[Federal Register Volume 84, Number 242 (Tuesday, December 17, 2019)]
[Proposed Rules]
[Pages 69182-69269]
[FR Doc No: 2019-24573]

Vol. 84

Tuesday,

No. 242

December 17, 2019

Part III

Environmental Protection Agency

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40 CFR Part 63

National Emission Standards for Hazardous Air Pollutants: Miscellaneous
Organic Chemical Manufacturing Residual Risk and Technology Review;
Proposed Rule

Federal Register / Vol. 84 , No. 242 / Tuesday, December 17, 2019 /
Proposed Rules

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 ENVIRONMENTAL PROTECTION AGENCY

 40 CFR Part 63

[EPA-HQ-OAR-2018-0746; FRL-10001-98-OAR]
RIN 2060-AT85

National Emission Standards for Hazardous Air Pollutants:
Miscellaneous Organic Chemical Manufacturing 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 Miscellaneous Organic Chemical
Manufacturing source category. The EPA is proposing decisions
concerning the residual risk and technology review (RTR), including
proposing amendments pursuant to the technology review for equipment
leaks and heat exchange systems, and also proposing amendments pursuant
to the risk review to specifically address ethylene oxide emissions
from storage tanks, process vents, and equipment leaks. 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, adding work practice standards for periods of SSM where
appropriate, and clarifying regulatory provisions for certain vent
control bypasses. Lastly, the EPA is proposing to add monitoring and
operational requirements for flares that control ethylene oxide
emissions and flares used to control emissions from processes that
produce olefins and polyolefins; and 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 (not including the potential
excess emission reductions from flares) would reduce hazardous air
pollutants (HAP) emissions from this source category by 116 tons per
year (tpy) and would reduce ethylene oxide emissions from this source
category by approximately 10 tpy.

DATES: Comments. Comments must be received on or before January 31,
2020. Under the Paperwork Reduction Act (PRA), comments on the
information collection provisions are best assured of consideration if
the Office of Management and Budget (OMB) receives a copy of your
comments on or before January 16, 2020.
    Public hearing. The EPA is planning to hold at least one public
hearing in response to this proposed action. Information about the
hearing, including location, date, and time, along with instructions on
how to register to speak at the hearing, will be published in a second
Federal Register document and posted at https://www.epa.gov/stationary-sources-air-pollution/miscellaneous-organic-chemical-manufacturing-national-emission. See SUPPLEMENTARY INFORMATION for information on
registering and attending a public hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2018-0746, 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_ADDRESS>Include Docket ID No. EPA-
HQ-OAR-2018-0746 in the subject line of the message.
     Fax:<PHONE_NUMBER>. Attention Docket ID No. EPA-HQ-OAR-
2018-0746.
     Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2018-0746, 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 Ms. Tegan Lavoie, Sector Policies and Programs Division
(E-143-01), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
and email address<EMAIL_ADDRESS>For specific information
regarding the risk modeling methodology, contact Mr. Matthew 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: (919)
541-1535; fax number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>For questions about monitoring and testing
requirements, contact Ms. Gerri Garwood, Sector Policies and Programs
Division (D243-05), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
and email address<EMAIL_ADDRESS>For information about the
applicability of the NESHAP to a particular entity, contact Mr. John
Cox, Office of Enforcement and Compliance Assurance, U.S. Environmental
Protection Agency, WJC South Building (Mail Code 2227A), 1200
Pennsylvania Avenue NW, Washington, DC 20460; telephone number: (202)
564-1395; and email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:
    Public hearing. The EPA is planning to hold at least one public
hearing in response to this proposed action. Information about the
hearing, including location, date, and time, along with instructions on
how to register to speak at the hearing will be published in a second
Federal Register document.
    Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2018-0746. All documents in the docket are
listed in 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. Publicly
available docket materials are available either electronically in
Regulations.gov or in hard copy at the EPA Docket Center, Room 3334,
WJC West Building, 1301 Constitution Avenue 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-
2018-0746. 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 information that you consider to be CBI or
otherwise protected through https://www.regulations.gov/ or email. This
type of information should be submitted by mail as discussed below.
    The EPA may publish any comment received to its public docket.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e., on the Web, cloud, or other
file sharing system). For additional submission methods, the full EPA
public comment policy, information about CBI or multimedia submissions,
and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    The https://www.regulations.gov/ website allows you to submit your
comment anonymously, which means the EPA will not know your identity or
contact information unless you provide it in the body of your comment.
If you send an email comment directly to the EPA without going through
https://www.regulations.gov/, your email address will be automatically
captured and included as part of the comment that is placed in the
public docket and made available on the internet. If you submit an
electronic comment, the EPA recommends that you include your name and
other contact information in the body of your comment and with any
digital storage media you submit. If the EPA cannot read your comment
due to technical difficulties and cannot contact you for clarification,
the EPA may not be able to consider your comment. Electronic files
should not include special characters or any form of encryption and be
free of any defects or viruses. For additional information about the
EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    Submitting CBI. Do not submit information containing CBI to the EPA
through https://www.regulations.gov/ or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
any digital storage media that you mail to the EPA, mark the outside of
the digital storage media as CBI and then identify electronically
within the digital storage media the specific information that is
claimed as CBI. In addition to one complete version of the comments
that includes information claimed as CBI, you must submit a copy of the
comments that does not contain the information claimed as CBI directly
to the public docket through the procedures outlined in Instructions
above. If you submit any digital storage media that does not contain
CBI, mark the outside of the digital storage media clearly that it does
not contain CBI. Information not marked as CBI will be included in the
public docket and the EPA's electronic public docket without prior
notice. Information marked as CBI will not be disclosed except in
accordance with procedures set forth in 40 Code of Federal Regulations
(CFR) part 2. Send or deliver information identified as CBI only to the
following address: OAQPS Document Control Officer (C404-02), OAQPS,
U.S. Environmental Protection Agency, Research Triangle Park, North
Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2018-0746.
    Preamble acronyms and abbreviations. We use multiple acronyms and
terms in this preamble. While this list may not be exhaustive, to ease
the reading of this preamble and for reference purposes, the EPA
defines the following terms and acronyms here:

ACA American Coatings Association
ACC American Chemistry Council
AEGL acute exposure guideline level
AERMOD air dispersion model used by the HEM-3 model
AFPM American Fuel & Petrochemical Manufacturers
AMEL alternative means of emission limitation
APCD air pollution control device
ATSDR Agency for Toxic Substances and Disease Registry
BAAQMD Bay Area Air Quality Management District
BACT best available control technology
Btu British thermal unit
Btu/scf British thermal unit per standard cubic foot
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CEMS continuous emission monitoring system(s)
CFR Code of Federal Regulations
ECHO Enforcement and Compliance History Online
EIS emissions inventory system
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guideline
ERT Electronic Reporting Tool
FID flame ionization detector
FTIR fourier transfer infrared spectrometry
GACT generally available control technologies
HAPV hazardous air pollutant(s)
HCl hydrochloric acid
HEM-3 Human Exposure Model
HF hydrogen fluoride
HI hazard index
HQ hazard quotient
HRVOC highly reactive volatile organic compounds
ICR Information Collection Request
IRIS Integrated Risk Information System
km kilometer
LAER lowest achievable emission rate
LDAR leak detection and repair
LEL lower explosive limit
MACT maximum achievable control technology
MCPU miscellaneous organic chemical manufacturing process unit
mg/m\3\ milligrams per cubic meter
MIR maximum individual risk
MON Miscellaneous Organic Chemical Manufacturing NESHAP
MPGF multi-point ground flare(s)
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NEI National Emission Inventory
NESHAP national emission standards for hazardous air pollutants
NHVcz net heating value in the combustion zone gas
NHVdil net heating value dilution parameter
NHVvg net heating value of flare vent gas
NRDC Natural Resources Defense Council
NSPS new source performance standards
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
OSHA Occupational Safety and Health Administration
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PDF portable document format
PDH propane dehydrogenation
POM polycyclic organic matter
ppm parts per million
ppmw parts per million by weight
ppmv parts per million by volume
PRA Paperwork Reduction Act
PRD pressure relief device(s)
psig pounds per square inch gauge
RACT reasonably available control technology
REL reference exposure level
RFA Regulatory Flexibility Act
RfC reference concentration
RTR residual risk and technology review
SAB Science Advisory Board
SCC source classification code
SSM startup, shutdown, and malfunction
TCEQ Texas Commission on Environmental Quality
TOSHI target organ-specific hazard index
tpy tons per year

TRIM.FaTE Total Risk Integrated Methodology.Fate, Transport, and
Ecological Exposure Model
UF uncertainty factor
[micro]g/m\3\ micrograms per cubic meter
UMRA Unfunded Mandates Reform Act
URE unit risk estimate
USGS U.S. Geological Survey
VCS voluntary consensus standards
VOC volatile organic compound(s)

    Organization of this document. The information in this preamble is
organized as follows below. In particular, section IV of this preamble
describes the majority of the Agency's rationale for the proposed
actions in this preamble. Section IV.A of this preamble specifies
proposed monitoring and operational requirements for a subset of flares
in the Miscellaneous Organic Chemical Manufacturing source category to
ensure that the level of control from the original maximum achievable
control technology (MACT) standards is achieved by these air pollution
control devices (APCD). To ensure that Clean Air Act (CAA) section 112
standards continuously apply (Sierra Club v. EPA, 551 F.3d 1019 (D.C.
Cir. 2008)), section IV.A of this preamble also proposes work practice
standards for periods of SSM for when flares are used as an APCD,
proposes work practice standards for periods of SSM for certain vent
streams (i.e., pressure relief device (PRD) releases and maintenance
vents), and proposes clarifications for vent control bypasses for
certain vent streams (i.e., closed vent systems containing bypass
lines, and flares connected to fuel gas systems).
    Section IV.B of this preamble summarizes the results of the risk
assessment while section IV.C summarizes our proposed decisions
regarding the results of the risk assessment, and proposes revisions
for storage tanks, process vents, and equipment leaks to reduce
emissions of ethylene oxide. Section IV.D of this preamble summarizes
the results of our technology review, and proposes revisions for heat
exchange systems and equipment leaks. Section IV.E of this preamble
summarizes other changes we are proposing, including general regulatory
language changes related to the removal of SSM exemptions, electronic
reporting, and other minor clarifications identified as part our review
of the NESHAP and as part of the other proposed revisions in this
proposal. Lastly, section IV.F of this preamble summarizes our
rationale for the compliance dates we are proposing.

