[Federal Register Volume 87, Number 168 (Wednesday, August 31, 2022)]
[Rules and Regulations]
[Pages 53381-53404]
[FR Doc No: 2022-18669]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R03-OAR-2022-0347; FRL-9333-02-R3]

Federal Implementation Plan Addressing Reasonably Available
Control Technology Requirements for Certain Sources in Pennsylvania

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is promulgating a
Federal implementation plan (FIP) for the Commonwealth of Pennsylvania
(Pennsylvania or the Commonwealth). This FIP sets emission limits for
nitrogen oxides (NOX) emitted from coal-fired electric
generating units (EGUs) equipped with selective catalytic reduction
(SCR) in Pennsylvania in order to meet the reasonably available control
technology (RACT) requirements for the 1997 and 2008 ozone national
ambient air quality standards (NAAQS). This action is being taken in
accordance with the requirements of the Clean Air Act (CAA).

DATES: This final rule is effective on September 30, 2022.

ADDRESSES: EPA has established a docket for this action under Docket ID
Number EPA-R03-OAR-2022-0347. All documents in the docket are listed on
the www.regulations.gov website. Although listed in the index, some
information is not publicly available, e.g., confidential business
information (CBI) or other information whose disclosure is restricted
by statute. Certain other material, such as copyrighted material, is
not placed on the internet and will be publicly available only in hard
copy form. Publicly available docket materials are available through
www.regulations.gov, or please contact the person identified in the FOR
FURTHER INFORMATION CONTACT section for additional availability
information.

FOR FURTHER INFORMATION CONTACT: David Talley, Permits Branch (3AD10),
Air & Radiation Division, U.S. Environmental Protection Agency, Region
III, Four Penn Center, 1600 John F. Kennedy Boulevard, Philadelphia,
Pennsylvania 19103. The telephone number is<PHONE_NUMBER>. Mr. Talley
can also be reached via electronic mail at [email protected].

SUPPLEMENTARY INFORMATION:

I. Background

    On May 25, 2022 (87 FR 31798), EPA published a notice of proposed
rulemaking (NPRM) addressing NOX emissions from coal-fired
power plants in the Commonwealth of Pennsylvania. In the NPRM, EPA
proposed a FIP in order to address the CAA's RACT requirements under
the 1997 and 2008 ozone NAAQS for large, coal-fired EGUs equipped with
SCR in Pennsylvania. As discussed in the NPRM, the FIP was proposed as
an outgrowth of a decision by the United States Court of Appeals for
the Third Circuit (``the Court''), which vacated and remanded to EPA a
portion of our prior approval of Pennsylvania's ``RACT II'' rule which
applied to the same universe of sources. See 87 FR 31798; 31799-39802.
    The Court directed that ``[o]n remand, the agency must either
approve a revised, compliant SIP within two years or formulate a new
Federal implementation plan.'' Sierra Club v. EPA, 972 F.3d 290, 309
(3rd Circuit 2020) (``Sierra Club''). On September 15, 2021, EPA
proposed disapproval of those portions of the prior approval which were
vacated by the Court. See 86 FR 51315. EPA took final action to
disapprove the vacated portions of our prior approval. 87 FR 50257,
August 16, 2022. EPA is now finalizing a FIP to fulfill the Court's
order.
    The collection of sources addressed by the RACT analysis in this
FIP has been determined by the scope of the Third Circuit's order in
the Sierra Club case and EPA's subsequent disapproval action. Herein,
EPA is finalizing RACT control requirements for the four facilities
that remain open and active that were subject to the SIP provision that
the Court vacated EPA's approval of and that EPA thereafter
disapproved: Conemaugh, Homer City, Keystone, and Montour. EPA's prior
approval action and the Court's decision related to source-specific
RACT determinations for the Cheswick, Conemaugh, Homer City, Keystone,
and Montour generating stations. The Bruce Mansfield and Cheswick
facilities ceased operation, so there is no longer a need to address
RACT requirements for those facilities, so are not at included in this
final action. Accordingly, there are a total of nine affected EGUs/
units at four facilities in this action: three at Homer City and two
each at Conemaugh, Keystone and Montour.
    The Pennsylvania Department of Environmental Protection (PADEP)
undertook efforts to develop a SIP revision addressing the deficiencies
identified by the Third Circuit in the Sierra Club decision. PADEP
proceeded to develop source specific (``case-by-case'') RACT
determinations for the generating stations at issue. By April 1, 2021,
each of the facilities had submitted permit applications to PADEP with
alternative RACT proposals in accordance with 25 Pa. Code 129.99.
Subsequently, PADEP issued technical deficiency notices to obtain more
information needed to support the facilities' proposed RACT
determinations. Although additional information was provided in
response to these notices, PADEP determined the proposals to be
insufficient and began developing its own RACT determination for each
facility. The outcome of this process was PADEP's issuance of draft
permits for each facility, which were

developed with the intention of submitting each case-by-case RACT
permit to be incorporated as a federally enforceable revision to the
Pennsylvania SIP. Each draft permit underwent a 30-day public comment
period,\1\ during which EPA provided source-specific comments to PADEP
for each permit. On May 26, 2022, PADEP submitted case-by-case RACT
determinations for Keystone, Conemaugh, and Homer City as a revision to
the Pennsylvania SIP. On June 9, 2022, PADEP submitted a case-by-case
RACT determination for Montour as a revision to the Pennsylvania SIP.
EPA has not yet fully evaluated those submittals and they are outside
of the scope of this action. Any action on those proposed SIP revisions
will be at a later date and under a separate action.
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    \1\ See 51 Pa.B. 5834, September 11, 2021 (Keystone); 51 Pa.B.
6259, October 2, 2021 (Conemaugh); 51 Pa.B. 6558, October 16, 2021
(Homer City); 51 Pa.B. 6930, November 6, 2021 (Montour); Allegheny
County Health Department Public Notices, December 2, 2021
(Cheswick).
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II. Summary of FIP and EPA Analysis

A. Overall Basis for Final Rule

    This section presents a summary of the basis for the final FIP. The
overall basis for the proposal was explained in detail in the NPRM. The
overall basis is largely unchanged from proposal, though as explained
in the responses to comments and section IV of this document on the
final limits, some adjustments were made to the resulting limits. For
more detail on what was proposed, please refer to the May 25, 2022
proposal publication (87 FR 31798).
    The basis for the final rule begins with the RACT definition. As
discussed in the NPRM, RACT is not defined in the CAA. However, EPA's
longstanding definition of RACT is ``the lowest emission limit that a
particular source is capable of meeting by the application of control
technology that is reasonably available considering technological and
economic feasibility.'' \2\ The Third Circuit decision ``assume[d]
without deciding'' that EPA's definition of RACT is correct. Sierra
Club at 294. EPA is using its longstanding definition of RACT to
establish the limits in this FIP.
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    \2\ See Memo, dated December 9, 1976, from Roger Strelow,
Assistant Administrator for Air and Waste Management, to Regional
Administrators, ``Guidance for Determining Acceptability of SIP
Regulations in Non-Attainment Areas,'' p. 2, available at https://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/19761209_strelow_ract.pdf (Strelow Memo), and 44 FR 53761, at 53762,
footnote 2 (September 17, 1979).
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    The EPA proposed that RACT limits in this FIP will apply throughout
the year. As discussed further in Section III of this preamble in
response to comments on this issue, the EPA is retaining year-round
limits because the limits herein are technologically and economically
feasible during the entire year. While other regulatory controls for
ozone, such as the Cross State Air Pollution Rule (CSAPR) and its
updates, may apply during a defined ozone season, the RACT limits
finalized herein do not authorize seasonal exemptions based on
atmospheric conditions or other factors. As explained, this action is
being finalized to meet the statutory requirement to implement RACT in
accordance with sections 182 and 184 of the Clean Air Act.
Implementation of RACT, and the definition of what is RACT, is not
constrained by the ozone season or atmospheric consideration.
Therefore, the limits finalized here apply throughout the year since
the RACT emissions rates are technologically and economically feasible
year-round. To the degree that the EPA analyses underlying the RACT
emissions limits here rely on past performance data, those calculations
typically use ozone season data. This is because ozone season data
generally represent the time period over which the NOX
emissions rate performance of these units is the best. Put another way,
the ozone season data for the facilities subject to these limits are a
reliable indicator of what is technologically and economically feasible
for these facilities, and EPA has no reason to believe that achieving
the same performance outside the ozone season would be technologically
or economically infeasible. As explained further in the next section,
no commenters presented compelling evidence to change EPA's conclusion
on this point.
    The EPA proposed to develop the FIP limits using a weighted rate
approach, and is retaining that overall approach here. EPA received
significant comments both for and against such an approach, which are
discussed in detail in the next section. Overall, upon consideration of
these comments, the EPA's judgment is that this approach is still the
best approach for addressing the Court decision and addressing SCR
operation during EGU cycling (the operation of EGUs turning on and off
or operating at varying loads levels based on electric demand). As we
discussed extensively at proposal, the cycling of units, combined with
the role of flue gas temperature in SCR performance, prompted EPA to
consider how best to establish RACT limits that address the Third
Circuit's concerns about allowing less stringent limits when flue gas
temperatures went below what it considered to be an arbitrary
temperature threshold. This is a challenging factor to consider in
cases when the operating temperature varies, and when the units spend
some time at temperatures where SCR is very effective, and some time at
temperatures where it is not.
    At proposal, EPA provided an assessment of whether the units in
this FIP exhibit a pattern of cycling between temperatures where SCR is
effective and where it is not. EPA evaluated years of data submitted by
these sources to EPA to characterize their variability in hours of
operation or level of operation.\3\ In particular, EPA used this
information to identify whether, or to what degree, the EGUs have
shifted from being ``baseload'' units (i.e., a steady-state heat input
rate generally within SCR optimal temperature range) to ``cycling''
units (i.e., variable heat input rates, possibly including periods
below the SCR optimal temperature range). All of these EGUs were
designed and built as baseload units, meaning the boilers were designed
to be operated at levels of heat input near their design capacity 24
hours per day, seven days per week, for much of the year. As a result,
the SCRs installed in the early 2000s were designed and built to work
in tandem with a baseload boiler.\4\ In particular, the SCR catalyst
and the reagent injection controls were designed for the consistently
higher flue gas temperatures created by baseload boiler operation. In
more recent years, for multiple reasons, these old, coal-fired baseload
units have struggled to remain competitive when bidding into the PJM
Interconnection (PJM) electricity market.\5\ Nationally, total electric
generation has generally remained consistent, but between 2010 and
2020, generation at coal-fired utilities has declined by 68%.\6\ As a
result, many of these units more recently have tended to cycle between
high heat inputs, when electricity demand is high, and lower heat
inputs or complete shutdowns,

