[Federal Register Volume 86, Number 5 (Friday, January 8, 2021)]
[Proposed Rules]
[Pages 1390-1418]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-00176]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2020-0535; FRL-10018-38-OAR]
RIN 2060-AU65


National Emission Standards for Hazardous Air Pollutants: Primary 
Magnesium Refining Residual Risk and Technology Review

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: This proposal presents the results of the U.S. Environmental 
Protection Agency's (EPA's) residual risk and technology review (RTR) 
for the National Emission Standards for the Hazardous Air Pollutants 
(NESHAP) for Primary Magnesium Refining, as required under the Clean 
Air Act (CAA). Based on the results of the risk review, the EPA is 
proposing that risks from emissions of air toxics from this source 
category are acceptable and that after removing the exemptions for 
startup, shutdown, and malfunction (SSM), the NESHAP provides an ample 
margin of safety. Furthermore, under the technology review, we are 
proposing one development in technology and practices that will require 
continuous pH monitoring for all control devices used to meet the acid 
gas emission limits of this subpart. In addition, as part of the 
technology review, the EPA is addressing a previously unregulated 
source of chlorine emissions, known as the chlorine bypass stack (CBS), 
by proposing a maximum achievable control technology (MACT) emissions 
standard for chlorine emissions from this source. The EPA also is 
proposing amendments to the regulatory provisions related to emissions 
during periods of SSM, including removing exemptions for periods of SSM 
and adding a work practice standard for malfunction events associated 
with the chlorine reduction burner (CRB); all emission limits will 
apply at all other times. In addition, the EPA is proposing electronic 
reporting of performance test results and performance evaluation 
reports.

DATES: Comments. Comments must be received on or before February 22, 
2021. 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 February 8, 2021.
    Public hearing: If anyone contacts us requesting a public hearing 
on or before January 13, 2021, 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-2020-0535, 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-2020-0535 in the subject line of the message.
     Fax: (202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-
2020-0535.
     Mail: U.S. Environmental Protection Agency, EPA Docket 
Center, Docket ID No. EPA-HQ-OAR-2020-0535, Mail Code 28221T, 1200 
Pennsylvania Avenue NW, Washington, DC 20460.
     Hand/Courier Delivery: EPA Docket Center, WJC West 
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. 
The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-
Friday (except federal holidays).
    Instructions: All submissions received must include the Docket ID 
No. for this rulemaking. Comments received may be posted without change 
to https://www.regulations.gov/, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the rulemaking process, see the SUPPLEMENTARY 
INFORMATION section of this document. Out of an abundance of caution 
for members of the public and our staff, the EPA Docket Center and 
Reading Room are closed to the public, with limited exceptions, to 
reduce the risk of transmitting COVID-19. Our Docket Center staff will 
continue to provide remote customer service via email, phone, and 
webform. We encourage the public to submit comments via https://www.regulations.gov/ or email, as there may be a delay in processing 
mail and faxes. Hand deliveries and couriers may be received by 
scheduled appointment only. For further information on EPA Docket 
Center services and the current status, please visit us online at 
https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed 
action, contact Michael Moeller, Sector Policies and Programs Division, 
Office of Air Quality Planning and Standards, U.S. Environmental 
Protection Agency, Research Triangle Park, North Carolina 27711; 
telephone number: (919) 541-2766; fax number: (919) 541-4991 and email 
address: [email protected]. For specific information regarding 
the risk modeling methodology, contact Jim Hirtz, Health and 
Environmental Impacts Division (C539-02), Office of Air Quality 
Planning and Standards, U.S. Environmental Protection Agency, Research 
Triangle Park, North Carolina 27711; telephone number: (919) 541-0881; 
fax number: (919) 541-0840; and email address: [email protected].

SUPPLEMENTARY INFORMATION: Participation in virtual public hearing. 
Please note that the EPA is deviating from its typical approach for 
public hearings because the President has declared a national 
emergency. Due to the current Centers for Disease Control and 
Prevention (CDC) recommendations, as well as state and

[[Page 1391]]

local orders for social distancing to limit the spread of COVID-19, the 
EPA cannot hold in-person public meetings at this time.
    To request a virtual public hearing, contact the public hearing 
team at (888) 372-8699 or by email at [email protected]. If 
requested, the virtual hearing will be held on January 25, 2021. The 
hearing will convene at 9:00 a.m. Eastern Time (ET) and will conclude 
at 3:00 p.m. ET. The EPA may close a session 15 minutes after the last 
pre-registered speaker has testified if there are no additional 
speakers. The EPA will announce further details at https://www.epa.gov/stationary-sources-air-pollution/primary-magnesium-refining-national-emissions-standards-hazardous/.
    The EPA will begin pre-registering speakers for the hearing upon 
publication of this document in the Federal Register, if a hearing is 
requested. 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-magnesium-refining-national-emissions-standards-hazardous/ or contact the public hearing team at (888) 372-
8699 or by email at [email protected]. The last day to pre-
register to speak at the hearing will be January 21, 2021. 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/stationary-sources-air-pollution/primary-magnesium-refining-national-emissions-standards-hazardous/.
    The EPA will make every effort to follow the schedule as closely as 
possible on the day of the hearing; however, please plan for the 
hearings to run either ahead of schedule or behind schedule.
    Each commenter will have 5 minutes to provide oral testimony. The 
EPA encourages commenters to provide the EPA with a copy of their oral 
testimony electronically (via email) by emailing it to Michael Moeller, 
email address: [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/stationary-sources-air-pollution/primary-magnesium-refining-national-emissions-standards-hazardous/. While the EPA expects the 
hearing to go forward as set forth above, please monitor our website or 
contact our public hearing team at (888) 372-8699 or by email at 
[email protected] to determine if there are any updates. The 
EPA does not intend to publish a document in the Federal Register 
announcing updates.
    If you require the services of a translator or a special 
accommodation such as audio description, please pre-register for the 
hearing with the public hearing team at the phone number or website 
provided above and describe your needs by January 15, 2021. 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-2020-0535. 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-
2020-0535. The EPA's policy is that all comments received will be 
included in the public docket without change and may be made available 
online at https://www.regulations.gov/, including any personal 
information provided, unless the comment includes information claimed 
to be CBI or other information whose disclosure is restricted by 
statute. Do not submit electronically any information that you consider 
to be CBI or other information whose disclosure is restricted by 
statute. This type of information should be submitted by mail as 
discussed below.
    The EPA may publish any comment received to its public docket. 
Multimedia submissions (audio, video, etc.) must be accompanied by a 
written comment. The written comment is considered the official comment 
and should include discussion of all points you wish to make. The EPA 
will generally not consider comments or comment contents located 
outside of the primary submission (i.e., on the web, cloud, or other 
file sharing system). For additional submission methods, the full EPA 
public comment policy, information about CBI or multimedia submissions, 
and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    The https://www.regulations.gov/ website allows you to submit your 
comment anonymously, which means the EPA will not know your identity or 
contact information unless you provide it in the body of your comment. 
If you send an email comment directly to the EPA without going through 
https://www.regulations.gov/, your email address will be automatically 
captured and included as part of the comment that is placed in the 
public docket and made available on the internet. If you submit an 
electronic comment, the EPA recommends that you include your name and 
other contact information in the body of your comment and with any 
digital storage media you submit. If the EPA cannot read your comment 
due to technical difficulties and cannot contact you for clarification, 
the EPA may not be able to consider your comment. Electronic files 
should not include special characters or any form of encryption and be 
free of any defects or viruses. For additional information about the 
EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    The EPA is temporarily suspending its Docket Center and Reading 
Room for public visitors, with limited exceptions, to reduce the risk 
of transmitting COVID-19. Our Docket Center staff will continue to 
provide remote customer service via email, phone, and webform. We 
encourage the public to submit comments via https://www.regulations.gov/ as there may be a delay in processing mail and 
faxes. Hand deliveries or couriers will be received by scheduled 
appointment only. For further information and updates on EPA Docket 
Center services, please visit us online at https://www.epa.gov/dockets.
    The EPA continues to carefully and continuously monitor information 
from the CDC, local area health departments, and our Federal partners 
so that we can respond rapidly as conditions change regarding COVID-19.
    Submitting CBI. Do not submit information containing CBI to the EPA 
through https://www.regulations.gov/ or email. Clearly mark the part or 
all of the information that you claim to be CBI. For CBI information on 
any digital storage media that you mail to the EPA, mark the outside of 
the digital storage

[[Page 1392]]

media as CBI and then identify electronically within the digital 
storage media the specific information that is claimed as CBI. In 
addition to one complete version of the comments that includes 
information claimed as CBI, you must submit a copy of the comments that 
does not contain the information claimed as CBI directly to the public 
docket through the procedures outlined in Instructions above. If you 
submit any digital storage media that does not contain CBI, mark the 
outside of the digital storage media clearly that it does not contain 
CBI. Information not marked as CBI will be included in the public 
docket and the EPA's electronic public docket without prior notice. 
Information marked as CBI will not be disclosed except in accordance 
with procedures set forth in 40 Code of Federal Regulations (CFR) part 
2. Send or deliver information identified as CBI only to the following 
address: OAQPS Document Control Officer (C404-02), OAQPS, U.S. 
Environmental Protection Agency, Research Triangle Park, North Carolina 
27711, Attention Docket ID No. EPA-HQ-OAR-2020-0535. Note that written 
comments containing CBI and submitted by mail may be delayed and no 
hand deliveries will be accepted.
    Preamble acronyms and abbreviations. We use multiple acronyms and 
terms in this preamble. While this list may not be exhaustive, to ease 
the reading of this preamble and for reference purposes, the EPA 
defines the following terms and acronyms here:

AEGL acute exposure guideline level
AERMOD air dispersion model used by the HEM-3 model
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CBS chlorine bypass stack
CDC Centers for Disease Control and Prevention
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CFR Code of Federal Regulations
CPMS continuous parameter monitoring system
CRB chlorine reduction burner
EPA Environmental Protection Agency
ERPG emergency response planning guideline
ERT Electronic Reporting Tool
HAP hazardous air pollutant(s)
HCl hydrochloric acid
HEM-3 Human Exposure Model, Version 1.5.5
HF hydrogen fluoride
HI hazard index
HQ hazard quotient
IRIS Integrated Risk Information System
km kilometer
LOAEL lowest-observed-adverse-effect-level
MACT maximum achievable control technology
mg/m3 milligrams per cubic meter
MIR maximum individual risk
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NESHAP national emission standards for hazardous air pollutants
NOAEL no-observed-adverse-effect-level
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PAH polycyclic aromatic hydrocarbons
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PM particulate matter
POM polycyclic organic matter
ppm parts per million
REL reference exposure level
RfC reference concentration
RfD reference dose
RTR residual risk and technology review
SAB Science Advisory Board
SSM startup, shutdown, and malfunction
TOSHI target organ-specific hazard index
tpy tons per year
TRIM.FaTE Total Risk Integrated Methodology.Fate, Transport, and 
Ecological Exposure model
UF uncertainty factor
[micro]g/m3 microgram per cubic meter
URE unit risk estimate
VCS voluntary consensus standards

    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 data collection activities were conducted to support 
this action?
    D. What other relevant background information and data are 
available?
III. Analytical Procedures and Decision-Making
    A. How do we consider risk in our decision-making?
    B. How do we perform the technology review?
    C. How do we estimate post-MACT risk posed by the source 
category?
IV. Analytical Results and Proposed Decisions
    A. What actions are we taking pursuant to CAA sections 112(d)(2) 
and 112(d)(3)?
    B. What are the results of the risk assessment and analyses?
    C. What are our proposed decisions regarding risk acceptability, 
ample margin of safety, and adverse environmental effect?
    D. What are the results and proposed decisions based on our 
technology review?
    E. What other actions are we proposing?
    F. What compliance dates are we proposing?
V. 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?
VI. Request for Comments
VII. Submitting Data Corrections
VIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Executive Order 13771: Reducing Regulations and Controlling 
Regulatory Costs
    C. Paperwork Reduction Act (PRA)
    D. Regulatory Flexibility Act (RFA)
    E. Unfunded Mandates Reform Act (UMRA)
    F. Executive Order 13132: Federalism
    G. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    H. Executive Order 13045: Protection of Children From 
Environmental Health Risks and Safety Risks
    I. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    J. National Technology Transfer and Advancement Act (NTTAA) and 
1 CFR Part 51
    K. 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 the 
Primary Magnesium Refining major sources regulated under 40 CFR part 
63, subpart TTTTT. The North American Industry Classification System 
(NAICS) code for the primary magnesium refining industry is 331410. 
This category and NAICS code are not intended to be exhaustive, but 
rather provide 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 Magnesium Refining source 
category is any facility engaged in producing metallic magnesium. The 
source category

[[Page 1393]]

includes, but is not limited to, metallic magnesium produced using the 
Dow sea-water process or the Pidgeon process. The Dow sea-water process 
involves the electrolysis of molten magnesium chloride. The Pidgeon 
process involves the thermal reduction of magnesium oxide with 
ferrosilicon.

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-magnesium-refining-national-emissions-standards-hazardous/. 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. 
Information on the overall RTR program is available at https://www.epa.gov/ttn/atw/rrisk/rtrpg.html.
    The proposed changes to the CFR that would be necessary to 
incorporate the changes proposed in this action are set out in an 
attachment to the memorandum titled Proposed Regulation Edits for 40 
CFR part 63, subpart TTTTT, available in the docket for this action 
(Docket ID No. EPA-HQ-OAR-2020-0535). The document includes the 
specific proposed amendatory language for revising the CFR and, for the 
convenience of interested parties, a redline version of the regulation. 
Following signature by the EPA Administrator, the EPA will also post a 
copy of this memorandum and the attachments to https://www.epa.gov/stationary-sources-air-pollution/primary-magnesium-refining-national-emissions-standards-hazardous/.

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 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 hazardous air pollutants (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 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.'' When the 
two reviews are combined into a single rulemaking, it is commonly 
referred to as the ``risk and 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 standards. For area sources, CAA 
section 112(d)(5) gives the EPA discretion 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 (the Court) 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 38045). If risks are 
unacceptable, the EPA must determine the emissions standards necessary 
to reduce risk 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,

[[Page 1394]]

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, we consider whether a 
more stringent standard is necessary to prevent, taking into 
consideration costs, energy, safety, and other relevant factors, an 
adverse environmental effect.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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. In 
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 required to 
address regulatory gaps, such as missing standards for listed air 
toxics known to be emitted from the source category. Louisiana 
Environmental Action Network (LEAN) v. EPA, 955 F.3d 1088 (D.C. Cir. 
2020).

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

    The EPA initially promulgated the Primary Magnesium Refining NESHAP 
on October 10, 2003 (68 FR 58615), and it is codified at 40 CFR part 
63, subpart TTTTT. This NESHAP regulates HAP emissions from new and 
existing primary magnesium refining facilities that are major sources 
of HAP. The source category is comprised of one plant that is owned by 
US Magnesium LLC and located in Rowley, Utah.
    The plant produces magnesium from brine (salt water) taken from the 
Great Salt Lake. The production process concentrates the magnesium 
salts in the brine, then processes the brine to remove impurities that 
would affect metal quality. After the brine solution is converted to a 
powder mixture of magnesium chloride and magnesium oxide in the spray 
dryers, the powder is conveyed to the melt/reactors. The melt/reactor 
melts the powder mixture and converts the remaining magnesium oxide to 
magnesium chloride by injecting chlorine into the molten salt. The 
purified molten salt is then transferred to the electrolytic cells 
where it is separated into magnesium metal and chlorine by 
electrolysis. The electrolysis process passes a direct electric current 
through the molten magnesium chloride, causing the dissociation of the 
salt and resulting in the generation of chlorine gas and magnesium 
metal. The magnesium metal is then transferred to the foundry for 
casting into ingots for sale. The chlorine produced is piped to a 
chlorine plant where it is liquefied for reuse or sale.
    The HAP emitted from the Primary Magnesium Refining source category 
are chlorine, hydrochloric acid (HCl), dioxin/furan, and trace amounts 
of HAP metals. Emission controls include various combinations of wet 
scrubbers (venturi and packed-bed scrubber) for acid gas and 
particulate matter (PM) control.
    Chlorine is emitted from the melting and purification of reactor 
cell product and is controlled by conversion to HCl in the CRB and 
subsequent absorption of the HCl in venturi and packed-bed scrubber. 
Using these control technologies, upwards of 99.9 percent control of 
chlorine is achieved. The electrowinning of the melted magnesium 
chloride to magnesium metal produces as a byproduct chlorine gas which 
is recovered at the chlorine plant. When the chlorine plant is 
inoperable, the chlorine produced at the electrolytic cells is routed 
through the CBS which contains a packed-bed scrubber and uses ferrous 
chloride as the adsorbing medium.
    HCl is emitted from the spray drying and storage of magnesium 
chloride powder and the melting and purification of reactor cell 
product prior to the electrowinning process. HCl emissions are 
controlled by venturi and packed-bed scrubbers.
    Dioxins/furans are generated in the melt/reactor and are subject to 
incidental control by the wet scrubbers used to control chlorine, HCl, 
and PM.
    The current rule requires compliance with emission limits, 
operating limits for control devices, and work practice standards. The 
emission limits include mass rate emission limits in pounds per hour 
(lbs/hr) for chlorine, HCl, PM, and particulate matter less than or 
equal to 10 microns (PM10). Additional emission limits in 
grains per dry standard cubic foot (gr/dscf) apply to magnesium 
chloride storage bins. The emission limits are shown in Table 1 of this 
preamble.

                                       Table 1--Mass Rate Emission Limits
                                                    [LBS/HR]
----------------------------------------------------------------------------------------------------------------
                 Emission point                      Chlorine           HCl             PM             PM10
----------------------------------------------------------------------------------------------------------------
Spray dryers....................................  ..............             200             100  ..............
Magnesium chloride storage bins \1\.............  ..............            47.5  ..............             2.7
Melt/reactor system.............................             100             7.2  ..............            13.1
Launder off-gas system..........................            26.0            46.0            37.5
----------------------------------------------------------------------------------------------------------------
\1\ Additional limits are 0.35 gr/dscf of HCl and 0.016 gr/dscf of PM10.

    The current rule also includes an emission limit for each melt/
reactor system of 36 nanograms of dioxin/furan toxicity equivalents per 
dry standard cubic meter corrected to 7 percent oxygen.
    Performance tests are required to demonstrate compliance with the 
emission limits and must be conducted at least twice during each title 
V operating permit term (at midterm and renewal). The source is also 
required to monitor operating parameters for control devices subject to 
operating limits established during the performance tests and carry out 
the procedures in their fugitive dust emissions control plan and their 
operation and maintenance plan. For wet scrubbers, the source is 
required to use continuous parameter monitoring systems (CPMS) to 
measure and record the hourly average pressure drop and scrubber water 
flow rate. To

[[Page 1395]]

demonstrate continuous compliance, the source must keep records 
documenting conformance with the monitoring requirements and the 
installation, operation, and maintenance requirements for CPMS.

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

    For the Primary Magnesium Refining source category, the EPA used 
emissions and supporting data from the 2017 National Emissions 
Inventory (NEI) as the primary data to develop the model input file for 
the residual risk assessment. The NEI is a database that contains 
information about sources that emit criteria air pollutants, their 
precursors, and HAP. The database includes estimates of annual air 
pollutant emissions from point, nonpoint, and mobile sources in the 50 
states, the District of Columbia, Puerto Rico, and the U.S. Virgin 
Islands. The EPA collects this information and releases an updated 
version of the NEI database every 3 years. The NEI includes data 
necessary for conducting risk modeling, including annual HAP emissions 
estimates from individual emission sources at facilities and the 
related emissions release parameters. Additional information on the 
development of the modeling file can be found in Appendix 1 to the 
Residual Risk Assessment for the Primary Magnesium Refining Source 
Category in Support of the 2020 Risk and Technology Review Proposed 
Rule, which is available in the docket for this proposed rule.

