[Federal Register Volume 88, Number 71 (Thursday, April 13, 2023)]
[Proposed Rules]
[Pages 22790-22857]
[FR Doc No: 2023-06676]

Vol. 88

Thursday,

No. 71

April 13, 2023

Part IV

Environmental Protection Agency

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40 CFR Part 63

National Emission Standards for Hazardous Air Pollutants: Ethylene
Oxide Emissions Standards for Sterilization Facilities Residual Risk
and Technology Review; Proposed Rule

Federal Register / Vol. 88, No. 71 / Thursday, April 13, 2023 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2019-0178; FRL-7055-03-OAR]
RIN 2060-AU37

National Emission Standards for Hazardous Air Pollutants:
Ethylene Oxide Emissions Standards for Sterilization Facilities
Residual Risk and Technology Review

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing
amendments to the National Emission Standards for Hazardous Air
Pollutants (NESHAP) for the Commercial Sterilization Facilities source
category. The EPA is proposing decisions concerning the risk and
technology review (RTR), including proposing amendments pursuant to the
technology review for certain point source emissions and proposing
amendments pursuant to the risk review to specifically address ethylene
oxide (EtO) emissions from point source and room air emissions from all
commercial sterilization facilities. The EPA is also proposing
amendments to correct and clarify regulatory provisions related to
emissions during periods of startup, shutdown, and malfunction (SSM),
including removing general exemptions for periods of SSM and adding
work practice standards for periods of SSM where appropriate. Lastly,
the EPA is proposing to revise monitoring and performance testing
requirements and to add provisions for electronic reporting of
performance test results and reports, performance evaluation reports,
and compliance reports. We estimate that, if finalized, these proposed
amendments would reduce EtO emissions from this source category by 19
tons per year (tpy) and reduce risks to public health to acceptable
levels.

DATES: Comments must be received on or before June 12, 2023. 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 May 15, 2023.
    Public hearing: The EPA will hold virtual public hearings on May 2
and May 3, 2023. See SUPPLEMENTARY INFORMATION for information on the
public hearings.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2019-0178, by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/
(our preferred method). Follow the online instructions for submitting
comments.
     Email: [email protected]. Include Docket ID No. EPA-
HQ-OAR-2019-0178 in the subject line of the message.
     Fax:<PHONE_NUMBER>. Attention Docket ID No. EPA-HQ-OAR-
2019-0178.
     Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2019-0178, Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.
     Hand/Courier Delivery: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-
Friday (except Federal holidays).
    Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov/, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the SUPPLEMENTARY
INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Jonathan Witt, Sector Policies and Programs Division
(E143-05), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; and email address:
[email protected]. For specific information regarding the risk modeling
methodology, contact Matt Woody, Health and Environmental Impacts
Division (C539-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; and email address:
[email protected].

SUPPLEMENTARY INFORMATION:
    Participation in virtual public hearing. The public hearings will
be held via virtual platform on May 2 and May 3, 2023, and will convene
at 11:00 a.m. Eastern Time (ET) and conclude at 7:00 p.m. ET each day.
On each hearing day, the EPA may close a session 15 minutes after the
last pre-registered speaker has testified if there are no additional
speakers. The EPA will announce further details at https://www.epa.gov/stationary-sources-air-pollution/ethylene-oxide-emissions-standards-sterilization-facilities. If the EPA receives a high volume of
registrations for the public hearing, we may continue the public
hearing on May 4, 2023.
    The EPA will begin pre-registering speakers for the hearing no
later than 1 business day following the publication of this document in
the Federal Register. To register to speak at the virtual hearing,
please use the online registration form available at https://www.epa.gov/stationary-sources-air-pollution/ethylene-oxide-emissions-standards-sterilization-facilities or contact the public hearing team
at<PHONE_NUMBER> or by email at [email protected]. The last
day to pre-register to speak at the hearing will be April 24, 2023.
Prior to the hearing, the EPA will post a general agenda that will list
pre-registered speakers in approximate order at: https://www.epa.gov/stationary-sources-air-pollution/ethylene-oxide-emissions-standards-sterilization-facilities.
    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 https://www.epa.gov/stationary-sources-air-pollution/ethylene-oxide-emissions-standards-sterilization-facilities.
While the EPA expects the hearing to go forward as set forth above,
please monitor our website or contact the public hearing team at (888)
372-8699 or by email at [email protected] to determine if there
are any updates. The EPA does not intend to publish a document in the
Federal Register announcing updates.
    If you require the services of a translator or special
accommodation such as audio description, please pre-

register for the hearing with the public hearing team and describe your
needs by April 18, 2023. The EPA may not be able to arrange
accommodations without advanced notice.
    Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2019-0178. All documents in the docket are
listed in https://www.regulations.gov/. Although listed, some
information is not publicly available, e.g., Confidential Business
Information (CBI) or other information whose disclosure is restricted
by statute. Certain other material, such as copyrighted material, is
not placed on the internet and will be publicly available only in hard
copy. With the exception of such material, publicly available docket
materials are available electronically in Regulations.gov. All publicly
available docket materials are available in hard copy at the EPA Docket
Center, EPA WJC West Building, Room 3334, 1301 Constitution Ave. NW,
Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30
p.m., Monday through Friday, excluding legal holidays. The telephone
number for the Public Reading Room is<PHONE_NUMBER>, and the telephone
number for the EPA Docket Center is<PHONE_NUMBER>.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2019-0178. The EPA's policy is that all comments received will be
included in the public docket without change and may be made available
online at https://www.regulations.gov/, including any personal
information provided, unless the comment includes information claimed
to be CBI or other information whose disclosure is restricted by
statute. Do not submit electronically to https://www.regulations.gov/
any information that you consider to be CBI or other information whose
disclosure is restricted by statute. 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 https://www.epa.gov/dockets/commenting-epa-dockets.
    The https://www.regulations.gov/ website allows you to submit your
comment anonymously, which means the EPA will not know your identity or
contact information unless you provide it in the body of your comment.
If you send an email comment directly to the EPA without going through
https://www.regulations.gov/, your email address will be automatically
captured and included as part of the comment that is placed in the
public docket and made available on the internet. If you submit an
electronic comment, the EPA recommends that you include your name and
other contact information in the body of your comment and with any
digital storage media you submit. If the EPA cannot read your comment
due to technical difficulties and cannot contact you for clarification,
the EPA may not be able to consider your comment. Electronic files
should not include special characters or any form of encryption and be
free of any defects or viruses. For additional information about the
EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    The EPA is soliciting comment on numerous aspects of this action.
The EPA has indexed each comment solicitation with an alpha-numeric
identifier (e.g., ``C-1,'' ``C-2,'' ``C-3'') to provide a consistent
framework for effective and efficient provision of comments.
Accordingly, the EPA asks that commenters include the corresponding
identifier when providing comments relevant to that comment
solicitation. The EPA asks that commenters include the identifier in
either a heading, or within the text of each comment (e.g., ``In
response to solicitation of comment C-1, . . .'') to make clear which
comment solicitation is being addressed. The EPA emphasizes that the
Agency is not limiting comment to these identified areas and encourages
provision of any other comments relevant to this action.
    Submitting CBI. Do not submit information containing CBI to the EPA
through https://www.regulations.gov/. Clearly mark the part or all of
the information that you claim to be CBI. For CBI information on any
digital storage media that you mail to the EPA, mark the outside of the
digital storage media as CBI and then identify electronically within
the digital storage media the specific information that is claimed as
CBI. In addition to one complete version of the comments that includes
information claimed as CBI, you must submit a copy of the comments that
does not contain the information claimed as CBI directly to the public
docket through the procedures outlined in Instructions above. If you
submit any digital storage media that does not contain CBI, mark the
outside of the digital storage media clearly that it does not contain
CBI 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
OAQPS CBI Office at the email address [email protected] 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 [email protected] to
request a file transfer link. If sending CBI information through the
postal service, please send it to the following address: OAQPS Document
Control Officer (C404-02), OAQPS, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711, Attention Docket ID No.
EPA-HQ-OAR-2019-0178. 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 document 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:

ADAF age-dependent adjustment factor
AEGL acute exposure guideline level
AERMOD air dispersion model used by the HEM model
AIHA American Industrial Hygiene Association
APCD air pollution control device
ARV aeration room vent
ASME American Society of Mechanical Engineers
ATSDR Agency for Toxic Substances and Disease Registry
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information

CEMS continuous emissions monitoring system
CEV chamber exhaust vent
CFR Code of Federal Regulations
cfs cubic feet per second
dscfm dry standard cubic feet per minute
EJ environmental justice
EPA Environmental Protection Agency
ERPG emergency response planning guideline
ERT Electronic Reporting Tool
EtO ethylene oxide
FIFRA Federal Insecticide, Fungicide, and Rodenticide Act
FR Federal Register
FTIR Fourier Transform Infrared Spectroscopy
GACT generally available control technology
GC gas chromatography
HAP hazardous air pollutant(s)
HCl hydrochloric acid
HEM Human Exposure Model
HF hydrogen fluoride
HQ hazard quotient
ICR Information Collection Request
IRIS Integrated Risk Information System
ISO International Organization for Standardization
km kilometer
lb/hr pounds per hour
LEL lower explosive limit
MACT maximum achievable control technology
MIR maximum individual risk
mg/L milligrams per liter
NAICS North American Industry Classification System
NDO natural draft opening
NEI National Emissions Inventory
NESHAP national emission standards for hazardous air pollutants
NIST National Institute of Standards and Technology
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PB-HAP hazardous air pollutants known to be persistent
and bio-accumulative in the environment
PID Proposed Interim Decision
ppbv parts per billion by volume
ppm parts per million
ppmv parts per million by volume
PoAHSM post-aeration handling of sterilized material
POM polycyclic organic matter
PpO propylene oxide
PRA Paperwork Reduction Act
PrAHSM pre-aeration handling of sterilized material
PS Performance Specification
PTE permanent total enclosure
RAC room air change
RBLC RACT/BACT/LAER Clearinghouse
REL reference exposure level
RDL Representative detection level
RFA Regulatory Flexibility Act
RfC reference concentration
RTR risk and technology review
SAB Science Advisory Board
SBAR Small Business Advocacy Review
SCV sterilization chamber vent
SSM startup, shutdown, and malfunction
TOSHI target organ-specific hazard index
tpy tons per year
TRIM.FaTE Total Risk Integrated Methodology, Environmental Fate,
Transport, and Ecological Exposure
UF uncertainty factor
UPL upper prediction limit
[micro]g/m3 microgram per cubic meter
URE unit risk estimate
VCS voluntary consensus standards
WebFIRE Web Factor and Information Retrieval

