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Proposed Rule2024-29466

Review of National Emission Standards for Hazardous Air Pollutants for Polyether Polyols Production Industry

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Published

December 27, 2024

Issuing agencies

Environmental Protection Agency

Abstract

The U.S. Environmental Protection Agency (EPA) is proposing amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) under the Clean Air Act (CAA) that apply to the Polyether Polyols (PEPO) Production industry (referred to as the PEPO NESHAP in this document). The EPA is proposing decisions resulting from the Agency's technology review of the PEPO NESHAP and decisions based on its reconsideration of certain issues raised in an administrative petition for reconsideration. Furthermore, the EPA is proposing to strengthen the emission standards for ethylene oxide (EtO) emissions after considering the results of a risk assessment for the PEPO NESHAP. The EPA is also proposing to require performance testing once every 5 years, to add work practice standards for certain activities where alternatives are appropriate, and to add provisions for electronic reporting. We estimate that the proposed amendments to the PEPO NESHAP, excluding the EtO emission standards, would reduce hazardous air pollutant (HAP) emissions from PEPO sources by approximately 157 tons per year (tpy). Additionally, the proposed EtO emission standards are expected to reduce EtO emissions by approximately 14 tpy. We also estimate that these proposed amendments to the NESHAP will reduce excess emissions of HAP from flares in the PEPO Production source category by an additional 75 tpy.

Full Text

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[Federal Register Volume 89, Number 248 (Friday, December 27, 2024)]
[Proposed Rules]
[Pages 105986-106061]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-29466]

[[Page 105985]]

Vol. 89

Friday,

No. 248

December 27, 2024

Part IV

Environmental Protection Agency

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40 CFR Part 63

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Review of National Emission Standards for Hazardous Air Pollutants for
Polyether Polyols Production Industry; Proposed Rule

Federal Register / Vol. 89 , No. 248 / Friday, December 27, 2024 /
Proposed Rules

[[Page 105986]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2023-0282; FRL-10854-01-OAR]
RIN 2060-AW01

Review of National Emission Standards for Hazardous Air
Pollutants for Polyether Polyols Production Industry

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing
amendments to the National Emission Standards for Hazardous Air
Pollutants (NESHAP) under the Clean Air Act (CAA) that apply to the
Polyether Polyols (PEPO) Production industry (referred to as the PEPO
NESHAP in this document). The EPA is proposing decisions resulting from
the Agency's technology review of the PEPO NESHAP and decisions based
on its reconsideration of certain issues raised in an administrative
petition for reconsideration. Furthermore, the EPA is proposing to
strengthen the emission standards for ethylene oxide (EtO) emissions
after considering the results of a risk assessment for the PEPO NESHAP.
The EPA is also proposing to require performance testing once every 5
years, to add work practice standards for certain activities where
alternatives are appropriate, and to add provisions for electronic
reporting. We estimate that the proposed amendments to the PEPO NESHAP,
excluding the EtO emission standards, would reduce hazardous air
pollutant (HAP) emissions from PEPO sources by approximately 157 tons
per year (tpy). Additionally, the proposed EtO emission standards are
expected to reduce EtO emissions by approximately 14 tpy. We also
estimate that these proposed amendments to the NESHAP will reduce
excess emissions of HAP from flares in the PEPO Production source
category by an additional 75 tpy.

DATES:
Comments. Comments must be received on or before February 25, 2025.
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 January 27, 2025.
Public hearing. If anyone contacts us requesting a public hearing
on or before January 3, 2025, 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-2023-0282, by any of the following methods:
<bullet> Federal eRulemaking Portal: <a href="https://www.regulations.gov">https://www.regulations.gov</a>
(our preferred method). Follow the online instructions for submitting
comments.
<bullet> Email: <a href="/cdn-cgi/l/email-protection#9bfab6faf5ffb6e9b6fff4f8f0feefdbfeebfab5fcf4ed">[email&#160;protected]</a>. Include Docket ID No. EPA-
HQ-OAR-2023-0282 in the subject line of the message.
<bullet> Fax: 202-566-9744. Attention Docket ID No. EPA-HQ-OAR-
2023-0282.
<bullet> Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2023-0282, Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.
<bullet> 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 <a href="https://www.regulations.gov/">https://www.regulations.gov/</a>, 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.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact U.S. EPA, Attn: Ms. Johanna Klein, Mail Drop: E143-01,
109 T.W. Alexander Drive, P.O. Box 12055, Research Triangle Park, North
Carolina 27711; telephone number: (919) 541-2283; and email address:
<a href="/cdn-cgi/l/email-protection#f893949d9196d692979099969699b89d8899d69f978e">[email&#160;protected]</a>. For specific information regarding the risk
modeling methodology, contact U.S. EPA, Attn: Ms. Dianna Francisco,
Mail Drop: C539-02, 109 T.W. Alexander Drive, P.O. Box 12055, Research
Triangle Park, North Carolina 27711; telephone number: (919) 541-3182;
and email address: <a href="/cdn-cgi/l/email-protection#fb9d899a959892889894d59f929a95959abb9e8b9ad59c948d">[email&#160;protected]</a>.

SUPPLEMENTARY INFORMATION:
Participation in virtual public hearing. To request a virtual
public hearing, contact the public hearing team at (888) 372-8699 or by
email at <a href="/cdn-cgi/l/email-protection#61323131251114030d080209040013080f06210411004f060e17">[email&#160;protected]</a>. If requested, the hearing will be
held via virtual platform. The EPA will announce the date of the
hearing and further details on the virtual public hearing at <a href="https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous">https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous</a>. The hearing will
convene at 11:00 a.m. Eastern Time (ET) and will conclude at 4:00 p.m.
ET. The EPA may close a session 15 minutes after the last pre-
registered speaker has testified if there are not additional speakers.
The EPA will begin pre-registering speakers for the hearing no
later than 1 business day after a request has been received. To
register to speak at the virtual hearing, please use the online
registration form available at <a href="https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous">https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous</a> or contact the public hearing team at (888) 372-8699 or by
email at <a href="/cdn-cgi/l/email-protection#9fcccfcfdbefeafdf3f6fcf7fafeedf6f1f8dffaeffeb1f8f0e9">[email&#160;protected]</a>. The last day to pre-register to
speak at the hearing will be January 13, 2025. Prior to the hearing,
the EPA will post a general agenda that will list pre-registered
speakers at: <a href="https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous">https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous</a>.
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 4 minutes to provide oral testimony. The
EPA encourages commenters to submit a copy of their 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 <a href="https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous">https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous</a>. While the EPA expects the hearing to go forward as set forth
above, please monitor these websites or contact the public hearing team
at (888) 372-8699 or by email at <a href="/cdn-cgi/l/email-protection#ebb8bbbbaf9b9e89878288838e8a9982858cab8e9b8ac58c849d">[email&#160;protected]</a> to determine
if there are any updates. The EPA does not intend to publish a document
in the Federal Register announcing updates.

[[Page 105987]]

If you require the services of a translator or a special
accommodation such as audio description, please pre-register for the
hearing with the public hearing team and describe your needs by January
7, 2025. The EPA may not be able to arrange accommodations without
advance notice.
Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2023-0282. All documents in the docket are
listed in <a href="https://www.regulations.gov">https://www.regulations.gov</a>. 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 <a href="http://Regulations.gov">Regulations.gov</a>.
Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2023-0282. 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a>, 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 to <a href="https://www.regulations.gov">https://www.regulations.gov</a>
any information that you consider to be CBI or other information whose
disclosure is restricted by statue. This type of information should be
submitted 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 <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>.
The <a href="https://www.regulations.gov">https://www.regulations.gov</a> 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
<a href="https://www.regulations.gov">https://www.regulations.gov</a>, 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 <a href="https://www.epa.gov/dockets">https://www.epa.gov/dockets</a>.
Submitting CBI. Do not submit information containing CBI to the EPA
through <a href="https://www.regulations.gov/">https://www.regulations.gov/</a>. 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, note the docket ID,
mark the outside of the digital storage media as CBI, and 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 and note the docket ID.
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.
Our preferred method to receive CBI is for it to be transmitted
electronically using email attachments, File Transfer Protocol (FTP),
or other online file sharing services (e.g., Dropbox, OneDrive, Google
Drive). Electronic submissions must be transmitted directly to the
Office of Air Quality Planning and Standards (OAQPS) CBI Office at the
email address <a href="/cdn-cgi/l/email-protection#4b242a3a3b382829220b2e3b2a652c243d">[email&#160;protected]</a> and, as described above, should include
clear CBI markings and note the docket ID. If assistance is needed with
submitting large electronic files that exceed the file size limit for
email attachments, and if you do not have your own file sharing
service, please email <a href="/cdn-cgi/l/email-protection#caa5abbbbab9a9a8a38aafbaabe4ada5bc">[email&#160;protected]</a> to request a file transfer link.
If sending CBI information through the postal service, please send it
to the following address: U.S. EPA, Attn: OAQPS Document Control
Officer, Mail Drop: C404-02, 109 T.W. Alexander Drive, P.O. Box 12055,
Research Triangle Park, North Carolina 27711, Attention Docket ID No.
EPA-HQ-OAR-2023-0282. The mailed CBI material should be double wrapped
and clearly marked. Any CBI markings should not show through the outer
envelope.
Preamble acronyms and abbreviations. Throughout this preamble the
use of ``we,'' ``us,'' or ``our'' is intended to refer to the EPA. 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:

ACC American Chemistry Council
ACS American Community Survey
ADAF age-dependent adjustment factor
AEGL acute exposure guideline levels
AERMOD American Meteorological Society/EPA Regulatory Model
dispersion modeling system
AIHA American Industrial Hygiene Association
ANSI American National Standards Institute
APCD air pollution control device
ASME American Society of Mechanical Engineers
ATSDR Agency for Toxic Substances and Disease Registry
1-BP 1-bromopropane
BACT best available control technology
BTU British thermal units
CAA Clean Air Act
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CFR Code of Federal Regulations
CMAS Chemical Manufacturing Area Sources
CMPU chemical manufacturing process unit
CO carbon monoxide
CO<INF>2</INF> carbon dioxide
DNA deoxyribonucleic acid
EAV equivalent annualized value
ECHO Enforcement and Compliance History Online
ECO extended cookout
EFR external floating roof
EIA Economic Impact Analysis
EJ environmental justice
EMACT Ethylene Production MACT
EPA Environmental Protection Agency
ERPG emergency response planning guidelines
ERT Electronic Reporting Tool
EtO ethylene oxide
FID flame ionization detector
FTIR Fourier transform infrared spectrometry
GACT generally available control technologies

[[Page 105988]]

HAP hazardous air pollutant(s)
HCl hydrochloric acid
HEM Human Exposure Model
HF hydrofluoric acid
HON Hazardous Organic NESHAP
HQ hazard quotient
HRVOC highly reactive volatile organic compound
ICR information collection request
IFR internal floating roof
IRIS Integrated Risk Information System
ISA Integrated Science Assessment
km kilometer
kPa kilopascals
LAER lowest achievable emission rate
lb/hr pounds per hour
LDAR leak detection and repair
LEAN Louisiana Environmental Action Network
LEL lower explosive limit
MACT maximum achievable control technology
MIR maximum individual lifetime [cancer] risk
MON Miscellaneous Organic Chemical Manufacturing NESHAP
MTVP maximum true vapor pressure
NAAQS National Ambient Air Quality Standard
NAICS North American Industry Classification System
NEI National Emissions Inventory
NESHAP national emission standards for hazardous air pollutants
NHVcz net heating value in the combustion zone gas
NHVdil net heating value dilution parameter
NHVvg net heating value in the vent gas
NO<INF>X</INF> nitrogen oxides
NRDC Natural Resources Defense Council
NSPS new source performance standards
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OAR Office of Air and Radiation
OLD Organic Liquids Distribution
OMB Office of Management and Budget
P&R I Group I Polymers and Resins NESHAP
PDF portable document format
PEPO polyether polyol
PMPU polyether polyol manufacturing process unit
POM polycyclic organic matter
ppmv parts per million by volume
ppmw parts per million by weight
PRA Paperwork Reduction Act
psia pounds per square inch absolute
psig pounds per square inch gauge
PRD pressure relief devices
PV present value
RACT reasonably available control technology
RDL representative detection limit
REL Reference Exposure Level
RFA Regulatory Flexibility Act
RfC reference concentration
RTR Risk and Technology Review
SAB Science Advisory Board
SCAQMD South Coast Air Quality Management District
scmm standard cubic meters per minute
scf standard cubic foot
SOCMI Synthetic Organic Chemical Manufacturing Industry
SO<INF>2</INF> sulfur dioxide
SSM startup, shutdown, and malfunction
TCEQ Texas Commission on Environmental Quality
THF tetrahydrofuran
TOC total organic compound
TOSHI target organ-specific hazard index
tpy tons per year
TRE total resource effectiveness
TRIM Total Risk Integrated Methodology
UF uncertainty factor
UMRA Unfunded Mandates Reform Act
URE unit risk estimate
U.S. United States
U.S.C. United States Code
USGS U.S. Geological Survey
VCS voluntary consensus standards
VOC volatile organic compound(s)
[mu]g/m3 micrograms per cubic meter

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 the source category and how do the current standards
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?
E. What outreach was conducted?
III. Analytical Procedures and Decision-Making
A. How do we consider risk in our decision-making?
B. How do we estimate post-MACT risk posed by the source
category?
C. How do we perform the technology review?
D. How do we determine a MACT floor and consider beyond-the-
floor?
IV. Analytical Results and Proposed Decisions
A. What are the results of the risk assessment and analyses?
B. What are our proposed decisions regarding risk acceptability,
ample margin of safety, and adverse environmental effect?
C. What are the results and proposed decisions based on our
technology review?
D. What actions are we taking pursuant to CAA sections 112(d)(2)
and (3) and 112(h)?
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?
F. What analysis of environmental justice did we conduct?
G. What analysis of children's environmental health did we
conduct?
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 14094: Modernizing Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
I. National Technology Transfer and Advancement Act (NTTAA) and
1 CFR Part 51
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations and Executive Order 14096: Revitalizing Our Nation's
Commitment to Environmental Justice for All

I. General Information

A. Does this action apply to me?

This action applies to the PEPO Production source category (and
whose facilities, sources, and processes we often refer to as ``PEPO''
for purposes of the NESHAP). The PEPO NESHAP is codified at 40 CFR part
63, subpart PPP. The North American Industry Classification System
(NAICS) code for PEPO facilities is 325199, although this is not
intended to be exhaustive but rather to 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 PEPO Production
source category is any facility which ``manufactures these polymers by
starting with cyclic ethers (e.g., oxides, epoxides) and initiating
polymerization by adding ethylene oxide, butylene oxide, propylene
oxide or other chemicals which would result in the potential emission
of HAPs. The reaction is base-catalyzed, with potassium hydroxide being
the most commonly used catalyst. The physical

[[Page 105989]]

properties of the polyols are influenced primarily by the functionality
of the initiator molecules and by the type and quantity of alkylene
oxide and hydroxyl groups present in the polyol.'' In the development
of NESHAP for this source category, the EPA considered emission sources
associated with equipment leaks (including leaks from heat exchange
systems), process vents, storage vessels, and wastewater collection and
treatment systems.

