[Federal Register Volume 89, Number 111 (Friday, June 7, 2024)]
[Proposed Rules]
[Pages 48523-48532]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-11175]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R03-OAR-2024-0024; FRL-11529-01-R3]


Air Plan Approval; Pennsylvania; Attainment Plan for the Indiana 
Nonattainment Area for the 2010 1-Hour Sulfur Dioxide National Ambient 
Air Quality Standard

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
approve a state implementation plan (SIP) revision submitted by the 
Commonwealth of Pennsylvania (Pennsylvania). This revision pertains to 
the attainment plan for the Indiana, Pennsylvania (PA) nonattainment 
area for the 2010 1-Hour Sulfur Dioxide (SO2) national 
ambient air quality standard (NAAQS). This action is being taken under 
the Clean Air Act (CAA).

DATES: Written comments must be received on or before July 8, 2024.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R03-
OAR-2024-0024 at www.regulations.gov, or via email to 
[email protected]. For comments submitted at Regulations.gov, follow 
the online instructions for submitting comments. Once submitted, 
comments cannot be edited or removed from Regulations.gov. For either 
manner of submission, the EPA may publish any comment received to its 
public docket. Do not submit electronically any information you 
consider to be confidential business information (CBI) or other 
information whose disclosure is restricted by statute. Multimedia 
submissions (audio, video, etc.) must be accompanied by a written 
comment. The written comment is considered the official comment and 
should include discussion of all points you wish to make. The EPA will 
generally not consider comments or comment contents located outside of 
the primary submission (i.e., on the web, cloud, or other file sharing 
system). For additional submission methods, please contact the person 
identified in the For Further Information Contact section. For the full 
EPA public comment policy, information about CBI or multimedia 
submissions, and general guidance on making effective comments, please 
visit www.epa.gov/dockets/commenting-epa-dockets.

[[Page 48524]]


FOR FURTHER INFORMATION CONTACT: Megan Goold, Planning & Implementation 
Branch (3AD30), Air & Radiation Division, U.S. Environmental Protection 
Agency, Region III, 1600 John F Kennedy Boulevard, Philadelphia, 
Pennsylvania 19103. The telephone number is (215) 814-2027. Ms. Goold 
can also be reached via electronic mail at [email protected].

SUPPLEMENTARY INFORMATION: On October 5, 2023, the Pennsylvania 
Department of Environmental Protection (PADEP) submitted a revision to 
its SIP to demonstrate attainment of the 2010 SO2 NAAQS in 
the Indiana, PA nonattainment area. This plan includes Pennsylvania's 
attainment demonstration and other attainment plan elements required 
under the CAA, including the requirement for meeting reasonable further 
progress (RFP) toward attainment of the NAAQS, reasonably available 
control measures and reasonably available control technology (RACM/
RACT), enforceable emission limitations and control measures, and 
contingency measures. Notably, the submission does not contain 
information regarding the required emissions inventory or the state's 
Nonattainment New Source Review (NNSR) program, as these were 
previously approved by the EPA (87 FR 50778, August 18, 2022).

I. Background

    On June 22, 2010, the EPA published a new 1-hour primary 
SO2 NAAQS of 75 parts per billion (ppb) at 40 CFR 50.17(a), 
which is met at an ambient air quality monitoring site when the 3-year 
average of the annual 99th percentile of daily maximum 1-hour average 
concentrations does not exceed 75 ppb, as determined in accordance with 
40 Code of Federal Regulations (CFR) part 50 appendix T (75 FR 35520, 
June 22, 2010). Under CAA section 107(d)(1), the EPA is required to 
designate areas as ``nonattainment,'' ``attainment,'' or 
``unclassifiable'' within two years of establishing a new or revising 
an existing standard. As part of this process, states must submit 
recommendations for area designations and boundaries to the EPA within 
one year of the effective date of the standard. Effective on October 4, 
2013,\1\ the Indiana Area (which encompasses Indiana County, and 
Plumcreek Township, South Bend Township and Eldertown Borough of 
Armstrong County) was designated as nonattainment for the 2010 
SO2 NAAQS for an area that encompasses the primary 
SO2 emitting sources: the Keystone Generating Station 
(Keystone), Conemaugh Generating Station (Conemaugh), Homer City 
Generating Station (Homer City), and Seward Generating Station (Seward) 
(hereafter referred to as ``the Indiana, PA NAA''). The October 4, 
2013, final designation triggered a requirement for Pennsylvania to 
submit by April 4, 2015 (within 18 months per CAA section 191(a)), a 
SIP revision with an attainment plan for how the Indiana, PA NAA would 
attain the 2010 SO2 NAAQS as expeditiously as practicable, 
but no later than October 4, 2018, (five years from the designation per 
CAA section 192(a)) in accordance with CAA sections 110(a), 172(c) and 
191-192.
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    \1\ 78 FR 47191 (August 5, 2013).
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    For a number of areas, including the Indiana, PA NAA, the EPA 
published a March 18, 2016 Finding of Failure to Submit, with an 
effective date of April 18, 2016, finding that Pennsylvania and other 
pertinent states had failed to submit the required SO2 
attainment plan by this submittal deadline. (see 81 FR 14736, March 18, 
2016). This finding initiated a deadline under CAA section 179(a) for 
the potential imposition of new source review and highway funding 
sanctions. However, as a result of Pennsylvania's October 11, 2017 
submittal (hereafter referred to as ``the 2017 SIP submittal''), and 
the EPA's subsequent October 13, 2017 letter to Pennsylvania finding 
the submittal complete, the CAA section 179(a) sanctions were not 
imposed. Additionally, under CAA section 110(c), the March 18, 2016, 
finding triggered a requirement that the EPA promulgate a Federal 
implementation plan (FIP) within two years of the effective date of the 
finding unless, by that time, the state has made the necessary complete 
submittal and the EPA has approved the submittal as meeting applicable 
requirements. The EPA took final action approving this attainment plan 
on October 19, 2020 (85 FR 66240, October 19, 2020), which removed the 
FIP obligation.
    On December 18, 2020, the Sierra Club, Clean Air Council, and 
Citizens for Pennsylvania's Future filed a petition for judicial review 
with the U.S. Court of Appeals for the Third Circuit, challenging that 
final approval.\2\ On April 5, 2021, the EPA filed a motion for 
voluntary remand without vacatur of its approval of the Indiana, PA 
SO2 attainment plan.
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    \2\ Sierra Club, et al. v. EPA, Case No. 20-3568 (3d Cir.).
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    On August 17, 2021, the U.S. Court of Appeals for the Third Circuit 
granted the EPA's request for remand without vacatur of the final 
approval of Pennsylvania's SO2 attainment plan for the 
Indiana, PA NAA, and required that the EPA take final action in 
response to the remand no later than one year from the date of the 
court's order.
    On August 18, 2022, the EPA revised and corrected its prior full 
approval action (85 FR 66240, October 19, 2020) without further 
submission from Pennsylvania (effective September 19, 2022) (87 FR 
50778, August 18, 2022). Specifically, the EPA retained the approval of 
the emissions inventory and NNSR program requirements, and disapproved 
the attainment demonstration, RACM/RACT requirements, RFP requirements, 
and contingency measures (hereafter referred to as the ``2022 Partial 
Approval/Partial Disapproval'') (87 FR 50778, August 18, 2022). The 
partial disapproval action initiated a sanctions clock under CAA 
section 179, providing for emission offset sanctions for new sources if 
EPA has not fully approved a revised attainment plan within 18 months 
(March 19, 2024) after final partial disapproval, and providing for 
highway funding sanctions if the EPA has not fully approved a revised 
plan within 6 months thereafter (September 19, 2024). The sanctions 
clock can be stopped only if the conditions of the EPA's regulations at 
40 CFR 52.31 are met. Also, under CAA section 110(c), the partial 
disapproval action initiated an obligation for EPA to promulgate a FIP 
within two years unless Pennsylvania has submitted, and EPA has fully 
approved, a plan addressing the disapproved attainment planning 
requirements.
    On October 5, 2023, Pennsylvania submitted a 2023 SO2 
Attainment Plan SIP Revision for the Indiana, PA NAA (hereafter 
referred to as the ``2023 SIP submittal''). The 2023 SIP submittal 
addresses the requirements of CAA sections 172(c), 191 and 192 and the 
disapproved attainment planning requirements in the EPA's 2022 Partial 
Approval/Partial Disapproval. Specifically, this SIP revision contains 
a modified attainment demonstration using dispersion modeling, 
evaluates sources for RACT/RACM purposes, gives an RFP explanation, and 
provides for contingency measures, and includes revised emissions 
limitations and control measures.
    Nonattainment area SO2 SIPs must meet the applicable 
requirements of the CAA, specifically CAA sections 110, 172, 191 and 
192. The EPA's regulations governing nonattainment area SIPs are set 
forth at 40 CFR part 51, with specific procedural requirements and 
control strategy requirements residing at subparts F and G, 
respectively. Soon

