Document ID: EPA-R03-OAR-2017-0615-0057
Agency: epa
Document Type: Proposed Rule
Title: Air Quality State Implementation Plans; Approvals and Promulgations: Pennsylvania; Attainment Plan for the Indiana, Pennsylvania Nonattainment Area for the 2010 Sulfur Dioxide Primary National Ambient Air Quality Standard
Posted Date: 2022-03-17T04:00Z

[Federal Register Volume 87, Number 52 (Thursday, March 17, 2022)]
[Proposed Rules]
[Pages 15166-15179]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-05398]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R03-OAR-2017-0615; FRL-9607-01-R3]

Air Plan Partial Approval and Partial Disapproval; Pennsylvania; 
Attainment Plan for the Indiana, Pennsylvania Nonattainment Area for 
the 2010 Sulfur Dioxide Primary 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 
revise its prior action that fully approved a state implementation plan 
(SIP) revision submitted by the Commonwealth of Pennsylvania, through 
the Pennsylvania Department of Environmental Protection (PADEP), to EPA 
on October 11, 2017, and supplemented on February 5, 2020. The SIP 
revision provided a plan for attainment of the 2010 sulfur dioxide 
(SO2) primary national ambient air quality standard (NAAQS) 
in the Indiana, Pennsylvania SO2 nonattainment area 
(hereafter referred to as the ``Indiana, PA NAA'' or ``Indiana Area''). 
The attainment plan submission included a base year emissions 
inventory, an analysis of the reasonably available control technology 
(RACT) and reasonably available control measure (RACM) requirements, 
enforceable emission limitations and control measures, a reasonable 
further progress (RFP) plan, a modeling demonstration of SO2 
attainment, and contingency measures for the Indiana Area. EPA is 
proposing to revise its prior action to partially approve and partially 
disapprove the SIP. This action is being taken under the Clean Air Act 
(CAA).

DATES: Written comments must be received on or before April 18, 2022.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R03-
OAR-2017-0615 at https://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, 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. 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 https://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Megan Goold, Planning & Implementation 
Branch (3AD30), Air & Radiation Division, U.S. Environmental Protection 
Agency, Region III, 1650 Arch Street, 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 11, 2017 and February 5, 2020, 
PADEP submitted a revision to its SIP for the purpose of providing for 
attainment of the 2010 SO2 primary NAAQS in the Indiana, PA 
NAA.

I. Background

    On June 2, 2010, the EPA Administrator signed a final rule 
establishing a new primary SO2 NAAQS as a 1-hour standard of 
75 parts per billion (ppb), based on a 3-year average of the annual 
99th percentile of daily maximum 1-hour average concentrations. See 75 
FR 35520 (June 22, 2010), codified at 40 CFR 50.17. This action also 
provided for revoking the 1971 primary, annual and 24-hour standards, 
subject to certain conditions.\1\ EPA established the NAAQS based on 
significant evidence and numerous health studies demonstrating that 
serious health effects are associated with short-term exposures to 
SO2 emissions ranging from five minutes to 24 hours, with an 
array of adverse respiratory effects including narrowing of the airways 
which can cause difficulty breathing (bronchoconstriction) and 
increased asthma symptoms. For more information regarding the health 
impacts of SO2, please refer to the June 22, 2010, final 
rule. See 75 FR 35520. Following promulgation of a new or revised 
NAAQS, EPA is required by the CAA to designate areas throughout the 
United States as attaining or not attaining the NAAQS; this designation 
process is described in section 107(d)(1)-(2) of the CAA. On August 5, 
2013, EPA promulgated initial air quality designations for 29 areas for 
the 2010 SO2 NAAQS (78 FR 47191), which became effective on 
October 4, 2013, based on violating air quality monitoring data for 
calendar years 2009-2011, where there was sufficient monitored data to 
support a nonattainment designation.
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    \1\ EPA's June 22, 2010 final action revoked the two 1971 
primary 24-hour standard of 140 ppb and the annual standard of 30 
ppb because they were determined not to add additional public health 
protection given a 1-hour standard at 75 ppb. See 75 FR 35520. 
However, the secondary 3-hour SO2 standard was retained. 
The 24-hour and annual standards became revoked for certain of those 
areas 1 year after the effective date of when the EPA designated 
them for the 2010 1-hour SO2 NAAQS. See 40 CFR 50.4(e).
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    Effective on October 4, 2013, 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, Conemaugh, Homer 
City, and Seward Electric Generating Units (EGUs). The October 4, 2013, 
final designation triggered a requirement for Pennsylvania to submit by 
April 4, 2015, a SIP revision with an attainment plan for how the 
Indiana Area would attain the 2010 SO2 NAAQS as 
expeditiously as practicable, but no later than October 4, 2018, in 
accordance with CAA sections 110(a), 172(c) and 191-192.
    For a number of areas, including the Indiana Area, EPA published a 
document on March 18, 2016, effective April 18, 2016, that Pennsylvania 
and other pertinent states had failed to

[[Page 15167]]

submit the required SO2 attainment plan by this submittal 
deadline. See 81 FR 14736. This finding initiated a deadline under CAA 
section 179(a) for the potential imposition of new source review and 
highway funding sanctions. However, pursuant to Pennsylvania's 
submittal of October 11, 2017, and EPA's subsequent completeness letter 
to Pennsylvania dated October 13, 2017, finding the submittal complete 
and noting the stopping of the sanctions' deadline, these sanctions 
under section 179(a) will not be imposed. Additionally, under CAA 
section 110(c), the March 18, 2016, finding triggered a requirement 
that 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 EPA has approved 
the submittal as meeting applicable requirements. EPA took final action 
approving this attainment plan on October 19, 2020 (85 FR 66240), which 
removed the FIP obligation.
    On December 18, 2020, the Sierra Club, Clean Air Council, and 
PennFuture 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, EPA filed a motion for voluntary remand without vacatur 
of its approval of the Indiana, PA SO2 attainment plan. In 
its motion, EPA explained that as part of its plan Pennsylvania relied 
on a particular type of computer modeling (i.e., mathematical programs 
that project the impact of certain emissions limits on air quality). 
EPA had not previously approved use of this type of modeling in the 
context of SO2 attainment for the purpose of demonstrating 
that certain source emission limits with averaging times greater than 
one hour included in the plan would demonstrate attainment with the 
2010 SO2 NAAQS. EPA further explained that a remand will 
allow EPA to revisit whether the specific modeling that Pennsylvania 
used to demonstrate that longer-term emission limits showed attainment 
was appropriate and will also allow EPA to further assess whether 
additional analyses are necessary to find that Pennsylvania has 
complied with the requirements of the CAA. Lastly, EPA explained that a 
remand will allow EPA to seek public comment on any new analyses and 
take other actions as appropriate.
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    \2\ Sierra Club, et al. v. EPA, Case No. 20-3568 (3rd Cir.).
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    In a short order without any commentary, on August 17, 2021, the 
U.S. Court of Appeals for the Third Circuit granted 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 EPA take final action in response to the remand no later than one 
year from the date of the court's order (i.e., by August 17, 2022). 
This action proposes EPA's response to the court's order.
    After reconsideration, for reasons described in the following 
sections, EPA is proposing that it was incorrect to fully approve the 
Indiana, PA SO2 attainment plan, and is proposing to revise 
its action to disapprove portions of the Indiana, PA SO2 
attainment plan while leaving certain other portions approved and while 
retaining incorporated emissions limits and control measures in the 
plan for limited SIP strengthening purposes. If EPA finalizes the 
partial disapproval proposed here, that action would initiate a 
sanctions clock under section 179, providing for emission offset 
sanctions for new sources if EPA has not fully approved a revised plan 
within 18 months after final partial disapproval, and providing for 
highway funding sanctions if EPA has not fully approved a revised plan 
within 6 months thereafter. The sanctions clock can be stopped only if 
the conditions of EPA's regulations at 40 CFR 52.31 are met. A final 
partial disapproval would also initiate an obligation for EPA to 
promulgate a FIP within 24 months unless Pennsylvania has submitted, 
and EPA has fully approved, a plan addressing these attainment planning 
requirements.
    Attainment plans for SO2 must meet the applicable 
requirements of the CAA, and specifically CAA sections 110, 172, 191, 
and 192. The required components of an SO2 attainment plan 
submittal are listed in section 172(c) of Title 1, part D of the CAA. 
EPA's regulations governing SO2 nonattainment 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, 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 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, EPA issued guidance (hereafter ``2014 
SO2 Nonattainment Guidance'') for how state submissions 
could address the statutory requirements for SO2 attainment 
plans.\3\ In this guidance, EPA described the statutory requirements 
for an attainment plan, which include: (1) An accurate base year 
emissions inventory of current emissions for all sources of 
SO2 within the nonattainment area (172(c)(3)); (2) an 
attainment demonstration that includes a modeling analysis showing that 
the enforceable emissions limitations and other control measures taken 
by the state will provide for expeditious attainment of the NAAQS 
(172(c) and (c)(6)); (3) demonstration of RFP (172(c)(2)); (4) 
implementation of RACM, including RACT (172(c)(1)); new source review 
(NSR) requirements (172(c)(5)); and (5) adequate contingency measures 
for the affected area (172(c)(9)). A synopsis of these requirements is 
provided in the notice of proposed rulemaking on the Illinois 
SO2 nonattainment plans, published on October 5, 2017, at 82 
FR 46434.
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    \3\ See ``Guidance for 1-Hour SO2 Nonattainment Area 
SIP Submissions'' (April 23, 2014), available at https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf.
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    In order for the EPA to fully approve a SIP as meeting the 
requirements of CAA sections 110, 172 and 191-192 and EPA's regulations 
at 40 CFR part 51, the SIP for the affected area must demonstrate to 
EPA's satisfaction that each of the aforementioned requirements have 
been met. Under CAA sections 110(l) and 193, 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 (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. The provisions in 40 CFR part 51, subpart G, 
further delineate the control strategy requirements that SIPs must 
meet, and EPA has long required that all SIPs and control strategies 
reflect four fundamental principles of quantification, enforceability, 
replicability, and accountability (57 FR 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