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. In accordance with 5 U.S.C.
553(b)(4), a brief summary of this rulemaking may be found at <a href="https://www.regulations.gov">https://www.regulations.gov</a>, Docket ID No. EPA-HQ-OAR-2023-0282. Following
signature by the EPA Administrator, the EPA will post a copy of this
proposed action at <a href="https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous">https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous</a>. 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.
A memorandum showing the edits that would be necessary to
incorporate the changes to the PEPO NESHAP (40 CFR part 63, subpart
PPP) proposed in this action is available in the docket (Docket ID No.
EPA-HQ-OAR-2023-0282). Following signature by the EPA Administrator,
the EPA also will post a copy of this document to <a href="https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous">https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous</a>.

II. Background

A. What is the statutory authority for this action?

1. NESHAP
The statutory authority for this action is provided by sections 112
and 301 of the CAA, as amended (42 U.S.C. 7401 et seq.). Section 112 of
the CAA establishes a two-stage regulatory process to develop standards
for emissions of HAP from stationary sources. Generally, the first
stage involves establishing technology-based standards and the second
stage involves evaluating those standards that are based on maximum
achievable control technology (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 listed under section 112(c) and 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 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,'' that the EPA must establish without
consideration of costs. Under CAA section 112(d)(2), the EPA must also
consider control options that are more stringent than the floor, taking
into consideration costs, non-air quality health and environmental
impacts, and energy requirements. Standards more stringent than the
floor are commonly referred to as ``beyond-the-floor'' or ``BTF''
standards. In certain instances, as provided in CAA section 112(h), the
EPA may set work practice standards in lieu of numerical emission
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 affirmed that CAA section 112(f)(2) incorporates the approach
established in the Benzene NESHAP. See Natural Resources Defense
Council (NRDC) v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008).
The approach incorporated into the CAA and used by the EPA to
evaluate residual risk and to develop standards under CAA section
112(f)(2) is a two-step approach. In the first step, the EPA determines
whether risks are acceptable. This determination ``considers all health
information, including risk estimation uncertainty, and includes a
presumptive limit on maximum individual lifetime [cancer] risk (MIR)
\1\ of approximately 1 in 10 thousand.'' (54 FR 38045). If risks are
unacceptable, the EPA must determine the emissions standards necessary
to reduce risk to an acceptable level without considering costs. In the
second step of the approach, the EPA

[[Page 105990]]

considers whether the emissions standards provide an ample margin of
safety to protect public health ``in consideration of all health
information, including the number of persons at risk levels higher than
approximately 1 in 1 million, as well as other relevant factors,
including costs and economic impacts, technological feasibility, and
other factors relevant to each particular decision.'' Id. The EPA must
promulgate emission standards necessary to provide an ample margin of
safety to protect public health or determine that the standards being
reviewed provide an ample margin of safety without any revisions. After
conducting the ample margin of safety analysis, we consider whether a
more stringent standard is necessary to prevent, taking into
consideration costs, energy, safety, and other relevant factors, an
adverse environmental effect.
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\1\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk if an individual were exposed to the maximum
level of a pollutant for a lifetime.
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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 floors that were
established during earlier rulemakings. NRDC v. EPA, 529 F.3d at 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 MACT
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).
The EPA conducted a residual risk and technology review (RTR) for
the PEPO NESHAP in 2014, concluding that there was no need to revise
the PEPO NESHAP under the provisions of either CAA sections 112(f) or
(d)(6). However, the EPA did address emissions during periods of
startup, shutdown, and malfunction (SSM), including from pressure
relief devices (PRDs) in organic HAP service that release to the
atmosphere, and also required electronic reporting of performance test
results (see 79 FR 17340, March 27, 2014). As part of the 2014 residual
risk review, the EPA conducted a risk assessment, and based on the
results of the risk assessment, determined that the then current level
of control called for by the existing MACT standards both reduced HAP
emissions to levels that presented an acceptable level of risk and
provided an ample margin of safety to protect public health.
This action constitutes another CAA section 112(d)(6) technology
review for the PEPO NESHAP. This action also constitutes an updated CAA
section 112(f) risk review based on new information for the PEPO
NESHAP. As noted above, CAA section 112(f)(2)(A) requires the EPA to
promulgate standards that ``provide an ample margin of safety to
protect public health'' and prevent ``an adverse environmental
effect.'' While CAA section 112(f) does not require the EPA to
periodically revisit a residual risk review, neither does it preclude
the EPA from exercising its inherent authority to revisit a previous
regulatory decision where new scientific, technical, or other relevant
information indicates such action is warranted. Moreover, the Act does
include a gap-filling provision that reinforces the authority for the
EPA to do so. CAA section 301(a)(1) provides authority to the
Administrator ``to prescribe such regulations as are necessary to carry
out his functions'' under the CAA. Such authority extends to the EPA's
discretion to revisit its section 112(f) residual risk review where the
Agency deems warranted. See NRDC v. EPA, 22 F.3d 1125, 1148 (D.C. Cir.
1994) (``[Section 301] is sufficiently broad to allow the promulgation
of rules that are necessary and reasonable to effect the purposes of
the Act.''). We note that although there is no statutory CAA obligation
under CAA section 112(f) for the EPA to conduct a second residual risk
review of the PEPO NESHAP, the EPA retains discretion to revisit its
residual risk reviews where the Agency deems that it is warranted. See,
e.g., Fed. Commc'ns Comm'n v. Fox Television Stations, Inc., 556 U.S.
502, 515 (2009); Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto.
Ins. Co., 463 U.S. 29, 42 (1983); Ethylene Oxide Emissions Standards
for Sterilization Facilities; Final Decision, 71 FR 17712, 17715 col. 1
(April 7, 2006) (in the 2006 residual risk review of the EtO emissions
standards for sterilization facilities, the EPA asserted its
``authority to revisit (and revise, if necessary) any rulemaking if
there is sufficient evidence that changes within the affected industry
or significant improvements to science suggests the public is exposed
to significant increases in risk as compared to the risk assessment
prepared for the rulemaking (e.g., CAA section 301).''). Here, the
specific changes to health information related to a certain pollutant
emitted by the PEPO Production source category led us to determine that
it is appropriate, in this case, to conduct this second residual risk
review under CAA section 112(f). In particular, the EPA is concerned
about the cancer risks posed from the PEPO Production source category
based on the EPA's 2016 updated Integrated Risk Information System
(IRIS) inhalation unit risk estimate (URE) for EtO, which shows EtO to
be significantly more toxic than previously known.\2\ The EPA's 2014
RTR could not have had the benefit of this updated URE at the time it
was conducted, but if it had the RTR would have necessarily resulted in
different conclusions about risk acceptability and the PEPO NESHAP's
provision of an ample margin of safety to protect public health. To
ensure our standards provide an ample margin of safety to protect
public health following the new IRIS inhalation URE for EtO, we are
exercising our discretion and conducting a risk assessment in this
action for PEPO Production sources. In sum, even though we do not have
a mandatory duty to conduct repeated residual risk reviews under CAA
sections 112(f)(2) and 301(a)(1), we have the authority to revisit any
rulemaking if there is sufficient evidence of changes within the
affected industry or significant new scientific information suggesting
the public is exposed to higher risks than previously understood. Our
conducting a discretionary second residual risk review for the PEPO
Production source category to account for the new IRIS inhalation URE
for EtO is consistent with recent similar actions regarding other
source categories. See 89 FR 24090, April 5, 2024, and 89 FR 42932, May
16, 2024.
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\2\ U.S. EPA. Evaluation of the Inhalation Carcinogenicity of
Ethylene Oxide (CASRN 75-21-8) In Support of Summary Information on
the Integrated Risk Information System (IRIS). December 2016. EPA/
635/R-16/350Fa. Available at: <a href="https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf">https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf</a>. See also, 87 FR
77985 (Dec. 21, 2022), Reconsideration of the 2020 National Emission
Standards for Hazardous Air Pollutants: Miscellaneous Organic
Chemical Manufacturing Residual Risk and Technology Review, Final
action; reconsideration of the final rule.
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2. Petition for Reconsideration
In addition to the proposed action under sections 112 and 301 of
the CAA described above, this action includes proposed amendments to
the PEPO NESHAP based on the EPA's reconsideration of certain aspects
of the NESHAP that were raised in an administrative petition submitted
pursuant to section 307(d)(7)(B) of the CAA. In May 2014, the EPA
received one petition for reconsideration of the PEPO NESHAP (40 CFR
part 63, subpart

[[Page 105991]]

PPP), Pesticide Active Ingredient Production NESHAP (40 CFR part 63,
subpart MMM), and Group IV Polymers and Resins NESHAP (40 CFR part 63,
subpart JJJ) pursuant to CAA section 307(d)(7)(B) from the Louisiana
Environmental Action Network, Ohio Valley Environmental Coalition, and
Sierra Club. A copy of the petition and subsequent EPA correspondence
granting reconsideration is provided in the docket for this rulemaking
(see Docket No. EPA-HQ-OAR-2023-0282).
For the PEPO NESHAP, the petitioners requested that the EPA: (1)
remove the affirmative defense provisions from the rules in light of
the court opinion in Natural Resources Defence Council v. EPA (D.C.
Cir. April 18, 2014); (2) provide adequate opportunity to comment on
the requirements associated with emissions from PRDs (including
associated compliance dates, the EPA's decision to not specifically
require electronic indicators and alarms to monitor PRD releases to the
atmosphere, and the standard's applicability to PRDs in organic HAP
service versus PRDs in total HAP service); (3) redo the risk assessment
using updated emission factors; (4) set additional monitoring
requirements for flares to reduce flaring emissions; (5) set fenceline
monitoring requirements; (6) reconsider its decision not to set
standards that account for developments in leak detection and repair
(LDAR); and (7) use existing regulatory authority to strengthen
chemical facility safety and prevent accidents in accordance with the
U.S. Chemical Safety and Hazard Investigation Board and Executive Order
13650. On August 26, 2014, the EPA sent a letter to the petitioners
informing them that the EPA was granting their request for
reconsideration at least on issues (1) and (2) above. A copy of the
August 26, 2014, letter is provided in the docket for this rulemaking
(see Docket No. EPA-HQ-OAR-2023-0282). In the letter, the EPA also
indicated that it would be initiating a notice and comment rulemaking
on the issues for which we granted reconsideration; therefore, one
purpose of this action is to formally respond to the issues raised in
the petition with respect to the PEPO NESHAP.\3\
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\3\ Although the issues identified in this paragraph (in
addition to one other issue related to alternative compliance
demonstration methods for periods of startup and shutdown) were also
raised for 40 CFR part 63, subparts JJJ and MMM; this action does
not respond to the reconsideration of these NESHAP, as the EPA is
not reviewing these subparts in this action.
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In a separate rulemaking (see 89 FR 52425, June 24, 2024), the EPA
is addressing issue (1), the affirmative defense against civil
penalties for violations occurring during malfunctions. That separate
rulemaking removes affirmative defense provisions from both NSPS and
NESHAP rules, including the PEPO NESHAP. Therefore, this proposed
action does not address removal of the affirmative defense provisions.
This action presents the EPA's proposed revisions to the PEPO
NESHAP based on the EPA's reconsideration of issue (2) in the petition
(see section IV.E.1 of this preamble for details about these proposed
amendments). Coincidentally, we also believe this action addresses
issues (3), (4), (5), and (6) in our normal course of review of the
PEPO NESHAP in accordance with sections 112 and 301 of the CAA. See
sections IV.A and IV.B of this preamble for our proposed decisions
relvant to issue (3), section IV.D.1 of this preamble for our proposed
decisions relevant to issue (4), section IV.C.6 of this preamble for
our proposed decisions relevant to issue (5), and sections IV.B.2.b and
IV.C.5 of this preamble for our proposed decisions relevant to issue
(6). With regard to issue (7), the EPA's authority to address
catastrophic releases under the NESHAP program was viewed as limited
under the pre-1990 CAA. Congress added CAA section 112(r) to address
this gap. In light of the extensive history and efforts of the agency
on inherently safer technology specifically and catastrophic accidents
generally under the section 112(r) program, and in light of the
statutory structure of section 112, we view the request to enact such
provisions in this rulemaking to be outside the scope of section
112(f)(2) and section 112(d)(6). We note that the EPA's regulations on
catastrophic releases appear in 40 CFR part 68. Prompted by Executive
Order 13650, ``Improving Chemical Facility Safety and Security,'' the
Risk Management Program regulations were amended on January 13, 2017,
to include new provisions on safer technology and alternatives analysis
and other prevention program elements; most recently, the regulations
were amended on March 11, 2024, to further enhance the accident
prevention and emergency preparedness requirements (89 FR 17622).

B. What is the source category and how do the current standards
regulate its HAP emissions?

The source category that is the subject of this proposal is the
PEPO Production source category subject to the PEPO NESHAP. The EPA
promulgated the PEPO NESHAP on June 1, 1999 (64 FR 29420), and codified
the NESHAP at 40 CFR part 63, subpart PPP. As promulgated in 1999, and
further amended on July 1, 2004 (69 FR 39862) and March 27, 2014 (59 FR
17340), the PEPO NESHAP regulates HAP emissions from polyether polyol
manufacturing process units (PMPUs) that produce PEPO as its primary
product.4 5 A PMPU consists of purification systems,
reactors and their associated product separators and recovery devices,
distillation units and their associated distillate receivers and
recovery devices, other associated unit operations, storage vessels,
surge control vessels, bottoms receivers, product transfer racks,
connected ducts and piping, combustion, recovery, or recapture devices
or systems. A PMPU also includes pumps, compressors, agitators, PRDs,
sampling connection systems, open-ended valves or lines, valves,
connectors, and instrumentation systems.
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\4\ PEPO are compounds formed through the polymerization of EtO
or propylene oxide or other cyclic ethers with compounds having one
or more reactive hydrogens (i.e., a hydrogen atom bonded to
nitrogen, oxygen, phosphorus, sulfur, etc.) to form polyethers
(i.e., compounds with two or more ether bonds). This definition of
PEPO excludes cellulose ethers (such as methyl cellulose,
carboxymethyl cellulose, hydroxyethyl cellulose, hydroxy ethyl
cellulose, and hydroxypropyl methyl cellulose) and materials
regulated under the HON, such as glycols and glycol ethers.
\5\ A PMPU also includes flexible operation process units when
an owner or operator cannot determine that a PEPO is not the primary
product, and a PEPO is produced or anticipated to be produced during
time spans described in 40 CFR 63.1420(e)(2).
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PEPO are used to make a variety of other products including
lubricants, adhesives, sealants, cosmetics, pharmaceuticals, soaps, and
a feedstock for polyurethanes production. Urethane grade PEPO (i.e.,
those that are free of water) are used as raw material in the
production of polyurethanes, including slabstock and molded flexible
foams, rigid foams and other polyurethanes, including microcellular
products, surface coatings, elastomers, fibers, adhesives, and
sealants.
PEPO can be produced by either polymerization of epoxides (i.e., a
three-membered cyclic ether, such as EtO or propylene oxide) or
tetrahydrofuran (THF). The former process is usually conducted as a
batch process, while production of polyols using THF is generally a
continuous process. EtO and propylene oxide are both HAP, but THF is
not. For the MACT regulation, the EPA created two subcategories of PEPO
based on the use of either epoxides or THF in polymerization.

