Document ID: EPA-R05-OAR-2015-0700-0022
Agency: epa
Document Type: Rule
Title: Final Approval of the Indiana Attainment Plan for the Southwest Indiana SO2 Nonattainment Area
Posted Date: 2020-08-17T04:00Z

[Federal Register Volume 85, Number 159 (Monday, August 17, 2020)]
[Rules and Regulations]
[Pages 49967-49975]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-16044]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R05-OAR-2015-0700; FRL-10012-09-Region 5]

Air Plan Approval; Indiana; Attainment Plan for the Southwest 
Indiana Sulfur Dioxide Nonattainment Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is approving as a 
State Implementation Plan (SIP) revision to the Southwest Indiana-
related elements of an Indiana submission to EPA dated October 2, 2015, 
as supplemented on November 15, 2017 and September 18, 2019. EPA 
concludes that Indiana has appropriately demonstrated that the plan 
provides for attainment of the 2010 sulfur dioxide (SO2) 
primary National Ambient Air Quality Standard (NAAQS) in the Southwest 
Indiana area by the applicable attainment date and that the plan meets 
the other applicable requirements under the Clean Air Act.

DATES: This final rule is effective on September 16, 2020.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-R05-OAR-2015-0700. All documents in the docket are listed on 
the www.regulations.gov website. Although listed in the index, some 
information is not publicly available, i.e., Confidential Business 
Information (CBI) or other information whose disclosure is restricted 
by statute. Certain other material, such as copyrighted material, is 
not placed on the internet and will be publicly available only in hard 
copy form. Publicly available docket materials are available through 
www.regulations.gov, or please contact the person identified in the FOR 
FURTHER INFORMATION CONTACT section for additional availability 
information.

FOR FURTHER INFORMATION CONTACT: John Summerhays at EPA Region 5, 
Attainment Planning and Maintenance

[[Page 49968]]

Section, Air Programs Branch (AR-18J), Environmental Protection Agency, 
Region 5, 77 West Jackson Boulevard, Chicago, Illinois 60604, (312) 
886-6067, summerhays.john@epa.gov.

SUPPLEMENTARY INFORMATION:

I. Summary of EPA's Notices of Proposed Rulemaking

    Following the promulgation in 2010 of a 1-hour primary 
SO2 NAAQS, on August 5, 2013, at 78 FR 47191, EPA designated 
an area in Southwest Indiana that included a township in each of 
Daviess and Pike Counties, Indiana as nonattainment for this NAAQS, in 
conjunction with designating three other areas in Indiana and multiple 
areas in other states as nonattainment. On October 2, 2015, the Indiana 
Department of Environmental Management (``Indiana'') submitted plans 
addressing all four of its SO2 nonattainment areas. EPA has 
taken separate action on Indiana's plans for its other nonattainment 
areas: EPA published final action on plans for the Indianapolis and 
Terre Haute areas on March 22, 2019, at 84 FR 10692, and published 
final action on the plan for the Morgan County area on September 23, 
2019, at 84 FR 49659.
    In addition to its October 2, 2015 submittal, Indiana made a 
supplemental submittal on November 15, 2017, providing clarifications 
on its inventory procedures and other elements of its four 
nonattainment plans. EPA published a proposed rule proposing to approve 
three of these plans (for the Southwest Indiana, Indianapolis, and 
Terre Haute areas) on August 15, 2018, at 83 FR 40487.
    In response to that proposed rule, EPA received comments objecting 
to, among other things, the manner in which Indiana calculated an 
adjustment to the level of the 30-day average limit for Indianapolis 
Power and Light's Petersburg power plant (IP&L-Petersburg or ``the 
facility''). These comments prompted Indiana to recalculate the 
adjustment factor used to determine the appropriate limits for this 
facility, resulting in the adoption of revised limits and submittal of 
these revised limits on September 18, 2019. Indiana also provided an 
email on November 19, 2019 clarifying the interrelationship between the 
commissioner's order containing the revised limits and the provisions 
in Indiana regulations, both of which Indiana requested be incorporated 
into the Indiana SIP.
    On February 24, 2020, at 85 FR 10350, EPA published a supplementary 
proposed rule addressing Indiana's revised plan. This action evaluated 
Indiana's revised 30-day average limits and the recalculated adjustment 
factor used to determine those limits. The original submittal relied on 
modeling to determine 1-hour emission limits that would provide for 
attainment (expressed in pounds per million British Thermal Units 
(MMBTU), known as critical emission rates), and imposed 30-day average 
limits determined by multiplying these 1-hour rates by 80 percent. 
Indiana's reevaluation concluded that a more appropriate adjustment 
factor was 68 percent. Indiana made no change to its modeling; its 
revised 30-day average limits reflect only this change in adjustment 
factor. Therefore, the supplemental proposed rule solicited comments 
only on this change to Indiana's plan.

