[Federal Register Volume 83, Number 50 (Wednesday, March 14, 2018)]
[Proposed Rules]
[Pages 11314-11341]
[FR Doc No: 2018-04939]

Vol. 83

Wednesday,

No. 50

March 14, 2018

Part II

Environmental Protection Agency

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40 CFR Part 63

National Emission Standards for Hazardous Air Pollutants: Leather
Finishing Operations Residual Risk and Technology Review; Proposed Rule

Federal Register / Vol. 83 , No. 50 / Wednesday, March 14, 2018 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2003-0194; FRL-9975-21-OAR]
RIN 2060-AT70

National Emission Standards for Hazardous Air Pollutants: Leather
Finishing Operations Residual Risk and Technology Review

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing
amendments to the National Emission Standards for Hazardous Air
Pollutants (NESHAP) for Leather Finishing Operations to address the
results of the residual risk and technology review (RTR) that the EPA
is required to conduct in accordance with section 112 of the Clean Air
Act (CAA). We found risks due to emissions of air toxics to be
acceptable from this source category and determined that the current
NESHAP provides an ample margin of safety to protect public health. We
identified no new cost-effective controls under the technology review
to achieve further emissions reductions. Therefore, we are proposing no
revisions to the numerical emission limits based on these analyses.
However, the EPA is proposing amendments to regulatory provisions
pertaining to emissions during periods of startup, shutdown, and
malfunction (SSM); amendments to add electronic reporting; and
amendments to clarify certain rule requirements and provisions. While
the proposed amendments would not result in reductions in emissions of
hazardous air pollutants (HAP), this action, if finalized, would result
in improved compliance and implementation of the rule.

DATES: Comments. Comments must be received on or before April 30, 2018.
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 April 13, 2018.
    Public Hearing. If a public hearing is requested by March 19, 2018,
then we will hold a public hearing on March 29, 2018 at the location
described in the ADDRESSES section. The last day to pre-register in
advance to speak at the public hearing will be March 27, 2018.

ADDRESSES: Comments. Submit your comments, identified by Docket ID No.
EPA-HQ-OAR-2003-0194, at http://www.regulations.gov. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from Regulations.gov. Regulations.gov is our
preferred method of receiving comments. However, other submission
formats are accepted. To ship or send mail via the United States Postal
Service, use the following address: U.S. Environmental Protection
Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2003-0194, Mail
Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460. Use the
following Docket Center address if you are using express mail,
commercial delivery, hand delivery, or courier: EPA Docket Center, EPA
WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington,
DC 20004. Delivery verification signatures will be available only
during regular business hours.
    Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. See section I.C of this preamble
for instructions on submitting CBI.
    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://www2.epa.gov/dockets/commenting-epa-dockets.
    Public Hearing. If a public hearing is requested, it will be held
at EPA Headquarters, EPA WJC East Building, 1201 Constitution Avenue
NW, Washington, DC 20004. If a public hearing is requested, then we
will provide details about the public hearing on our Web site at:
https://www.epa.gov/stationary-sources-air-pollution/leather-finishing-operations-national-emission-standards-hazardous. The EPA does not
intend to publish another document in the Federal Register announcing
any updates on the request for a public hearing. Please contact Ms.
Aimee St. Clair at<PHONE_NUMBER> or by email at [email protected]
to request a public hearing, to register to speak at the public
hearing, or to inquire as to whether a public hearing will be held.
    The EPA will make every effort to accommodate all speakers who
arrive and register. If a hearing is held at a U.S. government
facility, individuals planning to attend should be prepared to show a
current, valid state- or federal-approved picture identification to the
security staff in order to gain access to the meeting room. An expired
form of identification will not be permitted. Please note that the Real
ID Act, passed by Congress in 2005, established new requirements for
entering federal facilities. If your driver's license is issued by a
noncompliant state, you must present an additional form of
identification to enter a federal facility. Acceptable alternative
forms of identification include: Federal employee badge, passports,
enhanced driver's licenses, and military identification cards.
Additional information on the Real ID Act is available at https://www.dhs.gov/real-id-frequently-asked-questions. In addition, you will
need to obtain a property pass for any personal belongings you bring
with you. Upon leaving the building, you will be required to return
this property pass to the security desk. No large signs will be allowed
in the building, cameras may only be used outside of the building, and
demonstrations will not be allowed on federal property for security
reasons.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Mr. Bill Schrock, Natural Resources Group, Sector
Policies and Programs Division (E143-03), 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 protected].
For specific information regarding the risk modeling methodology,
contact 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:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>; and email
address: [email protected]. For information about the applicability
of the NESHAP to a particular entity, contact John Cox, Office of
Enforcement and Compliance Assurance, U.S. Environmental Protection
Agency, EPA WJC South Building (Mail Code 2227A), 1200 Pennsylvania
Avenue NW,

Washington DC 20460; telephone number:<PHONE_NUMBER>; and email
address: [email protected].

SUPPLEMENTARY INFORMATION:
    Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2003-0194. All documents in the docket are
listed in the Regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., 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, EPA 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
(202) 566-1744, and the telephone number for the EPA Docket Center is
(202) 566-1742.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2003-0194. 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 http://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 http://www.regulations.gov or email. This
type of information should be submitted by mail as discussed in section
1.C of this preamble. The http://www.regulations.gov Web site is an
``anonymous access'' system, 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 http://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 disk or CD-ROM 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 http://www.epa.gov/dockets.
    Preamble Acronyms and Abbreviations. We use multiple acronyms and
terms in this preamble. While this list may not be exhaustive, to ease
the reading of this preamble and for reference purposes, the EPA
defines the following terms and acronyms here:

AEGL acute exposure guideline level
AERMOD air dispersion model used by the HEM-3 model
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CFR Code of Federal Regulations
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guidelines
FR Federal Register
HAP hazardous air pollutant(s)
HCl hydrochloric acid
HEM-3 Human Exposure Model
HF hydrogen fluoride
HI hazard index
HQ hazard quotient
ICR information collection request
IRIS Integrated Risk Information System
km kilometer
MACT maximum achievable control technology
mg/m3 milligrams per cubic meter
MIR maximum individual risk
NAICS North American Industry Classification System
NESHAP national emission standards for hazardous air pollutants
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
QA/QC quality assurance/quality control
RBLC RACT/BACT/LAER Clearinghouse
REL reference exposure level
RFA Regulatory Flexibility Act
RfC reference concentration
RfD reference dose
RTO regenerative thermal oxidizer
RTR residual risk and technology review
SAB Science Advisory Board
SSM startup, shutdown, and malfunction
TOSHI target organ-specific hazard index
tpy tons per year
TSD technical support document
UF uncertainty factor
UMRA Unfunded Mandates Reform Act
URE unit risk estimate
VCS voluntary consensus standards

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

I. General Information
    A. Does this action apply to me?
    B. Where can I get a copy of this document and other related
information?
    C. What should I consider as I prepare my comments for the EPA?
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
    A. How do we consider risk in our decision-making?
    B. How do we perform the technology review?
    C. How did we estimate post-MACT risks posed by the source
category?
IV. Analytical Results and Proposed Decisions
    A. What are the results of the risk assessment and analyses?
    B. What are our proposed decisions regarding risk acceptability,
ample margin of safety, and adverse environmental effects?
    C. What are the results and proposed decisions based on our
technology review?
    D. What other actions are we proposing?
    E. 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)
    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, we published an initial list of source categories to be
regulated (57 FR 31576), Initial List of Categories of Sources Under
Section 112(c)(1) of the Clean Air Act Amendments of 1990. The Leather
Tanning and Finishing Operations source category was not included on
the initial list, but was added by an update to the list on June 4,
1996 (61 FR 28207), Revision of Initial List of Categories of Sources
and Schedule for Standards Under Sections 112(c) and (e) of the Clean
Air Act Amendments of 1990. On October 2, 2000, we proposed a NESHAP
for the Leather Finishing Operations source category (65 FR 58702). The
final rule was promulgated on February 27, 2002 (67 FR 9156)
(henceforth referred to as the ``Leather Finishing NESHAP''), which
modified the listing of this source category by deleting tanning
facilities from the definition and renaming the source category
``Leather Finishing Operations.'' The Revision of Initial List of
Categories of Sources and Schedule for Standards Under Sections 112(c)
and (e) of the Clean Air Act Amendments of 1990 (see 61 FR 28197,
28202, June 4, 1996), describes the Leather Finishing Operations source
category as ``any facility or process engaged in conditioning and
enhancement processes that give tanned leather distinctive and
desirable qualities required by end users of the material.''

