[Federal Register Volume 87, Number 27 (Wednesday, February 9, 2022)]
[Proposed Rules]
[Pages 7624-7673]
[FR Doc No: 2022-02343]

Vol. 87

Wednesday,

No. 27

February 9, 2022

Part III

Environmental Protection Agency

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40 CFR Part 63

National Emission Standards for Hazardous Air Pollutants: Coal- and
Oil-Fired Electric Utility Steam Generating Units--Revocation of the
2020 Reconsideration, and Affirmation of the Appropriate and Necessary
Supplemental Finding; Notice of Proposed Rulemaking; Proposed Rule

Federal Register / Vol. 87 , No. 27 / Wednesday, February 9, 2022 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2018-0794; FRL-6716.2-01-OAR]
RIN 2060-AV12

National Emission Standards for Hazardous Air Pollutants: Coal-
and Oil-Fired Electric Utility Steam Generating Units--Revocation of
the 2020 Reconsideration, and Affirmation of the Appropriate and
Necessary Supplemental Finding; Notice of Proposed Rulemaking

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The EPA is proposing to revoke a May 22, 2020 finding that it
is not appropriate and necessary to regulate coal- and oil-fired
electric utility steam generating units (EGUs) under Clean Air Act
(CAA) section 112, and to reaffirm the Agency's April 25, 2016 finding
that it remains appropriate and necessary to regulate hazardous air
pollutant (HAP) emissions from EGUs after considering cost. The Agency
is also reviewing another part of the May 22, 2020 action, a residual
risk and technology review (RTR) of Mercury and Air Toxics Standards
(MATS). Accordingly, in addition to soliciting comments on all aspects
of this proposal, the EPA is soliciting information on the performance
and cost of new or improved technologies that control HAP emissions,
improved methods of operation, and risk-related information to further
inform the Agency's review of the MATS RTR as directed by Executive
Order 13990.

DATES: Comments must be received on or before April 11, 2022.
    Public hearing: The EPA will hold a virtual public hearing on
February 24, 2022. See SUPPLEMENTARY INFORMATION for information on the
hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2018-0794, by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/
(our preferred method). Follow the online instructions for submitting
comments.
     Email: [email protected]. Include Docket ID No. EPA-
HQ-OAR-2018-0794 in the subject line of the message.
     Fax:<PHONE_NUMBER>. Attention Docket ID No. EPA-HQ-OAR-
2018-0794.
     Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2018-0794, Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.
     Hand/Courier Delivery: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-
Friday (except Federal holidays).
    Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov/, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the SUPPLEMENTARY
INFORMATION section of this document. Out of an abundance of caution
for members of the public and our staff, the EPA Docket Center and
Reading Room are closed to the public, with limited exceptions, to
reduce the risk of transmitting COVID-19. Our Docket Center staff will
continue to provide remote customer service via email, phone, and
webform. We encourage the public to submit comments via https://www.regulations.gov/ or email, as there may be a delay in processing
mail and faxes. Hand deliveries and couriers may be received by
scheduled appointment only. For further information on EPA Docket
Center services and the current status, please visit us online at
https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Melanie King, Sector Policies and Programs Division
(D243-01), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; and email address:
[email protected].

SUPPLEMENTARY INFORMATION: The EPA is proposing to revoke a May 22,
2020 finding that it is not appropriate and necessary to regulate coal-
and oil-fired EGUs under CAA section 112, and to reaffirm the Agency's
April 25, 2016 finding that it remains appropriate and necessary to
regulate HAP emissions from EGUs after considering cost. The 2016
finding was made in response to the U.S. Supreme Court's 2015 Michigan
v. EPA decision, where the Court held that the Agency had erred by not
taking cost into consideration when taking action on February 16, 2012,
to affirm a 2000 EPA determination that it was appropriate and
necessary to regulate HAP emissions from EGUs. In the same 2012 action,
the EPA also promulgated National Emission Standards for Hazardous Air
Pollutants (NESHAP) for coal- and oil-fired EGUs, commonly known as the
Mercury and Air Toxics Standards or MATS.
    Based on a re-evaluation of the administrative record and the
statute, the EPA proposes to conclude that the framework applied in the
May 22, 2020 finding was ill-suited to assessing and comparing the full
range of benefits to costs, and the EPA concludes that, after applying
a more suitable framework, the 2020 determination should be withdrawn.
For reasons explained in this notice, the EPA further proposes to
reaffirm that it is appropriate and necessary to regulate HAP emissions
from EGUs after weighing the volume of pollution that would be reduced
through regulation, the public health risks and harms posed by these
emissions, the impacts of this pollution on particularly exposed and
sensitive populations, the availability of effective controls, and the
costs of reducing this harmful pollution including the effects of
control costs on the EGU industry and its ability to provide reliable
and affordable electricity. This notice also presents information and
analysis that has become available since the 2016 finding, pertaining
to the health risks of mercury emissions and the costs of reducing HAP
emissions, that lend further support for this determination.
    The review that led to this proposal is consistent with the
direction in Executive Order 13990, ``Protecting Public Health and the
Environment and Restoring Science to Tackle the Climate Crisis,''
signed by President Biden on January 20, 2021. In response to the
Executive Order, the Agency is also reviewing another part of the May
22, 2020 action, a RTR of MATS. Accordingly, in addition to soliciting
comments on all aspects of this proposal, the EPA is soliciting
information on the performance and cost of new or improved technologies
that control HAP emissions, improved methods of operation, and risk-
related information to further inform the Agency's review of the MATS
RTR as directed by the Executive Order. Results of the EPA's review of
the RTR will be presented in a separate action.
    Participation in virtual public hearing. Please note that the EPA
is deviating from its typical approach for public hearings because the
President has declared a national emergency. Due to the current Centers
for Disease Control and Prevention (CDC) recommendations, as well as
state and local orders for social distancing to limit the spread of
COVID-19, the EPA

cannot hold in-person public meetings at this time.
    The virtual public hearing will be held via teleconference on
February 24, 2022 and will convene at 10:00 a.m. Eastern Time (ET) and
will conclude at 7:00 p.m. ET. The EPA may close a session 15 minutes
after the last pre-registered speaker has testified if there are no
additional speakers. For information or questions about the public
hearing, please contact the public hearing team at<PHONE_NUMBER> or by
email at [email protected]. The EPA will announce further
details at https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards.
    The EPA will begin pre-registering speakers for the hearing no
later than 1 business day following publication of this document in the
Federal Register. The EPA will accept registrations on an individual
basis. To register to speak at the virtual hearing, please use the
online registration form available at https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards or contact the
public hearing team at<PHONE_NUMBER> or by email at
[email protected]. The last day to pre-register to speak at the
hearing will be February 18, 2022. Prior to the hearing, the EPA will
post a general agenda that will list pre-registered speakers in
approximate order at: https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards.
    The EPA will make every effort to follow the schedule as closely as
possible on the day of the hearing; however, please plan for the
hearings to run either ahead of schedule or behind schedule.
    Each commenter will have 5 minutes to provide oral testimony. The
EPA encourages commenters to provide the EPA with a copy of their oral
testimony electronically (via email) by emailing it to
[email protected]. The EPA also recommends submitting the text of
your oral testimony as written comments to the rulemaking docket.
    The EPA may ask clarifying questions during the oral presentations
but will not respond to the presentations at that time. Written
statements and supporting information submitted during the comment
period will be considered with the same weight as oral testimony and
supporting information presented at the public hearing.
    Please note that any updates made to any aspect of the hearing will
be posted online at https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards. While the EPA expects the
hearing to go forward as set forth above, please monitor our website or
contact the public hearing team at<PHONE_NUMBER> or by email at
[email protected] to determine if there are any updates. The
EPA does not intend to publish a document in the Federal Register
announcing updates.
    If you require the services of a translator or a special
accommodation such as audio description, please pre-register for the
hearing with the public hearing team and describe your needs by
February 16, 2022. The EPA may not be able to arrange accommodations
without advanced notice.
    Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2018-0794.\1\ All documents in the docket are
listed in https://www.regulations.gov/. Although listed, some
information is not publicly available, e.g., Confidential Business
Information (CBI) or other information whose disclosure is restricted
by statute. Certain other material, such as copyrighted material, is
not placed on the internet and will be publicly available only in hard
copy. With the exception of such material, publicly available docket
materials are available electronically in https://www.regulations.gov/.
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    \1\ As explained in a memorandum to the docket, the docket for
this action includes the documents and information, in whatever
form, in Docket ID Nos. EPA-HQ-OAR-2009-0234 (National Emission
Standards for Hazardous Air Pollutants for Coal- and Oil-fired
Electric Utility Steam Generating Units), EPA-HQ-OAR-2002-0056
(National Emission Standards for Hazardous Air Pollutants for
Utility Air Toxics; Clean Air Mercury Rule (CAMR)), and Legacy
Docket ID No. A-92-55 (Electric Utility Hazardous Air Pollutant
Emission Study). See memorandum titled Incorporation by reference of
Docket Number EPA-HQ-OAR-2009-0234, Docket Number EPA-HQ-OAR-2002-
0056, and Docket Number A-92-55 into Docket Number EPA-HQ-OAR-2018-
0794 (Docket ID Item No. EPA-HQ-OAR-2018-0794-0005).
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    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2018-0794. The EPA's policy is that all comments received will be
included in the public docket without change and may be made available
online at https://www.regulations.gov/, including any personal
information provided, unless the comment includes information claimed
to be CBI or other information whose disclosure is restricted by
statute. Do not submit electronically any information that you consider
to be CBI or other information whose disclosure is restricted by
statute. This type of information should be submitted by mail as
discussed below.
    The EPA may publish any comment received to its public docket.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e., on the Web, cloud, or other
file sharing system). For additional submission methods, the full EPA
public comment policy, information about CBI or multimedia submissions,
and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    The https://www.regulations.gov/ website allows you to submit your
comment anonymously, which means the EPA will not know your identity or
contact information unless you provide it in the body of your comment.
If you send an email comment directly to the EPA without going through
https://www.regulations.gov/, your email address will be automatically
captured and included as part of the comment that is placed in the
public docket and made available on the internet. If you submit an
electronic comment, the EPA recommends that you include your name and
other contact information in the body of your comment and with any
digital storage media you submit. If the EPA cannot read your comment
due to technical difficulties and cannot contact you for clarification,
the EPA may not be able to consider your comment. Electronic files
should not include special characters or any form of encryption and be
free of any defects or viruses. For additional information about the
EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    The EPA is temporarily suspending its Docket Center and Reading
Room for public visitors, with limited exceptions, to reduce the risk
of transmitting COVID-19. Our Docket Center staff will continue to
provide remote customer service via email, phone, and webform. We
encourage the public to submit comments via https://www.regulations.gov/ as there may be a delay in processing mail and
faxes. Hand deliveries or couriers will be received by scheduled
appointment only. For further information and updates on EPA Docket
Center services, please visit us online at https://www.epa.gov/dockets.
    The EPA continues to carefully and continuously monitor information
from the CDC, local area health departments, and our Federal partners
so that we can respond rapidly as conditions change regarding COVID-19.
    Submitting CBI. Do not submit information containing CBI to the EPA

through https://www.regulations.gov/ or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
any digital storage media that you mail to the EPA, mark the outside of
the digital storage media as CBI and then identify electronically
within the digital storage media the specific information that is
claimed as CBI. In addition to one complete version of the comments
that includes information claimed as CBI, you must submit a copy of the
comments that does not contain the information claimed as CBI directly
to the public docket through the procedures outlined in Instructions
above. If you submit any digital storage media that does not contain
CBI, mark the outside of the digital storage media clearly that it does
not contain CBI. Information not marked as CBI will be included in the
public docket and the EPA's electronic public docket without prior
notice. Information marked as CBI will not be disclosed except in
accordance with procedures set forth in title 40 of the Code of Federal
Regulations (CFR) part 2. Send or deliver information identified as CBI
only to the following address: OAQPS Document Control Officer (C404-
02), OAQPS, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2018-
0794. Note that written comments containing CBI and submitted by mail
may be delayed and no hand deliveries will be accepted.
    Preamble acronyms and abbreviations. 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
ATSDR Agency for Toxic Substances and Disease Registry
ARP Acid Rain Program
BCA benefit-cost analysis
CAA Clean Air Act
CAAA Clean Air Act Amendments of 1990
CAMR Clean Air Mercury Rule
CBI Confidential Business Information
CFR Code of Federal Regulations
CVD cardiovascular disease
DSI dry sorbent injection
EGU electric utility steam generating unit
EIA Energy Information Administration
EPA Environmental Protection Agency
ESP electrostatic precipitator
EURAMIC European Multicenter Case-Control Study on Antioxidants,
Myocardial Infarction, and Cancer of the Breast Study
FF fabric filter
FGD flue gas desulfurization
FR Federal Register
GW gigawatt
HAP hazardous air pollutant(s)
HCl hydrogen chloride
HF hydrogen fluoride
IHD ischemic heart disease
IPM Integrated Planning Model
IRIS Integrated Risk Information System
KIHD Kuopio Ischaemic Heart Disease Risk Factor Study
kW kilowatt
MACT maximum achievable control technology
MATS Mercury and Air Toxics Standards
MI myocardial infarction
MIR maximum individual risk
MW megawatt
NAS National Academy of Sciences
NESHAP national emission standards for hazardous air pollutants
OMB Office of Management and Budget
O&M operation and maintenance
PM particulate matter
PUFA polyunsaturated fatty acid
RfD reference dose
RIA regulatory impact analysis
RTR residual risk and technology review
SCR selective catalytic reduction
SO2 sulfur dioxide
TSD technical support document
tpy tons per year