when demand is low, sometimes on a daily basis. This cycling behavior
can affect the ability of the EGUs to operate their SCRs because at
lower heat inputs the temperature of the flue gas can drop below the
operating temperature for which the SCR was designed.\7\ Nothing in the
comments undermined EPA's basic conclusion that this cycling pattern is
occurring. Accordingly, the final rule establishes limits that account
for the technical limits on SCR operation that can result from this
cycling behavior.
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    \3\ See the Excel spreadsheet entitled ``PA-MD-DE SCR unit data
2002-2020.xlsx'' in the docket for this action.
    \4\ This point is not applicable to the Conemaugh facility where
SCR was installed much later than other facilities at issue in this
rule. According to Key-Con's comment letter, ``KEY-CON Management
understood that compliance with the near-future MATS Rule and PADEP
RACT II Rule would preclude unit operations that bypassed the SCRs
at both stations.'' See Key-Con comments at 10.
    \5\ PJM is a regional transmission organization (RTO) or grid
operator which provides wholesale electricity throughout 13 states
and the District of Columbia.
    \6\ U.S. Energy Information Administration, ``Electric Power
Annual 2020,'' Table 3.1.A. Net Generation by Energy Source, https://www.eia.gov/electricity/annual/.
    \7\ U.S. EPA, ``EPA Alternative Control Techniques Document for
NOX Emissions from Utility Boilers'' EPA-453/R-94-023,
March 1994, p. 5-119, https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=2000INPN.txt.
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    In the proposal, we also noted that in RACT II, PADEP attempted to
address this cycling behavior by creating tiered emissions limits for
different modes of operation based on the flue gas temperature, which
its RACT II rule expressed as a transition from the 0.12 pounds of
NOX per million British thermal units (lb/MMBtu) rate to
much less stringent rates (between 0.35 and 0.4 lb/MMBtu, depending on
the type of boiler) based on a temperature cutoff of 600 degrees, with
the less stringent rate essentially representing a ``SCR-off'' mode
(i.e., an emission limit applicable at times when the SCR has been
idled or bypassed and is not actively removing NOX). The
Third Circuit rejected this approach because the selection of the
cutoff temperature was not sufficiently supported by the record. The
Third Circuit decision also questioned the need for the less stringent
rates, noting that nearby states do not have different emission rates
based on inlet temperatures. EPA considered the Court's concerns as
well as input received during the public comment period expressing both
support for, and opposition to, a tiered limit. We also considered the
practical and policy implications in structuring a tiered limit for
these cycling EGUs based on operating temperature. EPA has decided to
retain the proposed weighted approach instead of trying to develop a
tiered limit. As noted at proposal, the effectiveness of SCR does not
drop to zero at a single temperature point and defining the minimum
reasonable temperature range to begin reducing SCR operation for the
purposes of creating an enforceable RACT limit is a highly technical,
unit-specific determination that depends on several varying factors.\8\
We noted the complexity and detailed information necessary to produce a
justified and enforceable tiered limit that represents RACT and
addresses the Court's concerns about the basis and enforceability of
the tiers, and as explained further in the next section, none of the
comments, including those supporting the tiered limit, provided
sufficient basis for EPA to change its approach.
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    \8\ See Chapter 2, subsection 2.2.2 of the SCR Cost Manual, 7th
Edition, available at https://www.epa.gov/sites/default/files/2017-12/documents/scrcostmanualchapter7thedition_2016revisions2017.pdf.
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    In the proposal, EPA expressed an additional concern about
addressing cycling operation through a tiered RACT limit based on
operating temperature, which is that it would create an incentive for a
source to cycle to temperatures where SCR is not required, in order to
avoid SCR operating costs and potentially gain a competitive advantage.
In the case of the Pennsylvania limits addressed by the Third Circuit's
decision, there was no limit on how much time the units could spend in
SCR-off mode. In section C of the TSD for the proposed action,\9\ EPA
shows that over the last decade, some affected sources have varied the
gross load level to which they cycle down, hovering either just above
or just below the threshold at which the SCR can likely operate
effectively. Depending on the unit, this slight change in electricity
output could significantly affect SCR operation and the resulting
emissions output. Though instances of cycling below SCR thresholds
occurred in some cases prior to the implementation of Pennsylvania's
tiered RACT limit and thus the limit may not be the sole driver of the
behavior following its implementation, the tiered limit certainly
allows this behavior to occur. While EPA acknowledges the need for EGUs
to operate at times in modes where SCR cannot operate, EPA believes its
RACT limit should minimize incentives to do that, and a tiered rate
structure that effectively has no limit on SCR-off operation tends to
do the opposite. We received significant comments on this concern,
which are addressed in the response to comments section. EPA remains
concerned about essentially unlimited SCR-off operation, and continues
to believe that this is a key reason to retain the weighted rate
approach over a tiered approach.
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    \9\ EPA is not revising the TSD. Any new technical analysis will
be discussed directly in section III (EPA's Response to Comments) of
this preamble.
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    On the other hand, EPA also expressed concerns in the proposal
about a RACT limit that treats these EGUs as always operating as
baseload units by imposing a NOX emission rate that applies
at all times but can technically be achieved only if the boiler is
operating at high loads. Recent data indicate that these units are not
operating as baseload units and are not likely to do so in the
future.\10\ Selecting the best baseload rate (the rate reflecting SCR
operation in the optimal temperature range) and applying that rate at
all times does not account for, and could essentially prohibit, some
cycling operation of these units. Cycling has become more common at
coal-fired EGUs because they are increasingly outcompeted for baseload
power. In the past, these units were among the cheapest sources of
electricity and would often run close to maximum capacity. Other EGUs
can now generate electricity at lower costs than the coal-fired
units.\11\ Thus, the coal-fired units now cycle to lower loads during
hours with relatively low system demand (often overnight and especially
during the spring and fall ``shoulder'' seasons when space heating and
cooling demand is minimized) when their power is more expensive than
the marginal supply to meet lower load levels. Hence, they cycle up and
down as load- and demand-driven power prices rise and fall, and they
operate when the price meets or exceeds their cost to supply power. EPA
acknowledges that cycling down to a SCR-off mode may sometimes happen,
for example, when electricity demand drops unexpectedly, and other
units provide the power at a lower cost. The consideration of the
technical and economic feasibility of a given RACT limit should
reflect, to the extent possible, consideration of the past, current,
and future expected operating environment of a given unit. In electing
to finalize its weighted rate approach, EPA considered these
feasibility issues to establish a rate for each unit that reflects a
reasonable level of load-following (cycling) (e.g., a level consistent
with similar SCR-equipped units) but that also accounts for the lower
historic NOX rates that these units have achieved. While the
comments generally affirmed that a weighted rate could be structured to
address cycling, we did receive comments on the appropriate
considerations in choosing

the final rates, which are responded to later in this notice.
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    \10\ See section C of the TSD for the proposed action.
    \11\ The decreasing competitiveness of Pennsylvania's coal units
is illustrated by the fact that their share of the state's total
generation has declined from about 60% in 2001 to roughly 10% in
2021. See Energy Information Administration. Form EIA-923, Power
Plant Operations Report (2001-2021).
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B. Weighted Rates

    As discussed in the NPRM, in order to address the concerns
discussed previously in this section about how to determine RACT for
EGUs that cycle, EPA proposed to express the RACT NOX limits
for these units using a weighted rate limit. The weighted rate
incorporates both a lower ``SCR-on'' limit and a higher ``SCR-off''
limit. Through assignment of weights to these two limits based on the
proportion of operation in SCR-on and SCR-off modes during a historical
period that encompasses the range of recent operation, the SCR-on and
SCR-off limits are combined into a single RACT limit that applies at
all times. The weight given to the proposed SCR-off limit (established
as described later in this section) has the effect of limiting the
portion of time a cycling source can operate in SCR-off mode and
incentivizes a source to shift to SCR-on mode to preserve headroom
under the limit. While driving SCR operation, the weighted limit
accommodates the need for an EGU to occasionally cycle down to loads
below which the SCR can operate effectively and does not prohibit SCR-
off operation or dictate specific times when it must not occur. In this
way, this approach avoids the difficulty of precisely establishing the
minimum temperature point at which the SCR-off mode is triggered,
effectively acknowledging the more gradual nature of the transition
between modes where SCR is or is not effective. Finally, it is readily
enforceable through existing Continuous Emission Monitoring Systems
(CEMS), without the need for development of recordkeeping for
additional parameters that define the SCR-off mode. The approach is
described in more detail below.
    As a starting point for developing the proposed weighted rates for
each unit, EPA examined data related to the threshold at which these
facilities can effectively operate their SCR. Then, EPA calculated both
SCR-on and SCR-off rates using historic ozone season operating data for
the unit to determine when the SCR was likely running and when it was
likely not running, and then established rates based again on historic
operating data that represent the lowest emission limit that the source
is capable of meeting when the SCR is running and when it is not. EPA
did this by using the estimated minimum SCR operation threshold as
described in the proposed action, and then calculating average SCR-on
and SCR-off rates for each unit based on historic ozone season
operating data for that unit, when available, from 2003 to 2021. For
more detail on the development of the proposed rates, see section D of
the TSD for the proposed action. In particular, section D.1 addresses
the proposed threshold analysis. The SCR-on rate is an average of all
hours in which the SCR was likely running (operating above the
threshold at which it can run the SCR with an hourly NOX
emission rate below 0.2 lb/MMBtu) during each unit's third-best ozone
season from the period 2003 to 2021. The third-best ozone season was
identified based on the unit's overall average NOX emission
rate during each ozone season from 2003 to 2021. This time period
captures all years of SCR operation for each facility, though Conemaugh
only installed SCR in late 2014. EPA included all these years of data
in developing the proposed as well as the final limits because the
Agency did not identify, and commenters did not provide, a compelling
reason to exclude any of the years. This is in line with the Third
Circuit's decision, which questioned EPA's review of only certain years
of emissions data for these sources in determining whether to approve
Pennsylvania's RACT II NOX emission rate for these EGUs. The
use of the third-best year accounts for degradation of control
equipment over time, and it avoids biasing the limit with
uncharacteristically low emitting days, or under uncharacteristically
optimal operating conditions. EPA similarly used a third-best ozone
season approach for the Revised CSAPR Update (86 FR 23054, April 30,
2021) (RCU) and the proposed Good Neighbor Plan for the 2015 Ozone
NAAQS (87 FR 20036, April 6, 2022) (Good Neighbor Plan). The ``SCR-
off'' rate used to develop the proposal is an average of all hours in
which the unit's SCR was likely not running (operating below the
threshold at which it can run the SCR with an hourly NOX
rate above 0.2 lb/MMBtu) during all ozone seasons from 2003-2021
(except for Conemaugh). All ozone seasons in the time period were used
in order to increase the sample size of this subset of the data, as an
individual ozone season likely contains significantly fewer data points
of non-SCR operation.
    EPA then calculated the SCR-on and SCR-off ``weights,'' which
represent the amount of heat input spent above (SCR-on) or below (SCR-
off) the SCR threshold, for each EGU. For the weights used at the
proposal stage, EPA evaluated data from the 2011 to 2021 ozone seasons
and selected the year in which the EGU had its third highest proportion
of heat input spent above the SCR threshold during this time period,
using that year's weight (the ``third-best weight'') together with the
SCR-on/SCR-off rates described previously to calculate the weighted
rate. The years 2011-2021 were analyzed for purposes of the proposal
because they likely are representative of the time period that
encompasses the years when the units began to exhibit a greater cycling
pattern, and it is reasonable to expect that this pattern will continue
for the foreseeable future.
    Using these data, EPA proposed emissions limitations based on the
following equation:

(SCR-on weight * SCR-on mean rate) + (SCR off weight * SCR off mean
rate) = emissions limit in lb/MMBtu.

    Using this equation, EPA proposed the NOX emission
limits listed in Table 1, based on a 30-day rolling average:

                                 Table 1--Proposed NOX Emission Rate Limits \12\
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                                                                                Proposed
                                                Low range rate    High range     Weighted rate  facility-wide 30-
            Facility name                Unit     (lb/MMBtu)       rate (lb/      (lb/MMBtu)    day average rate
                                                                    MMBtu)                      limit (lb/MMBtu)
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Cheswick.............................        1           0.085           0.195           0.099             0.099
Conemaugh............................        1           0.071           0.132           0.091             0.091
Conemaugh............................        2           0.070           0.132           0.094  ................
Homer City...........................        1           0.102           0.190           0.102             0.088
Homer City...........................        2           0.088           0.126           0.088  ................
Homer City...........................        3           0.096           0.136           0.097  ................
Keystone.............................        1           0.046           0.170           0.076             0.074

Keystone.............................        2           0.045           0.172           0.074  ................
Montour..............................        1           0.047           0.131           0.069             0.069
Montour..............................        2           0.048           0.145           0.070  ................
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    EPA solicited comment on the proposed facility-wide average rate
limits, as well as the low and high range of potential limits. The
limits are calculated as a 30-day rolling average, and apply at all
times, including during operations when exhaust gas temperatures at the
SCR inlet are too low for the SCR to operate, or operate optimally. For
facilities with more than one unit, EPA proposed to allow facility-wide
averaging for compliance, but proposed that the average limit be based
on the weighted rate achieved by the best performing unit. A 30-day
average ``smooths'' operational variability by averaging the current
value with the prior values over a rolling 30-day period to determine
compliance. While some period of lb/MMBtu values over the compliance
rate can occur without triggering a violation, they must be offset by
corresponding periods where the lb/MMBtu rate is lower than the
compliance rate (i.e., the 30-day rolling average rate). EPA is
retaining its proposed overall approach to developing these limits, but
for reasons discussed in Section III of this preamble, EPA is changing
the way the rate calculation is done for facilities with more than one
unit, and is making additional adjustments to the rate calculation in
response to technical information received. These changes result in
some changes to the final rates, which are discussed in section IV of
this preamble.
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    \12\ See 87 FR 31806 (May 25, 2022).
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C. Daily NOX Mass Emission Rates

    EPA also proposed a unit-specific daily NOX mass
emission limit (i.e., lb/day) to complement the weighted facility-wide
30-day NOX emission rate limit and further ensure RACT is
applied continuously. High emissions days are a concern, given the 8-
hour averaging time of the underlying 1997 and 2008 ozone NAAQS. The
proposed daily NOX mass emission limit was calculated by
multiplying the proposed facility-wide 30-day rolling average
NOX emission limit (in lb/MMBtu) by each unit's heat input
maximum permitted rate capacity (in MMBtu/hr) by 24 hours. While the
30-day average rate limit ensures that SCR is operated where feasible
while reasonably accounting for cycling, EPA is concerned that units
meeting this limit might still occasionally have higher daily mass
emissions on one or more days where no or limited SCR operation occurs,
which could trigger exceedances of the ozone NAAQS if these high mass
emissions occur on days conducive to ozone formation, such as
especially hot summer days. EPA proposed a daily mass limit that would
govern over a full 24-hr, calendar day basis as an additional
constraint on SCR-off operation within a single day. The proposed limit
was designed to provide for some boiler operation without using the
SCR, which may be unavoidable during part of any given day, but also to
constrain such operation because the mass limit will necessitate SCR
operation (for example by raising heat input to a level where the SCR
can operate) if the unit is to continue to operate while remaining
below this limit. This provides greater consistency with the RACT
definition. Table 2 shows the unit-specific daily NOX mass
limits that were proposed in the NPRM.