II. Comments

    In response to its proposed rule of August 15, 2018, EPA received 
relevant comments from Sierra Club addressing the reliance on 30-day 
average emission limits for Indianapolis Power and Light's Petersburg 
power plant (IP&L-Petersburg). EPA also received two anonymous comments 
that address subjects outside the scope of our proposed action, do not 
explain (or provide a legal basis for) how the proposed action should 
differ in any way, and make no specific mention of the substantive 
aspects of the proposed action. Consequently, these comments are not 
germane to this rulemaking and require no further response. EPA 
received no comments on its supplemental proposed rule of February 24, 
2020.
    As noted above, Sierra Club had numerous comments on the 
calculation of the adjustment factor used to determine the original 30-
day average limits, which resulted in Indiana recalculating the 
adjustment factor and adopting revised limits, and which EPA then 
discussed in a supplemental notice of proposed rulemaking (NPRM). 
Consequently, some of Sierra Club's comments on the original Indiana 
submittal are either moot or have been subject to an additional 
solicitation of comments in light of the additional relevant available 
information. EPA received no comments on this supplemental NPRM. The 
following responses to Sierra Club's comments will identify the extent 
to which comments on specific aspects of Indiana's calculations of 30-
day average limits for IP&L-Petersburg are still germane.
    Comment: Sierra Club notes the health effects from exposure to 
SO2 ``in even very short time periods--such as five 
minutes.'' Sierra Club expresses concern that IP&L-Petersburg's 30-day 
average limit will allow spikes in emissions that cause spikes in 
concentrations sufficient to yield violations of the 1-hour air quality 
standard.
    Response: EPA believes that Indiana's establishment of a 30-day 
average limit at a lower level than the 1-hour limit indicated to be 
necessary by modeling will avoid some of the exceedances that would be 
expected with emissions constantly at the modeled level, such that the 
net effect of Indiana's lower, longer term average limit is to have 
similar air quality as would be expected with a 1-hour limit. Further 
discussion of this topic is provided below in response to more detailed 
comments. Sierra Club properly focuses on whether Indiana's plan 
provides for attainment of the 1-hour standard, and not on the shorter 
term (e.g., five minutes) exposures that the standard is designed in 
part to address. Nevertheless, EPA notes that suitably adjusted long 
term limits can be expected to provide adequate mitigation of even the 
shorter (sub-hour) exposures to SO2, for the same reasons 
that such limits suitably address the 1-hour standard.
    Comment: Sierra Club observes that EPA's April 2014 guidance \1\ 
acknowledges that EPA historically has required averaging times 
consistent with the averaging time of the standard, and specifically 
stated that EPA would not approve plans relying solely on 30-day 
average limits. Sierra Club cites other EPA statements that short term 
standards must be addressed with short term average limits. Sierra Club 
equates a 30-day average limit to a 720-hour average limit, and states 
that a 720-hour limit would not sufficiently limit hourly emissions to 
protect against violations of the air quality standard ``unless it was 
shown through air dispersion modeling that the maximum uncontrolled 
hourly emissions from a source'' would not result in violation of the 
standard. Sierra Club notes that Table 8-1 of EPA's modeling guideline 
``requires modeling for short term [standards] be based on the 
allowable emissions over the averaging time of the [standard].'' Sierra 
Club asserts that ``the maximum allowable hourly emission rate is 
difficult to predict from a 30-day average limit.''
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    \1\ See ``Guidance for 1-Hour SO2 Nonattainment Area 
SIP Submissions,'' available at https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf.
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    Response: The EPA statements that Sierra Club cites predate the 
2014 guidance, and thus reflect a time when EPA had not yet conducted 
the analyses and completed evaluation of methods

[[Page 49969]]