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

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?
II. Background
    A. Regulatory History
    B. Statutory Background
III. Proposed Determination Under CAA Section 112(n)(1)(A)
    A. Public Health Hazards Associated With Emissions From EGUs
    B. Consideration of Cost of Regulating EGUs for HAP
    C. Revocation of the 2020 Final Action
    D. The Administrator's Proposed Preferred Framework and Proposed
Conclusion
    E. The Administrator's Proposed Benefit-Cost Analysis Approach
and Proposed Conclusion
IV. Summary of Cost, Environmental, and Economic Impacts
V. Request for Comments and for Information To Assist With Review of
the 2020 RTR
VI. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act (NTTAA)
    J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. General Information

A. Executive Summary

    On January 20, 2021, President Biden signed Executive Order 13990,
``Protecting Public Health and the Environment and Restoring Science to
Tackle the Climate Crisis'' (86 FR 7037, January 25, 2021). The
Executive Order, among other things, instructs the EPA to review the
2020 final action titled, ``National Emission Standards for Hazardous
Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating
Units--Reconsideration of Supplemental Finding and Residual Risk and
Technology Review'' (85 FR 31286; May 22, 2020) (2020 Final Action) and
consider publishing a notice of proposed rulemaking suspending,
revising, or rescinding that action. Consistent with the Executive
Order, the EPA has undertaken a careful review of the 2020 Final
Action, in which the EPA reconsidered its April 25, 2016 supplemental
finding (81 FR 24420) (2016 Supplemental Finding). Based on that
review, the Agency proposes to find that the decisional framework for
making the appropriate and necessary determination under CAA section
112(n)(1)(A) that was applied in the 2020 Final Action was unsuitable
because it failed to adequately account for statutorily relevant
factors. Therefore, we propose to revoke the May 2020 determination
that it is not appropriate and necessary to regulate HAP emissions from
coal- and oil-fired EGUs under section 112 of the CAA. We further
propose to reaffirm our earlier determinations--made in 2000 (65 FR
79825; December 20, 2000) (2000 Determination), 2012 (77 FR 9304;
February 16, 2012) (2012 MATS Final Rule), and 2016--that it is
appropriate and necessary to regulate coal- and oil-fired EGUs under
section 112 of the CAA.
    In 1990, frustrated with the EPA's pace in identifying and
regulating HAP, Congress radically transformed its treatment of that
pollution. It rewrote section 112 of the CAA to require the EPA to
swiftly regulate 187 HAP with technology-based standards that would
require all major sources (defined by the quantity of pollution a
facility has the potential to emit) to meet the levels of reduction
achieved in practice by the best-performing similar sources. EGUs were
the one major source category excluded from automatic application of
these new standards. EGUs were treated differently primarily because
the 1990

Amendments to the CAA (1990 Amendments) included the Acid Rain Program
(ARP), which imposed criteria pollution reduction requirements on EGUs.
Congress recognized that the controls necessary to comply with this and
other requirements of the 1990 Amendments might reduce HAP emissions
from EGUs as well. Therefore, under CAA section 112(n)(1)(A), Congress
directed the EPA to regulate EGUs if, after considering a study of
``the hazards to public health reasonably anticipated to occur as a
result of [HAP] emissions by [EGUs] . . . after imposition of the [Acid
Rain Program and other] requirements of this chapter,'' the EPA
concluded that it ``is appropriate and necessary'' to do so. See CAA
section 112(n)(1)(A).
    The EPA completed that study in 1998 and, in 2000, concluded that
it is appropriate and necessary to regulate HAP emissions from coal-
and oil-fired EGUs. See 65 FR 79825 (December 20, 2000). The EPA
reaffirmed that conclusion in 2012, explaining that the other
requirements of the CAA, in particular the ARP, did not lead to the HAP
emission reductions that had been anticipated because many EGUs
switched to lower-sulfur coal rather than deploy pollution controls
that may have also reduced emissions of HAP. Indeed, the statute
contemplated that the EPA would be conducting the required study within
3 years of the 1990 Amendments; but when the EPA re-examined public
health hazards remaining after imposition of the Act's requirements in
2012, the Agency accounted for over 20 years of CAA regulation, and
EGUs still remained one of the largest sources of HAP pollution.
Specifically, in 2012, the EPA concluded that EGUs were the largest
domestic source of emissions of mercury, hydrogen fluoride (HF),
hydrogen chloride (HCl), and selenium; and among the largest domestic
contributors of emissions of arsenic, chromium, cobalt, nickel,
hydrogen cyanide, beryllium, and cadmium. The EPA further found that a
significant majority of EGUs were located at facilities that emitted
above the statutory threshold set for major sources (e.g., 10 tons per
year (tpy) of any one HAP or 25 tpy or more of any combination of HAP).
See 77 FR 9304 (February 16, 2012). In 2012, the EPA also established
limits for emissions of HAP from coal- and oil-fired EGUs. Id.
    Many aspects of the EPA's appropriate and necessary determination
and the CAA section 112 regulations were challenged in the U.S. Court
of Appeals for the District of Columbia Circuit (D.C. Circuit), and all
challenges were denied and the finding and standards upheld in full in
White Stallion Energy Center v. EPA, 748 F.3d 1222 (2014). The Supreme
Court granted review on a single issue and, in Michigan v. EPA, 576
U.S. 743 (2015), the Court held that the EPA erred when it failed to
consider the costs of its regulation in determining that it is
appropriate and necessary to regulate HAP emissions from EGUs, and
remanded that determination to the D.C. Circuit for further
proceedings. Following Michigan, in 2016 the EPA issued a Supplemental
Finding that it is appropriate and necessary to regulate EGU HAP after
considering the costs of such regulation. See 81 FR 24420 (April 25,
2016). In 2020, the Agency reversed that determination.\2\ In this
action, we conclude that the methodology we applied in 2020 is ill-
suited to the appropriate and necessary determination because, among
other reasons, it did not give adequate weight to the significant
volume of HAP emissions from EGUs and the attendant risks remaining
after imposition of the other requirements of the CAA, including many
adverse health and environmental effects of EGU HAP emissions that
cannot be quantified or monetized. We propose, therefore, to revoke the
2020 Final Action.
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    \2\ The 2020 Final Action, while reversing the 2016 Supplemental
Finding as to the EPA's determination that it was ``appropriate'' to
regulate HAP from EGUs, did not rescind the Agency's prior
determination that it was necessary to regulate. See 84 FR 2674
(February 7, 2019). Instead, the 2020 rulemaking stated that its
rescission was based on the appropriate prong alone: ``CAA section
112(n)(1)(A) requires the EPA to determine that both the appropriate
and necessary prongs are met. Therefore, if the EPA finds that
either prong is not satisfied, it cannot make an affirmative
appropriate and necessary finding. The EPA's reexamination of its
determination . . . focuses on the first prong of that analysis.''
Id.
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    We further propose to affirm, once again, that it is appropriate
and necessary to regulate coal- and oil-fired EGUs under CAA section
112. We first examine the benefits or advantages of regulation,
including new information on the risks posed by EGU HAP. We then
examine the costs or disadvantages of regulation, including both the
costs of compliance (which we explain we significantly overestimated in
2012) and how those costs affect the industry and the public. We then
weigh these benefits and costs to reach the conclusion that it is
appropriate and necessary to regulate using two alternative
methodologies.
    Our preferred methodology, as it was in the 2016 Supplemental
Finding, is to consider all of the impacts of the regulation--both
costs and benefits to society--using a totality-of the-circumstances
approach rooted in the Michigan court's direction to ``pay[ ] attention
to the advantages and disadvantages of [our] decision[ ].'' 576 U.S. at
753; see id. at 752 (``In particular, `appropriate' is `the classic
broad all-encompassing term that naturally includes consideration of
all relevant factors.''). To help determine the relevant factors to
weigh, we look to CAA section 112(n)(1)(A), the other provisions of CAA
section 112(n)(1), and to the statutory design of CAA section 112.
    Initially, we consider the human health advantages of reducing HAP
emissions from EGUs because in CAA section 112(n)(1)(A) Congress
directed the EPA to make the appropriate and necessary determination
after considering the results of a ``study of the hazards to public
health reasonably anticipated to occur as a result of [HAP] emissions''
from EGUs. See CAA section 112(n)(1)(A). We consider all of the
advantages of reducing emissions of HAP (i.e., the risks posed by HAP)
regardless of whether those advantages can be quantified or monetized,
and we explain why almost none of those advantages can be monetized.
Consistent with CAA section 112(n)(1)(B)'s direction to examine the
rate and mass of mercury emissions, and the design of CAA section 112,
which required swift reduction of the volume of HAP emissions based on
an assumption of risk, we conclude that we should place substantial
weight on reducing the large volume of HAP emissions from EGUs--both in
absolute terms and relative to other source categories--that, absent
MATS, was entering our air, water, and land, thus reducing the risk of
grave harms that can occur as a result of exposure to HAP. Also
consistent with the statutory design of CAA section 112, in considering
the advantages of HAP reductions, we consider the distribution of those
benefits, and the statute's clear goal in CAA section 112(n)(1)(C) and
other provisions of CAA section 112 to protect the most exposed and
susceptible populations, such as communities that are reliant on local
fish for their survival, and developing fetuses. We think it is highly
relevant that while EGUs generate power for all, and EGU HAP pollution
poses risks to all Americans exposed to such HAP, a smaller set of
Americans who live near EGUs face a disproportionate risk of being
significantly harmed by toxic pollution. Finally, we also consider the
identified risks to the environment posed by mercury and acid-gas HAP,
consistent with CAA section 112(n)(1)(B) and the general goal of CAA

