1362 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

distribution of power and 

responsibilities among the various 

levels of government. 

G. Executive Order 13175: Coordination 

With Indian Tribal Governments 

This action does not have tribal 

implications, as specified in Executive 

Order 13175, because the SIP is not 

approved to apply on any Indian 

reservation land or in any other area 

where the EPA or an Indian tribe has 

demonstrated that a tribe has 

jurisdiction, and will not impose 

substantial direct costs on tribal 

governments or preempt tribal law. 

Thus, Executive Order 13175 does not 

apply to this action. 

H. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

The EPA interprets Executive Order 

13045 as applying only to those 

regulatory actions that concern 

environmental health or safety risks that 

the EPA has reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive order. This action is not 

subject to Executive Order 13045 

because it does not impose additional 

requirements beyond those imposed by 

state law. 

I. Executive Order 13211: Actions 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) 

Section 12(d) of the NTTAA directs 

the EPA to use voluntary consensus 

standards in its regulatory activities 

unless to do so would be inconsistent 

with applicable law or otherwise 

impractical. The EPA believes that this 

action is not subject to the requirements 

of section 12(d) of the NTTAA because 

application of those requirements would 

be inconsistent with the CAA. 

K. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

The EPA lacks the discretionary 

authority to address environmental 

justice in this rulemaking. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Particulate matter, Reporting and 

recordkeeping requirements. 

Authority: 42 U.S.C. 7401 et seq. 

Dated: December 23, 2020. 

John Busterud, 

Regional Administrator, Region IX. 

[FR Doc. 2020–29092 Filed 1–7–21; 8:45 am] 

BILLING CODE 6560–50–P 

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. 

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 ChlorAlkali 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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 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 inperson 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-plantsnational-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-airpollution/mercury-cell-chloralkaliplants-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 preregistered speakers in approximate 

order at: https://www.epa.gov/ 

stationary-sources-air-pollution/ 

mercury-cell-chloralkali-plantsnational-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-plantsnational-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 preregister 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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1364 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

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 DecisionMaking 

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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
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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 ChlorAlkali Plants regulated under 40 CFR 

part 63, subpart IIIII. The North 

American Industry Classification 

System (NAICS) code for the chloralkali 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 chloralkali 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-plantsnational-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-airpollution/mercury-cell-chloralkaliplants-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 


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1Although 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. 

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. 

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 twostep 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). 

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, KelChlor process, and sodium chloride/sulfuric 

acid process.2

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 chloralkali 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 nonoven 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. 


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3Ashta 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. 

4The 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 doseresponse value; the HI is the sum of HQs for HAP 

that affect the same target organ or organ system. 

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. 

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: 

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, 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1368 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

5Recommendations 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/EPASAB-10-007-unsigned.pdf. 

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

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 


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6U.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. 

7For more information about HEM–3, go to 

https://www.epa.gov/fera/risk-assessment-andmodeling-human-exposure-model-hem. 

8U.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). 

9A census block is the smallest geographic area 

for which census statistics are tabulated. 

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 ChlorAlkali 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. 

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 chloralkali 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 EarthTM. 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 MACTallowable 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 MACTallowable 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 fullcapacity 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. 

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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
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10The 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/214C6E915BB04

E14852570CA007A682C/$File/ecadv02001.pdf. 

11See, 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). 

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. 

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 (mg/m3)) 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 doseresponse 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 doseresponse 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-assessinghealth-risks-associated-exposurehazardous-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. 

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-hotspots-program-guidance-manualpreparation-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-responseassessment-assessing-health-risksassociated-exposure-hazardous-airpollutants. 

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: 


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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 categoryspecific 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. 

13CalEPA 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-acute8-hour-and-chronic-reference-exposure-level-relsummary. 

14National 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). 

15ERPGS Procedures and Responsibilities. March 

2014. American Industrial Hygiene Association. 

Available at: https://www.aiha.org/get-involved/ 

AIHAGuidelineFoundation/EmergencyResponse

PlanningGuidelines/Documents/ 

ERPG%20Committee%20Standard

%20Operating%20Procedures%20%20-%20March

%202014%20Revision%20%28Updated%2010-2- 

2014%29.pdf. 

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. 

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 worstcase air dispersion conditions co-occur 

and that a person is present at the point 

of maximum exposure. 

To characterize the potential health 

risks associated with estimated acute 

inhalation exposures to a HAP, we 

generally use multiple acute doseresponse 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/m3 (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. 

ERPGs are ‘‘developed for emergency 

planning and are intended as healthbased 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. 

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-andmodeling-air-toxics-risk-assessmentreference-library). 

For the Mercury Cell Chlor-Alkali 

Plant source category, mercury 

emissions were the only PB–HAP 

emitted by the source category, so we 


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16Burger, J. 2002. Daily consumption of wild fish 

and game: Exposures of high end recreationists. 

International Journal of Environmental Health 

Research, 12:343–354. 