for formulating longer term average limits that would provide for 
attainment of a 1-hour air quality standard. Now that EPA has completed 
this work, the 2014 guidance, for purposes of implementing the 2010 
SO2 NAAQS, supersedes prior guidance on the topic.
    Sierra Club cites the requirement in EPA's modeling guideline \2\ 
to model the allowable emission rate based on a short term limitation, 
but does not address the guidance in appendix A of EPA's 2014 guidance 
(entitled ``Modeling Guidance for Nonattainment Areas''), which states 
that notwithstanding the orientation of Table 8-1 toward short term 
emission limits, ``current guidance . . . provides that after the state 
determines the 1-hour limit that would be necessary to provide for 
attainment, any longer term limit should be established at a level that 
is sufficiently lower to provide comparable stringency. Thus, in cases 
where a state wishes to apply a longer term average limit, the 
attainment analysis would be based not on the level of the longer term 
limit but rather on the level of the corresponding 1-hour emission 
limit.'' See page A-79 of EPA's 2014 guidance. This recommended 
approach avoids the unnecessary burden of defining an ensemble of 
variable emissions that may be considered to reflect allowable 
emissions and the burden of conducting a modeling analysis with such an 
inventory. Instead, EPA recommends relying on standard modeling 
approaches, as if a short-term limit were to be established. For 
reasons described in the guidance and described in more detail in the 
August 15, 2018 NPRM, EPA believes that a longer term limit that is 
determined to have comparable stringency to the corresponding 1-hour 
limit (generally, by applying an adjustment factor computed according 
to recommended methods) will yield comparable air quality (i.e., 
comparable assurance that the standard will not be violated) as the 1-
hour limit. For that reason, and for ease of implementation, EPA does 
not believe that an assessment of the range of emissions expected upon 
compliance with a long-term limit or an assessment of the associated 
air quality is warranted or necessary.
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    \2\ Title 40 Code of Federal Regulations part 51 appendix W, 
entitled ``Guideline on Air Quality Models.''
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    Comment: Sierra Club asserts that ``ambient air quality conditions 
can be rendered unsafe by as few as four hours of elevated emissions 
over the course of a year.''
    Response: Indiana, by imposing a 30-day average limit on IP&L-
Petersburg's emissions determined in accordance with EPA's guidance, 
allows a small number of occasions to have emissions above the critical 
emissions value but requires most occasions to have emissions well 
below this level, indeed requiring emissions on average to be 32 
percent below the critical emissions value. In modeling constant 
emissions, as in routine modeling to assess whether a particular set of 
1-hour emissions limits would provide for attainment, one makes no 
assessment of the impact of emissions sometimes being higher and other 
times being lower than the constant emission level. Sierra Club 
addresses only the occasions with higher emissions, noting their 
potential to result in exceedances beyond those expected with emissions 
always at the critical emissions value, thereby yielding a violation of 
the standard. However, Sierra Club does not address the impact of 
emissions generally being well below the critical emissions value. 
Thus, Sierra Club does not consider the likelihood that the more 
numerous occasions of emissions well below the critical emissions 
value, mandated by the downward adjusted longer term average emissions 
limit, would result in avoiding some of the exceedances that would be 
expected with emissions always at the critical emissions value. EPA 
does not dispute Sierra Club's contention that occasions with emissions 
above the critical emissions value create added risk of exceedances of 
the air quality standard (if these occasions occur when the meteorology 
is conducive toward high concentrations at locations where violations 
might occur), but Sierra Club does not dispute or otherwise address 
EPA's contention that other occasions with emissions well below the 
critical emissions value, which the downward adjusted 30-day average 
limit requires to occur often, can be expected to yield a compensating 
reduction in the frequency of concentrations above the level of the 
standard. As explained in the NPRM, EPA believes that the net effect of 
a properly downward adjusted longer-term limit is comparable to the 
effect of a corresponding 1-hour emission limit and provides equally 
for attainment.
    Comment: Sierra Club asserts that Indiana's modeling analysis, 
which does not directly assess emissions allowed by a long-term average 
emission limit, is contrary to the regulatory requirements in 40 CFR 
51.112(a). Separately, Sierra Club objects to EPA's assertion that the 
plan need not provide ``absolute certainty that attainment will in fact 
occur'' and that the plan need only provide ``an adequate level of 
confidence of prospective [attainment of the standard].'' Sierra Club 
quotes from Clean Air Act section 172(c)(1), that attainment plans 
``shall provide for attainment of the national primary ambient air 
quality standards.'' [Emphasis in comments.] Sierra Club concludes that 
``EPA has much more responsibility than just ensuring a plan provides 
`an adequate level of confidence' '' of attainment.
    Response: The requirement in 40 CFR 51.112(a) is that ``[e]ach plan 
must demonstrate that the measures, rules, and regulations contained in 
it are adequate to provide for the timely attainment and maintenance of 
the national standard that it implements.'' In this case, Indiana has 
conducted modeling to identify 1-hour emission limits that would 
provide for attainment. Indiana then provided an analysis of the degree 
of adjustment needed for 30-day average limits to be comparably 
stringent to those 1-hour limits, and Indiana adopted these 30-day 
average limits. Because Indiana has conducted a suitable analysis of 
appropriate 1-hour limits and suitably analyzed and adopted the 30-day 
average limits that are comparably stringent, EPA believes that Indiana 
has suitably demonstrated that the 30-day average limits in its plan 
are adequate to provide for timely attainment of the SO2 
standard, thereby satisfying the requirement of 40 CFR 51.112(a).
    Sierra Club has accurately quoted the requirement in the Clean Air 
Act for attainment plans to provide for attainment. Evidently Sierra 
Club believes that this requirement would have been met with 1-hour 
limits, despite the possibility that future violations might occur if, 
for example, future meteorology differs in unforeseeable ways from the 
historic meteorology analyzed in planning. EPA believes that the 30-day 
average limits adopted by Indiana provide comparable assurance of 
attainment as would have been provided by the 1-hour limits that 
Indiana would otherwise have relied on, and thus equally as well 
satisfy the requirement that, in all reasonably foreseeable 
circumstances, the plan provides for attainment.
    Comment: Sierra Club believes that the modeling analysis in 
appendix B of EPA's 2014 guidance does not suffice to demonstrate that 
30-day average limits at IP&L-Petersburg or elsewhere can protect 
against violations of the SO2 standard as well as 1-hour 
limits. Sierra Club believes that the appendix B analysis, by assuming 
a fixed distribution among stacks at the facility and assuming no 
changes in stack parameters pursuant to the addition of

[[Page 49970]]

