[Federal Register Volume 89, Number 178 (Friday, September 13, 2024)]
[Rules and Regulations]
[Pages 74836-74847]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-20598]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R03-OAR-2024-0024; FRL-11529-02-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: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is approving a state 
implementation plan (SIP) revision submitted by the Commonwealth of 
Pennsylvania (Pennsylvania or PA). The revision pertains to the 
attainment plan for the Indiana, PA nonattainment area for the 2010 1-
hour sulfur dioxide (SO2) national ambient air quality 
standard (NAAQS). The EPA is approving these revisions to the 
Pennsylvania SIP in accordance with the requirements of the Clean Air 
Act (CAA).

DATES: This final rule is effective on October 15, 2024.

ADDRESSES: EPA has established a docket for this action under Docket ID 
Number EPA-R03-OAR-2024-0024. All documents in the docket are listed on 
the www.regulations.gov website. Although listed in the index, some 
information is not publicly available, e.g., 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: 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:

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

[[Page 74837]]

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, PA Nonattainment Area (hereafter referred to as 
``the Indiana, PA NAA'') (which encompasses Indiana County, and 
Plumcreek Township, South Bend Township and Elderton Borough of 
Armstrong County) was designated as nonattainment for the 2010 
SO2 NAAQS. The area 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). 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 nonattainment new source review (NNSR) 
program requirements, and disapproved the attainment demonstration, 
reasonably available control measures and reasonably available control 
technology (RACM/RACT) requirements, reasonable further progress (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 the 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 the 
EPA to promulgate a FIP within two years unless Pennsylvania has 
submitted, and the EPA has fully approved, a plan addressing the 
disapproved attainment planning requirements.
    On October 12, 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, 
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 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;

[[Page 74838]]

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\ Memorandum from Stephen D. Page, ``Guidance for 1-Hour 
SO2 Nonattainment Area SIP Submissions'', April 23, 2014. 
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, 57 FR 13498 at 
13567-68 (April 16, 1992). SO2 attainment plans must consist 
of two components: (1) emission limits and other controls, including 
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).

II. Summary of SIP Revision and EPA Analysis

    On June 7, 2024 (89 FR 48523), the EPA published a notice of 
proposed rulemaking (NPRM) for Pennsylvania. In the NPRM, the EPA 
proposed approval of a revision to Pennsylvania's SIP to demonstrate 
attainment of the 2010 SO2 NAAQS in the Indiana, PA NAA. As 
noted, Pennsylvania submitted the formal SIP revision on October 12, 
2023. This submission includes Pennsylvania's attainment demonstration 
and other attainment plan elements required under the CAA, including 
the requirement for meeting RFP toward attainment of the NAAQS, 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 
NNSR program, as these were previously approved by the EPA (87 FR 
50778, August 18, 2022). In this action, the EPA is determining that 
the Pennsylvania 1-hour SO2 attainment plan for Indiana, PA 
meets the applicable statutory and regulatory requirements and is thus 
approving Pennsylvania's submission into its SIP. Also, the EPA is 
incorporating the following SO2 emission limits into the 
source-specific section of the PA SIP for the Keystone Plant, Conemaugh 
Station and Seward Station (as well as the compliance strategies listed 
in the unredacted portion of the Consent Order and Agreements (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. 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.
     Conemaugh--Add 3,080 lbs/hr combined on a 3-hour block 
average for Units 1 & 2 (Source IDs 031 & 032).
    Other specific requirements of the Indiana County attainment plan 
and the rationale for the EPA's action are explained in the NPRM, and 
its associated technical support document (TSD), and will not be 
restated here.

III. EPA's Response to Comments Received

    The EPA received four sets of comments in response to the NPRM. Two 
sets of comments were in opposition to the EPA's proposed action. The 
EPA also received one comment in support of the EPA's proposed action 
and one that was not relevant.
    Comment 1. The comment asserts that the EPA's interpretation of 
what contingency measures are permissible in an SO2 
attainment plan is not the ``best reading'' of the Clean Air Act. The 
comment cites section 172(c)(9), Contingency Measures, emphasizing that 
contingency measures take effect ``without further action by the State 
or Administrator.'' The comment takes issue with the approach to 
SO2 contingency measures set forth in the EPA's General 
Preamble, which states that ``contingency measures'' mean ``. . . the 
State agency has a comprehensive program to identify sources of 
violations of the SO2 NAAQS and to undertake an aggressive 
follow-up for compliance and enforcement.'' See 57 FR 13498 at 13547 
(April 16, 1992). The comment asserts that an enforcement action is 
``further action,'' which contradicts section 172(c)(9). Additionally, 
the comment claims that the EPA's citation to the state's authority to 
enforce its SIP is already required by CAA section 110(a)(2)(C) and 
does not necessarily meet the conditions of an enforcement program, let 
alone the contingency measure requirement, without a schedule and 
mechanism requiring action when violations occur. The comment suggests 
alternative contingency measures including switching to low-sulfur 
fuel, limiting operation until the SIP is revised, or a daily 
SO2 emission limit. Lastly, the comment states that the SIP 
lacks provisions to ensure ``aggressive follow-up'' can and will take 
place in the event the area fails to attain the NAAQS and therefore 
fails to meet the requirements of section 172(c)(9).
    Response 1. The EPA disagrees with this comment.
    First, as a general matter, the EPA's longstanding approach to 
contingency

[[Page 74839]]