section 112 to reduce risks posed by HAP to the environment.
    We next weigh those advantages against the disadvantages of
regulation, principally in the form of the costs incurred to control
HAP before they are emitted into the environment. Consistent with the
statutory design, we consider those costs comprehensively, examining
them in the context of the effect of those expenditures on the
economics of power generation more broadly, the reliability of
electricity, and the cost of electricity to consumers. These metrics
are relevant to our weighing exercise because they give us a more
complete picture of the disadvantages to producers and consumers of
electricity imposed by this regulation, and because our conclusion
might change depending on how this burden affects the ability of the
industry to thrive and to provide reliable, affordable electricity to
the benefit of all Americans. These metrics are relevant measures for
evaluating costs to the utility sector in part because they are the
types of metrics considered by the owners and operators of EGUs
themselves. See 81 FR 24428 (April 25, 2016). Per CAA section
112(n)(1)(B), we further consider the availability and cost of control
technologies, including the relationship of that factor to controls
installed under the ARP.
    As explained in detail in this document, we ultimately propose to
conclude that, weighing the risks posed by HAP emissions from EGUs
against the costs of reducing that pollution on the industry and
society as a whole, it is worthwhile (i.e., ``appropriate'') to
regulate those emissions to protect all Americans, and in particular
the most vulnerable populations, from the inherent risks posed by
exposure to HAP emitted by coal- and oil-fired EGUs. We propose to find
that this is true whether we are looking at the record in 2016 (i.e.,
information available as of the time of the 2012 threshold finding and
rulemaking) or at the updated record in 2021, in which we quantify
additional risks posed by HAP emissions from EGUs and conclude that the
actual cost of complying with MATS was almost certainly significantly
less than the EPA's projected estimate in the 2011 RIA, primarily
because fewer pollution controls were installed than projected and
because the unexpected increases in natural gas supply led to a
dramatic decrease in the price of natural gas.
    In the 2016 Supplemental Finding we did not consider non-HAP health
benefits that occur by virtue of controlling HAP from EGUs as a
relevant factor for our consideration under the preferred approach.
However, because the Supreme Court in Michigan directed us to consider
health and environmental effects beyond those posed by HAP,
``including, for instance, harms that regulation might do to human
health or the environment,'' and stressed that ``[n]o regulation is
`appropriate' if it does significantly more harm than good,'' 576 U.S.
at 752, we take comment on whether it is reasonable to also consider
the advantages associated with non-HAP emission reductions that result
from the application of HAP controls as part of our totality-of-the-
circumstances approach. In the 2012 MATS Final Rule, we found that
regulating EGUs for HAP resulted in substantial health benefits
accruing from coincidental reductions in particulate matter (PM)
pollution and its precursors. We also projected that regulating EGUs
for HAP would similarly result in an improvement in ozone pollution.
While we propose to reach the conclusion that HAP regulation is
appropriate even absent consideration of these additional benefits,
adding these advantages to the weighing inquiry would provide further
support for our proposed conclusion that the advantages of regulation
outweigh the disadvantages.
    We recognize, as we did in 2016, that our preferred, totality-of-
the-circumstances approach to making the appropriate and necessary
determination is an exercise in judgment, and that ``[r]easonable
people, and different decision-makers, can arrive at different
conclusions under the same statutory provision'' (81 FR 24431; April
25, 2016). However, this type of weighing of factors and circumstances
is an inherent part of regulatory decision-making, and we think it is a
reasonable approach where the factors the statute identifies as
important to consider cannot be quantified or monetized.
    Next, we turn to our alternative approach of a formal benefit-cost
analysis (BCA). This approach independently supports the determination
that it is appropriate to regulate EGU HAP. Based on the 2011
Regulatory Impacts Analysis (2011 RIA) \3\ performed as part of the
2012 MATS Final Rule, the total net benefits of MATS were overwhelming
even though the EPA was only able to monetize one of the many benefits
of reducing HAP emissions from EGUs. Like the preferred approach, this
conclusion is further supported by newer information on the risks posed
by HAP emissions from EGUs as well as the actual costs of implementing
MATS, which almost certainly were significantly lower than estimated in
the 2011 RIA.
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    \3\ U.S. EPA. 2011. Regulatory Impact Analysis for the Final
Mercury and Air Toxics Standards. EPA-452/R-11-011. Available at:
https://www3.epa.gov/ttn/ecas/docs/ria/utilities_ria_final-mats_2011-12.pdf.
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    Our proposal is organized as follows. In section II.A of this
preamble, we provide as background the regulatory and procedural
history leading up to this proposal. We also detail, in preamble
section II.B, the statutory design of HAP regulation that Congress
added to the CAA in 1990 in the face of the EPA's failure to make
meaningful progress in regulating HAP emissions from stationary
sources. In particular, we point out that many provisions of CAA
section 112 demonstrate the value Congress placed on reducing the
volume of HAP emissions from stationary sources as much as possible and
quickly, with a particular focus on reducing HAP related risks to the
most exposed and most sensitive members of the public. This background
assists in identifying the relevant statutory factors to weigh in
considering the advantages and disadvantages of HAP regulation.
    Against this backdrop, we propose to revoke the 2020 Final Action
and reaffirm the 2016 determination that it remains appropriate to
regulate HAP emissions from EGUs after a consideration of cost.
Specifically, in section III.A of this preamble, we review the long-
standing and extensive body of evidence, as well as new mercury-related
risk analyses performed since 2016, identifying substantial risks to
human health and the environment from HAP emissions from coal- and oil-
fired EGUs that support a conclusion that regulating HAP emissions from
EGUs is appropriate. In preamble section III.B, we analyze information
regarding how the power sector elected to comply with MATS, and how our
2012 projections for the cost of regulation almost certainly
overestimated the actual costs of the regulation by a significant
amount. In preamble section III.C, we explain our reasons for revoking
the 2020 Final Action, which applied an ill-suited framework for
evaluating cost because it gave little to no weight to the statutory
concern with reducing the volume of and risks from HAP emissions to
protect even the most exposed and most vulnerable members of the
public. In section III.D of this preamble, we describe and apply our
preferred, totality-of-the-circumstances approach, giving particular
weight to the factors identified in CAA section 112(n)(1) and 112 more
generally. We propose to conclude that after considering all of the

relevant factors and weighing the advantages of regulation against the
cost of doing so, it is appropriate and necessary to regulate EGUs
under CAA section 112. In section III.E of this preamble, we propose an
alternative formal benefit-cost approach for making the appropriate and
necessary determination. Under this approach, we propose to conclude
that it remains appropriate to regulate HAP emissions from EGUs after
considering cost because the BCA issued with the MATS rule indicated
that the total net benefits of MATS were overwhelming even though the
EPA was only able to monetize one of many statutorily identified
benefits of regulating HAP emissions from EGUs. The new information
examined by the EPA with respect to updated science and cost
information only strengthens our conclusions under either of these
methodologies. Section IV of this preamble notes that because this
proposal reaffirms prior determinations and does not impact
implementation of MATS, this action, if finalized, would not change
those standards.
    Finally, in preamble section V, in addition to soliciting comments
on all aspects of this proposed action, we separately seek comment on
any data or information that will assist in the EPA's ongoing review of
the RTR that the Agency completed for MATS in 2020.

B. Does this action apply to me?

    The source category that is the subject of this proposal is Coal-
and Oil-Fired EGUs regulated by NESHAP under 40 CFR 63, subpart UUUUU,
commonly known as MATS. The North American Industry Classification
System (NAICS) codes for the Coal- and Oil-Fired EGU source category
are 221112, 221122, and 921150. This list of NAICS codes is not
intended to be exhaustive, but rather provides a guide for readers
regarding the entities that this proposed action is likely to affect.

C. Where can I get a copy of this document and other related
information?

    In addition to being available in the docket, an electronic copy of
this action is available on the internet. Following signature by the
EPA Administrator, the EPA will post a copy of this proposed action at
https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards. Following publication in the Federal Register, the
EPA will post the Federal Register version of the proposal and key
technical documents at this same website.

II. Background

A. Regulatory History

    In the 1990 Amendments, Congress substantially modified CAA section
112 to address hazardous air pollutant emissions from stationary
sources. CAA section 112(b)(1) sets forth a list of 187 identified HAP,
and CAA sections 112(b)(2) and (3) give the EPA the authority to add or
remove pollutants from the list. CAA section 112(a)(1) and (2) specify
the two types of sources to be addressed: major sources and area
sources. A major source is any stationary source or group of stationary
sources at a single location and under common control that emits or has
the potential to emit, considering controls, 10 tpy or more of any HAP
or 25 tpy or more of any combination of HAP. CAA section 112(a)(1). Any
stationary source of HAP that is not a major source is an area
source.\4\ CAA section 112(a)(2). All major source categories, besides
EGUs, and certain area source categories, were required to be included
on an initial published list of sources subject to regulation under CAA
section 112. See CAA sections 112(a)(1) and (c)(1). The EPA is required
to promulgate emission standards under CAA section 112(d) for every
source category on the CAA section 112(c)(1) list.
---------------------------------------------------------------------------

    \4\ The statute includes a separate definition of ``EGU'' that
includes both major and area source power plant facilities. CAA
section 112(a)(8).
---------------------------------------------------------------------------

    The general CAA section 112(c) process for listing source
categories does not apply to EGUs. Instead, Congress enacted a special
provision, CAA section 112(n)(1)(A), which establishes a separate
process by which the EPA determines whether to add EGUs to the CAA
section 112(c) list of source categories that must be regulated under
CAA section 112. Because EGUs were subject to other CAA requirements
under the 1990 Amendments, most importantly the ARP, CAA section
112(n)(1)(A) directs the EPA to conduct a study to evaluate the hazards
to public health that are reasonably anticipated to occur as a result
of the HAP emissions from EGUs ``after imposition of the requirements
of this chapter.'' See CAA section 112(n)(1)(A); see also Michigan v.
EPA, 576 U.S. at 748 (``Quite apart from the hazardous-air-pollutants
program, the Clean Air Act Amendments of 1990 subjected power plants to
various regulatory requirements. The parties agree that these
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.''). The provision directs that the
EPA shall regulate EGUs under CAA section 112 if the Administrator
determines, after considering the results of the study, that such
regulation is ``appropriate and necessary.'' CAA section 112(n)(1)(A),
therefore, sets a unique process by which the Administrator is to
determine whether to add EGUs to the CAA section 112(c) list of sources
that must be subject to regulation under CAA section 112.
    The study required under CAA section 112(n)(1)(A) is one of three
studies commissioned by Congress under CAA section 112(n)(1), a
subsection entitled ``Electric utility steam generating units.'' The
first, which, as noted, the EPA was required to consider before making
the appropriate and necessary determination, was completed in 1998 and
was entitled the Study of Hazardous Air Pollutant Emissions from
Electric Utility Steam Generating Units-Final Report to Congress
(Utility Study).\5\ The Utility Study contained an analysis of HAP
emissions from EGUs, an assessment of the hazards and risks due to
inhalation exposures to these emitted pollutants, and a multipathway
(inhalation plus non-inhalation exposures) risk assessment for mercury
and a subset of other relevant HAP. The study indicated that mercury
was the HAP of greatest concern to public health from coal- and oil-
fired EGUs. The study also concluded that numerous control strategies
were available to reduce HAP emissions from this source category. The
second study commissioned by Congress under CAA section 112(n)(1)(B),
the Mercury Study Report to Congress (Mercury Study),\6\ was released
in 1997. Under this provision, the statute tasked the EPA with focusing
exclusively on mercury, but directed the Agency to look at other
stationary sources of mercury emission in addition to EGUs, the rate
and mass of emissions coming from those sources, available technologies
for controlling mercury and the costs of such technologies, and a
broader scope of impacts including environmental effects. As in the
Utility Study, the EPA confirmed that mercury is highly toxic,
persistent, and bioaccumulates in food chains. Fish consumption is the
primary pathway for human exposure to mercury, which can lead to higher
risks in certain populations. The third study, required under CAA
section 112(n)(1)(C),

directed the National Institute of Environmental Health Sciences
(NIEHS) to conduct a study to determine the threshold level of mercury
exposure below which adverse human health effects were not expected to
occur (NIEHS Study). The statute required that the study include a
threshold for mercury concentrations in the tissue of fish that could
be consumed, even by sensitive populations, without adverse effects to
public health. NIEHS submitted the required study to Congress in
1995.\7\ See 76 FR 24982 (May 3, 2011). Later, after submission of the
CAA section 112(n)(1) reports and as part of the fiscal year 1999
appropriations, Congress further directed the EPA to fund the National
Academy of Sciences (NAS) to perform an independent evaluation of the
data related to the health impacts of methylmercury, and, similar to
the CAA section 112(n)(1)(C) inquiry, specifically to advise the EPA as
to the appropriate reference dose (RfD) for methylmercury. Congress
also indicated in the 1999 conference report directing the EPA to fund
the NAS Study, that the EPA should not make the appropriate and
necessary regulatory determination until the EPA had reviewed the
results of the NAS Study. See H.R. Conf. Rep. No. 105-769, at 281-282
(1998). This last study, completed by the NAS in 2000, was entitled
Toxicological Effects of Methylmercury (NAS Study),\8\ and it presented
a rigorous peer-review of the EPA's RfD for methylmercury. Based on the
results of these studies and other available information, the EPA
determined on December 20, 2000, pursuant to CAA section 112(n)(1)(A),
that it is appropriate and necessary to regulate HAP emissions from
coal- and oil-fired EGUs and added such units to the CAA section 112(c)
list of source categories that must be regulated under CAA section 112.
See 65 FR 79825 (December 20, 2000) (2000 Determination).\9\
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    \5\ U.S. EPA. Study of Hazardous Air Pollutant Emissions from
Electric Utility Steam Generating Units--Final Report to Congress.
EPA-453/R-98-004a. February 1998.
    \6\ U.S. EPA. 1997. Mercury Study Report to Congress. EPA-452/R-
97-003 December 1997.
    \7\ National Institute of Environmental Health Sciences (NIEHS)
Report on Mercury; available in the rulemaking docket at EPA-HQ-OAR-
2009-0234-3053.
    \8\ National Research Council (NAS). 2000. Toxicological Effects
of Methylmercury. Committee on the Toxicological Effects of
Methylmercury, Board on Environmental Studies and Toxicology,
National Research Council. Many of the peer-reviewed articles cited
in this section are publications originally cited in the NAS report.
    \9\ In the same 2000 action, the EPA Administrator found that
regulation of HAP emissions from natural gas-fired EGUs is not
appropriate or necessary because the impacts due to HAP emissions
from such units are negligible. See 65 FR 79831 (December 20, 2000).
---------------------------------------------------------------------------