D. What other relevant background information and data are available?

    Information used to estimate emissions from the primary magnesium 
refining facility was obtained primarily from the EPA's 2017 NEI 
database, available at: https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data. Supplemental information 
was used from publicly available documents from the Utah Department of 
Environmental Quality (http://eqedocs.utah.gov/) and the EPA Region 8 
Superfund Remedial Investigation (https://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id=0802704). Data on the numbers, types, 
dimensions, and locations of the emission points for the facility were 
obtained from the NEI, Google Earth\TM\, and US Magnesium facility 
representatives. The HAP emissions from US Magnesium were categorized 
by source into one of the four emission process groups as follows: 
Spray dryers, magnesium chloride storage bins, melt/reactor system, and 
the CBS. Data on HAP emissions, including the HAP emitted, emission 
source, emission rates, stack parameters (such as temperature, 
velocity, flowrate, etc.), and latitude and longitude were compiled 
into a draft modeling file. To ensure the quality of the emissions 
data, the EPA subjected the draft modeling file to a variety of quality 
checks. The draft modeling file was made available to the facility to 
review the emission release parameters and the emission rates. Source 
latitudes and longitudes were checked in Google Earth\TM\ to verify 
accuracy and were corrected as needed. These and other quality control 
efforts resulted in a more accurate emissions dataset. Additional 
information on the development of the modeling file can be found in 
Appendix 1 to the Residual Risk Assessment for the Primary Magnesium 
Refining Source Category in Support of the 2020 Risk and Technology 
Review Proposed Rule, which is available in the docket for this 
proposed rule.

III. Analytical Procedures and Decision-Making

    In this section, we describe the analyses performed to support the 
proposed decisions for the RTR and other issues addressed in this 
proposal.

A. How do we consider risk in our decision-making?

    As discussed in section II.A of this preamble and in the Benzene 
NESHAP, in evaluating and developing standards under CAA section 
112(f)(2), we apply a two-step approach to determine whether or not 
risks are acceptable and to determine if the standards provide an ample 
margin of safety to protect public health. As explained in the Benzene 
NESHAP, ``the first step judgment on acceptability cannot be reduced to 
any single factor'' and, thus, ``[t]he Administrator believes that the 
acceptability of risk under section 112 is best judged on the basis of 
a broad set of health risk measures and information.'' (54 FR 38046). 
Similarly, with regard to the ample margin of safety determination, 
``the Agency again considers all of the health risk and other health 
information considered in the first step. Beyond that information, 
additional factors relating to the appropriate level of control will 
also be considered, including cost and economic impacts of controls, 
technological feasibility, uncertainties, and any other relevant 
factors.'' Id.
    The Benzene NESHAP approach provides flexibility regarding factors 
the EPA may consider in making determinations and how the EPA may weigh 
those factors for each source category. The EPA conducts a risk 
assessment that provides estimates of the MIR posed by emissions of HAP 
that are carcinogens from each source in the source category, the 
hazard index (HI) for chronic exposures to HAP with the potential to 
cause noncancer health effects, and the hazard quotient (HQ) for acute 
exposures to HAP with the potential to cause noncancer health 
effects.\2\ The assessment also provides estimates of the distribution 
of cancer risk within the exposed populations, cancer incidence, and an 
evaluation of the potential for an adverse environmental effect. The 
scope of the EPA's risk analysis is consistent with the explanation in 
EPA's response to comments on our policy under the Benzene NESHAP:
---------------------------------------------------------------------------

    \2\ The MIR is defined as the cancer risk associated with a 
lifetime of exposure at the highest concentration of HAP where 
people are likely to live. The HQ is the ratio of the potential HAP 
exposure concentration to the noncancer dose-response value; the HI 
is the sum of HQs for HAP that affect the same target organ or organ 
system.

    The policy chosen by the Administrator permits consideration of 
multiple measures of health risk. Not only can the MIR figure be 
considered, but also incidence, the presence of non-cancer health 
effects, and the uncertainties of the risk estimates. In this way, 
the effect on the most exposed individuals can be reviewed as well 
as the impact on the general public. These factors can then be 
weighed in each individual case. This approach complies with the 
Vinyl Chloride mandate that the Administrator ascertain an 
acceptable level of risk to the public by employing his expertise to 
assess available data. It also complies with the Congressional 
intent behind the CAA, which did not exclude the use of any 
particular measure of public health risk from the EPA's 
consideration with respect to CAA section 112 regulations, and 
thereby implicitly permits consideration of any and all measures of 
health risk which the Administrator, in his judgment, believes are 
---------------------------------------------------------------------------
appropriate to determining what will ``protect the public health''.

(54 FR 38057). Thus, the level of the MIR is only one factor to be 
weighed in determining acceptability of risk. The Benzene NESHAP 
explained that ``an MIR of approximately one in 10 thousand should 
ordinarily be the upper end of the range of acceptability. As risks 
increase above this benchmark, they become presumptively less 
acceptable under CAA section 112, and would be weighed with the other 
health risk measures and information in making an overall judgment on 
acceptability. Or, the Agency may find, in a particular case, that a 
risk that includes an MIR less than the presumptively acceptable level 
is unacceptable in the light of other health risk factors.'' Id. at 
38045. In other

[[Page 1396]]

words, risks that include an MIR above 100-in-1 million may be 
determined to be acceptable, and risks with an MIR below that level may 
be determined to be unacceptable, depending on all of the available 
health information. Similarly, with regard to the ample margin of 
safety analysis, the EPA stated in the Benzene NESHAP that: ``EPA 
believes the relative weight of the many factors that can be considered 
in selecting an ample margin of safety can only be determined for each 
specific source category. This occurs mainly because technological and 
economic factors (along with the health-related factors) vary from 
source category to source category.'' Id. at 38061. We also consider 
the uncertainties associated with the various risk analyses, as 
discussed earlier in this preamble, in our determinations of 
acceptability and ample margin of safety.
    The EPA notes that it has not considered certain health information 
to date in making residual risk determinations. At this time, we do not 
attempt to quantify the HAP risk that may be associated with emissions 
from other facilities that do not include the source category under 
review, mobile source emissions, natural source emissions, persistent 
environmental pollution, or atmospheric transformation in the vicinity 
of the sources in the category.
    The EPA understands the potential importance of considering an 
individual's total exposure to HAP in addition to considering exposure 
to HAP emissions from the source category and facility. We recognize 
that such consideration may be particularly important when assessing 
noncancer risk, where pollutant-specific exposure health reference 
levels (e.g., reference concentrations (RfCs)) are based on the 
assumption that thresholds exist for adverse health effects. For 
example, the EPA recognizes that, although exposures attributable to 
emissions from a source category or facility alone may not indicate the 
potential for increased risk of adverse noncancer health effects in a 
population, the exposures resulting from emissions from the facility in 
combination with emissions from all of the other sources (e.g., other 
facilities) to which an individual is exposed may be sufficient to 
result in an increased risk of adverse noncancer health effects. In May 
2010, the Science Advisory Board (SAB) advised the EPA ``that RTR 
assessments will be most useful to decision makers and communities if 
results are presented in the broader context of aggregate and 
cumulative risks, including background concentrations and contributions 
from other sources in the area.'' \3\
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    \3\ Recommendations of the SAB Risk and Technology Review 
Methods Panel are provided in their report, which is available at: 
https://yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.
---------------------------------------------------------------------------

    In response to the SAB recommendations, the EPA incorporates 
cumulative risk analyses into its RTR risk assessments. The Agency (1) 
conducts facility-wide assessments, which include source category 
emission points, as well as other emission points within the 
facilities; (2) combines exposures from multiple sources in the same 
category that could affect the same individuals; and (3) for some 
persistent and bioaccumulative pollutants, analyzes the ingestion route 
of exposure. In addition, the RTR risk assessments consider aggregate 
cancer risk from all carcinogens and aggregated noncancer HQs for all 
noncarcinogens affecting the same target organ or target organ system.
    Although we are interested in placing source category and facility-
wide HAP risk in the context of total HAP risk from all sources 
combined in the vicinity of each source, we are concerned about the 
uncertainties of doing so. Estimates of total HAP risk from emission 
sources other than those that we have studied in depth during this RTR 
review would have significantly greater associated uncertainties than 
the source category or facility-wide estimates. Such aggregate or 
cumulative assessments would compound those uncertainties, making the 
assessments too unreliable.

B. How do we perform the technology review?

    Our technology review primarily focuses on the identification and 
evaluation of developments in practices, processes, and control 
technologies that have occurred since the MACT standards were 
promulgated. Where we identify such developments, we analyze their 
technical feasibility, estimated costs, energy implications, and non-
air environmental impacts. We also consider the emission reductions 
associated with applying each development. This analysis informs our 
decision of whether it is ``necessary'' to revise the emissions 
standards. In addition, we consider the appropriateness of applying 
controls to new sources versus retrofitting existing sources. For this 
exercise, we consider any of the following to be a ``development'':
     Any add-on control technology or other equipment that was 
not identified and considered during development of the original MACT 
standards;
     Any improvements in add-on control technology or other 
equipment (that were identified and considered during development of 
the original MACT standards) that could result in additional emissions 
reduction;
     Any work practice or operational procedure that was not 
identified or considered during development of the original MACT 
standards;
     Any process change or pollution prevention alternative 
that could be broadly applied to the industry and that was not 
identified or considered during development of the original MACT 
standards; and
     Any significant changes in the cost (including cost 
effectiveness) of applying controls (including controls the EPA 
considered during the development of the original MACT standards).
    In addition to reviewing the practices, processes, and control 
technologies that were considered at the time we originally developed 
the NESHAP, we review a variety of data sources in our investigation of 
potential practices, processes, or controls. We also review the NESHAP 
and the available data to determine if there are any unregulated 
emissions of HAP within the source category and evaluate this data for 
use in developing new emission standards. See sections II.C and II.D of 
this preamble for information on the specific data sources that were 
reviewed as part of the technology review.

C. How do we estimate post-MACT risk posed by the source category?

    In this section, we provide a complete description of the types of 
analyses that we generally perform during the risk assessment process. 
In some cases, we do not perform a specific analysis because it is not 
relevant. For example, in the absence of emissions of HAP known to be 
persistent and bioaccumulative in the environment (PB-HAP), we would 
not perform a multipathway exposure assessment. Where we do not perform 
an analysis, we state that we do not and provide the reason. While we 
present all of our risk assessment methods, we only present risk 
assessment results for the analyses actually conducted (see section 
IV.B of this preamble).
    The EPA conducts a risk assessment that provides estimates of the 
MIR for cancer posed by the HAP emissions from each source in the 
source category, the HI for chronic exposures to HAP with the potential 
to cause noncancer health effects, and the HQ for acute exposures to 
HAP with the potential to

[[Page 1397]]

cause noncancer health effects. The assessment also provides estimates 
of the distribution of cancer risk within the exposed populations, 
cancer incidence, and an evaluation of the potential for an adverse 
environmental effect. The seven sections that follow this paragraph 
describe how we estimated emissions and conducted the risk assessment. 
The docket for this rulemaking contains the following document which 
provides more information on the risk assessment inputs and models: 
Residual Risk Assessment for the Primary Magnesium Refining Source 
Category in Support of the 2020 Risk and Technology Review Proposed 
Rule. The methods used to assess risk (as described in the seven 
primary steps below) are consistent with those described by the EPA in 
the document reviewed by a panel of the EPA's SAB in 2009; \4\ and 
described in the SAB review report issued in 2010. They are also 
consistent with the key recommendations contained in that report.
---------------------------------------------------------------------------

    \4\ U.S. EPA. Risk and Technology Review (RTR) Risk Assessment 
Methodologies: For Review by the EPA's Science Advisory Board with 
Case Studies--MACT I Petroleum Refining Sources and Portland Cement 
Manufacturing, June 2009. EPA-452/R-09-006. https://www.epa.gov/airtoxics/rrisk/rtrpg.html.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions 
release characteristics?
    The HAP emissions from US Magnesium fall into the following 
pollutant categories: Acid gases (i.e., HCl and chlorine), metals (HAP 
metals) and dioxins/furans. The HAP are emitted from several emission 
sources at US Magnesium which, for the purposes of the source category 
risk assessment, have been categorized into four emission process 
groups as follows: Spray dryers, magnesium chloride storage bins, melt/
reactor system, and the CBS. The main sources of emissions data include 
the NEI data submitted for calendar year 2017 and supplemental 
information gathered from the public domains of the Utah Department of 
Environmental Quality (DEQ) (http://eqedocs.utah.gov/) and the EPA 
Region 8 Superfund Remedial Investigation, available at: https://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id=0802704, and also 
available in the docket for this action (Docket ID No. EPA-HQ-OAR-2020-
0535). Data on the numbers, types, dimensions, and locations of the 
emission points for the facility were obtained from the NEI, Utah DEQ, 
Google Earth\TM\, and from representatives of the US Magnesium 
facility. A description of the data, approach, and rationale used to 
develop actual HAP emissions estimates is discussed in more detail in 
Appendix 1 to the Residual Risk Assessment for the Primary Magnesium 
Refining Source Category in Support of the 2020 Risk and Technology 
Review Proposed Rule, which is available in the docket (Docket ID No. 
EPA-HQ-OAR-2020-0535).
2. How did we estimate MACT-allowable emissions?
    The available emissions data in the RTR emissions dataset include 
estimates of the mass of HAP emitted during a specified annual time 
period. These ``actual'' emission levels are often lower than the 
emission levels allowed under the requirements of the current MACT 
standards. The emissions allowed under the MACT standards are referred 
to as the ``MACT-allowable'' emissions. We discussed the consideration 
of both MACT-allowable and actual emissions in the final Coke Oven 
Batteries RTR (70 FR 19992, 19998 and 19999, April 15, 2005) and in the 
proposed and final Hazardous Organic NESHAP RTR (71 FR 34421, 34428, 
June 14, 2006, and 71 FR 76603, 76609, December 21, 2006, 
respectively). In those actions, we noted that assessing the risk at 
the MACT-allowable level is inherently reasonable since that risk 
reflects the maximum level facilities could emit and still comply with 
national emission standards. We also explained that it is reasonable to 
consider actual emissions, where such data are available, in both steps 
of the risk analysis, in accordance with the Benzene NESHAP approach. 
(54 FR 38044.)
    Allowable emission rates for US Magnesium were developed based on 
the MACT emission limits. Specifically, given that the facility 
operates continuously throughout the year, the pound per hour emission 
limits for each emission process groups were used to calculate 
allowable emission totals. For sources without MACT limits in the 
current NESHAP, allowable emissions were assumed to equal to actual 
emissions since the facility operated continuously, at or near maximum 
capacity, during calendar year 2017. For a detailed description of the 
estimation of allowable emissions, see Appendix 1 to the Residual Risk 
Assessment for the Primary Magnesium Refining Source Category in 
Support of the 2020 Risk and Technology Review Proposed Rule, which is 
available in the docket (Docket ID No. EPA-HQ-OAR-2020-0535).
3. How do we conduct dispersion modeling, determine inhalation 
exposures, and estimate individual and population inhalation risk?
    Both long-term and short-term inhalation exposure concentrations 
and health risk from the source category addressed in this proposal 
were estimated using the Human Exposure Model (HEM-3).\5\ The HEM-3 
performs three primary risk assessment activities: (1) Conducting 
dispersion modeling to estimate the concentrations of HAP in ambient 
air, (2) estimating long-term and short-term inhalation exposures to 
individuals residing within 50 kilometers (km) of the modeled sources, 
and (3) estimating individual and population-level inhalation risk 
using the exposure estimates and quantitative dose-response 
information.
---------------------------------------------------------------------------

    \5\ For more information about HEM-3, go to https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem.
---------------------------------------------------------------------------

a. Dispersion Modeling
    The air dispersion model AERMOD, used by the HEM-3 model, is one of 
the EPA's preferred models for assessing air pollutant concentrations 
from industrial facilities.\6\ To perform the dispersion modeling and 
to develop the preliminary risk estimates, HEM-3 draws on three data 
libraries. The first is a library of meteorological data, which is used 
for dispersion calculations. This library includes 1 year (2016) of 
hourly surface and upper air observations from 824 meteorological 
stations selected to provide coverage of the United States and Puerto 
Rico. A second library of United States Census Bureau census block \7\ 
internal point locations and populations provides the basis of human 
exposure calculations (U.S. Census, 2010). In addition, for each census 
block, the census library includes the elevation and controlling hill 
height, which are also used in dispersion calculations. A third library 
of pollutant-specific dose-response values is used to estimate health 
risk. These are discussed below.
---------------------------------------------------------------------------

    \6\ U.S. EPA. Revision to the Guideline on Air Quality Models: 
Adoption of a Preferred General Purpose (Flat and Complex Terrain) 
Dispersion Model and Other Revisions (70 FR 68218, November 9, 
2005).
    \7\ A census block is the smallest geographic area for which 
census statistics are tabulated.
---------------------------------------------------------------------------

b. Risk From Chronic Exposure to HAP
    In developing the risk assessment for chronic exposures, we use the 
estimated annual average ambient air concentrations of each HAP emitted 
by each source in the source category. The HAP air concentrations at 
each nearby census block centroid located within 50 km of the facility 
are a surrogate for the chronic inhalation exposure concentration for 
all the people who reside in that census block. A distance of 50 km is 
consistent with both the analysis supporting the 1989 Benzene

[[Page 1398]]

NESHAP (54 FR 38044) and the limitations of Gaussian dispersion models, 
including AERMOD.
    For each facility, we calculate the MIR as the cancer risk 
associated with a continuous lifetime (24 hours per day, 7 days per 
week, 52 weeks per year, 70 years) exposure to the maximum 
concentration at the centroid of each inhabited census block. We 
calculate individual cancer risk by multiplying the estimated lifetime 
exposure to the ambient concentration of each HAP (in micrograms per 
cubic meter ([mu]g/m\3\)) by its unit risk estimate (URE). The URE is 
an upper-bound estimate of an individual's incremental risk of 
contracting cancer over a lifetime of exposure to a concentration of 1 
microgram of the pollutant per cubic meter of air. For residual risk 
assessments, we generally use UREs from the EPA's Integrated Risk 
Information System (IRIS). For carcinogenic pollutants without IRIS 
values, we look to other reputable sources of cancer dose-response 
values, often using California EPA (CalEPA) UREs, where available. In 
cases where new, scientifically credible dose-response values have been 
developed in a manner consistent with EPA guidelines and have undergone 
a peer review process similar to that used by the EPA, we may use such 
dose-response values in place of, or in addition to, other values, if 
appropriate. The pollutant-specific dose-response values used to 
estimate health risk are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
    To estimate individual lifetime cancer risks associated with 
exposure to HAP emissions from each facility in the source category, we 
sum the risks for each of the carcinogenic HAP \8\ emitted by the 
modeled facility. We estimate cancer risk at every census block within 
50 km of every facility in the source category. The MIR is the highest 
individual lifetime cancer risk estimated for any of those census 
blocks. In addition to calculating the MIR, we estimate the 
distribution of individual cancer risks for the source category by 
summing the number of individuals within 50 km of the sources whose 
estimated risk falls within a specified risk range. We also estimate 
annual cancer incidence by multiplying the estimated lifetime cancer 
risk at each census block by the number of people residing in that 
block, summing results for all of the census blocks, and then dividing 
this result by a 70-year lifetime.
---------------------------------------------------------------------------

    \8\ The EPA's 2005 Guidelines for Carcinogen Risk Assessment 
classifies carcinogens as: ``carcinogenic to humans,'' ``likely to 
be carcinogenic to humans,'' and ``suggestive evidence of 
carcinogenic potential.'' These classifications also coincide with 
the terms ``known carcinogen, probable carcinogen, and possible 
carcinogen,'' respectively, which are the terms advocated in the 
EPA's Guidelines for Carcinogen Risk Assessment, published in 1986 
(51 FR 33992, September 24, 1986). In August 2000, the document, 
Supplemental Guidance for Conducting Health Risk Assessment of 
Chemical Mixtures (EPA/630/R-00/002), was published as a supplement 
to the 1986 document. Copies of both documents can be obtained from 
https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944. Summing 
the risk of these individual compounds to obtain the cumulative 
cancer risk is an approach that was recommended by the EPA's SAB in 
their 2002 peer review of the EPA's National Air Toxics Assessment 
(NATA) titled NATA--Evaluating the National-scale Air Toxics 
Assessment 1996 Data--an SAB Advisory, available at https://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
---------------------------------------------------------------------------