[[Page 48525]]

after Congress enacted the 1990 amendments to the CAA, the EPA issued 
comprehensive guidance on SIPs in a document entitled the ``General 
Preamble for the Implementation of Title I of the Clean Air Act 
Amendments of 1990,'' published in the Federal Register at 57 FR 13498 
(April 16, 1992) (General Preamble). Among other things, the General 
Preamble addressed SO2 SIPs and fundamental principles for 
SIP control strategies. Id. at 13545-49, 13567-68. On April 23, 2014, 
the EPA issued guidance and recommendations for meeting the statutory 
requirements in SO2 SIPs addressing the 2010 primary NAAQS, 
in a document entitled, ``Guidance for 1-Hour SO2 
Nonattainment Area SIP Submissions'' (hereafter referred to as ``2014 
SO2 Nonattainment Guidance'').\3\ In the 2014 SO2 
Nonattainment Guidance, the EPA described the statutory requirements 
for a complete nonattainment area SIP, which include an accurate 
emissions inventory of current emissions for all sources of 
SO2 within the nonattainment area; an attainment 
demonstration; enforceable emissions limitations and control measures; 
demonstration of RFP; implementation of RACM (including RACT); 
nonattainment new source review; and adequate contingency measures for 
the affected area.
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    \3\ www.epa.gov/sites/default/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf.
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    For the EPA to fully approve a SIP as meeting the requirements of 
CAA sections 110, 172, 191, and 192 and the EPA's regulations at 40 CFR 
part 51, the SIP for the affected area needs to demonstrate to the 
EPA's satisfaction that each of the aforementioned requirements have 
been met. Under CAA sections 110(l) and 193, the EPA may not approve a 
SIP that would interfere with any applicable requirement concerning 
NAAQS attainment and RFP, or any other applicable requirement, and no 
requirement in effect before November 15, 1990 (or required to be 
adopted by an order, settlement, agreement, or plan in effect before 
November 15, 1990), in any area which is a nonattainment area for any 
air pollutant, may be modified in any manner unless it ensures 
equivalent or greater emission reductions of such air pollutant.
    CAA section 172(c)(1) directs states with areas designated as 
nonattainment to demonstrate that the submitted plan provides for 
attainment of the NAAQS. 40 CFR part 51, subpart G further delineates 
the control strategy requirements that SIPs must meet, and the EPA has 
long required that all SIPs and control strategies reflect the four 
fundamental principles of quantification, enforceability, 
replicability, and accountability. See General Preamble, at 13567-68. 
SO2 attainment plans must consist of two components: (1) 
emission limits and other control; measures that assure implementation 
of permanent, enforceable and necessary emission controls, and (2) a 
modeling analysis which meets the requirements of 40 CFR part 51, 
appendix W and demonstrates that these emission limits and control 
measures provide for timely attainment of the primary SO2 
NAAQS as expeditiously as practicable, but by no later than the 
attainment date for the affected area. In all cases, the emission 
limits and control measures must be accompanied by appropriate methods 
and conditions to determine compliance with the respective emission 
limits and control measures, and must be quantifiable (i.e., a specific 
amount of emission reduction can be ascribed to the measures), fully 
enforceable (specifying clear, unambiguous and measurable requirements 
for which compliance can be practicably determined), replicable (the 
procedures for determining compliance are sufficiently specific and 
non-subjective so that two independent entities applying the procedures 
would obtain the same result), and accountable (source-specific limits 
must be permanent and must reflect the assumptions used in the SIP 
demonstrations).
    The EPA's 2014 SO2 Nonattainment Guidance recommends 
that the emission limits established for the attainment demonstration 
be expressed as short-term average limits (e.g., addressing emissions 
averaged over one or three hours), but also describes the option to 
utilize emission limits with longer averaging times of up to 30 days so 
long as the state meets various suggested criteria. See 2014 
SO2 Nonattainment Guidance, pp. 22 to 39. The guidance 
recommends that--should states and sources utilize longer averaging 
times--the longer-term average limit should be set at an adjusted level 
that reflects a stringency comparable to the 1-hour average limit at 
the critical emission value (CEV) shown to provide for attainment that 
the plan otherwise would have set.
    The 2014 SO2 Nonattainment Guidance provides an 
extensive discussion of the EPA's rationale for concluding that 
appropriately set, comparably stringent limitations based on averaging 
times as long as 30 days can be found to provide for attainment of the 
2010 SO2 NAAQS. In evaluating this option, the EPA 
considered the nature of the standard, conducted detailed analyses of 
the impact of 30-day average limits on the prospects for attaining the 
standard, and carefully reviewed how best to achieve an appropriate 
balance among the various factors that warrant consideration in judging 
whether a state's plan provides for attainment. Id. at pp. 22-39, and 
Appendices B, C, and D.
    As specified in 40 CFR 50.17(b), the 1-hour primary SO2 
NAAQS is met at an ambient air quality monitoring site when the 3-year 
average of the annual 99th percentile of daily maximum 1-hour average 
concentrations is less than or equal to 75 ppb. In a year with 365 days 
of valid monitoring data, the 99th percentile would be the fourth 
highest daily maximum 1-hour value. The 2010 SO2 NAAQS, 
including this form of determining compliance with the standard, was 
upheld by the U.S. Court of Appeals for the District of Columbia 
Circuit in Nat'l Envt'l Dev. Ass'n's Clean Air Project v. EPA, 686 F.3d 
803 (D.C. Cir. 2012). Because the standard has this form, a single 
hourly exceedance of the 75 ppb NAAQS level does not by itself result 
in a violation of the standard. Instead, at issue is whether a source 
operating in compliance with a properly set longer-term average could 
cause multiple hourly exceedances over multiple days in a year, and if 
so, the resulting frequency and magnitude of such exceedances, and in 
particular, whether the EPA can have reasonable confidence that a 
properly set longer-term average limit will provide that the 3-year 
average of annual fourth highest daily maximum hourly values will be at 
or below 75 ppb. A synopsis of how the EPA evaluates whether such plans 
``provide for attainment,'' based on modeling of projected allowable 
emissions and in light of the SO2 NAAQS' form for 
determining attainment at monitoring sites, follows.
    For SO2 attainment plans based on 1-hour emission 
limits, the standard approach is to conduct modeling using fixed 1-hour 
emission rates. The maximum modeled emission rate that results in 
attainment is labeled the ``critical emissions value'' (CEV). The 
modeling process for identifying this CEV inherently considers the 
numerous variables that affect ambient concentrations of 
SO2, such as meteorological data, background concentrations, 
and topography. In the standard approach, the state would then provide 
for attainment by setting a continuously applicable 1-hour emission 
limit for each stationary SO2 source at this CEV.