                                  Table 2--Proposed Daily NOX Mass Limits \13\
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                                                                                Permitted max
                                                                                hourly heat     Proposed unit-
                           Facility name                               Unit      input rate       specific mass
                                                                               (MMBtu/hr) \14\   limit (lb/day)
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Cheswick...........................................................        1             6,000            14,256
Conemaugh..........................................................        1             8,280            18,084
Conemaugh..........................................................        2             8,280            18,084
Homer City.........................................................        1             6,792            14,345
Homer City.........................................................        2             6,792            14,345
Homer City.........................................................        3             7,260            15,333
Keystone...........................................................        1             8,717            15,481
Keystone...........................................................        2             8,717            15,481
Montour............................................................        1             7,317            12,117
Montour............................................................        2             7,239            11,988
----------------------------------------------------------------------------------------------------------------

    EPA solicited comment on the proposed daily mass limits. As
discussed in more detail in section III of this preamble, EPA
considered the comments received and made some changes to the final
limits. The final limits are discussed in section IV of this preamble.
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    \13\ See 87 FR 31807 (May 25, 2022).
    \14\ Title V Permit maximum heat input rates.
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III. EPA's Response to Comments Received

    EPA received 10 sets of comments on our May 25, 2022 proposed FIP.
A summary of the comments and EPA's response is provided herein. All
comments received are included in the docket for this action.
    Comment: Allegheny County Health Department (ACHD) submitted a

comment clarifying the operating status of the Cheswick Generating
Station.
    Response: EPA acknowledges the comment provided by ACHD. In our
NPRM, EPA described Cheswick as being in the process of closing,
despite ACHD having issued a title V permit modification that included
a provision requiring Boiler #1 to cease operations on April 1, 2022.
While that deadline had come and gone by the time the NPRM was
published, it was not entirely clear at the time of drafting the notice
that the closure was permanent and enforceable. ACHD's comment
addressed EPA's characterization of Cheswick's status in the NPRM and
affirmed that ACHD has verified that Cheswick's main boiler and
associated equipment have been permanently shut down. In the
intervening months since the NPRM, EPA has confirmed, with assistance
from ACHD, that the boiler has in fact ceased operating, and that
Cheswick's title V operating permit has been terminated. Therefore, EPA
finds that the closure is permanent and enforceable, and as such, is
not finalizing any RACT limits for Cheswick as proposed in our NPRM.
    Comment: Commenters assert that EPA must take action on PADEP's May
26, 2022 and June 9, 2022 SIP submittals, which included Pennsylvania's
own source specific RACT determinations, and which were intended to
address the deficiencies identified by the Third Circuit, prior to (or
concurrently with) promulgating a FIP.
    Response: Although EPA generally pursues a ``state first'' approach
to air quality management, giving deference to states to determine the
best strategy for addressing air quality concerns within their
boundaries in the first instance, EPA does not agree with the
commenters' assertion that EPA must act on PADEP's RACT SIP submittals
prior to or concurrently with finalizing a FIP. On September 15, 2021,
EPA proposed to disapprove those portions of Pennsylvania's May 16,
2016 SIP upon which EPA's prior approval had been vacated and remanded
by the Third Circuit, and that are encompassed in this FIP action. 86
FR 51315. EPA recently finalized that disapproval. 87 FR 50257. CAA
section 110(c)(1)(B) requires the Administrator to ``promulgate a
Federal implementation plan at any time within 2 years after the
Administrator disapproves a State implementation plan submission in
whole or in part, unless the State corrects the deficiency and the
Administrator approves the plan or plan revision, before the
Administrator promulgates such Federal implementation plan'' (emphasis
added). Following EPA's August 16, 2022 (87 FR 50257) final
disapproval, EPA has authority to promulgate a FIP under CAA section
110(c) at any time because EPA has not approved a plan or plan revision
from Pennsylvania correcting the deficiency. Nothing in the Clean Air
Act requires EPA to act upon a SIP submitted by a state to address a
deficiency identified in EPA's final disapproval prior to promulgating
a FIP, and the commenters have not provided any statutory basis for
such a position.
    As explained in the NPRM for this action, EPA may promulgate a FIP
contemporaneously with or immediately following the predicate final
disapproval action on a SIP (or finding that no SIP was submitted). EPA
v. EME Homer City Generation, L.P., 572 U.S. 489, 509 (2014) (``EPA is
not obliged to wait two years or postpone its action even a single day:
The Act empowers the Agency to promulgate a FIP `at any time' within
the two-year limit'') (internal citations omitted). In order to provide
for this, it cannot be true that EPA must take further action on SIP
submittals from the state prior to undertaking rulemaking for a FIP.
The practical effect of applying the procedure commenters allege, that
EPA must consider a new SIP submittal from the state prior to
promulgating a FIP, would be that EPA would either approve the state's
new SIP revision (thereby nullifying the need for a FIP) or EPA would
disapprove the state's new SIP revision, which would essentially
require a double disapproval from EPA in such circumstances. This
cannot be understood to be Congress's intent. When considering a
similar question, the Federal Court of Appeals for the Tenth Circuit
agreed with the interpretation EPA here states. Specifically, the Tenth
Circuit stated: ``The statute itself makes clear that the mere filing
of a SIP by Oklahoma does not relieve the EPA of its duty. And the
petitioners do not point to any language that requires the EPA to delay
its promulgation of a FIP until it rules on a proposed SIP. As the EPA
points out, such a rule would essentially nullify any time limits the
EPA placed on states. States could forestall the promulgation of a FIP
by submitting one inadequate SIP after another.'' Oklahoma v. EPA, 723
F.3d 1201, 1223 (10th Cir. 2013) (emphasis in original).
    EPA has not fully evaluated Pennsylvania's May 26 and June 9, 2022
submittals and has not yet proposed action on the SIP submittals. As
explained, this does not alter EPA's authority to finalize this action
promulgating a FIP. EPA intends to evaluate and take action on
Pennsylvania's submittal in accordance with the timelines established
in CAA section 110(k)(2). However, as noted in the NPRM, EPA submitted
extensive comments on the draft permits. In those comments, EPA raised
several concerns that remain unresolved, including whether
Pennsylvania's continued use of tiered limits (i.e., separate limits
for SCR-on and SCR-off operation) could be squared with the Court's
clear objection to our approval of such an approach in the past, and
whether Pennsylvania's record was adequate to support the limits
selected, the need for separate limits, and how to determine when each
limit applied.
    Comment: Several commenters asserted that EPA erred in the
selection of SCR as RACT. PADEP asserts that EPA's proposal does not
provide a source specific analysis of technological feasibility for
each unit, and that it does not identify any specific control
technology or technique as being technically feasible. They claim that
EPA's approach fails to comport with previous RACT approaches.
Keystone/Conemaugh (Key-Con) suggests that EPA overlooked the technical
and economic circumstances of the individual sources in determining
RACT. Additionally, one commenter, Talen Energy, alleged that EPA
should have selected feasible controls that ``represent RACT for each
mode of operation of the units, such as startup and shutdown.''
    Response: EPA disagrees with those comments suggesting that EPA's
FIP proposal did not follow the long-standing definition of RACT.
Courts have repeatedly concluded that the term ``reasonably available''
is ambiguous and therefore the statute does not specify which emission
controls must be considered ``reasonably available.'' See, e.g.,
Natural Resources Defense Council v. EPA, 571 F.3d 1245, 1252 (D.C.
Cir. 2009) (stating ``the term `reasonably available' within RACT is
also ambiguous'' and ``[g]iven this ambiguity, the EPA has discretion
reasonably to define the controls that will demonstrate compliance'').
See also, Sierra Club v. EPA, 294 F.3d 155, 162-63 (D.C. Cir. 2002)
(finding that the term ``reasonably available'' in the analogous
``reasonably available control measure'' is ambiguous and ``clearly
bespeaks [the Congress's] intention that the EPA exercise discretion in
determining which control measures must be implemented''). As stated in
the proposal, EPA's longstanding interpretation is that RACT is defined
as ``the lowest emission limitation that a particular source is capable
of meeting

by the application of control technology that is reasonably available
considering technological and economic feasibility.'' \15\ Commenters
correctly note that EPA has further explained that ``RACT for a
particular source is determined on a case-by-case basis, considering
the technological and economic circumstances of the individual
source.'' \16\
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    \15\ Memo, dated December 9, 1976, from Roger Strelow, Assistant
Administrator for Air and Waste Management, to Regional
Administrators, ``Guidance for Determining Acceptability of SIP
Regulations in Non-Attainment Areas,'' p. 2, available at https://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/19761209_strelow_ract.pdf and 44 FR 53762, footnote 2 (September 17,
1979) (Strelow Memo). See also Sierra Club v. EPA, 972 F.3d 290.
    \16\ Id.
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    EPA's action is in line with this longstanding guidance and other
Agency actions concerning RACT under section 182 of the Clean Air Act.
For each source, the EPA first selected a control technology that is
reasonably available, considering technical and economic feasibility,
and then identified the lowest emissions limitation that, in EPA's
judgment, the particular source is capable of meeting by application of
the technology (i.e., that a plant operator applying the selected
technology is capable of achieving economically and technologically).
With respect to the first step, for this set of sources EPA selected
SCR as the control technology that is reasonably available. For each of
the sources addressed in this final rule, SCR has already been
installed and each SCR has a clearly demonstrated operating history.
Most of the sources installed these SCRs in the early 2000s, with the
exception being Conemaugh, which only installed SCR in 2014. These
facts alone prove that SCR is a control technology that is reasonably
available for these sources. In the prior EPA-approved PADEP SIP
revision, SCR was selected as the control technology and that selection
was not disputed in comments on the action or in the subsequent
litigation, to which this FIP is a response. Additionally, no one
raised concerns about whether SCR was the appropriate control
technology when EPA initially proposed approval of PADEP's RACT
regulations, nor did anyone raise such concerns at the State level when
PADEP undertook notice and comment rulemaking in order to adopt the
regulation in the first place. To the extent that the commenters are
challenging EPA's judgment in choosing the emission limit that each
source is ``capable of meeting,'' those comments are addressed later in
this section. However, if the commenters are asserting that EPA has
selected a technology that is not ``reasonably available considering
technological and economic feasibility,'' the EPA disagrees based on
the fact that SCRs are present and operating at each of these sources.
    Regarding the comment that EPA should select RACT limits for each
mode of operation of the SCR, including startup and shutdown, the
proposed FIP accounts for this. Given that these sources already have
installed and operational SCRs, EPA determined it was appropriate to
consider modes of operation, as applicable, during the selection of the
emission limitation, rather than during the control technology
selection. Indeed, EPA's proposed statistical approach to develop the
rates is intended to select emissions limits that reasonably account
for different modes, including consideration of modes where the
selected RACT cannot be operated. As discussed in a comment response
later in this document, EPA considered whether it was appropriate to
create a tiered limit approach that also accounted for different modes
in the different tiers, but as explained here and in the proposal, were
EPA to define a mode where the chosen RACT technology need not operate
but also fail to provide constraints on the use of that mode, that
would essentially create an exemption from operating RACT when the
source is clearly capable of meeting a lower rate, and would thereby
create a regulatory incentive to operate at loads where the SCR is not
in operation.
    Comment: PADEP claims that it is inconsistent with RACT to use a
statistical approach for the selection of emissions limits. Key-Con
similarly claims that routine data are insufficient for a RACT
analysis.
    Response: As an initial matter, EPA affirms that a statistical
approach is a valid way to select the lowest emissions limit that the
source is capable of meeting through application of SCR. As explained
in the response to the prior comment, once a technology is selected
that is ``reasonably available considering technological and economic
feasibility,'' the second step is selection of the emission limit that
a plant operator applying the selected technology is economically and
technologically capable of achieving. In order to select the emission
limitation, EPA did an extensive statistical analysis of emissions data
from the affected facilities. The rationale underlying that approach is
outlined in significant detail in our proposal.
    EPA does not always have the benefit of a robust historic data set
that reflects actual operation of the selected control technology to
consider in selecting emission limits for purposes of establishing
RACT. When, as is the case here, we do have such data, it is reasonable
to use them. The proposal acknowledged several factors that affect the
degree to which the historic data set represents the lowest rate that
the source is capable of meeting and explains the adjustments EPA made
to its proposed emissions limits to account for those factors. There
are specific comments that take issue with certain choices EPA made in
applying the statistical approach, which EPA addresses later in this
notice, but nothing in the CAA or EPA rules or guidance precludes EPA
from using a statistical approach as it has done here.
    Comment: PADEP takes issue with EPA's decision to not do a
technical and economic feasibility analysis for other potential
NOX control technologies at these sources, such as
installation of newer low-NOX burners that achieve greater
NOX reductions during the combustion process. Key-Con
provided similar comments, asserting that our failure to analyze each
of these other potential NOX control technologies for their
economic and technological feasibility was not in keeping with RACT.
These commenters took issue with EPA's presumption ``that the
facilities have the flexibility to change their operations to emit less
NOX per unit of heat input.''
    Response: The statements discussing other potential NOX
control technologies that could be adopted, but that EPA was not
requiring, were provided as additional information, and as noted in the
proposal, ``EPA did not evaluate these technologies in the context of
our RACT analysis.'' Commenters appear to assume that EPA expressly
accounted for installation or increased use of these technologies when
determining limits that each source is capable of meeting. To the
contrary, this discussion was intended to clarify that these other
control techniques were not accounted for in EPA's development of each
source's limits; neither the rates nor the weights were adjusted to
require more use of these other control technologies. To the degree
that a source was using such other control technologies during the
period used in selecting the RACT limits, EPA's approach for developing
the limits assumed that the sources continued to operate these other
technologies without any change.
    Also, although PADEP did an analysis of other NOX
control technologies available to each source when setting the limits
in the permits, PADEP rejected all of these other control technologies
except boiler tuning, either