17U.S. EPA. Exposure Factors Handbook 2011 

Edition (Final). U.S. Environmental Protection 

Agency, Washington, DC, EPA/600/R–09/052F, 

2011. 

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 upperbound 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. 

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 sitespecific 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 waterVerDate Sep<11>2014 20:05 Jan 07, 2021 Jkt 253001 PO 00000 Frm 00070 Fmt 4702 Sfmt 4702 E:\FR\FM\08JAP1.SGM 08JAP1

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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-adverseeffect level, and no-observed-adverseeffect 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 backcalculate 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 wellbeing.’’ 

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 singletier 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 areaweighted 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 


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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 facilitywide 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 ChlorAlkali 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 facilitywide analyses, including all facilitywide 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 ChlorAlkali 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 


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18 IRIS glossary (https://ofmpub.epa.gov/sor_

internet/registry/termreg/searchandretrieve/ 

glossariesandkeywordlists/search.do?details=&

glossaryName=IRIS%20Glossary). 

19An 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. 

20See 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. 

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. 

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. 

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) cooccur. 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


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22The 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. 

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 hourby-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 chloralkali 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 chloralkali plant. As a result, we are only 

required to propose standards for 

chlorine emissions pursuant to CAA 

section 112(d)(2) and (3). 

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. 


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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 chloralkali 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 


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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 Beyondthe-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-thefloor 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 costeffectiveness 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 beyondVerDate Sep<11>2014 20:05 Jan 07, 2021 Jkt 253001 PO 00000 Frm 00076 Fmt 4702 Sfmt 4702 E:\FR\FM\08JAP1.SGM 08JAP1

tkelley on DSKBCP9HB2PROD with PROPOSALS
Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 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

Risk assessment Number of 

facilities 2

Maximum 

individual 

cancer risk 

(1-in-1 million) 3

Estimated 

population 

at increased 

risk of cancer 

≥ 1-in-1 million 

Estimated 

annual 

cancer 

incidence 

(cases per 

year) 

Maximum 

chronic 

noncancer 

TOSHI 4

Maximum 

screening 

acute 

noncancer HQ 5

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)

1Based 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. 

5The 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. 


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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. 

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 healthprotective 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 ChlorAlkali 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

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 


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well below 1 (0.0007). This information, 

in addition to the conservative (healthprotective) 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. 


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24Memorandum. 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. 

25PPG 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-atNatrium-Plant.aspx?Page=1&p=1. 

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 nonmercury 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-thefloor MACT determination under CAA 

section 112(d)(2) for existing source 

mercury emissions, as discussed above. 

For this proposal, the EPA reexamined 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

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 


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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 zeromercury 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. 


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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 datagathering 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 ‘‘§ 63.6(a)–(g), (i), 

(j)’’ to ‘‘§ 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 ‘‘§ 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 


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Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 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 ‘‘§ 63.7(a)(1), 

(b)–(h)’’ to ‘‘§ 63.7(a)–(h), except for 

(a)(2) and (e)(1)’’ and to add a new entry 

for ‘‘§ 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 crossreference 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 ‘‘§ 63.8(a)(1), (a)(3); 

(b); (c)(1)–(4), (6)–(8); (d); (e); and (f)(1)– 

(5)’’ to ‘‘§ 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 

‘‘§ 63.8(c)(1)(i) and (iii)’’ and 

‘‘§ 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 ‘‘§ 63.10(a); (b)(1); 

(b)(2)(i)–(xii), (xiv); (b)(3); (c); (d)(1)–(2), 

(4)–(5); (e); (f)’’ to ‘‘§ 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 ‘‘§ 63.10(b)(2)(i)–(v),’’ 

‘‘§ 63.10(c)(15),’’ and ‘‘§ 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). 


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26https://www.epa.gov/electronic-reporting-airemissions/electronic-reporting-tool-ert. 

27EPA’s Final Plan for Periodic Retrospective 

Reviews, August 2011. Available at: https://

www.regulations.gov/document?D=EPA-HQ-OA/ 

2011/0156/0154. 

28E-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/digitalgovernment/digital-government.html. 

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. 

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 agencywide 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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 1387 

Hazardous Air Pollutants (NESHAP) 

Rules, referenced earlier in this section. 

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 mg/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 mg/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 chloralkali 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. 


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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-plantsnational-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®

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® Excel 

files that are generated by the 

Microsoft® Access file. These files are 

provided on the project website at 

https://www.epa.gov/stationary-sourcesair-pollution/mercury-cell-chloralkaliplants-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/lawsregulations/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. 


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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 chloralkali 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, lowincome 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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1390 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

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] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 63 

[EPA–HQ–OAR–2020–0535; FRL–10018–38– 

OAR] 

RIN 2060–AU65 

National Emission Standards for 

Hazardous Air Pollutants: Primary 

Magnesium Refining Residual Risk and 

Technology Review 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: This proposal presents the 

results of the U.S. Environmental 

Protection Agency’s (EPA’s) residual 

risk and technology review (RTR) for the 

National Emission Standards for the 

Hazardous Air Pollutants (NESHAP) for 

Primary Magnesium Refining, as 

required under the Clean Air Act (CAA). 