measures in SO2 attainment plans, based on the Agency's 
technical expertise and understanding of control strategies addressing 
SO2, has been consistently applied by the EPA and states 
since shortly after the enactment of the 1990 Clean Air Act Amendments, 
including in the General Preamble, updated guidance memoranda \4\ and 
numerous SO2 SIP approval actions.\5\
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    \4\ SO2 Guideline Document, U.S. Environmental 
Protection Agency, Office of Air Quality Planning and Standards, 
Research Triangle Park, NC 27711, EPA-452/R-94-008, February 1994 
(1994 SO2 Guideline); Guidance for 1-Hour SO2 
Nonattainment Area SIP Submissions, Office of Air Quality Planning 
and Standards, Stephen D. Page, April 23, 2014 (2014 SO2 
Nonattainment Guidance).
    \5\ 87 FR 61514, 61522-61523 (October 12, 2022); 84 FR 51988, 
51994-51995 (October 1, 2019); 84 FR 32672, 32677 (July 9, 2019) 
(final rule 84 FR 49659 (September 23, 2019); 83 FR 51629, 51632-
51633 (October 12, 2018); 83 FR 40487, 40497 (August 15, 2018) 
(final rules 85 FR 49967 (August 17, 2020) and 84 FR 10692 (March 
22, 2019)); 82 FR 45242, 45251 (September 28, 2017) (final rule 83 
FR 25922 (June 5, 2018)); 82 FR 40086, 40097-40098 (August 24, 2017) 
(final rule 85 FR 73218 (November 17, 2020)).
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    Second, in response to the comment's specific objection that 
contingency measures are to take effect ``without further action,'' the 
EPA has interpreted ``without further action'' in the ozone, lead, and 
carbon monoxide contexts to mean no further rulemaking or legislative 
action, though the EPA recognized that certain actions such as 
notification of sources or modifications of permits would be needed for 
effective implementation. 57 FR 13498, 13512 and 13533 (April 16, 
1992), 58 FR 67748, 67752 (December 22, 1993). Undertaking enforcement 
against sources for violations of emission limitations that were 
necessary to provide for SO2 NAAQS attainment is consistent 
with the EPA's longstanding position across all of the NAAQS that 
ministerial actions to effectuate contingency measures, rather than 
additional rulemaking or legislative action to adopt new contingency 
measures, is appropriate to meet the requirements of CAA section 
172(c)(9). To commence an enforcement action when an emission 
limitation violation is identified, no further administrative or 
legislative action is necessary, and the state can expeditiously 
proceed to remedy the violation--even without needing to wait to 
determine whether such violation has caused or contributed to a 
violation of the NAAQS in the nonattainment area.
    Contrary to the comment's suggestion that Pennsylvania does not 
have a comprehensive enforcement program as required by CAA section 
110(a)(2)(C), Pennsylvania has such a program as specified in section 
4(27) of the Pennsylvania Air Pollution Control Act (APCA), 35 P.S. 
Sec.  4004(27), which authorizes the Pennsylvania Department of 
Environmental Protection (PADEP) to take any action it deems necessary 
or proper for the effective enforcement of the Act and the rules and 
regulations promulgated thereunder. Such actions include the issuance 
of orders (i.e., enforcement orders and orders to take corrective 
action to address air pollution or the danger of air pollution from a 
source) and the assessment of civil penalties. Any person in violation 
of the APCA, the rules and regulations, any order of PADEP, or a plan 
approval or operating permit conditions could also be subject to 
criminal fines upon conviction under section 9, 35 P.S. Sec.  4009. 
Section 7.1 of the APCA, 35 P.S. Sec.  4007.1, prohibits PADEP from 
issuing plan approvals and operating permits for any applicant, 
permittee, or a general partner, parent or subsidiary corporation of 
the applicant or the permittee that is placed on PADEP's Compliance 
Docket until the violations are corrected to the satisfaction of PADEP. 
Consequently, the EPA disagrees with the comment's assertion that in 
order to credit PADEP's comprehensive enforcement program as satisfying 
the CAA section 172(c)(9) SO2 contingency measure 
requirement, the program would have to include elements such as 
mandatory additional penalties or elimination of agency discretion to 
prosecute violations.
    Again, the enforcement process is more streamlined and targeted 
compared to rulemaking or legislation, which as discussed above, is 
considered disallowed ``further action'' for other criteria pollutants, 
and moreover enforcement is more akin to permissible implementation 
steps such as notification of sources and modification of permits. 
Compare 57 FR 13498, 13547 (April 16, 1992) (discussing a comprehensive 
program to identify violations and undertaking aggressive follow-up for 
compliance and enforcement) with 57 FR 13498, 13512 and 13533 (April 
16, 1992) (interpreting ``without further action'' to mean no further 
rulemaking or legislation but to allow implementation steps such as 
modification of permits and notification of sources) and 58 FR 67748, 
67752 (December 22, 1993). Thus, enforcement serves as an appropriate 
contingency measure for SO2 nonattainment SIPs.
    In addition to having a fully approved comprehensive enforcement 
program, PADEP has included what it refers to as additional contingency 
measures that are automatically triggered based on varying parameters, 
as described below.\6\ First, when any of the four sources' emissions 
in the NAA reach 99% of the SO2 emissions limit for the 
facility, within 48 hours the facility is required to undertake a full 
system audit of the SO2 emitting sources and submit a 
written report to PADEP within 15 days, and corrective actions shall be 
identified by PADEP as necessary. Second, if the Strongstown monitor in 
the NAA registers a daily maximum 1-hour average concentration 
exceeding 75 ppb, PADEP will notify the facilities in the NAA, and each 
facility is required to identify whether any of its SO2-
emitting sources were running at the time of the exceedance, and within 
a reasonable time period leading up to the exceedance, not to exceed 24 
hours. If any of the SO2-emitting sources were running at 
the time of the exceedance, the facility must then analyze the 
meteorological data on the day the hourly exceedance occurred to ensure 
that the exceedance was not due to SO2 emissions from the 
respective facility. The facility's findings must be submitted to PADEP 
within 30 days of being notified of the exceedance.\7\ These emissions-
threshold-activated and exceedance-activated measures further ensure 
that ``aggressive follow-up'' will occur without further regulatory 
steps taken by the state. They also further reduce the likelihood of a 
violation of the emission limits or NAAQS. These measures are in line 
with the additional contingency measures the EPA mentions in the 2014 
SO2 Nonattainment Guidance and in the General Preamble and 
are included in the Pennsylvania SIP.\8\ The most recent

[[Page 74840]]