    Table 1--NESHAP and Industrial Source Categories Affected by This
                             Proposed Action
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               NESHAP and source category                 NAICS code \1\
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Leather Finishing Operations...........................            3161
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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
http://www.epa.gov/stationary-sources-air-pollution/leather-finishing-operations-national-emission-standards-hazardous. Following publication
in the Federal Register, the EPA will post the Federal Register version
of the proposal and key technical documents at this same Web site.
Information on the overall RTR program is available at http://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.
    A redline version of the regulatory language that incorporates the
proposed changes in this action is available in the docket for this
action (Docket ID No. EPA-HQ-OAR-2003-0194).

C. What should I consider as I prepare my comments for the EPA?

    Submitting CBI. Do not submit information containing CBI to the EPA
through http://www.regulations.gov or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
a disk or CD-ROM that you mail to the EPA, mark the outside of the disk
or CD-ROM as CBI and then identify electronically within the disk or
CD-ROM 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 for inclusion in the public docket. If
you submit a CD-ROM or disk that does not contain CBI, mark the outside
of the disk or CD-ROM 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 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-2003-
0194.

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 so-called maximum achievable control
technology (MACT) standards to determine whether additional standards
are needed to further 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
tons per year (tpy) or more of a single HAP or 25 tpy or more of any
combination of HAP. All other sources are ``area sources.'' For major
sources, CAA section 112(d) 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). Section 112(f)(2) of the CAA requires the EPA to
determine for source categories subject to MACT standards 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 process 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 in the CAA process 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] [i.e., 100-in-1 million].'' 54 FR 38045, September
14, 1989. If risks are unacceptable, the EPA must determine the
emissions standards necessary to bring risks to an acceptable level
without considering costs. In the second step of the process, the EPA
considers whether the emissions standards provide an ample margin of
safety ``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. After conducting the ample margin of safety analysis, we
consider whether a more stringent standard is necessary to prevent an
adverse affect, taking into consideration costs, energy, safety, and
other relevant factors.
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    \1\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk if an individual were exposed to the maximum
level of a pollutant for a lifetime.
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    CAA section 112(d)(6) separately requires the EPA to review
standards promulgated under CAA section 112 and revise them ``as
necessary (taking into account developments in practices, processes,
and control technologies)'' no less frequently than every 8 years. In
conducting this so-called ``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 Leather Finishing NESHAP was promulgated on February 27, 2002
(67 FR 9156) and codified at 40 CFR part 63, subpart TTTT. The Leather
Finishing NESHAP defines ``leather finishing'' as ``a single process or
group of processes used to adjust and improve the physical and
aesthetic characteristics of the leather surface through the multistage
application of a coating comprised of dyes, pigments, film-forming
materials, and performance modifiers dissolved or suspended in liquid
carriers.'' 40 CFR 63.5460. The Leather Finishing NESHAP does not apply
to equipment used solely for leather tanning operations or to portions
of leather finishing operations using a solvent degreasing process
subject to the Halogenated Solvent Cleaning NESHAP (see 40 CFR
63.5290(c)).
    There are currently four existing leather finishing operations that
were identified as subject to the Leather Finishing NESHAP: S.B. Foot
Tanning Company of Red Wing, MN; Alliance Leather, Inc. of Peabody, MA;
Pearl Leather Finishers, Inc. of Johnstown, NY; and Tasman Leather
Group, LLC of Hartland, ME.
    In the overall process of leather products manufacturing, leather
finishing is considered a dry operation as opposed to the ``wet-end''
operations associated with leather tanning. Leather finishing
operations can be co-located with wet-end tannery operations or
performed in stand-alone facilities. None of the four existing
facilities subject to the Leather Finishing NESHAP perform the initial
wet-end tanning process that produces the commodity product known as
``wet blues'' or ``blue stock;'' however, based on information
available in the facility operating permits, the S.B. Foot and Tasman
facilities each perform retanning, coloring, and fat liquoring
operations. These are wet-end operations that soften, color, and
restore fats and oils to the blue stock. The equipment used solely for
leather tanning operations is not subject to the Leather Finishing
NESHAP.
    In the dry-end leather finishing operations, coatings are typically
applied to the leather substrate using spray, roll, and flow coating
techniques. The emission source types subject to the emission limits
under the Leather Finishing NESHAP include, but are not limited to
coating and spraying equipment, coating storage and mixing, and dryers.
Emissions of HAP occur from volatilization during the application of
the coating, drying, or curing of the coating, and from handling,
storage, and clean-up of the finishing materials. Wastewaters laden
with HAP are also a potential source of emissions at facilities that
use water curtains and water baths for particulate control. The
emission point types associated with these emission sources include
process vents, storage vessels, wastewater, and fugitive sources.
    In developing the Leather Finishing NESHAP, the EPA established
MACT standards for four types of leather product process operations:
(1) Upholstery leather with greater than or equal to 4 grams of add-on
finish per square foot of leather; (2) upholstery leather with less
than 4 grams of add-on finish per square foot of leather; (3)

water-resistant leather; and (4) nonwater-resistant leather. The MACT
standards limit emissions from new and existing leather finishing
operations and are expressed in terms of total HAP emissions per 1,000
square feet of leather processed over a rolling 12-month compliance
period. Sources must record the mass of HAP in coatings applied to the
leather either through an inventory mass balance or ``measure-as-
applied'' approach. Using the mass balance approach, sources may choose
to account for disposal of excess finish instead of assuming any excess
finish is also emitted. Emissions are calculated based on the
assumption that the entire HAP content of the applied finish is
released to the environment. Sources using an add-on control device may
account for the emission reduction achieved from the control device as
measured by a performance test conducted in accordance with the
requirements of the Leather Finishing NESHAP.
    Based on the data collected as described in section II.C and D of
this preamble, HAP emissions from this source category include propyl
cellosolve, glycol ethers, diethylene glycol monobutyl ether,
trimethylamine, diethylene glycol monomethyl ether, ethylene glycol,
toluene, methyl isobutyl ketone, and chromium (III) compounds.

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

    For this RTR, the EPA collected information from the 2014 National
Emissions Inventory (NEI, version 1), from facility permits and permit
applications, and through discussions with facility representatives and
state permitting authorities.
    The NEI is a database that contains information about sources that
emit criteria air pollutants, their precursors, and HAP. The database
includes estimates of annual air pollutant emissions from point,
nonpoint, and mobile sources in the 50 states, the District of
Columbia, Puerto Rico, and the Virgin Islands. The EPA collects this
information and releases an updated version of the NEI database every 3
years. The NEI includes information necessary for conducting risk
modeling, including annual HAP emissions estimates from individual
emission points at facilities and the related emissions release
parameters. We used NEI emissions and supporting data as the primary
source of information to develop the model input file for the risk
assessment (hereafter referred to as the ``RTR emissions dataset'').
For more details on the NEI, see https://www.epa.gov/air-emissions-inventories/national-emissions-inventory-nei.
    The EPA also gathered information on annual emissions, emission
points, air pollution control devices, and process operations from
facility construction and operating permits. We collected permits and
supporting documentation from state permitting authorities either
through direct contact with the agencies or through state-maintained
online databases. The NEI and facility permits contained much of the
information we used to develop the RTR emissions dataset. Supplemental
information was collected via communication with facility
representatives.
    The EPA contacted facility representatives for three of the four
leather finishing operations subject to the Leather Finishing NESHAP
(identified in section II.B of this preamble) to collect supplemental
and clarifying information for use in the RTR emissions dataset.
Facility representatives provided information including production
capacities, coating formulations, HAP emissions, and operating
schedules. We were unable to establish contact with facility
representatives for Alliance Leather, Inc. of Peabody, MA; however, the
Massachusetts Department of Environmental Protection confirmed the
facility was in operation at the time of our inquiry (November 2016)
and provided a facility annual emissions report for the 2015 reporting
year. Contacts with facility representatives, our review of permit
documentation, and our review of the 2014 NEI are documented in a
separate memorandum titled Leather Finishing: Residual Risk Modeling
File Supporting Documentation in the docket for this action.

