Rule2026-03638
National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units: Final Repeal
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
February 24, 2026
Effective
April 27, 2026
Issuing agencies
Environmental Protection Agency
Abstract
The U.S. Environmental Protection Agency (EPA) is finalizing the repeal of specific amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Coal- and Oil-Fired Electric Utility Steam Generating Units (EGUs), commonly referred to as the Mercury and Air Toxics Standards (MATS), that were promulgated on May 7, 2024. Specifically, the EPA is repealing the revised filterable particulate matter (fPM) emission standard, which serves as a surrogate for non-mercury hazardous air pollutant (HAP) metals for existing coal- fired EGUs; the revised fPM emission standard compliance demonstration requirements; and the revised mercury (Hg) emission standard for lignite-fired EGUs. The EPA is also making technical, non-substantive clarifications to electronic reporting requirements.
Full Text
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[Federal Register Volume 91, Number 36 (Tuesday, February 24, 2026)]
[Rules and Regulations]
[Pages 9088-9134]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-03638]
[[Page 9087]]
Vol. 91
Tuesday,
No. 36
February 24, 2026
Part IV
Environmental Protection Agency
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40 CFR Part 63
National Emission Standards for Hazardous Air Pollutants: Coal- and
Oil-Fired Electric Utility Steam Generating Units: Final Repeal; Final
Rule
Federal Register / Vol. 91, No. 36 / Tuesday, February 24, 2026 /
Rules and Regulations
[[Page 9088]]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 63
[EPA-HQ-OAR-2018-0794; FRL-6716.4-02-OAR]
RIN 2060-AW68
National Emission Standards for Hazardous Air Pollutants: Coal-
and Oil-Fired Electric Utility Steam Generating Units: Final Repeal
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: The U.S. Environmental Protection Agency (EPA) is finalizing
the repeal of specific amendments to the National Emission Standards
for Hazardous Air Pollutants (NESHAP) for Coal- and Oil-Fired Electric
Utility Steam Generating Units (EGUs), commonly referred to as the
Mercury and Air Toxics Standards (MATS), that were promulgated on May
7, 2024. Specifically, the EPA is repealing the revised filterable
particulate matter (fPM) emission standard, which serves as a surrogate
for non-mercury hazardous air pollutant (HAP) metals for existing coal-
fired EGUs; the revised fPM emission standard compliance demonstration
requirements; and the revised mercury (Hg) emission standard for
lignite-fired EGUs. The EPA is also making technical, non-substantive
clarifications to electronic reporting requirements.
DATES: The final rule is effective on April 27, 2026. The Director of
the Federal Register (FR) approved incorporation by reference (IBR) of
certain publications listed in the rule on April 16, 2012 and May 30,
2023.
ADDRESSES: The EPA established a docket for this action under Docket ID
No. EPA-HQ-OAR-2018-0794. All documents in the docket are available on
the <a href="https://www.regulations.gov">https://www.regulations.gov</a> website. Although listed, some
information is not publicly available, e.g., Confidential Business
Information or other information whose disclosure is restricted by
statute. The EPA does not place certain other material, such as
copyrighted material, on the internet; this material is publicly
available only as Portable Document Format (PDF) versions and
accessible only on EPA computers in the docket office reading room. The
public cannot download certain databases and physical items from the
docket but may request these items by contacting the docket office by
telephone at (202) 566-1744. The docket office has 10 business days to
respond to such requests. Except for these items, publicly available
docket materials are available electronically at <a href="https://www.regulations.gov">https://www.regulations.gov</a> or on the EPA computers in the docket office
reading room at the EPA Docket Center, WJC West Building, Room Number
3334, 1301 Constitution Ave. NW, Washington, DC. The Public Reading
Room hours of operation are 8:30 a.m. to 4:30 p.m. Eastern Time (ET),
Monday through Friday. The telephone number for the Public Reading Room
is (202) 566-1744, and the telephone number for the EPA Docket Center
is (202) 566-1742.
FOR FURTHER INFORMATION CONTACT: For information about this final rule,
contact Christopher Werner, Industrial Processing and Power Division
(IPPD) (D243-01), Office of Clean Air Programs (OCAP), U.S.
Environmental Protection Agency, P.O. Box 12055, Research Triangle
Park, North Carolina 27711; telephone number: (919) 541-5133; and email
address: <a href="/cdn-cgi/l/email-protection#017664736f64732f6269736872756e71696473416471602f666e77"><span class="__cf_email__" data-cfemail="2d5a485f43485f034e455f445e59425d45485f6d485d4c034a425b">[email protected]</span></a>. Individuals who are deaf or hard
of hearing, as well as individuals who have speech or communication
disabilities, may use a telecommunications relay service. To learn more
about how to make an accessible telephone call to any of the telephone
numbers shown in this preamble, please visit the web page (<a href="https://www.fcc.gov/trs">https://www.fcc.gov/trs</a>) for the relay service of the Federal Communications
Commission, and a list of relay services is available on their
directory page (<a href="https://www.fcc.gov/general/trs-state-and-territories">https://www.fcc.gov/general/trs-state-and-territories</a>).
SUPPLEMENTARY INFORMATION: Preamble acronyms and abbreviations.
Throughout this notice the use of ``we,'' ``us,'' or ``our'' refers to
the EPA. We use 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:
ACI activated carbon injection
BLDS bag leak detection systems
BTF beyond the floor
Btu British thermal units
CAA Clean Air Act
CEMS continuous emission monitoring system(s)
CFB circulating fluidized bed
CFR Code of Federal Regulations
CPMS continuous parametric monitoring system(s)
CRA Congressional Review Act
EAV equivalent annualized values
ECMPS Emissions Collection and Monitoring Plan System
EGU electric utility steam generating unit
EIA U.S. Energy Information Administration
ESP electrostatic precipitator
FF fabric filter
FGD flue gas desulfurization
fPM filterable particulate matter
FR Federal Register
GACT generally available control technologies
GWh gigawatt-hour
HAP hazardous air pollutant(s)
HCl hydrogen chloride
HF hydrogen fluoride
Hg mercury
HQ hazard quotient
ICR Information Collection Request
IGCC integrated gasification combined cycle
IPPD Industrial Processing and Power Division
IRA Inflation Reduction Act
lb pounds
LEE low emitting EGU
MATS Mercury and Air Toxics Standards
MMBtu million British thermal units of heat input
MW megawatt
NAICS North American Industry Classification System
NESHAP national emission standards for hazardous air pollutants
NTTAA National Technology Transfer and Advancement Act
OCAP Office of Clean Air Programs
OMB Office of Management and Budget
PDF Portable Document Format
PM particulate matter
PM CEMS particulate matter continuous emission monitoring system(s)
PRA Paperwork Reduction Act
PV present values
REL reference exposure level
RFA Regulatory Flexibility Act
RIA Regulatory Impact Analysis
RIN Regulatory Information Number
RTR residual risk and technology review
SO2 sulfur dioxide
SO3 sulfur trioxide
TBtu trillion British thermal units of heat input
TOSHI target organ-specific hazard index
tpy tons per year
UMRA Unfunded Mandates Reform Act
XML Extensible Markup Language
Table of Contents
I. General Information
A. Executive Summary
B. Does this action apply to me?
C. Where can I get a copy of this document and other related
information?
D. Judicial Review and Administrative Reconsideration
II. Background
A. What is the authority for this action?
B. What is the coal- and oil-fired EGU source category, and how
does the NESHAP regulate emissions from the source category?
C. Summary of the 2020 Final Rule
D. Summary of the 2024 Review of the 2020 Final Rule
E. Summary of the 2025 Proposed Repeal
III. Basis for Final Repeal of the 2024 Final Rule
A. Filterable PM Emission Standard for Existing Coal-Fired EGUs
B. Required Compliance Demonstration for the Filterable PM
Standard
[[Page 9089]]
C. Hg Emission Standard for Lignite-Fired EGUs
IV. Comments and Responses on the Relevance of Residual Risk to
Technology Reviews Under CAA Section 112(d)(6)
A. What did the EPA propose and solicit comment on regarding the
relevance of residual risk to technology reviews under CAA section
112(d)(6)?
B. What is the EPA finalizing regarding the relevance of
residual risk to technology reviews under CAA section 112(d)(6)?
C. What key comments did the EPA receive regarding the relevance
of residual risk to technology reviews under CAA section 112(d)(6),
and what are our responses?
V. What is the rationale for other final decisions and amendments
from the reevaluation of the 2024 Final Rule?
VI. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Executive Order 14192: Unleashing Prosperity Through
Deregulation
C. Paperwork Reduction Act (PRA)
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)
K. Congressional Review Act (CRA)
I. General Information
A. Executive Summary
In 2012, the EPA promulgated standards to address HAP emissions--
including mercury, lead, arsenic, chromium, nickel, and cadmium, as
well as hydrogen chloride from coal- and oil-fired EGUs (``2012 MATS
Rule'').\1\ Under CAA section 112, the EPA was required to review the
standards within eight years to identify and address any residual risk
to human health and the environment and, separately, to revise the
standards as ``necessary'' in light of developments in practices,
processes, and control technologies.\2\ The Agency timely completed
these reviews in 2020, finding, among other things, that the existing
standards in the 2012 MATS Rule protected public health with an ample
margin of safety and that further changes to the standards were not
``necessary'' because there were no cost-effective developments in
technology that supported revision (``2020 Final Rule'').\3\
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\1\ 77 FR 9304 (February 16, 2012).
\2\ CAA section 112(d)(6), (f)(2). CAA section 112 is codified
at 42 U.S.C. 7412.
\3\ 85 FR 31286 (May 22, 2020).
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Following a change in administration, however, an Executive Order
instructed the EPA to reconsider and suspend, revise, or rescind the
2020 Final Rule if appropriate.\4\ On May 7, 2024, the EPA finalized
several MATS amendments after initiating a rulemaking in response to
the Executive Order (``2024 Final Rule'').\5\ In the 2024 Final Rule,
the EPA confirmed that the 2020 risk review finding that the 2012 MATS
Rule protected public health and the environment with an ample margin
of safety as required by CAA section 112(f)(2) was correct.\6\
Nevertheless, upon reconsideration of the technology review under
section 112(d)(6), the Agency established more stringent standards for
the non-Hg metal HAP emissions and for fPM emissions (which serves as a
surrogate for non-Hg metal HAP) from coal-fired EGUs and for mercury
emissions from lignite-fired units and required all EGUs to install
continuous emissions monitoring systems (CEMS) to monitor emissions of
fPM, thereby removing existing compliance flexibilities in favor of a
uniform, one-size-fits-all approach. The Agency reasoned that the
revisions to MATS were warranted because ``the size and unique nature
of the coal-fired power sector'' made the revisions ``necessary,'' but
the revisions were based on relatively limited data concerning
potential improvements in control technology and established despite
the fact that the costs of the revisions were and are higher than
anything the Agency has previously determined ``necessary'' pursuant to
section 112(d)(6).\7\
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\4\ Executive Order 13990, ``Protecting Public Health and the
Environment and Restoring Science to Tackle the Climate Crisis,'' 86
FR 7037 (January 25, 2021), since rescinded by Executive Order
14148, ``Initial Rescissions of Harmful Executive Orders and
Actions,'' 90 FR 8237 (January 28, 2025).
\5\ 89 FR 38508 (May 7, 2024).
\6\ Id. at 38518; see 88 FR 24866 (April 24, 2023) (proposed
rule for the 2024 Final Rule).
\7\ 89 FR 38534 (May 7, 2024).
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On March 12, 2025, Administrator Zeldin announced that the Agency
would reconsider the 2024 Final Rule.\8\ On June 17, 2025, the EPA
undertook a review of the 2024 Final Rule and proposed to repeal most
of its amendments (``2025 Proposal'').\9\ This action was consistent
with several Executive Orders and other Presidential Actions. In
particular, Executive Order 14154, ``Unleashing American Energy,''
specifies that it is the policy of the United States to ``protect the
United States's economic and national security and military
preparedness by ensuring that an abundant supply of reliable energy is
readily accessible in every State and territory of the Nation'' and
``to ensure that all regulatory requirements related to energy are
grounded in clearly applicable law'' (among other considerations).\10\
The Executive Order directed the heads of all agencies to review all
existing regulations to identify 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 minerals, and nuclear energy resources.
This Executive Order also directed agencies, consistent with applicable
law, to suspend, revise, or rescind all agency actions identified as
unduly burdensome and revoked Executive Order 13990. This Executive
Order was followed by Executive Order 14179, ``Removing Barriers to
American Leadership in Artificial Intelligence;'' \11\ Executive Order
14192, ``Unleashing Prosperity Through Deregulation;'' \12\ Executive
Order 14262, ``Strengthening the Reliability and Security of the United
States Electric Grid;'' \13\ and Executive Order 14261,
``Reinvigorating America's Beautiful Clean Coal Industry and Amending
Executive Order 14241,'' 90 FR 15517 (April 14, 2025).
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\8\ <a href="https://www.epa.gov/newsreleases/epa-launches-biggest-deregulatory-action-us-history">https://www.epa.gov/newsreleases/epa-launches-biggest-deregulatory-action-us-history</a>.
\9\ 90 FR 25535 (June 17, 2025).
\10\ 90 FR 8353 (January 29, 2025).
\11\ 90 FR 8741 (January 31, 2025).
\12\ 90 FR 9065 (February 6, 2025).
\13\ 90 FR 15521 (April 14, 2025).
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In addition, on April 8, 2025, President Trump signed a
Proclamation titled ``Regulatory Relief for Certain Stationary Sources
to Promote American Energy.'' \14\ This Proclamation exempted certain
stationary sources, identified in Annex 1 of the Proclamation, from
compliance with the 2024 Final Rule pursuant to CAA section
112(i)(4).\15\ The President's exemption is for a period of two years
beyond the 2024 Final Rule's compliance date (i.e., for the period
beginning July 8, 2027, and concluding July 8, 2029). Sources
identified in Annex 1 will remain subject to the 2012 MATS Rule during
the two-year extension period. Copies of the Presidential Proclamation
and
[[Page 9090]]
Annex 1 are available in the rulemaking docket.\16\
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\14\ 90 FR 16777 (April 21, 2025).
\15\ ``Regulatory Relief for Certain Stationary Sources to
Further Promote American Energy'' was issued on July 17, 2025, and
added six sources to Annex 1. See 90 FR 34583 (July 23, 2025).
\16\ Document ID No. EPA-HQ-OAR-2018-0794-6980.
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In the 2025 Proposal, the EPA proposed to repeal the three key
amendments finalized in the 2024 Final Rule based on the EPA's
authority under CAA section 112 and the EPA's authority to reconsider
previous decisions taken under that authority to the extent permitted
by law and supported by a reasoned explanation.\17\ The Agency noted
that the proposed repeal was in accordance with the above-noted
Executive Orders and solicited comment on whether the 2024 Final Rule
had erred in evaluating cost-effectiveness and technical feasibility
when deciding that revisions were ``necessary.'' \18\ In addition, the
Agency sought comment on whether it should consider the potential for
meaningful risk reduction when evaluating costs as part of determining
whether revisions are ``necessary'' in a technology review.\19\
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\17\ FDA v. Wages & White Lion Invs., L.L.C., 604 U.S. 542, 568
(2025); FCC v. Fox Television Stations, Inc., 556 U.S. 502, 515
(2009); see also Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto.
Ins. Co., 463 U.S. 29, 42 (1983).
\18\ 90 FR 25544-45 (June 17, 2025).
\19\ Id. at 25545.
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In this final rule, the EPA is repealing the following three MATS
amendments from the 2024 Final Rule:
<bullet> The fPM emission standard for existing coal-fired EGUs,
which the EPA revised from 0.030 pounds per million British thermal
units (lb/MMBtu) to 0.010 lb/MMBtu;
<bullet> The compliance demonstration requirement for the fPM
emission standard for all coal- and oil-fired EGUs, which the EPA
revised from allowing EGU owners and operators to choose between use of
quarterly stack testing, use of continuous parametric monitoring
systems (CPMS), or use of PM continuous emission monitoring systems
(CEMS) to allowing only the use of PM CEMS; and
<bullet> The Hg emission standard for existing lignite-fired EGUs,
which the EPA revised from 4.0 pounds per trillion British thermal
units (lb/TBtu) to 1.2 lb/TBtu.
The EPA has reevaluated the 2024 Final Rule and, after considering
public comments, finds that the revisions to the emissions standards
were not ``necessary'' because they impose unwarranted compliance costs
or raise potential technical feasibility concerns. With respect to the
revised fPM emission standard, the EPA has two separate, and severable,
bases for this finding. First, the EPA finds that the cost-
effectiveness values associated with this standard (i.e., the cost per
mass of fPM or non-Hg HAP metal(s) reduced) are significantly higher
than cost-effectiveness values that the Agency previously accepted in
other technology reviews and related CAA section 112 actions for which
cost is a factor. Unlike in the 2024 Final Rule, the Agency does not
believe it is consistent with prior practice or reasonable to disregard
such cost-effectiveness comparators and does not believe that
differences between the EGU source category and other source categories
justify establishment of a new high-cost benchmark for fPM as a
surrogate for non-Hg metal HAP. Second, in undertaking review of the
2024 rule, the EPA also considered the Agency's conclusion from the
2020 residual risk review, confirmed by the 2024 Final Rule, that there
is little risk remaining from emissions of non-Hg HAP metals following
the implementation of the emissions standards promulgated in the 2012
MATS Rule. For the reasons set forth later in this preamble, the Agency
concludes that the low levels of remaining risk found in the prior
residual risk review are relevant to the cost reasonableness of revised
standards and therefore to whether it is ``necessary'' to promulgate
revised standards that impose additional costs.
With respect to the requirement to utilize PM CEMS for compliance
demonstrations, the EPA finds this requirement is an unnecessary
expense for coal- and oil-fired EGUs and that owners and operators
should retain the option of using other monitoring methods to
demonstrate compliance with the fPM emission standard. For the reasons
set forth later in this preamble, mandating the use of PM CEMS and
removing previously available compliance alternatives was not
``necessary'' pursuant to CAA section 112(d)(6). Furthermore, although
the EPA in the 2024 Final Rule invoked CAA section 114(a)(1)(C) as
offering additional authority for the PM CEMS requirement, that
provision is equally applicable to the alternative compliance
demonstration options restored in this final rule.
Finally, the EPA finds that the revised Hg emission standard for
lignite-fired EGUs is not achievable given the broad range of boiler
types and varying compositions of the different lignite fuels used at
those facilities. As set forth later in this preamble, in light of this
variability, the revised standard was based on insufficient data. As a
result, the EPA finds that these revisions to the emission standards
were not ``necessary'' under CAA section 112(d)(6), and is repealing
them. As noted above, this action is consistent with Executive Order
14192, ``Unleashing Prosperity Through Deregulation,'' \20\ Executive
Order 14154, ``Unleashing American Energy,'' \21\ and Executive Order
14261, ``Reinvigorating America's Beautiful Clean Coal Industry and
Amending Executive Order 14241,'' \22\ among other recent Presidential
actions.
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\20\ 90 FR 9065 (February 6, 2025).
\21\ 90 FR 8353 (January 29, 2025).
\22\ 90 FR 15517 (April 14, 2025).
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The EPA estimates that this action will result in present value
cost savings of $670 million at a 3 percent discount rate and $490
million at a 7 percent discount rate over the 2028 to 2037 timeframe,
with total annualized cost savings of $78 and $69 million per year,
respectively (in 2024 dollars).
B. Does this action apply to me?
Regulated entities. Table 1 of this preamble presents categories
and entities that this action potentially regulates.
Table 1--NESHAP and Industrial Source Categories Affected
by This Final Action
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NESHAP and source category NAICS \1\ code
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Coal and oil-fired EGUs (40 CFR part 63, subpart UUUUU). 221112,
221122, 921150
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\1\ North American Industry Classification System (NAICS).
[[Page 9091]]
The EPA does not intend Table 1 of this preamble to be exhaustive
but rather to provide a guide for readers regarding the entities that
this final action likely affects. To determine if this action affects
your facility, you should examine the applicability criteria in title
40 of the Code of Federal Regulations (CFR), part 63, subpart UUUUU. If
you have any questions regarding the applicability of any aspect of
this NESHAP, please contact the appropriate person listed in the
preceding FOR FURTHER INFORMATION CONTACT section of this preamble.