[[Page 48526]]

    The EPA recognizes that some sources have highly variable 
emissions, for example due to variations in fuel sulfur content and 
operating rate, that can make it extremely difficult, even with a well-
designed control strategy, to ensure in practice that emissions for any 
given hour do not exceed the CEV. The EPA also acknowledges the concern 
that longer-term emission limits can allow short periods with emissions 
above the CEV, which, if coincident with meteorological conditions 
conducive to high SO2 concentrations, could in turn create 
the possibility of an hourly NAAQS exceedance occurring on a day when 
an exceedance would not have occurred if emissions were continuously 
controlled at the level corresponding to the CEV. However, for several 
reasons, EPA believes that the approach recommended in its guidance 
document suitably addresses this concern.
    First, from a practical perspective, the EPA expects the actual 
emission profile of a source subject to an appropriately set longer-
term average limit to be similar to the emission profile of a source 
subject to an analogous 1-hour average limit. The EPA expects this 
similarity because it has recommended that the longer-term average 
limit be set at a level that is comparably stringent to the otherwise 
applicable 1-hour limit (reflecting a downward adjustment from the CEV) 
and that takes the source's emissions profile (and inherent level of 
emissions variability) into account. As a result, the EPA expects 
either form of emission limit to yield comparable air quality.
    Second, from a more theoretical perspective, the EPA has compared 
the likely air quality with a source having maximum allowable emissions 
under an appropriately set longer-term limit, to the likely air quality 
with the source having maximum allowable emissions under the comparable 
1-hour limit. In this comparison, in the 1-hour average limit scenario, 
the source is presumed at all times to emit at the CEV, and in the 
longer-term average limit scenario, the source is presumed occasionally 
to emit more than the CEV, but on average, and presumably at most 
times, to emit well below the CEV. In an ``average year,'' \4\ 
compliance with the 1-hour limit is expected to result in three 
exceedance days (i.e., three days with maximum hourly values above 75 
ppb) and a fourth day with a maximum hourly value at 75 ppb. By 
comparison, with the source complying with a longer-term limit, it is 
possible that additional hourly exceedances would occur that would not 
occur in the 1-hour limit scenario (if emissions exceed the CEV at 
times when meteorology is conducive to poor air quality). However, this 
comparison must also factor in the likelihood that exceedances that 
would be expected in the 1-hour limit scenario would not occur in the 
longer-term limit scenario. This result arises because the longer-term 
limit requires lower emissions most of the time (because the limit is 
set below the CEV), so a source complying with an appropriately set 
longer-term limit is likely to have lower emissions at critical times 
than would be the case if the source were emitting as allowed with a 1-
hour limit.
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    \4\ An ``average year'' is used to mean a year with average air 
quality. While 40 CFR part 50, appendix T, provides for averaging 
three years of annual 99th percentile daily maximum hourly values 
(e.g., the fourth highest maximum daily hourly concentration in a 
year with 365 days with valid data), this discussion and an example 
below uses a single ``average year'' in order to simplify the 
illustration of relevant principles.
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    To illustrate this point, the EPA conducted a statistical analysis 
using a range of scenarios using actual plant data. The analysis is 
described in appendix B of EPA's 2014 SO2 Nonattainment 
Guidance. Based on the analysis described in the 2014 SO2 
Nonattainment Guidance, the EPA expects that an emission profile with 
maximum allowable emissions under an appropriately set, comparably 
stringent 30-day average limit is likely to have the net effect of 
having a lower number of hourly exceedances and better air quality than 
an emission profile with maximum allowable emissions under a 1-hour 
emission limit at the CEV. This result provides a compelling policy 
rationale for allowing the use of a longer averaging period, in 
appropriate circumstances where the facts indicate this result can be 
expected to occur.
    The 2014 SO2 Nonattainment Guidance offers specific 
recommendations for determining an appropriate longer-term average 
limit. The recommended method starts with determination of the 1-hour 
emission limit that would provide for attainment (i.e., the CEV), and 
applies an adjustment factor to determine the (lower) level of the 
longer-term average emission limit that would be estimated to have a 
stringency comparable to the otherwise necessary 1-hour emission limit. 
This method uses a database of continuous emission data reflecting the 
type of control that the source will be using to comply with the SIP 
emission limits, which (if compliance requires new controls) may 
require use of an emission database from another source. The 
recommended method involves using these data to compute a complete set 
of emission averages, computed according to the averaging time and 
averaging procedures of the prospective emission limitation (i.e., 
using 1-hour historical emission values from the emissions database to 
calculate 30-day average emission values). In this recommended method, 
the ratio of the 99th percentile among these long-term averages to the 
99th percentile of the 1-hour values represents an adjustment factor 
that may be multiplied to the candidate 1-hour emission limit (CEV) to 
determine a longer-term average emission limit that may be considered 
comparably stringent.\5\
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    \5\ For example, if the CEV is 1,000 pounds of SO2 
per hour, and a suitable adjustment factor is determined to be 70 
percent, the recommended longer-term average limit would be 700 
pounds per hour.
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    The 2014 SO2 Nonattainment Guidance also addresses a 
variety of related topics, including the potential utility of setting 
supplemental emission limits, such as mass-based limits or work 
practice requirements for the operation of SO2 control 
equipment, to reduce the likelihood and/or magnitude of elevated 
emission levels that might occur under the longer-term emission rate 
limit.
    Preferred air quality models for use in regulatory applications are 
described in appendix A of the EPA's Guideline on Air Quality Models 
(40 CFR part 51, appendix W). In 2005, the EPA promulgated AERMOD as 
the Agency's preferred near-field dispersion modeling for a wide range 
of regulatory applications addressing stationary sources (for example 
in estimating SO2 concentrations) in all types of terrain 
based on extensive developmental and performance evaluation. 
Supplemental guidance on modeling for purposes of demonstrating 
attainment of the SO2 standard is provided in appendix A to 
the 2014 SO2 Nonattainment Guidance. Appendix A provides 
extensive guidance on the modeling domain, the source inputs, assorted 
types of meteorological data, and background concentrations. 
Consistency with the recommendations in this guidance is generally 
necessary for the attainment demonstration to offer adequately reliable 
assurance that the plan provides for attainment.
    Attainment demonstrations for the 2010 1-hour primary 
SO2 NAAQS must demonstrate future attainment and maintenance 
of the NAAQS in the entire area designated as nonattainment (i.e., not 
just at the violating monitor) by using air quality dispersion modeling 
(see appendix W to 40 CFR part 51) to show that the mix of sources and 
enforceable control measures and emission rates in an identified area 
will not lead to a violation of the SO2

