Document ID: EPA-HQ-OAR-2020-0560-0001
Agency: epa
Document Type: Proposed Rule
Title: National Emission Standards for Hazardous Air Pollutants: Mercury Cell Chlor-Alkali Plants Residual Risk and Technology Review
Posted Date: 2021-01-08T05:00Z

[Federal Register Volume 86, Number 5 (Friday, January 8, 2021)]
[Proposed Rules]
[Pages 1362-1390]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-00174]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2020-0560; FRL-10018-95-OAR]
RIN 2060-AU59

National Emission Standards for Hazardous Air Pollutants: Mercury 
Cell Chlor-Alkali Plants Residual Risk and Technology Review

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing 
the results of the residual risk and technology review (RTR) of the 
National Emission Standards for Hazardous Air Pollutants (NESHAP) for 
mercury emissions from Mercury Cell Chlor-Alkali Plants, as required by 
the Clean Air Act (CAA). The EPA is proposing to find risks due to 
emissions of hazardous air pollutants (HAP) to be acceptable from the 
Mercury Cell Chlor-Alkali Plants source category, and to determine that 
the current NESHAP provides an ample margin of safety to protect public 
health and that no more stringent standards are necessary to prevent, 
taking into consideration costs, energy, safety, and other relevant 
factors, an adverse environmental effect. The EPA is proposing to amend 
the requirements for cell room fugitive mercury emissions to require 
work practice standards for the cell rooms and to require instrumental 
monitoring of cell room fugitive mercury emissions under the technology 
review. Furthermore, under our technology review and maximum achievable 
control technology (MACT) analysis, we are proposing to not require 
conversion to non-mercury production technology and invite comments and 
data and information regarding this proposed determination. In 
addition, the EPA is proposing standards for fugitive chlorine 
emissions from mercury cell chlor-alkali plants, which are not 
currently regulated under the NESHAP. The EPA is proposing to address 
applicability for thermal mercury recovery units when chlorine and 
caustic are no longer produced in mercury cells. The EPA is also 
proposing revisions related to emissions during periods of startup, 
shutdown, and malfunction (SSM); provisions for electronic submission 
of performance test results, performance evaluation reports, and 
Notification of Compliance Status (NOCS) reports; and correction of 
various compliance errors in the current rule.

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-2020-0560, by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/ 
(our preferred method). Follow the online instructions for submitting 
comments.
     Email: a-and-r-docket@epa.gov. Include Docket ID No. EPA-
HQ-OAR-2020-0560 in the subject line of the message.
     Fax: (202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-
2020-0560.
     Mail: U.S. Environmental Protection Agency, EPA Docket 
Center, Docket ID No. EPA-HQ-OAR-2020-0560, Mail Code 28221T, 1200 
Pennsylvania Avenue NW, Washington, DC 20460.
     Hand Delivery or Courier (by scheduled appointment only): 
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

[[Page 1363]]

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 Phil Mulrine, Sector Policies and Programs Division 
(D243-02), Office of Air Quality Planning and Standards, U.S. 
Environmental Protection Agency, Research Triangle Park, North Carolina 
27711; telephone number: (919) 541-5289; fax number: (919) 541-4991; 
and email address: mulrine.phil@epa.gov. For specific information 
regarding the risk modeling methodology, contact James 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: hirtz.james@epa.gov.

SUPPLEMENTARY INFORMATION: 
    Participation in virtual public hearing. Please note that the EPA 
is deviating from its typical approach because the President has 
declared a national emergency. Due to the current Centers for Disease 
Control and Prevention (CDC) recommendations, as well as state and 
local orders for social distancing to limit the spread of COVID-19, the 
EPA cannot hold in-person public meetings at this time.
    To request a virtual public hearing, contact (888) 372-8699 or by 
email at SPPDpublichearing@epa.gov. 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 on the virtual public hearing at https://www.epa.gov//stationary-sources-air-pollution/mercury-cell-chloralkali-plants-national-emissions-standards.
    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/mercury-cell-chloralkali-plants-national-emissions-standards or contact the public hearing team at (888) 372-
8699 or by email at SPPDpublichearing@epa.gov. 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/mercury-cell-chloralkali-plants-national-emissions-standards.
    The EPA will make every effort to follow the schedule as closely as 
possible on the day of the hearing; however, please plan for the 
hearings to run either ahead of schedule or behind schedule.
    Each commenter will have 5 minutes to provide oral testimony. The 
EPA encourages commenters to provide the EPA with a copy of their oral 
testimony electronically (via email) by emailing it to Phil Mulrine at 
mulrine.phil@epa.gov. 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 is 
posted online at https://www.epa.gov/stationary-sources-air-pollution/mercury-cell-chloralkali-plants-national-emissions-standards. While the 
EPA expects the hearing to go forward as set forth above, please 
monitor our website or contact the public hearing team at (888) 372-
8699 or by email at SPPDpublichearing@epa.gov to determine if there are 
any updates. The EPA does not intend to publish a document in the 
Federal Register announcing updates.
    If you require the services of a translator or a special 
accommodation such as audio description, please pre-register for the 
hearing with the public hearing team and describe your needs by 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-2020-0560. In addition to this docket 
established for this rulemaking, relevant information can be found in 
dockets for previous rulemakings; EPA-HQ-OAR-2002-0016 and EPA HQ-OAR-
2002-0017. 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-
2020-0560. 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 
statue. 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

[[Page 1364]]

and included as part of the comment that is placed in the public docket 
and made available on the internet. If you submit an electronic 
comment, the EPA recommends that you include your name and other 
contact information in the body of your comment and with any digital 
storage media you submit. If the EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, the 
EPA may not be able to consider your comment. Electronic files should 
not include special characters or any form of encryption and be free of 
any defects or viruses. For additional information about the EPA's 
public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    The EPA is temporarily suspending its Docket Center and Reading 
Room for public visitors, with limited exceptions, to reduce the risk 
of transmitting COVID-19. Our Docket Center staff will continue to 
provide remote customer service via email, phone, and webform. We 
encourage the public to submit comments via https://www.regulations.gov/ as there may be a delay in processing mail and 
faxes. Hand deliveries or couriers will be received by scheduled 
appointment only. For further information and updates on EPA Docket 
Center services, please visit us online at https://www.epa.gov/dockets.
    The EPA continues to carefully and continuously monitor information 
from the CDC, local area health departments, and our Federal partners 
so that we can respond rapidly as conditions change regarding COVID-19.
    Submitting CBI. Do not submit information containing CBI to the EPA 
through https://www.regulations.gov/ or email. Clearly mark the part or 
all of the information that you claim to be CBI. For CBI information on 
any digital storage media that you mail to the EPA, mark the outside of 
the digital storage media as CBI and then identify electronically 
within the digital storage media the specific information that is 
claimed as CBI. In addition to one complete version of the comments 
that includes information claimed as CBI, you must submit a copy of the 
comments that does not contain the information claimed as CBI directly 
to the public docket through the procedures outlined in Instructions 
above. If you submit any digital storage media that does not contain 
CBI, mark the outside of the digital storage media clearly that it does 
not contain CBI. Information not marked as CBI will be included in the 
public docket and the EPA's electronic public docket without prior 
notice. Information marked as CBI will not be disclosed except in 
accordance with procedures set forth in 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-2020-0560. 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 two
AERMOD air dispersion model used by the HEM-3 model
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CFR Code of Federal Regulations
ECHO EPA's Enforcement and Compliance History Online database
EPA Environmental Protection Agency
ERPG emergency response planning guidelines
ERT Electronic Reporting Tool
GACT generally available control technology
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
ICR Information Collection Request
IRIS EPA's Integrated Risk Information System
km kilometer
MACT maximum achievable control technology
MIR maximum individual risk
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NEI National Emissions Inventory
NESHAP national emission standards for hazardous air pollutants
NOAEL No Observed Adverse Effect Level
NOCS Notification of Compliance Status report
NRDC Natural Resources Defense Council
NSPS new source performance standards
OMB Office of Management and Budget
OSHA Occupational Safety and Health Administration
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PDF portable document format
PM particulate matter
POM polycyclic organic matter
ppm parts per million
PRA Paperwork Reduction Act
REL reference exposure level
RfC reference concentration
RTR residual risk and technology review
SAB Science Advisory Board
SSM startup, shutdown, and malfunction
SV screening value
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
URE unit risk estimate
USGS U.S. Geological Survey

    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 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

[[Page 1365]]

    C. Paperwork Reduction Act (PRA)
    D. Regulatory Flexibility Act (RFA)
    E. Unfunded Mandates Reform Act (UMRA)
    F. Executive Order 13132: Federalism
    G. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    H. Executive Order 13045: Protection of Children From 
Environmental Health Risks and Safety Risks
    I. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    J. National Technology Transfer and Advancement Act (NTTAA)
    K. 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 Mercury 
Cell Chlor-Alkali Plants regulated under 40 CFR part 63, subpart IIIII. 
The North American Industry Classification System (NAICS) code for the 
chlor-alkali industry is 325180. 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.
    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 EPA 
listed the Chlorine Production source category. Subsequently, on 
December 19, 2003, the EPA divided the Chlorine Production source 
category into two subcategories because of the differences in the 
production methods and the HAP emitted. These subcategories are: (1) 
Mercury cell chlor-alkali plants; and (2) chlorine production plants 
that do not rely upon mercury cells for chlorine production (e.g., 
diaphragm cell chlor-alkali plants, membrane cell chlor-alkali plants, 
etc.). The EPA issued separate final actions in December 2003 to 
address emissions of mercury from the mercury cell chlor-alkali plant 
subcategory sources (68 FR 70904) and deleted the non-mercury cell 
subcategory (68 FR 70948). This action addresses the Mercury Cell 
Chlor-Alkali Plant source category, where a mercury cell chlor-alkali 
plant is any facility where mercury cells are used to manufacture 
product chlorine, product caustic, and by-product hydrogen and where 
mercury may be recovered from wastes.

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/mercury-cell-chloralkali-plants-national-emissions-standards. Following publication 
in the Federal Register, the EPA will post the Federal Register version 
of the proposal and key technical documents at this same website. 
Information on the overall RTR program is available at https://www3.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 IIIII, available in the docket for this action 
(Docket ID No. EPA-HQ-OAR-2020-0560). 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/mercury-cell-chloralkali-plants-national-emissions-standards.