    To assess the risk of noncancer health effects from chronic 
exposure to HAP, we calculate either an HQ or a target organ-specific 
hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is 
emitted. Where more than one noncancer HAP is emitted, we sum the HQ 
for each of the HAP that affects a common target organ or target organ 
system to obtain a TOSHI. The HQ is the estimated exposure divided by 
the chronic noncancer dose-response value, which is a value selected 
from one of several sources. The preferred chronic noncancer dose-
response value is the EPA RfC, defined as ``an estimate (with 
uncertainty spanning perhaps an order of magnitude) of a continuous 
inhalation exposure to the human population (including sensitive 
subgroups) that is likely to be without an appreciable risk of 
deleterious effects during a lifetime'' (https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary). In cases where an RfC 
from the EPA's IRIS is not available or where the EPA determines that 
using a value other than the RfC is appropriate, the chronic noncancer 
dose-response value can be a value from the following prioritized 
sources, which define their dose-response values similarly to the EPA: 
(1) The Agency for Toxic Substances and Disease Registry (ATSDR) 
Minimum Risk Level (https://www.atsdr.cdc.gov/mrls/index.asp); (2) the 
CalEPA Chronic Reference Exposure Level (REL) (https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0); or (3) as noted above, a scientifically 
credible dose-response value that has been developed in a manner 
consistent with the EPA guidelines and has undergone a peer review 
process similar to that used by the EPA. The pollutant-specific dose-
response values used to estimate health risks are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
c. Risk From Acute Exposure to HAP That May Cause Health Effects Other 
Than Cancer
    For each HAP for which appropriate acute inhalation dose-response 
values are available, the EPA also assesses the potential health risks 
due to acute exposure. For these assessments, the EPA makes 
conservative assumptions about emission rates, meteorology, and 
exposure location. As part of our efforts to continually improve our 
methodologies to evaluate the risks that HAP emitted from categories of 
industrial sources pose to human health and the environment,\9\ we 
revised our treatment of meteorological data to use reasonable worst-
case air dispersion conditions in our acute risk screening assessments 
instead of worst-case air dispersion conditions. This revised treatment 
of meteorological data and the supporting rationale are described in 
more detail in Residual Risk Assessment for Primary Magnesium Refining 
Source Category in Support of the 2020 Risk and Technology Review 
Proposed Rule and in Appendix 5 of the report: Technical Support 
Document for Acute Risk Screening Assessment. This revised approach has 
been used in this proposed rule and in all other RTR rulemakings 
proposed on or after June 3, 2019.
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    \9\ See, e.g., U.S. EPA. Screening Methodologies to Support Risk 
and Technology Reviews (RTR): A Case Study Analysis (Draft Report, 
May 2017. https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html).
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    To assess the potential acute risk to the maximally exposed 
individual, we use the peak hourly emission rate for each emission 
point,\10\ reasonable worst-case air dispersion conditions (i.e., 99th 
percentile), and the point of highest off-site exposure. Specifically, 
we assume that peak emissions from the source category and reasonable 
worst-case air dispersion conditions co-occur

[[Page 1399]]

and that a person is present at the point of maximum exposure.
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    \10\ In the absence of hourly emission data, we develop 
estimates of maximum hourly emission rates by multiplying the 
average actual annual emissions rates by a factor (either a 
category-specific factor or a default factor of 10) to account for 
variability. This is documented in Residual Risk Assessment for 
Primary Magnesium Refining Source Category in Support of the 2020 
Risk and Technology Review Proposed Rule and in Appendix 5 of the 
report: Technical Support Document for Acute Risk Screening 
Assessment. Both are available in the docket for this rulemaking.
---------------------------------------------------------------------------

    To characterize the potential health risks associated with 
estimated acute inhalation exposures to a HAP, we generally use 
multiple acute dose-response values, including acute RELs, acute 
exposure guideline levels (AEGLs), and emergency response planning 
guidelines (ERPG) for 1-hour exposure durations, if available, to 
calculate acute HQs. The acute HQ is calculated by dividing the 
estimated acute exposure concentration by the acute dose-response 
value. For each HAP for which acute dose-response values are available, 
the EPA calculates acute HQs.
    An acute REL is defined as ``the concentration level at or below 
which no adverse health effects are anticipated for a specified 
exposure duration.'' \11\ Acute RELs are based on the most sensitive, 
relevant, adverse health effect reported in the peer-reviewed medical 
and toxicological literature. They are designed to protect the most 
sensitive individuals in the population through the inclusion of 
margins of safety. Because margins of safety are incorporated to 
address data gaps and uncertainties, exceeding the REL does not 
automatically indicate an adverse health impact. AEGLs represent 
threshold exposure limits for the general public and are applicable to 
emergency exposures ranging from 10 minutes to 8 hours.\12\ They are 
guideline levels for ``once-in-a-lifetime, short-term exposures to 
airborne concentrations of acutely toxic, high-priority chemicals.'' 
Id. at 21. The AEGL-1 is specifically defined as ``the airborne 
concentration (expressed as ppm (parts per million) or mg/m\3\ 
(milligrams per cubic meter)) of a substance above which it is 
predicted that the general population, including susceptible 
individuals, could experience notable discomfort, irritation, or 
certain asymptomatic nonsensory effects. However, the effects are not 
disabling and are transient and reversible upon cessation of 
exposure.'' The document also notes that ``Airborne concentrations 
below AEGL-1 represent exposure levels that can produce mild and 
progressively increasing but transient and nondisabling odor, taste, 
and sensory irritation or certain asymptomatic, nonsensory effects.'' 
Id. AEGL-2 are defined as ``the airborne concentration (expressed as 
parts per million or milligrams per cubic meter) of a substance above 
which it is predicted that the general population, including 
susceptible individuals, could experience irreversible or other 
serious, long-lasting adverse health effects or an impaired ability to 
escape.'' Id.
---------------------------------------------------------------------------

    \11\ CalEPA issues acute RELs as part of its Air Toxics Hot 
Spots Program, and the 1-hour and 8-hour values are documented in 
Air Toxics Hot Spots Program Risk Assessment Guidelines, Part I, The 
Determination of Acute Reference Exposure Levels for Airborne 
Toxicants, which is available at https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary.
    \12\ National Academy of Sciences, 2001. Standing Operating 
Procedures for Developing Acute Exposure Levels for Hazardous 
Chemicals, page 2. Available at https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf. Note that the 
National Advisory Committee for Acute Exposure Guideline Levels for 
Hazardous Substances ended in October 2011, but the AEGL program 
continues to operate at the EPA and works with the National 
Academies to publish final AEGLs (https://www.epa.gov/aegl).
---------------------------------------------------------------------------

    ERPGs are ``developed for emergency planning and are intended as 
health-based guideline concentrations for single exposures to 
chemicals.'' \13\ Id. at 1. The ERPG-1 is defined as ``the maximum 
airborne concentration below which it is believed that nearly all 
individuals could be exposed for up to 1 hour without experiencing 
other than mild transient adverse health effects or without perceiving 
a clearly defined, objectionable odor.'' Id. at 2. Similarly, the ERPG-
2 is defined as ``the maximum airborne concentration below which it is 
believed that nearly all individuals could be exposed for up to one 
hour without experiencing or developing irreversible or other serious 
health effects or symptoms which could impair an individual's ability 
to take protective action.'' Id. at 1.
---------------------------------------------------------------------------

    \13\ ERPGS Procedures and Responsibilities. March 2014. American 
Industrial Hygiene Association. Available at: https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf.
---------------------------------------------------------------------------

    An acute REL for 1-hour exposure durations is typically lower than 
its corresponding AEGL-1 and ERPG-1. Even though their definitions are 
slightly different, AEGL-1s are often the same as the corresponding 
ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from 
our acute inhalation screening risk assessment typically result when we 
use the acute REL for a HAP. In cases where the maximum acute HQ 
exceeds 1, we also report the HQ based on the next highest acute dose-
response value (usually the AEGL-1 and/or the ERPG-1).
    For this source category, maximum hourly emission estimates were 
available, so we did not use the default emissions multiplier of 10. 
For the melt/reactor system and CBS, hourly emission estimates were 
initially based on an upper peak-to-mean ratio (i.e., 95th percentile) 
of the highest daily emission total and the daily average. This 
resulted in a factor of 8 for the melt/reactor system and 4.5 for the 
CBS. For all other processes, data from the CPMS of the associated wet 
scrubbers indicated that their operation was continuous and a factor of 
1 was used. As described in the risk assessment section of this 
preamble, we also assessed a worst-case acute risk scenario based on 
the estimated maximum hourly emissions rate (see risk assessment 
section for more details). A further discussion of why these factors 
were chosen can be found in Appendix 1 to the Residual Risk Assessment 
for the Primary Magnesium Refining Source Category in Support of the 
2020 Risk and Technology Review Proposed Rule, available in the docket 
for this rulemaking.
    In our acute inhalation screening risk assessment, acute impacts 
are deemed negligible for HAP for which acute HQs are less than or 
equal to 1, and no further analysis is performed for these HAP. In 
cases where an acute HQ from the screening step is greater than 1, we 
assess the site-specific data to ensure that the acute HQ is at an off-
site location. For this source category, the data refinements employed 
consisted of reviewing modeling results to ensure we were evaluating 
locations and risks that were off-site, in places where the public 
could congregate for an hour or more, and also evaluating further the 
potential peak estimated actual emissions reported by the facility, 
which we assume could occur during rebuild/rehabilitative maintenance 
of the melt/reactor CRB control device. The CRB has an infrequent, but, 
periodic rebuild cycle where the refractory needs to be replaced and 
rebuilt about every 6 to 7 years. During this period, based on 
available information, we estimate the acute factor could be as high as 
29, which is about 3.5 times higher than the initial modeled melt/
reactor acute factor. These refinements are discussed more fully in the 
Residual Risk Assessment for the Primary Magnesium Refining Source 
Category in Support of the 2020 Risk and Technology Review Proposed 
Rule, which is available in the docket for this source category.
4. How do we conduct the multipathway exposure and risk screening 
assessment?
    The EPA conducts a tiered screening assessment examining the 
potential for significant human health risks due to exposures via 
routes other than inhalation (i.e., ingestion). We first determine 
whether any sources in the

[[Page 1400]]

source category emit any HAP known to be persistent and bioaccumulative 
in the environment, as identified in the EPA's Air Toxics Risk 
Assessment Library (see Volume 1, Appendix D, at https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Primary Magnesium Refining source category, we identified 
potential PB-HAP emissions for arsenic compounds, lead compounds, 
cadmium compounds, mercury compounds, and dioxins/furans, so we 
proceeded to the next step of the evaluation. Except for lead, the 
human health risk screening assessment for PB-HAP consists of three 
progressive tiers. In a Tier 1 screening assessment, we determine 
whether the magnitude of the facility-specific emissions of PB-HAP 
warrants further evaluation to characterize human health risk through 
ingestion exposure. To facilitate this step, we evaluate emissions 
against previously developed screening threshold emission rates for 
several PB-HAP that are based on a hypothetical upper-end screening 
exposure scenario developed for use in conjunction with the EPA's Total 
Risk Integrated Methodology.Fate, Transport, and Ecological Exposure 
(TRIM.FaTE) model. The PB-HAP with screening threshold emission rates 
are arsenic compounds, cadmium compounds, chlorinated dibenzodioxins 
and furans, mercury compounds, and polycyclic organic matter (POM). 
Based on the EPA estimates of toxicity and bioaccumulation potential, 
these pollutants represent a conservative list for inclusion in 
multipathway risk assessments for RTR rules. (See Volume 1, Appendix D 
at https://www.epa.gov/sites/production/files/2013-08/documents/volume_1_reflibrary.pdf.) In this assessment, we compare the facility-
specific emission rates of these PB-HAP to the screening threshold 
emission rates for each PB-HAP to assess the potential for significant 
human health risks via the ingestion pathway. We call this application 
of the TRIM.FaTE model the Tier 1 screening assessment. The ratio of a 
facility's actual emission rate to the Tier 1 screening threshold 
emission rate is a ``screening value.''
    We derive the Tier 1 screening threshold emission rates for these 
PB-HAP (other than lead compounds) to correspond to a maximum excess 
lifetime cancer risk of 1-in-1 million (i.e., for arsenic compounds, 
polychlorinated dibenzodioxins and furans, and POM) or, for HAP that 
cause noncancer health effects (i.e., cadmium compounds and mercury 
compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP 
or combination of carcinogenic PB-HAP in the Tier 1 screening 
assessment exceeds the Tier 1 screening threshold emission rate for any 
facility (i.e., the screening value is greater than 1), we conduct a 
second screening assessment, which we call the Tier 2 screening 
assessment. The Tier 2 screening assessment separates the Tier 1 
combined fisher and farmer exposure scenario into fisher, farmer, and 
gardener scenarios that retain upper-bound ingestion rates.
    In the Tier 2 screening assessment, the location of each facility 
that exceeds a Tier 1 screening threshold emission rate is used to 
refine the assumptions associated with the Tier 1 fisher and farmer 
exposure scenarios at that facility. A key assumption in the Tier 1 
screening assessment is that a lake and/or farm is located near the 
facility. As part of the Tier 2 screening assessment, we use a U.S. 
Geological Survey (USGS) database to identify actual waterbodies within 
50 km of each facility and assume the fisher only consumes fish from 
lakes within that 50 km zone. We also examine the differences between 
local meteorology near the facility and the meteorology used in the 
Tier 1 screening assessment. We then adjust the previously-developed 
Tier 1 screening threshold emission rates for each PB-HAP for each 
facility based on an understanding of how exposure concentrations 
estimated for the screening scenario change with the use of local 
meteorology and the USGS lakes database.
    In the Tier 2 farmer scenario, we maintain an assumption that the 
farm is located within 0.5 km of the facility and that the farmer 
consumes meat, eggs, dairy, vegetables, and fruit produced near the 
facility. We may further refine the Tier 2 screening analysis by 
assessing a gardener scenario to characterize a range of exposures, 
with the gardener scenario being more plausible in RTR evaluations. 
Under the gardener scenario, we assume the gardener consumes home-
produced eggs, vegetables, and fruit products at the same ingestion 
rate as the farmer. The Tier 2 screen continues to rely on the high-end 
food intake assumptions that were applied in Tier 1 for local fish 
(adult female angler at 99th percentile fish consumption \14\) and 
locally grown or raised foods (90th percentile consumption of locally 
grown or raised foods for the farmer and gardener scenarios \15\). If 
PB-HAP emission rates do not result in a Tier 2 screening value greater 
than 1, we consider those PB-HAP emissions to pose risks below a level 
of concern. If the PB-HAP emission rates for a facility exceed the Tier 
2 screening threshold emission rates, we may conduct a Tier 3 screening 
assessment.
---------------------------------------------------------------------------

    \14\ Burger, J. 2002. Daily consumption of wild fish and game: 
Exposures of high end recreationists. International Journal of 
Environmental Health Research, 12:343-354.
    \15\ U.S. EPA. Exposure Factors Handbook 2011 Edition (Final). 
U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/
052F, 2011.
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    There are several analyses that can be included in a Tier 3 
screening assessment, depending upon the extent of refinement 
warranted, including validating that the lakes are fishable, locating 
residential/garden locations for urban and/or rural settings, 
considering plume-rise to estimate emissions lost above the mixing 
layer, and considering hourly effects of meteorology and plume-rise on 
chemical fate and transport (a time-series analysis). If necessary, the 
EPA may further refine the screening assessment through a site-specific 
assessment.
    In evaluating the potential multipathway risk from emissions of 
lead compounds, rather than developing a screening threshold emission 
rate, we compare maximum estimated chronic inhalation exposure 
concentrations to the level of the current National Ambient Air Quality 
Standard (NAAQS) for lead.\16\ Values below the level of the primary 
(health-based) lead NAAQS are considered to have a low potential for 
multipathway risk.
---------------------------------------------------------------------------

    \16\ In doing so, the EPA notes that the legal standard for a 
primary NAAQS--that a standard is requisite to protect public health 
and provide an adequate margin of safety (CAA section 109(b))--
differs from the CAA section 112(f) standard (requiring, among other 
things, that the standard provide an ``ample margin of safety to 
protect public health''). However, the primary lead NAAQS is a 
reasonable measure of determining risk acceptability (i.e., the 
first step of the Benzene NESHAP analysis) since it is designed to 
protect the most susceptible group in the human population--
children, including children living near major lead emitting 
sources. 73 FR 67002/3; 73 FR 67000/3; 73 FR 67005/1. In addition, 
applying the level of the primary lead NAAQS at the risk 
acceptability step is conservative, since that primary lead NAAQS 
reflects an adequate margin of safety.
---------------------------------------------------------------------------

    For further information on the multipathway assessment approach, 
see the Residual Risk Assessment for the Primary Magnesium Refining 
Source Category in Support of the Risk and Technology Review 2020 
Proposed Rule, which is available in the docket for this action.

[[Page 1401]]

5. How do we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect, Environmental HAP, and Ecological 
Benchmarks
    The EPA conducts a screening assessment to examine the potential 
for an adverse environmental effect as required under section 
112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines ``adverse 
environmental effect'' as ``any significant and widespread adverse 
effect, which may reasonably be anticipated, to wildlife, aquatic life, 
or other natural resources, including adverse impacts on populations of 
endangered or threatened species or significant degradation of 
environmental quality over broad areas.''
    The EPA focuses on eight HAP, which are referred to as 
``environmental HAP,'' in its screening assessment: Six PB-HAP and two 
acid gases. The PB-HAP included in the screening assessment are arsenic 
compounds, cadmium compounds, dioxins/furans, POM, mercury (both 
inorganic mercury and methyl mercury), and lead compounds. The acid 
gases included in the screening assessment are HCl and hydrogen 
fluoride (HF).
    HAP that persist and bioaccumulate are of particular environmental 
concern because they accumulate in the soil, sediment, and water. The 
acid gases, HCl and HF, are included due to their well-documented 
potential to cause direct damage to terrestrial plants. In the 
environmental risk screening assessment, we evaluate the following four 
exposure media: Terrestrial soils, surface water bodies (includes 
water-column and benthic sediments), fish consumed by wildlife, and 
air. Within these four exposure media, we evaluate nine ecological 
assessment endpoints, which are defined by the ecological entity and 
its attributes. For PB-HAP (other than lead), both community-level and 
population-level endpoints are included. For acid gases, the ecological 
assessment evaluated is terrestrial plant communities.
    An ecological benchmark represents a concentration of HAP that has 
been linked to a particular environmental effect level. For each 
environmental HAP, we identified the available ecological benchmarks 
for each assessment endpoint. We identified, where possible, ecological 
benchmarks at the following effect levels: Probable effect levels, 
lowest-observed-adverse-effect level (LOAEL), and no-observed-adverse-
effect level (NOAEL). In cases where multiple effect levels were 
available for a particular PB-HAP and assessment endpoint, we use all 
of the available effect levels to help us to determine whether 
ecological risks exist and, if so, whether the risks could be 
considered significant and widespread.
    For further information on how the environmental risk screening 
assessment was conducted, including a discussion of the risk metrics 
used, how the environmental HAP were identified, and how the ecological 
benchmarks were selected, see Appendix 9 of the Residual Risk 
Assessment for the Primary Magnesium Refining Source Category in 
Support of the Risk and Technology Review 2020 Proposed Rule, which is 
available in the docket for this action.
b. Environmental Risk Screening Methodology
    For the environmental risk screening assessment, the EPA first 
determined whether any facilities in the Primary Magnesium Refining 
source category emitted any of the environmental HAP. For the Primary 
Magnesium Refining source category, we identified emissions of HCl and 
dioxins, and potential emissions of arsenic, cadmium, and mercury. 
Because one or more of the environmental HAP evaluated are emitted by 
at least one facility in the source category, we proceeded to the 
second step of the evaluation.
c. PB-HAP Methodology
    The environmental screening assessment includes six PB-HAP, arsenic 
compounds, cadmium compounds, dioxins/furans, POM, mercury (both 
inorganic mercury and methyl mercury), and lead compounds. With the 
exception of lead, the environmental risk screening assessment for PB-
HAP consists of three tiers. The first tier of the environmental risk 
screening assessment uses the same health-protective conceptual model 
that is used for the Tier 1 human health screening assessment. 
TRIM.FaTE model simulations were used to back-calculate Tier 1 
screening threshold emission rates. The screening threshold emission 
rates represent the emission rate in tons of pollutant per year that 
results in media concentrations at the facility that equal the relevant 
ecological benchmark. To assess emissions from each facility in the 
category, the reported emission rate for each PB-HAP was compared to 
the Tier 1 screening threshold emission rate for that PB-HAP for each 
assessment endpoint and effect level. If emissions from a facility do 
not exceed the Tier 1 screening threshold emission rate, the facility 
``passes'' the screening assessment, and, therefore, is not evaluated 
further under the screening approach. If emissions from a facility 
exceed the Tier 1 screening threshold emission rate, we evaluate the 
facility further in Tier 2.
    In Tier 2 of the environmental screening assessment, the screening 
threshold emission rates are adjusted to account for local meteorology 
and the actual location of lakes in the vicinity of facilities that did 
not pass the Tier 1 screening assessment. For soils, we evaluate the 
average soil concentration for all soil parcels within a 7.5-km radius 
for each facility and PB-HAP. For the water, sediment, and fish tissue 
concentrations, the highest value for each facility for each pollutant 
is used. If emission concentrations from a facility do not exceed the 
Tier 2 screening threshold emission rate, the facility ``passes'' the 
screening assessment and typically is not evaluated further. If 
emissions from a facility exceed the Tier 2 screening threshold 
emission rate, we evaluate the facility further in Tier 3.
    As in the multipathway human health risk assessment, in Tier 3 of 
the environmental screening assessment, we examine the suitability of 
the lakes around the facilities to support life and remove those that 
are not suitable (e.g., lakes that have been filled in or are 
industrial ponds), adjust emissions for plume-rise, and conduct hour-
by-hour time-series assessments. If these Tier 3 adjustments to the 
screening threshold emission rates still indicate the potential for an 
adverse environmental effect (i.e., facility emission rate exceeds the 
screening threshold emission rate), we may elect to conduct a more 
refined assessment using more site-specific information. If, after 
additional refinement, the facility emission rate still exceeds the 
screening threshold emission rate, the facility may have the potential 
to cause an adverse environmental effect.
    To evaluate the potential for an adverse environmental effect from 
lead, we compared the average modeled air concentrations (from HEM-3) 
of lead around each facility in the source category to the level of the 
secondary NAAQS for lead. The secondary lead NAAQS is a reasonable 
means of evaluating environmental risk because it is set to provide 
substantial protection against adverse welfare effects which can 
include ``effects on soils, water, crops, vegetation, man-made 
materials, animals, wildlife, weather, visibility and climate, damage 
to and deterioration of property, and hazards to transportation, as 
well as effects on economic values and on personal comfort and well-
being.''

