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Proposed Rule2025-10991

Repeal of Greenhouse Gas Emissions Standards for Fossil Fuel-Fired Electric Generating Units

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Published

June 17, 2025

Issuing agencies

Environmental Protection Agency

Abstract

In this action, the U.S. Environmental Protection Agency (EPA) is proposing to repeal all greenhouse gas (GHG) emissions standards for fossil fuel-fired power plants. The EPA is proposing that the Clean Air Act (CAA) requires it to make a finding that GHG emissions from fossil fuel-fired power plants contribute significantly to dangerous air pollution, as a predicate to regulating GHG emissions from those plants. The EPA is further proposing to make a finding that GHG emissions from fossil fuel-fired power plants do not contribute significantly to dangerous air pollution. The EPA is also proposing, as an alternative, to repeal a narrower set of requirements that includes the emission guidelines for existing fossil fuel-fired steam generating units, the carbon capture and sequestration/storage (CCS)-based standards for coal-fired steam generating units undertaking a large modification, and the CCS-based standards for new base load stationary combustion turbines.

Full Text

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<title>Federal Register, Volume 90 Issue 115 (Tuesday, June 17, 2025)</title>
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[Federal Register Volume 90, Number 115 (Tuesday, June 17, 2025)]
[Proposed Rules]
[Pages 25752-25781]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-10991]

[[Page 25751]]

Vol. 90

Tuesday,

No. 115

June 17, 2025

Part II

Environmental Protection Agency

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40 CFR Part 60

Repeal of Greenhouse Gas Emissions Standards for Fossil Fuel-Fired
Electric Generating Units; Proposed Rule

Federal Register / Vol. 90 , No. 115 / Tuesday, June 17, 2025 /
Proposed Rules

[[Page 25752]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 60

[EPA-HQ-OAR-2025-0124; FRL-12674-01-OAR]
RIN 2060-AW55

Repeal of Greenhouse Gas Emissions Standards for Fossil Fuel-
Fired Electric Generating Units

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: In this action, the U.S. Environmental Protection Agency (EPA)
is proposing to repeal all greenhouse gas (GHG) emissions standards for
fossil fuel-fired power plants. The EPA is proposing that the Clean Air
Act (CAA) requires it to make a finding that GHG emissions from fossil
fuel-fired power plants contribute significantly to dangerous air
pollution, as a predicate to regulating GHG emissions from those
plants. The EPA is further proposing to make a finding that GHG
emissions from fossil fuel-fired power plants do not contribute
significantly to dangerous air pollution. The EPA is also proposing, as
an alternative, to repeal a narrower set of requirements that includes
the emission guidelines for existing fossil fuel-fired steam generating
units, the carbon capture and sequestration/storage (CCS)-based
standards for coal-fired steam generating units undertaking a large
modification, and the CCS-based standards for new base load stationary
combustion turbines.

DATES: Comments. Comments must be received on or before August 7, 2025.
Public Hearing. The EPA will hold a virtual public hearing on July
8, 2025. Please refer to the SUPPLEMENTARY INFORMATION section for
information on registering for the public hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2025-0124, by any of the following methods:
<bullet> Federal eRulemaking Portal: <a href="https://www.regulations.gov">https://www.regulations.gov</a>
(our preferred method). Follow the online instructions for submitting
comments.
<bullet> Email: <a href="/cdn-cgi/l/email-protection#accd81cdc2c881de81c8c3cfc7c9d8ecc9dccd82cbc3da">[email&#160;protected]</a>. Include Docket ID No. EPA-
HQ-OAR-2025-0124 in the subject line of the message.
<bullet> Fax: (202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-
2025-0124.
<bullet> Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2025-0124, Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.
<bullet> Hand/Courier Delivery: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-
Friday (except Federal holidays).
Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to <a href="https://www.regulations.gov">https://www.regulations.gov</a>, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the SUPPLEMENTARY
INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Ms. Lisa Thompson, Sector Policies and Programs
Division (D243-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number: (919) 541-5158; and email address:
<a href="/cdn-cgi/l/email-protection#15617d7a7865667a7b3b797c6674557065743b727a63">[email&#160;protected]</a>.

SUPPLEMENTARY INFORMATION:
Participation in virtual public hearing. The public hearing will be
held via virtual platform on July 8, 2025. The hearing will convene at
11 a.m. Eastern Time (ET) and conclude at 7 p.m. ET. The EPA may close
a session 15 minutes after the last pre-registered speaker has
testified if there are no additional speakers.
The EPA will begin pre-registering speakers for the hearing no
later than 1 business day following the publication of this document in
the Federal Register. To register to speak at the virtual hearing,
please use the online registration form available at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a> or contact the public hearing
team at (888) 372-8699 or by email at <a href="/cdn-cgi/l/email-protection#c093909084b0b5a2aca9a3a8a5a1b2a9aea780a5b0a1eea7afb6">[email&#160;protected]</a>. The
last day to pre-register to speak at the hearing will be June 29, 2025.
Prior to the hearing, the EPA will post a general agenda that will list
pre-registered speakers in approximate order at: <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>.
The EPA will make every effort to follow the schedule as closely as
possible on the day of the hearing; however, please plan for the
hearings to run either ahead of schedule or behind schedule.
Each commenter will have 4 minutes to provide oral testimony. The
EPA encourages commenters to submit a copy of their oral testimony as
written comments electronically to the rulemaking docket.
The EPA may ask clarifying questions during the oral presentations
but will not respond to the presentations at that time. Written
statements and supporting information submitted during the comment
period will be considered with the same weight as oral testimony and
supporting information presented at the public hearing.
Please note that any updates made to any aspect of the hearing will
be posted online at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>. While the EPA expects the hearing to go forward as described in
this section, please monitor our website or contact the public hearing
team at (888) 372-8699 or by email at <a href="/cdn-cgi/l/email-protection#d586858591a5a0b7b9bcb6bdb0b4a7bcbbb295b0a5b4fbb2baa3">[email&#160;protected]</a> to
determine if there are any updates. The EPA does not intend to publish
a document in the Federal Register announcing updates.
If you require a special accommodation such as audio description,
please pre-register for the hearing with the public hearing team and
describe your needs by June 24, 2025. The EPA may not be able to
arrange accommodations without advanced notice.
Docket. The EPA has established a docket for these rulemakings
under Docket ID No. EPA-HQ-OAR-2025-0124. All documents in the docket
are listed in the <a href="http://Regulations.gov">Regulations.gov</a> index. 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.
Written Comments. Direct your comments to Docket ID No. EPA-HQ-OAR-
2025-0124 at <a href="https://www.regulations.gov">https://www.regulations.gov</a> (our preferred method), or the
other methods identified in the ADDRESSES section. Once submitted,
comments cannot be edited or removed from the docket. The EPA may
publish any comment received to its public docket. Do not submit to the
EPA's docket at <a href="https://www.regulations.gov">https://www.regulations.gov</a> any information you
consider to be Confidential Business Information (CBI) or other
information whose disclosure is restricted by statute. This type of
information should be submitted as

[[Page 25753]]

discussed in the Submitting CBI section of this document.
The EPA is soliciting comment on numerous aspects of the proposed
rule. The EPA has indexed each comment solicitation with a unique
identifier (e.g., ``C-1'', ``C-2'', ``C-3'' . . .) to provide a
consistent framework for effective and efficient provision of comments.
Accordingly, we ask that commenters include the corresponding
identifier when providing comments relevant to that comment
solicitation. We ask that commenters include the identifier either in a
heading or within the text of each comment, to make clear which comment
solicitation is being addressed. We emphasize that we are not limiting
comment to these identified areas and encourage provision of any other
comments relevant to this proposed action.
Multimedia submissions (audio, video, etc.) must be accompanied by
a written comment. The written comment is considered the official
comment and should include discussion of all points you wish to make.
The EPA will generally not consider comments or comment contents
located outside of the primary submission (i.e., on the Web, cloud, or
other file sharing system). Please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a> for additional submission methods; the full EPA
public comment policy; information about CBI or multimedia submissions;
and general guidance on making effective comments.
The <a href="https://www.regulations.gov">https://www.regulations.gov</a> website allows you to submit your
comment anonymously, which means the EPA will not know your identity or
contact information unless you provide it in the body of your comment.
If you send an email comment directly to the EPA without going through
<a href="https://www.regulations.gov">https://www.regulations.gov</a>, your email address will be automatically
captured and included as part of the comment that is placed in the
public docket and made available on the internet. If you submit an
electronic comment, the EPA recommends that you include your name and
other contact information in the body of your comment and with any
digital storage media you submit. If the EPA cannot read your comment
due to technical difficulties and cannot contact you for clarification,
the EPA may not be able to consider your comment. Electronic files
should not include special characters or any form of encryption and
should be free of any defects or viruses.
Submitting CBI. Do not submit information containing CBI to the EPA
through <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Clearly mark the part or all of
the information that you claim to be CBI. For CBI information on any
digital storage media that you mail to the EPA, note the docket ID,
mark the outside of the digital storage media as CBI, and identify
electronically within the digital storage media the specific
information that is claimed as CBI. In addition to one complete version
of the comments that includes information claimed as CBI, you must
submit a copy of the comments that does not contain the information
claimed as CBI directly to the public docket through the procedures
outlined in Written Comments section of this document. If you submit
any digital storage media that does not contain CBI, mark the outside
of the digital storage media clearly that it does not contain CBI and
note the docket ID. Information not marked as CBI will be included in
the public docket and the EPA's electronic public docket without prior
notice. Information marked as CBI will not be disclosed except in
accordance with procedures set forth in 40 Code of Federal Regulations
(CFR) part 2.
Our preferred method to receive CBI is for it to be transmitted
electronically using email attachments, File Transfer Protocol (FTP),
or other online file sharing services (e.g., Dropbox, OneDrive, Google
Drive). Electronic submissions must be transmitted directly to the
Office of Air Quality Planning and Standards (OAQPS) CBI Office at the
email address <a href="/cdn-cgi/l/email-protection#6f000e1e1f1c0c0d062f0a1f0e41080019">[email&#160;protected]</a> and, as described above, should include
clear CBI markings and note the docket ID. If assistance is needed with
submitting large electronic files that exceed the file size limit for
email attachments, and if you do not have your own file sharing
service, please email <a href="/cdn-cgi/l/email-protection#b3dcd2c2c3c0d0d1daf3d6c3d29dd4dcc5">[email&#160;protected]</a> to request a file transfer link.
If sending CBI information through the U.S. Postal Service, please send
it to the following address: OAQPS Document Control Officer (C404-02),
OAQPS, U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2025-0124. The
mailed CBI material should be double wrapped and clearly marked. Any
CBI markings should not show through the outer envelope.
Preamble acronyms and abbreviations. Throughout this document the
use of ``we,'' ``us,'' or ``our'' is intended to refer to the EPA. The
EPA uses multiple acronyms and terms in this preamble. While this list
may not be exhaustive, to ease the reading of this preamble and for
reference purposes, the EPA defines the following terms and acronyms
here:

ACE Affordable Clean Energy [rule]
BSER best system of emission reduction
CAA Clean Air Act
CCS carbon capture and sequestration/storage
CFR Code of Federal Regulations
CO<INF>2</INF> carbon dioxide
CPS Carbon Pollution Standards
CPP Clean Power Plan
EGU electric generating unit
EPA Environmental Protection Agency
FR Federal Register
GHG greenhouse gas
MW megawatt
MWh megawatt-hour
NSPS new source performance standards
RIA regulatory impact analysis

Organization of this document. The information in this preamble
is organized as follows:

I. Executive Summary
II. General Information
A. Action Applicability
B. Where to Get a Copy of This Document and Other Related
Information
III. Background
A. Statutory Authority
1. Regulation of Emissions from New Sources
2. Regulation of Emissions From Existing Sources
3. Key Elements of Determining a Standard of Performance
4. EPA Promulgation of Emission Guidelines for States To
Establish Standards of Performance
B. EPA Regulation of GHG Emissions Under CAA Section 111
C. Carbon Pollution Standards
IV. Summary and Rationale of Primary Proposal
A. Summary of Proposed Action
B. Significant Contribution Finding for EGUs
1. Requirement for Significant Contribution Determination
2. Determination of Significant Contribution
C. Conclusion
V. Summary and Rationale of Alternative Proposal
A. Summary of Alternative Proposal
B. Emission Guidelines for Existing Fossil Fuel-Fired Steam
Generating Units
1. CCS-Based Requirements for Long-Term Existing Coal-Fired
Steam Generating Units
2. Natural Gas Co-Firing-Based Requirements for Existing Medium-
Term Coal-Fired Steam Generating Units
3. Requirements for Existing Natural Gas- and Oil-Fired Steam
Generating Units
4. Conclusion
C. CCS-Based Requirements for Coal-Fired Steam Generating Units
Undertaking a Large Modification
D. Phase 2 CCS-Based Requirements for New Combustion Turbine
EGUs
1. Adequately Demonstrated
2. Cost
3. Infrastructure
4. Conclusion
VI. Request for Comments
VII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive

[[Page 25754]]

Order 13563: Improving Regulation and Regulatory Review
B. Executive Order 14192: Unleashing Prosperity Through
Deregulation
C. Paperwork Reduction Act (PRA)
1. 40 CFR part 60, subpart TTTT
2. 40 CFR part 60, subpart TTTTa
3. 40 CFR part 60, subpart UUUUb
D. Regulatory Flexibility Act (RFA)
E. Unfunded Mandates Reform Act (UMRA)
F. Executive Order 13132: Federalism
G. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
H. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
I. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
J. National Technology Transfer and Advancement Act (NTTAA) and
1 CFR part 51

I. Executive Summary

In this action, the U.S. Environmental Protection Agency (EPA) is
proposing to repeal all greenhouse gas (GHG) standards for fossil fuel-
fired power plants. The EPA is proposing that Clean Air Act (CAA)
section 111 requires it to make a finding that GHG emissions from
fossil fuel-fired power plants contribute significantly to dangerous
air pollution, as a predicate to regulating GHG emissions from plants
in this source category. The EPA is further proposing to make a finding
that GHG emissions from fossil fuel-fired power plants do not
contribute significantly to dangerous air pollution within the meaning
of the statute. The EPA is also proposing, as an alternative, to repeal
a narrower set of requirements that include the emission guidelines for
existing fossil fuel-fired steam generating units, the carbon capture
and sequestration/storage (CCS)-based standards for coal-fired steam
generating units undertaking a large modification, and the CCS-based
standards for new base load stationary combustion turbines. In the
regulatory impact analysis, we present the potential impacts of the
proposal and alternative proposal in one shared set of estimates for
the years 2026 to 2047, discounting monetized estimates to 2025 under 3
and 7 percent discount rates. Over the 2026 to 2047 period, the present
value (PV) of the estimated compliance cost savings is $19 billion
under a 3 percent discount rate, and $9.6 billion under a 7 percent
discount rate for both the proposal and the alternative proposal.
With this action, the EPA proposes to resolve a decade's worth of
regulatory uncertainty brought on by the Agency's novel attempts to
regulate GHG emissions from fossil fuel-fired power plants under CAA
section 111. The EPA attempted to restrict GHG emissions from power
plants for the first time in 2015, when it issued both new source
performance standards for new power plants (the 2015 NSPS) \1\ and
emission guidelines for existing power plants (the Clean Power Plan
(CPP)).\2\ Despite in effect listing fossil fuel-fired power plants as
a new source category for the purpose of regulating GHG emissions, the
EPA interpreted CAA section 111 as authorizing the regulation of any
air pollutant so long as there was a rational basis for doing so, and
asserted that the Agency was not required to make a finding of
significant contribution to dangerous air pollution before regulating
sources within the new source category. In the alternative, the EPA
stated that it would make such a finding if required by the statute,
and based that finding on the absolute volume of GHG emissions from
fossil fuel-fired power plants.
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\1\ ``Standards of Performance for Greenhouse Gas Emissions From
New, Modified, and Reconstructed Stationary Sources: Electric
Utility Generating Units; Final Rule,'' 80 FR 64510 (October 23,
2015).
\2\ ``Carbon Pollution Emission Guidelines for Existing
Stationary Sources: Electric Utility Generating Units; Final Rule,''
80 FR 64662 (October 23, 2015).
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In West Virginia v. EPA, 597 U.S. 697 (2022), the U.S. Supreme
Court struck down these efforts in large part, ruling that CAA section
111 does not authorize the EPA to regulate fossil fuel-fired power
plants by capping GHG emissions at a level that forces a nationwide
transition away from the use of coal to generate electricity.\3\ Rather
than change course, however, the EPA responded by promulgating a new
rule that embraced the goals of the 2015 NSPS and CPP by expanding
restrictions on certain new sources and regulating existing sources in
a similarly stringent manner.
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\3\ See West Virginia v. EPA, 597 U.S. 697, 735 (2022) (Congress
did not give EPA authority to adopt a regulatory scheme that
``cap[s] carbon dioxide emissions at a level that will force a
nationwide transition away from the use of coal to generate
electricity'').
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The EPA's most recent effort to regulate GHG emissions from the
power sector, commonly referred to as the Carbon Pollution Standards
(CPS), includes standards of performance for new and reconstructed
fossil fuel-fired combustion turbines and for certain modified fossil
fuel-fired steam-generating power plants, as well as rules directing
States to set standards of performance for existing fossil fuel-fired
steam generating power plants.\4\ Aspects of these standards are
premised on one type of power plant--coal-fired plants--converting to
another type that would be partially fired with an entirely different
fuel, i.e., natural gas. Additionally, in the course of the rulemaking
and subsequent litigation over the CPS, numerous States, regulated
entities, and other stakeholders warned that these standards exceed the
EPA's authority to mandate already demonstrated technologies, not
technologies that will not be widely available until sometime in the
future, are based on inadequately demonstrated technologies, are
unachievable, threaten to impose massive costs on the power sector, and
do not adequately ensure the national interest in affordable, reliable
electricity.
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\4\ ``New Source Performance Standards for Greenhouse Gas
Emissions From New, Modified, and Reconstructed Fossil Fuel-Fired
Electric Generating Units; Emission Guidelines for Greenhouse Gas
Emissions From Existing Fossil Fuel-Fired Electric Generating Units;
and Repeal of the Affordable Clean Energy Rule; Final Rule,'' 89 FR
39798 (May 9, 2024).
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On January 20, 2025, President Trump issued Executive Order 14154,
``Unleashing American Energy,'' which directs federal agencies,
including the EPA, to review existing regulations ``to identify those
agency actions that impose an undue burden on the identification,
development, or use of domestic energy resources--with particular
attention to oil, natural gas, coal, hydropower, biofuels, critical
mineral, and nuclear energy resources.'' \5\ In the course of this
review, the EPA has identified GHG emissions standards \6\ for power
plants as one such action. The Executive Order further affirms that it
is, ``the policy of the United States to ensure that all regulatory
requirements related to energy are grounded in clearly applicable
law.'' \7\
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\5\ Executive Order 14154 section 3(a).
\6\ References to ``GHG standards'' here and elsewhere include
new source performance standards (NSPS) promulgated under CAA
section 111(b) and emission guidelines for existing sources
promulgated under CAA section 111(d).
\7\ Executive Order 14154, section 2.
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On February 19, 2025, President Trump issued an Executive Order
titled ``Ensuring Lawful Governance and Implementing the President's
`Department of Government Efficiency' Deregulatory Initiative.'' \8\
This Executive Order established a national policy requiring agencies,
including the EPA, to ``focus the executive branch's limited
enforcement resources on regulations squarely authorized by
constitutional Federal statutes'' and to ``initiate a process to review
all regulations subject to their sole or joint jurisdiction for
consistency with law