I. General Information
    A. Does this action apply to me?
    B. Where can I get a copy of this document and other related
information?
II. Background
    A. What is the statutory authority for this action?
    B. What is this source category and how does the current NESHAP
regulate its HAP emissions?
    C. What data collection activities were conducted to support
this action?
    D. What other relevant background information and data are
available?
III. Analytical Procedures and Decision-Making
    A. How do we consider risk in our decision-making?
    B. How do we perform the technology review?
    C. How do we estimate post-MACT risk posed by the source
category?
IV. Analytical Results and Proposed Decisions
    A. What actions are we taking in addition to those identified in
the risk and technology review?
    B. What are the results of the risk assessment and analyses?
    C. What are our proposed decisions regarding risk acceptability,
ample margin of safety, and adverse environmental effects?
    D. What are the results and proposed decisions based on our
technology review?
    E. What other actions are we proposing?
    F. What compliance dates are we proposing?
V. Summary of Cost, Environmental, and Economic Impacts
    A. What are the affected sources?
    B. What are the air quality impacts?
    C. What are the cost impacts?
    D. What are the economic impacts?
    E. What are the benefits?
VI. Request for Comments
VII. Submitting Data Corrections
VIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Executive Order 13771: Reducing Regulations and Controlling
Regulatory Costs
    C. Paperwork Reduction Act (PRA)
    D. Regulatory Flexibility Act (RFA)
    E. Unfunded Mandates Reform Act (UMRA)
    F. Executive Order 13132: Federalism
    G. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
    H. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
    I. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
    J. National Technology Transfer and Advancement Act (NTTAA) and
1 CFR Part 51
    K. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations

I. General Information

A. Does this action apply to me?

    Table 1 of this preamble lists the NESHAP and associated regulated
industrial source category that is the subject of this proposal. Table
1 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. On
July 16, 1992 (57 FR 31576), pursuant to specific listing requirements
in CAA section 112(c), the Agency published an initial list of 174
categories of major and area sources that would be subject to MACT
emission standards. Following this listing, in a November 7, 1996,
document (61 FR 57602), the Agency combined 21 of the 174 source
categories originally 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), and other organic chemical processes which were not included in
the original 174 source category list, into one source category called
the ``Miscellaneous Organic Chemical Processes'' source category. In a
November 18, 1999, document (64 FR 63035), the Agency divided the
``Miscellaneous Organic Chemical Processes'' source category into two
new source categories called the ``Miscellaneous Organic Chemical
Manufacturing'' source category and the ``Miscellaneous Coating
Manufacturing'' source category. The Miscellaneous Organic Chemical
Manufacturing source category includes any facility engaged in
benzyltrimethylammonium chloride production, carbonyl sulfide
production, chelating agents production, chlorinated paraffins
production, ethylidene norbornene production, explosives production,
hydrazine production, photographic chemicals production, phthalate
plasticizers production, rubber chemicals production, symmetrical
tetrachloropyridine production, oxybisphenoxarsine/1,3-diisocyanate
production, alkyd resins production, polyester resins production,
polyvinyl alcohol production, polyvinyl acetate emulsions production,
polyvinyl butyral production, polymerized vinylidene chloride
production, polymethyl methacrylate production, maleic

anhydride copolymers production, or any other organic chemical
processes not covered by another MACT standard. Many of these organic
chemical processes involve similar process equipment, similar emission
points and control equipment, and are in many cases co-located with
other source categories. For more information about the Miscellaneous
Organic Chemical Manufacturing source category, see section II.B of
this preamble.

    Table 1--NESHAP and Industrial Source Categories Affected by This
                             Proposed Action
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       Source category               NESHAP            NAICS code \1\
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Miscellaneous Organic         Miscellaneous         3251, 3252, 3253,
 Chemical Manufacturing.       Organic Chemical      3254, 3255, 3256,
                               Manufacturing.        and 3259, with
                                                     several exceptions.
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\1\ North American Industry Classification System.

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

    In addition to being available in the docket, an electronic copy of
this action is available on the internet. Following signature by the
EPA Administrator, the EPA will post a copy of this proposed action at
https://www.epa.gov/stationary-sources-air-pollution/miscellaneous-organic-chemical-manufacturing-national-emission. Following publication
in the Federal Register, the EPA will post the Federal Register version
of the proposal and key technical documents at this same website.
Information on the overall RTR program is available at https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.
    A redline version of the regulatory language that incorporates the
proposed changes is available in the docket for this action (Docket ID
No. EPA-HQ-OAR-2018-0746).

II. Background

A. What is the statutory authority for this action?

    The statutory authority for this action is provided by sections 112
and 301 of the CAA, as amended (42 U.S.C. 7401 et seq.). Section 112 of
the CAA establishes a two-stage regulatory process to develop standards
for emissions of HAP from stationary sources. Generally, the first
stage involves establishing technology-based standards and the second
stage involves evaluating those standards that are based on MACT to
determine whether additional standards are needed to address any
remaining risk associated with HAP emissions. This second stage is
commonly referred to as the ``residual risk review.'' In addition to
the residual risk review, the CAA also requires the EPA to review
standards set under CAA section 112 every 8 years to determine if there
are ``developments in practices, processes, or control technologies''
that may be appropriate to incorporate into the standards. This review
is commonly referred to as the ``technology review.'' When the two
reviews are combined into a single rulemaking, it is commonly referred
to as the ``risk and technology review.'' The discussion that follows
identifies the most relevant statutory sections and briefly explains
the contours of the methodology used to implement these statutory
requirements. A more comprehensive discussion appears in the document
titled CAA Section 112 Risk and Technology Reviews: Statutory Authority
and Methodology, in the docket for this rulemaking.
    In the first stage of the CAA section 112 standard setting process,
the EPA promulgates technology-based standards under CAA section 112(d)
for categories of sources identified as emitting one or more of the HAP
listed in CAA section 112(b). Sources of HAP emissions are either major
sources or area sources, and CAA section 112 establishes different
requirements for major source standards and area source standards.
``Major sources'' are those that emit or have the potential to emit 10
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.''
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. In certain instances, as
provided in CAA section 112(h), the EPA may set work practice standards
where it is not feasible to prescribe or enforce a numerical emission
standard. For area sources, CAA section 112(d)(5) gives the EPA
discretion to set standards based on generally available control
technologies or management practices (GACT standards) in lieu of MACT
standards.
    The second stage in standard-setting focuses on identifying and
addressing any remaining (i.e., ``residual'') risk according 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 Risk Report that the Agency intended to use
the Benzene NESHAP approach in making CAA section 112(f) residual risk
determinations (EPA-453/R-99-001, p. ES-11). The EPA subsequently
adopted this approach in its residual risk determinations and the
United States Court of Appeals for the District of Columbia Circuit
(the Court) upheld the EPA's interpretation that CAA section 112(f)(2)
incorporates the approach established in the Benzene NESHAP. See NRDC
v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008).
    The approach incorporated into the CAA and used by the EPA to
evaluate residual risk and to develop standards under CAA section
112(f)(2) is a two-step approach. In the first step, the EPA determines
whether risks are acceptable. This determination ``considers all health
information, including risk estimation uncertainty, and includes a
presumptive

limit on maximum individual lifetime [cancer] risk (MIR) \1\ of
approximately 1-in-10 thousand.'' 54 FR 38045, September 14, 1989. If
risks are unacceptable, the EPA must determine the emissions standards
necessary to reduce risk to an acceptable level without considering
costs. In the second step of the approach, the EPA considers whether
the emissions standards provide an ample margin of safety to protect
public health ``in consideration of all health information, including
the number of persons at risk levels higher than approximately 1-in-1
million, as well as other relevant factors, including costs and
economic impacts, technological feasibility, and other factors relevant
to each particular decision.'' Id. The EPA must promulgate emission
standards necessary to provide an ample margin of safety to protect
public health or determine that the standards being reviewed provide an
ample margin of safety without any revisions. After conducting the
ample margin of safety analysis, we consider whether a more stringent
standard is necessary to prevent, taking into consideration costs,
energy, safety, and other relevant factors, an adverse environmental
effect.
---------------------------------------------------------------------------

    \1\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk if an individual were exposed to the maximum
level of a pollutant for a lifetime.
---------------------------------------------------------------------------

    CAA section 112(d)(6) separately requires the EPA to review
standards promulgated under CAA section 112 and revise them ``as
necessary (taking into account developments in practices, processes,
and control technologies)'' no less often than every 8 years. In
conducting this review, which we call the ``technology review,'' the
EPA is not required to recalculate the MACT floor. Natural Resources
Defense Council (NRDC) v. EPA, 529 F.3d 1077, 1084 (D.C. Cir. 2008).
Association of Battery Recyclers, Inc. v. EPA, 716 F.3d 667 (D.C. Cir.
2013). The EPA may consider cost in deciding whether to revise the
standards pursuant to CAA section 112(d)(6).

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

    The current NESHAP, herein called the Miscellaneous Organic
Chemical Manufacturing NESHAP (MON) for the Miscellaneous Organic
Chemical Manufacturing source category was promulgated on November 10,
2003 (68 FR 63852), and codified at 40 CFR part 63, subpart FFFF. As
promulgated in 2003, and further amended on July 1, 2005 (70 FR 38562),
and July 14, 2006 (71 FR 40316), the MON regulates HAP emissions from
miscellaneous organic chemical manufacturing process units (MCPUs)
located at major sources. An MCPU includes a miscellaneous organic
chemical manufacturing process, as defined in 40 CFR 63.2550(i), and
must meet the following criteria: (1) It manufactures any material or
family of materials described in 40 CFR 63.2435(b)(1); it processes,
uses, or generates any of the organic HAP described in 40 CFR
63.2435(b)(2); and, except for certain process vents that are part of a
chemical manufacturing process unit, as identified in 40 CFR
63.100(j)(4), the MCPU is not an affected source or part of an affected
source under another subpart of 40 CFR part 63. An MCPU also includes
any assigned storage tanks and transfer racks; equipment in open
systems that is used to convey or store water having the same
concentration and flow characteristics as wastewater; and components
such as pumps, compressors, agitators, pressure relief devices,
sampling connection systems, open-ended valves or lines, valves,
connectors, and instrumentation systems that are used to manufacture
any material or family of materials described in 40 CFR 63.2435(b)(1).
Sources of HAP emissions regulated by the MON include the following:
process vents, storage tanks, transfer racks, equipment leaks,
wastewater streams, and heat exchange systems.
    As of November 6, 2018, the EPA identified 201 miscellaneous
organic chemical manufacturing facilities in operation and subject to
the MON standards, herein referred to as ``MON facilities'', using
methods described in section II.C of this preamble. A complete list of
known MON facilities is available in Appendix 1 of the document titled
Residual Risk Assessment for the Miscellaneous Organic Chemical
Manufacturing Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule, which is available in the docket for
this rulemaking.