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 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 
reqruirements. 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 defined in CAA section 112(a)(1) as 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 (not including motor vehicles or nonroad vehicles) are ``area 
sources,'' as defined in CAA section 112(a)(2). 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

[[Page 1366]]

promulgation of additional standards is needed to provide an ample 
margin of safety to protect public health or to prevent an adverse 
environmental effect. Section 112(d)(5) of the CAA provides that this 
residual risk review is not required for categories of area sources 
subject to GACT standards. Section 112(f)(2)(B) of the CAA further 
expressly preserves the EPA's use of the two-step approach for 
developing standards to address any residual risk and the Agency's 
interpretation of ``ample margin of safety'' developed in the National 
Emissions Standards for Hazardous Air Pollutants: Benzene Emissions 
from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene 
Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery 
Plants (Benzene NESHAP) (54 FR 38044, September 14, 1989). The EPA 
notified Congress in the Residual Risk Report that the Agency intended 
to use the Benzene NESHAP approach in making CAA section 112(f) 
residual risk determinations (EPA-453/R-99-001, p. ES-11). The EPA 
subsequently adopted this approach in its residual risk determinations 
and the United States Court of Appeals for the District of Columbia 
Circuit upheld the EPA's interpretation that CAA section 112(f)(2) 
incorporates the approach established in the Benzene NESHAP. See NRDC 
v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008).
    The approach incorporated into the CAA and used by the EPA to 
evaluate residual risk and to develop standards under CAA section 
112(f)(2) is a two-step approach. In the first step, the EPA determines 
whether risks are acceptable. This determination ``considers all health 
information, including risk estimation uncertainty, and includes a 
presumptive limit on maximum individual lifetime [cancer] risk (MIR) 
\1\ of approximately 1- in-10 thousand.'' (54 FR 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, 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'' as 
defined in CAA section 112(a)(7).
---------------------------------------------------------------------------

    \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 HAP 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 HAP emissions?

    The Chlorine Production source category was initially listed as a 
category of major sources of HAP pursuant to section 112(c)(1) of the 
CAA on July 16, 1992 (57 FR 31576). At the time of the initial listing, 
the EPA defined the Chlorine Production source category as follows:

    The Chlorine Production Source Category includes any facility 
engaged in the production of chlorine. The category includes, but is 
not limited to, facilities producing chlorine by the following 
production methods: Diaphragm cell, mercury cell, membrane cell, 
hybrid fuel cell, Downs cell, potash manufacture, hydrochloric acid 
decomposition, nitrosyl chloride process, nitric acid/salt process, 
Kel-Chlor process, and sodium chloride/sulfuric acid process.\2\
---------------------------------------------------------------------------

    \2\ Documentation for Developing the Initial Source Category 
List. U.S. Environmental Protection Agency. EPA-450/3-91-030. July 
1992. p. A-67. Available at: https://www3.epa.gov/ttn/atw/socatlst/socatpg.html.

    Based on the differences in the production methods and the HAP 
emitted, the EPA decided to divide the Chlorine Production source 
category into two subcategories: (1) Mercury cell chlor-alkali plants; 
and (2) chlorine production plants that do not rely upon mercury cells 
for chlorine production (diaphragm cell chlor-alkali plants, membrane 
cell chlor-alkali plants, etc.). On July 3, 2002, the EPA issued 
separate proposals to address emissions of mercury from the mercury 
cell chlor-alkali plant subcategory sources (67 FR 44672) and emissions 
of chlorine and hydrochloric acid (HCl) from both subcategories (67 FR 
44713). Separate final actions were taken on both proposals on December 
19, 2003. As part of these separate final actions, the EPA deleted the 
non-mercury cell subcategory under the authority of CAA section 
112(c)(9)(B)(ii) of the CAA (68 FR 70948).
    The final rule for the Mercury Cell Chlor-Alkali Plants subcategory 
(68 FR 70904, December 19, 2003, codified at 40 CFR part 63 subpart 
IIIII), which covers both major and area sources, included standards 
for mercury emissions from two types of affected sources at plant sites 
where chlorine and caustic are produced in mercury cells: Mercury cell 
chlor-alkali production facilty affected sources and mercury recovery 
facility affected sources. The rule prohibits mercury emissions from 
new and reconstructed mercury cell chlor-alkali production facilities. 
40 CFR 63.8190(a)(1). For existing mercury cell chlor-alkali production 
facilities, the standards include emission limitations for mercury 
emissions from process vents (including emissions from end-box 
ventilation systems and hydrogen systems) and work practices for 
fugitive mercury emissions from the cell room. 40 CFR 8190(a)(2), 
8192(a) through (f). For new, reconstructed, and existing mercury 
recovery facilities, the NESHAP includes emission limitations for 
mercury emissions from oven type thermal recovery unit vents and non-
oven type thermal recovery unit vents. 40 CFR 63.8190(a)(3). The rule 
did not include standards for chlorine or HCl, citing the authority of 
section 112(d)(4) of the CAA (68 FR 70906). In its 2003 action (68 FR 
70904), the EPA promulgated the initial Mercury Cell Chlor-Alkali 
Plants NESHAP pursuant to CAA section 112(d)(2) and added the source 
category to the EPA's Source Category List under CAA sections 
112(c)(1), as well as under (c)(3) and (k)(3)(B) and (c)(6), in each 
case because of the mercury emissions.

[[Page 1367]]

    Following promulgation of the 2003 Mercury Cell Chlor-Alkali Plants 
NESHAP, the EPA received a petition to reconsider several aspects of 
the rule from the Natural Resources Defense Council (NRDC). NRDC also 
filed a petition for judicial review of the rule in the U.S. Court of 
Appeals for the District of Columbia Circuit. In a letter dated April 
8, 2004, the EPA granted NRDC's petition for reconsideration and on 
July 20, 2004, the court placed the petition for judicial review in 
abeyance pending the EPA's action on reconsideration. The EPA issued 
proposals on June 11, 2008 (73 FR 33258), and on March 14, 2011 (76 FR 
13852), to respond to the reconsideration petition. We discuss the 
reconsideration and the 2008 and 2011 proposals further in section 
IV.A.2 of this preamble.
    The use of mercury cell technology has been declining for decades 
due to conversions to non-mercury processes and closures. For example, 
in 1993, there were about 13 facilities in the U.S., and when we 
initiated the development of this RTR proposed rule in early 2020, 
there were two facilities operating. Since that time, one facility 
(Ashta Chemicals in Ohio) ceased operating the mercury cell process.\3\ 
So, now only one mercury cell chlor-alkali plant remains in operation. 
The one remaining mercury cell chlor-alkali facility is owned by 
Westlake Chemical (operated by Eagle Natrium, LLC) and is located in 
Marshall County, West Virginia. This is a large integrated chemical 
production facility whose products include chlorine and caustic from 
their chlor-alkali processes. In addition to the mercury cell process, 
chlorine and caustic are also produced in diagraghm cells at the site.
---------------------------------------------------------------------------

    \3\ Ashta Chemicals in Ashtabula, Ohio, has stopped operating 
the mercury cell process, and is on schedule to complete the 
conversion to membrane cells by end of 2020. Source: Personal 
communication, phone conversation: Between Brittany Johnson, 
Environmental Manager, Ashta Chemicals and Phil Norwood, SC&A, 
Contractor for U.S. EPA, December 4, 2020.
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C. What data collection activities were conducted to support this 
action?

    Data sources used for this effort include the 2017 National 
Emissions Inventory (NEI), title V permit information, conversations 
with the West Virginia Department of Environmental Protection, and 
conversations with facility representatives. The NEI data were 
examined, and the processes and related emission sources associated 
with the mercury cell chlor-alkali plant were identified. In addition, 
information from data collection efforts from previous regulatory 
efforts for the source category were consulted, including studies that 
were conducted for the 2002 proposals, the 2003 final actions, and the 
2008 and 2011 proposals cited above.

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

    There are other sources that are often used by the EPA in obtaining 
information for RTRs. Examples include the EPA's Enforcement and 
Compliance History Online (ECHO) database, the Reasonably Available 
Control Technology/Best Available Control Technology/Lowest Achievable 
Emission Rate Clearinghouse, and NESHAP for similar industries. 
However, these sources were not utilized for the review for the Mercury 
Cell Chlor-Alkali Plants NESHAP because (1) the mercury cell processes 
are primarily sources of fugitive emissions and are unique such that 
control measures and work practices from other industries would not be 
applicable, and (2) since there is only one operating facility, it was 
more practical to focus on the specifics of that single facility.

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 at 
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.\4\ 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 
the EPA's response to comments on our policy under the Benzene NESHAP:
---------------------------------------------------------------------------

    \4\ 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 at 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,

[[Page 1368]]

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 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.'' \5\
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    \5\ 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 to consider. 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

[[Page 1369]]

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 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 Mercury Cell Chlor-Alkali Plant 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; \6\ and described in the 
SAB review report issued in 2010. They are also consistent with the key 
recommendations contained in that report.
---------------------------------------------------------------------------

    \6\ 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://www3.epa.gov/airtoxics/rrisk/rtrpg.html.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions 
release characteristics?
    The HAP emissions from the single mercury cell chlor-alkali plant 
includes mercury and chlorine. Hydrochloric acid historically had been 
associated with these facilities, but based on recent reviews of 
available information and discussions with Westlake Chemical, we 
conclude that any HCl emissions from the remaining operating facility 
in West Virginia are due to non-source category emissions sources such 
as HCl production operations (i.e., they are not emitted by an affected 
source subject to the standards applicable to mercury cell chlor-alkali 
plants). The mercury emissions are emitted from several emission 
sources within the mercury cell chlor-alkali facility affected source 
at the one operating mercury cell chlor-alkali plant, which, for the 
purposes of the source category risk assessment, have been categorized 
into two general emission process groups: (1) Process vents and (2) 
fugitives from the mercury cell room building. Based on available data, 
we conclude the chlorine emissions are mostly or entirely emitted as 
fugitive emissions associated with the cell room or from pipes or other 
equipment used to pump the product chlorine to the chlorine storage 
units or other associated equipment in the mercury cell chlor-alkali 
facility affected source. The main source of emissions data used in our 
analyses was the NEI data submitted for calendar year 2017. Data on the 
numbers, types, dimensions, and locations of the emission points and 
non-point sources for each facility were obtained from the NEI and 
Google Earth\TM\. A description of the data, approach, and rationale 
used to develop actual HAP emissions estimates is discussed in more 
detail in the document, Development of the Residual Risk Review 
Emissions Dataset for the Mercury Cell Chlor-Alkali Plants Source 
Category, which is available in the docket (Docket ID No. EPA-HQ-OAR-
2020-0560).
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 through 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)
    For the Mercury Cell Chlor-Alkali Plants source category, the EPA 
assumed actual emissions are equal to allowable emissions. Allowable 
emissions are the estimated emissions that would occur under normal 
full-capacity operating conditions and as allowed under the applicable 
MACT standards. There is no available data that suggests the facility 
is operating at less than full capacity. There is also no evidence that 
the facility is controlling point source emissions to a degree greater 
than the emission limitations or that they are performing practices in 
excess of the required work practices for the control of fugitive 
emissions. This means that they are not reducing emissions beyond the 
levels required by the MACT standards which would result in actual 
emissions being less than allowable emissions. In addition, a review of 
ECHO indicates no enforcement actions for violations of the title V 
operating limits over the last 5 years, which would result in actual 
emissions being greater than allowable. Therefore, we are comfortable 
with the assumption that actual emissions are equal to the allowable 
emissions.
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).\7\ 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.
---------------------------------------------------------------------------

