[Federal Register Volume 84, Number 107 (Tuesday, June 4, 2019)]
[Proposed Rules]
[Pages 25904-25973]
[FR Doc No: 2019-10068]

Vol. 84

Tuesday,

No. 107

June 4, 2019

Part II

Environmental Protection Agency

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40 CFR Part 63

National Emission Standards for Hazardous Air Pollutants: Surface
Coating of Metal Cans and Surface Coating of Metal Coil Residual Risk
and Technology Reviews; Proposed Rule

Federal Register / Vol. 84, No. 107 / Tuesday, June 4, 2019 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2017-0684, EPA-HQ-OAR-2017-0685; FRL-9993-45-OAR]
RIN 2060-AT51

National Emission Standards for Hazardous Air Pollutants: Surface
Coating of Metal Cans and Surface Coating of Metal Coil Residual Risk
and Technology Reviews

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing
amendments to address the results of the residual risk and technology
reviews (RTRs) that the EPA is required to conduct in accordance with
the Clean Air Act (CAA) with regard to the National Emissions Standards
for Hazardous Air Pollutants (NESHAP) for the Surface Coating of Metal
Cans and the NESHAP for the Surface Coating of Metal Coil. The EPA is
proposing to find the risks due to emissions of air toxics from these
source categories under the current standards to be acceptable and that
the standards provide an ample margin of safety to protect public
health. We are proposing no revisions to the numerical emission limits
based on these analyses. The EPA is proposing to amend provisions
addressing emissions during periods of startup, shutdown, and
malfunction (SSM); to amend provisions regarding electronic reporting
of performance test results; to amend provisions regarding monitoring
requirements; and to make miscellaneous clarifying and technical
corrections.

DATES: Comments. Comments must be received on or before July 19, 2019.
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 July 5, 2019.
    Public hearing. If anyone contacts us requesting a public hearing
on or before June 10, 2019, we will hold a hearing. Additional
information about the hearing, if requested, will be published in a
subsequent Federal Register document and posted at https://www.epa.gov/stationary-sources-air-pollution/surface-coating-metal-cans-national-emission-standards-hazardous and https://www.epa.gov/stationary-sources-air-pollution/surface-coating-metal-coil-national-emission-standards-hazardous. See SUPPLEMENTARY INFORMATION for information on
requesting and registering for a public hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2017-0684 for 40 Code of Federal Regulations (CFR) part 63, subpart
KKKK, Surface Coating of Metal Cans, and Docket ID No. EPA-HQ-OAR-2017-
0685 for 40 CFR part 63, subpart SSSS, Surface Coating of Metal Coil,
as applicable, by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/
(our preferred method). Follow the online instructions for submitting
comments.
     Email<EMAIL_ADDRESS>Include Docket ID No. EPA-
HQ-OAR-2017-0684 or EPA-HQ-OAR-2017-0685 (specify the applicable docket
number) in the subject line of the message.
     Fax:<PHONE_NUMBER>. Attention Docket ID No. EPA-HQ-OAR-
2017-0684 or EPA-HQ-OAR-2017-0685 (specify the applicable docket
number).
     Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2017-0684 or EPA-HQ-OAR-2017-0685
(specify the applicable docket number), Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.
     Hand/Courier Delivery: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-
Friday (except Federal holidays).
    Instructions: All submissions received must include the applicable
Docket ID No. for this rulemaking. Comments received may be posted
without change to https://www.regulations.gov/, including any personal
information provided. For detailed instructions on sending comments and
additional information on the rulemaking process, see the SUPPLEMENTARY
INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Ms. Paula Hirtz, Minerals and Manufacturing Group,
Sector Policies and Programs Division (D243-04), Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711; telephone number:<PHONE_NUMBER>;
fax number:<PHONE_NUMBER>; and email address<EMAIL_ADDRESS>For
specific information regarding the risk modeling methodology, contact
Mr. Chris Sarsony, 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_ADDRESS>For questions about monitoring and
testing requirements, contact Mr. Ketan Patel, Sector Policies and
Programs Division (D243-04), Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina 27711; telephone number:<PHONE_NUMBER>; fax
number:<PHONE_NUMBER>; and email address<EMAIL_ADDRESS>For
information about the applicability of any of these NESHAP to a
particular entity, contact Mr. John Cox, Office of Enforcement and
Compliance Assurance, U.S. Environmental Protection Agency, WJC South
Building (Mail Code 2227A), 1200 Pennsylvania Avenue NW, Washington, DC
20460; telephone number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:
    Public hearing. Please contact Ms. Nancy Perry at<PHONE_NUMBER> or
by email at<EMAIL_ADDRESS>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.
    Docket. The EPA has established two separate dockets for this
rulemaking. Docket ID No. EPA-HQ-OAR-2017-0684 has been established for
40 CFR part 63, subpart KKKK, Surface Coating of Metal Cans, and Docket
ID No. EPA-HQ-OAR-2017-0685 has been established for 40 CFR part 63,
subpart SSSS, Surface Coating of Metal Coil. All documents in the
dockets are listed in Regulations.gov. Although listed, some
information is not publicly available, e.g., Confidential Business
Information (CBI) or other information whose disclosure is restricted
by statute. Certain other material, such as copyrighted material, is
not placed on the internet and will be publicly available only in hard
copy. Publicly available docket materials are available either
electronically in Regulations.gov or in hard copy at the EPA Docket
Center, Room 3334, WJC West Building, 1301 Constitution Avenue NW,
Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30
p.m., Monday through Friday, excluding legal holidays. The telephone
number for the Public Reading Room is<PHONE_NUMBER>, and the telephone
number for the EPA Docket Center is<PHONE_NUMBER>.