design values at the Strongstown monitor in the NAA are 19 ppb in 2022, 
22 ppb in 2021, and 25 ppb in 2020, which are well below the 1-hour 
primary 2010 SO2 NAAQS of 75 ppb. The proactive nature of 
PADEP's emissions-threshold-activated and exceedance-activated 
measures, as well as the direct quantifiable impact of the 
SO2 control measures and the current design values in the 
NAA, make it very unlikely that a NAAQS violation could occur in this 
area while the sources are complying with their emission limits.
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    \6\ These measures enhance Pennsylvania's fully approved 
enforcement program that serves to meet the contingency measure 
requirement, are not necessary to meet applicable requirements of 
the CAA under section 110(a)(2)(A), and are already included in the 
SIP.
    \7\ Note the daily maximum 1-hour average concentration can be 
above 75 ppb multiple times in one year and still not violate the 
NAAQS due to the statistical nature of the design values. Therefore, 
this measure could be triggered multiple times before a design value 
of 75 ppb, and therefore a NAAQS violation, ever occurs.
    \8\ These exceedance-activated and emissions-threshold-activated 
measures were retained in the SIP, as explained in the partial 
disapproval, 87 FR 15166, 15177 (March 17, 2022) (final rule 
published 87 FR 50778 (August 18, 2022)), and the 2023 SIP 
submittal's attainment plan reiterates these requirements and the 
plan will be included in the SIP. For the sake of clarity and 
consistency, Keystone's COA will be removed from the SIP because the 
state has requested the removal of the 9600 lb/hr 24-hr 
SO2 emission limit which was approved into the SIP via a 
source-specific SIP revision based on the COA; included in that COA 
is the emissions-threshold activated measure which in the COA is 
based on the previously disapproved emissions limit. With the 
approval of the 2023 attainment plan into the SIP, the emissions-
threshold activated measure and the exceedance-activated measure for 
Keystone are still included in the SIP.
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    The comment listed several options for contingency measures that 
the comment suggests should be included in the SIP. The EPA 
acknowledges that one or more of these options may be appropriate in a 
specific situation, and for a specific source, if the area fails to 
achieve RFP or fails to attain the NAAQS by the statutory attainment 
date. However, because Indiana, PA is a multisource area with several 
emission units per facility, requiring one or more of these measures 
may not be appropriate depending on the cause of the potential 
violations of the SO2 standard, which would need to be 
evaluated at the time of occurrence. For example, triggering a fuel-
switch at one facility may not bring the area into attainment if the 
issue is caused by another facility violating its limit. Similarly, 
limiting operation of one facility may be appropriate if the subject 
facility is the cause of the problem, but requiring further measures at 
other facilities may not be warranted where the cause of the NAAQS 
violation was non-compliance with emission limits by a different 
facility and where the NAAQS violation can be most efficiently remedied 
by bringing that source into compliance with its established emission 
limits. Likewise, limiting operations at all SO2-emitting 
facilities in the area may not appropriately address the issue due to 
the localized nature of SO2 emissions and possible direct 
link between ambient concentrations and emissions from a specific 
facility. Similarly, changing the limits at all facilities, for example 
from a longer-term limit to a shorter-term limit, may appropriately 
address the problem, but it also may not, and the state would evaluate 
appropriate measures if and when an issue arises. These are 
illustrative examples, and while not exhaustive, they highlight the 
need for the state to be able to respond appropriately in a particular 
scenario due to the localized nature of SO2 impacts.
    In summary, the EPA's longstanding approach to implementing the 
section 172(c)(9) contingency measures requirement in SO2 
attainment plans via comprehensive enforcement programs is appropriate. 
This approach is based upon the EPA's technical expertise and in-depth 
understanding of SO2 control strategies and is consistent 
with the approaches undertaken for other criteria pollutants that have 
distinguished acceptable ministerial steps from regulatory or 
legislative action in satisfying the Act's requirement that contingency 
measures take effect ``without further action.'' Accordingly, in this 
case, Pennsylvania's fully approved comprehensive enforcement program, 
and as bolstered by the state's aforementioned requirements that are 
triggered automatically when emissions thresholds are reached or NAAQS 
exceedances are recorded, is approved as meeting the CAA section 
172(c)(9) contingency measure requirement.
    Comment 2. A comment takes issue with the EPA's approach to 
attainment determinations when an area initially fails to attain by the 
attainment date. The comment cites the requirement for the EPA to 
determine within six months of the attainment date whether the standard 
has been attained for a given area. Section 179(c)(1) of the Clean Air 
Act further states that if the Administrator has found that the area 
did not attain, the EPA ``may revise or supplement such determination 
at any time based on more complete information or analysis concerning 
the area's air quality as of the attainment date.'' The comment notes 
that the EPA's 1996 SO2 Memorandum \9\ and 2014 
SO2 Nonattainment Guidance do not require a new SIP 
submittal and further modeling is not required if the source 
characteristics are ``still reasonably represented.'' The comment 
claims that the EPA ought to require states to submit a demonstration 
that modeling assumptions have not changed. The comment states that 
because neither the EPA nor the state are reevaluating modeling 
assumptions, there is an added responsibility on the public to comment 
on the record on proposed attainment determinations. Lastly, the 
comment notes that this issue is magnified by the improper use of 30-
day rolling averages as emission limits, further complicating 
compliance.
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    \9\ Memorandum from Sally L. Shaver, ``Attainment Determination 
Policy for Sulfur Dioxide Nonattainment Areas'', January 26, 1996 
(1996 SO2 Memorandum).
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    Response 2. This comment is outside the scope of this action and 
does not require a response. The EPA notes that in this action, it is 
not implementing CAA section 179(c) or making a determination of 
attainment by the attainment date. To the extent the comment relates to 
objections to the emission limits adopted in the attainment plan, as 
explained elsewhere, the EPA concludes that the plan will provide for 
attainment, accounting for worst-case allowable emissions and 
meteorology.
    Comment 3. The comment asserts that the EPA's approach to 
reasonably available control measures (RACM) and reasonably available 
control technology (RACT) in the context of SO2 attainment 
plans is not the ``best reading'' of the Clean Air Act. The comment 
cites the EPA's 2014 SO2 Nonattainment Guidance, stating 
that the requirement to implement all RACM is fulfilled if a plan 
provides for attainment of the SO2 standards. The comment 
then cites requirements for attainment plans, 42 U.S.C. 7502(c)(1) 
(emphasis added):

    Such plan provisions shall provide for the implementation of all 
reasonably available control measures as expeditiously as 
practicable (including such reductions in emissions from existing 
sources in the area as may be obtained through the adoption, at a 
minimum, of reasonably available control technology) and shall 
provide for attainment of the national primary ambient air quality 
standards.

    In interpreting the provision, the comment highlights the word 
``and'' in these nonattainment plan provisions, stating that the 
requirement for all RACM and RACT must be fulfilled and the requirement 
for attainment must also be met. The comment also states that the EPA 
must give effect to every word and phrase in a statutory provision and 
that the EPA has failed to give effect to the requirement that all 
RACM/RACT be implemented. Next, the comment claims that the EPA fails 
to consider the plain meaning of statutory terms in reference to 
``available'' control options. The comment claims that the EPA's 
proposal fails to determine whether additional controls are needed and 
is lacking an analysis of control efficiencies for existing and 
potential controls, as well as costs for upgrades.
    Response 3. In identifying the ``best reading'' of a statutory 
requirement, the EPA has considered the overall and specific purpose of 
the requirement, the technical context in which it is imposed, and the 
most reasonable manner in which its obligations may be fulfilled. The 
Clean Air Act nonattainment planning requirements in section 172(c) 
applicable to states are set

[[Page 74841]]