emission controls, does not properly address the multi-stack situation 
at IP&L-Petersburg. Sierra Club objects further that the analysis in 
appendix B, by using an inventory of how the source would actually emit 
under a 30-day average limit, is not comparable to an analysis using 
the maximum permissible emissions under a 1-hour emission limit.
    Response: The differences between the plant modeled for appendix B 
(Canadys) and IP&L-Petersburg are not persuasive reasons to believe 
that the results found for Canadys would not also apply to IP&L-
Petersburg. There is no question that modeling to identify suitable 1-
hour emission limits must be done on a source-specific basis, 
considering the site-specific configurations of stacks, stack 
parameters (reflecting any influence of controls on those stack 
parameters), and other source-specific factors such as meteorology, 
terrain, and dimensions of nearby buildings. However, appendix B 
reflects a premise that a source-specific critical emission value 
(i.e., a candidate value for a 1-hour emission limit) has been 
identified. Appendix B addresses instead whether a 30-day average limit 
that reflects an adjustment in accordance with appendix C of EPA's 
guidance can be expected to result in attainment as well as imposition 
of a 1-hour limit at the critical emission value. The two scenarios 
addressed in appendix B (with and without a scrubber) reflect 
adjustment factors of 68 percent and 69 percent, respectively. Thus, 
the issue being addressed by appendix B is whether a 30-day average 
limit reflecting such adjustments (determined based on a source-
specific measure of variability) can be expected to ensure attainment 
as well as the corresponding 1-hour limit. EPA believes that this 
comparison between air quality with an adjusted 30-day average limit 
and air quality with the corresponding 1-hour limit applies to a broad 
range of circumstances. In particular, EPA believes that longer term 
limits established in accordance with EPA's guidance can provide for 
comparable air quality as the analogous 1-hour limits for a broad range 
of plants with various numbers of stacks, with various stack 
parameters, and with a broad range in the absolute magnitude of the 1-
hour limits that are necessary to assure attainment.
    Sierra Club is correct that the modeling described in appendix B 
for emissions in compliance with 30-day average limits is not directly 
comparable to the modeling that was done in establishing a suitable 1-
hour limit. As Sierra Club notes, modeling for the 30-day average limit 
scenarios reflected the expected distribution of emissions in 
compliance with such a limit, inherently reflecting a margin of 
compliance that sources routinely have at most times, whereas the 
modeling for the 1-hour limit scenarios reflected no such margin of 
compliance (i.e., these runs reflected emissions always at the 1-hour 
limit).
    To address this comment, EPA performed additional analyses designed 
to identify emission profiles with average emissions equal to the 
presumptive 30-day average limit and to estimate the air quality that 
would result. These analyses are described in detail in a document 
entitled ``Supplemental Assessment of the Air Quality Consequences of 
Applying Adjusted Long Term Average Emission Limits,'' which is 
included in the docket for this action.
    The emission profiles used in this supplemental assessment were 
generally based on the actual emissions variations found in the 30-day 
periods having 99th percentile level average emissions. Profiles were 
developed for two plants with limits established in recent attainment 
plans for 2010 SO2 nonattainment areas: IP&L-Petersburg 
(Unit 3) and Cardinal (Unit 1), a comparably large power plant in 
Jefferson County, Ohio. In each case, the analyses used data for a 
suitable period (3 years for IP&L-Petersburg and 5 years for Cardinal) 
during which the sources were complying with the attainment-level 
emission limit adopted by the state. Calculations were performed in 
accordance with appendix C of the 2014 guidance to determine the 99th 
percentile 30-day average emission rates and to determine appropriate 
adjustment factors to be applied in determining 30-day average emission 
limits. These calculations were performed separately on a pound per 
hour basis and on a pound per MMBTU basis, supporting identification of 
two actual emission profiles for each plant, one reflecting emission 
variations in the 30-day period with approximately the 99th percentile 
pound per hour value and one reflecting emission variations in the 30-
day period with approximately the 99th percentile pound per MMBTU 
value. Since the analysis used the modeling information for a separate 
plant (Canadys), the analyses used the critical emission value 
identified in that modeling. Allowable emissions (as a 30-day average) 
were calculated by multiplying this critical emission value by the 
applicable adjustment factor. Allowable emission profiles were then 
developed by scaling the actual emission profiles to the allowable 
level, i.e., multiplying the emissions for each hour times the ratio of 
the allowable emissions against the average emissions in the actual 
profile, as well as by substituting the allowable emission value for 
any time the plant was not operating in the actual profile period. 
These allowable emission profiles were applied repeatedly, in the first 
30 days and every successive 30 days, with the result that every 30-day 
period in the 5-year analysis had average emissions equal to the 
allowable emissions level.
    One of these profiles, namely for the 99th percentile pound per 
MMBTU profile at IP&L-Petersburg, included a brief period with 
exceptionally high emissions, reflecting minimal if any flue gas 
desulfurization. Based on the uniqueness of these emissions during this 
timeframe, EPA does not believe that such a profile, recurring every 30 
days, is a realistic representation of emission variations that 
routinely occur. The supplemental assessment document identified above 
provides further rationale for treating this as an unrepresentative 
profile, including evidence that such exceptional emissions are much 
more rare in practice, engineering reasons that such operation is prone 
to be damaging to the plant, and policy reasons that recurring 
occasions of exceptionally high emissions would be contrary to guidance 
to minimize the frequency and magnitude of occasions with emissions 
above the critical emissions value. Therefore, for this assessment, EPA 
replaced that profile with a profile based on emissions for the 30-day 
period with approximately the 98th percentile 30-day average pound per 
MMBTU value.
    The results of this assessment are shown in Table 1. For each of 
the four profiles, the resulting air quality is somewhat below the air 
quality standard. Since these profiles reflect allowable emissions at 
all times, these results may be compared to the results of modeling 
allowable emissions under the corresponding 1-hour limit (i.e., 
modeling emissions constantly at the critical emission value). Thus, 
this assessment supports a conclusion similar to the conclusion from 
appendix B, that establishment of a long term average emissions limit 
estimated to have comparable stringency to the corresponding 1-hour 
emission limit (calculated in accordance with the guidance in A C) can 
be expected to result in comparable air quality, and that such a limit 
provides comparable assurance of attainment.

