the sake of doing so under the guise of
imperceptible visibility improvements or solely for the sake of
reducing emissions. As discussed above, we considered all the statutory
factors, including the ``degree of improvement in visibility which may
reasonably be anticipated to result from the use of such [best
available retrofit] technology'' in our BART determinations. We do not
consider perceptibility as a threshold criterion for considering
improvements in visibility to be meaningful. Failing to consider less-
than-perceptible contributions to visibility impairment would ignore
the CAA's intent to have BART requirements apply to sources that
contribute to, as well as cause, such impairment.
    Comment: One commenter stated that the visibility benefits of some
of the required controls either individually or in combination will
result in perceptible visibility benefits. They also comment that the
regional haze regulations reflect EPA's finding that the Congressional
goal of eliminating haze can be achieved only by tackling the multitude
of sources that contribute to haze in national parks and wilderness
areas. For this reason, EPA has stated that ``visibility improvement
does not need to be perceptible to be deemed significant for BART
purposes.'' \253\
---------------------------------------------------------------------------

    \253\ 79 FR 5032, 5120 (January 30, 2014).
---------------------------------------------------------------------------

    Response: We agree with the commenter. As we discuss in response to
comments above, the Regional Haze Rule does not require that controls
on a source or group of sources result in perceptible visibility
improvement. We also agree that in some cases required controls either
individually or in combination with other required controls will result
in perceptible visibility improvements at impacted Class I areas on
some days.
3. Model Selection
    Comment: CALPUFF modeling cannot be used to justify controls at
Independence under the reasonable progress requirements. Using CALPUFF,
a single source model, for evaluating the reasonable progress benefits
of installing controls at Independence is misplaced and clearly in
error. EPA must demonstrate that additional controls are rational and
economically justifiable and that the amount of progress that would
result will be ``reasonable based upon the statutory factors.'' CALPUFF
is overly simplistic and greatly overstates the effect of single source
emissions.\254\ CALPUFF also fails to show the effects of multiple
sources, and is much less sophisticated in its treatment of the
chemical interactions of the different pollutants in the atmosphere
than CAMx. The commenters also state that the use of CALPUFF does not
reflect the interaction of pollutants in the atmosphere as accurately
as CAMx does.
---------------------------------------------------------------------------

    \254\ BART Guidelines, 70 FR 39104, 39121 (``there are other
features of our recommended modeling approach that are likely to
overstate the actual visibility effects of an individual source.
Most important, the simplified chemistry in the model tends to
magnify the actual visibility effects of that source.'')
---------------------------------------------------------------------------

    EPA used CALPUFF and did not perform refined, multi-state modeling
to determine the amount of visibility improvements that would be
achieved through the installation of controls because it would be
difficult, time-consuming, and expensive. Instead, the Agency took a
``thumbnail'' approach in an attempt to justify the proposed controls
based on how long it would take to achieve background levels.
    EPA recognized in their action on Texas regional haze that CAMx, a
photochemical transport 3-dimensional grid model, is a more appropriate
modeling tool for reasonable progress purposes.\255\ BART analyses
assess the impact of a single facility based on the maximum or 98th
percentile impacts, regardless of whether the Class I area was actually
experiencing high visibility impairment on any given day. Since CALPUFF
does not conduct an analysis considering all the emissions from all
potential sources, some of the days with the worst model-predicted
concentrations could be days that are not significantly impaired.
Reasonable progress modeling using a photochemical model, such as CAMx,
allows EPA to evaluate impacts from a source (with all other sources
included in the modeling) on a Class I area's best and worst days.\256\
---------------------------------------------------------------------------

    \255\ Proposed Texas Regional Haze FIP, 79 FR 74818, 74877,
74878.
    \256\ Id. at 74878.
---------------------------------------------------------------------------

    The draft EPA Modeling Guidance for Demonstrating Attainment of Air
Quality Goals for Ozone, PM2.5, and Regional Haze (Dec. 2014) (``Draft
Modeling Guidance'') discusses the use of photochemical grid models.
The Draft Modeling Guidance specifically notes that ``a modeling based
demonstration of the impacts of an emissions control scenario . . . as
part of a regional haze assessment usually necessitates the application
of a chemical transport grid model.'' \257\ Throughout the Draft
Modeling Guidance, the discussion is focused on items specific to
photochemical grid models such as CAMx, including emissions
inventories, supporting models, pre-processors, and applying a model to
changes in visibility.
---------------------------------------------------------------------------