[[Page 48527]]

NAAQS. For a short-term (i.e., 1-hour) standard, the EPA believes that 
dispersion modeling, using allowable emissions and addressing 
stationary sources in the affected area (and in some cases those 
sources located outside the nonattainment area which may affect 
attainment in the area) is technically appropriate, efficient, and 
effective in demonstrating attainment in nonattainment areas because it 
takes into consideration combinations of meteorological and emission 
source operating conditions that may contribute to peak ground-level 
concentrations of SO2.
    The meteorological data used in the analysis should generally be 
processed with the most recent version of AERMET. AERMET is a 
meteorological data preprocessor that incorporates air dispersion based 
on planetary boundary layer turbulence structure and scaling concepts. 
Estimated concentrations should include ambient background 
concentrations, should follow the form of the standard, and should be 
calculated as described in section 2.6.1.2 of the August 23, 2010, 
clarification memo on ``Applicability of Appendix W Modeling Guidance 
for the 1-hour SO2 National Ambient Air Quality Standard'' 
(U.S. EPA, 2010).

II. Summary of SIP Revision and EPA Analysis

    Pennsylvania's 2023 SIP submittal contained an attainment 
demonstration that located, identified, and quantified sources of 
emissions contributing to violations of the 2010 SO2 NAAQS 
in the Indiana, PA NAA; a determination that the control strategy for 
the primary SO2 sources (Keystone, Conemaugh, Homer City, 
and Seward) constitutes RACM/RACT; requirements for RFP toward 
attaining the SO2 NAAQS in the Indiana, PA NAA; contingency 
measures; and the request that emission limitations and compliance 
parameters for Keystone, Conemaugh, and Seward be incorporated into the 
SIP.\6\ The EPA disapproved these elements of PADEP's 2017 SIP 
submittal because they were based on longer-term averaging 
SO2 limits for Keystone and Seward that EPA could not 
approve. Those particular longer-term averaging limits were 
unsupportable because PADEP's modeling and analysis fell short of 
demonstrating that the longer-term limits were comparably stringent to 
the 1-hour CEV and that such limits would provide for attainment under 
worst-case emission scenarios, unlike the approach set forth in the 
2014 SO2 Nonattainment Guidance. But PADEP's 2023 SIP 
submittal includes appropriate modeling and revised longer-term 
averaging emission limits for Keystone, Conemaugh, and Seward that are 
comparably stringent to the 1-hour CEV for each facility. Therefore, 
the 2023 SIP submittal's attainment plan elements, the effectiveness of 
which are dependent upon correct longer-term averaging emission limits, 
are similarly approvable. The EPA already determined that Pennsylvania 
satisfied the emissions inventory and NNSR requirements and approved 
those elements of the attainment plan into Pennsylvania's SIP as stated 
in the 2022 Partial Approval/Partial Disapproval of Pennsylvania's 2017 
submittal (87 FR 50778, August 18, 2022).
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    \6\ SO2 emission limits for Homer City that were used 
in the attainment modeling were already approved into the SIP. (87 
FR 50778, August 18, 2022).
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A. Attainment Demonstration-Air Quality Modeling

    The SO2 attainment demonstration provides air quality 
dispersion modeling analyses to demonstrate that control strategies 
chosen to reduce SO2 source emissions will bring the 
Indiana, PA NAA into attainment. The modeling analyses, conducted 
pursuant to recommendations outlined in appendix W to 40 CFR part 51 
(EPA's Modeling Guidance), are used to assess the control strategy for 
a nonattainment area and establish emission limits that will provide 
for attainment. The analysis requires five years of meteorological data 
to simulate the dispersion of pollutant plumes from multiple point, 
area, or volume sources across the averaging times of interest.\7\ The 
modeling demonstration typically also relies on maximum allowable 
emissions from sources in the nonattainment area. Though the actual 
emissions are likely to be below the allowable emissions, sources have 
the ability to run at higher production rates or optimize controls such 
that emissions approach the allowable emissions limits. A modeling 
analysis that provides for attainment under all scenarios of operation 
for each source must therefore consider the worst-case scenario of both 
the meteorology (e.g., predominant wind directions, stagnation, etc.) 
and the maximum allowable emissions.
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    \7\ The period of meteorological data needed for an air-quality 
analysis is described in section 8.4.2(e) of Appendix W: ``The use 
of 5 years of adequately representative [National Weather Service] 
or comparable meteorological data, at least 1 year of site-specific, 
or at least 3 years of prognostic meteorological data, are 
required.''
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    Air dispersion modeling served as the basis for developing 
SO2 emission limits that provide for attainment of the 2010 
SO2 NAAQS throughout the Indiana, PA NAA. PADEP's air 
dispersion modeling methodology is fully described in appendix A of the 
state submittal, the Air Dispersion Modeling Technical Support 
Document.
    PADEP's air dispersion modeling utilized the AERMOD v22112 and its 
associated preprocessors, the building downwash preprocessor (BPIPPRM) 
v04274, the AERMOD terrain preprocessor (AERMAP) v18081, and the AERMOD 
meteorological preprocessor (AERMET) v22112.
    The modeling analysis included the following SO2 sources 
in the NAA: (1) Keystone's SO2 emission sources include two 
coal-fired boilers (Unit 1 & Unit 2 or Source ID 031 & 032). The 
SO2 emissions vent from each source to the atmosphere 
through separate flues within a common stack, which was characterized 
in AERMOD as a point source; (2) Homer City's SO2 emission 
sources include three coal-fired boilers (Unit 1, Unit 2 & Unit 3 or 
Source ID 031, 032 & 033). The SO2 emissions vent from each 
source to the atmosphere through separate stacks, which were each 
characterized in AERMOD as a point source; (3) Conemaugh's 
SO2 emission sources include two coal-fired boilers (Unit 1 
& Unit 2 or Source ID 031 & 032). The SO2 emissions vent 
from each source to the atmosphere through separate flues within a 
common stack, which was characterized in AERMOD as a point source; and 
(4) Seward's SO2 emission sources include two refuse coal-
fired boilers (Unit 1 & Unit 2 or Source ID 034 & 035). The 
SO2 emissions vent from each source to the atmosphere 
through a common stack, which was characterized in AERMOD as a point 
source.
    PADEP modeled three domains with three meteorological data sets. 
Domain 1, the Armstrong County portion of the Indiana, PA NAA, included 
SO2 emissions data from Keystone and Homer City in AERMOD. 
Domain 2, the Indiana County portion of the Indiana, PA NAA, included 
SO2 emissions data from all four power plant facilities in 
AERMOD. The air dispersion modeling in Domains 1 and 2 utilized 
representative meteorological datasets from the Johnstown--Cambria 
County Airport (KJST) meteorological site. The KJST meteorological 
dataset consists of a 5-year period of hourly records from January 1, 
2011, through December 31, 2015, consistent with the meteorological 
data period that was utilized in the air dispersion modeling for 
PADEP's 2017 SIP submittal for the Indiana, PA NAA. Additionally, a 
second KJST meteorological dataset was utilized, which consists of a 
more recent 5-year