[[Page 49971]]

       Table 1--Design Values Estimated for Each Emission Profile
------------------------------------------------------------------------
                                                           Design value
                         Profile                            ([micro]g/m
                                                            \3\ (ppb))
------------------------------------------------------------------------
Cardinal #/hour.........................................    181.2 (69.2)
Cardinal #/MMBTU........................................    190.6 (72.8)
Petersburg #/hour.......................................    156.3 (59.7)
Petersburg 98th %-ile #/MMBTU...........................    190.5 (72.7)
------------------------------------------------------------------------

    Comment: Sierra Club asserts that ``[n]either Indiana nor EPA 
evaluated the reasonably available control measures that could be 
utilized'' at IP&L-Petersburg. Sierra Club highlights a consultant's 
evaluation of such measures at this plant, as reported to the Indiana 
Utility Regulatory Commission. Sierra Club identifies several of the 
measures identified in this consultant's evaluation, and states that 
``EPA cannot justify allowing a 30-day average limit . . . without 
considering all reasonably available control measures.''
    Response: EPA guidance for implementing the SO2 NAAQS 
advises that a plan that provides for attainment may be considered to 
have implemented all reasonably available control measures. EPA 
believes that the 30-day average limits in Indiana's plan provide for 
attainment as well as would have been provided by 1-hour limits. 
Therefore, EPA believes that use of these 30-day average limits does 
not create a need for requirements for specific control measures 
(beyond the requirements inherent in the emission limit) that would not 
apply with the use of 1-hour limits. While the measures evaluated in 
the consultant's report may be useful approaches for the company to 
comply with Indiana's emission limits, EPA does not believe that 
approval of Indiana's plan should be contingent on Indiana adopting 
requirements for any of these specific measures.
    Comment: Sierra Club objects that Indiana ``did not conduct a unit-
specific analysis in determining emissions variability.'' Sierra Club 
believes that Indiana is not justified in evaluating emissions 
variability only for the FGD stack \3\ for Unit 2, rather than 
examining variability of emissions for all four units at IP&L-
Petersburg and including emissions from the bypass stacks (as 
applicable at Units 1 and 2). Sierra Club notes, in particular, that 
neither the 30-day average limits nor any other requirement will ensure 
that emissions from the bypass stacks will not occur. Sierra Club notes 
that the units differ significantly, as they use scrubbers of different 
vintages and these scrubbers have been upgraded recently, so that 
Indiana may not assume that the variability of the FGD stack emissions 
at Unit 2 in the period from 2006 to 2010 is representative of either 
the variability of emissions of the other three units at that time or 
of the variability of emissions that can be expected for any of the 
four units once the units meet the proposed SIP limits. Sierra Club 
thus implies that the data Indiana used are not appropriate for 
determining the degree of adjustment warranted for all four units for 
an attainment plan for this area.
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    \3\ The ``FGD stack'' refers to the stack that vents emissions 
from the unit's control device, and thus represents controlled 
emissions. The bypass stack vents the emissions from the unit when 
the control device is not controlling emissions properly.
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    Response: In response to this comment, Indiana provided further 
explanation of its reliance on data from the Unit 2 FGD stack, namely 
that these data, by exclusively reflecting controlled emissions and 
reflecting more stable control equipment operation than Unit 1, provide 
the best data set for representing the distribution of emissions for 
all four units once Indiana's limits take effect. An extensive 
discussion of Indiana's rationale is provided in the February 24, 2020 
supplemental NPRM, on which Sierra Club did not comment. Furthermore, 
additional analyses of variability at all four units at IP&L-Petersburg 
that were described in the supplemental NPRM provide additional support 
for EPA's belief that the 2006 to 2010 data for the Unit 2 FGD stack 
provide an appropriate data base for anticipating the variability that 
has in fact occurred in the time after Indiana's limits took effect. In 
absence of comments on this additional explanation, EPA maintains that 
Indiana's adjustment factor, based on 2006 to 2010 data for the FGD 
stack at Unit 2, is appropriate.
    Comment: Sierra Club notes that EPA's guidance recommends that 
variability analyses be based on ```an adequately robust data' with at 
least `3 to 5 years of stable data (without changes that significantly 
altered emissions variability)'.'' Sierra Club believes that the data 
set for IP&L-Petersburg's Unit 2 FGD stack does not meet these 
criteria. Sierra Club notes significant variability from year to year 
in the maximum 30-day average emissions (in pounds per hour) and 
emission rate (in pounds per MMBTU), which was permissible given the 
absence of a constraining emission limit. Sierra Club further notes 
that the emissions from the Unit 2 FGD stack were below Indiana's 
proposed 30-day average proposed SIP limit for two of the five years 
included in Indiana's analysis, yet even in those years those emissions 
(not including bypass stack emissions) exceeded the critical mass 
emissions value in 82 and 99 hours (in 2007 and 2008, respectively).
    Response: The February 24, 2020 supplemental NPRM addresses most of 
these comments. In particular, the supplemental action provided 
additional rationale for the use of historic data from the Unit 2 FGD 
stack for assessing the expected variability of emissions at all four 
units at IP&L-Petersburg, and the supplemental action described EPA's 
analysis of more recent data that help confirm Indiana's forecast of 
variability and that indicate that the three units that are complying 
with the revised limits are emitting above the critical emissions value 
less than one percent of the time. Because EPA received no comments on 
this supplemental action, EPA considers the supplemental information to 
address these comments on the initial NPRM.
    The supplemental NPRM did not address the portion of this comment 
that argued that year-to-year variability in emissions, expressed in 
terms of year-to-year variations in the maximum 30-day average pound 
per hour and pound per MMBTU, is too great to consider the 2006 to 2010 
period to be a period of stable operation with respect to emissions 
from the Unit 2 FGD stack. That portion of the comment is addressed 
here.
    The purpose of the relevant portion of EPA's guidance is to 
determine variability based on a data set that best reflects the degree 
of variability that can be expected once the facility complies with the 
limits in the plan. A data set with significant changes in control 
levels (e.g., two years of uncontrolled emissions and two years of well 
controlled emissions) would either (at the 99th percentile level) be 
dominated by the two years of uncontrolled emissions data or give a 
distorted picture of variability, thus giving results that are either 
insufficiently robust or misleading.
    However, Sierra Club has made no argument that the control regime 
for the Unit 2 emissions that are vented through the FGD stack changed 
during the 2006 to 2010 period. Instead, Sierra Club is effectively 
arguing that routine operation of the control equipment during that 
period results in significant variations in emissions from year to 
year. EPA expects year-to-year differences in plant operations, and 
indeed EPA seeks to include that variability in its recommended 
approach to assessing the appropriate degree of adjustment of longer-
term limits. Indeed, EPA's analysis of post-control data described in 
the supplemental NPRM suggests that the multi-year variability of 
current

