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 


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local orders for social distancing to limit 

the spread of COVID–19, the EPA 

cannot hold in-person public meetings 

at this time. 

To request a virtual public hearing, 

contact the public hearing team at (888) 

372–8699 or by email at 

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 at https://www.epa.gov/ 

stationary-sources-air-pollution/ 

primary-magnesium-refining-nationalemissions-standards-hazardous/. 

The EPA will begin pre-registering 

speakers for the hearing upon 

publication of this document in the 

Federal Register, if a hearing is 

requested. To register to speak at the 

virtual hearing, please use the online 

registration form available at https://

www.epa.gov/stationary-sources-airpollution/primary-magnesium-refiningnational-emissions-standardshazardous/ 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/ 

stationary-sources-air-pollution/ 

primary-magnesium-refining-nationalemissions-standards-hazardous/. 

The EPA will make every effort to 

follow the schedule as closely as 

possible on the day of the hearing; 

however, please plan for the hearings to 

run either ahead of schedule or behind 

schedule. 

Each commenter will have 5 minutes 

to provide oral testimony. The EPA 

encourages commenters to provide the 

EPA with a copy of their oral testimony 

electronically (via email) by emailing it 

to Michael Moeller, email address: 

moeller.michael@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 will be posted 

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

stationary-sources-air-pollution/ 

stationary-sources-air-pollution/ 

primary-magnesium-refining-nationalemissions-standards-hazardous/. While 

the EPA expects the hearing to go 

forward as set forth above, please 

monitor our website or contact our 

public hearing team at (888) 372–8699 

or by email at 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 at the phone number or 

website provided above and describe 

your needs by January 15, 2021. The 

EPA may not be able to arrange 

accommodations without advanced 

notice. 

Docket. The EPA has established a 

docket for this rulemaking under Docket 

ID No. EPA–HQ–OAR–2020–0535. All 

documents in the docket are listed in 

https://www.regulations.gov/. Although 

listed, some information is not publicly 

available, e.g., Confidential Business 

Information (CBI) or other information 

whose disclosure is restricted by statute. 

Certain other material, such as 

copyrighted material, is not placed on 

the internet and will be publicly 

available only in hard copy. With the 

exception of such material, publicly 

available docket materials are available 

electronically in Regulations.gov. 

Instructions. Direct your comments to 

Docket ID No. EPA–HQ–OAR–2020– 

0535. The EPA’s policy is that all 

comments received will be included in 

the public docket without change and 

may be made available online at https:// 

www.regulations.gov/, including any 

personal information provided, unless 

the comment includes information 

claimed to be CBI or other information 

whose disclosure is restricted by statute. 

Do not submit electronically any 

information that you consider to be CBI 

or other information whose disclosure is 

restricted by statute. This type of 

information should be submitted by 

mail as discussed below. 

The EPA may publish any comment 

received to its public docket. 

Multimedia submissions (audio, video, 

etc.) must be accompanied by a written 

comment. The written comment is 

considered the official comment and 

should include discussion of all points 

you wish to make. The EPA will 

generally not consider comments or 

comment contents located outside of the 

primary submission (i.e., on the web, 

cloud, or other file sharing system). For 

additional submission methods, the full 

EPA public comment policy, 

information about CBI or multimedia 

submissions, and general guidance on 

making effective comments, please visit 

https://www.epa.gov/dockets/ 

commenting-epa-dockets. 

The https://www.regulations.gov/ 

website allows you to submit your 

comment anonymously, which means 

the EPA will not know your identity or 

contact information unless you provide 

it in the body of your comment. If you 

send an email comment directly to the 

EPA without going through https://

www.regulations.gov/, your email 

address will be automatically captured 

and included as part of the comment 

that is placed in the public docket and 

made available on the internet. If you 

submit an electronic comment, the EPA 

recommends that you include your 

name and other contact information in 

the body of your comment and with any 

digital storage media you submit. If the 

EPA cannot read your comment due to 

technical difficulties and cannot contact 

you for clarification, the EPA may not 

be able to consider your comment. 

Electronic files should not include 

special characters or any form of 

encryption and be free of any defects or 

viruses. For additional information 

about the EPA’s public docket, visit the 

EPA Docket Center homepage at https:// 

www.epa.gov/dockets. 

The EPA is temporarily suspending 

its Docket Center and Reading Room for 

public visitors, with limited exceptions, 

to reduce the risk of transmitting 

COVID–19. Our Docket Center staff will 

continue to provide remote customer 

service via email, phone, and webform. 

We encourage the public to submit 

comments via https://

www.regulations.gov/ as there may be a 

delay in processing mail and faxes. 

Hand deliveries or couriers will be 

received by scheduled appointment 

only. For further information and 

updates on EPA Docket Center services, 

please visit us online at https://

www.epa.gov/dockets. 

The EPA continues to carefully and 

continuously monitor information from 

the CDC, local area health departments, 

and our Federal partners so that we can 

respond rapidly as conditions change 

regarding COVID–19. 

Submitting CBI. Do not submit 

information containing CBI to the EPA 

through https://www.regulations.gov/ or 

email. Clearly mark the part or all of the 

information that you claim to be CBI. 

For CBI information on any digital 

storage media that you mail to the EPA, 

mark the outside of the digital storage 


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media as CBI and then identify 

electronically within the digital storage 

media the specific information that is 

claimed as CBI. In addition to one 

complete version of the comments that 

includes information claimed as CBI, 

you must submit a copy of the 

comments that does not contain the 

information claimed as CBI directly to 

the public docket through the 

procedures outlined in Instructions 

above. If you submit any digital storage 

media that does not contain CBI, mark 

the outside of the digital storage media 

clearly that it does not contain CBI. 

Information not marked as CBI will be 

included in the public docket and the 

EPA’s electronic public docket without 

prior notice. Information marked as CBI 

will not be disclosed except in 

accordance with procedures set forth in 

40 Code of Federal Regulations (CFR) 

part 2. Send or deliver information 

identified as CBI only to the following 

address: OAQPS Document Control 

Officer (C404–02), OAQPS, U.S. 

Environmental Protection Agency, 

Research Triangle Park, North Carolina 

27711, Attention Docket ID No. EPA– 

HQ–OAR–2020–0535. Note that written 

comments containing CBI and 

submitted by mail may be delayed and 

no hand deliveries will be accepted. 

Preamble acronyms and 

abbreviations. We use multiple 

acronyms and terms in this preamble. 

While this list may not be exhaustive, to 

ease the reading of this preamble and for 

reference purposes, the EPA defines the 

following terms and acronyms here: 

AEGL acute exposure guideline level 

AERMOD air dispersion model used by the 

HEM–3 model 

CAA Clean Air Act 

CalEPA California EPA 

CBI Confidential Business Information 

CBS chlorine bypass stack 

CDC Centers for Disease Control and 

Prevention 

CDX Central Data Exchange 

CEDRI Compliance and Emissions Data 

Reporting Interface 

CFR Code of Federal Regulations 

CPMS continuous parameter monitoring 

system 

CRB chlorine reduction burner 

EPA Environmental Protection Agency 

ERPG emergency response planning 

guideline 

ERT Electronic Reporting Tool 

HAP hazardous air pollutant(s) 

HCl hydrochloric acid 

HEM–3 Human Exposure Model, Version 

1.5.5 

HF hydrogen fluoride 

HI hazard index 

HQ hazard quotient 

IRIS Integrated Risk Information System 

km kilometer 

LOAEL lowest-observed-adverse-effectlevel 

MACT maximum achievable control 

technology 

mg/m3 milligrams per cubic meter 

MIR maximum individual risk 

NAAQS National Ambient Air Quality 

Standards 

NAICS North American Industry 

Classification System 

NESHAP national emission standards for 

hazardous air pollutants 

NOAEL no-observed-adverse-effect-level 

OAQPS Office of Air Quality Planning and 

Standards 

OMB Office of Management and Budget 

PAH polycyclic aromatic hydrocarbons 

PB–HAP hazardous air pollutants known to 

be persistent and bio-accumulative in the 

environment 

PM particulate matter 

POM polycyclic organic matter 

ppm parts per million 

REL reference exposure level 

RfC reference concentration 

RfD reference dose 

RTR residual risk and technology review 

SAB Science Advisory Board 

SSM startup, shutdown, and malfunction 

TOSHI target organ-specific hazard index 

tpy tons per year 

TRIM.FaTE Total Risk Integrated 

Methodology.Fate, Transport, and 

Ecological Exposure model 

UF uncertainty factor 

mg/m3 microgram per cubic meter 

URE unit risk estimate 

VCS voluntary consensus standards 

Organization of this document. The 

information in this preamble is 

organized as follows: 

I. General Information 

A. Does this action apply to me? 

B. Where can I get a copy of this document 

and other related information? 

II. Background 

A. What is the statutory authority for this 

action? 

B. What is this source category and how 

does the current NESHAP regulate its 

HAP emissions? 

C. What data collection activities were 

conducted to support this action? 

D. What other relevant background 

information and data are available? 

III. Analytical Procedures and 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 

C. Paperwork Reduction Act (PRA) 

D. Regulatory Flexibility Act (RFA) 

E. Unfunded Mandates Reform Act 

(UMRA) 

F. Executive Order 13132: Federalism 

G. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

H. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

I. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

J. National Technology Transfer and 

Advancement Act (NTTAA) and 1 CFR 

Part 51 

K. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

I. General Information 

A. Does this action apply to me? 

The source category that is the subject 

of this proposal is the Primary 

Magnesium Refining major sources 

regulated under 40 CFR part 63, subpart 

TTTTT. The North American Industry 

Classification System (NAICS) code for 

the primary magnesium refining 

industry is 331410. This category and 

NAICS code are not intended to be 

exhaustive, but rather provide a guide 

for readers regarding the entities that 

this proposed action is likely to affect. 

The proposed standards, once 

promulgated, will be directly applicable 

to the affected sources. Federal, state, 

local, and tribal government entities 

would not be affected by this proposed 

action. As defined in the Initial List of 

Categories of Sources Under Section 

112(c)(1) of the Clean Air Act 

Amendments of 1990 (see 57 FR 31576, 

July 16, 1992) and Documentation for 

Developing the Initial Source Category 

List, Final Report (see EPA–450/3–91– 

030, July 1992), the Primary Magnesium 

Refining source category is any facility 

engaged in producing metallic 

magnesium. The source category 


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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. 

includes, but is not limited to, metallic 

magnesium produced using the Dow 

sea-water process or the Pidgeon 

process. The Dow sea-water process 

involves the electrolysis of molten 

magnesium chloride. The Pidgeon 

process involves the thermal reduction 

of magnesium oxide with ferrosilicon. 

B. Where can I get a copy of this 

document and other related 

information? 

In addition to being available in the 

docket, an electronic copy of this action 

is available on the internet. Following 

signature by the EPA Administrator, the 

EPA will post a copy of this proposed 

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

stationary-sources-air-pollution/ 

primary-magnesium-refining-nationalemissions-standards-hazardous/. 

Following publication in the Federal 

Register, the EPA will post the Federal 

Register version of the proposal and key 

technical documents at this same 

website. Information on the overall RTR 

program is available at https://

www.epa.gov/ttn/atw/rrisk/rtrpg.html. 

The proposed changes to the CFR that 

would be necessary to incorporate the 

changes proposed in this action are set 

out in an attachment to the 

memorandum titled Proposed 

Regulation Edits for 40 CFR part 63, 

subpart TTTTT, available in the docket 

for this action (Docket ID No. EPA–HQ– 

OAR–2020–0535). The document 

includes the specific proposed 

amendatory language for revising the 

CFR and, for the convenience of 

interested parties, a redline version of 

the regulation. Following signature by 

the EPA Administrator, the EPA will 

also post a copy of this memorandum 

and the attachments to https://

www.epa.gov/stationary-sources-airpollution/primary-magnesium-refiningnational-emissions-standardshazardous/. 

II. Background 

A. What is the statutory authority for 

this action? 

The statutory authority for this action 

is provided by sections 112 and 301 of 

the CAA, as amended (42 U.S.C. 7401 et 

seq.). Section 112 of the CAA 

establishes a two-stage regulatory 

process to develop standards for 

emissions of hazardous air pollutants 

(HAP) from stationary sources. 

Generally, the first stage involves 

establishing technology-based standards 

and the second stage involves 

evaluating those standards that are 

based on MACT to determine whether 

additional standards are needed to 

address any remaining risk associated 

with HAP emissions. This second stage 

is commonly referred to as the ‘‘residual 

risk review.’’ In addition to the residual 

risk review, the CAA also requires the 

EPA to review standards set under CAA 

section 112 every 8 years and revise the 

standards as necessary taking into 

account any ‘‘developments in 

practices, processes, or control 

technologies.’’ This review is commonly 

referred to as the ‘‘technology review.’’ 

When the two reviews are combined 

into a single rulemaking, it is commonly 

referred to as the ‘‘risk and technology 

review.’’ The discussion that follows 

identifies the most relevant statutory 

sections and briefly explains the 

contours of the methodology used to 

implement these statutory requirements. 

A more comprehensive discussion 

appears in the document titled CAA 

Section 112 Risk and Technology 

Reviews: Statutory Authority and 

Methodology, in the docket for this 

rulemaking. 

In the first stage of the CAA section 

112 standard setting process, the EPA 

promulgates technology-based standards 

under CAA section 112(d) for categories 

of sources identified as emitting one or 

more of the HAP listed in CAA section 

112(b). Sources of HAP emissions are 

either major sources or area sources, and 

CAA section 112 establishes different 

requirements for major source standards 

and area source standards. ‘‘Major 

sources’’ are those that emit or have the 

potential to emit 10 tons per year (tpy) 

or more of a single HAP or 25 tpy or 

more of any combination of HAP. All 

other sources are ‘‘area sources.’’ For 

major sources, CAA section 112(d)(2) 

provides that the technology-based 

NESHAP must reflect the maximum 

degree of emission reductions of HAP 

achievable (after considering cost, 

energy requirements, and non-air 

quality health and environmental 

impacts). These standards are 

commonly referred to as MACT 

standards. CAA section 112(d)(3) also 

establishes a minimum control level for 

MACT standards, known as the MACT 

‘‘floor.’’ In certain instances, as 

provided in CAA section 112(h), the 

EPA may set work practice standards in 

lieu of numerical emission standards. 

The EPA must also consider control 

options that are more stringent than the 

floor. Standards more stringent than the 

floor are commonly referred to as 

beyond-the-floor standards. For area 

sources, CAA section 112(d)(5) gives the 

EPA discretion to set standards based on 

generally available control technologies 

or management practices (GACT 

standards) in lieu of MACT standards. 

The second stage in standard-setting 

focuses on identifying and addressing 

any remaining (i.e., ‘‘residual’’) risk 

pursuant to CAA section 112(f). For 

source categories subject to MACT 

standards, section 112(f)(2) of the CAA 

requires the EPA to determine whether 

promulgation of additional standards is 

needed to provide an ample margin of 

safety to protect public health or to 

prevent an adverse environmental 

effect. Section 112(d)(5) of the CAA 

provides that this residual risk review is 

not required for categories of area 

sources subject to GACT standards. 

Section 112(f)(2)(B) of the CAA further 

expressly preserves the EPA’s use of the 

two-step approach for developing 

standards to address any residual risk 

and the Agency’s interpretation of 

‘‘ample margin of safety’’ developed in 

the National Emissions Standards for 

Hazardous Air Pollutants: Benzene 

Emissions from Maleic Anhydride 

Plants, Ethylbenzene/Styrene Plants, 

Benzene Storage Vessels, Benzene 

Equipment Leaks, and Coke By-Product 

Recovery Plants (Benzene NESHAP) (54 

FR 38044, September 14, 1989). The 

EPA notified Congress in the Residual 

Risk Report that the Agency intended to 

use the Benzene NESHAP approach in 

making CAA section 112(f) residual risk 

determinations (EPA–453/R–99–001, p. 

ES–11). The EPA subsequently adopted 

this approach in its residual risk 

determinations and the United States 

Court of Appeals for the District of 

Columbia Circuit (the Court) upheld the 

EPA’s interpretation that CAA section 

112(f)(2) incorporates the approach 

established in the Benzene NESHAP. 

See NRDC v. EPA, 529 F.3d 1077, 1083 

(D.C. Cir. 2008). 

The approach incorporated into the 

CAA and used by the EPA to evaluate 

residual risk and to develop standards 

under CAA section 112(f)(2) is a 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, 


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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. 

CAA section 112(d)(6) separately 

requires the EPA to review standards 

promulgated under CAA section 112 

and revise them ‘‘as necessary (taking 

into account developments in practices, 

processes, and control technologies)’’ no 

less often than every 8 years. In 

conducting this review, which we call 

the ‘‘technology review,’’ the EPA is not 

required to recalculate the MACT floor. 

Natural Resources Defense Council 

(NRDC) v. EPA, 529 F.3d 1077, 1084 

(D.C. Cir. 2008). Association of Battery 

Recyclers, Inc. v. EPA, 716 F.3d 667 

(D.C. Cir. 2013). The EPA may consider 

cost in deciding whether to revise the 

standards pursuant to CAA section 

112(d)(6). The EPA is required to 

address regulatory gaps, such as missing 

standards for listed air toxics known to 

be emitted from the source category. 

Louisiana Environmental Action 

Network (LEAN) v. EPA, 955 F.3d 1088 

(D.C. Cir. 2020). 

B. What is this source category and how 

does the current NESHAP regulate its 

HAP emissions? 

The EPA initially promulgated the 

Primary Magnesium Refining NESHAP 

on October 10, 2003 (68 FR 58615), and 

it is codified at 40 CFR part 63, subpart 

TTTTT. This NESHAP regulates HAP 

emissions from new and existing 

primary magnesium refining facilities 

that are major sources of HAP. The 

source category is comprised of one 

plant that is owned by US Magnesium 

LLC and located in Rowley, Utah. 

The plant produces magnesium from 

brine (salt water) taken from the Great 

Salt Lake. The production process 

concentrates the magnesium salts in the 

brine, then processes the brine to 

remove impurities that would affect 

metal quality. After the brine solution is 

converted to a powder mixture of 

magnesium chloride and magnesium 

oxide in the spray dryers, the powder is 

conveyed to the melt/reactors. The melt/ 

reactor melts the powder mixture and 

converts the remaining magnesium 

oxide to magnesium chloride by 

injecting chlorine into the molten salt. 

The purified molten salt is then 

transferred to the electrolytic cells 

where it is separated into magnesium 

metal and chlorine by electrolysis. The 

electrolysis process passes a direct 

electric current through the molten 

magnesium chloride, causing the 

dissociation of the salt and resulting in 

the generation of chlorine gas and 

magnesium metal. The magnesium 

metal is then transferred to the foundry 

for casting into ingots for sale. The 

chlorine produced is piped to a chlorine 

plant where it is liquefied for reuse or 

sale. 

The HAP emitted from the Primary 

Magnesium Refining source category are 

chlorine, hydrochloric acid (HCl), 

dioxin/furan, and trace amounts of HAP 

metals. Emission controls include 

various combinations of wet scrubbers 

(venturi and packed-bed scrubber) for 

acid gas and particulate matter (PM) 

control. 

