National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units: Final Repeal

Federal RegisterFeb 24, 2026

Ask Donna

What actually matters in this document.

Text

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.

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

https://www.regulations.gov

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

https://www.regulations.gov

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:

werner.christopher@epa.gov.

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 (

https://www.fcc.gov/trs

) for the relay service of the Federal Communications Commission, and a list of relay services is available on their directory page (

https://www.fcc.gov/general/trs-state-and-territories

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

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”).

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.

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”).

77 FR 9304 (February 16, 2012).

CAA section 112(d)(6), (f)(2). CAA section 112 is codified at 42 U.S.C. 7412.

85 FR 31286 (May 22, 2020).

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.

On May 7, 2024, the EPA finalized several MATS amendments after initiating a rulemaking in response to the Executive Order (“2024 Final Rule”).

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.

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).

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).

89 FR 38508 (May 7, 2024).

Id.

at 38518;

see

88 FR 24866 (April 24, 2023) (proposed rule for the 2024 Final Rule).

89 FR 38534 (May 7, 2024).

On March 12, 2025, Administrator Zeldin announced that the Agency would reconsider the 2024 Final Rule.

On June 17, 2025, the EPA undertook a review of the 2024 Final Rule and proposed to repeal most of its amendments (“2025 Proposal”).

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).

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;”

Executive Order 14192, “Unleashing Prosperity Through Deregulation;”

Executive Order 14262, “Strengthening the Reliability and Security of the United States Electric Grid;”

and Executive Order 14261, “Reinvigorating America's Beautiful Clean Coal Industry and Amending Executive Order 14241,” 90 FR 15517 (April 14, 2025).

https://www.epa.gov/newsreleases/epa-launches-biggest-deregulatory-action-us-history.

90 FR 25535 (June 17, 2025).

90 FR 8353 (January 29, 2025).

90 FR 8741 (January 31, 2025).

90 FR 9065 (February 6, 2025).

90 FR 15521 (April 14, 2025).

In addition, on April 8, 2025, President Trump signed a Proclamation titled “Regulatory Relief for Certain Stationary Sources to Promote American Energy.”

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).

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

Annex 1 are available in the rulemaking docket.

90 FR 16777 (April 21, 2025).

“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).

Document ID No. EPA-HQ-OAR-2018-0794-6980.

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.

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.”

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.

FDA

Wages & White Lion Invs., L.L.C.,

604 U.S. 542, 568 (2025);

FCC

Fox Television Stations, Inc.,

556 U.S. 502, 515 (2009);

see also Clean Water Action

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.”).

Nat'l Ass'n of Home Builders

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.

Clean Air Council

Pruitt,

862 F.3d 1, 8-9 (D.C. Cir. 2017).

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.

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

) may be used as a surrogate for all acid gas HAP if SO

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.

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.

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.

Selenium may be present in the filterable PM or the condensable fraction as the acid gas, SeO

Document ID No. EPA-HQ-OAR-2009-0234.

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.

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

since promulgation of the 2012 MATS Rule to determine whether revisions to the standards were otherwise “necessary.”

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.

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.

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.

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]

Number of

facilities

Maximum individual

cancer risk

(in 1 million)

Based on . . .

Actual

emissions

level

Allowable

emissions

level

Population at

increased risk of

cancer ≥1-in-1 million

Based on . . .

Actual

emissions

level

Allowable

emissions

level

Annual cancer

incidence

(cases per year)

Based on . . .

Actual

emissions

level

Allowable

emissions

level

Maximum chronic

noncancer TOSHI

Based on . . .

Actual

emissions

level

Allowable

emissions

level

Maximum screening acute noncancer HQ

Based on actual emissions level

322

193,000

636,000

0.04

0.1

0.2

0.4

REL

= 0.09 (arsenic).

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.

Maximum individual excess lifetime cancer risk due to HAP emissions from the source category.

Maximum target organ-specific hazard index (TOSHI). The target organ systems with the highest TOSHI for the source category are respiratory and immunological.

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.

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.,

, 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.

Document ID No. EPA-HQ-OAR-2018-0794-0015.

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.

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.

The EPA made the affirmative finding on March 6, 2023.

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).

