[Federal Register Volume 88, Number 140 (Monday, July 24, 2023)]
[Proposed Rules]
[Pages 47415-47437]
[FR Doc No: 2023-15303]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2020-0430; FRL-7522-04-OAR]
RIN 2060-AU63

National Emission Standards for Hazardous Air Pollutants: Primary
Copper Smelting

AGENCY: Environmental Protection Agency (EPA).

ACTION: Supplemental notice of proposed rulemaking.

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SUMMARY: This action supplements our proposed amendments to the
national emission standards for hazardous air pollutants (NESHAP) for
the Primary Copper Smelting source category published in the Federal
Register on January 11, 2022. In that action, the Environmental
Protection Agency (EPA) proposed amendments based on the residual risk
and technology review (RTR) for the major source category and the
technology review for the area source category. Although the proposal
included the technology review for the area source category, this
supplemental proposal does not include any changes for the area source
category. In order to complete the required technology review for the
major source category, the EPA is proposing additional hazardous air
pollutant (HAP) standards for the following pollutants: benzene,
toluene, hydrogen chloride (HCl), chlorine, polycyclic aromatic
hydrocarbons (PAH), naphthalene and dioxin/furans (D/F). The EPA also
evaluated the potential for changes to the previously proposed residual
risk assessment and the decisions related to risk. Furthermore, in this
action the EPA is also proposing revised standards for certain
provisions initially proposed in the January 11, 2022, RTR proposal
based on additional information gathered since the publication of the
2022 proposed rule.

DATES: Comments must be received on or before September 7, 2023. Under
the Paperwork Reduction Act (PRA), comments on the information
collection provisions are best assured of consideration if the Office
of Management and Budget (OMB) receives a copy of your comments on or
before August 23, 2023.
    Public hearing: If anyone contacts us requesting a public hearing
on or before July 31, 2023, we will hold a virtual public hearing. See
SUPPLEMENTARY INFORMATION for information on requesting and registering
for a public hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2020-0430, 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-2020-0430 in the subject line of the message.
     Fax:<PHONE_NUMBER>. Attention Docket ID No. EPA-HQ-OAR-
2020-0430.
     Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2020-0430, 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.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Tonisha Dawson, Sector Policies and Programs Division
(D243-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; and email address:
[email protected].

SUPPLEMENTARY INFORMATION:

    Participation in virtual public hearing. To request a virtual
public hearing, contact the public hearing team at<PHONE_NUMBER> or by
email at [email protected]. If requested, the hearing will be
held via virtual platform on August 8, 2023. The hearing will convene
at 11 a.m. Eastern Time (ET) and will conclude at 3 p.m. ET. The EPA
may close a session 15 minutes after the last pre-registered speaker
has testified if there are no additional speakers. The EPA will
announce further details at https://www.epa.gov/stationary-sources-air-pollution/primary-copper-smelting-national-emissions-standards-hazardous-air.
    If a public hearing is requested, the EPA will begin pre-
registering speakers for the hearing no later than 1 business day after
a request has been received. To register to speak at the virtual
hearing, please use the online registration form available at https://www.epa.gov/stationary-sources-air-pollution/primary-copper-smelting-national-emissions-standards-hazardous-air 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 August 7, 2023. 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/primary-copper-smelting-national-emissions-standards-hazardous-air.
    The EPA will make every effort to follow the schedule as closely as
possible on the day of the hearing; however, please plan for the
hearings to run either ahead of schedule or behind schedule.
    Each commenter will have 4 minutes to provide oral testimony. The
EPA encourages commenters to 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/primary-copper-smelting-national-emissions-standards-hazardous-air. 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 special
accommodation such as audio description, please pre-register for the
hearing with the public hearing team and describe your needs by July
31, 2023. 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-2020-0430. 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 Regulations.gov.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2020-0430. 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 to https://www.regulations.gov/
any information that you consider to be CBI or other information whose
disclosure is restricted by statute. This type of information should be
submitted 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.
    Submitting CBI. Do not submit information containing CBI to the EPA
through https://www.regulations.gov/. Clearly mark the part or all of
the information that you claim to be CBI. For CBI information on any
digital storage media that you mail to the EPA, note the docket ID,
mark the outside of the digital storage media as CBI, and identify
electronically within the digital storage media the specific
information that is claimed as CBI. In addition to one complete version
of the comments that includes information claimed as CBI, you must
submit a copy of the comments that does not contain the information
claimed as CBI directly to the public docket through the procedures
outlined in 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 and note the docket ID.
Information not marked as CBI will be included in the public docket and
the EPA's electronic public docket without prior notice. Information
marked as CBI will not be disclosed except in accordance with
procedures set forth in 40 Code of Federal Regulations (CFR) part 2.
    Our preferred method to receive CBI is for it to be transmitted
electronically using email attachments, File Transfer Protocol (FTP),
or other online file sharing services (e.g., Dropbox, OneDrive, Google
Drive). Electronic submissions must be transmitted

directly to the OAQPS CBI Office at the email address [email protected],
and as described above, should include clear CBI markings and note the
docket ID. If assistance is needed with submitting large electronic
files that exceed the file size limit for email attachments, and if you
do not have your own file sharing service, please email
[email protected] to request a file transfer link. If sending CBI
information through the postal service, please send it to the following
address: OAQPS Document Control Officer (C404-02), OAQPS, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711, Attention Docket ID No. EPA-HQ-OAR-2020-0430. The mailed CBI
material should be double wrapped and clearly marked. Any CBI markings
should not show through the outer envelope.
    Preamble acronyms and abbreviations. Throughout this preamble the
use of ``we,'' ``us,'' or ``our'' is intended to refer to the EPA. We
use multiple acronyms and terms in this preamble. While this list may
not be exhaustive, to ease the reading of this preamble and for
reference purposes, the EPA defines the following terms and acronyms
here:

ACI activated carbon injection
ADEQ Arizona Department of Environmental Quality
ADL above detection limit
ANSI American National Standards Institute
BDL below detection limit
BTF beyond-the-floor
CAA Clean Air Act
CBI Confidential Business Information
CFR Code of Federal Regulations
D/F dioxins and furans
DLL detection level limited
DSI dry sorbent injection
EPA Environmental Protection Agency
GACT generally available control technology
HAP hazardous air pollutant(s)
HCl hydrogen chloride
ICR Information Collection Request
km kilometers
lbs pounds
lbs/hr pounds per hour
lb/ton pounds per ton
LEAN Louisiana Environmental Action Network
MACT maximum achievable control technology
MIR maximum individual risk
mg/dscm milligram per dry standard cubic meter
NAICS North American Industry Classification System
NESHAP national emission standards for hazardous air pollutants
ng TEQ/Mg nanograms Toxic Equivalent per megagrams
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PAH polycyclic aromatic hydrocarbons
PM particulate matter
PRA Paperwork Reduction Act
RDL representative detection level
RFA Regulatory Flexibility Act
RTR risk and technology review
SO2 sulfur dioxide
SO3 sulfur trioxide
SSM startup, shutdown, and malfunction
TEF toxicity equivalence factors
TEQ toxic equivalency
THC Total hydrocarbons
tpy tons per year
ug/m\3\ micrograms per cubic meter
UMRA Unfunded Mandates Reform Act
UOM unit of measure
UPL upper predictive level
VCS voluntary consensus standards
WESP wet electrostatic precipitator

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

I. General Information
    A. Does this action apply to me?
    B. Where can I get a copy of this document and other related
information?
II. Background
    A. What is the statutory authority for this action?
    B. What is this source category and how does the current NESHAP
regulate its HAP emissions?
    C. What is the history of the Primary Copper Smelting Risk and
Technology Review?
    D. What was included in the 2022 proposed RTR affecting major
sources in the primary copper smelting source category?
    E. What data collection activities were conducted to support
this action?
III. Analytical Results and Proposed Decisions
    A. What are the results of our analyses of unregulated
pollutants and how did we establish the proposed MACT standards?
    B. What performance testing, monitoring, and recordkeeping and
reporting are we proposing relative to the unregulated HAP emission
limits?
    C. What revisions are we proposing specific to the emission
limit for process fugitive emissions from roof vents at the anode
refining operations from the 2022 proposed RTR?
    D. What revisions are we proposing specific to the emission
limit for mercury from the 2022 proposed RTR?
    E. What emissions standards are we proposing for the Aisle
Scrubber in this supplemental proposed rule that are different than
decisions proposed in the 2022 proposed RTR?
    F. What are the results of risk analyses completed for this
action?
    G. What other actions are we proposing, and what is the
rationale for those actions?
    H. What compliance dates are we proposing and what is the
rationale for the proposed compliance dates?
IV. Summary of Cost, Environmental, and Economic Impacts
    A. What are the affected sources?
    B. What are the air quality impacts?
    C. What are the cost impacts?
    D. What are the economic impacts?
    E. What are the benefits?
    F. What analysis of environmental justice did we conduct?
V. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 14094: Modernizing 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) and
1 CFR Part 51
    J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. General Information

A. Does this action apply to me?

    The source category that is the subject of this proposal is primary
copper smelting major sources regulated under 40 CFR part 63, subpart
QQQ. The North American Industry Classification System (NAICS) code for
the primary copper smelting industry is 331410. This list of categories
and 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. The proposed standards, once promulgated, will be
directly applicable to the affected sources. Federal, state, local, and
tribal government entities would not be affected by this proposed
action. As defined in the Initial List of Categories of Sources Under
Section 112(c)(1) of the Clean Air Act Amendments of 1990 (see 57 FR
31576; July 16, 1992) and Documentation for Developing the Initial
Source Category List, Final Report (see EPA-450/3-91-030, July 1992),
the primary copper smelting source category is any major source
facility engaged in the pyrometallurgical process used for the
extraction of copper from sulfur oxides, native ore concentrates, or
other copper bearing minerals. As originally defined, the category
includes, but is not limited to, the following smelting process units:
roasters, smelting furnaces, and converters. Affected sources under the
current major source NESHAP are

concentrate dryers, smelting furnaces, slag cleaning vessels,
converters, and fugitive emission sources.

B. 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/primary-copper-smelting-national-emissions-standards-hazardous-air. 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.
    A memorandum showing the rule edits that would be necessary to
incorporate the changes to 40 CFR part 63, subpart QQQ proposed in this
action is available in the docket (Docket ID No. EPA-HQ-OAR-2020-0430).
The EPA also will post a copy of this document to https://www.epa.gov/stationary-sources-air-pollution/primary-copper-smelting-national-emissions-standards-hazardous-air.