for technical feasibility or cost reasons, in setting the limits. This
rejection of most of the other control technologies as RACT by PADEP
essentially aligns with our own selection of SCR as RACT.
    Comment: Homer City objects to applying the RACT limit from the
lowest emitting of the three sources at the facility as a facility-wide
RACT NOX limit. Homer City asserts that the definition of
RACT, i.e. ``. . .the lowest emission limit that a particular source
[emphasis added] is capable of meeting. . .'' requires that EPA
establish FIP limits on a unit by unit basis, rather than by a facility
wide average.
    Response: Longstanding EPA policies have allowed for averaging to
meet RACT limits, including averaging across multiple emissions units.
The 1992 NOX supplement to the general preamble \17\ states
that it is appropriate for RACT to allow emissions averaging across
facilities within a nonattainment area (or Ozone Transport Region (OTR)
state, as is the case here). In practice EPA has allowed averaging
across units on a facility-wide basis, and even across facilities in
the same system under common control of the same owner/operator,
including its approval of PADEP's prior EGU RACT rules.\18\ EPA's
implementation rule for the 2008 ozone NAAQS allows nonattainment areas
to satisfy the NOX RACT requirement by using averaged area-
wide emissions reductions.\19\ EPA reasonably allows averaging for
compliance, so long as the underlying rates used as the basis for the
average meet the definition of RACT. The comments do not provide a
basis for EPA to reject its longstanding emissions averaging policies.
To the contrary, these policies provide additional flexibility for
sources to manage their SCR operation across units to ensure compliance
with the limits.
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    \17\ 57 FR 55620, November 25, 1992
    \18\ See 25 Pa Code Sec. Sec.  129.94 and 129.98, which allow
sources which cannot meet a presumptive RACT limit to average with
lower emitting sources, provided that aggregate emissions do not
exceed what would have been allowed under the presumptive limits.
    \19\ 80 FR at 12278-79 (``states may demonstrate as part of
their NOX RACT SIP submittal that the weighted average
NOX emission rate from all sources in the nonattainment
area subject to RACT meets NOX RACT requirements''). This
portion of the 2008 ozone SIP requirements rule was challenged, with
petitioners arguing that such a rule violated the Clean Air Act
because the statute at Sec.  182(b)(2) requires each individual
source to meet the NOX RACT requirement. The D.C. Circuit
rejected this argument, finding that the Clean Air Act ``does not
specify that `each one of' the individual sources within the
category of `all' `major sources' must implement RACT.'' South Coast
Air Quality Mgmt Dist. v. EPA, 882 F.3d 1138, 1154 (D.C. Cir. 2018).
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    Regarding the comments on EPA's proposal to base the facility-wide
average rate on the best performing unit, the EPA is finalizing a minor
change. In light of the unit-specific nature of EPA's weighted rate
analysis, the EPA expects that the unit-specific rates already
represent RACT for each unit, and that the most appropriate basis for a
facility-wide average would be the weighted rates for each of the units
at the facility. While some commenters felt that EPA should use the
lowest single unit rate to drive facilities to use their best
performing units most often, we expect that the stringent unit-specific
rates, when averaged together, will still provide sufficient incentive
to use the best performing units most often. See section IV of the
notice for additional information.
    Comment: Key-Con notes that only one of the designated
nonattainment areas in Pennsylvania is currently violating the 2015
ozone NAAQS, and expresses concern that EPA appears to have
inappropriately considered the potential for lower ozone levels in many
areas in setting RACT, and states that the requirement for
NOX RACT is simply tied to Pennsylvania's inclusion in the
OTR. Key-Con also asserts that it is more appropriate to use interstate
transport rules, not RACT, to address concerns about states'
obligations to eliminate significant contribution to nonattainment, or
interference with maintenance of NAAQS in other states.
    Response: The EPA agrees with the commenter's characterization that
Pennsylvania must implement RACT level controls statewide due to the
state's inclusion in the OTR, in accordance with CAA Sec.  184. The
statutory direction to require ``implementation of reasonably available
control technology'' in states included in an ozone transport region,
CAA Sec. Sec.  182(f), 184(b), is the same in substance as the
requirement for ozone nonattainment areas for ``implementation of
reasonably available control technology,'' CAA Sec.  182(b)(2).
Therefore, EPA's analytical method to determine what level of control
technology is reasonably available does not differ based on whether
RACT is being implemented in an ozone nonattainment area or the OTR.
    There are also areas of Pennsylvania that are still designated
nonattainment for both prior and current ozone NAAQS. EPA notes that
the implication of the commenter's statement, that an area's factual
attainment of an ozone NAAQS, as perhaps shown by a Clean Data
Determination, would have implications for whether that area needs to
implement RACT, is incorrect. An area designated nonattainment must
continue to meet the statutory requirement to implement RACT, if
otherwise applicable, until the area is redesignated to attainment or
unclassifiable under section 107(d)(3) of the CAA. While the EPA did
identify improved air quality in many areas, including remaining ozone
nonattainment areas, some of which are in other states, as a benefit of
the FIP emissions limits, we did not determine RACT through the
selection of control technology and identification of emission
limitations that the sources are capable of meeting based on the air
quality impact in any particular area(s). In other words, air quality
improvement in nonattainment areas in Pennsylvania or other states was
not a criterion in determining RACT in this action.
    Comment: Several commenters claim that EPA's economic feasibility
analysis for SCR optimization was flawed. First, commenters assert that
the economic analysis was flawed because it only considered the costs
of additional reagent, and ignored considerable capital costs such as
increased catalyst maintenance and replacement, and modifications to
ancillary equipment. Second, commenters assert that the actual $/ton
NOX costs far exceed what EPA's analysis claims, and are
more likely in the $150,000-200,000/ton range. Additionally, commenters
assert that EPA's analysis of reagent injection incorrectly assumes
that reagent costs will return to historic, lower prices.
    Response: EPA disagrees. First, commenters are incorrect in the
assertion that EPA did not consider capital costs, such as catalyst
maintenance and replacement. As discussed in the NPRM and TSD, EPA
relied on certain data from the recent evaluation of variable operating
and maintenance (VOM) costs (which include increased catalyst
maintenance and replacement costs), associated with increased use of
SCRs at EGUs used in a number of national rulemaking actions related to
the CAA's interstate transport requirements, including most recently
the proposed Good Neighbor Plan for the 2015 ozone NAAQS. In the ``EGU
NOX Mitigation Strategies Proposed Rule TSD'' (Good Neighbor
Plan TSD) for the proposed Good Neighbor Plan (included in the docket
for this action), EPA used the capital expenses and operation and
maintenance costs for installing and fully operating emission controls
based on the cost equations used within the Integrated Planning Model
(IPM) that were researched by Sargent & Lundy, a nationally

recognized architect/engineering firm with EGU sector expertise. See 87
FR 31808; TSD at 16-18. EPA's cost analysis for the proposed FIP only
related to increased use, or optimization, of the SCRs, since each
facility already had SCR installed. While that analysis was presented
on a national, fleetwide basis, for this action EPA used site specific
data in the ``Retrofit Cost Analyzer'' \20\ to perform a bounding
analysis to demonstrate that the cost assumptions made in the RCU and
Good Neighbor Plan were still accurate and reasonable for the current
RACT analysis. Using that methodology, EPA estimated a cost per ton for
these sources that ranged from $2,590 to $2,757, depending on the unit.
As previously stated, these estimates did include capital costs
associated with increased catalyst maintenance and replacement. Reagent
costs have actually dropped since the May 25, 2022 NPRM,\21\ and the
cost per ton of NOX removed is still well within a range
that should be considered economically feasible.
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    \20\ See TSD for proposed FIP at 16-18.
    \21\ Reagent prices have decreased since publication of the
NPRM, from an average of $1515/ton anhydrous ammonia to slightly
less than $1400/ton. See appendix 3 of the TSD for this action, and
https://mymarketnews.ams.usda.gov/filerepo/sites/default/files/3195/2022-07-28/614317/ams_3195_00065.pdf.
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    In Table 4 of the TSD for the proposed FIP, EPA calculated the
potential change in NOX mass emissions, based on the
proposed 30-day average NOX emission limits.\22\ Then, in
Table 5 of the proposed TSD, EPA calculated the cost per ton of
NOX removed based on the additional amount of reagent needed
to meet to those limits.\23\ EPA has made slight adjustments in
finalizing the emission limits after considering comments. Detailed
discussion of the rationale for and of the limits themselves can be
found elsewhere, but particularly in section IV of this preamble. Table
3 of this preamble shows the reductions these limits will realize when
compared to 2021 emissions data.
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    \22\ See Id. at 15.
    \23\ See Id. at 19.

                       Table 3--2021 Annual NOX Emissions and Rates Compared to FIP Rates
----------------------------------------------------------------------------------------------------------------
                                   2021                                                     Potential
                               Average NOX  30-Day  NOX    30-Day NOX       2021 NOX     change in  NOX
           Facility             rate  (lb/   rate (lb/   rate  vs. 2021     emissions         Mass
                                  MMBtu)       MMBtu)      average (%)       (tons)         Emissions
                                                                                (tons)
----------------------------------------------------------------------------------------------------------------
Conemaugh....................        0.149        0.072             -52           5,506          -2,837
Homer City...................        0.133        0.096             -28           3,144            -871
Keystone.....................        0.142        0.075             -47           5,481          -2,579
Montour......................        0.110        0.102              -7             649             -46
                              ----------------------------------------------------------------------------------
    Net......................  ...........  ...........  ..............          14,781          -6,333     -43%
----------------------------------------------------------------------------------------------------------------

    Based on the revised limits, and an updated cost of reagent, EPA
calculated the cost per ton of NOX removed for the final
limits:

                        Table 4--Cost per NOX ($/ton) Removed Based on Additional Reagent
----------------------------------------------------------------------------------------------------------------
                                       Predicted                                               Cost per ton  of
                                   reduction  (tons       Additional       Total annual cost    NOX removed for
            Facility              NOX per year  from  reagent  (tons per    for  additional   additional reagent
                                    2021  baseline)     year  from 2021     reagent [caret]         ($/ton) +
                                                          baseline) *
----------------------------------------------------------------------------------------------------------------
Conemaugh.......................               2,837               1,617          $2,263,800                $798
Homer City......................                 871                 496             694,400                 797
Keystone........................               2,579               1,470           2,058,000                 798
Montour.........................                  46                  26              36,400                 791
                                 -------------------------------------------------------------------------------
    Average cost/ton............  ..................  ..................  ..................                 796
----------------------------------------------------------------------------------------------------------------
* Additional reagent = predicted reduction (tons) x 0.57 tons reagent/ton NOX reduction.
[caret] Total cost = additional reagent x $1400/ton reagent.
+ Cost per ton = total cost/predicted reduction.