    Organization of this document. The information in this preamble is
organized as follows:

I. General Information
    A. Executive Summary
    B. Does this action apply to me?
    C. Where can I get a copy of this document and other related
information?
II. Background
    A. What is the statutory authority for this action?
    B. What is this source category and how does the current NESHAP
regulate its HAP emissions?
    C. What data collection activities were conducted to support
this action?
    D. How do we consider risk in our decision-making?
    E. How does the EPA perform the technology review?
    F. How do we estimate risk posed by the source category?
III. Analytical Results and Proposed Decisions
    A. How are we proposing to define affected sources?
    B. What actions are we taking pursuant to CAA sections
112(d)(2), 112(d)(3), and 112(d)(5)?
    C. What are the results of the risk assessment and analyses?
    D. What are our proposed decisions regarding risk acceptability,
ample margin of safety, and adverse environmental effect?
    E. What environmental justice analysis did we conduct?
    F. What are the results and proposed decisions based on our
technology review, and what is the rationale for those decisions?
    G. What other actions are we proposing, and what is the
rationale for those actions?
    H. What compliance dates are we proposing, and what is the
rationale for the proposed compliance dates?
IV. 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?
V. Request for Comments
VI. Incorporation by Reference
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and 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

I. General Information

A. Executive Summary

1. Purpose of the Regulatory Action
    The EPA is proposing to revise the NESHAP for Commercial
Sterilization Facilities by both amending existing standards and
establishing additional standards for this source category, exercising
authority under multiple provisions of section 112 of the Clean Air Act
(CAA). First, the EPA is proposing emission standards under CAA
sections 112(d)(2)-(3) or (d)(5) for a number of currently unregulated
emission sources of EtO. Second, the EPA is proposing risk-based
standards under CAA section 112(f)(2) in order to protect public health
with an ample margin of safety. Third, the EPA is proposing emission
standards under CAA section 112(d)(6) based on the Agency's review of
developments in practices, processes, and control technologies for this
source category.
    This proposed rulemaking reflects the EtO toxicological assessment
that the EPA's Integrated Risk Information System (IRIS) Program
completed in December 2016,\1\ which indicated that EtO is a far more
potent carcinogen than EPA had understood at the time of the previous
RTR for this source category. There are 86 commercial sterilization
facilities in this source category, many of which are located near
residences, schools, and other public facilities. Many of these
facilities are also located in communities with environmental justice
(EJ) concerns. The EPA has determined that approximately 23 of these
facilities pose elevated lifetime cancer risks to the surrounding
communities, some of which are exceptionally high. Throughout this
rulemaking process, we have engaged in

outreach activities to these communities, along with their state and
local governments.
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    \1\ Evaluation of the Inhalation Carcinogenicity of Ethylene
Oxide, December 2016, EPA/635/R-16/350Fc.
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    This important action, if finalized, will reduce EtO emissions and
lifetime cancer risks in multiple communities across the country,
including communities with EJ concerns, and it proposes to update our
standards considering proven and cost-effective control technologies
that are already in use at some facilities in this source category.
Recognizing that EPA now has additional information about the health
risks of EtO that was not available at the time of the last RTR, and in
order to ensure that EPA's standards for this source category
adequately protect public health, we have also conducted a second
residual risk review under CAA section 112(f)(2), as discussed in
section I.A.3 of this preamble.
    In deciding whether to conduct a second residual risk review, we
considered the advantages of EtO reductions and the distribution of
those reductions consistent with the clear goal of CAA section
112(f)(2) to protect the most exposed and susceptible populations,
which in this case include communities with EJ concerns. While
commercial medical device sterilizers provide a critical benefit for
the health of all, sparing Americans who live near commercial
sterilization facilities the disproportionate risk of being
significantly harmed by toxic pollution is also essential.
    Commercial sterilization facilities play a vital role in
maintaining an adequate supply of medical devices. According to the
U.S. Food and Drug Administration (FDA), ``Literature shows that about
fifty percent of all sterile medical devices in the U.S. are sterilized
with ethylene oxide.'' FDA also notes that, ``For many medical devices,
sterilization with ethylene oxide may be the only method that
effectively sterilizes and does not damage the device during the
sterilization process.'' \2\ In developing this proposed rule, EPA has
given careful consideration to the important function these facilities
serve, drawing from extensive engagement with industry stakeholders as
well as Federal agencies with expertise in and responsibility for the
medical supply chain.
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    \2\ https://www.fda.gov/medical-devices/general-hospital-devices-and-supplies/sterilization-medical-devices.
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    In order to ensure EPA's actions with respect to this source
category are based on the most accurate and complete information
possible, we have had many interactions with the EtO commercial
sterilization industry in recent years, including meetings, requests
for information, and outreach specific to this proposed rulemaking.
This has enabled EPA to work from the best possible information when
conducting the analyses to support this proposed rulemaking, including
the current configuration of facilities and the performance of control
technologies that are currently used.
    We have engaged with the U.S. Department of Health and Human
Services, particularly FDA, regarding the potential impacts of this
proposal on commercial sterilization facilities. These discussions have
focused on identifying and addressing any potential concerns regarding
the potential impact on the availability of certain medical devices
that are sterilized with EtO where alternative sterilization methods
are not readily available, including those that are (1) Experiencing or
at risk of experiencing a shortage, (2) in high demand as a result of
the COVID-19 pandemic, (3) used in pediatric services, and/or (4)
sterilized exclusively at a particular facility.
    In this rulemaking, we are proposing a set of standards that we
believe are achievable and reflect techniques and control technologies
that are currently used within the industry. We are also proposing to
provide sufficient time to enable these facilities to continue
sterilizing essential products while installing and testing new control
systems and associated equipment that will afford ample protection for
nearby communities. In terms of potential impacts to the medical device
supply chain, we project that the largest impacts are limited to a
handful of companies, and those that are also involved in sterilizing
the types of medical devices previously mentioned are already in the
planning stage for additional controls.
2. Summary of the Major Provisions of the Regulatory Action in Question
    The EPA is proposing numeric emission limits, operating limits, and
management practices under CAA sections 112(d)(2)-(3), (d)(5), and
(d)(6) for EtO emissions from certain emission sources and is also
proposing standards under CAA section 112(f)(2) for certain emission
sources in order to ensure that the standards provide an ample margin
of safety to protect public health.
    For the following emission sources that are currently
unregulated,\3\ the EPA is proposing to set standards under CAA
sections 112(d)(2)-(3) or (d)(5): sterilization chamber vent (SCV),
aeration room vent (ARV), and chamber exhaust vent (CEV) at facilities
where EtO use is less than 1 tpy, ARV and CEV at facilities where EtO
use is at least 1 tpy but less than 10 tpy, CEV at facilities where EtO
use is at least 10 tpy,\4\ and room air emissions.\5\
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    \3\ In 1992, pursuant to CAA section 112(c)(1), the EPA
published a list of major and area sources for regulation under CAA
section 112, including major and area sources of commercial
sterilizers. 57 FR 31576, 31586 (July 16, 1992). Area sources of
commercial sterilizers were listed for regulation under CAA section
112(c)(3) based on the EPA's finding that it presents a threat of
adverse effects to human health or the environment (by such sources
individually or in the aggregate) warranting regulation under that
section. Id. at 31586.
    \4\ The standards for CEVs were originally promulgated on
December 6, 1994. Following promulgation of the rule, the EPA
suspended certain compliance deadlines and ultimately removed the
standards for CEVs due to safety concerns. In the late 1990s, there
were multiple explosions at EtO commercial sterilization facilities
using oxidizers to control emissions from the CEV. For CEVs, it was
determined that the primary contributing issue leading to the
explosions was that EtO concentrations were above a safe level
(i.e., above the lower explosive limit (LEL)) within the CEV gas
streams. The EPA could not conclude at the time that the CEVs could
be safely controlled, so the standards for CEVs were removed on
November 2, 2001 (66 FR 55583) and have not been re-instated.
    \5\ As discussed in section II.F.1, room air emissions include
emissions resulting from indoor EtO storage, EtO dispensing, vacuum
pump operation, pre-aeration handling of sterilized material, and
post-aeration handling of sterilized material.
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    Next, based on the EPA's assessment of the residual risk after
considering the emission reductions from the current standards in
subpart O, as well as the proposed standards for the currently
unregulated sources, the EPA is proposing more stringent standards to
address risk for the following types of sources under CAA section
112(f)(2):
     SCVs at facilities where EtO use is at least 40 tpy.
     SCVs at facilities where EtO use is at least 10 tpy but
less than 40 tpy.
     SCVs at facilities where EtO use is at least 1 tpy but
less than 10 tpy.
     Group 2 room air emissions \6\ at area source facilities
where EtO use is at least 20 tpy.
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    \6\ As discussed in section III.B.8, Group 2 room air emissions
cover post-aeration handling of sterilized material.
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    Finally, under CAA section 112(d)(6), the EPA is proposing to
revise standards for the following sources that are regulated in the
current 40 CFR part 63, subpart O:
     SCVs at facilities where EtO use is at least 10 tpy.
     SCVs at facilities where EtO use is at least 1 tpy but
less than 10 tpy.
     ARVs at facilities where EtO use is at least 10 tpy.
    To demonstrate compliance with the emission limits, the EPA is
proposing