Based on the results of the risk review, 

the EPA is proposing that risks from 

emissions of air toxics from this source 

category are acceptable and that after 

removing the exemptions for startup, 

shutdown, and malfunction (SSM), the 

NESHAP provides an ample margin of 

safety. Furthermore, under the 

technology review, we are proposing 

one development in technology and 

practices that will require continuous 

pH monitoring for all control devices 

used to meet the acid gas emission 

limits of this subpart. In addition, as 

part of the technology review, the EPA 

is addressing a previously unregulated 

source of chlorine emissions, known as 

the chlorine bypass stack (CBS), by 

proposing a maximum achievable 

control technology (MACT) emissions 

standard for chlorine emissions from 

this source. The EPA also is proposing 

amendments to the regulatory 

provisions related to emissions during 

periods of SSM, including removing 

exemptions for periods of SSM and 

adding a work practice standard for 

malfunction events associated with the 

chlorine reduction burner (CRB); all 

emission limits will apply at all other 

times. In addition, the EPA is proposing 

electronic reporting of performance test 

results and performance evaluation 

reports. 

DATES: Comments. Comments must be 

received on or before February 22, 2021. 

Under the Paperwork Reduction Act 

(PRA), comments on the information 

collection provisions are best assured of 

consideration if the Office of 

Management and Budget (OMB) 

receives a copy of your comments on or 

before February 8, 2021. 

Public hearing: If anyone contacts us 

requesting a public hearing on or before 

January 13, 2021, we will hold a virtual 

public hearing. See SUPPLEMENTARY

INFORMATION for information on 

requesting and registering for a public 

hearing. 

ADDRESSES: You may send comments, 

identified by Docket ID No. EPA–HQ– 

OAR–2020–0535, by any of the 

following methods: 

• Federal eRulemaking Portal: 

https://www.regulations.gov/ (our 

preferred method). Follow the online 

instructions for submitting comments. 

• Email: a-and-r-docket@epa.gov. 

Include Docket ID No. EPA–HQ–OAR– 

2020–0535 in the subject line of the 

message. 

• Fax: (202) 566–9744. Attention 

Docket ID No. EPA–HQ–OAR–2020– 

0535. 

• Mail: U.S. Environmental 

Protection Agency, EPA Docket Center, 

Docket ID No. EPA–HQ–OAR–2020– 

0535, Mail Code 28221T, 1200 

Pennsylvania Avenue NW, Washington, 

DC 20460. 

• Hand/Courier Delivery: EPA Docket 

Center, WJC West Building, Room 3334, 

1301 Constitution Avenue NW, 

Washington, DC 20004. The Docket 

Center’s hours of operation are 8:30 

a.m.–4:30 p.m., Monday–Friday (except 

federal holidays). 

Instructions: All submissions received 

must include the Docket ID No. for this 

rulemaking. Comments received may be 

posted without change to https://

www.regulations.gov/, including any 

personal information provided. For 

detailed instructions on sending 

comments and additional information 

on the rulemaking process, see the 

SUPPLEMENTARY INFORMATION section of 

this document. Out of an abundance of 

caution for members of the public and 

our staff, the EPA Docket Center and 

Reading Room are closed to the public, 

with limited exceptions, to reduce the 

risk of transmitting COVID–19. Our 

Docket Center staff will continue to 

provide remote customer service via 

email, phone, and webform. We 

encourage the public to submit 

comments via https://

www.regulations.gov/ or email, as there 

may be a delay in processing mail and 

faxes. Hand deliveries and couriers may 

be received by scheduled appointment 

only. For further information on EPA 

Docket Center services and the current 

status, please visit us online at https:// 

www.epa.gov/dockets. 

FOR FURTHER INFORMATION CONTACT: For 

questions about this proposed action, 

contact Michael Moeller, Sector Policies 

and Programs Division, Office of Air 

Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, North Carolina 

27711; telephone number: (919) 541– 

2766; fax number: (919) 541–4991 and 

email address: moeller.michael@

epa.gov. For specific information 

regarding the risk modeling 

methodology, contact Jim Hirtz, Health 

and Environmental Impacts Division 

(C539–02), Office of Air Quality 

Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, North Carolina 

27711; telephone number: (919) 541– 

0881; fax number: (919) 541–0840; and 

email address: hirtz.james@epa.gov. 

SUPPLEMENTARY INFORMATION: 

Participation in virtual public hearing. 

Please note that the EPA is deviating 

from its typical approach for public 

hearings because the President has 

declared a national emergency. Due to 

the current Centers for Disease Control 

and Prevention (CDC) 

recommendations, as well as state and 


tkelley on DSKBCP9HB2PROD with PROPOSALS