    With respect to the assertion by commenters that the $/ton value is
actually in the $150,000-$200,000/ton of NOX removed range,
commenters have not supplied adequate data or analysis to substantiate
that assertion. Commenters (in this case, Montour) merely assert that
in order to meet the proposed limits, the units will need to run for
extended periods of time following a startup, even when electricity is
not being sold to the grid, in order to achieve a certain number of
hours of low hourly NOX emissions rates to offset the higher
hourly NOX emission rates during startup, or else the source
will not meet the proposed emission limits in the FIP. Montour claims
that it has more frequent start-ups and shut-downs during which it
cannot operate the SCRs. EPA notes that the comment did not provide any
analysis of potential alternate methods of compliant operation, and
merely submitted data relating to the extra cost of fuel oil during the
period of time they assert they will be required to run. For example,
it may be possible for the units to ramp up more quickly following
startup so as to spend less time in SCR-off mode. Additionally, it may
be possible for the units to spend more time ``hovering'' at a higher
heat input (i.e. SCR-on) in anticipation of a need for quick dispatch.
EPA acknowledges that the limits in the FIP may result in

the sources' needing to re-evaluate how they operate their EGUs in
order to meet the new RACT limit, which may require adjusting the
prices and certain operating parameters they specify to PJM when
bidding into the market. However, EPA views these as free-market
considerations, rather than an appropriate component of a RACT
determination. EPA has long held that ``[e]conomic feasibility rests
very little on the ability of a particular source to `afford' to reduce
emissions to the level of similar sources. Less efficient sources would
be rewarded by having to bear lower emission reduction costs if
affordability were given high consideration. Rather, economic
feasibility . . . is largely determined by evidence that other sources
in a source category have in fact applied the control technology in
question.'' \24\
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    \24\ E.P.A., State Implementation Plans; General Preamble for
the Implementation of Title I of the Clean Air Act Amendments of
1990; Supplemental, 57 FR 18,070, 18,073 (proposed April 28, 1992)
(first introducing RACT as a standard to regulate emissions from
existing sources).
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    EPA continues to believe that optimization of the SCRs to achieve
the NOX emission limits in this FIP is economically
feasible. Nothing submitted in the comments provided adequate
justification or data to make a determination to the contrary. Indeed,
evidence from the units' operating history supports EPA's view that
when it is economically advantageous to do so, these units have no
trouble meeting lower limits. Some of the lowest NOX
emissions EPA observed coincided with high NOX allowance
prices associated with the NOX SIP call which went into
effect in 2003.\25\ Additionally, data for some of these units from May
through June of the 2022 ozone season generally indicate SCR operating
patterns (and, as a result, NOX emissions) that match or are
among their best in the recent data record. EPA believes this is due,
at least in part, to the market prices of NOX allowances
needed for compliance with the RCU during this period, which were
reported to range between $20,000 and $40,000 per ton.\26\
---------------------------------------------------------------------------

    \25\ Finding of Significant Contribution and Rulemaking for
Certain States in the Ozone Transport Assessment Group Region for
Purposes of Reducing Regional Transport of Ozone (NOX SIP
Call), 63 FR 57356 (October 27, 1998) (codified in relevant part at
40 CFR 51.121 and 51.122).
    \26\ See S&P Global Capital IQ, capitaliq.spglobal.com
(subscription required).
---------------------------------------------------------------------------

    Comment: Commenters assert that EPA ignored equipment failure
issues and failed to consider the deleterious effects on both control
equipment and on the environment (ammonia slip, decreased mercury
removal) of excess ammonia injection, particularly when operating below
the catalysts' minimum effective temperature range. Commenters further
assert that EPA failed to consider an engineering analysis submitted by
Key-Con that PADEP relied upon in developing their case-by-case limit
for Key-Con.
    Response: EPA disagrees. First, EPA did not presume that the
proposed FIP limits would be met by simply injecting more reagent
during sub-optimal SCR operating conditions, and the FIP does not
require it. EPA continues to recognize that the NOX
reduction capabilities of the SCRs are flue gas temperature dependent,
and that the NOX removal efficiency curve decreases with
flue gas temperature until a point is reached where the SCR offers
little or no NOX control above what is achieved by the low
NOX burners (LNB) and overfire air (OFA) that are also
installed on all of the units subject to this FIP. We also recognize
that catalyst fouling, catalyst poisoning, ammonia slip and damage to
downstream equipment are all potential outcomes of excessive reagent
injection or injection during low temperature conditions. We further
recognize that there have been changes in the electricity market in
more recent years that result in greater periods of time when the units
are operating in SCR-off mode. EPA believes that because the
calculation of the limits uses actual past performance data from the
sources, which include times at low heat input and therefore time with
the SCR off, sources can meet these limits without injecting excessive
amounts of ammonia during unfavorable SCR operating conditions.
Additionally, using the third-best weight means that the SCR-off weight
is based on a recent year that is not the extreme SCR-on case in the
last decade and thus provides additional buffer.
    The data show that during times when boilers are operating at high
heat inputs and therefore SCRs are at optimum performance temperatures,
sources have shown that they are capable of achieving limits in the
0.05 to 0.07 lb/MMBtu range, so they could achieve additional
reductions during times when the SCR can be optimized to offset higher
emissions during times when the SCR may not be optimized, so as to meet
their 30-day rolling average and daily mass limit.
    Also, EPA did review and consider the Key-Con engineering report
referenced by the commenters. The information presented in that report
appears to have been submitted to Pennsylvania to contest condition
E.009 in PADEP's draft case-by-case RACT permit for Keystone, which
would have required Keystone to set the SCR controllers at a target
NOX emission rate of 0.06 lb/MMBtu.\27\ According to
Attachment 3 of Key-Con's comment letter, they additionally evaluated
operational data from 2019, which they claim is the last year of
typical operations.\28\ The report evaluated ammonia injection rates,
and purported to show that due to ammonia slip and fouling of
downstream appurtenances, the SCR could not and should not operate at a
set-point of 0.06 lb NOX/MMBtu. The report then determined
that ``a NOX rate of 0.09 lb/MMBtu is tolerable and will not
require air heater washes nearly as frequently as 0.08 lb/MMBtu \29\ or
less would.'' See page 10 of Appendix 3 to Key-Con's July 11, 2022
comment letter. The report also states that Key-Con conducted testing
on Conemaugh unit 1 during 18 days in May 2017 to determine if
continuous operation at a NOX setpoint of 0.04 lb/MMBtu was
sustainable. The report claimed that it was not, because emissions of
mercury spiked to a point where it appeared that Unit 1 would exceed
its Mercury Air Toxics Standard (MATS) limit, and the NOX
setpoint had to be increased to 0.07 lb/MMBtu to lower mercury
emissions. A similar test was conducted on Conemaugh Unit 2 towards the
end of the 2017 ozone season to determine if the 0.05 lb/MMBtu setpoint
was sustainable, and the report claims that after 25 days at the 0.05
setpoint, mercury emissions increased abruptly and nearly exceeded the
MATS limit, so the NOX setpoint had to be ``relaxed'' an
unspecified amount to decrease mercury emissions. P. 7 of Attachment 3.
---------------------------------------------------------------------------

    \27\ Per condition E.10 of the draft permit for Conemaugh, their
target was 0.05 lb NOX/MMBtu
    \28\ Commenters assert that 2020 and 2021 were excluded due to
low electricity demand and lack of coal supply, respectively.
    \29\ PADEP's proposed RACT limit.
---------------------------------------------------------------------------

    In response to the report, EPA notes that unlike Pennsylvania's
proposed RACT permit terms, EPA is not requiring that the sources
operate their SCRs at a certain set point below the 30-day rolling
daily average NOX rate limit, so the validity and relevance
of this testing to EPA's proposed limits is questionable. EPA is
expecting that the operators of Keystone and Conemaugh will operate
their SCRs in a way that balances concerns about catalyst and preheater
fouling and mercury emissions with the emission rates set by EPA--rates
which are based on operating data from these sources indicating
achievement of these emission rates in the past, including the recent
past. Also, we note that EPA's pounds of NOX per MMBtu of
heat

input emission rate limit is a 30-day rolling daily average emission
rate limit, whereas its daily limit is a mass limit. In contrast,
Pennsylvania's RACT permit had a daily (24 hour) average NOX
emissions rate, so EPA's 30-day rolling average emission rate limit
gives the source operators more flexibility in how they operate the
SCRs. That is, the operators do not need to keep the setpoint for the
SCRs at a very low level each day for an extended period of time, as
they would to meet Pennsylvania's daily average NOX rate.
The ability to average NOX hourly emission rates over 30
days allows the sources greater flexibility to vary NOX
emission rates from their SCRs, raising NOX emission rates
up or down in order to balance the various factors that must be taken
into account, such as catalyst or preheater fouling and mercury
emissions.
    Finally, EPA notes that the commenter did not perform a ``thorough
review of EPA's NOX emissions analyses'' because of EPA's
alleged technical failures and failure to understand current and
expected unit utilizations.\30\ However, the commenter did not provide
any information regarding expected unit utilization, and instead
criticized EPA's proposed rates as unobtainable during startup events
by providing 25 hours of minimal data regarding one cold-start of
Keystone Unit 1 in January 2022. Given that this data covered only 25
hours of startup, and was not then averaged with 29 other days of
emission data to arrive at a 30-day average hourly emission rate, it is
not proof that this one unit could not meet EPA's 30-day average rate.
Absent more robust data to support commenter's claim, EPA declines to
amend its proposed rates for the four units at Keystone and Conemaugh
based on the thin data presented.
---------------------------------------------------------------------------

    \30\ P. 11 of Key-Con's July 11, 2022 comments.
---------------------------------------------------------------------------

    Comment: PADEP asserts that EPA's weighted rate approach is flawed
because it relies on an analysis of past averages, which is contrary to
the court's instruction that ``. . . an average of the current
emissions being generated by existing systems will not usually be
sufficient to satisfy the RACT standard.''
    Response: EPA disagrees with the commenter's contention that the
analysis underlying EPA's RACT limits is flawed simply due to the fact
that EPA uses the mathematical function of averaging as part of the
Agency's overall calculation. As the commenter notes, the Sierra Club
decision does include language noting that ``an average of the current
emissions being generated by existing systems, will not usually be
sufficient to satisfy the RACT standard.'' 972 F.3d at 300. However, in
the preceding sentence, the court provides necessary context for its
statement and a helpful summary of what Pennsylvania provided in its
prior SIP, EPA's approval of which the Court was vacating. The Court
notes that the chosen emission limitation ``was selected as it
represents the average pollution output of the three plants that are
already compliant over the past five years.'' Id. Therefore, the court
did not take issue with the mathematical function of averaging; it took
issue with the quantity being averaged, and its application in setting
RACT. EPA does not believe that the court meant to forbid the use of
any averaging in the determination of RACT, so long as it fit within
the definition of RACT and the use of such averaging was adequately and
reasonably explained in the record.
    As explained elsewhere in this action, EPA has used a statistical
approach to establish the emission limitations contained in this FIP,
which necessarily involves averaging. However, there are significant
and meaningful differences between EPA's use of averaging and how PADEP
previously used averaging to determine the RACT limits at issue in the
Sierra Club decision. While Pennsylvania's limit was based on a five-
year ozone season average from three plants that were then averaged
together again to calculate a single limit required at five different
sources, EPA's approach uses a source-specific third-best ozone season
rate from a larger range of data. EPA's approach is consistent with the
RACT definition, including the interpretation of RACT contained in the
Sierra Club decision, because it is aimed at representing the lowest
rate the source is technologically and economically capable of
achieving, not the average rate it has already achieved. (As explained
elsewhere in this action, EPA used third-best to represent the source's
current capability, but the approach is still aimed at defining the
lowest rate, rather than a 5-year overall average).
    Comment: PADEP asserts that EPA's FIP is flawed because it relies
on the third-best approach used in the RCU and Good Neighbor Plan,
which is inappropriate because those rules evaluated more current data
sets, and that EPA's data set selection is not driven by RACT
regulations or guidance and does not set source specific limits
considering technological and economic feasibility.
    Response: EPA proposed to use the third-best ozone season rate for
each source based on the idea, which was also cited in both the RCU and
the Good Neighbor Plan, that the performance of SCRs degrades over
time, and that usually only one layer of catalyst is changed/
refurbished per year. Therefore, the SCRs may never be able to achieve
the same emission reduction rate as when they started operating and all
three catalyst layers were new. With the exception of the Conemaugh
plant, which installed its SCRs in late 2014, the other sources
installed their SCR by 2003.\31\ Thus, many other parts of the overall
SCR system, such as the reagent injection system, may also have
deteriorated in performance. The use of the third-best year for each
source is consistent with EPA's past practices in other rulemakings,
and also has a basis in the performance data of each source. The third-
best approach is a reasonable way of determining appropriate RACT
limits. It avoids biasing the SCR-on limit with uncharacteristically
low emitting ozone seasons, or under uncharacteristically optimal
operating conditions. As stated in the April 6, 2022 proposed Good
Neighbor Plan, the EPA found it prudent not to consider lowest or
second lowest ozone season NOX emissions rates, which may
reflect SCR systems that have all new components. Such data are
potentially not representative of ongoing achievable NOX
emission rates considering broken-in components and routine maintenance
schedules. Additionally, the fact that CSAPR and the Good Neighbor Plan
establish caps rather than limits does not preclude the use of the
third-best approach for the purposes of the FIP. EPA is finalizing the
use of the third-best year for all of the facilities except Conemaugh.
As discussed elsewhere in this action, EPA has determined it is
appropriate to use a different approach for establishing final RACT
limits for Conemaugh due to the fact that Conemaugh has newer SCRs. As
further discussed in section IV of this preamble, Conemaugh's final
limit was calculated using the second-best rate and the second-best
weight due to the more limited data set of years available for this
facility based on the more recent installation of SCR.\32\
---------------------------------------------------------------------------