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

    The EPA's Enforcement Compliance History Online (ECHO) database was
used as a tool to identify which leather finishing operations were
potentially subject to the Leather Finishing NESHAP. The ECHO database
provides integrated compliance and enforcement information for
approximately 800,000 regulated facilities nationwide. Using the search
feature in ECHO, the EPA identified 120 facilities that could
potentially be subject to the Leather Finishing NESHAP. The EPA also
reviewed the membership directory of the Leather Industries of America
trade association and supporting documentation for the 2002 rulemaking
and identified an additional 35 facilities with operations potentially
subject to the Leather Finishing NESHAP. We then searched state Web
sites for operating permits for these facilities to determine whether
the permits stated the facility contained leather finishing operations
subject to the rule. For facilities for which permits were unavailable,
we reviewed company Web sites, online news articles, and aerial imagery
to determine if the facility was still in operation. Of the 155
identified facilities, we determined that 24 facilities perform leather
finishing operations and 131 facilities are either closed or do not
perform leather finishing operations. Of the 24 facilities performing
leather finishing operations, only four are subject to the Leather
Finishing NESHAP. The 20 remaining facilities are area sources and not
subject to the Leather Finishing NESHAP.
    The EPA searched for Reasonably Available Control Technology
(RACT), Best Available Control Technology (BACT), and Lowest Achievable
Emission Rate (LAER) determinations in the RACT/BACT/LAER Clearinghouse
(RBLC). The RBLC is a database that contains case-specific information
of air pollution technologies that have been required to reduce the
emissions of air pollutants from stationary sources. Under the EPA's
New Source Review (NSR) program, if a facility is planning new
construction or a modification that will increase the air emissions by
a certain amount, an NSR permit must be obtained. This central database
promotes the sharing of information among permitting agencies and aids
in case-by-case determinations for NSR permits. We examined information
contained in the RBLC to determine what technologies are currently used
at leather finishing operations to reduce air emissions.
    The EPA also reviewed other information sources to determine
whether there have been developments in practices, processes, or
control technologies in the leather finishing operations source
category. We reviewed subsequent regulatory actions for sources similar
to leather finishing operations and conducted a review of literature
published by industry organizations, technical journals, and government
organizations. Additional details regarding our review of these
information sources is contained in the memorandum titled CAA section
112(d)(6) Technology Review for the Leather Finishing Source Category
in the docket for this action.

III. Analytical Procedures

    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 process 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 [previous] 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.\2\ The assessment
also provides estimates of the distribution of cancer risks within the
exposed populations, cancer incidence, and an evaluation of the
potential for adverse environmental effects. The scope of EPA's risk
analysis is consistent with EPA's response to comment on our policy
under the Benzene NESHAP where the EPA explained that:
---------------------------------------------------------------------------

    \2\ 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
exposure to the HAP to the level at or below which no adverse
chronic noncancer effects are expected; 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 [her] 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 [her] judgment, believes are
---------------------------------------------------------------------------
appropriate to determining what will `protect the public health'.''

    See 54 FR at 38057, September 14, 1989. Thus, the level of the MIR
is only one factor to be weighed in determining acceptability of risks.
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 MIR less than the
presumptively acceptable level is unacceptable in the light of other
health risk factors.'' Id. at 38045. 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 those HAP risks 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 risks, 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 increased risk of adverse noncancer health effects. In May
2010, the Science Advisory Board (SAB) advised the EPA ``that RTR
assessments will be most useful to decision makers and communities if
results are presented in the broader context of aggregate and
cumulative risks, including background concentrations and contributions
from other sources in the area.'' \3\
---------------------------------------------------------------------------

    \3\ The EPA's responses to this and all other key
recommendations of the SAB's advisory on RTR risk assessment
methodologies (which is available at: http://yosemite.epa.gov/sab/
sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-
007-unsigned.pdf) are outlined in a memorandum to this rulemaking
docket from David Guinnup titled, EPA's Actions in Response to the
Key Recommendations of the SAB Review of RTR Risk Assessment
Methodologies.
---------------------------------------------------------------------------

    In response to the SAB recommendations, the EPA is incorporating
cumulative risk analyses into its RTR risk assessments, including those
reflected in this proposal. The Agency is (1) Conducting facility-wide
assessments, which include source category emission points, as well as
other emission points within the facilities; (2) combining exposures
from multiple sources in the same category that could affect the same
individuals; and (3) for some persistent and bioaccumulative
pollutants, analyzing the ingestion route of exposure. In addition, the
RTR risk assessments have always considered aggregate cancer risk from
all carcinogens and aggregate noncancer HI from all noncarcinogens
affecting the same target organ system.
    Although we are interested in placing source category and facility-
wide HAP risks in the context of total HAP risks from all sources
combined in the

vicinity of each source, we are concerned about the uncertainties of
doing so. Because of the contribution to total HAP risk from emission
sources other than those that we have studied in depth during this RTR
review, such estimates of total HAP risks 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, in order to inform our decision of whether
it is ``necessary'' to revise the emissions standards, we analyze the
technical feasibility of applying these developments and the estimated
costs, energy implications, non-air environmental impacts, and we also
considered the emission reductions. In addition, we considered the
appropriateness of applying controls to new sources versus retrofitting
existing sources.
    Based on our analyses of the available data and information, we
identify potential developments in practices, processes, and control
technologies. 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 reviewed a variety of data sources in
our investigation of potential practices, processes, or controls to
consider. Among the sources we reviewed were the NESHAP for various
industries that were promulgated since the MACT standards being
reviewed in this action. We reviewed the regulatory requirements and/or
technical analyses associated with these regulatory actions to identify
any practices, processes, and control technologies considered in these
efforts that could be applied to emission sources in the Leather
Finishing Operations source category, as well as the costs, non-air
impacts, and energy implications associated with the use of these
technologies. Finally, we reviewed information from other sources, such
as state and/or local permitting agency databases and industry-
supported databases.

C. How did we estimate post-MACT risks posed by the source category?

    The EPA conducted 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 risks
within the exposed populations, cancer incidence, and an evaluation of
the potential for adverse environmental effects. 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 Leather
Finishing Operations Source Category in Support of the December 2017
Risk and Technology Review Proposed Rule. The methods used to assess
risks (as described in the eight primary steps below) are consistent
with those peer-reviewed by a panel of the EPA's SAB in 2009 and
described in their peer review report issued in 2010 \4\; they are also
consistent with the key recommendations contained in that report.
---------------------------------------------------------------------------

    \4\ U.S. EPA SAB. 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, May 2010.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions
release characteristics?
    Data for four leather finishing operations as described in section
II.C of this preamble were used to create the RTR emissions dataset.
The emission sources in the RTR emissions dataset include the following
types of emissions sources currently regulated by the Leather Finishing
NESHAP: Coating and spraying equipment, coating storage and mixing, and
dryers. The RTR emissions dataset also includes emissions from buffing
operations. This RTR emissions dataset is based primarily on emissions
data from the 2014 NEI, facility permits and permit supporting
documentation, a state-provided facility annual emissions report, and
information obtained through contact with facility representatives.
These data sources provided all of the emissions data in the RTR
emissions dataset and nearly all of the facility-specific data needed
to conduct the risk modeling analysis. However, there were a few
instances where default values were used to fill gaps in the facility-
specific data used in the risk modeling analysis. For example, default
values were used for fugitive release parameters. Use of defaults is
discussed in detail in the memorandum titled Leather Finishing:
Residual Risk Modeling File Supporting Documentation in the docket for
this action.
    The RTR emissions dataset was refined following an extensive
quality assurance (QA) check of source locations, emission release
characteristics, and annual emission estimates. We checked the
coordinates of each emission source in the dataset using a computer
program that renders a three-dimensional representation of Earth based
on satellite imagery to ensure the emission point locations were
correct. We also confirmed that each stack parameter was within
acceptable QA range check boundaries. For further information on the
EPA's QA review, see the memorandum titled Leather Finishing: Residual
Risk Modeling File Supporting Documentation in the docket for this
action.
2. How did we estimate MACT-allowable emissions?
    The available emissions data used to develop 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 required to comply with the current MACT
standards. The emissions level