    \7\ 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.\8\ 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 \9\ 
internal point locations and

[[Page 1370]]

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.
---------------------------------------------------------------------------

    \8\ 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).
    \9\ 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 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 \10\ 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.
---------------------------------------------------------------------------

    \10\ 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.
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    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,\11\ 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 the Mercury Cell Chlor-
Alkali Plant Source Category in Support of the 2020 Risk and Technology 
Review Proposed Rule, and in Appendix 5 of the report:

[[Page 1371]]

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.
---------------------------------------------------------------------------

    \11\ See, e.g., U.S. EPA. Screening Methodologies to Support 
Risk and Technology Reviews (RTR): A Case Study Analysis (Draft 
Report, May 2017. https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html).
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    To assess the potential acute risk to the maximally exposed 
individual, we use the peak hourly emission rate for each emission 
point,\12\ 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 and that a person is 
present at the point of maximum exposure.
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    \12\ 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 
Mercury Cell Chlor-alkali Plants 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.'' \13\ 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.\14\ 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.
---------------------------------------------------------------------------

    \13\ 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.
    \14\ 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.'' \15\ 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.
---------------------------------------------------------------------------

    \15\ 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, we used a default acute emissions 
multiplier of 10 as we have no information to suggest another factor to 
account for variability in hourly emissions data is more appropriate.
    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 estimating the highest HQ that might occur outside 
facility boundaries with the use of satellite imagery of the facility 
with receptor locations. These refinements are discussed more fully in 
the Residual Risk Assessment for the Mercury Cell Chlor-Alkali Plant 
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 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 Mercury Cell Chlor-Alkali Plant source category, mercury 
emissions were the only PB-HAP emitted by the source category, so we

[[Page 1372]]

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 (SV).''
    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 SV 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 \16\) and 
locally grown or raised foods (90th percentile consumption of locally 
grown or raised foods for the farmer and gardener scenarios \17\). If 
PB-HAP emission rates do not result in a Tier 2 SV 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.
---------------------------------------------------------------------------

    \16\ Burger, J. 2002. Daily consumption of wild fish and game: 
Exposures of high end recreationists. International Journal of 
Environmental Health Research, 12:343-354.
    \17\ 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.
    For further information on the multipathway assessment approach, 
see the Residual Risk Assessment for the Mercury Cell Chlor-Alkali 
Plant Source Category in Support of the Risk and Technology Review 2020 
Proposed Rule, which is available in the docket for this action.
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-

[[Page 1373]]

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, and no-observed-adverse-effect 
level. 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 Mercury Cell Chlor-Alkali Plant 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 Mercury Cell Chlor-Alkali 
Plant source category emitted any of the environmental HAP. For the 
Mercury Cell Chlor-Alkali Plant source category, we identified 
emissions of mercury and HCl. 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 National Ambient Air Quality Standards (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.''
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 SV 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 Mercury Cell Chlor-Alkali Plant 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

[[Page 1374]]

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 2014 NEI. The source category records 
of that NEI dataset were removed, evaluated, and updated as described 
in section II.C of this preamble. 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 Mercury Cell Chlor-Alkali Plant 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.
    For this source category, we conducted the facility-wide assessment 
using a dataset that the EPA compiled from the 2017 NEI. We used the 
NEI data for the facility and did not adjust any category or ``non-
category'' data. Therefore, there could be differences in the dataset 
from that used for the source category assessments described in this 
preamble. We analyzed 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, we 
made a reasonable attempt to identify the source category risks, and 
these risks were compared to the facility-wide risks to determine the 
portion of 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 Mercury Cell 
Chlor-Alkali Plant 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 
Mercury Cell Chlor-Alkali Plant 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 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

[[Page 1375]]

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, pages 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.\18\ 
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.\19\ 
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,\20\ 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.
---------------------------------------------------------------------------

    \18\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \19\ 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.
    \20\ 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.
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    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.
    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 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.\21\
---------------------------------------------------------------------------

    \21\ 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.

---------------------------------------------------------------------------

[[Page 1376]]

    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)?

1. MACT standards for Chlorine Emissions
    In addition to mercury, based on the NEI, the Westlake, West 
Virginia, mercury cell chlor-alkali facility emits an estimated 0.24 
tpy fugitive emissions of chlorine from the mercury cell chlor-alkali 
production facility affected source. Chlorine is not emitted from 
mercury thermal recovery units and furthermore, the facility does not 
have a mercury thermal recovery unit at the site. In the 2003 final 
rule, the EPA made the decision not to regulate chlorine and HCl in the 
Mercury Cell Chlor-Alkali Plant NESHAP based on the authority under 
section 112(d)(4) of the CAA. Specifically, the EPA based this decision 
on the ``determination that no further control is necessary because 
chlorine and HCl are ``health threshold pollutants,'' and chlorine and 
HCl levels emitted from chlorine production processes are below their 
threshold values within an ample margin of safety.'' (68 FR 70906, 
December 19, 2003).
    However, the EPA has determined that it must now propose standards 
for all HAP emissions from the source category, including emissions of 
chlorine, pursuant to CAA section 112(d)(2) and (3).\22\ As discussed 
in section III.C.1 above, while there are HCl emissions from the direct 
synthesis HCl production units at the Westlake, West Virginia, 
facility, they are not from processes that are part of the mercury cell 
chlor-alkali plant. Therefore, no emission limitations or work 
practices are being proposed for HCl since the emissions are not from 
parts of the site that are within the mercury cell chlor-alkali plant. 
As a result, we are only required to propose standards for chlorine 
emissions pursuant to CAA section 112(d)(2) and (3).
---------------------------------------------------------------------------

    \22\ The EPA not only has authority under CAA section 112(d)(2) 
and (3) to set MACT standards for previously unregulated HAP 
emissions at any time, but is required to address any previously 
unregulated HAP emissions as part of its periodic review of MACT 
standards under CAA section 112(d)(6). LEAN v. EPA, 955 F.3d at 
1091-1099.
---------------------------------------------------------------------------

    Fugitive chlorine emissions occur from equipment leaks in the cell 
room and throughout the other parts of the mercury cell chlor-alkali 
production facility affected source that handle and process the 
chlorine gas produced. As stated previously, mercury recovery units are 
not sources of chlorine emissions.

[[Page 1377]]

    Section 112 of the CAA generally directs that standards be 
specified as numerical emission standards, if possible. However, if it 
is determined that it is not feasible to prescribe or enforce a 
numerical emission standard, CAA section 112(h) indicates that a 
design, equipment, work practice, or operational standard may be 
specified, provided the criteria of CAA section 112(h)(2) are met. 
Those criteria define ``not feasible to prescribe or enforce an 
emission standard'' to mean any situation in which the EPA determines 
that: (1) A HAP 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 (2) the application of 
measurement methodology to a particular class of sources is not 
practicable due to technological and economic reasons. Most fugitive 
chlorine emission sources at mercury cell chlor-alkali plants are 
associated with cell rooms. Potential fugitive chlorine emissions are 
also located in the chlorine processing area. For both the cell room 
and the chlorine processing area, the fugitive chlorine emissions are 
primarily due to equipment leaks. Due to the nature of equipment leaks 
(i.e., low flow rate, occurring from individual pieces of equipment, 
high variability in time, and location of occurrence) it is 
technologically and economically impractical to collect the emissions 
and route them to a control device. As such, we believe that it is not 
feasible to either prescribe or enforce numerical emission limit(s) for 
fugitive chlorine emissions from cell rooms or any other location at 
the facility, under both of the criteria set forth in CAA section 
112(h)(2)(A) and (B). Consequently, these proposed standards address 
fugitive chlorine emission sources at existing mercury cell chlor-
alkali production facility affected sources through the establishment 
of work practice standards. As the NESHAP already effectively prohibits 
the construction or reconstruction of a mercury cell chlor-alkali 
production facility, there is no need to establish a new source MACT 
floor for fugitive chlorine emissions.
    There are many incentives for the identification and correction of 
chlorine leaks and to reduce fugitive chlorine emissions throughout the 
mecury cell chlor-alkali plant. First, chlorine is a primary product of 
the process, so lost chlorine equals lost product and lost profit. 
Second, chlorine, particularly ``wet'' chlorine, is very corrosive to 
process equipment. Therefore, prompt repair of chlorine leaks reduces 
damange to process equipment. These corrosive properties also mean that 
small leaks can quickly become large leaks, which could result in 
chlorine releases that are dangerous to plant workers and the 
surrounding community. For these reasons, the Westlake, West Virginia, 
facility has a program in place to identify and repair fugitive 
chlorine leaks across the plant. Specifically, Westlake operators 
perform inspections during each shift to identify leaks of chlorine. 
Therefore, leaks are detected and corrective actions implemented to 
minimize and reduce any fugitive chlorine emissions. Based on available 
information, we understand that the method Westlake uses to identify 
leaks of chlorine from each piece of equipment is olfactory 
observations of chlorine gas. If leaks are detected using the olfactory 
method, the facility takes immediate actions to fix the identified 
leaks. Furthermore, Westlake has chlorine sensors installed and 
operated throughout the relevant process units. If one of these sensors 
measures a chlorine concentration of 2 parts per million by volume 
(ppmv) or greater, the facility takes action to identify and fix leaks. 
Since there is only one currently operating mercury cell chlor-alkali 
plant in the country, the MACT floor for existing sources is 
represented by the practices in place at the Westlake facility to 
reduce chlorine fugitive emissions.
    As noted above, it is technologically and economically impractical 
to collect the emissions from every potential leak source at a facility 
and route them to a control device. The cell room building is generally 
under negative pressure and the air is routed through the roof vents. 
As a beyond-the-floor option for fugitive chlorine emissions, we 
considered requiring the air from the roof vents to be routed to a 
scrubber or other control device. However, the volume of the air flow 
from the Westlake cell room is over 700 million cubic feet per day, or 
almost 500,000 cubic feet per minute. It would be technically 
infeasible for any control device to handle this volume of gas 
throughput. Therefore, we rejected this beyond-the-floor option.
    Therefore, we are proposing the MACT floor level of control which 
represents the procedures in place at the Westlake, West Virginia, 
site. We developed the work practices in the proposed amendments to 
reflect these procedures, along with associated recordkeeping and 
reporting requirements to demonstrate compliance. Specifically, we are 
proposing that facilities must identify and inspect each piece of 
equipment that contains chlorine gas with a concentration of at least 5 
percent chlorine by volume throughout the mercury cell chlor-alkali 
production facility affected source for leaks at least once each 12 
hours. We are requesting comment on whether the 5 percent by volume 
threshold for defining equipment that must be inspected for chlorine 
leaks is the appropriate threshold for identifying equipment with the 
potential to generate fugitive emissions of chlorine gas. Equipment 
that is under negative pressure would be excluded from this 
requirement. The method that we are proposing to identify leaks of 
chlorine from each piece of equipment is olfactory observations of 
chlorine gas. However, we solicit comments regarding other methods 
(e.g., auditory or visual) that should also be allowed as a method to 
identify leaks.
    When a leak is detected, we are proposing that a first attempt at 
repair be conducted within 1 hour of detection and that the leak be 
repaired within 1 day of detection. We are proposing that a leak is 
repaired when the evidence of the olfactory observation is eliminated.
    Additionally, we are proposing that chlorine sensors be installed 
and operated continuously (at least one measure every 15 minutes) 
throughout the affected source. Each time one of these sensors measures 
a chlorine concentration of 2 ppmv or greater, the proposed rule would 
require a complete inspection for leaks of all equipment containing 5 
percent chlorine by volume within 1 hour of detection. The chlorine 
sensors that the facility uses must have a detection limit of 2 ppm or 
less. Furthermore, we propose the sensor must be calibrated and 
maintained following the manufacturer's recommendations.
    We are requesting comment on several aspects of the proposed 
requirements related to the use of chlorine sensors to identify leaks 
that may occur between the 12-hour regular inspections. First, we are 
requesting comment on where these ambient sensors should be located to 
ensure that chlorine emissions are detected by the ambient monitors. 
The proposed rule requires that they be placed throughout the mercury 
cell chlor-alkali manufacturing facility affected source, which 
includes ``all cell rooms and ancillary operations used in the 
manufacture of product chlorine, product caustic, and by-product 
hydrogen.'' We are requesting comment whether the rule should specify 
areas of the facility where sensors should be located and whether it 
should specify a