capture requirements. The EPA is also proposing that facilities either
monitor with an EtO continuous emissions monitoring system (CEMS) or
conduct initial and annual performance tests with continuous parameter
monitoring.
3. EPA Authority
    The EPA notes that it completed a residual risk and technology
review under CAA sections 112(f)(2) and 112(d)(6), respectively, for
this source category in 2006 (71 FR 17712). While CAA section 112(f)(2)
requires only a one-time risk review, which is to be conducted within
eight years of the date the initial standards are promulgated, it does
not limit the EPA's discretion or authority to conduct another risk
review should the EPA consider that such review is warranted. As
discussed in more detail in section III.C of this preamble, as our
understanding of the health effects of EtO developed, the EPA conducted
a second residual risk review under CAA section 112(f)(2) for
commercial sterilization facilities using ethylene oxide in order to
ensure that the standards provide an ample margin of safety to protect
public health.
    As discussed in further detail in section III.C, this second
residual risk review also encompasses certain area sources for which
EPA did not evaluate residual risk in its 2006 rulemaking. Although CAA
section 112(f)(5) states that a risk review is not required for
categories of area sources subject to generally available control
technology (GACT) standards, it does not prohibit such review. In 2006,
the EPA undertook a CAA section 112(f)(2) analysis only for area source
emissions standards that were issued as maximum achievable control
technology (MACT) standards and exercised its discretion under CAA
section 112(f)(5) to not do a CAA section 112(f)(2) analysis for those
emission points for which GACT standards were established (67 FR
17715). However, as the EPA made clear in that prior risk assessment,
``[w]e have the authority to revisit (and revise, if necessary) any
rulemaking if . . . significant improvements to science [suggest that]
the public is exposed to significant increases in risk as compared to
the [2006 risk assessment].'' Id. In light of the updated unit risk
estimate (URE) for EtO, which is approximately 60 times greater than
the value the EPA used in its previous risk assessment, the EPA is now
exercising its discretionary authority to conduct another CAA section
112(f)(2) analysis and to include in this analysis area sources of
commercial sterilizers using EtO for which the EPA has promulgated, or
is now proposing, GACT standards.
    Section 112(d)(6) of the CAA also requires the EPA to review and
revise, as necessary, standards promulgated under CAA section 112 at
least every 8 years, taking into account developments in practices,
processes, and control technologies. The EPA last completed this
required technology review for the Ethylene Oxide Commercial
Sterilization NESHAP (40 CFR 63, subpart O) in 2006. Accordingly, in
this proposed action the EPA is also conducting a CAA section 112(d)(6)
review for this source category.
4. Costs and Benefits
    Table 1 of this preamble summarizes the costs of this proposed
action for 40 CFR part 63, subpart O (Ethylene Oxide Commercial
Sterilization NESHAP).

                               Table 1--Summary of Costs of the Proposed Standards
                                                 [2021 Dollars]
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                                                                                Total annual
                                                   Total capital       Total       operation and   Total annual
                   Requirement                      investment      annualized      maintenance        cost
                                                                   capital costs       costs
----------------------------------------------------------------------------------------------------------------
Permanent total enclosure.......................     $65,798,622      $6,577,542        $430,729      $7,008,271
Additional gas/solid reactors...................     133,890,631      13,384,341      18,991,555      32,375,896
Cycle revalidations.............................               0               0       2,490,000       2,490,000
Monitoring and testing..........................      19,925,046       2,936,022       8,232,973      11,168,996
Recordkeeping and reporting.....................               0               0       8,618,124  \1\ 15,166,922
                                                 ---------------------------------------------------------------
    Total.......................................     219,614,299      22,897,905      38,763,381      68,210,084
----------------------------------------------------------------------------------------------------------------
\1\ This includes $6,548,798 of one-time annual costs for reading the rule, developing record systems, and
  initial title V permitting.

    Consistent with the compliance deadlines proposed in this rule, EPA
has assumed for purposes of this analysis that all capital costs and
one-time annual costs would be incurred within 18 months of the
publication of a final rule. The capital costs for permanent total
enclosure (PTE) and additional gas/solid reactors were annualized to 20
years. We estimate that, if finalized, these proposed amendments would
reduce EtO emissions from this source category by 19 tpy. Table 2 of
this preamble summarizes the cancer risk reductions that would result
from the proposed amendments.

               Table 2--Summary of Cancer Risk Reductions
------------------------------------------------------------------------
                                                        Cancer risks if
                                    Current cancer         proposed
                                         risks          amendments are
                                                           finalized
------------------------------------------------------------------------
Maximum Individual Risk (MIR)     6,000-in-1 million  100-in-1 million.
 \1\.
Number of People with Cancer      18,000............  0.
 Risks >100-in-1 million.
Number of People with Cancer      8.3 million.......  1.26 million. \2\
 Risks >=1-in-1 million.
Estimated Annual Cancer           0.9...............  0.1.
 Incidence (cases per year).
------------------------------------------------------------------------
\1\ The MIR is defined as the cancer risk associated with a lifetime of
  continuous exposure at the highest concentration of HAP where people
  are likely to live.
\2\ As discussed in section III, this value may be lower because the
  proposed Group 1 room air emission standards were not applied or
  accounted for in the risk assessment.

    As indicated in Table 2, EPA projects that the standards in the
proposed rule would significantly reduce incremental lifetime cancer
risks associated with emissions of EtO from this source category.
Currently, EPA estimates that the maximum increase in lifetime cancer
risk associated with any facility in this source category is 6,000-in-1
million, and that approximately 18,000 people are exposed to EtO from
this source category at levels that would correspond to a lifetime
cancer risk of greater than 100-in-1-million (which is EPA's
presumptive upper bound for acceptable health risks). Under the
proposed rule, no individual would be exposed to EtO at levels that
correspond to a lifetime cancer risk of greater than 100-in-1 million,
and the number of people with a potential risk of greater than or equal
to 1-in-1 million would be reduced by approximately 85 percent.
    See section IV of this preamble for further discussion of the costs
and a discussion of the benefits of the proposed standards. See section
III.G of this preamble for discussion of the proposed revisions to
monitoring, recordkeeping, reporting, and testing requirements. See
section III.C and III.D for discussion of the risk assessment results.

B. Does this action apply to me?

    The standards in 40 CFR part 63, subpart O, regulate emissions of
EtO from existing and new commercial sterilization operations. Table 3
of this preamble lists the NESHAP and some examples of regulated
industrial categories that are the subject of this proposal. Table 3 is
not intended to be exhaustive, but rather provides 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 Commercial
Sterilization Facilities source category is any facility engaged in the
use of EtO as a sterilant and fumigant following the production of
various products (e.g., medical equipment and supplies) and in
miscellaneous sterilization and fumigation operations at both major and
area sources. These commercial sterilization facilities use EtO as a
sterilant for heat- or moisture-sensitive materials and as a fumigant
to control microorganisms. Materials may be sterilized at the facility
that produces or uses the product, or by contract sterilizers (i.e.,
firms under contract to sterilize products manufactured by other
companies).

   Table 3--NESHAP and Industrial Categories Affected by This Proposed
                                 Action
------------------------------------------------------------------------
                                                              NAICS code
       Industrial category                  NESHAP               \1\
------------------------------------------------------------------------
Surgical and Medical Instrument    40 CFR part 63, subpart        339112
 Manufacturing.                     O.
Surgical Appliance and Supplies    40 CFR part 63, subpart        339113
 Manufacturing.                     O.
Pharmaceutical Preparation         40 CFR part 63, subpart        325412
 Manufacturing.                     O.
Spice and Extract Manufacturing..  40 CFR part 63, subpart        311942
                                    O.
Dried and Dehydrated Food          40 CFR part 63, subpart        311423
 Manufacturing.                     O.
Packaging and Labeling Services..  40 CFR part 63, subpart        561910
                                    O.
------------------------------------------------------------------------
\1\ North American Industry Classification System.

C. Where can I get a copy of this document and other related
information?

    In addition to being available in the docket, an electronic copy of
this action is available on the internet. Following signature by the
EPA Administrator, the EPA will post a copy of this proposed action at
https://www.epa.gov/ethylene-oxide-emissions-standards-sterilization-facilities. 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 rule edits that would be necessary to
incorporate the changes to 40 CFR part 63, subpart O, proposed in this
action is available in the docket (Docket ID No. EPA-HQ-OAR-2019-0178).
Following signature by the EPA Administrator, the EPA also will post a
copy of this document to https://www.epa.gov/stationary-sources-air-pollution/ethylene-oxide-emissions-standards-sterilization-facilities.

II. Background

A. What is the statutory authority for this action?

    The statutory authority for this action is provided by sections 112
and 301 of the Clean Air Act (CAA), as amended (42 U.S.C. 7401 et
seq.). Section 112 of the CAA establishes a two-stage regulatory
process to develop standards for emissions of hazardous air pollutants
(HAP) from stationary sources. Generally, the first stage involves
establishing technology-based standards and the second stage involves
evaluating those standards that are based on 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 MACT and GACT 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.'' The
discussion that follows identifies the most relevant statutory sections
and briefly explains the contours of the methodology used to implement
these statutory requirements. A more comprehensive discussion appears
in the document titled CAA Section 112 Risk and Technology Reviews:
Statutory Authority and Methodology, in the docket for this rulemaking.
    In the first stage of the CAA section 112 standard setting process,
the EPA promulgates technology-based standards under CAA section 112(d)
for categories of sources identified as emitting one or more of the HAP
listed in CAA section 112(b). Sources of HAP emissions are either major
sources or area sources, and CAA section 112 establishes different
requirements for major source standards and area source standards.
``Major sources'' are those that emit or have the potential to emit 10
tons per year (tpy) or more of a single HAP or 25 tpy or more of any
combination of HAP. All