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

    The EPA used several sources to develop the list of existing MON
facilities. All facilities in the 2014 National Emissions Inventory
(NEI) and the 2014 Toxics Release Inventory with a primary facility
NAICS code beginning with 325, representing the chemical manufacturing
sector, were queried to create a comprehensive base facility list. The
list was also supplemented using the Office of Enforcement and
Compliance Assurance's (OECA) Enforcement and Compliance History Online
(ECHO) tool (https://echo.epa.gov) and chemical sector facility lists
provided internally from the EPA's records. This starting chemical
manufacturing sector facility list included over 5,000 unique
facilities, 201 of which we found to be subject to the MON.
    To determine which facilities on the comprehensive chemical
manufacturing sector facility list were subject to the MON, title V air
permits were obtained from each state's online database. In cases where
the online database was incomplete, the Region and/or state was
contacted for help in obtaining the air permits, and internet searches
were performed to determine the status of the facility (e.g., open,
permanently closed, sold, etc.). The list was also shared with the
American Chemistry Council (ACC) and the American Coatings Association
(ACA) for voluntary input on rule applicability. This review and
analysis produced the final facility list of 201 MON facilities. For
MON facilities that reported emissions of ethylene oxide, we not only
reviewed the air permit, but we also contacted facilities to verify
process and operating information.\2\
---------------------------------------------------------------------------

    \2\ As discussed in section IV.C.2 of this preamble, we
specifically address ethylene oxide emissions from storage tanks,
process vents, and equipment leaks.
---------------------------------------------------------------------------

    In November 2018, the EPA issued a request, pursuant to CAA section
114, to gather information about process equipment, control
technologies, and emissions, and requested performance testing for
certain pollutants for one MCPU source emitting ethylene oxide. The
facility completed the survey and submitted responses (and follow-up
responses) to the EPA between January 2019 and February 2019. The
results of the performance testing were received on September 3, 2019,
and, therefore, were not included in the risk analysis. The Agency has
made the results publicly available in the docket for this rulemaking
to provide the public with an opportunity to review the data before
promulgation of the rule. Before final promulgation of this rulemaking,
the EPA intends to use the collected information to assist the Agency
in filling data gaps, establishing the baseline emissions and control
levels for purposes of the regulatory reviews, identifying the most
effective control measures, and estimating the environmental impacts
associated with the regulatory options considered and reflected in this
proposed action. The information not claimed as CBI by respondents and
received in time to be included in this proposal is available in

the memorandum titled Data Received from Information Collection Request
for the Miscellaneous Organic Chemical Manufacturing Source Category,
which is available in the docket for this rulemaking.

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

    We are relying on technical reports and memoranda that the EPA
developed for flares used as air pollution control devices in the
Petroleum Refinery Sector RTR and New Source Performance Standards
(NSPS) (80 FR 75178, December 1, 2015). These technical reports and
memoranda can be found in the Petroleum Refinery Sector RTR and NSPS
rulemaking docket, Docket ID No. EPA-HQ-OAR-2010-0682. The Petroleum
Refinery Sector docket contains several flare-related technical reports
and memoranda documenting numerous analyses the EPA conducted to
develop the final suite of operational and monitoring requirements for
refinery flares. For completeness of the rulemaking record for this
action and ease of reference in finding these items in the publicly
available refinery sector rulemaking docket, we are including a list of
the most relevant technical support documents in Table 1 of the
memorandum titled Control Option Impacts for Flares Located in the
Miscellaneous Organic Chemical Manufacturing Source Category, which is
available in the docket for this rulemaking.
    In addition, the EPA is incorporating into the docket for this
rulemaking materials associated with a number of site-specific
alternative means of emission limitation (AMEL) requests for facilities
electing to use multi-point ground flares (MPGF) as an APCD. These
site-specific AMEL requests for MPGF have been approved by the EPA
because the MPGF can achieve at least equivalent reductions in
emissions to the underlying flare operational standards in various
NESHAP and/or NSPS. The EPA receives these AMEL requests because MPGFs
are designed to operate above the current maximum permitted velocity
requirements for flares in the General Provisions at 40 CFR 63.11(b).
Given that the EPA has provided notice and sought comment on certain
specific AMEL requests, the underlying AMEL requests submitted by
industry, MPGF test data, technical memorandums, Federal Register
documents \3\ and other supporting and related material that formed the
basis of the AMEL requests and approved alternative operating
conditions have been placed in a publicly available docket at Docket ID
No. EPA-HQ-OAR-2014-0738. We consider all items in Docket ID No. EPA-
HQ-OAR-2014-0738 part of our rulemaking record as well, given that this
docket is specific to MPGF AMEL requests. We are, therefore,
referencing the materials in Docket ID No. EPA-HQ-OAR-2014-0738 for
this rule.
---------------------------------------------------------------------------

    \3\ 80 FR 8023, February 13, 2015; 80 FR 52426, August 31, 2015;
81 FR 23480, April 21, 2016; 82 FR 16392, April 4, 2017; 82 FR
27822, June 19, 2017; and 83 FR 18034, April 25, 2018.
---------------------------------------------------------------------------

    We are also relying on data gathered to support the RTR for
ethylene production processes, as well as memoranda documenting the
technology review for those processes. Many of the emission sources for
ethylene production facilities are similar to MON facilities, and
several of the control options analyzed for the MON were also analyzed
for the Ethylene Production RTR. The memoranda and background technical
information can be found in the Ethylene Production RTR rulemaking
docket, Docket ID No. EPA-HQ-OAR-2017-0357.
    Furthermore, the risk assessment presented here relies on the use
of the 2016 updated ethylene oxide unit risk estimate (URE) for
regulatory purposes. The EPA previously requested comment on the use of
this URE in the Hydrochloric Acid Production RTR proposed rule (84 FR
1584, February 4, 2019), the comment period for which closed on April
26, 2019. The Agency received a number of comments on the use of the
updated ethylene oxide URE. However, ethylene oxide is not emitted by
the Hydrochloric Acid Production source category but is emitted by the
Miscellaneous Organic Chemical Manufacturing source category.
Therefore, the EPA is incorporating these comments into the docket for
this rulemaking from Docket ID No. EPA-HQ-OAR-2018-0417 and, along with
comments received on this proposal, will address all comments in the
response to comments document of this final rulemaking. Note that all
comments received in the Hydrochloric Acid Production RTR proposal were
at least partially related to risks from ethylene oxide, and,
therefore, we are incorporating all comments from that rulemaking into
the docket for this action. (Note, additional discussion on the use of
the 2016 updated URE for ethylene oxide for this regulatory action is
provided in section IV.C.3 in this preamble.)
    Lastly, the EPA is incorporating into the docket for this
rulemaking all materials associated with the development of the current
MON standards from Docket ID No. A-96-04 and Docket ID No. OAR-2003-
0121. Publicly available docket materials are available either
electronically at https://www.regulations.gov/ or 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>.

III. Analytical Procedures and Decision-Making

    In this section, we describe the analyses performed to support the
proposed decisions for the RTR and other issues addressed in this
proposal.

A. How do we consider risk in our decision-making?

    As discussed in section II.A of this preamble and in the Benzene
NESHAP, in evaluating and developing standards under CAA section
112(f)(2), we apply a two-step approach to determine whether or not
risks are acceptable and to determine if the standards provide an ample
margin of safety to protect public health. As explained in the Benzene
NESHAP, ``the first step judgment on acceptability cannot be reduced to
any single factor'' and, thus, ``[t]he Administrator believes that the
acceptability of risk under section 112 is best judged on the basis of
a broad set of health risk measures and information.'' 54 FR 38046,
September 14, 1989. Similarly, with regard to the ample margin of
safety determination, ``the Agency again considers all of the health
risk and other health information considered in the first step. Beyond
that information, additional factors relating to the appropriate level
of control will also be considered, including cost and economic impacts
of controls, technological feasibility, uncertainties, and any other
relevant factors.'' Id.
The Benzene NESHAP approach provides flexibility regarding factors the
EPA may consider in making determinations and how the EPA may weigh
those factors for each source category. The EPA conducts a risk
assessment that provides estimates of the MIR posed by the HAP
emissions from each source in the source category, the hazard index
(HI) for chronic exposures to HAP with the potential to cause noncancer
health effects, and the

hazard quotient (HQ) for acute exposures to HAP with the potential to
cause noncancer health effects.\4\ The assessment also provides
estimates of the distribution of cancer risk within the exposed
populations, cancer incidence, and an evaluation of the potential for
an adverse environmental effect. The scope of the EPA's risk analysis
is consistent with the EPA's response to comments on our policy under
the Benzene NESHAP where the EPA explained that:
---------------------------------------------------------------------------

    \4\ The MIR is defined as the cancer risk associated with a
lifetime of exposure at the highest concentration of HAP where
people are likely to live. The HQ is the ratio of the potential HAP
exposure concentration to the noncancer dose-response value; the HI
is the sum of HQs for HAP that affect the same target organ or organ
system.

``[t]he 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'.''