    \257\ Draft Modeling Guidance at 22. The Draft Modeling Guidance
is available at http://www.epa.gov/scram001/guidance/guide/Draft_O3-PMRH_Modeling_Guidance-2014.pdf.
---------------------------------------------------------------------------

    Notably, EPA recently issued a proposal, which would remove CALPUFF
from EPA's preferred list of air dispersion models in its Guideline on
Air Quality Models \258\ (``Guideline''). Although EPA states that the
proposed changes to the Guideline would not affect its recommendation
that CALPUFF be used in the BART determination process, EPA made no
such assurances regarding the use of CALPUFF for a reasonable progress
analysis. EPA's proposal emphasizes the use of chemical transport
models for assessing visibility impacts from a single source or small
group of sources.
---------------------------------------------------------------------------

    \258\ Appendix W to 40 CFR part 51.
---------------------------------------------------------------------------

    EPA's Interagency Workgroup on Air Quality Modeling Phase 3 Summary
Report: Long Range Transport and Air Quality Related Values \259\ makes
clear that CALPUFF should not be used for a reasonable progress
analysis.
---------------------------------------------------------------------------

    \259\ Docket ID EPA-HQ-OAR-2015-0310-0004.
---------------------------------------------------------------------------

    Another commenter, EarthJustice, states that the other commenter's
assessment of the methodology used for Texas sources is incorrect. In
fact, EPA also used an emission ``scaling'' approach to determine the
effects of various control scenarios for their evaluation of Texas
sources that is

similar to that currently being applied for the evaluation of the
sources in Arkansas. EPA Region 6 did not run the CAMx model repeatedly
to determine the overall visibility effects of controlling individual
sources.
    Response: The commenters confuse the single source analysis for
evaluating the visibility impact and benefits of controls on units at
the Independence facility and the analysis to estimate the visibility
benefits of all controls on the 20% worst days in establishing a new
reasonable progress goal for 2018. We utilized CALPUFF modeling
following the same modeling protocol relied on for the BART analyses to
assess the visibility impacts and potential benefits of controls for
the units at the Independence facility. For estimating the total
visibility benefit from all controls and estimating a new reasonable
progress goal that reflects those controls, we relied on the CENRAP's
2018 CAMx modeling results, including source apportionment results, and
the projected emission inventories, and scaled the results as described
in the TSD. While we acknowledge that this approach is not as refined
an estimate as would be attained in performing a new photochemical
modeling run, it is based on scaling of earlier photochemical modeling
results and not on CALPUFF modeling, as the commenter suggests. We
disagree with the commenter's characterization of our analysis as a
``thumbnail'' approach and noted in our proposal that similar
approaches have been used in other actions in Hawaii and Arizona. As
discussed in the proposed action, our determination that controls were
reasonable for the Independence units was based on our evaluation of
the four factors and including consideration of the visibility benefit
of controls. For consideration of the visibility benefits, we relied on
the results of our CALPUFF modeling, the CENRAP CAMx source
apportionment results, and point source emission inventory data that
initially identified the Independence facility as having the greatest
potential to impact visibility at nearby Class I areas among all
sources not already controlled under the BART requirements.
    The 2005 BART Guidelines recommended the use of CALPUFF for
assessing visibility (secondary chemical impacts) but noted that
CALPUFF's chemistry was fairly simple. The visibility results from
CALPUFF could be used as one of the five factors in a BART evaluation
and the impacts should be utilized in a somewhat relative sense because
CALPUFF was not explicitly approved for full chemistry
calculations.\260\ The BART guidelines also provided the option to
potentially use photochemical grid models (such as CAMx) in the future
if modeling tools available were appropriate and EPA approved of the
technical approaches and how the model would be utilized.\261\ Appendix
W gives us discretionary authority in the selection of what models to
use for visibility assessments with modeling systems, and models such
as CALPUFF, CMAQ, REMSAD, and CAMx have all been used for that purpose.
Specifically for single-source reasonable progress assessments similar
to that done here for Independence, CALPUFF has been used for the
majority of sources, while CAMx has been used in some situations, most
notably and as noted by the commenter, in evaluating specific Texas
sources for reasonable progress. In 2006/7, EPA OAQPS and EPA Region 6
consulted with FLM representatives and approved Texas' BART screening
modeling protocol using source apportionment tools in CAMx.\262\
---------------------------------------------------------------------------