[[Page 49972]]

emissions is similar to the multi-year variability of Unit 2 FGD stack 
emissions in 2006 to 2010. ``Stable operation'' cannot be defined as 
operation without year-to-year variations; such a definition would 
defeat the purpose of forecasting the variability in emissions that can 
be expected into the future once the SIP control strategy is 
implemented. If anything, Sierra Club's comment highlights the 
importance of using the entirety of a multi-year data base (EPA 
recommends at least three to five years) for determining the relative 
stringency of a long term average limit as compared to a 1-hour limit, 
for a period with a stable control regime such as was the case here.
    Comment: Sierra Club objects that Indiana did not evaluate whether 
limits with an intermediate averaging period (e.g., 24 hours) might be 
more appropriate or whether supplemental limitations on peak hourly 
emissions might be warranted. Sierra Club provided statistics for each 
of the four units on the number of days since the limits took effect 
(using data from January 1, 2017 to June 30, 2018) during which at 
least one hour exceeded the critical emission rate, despite the four 
units all complying with Indiana's 30-day average emission limits. For 
Units 1 through 4 during that one and one half year period, Sierra Club 
noted 63 days, 138 days, 9 days, and 22 days, respectively, with at 
least one hour having more emissions than the unit's critical emissions 
value, representing respectively 11.5 percent, 25.3 percent, 1.7 
percent, and 4.0 percent of the days in that period. Sierra Club 
further notes eight hours during which total SO2 emissions 
exceeded the sum of the four units' critical emissions values (in 
approximate terms, a plant-wide critical emissions value). Sierra Club 
concludes that Indiana's 30-day average limits cannot be considered 
comparably stringent to 1-hour limits at the critical emissions value, 
that modeling of the critical emissions value does not suffice to 
demonstrate that the 30-day average limits provide for attainment, and 
that supplemental limits must be imposed to assure that ``actual 
occurrences of hourly emission rates above the critical emissions 
values will only occur on `rare' occasions.''
    Response: EPA's initial NPRM concluded that Indiana's 30-day 
average limits appeared to be sufficiently stringent to constrain 
hourly emissions to be only rarely above the critical emissions values, 
without the need for supplemental limits. The same logic would suggest 
that the use of limits with an intermediate averaging time such as 24 
hours is also not necessary to assure that hours with emissions above 
the critical emissions value will be rare.
    EPA's initial NPRM reported the results of an examination of five 
years of data from Unit 2 from before Indiana's limits took effect, 
noting that the unit exceeded the 30-day average limit for about seven 
percent of the averages and that the unit exceeded the critical 
emissions value for about six percent of the hours. Sierra Club uses a 
data set for 18 months starting when Indiana's limits took effect, 
which is a data set that is more indicative of operation in accordance 
with the limits in Indiana's plan. Sierra Club also examined data for 
all four units. Finally, EPA's supplemental NPRM, on which Sierra Club 
did not comment, reviewed the data for a 30-month period starting when 
Indiana's limits took effect. Specifically, for this 30-month period, 
Units 1, 3, and 4 complied with their revised 30-day average limits and 
had hourly emissions above the critical emissions value (i.e., the 
modeled mass emissions in pounds per hour) for 0.9 percent, 0.1 
percent, and 0.4 percent of the hours, respectively. Unit 2 exceeded 
its revised limit 17 percent of the 30-day averages, while exceeding 
the critical emission value 3 percent of the time. This suggests that 
the necessary improvements in scrubber efficiency at Unit 2 would 
likely yield a percentage of hours with emissions above the critical 
emission value that is similar to the percentages found for the three 
units that are already complying with limits. In absence of comments on 
this information, EPA continues to believe that Indiana's 30-day 
average limits are sufficient to constrain emissions to be only rarely 
above the critical emissions value, even without supplemental limits or 
limits set with a shorter averaging time.
    Comment: Sierra Club noted that Indiana determined its 30-day 
average limits on emission levels (in pounds per hour) on the basis of 
an adjustment factor calculated to reflect variability of emission 
rates (in pounds per MMBTU), to which Sierra Club objected as being 
inappropriate and contrary to EPA guidance.
    Response: EPA agrees that the variability of emission levels is 
prone to be different from the variability of emission rates, and 
Sierra Club is correct that EPA guidance recommends determining and 
applying separate adjustment factors for these two types of limits. 
Indiana's amended plan, including revised emission rate limits, no 
longer includes 30-day average mass emission level limits.\4\ EPA's 
supplemental NPRM provided EPA's review of this and other revisions 
Indiana made, and EPA received no comments on the revisions or on the 
review provided in its supplemental action. Thus, this comment is now 
moot.
---------------------------------------------------------------------------