    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2017-0684 for 40 CFR part 63, subpart KKKK, Surface Coating of Metal
Cans (Metal Cans Docket), or Docket ID No. EPA-HQ-OAR-2017-0685 for 40
CFR part 63, subpart SSSS, Surface Coating of Metal Coil (Metal Coil
Docket), as applicable to your comments. The EPA's policy is that all
comments received will be included in the public docket without change
and may be made available online at https://www.regulations.gov/,
including any personal information provided, unless the comment
includes information claimed to be CBI or other information whose
disclosure is restricted by statute. Do not submit information that you
consider to be CBI or otherwise protected through https://www.regulations.gov/ or email. This type of information should be
submitted by mail as discussed below.
    The EPA may publish any comment received to its public docket.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e., on the Web, cloud, or other
file sharing system). For additional submission methods, the full EPA
public comment policy, information about CBI or multimedia submissions,
and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    The https://www.regulations.gov/ website allows you to submit your
comment anonymously, which means the EPA will not know your identity or
contact information unless you provide it in the body of your comment.
If you send an email comment directly to the EPA without going through
https://www.regulations.gov/, your email address will be automatically
captured and included as part of the comment that is placed in the
public docket and made available on the internet. If you submit an
electronic comment, the EPA recommends that you include your name and
other contact information in the body of your comment and with any
digital storage media you submit. If the EPA cannot read your comment
due to technical difficulties and cannot contact you for clarification,
the EPA may not be able to consider your comment. Electronic files
should not include special characters or any form of encryption and be
free of any defects or viruses. For additional information about the
EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    Submitting CBI. Do not submit information containing CBI to the EPA
through https://www.regulations.gov or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
any digital storage media that you mail to the EPA, mark the outside of
the digital storage media as CBI and then identify electronically
within the digital storage media the specific information that is
claimed as CBI. In addition to one complete version of the comments
that includes information claimed as CBI, you must submit a copy of the
comments that does not contain the information claimed as CBI directly
to the public docket through the procedures outlined in Instructions
above. If you submit any digital storage media that does not contain
CBI, mark the outside of the digital storage media clearly that it does
not contain CBI. Information not marked as CBI will be included in the
public docket and the EPA's electronic public docket without prior
notice. Information marked as CBI will not be disclosed except in
accordance with procedures set forth in 40 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-2017-0684 for 40 CFR part 63,
subpart KKKK, Surface Coating of Metal Cans (Metal Cans Docket), or
Docket ID No. EPA-HQ-OAR-2017-0685 for 40 CFR part 63, subpart SSSS,
Surface Coating of Metal Coil (Metal Coil Docket), as applicable.
    Preamble acronyms and abbreviations. We use multiple acronyms and
terms in this preamble. While this list may not be exhaustive, to ease
the reading of this preamble and for reference purposes, the EPA
defines the following terms and acronyms here:

ACA American Coatings Association
AEGL acute exposure guideline level
AERMOD air dispersion model used by the HEM-3 model
ASTM American Society for Testing and Materials
BACT best available control technology
BPA bisphenol A
BPA-NI not intentionally containing BPA
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CEMS continuous emissions monitoring systems
CFR Code of Federal Regulations
DGME diethylene glycol monobutyl ether
ECHO Enforcement and Compliance History Online
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guideline
ERT Electronic Reporting Tool
FR Federal Register
GACT generally available control technology gal gallon
HAP hazardous air pollutant(s)
HCl hydrochloric acid
HEM-3 Human Exposure Model, Version 1.1.0
HF hydrogen fluoride
HI hazard index
HQ hazard quotient
HQREL hazard quotient recommended exposure limit
IBR incorporation by reference
ICAC Institute of Clean Air Companies
ICR Information Collection Request
IRIS Integrated Risk Information System
kg kilogram
km kilometer
LAER lowest achievable emission rate
lb pound
MACT maximum achievable control technology
mg/m\3\ milligrams per cubic meter
MIR maximum individual risk
mm millimeters
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NEI National Emission Inventory
NESHAP national emission standards for hazardous air pollutants
NSR New Source Review
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OCE overall control efficiency
OMB Office of Management and Budget
OSHA Occupational Safety and Health Administration
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PDF portable document format
POM polycyclic organic matter
ppmv parts per million by volume
PRA Paperwork Reduction Act
PTE permanent total enclosure
RACT reasonably available control technology
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
TRIM.FaTE Total Risk Integrated Methodology.Fate, Transport, and
Ecological Exposure model
UF uncertainty factor
[micro]g/m3 micrograms per cubic meter
UMRA Unfunded Mandates Reform Act

URE unit risk estimate
VCS voluntary consensus standards
VOC volatile organic compound

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

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

I. General Information

A. Does this action apply to me?

    Table 1 of this preamble lists the NESHAP and associated regulated
industrial source categories that are 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. As
defined in the Initial List of Categories of Sources Under Section
112(c)(1) of the Clean Air Act Amendments of 1990 (see 57 FR 31576,
July 16, 1992) and Documentation for Developing the Initial Source
Category List, Final Report (see EPA-450/3-91-030, July 1992), the
Surface Coating of Metal Cans source category includes any facility
engaged in the coating of metal cans, including: One- and two-piece
draw and iron can body coating, sheet coating, three-piece can body
assembly coating, or end coating. We estimate that five major source
facilities engaged in metal can coating would be subject to this
proposal. The Surface Coating of Metal Coil source category includes
any facility engaged in the surface coating of metal coil that is a
major source of hazardous air pollutant (HAP) emissions. Metal coil is
defined as any continuous metal strip (with a thickness of 0.15
millimeters (mm) or more) that is packaged in a roll or coil prior to
coating. We estimate that 48 major source facilities engaged in metal
coil coating would be subject to this proposal.

    Table 1--NESHAP and Industrial Source Categories Affected by This
                             Proposed Action
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                                                     Regulated entities
 NESHAP and source category      NAICS code \1\              \2\
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Surface Coating of Metal      332431, 332115,       Two-piece Beverage
 Cans.                         332116, 332812,       Can Facilities,
                               332999.               Three-piece Food
                                                     Can Facilities, Two-
                                                     piece Draw and Iron
                                                     Facilities, One-
                                                     piece Aerosol Can
                                                     Facilities.
                              332431..............  Can Assembly
                                                     Facilities.
                              332812..............  End Manufacturing
                                                     Facilities.
Surface Coating of Metal      325992..............  Photographic Film,
 Coil.                                               Paper, Plate, and
                                                     Chemical
                                                     Manufacturing.
                              326199..............  All Other Plastics
                                                     Product
                                                     Manufacturing.
                              331110..............  Iron and Steel Mills
                                                     and Ferroalloy
                                                     Manufacturing.
                              331221..............  Rolled Steel Shape
                                                     Manufacturing.
                              331315..............  Aluminum Sheet,
                                                     Plate, and Foil
                                                     Manufacturing.
                              331318..............  Other Aluminum
                                                     Rolling, Drawing,
                                                     and Extruding.
                              331420..............  Copper Rolling,
                                                     Drawing, Extruding,
                                                     and Alloying.
                              332311..............  Prefabricated Metal
                                                     Building and
                                                     Component
                                                     Manufacturing.
                              332312..............  Fabricated
                                                     Structural Metal
                                                     Manufacturing.
                              332322..............  Sheet Metal Work
                                                     Manufacturing.
                              \3\ 332812..........  Metal Coating,
                                                     Engraving (except
                                                     Jewelry and
                                                     Silverware), and
                                                     Allied Services to
                                                     Manufacturers.
                              332999..............  All Other
                                                     Miscellaneous
                                                     Fabricated Metal
                                                     Product
                                                     Manufacturing.
                              333249..............  Other Industrial
                                                     Machinery
                                                     Manufacturing.

                              337920..............  Blind and Shade
                                                     Manufacturing.
------------------------------------------------------------------------
\1\ North American Industry Classification System.
\2\ Regulated entities are major source facilities that apply surface
  coatings to these parts or products.
\3\ The majority of coil coating facilities are included in NAICS Code
  332812.