II. Background

A. What is the statutory authority for this action?

    The statutory authority for this action is provided by sections 112
and 301 of the Clean Air Act (CAA), as amended (42 U.S.C. 7401 et
seq.). Section 112 of the CAA establishes a two-stage regulatory
process to develop standards for emissions of HAP from stationary
sources. Generally, the first stage involves establishing technology-
based standards and the second stage involves evaluating those
standards that are based on maximum achievable control technology
(MACT) to determine whether additional standards are needed to address
any remaining risk associated with HAP emissions. This second stage is
commonly referred to as the ``residual risk review.'' In addition to
the residual risk review, the CAA also requires the EPA to review
standards set under CAA section 112 every 8 years and revise the
standards as necessary taking into account any ``developments in
practices, processes, or control technologies.'' This review is
commonly referred to as the ``technology review.'' The discussion that
follows identifies the most relevant statutory sections and briefly
explains the contours of the methodology used to implement these
statutory requirements. A more comprehensive discussion appears in the
document titled CAA Section 112 Risk and Technology Reviews: Statutory
Authority and Methodology, in the docket for this rulemaking.
    In the first stage of the CAA section 112 standard setting process,
the EPA promulgates technology-based standards under CAA section 112(d)
for categories of sources identified as emitting one or more of the HAP
listed in CAA section 112(b). Sources of HAP emissions are either major
sources or area sources, and CAA section 112 establishes different
requirements for major source standards and area source standards.
``Major sources'' are those that emit or have the potential to emit 10
tons per year (tpy) or more of a single HAP or 25 tpy or more of any
combination of HAP. All other sources are ``area sources.'' For major
sources, CAA section 112(d)(2) provides that the technology-based
NESHAP must reflect the maximum degree of emission reductions of HAP
achievable (after considering cost, energy requirements, and non-air
quality health and environmental impacts). These standards are commonly
referred to as MACT standards. CAA section 112(d)(3) also establishes a
minimum control level for MACT standards, known as the MACT ``floor.''
In certain instances, as provided in CAA section 112(h), the EPA may
set work practice standards in lieu of numerical emission standards.
The EPA must also consider control options that are more stringent than
the floor. Standards more stringent than the floor are commonly
referred to as beyond-the-floor (BTF) standards. For area sources, CAA
section 112(d)(5) allows the EPA to set standards based on generally
available control technologies or management practices (GACT standards)
in lieu of MACT standards.
    The second stage in standard-setting focuses on identifying and
addressing any remaining (i.e., ``residual'') risk pursuant to CAA
section 112(f). For source categories subject to MACT standards,
section 112(f)(2) of the CAA requires the EPA to determine whether
promulgation of additional standards is needed to provide an ample
margin of safety to protect public health or to prevent an adverse
environmental effect. Section 112(d)(5) of the CAA provides that this
residual risk review is not required for categories of area sources
subject to GACT standards. Section 112(f)(2)(B) of the CAA further
expressly preserves the EPA's use of the two-step approach for
developing standards to address any residual risk and the Agency's
interpretation of ``ample margin of safety'' developed in the 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). The EPA
notified Congress in the Residual Risk Report that the Agency intended
to use the Benzene NESHAP approach in making CAA section 112(f)
residual risk determinations (EPA-453/R-99-001, p. ES-11). The EPA
subsequently adopted this approach in its residual risk determinations,
and the United States Court of Appeals for the District of Columbia
Circuit upheld the EPA's interpretation that CAA section 112(f)(2)
incorporates the approach established in the Benzene NESHAP. See NRDC
v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008).
    The approach incorporated into the CAA and used by the EPA to
evaluate residual risk and to develop standards under CAA section
112(f)(2) is a two-step approach. In the first step, the EPA determines
whether risks are acceptable. This determination ``considers all health
information, including risk estimation uncertainty, and includes a
presumptive limit on maximum individual lifetime [cancer] risk (MIR)
\1\ of approximately 1-in-10 thousand.'' (54 FR at 38045). If risk is
unacceptable, the EPA must determine the emissions standards necessary
to reduce risks to an acceptable level without considering costs. In
the second step of the approach, the EPA considers whether the
emissions standards provide an ample margin of safety to protect public
health ``in consideration of all health information, including the
number of persons at risk levels higher than approximately 1-in-1
million, as well as other relevant factors, including costs and
economic impacts, technological feasibility, and other factors relevant
to each particular decision.'' Id. The EPA must promulgate emission
standards necessary to provide an ample margin of safety to protect
public health or determine that the standards being reviewed provide an
ample margin of safety without any revisions. After conducting the
ample margin of safety analysis, the Agency considers whether a more
stringent standard is necessary to prevent, taking into consideration
costs, energy, safety, and other relevant factors, an adverse
environmental effect.
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    \1\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk if an individual were exposed to the maximum
level of a pollutant for a lifetime.
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    CAA section 112(d)(6) separately requires the EPA to review
standards

promulgated under CAA section 112 and revise them ``as necessary
(taking into account developments in practices, processes, and control
technologies)'' no less often than every 8 years. While conducting this
review, which we call the ``technology review,'' the EPA is not
required to recalculate the MACT floor. Natural Resources Defense
Council (NRDC) v. EPA, 529 F.3d 1077, 1084 (D.C. Cir. 2008).
Association of Battery Recyclers, Inc. v. EPA, 716 F.3d 667 (D.C. Cir.
2013). The EPA may consider cost in deciding whether to revise the
standards pursuant to CAA section 112(d)(6). The EPA is also required
to address regulatory gaps, such as missing standards for listed air
toxics known to be emitted from the source category, and any new MACT
standards must be established under CAA sections 112(d)(2) and (3), or,
in specific circumstances, CAA sections 112(d)(4) or (h). Louisiana
Environmental Action Network (LEAN) v. EPA, 955 F.3d 1088 (D.C. Cir.
2020).
    As described in detail in section III of this preamble, pursuant to
the authorities described above in this section, this supplemental
proposed rule addresses additional currently unregulated emissions of
HAP from the primary copper smelting major source category. In addition
to the unregulated HAP addressed in the 2022 RTR proposed rule (87 FR
1616; January 11, 2022), available data indicate the following
unregulated pollutants are emitted from the source category: benzene,
dioxins and furans, HCl, chlorine, PAH including naphthalene, and
toluene. These pollutants are mainly emitted due to the combustion of
natural gas and coke. Therefore, the EPA is proposing amendments
establishing standards that reflect MACT for these pollutants emitted
by the source category, pursuant to CAA sections 112(d)(2) and (3).

B. What is this source category and how does the current NESHAP
regulate its HAP emissions?

    Consistent with the description in section II.A. of this preamble,
this supplemental proposal is applicable to major sources in the
primary copper smelting major source category. There is one area source
which is regulated by the primary copper smelting area source NESHAP
(40 CFR part 63, subpart EEEEEE), but the following description is
limited to the major source facilities consistent with this
supplemental proposed rule. The primary copper smelting major source
category includes any facility that is a major source of HAP and uses a
pyrometallurgical process to produce anode copper from copper ore
concentrates. Primary copper smelting begins with copper mines
supplying the ore concentrate (typically 30 percent copper). In most
cases, the moisture is reduced from the ore concentrate in dryers, and
the concentrate is then fed through a smelting furnace where it is
melted and reacts to produce copper matte. One existing smelter is able
to feed its copper concentrate directly to the smelting furnace without
prior drying. Copper matte is a molten solution of copper sulfide mixed
with iron sulfide and is about 60 percent copper. The solution is
further refined using converters to make blister copper, which is
approximately 98 percent copper. Converters use oxidation to remove
sulfide as sulfur dioxide (SO2) gas and the iron as a
ferrous oxide slag. The majority of the SO2 gases are sent
to a sulfuric acid plant. The slag is removed, cooled, and often
processed again to remove any residual copper. The blister copper is
reduced in the anode refining furnace to remove impurities and oxygen,
typically by injecting natural gas and steam, to produce a high purity
copper. The molten copper from the anode refining furnace is poured
into molds and cooled to produce solid copper ingots called anodes.
This process is known as casting. The anodes are sent to a copper
refinery, either on-site or at an off-site location, for further
purification using an electrolytic process to obtain high purity copper
that is sold as a product. The processing units of interest at primary
copper smelters, because of their potential to generate HAP emissions,
are the following: dryers, smelting furnaces, copper converters, anode
refining furnaces, and, if present, copper holding vessels, slag
cleaning vessels, and matte drying and grinding plants. The smelting
furnaces, converters and anode refining are sources of HAP emissions
from point sources (i.e., stacks, control devices) and process fugitive
emissions from roof vents. In addition, the transfers of matte,
converter slag, and blister copper are sources of process fugitive
emissions.
    There are two facilities (Asarco and Freeport--both located in
Arizona) which are major sources of HAP emissions and are subject to 40
CFR part 63, subpart QQQ, the major source NESHAP. The Asarco facility
uses an INCO brand flash smelting furnace. Flash smelting furnaces
consist of blowing fine, dried copper sulfide concentrate and silica
flux with air, oxygen-enriched air or oxygen into a hot hearth-type
furnace. The sulfide minerals in the concentrate react with oxygen
resulting in oxidation of the iron and sulfur, which produces heat and
therefore melting of the solids. The molten matte and slag are removed
separately from the furnace as they accumulate, and the matte is
transferred via ladles to the copper converters. The Freeport facility
uses an ISASMELT smelting furnace. The ISASMELT process involves
dropping wet feed through a feed port, such that dryers are not needed.
A mixture of air, oxygen, and natural gas is blown through a vertical
lance in the center of the furnace, generating heat and melting the
feed. The molten metal is then tapped from the bottom and sent to an
electric furnace to separate the matte from slag. The slag is removed
from the electric furnace through tapholes and is transferred to slag
pots via ladles. The matte is also removed from the electric furnace
through tapholes and transferred to the converter via ladles.
    Molten blister copper is transferred from the converting vessel to
an anode furnace for refining to further remove residual impurities and
oxygen. The blister copper is reduced in the anode refining furnace to
remove oxygen, typically by injecting natural gas and steam to produce
a high purity copper. The molten copper from the anode refining furnace
is poured into molds to produce solid copper ingots called anodes. The
anode copper is sent to a copper refinery, either on-site or at another
location, where it is further purified using an electrolytic process to
obtain the high purity copper that is sold as a product. The copper
refinery is not part of the primary copper smelting source category.
The current NESHAP for major sources (40 CFR part 63, subpart QQQ) was
proposed on April 20, 1998 (63 FR 19582), with a supplement to the
proposed rulemaking published on June 26, 2000 (65 FR 39326). The final
rule, promulgated on June 12, 2002 (67 FR 40478), established
particulate matter (PM) standards as a surrogate for HAP metals for
copper concentrate dryers, smelting furnaces, slag cleaning vessels,
and existing converters. The major source NESHAP applies to major
sources that use batch copper converters. Regarding new sources, the
NESHAP prohibits batch converters for new sources, which indirectly
means that any new source would need to install continuous converters
or another technology. The reason for this prohibition for new sources
is that continuous converters have lower process fugitive emissions
than batch converters. Further explanation is provided in the 2002

NESHAP final rule preamble (67 FR 40478; June 12, 2002).
    The converter building is subject to an opacity limit in the NESHAP
that only applies during performance testing. A fugitive dust plan is
required to minimize fugitive dust emissions. Subpart QQQ also
establishes requirements to demonstrate initial and continuous
compliance with all applicable emission limitations, work practice
standards, and operation and maintenance requirements. Annual
performance testing is required to demonstrate compliance with the PM
and opacity standards contained in the current NESHAP.

C. What is the history of the Primary Copper Smelting Risk and
Technology Review?

    On January 11, 2022, the EPA proposed the risk and technology
review required by CAA sections 112(d)(6) and 112(f)(2) for the NESHAP
for Copper Smelting (hereafter referred to as the ``2022 proposed
RTR'').\2\ Since the issuance of the 2022 proposed RTR, the EPA has
obtained additional information that impacts the decisions made for
certain amendments in the 2022 proposed RTR and that indicates there
are additional unregulated HAP for the source category. Therefore,
based on this new information, the EPA is proposing supplemental
amendments to the NESHAP to ensure that all emissions of HAP from
sources in the source category are regulated. Additionally, based on
this new information and as described in more detail in section III of
this preamble, we are proposing revised standards for certain
amendments that were initially included in the 2022 proposed RTR for
the copper smelting major source category.
---------------------------------------------------------------------------

    \2\ 87 FR 1616; January 11, 2022.
---------------------------------------------------------------------------