in place to provide for attainment and subsequent maintenance of the 
NAAQS in a designated nonattainment area--i.e., an area which the EPA 
has previously determined is not meeting the NAAQS. All section 172(c) 
requirements are targeted to remedy that NAAQS-violating occurrence. As 
the comment referenced, RACM/RACT is required under Clean Air Act 
section 172(c)(1) for nonattainment areas. Section 172(c)(1) of the CAA 
requires the implementation of all RACM as expeditiously as practicable 
(including such reductions in emissions from existing sources in the 
area as may be obtained through the adoption, at a minimum, of RACT) 
and shall provide for attainment of the NAAQS.
    The comment suggests that the RACM/RACT requirement of section 
172(c)(1) requires a state to assess and adopt measures that go further 
than what is necessary to attain the SO2 NAAQS in the 
nonattainment area, but such an approach undercuts the purpose of this 
provision as applied in the SO2 nonattainment plan context. 
At its core, this RACM/RACT requirement serves to remedy the status quo 
situation of an area not meeting the NAAQS, in order to prospectively 
achieve NAAQS attainment. This is clear from the requirement's 
placement within one of the two paragraphs in section 172(c)--along 
with section 172(c)(6)'s requirement that the plan include emissions 
limitations as necessary to provide for NAAQS attainment--that specify 
enumerated remedial measures that are not otherwise required absent an 
area's being designated nonattainment. Moreover, when applied in the 
SO2 nonattainment plan context, these provisions of section 
172(c) must be read in concert with the other applicable statutory 
provision that Congress enacted in 1990 specifically governing 
SO2 plans, section 192(a), that similarly stressed the need 
for remedial implementation plans to provide for NAAQS attainment. As 
explained elsewhere and further below, for SO2 the EPA has 
long taken the technical view that this source-oriented pollutant, 
compared to more regional pollutants like ozone and particulate matter, 
can be addressed via identification of necessary emission limits, and 
the control measures needed to meet them, that will provide for 
attaining air quality. When that analysis has been undertaken and 
appropriate attainment-providing emission limits have been devised, the 
central purpose of the section 172(c) attainment planning requirements 
will have been fulfilled, and it is not necessary to require additional 
controls. Consequently, the EPA does not consider that it would be the 
``best reading'' of the RACM/RACT requirement to interpret 
``reasonably'' in section 172(c)(1), when applied in the SO2 
SIP context, as requiring imposition of additional controls when those 
that are necessary to provide for NAAQS attainment have already been 
identified and required.
    For decades, the EPA has consistently defined RACT for 
SO2 as that control technology that will achieve the NAAQS 
within statutory timeframes. See, e.g., General Preamble, 57 FR 13498, 
13547 (April 16, 1992), which was published soon after the enactment of 
the 1990 Clean Air Act Amendments; see also, 1994 SO2 
Guideline at 6-39. RACT for certain other criteria pollutants is 
control technology that is reasonably available considering 
technological and economic feasibility (see December 9, 1976 memorandum 
from Roger Strelow, ``Guidance for Determining Acceptability of SIP 
Regulations in Non-Attainment Areas''). The EPA's definition of RACT 
for SO2, as that control technology which is necessary to 
achieve the NAAQS (40 CFR 51.100 (o)),\10\ is based on the specific 
characteristics of SO2. Since SO2 RACT is already 
defined as the technology necessary to achieve the SO2 
NAAQS, control technology that failed to achieve the NAAQS would fail 
to be SO2 RACT, and control technology beyond what is 
necessary to attain the SO2 NAAQS would be beyond the 
central purpose of the nonattainment planning requirements of section 
172(c).
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    \10\ RACT means devices, systems, process modifications, or 
other apparatus or techniques that are reasonably available taking 
into account: (1) The necessity of imposing such controls in order 
to attain and maintain a national ambient air quality standard; (2) 
The social, environmental, and economic impact of such controls; and 
(3) Alternative means of providing for attainment and maintenance of 
such standard. (This provision defines RACT for the purposes of 40 
CFR 51.341(b) only.)
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    When determining RACT for SO2, it is appropriate to take 
into account the necessity of the control in meeting the standard. As 
noted, the EPA's definition of RACT in the SO2 nonattainment 
context accounts for the characteristics of the specific pollutant. For 
a pollutant such as SO2, the relationship between an 
individual source's emissions and the overall air quality can be 
explicitly quantified, and the emission reductions necessary to attain 
the NAAQS are based on a limited number of sources in a NAA.\11\ 
Therefore, a state can explicitly calculate the emission reductions 
necessary to provide for attainment of the SO2 NAAQS, and it 
is appropriate not to require states to impose control measures 
requiring further reductions beyond what is necessary to achieve 
attainment.
---------------------------------------------------------------------------

    \11\ For reference, in the Indiana, PA NAA, 99.6% of the area's 
SO2 emissions inventory comes from the four facilities 
controlled in the attainment plan.
---------------------------------------------------------------------------

    For the Indiana, PA NAA, PADEP provided the necessary modeling, 
which demonstrated the specific hourly emission limits (and comparably 
stringent longer-term limits) that are required to provide for 
attainment of the standard. The EPA reviewed this modeling and 
determined it comports with the EPA's Guideline on Air Quality Models 
(40 CFR part 51, appendix W) and the EPA's 2014 SO2 
Nonattainment Guidance. Therefore, the EPA concluded that the emission 
limits established as RACM were shown to provide for attainment and 
thus met the longstanding definition of RACT for SO2. PADEP 
implemented these emission limits as expeditiously as practicable (with 
Keystone's and Conemaugh's limits effective immediately after August 
15, 2023, and Seward's limits effective immediately after August 17, 
2023 via Consent Orders and Agreements).
    While the comment disagrees with the EPA's approach to RACM/RACT 
for SO2 and characterizes its version as a better reading of 
the Act, the comment does not explain why its reading of the Act is a 
better reading specific to the SO2 NAAQS. The comment does 
not address the specific characteristics of the pollutant, 
characteristics that the EPA has considered while it has consistently 
defined RACT for SO2.\12\
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    \12\ The comment refers to the visibility program's method of 
determining retrofit controls. However, the visibility program 
operates under a different statutory and regulatory framework, and 
SO2 is one of many visibility impairing pollutants.
---------------------------------------------------------------------------

    As discussed above, this has been the EPA's longstanding definition 
and approach for SO2 RACT since the 1990 Clean Air Act 
Amendments. The EPA has consistently applied this definition of 
SO2 RACT and promulgated numerous implementation plan 
approvals using this approach.\13\ Consequently, the EPA disagrees with 
the comment's assertion that its approach does not reflect the ``best

[[Page 74842]]

reading'' of Clean Air Act section 172(c)(1) for SO2 
implementation plans.
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    \13\ 87 FR 61514, 61520-61521 (October 12, 2022); 84 FR 32672, 
32676-32677 (July 9, 2019) (final rule 84 FR 49659 (September 23, 
2019); 83 FR 50314, 50321-50324 (October 5, 2018) (final rule 84 FR 
51988 (October 1, 2019)); 83 FR 12516, 12519-12520 (March 22, 2018) 
(final rule 83 FR 51629 (October 12, 2018); 83 FR 40487, 40497 
(August 15, 2018) (final rules 85 FR 49967 (August 17, 2020) and 84 
FR 10692 (March 22, 2019)); 82 FR 45242, 45250-45251 (September 28, 
2017) (final rule 83 FR 25922 (June 5, 2018)); 82 FR 40086, 40096-
40097 (August 24, 2017) (final rule 85 FR 73218 (November 17, 
2020)).
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    Comment 4. Two comments claim that longer-term emission limits do 
not support attainment of the 1-hour SO2 standard. One 
comment states that the EPA's 2014 SO2 Nonattainment 
Guidance \14\ allows the use of 30-day emission limits as long as 
hourly emissions above the critical emission value \15\ (CEV) are rare 
and if the magnitude of emissions do not significantly exceed the CEV. 
The comment further states that the EPA justified 30-day emission 
limits to allow for operational flexibility at sources. Next, the 
comment claims that the EPA's 2014 SO2 Nonattainment 
Guidance highlights the value of supplemental limits, e.g., caps on the 
frequency or magnitude of elevated emissions, but fails to explain and 
justify approving longer-term emission limits in the absence of 
supplemental limits. Further, the comment states that the EPA's 
recognition of the value of supplemental limits in the 2014 
SO2 Nonattainment Guidance demonstrates that 30-day rolling 
averages, when used without supplemental limits, insufficiently protect 
the NAAQS.
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    \14\ www.epa.gov/sites/default/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf.
    \15\ The maximum modeled emission rate expressed as a 1-hour 
average that results in attainment is labeled the ``critical 
emissions value'' or CEV.
---------------------------------------------------------------------------