    \260\ 70 FR 39104, 39123, 39124. ``We understand the concerns of
commenters that the chemistry modules of the CALPUFF model are less
advanced than some of the more recent atmospheric chemistry
simulations. To date, no other modeling applications with updated
chemistry have been approved by EPA to estimate single source
pollutant concentrations from long range transport.'' and in
discussion of using other models with more advanced chemistry it
continues, ``A discussion of the use of alternative models is given
in the Guideline on Air Quality in appendix W, section 3.2.''
    \261\ 70 FR at 39123, 39124. ``The use of other models and
techniques to estimate if a source causes or contributes to
visibility impairment may be considered by the State, and the BART
guidelines preserve a State's ability to use other models. Regional
scale photochemical grid models may have merit, but such models have
been designed to assess cumulative impacts, not impacts from
individual sources. Such models are very resource intensive and time
consuming relative to CALPUFF, but States may consider their use for
SIP development in the future as they are adapted and demonstrated
to be appropriate for single source applications.''
    \262\ See Appendix 9-4: CAMx Modeling Protocol, Screening
Analysis of Potentially BART-Eligible Sources in Texas of the Texas
regional haze SIP.
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    Under the BART guidelines, CALPUFF should be used as a screening
tool and appropriate consultation with the reviewing authority is
required to use CALPUFF in a BART determination as part of a SIP or
FIP. The BART Guideline cited and referred to EPA's Guideline on Air
Quality Models (Appendix W) \263\ which includes provisions to obtain
approval through consultation with the reviewing authority. Moreover,
we also note that in EPA's document entitled Guidance on the Use of
Models and Other Analyses for Demonstrating Attainment of Air Quality
Goals for Ozone, PM2.5, and Regional Haze (EPA-454/B-07-
002), that Appendix W does not identify a particular modeling system as
`preferred' for modeling conducted in support of state implementation
plans under 40 CFR 51.308(b). A model should meet several general
criteria for it to be a candidate for consideration. These general
criteria are consistent with the requirements of 40 CFR 51.112 and 40
CFR 51, Appendix W. Therefore, it is correct to interpret that no model
system is considered `preferred' under 40 CFR 51, Appendix W, Section
3.1.1 (b) for either secondary particulate matter or for visibility
assessments. Under this general framework, we followed the general
recommendation in Appendix Y to use CALPUFF as a screening technique
since the modeling system has not been specifically approved for
chemistry. The use of CALPUFF is subject to Appendix W requirements in
section 3.0(b), 4, and 6.2.1(e) which includes an approved protocol to
use the current version.
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    \263\ 40 CFR part 51 Appendix W, Guideline on Air Quality
Models, 70 FR 68218 (November 9, 2005).
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    We and some states have used CALPUFF to model visibility benefits
as part of the reasonable progress analysis, and have used largely the
same methodology as in BART modeling (i.e. use of 24 hour or hourly
maximum emissions, a ``clean'' background condition, and a maximum or
98th percentile metric).\264\ This approach provides information on the
relative visibility benefits of controls to inform the evaluation of
cost-effectiveness as part of the four factor analysis and has the
benefit that it is immediately comparable to modeling used for BART
determinations. Compared to a CAMx modeling exercise, CALPUFF modeling
of one or more sources requires much less resources and time. However,
the CALPUFF approach models the impacts from the single facility with
limited chemistry and focuses on the maximum impacts from the source
rather than the visibility impairment on the 20% worst days. We agree
with the commenter that the CAMx model may be better suited for
evaluating the average visibility impairment due to individual sources
during the 20% worst days as part of reasonable progress analysis.
Photochemical models, like the CAMx model, provide a complete
representation of emissions, chemistry, transport, and deposition,
while CALPUFF treats a single source with simplified chemistry and
parameterized physical processes. Furthermore, the