other sources are ``area sources.'' For major sources, CAA section
112(d)(2) provides that the technology-based NESHAP must reflect the
maximum degree of emission reductions of HAP achievable (after
considering cost, energy requirements, and non-air quality health and
environmental impacts). These standards are commonly referred to as
MACT standards. CAA section 112(d)(3) also establishes a minimum
control level for MACT standards, known as the MACT ``floor.'' In
certain instances, as provided in CAA section 112(h), the EPA may set
work practice standards in lieu of numerical emission standards. The
EPA must also consider control options that are more stringent than the
floor. Standards more stringent than the floor are commonly referred to
as beyond-the-floor standards. For area sources, CAA section 112(d)(5)
allows the EPA to set standards based on GACT in lieu of MACT
standards. For categories of major sources and any area source
categories subject to 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). Section 112(f)
specifically states that EPA ``shall not be required'' to conduct risk
review under this subsection for categories of area sources subject to
GACT standards but does not limit the EPA's authority or discretion
from conducting such review. As discussed in more detail in section
III.C of this preamble, in light of the updated URE regarding EtO, the
EPA is choosing to exercise that discrection.
    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 upheld the EPA's interpretation that CAA section 112(f)(2)
incorporates the approach established in the Benzene NESHAP. See NRDC
v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008).
    The approach incorporated into the CAA and used by the EPA to
evaluate residual risk and to develop standards under CAA section
112(f)(2) is a two-step approach. In the first step, the EPA determines
whether risks are acceptable. This determination ``considers all health
information, including risk estimation uncertainty, and includes a
presumptive limit on maximum individual lifetime [cancer] risk (MIR)
\7\ of approximately 1-in-10 thousand.'' (54 FR 38045) If risks are
unacceptable, the EPA must determine the emissions standards necessary
to reduce risk to an acceptable level without considering costs. In the
second step of the approach, the EPA considers whether the emissions
standards provide an ample margin of safety to protect public health
``in consideration of all health information, including the number of
persons at risk levels higher than approximately 1-in-1 million, as
well as other relevant factors, including costs and economic impacts,
technological feasibility, and other factors relevant to each
particular decision.'' Id. The EPA must promulgate emission standards
necessary to provide an ample margin of safety to protect public health
or determine that the standards being reviewed provide an ample margin
of safety without any revisions. After conducting the ample margin of
safety analysis, we consider whether a more stringent standard is
necessary to prevent an adverse environmental effect, taking into
consideration costs, energy, safety, and other relevant factors.
---------------------------------------------------------------------------

    \7\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk if an individual were exposed to the maximum
level of a pollutant for a lifetime.
---------------------------------------------------------------------------

    CAA section 112(d)(6) separately requires the EPA to review
standards promulgated under CAA section 112 and revise them ``as
necessary (taking into account developments in practices, processes,
and control technologies)'' no less often than every 8 years. In
conducting this review, which we call the ``technology review,'' the
EPA is not required to recalculate the MACT floors that were
established in earlier rulemakings. Natural Resources Defense Council
(NRDC) v. EPA, 529 F.3d 1077, 1084 (D.C. Cir. 2008). Association of
Battery Recyclers, Inc. v. EPA, 716 F.3d 667 (D.C. Cir. 2013). The EPA
may consider cost in deciding whether to revise the standards pursuant
to CAA section 112(d)(6). The EPA is also required to address
regulatory gaps, such as missing standards for listed air toxics known
to be emitted from the source category, and any new MACT standards must
be established under CAA sections 112(d)(2) and (3), or, in specific
circumstances, CAA sections 112(d)(4) or (h). Louisiana Environmental
Action Network (LEAN) v. EPA, 955 F.3d 1088 (D.C. Cir. 2020).

B. What is this source category and how does the current NESHAP
regulate its HAP emissions?

    On July 16, 1992, pursuant to CAA section 112(c)(1), the EPA listed
certain major and area sources of HAP for regulation, including both
major and area sources of commercial sterilization facilities. 57 FR
31576, 31592. As explained in that document, area sources of commercial
sterilization facilities were listed pursuant to CAA section 112(c)(3)
based on a finding of a threat of adverse effects from commercial
sterilizers using EtO. Id at 31588. In 1994, the EPA promulgated the
Ethylene Oxide Emissions Standards for Sterilization Facilities NESHAP,
40 CFR part 63, subpart O (referred to in this proposed rulemaking as
the EtO Commercial Sterilization NESHAP) (59 FR 62589), which is
codified at 40 CFR part 63, subpart O. The EtO Commercial Sterilization
NESHAP regulates EtO emitted from commercial sterilization facilities.
The current NESHAP regulates point sources of emissions, specifically
SCVs and ARVs, at facilities that use at least 1 ton of EtO in
sterilization or fumigation operations in each 12-month period. In a
Federal Register document published on July 16, 1992 (57 FR 31576), the
EPA listed for regulation both major and area sources of EtO commercial
sterilization and fumigation operations pursuant to CAA section
112(c)(1) and 112(c)(3) (based on a finding of a threat of adverse
effects), respectively.
    EtO commercial sterilization covers the sterilizer process that
uses EtO to sterilize or fumigate materials (e.g., medical equipment
and supplies, spices, and other miscellaneous products and items). The
original

rulemaking addressed EtO emissions originating from three emission
points: SCV, ARV, and CEV. The SCV evacuates EtO from the sterilization
chamber following sterilization, fumigation, and any subsequent gas
washes before the chamber door is opened. The ARV evacuates EtO-laden
air from the aeration room or chamber that is used to facilitate off-
gassing of the sterile product and packaging. The CEV evacuates EtO-
laden air from the sterilization chamber after the chamber door is
opened for product unloading following the completion of sterilization
and associated gas washes. Other sources of emissions within this
source category are room air emissions from equipment used to charge
EtO into sterilization chambers, as well as residual EtO desorbing from
sterilized products within the facility, but the EtO Commercial
Sterilization NESHAP does not include standards for these emissions.
    In the chamber EtO sterilization process, products and items to be
sterilized are placed in a chamber and exposed to EtO gas at a
predetermined concentration, temperature, humidity, and pressure for a
period of time known as the dwell period. Following the dwell period,
the EtO gas is evacuated from the chamber, and the sterilized materials
are then aerated to remove residual EtO from the product. After the
aeration step, sterilized materials are typically moved to a shipping/
warehouse area for storage until they are ready to be distributed to
the customer. Sterilizer process equipment and emission control
configurations vary across facilities. The most common sterilizer
process equipment configuration includes a separate sterilizer chamber,
separate aeration room, and chamber exhaust on the sterilizer chamber
(also referred to as a back-vent). Another common configuration
includes a combination sterilizer where the sterilization and aeration
steps of the process occur within the same chamber, though this
configuration may or may not have a chamber exhaust.
    Another EtO sterilization process is single-item sterilization
where small individual items are sterilized in sealed pouches. EtO gas
is introduced into the sealed pouch, either by injection or use of an
EtO ampule, and the sealed pouch is then placed in a chamber where the
sterilization step and aeration step occur.
    Multiple control technologies were available for EtO commercial
sterilization at the time the EtO Commercial Sterilization NESHAP was
promulgated (December 1994). Control technologies for SCVs included:
acid-water scrubbers; thermal oxidizer/flares; catalytic oxidizers;
condensers/reclaimers; and a combination packed bed scrubber and gas-
solid reactor (dry bed reactor) systems. Control technologies for CEVs
included: packed bed scrubber; catalytic oxidizer; gas-solid reactor;
and a combination packed bed scrubber and gas-solid reactor. Control
technologies for ARVs included: acid-water scrubber, catalytic
oxidizer, and gas-solid reactor.
    In 2006, the EPA finalized a residual risk review and a technology
review under CAA section 112(f)(2) and CAA section 112(d)(6),
respectively (71 FR 17712, April 7, 2006). No changes were made to the
EtO Commercial Sterilization NESHAP in that action.
    The emission standards that currently apply to sterilization
facilities covered by 40 CFR part 63, subpart O, are shown in Table 4:

                            Table 4--Current EtO Standards for Commercial Sterilizers
----------------------------------------------------------------------------------------------------------------
 Existing and new sources subcategory
 (in any consecutive 12-month period)   Sterilization chamber      Aeration room vent      Chamber exhaust vent
                 \1\                          vent (SCV)                 (ARV)                  (CEV) \2\
----------------------------------------------------------------------------------------------------------------
Sources using 10 tons or more of EtO.  99 percent emission      1 part per million       No control.
                                        reduction (see 40 CFR    (ppm) maximum outlet
                                        63.362(c)).              concentration or 99
                                                                 percent emission
                                                                 reduction (see 40 CFR
                                                                 63.362(d)).
Sources using 1 ton or more of EtO     99 percent emission      No control.............  No control.
 but less than 10 tons of EtO.          reduction (see 40 CFR
                                        63.362(c)).
Sources using less than 1 ton of EtO.  No control required;     No control required;     No control required;
                                        minimal recordkeeping    minimal recordkeeping    minimal recordkeeping
                                        requirements apply       requirements apply       requirements apply
                                        (see 40 CFR              (see 40 CFR              (see 40 CFR
                                        63.367(c))).             63.367(c))).             63.367(c))).
----------------------------------------------------------------------------------------------------------------
\1\ Determined on a rolling 12-month basis.
\2\ The CEV emission source was included in the original standard but was later eliminated from the 40 CFR part
  63, subpart O, regulation in 2001.