    \4\ Indiana has provided modeling demonstrating that attainment 
is assured by a limit corresponding to the ``critical emission 
rate'' (which may be defined as the pound per MMBTU rate that at 
maximum load suffices to provide for attainment), and so Indiana's 
plan provides for attainment without need for an additional limit on 
pounds of emissions per hour.
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III. EPA's Final Action

    EPA is approving Indiana's SIP submission for the Southwest Indiana 
SO2 nonattainment area, which Indiana submitted to EPA on 
October 2, 2015 and supplemented on June 7, 2017, November 15, 2017, 
and September 18, 2019, and clarified on November 19, 2019. This 
SO2 nonattainment plan included Indiana's attainment 
demonstration for this area. The nonattainment plan also addressed 
requirements for emission inventories, reasonably available control 
technology/reasonably available control measures, reasonable further 
progress, and contingency measures. Indiana has previously addressed 
requirements regarding nonattainment area new source review.\5\ EPA has 
determined that Indiana's SO2 nonattainment plan for 
Southwest Indiana meets the applicable requirements of Clean Air Act 
sections 110, 172, 191, and 192.
---------------------------------------------------------------------------

    \5\ As noted in the NPRM, EPA approved Indiana's nonattainment 
new source review rules on October 7, 1994 (94 FR 24838).
---------------------------------------------------------------------------

    Underpinning Indiana's attainment plan for Southwest Indiana are 
three rules and a Commissioner's Order. The rule that is most pertinent 
to this action is Indiana Administrative Code, Title 326, Rule 7-4-15 
(326 IAC 7-4-15), entitled ``Pike County sulfur dioxide emission 
limitations'', effective January 1, 2017, which provides 1-hour 
emission limits for IP&L-Petersburg and the Frank E. Ratts facility and 
provide the terms under which IP&L may switch between being subject to 
the 1-hour limits in the rule and the 30-day average limits in the 
Commissioner's order. Two other rules, namely 326 IAC 7-1.1-3 
(``Compliance date'') and 326 IAC 7-2-1 (``Reporting requirements; 
methods to determine compliance''), are also pertinent to the Marion, 
Morgan, and Vigo County nonattainment plans and were approved in the 
context of action on the Marion and Vigo County action (See 84 FR 
10692, published March 22, 2019.) As a result of this action, the SIP 
will include Pike County limits (in

[[Page 49973]]

addition to previously approved limits for Marion, Morgan and Vigo 
Counties) as well as the implementing provisions in 326 IAC 7-1.1-3 and 
326 IAC 7-2-1, and no reapproval of these implementing provisions and 
indeed no SIP revision is needed for these implementing provisions to 
govern the implementation of the Pike County limits, as Indiana 
intended.\6\ In accordance with Indiana's request, EPA is approving 
paragraphs a, b, d, and e of 326 IAC 7-4-15. EPA is also approving 
Commissioner's Order Number 2019-2, issued on July 31, 2019 and 
effective on August 18, 2019. Indiana did not request approval of 326 
IAC 7-4-15(c), because these 30-day average limits have been superseded 
by the 30-day average limits in Commissioner's Order. As discussed in 
the supplemental NPRM, EPA is following Indiana's interpretation that 
compliance with the limits in the Commissioner's Order substitute for 
and supersede the limits in 326 IAC 7-4-15(c), and accordingly that the 
provisions of 326 IAC 7-4-15(d) describe how 30-day average emission 
rates are to be calculated to determine compliance with the limits in 
the Commissioner's Order, and that the provisions of 326 IAC 7-4-15(e) 
set the terms under which IP&L may elect to switch whether they must 
meet the 1-hour emission limits in 326 IAC 7-4-15(a) or the 30-day 
average limits in the Commissioner's Order.
---------------------------------------------------------------------------

    \6\ To avoid any potential for confusion, EPA wishes to note 
that the compliance deadline for the limits in the commissioner's 
order is specified in the commissioner's order and not in 326 IAC 7-
1.1-3.
---------------------------------------------------------------------------