[[Page 48528]]

period of hourly records from January 1, 2017, through December 31, 
2021.
    Domain 3, the portion of Indiana County near Conemaugh and Seward, 
included SO2 emissions data from those two plants. PADEP 
used data from the Conemaugh-Seward meteorological site to represent 
atmospheric conditions in the vicinity of Conemaugh and Seward. A 1-
year (September 1, 2015-August 31, 2016) Conemaugh-Seward 
meteorological dataset was utilized with AERMOD.
    Background SO2 was represented in AERMOD by temporally 
varying (by season and hour-of-day), 99th-percentile concentrations 
that were derived from data measured at the Allegheny County Health 
Department's South Fayette monitor (Site ID: 42-003-0067) for the 3-
year period, 2019-2021.
    AERMOD was used to determine the CEVs for Conemaugh, Keystone, and 
Seward where the modeled 1-hour emission rates demonstrate attainment 
of the 2010 1-hour SO2 NAAQS. The SO2 emission 
rates for Homer City were based on the unit 1, unit 2, and unit 3 
combined mass-based SO2 emission limits established in Plan 
Approval 32-00055H,\8\ which authorized the installation of Novel 
Integrated Desulfurization (NID) systems, often referred to as Dry Flue 
Gas Desulphurization (FGD) systems on unit 1 and unit 2. This 1-hour 
SO2 limit was based on air dispersion modeling that 
demonstrated attainment of the 2010 1-hour SO2 NAAQS. The 
CEV rates used in the demonstration analysis for each of the four 
sources are summarized in Table 1, in this document. The modeled 
emission rate in grams per second (g/s) was converted to pounds per 
hour (lbs/hr), which is the CEV.\9\
---------------------------------------------------------------------------

    \8\ Plan Approval 32-00055H was issued on April 2, 2012, and 
modified on April 4, 2013, by the DEP.
    \9\ Based on the National Institute of Standards and Technology 
conversion: 1 pound = 453.59237 grams.

  Table 1--Critical Emission Values (CEV) From Indiana, PA SIP Modeling
                              Demonstration
------------------------------------------------------------------------
                                           Modeled rate   CEV limit (lbs/
                Facility                       (g/s)            hr)
------------------------------------------------------------------------
Conemaugh Generating Station............       398.02731           3,159
Homer City Generating Station, Unit 1...       195.29672           1,550
Homer City Generating Station, Unit 2...       195.29672           1,550
Homer City Generating Station, Unit 3...       410.75310           3,260
Keystone Generating Station.............     1,224.44741           9,718
Seward Generating Station...............       482.57189           3,830
------------------------------------------------------------------------

    Using the EPA conversion factor for the SO2 NAAQS, the 
maximum 1-hour CEV model run design values for Domain 1 (196.00 [mu]g/
m\3\), Domain 2 (187.51 [mu]g/m\3\) and Domain 3 (195.99 [mu]g/m\3\) of 
the Indiana Area are less than 75 ppb.\10\ EPA has reviewed the 
modeling that Pennsylvania submitted to support the attainment 
demonstration for the Indiana Area and has determined that the AERMOD 
modeling is consistent with CAA requirements, appendix W to 40 CFR part 
51, and EPA's 2014 SO2 Guidance for SO2 
attainment demonstration modeling. Unlike the 2017 SIP submittal which 
the EPA partially disapproved in 2022 (87 FR 50778, August 18, 2022), 
PADEP's 2023 SIP submittal used an appropriate analysis to show that 
the modeled 1-hour CEV and longer-term emission limits were comparably 
stringent. In doing so, the 2023 SIP submission followed EPA guidance 
to develop an adjustment factor to convert the modeled 1-hour CEV to 
the comparably stringent longer-term emission limit. The 2023 SIP 
submission appropriately developed the adjustment factor by comparing 
the 99th percentile of historic hourly emissions to the 99th percentile 
of the longer-term averaged emissions of the same dataset to develop 
the longer-term emission limits. Conversely, the 2017 SIP submittal 
developed longer-term limits based on a novel modeling approach with a 
different variability metric without appropriate justification--PADEP 
had not demonstrated that the longer-term emission limits would provide 
for attainment under worst-case scenarios permissible under the limits. 
(87 FR 15166 at 15171-74, March 17, 2022).
---------------------------------------------------------------------------

    \10\ The SO2 NAAQS level is expressed in ppb but 
AERMOD gives results in [mu]g/m\3\. The conversion factor for 
SO2 (at the standard conditions applied in the ambient 
SO2 reference method) is 1 ppb = approximately 2.619 
[mu]g/m\3\. See Pennsylvania's SO2 Round 3 Designations 
Proposed Technical Support Document at www.epa.gov/sites/production/files/2017-08/documents/35_pa_so2_rd3-final.pdf.
---------------------------------------------------------------------------

    EPA's review supports PADEP's modeling methodology and conclusions. 
More information about EPA's review of PADEP's attainment demonstration 
and modeling can be found in EPA's March 2024 ``Technical Support 
Document the Critical Emissions Value Modeling Analysis for the 
Indiana, PA 1-Hour SO2 Nonattainment Area'' under Docket ID 
No. EPA-R03-OAR-2024-0024 and online at www.regulations.gov.
1. Longer-Term Emission Limits
    The 2017 SIP submittal established longer-term average 
SO2 limits for Keystone, Conemaugh, and Seward, and a 1-hour 
SO2 limit for Homer City. As described above, the limits in 
the 2017 submittal for Keystone and Seward were based on a novel 
modeling approach and an analysis that did not demonstrate that the 
longer-term emission limits were comparably stringent to the 1-hour 
CEV. (87 FR 15166 at 15171-74, March 17, 2022). EPA thus disapproved 
the longer-term average SO2 limits for Keystone and Seward 
as not properly characterizing maximally possible emissions. (87 FR 
15166 at 15173, March 17, 2022). Nonetheless, the EPA retained the 
limits as SIP strengthening in its partial approval and partial 
disapproval. (87 FR 15166 at 15176, March 17, 2022).
    PADEP's 2023 SIP submittal established revised longer-term average 
SO2 emission limits for Keystone, Conemaugh, and Seward 
facilities and retained the 1-hour SO2 emission limit 
previously established and approved for the Homer City facility.\11\ 
PADEP's 2023 SIP submittal established comparably stringent limits 
because PADEP used the ratio of the 99th percentile values of the 
hourly and longer-term emission rates as the adjustment factors for 
calculating