    We note that hospital sterilizers are regulated under a different
NESHAP (40 CFR part 63, subpart WWWWW), which is not addressed in this
rulemaking.\8\ We are aware of the potential risk posed by EtO
emissions from this source category and will address hospital
sterilizers in a future rulemaking.
---------------------------------------------------------------------------

    \8\ Hospitals are defined at 40 CFR 63.10448 to mean facilities
that provide medical care and treatment for patients who are acutely
ill or chronically ill on an inpatient basis under supervision of
licensed physicians and under nursing care offered 24 hours per day.
Hospitals include diagnostic and major surgery facilities but
exclude doctor's offices, clinics, or other facilities whose primary
purpose is to provide medical services to humans or animals on an
outpatient basis.
---------------------------------------------------------------------------

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

    The EPA used several sources to develop the list of existing
commercial sterilization facilities. We began with the facility list
used during the previous RTR and supplemented that with facilities
identified in the 2017 National Emissions Inventory (NEI), as well as
facilities identified using the Office of Enforcement and Compliance
Assurance's Enforcement and Compliance History Online tool (https://echo.epa.gov). We then reviewed available Federal, state, and local
data to determine whether any of these facilities had closed or ceased
using EtO for sterilization purposes. We also asked our EPA regional
offices to identify any commercial sterilization facilities that we
missed, and when we conducted the December 2019 CAA section 114
questionnaire and September 2021 CAA section 114 Information Collection
Request (ICR) (discussed below), we asked the parent companies to
identify

any commercial sterilization facilities they owned that we did not
identify. This review and analysis produced the final facility list of
86 commercial sterilization facilities. A complete list of known
commercial sterilization facilities is available in the document titled
Residual Risk Assessment for the Commercial Sterilization Facilities
Source Category in Support of the 2022 Risk and Technology Review
Proposed Rule, which is available in the docket for this rulemaking.
    For this RTR, the EPA investigated developments in practices,
processes, and control technologies through communications and direct
discussions with EPA regional offices, state and local agencies, Small
Business Environmental Assistance Program personnel, industry
representatives, and trade association representatives. Details of
these conversations are included in the memorandum titled Technical
Support Document for Proposed Rule--Industry Profile, Review of
Unregulated Emissions, CAA Section 112(d)(6) Technology Review, and CAA
Section 112(f) Risk Assessment for the Ethylene Oxide Emissions
Standards for Sterilization Facilities NESHAP (Technical Support
Document), available in the docket for this action (Docket ID No. EPA-
HQ-OAR-2019-0178). The EPA conducted literature reviews, operating
permit reviews, internet web searches, and site visits; published an
Advanced Notice of Proposed Rulemaking (84 FR 67889, December 12,
2019); reviewed public comments received; sent requests for information
to industry under the authority of CAA section 114; and searched the
EPA's Technology Transfer Network Clean Air Technology Center--RACT/
BACT/LAER Clearinghouse (RBLC) database.
    The RBLC provides several options for searching the permit database
online to locate applicable control technologies. We queried the RBLC
database for specific commercial sterilization Process Type 99.004
(Commercial Sterilization Facilities), as well as a related source
category, Process Type 99.008 (Hospital Sterilization Facilities). In
querying results dating back to January 1, 2006 (the date of the
residual risk and initial technology review), no results were returned
when searching for Process Type 99.004 and no results were returned for
Process Type 99.008. None of these searches returned relevant
information on developments in practices, processes, or control
technologies used in EtO commercial sterilization facilities. Full
details of the RBLC database search in support of this technology
review are included in the Technical Support Document, available in the
docket for this action (Docket ID No. EPA-HQ-OAR-2019-0178). Prior to
this proposed rulemaking, the EPA engaged in outreach activities to
communities we expect to be impacted most by the rulemaking.\9\ Any
information related to these outreach activities that we receive prior
to the conclusion of the comment period will be considered as part of
the final rulemaking, along with direct comments on this proposed
rulemaking. Any updated emissions information received during the EPA's
ongoing public outreach activities that may change the projected
impacts for these populations will be considered as part of the final
rulemaking, as well as direct comments received on this proposed
rulemaking.
---------------------------------------------------------------------------

    \9\ https://www.epa.gov/newsreleases/epa-launches-community-engagement-efforts-new-ethylene-oxide-risk-information.
---------------------------------------------------------------------------

    The EPA issued two requests to gather information about process
equipment, control technologies, and emissions from facilities in the
source category. In December 2019, the EPA issued a CAA section 114
request to a small number of entities that were operating 42 facilities
at the time (now 39) to gather information, including information about
types of process equipment, sterilization cycles, control technologies,
EtO usage and storage, room areas, movements of sterilized products,
and EtO concentration data. We also included requests for facility
documents (e.g., process flow diagrams, air permits, air permit
applications, process and instrumentation diagrams), performance test
reports, parametric monitoring data, startup shutdown and malfunction
plans, and EtO residual studies in products. These entities were
selected because, collectively, they comprised a significant portion of
the sterilization industry. All respondents completed the questionnaire
and submitted responses to the EPA in February 2020. Additionally, in
September 2021, the EPA issued an information collection request (ICR),
pursuant to CAA section 114, to gather information from all facilities
in the EtO commercial sterilization category. Additional questions in
the September 2021 ICR included information on non-EtO sterilization
techniques and stand-alone, non-co-located warehouses or distribution
centers.\10\ The facilities not included in the December 2019 request
were asked to respond to the full set of questions, and those
facilities were only asked to provide responses to the additional
questions. Responses to the ICR were due in November 2021.
---------------------------------------------------------------------------

    \10\ The EPA is not proposing requirements for these facilities
as part of this action. However, the EPA plans to evaluate the data
received and determine what requirements these facilities should be
subject to, if any.
---------------------------------------------------------------------------

    The Agency made the data results from the two questionnaires
available as part of a Freedom of Information Act request.\11\ The EPA
used the collected information to assist in filling data gaps,
establish the baseline emissions and control levels for purposes of the
regulatory reviews, identify the most effective control measures, and
estimate the environmental impacts associated with the regulatory
options considered and reflected in this proposed action. The responses
to the December 2019 and September 2021 questionnaires are listed in
the memorandum titled Documentation of Database Containing Information
from Responses to the December 2019 Questionnaire and the September
2021 Section 114 for the Ethylene Oxide Commercial Sterilization NESHAP
Review, which is available in the docket for this rulemaking. The
information not claimed as CBI by respondents and received in time to
be included in this proposal is available in the database titled Data
Received from Information Collection Requests for the Commercial
Sterilization Facilities Source Category, which is available in the
docket for this rulemaking.
---------------------------------------------------------------------------

    \11\ Results from the December 2019 questionnaire are available
at https://foiaonline.gov/foiaonline/action/public/submissionDetails?trackingNumber=EPA-2020-004133&type=Request, and
results from the September 2021 ICR are available at https://foiaonline.gov/foiaonline/action/public/submissionDetails?trackingNumber=EPA-2022-003690&type=Request.
---------------------------------------------------------------------------

D. 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 the
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 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.\12\ The assessment also provides estimates of the distribution
of cancer risk within the exposed populations, cancer incidence, and an
evaluation of the potential for an adverse environmental effect. The
scope of the EPA's risk analysis is consistent with the explanation in
the EPA's response to comments on our policy under the Benzene NESHAP.
The policy chosen by the Administrator permits consideration of
multiple measures of health risk. Not only can the MIR figure be
considered, but also incidence, the presence of non-cancer health
effects, and the uncertainties of the risk estimates. In this way, the
effect on the most exposed individuals can be reviewed as well as the
impact on the general public. These factors can then be weighed in each
individual case. This approach complies with the Vinyl Chloride mandate
that the Administrator ascertain an acceptable level of risk to the
public by employing his expertise to assess available data. It also
complies with the congressional intent behind the CAA, which did not
exclude the use of any particular measure of public health risk from
the EPA's consideration with respect to CAA section 112 regulations,
and thereby implicitly permits consideration of any and all measures of
health risk which the Administrator, in his judgment, believes are
appropriate to determining what will ``protect the public health'' (54
FR 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 may be determined to
be acceptable, and risks with an MIR below that level may be determined
to be unacceptable, depending on all of the available health
information. Similarly, with regard to the ample margin of safety
analysis, the EPA stated in the Benzene NESHAP that: ``EPA believes the
relative weight of the many factors that can be considered in selecting
an ample margin of safety can only be determined for each specific
source category. This occurs mainly because technological and economic
factors (along with the health-related factors) vary from source
category to source category.'' Id. at 38061. We also consider the
uncertainties associated with the various risk analyses, as discussed
earlier in this preamble, in our determinations of acceptability and
ample margin of safety.
---------------------------------------------------------------------------

    \12\ The MIR is defined as the cancer risk associated with a
lifetime of continuous 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 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.'' \13\
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    \13\ Recommendations of the SAB Risk and Technology Review
Methods Panel are provided in their report, which is available at:
https://www.epa.gov/sites/default/files/2021-02/documents/epa-sab-10-007-unsigned.pdf.
---------------------------------------------------------------------------

    In response to the SAB recommendations, the EPA incorporates
cumulative risk analyses into its RTR risk assessments. The Agency (1)
Conducts facility-wide assessments, which include source category
emission points, as well as other emission points within the
facilities; (2) combines exposures from multiple sources in the same
category that could affect the same individuals; and (3) for some
persistent and bioaccumulative pollutants, analyzes the ingestion route
of exposure. In addition, the RTR risk assessments consider aggregate
cancer risk from all carcinogens and aggregated noncancer HQs for all
noncarcinogens affecting the same target organ or target organ system.
    Although we are interested in placing source category and facility-
wide HAP risk in the context of total HAP risk from all sources
combined in the vicinity of each source, we are concerned about the
uncertainties of doing so. Estimates of total HAP risk from emission
sources other than those that we have studied in depth during this RTR
review would have significantly greater associated uncertainties than
the source category or facility-wide estimates. Such aggregate or
cumulative assessments would compound those uncertainties, making the
assessments too unreliable.

E. How does the EPA perform the technology review?

    Our technology review primarily focuses on the identification and
evaluation of developments in practices, processes, and control
technologies that have occurred since the MACT and GACT standards were
promulgated. Where we identify such developments, we analyze their
technical feasibility, estimated costs, energy implications, and non-
air environmental impacts. We also consider the emission reductions

associated with applying each development. This analysis informs our
decision of whether it is ``necessary'' to revise the emissions
standards. In addition, we consider the appropriateness of applying
controls to new sources versus retrofitting existing sources. For this
exercise, we consider any of the following to be a ``development'':
     Any add-on control technology or other equipment that was
not identified and considered during development of the original MACT
and GACT standards;
     Any improvements in add-on control technology or other
equipment (that were identified and considered during development of
the original MACT and GACT standards) that could result in additional
emissions reduction;
     Any work practice or operational procedure that was not
identified or considered during development of the original MACT and
GACT standards;
     Any process change or pollution prevention alternative
that could be broadly applied to the industry and that was not
identified or considered during development of the original MACT and
GACT standards; and
     Any significant changes in the cost (including cost
effectiveness) of applying controls (including controls the EPA
considered during the development of the original MACT and GACT
standards).
    In addition to reviewing the practices, processes, and control
technologies that were considered at the time we originally developed
or last reviewed the NESHAP, we review a variety of data sources in our
investigation of potential practices, processes, or controls to
consider. We also review the NESHAP and the available data to determine
if there are any unregulated emissions of HAP within the source
category and evaluate 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.