allowed to be emitted by the MACT standards is referred to as the
``MACT-allowable'' emissions level. We discussed the use 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 RTRs (71 FR 34428, June 14, 2006, and 71 FR 76609,
December 21, 2006, respectively). In those actions, we noted that
assessing the risks at the MACT-allowable level is inherently
reasonable since these risks reflect 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).
    We used the RTR emissions dataset discussed in section III.C.1 of
this preamble to estimate allowable emissions levels. The types and
sources of data we used to estimate allowable emissions vary by
facility and leather finishing operation type. Because the Leather
Finishing NESHAP MACT limits are production-based limits (i.e., pounds
HAP per square feet of leather processed), estimating MACT-allowable
emissions for the Leather Finishing Operations source category would be
accomplished by using the actual production level per leather finishing
operation type to calculate emissions at the MACT limit per leather
finishing operation type. However, we do not have actual production
data (quantity and type of leather) for each permitted leather
finishing operation because we did not petition facilities for this
information with an information collection request (ICR). As a result,
different methods for estimating allowable emissions were warranted for
each facility and leather finishing operation type. This section
provides a summary of our method for estimating allowable emissions for
each facility. Refer to the memorandum titled Leather Finishing:
Residual Risk Modeling File Supporting Documentation in the docket for
this action for a more detailed discussion of the data and methods we
used to calculate allowable emissions for these facilities.
    For Alliance Leather, we estimated allowable emissions for organic
HAP using the Leather Finishing NESHAP limit on total HAP emissions
that is specified in the facility's permit, which is 3.7 pounds of HAP
emitted per 1,000 square feet of leather processed. The facility's
total allowable annual HAP emission rate was estimated to be the
product of this HAP limit (3.7 pounds per 1,000 square feet of leather
processed), the design production capacity of the leather finishing
process specified in the operating permit (16,200 square feet per
hour), and the annual operating schedule contained in the 2014 NEI
(2,000 hours per year). Given that we do not have actual production
data for this leather finishing operation, we could not calculate the
MACT-allowable emissions level as described above. However, using
design production capacity in place of actual production is a more
conservative approach, yielding a higher estimate for allowable organic
HAP emissions. As further detailed in the memorandum cited above in
this section, this approach yielded a total allowable annual HAP
emission rate of 60 tpy, equivalent to 118 times the actual emission
rate. Allowable organic HAP emissions for the risk modeling file were
estimated by multiplying by 118 the actual organic HAP emission rates
for each emission release point, emission process, and emission unit
combination.
    For S.B. Foot Tanning Co. and Pearl Leather Finishers, Inc, we also
do not have actual production data. Further, S.B. Foot has multiple
leather finishing operations, each subject to a different production-
based NESHAP limit. To calculate the MACT-allowable emissions level for
each leather finishing operation at the facility, we would need the
actual production data for each leather finishing operation. Given our
data limitations for these two facilities, we identified an alternative
approach for estimating allowable emissions that was not available for
Alliance Leather. S.B. Foot and Pearl Leather Finishers are subject to
permitted mass-based limits on volatile organic compound(s) (VOC)
emissions in tpy. We determined that we could use each facility's
permitted VOC limit to estimate allowable organic HAP emissions because
all organic HAP emitted are VOC and, in the coating formulations, there
is little variation in the ratio of total organic HAP to total VOC.
Using the ratio of each facility's permitted VOC emission limit to its
reported \5\ annual VOC emissions, we estimated allowable organic HAP
emissions as the product of actual organic HAP emissions and this
ratio. For example, for S.B. Foot, permitted VOC emissions are 200 tpy
and reported VOC emissions are 88.61 tpy, which yields a ratio of 2.26.
For Pearl Leather Finishers, permitted VOC emissions are 194,180 pounds
per year and reported VOC emissions are 41,926 pounds, which yields a
ratio of 4.63. Using these ratios, we estimated allowable organic HAP
emissions as the product of actual organic HAP emissions and the ratio.
For S.B. Foot, actual organic HAP emissions are 16.18 tpy, which
multiplied by 2.26 yields 36.5 tpy allowable organic HAP emissions.
Using this same method for Pearl Leather Finishers yields an allowable
organic HAP emission level of 5.1 tpy. Allowable organic HAP emissions
for the risk modeling file were estimated for each facility by
multiplying the actual organic HAP emission rates for each emission
release point, emission process, and emission unit combination by the
ratio. Refer to the memorandum cited above in this section for a
detailed discussion about these data sources and calculations. We
solicit comment on this proposed method of calculating allowable
organic HAP emissions for S.B. Foot and Pearl Leather Finishers.
---------------------------------------------------------------------------

    \5\ Reported to the 2014 NEI.
---------------------------------------------------------------------------

    For Tasman Leather Group, LLC., allowable emissions were estimated
using the maximum HAP emissions allowed for area sources, which is 10
tpy for all HAP emitted (refer to the memorandum, Leather Finishing:
Residual Risk Modeling File Supporting Documentation, in the docket for
this action for further discussion on the status of this facility as an
area source). Allowable emissions for organic HAP were set equivalent
to this total annual HAP emission limit of 10 tpy. Allowable organic
HAP emissions for the risk modeling file were estimated by multiplying
the actual organic HAP emission rate (as reported in the 2014 NEI) for
each emission release point, emission process, and emission unit
combination by a factor of 2.78, which is the ratio of allowable total
HAP emissions (10 tpy) to actual facility-wide emissions of HAP (3.59
tpy). Refer to the memorandum cited above in this section for a
detailed discussion about these data sources and calculations.
    We estimated allowable chromium (III) emissions from buffing
operations as follows. For S.B. Foot, the allowable rate for each
chromium-emitting emission release point was set equal to the potential
to emit value in the facility's permit technical support document
(TSD), which is 0.319 tpy chromium (III). No additional restrictions on
chromium (III) emissions were identified. For Pearl Leather Finishers
and Tasman Leather Group, we used emission factors presented in the
S.B. Foot permit TSD to estimate the allowable emission rate for each
chromium emission release point. For Pearl Leather Finishers, based on
communication with facility representatives regarding average

production rate, design production capacity, and dust capture, and
assuming a 90-percent control efficiency, we calculated an allowable
chromium (III) emission rate of 0.266 tpy. For Tasman Leather Group,
based on communication with facility representatives, we identified the
design capacity of each buffing operation and established that four
buffing operations currently operate. Using this design capacity, we
calculated allowable chromium emissions based on permit special
conditions for the facility allowing the operation of 12 such buffing
units at any given time and requiring a 90-percent particulate removal
efficiency. Based on these permitted conditions, we calculated an
allowable chromium (III) emission rate of 4.98 tpy. Refer to the
memorandum cited above in this section for a detailed discussion about
these data sources and calculations. We identified no buffing
operations at Alliance Leather.
    We solicit comment on our proposed methods for estimating allowable
emissions. In addition to general comments on these proposed methods,
we are interested in additional data that may improve our estimation of
allowable emissions.
3. How did we conduct dispersion modeling, determine inhalation
exposures, and estimate individual and population inhalation risks?
    Both long-term and short-term inhalation exposure concentrations
and health risks from the source category addressed in this proposal
were estimated using the Human Exposure Model (HEM-3). 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 risks
using the exposure estimates and quantitative dose-response
information.
a. Dispersion Modeling
    The air dispersion model AERMOD, used by the HEM-3 model, is one of
the EPA's preferred models for assessing air pollutant concentrations
from industrial facilities.\6\ To perform the dispersion modeling and
to develop the preliminary risk estimates, HEM-3 draws on three data
libraries. The first is a library of meteorological data, which is used
for dispersion calculations. This library includes 1 year (2016) of
hourly surface and upper air observations from 824 meteorological
stations, selected to provide coverage of the United States and Puerto
Rico. A second library of United States Census Bureau census block \7\
internal point locations and populations provides the basis of human
exposure calculations (U.S. Census, 2010). In addition, for each census
block, the census library includes the elevation and controlling hill
height, which are also used in dispersion calculations. A third library
of pollutant-specific dose-response values is used to estimate health
risks. These dose-response values are the latest values recommended by
the EPA for HAP. They are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants and are discussed in more detail later in this
section.
---------------------------------------------------------------------------

    \6\ 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).
    \7\ A census block is the smallest geographic area for which
census statistics are tabulated.
---------------------------------------------------------------------------

b. Risk From Chronic Exposure to HAP That May Cause Cancer
    In developing the risk assessment for chronic exposures, we use the
estimated annual average ambient air concentrations of each HAP emitted
by each source for which we have emissions data in the source category.
The air concentrations at each nearby census block centroid are used as
a surrogate for the chronic inhalation exposure concentration for all
the people who reside in that census block. We calculate the MIR for
each facility as the cancer risk associated with a continuous lifetime
(24 hours per day, 7 days per week, 52 weeks per year, for a 70-year
period) exposure to the maximum concentration at the centroid of
inhabited census blocks. Individual cancer risks are calculated by
multiplying the estimated lifetime exposure to the ambient
concentration of each HAP (in micrograms per cubic meter) by its unit
risk estimate (URE). The URE is an upper bound estimate of an
individual's probability 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 the 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.
    To estimate incremental individual lifetime cancer risks associated
with emissions from the facilities in the source category, the EPA sums
the risks for each of the carcinogenic HAP \8\ emitted by the modeled
sources. Cancer incidence and the distribution of individual cancer
risks for the population within 50 km of the sources are also estimated
for the source category by summing individual risks. 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.
---------------------------------------------------------------------------

