[Federal Register Volume 87, Number 52 (Thursday, March 17, 2022)]
[Proposed Rules]
[Pages 15166-15179]
[FR Doc No: 2022-05398]

-----------------------------------------------------------------------

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.

-----------------------------------------------------------------------

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<PHONE_NUMBER>. 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.
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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

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.
---------------------------------------------------------------------------

    \2\ Sierra Club, et al. v. EPA, Case No. 20-3568 (3rd Cir.).
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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

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

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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \6\ EPA published revisions to the ``Guideline on Air Quality
Models'' on January 17, 2017.
---------------------------------------------------------------------------

    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 <IP_ADDRESS> 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

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.
---------------------------------------------------------------------------

    \7\ Sierra Club, et al. v. EPA, Case No. 20-3568 (3rd Cir.).
---------------------------------------------------------------------------

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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    Section 172(c)(5) of the CAA requires that an attainment plan
require permits

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.
---------------------------------------------------------------------------

    \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.''
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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\

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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \13\ Plan Approval 32-00055H was issued on April 2, 2012, and
modified on April 4, 2013, by PADEP.
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \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

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\
---------------------------------------------------------------------------

    \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.''
---------------------------------------------------------------------------

    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

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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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

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

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

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

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

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