[[Page 15168]]

meeting the requirements of 40 CFR part 51, appendix W, which 
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 (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).
    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 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, 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 
exceedance does not create a violation of the standard. Instead, at 
issue is whether a source operating in compliance with a properly set 
longer term average could cause exceedances, and if so, the resulting 
frequency and magnitude of such exceedances, and in particular, whether 
EPA can have reasonable confidence that a properly set longer term 
average limit will provide that the average fourth highest daily 
maximum value will be at or below 75 ppb. A synopsis of how EPA 
evaluates whether such plans ``provide for attainment,'' based on 
modeling of projected allowable emissions and in light of the 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 ``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.
    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. 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 a 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, 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. 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, EPA expects either form of emission limit to yield comparable 
air quality.
    Second, from a more theoretical perspective, EPA has compared the 
likely air quality with a source having maximum allowable emissions 
under an appropriately set longer term limit, as compared 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 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 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

[[Page 15169]]

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 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, 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, 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 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 by 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 1000 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, 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).'' \6\ In 2005, the EPA promulgated the 
American Meteorological Society/Environmental Protection Agency 
Regulatory Model (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.
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    \6\ EPA published revisions to the ``Guideline on Air Quality 
Models'' on January 17, 2017.
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    As stated previously, 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 
NAAQS. For a short-term (i.e., 1-hour) standard, 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, the Meteorological 
data preprocessor for AERMOD. 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-hr SO2 National Ambient Air 
Quality Standard'' (U.S. EPA, 2010) and EPA's March 11, 2011 
clarification memo, ``Additional Clarification Regarding Application of 
Appendix W Modeling Guidance for the 1-hour NO2 National 
Ambient Air Quality Standard.''

II. Summary of Pennsylvania's SIP Revision and EPA Analysis

    In accordance with section 172(c) of the CAA, the Pennsylvania 
attainment plan for the Indiana Area includes: (1) An emissions 
inventory for SO2 for the plan's base year (2011); and (2) 
an attainment demonstration. The attainment demonstration includes the 
following: (1) Analyses that locate, identify, and quantify sources of 
emissions contributing to violations of the 2010 SO2 NAAQS; 
(2) a determination that the control strategy for the primary 
SO2 sources within the nonattainment areas constitutes RACM/
RACT; (3) a dispersion modeling analysis of an emissions control 
strategy for the primary SO2 sources (Keystone, Conemaugh, 
Homer City, and Seward) purporting to show attainment of the 
SO2 NAAQS by the October 4, 2018, attainment date; (4) 
requirements for RFP toward attaining the SO2 NAAQS in the 
Area; (5) contingency measures; (6) the assertion that Pennsylvania's 
existing SIP-approved NSR program meets the applicable requirements for 
SO2; and (7) the request that emission limitations and 
compliance parameters for Keystone, Conemaugh, Homer City, and Seward 
be incorporated into the SIP.
    On July 13, 2018 (83 FR 32606), EPA published a notice of proposed 
rulemaking (NPRM) in which EPA proposed full approval of Pennsylvania's 
Indiana, PA SO2 attainment plan and SO2 emission 
limits and associated compliance parameters for the Keystone, Homer 
City, Conemaugh and Seward sources. During

[[Page 15170]]

the public comment period, the Sierra Club (in conjunction with the 
National Parks Conservation Association, PennFuture, Earthjustice, and 
Clean Air Council) submitted a modeling analysis which showed that the 
emission limits in the attainment plan did not assure attainment 
because one modeled receptor within the nonattainment area had a 
modeled design value that was above the SO2 NAAQS. Sierra 
Club's modeling also showed violations of the SO2 NAAQS 
outside of the nonattainment area. In response to this comment, on 
February 5, 2020, PADEP submitted supplemental information in support 
of the attainment plan. The February 5, 2020 submittal included: (1) A 
supplemental air dispersion modeling report; (2) supplemental air 
dispersion modeling data; (3) a supplemental air dispersion modeling 
protocol; (4) a meteorological monitoring plan; (5) meteorological 
monitoring data; (6) meteorological monitoring quality assurance, 
quality control, and audit reports; (7) Clean Air Markets Division 
(CAMD) emissions data for 2010-2018; and (8) Continuous Emissions 
Monitoring (CEM) data for 2010 through the third quarter of 2019. The 
supplemental air dispersion modeling used a more refined model receptor 
grid than that in the original submittal, meteorological data collected 
near the controlling modeled source (Seward), and more recent (2016-18) 
background concentrations from the South Fayette SO2 monitor 
(the monitor used to determine background concentrations in the 
original modeling analysis). The supplemental modeling did not address 
the violations occurring outside the nonattainment area that Sierra 
Club's modeling identified. In order to allow for public comment on 
this supplemental information and modeling, on March 9, 2020 (85 FR 
13602), EPA published a notice of data availability (NODA) for the 
February 5, 2020, submittal. During that public comment period, Sierra 
Club submitted new comments raising issues with the supplemental 
modeling.
    On October 19, 2020 (85 FR 66240), EPA finalized full approval of 
the Pennsylvania SO2 attainment plan for the Indiana, PA NAA 
(hereafter referred to as the ``October 2020 final rule action'' or the 
``October 2020 final action''). On December 18, 2020, the Sierra Club, 
Clean Air Council, and PennFuture filed a petition for judicial review 
with the U.S. Court of Appeals for the Third Circuit, challenging that 
final approval.\7\ As mentioned earlier, on August 17, 2021, the U.S. 
Court of Appeals for the Third Circuit granted EPA's request for remand 
without vacatur of the final approval of Pennsylvania's SO2 
attainment plan for the Indiana, PA NAA. The court ordered EPA to take 
final action to respond to the remand no later than August 17, 2022. 
EPA has reconsidered that final action and is proposing to revise its 
prior full approval to a partial approval and partial disapproval based 
on the analysis and explanation below. EPA now proposes to determine 
that it was in error to fully approve the Indiana, PA SO2 
attainment plan, and is in the same manner as the prior full approval 
revising its prior action. See, CAA section 110(k)(6). EPA is proposing 
to retain the approval of the emissions inventory and nonattainment New 
Source Review (NNSR) program requirements, and is proposing disapproval 
of the attainment demonstration, RACM/RACT requirements, RFP 
requirements and contingency measures.
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    \7\ Sierra Club, et al. v. EPA, Case No. 20-3568 (3rd Cir.).
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A. Emissions Inventory Requirements

    States are required under section 172(c)(3) of the CAA to develop 
comprehensive, accurate and current emissions inventories of all 
sources of the relevant pollutant or pollutants in the nonattainment 
area. These inventories provide detailed accounting of all emissions 
and emissions sources of the pollutant or precursors. In addition, 
inventories are used in air quality modeling to demonstrate that 
attainment of the NAAQS is as expeditious as practicable. The 
SO2 Nonattainment Guidance provides that the emissions 
inventory should be consistent with the Air Emissions Reporting 
Requirements (AERR) at Subpart A to 40 CFR part 51.\8\
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    \8\ The AERR at subpart A to 40 CFR part 51 cover overarching 
federal reporting requirements for the states to submit emissions 
inventories for criteria pollutants to EPA's Emissions Inventory 
System. EPA uses these submittals, along with other data sources, to 
build the National Emissions Inventory.
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    For the base year inventory of actual emissions, a ``comprehensive, 
accurate and current'' inventory can be represented by a year that 
contributed to the three-year design value used for the original 
nonattainment designation. The 2014 SO2 Nonattainment 
Guidance notes that the base year inventory should include all sources 
of SO2 in the nonattainment area as well as any sources 
located outside the nonattainment area which may affect attainment in 
the area. Pennsylvania appropriately elected to use 2011 as the base 
year because the designation of nonattainment was based on data from 
2009-2011. Actual emissions from all the sources of SO2 in 
the Indiana Area were reviewed and compiled for the base year emissions 
inventory requirement. The primary SO2-emitting point 
sources located within the Indiana Area are Keystone, Conemaugh, Homer 
City, and Seward, all coal-fired power plants. Keystone and Conemaugh 
each have two pulverized coal-fired (PC) boilers; Homer City has three 
coal-fired boilers; and Seward has two circulating fluidized bed (CFB) 
waste coal-fired boilers. More information about the emissions 
inventory for the Indiana Area (and analysis of the inventory) can be 
found in Pennsylvania's October 11, 2017, submittal as well as EPA's 
emissions inventory technical support document (TSD), which can be 
found under Docket ID No. EPA-R03-OAR-2017-0615 and online at 
www.regulations.gov.
    Table 1 in this document shows the level of emissions, expressed in 
tons per year (tpy), in the Indiana Area for the 2011 base year by 
emissions source category. The point source category includes all 
sources within the Area.