    \8\ EPA 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 risks of these individual compounds to obtain the cumulative
cancer risks 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 http://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
---------------------------------------------------------------------------

c. Risk From Chronic Exposure to HAP That May Cause Health Effects
Other Than Cancer
    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 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 (https://iaspub.epa.gov/sor_internet/registry/termreg/
searchandretrieve/glossariesandkeywordlists/

search.do?details=&vocabName=IRIS%20Glossary), 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.'' In cases where an RfC from
the EPA's IRIS database 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 (http://www.atsdr.cdc.gov/mrls/index.asp);
(2) the CalEPA Chronic Reference Exposure Level (REL) (http://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.
d. 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. We use the peak hourly emission rate,\9\ worst-case
dispersion conditions, and, in accordance with our mandate under
section 112 of the CAA, the point of highest off-site exposure to
assess the potential risk to the maximally exposed individual.
---------------------------------------------------------------------------

    \9\ In the absence of hourly emission data, we develop estimates
of peak hourly emission rates by multiplying the average actual
annual emissions rates by a default factor (usually 10) to account
for variability. This is documented in Residual Risk Assessment for
the Leather Finishing Operations Source Category in Support of the
December 2017 Risk and Technology Review Proposed Rule and in
Appendix 5 of the report: Analysis of Data on Short-term Emission
Rates Relative to Long-term Emission Rates. Both are available in
the docket for this rulemaking.
---------------------------------------------------------------------------

    To characterize the potential health risks associated with
estimated acute inhalation exposures to a HAP, we generally use
multiple acute dose-response values, including acute RELs, acute
exposure guideline levels (AEGLs), and emergency response planning
guidelines (ERPG) for 1-hour exposure durations), if available, to
calculate acute HQs. The acute HQ is calculated by dividing the
estimated acute exposure 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.'' \10\ 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.\11\ They are
guideline levels for ``once-in-a-lifetime, short-term exposures to
airborne concentrations of acutely toxic, high-priority chemicals.''
Id. at 21. The AEGL-1 is specifically defined as ``the airborne
concentration (expressed as ppm (parts per million) or mg/m3
(milligrams per cubic meter)) of a substance above which it is
predicted that the general population, including susceptible
individuals, could experience notable discomfort, irritation, or
certain asymptomatic nonsensory effects. However, the effects are not
disabling and are transient and reversible upon cessation of
exposure.'' 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.
---------------------------------------------------------------------------

    \10\ 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 http://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary.
    \11\ National Academy of Sciences (NAS), 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).
---------------------------------------------------------------------------

    ERPGs are developed for emergency planning and are intended as
health-based guideline concentrations for single exposures to
chemicals.'' \12\ 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.
---------------------------------------------------------------------------

    \12\ 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.
---------------------------------------------------------------------------

    An acute REL for 1-hour exposure durations is typically lower than
its corresponding AEGL-1 and ERPG-1. Even though their definitions are
slightly different, AEGL-1s are often the same as the corresponding
ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from
our acute inhalation screening risk assessment typically result when we
use the acute REL for a HAP. In cases where the maximum acute HQ
exceeds 1, we also report the HQ based on the next highest acute dose-
response value (usually the AEGL-1 and/or the ERPG-1).
    For this source category, facility-specific actual emissions were
used to calculate peak hourly emissions in our acute inhalation
screening risk assessment. For each HAP emitted by a facility, the peak
hourly emission rate was calculated by dividing the actual annual
emission rate by facility-specific annual operating hours and
multiplying this hourly rate by an acute emission multiplier of 1.8.
The multiplier was developed using U.S. census data reported in 2012
through 2017 for leather finishing operations production capacity
utilization over the period 2011 through 2016. The multiplier was
calculated as the ratio of the highest

production rate capacity use factor (87.5) to the lowest production
rate capacity use factor (46.6). Emissions from leather finishing
operations are primarily from coatings operations. The production
capacity of leather finishing operations is constrained by the amount
of time it takes to apply and cure coatings, and machines are running
more or less continuously, which gives a smooth temporal profile and,
thus, a low emission adjustment factor. Consequently, actual emissions
and acute hourly emissions will be similar, and the selected adjustment
factor of 1.8 was selected over the default adjustment factor of 10.
The description of how peak hourly emissions were calculated and
additional information regarding operating hours at each facility in
the source category can be found in Appendix 1--Emissions Inventory
Support Document of the document titled Residual Risk Assessment for
the Leather Finishing Operations Source Category in Support of the
December 2017 Risk and Technology Review Proposed Rule in the docket
for this rulemaking.
    In our acute inhalation screening risk assessment, acute impacts
are deemed negligible for HAP where acute HQs are less than or equal to
1 (even under the conservative assumptions of the screening
assessment), and no further analysis is performed for these HAP. In
cases where an acute HQ from the screening step is greater than 1, we
consider additional site-specific data to develop a more refined
estimate of the potential for acute impacts of concern. 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. Also in estimating acute
risks for the Leather Finishing Operations source category, we employed
the following data refinements in calculating peak hourly emissions, as
described above in this section: Used facility-specific operating hour
data and developed an industry-specific multiplier based on industry-
specific U.S. census data. These refinements are discussed more fully
in the Residual Risk Assessment for the Leather Finishing Operations
Source Category in Support of the December 2017 Risk and Technology
Review Proposed Rule, which is available in the docket for this action.
4. How did we conduct the multipathway exposure and risk screening
assessment?
    The EPA conducted 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 determined
whether any sources in the source category emitted any HAP known to be
persistent and bioaccumulative in the environment (PB-HAP), as
identified in the EPA's Air Toxics Risk Assessment Library (See Volume
1, Appendix D, at http://www2.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Leather Finishing Operations source category, we did not
identify emissions of any PB-HAP. Because we did not identify PB-HAP
emissions, no further evaluation of multipathway risk was conducted for
this source category.
5. How did we assess risks considering emissions control options?
    While emission control technologies were considered, the analysis
determined the available control technologies were not cost effective
for reducing HAP emissions from leather finishing operations.
Therefore, we did not assess risk on the emission control options. For
more information regarding analysis of available control technologies,
see the memorandum, CAA section 112(d)(6) Technology Review for the
Leather Finishing Source Category, which is available in the docket for
this action.
6. How did we conduct the environmental risk screening assessment?
a. Adverse Environmental Effects, Environmental HAP, and Ecological
Benchmarks
    The EPA conducts a screening assessment to examine the potential
for adverse environmental effects 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, polycyclic organic
matter, 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, were 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 the Leather Finishing Operations source category, we did not
identify emissions of any PB-HAP. Because we did not identify PB-HAP
emissions, no further evaluation of ecological impacts was conducted
for this source category.
    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 Leather Finishing Operations Source Category in Support
of the Risk and Technology Review December 2017 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 Leather

Finishing Operations source category emitted any of the environmental
HAP. For this source category, we did not identify emissions of any of
the eight environmental HAP included in the screen. Because we did not
identify environmental HAP emissions, no further evaluation of
environmental risk was conducted.
7. How did 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 that the EPA compiled from the 2014 NEI. We used the
NEI data for the facility and did not adjust any category or ``non-
category'' data. Therefore, there could be differences in the dataset
from that used for the source category assessments described in this
preamble. We analyzed risks due to the inhalation of HAP that are
emitted ``facility-wide'' for the populations residing within 50 km of
each facility, consistent with the methods used for the source category
analysis described above. For these facility-wide risk analyses, we
made a reasonable attempt to identify the source category risks, and
these risks were compared to the facility-wide risks to determine the
portion of facility-wide risks that could be attributed to the source
category addressed in this proposal. We also specifically examined the
facility that was associated with the highest estimate of risk and
determined the percentage of that risk attributable to the source
category of interest. The Residual Risk Assessment for the Leather
Finishing Operations Source Category in Support of the Risk and
Technology Review December 2017 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 did 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
Leather Finishing Operations Source Category in Support of the Risk and
Technology Review December 2017 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 QA/
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 risks 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 Cancer Guidelines; 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'' (EPA's 2005 Cancer Guidelines, pages 1-7). This
is the approach followed here as summarized in the next paragraphs.
    Cancer UREs used in our risk assessments are those that have been
developed to generally provide an upper bound estimate of risk. That
is, they represent a ``plausible upper limit to the true value of a
quantity'' (although this is usually not a true statistical confidence
limit).\13\ In some circumstances, the true risk could be as low as
zero; however, in other circumstances the risk could be greater.\14\
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 (U.S. EPA, 1993 and 1994) 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.
---------------------------------------------------------------------------