[[Page 1402]]

d. Acid Gas Environmental Risk Methodology
    The environmental screening assessment for acid gases evaluates the 
potential phytotoxicity and reduced productivity of plants due to 
chronic exposure to HF and HCl. The environmental risk screening 
methodology for acid gases is a single-tier screening assessment that 
compares modeled ambient air concentrations (from AERMOD) to the 
ecological benchmarks for each acid gas. To identify a potential 
adverse environmental effect (as defined in section 112(a)(7) of the 
CAA) from emissions of HF and HCl, we evaluate the following metrics: 
The size of the modeled area around each facility that exceeds the 
ecological benchmark for each acid gas, in acres and square kilometers; 
the percentage of the modeled area around each facility that exceeds 
the ecological benchmark for each acid gas; and the area-weighted 
average screening value around each facility (calculated by dividing 
the area-weighted average concentration over the 50-km modeling domain 
by the ecological benchmark for each acid gas). For further information 
on the environmental screening assessment approach, see Appendix 9 of 
the Residual Risk Assessment for the Primary Magnesium Refining Source 
Category in Support of the Risk and Technology Review 2020 Proposed 
Rule, which is available in the docket for this action.
6. How do we conduct facility-wide assessments?
    To put the source category risks in context, we typically examine 
the risks from the entire ``facility,'' where the facility includes all 
HAP-emitting operations within a contiguous area and under common 
control. In other words, we examine the HAP emissions not only from the 
source category emission points of interest, but also emissions of HAP 
from all other emission sources at the facility for which we have data. 
For this source category, we conducted the facility-wide assessment 
using a dataset compiled from the 2017 NEI. The source category records 
of that NEI dataset were removed, evaluated, and updated as described 
in section II.C of this preamble: What data collection activities were 
conducted to support this action? Once a quality assured source 
category dataset was available, it was placed back with the remaining 
records from the NEI for that facility. The facility-wide file was then 
used to analyze risks due to the inhalation of HAP that are emitted 
``facility-wide'' for the populations residing within 50 km of each 
facility, consistent with the methods used for the source category 
analysis described above. For these facility-wide risk analyses, the 
modeled source category risks were compared to the facility-wide risks 
to determine the portion of the facility-wide risks that could be 
attributed to the source category addressed in this proposal. We also 
specifically examined the facility that was associated with the highest 
estimate of risk and determined the percentage of that risk 
attributable to the source category of interest. The Residual Risk 
Assessment for the Primary Magnesium Refining Source Category in 
Support of the Risk and Technology Review 2020 Proposed Rule, available 
through the docket for this action, provides the methodology and 
results of the facility-wide analyses, including all facility-wide 
risks and the percentage of source category contribution to facility-
wide risks.
7. How do we consider uncertainties in risk assessment?
    Uncertainty and the potential for bias are inherent in all risk 
assessments, including those performed for this proposal. Although 
uncertainty exists, we believe that our approach, which used 
conservative tools and assumptions, ensures that our decisions are 
health and environmentally protective. A brief discussion of the 
uncertainties in the RTR emissions dataset, dispersion modeling, 
inhalation exposure estimates, and dose-response relationships follows 
below. Also included are those uncertainties specific to our acute 
screening assessments, multipathway screening assessments, and our 
environmental risk screening assessments. A more thorough discussion of 
these uncertainties is included in the Residual Risk Assessment for the 
Primary Magnesium Refining Source Category in Support of the Risk and 
Technology Review 2020 Proposed Rule, which is available in the docket 
for this action. If a multipathway site-specific assessment was 
performed for this source category, a full discussion of the 
uncertainties associated with that assessment can be found in Appendix 
11 of that document, Site-Specific Human Health Multipathway Residual 
Risk Assessment Report.
a. Uncertainties in the RTR Emissions Dataset
    Although the development of the RTR emissions dataset involved 
quality assurance/quality control processes, the accuracy of emissions 
values will vary depending on the source of the data, the degree to 
which data are incomplete or missing, the degree to which assumptions 
made to complete the datasets are accurate, errors in emission 
estimates, and other factors. The emission estimates considered in this 
analysis generally are annual totals for certain years, and they do not 
reflect short-term fluctuations during the course of a year or 
variations from year to year. The estimates of peak hourly emission 
rates for the acute effects screening assessment were based on an 
emission adjustment factor applied to the average annual hourly 
emission rates, which are intended to account for emission fluctuations 
due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration 
estimates associated with any model, including the EPA's recommended 
regulatory dispersion model, AERMOD. In using a model to estimate 
ambient pollutant concentrations, the user chooses certain options to 
apply. For RTR assessments, we select some model options that have the 
potential to overestimate ambient air concentrations (e.g., not 
including plume depletion or pollutant transformation). We select other 
model options that have the potential to underestimate ambient impacts 
(e.g., not including building downwash). Other options that we select 
have the potential to either under- or overestimate ambient levels 
(e.g., meteorology and receptor locations). On balance, considering the 
directional nature of the uncertainties commonly present in ambient 
concentrations estimated by dispersion models, the approach we apply in 
the RTR assessments should yield unbiased estimates of ambient HAP 
concentrations. We also note that the selection of meteorology dataset 
location could have an impact on the risk estimates. As we continue to 
update and expand our library of meteorological station data used in 
our risk assessments, we expect to reduce this variability.
c. Uncertainties in Inhalation Exposure Assessment
    Although every effort is made to identify all of the relevant 
facilities and emission points, as well as to develop accurate 
estimates of the annual emission rates for all relevant HAP, the 
uncertainties in our emission inventory likely dominate the 
uncertainties in the exposure assessment. Some uncertainties in our 
exposure assessment include human mobility, using the centroid of each 
census block, assuming lifetime exposure, and

[[Page 1403]]

assuming only outdoor exposures. For most of these factors, there is 
neither an under nor overestimate when looking at the maximum 
individual risk or the incidence, but the shape of the distribution of 
risks may be affected. With respect to outdoor exposures, actual 
exposures may not be as high if people spend time indoors, especially 
for very reactive pollutants or larger particles. For all factors, we 
reduce uncertainty when possible. For example, with respect to census-
block centroids, we analyze large blocks using aerial imagery and 
adjust locations of the block centroids to better represent the 
population in the blocks. We also add additional receptor locations 
where the population of a block is not well represented by a single 
location.
d. Uncertainties in Dose-Response Relationships
    There are uncertainties inherent in the development of the dose-
response values used in our risk assessments for cancer effects from 
chronic exposures and noncancer effects from both chronic and acute 
exposures. Some uncertainties are generally expressed quantitatively, 
and others are generally expressed in qualitative terms. We note, as a 
preface to this discussion, a point on dose-response uncertainty that 
is stated in the EPA's 2005 Guidelines for Carcinogen Risk Assessment; 
namely, that ``the primary goal of EPA actions is protection of human 
health; accordingly, as an Agency policy, risk assessment procedures, 
including default options that are used in the absence of scientific 
data to the contrary, should be health protective'' (the EPA's 2005 
Guidelines for Carcinogen Risk Assessment, page 1 through 7). This is 
the approach followed here as summarized in the next paragraphs.
    Cancer UREs used in our risk assessments are those that have been 
developed to generally provide an upper bound estimate of risk.\17\ 
That is, they represent a ``plausible upper limit to the true value of 
a quantity'' (although this is usually not a true statistical 
confidence limit). In some circumstances, the true risk could be as low 
as zero; however, in other circumstances the risk could be greater.\18\ 
Chronic noncancer RfC and reference dose (RfD) values represent chronic 
exposure levels that are intended to be health-protective levels. To 
derive dose-response values that are intended to be ``without 
appreciable risk,'' the methodology relies upon an uncertainty factor 
(UF) approach,\19\ which considers uncertainty, variability, and gaps 
in the available data. The UFs are applied to derive dose-response 
values that are intended to protect against appreciable risk of 
deleterious effects.
---------------------------------------------------------------------------

    \17\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \18\ An exception to this is the URE for benzene, which is 
considered to cover a range of values, each end of which is 
considered to be equally plausible, and which is based on maximum 
likelihood estimates.
    \19\ See A Review of the Reference Dose and Reference 
Concentration Processes, U.S. EPA, December 2002, and Methods for 
Derivation of Inhalation Reference Concentrations and Application of 
Inhalation Dosimetry, U.S. EPA, 1994.
---------------------------------------------------------------------------

    Many of the UFs used to account for variability and uncertainty in 
the development of acute dose-response values are quite similar to 
those developed for chronic durations. Additional adjustments are often 
applied to account for uncertainty in extrapolation from observations 
at one exposure duration (e.g., 4 hours) to derive an acute dose-
response value at another exposure duration (e.g., 1 hour). Not all 
acute dose-response values are developed for the same purpose, and care 
must be taken when interpreting the results of an acute assessment of 
human health effects relative to the dose-response value or values 
being exceeded. Where relevant to the estimated exposures, the lack of 
acute dose-response values at different levels of severity should be 
factored into the risk characterization as potential uncertainties.
    Uncertainty also exists in the selection of ecological benchmarks 
for the environmental risk screening assessment. We established a 
hierarchy of preferred benchmark sources to allow selection of 
benchmarks for each environmental HAP at each ecological assessment 
endpoint. We searched for benchmarks for three effect levels (i.e., no-
effects level, threshold-effect level, and probable effect level), but 
not all combinations of ecological assessment/environmental HAP had 
benchmarks for all three effect levels. Where multiple effect levels 
were available for a particular HAP and assessment endpoint, we used 
all of the available effect levels to help us determine whether risk 
exists and whether the risk could be considered significant and 
widespread.
    Although we make every effort to identify appropriate human health 
effect dose-response values for all pollutants emitted by the sources 
in this risk assessment, some HAP emitted by this source category are 
lacking dose-response assessments. Accordingly, these pollutants cannot 
be included in the quantitative risk assessment, which could result in 
quantitative estimates understating HAP risk. To help to alleviate this 
potential underestimate, where we conclude similarity with a HAP for 
which a dose-response value is available, we use that value as a 
surrogate for the assessment of the HAP for which no value is 
available. To the extent use of surrogates indicates appreciable risk, 
we may identify a need to increase priority for an IRIS assessment for 
that substance. We additionally note that, generally speaking, HAP of 
greatest concern due to environmental exposures and hazard are those 
for which dose-response assessments have been performed, reducing the 
likelihood of understating risk. Further, HAP not included in the 
quantitative assessment are assessed qualitatively and considered in 
the risk characterization that informs the risk management decisions, 
including consideration of HAP reductions achieved by various control 
options.
    For a group of compounds that are unspeciated (e.g., glycol 
ethers), we conservatively use the most protective dose-response value 
of an individual compound in that group to estimate risk. Similarly, 
for an individual compound in a group (e.g., ethylene glycol diethyl 
ether) that does not have a specified dose-response value, we also 
apply the most protective dose-response value from the other compounds 
in the group to estimate risk.
e. Uncertainties in Acute Inhalation Screening Assessments
    In addition to the uncertainties highlighted above, there are 
several factors specific to the acute exposure assessment that the EPA 
conducts as part of the risk review under section 112 of the CAA. The 
accuracy of an acute inhalation exposure assessment depends on the 
simultaneous occurrence of independent factors that may vary greatly, 
such as hourly emissions rates, meteorology, and the presence of a 
person. In the acute screening assessment that we conduct under the RTR 
program, we assume that peak emissions from the source category and 
reasonable worst-case air dispersion conditions (i.e., 99th percentile) 
co-occur. We then include the additional assumption that a person is 
located at this point at the same time. Together, these assumptions 
represent a reasonable worst-case actual exposure scenario. In most 
cases, it is unlikely that a person would be located at the point of 
maximum exposure during the time when peak emissions and

[[Page 1404]]

reasonable worst-case air dispersion conditions occur simultaneously.
f. Uncertainties in the Multipathway and Environmental Risk Screening 
Assessments
    For each source category, we generally rely on site-specific levels 
of PB-HAP or environmental HAP emissions to determine whether a refined 
assessment of the impacts from multipathway exposures is necessary or 
whether it is necessary to perform an environmental screening 
assessment. This determination is based on the results of a three-
tiered screening assessment that relies on the outputs from models--
TRIM.FaTE and AERMOD--that estimate environmental pollutant 
concentrations and human exposures for five PB-HAP (dioxins, POM, 
mercury, cadmium, and arsenic) and two acid gases (HF and HCl). For 
lead, we use AERMOD to determine ambient air concentrations, which are 
then compared to the secondary NAAQS standard for lead. Two important 
types of uncertainty associated with the use of these models in RTR 
risk assessments and inherent to any assessment that relies on 
environmental modeling are model uncertainty and input uncertainty.\20\
---------------------------------------------------------------------------

    \20\ In the context of this discussion, the term ``uncertainty'' 
as it pertains to exposure and risk encompasses both variability in 
the range of expected inputs and screening results due to existing 
spatial, temporal, and other factors, as well as uncertainty in 
being able to accurately estimate the true result.
---------------------------------------------------------------------------

    Model uncertainty concerns whether the model adequately represents 
the actual processes (e.g., movement and accumulation) that might occur 
in the environment. For example, does the model adequately describe the 
movement of a pollutant through the soil? This type of uncertainty is 
difficult to quantify. However, based on feedback received from 
previous EPA SAB reviews and other reviews, we are confident that the 
models used in the screening assessments are appropriate and state-of-
the-art for the multipathway and environmental screening risk 
assessments conducted in support of RTRs.
    Input uncertainty is concerned with how accurately the models have 
been configured and parameterized for the assessment at hand. For Tier 
1 of the multipathway and environmental screening assessments, we 
configured the models to avoid underestimating exposure and risk. This 
was accomplished by selecting upper-end values from nationally 
representative datasets for the more influential parameters in the 
environmental model, including selection and spatial configuration of 
the area of interest, lake location and size, meteorology, surface 
water, soil characteristics, and structure of the aquatic food web. We 
also assume an ingestion exposure scenario and values for human 
exposure factors that represent reasonable maximum exposures.
    In Tier 2 of the multipathway and environmental screening 
assessments, we refine the model inputs to account for meteorological 
patterns in the vicinity of the facility versus using upper-end 
national values, and we identify the actual location of lakes near the 
facility rather than the default lake location that we apply in Tier 1. 
By refining the screening approach in Tier 2 to account for local 
geographical and meteorological data, we decrease the likelihood that 
concentrations in environmental media are overestimated, thereby 
increasing the usefulness of the screening assessment. In Tier 3 of the 
screening assessments, we refine the model inputs again to account for 
hour-by-hour plume-rise and the height of the mixing layer. We can also 
use those hour-by-hour meteorological data in a TRIM.FaTE run using the 
screening configuration corresponding to the lake location. These 
refinements produce a more accurate estimate of chemical concentrations 
in the media of interest, thereby reducing the uncertainty with those 
estimates. The assumptions and the associated uncertainties regarding 
the selected ingestion exposure scenario are the same for all three 
tiers.
    For the environmental screening assessment for acid gases, we 
employ a single-tiered approach. We use the modeled air concentrations 
and compare those with ecological benchmarks.
    For all tiers of the multipathway and environmental screening 
assessments, our approach to addressing model input uncertainty is 
generally cautious. We choose model inputs from the upper end of the 
range of possible values for the influential parameters used in the 
models, and we assume that the exposed individual exhibits ingestion 
behavior that would lead to a high total exposure. This approach 
reduces the likelihood of not identifying high risks for adverse 
impacts.
    Despite the uncertainties, when individual pollutants or facilities 
do not exceed screening threshold emission rates (i.e., screen out), we 
are confident that the potential for adverse multipathway impacts on 
human health is very low. On the other hand, when individual pollutants 
or facilities do exceed screening threshold emission rates, it does not 
mean that impacts are significant, only that we cannot rule out that 
possibility and that a refined assessment for the site might be 
necessary to obtain a more accurate risk characterization for the 
source category.
    The EPA evaluates the following HAP in the multipathway and/or 
environmental risk screening assessments, where applicable: Arsenic, 
cadmium, dioxins/furans, lead, mercury (both inorganic and methyl 
mercury), POM, HCl, and HF. These HAP represent pollutants that can 
cause adverse impacts either through direct exposure to HAP in the air 
or through exposure to HAP that are deposited from the air onto soils 
and surface waters and then through the environment into the food web. 
These HAP represent those HAP for which we can conduct a meaningful 
multipathway or environmental screening risk assessment. For other HAP 
not included in our screening assessments, the model has not been 
parameterized such that it can be used for that purpose. In some cases, 
depending on the HAP, we may not have appropriate multipathway models 
that allow us to predict the concentration of that pollutant. The EPA 
acknowledges that other HAP beyond these that we are evaluating may 
have the potential to cause adverse effects and, therefore, the EPA may 
evaluate other relevant HAP in the future, as modeling science and 
resources allow.