[[Page 25755]]

and Administration policy.'' \9\ Among other things, the Executive
Order instructed agencies to identify ``regulations that are based on
anything other than the best reading of the underlying statutory
authority or prohibition'' \10\ and ``regulations that implicate
matters of social, political, or economic significance that are not
authorized by clear statutory authority.'' \11\ In the course of this
review, the EPA has identified GHG standards for power plants as
regulations that may be based on interpretations that are inconsistent
with the best reading of CAA section 111 and address a significant
issue without clear statutory authorization.
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\8\ Executive Order 14219.
\9\ Id. sections 1, 2(a).
\10\ Id. section 2(a)(iii).
\11\ Id. section 2(a)(iv).
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On April 8, 2025, President Trump issued an Executive Order titled,
``Reinvigorating America's Beautiful Clean Coal Industry and Amending
Executive Order 14241.'' \12\ This Executive Order stated that ``coal
is essential to our national and economic security'' and established
``a national priority to support the domestic coal industry by removing
Federal regulatory barriers that undermine coal production.'' \13\ The
Executive Order specifically found that ``beautiful clean coal
resources will be critical to meeting the rise in electricity demand
due to the resurgence of domestic manufacturing and the construction of
artificial intelligence data processing centers'' and to increasing
``energy supply,'' lowering ``electricity costs,'' stabilizing the
power grid, creating ``high paying jobs,'' supporting ``burgeoning
industries,'' and assisting allies abroad.\14\ Accordingly, the
Executive Order directed the EPA, among other agencies, to ``identify
any guidance, regulations, programs, and policies within their
respective executive department or agency that seek to transition the
Nation away from coal production and electricity generation'' \15\ and
``consider revising or rescinding Federal actions identified in
subsection (a) of this section consistent with applicable law.'' \16\
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\12\ Executive Order 14261.
\13\ Id. section 2.
\14\ Id. section 1.
\15\ Id. section 6(a).
\16\ Id. section 6(b).
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The EPA has concluded its initial review of GHG emissions standards
for the power sector, as directed by Executive Order 14154, Executive
Order 14219, and Executive Order 14261, and has substantial concerns
about the legal and technical underpinnings of its efforts since 2015
to regulate GHG emissions from fossil fuel-fired power plants. Based on
a reassessment of the legal and technical conclusions in the 2015 NSPS
and CPS, the EPA is proposing to repeal the GHG emissions standards for
new and existing sources in the fossil fuel-fired power plant source
category.
Specifically, the EPA is proposing to conclude that CAA section 111
is best read to require, or at least authorize the EPA to require, an
Administrator's determination that an air pollutant emitted by a source
category causes, or contributes significantly to, air pollution which
may reasonably be anticipated to endanger public health or welfare as a
predicate to establishing emission standards for that pollutant. As
relevant to this action, in the 2015 NSPS the EPA listed all fossil
fuel-fired electric generating units (EGUs)--combining the previously
existing steam generator and combustion turbine categories--as a
distinct source category for purposes of promulgating standards for GHG
emissions. Nevertheless, the EPA asserted in 2015 that it was not
required to make a significant contribution finding for the newly
listed category because sources within the category had previously been
listed under CAA section 111(b)(1).\17\
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\17\ 80 FR 64529-32 (October 23, 2015).
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As such, the EPA proposes to conclude that, at a minimum, the
Administrator must make a significant contribution finding before
issuing GHG emission standards for a new source category even if
covered sources had previously been listed under a distinct category.
The EPA is further proposing to determine, in a change from the
2015 NSPS and CPS, that GHG emissions from fossil fuel-fired power
plants do not contribute significantly to dangerous air pollution as
required for the promulgation of new and existing source standards. The
Agency is proposing that a determination of significant contribution
must consider whether such determination would have an influence or
effect on the targeted air pollution and the public health or welfare
impacts attributed to such air pollution. This inquiry necessarily
entails considering the policies that would inform the resulting
regulation. In this instance, the EPA is proposing to find that any
regulation of GHG emissions from fossil fuel-fired EGUs under CAA
section 111 would not have a significant effect on GHG air pollution
and the public health or welfare impacts attributed to such air
pollution, and that the contribution of this source category is
therefore not significant, because GHG emissions from those sources are
a small and decreasing part of global emissions; cost-effective control
measures are not reasonably available; and because this
Administration's priority is to promote the public health or welfare
through energy dominance and independence secured by using fossil fuels
to generate power. On this basis of proposing to find that GHG
emissions from fossil fuel-fired power plants do not contribute
significantly to dangerous air pollution, the EPA is proposing to
repeal all GHG emissions standards for the power sector under CAA
section 111, specifically the 2015 NSPS, codified in 40 CFR part 60,
subpart TTTT; and the CPS codified in 40 CFR part 60, subparts TTTTa
and UUUUb.
Further, in the course of its review, the EPA reexamined the best
systems of emission reduction (BSERs) for fossil fuel-fired power
plants in the recently promulgated CPS to ensure that all regulatory
requirements related to energy are grounded in clearly applicable
law.\18\ As discussed below, the EPA is proposing, as an alternative to
repealing the GHG emissions standards for new and existing sources in
subparts TTTT, TTTTa, and UUUUb on the basis of a proposed
determination that GHG emissions from fossil fuel-fired power plants do
not significantly contribute to dangerous air pollution, to revise the
BSER determinations in the CPS as follows.
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\18\ Executive Order 14154, section 2(d).
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First, the EPA is proposing to determine that 90 percent CCS is not
the BSER for existing long-term coal-fired steam generating units
because 90 percent CCS has not been adequately demonstrated and its
costs are not reasonable. In a change from the CPS, the EPA proposes to
conclude that experimental projects aiming to achieve 90 percent CCS
were not a sufficient basis to conclude the technology has already been
adequately demonstrated. Furthermore, because it is extremely unlikely
that the infrastructure necessary for CCS can be deployed by the
January 1, 2032 compliance date, the EPA is proposing to determine that
the degree of emission limitation in the CPS for long-term coal-fired
steam generating units is not achievable. The EPA proposes to conclude
that its contrary determination in the CPS was inadequately supported
and exceeded the Agency's authority by mandating a degree of emission
reduction that would not be achievable until sometime in the future
when the relevant technologies are sufficiently available.

[[Page 25756]]

Second, the EPA is proposing to determine that 40 percent natural
gas co-firing is not the BSER for existing medium-term coal-fired steam
generating units because a thorough consideration of the ``energy
requirements'' BSER factor in CAA section 111(a)(1) shows that natural
gas co-firing in a steam generating unit is an inefficient use of
natural gas. Additionally, the EPA is proposing to conclude that 40
percent natural gas co-firing constitutes impermissible generation
shifting under West Virginia, and that the Agency erred in the CPS by
construing West Virginia too narrowly in this respect. Moreover, the
EPA proposes that the associated degree of emission limitation is not
achievable because it is extremely unlikely the necessary pipeline
infrastructure can be deployed in the time provided under the CPS.
Based on these proposed conclusions, the EPA is proposing to repeal the
requirements in the emission guidelines related to existing long-term
and medium-term coal-fired steam generating units.
Third, the EPA is proposing to repeal the requirements in the
emission guidelines related to natural gas-c9and oil-fired steam
generating units because it would be an inefficient use of State
resources to develop, submit, and implement State plans solely for
natural gas-and oil-fired steam generating units, which comprise a
relatively small part of the source category and would result in few or
no emission reductions under the existing emission guidelines.
Consequently, the EPA is proposing to repeal the emission guidelines
for existing fossil fuel-fired steam generating units in their
entirety.
Fourth, because the EPA is proposing that 90 percent CCS is neither
adequately demonstrated nor cost-reasonable, the EPA is proposing to
repeal the CCS-based requirements for coal-fired steam generating units
undertaking a large modification.
Finally, the EPA is proposing that 90 percent CCS is neither
adequately demonstrated nor cost-reasonable for new base load
combustion turbines. Furthermore, because it is extremely unlikely that
the infrastructure necessary for CCS can be deployed by the January 1,
2032 compliance date, the EPA is proposing to determine that the phase
2 standards of performance in the CPS for new base load combustion
turbines are not achievable. The contrary determinations in the CPS
appear to be in error for many of the same reasons that apply to
existing coal-fired steam generating units. Consequently, the EPA is
proposing to repeal the phase 2 CCS-based requirements for new base
load stationary combustion turbines.

II. General Information

A. Action Applicability

The source category that is the subject of this action is composed
of fossil fuel-fired electric utility steam generating units. The 2022
North American Industry Classification System (NAICS) code for the
source category is 221112. This is not intended to be exhaustive but
rather provides a guide for readers regarding the entities that this
proposed action is likely to affect.
The proposed repeal of 40 CFR part 60, subpart UUUUb, once
promulgated, would be applicable to States currently required to
develop and submit State plans pursuant to Clean Air Act (CAA) section
111(d). The proposed repeal of 40 CFR part 60, subpart TTTT, once
promulgated, would be applicable to affected facilities that commenced
construction or modification after January 8, 2014, or reconstruction
after June 18, 2014, and on or before May 23, 2023. The proposed repeal
of 40 CFR part 60, subpart TTTTa, once promulgated, would be applicable
to affected facilities that began construction, reconstruction, or
modification after May 23, 2023. Federal, State, local, and Tribal
government entities that own and/or operate electric generating units
(EGUs) subject to 40 CFR part 60, subparts TTTT and TTTTa would be
affected by this proposed action.
In the alternate proposal, the proposed repeal of 40 CFR part 60,
subpart UUUUb, once promulgated, would be applicable to States
currently required to develop and submit State plans pursuant to CAA
section 111(d). The proposed revisions to 40 CFR part 60, subpart
TTTTa, once promulgated, would be applicable to affected facilities
that began construction, reconstruction, or modification after May 23,
2023. Federal, State, local, and Tribal government entities that own
and/or operate EGUs subject to 40 CFR part 60, subpart TTTTa would be
affected by this proposed action.

B. Where to Get a Copy of This Document and Other Related Information

In addition to being available in the docket, an electronic copy of
this proposed rulemaking is available on the internet at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>. Following signature by the EPA
Administrator, the EPA will post a copy of this proposed action at this
same website. Following publication in the Federal Register, the EPA
will post the Federal Register version of the proposed action and key
technical documents at this same website.
Memoranda showing the edits that would be necessary to incorporate
the changes under the two alternate proposals to 40 CFR part 60,
subparts TTTT, TTTTa, and UUUUb are available in the docket for this
action. Following signature by the EPA Administrator, the EPA also will
post a copy of the documents at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>.

III. Background

A. Statutory Authority

As described in this section of the preamble, CAA section 111
authorizes the EPA to establish emission standards for new stationary
sources and emission guidelines for existing stationary sources under
certain conditions. This provision, along with agencies' authority to
reconsider prior regulations, provides the EPA's statutory authority
for this proposed action.\19\
---------------------------------------------------------------------------

\19\ See Clean Air Council v. Pruitt, 862 F.3d 1, 8 (D.C. Cir.
2017) (``Agencies obviously have broad discretion to reconsider a
regulation at any time.''); see also FDA v. Wages & White Lion
Invs., LLC, 145 S. Ct. 898 (2025); FCC v. Fox TV Stations, Inc., 556
U.S. 502 (2009); Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto.
Ins. Co., 463 U.S. 29 (1983).
---------------------------------------------------------------------------

1. Regulation of Emissions From New Sources
CAA section 111(b)(1)(A) requires the EPA Administrator to
promulgate a list of categories of stationary sources that the
Administrator, ``in his judgment,'' finds ``causes, or contributes
significantly to, air pollution which may reasonably be anticipated to
endanger public health or welfare.'' The EPA has the authority to
define the scope of the source categories, determine the pollutants for
which standards should be developed, and distinguish among classes,
types, and sizes within categories in establishing the standards. Once
the EPA lists a source category that contributes significantly to
dangerous air pollution, the EPA must, under CAA section 111(b)(1)(B),
establish ``standards of performance'' for ``new sources'' in the
source category. These standards are referred to as new source
performance standards, or NSPS. The NSPS are national requirements that
apply directly to the sources subject to them.
Under CAA section 111(a)(1), a ``standard of performance'' is
defined as

[[Page 25757]]

``a standard for emissions of air pollutants'' that is determined in a
specified manner. Under CAA section 111(a)(2), a ``new source'' is
defined as ``any stationary source, the construction or modification of
which is commenced after the publication of regulations (or, if
earlier, proposed regulations) prescribing a standard of performance
under this section, which will be applicable to such source.'' Under
CAA section 111(a)(4), ``modification'' means ``any physical change in,
or change in the method of operation of, a stationary source which
increases the amount of any air pollutant emitted by such source or
which results in the emission of any air pollutant not previously
emitted.'' While this provision treats modified sources as new sources,
EPA regulations also treat a source that undergoes ``reconstruction,''
by substantially replacing its components, as a new source.\20\
---------------------------------------------------------------------------

\20\ 40 CFR 60.15.
---------------------------------------------------------------------------

When the EPA establishes or revises a performance standard, CAA
section 111(a)(1) provides that such standard must ``reflect[ ] the
degree of emission limitation achievable through the application of the
best system of emission reduction which (taking into account the cost
of achieving such reduction and any nonair quality health and
environmental impact and energy requirements) the Administrator
determines has been adequately demonstrated.'' Thus, the term
``standard of performance'' as used in CAA section 111 makes clear that
the EPA must determine both the ``best system of emission reduction . .
. adequately demonstrated'' (BSER) for emissions of the relevant air
pollutants by regulated sources in the source category and the ``degree
of emission limitation achievable through the application of the
[BSER].'' \21\ As explained further below, to determine the BSER, the
EPA first identifies the ``system[s] of emission reduction'' that are
``adequately demonstrated,'' and then determines the ``best'' of those
adequately demonstrated systems, ``taking into account'' factors
including ``cost,'' ``nonair quality health and environmental impact,''
and ``energy requirements.'' The EPA then derives from that system an
``achievable'' ``degree of emission limitation.'' The EPA must then,
under CAA section 111(b)(1)(B), promulgate ``standard[s] for
emissions''--the NSPS--that reflect that level of stringency. The EPA
may determine that different sets of sources have different
characteristics relevant for determining the BSER for emissions of the
relevant air pollutants and may subcategorize sources accordingly.\22\
---------------------------------------------------------------------------

\21\ West Virginia v. EPA, 597 U.S. 697, 709 (2022).
\22\ CAA section 111(b)(2).
---------------------------------------------------------------------------

2. Regulation of Emissions From Existing Sources
The EPA has generally used CAA section 111 to establish standards
for emissions of air pollutants from new sources within a category. In
the rare instances in which the new stationary source standards concern
air pollutants that are not regulated under the National Ambient Air
Quality Standards (NAAQS) program pursuant to CAA sections 108-110, or
the National Emission Standards for Hazardous Air Pollutants (NESHAP)
program pursuant to CAA section 112, the promulgation of standards for
new stationary sources triggers a requirement that the EPA also
promulgate regulations for emissions of that pollutant from existing
sources within the same category under CAA section 111(d).\23\
---------------------------------------------------------------------------

\23\ See CAA section 111(d)(1)(A)(i) and (ii); West Virginia,
597 U.S. at 710 (``[r]eflecting the ancillary nature of Section
111(d), EPA has used it only a handful of times since the enactment
of the statute in 1970.'').
---------------------------------------------------------------------------

CAA section 111(d) establishes a framework of ``cooperative
federalism for the regulation of existing sources.'' \24\ Under CAA
section 111(d)(1)(A)-(B), the EPA must ``prescribe regulations'' that
require ``[e]ach state . . . to submit to [EPA] a plan . . . which
establishes standards of performance for any existing stationary source
for'' the air pollutant at issue, and which ``provides for the
implementation and enforcement of such standards of performance.'' CAA
section 111(a)(6) defines an ``existing source'' as ``any stationary
source other than a new source.''
---------------------------------------------------------------------------

\24\ American Lung Ass'n v. EPA, 985 F.3d 914, 931 (D.C. Cir.
2021) rev'd in part, West Virginia v. EPA, 597 U.S. 697 (2022).
---------------------------------------------------------------------------

As part of carrying out this obligation, the EPA promulgates
``emission guidelines'' for States that identify the BSER and the
degree of emission limitation achievable through the application of the
BSER. Each State must then establish standards of performance for
emissions of the air pollutant at issue by covered sources that reflect
that level of stringency.\25\ States need not compel regulated sources
to adopt the particular components of the BSER itself; rather, States
have discretion in designing the policies and rules their sources will
use to achieve the degree of emission limitation required by the EPA's
emission guidelines. The statute also requires the EPA's regulations to
permit a State, ``in applying a standard of performance to any
particular source,'' to ``take into consideration, among other factors,
the remaining useful life of the existing source to which such standard
applies.'' \26\ Once the EPA approves a State's plan, the provisions in
the plan become federally enforceable against the source, in the same
manner as the provisions of an approved State Implementation Plan (SIP)
under the CAA.\27\ If a State elects not to submit a plan or submits a
plan that the EPA does not find ``satisfactory,'' the EPA is authorized
to promulgate a plan that establishes Federal standards of performance
for the State's existing sources.\28\
---------------------------------------------------------------------------

\25\ As discussed below, CAA section 111(d)(1)(B) provides that,
in certain circumstances, States may apply standards of performance
that are less stringent than the degree of emission limitation the
EPA determines in the emission guidelines.
\26\ CAA section 111(d)(1).
\27\ CAA section 111(d)(2)(B).
\28\ CAA section 111(d)(2)(A).
---------------------------------------------------------------------------

3. Key Elements of Determining a Standard of Performance
Congress first defined the term ``standard of performance'' when
enacting CAA section 111 in the 1970 Clean Air Act, amended the
definition in the Clean Air Act Amendments (CAAA) of 1977, and then
amended the definition again in the 1990 CAAA to largely restore the
definition as it read in the 1970 CAA. The D.C. Circuit has reviewed
CAA section 111 rulemakings on numerous occasions since 1973 and has
developed a body of caselaw that interprets the term.\29\
---------------------------------------------------------------------------

\29\ Portland Cement Ass'n v. Ruckelshaus, 486 F.2d 375 (D.C.
Cir. 1973); Essex Chemical Corp. v. Ruckelshaus, 486 F.2d 427 (D.C.
Cir. 1973); Sierra Club v. Costle, 657 F.2d 298 (D.C. Cir. 1981);
Lignite Energy Council v. EPA, 198 F.3d 930 (D.C. Cir. 1999);
Portland Cement Ass'n v. EPA, 665 F.3d 177 (D.C. Cir. 2011);
American Lung Ass'n v. EPA, 985 F.3d 914 (D.C. Cir. 2021), rev'd in
part, West Virginia v. EPA, 597 U.S. 697 (2022). See also Delaware
v. EPA, No. 13-1093 (D.C. Cir. May 1, 2015).
---------------------------------------------------------------------------

The basis for standards of performance, whether promulgated by the
EPA under CAA section 111(b) or established by the States under CAA
section 111(d) in response to emission guidelines promulgated by the
Agency, is the ``degree of emission limitation'' that is ``achievable''
by sources in the source category by application of the ``best system
of emission reduction'' that the EPA determines is ``adequately
demonstrated'' (BSER). As explained further below in this section, the
D.C. Circuit has explained that systems are not ``adequately
demonstrated'' if they are ``purely theoretical or experimental.'' \30\
The D.C. Circuit has stated that in determining the ``best''

[[Page 25758]]

adequately demonstrated system for the pollutants at issue, the EPA
must also take into account ``the amount of air pollution''
reduced.\31\ The D.C. Circuit has also stated that the EPA may weigh
the various factors identified in the statute and caselaw to determine
the ``best'' system and has emphasized that the EPA has significant
discretion in weighing the factors.\32\
---------------------------------------------------------------------------

\30\ Essex Chem. Corp. v. Ruckelshaus, 486 F.2d 427, 433-34
(D.C. Cir. 1973).
\31\ See Sierra Club v. Costle, 657 F.2d 298, 326 (D.C. Cir.
1981). The D.C. Circuit has stated that EPA must also take into
account ``technological innovation.'' See id. at 347.
\32\ See Lignite Energy Council, 198 F.3d at 933 (``Because
section 111 does not set forth the weight that should be assigned to
each of these factors, we have granted the agency a great degree of
discretion in balancing them.'').
---------------------------------------------------------------------------

After determining the BSER, the EPA sets an achievable emission
limit based on application of the BSER.\33\ For a CAA section 111(b)
rule, the EPA determines the standard of performance that reflects the
achievable emission limit. For a CAA section 111(d) rule, the States
have the obligation of establishing standards of performance for the
affected sources that reflect the degree of emission limitation that
the EPA has determined and provided to States as part of an emission
guideline. In applying these standards to existing sources, States are
permitted to take a source's remaining useful life and other factors
into account.
---------------------------------------------------------------------------