[[Page 1378]]

minimum number of sensors. We are requesting comment on the types 
(i.e., detection methodology) of devices that should be used, the 
appropriate detection limit for these devices, and whether the devices 
should be subject to the continuous parameter monitoring requirements 
in 40 CFR 63.8 of the General Provisions of part 63. We are requesting 
comment on the appropriate sampling time and whether the proposed 
requirement that a measurement be taken every 15 minutes is 
appropriate, as well as the proposed 2 ppmv concentration level that 
triggers action (i.e., additional inspections). In conjunction, we are 
requesting comment on whether action should be required based on a 
single measurement above the 2 ppmv action level, or whether it should 
be required when measurements averaged over a specified time period 
exceed 2 ppmv (e.g., if the one-hour average concentration is greater 
than 2 ppmv). Finally, the proposed rule generically requires that 
records of all chlorine concentration measurements be maintained. We 
are requesting comments on whether the rule should include data 
acquisition system and data format requirements, and if so, what 
associated requirements might be appropriate.
    The proposed rule would require that initial attempts at corrective 
actions of leaks be taken within 1 hour of detection, and the leak be 
repaired within 1 day of the date of detection. Records would be 
required to document the equipment containing more than 5 percent by 
volume of chlorine and the dates and times the inspections occurred. 
For each leak identified, records would also be required identifying 
the piece of equipment with the leak, the date and time it was 
identified, the date and time a first attempt to repair the leak was 
performed, the date and time the leak was stopped and repaired, and a 
description of the repair made to stop the leak. Records would also be 
required of any deviation from these work practices. Also, the number 
of leaks found and repaired during the reporting timeframe and any 
deviations from the work practices would be included in the periodic 
report.
2. Reconsideration Petition and Beyond-the-Floor Analysis for Mercury
    In early 2004, the EPA received a petition for reconsideration 
pursuant to CAA section 307(d)(7)(B) and a petition for judicial review 
under CAA section 307(b)(1) from the NRDC regarding the 2003 Mercury 
Cell Chlor-Alkali MACT standards. In the petition for reconsideration, 
NRDC claimed that the EPA failed to conduct the required beyond-the-
floor analysis under CAA section 112(d)(2) regarding whether to 
prohibit mercury emissions from existing sources, as the rule did for 
new and reconstructed sources. In a letter dated April 8, 2004, the EPA 
informed NRDC that it had granted the petition for reconsideration and 
would respond to NRDC's petition in a subsequent notice of proposed 
rulemaking. On July 20, 2004, the court put the litigation into 
abeyance and directed the EPA to file periodic status reports.
    In 2006 and 2007, the EPA conducted a testing program to measure 
fugitive mercury emissions at two selected facilities to inform the 
reconsideration. The EPA provided final reports regarding the results 
of the study to NRDC as required by a joint stipulation filed in the 
litigation. Both of the studied facilities are no longer operational. 
On June 11, 2008 (73 FR 33258), the EPA published a proposed rule that 
provided the EPA's proposed response to the petition for 
reconsideration, which would require facilities to install and operate 
a continuous mercury monitoring system in the ``upper portions of the 
cell room'' and continue to perform the work practice standards (with 
reduced recordkeeping and reporting requirements and no floor-level 
monitoring). The EPA received comments from Oceana, PPG Industries, the 
Chlorine Institute, Olin Chlor-alkali Products, and an anonymous 
submittal.
    Subsequently, in 2011, the EPA published a new proposed rulemaking 
in response to the petition for reconsideration (76 FR 13852, March 14, 
2011). The new proposed rule contained two options that the EPA was 
considering. The first option was to require remaining existing 
facilities to convert to a non-mercury technology to produce chlorine 
as a beyond-the-floor measure under CAA section 112(d)(2). The second 
option included the combination of the continuous cell room monitoring 
program and work practice program originally proposed in 2008 as a 
beyond-the-floor measure. Like for the 2008 proposed rule, the EPA 
received a number of comments from various stakeholders both for and 
against the 2011 proposed rulemaking. All of the EPA's technical 
analyses for the proposed rulemakings, public comments, and other 
supporting information regarding the 2008 and 2011 proposals are 
available in the docket for the proposals (Docket ID No. EPA-HQ-OAR-
2002-0017). No final action has been taken on the 2008 or 2011 
proposals, or to respond to the petition for reconsideration, and the 
litigation concerning the 2003 NESHAP remains in abeyance with the EPA 
still subject to the court's order to file periodic status reports.
    In conjunction with this proposed RTR action under CAA sections 
112(d)(6) and 112(f)(2), the EPA, pursuant to CAA sections 112(d)(2) 
and (3), re-evaluated whether a beyond-the-floor requirement that 
facilities must convert to a non-mercury technology within 3 years 
would still be appropriate based on updated analyses compared to those 
supporting the 2011 proposal. In 2011 there were four such facilities 
still in operation. Two of these facilities were the subject of the 
EPA's studies of fugitive mercury emissions over 2006 and 2007, and 
they have since shut down. As described above, only one operating 
facility remains in the U.S. that uses the mercury cell process to 
produce chlorine. Based on our updated analysis, contained in the 
docket for this proposed rule, we estimate the capital costs would be 
about $69 million for the one remaining facility to convert to a non-
mercury process. However, there would be savings over time due to the 
elimination of compliance costs associated with mercury and the higher 
efficiency and energy savings of switching to the membrane technology. 
The estimated annual costs, after accounting for the expected savings, 
are $2.8 million per year for the one remaining mercury cell facility. 
Based on reported mercury emissions, the cost effectiveness of the 
conversion is estimated to be $22,000 per pound of mercury emissions 
eliminated. However, we also note that the cost-effectiveness estimate 
is uncertain because, first, mercury emissions are based on 
calculations and assumptions regarding the facility's emissions (no 
test data are available for this facility), and second, because there 
are uncertainties with the cost estimates from the 2011 proposal as 
being transferable to the remaining facility. In the 2011 proposal, the 
estimated cost effectiveness was $20,000 per pound for the industry 
(see 76 FR 13852, March 14, 2011), but this was substantially based on 
the studies conducted for the two no longer operating sources.
    Based on consideration of the updated costs and cost effectiveness 
and uncertainties, and given the passage of time, and the fact that the 
cost-effectiveness data and analysis done in 2011 were based on two 
facilities that are no longer operating, we question whether those 2011 
analyses would still be transferable to the one remaining operating 
facility. Consequently, we are not proposing in this action to require 
the elimination of mercury as a beyond-

[[Page 1379]]

the-floor standard under CAA section 112(d)(2). However, we are 
soliciting comments, data, and other information regarding this 
proposed decision, including data and information regarding the capital 
and annual costs, cost effectiveness, non-air impacts, and other 
relevant information that would be relevant for the remaining facility 
regarding whether the NESHAP should include a zero-mercury standard as 
a beyond-the-floor MACT standard. We intend to consider any such 
submitted data and information, in addition to the data and information 
contained in the records for the 2008 and 2011 proposals and in this 
proposal, in reaching final conclusions under CAA section 112(d)(2) 
regarding a zero-mercury standard beyond-the-floor.

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

    As described above, for the Mercury Cell Chlor-Alkali Plant source 
category, we conducted an inhalation risk assessment for all HAP 
emitted, a multipathway screening assessment for the PB-HAP emitted, 
and an environmental risk screening assessment for the PB-HAP emitted 
from the source category. When we initiated this RTR and developed the 
risk input files, there were two facilities operating in the source 
category (Ashta in Ohio and Westlake in West Virginia); however, as 
noted above, Ashta has since permanently shut down the mercury cell 
process. We also conducted an environmental screening for HCl, because 
we initially had some HCl emissions in our data set, but as described 
above, after further review, we conclude those HCl emissions are due to 
non-category sources. We present results of the risk assessment briefly 
below and in more detail in the Residual Risk Assessment for the 
Mercury Cell Chlor-Alkali Plant Source Category in Support of the Risk 
and Technology Review 2020 Proposed Rule, which is available in the 
docket for this action.
1. Chronic Inhalation Risk Assessment Results
    The EPA estimated inhalation risk is based on actual and allowable 
emissions. The estimated baseline MIR posed by the source category is 
less than 1-in-1 million based on actual emissions and MACT-allowable 
emissions. The total estimated cancer incidence based on actual or 
allowable emission levels is 0.0000003 excess cancer cases per year, or 
one case every 3 million years. Emissions of 1,3-dichloropropene from 
the mercury cell building at Ashta accounted for 100 percent of the 
cancer incidence. No one is exposed to cancer risk greater than or 
equal to 1-in-1 million based upon actual and allowable emissions (see 
Table 1 of this preamble). However, based on the available data, the 
1,3-dichloropropene was only emitted from Ashta, which is no longer 
operating as a mercury cell facility, as discussed above. Furthermore, 
we have no indication or data suggesting that this pollutant is emitted 
from the one remaining facility.
    The maximum chronic noncancer TOSHI values for the source category 
were estimated to be less than 1 (0.05) based on actual and allowable 
emissions. For both actual and allowable emissions, respiratory risks 
were driven by chlorine emissions from the mercury cell building.