F. How do we estimate risk posed by the source category?

    In this section, we provide a complete description of the types of
analyses that we generally perform during the risk assessment process.
In some cases, we do not perform a specific analysis because it is not
relevant. For example, in the absence of emissions of HAP known to be
persistent and bioaccumulative in the environment (PB-HAP), we would
not perform a multipathway exposure assessment. Where we do not perform
an analysis, we state that we do not and provide the reason. While we
present all of our risk assessment methods, we only present risk
assessment results for the analyses actually conducted (see section
IV.B of this preamble).
    The EPA conducts a risk assessment that provides estimates of the
MIR for cancer posed by the HAP emissions from each source in the
source category, the hazard index 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
eight sections that follow this paragraph describe how we estimated
emissions and conducted the risk assessment. The docket for this
rulemaking contains the following document that provides more
information on the risk assessment inputs and models: Residual Risk
Assessment for the Commercial Sterilization Facilities Source Category
in Support of the 2022 Risk and Technology Review Proposed Rule. The
methods used to assess risk (as described in the eight 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, and described in the SAB
review report issued in 2010. They are also consistent with the key
recommendations contained in that report.
1. How did we estimate actual emissions and identify the emissions
release characteristics?
    Commercial sterilizers using EtO were listed for regulation in 1992
as described in section II.B of this preamble. The standards in the
current NESHAP subpart O are based on facilities' EtO usage amount.
Specifically, 40 CFR part 63, subpart O, contains SCV and ARV standards
for facilities where EtO use is at least 10 tpy and a separate SCV
standard for facilities where EtO use is at least 1 tpy but less than
10 tpy. Currently there are 86 facilities in the source category. Based
on actual EtO usage data, 47 facilities are sterilization sources where
EtO use is at least 10 tpy, 20 facilities are sterilization sources
where EtO use is at least 1 tpy but less than 10 tpy, and 19 facilities
are sterilization sources where EtO use is less than 1 tpy. The EPA
also identified, based on permits and responses to the December 2019
questionnaire and September 2021 ICR, 11 research facilities, as
defined under CAA 112(c)(7), which are not part of the source category.
    For these facilities, the emissions information that was derived
from the 2014 NEI was, in general, found to be insufficient to set
appropriate standards. Most notably, for most facilities, room air
emissions were not accounted for in the NEI. In addition, 28 facilities
had no Emissions Inventory System ID and, therefore, no emissions data
to pull from the NEI. Therefore, the EPA generated new EtO emissions
data as described below. The complete Commercial Sterilization facility
list is available in Appendix 1 of the document titled Residual Risk
Assessment for the Commercial Sterilization Facilities Source Category
in Support of the 2022 Risk and Technology Review Proposed Rule, which
is available in the docket for this rulemaking.
    In general, emissions were estimated using a mass balance approach,
beginning with annual EtO use (i.e., the previous consecutive 12-month
period of EtO use). Where available, the latest annual EtO usage for
each facility was used. Where we lacked data, we assumed that the
facility was using 50 percent of the maximum usage listed in state and
local permits because this is the industry average. Then, EtO use was
apportioned to the different emission process groups using emission
factors. Emission sources from Commercial Sterilization Facilities
include SCVs, ARVs, CEVs, and room air emission sources (descriptions
of SCV, ARV, and CEV emission sources are provided in section II.B).
The room air emission sources are:
     Indoor EtO storage: EtO drums and cylinders are often
stored in storage areas inside the facility, and emissions may occur
from improperly sealed/leaking drums and cylinders into the storage
room area.
     EtO dispensing: This includes connecting pressurized lines
from the storage drum or cylinder valve to the sterilization chamber to
charge EtO to the process cycle. EtO is often moved from the drum to
the sterilizer chamber using nitrogen. EtO drums or cylinders may sit
in a separate room for dispensing, or the drum or cylinder may be
placed near the sterilization chamber. In either scenario, emissions
may occur from connectors and valves on the pressurized lines that
connect the storage drum or cylinder to the chamber.
     Vacuum pump operation: These are often used to evacuate
sterilization chambers before the chamber door is opened. The vacuum
pump feeds into a separation tank where the recirculating

pump fluid is returned to the pump and the EtO and other gases
(nitrogen and air) are vented to a control system or to the atmosphere.
Emissions from leaks may occur from the vacuum pump during operation.
     Pre-aeration handling of sterilized material (PrAHSM):
Following the sterilization cycle, emissions may occur from the
sterilized materials when moving the material from the sterilization
chamber to the aeration room or when holding the material within the
facility areas. PrAHSM includes activities such as removing the
sterilized materials from the sterilization chamber, transferring
sterilized materials from the sterilization chamber to the aeration
room, placing or holding of sterilized materials outside of process
equipment for short periods of time, and, at some facilities, during
aeration transfers where there are primary and secondary aeration
chambers. Emissions may occur from off-gassing of residual EtO that is
contained in the materials following exposure to EtO.
     Post-aeration handling of sterilized material (PoAHSM):
Following the aeration step, emissions may continue to occur from the
sterilized and aerated materials when moving the material and holding
the material within the facility areas. PoAHSM includes activities such
as removing the sterilized/aerated materials from the aeration room,
transferring the sterilized/aerated materials from the aeration room to
holding areas, placing or holding of the sterilized/aerated materials
in a quarantine area while awaiting confirmation of sterility, and
holding of sterilized/aerated materials in shipping and warehouse areas
at the facility. Emissions may occur from continued off-gassing of
residual EtO that remains in the materials even after the aeration
step.
     Non-oxidizer air pollution control device (APCD) area:
Non-oxidizer APCDs, such as acid-water scrubbers and gas-solid
reactors, are typically housed within the sterilization building.
Through the responses to the section 114 requests, we learned that
elevated EtO concentrations were observed in the rooms where these
APCDs were located. This is likely due to equipment leaks and/or
emissions not being fully captured or routed under negative pressure.
    In the original rulemaking, we assumed there were no room air
emissions. Using the emission source apportionment data available at
that time, we assumed that 95 percent of the EtO usage was emitted
through the SCV, 2 percent was emitted through the CEV, and 3 percent
was emitted through the ARV.\14\ The EPA now understands that in
addition to emissions from point sources such as SCVs, CEVs, and ARVs,
room air emissions also occur at commercial sterilization facilities.
In recent years, the industry has assumed a range of room air
emissions, anywhere from 0.01 to 1.5 percent of total usage. However,
there is little to no documentation for these assumptions or what
emission sources were included. In 2019, the EPA examined ambient air
monitoring data collected around a commercial sterilization facility in
Willowbrook, Illinois, and derived a room air emissions factor that
equates to approximately 0.6 percent of total EtO usage.\15\
---------------------------------------------------------------------------

    \14\ U.S. EPA. Ethylene Oxide Emissions from Commercial
Sterilization/Fumigation Operations, Background Information for
Proposed Standards. EPA Publication No. EPA-453/D-93-016. October
1992.
    \15\ https://www.epa.gov/sites/default/files/2019-08/documents/appendix_1_to_the_sterigenics_willowbrook_risk_assessment.pdf, Table
1.
---------------------------------------------------------------------------

    Under this rule review, the EPA reassessed the emission
apportionment across the emission sources at commercial sterilization
facilities. The EPA analyzed the responses from the December 2019
questionnaire and September 2021 ICR to update the fraction of EtO that
is apportioned to SCV, ARV, CEV, and room air emissions.
     The data for the ARV analyses included flow rate (or room
volume combined with air changeover rate), EtO concentration, and
average aeration room temperature to estimate ARV emissions.
     The data for the CEV analyses included flow rate, EtO
concentration, and the sterilizer chamber temperature to estimate CEV
emissions.
     The data for the room area analyses included the flow
rate, EtO concentration, temperature information, and annual operating
hours to estimate the EtO emission for each emission source.
    The estimated EtO emissions were compared to the annual actual EtO
usage to develop the fraction of EtO use that goes to each emission
source before controls. Under the recent emission source apportionment
analysis, the EPA determined 4 percent of EtO used goes to the ARV, 1
percent goes to the CEV, 0.1 percent goes to EtO dispensing, 0.1
percent goes to vacuum pump operations, 0.2 percent goes to pre-
aeration handling of sterilized material, 0.2 percent goes to post-
aeration handling of sterilized material, and 0.04 percent goes to non-
oxidizer APCD operation. We estimate that another 1 percent of EtO used
leaves the facility still in the product. The portion of EtO usage that
is emitted from SCV is the balance of the EtO usage (i.e., 93.36
percent). However, the value varies depending on the equipment
configuration (traditional sterilizer chamber, combination chamber,
etc.) and may range from 93.36 to 98.32 percent. The EPA was not able
to quantify what percentage of EtO use is emitted from indoor EtO
storage, which could result in a slight underestimation of the risk.
Based on our review of the data, we do not believe that emissions from
indoor EtO storage are significant. See memorandum Development of
Ethylene Oxide Usage Fractions for Ethylene Oxide Commercial
Sterilization--Proposal, which is available in the docket for this
rulemaking.
    Finally, the performance of the control systems used to reduce
emissions, if available, was considered. Data from the CAA section 114
requests, as well as state and local permitting data, were also used to
develop the other parameters needed to perform the risk modeling
analysis, including the emissions release characteristics, such as
stack heights, stack diameters, flow rates, temperatures, and emission
release point locations.
    The RTR emissions dataset developed using the data and estimates
described immediately above was refined following an extensive quality
assurance check of source locations, emission release point parameters,
and annual emission estimates. The EPA reviewed the locations of
emission release points at each facility and revised each record as
needed to ensure that all release points were located correctly. If an
emission release point was located outside of the facility fenceline or
on an obviously incorrect location within the fenceline (e.g., parking
lot, lake, etc.) then the emission release point was relocated to
either the true location of the equipment, if known, or the approximate
center of the facility.
    The emission release point parameters for stacks in the modeling
input files include stack height, exit gas temperature, stack diameter,
exit gas velocity, and exit gas flow rate. If emission release point
parameters were outside of typical quality assurance range checks or
missing, then an investigation was done to determine whether these
values were accurate. If this information could not be found, then
surrogate values were assigned based on similar values observed for the
control device and process group. In some cases, missing emission
release point parameters were calculated using