\33\ See, e.g., Oil and Natural Gas Sector: New Source
Performance Standards and National Emission Standards for Hazardous
Air pollutants Reviews (77 FR 49494; August 16, 2012) (describing
the three-step analysis in setting a standard of performance).
---------------------------------------------------------------------------

In identifying ``system[s] of emission reduction, the EPA has
historically followed a ``technology-based approach'' that focuses on
``measures that improve the pollution performance of individual
sources,'' such as ``add-on controls.'' \34\ The EPA departed from its
historical approach in a significant way in the CPP by setting a BSER
in which the ``system'' of emissions reduction involved shifting
electricity generation from one type of fuel to another. In West
Virginia, the Supreme Court applied the major questions doctrine to
hold that the term ``system'' did not provide the requisite clear
authorization to support the CPP's BSER, which the Court described as
``carbon emissions caps based on a generation shifting approach'' \35\
that capped GHG ``emissions at a level that will force a nationwide
transition away from the use of coal to generate electricity[.]'' \36\
The Court explained that the EPA's BSER ``forc[es] a shift throughout
the power grid from one type of energy source to another,'' which
constituted `` `unprecedented power over American industry' '' and was
different in kind from the type of ``system'' of emissions reduction
envisioned by CAA section 111(d).\37\
---------------------------------------------------------------------------

\34\ See West Virginia v. EPA, 597 U.S. at 727 (quoting the
CPP).
\35\ Id. at 732.
\36\ Id. at 734.
\37\ Id. at 728 (citation omitted).
---------------------------------------------------------------------------

To qualify for selection as the BSER, the system of emission
reduction must be ``adequately demonstrated'' as ``the Administrator
determines.'' The plain text of CAA section 111(a)(1), and in
particular the terms ``adequately'' and ``the Administrator
determines,'' confer discretion to the EPA in identifying the
appropriate system, including making scientific and technological
determinations and considering a broad range of policy
considerations.\38\ However, the terms ``adequately'' and
``demonstrated,'' as well as applicable caselaw, make clear that the
EPA may not determine that a ``purely theoretical or experimental''
system is ``adequately demonstrated.'' \39\ Moreover, applicable case
law and the text and structure of CAA section 111, including, in
particular, the eight-year review requirement in CAA section
111(b)(1)(B), place an outer bound on any discretion the EPA may have
to project technological development into the future. The EPA has
historically taken the position that because the regulated sources must
be able to use the system to meet the applicable standards of
performance for the relevant air pollutants by the applicable
compliance date, the system must be available to the sources in time to
achieve the standards. A system that will not be generally available
for use in achieving the standard until technological enhancements have
been developed, which may occur until years into the future, is
therefore not ``adequately demonstrated.'' In the CPS, the EPA departed
from this historical position by selecting a BSER of 90 percent CCS
that might not, if ever, be demonstrated and widely available as a
general matter until sometime in the future. Because the CPP attempted
a different approach to regulating fossil fuel-fired power plants, the
Supreme Court's decision in West Virginia did not address this aspect
of the EPA's approach in the CPS.
---------------------------------------------------------------------------

\38\ Nat'l Asphalt Pavement Ass'n v. Train, 539 F.2d 775, 786
(D.C. Cir. 1976); Essex Chem. Corp. v. Ruckelshaus, 486 F.2d 427,
434 (D.C. Cir. 1973).
\39\ Essex Chem. Corp., 486 F.2d at 433-34; see Portland Cement
Assn. v. Ruckelshaus, 486 F.2d 375, 391-92 (D.C. Cir. 1973) (EPA may
not base an ``adequately demonstrated'' determination on a ``
`crystal ball' inquiry'') (citation omitted).
---------------------------------------------------------------------------

In addition, CAA section 111(a)(1) requires the EPA to account for
``the cost of achieving [the emission] reduction'' in determining the
adequately demonstrated BSER. Although the CAA does not describe how
the EPA is to account for costs to affected sources, the D.C. Circuit
has formulated the cost standard in various ways, including stating
that the EPA may not adopt a standard the cost of which would be
``excessive'' or ``unreasonable.'' \40\ The EPA has discretion in
considering cost under section 111(a), both in determining the
appropriate level of costs and in balancing costs with other BSER
factors.\41\ The D.C. Circuit has repeatedly upheld the EPA's
consideration of cost in reviewing standards of performance.\42\
---------------------------------------------------------------------------

\40\ Sierra Club v. Costle, 657 F.2d 298, 343 (D.C. Cir. 1981).
See 79 FR 1430, 1464 (January 8, 2014); Lignite Energy Council, 198
F.3d at 933 (costs may not be ``exorbitant''); Portland Cement Ass'n
v. EPA, 513 F.2d 506, 508 (D.C. Cir. 1975) (costs may not be
``greater than the industry could bear and survive'').
\41\ Sierra Club v. Costle, 657 F.2d 298, 343 (D.C. Cir. 1981).
\42\ See Essex Chemical Corp. v. Ruckelshaus, 486 F.2d 427, 440
(D.C. Cir. 1973); Portland Cement Ass'n v. Ruckelshaus, 486 F.2d
375, 387-88 (D.C. Cir. 1973); Sierra Club v. Costle, 657 F.2d 298,
313 (D.C. Cir. 1981).
---------------------------------------------------------------------------

Under CAA section 111(a)(1), the EPA is required to take into
account ``any nonair quality health and environmental impact and energy
requirements'' in determining the BSER. Nonair quality health and
environmental impacts may include the impacts of the disposal of
byproducts of the air pollution controls, or requirements of the air
pollution control equipment for water.\43\ Energy requirements may
include the impact, if any, of the air pollution controls on the
source's own energy needs.\44\ In addition, based on the D.C. Circuit's
interpretations of CAA section 111, energy requirements may also
include the impact, if any, of the air pollution controls on the energy
supply for a particular area or nationwide.\45\ In addition, the EPA
has considered under this statutory factor whether possible controls
would create risks to the reliability of the electricity system.
---------------------------------------------------------------------------

\43\ Portland Cement Ass'n v. Ruckelshaus, 465 F.2d 375, 387-88
(D.C. Cir. 1973), cert. denied, 417 U.S. 921 (1974).
\44\ For details on the modeled energy requirements associated
with CCS, please see section 6.4 of the RIA for this rule.
\45\ See Sierra Club v. Costle, 657 F.2d at 327-28 (quoting 44
FR 33583-84; June 11, 1979); 79 FR 1430, 1465 (January 8, 2014)
(citing Sierra Club v. Costle, 657 F.2d at 351).
---------------------------------------------------------------------------

The D.C. Circuit has also held that the term ``best'' authorizes
the EPA to consider factors in addition to the ones enumerated in CAA
section 111(a)(1) that further the purpose of the statute. In
particular, consistent with the plain

[[Page 25759]]

language and the purpose of CAA section 111(a)(1), which requires the
EPA to determine the ``best system of emission reduction'' (emphasis
added), the EPA must consider the quantity of emissions at issue.\46\
In determining which adequately demonstrated system of emission
reduction is the ``best,'' the EPA has broad discretion. In Sierra Club
v. Costle, 657 F.2d 298 (D.C. Cir. 1981), the court explained that
``section 111(a) explicitly instructs the EPA to balance multiple
concerns when promulgating a NSPS'' \47\ and emphasized that ``[t]he
text gives the EPA broad discretion to weigh different factors in
setting the standard,'' including the amount of emission reductions,
the cost of the controls, and the non-air quality environmental impacts
and energy requirements.\48\
---------------------------------------------------------------------------

\46\ Sierra Club v. Costle, 657 F.2d 298, 326 (D.C. Cir. 1981).
The D.C. Circuit has also held that Congress intended for CAA
section 111 to create incentives for new technology and therefore
that the EPA is required to consider technological innovation as one
of the factors in determining the ``best system of emission
reduction.'' See id. at 346-47.
\47\ See AEP v. Connecticut, 564 U.S. 410, 427 (2011); Sierra
Club v. Costle, 657 F.2d at 319.
\48\ Sierra Club v. Costle, 657 F.2d at 321; New York v. Reilly,
969 F.2d at 1150.
---------------------------------------------------------------------------

A standard of performance is ``achievable'' if a technology can
reasonably be projected to be available to an individual source at the
time it is constructed so as to allow it to meet the standard.\49\
Although the courts have established this approach for achievability in
cases concerning CAA section 111(b) new source standards of
performance, a generally comparable approach should apply under CAA
section 111(d), although the BSER may differ in some cases as between
new and existing sources due to, for example, higher costs of
retrofit.\50\ For existing sources, CAA section 111(d)(1) requires the
EPA to establish regulations for State plans that, in turn, must
include ``standards of performance.'' As the Supreme Court has
recognized, this provision requires the EPA to promulgate emission
guidelines that determine the BSER for a source category and then
identify the degree of emission limitation achievable by application of
the BSER.\51\
---------------------------------------------------------------------------

\49\ Sierra Club v. Costle, 657 F.2d 298, 364, n.276 (D.C. Cir.
1981).
\50\ 40 FR 53340 (November 17, 1975).
\51\ See West Virginia v. EPA, 597 U.S. at 710; 40 CFR 60.21(e),
60.21a(e) (definition of ``emission guideline'' includes provision
of the degree of emission limitation achievable through the
application of the BSER as determined by the Administrator).
---------------------------------------------------------------------------

4. EPA Promulgation of Emission Guidelines for States To Establish
Standards of Performance
CAA section 111(d)(1) directs the EPA to promulgate regulations
establishing a procedure similar to that provided by CAA section 110
under which States submit State plans that establish and implement
``standards of performance'' for emissions of certain air pollutants
from existing sources which, if they were new sources, would be
regulated under CAA section 111(b). The term ``standard of
performance'' is defined under CAA section 111(a)(1), as quoted earlier
in this preamble. Thus, CAA sections 111(a)(1) and (d)(1) collectively
require the EPA to determine the degree of emission limitation
achievable through application of the BSER to existing sources and to
promulgate regulations under which States establish standards of
performance reflecting that degree of emission limitation. The EPA
addresses both responsibilities through its emission guidelines, as
well as through its general implementing regulations for CAA section
111(d).
Following the EPA's promulgation of emission guidelines, each State
must establish standards of performance with respect to the relevant
air pollutants for its existing sources, which the EPA's regulations
call ``designated facilities.'' \52\ Such standards of performance must
reflect the degree of emission limitation achievable through
application of the best system of emission reduction for the relevant
pollutants as determined by the EPA, which the Agency may express as a
presumptive standard of performance in the applicable emission
guidelines.
---------------------------------------------------------------------------

\52\ 40 CFR 60.21a(b), 60.24a(b).
---------------------------------------------------------------------------

While the standards of performance that States establish in their
plans must generally be no less stringent than the degree of emission
limitation determined by the EPA,\53\ CAA section 111(d)(1) also
requires that the EPA's regulations ``permit the State in applying a
standard of performance to any particular source . . . to take into
consideration, among other factors, the remaining useful life of the
existing source to which such standard applies.'' The EPA's
implementing regulations for CAA section 111(d) provide a framework for
States' consideration of a facility's remaining useful life and other
factors (referred to as ``RULOF'') when applying a standard of
performance to a particular source. The State must include the
standards of performance in the plan submitted to the EPA for review
according to the procedures established in the Agency's implementing
regulations for CAA section 111(d).\54\ Under CAA section 111(d)(2)(A),
the EPA must approve State plans that are determined to be
``satisfactory.'' CAA section 111(d)(2)(A) also gives the Agency ``the
same authority'' as that conferred under CAA section 110(c) to
promulgate a Federal plan in cases where a State fails to submit a
satisfactory plan.
---------------------------------------------------------------------------

\53\ 40 CFR 60.24(c), 60.24a(c).
\54\ See generally 40 CFR 60.23a-60.28a.
---------------------------------------------------------------------------

B. EPA Regulation of GHG Emissions Under CAA Section 111

This section discusses the EPA's efforts since 2015 to regulate GHG
emissions under CAA section 111, including the regulation of electric
generating units (EGUs) and the associated caselaw, insofar as it is
relevant to this action. This background is relevant because it
explains the current rules that are directly affected by this proposed
action, as well as the EPA's asserted legal basis for regulating GHG
emissions under CAA section 111, which is implicated by this proposed
action.
The EPA has regulated air pollutants from power plants under CAA
section 111 since 1971, when the Agency listed ``fossil fuel-fired
steam generators of more than 250 million Btu per hour heat input'' as
a source category under CAA section 111(b)(1)(A) \55\ and subsequently
promulgated NSPS for certain air pollutants.\56\ In 1977, the EPA
listed fossil fuel-fired stationary combustion turbines in a category
under CAA section 111(b)(1)(A) \57\ and subsequently promulgated NSPS
for certain air pollutants.\58\ However, the EPA did not invoke CAA
section 111 to regulate GHG emissions from power plants until 2015,
when it promulgated the 2015 NSPS, which addressed GHG emissions, as
measured by the equivalent of CO<INF>2</INF> emissions, from new fossil
fuel-fired EGUs under CAA section 111(b),\59\ and the CPP, which set
emission guidelines directing States to regulate GHG emissions, as
measured by the equivalent of CO<INF>2</INF> emissions, from existing
EGUs under CAA section 111(d).\60\
---------------------------------------------------------------------------

\55\ 36 FR 5931 (March 31, 1971) (listing).
\56\ See, e.g., 36 FR 24876 (December 23, 1971); 40 CFR 60
subpart Da.
\57\ 42 FR 53657 (October 3, 1977) (listing ``stationary gas
turbines'').
\58\ See, e.g., 44 FR 62792 (September 10, 1979); 40 CFR 60
subpart KKKK.
\59\ ``Standards of Performance for Greenhouse Gas Emissions
From New, Modified, and Reconstructed Stationary Sources: Electric
Utility Generating Units; Final Rule,'' 80 FR 64510 (October 23,
2015).
\60\ ``Carbon Pollution Emission Guidelines for Existing
Stationary Sources: Electric Utility Generating Units; Final Rule,''
80 FR 64662 (October 23, 2015).

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[[Page 25760]]

In the 2015 NSPS, the Agency asserted that it was not required to
make a finding of significant contribution under CAA section 111 before
regulating GHG emissions. The EPA explained the legal basis for this
interpretation as follows: The EPA noted that it had listed fossil
fuel-fired steam generators as a source category in 1971 and combustion
turbines as a source category in 1979, in each case on the basis of the
sources' emissions of non-GHG air pollutants, and the EPA acknowledged
that it had not considered GHG emissions at the time of those listings.
Even so, in the 2015 NSPS, the EPA stated that it interpreted CAA
section 111 to provide that once the EPA had listed a source category
once, it was authorized to promulgate NSPS for any air pollutant from a
source listed in that source category, so long as it had a rational
basis for doing so.\61\
---------------------------------------------------------------------------

\61\ 80 FR 64529-31 (October 23, 2015).
---------------------------------------------------------------------------

The EPA received comments on the 2015 NSPS stating that CAA section
111 did not authorize regulation of GHGs from EGUs until the Agency
first makes a finding that emissions of GHGs from EGUs contribute
significantly to air pollution which may reasonably be anticipated to
endanger public health or welfare. Such a finding is shorthanded here
as a pollutant-specific significant contribution finding, and such air
pollution is shorthanded here as dangerous air pollution. The EPA
disagreed with those comments. The EPA explained that CAA section
111(b)(1)(A), 111(b)(1)(B), and 111(a)(1), read together, authorize the
EPA to regulate an air pollutant from a listed source category, subject
to the standards of rationality under CAA section 307(d)(9)(A),\62\ and
do not require the EPA to make an additional determination, as a
predicate for regulation, that the air pollutant contributes
significantly to dangerous air pollution.
---------------------------------------------------------------------------

\62\ Promulgation of NSPS under CAA section 111(b)(1)(B) is
subject to the requirements of CAA section 307(d), under CAA section
307(d)(1)(C).
---------------------------------------------------------------------------

In the 2015 NSPS, the EPA took the additional step of ``combining
the steam generator and combustion turbine categories into a single
category of fossil fuel-fired electricity generating units for purposes
of promulgating standards of performance for GHG emissions.'' \63\ The
EPA explained that ``[c]ombining the two categories is reasonable
because they both provide the same product: Electricity services,'' and
that doing so was consistent with the Agency's decision to combine the
categories ``in the CAA section 111(d) rule for existing sources that
accompanies this rule,'' i.e., in the CPP.\64\ The EPA added that it
did not consider this combining of the source categories to constitute
a new listing of the resultant source category.\65\
---------------------------------------------------------------------------

\63\ 80 FR 64531 (October 23, 2015).
\64\ Id.
\65\ Id. at 64532.
---------------------------------------------------------------------------

In the 2015 NSPS, notwithstanding its position that CAA section 111
does not require a pollutant-specific significant contribution finding
for GHG emissions, the EPA added, in the alternative, that it was
making that finding for GHG emissions from EGUs. The EPA explained that
it based this finding on the volume of GHG emissions emitted by EGUs,
coupled with the EPA's 2009 determination that GHG air pollution
endangered public health or welfare and subsequently available
information.\66\
---------------------------------------------------------------------------

\66\ Id. at 64530-31.
---------------------------------------------------------------------------

The 2015 NSPS promulgated standards of performance to limit
emissions of GHGs, manifested as CO<INF>2</INF>, from newly
constructed, modified, and reconstructed fossil fuel-fired electric
utility steam generating units, i.e., utility boilers and integrated
gasification combined cycle (IGCC) combustion turbines and newly
constructed and reconstructed stationary combustion turbines. These
final standards are codified in 40 CFR part 60, subpart TTTT. In
promulgating the 2015 NSPS for newly constructed fossil fuel-fired
steam generating units, the EPA determined the BSER to be a new, highly
efficient, supercritical pulverized coal (SCPC) EGU that implements
post-combustion partial CCS technology.
The 2015 NSPS also included standards of performance for steam
generating units that undergo a ``reconstruction'' as well as units
that implement ``large modifications'' (i.e., modifications resulting
in an increase in hourly CO<INF>2</INF> emissions of more than 10
percent). The 2015 NSPS did not establish standards of performance for
steam generating units that undertake ``small modifications'' (i.e.,
modifications resulting in an increase in hourly CO<INF>2</INF>
emissions of less than or equal to 10 percent), due to the limited
information available to inform the analysis of a BSER and
corresponding standard of performance.
The 2015 NSPS also finalized standards of performance for newly
constructed and reconstructed natural gas-fired stationary combustion
turbines that operate at base load and non-base load, based on
efficient natural gas combined cycle (NGCC) technology or the use of
lower-emitting fuels (referred to as clean fuels in the 2015 NSPS) as
the BSER. The EPA did not promulgate final standards of performance for
modified stationary combustion turbines under CAA section 111(d) due to
lack of information.
The 2015 NSPS was challenged in the D.C. Circuit, but the case has
been held in abeyance in light of the EPA's subsequent rulemakings.
In the CPP--promulgated at the same time that the EPA promulgated
the 2015 NSPS--the EPA interpreted CAA section 111(d) to require the
Agency to regulate GHG emissions from existing sources in the newly
combined source category because the EPA had promulgated NSPS for GHG
emissions from new sources in that source category.\67\ The EPA
determined that the BSER for existing fossil fuel-fired EGUs consisted
primarily of generation shifting measures, as described earlier in this
preamble.\68\ The Supreme Court stayed the CPP pending review in
February 2016,\69\ and the D.C. Circuit held the litigation in abeyance
and ultimately dismissed it in light of subsequent developments.\70\
---------------------------------------------------------------------------

\67\ 80 FR 64702 (October 23, 2015).
\68\ Id. at 64728-29.
\69\ West Virginia v. EPA, 577 U.S. 1126 (2016).
\70\ American Lung Ass'n, 985 F.3d at 937.
---------------------------------------------------------------------------

In 2018, the EPA proposed to revise the NSPS for new, modified, and
reconstructed fossil fuel-fired steam generating units and IGCC units
(2018 NSPS Proposal).\71\ The EPA proposed to revise the NSPS for newly
constructed units, based on a revised BSER of a highly efficient EGU
without partial CCS. The EPA also proposed to revise the NSPS for
modified and reconstructed units. As explained later in this section,
the 2018 NSPS Proposal was never finalized and, as noted below, was
rescinded as part of the Carbon Pollution Standards.
---------------------------------------------------------------------------