C. Where can I get a copy of this document and other related
information?
In addition to the docket, an electronic copy of this final rule is
available on the internet. A brief summary of this rule is available at
<a href="https://www.regulations.gov">https://www.regulations.gov</a>, Docket ID No. EPA-HQ-OAR-2018-0794.
Following signature by the EPA Administrator, the EPA will post a copy
of this rule at: <a href="https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards">https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards</a>. Following publication in the Federal
Register, the EPA will post the Federal Register version and key
technical documents at this same website.
The changes to the regulatory text are being finalized in this
rule. In addition, a redline strikeout memorandum showing the rule
edits necessary to incorporate the changes to 40 CFR part 63, subpart
UUUUU, finalized in this action is available in the docket. Following
signature by the Administrator, the EPA also will post a copy of this
preamble to <a href="https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards">https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards</a>.
D. Judicial Review and Administrative Reconsideration
Under CAA section 307(b)(1), judicial review of this final action
is available only by filing a petition for review in the United States
Court of Appeals for the District of Columbia Circuit (``D.C.
Circuit'') by April 27, 2026. CAA section 307(b)(2) prohibits a party
from challenging this final rule separately in any civil or criminal
proceedings brought by the EPA for enforcement.
CAA section 307(d)(7)(B) further provides that only an objection to
a rule or procedure that was raised with reasonable specificity during
the period for public comment (including any public hearing) may be
raised during judicial review. This section also requires the EPA to
reconsider the rule if the person raising an objection can demonstrate
to the Administrator that it was impracticable to raise such objection
within the period for public comment or if the grounds for such
objection arose after the period for public comment (but within the
time specified for judicial review) and if such objection is of central
relevance to the outcome of the rule. Any person seeking to make such a
demonstration should submit a Petition for Reconsideration to the
Office of the Administrator, U.S. EPA, Room 3000, WJC South Building,
1200 Pennsylvania Ave. NW, Washington, DC 20460, with a copy to both
the person(s) listed in the preceding FOR FURTHER INFORMATION CONTACT
section and the Associate General Counsel for the Air and Radiation Law
Office, Office of General Counsel (Mail Code 2344A), U.S. EPA, 1200
Pennsylvania Ave. NW, Washington, DC 20460.
II. Background
A. What is the authority for this action?
1. What is the statutory authority for this action?
The statutory authority for this action is provided by CAA section
112, as amended (42 U.S.C. 7412). CAA section 112 establishes a multi-
stage regulatory process to develop standards for emissions of HAP from
stationary sources. Generally, the first stage involves establishing
technology-based standards that reflect the maximum achievable control
technology (MACT) or an appropriate alternative.\23\ The second stage
involves evaluating those standards within eight years under CAA
section 112(f)(2) to determine whether additional standards are needed
to address any remaining risk associated with HAP emissions.\24\ This
second stage is commonly referred to as the ``residual risk review.''
In addition to the residual risk review, CAA section 112(d)(6) also
requires the EPA to review the standards every eight years and ``revise
as necessary'' taking into account ``developments in practices,
processes, and control technologies.'' \25\ This review is commonly
referred to as the ``technology review.'' The discussion that follows
identifies the most relevant statutory sections and briefly explains
the contours of the methodology used to implement these statutory
requirements.
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\23\ 42 U.S.C. 7412(d)(1)-(4).
\24\ Id. 7412(f)(2).
\25\ Id. 7412(d)(6).
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In the first stage of the CAA section 112 standard-setting process,
the EPA promulgates technology-based standards under CAA section 112(d)
for categories of sources identified as emitting one or more of the HAP
listed in CAA section 112(b). Sources of HAP emissions are either major
sources or area sources, and CAA section 112 establishes different
requirements for major source standards and area source standards. The
requirements for major sources are the relevant requirements for the
present rulemaking. ``Major sources'' are those that emit or have the
potential to emit 10 tons per year (tpy) or more of a single HAP or 25
tpy or more of any combination of HAP.\26\ For major sources, CAA
section 112(d)(2) provides that the technology-based NESHAP must
reflect the maximum degree of reduction in emissions of HAP achievable
(after considering cost, energy requirements, and non-air quality
health and environmental impacts). These standards are commonly
referred to as MACT standards. CAA section 112(d)(3) also establishes a
minimum control level for MACT standards, known as the MACT ``floor,''
which is based on emission controls achieved in practice by a certain
percentage of the best performing sources. The EPA also considers
control options that are more stringent than the floor. Standards more
stringent than the floor are commonly referred to as ``beyond-the-
floor'' standards.
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\26\ Id. 7412(a)(1).
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The next stage in standard-setting focuses on identifying and
addressing any remaining (i.e., ``residual'') risk within eight years
pursuant to CAA section 112(f)(2) and concurrently conducting a
technology review pursuant to CAA section 112(d)(6). This latter
provision requires the EPA to review standards promulgated under CAA
section 112 and revise them ``as necessary (taking into account
developments in practices, processes, and control technologies)'' no
less often than every eight years. In conducting this review, which we
call the ``technology review,'' the EPA is not required to recalculate
the MACT floors that were established in earlier rulemakings.\27\ The
EPA considers cost in deciding whether to revise the standards pursuant
to CAA section 112(d)(6).
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\27\ Ass'n of Battery Recyclers, Inc. v. EPA, 716 F.3d 667 (D.C.
Cir. 2013); Natural Resources Def. Council (NRDC) v. EPA, 529 F.3d
1077, 1084 (D.C. Cir. 2008).
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CAA section 112(d)(6) and relevant case law provide the EPA with
flexibility to consider additional relevant factors other than those
enumerated in section 112(d)(6) when deciding whether revisions to
existing
[[Page 9092]]
standards are ``necessary.'' The D.C. Circuit has held that the CAA
section 112(d)(6) requirement to periodically review and revise CAA
section 112 emission standards ``as necessary'' is not limited to the
consideration of ``developments in practices, processes and control
technologies.'' \28\ Rather, ``the operative standard is `revise as
necessary,' with the parenthetical pointing to a non-exhaustive list of
considerations.'' \29\ The Supreme Court also emphasized in Michigan v.
EPA that unless the statute provides otherwise, broad terms such as
``necessary'' direct the relevant agency to consider all relevant
factors, including by assessing the cost of an action relative to the
anticipated benefits.\30\ That decision is particularly relevant here
because the Court was interpreting a related provision of CAA section
112 that instructs the Administrator to determine whether it is
``appropriate and necessary'' to regulate HAP emissions from EGUs.\31\
Thus, under relevant case law, when the EPA is deciding whether it is
``necessary'' to revise standards pursuant to CAA section 112(d)(6),
the Agency can consider the costs of any developments in practices,
processes, and control technologies.
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\28\ La. Envtl. Action Network (LEAN) v. EPA, 955 F.3d 1088,
1097 (D.C. Cir. 2020).
\29\ Id.; see also Nat'l Ass'n for Surface Finishing v. EPA, 795
F.3d 1, 11 (D.C. Cir. 2015); Ass'n of Battery Recyclers, 716 F.3d at
673-74.
\30\ 576 U.S. 743, 752-53 (2015).
\31\ See id. (interpreting 42 U.S.C. 7412(n)(1)(A)).
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The EPA is also finalizing that the results of a prior residual
risk review under CAA section 112(f)(2) can be relevant under certain
circumstances when evaluating whether it is ``necessary'' to revise
standards under CAA section 112(d)(6). Specifically, as relevant here,
where the remaining risk of cancer from the sources in this category is
below 1-in-1 million, cost considerations bear additional weight in
determining whether revised standards are ``necessary'' under CAA
section 112(d)(6). In section III.A.2 of this preamble, we elaborate on
this approach, including discussing its basis in CAA section 112 and
its consistency with prior NESHAP technology reviews.
2. What is the authority for revisiting the 2024 Final Rule?
The EPA's authority to revisit existing regulations under CAA
section 112 is well-grounded in law. Specifically, the EPA has
authority to reconsider, repeal, or revise past decisions to the extent
permitted by law so long as the Agency provides a reasoned
explanation.\32\ This is true when, as is the case here, an agency
reconsiders a prior regulation after a change in administration.\33\
When permitted by the statutory scheme, ``[a]gencies obviously have
broad discretion to reconsider a regulation at any time.'' \34\
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\32\ See, e.g., Motor Vehicle Mfrs. Ass'n, 463 U.S. at 42
(``[R]egulatory agencies do not establish rules of conduct to last
forever [and] an agency must be given able latitude to adapt their
rules and policies to . . . changing circumstances.''); see also
Clean Water Action v. EPA, 936 F.3d 308, 313 (5th Cir. 2019) (``EPA
correctly surmised that, in addition to its statutory authority to
revise rules . . . administrative agencies possess the inherent
authority to revise previously-promulgated rules, so long as they
follow the proper administrative requirements and provide a reasoned
basis for the agency decision.'').
\33\ Nat'l Ass'n of Home Builders v. EPA, 682 F.3d 1032, 1038,
1043 (D.C. Cir. 2012) (explaining that an agency's ``reevaluation of
which policy would be better in light of the facts'' is ``well
within'' its discretion and that a change in administration is a
``perfectly reasonable basis for an executive agency's reappraisal
of the costs and benefits of its programs and regulations''
(internal quotation marks omitted)). For this rulemaking, no
commenters contested that the EPA has authority to reconsider a
prior rule under CAA section 112(d)(6), although some argued that
the EPA is impermissibly weakening a prior CAA section 112 rule.
\34\ Clean Air Council v. Pruitt, 862 F.3d 1, 8-9 (D.C. Cir.
2017).
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B. What is the coal- and oil-fired EGU source category, and how does
the NESHAP regulate emissions from the source category?
The EPA promulgated the Mercury and Air Toxics Standards on
February 16, 2012. The standards are codified at 40 CFR part 63,
subpart UUUUU. Coal- and oil-fired EGUs are combustion units of more
than 25 megawatts (MW) that serve a generator that produces electricity
for sale and are located at both major and area sources of HAP
emissions.\35\ For coal-fired EGUs, the 2012 MATS Rule established
standards to limit emissions of Hg, acid gas HAP (e.g., hydrogen
chloride (HCl), hydrogen fluoride (HF)), non-Hg HAP metals (e.g.,
nickel, lead, chromium), and organic HAP (e.g., formaldehyde, dioxin/
furan). Emission standards for HCl serve as a surrogate for all the
acid gas HAP. For coal-fired EGUs with flue gas desulfurization (FGD),
an alternate standard for sulfur dioxide (SO<INF>2</INF>) may be used
as a surrogate for all acid gas HAP if SO<INF>2</INF> CEMS are
installed and operational. Standards for fPM serve as a surrogate for
the non-Hg HAP metals, with total and individual HAP metals standards
provided as an alternative. The EPA chose fPM as a surrogate for non-Hg
HAP metals because non-Hg HAP metals are predominantly a component of
the filterable fraction of total PM (which is composed of a filterable
and condensable fraction), and control of fPM emissions also results in
control of emissions of non-Hg HAP metals.\36\ Additionally, not all
fuels emit the same type and amount of non-Hg HAP metals, but most
generally emit fPM that includes some amount and combination of all the
non-Hg HAP metals. Finally, using fPM as a surrogate eliminates the
cost of performance testing to demonstrate compliance with numerous
standards for individual non-Hg HAP metals.\37\
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\35\ A unit that cogenerates steam and electricity and supplies
more than one-third of its potential electric output capacity and
more than 25 MW electrical output to any utility power distribution
system for sale is also an electric utility steam generating unit.
\36\ Selenium may be present in the filterable PM or the
condensable fraction as the acid gas, SeO<INF>2.</INF>
\37\ Document ID No. EPA-HQ-OAR-2009-0234.
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In addition, the EPA established work practice standards to limit
the formation and emissions of organic HAP. For oil-fired EGUs, the
2012 MATS Rule established standards to limit emissions of HCl and HF,
total HAP metals (e.g., Hg, nickel, lead), and organic HAP (e.g.,
formaldehyde, dioxin/furan). Standards for fPM also serve as a
surrogate for total HAP metals, with standards for total and individual
HAP metals provided as alternative equivalent standards.
C. Summary of the 2020 Final Rule
The 2020 Final Rule included two separate decisions. First, the EPA
responded to the Supreme Court's remand in Michigan by concluding that
it is not ``appropriate and necessary'' pursuant to CAA section
112(n)(1)(A) to regulate coal- and oil-fired EGUs under CAA section
112.\38\ Second, the EPA completed the combined RTR for MATS due 8
years from the promulgation of the 2012 MATS Rule. As part of the RTR,
the EPA conducted the residual risk review (``2020 Residual Risk
Review'') pursuant to CAA section 112(f)(2), which requires the EPA to
determine whether promulgation of additional standards is needed to
provide an ample margin of safety to protect public health or to
prevent an adverse environmental effect. Also, the EPA conducted a
technology review (``2020 Technology Review'') pursuant to CAA section
112(d)(6), which focused on identifying and evaluating developments in
practices, processes, and control technologies that occurred
[[Page 9093]]
since promulgation of the 2012 MATS Rule to determine whether revisions
to the standards were otherwise ``necessary.''
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\38\ As noted below, in 2023, the EPA reversed its position from
the 2020 Final Rule and concluded that regulation of coal- and oil-
fired EGUs is ``appropriate and necessary'' under CAA section
112(n)(1)(A). 88 FR 13956 (March 6, 2023) (``2023 Final Rule''). In
the present rulemaking, the EPA is not reconsidering the
``appropriate and necessary'' finding in the 2020 Final Rule or 2023
Final Rule.
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The EPA presented the results of the 2020 Residual Risk Review,
including the Agency's decisions regarding risk acceptability, ample
margin of safety, and adverse environmental effects, in the 2020 Final
Rule. Table 2 below summarizes the results of the risk assessment; more
detail is available in the document entitled Residual Risk Assessment
for the Coal- and Oil-Fired EGU Source Category in Support of the 2020
Risk and Technology Review Final Rule, which is available in the docket
for this rulemaking.\39\ The EPA found the residual risk due to
emissions of air toxics from this source category to be acceptable and
determined that the 2012 MATS Rule provided an ample margin of safety
to protect public health and prevent adverse environmental effects.
Therefore, the EPA did not make any revisions to the 2012 MATS Rule to
address residual risk.
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\39\ Document ID No. EPA-HQ-OAR-2018-0794-4553.
Table 2--Coal- and Oil-Fired EGU Inhalation Risk Assessment Results in the 2020 Final Rule
[85 FR 31286, May 22, 2020]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Maximum individual Population at increased Annual cancer incidence Maximum chronic Maximum screening
cancer risk (in 1 risk of cancer >=1-in-1 (cases per year) noncancer TOSHI \3\ acute noncancer HQ
million) \2\ million -------------------------------------------------- \4\
-------------------------------------------------- Based on . . . Based on . . . --------------------
Number of facilities \1\ Based on . . . Based on . . . --------------------------------------------------
--------------------------------------------------
Actual Allowable Actual Allowable Actual Allowable Actual Allowable Based on actual
emissions emissions emissions emissions emissions emissions emissions emissions emissions level
level level level level level level level level
--------------------------------------------------------------------------------------------------------------------------------------------------------
322............................ 9 10 193,000 636,000 0.04 0.1 0.2 0.4 HQREL = 0.09
(arsenic).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Number of facilities evaluated in the risk analysis. At the time of the risk analysis there were an estimated 323 facilities in the coal- and oil-
fired EGU source category; however, one facility is in Guam, which was beyond the geographic range of the model used to estimate risks. Therefore, the
Guam facility was not modeled and the emissions for that facility were not included in the assessment.
\2\ Maximum individual excess lifetime cancer risk due to HAP emissions from the source category.
\3\ Maximum target organ-specific hazard index (TOSHI). The target organ systems with the highest TOSHI for the source category are respiratory and
immunological.
\4\ The maximum estimated acute exposure concentration was divided by available short-term threshold values to develop an array of hazard quotient (HQ)
values. HQ values shown use the lowest available acute threshold value, which in most cases is the reference exposure level (REL). When an HQ exceeds
1.0, we also show the HQ using the next lowest available acute dose-response value.
The 2020 Residual Risk Review also included more particularized
risk determinations. As relevant here, these included determining that
the maximum lifetime cancer risk from coal-fired EGUs ranged from
0.002-in-1 million to 0.3-in-1 million.\40\
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\40\ Residual Risk Assessment for the Coal- and Oil-Fired EGU
Source Category in Support of the 2020 Risk and Technology Review
Final Rule. This report is referred to as the 2020 Residual Risk
Review throughout the preamble.
---------------------------------------------------------------------------
The 2020 Final Rule also presented the results of the 2020
Technology Review, which focused on identifying and evaluating
developments in practices, processes, and control technologies that
occurred since promulgation of the 2012 MATS Rule to determine whether
revisions are ``necessary'' in light of all relevant considerations.
Control technologies typically used to minimize emissions of pollutants
that have numeric emission limits under the 2012 MATS Rule include
electrostatic precipitators (ESPs) and fabric filters (FFs) for control
of fPM as a surrogate for non-Hg HAP metals; wet scrubbers, dry
scrubbers, and dry sorbent injection for control of acid gases (e.g.,
SO<INF>2</INF>, HCl, and HF); and activated carbon injection (ACI) and
other Hg-specific technologies for control of Hg. In the 2020
Technology Review, the EPA did not identify any developments in
practices, processes, or control technologies that would achieve
further cost-effective emissions reductions and thus did not make any
changes to the emission standards or other requirements in the 2012
MATS Rule. More information on the 2020 Technology Review is presented
in the memorandum entitled Technology Review for the Coal- and Oil-
Fired EGU Source Category, which is available in the docket for this
rulemaking.\41\
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\41\ Document ID No. EPA-HQ-OAR-2018-0794-0015.
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D. Summary of the 2024 Review of the 2020 Final Rule
Executive Order 13990, ``Protecting Public Health and the
Environment and Restoring Science to Tackle the Climate Crisis,''
instructed the EPA to review the 2020 Final Rule and to consider
publishing a notice of proposed rulemaking suspending, revising, or
rescinding that action.\42\ The EPA reviewed the finding in the 2020
Final Rule that it was not appropriate and necessary to regulate coal-
and oil-fired EGUs under CAA section 112 and, on February 9, 2022,
proposed to find that it is appropriate and necessary to regulate coal-
and oil-fired EGUs under CAA section 112.\43\ The EPA made the
affirmative finding on March 6, 2023.\44\
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\42\ 86 FR 7037 (January 25, 2021), rescinded by Executive Order
14148, ``Initial Rescissions of Harmful Executive Orders and
Actions,'' 90 FR 8237 (January 28, 2025).
\43\ 87 FR 7624 (February 9, 2022).
\44\ 88 FR 13956 (March 6, 2023).
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On April 24, 2023, the EPA proposed the results of the Agency's
review of the RTR from the 2020 Final Rule.\45\ In the 2023 proposed
rule, the EPA noted the conclusions from the 2020 Residual Risk Review,
as shown in Table 2 of this preamble, including the finding that
residual risk due to emissions of air toxics from this source category
was acceptable and that the 2012 MATS Rule provided an ample margin of
safety to protect public health and prevent adverse environmental
effects. Further, the EPA explained that it had ``review[ed] the 2020
residual risk analysis, [and] . . . determined that the risk analysis
was rigorous, robust, and conducted using approaches and methodologies
that are consistent with those that have been utilized in residual risk
analyses and reviews for other industrial sectors.'' \46\ For these
reasons, the EPA did not reopen the 2020 Residual Risk Review and did
not propose changes to any emissions standards or other requirements
for the purpose of addressing the remaining risk.\47\
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\45\ 88 FR 24854 (April 24, 2023).
\46\ Id. at 24866.
\47\ Id.