[[Page 105992]]

The HAP emission sources at PEPO facilities include process vents,
storage vessels, equipment leaks, and wastewater. Additionally, some
facilities have cooling towers or other heat exchangers which could
become HAP emission sources if process fluids leak into the heat
exchange water. In the production of PEPO, HAP are used primarily as
reactants or extraction solvents. HAP emitted from PEPO facilities
include EtO, propylene oxide, toluene, methanol, and glycol ethers. The
MACT standards for PEPO production include emission limits for process
vents; a combination of equipment standards and work practices for
storage vessels, wastewater, and equipment leaks; and work practice
standards for cooling towers.
As of March 1, 2024, the EPA identified 25 PEPO facilities in
operation that are subject to the PEPO NESHAP. The list of facilities
located in the United States that are part of the PEPO Production
source category with processes subject to the PEPO NESHAP is presented
in the document titled List of Facilities Subject to the PEPO NESHAP,
which is available in the docket for this action (Docket ID No. EPA-HQ-
OAR-2023-0282).

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

The EPA used several data sources to determine the facilities that
are subject to the PEPO NESHAP discussed in section II.B of this
preamble. We identified facilities in the 2017 National Emissions
Inventory (NEI) and the Toxics Release Inventory system having a
primary facility NAICS code beginning with 325, Chemical Manufacturing.
We also used information from the 2014 PEPO NESHAP RTR, other facility
lists from the EPA's recent chemical sector rulemakings (e.g., HON),
and the Office of Enforcement and Compliance Assurance's Enforcement
and Compliance History Online (ECHO) tool (<a href="https://echo.epa.gov">https://echo.epa.gov</a>). To
inform our reviews of the Agency's emission standards, we reviewed the
EPA's Reasonably Available Control Technology (RACT)/Best Available
Control Technology (BACT)/Lowest Achievable Emission Rate (LAER)
Clearinghouse and regulatory development efforts for similar sources
published after the PEPO NESHAP was developed. The EPA also reviewed
air emissions permits issued by State regulatory agencies to determine
facilities subject to the PEPO NESHAP. Additionally, we met with
industry representatives from the American Chemistry Council (ACC) to
collect data and discuss industry practices.
In January 2022, the EPA issued requests, pursuant to CAA section
114, to collect information from synthetic organic chemical
manufacturing industry (SOCMI) facilities subject to the hazardous
organic NESHAP (HON) at 40 CFR part 63, subparts F, G, and H (nine
facilities being also subject to the PEPO NESHAP) owned and operated by
eight entities (i.e., corporations). Many of the entities chosen for
the CAA section 114 request own or operate facilities that produce,
use, and emit EtO, which is a pollutant with considerable concern for
cancer risk for the PEPO Production source category. This CAA section
114 request focused on gathering comprehensive information about
process equipment, control technologies, point and fugitive emissions,
and other aspects of facility operations. Additionally, the EPA
requested stack testing for certain emission sources (e.g., pollutants
for vent streams associated with each EtO production line). Also, the
EPA required, as part of the January 2022 CAA section 114 request, that
facilities conduct fugitive emission testing (i.e., fenceline
monitoring) for any of six specific HAP they emit: benzene; 1,3-
butadiene; chloroprene; EtO; ethylene dichloride; and vinyl chloride.
Companies submitted responses (and follow-up responses) and testing
results to the EPA during the summer and fall of 2022. The EPA used the
collected information to fill data gaps, establish the baseline
emissions and control levels for purposes of the regulatory reviews,
identify the most effective control measures, and estimate the public
health and environmental and cost impacts associated with the
regulatory options considered and reflected in this proposed action.
The information not claimed as CBI by respondents is available in the
document titled Data Received from Information Collection Request for
Chemical Manufacturers, in the docket for this action, Docket ID No.
EPA-HQ-OAR-2023-0282.

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

As mentioned above, this action includes proposed amendments to the
current flare requirements in the PEPO NESHAP. In proposing these
amendments, we relied on certain technical reports and memoranda that
the EPA developed for flares used as air pollution control devices
(APCDs) in the Petroleum Refinery Sector RTR and new source performance
standards (NSPS) rulemaking (80 FR 75178, December 1, 2015). The
Petroleum Refinery Sector rulemaking docket is at Docket ID No. EPA-HQ-
OAR-2010-0682. For completeness of the rulemaking record for this
action and for ease of reference in finding these items in the publicly
available Petroleum Refinery Sector rulemaking docket, we are including
the most relevant flare-related technical support documents in the
docket for this proposed action (Docket ID No. EPA-HQ-OAR-2023-0282)
and including a list of all documents used to inform the 2015 flare
provisions in the Petroleum Refinery Sector RTR and NSPS rulemaking in
the document titled Control Option Impacts for Flares in the PEPO
Production Source Category that Control Emissions from Processes
Subject to the PEPO NESHAP, which is available in the docket for this
rulemaking.
We are also relying on data gathered to support the rulemakings for
the EMACT standards, HON, and MON, as well as memoranda documenting the
technology reviews for those processes. Many of the emission sources
for ethylene production facilities, HON facilities, and MON facilities
are similar to PEPO facilities, so the EPA analyzed several control
options for the PEPO NESHAP that the Agency also analyzed for the
rulemakings for the EMACT standards, HON, and MON. The memoranda and
background technical information can be found in the Ethylene
Production RTR rulemaking docket (Docket ID No. EPA-HQ-OAR-2017-0357),
the HON rulemaking docket (Docket ID No. EPA-HQ-OAR-2022-0730), and the
MON RTR rulemaking docket (Docket ID No. EPA-HQ-OAR-2018-0746).
Additional information related to the promulgation and subsequent
amendments of the PEPO NESHAP is available in Docket ID Nos. A-96-38,
EPA-HQ-OAR-2004-0467, and EPA-HQ-OAR-2011-0435.

E. What outreach was conducted?

We conducted pre-proposal outreach by sharing an overview of the
industry and planned rulemaking to the EPA's national environmental
justice (EJ) engagement call on August 20, 2024, and the EPA's monthly
call with the National Tribal Air Association on August 31, 2023, and
August 29, 2024. We also met with members of the ACC on August 13,
2024. The EPA also previously engaged in outreach activities with
communities we expected to be impacted by chemical plants emitting EtO
in 2021.\6\
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\6\ <a href="https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/inspector-general-follow-ethylene-oxide-0">https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/inspector-general-follow-ethylene-oxide-0</a>.

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[[Page 105993]]

III. Analytical Procedures and Decision-Making

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.\7\ The assessment also provides estimates of the distribution
of cancer risk within the exposed populations, cancer incidence, and an
evaluation of the potential for an adverse environmental effect. The
scope of the EPA's risk analysis is consistent with the explanation in
the EPA's response to comments on our policy under the 1989 Benzene
NESHAP:
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\7\ The MIR is defined as the cancer risk associated with a
lifetime of exposure at the highest concentration of HAP where
people are likely to live. The HQ is the ratio of the potential HAP
exposure concentration to the noncancer dose-response value; the HI
is the sum of HQs for HAP that affect the same target organ or organ
system.

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

(54 FR 38057). Thus, the level of the MIR is only one factor to be
weighed in determining acceptability of risk. The Benzene NESHAP
explained that ``an MIR of approximately one in 10 thousand should
ordinarily be the upper end of the range of acceptability. As risks
increase above this benchmark, they become presumptively less
acceptable under CAA section 112, and would be weighed with the other
health risk measures and information in making an overall judgment on
acceptability. Or, the Agency may find, in a particular case, that a
risk that includes an MIR less than the presumptively acceptable level
is unacceptable in the light of other health risk factors.'' Id. at
38045. In other words, risks that include an MIR above 100-in-1 million
(1-in-10 thousand) 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 1989 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.'' \8\
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\8\ Recommendations of the SAB Risk and Technology Review
Methods Panel are provided in their report, which is available at:
<a href="https://www.epa.gov/sites/default/files/2021-02/documents/epa-sab-10-007-unsigned.pdf">https://www.epa.gov/sites/default/files/2021-02/documents/epa-sab-10-007-unsigned.pdf</a>.
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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

[[Page 105994]]

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. While we evaluated the risk from HAP
emitted by all stationary point sources near facilities within this
source category in the community-based risk assessment, that assessment
is intended to provide additional context to the public and was not
used for decision-making in this proposed rule.

B. 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.A 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 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 nine 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
Polyether Polyols (PEPO) Production Source Category in Support of the
2024 Risk and Technology Review Proposed Rule. The methods used to
assess risk (as described in the nine 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; \9\ and described in the SAB review
report issued in 2010. They are also consistent with the key
recommendations contained in that report.
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\9\ U.S. EPA. Risk and Technology Review (RTR) Risk Assessment
Methodologies: For Review by the EPA's Science Advisory Board with
Case Studies--MACT I Petroleum Refining Sources and Portland Cement
Manufacturing, June 2009. EPA-452/R-09-006. <a href="https://www3.epa.gov/airtoxics/rrisk/rtrpg.html">https://www3.epa.gov/airtoxics/rrisk/rtrpg.html</a>.
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1. How did we estimate actual emissions and identify the emissions
release characteristics?
As previously discussed, we updated the risk assessment in this
action for the PEPO Production source category because the source
category has sources that emit EtO. The EPA developed the list of 25
facilities for the PEPO Production source category as described in
section II.B of this preamble. We developed the emissions modeling
input files using the EPA's 2017 NEI. However, in a few instances where
facility-specific data were not available or not reflective of current
controls in the 2017 NEI, we obtained data from a more recent dataset
(e.g., review of emissions inventory data from our CAA section 114
request, more recent inventories submitted to States, or 2018 NEI). The
EPA also used the NEI data to develop the other parameters needed to
perform the risk modeling analysis including the emissions release
characteristics, such as stack heights, stack diameters, volumetric
flow rates, temperatures, and emission release point locations. For
further details on the assumptions and methodologies used to estimate
actual emissions, see appendix 1 of the document titled Residual Risk
Assessment for the Polyether Polyols (PEPO) Production Source Category
in Support of the 2024 Risk and Technology Review Proposed Rule, which
is available in the docket for this rulemaking.
2. How did we estimate MACT-allowable emissions?
The available emissions data in the RTR emissions dataset include
estimates of the mass of HAP emitted during a specified annual time
period. These ``actual'' emission levels are often lower than the
emission levels allowed under the requirements of the current MACT
standards. The emissions allowed under the MACT standards are referred
to as the ``MACT-allowable'' emissions. We discussed the consideration
of both MACT-allowable and actual emissions in the 2005 final RTR for
Coke Oven Batteries (70 FR 19992, 19998-99, April 15, 2005) and in the
2006 proposed and final RTR for the HON (71 FR 34421, 34428, June 14,
2006, and 71 FR 76603, 76609, December 21, 2006, respectively). In
those actions, we noted that assessing the risk at the MACT-allowable
level is inherently reasonable since that risk reflects the maximum
level facilities could emit and still comply with national emission
standards. We also explained that it is reasonable to consider actual
emissions, where such data are available, in both steps of the risk
analysis, in accordance with the Benzene NESHAP approach. (54 FR
38044.)
For this analysis, we have determined that the actual emissions
data are reasonable estimates of the MACT-allowable emissions levels
for the PEPO Production source category, as we are not generally aware
of any situations in which a facility is conducting additional work
practices or operating a control device such that it achieves a far
greater emission reduction than required by the NESHAP. However, in
cases where we encountered a permit emissions limit that appeared to be
higher than the reported emissions, we recorded that in the allowable
emissions column of the modeling file to assess the risk of allowable
emissions. For further details on the assumptions and methodologies
used to estimate MACT-allowable emissions, see appendix 1 of the
document titled Residual Risk Assessment for the Polyether Polyols
(PEPO) Production Source Category in Support of the 2024 Risk and
Technology Review Proposed Rule, which is available in the docket for
this rulemaking.
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-4).\10\ The HEM-4
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.
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\10\ For more information about HEM-4, go to <a href="https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem">https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem</a>.

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[[Page 105995]]

a. Dispersion Modeling
The air dispersion model AERMOD (American Meteorological Society/
EPA Regulatory Model dispersion modeling system), used by the HEM-4, is
one of the EPA's preferred models for assessing air pollutant
concentrations from industrial facilities.\11\ To perform the
dispersion modeling and to develop the preliminary risk estimates, HEM-
4 draws on three data libraries. The first is a library of
meteorological data, which is used for dispersion calculations. This
library includes 1 year (2019) of hourly surface and upper air
observations from over 800 meteorological stations, selected to provide
coverage of the United States and Puerto Rico. A second library of
United States Census Bureau census block \12\ internal point locations
and populations provides the basis of human exposure calculations (U.S.
Census, 2020). 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.
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\11\ U.S. EPA. Revision to the Guideline on Air Quality Models:
Adoption of a Preferred General Purpose (Flat and Complex Terrain)
Dispersion Model and Other Revisions (70 FR 68218, November 9,
2005).
\12\ A census block is the smallest geographic area for which
census statistics are tabulated.
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b. Risk From Chronic Exposure to HAP
In developing the risk assessment for chronic exposures, we use the
estimated annual average ambient air concentrations of each HAP emitted
by each source in the source category. The HAP air concentrations at
each nearby census block centroid located within 50 km of the facility
are a surrogate for the chronic inhalation exposure concentration for
all the people who reside in that census block. A distance of 50 km is
consistent with both the analysis supporting the 1989 Benzene NESHAP
(54 FR 38044) and the limitations of Gaussian dispersion models,
including AERMOD.
For each facility, we calculate the MIR as the cancer risk
associated with a continuous lifetime (24 hours per day, 7 days per
week, 52 weeks per year, 70 years) exposure to the maximum annual
average concentration at the centroid of each inhabited census block.
We calculate individual cancer risk by multiplying the estimated
lifetime exposure to the ambient concentration of each HAP (in
micrograms per cubic meter ([mu]g/m\3\)) by its 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 [mu]g/m\3\
of air. For residual risk assessments, we generally use UREs from the
EPA's IRIS. For carcinogenic pollutants without IRIS values, we look to
other reputable sources of cancer dose-response values, often using
California EPA (CalEPA) UREs, where available. In cases where new,
scientifically credible dose-response values have been developed in a
manner consistent with EPA guidelines and have undergone a peer review
process similar to that used by the EPA, we may use such dose-response
values in place of, or in addition to, other values, if appropriate.
The pollutant-specific dose-response values used to estimate health
risk are available at <a href="https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants">https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants</a>.
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 \13\ 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.
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\13\ The EPA's 2005 Guidelines for Carcinogen Risk Assessment
classifies carcinogens as: ``carcinogenic to humans,'' ``likely to
be carcinogenic to humans,'' and ``suggestive evidence of
carcinogenic potential.'' These classifications also coincide with
the terms ``known carcinogen,'' ``probable carcinogen,'' and
``possible carcinogen,'' respectively, which are the terms advocated
in the EPA's Guidelines for Carcinogen Risk Assessment, published in
1986 (51 FR 33992, September 24, 1986). In August 2000, the
document, Supplemental Guidance for Conducting Health Risk
Assessment of Chemical Mixtures (EPA/630/R-00/002), was published as
a supplement to the 1986 document. Copies of both documents can be
obtained from <a href="https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944">https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944</a>. Summing
the risk of these individual compounds to obtain the cumulative
cancer risk is an approach that was recommended by the EPA's SAB in
their 2002 peer review of the EPA's National Air Toxics Assessment
(NATA) titled NATA--Evaluating the National-scale Air Toxics
Assessment 1996 Data--an SAB Advisory, available at https://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
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To assess the risk of noncancer health effects from chronic
exposure to HAP, we calculate either an HQ or a target organ-specific
hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is
emitted. Where more than one noncancer HAP is emitted, we sum the HQ
for each of the HAP that affects a common target organ or target organ
system to obtain a TOSHI. The HQ is the estimated exposure divided by
the chronic noncancer dose-response value, which is a value selected
from one of several sources. The preferred chronic noncancer dose-
response value is the EPA RfC, defined as ``an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure to the human population (including sensitive
subgroups) that is likely to be without an appreciable risk of
deleterious effects during a lifetime'' (<a href="https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary">https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary</a>). 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)
Minimal Risk Level (<a href="https://www.atsdr.cdc.gov/mrls/index.asp">https://www.atsdr.cdc.gov/mrls/index.asp</a>); (2) the
CalEPA Chronic Reference Exposure Level (REL) (<a href="https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0">https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0</a>); 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 <a href="https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants">https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants</a>.
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 health
protective