    In 2005, the EPA revised the original 2000 Determination and
concluded that it was neither appropriate nor necessary to regulate
EGUs under CAA section 112 in part because the EPA concluded it could
address risks from EGU HAP emissions under a different provision of the
statute. See 70 FR 15994 (March 29, 2005) (2005 Revision). Based on
that determination, the EPA removed coal- and oil-fired EGUs from the
CAA section 112(c) list of source categories to be regulated under CAA
section 112. In a separate but related 2005 action, the EPA also
promulgated the Clean Air Mercury Rule (CAMR), which established CAA
section 111 standards of performance for mercury emissions from EGUs.
See 70 FR 28605 (May 18, 2005). Both the 2005 Revision and the CAMR
were vacated by the D.C. Circuit in 2008. New Jersey v. EPA, 517 F.3d
574 (DC Cir. 2008). The D.C. Circuit held that the EPA failed to comply
with the requirements of CAA section 112(c)(9) for delisting source
categories, and consequently also vacated the CAA section 111
performance standards promulgated in CAMR, without addressing the
merits of those standards. Id. at 582-84.
    Subsequent to the New Jersey decision, the EPA conducted additional
technical analyses, including peer-reviewed risk assessments on human
health effects associated with mercury (2011 Final Mercury TSD) \10\
and non-mercury metal HAP emissions from EGUs (2011 Non-Hg HAP
Assessment).\11\ Those analyses, which focused on populations with
higher fish consumption (e.g., subsistence fishers) and residents
living near the facilities who experienced increased exposure to HAP
through inhalation, found that mercury and non-mercury HAP emissions
from EGUs remain a public health hazard and that EGUs were the largest
anthropogenic source of mercury emissions to the atmosphere in the U.S.
Based on these findings, and other relevant information regarding the
volume of HAP, environmental effects, and availability of controls, in
2012, the EPA affirmed the original 2000 Determination that it is
appropriate and necessary to regulate EGUs under CAA section 112. See
77 FR 9304 (February 16, 2012).
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    \10\ U.S. EPA. 2011. Revised Technical Support Document:
National-Scale Assessment of Mercury Risk to Populations with High
Consumption of Self-caught Freshwater Fish in Support of the
Appropriate and Necessary Finding for Coal- and Oil-Fired Electric
Generating Units. Office of Air Quality Planning and Standards.
December 2011. EPA-452/R-11-009. Docket ID Item No. EPA-HQ-OAR-2009-
0234-19913 (2011 Final Mercury TSD).
    \11\ U.S. EPA. 2011. Supplement to the Non-Hg Case Study Chronic
Inhalation Risk Assessment In Support of the Appropriate and
Necessary Finding for Coal- and Oil-Fired Electric Generating Units.
Office of Air Quality Planning and Standards. November 2011. EPA-
452/R-11-013. Docket ID Item No. EPA-HQ-OAR-2009-0234-19912 (2011
Non-Hg HAP Assessment).
---------------------------------------------------------------------------

    In the same 2012 action, the EPA established a NESHAP, commonly
referred to as MATS, that required coal- and oil-fired EGUs to meet HAP
emission standards reflecting the application of the maximum achievable
control technology (MACT) for all HAP emissions from EGUs.\12\ MATS
applies to existing and new coal- and oil-fired EGUs located at both
major and area sources of HAP emissions. An EGU is a fossil fuel-fired
steam generating combustion unit of more than 25 megawatts (MW) that
serves a generator that produces electricity for sale. See CAA section
112(a)(8) (defining EGU). A unit that cogenerates steam and electricity
and supplies more than one-third of its potential electric output
capacity and more than 25 MW electric output to any utility power
distribution system for sale is also an EGU. Id.
---------------------------------------------------------------------------

    \12\ Although the 2012 MATS Final Rule has been amended several
times, the amendments are not a result of actions regarding the
appropriate and necessary determination and, therefore, are not
discussed in this preamble. Detail regarding those amendatory
actions can be found at https://www.epa.gov/stationary-sources-air-pollution/mercury-and-air-toxics-standards.
---------------------------------------------------------------------------

    For coal-fired EGUs, MATS includes standards to limit emissions of
mercury, acid gas HAP, non-mercury HAP metals (e.g., nickel, lead,
chromium), and organic HAP (e.g., formaldehyde, dioxin/furan).
Standards for HCl serve as a surrogate for the acid gas HAP, with an
alternate standard for sulfur dioxide (SO2) that may be used
as a surrogate for acid gas HAP for those coal-fired EGUs with flue gas
desulfurization (FGD) systems and SO2 continuous emissions
monitoring systems that are installed and operational. Standards for
filterable PM serve as a surrogate for the non-mercury HAP metals, with
standards for total non-mercury HAP metals and individual non-mercury
HAP metals provided as alternative equivalent standards. Work practice
standards that require periodic combustion process tune-ups were
established to limit formation and emissions of the organic HAP.
    For oil-fired EGUs, MATS includes standards to limit emissions of
HCl and HF, total HAP metals (e.g., mercury, nickel, lead), and organic
HAP (e.g., formaldehyde, dioxin/furan). Standards for filterable PM
serve as a surrogate for total HAP metals, with standards for total HAP
metals and individual HAP metals provided as alternative equivalent
standards. Periodic combustion process tune-up work practice standards
were established to

limit formation and emissions of the organic HAP.
    Additional detail regarding the types of units regulated under MATS
and the regulatory requirements that they are subject to can be found
in 40 CFR 63, subpart UUUUU.\13\ The existing source compliance date
was April 16, 2015, but many existing sources were granted an
additional 1-year extension of the compliance date for the installation
of controls.
---------------------------------------------------------------------------

    \13\ Available at www.ecfr.gov/cgi-bin/text-idx?node=sp40.15.63.uuuuu.
---------------------------------------------------------------------------

    After MATS was promulgated, both the rule itself and many aspects
of the EPA's appropriate and necessary determination were challenged in
the D.C. Circuit. In White Stallion Energy Center v. EPA, the D.C.
Circuit unanimously denied all challenges to MATS, with one exception
discussed below in which the court was not unanimous. 748 F.3d 1222
(D.C. Cir. 2014). As part of its decision, the D.C. Circuit concluded
that the ``EPA's `appropriate and necessary' determination in 2000, and
the reaffirmation of that determination in 2012, are amply supported by
EPA's findings regarding the health effects of mercury exposure.'' Id.
at 1245.\14\ While joining the D.C. Circuit's conclusions as to the
adequacy of the EPA's identification of public health hazards, one
judge dissented on the issue of whether the EPA erred by not
considering costs together with the harms of HAP pollution when making
the ``appropriate and necessary'' determination, finding that cost was
a required consideration under that determination. Id. at 1258-59
(Kavanaugh, J., dissenting).
---------------------------------------------------------------------------

    \14\ In discussing the 2011 Final Mercury TSD, the D.C. Circuit
concluded that the EPA considered the available scientific
information in a rational manner, and stated:
    As explained in the technical support document (TSD)
accompanying the Final Rule, EPA determined that mercury emissions
posed a significant threat to public health based on an analysis of
women of child-bearing age who consumed large amounts of freshwater
fish. See [2011 Final] Mercury TSD . . . . The design of EPA's TSD
was neither arbitrary nor capricious; the study was reviewed by
EPA's independent Science Advisory Board, stated that it
``support[ed] the overall design of and approach to the risk
assessment'' and found ``that it should provide an objective,
reasonable, and credible determination of potential for a public
health hazard from mercury emissions emitted from U.S. EGUs.'' . . .
In addition, EPA revised the final TSD to address SAB's remaining
concerns regarding EPA's data collection practices.
    Id. at 1245-46.
---------------------------------------------------------------------------

    The U.S. Supreme Court subsequently granted certiorari, directing
the parties to address a single question posed by the Court itself:
``Whether the Environmental Protection Agency unreasonably refused to
consider cost in determining whether it is appropriate to regulate
hazardous air pollutants emitted by electric utilities.'' Michigan v.
EPA, 135 S. Ct. 702 (Mem.) (2014). In 2015, the U.S. Supreme Court held
that ``EPA interpreted [CAA section 112(n)(1)(A)] unreasonably when it
deemed cost irrelevant to the decision to regulate power plants.''
Michigan, 576 U.S. at 760. In so holding, the U.S. Supreme Court found
that the EPA ``must consider cost-including, most importantly, cost of
compliance-before deciding whether regulation is appropriate and
necessary.'' Id. at 2711. It is ``up to the Agency,'' the Court added,
``to decide (as always, within the limits of reasonable interpretation)
how to account for cost.'' Id. The rule was ultimately remanded back to
the EPA to complete the required cost analysis, and the D.C. Circuit
left the MATS rule in place pending the completion of that analysis.
White Stallion Energy Center v. EPA, No. 12-1100, ECF No. 1588459 (D.C.
Cir. December 15, 2015).
    In response to the U.S. Supreme Court's direction, the EPA
finalized a supplemental finding on April 25, 2016, that evaluated the
costs of complying with MATS and concluded that the appropriate and
necessary determination was still valid. The 2016 Supplemental Finding
promulgated two different approaches to incorporate cost into the
decision-making process for the appropriate and necessary
determination. See 81 FR 24420 (April 25, 2016). The EPA determined
that both approaches independently supported the conclusion that
regulation of HAP emissions from EGUs is appropriate and necessary.
    The EPA's preferred approach to incorporating cost evaluated
estimated costs of compliance with MATS against several cost metrics
relevant to the EGU sector (e.g., historical annual revenues, annual
capital expenditures, and impacts on retail electricity prices), and
found that the projected costs of MATS were reasonable for the sector
in comparison with historical data on those metrics. The evaluation of
cost metrics that the EPA applied was consistent with approaches
commonly used to evaluate environmental policy cost impacts.\15\ The
EPA also examined as part of its cost analysis what the impact of MATS
would be on retail electricity prices and the reliability of the power
grid. Using a totality-of-the-circumstances approach, the EPA weighed
these supplemental findings as to cost against the existing
administrative record detailing the identified hazards to public health
and the environment from mercury, non-mercury metal HAP, and acid gas
HAP that are listed under CAA section 112, and the other advantages to
regulation. Based on that balancing, the EPA concluded under the
preferred approach that it remains appropriate to regulate HAP
emissions from EGUs after considering cost. See 81 FR 24420 (April 25,
2016) (``After evaluating cost reasonableness using several different
metrics, the Administrator has, in accordance with her statutory duty
under CAA section 112(n)(1)(A), weighed cost against the previously
identified advantages of regulating HAP emissions from EGUs--including
the agency's prior conclusions about the significant hazards to public
health and the environment associated with such emissions and the
volume of HAP that would be reduced by regulation of EGUs under CAA
section 112.'')
---------------------------------------------------------------------------

    \15\ For example, see ``Economic Impact and Small Business
Analysis-Mineral Wool and Wool Fiberglass RTRs and Wool Fiberglass
Area Source NESHAP'' (U.S. EPA, 2015; https://www.epa.gov/sites/default/files/2020-07/documents/mwwf_eia_neshap_final_07-2015.pdf)
or ``Economic Impact Analysis of Final Coke Ovens NESHAP'' (U.S.
EPA, 2002; https://www.epa.gov/sites/default/files/2020-07/documents/coke-ovens_eia_neshap_final_08-2002.pdf).
---------------------------------------------------------------------------

    In a second alternative and independent approach (referred to as
the alternative approach), the EPA considered the BCA in the 2011 RIA
for the 2012 MATS Final Rule. Id. at 24421. In that analysis, even
though the EPA was only able to monetize one HAP-specific endpoint, the
EPA estimated that the final MATS rule would yield annual monetized net
benefits (in 2007 dollars) of between $37 billion to $90 billion using
a 3-percent discount rate and between $33 billion to $81 billion using
a 7-percent discount rate, in comparison to the projected $9.6 billion
in annual compliance costs. See id. at 24425. The EPA therefore
determined that the alternative approach also independently supported
the conclusion that regulation of HAP emissions from EGUs remains
appropriate after considering cost. Id.
    Several state and industry groups petitioned for review of the 2016
Supplemental Finding in the D.C. Circuit. Murray Energy Corp. v. EPA,
No. 16-1127 (D.C. Cir. filed April 25, 2016). In April 2017, the EPA
moved the D.C. Circuit to continue oral argument and hold the case in
abeyance in order to give the then-new Administration an opportunity to
review the 2016 action, and the D.C. Circuit ordered that the
consolidated challenges to the 2016

Supplemental Finding be held in abeyance (i.e., temporarily on
hold).\16\
---------------------------------------------------------------------------

    \16\ Order, Murray Energy Corp. v. EPA, No. 16-1127 (D.C. Cir.
April 27, 2017), ECF No. 1672987. In response to a joint motion from
the parties to govern future proceedings, the D.C. Circuit issued an
order in February 2021 to continue to hold the consolidated cases in
Murray Energy Corp. v. EPA in abeyance. Order, Murray Energy Corp.
v. EPA, No. 16-1127 (D.C. Cir. February 25, 2021), ECF No. 1887125.
---------------------------------------------------------------------------