\71\ ``Review of Standards of Performance for Greenhouse Gas
Emissions From New, Modified, and Reconstructed Stationary Sources:
Electric Utility Generating Units; Proposed Rule,'' 83 FR 65424
(December 20, 2018).
---------------------------------------------------------------------------

In 2019, the EPA repealed the CPP and replaced it with the
Affordable Clean Energy (ACE) Rule.\72\ In contrast to the CPP, the EPA
determined in the ACE Rule that under the provisions of CAA section
111, a system of emission reduction is limited to measures that can be
applied to at the level of the individual source and cannot include
generation shifting measures.\73\ Instead, the EPA determined the BSER
for existing coal-fired EGUs to be heat rate improvements alone.
Specifically, the

[[Page 25761]]

EPA listed various technologies that could improve heat rate and
identified the ``degree of emission limitation achievable'' by
providing ranges of expected emission reductions associated with each
of the technologies.\74\ The EPA also explained that it was not
determining CCS to be the BSER in part because of its unreasonable
expense, and was not determining natural gas co-firing to be the BSER
because it was an inefficient use of natural gas.\75\
---------------------------------------------------------------------------

\72\ ``Repeal of the Clean Power Plan; Emission Guidelines for
Greenhouse Gas Emissions From Existing Electric Utility Generating
Units; Revisions to Emission Guidelines Implementing Regulations;
Final Rule,'' 84 FR 32520 (July 8, 2019).
\73\ 84 FR 32523-24 (July 8, 2019).
\74\ Id. at 32535-38.
\75\ Id. at 32545.
---------------------------------------------------------------------------

In 2021, the D.C. Circuit vacated the ACE Rule, including the CPP
Repeal.\76\ The court held, among other things, that CAA section 111
did not limit the EPA, in determining the BSER, to measures applied at
and to an individual source, and that CAA section 111 did authorize the
EPA to determine generation shifting as the BSER. The D.C. Circuit
concluded that as a result, both the CPP Repeal and the ACE Rule should
be vacated.\77\ The court did not address most other challenges to the
ACE Rule, including the arguments concerning the heat rate improvement
BSER.
---------------------------------------------------------------------------

\76\ American Lung Ass'n v. EPA, 985 F.3d 914 (D.C. Cir. 2021).
\77\ 985 F.3d at 995.
---------------------------------------------------------------------------

Several petitioners argued that the ACE Rule was invalid on the
grounds that the EPA had predicated regulation of GHG emissions from
existing EGUs on the new source GHG emissions standards in the 2015
NSPS, and that those standards were flawed because CAA section 111
required them to be predicated on a pollutant-specific significant
contribution finding with identified standards or criteria for
determining significance. The D.C. Circuit held that it did not need to
decide whether CAA section 111 requires a pollutant-specific
significant contribution finding for GHG emissions from EGUs as a
predicate for CAA section 111 regulation because the EPA had made such
a finding in the alternative. The court rejected the Petitioners'
argument that the significant contribution finding was flawed due to
lack of identified criteria for significance and explained that the
magnitude of GHG emissions from EGUs supported the significance finding
without identified criteria for significance.\78\
---------------------------------------------------------------------------

\78\ Id. at 974-77.
---------------------------------------------------------------------------

In 2022, the Supreme Court in West Virginia reversed the D.C.
Circuit's decision to vacate the ACE Rule's embedded repeal of the
CPP.\79\ As noted above, the Court concluded that the CPP's BSER of
``generation shifting'' implicated the major questions doctrine and
exceeded the EPA's statutory authority because CAA section 111 did not
clearly authorize the Agency to cap GHG emissions at a level that
forces a nationwide transition away from using coal to generate
electricity.\80\
---------------------------------------------------------------------------

\79\ West Virginia v. EPA, 597 U.S. 697 (2022).
\80\ Id. at 734-35.
---------------------------------------------------------------------------

On October 27, 2022, the D.C. Circuit responded to the Supreme
Court's decision by taking steps to, among other things, ensure that
the CPP remained repealed but that the ACE Rule came back into effect.
Following a change in administration, the EPA informed the court that
it intended to replace the ACE Rule. Accordingly, the court stayed
further proceedings with respect to the ACE Rule, including the various
challenges to the heat rate improvement BSER.\81\
---------------------------------------------------------------------------

\81\ American Lung Ass'n v. EPA, No. 19-1140, Order (October 27,
2022).
---------------------------------------------------------------------------

C. Carbon Pollution Standards

On May 9, 2024, the EPA promulgated the Carbon Pollution Standards
(CPS), which consisted of several rules and actions.\82\ The first
action was the repeal of the ACE Rule. The EPA explained, among other
things, that the suite of heat rate improvements that was identified in
the ACE Rule as the BSER is not an appropriate BSER for existing coal-
fired EGUs.\83\
---------------------------------------------------------------------------

\82\ ``New Source Performance Standards for Greenhouse Gas
Emissions From New, Modified, and Reconstructed Fossil Fuel-Fired
Electric Generating Units; Emission Guidelines for Greenhouse Gas
Emissions From Existing Fossil Fuel-Fired Electric Generating Units;
and Repeal of the Affordable Clean Energy Rule; Final Rule'', 89 FR
39798 (May 9, 2024).
\83\ In the CPS, the EPA also withdrew the separate proposed
revisions to the New Source Review (NSR) regulations that were
included the ACE Rule proposal (83 FR 44773-83, August 31, 2018).
---------------------------------------------------------------------------

In addition, the CPS included emission guidelines for GHG emissions
from existing fossil fuel-fired steam generating units, which include
the separate subcategories of coal-fired units, oil-fired units, and
gas-fired units.\84\ For long-term coal-fired units, the EPA finalized
90 percent CCS as the BSER, with a presumptive standard of an 88.4
percent reduction in annual emission rate and a compliance deadline of
January 1, 2032. The EPA asserted that 90 percent CCS is an adequately
demonstrated technology that achieves significant emissions reduction
and is cost-reasonable, taking into account the supposedly declining
costs of the technology and the IRC section 45Q tax credit available
for a certain number of years to generating sources that use CCS
technology. In recognition of the significant capital expenditures
involved in deploying CCS technology and the fact that a number of
regulated units had announced retirement dates, the EPA finalized a
separate subcategory for existing coal-fired units that demonstrate
that they plan to permanently cease operation before January 1, 2039.
For this subcategory, the BSER is co-firing with natural gas, at a
level of 40 percent of the unit's annual heat input, the presumptive
standard is a 16 percent reduction in annual emission rate, and the
compliance deadline is January 1, 2030. In addition, the EPA exempted
existing coal-fired units demonstrating that they plan to permanently
cease operation prior to January 1, 2032. The EPA determined that these
controls were cost-effective primarily by reference to two metrics it
used in prior rulemakings. The first determines the cost in dollars for
each ton or other quantity of the regulated air pollutant removed
through the system of emission reduction. The second, which the EPA
particularly relied on in rules for the electric power sector,
determines the dollar increase in the cost of a MWh of electricity
generated by the affected sources due to the emission controls, which
shows the cost of controls relative to the output of electricity.\85\
---------------------------------------------------------------------------

\84\ Although, in the proposed CPS, the EPA proposed emission
guidelines for GHG emissions from existing fossil fuel-fired
combustion turbines, it did not finalize those guidelines.
\85\ 89 FR 39882 (May 9, 2024).
---------------------------------------------------------------------------

For existing gas- and oil-fired steam generating units, the EPA
further subcategorized them into base load (units with annual capacity
factors greater than or equal to 45 percent), intermediate load (units
with annual capacity factors greater than or equal to 8 percent and
less than 45 percent), and low load (units with annual capacity factors
less than 8 percent) subcategories. The EPA finalized routine methods
of operation and maintenance as the BSER for base load and intermediate
load units, with presumptive standards for base load units of 1,400 lb
CO<INF>2</INF>/MWh-gross, and for intermediate load units of 1,600 lb
CO<INF>2</INF>/MWh-gross. For low load units, the EPA finalized a
uniform fuels BSER and a presumptive input-based standard of 170 lb
CO<INF>2</INF>/MMBtu for oil-fired sources and a presumptive standard
of 130 lb CO<INF>2</INF>/MMBtu for natural gas-fired sources.
The CPS also includes standards of performance for new and
reconstructed combustion turbines, organized into three subcategories:
base load, intermediate load, and low load. For base load turbines, the
standard consists of two components to be implemented in two phases.
The first component is

[[Page 25762]]

based on a BSER of highly efficient generation, which is determined
according to the emission rates that the best performing units are
achieving, and compliance was required upon the effective date of the
CPS. The second component is based on a BSER of 90 percent CCS, and
compliance is required on January 1, 2032. For intermediate load
turbines, the EPA determined the BSER to be highly efficient simple-
cycle generation; and for low load combustion turbines, the EPA
determined the BSER to be the use of lower-emitting fuels.
In addition, the EPA revised the standards of performance for coal-
fired steam generating units that undertake a large modification (i.e.,
a modification that increases its hourly emission rate by more than 10
percent) to be based on the BSER of 90 percent CCS. Finally, the EPA
withdrew the 2018 proposed amendments \86\ to the NSPS for GHG
emissions from coal-fired EGUs.
---------------------------------------------------------------------------

\86\ 83 FR 65424 (December 20, 2018).
---------------------------------------------------------------------------

Following promulgation of the CPS, 27 States and numerous industry
groups filed petitions for review in the D.C. Circuit, and many
subsequently filed motions to stay the rule. The D.C. Circuit denied
the stay motions on July 19, 2024,\87\ and the Supreme Court denied
them on October 16, 2024.\88\ However, Justice Thomas would have
granted a stay and Justice Kavanaugh, joined by Justice Gorsuch, wrote
that ``the applicants have shown a strong likelihood of success on the
merits as to at least some of their challenges to the [EPA's] rule.''
\89\ The merits case was briefed, and oral argument was held before the
D.C. Circuit on December 6, 2024. Following a change in administration,
the D.C. Circuit agreed to hold the case in abeyance pending further
actions by the Agency.
---------------------------------------------------------------------------

\87\ West Virginia v. EPA, No. 2420 Order, 2024 U.S. App. LEXIS
17856 (July 19, 2024).
\88\ West Virginia v. EPA, 145 S. Ct. 2 (2024).
\89\ Id.
---------------------------------------------------------------------------

IV. Summary and Rationale of Primary Proposal

A. Summary of Proposed Action

The EPA is proposing that CAA section 111 is best read to require,
or at least authorize the EPA to require, an Administrator's
determination that an air pollutant emitted by a source category
causes, or contributes significantly to, dangerous air pollution as a
predicate to establishing emissions standards for that pollutant. In
the context of the 2015 NSPS and CPS, the mandatory form of this
interpretation would require the EPA to determine that GHG emissions
from EGUs contribute significantly to dangerous air pollution before
regulating GHG emissions from fossil fuel-fired EGUs. This proposal
would reverse the EPA's most recent interpretation on that point, which
asserted that the EPA could regulate GHG emissions from existing source
categories of fossil fuel-fired EGUs and, in fact, combine those source
categories into a single source category and regulate it solely on the
basis of GHG emissions, without making the significant contribution
finding for GHG emissions.
The EPA is further proposing to determine, as an exercise of the
Administrator's judgement and based on the available evidence, that GHG
emissions from fossil fuel-fired EGUs do not contribute significantly
to dangerous air pollution for purposes of CAA section 111(b). This
proposal would rescind the EPA's prior, alternative determination to
the contrary in the 2015 NSPS as carried over into the CPS. On this
basis, the EPA is proposing to repeal all GHG emissions standards and
emission guidelines for the power sector, specifically the 2015 NSPS
codified in 40 CFR part 60, subpart TTTT (80 FR 64510; October 23,
2015), and the CPS codified in 40 CFR part 60, subparts TTTTa and UUUUb
(89 FR 39798; May 9, 2024).
As explained below, the EPA seeks comment on its proposed
interpretation of CAA section 111 to require, or at least authorize the
EPA to require, an Administrator's determination of significant
contribution for the air pollutant under consideration. Separately, the
EPA seeks comment on whether CAA section 111 requires a significant
contribution finding for the fossil fuel-fired EGU source category
first created in the 2015 NSPS. Finally, the EPA seeks comment on its
interpretation of what it means for a source category to contribute
``significantly'' to dangerous air pollution, and on the proposed
Administrator's determination that GHG emissions from sources within
the fossil fuel-fired EGU source category do not contribute
significantly to such pollution. The EPA encourages commenters to
present any other relevant arguments and information, including with
respect to legitimate reliance interests on the 2015 NSPS and CPS.

B. Significant Contribution Finding for EGUs

In this section, the EPA first explains the legal bases for its
proposal that CAA section 111 requires, or at least authorizes the EPA
to require, that the EPA determine that GHG from the fossil fuel-fired
EGU source category contribute significantly to dangerous air pollution
as a predicate for regulation. The EPA then explains its reasons for
proposing to determine that GHG emissions from this source category do
not contribute significantly to dangerous air pollution within the
meaning of CAA section 111.
1. Requirement for Significant Contribution Determination
a. Requirement for a Significant Contribution Determination Concerning
GHG Emissions From the EGU Source Category
As noted in section III.B above, prior to the 2015 NSPS, the EPA
had listed two separate source categories of electricity generating
sources--steam generators and combustion turbines--under CAA section
111(b)(1)(A), which requires the EPA to list a source category for
regulation if it determines that the source category ``causes, or
contributes significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' The EPA had
previously promulgated NSPS only for different, non-GHG air pollutants
from those source categories. In the 2015 NSPS, the EPA combined the
two source categories into a single source category--``fossil fuel-
fired electricity generating units''--solely for the purpose of
regulating GHG emissions, but did not otherwise revise the prior source
category listings or promulgated NSPS. The EPA stated that combining
the source categories in this fashion did not constitute a listing of a
new source category under CAA section 111(b)(1)(A),\90\ and interpreted
CAA section 111 to authorize it to regulate GHG emissions from the new,
combined source category as long as it had a rational basis for doing
so. The EPA went on to determine that, in light of the amount of GHG
emissions from the source category relative to other source categories,
the EPA had a rational basis to regulate GHG emissions. The EPA added
that even if it were required to determine that GHG emissions from the
source category contribute significantly to dangerous air pollution as
a predicate

[[Page 25763]]

for regulation, it was making that determination in the alternative,
and cited the same facts it relied on for the rational basis
determination.
---------------------------------------------------------------------------

\90\ Specifically, the EPA stated, ``Because these two source
categories are pre-existing listed source categories and the EPA
will not be subjecting any additional sources in the categories to
CAA regulation for the first time, the combination of these two
categories is not considered a new source category subject to the
listing requirements of CAA section 111(b)(1)(A). As a result, this
final rule does not list a new category under CAA section
111(a)(1)(A), nor does this final rule revise either of the two
source categories. Thus, the EPA is not required to make a new
endangerment and contribution finding for the combination of the two
categories. . . .'' 80 FR 64532 (October 23, 2015).
---------------------------------------------------------------------------

Notwithstanding the EPA's statements in the 2015 NSPS, its action
in combining the two source categories for purpose of regulating GHG
emissions had the effect of listing a new combined source category
under CAA section 111(b)(1)(A) based solely on the emission of GHGs by
sources within the new category. In light of the CAA section
111(b)(1)(A) requirement that a source category may be listed only if
``it causes, or contributes significantly to, [dangerous] air
pollution,'' the EPA proposes that the creation of a single source
category solely on the basis of GHG emissions is justifiable only if
the GHG emissions ``cause[], or contribute[] significantly to,
[dangerous] air pollution.'' \91\ In a change from its position in the
2015 NSPS, the EPA proposes to conclude that a new source category,
whether consisting of previously unregulated sources or sources
previously regulated under distinct categories, cannot be listed
without the Administrator's determination of significant contribution
required by the statute. Relatedly, the EPA proposes to conclude that
Congress required the EPA to identify more than a rational basis for
regulating emissions from a source category, as evidenced by the
statute's use of ``cause, or contributes significantly'' in relation to
``air pollution which may reasonably be anticipated to endanger public
health or welfare.''
---------------------------------------------------------------------------

\91\ Note that the reference in the CAA section 111(b)(1)(A)
endangerment provision to ``causes'' generally refers to emissions
that are the sole part of the air pollution problem. The EPA has
defined the same term in similar CAA endangerment provisions the
same way. See ``Endangerment and Cause or Contribute Findings for
Greenhouse Gases Under Section 202(a) of the Clean Air Act,'' 74 FR
66506 (December 15, 2009) (interpreting the CAA section 202(a)(1)
endangerment provision as follows: ``In addition, by instructing the
Administrator to consider whether emissions of an air pollutant
cause or contribute to air pollution, the statute is clear that she
need not find that emissions from any one sector or group of sources
are the sole or even the major part of an air pollution problem. The
use of the term `contribute' clearly indicates a lower threshold
than the sole or major cause.'').
---------------------------------------------------------------------------

In the 2015 NSPS, the EPA purported, in the alternative, to make a
significant contribution finding for GHG emissions from EGUs within the
newly established source category. Under the interpretation the EPA is
proposing in this action, this finding was, and is, a necessary
predicate for regulation. In a change from this alternative finding,
and as discussed later in this section, the EPA is now proposing to
determine that GHG emissions from fossil fuel-fired EGUs do not
contribute significantly to dangerous air pollution within the meaning
of CAA section 111. This determination would preclude the EPA from
regulating GHG emissions from fossil fuel-fired EGUs. The EPA proposes
to conclude that such a determination would be consistent with
agencies' authority to reconsider prior decisions,\92\ and with the
relevant statutory text. In particular, CAA section 111(b)(1)(A)
instructs the Administrator to use ``his judgment'' in making
significant contribution findings, and further authorizes the EPA to
``from time to time . . . revise'' the list of source categories
regulated under CAA section 111. In effect, the EPA is proposing to
revise the list of source categories to remove the combined source
category of fossil fuel-fired EGUs that emit GHGs that was created for
the first time in the 2015 NSPS, while retaining pre-existing source
categories for EGUs and related regulations for different, non-GHG
pollutants.
---------------------------------------------------------------------------

\92\ See FDA v. Wages & White Lion Invs., LLC, 145 S. Ct. 898
(2025); FCC v. Fox TV Stations, Inc., 556 U.S. 502 (2009); Motor
Vehicle Mfrs. Ass'n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29
(1983); Clean Air Council v. Pruitt, 862 F.3d 1, 8 (D.C. Cir. 2017).
---------------------------------------------------------------------------

b. Requirement for Pollutant-Specific Significant Contribution Finding
As noted in section III.B of this preamble, in the 2015 NSPS, the
EPA justified its regulation of GHG emissions from fossil fuel-fired
steam generators and combustion turbines primarily by interpretating
CAA section 111 to authorize the regulation of air pollutants emitted
by sources within an existing source category without an
Administrator's determination of significant contribution to dangerous
air pollution, so long as the EPA had a rational basis for such
regulation. In this action, the EPA proposes to interpret CAA section
111 as requiring the EPA to determine that emissions of an air
pollutant from an existing source category significantly contribute to
dangerous air pollution before imposing standards of performance for
that air pollutant on the relevant source categories.
The EPA proposes to conclude that CAA section 111 is best read to
require an Administrator's determination as a predicate for regulating
emissions of an air pollutant by an existing source category. Once the
EPA lists a source category for regulation under CAA section
111(b)(1)(A) on grounds that the EPA determines that ``it causes, or
contributes significantly to, [dangerous] air pollution,'' the EPA is
required, under CAA section 111(b)(1)(B), to promulgate ``standards of
performance'' for new sources in the category. CAA section 111(a)(1)
defines ``standard of performance'' as ``a standard for emissions of
air pollutants'' determined in a specified manner. Thus, CAA section
111(b)(1)(B) requires that the EPA promulgate standards for ``emissions
of air pollutants.'' Under longstanding practice, ``EPA undertakes this
analysis on a pollutant-by-pollutant basis, establishing different
standards of performance with respect to different pollutants emitted
from the same source category.'' \93\
---------------------------------------------------------------------------

\93\ West Virginia, 597 U.S. at 709.
---------------------------------------------------------------------------