[[Page 48529]]

the longer-term limits.\12\ The revised longer-term emission limits 
were calculated from the 1-hour SO2 CEVs using adjustment 
factors that correspond to the averaging periods already established in 
emission limits for each facility (i.e., Seward's emission limit uses a 
30-operating day averaging period, Keystone uses a 24-hour block 
averaging period, and Conemaugh uses a 3-hour block averaging period). 
The adjustment factors which are used for deriving longer-term emission 
limits that are as comparably stringent as the 1-hour SO2 
CEVs were calculated in accordance with the EPA's 2014 SO2 
Nonattainment Guidance. All and only operating hours with measured 
values were used in the calculations.\13\ PADEP utilized four years of 
stable operations hourly emissions data from 2018-2022. In accordance 
with the 2014 SO2 Nonattainment Guidance's recommendation to 
use data from years with stable operations, data from March through 
September of 2020, during which operations at Keystone and Conemaugh 
shifted toward low-load conditions as a result of the COVID-19 
pandemic, were excluded from adjustment factor calculations for both 
stations. To have a complete four calendar years' worth of data, data 
from March through September of 2022 were used as replacement for the 
March through September of 2020 data. The calculation of the adjustment 
factors is described in detail in appendix B of the state submittal and 
was based on the data reduction criteria and average emission rate 
calculation established for demonstrating compliance with the longer-
term emission limits. For example, Seward's 30-operating day rolling 
average is the average of all the hourly emission data, using only 
hours during which fuel is combusted from the preceding 30 operating 
days. An operating day is defined as a 24-hour period between 
12midnight and the following 12 midnight during which any fuel is 
combusted at any time. This compliance approach is the same as the 
calculations and definitions used in developing the adjustment factor 
for this source.
---------------------------------------------------------------------------

    \11\ While at the time of publication, the evidence suggests 
that Homer City's three units have ceased operations, EPA's approval 
of this attainment plan is independent of Homer City's ceasing 
operations. Emissions data indicates that Units 1 and 2 last emitted 
on March 24, 2023, and December 11, 2022, and Unit 3 on May 17, 
2023. However, as the EPA is not aware of PADEP rescinding Homer 
City's operating permits,-Homer City ceasing operations does not 
guarantee that the units are permanently and enforceably shutdown. 
Importantly, PADEP's 2023 SIP submittal and the accompanying 
attainment demonstration, which the EPA is proposing to approve, 
properly accounted for Homer City's continued operation. To be 
clear, the EPA's proposed approval of this attainment plan is based 
on Homer City's possible continued operation.
    \12\ Conemaugh's 3-hour block average emission limits in PADEP's 
October 11, 2017 submission for each individual unit was roughly in 
line with the CEV modeled limit and the ratio from appendix C in 
EPA's 2014 SO2 Guidance. (87 FR 15166 at 15175, March 17, 
2022). Nonetheless, in its 2023 SIP submittal PADEP included a 
combined 3-hour block average emission limit using the 99th 
percentile ratio to develop the adjustment factor to calculate 
Conemaugh's 3-hour block combined averaging SO2 limit.
    \13\ Substituted values and nonoperating hours were not used in 
the calculations.
---------------------------------------------------------------------------

    The 1-hour SO2 CEVs, the adjustment factors, the longer-
term SO2 emission limits, and the averaging periods for the 
three other facilities are summarized in Table 2, in this document.

                    Table 2--Sources in Indiana, PA NAA With Longer-Term SO2 Emission Limits
----------------------------------------------------------------------------------------------------------------
                                        1-Hour CEV      Adjustment    Longer-term limit
               Source                    (lbs/hr)         factor           (lbs/hr)          Averaging period
----------------------------------------------------------------------------------------------------------------
Keystone............................           9,718           0.857              8,328  24-hr block.
Conemaugh...........................           3,159           0.975              3,080  3-hour block.
Seward..............................           3,830           0.756              2,895  30-operating day
                                                                                          rolling.
----------------------------------------------------------------------------------------------------------------

    Additionally, PADEP implemented a supplemental measure to control 
any potential hourly emissions spikes at Seward station. Seward shall 
inject limestone into Source ID 034 and Source ID 035 during initial 
firing each time Source ID 034 and Source ID 035 are operated to reduce 
the magnitude and frequency of SO2 emission spikes in 
accordance with good air pollution control practices.
    The EPA reviewed PADEP's adjustment factor calculations, including 
the selected years of emissions data and the exclusion of March through 
September of 2020 due to the COVID pandemic and the claim that the 
operation of Keystone and Conemaugh was not considered stable during 
that time period. The EPA notes that removing this period of time, and 
adding the period of March through September of 2022, produced similar 
adjustment factors as would have been calculated without replacing the 
data. The EPA reviewed the justification provided by PADEP regarding 
this issue and concludes that PADEP properly characterized the hourly 
load impact of the COVID pandemic in the data (i.e., shift from high 
load to low load operation during this time), and properly included 
data where stable operation of the sources was verified. PADEP followed 
the EPA's 2014 SO2 Nonattainment Guidance in developing the 
comparably stringent longer-term limits for Seward, Conemaugh and 
Keystone. The EPA is proposing to approve the longer-term emission 
limits described above as being comparably stringent to the 1-hour CEV 
for Seward, Conemaugh and Keystone, and as correcting the deficiencies 
of the 2017 submittal previously identified in 2022 by removing the 
previously approved (and retained as SIP strengthening) longer-term 
averaging SO2 limits for Keystone, Conemaugh, and Seward as 
described in the RACM/RACT section that follows.

B. RACM/RACT and Enforceable Emission Limitations

    Section 172(c)(1) of the CAA requires states to adopt and submit 
all RACM, including RACT, as needed to attain the standards as 
expeditiously as practicable. Section 172(c)(6) requires the SIP to 
contain enforceable emission limits and control measures necessary to 
provide for timely attainment of the standard.
    Pennsylvania's submittal discusses that the main SO2 
emitting sources at Conemaugh, Homer City, Keystone, and Seward are all 
equipped with FGD systems (wet limestone scrubbers, dry FGD, or in-
furnace limestone injection systems) to reduce SO2 
emissions. Table 3, in this document, lists the control technology at 
each of the main SO2 emitting sources at each facility.