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The EPA's review of the 2020 Technology Review included evaluating
the technology review \48\ and focused on
[[Page 9094]]
the identification of any developments in practices, processes, and
control technologies that have occurred since the finalization of the
2012 MATS Rule and since publishing the 2020 Technology Review. Based
on that review, the EPA concluded that revisions to certain standards
were warranted and proposed three changes. First, the EPA proposed to
revise the existing coal-fired EGU fPM emissions standard, which is a
surrogate for non-Hg HAP metals, from 0.030 lb/MMBtu to 0.010 lb/MMBtu,
and proposed corresponding reductions in the alternative emission
standards for total and individual non-Hg HAP metals. Second, the EPA
proposed to require that all coal- and oil-fired EGUs demonstrate
compliance with the applicable fPM emission standard exclusively by
using PM CEMS, and to remove the option of using alternative compliance
demonstrations. Third, the EPA proposed to revise the Hg emission
standard for lignite-fired EGUs from 4.0 lb/TBtu to 1.2 lb/TBtu with an
alternative output-based standard of 0.013 lb/gigawatt-hour (GWh). All
proposed changes were ultimately promulgated in the 2024 Final
Rule.\49\
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\48\ Described in Document ID No. EPA-HQ-OAR-2018-0794-0015.
\49\ In the 2024 Final Rule, the EPA also removed paragraph (2)
of the definition of ``startup'' in 40 CFR 63.10042. See 89 FR 38550
(May 7, 2024). The regulation now requires that all EGUs use the
work practice standards in paragraph (1) of the definition of
``startup'' in 40 CFR 63.10042, which was already being used by
virtually all affected EGUs. The EPA made this revision in response
to Chesapeake Climate Action Network v. EPA, 952 F.3d 310 (D.C. Cir.
2020), in which the D.C. Circuit remanded the alternative
``startup'' work practice standard in paragraph (2) to the EPA for
reconsideration. The compliance deadline for the changes to the
``startup'' definition was January 2, 2025. The EPA did not propose
amendments to this aspect of the 2024 Final Rule and is not
finalizing any changes to the ``startup'' definition at this time.
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In the 2024 Final Rule, the EPA established a substantially more
stringent fPM emission standard, which serves as a surrogate for the
non-Hg HAP metals. The fPM standard was lowered from 0.030 lb/MMBtu to
0.010 lb/MMBtu for all existing coal-fired EGUs. The 2024 Final Rule
also proportionally lowered the individual and total non-Hg HAP metal
emission limits.
In the 2024 Final Rule, the EPA revised its conclusion in the 2020
Final Rule by finding that there were developments in practices,
processes, and control technologies to reduce fPM emissions, that the
costs to comply with the more stringent fPM standard based on these
developments were reasonable, and in light of those considerations,
that the revised standard was ``necessary.'' The EPA stated that it had
considered costs in several ways, including cost effectiveness, the
total capital costs of proposed measures, annual costs, and costs
compared to total revenues. In addition, in the 2024 Final Rule, the
EPA found that most existing coal-fired EGUs had reporting fPM levels
that were below the 2012 MATS Rule 0.030 lb/MMBtu emission limit and
that costs were lower than estimated during promulgation of the 2012
MATS Rule fPM emission limit.\50\
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\50\ For instance, the EPA found at the time that the median fPM
rate of the 296 coal-fired EGUs assessed in the 2024 Final Rule was
0.004 lb/MMBtu, or 60 percent below the revised fPM limit of 0.010
lb/MMBtu. See 89 FR 38522 (May 7, 2024).
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E. Summary of the 2025 Proposed Repeal
On June 17, 2025, the EPA proposed to repeal the amendments to MATS
in the 2024 Final Rule.\51\ Based on our reevaluation of the 2024 Final
Rule, we proposed to repeal the fPM emission standard for all existing
coal-fired EGUs of 0.010 lb/MMBtu, the requirement for all coal- and
oil-fired EGUs to demonstrate compliance with the fPM emission standard
by using PM CEMS, and the Hg emission standard for lignite-fired EGUs
of 1.2 lb/TBtu. The Agency proposed to find that the cost-effectiveness
values associated with the revised fPM emission standard are
significantly higher than cost-effectiveness values that we previously
rejected in other technology reviews and related actions under CAA
section 112. The EPA also proposed to find that the requirement
utilizing PM CEMS for compliance demonstration was an unnecessary
expense for coal- and oil-fired EGUs and that the owners and operators
of such sources should maintain the option to utilize other monitoring
methods to demonstrate compliance with the fPM emission standard.
Lastly, the EPA proposed to find that the Agency failed to demonstrate
that the revised Hg emission standard for lignite-fired EGUs is
achievable across the broad range of boiler types and varying
compositions of the different lignite fuels. The Agency also took
comment on whether we should consider the potential for meaningful risk
reduction when weighing costs to determine if it is necessary to revise
standards in a CAA section 112(d)(6) technology review.
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\51\ 90 FR 25535 (June 17, 2025).
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III. Basis for Final Repeal of the 2024 Final Rule
In this section, the EPA describes what aspects of the proposal the
Agency is finalizing, a summary of key comments and responses, and the
rationale for each final decision. For all comments not discussed in
this preamble, comment excerpts and the EPA's responses are available
in the comment summary and response document entitled National Emission
Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric
Utility Steam Generating Units, Repeal of Amendments, Summary of Public
Comments and Responses on Proposed Rule, available in the docket for
this rulemaking.\52\
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\52\ Docket ID No. EPA-HQ-OAR-2018-0794.
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Because this final rule repeals three requirements of the 2024
Final Rule--revisions to the emissions standards for fPM as a surrogate
for non-Hg HAP metals for existing coal-fired EGUs, the fPM emission
standard compliance demonstration requirements, and the Hg emission
standard for lignite-fired EGUs--the EPA intends the repeal of each
requirement to be severable from one another. Just as each requirement
added in the 2024 Final Rule addressed distinct aspects of MATS and
employed a distinct rationale, so also is the EPA finalizing the repeal
of each requirement for separate and independent reasons. When the EPA
adopted these three requirements in the 2024 Final Rule, the EPA
explained that each of the three requirements were severable from each
other as each is ``multifaceted and addresses several distinct aspects
of MATS for independent reasons.'' \53\ By the same token, the repeal
of each of requirement is severable from the repeal of the remaining
requirements.
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\53\ 90 FR 38518 (May 7, 2024).
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The EPA intends that the various components of this final rule
operate independently of the other and be considered independently. For
example, the EPA notes that our justifications for repealing the
revised fPM standard as a surrogate for non-Hg HAP metals (and related
revised standards for each non-Hg HAP metal) are rooted in the poor
cost-effectiveness of the controls, while our justifications for
repealing the requirements for lignite-fired EGUs to meet the same
standard for Hg emissions as other coal- and oil-fired EGUs rest on a
separate analysis specific to the variability of lignite-fired units
and lack of sufficient data. Similarly, our justifications for
repealing the changes to the fPM compliance demonstration requirement
are based on the cost of CEMs and the determination that it is not
necessary to make CEMS the exclusive means of demonstrating compliance
to further transparency and informational values.
Each of these actions is independent from each other. In
particular, the repeal of the revised emission standard for fPM
[[Page 9095]]
as a surrogate for non-Hg HAP metals (and related revised standards for
each non-Hg HAP metal) and the repeal of the fPM compliance
demonstration requirement to utilize PM CEMS are independent and based
on separate rationales. While the EPA considered the technical
feasibility of PM CEMS in establishing the revised fPM standard, the
EPA finds there are independent reasons for repealing each requirement,
as just noted. If the EPA were to repeal any one or two of the three
requirements, but not the other one or two, each repeal would reinstate
requirements from the 2012 MATS Rule that continue to be workable
without the other one or two revisions in place.
Accordingly, the EPA finds that the repeal of each set of revised
standards and requirements is severable from the repeal of the other
revised standards and requirements. Thus, the EPA has independently
considered and adopted each portion of this final rule, which includes
the repeal of the revised fPM emission standard as a surrogate for non-
Hg HAP metals (and related revised standards for each non-Hg HAP
metal), the repeal of the fPM compliance demonstration requirement, and
the repeal of the revised Hg emission standard for lignite-fired units,
and each is severable should there be judicial review. If a court were
to invalidate any one of these elements of the final rule, the EPA
intends the remainder of this action to remain effective. Importantly,
the EPA designed the different elements of this final rule to function
sensibly and independently. Further, the supporting bases for each
element of the final rule reflect the Agency's judgment that the
element is independently justified and appropriate, and that each
element can function independently even if one or more other parts of
the rule has been set aside.
A. Filterable PM Emission Standard for Existing Coal-Fired EGUs
1. What is the EPA finalizing for the filterable PM emission standard
for existing coal-fired EGUs?
The EPA proposed repealing the lower fPM limit of 0.010 lb/MMBtu
for existing coal-fired EGUs based on a determination that the cost of
the revision to the standard are unreasonable, and thus, not
``necessary'' as required by CAA section 112(d)(6). The EPA also
proposed to revert the corresponding total and individual HAP metal
emission standards to the limits that were promulgated in the 2012 MATS
Rule if the repeal of the more stringent fPM limit were finalized. The
EPA solicited comment on whether the cost-effectiveness rationale used
to justify the revised fPM emission standard is consistent with the
Agency's prior CAA section 112(d)(6) technology review determinations
(Question #1) and on whether there are other cost-effective and
achievable alternative standards that the EPA should consider as an
alternative to a standalone repeal of the 0.010 lb/MMBtu fPM emission
standard (Question #2). The EPA also took comment on whether risk
should be a factor that the Agency considers when conducting technology
reviews and if so, how.
The EPA is finalizing its proposal to repeal the more stringent fPM
emission standard and the corresponding total and individual non-Hg HAP
metal standards that were promulgated in the 2024 Final Rule and to
revert to the limits set in the 2012 MATS Rule, which reduce risk to
acceptable levels and provide an ample margin of safety. Commenters
provided both supportive and opposing arguments for issues regarding
the fPM emission standard. Neither these comments nor the Agency's
updated analyses altered the EPA's views of the conclusions proposed or
required changes to the proposed regulatory language.
2. What is the rationale for the EPA's final decision to repeal the
filterable PM standard for existing coal-fired EGUs?
In this final rule, the EPA is repealing the lower fPM standard of
0.010 lb/MMBtu for existing coal-fired EGUs that the EPA established in
the 2024 Final Rule, as well as the alternative total and individual
non-Hg HAP metal limits and returning all of them to the emissions
standards promulgated in the 2012 MATS Rule. As discussed in this
section, the EPA determines upon further review that the cost-
effectiveness of the revised standards is not reasonable and compares
unfavorably to prior Agency decisions on cost-reasonableness across
other technology reviews and other section 112 actions where costs are
considered. In addition, after reviewing the comments the EPA received
concerning the consideration of risk in the context of a CAA section
112(d)(6) review, the Agency concludes that the results of the residual
risk review may be considered when evaluating whether revisions to the
emission standards are cost-reasonable and therefore ``necessary''
under CAA section 112(d)(6). As explained further in section III.A of
this preamble, the EPA finds that it is appropriate to consider the
conclusions of the section 112(f)(2) risk review in all subsequent
section 112(d)(6) reviews. For a risk review, the Agency determines the
risk remaining from HAP emissions from every source in a source
category, and the statute includes specific risk thresholds for
remaining cancer risk. Specifically, the statute incorporates a
rebuttable presumption that a cancer risk above 100 in 1 million is
unacceptable \54\ and establishes an aspirational goal of using
standards to reduce cancer risk for each source in a category to no
greater than one in one million.\55\ The Agency finds that the results
of the residual risk review can be considered in technical reviews
going forward to inform the potential for meaningful risk reduction
when evaluating cost.
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\54\ See CAA section 112(f)(2)(B), 42 U.S.C. 7412(f)(2)(B)
(preserving the EPA's approach in the Benzene NESHAP, under which
cancer risk above 100 in 1 million is presumptively unacceptable
unless the presumption is overcome on a category-specific basis).
\55\ See CAA section 112(f)(2)(A), 42 U.S.C. 7412(f)(2)(A)
(requiring the EPA to promulgate standards if the cancer risk to the
most exposed individual exceeds one-in-one million eight years after
the EPA established MACT standards for the source category.
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In this case, the MACT standard for non-Hg HAP metals in the 2012
MATS Rule lowered the maximum individual lifetime cancer risk (cancer
MIR) from such HAP metals to below one-in-one million for every coal-
fired EGU in the country, thereby achieving the aspirational goal of
CAA section 112(f)(2)(A). In such cases, the EPA now concludes that a
greater emphasis on cost is warranted in light of the low potential for
further risk reduction, and that additional controls would generally
only be ``necessary'' when the costs are on the lower end of what has
been found acceptable from a cost perspective in prior CAA section 112
actions. For emissions of non-Hg HAP metals from coal-fired EGUs, in
light of the high cost of the controls, a common metric the EPA
considers in CAA section 112(d)(6) technology reviews, and the low
remaining risk of cancer from these emissions, the Agency concludes
that the 2024 revisions are not necessary. The EPA views each of the
rationales set out in this section--a change of views on cost
reasonableness of the additional controls evaluated in the 2024 Final
Rule and the additional consideration of the low remaining risk for
this source category--as separate and independent bases for repeal,
either one of which would lead the Agency to conclude that the revised
standards in the 2024 Final Rule were not ``necessary'' under CAA
section 112(d)(6).
As the EPA noted in the 2024 Final Rule, the Agency considers costs
in various ways depending on the rule and
[[Page 9096]]
the affected sector. For example, the EPA has considered the cost
effectiveness of controls in the vast majority of CAA section 112
rulemakings where costs are considered, and the Agency has also
considered total capital costs of control measures, annual compliance
costs, and the compliance costs compared to total revenues (e.g., cost-
to-revenue ratios). In the 2024 Final Rule and, by the same token, in
this rule, the most important indicator of cost is cost effectiveness,
which is the relationship of costs to emission reductions, because that
indicator sheds the most light on whether the revised emissions
standard that is based on those controls is ``necessary'' under CAA
section 112(d)(6). As the EPA acknowledged in the 2024 Final Rule, the
cost-effectiveness ratio of the revised 0.010 lb/MMBtu fPM standard was
significantly higher than cost-effectiveness ratios the EPA rejected in
past technology reviews conducted under CAA section 112(d)(6) for other
source categories.\56\ Moreover, the cost effectiveness values for the
specific non-Hg HAP metals (i.e., the metals for which fPM serves as a
surrogate) emitted from EGUs are almost an order of magnitude higher
than the highest values accepted for such HAP metals under CAA section
112(d)(6) reviews for other source categories. See section III.A.3 of
this preamble, below, for a more detailed discussion. The EPA now finds
that the costs for this source category to achieve the revised
standard, in relation to the amount of emission reductions, are
unreasonable, such that the revised standard is not ``necessary'' under
CAA section 112(d)(6). As noted below, the EPA also finds that the
limited risk posed by emissions from coal-fired power plants, coupled
with the high cost-effectiveness values, are a separate and additional
reason for its determination that the revised standard is not
``necessary'' under CAA section 112(d)(6).
---------------------------------------------------------------------------
\56\ 89 FR 38533-34 (May 7, 2024). These rules are also noted in
section III.A.3 of this preamble.
---------------------------------------------------------------------------
In the 2024 Final Rule, the EPA estimated the cost effectiveness
for EGUs that were reporting average fPM rates above the 0.010 lb/MMBtu
fPM emission standard to be $10.5 million per ton of non-Hg HAP metals
and $34,500 per ton of fPM (2019$). The EPA has since revised these
cost effectiveness estimates based on updated expectations regarding
the existing coal-fired EGU fleet, reflecting fewer planned
retirements. Table 3 of this preamble summarizes the updated cost
effectiveness of the more stringent fPM emission standard. For the
purpose of estimating cost effectiveness, the analysis presented in
this table is based on the observed emission rates of all existing
coal-fired EGUs except those with retirements reported to the U.S.
Energy Information Administration (EIA) via EIA Form 860.\57\ The
analysis presented in Table 3 estimated the costs associated for each
unit to upgrade its existing PM controls to meet a fPM emission
standard of 0.010 lb/MMBtu, using the same methodology as the 2024
Final Rule. In the cases where existing PM controls would not achieve
the necessary reductions, unit-specific FF installation costs were
estimated.\58\
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\57\ This is described in detail in the 2023 Technical Memo,
2024 Technical Memo, and the 2025 Update to the 2024 Technology
Review for the Coal- and Oil-Fired EGU Source Category memorandum
(``2025 Technical Memo'') available in the rulemaking docket (Docket
ID No. EPA-HQ-OAR-2018-0794).
\58\ Note that unlike the cost projections presented in the
Regulatory Impact Analysis (RIA), the updated estimates do not
account for the two-year compliance extensions for units listed on
Annex 1 of the Presidential Proclamation or any future changes in
the composition of the operational coal-fired EGU fleet that may
occur by 2028 as a result of other factors affecting the power
sector.
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Based on this updated analysis, total annual costs are estimated to
be approximately $93.7 million with a cost effectiveness of $11.1
million per ton of non-Hg HAP metals, and $36,502 per ton of fPM, for
the 0.010 lb/MMBtu fPM emission standard, which is about 5 percent
higher than the 2024 Final Rule estimated.
Table 3--Summary of Revised Cost Effectiveness Analysis for the
Updated fPM Emission Limit
(i.e., 0.010 lb/MMBtu)
------------------------------------------------------------------------
2025 Final
Repeal Rule
------------------------------------------------------------------------
Number of Affected Units (Capacity, GW)................. 37 (16.8)
Annual Cost, ($M, 2019 dollars)......................... 93.7
fPM Reductions (tpy).................................... 2,567
Total Non-Hg HAP Metals Reductions (tpy)................ 8.4
Total Non-Hg HAP Metals Cost Effectiveness ($M/ton)..... 11.1
Total Non-Hg HAP Metals Cost Effectiveness ($/lb)....... 5,600
------------------------------------------------------------------------
Upon reconsideration, the EPA is finalizing the repeal of the more
stringent fPM standard and corresponding total and individual HAP metal
standards promulgated in the 2024 Final Rule because the cost
effectiveness of the revised standard is inconsistent with that of the
EPA's prior technology review determinations. In the 2024 Final Rule,
the EPA asserted that differences between the power sector and the
other source categories subject to previous technology reviews
justified accepting an unusually high cost-effectiveness ratio. Upon
further review, the Agency no longer believes the unique nature of the
utility power industry supports the decision to revise the fPM standard
for coal-fired EGU's.
In particular, the EPA stated in the 2024 Final Rule that the large
size of the power sector relative to other industrial sectors meant
that the amount of its emissions were relatively greater than other
source categories.\59\ The EPA added that the size of the sector also
includes relatively large revenues, which the Agency believed at the
time further justified the control costs.\60\ The EPA also stated in
the 2024 Final Rule that because of the emission rates already achieved
by most of the coal-fired EGUs in the source category, the costs of
complying with the revised standard would be borne by only some of the
sources in the source category.\61\ On that basis, the EPA asserted
that the controls would not have ``significant effects'' on the
industry, i.e., the power sector.\62\ Finally, the EPA claimed that the
cost effectiveness of the controls should be considered in light of
these characteristics of the source category, which distinguish it from
other source
[[Page 9097]]
categories that the EPA has regulated under CAA section 112.\63\
---------------------------------------------------------------------------
\59\ 90 FR 38524 (May 7, 2024).
\60\ Id. at 38534.
\61\ Id.
\62\ Id. at 38524.
\63\ Id.
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The EPA now believes that it was inappropriate to rely on the
differences between the EGU sector and other sectors with respect to
consideration of costs in the development of standards. The EPA has
consistently maintained that the statute treats the EGU source category
the same as all other major source categories with respect to
regulation under CAA section 112(d) once the Agency decides pursuant to
CAA section 112(n)(1)(A) to add the EGU source category to the list of
regulated major sources under CAA section 112(c)(1).\64\ In the 2024
Final Rule, however, the Agency ignored that position and used certain
unique factors about the power sector in an attempt justify otherwise
unreasonable costs. Specifically, the Agency no longer believes it was
reasonable to establish a fPM standard with one of the highest cost-
effectiveness values ever accepted for fPM under CAA section 112(d)(6),
particularly when the cost-effectiveness ratio for the actual non-Hg
HAP metal emissions was approximately an order of magnitude higher than
any cost-effectiveness value the Agency has ever found reasonable for
non-Hg HAP metals. The longstanding use of fPM as a surrogate for non-
Hg HAP metals does not excuse the Agency from considering cost-
effectiveness as to the non-Hg HAP metals themselves. The purpose of
CAA section 112 is to regulate HAP emissions, and when there exists a
disparity in cost effectiveness between a surrogate and the associated
HAP, it is important to give sufficient consideration to that
disparity, but the Agency failed to do so in the 2024 Final Rule. Thus,
although the Agency identified what it considered at the time to be
``developments'' in some control strategies in the 2024 Final Rule, the
costs for the power sector to implement those developments are not
reasonable, such that the revised standards are not ``necessary'' under
CAA section 112(d)(6). As a result of this final rule, the fPM and
corresponding total and individual non-Hg HAP metal emission standards
will revert to the standards that were promulgated in the 2012 MATS
Rule (e.g., 0.030 lb/MMBtu for fPM and associated prior standards for
non-Hg HAP metals).