Read together, CAA section 111(b)(1)(A) and 111(b)(1)(B)
demonstrate that CAA section 111 directs the EPA to establish standards
for air pollutants that significantly contribute to dangerous air
pollution. Importantly, the source categories that the EPA is required
to list under CAA section 111(b)(1)(A) typically emit multiple air
pollutants, but CAA section 111(b)(1)(B) does not specify the air
pollutants for which the EPA must promulgate standards. These
provisions must be read in context as a cohesive whole. Interpreting
CAA section 111(b)(1)(A) in isolation to authorize the EPA to list a
source category based on a significance finding for one pollutant fails
to give independent meaning to the broader term ``air pollution'' and
effectively reads the ``contributes significantly'' requirement out of
the statute with respect to all other pollutants. On one hand, this
interpretation allows the EPA to evade the ``contributes
significantly'' requirement by listing a source category based on one
pollutant in order to regulate other pollutants for which it has not,
or cannot, make a credible finding of significant contribution to
dangerous air pollution. On the other, this interpretation would
trigger the requirement that the EPA promulgate standards of
performance under CAA section 111(b)(1)(B) for all air pollutants
emitted by the listed source category under the definition of
``standard of performance'' in CAA section 111(a)(1). Nothing in CAA
section 111 suggests that Congress intended the EPA to regulate
emissions of any and all air pollutants regardless of the magnitude of
emissions (i.e., including de minimis emissions) and regardless of
those emissions' contribution to dangerous air pollution (i.e.,
including pollutants that are not dangerous to health or welfare).
Rather, the EPA is necessarily required to exercise judgment in
determining which air pollutants to regulate, and Congress directed
that judgment must

[[Page 25764]]

be applied by determining whether an air pollutant contributes
significantly to dangerous air pollution.
By analogy, the Supreme Court held in Utility Air Regulatory Group
v. EPA, 573 U.S. 302, 322-23 (2014), that the phrase ``any air
pollutant'' in the new source review prevention of significant
deterioration (PSD) requirements under CAA sections 165(a)(1) and
169(1), which apply the PSD requirements to stationary sources that
emit specified amounts of ``any air pollutant,'' do not, based on their
statutory context, include GHGs, even though GHGs had been understood
as air pollutants.\94\ By the same token, because CAA section
111(b)(1)(A) authorizes the EPA to list a source category for
regulation only if it ``contributes significantly'' to dangerous air
pollution, it is appropriate to limit GHG emissions from a source
category only if they contribute significantly to such dangerous air
pollution. This interpretation is merited in part because the EPA did
not consider GHG emissions when the Agency initially listed the fossil
fuel-fired power plant source categories in the 1970s. In addition,
limiting the EPA's authority to regulate GHG emissions only if they
contribute significantly to dangerous air pollution is consistent with
prior EPA decisions not to regulate certain air pollutants under CAA
section 111 on grounds that they had little impact or that no effective
controls were available.\95\
---------------------------------------------------------------------------

\94\ In UARG, the Court interpreted the similar provisions of
the title V permit program, CAA sections 501(2)(B) and 302(j), the
same way. 573 U.S. at 323-24.
\95\ See National Lime Assoc. v. EPA, 627 F.2d 416, 426 & n.27
(D.C. Cir. 1980) (noting EPA did not promulgate standards for oxides
of nitrogen (NO<INF>X</INF>), sulfur dioxide (SO<INF>2</INF>) and CO
from lime plants due to limited amounts of emissions and lack of
effective controls).
---------------------------------------------------------------------------

Additional context and structure in CAA section 111 suggests that
CAA section 111(b)(1) is best read to require pollutant-specific
contribution findings. CAA section 111(b)(3) requires the EPA to
``issue information on pollution control techniques for categories of
new sources and air pollutants subject to the provisions of this
section.'' \96\ This language treats ``categories of new sources'' and
``air pollutants'' in the same breath, suggesting that the required
findings in ``this section'' apply to both phrases. CAA section 111(h),
which authorizes the EPA to impose design, equipment, work practice, or
operational standards when standards of performance are not feasible,
provides that standards of performance are not feasible when ``a
pollutant or pollutants cannot be emitted through a conveyance designed
and constructed to emit or capture such pollutant.'' \97\ That language
recognizes that CAA section 111(b)(1) is ultimately concerned with
controlling particular pollutants, and reinforces the importance of
making significant contribution determinations for such pollutants.
Finally, CAA section 111(j) authorizes the EPA to waive requirements
under certain conditions ``with respect to any air pollutant,'' meaning
waivers are granted on a pollutant-by-pollutant, in addition to source-
by-source, basis.\98\ This language supports the conclusion that the
EPA must analyze the contribution of pollutants to dangerous air
pollution under CAA section 111 generally.
---------------------------------------------------------------------------

\96\ CAA section 111(b)(3) (emphases added).
\97\ CAA section 111(h)(2) (emphases added).
\98\ CAA section 111(j)(1)(A).
---------------------------------------------------------------------------

The EPA solicits comment on the interpretation that it is
appropriate to regulate emissions of an air pollutant--here, GHGs--from
a source category only if those emissions contribute significantly to
dangerous air pollution. In particular, the EPA seeks comment with
respect to the textual requirements of CAA section 111(b), relevant
context from the remainder of CAA section 111, and relevant structural
arguments regarding the CAA more generally, including statutory
provisions not specifically discussed in this proposal.
In the alternative, the EPA proposes to interpret CAA section 111
to at least authorize the EPA to require a determination that an air
pollutant--here, GHG emissions from the power sector--significantly
contributes to dangerous air pollution as a predicate to imposing
standards of performance. Specifically, under this alternative, the EPA
proposes to interpret CAA section 111 as granting the EPA discretion to
determine which air pollutants to regulate under CAA section
111(b)(1)(B). As noted above, that provision directs the EPA to
establish standards for ``emissions of air pollutants,'' but those
provisions do not indicate which air pollutants within a potential
source category must be regulated. The EPA is proposing to interpret
this language to permit the EPA to choose which pollutants to regulate
based on the significant contribution standard in CAA section
111(b)(1)(A).
This alternative interpretation, under which the EPA determines
that the air pollutants for which it establishes standards are those
that contribute significantly to dangerous air pollution, is consistent
with the overall purpose of CAA section 111 to protect the public
health or welfare from source categories that contribute significantly
to dangerous air pollution. This interpretation is also consistent with
the discretion that CAA section 111 confers to the EPA at each stage of
the rulemaking process. That is, the EPA exercises ``judgment'' in
determining which source categories to list for regulation under CAA
section 111(b)(1)(A)); after listing a source category, the EPA has
discretion in determining which pollutants to regulate; and once the
EPA has determined to regulate a particular air pollutant, it has
discretion in determining the type of emission controls (BSER) that
serve as the basis for the regulation under CAA section 111(a)(1).
The EPA seeks comment on this alternative interpretation, including
with respect to whether the text of CAA section 111(b) confers
sufficient discretion on the EPA and whether additional provisions of
CAA section 111 or the CAA more generally inform the scope of that
discretion. The EPA also seeks comment on whether it erred in
determining that it was not required to make a significant contribution
finding in the 2015 NSPS or in not revisiting the issue in the CPS, and
whether or not it would be appropriate to exercise its discretion here
by requiring such a finding for GHG emissions from the fossil fuel-
fired power plant source category.
The EPA recognizes that the proposals discussed in this section
constitute a change from the EPA's approaches to statutory
interpretation in the 2015 NSPS. The EPA notes that the 2015 NSPS,
which asserted that the EPA need only have a rational basis for
regulating additional pollutants emitted from a new category comprised
of previously regulated sources, was itself a departure from the EPA's
prior implementation of CAA section 111. The 2015 NSPS regulated GHG
emissions from certain new sources in the power sector for the first
time since the enactment of CAA section 111(b) in 1970, and for the
first time specifically articulated the rational basis interpretation
as allowing the EPA to regulate additional pollutants without ever
having made a significant contribution finding for that pollutant.
The EPA seeks comment on this change in interpretation, including
any specific reliance interests relevant to the interpretation taken in
the 2015 NSPS, as carried over into the CPS, and the relative strength
of the rationale for these respective interpretations. The EPA also
seeks comment on whether and how the Supreme Court's recent decision in
Loper Bright Enterprises v.

[[Page 25765]]

Raimondo,\99\ should inform the EPA's approach to interpreting CAA
section 111 and selecting which interpretation better reflects the best
reading of the statute.
---------------------------------------------------------------------------

\99\ Loper Bright v. Raimondo, 144 S. Ct. 2244, 2263 & n.5
(2024).
---------------------------------------------------------------------------

The EPA is also requesting comment on whether its proposed
interpretation of CAA section 111(b)(1)(A) as requiring a pollutant-
specific significant contribution finding is necessary to avoid
implicating the major questions doctrine as articulated by the Supreme
Court in West Virginia. Specifically, the EPA is seeking input on
whether the proposed interpretations in this section are necessary to
prevent the Agency from improperly expanding its regulatory authority
by determining that emissions of de minimis amounts of air pollutants,
or non-harmful substances that may nevertheless be defined as air
pollutants, should be regulated under CAA section 111.
2. Determination of Significant Contribution
As noted above, CAA section 111(b)(1)(A) requires the Administrator
to list a source category for regulation ``if in his judgment it
causes, or contributes significantly to, [dangerous] air pollution.''
The EPA proposes to interpret this provision, in conjunction with other
provisions in CAA section 111, to require, as a predicate for
regulation of GHG emissions from a source category, that the EPA
determine that such emissions ``contribute[ ] significantly'' to
dangerous air pollution. By its explicit reference to the
Administrator, this provision expressly delegates to the EPA the
authority to determine when emissions ``contribute[ ] significantly.''
\100\ This section sets out the EPA's proposed interpretation of CAA
section 111's significant contribution standard and seeks comment on
the strength of this interpretation and its application to GHG
emissions by EGUs.
---------------------------------------------------------------------------

\100\ Id.
---------------------------------------------------------------------------

a. Proposed Interpretation of ``Significantly Contributes''
The EPA proposes to interpret ``significantly contributes'' as used
in CAA section 111 as conferring discretion on the Administrator based
on the statutory text, structure, and background principles of law.
First, the EPA proposes to conclude that the term ``significantly
contributes'' (emphasis added), in conjunction with the explicit grant
of authority to the Administrator to exercise ``judgment,'' confers
discretion to consider policy issues inherent in the statutory
structure, including effectiveness of emissions reduction controls,
cost-reasonableness of those controls, impacts on the affected
industry, and impacts of the emissions on public health and welfare.
Second, the EPA proposes to conclude that ``significantly contributes''
incorporates background legal principles of proximate cause that inform
both whether an air pollutant contributes to dangerous air pollution
and the extent of contribution required to trigger regulation based on
the particular form of dangerous air pollution identified.
Consistent with its ordinary meaning, the term ``significant[ ]''
is defined as ``having or likely to have influence or effect:
important.'' \101\ ``Important'' is similarly defined, in turn, as
``marked by or indicative of significant worth or consequence :
valuable in content or relationship.'' \102\ Whether a source
category's contribution to air pollution should be considered
``important'' or ``valuable'' entails consideration of the influence,
effect, or usefulness of finding such contribution. If regulating
emissions of a particular pollutant from a source category would have
little effect on dangerous air pollution, that source category's
contribution to the air pollution is not significant. By the same
token, if regulating emissions would not be useful, taking into
account, inter alia, the impacts on, and the Administration's policies
concerning, the source category, that source category's contribution to
the air pollution is not significant. An inquiry into the effect of a
finding of significance necessarily involves policy considerations that
will inform any subsequent regulation when making the significance
determination in the first instance.\103\
---------------------------------------------------------------------------

\101\ Merriam-Webster. Dictionary Definition: Significant.
<a href="https://www.merriam-webster.com/dictionary/significant">https://www.merriam-webster.com/dictionary/significant</a>.
\102\ Merriam-Webster. Dictionary Definition: Important. <a href="https://www.merriam-webster.com/dictionary/important">https://www.merriam-webster.com/dictionary/important</a>.
\103\ Because CAA section 111 delegates to the EPA the authority
to consider policy goals in determining whether emissions contribute
``significant[ly]'' and does not limit the meaning of
``significantly'' to some specified level of emissions, the EPA
proposes to conclude that it is not necessary to identify standards
or criteria for determining whether a particular level of emissions
contributes ``significantly.''
---------------------------------------------------------------------------

This interpretation of ``significantly contributes'' accords with
the structure and language of the remainder of the statutory provision.
CAA section 111(b)(1)(A) does not require the EPA to conduct separate
analyses of contribution and endangerment or imply that significance is
divorced from the policy and regulatory tools available to address an
identified danger. To the contrary, Congress required the Administrator
to exercise ``judgment'' in determining whether emissions of an air
pollutant from a category of sources contribute significantly to
dangerous air pollution such that emissions reductions can reasonably
be required. This explicit authorization to the Administrator to
exercise ``judgment'' reinforces interpreting ``significantly'' to
include the Administrator's policy considerations associated with
reducing emissions. When Congress intends to require the EPA to
evaluate the significance of a risk separately from risk mitigation, it
knows how to do so. For example, unlike key provisions of the Safe
Drinking Water Act (SDWA) and the Toxic Substances Control Act (TSCA),
CAA section 111 uses discretionary language and does not purport to
exclude any standard administrative considerations from the scope of
the EPA's significance analysis.\104\
---------------------------------------------------------------------------

\104\ See Michigan v. EPA, 576 U.S. 743, 753 (2015).
---------------------------------------------------------------------------

Notably, this interpretation of significance is not foreclosed by
the D.C. Circuit's decision in American Lung Association v. EPA. There,
the court addressed the question whether EPA had to consider certain
metrics or factors when determining if a source category's contribution
is significant.\105\ The court declined to answer this question,
finding that it was not necessary to do so in that case.\106\ Under the
interpretation of ``contributes significantly'' proposed here,
significance would be determined not with regard to a quantitative
threshold, but rather based on the impact of the resulting regulation.
The American Lung Association decision does not speak to this
interpretation, and thus does not purport to restrict the
Administrator's discretion to exercise judgment by factoring in
statutory policy considerations when determining significance.
---------------------------------------------------------------------------

\105\ American Lung Ass'n v. EPA, 985 F.3d 914, 977 (D.C. Cir.
2021), rev'd in part, West Virginia v. EPA, 597 U.S. 697 (2022).
\106\ Id.
---------------------------------------------------------------------------

The CAA, and specifically the factors laid out in section
111(a)(1), provides guidance on the scope of the considerations
relevant to assessing whether an air pollutant contributes
significantly to dangerous air pollution. As noted above, the EPA has
discretion to consider statutory policies, including risk management
considerations, in determining whether emissions contribute
``significantly,'' and CAA section 111(a)(1) includes the factors

[[Page 25766]]

that EPA must consider in determining emission standards to manage
risk. Specifically, CAA section 111(a) requires that the EPA determine
the level of emission reductions that will be required based on
consideration of, among other things, the cost of achieving those
reductions. If the cost is unreasonable, the associated emission
reductions are not warranted. Thus, when determining if a source
category contributes significantly to dangerous air pollution, the EPA
will look to the availability of achievable, cost-effective emission
reductions. If no such reductions are available, the influence or
effect of regulating the source category for that pollutant is null and
its contribution to air pollution is not significant.
The EPA has long interpreted a similar phrase in CAA section
110(a)(2)(D)(i)(I) to include cost considerations. That provision
requires that state implementation plans contain provisions that
prohibit sources from ``emitting any air pollutant in amounts which
will contribute significantly to'' downwind air quality problems. Based
on this provision, the EPA has promulgated several region-wide rules,
beginning in 1998, to limit emissions of air pollutants that affect
downwind air quality. In these rules, the EPA has consistently
interpreted the term ``significantly'' to include consideration of the
cost-effectiveness of controls in determining the overall amount of
required emission reductions.\107\ Although not addressing the EPA's
specific interpretation, the Supreme Court read the phrase ``amounts
which will contribute significantly'' to authorize the consideration of
cost effectiveness.\108\
---------------------------------------------------------------------------

\107\ See EPA v. EME Homer City Generation, L.P., 572 U.S. 489,
499-503 (2014) (recounting history of EPA regulatory action and
statutory interpretation, beginning with the ``NOx SIP Call,'' 63 FR
57356, 57358 (October 27, 1998)).
\108\ Id. at 518-19.
---------------------------------------------------------------------------

As the EPA has explained previously in examining alternatives to
reduce emissions of GHGs from fossil fuel-fired EGUs, there are four
main approaches to controls that can potentially be used given the
continued (and increasing) demand for electricity generation.\109\
Serious flaws in each of these potential controls demonstrates not only
that emissions reductions are not readily achievable, but also that the
contribution to dangerous air pollution that the EPA previously relied
upon to regulate GHG emissions is not significant within the meaning of
CAA section 111 when read in context with an eye towards the
provision's structure.
---------------------------------------------------------------------------

\109\ CPP was based on generation shifting as BSER, ACE was
based on HRI as BSER, and CPS was based on co-firing and CCS as
BSERs. Those prior rulemakings examine various aspects of those
approaches. See CPP proposal at 79 FR 34830 (June 18, 2014), CPP
final at 80 FR 64662 (October 23, 2015), ACE proposal at 83 FR 44746
(August 31, 2018), ACE final at 84 FR 32520 (July 8, 2019), CPS
proposal at 88 FR 33240 (May 23, 2023), and CPS final at 89 FR 39798
(May 9, 2024). See also previous technical support documents at
Docket ID No. EPA-HQ-OAR-2013-0602-36852, EPA-HQ-OAR-2023-0072-9095,
and EPA-HQ-OAR-2023-0072-9099.
---------------------------------------------------------------------------

The first approach is generation shifting, which the Supreme Court
held in West Virginia cannot be considered as part of BSER. The second
is the use of CCS technology at fossil fuel-fired power plants. As
explained below, there is very limited use of CCS on fossil fuel-fired
EGUs either in the U.S. or internationally, and the projects using CCS
on a cutting-edge basis have demonstrated significantly less than 90
percent capture. Moreover, as discussed in sections V.B.1.b-c and V.2
of this preamble, the EPA is proposing to find that the cost of 90
percent CCS is unreasonable, and therefore that the associated emission
reductions are not achievable. The third approach to reducing GHG
emissions is natural gas co-firing. As further explained in section
V.B.2 of this preamble, the EPA is proposing that basing the BSER on a
switch from one fuel to an entirely different fuel would constitute
impermissible generation shifting. Even if switching to natural gas
were an allowable BSER for coal-fired steam generating units, in
considering energy requirements, natural gas co-firing is an
inefficient use of that natural gas, and natural gas is also an
important and limited resource necessary to public welfare. Finally,
efficiency, or heat rate improvements (HRI) can be used. For new
sources, this is unlikely to have a significant impact on emissions
because sources already have a significant incentive to use the most
efficient technology available even without regulatory drivers. For
existing sources, efficiency improvements decrease emissions per MWh of
electricity generated but can result in a ``rebound effect'' where
emissions at the individual EGU increase due to increased generation
from the unit. Because an EGU applying HRI is more fuel efficient and
may have lower dispatch costs, it may also displace generation from
lower emitting EGUs (e.g., an existing source displaces generation from
a new natural gas combined cycle unit) so that overall emissions from
the power sector may increase. As a result, HRI may be unsuitable as
BSER due to the uncertainty as to whether the technology results in
overall emission reductions.
Thus, the control options available to reduce GHGs from fossil
fuel-fired EGUs are not permissible as BSER, not adequately
demonstrated, cost unreasonable, or potentially ineffective in reducing
emissions. Because it is likely that the Agency may be unable to
develop a BSER that would result in any meaningful, cost-reasonable GHG
emission reductions, the contribution of this source category to GHG
air pollution is not significant. In particular, because, as discussed
below, only extraordinary emissions reductions on a global scale would
have any impact on the potential endangerment of public health and
welfare in this context, the EPA is proposing to determine that GHG
emissions from the EGU source category do not contribute significantly
to dangerous air pollution.
The EPA proposes to conclude based on this interpretation of CAA
section 111 that the significant contribution analysis is informed by
considerations of national policy regarding the public welfare and the
ability of the CAA section 111 regulatory mechanism to achieve
meaningful reductions in air pollution that are cost-reasonable and
achievable. As such, the significance analysis is informed by this
Administration's national policy that energy production is essential to
the public welfare. This entails continued and increasing reliance on
fossil fuels to meet increasing demands for electricity generation,
including to power artificial intelligence (AI) and related
technologies with critical implications for national security and
economic growth. Such considerations fit within the meaning of the term
``significant,'' as well as within the CAA's broad understanding of the
term ``welfare'' as including (but not limited to) ``effects on
economic values and on personal comfort and well-being.'' \110\
---------------------------------------------------------------------------