[[Page 48530]]



                  Table 3--Control Technology at the Four Major SO2 Sources in the Indiana Area
----------------------------------------------------------------------------------------------------------------
                                                                                                      Control
                Facility                             Unit                     SO2 control          installation
                                                                                                       date
----------------------------------------------------------------------------------------------------------------
Conemaugh...............................  031--Main Boiler 1........  Wet limestone scrubber....           ~1994
                                          031--Main Boiler 2........  Wet limestone scrubber....           ~1995
Homer City..............................  031--Boiler 1.............  Dry FGD...................      11/18/2015
                                          032--Boiler 2.............  Dry FGD...................       5/23/2016
                                          033--Boiler 3.............  Wet limestone scrubber....           ~2002
Keystone................................  031--Boiler 1.............  Wet limestone scrubber....       9/24/2009
                                          032--Boiler 2.............  Wet limestone scrubber....      11/22/2009
Seward..................................  034--CFB Boiler 1.........  In-furnace limestone                 ~2004
                                                                       injection.
                                          035--CFB Boiler 2.........  In-furnace limestone                 ~2004
                                                                       injection.
----------------------------------------------------------------------------------------------------------------

    With these controls installed, Pennsylvania's submittal discusses 
facility-specific control measures, namely SO2 emission 
limits for Homer City, Conemaugh, Seward and Keystone. Homer City has a 
1-hour averaging period emission limit which was previously in its 
existing Title V Operating Permit (TVOP). The 1-hour SO2 CEV 
is equivalent to the 1-hour SO2 emission limit in the 
current TVOP #32-00055.
    PADEP issued Consent Order and Agreements (COAs) with both Keystone 
and Conemaugh on August 15, 2023, as well as Seward on August 17, 2023 
(2023 COAs), which established new emission limits that were 
demonstrated to provide for attainment in the Indiana, PA Area. PADEP 
has asked the EPA to incorporate into the SIP the following updated 
combination of SO2 emission limits for these three 
facilities (as well as the compliance strategies listed in the 
unredacted portion of the COAs found in appendix C of the state 
submittal):
     Keystone--Remove 9,600 lbs/hr on a 24-hour (daily) block 
average and replace with 8,328 lbs/hr combined based on a 24-hour block 
average for Boiler 1 & Boiler 2 (Source IDs 031 & 032).
     Seward--Remove 3,038.4 lbs/hr and replace with 2,895 lbs/
hr combined based on a 30-day operating hours average rolling by one 
day for Source IDs 034 & 035. Remove 13,308 tpy and replace with 12,680 
tpy combined for Source IDs 034 & 035.\14\ Add the requirement to 
inject limestone into Source ID 034 and Source ID 035 during initial 
firing each time Source ID 034 and Source ID 035 are operated to reduce 
the magnitude and frequency of SO2 emission spikes in 
accordance with good air pollution control practices.
---------------------------------------------------------------------------

    \14\ The new annual limit is calculated to be consistent with 
the new 30-day limit, and is considered a supplemental limit.
---------------------------------------------------------------------------

     Conemaugh--Add 3,080 lbs/hr combined on a 3-hour block 
average for Units 1 & 2 (Source IDs 031 & 032).\15\
---------------------------------------------------------------------------

    \15\ Conemaugh's new 3,080 lbs/hr combined 3-hour block average 
limit for Units 1 and 2 is in addition to the emission limits 
retained as SIP strengthening in the 2022 Partial Approval/Partial 
Disapproval. Specifically, this action does not remove the 1,656 
lbs/hr emission limit on a 3-hour block average for Units 1 and 2 
individually.
---------------------------------------------------------------------------

    These emissions limits and associated compliance parameters will be 
federally enforceable upon the EPA's approval of the SIP. The EPA 
retained Homer City's 1-hour SO2 emission limit as a SIP 
strengthening measure in its 2022 Partial Approval/Partial Disapproval 
and now proposes to retain that limit as part of PADEP's attainment 
demonstration here.
    The emission limits described here have been shown to provide for 
attainment of the NAAQS, and thus the EPA is proposing to determine 
that these are emissions limitations as defined under CAA section 
302(k) that are necessary and appropriate to meet the applicable 
requirements of the CAA under CAA section 110(a)(2)(A), including that 
the state's plan satisfies requirements for RACM/RACT under CAA section 
172(c)(1) and includes enforceable emission limitations as may be 
necessary and appropriate to provide for attainment of the NAAQS under 
CAA section 172(c)(6). The EPA is also proposing to determine that the 
removal of Keystone and Seward's previously SIP-approved SO2 
emission limits (87 FR 50778, August 18, 2022) and replacement with the 
new SO2 emission limits listed in Table 2 of this document 
does not pose an issue with respect to CAA section 110(l) or 193.\16\
---------------------------------------------------------------------------

    \16\ Under CAA sections 110(l) and 193, the EPA may not approve 
a SIP that would interfere with any applicable requirement 
concerning NAAQS attainment and RFP, or any other applicable 
requirement, and no requirement in effect before November 15, 1990 
(or required to be adopted by an order, settlement, agreement, or 
plan in effect before November 15, 1990), in any area which is a 
nonattainment area for any air pollutant, may be modified in any 
manner unless it ensures equivalent or greater emission reductions 
of such air pollutant. The newly established emissions limit for 
Keystone of 8,328 on 24-hour block period is more stringent that the 
previously SIP-approved emission limit of 9,600 lb/hr on a 24-hour 
block period, and the newly established emission limits for Seward 
of 2,895 lb/hr on a 30-operating day rolling average is more 
stringent that the previously SIP-approved emission limit of 3,084.4 
lb/hr on a 30-operating day rolling average.
---------------------------------------------------------------------------

C. Reasonable Further Progress (RFP)

    Section 172 of the CAA requires Pennsylvania's attainment plan to 
provide for RFP toward attainment. The relationship between 
SO2 and sources is more directly quantifiable as compared to 
other NAAQS pollutants, and there is usually a single step between pre-
control nonattainment and post-control attainment. Therefore, for 
SO2 SIPs, which address a small number of affected sources, 
requiring expeditious compliance with attainment emission limits can 
address the RFP requirement. To be approved by the EPA under CAA 
section 192(a), attainment plans need to provide for future attainment 
of the NAAQS as expeditiously as practicable, but no later than 5 years 
from the effective date of the area's designation as nonattainment. For 
areas designated nonattainment effective October 4, 2013, attainment 
plans were required to contain demonstrations that the area would 
attain as expeditiously as practicable, but no later than October 4, 
2018.
    The four sources in the Indiana, PA NAA were subject to federally 
enforceable SO2 emissions limits since the EPA's initial 
approval of the 2017 SIP submittal on October 19, 2020 (85 FR 66240, 
October 19, 2020). After the 2022 Partial Approval/Partial Disapproval 
of the 2017 SIP submittal, those emission limits remained in the SIP as 
SIP strengthening measures. The appropriate SO2 limits were 
already established for Homer City effective February 28, 2017 in the 
state permit, and remain the same as they were since being incorporated 
into the SIP effective November 18, 2020. For the remaining three 
sources, Keystone, Seward, and

[[Page 48531]]

Conemaugh, due to the timeline of events, it was not practical for 
Pennsylvania to have a compliance schedule which provided for 
attainment no later than 5 years from the area's designation of 
nonattainment (i.e., October 4, 2018). However, in response to the 
EPA's 2022 partial disapproval of its SIP for the Indiana, PA NAA, 
Pennsylvania acted quickly in establishing new emission limits which 
provide for attainment in the Indiana, PA NAA as expeditiously as 
practicable with this 2023 SIP submittal. Through the aforementioned 
COAs dated August 15, 2023 for Keystone and Conemaugh and August 17, 
2023 for Seward, the new limits were effective immediately after the 
date of each of the 2023 COAs. The EPA asserts that PADEP established 
the emission limits as expeditiously as practicable to provide for 
attainment in the Indiana, PA NAA and to remedy the EPA's 2022 partial 
disapproval, and therefore the EPA proposes to find that Pennsylvania's 
plan provides for RFP, based on the proposed determination that the 
revised emissions limitations as defined under CAA section 302(k) are 
necessary and appropriate to meet the applicable requirements of the 
CAA, including the RFP requirement of CAA section 172(c)(2).