    \31\ As noted in the NPRM, the limits proposed for Conemaugh
were based on the second-best ozone season, since Conemaugh's SCR
was only installed in late 2014 and EPA therefore doesn't have the
same volume of operating data as for the other sources.
    \32\ The proposed limit used the second best rate and the third
best weight.
---------------------------------------------------------------------------

    Regarding the claim that the RCU and Good Neighbor Plan used more
current data sets, this is because those rulemakings were undertaken
under a completely different statutory provision with different
requirements and purpose than this FIP. Both the RCU and Good

Neighbor Plan FIPs were addressing the requirement in section
110(a)(2)(D)(i)(I) of the CAA to ensure that emissions from upwind
sources, including EGUs, were not significantly contributing to
nonattainment or interfering with maintenance in downwind areas. The
RCU addressed upwind significant contributions to downwind areas for
the 2008 ozone NAAQS, while the proposed Good Neighbor Plan addressed
upwind emissions for the 2015 ozone NAAQS. As such, for both rules, EPA
needed to use the most recently available and up-to-date data for both
source emissions and ambient air monitoring results in order to
identify upwind emissions currently affecting downwind monitors for the
2008 and 2015 ozone NAAQS. Here, the purpose is to identify RACT, as
required under subsections 182(b)(2), 182 (f)(1), and 184 of the CAA,
which requires that major sources of NOX and/or VOCs in
nonattainment areas, or in the OTR, meet RACT, which EPA defines as
``the lowest emission limit that a particular source is capable of
meeting by the application of control technology that is reasonably
available considering technological and economic feasibility.'' Given
this different purpose, the examination of historic operating data for
the SCRs is relevant to the determination of the NOX
emission rates each source attained while running their SCRs, and which
the source was therefore capable of meeting. Also, EPA did consider
ozone season emission rates from each source through 2021, which was
the most recent data available at the time of the proposal, so PADEP's
claim that EPA did not consider recent data is incorrect.
    Comment: PADEP further asserts that EPA's FIP is flawed because it
only considers ozone season data, so fails to consider emissions for a
major part of the year. Commenters claim the court acknowledged that
their presumptive limit did account for seasonal variability. They cite
to Motor Vehicles Mfrs. Ass'n of the U.S., Inc. v. State Farm Mut.
Auto. Ins. Co., 463 U.S. 29, 43 (1983) (``State Farm'') (Providing that
``the agency must examine the relevant data and articulate a
satisfactory explanation for its action including a ``rational
connection between the facts found and the choice made,'' and claim
that because EPA failed to consider the majority of the operational
emissions data (i.e., non-ozone season), EPA failed to adequately
demonstrate that the proposed limits are technically and economically
feasible year-round.
    Response: EPA disagrees with PADEP's claim that EPA should consider
non-ozone season data for several reasons. Although these sources were
subject to the CAIR annual NOX requirements starting in 2009
and the CSAPR annual NOX requirements starting in 2015,
these cap and trade programs initially set annual NOX
emission budgets for states based on a NOX emission rate of
0.15 lb/MMBtu starting in 2009, then based on a cost-effectiveness
level starting in 2015, and allowed individual sources to exceed their
allocated allowances by a certain percent by purchasing additional
NOX allowances from other sources. As such, the non-ozone
season emissions data beginning in 2009 does not necessarily reflect
the NOX emission rates these SCRs are capable of achieving
outside of the ozone season because the SCRs were not required to meet
a specific NOX emission rate. Second, post-2017 (when
Pennsylvania's RACT II limit of 0.12lb/MMBtu was effective), data show
the sources generally did not operate the SCRs for significant time
periods outside of ozone season. Hourly operating data submitted by
Keystone and Conemaugh to PADEP show that in 2017, the SCRs did not
consistently operate outside of ozone season, with the units at each
source often cycling down to low heat inputs at night and therefore not
operating their SCRs.\33\ Third, Pennsylvania also based the 0.12 lb/
MMBtu emission rate in its RACT II rule solely on ozone season
emissions data. Finally, PADEP does not explain why EPA's determination
of RACT for these sources would be altered by consideration of non-
ozone season data.
---------------------------------------------------------------------------

    \33\ For examples of this SCR-off operation, see the xl
spreadsheet in the docket entitled ``KEY_Hourly emissions and
operating data 2017-2020_06-24-21.'' For Keystone Unit 1, see
February 5th to 28th, 2017, and for Unit 2 see October 1 through
30th, 2017. For Conemaugh, see the spreadsheet in the docket
entitled ``CON_Hourly emissions and operating data 2017-2020_6-24-
21.'' For Unit 1, see January 21 through 23rd, 2017 and for Unit 2
see April 15th through 17th, 2017.
---------------------------------------------------------------------------

    Comment: Several commenters objected to EPA's methodology (and
thus, results) in calculating the SCR-on/SCR-off thresholds. PADEP in
particular asserts that by assigning an operating threshold for SCR
operation at each facility, EPA has run afoul of the Court's objection
to the 600-degree threshold in Pennsylvania's original RACT II
regulation. Further, PADEP asserts that because EPA had only limited
information from Key-Con and none from the other facilities, and
because we failed to seek such information from the other facilities,
the resulting emission limits are unsupported. Another commenter
asserted that EPA's visual evaluation of scatterplot data to develop
the thresholds was flawed, and that rather than accurately depicting
the SCR-on/SCR-off thresholds, the diagrams actually depict the minimum
sustainable load for the unit, which is ``. . . typically the level at
which PJM places a unit at low load for spinning reserve during periods
of low demand.'' See Homer City Comments at 2. Additionally, commenters
assert that the use of 0.2 lb/MMBtu as an indicator of when the SCRs
are or are not running is arbitrary, since there are times when an SCR
is off, but the NOX emissions are below 0.2 lb/MMBtu, and
conversely, there are times when an SCR is running, but the
NOX emissions are greater than 0.2 lb/MMBtu.
    Response: First, EPA disagrees with Pennsylvania's assertion that
the methodology for determining the SCR-on and SCR-off weights and
rates using observed SCR thresholds in the data for purposes of
developing an emissions limit that would restrict SCR-off operation is
substantially similar to PADEP's use of the 600-degree threshold to
justify essentially unlimited SCR-off operation. EPA further disagrees
that the Sierra Club adverse decision concerning the 600-degree
threshold has direct relevance to the permissibility of the approach
used by EPA in utilizing SCR-on and SCR-off weights and rates. The
Court found that Pennsylvania's blanket 600-degree temperature
threshold, which Pennsylvania applied uniformly to all the sources
regardless of the differences in SCRs at each source, was inadequately
explained or supported by the record. 972 F.3d at 303 (``Regarding the
threshold, neither the EPA nor DEP can explain why it is necessary at
all. . . . [E]ven assuming such a temperature threshold were
reasonable, the record does not support the conclusion that 600 degrees
Fahrenheit is the proper limit.'') EPA's SCR-on and SCR-off thresholds
were derived through careful unit-by-unit observation of actual
operating data. Furthermore, rather than drawing a regulatory line
below which less stringent emissions limits apply without any
restriction on operating time, EPA used the 0.2 lb/MMBtu threshold to
divide the operational data into SCR-on and SCR-off categories, then
used those data to establish both average SCR-on and -off rates for
each unit, and to identify the unit's past percentage of ozone season
time with the SCR on or off to establish the weight applied to the
respective rates. As such, the 0.2 lb/MMBtu is not an enforceable
limit, but merely a data point that was one component of EPA's approach
to use historical operating data to derive the lowest emission limit
that these particular sources are capable

of meeting by the application of control technology that is reasonably
available considering technological and economic feasibility.
    As for the assertion that the 0.2 lb/MMBtu cutpoint is arbitrary,
EPA conducted a fleetwide analysis of EGUs with combustion and post-
combustion NOX controls and found that this rate indicates
that the SCR is running to some extent.\34\ Nevertheless, in response
to our May 25, 2022 (87 FR 31798) proposal, EPA did in fact receive
additional information from certain sources (Montour and Homer City)
regarding what they consider the proper megawatt (MW) threshold for
operation of their SCRs. As described in section IV of this preamble,
we have taken that information into account in developing the
NOX emission limits finalized in this action.
---------------------------------------------------------------------------

    \34\ See ``Attachment 3-1 NOX Rate Development in EPA
Platform v6'' for EPA's Power Sector Modeling Platform (IPM) at
https://www.epa.gov/system/files/documents/2022-02/attachment-3-1-nox-rate-development-in-epa-platform-v6-summer-2021-reference-case.pdf.
---------------------------------------------------------------------------

    Comment: PADEP asserts that EPA's statistical approach to RACT in
this case has led to absurd results, specifically a higher limit for
Conemaugh than for Homer City and Keystone, despite the fact that
Conemaugh's SCRs are newer and technically capable of achieving lower
NOX emission rates.
    Response: EPA has developed the emissions limits for each source
based on analysis of historical data for each source demonstrating what
emissions the sources are capable of achieving through operation of
their installed SCR equipment. The emission limits being established
for Keystone are based on analysis of historical data extending back to
2003, while the emissions limits being established for Conemaugh are
based on historical data extending only back to 2015 due to the more
recent SCR installations at Conemaugh. Because the shorter historical
period of the Conemaugh data set does not contain periods with high
NOX allowance prices that would necessarily have motivated
Conemaugh to try to achieve the lowest possible emissions, it is
possible that EPA's resulting emissions limits for Conemaugh are less
stringent than would have been established with a more extensive data
set. However, the limitations of the data available for Conemaugh in no
way render the Keystone emission limits unreasonable. Nevertheless, the
comment does illustrate that EPA should adjust its approach to account
for the more limited Conemaugh data. As further discussed in section IV
of this preamble, in response to comments received, EPA is finalizing
limits that differ slightly from what was proposed, including an
adjustment for Conemaugh that better accounts for the more limited set
of ozone seasons from which to draw data for this source, while also
addressing the circumstances that prompted the PADEP comment regarding
absurd results. The Agency determined that for Conemaugh, it is
reasonable to use the second-best weight instead of the third-best.
    Comment: PADEP asserts that EPA should have considered tiered
limits as they did, and that such a limit structure would, in fact,
result in optimized SCR operation.
    Response: EPA disagrees that we needed to establish a tiered limit
structure like the one that was vacated by the Court, or the similar
approach used by PADEP in their case-by-case permits. As explained in
the proposal and the earlier section of this preamble, EPA did consider
the appropriateness of tiered limits and opted to not propose such an
approach for several reasons. First, while the Court did not explicitly
preclude the threshold approach, they were clearly suspicious of its
appropriateness: ``Regarding the threshold, neither the EPA nor DEP can
explain why it is necessary at all. It is not a common exemption.''
Sierra at 20. Upon reconsideration, EPA believes that it is not
necessary. EPA continues to believe that constraining SCR-off operation
to the extent possible based on data reflecting the recent operations
of each source is the appropriate means of implementing emission limits
consistent with RACT. As EPA raised in the on-record comments we
submitted to PADEP on draft permits,\35\ it is not clear to EPA how a
tiered limit approach constrains SCR-off operation in any meaningful or
enforceable way.\36\ Moreover, unconstrained SCR-off operation would be
inconsistent with the Court's directive that the RACT limit must be
technology-forcing.\37\ A set of limits that does not place limits on
the source operating without its NOX control technology is
not technology-forcing. Accordingly, EPA has chosen to forgo the tiered
limit approach, and instead use a weighted rate approach, which we
continue to believe provides the sources flexibility to address current
operational realities (i.e., increased cycling), while at the same time
providing meaningful constraint on SCR-off operation and objective
enforceability.
---------------------------------------------------------------------------