other parameters within the modeling input file. For example, missing
exit gas flow rates were calculated using the reported diameter and
velocity.
    Additionally, the EPA compared the emission release point type
(i.e., fugitive, stack) to the emission unit and process descriptions
for the modeling file records. In cases where information was
conflicting (i.e., equipment leaks being modeled as a vertical stack,
or process vent emissions being modeled as a fugitive area), we updated
the emission release point type to the appropriate category and
supplemented the appropriate emission release parameters using either
permitted values, when available, or default values.
2. 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). The HEM performs
three primary risk assessment activities: (1) Conducting dispersion
modeling to estimate the concentrations of HAP in ambient air, (2)
estimating long-term and short-term inhalation exposures to individuals
residing within 50 kilometers (km) of the modeled sources, and (3)
estimating individual and population-level inhalation risk using the
exposure estimates and quantitative dose-response information.
a. Dispersion Modeling
    AERMOD, the air dispersion model used by the HEM model, is one of
the EPA's preferred models for assessing air pollutant concentrations
from industrial facilities. To perform the dispersion modeling and to
develop the preliminary risk estimates, HEM draws on three data
libraries. The first is a library of meteorological data, which is used
for dispersion calculations. This library includes hourly surface and
upper air observations for years ranging from 2016-2019 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 internal point locations and populations provides the
basis of human exposure calculations (U.S. Census, 2010). In addition,
for each census block, the census library includes the elevation and
controlling hill height, which are also used in dispersion
calculations. A third library of pollutant-specific dose-response
values is used to estimate health risk. These are discussed below.
b. Risk From Chronic Exposure to HAP
    In developing the risk assessment for chronic exposures, we use the
estimated annual average ambient air concentrations of each HAP emitted
by each source in the source category. The HAP air concentrations at
each nearby census block centroid located within 50 km of the facility
are a surrogate for the chronic inhalation exposure concentration for
all the people who reside in that census block. A distance of 50 km is
consistent with both the analysis supporting the 1989 Benzene NESHAP
(54 FR 38044) and the limitations of Gaussian dispersion models,
including AERMOD.
    For each facility, we calculate the MIR as the cancer risk
associated with a continuous lifetime (24 hours per day, 7 days per
week, 52 weeks per year, 70 years) exposure to the maximum
concentration at the centroid of each inhabited census block. We
calculate individual cancer risk by multiplying the estimated lifetime
exposure to the ambient concentration of each HAP (in [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 microgram of the pollutant per cubic meter 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 CalEPA
UREs, where available. In cases where new, scientifically credible
dose-response values have been developed in a manner consistent with
EPA guidelines and have undergone a peer review process similar to that
used by the EPA, we may use such dose-response values in place of, or
in addition to, other values, if appropriate. The pollutant-specific
dose-response values used to estimate health risk are available at
https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
    To estimate individual lifetime cancer risks associated with
exposure to HAP emissions from each facility in the source category, we
sum the risks for each of the carcinogenic HAP emitted by the modeled
facility. We estimate cancer risk at every census block within 50 km of
every facility in the source category. The MIR is the highest
individual lifetime cancer risk estimated for any of those census
blocks. In addition to calculating the MIR, we estimate the
distribution of individual cancer risks for the source category by
summing the number of individuals within 50 km of the sources whose
estimated risk falls within a specified risk range. We also estimate
annual cancer incidence by multiplying the estimated lifetime cancer
risk at each census block by the number of people residing in that
block, summing results for all of the census blocks, and then dividing
this result by a 70-year lifetime.
    To assess the risk of noncancer health effects from chronic
exposure to HAP, we calculate either an HQ or a target organ-specific
hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is
emitted. Where more than one noncancer HAP is emitted, we sum the HQ
for each of the HAP that affects a common target organ or target organ
system to obtain a TOSHI. The HQ is the estimated exposure divided by
the chronic noncancer dose-response value, which is a value selected
from one of several sources. The preferred chronic noncancer dose-
response value is the EPA RfC, defined as ``an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure to the human population (including sensitive
subgroups) that is likely to be without an appreciable risk of
deleterious effects during a lifetime'' (https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary). In cases where an RfC
from the EPA's IRIS is not available or where the EPA determines that
using a value other than the RfC is appropriate, the chronic noncancer
dose-response value can be a value from the following prioritized
sources, which define their dose-response values similarly to the EPA:
(1) the Agency for Toxic Substances and Disease Registry (ATSDR)
Minimal Risk Level (https://www.atsdr.cdc.gov/minimalrisklevels/index.html); (2) the CalEPA Chronic Reference Exposure Level (REL)
(https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0); or (3) as noted
above, a scientifically credible dose-response value that has been
developed in a manner consistent with the EPA guidelines and has
undergone a peer review process similar to that used by the EPA. The
pollutant-specific dose-response values used to estimate health risks
are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.

c. Risk From Acute Exposure to HAP That May Cause Health Effects Other
Than Cancer
    For each HAP for which appropriate acute inhalation dose-response
values are available, the EPA also assesses the potential health risks
due to acute exposure. For these assessments, the EPA makes
conservative assumptions about emission rates, meteorology, and
exposure location. As part of our efforts to continually improve our
methodologies to evaluate the risks that HAP emitted from categories of
industrial sources pose to human health and the environment, we revised
our treatment of meteorological data to use reasonable worst-case air
dispersion conditions in our acute risk screening assessments instead
of worst-case air dispersion conditions. This revised treatment of
meteorological data and the supporting rationale are described in more
detail in Residual Risk Assessment for Commercial Sterilization
Facilities Source Category in Support of the 2022 Technology Review
Proposed Rule and in Appendix 5 of the report: Technical Support
Document for Acute Risk Screening Assessment. This revised approach has
been used in this proposed rule and in all other RTR rulemakings
proposed on or after June 3, 2019.
    To assess the potential acute risk to the maximally exposed
individual, we use the peak hourly emission rate for each emission
point, 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.
    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 reference exposure level (REL) is defined as ``the
concentration level at or below which no adverse health effects are
anticipated for a specified exposure duration.'' 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.
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 or milligrams per cubic meter)
of a substance above which it is predicted that the general population,
including susceptible individuals, could experience notable discomfort,
irritation, or certain asymptomatic nonsensory effects. However, the
effects are not disabling and are transient and reversible upon
cessation of exposure.'' The document also notes that ``Airborne
concentrations below AEGL-1 represent exposure levels that can produce
mild and progressively increasing but transient and nondisabling odor,
taste, and sensory irritation or certain asymptomatic, nonsensory
effects.'' Id. AEGL-2 are defined as ``the airborne concentration
(expressed as parts per million or milligrams per cubic meter) of a
substance above which it is predicted that the general population,
including susceptible individuals, could experience irreversible or
other serious, long-lasting adverse health effects or an impaired
ability to escape.'' Id.
    ERPGs are developed 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 one hour without experiencing or
developing irreversible or other serious health effects or symptoms
which could impair an individual's ability to take protective action.
    An acute REL for 1-hour exposure durations is typically lower than
its corresponding AEGL-1 and ERPG-1. Even though their definitions are
slightly different, AEGL-1s are often the same as the corresponding
ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from
our acute inhalation screening risk assessment typically result when we
use the acute REL for a HAP. In cases where the maximum acute HQ
exceeds 1, we also report the HQ based on the next highest acute dose-
response value (usually the AEGL-1 and/or the ERPG-1).
    For this source category, an acute emissions multiplier value of
1.2 was used because, overall, sterilization operations tend to be
steady-state without much variation. A further discussion of why this
factor was chosen can be found in Appendix 1 of the document titled
Residual Risk Assessment for the Commercial Sterilization Facilities
Source Category in Support of the 2022 Risk and Technology Review
Proposed Rule, available in the docket for this rulemaking.
    In our acute inhalation screening risk assessment, acute impacts
are deemed negligible for HAP for which acute HQs are less than or
equal to 1, and no further analysis is performed for these HAP. In
cases where an acute HQ from the screening step is greater than 1, we
assess the site-specific data to ensure that the acute HQ is at an off-
site location. For this source category, all acute HQs were less than
or equal to 1, and no further analysis was performed.
3. How do we conduct the multipathway exposure and risk screening
assessment?
    The EPA conducts a tiered screening assessment examining the
potential for significant human health risks due to exposures via
routes other than inhalation (i.e., ingestion). We first determine
whether any sources in the source category emit any HAP known to be
persistent and bioaccumulative in the environment, as identified in the
EPA's Air Toxics Risk Assessment Library (see Volume 1, Appendix D, at
https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Commercial Sterilization Facilities source category, we did
not identify emissions of any PB-HAP. Because we did not identify any
PB-HAP emissions, no further evaluation of multipathway risk was
conducted for this source category.