See 54 FR 38057, September 14, 1989. 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.
    The EPA notes that it has not considered certain health information
to date in making residual risk determinations. At this time, we do not
attempt to quantify the HAP risk that may be associated with emissions
from other facilities that do not include the source category under
review, mobile source emissions, natural source emissions, persistent
environmental pollution, or atmospheric transformation in the vicinity
of the sources in the category.
    The EPA understands the potential importance of considering an
individual's total exposure to HAP in addition to considering exposure
to HAP emissions from the source category and facility. We recognize
that such consideration may be particularly important when assessing
noncancer risk, where pollutant-specific exposure health reference
levels (e.g., reference concentrations (RfCs)) are based on the
assumption that thresholds exist for adverse health effects. For
example, the EPA recognizes that, although exposures attributable to
emissions from a source category or facility alone may not indicate the
potential for increased risk of adverse noncancer health effects in a
population, the exposures resulting from emissions from the facility in
combination with emissions from all of the other sources (e.g., other
facilities) to which an individual is exposed may be sufficient to
result in an increased risk of adverse noncancer health effects. In May
2010, the Science Advisory Board (SAB) advised the EPA ``that RTR
assessments will be most useful to decision makers and communities if
results are presented in the broader context of aggregate and
cumulative risks, including background concentrations and contributions
from other sources in the area.'' \5\
---------------------------------------------------------------------------

    \5\ Recommendations of the SAB Risk and Technology Review
Methods Panel are provided in their report, which is available at:
https://yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.
---------------------------------------------------------------------------

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

B. How do we perform the technology review?

    Our technology review focuses on the identification and evaluation
of developments in practices, processes, and control technologies that
have occurred since the MACT standards were promulgated. Where we
identify such developments, we analyze their technical feasibility,
estimated costs, energy implications, and non-air environmental
impacts. We also consider the emission reductions associated with
applying each development. This analysis informs our decision of
whether it is ``necessary'' to revise the emissions standards. In
addition, we consider the appropriateness of applying controls to new
sources versus retrofitting existing sources. For this exercise, we
consider any of the following to be a ``development'':
     Any add-on control technology or other equipment that was
not identified and considered during development of the original MACT
standards;
     Any improvements in add-on control technology or other
equipment (that were identified and considered during development of
the original

MACT standards) that could result in additional emissions reduction;
     Any work practice or operational procedure that was not
identified or considered during development of the original MACT
standards;
     Any process change or pollution prevention alternative
that could be broadly applied to the industry and that was not
identified or considered during development of the original MACT
standards; and
     Any significant changes in the cost (including cost-
effectiveness) of applying controls (including controls the EPA
considered during the development of the original MACT standards).
    In addition to reviewing the practices, processes, and control
technologies that were considered at the time we originally developed
(or last updated) the NESHAP, we review a variety of data sources in
our investigation of potential practices, processes, or controls to
consider. See sections II.C and II.D of this preamble for information
on the specific data sources that were reviewed as part of the
technology review.

C. How do we estimate post-MACT risk posed by the source category?

    In this section, we provide a complete description of the types of
analyses that we generally perform during the risk assessment process.
In some cases, we do not perform a specific analysis because it is not
relevant. For example, in the absence of emissions of HAP known to be
persistent and bioaccumulative in the environment (PB-HAP), we would
not perform a multipathway exposure assessment. Where we do not perform
an analysis, we state that we do not and provide the reason. While we
present all of our risk assessment methods, we only present risk
assessment results for the analyses actually conducted (see section
IV.B of this preamble).
    The EPA conducts a risk assessment that provides estimates of the
MIR for cancer posed by the HAP emissions from each source in the
source category, the HI for chronic exposures to HAP with the potential
to cause noncancer health effects, and the HQ for acute exposures to
HAP with the potential to 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 which provides more information on the risk
assessment inputs and models: Residual Risk Assessment for the
Miscellaneous Organic Chemical Manufacturing Source Category in Support
of the 2019 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; \6\ and described in the SAB review
report issued in 2010. They are also consistent with the key
recommendations contained in that report.
---------------------------------------------------------------------------

    \6\ U.S. EPA. Risk and Technology Review (RTR) Risk Assessment
Methodologies: For Review by the EPA's Science Advisory Board with
Case Studies--MACT I Petroleum Refining Sources and Portland Cement
Manufacturing, June 2009. EPA-452/R-09-006. https://www3.epa.gov/airtoxics/rrisk/rtrpg.html.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions
release characteristics?
    The MON facility list was developed as described in section II.C of
this preamble and consists of 201 facilities. The emissions modeling
input files were developed using the EPA's 2014 NEI. Two modeling input
files were developed, one that contains the whole facility emissions
and one that contains only emissions from MON processes, or the source
category. For the 201 MON facilities, only 197 had reported HAP
emissions in the 2014 NEI. Of the four facilities without HAP
emissions, two had reported no HAP data to the 2014 NEI and two had no
Emissions Inventory System (EIS) ID and, therefore, no emissions data
to pull from the NEI. Of the 197 facilities with reported HAP
emissions, three facilities did not report any HAP emissions that could
be identified as attributed to MON processes and, therefore, emissions
data for these three facilities could not be modeled. Therefore, due to
lack of available data, source category risk modeling was not conducted
for seven of the 201 MON facilities, which could potentially result in
an underestimation of risk for the source category. The complete MON
facility list is available in Appendix 1 of the document titled
Residual Risk Assessment for the Miscellaneous Organic Chemical
Manufacturing Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule, which is available in the docket for
this rulemaking.
    The EPA created the whole facility modeling file using all HAP
emissions records from the 2014 NEI for the list of 197 EIS IDs which
had available HAP data. The NEI 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 EPA then created the source category modeling input file by
identifying the specific NEI emissions records in the whole facility
modeling input file that are subject to the MON by reviewing the
facilities' title V air permits, unit source classification code (SCC),
emission unit descriptions, and process descriptions. The EPA also used
SCC codes, emission unit descriptions, and process descriptions to
identify units that are not subject to the MON (e.g., boilers, engines,
etc.) and removed them from the source category modeling file. In
general, ambiguous NEI records were assumed to be subject to the MON to
be conservatively inclusive, with the intention of verifying the rule
applicability later if the risk analysis revealed these unit emissions
to be risk drivers for the source category. As mentioned previously, of
the 197 facilities with reported HAP emissions at the whole facility
level, three facilities did not report any HAP emissions that could be
identified as attributed to MON processes and, therefore, emissions
data for 194 facilities was included in the source category modeling
file. After determining which NEI records were subject to the MON, the
record was assigned to an emission process group, identified in Table
2.

  Table 2--Emission Process Groups Related to the Miscellaneous Organic
                 Chemical Manufacturing Source Category
------------------------------------------------------------------------
                                               Emission process group
  Emission process group abbreviation \1\          description \1\
------------------------------------------------------------------------
PV........................................  Process Vent.
ST........................................  Storage Tank.
TR........................................  Transfer Operation.
HE........................................  Heat Exchange System.
EL........................................  Equipment Leak.
WS........................................  Wastewater.
FL........................................  Flare.
IN \2\....................................  Potential MON Process
                                             Group.\2\
UK \3\....................................  Unknown Process Group.\3\
OT \4\....................................  Non-MON Process Group.\4\
------------------------------------------------------------------------
\1\ Sometimes the record includes co-mingled emissions from more than
  one emission process group due to a shared control device.

\2\ These are emission records at the facility from sources that may
  potentially be subject to the MON, based on their SCC code, emission
  unit description, or process description, but could not be verified
  due to lack of available information.
\3\ These are emission records at the facility from sources that are
  subject to the MON but lack specific details in the NEI record to
  allow identification of an appropriate emission process group.
\4\ These are emission records at the facility from sources that are not
  subject to the MON. Therefore, this emission process group will only
  appear in the whole facility modeling file, and not in the source
  category modeling file.

    The RTR emissions dataset 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 within
the fenceline of the facility. 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 re-located 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 the air permit was used to try and determine the
permitted value. If this information could not be found within the air
permit, then a surrogate value was assigned based on either the NAICS
code, the regulatory code, or the SCC. 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 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 defaulted values.
    In some cases, the EPA coordinated with Regional offices, state
agencies, and/or industry on a specific emission record if it was
unknown whether the emissions belonged to a MON process and preliminary
risk analysis indicated that this pollutant might be a risk driver.
This specific inquiry was done to ensure that only MON emissions were
included in the source category modeling file. To further improve the
quality of the modeling file, in September 2017, the EPA provided
member companies of ACC and ACA with the emissions modeling input
records. The emissions records were also sent directly to several
companies. This allowed companies the opportunity to review and revise
emission values, emission release point parameters, and coordinates, as
needed. Any changes received between September 2017 and November 2018
were incorporated into the RTR modeling file. Changes received after
November 2018 will be considered for incorporation in the final rule. A
list of responses received from the Regional offices, state agencies,
and chemical companies can be found in Appendix 1 of the document
titled Residual Risk Assessment for the Miscellaneous Organic Chemical
Manufacturing Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule, which is available in the docket for
this rulemaking. This memorandum provides a description of the
information received, the file name of the response received, and
details on how the information was used to supplement the modeling
file. This memorandum also provides records of all changes made to the
source category and whole facility modeling input files throughout the
quality assurance and quality control process, and additional details
on the data and methods used to develop actual emissions estimates for
the risk modeling, including the EPA's quality assurance review.
2. How did we estimate MACT-allowable emissions?
    The available emissions data in the RTR emissions dataset include
estimates of the mass of HAP emitted during a specified annual time
period. These ``actual'' emission levels are often lower than the
emission levels allowed under the requirements of the current MACT
standards. The emissions allowed under the MACT standards are referred
to as the ``MACT-allowable'' emissions. We discussed the consideration
of both MACT-allowable and actual emissions in the final Coke Oven
Batteries RTR (70 FR 19998-19999, April 15, 2005) and in the proposed
and final Hazardous Organic NESHAP RTR (71 FR 34428, June 14, 2006, and
71 FR 76609, December 21, 2006, respectively). In those actions, we
noted that assessing the risk at the MACT-allowable level is inherently
reasonable since that risk reflects the maximum level facilities could
emit and still comply with national emission standards. We also
explained that it is reasonable to consider actual emissions, where
such data are available, in both steps of the risk analysis, in
accordance with the Benzene NESHAP approach. (54 FR 38044, September
14, 1989.)
    For this analysis, we have determined that the actual emissions
data are reasonable estimates of the MACT-allowable emissions levels
for the Miscellaneous Organic Chemical Manufacturing source category.
The ability to estimate MACT-allowable emissions from the actual
emissions dataset is largely dependent on the format of the standard
for a given emissions source as well as the types of controls employed
for the source. For further details on the assumptions and
methodologies used to estimate MACT-allowable emissions, see Appendix 1
of the document titled Residual Risk Assessment for the Miscellaneous
Organic Chemical Manufacturing Source Category in Support of the 2019
Risk and Technology Review Proposed Rule, which is available in the
docket for this rulemaking.
3. How do we conduct dispersion modeling, determine inhalation
exposures, and estimate individual and population inhalation risk?
    Both long-term and short-term inhalation exposure concentrations
and health risk from the source category addressed in this proposal
were estimated using the Human Exposure Model (HEM-3).\7\ The HEM-3
performs three primary risk assessment activities: (1) Conducting
dispersion modeling to estimate the concentrations of HAP in ambient
air, (2) estimating long-term and short-term inhalation exposures to
individuals residing within 50 kilometers (km) of the modeled sources,
and (3) estimating individual and population-level inhalation risk
using the exposure estimates and quantitative dose-response
information.
---------------------------------------------------------------------------