IV. Analytical Results and Proposed Decisions

A. What actions are we taking pursuant to CAA sections 112(d)(2) and 
112(d)(3)?

    In this proposal, pursuant to CAA section 112(d)(2) and (3) , we 
are proposing to establish an emission standard requiring MACT level 
control of chlorine emissions from the CBS. The results and proposed 
decisions based on the analyses performed pursuant to CAA section 
112(d)(2) and (3) are presented below.
    In the primary magnesium refining process, the electrowinning of 
the melted magnesium chloride to magnesium metal produces as a 
byproduct chlorine gas which is piped to, and recovered at, the co-
located chlorine plant. At the chlorine plant, the chlorine gas is 
liquified and then stored for either reuse back into the magnesium 
refining process or sold to the market. When the chlorine plant is 
inoperable (e.g., due to a malfunction or planned maintenance), the 
chlorine gas produced at the electrolytic cells is routed through the 
CBS. The CBS contains a packed-bed scrubber which uses ferrous chloride 
as the adsorbing

[[Page 1405]]

medium to control chlorine emissions. The reaction of chlorine with 
ferrous chloride in the scrubbing medium creates a valuable by-product, 
ferric chloride, which the facility sells to the market. Since the CBS 
produces this valuable product, in addition to routing chlorine gas to 
the CBS when the chlorine plant is inoperable, the facility also 
routinely intentionally routes smaller amounts of chlorine gas (also 
known as tail gas) from the chlorine plant to the CBS during normal 
operations to produce ferric chloride.
    Based on available information from the facility and the current 
title V permit, we estimate the scrubbers achieve at least 95 percent 
control efficiency and that the remaining chlorine gas (up to 5 
percent) is emitted to the atmosphere. As a potentially significant 
source of chlorine emissions from the refining process, we are 
proposing to establish an emission standard requiring MACT level 
control of chlorine emissions from the CBS.
    MACT standards must reflect the maximum degree of emissions 
reduction achievable through the application of measures, processes, 
methods, systems or techniques, including, but not limited to, measures 
that: (1) Reduce the volume of or eliminate pollutants through process 
changes, substitution of materials or other modifications; (2) enclose 
systems or processes to eliminate emissions; (3) capture or treat 
pollutants when released from a process, stack, storage, or fugitive 
emissions point; (4) are design, equipment, work practice, or 
operational standards (including requirements for operator training or 
certification); or (5) are a combination of the above. See CAA section 
112(d)(2)(A) through (E). The MACT standards may take the form of 
design, equipment, work practice, or operational standards where the 
EPA determines either that: (1) A pollutant cannot be emitted through a 
conveyance designed and constructed to emit or capture the pollutant, 
or that any requirement for, or use of, such a conveyance would be 
inconsistent with law; or (2) the application of measurement 
methodology to a particular class of sources is not practicable due to 
technological and economic limitations. See CAA section 112(h)(1) and 
(2).
    The MACT ``floor'' is the minimum control level required for MACT 
standards promulgated under CAA section 112(d) and may not be based on 
cost considerations. For new sources, the MACT floor cannot be less 
stringent than the emissions control that is achieved in practice by 
the best-controlled similar source. The MACT floor for existing sources 
can be less stringent than floors for new sources, but not less 
stringent than the average emissions limitation achieved by the best-
performing 12 percent of existing sources in the category or 
subcategory (or the best-performing five sources for categories or 
subcategories with fewer than 30 sources). Once the EPA has set the 
MACT floor, it may then impose stricter standards (``beyond-the-floor'' 
limits) if the EPA determines them to be achievable taking into 
consideration the cost of achieving the emission reductions, any non-
air quality health and environmental impacts, and energy requirements.
    Since there is only one primary magnesium refinery in the source 
category, the MACT floor for new and existing sources is established by 
the emission limitation achieved at that source. As described above, 
currently the CBS chlorine emissions are controlled by a ferrous 
chloride packed-bed scrubber. A representative from US Magnesium 
explained that chlorine removal can be calculated to be up to 100 
percent stoichiometrically under fixed mass flow and ferric chloride 
recirculation rates. However, due to high variability in flow rates 
during the range of normal operations, the actual efficiency is 
expected to be less than 100 percent (for more information see email 
from Rob Hartman, US Magnesium, to Michael Moeller, EPA, which is 
available in the docket for this proposed rulemaking). Based on the 
limited available information and applying engineering judgement as 
described above, the facility and the state of Utah assume that the 
scrubbers achieve an average removal efficiency of 95 percent for 
purposes of determining and reporting daily chlorine emissions as 
required by the tile V permit. However, there are no stack test data 
available to confirm this value. Therefore, based on the available 
information, we propose 95 percent reduction of chlorine emissions as 
the MACT floor for the CBS for new and existing sources in the source 
category.
    In addition to determining the MACT floor level of control, as part 
of our development of the proposed MACT standard, we assessed whether 
stricter standards (``beyond-the-floor'' limits) are achievable taking 
into consideration the cost of achieving additional emission 
reductions, any non-air quality health and environmental impacts, and 
energy requirements. We identified one potential control option, using 
a combination of a thermal incinerator coupled with a wet scrubber, 
that could achieve chlorine control efficiencies greater than the 
current 95 percent. The thermal incinerator reacts chlorine with 
natural gas to produce HCl gas. This process is highly efficient at 
converting chlorine into HCl and based on the available information, we 
estimate that 99 percent of the chlorine is converted to HCl. The HCl 
gas stream, which has greater solubility than chlorine, is then 
controlled through absorption via a wet scrubber. The wet scrubber 
removal efficiency of HCl is estimated to be 99 percent. This 
combination of controls could be expected to achieve 98 percent 
reduction of chlorine emissions. With regard to costs of achieving 
these additional emission reductions, based on limited information, we 
estimate the capital costs for these beyond-the-floor controls would be 
about $1.3 million, annualized costs would be about $1.4 million, and 
would achieve an estimated 300 tpy reduction, with estimated cost 
effectiveness of $4,657 per ton of chlorine reductions. However, as 
explained in the technical memorandum cited below, we note that there 
are substantial uncertainties with the baseline emissions estimates, 
the emissions reductions that would be achieved, and the cost 
estimates. This is primarily due to lack of test data and lack of 
information regarding flow rates, renovation costs, and other factors. 
For example, without test data to corroborate, the actual efficiency of 
the current control could be higher (or lower) than the estimated 95 
percent. The facility has determined that chlorine removal, under 
stoichiometrically ideal conditions, can be calculated to be up to 100 
percent. If the current control is higher than the 95 percent, the 
additional emission reductions and the cost effectiveness would be 
reduced. If the current control approaches 98 percent, there would be 
no additional reductions to achieve. In regard to uncertainties with 
the cost estimates, there is a large range of values for the costs 
associated with the installation and operating of a thermal incinerator 
and wet scrubber devices. To account for this, we used the midpoint of 
the cost range; however, due to the unique nature of this industry and 
without additional information about the CBS, the actual costs could be 
anywhere within the range and even beyond it. Using the upper end 
estimates of the cost range, capital costs could be as high as $2.1 
million, annualized costs up to $2.5 million and an estimated cost 
effectiveness of $8,152 per ton. In addition, there would be additional 
economic impacts beyond these estimated costs due to the loss of 
facility revenue from the elimination of the production of a valuable 
by-product

[[Page 1406]]

that is created with the current controls. For more information 
regarding the beyond-the-floor analysis, the uncertainties and our 
conclusions, see the Beyond-the-floor Assessment for the Chlorine 
Bypass Stack memorandum, which is available in the docket for this 
proposed action.
    We note that the cost-effectiveness is within the range of cost 
effectiveness accepted for beyond-the-floor controls for some other HAP 
in NESHAP for other source categories (e.g., Secondary Lead Smelting, 
77 FR 3, January 5, 2012, and Ferroalloys Production, 80 FR 125, June 
30, 2015). We have not identified any previous NESHAP that accepted or 
rejected such cost-effectiveness estimates specifically for chlorine.
    Nevertheless, given the issues and substantial uncertainties 
described above, we are not proposing this beyond-the-floor standard. 
We also note that we did not identify any relevant non-air quality 
health and environmental impacts, and energy requirements. Although we 
are not proposing this beyond-the-floor standard, we are soliciting 
comments, data and other information regarding the beyond-the-floor 
analysis (including costs estimates, baseline emissions, emissions 
reductions, and loss of product/revenue), and we are soliciting 
comments regarding our proposed determination and whether it would be 
appropriate to require these beyond-the-floor controls under the 
NESHAP, and if so, why.
    Therefore, based on all the analyses presented above, we are 
proposing a MACT floor emissions standard for the CBS that will require 
new and existing sources in the source category to operate the control 
device and demonstrate 95 percent reduction of chlorine emissions. 
Specifically, we propose the following conditions: The facility must 
operate the control device (e.g., a CBS scrubber) at all times when 
chlorine emissions are being routed to the CBS; except for 
circumstances under which emissions are routed to the CBS due to a 
chlorine plant malfunction and the CBS control device is not in 
operation, the CBS control device must be operating as soon as 
practicable but no later than 15 minutes after the routing of the 
chlorine emissions to the CBS. The facility must also document, and 
keep records, regarding each malfunction event, as described below. To 
demonstrate 95 percent control efficiency is achieved, we are proposing 
to require that new and existing sources in the source category conduct 
periodic performance tests that include inlet and outlet test samples. 
These tests would be conducted no less frequently than twice per permit 
term of a source's title V permit (at mid-term and renewal), which 
would be at least two tests every 5 years. We are proposing to require 
that new and existing sources in the source category use EPA Method 26A 
in 40 CFR part 60, appendix A (i.e., the reference method for chlorine) 
to demonstrate compliance with the MACT standard. In addition to the 
performance compliance tests, with regard to parametric monitoring, we 
are proposing to require that new and existing sources in the source 
category measure and record the pH, liquid flow, and pressure drop of 
the control device on an on-going basis to demonstrate continuous 
compliance with the chlorine standard, and maintain such records. 
During a malfunction event, the owner or operator would be required to 
follow the typical recordkeeping and reporting associated with 
malfunction events (described in section IV.E), and also keep records 
of the date and time the control device was started, and also conduct 
the same measurements and monitoring of the parameters described above 
(i.e., pH, liquid flow, and pressure drop). However, we are also 
seeking comments regarding these proposed requirements, and whether the 
EPA should consider alternative standards, or methodology modifications 
or parameters to demonstrate compliance and, if so, an explanation of 
those alternatives and why they would be appropriate.
    Although we are proposing a MACT floor level of control for new and 
existing sources of 95 percent reduction of chlorine emissions based on 
the information presented above, we acknowledge there are some 
uncertainties regarding the actual control efficiency achieved under 
normal variable operations. Therefore, we are soliciting comments, 
data, or other information regarding the 95 percent control efficiency 
limit and whether a different limit, higher or lower, would be 
appropriate and, if so, why such a different limit would be appropriate 
to represent the MACT floor level of control. As described above, we 
are not proposing a beyond-the-floor option primarily due to 
significant uncertainties in the emissions and in the costs of 
achieving additional emission reductions. We conclude that the current 
scrubbing system represents MACT for the CBS. However, we are 
soliciting comments, data, and other information regarding the analyses 
for our proposed MACT floor standard and the beyond-the-floor option 
and our determinations. For more information regarding the beyond-the-
floor analysis and our conclusions, see the Beyond-the-floor Assessment 
for the Chlorine Bypass Stack memorandum, which is available in the 
docket for this proposed action.

B. What are the results of the risk assessment and analyses?

1. Chronic Inhalation Risk Assessment Results
    Table 2 of this preamble provides a summary of the results of the 
chronic inhalation risk assessment for HAP emissions for the source 
category, and an upper-end assessment of acute inhalation risks (based 
on the 95th percentile of 2017 hourly emissions estimates). Additional 
analyses and refinements regarding potential acute risks, including 
potential higher-end acute risks, are described later in this section. 
More detailed information on the risk assessment can be found in the 
document titled Residual Risk Assessment for the Primary Magnesium 
Refining Source Category in Support of the Risk and Technology Review 
2020 Proposed Rule, available in the docket for this rule.

[[Page 1407]]



                                                     Table 2--Primary Magnesium Refining Source Category Inhalation Risk Assessment Results
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                              Maximum individual      Population at increased   Annual cancer incidence       Maximum chronic         Maximum screening acute noncancer HQ \3\
                                               cancer risk (in 1     risk of cancer >= 1-in-1   (cases per year)  based   noncancer TOSHI  based                   based on . . .
                                           million) \2\  based on .    million based on . . .          on . . .                  on . . .         ----------------------------------------------
        Number of  facilities \1\                     . .           ------------------------------------------------------------------------------
                                          --------------------------
                                              Actual     Allowable      Actual     Allowable      Actual     Allowable      Actual     Allowable        95th percentile of actual emissions
                                            emissions    emissions    emissions    emissions    emissions    emissions    emissions    emissions
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1........................................         0.08         0.08            0            0      0.00001      0.00001          * 1        * 0.6  3-REL
                                                                                                                                                   <1 AEGL-1
                                                                                                                                                   (chlorine).
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Number of facilities evaluated in the risk analysis.
\2\ Maximum individual excess lifetime cancer risk due to HAP emissions from the source category.
\3\ Arsenic REL. The maximum estimated acute exposure concentration was divided by available short-term dose-response values to develop an array of HQ values. HQ values shown use the lowest
  available acute dose-response value, which in most cases is the REL. When an HQ exceeds 1, we also show the HQ using the next lowest available acute dose-response value.
* (Respiratory).

    Results of the inhalation risk assessment based on estimates of 
actual emissions indicate that the maximum lifetime individual cancer 
risk (or MIR) posed by the single facility is 0.08-in-1 million, with 
arsenic compounds, dioxins/furans, chromium (VI) compounds, and nickel 
compounds predominantly emitted from spray dryers and the melt/reactor 
system as the major contributors to the risk. The total estimated 
cancer incidence from this source category is 0.00001 excess cancer 
cases per year, or one excess case in every 100,000 years. No people 
are estimated to have inhalation cancer risks above 1-in-1 million due 
to HAP emitted from the facility in this source category. The HEM-3 
model predicted the maximum chronic noncancer HI value for the source 
category could be up to 2 (respiratory effects), driven by emissions of 
chlorine from the melt/reactor system and that two people could be 
expected to be exposed to TOSHI levels above 1. However, due to the 
large distance to the nearest residential areas, the MIR and maximum 
chronic HI receptor is approximately 26 km from the plant. Based upon 
the distance of the plant to the MIR receptor with a local average wind 
of 5 meters per second, the facility's plume would reach this receptor 
in approximately 1.4 hours. After reviewing the decay rates for 
chlorine and receptor distances for this facility, we determined that 
these emission sources should be modeled taking photo-decay into 
account. The HEM-3 model does not consider photo-decay. Therefore, a 
separate refined analysis considering decay was performed to assess the 
impact on the chronic noncancer HI. Based upon the reactivity of 
chlorine and the time to reach the MIR location, we would expect the 
chlorine concentration at the MIR to decrease by approximately 44 
percent when accounting for photo-decay, resulting in a chronic 
noncancer HI value for the source category of 1 (respiratory) with no 
people expected to be exposed to a HI of greater than 1. Details on 
this refinement is presented in Appendix 12 of the source category risk 
report, which is available in the docket for this action.
    Considering MACT-allowable emissions, results of the inhalation 
risk assessment indicate that the cancer MIR is 0.08-in-1 million, 
again with arsenic compounds, dioxins/furans, chromium (VI) compounds, 
and nickel compounds predominantly emitted from spray dryers and the 
melt/reactor system as the major contributors to the risk. The total 
estimated cancer incidence from this source category based on allowable 
emissions is 0.00001 excess cancer cases per year, or one excess case 
in every 100,000 years. No people are estimated to have cancer risks 
above 1-in-1 million from HAP emitted from the facility in this source 
category. No individuals are estimated to have exposures that result in 
a noncancer HI at or above 1 at allowable emission rates.
2. Screening Level Acute Risk Assessment Results
    To better characterize the potential health risks associated with 
estimated worst-case acute exposures to HAP, and in response to a key 
recommendation from the SAB's peer review of the EPA's RTR risk 
assessment methodologies, we examined a wider range of available acute 
health metrics than we do for our chronic risk assessments. This is in 
acknowledgement that there are generally more data gaps and 
uncertainties in acute reference values than there are in chronic 
reference values. By definition, the acute REL represents a health-
protective level of exposure, with effects not anticipated below those 
levels, even for repeated exposures. However, the level of exposure 
that would cause health effects is not specifically known. Therefore, 
when an REL is exceeded and an AEGL-1 or ERPG-1 level is available 
(i.e., levels at which mild, reversible effects are anticipated in the 
general public for a single exposure), we typically use them as an 
additional comparative measure, as they provide an upper bound for 
exposure levels above which exposed individuals could experience 
effects. As the exposure concentration increases above the acute REL, 
the potential for effects increases.
    Based on our initial acute risk assessment, the maximum acute HQs 
from actual baseline emissions, based on a review of all modeled 
receptors for the US Magnesium facility, identified an exceedance of 
one acute benchmark (for chlorine) with an HQ of 8 based on the 1-hour 
REL, but that receptor is located on-site with no public access. We 
then evaluated the off-site receptors, which resulted in a highest 
refined (off-site) screening acute HQ for chlorine of 3 (based on the 
acute REL for chlorine). For this initial model run, we assumed an 
upper-end estimate of hourly potential acute emissions from the primary 
source of the chlorine emissions (i.e., the melt/reactor system) of 8 
times higher than the annual average emissions rate (which is the 
estimated 95 percent value of the range of estimated emissions in 
2017). Further, this exceedance was only predicted to occur in a non-
residential area with limited public access in a parking lot shared 
with a neighboring facility (ATI Titanium LLC). A review of the other 
surrounding property off-site of the US Magnesium facility identified 
public land managed by the Bureau of Land Management with an HQ (REL) 
of 2, access highways to the facilities off of the Interstate (I-80) 
with an HQ of 0.4 and the MIR residential location for the source 
category having an HQ of 0.3. No facilities were estimated to have an 
HQ based on AEGL or EPRG benchmarks greater than 1. Based on these 
initial estimated actual acute emissions (95th percentile), the refined 
acute results (with maximum acute HQ of 3) indicate that these upper 
end emissions are unlikely to pose significant risk to the general 
public.

[[Page 1408]]

    However, we also evaluated the potential acute HQ values based on 
estimated worst-case emissions, which we understand have occurred 
during periodic rebuilding and rehabilitative maintenance events of the 
melt/reactor control device (i.e., the CRB), as discussed previously in 
section III.C.3.c. Because of the infrequent nature of the CRB rebuilds 
(every 6 to 7 years) chronic risks are not expected to change; however, 
acute risks could increase significantly during these time periods. 
Based on available information, we estimate the worst-case chlorine 
emissions from the melt/reactor to be as high as 3.6 times the acute 
emissions modeled initially (i.e., the 95th percentile estimate), or 29 
times annual average emissions rates. During these events, assuming a 
linear increase in risks compared to emissions, we estimate the maximum 
off-site acute HQs could be up to 11 in the parking lot shared with the 
neighboring facility, 7 on public uninhabited lands and 1 at the 
nearest residential location. Further details on the acute HQ risk 
analyses and results are provided in Appendix 10 of the risk report for 
this source category.
3. Multipathway Risk Screening Results
    The lone facility in the source category reported estimated 
emissions of carcinogenic PB-HAP (arsenic and dioxins) and non-
carcinogenic PB-HAP (cadmium and mercury). The facility reported 
emissions of carcinogenic PB-HAP (arsenic and dioxins) that exceeded a 
Tier 1 cancer screening threshold emission rate and reported emissions 
of non-carcinogenic PB-HAP (mercury) that exceeded a Tier 1 noncancer 
screening threshold emission rate. Because the facility exceeded the 
Tier 1 multipathway screening threshold emission rate for one or more 
PB-HAP, we used additional facility site-specific information to 
perform a Tier 2 assessment and determine the maximum chronic cancer 
and noncancer impacts for the source category. Based on the Tier 2 
multipathway cancer assessment, the dioxin emissions exceeded the Tier 
2 screening threshold emission rate by a factor of 20 and a factor of 
40 for arsenic. The multipathway risk screening Tier 2 assessment 
resulted in a combined dioxin and arsenic emission rate that exceeded 
the Tier 2 cancer screening value by a factor of 60 for the gardener 
scenario. The Tier 2 screening value for all other PB-HAP potentially 
emitted from the source category (mercury compounds and cadmium 
compounds) were less than 1.
    A Tier 3 cancer screening assessment was conducted for both the 
fisher and gardener scenarios. Based on this Tier 3 screening 
assessment, a refined lake screening was conducted as well as 
identification of a residential receptor location (i.e., MIR location 
from the inhalation assessment) for the gardener scenario. This review 
resulted in the removal of multiple lakes and the placement of the 
residential receptor approximately 20 km south of the facility. Based 
upon these refinements, the fisher scenario resulted in a cancer 
screening value of 7 and the gardener scenario resulted in a cancer 
screening value of 1.
    An exceedance of a screening threshold emission rate in any of the 
tiers cannot be equated with a risk value or an HQ (or HI). Rather, it 
represents a high-end estimate of what the risk or hazard may be. For 
example, screening threshold emission rate of 2 for a non-carcinogen 
can be interpreted to mean that we are confident that the HQ would be 
lower than 2. Similarly, a tier screening threshold emission rate of 7 
for a carcinogen means that we are confident that the risk is lower 
than 7-in-1 million. Our confidence comes from the conservative, or 
health-protective, assumptions encompassed in the screening tiers: We 
choose inputs from the upper end of the range of possible values for 
the influential parameters used in the screening tiers, and we assume 
that the exposed individual exhibits ingestion behavior that would lead 
to a high total exposure.
4. Environmental Risk Screening Results
    As described in section III.A of this document, we conducted an 
environmental risk screening assessment for the Primary Magnesium 
Refining source category for the following pollutants: Arsenic, 
cadmium, dioxins/furans, HCl, lead, and mercury.
    In the Tier 1 screening analysis for PB-HAP (other than lead, which 
was evaluated differently), arsenic, cadmium, and divalent mercury 
emissions had no Tier 1 exceedances for any ecological benchmark. 
Dioxin/furan emissions at one facility had Tier 1 exceedances for the 
surface soil NOAEL (mammalian insectivores--shrew) benchmark by a 
maximum screening value of 400. Methyl mercury at one facility had Tier 
1 exceedances for the surface soil NOAEL (avian ground insectivores--
woodcock) by a maximum screening value of 2.
    A Tier 2 screening assessment was performed for methyl mercury and 
dioxin/furan emissions. Methyl mercury had no Tier 2 exceedances for 
any ecological benchmark. Dioxin/furan emissions had Tier 2 exceedances 
for the surface soil NOAEL (mammalian insectivores--shrew) benchmark by 
a maximum screening value of 4. This screening value was refined by 
removing soil areas located on-site. The refined Tier 2 screening value 
for dioxins/furans is 3.
    A Tier 3 screening analysis was performed for dioxin emissions. In 
the Tier 3 screen, after incorporating chemical losses due to plume-
rise into the calculation, the screening value remained 3 (surface soil 
NOAEL). Also in the Tier 3 screen, we conducted runs of the screening 
scenario within TRIM.FaTE with the following site-specific time-series 
data: Hourly meteorology, time series of leaf litterfall and air-leaf 
chemical exchanges, facility emissions, and hourly values of emission 
release height equivalent to hourly plume-rise height. After 
incorporating these time-series data in the analysis, the screening 
value is 2 (surface soil NOAEL). No other dioxin/furan benchmarks were 
exceeded in Tier 2 or 3. Specifically, the following dioxin/furan 
benchmarks were not exceeded in the Tier 2 or 3 screen:

 Fish--Avian Piscivores (NOAEL, geometric-maximum-allowable-
toxicant-level (GMATL), and LOAEL)
 Fish--Mammalian Piscivores (NOAEL, GMATL, and LOAEL)
 Sediment Community (No-effect, Threshold, and Probable-Effect)
 Surface Soil (Threshold)
 Water-column Community (Threshold, Frank-Effect)

    For lead, we did not estimate any exceedances of the secondary lead 
NAAQS.
    For HCl, the average modeled concentration around the facility 
(i.e., the average concentration of all off-site data points in the 
modeling domain) did not exceed any ecological benchmark. In addition, 
each individual modeled concentration of HCl (i.e., each off-site data 
point in the modeling domain) was below the ecological benchmarks for 
the facility.
    Based on the results of the environmental risk screening analysis, 
we do not expect an adverse environmental effect as a result of HAP 
emissions from this source category.
5. Facility-Wide Risk Results
    Facility-wide risks were estimated using the NEI-based data 
described in section III.C of this preamble. The maximum facility-wide 
cancer MIR is 0.08-in-1 million, mainly driven by arsenic compounds, 
dioxins/furans, chromium (VI) compounds, and nickel compounds 
predominantly emitted

[[Page 1409]]

from spray dryers and the melt/reactor system. The total estimated 
cancer incidence from the whole facility is 0.00001 excess cancer cases 
per year, or one excess case in every 100,000 years. No people are 
estimated to have cancer risks above 1-in-1 million from exposure to 
HAP emitted from both MACT and non-MACT sources at the single facility 
in this source category. The maximum facility-wide TOSHI for the source 
category is estimated by HEM-3 to be 2, mainly driven by emissions of 
chlorine from the melt/reactor system. Approximately two people are 
exposed to noncancer HI levels above 1, based on facility-wide 
emissions from the facility in this source category. However, once 
refined for photo-decay, the maximum facility-wide TOSHI for the source 
category is estimated to be 1 and no one is exposed to an HI greater 
than 1.
6. What demographic groups might benefit from this regulation?
    To examine the potential for any environmental justice issues that 
might be associated with the source category, we performed a 
demographic analysis, which is an assessment of risk to individual 
demographic groups of the populations living near the facilities at 
different risk levels. However, because no one is exposed to a cancer 
risk greater than 1-in-1 million or a chronic noncancer HQ greater than 
1, we only evaluated the population distributions living near the 
facility.
    The results of the demographic analysis are summarized in Table 3 
below. These results, for various demographic groups, are based on the 
population living within 50 km of the facility (the nearest resident is 
over 20 km from the facility).
    The results of the Primary Magnesium Refining source category 
demographic analysis indicate that for the population subgroups living 
within 50-km of the facility only one subgroup (people 0 to 17 years) 
is above its corresponding national average (40 percent versus 23 
percent nationally).
    The methodology and the results of the demographic analysis are 
presented in further details in a technical report, Risk and Technology 
Review--Analysis of Demographic Factors for Populations Living Near 
Primary Magnesium Refining Source Category Operations, available in the 
docket for this action.

                              Table 3--Summary of Demographic Assessment for the Primary Magnesium Refining Source Category
                                                                   [Demographic group]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                        Over 25
                         Minority   African     Native    Other and    Hispanic   Ages 0 to    Ages 18 to   Ages 65    without a   Below the  Linguistic
         Total             \1\      American   American  multiracial  or Latino     17 (%)       64 (%)      and up    HS diploma   poverty    isolation
                                      (%)        (%)         (%)         (%)                                  (%)         (%)      level (%)      (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                    National Averages
--------------------------------------------------------------------------------------------------------------------------------------------------------
317,746,049...........         38         12        0.8           7          18           23           63         14           14         14           6
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                Population Surrounding the Source Category Emissions \2\
--------------------------------------------------------------------------------------------------------------------------------------------------------
20,598................          9        0.2        0.1           2           6           40           54          6            5          7           1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Minority population is the total population minus the white population.
\2\ Proximity population statistics are provided irrespective of cancer and noncancer risk living within 50 km of the facility.

C. What are our proposed decisions regarding risk acceptability, ample 
margin of safety, and adverse environmental effect?

1. Risk Acceptability
    As noted in section III of this preamble, the EPA sets standards 
under CAA section 112(f)(2) using ``a two-step standard-setting 
approach, with an analytical first step to determine an `acceptable 
risk' that considers all health information, including risk estimation 
uncertainty, and includes a presumptive limit on MIR of approximately 
1-in-10 thousand'' (see 54 FR 38045, September 14, 1989). In this 
proposal, the EPA estimated risks based on actual and allowable 
emissions under the current NESHAP from the Primary Magnesium Refining 
source category.
    The estimated inhalation cancer risk to the individual most exposed 
to actual or allowable emissions from the source category is 0.08-in-1 
million. The estimated incidence of cancer due to inhalation exposures 
is 0.00001 excess cancer cases per year, or 1 excess case every 100,000 
years. No people are estimated to have cancer risks above 1-in-1 
million from HAP emitted from the facility in this source category.
    The estimated, refined, maximum chronic noncancer TOSHI from 
inhalation exposure for this source category is 1, indicating low 
likelihood of adverse noncancer effects from long-term inhalation 
exposures.
    The multipathway risk assessment results indicate a maximum cancer 
risk of 7-in-1 million based on ingestion exposures estimated for 
dioxins using the health protective risk screening assumptions of a 
Tier 3 fisher exposure scenario.
    The initial acute risk screening assessment of upper-end estimates 
of acute inhalation impacts (which were based on the 95th percentile 
estimate of hourly emissions) indicates a maximum off-site acute HQ 
(REL) of 3, located at an adjacent facility. A review of the 
surrounding property off-site of the US Magnesium facility also 
identified public land managed by the Bureau of Land Management with an 
HQ of 2. Access highways to the facilities off of the highway (I-80) 
show an HQ of 0.4, with the MIR residential location for the source 
category having an HQ of 0.3.
    After the initial acute risk assessment, we also evaluated the 
potential risks associated with an estimate of the worst-case actual 
hourly peak emissions, which we understand can occur during rebuilding/
rehabilitative maintenance events of the CRB. During these events, we 
estimate that maximum off-site acute HQ (REL) can be as high as 11 in 
the parking lot shared with the neighboring facility, 7 on public 
uninhabited lands, and 1 at the nearest residential location. However, 
as is discussed in section IV.E of this preamble, by removing the SSM 
exemptions in this proposed action, proposing work practice standards 
for periods of malfunction, and with current emission limits in the 
NESHAP applying at all other times, including rebuild/rehabilitative 
maintenance of the CRB, this potential elevated acute risk will be 
significantly reduced. Therefore, based on this assessment, the refined 
acute results indicate that at baseline, the acute HQ could be as high 
as 11, but once the proposed rule is finalized, including the removal 
of the exemptions, peak emissions are unlikely to pose significant 
risk.
    Considering all of the health risk information and factors 
discussed

[[Page 1410]]

above, including the uncertainties discussed in section III of this 
preamble, the EPA proposes that the risks for this source category 
under the current NESHAP provisions are acceptable. However, we note 
that we have some concerns regarding the potential acute risks 
estimated for the baseline scenario, but as described above, and below 
in the ample margin of safety analysis section, these potential risks 
will be significantly reduced once this proposed rule is finalized.
2. Ample Margin of Safety Analysis
    As directed by CAA section 112(f)(2), we conducted an analysis to 
determine whether the current emissions standards provide an ample 
margin of safety to protect public health. Under the ample margin of 
safety analysis, the EPA considers all health factors evaluated in the 
risk assessment and evaluates the cost and feasibility of available 
control technologies and other measures (including the controls, 
measures, and costs reviewed under the technology review) that could be 
applied to this source category to further reduce the risks (or 
potential risks) due to emissions of HAP identified in our risk 
assessment. In this analysis, we considered the results of the 
technology review, risk assessment, and other aspects of the NESHAP 
review to determine whether there are any emission reduction measures 
necessary to provide an ample margin of safety with respect to the 
risks associated with these emissions.
    The inhalation cancer risk due to HAP emissions from the Primary 
Magnesium Refining source category is less than 1-in-1 million and the 
chronic noncancer TOSHI due to inhalation exposures is estimated to be 
1 and no one exposed to an HI greater than 1. Additionally, the results 
of the acute screening analysis showed that risks were below a level of 
concern during normal operations.
    As described above, there are potential elevated acute risks 
associated with CRB controls on the melt/reactor; however, by removing 
the SSM exemptions in this proposed action, proposing work practice 
standards for periods of malfunction, and with current emission limits 
applying at all other times, including rebuild/rehabilitative 
maintenance of the CRB, these potential elevated acute risks will be 
significantly reduced.
    With regard to PB-HAP, we identified and investigated the 
installation of activated carbon injection (ACI) and a baghouse with 
catalytic filters as an option to further reduce dioxin emissions and 
risks. The use of ACI plus catalytic filters to reduce dioxin emissions 
was evaluated and determined not to be cost effective during the 
original NESHAP. Based on our current review of that information, we do 
not believe the associated costs for installing and operating a 
baghouse have changed significantly since the original NESHAP. When 
evaluating the cost effectiveness of installing ACI and a baghouse with 
catalytic filters during the development of the 2003 Primary Magnesium 
Refining NESHAP, a full cost analysis was performed for the facility. 
Based on our reevaluation of this information and an updated analysis, 
we estimate these controls would have capital cost of about $1 million, 
annual costs of $600,000, and would achieve about 2 grams reduction per 
year (95 percent reduction), with cost effectiveness of $289,000 per 
gram of dioxin removal, and the maximum cancer risk would be reduced 
from 7-in-1 million to about 1-in-1 million (for more details see 
Legacy Docket A-2002-0043, Document II-B-5). Due to the relatively high 
cost, coupled with the small reduction in dioxin emissions, we conclude 
that these controls are not cost effective, and would only achieve 
modest reduction in risks. We did not identify any relevant non-air 
quality health and environmental impacts, and energy requirements. 
Based upon the relatively low baseline risks, minimal available risk 
reductions, and lack of cost-effective control options to reduce 
emissions, we are not proposing revised standards for dioxins and 
furans in this action.
    In summary, we are proposing that baseline risks from the source 
category are acceptable, and we are proposing rule changes (described 
above) to remove SSM exemptions and add work practice standards for CRB 
malfunction events. With these proposed revisions along with the 
current emissions limits for chlorine and other HAP applying at all 
times, the potential acute risks of chlorine will be addressed. 
Furthermore, we did not identify cost-effective controls for dioxins. 
Therefore, we are proposing that after the rule changes described above 
are finalized, the NESHAP will provide an ample margin of safety to 
protect public health. Since the removal of the SSM exemptions and 
addition of work practices for malfunctions help address the acute 
risks, we are proposing to adopt these amendments under CAA section 
112(f), in addition to authorities 112(d)(2), 112(d)(3), or 112(h), as 
described elsewhere in this preamble.
3. Adverse Environmental Effect
    As described in section III.A of this preamble, we conducted an 
environmental risk screening assessment for the Primary Magnesium 
Refining source category. We do not expect there to be an adverse 
environmental effect as a result of HAP emissions from this source 
category and we are proposing that it is not necessary to set any 
additional standards, beyond those described above, to prevent, taking 
into consideration costs, energy, safety, and other relevant factors, 
an adverse environmental effect.

D. What are the results and proposed decisions based on our technology 
review?

    As described in section III.B of this preamble, the technology 
review focuses on the identification and evaluation of developments in 
practices, processes, and control technologies that have occurred since 
the MACT standards were promulgated. We also evaluate, during the 
technology review, whether there are any unregulated emissions of HAP 
within the source category, and we establish standards if we identify 
unregulated emissions. In conducting the technology review, we reviewed 
various informational sources regarding the emissions from the Primary 
Magnesium Refining source category. The review included a search of the 
internet and Reasonably Available Control Technology, Best Available 
Control Technology, and Lowest Achievable Emission Rate Clearinghouse 
database, reviews of air permits, and discussions with industry 
representatives. We reviewed these data sources for information on 
practices, processes, and control technologies that were not considered 
during the development of the Primary Magnesium Refining NESHAP. We 
also looked for information on improvements in practices, processes, 
and control technologies that have occurred since the development of 
the Primary Magnesium Refining NESHAP.
    Based on this review, the EPA identified a development in 
technology and practices regarding pH monitoring for acid gas control 
devices. Specifically, the EPA is proposing to amend the emission 
limitations and operating parameters set forth in 40 CFR 63.9890(b) to 
include pH as an additional operational parameter for all control 
devices used to meet the acid gas emission limits of this subpart. We 
have determined that this change reflects a development in technology 
and practices pursuant to CAA section 112(d)(6), that is consistent 
with other

[[Page 1411]]

NESHAP that cover acid-gas emitting source categories, such as the HCl 
Production source category, that requires pH as an operational 
parameter. Monitoring and maintaining the appropriate pH levels are 
important to ensure the effectiveness of acid gas control devices 
(i.e., wet scrubbers). This is particularly relevant to this source 
category since each stack covered in this subpart is subject to an acid 
gas emissions limitation (either chlorine, HCl, or both). Therefore, in 
addition to maintaining the hourly average pressure drops and scrubber 
liquid flow rates, we are proposing that pH must also be measured and 
maintained within the operating range values established during the 
performance test for all control devices used to meet the acid gas 
emission limits of this subpart. The proposed installation, operation, 
and maintenance requirements specifically for pH are included in 40 CFR 
63.9921(a)(3). In addition, there are minor amendments to 40 CFR 
63.9916, 63.9917, 63.9920, and 63.9923 to include pH in all CPMS 
related requirements.
    Furthermore, as described above in section IV.A, we evaluated the 
potential to require an incinerator and wet scrubber to achieve 
additional reductions of chlorine from the CBS, however, due to 
significant uncertainties in emissions and costs of controls, we are 
not proposing such controls under CAA section 112(d)(2) or (d)(3). For 
the same reasons, we are also not proposing such controls under CAA 
section 112(d)(6).
    In addition, as part of the technology review, we identified a 
previously unregulated process and pollutant, and are regulating them 
under CAA sections 112(d)(2) and (3), as described in section IV.A, 
above.
    In summary, after reviewing all of this information, we identified 
one development in technology and practices regarding pH monitoring for 
acid gas control devices. We did not identify any additional cost-
effective developments in practices, processes, or control technologies 
used at primary magnesium refining facilities since promulgation of the 
MACT standard that warrant revision to the NESHAP pursuant to CAA 
section 112(d)(6) at this time. For all four emission points, US 
Magnesium uses wet scrubbers (packed-bed and venturi scrubbers) to 
achieve the emission limits. We concluded that wet scrubbing systems 
are the most appropriate and practical control systems and that there 
is no other control equipment or methods of control that would be more 
effective for reducing their emissions taking into consideration cost, 
feasibility, and uncertainties.

E. What other actions are we proposing?

    In addition to the proposed actions described above, we are 
proposing additional revisions to the NESHAP. We are proposing 
revisions to the SSM provisions of the MACT rule in order to ensure 
that they are consistent with the decision in Sierra Club v. EPA, 551 
F. 3d 1019 (D.C. Cir. 2008), in which the court vacated two provisions 
that exempted sources from the requirement to comply with otherwise 
applicable CAA section 112(d) emission standards during periods of SSM. 
We are also proposing various other changes, including an alternative 
standard for malfunction events for the CRB and the addition of 
electronic reporting. Our analyses and proposed changes related to 
these issues are discussed below.
1. SSM
    In its 2008 decision in Sierra Club v. EPA, 551 F.3d 1019 (D.C. 
Cir. 2008), the court vacated portions of two provisions in the EPA's 
CAA section 112 regulations governing the emissions of HAP during 
periods of SSM. Specifically, the court vacated the SSM exemption 
contained in 40 CFR 63.6(f)(1) and (h)(1), holding that under section 
302(k) of the CAA, emissions standards or limitations must be 
continuous in nature and that the SSM exemption violates the CAA's 
requirement that some CAA section 112 standards apply continuously.
    Consistent with Sierra Club v. EPA, we are proposing the 
elimination of the SSM exemptions in this NESHAP and we are proposing 
that emissions standards will apply at all times. As described below, 
we are proposing new work practice standards pursuant to CAA section 
112(h) that will apply to CRB malfunctions. For all other sources, 
scenarios, and HAP, we are simply removing the SSM exemptions such that 
the current emissions limits will apply at all times. We are also 
proposing several revisions to Table 5 (the General Provisions 
Applicability Table) which are explained in more detail below. For 
example, we are proposing to eliminate the incorporation of the General 
Provisions' requirement that sources develop an SSM plan. We also are 
proposing to eliminate and revise certain recordkeeping and reporting 
requirements related to the SSM exemption as described below.
    The EPA has attempted to ensure that the provisions we are 
proposing to eliminate are inappropriate, unnecessary, or redundant in 
the absence of the SSM exemption. We are specifically seeking comment 
on whether we have successfully done so.
    In proposing the standards in this rule, the EPA has considered 
startup and shutdown periods and, for the reasons explained below, is 
not proposing alternate standards for those periods. The primary 
magnesium refining production process is continuous, with control 
equipment operating at all times. The industry has not identified (and 
there are no data indicating) any specific problems with removing the 
provisions for startup and shutdown. However, we solicit comment on 
whether any situations exist where separate standards, such as work 
practices, would be more appropriate during periods of startup and 
shutdown rather than the current standard.
    Periods of startup, normal operations, and shutdown are all 
predictable and routine aspects of a source's operations. Malfunctions, 
in contrast, are neither predictable nor routine. Instead they are, by 
definition, sudden, infrequent, and not reasonably preventable failures 
of emissions control, process, or monitoring equipment. (40 CFR 63.2) 
(definition of malfunction). The EPA interprets CAA section 112 as not 
requiring emissions that occur during periods of malfunction to be 
factored into development of CAA section 112 standards and this reading 
has been upheld as reasonable by the court in U.S. Sugar Corp. v. EPA, 
830 F.3d 579, 606-610 (2016). Under section 112, emissions standards 
for new sources must be no less stringent than the level ``achieved'' 
by the best controlled similar source and for existing sources 
generally must be no less stringent than the average emission 
limitation ``achieved'' by the best performing 12 percent of sources in 
the category (or the average emission limitation achieved by the best 
performing sources where, as here, there are fewer than 30 sources in 
the source category). There is nothing in CAA section 112 that directs 
the Agency to consider malfunctions in determining the level 
``achieved'' by the best performing sources when setting emission 
standards. As the court has recognized, the phrase ``average emissions 
limitation achieved by the best performing 12 percent of sources ``says 
nothing about how the performance of the best units is to be 
calculated.'' Nat'l Ass'n of Clean Water Agencies v. EPA, 734 F.3d 
1115, 1141 (D.C. Cir. 2013). While the EPA accounts for variability in 
setting emissions standards, nothing in CAA section 112 requires the 
Agency to consider malfunctions as part of that analysis. The EPA is 
not required to