D. What was included in the 2022 proposed RTR affecting major sources
in the primary copper smelting source category?

    Consistent with the statutory requirements described in section
II.A of this preamble, the 2022 proposed RTR included a risk review
pursuant to CAA section 112(f)(2) and a technology review pursuant to
CAA section 112(d)(6) for the major source category. Additionally, the
Agency reviewed available data to determine whether there were any
unregulated emissions of HAP within the source category and evaluated
the data for use in developing new emission standards.
    As described in the 2022 proposed RTR, as part of the technology
review for the major source category, the EPA identified previously
unregulated processes and pollutants and proposed to regulate them
under CAA section 112(d)(2) and (3) for the major source NESHAP (40 CFR
part 63, subpart QQQ), as follows:
     PM limits, as a surrogate for metal HAP, for anode
refining point sources at existing and new sources.
     PM limits, as a surrogate for metal HAP, for process
fugitive emissions from roofline vents of smelting furnaces at existing
and new sources.
     PM limits, as a surrogate for metal HAP, for process
fugitive emissions from converters at existing and new sources.
     PM limits, as a surrogate for metal HAP, for process
fugitive emissions from roof vents at anode refining operations at
existing and new sources.
     Mercury limits for any existing and new combination of
stacks or other vents from the copper concentrate dryers, converting
department, the anode refining department, and the smelting vessels
affected sources.
     PM limits, as a surrogate for metal HAP, for new
converters.
    The Agency also completed a review of residual risk for the source
category consistent with CAA section 112(f). Based on the results of
the risk review, the EPA proposed that risks from emissions of air
toxics from the major source category were unacceptable due to HAP
metal (primarily lead and arsenic) emissions. The largest contributor
to risk was the process fugitive emissions from roof vents at anode
refining operations (constituting about 71 percent of the MIR) followed
by the aisle scrubber (constituting about 23 percent of the MIR) at the
Freeport facility. In the 2022 proposed RTR, the EPA concluded that the
emission limits proposed under CAA section 112(d)(2) and (3) for the
process fugitive emissions from roof vents at anode refining operations
will require additional controls that are expected to provide enough
emissions reduction to reduce risks to an acceptable level; therefore,
they were also proposed pursuant to CAA section 112(f)(2). The Agency
also considered proposing additional control requirements for the aisle
scrubber as part of the Agency's ample margin of safety analysis. The
EPA did not propose any control requirements for the aisle scrubber in
the 2022 proposed RTR but did seek comment on its analysis (including
the costs, costs effectiveness, and risk reductions) and whether the
EPA should establish more stringent standards to reduce HAP metal
emissions from the aisle scrubber. Also, as part of the ample margin of
safety analysis, the EPA evaluated additional work practices to reduce
fugitive dust emissions, consistent with Asarco's current consent
decree. The Agency found that the implementation of a more robust
fugitive dust plan would result in an unquantified reduction of HAP, at
minimal cost for implementation, and therefore proposed this
requirement in the 2022 proposed RTR. In the 2022 proposed RTR, the EPA
proposed that the combination of the standards for anode refining roof
vents, fugitive dust plan and all other current standards in the NESHAP
would ensure the NESHAP provides an ample margin of safety to protect
public health.
    The EPA did not identify developments in practices, processes, or
control technologies pursuant to CAA section 112(d)(6) to achieve
further emissions reductions beyond the controls and reductions
proposed under the risk review for major sources.
    The EPA also proposed to remove exemptions for periods of startup,
shutdown, and malfunction (SSM) and specified that the emission
standards apply at all times and proposed a requirement for electronic
reporting of performance test results and notification of compliance
reports.
    Of central relevance to this supplemental proposal are the proposed
emission limits for the process fugitive emissions from roof vents at
anode refining operations at new and existing sources; the mercury
limits for any existing and new combination of stacks or other vents
from the copper concentrate dryers, converting department, the anode
refining department, and the smelting vessels affected sources; the
potential control options for metal HAP at the aisle scrubber; and the
proposed MACT limits for additional unregulated HAP. As detailed in the
next section II.E of this preamble, the EPA has obtained additional
information relative to these processes and pollutants. As a result of
evaluating this new information, we are proposing both revised and new
requirements in this supplemental proposed rulemaking (compared to the
proposed requirements in the 2022 proposed RTR) for these processes and
pollutants. A detailed discussion is provided in section III of this
preamble, which covers what was proposed for these processes and
pollutants in the 2022 proposed RTR, the evaluation of new information,
and what we are proposing for these processes and pollutants in this
supplemental proposed rulemaking.

E. What data collection activities were conducted to support this
action?

    The 2022 proposed RTR was published in the Federal Register on
January 11, 2022 (87 FR 1616). The initial 45-day comment period was
extended by 60 days and ended on April 26, 2022. During the comment
period, the EPA received public comments from industry, tribal nations,
two environmental groups, Arizona Department of Environmental Quality
(ADEQ), and private citizens. Some of the comments on the proposed
rulemaking claimed that there are additional unregulated HAP from the
source category beyond those the EPA addressed in the 2022 proposed
RTR. In response to these public comments, the EPA issued a CAA section
114 information request to collect further information. The section 114
information request was sent to the Freeport facility only, as the
Asarco facility has been idled since October 2019. The section 114
information request was delivered to the Freeport facility on August
31, 2022. The key components of the response to the request included
the following:
     Results of performance testing which was required to be
conducted in two phases. Initially, performance tests were conducted at
the vent fume and aisle scrubber stacks of the Freeport facility for
the following compounds: benzene, 1,4-dichlorobenzene, formaldehyde,
hexane, hydrogen fluoride, hydrochloric acid, toluene, total
hydrocarbons, polycyclic aromatic hydrocarbons including naphthalene,
and dioxins and furans. For compounds that were detected at the vent
fume and aisle scrubber, additional performance testing and reporting
were required to be conducted at the acid plant tail gas stack. The
Agency did not request chlorine testing; however, chlorine test results
were included in respective test reports.
     Data regarding the costs and feasibility of installing
additional controls for the aisle scrubber. This included the
evaluation of two options: (1) installing a wet electrostatic
precipitator (WESP) which would operate in series with the aisle
scrubber to provide further emissions reductions, and (2) installing a
baghouse which would control the secondary converter emissions before
they enter the aisle scrubber.
     Detailed information regarding all input materials.
    In addition to the information collected through the section 114
information request, the EPA also received information during and after
the public comment period of the 2022 proposed RTR. This additional
information included cost estimates for the control devices which would
be required by the emission limits proposed in the 2022 proposed RTR
(e.g., for mercury, lead and arsenic). It also included additional
performance testing results for the roofline vents, vent fume, aisle
scrubber, and acid plant. Finally, Freeport also voluntarily performed
an additional performance test for mercury in 2022 and submitted those
results to the EPA. The data collected and used in this action are
provided in the docket for this action.
    Regarding the anode roofline vents, we received one additional
stack test that resulted in a small increase to the annual emissions of
lead, which we now estimate to be 4.47 tons/yr, relative to the
estimate in the 2022 proposed rule, which was 4.09 tons/yr. For
mercury, based on the additional mercury test, we now estimate mercury
emissions from point and non-point sources at the Freeport facility to
be 139 lb/yr, while the Asarco mercury emissions are unchanged from the
2022 Proposed RTR (10 lb/yr). Finally, we received two new stack tests
for the aisle scrubber at the Freeport facility, and based on these new
test data, the estimates of PM metals emissions from the aisle scrubber
are slightly lower compared to the 2022 proposed RTR, but only have a
small effect on the overall risk assessment results. Nevertheless, we
updated our risk analysis based on the additional data and concluded
that the new data would not change our proposed determination that risk
is unacceptable at baseline. We did not revise or redo the demographic
analysis. The 2022 risk assessment and demographics analyses conducted
for this action are available in the preamble of the 2022 proposed rule
(87 FR 1616; January 11, 2022) and associated technical documents cited
in that 2022 preamble. These documents can also be found in the docket
of this supplemental proposal. Aspects of the updated risk review are
summarized in sections III.C. and II.E of this preamble, and a more
detailed discussion is provided in section III.F of this preamble.

III. Analytical Results and Proposed Decisions

    In this section, the EPA describes the analytical results and
proposed decisions for addressing the additional unregulated HAP for
the major source category. Additionally, this section discusses
analytical results and revised decisions for certain provisions of the
2022 proposed RTR. For more information regarding the types of
analytical procedures used and the types of information the EPA
evaluates for actions, see section III of the 2022 proposed rule (87 FR
1616; January 11, 2022). These revised decisions affect the proposed
emission limits for the process fugitive emissions from roof vents at
anode refining operations at new and existing sources; the mercury
limits for any existing and new combination of stacks or other vents
from the copper concentrate dryers, converting department, the anode
refining department, and the smelting vessels affected sources; and the
proposed regulatory options for the particulate metal HAP (e.g., lead,
arsenic) for the aisle scrubber at the Freeport facility. Finally, the
EPA is proposing amendments to address the use of bypass stacks for
major sources within the primary copper smelting category.

A. What are the results of our analyses of unregulated pollutants and
how did we establish the proposed MACT standards?

    As mentioned in section II.E of this preamble, the EPA received
comments on the 2022 proposed RTR concerning unregulated HAP from the
major sources within the primary copper smelting category. In response,
the EPA issued a CAA section 114 information request to the Freeport
facility on August 31, 2022. The CAA section 114 information request
required performance testing in two phases. Initially, performance
testing was to be conducted for the required HAP at the vent fume and
aisle scrubber. The acid plant stack was required to be tested for a
required HAP only if the preliminary test results from the vent fume
stack demonstrated that the pollutant is emitted above detection levels
(ADL) for at least one sample run. Any pollutant that was not ADL at
the vent fume stack was not required to be tested at the acid plant
stack because it was assumed that the pollutant would not be detected
at the acid plant stack as well. A summary of the HAP tested, the EPA
test method, and the results by stack by detection classification
(e.g., ADL; below detection levels (BDL); detection level limited
(DLL)) are shown in Table 1. We note that while not required, the test
report for the vent fume and aisle scrubber included results for
chlorine. Complete copies of the stack test reports for the vent fume
and aisle scrubber as well as the acid plant are available in the
docket for this supplemental rule.\3\
---------------------------------------------------------------------------

    \3\ The vent fume and aisle scrubber test report was initially
submitted to the EPA on November 25, 2022. The EPA sent Freeport
several questions on the test report and Freeport submitted a
revised version of the test report on February 10, 2023. All
versions of the test report and related EPA correspondence are
available in the docket EPA-HQ-OAR-2020-0430.

 Table 1--Summary of Unregulated HAP Performance Testing for the Major Source Copper Smelting Source Category in
                                                    2022-2023
----------------------------------------------------------------------------------------------------------------
                                                                    Vent fume/aisle
                 HAP                         Test method                scrubber                Acid plant
----------------------------------------------------------------------------------------------------------------
Benzene..............................  EPA Method 18..........  DLL....................  BDL.
1,4-dichlorobenzene..................  EPA Method 18..........  BDL....................  Not tested.
Hexane...............................  EPA Method 18..........  BDL....................  Not tested.
Toluene..............................  EPA Method 18..........  DLL....................  BDL.
Formaldehyde.........................  EPA Method 320.........  BDL....................  Not tested.
THC..................................  EPA Method 25A.........  N/A....................  N/A.
HCl..................................  EPA Method 26A.........  ADL....................  ADL.
Chlorine.............................  EPA Method 26A.........  ADL....................  Not tested.
Hydrogen Fluoride....................  EPA Method 26A.........  BDL....................  Not tested.
PAH (including Naphthalene)..........  EPA OTM 46.............  DLL....................  DLL.
Dioxins and Furans...................  EPA OTM 46.............  DLL....................  DLL.
----------------------------------------------------------------------------------------------------------------
* Revisions of Method 23 finalized March 20, 2023, is equivalent to OTM-46.