---------------------------------------------------------------------------
\64\ After the EPA makes the ``appropriate and necessary''
finding for the EGU source category required in CAA section
112(n)(1)(A), the EGU source category becomes included in the ``list
of all categories and subcategories of major sources'' in CAA
subsection 112(c)(1). 42 U.S.C. 7412(c)(1), (n)(1)(A). That listing,
in turn, triggers the same, general regulatory requirements for the
EGU source category as apply to the other listed source categories,
under CAA section 112. See, e.g., 42 U.S.C. 7412(c)(2); 88 FR 13956,
13960-61 (March 6, 2023) (recounting the EPA's position since 2000
that an affirmative ``appropriate and necessary'' finding puts the
EGU source category in the same position as all source categories
listed in CAA section 112(c)(1)).
---------------------------------------------------------------------------
In addition to finding that the costs are unreasonable on their
face, circumstances have changed materially since promulgation of the
2024 Final Rule. Fewer coal-fired EGUs are likely to retire instead of
complying with MATS because of an increasing need for electricity
generation, including to support growing demand from the technology
sector. Moreover, Congress recently passed, and President Trump signed
into law, new legislation that repealed, amended, or defunded relevant
provisions of the Inflation Reduction Act (IRA), including tax credits
for solar and wind generation that the EPA cited in the 2024 Final Rule
to predict an ``accelerated'' transition away from coal- and oil-fired
generation.\65\ Coupled with the Executive Orders discussed earlier in
this preamble that establish different policies and programs to promote
power generation from this source category, the EPA's prior predictions
about the future of the power sector and conclusion that the unique
characteristics of the power sector support a finding that the
additional controls are ``necessary'' are no longer accurate.\66\
Instead, that unique character of the power sector and the increasing
demand supports this repeal because any unnecessary downward pressure
on the power industry at this time is not in the national interest or
in the interest of consumers.
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\65\ Compare 89 FR 38534 (May 7, 2024) (citing Pub. L. 117-169
(2022)), with Pub. L. 119-21 (2025).
\66\ The EPA further clarifies that statements in the 2024 Final
Rule regarding planned EGU retirements ``due to factors independent
of the EPA's regulation'' were overbroad and did not reflect a
detailed, source-by-source analysis of the costs of regulation. See,
e.g., 89 FR 38524-25 (May 7, 2024). In several recent cases, the
Supreme Court has vacated EPA rules for misusing statutory authority
and failing to consider the costs of regulation. See West Virginia
v. EPA, 597 U.S. 697 (2022) (vacating CAA section 111(d) standards
for pursuing generation shifting in violation of the major questions
doctrine); Michigan, 576 U.S. at 749-50 (faulting the EPA's decision
to regulate EGUs under CAA section 112 for failing to account for an
estimated $9.6 billion in annual compliance costs). Although trends
in a source category can be relevant under CAA section 112(d)(6),
the inherent difficulty in determining whether a planned retirement
is independent of regulatory pressure cautions against making such
an assumption for regulatory purposes absent more direct engagement
with and analysis of each source.
---------------------------------------------------------------------------
The EPA's decision to repeal these standards from the 2024 Final
Rule is further supported by the low remaining cancer risk attributed
to HAP emissions from this source category. As noted in section II.A.1
of this preamble and discussed in greater detail in section IV of this
preamble, CAA section 112(d)(6) and relevant case law support
considering additional factors beyond developments in technology when
deciding whether revisions to existing standards are ``necessary,''
including cost. Considering risk in the context of the first technology
review would be duplicative of the one-time risk review requirement,
which is conducted at the same time and which generally includes an
ample-margin-of-safety analysis that takes the costs of controls into
account. However, Congress did include risk benchmarks in CAA section
112(f), and considering those benchmarks in subsequent technology
reviews is consistent with the broad scope of the term ``necessary''
and reasonable because that information is part of the overall CAA
section 112 record for each source category. Specifically, CAA section
112(f)(2)(A) directs the EPA to ``promulgate standards'' if the cancer
risk to the most exposed individual is greater than one-in-one
million.\67\ Additionally, CAA section 112(f)(2)(B) incorporates the
Benzene NESHAP approach, which generally presumes that a cancer risk of
greater than 1-in-10,000 is unacceptable unless such presumption is
overcome.\68\
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\67\ 42 U.S.C. 7412(f)(2)(A).
\68\ Id. 7412(f)(2)(B).
---------------------------------------------------------------------------
The decision to consider the low remaining risk in the prior
residual risk assessment in assessing the need for additional standards
in the second and subsequent CAA section 112(d)(6) reviews is
consistent with the ordinary meaning of the term ``necessary,'' which
is ``required,'' ``compulsory,'' or ``determined or produced by the
previous condition of things.'' \69\ CAA section 112(d)(6), by its
terms, expressly requires the EPA to consider ``developments in
practices, processes, and control technologies'' when determining
whether it is ``necessary'' to revise existing section 112 standards
(e.g., standards based on the MACT floor, a beyond-the-floor level of
control, or a risk review). The EPA also considers the costs of
potential revisions even though CAA section 112(d)(6) does not
explicitly reference cost. The D.C. Circuit has upheld that
interpretation,\70\ and it is consistent with the Supreme Court's
interpretation of the term ``appropriate and necessary'' in another
[[Page 9098]]
provision of CAA section 112.\71\ As with costs, the EPA interprets CAA
section 112(d)(6) to authorize the EPA to take the low remaining risk
identified in the prior residual risk review into account even though
the provision does not explicitly refer to health risks. When the
Agency has previously determined that residual risk for a source
category is consistent with Congress' risk-reduction goals, that
relatively low risk is relevant to determining whether additional
standards are ``necessary'' and, if so, which standards are
``necessary.'' That follows from the overall purpose of CAA section
112, which is to promote public health by reducing the hazards
presented by the emission of air toxics, and from Congress' decision to
establish and adopt the particular risk thresholds in the statute
described above.
---------------------------------------------------------------------------
\69\ Webster's Ninth New Collegiate Dictionary 790 (1984).
\70\ Ass'n of Battery Recyclers, 716 F.3d at 673-74.
\71\ Michigan, 576 U.S. at 748-49.
---------------------------------------------------------------------------
This interpretation is consistent with how the EPA has interpreted
``necessary'' under CAA section 112(n)(1)(A) by taking into
consideration health risks. The Supreme Court explained the provisions
of CAA section 112(n)(1)(A), including their background and context, in
Michigan v. EPA, as follows:
[T]he Clean Air Act Amendments of 1990 subjected power plants to
various regulatory requirements. . . . [T]hese requirements were
expected to have the collateral effect of reducing power plants'
emissions of hazardous air pollutants, although the extent of the
reduction was unclear. Congress directed the Agency to ``perform a
study of the hazards to public health reasonably anticipated to
occur as a result of emissions by [power plants] of [hazardous air
pollutants] after imposition of the requirements of this chapter.''
If the Agency ``finds . . . regulation is appropriate and necessary
after considering the results of the study,'' it ``shall regulate
[power plants] under [CAA section 112].'' \72\
---------------------------------------------------------------------------
\72\ Michigan, 576 U.S. at 748 (quoting 42 U.S.C.
7412(n)(1)(A)).
The Court went on to explain, with approval, the EPA's
interpretation of ``necessary,'' which, as noted, takes into
---------------------------------------------------------------------------
consideration health risks:
In 2012, [the EPA] reaffirmed [its prior] appropriate-and-
necessary finding. . . . The Agency found regulation ``appropriate''
because (1) power plants' emissions of mercury and other hazardous
air pollutants posed risks to human health and the environment and
(2) controls were available to reduce these emissions. It found
regulation ``necessary'' because the imposition of the Act's other
requirements did not eliminate these risks.\73\
---------------------------------------------------------------------------
\73\ Id. at 749 (citing 77 FR 9304, 9363 (February 16, 2012)).
Interpreting ``necessary'' to authorize consideration of the prior
residual risk review in the way described in this preamble is also
consistent with CAA section 112(d)(6)'s direction to revise ``emission
standards promulgated under this section.'' Specifically, after the EPA
conducts the mandatory section 112(f)(2) residual risk review,
subsequent section 112(d)(6) technology reviews will include a review
and potential revision of all section 112 standards.\74\ Considering
the findings of the prior risk review, which are part of the record
before the Agency, during those technology reviews is reasonable and
accounts for CAA section 112's purpose of protecting public health.
---------------------------------------------------------------------------
\74\ Ass'n of Battery Recyclers, 716 F.3d at 673.
---------------------------------------------------------------------------
The approach that the EPA is taking in this rulemaking, i.e.,
considering the low residual risk findings from the 2020 Residual Risk
Review, marks a change from the Agency's stated approach in the 2024
Final Rule, in which the Agency declined to consider the health-risk
findings from the 2020 Residual Risk Review as part of the technology
review. Specifically, the EPA stated that it was ``not compel[led]'' to
``consider[] risks as a factor'' in technology reviews under CAA
section 112(d)(6).\75\ The EPA explained that the CAA section 112(d)(6)
technology review and the section 112(f) residual risk determination
were ``independent'' of each other, and that ``a determination under
section 112(f) of an ample margin of safety and no adverse
environmental effects alone will [not] . . . cause us to determine that
a revision is not necessary under CAA section 112(d)(6).'' \76\
---------------------------------------------------------------------------
\75\ 89 FR 38525 (May 7, 2024).
\76\ Id. (quotation marks omitted).
---------------------------------------------------------------------------
However, in the 2024 Final Rule, the EPA did not say that CAA
section 112 precludes the Agency from considering risks in connection
with a CAA section 112(d)(6) technology review. Moreover, the EPA
acknowledged that in some prior section 112(d)(6) reviews, the Agency
has considered risks.\77\
---------------------------------------------------------------------------
\77\ Id. at 38525 & n.31 (citing National Emission Standards for
Organic Hazardous Air Pollutants From the Synthetic Organic Chemical
Manufacturing Industry, 71 FR 76603, 76606 (December 21, 2006), and
Proposed Rules: National Emission Standards for Halogenated Solvent
Cleaning, 73 FR 62384, 62404 (October 20, 2008)).
---------------------------------------------------------------------------
For all of these reasons, the EPA concludes that it is reasonable
to consider the low remaining risks identified in a prior residual risk
review--particularly where, as here, such risks are consistent with the
thresholds Congress set out or adopted by statute--when determining in
a second and subsequent CAA section 112(d)(6) review whether additional
standards are ``necessary.'' For this rule, the Agency considered the
2020 Residual Risk Review of MATS in the manner and for the reasons
described elsewhere in this final action.
Having concluded that CAA section 112(d)(6) allows the EPA to
consider the results of an earlier CAA section 112(f)(2) residual risk
review in subsequent technology reviews, we must determine how and to
what extent the Agency may consider risk in determining whether revised
standards are ``necessary.'' As noted above, the clearest benchmark is
in CAA section 112(f)(2)(A), which the EPA has long interpreted as
requiring an ample-margin-of-safety analysis but not mandating that the
Agency require additional reductions in HAP emissions after considering
costs and other factors. The D.C. Circuit upheld this interpretation,
describing the one-in-one million risk level as an ``aspirational
goal'' of the statute for sources of HAP emissions and not as the level
that every source category must achieve under CAA section
112(f)(2).\78\
---------------------------------------------------------------------------
\78\ NRDC, 529 F.3d at 1082 (rejecting the argument that risks
must be reduced to the one-in-one million threshold).
---------------------------------------------------------------------------
The EPA thus concludes that the statutory benchmarks for risk
provide relevant guidance on whether additional regulation is
``necessary'' under CAA section 112(d)(6). If the remaining risk found
during a prior residual risk review is below the one-in-one million
risk level, the EPA may place greater emphasis on costs of the new
controls. Over the years of implementing CAA section 112, the EPA
developed cost metrics for evaluating whether it is reasonable to
consider a particular control to be ``necessary,'' and the Agency uses
those metrics when evaluating whether controls are reasonable in
several CAA section 112 contexts (e.g., beyond the floor (BTF), ample
margin of safety, generally available control technologies (GACT)). The
EPA also uses these metrics when determining whether additional
controls are necessary under CAA section 112(d)(6) on the theory that
if the costs of such controls are within the range of what had been
found reasonable in one rule, then those same costs are potentially
reasonable for other source categories. If additional controls cost
more than the historical range, we generally conclude that such
controls are unnecessary. The EPA maintains that this approach is
appropriate when the CAA section 112(f)(2) risk analysis shows
remaining risks above statutorily set benchmarks (e.g., risks greater
than one-in-one million) or where noncancer risk from the source
category emissions exceed a level adequate to protect
[[Page 9099]]
public health with an ample margin of safety. However, where the MACT
standard lowers cancer risks to below the statutory one-in-one million
cancer risk threshold, the EPA concludes that more emphasis may be
placed on cost in determining whether additional controls are
``necessary'' under CAA section 112(d)(6) within the context of the
statute as a whole.
The statute makes clear that CAA section 112(d)(6) technology
reviews are required even when a CAA section 112(f)(2) residual risk
review finds cancer risk is below the one-in-one million threshold, and
additional controls may be ``necessary'' when ongoing reductions in HAP
are possible at relatively low cost. In cases like MATS, however, the
EPA maintains that the effectiveness of the original MACT standard at
lowering risks should be given greater weight. As noted in the 2020
Final Rule, no coal-fired EGU facility posed a cancer risk greater than
one-in-one million. In fact, the highest cancer risk from non-Hg HAP
metals from a coal-fired EGU was 0.3-in-one million, and most coal-
fired EGUs were assessed to pose considerably lower cancer risks from
such HAP emissions.\79\ Despite these facts, in the 2024 Final Rule,
the EPA established CAA section 112(d)(6) standards for emissions of
fPM and corresponding standards for emissions of non-Hg HAP metals
though the cost-effectiveness values of such controls were the highest
(or among the highest) of any CAA section 112(d)(6) standard the Agency
has established.\80\ We now conclude it was not ``necessary'' to
establish a new high-cost benchmark for non-Hg HAP metals from EGUs
because the MACT standards in the 2012 MATS Rule achieved the
aspirational goal for cancer risks from such HAP emissions. Instead, in
such situations, the EPA believes a harder look at costs should be
conducted and additional controls will be considered unnecessary unless
the costs of such controls are at the lower range of cost
acceptability. Imposing costs that are below historically accepted
levels will continue to satisfy the statutory goal of continuing to
reduce HAP emissions without unreasonably burdening source categories
that pose very low risks due to HAP emissions. In addition, as noted
above, even if the EPA did not consider the low remaining risks from
the 2012 MACT standards as determined in the 2020 Final Rule, the EPA
would conclude that the costs of the 2024 standards are unacceptably
high in light of their high cost-effectiveness values, such that the
2024 standards are not necessary.
---------------------------------------------------------------------------
\79\ Document ID No. EPA-HQ-OAR-2018-0794-0070.
\80\ 89 FR 38530-35 (May 7, 2024).
---------------------------------------------------------------------------
3. What key comments did the EPA receive on the filterable PM emission
standard for existing coal-fired EGUs and what are our responses?
Comment: Some commenters agreed with the EPA's proposal that the
costs for the power sector to achieve the more stringent fPM standard
are too high and are inconsistent with other technology review
determinations. In the 2024 Final Rule, the EPA estimated that the
cost-effectiveness for the 0.010 lb/MMBtu fPM emission limit was $10.5
million per ton of non-Hg HAP metals and $34,500 per ton of fPM.
Commenters stated that these costs are not reasonable when compared to
other technology reviews, including those cited by the EPA in the
proposed rule, that rejected controls as not cost-effective. These
technology reviews included the Petroleum Refinery Sector technology
review \81\ ($10 million per ton of total non-Hg HAP metals reduced),
the Integrated Iron and Steel Manufacturing Facilities technology
review \82\ ($7 million per ton of non-Hg HAP metals reduced), and the
Taconite Iron Ore Processing RTR \83\ ($16 million per ton of non-Hg
HAP metals reduced). Furthermore, commenters noted that the EPA has
rejected similar or even smaller cost-effectiveness values in other CAA
section 112 rulemakings:
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\81\ Petroleum Refinery Sector Risk and Technology Review and
New Source Performance Standards, 80 FR 75178, 75201 (December 1,
2015).
\82\ National Emission Standards for Hazardous Air Pollutants:
Integrated Iron and Steel Manufacturing Facilities Residual Risk and
Technology Review, 85 FR 42074, 42088 (July 13, 2020).
\83\ National Emission Standards for Hazardous Air Pollutants:
Taconite Iron Ore Processing Residual Risk and Technology Review, 85
FR 45476, 45483 (July 28, 2020).
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<bullet> In the Hazardous Waste Combustors NESHAP beyond-the-floor
analysis,\84\ the EPA declined to impose a more stringent dioxin/furan
emission limit because of cost, finding $2.5 million to $4.9 million
per gram toxicity equivalence of dioxin/furan removed.
---------------------------------------------------------------------------
\84\ National Emission Standards for Hazardous Air Pollutants:
Final Standards for Hazardous Air Pollutants for Hazardous Waste
Combustors (Phase I Final Replacement Standards and Phase II), 70 FR
59402, 59462 (October 12, 2005).
---------------------------------------------------------------------------
<bullet> In the Shipbuilding and Ship Repair NESHAP RTR,\85\ the
EPA declined to revise the formaldehyde emission limit after finding
that spray line reconfiguration would cost $43,000 per ton of
formaldehyde reduced.
---------------------------------------------------------------------------
\85\ National Emission Standards for Hazardous Air Pollutants
for Shipbuilding and Ship Repair (Surface Coating); National
Emission Standards for Wood Furniture Manufacturing Operations, 76
FR 72050, 72056 (November 21, 2011).
---------------------------------------------------------------------------
<bullet> In the Pulp and Paper NESHAP RTR,\86\ the EPA declined to
update standards in the final rule \87\ for controlling kraft
condensates emissions that would cost $1,000 per ton of HAP removed or
$4 million per year.
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\86\ National Emission Standards for Hazardous Air Pollutants:
Pulp and Paper Residual Risk and Technology Review, 76 FR 81328,
81345 (December 27, 2011).
\87\ National Emission Standards for Hazardous Air Pollutants:
Pulp and Paper Residual Risk and Technology Review, 77 FR 55698,
55701 (September 11, 2012).
---------------------------------------------------------------------------
Additionally, commenters stated that the cost analysis for the 2024
Final Rule underestimates overall compliance costs, as the EPA failed
to identify all sources that would need to make air pollution control
device upgrade investments and to account for unit-level operational
challenges that could increase compliance costs. For example,
commenters cited declarations submitted as part of challenges to the
2024 Final Rule, which stated that compliance with the 0.010 lb/MMBtu
fPM emission standard at the Colstrip facility would have cost over
$350 million, with more recent estimates of over $500 million that
incorporate more accurate wage rates, structural steel install rates,
scaffolding costs, duct installation costs, and total delivery
costs.\88\ Commenters pointed to the 2025 Proposal and stated that
industrywide cost-effectiveness was at minimum $10.5 million per ton of
non-Hg HAP metals controlled, but the largest costs were found
predominantly at Colstrip which results in approximately $16 million
per ton of non-Hg HAP metals reductions using the EPA's
``underestimated'' costs.
---------------------------------------------------------------------------
\88\ Document ID No. EPA-HQ-OAR-2018-0794-7154.
---------------------------------------------------------------------------
Other commenters argued that the EPA was wrong in proposing that
the cost effectiveness of the 0.010 lb/MMBtu fPM emission standard (as
estimated in the 2024 Final Rule) is too high. Commenters stated that
the examples rejecting high cost-effectiveness values that the EPA
provided in the 2025 Proposal are flawed and should not be relied upon.