\110\ CAA section 302(h).
---------------------------------------------------------------------------

In the 2015 NSPS, the EPA took a materially different view when
making, in the alternative, a significant contribution finding for GHG
emissions from fossil fuel-fired power plants. There, the EPA based the
finding solely on the quantity of GHG emissions and did not consider
the potential impacts of its policy.\111\ The limitations of this
approach became evident in the CPS, where the EPA assessed impacts on
the fossil fuel-fired power plants that it regulated; the Agency
estimated that the CPS would result in significant coal retirements of
5 GW by 2030, an

[[Page 25767]]

incremental 21 GW by 2035, and an incremental 14 GW by 2040, relative
to a baseline without the CPS.\112\ The EPA further estimated that CPS
resulted in lower amounts of generation from new gas turbines and fewer
natural gas combined cycle turbines being built.\113\ Notwithstanding
these estimates, the Agency did not revisit its prior finding of
significant contribution, and instead assumed that GHG emissions from
such sources should be regulated as contributing significantly to a
danger to public health and welfare, without accounting for the
consequences to public health and welfare of taking action that
resulted in plant closures.
---------------------------------------------------------------------------

\111\ 89 FR 64531 (October 23, 2015).
\112\ U.S. EPA. Regulatory Impact Analysis for the New Source
Performance Standards for Greenhouse Gas Emissions from New,
Modified, and Reconstructed Fossil Fuel-Fired Electric Generating
Units; Emission Guidelines for Greenhouse Gas Emissions from
Existing Fossil Fuel-Fired Electric Generating Units; and Repeal of
the Affordable Clean Energy Rule. May 2024. Document ID No. EPA-HQ-
OAR-2023-0072-8913. Page 3-28.
\113\ Id. Page 3-29.
---------------------------------------------------------------------------

In enacting and amending CAA section 111, Congress legislated
against background legal principles, including principles of causation
and proximate cause.\114\ These ``default rules'' are ``presumed to
have [been] incorporated, absent an indication to the contrary in the
statute itself.'' \115\ CAA section 111(b)(1)(A) incorporates these
principles by using the term ``cause'' and the phrase ``significantly
contribute'' without accompanying language that suggests an intent to
depart from ordinary rules of legal meaning. The EPA proposes to
interpret CAA section 111(b)(1)(A) as incorporating ordinary causation
and proximate cause principles that must be considered in determining
whether the emission of an air pollutant ``significantly contributes''
to dangerous air pollution in light of the directness and degree of the
supposed contribution.\116\
---------------------------------------------------------------------------

\114\ See, e.g., Bank of Am. Corp. v. City of Miami, 581 U.S.
189, 201 (2017); Lexmark Int'l, Inc. v. Static Control Components,
Inc., 572 U.S. 118, 132 (2014); Univ. of Tex. Sw. Med. Ctr. v.
Nassar, 570 U.S. 338, 347 (2013).
\115\ Nassar, 570 U.S. at 347.
\116\ The Supreme Court has explained, ``[t]he proximate-cause
analysis asks `whether the harm alleged has a sufficiently close
connection to the conduct the statute prohibits.' '' Bank of Am.
Corp. v. City of Miami, 581 U.S. at 190 (quoting Lexmark Int'l, Inc.
v. Static Control Components, Inc., 572 U.S. at 133. In the present
context, this analysis asks whether the air pollutant emissions have
a sufficiently close connection to the endangerment caused by the
air pollution.
---------------------------------------------------------------------------

In the 2015 NSPS, the EPA assigned itself a particularly demanding
analytical task by evaluating the significance of contribution to
global, well-mixed air pollution that results from a combination of
pollutants from a large and diverse array of sources that in turn,
creates elevated global concentrations that, in turn, the Agency
determined play a causal role in environmental phenomena that, in turn,
the Agency determined adversely affect the public health and welfare.
The global scale of that analysis and attenuated chain of causation
stands in marked contrast to the EPA's prior listing and regulatory
efforts under CAA section 111. None of those listings and regulatory
efforts concerned air pollutants that can be connected to adverse
public health and welfare impacts only when aggregated into global
emissions from all potential global sources.
The threshold for significant contribution under this theory is
heightened by the multiple intervening actors, uncertainties, and
extrapolations necessary to draw a connection between emissions by a
source category and dangerous air pollution in the form of adverse
effects in the U.S. from anthropogenic climate change, as discussed
further below. Under the EPA's proposed interpretation, this attenuated
causal chain would require a greater volume and percentage of
contribution than a more direct causal relationship to account for the
degree of uncertainty and extrapolations involved. In other words,
emissions of an air pollutant by a source category cannot be said to
contribute significantly to a third or fourth order adverse consequence
involving multiple independent domestic and global actors unless the
contribution is sufficiently significant that regulation would have a
discernable impact on the potential danger.
b. Proposed Application of ``Significantly Contributes''
In the 2015 NSPS, the EPA found, in the alternative, that GHG
emissions from domestic fossil fuel-fired EGUs ``significantly
contribute'' to dangerous air pollution based exclusively on the volume
of GHG emissions from the source category.\117\ In addition, the Agency
relied on its conclusion in the 2009 Endangerment Finding that global
GHG air pollution causes anthropogenic climate change that, in turn,
caused adverse domestic impacts.\118\ The EPA's theory at the time can
be summarized as follows: (1) GHG emissions from U.S. fossil fuel-fired
EGUs combine with GHGs emitted from other U.S. sources; (2) U.S. GHG
emissions combine with global emissions of GHGs from all sources in all
countries to produce a combined concentration of GHGs in the
atmosphere; (3) that combined concentration of GHGs in the atmosphere
plays a causal role in a net trend toward increasing temperatures; (4)
that net trend toward increasing temperatures plays a causal role in
global environmental, climate, weather, and oceanographic patterns; and
(5) those global changes play a causal role in producing adverse
domestic environmental, climate, weather, and oceanographic phenomena
that (6) endanger the public health and welfare.
---------------------------------------------------------------------------

\117\ 80 FR 64531 (October 23, 2015).
\118\ See id. at 6430-31 (citing ``Endangerment and Cause or
Contribute Findings for Greenhouse Gases Under Section 202(a) of the
Clean Air Act,'' 74 FR 66496 (December 15, 2009)).
---------------------------------------------------------------------------

The EPA now proposes to adopt a statutory interpretation that is
centered on the impacts and effects of statutory policy considerations
in determining whether a source category's contribution is significant,
rather than a purely quantitative measure of significance resting on
the absolute volume of emissions from a source category.\119\ Based on
this interpretation, the Agency proposes to conclude, as an exercise of
the Administrator's informed judgment, that the volume of GHG emissions
from U.S. fossil fuel-fired EGUs does not demonstrate the significant
contribution to dangerous air pollution required to invoke the Agency's
regulatory authority under CAA section 111. This proposed determination
is based on the considerations of statutory structure and policy
regarding public welfare discussed in the previous section, available
information on the declining share of GHG emissions from U.S. EGUs
relative to global emissions, and the attenuated nature of the causal
chain between the volume of GHG emissions from the EGU source category
and potential danger to public health and welfare arising from
anthropogenic climate change.
---------------------------------------------------------------------------

\119\ This proposed interpretation of CAA section 111(b)(1)(A)
represents a departure from the EPA's previous interpretations of
what it means for a source category to ``contribute[] significantly
to'' dangerous air pollution. Given this different starting point,
the D.C. Circuit's discussion of significance in American Lung
Ass'n, 985 F.3d 914, 975-77, is inapposite.
---------------------------------------------------------------------------

Unlike other air pollutants that can have a localized or regional
impact and direct consequences to human health, GHGs are global
pollutants. The share of GHG emissions from the U.S. power sector,
including CO<INF>2</INF>, to global concentrations of GHGs in the
atmosphere is relatively minor and has been declining over time. In
2005, U.S. electric power sector GHG emissions comprised 5.5 percent of
total global GHG emissions. This percentage has fallen steadily since
then to 4.6 percent

[[Page 25768]]

in 2010, to 3.7 percent in 2015, and comprising 3 percent of total
global emissions by 2022.\120\ This relative decline is driven in part
by increases in GHG emissions from developing countries that are
rapidly electrifying and increasing their energy demands, including
through the robust deployment of fossil fuel-fired EGUs--a trend that
is likely to persist going forward. Further, many other countries burn
much more coal than is utilized by the U.S. power sector. For example,
in 2024, China used more than 13 times as much coal as the U.S.\121\
Despite the fact that coal use in the U.S. has declined nearly 62
percent from its historic high in 2007,\122\ global coal use continues
to grow--with 2024 seeing the most coal use ever.\123\ Limiting the use
of coal and other fossil fuels in U.S. EGUs does not significantly
impact global GHG concentrations when other countries continue to
increase their use of fossil fuels. The EPA proposes to find that the
large and growing share of GHG emissions from international sources
strengthens the conclusion that U.S. fossil fuel-fired electricity
generation, including U.S. coal use for electricity generation, does
not contribute significantly to globally elevated concentrations of
GHGs in the atmosphere.\124\
---------------------------------------------------------------------------

\120\ Calculations based on U.S. EPA, ``Inventory of GHG Sources
and Sinks.'' <a href="https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks">https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks</a>, and U.S. EPA, ``Global
Greenhouse Overview.'' <a href="https://www.epa.gov/ghgemissions/global-greenhouse-gas-overview">https://www.epa.gov/ghgemissions/global-greenhouse-gas-overview</a>.
\121\ Institute for Energy Research, ``Global Coal Use Hits
Another Historic Record in 2024.'' January 21, 2025. <a href="https://www.instituteforenergyresearch.org/fossil-fuels/coal/global-coal-use-hits-another-historic-record-in-2024/">https://www.instituteforenergyresearch.org/fossil-fuels/coal/global-coal-use-hits-another-historic-record-in-2024/</a>.
\122\ EIA Annual Coal Report 2023 and 2007. <a href="https://www.eia.gov/coal/annual/">https://www.eia.gov/coal/annual/</a>.
\123\ Institute for Energy Research, ``Global Coal Use Hits
Another Historic Record in 2024.'' January 21, 2025. <a href="https://www.instituteforenergyresearch.org/fossil-fuels/coal/global-coal-use-hits-another-historic-record-in-2024/">https://www.instituteforenergyresearch.org/fossil-fuels/coal/global-coal-use-hits-another-historic-record-in-2024/</a>.
\124\ In American Lung Ass'n, the D.C. Circuit noted that what
it viewed as U.S. power plants' relatively large share of global GHG
emissions supported the EPA's view in the 2015 New Source Rule that
those power plant emissions were significant. American Lung Ass'n,
985 F.3d at 977. Since then, the U.S. power plants' share of global
GHG emissions has declined. Most importantly, the EPA is now
proposing to interpret ``contribute significantly'' to include
policy considerations, as noted above.
---------------------------------------------------------------------------

Aside from these relative trends, the percentage contribution of
GHG emissions from U.S. fossil fuel-fired EGUs may not be a significant
contribution to global GHG concentrations in the atmosphere,
particularly given the discretion conferred by the term
``significant.'' The 3 percent contribution figure from 2022 suggests
that the risks to public health and welfare attributed to anthropogenic
climate change would not be meaningfully different even if the fossil
fuel-fired EGU source category were to cease all GHG emissions.
The EPA solicits comment on the proposed determination that GHG
emissions from the EGU source category do not ``contribute
significantly'' to dangerous air pollution under CAA section
111(b)(1)(A).

C. Conclusion

In conclusion, the EPA is proposing to interpret CAA section 111 to
require, or at least authorize the EPA to require, that the EPA must
determine that GHG emissions from EGUs contribute significantly to
dangerous air pollution as a predicate to regulation of GHG emissions
from fossil fuel-fired EGUs. The EPA is further proposing to determine
that GHG emissions from fossil fuel-fired EGUs do not contribute
significantly to dangerous air pollution. On this basis, the EPA is
proposing to repeal all greenhouse gas standards for the power sector,
specifically the 2015 NSPS and the CPS.

V. Summary and Rationale of Alternative Proposal

As an alternative to the proposal to determine that fossil fuel-
fired EGUs do not contribute significantly to GHG air pollution and to
repeal 40 CFR part 60, subparts TTTT, TTTTa, and UUUUb in their
entirety on that basis, the EPA is, based on different rationales,
proposing to repeal specific portions of these subparts. Those subparts
are the emission guidelines for existing fossil fuel-fired steam
generating units in 40 CFR part 60, subpart UUUUb; as well as the
requirements for coal-fired steam generating units undertaking a large
modification and the phase 2 CCS-based requirements for new base load
combustion turbine EGUs in 40 CFR part 60, subpart TTTTa.
If the EPA does not finalize the primary proposal, it may finalize
this alternative proposal. Under this alternative, the EPA is not
reopening the BSER determinations or standards of performance and
related requirements for new and reconstructed intermediate load and
low load fossil fuel-fired stationary combustion turbines or for phase
1 for new and reconstructed base load fossil fuel-fired stationary
combustion turbines. Similarly, under the alternative proposal, the EPA
is not reopening the 2015 NSPS or substantive elements of 40 CFR part
60, subpart TTTT. However, the EPA still requests comment on these
issues in general and may, if appropriate, engage in further rulemaking
at a future date if this alternative proposal is finalized.

A. Summary of Alternative Proposal

The EPA is proposing to determine that 90 percent CCS is not the
BSER for existing long-term coal-fired steam generating units because
it has not been adequately demonstrated and because the costs are not
reasonable. Furthermore, because it is unlikely that the infrastructure
necessary for CCS can be deployed by the January 1, 2032, compliance
date, the EPA is proposing to determine that the degree of emission
limitation in the CPS for long-term coal-fired steam generating units
is not achievable. The EPA is proposing to determine that 40 percent
natural gas co-firing is not the BSER for existing medium-term coal-
fired steam generating units because consideration of the energy
requirements shows that 40 percent natural gas co-firing in a steam
generating unit is an inefficient use of natural gas, as detailed in
section V.B.2 of this preamble, particularly compared to use in a
natural gas-fired combined cycle EGU. Therefore, the EPA is proposing
to repeal the BSER determinations, presumptive standards of
performance, and all related requirements in the emission guidelines
for existing long-term and medium-term coal-fired steam generating
units.
The EPA is additionally proposing to repeal the requirements for
existing natural gas- and oil-fired steam generating units because it
would be an inefficient use of State resources to develop, submit, and
implement State plans solely for natural gas- and oil-fired steam
generating units, which comprise a relatively small part of the source
category and would contribute few or no emission reductions under the
existing emission guidelines. That is, it would not be reasonable for
the EPA to require States to prepare plans for existing natural gas-
and oil-fired steam generating units if the EPA is repealing the
requirements for existing coal-fired steam generating units. Because
the EPA would repeal the substantive requirements for all regulated
subcategories, it is proposing to repeal the emission guidelines for
existing fossil fuel-fired steam generating units in its entirety.
Because the EPA is proposing to determine that 90 percent CCS is
not the BSER for existing long-term coal-fired steam generating units,
the EPA is further proposing to repeal the CCS-based requirements for
coal-fired steam generating units undertaking a large modification.
Finally, the EPA is proposing to determine that 90 percent CCS is not
the BSER for new base load

[[Page 25769]]

combustion turbine EGUs because the EPA is proposing that it has not
been adequately demonstrated and the costs are not reasonable.
Furthermore, because it is unlikely that infrastructure necessary for
CCS can be deployed by the January 1, 2032, compliance date, the EPA is
proposing to determine that the phase 2 standards of performance in the
CPS for new base load combustion turbines are not achievable.
Consequently, the EPA is proposing to repeal the phase 2 CCS-based
requirements for new base load combustion turbine EGUs.
This section details the rationale for the alternative proposal to
repeal the emission guidelines for existing fossil fuel-fired steam
generating units, the CCS-based requirements for coal-fired steam
generating units undertaking a large modification, and the phase 2 CCS-
based requirements for new base load combustion turbine EGUs.

B. Emission Guidelines for Existing Fossil Fuel-Fired Steam Generating
Units

1. CCS-Based Requirements for Long-Term Existing Coal-Fired Steam
Generating Units
The EPA is proposing to determine that CCS with 90 percent capture
is not the BSER for long-term existing coal-fired steam generating
units because it has not been adequately demonstrated, and the costs
are unreasonable. Furthermore, as detailed in section V.B.1.c of this
preamble, it is unlikely that infrastructure necessary for CCS can be
deployed by the January 1, 2032, compliance date, and the EPA is
therefore proposing to determine that the degree of emission limitation
in the CPS for long-term coal-fired steam generating units is not
achievable. Consequently, the EPA is proposing to repeal the
requirements in the emission guidelines pertaining to long-term
existing coal-fired steam generating units.
a. Adequately Demonstrated
CCS with 90 percent capture involves the capture of 90 percent of
the CO<INF>2</INF> from the flue gas of the EGU, transport of the
compressed CO<INF>2</INF> via pipeline, and sequestration in geologic
storage. The foundation of the EPA's prior BSER determination fails at
the first step in the process because 90 percent capture of the
CO<INF>2</INF> from flue gas of an EGU has not been adequately
demonstrated and should not have been considered or selected as the
BSER.
As explained previously, the EPA has discretion under CAA section
111 to determine whether technologies are adequately demonstrated such
that they are appropriate for consideration and potential selection as
the BSER. In the CPS, the EPA interpreted CAA section 111, its
legislative history, and the D.C. Circuit caselaw to take the position
that this discretion includes a degree of forward-looking prediction on
whether a technology has been ``adequately demonstrated'' such that it
could be the BSER for a given source category.\125\ The text and
structure of CAA section 111 and applicable case law demonstrate,
however, that even if the EPA has discretion in this regard, it is not
unbounded. The statute requires the EPA to ``review and, if
appropriate, revise'' new source standards for a listed category at
least every eight years.\126\ This provision indicates that
technologies requiring enhancements and development that would take
significant time, and certainly that would take an entire review cycle
or longer, cannot be considered ``adequately demonstrated'' and thus
are not appropriate for selection as the BSER. Rather, the EPA should
review the state of the technology at the next eight-year review cycle,
and consider at that time whether it is ``adequately demonstrated.''
For the reasons detailed in this section of the preamble, the EPA is
proposing 90 percent CCS is not adequately demonstrated. As a result,
even if the EPA has authority to take into account future technological
development in determining adequately demonstrated, and even if 90
percent capture were achievable in the future, additional time would be
required for the CCS technology to develop. The EPA proposes to find
that it erred in the CPS, and is proposing that 90 percent CCS cannot
be BSER, because the CPS record did not demonstrate that CCS technology
would develop further so that 90 percent capture is achievable, did not
demonstrate the period of time over which the technology would develop,
and, by the same token, did not demonstrate that any such development
would occur, at minimum, within the next eight years.
---------------------------------------------------------------------------

\125\ 89 FR 39830-32 (May 9, 2024).
\126\ CAA section 111(b)(1)(B).
---------------------------------------------------------------------------

In the CPS, the argument that 90 percent capture was adequately
demonstrated relied in large part on the operation of amine solvent-
based CO<INF>2</INF> capture at Boundary Dam Unit 3. However, between
2014 and 2022, Boundary Dam achieved a total capture efficiency of not
more than 63 percent over the course of a calendar year \127\ (the
timeframe relevant to the emission reduction requirements in the
emission guidelines), which is substantially below the 90 percent
capture level specified by the BSER. While the EPA had acknowledged the
challenges and underperformance of the capture system at Boundary Dam,
it asserted that fixes were available or could be made to address those
issues. However, many of those fixes were already made, and performance
remained below the design capture efficiency. Furthermore, the
operating availability of capture systems has been, to date, less than
100 percent. The EPA previously argued that new solvents were available
that could capture CO<INF>2</INF> at higher rates to address these
gaps, but the experience at Boundary Dam suggests it would be
reasonable to anticipate the possibility that those solvents would
similarly underperform. Considering these factors, the EPA is proposing
to determine that CCS with 90 percent capture is not adequately
demonstrated for existing coal-fired steam generating units. The
following subsections provide further explanation.
---------------------------------------------------------------------------