    As described in more detail in the following sections III.A.1
through III.A.5 of this preamble, the EPA is proposing a source
category MACT emission limit pursuant to CAA section 112(d)(2) and (3)
for each unregulated HAP that was found to be emitted through these
performance tests. The EPA contemplated using the total hydrocarbons
(THC) results as a surrogate for some of the organics (e.g., benzene,
toluene) but has decided to not propose THC as a surrogate, since the
THC test was not conducted in accordance with all of the requirements
of the EPA test method.
    The ``MACT floor'' for existing sources is calculated based on the
average performance of the best-performing units in each category or
subcategory and on a consideration of the variability of HAP emissions
from these units. The MACT floor for new sources is based on the single
best-performing source, with a similar consideration of variability.
The MACT floor for new sources cannot be less stringent than the
emissions performance that is achieved in practice by the best-
controlled similar source. Also as described in section II.E of this
preamble, the section 114 request was issued to the only currently
operating major source copper smelting facility, Freeport. Therefore,
the proposed MACT floor for existing and new sources will be determined
using these data (i.e., the proposed MACT emission limits are the same
for existing and new sources). To account for variability in the copper
smelting operations and resulting emissions, we calculated the MACT
floors using the 99 percent Upper Predictive Limit (UPL) using all
available stack test data.\4\ We are proposing MACT floor limits in
units of mass of emissions allowed per mass of concentrate feed (for
example, a proposed emissions limit of 0.0017 lbs of benzene per ton
concentrated ore fed).
---------------------------------------------------------------------------

    \4\ For more information regarding the general use of the UPL
and why it is appropriate for calculating MACT floors, see Use of
Upper Prediction Limit for Calculating MACT Floors (UPL Memo), which
is available in the docket for this action.
---------------------------------------------------------------------------

    The UPL approach addresses variability of emissions data from the
best-performing source or sources in setting MACT standards. The UPL
also accounts for uncertainty associated with emission values in a
dataset, which can be influenced by components such as the number of
samples available for developing MACT standards and the number of
samples that will be collected to assess compliance with the emission
limit. The UPL approach has been used in many environmental science
applications. As explained in more detail in the UPL Memo cited above,
the EPA uses the UPL approach to reasonably estimate the emissions
performance of the best-performing source or sources to establish MACT
floor standards.
    Additionally, we reviewed the December 13, 2011, memorandum from
Peter Westlin and Ray Merrill titled Data and procedure for handling
below detection level data in analyzing various pollutant emissions
databases for MACT and RTR emissions limits (Docket ID No. EPA-HQ-OAR-
2017-0015), which describes the procedure for handling BDL data and
developing representative detection level (RDL) data when setting MACT
emission limits. In accordance with these guidance documents, the
proposed new and existing UPL emission standards for each applicable
compound (i.e., benzene, toluene, HCl, chlorine, PAH (excluding
naphthalene), naphthalene, and D/F) were compared to the emission limit
value determined to be equivalent to 3 times the RDL (3xRDL) \5\ of the
test method. If the 3xRDL value was larger than the MACT Floor 99
percent UPL value, then the proposed MACT floor limit is proposed as
the 3xRDLvalue of the test method.
---------------------------------------------------------------------------

    \5\ The factor of three used in the 3xRDL calculation is based
on a scientifically accepted definition of level of quantitation--
simply stated, the level where a test method performs with
acceptable precision. The level of quantitation has been defined as
ten times the standard deviation of seven replicate analyses of a
sample at a concentration level close to the MDL units of the
emission standard is then compared to the MACT floor value to ensure
that the resulting emission limit is in a range that can be measured
with reasonable precision. In other words, if the 3xRDL value were
less than the calculated floor (e.g., calculated from the UPL), we
would conclude that measurement variability has been adequately
addressed; if it were greater than the calculated floor, we would
adjust the emissions limit to comport with the 3xRDL value to
address measurement variability.
---------------------------------------------------------------------------

    Further information on the development of the 99 percent UPL and
3xRDL values for compounds for which emission standards are being
proposed is included in a memorandum entitled, Proposed Maximum
Achievable Control Technology (MACT) Floor Analysis for Unregulated HAP
for the Primary Copper Smelting Major Source Category which is
available in the docket for this rulemaking (Docket ID EPA-HQ-OAR-2020-
0430).
    In addition, the EPA must examine more stringent BTF regulatory
options to determine MACT. Unlike the floor minimum stringency
requirements, the EPA must consider various impacts (such as costs and
cost effectiveness) of the more stringent regulatory options in
determining whether MACT standards should reflect beyond-the-floor
requirements. If the EPA concludes that the more stringent regulatory
options have unreasonable impacts, the EPA

selects the MACT floor as MACT. However, if the EPA concludes that
impacts associated with beyond-the-floor levels of control are
reasonable in light of additional emissions reductions achieved, the
EPA selects those BTF levels as MACT.
1. Benzene
    The performance testing conducted at Freeport included the results
of stack testing for benzene using EPA Method 18. The proposed MACT
floor emissions limit was calculated by summing the emission rates from
the vent fume, aisle scrubber and acid plant combined, accounting for
variability using the 99 percent UPL. Using this approach, we
calculated a source category MACT floor emissions limit of 0.0017 lbs
benzene/ton concentrated ore fed for new and existing sources. Based on
the available data, the Agency concludes that both facilities in the
major source copper smelting source category would be able to meet the
MACT floor emissions limit with no additional controls.
    We then evaluated and considered a BTF option to further reduce
emissions of benzene from new and existing sources. Based on the
available test data, the Agency estimates that the aisle scrubber is
the largest source of benzene emissions at Freeport, accounting for 87
percent of the total, with an estimated 414 lbs/yr of benzene
emissions. The BTF option for existing sources would require Freeport
to install and operate an activated carbon injection (ACI) system with
the existing air pollution control device (i.e., aisle scrubber). The
Agency estimates the ACI system would achieve approximately 60 percent
reduction of benzene from the aisle scrubber (i.e., 248 lbs/yr
reduction of benzene). The EPA estimates $0.6 million for capital
costs, and annualized costs are $2.7 million. This results in a cost
effectiveness of approximately $22 million per ton of benzene reduced.
We do not find costs associated with this BTF option to be reasonable
and are therefore not proposing a BTF emission limit for benzene.
Instead, we are proposing the source category MACT floor emissions
limit of 0.0017 lbs benzene/ton concentrated ore fed for new and
existing sources. A detailed description of the analysis of benzene
emissions, the controls necessary to reduce benzene emissions, and the
cost of these controls is included in the document, Estimated Cost for
Beyond-the-floor Controls for HAP Emissions from Primary Copper
Smelting Facilities, located in the docket (Docket ID No. EPA-HQ-OAR-
2020-0430).
2. Toluene
    The performance testing conducted at Freeport included the results
of stack testing for toluene using EPA Method 18. The proposed MACT
floor emissions limit was calculated by summing the emission rates from
the vent fume, aisle scrubber and acid plant combined, accounting for
variability using the 99 percent UPL. Using this approach, we
calculated a source category MACT floor emissions limit of 0.00084 lbs
toluene/ton concentrated ore fed for new and existing sources. Based on
the available data, the Agency concludes that both facilities in the
major source copper smelting source category would be able to meet the
MACT floor emissions limit with no additional controls.
    We then evaluated and considered a BTF option to further reduce
emissions of toluene from new and existing sources. Based on the
available test data, the Agency estimates that the aisle scrubber is
the largest source of toluene emissions at Freeport, accounting for 66
percent of the total, with an estimated 187 lbs/yr of toluene
emissions. The BTF option for existing sources would require Freeport
to install and operate an ACI system with the existing air pollution
control device (i.e., aisle scrubber). The Agency estimates the ACI
system would achieve approximately 60 percent reduction of toluene from
the aisle scrubber (i.e., 112 lbs/yr reduction of toluene). The EPA
estimates $0.6 million for capital costs, and annualized costs are $2.7
million. This results in a cost effectiveness of approximately $48
million per ton of toluene reduced. We do not find costs associated
with this BTF option to be reasonable and are therefore not proposing a
BTF emission limit for toluene. Instead, we are proposing the source
category MACT floor emissions limit of 0.00084 lbs toluene/ton
concentrated ore fed for new and existing sources. A detailed
description of the analysis of toluene emissions, the controls
necessary to reduce toluene emissions, and the cost of these controls
is included in the document, Estimated Cost for Beyond-the-floor
Controls for HAP Emissions from Primary Copper Smelting Facilities,
located in the docket (Docket ID No. EPA-HQ-OAR-2020-0430).
3. HCl
    The performance testing conducted at Freeport included the results
of stack testing for HCl using EPA Method 26A. The proposed MACT floor
emissions limit was calculated by summing the emission rates from the
vent fume, aisle scrubber and acid plant combined, accounting for
variability using the 99 percent UPL. The 99 percent UPL value HCl was
0.0013. The 3xRDL was found to be slightly larger, 0.0015 pounds per
ton (lb/ton) concentrated ore fed, so consistent with EPA guidelines,
we have determined that the 3xRDL value (0.0015 lb/ton) represents the
MACT floor emissions limit for new and existing sources. Based on the
available data, the Agency concludes that both facilities in the major
source copper smelting source category would be able to meet the
emissions limit with no additional controls.
    We then evaluated and considered a BTF option to further reduce
emissions of HCl from new and existing sources. Based on the available
test data, the Agency estimates that the aisle scrubber is the largest
source of HCl emissions at Freeport, accounting for 55 percent of the
total, with an estimated 682 lbs/yr of HCl emissions. The BTF option
for existing sources would require Freeport to install and operate a
dry sorbent injection (DSI) system with the existing air pollution
control device (i.e., aisle scrubber). The Agency estimates the DSI
system would achieve approximately 98 percent reduction of HCl from the
aisle scrubber (i.e., 668 lbs/yr reduction of HCl). The EPA estimates
$0.6 million for capital costs, and annualized costs are $0.5 million.
This results in a cost effectiveness of approximately $1.5 million per
ton of HCl reduced. We do not find costs associated with this BTF
option to be reasonable and are therefore not proposing a BTF emission
limit for HCl. Instead, we are proposing the source category MACT floor
emissions limit of 0.0015 lb/ton concentrated ore fed for HCl for new
and existing sources. A detailed description of the analysis of HCl
emissions, the controls necessary to reduce HCl emissions, and the cost
of these controls is included in the document, Estimated Cost for
Beyond-the-floor Controls for HAP Emissions from Primary Copper
Smelting Facilities, located in the docket (Docket ID No. EPA-HQ-OAR-
2020-0430).
4. Chlorine
    The EPA did not require facilities to test for chlorine, however
the performance testing conducted at Freeport included the results of
stack testing for chlorine using EPA Method 26A. Because the acid plant
had no data for chlorine, a percentage was calculated from the ratio of
HCl to chlorine at the aisle scrubber and vent fume stack. The highest
average ratio was used to estimate the chlorine emissions for the acid
plant. The proposed MACT floor emissions limit was calculated by
summing the