These commenters asserted that the RTR for the Integrated Iron and
Steel NESHAP also estimated a fPM cost effectiveness of $160,000 per
ton, well above the $35,000 per ton of fPM estimated for the 2024 Final
Rule. Further, these commenters stated that if the cost per ton of any
of the non-Hg HAP metals is reasonable, then the control costs should
also be regarded as reasonable. These commenters stated
[[Page 9100]]
that the EPA has previously accepted Hg cost effectiveness values of up
to approximately $32,000 per pound, which is the equivalent of $64
million per ton reduced. Commenters noted that the rejected cost
effectiveness values from the Petroleum Refinery NESHAP RTR ($10
million per ton) and Integrated Iron and Steel NESHAP ($7 million per
ton) are at the low end of the accepted Hg cost-effectiveness value,
highlighting that the EPA has approved higher dollar per ton values in
the past. Lastly, commenters argued that the EPA ignored the 2024 Final
Rule's explanation for why the Petroleum Refinery Sector and Integrated
Iron and Steel Manufacturing Facilities reviews were not
comparable,\89\ and that the Agency also ignored the 2024 Final Rule's
comparison of cost-effectiveness values with the Ferroalloys Production
source category, in which the EPA approved higher cost-effectiveness
values for PM than those estimated in the 2024 Final Rule.
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\89\ In the 2024 Final Rule, the EPA noted that the 2020
Integrated Iron and Steel Manufacturing rulemaking source category
only covered 11 facilities with 3 tons per year (tpy) of HAP and 120
tpy of PM reductions, compared to MATS, which affected 314 coal-
fired EGUs with estimated reductions of 8.3 tpy HAP and 2,537 tpy of
fPM. See 89 FR 38524 (May 7, 2024).
---------------------------------------------------------------------------
Other commenters stated that the cost effectiveness comparison for
a single facility bearing the highest costs under the 2024 Final Rule
is inappropriate and arbitrary, as the cost-effectiveness ratio across
an entire sector is very different than the cost-effectiveness ratio of
a single facility. Commenters argued that it is expected that some
facilities would face higher costs than others for a given regulation
given differences in air pollution control devices. The commenters
stated that it is irrational for the EPA to imply that the highest-cost
facility's cost-effectiveness ratio cannot exceed a ratio rejected for
a fleetwide average.
Response: The EPA generally agrees with commenters that cost
effectiveness (i.e., the costs per unit of emissions reduction) is a
metric that the Agency consistently considers, alongside other cost
metrics, in CAA section 112 rulemakings where it can consider costs.
The EPA also agrees that the Agency has the discretion in how it
considers statutory factors, including costs, under CAA section
112(d)(6).\90\ The Agency disagrees, however, that there is any
particular threshold that renders a potential control technology cost-
effective or not.\91\
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\90\ See, e.g., Ass'n of Battery Recyclers, 716 F.3d at 673-74
(allowing that the EPA may consider costs in conducting technology
reviews under CAA section 112(d)(6)); Nat'l Ass'n for Surface
Finishing, 795 F.3d at 11.
\91\ See, e.g., National Emissions Standards for Hazardous Air
Pollutants: Ferroalloys Production, 80 FR 37366, 37381 (June 30,
2015) (``[I]t is important to note that there is no bright line for
determining acceptable cost effectiveness for HAP metals. Each
rulemaking is different, and various factors must be considered.'').
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The EPA disagrees with the commenters who sought to distinguish
prior rules in which the EPA declined to revise standards for non-Hg
HAP metals due to the high cost-effectiveness values of those
standards. As noted above, the cost-effectiveness of the 2024 Final
Rule's revised standards for non-Hg HAP metals is substantially less
favorable than in any other rule the EPA has promulgated under CAA
section 112(d)(6). In several rules under CAA section 112(d)(6), the
EPA declined to revise standards for non-Hg metal HAPs on grounds that
the cost-effectiveness values were in the millions of dollars per ton
reduced, which are roughly comparable to the cost-effectiveness values
in the 2024 Final Rule. As commenters point out, in some of those
cases, the EPA also noted industry-specific reasons for declining to
adopt the revised standards, but the key reason in those rules, as
here, was the high cost-effectiveness values. In addition, the
commenters point to multiple cost-effectiveness values that the EPA has
accepted in past actions for Hg control that are significantly higher
than the values that the agency is rejecting for control of non-Hg HAP
metals, but the EPA considers those values inappropriate for
determining cost effectiveness of non-Hg HAP metals.
The EPA disagrees with commenters who argued that the 2025 Proposal
focused on costs to a single facility. Although the EPA pointed out at
proposal that the units at the Colstrip facility accounted for almost
half of the 2024 Final Action's total compliance costs, that was not
the basis for the proposed repeal and it is not the rationale for this
final action repealing the more stringent fPM standard. Rather, the
rationale is the high cost-effectiveness values, especially when
coupled with the limited risk, including from the Colstrip facility.
Comment: Some commenters argued that the EPA failed to adequately
explain why it is ``necessary'' under CAA section 112(d)(6) to revert
to the 2012 MATS Rule standards when the CAA requires that the Agency
``take into account developments in practices, processes, and control
technologies'' that have occurred since the EPA promulgated the
original 2012 MATS Rule.\92\ Commenters further asserted that the EPA
must explain why the 2012 emissions standards are the maximum
achievable emissions standards given major developments in control
technology since 2012, including reduced costs and improvements of
existing control technologies, better practices for monitoring the
operation of ESPs, and more durable filter bag materials for FF, which
commenters asserted the EPA did not dispute in the proposed rule.
Commenters stated the EPA chose to disregard these developments and
that the Agency's own analysis in the 2024 Final Rule showed that at
least 93 percent of the industry is already attaining a 0.010 lb/MMBtu
fPM emission standard.
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\92\ See CAA section 112(d)(6), 42 U.S.C. 7412(d)(6) (requiring
the Administrator to ``review, and revise as necessary (taking into
account developments in practices, processes, and control
technologies), emission standards promulgated under [section 112] no
less often than every 8 years'').
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Response: The EPA notes that it has authority to reconsider past
decisions and to revise, replace, or repeal a decision to the extent
permitted by law and supported by a reasoned explanation.\93\ In this
case, as in the 2024 Final Rule, the EPA did not conduct a new
mandatory technology review but, instead, reviewed a prior technology
review. The next technology review for this source category is due
within 8 years of the prior review, which was finalized in 2020. The
EPA further disagrees with these commenters to the extent they suggest
that CAA section 112(d)(6) requires the Agency to select the maximum
degree of emissions reductions in setting standards. The technology
review under CAA section 112(d)(6) does not allow the Agency to
recalculate the MACT floor for any currently regulated HAPs. Rather,
CAA section 112(d)(2) provides that the EPA must require the maximum
degree of reduction in emissions of HAP that the Administrator
determines to be achievable, taking into consideration cost, non-air
quality health and environmental impacts, and energy requirements, and
CAA section 112(d)(3) prescribes specific requirements for calculating
the MACT. The EPA's task under CAA section 112(d)(6) is not to
recalculate a new, lower MACT, but to determine whether, taking into
account developments in technology and other relevant information, it
is ``necessary'' to revise the standards. Further, EPA regulated all
HAP emitted from EGUs in 2012 so there are no gaps to fill.
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\93\ See, e.g., Fox Television Stations, 556 U.S. at 515; Motor
Vehicle Mfrs. Ass'n, 463 U.S. at 42.
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[[Page 9101]]
In this instance, the EPA reevaluated the 2024 Final Rule and
determined that a more stringent fPM emission standard is not
``necessary,'' including because of cost-effectiveness estimates, in
light of the Agency's 2020 Technology Review. In this action, the EPA
updated its evaluation of fPM compliance data for the coal-fired fleet
and associated costs of PM controls to achieve a lower standard;
specifically, total annual costs are estimated to be approximately
$93.7 million with a cost effectiveness of $11.1 million per ton of
non-Hg HAP metals for the 0.010 lb/MMBtu fPM emission standard.\94\ The
EPA acknowledges the reduced costs and improvements of existing ESP and
FF control technologies compared to estimates from the 2012 MATS Rule
and acknowledges that the fleet is largely overperforming with the fPM
emission standard, but that fact alone does not make the high cost-
effectiveness number reasonable or necessary under section 112(d)(6),
particularly in light of the low remaining risk.
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\94\ Updates and revisions to the 2024 Technical Memo are
described in detail in the 2025 Update to the 2024 Technology Review
for the Coal- and Oil-Fired EGU Source Category memorandum (``2025
Technical Memo'') available in the rulemaking docket (Docket ID No.
EPA-HQ-OAR-2018-0794).
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Comment: Several commenters generally supportive of the proposal
urged the EPA to acknowledge additional considerations for rejecting
the 0.010 lb/MMBtu fPM emission standard. First, commenters stated that
the 2024 Final Rule's reliance on ``considering cost in various
ways''--such as comparing them to typical capital and total
expenditures for the power sector, total power sector sales, and total
PM upgrade control costs and emissions of the fleet--to explain its
acceptance of high cost-effectiveness values should be rejected.
Commenters questioned the use of compliance costs compared to revenues,
arguing that the EPA would be hard-pressed to find that the utility
sector as a whole cannot afford the cost of virtually any regulatory
action, especially when such action is viewed in isolation. Commenters
argued that the framing of considering costs in various ways in the
2024 Final Rule departed from the EPA's longstanding precedent
regarding cost consideration in an RTR.
Second, a commenter requested that the EPA also reject the 0.010
lb/MMBtu fPM emission standard because of a flawed technical analysis
based on truncated and unrepresentative data. Commenters noted that,
for many units, the EPA relied on only two quarters of data and failed
to explain the reasoning behind the EPA's decision to not incorporate
all compliance data. Commenters also said that the cost analysis should
account for other indirect impacts on grid reliability, such as
security risks associated with temporarily reduced electric generation
capacity and lost revenues during the downtime required to engineer and
retrofit additional control technologies required to comply with the
2024 Final Rule.
Alternatively, other commenters said that the EPA reasonably
explained costs in the 2024 Final Rule and that the EPA's proposal to
repeal the fPM emission standard based on high costs is arbitrary and
capricious. These commenters argued that the EPA's view about what is
cost-effective is subjective and has nothing to do with what can be
achieved--considering costs or otherwise. Commenters stated that the
EPA did not cite any example of cost being the sole factor supporting a
decision to revise or not to revise standards, as it did in the
proposed rule here.
Response: The EPA disagrees in part with commenters stating that
the Agency does not consider costs in various ways in CAA section 112
rulemakings. As stated earlier in this preamble, the EPA routinely
considers cost effectiveness metrics together with additional factors,
such as other relevant cost metrics (e.g., total costs, annual costs,
and costs compared to revenues), and impacts to the regulated industry,
to determine whether, taking into account developments in practices,
processes, and control technologies, it is ``necessary'' to revise
emissions standards pursuant to CAA section 112(d)(6). For example, in
the 2015 Ferroalloys rulemaking, the EPA rejected a potential control
option due to concerns about technical feasibility and the significant
economic impacts the option would create for the industry, including
potential facility closures that would impact significant portions of
industry production.\95\ The EPA agrees with these commenters, however,
that the Agency's statements about the power sector in the 2024 Final
Rule are not appropriate reasons to accept higher cost-effectiveness
values relative to other source categories. As explained in section
III.A.1 of this preamble, cost-effectiveness metrics are an important
means of evaluating whether developments in technology make a revision
``necessary'' because they present the emission-reduction benefit
relative to the cost of such emission reduction. Characteristics of the
power sector such as number of units and quantity of emissions do not
mean that metric is not reasonable, because the metric is already keyed
to ton of HAP emissions reduced.
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\95\ 79 FR 60238, 60273 (October 6, 2014) (supplemental proposed
rule).
---------------------------------------------------------------------------
With respect to commenters' argument that the EPA's view about what
is cost effective is subjective and therefore an improper basis for
repealing the revised standards in the 2024 Final Rule, the EPA
disagrees. Congress vested the EPA with authority to make judgments
about when a revision is ``necessary'' under CAA section 112(d)(6), and
cost-effectiveness metrics are an important input to the exercise of
that reasoned judgment. To the extent that the EPA's view now differs
from the view adopted in the 2024 Final Rule, the law is clear that the
Agency has authority to reconsider, repeal, or revise past decisions to
the extent permitted by law so long as the EPA provides a reasoned
explanation.\96\ Indeed, the position taken in the 2024 Final Rule was
itself a departure from the conclusions reached in the 2020 Final Rule,
as the Agency acknowledged at the time and asserted was permissible
under the same legal doctrine supporting this reconsideration.\97\ As
noted in the 2024 Final Rule, the cost effectiveness ratio of the
revised fPM standard for non-Hg metal HAPs was significantly higher
than the cost-effectiveness ratios for those HAPs the EPA has rejected
in the past in technology reviews conducted under CAA section 112(d)(6)
for other industries.\98\ The cost effectiveness ratio of the revised
fPM standard was also higher than cost-effectiveness ratios that the
EPA accepted for fPM emissions in other industries in other CAA section
112(d)(6) reviews. The EPA now finds that the costs for the power
sector to achieve the revised standard are too high, and, separately,
certainly too high in light of the low remaining risks, such that the
revised standard is not necessary under CAA section 112(d)(6).
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\96\ See, e.g., Motor Vehicle Mfrs. Ass'n, 463 U.S. at 42
(``[R]egulatory agencies do not establish rules of conduct to last
forever [and] an agency must be given latitude to adapt their rules
and policies to . . . changing circumstances.'').
\97\ 89 FR 38513 (May 7, 2024).
\98\ Id. at 38533-34.
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B. Required Compliance Demonstration for the Filterable PM Standard
1. What is the EPA finalizing for the compliance demonstration
requirements for the filterable PM standard?
The EPA proposed to repeal the requirement that sources must use PM
CEMS exclusively for demonstrating
[[Page 9102]]
compliance with the fPM emission standard, as well as the adjusted QA
criteria,\99\ and to return to the previous regulatory language from
the 2012 MATS Rule and 2020 Final Rule that allowed owners and
operators to demonstrate compliance using either quarterly stack
testing, PM CPMS, or PM CEMS. The EPA solicited comment on the
rationale that the higher costs for EGUs not currently utilizing PM
CEMS, the availability of other air pollution control performance
indicators that can inform operators of malfunctions, and the adequacy
of current compliance options support repealing the requirement that
all coal- and oil-fired EGUs must use PM CEMS (Question #3). The EPA
also proposed and solicited comment on reinstating the low emitting EGU
(LEE) program for fPM and non-Hg HAP metals, which reduces the required
stack testing frequency for sources that demonstrated that their
emissions are less than 50 percent of the corresponding emissions limit
for 3 consecutive years (Question #4). Lastly, the EPA proposed
retaining the updated fPM measurement requirements of allowing either
an increased minimum volume per run or the collection of a minimum mass
per run.\100\ The EPA solicited comment on these measurement
requirements for fPM compliance demonstration, as the Agency believed
retaining the additional option of sample mass would reduce measurement
uncertainty and may reduce test durations and, therefore, reduce fPM
testing costs (Question #5).
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\99\ Emission standards are used to determine the acceptable
tolerance interval when correlating PM CEMS. In the 2024 Final Rule,
the EPA instructed the use of 0.015 lb/MMBtu, instead of the
finalized more stringent limit of 0.010 lb/MMBtu, when developing PM
CEMS correlations to ease difficulties correlating PM CEMS. See 89
FR 38535 (May 7, 2024).
\100\ For coal- and solid oil-fired EGUs, the 2024 Final Rule
required a minimum catch for fPM of 6.0 mg or a minimum sample
volume of 4 dry standard cubic meters (dscm) per run. Requirements
for IGCCs included a minimum catch for fPM of 3 mg or a minimum
sample volume of 2 dscm. There were no changes to the minimum catch
and sample volume requirements for oil-fired EGUs.
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Commenters provided both supportive and opposing arguments
regarding the EPA's proposed compliance demonstration requirements for
fPM. With several minor, technical exceptions, comments received on the
proposed repeal of the PM CEMS compliance demonstration requirement for
fPM did not result in a change to the position the Agency set out in
the proposed rule. Therefore, the EPA is repealing the requirement to
use PM CEMS for compliance demonstration with the fPM emission standard
and restoring flexibility to owners and operators to choose between the
fPM compliance demonstration options as proposed. The EPA is also
reinstating the LEE program for fPM and non-Hg HAP metals as proposed.
The EPA received comments that supported retaining the flexibility of a
minimum volume per run or minimum mass per run sampling requirements
but argued that the updated minimum volume per run sampling requirement
would result in longer test runs and impose significant burdens on
operators. Based on these comments, along with an additional review of
the accuracy of PM CEMS at low levels, the EPA is finalizing as
proposed but with minor technical revisions to the sampling
requirements based on the purpose of the fPM testing. If PM CEMS are
used for the compliance demonstration, owners and operators are
required to follow the updated sampling requirements for minimum volume
per run or minimum mass per run, as proposed in the 2025 Proposal. For
all other compliance demonstration options, owners and operators are
required to collect a lower minimum sample volume as originally
required in the 2012 MATS Rule.
2. What is the rationale for the EPA's final approach and decisions on
the compliance demonstration requirements for the filterable PM
standard?
Upon further review, the EPA concludes that mandating the use of PM
CEMS and removing previously available compliance alternatives was not
``necessary'' pursuant to CAA section 112(d)(6). As discussed in
section III.A of this preamble, the EPA is finalizing the proposed
repeal of the more stringent fPM emission standard from the 2024 Final
Rule and returning to the fPM emission standard set in the 2012 MATS
Rule and reaffirmed in the 2020 Final Rule. Therefore, the EPA's
conclusion in the 2024 Final Rule that the costs for PM CEMS are
commensurate with the costs for stack testing \101\ no longer applies,
because longer duration runs that increase stack testing costs are no
longer necessary to demonstrate compliance with a lower fPM. Many
sources also use the stack testing compliance option to efficiently
merge their PM and HCl testing programs into a single testing
mobilization to test for those pollutants in conjunction, possibly
yielding further cost savings. Further, the Agency finds that although
the 2024 Final Rule invoked CAA section 114(a)(1)(C) as offering
additional authority for the PM CEMS requirement,\102\ the provision is
equally applicable to the alternative compliance demonstration options
restored in this final rule.\103\
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\101\ 89 FR 38535-37 (May 7, 2024).
\102\ Id. at 38535.
\103\ See CAA section 114(a)(1), (a)(1)(C)-(D), 42 U.S.C.
7414(a)(1), (a)(1)(C)-(D) (authorizing the EPA to require source
owners or operators to ``install, use and maintain such monitoring
equipment, and use such audit procedures, or methods'' and ``sample
such emissions'' as required by the Administrator).
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The 2024 Final Rule requirement to use PM CEMS to demonstrate
compliance meant that up to two-thirds of EGU owners and operators
would face higher compliance costs than when allowed to use quarterly
stack testing or PM CPMS. As shown in more detail in the RIA for this
final rule, the EPA estimates a cost savings of $2.9 million per year
related to the repeal of the PM CEMS requirement, after the two-year
exemption period (2030 to 2037); the estimated cost savings during the
two-year exemption period (2028 to 2029) is $1.2 million per year.
While the EPA concluded in the 2024 Final Rule that the use of PM CEMS
would allow for more efficient pollutant abatement and increased
transparency of EGU emissions,\104\ the Agency no longer believes that
those advantages outweigh the increased cost of PM CEMS compared to the
two other compliance options (i.e., PM CPMS and quarterly stack
testing) that were determined to be appropriate for demonstrating
compliance with the fPM emission standard in the 2012 MATS Rule.
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\104\ 89 FR 38535 (May 7, 2024).