                           Table 1--Inhalation Risk Assessment Summary for Mercury Cell Chlor-Alkali Plant \1\ Source Category
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Maximum        Estimated       Estimated
                                                         individual     population at   annual cancer
           Risk assessment                Number of      cancer risk   increased risk     incidence         Maximum chronic      Maximum screening acute
                                       facilities \2\      (1-in-1     of cancer >= 1-   (cases per       noncancer TOSHI \4\        noncancer HQ \5\
                                                        million) \3\    in-1 million        year)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                Baseline Actual Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source Category......................               2           0.004               0       0.0000003  0.05 (respiratory)......  2 (REL), 7E-4 (AEGL2).
Facility-Wide........................               2             0.3               0          0.0001  0.05 (respiratory)......  .......................
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                              Baseline Allowable Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source Category......................               2           0.004               0       0.0000003  0.05 (respiratory)......  .......................
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Based on actual and allowable emissions.
\2\ Number of facilities in the risk assessment includes two facilities subject to 40 CFR part 63, subpart IIIII.
\3\ Maximum individual excess lifetime cancer risk due to HAP emissions from the source category.
\4\ Maximum TOSHI. The target organ with the highest TOSHI for the source category is the respiratory system.
\5\ The maximum estimated acute exposure concentration was divided by available short-term threshold values to develop an array of HQ values. The acute
  HQ shown was based upon the lowest acute 1-hour dose-response value, the REL for mercury (elemental). When an HQ exceeds 1, we also show the HQ using
  the next lowest available acute dose-response value.

2. Screening Level Acute Risk Assessment Results
    Based on our refined screening analysis of reasonable worst-case 
acute exposure to actual emissions from the category, both facilities 
exceeded an HQ of 1 (the HQ was 2) when compared to the 1-hour REL for 
mercury (elemental). As discussed in section III.C.3.c of this 
preamble, we used an acute hourly multiplier of 10 for all emission 
processes. For this HAP, there are no AEGL-1 or ERPG-1 values for 
comparison, but AEGL-2 or ERPG-2 values are available. For elemental 
mercury, when the maximum off-site concentration is compared with the 
AEGL-2 and ERPG-2, the maximum acute noncancer HQ is well below 1 
(0.0007).
3. Multipathway Risk Screening Results
    PB-HAP emissions (based on estimates of actual emissions) were 
reported from both facilities in the source category with both 
exceeding the Tier 1 non-cancer screening threshold emission rate for 
mercury. A Tier 2 screening analysis was conducted with no facilities 
having an SV greater than 1 for any scenario (the fisher and farmer had 
the highest SV at 0.4). There are no carcinogenic PB-HAP emitted from 
the source category. So, there are no cancer SVs to report. Further 
details on the Tier 2 screening analysis can be found in the Residual 
Risk Assessment for the Mercury Cell Chlor-Alkali Plant Source Category 
in Support of the Risk and Technology Review 2020 Proposed Rule, and 
Appendix 10 of this report.

[[Page 1380]]

    An SV in any of the tiers is not an estimate of the cancer risk or 
a noncancer HQ. Rather, an SV represents a high-end estimate of what 
the risk or HQ may be. For example, facility emissions resulting in an 
SV of 2 for a non-carcinogen can be interpreted to mean that we are 
confident that the HQ would be lower than 2. Similarly, facility 
emissions resulting in a cancer SV of 20 for a carcinogen means that we 
are confident that the cancer risk is lower than 20-in-1 million. Our 
confidence comes from the health-protective assumptions that are 
incorporated into the screens: we choose inputs from the upper end of 
the range of possible values for the influential parameters used in the 
screens, and we assume food consumption behaviors that would lead to 
high total exposure. This risk assessment estimates the maximum hazard 
for mercury through fish consumption based on upper bound screens. As 
discussed above, the maximum mercury Tier 2 noncancer SV based upon the 
fisher scenario resulted in an SV less than 1.
4. Environmental Risk Screening Results
    As described in section III.A of this preamble, we conducted an 
environmental risk screening assessment for the Mercury Cell Chlor-
Alkali Plant source category for the following pollutants: HCl and 
mercury (methyl mercury and mercuric chloride). However, as noted 
above, we subsequently determined that the HCl emissions are due to 
non-category sources such as co-located HCl production.
    In the Tier 1 screening analysis, methyl mercury and divalent 
mercury resulted in exceedances of ecological benchmarks by two 
facilities. Divalent mercury emissions had Tier 1 exceedances for the 
following benchmarks: Surface soil threshold level--invertebrate 
communities by a maximum SV of 4. Methyl mercury had Tier 1 exceedances 
for the following benchmarks: No Observed Adverse Effect Level 
(NOAEL)--avian ground insectivores (woodcock) by a maximum SV of 6.
    A Tier 2 screening analysis was performed for divalent mercury and 
methyl mercury. In the Tier 2 screening analysis, divalent mercury 
emissions had no Tier 2 exceedances. Methyl mercury had Tier 2 
exceedances for one facility exceeding the following benchmark: Surface 
soil NOAEL for avian ground insectivores (woodcock) by a maximum SV of 
2 with 0.1 percent of the soil area being above an SV of 2.
    For HCl, only one facility reported emissions. The average modeled 
concentration around this 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. However, as explained 
above, after further investigation, we conclude that the reported HCl 
emissions are due to non-category sources.
5. Facility-Wide Risk Results
    The EPA estimated inhalation risk based on facility-wide emissions 
to be 0.3-in-1 million, with an 0.0001 excess cancer cases per year, or 
one case every 10,000 years. Emissions of metals (arsenic, chromium VI, 
and nickel) from non-category sources account for 100 percent of the 
cancer incidence. No one is exposed to cancer risk greater than or 
equal to 1-in-1 million (see Table 1 of this preamble). The maximum 
chronic noncancer TOSHI value for the source category was the same for 
both actual emissions and allowable emissions with an HI less than 1 
(0.05) for respiratory risks driven by chlorine emissions from the 
mercury cell building.
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 risks to individual 
demographic groups of the populations living within 5 km and within 50 
km of the facilities. In the analysis, we evaluated the distribution of 
HAP-related cancer and noncancer risks from the mercury cell chlor-
alkali plant source category across different demographic groups within 
the populations living near the two facilities.\23\
---------------------------------------------------------------------------

    \23\ Demographic groups included in the analysis are: White, 
African American, Native American, other races and multiracial, 
Hispanic or Latino, children 17 years of age and under, adults 18 to 
64 years of age, adults 65 years of age and over, adults without a 
high school diploma, people living below the poverty level, people 
living two times the poverty level, and linguistically isolated 
people.
---------------------------------------------------------------------------

    Results of the demographic analysis indicate that, for three of the 
11 demographic groups, age greater than or equal to 65, age greater 
than or equal to 25 years of age without a high school diploma, and 
people below the poverty level, the percentage of the population living 
within 5 km of facilities in the source category is greater than the 
corresponding national percentage for the same demographic groups. When 
examining the risk levels of those exposed to emissions from mercury 
cell chlor-alkali plant facilities, we find that no one is exposed to a 
cancer risk at or above 1-in-1 million or to a chronic noncancer TOSHI 
greater than 1.
    The methodology and the results of the demographic analysis are 
presented in a technical report, Risk and Technology Review--Analysis 
of Demographic Factors for Populations Living Near Mercury Cell Chlor-
Alkali Plant Source Category Operations, available in the docket for 
this action.

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

1. Risk Acceptability
    As explained in section II.A 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'' (54 FR 38045, September 14, 1989). The 
EPA weighed all health risk measures and information, including science 
policy assumptions and estimation uncertainties, in determining whether 
risk posed by emissions from the source category is acceptable.
    As described above, the maximum cancer risk for inhalation exposure 
to actual and allowable emissions from the Mercury Cell Chlor-Alkali 
Plant source category is 0.004-in-1 million, which is more than four 
orders of magnitude below 100-in-1 million, which is the presumptive 
upper limit of acceptable risk. The EPA estimates emissions from the 
category would result in a cancer incidence of 0.0000003 excess cancer 
cases per year, or one case every 3 million years. Furthermore, as 
described above, the facility estimated to pose those cancer risks is 
no longer operating as a mercury cell facility. Inhalation exposures to 
HAP associated with chronic noncancer health effects result in a TOSHI 
of 0.05 based on actual and allowable emissions, 20 times below an 
exposure that the EPA has determined is without appreciable risk of 
adverse health effects. Exposures to HAP associated with acute 
noncancer health effects result in an HQ less than or equal to 2 based 
upon the 1-hour REL for elemental mercury, and when the maximum off-
site concentration is compared with the AEGL-2 and ERPG-2, the maximum 
acute noncancer HQ is

[[Page 1381]]

well below 1 (0.0007). This information, in addition to the 
conservative (health-protective) assumptions built into the screening 
assessment, leads us to conclude that adverse effects from acute 
exposure to emissions of this HAP from this source category are not 
anticipated. Maximum noncancer hazard due to ingestion exposures 
estimated using health-protective risk screening assumptions are below 
an HQ of 1 (0.4) for the Tier 2 fisher scenario. The estimated 
ingestion cancer risk is zero since we did not identify any 
carcinogenic HAP emitted from the source category. Considering all of 
the health risk information and factors discussed above, as well as the 
uncertainties discussed in section III of this preamble, we propose 
that the risks posed by emissions from the Mercury Cell Chlor-Alkali 
Plant source category are acceptable.
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, we evaluated 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 from the source category.
    As described above, the only HAP emitted from this source category 
posing any risks of potential concern is elemental mercury, with a 
maximum noncancer acute HQ of 2 based on the REL. Therefore, we 
considered potential options to reduce mercury emissions under the 
ample margin of safety analysis. The options we considered under the 
ample margin of safety analysis are the exact same control options 
described under the technology review section of this preamble (see 
section IV.D below).
    First, as described in greater detail under the technology review 
section, we evaluated the option of requiring a combination of 
implementing a cell room monitoring program and performing work 
practices as an approach to minimize mercury emissions. Under the 
technology review section, we determined that this option does 
constitutes a development in emissions control practices pursuant to 
CAA section 112(d)(6) with very low costs, and, therefore, we are 
proposing these requirements under the technology review. However, 
since the one operating facility already conducts these two actions, we 
do not expect any actual reductions in emissions and, therefore, we 
would expect no actual reductions in risks. Since this option is not 
expected to result in any risk reductions, we are not proposing to 
adopt those requirements pursuant to CAA section 112(f).
    The other option we considered under the CAA section 112(d)(6) 
technology review (described in section IV.D of this preamble) as well 
as under CAA sections 112(d)(2) and (3), as described in section IV.A 
of this preamble, is to require zero mercury emissions from existing 
sources, which is the requirement for new and reconstructed mercury 
cell chlor-alkali production sources. This option would eliminate 
process vent and fugitive mercury emissions as it would force the 
remaining facility to convert the operation to a non-mercury process or 
close the mercury cell operation. As described in more detail in 
sections IV.A and IV.D of this preamble, we estimate the capital cost 
of converting the one remaining mercury cell facility to membrane cells 
is just over $69 million. The estimated emissions of mercury would be 
reduced from 126 pounds to zero pounds per year. Considering the costs 
of conversion annualized over a time period of 20 years, the annual 
costs are estimated to be approximately $2.8 million, which results in 
a cost effectiveness of approximately $22,000 per pound of mercury 
emissions eliminated. With regard to reductions in risks due to HAP 
emissions as a result of this option, since this option would force 
conversion or closure of the remaining one mercury cell facility, the 
risks due to emissions of HAP for the source category would be zero, 
since there would be no facilities in the source category.
    Nevertheless, after considering the options described above, since 
the risks due to mercury emissions are already low (with a maximum 
acute noncancer HQ of less than or equal to 2 based upon the 1-hour REL 
and a maximum HQ of 0.0007 based on AEGL-2 and ERPG-2), and given the 
costs described above, and because of the substantial uncertainties in 
the emissions estimates and cost estimates, we are not proposing any 
additional standards for mercury under CAA section 112(f).
    In summary, considering the very low cancer risks (MIR far less 
than 1-in-1 million) and very low chronic noncancer risks (HI of 0.05) 
to individuals exposed to HAP emitted from this source category, and 
after considering possible options for mercury as described above, we 
are proposing a determination that the existing standards provide an 
ample margin of safety to protect public health.
3. Adverse Environmental Effect
    Based on the results of the environmental risk screening analysis, 
we do not expect an adverse environmental effect, as defined by CAA 
section 112(a)(7), as a result of HAP emissions from this source 
category, and we are proposing that it is not necessary to set a more 
stringent standard 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 noted above, 40 CFR part 63, subpart IIIII currently includes 
emission limitations for mercury emissions from process vents 
(including emissions from end-box ventilation systems, hydrogen 
systems, and mercury recovery facilities) and work practices for 
fugitive mercury emissions from the cell room. We have identified a 
development for cell room fugitive mercury emissions.
    With regard to fugitive mercury emissions from the cell room, the 
current rule at 40 CFR 63.8192(a) through (f) requires a suite of 
equipment standards and work practices. It also provides the option, in 
lieu of the work practices otherwise required under CAA sections 
63.8192(a) through (d), to institute a cell room monitoring program to 
continuously monitor the mercury vapor concentration in the upper 
portion of each cell room. See 40 CFR 63.8192 introductory text, and 40 
CFR 63.8192(g). The single mercury cell facility still operating 
complies via this alternative. However, while not required to do so 
under the current regulation, the facility also performs all the work 
practices. Therefore, the EPA determined that the combination of 
implementing a cell room monitoring program and performing work 
practices constitutes a development in emissions control practices. 
This combination was the proposed option in the June 11, 2008, action 
(73 FR 33258), and also included as a co-proposal in the March 14, 2011 
(76 FR 13852), action. Since the only facility in the source category 
is already implementing the monitoring program and performing these 
work practices, there would be no costs (with the exception of 
additional recordkeeping and reporting costs) or additional mercury 
emission reductions associated with implementing a standard that 
requires a combination of these practices.