  Table 1--2011 Base Year SO2 Emissions Inventory for the Indiana Area
------------------------------------------------------------------------
                                                           SO2 emissions
                Emission source category                       (tpy)
 
------------------------------------------------------------------------
Point...................................................     144,269.017
Area....................................................         555.610
Non-road................................................           1.025
On-road.................................................           7.730
                                                         ---------------
    Total...............................................     144,833.382
------------------------------------------------------------------------

    EPA has evaluated Pennsylvania's 2011 base year emissions inventory 
for the Indiana Area and has made the preliminary determination that 
this inventory was developed in a manner consistent with EPA's guidance 
and that EPA appropriately approved this element of the attainment plan 
in its prior action. Therefore, pursuant to section 172(c)(3), EPA is 
not proposing to change its approval of Pennsylvania's 2011 base year 
emissions inventory for the Indiana Area to a disapproval, as it meets 
CAA requirements. Instead, EPA is proposing that the plan retain its 
approval with respect to the base year emissions inventory element.

B. New Source Review \9\
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    \9\ The CAA NSR program is composed of three separate programs: 
Prevention of significant deterioration (PSD), NNSR, and Minor NSR. 
PSD is established in part C of title I of the CAA and applies in 
undesignated areas and in areas that meet the NAAQS--designated 
``attainment areas''--as well as areas where there is insufficient 
information to determine if the area meets the NAAQS--designated 
``unclassifiable areas.'' The NNSR program is established in part D 
of title I of the CAA and applies in areas that are not in 
attainment of the NAAQS--designated ``nonattainment areas.'' The 
Minor NSR program addresses construction or modification activities 
that do not qualify as ``major'' and applies regardless of the 
designation of the area in which a source is located. Together, 
these programs are referred to as the NSR programs. Section 173 of 
the CAA lays out the NNSR program for preconstruction review of new 
major sources or major modifications to existing sources, as 
required by CAA section 172(c)(5). The programmatic elements for 
NNSR include, among other things, compliance with the lowest 
achievable emissions rate and the requirement to obtain emissions 
offsets.
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    Section 172(c)(5) of the CAA requires that an attainment plan 
require permits

[[Page 15171]]

for the construction and operation of new or modified major stationary 
sources in a nonattainment area. Pennsylvania has a fully implemented 
Nonattainment New Source Review (NNSR) program for criteria pollutants 
in 25 Pennsylvania Code Chapter 127, Subchapter E, which was approved 
into the Pennsylvania SIP on December 9, 1997 (62 FR 64722). On May 14, 
2012 (77 FR 28261), EPA approved a SIP revision pertaining to the pre-
construction permitting requirements of Pennsylvania's NNSR program to 
update the regulations to meet EPA's 2002 NSR reform regulations. EPA 
then approved an update to Pennsylvania's NNSR regulations on July 13, 
2012 (77 FR 41276), and on June 11, 2021 (86 FR 25951). These rules 
provide for appropriate NSR as required by CAA sections 172(c)(5) and 
173 and 40 CFR 51.165 for SO2 sources undergoing 
construction or major modification in the Indiana Area without need for 
modification of the approved rules. Therefore, in its prior approval 
action, EPA concluded that the Pennsylvania SIP meets the requirements 
of section 172(c)(5) for the Indiana Area. EPA continues to believe 
that the Pennsylvania SIP meets this requirement and is not proposing 
to change its action to disapproval for the NNSR element. Instead, EPA 
is proposing that the plan retain its approval with respect to the NNSR 
element.

C. Attainment Demonstration

    The SO2 attainment demonstration provides air quality 
dispersion modeling analyses intended to demonstrate that control 
strategies chosen to reduce SO2 source emissions will bring 
the area into attainment by the statutory attainment date of October 4, 
2018. The modeling analyses are used to assess the control strategy for 
a nonattainment area and establish emission limits that will provide 
for attainment. The analyses require 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.\10\ The 
modeling demonstration typically also relies on maximum allowable 
emissions from sources in the nonattainment area. Modeling analyses 
that provide for attainment under all scenarios of operation for each 
source must, therefore, consider the worst-case scenario of both the 
representative meteorology (e.g., predominant wind directions, 
stagnation, etc.) and the maximum allowable emissions. In this way, the 
attainment demonstration shows that the emissions limits in the SIP 
provide for attainment under all worst-case meteorological and 
emissions scenarios that are permissible under the limits.
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    \10\ The period of meteorological data needed for an air-quality 
analysis is described in section 8.4.2 (e) of appendix W: ``[T]he 
use of five years of adequately representative National Weather 
Service or comparable meteorological data, at least one year of 
site-specific, or at least three years of prognostic meteorological 
data, are required.''
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    In its October 11, 2017, and February 5, 2020, submissions, PADEP 
provided multiple modeling analyses as their attainment demonstration. 
In order to better explain our review of each analysis, EPA has 
categorized them--first to address Pennsylvania's request to use an 
alternative model option (AERMOIST) in the attainment plan, and then to 
address the modeling used to develop emission limits for the four main 
sources of SO2 emissions. This is the same approach EPA used 
to review the modeling analyses for the October 2020 final rule action 
that fully approved the plan.
    In relation to the alternative model request, PADEP provided: (1) 
An analysis using the default option in EPA's preferred dispersion 
modeling system, AERMOD; and (2) an analysis utilizing AERMOD but 
including a procedure called AERMOIST, an alternative model option 
which accounts for additional plume rise associated with the latent 
heat release of condensation due to moisture in a stack's plume. 
AERMOIST is currently not approved by EPA for regulatory use.
    On July 13, 2018, EPA rejected PADEP's request to use AERMOIST in 
its attainment demonstration. 83 FR 32606. EPA is not proposing to 
change our previous rejection of the AERMOIST procedure in this action, 
nor did we in the October 2020 final action. EPA's conclusion from its 
review of AERMOIST in the previous action still applies, which was that 
the AERMOIST procedure is not an appropriate option for use in the 
Indiana attainment plan for the following reasons: (1) There is no 
multi-monitor database of SO2 monitoring data available for 
the four major sources of SO2 in the Indiana Area to conduct 
a source-specific statistical test to determine if AERMOIST provides a 
definitive improvement over the current regulatory default version of 
AERMOD; (2) AERMOIST was universally applied to all the major sources 
in the Indiana Area regardless of whether the source plumes are 
actually saturated; and (3) there is a lack of supporting analysis for 
using relative humidity measurements in AERMOIST.\11\
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    \11\ A detailed discussion of the deficiencies of the AERMOIST 
modeling analysis submitted for the Indiana Area can be found in 
EPA's AERMOIST modeling TSD for the Indiana Area which can be found 
under Docket ID No. EPA-R03-OAR-2017-0615 and available online at 
www.regulations.gov.
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    PADEP submitted multiple additional modeling analyses not relying 
upon AERMOIST to develop and/or support emission limits for the four 
main sources of SO2 emissions in the Indiana Area: (1) A 
February 5, 2020 modeling analysis using randomly reassigned emission 
(RRE) values to support the 30-day limit for Seward; (2) an October 11, 
2017 modeling analysis using RRE values to support the 30-day limit for 
Seward; (3) an October 11, 2017 modeling analysis using RRE values to 
develop a 24-hour emission limit for Keystone; (4) a February 5, 2020 
modeling analysis to reexamine the Critical Emission Value (CEVs) for 
Keystone, Conemaugh, Homer City and Seward; and (5) an October 11, 2017 
modeling analysis to determine the CEVs for the four main 
SO2 sources: Keystone, Conemaugh, Homer City and Seward.
    In the October 2020 final action, EPA focused our review on the CEV 
and RRE modeling from the February 5, 2020, submittal used to support 
Seward's longer-term limit and on review of the CEV and RRE modeling in 
the October 11, 2017 submittal used to develop Keystone's longer-term 
limit. Our reconsideration of these reviews, and the reasons for why we 
now think we were in error to fully approve the analyses, is explained 
in detail below.
    EPA reviewed the October 11, 2017, and the February 5, 2020, 
modeling analyses, which were used by PADEP to determine the CEVs for 
Keystone, Conemaugh, Seward and Homer City.\12\

[[Page 15172]]