Chlorine is emitted from the melting 

and purification of reactor cell product 

and is controlled by conversion to HCl 

in the CRB and subsequent absorption 

of the HCl in venturi and packed-bed 

scrubber. Using these control 

technologies, upwards of 99.9 percent 

control of chlorine is achieved. The 

electrowinning of the melted 

magnesium chloride to magnesium 

metal produces as a byproduct chlorine 

gas which is recovered at the chlorine 

plant. When the chlorine plant is 

inoperable, the chlorine produced at the 

electrolytic cells is routed through the 

CBS which contains a packed-bed 

scrubber and uses ferrous chloride as 

the adsorbing medium. 

HCl is emitted from the spray drying 

and storage of magnesium chloride 

powder and the melting and 

purification of reactor cell product prior 

to the electrowinning process. HCl 

emissions are controlled by venturi and 

packed-bed scrubbers. 

Dioxins/furans are generated in the 

melt/reactor and are subject to 

incidental control by the wet scrubbers 

used to control chlorine, HCl, and PM. 

The current rule requires compliance 

with emission limits, operating limits 

for control devices, and work practice 

standards. The emission limits include 

mass rate emission limits in pounds per 

hour (lbs/hr) for chlorine, HCl, PM, and 

particulate matter less than or equal to 

10 microns (PM10). Additional emission 

limits in grains per dry standard cubic 

foot (gr/dscf) apply to magnesium 

chloride storage bins. The emission 

limits are shown in Table 1 of this 

preamble. 

TABLE 1—MASS RATE EMISSION LIMITS

[LBS/HR] 

Emission point Chlorine HCl PM PM10

Spray dryers .................................................................................................... ........................ 200 100 ........................

Magnesium chloride storage bins 1 .................................................................. ........................ 47.5 ........................ 2.7 

Melt/reactor system ......................................................................................... 100 7.2 ........................ 13.1 

Launder off-gas system ................................................................................... 26.0 46.0 37.5 

1Additional limits are 0.35 gr/dscf of HCl and 0.016 gr/dscf of PM10. 

The current rule also includes an 

emission limit for each melt/reactor 

system of 36 nanograms of dioxin/furan 

toxicity equivalents per dry standard 

cubic meter corrected to 7 percent 

oxygen. 

Performance tests are required to 

demonstrate compliance with the 

emission limits and must be conducted 

at least twice during each title V 

operating permit term (at midterm and 

renewal). The source is also required to 

monitor operating parameters for 

control devices subject to operating 

limits established during the 

performance tests and carry out the 

procedures in their fugitive dust 

emissions control plan and their 

operation and maintenance plan. For 

wet scrubbers, the source is required to 

use continuous parameter monitoring 

systems (CPMS) to measure and record 

the hourly average pressure drop and 

scrubber water flow rate. To 


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2The 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. 

demonstrate continuous compliance, 

the source must keep records 

documenting conformance with the 

monitoring requirements and the 

installation, operation, and maintenance 

requirements for CPMS. 

C. What data collection activities were 

conducted to support this action? 

For the Primary Magnesium Refining 

source category, the EPA used emissions 

and supporting data from the 2017 

National Emissions Inventory (NEI) as 

the primary data to develop the model 

input file for the residual risk 

assessment. The NEI is a database that 

contains information about sources that 

emit criteria air pollutants, their 

precursors, and HAP. The database 

includes estimates of annual air 

pollutant emissions from point, 

nonpoint, and mobile sources in the 50 

states, the District of Columbia, Puerto 

Rico, and the U.S. Virgin Islands. The 

EPA collects this information and 

releases an updated version of the NEI 

database every 3 years. The NEI 

includes data necessary for conducting 

risk modeling, including annual HAP 

emissions estimates from individual 

emission sources at facilities and the 

related emissions release parameters. 

Additional information on the 

development of the modeling file can be 

found in Appendix 1 to the Residual 

Risk Assessment for the Primary 

Magnesium Refining Source Category in 

Support of the 2020 Risk and 

Technology Review Proposed Rule, 

which is available in the docket for this 

proposed rule. 

D. What other relevant background 

information and data are available? 

Information used to estimate 

emissions from the primary magnesium 

refining facility was obtained primarily 

from the EPA’s 2017 NEI database, 

available at: https://www.epa.gov/airemissions-inventories/2017-nationalemissions-inventory-nei-data. 

Supplemental information was used 

from publicly available documents from 

the Utah Department of Environmental 

Quality (http://eqedocs.utah.gov/) and 

the EPA Region 8 Superfund Remedial 

Investigation (https://cumulis.epa.gov/ 

supercpad/cursites/csitinfo.cfm?id=

0802704). Data on the numbers, types, 

dimensions, and locations of the 

emission points for the facility were 

obtained from the NEI, Google EarthTM, 

and US Magnesium facility 

representatives. The HAP emissions 

from US Magnesium were categorized 

by source into one of the four emission 

process groups as follows: Spray dryers, 

magnesium chloride storage bins, melt/ 

reactor system, and the CBS. Data on 

HAP emissions, including the HAP 

emitted, emission source, emission 

rates, stack parameters (such as 

temperature, velocity, flowrate, etc.), 

and latitude and longitude were 

compiled into a draft modeling file. To 

ensure the quality of the emissions data, 

the EPA subjected the draft modeling 

file to a variety of quality checks. The 

draft modeling file was made available 

to the facility to review the emission 

release parameters and the emission 

rates. Source latitudes and longitudes 

were checked in Google EarthTM to 

verify accuracy and were corrected as 

needed. These and other quality control 

efforts resulted in a more accurate 

emissions dataset. Additional 

information on the development of the 

modeling file can be found in Appendix 

1 to the Residual Risk Assessment for 

the Primary Magnesium Refining Source 

Category in Support of the 2020 Risk 

and Technology Review Proposed Rule, 

which is available in the docket for this 

proposed rule. 

III. Analytical Procedures and 

Decision-Making 

In this section, we describe the 

analyses performed to support the 

proposed decisions for the RTR and 

other issues addressed in this proposal. 

A. How do we consider risk in our 

decision-making? 

As discussed in section II.A of this 

preamble and in the Benzene NESHAP, 

in evaluating and developing standards 

under CAA section 112(f)(2), we apply 

a two-step approach to determine 

whether or not risks are acceptable and 

to determine if the standards provide an 

ample margin of safety to protect public 

health. As explained in the Benzene 

NESHAP, ‘‘the first step judgment on 

acceptability cannot be reduced to any 

single factor’’ and, thus, ‘‘[t]he 

Administrator believes that the 

acceptability of risk under section 112 is 

best judged on the basis of a broad set 

of health risk measures and 

information.’’ (54 FR 38046). Similarly, 

with regard to the ample margin of 

safety determination, ‘‘the Agency again 

considers all of the health risk and other 

health information considered in the 

first step. Beyond that information, 

additional factors relating to the 

appropriate level of control will also be 

considered, including cost and 

economic impacts of controls, 

technological feasibility, uncertainties, 

and any other relevant factors.’’ Id. 

The Benzene NESHAP approach 

provides flexibility regarding factors the 

EPA may consider in making 

determinations and how the EPA may 

weigh those factors for each source 

category. The EPA conducts a risk 

assessment that provides estimates of 

the MIR posed by emissions of HAP that 

are carcinogens from each source in the 

source category, the hazard index (HI) 

for chronic exposures to HAP with the 

potential to cause noncancer health 

effects, and the hazard quotient (HQ) for 

acute exposures to HAP with the 

potential to cause noncancer health 

effects.2 The assessment also provides 

estimates of the distribution of cancer 

risk within the exposed populations, 

cancer incidence, and an evaluation of 

the potential for an adverse 

environmental effect. The scope of the 

EPA’s risk analysis is consistent with 

the explanation in EPA’s response to 

comments on our policy under the 

Benzene NESHAP: 

The policy chosen by the Administrator 

permits consideration of multiple measures 

of health risk. Not only can the MIR figure 

be considered, but also incidence, the 

presence of non-cancer health effects, and the 

uncertainties of the risk estimates. In this 

way, the effect on the most exposed 

individuals can be reviewed as well as the 

impact on the general public. These factors 

can then be weighed in each individual case. 

This approach complies with the Vinyl 

Chloride mandate that the Administrator 

ascertain an acceptable level of risk to the 

public by employing his expertise to assess 

available data. It also complies with the 

Congressional intent behind the CAA, which 

did not exclude the use of any particular 

measure of public health risk from the EPA’s 

consideration with respect to CAA section 

112 regulations, and thereby implicitly 

permits consideration of any and all 

measures of health risk which the 

Administrator, in his judgment, believes are 

appropriate to determining what will 

‘‘protect the public health’’. 

(54 FR 38057). Thus, the level of the 

MIR is only one factor to be weighed in 

determining acceptability of risk. The 

Benzene NESHAP explained that ‘‘an 

MIR of approximately one in 10 

thousand should ordinarily be the upper 

end of the range of acceptability. As 

risks increase above this benchmark, 

they become presumptively less 

acceptable under CAA section 112, and 

would be weighed with the other health 

risk measures and information in 

making an overall judgment on 

acceptability. Or, the Agency may find, 

in a particular case, that a risk that 

includes an MIR less than the 

presumptively acceptable level is 

unacceptable in the light of other health 

risk factors.’’ Id. at 38045. In other 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1396 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

3Recommendations 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/4AB3966E263D943

A8525771F00668381/$File/EPA-SAB-10-007- 

unsigned.pdf. 

words, risks that include an MIR above 

100-in-1 million may be determined to 

be acceptable, and risks with an MIR 

below that level may be determined to 

be unacceptable, depending on all of the 

available health information. Similarly, 

with regard to the ample margin of 

safety analysis, the EPA stated in the 

Benzene NESHAP that: ‘‘EPA believes 

the relative weight of the many factors 

that can be considered in selecting an 

ample margin of safety can only be 

determined for each specific source 

category. This occurs mainly because 

technological and economic factors 

(along with the health-related factors) 

vary from source category to source 

category.’’ Id. at 38061. We also 

consider the uncertainties associated 

with the various risk analyses, as 

discussed earlier in this preamble, in 

our determinations of acceptability and 

ample margin of safety. 

The EPA notes that it has not 

considered certain health information to 

date in making residual risk 

determinations. At this time, we do not 

attempt to quantify the HAP risk that 

may be associated with emissions from 

other facilities that do not include the 

source category under review, mobile 

source emissions, natural source 

emissions, persistent environmental 

pollution, or atmospheric 

transformation in the vicinity of the 

sources in the category. 

The EPA understands the potential 

importance of considering an 

individual’s total exposure to HAP in 

addition to considering exposure to 

HAP emissions from the source category 

and facility. We recognize that such 

consideration may be particularly 

important when assessing noncancer 

risk, where pollutant-specific exposure 

health reference levels (e.g., reference 

concentrations (RfCs)) are based on the 

assumption that thresholds exist for 

adverse health effects. For example, the 

EPA recognizes that, although exposures 

attributable to emissions from a source 

category or facility alone may not 

indicate the potential for increased risk 

of adverse noncancer health effects in a 

population, the exposures resulting 

from emissions from the facility in 

combination with emissions from all of 

the other sources (e.g., other facilities) to 

which an individual is exposed may be 

sufficient to result in an increased risk 

of adverse noncancer health effects. In 

May 2010, the Science Advisory Board 

(SAB) advised the EPA ‘‘that RTR 

assessments will be most useful to 

decision makers and communities if 

results are presented in the broader 

context of aggregate and cumulative 

risks, including background 

concentrations and contributions from 

other sources in the area.’’ 3

In response to the SAB 

recommendations, the EPA incorporates 

cumulative risk analyses into its RTR 

risk assessments. The Agency (1) 

conducts facility-wide assessments, 

which include source category emission 

points, as well as other emission points 

within the facilities; (2) combines 

exposures from multiple sources in the 

same category that could affect the same 

individuals; and (3) for some persistent 

and bioaccumulative pollutants, 

analyzes the ingestion route of 

exposure. In addition, the RTR risk 

assessments consider aggregate cancer 

risk from all carcinogens and aggregated 

noncancer HQs for all noncarcinogens 

affecting the same target organ or target 

organ system. 

Although we are interested in placing 

source category and facility-wide HAP 

risk in the context of total HAP risk 

from all sources combined in the 

vicinity of each source, we are 

concerned about the uncertainties of 

doing so. Estimates of total HAP risk 

from emission sources other than those 

that we have studied in depth during 

this RTR review would have 

significantly greater associated 

uncertainties than the source category or 

facility-wide estimates. Such aggregate 

or cumulative assessments would 

compound those uncertainties, making 

the assessments too unreliable. 

B. How do we perform the technology 

review? 

Our technology review primarily 

focuses on the identification and 

evaluation of developments in practices, 

processes, and control technologies that 

have occurred since the MACT 

standards were promulgated. Where we 

identify such developments, we analyze 

their technical feasibility, estimated 

costs, energy implications, and non-air 

environmental impacts. We also 

consider the emission reductions 

associated with applying each 

development. This analysis informs our 

decision of whether it is ‘‘necessary’’ to 

revise the emissions standards. In 

addition, we consider the 

appropriateness of applying controls to 

new sources versus retrofitting existing 

sources. For this exercise, we consider 

any of the following to be a 

‘‘development’’: 

• Any add-on control technology or 

other equipment that was not identified 

and considered during development of 

the original MACT standards; 

• Any improvements in add-on 

control technology or other equipment 

(that were identified and considered 

during development of the original 

MACT standards) that could result in 

additional emissions reduction; 

• Any work practice or operational 

procedure that was not identified or 

considered during development of the 

original MACT standards; 

• Any process change or pollution 

prevention alternative that could be 

broadly applied to the industry and that 

was not identified or considered during 

development of the original MACT 

standards; and 

• Any significant changes in the cost 

(including cost effectiveness) of 

applying controls (including controls 

the EPA considered during the 

development of the original MACT 

standards). 

In addition to reviewing the practices, 

processes, and control technologies that 

were considered at the time we 

originally developed the NESHAP, we 

review a variety of data sources in our 

investigation of potential practices, 

processes, or controls. We also review 

the NESHAP and the available data to 

determine if there are any unregulated 

emissions of HAP within the source 

category and evaluate this data for use 

in developing new emission standards. 

See sections II.C and II.D of this 

preamble for information on the specific 

data sources that were reviewed as part 

of the technology review. 

C. How do we estimate post-MACT risk 

posed by the source category? 

In this section, we provide a complete 

description of the types of analyses that 

we generally perform during the risk 

assessment process. In some cases, we 

do not perform a specific analysis 

because it is not relevant. For example, 

in the absence of emissions of HAP 

known to be persistent and 

bioaccumulative in the environment 

(PB–HAP), we would not perform a 

multipathway exposure assessment. 

Where we do not perform an analysis, 

we state that we do not and provide the 

reason. While we present all of our risk 

assessment methods, we only present 

risk assessment results for the analyses 

actually conducted (see section IV.B of 

this preamble). 

The EPA conducts a risk assessment 

that provides estimates of the MIR for 

cancer posed by the HAP emissions 

from each source in the source category, 

the HI for chronic exposures to HAP 

with the potential to cause noncancer 

health effects, and the HQ for acute 

exposures to HAP with the potential to 


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4U.S. EPA. Risk and Technology Review (RTR) 

Risk Assessment Methodologies: For Review by the 

EPA’s Science Advisory Board with Case Studies— 

MACT I Petroleum Refining Sources and Portland 

Cement Manufacturing, June 2009. EPA–452/R–09– 

006. https://www.epa.gov/airtoxics/rrisk/rtrpg.html. 

5For more information about HEM–3, go to 

https://www.epa.gov/fera/risk-assessment-andmodeling-human-exposure-model-hem. 6U.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). 7A census block is the smallest geographic area 

for which census statistics are tabulated. 

cause noncancer health effects. The 

assessment also provides estimates of 

the distribution of cancer risk within the 

exposed populations, cancer incidence, 

and an evaluation of the potential for an 

adverse environmental effect. The seven 

sections that follow this paragraph 

describe how we estimated emissions 

and conducted the risk assessment. The 

docket for this rulemaking contains the 

following document which provides 

more information on the risk assessment 

inputs and models: Residual Risk 

Assessment for the Primary Magnesium 

Refining Source Category in Support of 

the 2020 Risk and Technology Review 

Proposed Rule. The methods used to 

assess risk (as described in the seven 

primary steps below) are consistent with 

those described by the EPA in the 

document reviewed by a panel of the 

EPA’s SAB in 2009; 4 and described in 

the SAB review report issued in 2010. 

They are also consistent with the key 

recommendations contained in that 

report. 

1. How did we estimate actual 

emissions and identify the emissions 

release characteristics? 

The HAP emissions from US 

Magnesium fall into the following 

pollutant categories: Acid gases (i.e., 

HCl and chlorine), metals (HAP metals) 

and dioxins/furans. The HAP are 

emitted from several emission sources at 

US Magnesium which, for the purposes 

of the source category risk assessment, 

have been categorized into four 

emission process groups as follows: 

Spray dryers, magnesium chloride 

storage bins, melt/reactor system, and 

the CBS. The main sources of emissions 

data include the NEI data submitted for 

calendar year 2017 and supplemental 

information gathered from the public 

domains of the Utah Department of 

Environmental Quality (DEQ) (http://

eqedocs.utah.gov/) and the EPA Region 

8 Superfund Remedial Investigation, 

available at: https://cumulis.epa.gov/ 

supercpad/cursites/csitinfo.

cfm?id=0802704, and also available in 

the docket for this action (Docket ID No. 

EPA–HQ–OAR–2020–0535). Data on the 

numbers, types, dimensions, and 

locations of the emission points for the 

facility were obtained from the NEI, 

Utah DEQ, Google EarthTM, and from 

representatives of the US Magnesium 

facility. A description of the data, 

approach, and rationale used to develop 

actual HAP emissions estimates is 

discussed in more detail in Appendix 1 

to the Residual Risk Assessment for the 

Primary Magnesium Refining Source 

Category in Support of the 2020 Risk 

and Technology Review Proposed Rule, 

which is available in the docket (Docket 

ID No. EPA–HQ–OAR–2020–0535). 

2. How did we estimate 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 and 19999, April 15, 

2005) and in the proposed and final 

Hazardous Organic NESHAP RTR (71 

FR 34421, 34428, June 14, 2006, and 71 

FR 76603, 76609, December 21, 2006, 

respectively). In those actions, we noted 

that assessing the risk at the 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.) 

Allowable emission rates for US 

Magnesium were developed based on 

the MACT emission limits. Specifically, 

given that the facility operates 

continuously throughout the year, the 

pound per hour emission limits for each 

emission process groups were used to 

calculate allowable emission totals. For 

sources without MACT limits in the 

current NESHAP, allowable emissions 

were assumed to equal to actual 

emissions since the facility operated 

continuously, at or near maximum 

capacity, during calendar year 2017. For 

a detailed description of the estimation 

of allowable emissions, see Appendix 1 

to the Residual Risk Assessment for the 

Primary Magnesium Refining Source 

Category in Support of the 2020 Risk 

and Technology Review Proposed Rule, 

which is available in the docket (Docket 

ID No. EPA–HQ–OAR–2020–0535). 