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

    In addition to being available in the dockets for this action, an
electronic copy of this action is available on the internet. Following
signature by the EPA Administrator, the EPA will post a copy of this
proposed action at https://www.epa.gov/stationary-sources-air-pollution/surface-coating-metal-cans-national-emission-standards-hazardous and https://www.epa.gov/stationary-sources-air-pollution/surface-coating-metal-coil-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
these same websites. Information on the overall RTR program is
available at https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.
    Redline versions of the regulatory language that incorporates the
proposed changes in this action are available in the Metal Cans and the
Metal Coil Dockets (Docket ID No. EPA-HQ-OAR-2017-0684 and Docket ID
No. EPA-HQ-OAR-2017-0685, respectively).

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.).\1\ Section 112
of the CAA establishes a two-stage regulatory process to develop
standards for emissions of HAP from stationary sources. Generally, the
first stage involves establishing technology-based standards and the
second stage involves evaluating those standards that are based on
maximum achievable control technology (MACT) to determine whether
additional standards are needed to address any remaining risk
associated with HAP emissions. This second stage is commonly referred
to as the ``residual risk review.'' In addition to the residual risk
review, the CAA also requires the EPA to review standards set under CAA
section 112 every 8 years 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 dockets for each subpart in this rulemaking (Docket ID No. EPA-HQ-
OAR-2017-0684 for Metal Cans Coating and Docket ID No. EPA-HQ-OAR-2017-
0685 for Metal Coil Coating).
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    \1\ In addition, section 301 of the CAA provides general
authority for the Administrator to ``prescribe such regulations as
are necessary to carry out his functions'' under the CAA.
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    In the first stage of the CAA section 112 standard setting process,
the EPA promulgates technology-based standards under CAA section112(d)
for categories of sources identified as emitting one or more of the HAP
listed in CAA section 112(b). Sources of HAP emissions are either major
sources or area sources, and CAA section 112 establishes different
requirements for major source standards and area source standards.
``Major sources'' are those that emit or have the potential to emit 10
tons per year (tpy) or more of a single HAP or 25 tpy or more of any
combination of HAP. All other sources are ``area sources.'' For major
sources, CAA section 112(d)(2) provides that the technology-based
NESHAP must reflect the maximum degree of emission reductions of HAP
achievable (after considering cost, energy requirements, and non-air
quality health and environmental impacts). These standards are commonly
referred to as MACT standards. CAA section 112(d)(3) also establishes a
minimum control level for MACT standards, known as the MACT ``floor.''
The EPA must also consider control options that are more stringent than
the floor. Standards more stringent than the floor are commonly
referred to as beyond-the-floor standards. In certain instances, as
provided in CAA section 112(h), the EPA may set work practice standards
where it is not feasible to prescribe or enforce a numerical emission
standard. For area sources, CAA section 112(d)(5) gives the EPA
discretion to set standards based on generally available control
technologies or management practices (GACT standards) in lieu of MACT
standards.
    The second stage in standard-setting focuses on identifying and
addressing any remaining (i.e., ``residual'') risk according to CAA
section 112(f). For source categories subject to MACT standards,
section 112(f)(2) of the CAA requires the EPA to determine whether
promulgation of additional standards is needed to provide an ample
margin of safety to protect public health or to prevent an adverse
environmental effect. Section 112(d)(5) of the CAA provides that this
residual risk review is not required for categories of area sources
subject to GACT standards. Section 112(f)(2)(B) of the CAA further
expressly preserves the EPA's use of the two-step approach for
developing standards to address any residual risk and the Agency's
interpretation of ``ample margin of safety'' developed in the National
Emissions Standards for Hazardous Air Pollutants: Benzene Emissions
from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene
Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery
Plants (Benzene NESHAP) (54 FR 38044, September 14, 1989). The EPA
notified Congress in the Risk Report that the Agency intended to use
the Benzene NESHAP approach in making CAA section 112(f) residual risk
determinations (EPA-453/R-99-001, p. ES-11). The EPA subsequently
adopted this approach in its residual risk determinations and the
United States Court of Appeals for the District of Columbia Circuit
(the Court) upheld the EPA's interpretation that CAA section 112(f)(2)
incorporates the approach established in the Benzene NESHAP. See NRDC
v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008).
    The approach incorporated into the CAA and used by the EPA to
evaluate residual risk and to develop standards under CAA section
112(f)(2) is a two-step approach. In the first step, the EPA determines
whether risks are acceptable. This determination ``considers all health

information, including risk estimation uncertainty, and includes a
presumptive limit on maximum individual lifetime [cancer] risk (MIR)
\2\ of approximately 1-in-10 thousand.'' 54 FR 38045, September 14,
1989. If risks are unacceptable, the EPA must determine the emissions
standards necessary to reduce risk to an acceptable level without
considering costs. In the second step of the approach, the EPA
considers whether the emissions standards provide an ample margin of
safety to protect public health ``in consideration of all health
information, including the number of persons at risk levels higher than
approximately 1-in-1 million, as well as other relevant factors,
including costs and economic impacts, technological feasibility, and
other factors relevant to each particular decision.'' Id. The EPA must
promulgate emission standards necessary to provide an ample margin of
safety to protect public health. After conducting the ample margin of
safety analysis, we consider whether a more stringent standard is
necessary to prevent, taking into consideration costs, energy, safety,
and other relevant factors, an adverse environmental effect.
---------------------------------------------------------------------------

    \2\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk if an individual were exposed to the maximum
level of a pollutant for a lifetime.
---------------------------------------------------------------------------