    \7\ For more information about HEM-3, go to https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem.
---------------------------------------------------------------------------

a. Dispersion Modeling
    The air dispersion model AERMOD, used by the HEM-3 model, is one of
the EPA's preferred models for assessing air pollutant concentrations
from industrial facilities.\8\ To perform the dispersion modeling and
to develop the

preliminary risk estimates, HEM-3 draws on three data libraries. The
first is a library of meteorological data, which is used for dispersion
calculations. This library includes 1 year (2016) of hourly surface and
upper air observations from 824 meteorological stations, selected to
provide coverage of the United States and Puerto Rico. A second library
of United States Census Bureau census block \9\ internal point
locations and populations provides the basis of human exposure
calculations (U.S. Census, 2010). In addition, for each census block,
the census library includes the elevation and controlling hill height,
which are also used in dispersion calculations. A third library of
pollutant-specific dose-response values is used to estimate health
risk. These are discussed below.
---------------------------------------------------------------------------

    \8\ U.S. EPA. Revision to the Guideline on Air Quality Models:
Adoption of a Preferred General Purpose (Flat and Complex Terrain)
Dispersion Model and Other Revisions (70 FR 68218, November 9,
2005).
    \9\ A census block is the smallest geographic area for which
census statistics are tabulated.
---------------------------------------------------------------------------

b. Risk From Chronic Exposure to HAP
    In developing the risk assessment for chronic exposures, we use the
estimated annual average ambient air concentrations of each HAP emitted
by each source in the source category. The HAP air concentrations at
each nearby census block centroid located within 50 km of the facility
are a surrogate for the chronic inhalation exposure concentration for
all the people who reside in that census block. A distance of 50 km is
consistent with both the analysis supporting the 1989 Benzene NESHAP
(54 FR 38044, September 14, 1989) and the limitations of Gaussian
dispersion models, including AERMOD.
    For each facility, we calculate the MIR as the cancer risk
associated with a continuous lifetime (24 hours per day, 7 days per
week, 52 weeks per year, 70 years) exposure to the maximum
concentration at the centroid of each inhabited census block. We
calculate individual cancer risk by multiplying the estimated lifetime
exposure to the ambient concentration of each HAP (in micrograms per
cubic meter ([mu]g/m\3\)) by its URE. The URE is an upper-bound
estimate of an individual's incremental risk of contracting cancer over
a lifetime of exposure to a concentration of 1 microgram of the
pollutant per cubic meter of air. For residual risk assessments, we
generally use UREs from the EPA's Integrated Risk Information System
(IRIS). For carcinogenic pollutants without IRIS values, we look to
other reputable sources of cancer dose-response values, often using
California EPA (CalEPA) UREs, where available. In cases where new,
scientifically credible dose-response values have been developed in a
manner consistent with EPA guidelines and have undergone a peer review
process similar to that used by the EPA, we may use such dose-response
values in place of, or in addition to, other values, if appropriate.
The pollutant-specific dose-response values used to estimate cancer
health risk are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
    To estimate individual lifetime cancer risks associated with
exposure to HAP emissions from each facility in the source category, we
sum the risks for each of the carcinogenic HAP \10\ emitted by the
modeled facility. We estimate cancer risk at every census block within
50 km of every facility in the source category. The MIR is the highest
individual lifetime cancer risk estimated for any of those census
blocks. In addition to calculating the MIR, we estimate the
distribution of individual cancer risks for the source category by
summing the number of individuals within 50 km of the sources whose
estimated risk falls within a specified risk range. We also estimate
annual cancer incidence by multiplying the estimated lifetime cancer
risk at each census block by the number of people residing in that
block, summing results for all of the census blocks, and then dividing
this result by a 70-year lifetime.
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    \10\ The EPA's 2005 Guidelines for Carcinogen Risk Assessment
classifies carcinogens as: ``carcinogenic to humans,'' ``likely to
be carcinogenic to humans,'' and ``suggestive evidence of
carcinogenic potential.'' These classifications also coincide with
the terms ``known carcinogen, probable carcinogen, and possible
carcinogen,'' respectively, which are the terms advocated in the
EPA's Guidelines for Carcinogen Risk Assessment, published in 1986
(51 FR 33992, September 24, 1986). In August 2000, the document,
Supplemental Guidance for Conducting Health Risk Assessment of
Chemical Mixtures (EPA/630/R-00/002), was published as a supplement
to the 1986 document. Copies of both documents can be obtained from
https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944. Summing
the risk of these individual compounds to obtain the cumulative
cancer risk is an approach that was recommended by the EPA's SAB in
their 2002 peer review of the EPA's National Air Toxics Assessment
(NATA) titled NATA--Evaluating the National-scale Air Toxics
Assessment 1996 Data--an SAB Advisory, available at https://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
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    To assess the risk of noncancer health effects from chronic
exposure to HAP, we calculate either an HQ or a target organ-specific
hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is
emitted. Where more than one noncancer HAP is emitted, we sum the HQ
for each of the HAP that affects a common target organ or target organ
system to obtain a TOSHI. The HQ is the estimated exposure divided by
the chronic noncancer dose-response value, which is a value selected
from one of several sources. The preferred chronic noncancer dose-
response value is the EPA RfC, defined as ``an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure to the human population (including sensitive
subgroups) that is likely to be without an appreciable risk of
deleterious effects during a lifetime'' (https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary). In cases where an RfC
from the EPA's IRIS is not available or where the EPA determines that
using a value other than the RfC is appropriate, the chronic noncancer
dose-response value can be a value from the following prioritized
sources, which define their dose-response values similarly to the EPA:
(1) The Agency for Toxic Substances and Disease Registry (ATSDR)
Minimum Risk Level (https://www.atsdr.cdc.gov/mrls/index.asp); (2) the
CalEPA Chronic Reference Exposure Level (REL) (https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0); or (3) as noted above, a scientifically
credible dose-response value that has been developed in a manner
consistent with the EPA guidelines and has undergone a peer review
process similar to that used by the EPA. The pollutant-specific dose-
response values used to estimate chronic noncancer 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. In this proposed rulemaking, as part of our efforts
to continually improve our methodologies to evaluate the risks that HAP
emitted from categories of industrial sources pose to human health and
the

environment,\11\ we are revising our treatment of meteorological data
to use reasonable worst-case air dispersion conditions in our acute
risk screening assessments instead of worst-case air dispersion
conditions. This revised treatment of meteorological data and the
supporting rationale are described in more detail in Residual Risk
Assessment for the Miscellaneous Organic Chemical Manufacturing Source
Category in Support of the 2019 Risk and Technology Review Proposed
Rule and in Appendix 5 of the report: Technical Support Document for
Acute Risk Screening Assessment. We will be applying this revision in
RTR rulemakings proposed on or after June 3, 2019.
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    \11\ See, e.g., U.S. EPA. Screening Methodologies to Support
Risk and Technology Reviews (RTR): A Case Study Analysis, Draft
Report, May 2017. https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.
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    To assess the potential acute risk to the maximally exposed
individual, we use the peak hourly emission rate for each emission
point,\12\ reasonable worst-case air dispersion conditions (i.e., 99th
percentile), and the point of highest off-site exposure. Specifically,
we assume that peak emissions from the source category and reasonable
worst-case air dispersion conditions co-occur and that a person is
present at the point of maximum exposure.
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    \12\ In the absence of hourly emission data, we develop
estimates of maximum hourly emission rates by multiplying the
average actual annual emissions rates by a factor (either a
category-specific factor or a default factor of 10) to account for
variability. This is documented in Residual Risk Assessment for
Miscellaneous Organic Chemical Manufacturing Source Category in
Support of the 2019 Risk and Technology Review Proposed Rule and in
Appendix 5 of the report: Technical Support Document for Acute Risk
Screening Assessment. Both are available in the docket for this
rulemaking.
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    To characterize the potential health risks associated with
estimated acute inhalation exposures to a HAP, we generally use
multiple acute dose-response values, including acute RELs, acute
exposure guideline levels (AEGLs), and emergency response planning
guidelines (ERPG) for 1-hour exposure durations, if available, to
calculate acute HQs. The acute HQ is calculated by dividing the
estimated acute exposure concentration by the acute dose-response
value. For each HAP for which acute dose-response values are available,
the EPA calculates acute HQs.
    An acute REL is defined as ``the concentration level at or below
which no adverse health effects are anticipated for a specified
exposure duration.'' \13\ Acute RELs are based on the most sensitive,
relevant, adverse health effect reported in the peer-reviewed medical
and toxicological literature. They are designed to protect the most
sensitive individuals in the population through the inclusion of
margins of safety. Because margins of safety are incorporated to
address data gaps and uncertainties, exceeding the REL does not
automatically indicate an adverse health impact. AEGLs represent
threshold exposure limits for the general public and are applicable to
emergency exposures ranging from 10 minutes to 8 hours.\14\ They are
guideline levels for ``once-in-a-lifetime, short-term exposures to
airborne concentrations of acutely toxic, high-priority chemicals.''
Id. at 21. The AEGL-1 is specifically defined as ``the airborne
concentration (expressed as ppm (parts per million) or mg/m\3\
(milligrams per cubic meter)) of a substance above which it is
predicted that the general population, including susceptible
individuals, could experience notable discomfort, irritation, or
certain asymptomatic nonsensory effects. However, the effects are not
disabling and are transient and reversible upon cessation of
exposure.'' The document also notes that ``Airborne concentrations
below AEGL-1 represent exposure levels that can produce mild and
progressively increasing but transient and nondisabling odor, taste,
and sensory irritation or certain asymptomatic, nonsensory effects.''
Id. AEGL-2 are defined as ``the airborne concentration (expressed as
parts per million or milligrams per cubic meter) of a substance above
which it is predicted that the general population, including
susceptible individuals, could experience irreversible or other
serious, long-lasting adverse health effects or an impaired ability to
escape.'' Id.
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    \13\ CalEPA issues acute RELs as part of its Air Toxics Hot
Spots Program, and the 1-hour and 8-hour values are documented in
Air Toxics Hot Spots Program Risk Assessment Guidelines, Part I, The
Determination of Acute Reference Exposure Levels for Airborne
Toxicants, which is available at https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary.
    \14\ National Academy of Sciences, 2001. Standing Operating
Procedures for Developing Acute Exposure Levels for Hazardous
Chemicals, page 2. Available at https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf. Note that the
National Advisory Committee for Acute Exposure Guideline Levels for
Hazardous Substances ended in October 2011, but the AEGL program
continues to operate at the EPA and works with the National
Academies to publish final AEGLs (https://www.epa.gov/aegl).
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    ERPGs are ``developed for emergency planning and are intended as
health-based guideline concentrations for single exposures to
chemicals.'' \15\ Id. at 1. The ERPG-1 is defined as ``the maximum
airborne concentration below which it is believed that nearly all
individuals could be exposed for up to 1 hour without experiencing
other than mild transient adverse health effects or without perceiving
a clearly defined, objectionable odor.'' Id. at 2. Similarly, the ERPG-
2 is defined as ``the maximum airborne concentration below which it is
believed that nearly all individuals could be exposed for up to one
hour without experiencing or developing irreversible or other serious
health effects or symptoms which could impair an individual's ability
to take protective action.'' Id. at 1.
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    \15\ ERPGS Procedures and Responsibilities. March 2014. American
Industrial Hygiene Association. Available at: https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf.
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    An acute REL for 1-hour exposure durations is typically lower than
its corresponding AEGL-1 and ERPG-1. Even though their definitions are
slightly different, AEGL-1s are often the same as the corresponding
ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from
our acute inhalation screening risk assessment typically result when we
use the acute REL for a HAP. In cases where the maximum acute HQ
exceeds 1, we also report the HQ based on the next highest acute dose-
response value (usually the AEGL-1 and/or the ERPG-1).
    For the acute inhalation risk assessment of the Miscellaneous
Organic Chemical Manufacturing source category, we used process level-
specific acute emissions multipliers, ranging from a factor of 2 to 10.
In general, hourly emissions estimates were based on peak-to-mean
ratios for 37 emission process groups, with emissions from transfer
racks and other emission process groups where sufficient information
did not exist to adequately assess peak hourly emissions (e.g., flares
controlling various unknown emissions sources) having the highest
hourly peak emissions at a factor of 10 times the annual average. A
further discussion of why these factors were selected can be found in
Appendix 1 of the document titled Residual Risk Assessment for the
Miscellaneous Organic Chemical Manufacturing Source Category in Support
of the 2019 Risk and Technology Review Proposed Rule, which is
available in the docket for this rulemaking.
    In our acute inhalation screening risk assessment, acute impacts
are deemed negligible for HAP for which acute HQs are less than or
equal to 1, and no further analysis is performed for these