3. How do we conduct dispersion 

modeling, determine inhalation 

exposures, and estimate individual and 

population inhalation risk? 

Both long-term and short-term 

inhalation exposure concentrations and 

health risk from the source category 

addressed in this proposal were 

estimated using the Human Exposure 

Model (HEM–3).5 The HEM–3 performs 

three primary risk assessment activities: 

(1) Conducting dispersion modeling to 

estimate the concentrations of HAP in 

ambient air, (2) estimating long-term 

and short-term inhalation exposures to 

individuals residing within 50 

kilometers (km) of the modeled sources, 

and (3) estimating individual and 

population-level inhalation risk using 

the exposure estimates and quantitative 

dose-response information. 

a. Dispersion Modeling 

The air dispersion model AERMOD, 

used by the HEM–3 model, is one of the 

EPA’s preferred models for assessing air 

pollutant concentrations from industrial 

facilities.6 To perform the dispersion 

modeling and to develop the 

preliminary risk estimates, HEM–3 

draws on three data libraries. The first 

is a library of meteorological data, 

which is used for dispersion 

calculations. This library includes 1 

year (2016) of hourly surface and upper 

air observations from 824 

meteorological stations selected to 

provide coverage of the United States 

and Puerto Rico. A second library of 

United States Census Bureau census 

block 7 internal point locations and 

populations provides the basis of 

human exposure calculations (U.S. 

Census, 2010). In addition, for each 

census block, the census library 

includes the elevation and controlling 

hill height, which are also used in 

dispersion calculations. A third library 

of pollutant-specific dose-response 

values is used to estimate health risk. 

These are discussed below. 

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 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1398 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

8The EPA’s 2005 Guidelines for Carcinogen Risk 

Assessment classifies carcinogens as: ‘‘carcinogenic 

to humans,’’ ‘‘likely to be carcinogenic to humans,’’ 

and ‘‘suggestive evidence of carcinogenic 

potential.’’ These classifications also coincide with 

the terms ‘‘known carcinogen, probable carcinogen, 

and possible carcinogen,’’ respectively, which are 

the terms advocated in the EPA’s Guidelines for 

Carcinogen Risk Assessment, published in 1986 (51 

FR 33992, September 24, 1986). In August 2000, the 

document, Supplemental Guidance for Conducting 

Health Risk Assessment of Chemical Mixtures 

(EPA/630/R–00/002), was published as a 

supplement to the 1986 document. Copies of both 

documents can be obtained from https://

cfpub.epa.gov/ncea/risk/recordisplay.

cfm?deid=20533&CFID=70315376&CFTOKEN=

71597944. Summing the risk of these individual 

compounds to obtain the cumulative cancer risk is 

an approach that was recommended by the EPA’s 

SAB in their 2002 peer review of the EPA’s National 

Air Toxics Assessment (NATA) titled NATA— 

Evaluating the National-scale Air Toxics 

Assessment 1996 Data—an SAB Advisory, available 

at https://yosemite.epa.gov/sab/sabproduct.nsf/ 

214C6E915BB04E14852570CA007A682C/$File/ 

ecadv02001.pdf. 

9See, 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). 

10 In the absence of hourly emission data, we 

develop estimates of maximum hourly emission 

rates by multiplying the average actual annual 

emissions rates by a factor (either a categoryspecific factor or a default factor of 10) to account 

for variability. This is documented in Residual Risk 

Assessment for Primary Magnesium Refining 

Source Category in Support of the 2020 Risk and 

Technology Review Proposed Rule and in Appendix 

5 of the report: Technical Support Document for 

Acute Risk Screening Assessment. Both are 

available in the docket for this rulemaking. 

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 8 emitted 

by the modeled facility. We estimate 

cancer risk at every census block within 

50 km of every facility in the source 

category. The MIR is the highest 

individual lifetime cancer risk estimated 

for any of those census blocks. In 

addition to calculating the MIR, we 

estimate the distribution of individual 

cancer risks for the source category by 

summing the number of individuals 

within 50 km of the sources whose 

estimated risk falls within a specified 

risk range. We also estimate annual 

cancer incidence by multiplying the 

estimated lifetime cancer risk at each 

census block by the number of people 

residing in that block, summing results 

for all of the census blocks, and then 

dividing this result by a 70-year 

lifetime. 

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/glossaries

andkeywordlists/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,9 we revised our 

treatment of meteorological data to use 

reasonable worst-case air dispersion 

conditions in our acute risk screening 

assessments instead of worst-case air 

dispersion conditions. This revised 

treatment of meteorological data and the 

supporting rationale are described in 

more detail in Residual Risk Assessment 

for Primary Magnesium Refining Source 

Category in Support of the 2020 Risk 

and Technology Review Proposed Rule 

and in Appendix 5 of the report: 

Technical Support Document for Acute 

Risk Screening Assessment. This revised 

approach has been used in this 

proposed rule and in all other RTR 

rulemakings proposed on or after June 3, 

2019. 

To assess the potential acute risk to 

the maximally exposed individual, we 

use the peak hourly emission rate for 

each emission point,10 reasonable 

worst-case air dispersion conditions 

(i.e., 99th percentile), and the point of 

highest off-site exposure. Specifically, 

we assume that peak emissions from the 

source category and reasonable worstcase air dispersion conditions co-occur 


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11CalEPA 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. 

12National 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). 

13ERPGS Procedures and Responsibilities. March 

2014. American Industrial Hygiene Association. 

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

AIHAGuidelineFoundation/EmergencyResponse

PlanningGuidelines/Documents/ERPG%20

Committee%20Standard%20Operating%20

Procedures%20%20-%20March%202014

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

2014%29.pdf. 

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.’’ 11

Acute RELs are based on the most 

sensitive, relevant, adverse health effect 

reported in the peer-reviewed medical 

and toxicological literature. They are 

designed to protect the most sensitive 

individuals in the population through 

the inclusion of margins of safety. 

Because margins of safety are 

incorporated to address data gaps and 

uncertainties, exceeding the REL does 

not automatically indicate an adverse 

health impact. AEGLs represent 

threshold exposure limits for the general 

public and are applicable to emergency 

exposures ranging from 10 minutes to 8 

hours.12 They are guideline levels for 

‘‘once-in-a-lifetime, short-term 

exposures to airborne concentrations of 

acutely toxic, high-priority chemicals.’’ 

Id. at 21. The AEGL–1 is specifically 

defined as ‘‘the airborne concentration 

(expressed as ppm (parts per million) or 

mg/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.’’ 13 Id. at 

1. The ERPG–1 is defined as ‘‘the 

maximum airborne concentration below 

which it is believed that nearly all 

individuals could be exposed for up to 

1 hour without experiencing other than 

mild transient adverse health effects or 

without perceiving a clearly defined, 

objectionable odor.’’ Id. at 2. Similarly, 

the ERPG–2 is defined as ‘‘the 

maximum airborne concentration below 

which it is believed that nearly all 

individuals could be exposed for up to 

one hour without experiencing or 

developing irreversible or other serious 

health effects or symptoms which could 

impair an individual’s ability to take 

protective action.’’ Id. at 1. 

An acute REL for 1-hour exposure 

durations is typically lower than its 

corresponding AEGL–1 and ERPG–1. 

Even though their definitions are 

slightly different, AEGL–1s are often the 

same as the corresponding ERPG–1s, 

and AEGL–2s are often equal to ERPG– 

2s. The maximum HQs from our acute 

inhalation screening risk assessment 

typically result when we use the acute 

REL for a HAP. In cases where the 

maximum acute HQ exceeds 1, we also 

report the HQ based on the next highest 

acute dose-response value (usually the 

AEGL–1 and/or the ERPG–1). 

For this source category, maximum 

hourly emission estimates were 

available, so we did not use the default 

emissions multiplier of 10. For the melt/ 

reactor system and CBS, hourly 

emission estimates were initially based 

on an upper peak-to-mean ratio (i.e., 

95th percentile) of the highest daily 

emission total and the daily average. 

This resulted in a factor of 8 for the 

melt/reactor system and 4.5 for the CBS. 

For all other processes, data from the 

CPMS of the associated wet scrubbers 

indicated that their operation was 

continuous and a factor of 1 was used. 

As described in the risk assessment 

section of this preamble, we also 

assessed a worst-case acute risk scenario 

based on the estimated maximum 

hourly emissions rate (see risk 

assessment section for more details). A 

further discussion of why these factors 

were chosen can be found in Appendix 

1 to the Residual Risk Assessment for 

the Primary Magnesium Refining Source 

Category in Support of the 2020 Risk 

and Technology Review Proposed Rule, 

available in the docket for this 

rulemaking. 

In our acute inhalation screening risk 

assessment, acute impacts are deemed 

negligible for HAP for which acute HQs 

are less than or equal to 1, and no 

further analysis is performed for these 

HAP. In cases where an acute HQ from 

the screening step is greater than 1, we 

assess the site-specific data to ensure 

that the acute HQ is at an off-site 

location. For this source category, the 

data refinements employed consisted of 

reviewing modeling results to ensure we 

were evaluating locations and risks that 

were off-site, in places where the public 

could congregate for an hour or more, 

and also evaluating further the potential 

peak estimated actual emissions 

reported by the facility, which we 

assume could occur during rebuild/ 

rehabilitative maintenance of the melt/ 

reactor CRB control device. The CRB 

has an infrequent, but, periodic rebuild 

cycle where the refractory needs to be 

replaced and rebuilt about every 6 to 7 

years. During this period, based on 

available information, we estimate the 

acute factor could be as high as 29, 

which is about 3.5 times higher than the 

initial modeled melt/reactor acute 

factor. These refinements are discussed 

more fully in the Residual Risk 

Assessment for the Primary Magnesium 

Refining Source Category in Support of 

the 2020 Risk and Technology Review 

Proposed Rule, which is available in the 

docket for this source category. 

4. How do we conduct the 

multipathway exposure and risk 

screening assessment? 

The EPA conducts a tiered screening 

assessment examining the potential for 

significant human health risks due to 

exposures via routes other than 

inhalation (i.e., ingestion). We first 

determine whether any sources in the 


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14Burger, J. 2002. Daily consumption of wild fish 

and game: Exposures of high end recreationists. 

International Journal of Environmental Health 

Research, 12:343–354. 

15U.S. EPA. Exposure Factors Handbook 2011 

Edition (Final). U.S. Environmental Protection 

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

2011. 

16 In doing so, the EPA notes that the legal 

standard for a primary NAAQS—that a standard is 

requisite to protect public health and provide an 

adequate margin of safety (CAA section 109(b))— 

differs from the CAA section 112(f) standard 

(requiring, among other things, that the standard 

provide an ‘‘ample margin of safety to protect 

public health’’). However, the primary lead NAAQS 

is a reasonable measure of determining risk 

acceptability (i.e., the first step of the Benzene 

NESHAP analysis) since it is designed to protect the 

most susceptible group in the human population— 

children, including children living near major lead 

emitting sources. 73 FR 67002/3; 73 FR 67000/3; 73 

FR 67005/1. In addition, applying the level of the 

primary lead NAAQS at the risk acceptability step 

is conservative, since that primary lead NAAQS 

reflects an adequate margin of safety. 

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 Primary Magnesium Refining 

source category, we identified potential 

PB–HAP emissions for arsenic 

compounds, lead compounds, cadmium 

compounds, mercury compounds, and 

dioxins/furans, so we proceeded to the 

next step of the evaluation. Except for 

lead, the human health risk screening 

assessment for PB–HAP consists of three 

progressive tiers. In a Tier 1 screening 

assessment, we determine whether the 

magnitude of the facility-specific 

emissions of PB–HAP warrants further 

evaluation to characterize human health 

risk through ingestion exposure. To 

facilitate this step, we evaluate 

emissions against previously developed 

screening threshold emission rates for 

several PB–HAP that are based on a 

hypothetical upper-end screening 

exposure scenario developed for use in 

conjunction with the EPA’s Total Risk 

Integrated Methodology.Fate, Transport, 

and Ecological Exposure (TRIM.FaTE) 

model. The PB–HAP with screening 

threshold emission rates are arsenic 

compounds, cadmium compounds, 

chlorinated dibenzodioxins and furans, 

mercury compounds, and polycyclic 

organic matter (POM). Based on the EPA 

estimates of toxicity and 

bioaccumulation potential, these 

pollutants represent a conservative list 

for inclusion in multipathway risk 

assessments for RTR rules. (See Volume 

1, Appendix D at https://www.epa.gov/ 

sites/production/files/2013-08/ 

documents/volume_1_reflibrary.pdf.) In 

this assessment, we compare the 

facility-specific emission rates of these 

PB–HAP to the screening threshold 

emission rates for each PB–HAP to 

assess the potential for significant 

human health risks via the ingestion 

pathway. We call this application of the 

TRIM.FaTE model the Tier 1 screening 

assessment. The ratio of a facility’s 

actual emission rate to the Tier 1 

screening threshold emission rate is a 

‘‘screening value.’’ 

We derive the Tier 1 screening 

threshold emission rates for these PB– 

HAP (other than lead compounds) to 

correspond to a maximum excess 

lifetime cancer risk of 1-in-1 million 

(i.e., for arsenic compounds, 

polychlorinated dibenzodioxins and 

furans, and POM) or, for HAP that cause 

noncancer health effects (i.e., cadmium 

compounds and mercury compounds), a 

maximum HQ of 1. If the emission rate 

of any one PB–HAP or combination of 

carcinogenic PB–HAP in the Tier 1 

screening assessment exceeds the Tier 1 

screening threshold emission rate for 

any facility (i.e., the screening value is 

greater than 1), we conduct a second 

screening assessment, which we call the 

Tier 2 screening assessment. The Tier 2 

screening assessment separates the Tier 

1 combined fisher and farmer exposure 

scenario into fisher, farmer, and 

gardener scenarios that retain 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 14) and locally grown 

or raised foods (90th percentile 

consumption of locally grown or raised 

foods for the farmer and gardener 

scenarios 15). If PB–HAP emission rates 

do not result in a Tier 2 screening value 

greater than 1, we consider those PB– 

HAP emissions to pose risks below a 

level of concern. If the PB–HAP 

emission rates for a facility exceed the 

Tier 2 screening threshold emission 

rates, we may conduct a Tier 3 

screening assessment. 

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. 

In evaluating the potential 

multipathway risk from emissions of 

lead compounds, rather than developing 

a screening threshold emission rate, we 

compare maximum estimated chronic 

inhalation exposure concentrations to 

the level of the current National 

Ambient Air Quality Standard (NAAQS) 

for lead.16 Values below the level of the 

primary (health-based) lead NAAQS are 

considered to have a low potential for 

multipathway risk. 

For further information on the 

multipathway assessment approach, see 

the Residual Risk Assessment for the 

Primary Magnesium Refining Source 

Category in Support of the Risk and 

Technology Review 2020 Proposed Rule, 

which is available in the docket for this 

action. 


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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 watercolumn 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 (LOAEL), and no-observedadverse-effect level (NOAEL). In cases 

where multiple effect levels were 

available for a particular PB–HAP and 

assessment endpoint, we use all of the 

available effect levels to help us to 

determine whether ecological risks exist 

and, if so, whether the risks could be 

considered significant and widespread. 

For further information on how the 

environmental risk screening 

assessment was conducted, including a 

discussion of the risk metrics used, how 

the environmental HAP were identified, 

and how the ecological benchmarks 

were selected, see Appendix 9 of the 

Residual Risk Assessment for the 

Primary Magnesium Refining Source 

Category in Support of the Risk and 

Technology Review 2020 Proposed Rule, 

which is available in the docket for this 

action. 

b. Environmental Risk Screening 

Methodology 

For the environmental risk screening 

assessment, the EPA first determined 

whether any facilities in the Primary 

Magnesium Refining source category 

emitted any of the environmental HAP. 

For the Primary Magnesium Refining 

source category, we identified emissions 

of HCl and dioxins, and potential 

emissions of arsenic, cadmium, and 

mercury. Because one or more of the 

environmental HAP evaluated are 

emitted by at least one facility in the 

source category, we proceeded to the 

second step of the evaluation. 

c. PB–HAP Methodology 

The environmental screening 

assessment includes six PB–HAP, 

arsenic compounds, cadmium 

compounds, dioxins/furans, POM, 

mercury (both inorganic mercury and 

methyl mercury), and lead compounds. 

With the exception of lead, the 

environmental risk screening 

assessment for PB–HAP consists of three 

tiers. The first tier of the environmental 

risk screening assessment uses the same 

health-protective conceptual model that 

is used for the Tier 1 human health 

screening assessment. TRIM.FaTE 

model simulations were used to 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 

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.’’ 


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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 screening value 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 

Primary Magnesium Refining Source 

Category in Support of the Risk and 

Technology Review 2020 Proposed Rule, 

which is available in the docket for this 

action. 

6. How do we conduct facility-wide 

assessments? 

To put the source category risks in 

context, we typically examine the risks 

from the entire ‘‘facility,’’ where the 

facility includes all HAP-emitting 

operations within a contiguous area and 

under common control. In other words, 

we examine the HAP emissions not only 

from the source category emission 

points of interest, but also emissions of 

HAP from all other emission sources at 

the facility for which we have data. For 

this source category, we conducted the 

facility-wide assessment using a dataset 

compiled from the 2017 NEI. The source 

category records of that NEI dataset 

were removed, evaluated, and updated 

as described in section II.C of this 

preamble: What data collection 

activities were conducted to support 

this action? Once a quality assured 

source category dataset was available, it 

was placed back with the remaining 

records from the NEI for that facility. 

The facility-wide file was then used to 

analyze risks due to the inhalation of 

HAP that are emitted ‘‘facility-wide’’ for 

the populations residing within 50 km 

of each facility, consistent with the 

methods used for the source category 

analysis described above. For these 

facility-wide risk analyses, the modeled 

source category risks were compared to 

the facility-wide risks to determine the 

portion of the facility-wide risks that 

could be attributed to the source 

category addressed in this proposal. We 

also specifically examined the facility 

that was associated with the highest 

estimate of risk and determined the 

percentage of that risk attributable to the 

source category of interest. The Residual 

Risk Assessment for the Primary 

Magnesium Refining Source Category in 

Support of the Risk and Technology 

Review 2020 Proposed Rule, available 

through the docket for this action, 

provides the methodology and results of 

the facility-wide analyses, including all 

facility-wide risks and the percentage of 

source category contribution to facilitywide risks. 

7. How do we consider uncertainties in 

risk assessment? 