    \13\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \14\ 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.
---------------------------------------------------------------------------

    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 every effort is made to identify appropriate human health
effect dose-response values for all pollutants emitted by the sources
in this risk assessment, some HAP emitted by this source category are
lacking dose-response assessments. Accordingly, these pollutants cannot
be included in the quantitative risk assessment, which could result in
quantitative estimates understating HAP risk. To help to alleviate this
potential underestimate, where we conclude similarity with a HAP for
which a dose-response value is available, we use that value as a
surrogate for the assessment of the HAP for which no value is
available. To the extent use of surrogates indicates appreciable risk,
we may identify a need to increase priority for an IRIS assessment for
that substance. We additionally note that, generally speaking, HAP of
greatest concern due to environmental exposures and hazard are those
for which dose-response assessments have been performed, reducing the
likelihood of understating risk. Further, HAP not included in the
quantitative assessment are assessed qualitatively and considered in
the risk characterization that informs the risk management decisions,
including consideration of HAP reductions achieved by various control
options.
    For a group of compounds that are unspeciated (e.g., glycol
ethers), we conservatively use the most protective dose-response value
of an individual compound in that group to estimate risk. Similarly,
for an individual compound in a group (e.g., ethylene glycol diethyl
ether) that does not have a specified dose-response value, we also
apply the most protective dose-response value from the other compounds
in the group to estimate risk.
e. Uncertainties in Acute Inhalation Screening Assessments
    In addition to the uncertainties highlighted above, there are
several factors specific to the acute exposure assessment that the EPA
conducts as part of the risk review under section 112 of the CAA. The
accuracy of an acute inhalation exposure assessment depends on the
simultaneous occurrence of independent factors that may vary greatly,
such as hourly emissions rates, meteorology, and the presence of humans
at the location of the maximum concentration. In the acute screening
assessment that we conduct under the RTR program, we assume that peak
emissions from the source category and worst-case meteorological
conditions co-occur, thus, resulting in maximum ambient concentrations.
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 during this same time period.
For this source category, these assumptions would tend to be worst-case
actual exposures as it is unlikely that a person would be located at
the point of maximum exposure during the time when peak emissions and
worst-case meteorological conditions occur simultaneously.

IV. Analytical Results and Proposed Decisions

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

    We present results of the Leather Finishing Operations source
category risk assessment briefly below and in more detail in the
residual risk document, Residual Risk Assessment for the Leather
Finishing Operations Source Category in Support of the December 2017
Risk and Technology Review Proposed Rule, in the docket for this
action.
1. Inhalation Risk Assessment Results
    Table 2 of this preamble provides a summary of the results of the
inhalation risk assessment for the source category.

                                        Table 2--Leather Finishing Operations Inhalation Risk Assessment Results
--------------------------------------------------------------------------------------------------------------------------------------------------------
                        Maximum  individual      Estimated population  at    Estimated  annual cancer     Maximum  chronic  non-      Maximum screening
                        cancer risk  (in 1       increased  risk of cancer     incidence  (cases per         cancer  TOSHI \3\       acute non-cancer HQ
                           million) \2\              >= 1-in-1 million                 year)           ----------------------------          \4\
     Number of     ------------------------------------------------------------------------------------                            ---------------------
  facilities \1\      Based on      Based on      Based on      Based on      Based on      Based on      Based on      Based on
                       actual       allowable      actual       allowable      actual        actual        actual       allowable      Based on actual
                      emissions     emissions     emissions     emissions     emissions     emissions     emissions     emissions      emissions level
                      level \2\       level       level \2\       level         level         level         level         level
--------------------------------------------------------------------------------------------------------------------------------------------------------
4.................            0             0             0             0             0             0          0.04           0.3   HQREL = 3 (propyl
                                                                                cellosolve and
                                                                                glycol ethers)
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Number of facilities evaluated in the risk analysis.
\2\ Maximum individual excess lifetime cancer risk due to HAP emissions from the source category.
\3\ Maximum TOSHI. The target organ with the highest TOSHI for the Leather Finishing Operations source category is the reproductive target organ.
\4\ The maximum estimated acute exposure concentration was divided by available short-term threshold values to develop an array of HQ values. HQ values
  shown use the lowest available acute threshold value, which in most cases is the REL. When an HQ exceeds 1, we also show the HQ using the next lowest
  available acute dose-response value.

    The results of the inhalation risk modeling using actual emissions
data, as shown in Table 2 of this preamble, indicate the maximum
chronic noncancer TOSHI value could be up to 0.04. While we would have
estimated incremental individual lifetime cancer risks as discussed in
section III.C.3.b of this preamble, there were no carcinogenic HAP
emissions from this source category, so the maximum lifetime individual
cancer risk is 0 and the total estimated national cancer incidence from
these facilities based on actual emission levels is no excess cancer
cases per year.
2. Acute Risk Results
    Table 2 of this preamble indicates that for the Leather Finishing
Operations source category, the maximum HQ is 3, driven by propyl
cellosolve and glycol ethers. The only acute dose-response value for
propyl cellosolve and glycol ethers is the REL; therefore, only the
HQREL is provided. Refinement of the acute risk results was
performed using aerial photos to ensure that the location where the
maximum risk was projected to occur was, in fact, a location where the
general public could be exposed. The result of this refinement
confirmed that the maximum acute risk result occurred where the public
could potentially be exposed. This refinement, therefore, had no impact
on the maximum HQ. For more detailed acute risk results refer to the
draft residual risk document, Residual Risk Assessment for the Leather
Finishing Operations Source Category in Support of the December 2017
Risk and Technology Review Proposed Rule, in the docket for this
action.
3. Multipathway Risk Screening Results
    There are no PB-HAP emitted by facilities in this source category.
Therefore, we do not expect any human health multipathway risks as a
result of HAP emissions from this source category.
4. Environmental Risk Screening Results
    There are no ``environmental HAP'' emitted by facilities in this
source category. Therefore, we do not expect an adverse environmental
effect as a result of HAP emissions from this source category.
5. Facility-Wide Risk Results
    An assessment of risk from facility-wide emissions was performed to
provide context for the source category risks. Using the NEI data
described in sections II.C and III.C of this preamble, the maximum
cancer risk in the facility-wide assessment was 0.09-in-1 million and
the maximum chronic noncancer HI index was 0.1 (for the reproductive
system), both driven by emissions from external combustion boilers.
6. What demographic groups might benefit from this regulation?
    To examine the potential for any environmental justice issues that
might be associated with the source category, we performed a
demographic analysis, which is an assessment of risks to individual
demographic groups of the populations living within 5 km and within 50
km of the facilities. In the analysis, we evaluated the distribution of
HAP-related cancer and noncancer risks from the Leather Finishing
Operations source category across different demographic groups within
the populations living near facilities.\15\
---------------------------------------------------------------------------

    \15\ Demographic groups included in the analysis are: White,
African American, Native American, other races and multiracial,
Hispanic or Latino, children 17 years of age and under, adults 18 to
64 years of age, adults 65 years of age and over, adults without a
high school diploma, people living below the poverty level, people
living two times the poverty level, and linguistically isolated
people.
---------------------------------------------------------------------------

    Results of the demographic analysis indicate that, for 1 of the 11
demographic groups, Ages 65 and up, the percentage of the population
living within 5 km of facilities in the source category is greater than
the corresponding national percentage for the same demographic groups.
When examining the risk levels of those exposed to emissions from
leather finishing operations, we find that no one is exposed to a
cancer risk at or above 1-in-1 million or to a chronic noncancer TOSHI
greater than 1.
    The methodology and the results of the demographic analysis are
presented in a technical report, Risk and Technology Review--Analysis
of Demographic Factors for Populations Living Near Leather Finishing
Operations, available in the docket for this action.