[[Page 105996]]

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,\14\ 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 the document titled Residual Risk Assessment for the
Polyether Polyols (PEPO) Production Source Category in Support of the
2024 Risk and Technology Review Proposed Rule and in appendix 5 of the
report Technical Support Document for Acute Risk Screening Assessment,
which are available in the docket for this rulemaking. This revised
approach has been used in this proposed rule and in all other RTR
rulemakings proposed on or after June 3, 2019.
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\14\ See, e.g., U.S. EPA. Screening Methodologies to Support
Risk and Technology Reviews (RTR): A Case Study Analysis (Draft
Report, May 2017. (<a href="https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html">https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html</a>).
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To assess the potential acute risk to the maximally exposed
individual, we use the peak hourly emission rate for each emission
point,\15\ reasonable worst-case air dispersion conditions (i.e., 99th
percentile), and the point of highest off-site exposure. Specifically,
we assume that peak emissions from the source category and reasonable
worst-case air dispersion conditions co-occur and that a person is
present at the point of maximum exposure.
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\15\ In the absence of hourly emission data, we develop
estimates of maximum hourly emission rates by multiplying the
average actual annual emissions rates by a factor (either a
category-specific factor or a default factor of 10) to account for
variability. This is documented in Residual Risk Assessment for the
Polyether Polyols (PEPO) Production Source Category in Support of
the 2024 Risk and Technology Review Proposed Rule, and in appendix 5
of the report: Technical Support Document for Acute Risk Screening
Assessment. Both of these documents are available in the docket for
this rulemaking.
---------------------------------------------------------------------------

To characterize the potential health risks associated with
estimated acute inhalation exposures to a HAP, we generally use
multiple acute dose-response values, including acute RELs, acute
exposure guideline levels (AEGLs), and emergency response planning
guidelines (ERPG) for 1-hour exposure durations, if available, to
calculate acute HQs. The acute HQ is calculated by dividing the
estimated acute exposure concentration by the acute dose-response
value. For each HAP for which acute dose-response values are available,
the EPA calculates acute HQs.
An acute REL is defined as ``the concentration level at or below
which no adverse health effects are anticipated for a specified
exposure duration.'' \16\ 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.\17\ 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.
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\16\ CalEPA issues acute RELs as part of its Air Toxics Hot
Spots Program, and the 1-hour and 8-hour values are documented in
Air Toxics Hot Spots Program Risk Assessment Guidelines, Part I, The
Determination of Acute Reference Exposure Levels for Airborne
Toxicants, which is available at <a href="https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary">https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary</a>.
\17\ National Academy of Sciences, 2001. Standing Operating
Procedures for Developing Acute Exposure Levels for Hazardous
Chemicals, page 2. Available at <a href="https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf">https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf</a>. 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 (<a href="https://www.epa.gov/aegl">https://www.epa.gov/aegl</a>).
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ERPGs are developed, by the American Industrial Hygiene Association
(AIHA), for emergency planning and are intended to be health-based
guideline concentrations for single exposures to chemicals. The ERPG-1
is the maximum airborne concentration, established by AIHA, 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.
Similarly, the ERPG-2 is the maximum airborne concentration,
established by AIHA, below which it is believed that nearly all
individuals could be exposed for up to 1 hour without experiencing or
developing irreversible or other serious health effects or symptoms
which could impair an individual's ability to take protective action.
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 the PEPO Production source category, we did not use a default
acute emissions multiplier of 10, but rather we used process level-
specific acute emissions multipliers, generally ranging from a factor
of 2 to 10 as was done in past chemical and petrochemical residual risk
reviews such as for the 2015 Petroleum Refinery Sector rule, 2024 HON
rulemaking, 2020 MON RTR, and 2020 EMACT standards RTR, where similar
emission sources and standards exist. These refinements are discussed
more fully in appendix 1 of the document titled Residual Risk
Assessment for the Polyether Polyols (PEPO) Production Source Category
in Support of the 2024 Risk and Technology Review Proposed Rule, which
is 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

[[Page 105997]]

that the acute HQ is at an off-site location. For the PEPO Production
source category, the data refinements employed consisted of reviewing
satellite imagery of the locations of the maximum acute HQ values to
determine if the maximum was off facility property. For any maximum
value that was determined to be on facility property, the next highest
value that was off facility property was used. These refinements are
discussed more fully in the document titled Residual Risk Assessment
for the Polyether Polyols (PEPO) Production Source Category in Support
of the 2024 Risk and Technology Review Proposed Rule, which is
available in the docket for this rulemaking.
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 (e.g., ingestion). We first determine
whether any sources in the source category emit any HAP known to be
persistent and bioaccumulative in the environment, as identified in the
EPA's Air Toxics Risk Assessment Library (see Volume 1, appendix D, at
<a href="https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library">https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library</a>).
For the PEPO Production source category, we identified PB-HAP
emissions of arsenic compounds, cadmium compounds, polycyclic organic
matter (POM), and mercury, 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 POM.
Based on the EPA estimates of toxicity and bioaccumulation potential,
these pollutants represent a health protective list for inclusion in
multipathway risk assessments for RTR rules. (See Volume 1, Appendix D
at <a href="https://www.epa.gov/sites/production/files/2013-08/documents/volume_1_reflibrary.pdf">https://www.epa.gov/sites/production/files/2013-08/documents/volume_1_reflibrary.pdf</a>.) In this assessment, we compare the facility-
specific emission rates of these PB-HAP to the screening threshold
emission rates for each PB-HAP to assess the potential for significant
human health risks via the ingestion pathway. We call this application
of the TRIM.FaTE model the Tier 1 screening assessment. The ratio of a
facility's actual emission rate to the Tier 1 screening threshold
emission rate is a ``screening value.''
We derive the Tier 1 screening threshold emission rates for these
PB-HAP (other than lead compounds) to correspond to a maximum excess
lifetime cancer risk of 1-in-1 million (i.e., for arsenic compounds,
polychlorinated dibenzodioxins and furans, and POM) or, for HAP that
cause noncancer health effects (i.e., cadmium compounds and mercury
compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP
or combination of carcinogenic PB-HAP in the Tier 1 screening
assessment exceeds the Tier 1 screening threshold emission rate for any
facility (i.e., the screening value is greater than 1), we conduct a
second screening assessment, which we call the Tier 2 screening
assessment. The Tier 2 screening assessment separates the Tier 1
combined fisher and farmer exposure scenario into fisher, farmer, and
gardener scenarios that retain upper-bound ingestion rates.
In the Tier 2 screening assessment, the location of each facility
that exceeds a Tier 1 screening threshold emission rate is used to
refine the assumptions associated with the Tier 1 fisher and farmer
exposure scenarios at that facility. A key assumption in the Tier 1
screening assessment is that a lake and/or farm is located near the
facility. As part of the Tier 2 screening assessment, we use a U.S.
Geological Survey (USGS) database to identify actual waterbodies within
50 km of each facility and assume the fisher only consumes fish from
lakes within that 50-km zone. We also examine the differences between
local meteorology near the facility and the meteorology used in the
Tier 1 screening assessment. We then adjust the previously-developed
Tier 1 screening threshold emission rates for each PB-HAP for each
facility based on an understanding of how exposure concentrations
estimated for the screening scenario change with the use of local
meteorology and the USGS lakes database.
In the Tier 2 farmer scenario, we maintain an assumption that the
farm is located within 0.5 km of the facility and that the farmer
consumes meat, eggs, dairy, vegetables, and fruit produced near the
facility. We may further refine the Tier 2 screening analysis by
assessing a gardener scenario to characterize a range of exposures,
with the gardener scenario being more plausible in RTR evaluations.
Under the gardener scenario, we assume the gardener consumes home-
produced eggs, vegetables, and fruit products at the same ingestion
rate as the farmer. The Tier 2 screen continues to rely on the high-end
food intake assumptions that were applied in Tier 1 for local fish
(adult female angler at 99th percentile fish consumption \18\) and
locally grown or raised foods (90th percentile consumption of locally
grown or raised foods for the farmer and gardener scenarios \19\). 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.
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\18\ Burger, J. 2002. Daily consumption of wild fish and game:
Exposures of high end recreationists. International Journal of
Environmental Health Research, 12:343-354.
\19\ U.S. EPA. Exposure Factors Handbook 2011 Edition (Final).
U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/
052F, 2011.
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There are several analyses that can be included in a Tier 3
screening assessment, depending upon the extent of refinement
warranted, including validating that the lakes are fishable, locating
residential/garden locations for urban and/or rural settings,
considering plume-rise to estimate emissions lost above the mixing
layer, and considering hourly effects of meteorology and plume-rise on
chemical fate and transport (a time-series analysis). If necessary, the
EPA may further refine the screening assessment through a site-specific
assessment.
In evaluating the potential multipathway risk from emissions of
lead compounds, rather than developing a screening threshold emission
rate, we compare maximum estimated chronic inhalation exposure
concentrations to the level of the current National Ambient Air Quality
Standard (NAAQS) for lead.\20\ Values below the level of the

[[Page 105998]]

primary (health-based) lead NAAQS are considered to have a low
potential for multipathway risk.
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\20\ 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 1989 Benzene NESHAP analysis) since it is designed
to protect the most susceptible group in the human population--
children, including children living near major lead emitting
sources. 73 FR 67002/3; 73 FR 67000/3; 73 FR 67005/1. In addition,
applying the level of the primary lead NAAQS at the risk
acceptability step is conservative, since that primary lead NAAQS
reflects an adequate margin of safety.
---------------------------------------------------------------------------

For further information on the multipathway assessment approach,
see the document titled Residual Risk Assessment for the Polyether
Polyols (PEPO) Production Source Category in Support of the 2024 Risk
and Technology Review Proposed Rule, which is available in the docket
for this rulemaking.
5. How do we assess risks considering emissions control options?
In addition to assessing baseline inhalation risks and screening
for potential multipathway risks, we also estimate risks considering
the potential emission reductions that would be achieved by the control
options under consideration. In these cases, the expected emission
reductions are applied to the specific HAP and emission points in the
RTR emissions dataset to develop corresponding estimates of risk and
incremental risk reductions.
6. 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 hydrochloric acid (HCl)
and hydrofluoric acid (HF).
HAP that persist and bioaccumulate are of particular environmental
concern because they accumulate in the soil, sediment, and water. The
acid gases, HCl and HF, are included due to their well-documented
potential to cause direct damage to terrestrial plants. In the
environmental risk screening assessment, we evaluate the following four
exposure media: terrestrial soils, surface water bodies (includes
water-column and benthic sediments), fish consumed by wildlife, and
air. Within these four exposure media, we evaluate nine ecological
assessment endpoints, which are defined by the ecological entity and
its attributes. For PB-HAP (other than lead), both community-level and
population-level endpoints are included. For acid gases, the ecological
assessment evaluated is terrestrial plant communities.
An ecological benchmark represents a concentration of HAP that has
been linked to a particular environmental effect level. For each
environmental HAP, we identified the available ecological benchmarks
for each assessment endpoint. We identified, where possible, ecological
benchmarks at the following effect levels: probable effect levels,
lowest-observed-adverse-effect level, and no-observed-adverse-effect
level. In cases where multiple effect levels were available for a
particular PB-HAP and assessment endpoint, we use all of the available
effect levels to help us to determine whether ecological risks exist
and, if so, whether the risks could be considered significant and
widespread.
For further information on how the environmental risk screening
assessment was conducted, including a discussion of the risk metrics
used, how the environmental HAP were identified, and how the ecological
benchmarks were selected, see appendix 9 of the document titled
Residual Risk Assessment for the Polyether Polyols (PEPO) Production
Source Category in Support of the 2024 Risk and Technology Review
Proposed Rule, which is available in the docket for this rulemaking.
b. Environmental Risk Screening Methodology
For the environmental risk screening assessment, the EPA first
determined whether any facilities in the PEPO Production source
category emitted any of the environmental HAP. For the PEPO Production
source category, we identified emissions of arsenic compounds, cadmium
compounds, POM, and mercury.\21\ Because one or more of the
environmental HAP evaluated are emitted by at least one facility in the
PEPO Production source category, we proceeded to the second step of the
evaluation.
---------------------------------------------------------------------------

\21\ We note that in many instances, we did not have sufficient
information to parse out emissions from PEPO processes from
facility-wide emissions inventories; thus, to avoid underestimating
emissions from PEPO sources, we modeled most or all of certain
facilities' emissions records as if they all are from the PEPO
Production source category.
---------------------------------------------------------------------------

c. PB-HAP Methodology
The environmental screening assessment includes six PB-HAP, arsenic
compounds, cadmium compounds, dioxins/furans, POM, mercury (both
inorganic mercury and methyl mercury), and lead compounds. With the
exception of lead, the environmental risk screening assessment for PB-
HAP consists of three tiers. The first tier of the environmental risk
screening assessment uses the same health-protective conceptual model
that is used for the Tier 1 human health screening assessment.
TRIM.FaTE model simulations were used to back-calculate Tier 1
screening threshold emission rates. The screening threshold emission
rates represent the emission rate in tons of pollutant per year that
results in media concentrations at the facility that equal the relevant
ecological benchmark. To assess emissions from each facility in the
category, the reported emission rate for each PB-HAP was compared to
the Tier 1 screening threshold emission rate for that PB-HAP for each
assessment endpoint and effect level. If emissions from a facility do
not exceed the Tier 1 screening threshold emission rate, the facility
``passes'' the screening assessment, and, therefore, is not evaluated
further under the screening approach. If emissions from a facility
exceed the Tier 1 screening threshold emission rate, we evaluate the
facility further in Tier 2.
In Tier 2 of the environmental screening assessment, the screening
threshold emission rates are adjusted to account for local meteorology
and the actual location of lakes in the vicinity of facilities that did
not pass the Tier 1 screening assessment. For soils, we evaluate the
average soil concentration for all soil parcels within a 7.5-km radius
for each facility and PB-HAP. For the water, sediment, and fish tissue
concentrations, the highest value for each facility for each pollutant.
If emissions from a facility do not exceed the Tier 2 screening
threshold emission rate, the facility ``passes'' the screening

[[Page 105999]]