CAMx model can be used to evaluate a large number of individual
sources, and there are concerns in using CALPUFF for modeling impacts
at distances much greater than 300 km from the source. In our analysis
of source-specific impacts of Texas sources, we determined that CAMx
was best suited for the complex analysis that we needed to perform in
evaluating a large number of sources (38 separate facilities for our
initial analysis) at distances from impacted Class I areas much larger
than 300km, and in focusing on the 20% worst days. We discuss our
selection of CAMx modeling in our Texas analysis in depth in the RTC
document that accompanies that action.\265\ As noted by EarthJustice,
we did not perform a final CAMx model scenario to obtain the new RPGs
in our Texas action, and instead relied on a scaling analysis similar
to the methodology used in this action to adjust the CENRAP modeled RPG
values based on the source apportionment data and emissions data
available. As discussed above, RPGs were adjusted in actions in
Arizona, Hawaii, Texas/Oklahoma and in this action by estimating the
visibility improvement due to required controls based on scaling the
anticipated emission reductions and the source apportionment modeling.
In Texas/Oklahoma, source-specific source apportionment data and
emissions were utilized. In the other states, emissions and source-
apportionment data on a state and source category level were utilized.
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    \264\ For example see summary of the reasonable progress
analyses for specific sources in Arizona (79 FR 9353), North Dakota
(76 FR 58631), Montana (77 FR 24065), and Wyoming (78 FR 34785).
    \265\ Texas Regional Haze FIP, EPA Response to Comments
Document, available at www.regulations.gov, Document ID: EPA-R06-
OAR-2014-0754-0087.
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    Consistent with the examples discussed above,\266\ in evaluating
the sources in Arkansas, we determined that CALPUFF was adequate since
we determined that only one source needed to be assessed for a
reasonable progress evaluation, and that source was well within the
recommended range for CALPUFF modeling of under 300km from the Class I
areas of interest. In fact, three of the four impacted Class I areas
lie within 200km of the source. We discuss comments concerning why our
reasonable progress screening analysis focused on NOX and
SO2 emissions from Arkansas point sources and our
determination that additional analysis was necessary for the
Independence facility in response to comments elsewhere in this
document. In evaluating visibility impacts and benefits for those
sources subject to BART, we relied on CALPUFF modeling prepared by the
facilities. Utilizing CALPUFF for the reasonable progress analysis on
Independence provided for a consistent approach for all facilities and
allowed for direct comparison of the visibility impacts and benefits
across all facilities impacted by the proposed rulemaking. In some
situations, the CALPUFF modeled maximum or 98th percentile impacts of
the facility may not coincide with the days that make up the worst 20%
monitored days at the Class I area. Therefore, the visibility benefits
modeled by CALPUFF are not directly comparable to the visibility
benefits that would be anticipated on the 20% worst days from those
specific controls. However, our analysis of the CENRAP 2018 CAMx
photochemical modeling showed that: On the 20% worst days, Arkansas
point sources contribute significantly to visibility impairment at
Arkansas' Class I areas (greater than 4% of total visibility impairment
at each Arkansas Class I area); review of the emission inventory
revealed that a very small number of point sources are responsible for
the majority of the point source emissions of NOX and
SO2 and therefore a very small number of point sources are