[[Page 1382]]

    We also identified the option to require zero mercury emissions 
from existing sources, which is the requirement for new and 
reconstructed mercury cell chlor-alkali production sources. This option 
would eliminate process vent and fugitive mercury emissions as it would 
force the remaining facility to convert the operation to a non-mercury 
process, or close the mercury cell operation, by a date no later than 3 
years of the date of publication of the final rule. See CAA section 
112(i)(3)(A). When the EPA originally listed the Chlorine Production 
source category in 1992, there were 13 mercury cell chlor-alkali plants 
in the U.S. Since that time, the number of facilities has steadily 
declined to the current situation with only one facility. Many owners 
of mercury cell facilities converted to the more efficient and more 
environmentally friendly membrane cell technology, while other mercury 
cell chlor-alkali plant owners have concluded the investment decision 
was currently not in their company's interest given their assessment of 
future economic conditions and have shut down their mercury cell chlor-
alkali plants entirely. Therefore, the zero mercury emissions option is 
a demonstrated potential development in processes pursuant to CAA 
section 112(d)(6).
    The EPA has considered this option previously since the 
promulgation of the regulation in 2003, in the context of evaluating 
whether a prohibition on mercury emissions would be a reasonable 
beyond-the-floor MACT measure under CAA section 112(d)(2). As discussed 
above, in 2008, the EPA proposed amendments to 40 CFR part 63, subpart 
IIIII (73 FR 33258, June 11, 2008). One of the options evaluated for 
this 2008 proposal was to require zero mercury emissions, and the EPA 
evaluated the impacts of requiring conversion of mercury cell chlor-
alkali production plants to non-mercury technology. The EPA proposed 
``to reject conversion to non-mercury technology as a beyond-the-floor 
control requirement because of the high cost impact this forced 
conversion would impose on the facilities in the industry.'' As noted 
above, the EPA proposed the combination of mercury cell room monitoring 
and work practices in the 2008 action (73 FR 33275).
    Considering comments received on the 2008 proposed cost and impacts 
analysis of the option to convert to non-mercury technology, the EPA 
significantly refined the analysis. The results of the revised analyses 
were published in 2011, along with two proposed options to reduce 
mercury emissions. One was an option to require all mercury cell chlor-
alkali facilities to comply with a zero-mercury emissions limitation 
within 3 years of the finalization of the proposal (76 FR 13852, March 
14, 2011). The other proposed option was to require continuous 
monitoring of mercury in the upper regions of the cell room along with 
work practices, as under the 2008 proposal (and as being proposed here 
under CAA section 112(d)(6)). The revised analysis of the impacts of 
conversion from mercury cells to membrane cells is discussed in detail 
in the 2011 proposal and supporting documentation.
    Comments were received on the updated analysis and supplemental 
2011 proposal. An environmental advocacy commenter (Docket Item No. 
EPA-HQ-OAR-2002-0017-0152) supported the proposed zero-mercury option 
but also commented that the EPA had overstated the costs and 
understated the emission reductions and other benefits. Conversely, 
three industry representatives (Docket Item Nos. EPA-HQ-OAR-2002-0017-
0150, -0151, and -0157) commented that the EPA's revised analysis had 
underestimated the costs and negative economic impacts and overstated 
the benefits. One industry representative (Docket ID No.EPA-HQ-OAR-
2002-0150) provided an analysis of the impacts of conversion specific 
to the West Virginia facility (which is, as discussed previously, the 
only mercury cell plant currently still in operation). The commenter 
indicated that the cost of conversion estimated by the EPA for this 
facility (around $43 million) was considerably less than the estimates 
calculated by the facility (around $60 million). The commenter also 
provided a cost-effectiveness analysis, which showed a cost of over 
$77,000 per pound of mercury emissions eliminated for this facility. 
The EPA has not yet finalized either of the options included in the 
2011 supplemental proposal, or otherwise issued a final beyond-the-
floor MACT determination under CAA section 112(d)(2) for existing 
source mercury emissions, as discussed above.
    For this proposal, the EPA re-examined the impacts of a zero-
mercury option. Specifically, the EPA evaluated the costs and cost 
effectiveness of the replacement of the West Virginia mercury cell 
facility with a membrane cell facility. As pointed out above, the EPA's 
2011 estimate for the capital cost to convert the West Virginia 
facility was just over $43 million and an annual cost of $2.6 million 
per year. The EPA updated this estimate by adjusting the costs to 2019 
dollars and incorporating the actual costs of conversion incurred by 
the Ohio facility for their 2019/2020 conversion. The resulting updated 
estimate is that the capital cost of converting the West Virginia 
mercury cell facility to membrane cells is just over $69 million. The 
estimated emissions of mercury would be reduced from 126 pounds to zero 
pounds per year. Considering the costs of conversion annualized over a 
time period of 20 years, the annual costs are estimated to be 
approximately $2.8 million, which results in a cost effectiveness of 
approximately $22,000 per pound of mercury emissions eliminated.\24\ 
While some commenters have suggested that the EPA's estimates of 
mercury emissions from mercury cell chlor-alkali facilities are 
underestimated due to ``unaccounted for'' mercury, the EPA's detailed 
study conducted prior to the 2008 proposal demonstrated otherwise. 
Specifically, the EPA stated ``The results of the almost one million 
dollar study of fugitive emissions from mercury cell chlor-alkali 
plants sponsored by EPA enables us to conclude that the levels of 
fugitive emissions for mercury chlor-alkali plants are much closer to 
the assumed emissions in the part 61 Mercury NESHAP, of 1,300 grams/
day/plant (around 0.5 tons/yr/plant) than the levels assumed by NRDC (3 
to 5 tons/yr/plant). The results of this study suggest that the 
emissions are routinely less than half of the 1,300 grams/day level, 
with overall fugitive emissions from the five operating facilities 
estimated at less than 1 ton per year of mercury.'' (73 FR 32666). This 
study, and the EPA's basis for their conclusion regarding the magnitude 
of mercury emissions from these facilities, is discussed in detail in 
the 2008 proposal (73 FR 33262 through 33267). In addition, the West 
Virginia facility is required under an agreement with the Attorney 
General of Maryland to limit mercury emissions from the facility to 
less than 150 pounds per year.\25\
---------------------------------------------------------------------------

    \24\ Memorandum. Norwood, P., SC&A, Inc. to Mulrine, P., EPA. 
Updated Cost Analysis for Conversion of Mercury Cell Chlor-Alkali 
Plants to Membrane Cells. December 3, 2020.
    \25\ PPG to Lower Mercury Emissions at Natrium Plant. 
Environmental Protection Online. August 25, 2009. Available at 
https://eponline.com/Articles/2009/08/25/PPG-to-Lower-Mercury-Emissions-at-Natrium-Plant.aspx?Page=1&p=1.
---------------------------------------------------------------------------

    The EPA also examined the non-air impacts associated with switching 
from mercury cell to non-mercury cell processes. For 2019, the West 
Virginia facility reported a total of 898.1 pounds of non-air mercury 
releases. This consists of 9 pounds to streams/water bodies, 883.3 
pounds to Resource

[[Page 1383]]

Conservation and Recovery Act, Subtitle C Landfills, and 5.8 pounds to 
other offsite sources. All these releases would be eliminated with the 
conversion to non-mercury cell processes. While the promulgation of a 
zero-mercury standard would eliminate these ongoing releases, there 
would be environmental impacts associated with the dismantling and 
decommissioning of the West Virginia mercury cell plant. In 2008, the 
EPA estimated that these activities would result in over 4,000 pounds 
of mercury in wastes (for example, from contaminated piping and other 
equipment). We believe this estimate still represents a reasonable 
estimate of the wastes that would be generated. In addition, the 
facility would need to deal with the several hundred tons of elemental 
mercury that is currently contained in the cells. The options for 
storing this mercury are limited by the Mercury Export Ban Act of 2008. 
The only realistic options for long-term storage of this mercury are to 
send it to U.S. Department of Energy storage facilities or to continue 
to store it onsite, both of which would result in ongoing costs to the 
facility.
    Based on these factors, we are not proposing the option of a zero-
mercury standard as part of our CAA section 112(d)(6) technology review 
for this source category at this time. Moreover, as we are now 
uncertain whether the assessments supporting the 2011 proposed option 
to require elimination of mercury emissions from existing sources 
continue to represent accurate estimates of the costs of requiring such 
elimination at the single remaining plant, we are proposing that 
promulgating a zero-mercury standard for existing sources would not be 
a reasonable beyond-the-floor MACT standard under CAA section 
112(d)(2). However, we are soliciting comments, data, and other 
information regarding these proposed decisions, including data and 
information regarding the costs, cost effectiveness, non-air, and 
economic impacts and other relevant information regarding whether the 
NESHAP should include a zero-mercury standard as either a beyond-the-
floor MACT standard or a revised standard under the technology review, 
and whether the proposed work practices for chlorine emissions and 
proposed amendments to the mercury work practices would be necessary if 
a zero-mercury standard were to be adopted. We intend to consider any 
such submitted data and information, in addition to the data and 
information contained in the records for the 2008 and 2011 proposals 
and in this proposal, in reaching final conclusions under CAA sections 
112(d)(2) and (6) regarding a zero-mercury standard.
    Based on the analyses discussed above, we are proposing the first 
option, which is to amend the rule to require both a cell room 
monitoring program and work practice standards. Specifically, the 
proposed amendments would require, beginning 6 months after the final 
rule is published, compliance with all work practices in the rule and 
associated recordkeeping and reporting requirements plus the cell room 
monitoring program. The exception is the work practice to develop and 
follow a floor-level mercury vapor measurement program required at 40 
CFR 63.8192(d). The cell room monitoring program is similar to the 
floor-level program, except that it is more comprehensive and effective 
as it detects increased mercury levels throughout the cell room, while 
the floor-level program only detects increased levels near the floor-
level walkways.