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

B. What are the source categories and how do the current NESHAP
regulate their HAP emissions?

1. What is the Surface Coating of Metal Cans source category and how
does the current NESHAP regulate its HAP emissions?
a. Source Category Description
    The NESHAP for the Surface Coating of Metal Cans source category
was promulgated on November 13, 2003 (68 FR 64432), and is codified at
40 CFR part 63, subpart KKKK. Technical corrections and clarifying
amendments were promulgated on January 6, 2006 (71 FR 1386). The
Surface Coating of Metal Cans NESHAP applies to the surface coating and
related operations at each new, reconstructed, and existing affected
source of HAP emissions at facilities that are major sources and are
engaged in the surface coating of metal cans and ends (including
decorative tins) and metal crowns and closures. The Surface Coating of
Metal Cans NESHAP (40 CFR 63.3561) defines a ``metal can'' as ``a
single-walled container manufactured from metal substrate equal to or
thinner than 0.3785 mm (0.0149 inch)'' and includes coating operations
for the four following subcategories:
     One- and two-piece draw and iron can body coating--
includes one-piece aerosol cans, defined as an ``aerosol can formed by
the draw and iron process to which no ends are attached and a valve is
placed directly on top'' and two-piece draw and iron cans, defined as a
``steel or aluminum can manufactured by the draw and iron process.''
These include two-piece beverage cans manufactured to contain drinkable
liquids, such as beer, soft drinks, or fruit juices, and two-piece food
cans designed to contain edible products other than beverages and to be
hermetically sealed.
     Sheetcoating--includes all the flat metal sheetcoating
operations associated with the manufacture of three-piece cans,
decorative tins, crowns, and closures.
     Three-piece can body assembly coating--includes three-
piece aerosol cans, defined as a ``steel aerosol can formed by the
three-piece can assembly process manufactured to contain food or
nonfood products,'' and three-piece food cans, defined as a ``steel can
formed by the three-piece can assembly process manufactured to contain
edible products and designed to be hermetically sealed.''
     End coating--includes the application of end seal
compounds and repair spray coatings to metal can ends and includes
three distinct coating type segments reflecting different end uses:
Aseptic end seal compounds, non-aseptic end seal compounds, and repair
spray coatings.
    The Surface Coating of Metal Cans NESHAP defines a ``decorative
tin'' as ``a single-walled container, designed to be covered or
uncovered that is manufactured from metal substrate equal to or thinner
than 0.3785 mm (0.0149 inch) and is normally coated on the exterior
surface with decorative coatings. Decorative tins may contain foods but
are not hermetically sealed and are not subject to food processing
steps such as retort or pasteurization. Interior coatings are not
usually applied to protect the metal and contents from chemical
interaction.''
    The Surface Coating of Metal Cans NESHAP also defines a ``coating''
as ``a material that is applied to a substrate for decorative,
protective, or functional purposes. Such materials include, but are not
limited to, paints, sealants, caulks, inks, adhesives, and maskants.''
Fusion pastes, ink jet markings, mist solutions, and lubricants, as
well as decorative, protective, or functional materials that consist
only of protective oils for metals, acids, bases, or any combination of
these substances, are not considered coatings under 40 CFR part 63,
subpart KKKK.
    Based on our search of the National Emission Inventory (NEI)
(www.epa.gov/air-emissions-inventories/national-emissions-inventory-nei) and the EPA's Enforcement and Compliance History Online (ECHO)
database (echo.epa.gov) and a review of active air emissions permits,
we estimate that five facilities are subject to the Surface Coating of
Metal Cans NESHAP. A complete list of facilities subject to the Surface
Coating of Metal Cans NESHAP is available in Appendix 1 to the
memorandum titled Technology Review for Surface Coating Operations in
the Metal Cans Category, in the Metal Cans Docket (Docket ID No. EPA-
HQ-OAR-2017-0684).
b. HAP Emission Sources
    The primary HAP emitted from metal can surface coating operations
are organic HAP and include glycol ethers, formaldehyde, xylenes,
toluene, methyl isobutyl ketone, 2-(hexyloxy) ethanol, ethyl benzene,
and methanol. These HAP account for 99 percent of the HAP emissions
from the source category. The HAP emissions from the metal cans
category occur from coating application lines, drying and curing ovens,
mixing and thinning areas, and cleaning of equipment. The coating
application lines and the drying and curing ovens are the largest
sources of HAP emissions. The coating application lines apply an
exterior base coat to two- and three-piece cans using a lithographic/
printing (i.e., roll) application process. The inside, side seam, and
repair coatings are spray applied using airless spray equipment and are
a minor portion of the can coating operations. As indicated by the
name, repair spray coatings are used to cover breaks in the coating
that are caused during the formation of the score in easy-open ends or
to provide, after the manufacturing process, an additional protective
layer for corrosion resistance.

    Inorganic HAP emissions were considered in the development of the
Surface Coating of Metal Cans NESHAP. Inorganic HAP, including chromium
and manganese compounds, are contained in some of the coatings used by
this source category. However, the EPA determined that no controls were
needed because the coatings used that may contain inorganic HAP were
not spray applied. Instead, these coatings were roll applied through
direct contact (similar to lithographic printing) with the surface to
which they were being applied, and the inorganic HAP became part of the
cured coating.\3\ No inorganic HAP were reported in the NEI data used
for this RTR for surface coating operations at major source metal can
coating facilities.
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    \3\ National Emission Standards for Hazardous Air Pollutants:
Surface Coating of Metal Cans Background Information for Final
Standards. Summary of Public Comments and Responses. EPA 453/R-03-
009. August 2003. Section 2.5.4.
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c. NESHAP Requirements for Control of HAP
    We estimated that the Surface Coating of Metal Cans NESHAP
requirements would reduce the emissions of organic HAP from the source
category by 71 percent or 6,800 tpy (68 FR 2110, January 15, 2003).
This estimate included two HAP that were since delisted. The delisting
of ethylene glycol monobutyl ether occurred in 2004, and the delisting
of methyl ethyl ketone occurred in 2005.
    The NESHAP specifies numerical emission limits for existing sources
and for new and reconstructed sources for organic HAP emissions
according to four can coating subcategories. The organic HAP emission
limits for existing sources conducting: (1) One- and two-piece draw and
iron can body coating (includes two-piece beverage cans, two-piece food
cans, and one-piece aerosol cans) ranges from 0.07 to 0.12 kilogram
(kg) HAP/liter of coating solids (or 0.59 to 0.99 pound/gallon (lb/
gal)); (2) sheet coating is 0.03 kg HAP/liter of coating solids (or
0.26 lb/gal); (3) three piece can assembly (includes inside spray,
aseptic, and non-aseptic side seam stripes on food cans, side seam
stripes on general line non-food cans, and side seam stripes on aerosol
cans) ranges from 0.29 to 1.94 kg HAP/liter of coating solids (or 2.43
to 16.16 lb/gal); and (4) end coating (includes aseptic and non-aseptic
end seal compounds and repair spray coatings) ranges from zero to 2.06
kg HAP/liter of coating solids (or zero to 17.17 lb/gal). The organic
HAP emission limits for new and reconstructed sources conducting: (1)
One and two-piece draw and iron can body coating ranges from 0.04 to
0.08 kg HAP/liter of coating solids (or 0.31 to 0.65 lb/gal); (2) sheet
coating is 0.02 kg HAP/liter of coating solids (or 0.17 lb/gal); (3)
three piece can assembly ranges from 0.12 to 1.48 kg HAP/liter of
coating solids (or 1.03 to 12.37 lb/gal); and (4) end coating ranges
from zero to 0.64 kg HAP/liter of coating solids (or zero to 5.34 lb/
gal). The specific organic HAP emission limits for each can coating
subcategory are listed in Table 3 of the memorandum titled Technology
Review for Surface Coating Operations in the Metal Cans Category, in
the Metal Cans Docket (Docket ID No. EPA-HQ-OAR-2017-0684).
    Compliance with the Surface Coating of Metal Cans NESHAP emission
limits can be achieved using several different options, including a
compliant material option, an emission rate without add-on controls
option (averaging option), an emission rate with add-on controls
option, or a control efficiency/outlet concentration. For any coating
operation(s) on which the facility uses the compliant material option
or the emission rate without add-on controls option, the facility is
not required to meet any work practice standards.
    If the facility uses the emission rate with add-on controls option,
the facility must develop and implement a work practice plan to
minimize organic HAP emissions from the storage, mixing, and conveying
of coatings, thinners, and cleaning materials used in, and waste
materials generated by, the coating operation(s) using that option. The
plan must specify practices and procedures to ensure that a set of
minimum work practices specified in the NESHAP are implemented. The
facility must also comply with site-specific operating limits for the
emission capture and control system.
2. What is the Surface Coating of Metal Coil source category and how
does the current NESHAP regulate its HAP emissions?
a. Source Category Description
    The NESHAP for the Surface Coating of Metal Coil source category
was promulgated on June 10, 2002 (67 FR 39794), and is codified at 40
CFR part 63, subpart SSSS. A technical correction to the final rule was
published on March 17, 2003 (68 FR 12590). The Surface Coating of Metal
Coil NESHAP applies to owners or operators of metal coil surface
coating operations at facilities that are major sources of HAP.
    The Surface Coating of Metal Coil NESHAP (40 CFR 63.5100) applies
to the collection of all coil coating lines at a facility and defines a
coil coating line as the process for metal coil coating that includes
the web unwind or feed station, a series of one or more coating
stations, associated curing ovens, wet sections, and quench stations. A
coil coating line does not include ancillary operations such as mixing/
thinning, cleaning, wastewater treatment, and storage of coating
material. The Surface Coating of Metal Coil NESHAP (40 CFR 63.5110)
defines a coil coating operation as the collection of equipment used to
apply an organic coating to the surface of any continuous metal strip
that is 0.006 inch (0.15 millimeter (mm)) thick or more that is
packaged in a roll or coil. The Surface Coating of Metal Coil NESHAP
also defines a coating material as the coating and other products
(e.g., a catalyst and resin in multi-component coatings) combined to
make a single material at the coating facility that is applied to metal
coil and includes organic solvents used to thin a coating prior to
application to the metal coil.
    Based on our search of the NEI and EPA's ECHO database and a review
of active air emission permits, we estimate that 48 facilities are
subject to the Surface Coating of Metal Coil NESHAP. A complete list of
facilities we identified as subject to the Surface Coating of Metal
Coil NESHAP is available in Appendix 1 to the memorandum titled
Residual Risk Assessment for the Surface Coating of Metal Coil Source
Category in Support of the 2019 Risk and Technology Review Proposed
Rule (hereafter referred to as the Metal Coil Risk Assessment Report),
in the Surface Coating of Metal Coil Docket (Docket ID No. EPA-HQ-OAR-
2017-0685).
b. HAP Emission Sources
    The primary HAP emitted from metal coil coating operations are
organic HAP and include xylenes, glycol ethers, naphthalene,
isophorone, toluene, diethylene glycol monobutyl ether (DGME), and
ethyl benzene. The majority of organic HAP emissions are from the
coating application and the curing ovens.
    Inorganic HAP emissions were considered in the development of the
Surface Coating of Metal Coil NESHAP. Based on information reported in
survey responses during the development of the 2002 proposed NESHAP,
inorganic HAP were present in the pigments and film-forming components
of some coatings used by this source category. However, we concluded
that inorganic HAP are not likely to be emitted from these sources
because of the application techniques used (67 FR 46032, July 11,
2002). The data obtained from the NEI and the Toxics Release Inventory
for