In the October 11, 2017, submittal, the Indiana Area was divided into 
two separate modeling domains. One domain included portions of 
Armstrong County which only addressed emissions from Keystone as a 
source. The other domain covered all of Indiana County and addressed 
emissions from all four sources in the nonattainment area. For both 
domains, background concentrations included impacts from non-modeled 
sources. Each separate model domain used its own (different) background 
concentration. EPA continues to agree with Pennsylvania that two 
modeling domains are appropriate due to the long distance between 
Keystone and the other three sources, and the predominant wind 
direction. EPA also continues to assert that the use of a different, 
and higher background for the Keystone CEV modeling, while not 
required, provides additional assurances that the CEV for Keystone is 
protective of the NAAQS. 85 FR 66420.
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    \12\ Refer to EPA's Modeling TSDs for the Indiana Area under 
Docket ID EPA-R03-OAR-2017-0615, available at www.regulations.gov 
for EPA's review of the modeling domains (TSD For the Modeling 
Portions of the Document Entitled ``State Implementation Plan 
Revision: Attainment Demonstration and Base Year Inventory Indiana, 
PA Nonattainment Area for the 2010 1-Hour Sulfur Dioxide National 
Ambient Air Quality Standard,'' dated October 2017 pages 9-14, and 
TSD For the Modeling Portions of the Document Entitled 
``Supplemental Information to Address a Comment Received by the EPA 
on Pennsylvania's 1-hour Sulfur Dioxide Attainment Demonstration for 
the Indiana, Pennsylvania Nonattainment Area'' submitted on February 
5, 2020 pages 12-15) and 85 FR 66240 at 66247-66248.
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    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,\13\ 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.
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    \13\ Plan Approval 32-00055H was issued on April 2, 2012, and 
modified on April 4, 2013, by PADEP.
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    In the February 5, 2020, modeling analysis, an alternative finer 
scale grid in the southeast corner of the original Indiana County 
domain was used, as well as multi-level site-specific meteorological 
data that were generated during the period from September 2015 through 
August 2016, and updated background concentrations. When all the 
updates were modeled, Seward's 1-hour CEV had to be reduced 
approximately 11% from the original CEV to show attainment with the 
NAAQS (CEV changed from 5,079 lb/hr to 4,500 lb/hr). The CEVs for the 
other three SIP sources did not change. The CEV rates used in the 
demonstration analysis for each of the four sources are summarized in 
the following table. The modeled emission rate in grams per second was 
converted to pounds per hour, which is the CEV for each source.\14\ 
Upon reconsideration, EPA is not proposing to change the October 2020 
decision that the CEVs were modeled correctly.\15\
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    \14\ Based on the National Institute of Standards and Technology 
conversion: 1 pound = 453.59237 grams
    \15\ While the current CEV modeling is not a reason for 
disapproval, as discussed later in the preamble, EPA encourages 
Pennsylvania to ensure that the revised attainment plan includes 
modeling that provides for attainment in all areas with known NAAQS 
violations.

                      Table 2--February 5, 2020 Model Run Results--Critical Emission Values
----------------------------------------------------------------------------------------------------------------
                                                                Critical emission value  Critical emission value
                                                                  - SO2 emission rates     - SO2 emission rates
                            Source                               modeled in attainment    modeled in attainment
                                                                    model run (g/s)         model run (lb/hr)
 
----------------------------------------------------------------------------------------------------------------
Seward........................................................                   566.99                   4500.0
Homer City Unit 1.............................................                   195.30                   1550.0
Homer City Unit 2.............................................                   195.30                   1550.0
Homer City Unit 3.............................................                   410.75                   3260.0
Keystone......................................................                  1223.60                   9711.1
Conemaugh.....................................................                   426.00                   3381.0
----------------------------------------------------------------------------------------------------------------

    The October 11, 2017, submittal also included a modeling analysis 
using randomly reassigned historical hourly emissions for Keystone for 
100 AERMOD simulations (referred to as RRE Modeling). The hourly 
modeled emission values were based on 2016 actual hourly emissions that 
reflect emission patterns based on plant operations and reassigned to 
determined fixed values through a binning approach in which the upper 
limit for each corresponding bin was used as the modeled emission rate. 
The emissions profile was such that the actual emission rate for 15% of 
the hours per year were above the CEV of 9,711 lb/hr, and those hours 
fell within 15 days in each month. Because of this pattern, where 
hourly actual emissions values above the CEV were clustered together on 
a limited number of days rather than individually dispersed throughout 
the year, Pennsylvania created a ``rule'' in the modeling of binned 
reassigned fixed values, whereby the actual hours over the CEV were 
modeled in separate clusters which Pennsylvania calls ``high emission 
event days.'' The total amount of SO2 emissions each day, 
however, are constrained by a limit which restricts the total pounds of 
SO2 emissions, on a 24-hour block average basis, to be at or 
below 9,600 lb/hr. The hours for which the emissions were modeled above 
the CEV were not randomly dispersed individually throughout the year 
because the plant did not and likely will not operate that way in order 
to meet the limit. Thus, these high emission events were modeled in a 
way that is representative of the variability in the historic (2016) 
emissions data and of expected emissions performance occurring in 
compliance with the allowable emissions limit (as asserted in 
Pennsylvania's submittal).
    The ``rule'' constrained the high emission events days to not 
exceed 9,604 lb/hr on a 24-hour block average; however, not every day 
was modeled with hourly emission rates resulting in a 24-hour block 
average approaching or equal to 9,604 lbs/hr. As previously described, 
the historical emissions data demonstrate that not every day is a high 
emission event day based on the historic variability of the source. 
Pennsylvania modeled about 50% of the days in a month where binned 
reassigned hourly SO2 emissions were always below the CEV 
value and about 50% of the days in a month as high emission event days 
where there were at least three hours of binned reassigned emissions 
over the CEV during those 24 hours. The high

[[Page 15173]]

emission events days included nine days (30% of the days) in a month 
where the 24-hour averages were near 9,600 lb/hr. The remaining six 
high emission event days per month experienced three hours of emissions 
above the CEV, yet emissions during the remaining hours of the day 
resulted in the 24-hour daily average falling at 6,333 lb/hr for five 
of the six days and at 8,964 lb/hr for one of the six days. However, 
the other hours in these days were assigned values at or below the CEV, 
reflecting the predominance of values below the CEV in the modeled 
emissions distribution (which in turn reflected the predominance of 
values below the CEV in the historical record), resulting in daily 
average emission rates for these days below 9,600 lb/hr. The remaining 
days (not categorized as high emission events days) had 24-hour daily 
average emissions between 5,000 lb/hr and 6,200 lb/hr.
    Pennsylvania developed 100 different annual emission profiles using 
the historic data of high emission event days, and randomly re-
assigning the other hourly emissions such that the 24-hour limit of 
9,600 lbs/hr is modeled during 30% of the days across each month. These 
emission files provide a large array of temporally varying hourly 
actual emissions which take into account the ``rule'' where hourly 
actual emissions above the CEV are clustered together into high 
emission event days, reflecting the variability in the historic 
emissions data and historic plant operations. Each of the 100 emissions 
scenarios were modeled with five years of meteorological data using 
AERMOD. For each of the 100 5-year AERMOD simulations for Keystone, the 
5-year average of the 99th percentile of the daily maximum 1-hour 
SO2 modeled concentrations were below the NAAQS.\16\
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    \16\ See EPA's March 1, 2011 clarification memo ``Additional 
Clarification Regarding Application of Appendix W Modeling Guidance 
for the 1-hour NO2 National Ambient Air Quality 
Standard.''
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    When reconsidering the RRE modeling for Keystone, EPA examined 
whether the RRE modeling provided the necessary analysis to determine 
if the longer term limits were comparably stringent to the modeled 1-
hour CEVs and whether the RRE approach demonstrated that the longer 
term limits provided for attainment.
    While the 2014 SO2 Nonattainment Guidance did not 
preclude states from using other approaches to determine appropriate 
longer term average limits, EPA did recommend that in all cases the 
analysis begin with the determination of the CEV (a constant hourly 
emissions level at which attainment is modeled to occur) and include an 
assessment showing that the longer term limits are of comparable 
stringency to the 1-hour CEV. This is a critical element in the 
attainment demonstration because it provides a similar level of 
assurance that complying with the longer term limit, in lieu of the 
hourly limit reflecting the modeled CEV, will also provide for 
attainment.
    As described earlier, Pennsylvania provided adequate CEV modeling 
for Keystone, Seward, Homer City, and Conemaugh, but Pennsylvania did 
not provide evidence that the longer term limits derived via the 
application of RRE modeling were comparable in stringency to the 9,711 
lb/hr CEV for Keystone. Essentially, the necessary steps to establish 
the comparably stringent relationship between a modeled 1-hour CEV and 
longer term limits were not taken.
    In the October 2020 final rule action, EPA did not address whether 
the longer term limits derived via the RRE modeling of binned 
reassigned historical emissions were in fact comparably stringent to 
the 1-hour CEV, and at that time only focused our review on whether the 
RRE modeling of binned re-assigned historical actual emissions 
projected future emissions performance that would result in NAAQS 
attainment. In that final rule, EPA stated that ``the RRE modeling 
provided enough permutations of emissions and meteorology that we can 
be reasonably confident that Keystone's longer-term limit is protective 
of the NAAQS. This conclusion is based upon the large number of 
emission distribution profiles (100), the frequency and distribution of 
high emission event days, the 9,600 lb/hr 24-hour emission limit 
modeled 30% of the days per month, emissions inputs reflective of the 
variability in historic plant operations, and meteorological data (five 
years of National Weather Service data).'' (85 FR 66240 at 66244).
    Upon reconsideration, EPA has determined that without a comparably 
stringent analysis and a clear link between the modeled 1-hour CEV and 
the longer term limit, EPA does not have adequate assurance that 
Keystone's longer term limit, considering worst case emissions 
scenarios permissible under the limit, is protective of the 1-hour 
SO2 standard. EPA did not address this issue clearly in the 
October 2020 final action; however, EPA was clear in the 2014 
SO2 Guidance, which states, ``A comparison of the 1-hour 
limit and the proposed longer term limit, in particular an assessment 
of whether the longer term average limit may be considered to be of 
comparable stringency to a 1-hour limit at the critical emission value, 
would be a critical element of a demonstration that any longer term 
average limits in the SIP will help provide adequate assurance that the 
plan will provide for attainment and maintenance of the 1-hour NAAQS.'' 
(pg. 26).
    In addition to not having established that the longer term limits 
are comparably stringent to the 1-hour CEV, Pennsylvania's binning 
approach used in the RRE modeling was dependent upon historical 
emissions performance and assumed continued performance that was well 
below that which is permissible under the limit. The binned emissions 
approach may have been a valid way to characterize factual air quality 
resulting from actual emissions and may be useful in a designations or 
attainment determination context. However, because the approach did not 
characterize maximally possible emissions that could occur in 
compliance with the emission limit nor provide a comparably stringent 
analysis, EPA now considers that it falls short of demonstrating that 
the limits will provide for attainment under all worst case emissions 
scenarios that are permissible under the limit, and that it was 
incorrect for EPA to fully approve the attainment demonstration in the 
absence of this demonstration.
    In order to establish the comparable stringency of a longer term 
limit to a modeled attaining 1-hour CEV, EPA's 2014 Guidance 
recommended using a comparison of the 99th percentile of historic 
hourly emissions to the 99th percentile of the longer term averaged 
emissions of the same dataset to develop an adjustment factor for use 
in converting the modeled 1-hour CEV to a comparably stringent longer 
term limit. The focus on the 99th percentile of data is purposeful to 
ensure that extreme hourly variability was correctly accounted for in 
developing the longer term limits and showing that the longer term 
limits account for the worst case emissions performance that is 
permissible under the limits. Generally, when applying EPA's 
recommended methodology for developing a comparably stringent longer 
term limit, a source with a history of frequent spikes of high hourly 
emissions will have a lower adjustment factor, resulting in a greater 
reduction in the numeric value of the comparably stringent longer term 
limit, than a source with less frequent spikes of high hourly 
emissions. Development of a longer term limit based on a variability 
metric other than the 99th percentile metric of the historic emissions 
variability should be accompanied by