    Accordingly, the EPA reviewed the 2016 action, and on May 22, 2020,
finalized a revised response to the Michigan decision. See 85 FR 31286
(May 22, 2020). In the 2020 Final Action, after primarily comparing the
projected costs of compliance to the one post control HAP emission
reduction benefit that could be monetized, the EPA reconsidered its
previous determination and found that it is not appropriate to regulate
HAP emissions from coal- and oil-fired EGUs after a consideration of
cost, thereby reversing the Agency's conclusion under CAA section
112(n)(1)(A), first made in 2000 and later affirmed in 2012 and 2016.
Specifically, in its reconsideration, the Agency asserted that the 2016
Supplemental Finding considering the cost of MATS was flawed based on
its assessment that neither of the two approaches to considering cost
in the 2016 Supplemental Finding satisfied the EPA's obligation under
CAA section 112(n)(1)(A), as that provision was interpreted by the U.S.
Supreme Court in Michigan. Additionally, the EPA determined that, while
finalizing the action would reverse the 2016 Supplemental Finding, it
would not remove the Coal- and Oil-Fired EGU source category from the
CAA section 112(c)(1) list, nor would it affect the existing CAA
section 112(d) emissions standards regulating HAP emissions from coal-
and oil-fired EGUs that were promulgated in the 2012 MATS Final
Rule.\17\ See 85 FR 31312 (May 22, 2020).
---------------------------------------------------------------------------

    \17\ This finding was based on New Jersey v. EPA, 517 F.3d 574
(D.C. Cir. 2008), which held that the EPA is not permitted to remove
source categories from the CAA section 112(c)(1) list unless the CAA
section 112(c)(9) criteria for delisting have been met.
---------------------------------------------------------------------------

    In the 2020 Final Action, the EPA also finalized the risk review
required by CAA section 112(f)(2) and the first technology review
required by CAA section 112(d)(6) for the Coal- and Oil-Fired EGU
source category regulated under MATS.\18\ The EPA determined that
residual risks due to emissions of air toxics from the Coal- and Oil-
Fired EGU source category are acceptable and that the current NESHAP
provides an ample margin of safety to protect public health and to
prevent an adverse environmental effect. In the technology review, the
EPA did not identify any new developments in HAP emission controls to
achieve further cost-effective emissions reductions. Based on the
results of these reviews, the EPA found that no revisions to MATS were
warranted. See 85 FR 31314 (May 22, 2020).
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    \18\ CAA section 112(f)(2) requires the EPA to conduct a one-
time review of the risks remaining after imposition of MACT
standards under CAA section 112(d)(2) within 8 years of the
effective date of those standards (risk review). CAA section
112(d)(6) requires the EPA to conduct a review of all CAA section
112(d) standards at least every 8 years to determine whether it is
necessary to establish more stringent standards after considering,
among other things, advances in technology and costs of additional
control (technology review). The EPA has always conducted the first
technology review at the same time it conducts the risk review and
collectively the actions are known at RTRs.
---------------------------------------------------------------------------

    Several states, industry, public health, environmental, and civil
rights groups petitioned for review of the 2020 Final Action in the
D.C. Circuit. American Academy of Pediatrics v. Regan, No. 20-1221 and
consolidated cases (D.C. Cir. filed June 19, 2020). On September 28,
2020, the D.C. Circuit granted the EPA's unopposed motion to sever from
the lead case and hold in abeyance two of the petitions for review:
Westmoreland Mining Holdings LLC v. EPA, No. 20-1160 (D.C. Cir. filed
May 22, 2020) (challenging the 2020 Final Action as well as prior EPA
actions related to MATS, including a challenge to the MATS CAA section
112(d) standards on the basis that the 2020 Final Action's reversal of
the appropriate and necessary determination provided a ``grounds
arising after'' for filing a petition outside the 60-day window for
judicial review of MATS), and Air Alliance Houston v. EPA, No. 20-1268
(D.C. Cir. filed July 21, 2020) (challenging only the RTR portion of
the 2020 Final Action).\19\
---------------------------------------------------------------------------

    \19\ Order, Westmoreland Mining Holdings LLC v. EPA, No. 20-1160
(D.C. Cir. September 28, 2020), ECF No. 1863712.
---------------------------------------------------------------------------

    On January 20, 2021, President Biden signed Executive Order 13990,
``Protecting Public Health and the Environment and Restoring Science to
Tackle the Climate Crisis.'' The Executive Order, among other things,
instructs the EPA to review the 2020 Final Action and consider
publishing a notice of proposed rulemaking suspending, revising, or
rescinding that action. In February 2021, the EPA moved the D.C.
Circuit to hold American Academy of Pediatrics and consolidated cases
in abeyance, pending the Agency's review of the 2020 Final Action as
prompted in Executive Order 13990, and on February 16, 2021, the D.C.
Circuit granted the Agency's motion.\20\
---------------------------------------------------------------------------

    \20\ Order, American Academy of Pediatrics v. Regan, No. 20-1221
(D.C. Cir. February 16, 2021), ECF No. 1885509.
---------------------------------------------------------------------------

    In the meantime, the requirements of MATS have been fully
implemented, resulting in significant reductions in HAP emissions from
EGUs and the risks associated with those emissions. The EPA had
projected that annual EGU mercury emissions would be reduced by 75
percent with MATS implementation. In fact, EGU emission reductions have
been far more substantial (down to approximately 4 tons in 2017), which
represents an 86 percent reduction compared to 2010 (pre-MATS) levels.
See Table 4 at 84 FR 2689 (February 7, 2019). Acid gas HAP and non-
mercury metal HAP have similarly been reduced--by 96 percent and 81
percent, respectively--as compared to 2010 levels. Id. MATS is the only
Federal requirement that guarantees this level of HAP control from
EGUs.
    The EPA is now proposing to revoke the 2020 reconsideration of the
2016 Supplemental Finding and to reaffirm once again that it is
appropriate and necessary to regulate emissions of HAP from coal- and
oil-fired EGUs. We will provide notice of the results of our review of
the 2020 RTR in a separate future action.

B. Statutory Background

    Additional statutory context is useful to help identify the
relevant factors that the Administrator should weigh when making the
appropriate and necessary determination.
1. Pre-1990 History of HAP Regulation
    In 1970, Congress enacted CAA section 112 to address the millions
of pounds of HAP emissions that were estimated to be emitted from
stationary sources in the country. At that time, the CAA defined HAP as
``an air pollutant to which no ambient air quality standard is
applicable and which, in the judgment of the Administrator may cause,
or contribute to, an increase in mortality or an increase in serious
irreversible, or incapacitating reversible, illness,'' but the statute
left it to the EPA to identify and list pollutants that were HAP. Once
a HAP was listed, the statute required the EPA to regulate sources of
that identified HAP ``at the level which in [the Administrator's]
judgment provides an ample margin of safety to protect the public
health from such hazardous air pollutants.'' CAA section 112(b)(1)(B)
(pre-1990 amendments); Legislative History of the CAA Amendments of
1990 (``Legislative

History''), at 3174-75, 3346 (Comm. Print 1993). The statute did not
define the term ``ample margin of safety'' or provide a risk metric on
which the EPA was to establish standards, and initially the EPA
endeavored to account for costs and technological feasibility in every
regulatory decision. In Natural Resources Defense Council (NRDC) v.
EPA, 824 F.2d 1146 (D.C. Cir. 1987), the D.C. Circuit concluded that
the CAA required that in interpreting what constitutes ``safe,'' the
EPA was prohibited from considering cost and technological feasibility.
Id. at 1166.
    The EPA subsequently issued the NESHAP for benzene in accordance
with the NRDC holding.\21\ Among other things, the Benzene NESHAP
concluded that there is a rebuttable presumption that any cancer risk
greater than 100-in-1 million to the most exposed individual is
unacceptable, and per NRDC, must be addressed without consideration of
cost or technological feasibility. The Benzene NESHAP further provided
that, after evaluating the acceptability of cancer risks, the EPA must
evaluate whether the current level of control provides an ample margin
of safety for any risk greater than 1-in-1 million and, if not, the EPA
will establish more stringent standards as necessary after considering
cost and technological feasibility.\22\
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    \21\ National Emissions Standards for Hazardous Air Pollutants:
Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene
Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke
By-Product Recovery Plants (Benzene NESHAP). 54 FR 38044 (September
14, 1989).
    \22\ ``In protecting public health with an ample margin of
safety under section 112, EPA strives to provide maximum feasible
protection against risks to health from hazardous air pollutants by
(1) protecting the greatest number of persons possible to an
individual lifetime risk level no higher than approximately 1 in 1
million and (2) limiting to no higher than approximately 1 in 10
thousand the estimated risk that a person living near a plant would
have if he or she were exposed to the maximum pollutant
concentrations for 70 years.'' Benzene NESHAP, 54 FR 38044-5,
September 14, 1989.
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2. Clean Air Act 1990 Amendments to Section 112
    In 1990, Congress radically transformed section 112 of the CAA and
its treatment of hazardous air pollution. The legislative history of
the amendments indicates Congress' dissatisfaction with the EPA's slow
pace addressing these pollutants under the 1970 CAA: ``In theory,
[hazardous air pollutants] were to be stringently controlled under the
existing Clean Air Act section 112. However, . . . only seven of the
hundreds of potentially hazardous air pollutants have been regulated by
EPA since section 112 was enacted in 1970.'' H.R. Rep. No. 101-490, at
315 (1990); see also id. at 151 (noting that in 20 years, the EPA's
establishment of standards for only seven HAP covered ``a small
fraction of the many substances associated . . . with cancer, birth
defects, neurological damage, or other serious health impacts.'').
Congress was concerned with how few sources had been addressed during
this time. Id. (``[The EPA's] regulations sometimes apply only to
limited sources of the relevant pollutant. For example, the original
benzene standard covered just one category of sources (equipment
leaks). Of the 50 toxic substances emitted by industry in the greatest
volume in 1987, only one--benzene--has been regulated even partially by
EPA.''). Congress noted that state and local regulatory efforts to act
in the face of ``the absence of Federal regulations'' had ``produced a
patchwork of differing standards,'' and that ``[m]ost states . . .
limit the scope of their program by addressing a limited number of
existing sources or source categories, or by addressing existing
sources only on a case-by-case basis as problem sources are
identified'' and that ``[o]ne state exempts all existing sources from
review.'' Id.
    In enacting the 1990 Amendments with respect to the control of
hazardous air pollution, Congress noted that ``[p]ollutants controlled
under [section 112] tend to be less widespread than those regulated
[under other sections of the CAA], but are often associated with more
serious health impacts, such as cancer, neurological disorders, and
reproductive dysfunctions.'' Id. at 315. In its substantial 1990
Amendments, Congress itself listed 189 HAP (CAA section 112(b)) and set
forth a statutory structure that would ensure swift regulation of a
significant majority of these HAP emissions from stationary sources.
Specifically, after defining major and area sources and requiring the
Agency to list all major sources and many area sources of the listed
pollutants (CAA section 112(c)), the new CAA section 112 required the
Agency to establish technology-based emission standards for listed
source categories on a prompt schedule and to revisit those technology-
based standards every 8 years (CAA section 112(d) (emission standards);
CAA section 112(e) (schedule for standards and review)). The 1990
Amendments also obligated the EPA to evaluate the residual risk within
8 years of promulgation of technology-based standards. CAA section
112(f)(2).
    In setting the standards, CAA section 112(d) requires the Agency to
establish technology-based standards that achieve the ``maximum degree
of reduction,'' ``including a prohibition on such emissions where
achievable.'' CAA section 112(d)(2). Congress specified that the
maximum degree of reduction must be at least as stringent as the
average level of control achieved in practice by the best performing
sources in the category or subcategory based on emissions data
available to the Agency at the time of promulgation. This technology-
based approach permitted the EPA to swiftly set standards for source
categories without determining the risk or cost in each specific case,
as the EPA had done prior to the 1990 Amendments. In other words, this
approach to regulation quickly required that all major sources and many
area sources of HAP install control technologies consistent with the
top performers in each category, which had the effect of obtaining
immediate reductions in the volume of HAP emissions from stationary
sources. The statutory requirement that sources obtain levels of
emission limitation that have actually been achieved by existing
sources, instead of levels that could theoretically be achieved,
inherently reflects a built-in cost consideration.\23\
---------------------------------------------------------------------------

    \23\ Congress recognized as much:
    ``The Administrator may take the cost of achieving the maximum
emission reduction and any non-air quality health and environmental
impacts and energy requirements into account when determining the
emissions limitation which is achievable for the sources in the
category or subcategory. Cost considerations are reflected in the
selection of emissions limitations which have been achieved in
practice (rather than those which are merely theoretical) by sources
of a similar type or character.''
    A Legislative History of the Clean Air Act Amendments of 1990
(CAA Legislative History), Vol 5, pp. 8508 -8509 (CAA Amendments of
1989; p. 168-169; Report of the Committee on Environment and Public
Works S. 1630).
---------------------------------------------------------------------------