[[Page 1412]]

treat a malfunction in the same manner as the type of variation in 
performance that occurs during routine operations of a source. A 
malfunction is a failure of the source to perform in a ``normal or 
usual manner'' and no statutory language compels the EPA to consider 
such events in setting CAA section 112 standards.
    As the court recognized in U.S. Sugar Corp., accounting for 
malfunctions in setting standards would be difficult, if not 
impossible, given the myriad different types of malfunctions that can 
occur across all sources in the category and given the difficulties 
associated with predicting or accounting for the frequency, degree, and 
duration of various malfunctions that might occur. Id. at 608 (``the 
EPA would have to conceive of a standard that could apply equally to 
the wide range of possible boiler malfunctions, ranging from an 
explosion to minor mechanical defects. Any possible standard is likely 
to be hopelessly generic to govern such a wide array of 
circumstances.''). As such, the performance of units that are 
malfunctioning is not ``reasonably'' foreseeable. See, e.g., Sierra 
Club v. EPA, 167 F.3d 658, 662 (D.C. Cir. 1999) (``The EPA typically 
has wide latitude in determining the extent of data-gathering necessary 
to solve a problem. We generally defer to an agency's decision to 
proceed on the basis of imperfect scientific information, rather than 
to `invest the resources to conduct the perfect study.' ''). See also, 
Weyerhaeuser v. Costle, 590 F.2d 1011, 1058 (D.C. Cir. 1978) (``In the 
nature of things, no general limit, individual permit, or even any 
upset provision can anticipate all upset situations. After a certain 
point, the transgression of regulatory limits caused by `uncontrollable 
acts of third parties,' such as strikes, sabotage, operator 
intoxication or insanity, and a variety of other eventualities, must be 
a matter for the administrative exercise of case-by case enforcement 
discretion, not for specification in advance by regulation.''). In 
addition, emissions during a malfunction event can be significantly 
higher than emissions at any other time of source operation. For 
example, if an air pollution control device with 99 percent removal 
goes offline as a result of a malfunction (as might happen if, for 
example, the bags in a baghouse catch fire) and the emission unit is a 
steady state type unit that would take days to shut down, the source 
would go from 99 percent control to zero control until the control 
device was repaired. The source's emissions during the malfunction 
would be 100 times higher than during normal operations. As such, the 
emissions over a 4-day malfunction period would exceed the annual 
emissions of the source during normal operations. As this example 
illustrates, accounting for malfunctions could lead to standards that 
are not reflective of (and significantly less stringent than) levels 
that are achieved by a well performing non-malfunctioning source. It is 
reasonable to interpret CAA section 112 to avoid such a result. The 
EPA's approach to malfunctions is consistent with CAA section 112 and 
is a reasonable interpretation of the statute.
    Although no statutory language compels the EPA to set separate 
standards for malfunctions, the EPA has the discretion to do so where 
feasible. For example, in the Petroleum Refinery Sector RTR, the EPA 
established a work practice standard for unique types of malfunction 
that result in releases from pressure relief devices or emergency 
flaring events because the EPA had information to determine that such 
work practices reflected the level of control that applies to the best 
performers. 80 FR 75178, 75211 through 14 (December 1, 2015). The EPA 
will consider whether circumstances warrant setting standards for a 
particular type of malfunction and, if so, whether the EPA has 
sufficient information to identify the relevant best performing sources 
and establish a standard for such malfunctions. (We also encourage 
commenters to provide any such information.)
    Given the EPA's discretion to set separate standards for 
malfunctions, we are proposing a standard for this source category to 
address the CRB emission point. Based on our knowledge of the processes 
and engineering judgement, we expect that the standard for normal 
operations for the melt/reactor (100 lbs/hr) cannot be met during 
malfunctions of the CRB (unavoidable and unanticipated breakdowns), 
unless the melt/reactor is stopped, which the facility has indicated 
cannot be done instantaneously due to the molten process. The CRB is 
the primary chlorine control device for the melt/reactor system. The 
CRB converts the chlorine gas stream from the melt/reactor to HCl. A 
high percentage of the HCl is then captured through a series of wet 
scrubbers. If the CRB is offline, the chlorine emissions continue to 
pass through the wet scrubbers; however, without the conversion to HCl, 
removal is significantly reduced. Therefore, the EPA anticipates that 
malfunctions of the CRB will result in violations of the current 
chlorine standard (i.e., 100 lbs/hr) during a significant portion of 
the malfunction events if the melt reactor process continues to 
operate. To address this issue, the EPA is proposing work practice 
standards in Table 4 to 40 CFR part 63, subpart TTTTT to apply during 
CRB malfunctions to ensure that a CAA section 112 standard applies 
continuously. Based on discussions with the facility, CRB malfunctions 
are infrequent, unpredictable, and highly variable in nature. 
Furthermore, these events are typically short, requiring a few hours 
for the facility to replace or repair the malfunctioning equipment. 
Because of this, it is not technically feasible to measure emissions 
during the brief periods when these situations occur (i.e., 
unpredictable, highly variable, and short in duration).
    As noted in CAA section 112(h)(1), ``if it is not feasible in the 
judgment of the Administrator to prescribe or enforce an emission 
standard for control of a hazardous air pollutant or pollutants, the 
Administrator may, in lieu thereof, promulgate a design, equipment, 
work practice, or operational standard, or combination thereof, which 
in the Administrator's judgment is consistent with the provisions of 
subsection (d) or (f).'' CAA section 112(h)(2) defines the phrase ``not 
feasible to prescribe or enforce an emission standard'' as any 
situation in which the Administrator determines that either ``a 
hazardous air pollutant or pollutants cannot be emitted through a 
conveyance designed and constructed to emit or capture such pollutant, 
or that any requirement for, or use of, such a conveyance would be 
inconsistent with any Federal, State or local law'' or ``the 
application of measurement methodology to a particular class of sources 
is not practicable due to technological and economic limitations.''
    Based on the information described above, the EPA is proposing work 
practice standards pursuant to CAA section 112(h) that will apply to 
the melt/reactor and the CRB during periods when a malfunction occurs 
to the CRB. We are proposing the following work practices for these 
periods that include the following requirements: (1) During unplanned/
unavoidable CRB malfunction events, the facility must shutdown the 
reactor as soon as practicable but not later than 15 minutes after such 
event occurs and keep the reactor offline during the CRB repair 
process; and (2) operators must perform a root cause analysis/
corrective action. This includes conducting a root cause analysis to 
determine the source, nature, and cause of each malfunction event and 
identifying corrective measures to prevent future such malfunction 
events as soon as practicable, but no later than 45 days after a 
malfunction event.

[[Page 1413]]

Corrective actions must be implemented as soon as practicable, but no 
later than 45 days after a malfunction event or as soon thereafter as 
practicable. If there is a second release event in a 12-month period 
with the same root cause on the same equipment, it would be a deviation 
of the work practice standard. However, as an alternative to this work 
practice standard, we propose that facility would be allowed to keep 
melt reactor operating if they reroute the emissions to an equally 
effective back-up control device configuration, such as a back-up CRB 
and wet scrubber.
    With regard to other emissions sources (e.g., spray dryers, 
magnesium chloride storage bins, launder off-gas systems), the EPA 
anticipates that it is unlikely that a malfunction will result in a 
violation of the standard because the air pollution control equipment 
or other measures used to limit the emissions from these processes 
would still be operational. If the malfunction occurs in the pollution 
control equipment for these other processes, the operators should 
discontinue process operations until such time that the air pollution 
control systems are operable in order to comply with the requirements 
to minimize emissions and operate according to good air pollution 
practices. In general, process operations should be able to be shut 
down quickly enough to avoid a violation of an emissions limitation. 
Nevertheless, we expect there could be situations where a malfunction 
in the control equipment could result in a violation of the standard 
depending on how quickly emissions decline upon process shut down. In 
this case, owners or operators must report the deviation, the quantity 
of HAP emitted over the emissions limit, the cause of the deviation, 
and the corrective action taken to limit the emissions during the 
event.
    In the unlikely event that a source fails to comply with the 
applicable CAA section 112(d) standards as a result of a malfunction 
event, the EPA would determine an appropriate response based on, among 
other things, the good faith efforts of the source to minimize 
emissions during malfunction periods, including preventative and 
corrective actions, as well as root cause analyses to ascertain and 
rectify excess emissions. The EPA would also consider whether the 
source's failure to comply with the CAA section 112(d) standard was, in 
fact, sudden, infrequent, not reasonably preventable, and was not 
instead caused, in part, by poor maintenance or careless operation. 40 
CFR 63.2 (definition of malfunction).
    If the EPA determines in a particular case that an enforcement 
action against a source for violation of an emission standard is 
warranted, the source can raise any and all defenses in that 
enforcement action and the federal district court will determine what, 
if any, relief is appropriate. The same is true for citizen enforcement 
actions. Similarly, the presiding officer in an administrative 
proceeding can consider any defense raised and determine whether 
administrative penalties are appropriate.
    In summary, the EPA interpretation of the CAA and, in particular, 
CAA section 112, is reasonable and encourages practices that will avoid 
malfunctions and judicial procedures for addressing exceedances of the 
standards fully recognize that violations may occur despite good faith 
efforts to comply and can accommodate those situations. U.S. Sugar 
Corp. v. EPA, 830 F.3d 579, 606-610 (2016).
    We are also proposing several revisions to the General Provisions 
Applicability Table (Table 5) which are explained in more detail below 
as follows. We are proposing to revise the General Provisions 
Applicability Table (Table 5) entry for 40 CFR 63.6(e)(1)(i) by 
changing the ``yes'' in the column titled ``Applies to Subpart TTTTT'' 
to a ``no.'' Section 63.6(e)(1)(i) describes the general duty to 
minimize emissions. Some of the language in that section is no longer 
necessary or appropriate in light of the elimination of the SSM 
exemption. We are proposing instead to add general duty regulatory text 
at 40 CFR 63.9910(b) that reflects the general duty to minimize 
emissions while eliminating the reference to periods covered by an SSM 
exemption. The current language in 40 CFR 63.6(e)(1)(i) characterizes 
what the general duty entails during periods of SSM. With the 
elimination of the SSM exemption, there is no need to differentiate 
between normal operations and SSM events in describing the general 
duty. Therefore, the language the EPA is proposing for 40 CFR 
63.9910(b) does not include that language from 40 CFR 63.6(e)(1).
    We are also proposing to revise the General Provisions 
Applicability Table (Table 5) entry for 40 CFR 63.6(e)(1)(ii) by 
changing the ``yes'' in the column titled ``Applies to Subpart TTTTT'' 
to a ``no.'' Section 63.6(e)(1)(ii) imposes requirements that are not 
necessary with the elimination of the SSM exemption or are redundant 
with the general duty requirement being added at 40 CFR 63.9910(b).
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.6(e)(3) by changing the ``yes'' in 
the column titled ``Applies to Subpart TTTTT'' to a ``no.'' Generally, 
these paragraphs require development of an SSM plan and specify SSM 
recordkeeping and reporting requirements related to the SSM plan. As 
noted, the EPA is proposing to remove the SSM exemptions. Therefore, 
affected units will be subject to an emission standard during such 
events. The applicability of a standard during such events will ensure 
that sources have ample incentive to plan for and achieve compliance 
and, thus, the SSM plan requirements are no longer necessary.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.6(f)(1) by changing the ``yes'' in 
the column titled ``Applies to Subpart TTTTT'' to a ``no.'' The current 
language of 40 CFR 63.6(f)(1) exempts sources from nonopacity standards 
during periods of SSM. As discussed above, the court in Sierra Club v. 
EPA vacated the exemptions contained in this provision and held that 
the CAA requires that some CAA section 112 standards apply 
continuously. Consistent with Sierra Club v. EPA, the EPA is proposing 
to revise standards in this rule to apply at all times and proposing a 
new work practice standard for CRB malfunction events.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.7(e)(1) by changing the ``yes'' in 
the column titled ``Applies to Subpart TTTTT'' to a ``no.'' Section 
63.7(e)(1) describes performance testing requirements. The EPA is 
instead proposing to add a performance testing requirement at 40 CFR 
63.9913(a). The performance testing requirements we are proposing to 
add differ from the General Provisions performance testing provisions 
in several respects. The regulatory text removes the cross-reference to 
40 CFR 63.7(e)(1) and does not include the language in 40 CFR 
63.7(e)(1) that restated the SSM exemption and language that precluded 
startup and shutdown periods from being considered ``representative'' 
for purposes of performance testing. The proposed performance testing 
provisions will not allow performance testing during malfunctions. As 
in 40 CFR 63.7(e)(1), performance tests conducted under this subpart 
should not be conducted during malfunctions because conditions during 
malfunctions are often not representative of normal operating 
conditions. The EPA is proposing to add language that requires the 
owner or operator to record the process information that is necessary 
to document operating conditions during

[[Page 1414]]

the test and include in such record an explanation to support that such 
conditions represent normal operation. Section 63.7(e) requires that 
the owner or operator make available to the Administrator such records 
``as may be necessary to determine the condition of the performance 
test'' available to the Administrator upon request but does not 
specifically require the information to be recorded. The regulatory 
text the EPA is proposing to add to this provision builds on that 
requirement and makes explicit the requirement to record the 
information.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.8(c)(1)(i) and (iii) by changing 
the ``yes'' in the column titled ``Applies to Subpart TTTTT'' to a 
``no.'' The cross-references to the general duty and SSM plan 
requirements in those subparagraphs are not necessary in light of other 
requirements of 40 CFR 63.8 that require good air pollution control 
practices (40 CFR 63.8(c)(1)) and that set out the requirements of a 
quality control program for monitoring equipment (40 CFR 63.8(d)).
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.10(b)(2)(i) by changing the ``yes'' 
in the column titled ``Applies to Subpart TTTTT'' to a ``no.'' Section 
63.10(b)(2)(i) describes the recordkeeping requirements during startup 
and shutdown. These recording provisions are no longer necessary 
because the EPA is proposing that recordkeeping and reporting 
applicable to normal operations will apply to startup and shutdown. In 
the absence of special provisions applicable to startup and shutdown, 
such as a startup and shutdown plan, there is no reason to retain 
additional recordkeeping for startup and shutdown periods.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.10(b)(2)(ii) by changing the 
``yes'' in the column titled ``Applies to Subpart TTTTT'' to a ``no.'' 
Section 63.10(b)(2)(ii) describes the recordkeeping requirements during 
a malfunction. The EPA is proposing to add such requirements to 40 CFR 
63.9932. The regulatory text we are proposing to add differs from the 
General Provisions it is replacing in that the General Provisions 
requires the creation and retention of a record of the occurrence and 
duration of each malfunction of process, air pollution control, and 
monitoring equipment. The EPA is proposing that this requirement apply 
to any failure to meet an applicable standard and is requiring that the 
source record the date, time, and duration of the failure rather than 
the ``occurrence.'' The EPA is also proposing to add to 40 CFR 63.9932 
a requirement that sources keep records that include a list of the 
affected source or equipment and actions taken to minimize emissions, 
an estimate of the quantity of each regulated pollutant emitted over 
the standard for which the source failed to meet the standard, and a 
description of the method used to estimate the emissions. Examples of 
such methods would include product loss calculations, mass balance 
calculations, measurements when available, or engineering judgment 
based on known process parameters. The EPA is proposing to require that 
sources keep records of this information to ensure that there is 
adequate information to allow the EPA to determine the severity of any 
failure to meet a standard, and to provide data that may document how 
the source met the general duty to minimize emissions when the source 
has failed to meet an applicable standard.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.10(b)(2)(iv) by changing the 
``yes'' in the column titled ``Applies to Subpart TTTTT'' to a ``no.'' 
When applicable, the provision requires sources to record actions taken 
during SSM events when actions were inconsistent with their SSM plan. 
The requirement is no longer appropriate because SSM plans will no 
longer be required. The requirement previously applicable under 40 CFR 
63.10(b)(2)(iv)(B) to record actions to minimize emissions and record 
corrective actions is now applicable by reference to 40 CFR 63.9932.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.10(b)(2)(v) by changing the ``yes'' 
in the column titled ``Applies to Subpart TTTTT'' to a ``no.'' When 
applicable, the provision requires sources to record actions taken 
during SSM events to show that actions taken were consistent with their 
SSM plan. The requirement is no longer appropriate because SSM plans 
will no longer be required.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.10(c)(15) by changing the ``yes'' 
in the column titled ``Applies to Subpart TTTTT'' to a ``no.'' The EPA 
is proposing that 40 CFR 63.10(c)(15) no longer applies. When 
applicable, the provision allows an owner or operator to use the 
affected source's SSM plan or records kept to satisfy the recordkeeping 
requirements of the SSM plan, specified in 40 CFR 63.6(e), to also 
satisfy the requirements of 40 CFR 63.10(c)(10) through (12). The EPA 
is proposing to eliminate this requirement because SSM plans would no 
longer be required, and, therefore, 40 CFR 63.10(c)(15) no longer 
serves any useful purpose for affected units.
    We are proposing to revise the General Provisions Applicability 
Table (Table 5) entry for 40 CFR 63.10(d)(5) by changing the ``yes'' in 
the column titled ``Applies to Subpart TTTTT'' to a ``no.'' Section 
63.10(d)(5) describes the reporting requirements for startups, 
shutdowns, and malfunctions. To replace the General Provisions 
reporting requirement, the EPA is proposing to add reporting 
requirements to 40 CFR 63.9931(b)(4). The replacement language differs 
from the General Provisions requirement in that it eliminates periodic 
SSM reports as a stand-alone report. We are proposing language that 
requires sources that fail to meet an applicable standard at any time 
to report the information concerning such events in the semi-annual 
compliance report already required under this rule. We are proposing 
that the report must contain the number, date, time, duration, and the 
cause of such events (including unknown cause, if applicable), a list 
of the affected source or equipment, an estimate of the quantity of 
each regulated pollutant emitted over any emission limit, and a 
description of the method used to estimate the emissions. Examples of 
such methods would include product-loss calculations, mass balance 
calculations, measurements when available, or engineering judgment 
based on known process parameters. The EPA is proposing this 
requirement to ensure that there is adequate information to determine 
compliance, to allow the EPA to determine the severity of the failure 
to meet an applicable standard, and to provide data that may document 
how the source met the general duty to minimize emissions during a 
failure to meet an applicable standard.
    We will no longer require owners or operators to determine whether 
actions taken to correct a malfunction are consistent with an SSM plan, 
because SSM plans would no longer be required. The proposed amendments, 
therefore, eliminate the cross-reference to 40 CFR 63.10(d)(5)(i) that 
contains the description of the previously required SSM report format 
and submittal schedule from this section. These specifications are no 
longer necessary because the events will be reported in otherwise 
required reports with similar format and submittal requirements.
    The proposed amendments eliminate the cross-reference to 40 CFR 
63.10(d)(5)(ii), which requires an

[[Page 1415]]

immediate report for SSM when a source failed to meet an applicable 
standard but did not follow the SSM plan. We will no longer require 
owners and operators to report when actions taken during a startup, 
shutdown, or malfunction were not consistent with an SSM plan, because 
SSM plans would no longer be required.
2. Electronic Reporting
    The EPA is proposing that owners and operators of primary magnesium 
refining facilities submit electronic copies of required performance 
test reports and performance evaluation reports through the EPA's 
Central Data Exchange (CDX) using the Compliance and Emissions Data 
Reporting Interface (CEDRI). A description of the electronic data 
submission process is provided in the memorandum, Electronic Reporting 
Requirements for New Source Performance Standards (NSPS) and National 
Emission Standards for Hazardous Air Pollutants (NESHAP) Rules, 
available in the docket for this action. The proposed rule requires 
that performance test results collected using test methods that are 
supported by the EPA's Electronic Reporting Tool (ERT) as listed on the 
ERT website \21\ at the time of the test be submitted in the format 
generated through the use of the ERT or an electronic file consistent 
with the xml schema on the ERT website, and other performance test 
results be submitted in portable document format (PDF) using the 
attachment module of the ERT.
---------------------------------------------------------------------------