HAP. In cases where an acute HQ from the screening step is greater than
1, we assess the site-specific data to ensure that the acute HQ is at
an off-site location. For this source category, the data refinements
employed consisted of ensuring the locations where the maximum HQ
occurred were off facility property and where the public could
potentially be exposed. These refinements are discussed more fully in
the Residual Risk Assessment for the Miscellaneous Organic Chemical
Manufacturing Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule, which is available in the docket for
this source category.
4. How do we conduct the multipathway exposure and risk screening
assessment?
    The EPA conducts a tiered screening assessment examining the
potential for significant human health risks due to exposures via
routes other than inhalation (i.e., ingestion). We first determine
whether any sources in the source category emit any HAP known to be
persistent and bioaccumulative in the environment, as identified in the
EPA's Air Toxics Risk Assessment Library (see Volume 1, Appendix D, at
https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Miscellaneous Organic Chemical Manufacturing source
category, we identified PB-HAP emissions of polycyclic organic matter
(POM) (of which polycyclic aromatic hydrocarbons is a subset), lead
compounds, mercury compounds, cadmium compounds, and arsenic compounds,
so we proceeded to the next step of the evaluation. Except for lead,
the human health risk screening assessment for PB-HAP consists of three
progressive tiers. In a Tier 1 screening assessment, we determine
whether the magnitude of the facility-specific emissions of PB-HAP
warrants further evaluation to characterize human health risk through
ingestion exposure. To facilitate this step, we evaluate emissions
against previously developed screening threshold emission rates for
several PB-HAP that are based on a hypothetical upper-end screening
exposure scenario developed for use in conjunction with the EPA's Total
Risk Integrated Methodology.Fate, Transport, and Ecological Exposure
(TRIM.FaTE) model. The PB-HAP with screening threshold emission rates
are arsenic compounds, cadmium compounds, chlorinated dibenzodioxins
and furans, mercury compounds, and POM. Based on the EPA estimates of
toxicity and bioaccumulation potential, these pollutants represent a
conservative list for inclusion in multipathway risk assessments for
RTR rules. (See Volume 1, Appendix D at https://www.epa.gov/sites/production/files/2013-08/documents/volume_1_reflibrary.pdf). In this
assessment, we compare the facility-specific emission rates of these
PB-HAP to the screening threshold emission rates for each PB-HAP to
assess the potential for significant human health risks via the
ingestion pathway. We call this application of the TRIM.FaTE model the
Tier 1 screening assessment. The ratio of a facility's actual emission
rate to the Tier 1 screening threshold emission rate is a ``screening
value'' (SV).
    We derive the Tier 1 screening threshold emission rates for these
PB-HAP (other than lead compounds) to correspond to a maximum excess
lifetime cancer risk of 1-in-1 million (i.e., for arsenic compounds,
polychlorinated dibenzodioxins and furans and POM) or, for HAP that
cause noncancer health effects (i.e., cadmium compounds and mercury
compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP
or combination of carcinogenic PB-HAP in the Tier 1 screening
assessment exceeds the Tier 1 screening threshold emission rate for any
facility (i.e., the SV is greater than 1), we conduct a second
screening assessment, which we call the Tier 2 screening assessment.
The Tier 2 screening assessment separates the Tier 1 combined fisher
and farmer exposure scenario into fisher, farmer, and gardener
scenarios that retain upper-bound ingestion rates.
    In the Tier 2 screening assessment, the location of each facility
that exceeds a Tier 1 screening threshold emission rate is used to
refine the assumptions associated with the Tier 1 fisher and farmer
exposure scenarios at that facility. A key assumption in the Tier 1
screening assessment is that a lake and/or farm is located near the
facility. As part of the Tier 2 screening assessment, we use a U.S.
Geological Survey (USGS) database to identify actual waterbodies within
50 km of each facility and assume the fisher only consumes fish from
lakes within that 50 km zone. We also examine the differences between
local meteorology near the facility and the meteorology used in the
Tier 1 screening assessment. We then adjust the previously-developed
Tier 1 screening threshold emission rates for each PB-HAP for each
facility based on an understanding of how exposure concentrations
estimated for the screening scenario change with the use of local
meteorology and USGS lakes database.
    In the Tier 2 farmer scenario, we maintain an assumption that the
farm is located within 0.5 km of the facility and that the farmer
consumes meat, eggs, dairy, vegetables, and fruit produced near the
facility. We may further refine the Tier 2 screening analysis by
assessing a gardener scenario to characterize a range of exposures,
with the gardener scenario being more plausible in RTR evaluations.
Under the gardener scenario, we assume the gardener consumes home-
produced eggs, vegetables, and fruit products at the same ingestion
rate as the farmer. The Tier 2 screen continues to rely on the high-end
food intake assumptions that were applied in Tier 1 for local fish
(adult female angler at 99th percentile fish consumption \16\) and
locally grown or raised foods (90th percentile consumption of locally
grown or raised foods for the farmer and gardener scenarios \17\). If
PB-HAP emission rates do not result in a Tier 2 SV greater than 1, we
consider those PB-HAP emissions to pose risks below a level of concern.
If the PB-HAP emission rates for a facility exceed the Tier 2 screening
threshold emission rates, we may conduct a Tier 3 screening assessment.
---------------------------------------------------------------------------

    \16\ Burger, J. 2002. Daily consumption of wild fish and game:
Exposures of high end recreationists. International Journal of
Environmental Health Research 12:343-354.
    \17\ U.S. EPA. Exposure Factors Handbook 2011 Edition (Final).
U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/
052F, 2011.
---------------------------------------------------------------------------

    There are several analyses that can be included in a Tier 3
screening assessment, depending upon the extent of refinement
warranted, including validating that the lakes are fishable, locating
residential/garden locations for urban and/or rural settings,
considering plume-rise to estimate emissions lost above the mixing
layer, and considering hourly effects of meteorology and plume rise on
chemical fate and transport (a time-series analysis). If necessary, the
EPA may further refine the screening assessment through a site-specific
assessment.
    In evaluating the potential multipathway risk from emissions of
lead compounds, rather than developing a screening threshold emission
rate, we compare maximum estimated chronic inhalation exposure
concentrations to the level of the current National Ambient Air Quality
Standard (NAAQS) for lead.\18\ Values below the level of the

primary (health-based) lead NAAQS are considered to have a low
potential for multipathway risk.
---------------------------------------------------------------------------

    \18\ In doing so, the EPA notes that the legal standard for a
primary NAAQS--that a standard is requisite to protect public health
and provide an adequate margin of safety (CAA section 109(b))--
differs from the CAA section 112(f) standard (requiring, among other
things, that the standard provide an ``ample margin of safety to
protect public health''). However, the primary lead NAAQS is a
reasonable measure of determining risk acceptability (i.e., the
first step of the Benzene NESHAP analysis) since it is designed to
protect the most susceptible group in the human population--
children, including children living near major lead emitting
sources. 73 FR 67002/3; 73 FR 67000/3; 73 FR 67005/1. In addition,
applying the level of the primary lead NAAQS at the risk
acceptability step is conservative, since that primary lead NAAQS
reflects an adequate margin of safety.
---------------------------------------------------------------------------