[[Page 15174]]

justification of how the longer term limit is comparably stringent to 
the 1-hour CEV. In the RRE analysis for Keystone, the Commonwealth of 
Pennsylvania used the actual hourly emissions distribution of one year 
(2016) to generate 100 hourly emissions profiles to use in the 
modeling. Pennsylvania's analysis (i.e., RRE approach) was an 
assessment of hourly emissions with no assurance (via a comparably 
stringent consideration) that prospective (future) hourly emissions 
when complying with the longer term limit (potentially worst case 
scenarios) were properly accounted for. Pennsylvania did not provide a 
justification for using a metric other than the 99th percentile of 
hourly emissions data to support Keystone's longer-term limit. This 
means that Pennsylvania did not establish that the longer term limit 
for Keystone was comparably stringent to an attaining 1-hour CEV, and 
that EPA erred in approving the attainment demonstration and limit as 
providing for NAAQS attainment. Thus, EPA is proposing to correct its 
prior approval to a disapproval of the attainment demonstration for 
Keystone.
    In the February 5, 2020, submittal, Pennsylvania included an RRE 
analysis for Seward to support its already established 30-day average 
SO2 limit of 3,038.4 lb/hr. First, Pennsylvania determined 
Seward's CEV of 4,500 lb/hr using AERMOD.\17\ Then, using 2016-2018 
emissions from Seward, Pennsylvania developed a binned emissions 
dataset to be used in formulating the inventories modeled in 100 AERMOD 
simulations. Pennsylvania used a total of 13 bins, including five bins 
ranging from an upper level of 2,000 lbs/hour to an upper level of 
4,500 lbs/hour and eight bins at various ranges above the CEV. Hours 
without operation were represented as hours with 2,000 lbs/hour, and 
all the other hours were represented with the upper level of the 
applicable bin. The dataset included 2.5% of hourly emissions above the 
CEV (or 220 hours). This was based on how the plant historically 
operated while complying with this 30-day limit during the appliable 
time period and how it is expected to operate into the future while in 
compliance with the 30-day limit. The hours above the CEV were 
distributed across four high emission events, where the duration of 
each event was 4, 7, 12, or 16 hours, with the frequency of those 
events being twice per month, monthly, every six months and once per 
year, respectively, such that these 220 hours above the CEV were spread 
across 39 days. The remaining 97.5% of hourly emissions were below the 
CEV and randomly assigned throughout the annual emissions profile.
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    \17\ This CEV and the description provided are based on 
Pennsylvania's updated analysis which was provided to EPA on 
February 5, 2020. The CEV for Seward in the October 11, 2018 
submittal was 5,079 lb/hr.
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    Pennsylvania calculated a weighted average of the hourly emissions 
in the binned inventory by multiplying the bin level times the 
percentage of hours in each bin and summing the results. This sum, 
representing the average of the modeled emissions, equaled 3,088 lb/hr. 
Despite minor variations resulting from the random distribution 
process, each of the 100 AERMOD simulations had approximately this 
average level of emissions.
    Pennsylvania developed 100 different annual emission profiles using 
the historic data of high emission event days, and randomly assigning 
the other hourly emissions such that the average of the 30-day averages 
of each simulation was close to 3,088 lb/hr. Seward's SO2 
emissions limit of 3,038.4 lb/hr on a 30-day rolling average basis is 
approximately 50 lb/hr less than the approximate average emissions 
value used in the AERMOD simulations.
    As similarly described above for Keystone, when reconsidering the 
RRE modeling for Seward, EPA has now examined whether the RRE modeling 
provided the necessary analysis to determine if the longer term limits 
were comparably stringent to the modeled 1-hour CEVs. Upon 
reconsideration, EPA has found that the RRE modeling used to support 
Seward's longer term limit did not provide evidence that the longer 
term limit is comparably stringent to Seward's CEV of 4,500 lb/hr. As 
noted previously in the preamble, the CEV for Seward decreased 11% from 
5,079 lb/hr in the October 11, 2017, submittal to 4,500 lb/hr in the 
February 5, 2020, submittal, due to updates to model inputs, in 
particular, site specific meteorology data, a more refined receptor 
grid, and updated emissions data. The RRE derived longer-term limit, 
however, did not change from one submittal to the next. This highlights 
the failed linkage of the modeled CEV to this longer term limit. In the 
October 2020 final action, EPA failed to address this critical element 
in determining whether the State had adequately shown that allowable 
emissions performance in compliance with a longer term limit for Seward 
ensures NAAQS attainment.
    In relation to whether the binned approach used for Seward's RRE 
modeling provided adequate assurance that hourly emissions when in 
compliance with the longer term limit provided for attainment, EPA 
notes that the binned approach did not account for the 99th percentile 
of historic hourly data, nor did it provide evidence that an analysis 
based on a metric other than 99th percentile of hourly emissions data 
could result in a comparably stringent longer term limit. This means 
that PADEP did not establish that the longer term limit for Seward was 
comparably stringent to an attaining 1-hour CEV, and that EPA erred in 
approving the attainment demonstration and limit as providing for NAAQS 
attainment. Thus, EPA is proposing to correct its prior approval to a 
disapproval of the attainment demonstration for Seward.

D. RACM/RACT

    CAA section 172(c)(1) requires that each attainment plan provide 
for the implementation of all reasonably available control measures 
(i.e., RACM) as expeditiously as practicable and shall provide for 
attainment of the NAAQS. Section 172(c)(6) requires SIPs to contain 
enforceable emission limitations and control measures as may be 
necessary or appropriate to provide for NAAQS attainment. EPA 
interprets RACM, including RACT, under section 172 as measures that a 
state determines to be both reasonably available and contribute to 
attainment as expeditiously as practicable ``for existing sources in 
the area.''
    Pennsylvania's October 11, 2017, submittal discusses Federal and 
state measures that Pennsylvania asserts will provide emission 
reductions leading to attainment and maintenance of the 2010 
SO2 NAAQS. With regard to state rules, Pennsylvania cites 
its low sulfur fuel rules, which were SIP-approved on July 10, 2014 (79 
FR 39330). Pennsylvania's low sulfur fuel oil provisions apply to 
refineries, pipelines, terminals, retail outlet fuel storage 
facilities, commercial and industrial facilities, and facilities with 
units burning regulated fuel oil to produce electricity and domestic 
home heaters. These low sulfur fuel oil rules reduce the amount of 
sulfur in fuel oils used in combustion units, thereby reducing 
SO2 emissions and the formation of sulfates that cause 
decreased visibility.
    The October 11, 2017, submittal also 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

[[Page 15175]]

the main SO2 emitting sources at each facility.