    \35\ See document ID EPA-R03-OAR-2022-0347-0067 in the docket
for this action at www.regulations.gov.
    \36\ EPA has not yet evaluated and is not pre-determining the
approvability Pennsylvania's ultimate SIP revisions, which were
submitted on May 26, 2020 and June 9, 2022.
    \37\ Sierra Club at 309.
---------------------------------------------------------------------------

    Comment: Talen Energy (Montour) asserts that EPA's limits are so
restrictive that they extend the regulatory regime beyond the customary
regulation of air pollutant emissions, and in effect dictate operation
of units and may severely limit the ability of the units to run as
directed by PJM and potentially compromise grid reliability.
    Response: EPA disagrees that these FIP limits are too restrictive
or that they extend the regulatory regime beyond EPA's Clean Air Act
authority or customary EPA action in a way that is inappropriate or
inconsistent with past CAA implementation. Emission limitations are, by
definition, a limitation on the amount of pollutants that may be
emitted by a source and therefore all emission limits place
restrictions on how sources operate in some fashion. For example,
states or EPA may place enforceable requirements on sources for
throughput limitations; federally enforceable requirements of this
nature are a standard practice that substitutes for major source
applicability of new source review (NSR) or national emission standards
for hazardous air pollutants (NESHAPs). Some emission limitations may
also take the form of work practice standards, which could place
requirements on the type of fuel a source may use or limit the amount
of time a source may operate under a certain status. These FIP limits
do not prescribe when or how the affected units should operate in order
to generate electricity. Rather, these limits ensure that when the
units are operating, their already installed SCRs are also operated in
a way that achieves the lowest emission rates that are technically and
economically feasible.
    As discussed previously in this notice, EPA acknowledges that the
weight given to the proposed SCR-off limit has the effect of limiting
the portion of time a cycling source can operate in SCR-off mode and
incentivizes a source to shift to SCR-on mode to preserve headroom
under the limit. While driving SCR operation, the weighted limit
accommodates the need for an EGU to occasionally cycle down to loads
below which SCR can operate effectively. Nothing in the FIP being
finalized in this document is intended to prohibit SCR-off operation,
nor does it dictate specific times when SCR-off operation would not be
permitted to occur.
    Comment: Montour commented that the compliance date should be
extended and not be the same date as the effective

date of the regulation. Citing the need to identify and evaluate the
updates/changes necessary, update programming for the CEMS and process
control equipment, provide training to staff, and complete operational
trials, Montour suggested extending the compliance date by six months.
Other sources commented that EPA should not proceed at all with a final
rule at this time and instead seek an extension from the Court to
reconsider the proposed limits.
    Response: Before addressing the substance of this comment, EPA
would like to correct an error in the NPRM regarding the effective date
of the FIP. The effective date of the regulation was intended to be
conveyed as an editorial note that the rule would be effective 30 days
after publication of the final rule. Instead, the editorial note was
converted into an actual date by the publisher, which was 30 days after
the date the proposed rulemaking was published: June 24, 2022. This was
a typographical error that produced an absurd result: the rule could
not possibly be effective before a final approval, or indeed, even
before the public comment period had ended (on July 11, 2022). The
proposed compliance date was accurately described to ``commence
immediately upon the effective date.'' \38\
---------------------------------------------------------------------------

    \38\ The proposal erroneously published the effective date of
the rule as June 24, 2022 and not as an editorial note that the rule
would be effective 30 days after the publication of the final rule.
See 87 FR 31813.
---------------------------------------------------------------------------

    With regard to Montour's request to extend the compliance date, EPA
agrees there will be a certain amount of time required for the
facilities to adjust to the new requirements and make certain technical
and administrative changes to ensure operations comply with the new
RACT limits. After considering comments received on this rulemaking,
EPA has determined that it is appropriate to extend the compliance date
past the initial proposal of 30 days after the effective date of these
regulations. The commenters have raised compelling concerns about being
able to meet new, more stringent limits on the accelerated timeline. In
light of the comment received from Montour, EPA is finalizing a
compliance date of 180 days after the effective date of the FIP. EPA is
under Court Order to ``. . . either approve a revised, compliant SIP
within two years or formulate a new [FIP],'' which EPA interprets as
requiring a final rule by August 27, 2022. Therefore, EPA will finalize
the final rule in compliance with the Court.
    Comment: Homer City asserted that EPA's description of the
methodology for determining SCR-on and SCR-off weighting is inadequate
to allow for independent verification. Also, Homer City also commented
that there is no explanation as to why the SCR-off weights (0.00 or
0.01) are so small, which leave no margin for SCR-off operation.
    Response: The commenter did not provide adequate explanation as to
why or where it had difficulty in understanding or replicating the
calculations EPA outlined in the proposed notice. Homer City also did
not submit its attempted calculations for EPA's consideration. All of
the data EPA used to develop the proposed emission limits (including
that which was used to establish the SCR-on and SCR-off weights) was
either available in the docket, or, because of file type and size
limitations of www.regulations.gov, was available upon request.\39\
Other commenters were able to replicate and/or modify EPA's
methodology. Homer City's weights are representative of their ozone
season operation over the time period analyzed for the weights (2011 to
2021). Further discussion of their revised weights can be found in
section IV of this preamble.
---------------------------------------------------------------------------

    \39\ See ``Memo to Docket--Availability of Additional
Information,'' document number EPA-R03-OAR-2022-0347-0060.
---------------------------------------------------------------------------

    Comment: Sierra Club asserts that the requirement that the sources
submit reports of their compliance every six months should be shortened
to every three months (quarterly), because the information needed to
demonstrate compliance with the FIP is already submitted to EPA for
various purposes on a quarterly basis, and that it does not make sense
for the FIP to require less frequent (biannual) reporting. In addition,
if EPA elects to keep the FIP reporting data separate from reporting to
the Clean Air Markets Division, Sierra Club requests that EPA put a
mechanism into the FIP by which the public can readily access this data
to ensure compliance, such as posting that data to the Clean Air
Markets Program Data tool. Finally, the commenter requests that the FIP
recordkeeping requirements be updated to include information about SCR
runtime and/or bypass as well as reagent usage.
    Response: EPA selected the six-month reporting period in order to
be consistent and streamlined with the sources' existing title V
reporting requirements. These title V reports are submitted to EPA
Region 3 and the state for review. The fact that certain data used to
determine compliance with the FIP requirements are also reported
quarterly to other EPA offices under various programs, such as the Acid
Rain program and Cross State Air Pollution Rule, and then placed into
EPA's Clean Air Markets Data Program online tool, does not provide a
sufficient basis to increase the frequency of reporting compliance with
the FIP requirements to match the reporting frequency for the
underlying data. There is nothing about the FIP limits that would
necessitate a reporting frequency greater than the reporting frequency
required by title V. The FIP does require deviation reports to be
submitted to EPA when NOX emission limits have been exceeded
for three or more days in any 30-day period.
    With respect to the assertion that the reporting requirements
should be updated to include SCR runtime and reagent injection data,
EPA believes that reporting of CEMS data consistent with title V
requirements is sufficient for compliance demonstration purposes. EPA
has not tied the emission limits directly to SCR operating parameters
in a way that would necessitate the submission of additional SCR data.
Compliance with the emission limits is the ultimate regulatory
requirement, and this is adequately demonstrated through submission of
CEMS data. EPA does not believe it is appropriate at this time to
include reporting requirements to this FIP that are not directly
necessary to show compliance with the regulatory requirements finalized
herein.
    Regarding the assertion that EPA should provide mechanism by which
the public can readily access additional data beyond the regularly
reported emissions data to ensure compliance, such as posting that
additional data to the Clean Air Markets Program Data tool, EPA is not
taking that step at this time. There is nothing about the
NOX limits in this FIP which would require EPA to provide a
novel approach to providing access to additional compliance data.
Further, the tools EPA makes available for providing the public with
access to reported emissions data are not at issue in this proceeding,
and comments requesting changes to those tools are outside the scope of
the rule.
    Comment: Sierra Club asserts that EPA should have used the best
year, rather than the third-best, which is what EPA used in
establishing the SCR-on rate. First, they assert that EPA has not
established that control equipment degrades over time, and that by
selecting the third-best ozone season, EPA is allowing sources to forgo
maintenance and good operating practices that would allow them to
otherwise meet limits that were established on a best ozone season
basis. Further, pointing to the rates achieved during the period of
2003-2010 when NOX allowance prices were high due to

the NOX SIP call, Sierra Club asserts that the decline in
SCR performance is due not to equipment degradation, but to the lack of
a regulatory requirement to achieve better emissions. Finally, Sierra
Club asserts that an examination of the best performing years does not
support the idea that equipment degradation due to the passage of time
necessarily leads to an inability to meet lower limits, and again
asserts that higher emissions rates are tied to less stringent
regulatory requirements rather than equipment degradation.
    Response: EPA disagrees that we should have used the best ozone
season instead of the third-best to establish the SCR-on rate. First,
although equipment degradation is not the only consideration we
evaluated when selecting the third-best approach, it is certainly a
contributing factor. While degradation can be slowed or mitigated
through proper operation, there is little question that it occurs and
can impact the removal efficiency. EPA has explained this previously
that ``[o]ver time, . . . the catalyst activity decreases, requiring
replacement, washing/cleaning, rejuvenation, or regeneration of the
catalyst.'' \40\ EPA acknowledges that catalyst management practices
can be adapted to address catalyst degradation, but that does not mean
that the degradation does not occur.
---------------------------------------------------------------------------

    \40\ See https://www.epa.gov/sites/default/files/2017-12/documents/scrcostmanualchapter7thedition_2016revisions2017.pdf at
16.
---------------------------------------------------------------------------

    In addition, EPA's longstanding interpretation of RACT does not
require RACT-level controls to be equivalent to the ``best.'' The Court
agreed with this interpretation in the Sierra Club decision: ``we do
not suggest that Pennsylvania must achieve the absolute lowest level of
emissions that is technologically possible for the approved limit to
satisfy RACT.'' \41\ As explained in the NPRM and in response to the
previous comment, EPA believes that the third-best approach is a
reasonable way of establishing appropriate RACT limits. Use of the
third-best year avoids biasing the limit with uncharacteristically low
emitting ozone seasons, or under uncharacteristically optimal operating
conditions.
---------------------------------------------------------------------------

    \41\ 972 F.3d at 302.
---------------------------------------------------------------------------