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-4)
of lead around each facility in the source category to the level of the
secondary NAAQS for lead. The secondary lead NAAQS is a reasonable
means of evaluating environmental risk because it is set to provide
substantial protection against adverse welfare effects which can
include ``effects on soils, water, crops, vegetation, man-made
materials, animals, wildlife, weather, visibility and climate, damage
to and deterioration of property, and hazards to transportation, as
well as effects on economic values and on personal comfort and well-
being.''
d. Acid Gas Environmental Risk Methodology
The environmental screening assessment for acid gases evaluates the
potential phytotoxicity and reduced productivity of plants due to
chronic exposure to HF and HCl. The environmental risk screening
methodology for acid gases is a single-tier screening assessment that
compares modeled ambient air concentrations (from AERMOD) to the
ecological benchmarks for each acid gas. To identify a potential
adverse environmental effect (as defined in section 112(a)(7) of the
CAA) from emissions of HF and HCl, we evaluate the following metrics:
the size of the modeled area around each facility that exceeds the
ecological benchmark for each acid gas, in acres and square km; the
percentage of the modeled area around each facility that exceeds the
ecological benchmark for each acid gas; and the area-weighted average
screening value around each facility (calculated by dividing the area-
weighted average concentration over the 50-km modeling domain by the
ecological benchmark for each acid gas). For further information on the
environmental screening assessment approach, see appendix 9 of the
document titled Residual Risk Assessment for the Polyether Polyols
(PEPO) Production Source Category in Support of the 2024 Risk and
Technology Review Proposed Rule, which is available in the docket for
this rulemaking.
7. 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 the PEPO Production source category, we conducted the facility-wide
assessment using a dataset compiled from the 2017 NEI and other
emissions information discussed in section II.C of this preamble. Once
a quality assured source category dataset was available, it was placed
back with the remaining records from the NEI for that facility (which
in most instances was 2017 NEI data). 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 document titled
Residual Risk Assessment for the Polyether Polyols (PEPO) Production
Source Category in Support of the 2024 Risk and Technology Review
Proposed Rule, available through the docket for this rulemaking,
provides the methodology and results of the facility-wide analyses,
including all facility-wide risks and the percentage of source category
contribution to facility-wide risks.
8. How do we conduct community-based risk assessments?
In addition to the source category and facility-wide risk
assessments, we also assessed the combined inhalation cancer risk from
all local stationary sources of HAP for which we have emissions data.
Specifically, we combined the modeled impacts from the facility-wide
assessment (which includes category and non-category sources) with
other nearby stationary point source model results. Section II.C of
this preamble discusses the facility-wide emissions used in this
assessment. For the other nearby point sources, we used AERMOD model
results with emissions based primarily on the 2020 NEI. After combining
these model results, we assessed cancer risks due to the inhalation of
all HAP emitted by point sources for the populations residing within 10
km (~6.2 miles) of PEPO facilities. In the community-based risk
assessment, we compared the modeled source category and facility-wide
cancer risks to the cancer risks from other nearby point sources to
determine the portion of the risks that could be attributed to the
source category addressed in this proposal. The document titled
Residual Risk Assessment for the Polyether Polyols (PEPO) Production
Source Category in Support of the 2024 Risk and Technology Review
Proposed Rule, which is available in the docket for this rulemaking,
provides the methodology and results of the community-based risks
analyses.
9. 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 health
protective 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 document titled Residual Risk
Assessment for the Polyether Polyols (PEPO) Production

[[Page 106000]]

Source Category in Support of the 2024 Risk and Technology Review
Proposed Rule, which is available in the docket for this rulemaking. 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 emissions inventory likely dominate the
uncertainties in the exposure assessment. Some uncertainties in our
exposure assessment include human mobility, using the centroid of each
census block, assuming lifetime exposure, and assuming only outdoor
exposures. For most of these factors, there is neither an under nor
overestimate when looking at the maximum individual risk or the
incidence, but the shape of the distribution of risks may be affected.
With respect to outdoor exposures, actual exposures may not be as high
if people spend time indoors, especially 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 1-7). 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.\22\
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.\23\
Chronic noncancer RfC and reference dose 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,\24\ 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.
---------------------------------------------------------------------------

\22\ IRIS glossary (<a href="https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary">https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary</a>).
\23\ An exception to this is the URE for benzene, which is
considered to cover a range of values, each end of which is
considered to be equally plausible, and which is based on maximum
likelihood estimates.
\24\ See A Review of the Reference Dose and Reference
Concentration Processes, U.S. EPA, December 2002, and Methods for
Derivation of Inhalation Reference Concentrations and Application of
Inhalation Dosimetry, U.S. EPA, 1994.
---------------------------------------------------------------------------

Many of the UFs used to account for variability and uncertainty in
the development of acute dose-response values are quite similar to
those developed for chronic durations. Additional adjustments are often
applied to account for uncertainty in extrapolation from observations
at one exposure duration (e.g., 4 hours) to derive an acute dose-
response value at another exposure duration (e.g., 1 hour). Not all
acute dose-response values are developed for the same purpose, and care
must be taken when interpreting the results of an acute assessment of
human health effects relative to the dose-response value or values
being exceeded. Where relevant to the estimated exposures, the lack of
acute dose-response values at different levels of severity should be
factored into the risk characterization as potential uncertainties.
Uncertainty also exists in the selection of ecological benchmarks
for the environmental risk screening assessment. We established a
hierarchy of preferred benchmark sources to allow selection of
benchmarks for each environmental HAP at each ecological assessment
endpoint. We searched for benchmarks for three effect levels (i.e., no-
effects level, threshold-effect level,

[[Page 106001]]

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 the source category are
lacking dose-response assessments. Accordingly, these pollutants cannot
be included in the quantitative risk assessment, which could result in
quantitative estimates understating HAP risk. To help to alleviate this
potential underestimate, where we conclude similarity with a HAP for
which a dose-response value is available, we use that value as a
surrogate for the assessment of the HAP for which no value is
available. To the extent use of surrogates indicates appreciable risk,
we may identify a need to increase priority for an IRIS assessment for
that substance. We additionally note that, generally speaking, HAP of
greatest concern due to environmental exposures and hazard are those
for which dose-response assessments have been performed, reducing the
likelihood of understating risk. Further, HAP not included in the
quantitative assessment are assessed qualitatively and considered in
the risk characterization that informs the risk management decisions,
including consideration of HAP reductions achieved by various control
options.
For a group of compounds that are unspeciated (e.g., groups of
compounds that we do not know the exact composition of like glycol
ethers), we conservatively use the most protective dose-response value
of an individual compound in that group to estimate risk. Similarly,
for an individual compound in a group (e.g., ethylene glycol diethyl
ether) that does not have a specified dose-response value, we also
apply the most protective dose-response value from the other compounds
in the group to estimate risk.
e. Uncertainties in Acute Inhalation Screening Assessments
In addition to the uncertainties highlighted above, there are
several factors specific to the acute exposure assessment that the EPA
conducts as part of the risk review under section 112 of the CAA. The
accuracy of an acute inhalation exposure assessment depends on the
simultaneous occurrence of independent factors that may vary greatly,
such as hourly emissions rates, meteorology, and the presence of a
person. In the acute screening assessment that we conduct under the RTR
program, we assume that peak emissions from the source category and
reasonable worst-case air dispersion conditions (i.e., 99th percentile)
co-occur. We then include the additional assumption that a person is
located at this point at the same time. Together, these assumptions
represent a reasonable worst-case actual exposure scenario. In most
cases, it is unlikely that a person would be located at the point of
maximum exposure during the time when peak emissions and reasonable
worst-case air dispersion conditions occur simultaneously.
f. Uncertainties in the Multipathway and Environmental Risk Screening
Assessments
For each source category, we generally rely on site-specific levels
of PB-HAP or environmental HAP emissions to determine whether a refined
assessment of the impacts from multipathway exposures is necessary or
whether it is necessary to perform an environmental screening
assessment. This determination is based on the results of a three-
tiered screening assessment that relies on the outputs from models--
TRIM.FaTE and AERMOD--that estimate environmental pollutant
concentrations and human exposures for five PB-HAP (dioxins, POM,
mercury, cadmium, and arsenic) and two acid gases (HF and HCl). For
lead, we use AERMOD to determine ambient air concentrations, which are
then compared to the secondary NAAQS standard for lead. Two important
types of uncertainty associated with the use of these models in RTR
risk assessments and inherent to any assessment that relies on
environmental modeling are model uncertainty and input uncertainty.\25\
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\25\ In the context of this discussion, the term ``uncertainty''
as it pertains to exposure and risk encompasses both variability in
the range of expected inputs and screening results due to existing
spatial, temporal, and other factors, as well as uncertainty in
being able to accurately estimate the true result.
---------------------------------------------------------------------------

Model uncertainty concerns whether the model adequately represents
the actual processes (e.g., movement and accumulation) that might occur
in the environment. For example, does the model adequately describe the
movement of a pollutant through the soil? This type of uncertainty is
difficult to quantify. However, based on feedback received from
previous EPA SAB reviews and other reviews, we are confident that the
models used in the screening assessments are appropriate and state-of-
the-art for the multipathway and environmental screening risk
assessments conducted in support of RTRs.
Input uncertainty is concerned with how accurately the models have
been configured and parameterized for the assessment at hand. For Tier
1 of the multipathway and environmental screening assessments, we
configured the models to avoid underestimating exposure and risk. This
was accomplished by selecting upper-end values from nationally
representative datasets for the more influential parameters in the
environmental model, including selection and spatial configuration of
the area of interest, lake location and size, meteorology, surface
water, soil characteristics, and structure of the aquatic food web. We
also assume an ingestion exposure scenario and values for human
exposure factors that represent reasonable maximum exposures.
In Tier 2 of the multipathway and environmental screening
assessments, we refine the model inputs to account for meteorological
patterns in the vicinity of the facility versus using upper-end
national values, and we identify the actual location of lakes near the
facility rather than the default lake location that we apply in Tier 1.
By refining the screening approach in Tier 2 to account for local
geographical and meteorological data, we decrease the likelihood that
concentrations in environmental media are overestimated, thereby
increasing the usefulness of the screening assessment. In Tier 3 of the
screening assessments, we refine the model inputs again to account for
hour-by-hour plume-rise and the height of the mixing layer. We can also
use those hour-by-hour meteorological data in a TRIM.FaTE run using the
screening configuration corresponding to the lake location. These
refinements produce a more accurate estimate of chemical concentrations
in the media of interest, thereby reducing the uncertainty with those
estimates. The assumptions and the associated uncertainties regarding
the selected ingestion exposure scenario are the same for all three
tiers.
For the environmental screening assessment for acid gases, we
employ a single-tiered approach. We use the modeled air concentrations
and compare those with ecological benchmarks.
For all tiers of the multipathway and environmental screening
assessments, our approach to addressing model input uncertainty is
generally cautious. We

[[Page 106002]]

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.

C. 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 previous PEPO NESHAP
technology review was 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 CAA section 112 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'':
<bullet> Any add-on control technology or other equipment that was
not identified and considered during development of the original MACT
standards;
<bullet> 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;
<bullet> Any work practice or operational procedure that was not
identified or considered during development of the original MACT
standards;
<bullet> 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
<bullet> 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
(or last updated) the PEPO NESHAP, we review a variety of data sources
in our investigation of potential practices, processes, or controls to
consider. We also review the NESHAP and the available data to determine
if there are any unregulated emissions of HAP within the source
category, and evaluate these 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.

D. How do we determine a MACT floor and consider beyond-the-floor?

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. CAA section
112(d)(2)(A)-(E). The MACT standards may take the form of design,
equipment, work practice or operational standards where the EPA first
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. CAA section 112(h)(1)-(2).
The MACT ``floor'' is the minimum control level allowed for MACT
standards promulgated under CAA section 112(d)(3) and may not be based
on cost considerations. For new sources located at facilities that are
major sources of HAP, section 112 of the CAA requires the EPA to
establish standards that are no less stringent than the emissions
control that is achieved in practice by the best controlled similar
source. The statute does not define ``achieved in practice'' nor does
it dictate the manner in which the agency determines which source is
the best controlled similar source, instead leaving it to the agency's
discretion to make those determinations. For existing sources located
at facilities that are major sources of HAP, standards must be no less
stringent than the average emissions limitation achieved by the best
performing sources for which the EPA has emissions information. Again,
the CAA leaves to the EPA's discretion the manner in which to calculate
``the average emission limitation achieved'' by the best performing
sources. Under section 112, the CAA recognizes that source categories
and subcategories have differing numbers of sources and provides
category size-specific instructions on determining standard stringency
for existing sources. Specifically, standards for categories or
subcategories with fewer than 30 sources must be based on the average
emission limitation achieved by the best performing 5 sources, and
standards for categories or subcategories with 30 or more sources must
be based on the average emission limitation achieved by the best
performing 12 percent of sources for which the EPA has emissions
information. In developing MACT standards, the EPA must also

[[Page 106003]]

consider control options that are more stringent than the floor (i.e.,
``beyond-the-floor'' options) under CAA section 112(d)(2). We may
establish beyond-the-floor standards more stringent than the floor
based on considerations of the cost of achieving the emission
reductions, any non-air quality health and environmental impacts, and
energy requirements.

IV. Analytical Results and Proposed Decisions

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

As previously discussed, we conducted a risk assessment for the
PEPO Production source category. We previously identified EtO as a
cancer risk driver from facilities with PEPO NESHAP-subject processes
in the first risk assessment we conducted in 2014. However, the EPA's
IRIS inhalation URE for EtO was revised in 2016,\26\ based on new data,
showing EtO to be more carcinogenic than previously understood (i.e.,
resulting in a URE 60 times greater than the previous URE over a 70-
year lifetime). We briefly present the results of the risk assessment
below and in more detail in the document titled Residual Risk
Assessment for the Polyether Polyols (PEPO) Production Source Category
in Support of the 2024 Risk and Technology Review Proposed Rule, which
is available in the docket for this rulemaking.
---------------------------------------------------------------------------

\26\ U.S. EPA. Evaluation of the Inhalation Carcinogenicity of
Ethylene Oxide (CASRN 75-21-8) In Support of Summary Information on
the Integrated Risk Information System (IRIS). December 2016. EPA/
635/R-16/350Fa. Available at: <a href="https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf">https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf</a>.
---------------------------------------------------------------------------

1. Chronic Inhalation Risk Assessment Results
Out of the 25 facilities identified as subject to the PEPO NESHAP,
two facilities do not have source category emissions included in our
risk assessment. One facility has a PEPO source under construction
while the other facility did not report records in its emissions
inventory with names that that could be linked to its PEPO process and
thus we did not have sufficient information to parse out the source
category records.\27\ The results of the chronic baseline inhalation
cancer risk assessment, which are estimated using modeling and is the
case for all risk results presented here and in subsequent sections,
indicate that, based on estimates of current actual emissions, the MIR
posed by the source category is 1,000-in-1 million, driven by EtO
emissions from wastewater (77 percent) and equipment leaks (21
percent). The total estimated cancer incidence based on actual emission
levels is 0.3 excess cancer cases per year (or 1 cancer case every 3.3
years). EtO emissions contribute 99.6 percent of the total cancer
incidence. Within 50 km of PEPO NESHAP-subject facilities, the
population exposed to cancer risk greater than 100-in-1 million for
PEPO NESHAP actual emissions is approximately 3,300 people, and the
population exposed to cancer risk greater than or equal to 1-in-1
million is approximately 3.8 million people. Of the 23 facilities that
the EPA assessed for source category risk, 6 facilities have an
estimated maximum cancer risk greater than 100-in-1 million. In
addition, the maximum modeled chronic noncancer TOSHI for the source
category based on actual emissions is estimated to be 0.1 (for
respiratory effects). No populations are estimated to be exposed to a
TOSHI greater than 1.
---------------------------------------------------------------------------

\27\ When considering all emissions reported by the facility for
which we could not identify PEPO emissions records, we estimated a
facility-wide maximum cancer risk of 70-in-1 million, so including
this facility in the PEPO source category risk assessment would not
have changed our decisions on standards to address unacceptable
risk.
---------------------------------------------------------------------------

Of the 23 facilities that the EPA assessed for the source category
risk, 5 facilities have allowable emissions that differ from the actual
emissions (see section III.B.2 of this preamble). For the other 18
facilities, actual emissions equal allowable emissions, and therefore,
actual risks equal allowable risks for these 18 facilities. Our risk
assessment based on allowable emissions includes all 23 facilities.
This assessment estimates the MIR posed by the source category is
unchanged at 1,000-in-1 million, driven by EtO emissions from
wastewater (77 percent) and equipment leaks (21 percent). The total
estimated cancer incidence is 0.4 excess cancer cases per year (or 1
cancer case every 2.5 years). EtO emissions contribute 99.6 percent of
the total cancer incidence. Within 50 km of PEPO NESHAP-subject
facilities, the population exposed to cancer risk greater than 100-in-1
million for PEPO NESHAP allowable emissions is approximately 6,700
people, and the population exposed to cancer risk greater than or equal
to 1-in-1 million is approximately 4.7 million people. Of the 23
facilities that the EPA assessed for source category risk, 8 facilities
have an estimated maximum cancer risk greater than 100-in-1 million. In
addition, the EPA estimated the maximum modeled chronic noncancer TOSHI
for the source category based on allowable emissions to be less than 1.
See table 1 of this preamble for a summary of the PEPO NESHAP
inhalation risk assessment results.