responsible for the portion of visibility impairment due to Arkansas
point sources on the 20% worst days; and the Independence facility is
one of the very largest emission sources and it is located relatively
close (under 200 km) to three Class I areas. Therefore, we identified
Independence as having the greatest potential to impact visibility on
the 20% worst days based on emissions and location and should be
evaluated for reasonable progress controls. We determined that CALPUFF
modeling was appropriate and sufficient to provide information on the
degree of visibility benefits of controls on Independence to inform the
reasonable progress assessment. Through our evaluation of the four
statutory factors, we identified cost-effective controls. We then
considered visibility benefits of the cost-effective controls. We
conducted CALPUFF modeling to determine the level of visibility impacts
and benefits anticipated by SO2 and NOX controls
at nearby impacted Class I areas, evaluating the 98th percentile
visibility impacts.\267\
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    \266\ For example see summary of the reasonable progress
analyses for specific sources in Arizona (79 FR 9321, 9353), North
Dakota (76 FR 58570, 58631 (September 21, 2011)), Montana (77 FR
23988, 24065 (April 20, 2012)), and Wyoming (78 FR 34738, 34785
(June 10, 2013)).
    \267\ See Summary of Additional Modeling for Entergy
Independence and Appendix C to the TSD.
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    As we discuss elsewhere in this final rule, Entergy submitted CAMx
model results as part of their comments. The modeled contribution to
visibility impairment due to baseline emissions from the Independence
facility alone were approximately 1.3% of the total visibility
impairment at each Arkansas Class I area. In terms of deciviews, the
average impact over the 20% worst days based on Entergy's CAMx modeling
(adjusting to natural background conditions) is over 0.5 dv at the
Arkansas Class I areas and even larger at the Class I areas in
Missouri. These results estimate the visibility impacts from the source
on the 20% worst days and confirm and provide additional support to our
determination that Independence significantly impacts visibility, both
in terms of maximum visibility impairment and visibility impairment on
the 20% worst days, and that emissions controls provide for meaningful
visibility benefits towards the goal of natural visibility conditions.
In conclusion, both approaches, CALPUFF and CAMx, support the
determination that the required controls are reasonable.
    The commenter cites the BART guidelines and asserts that EPA
recognizes that the CALPUFF model is overly simplistic and overstates
the effect of single-source emissions. This is not an accurate
characterization. EPA recognized the uncertainty in the CALPUFF
modeling results when EPA made the decision, in the final BART
Guidelines, to recommend that the model be used to estimate the 98th
percentile visibility impairment rather than the highest daily impact
value. We made the decision to consider the less conservative 98th
percentile primarily because the chemistry modules in the CALPUFF model
are simplified and likely to provide conservative (higher) results for
peak impacts. Since CALPUFF's simplified chemistry could lead to model
over predictions and thus be conservative, EPA decided to use the less
conservative 98th percentile.\268\ While recognizing the limitations of
the CALPUFF model in the preamble, EPA concluded that, for the specific
purposes of the Regional Haze Rule's BART provisions, CALPUFF is
sufficiently reliable to inform the decision making process.\269\ More
recent evaluations demonstrate that the CALPUFF model can both under-
predict and over-predict visibility impacts. For example, the 2012
ENVIRON report on