    Further, after determining the minimum stringency level of control,
or MACT floor, CAA section 112(d)(2) requires the Agency to determine
whether more stringent standards are achievable after considering the
cost of achieving such standards and any non-air-quality health and
environmental impacts and energy requirements of additional control. In
doing so, the statute further specifies in CAA section 112(d)(2) that
the EPA should consider requiring sources to apply measures that, among
other things, ``reduce the volume of, or eliminate emissions of, such
pollutants . . .'' (CAA section 112(d)(2)(A)), ``enclose systems or
processes to eliminate emissions'' (CAA section 112(d)(2)(B)), and
``collect, capture, or treat such pollutants when released . . .'' (CAA
section 112(d)(2)(C)). The 1990 Amendments also built in a regular
review of new

technologies and a one-time review of risks that remain after
imposition of MACT standards. CAA section 112(d)(6) requires the EPA to
evaluate every NESHAP no less often than every 8 years to determine
whether additional control is necessary after taking into consideration
``developments in practices, processes, and control technologies,''
without regard to risk. CAA section 112(f) requires the EPA to ensure
that the risks are acceptable and that the MACT standards provide an
ample margin of safety.
    The statutory requirement to establish technology-based standards
under CAA section 112 avoided the need for the EPA to identify hazards
to public health and the environment in order to justify regulation of
HAP emissions from stationary sources, reflecting Congress' judgment
that such emissions are inherently dangerous. See S. Rep. No. 101-228,
at 148 (``The MACT standards are based on the performance of
technology, and not on the health and environmental effects of the
[HAP].''). The technology review required in CAA section 112(d)(6)
further mandates that the EPA continually evaluate standards to
determine if additional reductions can be obtained, without
consideration of the specific risk associated with the HAP emissions
that would be reduced. Notably, the CAA section 112(d)(6) review of
what additional reductions may be obtained based on new technology is
required even after the Agency has conducted the CAA section 112(f)(2)
review and determined that the existing standard will protect the
public with an ample margin of safety.
    The statutory structure and legislative history also demonstrate
Congress' concern with the many ways that HAP can harm human health and
Congress' goal of protecting the most exposed and vulnerable members of
society. The committee report accompanying the 1990 Amendments
discussed the scientific understanding regarding HAP risk at the time,
including the 1989 report on benzene performed by the EPA noted above.
H.R. Rep. No. 101-490, at 315. Specifically, Congress highlighted the
EPA's findings as to cancer incidence, and importantly, lifetime
individual risk to the most exposed individuals. Id. The report also
notes the limitations of the EPA's assessment: ``The EPA estimates
evaluated the risks caused by emissions of a single toxic air pollutant
from each plant. But many facilities emit numerous toxic pollutants.
The agency's risk assessments did not consider the combined or
synergistic effects of exposure to multiple toxics, or the effect of
exposure through indirect pathways.'' Id. Congress also noted the EPA's
use of the maximum exposed individual (MEI) tool to assess risks faced
by heavily exposed citizens. Id. The report cited particular scientific
studies demonstrating that some populations are more affected than
others--for example, it pointed out that ``[b]ecause of their small
body weight, young children and fetuses are especially vulnerable to
exposure to PCB-contaminated fish. One study has found long-term
learning disabilities in children who had eaten high-levels of Great
Lakes fish.'' Id.
    The statutory structure confirms Congress' approach to risk and
sensitive populations. As noted, the CAA section 112(f)(2) residual
risk review requires the EPA to consider whether, after imposition of
the CAA section 112(d)(2) MACT standard, there are remaining risks from
HAP emissions that warrant more stringent standards to provide an ample
margin of safety to protect public health or to prevent an adverse
environmental effect. See CAA section 112(f)(2)(A). Specifically, the
statute requires the EPA to promulgate standards under the risk review
provision if the CAA section 112(d) standard does not ``reduce lifetime
excess cancer risks to the individual most exposed to emissions from a
source in the category or subcategory to less than one in one
million.'' Id. Thus, even after the application of MACT standards, the
statute directs the EPA to conduct a rulemaking if even one person has
a risk, not a guarantee, of getting cancer. This demonstrates the
statutory intent to protect even the most exposed member of the
population from the harms attendant to exposure to HAP emissions.
    If a residual risk rulemaking is required, as noted above, the
statute incorporates the detailed rulemaking approach set forth in the
Benzene NESHAP for determining whether HAP emissions from stationary
sources pose an unacceptable risk and whether standards provide an
ample margin of safety. See CAA section 112(f)(2)(B) (preserving the
prior interpretation of ``ample margin of safety'' set forth in the
Benzene NESHAP). That approach includes a rebuttable presumption that
any cancer risk greater than 100-in-1 million to the most exposed
person is per se unacceptable. For non-cancer chronic and acute risks,
the EPA has more discretion to determine what is acceptable, but even
then, the statute requires the EPA to evaluate the risks to the most
exposed individual and our RfDs are developed with the goal of being
protective of even sensitive members of the population. See e.g., CAA
section 112(n)(1)(C) (requiring, in part, the development of ``a
threshold for mercury concentration in the tissue of fish which may be
consumed (including consumption by sensitive populations) without
adverse effects to public health''). If risks are found to be
unacceptable, the EPA must impose additional control requirements to
ensure that post CAA section 112(f) risks from HAP emissions are at an
acceptable level, regardless of cost and technological feasibility.
    After determining whether the risks are acceptable and developing
standards to achieve an acceptable level of risk if necessary, the EPA
must then determine whether more stringent standards are necessary to
provide an ample margin of safety to protect public health, and at this
stage we must take into consideration cost, technological feasibility,
uncertainties, and other relevant factors. As stated in the Benzene
NESHAP, ``In protecting public health with an ample margin of safety
under section 112, EPA strives to provide maximum feasible protection
against risks to health from hazardous air pollutants by . . .
protecting the greatest number of persons possible to an individual
lifetime risk level no higher than approximately 1 in 1 million.'' See
54 FR 38044-45 (September 14, 1989); see also NRDC v. EPA, 529 F.3d
1077, 1082 (D.C. Cir. 2008) (finding that ``the Benzene NESHAP standard
established a maximum excess risk of 100-in-one million, while adopting
the one-in-one million standard as an aspirational goal.'').
    The various listing and delisting provisions of CAA section 112
further demonstrate a statutory intent to reduce risk and protect the
most exposed members of the population from HAP emissions. See, e.g.,
CAA section 112(b)(2) (requiring the EPA to add pollutants to the HAP
list if the EPA determines the HAP ``presents, or may present'' adverse
human health or adverse environmental effects); id. at CAA section
112(b)(3)(B) (requiring the EPA to add a pollutant to the list if a
petitioner shows that a substance is known to cause or ``may reasonably
be anticipated to cause adverse effects to human health or adverse
environmental effects''); id. at CAA section 112(b)(3) (authorizing the
EPA to delete a substance only on a showing that ``the substance may
not reasonably be anticipated to cause any adverse effects to human
health or adverse environmental effects.''); id. at CAA section
112(c)(9)(B)(i) (prohibiting the EPA from delisting a source category
if even one source in the category causes

a lifetime cancer risk greater than 1-in-1 million to ``the individual
in the population who is most exposed to emissions of such pollutants
from the source.''); id. at CAA section 7412(c)(9)(B)(i) (prohibiting
the EPA from delisting a source category unless the Agency determines
that the non-cancer causing HAP emitted from the source category do not
``exceed a level which is adequate to protect public health with an
ample margin of safety and no adverse environmental effect will result
from emissions of any source'' in the category); id. at CAA section
112(n)(1)(C) (requiring a study to determine the level of mercury in
fish tissue that can be consumed by even sensitive populations without
adverse effect to public health).
    The deadlines for action included in the 1990 Amendments indicate
that Congress wanted HAP pollution addressed quickly. The statute
requires the EPA to list all major source categories within 1 year of
the 1990 Amendments and to regulate those listed categories on a strict
schedule that prioritizes the source categories that are known or
suspected to pose the greatest risks to the public. See CAA sections
112(c)(1), 112(e)(1) and 112(e)(2). For area sources, where the statute
provides the EPA with greater discretion to determine the sources to
regulate, it also directs the Agency to collect the information
necessary to make the listing decision for many area source categories
and requires the Agency to act on that information by a date certain.
    For example, CAA section 112(k) establishes an area source program
designed to identify and list at least 30 HAP that pose the greatest
threat to public health in the largest number of urban areas (urban
HAP) and to list for regulation area sources that account for at least
90 percent of the area source emissions of the 30 urban HAP. See CAA
sections 112(k) and 112(c)(3). In addition to the urban air toxics
program, CAA section 112(c)(6) directs the EPA to identify and list
sufficient source categories to ensure that at least 90 percent of the
aggregate emissions of seven bioaccumulative and persistent HAP,
including mercury, are subject to standards pursuant to CAA sections
112(d)(2) or (d)(4). See CAA section 112(c)(6). Notably, these
requirements were in addition to any controls on mercury and other CAA
section 112(c)(6) HAP that would be imposed if the EPA determined it
was appropriate and necessary to regulate EGUs under CAA section 112.
This was despite the fact that it was known at the time of enactment
that other categories with much lower emissions of mercury would have
to be subject to MACT standards because of the exclusion of EGUs from
CAA section 112(c)(6).
    As the preceding discussion demonstrates, throughout CAA section
112 and its legislative history, Congress made clear its intent to
quickly secure large reductions in the volume of HAP emissions from
stationary sources because of its recognition of the hazards to public
health and the environment inherent in exposure to such emissions. CAA
section 112 and its legislative history also reveal Congress'
understanding that fully characterizing the risks posed by HAP
emissions was exceedingly difficult; thus, Congress purposefully
replaced a regime that required an assessment of risk in the first
instance with one that assumed that risk and directed swift and
substantial reductions. The statutory design and direction also
repeatedly emphasize that the EPA should regulate with the most exposed
and most sensitive members of the population in mind in order to
achieve an acceptable level of HAP emissions with an ample margin of
safety. As explained further below, this statutory context informs the
EPA's judgment as to the relevant factors to weigh in the analysis of
whether regulation remains appropriate after a consideration of cost.

III. Proposed Determination Under CAA Section 112(n)(1)(A)

    In this action, the EPA is proposing to revoke the 2020 Final
Action and to reaffirm the appropriate and necessary determination made
in 2000, and reaffirmed in 2012 and 2016.\24\ We propose to find that,
under either our preferred totality-of-the-circumstances framework or
our alternative formal BCA framework, the information that would have
been available to the Agency as of the time of the 2012 rulemaking
supports a determination that it is appropriate and necessary to
regulate HAP from EGUs. We also consider new information regarding the
hazards to public health and the environment and the costs of
compliance with MATS that has become available since the 2016
Supplemental Finding, and find that the updated information strengthens
the EPA's conclusion that it is appropriate and necessary to regulate
HAP from coal- and oil-fired EGUs.
---------------------------------------------------------------------------

    \24\ Our proposal focuses on an analysis of the ``appropriate''
prong of the CAA section 112(n)(1)(A). The Michigan decision and
subsequent EPA actions addressing that decision have been centered
on supplementing the Agency's record with a consideration of the
cost of regulation as part of the ``appropriate'' aspect of the
overall determination. As noted, the 2020 Final Action, while
reversing the 2016 Supplemental Finding as to the EPA's
determination that it was ``appropriate'' to regulate HAP from EGUs,
did not rescind the Agency's prior determination that it was
necessary to regulate. See 84 FR 2674 (February 7, 2019) (``CAA
section 112(n)(1)(A) requires the EPA to determine that both the
appropriate and necessary prongs are met. Therefore, if the EPA
finds that either prong is not satisfied, it cannot make an
affirmative appropriate and necessary finding. The EPA's
reexamination of its determination . . . focuses on the first prong
of that analysis.''). The ``necessary'' determination rested on two
primary bases: (1) In 2012, the EPA determined that the hazards
posed to human health and the environment by HAP emissions from EGUs
would not be addressed in its future year modeling, which accounted
for all CAA requirements to that point; and (2) our conclusion that
the only way to ensure permanent reductions in U.S. EGU emissions of
HAP and the associated risks to public health and the environment
was through standards set under CAA section 112. See 76 FR 25017
(May 23, 2011). We therefore continue our focus in this proposal on
reinstating the ``appropriate'' prong of the determination, leaving
undisturbed the Agency's prior conclusions that regulation of HAP
from EGUs is ``necessary.'' See 65 FR 79830 (December 20, 2000); 76
FR 25017 (May 3, 2011); 77 FR 9363 (February 16, 2012).
---------------------------------------------------------------------------