    The second comment states that the SO2 limit was set as 
a 1-hour standard to protect human health from harmful, short-term 
exposures of SO2 and that Seward's and Keystone's emission 
limits are not protective under that standard. The comment claims that 
the Seward and Keystone generating stations ``regularly and 
frequently'' exceed their hourly CEV. Citing data from January 1, 2018 
through March 31, 2024, the comment asserts that Keystone exceeded the 
9,718 lbs/hr CEV on 532 occasions and that Seward exceeded the 3,830 
lbs/hr CEV on 349 occasions, which occurred on 28 separate days in 
2018, 7 days in 2019, 13 days in 2020, 31 days in 2021, 58 days in 
2022, 40 days in 2023, and 16 days in 2024. The comment claims that the 
PADEP justification for disregarding these exceedances, i.e., because 
they ``occurred over a large number of possible operating hours per 
year,'' is dismissive of the fact that the SO2 standard is a 
short-term standard and that just four hours on four days with 
SO2 concentrations over 75 ppb will lead to nonattainment of 
the NAAQS.
    Response 4. The EPA disagrees with the assertion that longer-term 
limits cannot be protective of a 1-hour SO2 standard. As 
explained in the NPRM for this action, and in the EPA's 2014 
SO2 Nonattainment Guidance, the EPA believes that 
appropriately set longer-term limits can be protective of the 1-hour 
SO2 NAAQS.
    The EPA 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, the 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. This downward adjustment of the 
limit is to compensate for the loss of stringency inherent in applying 
a longer-term average limit, by requiring most values to be lower than 
they are required to be with a 1-hour limit at the CEV. 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,'' \16\ 
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.
---------------------------------------------------------------------------

    \16\ 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'' to simplify the illustration of 
relevant principles.
---------------------------------------------------------------------------

    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 the 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. PADEP correctly followed the recommendations in devising the 
longer-term limits for Seward and Keystone. The 24-hour average limit 
of 8,328 lbs/hr went into effect for Keystone on August 15, 2023, and 
the 30-day average limit of 2,895 lbs/hr went into effect for Seward on 
August 17, 2023. The EPA reviewed the comment's hourly data files for 
Seward and Keystone from January 1, 2018 through March 31, 2024, in 
which the CEV at Keystone was exceeded on 532

[[Page 74843]]

separate occasions, and the CEV at Seward was exceeded on 349 separate 
occasions. During the majority of this time period, the sources were 
not subject to the new limits developed for this attainment plan. 
Additionally, the stated number of occasions over the CEV for Seward 
and Keystone during the six and one quarter years of data equate to 
less than one percent of the hours for each source, which EPA considers 
to be a minimal amount of occasions over the CEV. The EPA disagrees 
with the comment on the air quality consequences of these occasions of 
elevated emissions. While there were times after the new 30-day limit 
went into effect where hourly emissions were above the CEV, there is no 
evidence that these emissions caused an exceedance of the NAAQS. The 
EPA believes that a full analysis of the air quality impact of 
Pennsylvania's limits must consider these hours of elevated emissions 
in conjunction with the far greater number of hours when emissions are 
required to be well below the level that would model violations (i.e., 
the CEV). The comment provided no modeling analysis that incorporated 
both the hours of emissions above the CEV and the hours below. For 
reasons described in more detail in the EPA's guidance, the NPRM and 
the EPA's Technical Support Document: Critical Emission Value Modeling 
Analysis for the Indiana, PA 1-Hour SO2 Nonattainment Area 
(EPA Modeling TSD) for this action, the EPA believes that the net 
effect of these compensating factors is that PADEP's limits provide 
adequate assurance that the area will attain the SO2 
standard.
    The EPA disagrees with the comment's assertion that supplemental 
limits must be required to limit the magnitude of emissions spikes when 
a longer-term limit is established. As explained in detail above, a 
comparably stringent longer-term limit can provide for protection of 
the NAAQS, even without supplemental limits. In any event, PADEP 
exercised additional options for restricting the frequency and 
magnitude of occurrences of elevated emissions per the 2014 
SO2 Nonattainment Guidance,\17\ such as setting averaging 
times shorter than thirty days or analyzing emissions data \18\ to 
determine when to target emission episodes using supplemental limits. 
For Keystone, PADEP applied a shorter averaging time of 24 hours. For 
Seward, which has a 30-day limit, PADEP included a supplemental limit 
in the form of a work practice requirement of injecting limestone into 
the combustor during initial firing which was deemed appropriate due to 
specific emissions data patterns experienced during those periods.
---------------------------------------------------------------------------

    \17\ According to the 2014 SO2 Nonattainment 
Guidance, p. 34, states have several additional options for 
restricting the frequency and magnitude of occurrences of elevated 
emissions. First, states may apply shorter averaging times, such as 
24 hours, which provide less allowance of emission spikes than would 
longer averaging times, such as 30 days. Second, for sources that 
are or will be operating emission control equipment, states may 
establish requirements for the operation of this control equipment. 
For such sources, a substantial component of the variability in 
emissions often arises from variations in the operation of the 
control equipment, perhaps including operating the source when the 
control equipment is not operating. States have multiple options for 
requiring less variability in control equipment operation. One 
option would be a direct work practice requirement for operation of 
the control equipment, perhaps specifying some minimum level of 
control efficiency and associated monitoring, recordkeeping, and 
reporting requirements.
    \18\ If this type of information on historic emission patterns 
is not available, it may be difficult to determine supplemental 
limits.
---------------------------------------------------------------------------