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 
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 also are proposing various other changes to require electronic 
reporting of performance test results, notifications, and reports. We 
are also proposing two amendments to correct errors and improve the 
compliance provisions in the rule, as well as proposing amendments to 
address applicability for thermal mercury recovery units when chlorine 
and caustic are no longer produced in mercury cells. 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 the emissions standards 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. In 2011, the EPA 
proposed similar revisions to the SSM provisions as those being 
proposed here. During the comment period for the 2011 rule, the mercury 
cell chlor-alkali industry indicated that there were safety concerns 
associated with complying with the emissions standards during startup 
for the hydrogen vent stream. The industry provided general information 
that suggested that the control device could not be operated until the 
exhaust stream composition could be regulated. However, no additional 
data or information has been received since 2011, and it is unclear 
whether the one operating facility in the source category would violate 
its emissions standards during these startup times, whether the 
facility has changed operations since the 2011 rule to be able to 
comply with the emissions standards during startup, or whether there 
are other practices or standards that could apply during these periods 
to ensure emissions are limited or reduced. In the absence of evidence 
that the emissions standards cannot be met during startup, the EPA is 
proposing that the emissions standards apply at all times. However, we 
solicit comment and detailed information for any situations where 
separate standards, such as work practices, would be more appropriate 
during periods of startup and shutdown rather than the current 
standard.

[[Page 1384]]

    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 CAA 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 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.
    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).
a. General Duty, SSM Plan, and Compliance with Standards
    We are proposing to revise the General Provisions Applicability 
Table (Table 10) entry for ``Sec.  63.6(a)-(g), (i), (j)'' to ``Sec.  
63.6(a)-(g), (i), (j), except for (e)(1)(i) and (ii), (e)(3), and 
(f)(1)'' and to add a new entry for ``Sec.  63.6(e)(1)(i) and (ii), 
(e)(3), and (f)(1),'' in which a ``No'' entry would be included in the 
column, ``Applies to Subpart IIIII.'' 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 63.8222 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

[[Page 1385]]

and SSM events in describing the general duty. Therefore, the language 
the EPA is proposing for 40 CFR 63.8222 does not include that language 
from 40 CFR 63.6(e)(1). In addition, 40 CFR 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 63.8222. Generally, 40 CFR 63.6(e)(3) requires 
development of an SSM plan and specifies 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. 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 that the 
standards in this rule apply at all times.
b. Performance Testing
    We are proposing to revise the General Provisions Applicability 
Table (Table 10) entry for ``Sec.  63.7(a)(1), (b)-(h)'' to ``Sec.  
63.7(a)-(h), except for (a)(2) and (e)(1)'' and to add a new entry for 
``Sec.  63.7(e)(1),'' in which a ``No'' entry would be included in the 
column, ``Applies to Subpart IIIII.'' Section 63.7(e)(1) describes 
performance testing requirements. The EPA is instead proposing to add a 
performance testing requirement at 40 CFR 63.8232(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 startup and shutdown events. 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 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.
c. Monitoring
    We are proposing to revise the General Provisions Applicability 
Table (Table 10) entry for ``Sec.  63.8(a)(1), (a)(3); (b); (c)(1)-(4), 
(6)-(8); (d); (e); and (f)(1)-(5)'' to ``Sec.  63.8(a)(1), (a)(3); (b); 
(c)(1)(ii), (2)-(4), (6)-(8); (d)(1)-(2); (e); and (f)(1)-(5)'' and to 
add entries for ``Sec.  63.8(c)(1)(i) and (iii)'' and ``Sec.  
63.8(d)(3)'' in which a ``No'' entry would be included in the column, 
``Applies to Subpart IIIII,'' for the new entries. The cross-references 
to the general duty and SSM plan requirements in subparagraphs 40 CFR 
63.8(c)(1)(i) and (iii) 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)). In 
addition, the final sentence in 40 CFR 63.8(d)(3) refers to the General 
Provisions' SSM plan requirement which is no longer applicable. The EPA 
is proposing to add to the rule at 40 CFR 63.8242(a)(3)(v) text that is 
identical to 40 CFR 63.8(d)(3) except for the final sentence with the 
reference to SSM.
d. Recordkeeping and Reporting
    We are proposing to revise the General Provisions Applicability 
Table (Table 10) entry for ``Sec.  63.10(a); (b)(1); (b)(2)(i)-(xii), 
(xiv); (b)(3); (c); (d)(1)-(2), (4)-(5); (e); (f)'' to ``Sec.  
63.10(a); (b)(1); (b)(2)(vi)-(xii), (xiv); (b)(3); (c)(1)-(14); (d)(1)-
(2), (4); (e); (f)'' and to add entries for ``Sec.  63.10(b)(2)(i)-
(v),'' ``Sec.  63.10(c)(15),'' and ``Sec.  63.10(d)(5),'' in which a 
``No'' entry would be included in the column, ``Applies to Subpart 
IIIII,'' for the new entries. 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.
    Section 63.10(b)(2)(ii) describes the recordkeeping requirements 
during a malfunction. The EPA is proposing to add such requirement to 
40 CFR 63.8256(a)(2). 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 deviation from an applicable requirement, 
which would include malfunctions, and is requiring that the source 
record the date, time, and duration of the deviation rather than the 
``occurrence.'' The EPA is also proposing to add requirements to 40 CFR 
63.8256(a)(2) 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 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.
    When applicable, 40 CFR 63.10(b)(2)(iv) 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 required by 40 CFR 63.8256(a)(2).

[[Page 1386]]

    When applicable, 40 CFR 63.10(b)(2)(v) 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.
    The EPA is also 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.
    Section 63.10(d)(5) describes the reporting requirements for SSM. 
To replace the General Provisions reporting requirement, the EPA is 
proposing to add reporting requirements to 40 CFR 63.8254(b)(8) and 
(9). This language differs from the General Provisions requirement in 
that it does not require a stand-alone report. With this revision, we 
are proposing that sources that fail to meet an applicable standard or 
regulatory requirement at any time 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.
    Section 63.10(d)(5)(ii) describes an immediate report for startups, 
shutdown, and malfunctions when a source failed to meet an applicable 
standard but did not follow the SSM plan. We will no longer require 
owners or operators to report when actions taken during a startup, 
shutdown, or malfunction were not consistent with an SSM plan, because 
plans would no longer be required.
2. Electronic Reporting
    The EPA is proposing that owners and operators of mercury cell 
chlor-alkali plants submit electronic copies of required performance 
test reports, notifications, and 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 \26\ 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. The proposed rule requires that each 
notification--such as a Revised NOCS--and each report--such as a 
semiannual report--be submitted as a PDF upload in CEDRI.
---------------------------------------------------------------------------

    \26\ 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 \27\ to 
implement Executive Order 13563 and is in keeping with the EPA's 
agency-wide policy \28\ developed in response to the White House's 
Digital Government Strategy.\29\ 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

[[Page 1387]]

Hazardous Air Pollutants (NESHAP) Rules, referenced earlier in this 
section.
---------------------------------------------------------------------------

    \27\ EPA's Final Plan for Periodic Retrospective Reviews, August 
2011. Available at: https://www.regulations.gov/document?D=EPA-HQ-OA/2011/0156/0154.
    \28\ 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.
    \29\ 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.
---------------------------------------------------------------------------

3. Compliance Provisions Rule Corrections
    We are proposing amendments to correct errors and improve the 
compliance provisions of the rule. These changes, which are described 
below, were included in the March 14, 2011, proposal (76 FR 13865) and 
the June 2008 proposal (73 FR 33275).
a. Detection Limit for Mercury Monitor Analyzers
    Paragraph 63.8242 (a)(2) requires mercury continuous monitor 
analyzers to have a detector capable of detecting a mercury 
concentration at or below 0.5 times the mercury concentration level 
measured during the performance test. Since promulgation of the NESHAP, 
we have realized that detecting a concentration of 0.5 times the 
mercury concentration could, in cases of low mercury concentrations, be 
infeasible for the monitoring devices on the market. Information 
available to us at this time shows that 0.1 [mu]g/m3 is the detection 
limit of commonly commercially available analyzers. Analyzers with 
detection limits at this level are more than sufficient to determine 
compliance with the limitations in the NESHAP. Therefore, we are 
proposing to revise this paragraph to require a detector capable of 
detecting a mercury concentration at or below 0.5 times the mercury 
concentration measured during the test or 0.1 [mu]g/m3.
b. Averaging Period for Mercury Recovery Unit Compliance
    The NESHAP is inconsistent as to whether the rule requires a daily 
average or an hourly average to determine continuous compliance with 
the emissions standard for mercury recovery units. While 40 CFR 
63.8243(b) indicates that this averaging period is daily, another 
paragraph, 40 CFR 63.8246(b), states that limit is based on the average 
hourly concentration of mercury. It was our intention for compliance to 
be based on a daily average, and the inclusion of ``hourly'' in 40 CFR 
63.8246 (b) was a drafting error. Therefore, we are proposing to 
correct this error by replacing ``hourly'' in 40 CFR 63.8246(b) with 
``daily.''
4. Applicability for Mercury Recovery Units
    As discussed previously, all but one mercury cell plant has closed 
or converted to membrane cells since the promulgation of the 2003 
Mercury Cell Chlor-Alkali Plants MACT. When these situations have 
occurred at plants with on-site thermal mercury recovery units, it has 
been common for these units to continue to operate to assist in the 
treatment of wastes associated with the shutdown/conversion. We are not 
aware of any mercury recovery units still in operation and the 
Westlake, West Virginia, facility does not operate a thermal mercury 
recovery unit that is subject to the emission limitations in the rule. 
Regardless, under the applicability of the 2003 Mercury Cell Chlor-
Alkali Plants MACT, these units would no longer be an affected source 
after the chlorine production facility ceased operating. Furthermore, 
while the NESHAP already effectively prohibits the construction or 
reconstruction of a new mercury cell chlor-alkali production facility, 
it does not do the same for mercury recovery facilities. Therefore, 
there exists the possibility that there is an existing mercury recovery 
unit of which we are unaware or that a mercury recovery facility 
subject to new source standards could be constructed or reconstructed. 
Therefore, these proposed amendments would require any mercury recovery 
unit to comply with the requirements of the Mercury Cell Chlor-Alkali 
Plants MACT for such units, as long as the mercury recovery unit 
operates to recover mercury from wastes generated by a mercury cell 
chlor-alkali plant.