                  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, the October 11, 2017, submittal 
discusses facility-specific control measures, namely SO2 
emission limits for Conemaugh, Homer City, and Seward, and new 
SO2 emission limits for Keystone. Keystone's new limits were 
developed through air dispersion modeling (default AERMOD as described 
below) submitted by PADEP. In order to ensure that the Indiana Area 
demonstrates attainment with the SO2 NAAQS, PADEP asserts 
that the following combination of emission limits at the four 
facilities is sufficient for the Indiana Area to meet the 
SO2 NAAQS and serve as RACM/RACT:
     Conemaugh's current SO2 emission limits 
contained in the Title V Operating Permit (TVOP) 32-00059 because the 
emission limits for Conemaugh determined by the modeling as necessary 
for SO2 attainment would be less stringent;
     Seward's current SO2 emission limit in TVOP 32-
00040 because the emission limits for Seward determined by the modeling 
as necessary for SO2 attainment would be less stringent;
     Homer City's current SO2 emission limits 
established in Plan Approval 32-00055H and Plan Approval 32-00055I; and
     A new, more stringent combined SO2 emission 
limit for Keystone Unit 1 and Unit 2 of 9,600 lbs/hr block 24-hour 
average limit.

The emission limits for each of the SO2-emitting facilities 
are listed in Table 4 in this document.

                            Table 4--SO2 Emission Limits for Indiana Area Facilities
----------------------------------------------------------------------------------------------------------------
              Facility                 Source description      Emission limit (lbs/hr)       Averaging period
----------------------------------------------------------------------------------------------------------------
Conemaugh..........................  Unit 1................  1,656 (TVOP 32-00059)......  3-hour block.
                                     Unit 2................
Homer City.........................  Unit 1................  6,360 (Plan Approval 32-     1-hour block.
                                     Unit 2................   00055H) and limits
                                     Unit 3................   specified in Plan Approval
                                                              32-00055I.
Keystone...........................  Unit 1................  9,600 (New limit based on    24-hour block.
                                     Unit 2................   default AERMOD).
Seward.............................  Unit 1................  3,038.4 (TVOP 32-00040)....  30-day rolling.
                                     Unit 2................
----------------------------------------------------------------------------------------------------------------

    The emission limits for Conemaugh, Keystone and Seward have 
averaging times greater than 1-hour (ranging between three hours and 30 
days). The SO2 limits at Conemaugh are set to a 3-hour block 
average. This average is roughly in line with the CEV modeled limit and 
the ratio from Appendix C in EPA's 2014 SO2 Nonattainment 
Guidance. Keystone's limits were set to a 24-hour block average based 
on the 100 RRE simulation method discussed in the Attainment 
Demonstration section in this proposed rulemaking. A similar approach 
was used to establish a 30-day rolling average for Seward. Appendices 
C-1a and C-4 of Pennsylvania's October 11, 2017, SIP submittal, and the 
modeling report of the February 5, 2020, submittal, provide detailed 
explanation of the longer-term emission limits.
    EPA expects to consider the following factors in evaluating the 
adequacy of plans with limits based on longer averaging times: (l) 
Whether the numerical value of the mass emissions limit averaged over a 
longer time is comparably stringent to a 1-hour limit at the CEV; and 
(2) whether the longer-term average limit, potentially in combination 
with other limits, can be expected to constrain emissions sufficiently 
so that any occasions of emissions above the CEV will be limited in 
frequency and magnitude and, if they occur, would not be expected to 
result in NAAQS violations.
    EPA analyzed the last five years of emissions data for Keystone and 
Seward in order to understand the source's historic emissions 
variability. EPA used the methodology described in Appendix C of the 
2014 SO2 Nonattainment Guidance to calculate adjustment 
factors for each source. Refer to EPA's TSD entitled Reconsideration of 
the Attainment Plan for the Indiana, PA 1-Hour SO2 
Nonattainment Area (January 2022) for a detailed description of EPA's 
analysis.
    The 2014 SO2 Nonattainment Guidance recommends the use 
of a data set that reflects hourly data for at least 3 to 5 years of 
stable operation (i.e., without changes that significantly alter 
emissions variability) to obtain a suitably reliable analysis. EPA 
analyzed two 3-year periods and one 5-year period for Keystone, and one 
3-year

[[Page 15176]]

period and one 5-year period for Seward for illustrative purposes. 
Because the analyses for Seward and Keystone were done for illustrative 
purposes, the adjustment factors resulting from the analyses are also 
only for illustrative purposes. Using the current CEV for Keystone of 
9,711 lb/hr, and depending upon the years of data used, Keystone's 24-
hour block limits could be either 8,573.0 lbs/hr, 8,959.5 lb/hr, or 
8,225.3 lbs/hr. Using Seward's CEV determined by Pennsylvania's 
supplemental analysis (4,500 lbs/hr) the 30-day rolling limit would be 
3,484.3 lbs/hr using the 3-year adjustment factor and 2,575.3 lbs/hr 
using the 5-year adjustment factor.
    EPA compared these values to Pennsylvania's RRE modeling derived 
24-hr limit for Keystone (9,600 lb/r) and the 30-day limit for Seward 
(3,038 lb/hr). For Keystone, the comparably stringent values calculated 
by EPA are between 640 and 1,375 lb/hr less than the limit Pennsylvania 
claimed was protective of the standard, which was 9,600 lb/hr on a 24-
hour block basis. The significant difference between Pennsylvania's 
RRE-derived 24-hour limit for Keystone and the potential 24-hour limits 
calculated by EPA using Appendix C of the 2014 SO2 Guidance 
calls into question whether Keystone's RRE-derived 24-hour limit of 
9,600 lb/hr is comparably stringent to the 1-hr CEV. If the RRE-derived 
limit is not comparably stringent to the CEV that was modeled to show 
attainment of the SO2 NAAQS, then it is uncertain whether 
the longer-term 24-hour limit will provide for attainment of the NAAQS.
    For Seward, when using the last three years of available emissions 
data (2018-2020), EPA calculated 30-day emission limit following the 
Appendix C methodology is 446 lb/hr more than the adopted limit of 
3,038 lb/hr. When using the last five years of available emissions data 
(2016-2020), EPA calculated 30-day limit is 463 lb/hr less than 
Seward's current limit. The large difference in these 30-day limits 
probably results from the decrease in SO2 emission spikes at 
Seward, both in frequency and magnitude, that occurred after 2017. 
Seward's SO2 emissions spikes have declined in magnitude and 
frequency over the last 3 years, which may be due to the operational 
changes referenced in the February 5, 2020, submittal. The 30-day 
average SO2 limit for Seward has been in place since 2001 
and has not been supplemented with additional limits to reflect the 
operational changes noted. As mentioned earlier in the preamble, EPA 
must consider whether the longer-term average limit can be expected to 
constrain emissions sufficiently so that emissions above the CEV will 
be limited in frequency and magnitude and, if they occur, would not be 
expected to result in NAAQS violations. Historic hourly emissions 
(described in the January 2022 TSD) before 2018 show that it is 
possible for this source to be in compliance with the 30-day limit of 
3,038 lb/hr yet have up to 171 hours over the CEV. This data supports 
EPA's earlier conclusion that the current limit, by itself, does not 
adequately constrain the frequency and magnitude of hourly exceedances 
of the CEV and is not comparably stringent to the CEV.
    As described earlier in the preamble, in EPA's October 2020 final 
action on this attainment plan, EPA failed to consider a critical 
aspect of longer-term limits in relation to the 1-hour SO2 
NAAQS, which was whether the longer-term limits for Keystone and Seward 
were comparably stringent to their CEVs and therefore support a 
conclusion that compliance with the longer term limits will provide for 
NAAQS attainment, which is necessary to meet the RACM/RACT requirement 
under EPA's SO2 policy. Absent a comparably stringent 
analysis from Pennsylvania, EPA is proposing that it erred in 
previously approving the RACM/RACT element for the Indiana Area SIP and 
proposes to change its prior approval of the RACM/RACT element to a 
disapproval of the RACT/RACM element for Seward and Keystone.
    The emission limits of the four SIP sources and all related 
compliance parameters (i.e., the measures which include system audits, 
record-keeping and reporting, and corrective actions) have been 
incorporated into the SIP via EPA's final approval of the Indiana, PA 
SO2 attainment plan (85 FR 66240, October 19, 2020) which 
made these changes federally enforceable. EPA is proposing to retain 
the emission limits and compliance parameters for the main sources of 
SO2 in the SIP as SIP strengthening measures while 
Pennsylvania works on revised limits for its attainment plan. 
Maintaining these limits and measures as SIP strengthening measures is 
appropriate for limits that improve air quality but do not meet a 
specific CAA requirement (see 86 FR 14827 at 14828, March 19, 2021).