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

1. Risk Acceptability
    We weigh all health risk factors in our risk acceptability
determination, including the cancer MIR, the number of persons in
various cancer and non-cancer risk ranges, cancer incidence, the
maximum non-cancer TOSHI, the maximum acute non-cancer HQ, the extent
of non-cancer risks, the distribution of cancer and non-cancer risks in
the exposed population, and risk estimation uncertainties (54 FR 38044,
September 14, 1989).
    For the Leather Finishing Operations source category, the risk
analysis indicates that the cancer risks to the individual most exposed
are below 1-in-1 million from both actual and allowable emissions.
These risks are considerably less than 100-in-1 million, which is the
presumptive upper limit of acceptable risk. The risk analysis also
shows no cancer incidence, as well as maximum chronic noncancer TOSHI
value of 0.04, which is significantly below 1. In addition, the risk
assessment indicates no significant potential for multi-pathway health
effects. The acute

non-cancer risks indicate a maximum HQ of 3.
    Considering all the health risk information and factors discussed
above, including the uncertainties, we propose to find that the risks
from the Leather Finishing Operations source category are acceptable.
2. Ample Margin of Safety Analysis
    Although we are proposing that the risks from the Leather Finishing
Operations source category are acceptable, risk estimates indicate the
maximum acute non-cancer HQ screening estimate was greater than 1,
driven by emissions of propyl cellosolve and glycol ethers and based on
allowable emissions, as further discussed in section IV.A.2 of this
preamble. We considered options for further reducing gaseous organic
HAP emissions from leather finishing operations. The greatest reduction
in organic HAP emissions that could be achieved for these operations
would result from use of a concentrator followed by a regenerative
thermal oxidizer (RTO), which we estimate would remove 98 percent of
organic HAP emissions. Biological treatment together with use of a
concentrator would achieve 84-percent removal of organic HAP emissions.
Section IV.C of this preamble discusses the costs and impacts
associated with use of these control technologies. The resulting cost-
effectiveness values for operating the concentrator followed by a RTO
and for operating the concentrator plus biological treatment are
$54,000 and $62,000 per ton of HAP removed, respectively. Due to our
determinations that cancer risks are below 1-in-1 million and that the
maximum chronic noncancer TOSHI value is below 1, uncertainties
associated with the acute screening risk estimate (refer to the risk
report titled Residual Risk Assessment for the Leather Finishing
Operations Source Category in Support of the December 2017 Risk and
Technology Review Proposed Rule in the docket for this action), and the
substantial costs associated with the control options, we are proposing
that additional standards for this source category are not required to
provide an ample margin of safety to protect public health, and that
the current standards provide an ample margin of safety to protect
public health.
3. Adverse Environmental Effects
    We did not identify emissions of any of the eight environmental HAP
included in our environmental risk screening, and we are unaware of any
adverse environmental effects caused by HAP emitted by this source
category. Therefore, we do not expect there to be an adverse
environmental effect as a result of HAP emissions from this source
category, and we are proposing that it is not necessary to promulgate a
more stringent standard to prevent an adverse environmental effect,
taking into consideration costs, energy, safety, and other relevant
factors.
    For the reasons above, we are not proposing to make any amendments
to the existing NESHAP pursuant to CAA section 112(f)(2).

C. What are the results and proposed decisions based on our technology
review?

    As described in section III.B of this preamble, our technology
review focused on identifying developments in the practices, processes,
and control technologies for the Leather Finishing Operations source
category. The EPA reviewed various information sources regarding
emissions sources that are currently regulated by the Leather Finishing
NESHAP, which include, but are not limited to, coating and spraying
equipment, coating storage and mixing, and dryers.
    As discussed further in sections II.C and D of this preamble, we
conducted a search of the RBLC, other regulatory actions (MACT
standards, area source standards, and residual risk standards) since
the 2002 Leather Finishing NESHAP, literature related to research
conducted for emission reductions from leather finishing operations
emission sources, and state permits.
    We reviewed these data sources for information on add-on control
technologies, other treatment units, work practices, procedures, and
process alternatives that were not considered during the development of
the Leather Finishing NESHAP. We also looked for information on
improvements in add-on control technology, other treatment units, work
practices, procedures, and process changes or pollution prevention
alternatives that have occurred since development of the Leather
Finishing NESHAP.
    After reviewing information from the aforementioned sources, we
identified two control technologies for further evaluation that are
technically feasible for use at leather finishing operations, but were
not investigated during the original rule development: biological
treatment and concentrators. Biological treatment was identified as a
result of our literature review. In biological treatment, organic
pollutants are converted to water and carbon dioxide after being
consumed as food by microbes. Biological treatment can include
biofilters, bio-trickling filters, and bioscrubbers among others. The
use of a concentrator was identified by our review of residual risk
standards. The technology review conducted for the Ship Building and
Ship Repair source category identified the use of a concentrator,
combined with an RTO, to control emissions from spray booths (75 FR
80239). A concentrator uses an adsorbent to remove organic pollutants
from an exhaust stream. Those pollutants are then desorbed from the
adsorbent material using a stream much smaller in volume than the
original exhaust stream. This lower flow rate stream is then directed
to an RTO to destroy the desorbed pollutants. By using a concentrator,
the resulting low flow rate, higher pollutant concentration stream is
more economical to treat in an RTO than a high volume low concentration
stream. The economics of operating a biological treatment unit could
also potentially be improved in a similar manner by use of a
concentrator.
    We evaluated the annual cost and emissions reductions of using
biological treatment to reduce HAP emissions at each of the four
leather finishing operations subject to the Leather Finishing NESHAP.
Annual costs for each facility ranged from $43,000 to $417,000 per year
for a total of approximately $840,000 for the industry. Assuming a
control efficiency of 85 percent, HAP emissions would be reduced by
approximately 0.43 tpy for the facility with the smallest projected
reduction to 14 tpy for the facility with the largest projected
reduction, for a cumulative total of 18 tpy for the four facilities
subject to the Leather Finishing NESHAP. To install biological
treatment at each facility, the resulting cost effectiveness ranged
from $30,000 to $110,000 per ton of HAP reduced. Considering the high
costs per ton of HAP reduced associated with the installation of
biological treatment, we did not consider this technology to be cost
effective for further reducing HAP emissions from leather finishing
operations.
    During proposal of the Leather Finishing NESHAP, we considered the
use of an RTO to control HAP emissions from leather finishing
operations as a ``beyond-the-floor'' option; however, we rejected it
because of a significantly higher cost per ton of emissions reductions
(65 FR 58706). Our technology review revealed the use of a concentrator
in addition to an RTO as a potential improvement in add-on control
technology. We evaluated the annual cost and emissions reductions of
using a rotary concentrator combined with an RTO and, as an
alternative, a rotary concentrator combined with a

biological treatment unit for a model facility. Our analysis evaluated
the annual costs of only the rotary concentrator on the basis that if
operation of the concentrator is not cost effective, then operating
both the concentrator and an RTO or biological treatment unit is also
not cost effective. We calculated a total annual cost of operating the
rotary concentrator of approximately $284,000 per year. Applying a
control efficiency of 98 percent for the rotary concentrator and RTO,
we calculated annual HAP emission reductions of 5.2 tpy. Assuming a
control efficiency of 84 percent for the rotary concentrator and
biological treatment combination, we calculated an annual HAP emission
reduction of 4.5 tpy. The resulting cost-effectiveness values for the
concentrator plus RTO and concentrator plus biological treatment are
$54,000 and $62,000 per ton of HAP reduced, respectively; however,
these dollar values only represent the cost of operating the
concentrator and not the RTO or biological treatment process.
Considering the high costs per ton of HAP reduced associated with only
the operation of the rotary concentrator, we did not consider a
concentrator and RTO or a concentrator and biological treatment to be
cost effective for further reducing HAP emissions from leather
finishing operations. Additional information about the assumptions and
methodologies used in these calculations is documented in the
memorandum titled CAA section 112(d)(6) Technology Review for the
Leather Finishing Operations Source Category in the docket for this
action.
    Considering the results of the technology review, we conclude that
changes to the leather finishing operations emission limits are not
warranted pursuant to CAA section 112(d)(6). We are, therefore, not
proposing to make any amendments to the existing NESHAP pursuant to CAA
section 112(d)(6). We solicit comment on our proposed decision.