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The EPA noted in the 2024 Final Rule that CEMS enable power plant
operators to quickly identify and correct problems with air pollution
control devices.\105\ However, there are other ways that owners and
operators can become aware of air pollution control malfunctions
without employing PM CEMS. For example, operators at EGUs with an ESP
can instantaneously track and record opacity, secondary corona power,
secondary voltage (i.e., the voltage across the electrodes), secondary
current (i.e., the current to the electrodes), spark rate, and alarm
and fault indicators to ensure proper functionality of the ESP in real
time. For EGUs with technology such as FFs, bag leak detection systems
(BLDS) and parameters like pressure differential (i.e., pressure drop),
inlet temperature, temperature differential, exhaust gas flow rate,
cleaning mechanism and cycle operation, and fan current and speed can
serve as reliable indicators of process operations. These indicators
also provide valuable data for analyzing trends and making informed
[[Page 9103]]
decisions about operational improvements and investments. As noted
earlier in this preamble and in the 2024 Final Rule, a large majority
of sources are already reporting measured compliance data showing fPM
emissions that are below the previous fPM standard of 0.030 lb/MMBtu
(via either PM CEMS or the stack testing compliance option), which
further illustrates that the various options for demonstrating
compliance with the fPM standards have been appropriate and
effective.\106\
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\105\ Id. at 38536.
\106\ Additionally, all fPM compliance data can be accessed by
the public via the EPA's Web Factor Information Retrieval System
(WebFIRE) at <a href="https://cfpub.epa.gov/webfire">https://cfpub.epa.gov/webfire</a>, which maintains the
availability and transparency of fPM emissions.
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Therefore, the EPA is repealing the requirement to use PM CEMS for
demonstrating compliance with the fPM emission standard, as well as the
adjusted QA criteria,\107\ and returning to the previous requirement
that allowed owners and operators to demonstrate compliance using
quarterly stack testing, PM CPMS, or PM CEMS. This provides greater
flexibility to owners and operators and reduces the compliance burden,
while still assuring compliance with the fPM emission standard.
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\107\ New PM CEMS installations must follow Performance
Specification 11 (PS-11), which requires the development of a site-
specific correlation curve to relate PM CEMS readings to the PM
reference method values. Emission standards are used to determine
the acceptable tolerance interval when correlating PM CEMS. In the
2024 Final Rule, the EPA instructed the use of 0.015 lb/MMBtu,
instead of the finalized more stringent limit of 0.010 lb/MMBtu,
when developing PM CEMS correlations to ease difficulties
correlating PM CEMS. See 89 FR 38535 (May 7, 2024).
---------------------------------------------------------------------------
The EPA is also reinstating the LEE program for fPM and non-Hg HAP
metals, which reduces the stack testing frequency for sources that have
demonstrated that their emissions are less than 50 percent of the
applicable emission limit for 3 consecutive years. Sources that had
previously demonstrated that they qualify for LEE status would not have
to re-demonstrate that qualification. In the 2024 Final Rule, the EPA
found that the optional LEE program was ``superfluous'' due to the PM
CEMS requirement and the revised fPM emission standard.\108\ However,
as the EPA is repealing those requirements, reinstating the LEE program
for fPM and non-Hg HAP metals will further reduce the costs associated
with stack testing for sources that opt in, while still assuring
compliance with the emission standard.\109\ As mentioned earlier in
this section, since LEE testing is only required once every 3 years
once a source has attained LEE status, the ongoing LEE testing program
is approximately 8 to 10 percent of the cost of a quarterly stack
testing program.
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\108\ 89 FR 38510 (May 7, 2024).
\109\ The LEE provisions are designed to ensure emissions are
minimized. For example, EGUs equipped with a main stack and a bypass
stack or bypass duct configuration that allows the effluent to
bypass any pollutant control device are not allowed to pursue the
LEE option under 40 CFR 63.10000(c). Furthermore, under 40 CFR
63.10000(c)(1)(i)(D), EGUs claiming LEE status may bypass a control
device during emergency periods for no more than 2 percent of the
EGU's annual operating hours.
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Finally, the EPA is also updating the fPM measurement requirements
that allow either an increased minimum volume per run or the collection
of a minimum mass per run. As stated in section III.A of this preamble,
a large majority of sources have reported measured compliance data
showing fPM emissions below the 0.030 lb/MMBtu fPM standard. It is
important that a sufficient quantity (i.e., mg of mass) of fPM be
collected during these fPM test runs to allow for the accurate
measurement of PM emissions, especially when the testing is being
conducted to correlate or certify a PM CEMS. For these reasons, we have
modified the fPM testing requirement to collect either a minimum catch
of 6.0 mg or a minimum sample volume of 4 dscm per run if using a PM
CEMS for compliance, whereas all other compliance demonstration options
will be required to collect a minimum sample volume of 1 dscm per PM
test run.
3. What key comments did the EPA receive on the compliance
demonstration requirements for the filterable PM standard and what are
our responses?
Comment: Some commenters agreed that there are other air pollution
control indicators such as opacity, ESP power, and baghouse
differential pressure that are used to provide timely information on
potential equipment performance issues or malfunctions. Additionally,
commenters said that the PM CEMS requirement falsely assumed the data
would provide a better indicator of control equipment performance,
which may not always be the case since PM CEMS measurements can be
influenced by a variety of factors. Commenters stated that sources are
required to comply with limits at all times, including between
performance tests, and that under 40 CFR 63.10000(b), EGUs ``must
operate and maintain any affected source, including associated air
pollution control equipment and monitoring equipment, in a manner
consistent with safety and good air pollution control practices for
minimizing emissions.''
Commenters also stated that owners and operators have multiple
tools beyond CEMS to identify malfunctions in air pollution control
equipment. These commenters agreed with the EPA's explanation in the
proposed rule that facilities equipped with ESPs can monitor parameters
such as opacity levels which can indicate higher than normal levels of
particulates in the exhaust gas; secondary corona power, secondary
voltage, and secondary current (indicating the collection of
particulates on the plates and wires) to verify proper operation; power
levels to the rappers and vibrators (used to clean the plates and
wires); and the continued operation of the ash removal system to
prevent system backup. For units with FFs, commenters stated that
operators can rely on, as indicators of control performance, BLDS;
pressure differential (indicates a bag leak or excessive buildup of the
ash layer on the filters); temperature differential (for optimal bag/
filter conditions); exhaust gas flow rate to detect unfiltered gas
escaping the system; power levels and operations of the bag vibrators
or reverse-air systems to ensure proper bag cleaning activity; fan
current which can indicate plugged bags; and opacity monitors.
According to commenters, these monitoring practices, which are already
in use across the industry, provide meaningful and timely insight into
equipment condition and emissions performance without necessitating
continuous emissions data. Additionally, other commenters stated that
there are sufficient compliance indicators in place to ensure that PM
(and HCl) emissions remain low between stack tests, such as operation
of scrubber technology.
Alternatively, other commenters argued the EPA did not provide
evidence that other parameters can be a substitute for complying with
the fPM limit or be used in ways to quickly identify problems with
pollution controls. Commenters also stated that the EPA did not
demonstrate that these alternative parameters will provide the same or
similar benefits as PM CEMS. Commenters disagreed that other
performance indicators are as reliable as PM CEMS to identify
malfunctions with the same sensitivity and that there is no requirement
to continuously monitor and maintain a record of each of these
parameters. Further, commenters argued that while monitoring of
operational parameters of control technologies may
[[Page 9104]]
reveal anomalous conditions broadly, it does not quantify the mass or
concentration of increased fPM emissions.
Response: The EPA agrees that there are reliable performance
indicators that are continuously monitored and recorded, which are used
to provide timely information on potential equipment performance and
control device issues or malfunctions. As discussed in section III.B of
this preamble, the EPA noted in the 2024 Final Rule that PM CEMS enable
power plant operators to quickly identify and correct problems with air
pollution control devices.\110\ However, there are other ways that
owners and operators become aware of air pollution control malfunctions
without employing PM CEMS. For example, for proper process operations
purposes of the unit, operators of EGUs with an ESP can instantaneously
track and record opacity, secondary corona power, secondary voltage
(i.e., the voltage across the electrodes), secondary current (i.e., the
current to the electrodes), spark rate, and alarm and fault indicators
to ensure proper functionality of the ESP in real time. Similarly, for
EGUs with technology such as FFs, BLDS and parameters like pressure
differential (i.e., pressure drop), inlet temperature, temperature
differential, exhaust gas flow rate, cleaning mechanism and cycle
operation, and fan current and speed can serve as reliable indicators
of process operations. These indicators, which are routinely monitored
and recorded regardless of any regulatory requirement, also provide
valuable data for analyzing trends and making informed decisions about
operational improvements and investments. Moreover, these indicators
help ensure that EGUs are operated and maintained, including associated
air pollution control equipment and monitoring equipment, in a manner
consistent with safety and good air pollution control practices for
minimizing emissions. As noted earlier in this preamble and in the 2024
Final Rule, a large majority of sources are already reporting measured
compliance data showing fPM emissions well below the previous fPM
standard of 0.030 lb/MMBtu (either via PM CEMS or the stack testing
compliance option), which further illustrates that the various options
for demonstrating compliance with the fPM standards have been
appropriate and effective.
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\110\ 89 FR 38536 (May 7, 2024).
---------------------------------------------------------------------------
Comment: Commenters agreed with the EPA that the costs of
installing PM CEMS are significant and the 2024 Final Rule failed to
articulate why such costs were justified as compared to the other
compliance methods permitted since 2012. Commenters argued that the EPA
did not consider the fact that certain CEMS technologies, based on
their designs and models, might not have replacement parts readily
available from the original equipment manufacturers; therefore, when a
critical component of the CEMS breaks or needs replacement, repairs
could require costly expenditures or even a total replacement of the
CEMS. Commenters also provided examples of how stack testing or CPMS
costs could be much less than the cost of PM CEMS. For instance,
commenters said that some sources conduct quarterly testing for HCl
along with fPM to reduce stack testing costs further by merging the HCl
testing and fPM testing into the same testing program mobilization,
which would be noticeably cheaper than testing for HCl and fPM
separately. Commenters also noted that testing costs for EGUs that
previously qualified for PM LEE status were much less than the cost of
PM CEMS, by some estimates as much as 20 to 30 times lower. Lastly,
commenters explained that CPMS provide lower testing costs, simpler
procedures for establishing operating limits, and fewer operational
burdens compared to PM CEMS.
Other commenters disagreed that the higher costs of PM CEMS justify
repealing the PM-CEMS-only compliance demonstration requirement from
the 2024 Final Rule. Further, commenters said that the benefits of
reduced pollution through the use of PM CEMS would exceed the minor
incremental cost between PM CEMS and stack testing.
Response: As discussed in section III.A of this preamble, the EPA
is finalizing the repeal of the more stringent fPM emission standard.
The more stringent fPM standard required longer duration runs, which
would increase the relative costs of stack testing. Therefore, the
EPA's conclusion in the 2024 Final Rule that the costs for PM CEMS are
commensurate with the costs for stack testing no longer applies because
stack testing costs are not increasing due to longer duration runs.
However, the EPA disagrees that sources that elect to conduct
quarterly testing for HCl tests combined with fPM would greatly reduce
stack testing costs. On the contrary, adding HCl testing to an fPM
testing program (or adding fPM testing to an HCl testing program) would
result in an increased cost for testing, as opposed to lowering the
cost. While some cost savings would be realized by efficiently
``merging'' a fPM and HCl testing programs into a single testing
mobilization to test for those pollutants in conjunction, this approach
would not result in a lower cost than what would be realized if testing
for PM only.\111\ Nevertheless, the EPA understands that testing for
fPM and HCl would not double the cost of an ``fPM only'' test program,
since the fPM and HCl testing would occur concurrently without needing
separate testing mobilizations, equipment setups, and equipment tear
downs.
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\111\ Commenters claim that quarterly stack testing for fPM
costs $57,100/year, while merging the fPM testing with the HCl
testing into the same testing mobilization would lower the testing
costs to $37,500/year, yielding almost $20,000/year in cost savings.
The EPA disagrees that costs for merging the stack testing for fPM
and HCl would be lower than testing for fPM only.
---------------------------------------------------------------------------
The EPA agrees that testing costs for EGUs that previously
qualified for PM LEE status will be much lower than the cost of PM
CEMS, yielding further cost savings. Since LEE testing is only required
once every 3 years once a source has attained LEE status, the EPA
estimates that an ongoing LEE testing program is approximately 8 to 10
percent of the cost of a quarterly stack testing program.\112\
---------------------------------------------------------------------------
\112\ Per 40 CFR 63.10000(c)(1)(iii), an ongoing LEE PM testing
program is required at least once every 36 months (or at 1/12th the
frequency (i.e., 8.3 percent)) of a quarterly PM testing program to
demonstrate continued LEE status.
---------------------------------------------------------------------------
Comment: Some commenters argued that the EPA failed to adequately
explain its changed view of PM CEMS in terms of superior accuracy,
transparency, and pollution reduction afforded by using PM CEMS,
asserting that PM CEMS are already widely used throughout the industry
and that the costs are small compared to a facility's overall operating
expenses. These commenters stated that the EPA did not demonstrate that
the other compliance demonstration options will provide the same or
similar benefits as PM CEMS. Commenters asserted that PM CEMS have the
benefits of greater reliability and accuracy and that continuous
monitoring allows rapid detection of pollution problems so violations
can be prevented or quickly fixed. Commenters also asserted that real-
time information on pollution has more operational relevance for plant
managers than do stack tests because real-time CEMS data allow managers
to find the reasons for problems and provide learning that can have
significant long-term benefits. Specifically, commenters stated that in
the 2024 Final Rule, the EPA found that requiring the use of PM CEMS
would provide 35,040 15-minute values for each EGU during a 1-year
period, which is 243 times more information than is
[[Page 9105]]
provided by quarterly stack testing under the 2012 MATS Rule.
Commenters also asserted that continuous monitoring can reveal wide
variability that is obscured with stack tests that occur once a
quarter, once a year, or even less frequently; and that continuous
monitoring allows an automated response that can fix the problem before
noncompliance occurs, or an alarm that notifies relevant personnel that
a problem is occurring. Commenters also asserted that continuous
monitoring is also a deterrent to negligence and fraud; when companies
know that increases in pollution can be detected in real time, they are
less likely to engage in risky or prohibited practices. Commenters also
asserted that CEMS monitoring data allows the facility, neighbors, and
regulatory entities to see if the facility is complying with the
standard, as it does not rely on an outdated monitoring method and
assumption that emissions will consistently remain at the level found
during an unreliable stack test.
Further, commenters asserted that State regulatory programs rely on
PM CEMS data to effectively limit emissions. For example, the Illinois
Control Board recently relied on PM CEMS data in promulgating emissions
limits for industrial facilities, including coal-fired power plants,
during period of ``start-up, malfunction, or breakdown.'' Commenters
said that this analysis would have been difficult to perform if only
stack testing data were available, which would not comprehensively
capture emissions levels during atypical startup, malfunction, or
breakdown periods.
Response: The EPA recognizes that PM CEMS may have certain
advantages over periodic stack testing in some situations. However, as
discussed in section III.B of this preamble, pursuant to CAA section
112(d)(6), the EPA must consider cost in deciding whether it is
``necessary'' to revise the requirements and has broad discretion in
selecting reasonable compliance demonstration methods under CAA section
112 and 114(a)(1). Stack testing under MATS has been shown to be less
costly than operating and maintaining a PM CEMS on an annualized cost
basis.\113\ Moreover, sources subject to both an applicable PM and HCl
standard under MATS may use the stack testing compliance option to
efficiently merge their PM and HCl testing programs into a single
testing mobilization to test for those pollutants concurrently,
possibly yielding further cost savings. The EPA also notes that stack
testing for fPM under MATS continues to be required on a quarterly
basis, which is more frequent than typical stack test programs which
are required at either annual or multi-year frequencies.\114\ Finally,
there is no indication in the record that EGUs are in noncompliance
with the fPM standard. The record demonstrates consistent
overperformance of the standard by a large percentage of the regulated
community. In light of this, it is reasonable to continue to provide
flexibility, and it renders the additional cost of mandating PM CEMS
unnecessary.
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\113\ Memo from Barrett Parker, EPA to Docket ID No: EPA-HQ-OAR-
2018-0794, ``Revised Estimated Non-Beta Gauge PM CEMS and Filterable
PM Testing Costs'' (December 21, 2023).
\114\ For example, industrial boilers subject to 40 CFR part 63,
subpart DDDDD, are required to perform fPM testing on either an
annual or 3-year frequency, depending on the PM emission rate during
testing. For stationary reciprocating internal combustion engines
subject to 40 CFR part 63, subpart ZZZZ, testing for carbon monoxide
(CO) is required every 8,760 hours or 3 years, whichever comes
first. For stationary combustion turbines subject to 40 CFR part 63,
subpart YYYY, testing for formaldehyde is required on an annual
basis. However, testing for fPM is not required for stationary
combustion turbines under 40 CFR part 63, subpart YYYY, or 40 CFR
part 630, subpart KKKK, and is instead at the discretion of the
delegated authority.
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Comment: Regarding stack testing for fPM, commenters generally
agreed with the EPA's proposal to retain the option of allowing either
an increased minimum volume per run or the collection of a minimum mass
per run, since that option would provide owners and operators greater
flexibility that may reduce measurement uncertainty, lower test
durations, and therefore lower the fPM stack testing costs. However,
commenters requested that the proposed updated minimum volume per run
of 4 dscm should instead return to the 1 dscm level of the 2012 MATS
Rule. Commenters said that a 4 dscm minimum volume per run for all
compliance demonstration options would require longer duration stack
test runs of approximately 9 hours, posing larger costs, emissions, and
operational difficulties for units.
Further, commenters argued that if the EPA finalized the repeal of
the more stringent fPM limit and the PM-CEMS-only compliance
demonstration requirement, the increase to 4 dscm minimum volume for
each fPM stack testing run would no longer be prudent for all
compliance demonstration purposes. While commenters stated that higher
sample volumes could be useful to reduce measurement uncertainty for
sources operating near emission limits or with low-level test
measurements, individual owners and operators are best able to make
such decisions based on the unit-specific compliance strategies.
Commenters who disagreed with the EPA's proposal to retain these
updated sampling requirements argued that more mass or volume does not
create a more accurate correlation with PM CEMS, as the overall shape
of the correlation curve is defined by mid- and high-level test
conditions that have sufficient fPM mass due to artificially detuned
conditions. A few commenters asserted that a minimum mass option is not
feasible, as the amount of PM mass collected on the filter during stack
testing is not known until after the run is completed and the filters
are dried and weighed. While historical test results should enable
sources to reasonably estimate the mass that will be collected during
each fPM stack test run, commenters argued that sources should not be
required to repeat test runs based solely on the collection of less
mass than expected.
Other commenters argued that the updates to the sampling
requirements in the 2024 Final Rule are necessary to ensure reliable
test results, particularly at the low levels of fPM many EGUs are
measuring. However, commenters expressed concern that the updates to
the sampling requirements combined with the repeal of the more
stringent fPM emission limit could result in emission spikes during
stack testing. Commenters argued that the lower fPM emission standard
combined with the sampling requirements in the 2024 Final Rule would
have required plants to maintain the low emission rates they have been
demonstrating and better protect surrounding communities.
Response: The EPA agrees that sampling requirements that allow
either an increased minimum volume per run or the collection of a
minimum mass per run would provide EGU owners and operators greater
flexibility. The EPA also recognizes that a 4 dscm minimum volume per
run would require longer duration stack test runs and that those longer
test runs are not necessary for all fPM compliance demonstration
options.
However, the EPA disagrees with the assertion that more mass or
volume does not create a more accurate correlation with PM CEMS. While
the mid- and high-level test conditions during PM CEMS correlations or
verifications will most likely use the minimum catch value of 6.0
milligrams (mg) per run, it is still necessary to accurately measure
values for the low-level test conditions. The EPA agrees with
commenters that historical test data provides sources with a reasonable
indicator and estimate of the potential mass that would be collected
during each test run, therefore making it unnecessary to utilize the
[[Page 9106]]
minimum volume requirement, especially at the mid- and high-level test
conditions.