Table 1--PEPO Production Source Category Inhalation Risk Assessment Results Based on Actual and Allowable Emissions \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Maximum Estimated population at Estimated Refined
individual increased risk of cancer annual maximum
Number of cancer risk -------------------------- cancer Maximum chronic noncancer screening
Risk assessment facilities (-in-1 incidence TOSHI acute
\2\ million) >=1-in-1 >100-in-1 (cases per noncancer
\3\ million million year) HQ
--------------------------------------------------------------------------------------------------------------------------------------------------------
Baseline (Pre-control) Actual Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source Category............................ 23 1,000 3.8 3,300 0.3 0.1 (respiratory)............ 1
Facility-wide \4\.......................... 25 2,000 7.3 4,000 0.6 3 (respiratory)..............
--------------------------------------------------------------------------------------------------------------------------------------------------------
Baseline (Pre-control) Allowable Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source Category \1\........................ 23 1,000 4.7 6,700 0.4 0.1 (respiratory)............
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ There are allowable emissions for 5 facilities. For the other 18 facilities, actual emissions equal allowable emissions.
\2\ There are 25 PEPO production facilities; however, only 23 of these facilities are included in the source category risk assessment based on available
data.
\3\ Maximum individual excess lifetime cancer risk due to HAP emissions.
\4\ See ``Facility-Wide Risk Results'' in section IV.A.5 of this preamble for more details on this risk assessment.

[[Page 106004]]

2. Screening Level Acute Risk Assessment Results
As presented in table 1 of this preamble, the estimated worst-case
off-site acute inhalation exposures to emissions from the PEPO
Production source category result in a maximum modeled acute noncancer
HQ equal to 1 based on the REL for methoxytriglycol (a glycol ether).
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. The main body and appendix 10 of the document titled Residual Risk
Assessment for the Polyether Polyols (PEPO) Production Source Category
in Support of the 2024 Risk and Technology Review Proposed Rule, which
is available in the docket for this rulemaking, provides detailed
information about the assessment, including evaluation of the
screening-level acute risk assessment results.
3. Multipathway Risk Screening Results
For the PEPO Production source category, three facilities emitted
at least 1 PB-HAP, including arsenic, cadmium, mercury, and POM.\28\
Emissions of these PB-HAP from each facility were compared to the
respective pollutant-specific Tier 1 screening emission thresholds. The
Tier 1 screening analysis for PB-HAP (other than lead, which was
evaluated differently), indicated no facilities exceeded the Tier 1
emission threshold for arsenic, cadmium, mercury, or POM.
---------------------------------------------------------------------------

\28\ Note that while the multipathway risk screening results
includes metals (e.g., arsenic, cadmium, mercury) and POM, the EPA
used a health-protective approach and included emissions inventory
records that were not clearly labeled (not easily categorized) in
modeling of emissions from the PEPO Production source category. This
means that emissions from other source categories were likely
included for this analysis in certain instances. We have no
information suggesting that metals or POM are emitted from PEPO
processes. See appendix 1 of the document titled Residual Risk
Assessment for the Polyether Polyols (PEPO) Production Source
Category in Support of the 2024 Risk and Technology Review Proposed
Rule, which is available in the docket for this rulemaking, for more
details about development of the risk modeling file.
---------------------------------------------------------------------------

In evaluating the potential for multipathway risk from emissions of
lead, the modeled maximum annual ambient lead concentration (0.000002
[mu]g/m\3\) was compared to the NAAQS for lead (0.15 [mu]g/m\3\, 3-
month rolling average). We did not estimate any exceedance of the NAAQS
for lead. The modeled maximum annual lead concentration is well below
the NAAQS for lead, indicating low potential for multipathway risk of
concern due to lead emissions.
Detailed information about the assessment is provided in the
document titled Residual Risk Assessment for the Polyether Polyols
(PEPO) Production Source Category in Support of the 2024 Risk and
Technology Review Proposed Rule, which is available in the docket for
this rulemaking.
4. Environmental Risk Screening Results
As described in section IV.A of this preamble, we conducted a
screening assessment for adverse environmental effects for the PEPO
Production source category. The environmental screening assessment
included the following HAP: arsenic, cadmium, methyl mercury, divalent
mercury, and POM.\29\
---------------------------------------------------------------------------

\29\ Note that while the environmental risk screening results
includes metals (e.g., arsenic, cadmium, lead, mercury), POM, and
acid gases (e.g., HCl), the EPA used a health-protective approach
and included emissions inventory records that were not clearly
labeled (not easily categorized) in modeling of emissions from the
PEPO Production source category to avoid underestimating emissions
from PEPO sources. This means that emissions from other source
categories were likely included for this analysis in certain
instances. We have no information suggesting that metals, POM, or
HCl are emitted from PEPO processes. See appendix 1 of the document
titled Residual Risk Assessment for the Polyether Polyols (PEPO)
Production Source Category in Support of the 2024 Risk and
Technology Review Proposed Rule, which is available in the docket
for this rulemaking, for more details about development of the risk
modeling file.
---------------------------------------------------------------------------

In the Tier 1 screening analysis for PB-HAP (other than lead, which
was evaluated differently), none of the PB-HAP had exceedances for any
ecological benchmark.
In evaluating the potential adverse environmental risks associated
with emissions of lead, the modeled maximum annual ambient lead
concentration (0.000002 [mu]g/m\3\) was compared to the NAAQS for lead
(0.15 [mu]g/m\3\, 3-month rolling average). We did not estimate any
exceedance of the NAAQS for lead. The modeled maximum annual lead
concentration is well below the NAAQS for lead, indicating low
potential for environmental risk of concern due to lead emissions.
We also conducted an environmental risk screening assessment
specifically for acid gases (i.e., HCl and HF) for the PEPO Production
source category. There are no facilities with HF emissions. There are
three facilities with HCl emissions. For HCl, the average modeled
concentration around each 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 all facilities.
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. Detailed information about the
assessments is provided in the document titled Residual Risk Assessment
for the Polyether Polyols (PEPO) Production Source Category in Support
of the 2024 Risk and Technology Review Proposed Rule, which is
available in the docket for this rulemaking.
5. Facility-Wide Risk Results
We assessed facility-wide risk, as described in section III.B.7 of
this preamble, to characterize the source category risk in the context
of ``whole facility'' risk using the NEI-based data described in
section II.C of this preamble. Facility-wide risk was modeled using
post-control emissions from the processes subject to the HON to reflect
the emissions reductions expected from the HON rulemaking that was
signed in early 2024 (89 FR 42932). The maximum lifetime individual
cancer risk posed by the 25 modeled facilities based on facility-wide
emissions is 2,000-in-1 million with EtO emissions from wastewater (72
percent) and equipment leaks (20 percent) from PEPO production source
category emissions driving the risk. The total estimated cancer
incidence based on facility-wide emission levels is 0.6 excess cancer
cases per year. EtO emissions contribute 94 percent of the total cancer
incidence. Within 50 km of PEPO NESHAP-subject facilities, the
population exposed to cancer risk greater than 100-in-1 million for
PEPO facility-wide emissions is approximately 4,000 people, and the
population exposed to cancer risk greater than or equal to 1-in-1
million is approximately 7.3 million people. The maximum chronic
noncancer TOSHI due to facility-wide emissions is estimated to be 3
(for respiratory effects) due to emissions of chlorine from 1 facility.
A different facility has a chronic noncancer TOSHI of 2 (for
respiratory effects) due to facility-wide emissions of maleic
anhydride. Approximately 60 people are estimated to be exposed to a
TOSHI greater than 1 due to facility-wide emissions. Of the
approximately 60 people, 44 people are exposed to a TOSHI of 3 due to
emissions of chlorine and 16 people are exposed to a TOSHI of 2 due to
emissions of maleic anhydride.
After the controls proposed in this action are implemented for the
PEPO Production source category (see section IV.B.2 of this preamble),
the post-

[[Page 106005]]

control facility-wide cancer risk remains greater than 100-in-1 million
at two facilities.
6. Community-Based Risk Assessment
We also conducted a community-based risk assessment for PEPO
NESHAP-subject facilities. The goal of this assessment was to estimate
cancer risk from HAP emitted from all local stationary point sources
for which we have emissions data. We estimated the overall inhalation
cancer risk due to emissions from all stationary point sources
impacting census blocks within 10 km of the 25 PEPO production
facilities. Specifically, we combined the modeled impacts from category
and non-category HAP sources at PEPO production facilities, as well as
other stationary point source HAP emissions. Within 10 km of PEPO
NESHAP-subject facilities, we identified 823 non-source category
facilities that could potentially also contribute to HAP inhalation
exposures. Similar to the facility-wide risk assessment, the community-
based risk assessment uses post-control emissions from the processes
subject to the HON to reflect the emissions reductions expected from
the HON rulemaking that was signed in early 2024 (89 FR 42932).
We first looked at what the maximum cancer risk is for communities
around PEPO production facilities. The results indicate that the
community-level maximum individual cancer risk is the same as both the
source category MIR and the maximum individual cancer risk for the
facility-wide assessment, 2,000-in-1 million. The community-based risk
assessment estimated that greater than 99 percent of the community-
level maximum individual cancer risk is attributable to emissions from
PEPO production facilities (including both source category and non-
category emissions). We then looked at the risks to the communities
from all emissions sources for which we had data. Within 10 km, the
population exposed to cancer risks greater than 100-in-1 million from
all nearby emissions is approximately 5,300. For comparison,
approximately 3,300 people have cancer risks greater than 100-in-1
million due to PEPO production emissions and approximately 4,000 people
have cancer risks greater than 100-in-1 million due to PEPO facility-
wide emissions (see table 2 of this preamble). The overall cancer
incidence for this exposed population (i.e., populations with risks
greater than 100-in-1 million living within 10 km of PEPO production
facilities) is 0.02, with 84 percent of the cancer incidence from PEPO
production processes, 9 percent from non-PEPO processes at PEPO
production facilities (a total of 93 percent from PEPO production
facilities), and 7 percent from other nearby stationary point sources
that are not PEPO production facilities.
The population exposed to cancer risks greater than or equal to 1-
in-1 million in the community-based assessment is approximately 1.2
million people. For comparison, approximately 830,000 people have
cancer risks greater than or equal to 1-in-1 million due to PEPO
production process emissions and approximately 1.1 million people have
cancer risks greater than 1-in-1 million due to PEPO facility-wide
emissions (see table 2 of this preamble). The overall cancer incidence
for this exposed population (i.e., people with risks greater than or
equal to 1-in-1 million and living within 10 km of PEPO production
facilities) is 0.4, with 34 percent of the incidence due to emissions
from PEPO production processes, 30 percent from emissions of non-PEPO
processes at PEPO production facilities (that is, a total of 64 percent
from emissions from PEPO production facilities) and 36 percent from
emissions from other nearby stationary sources that are not PEPO
production facilities.
After the controls proposed in this action are implemented for the
PEPO Production source category (see section IV.B.2 of this preamble),
the community-level maximum individual cancer risk will be reduced to
the same as the facility-wide assessment, 300-in-1 million. The
assessment estimated that 51 percent of the MIR is attributable to
emissions from non-PEPO processes at a PEPO production facility, 43
percent from PEPO processes and 6 percent from other nearby stationary
point sources that are not PEPO production facilities. The population
(within 10 km of PEPO facilities) exposed to cancer risks greater than
100-in-1 million from all nearby emissions will be significantly
reduced from 5,300 people to 500 people; a 91 percent reduction from
the baseline. The populations exposed to cancer risks greater than 100-
in-1 million from the PEPO Production source category and facility-wide
emissions are similarly reduced, from 3,300 people to 0 for source
category emissions and from 4,000 to 200 for facility-wide emissions
(see table 2 of this preamble). Furthermore, the overall cancer
incidence for this exposed population is expected to be reduced from
0.02 to 0.001. The percentage of cancer incidence due to emissions from
PEPO processes is reduced from 84 percent to 28 percent. The percentage
of the cancer incidence due to emissions from non-PEPO processes at
PEPO production facilities and emissions from other nearby stationary
sources proportionately shifts to 46 percent and 26 percent
respectively. EtO emissions across these sources remain the largest
source of incidence, accounting for 93 percent of the overall cancer
incidence for this exposed population.
The post-control population exposed to cancer risks greater than or
equal to 1-in-1 million will be reduced from 1.2 million to 1.1
million. In comparison, after the controls proposed in this action, the
number of people with risks greater than or equal to 1-in-1 million due
to source category emissions would reduce from 830,000 to 560,000 and
due to facility-wide emissions from 1.1 million to 1 million (see table
2 of this preamble). The overall cancer incidence for this exposed
population is expected to be reduced from 0.4 to 0.3. The percentage of
cancer incidence from PEPO processes is expected to decrease from 34 to
11 percent. The cancer incidence from non-PEPO processes at PEPO
production facilities and from other nearby stationary sources are
expected to proportionately shift to 40 percent and 49 percent,
respectively.
More results from the community-based assessment are provided in
the document titled Analysis of Demographic Factors For Populations
Living Near Polyether Polyols (PEPO) Production Facilities--Community-
Based Assessment, which is available in the docket for this rulemaking.