    At the outset, we note that CAA section 112(n)(1)(A) is silent as
to whether the EPA may consider updated information when acting on a
remand of the appropriate and necessary determination. CAA section
112(n)(1)(A) directs the EPA to conduct the Utility Study within 3
years, and requires the EPA to regulate EGUs if the Administrator makes
a finding that it is appropriate and necessary to do so ``after''
considering the results of the Utility Study. Consistent with the EPA's
interpretation in 2005, 2012, 2016, and 2020, we do not read this
language to require the EPA to consider the most-up-to-date information
where the Agency is compelled to revisit the determination, but nor do
we interpret the provision to preclude consideration of new information
where reasonable. See 70 FR 16002 (March 29, 2005); 77 FR 9310
(February 16, 2012); 81 FR 24432 (April 25, 2016); 85 FR 31306 (May 22,
2020). As such, the Agency has applied its discretion in determining
when to consider new information under this provision based on the
circumstances. For example, when the EPA was revisiting the
determination in 2012, we noted that ``[b]ecause several years had
passed since the 2000 finding, the EPA performed additional technical
analyses for the proposed rule, even though those analyses were not
required.'' 77 FR 9310 (February 16, 2012).\25\ Similarly, we think
that it is reasonable to consider new information in the context of
this proposal, given that almost a decade has passed since we last
considered updated information. In this proposed reconsideration of the

determination per the President's Executive Order, both the growing
scientific understanding of public health risks associated with HAP
emissions and a clearer picture of the cost of control technologies and
the make-up of power sector generation over the last decade may inform
the question of whether it is appropriate to regulate, and, in
particular, help address the inquiry that the Supreme Court directed us
to undertake in Michigan. We believe the evolving scientific
information with regard to benefits and the advantage of hindsight with
regard to costs warrant considering currently available information in
making this determination. To the extent that our determination should
flow from information that would have been available at the ``initial
decision to regulate,'' Michigan, 576 U.S. at 754, we propose
conclusions here based on analyses limited to this earlier record. But
we also believe it is reasonable to consider new data, and propose to
find that the new information regarding both public health risks and
costs bolsters the finding and supports a determination that it is
appropriate and necessary to regulate EGUs for HAP.
---------------------------------------------------------------------------

    \25\ The EPA was not challenged on this interpretation in White
Stallion.
---------------------------------------------------------------------------

    In section III.A of this preamble, we first describe the advantages
of regulation--the reduction in emissions of HAP and attendant
reduction of risks to human health and the environment, including the
distribution of these health benefits. We carefully document the
numerous risks to public health and the environment posed by HAP
emissions from EGUs. This includes information previously recognized
and documented in the statutorily mandated CAA section 112(n)(1)
studies, the 2000 Determination, the 2012 MATS Final Rule, and the 2016
Supplemental Finding about the nature and extent of health and
environmental impacts from HAP that are emitted by EGUs, as well as
additional risk analyses supported by new scientific studies.
Specifically, new risk screening analyses on the connection between
mercury and heart disease as well as IQ loss in children across the
U.S. further supports the conclusion that HAP emissions from EGUs pose
hazards to public health and the environment warranting regulating
under CAA section 112. The EPA also discusses the challenges associated
with fully quantifying and monetizing the human health and
environmental effects associated with HAP emissions. Finally, we note
that in addition to reducing the identified risks posed by HAP
emissions from EGUs, regulation of such HAP emissions results in
significant health and environmental co-benefits.
    We then turn in preamble section III.B. to the disadvantages of
regulation--the costs associated with reducing EGU HAP emissions and
other potential impacts to the sector and the economy associated with
MATS. With the benefit of hindsight, we first consider whether MATS
actually cost what we projected in the 2011 RIA and conclude that the
projection in the 2011 RIA was almost certainly a significant
overestimate of the actual costs. We then evaluate the costs estimated
in the 2011 RIA against several metrics relevant to the impacts those
costs have on the EGU sector and American electricity consumers (e.g.,
historical annual revenues, annual capital and production expenditures,
impacts on retail electricity prices, and impacts on resource adequacy
and reliability). These analyses, based on data available in 2012 and
based on updated data, all show that the costs of MATS were within the
bounds of typical historical fluctuations and that the industry would
be able to comply with MATS and continue to provide a reliable source
of electricity without price increases that were outside the range of
historical variability.
    In section III.C of this preamble, we explain why the methodology
used in our 2020 Finding was ill-suited to determining whether EGU HAP
regulation is appropriate and necessary because it gave virtually no
weight to the volume of HAP that would be reduced, and the vast
majority of the benefits of reducing EGU HAP, including the reduction
of risk to sensitive populations, based on the Agency's inability to
quantify or monetize post-control benefits of HAP regulations.
    In preamble section III.D, we explain our preferred totality-of-
the-circumstances methodology that we propose to use to make the
appropriate determination, and our application of that methodology.
This approach looks to the statute, and particularly CAA section
112(n)(1)(A) and the other provisions in CAA section 112(n)(1), to help
identify the relevant factors to weigh and what weight to afford those
factors. Under that methodology we weigh the significant health and
environmental advantages of reducing EGU HAP, and in particular the
benefits to the most exposed and sensitive individuals, against the
disadvantages of expending money to achieve those benefits--i.e., the
effects on the electric generating industry and its ability to provide
reliable and affordable electricity. We ultimately propose to conclude
that the advantages outweigh the disadvantages whether we look at the
record from 2012 or at our new record, which includes an expanded
understanding of the health risks associated with HAP emissions and
finds that the costs projected in the 2011 RIA were almost certainly
significantly overestimated. We further consider that, if we also
account for the non-HAP benefits in our preferred totality-of-the-
circumstances approach, such as the benefits (including reduced
mortality) of coincidental reductions in PM and ozone that flow from
the application of controls on HAP, the balance weighs even more
heavily in favor of regulating HAP emissions from coal- and oil-fired
EGUs.
    Finally, in section III.E, we consider an alternative methodology
to make the appropriate determination, using a formal BCA of MATS that
was conducted consistent with economic principles. This methodology is
not our preferred way to consider advantages and disadvantages for the
CAA section 112(n)(1)(A) determination, because the EPA's inability to
generate a monetized estimate of the full benefits of HAP reductions
can lead to an underestimate of the monetary value of the net benefits
of regulation. To the extent that a formal BCA is appropriate for
making the CAA section 112(n)(1)(A) determination, however, that
approach demonstrates that the monetized benefits of MATS outweigh the
monetized costs by a considerable margin, whether we look at the 2012
record or our updated record. We therefore propose that it is
appropriate to regulate EGUs for HAP applying a BCA approach as well.
    In sum, the EPA proposes to conclude that it is appropriate and
necessary to regulate HAP emissions from coal- and oil-fired EGUs,
whether we are applying the preferred totality-of-the-circumstances
methodology or the alternative formal benefit-cost approach, and
whether we are considering only the administrative record as of the
original EPA response on remand to Michigan in 2016 or based on new
information made available since that time. The information and data
amassed by the EPA over the decades of administrative analysis and
rulemaking devoted to this topic overwhelmingly support the conclusion
that the advantages of regulating HAP emissions from coal- and oil-
fired EGUs outweigh the costs. The EPA requests comment on this
proposed finding and on the supporting information presented in this
proposal, including information related to the risks associated with
HAP emissions from U.S. EGUs and the actual costs incurred by the power
sector due to MATS, as well as on the

preferred and alternative methodologies for reaching the proposed
conclusion.

A. Public Health Hazards Associated With Emissions From EGUs

1. Overview
    The administrative record for the MATS rule detailed several
hazards to public health and the environment from HAP emitted by EGUs
that remained after imposition of the ARP and other CAA requirements.
See 80 FR 75028-29 (December 1, 2015). See also 65 FR 79825-31
(December 20, 2000); 76 FR 24976-25020 (May 3, 2011); 77 FR 9304-66
(February 16, 2012). The EPA considered all of this information again
in the 2016 Supplemental Finding, noting that this sector represented a
large fraction of U.S. emissions of mercury, non-mercury metal HAP, and
acid gases. Specifically, the EPA found that even after imposition of
the other requirements of the CAA, but absent MATS, EGUs remained the
largest domestic source of mercury, HF, HCl, and selenium and among the
largest domestic contributors of arsenic, chromium, cobalt, nickel,
hydrogen cyanide, beryllium, and cadmium, and that a significant
majority of EGU facilities emitted above the major source thresholds
for HAP emissions.
    Further, the EPA noted that the totality of risks that accrue from
these emissions were significant. These hazards include potential
neurodevelopmental impairment, increased cancer risks, contribution to
chronic and acute health disorders, as well as adverse impacts on the
environment. Specifically, the EPA pointed to results from its revised
nationwide Mercury Risk Assessment (contained in the 2011 Final Mercury
TSD) \26\ as well as an inhalation risk assessment (2011 Non-Hg HAP
Assessment) for non-mercury HAP (i.e., arsenic, nickel, chromium,
selenium, cadmium, HCl, HF, hydrogen cyanide, formaldehyde, benzene,
acetaldehyde, manganese, and lead). The EPA estimated lifetime cancer
risks for inhabitants near some coal- and oil-fired EGUs to exceed 1-
in-1 million \27\ and noted that this case-study-based estimate likely
underestimated the true maximum risks for the EGU source category. See
77 FR 9319 (February 16, 2012). The EPA also found that mercury
emissions pose a hazard to wildlife, adversely affecting fish-eating
birds and mammals, and that the large volume of acid gas HAP associated
with EGUs also pose a hazard to the environment.\28\ These technical
analyses were all challenged in the White Stallion case, and the D.C.
Circuit found that the EPA's risk finding as to mercury alone--that is,
before reaching any other risk finding--established a significant
public health concern. The court stated that ``EPA's `appropriate and
necessary' determination in 2000, and its reaffirmation of that
determination in 2012, are amply supported by EPA's finding regarding
the health effects of mercury exposure.'' White Stallion Energy Center
v. EPA, 748 F.3d 1222, 1245 (D.C. Cir. 2014). Additional scientific
evidence about the human health hazards associated with EGU HAP
emissions that has been collected since the 2016 Supplemental Finding
and is discussed in this section has extended our confidence that these
emissions pose an unacceptable risk to the American public and in
particular, to vulnerable, exposed populations.
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    \26\ U.S. EPA. 2011. Revised Technical Support Document:
National-Scale Assessment of Mercury Risk to Populations with High
Consumption of Self-caught Freshwater Fish In Support of the
Appropriate and Necessary Finding for Coal- and Oil-Fired Electric
Generating Units. Office of Air Quality Planning and Standards.
November. EPA-452/R-11-009. Docket ID Item No. EPA-HQ-OAR-2009-0234-
19913.
    \27\ The EPA determined the 1-in-1 million standard was the
correct metric in part because CAA section 112(c)(9)(B)(1) prohibits
the EPA from removing a source category from the list if even one
person is exposed to a lifetime cancer risk greater than 1-in-1
million, and CAA section 112(f)(2)(A) directs the EPA to conduct a
residual risk rulemaking if even one person is exposed to a lifetime
excess cancer risk greater than 1-in-1 million. See White Stallion
at 1235-36 (agreeing it was reasonable for the EPA to consider the
1-in-1 million delisting criteria in defining ``hazard to public
health'' under CAA section 112(n)(1)(A)).
    \28\ The EPA had determined it was reasonable to consider
environmental impacts of HAP emissions from EGUs in the appropriate
determination because CAA section 112 directs the EPA to consider
impacts of HAP emissions on the environment, including in the CAA
section 112(n)(1)(B) Mercury Study. See White Stallion at 1235-36
(agreeing it was reasonable for the EPA to consider the
environmental harms when making the appropriate and necessary
determination).
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    This section of the preamble starts by briefly reviewing the long-
standing and extensive body of evidence, including new scientific
information made available since the 2016 Supplemental Finding, which
demonstrates that HAP emissions from oil- and coal-fired EGUs present
hazards to public health and the environment warranting regulation
under CAA section 112 (section III.A.2). This is followed by an
expanded discussion of the health risks associated with domestic EGU
mercury emissions based on additional evidence regarding cardiovascular
effects that has become available since the 2016 Supplemental Finding
(section III.A.3). In section III.A.4, the EPA describes the reasons
why it is extremely difficult to estimate the full health and
environmental impacts associated with exposure to HAP. We note the
longstanding challenges associated with quantifying and monetizing
these effects, which may be permanent and life-threatening and are
often distributed unevenly (i.e., concentrated among highly exposed
individuals). Next, the section provides an expanded discussion of some
identified environmental justice (EJ) issues associated with these
emissions (section III.A.5). Section III.A.6 identifies health effects
associated with other, non-HAP emissions from EGUs such as
SO2, direct PM2.5 and other PM2.5 and
ozone precursors. Because these pollutants are co-emitted with HAP, the
controls necessary to reduce HAP emissions from EGUs often reduce these
pollutants as well. After assessing all the evidence, the EPA concludes
again (section III.A.7) that regulation of HAP emissions from EGUs
under CAA section 112 greatly improves public health for Americans by
reducing the risks of premature mortality from heart attacks, cancer,
and neurodevelopmental delays in children, and by helping to restore
economically vital ecosystems used for recreational and commercial
purposes. Further, we conclude that these public health improvements
will be particularly pronounced for certain segments of the American
population that are especially vulnerable (e.g., subsistence fishers
\29\ and their children) to impacts from EGU HAP emissions. In
addition, the concomitant reductions in co-emitted pollutants will also
provide substantial public health and environmental benefits.
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    \29\ Subsistence fishers, who by definition obtain a substantial
portion of their dietary needs from self-caught fish consumption,
can experience elevated levels of exposure to chemicals that
bioaccumulate in fish including, in particular, methylmercury.
Subsistence fishing activity can be related to a number of factors
including socio-economic status (poverty) and/or cultural practices,
with ethnic minorities and tribal populations often displaying
increased levels of self-caught fish consumption (Burger et al.,
2002, Shilling et al., 2010, Dellinger 2004).
    Burger J, (2002). Daily consumption of wild fish and game:
exposures of high end recreationalists. International Journal of
Environmental Health Research 12:4, p. 343-354.
    Shilling F, White A, Lippert L, Lubell M, (2010). Contaminated
fish consumption in California's Central Valley Delta. Environmental
Research 110, p. 334-344.
    Dellinger J, (2004). Exposure assessment and initial
intervention regarding fish consumption of tribal members in the
Upper Great Lakes Region in the United States. Environmental
Research 95, p. 325-340.
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2. Overview of Health Effects Associated With Mercury and Non-Mercury
HAP
    In calling for the Agency to consider the regulation of HAP from
EGUs, the