emission rates from the vent fume and aisle scrubber and the estimated
emission rate from the acid plant, accounting for variability using the
99 percent UPL. Using this approach, we calculated a source category
MACT floor emissions limit of 0.0054 lbs chlorine/ton concentrated ore
fed for new and existing sources. Based on the available data, the
Agency concludes that both facilities in the major source copper
smelting source category would be able to meet the emissions limit with
no additional controls.
    We then evaluated and considered a BTF option to further reduce
emissions of chlorine from new and existing sources. Based on the
available test data, the Agency estimates that the aisle scrubber is
the largest source of chlorine emissions at Freeport, accounting for 53
percent of the total, with an estimated 2,490 lbs/yr of chlorine
emissions. The BTF option for existing sources would require Freeport
to install and operate a DSI system with the existing air pollution
control device (i.e., aisle scrubber). The Agency estimates the DSI
system would achieve approximately 98 percent reduction of chlorine
from the aisle scrubber (i.e., 2,440 lbs/yr reduction of chlorine). The
EPA estimates $0.6 million for capital costs, and annualized costs are
$0.5 million. This results in a cost effectiveness of approximately
$0.4 million per ton of chlorine reduced. We do not find costs
associated with BTF options to be reasonable and are therefore not
proposing a BTF emission limit for chlorine. Instead, we are proposing
the source category MACT floor emissions limit of 0.0054 lbs chlorine/
ton concentrated ore fed for new and existing sources. A detailed
description of the analysis of chlorine emissions, the controls
necessary to reduce chlorine emissions, and the cost of these controls
is included in the document, Estimated Cost for Beyond-the-floor
Controls for HAP Emissions from Primary Copper Smelting Facilities,
located in the docket (Docket ID No. EPA-HQ-OAR-2020-0430).
5. PAH
    The performance testing conducted at Freeport included the results
of stack testing for PAH using EPA OTM-46. EPA OTM-46 is nearly
identical to the updated EPA Method 23, for which revisions were
promulgated on March 20, 2023 (88 FR 16732). In reviewing the test
results, we found that approximately 70 percent of the PAH measured was
naphthalene; therefore, we are proposing a PAH MACT floor emissions
limit excluding naphthalene and a separate naphthalene MACT floor
emissions limit. These proposed MACT floor emissions limits were
calculated by summing the emission rates from the vent fume, aisle
scrubber and acid plant combined, accounting for variability using the
99 percent UPL. We are proposing a source category MACT floor emissions
limit for PAH excluding naphthalene of 0.0001 lbs PAH excluding
naphthalene/ton concentrated ore fed for new and existing sources. We
are proposing a source category MACT floor emissions limit for
naphthalene of 0.00028 lbs naphthalene/ton concentrated ore fed for new
and existing sources. Based on the available data, the Agency concludes
that both facilities in the major source copper smelting source
category would be able to meet these MACT floor emissions limits with
no additional controls.
    We also evaluated and considered a BTF option to further reduce
emissions of PAH and naphthalene from new and existing sources. Based
on the available test data, the Agency estimates that the aisle
scrubber is the largest source of PAH and naphthalene emissions at
Freeport, accounting for 77 percent of the total, with an estimated 97
lbs/yr of PAH emissions. The BTF option for existing sources would
require Freeport to install and operate an ACI system with the existing
air pollution control device (i.e., aisle scrubber). The Agency
estimates the ACI system would achieve approximately 60 percent
reduction of PAH from the aisle scrubber (i.e., 58 lbs/yr reduction of
PAH). The EPA estimates $0.6 million for capital costs, and annualized
costs are $2.7 million. This results in a cost effectiveness of
approximately $92 million per ton of PAH reduced. We do not find costs
associated with BTF options to be reasonable and are therefore not
proposing a BTF emission limit for PAH. Because it was not cost
effective to propose further control of PAH, and since naphthalene is
one compound in this group, we conclude it is also not cost effective
to require BTF controls for naphthalene. Therefore, we are proposing
the MACT floor limits for PAHs and naphthalene described previously in
this section. A detailed description of the analysis of PAH emissions,
the controls necessary to reduce PAH emissions, and the cost of these
controls is included in the document, Estimated Cost for Beyond-the-
floor Controls for HAP Emissions from Primary Copper Smelting
Facilities, located in the docket (Docket ID No. EPA-HQ-OAR-2020-0430).
6. D/F
    The performance testing conducted at Freeport included the results
of stack testing for congeners of D/F using EPA OTM-46. The proposed
MACT floor emissions limit was calculated by summing the emission rates
from the vent fume, aisle scrubber and acid plant combined, accounting
for variability using the 99 percent UPL. We are proposing a source
category MACT floor emissions limit of 60 nanograms D/F Toxic
Equivalent (TEQ)/Mg concentrated ore fed for new and existing sources.
Based on the available data, the Agency concludes that both facilities
in the major source copper smelting source category would be able to
meet the MACT floor emissions limit with no additional controls.
    We also evaluated and considered a BTF option to further reduce
emissions of D/F from new and existing sources. Based on the available
test data, the Agency estimates that the aisle scrubber is the largest
source of D/F emissions at Freeport, accounting for 83 percent of the
total, with an estimated 0.04 grams/yr of D/F TEQ emissions. The BTF
option for existing sources would require Freeport to install and
operate an ACI system with the existing air pollution control device
(i.e., aisle scrubber). The Agency estimates the ACI system would
achieve approximately 85 percent reduction of D/F from the aisle
scrubber (i.e., 0.03 grams/yr reduction of D/F TEQ). The EPA estimates
$0.6 million for capital costs, and annualized costs are $2.7 million.
This results in a cost effectiveness of approximately $83 million per
gram of D/F TEQ reduced. We do not find costs associated with the BTF
option to be reasonable and are therefore not proposing a BTF emission
limit for D/F. Therefore, we are proposing the MACT floor limit
described previously in this section. A detailed description of the
analysis of D/F emissions, the controls necessary to reduce D/F
emissions, and the cost of these controls is included in the document,
Estimated Cost for Beyond-the-floor Controls for HAP Emissions from
Primary Copper Smelting Facilities, located in the docket (Docket ID
No. EPA-HQ-OAR-2020-0430).
7. Summary of Proposed New and Existing Source Limits for Copper
Smelting
    The proposed emission limits for new and existing sources in the
major source copper smelting source category are summarized in Table 2.

 Table 2--Summary of Proposed New and Existing Source MACT Emission Limits for the Major Source Copper Smelting
                                                 Source Category
----------------------------------------------------------------------------------------------------------------
                                               Existing source                           New source
                HAP                -----------------------------------------------------------------------------
                                         Limit      Unit of Measure (UOM)       Limit               UOM
----------------------------------------------------------------------------------------------------------------
Benzene...........................         1.7E-03  lb/ton concentrated           1.7E-03  lb/ton concentrated
                                                     ore fed.                               ore fed.
Toluene...........................         8.4E-04  lb/ton concentrated           8.4E-04  lb/ton concentrated
                                                     ore fed.                               ore fed.
HCl...............................         1.5E-03  lb/ton concentrated           1.5E-03  lb/ton concentrated
                                                     ore fed.                               ore fed.
Chlorine..........................         5.4E-03  lb/ton concentrated           5.4E-03  lb/ton concentrated
                                                     ore fed.                               ore fed.
PAH (excluding Naphthalene).......         1.0E-04  lb/ton concentrated           1.0E-04  lb/ton concentrated
                                                     ore fed.                               ore fed.
Naphthalene.......................         2.8E-04  lb/ton concentrated           2.8E-04  lb/ton concentrated
                                                     ore fed.                               ore fed.
Dioxins and Furans................              60  ng TEQ/Mg                          60  ng TEQ/Mg
                                                     concentrated ore fed.                  concentrated ore
                                                                                fed.
----------------------------------------------------------------------------------------------------------------

B. What performance testing, monitoring, and recordkeeping and
reporting are we proposing relative to the unregulated HAP emission
limits?

    We are proposing, based on the new and existing source emissions
limits for copper smelting, that new sources demonstrate initial
compliance upon start-up, and existing sources demonstrate initial
compliance within 1 year after the promulgation of the final rule. We
are proposing that the initial performance tests to demonstrate
compliance with the MACT standards of Table 2 of this preamble are
conducted using the methods identified in Table 3.

                Table 3--Summary of Proposed Test Methods
------------------------------------------------------------------------
                 Pollutant                           EPA method
------------------------------------------------------------------------
Benzene...................................  EPA Method 18.
Toluene...................................  EPA Method 18.
HCl.......................................  EPA Method 26A.
Chlorine..................................  EPA Method 26A.
PAH (excluding Naphthalene)...............  EPA Method 23.
Naphthalene...............................  EPA Method 23.
Dioxins and Furans........................  EPA Method 23.
------------------------------------------------------------------------

    Additionally, we are proposing that subsequent performance testing
will be required every five years, using the methods identified in
Table 3.
    Under this proposal, and consistent with existing requirements in
the Primary Copper Smelting NESHAP, a source owner will be required to
submit semiannual compliance summary reports which document both
compliance with the requirements of the Primary Copper Smelting NESHAP
and any deviations from compliance with any of those requirements.
    Owners and operators would be required to maintain the records
specified by 40 CFR 63.10 and, in addition, would be required to
maintain records of all inspection and monitoring data, in accordance
with the Primary Copper Smelting NESHAP (40 CFR 63.1456).
    We considered the possibility of proposing a fenceline monitoring
requirement. However, we determined that fenceline monitoring is not
appropriate for this source category primarily because the main
emissions of interest for this source category are process fugitive
emissions that are released from roofline vents that are at about 100
feet elevation (i.e., not ``ground level'' like the source categories
where we have required or proposed fenceline monitoring). Due to the
elevation of the fugitive release points, the emissions would pass over
the fenceline monitors and would not be effectively measured. In
addition, EPA has determined that there are effective technologies for
capturing these process fugitive emissions and routing them to control
devices, and is proposing to require the use of such approaches in this
rulemaking. Unlike many other source categories, it is also feasible to
measure the process fugitive emissions at these facilities. These
characteristics suggest that fenceline monitoring--which is typically
used to detect emissions that can be difficult to control or measure at
the points where they are emitted, and to identify the need for follow-
up investigation and corrective action--would have relatively limited
value in the context of this source category.

C. What revisions are we proposing specific to the emission limit for
process fugitive emissions from roof vents at the anode refining
operations from the 2022 proposed RTR?

    As described in the 2022 proposed RTR, the current NESHAP does not
include standards for process fugitive emissions from the rooflines of
smelting furnaces, converters, or anode refining operations, except for
an opacity limit for converter roof vents that applies during testing.
During the development of the 2022 proposed RTR, the EPA determined
that risk for the major source category was unacceptable. One of the
main risk drivers was metal HAP emissions (mainly lead and arsenic)
from the anode refining roofline at the Freeport facility, which
comprised 71 percent of the MIR. Therefore, in the 2022 proposed RTR,
pursuant to CAA sections 112(d)(2) and (3) for new and existing major
sources, PM limits were proposed for process fugitive emissions from
the rooflines of the converters and smelting furnaces. Pursuant to CAA
sections 112(d)(2), (d)(3), and (f)(2) PM limits were proposed for
process fugitive emissions for new and existing major sources' anode
refining operations roofline vents.
    In the 2022 proposed RTR for converter and smelting furnace
rooflines, we developed MACT floor emissions limits for PM, as a
surrogate for particulate HAP metals, which include antimony, arsenic,
beryllium, cadmium, chromium, cobalt, lead, manganese, nickel, and
selenium compounds, based on the available test data. The use of PM as
a surrogate for particulate metal HAP is consistent with the approach
used to limit particulate metal HAP emissions from other copper
smelting processes in the current NESHAP and for many other source
categories (i.e., Ferroalloys Production, Integrated Iron and Steel
Manufacturing, and Integrated Iron and Steel Foundries). The data used
in the MACT floor emission limit development was from the Freeport
facility. The Agency used the UPL methodology to develop the emission
limits. The development of the MACT floor limits included in the 2022
proposed RTR is described in detail in the memorandum entitled, Draft
MACT Floor Analyses for the Primary Copper Smelting Source Category
(Docket Item No. EPA-HQ-OAR-2020-0430-0055), which is available in the
docket. Based on these analyses, the proposed MACT floor emission
limits included in the 2022 proposed RTR were 1.7 pounds per hour (lbs/
hr) PM for process fugitive emissions for existing and new converter
rooflines and 4.3 lbs/hr PM for existing and new smelting furnace
rooflines. We also evaluated BTF PM limits for smelting furnace and