Uncertainty and the potential for bias 

are inherent in all risk assessments, 

including those performed for this 

proposal. Although uncertainty exists, 

we believe that our approach, which 

used conservative tools and 

assumptions, ensures that our decisions 

are health and environmentally 

protective. A brief discussion of the 

uncertainties in the RTR emissions 

dataset, dispersion modeling, inhalation 

exposure estimates, and dose-response 

relationships follows below. Also 

included are those uncertainties specific 

to our acute screening assessments, 

multipathway screening assessments, 

and our environmental risk screening 

assessments. A more thorough 

discussion of these uncertainties is 

included in the Residual Risk 

Assessment for the Primary Magnesium 

Refining Source Category in Support of 

the Risk and Technology Review 2020 

Proposed Rule, which is available in the 

docket for this action. If a multipathway 

site-specific assessment was performed 

for this source category, a full 

discussion of the uncertainties 

associated with that assessment can be 

found in Appendix 11 of that document, 

Site-Specific Human Health 

Multipathway Residual Risk Assessment 

Report. 

a. Uncertainties in the RTR Emissions 

Dataset 

Although the development of the RTR 

emissions dataset involved quality 

assurance/quality control processes, the 

accuracy of emissions values will vary 

depending on the source of the data, the 

degree to which data are incomplete or 

missing, the degree to which 

assumptions made to complete the 

datasets are accurate, errors in emission 

estimates, and other factors. The 

emission estimates considered in this 

analysis generally are annual totals for 

certain years, and they do not reflect 

short-term fluctuations during the 

course of a year or variations from year 

to year. The estimates of peak hourly 

emission rates for the acute effects 

screening assessment were based on an 

emission adjustment factor applied to 

the average annual hourly emission 

rates, which are intended to account for 

emission fluctuations due to normal 

facility operations. 

b. Uncertainties in Dispersion Modeling 

We recognize there is uncertainty in 

ambient concentration estimates 

associated with any model, including 

the EPA’s recommended regulatory 

dispersion model, AERMOD. In using a 

model to estimate ambient pollutant 

concentrations, the user chooses certain 

options to apply. For RTR assessments, 

we select some model options that have 

the potential to overestimate ambient air 

concentrations (e.g., not including 

plume depletion or pollutant 

transformation). We select other model 

options that have the potential to 

underestimate ambient impacts (e.g., not 

including building downwash). Other 

options that we select have the potential 

to either under- or overestimate ambient 

levels (e.g., meteorology and receptor 

locations). On balance, considering the 

directional nature of the uncertainties 

commonly present in ambient 

concentrations estimated by dispersion 

models, the approach we apply in the 

RTR assessments should yield unbiased 

estimates of ambient HAP 

concentrations. We also note that the 

selection of meteorology dataset 

location could have an impact on the 

risk estimates. As we continue to update 

and expand our library of 

meteorological station data used in our 

risk assessments, we expect to reduce 

this variability. 

c. Uncertainties in Inhalation Exposure 

Assessment 

Although every effort is made to 

identify all of the relevant facilities and 

emission points, as well as to develop 

accurate estimates of the annual 

emission rates for all relevant HAP, the 

uncertainties in our emission inventory 

likely dominate the uncertainties in the 

exposure assessment. Some 

uncertainties in our exposure 

assessment include human mobility, 

using the centroid of each census block, 

assuming lifetime exposure, and 


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

internet/registry/termreg/searchandretrieve/ 

glossariesandkeywordlists/search.do?details=&

glossaryName=IRIS%20Glossary). 

18An 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. 

19See 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. 

assuming only outdoor exposures. For 

most of these factors, there is neither an 

under nor overestimate when looking at 

the maximum individual risk or the 

incidence, but the shape of the 

distribution of risks may be affected. 

With respect to outdoor exposures, 

actual exposures may not be as high if 

people spend time indoors, especially 

for very reactive pollutants or larger 

particles. For all factors, we reduce 

uncertainty when possible. For 

example, with respect to census-block 

centroids, we analyze large blocks using 

aerial imagery and adjust locations of 

the block centroids to better represent 

the population in the blocks. We also 

add additional receptor locations where 

the population of a block is not well 

represented by a single location. 

d. Uncertainties in Dose-Response 

Relationships 

There are uncertainties inherent in 

the development of the dose-response 

values used in our risk assessments for 

cancer effects from chronic exposures 

and noncancer effects from both chronic 

and acute exposures. Some 

uncertainties are generally expressed 

quantitatively, and others are generally 

expressed in qualitative terms. We note, 

as a preface to this discussion, a point 

on dose-response uncertainty that is 

stated in the EPA’s 2005 Guidelines for 

Carcinogen Risk Assessment; namely, 

that ‘‘the primary goal of EPA actions is 

protection of human health; 

accordingly, as an Agency policy, risk 

assessment procedures, including 

default options that are used in the 

absence of scientific data to the 

contrary, should be health protective’’ 

(the EPA’s 2005 Guidelines for 

Carcinogen Risk Assessment, page 1 

through 7). This is the approach 

followed here as summarized in the 

next paragraphs. 

Cancer UREs used in our risk 

assessments are those that have been 

developed to generally provide an upper 

bound estimate of risk.17 That is, they 

represent a ‘‘plausible upper limit to the 

true value of a quantity’’ (although this 

is usually not a true statistical 

confidence limit). In some 

circumstances, the true risk could be as 

low as zero; however, in other 

circumstances the risk could be 

greater.18 Chronic noncancer RfC and 

reference dose (RfD) values represent 

chronic exposure levels that are 

intended to be health-protective levels. 

To derive dose-response values that are 

intended to be ‘‘without appreciable 

risk,’’ the methodology relies upon an 

uncertainty factor (UF) approach,19

which considers uncertainty, variability, 

and gaps in the available data. The UFs 

are applied to derive dose-response 

values that are intended to protect 

against appreciable risk of deleterious 

effects. 

Many of the UFs used to account for 

variability and uncertainty in the 

development of acute dose-response 

values are quite similar to those 

developed for chronic durations. 

Additional adjustments are often 

applied to account for uncertainty in 

extrapolation from observations at one 

exposure duration (e.g., 4 hours) to 

derive an acute dose-response value at 

another exposure duration (e.g., 1 hour). 

Not all acute dose-response values are 

developed for the same purpose, and 

care must be taken when interpreting 

the results of an acute assessment of 

human health effects relative to the 

dose-response value or values being 

exceeded. Where relevant to the 

estimated exposures, the lack of acute 

dose-response values at different levels 

of severity should be factored into the 

risk characterization as potential 

uncertainties. 

Uncertainty also exists in the 

selection of ecological benchmarks for 

the environmental risk screening 

assessment. We established a hierarchy 

of preferred benchmark sources to allow 

selection of benchmarks for each 

environmental HAP at each ecological 

assessment endpoint. We searched for 

benchmarks for three effect levels (i.e., 

no-effects level, threshold-effect level, 

and probable effect level), but not all 

combinations of ecological assessment/ 

environmental HAP had benchmarks for 

all three effect levels. Where multiple 

effect levels were available for a 

particular HAP and assessment 

endpoint, we used all of the available 

effect levels to help us determine 

whether risk exists and whether the risk 

could be considered significant and 

widespread. 

Although we make every effort to 

identify appropriate human health effect 

dose-response values for all pollutants 

emitted by the sources in this risk 

assessment, some HAP emitted by this 

source category are lacking doseresponse assessments. Accordingly, 

these pollutants cannot be included in 

the quantitative risk assessment, which 

could result in quantitative estimates 

understating HAP risk. To help to 

alleviate this potential underestimate, 

where we conclude similarity with a 

HAP for which a dose-response value is 

available, we use that value as a 

surrogate for the assessment of the HAP 

for which no value is available. To the 

extent use of surrogates indicates 

appreciable risk, we may identify a need 

to increase priority for an IRIS 

assessment for that substance. We 

additionally note that, generally 

speaking, HAP of greatest concern due 

to environmental exposures and hazard 

are those for which dose-response 

assessments have been performed, 

reducing the likelihood of understating 

risk. Further, HAP not included in the 

quantitative assessment are assessed 

qualitatively and considered in the risk 

characterization that informs the risk 

management decisions, including 

consideration of HAP reductions 

achieved by various control options. 

For a group of compounds that are 

unspeciated (e.g., glycol ethers), we 

conservatively use the most protective 

dose-response value of an individual 

compound in that group to estimate 

risk. Similarly, for an individual 

compound in a group (e.g., ethylene 

glycol diethyl ether) that does not have 

a specified dose-response value, we also 

apply the most protective dose-response 

value from the other compounds in the 

group to estimate risk. 

e. Uncertainties in Acute Inhalation 

Screening Assessments 

In addition to the uncertainties 

highlighted above, there are several 

factors specific to the acute exposure 

assessment that the EPA conducts as 

part of the risk review under section 112 

of the CAA. The accuracy of an acute 

inhalation exposure assessment 

depends on the simultaneous 

occurrence of independent factors that 

may vary greatly, such as hourly 

emissions rates, meteorology, and the 

presence of a person. In the acute 

screening assessment that we conduct 

under the RTR program, we assume that 

peak emissions from the source category 

and reasonable worst-case air dispersion 

conditions (i.e., 99th percentile) 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 


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20 In the context of this discussion, the term 

‘‘uncertainty’’ as it pertains to exposure and risk 

encompasses both variability in the range of 

expected inputs and screening results due to 

existing spatial, temporal, and other factors, as well 

as uncertainty in being able to accurately estimate 

the true result. 

reasonable worst-case air dispersion 

conditions occur simultaneously. 

f. Uncertainties in the Multipathway 

and Environmental Risk Screening 

Assessments 

For each source category, we 

generally rely on site-specific levels of 

PB–HAP or environmental HAP 

emissions to determine whether a 

refined assessment of the impacts from 

multipathway exposures is necessary or 

whether it is necessary to perform an 

environmental screening assessment. 

This determination is based on the 

results of a three-tiered screening 

assessment that relies on the outputs 

from models—TRIM.FaTE and 

AERMOD—that estimate environmental 

pollutant concentrations and human 

exposures for five PB–HAP (dioxins, 

POM, mercury, cadmium, and arsenic) 

and two acid gases (HF and HCl). For 

lead, we use AERMOD to determine 

ambient air concentrations, which are 

then compared to the secondary 

NAAQS standard for lead. Two 

important types of uncertainty 

associated with the use of these models 

in RTR risk assessments and inherent to 

any assessment that relies on 

environmental modeling are model 

uncertainty and input uncertainty.20

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)? 

In this proposal, pursuant to CAA 

section 112(d)(2) and (3) , we are 

proposing to establish an emission 

standard requiring MACT level control 

of chlorine emissions from the CBS. The 

results and proposed decisions based on 

the analyses performed pursuant to 

CAA section 112(d)(2) and (3) are 

presented below. 

In the primary magnesium refining 

process, the electrowinning of the 

melted magnesium chloride to 

magnesium metal produces as a 

byproduct chlorine gas which is piped 

to, and recovered at, the co-located 

chlorine plant. At the chlorine plant, the 

chlorine gas is liquified and then stored 

for either reuse back into the 

magnesium refining process or sold to 

the market. When the chlorine plant is 

inoperable (e.g., due to a malfunction or 

planned maintenance), the chlorine gas 

produced at the electrolytic cells is 

routed through the CBS. The CBS 

contains a packed-bed scrubber which 

uses ferrous chloride as the adsorbing 


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medium to control chlorine emissions. 

The reaction of chlorine with ferrous 

chloride in the scrubbing medium 

creates a valuable by-product, ferric 

chloride, which the facility sells to the 

market. Since the CBS produces this 

valuable product, in addition to routing 

chlorine gas to the CBS when the 

chlorine plant is inoperable, the facility 

also routinely intentionally routes 

smaller amounts of chlorine gas (also 

known as tail gas) from the chlorine 

plant to the CBS during normal 

operations to produce ferric chloride. 

Based on available information from 

the facility and the current title V 

permit, we estimate the scrubbers 

achieve at least 95 percent control 

efficiency and that the remaining 

chlorine gas (up to 5 percent) is emitted 

to the atmosphere. As a potentially 

significant source of chlorine emissions 

from the refining process, we are 

proposing to establish an emission 

standard requiring MACT level control 

of chlorine emissions from the CBS. 

MACT standards must reflect the 

maximum degree of emissions reduction 

achievable through the application of 

measures, processes, methods, systems 

or techniques, including, but not limited 

to, measures that: (1) Reduce the volume 

of or eliminate pollutants through 

process changes, substitution of 

materials or other modifications; (2) 

enclose systems or processes to 

eliminate emissions; (3) capture or treat 

pollutants when released from a 

process, stack, storage, or fugitive 

emissions point; (4) are design, 

equipment, work practice, or 

operational standards (including 

requirements for operator training or 

certification); or (5) are a combination of 

the above. See CAA section 112(d)(2)(A) 

through (E). The MACT standards may 

take the form of design, equipment, 

work practice, or operational standards 

where the EPA determines either that: 

(1) A pollutant cannot be emitted 

through a conveyance designed and 

constructed to emit or capture the 

pollutant, or that any requirement for, or 

use of, such a conveyance would be 

inconsistent with law; or (2) the 

application of measurement 

methodology to a particular class of 

sources is not practicable due to 

technological and economic limitations. 

See CAA section 112(h)(1) and (2). 

The MACT ‘‘floor’’ is the minimum 

control level required for MACT 

standards promulgated under CAA 

section 112(d) and may not be based on 

cost considerations. For new sources, 

the MACT floor cannot be less stringent 

than the emissions control that is 

achieved in practice by the bestcontrolled similar source. The MACT 

floor for existing sources can be less 

stringent than floors for new sources, 

but not less stringent than the average 

emissions limitation achieved by the 

best-performing 12 percent of existing 

sources in the category or subcategory 

(or the best-performing five sources for 

categories or subcategories with fewer 

than 30 sources). Once the EPA has set 

the MACT floor, it may then impose 

stricter standards (‘‘beyond-the-floor’’ 

limits) if the EPA determines them to be 

achievable taking into consideration the 

cost of achieving the emission 

reductions, any non-air quality health 

and environmental impacts, and energy 

requirements. 

Since there is only one primary 

magnesium refinery in the source 

category, the MACT floor for new and 

existing sources is established by the 

emission limitation achieved at that 

source. As described above, currently 

the CBS chlorine emissions are 

controlled by a ferrous chloride packedbed scrubber. A representative from US 

Magnesium explained that chlorine 

removal can be calculated to be up to 

100 percent stoichiometrically under 

fixed mass flow and ferric chloride 

recirculation rates. However, due to 

high variability in flow rates during the 

range of normal operations, the actual 

efficiency is expected to be less than 

100 percent (for more information see 

email from Rob Hartman, US 

Magnesium, to Michael Moeller, EPA, 

which is available in the docket for this 

proposed rulemaking). Based on the 

limited available information and 

applying engineering judgement as 

described above, the facility and the 

state of Utah assume that the scrubbers 

achieve an average removal efficiency of 

95 percent for purposes of determining 

and reporting daily chlorine emissions 

as required by the tile V permit. 

However, there are no stack test data 

available to confirm this value. 

Therefore, based on the available 

information, we propose 95 percent 

reduction of chlorine emissions as the 

MACT floor for the CBS for new and 

existing sources in the source category. 

In addition to determining the MACT 

floor level of control, as part of our 

development of the proposed MACT 

standard, we assessed whether stricter 

standards (‘‘beyond-the-floor’’ limits) 

are achievable taking into consideration 

the cost of achieving additional 

emission reductions, any non-air quality 

health and environmental impacts, and 

energy requirements. We identified one 

potential control option, using a 

combination of a thermal incinerator 

coupled with a wet scrubber, that could 

achieve chlorine control efficiencies 

greater than the current 95 percent. The 

thermal incinerator reacts chlorine with 

natural gas to produce HCl gas. This 

process is highly efficient at converting 

chlorine into HCl and based on the 

available information, we estimate that 

99 percent of the chlorine is converted 

to HCl. The HCl gas stream, which has 

greater solubility than chlorine, is then 

controlled through absorption via a wet 

scrubber. The wet scrubber removal 

efficiency of HCl is estimated to be 99 

percent. This combination of controls 

could be expected to achieve 98 percent 

reduction of chlorine emissions. With 

regard to costs of achieving these 

additional emission reductions, based 

on limited information, we estimate the 

capital costs for these beyond-the-floor 

controls would be about $1.3 million, 

annualized costs would be about $1.4 

million, and would achieve an 

estimated 300 tpy reduction, with 

estimated cost effectiveness of $4,657 

per ton of chlorine reductions. However, 

as explained in the technical 

memorandum cited below, we note that 

there are substantial uncertainties with 

the baseline emissions estimates, the 

emissions reductions that would be 

achieved, and the cost estimates. This is 

primarily due to lack of test data and 

lack of information regarding flow rates, 

renovation costs, and other factors. For 

example, without test data to 

corroborate, the actual efficiency of the 

current control could be higher (or 

lower) than the estimated 95 percent. 

The facility has determined that 

chlorine removal, under 

stoichiometrically ideal conditions, can 

be calculated to be up to 100 percent. 

If the current control is higher than the 

95 percent, the additional emission 

reductions and the cost effectiveness 

would be reduced. If the current control 

approaches 98 percent, there would be 

no additional reductions to achieve. In 

regard to uncertainties with the cost 

estimates, there is a large range of values 

for the costs associated with the 

installation and operating of a thermal 

incinerator and wet scrubber devices. 

To account for this, we used the 

midpoint of the cost range; however, 

due to the unique nature of this industry 

and without additional information 

about the CBS, the actual costs could be 

anywhere within the range and even 

beyond it. Using the upper end 

estimates of the cost range, capital costs 

could be as high as $2.1 million, 

annualized costs up to $2.5 million and 

an estimated cost effectiveness of $8,152 

per ton. In addition, there would be 

additional economic impacts beyond 

these estimated costs due to the loss of 

facility revenue from the elimination of 

the production of a valuable by-product 


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that is created with the current controls. 

For more information regarding the 

beyond-the-floor analysis, the 

uncertainties and our conclusions, see 

the Beyond-the-floor Assessment for the 

Chlorine Bypass Stack memorandum, 

which is available in the docket for this 

proposed action. 

We note that the cost-effectiveness is 

within the range of cost effectiveness 

accepted for beyond-the-floor controls 

for some other HAP in NESHAP for 

other source categories (e.g., Secondary 

Lead Smelting, 77 FR 3, January 5, 2012, 

and Ferroalloys Production, 80 FR 125, 

June 30, 2015). We have not identified 

any previous NESHAP that accepted or 

rejected such cost-effectiveness 

estimates specifically for chlorine. 

Nevertheless, given the issues and 

substantial uncertainties described 

above, we are not proposing this 

beyond-the-floor standard. We also note 

that we did not identify any relevant 

non-air quality health and 

environmental impacts, and energy 

requirements. Although we are not 

proposing this beyond-the-floor 

standard, we are soliciting comments, 

data and other information regarding the 

beyond-the-floor analysis (including 

costs estimates, baseline emissions, 

emissions reductions, and loss of 

product/revenue), and we are soliciting 

comments regarding our proposed 

determination and whether it would be 

appropriate to require these beyond-thefloor controls under the NESHAP, and 

if so, why. 

Therefore, based on all the analyses 

presented above, we are proposing a 

MACT floor emissions standard for the 

CBS that will require new and existing 

sources in the source category to operate 

the control device and demonstrate 95 

percent reduction of chlorine emissions. 