    EPA does agree with the commenter that there does appear to be a
correlation between increased SCR operation (and correspondingly lower
NOX emissions), and periods when new regulatory requirements
such as CAIR, CSAPR, the CSAPR Update, and the RCU, have created
meaningfully more stringent NOX emission budgets. More
stringent emissions budgets can compel EGUs to operate their SCRs more
often and at lower NOX emission rates to meet these new
budgets. They accomplish this result by raising the cost of
NOX allowances, creating an economic incentive for EGUs to
operate their SCRs more often and at lower NOX emission
rates to either avoid having to purchase costly allowances or to
generate NOX allowances to sell. EPA continues to believe
that our proposed weighted rate approach takes these factors into
consideration and establishes appropriate limits that are consistent
with the CAA's RACT requirements.
    Comment: Similar to comments relating to EPA's consideration of
operating data from years when the units were operating in a base load
capacity, commenters assert that ozone season operations are not
consistent with year-round operations and therefore should not be the
sole timeframe considered in development of the limits that apply all
the time. Further, Key-Con in particular noted that the SCRs at
Keystone were designed to only run during ozone season, and that in the
past, they had considerable down time for cleaning and maintenance of
the controls. Additionally, they assert that ammonium bisulfate salts
(ABS) form more readily in colder ambient temperatures, leading to
increased fouling.
    Response: EPA acknowledges some of the technical challenges
associated with temperature and SCR activity. Because of this, among
other reasons, we performed an analysis of actual operating and
emissions data and developed reasonable limits to account for
challenges such as seasonal ambient temperature changes and increased
cycling operation rather than selecting the absolute lowest rates that
these units have ever achieved. EPA primarily used ozone season data to
develop these limits, which is appropriate, not only because the ozone
season generally represents a period of increased electricity demand
and operation at these sources, but also because it is indicative of
what these units can achieve when there are additional regulatory
constraints and economic disincentives against sub-optimal SCR
operation in place.
    To the degree that the comment is suggesting that this RACT FIP
should create seasonal limits that do not require SCR operations in
non-ozone-season months, the EPA does not believe that this would be
consistent with the CAA RACT requirement. As noted in the background of
this preamble, NOX RACT for major sources is required to be
applied year-round. There are numerous coal-fired EGUs operating in the
OTR that operate SCR controls on an annual basis. Additionally, there
are coal-fired EGUs operating outside the OTR subject to other
regulations that mandate SCR controls be operated throughout the year
as well. Like the four Pennsylvania facilities addressed in this
notice, many of these other coal-fired EGUs were built in the same era
(1960s and 1970s) and then later retrofitted with SCRs in response to
the EPA interstate transport requirements for ozone season
NOX emissions, which began in 2003. So, while EPA has
applied RACT on a case-by-case, source-specific basis, EPA cannot
ignore the fact that there are many coal-fired EGUs, outside of
Pennsylvania, that can, and do, operate their SCR controls year-round
with NOX emission limits similar to the final limits
determined in this notice for the purposes of NOX RACT as
well as for other regulatory requirements.\42\
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    \42\ Delaware Administrative Code, Title 7 Natural Resources &
Environmental Control, 1100 Air Quality Management Section, 1146
``Electric Generating Unit (EGU) Multi-Pollutant Regulation''.
    Maryland--Code of Maryland Regulations (COMAR), Title 26
Department of the Environment, Subtitle 11 Air Quality, Chapter 38,
``Control of NOX Emissions from Coal-Fired Electric
Generating Units''.
    New Jersey State Department of Environmental Protection, New
Jersey Administrative Code, Title 7, Chapter 27, Subchapter 19,
``Control and Prohibition of Air Pollution from Oxides of
Nitrogen''.
    ``Coal-Fired Power Plant Enforcement'' US EPA, retrieved August
2022. See https://www.epa.gov/enforcement/coal-fired-power-plant-enforcement.
---------------------------------------------------------------------------

    EPA also disagrees that the Keystone units cannot operate their
SCRs effectively outside of the ozone season or that the rates must be
further adjusted to account for seasonal effects. In response to
Keystone's comment, EPA further reviewed non-ozone season emissions
data reports for Keystone units and found that between 2009 and 2010,
both Keystone units operated their SCRs in non-ozone season months for
extended periods whereby their NOX emissions were generally
below the final NOX emission limits determined in this
notice.\43\ Therefore, EPA cannot justify exempting Keystone from
operating its SCRs, with reasonable effectiveness, for NOX
RACT during non-ozone season months.
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    \43\ ``Custom Data Download'' US EPA Clean Air Markets Program
Data, retrieved August 2022, see https://campd.epa.gov/data/custom-data-download.
---------------------------------------------------------------------------

    Comment: Key-Con asserts that EPA's limits severely and
inappropriately limit the amount of time either facility can operate
without ammonia injection, especially during start-up and low load

operation. They further assert that the duration of a cold start-up is
18-24 hours, and that at loads between the minimum sustainable load
(340 MW) and the unit load (which they do not identify) where the
minimum continuous operating temperature (MCOT) of the SCR is reached,
emissions can reach 0.35 lb/MMBtu for Keystone units, and 0.30 lb/MMBtu
for Conemaugh. They assert that Keystone units 1 and 2 in particular
would be unable to demonstrate compliance if there was one cold start-
up in a 30-day period, even if they spent the rest of the time
operating at the proposed limit of 0.074 lb/MMBtu.
    Response: Key-Con's comment is not sufficient to demonstrate an
inability to meet the proposed FIP limits. Key-Con presented no data to
justify the amount of time spent in a cold start-up during which the
unit load is above the sustainable limit, but below whatever threshold
is necessary to bring flue gas up to the MCOT of the SCR and begin
ammonia injection. As noted in a previous response, Key-Con did not
provide any information regarding expected unit utilization, and
instead criticized EPA's proposed rates as unobtainable during startup
events by providing 25 hours of minimal data regarding one cold-start
of Keystone Unit 1 in January 2022. Given that this data covered only
25 hours of startup, and was not then averaged with 29 other days of
emission data to arrive at a 30-day average hourly emission rate, it is
not proof that this one unit could not meet EPA's 30-day average rate.
    In response to this comment, EPA further reviewed startup data for
Keystone in non-ozone season months. On November 5, 2009, Keystone Unit
1 started operations after having been inoperable since October 20,
2009. During the first three days of operation, the daily
NOX emission rates were 0.229, 0.160, and 0.058 lb/MMBtu
respectively. During the subsequent days of operation, up until
reaching 30 operating days, the daily NOX emissions varied
from a low of 0.046 to a high of 0.116 lb/MMBtu. The resultant 30-day
NOX emission rate after 30 days of operation was 0.064 lb/
MMBtu.\44\ This is well below the final NOX emission rate
limit determined in this notice of 0.075 lb/MMBtu. This example
illustrates that the unit is entirely capable of achieving the emission
rate limits in this notice, with startup periods, provided the normal
operating days are sufficiently controlled and the facility was able to
achieve these results without a specific 30-day regulatory requirement
to do so. Moreover, EPA has purposely granted an emission rate averaged
over 30 days, which is the maximum averaging time EPA can grant for
NOX RACT. EPA has also issued facility-wide emission rate
limits to allow the facilities to further average the emission rates
amongst their units. This amount of dual averaging, in terms of
averaging days and then units, affords Key-Con, and the other
facilities, additional flexibility to manage startup operations.
---------------------------------------------------------------------------

    \44\ See ``Keystone winter-time SCR use unit 1.xlsx'' in the
docket for this action.
---------------------------------------------------------------------------

    Further, even if we are to accept this claim on its face, Key-Con's
argument fails because they merely point out the obvious mathematical
certainty that any appreciable amount of time spent operating above the
average limit would lead to a violation if the entirety of the
remaining averaging period was spent operating exactly at the limit.
The entire purpose of establishing average limits (and in this case a
30-day average) is to smooth out the peaks and valleys of shorter-term
emissions and arrive at a limit that can be met by offsetting periods
when the units emit above the limit (generally, SCR-off periods), with
periods of optimal operation where the units emit below the limit
(generally, SCR-on periods). This is one of the reasons that we did not
select the lowest achievable SCR-on rate as RACT. EPA's limits provide
for some level of SCR-off operation, while still representing the
lowest rate the source is capable of meeting over such period through
the application of control technology that is reasonably available
considering technological and economic feasibility. To the degree that
this limit acts as a constraint on low-load operation without the SCR,
the commenter did not explain why such a constraint is inappropriate.
In light of the high NOX emissions that can occur with such
operation, the EPA believes this is a reasonable approach to define a
limit that represents the application of RACT. Moreover, Key-Con's own
analysis appears to support an ability to meet 0.075 lb/MMBtu, even
based on cold start-ups taking place in January.\45\ As discussed in
section IV of this preamble, EPA has re-evaluated our proposed limits,
with the resulting limits being consistent with what Key-Con's comments
appear to show is attainable.
---------------------------------------------------------------------------

    \45\ Id.
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    Comment: Homer City asserts that because the proposed 24-hour mass
limits are based on the 30-day average rate limits, the mass limits do
not provide adequate margin for periods of start-up and shut down.
    Response: EPA disagrees. First, as previously discussed, the 30-day
rate-based limits upon which the daily mass limits are based were
derived in such a way as to incorporate several layers of flexibility,
or margin, including emissions during periods of startup and shutdown.
We used weighted averages considering years when the units were
operating in more of a load-following mode rather than as baseload, we
used a 30-day averaging period to ``smooth'' variability of shorter-
term emissions, and we used the ``third-best'' rather than the ``best''
approach in order to add additional buffer and still establish limits
that represent RACT. Additionally, it is not clear what period of time
the commenter is considering as ``startup,'' nor have they established
that they could not begin operating the SCRs sooner. While emission
rates during the startup process do tend to be higher before the
control equipment is fully operational, mass emissions are typically
lower for most startup hours, since startup generally happens at lower
levels of fuel combustion. Finally, commenters have not presented any
actual operating data to demonstrate that they cannot meet the proposed
limits. Indeed, EPA's review of historical data, and in fact, some data
from the 2022 ozone season reported so far, supports a determination
that the sources can achieve EPA's final 30-day NOX emission
rate limits, and that when the units operate in compliance with the 30-
day rate limit, they have generally operated below the final daily
NOX mass emission limits.
    Comment: Homer City claims that EPA's proposed limits are not
technically feasible because, they assert, from 2010-2021, only
Keystone and Conemaugh Units 1 and 2 have been able to achieve EPA's
proposed limits on a 30-day basis, and even then, it was only 7
instances or 6.36% of the time.
    Response: First, if sources were not meeting the proposed limits in
the selected years during which there was no regulatory requirement or
economic incentive to do so, it is not necessarily proof that they
could not have. Nor is it proof that they cannot in the future. EPA
notes that in rejecting EPA's approval of PADEP's original 0.12 lb/
MMBtu limit as ``a mere acceptance of the status quo,'' 972 F.3d at
302, the Court in Sierra Club affirmed that ``an average of the current
emissions being generated by existing systems, will not usually be
sufficient to satisfy the RACT standard,'' id. at 300. Homer City
rejects EPA's limits, but presents no data or analysis that
demonstrates what they are in fact capable of achieving, and what EPA
should establish as RACT for these

units. EPA has demonstrated that the limits are achievable when the
regulatory environment requires it, and that the limits in the FIP
represent RACT for these sources.
    Comment: PADEP asserts that EPA's FIP is based on an incomplete
record. First, PADEP asserts that EPA ignored information that the
Department obtained from the sources and failed to obtain additional
information that would be necessary to conduct a source specific RACT
analysis. Additionally, PADEP claims that meetings between EPA staff
and the Maryland Department of the Environment (MDE) prior to our
proposal may be relevant to the development of the FIP, and that
records from that meeting should have been in the docket.
    Response: EPA disagrees. First, to the extent it was relevant to
our approach, we did consider the information that PADEP obtained and
submitted, and in fact cited to it on numerous occasions, and included
it in the record as appropriate. EPA had a sufficient technical basis,
that is thoroughly documented in the rulemaking record, to support the
RACT limits included in this FIP. To the extent that PADEP or the
sources at issue in this rulemaking believe the Agency should have
considered additional or alternative data, the 45-day comment period
provided an opportunity for the sources to submit such information. EPA
considered all of the additional information submitted prior to
finalizing the FIP. With respect to the assertion that records from
EPA's discussions with MDE prior to EPA proposing this action should
have been contained in the record, EPA disagrees. All documentation and
information that EPA relied upon in developing this rule action have
been included in the record. The cited discussion with MDE did not
contain information that was relied upon for development of the FIP
approach and limits.
    Comment: Montour submitted a technical analysis which built upon
EPA's methodology in the May 25, 2022 (87 FR 31798) NPRM in order to
demonstrate what they felt are more achievable limits, based on a
dataset that represents what Montour contends are more consistent with
current operating parameters. Montour asserts that EPA should have only
considered ozone season data from 2017-2021, that the correct SCR
threshold is 440MW, and that as a result, Montour should have a
facility-wide, 30-day NOX emission rate limit of 0.099 lb/
MMBtu, with daily mass-based limits of 17,385 and 17,200 lb
NOX/day for Units 1 and 2, respectively.
    Response: As further discussed in section IV of this preamble, as a
result of comments received and while largely retaining the methodology
described in the NPRM, EPA has revised some of the limits from the
proposal based on the submittal of additional data or the
reconsideration of some of the weights in the case of Conemaugh.
Specifically, in cases such as Montour where a facility submitted SCR
threshold data to counter that which EPA used in the proposal, EPA
recalculated the NOX rate limits using the facility's
information, but EPA's original methodology. In the case of Montour,