converter rooflines based on the potential addition of capture and
control equipment designed to achieve approximately 90 percent
reduction in process fugitive emissions. Based on the results of these
analyses, the Agency did not propose BTF limits in the 2022 proposed
RTR for converters or smelting furnaces because of the high costs and
poor cost effectiveness and uncertainties in the estimates of
emissions, emissions reductions and costs. Further details of these BTF
analyses included in the 2022 proposed RTR are provided in the
technical memo, Evaluation of Beyond-the-floor and Ample Margin of
Safety Control Options and Costs for Process Fugitive Emissions from
Smelting Furnaces and Converters, and for Point Source Emissions from
Anode Refining Furnaces and for the Combined Emissions Stream Emitted
from the Freeport Aisle Scrubber (Docket Item No. EPA-HQ-OAR-2020-0430-
0060).
    In the 2022 proposed RTR for the roofline vents of anode refining
operations, we initially developed a MACT floor emissions PM limit of
15.2 lbs/hr using the available test data and application of the UPL
methodology. For this standard, PM also serves as a surrogate for
particulate metal HAP similar to the other PM limits in the NESHAP.
Subsequently, we evaluated a BTF emission limit for the anode refining
operation roofline vents. The BTF emission limit was set at 90 percent
lower than the MACT floor, or 1.6 lb PM/hr. As described in the 2022
proposed RTR, in order to comply with the proposed anode refining
operation BTF limit, the EPA expected that Freeport would need to
install improved capture systems, including hoods, ductwork, and fans,
and one additional baghouse. These improved capture systems would need
to be applied to four units including the two-anode refining furnace
pouring operations, the anode casting wheel, and the holding vessel. In
the January 2022 proposed RTR, we estimated a total capital cost of
$5,887,000 (2019 dollars), a total O&M cost of $1,002,000 (2019
dollars) and total annualized costs of $1,558,000 (2019 dollars). The
expected emission reductions were 4.25 tpy of lead and arsenic. The
resulting cost effectiveness was $367,000/ton (2019 dollars). We
concluded that this option was cost effective and proposed the BTF PM
emission limit for the anode refining roofline vents. The same emission
limit proposed pursuant to CAA 112(d)(2) and (3) for the anode refining
operation roofline vent was also proposed to reduce risks to an
acceptable level pursuant to CAA section 112(f)(2). Further information
on the development of the proposed emission limit and the related cost
estimates for control equipment are included in the record for the 2022
proposed RTR in the memorandums entitled, Draft MACT Floor Analyses for
the Primary Copper Smelting Source Category (Docket Item No. EPA-HQ-
OAR-2020-0430-0055) and Development of Estimated Costs for Enhanced
Capture and Control of Process Fugitive Emissions form from Anode
Refining Operations at Freeport (Docket Item No. EPA-HQ-OAR-2020-0430-
0061).
    During the public comment period for the 2022 proposed RTR, the EPA
received comments from industry stakeholders that a combined limit
would be preferred over individual limits. Commenters noted several
reasons for this:
     Increased flexibility with respect to compliance options
resulting in lower costs to comply;
     Lack of physical separation between departments and
potential for emissions transfer; and
     Variability of department-specific emissions driven by the
type of material being processed rather than by lack of emissions
prevention measures.
    The Freeport facility also provided additional test data for the
roofline vents for all three process areas in Appendices H1 and H2 of
their public comment letter (Docket Item No. EPA-HQ-OAR-2020-0430-
0134). In reviewing these additional test data, we note that for
completeness they should be included in the calculation of emission
limits for these emission sources.
    In their comment letter, Freeport noted that the emission rates
from the test data underlying the MACT floor emission limits from each
smelter (electric and ISASMELT) should be added together rather than
averaged since they are two distinct emission points. In reviewing the
test data, we agree that the emission rates for the smelters should be
added rather than averaged. This change is incorporated in our revised
analyses included in this supplemental proposal for these emission
sources.
    In response to the comments the EPA received on combining the three
proposed roofline emission limits (i.e., from the smelters, converters,
and anode refining rooflines) into a single combined emission limit, we
performed an evaluation of the approach used in the 2022 proposed RTR
and an evaluation of combining the emissions data to develop the
emissions limit. The evaluations use all test data now available and
incorporate the change to the processing of the smelter test data
(i.e., adding the emission rates from each smelter rather than
averaging them). Our evaluation of separate emission limits for
filterable PM from the converter, smelter, and anode refining rooflines
using the methodology in the 2022 proposed RTR, results in PM MACT
floor emission limits of 2.4 lbs/hr for the converter roofline and 5.7
lbs/hr for the smelting roofline, and a BTF emission limit (assuming 90
percent control) of 1.6 lbs/hr for the anode refining roofline.
    We also evaluated the development of a combined emission limit for
all the rooflines. This new emission limit is also calculated using the
99 percent UPL methodology. Specifically, for calculating the combined
emission limit, we first determined the 99 percent UPL of the combined
emission rates based on all test data now available for filterable PM.
We then determined the average fraction of emissions which are
attributable to the anode refining roof vent (72 percent). Then we
adjusted the anode refining roof vent's portion of the 99 percent UPL
by reducing that portion of the value by 90 percent. This results in a
combined filterable PM emission limit of 6.3 lbs/hr. We note that this
emission limit is still expected to require 90 percent control of the
anode refining roofline vent at the Freeport facility, and we expect
the Freeport facility will still have to apply controls at this
emission source. Therefore, despite the emission limit changing in
format (i.e., becoming a single limit as opposed to three separate
limits), we expect slightly higher emission reductions (i.e., 4.59 tpy
of lead and arsenic). While we expect the Freeport facility will need
to apply some control of the anode refining source, a combined limit
would provide the facility with options to determine which source or
combination of sources to control and to what level to achieve the
overall needed emission reductions to comply with the combined emission
limit. Because the option is expected to provide the same emission
reductions as separate emission limits while also providing some
flexibility for subject facilities, we are proposing a single combined
emission limit for the converter, smelting, and anode refining roofline
vents in this supplemental proposed rulemaking. Further information on
our evaluation of separate and combined emission limits using all test
data are available in the memorandum entitled Revised MACT Floor
Analysis for the Fugitive Process Emission Sources in the docket for
this

rulemaking (Docket ID EPA-HQ-OAR-2020-0430).
    The EPA also received comments from the Freeport facility
concerning its cost estimates for the anode refining process fugitive
roofline emissions controls. In their public comment letter on the 2022
proposed RTR, the Freeport facility suggested that the EPA had
underestimated costs for controlling the anode refining operations'
process fugitive emissions. They provided their own cost assessment
data in Attachment F of their comment letter (Docket Item No. EPA-HQ-
OAR-2020-0430-0134).
    After evaluating the comment letter and associated documents
provided by Freeport, we determined that it is appropriate to update
certain data input parameters in the cost estimates to reflect design
requirements at the Freeport facility primarily by increasing the
baghouse flowrate, lowering the air to cloth ratio, and adding a lime
injection system to treat any acid gases in the exhaust stream.
Additionally, the cost estimates have been updated to reflect 2022
dollars and using an updated bank prime interest rate. The Agency now
estimates that the BTF standard for the process fugitive emissions from
the roofline at the Freeport facility would have capital costs of
$10,239,666 and annualized costs of $2,143,972 and achieve about 4.59
tpy reduction of lead and arsenic, with cost effectiveness of $467,000/
ton lead and arsenic, which is a level that, while higher than the cost
effectiveness in the 2022 proposed RTR, we consider to be cost
effective for these pollutants. Further information on our revised cost
estimates can be found in the memorandum entitled, Cost Estimates for
Enhanced Capture and Control of Process Fugitive Emissions from the
Anode Refining Operations at Freeport in the docket for this rulemaking
(Docket ID EPA-HQ-OAR-2020-0430). As described above, we are
maintaining a proposed BTF emission limit for the roof vents in this
supplemental proposal because it is cost effective and feasible to
achieve. We also note that this BTF limit would ensure that risks are
acceptable. We estimate that this BTF limit would reduce the cancer MIR
near Freeport from 70-in-1 million to 20-in-1 million, ensure 3-month
rolling average ambient lead concentrations remain well below the lead
NAAQS near Freeport, and reduce the maximum noncancer acute HQ (for
arsenic) from 7 to 2. Furthermore, this BTF limit would reduce the
number of people with an estimated increased risk of cancer of greater
than or equal to 1-in-1 million from 22,900 people (at baseline) to
17,400 (post-control) and decrease the estimated cancer incidence from
0.002 cases per year to 0.001 cases per year. The cancer MIR for Asarco
would remain at 60-in-1 million.
    Consistent with the analysis provided in the 2022 proposed RTR, we
expect the costs for the other major source copper smelting facility,
Asarco, to be limited to emissions compliance testing and recordkeeping
and reporting requirements. Also, consistent with the analysis provided
in the 2022 proposed RTR, the EPA estimates the costs for the Asarco
facility are $107,581 per year (after adjusting to 2022 dollars) to
comply with the proposed testing and recordkeeping and reporting
requirements for process fugitive lead emissions from its three
roofline vents (i.e., for the anode, converter, and smelting furnace
rooflines). While we are proposing a combined roofline emissions limit
in this supplemental proposal, instead of separate limits for each
department, we expect the testing costs to remain the same as those
estimated in the 2022 proposed RTR since all three sources will have to
be tested to compare to the proposed combined emission limit included
in this supplemental proposal. This estimate is based on the EPA's
experience and knowledge of typical costs associated with these types
of testing requirements. We also note that the Freeport facility
already performs the emissions testing that is required by the
emissions limit in this supplemental proposal, thus this proposed rule
does not impose any additional costs related to emissions testing and
recordkeeping and reporting on the Freeport facility because these
costs would be incurred in the absence of the supplemental proposed
rule.
    We are proposing that existing facilities would need to comply
within two years after promulgation of the final rule and that
compliance would be demonstrated through an initial performance test
followed by a compliance test once per year. Moreover, facilities would
need to monitor control parameters (e.g., fan speed, amperage, pressure
drops, and/or damper positioning), as applicable, on a continuous basis
to ensure the control systems are working properly. All new or
reconstructed facilities must comply with all requirements in the final
rule upon startup.

D. What revisions are we proposing specific to the emission limit for
mercury from the 2022 proposed RTR?

    As described in the 2022 proposed RTR, the current NESHAP does not
include standards for mercury. Using the test data available during the
development of the 2022 proposed RTR, the source category was estimated
to emit 55 pounds per year of mercury with 45 pounds per year emitted
from the Freeport facility. Because of the temperatures of the exhaust
gas streams encountered at primary copper smelting operations, much of
the mercury emitted is in vapor form, not in particulate form. The
vapor form of mercury is not captured by the controls used to reduce PM
emission. Therefore, the PM limits in the NESHAP do not serve as a
surrogate for mercury. Therefore, in the 2022 proposed RTR, pursuant to
CAA sections 112(d)(2) and (3) for new and existing major sources,
mercury limits were proposed. In the 2022 proposed RTR, the Agency used
the available test data from Asarco and Freeport to develop the mercury
standards for new and existing sources (details can be found in Draft
MACT Floor Analyses for the Primary Copper Smelting Source Category
(Docket Item No. EPA-HQ-OAR-2020-0430-0055)).
    In the 2022 proposed RTR, the new source standard was based on the
best performer, Asarco. The Agency evaluated proposing a BTF emission
standard for new sources based on Asarco data in the 2022 proposed RTR
but rejected this option based on the cost effectiveness, uncertainty
in the quantity of emission reductions, and the fact that the new
source MACT floor standard is significantly lower than the limit for
existing sources. The proposed emission standard for new sources in the
2022 proposed RTR was 0.00097 lbs/hr. The Agency has not received any
new information relative to the new source standard included in the
2022 proposed RTR and, therefore, maintains this proposed MACT floor
emission limit for new sources.
    In the 2022 proposed RTR, the MACT floor emissions limit for
existing sources was calculated based on the average of all the
emissions tests from both facilities, accounting for variability using
the 99 percent UPL. A MACT floor based on the 99 percent UPL for the
combined facility-wide sources was 0.01 lbs/hr. The Agency also
evaluated a BTF emission standard for existing sources, a value of
0.0043 lbs/hr. The BTF standard was based on the addition of controls
at the Freeport facility's acid plant which was identified as the
largest source of mercury emissions at the Freeport facility using data
available at the time. The additional controls were expected to include
the installation of a polishing baghouse with activated carbon
injection. The expected emission reductions were 26 lb/yr, based on 90
percent control of the emissions from Freeport's acid plant. The
estimated