E. RFP Plan

    Section 172(c)(2) of the CAA requires that an attainment plan 
include a demonstration that shows RFP for meeting air quality 
standards will be achieved through generally linear, incremental 
improvements in air quality. Section 171(1) of the CAA defines RFP as 
``such annual incremental reductions in emissions of the relevant air 
pollutant as are required by this part (part D) or may reasonably be 
required by EPA for the purpose of ensuring attainment of the 
applicable NAAQS by the applicable attainment date.'' As stated 
originally in the 1994 SO2 Guidelines Document \18\ and 
repeated in the 2014 SO2 Nonattainment Guidance, EPA 
continues to believe that this definition is most appropriate for 
pollutants that are emitted from numerous and diverse sources, where 
the relationship between emissions from these numerous and diverse 
sources and the effect of those emissions on ambient air quality are 
difficult to ascertain. In such cases, emissions reductions may be 
required from numerous and varying types of sources in numerous 
locations. The relationship between ambient SO2 
concentrations and the sources of SO2 emissions is much more 
discernable and definable. That is, it is easier to determine the 
effect on ambient SO2 concentrations that SO2 
emission reductions from certain sources will produce. Moreover, the 
emissions reductions from these few sources necessary to attain the 
SO2 NAAQS usually occur in one step, which often (but not 
always) results from installation of new or better controls on a few 
sources that represent a knowable, specific amount of SO2 
reductions, rather than the piecemeal and gradual adoption of controls 
or measures by numerous sources. Therefore, EPA interpreted RFP for 
SO2 as adherence to an ambitious compliance schedule for the 
adoption of controls or newer limits on these SO2 sources in 
both the 1994 SO2 Guideline Document and the 2014 
SO2 Nonattainment Guidance.
---------------------------------------------------------------------------

    \18\ 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. 
Located at: https://www.epa.gov/ttn/oarpg/t1pgm.html.
---------------------------------------------------------------------------

    The purpose of an ambitious compliance schedule is to ensure that 
SO2 sources reach the SO2 emission limits that 
were modeled to show attainment as soon as possible, but no later than 
the compliance date. If the emission limits themselves have not been 
shown to model attainment, then an ambitious compliance schedule will 
not necessarily result in attainment, and reasonable further progress 
toward attainment may not lead to attainment. As noted, on 
reconsideration EPA does not view the longer term emission limits 
derived by Pennsylvania using RRE modeling to be comparably stringent 
to the CEVs used in the modeling that

[[Page 15177]]

demonstrated future attainment of the NAAQS. Therefore, EPA finds there 
is a lack of evidence showing that these longer term limits will yield 
a sufficient reduction in SO2 emissions in the Indiana NAA 
to attain the NAAQS. As a result, EPA is proposing to determine that 
Pennsylvania's SO2 attainment plan for the Indiana Area is 
not adequate to achieve attainment of the NAAQS because the RRE-derived 
longer term limits have not been adequately shown to provide for 
sufficient SO2 emission reductions in the Indiana Area. 
Without this assurance, EPA is proposing to determine that it erred in 
previously approving the RFP element of Pennsylvania's SO2 
attainment plan for the Indiana Area. EPA proposes to change its prior 
approval of the RFP element to a disapproval of Pennsylvania's 
attainment plan with respect to the RFP requirements.

F. Contingency Measures

    In accordance with section 172(c)(9) of the CAA, contingency 
measures are required as additional measures to be implemented in the 
event that an area fails to meet the RFP requirements or fails to 
attain the standard by its attainment date. These measures must be 
fully adopted rules or control measures that can be implemented quickly 
and without additional EPA or state action if the area fails to meet 
RFP requirements or fails to meet its attainment date and should 
contain trigger mechanisms and an implementation schedule. However, 
SO2 presents special considerations. As stated in the final 
2010 SO2 NAAQS promulgation on June 22, 2010 (75 FR 35520), 
and in the 2014 SO2 Nonattainment Guidance, EPA explained 
that because of the quantifiable relationship between SO2 
sources and control measures, provided that the attainment plan 
demonstrates that emissions performance under the allowable emissions 
limits in the SIP provide for NAAQS attainment, it is appropriate that 
state agencies develop a comprehensive program to identify sources of 
violations of the SO2 NAAQS and undertake an aggressive 
follow-up for compliance and enforcement of those emission limits.
    The Consent Order and Agreements (COAs) or Consent Orders (COs) for 
Conemaugh, Homer City, Keystone, and Seward (see Appendices B-1 through 
B-4 of the October 11, 2017 submittal and updated permits submitted on 
February 5, 2020) each contain the following measures that are designed 
to keep the Indiana Area from triggering an exceedance or violation of 
the SO2 NAAQS: (1) Upon execution of the COA or CO, if 
SO2 emissions from the combined SO2 emitting 
sources at the facility exceed 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; and (2) upon 
execution of the COA or CO, if the Strongstown monitor (ID 42-063-0004) 
measures a 1-hour concentration exceeding 75 ppb, PADEP will notify the 
facility in the NAA, and the facility is required to identify whether 
any of the SO2-emitting sources at the respective facility 
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 daily exceedance occurred to ensure that the daily 
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.
    Additionally, if PADEP identifies a daily maximum SO2 
concentration exceeding 75 ppb at a PADEP-operated SO2 
ambient air quality monitor in the Indiana Area, within 5 days, PADEP 
will contact Conemaugh, Homer City, Keystone, and Seward to trigger the 
implementation of the daily exceedance report contingency measure 
described in section VIII.C. of the October 11, 2017, submittal. If 
necessary, section 4(27) of the Pennsylvania Air Pollution Control Act 
(APCA) authorizes PADEP to take any action it deems necessary or proper 
for the effective enforcement of APCA and the rules and regulations 
promulgated under APCA. Such actions include the issuance of orders and 
the assessment of civil penalties. A more detailed description of the 
contingency measures can be found in section VIII of the October 11, 
2017, submittal as well as the COAs and COs included in the submittal 
and included for incorporation by reference into the SIP.
    EPA is proposing to change its prior finding that Pennsylvania's 
October 11, 2017 and February 5, 2020 submittals include sufficient 
contingency measures, since EPA is now proposing that they are based on 
the emission limits, including longer term emission limits, that on 
reconsideration EPA believes have not been shown as comparably 
stringent to the CEVs used in the modeling that demonstrated attainment 
and consequently cannot support a conclusion that compliance with the 
allowable limits in the attainment plan will provide for NAAQS 
attainment. Therefore, on reconsideration EPA proposes that it erred in 
previously approving the contingency measures submitted by 
Pennsylvania, and now proposes to correct this error by proposing to 
change its approval of this element to disapproval because they do not 
follow the 2014 SO2 Nonattainment Guidance and do not meet 
the section 172(c)(9) requirements. Nevertheless, EPA is proposing to 
retain the contingency measures in the SIP which were approved into the 
SIP on October 19, 2020 (85 FR 66240), as SIP strengthening measures. 
Specific needed amendments to the contingency measures can be evaluated 
and determined in the context of developing a new attainment plan that 
appropriately demonstrates that its emission limits and control 
measures will provide for NAAQS attainment.

III. Summary of Sierra Club Modeling Analysis for Westmoreland and 
Cambria Counties Submitted During the Public Comment Period (83 FR 
32606, July 13, 2018) and EPA Considerations

A. Modeled Violations in Westmoreland and Cambria Counties

    During the public comment period for the proposed approval of this 
attainment plan (83 FR 32606, July 13, 2018), the Sierra Club (in 
conjunction with the National Parks Conservation Association, 
PennFuture, Earthjustice, and Clean Air Council) submitted a modeling 
analysis using actual emissions and the CEVs for Conemaugh and Seward 
which claimed to show violations of the SO2 NAAQS outside of 
the nonattainment area, beyond the eastern border of Indiana county 
within nearby portions of Westmoreland and Cambria counties. The 
modeling used the same meteorological data, stack parameters, 
background concentrations and building downwash as Pennsylvania's 
October 11, 2017, submittal. The Sierra Club modeling used emission 
inputs of actual historical emissions (2013- 2018 quarter 1) and a 
finer receptor grid that included receptors outside Indiana County. 
When modeling 2015-2017 emissions, the resulting design value was 293.4 
ug/m\3\, and when modeling 2013-2017 emissions, the resulting design 
value was 267.2 ug/m\3\.\19\ The comment letter

[[Page 15178]]

and modeling results can be found in the Docket for this action.
---------------------------------------------------------------------------

    \19\ In the Round 3 intended designations (82 FR 41903) 
published September 5, 2017, EPA endorsed a value of 196.4 [micro]g/
m\3\ (based on calculations using all available significant figures) 
as equivalent to the 2010 SO2 standard. To avoid 
confusion, EPA is expecting attainment demonstrations to show 
achievement with concentrations at or below precisely 196.4 
[micro]g/m\3\.
---------------------------------------------------------------------------

    Under reconsideration, EPA notes that Sierra Club's modeling, using 
actual emissions and the CEVs for Conemaugh and Seward, although using 
slightly different data from PA's modeling, suggests that there are 
modeled SO2 nonattainment violations outside the NAA, and 
nothing in PA's submittal rebuts the finding of nonattainment outside 
the NAA.
    As stated in the October 2020 final rule action, although EPA does 
not consider that a failure to include an analysis of modeled 
SO2 concentrations outside of the boundaries of the NAA is 
an independent basis on which to disapprove this attainment plan, EPA 
is now proposing to revise its prior full approval of the attainment 
plan to a partial disapproval in order to correct errors made in 
approving the attainment demonstration, and the RACM/RACT, RFP and 
contingency measure elements. EPA encourages the state, when developing 
a new attainment plan that would respond to this partial disapproval, 
if finalized, to additionally ensure that any revised attainment plan 
demonstrates attainment for all known modeled violations. EPA is also 
considering taking a separate statutory action under the Clean Air Act 
to address the modeled violations in Westmoreland and Cambria counties.