    Comment 5. The comment states that the CEVs set for each stationary 
SO2 source impacting nonattainment in Indiana County are not 
protective of the NAAQS. The comment cites an assessment of the EPA's 
modeling analysis which asserts that the CEVs yield peak concentrations 
approximately 50 micrograms per cubic meter above the NAAQS. Steven 
Klafka, Conemaugh, Homer City, Keystone and Seward Generating Stations 
Indiana County, Pennsylvania Evaluation of Compliance with the 1-hour 
NAAQS for SO2, (Wingra Engineering July 8, 2024).
    Response 5: The EPA has reviewed the July 8, 2024 modeling analysis 
prepared for the Sierra Club by Wingra Engineering (July 2024 Wingra 
Analysis) and found several deficiencies with it. These include the 
choice of meteorological data and the combining of emission sources 
across an amalgamated modeling domain. The July 2024 Wingra Analysis 
otherwise utilizes the same modeling system components (receptor grid 
locations/elevations/hill-height scales, building downwash parameters, 
surface characteristics, etc.) as those used in the modeling analysis 
performed by Pennsylvania and reviewed by the EPA. For consistency 
purposes, the comment's July 2024 Wingra Analysis utilized the same 
versions of the AERMOD platform used by Pennsylvania.
    As described in section 6 of PADEP's Air Dispersion Modeling 
Technical Support Document (Docket file EPA-R03-OAR-2024-0024-
0003_attachment_9) the air dispersion modeling for the Indiana, PA NAA 
utilized representative meteorological datasets from two sites. Data 
from the Johnstown-Cambria County Airport (KJST) meteorological site 
represented atmospheric conditions in the vicinity of Keystone and 
Homer City power plants. The KJST meteorological site is approximately 
58 kilometers southeast of Keystone and approximately 38 kilometers 
southeast of Homer City. Data from the Ash Site #1 meteorological site 
represented atmospheric conditions in the vicinity of Conemaugh and 
Seward. The Conemaugh-Seward (Ash Site #1) meteorological site is 
located between the two power plants, approximately 1.9 kilometers 
northeast of the Conemaugh power plant and approximately 1.7 kilometers 
south-southwest of the Seward power plant.
    Based on the EPA's Guideline on Air Quality Models (40 CFR part 51, 
appendix W), meteorological data used as input to a dispersion model 
should be selected on the basis of spatial and climatological 
(temporal) representativeness as well as the ability of the individual 
parameters selected to characterize the transport and dispersion 
conditions in the area of concern. Representativeness of the 
meteorological data is dependent on numerous factors. These factors 
include but are not limited to: (1) the proximity of the meteorological 
monitoring site to the area under consideration; (2) the complexity of 
the terrain; (3) the exposure of the meteorological monitoring site; 
and (4) the period of time during which data are collected. Both 
meteorological data sets used in Pennsylvania's modeling analysis meet 
applicable completeness requirements.
    While the July 2024 Wingra Analysis claims that the Ash Site #1 is 
representative of impacts from emissions released by all four plants, 
the EPA disagrees because of the difference in local topography around 
the modeled sources. The decision to utilize the KJST meteorological 
site for the Homer City and Keystone power plants and the Ash Site #1 
for the Conemaugh and Seward power plants was largely based on the 
modeled sources' topographical settings (terrain features). Each of the 
meteorological sites were best suited to capture the proper boundary 
layer characteristics for their respective sources.
    The Indiana, PA NAA sits along the Allegheny Plateau physiographic 
province of the Appalachian Mountains system west of the eastern 
continental divide. Maps depicting topographical elevations in the 
vicinity of the Indiana, PA NAA showing the locations of the Conemaugh, 
Homer City, Keystone and Seward power plants and the KJST and

[[Page 74844]]

Ash Site #1 meteorological sites can be found in the EPA's technical 
support document that is part of the public record in the docket for 
this action (Figures 1 and 2 of the EPA Modeling TSD). Relatively flat 
terrain resides in the western portion of the nonattainment area where 
the Homer City and Keystone power plants are located. Both power plants 
sit at significantly lower elevations than the KJST site. Furthermore, 
the KJST site is located on some of the highest terrain in western 
Pennsylvania and no topographic features between the KJST site and 
Homer City and Keystone would unduly influence the wind fields at the 
KJST site. In contrast, the Conemaugh and Seward power plants are 
located along the Conemaugh River in the southeastern part of the 
Indiana, PA NAA between the Chestnut (west) and Laurel (east) ridges 
that define the northern terminus of the Ligonier Valley. The latter 
two power plants reside within a valley marked by higher terrain to the 
east and west. This valley impacts local meteorological parameters such 
as wind fields and atmospheric stability. Air flow can become channeled 
within valley features, and topography can influence vertical 
atmospheric stability, especially at night, setting up potentially 
strong vertical temperature inversions.
    The July 2024 Wingra Analysis amalgamates all of the model 
receptors Pennsylvania utilized in its three modeling domains covering 
the entire Indiana, PA NAA. The rationale for dividing the Indiana, PA 
NAA into three separate modeling domains (with different sources and 
meteorological data) was explained in the Air Dispersion Modeling 
Technical Support Document from PADEP (pages 6-8 to 6-9, 6-15 to 6-17, 
and 8-1 to 8-3) and in the EPA Modeling TSD (pages 63 and 70) that are 
part of the public docket for this action.
    No rationale was provided in the July 2024 Wingra Analysis 
submitted during the public comment period to support combining the 
three modeling domains utilized in PADEP's SIP modeling demonstration. 
Additionally, no rationale was provided to refute the division of the 
Indiana, PA NAA into three distinct modeling domains. The EPA believes, 
therefore, that Wingra Engineering's modeling analysis erred on its 
modeling domain setup by combining all sources into one amalgamated 
receptor domain.
    Noting the deficiencies in the July 2024 Wingra Analysis, the EPA 
concludes that the modeling analysis presented by PADEP demonstrates 
the validity of the CEVs established for the Conemaugh, Homer City, 
Keystone and Seward power plants.
    Comment 6. The comment states that the adjustment factor of 0.756, 
used to convert the Seward generating station's CEV to a 30-day rolling 
average, is too high. The comment claims that Pennsylvania's proposed 
adjustment factor results in 20% higher emission limits when compared 
to emission limits calculated with the EPA's adjustment factor of 0.63. 
The comment states that if the January 2019 through March 2023 dataset 
is used instead of the 2018-2021 dataset used by PADEP, the Seward 
adjustment factor would be reduced to 0.712. Next, the comment provided 
seven different adjustment factors calculated based on differing 
historic data periods. Additionally, the comment asserts that Seward's 
SO2 emissions have increased since 2013, and the proposed 
30-day limit increases the likelihood of continued nonattainment if 
emission reductions are not established.
    Response 6. The spreadsheet submitted as Attachment C to the 
comment, included incorrect calculations for the 30-day average values. 
As specified in the state submittal, the 30-day rolling average for 
Seward should be calculated for each operating day, by calculating the 
average of all the hourly emission data, using only hours during which 
fuel is combusted from the preceding 30 operating days. In the 
spreadsheet calculations, the comment always averaged the previous 30-
days using 720 hours (total number of hours in 30 days) as opposed to 
the number of hours when fuel was actually burned. In the SIP 
submittal, PADEP correctly calculated the 30-day average emission 
values in developing the adjustment factors for Seward. PADEP also 
justified the period of time used for the calculations by explaining 
that, in line with the EPA's 2014 SO2 Nonattainment 
Guidance, PADEP used data from years of stable operation. As PADEP 
described, when the SIP analysis began in 2022, it initially considered 
emission data for years 2017 through 2021. However, in 2017, there was 
an operational change at Seward \19\ that could have affected the 
emission variability. Because of operational changes at Seward in 2017 
and in an effort to have one consistent emission dataset for all three 
facilities with longer-term SO2 emission limits, PADEP 
calculated the adjustment factors using emission data for years 2018 
through 2021. The EPA believes this is consistent with the 
recommendation on emission data use in the 2014 SO2 
Nonattainment Guidance, pages 29-30.
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    \19\ After a change of ownership in December 2016, Seward 
implemented a startup operational change, which is the addition of 
limestone to the combustor during initial firing to reduce 
SO2 emissions.
---------------------------------------------------------------------------