87 FR 7624 (February 9, 2022).

88 FR 13956 (March 6, 2023).

On April 24, 2023, the EPA proposed the results of the Agency's review of the RTR from the 2020 Final Rule.

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.”

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.

88 FR 24854 (April 24, 2023).

Id.

at 24866.

Id.

The EPA's review of the 2020 Technology Review included evaluating the technology review

and focused on

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.

Described in Document ID No. EPA-HQ-OAR-2018-0794-0015.

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

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.

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.

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).

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.

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.

90 FR 25535 (June 17, 2025).

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.

Docket ID No. EPA-HQ-OAR-2018-0794.

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.”

By the same token, the repeal of each of requirement is severable from the repeal of the remaining requirements.

90 FR 38518 (May 7, 2024).

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

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

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.

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.

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).

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.

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

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.

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).

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.

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.

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).

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.

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.

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.

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.

On that basis, the EPA asserted that the controls would not have “significant effects” on the industry,

i.e.,

the power sector.

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

categories that the EPA has regulated under CAA section 112.

90 FR 38524 (May 7, 2024).

Id.

at 38534.

Id.

at 38524.

Id.

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).

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).

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.

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.

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.

Compare

89 FR 38534 (May 7, 2024) (citing Pub. L. 117-169 (2022)),

with

Pub. L. 119-21 (2025).

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

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.

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.

42 U.S.C. 7412(f)(2)(A).

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.”

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,

and it is consistent with the Supreme Court's interpretation of the term “appropriate and necessary” in another

provision of CAA section 112.

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.

Webster's Ninth New Collegiate Dictionary 790 (1984).

Ass'n of Battery Recyclers,

716 F.3d at 673-74.

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

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].”

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.

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.

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.

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).

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).”

89 FR 38525 (May 7, 2024).

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.

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).

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

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.

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.

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.

Document ID No. EPA-HQ-OAR-2018-0794-0070.

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

($10 million per ton of total non-Hg HAP metals reduced), the Integrated Iron and Steel Manufacturing Facilities technology review

($7 million per ton of non-Hg HAP metals reduced), and the Taconite Iron Ore Processing RTR

($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:

Petroleum Refinery Sector Risk and Technology Review and New Source Performance Standards,

80 FR 75178, 75201 (December 1, 2015).

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).

National Emission Standards for Hazardous Air Pollutants: Taconite Iron Ore Processing Residual Risk and Technology Review,

85 FR 45476, 45483 (July 28, 2020).

• In the Hazardous Waste Combustors NESHAP beyond-the-floor analysis,

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.

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).

• In the Shipbuilding and Ship Repair NESHAP RTR,

the EPA declined to revise the formaldehyde emission limit after finding that spray line reconfiguration would cost $43,000 per ton of formaldehyde reduced.

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).

• In the Pulp and Paper NESHAP RTR,

the EPA declined to update standards in the final rule

for controlling kraft condensates emissions that would cost $1,000 per ton of HAP removed or $4 million per year.

National Emission Standards for Hazardous Air Pollutants: Pulp and Paper Residual Risk and Technology Review,

76 FR 81328, 81345 (December 27, 2011).

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.

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.

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

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,

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.

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).

The Agency disagrees, however, that there is any particular threshold that renders a potential control technology cost-effective or not.

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.

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.”).

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.

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.

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”).

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.

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.

See, e.g., Fox Television Stations,

556 U.S. at 515;

Motor Vehicle Mfrs. Ass'n,

463 U.S. at 42.

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.

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.

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).

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.

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.

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.

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.

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.

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).

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.”).

89 FR 38513 (May 7, 2024).

Id.

at 38533-34.

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

compliance with the fPM emission standard, as well as the adjusted QA criteria,

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).

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.

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

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).

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.

104

89 FR 38535 (May 7, 2024).

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.,

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

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

https://cfpub.epa.gov/webfire,

which maintains the availability and transparency of fPM emissions.

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.

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.

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.

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

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.

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.

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

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

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.

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.

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

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

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

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

) in the flue gas stream. SO

, 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.

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

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.

https://www.eia.gov/electricity/data/eia923/.

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

-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

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

This text is long and has been trimmed here. Open the source document for the complete record.

This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.