D. Contingency Measures

    Section 172 of the CAA requires that attainment plans include 
additional measures, called contingency measures, which will take 
effect if an area fails to meet RFP or fails to attain the standard by 
the attainment date. The EPA's 2014 SO2 Nonattainment 
Guidance describes special features of SO2 planning that 
influence the suitability of alternative means of addressing the 
requirement in CAA section 172(c)(9) for contingency measures for 
SO2. That is, SO2 control measures are based on 
what is directly and quantifiably necessary to attain the 
SO2 NAAQS, and consequently, an area that implements such 
control measures would be unlikely to fail to attain the NAAQS.\17\ 
Therefore, an appropriate means of satisfying the contingency measures 
requirement is for the state to have a comprehensive enforcement 
program that identifies sources of violations of the SO2 
NAAQS and for the state to undertake aggressive follow-up for 
compliance and enforcement. Pennsylvania's plan provides for satisfying 
the contingency measure requirement in this manner for the 
nonattainment area. PADEP has a comprehensive compliance and 
enforcement program to identify sources of violations of the 2010 1-
hour SO2 NAAQS and can undertake aggressive follow-up for 
compliance and enforcement including the ability to enact a COA in a 
timely manner (section 4(27) of the Pennsylvania Air Pollution Control 
Act, 35 P.S. section 4004(27)). The EPA is proposing to approve the 
emissions limits from the 2023 SIP submittal as enforceable limitations 
under CAA section 302(k) which are necessary and appropriate to provide 
for attainment of the standard in the Indiana, PA NAA and meet the 
requirements of the CAA, including sections 110(a)(2)(A), 172(c)(1), 
172(c)(2), and 172(c)(6). Consequently, the EPA is proposing to find 
that PA's comprehensive enforcement program for such necessary and 
appropriate emission limitations is an appropriate contingency measure 
for this area and meets the requirement of CAA section 172(c)(9).
---------------------------------------------------------------------------

    \17\ See 75 FR 35520 at 35576 (June 22, 2010) and the 2014 
SO2 Nonattainment Guidance.
---------------------------------------------------------------------------

III. Proposed Action

    The EPA is proposing to approve Pennsylvania's SIP revision 
submitted to the EPA on October 5, 2023, for the purpose of attaining 
the 2010 1-hour SO2 NAAQS for the Indiana, PA NAA. 
Specifically, the EPA is proposing to approve the following elements of 
this SO2 attainment plan: Pennsylvania's attainment 
demonstration for the nonattainment area, RACT/RACM and emission 
limitations, RFP plan, and contingency measures. The EPA previously 
approved Pennsylvania's attainment plan requirements regarding 
nonattainment area Emissions Inventory and NNSR.
    The EPA is proposing to conclude that the modeling and comparably 
stringent longer-term emission limits in Pennsylvania's plan adequately 
demonstrate that the control requirements in the COAs provide for 
attainment in the area. This attainment plan also properly addresses 
requirements for RACT/RACM and emission limitations, RFP, and 
contingency measures because the plan now includes emission limits that 
provide for attainment. Thus, the EPA is proposing to determine that 
Pennsylvania's Indiana Area SO2 attainment plan meets the 
applicable requirements of CAA sections 172, 191, and 192. The EPA is 
taking public comments for thirty days following the publication of 
this proposed action in the Federal Register. The EPA will take these 
comments into consideration in our final action.

IV. Incorporation by Reference

    In accordance with requirements of 1 CFR 51.5, the EPA is proposing 
to incorporate by reference the SO2 emission limits and 
compliance parameters established in (the unredacted portions of) the 
COAs for Seward, Conemaugh and Keystone facilities as discussed in 
section II. of this document. The EPA has made, and will continue to 
make, these materials generally available through https://www.regulations.gov and at the EPA Region III Office (please contact 
the person identified in the FOR FURTHER INFORMATION CONTACT section of 
this preamble for more information).

V. Statutory and Executive Order Reviews

    Under the CAA, the Administrator is required to approve a SIP 
submission that complies with the provisions of the CAA and applicable 
Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in 
reviewing SIP submissions, the EPA's role is to approve state choices, 
provided that they meet the criteria of the CAA. 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 proposed 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);
     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); and

[[Page 48532]]

     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.
    Executive Order 12898 (Federal Actions to Address Environmental 
Justice in Minority Populations and Low-Income Populations, 59 FR 7629, 
February 16, 1994) directs Federal agencies to identify and address 
``disproportionately high and adverse human health or environmental 
effects'' of their actions on minority populations and low-income 
populations to the greatest extent practicable and permitted by law. 
The EPA defines environmental justice (EJ) as ``the fair treatment and 
meaningful involvement of all people regardless of race, color, 
national origin, or income with respect to the development, 
implementation, and enforcement of environmental laws, regulations, and 
policies.'' The EPA further defines the term fair treatment to mean 
that ``no group of people should bear a disproportionate burden of 
environmental harms and risks, including those resulting from the 
negative environmental consequences of industrial, governmental, and 
commercial operations or programs and policies.'' PADEP did not 
evaluate environmental justice considerations as part of its SIP 
submittal; the CAA and applicable implementing regulations neither 
prohibit nor require such an evaluation. The EPA did not perform an EJ 
analysis and did not consider EJ in this action. Due to the nature of 
the action being taken here, this action is expected to have a neutral 
to positive impact on the air quality of the affected area. 
Consideration of EJ is not required as part of this action, and there 
is no information in the record inconsistent with the stated goal of 
E.O. 12898 of achieving environmental justice for people of color, low-
income populations, and Indigenous peoples.
    In addition, this proposed rulemaking, approval of Pennsylvania's 
Indiana Area SO2 attainment plan, does not have tribal 
implications as specified by Executive Order 13175 (65 FR 67249, 
November 9, 2000), because the SIP is not approved to apply in Indian 
country located in the State, and EPA notes that it will not impose 
substantial direct costs on tribal governments or preempt tribal law.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Intergovernmental relations, Reporting and recordkeeping 
requirements, Sulfur oxides.

Adam Ortiz,
Regional Administrator, Region III.
[FR Doc. 2024-11175 Filed 6-6-24; 8:45 am]
BILLING CODE 6560-50-P