After considering comments, and because the EPA is finalizing the
repeal of the PM CEMS requirement and again allowing other fPM
compliance demonstration options, the EPA is also finalizing minor
technical revisions to the fPM sampling requirements. Specifically, the
EPA is finalizing the requirement that allows EGU owners and operators
using PM CEMS for compliance to collect either a minimum catch of 6.0
mg or a minimum sample volume of 4 dscm per run, in order to provide
additional testing flexibility while also ensuring that a sufficient PM
CEMS correlation sample is obtained. For EGU owners and operators using
any other compliance demonstration option, the EPA is finalizing the
revised minimum sample volume of 1 dscm per PM test run, which is
considered sufficient for a representative gravimetric assessment of a
source's PM compliance status.\115\
---------------------------------------------------------------------------
\115\ More specifically, the 4 dscm sample volume (or 6.0 mg
sample catch) requirement would apply to any test associated with PM
CEMS testing (e.g., Performance Specification 11 (PS-11) correlation
curves, relative response audits (RRAs), and response correlation
audits (RCAs)), whereas the 1 dscm sample volume requirement would
apply to quarterly PM compliance testing. PM LEE testing programs
would also be based upon the 1 dscm sample volume requirement, yet
the required minimum sample volume for LEE testing will continue to
be increased nominally by a factor of 2 (i.e., at least 2 dscm), per
40 CFR part 63, subpart UUUUU, table 2.
---------------------------------------------------------------------------
C. Hg Emission Standard for Lignite-Fired EGUs
1. What are we finalizing as the Hg emission standard for lignite-fired
EGUs?
In the proposed rule, the EPA proposed to repeal the Hg standard
for lignite-fired EGUs in the 2024 Final Rule and to return to the 4.0
lb/TBtu emission standard promulgated in the 2012 MATS Rule and
retained in the 2020 Final Rule. The EPA solicited comment on whether
there is sufficient data demonstrating that the standard can be met by
lignite-fired EGUs with a range of boiler types and variable fuel
composition (Question #6). The EPA also solicited comment on other
achievable and cost-effective Hg standards for lignite-fired EGUs that
are based on developments in practices, processes, and control
technologies that the EPA should consider as an alternative to a
standalone repeal of the 1.2 lb/TBtu standard (Question #7).
Upon further consideration and after reviewing comments received,
the EPA is repealing the 1.2 lb/TBtu Hg limit for lignite-fired EGUs
that was promulgated in the 2024 Final Rule and reverting to the 4.0
lb/TBtu Hg limit that was set in the 2012 MATS Rule and retained in the
2020 Final Rule.
2. What is the rationale for our final approach and decisions on the Hg
emission standard for lignite-fired EGUs?
In the 2012 MATS Rule, the EPA promulgated a beyond-the-floor
standard for Hg for the subcategory of existing coal-fired units
designed for ``low rank'' virgin coal (i.e., lignite) based on the use
of ACI for Hg control.\116\ The EPA established a Hg emission standard
of 4.0 lb/TBtu for lignite-fired utility boilers and 1.2 lb/TBtu for
utility boilers firing all other types of coal (e.g., anthracitic coal,
bituminous coal, subbituminous coal, and coal refuse).
---------------------------------------------------------------------------
\116\ 77 FR 9304 (February 16, 2012).
---------------------------------------------------------------------------
The 2024 Final Rule lowered the Hg standard for lignite-fired EGUs
from 4.0 lb/TBtu to 1.2 lb/TBtu based on the EPA's determination that
commercially available control technologies and improved methods of
operation would allow lignite-fired EGUs to meet a more stringent
emission standard. The more stringent Hg emission standard brought the
requirement for lignite-fired EGUs in line with the emission limitation
requirements of EGUs firing all other types of coal. In the 2024 Final
Rule, the EPA reviewed coal composition information and concluded that
the Hg content, the halogen content, and the alkalinity were similar
between various lignite and subbituminous coals. In 2021, EGUs firing
subbituminous coal emitted Hg at an average annual rate of 0.6 lb Hg/
TBtu with measured values as low as 0.1 lb/TBtu, which the Agency found
demonstrated that EGUs burning subbituminous coal have utilized control
options to meet the 1.2 lb/TBtu emission standard despite the
challenges presented by the low halogen content in the coal (which
results in difficult-to-control elemental Hg vapor in the flue gas
stream).\117\ The Agency asserted that its cost-effectiveness estimates
for a model 800 MW lignite-fired EGU using a range of sorbent injection
rates to meet the revised Hg emission standard were lower or consistent
with cost-effectiveness values for Hg controls that the EPA has found
to be acceptable in previous rulemakings.
---------------------------------------------------------------------------
\117\ 88 FR 24880 (April 23, 2023).
---------------------------------------------------------------------------
After reviewing the revised emission standard that was promulgated
in the 2024 Final Rule, the EPA is repealing the revised Hg emission
limit for lignite-fired EGUs because the revised standard was based on
insufficient data to demonstrate that lignite units can meet the lower
limit over the range of boiler types and variable compositions of fuels
used at lignite-fired EGUs. Commenters provided both supportive and
opposing arguments for issues regarding the Hg limit for lignite-fired
EGUs. Comments received on the proposed repeal of the Hg limit for
lignite-fired EGUs did not persuade the Agency to change its position
from that set out in the proposed rule.
While the EPA found that all 22 existing lignite-fired EGUs at 12
facilities would need to control their Hg emissions to 95 percent or
less to meet an emission standard of 1.2 lb/TBtu in the 2024 Final
Rule,\118\ the Agency did not demonstrate that this high level of Hg
removal is generally achievable for all lignite-fired units in the
source category while taking into account the wide-ranging and highly
variable Hg content of the various lignite fuels. In fact, Hg emission
rates reported in the 2024 Final Rule from units at 11 of the 12
lignite facilities were well above the final 1.2 lb/TBtu emission
standard.\119\ The EPA instead primarily relied on the emission
reduction performance of only two units (at the Twin Oaks facility in
Texas) that achieved the revised emission standard.\120\ Between August
1 and September 19, 2023, a series of Hg emissions performance tests
were conducted on Twin Oaks units 1 and 2. The average Hg emissions
rates for the 30-boiler operating day performance tests were 1.1 lb/
TBtu for unit 1 and 0.9 lb/TBtu for unit 2.\121\ Further, in
performance testing for the previous year (2022), the average Hg
emissions rates for the 30-boiler operating day performance test were
0.9 lb/TBtu for unit 1 and 0.6 lb/TBtu for unit 2. However, these tests
were conducted over a limited operating period and are not sufficient
to establish that meeting a 1.2 lb/TBtu standard continuously is
possible for all lignite-fired EGUs.
---------------------------------------------------------------------------
\118\ Since the 2024 Final Rule, the Martin Lake and Limestone
facilities have undergone permit changes that no longer allow the
burning of lignite coal.
\119\ 89 FR 38546 (May 7, 2024).
\120\ Id. at 38539.
\121\ Id. at 38540.
---------------------------------------------------------------------------
Furthermore, the Twin Oaks facility, constructed in the early
1990s, is one of the newest lignite units and uses a circulating
fluidized bed (CFB) combustor, which affects Hg emissions. Conventional
boilers use coal that is pulverized to a very fine particle size (i.e.,
powdered) to maximize combustion efficiency and to minimize unburned
carbon. In contrast, the design
[[Page 9107]]
of CFB combustors permits the burning of larger-sized coal particles.
Fluidized bed units typically operate at lower temperatures compared to
conventional boilers and have longer fuel residence times. As a result,
CFB combustors typically have higher levels of unburned carbon present
in the fly ash. The unburned carbon particles can behave much like
injected activated carbon sorbent and, coupled with the lower operating
temperature and longer residence time, can promote more efficient Hg
removal as compared to that observed from units using non-CFB boilers
with conventional pulverized coal combustors.
Other lignite-fired EGUs that utilize a CFB combustor also had
generally lower Hg emission rates. For instance, the 2022 measured Hg
rates reported in the 2024 Final Rule for the Red Hills facility in
Mississippi, which also employs CFB combustors, was 1.7 lb/TBtu,
compared to a range of 2.5 to 3.0 lb/TBtu for other lignite-fired EGUs
in the southern U.S.\122\ Additionally, the lowest 2022 Hg emissions
from lignite-fired facilities in North Dakota were found at Spiritwood
Station, which also utilizes a CFB combustor. In revising the Hg
emission standard for lignite-fired EGUs in the 2024 Final Rule, the
EPA failed to evaluate the achievability of the revised Hg emission
standard by affected sources that are not using the better performing
CFB combustor technology.
---------------------------------------------------------------------------
\122\ Id. at 38548.
---------------------------------------------------------------------------
In addition, the EPA assumed in the 2024 Final Rule that the
revised Hg standard of 1.2 lb/TBtu could be met by injecting better
performing powdered sorbents using existing sorbent injection systems
without the need for equipment modifications or additions. However,
industry commenters noted that existing equipment at lignite-fired
power plants may not be able to achieve the 1.2 lb/TBtu Hg limit and
that demonstration testing would be required to determine a sorbent
dosage rate, guaranteed injection rate, and the emissions rate that can
be achieved when considering the Hg content variability of the lignite.
Commenters stated that modifications to Hg control systems may be
required to meet the 1.2 lb/TBtu emission limit. The EPA did not
consider such cost in the final analysis for the 2024 Final Rule.
In addition, the Agency did not sufficiently investigate the
complex composition of lignite coals in the 2024 Final Rule, including
the variability of the Hg content in the inlet fuel source and the
corresponding reductions needed to comply with the 1.2 lb/TBtu Hg
emission standard. In the 2023 proposed rule, the EPA explained how the
halogen content of coal influences the oxidation state of Hg in the
flue gas stream, and thus the partitioning of Hg into elemental Hg
vapor, oxidized Hg vapor, or particle-bound Hg, which impacts the Hg
control approaches.\123\ Lignite and subbituminous coals both have a
lower halogen content compared to bituminous coals, and the Hg in the
flue gas from boilers firing those fuels tends to stay in the elemental
vapor state, which is more challenging to control. The EPA noted that
pre-halogenated (typically brominated) sorbents have been effectively
utilized to control Hg emissions at power plants firing low-halogen
content subbituminous coals. However, the EPA also noted that lignite
coals tend to contain higher amounts of sulfur (more similar to some
bituminous coals), which, under certain circumstances, can result in
the production of sulfur trioxide (SO<INF>3</INF>) in the flue gas
stream. SO<INF>3</INF>, in turn, is known to inhibit the effectiveness
of some sorbents that are used for Hg control. The EPA acknowledged the
challenges with higher sulfur content coals but noted that bituminous
coal-fired power plants found ways to overcome those challenges--
sometimes by utilizing newly developed sulfur-tolerant sorbents.
However, while the EPA acknowledged the respective challenges that the
halogen and sulfur contents of coal can have on Hg control in the 2024
Final Rule, the EPA failed to address the impact of lower halogen
content coupled with higher sulfur content on Hg control for lignite-
fired power plants. Subbituminous coals tend to have low contents of
both halogen and sulfur, while bituminous coals tend to contain higher
levels of both halogen and sulfur. In comparison, lignites tend to have
low halogen content (similar to subbituminous coals) and higher sulfur
content (similar to bituminous coals).
---------------------------------------------------------------------------
\123\ 88 FR 24875 (April 24, 2023).
---------------------------------------------------------------------------
Commenters also provided data challenging the assumed inlet value
of 25.0 lb/TBtu used in modeling in the 2024 Final Rule. For example,
historical data indicate that lignite seams near the San Miguel plant
in Texas result in coal feeds that have an average Hg inlet content of
34.0 lb/TBtu.\124\ As a result, San Miguel would need to achieve an
average control rate of 96.3 percent to meet the standard in the 2024
Final Rule, compared to an 87.8 capture percentage for the 4.0 lb/TBtu
emission limit .\125\ Additionally, monthly fluctuations in Hg content
could require even higher control levels at least half the time.
Ignoring monthly variability not only leads to an underestimation of
costs associated with Hg removal but also overlooks control device
modifications and enhancements required to achieve pollution control
levels exceeding 90 percent.
---------------------------------------------------------------------------
\124\ Document ID No. EPA-HQ-OAR-2018-0794-5965.
\125\ Document ID No. EPA-HQ-OAR-2018-0794-5965.
---------------------------------------------------------------------------
It was not necessary to revise the Hg limit for lignite-fired EGUs
in the 2024 Final Rule. This revised emission standard was based on
insufficient data, and furthermore, the EPA did not demonstrate that
the high level of Hg removal it required was generally achievable for
all lignite-fired units in the source category while taking into
account the wide-ranging and highly variable Hg content of the various
lignite fuels. In addition, the Agency failed to evaluate its
achievability by affected sources that are not using CFB combustor
technology and assumed the revised standard could be met by injecting
better performing sorbents without equipment modifications. The EPA
also did not sufficiently investigate the complex composition of
lignite coals, including the variability of the Hg content in the inlet
fuel source, and ignored monthly variability, leading to an
underestimation of costs. For these reasons, the EPA is finalizing the
repeal of the Hg emission limit for lignite-fired EGUs that was
promulgated in the 2024 Final Rule--1.2 lb/TBtu--and reverting to the
Hg emission limit--4.0 lb/TBtu--that was promulgated in the 2012 MATS
Rule.
3. What key comments did we receive on the Hg emission standard for
lignite-fired EGUs and what are our responses?
Comment: Some commenters agreed with the EPA's proposed
reconsideration of the Twin Oaks Hg data that the EPA relied upon in
the 2024 Final Rule. First, commenters agreed the performance tests
were conducted over a limited operating period and not sufficient to
establish a more stringent Hg emission standard continuously for all
units. Commenters argued that this facility was not representative of
the national fleet because lignite seams burned at Twin Oaks differ
from lignite at North Dakota lignite facilities and at other Texas
lignite facilities. Second, commenters agreed that the CFB boiler
design at the Twin Oaks and Red Hills facilities promote more efficient
Hg removal compared to units using other types of boilers.
[[Page 9108]]
Other commenters disagreed with the EPA's proposed reconsideration
of the Twin Oaks and Red Hills Hg data, arguing that the facilities'
use of baghouses is an additional reason for highly effective Hg
capture. These commenters asserted that while both facilities are
equipped with ACI and would have very low SO<INF>3</INF> present in the
flue gas due to high free lime content, the presence of a baghouse
makes the ACI, as well as any intrinsic capture of fly ash, much more
effective. These commenters stated that if an ESP was installed instead
of a baghouse, Hg capture would be more difficult. However, commenters
asserted that every lignite unit is already configured in a manner for
potentially higher Hg capture. These commenters stated that lignite
facilities equipped with baghouses include Antelope Valley, Coyote,
Spiritwood, Twin Oaks, Oak Grove, and Red Hills, and that some of those
facilities also have an upstream dry scrubber (Antelope Valley, Coyote,
Spiritwood) that helps make Hg capture with ACI more effective. The
remainder of the lignite facilities (Coal Creek, Leland Olds, Milton R
Young, Limestone, Martin Lake, and San Miguel) installed ESPs followed
by a wet FGD, which enable additional Hg capture beyond what is
achieved with ACI because wet FGD removes oxidized Hg very efficiently.
These commenters further asserted that higher Hg capture is
possible for lignite plants with pulverized coal boilers (i.e., non-CFB
units) and pointed to the Conemaugh power plant in Pennsylvania as an
example. The Conemaugh facility is equipped with an ESP and wet FGD and
burns bituminous coal. These commenters attempted to calculate the Hg
content of coals burned at Conemaugh using EIA-923 data from 2016 to
2022, finding an average Hg content ranging from approximately 10 lb/
TBtu to over 50 lb/TBtu with a standard deviation ranging from near
zero to almost 40 lb/TBtu.\126\ These commenters also asserted that
most bituminous and subbituminous units receive coal from multiple
mines and therefore face much greater variability in Hg content than
lignite units, which are mine-mouth and only receive coal from one
mine. Using the inferred Hg content information, commenters estimated
that the Hg capture rate at the Conemaugh facility exceeded 95 percent
every year, demonstrating that higher Hg capture at lignite units with
lower Hg variability is possible using this configuration.
---------------------------------------------------------------------------
\126\ The survey Form EIA-923 collects detailed electric power
data--monthly and annually--on electricity generation, fuel
consumption, fossil fuel stocks, and receipts at the power plant and
prime mover level. <a href="https://www.eia.gov/electricity/data/eia923/">https://www.eia.gov/electricity/data/eia923/</a>.
---------------------------------------------------------------------------
Response: The EPA agrees that baghouses are another technology for
efficient Hg capture. However, the Agency did not demonstrate that
higher Hg removal is achievable for all lignite-fired units once the
wide-ranging and highly variable Hg content of the various lignite
fuels is taken into account. As noted in the 2024 Final Rule,
bituminous coals from Pennsylvania exhibit large Hg content variability
similar to that of lignite, but bituminous coals also have higher
natural chlorine content than lignite coal, which aids in the Hg
removal efficiency.\127\ Therefore, the Agency does not agree with the
commenters' example that a facility burning bituminous coal using a
pulverized coal boiler demonstrates that a similar lignite-fired unit
can achieve a similar level of Hg control.
---------------------------------------------------------------------------
\127\ 89 FR 38543 (May 7, 2024).
---------------------------------------------------------------------------
Comment: Commenters argued that the EPA failed to adequately
justify returning to the 2012 MATS Rule Hg emission standard for
lignite-fired EGUs in the proposed rule, as power plants that burn
lignite coal represent a disproportionally large share of Hg emissions
across all coal-fired EGUs. Specifically, commenters cited the 2023
proposal, in which the EPA provided that 16 of the top 20 Hg-emitting
EGUs were lignite-fired and that lignite EGUs were responsible for
about 30 percent of all Hg emitted from all coal-fired EGUs in 2021,
while generating about 7 percent of total 2021 MW-hours.\128\
Commenters noted that the 2012 MATS Rule resulted in a 90 percent
reduction of Hg from power plants, but few reductions came from plants
that burn lignite coal. The commenters explained that lignite-fired
EGUs are concentrated geographically in North Dakota and Texas, which
increases the cumulative burden of such pollutants on surrounding and
downwind vulnerable communities.
---------------------------------------------------------------------------
\128\ 88 FR 24876 (April 24, 2023).
---------------------------------------------------------------------------
Response: The EPA took all relevant comments and information,
including information referenced above, into consideration when
deciding whether to finalize the proposed repeal. Since the 2024 Final
Rule, the Agency obtained updated information on the fleet of power
plants burning lignite coal, finding that the Martin Lake and Limestone
facilities (both in Texas) are no longer permitted to burn lignite and
are now subject to a 1.2 lb/TBtu Hg emission standard. As mentioned
earlier in this preamble, the 2020 Residual Risk Review found the
residual risks due to emissions of air toxics to be acceptable from the
coal- and oil-fired EGU source category and determined that the current
NESHAP (as promulgated in the 2012 MATS Rule) provided an ample margin
of safety to protect human health and prevent an adverse environmental
effect. Risk from near-field deposition of Hg to subsistence fishers
was evaluated, using a site-specific assessment of a lake near three
lignite-fired facilities.\129\ The results suggest that methylmercury
(MeHg) exposure to subsistence fishers from lignite-fired units alone
is below the RfD for MeHg neurodevelopmental toxicity or IQ loss, with
an estimated hazard quotient (HQ) of 0.06. In general, the EPA believes
that exposures at or below the RfD are unlikely to be associated with
appreciable risk of deleterious effects. The EPA reaffirmed its 2020
Residual Risk Review, which showed that emissions of HAP from coal- and
oil-fired power plants have been reduced such that residual risk is at
an acceptable level and provides an ample margin of safety, in the 2024
Final Rule.\130\
---------------------------------------------------------------------------
\129\ . Document ID No. EPA-HQ-OAR-2018-0794-0070
\130\ In the 2024 Final Rule, the EPA stated: ``In the 2023
Proposal, the EPA determined not to reopen the 2020 Residual Risk
Review, and accordingly did not propose any revisions to that
review. As the EPA explained in the proposal, the EPA found in the
2020 RTR that risks from the Coal- and Oil-Fired EGU source category
due to emissions of air toxics are acceptable and that the existing
NESHAP provides an ample margin of safety to protect public
health.'' 89 FR 38518 (May 7, 2024).