Specifically, we propose the following 

conditions: The facility must operate the 

control device (e.g., a CBS scrubber) at 

all times when chlorine emissions are 

being routed to the CBS; except for 

circumstances under which emissions 

are routed to the CBS due to a chlorine 

plant malfunction and the CBS control 

device is not in operation, the CBS 

control device must be operating as 

soon as practicable but no later than 15 

minutes after the routing of the chlorine 

emissions to the CBS. The facility must 

also document, and keep records, 

regarding each malfunction event, as 

described below. To demonstrate 95 

percent control efficiency is achieved, 

we are proposing to require that new 

and existing sources in the source 

category conduct periodic performance 

tests that include inlet and outlet test 

samples. These tests would be 

conducted no less frequently than twice 

per permit term of a source’s title V 

permit (at mid-term and renewal), 

which would be at least two tests every 

5 years. We are proposing to require that 

new and existing sources in the source 

category use EPA Method 26A in 40 

CFR part 60, appendix A (i.e., the 

reference method for chlorine) to 

demonstrate compliance with the 

MACT standard. In addition to the 

performance compliance tests, with 

regard to parametric monitoring, we are 

proposing to require that new and 

existing sources in the source category 

measure and record the pH, liquid flow, 

and pressure drop of the control device 

on an on-going basis to demonstrate 

continuous compliance with the 

chlorine standard, and maintain such 

records. During a malfunction event, the 

owner or operator would be required to 

follow the typical recordkeeping and 

reporting associated with malfunction 

events (described in section IV.E), and 

also keep records of the date and time 

the control device was started, and also 

conduct the same measurements and 

monitoring of the parameters described 

above (i.e., pH, liquid flow, and pressure 

drop). However, we are also seeking 

comments regarding these proposed 

requirements, and whether the EPA 

should consider alternative standards, 

or methodology modifications or 

parameters to demonstrate compliance 

and, if so, an explanation of those 

alternatives and why they would be 

appropriate. 

Although we are proposing a MACT 

floor level of control for new and 

existing sources of 95 percent reduction 

of chlorine emissions based on the 

information presented above, we 

acknowledge there are some 

uncertainties regarding the actual 

control efficiency achieved under 

normal variable operations. Therefore, 

we are soliciting comments, data, or 

other information regarding the 95 

percent control efficiency limit and 

whether a different limit, higher or 

lower, would be appropriate and, if so, 

why such a different limit would be 

appropriate to represent the MACT floor 

level of control. As described above, we 

are not proposing a beyond-the-floor 

option primarily due to significant 

uncertainties in the emissions and in 

the costs of achieving additional 

emission reductions. We conclude that 

the current scrubbing system represents 

MACT for the CBS. However, we are 

soliciting comments, data, and other 

information regarding the analyses for 

our proposed MACT floor standard and 

the beyond-the-floor option and our 

determinations. For more information 

regarding the beyond-the-floor analysis 

and our conclusions, see the Beyondthe-floor Assessment for the Chlorine 

Bypass Stack memorandum, which is 

available in the docket for this proposed 

action. 

B. What are the results of the risk 

assessment and analyses? 

1. Chronic Inhalation Risk Assessment 

Results 

Table 2 of this preamble provides a 

summary of the results of the chronic 

inhalation risk assessment for HAP 

emissions for the source category, and 

an upper-end assessment of acute 

inhalation risks (based on the 95th 

percentile of 2017 hourly emissions 

estimates). Additional analyses and 

refinements regarding potential acute 

risks, including potential higher-end 

acute risks, are described later in this 

section. More detailed information on 

the risk assessment can be found in the 

document titled Residual Risk 

Assessment for the Primary Magnesium 

Refining Source Category in Support of 

the Risk and Technology Review 2020 

Proposed Rule, available in the docket 

for this rule. 


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TABLE 2—PRIMARY MAGNESIUM REFINING SOURCE CATEGORY INHALATION RISK ASSESSMENT RESULTS

Number of 

facilities 1

Maximum individual cancer 

risk (in 1 million) 2

based on . . . 

Population at increased 

risk of cancer ≥ 1-in-1 

million based on . . . 

Annual cancer incidence 

(cases per year) 

based on . . . 

Maximum chronic noncancer TOSHI 

based on . . . 

Maximum screening acute 

noncancer HQ 3

based on . . . 

Actual 

emissions 

Allowable 

emissions 

Actual 

emissions 

Allowable 

emissions 

Actual 

emissions 

Allowable 

emissions 

Actual 

emissions 

Allowable 

emissions 

95th percentile of 

actual emissions 

1 ................... 0.08 0.08 0 0 0.00001 0.00001 * 1 * 0.6 3–REL 

<1 AEGL–1 

(chlorine). 

1 Number of facilities evaluated in the risk analysis. 

2 Maximum individual excess lifetime cancer risk due to HAP emissions from the source category. 

3Arsenic REL. The maximum estimated acute exposure concentration was divided by available short-term dose-response values to develop an array of HQ values. 

HQ values shown use the lowest available acute dose-response value, which in most cases is the REL. When an HQ exceeds 1, we also show the HQ using the 

next lowest available acute dose-response value. 

* (Respiratory). 

Results of the inhalation risk 

assessment based on estimates of actual 

emissions indicate that the maximum 

lifetime individual cancer risk (or MIR) 

posed by the single facility is 0.08-in-1 

million, with arsenic compounds, 

dioxins/furans, chromium (VI) 

compounds, and nickel compounds 

predominantly emitted from spray 

dryers and the melt/reactor system as 

the major contributors to the risk. The 

total estimated cancer incidence from 

this source category is 0.00001 excess 

cancer cases per year, or one excess case 

in every 100,000 years. No people are 

estimated to have inhalation cancer 

risks above 1-in-1 million due to HAP 

emitted from the facility in this source 

category. The HEM–3 model predicted 

the maximum chronic noncancer HI 

value for the source category could be 

up to 2 (respiratory effects), driven by 

emissions of chlorine from the melt/ 

reactor system and that two people 

could be expected to be exposed to 

TOSHI levels above 1. However, due to 

the large distance to the nearest 

residential areas, the MIR and maximum 

chronic HI receptor is approximately 26 

km from the plant. Based upon the 

distance of the plant to the MIR receptor 

with a local average wind of 5 meters 

per second, the facility’s plume would 

reach this receptor in approximately 1.4 

hours. After reviewing the decay rates 

for chlorine and receptor distances for 

this facility, we determined that these 

emission sources should be modeled 

taking photo-decay into account. The 

HEM–3 model does not consider photodecay. Therefore, a separate refined 

analysis considering decay was 

performed to assess the impact on the 

chronic noncancer HI. Based upon the 

reactivity of chlorine and the time to 

reach the MIR location, we would 

expect the chlorine concentration at the 

MIR to decrease by approximately 44 

percent when accounting for photodecay, resulting in a chronic noncancer 

HI value for the source category of 1 

(respiratory) with no people expected to 

be exposed to a HI of greater than 1. 

Details on this refinement is presented 

in Appendix 12 of the source category 

risk report, which is available in the 

docket for this action. 

Considering MACT-allowable 

emissions, results of the inhalation risk 

assessment indicate that the cancer MIR 

is 0.08-in-1 million, again with arsenic 

compounds, dioxins/furans, chromium 

(VI) compounds, and nickel compounds 

predominantly emitted from spray 

dryers and the melt/reactor system as 

the major contributors to the risk. The 

total estimated cancer incidence from 

this source category based on allowable 

emissions is 0.00001 excess cancer cases 

per year, or one excess case in every 

100,000 years. No people are estimated 

to have cancer risks above 1-in-1 million 

from HAP emitted from the facility in 

this source category. No individuals are 

estimated to have exposures that result 

in a noncancer HI at or above 1 at 

allowable emission rates. 

2. Screening Level Acute Risk 

Assessment Results 

To better characterize the potential 

health risks associated with estimated 

worst-case acute exposures to HAP, and 

in response to a key recommendation 

from the SAB’s peer review of the EPA’s 

RTR risk assessment methodologies, we 

examined a wider range of available 

acute health metrics than we do for our 

chronic risk assessments. This is in 

acknowledgement that there are 

generally more data gaps and 

uncertainties in acute reference values 

than there are in chronic reference 

values. By definition, the acute REL 

represents a health-protective level of 

exposure, with effects not anticipated 

below those levels, even for repeated 

exposures. However, the level of 

exposure that would cause health effects 

is not specifically known. Therefore, 

when an REL is exceeded and an AEGL– 

1 or ERPG–1 level is available (i.e., 

levels at which mild, reversible effects 

are anticipated in the general public for 

a single exposure), we typically use 

them as an additional comparative 

measure, as they provide an upper 

bound for exposure levels above which 

exposed individuals could experience 

effects. As the exposure concentration 

increases above the acute REL, the 

potential for effects increases. 

Based on our initial acute risk 

assessment, the maximum acute HQs 

from actual baseline emissions, based 

on a review of all modeled receptors for 

the US Magnesium facility, identified an 

exceedance of one acute benchmark (for 

chlorine) with an HQ of 8 based on the 

1-hour REL, but that receptor is located 

on-site with no public access. We then 

evaluated the off-site receptors, which 

resulted in a highest refined (off-site) 

screening acute HQ for chlorine of 3 

(based on the acute REL for chlorine). 

For this initial model run, we assumed 

an upper-end estimate of hourly 

potential acute emissions from the 

primary source of the chlorine 

emissions (i.e., the melt/reactor system) 

of 8 times higher than the annual 

average emissions rate (which is the 

estimated 95 percent value of the range 

of estimated emissions in 2017). 

Further, this exceedance was only 

predicted to occur in a non-residential 

area with limited public access in a 

parking lot shared with a neighboring 

facility (ATI Titanium LLC). A review of 

the other surrounding property off-site 

of the US Magnesium facility identified 

public land managed by the Bureau of 

Land Management with an HQ (REL) of 

2, access highways to the facilities off of 

the Interstate (I–80) with an HQ of 0.4 

and the MIR residential location for the 

source category having an HQ of 0.3. No 

facilities were estimated to have an HQ 

based on AEGL or EPRG benchmarks 

greater than 1. Based on these initial 

estimated actual acute emissions (95th 

percentile), the refined acute results 

(with maximum acute HQ of 3) indicate 

that these upper end emissions are 

unlikely to pose significant risk to the 

general public. 


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However, we also evaluated the 

potential acute HQ values based on 

estimated worst-case emissions, which 

we understand have occurred during 

periodic rebuilding and rehabilitative 

maintenance events of the melt/reactor 

control device (i.e., the CRB), as 

discussed previously in section III.C.3.c. 

Because of the infrequent nature of the 

CRB rebuilds (every 6 to 7 years) 

chronic risks are not expected to 

change; however, acute risks could 

increase significantly during these time 

periods. Based on available information, 

we estimate the worst-case chlorine 

emissions from the melt/reactor to be as 

high as 3.6 times the acute emissions 

modeled initially (i.e., the 95th 

percentile estimate), or 29 times annual 

average emissions rates. During these 

events, assuming a linear increase in 

risks compared to emissions, we 

estimate the maximum off-site acute 

HQs could be up to 11 in the parking 

lot shared with the neighboring facility, 

7 on public uninhabited lands and 1 at 

the nearest residential location. Further 

details on the acute HQ risk analyses 

and results are provided in Appendix 10 

of the risk report for this source 

category. 

3. Multipathway Risk Screening Results 

The lone facility in the source 

category reported estimated emissions 

of carcinogenic PB–HAP (arsenic and 

dioxins) and non-carcinogenic PB–HAP 

(cadmium and mercury). The facility 

reported emissions of carcinogenic PB– 

HAP (arsenic and dioxins) that 

exceeded a Tier 1 cancer screening 

threshold emission rate and reported 

emissions of non-carcinogenic PB–HAP 

(mercury) that exceeded a Tier 1 

noncancer screening threshold emission 

rate. Because the facility exceeded the 

Tier 1 multipathway screening 

threshold emission rate for one or more 

PB–HAP, we used additional facility 

site-specific information to perform a 

Tier 2 assessment and determine the 

maximum chronic cancer and 

noncancer impacts for the source 

category. Based on the Tier 2 

multipathway cancer assessment, the 

dioxin emissions exceeded the Tier 2 

screening threshold emission rate by a 

factor of 20 and a factor of 40 for 

arsenic. The multipathway risk 

screening Tier 2 assessment resulted in 

a combined dioxin and arsenic emission 

rate that exceeded the Tier 2 cancer 

screening value by a factor of 60 for the 

gardener scenario. The Tier 2 screening 

value for all other PB–HAP potentially 

emitted from the source category 

(mercury compounds and cadmium 

compounds) were less than 1. 

A Tier 3 cancer screening assessment 

was conducted for both the fisher and 

gardener scenarios. Based on this Tier 3 

screening assessment, a refined lake 

screening was conducted as well as 

identification of a residential receptor 

location (i.e., MIR location from the 

inhalation assessment) for the gardener 

scenario. This review resulted in the 

removal of multiple lakes and the 

placement of the residential receptor 

approximately 20 km south of the 

facility. Based upon these refinements, 

the fisher scenario resulted in a cancer 

screening value of 7 and the gardener 

scenario resulted in a cancer screening 

value of 1. 

An exceedance of a screening 

threshold emission rate in any of the 

tiers cannot be equated with a risk value 

or an HQ (or HI). Rather, it represents 

a high-end estimate of what the risk or 

hazard may be. For example, screening 

threshold emission rate of 2 for a noncarcinogen can be interpreted to mean 

that we are confident that the HQ would 

be lower than 2. Similarly, a tier 

screening threshold emission rate of 7 

for a carcinogen means that we are 

confident that the risk is lower than 7- 

in-1 million. Our confidence comes 

from the conservative, or healthprotective, assumptions encompassed in 

the screening tiers: We choose inputs 

from the upper end of the range of 

possible values for the influential 

parameters used in the screening tiers, 

and we assume that the exposed 

individual exhibits ingestion behavior 

that would lead to a high total exposure. 

4. Environmental Risk Screening Results 

As described in section III.A of this 

document, we conducted an 

environmental risk screening 

assessment for the Primary Magnesium 

Refining source category for the 

following pollutants: Arsenic, cadmium, 

dioxins/furans, HCl, lead, and mercury. 

In the Tier 1 screening analysis for 

PB–HAP (other than lead, which was 

evaluated differently), arsenic, 

cadmium, and divalent mercury 

emissions had no Tier 1 exceedances for 

any ecological benchmark. Dioxin/furan 

emissions at one facility had Tier 1 

exceedances for the surface soil NOAEL 

(mammalian insectivores—shrew) 

benchmark by a maximum screening 

value of 400. Methyl mercury at one 

facility had Tier 1 exceedances for the 

surface soil NOAEL (avian ground 

insectivores—woodcock) by a maximum 

screening value of 2. 

A Tier 2 screening assessment was 

performed for methyl mercury and 

dioxin/furan emissions. Methyl mercury 

had no Tier 2 exceedances for any 

ecological benchmark. Dioxin/furan 

emissions had Tier 2 exceedances for 

the surface soil NOAEL (mammalian 

insectivores—shrew) benchmark by a 

maximum screening value of 4. This 

screening value was refined by 

removing soil areas located on-site. The 

refined Tier 2 screening value for 

dioxins/furans is 3. 

A Tier 3 screening analysis was 

performed for dioxin emissions. In the 

Tier 3 screen, after incorporating 

chemical losses due to plume-rise into 

the calculation, the screening value 

remained 3 (surface soil NOAEL). Also 

in the Tier 3 screen, we conducted runs 

of the screening scenario within 

TRIM.FaTE with the following sitespecific time-series data: Hourly 

meteorology, time series of leaf litterfall 

and air-leaf chemical exchanges, facility 

emissions, and hourly values of 

emission release height equivalent to 

hourly plume-rise height. After 

incorporating these time-series data in 

the analysis, the screening value is 2 

(surface soil NOAEL). No other dioxin/ 

furan benchmarks were exceeded in 

Tier 2 or 3. Specifically, the following 

dioxin/furan benchmarks were not 

exceeded in the Tier 2 or 3 screen: 

• Fish—Avian Piscivores (NOAEL, 

geometric-maximum-allowabletoxicant-level (GMATL), and LOAEL) 

• Fish—Mammalian Piscivores 

(NOAEL, GMATL, and LOAEL) 

• Sediment Community (No-effect, 

Threshold, and Probable-Effect) 

• Surface Soil (Threshold) 

• Water-column Community 

(Threshold, Frank-Effect) 

For lead, we did not estimate any 

exceedances of the secondary lead 

NAAQS. 

For HCl, the average modeled 

concentration around the facility (i.e., 

the average concentration of all off-site 

data points in the modeling domain) did 

not exceed any ecological benchmark. In 

addition, each individual modeled 

concentration of HCl (i.e., each off-site 

data point in the modeling domain) was 

below the ecological benchmarks for the 

facility. 

Based on the results of the 

environmental risk screening analysis, 

we do not expect an adverse 

environmental effect as a result of HAP 

emissions from this source category. 

5. Facility-Wide Risk Results 

Facility-wide risks were estimated 

using the NEI-based data described in 

section III.C of this preamble. The 

maximum facility-wide cancer MIR is 

0.08-in-1 million, mainly driven by 

arsenic compounds, dioxins/furans, 

chromium (VI) compounds, and nickel 

compounds predominantly emitted 


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from spray dryers and the melt/reactor 

system. The total estimated cancer 

incidence from the whole facility is 

0.00001 excess cancer cases per year, or 

one excess case in every 100,000 years. 

No people are estimated to have cancer 

risks above 1-in-1 million from exposure 

to HAP emitted from both MACT and 

non-MACT sources at the single facility 

in this source category. The maximum 

facility-wide TOSHI for the source 

category is estimated by HEM–3 to be 2, 

mainly driven by emissions of chlorine 

from the melt/reactor system. 

Approximately two people are exposed 

to noncancer HI levels above 1, based on 

facility-wide emissions from the facility 

in this source category. However, once 

refined for photo-decay, the maximum 

facility-wide TOSHI for the source 

category is estimated to be 1 and no one 

is exposed to an HI greater than 1. 

6. What demographic groups might 

benefit from this regulation? 

To examine the potential for any 

environmental justice issues that might 

be associated with the source category, 

we performed a demographic analysis, 

which is an assessment of risk to 

individual demographic groups of the 

populations living near the facilities at 

different risk levels. However, because 

no one is exposed to a cancer risk 

greater than 1-in-1 million or a chronic 

noncancer HQ greater than 1, we only 

evaluated the population distributions 

living near the facility. 

The results of the demographic 

analysis are summarized in Table 3 

below. These results, for various 

demographic groups, are based on the 

population living within 50 km of the 

facility (the nearest resident is over 20 

km from the facility). 

The results of the Primary Magnesium 

Refining source category demographic 

analysis indicate that for the population 

subgroups living within 50-km of the 

facility only one subgroup (people 0 to 

17 years) is above its corresponding 

national average (40 percent versus 23 

percent nationally). 

The methodology and the results of 

the demographic analysis are presented 

in further details in a technical report, 

Risk and Technology Review—Analysis 

of Demographic Factors for Populations 

Living Near Primary Magnesium 

Refining Source Category Operations, 

available in the docket for this action. 