this RTR included low quantities of inorganic HAP for major source
facilities that conduct metal coil operations. Further investigation of
these sources concluded that these inorganic emissions were reported in
error.
c. NESHAP Requirements for Control of HAP
    We estimated that the Surface Coating of Metal Coil NESHAP
requirements would reduce the emissions of organic HAP from the source
category by approximately 55 percent or 1,318 tpy (65 FR 44616, July
18, 2000). The NESHAP specifies numerical emission limits for organic
HAP emissions from the coating application stations and associated
curing ovens. The Surface Coating of Metal Coil NESHAP provides options
for limiting organic HAP emissions to one of the four specified levels:
(1) Use only individually compliant coatings with an organic HAP
content that does not exceed 0.046 kg/liter of solids applied, (2) use
coatings with an average organic HAP content of 0.046 kg/liter of
solids on a rolling 12-month average, (3) use a capture system and add-
on control device to either reduce emissions by 98 percent or use a
100-percent efficient capture system (permanent total enclosure (PTE))
and an oxidizer to reduce organic HAP emissions to no more than 20
parts per million by volume (ppmv) as carbon, or (4) use a combination
of compliant coatings and control devices to maintain an average
equivalent emission rate of organic HAP not exceeding 0.046 kg/liter of
solids on a rolling 12-month average basis. These compliance options
apply to an individual coil coating line, to multiple lines as a group,
or to the entire affected source.
    Compliant coatings must contain no organic HAP (each organic HAP
that is not an Occupational Safety and Health Administration (OSHA)-
defined carcinogen that is measured to be present at less than 1
percent by weight is counted as zero). The NESHAP also sets operating
limits for the emission capture and add-on control devices.

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

    For the risk modeling portion of these RTRs, the EPA used data from
the 2011 and 2014 NEI. 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 data 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 data to develop
the model input files for the risk assessments for each of these three
source categories. Detailed information on the development of the
modeling file for the Surface Coating of Metal Cans source category can
be found in Appendix 1 to the Residual Risk Assessment for the Surface
Coating of Metal Cans Source Category in Support of the 2019 Risk and
Technology Review Proposed Rule (hereafter referred to as the Metal
Cans Risk Assessment Report), in the Metal Cans Docket (Docket ID No.
EPA-HQ-OAR-2017-0684). Detailed information on the development of the
modeling file for the Surface Coating of Metal Coil source category can
be found in Appendix 1 to the Metal Coil Risk Assessment Report, in the
Metal Coil Docket (Docket ID No. EPA-HQ-OAR-2017-0685).
    For both the risk modeling and technology review portion of these
RTRs, we also gathered data from facility construction and operating
permits regarding emission points, air pollution control devices, and
process operations. We collected permits and supporting documentation
from state permitting authorities through state-maintained online
databases. The facility permits were also used to confirm that the
facilities were major sources of HAP and were subject to the NESHAP
that are the subject of these risk assessments. In certain cases, we
contacted industry associations and facility owners or operators to
confirm and clarify the sources of emissions that were reported in the
NEI. No formal information collection request (ICR) was conducted for
this action.
    For the technology review portion of these RTRs, we also used
information from the EPA's ECHO database as a tool to identify which
facilities were potentially subject to the 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 facilities that could potentially
be subject to each of these two NESHAP. We then reviewed operating
permits for these facilities, when available, to confirm that they were
major sources of HAP with emission sources subject to these NESHAP.
    Also for the technology reviews, we collected information from the
reasonably available control technology (RACT), best available control
technology (BACT), and lowest achievable emission rate (LAER)
determinations in the EPA's RACT/BACT/LAER Clearinghouse (RBLC).\4\
This is a database that contains case-specific information on 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 large 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 for these
surface coating operations to reduce air emissions.
---------------------------------------------------------------------------

    \4\ https://www.epa.gov/catc/ractbactlaer-clearinghouse-rblc-basic-information.
---------------------------------------------------------------------------

    Additional information about these data collection activities for
the technology reviews is contained in the technology review memoranda
titled Technology Review for Surface Coating Operations in the Metal
Cans Category, May 2017 (hereafter referred to as the Metal Cans
Technology Review Memo), and the Technology Review for Surface Coating
Operations in the Metal Coil Category, September 2017 (hereafter
referred to as the Metal Coil Technology Review Memo), available in the
respective Metal Cans and Metal Coil Dockets.