    For further information on the multipathway assessment approach,
see the Residual Risk Assessment for the Miscellaneous Organic Chemical
Manufacturing Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule, which is available in the docket for
this action.
5. How do we assess risks considering emissions control options?
    In addition to assessing baseline inhalation risks and screening
for potential multipathway risks, we also estimate risks considering
the potential emission reductions that would be achieved by the control
options under consideration. In these cases, the expected emission
reductions are applied to the specific HAP and emission points in the
RTR emissions dataset to develop corresponding estimates of risk and
incremental risk reductions.
6. How do we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect, Environmental HAP, and Ecological
Benchmarks
    The EPA conducts a screening assessment to examine the potential
for an adverse environmental effect as required under section
112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines ``adverse
environmental effect'' as ``any significant and widespread adverse
effect, which may reasonably be anticipated, to wildlife, aquatic life,
or other natural resources, including adverse impacts on populations of
endangered or threatened species or significant degradation of
environmental quality over broad areas.''
    The EPA focuses on eight HAP, which are referred to as
``environmental HAP,'' in its screening assessment: Six PB-HAP and two
acid gases. The PB-HAP included in the screening assessment are arsenic
compounds, cadmium compounds, dioxins/furans, POM, mercury (both
inorganic mercury and methyl mercury), and lead compounds. The acid
gases included in the screening assessment are hydrochloric acid (HCl)
and hydrogen fluoride (HF).
    HAP that persist and bioaccumulate are of particular environmental
concern because they accumulate in the soil, sediment, and water. The
acid gases, HCl and HF, are included due to their well-documented
potential to cause direct damage to terrestrial plants. In the
environmental risk screening assessment, we evaluate the following four
exposure media: Terrestrial soils, surface water bodies (includes
water-column and benthic sediments), fish consumed by wildlife, and
air. Within these four exposure media, we evaluate nine ecological
assessment endpoints, which are defined by the ecological entity and
its attributes. For PB-HAP (other than lead), both community-level and
population-level endpoints are included. For acid gases, the ecological
assessment evaluated is terrestrial plant communities.
    An ecological benchmark represents a concentration of HAP that has
been linked to a particular environmental effect level. For each
environmental HAP, we identified the available ecological benchmarks
for each assessment endpoint. We identified, where possible, ecological
benchmarks at the following effect levels: Probable effect levels,
lowest-observed-adverse-effect level, and no-observed-adverse-effect
level. In cases where multiple effect levels were available for a
particular PB-HAP and assessment endpoint, we use all of the available
effect levels to help us to determine whether ecological risks exist
and, if so, whether the risks could be considered significant and
widespread.
    For further information on how the environmental risk screening
assessment was conducted, including a discussion of the risk metrics
used, how the environmental HAP were identified, and how the ecological
benchmarks were selected, see Appendix 9 of the Residual Risk
Assessment for the Miscellaneous Organic Chemical Manufacturing Source
Category in Support of the 2019 Risk and Technology Review Proposed
Rule, which is available in the docket for this action.
b. Environmental Risk Screening Methodology
    For the environmental risk screening assessment, the EPA first
determined whether any facilities in the Miscellaneous Organic Chemical
Manufacturing source category emitted any of the environmental HAP. For
the Miscellaneous Organic Chemical Manufacturing source category, we
identified emissions of POM, lead compounds, mercury compounds, cadmium
compounds, arsenic compounds, HCl, and HF. Because one or more of the
environmental HAP evaluated are emitted by at least one facility in the
source category, we proceeded to the second step of the evaluation.
c. PB-HAP Methodology
    The environmental screening assessment includes six PB-HAP, arsenic
compounds, cadmium compounds, dioxins/furans, POM, mercury (both
inorganic mercury and methyl mercury), and lead compounds. With the
exception of lead, the environmental risk screening assessment for PB-
HAP consists of three tiers. The first tier of the environmental risk
screening assessment uses the same health-protective conceptual model
that is used for the Tier 1 human health screening assessment.
TRIM.FaTE model simulations were used to back-calculate Tier 1
screening threshold emission rates. The screening threshold emission
rates represent the emission rate in tons of pollutant per year that
results in media concentrations at the facility that equal the relevant
ecological benchmark. To assess emissions from each facility in the
category, the reported emission rate for each PB-HAP was compared to
the Tier 1 screening threshold emission rate for that PB-HAP for each
assessment endpoint and effect level. If emissions from a facility do
not exceed the Tier 1 screening threshold emission rate, the facility
``passes'' the screening assessment, and, therefore, is not evaluated
further under the screening approach. If emissions from a facility
exceed the Tier 1 screening threshold emission rate, we evaluate the
facility further in Tier 2.
    In Tier 2 of the environmental screening assessment, the screening
threshold emission rates are adjusted to account for local meteorology
and the actual location of lakes in the vicinity of facilities that did
not pass the Tier 1 screening assessment. For soils, we evaluate the
average soil concentration for all soil parcels within a 7.5-km radius
for each facility and PB-HAP. For the water, sediment, and fish tissue
concentrations, the highest value for each facility for each pollutant
is used. If emission concentrations from a facility do not exceed the
Tier 2 screening threshold emission rate, the facility ``passes'' the
screening assessment and typically is not evaluated further. If
emissions from a

facility exceed the Tier 2 screening threshold emission rate, we
evaluate the facility further in Tier 3.
    As in the multipathway human health risk assessment, in Tier 3 of
the environmental screening assessment, we examine the suitability of
the lakes around the facilities to support life and remove those that
are not suitable (e.g., lakes that have been filled in or are
industrial ponds), adjust emissions for plume-rise, and conduct hour-
by-hour time-series assessments. If these Tier 3 adjustments to the
screening threshold emission rates still indicate the potential for an
adverse environmental effect (i.e., facility emission rate exceeds the
screening threshold emission rate), we may elect to conduct a more
refined assessment using more site-specific information. If, after
additional refinement, the facility emission rate still exceeds the
screening threshold emission rate, the facility may have the potential
to cause an adverse environmental effect.
    To evaluate the potential for an adverse environmental effect from
lead, we compared the average modeled air concentrations (from HEM-3)
of lead around each facility in the source category to the level of the
secondary NAAQS for lead. The secondary lead NAAQS is a reasonable
means of evaluating environmental risk because it is set to provide
substantial protection against adverse welfare effects which can
include ``effects on soils, water, crops, vegetation, man-made
materials, animals, wildlife, weather, visibility and climate, damage
to and deterioration of property, and hazards to transportation, as
well as effects on economic values and on personal comfort and well-
being.''
d. Acid Gas Environmental Risk Methodology
    The environmental screening assessment for acid gases evaluates the
potential phytotoxicity and reduced productivity of plants due to
chronic exposure to HF and HCl. The environmental risk screening
methodology for acid gases is a single-tier screening assessment that
compares modeled ambient air concentrations (from AERMOD) to the
ecological benchmarks for each acid gas. To identify a potential
adverse environmental effect (as defined in section 112(a)(7) of the
CAA) from emissions of HF and HCl, we evaluate the following metrics:
The size of the modeled area around each facility that exceeds the
ecological benchmark for each acid gas, in acres and km\2\; the
percentage of the modeled area around each facility that exceeds the
ecological benchmark for each acid gas; and the area-weighted average
SV around each facility (calculated by dividing the area-weighted
average concentration over the 50-km modeling domain by the ecological
benchmark for each acid gas). For further information on the
environmental screening assessment approach, see Appendix 9 of the
Residual Risk Assessment for the Miscellaneous Organic Chemical
Manufacturing Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule, which is available in the docket for
this action.
7. How do we conduct facility-wide assessments?
    To put the source category risks in context, we typically examine
the risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, we examine the HAP emissions not only from the
source category emission points of interest, but also emissions of HAP
from all other emission sources at the facility for which we have data.
For this source category, we conducted the facility-wide assessment
using a dataset compiled from the 2014 NEI. The source category records
of that NEI dataset were flagged within the dataset, as described in
section II.C of this preamble: What data collection activities were
conducted to support this action? Quality assurance and quality control
was performed on the whole facility dataset, which included the flagged
source category records. 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 Miscellaneous Organic Chemical Manufacturing Source
Category in Support of the 2019 Risk and Technology Review 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.
8. 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
Miscellaneous Organic Chemical Manufacturing Source Category in Support
of the 2019 Risk and Technology Review Proposed Rule, which is
available in the docket for this action. If a multipathway site-
specific assessment was performed for this source category, a full
discussion of the uncertainties associated with that assessment can be
found in Appendix 11 of that document, Site-Specific Human Health
Multipathway Residual Risk Assessment Report.
a. Uncertainties in the RTR Emissions Dataset
    Although the development of the RTR emissions dataset involved
quality assurance/quality control processes, the accuracy of emissions
values will vary depending on the source of the data, the degree to
which data are incomplete or missing, the degree to which assumptions
made to complete the datasets are accurate, errors in emission
estimates, and other factors. The emission estimates considered in this
analysis generally are annual totals for certain years, and they do not
reflect short-term fluctuations during the course of a year or
variations from year to year. The estimates of peak hourly emission
rates for the acute effects screening assessment were based on an
emission adjustment factor applied to the average annual hourly
emission rates, which are intended to account for emission fluctuations
due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration
estimates associated with any model, including