TABLE 3—SUMMARY OF DEMOGRAPHIC ASSESSMENT FOR THE PRIMARY MAGNESIUM REFINING SOURCE CATEGORY

[Demographic group] 

Total Minority 1

African 

American 

(%) 

Native 

American 

(%) 

Other and 

multiracial 

(%) 

Hispanic or 

Latino 

(%) 

Ages 0 to 17 

(%) 

Ages 18 to 

64 

(%) 

Ages 65 

and up 

(%) 

Over 25 

without a 

HS diploma 

(%) 

Below the 

poverty 

level 

(%) 

Linguistic 

isolation 

(%) 

National Averages 

317,746,049 .. 38 12 0.8 7 18 23 63 14 14 14 6 

Population Surrounding the Source Category Emissions 2

20,598 ........... 9 0.2 0.1 2 6 40 54 6 5 7 1 

1 Minority population is the total population minus the white population. 

2Proximity population statistics are provided irrespective of cancer and noncancer risk living within 50 km of the facility. 

C. What are our proposed decisions 

regarding risk acceptability, ample 

margin of safety, and adverse 

environmental effect? 

1. Risk Acceptability 

As noted in section III of this 

preamble, the EPA sets standards under 

CAA section 112(f)(2) using ‘‘a two-step 

standard-setting approach, with an 

analytical first step to determine an 

‘acceptable risk’ that considers all 

health information, including risk 

estimation uncertainty, and includes a 

presumptive limit on MIR of 

approximately 1-in-10 thousand’’ (see 

54 FR 38045, September 14, 1989). In 

this proposal, the EPA estimated risks 

based on actual and allowable emissions 

under the current NESHAP from the 

Primary Magnesium Refining source 

category. 

The estimated inhalation cancer risk 

to the individual most exposed to actual 

or allowable emissions from the source 

category is 0.08-in-1 million. The 

estimated incidence of cancer due to 

inhalation exposures is 0.00001 excess 

cancer cases per year, or 1 excess case 

every 100,000 years. No people are 

estimated to have cancer risks above 

1-in-1 million from HAP emitted from 

the facility in this source category. 

The estimated, refined, maximum 

chronic noncancer TOSHI from 

inhalation exposure for this source 

category is 1, indicating low likelihood 

of adverse noncancer effects from longterm inhalation exposures. 

The multipathway risk assessment 

results indicate a maximum cancer risk 

of 7-in-1 million based on ingestion 

exposures estimated for dioxins using 

the health protective risk screening 

assumptions of a Tier 3 fisher exposure 

scenario. 

The initial acute risk screening 

assessment of upper-end estimates of 

acute inhalation impacts (which were 

based on the 95th percentile estimate of 

hourly emissions) indicates a maximum 

off-site acute HQ (REL) of 3, located at 

an adjacent facility. A review of the 

surrounding property off-site of the US 

Magnesium facility also identified 

public land managed by the Bureau of 

Land Management with an HQ of 2. 

Access highways to the facilities off of 

the highway (I–80) show an HQ of 0.4, 

with the MIR residential location for the 

source category having an HQ of 0.3. 

After the initial acute risk assessment, 

we also evaluated the potential risks 

associated with an estimate of the worstcase actual hourly peak emissions, 

which we understand can occur during 

rebuilding/rehabilitative maintenance 

events of the CRB. During these events, 

we estimate that maximum off-site acute 

HQ (REL) can be as high as 11 in the 

parking lot shared with the neighboring 

facility, 7 on public uninhabited lands, 

and 1 at the nearest residential location. 

However, as is discussed in section IV.E 

of this preamble, by removing the SSM 

exemptions in this proposed action, 

proposing work practice standards for 

periods of malfunction, and with 

current emission limits in the NESHAP 

applying at all other times, including 

rebuild/rehabilitative maintenance of 

the CRB, this potential elevated acute 

risk will be significantly reduced. 

Therefore, based on this assessment, the 

refined acute results indicate that at 

baseline, the acute HQ could be as high 

as 11, but once the proposed rule is 

finalized, including the removal of the 

exemptions, peak emissions are unlikely 

to pose significant risk. 

Considering all of the health risk 

information and factors discussed 


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above, including the uncertainties 

discussed in section III of this preamble, 

the EPA proposes that the risks for this 

source category under the current 

NESHAP provisions are acceptable. 

However, we note that we have some 

concerns regarding the potential acute 

risks estimated for the baseline scenario, 

but as described above, and below in the 

ample margin of safety analysis section, 

these potential risks will be significantly 

reduced once this proposed rule is 

finalized. 

2. Ample Margin of Safety Analysis 

As directed by CAA section 112(f)(2), 

we conducted an analysis to determine 

whether the current emissions standards 

provide an ample margin of safety to 

protect public health. Under the ample 

margin of safety analysis, the EPA 

considers all health factors evaluated in 

the risk assessment and evaluates the 

cost and feasibility of available control 

technologies and other measures 

(including the controls, measures, and 

costs reviewed under the technology 

review) that could be applied to this 

source category to further reduce the 

risks (or potential risks) due to 

emissions of HAP identified in our risk 

assessment. In this analysis, we 

considered the results of the technology 

review, risk assessment, and other 

aspects of the NESHAP review to 

determine whether there are any 

emission reduction measures necessary 

to provide an ample margin of safety 

with respect to the risks associated with 

these emissions. 

The inhalation cancer risk due to HAP 

emissions from the Primary Magnesium 

Refining source category is less than 

1-in-1 million and the chronic 

noncancer TOSHI due to inhalation 

exposures is estimated to be 1 and no 

one exposed to an HI greater than 1. 

Additionally, the results of the acute 

screening analysis showed that risks 

were below a level of concern during 

normal operations. 

As described above, there are 

potential elevated acute risks associated 

with CRB controls on the melt/reactor; 

however, by removing the SSM 

exemptions in this proposed action, 

proposing work practice standards for 

periods of malfunction, and with 

current emission limits applying at all 

other times, including rebuild/ 

rehabilitative maintenance of the CRB, 

these potential elevated acute risks will 

be significantly reduced. 

With regard to PB–HAP, we identified 

and investigated the installation of 

activated carbon injection (ACI) and a 

baghouse with catalytic filters as an 

option to further reduce dioxin 

emissions and risks. The use of ACI plus 

catalytic filters to reduce dioxin 

emissions was evaluated and 

determined not to be cost effective 

during the original NESHAP. Based on 

our current review of that information, 

we do not believe the associated costs 

for installing and operating a baghouse 

have changed significantly since the 

original NESHAP. When evaluating the 

cost effectiveness of installing ACI and 

a baghouse with catalytic filters during 

the development of the 2003 Primary 

Magnesium Refining NESHAP, a full 

cost analysis was performed for the 

facility. Based on our reevaluation of 

this information and an updated 

analysis, we estimate these controls 

would have capital cost of about $1 

million, annual costs of $600,000, and 

would achieve about 2 grams reduction 

per year (95 percent reduction), with 

cost effectiveness of $289,000 per gram 

of dioxin removal, and the maximum 

cancer risk would be reduced from 

7-in-1 million to about 1-in-1 million 

(for more details see Legacy Docket A– 

2002–0043, Document II–B–5). Due to 

the relatively high cost, coupled with 

the small reduction in dioxin emissions, 

we conclude that these controls are not 

cost effective, and would only achieve 

modest reduction in risks. We did not 

identify any relevant non-air quality 

health and environmental impacts, and 

energy requirements. Based upon the 

relatively low baseline risks, minimal 

available risk reductions, and lack of 

cost-effective control options to reduce 

emissions, we are not proposing revised 

standards for dioxins and furans in this 

action. 

In summary, we are proposing that 

baseline risks from the source category 

are acceptable, and we are proposing 

rule changes (described above) to 

remove SSM exemptions and add work 

practice standards for CRB malfunction 

events. With these proposed revisions 

along with the current emissions limits 

for chlorine and other HAP applying at 

all times, the potential acute risks of 

chlorine will be addressed. 

Furthermore, we did not identify costeffective controls for dioxins. Therefore, 

we are proposing that after the rule 

changes described above are finalized, 

the NESHAP will provide an ample 

margin of safety to protect public health. 

Since the removal of the SSM 

exemptions and addition of work 

practices for malfunctions help address 

the acute risks, we are proposing to 

adopt these amendments under CAA 

section 112(f), in addition to authorities 

112(d)(2), 112(d)(3), or 112(h), as 

described elsewhere in this preamble. 

3. Adverse Environmental Effect 

As described in section III.A of this 

preamble, we conducted an 

environmental risk screening 

assessment for the Primary Magnesium 

Refining source category. We do not 

expect there to be an adverse 

environmental effect as a result of HAP 

emissions from this source category and 

we are proposing that it is not necessary 

to set any additional standards, beyond 

those described above, to prevent, 

taking into consideration costs, energy, 

safety, and other relevant factors, an 

adverse environmental effect. 

D. What are the results and proposed 

decisions based on our technology 

review? 

As described in section III.B of this 

preamble, the technology review focuses 

on the identification and evaluation of 

developments in practices, processes, 

and control technologies that have 

occurred since the MACT standards 

were promulgated. We also evaluate, 

during the technology review, whether 

there are any unregulated emissions of 

HAP within the source category, and we 

establish standards if we identify 

unregulated emissions. In conducting 

the technology review, we reviewed 

various informational sources regarding 

the emissions from the Primary 

Magnesium Refining source category. 

The review included a search of the 

internet and Reasonably Available 

Control Technology, Best Available 

Control Technology, and Lowest 

Achievable Emission Rate 

Clearinghouse database, reviews of air 

permits, and discussions with industry 

representatives. We reviewed these data 

sources for information on practices, 

processes, and control technologies that 

were not considered during the 

development of the Primary Magnesium 

Refining NESHAP. We also looked for 

information on improvements in 

practices, processes, and control 

technologies that have occurred since 

the development of the Primary 

Magnesium Refining NESHAP. 

Based on this review, the EPA 

identified a development in technology 

and practices regarding pH monitoring 

for acid gas control devices. 

Specifically, the EPA is proposing to 

amend the emission limitations and 

operating parameters set forth in 40 CFR 

63.9890(b) to include pH as an 

additional operational parameter for all 

control devices used to meet the acid 

gas emission limits of this subpart. We 

have determined that this change 

reflects a development in technology 

and practices pursuant to CAA section 

112(d)(6), that is consistent with other 


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Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 1411 

NESHAP that cover acid-gas emitting 

source categories, such as the HCl 

Production source category, that 

requires pH as an operational parameter. 

Monitoring and maintaining the 

appropriate pH levels are important to 

ensure the effectiveness of acid gas 

control devices (i.e., wet scrubbers). 

This is particularly relevant to this 

source category since each stack covered 

in this subpart is subject to an acid gas 

emissions limitation (either chlorine, 

HCl, or both). Therefore, in addition to 

maintaining the hourly average pressure 

drops and scrubber liquid flow rates, we 

are proposing that pH must also be 

measured and maintained within the 

operating range values established 

during the performance test for all 

control devices used to meet the acid 

gas emission limits of this subpart. The 

proposed installation, operation, and 

maintenance requirements specifically 

for pH are included in 40 CFR 

63.9921(a)(3). In addition, there are 

minor amendments to 40 CFR 63.9916, 

63.9917, 63.9920, and 63.9923 to 

include pH in all CPMS related 

requirements. 

Furthermore, as described above in 

section IV.A, we evaluated the potential 

to require an incinerator and wet 

scrubber to achieve additional 

reductions of chlorine from the CBS, 

however, due to significant 

uncertainties in emissions and costs of 

controls, we are not proposing such 

controls under CAA section 112(d)(2) or 

(d)(3). For the same reasons, we are also 

not proposing such controls under CAA 

section 112(d)(6). 

In addition, as part of the technology 

review, we identified a previously 

unregulated process and pollutant, and 

are regulating them under CAA sections 

112(d)(2) and (3), as described in section 

IV.A, above. 

In summary, after reviewing all of this 

information, we identified one 

development in technology and 

practices regarding pH monitoring for 

acid gas control devices. We did not 

identify any additional cost-effective 

developments in practices, processes, or 

control technologies used at primary 

magnesium refining facilities since 

promulgation of the MACT standard 

that warrant revision to the NESHAP 

pursuant to CAA section 112(d)(6) at 

this time. For all four emission points, 

US Magnesium uses wet scrubbers 

(packed-bed and venturi scrubbers) to 

achieve the emission limits. We 

concluded that wet scrubbing systems 

are the most appropriate and practical 

control systems and that there is no 

other control equipment or methods of 

control that would be more effective for 

reducing their emissions taking into 

consideration cost, feasibility, and 

uncertainties. 

E. What other actions are we proposing? 

In addition to the proposed actions 

described above, we are proposing 

additional revisions to the NESHAP. We 

are proposing revisions to the SSM 

provisions of the MACT rule in order to 

ensure that they are consistent with the 

decision in Sierra Club v. EPA, 551 F. 

3d 1019 (D.C. Cir. 2008), in which the 

court vacated two provisions that 

exempted sources from the requirement 

to comply with otherwise applicable 

CAA section 112(d) emission standards 

during periods of SSM. We are also 

proposing various other changes, 

including an alternative standard for 

malfunction events for the CRB and the 

addition of electronic reporting. Our 

analyses and proposed changes related 

to these issues are discussed below. 

1. SSM 

In its 2008 decision in Sierra Club v. 

EPA, 551 F.3d 1019 (D.C. Cir. 2008), the 

court vacated portions of two provisions 

in the EPA’s CAA section 112 

regulations governing the emissions of 

HAP during periods of SSM. 

Specifically, the court vacated the SSM 

exemption contained in 40 CFR 

63.6(f)(1) and (h)(1), holding that under 

section 302(k) of the CAA, emissions 

standards or limitations must be 

continuous in nature and that the SSM 

exemption violates the CAA’s 

requirement that some CAA section 112 

standards apply continuously. 

Consistent with Sierra Club v. EPA, 

we are proposing the elimination of the 

SSM exemptions in this NESHAP and 

we are proposing that emissions 

standards will apply at all times. As 

described below, we are proposing new 

work practice standards pursuant to 

CAA section 112(h) that will apply to 

CRB malfunctions. For all other sources, 

scenarios, and HAP, we are simply 

removing the SSM exemptions such that 

the current emissions limits will apply 

at all times. We are also proposing 

several revisions to Table 5 (the General 

Provisions Applicability Table) which 

are explained in more detail below. For 

example, we are proposing to eliminate 

the incorporation of the General 

Provisions’ requirement that sources 

develop an SSM plan. We also are 

proposing to eliminate and revise 

certain recordkeeping and reporting 

requirements related to the SSM 

exemption as described below. 

The EPA has attempted to ensure that 

the provisions we are proposing to 

eliminate are inappropriate, 

unnecessary, or redundant in the 

absence of the SSM exemption. We are 

specifically seeking comment on 

whether we have successfully done so. 

In proposing the standards in this 

rule, the EPA has considered startup 

and shutdown periods and, for the 

reasons explained below, is not 

proposing alternate standards for those 

periods. The primary magnesium 

refining production process is 

continuous, with control equipment 

operating at all times. The industry has 

not identified (and there are no data 

indicating) any specific problems with 

removing the provisions for startup and 

shutdown. However, we solicit 

comment on whether any situations 

exist where separate standards, such as 

work practices, would be more 

appropriate during periods of startup 

and shutdown rather than the current 

standard. 

Periods of startup, normal operations, 

and shutdown are all predictable and 

routine aspects of a source’s operations. 

Malfunctions, in contrast, are neither 

predictable nor routine. Instead they 

are, by definition, sudden, infrequent, 

and not reasonably preventable failures 

of emissions control, process, or 

monitoring equipment. (40 CFR 63.2) 

(definition of malfunction). The EPA 

interprets CAA section 112 as not 

requiring emissions that occur during 

periods of malfunction to be factored 

into development of CAA section 112 

standards and this reading has been 

upheld as reasonable by the court in 

U.S. Sugar Corp. v. EPA, 830 F.3d 579, 

606–610 (2016). Under section 112, 

emissions standards for new sources 

must be no less stringent than the level 

‘‘achieved’’ by the best controlled 

similar source and for existing sources 

generally must be no less stringent than 

the average emission limitation 

‘‘achieved’’ by the best performing 12 

percent of sources in the category (or the 

average emission limitation achieved by 

the best performing sources where, as 

here, there are fewer than 30 sources in 

the source category). There is nothing in 

CAA section 112 that directs the Agency 

to consider malfunctions in determining 

the level ‘‘achieved’’ by the best 

performing sources when setting 

emission standards. As the court has 

recognized, the phrase ‘‘average 

emissions limitation achieved by the 

best performing 12 percent of sources 

‘‘says nothing about how the 

performance of the best units is to be 

calculated.’’ Nat’l Ass’n of Clean Water 

Agencies v. EPA, 734 F.3d 1115, 1141 

(D.C. Cir. 2013). While the EPA 

accounts for variability in setting 

emissions standards, nothing in CAA 

section 112 requires the Agency to 

consider malfunctions as part of that 

analysis. The EPA is not required to 


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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. 

Although no statutory language 

compels the EPA to set separate 

standards for malfunctions, the EPA has 

the discretion to do so where feasible. 

For example, in the Petroleum Refinery 

Sector RTR, the EPA established a work 

practice standard for unique types of 

malfunction that result in releases from 

pressure relief devices or emergency 

flaring events because the EPA had 

information to determine that such work 

practices reflected the level of control 

that applies to the best performers. 80 

FR 75178, 75211 through 14 (December 

1, 2015). The EPA will consider whether 

circumstances warrant setting standards 

for a particular type of malfunction and, 

if so, whether the EPA has sufficient 

information to identify the relevant best 

performing sources and establish a 

standard for such malfunctions. (We 

also encourage commenters to provide 

any such information.) 

Given the EPA’s discretion to set 

separate standards for malfunctions, we 

are proposing a standard for this source 

category to address the CRB emission 

point. Based on our knowledge of the 

processes and engineering judgement, 

we expect that the standard for normal 

operations for the melt/reactor (100 lbs/ 

hr) cannot be met during malfunctions 

of the CRB (unavoidable and 

unanticipated breakdowns), unless the 

melt/reactor is stopped, which the 

facility has indicated cannot be done 

instantaneously due to the molten 

process. The CRB is the primary 

chlorine control device for the melt/ 

reactor system. The CRB converts the 

chlorine gas stream from the melt/ 

reactor to HCl. A high percentage of the 

HCl is then captured through a series of 

wet scrubbers. If the CRB is offline, the 

chlorine emissions continue to pass 

through the wet scrubbers; however, 

without the conversion to HCl, removal 

is significantly reduced. Therefore, the 

EPA anticipates that malfunctions of the 

CRB will result in violations of the 

current chlorine standard (i.e., 100 lbs/ 

hr) during a significant portion of the 

malfunction events if the melt reactor 

process continues to operate. To address 

this issue, the EPA is proposing work 

practice standards in Table 4 to 40 CFR 

part 63, subpart TTTTT to apply during 

CRB malfunctions to ensure that a CAA 

section 112 standard applies 

continuously. Based on discussions 

with the facility, CRB malfunctions are 

infrequent, unpredictable, and highly 

variable in nature. Furthermore, these 

events are typically short, requiring a 

few hours for the facility to replace or 

repair the malfunctioning equipment. 