IV. Incorporation by Reference

    In this rule, EPA is finalizing regulatory text that includes 
incorporation by reference. In accordance with requirements of 1 CFR 
51.5, EPA is finalizing the incorporation by reference of an Indiana 
regulation described in the amendments to 40 CFR part 52 set forth 
below. EPA has made, and will continue to make, these documents 
generally available through www.regulations.gov, and at the EPA Region 
5 Office (please contact the applicable person identified in the FOR 
FURTHER INFORMATION CONTACT section of this preamble for more 
information). Therefore, these materials have been approved by EPA for 
inclusion in the SIP, have been incorporated by reference by EPA into 
that plan, are fully federally enforceable under sections 110 and 113 
of the Clean Air Act as of the effective date of the final rulemaking 
of EPA's approval, and will be incorporated by reference in the next 
update to the SIP compilation.\7\
---------------------------------------------------------------------------

    \7\ 62 FR 27968 (May 22, 1997).
---------------------------------------------------------------------------

V. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Clean Air Act 
and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, EPA's role is to approve state 
choices, provided that they meet the criteria of the Clean Air Act. 
Accordingly, this action merely approves state law as meeting Federal 
requirements and does not impose additional requirements beyond those 
imposed by state law. For that reason, this action:
     Is not a significant regulatory action subject to review 
by the Office of Management and Budget under Executive Orders 12866 (58 
FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 2011);
     Is not an Executive Order 13771 (82 FR 9339, February 2, 
2017) regulatory action because SIP approvals are exempted under 
Executive Order 12866;
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Is not subject to requirements of Section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act; and
     Does not provide EPA with the discretionary authority to 
address, as appropriate, disproportionate human health or environmental 
effects, using practicable and legally permissible methods, under 
Executive Order 12898 (59 FR 7629, February 16, 1994).
    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction. In those areas of Indian 
country, the rule does not have tribal implications and will not impose 
substantial direct costs on tribal governments or preempt tribal law as 
specified by Executive Order 13175 (65 FR 67249, November 9, 2000).
    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. EPA will submit a report containing this action and 
other required information to the U.S. Senate, the U.S. House of 
Representatives, and the Comptroller General of the United States prior 
to publication of the rule in the Federal Register. A major rule cannot 
take effect until 60 days after it is published in the Federal 
Register. This action is not a ``major rule'' as defined by 5 U.S.C. 
804(2).
    Under section 307(b)(1) of the Clean Air Act, petitions for 
judicial review of this action must be filed in the United States Court 
of Appeals for the appropriate circuit by October 16, 2020. Filing a 
petition for reconsideration by the Administrator of this final rule 
does not affect the finality of this action for the purposes of 
judicial review nor does it extend the time within which a petition for 
judicial review may be filed, and shall not postpone the effectiveness 
of such rule or action. This action may not be challenged later in 
proceedings to enforce its requirements. (See section 307(b)(2).)

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
Reference, Reporting and recordkeeping requirements, Sulfur oxides.

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

    Dated: July 16, 2020.
Kurt Thiede,
Regional Administrator, Region 5.

    For the reasons stated in the preamble, the EPA amends 40 CFR part 
52 as follows:

[[Page 49974]]

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

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

0
2. In Sec.  52.770:
0
a. In paragraph (c) amend the table by adding an entry for ``7-4-15'' 
under ``Article 7. Sulfur Dioxide Rules,'' ``Rule 4. Emission 
Limitations and Requirements by County'';
0
b. In paragraph (d) amend the table by adding an entry at the end with 
a CO date of ``7/31/2019'' for ``IP&L-Petersburg''; and
0
c. In paragraph (e) amend the table by adding an entry for ``Southwest 
Indiana 2010 Sulfur Dioxide (SO2) Attainment Plan'' after 
the entry for ``Ozone (8-Hour, 1997): South Bend-Elkhart, IN (Elkhart 
and St. Joseph Counties)''.
    The additions read as follows:

Sec.  52.770  Identification of plan.

* * * * *
    (c) * * *

                                        EPA--Approved Indiana Regulations
----------------------------------------------------------------------------------------------------------------
                                                        Indiana
      Indiana citation              Subject         effective date    EPA approval date            Notes
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                         Article 7. Sulfur Dioxide Rules
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                             Rule 4. Emission Limitations and Requirements by County
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
7-4-15.....................  Pike County sulfur          10/5/2015  8/17/2020, [insert     Only (a), (b), (d),
                              dioxide emission                       Federal Register       and (e). EPA is
                              limitations.                           citation].             approving a
                                                                                            commissioner's order
                                                                                            in place of (c).
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------

* * * * *
    (d) * * *

                       EPA--Approved Indiana Nonregulatory and Quasi-Regulatory Provisions
----------------------------------------------------------------------------------------------------------------
          CO date                    Title             SIP rule          EPA approval           Explanation
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
7/31/2019..................  IP&L-Petersburg......          7-4-15  8/17/2020, [insert     30-day average
                                                                     Federal Register       limits.
                                                                     citation].
----------------------------------------------------------------------------------------------------------------

* * * * *
    (e) * * *

                       EPA--Approved Indiana Nonregulatory and Quasi-Regulatory Provisions
----------------------------------------------------------------------------------------------------------------
                Title                  Indiana date           EPA approval                   Explanation
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Southwest Indiana 2010 Sulfur                10/2/15  8/17/2020, [insert Federal
 Dioxide (SO2) Attainment Plan.                        Register citation].
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------

* * * * *
[FR Doc. 2020-16044 Filed 8-14-20; 8:45 am]
BILLING CODE 6560-50-P