[[Page 106006]]

Table 2--Inhalation Cancer Risk Assessment Results for Communities Living Within 10 km of PEPO Production
Facilities
----------------------------------------------------------------------------------------------------------------
Estimated population at
Maximum increased risk of cancer
Risk assessment individual -------------------------------
cancer risk (- >100-in-1 >=1-in-1
in-1 million) million million
----------------------------------------------------------------------------------------------------------------
Baseline (Pre-control)
----------------------------------------------------------------------------------------------------------------
PEPO Production Source Category................................. 1,000 3,300 830,000
Facility-wide................................................... 2,000 4,000 1.1 million
Community-based................................................. 2,000 5,300 1.2 million
----------------------------------------------------------------------------------------------------------------
After Implementation of Proposed Controls (Post-control)
----------------------------------------------------------------------------------------------------------------
PEPO Production Source Category................................. 100 0 560,000
Facility-wide................................................... 300 200 1 million
Community-based................................................. 300 500 1.1 million
----------------------------------------------------------------------------------------------------------------

7. What demographic groups might benefit from this regulation?
To examine the potential for EJ concerns, the EPA conducted three
different demographic analyses: a proximity analysis, baseline cancer
risk-based analysis (i.e., before implementation of any controls
required by this proposed action), and post-control cancer risk-based
analysis (i.e., after implementation of the controls required by this
proposed action). The proximity demographic analysis is an assessment
of individual demographic groups in the total population living within
10 km (~6.2 miles) and 50 km (~31 miles) of the facilities. The
baseline risk-based demographic analysis is an assessment of risks to
individual demographic groups in the population living within 10 km and
50 km of the facilities prior to the implementation of any controls
required by this proposed action (``baseline''). The post-control risk-
based demographic analysis is an assessment of risks to individual
demographic groups in the population living within 10 km and 50 km of
the facilities after implementation of the controls required by this
proposed action (``post-control''). Each of these demographic analyses
were performed for the following three different HAP emissions
scenarios: PEPO category HAP emissions (10 km and 50 km), whole-
facility HAP emissions (10 km and 50 km), and community HAP emissions
(10 km only). Demographic groups included in the analyses are: White,
Black, American Indian and Alaskan Native, other races and multiracial,
Hispanic or Latino, children 17 years of age and under, adults 18 to 64
years of age, adults 65 years of age and over, adults over 25 without a
high school diploma, people living below the poverty level, people
living below two times the poverty level, and linguistically isolated
people. For a detailed discussion of the types of EJ analyses performed
for this proposal and their results see section V.F of this preamble,
``What analysis of environmental justice did we conduct?''

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

1. Risk Acceptability Under the Current MACT Standards
As noted in section III.A of this preamble, we weigh a wide range
of health risk measures and factors in our risk acceptability
determination, including the cancer MIR, the number of persons in
various cancer and noncancer risk ranges, cancer incidence, the maximum
noncancer TOSHI, the maximum acute noncancer HQ, the extent of
noncancer risks, the distribution of cancer and noncancer risks in the
exposed population, and risk estimation uncertainties (54 FR 38044,
September 14, 1989).
Under the current MACT standards for the PEPO Production source
category, the risk results indicate that the MIR is 1,000-in-1 million,
driven by emissions of EtO, and well above 100-in-1 million, which is
the presumptive limit of acceptability. The estimated incidence of
cancer due to inhalation exposures is 0.3 excess cancer case per year.
The population estimated to be exposed to cancer risks greater than
100-in-1 million is approximately 3,300, and the population estimated
to be exposed to cancer risks greater than or equal to 1-in-1 million
is approximately 3.8 million. The estimated maximum chronic noncancer
TOSHI from inhalation exposure for this source category is 0.1 (for
respiratory effects). The acute risk screening assessment of reasonable
worst-case inhalation impacts indicates a maximum acute noncancer HQ of
1.
Considering all of the health risk information and factors
discussed above, particularly the high MIR for the PEPO Production
source category, the EPA proposes that the risks for the source
category are unacceptable. As noted in section II.A of this preamble,
when risks are unacceptable, under the 1989 Benzene NESHAP approach and
CAA section 112(f)(2)(A), the EPA must first determine the emissions
standards necessary to reduce risk to an acceptable level, and then
determine whether further HAP emissions reductions are necessary to
provide an ample margin of safety to protect public health or to
prevent, taking into consideration costs, energy, safety, and other
relevant factors, an adverse environmental effect. Therefore, pursuant
to CAA section 112(f)(2), we are proposing certain standards for
emission sources of EtO in the PEPO Production source category that are
more protective than the current PEPO NESHAP MACT standards.
2. Proposed Controls To Address Unacceptable Risks
As previously discussed, we conducted a risk assessment of the PEPO
Production source category because the 2016 revision to the EPA's IRIS
inhalation URE for EtO showed that EtO is more toxic than previously
known.
For the PEPO Production source category, we identified EtO as the
cancer risk driver from PEPO sources. We are aware of 20 PEPO
facilities reporting EtO emissions in their emissions inventories from
PEPO production processes. From our residual risk assessment, six
facilities with emissions of EtO from process vents, storage vessels,
equipment leaks, and wastewater have estimated cancer risks

[[Page 106007]]

greater than 100-in-1 million in nearby communities. Additionally, an
allowable leak of EtO from a heat exchange system contributes to cancer
risks greater than 100-in-1 million. Thus, to reduce emissions of EtO
from PEPO processes, the EPA is proposing more stringent control
requirements for process vents, storage vessels, equipment leaks, heat
exchange systems, and wastewater that emit or have the potential to
emit EtO. As discussed later in this preamble, we are proposing that
these requirements will reduce risk to an acceptable level and provide
an ample margin of safety to protect public health, and no additional
requirements are needed to prevent an adverse environmental effect.
We discuss the control options we evaluated for reducing EtO
emissions from PEPO processes in sections IV.B.2.a through IV.B.2.e of
this preamble.
a. Process Vents and Storage Vessels
Process vents that emit EtO are primarily associated with reactors
(from batch unit operations and continuous unit operations) that
produce PEPO products using epoxides as a reactant. Other unit
operations within the PMPU may also have process vents that emit EtO,
such as process vents on condensers and distillation units.
The PEPO NESHAP (40 CFR 63.1425) specifies control requirements for
process vents, based on the PEPO polymerization process (i.e.,
polymerization using epoxides versus using THF). For PEPO processes
that use epoxides as the reactant, the PEPO NESHAP specifies emissions
limits for: (1) epoxide emissions, (2) nonepoxide organic HAP emissions
from processes that use nonepoxide HAP to make or modify the product,
and (3) nonepoxide organic HAP emissions from catalyst extraction. For
the epoxide standards, the PEPO NESHAP (40 CFR 63.1425(b)) requires
owners or operators to either: (1) reduce emissions at existing sources
by 98 percent and new sources by 99.9 percent; (2) control emissions
using a flare (existing sources only); (3) achieve an outlet
concentration of 20 parts per million by volume (ppmv) or less; or (4)
limit emissions to 1.69 x 10-2 kilogram of epoxide per
megagram of product at existing sources and 4.43 x 10-3
kilogram of epoxide per megagram of product at new sources. We provide
more details about process vents in our technology review discussion
(see section IV.C.3 of this preamble) including specifics about the
process vent standards for nonepoxide organic HAP emissions from
processes that use nonepoxide HAP to make or modify the product, and
for nonepoxide organic HAP emissions from catalyst extraction.
PEPO facilities use storage vessels to hold liquid and gaseous
feedstocks for use in a process, as well as to store liquid and gaseous
products from a process. Facilities typically store EtO under pressure
as a liquified gas, but EtO may also be found in small amounts in
atmospheric storage vessels storing liquid products that use EtO as a
reactant in their production. Typical emissions from atmospheric
storage tanks occur from working and breathing losses, while pressure
vessels are considered closed systems and, if properly maintained and
operated, should have virtually no emissions. In some instances, there
may be low levels of fugitive emissions from pressure vessels, and
pressure vessels storing liquefied gases may be vented periodically to
purge inerts.
The PEPO NESHAP (40 CFR 63.1432) cites the control provisions
specified in the HON (40 CFR 63.119 through 63.123) which require
owners or operators determine Group 1 or Group 2 designations of
affected storage vessels, based on the volume of the storage vessel and
maximum true vapor pressure (MTVP) of the material stored. Group 1
storage vessels are those with capacities between 75 m\3\ (inclusive)
and 151 m\3\ and a MTVP greater than or equal to 13.1 kilopascals
(kPa), and those with capacities greater than or equal to 151 m\3\ and
a MTVP greater than or equal to 5.2 kPa. The HON storage vessel
standards that PEPO affected sources are currently subject to \30\
require Group 1 storage vessels to reduce total HAP emissions by 95
percent (or 90 percent if the storage vessel was installed on or before
December 31, 1992) by venting emissions through a closed vent system to
any combination of control devices or to vent emissions through a
closed vent system to a flare. Owners and operators of Group 1 storage
vessels storing a liquid with a MTVP of total organic HAP less than
76.6 kPa are also allowed to reduce organic HAP by utilizing an
internal floating roof (IFR), an external floating roof (EFR), an EFR
converted to an IFR, vapor balancing, or by routing the emissions to a
process or a fuel gas system. For Group 1 storage vessels storing a
liquid with a MTVP of total organic HAP greater than or equal to 76.6
kPa, owners and operators can reduce organic HAP emissions by 95
percent by venting emissions through a closed vent system to any
combination of control devices, controlling emissions by routing them
to a process or a fuel gas system, or by using vapor balancing.
Pressure vessels (operating in excess of 204.9 kPa without emissions to
the atmosphere) may also store materials with EtO. For storage vessels,
the PEPO NESHAP, by reference to the HON, allows use of a design
evaluation instead of a performance test to determine the percent
reduction of control devices for any quantity of total uncontrolled
organic HAP emissions being sent to the control device. We provide more
details about storage vessels in our technology review discussion (see
section IV.C.2 of this preamble).
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\30\ The HON requirements that were added in 2024 (89 FR 42932,
May 16, 2024) apply to only the SOCMI source category; therefore,
those 2024 HON amendments are currently not applicable to the PEPO
Production source category. In other words, when we discuss the
current PEPO NESHAP requirements that refer to HON, we mean pre-2024
HON requirements.
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Based on results from the risk assessment, we determined that the
current MACT standards for PEPO process vents and storage vessels do
not result in sufficient control of EtO emissions to prevent
unacceptable risk. For example, emissions of EtO from PEPO process
vents and storage vessels contribute to 72 percent of one facility's
maximum individual cancer risk of 500-in-1 million. Therefore, we
evaluated available control technologies with a higher level of
control, as discussed below.
To lower the risk for PEPO facilities with EtO emissions, we
analyzed a control option for process vents and storage vessels that
are in EtO service which requires all process vents and storage vessels
in EtO service to be controlled. This control option is based on
requirements that were recently finalized in the MON and HON because of
unacceptable risk (see 85 FR 49084, August 12, 2020, and 89 FR 42932,
May 16, 2024, respectively). The definitions of process vents and
storage vessels ``in ethylene oxide service'' from the MON and HON are
presented here:
<bullet> For process vents, ``in ethylene oxide service'' means,
when uncontrolled, each process vent contains a concentration of
greater than or equal to 1 ppmv undiluted EtO, and when combined, the
sum of all process vents within the process would emit uncontrolled EtO
emissions greater than or equal to 5 lb/yr.
<bullet> For storage vessels of any capacity and vapor pressure,
``in ethylene oxide service'' means that the concentration of EtO
within the tank liquid is greater than or equal to 0.1 percent by
weight.
The MON and HON standards for process vents and storage vessels in
EtO service, require owners and operators to route emissions through a
closed vent

[[Page 106008]]

system to a: (1) control device that reduces EtO by at least 99.9
percent by weight or to a concentration less than 1 ppmv for each
process vent and storage vessel vent (or, for multiple process vents
within a process, to less than 5 lb/yr for all combined process vents),
or (2) flare meeting certain flare operating and monitoring
requirements.
To ensure emissions from PEPO affected sources are controlled to an
acceptable level of risk under the PEPO NESHAP, we are proposing to
incorporate the same EtO emissions standards for process vents and
storage vessels from the MON and HON into the PEPO NESHAP.
Specifically, we are proposing at 40 CFR 63.1423(b) to refer to subpart
F of the HON which defines the term ``in ethylene oxide service'' for
process vents to mean each process vent in a process that, when
uncontrolled, contains a concentration of greater than or equal to 1
ppmv undiluted EtO, and when combined, the sum of all these process
vents within the process would emit uncontrolled EtO emissions greater
than or equal to 5 pounds per year (lb/yr) (2.27 kilograms per year,
kg/yr). We are also proposing to update the definition of ``process
vent'' at 40 CFR 63.1423(b) to align with this proposed change. We are
also proposing in the PEPO NESHAP at 40 CFR 63.1423(b) to refer to
subpart F of the HON which defines the term ``in ethylene oxide
service'' for storage vessels to mean that the concentration of EtO of
the stored liquid is at least 0.1 percent by weight. We are also
proposing that the exemption for ``vessels and equipment storing and/or
handling material that contains no organic HAP, or organic HAP as
impurities only'' listed in the definition of ``storage vessel'' at 40
CFR 63.1423(b) does not apply for storage vessels in EtO service. We
are proposing procedures for determining whether process vents and/or
storage vessels are in EtO service within the proposed definition of
the term ``in ethylene oxide service'' (by reference to 40 CFR 63.109
for PEPO process vents and storage vessels in EtO service). We are
proposing at 40 CFR 63.1425(g) that PEPO process vents in EtO service
either reduce emissions of EtO by: (1) venting emissions through a
closed vent system to a non-flare control device that reduces EtO by at
least 99.9 percent by weight, or to a concentration less than 1 ppmv
for each process vent, or to less than 5 lb/yr for all combined process
vents within the process; or (2) routing emissions through a closed
vent system to a flare meeting the proposed flare operating
requirements discussed in section IV.D.1 of this preamble (see proposed
40 CFR 63.1436). We are proposing at 40 CFR 63.1432(a) by reference to
the HON (40 CFR 63.119(a)(5)) that PEPO storage vessels in EtO service
either reduce emissions of EtO by: (1) venting emissions through a
closed vent system to a non-flare control device that reduces EtO by at
least 99.9 percent by weight or to a concentration less than 1 ppmv for
each storage tank vent; or (2) venting emissions through a closed vent
system to a flare meeting the proposed flare operating requirements
discussed in section IV.D.1 of this preamble (see proposed 40 CFR
63.1436). We are proposing procedures to determine compliance with
these proposed EtO standards at 40 CFR 63.1426(g) (by reference to 40
CFR 63.124 for PEPO process vents in EtO service) and 40 CFR 63.1432(v)
(by reference to 40 CFR 63.124 for PEPO storage vessels in EtO
service). In section IV.D.1 of this preamble, we recognized flares
cannot achieve 99.9 percent EtO reduction. We also noted that as part
of the CAA section 114 request, five facilities measured EtO emissions
from their EtO emission points and only one of these five facilities
currently use a flare to control EtO emissions from process vents or
storage vessels. Even so, our modeling file does include several other
PEPO facilities that do use flares to control process vents and storage
vessels that emit EtO. Therefore, we accounted for these flares
operating at 98 percent EtO reduction in our risk assessment and
determined that it is not necessary for flares to achieve 99.9 percent
EtO reduction to reduce risk to an acceptable level and provide an
ample margin of safety to protect public health (provided that owners
and operators still comply with the entire suite of EtO control
requirements that we are proposing in this action).
Additionally, we propose removing the option to allow use of a
design evaluation in lieu of performance testing to demonstrate
compliance for storage vessels in EtO service to ensure that the
required level of control is achieved (see proposed 40 CFR 63.1432(v)
by reference to the HON (40 CFR 63.124(a)(2)(i) and (b)(3))). We are
also proposing that after promulgation of the rule, owners or operators
that choose to control emissions with a non-flare control device
conduct an initial performance test according to proposed 40 CFR
63.1426(g) and 63.1432(v) by reference to the HON (40 CFR 63.124) on
each existing control device in EtO service and on each newly installed
control device in EtO service to verify performance at the required
level of control. We are also proposing at 40 CFR 63.1426(g) and
63.1432(v) by reference to the HON (40 CFR 63.124(b)) that owners or
operators conduct periodic performance testing on non-flare control
devices in EtO service every 5 years.
Finally, we are proposing at 40 CFR 63.1427(a) that owners and
operators may not use the extended cookout (ECO) pollution prevention
technique to show compliance with the proposed standard for PEPO
process vents in EtO service. The PEPO NESHAP at 40 CFR 63.1427(a)
allows the use of ECO as a means of reducing epoxide emissions by the
required percentage (98 or 99.9 percent) or complying with the
production-based limit (<=1.69 x 10-2 or 4.43 x
10-3 kilograms of epoxide emissions per megagram of product
made). This pollution prevention technique reduces emissions by
extending the time of reaction, thus leaving less unreacted epoxides to
be emitted downstream. To demonstrate a percent efficiency, it is
necessary to designate the basis, or the ``uncontrolled'' emissions,
for assessing the percent reduction. The point where uncontrolled
emissions are to be assessed, called the ``onset'' of the ECO, is
defined in the PEPO NESHAP at 40 CFR 63.1427(c) as the point when the
epoxide concentration in the reactor liquid is equal to 25 percent of
the concentration of epoxide in the liquid at the end of the epoxide
feed. Procedures to calculate epoxide emissions at the end of ECO are
provided in 40 CFR 63.1427(d). The EPA determined the default onset of
ECO based on CBI from the Society of the Plastics Industry, which
indicated the economic breakpoint for when a cookout is no longer
economically advantageous (see 62 FR 46804, September 4, 1997).
However, new economic conditions suggest the ECO compliance option may
no longer be viable. For instance, one facility reported, in response
to the EPA's CAA section 114 request, that their customers require less
than 1 ppm residual EtO, i.e., it is economically advantageous to
continue the reaction until 1 ppm is reached. It is impractical to
achieve a 99.9 percent reduction from an onset of 1 ppm. Additionally,
using the current definition of onset, ECO could lead to high EtO
emissions relative to the starting amount of epoxide used. Therefore,
we believe it is not appropriate to continue allowing the ECO pollution
prevention technique to demonstrate compliance with the proposed EtO
emissions standards (i.e., reduce EtO by at least 99.9 percent by
weight) that are intended to control