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

    We also reviewed the NESHAP for other surface coating source
categories that were promulgated after the Surface Coating of Metal
Cans and the Surface Coating of Metal Coil NESHAP as part of the
technology review for these source categories. We reviewed the
regulatory requirements and/or technical analyses associated with these
later regulatory actions to identify any practices, processes, and
control technologies considered in those rulemakings that could be
applied to emission sources in the Surface Coating of Metal Cans and
the Surface Coating of Metal Coil source categories, as well as the
costs, non-air impacts, and energy implications associated with the use
of those technologies. We also reviewed

information available in the American Coatings Association's (ACA)
Industry Market Analysis, 9th Edition (2014-2019).\5\ The ACA Industry
Market Analysis provided information on trends in coatings technology
that can affect emissions from the Surface Coating of Metal Cans and
the Surface Coating of Metal Coil source categories. Additional details
regarding our review of these information sources are contained in the
Metal Cans Technology Review Memo, and the Metal Coil Technology Review
Memo, available in the respective Metal Cans and Metal Coil Dockets.
---------------------------------------------------------------------------

    \5\ Prepared for the ACA, Washington, DC, by The ChemQuest
Group, Inc., Cincinnati, Ohio. 2015.
---------------------------------------------------------------------------

III. Analytical Procedures and Decision Making

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

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

    As discussed in section II.A of this preamble and in the Benzene
NESHAP, in evaluating and developing standards under CAA section
112(f)(2), we apply a two-step approach to determine whether or not
risks are acceptable and to determine if the standards provide an ample
margin of safety to protect public health. As explained in the Benzene
NESHAP, ``the first step judgment on acceptability cannot be reduced to
any single factor'' and, thus, ``[t]he Administrator believes that the
acceptability of risk under section 112 is best judged on the basis of
a broad set of health risk measures and information.'' 54 FR 38046,
September 14, 1989. Similarly, with regard to the ample margin of
safety determination, ``the Agency again considers all of the health
risk and other health information considered in the first step. Beyond
that information, additional factors relating to the appropriate level
of control will also be considered, including cost and economic impacts
of controls, technological feasibility, uncertainties, and any other
relevant factors.'' Id.
    The Benzene NESHAP approach provides flexibility regarding factors
the EPA may consider in making determinations and how the EPA may weigh
those factors for each source category. The EPA conducts a risk
assessment that provides estimates of the MIR posed by the HAP
emissions from each source in the source category, the hazard index
(HI) for chronic exposures to HAP with the potential to cause noncancer
health effects, and the hazard quotient (HQ) for acute exposures to HAP
with the potential to cause noncancer health effects.\6\ The assessment
also provides estimates of the distribution of cancer risk within the
exposed populations, cancer incidence, and an evaluation of the
potential for an adverse environmental effect. The scope of the EPA's
risk analysis is consistent with the EPA's response to comments on our
policy under the Benzene NESHAP where the EPA explained that:
---------------------------------------------------------------------------

    \6\ 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 non-cancer 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 noncancer health
effects, and the uncertainties of the risk estimates. In this way, the
effect on the most exposed individuals can be reviewed as well as the
impact on the general public. These factors can then be weighed in each
individual case. This approach complies with the Vinyl Chloride mandate
that the Administrator ascertain an acceptable level of risk to the
public by employing his expertise to assess available data. It also
complies with the Congressional intent behind the CAA, which did not
exclude the use of any particular measure of public health risk from
the EPA's consideration with respect to CAA section 112 regulations,
and thereby implicitly permits consideration of any and all measures of
health risk which the Administrator, in his judgment, believes are
---------------------------------------------------------------------------
appropriate to determining what will `protect the public health'.''

    See 54 FR 38057, September 14, 1989. Thus, the level of the MIR is
only one factor to be weighed in determining acceptability of risk. The
Benzene NESHAP explained that ``an MIR of approximately one in 10
thousand should ordinarily be the upper end of the range of
acceptability. As risks increase above this benchmark, they become
presumptively less acceptable under CAA section 112, and would be
weighed with the other health risk measures and information in making
an overall judgment on acceptability. Or, the Agency may find, in a
particular case, that a risk that includes an MIR less than the
presumptively acceptable level is unacceptable in the light of other
health risk factors.'' Id. at 38045. Similarly, with regard to the
ample margin of safety analysis, the EPA stated in the Benzene NESHAP
that the: ``EPA believes the relative weight of the many factors that
can be considered in selecting an ample margin of safety can only be
determined for each specific source category. This occurs mainly
because technological and economic factors (along with the health-
related factors) vary from source category to source category.'' Id. at
38061. We also consider the uncertainties associated with the various
risk analyses, as discussed earlier in this preamble, in our
determinations of acceptability and ample margin of safety.
    The EPA notes that it has not considered certain health information
to date in making residual risk determinations. At this time, we do not
attempt to quantify the HAP risk that may be associated with emissions
from other facilities that do not include the source categories under
review, mobile source emissions, natural source emissions, persistent
environmental pollution, or atmospheric transformation in the vicinity
of the sources in the categories.
    The EPA understands the potential importance of considering an
individual's total exposure to HAP in addition to considering exposure
to HAP emissions from the source category and facility. We recognize
that such consideration may be particularly important when assessing
noncancer risk, where pollutant-specific exposure health reference
levels (e.g., reference concentrations (RfCs)) are based on the
assumption that thresholds exist for adverse health effects. For
example, the EPA recognizes that, although exposures attributable to
emissions from a source category or facility alone may not indicate the
potential for increased risk of adverse noncancer health effects in a
population, the exposures resulting from emissions from the facility in
combination with emissions from all of the other sources (e.g., other
facilities) to which an individual is exposed may be sufficient to
result in an increased risk of adverse noncancer health effects. In May
2010, the Science Advisory Board (SAB) advised the EPA ``that RTR
assessments will be most useful to decision makers and communities if
results are presented in the broader context of aggregate and
cumulative risks, including background concentrations and contributions
from other sources in the area.'' \7\
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    \7\ Recommendations of the SAB Risk and Technology Review (RTR)
Panel are provided in their report, which is available at: http://
yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.