Because of this, it is not technically 

feasible to measure emissions during the 

brief periods when these situations 

occur (i.e., unpredictable, highly 

variable, and short in duration). 

As noted in CAA section 112(h)(1), ‘‘if 

it is not feasible in the judgment of the 

Administrator to prescribe or enforce an 

emission standard for control of a 

hazardous air pollutant or pollutants, 

the Administrator may, in lieu thereof, 

promulgate a design, equipment, work 

practice, or operational standard, or 

combination thereof, which in the 

Administrator’s judgment is consistent 

with the provisions of subsection (d) or 

(f).’’ CAA section 112(h)(2) defines the 

phrase ‘‘not feasible to prescribe or 

enforce an emission standard’’ as any 

situation in which the Administrator 

determines that either ‘‘a hazardous air 

pollutant or pollutants cannot be 

emitted through a conveyance designed 

and constructed to emit or capture such 

pollutant, or that any requirement for, or 

use of, such a conveyance would be 

inconsistent with any Federal, State or 

local law’’ or ‘‘the application of 

measurement methodology to a 

particular class of sources is not 

practicable due to technological and 

economic limitations.’’ 

Based on the information described 

above, the EPA is proposing work 

practice standards pursuant to CAA 

section 112(h) that will apply to the 

melt/reactor and the CRB during periods 

when a malfunction occurs to the CRB. 

We are proposing the following work 

practices for these periods that include 

the following requirements: (1) During 

unplanned/unavoidable CRB 

malfunction events, the facility must 

shutdown the reactor as soon as 

practicable but not later than 15 minutes 

after such event occurs and keep the 

reactor offline during the CRB repair 

process; and (2) operators must perform 

a root cause analysis/corrective action. 

This includes conducting a root cause 

analysis to determine the source, nature, 

and cause of each malfunction event 

and identifying corrective measures to 

prevent future such malfunction events 

as soon as practicable, but no later than 

45 days after a malfunction event. 


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Corrective actions must be implemented 

as soon as practicable, but no later than 

45 days after a malfunction event or as 

soon thereafter as practicable. If there is 

a second release event in a 12-month 

period with the same root cause on the 

same equipment, it would be a 

deviation of the work practice standard. 

However, as an alternative to this work 

practice standard, we propose that 

facility would be allowed to keep melt 

reactor operating if they reroute the 

emissions to an equally effective backup control device configuration, such as 

a back-up CRB and wet scrubber. 

With regard to other emissions 

sources (e.g., spray dryers, magnesium 

chloride storage bins, launder off-gas 

systems), the EPA anticipates that it is 

unlikely that a malfunction will result 

in a violation of the standard because 

the air pollution control equipment or 

other measures used to limit the 

emissions from these processes would 

still be operational. If the malfunction 

occurs in the pollution control 

equipment for these other processes, the 

operators should discontinue process 

operations until such time that the air 

pollution control systems are operable 

in order to comply with the 

requirements to minimize emissions 

and operate according to good air 

pollution practices. In general, process 

operations should be able to be shut 

down quickly enough to avoid a 

violation of an emissions limitation. 

Nevertheless, we expect there could be 

situations where a malfunction in the 

control equipment could result in a 

violation of the standard depending on 

how quickly emissions decline upon 

process shut down. In this case, owners 

or operators must report the deviation, 

the quantity of HAP emitted over the 

emissions limit, the cause of the 

deviation, and the corrective action 

taken to limit the emissions during the 

event. 

In the unlikely event that a source 

fails to comply with the applicable CAA 

section 112(d) standards as a result of a 

malfunction event, the EPA would 

determine an appropriate response 

based on, among other things, the good 

faith efforts of the source to minimize 

emissions during malfunction periods, 

including preventative and corrective 

actions, as well as root cause analyses 

to ascertain and rectify excess 

emissions. The EPA would also 

consider whether the source’s failure to 

comply with the CAA section 112(d) 

standard was, in fact, sudden, 

infrequent, not reasonably preventable, 

and was not instead caused, in part, by 

poor maintenance or careless operation. 

40 CFR 63.2 (definition of malfunction). 

If the EPA determines in a particular 

case that an enforcement action against 

a source for violation of an emission 

standard is warranted, the source can 

raise any and all defenses in that 

enforcement action and the federal 

district court will determine what, if 

any, relief is appropriate. The same is 

true for citizen enforcement actions. 

Similarly, the presiding officer in an 

administrative proceeding can consider 

any defense raised and determine 

whether administrative penalties are 

appropriate. 

In summary, the EPA interpretation of 

the CAA and, in particular, CAA section 

112, is reasonable and encourages 

practices that will avoid malfunctions 

and judicial procedures for addressing 

exceedances of the standards fully 

recognize that violations may occur 

despite good faith efforts to comply and 

can accommodate those situations. U.S. 

Sugar Corp. v. EPA, 830 F.3d 579, 606– 

610 (2016). 

We are also proposing several 

revisions to the General Provisions 

Applicability Table (Table 5) which are 

explained in more detail below as 

follows. We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.6(e)(1)(i) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ Section 63.6(e)(1)(i) describes the 

general duty to minimize emissions. 

Some of the language in that section is 

no longer necessary or appropriate in 

light of the elimination of the SSM 

exemption. We are proposing instead to 

add general duty regulatory text at 40 

CFR 63.9910(b) that reflects the general 

duty to minimize emissions while 

eliminating the reference to periods 

covered by an SSM exemption. The 

current language in 40 CFR 63.6(e)(1)(i) 

characterizes what the general duty 

entails during periods of SSM. With the 

elimination of the SSM exemption, 

there is no need to differentiate between 

normal operations and SSM events in 

describing the general duty. Therefore, 

the language the EPA is proposing for 40 

CFR 63.9910(b) does not include that 

language from 40 CFR 63.6(e)(1). 

We are also proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.6(e)(1)(ii) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ Section 63.6(e)(1)(ii) imposes 

requirements that are not necessary with 

the elimination of the SSM exemption 

or are redundant with the general duty 

requirement being added at 40 CFR 

63.9910(b). 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.6(e)(3) by 

changing the ‘‘yes’’ in the column titled 

‘‘Applies to Subpart TTTTT’’ to a ‘‘no.’’ 

Generally, these paragraphs require 

development of an SSM plan and 

specify SSM recordkeeping and 

reporting requirements related to the 

SSM plan. As noted, the EPA is 

proposing to remove the SSM 

exemptions. Therefore, affected units 

will be subject to an emission standard 

during such events. The applicability of 

a standard during such events will 

ensure that sources have ample 

incentive to plan for and achieve 

compliance and, thus, the SSM plan 

requirements are no longer necessary. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.6(f)(1) by 

changing the ‘‘yes’’ in the column titled 

‘‘Applies to Subpart TTTTT’’ to a ‘‘no.’’ 

The current language of 40 CFR 

63.6(f)(1) exempts sources from 

nonopacity standards during periods of 

SSM. As discussed above, the court in 

Sierra Club v. EPA vacated the 

exemptions contained in this provision 

and held that the CAA requires that 

some CAA section 112 standards apply 

continuously. Consistent with Sierra 

Club v. EPA, the EPA is proposing to 

revise standards in this rule to apply at 

all times and proposing a new work 

practice standard for CRB malfunction 

events. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.7(e)(1) by 

changing the ‘‘yes’’ in the column titled 

‘‘Applies to Subpart TTTTT’’ to a ‘‘no.’’ 

Section 63.7(e)(1) describes performance 

testing requirements. The EPA is instead 

proposing to add a performance testing 

requirement at 40 CFR 63.9913(a). The 

performance testing requirements we 

are proposing to add differ from the 

General Provisions performance testing 

provisions in several respects. The 

regulatory text removes the 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 malfunctions. As in 40 

CFR 63.7(e)(1), performance tests 

conducted under this subpart should 

not be conducted during malfunctions 

because conditions during malfunctions 

are often not representative of normal 

operating conditions. The EPA is 

proposing to add language that requires 

the owner or operator to record the 

process information that is necessary to 

document operating conditions during 


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1414 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

the test and include in such record an 

explanation to support that such 

conditions represent normal operation. 

Section 63.7(e) requires that the owner 

or operator make available to the 

Administrator such records ‘‘as may be 

necessary to determine the condition of 

the performance test’’ available to the 

Administrator upon request but does 

not specifically require the information 

to be recorded. The regulatory text the 

EPA is proposing to add to this 

provision builds on that requirement 

and makes explicit the requirement to 

record the information. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.8(c)(1)(i) 

and (iii) by changing the ‘‘yes’’ in the 

column titled ‘‘Applies to Subpart 

TTTTT’’ to a ‘‘no.’’ The cross-references 

to the general duty and SSM plan 

requirements in those subparagraphs are 

not necessary in light of other 

requirements of 40 CFR 63.8 that require 

good air pollution control practices (40 

CFR 63.8(c)(1)) and that set out the 

requirements of a quality control 

program for monitoring equipment (40 

CFR 63.8(d)). 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.10(b)(2)(i) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ Section 63.10(b)(2)(i) describes 

the recordkeeping requirements during 

startup and shutdown. These recording 

provisions are no longer necessary 

because the EPA is proposing that 

recordkeeping and reporting applicable 

to normal operations will apply to 

startup and shutdown. In the absence of 

special provisions applicable to startup 

and shutdown, such as a startup and 

shutdown plan, there is no reason to 

retain additional recordkeeping for 

startup and shutdown periods. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.10(b)(2)(ii) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ Section 63.10(b)(2)(ii) describes 

the recordkeeping requirements during 

a malfunction. The EPA is proposing to 

add such requirements to 40 CFR 

63.9932. The regulatory text we are 

proposing to add differs from the 

General Provisions it is replacing in that 

the General Provisions requires the 

creation and retention of a record of the 

occurrence and duration of each 

malfunction of process, air pollution 

control, and monitoring equipment. The 

EPA is proposing that this requirement 

apply to any failure to meet an 

applicable standard and is requiring that 

the source record the date, time, and 

duration of the failure rather than the 

‘‘occurrence.’’ The EPA is also 

proposing to add to 40 CFR 63.9932 a 

requirement that sources keep records 

that include a list of the affected source 

or equipment and actions taken to 

minimize emissions, an estimate of the 

quantity of each regulated pollutant 

emitted over the standard for which the 

source failed to meet the standard, and 

a description of the method used to 

estimate the emissions. Examples of 

such methods would include product 

loss calculations, mass balance 

calculations, measurements when 

available, or engineering judgment 

based on known process parameters. 

The EPA is proposing to require that 

sources keep records of this information 

to ensure that there is adequate 

information to allow the EPA to 

determine the severity of any failure to 

meet a standard, and to provide data 

that may document how the source met 

the general duty to minimize emissions 

when the source has failed to meet an 

applicable standard. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.10(b)(2)(iv) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ When applicable, the provision 

requires sources to record actions taken 

during SSM events when actions were 

inconsistent with their SSM plan. The 

requirement is no longer appropriate 

because SSM plans will no longer be 

required. The requirement previously 

applicable under 40 CFR 

63.10(b)(2)(iv)(B) to record actions to 

minimize emissions and record 

corrective actions is now applicable by 

reference to 40 CFR 63.9932. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.10(b)(2)(v) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ When applicable, the provision 

requires sources to record actions taken 

during SSM events to show that actions 

taken were consistent with their SSM 

plan. The requirement is no longer 

appropriate because SSM plans will no 

longer be required. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.10(c)(15) 

by changing the ‘‘yes’’ in the column 

titled ‘‘Applies to Subpart TTTTT’’ to a 

‘‘no.’’ The EPA is proposing that 40 CFR 

63.10(c)(15) no longer applies. When 

applicable, the provision allows an 

owner or operator to use the affected 

source’s SSM plan or records kept to 

satisfy the recordkeeping requirements 

of the SSM plan, specified in 40 CFR 

63.6(e), to also satisfy the requirements 

of 40 CFR 63.10(c)(10) through (12). The 

EPA is proposing to eliminate this 

requirement because SSM plans would 

no longer be required, and, therefore, 40 

CFR 63.10(c)(15) no longer serves any 

useful purpose for affected units. 

We are proposing to revise the 

General Provisions Applicability Table 

(Table 5) entry for 40 CFR 63.10(d)(5) by 

changing the ‘‘yes’’ in the column titled 

‘‘Applies to Subpart TTTTT’’ to a ‘‘no.’’ 

Section 63.10(d)(5) describes the 

reporting requirements for startups, 

shutdowns, and malfunctions. To 

replace the General Provisions reporting 

requirement, the EPA is proposing to 

add reporting requirements to 40 CFR 

63.9931(b)(4). The replacement language 

differs from the General Provisions 

requirement in that it eliminates 

periodic SSM reports as a stand-alone 

report. We are proposing language that 

requires sources that fail to meet an 

applicable standard at any time to report 

the information concerning such events 

in the semi-annual compliance report 

already required under this rule. We are 

proposing that the report must contain 

the number, date, time, duration, and 

the cause of such events (including 

unknown cause, if applicable), a list of 

the affected source or equipment, an 

estimate of the quantity of each 

regulated pollutant emitted over any 

emission limit, and a description of the 

method used to estimate the emissions. 

Examples of such methods would 

include product-loss calculations, mass 

balance calculations, measurements 

when available, or engineering 

judgment based on known process 

parameters. The EPA is proposing this 

requirement to ensure that there is 

adequate information to determine 

compliance, to allow the EPA to 

determine the severity of the failure to 

meet an applicable standard, and to 

provide data that may document how 

the source met the general duty to 

minimize emissions during a failure to 

meet an applicable standard. 

We will no longer require owners or 

operators to determine whether actions 

taken to correct a malfunction are 

consistent with an SSM plan, because 

SSM plans would no longer be required. 

The proposed amendments, therefore, 

eliminate the cross-reference to 40 CFR 

63.10(d)(5)(i) that contains the 

description of the previously required 

SSM report format and submittal 

schedule from this section. These 

specifications are no longer necessary 

because the events will be reported in 

otherwise required reports with similar 

format and submittal requirements. 

The proposed amendments eliminate 

the cross-reference to 40 CFR 

63.10(d)(5)(ii), which requires an 


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21https://www.epa.gov/electronic-reporting-airemissions/electronic-reporting-tool-ert. 

22EPA’s Final Plan for Periodic Retrospective 

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

www.regulations.gov/document?D=EPA-HQ-OA2011-0156-0154. 

23E-Reporting Policy Statement for EPA 

Regulations, September 2013. Available at: https:// 

www.epa.gov/sites/production/files/2016-03/ 

documents/epa-ereporting-policy-statement-2013- 

09-30.pdf. 

24 Digital Government: Building a 21st Century 

Platform to Better Serve the American People, May 

2012. Available at: https://obamawhitehouse.

archives.gov/sites/default/files/omb/egov/digitalgovernment/digital-government.html. 

immediate report for SSM when a 

source failed to meet an applicable 

standard but did not follow the SSM 

plan. We will no longer require owners 

and operators to report when actions 

taken during a startup, shutdown, or 

malfunction were not consistent with an 

SSM plan, because SSM plans would no 

longer be required. 

2. Electronic Reporting 

The EPA is proposing that owners and 

operators of primary magnesium 

refining facilities submit electronic 

copies of required performance test 

reports and performance evaluation 

reports through the EPA’s Central Data 

Exchange (CDX) using the Compliance 

and Emissions Data Reporting Interface 

(CEDRI). A description of the electronic 

data submission process is provided in 

the memorandum, Electronic Reporting 

Requirements for New Source 

Performance Standards (NSPS) and 

National Emission Standards for 

Hazardous Air Pollutants (NESHAP) 

Rules, available in the docket for this 

action. The proposed rule requires that 

performance test results collected using 

test methods that are supported by the 

EPA’s Electronic Reporting Tool (ERT) 

as listed on the ERT website 21 at the 

time of the test be submitted in the 

format generated through the use of the 

ERT or an electronic file consistent with 

the xml schema on the ERT website, and 

other performance test results be 

submitted in portable document format 

(PDF) using the attachment module of 

the ERT. 

Additionally, the EPA has identified 

two broad circumstances in which 

electronic reporting extensions may be 

provided. These circumstances are (1) 

outages of the EPA’s CDX or CEDRI 

which preclude an owner or operator 

from accessing the system and 

submitting required reports and (2) force 

majeure events, which are defined as 

events that will be or have been caused 

by circumstances beyond the control of 

the affected facility, its contractors, or 

any entity controlled by the affected 

facility that prevent an owner or 

operator from complying with the 

requirement to submit a report 

electronically. Examples of force 

majeure events are acts of nature, acts 

of war or terrorism, or equipment failure 

or safety hazards beyond the control of 

the facility. The EPA is providing these 

potential extensions to protect owners 

and operators from noncompliance in 

cases where they cannot successfully 

submit a report by the reporting 

deadline for reasons outside of their 

control. In both circumstances, the 

decision to accept the claim of needing 

additional time to report is within the 

discretion of the Administrator, and 

reporting should occur as soon as 

possible. 

The electronic submittal of the reports 

addressed in this proposed rulemaking 

will increase the usefulness of the data 

contained in those reports, is in keeping 

with current trends in data availability 

and transparency, will further assist in 

the protection of public health and the 

environment, will improve compliance 

by facilitating the ability of regulated 

facilities to demonstrate compliance 

with requirements, and by facilitating 

the ability of delegated state, local, 

tribal, and territorial air agencies and 

the EPA to assess and determine 

compliance, and will ultimately reduce 

burden on regulated facilities, delegated 

air agencies, and the EPA. Electronic 

reporting also eliminates paper-based, 

manual processes, thereby saving time 

and resources, simplifying data entry, 

eliminating redundancies, minimizing 

data reporting errors, and providing data 

quickly and accurately to the affected 

facilities, air agencies, the EPA, and the 

public. Moreover, electronic reporting is 

consistent with the EPA’s plan 22 to 

implement Executive Order 13563 and 

is in keeping with the EPA’s agencywide policy 23 developed in response to 

the White House’s Digital Government 

Strategy.24 For more information on the 

benefits of electronic reporting, see the 

memorandum, Electronic Reporting 

Requirements for New Source 

Performance Standards (NSPS) and 

National Emission Standards for 

Hazardous Air Pollutants (NESHAP) 

Rules, referenced earlier in this section. 

F. What compliance dates are we 

proposing? 

The EPA is proposing two separate 

compliance dates for affected facilities, 

based on the different amendments in 

the rulemaking. For the proposed 

amendments regarding the MACT 

standard for the CBS, the work practice 

standard for CRB malfunctions, the 

elimination of SSM exemptions, and 

electronic reporting requirements, we 

are proposing that affected facilities that 

have constructed or reconstructed on or 

before January 8, 2021, must comply by 

the effective date of the final rule. For 

the proposed requirement to add pH as 

an additional control device operational 

parameter, we propose that the affected 

facilities that have constructed or 

reconstructed on or before January 8, 

2021, must comply no later than 180 

days after the effective date of the final 

rule. For affected facilities that 

commence construction or 

reconstruction after January 8, 2021, 

owners or operators must comply with 

all requirements of the subpart, 

including all the amendments being 

proposed, no later than the effective 

date of the final rule or upon startup, 

whichever is later. 