[[Page 106009]]

emissions from process vents and storage vessels to an acceptable risk
level. We are also proposing that it is not appropriate to continue to
allow the existing production-based limits (i.e., <=1.69 x
10-2 or 4.43 x 10-3 kilograms of epoxide
emissions per megagram of product made) in place of the new EtO
emissions standards. The 1.69 x 10-3 production-based limit
is an alternative to the 98 percent emission reduction standard for
existing affected sources which is not as stringent as the proposed
99.9 percent emission reduction standard for EtO. While the 4.43 x
10-3 production-based limit is an alternative to the 99.9
percent emission reduction standard for new affected sources, it is
related to the aggregate reduction of total epoxide emissions and not
specifically to EtO emissions. Additionally, it is not clear how these
production-based limits (also referred to ``as emission factors'') were
derived \31\ and we do not have enough information to set a new
production-based limit that would be equivalent to the proposed EtO
emissions standards.
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\31\ Although the original proposal for the PEPO NESHAP (62 FR
46804, September 4, 1997) mentions that the method for determining
these emission factors is detailed in the Supplementary Information
Document, we could not locate this derivation in the document titled
Hazardous Air Pollutant Emissions from the Production of Polyether
Polyols--Supplementary Information Document for Proposed Standards.
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See the document titled Analysis of Control Options for Process
Vents and Storage Vessels to Reduce Residual Risk of Ethylene Oxide in
the PEPO Production Source Category, which is available in the docket
for this action, for more information on the control option the EPA
evaluated to reduce EtO risk from PEPO process vents and storage
vessels.
b. Equipment Leaks
Emissions of EtO from equipment leaks occur in the form of gases or
liquids that escape to the atmosphere through connection points (e.g.,
threaded fittings) or through the moving parts of valves, pumps,
compressors, PRDs, and certain types of process equipment. The PEPO
NESHAP defines equipment leaks as ``emissions of organic HAP from a
connector, pump, compressor, agitator, pressure relief device, sampling
connection system, open-ended valve or line, valve, surge control
vessel, bottoms receiver, or instrumentation system in organic HAP
service.'' The equipment leak requirements apply to equipment that
contain or contact material that are 5 percent by weight or more of
organic HAP, operate 300 hours per year or more, and are not in vacuum
service.
The PEPO NESHAP requirements for equipment leaks directly reference
the provisions in 40 CFR part 63, subpart H (which is part of the HON).
The HON equipment leak requirements vary by equipment component type,
but require LDAR using monitoring with EPA Method 21 of appendix A-7 to
40 CFR part 60 at certain frequencies (e.g., monthly, quarterly, every
2 quarters, annually) and varying leak definitions (e.g., 500 ppmv;
1,000 ppmv; 10,000 ppmv) depending on the type of service (e.g., gas
and vapor service or in light liquid service). The LDAR requirements
for components in heavy liquid service include sensory monitoring and
the use of EPA Method 21 monitoring if a leak is identified. We provide
more details about equipment leaks in our technology review discussion
(see section IV.C.5 of this preamble).
Results from our risk assessment indicate that, for the source
category MIR of 1,000-in-1 million, more than 20 percent is from
emissions of EtO related to PEPO equipment leaks. We also note that the
risk from EtO from PEPO equipment leaks at three facilities (including
the facility driving the MIR) is >=100-in-1 million. To help reduce the
risk associated with EtO emissions from equipment leaks in the PEPO
Production source category, we performed a review of available measures
for reducing EtO emissions from components that are most likely to be
in EtO service, which include connectors (in gas and vapor service or
light liquid service), pumps (in light liquid service), and valves (in
gas or light liquid service). We identified options for further
strengthening LDAR practices to find and repair equipment leaks from
these three pieces of equipment more quickly, including lowering the
leak definitions and/or requiring more frequent monitoring with EPA
Method 21 of appendix A-7 to 40 CFR part 60, which align with the
recently finalized EtO standards for equipment leaks in the HON (89 FR
42932, May 16, 2024).
For gas/vapor and light liquid connectors in EtO service, we
identified two options: (1) require connector monitoring at a leak
definition of 500 ppmv with annual monitoring and no reduction in
monitoring frequency (i.e., no skip periods), and (2) require connector
monitoring at a leak definition of 100 ppmv with annual monitoring and
no reduction in monitoring frequency.
For light liquid pumps in EtO service, we identified three options:
(1) lower the leak definition from 1,000 ppmv to 500 ppmv with monthly
monitoring, (2) lower the leak definition from 1,000 ppmv to 100 ppmv
with monthly monitoring, or (3) require the use of leakless pumps
(i.e., canned pumps, magnetic drive pumps, diaphragm pumps, pumps with
tandem mechanical seals, pumps with double mechanical seals) with
annual monitoring and a leak defined as any reading above background
concentration levels.
For gas/vapor and light liquid valves in EtO service, we identified
two options: (1) require a leak definition of 500 ppmv with monthly
monitoring and no reduction in monitoring frequency, and (2) lower the
leak definition from 500 ppmv to 100 ppmv with monthly monitoring and
no reduction in monitoring frequency.
Due to the high residual risk for some of the facilities from
equipment leaks of EtO and the potential need for greater emission
reduction to meet an acceptable level of risk for the PEPO Production
source category, we also evaluated a more stringent combined option
which requires monthly monitoring for valves (in gas/vapor and light
liquid service), connectors (in gas/vapor and light liquid service),
and pumps (light liquid service) in EtO service at a leak definition of
100 ppmv for valves and connectors and 500 ppmv for light liquid pumps
using EPA Method 21 of appendix A-7 to 40 CFR part 60. This combined
option also does not allow equipment in EtO service to be monitored
less frequently with skip periods, nor does the option allow facilities
to take advantage of the delay of repair provisions. We analyzed
increasing the monitoring frequency to monthly for connectors because
they are the most numerous equipment components at chemical facilities,
and they are the most significant contribution to the baseline
emissions from leaking equipment at the EtO-emitting facilities.
For the component-specific control options, we calculated the EtO
baseline emissions and emissions after implementation of controls for
each facility using average volatile organic compound (VOC) emission
rates for each component, and the component counts and the EtO weight
percent of the process from the responses to the EPA's CAA section 114
request. For the combined option of monthly monitoring of gas and light
liquid valves and connectors at 100 ppmv and light liquid pumps at 500
ppmv, we do not have emission factors to estimate reductions for
increased monitoring frequencies for connectors. Where a simplified
emission factor method for determining the potential reductions of
applying the

[[Page 106010]]

option did not exist, we estimated emissions reductions based on the
approach used in other rules,\32\ where detailed leak data or an
assumed leak distribution were available. The equipment leaks model
uses a Monte Carlo analysis to estimate emissions from EtO facility
equipment leaks. The memorandum Analysis of Control Options for
Equipment Leaks to Reduce Residual Risk of Ethylene Oxide in the PEPO
Production Source Category, which is available in the docket for this
action, provides a detailed discussion of the model.
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\32\ Gas Plant Equipment Leak Monte Carlo Model Code and
Instructions. October 21, 2021. EPA Docket No. EPA-HQ-OAR-2021-0317.
Control Options for Equipment Leaks at Gasoline Distribution
Facilities. October 20, 2021. EPA Docket No. EPA-HQ-OAR-2020-0371.
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In this action, we are also proposing the same definition for the
term ``in ethylene oxide service'' for equipment as used in the final
amendments to the HON (89 FR 42932, May 16, 2024).\33\ For equipment
leaks, we are proposing to define ``in ethylene oxide service'' in the
PEPO NESHAP at 40 CFR 63.1423(b) (by reference to 40 CFR 63.101) to
mean any equipment that contains or contacts a fluid (liquid or gas)
that is at least 0.1 percent by weight of EtO. We are proposing
procedures for determining whether equipment is in EtO service within
the proposed definition of the term ``in ethylene oxide service'' (by
reference to 40 CFR 63.109 for PEPO equipment in EtO service). We are
proposing that any piece of equipment that is in ethylene oxide service
is also in organic HAP service. For PEPO equipment in EtO service, to
achieve greater emissions reductions to help meet an acceptable level
of risk for the PEPO Production source category, we are proposing the
following combined requirements: monitoring of connectors in gas/vapor
and light liquid service at a leak definition of 100 ppmv on a monthly
basis with no reduction in monitoring frequency or delay of repair;
monthly monitoring of light liquid pumps at a leak definition of 500
ppmv; and monthly monitoring of gas/vapor and light liquid valves at a
leak definition of 100 ppmv with no reduction in monitoring frequency
or delay of repair (see proposed 40 CFR 63.1434(a) by reference to the
HON). The document titled Analysis of Control Options for Equipment
Leaks to Reduce Residual Risk of Ethylene Oxide in the PEPO Production
Source Category, which is available in the docket for this action,
provides additional information on all evaluated control options to
reduce EtO risk from PEPO equipment leaks.
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\33\ See 40 CFR 63.101.
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c. Heat Exchange Systems
Emissions of EtO from heat exchange systems occur due to corrosion
or cracks in internal tubing materials, which allows some process
fluids to mix or become entrained with the cooling water. Pollutants
(e.g., EtO) in the process fluids may subsequently be released from the
cooling water into the atmosphere when the water is exposed to air
(e.g., in a cooling tower for closed-loop systems or trenches/ponds in
a once-through system). The HON heat exchange system standards that
PEPO affected sources are currently subject to require owners or
operators to monitor heat exchange systems for leaks of process fluids
into cooling water and take actions to repair leaks within 45 days if
they are detected (facilities may delay the repair of leaks if they
meet certain criteria). To comply with the provisions, owners or
operators can use any method listed in 40 CFR part 136 to sample
cooling water for leaks for the HAP listed in table 4 to subpart F
(recirculating systems) and table 9 to subpart G (once-through systems)
(and other representative substances such as total organic compounds
(TOC) or VOC that can indicate the presence of a leak can also be
used). In addition, owners or operators can monitor for leaks using a
surrogate indicator (e.g., ion specific electrode monitoring, pH,
conductivity), provided that they meet certain criteria in 40 CFR
63.104(c). We provide more details about heat exchange systems in our
technology review discussion (see section IV.C.1 of this preamble).
For heat exchange systems, we found that, while we did not identify
a report of EtO emissions from a PEPO heat exchange system leak, a
model using representative leaks (and the current standards for
monitoring and repair) indicated that a potential leak currently
allowed by the PEPO NESHAP containing EtO from a facility's cooling
tower could significantly contribute to unacceptable risk. Thus, we are
proposing to use the same definition of the term ``in ethylene oxide
service'' as used in the final amendments to the HON (89 FR 42932, May
16, 2024). We are proposing in the PEPO NESHAP at 40 CFR 63.1423 to
refer to subpart F of the HON which defines the term ``in ethylene
oxide service'' for heat exchange systems to mean any heat exchange
system in a process that cools process fluids (liquid or gas) that are
0.1 percent or greater by weight of EtO. We are proposing procedures
for determining whether heat exchange systems are in EtO service within
the proposed definition of the term ``in ethylene oxide service'' (by
reference to 40 CFR 63.109 for PEPO heat exchange systems in EtO
service). We are proposing that any heat exchange system that is in
ethylene oxide service is also in organic HAP service. To address risk
from EtO allowable emissions due to PEPO heat exchange system leaks, we
evaluated the following option for PEPO heat exchange systems ``in
ethylene oxide service'' which: (1) requires use of the Modified El
Paso Method (see section IV.C.1 of this preamble), (2) requires
quarterly monitoring using the Modified El Paso Method, (3) reduces the
allowed amount of repair time from 45 days after finding a leak to 15
days from the sampling date, and (4) prohibits delay of repair. We also
evaluated this same option except with varying monitoring frequencies
(i.e., monthly and weekly) instead of quarterly. Using equation 7-2
from appendix P of the Texas Commission on Environmental Quality's
(TCEQ) Sampling Procedures Manual,\34\ model leak distributions and
concentrations, and other model input parameters, we anticipate the
quarterly option would reduce EtO emissions from leaking PEPO heat
exchange systems by 54 percent because owners or operators would
identify and repair leaks more quickly, which is needed to help reduce
potential unacceptable risk from the PEPO Production source category.
See section IV.B.4 of this preamble for an analysis of the monthly and
weekly options to provide an ample margin of safety. We are proposing
weekly monitoring at 40 CFR 63.1435(a) by reference to the HON (40 CFR
63.104(g)(6)) based on that ample margin of safety analysis. The
document titled Analysis of Control Options for Heat Exchange Systems
to Reduce Residual Risk of Ethylene Oxide in the PEPO Production Source
Category, which is available in the docket for this action, provides
additional information on this evaluated control option to reduce EtO
risk from PEPO heat exchange systems.
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\34\ See appendix B in the document titled: The Air Stripping
Method (Modified El Paso Method) for Determination of Volatile
Organic Compound (VOC) Emissions from Water Sources, which is
included in the docket for this rulemaking.
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d. Wastewater
EtO is emitted from wastewater collection, storage, and treatment
systems that are uncovered or open to the atmosphere through
volatilization of the compound at the liquid surface. Emissions occur
by diffusive or convective me

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