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

B. How do we perform the technology review?

    Our technology review focuses on the identification and evaluation
of developments in practices, processes, and control technologies that
have occurred since the MACT standards were promulgated. Where we
identify such developments, we analyze their technical feasibility,
estimated costs, energy implications, and non-air environmental
impacts. We also consider the emission reductions associated with
applying each development. This analysis informs our decision of
whether it is ``necessary'' to revise the emissions standards. In
addition, we consider the appropriateness of applying controls to new
sources versus retrofitting existing sources. For this exercise, we
consider any of the following to be a ``development'':
     Any add-on control technology or other equipment that was
not identified and considered during development of the original MACT
standards;
     Any improvements in add-on control technology or other
equipment (that were identified and considered during development of
the original MACT standards) that could result in additional emissions
reduction;
     Any work practice or operational procedure that was not
identified or considered during development of the original MACT
standards;
     Any process change or pollution prevention alternative
that could be broadly applied to the industry and that was not
identified or considered during development of the original MACT
standards; and
     Any significant changes in the cost (including cost
effectiveness) of applying controls (including controls the EPA
considered during the development of the original MACT standards).
    In addition to reviewing the practices, processes, and control
technologies that were considered at the time we originally developed
the NESHAP (i.e., the 2003 Surface Coating of Metal Cans NESHAP; and
the 2002 Surface Coating of Metal Coil NESHAP) we review a variety of
data sources in our investigation of potential practices, processes, or
controls that may have not been considered for each of the two source
categories during development of the NESHAP. Among the sources we
reviewed were the NESHAP for various industries that were promulgated
after the MACT standards being reviewed in this action (e.g., NESHAP
for Miscellaneous Metal Parts and Products (40 CFR part 63, subpart
MMMM)). We also reviewed the results of other technology reviews for
other surface coating source categories since the promulgation of the
NESHAP (e.g., the technology reviews conducted for the Shipbuilding and
Ship Repair (Surface Coating) NESHAP (40 CFR part 63, subpart II) and
the Wood Furniture Manufacturing Operations NESHAP (40 CFR part 63,
subpart JJ)). 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 Surface
Coating of Metal Cans and the Surface Coating of Metal Coil source
categories, 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-sponsored market analyses and
trade journals, to research advancements in add-on controls and lower
HAP technology for coatings and solvents. For a more detailed
discussion of our methods for performing these technology reviews,
refer to the Metal Cans Technology Review Memo and the Metal Coil
Technology Review Memo, which are available in the respective Metal
Cans and Metal Coil dockets.

C. How do we estimate post-MACT risk posed by these source categories?

    In this section, we provide a complete description of the types of
analyses that we generally perform during the risk assessment process.
In some cases, we do not perform a specific analysis because it is not
relevant. For example, in the absence of emissions of HAP known to be
persistent and bioaccumulative in the environment (PB-HAP), we would
not perform a multipathway exposure assessment. Where we do not perform
an analysis, we state that we do not and provide the reason. While we
present all of our risk assessment methods, we only present risk
assessment results for the analyses actually conducted (see section
IV.B of this preamble).
    The EPA conducts a risk assessment that provides estimates of the
MIR for cancer posed by the HAP emissions from each source in the
source category, the HI for chronic exposures to HAP with the potential
to cause noncancer health effects, and the HQ for acute exposures to
HAP with the potential to cause noncancer health effects. The
assessment also provides estimates of the distribution of cancer risk
within the exposed populations, cancer incidence, and an evaluation of
the potential for an adverse environmental effect. The seven sections
that follow this paragraph describe how we estimated emissions and
conducted the risk assessments in this action. The dockets for this
rulemaking contain the following documents which provide more
information on the risk assessment inputs and models: Metal Cans Risk
Assessment Report and the Metal Coil Risk Assessment Report. The
methods used to assess risk (as described in the seven primary steps
below) are consistent with those described by the EPA in the document
reviewed by a panel of the EPA's SAB in 2009; \8\ and described in the
SAB review report issued in 2010. They are also consistent with the key
recommendations contained in that report.
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    \8\ U.S. EPA. Risk and Technology Review (RTR) Risk Assessment
Methodologies: For Review by the EPA's Science Advisory Board with
Case Studies--MACT I Petroleum Refining Sources and Portland Cement
Manufacturing, June 2009. EPA-452/R-09-006. https://www3.epa.gov/airtoxics/rrisk/rtrpg.html.

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1. How did we estimate actual emissions and identify the emissions
release characteristics?
    The actual emissions and the emission release characteristics for
each facility were obtained primarily from either the 2011 NEI or the
2014 NEI. The 2011 version of the NEI was the most recent version
available during the data collection phase of this rulemaking;
therefore, most data were obtained from the 2011 NEI. The 2014 NEI was
used to supplement the dataset with HAP data for emission units or
processes for which the 2011 NEI included only volatile organic
compounds (VOC) or particulate matter. In some cases, the industry
association or the specific facilities were contacted to confirm
emissions that appeared to be outliers, that were otherwise
inconsistent with our understanding of the industry, or that were
associated with high risk values in our initial risk screening
analyses. When appropriate, emission values and release characteristics
were revised based on these facility contacts, and these changes were
documented. Additional information on the development of the modeling
file for each source category, including the development of the actual
emissions estimates and emissions release characteristics, can be found
in Appendix 1 to the Metal Cans Risk Assessment Report, in the Metal
Cans Docket and Appendix 1 to the Metal Coil Risk Assessment Report, in
the Metal Coil Docket.
2. How did we estimate MACT-allowable emissions?
    The available emissions data in the RTR emissions dataset include
estimates of the mass of HAP emitted during a specified annual time
period. These ``actual'' emission levels are often lower than the
emission levels allowed under the requirements of the current MACT
standards. The emissions allowed under the MACT standards are referred
to as the ``MACT-allowable'' emissions. We discussed the consideration
of both MACT-allowable and actual emissions in the final Coke Oven
Batteries RTR (70 FR 19998-19999, April 15, 2005) and in the proposed
and final Hazardous Organic NESHAP RTRs (71 FR 34428, June 14, 2006,
and 71 FR 76609, December 21, 2006, respectively). In those actions, we
noted that assessing the risk at the MACT-allowable level is inherently
reasonable since that risk reflects the maximum level facilities could
emit and still comply with national emission standards. We also
explained that it is reasonable to consider actual emissions, where
such data are available, in both steps of the risk analysis, in
accordance with the Benzene NESHAP approach. (54 FR 38044, September
14, 1989.)
    For both the Surface Coating of Metal Cans and the Surface Coating
of Metal Coil source categories, the EPA calculated allowable emissions
by developing source category-specific multipliers of 1.1 that was
applied to the current emissions for each category to estimate the
allowable emissions. The multipliers were based on information obtained
from the facility operating permits and the add-on control device
control efficiencies for metal can and metal coil coating operations.
Both categories have facilities that employ the use of add-on controls
with efficiencies that are slightly above the control efficiency level
required by the respective NESHAP, which suggests that the actual
emissions are slightly lower than the NESHAP allowable levels.
    For more details on how the EPA estimated the MACT allowable
emissions for the Surface Coating of Metal Cans source category, please
see Appendix 1 to the Metal Cans Risk Assessment Report, in the Metal
Cans Docket (Docket ID No. EPA-HQ-OAR-2017-0684). For more details on
how the EPA calculated the MACT allowable emissions for the Surface
Coating of Metal Coil source category, please see Appendix 1 to the
Metal Coil Risk Assessment Report, in the Metal Coil Docket (Docket ID
No. EPA-HQ-OAR-2017-0685).
3. How do we conduct dispersion modeling, determine inhalation
exposures, and estimate individual and population inhalation risk?
    Both long-term and short-term inhalation exposure concentrations
and health risk from the source categories addressed in this proposal
were estimated using the Human Exposure Model (HEM-3).\9\ The HEM-3
performs three primary risk assessment activities: (1) Conducting
dispersion modeling to estimate the concentrations of HAP in ambient
air, (2) estimating long-term and short-term inhalation exposures to
individuals residing within 50 kilometers (km) of the modeled sources,
and (3) estimating individual and population-level inhalation risk
using the exposure estimates and quantitative dose-response
information.
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    \9\ For more information about HEM-3, go to https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem.
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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.\10\ 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 U.S. and Puerto Rico. A
second library of U.S. Census Bureau census block \11\ internal point
locations and populations provides the basis of human exposure
calculations (U.S. Census, 2010). In addition, for each census block,
the census library includes the elevation and controlling hill height,
which are also used in dispersion calculations. A third library of
pollutant-specific dose-response values is used to estimate health
risk. These are discussed below.
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    \10\ 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).
    \11\ A census block is the smallest geographic area for which
census statistics are tabulated.
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b. Risk From Chronic Exposure to HAP
    In developing the risk assessment for chronic exposures, we use the
estimated annual average ambient air concentrations of each HAP emitted
by each source in the source categories. The HAP air concentrations at
each nearby census block centroid located within 50 km of the facility
are a surrogate for the chronic inhalation exposure concentration for
all the people who reside in that census block. A distance of 50 km is
consistent with both the analysis supporting the 1989 Benzene NESHAP
(54 FR 38044, September 14, 1989) and the limitations of Gaussian
dispersion models, including AERMOD.
    For each facility, we calculate the MIR as the cancer risk
associated with a continuous lifetime (24 hours per day, 7 days per
week, 52 weeks per year, 70 years) exposure to the maximum
concentration at the centroid of each inhabited census block. We
calculate individual cancer risk by multiplying the estimated lifetime
exposure to the ambient concentration of each HAP (in micrograms per
cubic meter ([mu]g/m\3\)) by its unit risk estimate (URE). The URE is
an upper-bound estimate of an individual's incremental risk of
contracting cancer over a lifetime of exposure to a concentration of 1
microgram of the pollutant per cubic meter of air. For residual risk