Based on our understanding of the 

facility operations and experience with 

similar industries, we believe that the 

effective date of the final rule is 

appropriate for the proposed MACT 

CBS standard, CRB work practice 

standard, elimination of SSM 

exemptions, and electronic reporting 

requirement. Regarding these new 

proposed CBS and CRB requirements, 

the facility already routinely performs 

these operations. The CRB work practice 

for malfunctions require minimal 

additional effort to implement (i.e. 

shutting down the melt/reactor process). 

Furthermore, it is current facility policy 

to perform a root cause analysis on any 

CRB malfunction events. The CBS 

control device operational requirements 

are largely being met during current 

plant operations. Regarding the 

compliance testing requirements, 

depending on the configuration of the 

stack, adjustments may need to be made 

in order to perform the required 

performance tests, such as the 

installation of inlet and outlet sampling 

ports at the CBS control device stack. 

However, provisions in 40 CFR 63.9911, 

regarding performance tests and initial 

compliance demonstrations, allow up to 

180 days after the compliance date to 

conduct such tests, which we believe is 

sufficient time for the facility to 

demonstrate compliance with the 

proposed CBS standard. The electronic 

reporting burden is minimal as it 

eliminates paper-based, manual 

processes, thereby saving time and 

resources as well as simplifying data 

entry. We do not expect that the 

proposed SSM revisions will require 

any new control systems and very few, 

if any, operational changes. The primary 

magnesium refining is a continuous 

operation, with minimal startup and 

shutdown, and control devices 

operating at all times. Additionally, 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1416 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

much of the revisions are eliminating 

additional records and reports related to 

SSM. These changes can be 

implemented quickly by the owner or 

operator at no cost (and likely some cost 

savings) and if these records are still 

collected after the final rule is 

promulgated, the facility will still be in 

compliance with the proposed 

requirements. Therefore, based on the 

reasoning above, we are proposing that 

affected facilities will need to comply 

with these amendments by the effective 

date of the final rule. For affected 

facilities that commence construction or 

reconstruction after January 8, 2021, 

owners or operators must comply with 

all requirements of the subpart, 

including all the amendments being 

proposed, no later than the effective 

date of the final rule or upon startup, 

whichever is later. 

The EPA is also proposing to amend 

the emission limitations and operating 

parameters set forth in 40 CFR 

63.9890(b) to include pH as an 

additional operational parameter for all 

control devices used to meet the acid 

gas emission limits of this subpart. The 

facility currently monitors and 

maintains the hourly average pressure 

drops and liquid flow rates for all 

control devices; however, the additional 

requirement to monitor pH would 

require the installation and 

implementation of continuous pH 

monitors. Therefore, in order to provide 

time for implementation, we are 

proposing that it is necessary to provide 

180 days after the effective date of the 

final rule for all affected facilities that 

have constructed or reconstructed on or 

before January 8, 2021, to comply with 

the new pH operational parameters. For 

affected facilities that commence 

construction or reconstruction after 

January 8, 2021, we are proposing 

owners or operators comply with the 

new pH operational parameters by the 

effective date of the final rule (or upon 

startup, whichever is later). 

We solicit comment on the proposed 

compliance periods, and we specifically 

request submission of information from 

sources in this source category regarding 

specific actions that would need to be 

undertaken to comply with the 

proposed amended requirements and 

the time needed to make the 

adjustments for compliance with any of 

the revised requirements. 

V. Summary of Cost, Environmental, 

and Economic Impacts 

A. What are the affected sources? 

The Primary Magnesium Refining 

source category comprises one plant, US 

Magnesium, located in Rowley, Utah. 

US Magnesium was the sole facility 

when the original NESHAP was 

promulgated in 2011; this has not 

changed since then nor are there new 

facilities anticipated. 

B. What are the air quality impacts? 

We are proposing to establish an 

emission standard requiring MACT 

level control of chlorine emissions from 

the CBS that requires the facility to 

operate the associated control device 

and demonstrate 95 percent control 

efficiency of chlorine emissions. Since 

the facility already routinely operates 

the CBS control device, we expect 

minimal associated emissions 

reductions. However, this will ensure 

that the emissions remain controlled 

and minimized moving forward. The 

proposed amendments also include 

removal of the SSM exemptions and the 

addition of a work practice standard for 

malfunction events related to the melt/ 

reactor system. Although we are unable 

to quantify the emission reduction 

associated with these changes, we 

expect that emissions will be reduced 

by requiring the facility to meet the 

applicable standard during periods of 

SSM and that the work practice 

standard will minimize malfunction 

related emissions. 

C. What are the cost impacts? 

The proposed amendments include a 

work practice standard for malfunctions 

of the CRB and a MACT level chlorine 

emission standard for the CBS. The 

costs associated with the proposed 

amendments are expected to be 

minimal. The CRB work practice 

standard will require labor related with 

the root cause analysis condition. 

However, it is current facility policy to 

conduct such analyses following a 

malfunction related event; therefore, we 

expect no additional associated costs to 

comply with the proposed work practice 

standard. The proposed emission 

standard for the CBS will have costs 

related to recordkeeping and repeat 

performance testing. The additional 

inlet and outlet performance test is 

expected to cost an estimated $30,000 

every 2.5 years. There will likely also be 

some initial costs to drill and establish 

inlet and outlet ports on the current 

stack, which currently has no ports. We 

expect no further costs associated with 

the CBS standard (e.g., add-on controls 

or operation costs) since the facility 

already has a CBS control device and 

routinely operates it. With regard to the 

proposed electronic reporting 

requirements, which will eliminate 

paper-based manual processes, we 

expect a small initial unquantified cost 

to transition to electronic reporting, but 

that these costs will be off-set with 

savings over time such that ultimately 

there will be an unquantified reduction 

in costs to the affected facility. 

D. What are the economic impacts? 

Economic impact analyses focus on 

changes in market prices and output 

levels that result from compliance costs 

imposed as a result of this action. 

Because the costs associated with the 

proposed revisions are minimal, no 

significant economic impacts from the 

proposed amendments are anticipated. 

E. What are the benefits? 

Although the EPA does not anticipate 

any significant reductions in HAP 

emissions as a result of the proposed 

amendments, we believe that the action, 

if finalized as proposed, would result in 

some unquantified reductions in 

chlorine emissions—albeit minimal— 

and improvements to the rule and the 

further protection of public health and 

the environment. Furthermore, pursuant 

to CAA section 112(d)(2) and (3), by 

establishing a MACT standard for 

chlorine emissions from the CBS, we are 

ensuring that the associated control 

device is operational during any 

emission release and meets 

demonstratable performance criteria. 

Additionally, the proposed amendments 

requiring electronic submittal of initial 

notifications, performance test results, 

and semiannual reports will increase 

the usefulness of the data, are in 

keeping with current trends of data 

availability, will further assist in the 

protection of public health and the 

environment, and will ultimately result 

in less burden on the regulated 

community. See section IV.D.3 of this 

preamble for more information. 

VI. Request for Comments 

We solicit comments on this proposed 

action. In addition to general comments 

on this proposed action, we are also 

interested in additional data that may 

improve the risk assessments and other 

analyses. We are specifically interested 

in receiving any improvements to the 

data used in the site-specific emissions 

profiles used for risk modeling. Such 

data should include supporting 

documentation in sufficient detail to 

allow characterization of the quality and 

representativeness of the data or 

information. Section VII of this 

preamble provides more information on 

submitting data. 

VII. Submitting Data Corrections 

The site-specific emissions profiles 

used in the source category risk and 

demographic analyses and instructions 

are available for download on the RTR 


tkelley on DSKBCP9HB2PROD with PROPOSALS
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website at https://www.epa.gov/ 

stationary-sources-air-pollution/ 

primary-magnesium-refining-nationalemissions-standards-hazardous/. The 

data files include detailed information 

for each HAP emissions release point for 

the facilities in the source category. 

If you believe that the data are not 

representative or are inaccurate, please 

identify the data in question, provide 

your reason for concern, and provide 

any ‘‘improved’’ data that you have, if 

available. When you submit data, we 

request that you provide documentation 

of the basis for the revised values to 

support your suggested changes. To 

submit comments on the data 

downloaded from the RTR website, 

complete the following steps: 

1. Within this downloaded file, enter 

suggested revisions to the data fields 

appropriate for that information. 

2. Fill in the commenter information 

fields for each suggested revision (i.e., 

commenter name, commenter 

organization, commenter email address, 

commenter phone number, and revision 

comments). 

3. Gather documentation for any 

suggested emissions revisions (e.g., 

performance test reports, material 

balance calculations). 

4. Send the entire downloaded file 

with suggested revisions in Microsoft®

Access format and all accompanying 

documentation to Docket ID No. EPA– 

HQ–OAR–2020–0535 (through the 

method described in the ADDRESSES

section of this preamble). 

5. If you are providing comments on 

a single facility or multiple facilities, 

you need only submit one file for all 

facilities. The file should contain all 

suggested changes for all sources at that 

facility (or facilities). We request that all 

data revision comments be submitted in 

the form of updated Microsoft® 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/primary-magnesiumrefining-national-emissions-standardshazardous/. 

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 Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is not a significant 

regulatory action and was, therefore, not 

submitted to OMB for review. 

B. Executive Order 13771: Reducing 

Regulations and Controlling Regulatory 

Costs 

This action is not expected to be an 

Executive Order 13771 regulatory action 

because this action is not significant 

under Executive Order 12866. 

C. Paperwork Reduction Act (PRA) 

The information collection activities 

in this proposed rule have been 

submitted for approval to OMB under 

the PRA. The Information Collection 

Request (ICR) document that the EPA 

prepared has been assigned EPA ICR 

number 2098.09. You can find a copy of 

the ICR in the docket for this rule, and 

it is briefly summarized here. 

These amendments require electronic 

reporting; remove the SSM exemptions; 

and impose other revisions that affect 

reporting and recordkeeping for primary 

magnesium refining facilities. This 

information is collected to assure 

compliance with 40 CFR part 63, 

subpart TTTTT. 

Respondents/affected entities: 

Owners and operators of Primary 

Magnesium Refining Facilities. 

Respondent’s obligation to respond: 

Mandatory (40 CFR part 63, subpart 

TTTTT). 

Estimated number of respondents: 

One. 

Frequency of response: Semiannually. 

Total estimated burden: 625 hours 

(per year). Burden is defined at 5 CFR 

1320.3(b). 

Total estimated cost: $73,100 

annualized capital or operation and 

maintenance costs. 

An agency may not conduct or 

sponsor, and a person is not required to 

respond to, a collection of information 

unless it displays a currently valid OMB 

control number. The OMB control 

numbers for the EPA’s regulations in 40 

CFR are listed in 40 CFR part 9. 

Submit your comments on the 

Agency’s need for this information, the 

accuracy of the provided burden 

estimates, and any suggested methods 

for minimizing respondent burden to 

the EPA using the docket identified at 

the beginning of this rule. You may also 

send your ICR-related comments to 

OMB’s Office of Information and 

Regulatory Affairs via email to OIRA_

submission@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. Based on the Small Business 

Administration size category for this 

source category, no small entities are 

subject to this action. 

E. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain any 

unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538, and does 

not significantly or uniquely affect small 

governments. The action imposes no 

enforceable duty on any state, local, or 

tribal governments or the private sector. 

F. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government. 

G. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have tribal 

implications as specified in Executive 

Order 13175. No tribal governments 

own facilities subject to this proposed 

action. Thus, Executive Order 13175 

does not apply to this action. However, 

since a magnesium facility is located 

within 50 miles of tribal lands, 

consistent with the EPA Policy on 

Consultation and Coordination with 

Indian Tribes, we will offer tribal 

consultation for this rulemaking. 

H. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

This action is not subject to Executive 

Order 13045 because it is not 

economically significant as defined in 

Executive Order 12866, and because the 

EPA does not believe the environmental 

health or safety risks addressed by this 

action present a disproportionate risk to 

children. This action’s health and risk 

assessments are contained in section IV 

of this preamble and in the Primary 

Magnesium Refining Risk Report, which 

is available in the docket. 

I. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This action is not subject to Executive 

Order 13211, because it is not a 


tkelley on DSKBCP9HB2PROD with PROPOSALS
1418 Federal Register / Vol. 86, No. 5 / Friday, January 8, 2021 / Proposed Rules 

significant regulatory action under 

Executive Order 12866. 

J. National Technology Transfer and 

Advancement Act (NTTAA) and 1 CFR 

Part 51 

This action involves technical 

standards. Therefore, the EPA 

conducted searches for National 

Emission Standards for Hazardous Air 

Pollutants: Primary Magnesium Refining 

Residual Risk and Technology Review 

through the Enhanced NSSN Database 

managed by the American National 

Standards Institute (ANSI). We also 

contacted voluntary consensus 

standards (VCS) organizations and 

accessed and searched their databases. 

Searches were conducted for EPA 

Methods 1, 2, 2F, 2G, 3, 3A, 3B, 4, 5, 

5D, 23, 26, 26A, of 40 CFR part 60, 

appendix A, and EPA Methods 201 and 

201A of 40 CFR part 51, appendix M. 

No applicable VCS were identified for 

EPA Methods 1, 2, 2F, 2G, 5D, 23, 201 

and 201A. 

During the search, if the title or 

abstract (if provided) of the VCS 

described technical sampling and 

analytical procedures that are similar to 

the EPA’s reference method, the EPA 

considered it as a potential equivalent 

method. All potential standards were 

reviewed to determine the practicality 

of the VCS for this rule. This review 

requires significant method validation 

data which meets the requirements of 

EPA Method 301 for accepting 

alternative methods or scientific, 

engineering, and policy equivalence to 

procedures in EPA reference methods. 

The EPA may reconsider determinations 

of impracticality when additional 

information is available for particular 

VCS. 

Two VCS were identified as an 

acceptable alternative to EPA test 

methods for the purposes of this rule. 

The VCS, ANSI/ASME PTC 19–10–1981 

Part 10 (2010), ‘‘Flue and Exhaust Gas 

Analyses,’’ is an acceptable alternative 

to EPA Method 3B manual portion only 

and not the instrumental portion. The 

VCS, ASTM D6735–01(2009), ‘‘Standard 

Test Method for Measurement of 

Gaseous Chlorides and Fluorides from 

Mineral Calcining Exhaust Sources 

Impinger Method,’’ is an acceptable 

alternative to EPA Method 26 and 26A. 

The search identified 18 VCS that were 

potentially applicable for these rules in 

lieu of EPA reference methods. After 

reviewing the available standards, the 

EPA determined that 18 candidate VCS 

(ASTM D3154–00 (2014), ASTM 

D3464–96 (2014), ASTM 3796–09 

(2016), ISO 10780:1994 (2016), ASME 

B133.9–1994 (2001), ISO 10396:(2007), 

ISO 12039:2001(2012), ASTM D5835–95 

(2013), ASTM D6522–11, CAN/CSA 

Z223.2–M86 (R1999), ISO 9096:1992 

(2003), ANSI/ASME PTC–38–1980 

(1985), ASTM D3685/D3685M–98–13, 

CAN/CSA Z223.1–M1977, ISO 

10397:1993, ASTM D6331 (2014), EN 

1948–3 (1996), EN 1911:2010) identified 

for measuring emissions of pollutants or 

their surrogates subject to emission 

standards in the rule would not be 

practical due to lack of equivalency, 

documentation, validation data, and 

other important technical and policy 

considerations. Additional information 

for the VCS search and determinations 

can be found in the memorandum, 

Voluntary Consensus Standard Results 

for National Emission Standards for 

Hazardous Air Pollutants: Primary 

Magnesium Refining Residual Risk and 

Technology Review, which is available 

in the docket for this action. Under 40 

CFR 63.7(f) and 40 CFR 63.8(f) of 

subpart A of the General Provisions, a 

source may apply to the EPA to use 

alternative test methods or alternative 

monitoring requirements in place of any 

required testing methods, performance 

specifications, or procedures in the final 

rule or any amendments. 

The EPA welcomes comments on this 

aspect of the proposed rulemaking and, 

specifically, invites the public to 

identify potentially applicable VCS and 

to explain why such standards should 

be used in this regulation. 

K. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

The EPA believes that this action does 

not have disproportionately high and 

adverse human health or environmental 

effects on minority populations, lowincome populations, and/or indigenous 

peoples, as specified in Executive Order 

12898 (59 FR 7629, February 16, 1994). 

This action’s health and risk 

assessments are contained in section IV 

of this preamble. The documentation for 

this decision is contained in section 

IV.A.1 of this preamble and in the 

Primary Magnesium Refining Risk 

Report, which is available in Docket ID 

No. EPA–HQ–OAR–2020–0535. 

List of Subjects in 40 CFR Part 63 

Environmental protection, Air 

pollution control, Hazardous 

substances, Incorporation by reference, 

Reporting and recordkeeping 

requirements. 

Andrew Wheeler, 

Administrator. 

[FR Doc. 2021–00176 Filed 1–7–21; 8:45 am] 

BILLING CODE 6560–50–P 

DEPARTMENT OF TRANSPORTATION 

Federal Railroad Administration 

49 CFR Part 219 

[Docket No. FRA–2019–0071, Notice No. 1] 

RIN 2130–AC80 

Control of Alcohol and Drug Use: 

Coverage of Mechanical Employees 

and Miscellaneous Amendments 

AGENCY: Federal Railroad 

Administration (FRA), Department of 

Transportation (DOT). 

ACTION: Notice of proposed rulemaking. 

SUMMARY: In response to a Congressional 

mandate in the Substance Use-Disorder 

Prevention that Promotes Opioid 

Recovery and Treatment for Patients 

and Communities Act (SUPPORT Act), 

FRA is proposing to expand the scope 

of its alcohol and drug regulation to 

cover mechanical (MECH) employees 

who test or inspect railroad rolling 

equipment. FRA is also proposing 

miscellaneous, clarifying amendments 

to its alcohol and drug regulation. 

DATES: Written comments on this 

proposed rule must be received on or 

before March 9, 2021. Comments 

received after that date will be 

considered to the extent possible 

without incurring additional expense or 

delay. 

ADDRESSES: Comments: Comments 

related to Docket No. FRA–2019–0071 

may be submitted by going to http://

www.regulations.gov and following the 

online instructions for submitting 

comments. 

Instructions: All submissions must 

include the agency name and docket 

number or Regulatory Identification 

Number (RIN) for this rulemaking. Note 

that all comments received will be 

posted without change to http://

www.regulations.gov including any 

personal information provided. Please 

see the Privacy Act heading in the 

SUPPLEMENTARY INFORMATION section of 

this document for Privacy Act 

information related to any submitted 

comments or materials. 

Docket: For access to the docket to 

read background documents, petitions 

for reconsideration, or comments 

received, go to http://

www.regulations.gov and follow the 

online instructions for accessing the 

docket. 

FOR FURTHER INFORMATION CONTACT: 

Gerald Powers, Drug and Alcohol 

Program Manager, Office of Railroad 

Safety—Office of Technical Oversight, 

telephone: 202–493–6313; email: 


tkelley on DSKBCP9HB2PROD with PROPOSALS