\127\ Jacobs, B., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Reducing the CO2 Emission Intensity of Boundary Dam Unit 3 Through
Optimization of Operating Parameters of the Power Plant and Carbon
Capture Facilities. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430</a>.
---------------------------------------------------------------------------

i. Boundary Dam Unit 3
In the CPS, the EPA relied heavily on the operation of carbon
capture at the 110 MW coal-fired Boundary Dam Unit 3 (Saskatchewan,
Canada) to demonstrate 90 percent capture. CCS at Boundary Dam has been
operated since 2014. The unit uses Shell's amine-based CANSOLV[supreg]
solvent technology to capture CO<INF>2</INF> from the post-combustion
flue gas of the coal-fired boiler.\128\ Captured CO<INF>2</INF> is then
compressed, transported by pipeline, and used for enhanced oil recovery
or stored in a saline aquifer at the Aquistore site.\129\ While
Boundary Dam Unit 3 achieved 89.7 percent capture over a 3-day test
early in its operation, longer-term capture levels have been
lower.\130\ Between 2015 and 2022, Boundary Dam achieved a total
capture efficiency of not more than 63 percent in a calendar

[[Page 25770]]

year,\131\ which is substantially below the 90 percent capture
efficiency of the BSER.
---------------------------------------------------------------------------

\128\ Giannaris, S., et al. Proceedings of the 15th
International Conference on Greenhouse Gas Control Technologies
(March 15-18, 2021). SaskPower's Boundary Dam Unit 3 Carbon Capture
Facility--The Journey to Achieving Reliability. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3820191">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3820191</a>.
\129\ Aquistore. <a href="https://ptrc.ca/aquistore">https://ptrc.ca/aquistore</a>.
\130\ SaskPower Annual Report (2015-16). https://
www.saskpower.com/about-us/Our-Company/~/
link.aspx?_id=29E795C8C20D48398EAB5E3273C256AD&_z=z.
\131\ Jacobs, B., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Reducing the CO2 Emission Intensity of Boundary Dam Unit 3 Through
Optimization of Operating Parameters of the Power Plant and Carbon
Capture Facilities. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430</a>.
---------------------------------------------------------------------------

This lower total capture efficiency is due to, among other things,
the capture system at Boundary Dam Unit 3 typically processing less
than all of the flue gas, in part to ``maintain long-term reliable
operation.'' \132\ Prior to 2023, the CO<INF>2</INF> capture system at
Boundary Dam Unit 3 processed up to about 75 percent of the flue gas
when operating, with 90 percent CO<INF>2</INF> capture from the
processed flue gas when operating.\133\ The EPA argued in the CPS that
such capture from the majority of the flue gas was supportive of the
determination of 90 percent capture from all of the flue gas as
adequately demonstrated; however, this does not account for the
differences in performance when a system is processing less than all of
the flue gas.
---------------------------------------------------------------------------

\132\ SaskPower. ``Docket ID No. EPA-HQ-OAR-2023-0072: SaskPower
Correction of Reference to Boundary Dam Unit 3 Emissions Performance
in Proposed Rule.'' August 4, 2023. Document ID No. EPA-HQ-OAR-2023-
0072-0687.
\133\ Jacobs, B., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Reducing the CO2 Emission Intensity of Boundary Dam Unit 3 Through
Optimization of Operating Parameters of the Power Plant and Carbon
Capture Facilities. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430</a>.
---------------------------------------------------------------------------

Opponents of the CPS argued before the D.C. Circuit that there is a
meaningful difference between instances where an emissions control
device processes a ``slipstream'' (a portion of the flue gas) and where
a control device processes all of the flue gas. They further suggested
that the capture efficiencies achieved for a system processing a
portion of the flue gas would not be indicative of potential capture
efficiencies for a system processing all of the flue gas.\134\ In
essence, they asserted that processing a portion of the flue gas
``functions reliably because gas pressures and volumes are static and
controllable,'' whereas a capture system processing all of the flue gas
``would need to contend with dynamic pressure and volume, shifting as
the facility responds to electricity demand.'' \135\
---------------------------------------------------------------------------

\134\ West Virginia v. EPA, No. 24-1120 (D.C. Cir. 2024), Doc.
#2083273, at 46-47 (Opening Brief of Petitioners).
\135\ Id.
---------------------------------------------------------------------------

In general, Boundary Dam Unit 3 operates as a base load unit,
typically operating at high capacity factors such that the unit
experiences less variation in operation than a load-following unit. The
CO<INF>2</INF> capture system uses steam and electricity from the host
EGU (i.e., integrated steam and power). While reports on Boundary Dam's
operation document increases in capture efficiency at reduced
throughputs to the CO<INF>2</INF> absorber,\136\ it is unclear whether
those reductions in throughput coincided with decreases in load of the
host EGU in response to changes in demand. Because the flue gas can
bypass the CO<INF>2</INF> capture system, it is possible that the
throughput to the capture system could be changed independently of the
changes in steam load or electricity generation. While other control
schemes may be applicable, and it may be that further optimization
could be undertaken when processing all of the flue gas,\137\ a
CO<INF>2</INF> capture system required to process all of the flue gas
at all times may not have the same flexibility in process control that
is available to a system processing a portion of the flue gas.
Regardless, the total capture from the facility has been substantially
less than 90 percent.
---------------------------------------------------------------------------

\136\ Jacobs, B., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Reducing the CO2 Emission Intensity of Boundary Dam Unit 3 Through
Optimization of Operating Parameters of the Power Plant and Carbon
Capture Facilities. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430</a>.
\137\ Id.
---------------------------------------------------------------------------

Around 2024, additional improvements at Boundary Dam Unit 3 were
made to increase throughputs, and SaskPower noted that a greater
portion of the flue gas was being processed by the capture system (up
to 95 percent of the flue gas, with 87 percent capture from the
processed flue gas, resulting in 83 percent total capture when
operating).\138\ Whether that performance has been maintained in the
long term has not been reported. Notably, at those higher throughputs,
the capture efficiency from the processed flue gas is lower. Moreover,
even with those improvements, Boundary Dam continues to operate with
capture efficiencies below design specification.
---------------------------------------------------------------------------

\138\ U.S. EPA, ``Meeting with SaskPower to Discuss CCS at
Boundary Dam Unit 3.'' January 18, 2024. Document ID No. EPA-HQ-OAR-
2023-0072-8906.
---------------------------------------------------------------------------

Finally, availability of the capture system at Boundary Dam Unit 3
has been less than 100 percent. Between 2015 and 2022, annual
availability of the capture plant relative to the EGU varied between 58
and 94 percent.\139\ In 2024, average quarterly availability of the
capture plant was about 85 percent.\140\ Lower availabilities further
contribute to lower total capture efficiencies.
---------------------------------------------------------------------------

\139\ Jacobs, B., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Reducing the CO2 Emission Intensity of Boundary Dam Unit 3 Through
Optimization of Operating Parameters of the Power Plant and Carbon
Capture Facilities. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430</a>.
\140\ SaskPower. BD3 Status Update: Q4 2024. <a href="https://saskpower.com/about-us/our-company/blog/2025/bd3-status-update-q4-2024">https://saskpower.com/about-us/our-company/blog/2025/bd3-status-update-q4-2024</a>.
---------------------------------------------------------------------------

The total capture efficiency at Boundary Dam Unit 3 has been less
than 90 percent because the capture system has not processed all of the
flue gas, the capture efficiency is still less than 90 percent when the
capture system is operating even after applying fixes, and the
availability of the capture system is less than 100 percent.
Considering this, the EPA is proposing to conclude that the experience
at Boundary Dam Unit 3 does not support 90 percent CCS as adequately
demonstrated.
ii. CO<INF>2</INF> Capture at Other Coal-Fired Steam Generating Units
To support the prior determination of 90 percent capture as
adequately demonstrated, the EPA cited other applications of CCS at
coal-fired steam generating units. These included CO<INF>2</INF>
capture at the Argus Cogeneration Plant (Trona, California) as well as
at AES's Warrior Run (Cumberland, Maryland) and Shady Point (Panama,
Oklahoma) plants.\141\ In general, these projects were not of an
equivalent size to commercial scale or, in the case of the Argus
Cogeneration Plant, captured far less than 90 percent of
CO<INF>2</INF>.
---------------------------------------------------------------------------

\141\ Dooley, J.J., et al. (2009). ``An Assessment of the
Commercial Availability of Carbon Dioxide Capture and Storage
Technologies as of June 2009.'' U.S. DOE, Pacific Northwest National
Laboratory, under Contract DE-AC05-76RL01830.
---------------------------------------------------------------------------

The EPA also cited Energy Policy Act of 2005 (EPAct05) assisted
projects including a pilot-scale project at Plant Barry (Mobile,
Alabama) and Petra Nova at W.A. Parish Unit 8 (Thompsons, Texas). The
25 MWe (megawatt-equivalent) project at Plant Barry is not reflective
of commercial scale operation.
The Petra Nova project began operation in 2017 and was put into
reserve shutdown (i.e., idled) in May 2020, citing the poor economics
of utilizing captured CO<INF>2</INF> for enhanced oil recovery (EOR) at
that time. On September 13, 2023, it was announced that the carbon
capture facility at Petra Nova had been restarted.\142\ A final report
from the National Energy Technology Laboratory (NETL) details the
challenges faced by the project over

[[Page 25771]]

an initial 3-year period. These included leaks from heat exchangers,
build-up of slurry and solids on the flue gas blower, and build-up of
scale on various components.\143\ While Petra Nova captured 92.4
percent of the CO<INF>2</INF> from the 240 MWe flue gas it processed
over a 3-year period, maintenance to address outages directly
attributable to the CO<INF>2</INF> capture facility were about 10
percent of the year on average over that timeframe. Accounting for
those outages results in a total capture efficiency less than 90
percent. Furthermore, Petra Nova processes a 240 MWe portion of the
flue gas from the 610 MW W. A. Parish Unit 8. At full load, that would
equate to a capture efficiency of about 36 percent of the emissions
from the coal-fired steam generating unit. Additionally, the 90 percent
CCS BSER in the CPS was premised on the CO<INF>2</INF> capture plant
using integrated steam and electricity from the host EGU. However,
Petra Nova uses an auxiliary natural gas-fired combustion turbine
cogeneration unit to provide steam and electricity to the
CO<INF>2</INF> capture process and CO<INF>2</INF> emissions from the
auxiliary cogeneration unit were not captured. Accounting for emissions
from the auxiliary cogeneration unit would lower the capture efficiency
further.
---------------------------------------------------------------------------

\142\ JX Nippon Oil & Gas Exploration Corporation. Restart of
the large-scale Petra Nova Carbon Capture Facility in the U.S.
(September 2023). <a href="https://www.nex.jx-group.co.jp/english/newsrelease/upload_files/20230913EN.pdf">https://www.nex.jx-group.co.jp/english/newsrelease/upload_files/20230913EN.pdf</a>.
\143\ W.A. Parish Post-Combustion CO<INF>2</INF> Capture and
Sequestration Demonstration Project, Final Scientific/Technical
Report (March 2020). <a href="https://www.osti.gov/servlets/purl/1608572">https://www.osti.gov/servlets/purl/1608572</a>.
---------------------------------------------------------------------------

It is unclear whether the auxiliary cogeneration unit provided
additional operational flexibility in how the capture facility was able
to respond to changes in flue gas conditions. Generally, automatic
controls will adjust operation of the capture facility (e.g., flue gas
blower operation, steam load to the reboiler) in response to changing
load and changes in flue gas flowrate and CO<INF>2</INF>
concentration.\144\ When flue gas CO<INF>2</INF> concentrations are at
design levels, the capture facility can maintain design throughput
(i.e., on a lb CO<INF>2</INF>/hr basis) with the host EGU operating as
low as 50 percent load. At lower loads, the capture throughput
decreases proportionally. Generally, the capture facility can operate
between 50 to 100 percent of its design throughput. However,
independent of the capture facility, challenges specific to the
auxiliary cogeneration unit (e.g., handling excess steam) were observed
below 70 percent design throughput, limiting operation at lower
throughputs. Furthermore, the auxiliary cogeneration unit contributed
to additional outages (67 days in 2017, 1 day in 2018, and 20 days in
2019).
---------------------------------------------------------------------------

\144\ Id.
---------------------------------------------------------------------------

iii. Variations in Performance of Capture
The determinations in the CPS assumed that the CO<INF>2</INF>
capture system is available every hour the EGU is operational and
performs at its design capture efficiency (or better) during each of
those hours. The EPA is now proposing to find that it did not
adequately account for variations in performance of CO<INF>2</INF>
capture that would result in a lower capture efficiency. In the CPS,
the EPA did not account for changes in seasonal performance of the
capture system. Both Boundary Dam Unit 3 and Petra Nova reported
challenges during periods of high heat and humidity. At Boundary Dam
Unit 3, ``[t]he third quarter of 2024 (July 1 to September 30) included
an abnormally hot and humid summer, resulting in a slightly lower daily
average capture of 2,675 [metric tons] per day [. . .].'' \145\ For
other quarters, daily average capture rates were 2,867 in the second
quarter of 2024,\146\ 2,484 metric tons per day in the fourth quarter
of 2024,\147\ and 2,553 metric tons per day in the first quarter of
2025.\148\ Reasons for the lower average rate of capture in other
quarters was not provided. At Petra Nova, while the target capture rate
was maintained, a combination of factors including, ``summer ambient
conditions [. . .] resulted in the loss of excess margin in the cooling
system stressing the ability to maintain [. . .] capture [. . .].''
\149\
---------------------------------------------------------------------------

\145\ SaskPower. BD3 Status Update: Q3 2024. <a href="https://www.saskpower.com/about-us/our-company/blog/2024/bd3-status-update-q3-2024">https://www.saskpower.com/about-us/our-company/blog/2024/bd3-status-update-q3-2024</a>.
\146\ SaskPower. BD3 Status Update: Q2 2024. <a href="https://www.saskpower.com/about-us/our-company/blog/2024/bd3-status-update-q2-2024">https://www.saskpower.com/about-us/our-company/blog/2024/bd3-status-update-q2-2024</a>.
\147\ SaskPower. BD3 Status Update: Q4 2024. <a href="https://saskpower.com/about-us/our-company/blog/2025/bd3-status-update-q4-2024">https://saskpower.com/about-us/our-company/blog/2025/bd3-status-update-q4-2024</a>.
\148\ SaskPower. BD3 Status Update: Q1 2025. <a href="https://saskpower.com/about-us/our-company/blog/2025/bd3-status-update-q1-2025">https://saskpower.com/about-us/our-company/blog/2025/bd3-status-update-q1-2025</a>.
\149\ W.A. Parish Post-Combustion CO<INF>2</INF> Capture and
Sequestration Demonstration Project, Final Scientific/Technical
Report (March 2020). <a href="https://www.osti.gov/servlets/purl/1608572">https://www.osti.gov/servlets/purl/1608572</a>.
---------------------------------------------------------------------------

The EPA also did not account for periodic decreases in the
performance of the CO<INF>2</INF> capture system due to solvent
degradation and fouling of components between maintenance cycles.
Boundary Dam Unit 3 experienced challenges with respect to solvent
foaming, biological fouling, scaling, and fouling from fly-
ash.150 151 While actions can be taken to address those
issues, performance and capture efficiency would necessarily decrease
in between treatments or maintenance (e.g., fouling would steadily
accumulate after cleaning). On average, the capture efficiency would
therefore be less than optimal. SaskPower indicated that even after
applying such fixes, Boundary Dam Unit 3 achieved at best a total
capture efficiency of 83 percent when the capture system was
operating.\152\
---------------------------------------------------------------------------

\150\ Giannaris, S., et al. Proceedings of the 15th
International Conference on Greenhouse Gas Control Technologies
(March 15-18, 2021). SaskPower's Boundary Dam Unit 3 Carbon Capture
Facility--The Journey to Achieving Reliability. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3820191">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3820191</a>.
\151\ Pradoo, P., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Improving the Operating Availability of the Boundary Dam Unit 3
Carbon Capture Facility. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286503">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286503</a>.
\152\ U.S. EPA, ``Meeting with SaskPower to Discuss CCS at
Boundary Dam Unit 3.'' January 18, 2024. Document ID No. EPA-HQ-OAR-
2023-0072-8906.
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Furthermore, the EPA did not adequately account for periods of
startup on the availability of the capture system and only provided a
qualitative rationale for why its approach was reasonable.\153\ After
absorption, thermal energy (heat) in the form of steam is required to
release the CO<INF>2</INF> from the CO<INF>2</INF>-rich solvent and
electricity is required to power the compressor to compress the
CO<INF>2</INF> for transport via pipeline. However, prior to
substantial production of steam and electricity, major components of
the capture process may be offline. The EPA cited unspecified process
techniques to address the availability of the capture system at
startup.\154\ Even assuming the capture system could consistently
capture 90 percent CO<INF>2</INF> when operating, any CO<INF>2</INF>
emitted prior to operation of the capture equipment would necessarily
result in the average capture efficiency being less than 90 percent.
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\153\ 89 FR 39854 (May 9, 2024).
\154\ U.S. EPA, Response to Comments Document, April 2024.
Chapter 4.1.5, page 33. Document ID No. EPA-HQ-OAR-2023-0072-8914.
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To consistently achieve 90 percent capture on average, the source
would have to overperform during certain hours. The EPA cited results
from Boundary Dam \155\ that suggested higher capture efficiencies were
achieved at lower throughputs. However, in its justification of the
BSER, the EPA relied on an assumption that sources would be operating
at high capacity throughout the course of the year. If that were the
case, the hypothetical higher capture efficiencies potentially achieved
at lower throughputs would not be observed when the CO<INF>2</INF>
capture system is operated in practice. To otherwise achieve an annual
average capture