capital costs for the polishing baghouse with activated carbon
injection were $1.5 million (2019 dollars), and the estimated
annualized costs were $714,000 (2019 dollars), for a cost effectiveness
of $27,500 (2019 dollars) per pound of mercury reduced. In the 2022
proposed RTR, the Agency proposed the BTF standard of 0.0043 lbs/hr for
existing sources. The development of this beyond-the-floor limit is
described in detail in the memorandum entitled, Estimated Costs for
Beyond-the-floor Controls for Mercury Emissions from Primary Copper
Smelting Facilities (Docket Item No. EPA-HQ-OAR-2020-0430-0059).
    Since the 2022 proposed RTR, the EPA received comments on the
proposed existing source mercury standard and new information from the
Freeport facility through the CAA section 114 information request
described in II.E of this preamble. Freeport provided additional
mercury performance test reports with results for the vent fume, aisle
scrubber and acid plant covering calendar years 2019-2021. The Freeport
facility noted that these test reports used a variation of EPA Method
29 that may result in mercury emissions measurements that are biased
low. These mercury tests conducted in 2019-21 were not done according
to the EPA method. The facility voluntarily completed an additional
mercury performance test at the vent fume, aisle scrubber, and acid
plant in 2022 which fully followed EPA Method 29. These test reports
are available in the docket for this rulemaking (Docket ID EPA-HQ-OAR-
2020-0430).
    In their public comment letter, Freeport provided comments
specifically on controlling emissions from the acid plant. The facility
questioned the technical feasibility of these controls, stating that
they are unaware of a polishing baghouse with ACI operating downstream
of a wet scrubber on an acid plant. They explained that the conditions
of the acid plant exhaust streams are unsuited for ACI since the stream
has a high moisture content, low mercury concentrations, and high
concentrations of SO2/SO3 which inhibit mercury
removal.
    Freeport argued that even if it was technically feasible, the EPA
had underestimated costs and overstated reductions. Freeport submitted
their own cost estimates for ACI plus a polishing baghouse on the acid
plant as part of their comment letter on the 2022 proposed RTR (see
Attachment I of Docket Item No. EPA-HQ-OAR-2020-0430-0134). The
facility subsequently revised and resubmitted their evaluation of the
baghouse with activated carbon injection control option for the acid
plant to the EPA on March 12, 2023 (Docket ID EPA-HQ-OAR-2020-0430). In
this evaluation, the Freeport facility estimated the emission
reductions of mercury to be between 50 and 75 percent using a polishing
baghouse with ACI, or about 15 to 22 lbs of mercury. The cost estimate
from Freeport provided capital costs of $16.4M, annualized costs of
$4.4 million and a cost effectiveness of about $169,000 per pound.
    The EPA has performed a review of all available mercury test data
from Freeport and the cost estimate provided by Freeport. In reviewing
the test data, we decided that only the test which was fully compliant
with EPA Method 29 should be used to calculate emission limits and to
estimate the quantity of potential emissions reductions. Using the data
from this test report, the point and non-point source emissions from
Freeport are estimated to be 139 lbs/yr which, when combined with the
test report from Asarco which indicates that 10 lbs/yr are estimated to
be emitted from that facility, results in an estimated total of 149
lbs/yr mercury emitted from the source category. In Freeport's 2022
mercury test which complied fully with EPA Method 29, the emissions
were more evenly distributed between the three stacks at the facility
with an estimated 45 lbs/yr from the vent fume stack, an estimated 49.3
lbs/yr estimated from the aisle scrubber and an estimated 38.5 lbs/yr
from the acid plant.
    Using the 2022 mercury test from Freeport and the performance test
from Asarco, we calculated the MACT floor limit for existing sources by
averaging all the test results from both facilities, accounting for
variability using the 99 percent UPL. A MACT floor based on the 99
percent UPL for the combined facility-wide limit for existing sources
is 0.033 lbs/hr. Based on the available data, we conclude that both
facilities would be able to meet the MACT floor limit with no
additional controls. For new sources, we are maintaining the MACT floor
limit of 0.00097 lbs/hr provided in the 2022 proposed RTR which was
based on data from the best performer, Asarco. We have no new data with
which to update this value. A detailed analysis and documentation of
the revised MACT floor calculations for existing sources can be found
in the technical document, Revised MACT Floor Analysis for Mercury,
available in the docket (Docket ID EPA-HQ-2020-0430).
    As discussed previously, the Freeport facility submitted comments
indicating several technical reasons that control of mercury from the
acid plant would be difficult. In reviewing the 2022 mercury test from
Freeport, we find that the mercury emissions were distributed more
evenly among the facility's three stacks when compared to the other
test reports which included mercury from 2018-2021. We have evaluated
the technical aspects of Freeport's comment letter regarding mercury
control from the acid plant and agree characteristics of the exhaust
stream and equipment configuration may inhibit mercury control (e.g.,
moisture content, acid gas content, mercury concentration). Considering
this, and the emissions distribution from the 2022 mercury test, we
examined other control options to determine whether there is a more
technically suitable and cost-effective option for controlling mercury
emissions at Freeport. When reviewing the stack characteristics, we
find that the aisle scrubber has a high flowrate, typically in excess
of one million cubic feet per minute, and a very similar quantity of
mercury emissions compared to the other two stacks based on the 2022
test. The aisle scrubber also combines streams which are currently
uncontrolled (i.e., secondary converter) with streams that are
controlled (i.e., primary anode refining baghouse emissions). On the
other hand, the vent fume stack handles emissions from the secondary
capture system for the furnaces and has a lower flowrate than the aisle
scrubber. Often, a higher flowrate and the complexity of combining
multiple streams increase control costs. When evaluating beyond-the-
floor options for controlling mercury, we estimated costs and emissions
reductions for controlling the vent fume exhaust stream because we
expect the more simplistic exhaust stream configuration, lower
flowrate, and similar quantity of expected reductions to be more
favorable for controlling mercury than the aisle scrubber. For the BTF
option, we estimated costs and emissions reductions associated with a
baghouse with lime injection and activated carbon injection with an
expected control efficiency of 90 percent for mercury from the vent
fume. The estimated reduction would be 40.5 lbs of mercury from the
vent fume stack. The overall reduction of mercury emissions that would
occur from the Freeport facility with this BTF option is estimated to
be 30 percent (i.e., the facility-wide total emissions of 139 lbs
mercury would be reduced by 40.5 lbs mercury). The capital costs of the
baghouse with lime injection and activated carbon injection

are estimated to be $6.04M, with annualized costs of $1.91M and a cost
effectiveness of $47,000/lb mercury reduced. We do not find costs
associated with the BTF option to be reasonable and are therefore not
proposing a BTF emission limit for existing sources for mercury. We
also considered other BTF options, but all other options were less cost
effective than the option presented in this section. The EPA is
requesting comment on the BTF options evaluated for mercury and whether
the EPA should determine in this case that $47,000/lb mercury is cost-
effective for mercury control and include a BTF limit in the final
rule. A detailed description of the BTF analysis of mercury emissions,
the controls necessary to reduce mercury emissions, and the cost of
these BTF controls are included in the document, Estimated Cost for
Beyond-the-floor Controls for Mercury Emissions from Primary Copper
Smelting Facilities, located in the docket (Docket ID No. EPA-HQ-OAR-
2020-0430). Since we have not identified a cost-effective BTF option,
we are proposing the MACT floor limit for the combined facility-wide
limit for mercury of 0.033 lbs/hr for existing sources.
    The EPA is proposing that compliance with the mercury emissions
limits for existing sources will be demonstrated through an initial
compliance test for each of the affected sources (e.g., furnaces,
converters, anode refining) within 1 year of publication of the rule
followed by a compliance test at least once every year. We estimate
that Freeport and Asarco will incur performance testing costs for
mercury of $49,940 per facility per year. For newly affected
facilities, compliance is to be achieved no later than the effective
date of the final rule or upon startup, whichever is later.

E. What emissions standards are we proposing for the Aisle Scrubber in
this supplemental proposed rule that are different than decisions
proposed in the 2022 proposed RTR?

    As discussed in the preamble of the 2022 proposed RTR, we proposed
that the risks for the major source category were unacceptable. The EPA
identified controls to reduce risk to an acceptable level, which were
proposed to be achieved by controlling the anode refining roofline
vents (as described in section III.C. of this preamble). Then, the EPA
considered whether additional measures were required to provide an
ample margin of safety to protect public health. An aisle scrubber
located at one of the two major source facilities (Freeport) was
estimated to emit 9.2 tpy metal HAP (mostly lead and arsenic) and was
identified as an emission source that contributed significantly to risk
at the Freeport facility (e.g., 23 percent of the cancer MIR).
Therefore, the EPA evaluated the cost, the emissions reductions and
risk reductions that could be achieved by additional controls for the
aisle scrubber as part of the ample margin of safety analysis.
    Specifically. In the 2022 proposed RTR the EPA evaluated the cost
and emission reductions of adding a WESP to the combined emissions
stream from the aisle scrubber. The evaluation is described in the
memorandum entitled Evaluation of Beyond-the-floor and Ample Margin of
Safety Control Options and Costs for Process Fugitive Emissions from
Smelting Furnaces and Converters, and for Point Source Emissions from
Anode Refining Furnaces and for the Combined Emissions Stream Emitted
from the Freeport Aisle Scrubber--REVISED (Docket Item No. EPA-HQ-OAR-
0430-0108). Based on the analysis included in the 2022 Proposed RTR,
the estimated capital costs were $67 million (2019 dollars), and the
estimated annualized costs were $17 million (2019 dollars). The
associated emissions reduction achieved were estimated to be 8.7 tpy
total metal HAP of which 7.6 tpy were estimated to be lead and arsenic
resulting in a cost effectiveness of $2 million/ton (2019 dollars).
    The aisle scrubber at the Freeport facility is used to control the
combined secondary emissions from the converter plus the emissions
exiting the baghouse used to control primary anode refining point
source emissions. Currently, there are emission limits for secondary
capture systems from existing converter departments in 40 CFR
63.1444(d)(6). Furthermore, the EPA proposed emissions limits for new
and existing anode refining departments in the 2022 proposed RTR (i.e.,
proposed limits for 40 CFR 63.1444(i)(1)). In this supplemental
proposal, the EPA is co-proposing regulatory options for additional
control of either the secondary capture system for the converter
department or additional control of the combined emissions stream of
the secondary capture system for the converter department and the point
source emissions from the anode refining department. These control
options would result in more stringent emissions standards for these
emission sources than what is currently required by the Primary Copper
Smelting NESHAP as discussed more below. These standards are being
proposed as technology developments pursuant to CAA section 112(d)(6)
and to provide an ample margin of safety to protect public health
pursuant to CAA section 112(f)(2).
    In order to best inform these options for additional controls,
after the January 2022 proposal the EPA issued a CAA section 114
information request to the Freeport facility as described in section
II.E of this preamble. The CAA section 114 information request
requested that Freeport perform a feasibility analysis of whether
Freeport could further reduce the HAP metal emissions either from the
secondary capture system for the converter department or from the
combined emissions stream entering the aisle scrubber (i.e., the
emissions stream from the secondary capture system for the converter
department and the anode refining department).
    The Freeport facility subsequently provided the EPA with an
evaluation of control options for the aisle scrubber, including:
     Option 1--Addition of a WESP downstream of the aisle
scrubber to provide additional control of the combined emissions stream
from the secondary capture system for the converter department and the
anode refining department (i.e., the same option evaluated by the EPA
in the ample margin of safety analysis included in the January 2022
proposal);
     Option 2--Addition of a baghouse upstream of the aisle
scrubber to provide additional control of the secondary capture system
for the converter department.
    The Freeport facility regularly conducts performance testing of its
aisle scrubber for filterable PM and metals. The EPA has obtained
copies of the performance test results from 2018, 2019, 2020, 2021 and
2022 for the aisle scrubber, which are available in the docket for this
rulemaking (Docket ID No. EPA-HQ-OAR-2020-0430). We used these
performance tests to estimate the baseline emissions and subsequently
estimate the quantity of emissions reductions for the options for
controlling the aisle scrubber at the Freeport facility. Using these
test data, we now estimate the annual emissions of metal HAP to be 6.63
tpy, of which more than 90 percent is lead and arsenic, on average. We
also used the test reports to inform the development of potential
emissions standards. Initially we developed a limit that represents
current emissions from the aisle scrubber, accounting for variability
using the 99 percent UPL. The resulting limit based on the 99 percent
UPL for the combined emissions stream from the secondary capture system
for the converter department and the anode refining department is 7.48
milligram