Comparison of Single-Source Air Quality Assessment Techniques for
Ozone, PM2.5, other criteria pollutants and AQRVs found that CALPUFF
predicted highest 24-hr nitrate and sulfate concentrations lower than
those predicted by the CAMx photochemical grid model in some areas
within the modeling domain.\270\ In a presentation for the 2010 annual
Community Modeling and Analysis System conference, Anderson et al.
(2010) \271\ found that the CALPUFF model frequently predicted lower
nitrate concentrations compared to the CAMx photochemical grid model
which has a much more rigorous treatment of photochemical reactions. As
we stated in promulgating the BART Guidelines, we are confident that
CALPUFF distinguishes, comparatively, the relative contributions from
sources such that the differences in source configurations, sizes,
emission rates, and visibility impacts are well-reflected in the model
results.\272\
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    \268\ ``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.''
    \269\ 70 FR at 39123.
    \270\ Comparison of Single[hyphen]Source Air Quality Assessment
Techniques for Ozone, PM2.5, other Criteria Pollutants
and AQRVs, ENVIRON, September 2012.
    \271\ Anderson, B., K. Baker, R. Morris, C. Emery, A. Hawkins,
E. Snyder ``Proof-of-Concept Evaluation of Use of Photochemical Grid
Model Source Apportionment Techniques for Prevention of Significant
Deterioration of Air Quality Analysis Requirements'' Presentation
for Community Modeling and Analysis System (CMAS) 2010 Annual
Conference, (October 11-15, 2010) can be found at http://www.cmascenter.org/conference/2010/agenda.cfm.
    \272\ 70 FR 39104, 39122.
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    With regard to comments concerning the draft EPA modeling Guidance
for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and
Regional Haze (Dec. 2014), the commenter confuses the single-source
analysis to evaluate visibility impacts and benefits of controls on an
individual source with the analysis of overall visibility conditions at
a Class I area due to the complete emission control strategy for all
sources developed under the reasonable progress and long-term strategy
requirements. The draft modeling guidance (as does the current guidance
\273\) discusses the projection of overall visibility conditions and
the need for photochemical grid modeling to account for all emission
sources to model current visibility conditions and project future
visibility conditions in response to the overall emission control
scenarios. The section of the modeling guidance on regional haze \274\
describes the recommended modeling analysis to assess overall future
visibility improvement relative to the uniform rate of progress or
``glidepath'' (for each Class I area) as part of a reasonable progress
analysis, and does not discuss source-specific analyses that may be
completed to inform a reasonable progress assessment.\275\ Because the
CALPUFF model only evaluates visibility impacts from a single-source or
a limited group of sources, it is not capable of projecting overall
visibility conditions due to all sources and controls. Consistent with
this draft guidance and the current guidance, CENRAP and Arkansas
utilized CAMx and CMAQ modeling to project future visibility conditions
for 2018 for establishment of the RPGs and comparison with the URP.
Similarly, we utilized the CENRAP CAMx model results and adjusted them
based on source apportionment and emissions data, to estimate the new
RPGs for the Arkansas Class I areas considering the anticipated changes
in emissions due to all required controls. We discuss the selection of
models for assessing individual visibility impacts and benefits of
controls above.
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    \273\ 2007 EPA modeling Guidance for Demonstrating Attainment of
Air Quality Goals for Ozone, PM2.5, and Regional Haze.
    \274\ Draft EPA modeling Guidance for Demonstrating Attainment
of Air Quality Goals for Ozone, PM2.5, and Regional Haze
(December 2014) Section 4.8 ``What Is The Recommended Modeling
Analysis for Regional Haze?''
    \275\ Draft EPA modeling Guidance for Demonstrating Attainment
of Air Quality Goals for Ozone, PM2.5, and Regional Haze (December
2014) at 173: ``The modeling can be used to determine the predicted
improvement in visibility and whether the visibility levels are on,
above, or below the glidepath. It cannot by itself determine the
reasonable progress goals or determine whether the reasonable
progress goal is met, and it does not satisfy the requirements for
the statutory four factor analysis. See the Regional Haze Rule and
related guidance documents for more information on the four factor
analysis, including control strategy analysis for single sources.''
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    The commenters cite to the proposed revisions to the Guideline on
Air Quality Models (Appendix W) \276\ and the IWAQM Phase 3 modeling
report \277\ and assert that they support the conclusion that the use
of CALPUFF for Independence was inappropriate. We disagree with the
commenter. As we discuss above, we agree with the commenter that the
CAMx model, may be better suited for a reasonable progress analysis in
certain situations. Proposed revisions to Appendix W discuss removing
the requirement to use CALPUFF for long-range transport assessments and
as a preferred model due to the need to provide flexibility in
estimating single-source secondary pollutant impacts and concerns about
management and maintenance of the CALPUFF modeling code.\278\ These
proposed changes do not affect EPA's recommendation that States use
CALPUFF to determine the applicability and level of BART in regional
haze implementation plans. The proposed changes also do not preclude
the use of CALPUFF for any other non-BART analysis, such as long-range
transport PSD increment assessment, but recognize that modern chemical
transport models have evolved sufficiently and provide a credible
platform for estimating potential visibility impacts from a single or
small group of emission sources.\279\ The proposed Appendix W rule
simply proposes to remove CALPUFF as a preferred model. If the proposed
changes are finalized, CALPUFF or any other model can still be used for
non-BART analyses with the appropriate justification as an
``alternative model''.
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    \276\ 80 FR 45340 (July 29, 2015).
    \277\ Interagency Workgroup on Air Quality Modeling Phase 3
Summary Report: Long Range Transport and Air Quality Related Values.
    \278\ 80 CFR 45340, 45349: ``In order to provide the user
community flexibility in estimating single-source secondary
pollutant impacts and given the availability of more appropriate
modeling techniques, such as photochemical transport models (which
address limitations of models like CALPUFF [37]), the EPA is
proposing that the Guideline no longer contain language that
requires the use of CALPUFF or another Lagrangian puff model for
long-range transport assessments. Additionally, the EPA is proposing
to remove the CALPUFF modeling system as an EPA-preferred model for
long-range transport due to concerns about the management and
maintenance of the model code given the frequent change in ownership
of the model code since promulgation in the previous version of the
Guideline. [38] The EPA recognizes that long-range transport
assessments may be necessary in certain limited situations for PSD