    \21\ https://www.epa.gov/electronic-reporting-air-emissions/electronic-reporting-tool-ert.
---------------------------------------------------------------------------

    Additionally, the EPA has identified two broad circumstances in 
which electronic reporting extensions may be provided. These 
circumstances are (1) outages of the EPA's CDX or CEDRI which preclude 
an owner or operator from accessing the system and submitting required 
reports and (2) force majeure events, which are defined as events that 
will be or have been caused by circumstances beyond the control of the 
affected facility, its contractors, or any entity controlled by the 
affected facility that prevent an owner or operator from complying with 
the requirement to submit a report electronically. Examples of force 
majeure events are acts of nature, acts of war or terrorism, or 
equipment failure or safety hazards beyond the control of the facility. 
The EPA is providing these potential extensions to protect owners and 
operators from noncompliance in cases where they cannot successfully 
submit a report by the reporting deadline for reasons outside of their 
control. In both circumstances, the decision to accept the claim of 
needing additional time to report is within the discretion of the 
Administrator, and reporting should occur as soon as possible.
    The electronic submittal of the reports addressed in this proposed 
rulemaking will increase the usefulness of the data contained in those 
reports, is in keeping with current trends in data availability and 
transparency, will further assist in the protection of public health 
and the environment, will improve compliance by facilitating the 
ability of regulated facilities to demonstrate compliance with 
requirements, and by facilitating the ability of delegated state, 
local, tribal, and territorial air agencies and the EPA to assess and 
determine compliance, and will ultimately reduce burden on regulated 
facilities, delegated air agencies, and the EPA. Electronic reporting 
also eliminates paper-based, manual processes, thereby saving time and 
resources, simplifying data entry, eliminating redundancies, minimizing 
data reporting errors, and providing data quickly and accurately to the 
affected facilities, air agencies, the EPA, and the public. Moreover, 
electronic reporting is consistent with the EPA's plan \22\ to 
implement Executive Order 13563 and is in keeping with the EPA's 
agency-wide policy \23\ developed in response to the White House's 
Digital Government Strategy.\24\ For more information on the benefits 
of electronic reporting, see the memorandum, Electronic Reporting 
Requirements for New Source Performance Standards (NSPS) and National 
Emission Standards for Hazardous Air Pollutants (NESHAP) Rules, 
referenced earlier in this section.
---------------------------------------------------------------------------

    \22\ EPA's Final Plan for Periodic Retrospective Reviews, August 
2011. Available at: https://www.regulations.gov/document?D=EPA-HQ-OA-2011-0156-0154.
    \23\ E-Reporting Policy Statement for EPA Regulations, September 
2013. Available at: https://www.epa.gov/sites/production/files/2016-03/documents/epa-ereporting-policy-statement-2013-09-30.pdf.
    \24\ Digital Government: Building a 21st Century Platform to 
Better Serve the American People, May 2012. Available at: https://obamawhitehouse.archives.gov/sites/default/files/omb/egov/digital-government/digital-government.html.
---------------------------------------------------------------------------

F. What compliance dates are we proposing?

    The EPA is proposing two separate compliance dates for affected 
facilities, based on the different amendments in the rulemaking. For 
the proposed amendments regarding the MACT standard for the CBS, the 
work practice standard for CRB malfunctions, the elimination of SSM 
exemptions, and electronic reporting requirements, we are proposing 
that affected facilities that have constructed or reconstructed on or 
before January 8, 2021, must comply by the effective date of the final 
rule. For the proposed requirement to add pH as an additional control 
device operational parameter, we propose that the affected facilities 
that have constructed or reconstructed on or before January 8, 2021, 
must comply no later than 180 days after the effective date of the 
final rule. For affected facilities that commence construction or 
reconstruction after January 8, 2021, owners or operators must comply 
with all requirements of the subpart, including all the amendments 
being proposed, no later than the effective date of the final rule or 
upon startup, whichever is later.
    Based on our understanding of the facility operations and 
experience with similar industries, we believe that the effective date 
of the final rule is appropriate for the proposed MACT CBS standard, 
CRB work practice standard, elimination of SSM exemptions, and 
electronic reporting requirement. Regarding these new proposed CBS and 
CRB requirements, the facility already routinely performs these 
operations. The CRB work practice for malfunctions require minimal 
additional effort to implement (i.e. shutting down the melt/reactor 
process). Furthermore, it is current facility policy to perform a root 
cause analysis on any CRB malfunction events. The CBS control device 
operational requirements are largely being met during current plant 
operations. Regarding the compliance testing requirements, depending on 
the configuration of the stack, adjustments may need to be made in 
order to perform the required performance tests, such as the 
installation of inlet and outlet sampling ports at the CBS control 
device stack. However, provisions in 40 CFR 63.9911, regarding 
performance tests and initial compliance demonstrations, allow up to 
180 days after the compliance date to conduct such tests, which we 
believe is sufficient time for the facility to demonstrate compliance 
with the proposed CBS standard. The electronic reporting burden is 
minimal as it eliminates paper-based, manual processes, thereby saving 
time and resources as well as simplifying data entry. We do not expect 
that the proposed SSM revisions will require any new control systems 
and very few, if any, operational changes. The primary magnesium 
refining is a continuous operation, with minimal startup and shutdown, 
and control devices operating at all times. Additionally,

[[Page 1416]]

much of the revisions are eliminating additional records and reports 
related to SSM. These changes can be implemented quickly by the owner 
or operator at no cost (and likely some cost savings) and if these 
records are still collected after the final rule is promulgated, the 
facility will still be in compliance with the proposed requirements. 
Therefore, based on the reasoning above, we are proposing that affected 
facilities will need to comply with these amendments by the effective 
date of the final rule. For affected facilities that commence 
construction or reconstruction after January 8, 2021, owners or 
operators must comply with all requirements of the subpart, including 
all the amendments being proposed, no later than the effective date of 
the final rule or upon startup, whichever is later.
    The EPA is also proposing to amend the emission limitations and 
operating parameters set forth in 40 CFR 63.9890(b) to include pH as an 
additional operational parameter for all control devices used to meet 
the acid gas emission limits of this subpart. The facility currently 
monitors and maintains the hourly average pressure drops and liquid 
flow rates for all control devices; however, the additional requirement 
to monitor pH would require the installation and implementation of 
continuous pH monitors. Therefore, in order to provide time for 
implementation, we are proposing that it is necessary to provide 180 
days after the effective date of the final rule for all affected 
facilities that have constructed or reconstructed on or before January 
8, 2021, to comply with the new pH operational parameters. For affected 
facilities that commence construction or reconstruction after January 
8, 2021, we are proposing owners or operators comply with the new pH 
operational parameters by the effective date of the final rule (or upon 
startup, whichever is later).
    We solicit comment on the proposed compliance periods, and we 
specifically request submission of information from sources in this 
source category regarding specific actions that would need to be 
undertaken to comply with the proposed amended requirements and the 
time needed to make the adjustments for compliance with any of the 
revised requirements.

V. Summary of Cost, Environmental, and Economic Impacts

A. What are the affected sources?

    The Primary Magnesium Refining source category comprises one plant, 
US Magnesium, located in Rowley, Utah. US Magnesium was the sole 
facility when the original NESHAP was promulgated in 2011; this has not 
changed since then nor are there new facilities anticipated.

B. What are the air quality impacts?

    We are proposing to establish an emission standard requiring MACT 
level control of chlorine emissions from the CBS that requires the 
facility to operate the associated control device and demonstrate 95 
percent control efficiency of chlorine emissions. Since the facility 
already routinely operates the CBS control device, we expect minimal 
associated emissions reductions. However, this will ensure that the 
emissions remain controlled and minimized moving forward. The proposed 
amendments also include removal of the SSM exemptions and the addition 
of a work practice standard for malfunction events related to the melt/
reactor system. Although we are unable to quantify the emission 
reduction associated with these changes, we expect that emissions will 
be reduced by requiring the facility to meet the applicable standard 
during periods of SSM and that the work practice standard will minimize 
malfunction related emissions.

C. What are the cost impacts?

    The proposed amendments include a work practice standard for 
malfunctions of the CRB and a MACT level chlorine emission standard for 
the CBS. The costs associated with the proposed amendments are expected 
to be minimal. The CRB work practice standard will require labor 
related with the root cause analysis condition. However, it is current 
facility policy to conduct such analyses following a malfunction 
related event; therefore, we expect no additional associated costs to 
comply with the proposed work practice standard. The proposed emission 
standard for the CBS will have costs related to recordkeeping and 
repeat performance testing. The additional inlet and outlet performance 
test is expected to cost an estimated $30,000 every 2.5 years. There 
will likely also be some initial costs to drill and establish inlet and 
outlet ports on the current stack, which currently has no ports. We 
expect no further costs associated with the CBS standard (e.g., add-on 
controls or operation costs) since the facility already has a CBS 
control device and routinely operates it. With regard to the proposed 
electronic reporting requirements, which will eliminate paper-based 
manual processes, we expect a small initial unquantified cost to 
transition to electronic reporting, but that these costs will be off-
set with savings over time such that ultimately there will be an 
unquantified reduction in costs to the affected facility.

D. What are the economic impacts?

    Economic impact analyses focus on changes in market prices and 
output levels that result from compliance costs imposed as a result of 
this action. Because the costs associated with the proposed revisions 
are minimal, no significant economic impacts from the proposed 
amendments are anticipated.

E. What are the benefits?

    Although the EPA does not anticipate any significant reductions in 
HAP emissions as a result of the proposed amendments, we believe that 
the action, if finalized as proposed, would result in some unquantified 
reductions in chlorine emissions--albeit minimal--and improvements to 
the rule and the further protection of public health and the 
environment. Furthermore, pursuant to CAA section 112(d)(2) and (3), by 
establishing a MACT standard for chlorine emissions from the CBS, we 
are ensuring that the associated control device is operational during 
any emission release and meets demonstratable performance criteria. 
Additionally, the proposed amendments requiring electronic submittal of 
initial notifications, performance test results, and semiannual reports 
will increase the usefulness of the data, are in keeping with current 
trends of data availability, will further assist in the protection of 
public health and the environment, and will ultimately result in less 
burden on the regulated community. See section IV.D.3 of this preamble 
for more information.

VI. Request for Comments

    We solicit comments on this proposed action. In addition to general 
comments on this proposed action, we are also interested in additional 
data that may improve the risk assessments and other analyses. We are 
specifically interested in receiving any improvements to the data used 
in the site-specific emissions profiles used for risk modeling. Such 
data should include supporting documentation in sufficient detail to 
allow characterization of the quality and representativeness of the 
data or information. Section VII of this preamble provides more 
information on submitting data.

VII. Submitting Data Corrections

    The site-specific emissions profiles used in the source category 
risk and demographic analyses and instructions are available for 
download on the RTR

[[Page 1417]]

website at https://www.epa.gov/stationary-sources-air-pollution/primary-magnesium-refining-national-emissions-standards-hazardous/. The 
data files include detailed information for each HAP emissions release 
point for the facilities in the source category.
    If you believe that the data are not representative or are 
inaccurate, please identify the data in question, provide your reason 
for concern, and provide any ``improved'' data that you have, if 
available. When you submit data, we request that you provide 
documentation of the basis for the revised values to support your 
suggested changes. To submit comments on the data downloaded from the 
RTR website, complete the following steps:
    1. Within this downloaded file, enter suggested revisions to the 
data fields appropriate for that information.
    2. Fill in the commenter information fields for each suggested 
revision (i.e., commenter name, commenter organization, commenter email 
address, commenter phone number, and revision comments).
    3. Gather documentation for any suggested emissions revisions 
(e.g., performance test reports, material balance calculations).
    4. Send the entire downloaded file with suggested revisions in 
Microsoft[supreg] Access format and all accompanying documentation to 
Docket ID No. EPA-HQ-OAR-2020-0535 (through the method described in the 
ADDRESSES section of this preamble).
    5. If you are providing comments on a single facility or multiple 
facilities, you need only submit one file for all facilities. The file 
should contain all suggested changes for all sources at that facility 
(or facilities). We request that all data revision comments be 
submitted in the form of updated Microsoft[supreg] Excel files that are 
generated by the Microsoft[supreg] Access file. These files are 
provided on the project website at https://www.epa.gov/stationary-sources-air-pollution/primary-magnesium-refining-national-emissions-standards-hazardous/.

VIII. Statutory and Executive Order Reviews

    Additional information about these statutes and Executive Orders 
can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    This action is not a significant regulatory action and was, 
therefore, not submitted to OMB for review.

B. Executive Order 13771: Reducing Regulations and Controlling 
Regulatory Costs

    This action is not expected to be an Executive Order 13771 
regulatory action because this action is not significant under 
Executive Order 12866.

C. Paperwork Reduction Act (PRA)

    The information collection activities in this proposed rule have 
been submitted for approval to OMB under the PRA. The Information 
Collection Request (ICR) document that the EPA prepared has been 
assigned EPA ICR number 2098.09. You can find a copy of the ICR in the 
docket for this rule, and it is briefly summarized here.
    These amendments require electronic reporting; remove the SSM 
exemptions; and impose other revisions that affect reporting and 
recordkeeping for primary magnesium refining facilities. This 
information is collected to assure compliance with 40 CFR part 63, 
subpart TTTTT.
    Respondents/affected entities: Owners and operators of Primary 
Magnesium Refining Facilities.
    Respondent's obligation to respond: Mandatory (40 CFR part 63, 
subpart TTTTT).
    Estimated number of respondents: One.
    Frequency of response: Semiannually.
    Total estimated burden: 625 hours (per year). Burden is defined at 
5 CFR 1320.3(b).
    Total estimated cost: $73,100 annualized capital or operation and 
maintenance costs.
    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collection of information unless it displays a 
currently valid OMB control number. The OMB control numbers for the 
EPA's regulations in 40 CFR are listed in 40 CFR part 9.
    Submit your comments on the Agency's need for this information, the 
accuracy of the provided burden estimates, and any suggested methods 
for minimizing respondent burden to the EPA using the docket identified 
at the beginning of this rule. You may also send your ICR-related 
comments to OMB's Office of Information and Regulatory Affairs via 
email to [email protected], Attention: Desk Officer for the 
EPA. Since OMB is required to make a decision concerning the ICR 
between 30 and 60 days after receipt, OMB must receive comments no 
later than February 8, 2021. The EPA will respond to any ICR-related 
comments in the final rule.

D. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities. Based on the 
Small Business Administration size category for this source category, 
no small entities are subject to this action.

E. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in 
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect 
small governments. The action imposes no enforceable duty on any state, 
local, or tribal governments or the private sector.

F. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the states, on the relationship between 
the national government and the states, or on the distribution of power 
and responsibilities among the various levels of government.

G. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    This action does not have tribal implications as specified in 
Executive Order 13175. No tribal governments own facilities subject to 
this proposed action. Thus, Executive Order 13175 does not apply to 
this action. However, since a magnesium facility is located within 50 
miles of tribal lands, consistent with the EPA Policy on Consultation 
and Coordination with Indian Tribes, we will offer tribal consultation 
for this rulemaking.

H. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

    This action is not subject to Executive Order 13045 because it is 
not economically significant as defined in Executive Order 12866, and 
because the EPA does not believe the environmental health or safety 
risks addressed by this action present a disproportionate risk to 
children. This action's health and risk assessments are contained in 
section IV of this preamble and in the Primary Magnesium Refining Risk 
Report, which is available in the docket.

I. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use

    This action is not subject to Executive Order 13211, because it is 
not a

[[Page 1418]]

significant regulatory action under Executive Order 12866.

J. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR 
Part 51

    This action involves technical standards. Therefore, the EPA 
conducted searches for National Emission Standards for Hazardous Air 
Pollutants: Primary Magnesium Refining Residual Risk and Technology 
Review through the Enhanced NSSN Database managed by the American 
National Standards Institute (ANSI). We also contacted voluntary 
consensus standards (VCS) organizations and accessed and searched their 
databases. Searches were conducted for EPA Methods 1, 2, 2F, 2G, 3, 3A, 
3B, 4, 5, 5D, 23, 26, 26A, of 40 CFR part 60, appendix A, and EPA 
Methods 201 and 201A of 40 CFR part 51, appendix M. No applicable VCS 
were identified for EPA Methods 1, 2, 2F, 2G, 5D, 23, 201 and 201A.
    During the search, if the title or abstract (if provided) of the 
VCS described technical sampling and analytical procedures that are 
similar to the EPA's reference method, the EPA considered it as a 
potential equivalent method. All potential standards were reviewed to 
determine the practicality of the VCS for this rule. This review 
requires significant method validation data which meets the 
requirements of EPA Method 301 for accepting alternative methods or 
scientific, engineering, and policy equivalence to procedures in EPA 
reference methods. The EPA may reconsider determinations of 
impracticality when additional information is available for particular 
VCS.
    Two VCS were identified as an acceptable alternative to EPA test 
methods for the purposes of this rule. The VCS, ANSI/ASME PTC 19-10-
1981 Part 10 (2010), ``Flue and Exhaust Gas Analyses,'' is an 
acceptable alternative to EPA Method 3B manual portion only and not the 
instrumental portion. The VCS, ASTM D6735-01(2009), ``Standard Test 
Method for Measurement of Gaseous Chlorides and Fluorides from Mineral 
Calcining Exhaust Sources Impinger Method,'' is an acceptable 
alternative to EPA Method 26 and 26A. The search identified 18 VCS that 
were potentially applicable for these rules in lieu of EPA reference 
methods. After reviewing the available standards, the EPA determined 
that 18 candidate VCS (ASTM D3154-00 (2014), ASTM D3464-96 (2014), ASTM 
3796-09 (2016), ISO 10780:1994 (2016), ASME B133.9-1994 (2001), ISO 
10396:(2007), ISO 12039:2001(2012), ASTM D5835-95 (2013), ASTM D6522-
11, CAN/CSA Z223.2-M86 (R1999), ISO 9096:1992 (2003), ANSI/ASME PTC-38-
1980 (1985), ASTM D3685/D3685M-98-13, CAN/CSA Z223.1-M1977, ISO 
10397:1993, ASTM D6331 (2014), EN 1948-3 (1996), EN 1911:2010) 
identified for measuring emissions of pollutants or their surrogates 
subject to emission standards in the rule would not be practical due to 
lack of equivalency, documentation, validation data, and other 
important technical and policy considerations. Additional information 
for the VCS search and determinations can be found in the memorandum, 
Voluntary Consensus Standard Results for National Emission Standards 
for Hazardous Air Pollutants: Primary Magnesium Refining Residual Risk 
and Technology Review, which is available in the docket for this 
action. Under 40 CFR 63.7(f) and 40 CFR 63.8(f) of subpart A of the 
General Provisions, a source may apply to the EPA to use alternative 
test methods or alternative monitoring requirements in place of any 
required testing methods, performance specifications, or procedures in 
the final rule or any amendments.
    The EPA welcomes comments on this aspect of the proposed rulemaking 
and, specifically, invites the public to identify potentially 
applicable VCS and to explain why such standards should be used in this 
regulation.

K. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    The EPA believes that this action does not have disproportionately 
high and adverse human health or environmental effects on minority 
populations, low-income populations, and/or indigenous peoples, as 
specified in Executive Order 12898 (59 FR 7629, February 16, 1994). 
This action's health and risk assessments are contained in section IV 
of this preamble. The documentation for this decision is contained in 
section IV.A.1 of this preamble and in the Primary Magnesium Refining 
Risk Report, which is available in Docket ID No. EPA-HQ-OAR-2020-0535.

List of Subjects in 40 CFR Part 63

    Environmental protection, Air pollution control, Hazardous 
substances, Incorporation by reference, Reporting and recordkeeping 
requirements.

Andrew Wheeler,
Administrator.
[FR Doc. 2021-00176 Filed 1-7-21; 8:45 am]
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