4. 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.
5. How do we conduct the environmental risk screening assessment?
    The EPA conducts a screening assessment to examine the potential
for an adverse environmental effect. 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, polycyclic organic matter
(POM), mercury (both inorganic mercury and methyl mercury), and lead
compounds. The acid gases included in the screening assessment are
hydrochloric acid (HCl) and hydrogen fluoride (HF).
    For the Commercial Sterilization Facilities source category, we did
not identify emissions of any environmental HAP. Because we did not
identify any environmental HAP emissions, no further evaluation of
environmental risk was conducted for this source category.
6. How do we conduct facility-wide assessments?
    To put the source category risks in context, we typically examine
the risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, we examine the HAP emissions not only from the
source category emission points of interest, but also emissions of HAP
from all other emission sources at the facility for which we have data.
For this source category, we conducted the facility-wide assessment
using a dataset compiled from the 2017 NEI. The source category records
of that NEI dataset were removed, evaluated, and updated as described
in section II.C of this preamble: What data collection activities were
conducted to support this action? Once a quality assured source
category dataset was available, it was placed back with the remaining
records from the NEI for that facility. The facility-wide file was then
used to analyze risks due to the inhalation of HAP that are emitted
``facility-wide'' for the populations residing within 50 km of each
facility, consistent with the methods used for the source category
analysis described above. For these facility-wide risk analyses, the
modeled source category risks were compared to the facility-wide risks
to determine the portion of the facility-wide risks that could be
attributed to the source category addressed in this proposal. We also
specifically examined the facility that was associated with the highest
estimate of risk and determined the percentage of that risk
attributable to the source category of interest. The Residual Risk
Assessment for the Commercial Sterilization Facilities Source Category
in Support of the Risk and Technology Review 2022 Proposed Rule,
available through the docket for this action, provides the methodology
and results of the facility-wide analyses, including all facility-wide
risks and the percentage of source category contribution to facility-
wide risks.
7. How do we consider uncertainties in risk assessment?
    Uncertainty and the potential for bias are inherent in all risk
assessments, including those performed for this proposal. Although
uncertainty exists, we believe that our approach, which used
conservative tools and assumptions, ensures that our decisions are
health and environmentally protective. A brief discussion of the
uncertainties in the RTR emissions dataset, dispersion modeling,
inhalation exposure estimates, and dose-response relationships follows
below. Also included are those uncertainties specific to our acute
screening assessments, multipathway screening assessments, and our
environmental risk screening assessments. A more thorough discussion of
these uncertainties is included in the Residual Risk Assessment for the
Commercial Sterilization Facilities Source Category in Support of the
Risk and Technology Review 2022 Proposed Rule, which is available in
the docket for this action. If a multipathway site-specific assessment
was performed for this source category, a full discussion of the
uncertainties associated with that assessment can be found in Appendix
11 of that document, Site-Specific Human Health Multipathway Residual
Risk Assessment Report.
a. Uncertainties in the RTR Emissions Dataset
    Although the development of the RTR emissions dataset involved
quality assurance/quality control processes, the accuracy of emissions
values will vary depending on the source of the data, the degree to
which data are incomplete or missing, the degree to which assumptions
made to complete the datasets are accurate, errors in emission
estimates, and other factors. The emission estimates considered in this
analysis generally are annual totals for certain years, and they do not
reflect short-term fluctuations during the course of a year or
variations from year to year. The estimates of peak hourly emission
rates for the acute effects screening assessment were based on an
emission adjustment factor applied to the average annual hourly
emission rates, which are intended to account for emission fluctuations
due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration
estimates associated with any model, including the EPA's recommended
regulatory dispersion model, AERMOD. In using a model to estimate
ambient pollutant concentrations, the user chooses certain options to
apply. For RTR assessments, we select some model options that have the
potential to overestimate ambient air concentrations (e.g., not
including plume depletion or pollutant transformation). We select other
model options that have the potential to underestimate ambient impacts.
Other options that we select have the potential to either under- or
overestimate ambient levels (e.g., meteorology and receptor locations).
On balance, considering the directional nature of the uncertainties
commonly present in ambient concentrations estimated by dispersion
models, the approach we apply in the RTR assessments should yield
unbiased estimates of ambient HAP concentrations. We also note that the
selection of meteorology dataset location could have an impact on the
risk estimates. As we continue to update and expand our library of
meteorological station data used in our risk assessments, we expect to
reduce this variability.

c. Uncertainties in Inhalation Exposure Assessment
    Although every effort is made to identify all of the relevant
facilities and emission points, as well as to develop accurate
estimates of the annual emission rates for all relevant HAP, the
uncertainties in our emission inventory likely dominate the
uncertainties in the exposure assessment. Some uncertainties in our
exposure assessment include human mobility, using the centroid of each
census block, assuming lifetime exposure, and assuming only outdoor
exposures. For most of these factors, there is neither an under- nor
overestimate when looking at the maximum individual risk or the
incidence, but the shape of the distribution of risks may be affected.
With respect to outdoor exposures, actual exposures may not be as high
if people spend time indoors, especially 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. 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. 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, which considers uncertainty, variability, and gaps in the
available data. The UFs are applied to derive dose-response values that
are intended to protect against appreciable risk of deleterious
effects.
    Many of the UFs used to account for variability and uncertainty in
the development of acute dose-response values are quite similar to
those developed for chronic durations. Additional adjustments are often
applied to account for uncertainty in extrapolation from observations
at one exposure duration (e.g., 4 hours) to derive an acute dose-
response value at another exposure duration (e.g., 1 hour). Not all
acute dose-response values are developed for the same purpose, and care
must be taken when interpreting the results of an acute assessment of
human health effects relative to the dose-response value or values
being exceeded. Where relevant to the estimated exposures, the lack of
acute dose-response values at different levels of severity should be
factored into the risk characterization as potential uncertainties.
    Uncertainty also exists in the selection of ecological benchmarks
for the environmental risk screening assessment. We established a
hierarchy of preferred benchmark sources to allow selection of
benchmarks for each environmental HAP at each ecological assessment
endpoint. We searched for benchmarks for three effect levels (i.e., no-
effects level, threshold-effect level, and probable effect level), but
not all combinations of ecological assessment/environmental HAP had
benchmarks for all three effect levels. Where multiple effect levels
were available for a particular HAP and assessment endpoint, we used
all of the available effect levels to help us determine whether risk
exists and whether the risk could be considered significant and
widespread.
    Although we make every effort to identify appropriate human health
effect dose-response values for all pollutants emitted by the sources
in this risk assessment, some HAP emitted by this source category are
lacking dose-response assessments. Accordingly, these pollutants cannot
be included in the quantitative risk assessment, which could result in
quantitative estimates understating HAP risk. To help to alleviate this
potential underestimate, where we conclude similarity with a HAP for
which a dose-response value is available, we use that value as a
surrogate for the assessment of the HAP for which no value is
available. To the extent use of surrogates indicates appreciable risk,
we may identify a need to increase priority for an IRIS assessment for
that substance. We additionally note that, generally speaking, HAP of
greatest concern due to environmental exposures and hazard are those
for which dose-response assessments have been performed, reducing the
likelihood of understating risk. Further, HAP not included in the
quantitative assessment are assessed qualitatively and considered in
the risk characterization that informs the risk management decisions,
including consideration of HAP reductions achieved by various control
options.
    For a group of compounds that are unspeciated (e.g., glycol
ethers), we conservatively use the most protective dose-response value
of an individual compound in that group to estimate risk. Similarly,
for an individual compound in a group (e.g., ethylene glycol diethyl
ether) that does not have a specified dose-response value, we also
apply the most protective dose-response value from the other compounds
in the group to estimate risk.
e. Uncertainties in Acute Inhalation Screening Assessments
    In addition to the uncertainties highlighted above, there are
several factors specific to the acute exposure assessment that the EPA
conducts as part of the risk review under section 112 of the CAA. The
accuracy of an acute inhalation exposure assessment depends on the
simultaneous occurrence of independent factors that may vary greatly,
such as hourly emissions rates, meteorology, and the presence of a
person. In the acute screening assessment that we conduct under the RTR
program, we assume that peak emissions from the source category and
reasonable worst-case air dispersion conditions (i.e., 99th percentile)
co-occur. We then include the additional assumption that a person is
located at this point at the same time. Together, these assumptions
represent a reasonable worst-case actual exposure scenario. In most
cases, it is unlikely that a person would be located at the point of
maximum exposure during the time when peak emissions and 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 American Meteorological Society (AMS)/Environmental
Protection Agency (EPA) Regulatory Model (AERMOD)--that estimate
environmental pollutant concentrations and human exposures for five PB-
HAP (dioxins/furans, POM, mercury (both inorganic and methyl mercury),
cadmium, and arsenic) and two acid gases (HF and HCl). For lead, the
other PB-HAP, we use AERMOD to determine ambient air concentrations,
which are then compared to the secondary National Ambient Air Quality
Standards 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.
    Model uncertainty concerns whether the model adequately represents
the actual processes that might occur in the environment, such as the
movement of a pollutant through soil or accumulation of the pollutant
over time. 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 adopts
conservative assumptions that are intended to be protective of public
health. We choose model inputs from the upper end of the range of
possible values for the influential parameters used in the models, and
we assume that the exposed individual exhibits ingestion behavior that
would lead to a high total exposure. This approach reduces the
likelihood of not identifying high risks for adverse impacts.
    Despite the uncertainties, when individual pollutants or facilities
do not exceed screening threshold emission rates (i.e., screen out), we
are confident that the potential for adverse multipathway impacts on
human health is very low. On the other hand, when individual pollutants
or facilities do exceed screening threshold emission rates, it does not
mean that impacts are significant, only that we cannot rule out that
possibility and that a refined assessment for the site might be
necessary to obtain a more accurate risk characterization for the
source category.
    The EPA evaluates the following HAP in the multipathway and/or
environmental risk screening assessments, where applicable: arsenic,
cadmium, dioxins/furans, lead, mercury (both inorganic and methyl
mercury), POM, HCl, and HF. These HAP represent pollutants that can
cause adverse impacts either through direct exposure to HAP in the air
or through exposure to HAP that are deposited from the air onto soils
and surface waters and then through the environment into the food web.
These HAP represent those HAP for which we can conduct a meaningful
multipathway or environmental screening risk assessment. For other HAP
not included in our screening assessments, the model has not been
parameterized such that it can be used for that purpose. In some cases,
depending on the HAP, we may not have appropriate multipathway models
that allow us to predict the concentration of that pollutant. The EPA
acknowledges that other HAP beyond these that we are evaluating may
have the potential to cause adverse effects and, therefore, the EPA may
evaluate other relevant HAP in the future, as modeling science and
resources allow.

III. Analytical Results and Proposed Decisions

    In this section, we describe the analyses performed to support the
proposed decisions for establishing standards for previously
unregulated processes and pollutants, the residual risk assessment, the
technology review, and other issues addressed in this proposal. We also
describe the proposed standards that result from this series of
analyses. To develop the proposed standards, we first determined the
proposed standards for previously unregulated emission sources under
CAA section 112(d)(2)-(3) (MACT) or 112(d)(5) (GACT). Next, we assessed
the remaining risks, taking into account the current standards and the
proposed standards we developed under the first analysis for the
currently unregulated sources. Based on the risk assessment, we