[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]
-----------------------------------------------------------------------
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.
-----------------------------------------------------------------------
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\
---------------------------------------------------------------------------
\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.
---------------------------------------------------------------------------
\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).
---------------------------------------------------------------------------
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.
---------------------------------------------------------------------------
\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.
---------------------------------------------------------------------------
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]
BILLING CODE 6560-50-P