the EPA's recommended regulatory dispersion model, AERMOD. In using a
model to estimate ambient pollutant concentrations, the user chooses
certain options to apply. For RTR assessments, we select some model
options that have the potential to overestimate ambient air
concentrations (e.g., not including plume depletion or pollutant
transformation). We select other model options that have the potential
to underestimate ambient impacts (e.g., not including building
downwash). Other options that we select have the potential to either
under- or overestimate ambient levels (e.g., meteorology and receptor
locations). On balance, considering the directional nature of the
uncertainties commonly present in ambient concentrations estimated by
dispersion models, the approach we apply in the RTR assessments should
yield unbiased estimates of ambient HAP concentrations. We also note
that the selection of meteorology dataset location could have an impact
on the risk estimates. As we continue to update and expand our library
of meteorological station data used in our risk assessments, we expect
to reduce this variability.
c. Uncertainties in Inhalation Exposure Assessment
    Although every effort is made to identify all of the relevant
facilities and emission points, as well as to develop accurate
estimates of the annual emission rates for all relevant HAP, the
uncertainties in our emission inventory likely dominate the
uncertainties in the exposure assessment. Some uncertainties in our
exposure assessment include human mobility, using the centroid of each
census block, assuming lifetime exposure, and assuming only outdoor
exposures. For most of these factors, there is neither an under nor
overestimate when looking at the maximum individual risk or the
incidence, but the shape of the distribution of risks may be affected.
With respect to outdoor exposures, actual exposures may not be as high
if people spend time indoors, especially 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.\19\
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.\20\
Chronic noncancer RfC and reference dose (RfD) values represent chronic
exposure levels that are intended to be health-protective levels. To
derive dose-response values that are intended to be ``without
appreciable risk,'' the methodology relies upon an uncertainty factor
(UF) approach,\21\ 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.
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    \19\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \20\ An exception to this is the URE for benzene, which is
considered to cover a range of values, each end of which is
considered to be equally plausible, and which is based on maximum
likelihood estimates.
    \21\ See A Review of the Reference Dose and Reference
Concentration Processes, U.S. EPA, December 2002, and Methods for
Derivation of Inhalation Reference Concentrations and Application of
Inhalation Dosimetry, U.S. EPA, 1994.
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    Many of the UFs used to account for variability and uncertainty in
the development of acute dose-response values are quite similar to
those developed for chronic durations. Additional adjustments are often
applied to account for uncertainty in extrapolation from observations
at one exposure duration (e.g., 4 hours) to derive an acute dose-
response value at another exposure duration (e.g., 1 hour). Not all
acute dose-response values are developed for the same purpose, and care
must be taken when interpreting the results of an acute assessment of
human health effects relative to the dose-response value or values
being exceeded. Where relevant to the estimated exposures, the lack of
acute dose-response values at different levels of severity should be
factored into the risk characterization as potential uncertainties.
    Uncertainty also exists in the selection of ecological benchmarks
for the environmental risk screening assessment. We established a
hierarchy of preferred benchmark sources to allow selection of
benchmarks for each environmental HAP at each ecological assessment
endpoint. We searched for benchmarks for three effect levels (i.e., no-
effects level, threshold-effect level, and probable effect level), but
not all combinations of ecological assessment/environmental HAP had
benchmarks for all three effect levels. Where multiple effect levels
were available for a particular HAP and assessment endpoint, we used
all of the available effect levels to help us determine whether risk
exists and whether the risk could be considered significant and
widespread.
    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 emission 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. These two events are unlikely to occur at the same time,
making these assumptions conservative. 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 exposure
scenario. In most cases, it is unlikely that a person would be located
at the point of maximum exposure during the time when peak emissions
and reasonable worst-case air dispersion conditions occur
simultaneously.
f. Uncertainties in the Multipathway and Environmental Risk Screening
Assessments
    For each source category, we generally rely on site-specific levels
of PB-HAP or environmental HAP emissions to determine whether a refined
assessment of the impacts from multipathway exposures is necessary or
whether it is necessary to perform an environmental screening
assessment. This determination is based on the results of a three-
tiered screening assessment that relies on the outputs from models--
TRIM.FaTE and AERMOD--that estimate environmental pollutant
concentrations and human exposures for five PB-HAP (dioxins, POM,
mercury, cadmium, and arsenic) and two acid gases (HF and HCl). For
lead, we use AERMOD to determine ambient air concentrations, which are
then compared to the secondary NAAQS standard for lead. Two important
types of uncertainty associated with the use of these models in RTR
risk assessments and inherent to any assessment that relies on
environmental modeling are model uncertainty and input uncertainty.\22\
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    \22\ In the context of this discussion, the term ``uncertainty''
as it pertains to exposure and risk encompasses both variability in
the range of expected inputs and screening results due to existing
spatial, temporal, and other factors, as well as uncertainty in
being able to accurately estimate the true result.
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    Model uncertainty concerns whether the model adequately represents
the actual processes (e.g., movement and accumulation) that might occur
in the environment. For example, does the model adequately describe the
movement of a pollutant through the soil? This type of uncertainty is
difficult to quantify. However, based on feedback received from
previous EPA SAB reviews and other reviews, we are confident that the
models used in the screening assessments are appropriate and state-of-
the-art for the multipathway and environmental screening risk
assessments conducted in support of RTR.
    Input uncertainty is concerned with how accurately the models have
been configured and parameterized for the assessment at hand. For Tier
1 of the multipathway and environmental screening assessments, we
configured the models to avoid underestimating exposure and risk. This
was accomplished by selecting upper-end values from nationally
representative datasets for the more influential parameters in the
environmental model, including selection and spatial configuration of
the area of interest, lake location and size, meteorology, surface
water, soil characteristics, and structure of the aquatic food web. We
also assume an ingestion exposure scenario and values for human
exposure factors that represent reasonable maximum exposures.
    In Tier 2 of the multipathway and environmental screening
assessments, we refine the model inputs to account for meteorological
patterns in the vicinity of the facility versus using upper-end
national values, and we identify the actual location of lakes near the
facility rather than the default lake location that we apply in Tier 1.
By refining the screening approach in Tier 2 to account for local
geographical and meteorological data, we decrease the likelihood that
concentrations in environmental media are overestimated, thereby
increasing the usefulness of the screening assessment. In Tier 3 of the
screening assessments, we refine the model inputs again to account for
hour-by-hour plume rise and the height of the mixing layer. We can also
use those hour-by-hour meteorological data in a TRIM.FaTE run using the
screening configuration corresponding to the lake location. These
refinements produce a more accurate estimate of chemical concentrations
in the media of interest, thereby reducing the uncertainty with those
estimates. The assumptions and the associated uncertainties regarding
the selected ingestion exposure scenario are the same for all three
tiers.
    For the environmental screening assessment for acid gases, we
employ a single-tiered approach. We use the modeled air concentrations
and compare those with ecological benchmarks.
    For all tiers of the multipathway and environmental screening
assessments, our approach to addressing model input uncertainty is
generally cautious. We choose model inputs from the upper end of the
range of possible values for the influential parameters used in the
models, and we assume that the exposed individual exhibits ingestion
behavior that would lead to a high total exposure. This approach
reduces the likelihood of not identifying high risks for adverse
impacts.
    Despite the uncertainties, when individual pollutants or facilities
do not exceed screening threshold emission rates (i.e., screen out), we
are confident that the potential for adverse multipathway impacts on
human health is very low. On the other hand, when individual pollutants
or facilities do exceed screening threshold emission rates, it does not
mean that impacts are significant, only that we cannot rule out that
possibility and that a refined assessment for the site might be
necessary to obtain a more accurate risk characterization for the
source category.
    The EPA evaluates the following HAP in the multipathway and/or
environmental risk screening assessments, where applicable: Arsenic,
cadmium, dioxins/furans, lead, mercury (both inorganic and methyl
mercury), POM, HCl, and HF. These HAP represent pollutants that can
cause adverse impacts either through direct exposure to HAP in the air
or through exposure to HAP that are deposited from the air onto soils
and surface waters and then through the environment into the food web.
These HAP represent those HAP for which we can conduct a meaningful
multipathway

or environmental screening risk assessment. For other HAP not included
in our screening assessments, the model has not been parameterized such
that it can be used for that purpose. In some cases, depending on the
HAP, we may not have appropriate multipathway models that allow us to
predict the concentration of that pollutant. The EPA acknowledges that
other HAP beyond these that we are evaluating may have the potential to
cause adverse effects and, therefore, the EPA may evaluate other
relevant HAP in the future, as modeling science and resources allow.

IV. Analytical Results and Proposed Decisions

A. What actions are we taking in addition to those identified in the
risk and technology review?

    In addition to the proposed actions on the risk review and
technology review discussed further in this section, we are proposing
the following: (1) Adding monitoring and operational requirements for
flares that control ethylene oxide emissions and flares used to control
emissions from processes that produce olefins and polyolefins, with the
option for an owner or operator of a flare outside of this subset to
choose to opt in to the proposed requirements in lieu of complying with
the current flare standards, and (2) consistent with Sierra Club v.
EPA, 551 F.3d 1019 (D.C. Cir. 2008), ensuring that CAA section 112
standards apply continuously by proposing work practice standards for
periods of SSM for certain vent streams (i.e., PRD releases and
maintenance vents), and proposing clarifications for vent control
bypasses for certain vent streams (i.e., closed vent systems containing
bypass lines, and flares connected to fuel gas systems). The results
and proposed decisions based on the analyses performed pursuant to CAA
section 112(d)(2) and (3) are presented below.
1. Flares
    The EPA is proposing under CAA section 112(d)(2) and (3) to amend
the operating and monitoring requirements for a subset of flares used
as APCDs in the Miscellaneous Organic Chemical Manufacturing source
category because we have determined that the current requirements for
flares in this subset are not adequate to ensure the level of
destruction efficiency needed to conform with the MACT standards in the
MON. This subset includes flares that either (1) control ethylene oxide
emissions, (2) control emissions from processes that produce olefins,
or (3) control emissions from processes that produce polyolefins.
Flares falling into one of these categories are referred to as the
flare ``subset'' in this preamble, and for clarification, it is our
intention that, as part of this proposal, flares controlling propane
dehydrogenation (PDH) processes be included in this flare subset since
the PDH process produces olefins such as propylene. The EPA is also
proposing that, for flares outside of this subset, an owner or operator
may choose to comply with the updated standards in lieu of complying
with the current flare standards. Therefore, all proposed flare
standards in section IV.A.1 of this preamble are intended to apply to
only the specified flare subset and to flares at MON facilities where
the owner or operator has chosen to opt in to the proposed standards.
Flares outside of this subset, or at MON facilities where the owner or
operator has chosen not to opt in to the proposed standards, will be
subject to the current provisions for flares in the MON standard.
    The specified flare subset was selected on the basis that the
current requirements for flares may be inadequate to ensure the level
of destruction efficiency needed to conform with the MACT standards in
the MON. Flares are commonly used within the Miscellaneous Organic
Chemical Manufacturing source category. The requirements applicable to
flares, which are used to control emissions from various emission
sources in the Miscellaneous Organic Chemical Manufacturing source
category (e.g., process vents, storage tanks, transfer racks, equipment
leaks, wastewater streams), are set forth in the General Provisions to
40 CFR part 63 and are cross-referenced in 40 CFR part 63, subpart G
(for wastewater), and 40 CFR part 63, subpart SS (for process vents,
storage tanks, transfer racks, and equipment leaks). In general, flares
used as APCDs are expected to achieve 98-percent HAP destruction