    Also, the comment appears to misunderstand the adjustment factor of 
0.63 included in table 1 of appendix B of the 2014 SO2 
Nonattainment Guidance. The EPA's 2014 SO2 Nonattainment 
Guidance did not calculate nor provide source-specific adjustment 
factors for Seward, but rather, calculated the average adjustment 
factor for 90 sources equipped with a dry scrubber. The EPA believes 
that if continuous emissions monitoring systems (CEMs) data is 
available for a source, it is most appropriate to use that data for 
developing adjustment factors, as long as it continues to represent the 
distribution of emissions that is expected once the attainment plan is 
implemented. This was the case with Seward. The EPA concludes that the 
adjustment factor of 0.756 calculated for Seward is more appropriate 
because it is source-specific, based on CEMS data and provides for a 
comparably stringent 30-day average emission limit.
    Regarding the comment about the annual SO2 emissions 
increases since 2013, the EPA reviewed the data and notes that 
SO2 emissions increased from 2013-2018. However, after that 
period the emissions remained in a similar range. Additionally, annual 
emissions are not a direct indicator of compliance with the NAAQS nor 
with the 30-day emission limit which the EPA is approving as providing 
for attainment in this plan.
    Comment 7. The comment claims that the EPA ignores the ongoing 
negative impacts of Indiana County's major SO2 sources on 
neighboring Westmoreland and Cambria counties. The comment states that 
Pennsylvania has failed to meaningfully address SO2 sources 
in Indiana County and that the EPA should encourage Pennsylvania to 
implement more protective SO2 limits to wholly address 
nonattainment caused by these sources and to be protective of 
vulnerable populations in Indiana County and neighboring areas.
    Response 7. The comment's concern regarding negative impacts 
outside of the Indiana, PA NAA boundaries from the Indiana County 
SO2 sources is beyond the scope of this action.
    Section 171(2) of the CAA defines nonattainment area to mean for 
any air pollutant, an area which is designated ``nonattainment'' with 
respect to that pollutant within the meaning of section 107(d) of this 
title. In an earlier, separate action, the boundaries of the Indiana,

[[Page 74845]]

PA NAA were set and finalized in August 2013 in ``Round One'' of EPA's 
designations for the 2010 SO2 NAAQS under section 107(d) of 
the CAA, and these boundaries were not challenged.\20\ Westmoreland and 
Cambria counties are not included within those boundaries.
---------------------------------------------------------------------------

    \20\ 78 FR 47191 (August 5, 2013); www.epa.gov/sulfur-dioxide-designations/so2-designations-state-designations-round-1.
---------------------------------------------------------------------------

    Pennsylvania's obligation under section 110(a) of the CAA is to 
submit `` . . . a plan which provides for implementation, maintenance, 
and enforcement of such primary standard in each air quality control 
region (or portion thereof) within such State.'' CAA section 110(a)(1). 
Section 110 further provides that ``[i]n the case of a plan or plan 
revision for an area designated as a nonattainment area, [the plan 
shall] meet the applicable requirements of part D of this subchapter 
(relating to nonattainment areas).'' CAA section 110(a)(2)(I). Section 
172(c)(6) then requires the SIP for a nonattainment area to include 
enforceable emission limitations and control measures as necessary or 
appropriate to provide for NAAQS attainment ``in such area.'' In this 
case, Pennsylvania's attainment plan for the Indiana, PA NAA includes 
limits on SO2 sources and a modeling demonstration showing 
that SO2 concentrations throughout the nonattainment area 
are at or below the NAAQS.
    Further, the EPA's role is limited to determining whether the 
submitted SIP meets the requirements of the CAA, see section 110(k)--in 
this action, Pennsylvania's 2023 SIP submittal does not address areas 
outside the defined nonattainment area. Absent a clear requirement that 
Pennsylvania must include model receptors outside of the nonattainment 
area in its submission, the EPA will confine its analysis to whether 
the attainment SIP demonstrates attainment within the designated 
nonattainment area.
    On February 12, 2024, EPA published notice in a separate action of 
its intent to redesignate portions of Cambria and Westmoreland Counties 
\21\ to nonattainment for the 2010 SO2 NAAQS (89 FR 9815). 
The CAA provides the EPA with the authority to revise designations of, 
or ``redesignate,'' areas under CAA section 107(d)(3). Such 
redesignations can originate as requests by states (per CAA section 
107(d)(3)(D)), and the EPA can also notify a state at any time that a 
designation of any area or portion of an area should be revised, on the 
basis of air quality data, planning and control considerations, or any 
other air quality-related considerations the EPA Administrator deems 
appropriate. If finalized, the nonattainment designation for these 
counties will require the state to submit nonattainment area 
requirements per CAA section 172.
---------------------------------------------------------------------------

    \21\ EPA designated Cambria County unclassifiable and 
Westmoreland County attainment/unclassifiable for the 2010 1-hour 
SO2 NAAQS effective April 9, 2018. 83 FR 1098 (January 9, 
2018).
---------------------------------------------------------------------------

    Comment 8. The comment states that the SIP should incorporate the 
closure of the Homer City generating station, as well as the projected 
2028 retirements of the Keystone and Conemaugh generating stations. 
Further, the comment asserts that the SIP should not be approvable 
until the SO2 emission limits for these plants are removed.
    Response 8. The EPA disagrees with the comment. CAA section 
172(c)(6) requires the SIP for a nonattainment area to include 
enforceable emission limitations and control measures as necessary or 
appropriate to provide for NAAQS attainment in the area. With this 
action, the EPA is approving the emission limits for the four sources 
in the Indiana, PA NAA as meeting this requirement. As such, it is not 
necessary to include the Homer City retirement nor the projected 
retirements of Keystone and Conemaugh in the SIP as enforceable 
measures. And as explained in the NPRM, as the EPA is not aware of 
PADEP rescinding Homer City's operating permit, Homer City ceasing 
operations does not guarantee that the units are permanently and 
enforceably shutdown. 89 FR 48523, 48528 (June 7, 2024). Nor did 
PADEP's 2023 SIP submittal request to incorporate the pending closure 
of Homer City into the SIP. Similarly for Keystone and Conemaugh, the 
EPA is not aware of PADEP rescinding the permits for these two sources 
nor did PADEP's 2023 SIP submittal request their projected retirements 
be included in the SIP. The approval of this attainment plan is thus 
properly based on Homer City's possible continued operation, as well as 
Keystone's and Conemaugh's continued operations.