---------------------------------------------------------------------------
Comment: Many commenters agreed that the EPA did not appropriately
consider costs for lignite EGUs to meet a revised Hg emission standard
in the 2024 Final Rule. Commenters stated the cost to comply with the
revised Hg emission standard depends on the amount and type of sorbent
required and ACI equipment additions or modifications, and since the
amount of sorbent needed to achieve a more stringent standard is
unclear and unit-specific, the sorbent cost cannot be reliably
calculated. Commenters also disagreed with the EPA's claim in the 2024
Final Rule that SO<INF>3</INF>-tolerant sorbents could be used at lower
feed rates to achieve greater Hg capture. Commenters stated that the
EPA underestimated costs in the 2024 Final Rule by not considering the
costs of modifications to the Hg control systems to meet a more
stringent Hg emission standard, especially for units equipped with an
ESP instead of a FF. Commenters stated that compliance costs cannot be
accurately estimated because no lignite EGU has demonstrated that the
revised Hg
[[Page 9109]]
emission standard can be met on a continuous basis. Commenters stated
that these deficiencies in the Agency's cost analysis (e.g., failure to
include annual capitalized costs for the Hg control system, updated
sorbent costs, and costs based on theoretical sorbent usage) resulted,
for example, in at least a $2.6 million underestimate for Milton R
Young Station's Unit 2.
Other commenters claimed that the EPA provided no evidence in the
proposed rule, and did not appear to conclude, that costs of possible
modifications to Hg control systems render the Hg standard either not
``achievable'' or not cost-effective. These commenters stated that
although the EPA asserted in the proposed rule that it did not
previously consider the cost of possible modifications to control
systems to meet the revised Hg standard, the Agency had in fact
considered these costs in the 2024 Final Rule and found them to be
reasonable.\131\ One of these commenters quoted a portion of the 2024
Final Rule in which the commenter believed that the EPA considered the
costs of potential control system modifications and found that the need
for ``significant additional capital investment is unlikely.'' \132\
Commenters asserted that the EPA stated in the 2024 Final Rule that the
Agency expected sources to ``be able to meet the revised emission
standard using existing controls (e.g., using existing sorbent
injection equipment)'' and that ``if site-specific conditions
necessitate minor capital improvements to the ACI control technology, .
. . any incremental capital cost would be small relative to ongoing
sorbent costs accounted for in this analysis.'' \133\
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\131\ Document ID No. EPA-HQ-OAR-2018-0794-7609 (citing 89 FR
38508 (May 7, 2024).
\132\ Id. (citing 89 FR 38549 (May 7, 2024)).
\133\ Id.
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Response: The EPA agrees with the commenters asserting that the
Agency did not appropriately consider costs associated with Hg removal
and overlooked costs for control device modification and enhancement
required to achieve pollution control levels exceeding 90 percent
within the 2024 Final Rule. In the 2024 Final Rule, the EPA noted that
pre-halogenated (typically brominated) and sulfur-tolerant sorbents
have effectively utilized to control Hg emissions at power plants
firing low-halogen subbituminous coals. However, in the 2024 Final
Rule, the EPA did not consider that the SO<INF>3</INF>-tolerant
sorbents had not been extensively tested on lignite-fired EGUs and thus
the feed rates and associated costs are uncertain and therefore
disagrees with those commenters that asserted costs for these sorbents
are reasonable. Since subbituminous coals tend to have low content of
both halogen and sulfur and bituminous coals tend to contain higher
levels of both halogen and sulfur, whereas lignites generally have the
combined characteristics of low halogen content and higher sulfur
content, the EPA disagrees with those commenters that asserted
associated costs to achieve greater Hg capture in lignite-fired EGUs
were properly considered in the 2024 Final Rule.
IV. Comments and Responses on the Relevance of Residual Risk to
Technology Reviews Under CAA Section 112(d)(6)
A. What did the EPA propose and solicit comment on regarding the
relevance of residual risk to technology reviews under CAA section
112(d)(6)?
The EPA is finalizing the position that the Agency may consider the
results of the one-time residual risk review requirement under CAA
section 112(f)(2) in determining whether it is ``necessary'' to revise
standards at the conclusion of subsequent CAA section 112(d)(6)
technology reviews. Under CAA section 112(d)(6), the EPA is required
``to review, and revise as necessary (taking into account developments
in practices, processes, and control technologies), emission standards
promulgated under this section no less often than every 8 years''
(emphasis added). As noted in section II.A.1 of this preamble, the
breadth of the term ``necessary'' in CAA section 112(d)(6) authorizes
the EPA to consider the costs of revising standards in addition to the
emissions-reduction potential of developments in practices, processes,
and control technologies. Given the high costs and potential technical
feasibility concerns with implementing the revised standards
promulgated in the 2024 Final Rule, the EPA proposed to find that the
2024 revisions were not ``necessary'' under CAA section 112(d)(6) and
solicited comment on whether and how the extent of further meaningful
risk reduction opportunities should be considered in making that CAA
section 112(d)(6) determination (Question #8). As explained in section
II of this preamble, the EPA found in its 2020 Residual Risk Review
that the residual risks due to HAP emissions from this source category
are acceptable and determined that the current NESHAP (as promulgated
in the 2012 MATS Rule) provided an ample margin of safety to protect
public health and prevent an adverse environmental effect. The EPA
reaffirmed the 2020 Final Rule, and did not reopen any of the
underlying findings or conclusions of the one-time residual risk review
requirement for MATS, in the 2024 Final Rule.\134\
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\134\ See 89 FR 38518 (May 7, 2024). The results of the risk
analysis indicated that both the actual and allowable inhalation
cancer risk to the individual most exposed was well below 100-in-1
million, which is the EPA's presumptive limit of acceptability under
the Benzene NESHAP. The results of the chronic inhalation cancer
risk assessment based on actual emissions, as shown in Table 2 of
this preamble, indicated that the estimated maximum individual
lifetime cancer risk (cancer MIR) was 9-in-1 million, with nickel
emissions from certain oil-fired EGUs as the major contributor to
the risk. Approximately 193,000 people were estimated to have cancer
risks at or above 1-in-1 million from HAP emitted from four
facilities in this source category--all from oil-fired sources in
Puerto Rico. However, the 2024 Final Rule only required controls for
certain types of coal-fired EGUs and would not impact emissions from
these oil-fired facilities.
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B. What is the EPA finalizing regarding the relevance of residual risk
to technology reviews under CAA section 112(d)(6)?
As previewed in section III.A of this preamble, the EPA concludes
that subsequent technology reviews under CAA section 112(d)(6) may
consider the results of the one-time residual risk review requirement
under CAA section 112(f)(2) in determining whether revisions are
``necessary.'' Specifically, the EPA will generally place greater
weight on the cost of revising standards when the results of the one-
time residual risk review requirement indicate that cancer risk from
HAP emissions are less than the statute's aspirational goal of one in
one million. Under those circumstances, revisions will generally be
``necessary'' only when costs are at the low end of the range of
acceptability. This interpretation follows from the term ``necessary''
in CAA section 112(d)(6), which gives the Agency discretion to consider
relevant factors and information, including information in the record
for the NESHAP under review.\135\ It is also consistent with the risk
thresholds that Congress wrote into the statute, including the
requirement to promulgate additional standards when cancer risk exceeds
the aspirational goal of one in one million and the
[[Page 9110]]
presumptive unacceptability threshold of 100 in one million expressly
incorporated as part of the Benzene NESHAP approach.\136\
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\135\ LEAN, 955 F.3d at 1097 (parenthetical in CAA section
112(d)(6) points to non-exhaustive list of considerations); see also
Michigan, 576 U.S. at 752-53 (the term ``appropriate and necessary''
in CAA section 112(n)(1) directs agency to consider all relevant
factors in exercising discretion); Nat'l Ass'n for Surface
Finishing, 795 F.3d at 9-11 (discussing the EPA's discretion to
consider relevant information when determining relevant information
is ``necessary''); Ass'n of Battery Recyclers, 716 F.3d at 673-74
(similar).
\136\ CAA section 112(f)(2)(B), 42 U.S.C. 7412(f)(2)(B).
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Commenters provided supportive and opposing arguments as to whether
a technology review conducted under CAA section 112(d)(6) should take
into consideration whether any meaningful risk reduction would be
obtained from further reducing HAP emissions under the technology
review given the results of the residual risk review. The EPA has taken
these comments into account in finalizing its position on the question
and summarizes and responds to many of the most significant comments in
the following section. Additional discussion, including further comment
summaries and responses, are available in the Response to Comment
document available in the docket for this rule.
C. What key comments did the EPA receive regarding the relevance of
residual risk to technology reviews under CAA section 112(d)(6), and
what are our responses?
Comment: Commenters agreed that the EPA should consider the
potential for and materiality of risk reductions when conducting a CAA
section 112(d)(6) technology review, citing multiple reasons. First,
commenters argued that CAA section 112(d)(6) allows the EPA to revise
standards only when ``necessary,'' which should be determined by
assessing whether new regulations protect human health and the
environment. Commenters stated that in Michigan, the Supreme Court
explained that the EPA must consider costs when it evaluates benefits
in deciding whether the 2012 MATS Rule was ``appropriate and
necessary,'' and that case should similarly require the Agency to
conduct a cost-benefit analysis to any new revisions under CAA section
112(d)(6). Commenters listed previous rules where the Agency used the
lack of meaningful risk reduction as a factor in its cost analysis,
such as the Industrial Process Cooling Towers NESHAP RTR,\137\
Petroleum Refineries NESHAP RTR,\138\ Halogenated Solvent Cleaning
NESHAP reconsideration proposal,\139\ and Organic Hazards Air
Pollutants from the Synthetic Organic Chemical Manufacturing Industry
NESHAP RTR.\140\ Commenters also noted that in the RTR for the Coke
Oven Batteries NESHAP, the EPA stated generally that findings
concerning risk that the EPA makes in a section 112(f)(2) determination
may be relevant in making any subsequent 112(d)(6) determinations for
the related 112(d) standard.\141\
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\137\ National Emission Standards for Hazardous Air Pollutants
for Industrial Process Cooling Towers, 71 FR 17729, 17731-32 (April
7, 2006).
\138\ National Emission Standards for Hazardous Air Pollutants
from Petroleum Refineries, 72 FR 50716, 50730 (September 4, 2007).
\139\ National Emission Standards for Hazardous Air Pollutants
for Halogenated Solvent Cleaning, 73 FR 62384, 62404 (October 20,
2008).
\140\ National Emission Standards for Hazardous Air Pollutants
for Organic Hazardous Air Pollutants from the Synthetic Organic
Chemical Manufacturing Industry, 71 FR 76603, 76606 (December 21,
2006).
\141\ National Emission Standards for Coke Oven Batteries, 70 FR
19992, 20009 (April 15, 2005).
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Second, commenters noted that the residual risk of HAP emissions
from coal-fired EGUs are minimal under the MACT standards from the 2012
MATS Rule. Specifically, commenters noted that the EPA's 2020 Residual
Risk Review found that the maximum lifetime cancer risk from coal-fired
EGUs ranged from 0.002 to 0.344 in 1 million, which, commenters
asserted, are orders of magnitude below what commenters further
asserted is Congress's threshold for deregulating the source category.
Commenters argued that further reducing cancer risks that are already
less than one in one million yields negligible benefits, if any.
Other commenters disagreed that the EPA should consider residual
risk during a CAA section 112(d)(6) technology review, arguing that the
proposed rule misconstrues the technology review process under CAA
section 112(d)(6) and fails to apply the best reading of the statute.
These commenters stated that the EPA must review any new developments
in control technologies and explain why those new developments make it
necessary to adopt new standards. These commenters stated that the
proposed rule is arbitrary and capricious because the EPA failed to
consider any developments in practices, processes, and control
technologies in finding that rescission is necessary. In the proposed
rule, the Agency stated that ``[g]iven the high costs and potential
feasibility concerns with implementing the revised standards . . . the
2024 changes were not necessary under CAA section 112(d)(6).'' \142\
However, these commenters argued that the EPA added no new information
or analysis concerning developments in practices, processes, and
control technologies--the rulemaking record is essentially identical to
that underlying the 2024 Final Rule, as the EPA recognized in its 2025
RIA. Instead, these commenters argued, the EPA now determines that the
2024 changes were not necessary in a conclusory manner, only citing
changes in the Administrator's policy preferences at the EPA as
``developments'' rather than citing any factual developments in
practices, processes, or control technologies at emissions sources.
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\142\ 90 FR 25544 (June 17, 2025).
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Lastly, these commenters claimed that CAA section 112(d)(6) does
not allow the EPA to withdraw revised standards based on its claim that
otherwise achievable controls produce no ``meaningful risk reduction.''
These commenters also argued that the EPA provided no reasonable basis
to conclude that the 2012 MATS Rule still provides the maximum degree
of emission reduction achievable under CAA section 112(d)(2),
instructing the EPA to ``tak[e] into account developments in practices,
processes, and control technologies.'' These commenters asserted that
the EPA may not decline to make otherwise ``necessary'' revisions based
on its appraisal of risk reduction.
Response: The EPA agrees that the Agency has an independent
statutory authority and obligation to conduct technology reviews every
8 years separate from the EPA's obligation to conduct a one-time
residual risk review within 8 years of setting the MACT. The D.C.
Circuit has recognized the CAA section 112(d)(6) technology review and
CAA section 112(f)(2) residual risk review are ``distinct, parallel
analyses'' that the EPA undertakes ``[s]eparately.'' \143\ It would be
inconsistent with the text, structure, and legislative history of the
CAA for the EPA to conclude that Congress intended the statute's
technology-based approach to be sidelined after the Agency concludes
the risk review, particularly because technology reviews, unlike the
residual risk review, must be completed every 8 years on an ongoing
basis. In the past, the EPA has occasionally determined that additional
controls were warranted under technology reviews pursuant to CAA
section 112(d)(6) although additional standards were not necessary to
maintain an ample margin of safety under CAA
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\143\ Nat'l Ass'n for Surface Finishing, 795 F.3d at 5.
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[[Page 9111]]
section 112(f)(2).\144\ The EPA has also previously stated that it
``disagree[s] with the view that a determination under CAA section
112(f) of an [ample margin of safety] and no adverse environmental
effects alone will, in all cases, cause us to determine that a revision
is not necessary under CAA section 112(d)(6).'' \145\
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\144\ See, e.g., National Emission Standards for Hazardous Air
Pollutants: Refractory Products Manufacturing Residual Risk and
Technology Review, 86 FR 66045 (November 19, 2021); National
Emission Standards for Hazardous Air Pollutants: Site Remediation
Residual Risk and Technology Review, 85 FR 41680 (July 10, 2020);
National Emission Standards for Hazardous Air Pollutants: Organic
Liquids Distribution (Non-Gasoline) Residual Risk and Technology
Review, 85 FR 40740, 40745 (July 7, 2020); National Emission
Standards for Hazardous Air Pollutants: Generic Maximum Achievable
Control Technology Standards Residual Risk and Technology Review for
Ethylene Production, 85 FR 40386, 40389 (July 6, 2020); National
Emission Standards for Hazardous Air Pollutants for Chemical
Recovery Combustion Sources at Kraft, Soda, Sulfite, and Stand-Alone
Semichemical Pulp Mills, 82 FR 47328 (October 11, 2017); National
Emission Standards for Hazardous Air Pollutants: Generic Maximum
Achievable Control Technology Standards; and Manufacture of Amino/
Phenolic Resins, 79 FR 60898, 60901 (October 8, 2014).
\145\ National Emission Standards for Hazardous Air Pollutant
Emissions: Group I Polymers and Resins; Marine Tank Vessel Loading
Operations; Pharmaceuticals Production; and the Printing and
Publishing Industry, 76 FR 22566, 22577 (April 21, 2011).
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However, the EPA also agrees with commenters' assertions that costs
should be considered in relation to potential benefits when evaluating
whether revisions are ``necessary'' under CAA section 112(d)(6). That
concept is inherent in the EPA's consideration of standard cost
metrics, including cost effectiveness expressed as cost per ton of HAP
emissions abated. HAP emissions figures are important because of the
health and environmental impacts they represent, and it is reasonable
to consider such impacts when determining whether to regulate. As noted
earlier in this preamble, the EPA has long evaluated cost effectiveness
in the context of particular HAP because different HAPs present
different physical and risk characteristics. That concept is also
inherent in the nature of cost consideration. As the Supreme Court
explained in Michigan, ``[c]onsideration of cost reflects the
understanding that reasonable regulation ordinarily requires paying
attention to the advantages and the disadvantages of agency
decisions,'' and it would be irrational ``to impose billions of dollars
in economic costs in return for a few dollars in health or
environmental benefits.'' \146\
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\146\ 576 U.S. at 752-53.
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As explained in section III.A of this preamble, there are
circumstances in which the EPA may consider risk in a CAA section
112(d)(6) rulemaking as part of its determination of whether revisions
to emission standards are ``necessary.'' The EPA concludes that in the
present rulemaking, it may consider the small remaining risk from the
non-HG HAP metals emitted from the source category--the cancer risks
are less than one in one million for every coal-fired EGU in the source
category--in assessing whether the costs of controls for those
pollutants are too high, such that a revision to the standards based on
those controls is not ``necessary.'' This conclusion is consistent with
previous rules under CAA section 112(d)(6) in which the EPA has
considered risk.
V. What is the rationale for other final decisions and amendments from
the reevaluation of the 2024 Final Rule?
In 2020, the EPA finalized electronic data reporting requirements
of MATS, including requiring data availability in Extensible Markup
Language (XML) format and amending the reporting and recordkeeping
requirements associated with performance stack tests, PM and HCl CEMS,
and PM CPMS.\147\ As a result, sources are required to use the
Emissions Collection and Monitoring Plan System (ECMPS) Client Tool to
submit all required reports. The deadline to meet changes in electronic
reporting was December 31, 2023, which has since been tentatively
extended to the 1st quarter of 2026.
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\147\ 85 FR 55744 (September 9, 2020).
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As part of this rulemaking, the EPA is finalizing two minor
technical, non-substantive clarifications to the relevant electronic
data reporting requirements, such as (i) removing references to
``ECMPS'' and replacing with ``ECMPS Reporting Tool'' and (ii) revising
the XML file format requirement to any file format specified by the
Administrator. The main effect of these minor technical clarifications
is that they make clear that the EPA will accept MATS reports in both
XML and PDF (or other) formats, as opposed to only XML. These minor
technical clarifications will better clarify and enable the reporting
of electronic compliance data, in light of the fact that some reporting
aspects are not supported by XML.
The EPA is making these non-substantive clarifications including
under the ``good cause'' exception to notice-and-comment rulemaking
incorporated by reference into the statute in CAA section 307. Under
section 553(b)(B) of the Administrative Procedure Act, an agency may
forego notice-and-comment rulemaking when it ``for good cause find[s]''
that providing notice and an opportunity for comment would be
``impracticable, unnecessary, or contrary to the public interest.''
Here, providing notice is ``unnecessary'' because of the minor, non-
substantive nature of the technical clarifications.\148\ As these
changes do not alter the substantive reporting requirements, there is
good cause to make them without prior notice and comment. The Agency
emphasizes that these non-substantive clarifications are separate and
independent from any other change made in this final rule.
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\148\ See Mack Trucks, Inc. v. EPA, 682 F.3d 87, 94 (D.C. Cir.
2012) (``This prong of the good cause inquiry is `confined to those
situations in which the administrative rule is a routine
determination, insignificant in nature and impact, and
inconsequential to the industry and to the public.' '') (quoting
Util. Solid Waste Activities Grp. v. EPA, 236 F.3d 749, 755 (D.C.
Cir. 2001)).
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VI. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders is
available at <a href="https://www.epa.gov/laws-regulations/laws-and-executive-orders">https://www.epa.gov/laws-regulations/laws-and-executive-orders</a>.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is a significant action under E.O. 12866 section
3(f)(1) that was submitted to the OMB for review. Any changes made in
response to E.O. 12866 review have been documented in the docket. The
EPA prepared an analysis of the potential costs and benefits associated
with this action. This analysis, Regulatory Impact Analysis for the
Final Repeal of Amendments to National Emission Standards for Hazardous
Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating
Units, is available in the docket.\149\
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\149\ Docket ID No. EPA-HQ-OAR-2018-0794.
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We present the estimated present values (PV) and equivalent
annualized values (EAV) of the estimated cost savings of repealing the
2024 Final Rule in 2024 dollars over the 2028 to 2037 period,
discounted to 2025. In addition, the Agency presents the assessment for
specific snapshot years, consistent with historic practice. These
snapshot years are 2028, 2030, and 2035. The power industry's cost
savings are represented in this analysis as the change in electric
power generation cost
[…truncated; see source link]Indexed from Federal Register on February 24, 2026.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.