CAA stipulated that the EPA complete three studies (all of which were
extensively peer-reviewed) exploring various aspects of risk posed to
human health and the environment by HAP released from EGUs. The first
of these studies, the Utility Study, published in 1998, focused on the
hazards to public health specifically associated with EGU-sourced HAP
including, but not limited to, mercury. See CAA section 112(n)(1)(A). A
second study, the Mercury Study, released in 1997, while focusing
exclusively on mercury, was broader in scope including not only human
health, but also environmental impacts and specifically addressed the
potential for mercury released from multiple emissions sources (in
addition to EGUs) to affect human health and the environment. See CAA
section 112(n)(1)(B). The third study, required under CAA section
112(n)(1)(C), the NIEHS Study, submitted to Congress in 1995,
considered the threshold level of mercury exposure below which adverse
human health effects were not expected to occur. An additional fourth
study, the NAS Study, directed by Congress in 1999 and completed in
2000, focused on determining whether a threshold for mercury health
effects could be identified for sensitive populations and, as such,
presented a rigorous peer review of the EPA's RfD for methylmercury.
The aggregate results of these peer-reviewed studies commissioned by
Congress as part of CAA section 112(n)(1) supported the determination
that HAP emissions from EGUs represented a hazard to public health and
the environment that would not be addressed through imposition of the
other requirements of the CAA. In the 2 decades that followed, the EPA
has continued to conduct additional research and risk assessments and
has surveyed the latest science related to the risk posed to human
health and the environment by HAP released from EGUs.
a. Review of Health Effects and Previous Risk Analyses for
Methylmercury
    Mercury is a persistent and bioaccumulative toxic metal that, once
released from power plants into the ambient air, can be readily
transported and deposited to soil and aquatic environments where it is
transformed by microbial action into methylmercury. See Mercury Study;
76 FR 24976 (May 3, 2011) (2011 NESHAP Proposal); 80 FR 75029 (December
1, 2015) (2015 Proposal). Methylmercury bioaccumulates in the aquatic
food web eventually resulting in highly concentrated levels of
methylmercury within the larger and longer-living fish, which can then
be consumed by humans.\30\ As documented in both the NAS Study and the
Mercury Study, fish and seafood consumption is the primary route of
human exposure to methylmercury, with populations engaged in
subsistence-levels of consumption being of particular concern.\31\ The
NAS Study reviewed the effects of methylmercury on human health,
concluding that it is highly toxic to multiple human and animal organ
systems. Of particular concern is chronic prenatal exposure via
maternal consumption of foods containing methylmercury. Elevated
exposure has been associated with developmental neurotoxicity and
manifests as poor performance on neurobehavioral tests, particularly on
tests of attention, fine motor function, language, and visual-spatial
ability. Evidence also suggests potential for adverse effects on the
cardiovascular system, adult nervous system, and immune system, as well
as potential for causing cancer.\32\ Below we review the broad range of
public health hazards associated with methylmercury exposure.
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    \30\ We recognize that mercury deposition over land with
subsequent impacts to agricultural-sourced food may also represent a
public health concern, however as noted below, primary exposure to
the U.S. population is through fish consumption.
    \31\ In light of the methylmercury impacts, the EPA and the Food
and Drug Administration have collaborated to provide advice on
eating fish and shellfish as part of a healthy eating pattern
(https://www.fda.gov/food/consumers/advice-about-eating-fish). In
addition, states provide fish consumption advisories designed to
protect the public from eating fish from waterbodies within the
state that could harm their health based on local fish tissue
sampling.
    \32\ National Research Council. 2000. Toxicological Effects of
Methylmercury. Washington, DC: The National Academies Press. https://doi.org/10.17226/9899.
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    Neurodevelopmental Effects of Exposure to Methylmercury.
Methylmercury is a powerful neurotoxin. Because the impacts of the
neurodevelopmental effects of methylmercury are greatest during periods
of rapid brain development, developing fetuses and young children are
particularly vulnerable. Children born to populations with high fish
consumption (e.g., people consuming fish as a dietary staple) or
impaired nutritional status (e.g., people with iron or vitamin C
deficiencies) are especially vulnerable to adverse neurodevelopmental
outcomes. These dietary and nutritional vulnerabilities are often
particularly pronounced in underserved communities with minority
populations and low-income populations that have historically faced
economic and environmental injustice and are overburdened by cumulative
levels of pollution.\33\
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    \33\ Burger J, 2002. Daily consumption of wild fish and game:
Exposures of high end recreationalists. International Journal of
Environmental Health Research 12:4, p. 343-354.
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    Infants in the womb can be exposed to methylmercury when their
mothers eat fish and shellfish that contain methylmercury. This
exposure can adversely affect unborn infants' growing brains and
nervous systems. Children exposed to methylmercury while they are in
the womb can have impacts to their cognitive thinking, memory,
attention, language, fine motor skills, and visual spatial skills.
Based on scientific evidence reflecting concern about a range of
neurodevelopmental effects seen in children exposed in utero to
methylmercury, the EPA defined an RfD of 0.0001 mg/kg-day for
methylmercury.\34\ An RfD is defined as an estimate (with uncertainty
spanning perhaps an order of magnitude) of a daily exposure to the
human population (including sensitive subgroups) that is likely to be
without an appreciable risk of deleterious effects during a lifetime
(EPA, 2002).\35\
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    \34\ U.S. EPA. 2001. IRIS Summary for Methylmercury. U.S.
Environmental Protection Agency, Washington, DC. (USEPA, 2001).
    \35\ U.S. EPA. 2002. A Review of the Reference Dose and
Reference Concentration Processes. EPA/630/P-02/002F, December 2002.
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    Prenatal exposure to methylmercury from maternal consumption of
fish has been associated with several adverse neurodevelopmental
outcomes in various fish consuming populations. Although data are
limited, the EPA has focused on several subpopulations likely to be at
higher risk from methylmercury exposure associated with EGU HAP due to
fish consumption. As part of the 2011 Final Mercury TSD, the EPA
completed a national-scale risk assessment focused on mercury emissions
from domestic EGUs. Specifically, we examined risk associated with
mercury released from U.S. EGUs that deposits to watersheds within the
continental U.S., bioaccumulates in fish as methylmercury, and is
consumed when fish are eaten by female subsistence fishers of child-
bearing age and other freshwater self-caught fish consumers. There is
increased risk for in utero exposure and adverse outcomes in children
born to female subsistence fishers with elevated exposure to
methylmercury. The risk assessment modeled scenarios representing high-
end self-caught fish consumers active at inland freshwater lakes and
streams. The analysis estimated that 29 percent of the watersheds
studied would lead to

female subsistence fishers having exposures which exceeded the
methylmercury RfD, based on in utero effects, due in whole or in part
to the contribution of domestic EGU emissions of mercury. This included
up to 10 percent of modeled watersheds where deposition from U.S. EGUs
alone leads to potential exposures that exceed the RfD.\36\
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    \36\ The EPA chose this risk metric in part because CAA section
112(n)(1)(C) directed the NIEHS to develop a threshold for mercury
concentration in fish tissue that can be consumed by even sensitive
populations without adverse effect and because CAA section 112(c)(6)
demonstrates a special interest in protecting the public from
exposure to mercury.
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    In addition to the 2011 Final Mercury TSD focusing on subsistence
fishers referenced above, the EPA also completed a RIA in 2011
including the characterization of benefits associated with the
prospective reduction of U.S. EGU mercury emissions under MATS.\37\
However, due to limitations on the available data with regard to the
extent of subsistence fishing activity in the U.S., which prevented the
enumeration of subsistence fisher populations, the EPA was unable to
develop a quantitative estimate of the reduction in population-level
risk or associated dollar benefits for children of female subsistence
fishers. Instead, in the 2011 MATS RIA, the EPA focused on a different
population of self-caught fish consumers that could be enumerated.
Specifically, we quantitatively estimated the amount and value of IQ
loss associated with prenatal methylmercury exposure among the children
of recreational anglers consuming self-caught fish from inland
freshwater lakes, streams and rivers (unlike subsistence fishers,
available data allow the characterization of recreational fishing
activity across the U.S. including enumeration of these populations).
Although the EPA acknowledged uncertainty about the size of the
affected population and acknowledged that it could be underestimated,
these unborn children associated with recreational anglers represented
precisely the type of sensitive population most at risk from mercury
exposure that CAA section 112 is designed to protect. The results
generated in the 2011 RIA for recreational anglers suggested that by
reducing methylmercury exposure, MATS was estimated to yield an
additional 511 IQ points among the affected population of children,
which would increase their future lifetime earnings. The EPA noted at
the time that the analysis likely underestimated potential benefits for
children of recreational anglers since, due to data limitations, it did
not cover consumption of recreationally caught seafood from estuaries,
coastal waters, and the deep ocean which was expected to contribute
significantly to overall exposure. Nevertheless, this single endpoint
alone, evaluated solely for the recreational angler, provides evidence
of potentially significant health harm from methylmercury exposure.
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    \37\ The 2011 MATS RfD-based risk assessment focusing on the
subsistence fisher population was designed as a screening-level
analysis to inform consideration for whether U.S. EGU-sourced
mercury represented a public health hazard. As such, the most
appropriate risk metric was modeled exposure (for highly-exposed
subsistence fishers) compared to the RfD for methylmercury. By
contrast, the 2011 RIA was focused on estimating the dollar benefits
associated with MATS and as such focused on a health endpoint which
could be readily enumerated and then monetized, which at the time
was IQ for infants born to recreational anglers.
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    In 2011 we noted that other, more difficult to quantify endpoints
may also contribute to the overall burden across a broader range of
subgroups. The metrics studied in addition to IQ include those measured
by performance on neurobehavioral tests, particularly on tests of
attention, fine motor-function, language, and visual spatial ability
(USEPA, 2001; Agency for Toxic Substances and Disease Registry (ATSDR),
1999).\38\ Such adverse neurodevelopmental effects are well documented
in cohorts of subsistence fisher populations (i.e., Faroe Islands and
the Nunavik region of Arctic Canada).
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    \38\ Agency for Toxic Substances and Disease Registry (ATSDR).
1999. Toxicological profile for mercury. Atlanta, GA: U.S.
Department of Health and Human Services, Public Health Service.
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    At this time, the EPA is conducting an updated methylmercury IRIS
assessment and recently released preliminary assessment materials, an
IRIS Assessment Plan (IAP) and Systematic Review Protocol for
methylmercury.\39\ The update to the methylmercury IRIS assessment will
focus on updating the quantitative aspects of neurodevelopmental
outcomes associated with methylmercury exposure. As noted in these
early assessment materials, new studies are available, since 2001,
assessing the effects of methylmercury exposure on cognitive function,
motor function, behavioral, structural, and electrophysiological
outcomes at various ages following prenatal or postnatal exposure to
methylmercury (USEPA, 2001; NAS Study; 84 FR 13286 (April 4, 2019);
\40\ 85 FR 32037 (May 8, 2020)).\41\
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    \39\ https://iris.epa.gov/ChemicalLanding/&substance_nmbr=73.
    \40\ Availability of the IRIS Assessment Plan for Methylmercury.
84 FR 13286 (April 4, 2019).
    \41\ Availability of the Systematic Review Protocol for the
Methylmercury Integrated Risk Information System (IRIS) Assessment.
85 FR 32037 (May 28, 2020).
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    Cardiovascular Impacts of Exposure to Methylmercury. The NAS Study