IV. Final Action

    The EPA is approving the attainment plan for the Indiana, PA NAA 
for the 2010 1-hour SO2 NAAQS, which Pennsylvania submitted 
on October 12, 2023, as a revision to the Pennsylvania SIP. 
Specifically, the EPA is approving the attainment demonstration, RACM/
RACT requirements, RFP requirements, and contingency measures of the 
attainment plan. The EPA previously approved the emissions inventory 
and NNSR program elements of the attainment plan.
    This approval terminates the highway funding sanction and FIP 
clocks started under CAA sections 179 and 110, respectively, resulting 
from EPA's partial disapproval of the prior SIP submittal. It also 
removes the permitting offset sanction that has been in place since 
March 19, 2024.

V. Incorporation by Reference

    In this document, the 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 
SO2 emission limits and compliance parameters established in 
(the unredacted portions of) the COAs for the Seward, Conemaugh and 
Keystone facilities, as discussed in section II of this preamble and 
described in the amendments to 40 CFR part 52 set forth below. The EPA 
has made, and will continue to make, these materials generally 
available through 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). Therefore, 
these materials have been approved by the EPA for inclusion in the SIP, 
have been incorporated by reference by the EPA into that plan, are 
fully federally enforceable under sections 110 and 113 of the CAA as of 
the effective date of the final rulemaking of the EPA's approval, and 
will be incorporated by reference in the next update to the SIP 
compilation.\22\
---------------------------------------------------------------------------

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

VI. Statutory and Executive Order Reviews

A. General Requirements

    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 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);

[[Page 74846]]

     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
     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 CAA.
    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 final rule approving Pennsylvania's Indiana, PA 
NAA 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 the EPA notes that it will not impose substantial direct 
costs on tribal governments or preempt tribal law.

B. Submission to Congress and the Comptroller General

    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. The 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).

C. Petitions for Judicial Review

    Under section 307(b)(1) of the CAA, petitions for judicial review 
of this action must be filed in the United States Court of Appeals for 
the appropriate circuit by November 12, 2024. 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 approving the Indiana, PA attainment plan for the 
2010 1-hour SO2 NAAQS 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, Intergovernmental relations, Reporting and recordkeeping 
requirements, Sulfur oxides.

Adam Ortiz,
Regional Administrator, Region III.

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

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.

Subpart NN--Pennsylvania

0
2. In Sec.  52.2020:
0
a. Amend the table in paragraph (d)(3) by:
0
i. Adding entries for ``Keystone Generating Station'', ``Conemaugh 
Generating Station'', and ``Seward Generating Station'' at the end of 
the table; and
0
ii. Removing the first entry for ``Seward Station''; and the entry for 
``Keystone Plant''.
0
b. Adding in paragraph (e)(1) table the entry ``Attainment Plan for the 
Indiana County, Pennsylvania Nonattainment Area for the 2010 Sulfur 
Dioxide Primary National Ambient Air Quality Standard'' at the end of 
the table.
    The additions read as follows:


Sec.  52.2020  Identification of plan.

* * * * *
    (d) * * *
    (3) * * *

[[Page 74847]]



----------------------------------------------------------------------------------------------------------------
                                                                                                    Additional
                                                                       State     EPA  approval     explanation/
        Name of source            Permit No.           County        effective        date        Sec.   52.2063
                                                                       date                          citation
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Keystone Generating Station..  Consent Order     Armstrong........    08/15/23  9/13/2024,       For Source IDs
                                and Agreement.                                   [INSERT          031 and 032:
                                                                                 Federal          Combined SO2
                                                                                 Register         emission
                                                                                 CITATION].       limit; CEMS
                                                                                                  monitoring;
                                                                                                  definition of
                                                                                                  ``24-hour
                                                                                                  block'';
                                                                                                  Quarterly
                                                                                                  emission
                                                                                                  reporting
                                                                                                  requirement;
                                                                                                  and reporting
                                                                                                  of hourly SO2
                                                                                                  lbs/hr
                                                                                                  emission
                                                                                                  averages.
Conemaugh Generating Station.  Consent Order     Indiana..........    08/15/23  9/13/2024,       For Source IDs
                                and Agreement.                                   [INSERT          031 and 032:
                                                                                 Federal          Combined SO2
                                                                                 Register         emission
                                                                                 CITATION].       limit; CEMS
                                                                                                  monitoring;
                                                                                                  definition of
                                                                                                  ``3-hour
                                                                                                  block'';
                                                                                                  Quarterly
                                                                                                  emission
                                                                                                  reporting
                                                                                                  requirement;
                                                                                                  and reporting
                                                                                                  of hourly SO2
                                                                                                  lbs/hr
                                                                                                  emission
                                                                                                  averages.
Seward Generating Station....  Consent Order     Indiana..........    08/17/23  9/13/2024,       For Source IDs
                                and Agreement.                                   [INSERT          034 and 035:
                                                                                 Federal          Combined SO2
                                                                                 Register         emission
                                                                                 CITATION].       limit; CEMS
                                                                                                  monitoring;
                                                                                                  definition of
                                                                                                  ``operating
                                                                                                  day'';
                                                                                                  reporting of
                                                                                                  hourly SO2 lbs/
                                                                                                  hr emission
                                                                                                  rate;
                                                                                                  injection of
                                                                                                  limestone
                                                                                                  during initial
                                                                                                  firing; and
                                                                                                  quarterly
                                                                                                  submission of
                                                                                                  ``Hourly
                                                                                                  Injection
                                                                                                  Reports.''
----------------------------------------------------------------------------------------------------------------

* * * * *
    (e) * * *
    (1) * * *

----------------------------------------------------------------------------------------------------------------
                                                            State
    Name of non-regulatory SIP          Applicable        submittal   EPA  approval date  Additional explanation
             revision                 geographic area       date
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Attainment Plan for the Indiana,   Indiana County and      10/12/23  9/13/2024, [INSERT   52.2033(g).
 Pennsylvania Nonattainment Area    portions of                       Federal.
 for the 2010 Sulfur Dioxide        Armstrong County                 Register CITATION].
 Primary National Ambient Air       (Plumcreek
 Quality Standard.                  Township, South
                                    Bend Township, and
                                    Elderton Borough).
----------------------------------------------------------------------------------------------------------------

* * * * *

0
3. Amend Sec.  52.2033 by adding paragraph (g) to read as follows:


Sec.  52.2033  Control strategy: Sulfur oxides.

* * * * *
    (g) EPA approves the Attainment Plan for the Indiana, PA 
Nonattainment Area for the 2010 Sulfur Dioxide National Ambient Air 
Quality Standard submitted by the Pennsylvania Department of 
Environmental Protection on October 12, 2023. EPA approves the 
attainment demonstration and other attainment plan elements, including 
Reasonably Available Control Technology (RACT)/Reasonably Available 
Control Measures (RACM) determination, Reasonable Further Progress 
(RFP) requirements, and contingency measures.

[FR Doc. 2024-20598 Filed 9-12-24; 8:45 am]
BILLING CODE 6560-50-P