D. What other actions are we proposing?

    In addition to the proposed actions described above, we are
proposing additional revisions. We are proposing revisions to the SSM
provisions of the MACT rule in order to ensure that they are consistent
with the Court decision in Sierra Club v. EPA, 551 F. 3d 1019 (D.C.
Cir. 2008), which vacated two provisions that exempted sources from the
requirement to comply with otherwise applicable CAA section 112(d)
emission standards during periods of SSM. We also are proposing a
process to increase the ease and efficiency of performance test data
submittal while improving data accessibility through the use of
electronic data reporting. Finally, we are proposing clarifications to
the regulatory text. Our analyses and proposed changes related to these
issues are discussed below.
1. Startup, Shutdown, and Malfunction Requirements
    In its 2008 decision in Sierra Club v. EPA, 551 F.3d 1019 (D.C.
Cir. 2008), the Court vacated portions of two provisions in the EPA's
CAA section 112 regulations governing the emissions of HAP during
periods of SSM. Specifically, the Court vacated the SSM exemption
contained in 40 CFR 63.6(f)(1) and 40 CFR 63.6(h)(1), holding that
under section 302(k) of the CAA, emissions standards or limitations
must be continuous in nature and that the SSM exemption violates the
CAA's requirement that some CAA section 112 standards apply
continuously.
    The Leather Finishing NESHAP currently requires that the standards
apply at all times, consistent with Sierra Club v. EPA. The NESHAP
specifies in 40 CFR 63.5320(a) ``All affected sources must be in
compliance with the requirements of this subpart at all times,
including periods of startup, shutdown, and malfunction.'' However, the
NESHAP includes provisions related to SSM that are not consistent with
Sierra Club v. EPA or 40 CFR 63.5320(a). For example, Table 2 to the
Leather Finishing NESHAP (i.e., the General Provisions applicability
table, hereafter referred to as the ``General Provisions table to
subpart TTTT'') incorporates all of the introductory paragraph to 40
CFR 63.6(e), which provides that the standards do not apply at all
times: ``The general duty to minimize emissions during a period of
startup, shutdown, or malfunction does not require the owner or
operator to achieve emission levels that would be required by the
applicable standard at other times if this is not consistent with
safety and good air pollution control practices, nor does it require
the owner or operator to make any further efforts to reduce emissions
if levels required by the applicable standard have been achieved.''
Further, the introductory paragraph to 40 CFR 63.6(e) refers to the SSM
plan, which is not consistent with the NESHAP's exclusion (as specified
in the General Provisions table to subpart TTTT) of the SSM plan in 40
CFR 63.6(e)(3), SSM recordkeeping in 40 CFR 63.10(b)(2), and SSM
reporting in 40 CFR 63.10(d)(5). In order to remove these
inconsistencies within the NESHAP, to clarify the EPA's original intent
that the standards apply at all times, and to ensure that the subpart
requirements are consistent with the court decision cited above, we are
proposing to unincorporate all General Provisions related to the SSM
exemption and move any applicable portion of these General Provisions
to the NESHAP.
    As is explained in more detail below, we are proposing two
revisions to the General Provisions table to subpart TTTT to eliminate
two General Provisions that include rule language providing an
exemption for periods of SSM. Additionally, we are proposing to
eliminate language related to SSM that treats periods of startup and
shutdown the same as periods of malfunction, as explained further
below. Finally, we are proposing to revise the Deviation Notification
Report and related records as they relate to malfunctions, as further
described below.
    The EPA has attempted to ensure that the provisions we are
proposing to eliminate are inappropriate, unnecessary, or redundant in
the absence of the SSM exemption. We are specifically seeking comment
on whether we have successfully done so.
    The current rule specifies that the standards apply at all times.
In promulgating the original NESHAP for Leather Finishing Operations,
the EPA took into account startup and shutdown periods by applying a
standard based on total coating used and HAP content and requiring a
mass balance compliance method that was applicable for all operations,
even periods of startup and shutdown. As a result, the EPA is not
proposing any changes to the current requirement that all standards
apply during those periods. However, as noted above and discussed
further below, the current rule incorporates two general provisions
that include rule language providing an exemption for periods of SSM,
and the rule includes language that differentiates between normal
operations, startup and shutdown, and malfunction events in describing
the general duty, and these provisions are not necessary or appropriate
in light of the requirement that the standards apply at all times.
Periods of startup, normal operations, and shutdown are all predictable
and routine aspects of a source's operations. Malfunctions, in
contrast, are neither predictable nor routine. Instead they are, by
definition, sudden, infrequent, and not reasonably preventable failures
of emissions control, process, or monitoring equipment. (40 CFR 63.2)
(Definition of malfunction). The EPA interprets CAA section 112 as not
requiring emissions that occur during periods of

malfunction to be factored into development of CAA section 112
standards and this reading has been upheld as reasonable by the Court
in U.S. Sugar Corp. v. EPA, 830 F.3d 579, 606-610 (2016). Under CAA
section 112, emissions standards for new sources must be no less
stringent than the level ``achieved'' by the best controlled similar
source and for existing sources generally must be no less stringent
than the average emission limitation ``achieved'' by the best
performing 12 percent of sources in the category. There is nothing in
CAA section 112 that directs the Agency to consider malfunctions in
determining the level ``achieved'' by the best performing sources when
setting emission standards. As the Court has recognized, the phrase
``average emissions limitation achieved by the best performing 12
percent of'' sources ``says nothing about how the performance of the
best units is to be calculated.'' Nat'l Ass'n of Clean Water Agencies
v. EPA, 734 F.3d 1115, 1141 (D.C. Cir. 2013). While the EPA accounts
for variability in setting emissions standards, nothing in CAA section
112 requires the Agency to consider malfunctions as part of that
analysis. The EPA is not required to treat a malfunction in the same
manner as the type of variation in performance that occurs during
routine operations of a source. A malfunction is a failure of the
source to perform in a ``normal or usual manner,'' and no statutory
language compels the EPA to consider such events in setting CAA section
112 standards.
    As the Court recognized in U.S. Sugar Corp, accounting for
malfunctions in setting standards would be difficult, if not
impossible, given the myriad different types of malfunctions that can
occur across all sources in the category and given the difficulties
associated with predicting or accounting for the frequency, degree, and
duration of various malfunctions that might occur. Id. at 608 (``the
EPA would have to conceive of a standard that could apply equally to
the wide range of possible boiler malfunctions, ranging from an
explosion to minor mechanical defects. Any possible standard is likely
to be hopelessly generic to govern such a wide array of
circumstances.''). As such, the performance of units that are
malfunctioning is not ``reasonably'' foreseeable. See, e.g., Sierra
Club v. EPA, 167 F.3d 658, 662 (D.C. Cir. 1999) (``The EPA typically
has wide latitude in determining the extent of data-gathering necessary
to solve a problem. We generally defer to an agency's decision to
proceed on the basis of imperfect scientific information, rather than
to `invest the resources to conduct the perfect study.' '') See also,
Weyerhaeuser v. Costle, 590 F.2d 1011, 1058 (D.C. Cir. 1978) (``In the
nature of things, no general limit, individual permit, or even any
upset provision can anticipate all upset situations. After a certain
point, the transgression of regulatory limits caused by `uncontrollable
acts of third parties,' such as strikes, sabotage, operator
intoxication or insanity, and a variety of other eventualities, must be
a matter for the administrative exercise of case-by-case enforcement
discretion, not for specification in advance by regulation.''). In
addition, emissions during a malfunction event can be significantly
higher than emissions at any other time of source operation. For
example, if an air pollution control device with 99-percent removal
goes off-line as a result of a malfunction (as might happen if, for
example, the bags in a baghouse catch fire) and the emission unit is a
steady state type unit that would take days to shut down, the source
would go from 99-percent control to zero control until the control
device was repaired. The source's emissions during the malfunction
would be 100 times higher than during normal operations. As such, the
emissions over a 4-day malfunction period would exceed the annual
emissions of the source during normal operations. As this example
illustrates, accounting for malfunctions could lead to standards that
are not reflective of (and significantly less stringent than) levels
that are achieved by a well-performing non-malfunctioning source. It is
reasonable to interpret CAA section 112 to avoid such a result. The
EPA's approach to malfunctions is consistent with CAA section 112 and
is a reasonable interpretation of the statute.
    Although no statutory language compels the EPA to set standards for
malfunctions, the EPA has the discretion to do so where feasible. For
example, in the Petroleum Refinery Sector RTR, the EPA established a
work practice standard for unique types of malfunction that result in
releases from pressure relief devices or emergency flaring events
because we had information to determine that such work practices