[[Page 25772]]

efficiency of 90 percent, higher instantaneous capture efficiencies
would likely need to be achievable. In the CPS, the EPA cited vendor
statements of pilot tests for different commercial amine solvents where
higher capture efficiencies were observed under specific
conditions,\156\ although those capture rates have not been
demonstrated at the commercial scale over the course of a calendar
year. Regardless, the experience at Boundary Dam has shown that it
would be reasonable to anticipate that total capture efficiencies
achieved in practice would be less than design specifications.
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\155\ Jacobs, B., et al. Proceedings of the 16th International
Conference on Greenhouse Gas Control Technologies (October 2022).
Reducing the CO2 Emission Intensity of Boundary Dam Unit 3 Through
Optimization of Operating Parameters of the Power Plant and Carbon
Capture Facilities. <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430">https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4286430</a>.
\156\ 89 FR 39852 (May 9, 2024).
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iv. Projects and Technologies in Development
There are no new post-combustion CCS applications in operation that
are achieving 90 percent capture over the course of a calendar year at
commercial scale. Rather, some of the planned projects cited in the CPS
either have been abandoned or have faced other challenges. Project
Diamond Vault was a planned project to capture up to 95 percent of
CO<INF>2</INF> emissions from the 600 MW Madison Unit 3 at Brame Energy
Center in Lena, Louisiana.\157\ The Front-End Engineering Design (FEED)
study and current plans for carbon capture were abandoned in late
2024.\158\ Project Tundra is a carbon capture project in North Dakota
at the Milton R. Young Station lignite coal-fired power plant. The plan
has been for the capture plant to treat the flue gas from the 455 MW
Unit 2 and some additional flue gas from the 250 MW Unit 1 (an
equivalent capacity of 530 MW in total).\159\ TC Energy, a primary
sponsor of Project Tundra, has since withdrawn from the project,
although the project may continue to move forward depending on various
factors.\160\ The timeframes for several other CCS projects on coal-
fired EGUs are unclear.\161\
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\157\ Project Diamond Vault Overview. <a href="https://www.cleco.com/docs/default-source/diamond-vault/project_diamond_vault_overview.pdf">https://www.cleco.com/docs/default-source/diamond-vault/project_diamond_vault_overview.pdf</a>.
\158\ Cleco Corporate Holdings, LLC SEC Form 10Q, at 51 (August
18, 2024). <a href="https://www.sec.gov/Archives/edgar/data/18672/000108981924000026/cnl-20240630.htm">https://www.sec.gov/Archives/edgar/data/18672/000108981924000026/cnl-20240630.htm</a>.
\159\ ``An Overview of Minnkota's Carbon Capture Initiative--
Project Tundra,'' 2023 LEC Annual Meeting, October 5, 2023.
\160\ Power Engineering. Key partner withdraws from large-scale
CO2 capture project. <a href="https://www.power-eng.com/environmental-emissions/carbon-capture-storage/key-partner-withdraws-from-large-scale-co2-capture-project/">https://www.power-eng.com/environmental-emissions/carbon-capture-storage/key-partner-withdraws-from-large-scale-co2-capture-project/</a>.
\161\ Inside Climate News. A Carbon Capture Project Faces a New
Delay in a Year of Slow Progress for Coal Power Plants Looking for
Retrofits. <a href="https://insideclimatenews.org/news/10122024/north-dakota-coal-plant-carbon-capture-project-faces-new-delay/">https://insideclimatenews.org/news/10122024/north-dakota-coal-plant-carbon-capture-project-faces-new-delay/</a>.
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Finally, the EPA based its prior determination on the assessment of
CO<INF>2</INF> capture using an amine solvent. While other technologies
may be applied for post-combustion CO<INF>2</INF> capture (membranes,
molten salts, cryogenic methods), they are in general less developed
and have yet to be applied at large scale. Some, such as membranes,
while achieving lower capture efficiencies (closer to 70 percent for
membranes), could have the benefit of fewer byproduct emissions and
potentially lower water and/or energy requirements (process steam for
heating) in comparison to amine solvent technologies.\162\ The EPA
notes that higher capture efficiencies of 90 percent could otherwise
complicate commercial deployment of those other technologies.
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\162\ Merkel, Tim, et al. ``Commercial-Scale Front-End
Engineering Design (Feed) Study for MTR's Membrane CO2 Capture
Process.'' November 2022. <a href="https://www.osti.gov/biblio/1897679">https://www.osti.gov/biblio/1897679</a>.
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b. Cost
The EPA has re-evaluated the costs and associated assumptions
underlying the cost analysis of 90 percent CCS on existing long-term
coal-fired steam generating units and is proposing to determine that
the costs are not reasonable. In the CPS, costs for CCS on existing
coal-fired steam generating units were determined assuming a best-case
scenario. Specifically, the cost assessment assumed sources operated at
high annual capacity factors (80 percent) and that the CO<INF>2</INF>
capture equipment was available and performing optimally every hour the
EGU was operating. However, as detailed in the preceding section of
this document, even with a design capture efficiency of 90 percent, the
effective annual capture efficiency is lower, and under some
circumstances significantly lower. Moreover, in 2023, coal-fired EGUs
had an average capacity factor of 42 percent.\163\ Lower capacity
factors typically result in less revenue from electricity generation.
Additionally, less CO<INF>2</INF> captured (lower actual capture
efficiency, lower EGU capacity factor, or both) results in higher costs
due to reduced revenue from the IRC section 45Q tax credit.
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\163\ U.S. Energy Information Administration. Electric Power
Annual. <a href="https://www.eia.gov/electricity/annual/">https://www.eia.gov/electricity/annual/</a>.
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In the CPS, the costs of CCS for existing coal-fired steam
generating units accounted for the IRC 45Q tax credit by reducing the
direct costs to the source for every ton of CO<INF>2</INF> reduced, and
costs were assessed over a period consistent with the 12-year
availability of the IRC section 45Q tax credit. Additionally, rather
than directly considering the costs for any operation after the
expiration of availability of the IRC section 45Q tax credit for
existing coal-fired steam generating units in the CPS, the EPA
committed to review the requirements of the emission guidelines
pertaining to existing coal-fired steam generating units by January 1,
2041, and posited that other mechanisms for potential valuation of EGUs
operating with 90 percent CCS could arise in the future.\164\ However,
those assumptions are no longer reasonable because the EPA believes
that coal-fired steam generating units are now more likely to operate
longer than they will be able to claim the tax credit.
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\164\ 89 FR 39902 (May 9, 2024).
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Under a more realistic set of assumptions that reflect, among other
things, lower capacity factors and the limited availability of the IRC
section 45Q tax credit,\165\ the costs are substantially higher ($53.7/
MWh, $77/ton of CO<INF>2</INF> reduced) than those determined in the
CPS and more than two times higher on a $/MWh basis than the costs the
EPA has previously determined to be reasonable ($18.50/MWh).\166\ Such
high costs, particularly on a $/MWh basis, are not reasonable and do
not support 90 percent CCS as BSER. Additionally, parties that
challenged the CPS in the D.C. Circuit argued that the tax credit
shifts the costs of CCS to taxpayers and that the EPA failed to account
for those costs.\167\ The EPA proposes that this type of cost
calculation is an incorrect accounting for the costs of control as the
EPA should not be considering tax credits when determining the cost of
the control and is specifically taking comment on this position.
Additionally, companies finance cost of controls in various different
ways (e.g., debt financing), and can obtain different interest rates
that are historically not individually calculated when developing
regulations. Moreover, legislation has been introduced in

[[Page 25773]]

Congress to repeal the IRC section 45Q tax credit,\168\ so that owners/
operators cannot be assured that it will be available for purposes of
compliance with the CPS. The costs of 90 percent CCS are not reasonable
without taking into account the tax credit.
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\165\ Capital equipment, etc., consistent with 90 percent design
capture rate, 75 percent actual capture rate, a fixed 40 percent
capacity factor, and 15-year booklife (12 years of 45Q availability,
3 years without). Costs are expressed in 2019$. See memorandum
Updated Evaluation of Best System of Emission Reduction Costs of
Carbon Capture and Sequestration/Storage at Existing Coal-Fired
Electric Generating Units, available in the docket.
\166\ Costs are expressed in 2019$. In a variety of rulemakings,
the EPA has required coal-fired EGUs to install and operate flue gas
desulfurization (FGD, or wet scrubbers) to reduce their
SO<INF>2</INF> emissions. The annualized cost of installing these
controls on a representative 700 to 300 MW coal-fired steam
generating unit are $14.80 to $18.50/MWh. Hence control costs that
are generally consistent with these values should be considered
reasonable. 89 FR 39882 (May 9, 2024).
\167\ West Virginia v. EPA, No. 24-1120 (D.C. Cir. 2024), Doc.
#2083273, at 79-89.
\168\ 119th Congress. H.R.1946--45Q Repeal Act of 2025. <a href="https://www.congress.gov/bill/119th-congress/house-bill/1946/text">https://www.congress.gov/bill/119th-congress/house-bill/1946/text</a>.
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c. Infrastructure
The CPS determined that the capture, pipeline, and sequestration
infrastructure necessary for the affected sources to meet the standards
could be deployed by the compliance date of January 1, 2032. However,
that position relied on the assumption of best-case scenarios. The
equipment for the capture of CO<INF>2</INF> takes time to design,
permit, and install. In the CPS, the Agency assumed an aggressive
timeline for deployment of capture equipment. Of the project schedules
in a report developed by Sargent and Lundy,\169\ the EPA based the
timeline for installation of capture equipment off the more aggressive
schedule that included a 12-month FEED study in place of an 18-month
FEED study. The EPA further abbreviated that schedule by 2 months based
on its own assumptions by shortening the duration for commercial
arrangements from 9 months to 7 months, assuming sources immediately
begin sitework as soon as permitting is complete, and accounting for 13
months (rather than 14) for startup and testing.\170\ However, those
assumptions may not reflect what is achievable for the average source,
and those assumptions furthermore ignore any potential delays.
Regarding transport of CO<INF>2</INF>, there is not an existing network
of CO<INF>2</INF> pipelines with the capacity capable of meeting the
demands in the CPS. While there are about 5,000 miles of CO<INF>2</INF>
pipelines operational in the U.S.,\171\ they are largely not located
near existing coal-fired sources. Planned CO<INF>2</INF> pipelines
continue to face delays due to factors including State permitting and
the challenges associated with eminent domain authority and negotiating
rights-of-way. Summit Carbon Solutions' application for a pipeline in
South Dakota was paused after the State banned eminent domain for
CO<INF>2</INF> pipelines.172 173 A similar law is
progressing through the Iowa State legislature.\174\ Furthermore, while
the U.S. has broad availability of the geologic formations that may
potentially be suitable for CO<INF>2</INF> sequestration, existing
storage infrastructure for sequestration of CO<INF>2</INF> is limited.
In the CPS, the EPA based its assumptions on the availability of
``potential'' storage sites; however, it takes time to characterize
those sites, and it is possible that the nearest available
``potential'' site may not ultimately be suitable. Development of
planned storage sites may also face delays due to permitting and other
issues. Considering these factors, it is unlikely that infrastructure
necessary for CCS can be deployed by the January 1, 2032, compliance
date, and the EPA is therefore proposing that the degree of emission
limitation in the CPS for long-term coal-fired steam generating units
is not achievable.
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\169\ CO<INF>2</INF> Capture Project Schedule and Operations
Memo, Sargent & Lundy (2024). Document ID EPA-HQ-OAR-2023-0072-9095,
Attachment 17.
\170\ 89 FR 39875 (May 9, 2024).
\171\ Congressional Research Service. 2022. Carbon Dioxide
Pipelines: Safety Issues, CRS Reports, June 3, 2022. <a href="https://crsreports.congress.gov/product/pdf/IN/IN11944">https://crsreports.congress.gov/product/pdf/IN/IN11944</a>.
\172\ South Dakota Public Broadcasting. Summit pauses CO2
pipeline application in South Dakota. <a href="https://www.sdpb.org/business-economics/2025-03-12/summit-pauses-co2-pipeline-application-in-south-dakota">https://www.sdpb.org/business-economics/2025-03-12/summit-pauses-co2-pipeline-application-in-south-dakota</a>.
\173\ South Dakota Legislature House Bill 1052. <a href="https://sdlegislature.gov/Session/Bill/25581">https://sdlegislature.gov/Session/Bill/25581</a>.
\174\ Iowa Capital Dispatch. House votes to ban eminent domain
for CO2 pipelines. <a href="https://iowacapitaldispatch.com/2025/03/26/house-votes-to-ban-eminent-domain-for-co2-pipelines/">https://iowacapitaldispatch.com/2025/03/26/house-votes-to-ban-eminent-domain-for-co2-pipelines/</a>.
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d. Conclusion
Because the EPA is proposing to find that 90 percent CCS is not an
adequately demonstrated system of emission reduction and that the cost
of 90 percent CCS for long-term coal-fired steam generating units is
not reasonable, it is proposing to determine that 90 percent carbon
capture and storage is not BSER for long-term coal-fired steam
generating units. Furthermore, because it is unlikely that
infrastructure necessary for CCS can be deployed by the January 1,
2032, compliance date, the EPA is proposing to determine that the
degree of emission limitation in the CPS for long-term coal-fired steam
generating units is not achievable. Consequently, the EPA is proposing
to accordingly repeal the requirements in emission guidelines
pertaining to long-term coal-fired steam generating units. In this
proposed repeal, the EPA is addressing only CCS with 90 percent
capture, because that was the BSER determination in the CPS. Whether
CCS with other, lower rates of capture could be the BSER is outside the
scope of this repeal action.
The EPA solicits comment on the arguments for repealing the 90
percent CCS-based requirements of the emission guidelines pertaining to
long-term coal-fired steam generating units. The EPA solicits comment
on its proposed conclusion that 90 percent CCS is not an adequately
demonstrated system of emission reduction. In particular, the EPA is
requesting input on its proposal that the performance of the
CO<INF>2</INF> capture system at Boundary Dam Unit 3 is not a
sufficient basis for determining that 90 percent CCS is adequately
demonstrated for coal-fired steam generating units. The Agency further
solicits comment on the status and performance of CCS projects and
technologies more generally, especially on projects that inform the
question of whether 90 percent CCS is adequately demonstrated. The EPA
is also requesting comment on its proposed conclusions regarding the
impacts of startup and of variability more generally on CCS
performance, as well as on methods to control process parameters
(pressure, velocity, etc.) and capture efficiencies under startup and
variable load, and what differences in those methods exist where the
CO<INF>2</INF> capture system processes all or part of the flue gas.
The EPA also solicits comment on its proposed conclusion that the
cost of 90 percent CCS for long-term coal-fired steam generating units
is not reasonable, including on any considerations related to taking
the IRC section 45Q tax credit into account when calculating the costs
of CCS in the context of a BSER analysis. The EPA further requests
comment on the costs of CCS for existing coal-fired steam generating
units, including on the interplay of design capture efficiency, actual
capture efficiency, and cost effectiveness.
The EPA also solicits comment on its proposed determination that,
because the infrastructure for CCS is unlikely to be deployed by the
January 1, 2032 compliance date, the degree of emission limitation is
not achievable for long-term coal-fired steam generating units.
2. Natural Gas Co-Firing-Based Requirements for Existing Medium-Term
Coal-Fired Steam Generating Units
The EPA is proposing to determine that 40 percent natural gas co-
firing is not the BSER for medium-term coal-fired steam generating
units. As part of determining the BSER, the EPA takes into account
energy requirements.\175\ As discussed in section III.A. of this
preamble, energy requirements may include the impacts, if any, of the
air pollution controls on the source's own energy needs. The EPA may
further assess energy requirements as they pertain to the energy system
as a whole, on a sector-wide, regional, or national

[[Page 25774]]

basis, as appropriate. In the ACE Rule, the EPA concluded that natural
gas co-firing in a coal-fired steam generating unit, particularly in
high proportions, is an inefficient use of natural gas.\176\ While
coal-fired steam generating units may use small amounts of natural gas
for startup purposes, relatively few use natural gas in proportions
that would have been consistent with the requirements for medium-term
coal-fired steam generating units in the CPS. The higher hydrogen
content of natural gas relative to coal reduces the efficiency of the
boiler; 40 percent natural gas co-firing would result in a decrease in
the boiler efficiency by about 2 percent (to a total efficiency less
than 40 percent). In the CPS, the EPA argued that this decline in
efficiency could be partially offset by decreases in auxiliary power
demand related to coal handling and emissions controls but acknowledged
that there was uncertainty about whether this would be true in all
circumstances.\177\ The EPA explained that the determination in the ACE
Rule that natural gas co-firing was an inefficient use of gas was
informed by the more limited supply of natural gas and the larger
amount of coal-fired EGU capacity and generation that were present when
that rule was promulgated in 2019 relative to when the CPS was
finalized. The CPS rationale went on to say that, since the expected
supply of natural gas had expanded since 2019 and the capacity and
generation of existing coal-fired EGUs had decreased, the total mass of
natural gas that might be required to implement co-firing could be
reduced to reasonable levels.\178\
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\175\ CAA section 111(a)(1).
\176\ 84 FR 32545 (July 8, 2019).
\177\ 89 FR 39895 (May 9, 2024).
\178\ Id.
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The EPA now proposes to find the reasoning in the CPS regarding the
availability of natural gas and the demand that would be associated
with 40 percent co-firing natural gas in coal-fired steam boilers to be
an insufficient basis for determining there would be no significant
adverse consequences related to energy requirements. The EPA believes
that coal-fired steam generating unit capacity and generation will
continue to comprise a substantial portion of the nation's electricity
supply; a number of coal-fired steam generating units are delaying or
canceling their scheduled retirements in light of increasing
electricity demand.\179\ Additionally, the U.S. Energy Information
Administration (EIA) projects that the demand for natural gas, driven
by domestic consumption and liquefied natural gas exports, will grow
both in the near term \180\ as well as in the long term.\181\ Thus, it
is not reasonable to assume that the total volume of natural gas that
would be needed to implement co-firing would be reduced in the CPS
relative to what the EPA expected in 2019 or that diverting that
natural gas from other uses would have no significant adverse impacts
on the energy system. Furthermore, the fact remains that natural gas
may be more efficiently used in natural gas-fired combined cycle EGUs.
New natural gas-fired combined cycle EGUs generally have operating
efficiency of greater than 50 percent. For base load units, heat rates
in new natural gas-fired combined cycle EGUs are approximately 6,700
Btu/kWh whereas heat rates in existing 100 percent natural gas-fired
steam generating units can be more than about 11,000 Btu/kWh. The use
of large amounts of natural gas for combustion in combined cycle EGUs
is more efficient. Considering the energy requirements, the EPA is
proposing that 40 percent natural gas co-firing is not a suitable BSER
for existing coal-fired steam generating units. The EPA solicits
comment on its proposed repeal of the 40 percent co-firing BSER. In
particular, the Agency requests input on considerations related to the
supply of and demand for natural gas, and on how the diversion of
natural gas to coal-fired steam generating units would impact the
energy system. The EPA additionally requests any information related to
the relative efficiency of co-firing natural gas versus using it in a
combustion turbine to generate electricity.
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\179\ Power. U.S. Coal Plants Get Reprieve as Market and
Policies Change. <a href="https://www.powermag.com/u-s-coal-plants-get-reprieve-as-market-and-policies-change/">https://www.powermag.com/u-s-coal-plants-get-reprieve-as-market-and-policies-change/</a>.
\180\ U.S. Energy Information Administration. EIA expects higher
wholesale U.S. natural gas prices as demand increases. <a href="https://www.eia.gov/todayinenergy/detail.php?id=64344">https://www.eia.gov/todayinenergy/detail.php?id=64344</a>.
\181\ U.S. Energy Information Administration, Annual Energy
Outlook 2025. <a href="https://www.eia.gov/outlooks/aeo/data/browser/#/?id=13-AEO2025&cases=ref2025&sourcekey=0">https://www.eia.gov/outlooks/aeo/data/browser/#/?id=13-AEO2025&cases=ref2025&sourcekey=0</a>.
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Additionally or in the alternative, the EPA proposes to find that
40 percent co-firing with natural gas is not the BSER for existing
medium-term coal-fired steam generating EGUs because it constitutes
generation shifting and is therefore beyond the EPA's authority to
require under CAA section 111.\182\ While the EPA considered whether
co-firing natural gas in a coal-fired boiler would constitute
generation shifting in the CPS and concluded that it would not,\183\
the Agency has reexamined the question and is now proposing to find
that a requiring a utility to use a completely different fuel type that
in many cases requires significant new infrastructure to be added to
supply the facility, and can require modification/addition of burners
to the boiler, is impermissible generation shifting. The parties that
challenged the validity of the CPS in the D.C. Circuit similarly
distinguished fuel switching between the same type of fuel (e.g.,
switching from high-sulfur coal to lower sulfur-coal) from fuel
switching between different types of fuel (e.g., switching from coal to
gas in a steam generating boiler) \184\ and argued that the latter runs
afoul of the Supreme Court's decision in West Virginia \185\ that the
EPA cannot base BSER on shifting generation. Similarly, the EPA
proposes to find that a BSER based on forcing a coal-fired EGU to
become a partially natural gas-fired steam generating units shifts that
unit's generation from coal to natural gas and is impermissible under
the Court's precedent because it is an attempt to dictate the market
share of coal versus natural gas. The EPA requests comment on its
proposed conclusion that 40 percent natural gas co-firing cannot be the
BSER for a coal-fired steam generating units because it constitutes
generation shifting.
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\182\ West Virginia v. EPA, No. 24-1120 (D.C. Cir. 2024), Doc.
#2083273, at 110-14.
\183\ U.S. EPA, Response to Comments Document, April 2024.
Chapter 2.7.2, page 101-02. Document ID No. EPA-HQ-OAR-2023-0072-
8914.
\184\ Id. at 112-13.
\185\ 597 U.S. 697 (2022).
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Finally, the EPA proposes to determine that a degree of emission
limitation based on 40 percent natural gas co-firing is not achievable
because it is unlikely that the pipeline infrastructure necessary can
be deployed by the compliance date of January 1, 2030. In the CPS, the
EPA estimated that the maximum aggregate amount of pipeline capacity
needed to implement 40 percent natural gas co-firing would be nearly
14.7 billion cubic feet per day, which would require about 3,500 miles
of pipeline.\186\ The CPS further assumed that sources could obtain the
permits necessary to construct

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