F. What compliance dates are we proposing?

    From our assessment of the time frame needed for compliance with 
the entirety of the revised requirements, the EPA considers a period of 
6 months to be the most expeditious compliance period practicable and, 
thus, is proposing that the affected source be in compliance with all 
of this regulation's revised requirements within 6 months of the 
regulation's effective date.
    For existing sources, we are proposing two changes to the work 
practice standards. While these proposed work practice standards are 
based on the practices in place at the single facility in the source 
category, they will require some modifications to the procedures 
currently employed at the facility. Specifically, they will need to 
develop and implement a recordkeeping system to record and maintain the 
records required for the mercury cell work practices and to incorporate 
the required material in the requisite reports. Also, while the 
facility has standard operating procedures in place to reduce fugitive 
emissions of chlorine upon which the proposed requirements are based, 
they will need to develop and implement a recordkeeping system to 
record and maintain the records required for the fugitive chlorine 
inspection requirements and to incorporate the required material in the 
requisite reports. We propose that a 6-month period of time would be 
adequate for these activities.
    In addition, we are proposing to add a requirement that 
notifications, performance test results, and compliance reports be 
submitted electronically. We are also proposing to change the 
requirements for SSM by removing the exemption from the requirements to 
meet the standards during SSM periods and by removing the requirement 
to develop and implement an SSM plan. Our experience with similar 
industries that are required to convert reporting mechanisms to install 
necessary hardware and software, become familiar with the process of 
submitting performance test results electronically through the EPA's 
CEDRI, test these new electronic submission capabilities, and reliably 
employ electronic reporting shows that a time period of a minimum of 3 
months, and, more typically, 6 months is generally necessary to 
successfully accomplish these revisions. Our experience with similar 
industries further shows that this sort of regulated facility generally 
requires a time period of 6 months to read and understand the amended 
rule requirements; to evaluate their operations to ensure that they can 
meet the standards during periods of startup and shutdown as defined in 
the rule and make any necessary adjustments; and to update their 
operation, maintenance, and monitoring plans to reflect the revised 
requirements.
    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. We note that information provided may result in 
changes to the proposed compliance dates.

V. Summary of Cost, Environmental, and Economic Impacts

A. What are the affected sources?

    There is only one mercury cell chlor-alkali facility currently 
operating in the U.S. The facility will be subject to the Mercury Cell 
Chlor-Alkali Plants NESHAP affected by the proposed amendments to 40 
CFR part 63, subpart IIIII.

[[Page 1388]]

B. What are the air quality impacts?

    We are not proposing revisions to the mercury emission limits for 
process vents other than to make them applicable during SSM periods, 
and we do not anticipate any air quality impacts as a result of this 
proposed amendment, since the one subject facility is already in 
compliance with emission limits during all periods, including SSM. We 
are proposing changes to require both the mercury cell room monitoring 
program and the work practice standards for fugitive mercury emissions, 
and are proposing new work practice standards for fugitive chlorine 
emissions. However, these proposed changes are based on the current 
practices in place at the one subject facility. Therefore, we also do 
not anticipate any air quality impacts as a result of these proposed 
amendments to the work practices.

C. What are the cost impacts?

    As noted earlier, the single facility in the source category is 
complying with the alternative cell room monitoring program. While not 
currently required, the facility is also implementing the work 
practices. Therefore, the only costs that would be incurred with the 
proposed requirement to comply with both the cell room monitoring 
program and the work practices are those costs associated with the work 
practice recordkeeping and reporting. We estimate these costs to be 
$36,000 per year for the mercury work practices recordkeeping and 
reporting and $49,000 for the chlorine inspection program recordkeeping 
and reporting (all costs in 2020 dollars). Another way to present these 
costs is to show them in terms of present value, in which the stream 
over time of costs per year for the proposal requirement is discounted 
to the present day. For this proposal, the present value of the costs 
in total is $445,000 in 2020 dollars, calculated over an 8-year period 
from 2022 to 2029 (assuming promulgation in 2021), estimated at a 7 
percent discount rate and discounted to 2020. The equivalent annualized 
value of these costs, which is an annualized value of costs consistent 
with the present value, is $74,500 in 2020 dollars, and also estimated 
at a 7 percent discount rate and discounted to 2020.

D. What are the economic impacts?

    Economic impact analyses focus on changes in market prices and 
output levels. If changes in market prices and output levels in the 
primary markets as a result of complying with the rule are significant 
enough, impacts on other markets may also be examined. Both the 
magnitude of costs needed to comply with a proposed rule and the 
distribution of these costs among affected facilities can have a role 
in determining how the market prices and output levels will change in 
response to a proposed rule. The total cost associated with this 
proposed rule is estimated to be $85,000 per year in 2020 dollars, 
which is the cost associated with additional recordkeeping and 
reporting costs. The economic impact associated with this cost, 
calculated as an annual cost per sales, for the parent firm owning the 
single affected facility is 0.001 percent, and is not expected to 
result in a significant market impact, regardless of whether it is 
fully passed on to the consumer or fully absorbed by the affected firm.

E. What are the benefits?

    The EPA does not anticipate reductions in HAP emissions as a result 
of the proposed amendments to the Mercury Cell Chlor-Alkali Plants 
NESHAP. However, the proposed amendments would improve the rule by 
codifying the existing practices to reduce emissions into enforceable 
requirements, ensuring that the standards apply at all times. Also, 
requiring electronic submittal of initial notifications, performance 
test results, and reports will increase the usefulness of the data and 
ultimately result in less burden on the regulated community. Because 
these proposed amendments are not considered economically significant, 
as defined by Executive Order 12866, and because no emission reductions 
were estimated, we did not estimate any health benefits from reducing 
emissions.

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 website at https://www.epa.gov/stationary-sources-air-pollution/mercury-cell-chloralkali-plants-national-emissions-standards. 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-2020-0560 (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/mercury-cell-chloralkali-plants-national-emissions-standards.

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 Orders 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.

[[Page 1389]]

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 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 2046.10. You can find a copy of the ICR in the docket for this 
rule, and it is briefly summarized here.
    The information requirements in this rulemaking are based on the 
notification, recordkeeping, and reporting requirements in the NESHAP 
General Provisions (40 CFR part 63, subpart A), which are mandatory for 
all operators subject to national emission standards. These 
notifications, reports, and records are essential in determining 
compliance, and are specifically authorized by CAA section 114 (42 
U.S.C. 7414). All information submitted to the EPA pursuant to the 
recordkeeping and reporting requirements for which a claim of 
confidentiality is made is safeguarded according to Agency policies set 
forth in 40 CFR part 2, subpart B.
    The EPA is proposing amendments that revise provisions pertaining 
to emissions during periods of SSM; add requirements for electronic 
reporting of notifications and reports and performance test results; 
and make other minor clarifications and corrections. This information 
will be collected to assure compliance with the Mercury Cell Chlor-
Alkali Plants NESHAP.
    Respondents/affected entities: Owners or operators of mercury cell 
chlor-alkali facilities.
    Respondent's obligation to respond: Mandatory (42 U.S.C. 7414).
    Estimated number of respondents: One total for the source category. 
This facility is already a respondent and no new facilities are 
expected to become respondents as a result of this proposed action.
    Frequency of response: Initially, occasionally, and semi-annually.
    Total estimated burden: 3,567 total hours (per year) for the source 
category, of which 1,680 are estimated as a result of this action. 
Burden is defined at 5 CFR 1320.3(b).
    Total estimated cost: The total estimated cost of the rule is 
$428,000 (per year) for the source category, including $8,200 
annualized capital or operation and maintenance costs. We estimate that 
$0 of the $8,200 in total annualized capital or operation and 
maintenance costs is a result of this proposed action. Recordkeeping 
and reporting costs of $205,000 estimated as a result of this action 
are included in the $428,000 in total 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 OIRA_submissions@omb.eop.gov, 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. The parent 
company for the single affected facility in the source category is not 
a small entity given the Small Business Administration small business 
size definition for this industry (1,000 employees or greater for NAICS 
325180).

E. Unfunded Mandates Reform Act (UMRA)

    This action does not contain an unfunded mandate of $100 million or 
more 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. The mercury cell chlor-alkali plant affected by 
this proposed action is not owned or operated by tribal governments or 
located within tribal lands. Thus, Executive Order 13175 does not apply 
to this action.

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. As the proposed rule amendments would not change emissions of 
HAP and risk to anyone exposed, the EPA estimates that the proposed 
rule amendments would have no effect on risks to children. This 
action's health and risk assessments are contained in section IV.B of 
this preamble and the document, Residual Risk Assessment for the 
Mercury Cell Chlor-Alkali Plant Source Category in Support of the Risk 
and Technology Review 2020 Proposed Rule, which is available in the 
docket for this rulemaking.

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 significant regulatory action under Executive Order 12866.

J. National Technology Transfer and Advancement Act (NTTAA)

    This rulemaking does not change the existing technical standards in 
the rule.

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) 
because it does not change the level of environmental protection for 
any affected populations and does not have any disproportionately high 
and adverse human health or environmental effects on any population, 
including any

[[Page 1390]]

minority, low income, or indigenous populations.
    To gain a better understanding of the source category and near 
source populations, the EPA conducted a demographic analysis for 
mercury cell chlor-alkali facilities to identify any overrepresentation 
of minority, low income, or indigenous populations with cancer risks 
above 1-in-1 million. This analysis only gives some indication of the 
prevalence of sub-populations that may be exposed to air pollution from 
the sources; it does not identify the demographic characteristics of 
the most highly affected individuals or communities, nor does it 
quantify the level of risk faced by those individuals or communities. 
More information on the source category's risk can be found in section 
IV of this preamble. The complete demographic analysis results and the 
details concerning its development are presented in the technical 
report, Risk and Technology Review--Analysis of Demographic Factors for 
Populations Living Near Mercury Cell Chlor-Alkali Facilities, available 
in the docket for this action.

List of Subjects in 40 CFR Part 63

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

Andrew Wheeler,
Administrator.
[FR Doc. 2021-00174 Filed 1-7-21; 8:45 am]
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