B. Environmental Justice Considerations

    EPA conducted an environmental justice (EJ) analysis on the Indiana 
NAA and Westmoreland and Cambria counties. The consideration of 
environmental justice concerns is consistent with the EPA 
Administrator's directive and presidential executive orders.\20\ The 
EPA has defined environmental justice 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.'' \21\ A detailed description of the EJ analysis is available 
in the TSD for this action, which can be found under Docket ID No. EPA-
R03-OAR-2017-0615 and online at www.regulations.gov.
---------------------------------------------------------------------------

    \20\ On April 7, 2021, the Administrator directed all EPA 
offices to take immediate and affirmative steps to incorporate EJ 
considerations into their work, including assessing impacts to 
pollution-burdened, underserved, and Tribal communities in 
regulatory development processes and considering regulatory options 
to maximize benefits to these communities. Message from the EPA 
Administrator, Our Commitment to Environmental Justice (issued April 
7, 2021) at https://www.epa.gov/sites/production/files/2021-04/documents/regan-messageoncommitmenttoenvironmentaljustice-april072021.pdf; ``Executive Order on Advancing Racial Equity and 
Support for Underserved Communities Through the Federal Government'' 
(E.O. 13985, issued January 20, 2021) at https://www.whitehouse.gov/briefing-room/presidential-actions/2021/01/20/executive-order-advancing-racial-equity-and-support-for-underserved-communities-through-the-federal-government/ and 86 FR 7009 (January 25, 2021).
    \21\ See https://www.epa.gov/environmentaljustice/learn-about-environmental-justice.
---------------------------------------------------------------------------

    Vulnerable populations (characterized by the low-income criteria as 
discussed in the TSD) are found inside and outside the SO2 
nonattainment area boundary. In particular, the areas identified by the 
Sierra Club modeling outside the NAA in Westmoreland and Cambria 
counties are also identified as vulnerable populations. EPA recommends 
that Pennsylvania's response to our action, if finalized, should be as 
expeditious as practicable and take into account the emissions impact 
on the vulnerable populations both inside the current nonattainment 
area, and in adjacent areas. EPA is committed to environmental justice 
for all people and expects PADEP in its CAA obligations to ensure that 
public health protection of all people in the Commonwealth is 
consistent with both EPA's and PADEP's commitments.

IV. Proposed Action

    EPA is proposing to amend its prior full approval of the Indiana 
Area SO2 attainment plan to a partial approval and partial 
disapproval. Specifically, EPA is proposing to retain approval of the 
emissions inventory and NNSR elements of Pennsylvania SIP revision and 
disapprove the attainment plan, RACM/RACT demonstration, RFP element, 
and contingency measures which were submitted on October 11, 2017, and 
February 5, 2020. EPA is soliciting public comments on the issues 
discussed in this document. These comments will be considered before 
taking final action.

V. Incorporation by Reference

    In this document, EPA is proposing to include in a final EPA rule 
regulatory text that includes incorporation by reference. In accordance 
with requirements of 1 CFR 51.5, EPA is proposing to retain the 
following information as SIP strengthening measures. These measures 
were incorporated by reference into the SIP under the approval of this 
attainment plan (85 FR 66240, October 19, 2020). If this proposed 
disapproval is finalized, EPA does not intend to remove these measures, 
but to retain them. The measures are: The portions of the COAs or COs 
entered between Pennsylvania and Conemaugh, Homer City, Keystone, and 
Seward that are not redacted, as well as the unredacted portions of the 
TVOPs or Plan Approval included in the October 11, 2017 submittal and 
the corrected documents in the February 5, 2020 submittal. These 
include emission limits and associated compliance parameters (i.e., the 
measures which include system audits, record-keeping and reporting, and 
corrective actions). 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).

VI. Statutory and Executive Order Reviews

Executive Orders 12866 and 13563: Regulatory Planning and Review

    Under Executive Orders 12866 (58 FR 51735, October 4, 1993) and 
13563 (76 FR 3821, January 21, 2011), this action is not a 
``significant regulatory action'' and, therefore, is not subject to 
review by the Office of Management and Budget.

Executive Order 13771: Reducing Regulations and Controlling Regulatory 
Costs

    This action is not an Executive Order 13771 regulatory action 
because this action is not significant under Executive Order 12866.

Paperwork Reduction Act

    This rulemaking does not impose an information collection burden 
under the provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 
3501 et seq.).

Regulatory Flexibility Act

    This action merely proposes to disapprove state requirements as not 
meeting Federal requirements and imposes no additional requirements 
beyond those imposed by state law. Accordingly, the Administrator 
certifies that this rulemaking will not have a significant economic 
impact on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.).

Unfunded Mandates Reform Act

    Because this rulemaking proposes to disapprove pre-existing 
requirements under state law and does not impose any additional 
enforceable duty beyond that required by state law, it does not contain 
any unfunded mandate or significantly or uniquely affect small

[[Page 15179]]

governments, as described in the Unfunded Mandates Reform Act of 1995 
(Pub. L. 104-4).

Executive Order 13132: Federalism

    This action also does not have federalism implications because it 
does not have substantial direct effects on the states, on the 
relationship between the National Government and the states, or on the 
distribution of power and responsibilities among the various levels of 
government, as specified in Executive Order 13132 (64 FR 43255, August 
10, 1999). This action merely proposes to disapprove a state 
requirement and does not alter the relationship or the distribution of 
power and responsibilities established in the CAA.

Executive Order 13175: Consultation and Coordination With Indian Tribal 
Governments

    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction. In those areas of Indian 
country, the rulemaking does not have tribal implications and will not 
impose substantial direct costs on tribal governments or preempt tribal 
law as specified by Executive Order 13175 (65 FR 67249, November 9, 
2000).

Executive Order 13045: Protection of Children From Environmental Health 
and Safety Risks

    This rulemaking also is not subject to Executive Order 13045 
``Protection of Children from Environmental Health Risks and Safety 
Risks'' (62 FR 19885, April 23, 1997), because it proposes to 
disapprove a state rule.

Executive Order 13211: Actions That Significantly Affect Energy Supply, 
Distribution, or Use

    Because it is not a ``significant regulatory action'' under 
Executive Order 12866 or a ``significant energy action,'' this action 
is also not subject to Executive Order 13211 (66 FR 28355, May 22, 
2001).

National Technology Transfer Advancement Act

    In reviewing state submissions, EPA's role is to approve state 
choices, provided that they meet the criteria of the CAA. In this 
context, in the absence of a prior existing requirement for the state 
to use voluntary consensus standards (VCS), EPA has no authority to 
disapprove a state submission for failure to use VCS. It would thus be 
inconsistent with applicable law for EPA, when it reviews a state 
submission, to use VCS in place of a state submission that otherwise 
satisfies the provisions of the CAA. Thus, the requirements of section 
12(d) of the National Technology Transfer and Advancement Act of 1995 
(15 U.S.C. 272 note) do not apply.

Executive Order 12898: Federal Actions To Address Environmental Justice 
in Minority Populations and Low-Income Populations

    Executive Order 12898 (59 FR 7629 (February 16, 1994)) establishes 
Federal executive policy on environmental justice. Its main provision 
directs Federal agencies, to the greatest extent practicable and 
permitted by law, to make environmental justice part of their mission 
by identifying and addressing, as appropriate, disproportionately high 
and adverse human health or environmental effects of their programs, 
policies, and activities on minority populations and low-income 
populations in the United States. EPA lacks the discretionary authority 
to address environmental justice in this action. In reviewing SIP 
submissions, EPA's role is to approve or disapprove state choices, 
based on the criteria of the CAA.
    Accordingly, this action proposing partial disapproval of 
Pennsylvania's SO2 attainment plan for the Indiana Area, 
merely disapproves certain state requirements and retains certain state 
requirements as SIP strengthening measures in the SIP under section 110 
of the CAA and will not in-and-of itself create any new requirements. 
Accordingly, it does not provide EPA with the discretionary authority 
to address, as appropriate, disproportionate human health or 
environmental effects, using practicable and legally permissible 
methods, under Executive Order 12898.

List of Subjects in 40 CFR Part 52

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

    Dated: March 8, 2022.
Diana Esher,
Acting Regional Administrator, Region III.
[FR Doc. 2022-05398 Filed 3-16-22; 8:45 am]
BILLING CODE 6560-50-P