per dry cubic standard meter (mg/dscm). This UPL served as the baseline
for the development of the two control options described in this
section. A detailed discussion of the option-specific control
equipment, expected emission reductions, associated emissions standard,
and control costs are described in the following paragraphs.
    For Option 1, as described previously, the WESP would be located
downstream of the aisle scrubber and therefore further control the
combined emissions stream from the secondary capture system for the
converter department and the anode refining department. The expected
control efficiency for the WESP is 95 percent, thus expected emission
reductions from this option are 95 percent of the baseline emissions
(6.63 tpy metal HAP) or 6.3 tpy metal HAP. The EPA updated the expected
flowrate for the WESP in its cost estimates from the value used in the
cost estimate we provided in the 2022 proposed RTR based on comments
from Freeport. We also updated the cost estimate to reflect 2022
dollars and updated the bank prime interest rate. Based on our
analysis, the estimated capital costs for the WESP are $98.5 million,
the annualized costs are $25.2 million, and estimated reductions are
6.3 tpy reduction of metal HAP, with cost effectiveness of $4.0
million/ton metal HAP. The emission limit for this option would be
0.374 mg/dscm, which is based on applying the expected control of 95
percent to the 99 percent UPL for the combined emissions stream from
the secondary capture system for the converter department and the anode
refining department.
    As described in the previous section III.C. of this preamble, we
estimate the reductions of process fugitive emissions from the roof
vents would reduce the MIR at Freeport from 70-in-1 million to 20-in-1
million; reduce the number of people with cancer risk greater than 1-
in-1 million from 22,900 to 17,400; reduce ambient lead exposures below
the lead NAAQS; and reduce the maximum HQ (due to arsenic emissions)
from 7 to 2. We estimate that the proposed limit of 0.374 mg/dscm for
the aisle scrubber (option 1) would reduce the incremental cancer risk
of an additional 1,900 people below 1-in-1 million (from 17,400 to
15,500). Furthermore, the maximum acute HQ due to arsenic emissions
would be reduced from 2 to 1. Option 1 would result in a small
additional reduction in the MIR at Freeport, but after rounding up (to
1 significant figure) the MIR remains at 20-in-1 million. However, we
note that the estimated cancer MIR for the source category would be 60-
in-1 million, which is the maximum cancer risk near the Asarco
facility.
    Option 2, as described previously, would require a baghouse
upstream of the aisle scrubber which would be designed to control the
secondary capture system for the converter department. Currently, the
uncontrolled emissions from the secondary capture system for the
converter department combine with the baghouse-controlled primary anode
refining point source emissions and route to the aisle scrubber. Unlike
the aisle scrubber which is routinely tested for particulate matter and
lead emissions, the secondary converter duct is not sampled at any
regular frequency. However, in an engineering evaluation submitted by
Freeport as part of the CAA section 114 information request in which
the converter duct was sampled, the facility explained that
approximately 75 percent of the emissions from the aisle scrubber are
attributable to the secondary capture system for the converter
department. Therefore, we estimate that average annual metal HAP
emissions from the secondary capture system for the converter
department are 4.97 tpy (75 percent of the estimated total average
annual metal HAP emissions from the aisle scrubber, which is 6.63 tpy).
To estimate the expected reductions from this option, we applied the
expected control efficiency of the baghouse (90 percent) to the
emissions which are estimated to be from the secondary capture system
for the converter department (4.97 tpy). This results in an estimated
emissions reduction of 4.5 tpy metal HAP from the aisle scrubber, which
is about a 68 percent reduction of emissions from the aisle scrubber.
We estimate these controls (i.e., baghouse) will have capital costs of
$37M, annualized costs of $6.2 million and achieve about a 4.5 tpy
reduction in metal HAP with cost effectiveness of $1.38 million/ton
metal HAP. The emission standard for this option was calculated by
first determining the fraction of the 99 percent UPL that is estimated
to be from the secondary capture system for the converter department,
5.61 mg/dscm, and then applying the expected control efficiency of the
baghouse (i.e., 90 percent) to determine the reduction in the emission
limit (5.09 mg/dscm). The resulting emissions limit under option 2
would be 2.43 mg/dscm for additional controls on the secondary capture
system for the converter department.
    As described in the previous section III.C. of this preamble, we
estimate the reductions of process fugitive emissions from the roof
vents would reduce the MIR at Freeport from 70-in-1 million to 20-in-1
million; reduce the number of people with cancer risk greater than 1-
in-1 million from 22,900 to 17,400; reduce ambient lead exposures below
the lead NAAQS; and reduce the maximum HQ (due to arsenic emissions)
from 7 to 2. We estimate that the proposed limit of 2.43 mg/dscm (based
on addition of a baghouse on the secondary capture system for the
converter department--option 2) would reduce the incremental cancer
risk of an additional 700 people to below 1-in-1 million (from 17,400
to 16,700). Furthermore, the maximum acute HQ due to arsenic emissions
would be reduced from 2 to 1. Option 2 would also result in a small
additional reduction in the maximum cancer risk at Freeport, but after
rounding up (to 1 significant figure) the maximum risk would remain at
20-in-1 million. The estimated cancer MIR for the source category would
be 60-in-1 million, which is the maximum cancer risk near the Asarco
facility.
    As discussed below, based on consideration and evaluation of both
options, the EPA is proposing both options pursuant to CAA section
112(d)(6) and CAA section 112(f). We propose that both options are
feasible, achieve significant reductions of the HAP metals and risk
reduction, and that the cost impacts are reasonable. Therefore, both
options represent cost-effective developments in control technology
pursuant to CAA section 112(d)(6) and ensure the NESHAP will provide an
ample margin of safety to protect public health pursuant to CAA section
112(f). We expect that the Asarco facility can comply with either
option without the need to install additional controls. We are
proposing that facilities would need to comply within two years after
promulgation of the final rule and that compliance would be
demonstrated through an initial performance test followed by a
compliance test once per year. Moreover, facilities would need to
monitor control parameters (e.g., fan speed, amperage, pressure drops,
and/or damper positioning), as applicable, on a continuous basis to
ensure the control systems are working properly.
    Further information regarding our estimated control costs,
associated emission reductions, and estimated cost effectiveness can be
found in the memorandum entitled, Cost Estimates for Additional
Controls of Freeport's Aisle Scrubber which is available in the docket
for this rulemaking (Docket ID No. EPA-HQ-OAR-2020-0430). Further
information regarding the development of the proposed emission
standards for

each option can be found in the memorandum entitled, Emission Standard
Development for the Options to Provide Additional Controls for the
Secondary Capture System for the Converter Department and Anode
Refining Department which is available in the docket for this
rulemaking (Docket ID No. EPA-HQ-OAR-2020-0430).
    The EPA is presenting both options (described in this section) in
this supplemental proposal as potential regulatory options that we may
finalize for this source category under CAA section 112(d)(6) and/or
CAA section 112(f) after consideration of public comments. Under CAA
section 112(d)(6) we propose that both options represent cost-effective
developments in control technology and that it is necessary to revise
the standards to reduce emissions from the aisle scrubber. In addition
to the controls described above, we note that in the 2022 RTR Proposed
Rule we also proposed a requirement that facilities develop and operate
according to a fugitive dust minimization plan, which would provide
some additional unquantified health protection. We are not proposing
any changes to that proposed fugitive dust minimization requirement in
this action.
    Noting that in setting standards to provide ample margin of safety
to protect public health EPA strives to provide protection to the
greatest number of persons possible to an individual lifetime risk
level no higher than approximately 1-in-1 million (54 FR 38044;
September 14, 1989), and after considering the risk reduction achieved
under both options as well as the cost and feasibility of controls,
along with the fugitive dust plan, we propose that either option
provides an ample margin of safety to protect public health under CAA
section 112(f). We are seeking comments on the technical feasibility,
costs, expected emission reductions, and risk reductions achieved and
whether one option is preferable over the other and why.

F. What are the results of risk analyses completed for this action?

    In the January 11, 2022, proposed amendments to the Primary Copper
Smelting RTR rule (87 FR 1616; January 11, 2022), the EPA conducted a
residual risk assessment and determined that risks from the primary
copper smelting source category were unacceptable due to HAP metal
(primarily lead and arsenic) emissions and proposed standards to reduce
risk to an acceptable level and provide an ample margin of safety to
protect public health. The risk analysis supporting the proposed rule
indicated exceedances of the lead NAAQS at the baseline (i.e., based on
current HAP emissions). That risk analysis also indicated that the
cancer risk for the individual most exposed could be up to 80-in-1
million based on actual emissions and up to 90-in-1 million based on
allowable emissions. In addition to the noncancer risk from lead, the
analysis also indicated a chronic HI of 1 due to arsenic and a maximum
acute HQ of 7 for arsenic (see Docket No. EPA-HQ-OAR-2020-0430). Since
issuance of the proposal, the EPA has received new facility operation
and HAP emissions data from the Freeport facility through the public
comments and issuance of a 2022 CAA section 114 information request.
Detailed information on the new data is provided in the memorandum
Updated Stack/Emissions Data Collected for 2023 Primary Copper Smelting
Risk Review, which is available in the docket for this action (Docket
ID No. EPA-HQ-OAR-2020-0430).
    Based on the updated stack and performance tests submitted by
Freeport as part of the section 114 request, we updated the baseline
risk assessment for this supplemental proposal. The new assessment
reflects emissions changes to the known risk drivers (arsenic and lead)
and a potential risk driver (mercury) at Freeport. Since this
supplemental proposal only reflects emissions changes for the Freeport
facility, we only updated the risk assessment for this facility.
    Also, this supplemental proposal includes an updated control option
1 and a new control option 2 that affect the Freeport facility only, as
described in Table 4. Because of these changes, we conducted for this
supplemental proposal an updated assessment of post-control risk for
both of these emission control scenarios for Freeport. The risk results
for the Asarco facility have not changed since the 2022 proposal. The
details of the risk assessment for Asarco are described in the 2022
proposal Federal Register publication (87 FR 1616; January 11, 2022)
for details and the 2022 risk report, which is available in the docket
for this proposed rule.

  Table 4--Comparison of the Primary Copper Smelting Baseline Inhalation Risk Assessment Results for Freeport With Post-Control Risk Estimates for Two
                                                       2023 Proposed Supplemental Control Options
                                                       [Estimated risks based on actual emissions]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Population at                                      Maximum      Max predicted
                                              Maximum     increased risk   Annual cancer      Maximum       residential       3-month
      Risk assessment scenario \1\          individual       of cancer       incidence        chronic        annual Pb      modeled Pb    Acute HQ (REL)
                                            cancer risk   [gteqt]  1-in-    (cases per       noncancer      conc. (ug/      conc. (ug/          \5\
                                          (in-1 million)     1 million         year)         TOSHI \2\       m\3\) \3\       m\3\)\4\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Rule (original baseline).......         80 (As)          24,400           0.002          1 (As)            0.12       0.17 (Pb)          7 (As)
Supplemental Proposal (revised baseline)         70 (As)          22,900           0.002          1 (As)            0.12       0.17 (Pb)          7 (As)
Supplemental Proposal Post-Control for           20 (As)          17,400           0.001        0.3 (As)           0.041       0.06 (Pb)          2 (As)
 Anode Roofline.........................
Supplemental Proposal Post-Control               20 (As)          15,500          0.0006        0.3 (As)           0.026       0.04 (Pb)          1 (As)
 Option 1 for Aisle Scrubber \6\........
Supplemental Proposal Post-Control               20 (As)          16,700          0.0006        0.3 (As)           0.028       0.04 (Pb)          1 (As)
 Option 2 for Aisle Scrubber \7\........
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ All values provided in this table are based upon only arsenic and lead emissions from Freeport (Miami, AZ).
\2\ TOSHI value for developmental effects does not include contribution from lead.
\3\ The maximum annual concentration for lead is based upon the MIR location which is also the maximum off-site exposure location for Freeport.
\4\ The maximum predicted 3-month Pb (lead) conc based on actual emissions at the time of proposal was based on AERMOD modeling with LEAD_POST, while
  the maximum predicted 3-month Pb conc for the supplemental proposal are based upon extrapolations of the HEM-4 annual Pb concentrations using the
  annual and 3-month modeled results from proposal.
\5\ The HQ values are based upon the lowest 1-hour acute health benchmark, the reference exposure level (REL) for arsenic. Arsenic also has an AEGL-2
  value (irreversible or escape-impairing effects) which resulted in a maximum HQ value of 0.0006 based upon actual emissions estimated in this
  supplemental proposal.
\6\ Option 1 represents controls on anode roofline (described in section III.C of this preamble) +WESP on aisle scrubber (described in section III.E of
  this preamble).
\7\ Option 2 represents controls on anode roofline (described in section III.C of this preamble) + baghouse upstream of aisle scrubber (described in
  section III.E of this preamble).

    The methodologies used for the updated baseline risk analysis are
described in section III.C. of the preamble to the January 11, 2022,
proposed rule National Emission Standards for Hazardous Air Pollutants:
Primary Copper Smelting Residual Risk and Technology Review (87 FR
1616; January 11, 2022). We present the results of the updated baseline
risk analysis for Freeport and the analysis of the proposed control
options in Table 4 of this preamble (rows labeled ``Supplemental
Proposal Post-Control Option 1'' and ``Supplemental Proposal Post-
Control Option 2'') and in more detail in the document: Revised
Residual Risk Assessment for the Freeport Smelter (Miami, AZ) in
Support of the 2023 Supplemental Proposal for the Primary Copper
Smelting Source Category, available in the docket for this action
(Docket No. EPA-HQ-OAR-2020-0430). For more detail on the proposed
control options, refer to sections III.C and III.E. of this preamble.
    The updated baseline risk assessment did not result in a