assessments, we generally use UREs from the EPA's Integrated Risk
Information System (IRIS). For carcinogenic pollutants without IRIS
values, we look to other reputable sources of cancer dose-response
values, often using California EPA (CalEPA) UREs, where available. In
cases where new, scientifically credible dose-response values have been
developed in a manner consistent with EPA guidelines and have undergone
a peer review process similar to that used by the EPA, we may use such
dose-response values in place of, or in addition to, other values, if
appropriate. The pollutant-specific dose-response values used to
estimate health risk are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
    To estimate individual lifetime cancer risks associated with
exposure to HAP emissions from each facility in the source category, we
sum the risks for each of the carcinogenic HAP \12\ emitted by the
modeled facility. We estimate cancer risk at every census block within
50 km of every facility in the source category. The MIR is the highest
individual lifetime cancer risk estimated for any of those census
blocks. In addition to calculating the MIR, we estimate the
distribution of individual cancer risks for the source category by
summing the number of individuals within 50 km of the sources whose
estimated risk falls within a specified risk range. We also estimate
annual cancer incidence by multiplying the estimated lifetime cancer
risk at each census block by the number of people residing in that
block, summing results for all of the census blocks, and then dividing
this result by a 70-year lifetime.
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    \12\ The EPA's 2005 Guidelines for Carcinogen Risk Assessment
classifies carcinogens as: ``carcinogenic to humans,'' ``likely to
be carcinogenic to humans,'' and ``suggestive evidence of
carcinogenic potential.'' These classifications also coincide with
the terms ``known carcinogen, probable carcinogen, and possible
carcinogen,'' respectively, which are the terms advocated in the
EPA's Guidelines for Carcinogen Risk Assessment, published in 1986
(51 FR 33992, September 24, 1986). In August 2000, the document,
Supplemental Guidance for Conducting Health Risk Assessment of
Chemical Mixtures (EPA/630/R-00/002), was published as a supplement
to the 1986 document. Copies of both documents can be obtained from
https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944. Summing
the risk of these individual compounds to obtain the cumulative
cancer risk is an approach that was recommended by the EPA's SAB in
their 2002 peer review of the EPA's National Air Toxics Assessment
(NATA) titled NATA--Evaluating the National-scale Air Toxics
Assessment 1996 Data--a SAB Advisory, available at https://
yosemite.epa.gov/sab/sabproduct.nsf/
214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.
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    To assess the risk of noncancer health effects from chronic
exposure to HAP, we calculate either an HQ or a target organ-specific
hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is
emitted. Where more than one noncancer HAP is emitted, we sum the HQ
for each of the HAP that affects a common target organ or target organ
system to obtain a TOSHI. The HQ is the estimated exposure divided by
the chronic noncancer dose-response value, which is a value selected
from one of several sources. The preferred chronic noncancer dose-
response value is the EPA RfC, defined as ``an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure to the human population (including sensitive
subgroups) that is likely to be without an appreciable risk of
deleterious effects during a lifetime'' (https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary). In cases where an RfC
from the EPA's IRIS is not available or where the EPA determines that
using a value other than the RfC is appropriate, the chronic noncancer
dose-response value can be a value from the following prioritized
sources, which define their dose-response values similarly to the EPA:
(1) The Agency for Toxic Substances and Disease Registry (ATSDR)
Minimum Risk Level (https://www.atsdr.cdc.gov/mrls/index.asp); (2) the
CalEPA Chronic Reference Exposure Level (REL) (https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0); or (3) as noted above, a scientifically
credible dose-response value that has been developed in a manner
consistent with the EPA guidelines and has undergone a peer review
process similar to that used by the EPA. The pollutant-specific dose-
response values used to estimate health risks are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
c. Risk From Acute Exposure to HAP That May Cause Health Effects Other
Than Cancer
    For each HAP for which appropriate acute inhalation dose-response
values are available, the EPA also assesses the potential health risks
due to acute exposure. For these assessments, the EPA makes
conservative assumptions about emission rates, meteorology, and
exposure location. We use the peak hourly emission rate,\13\ 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.
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    \13\ In the absence of hourly emission data, we develop
estimates of maximum hourly emission rates by multiplying the
average actual annual emissions rates by a factor (either a
category-specific factor or a default factor of 10) to account for
variability. This is documented in the Metal Cans Risk Assessment
Report and the Metal Coil Risk Assessment Report and in Appendix 5
of the report: Analysis of Data on Short-term Emission Rates
Relative to Long-term Emission Rates. These documents are available
in the Metal Cans Docket and the Metal Coil Docket.
---------------------------------------------------------------------------

    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.'' \14\ 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.\15\ They are
guideline levels for

``once-in-a-lifetime, short-term exposures to airborne concentrations
of acutely toxic, high-priority chemicals.'' Id. at 21. The AEGL-1 is
specifically defined as ``the airborne concentration (expressed as ppm
(parts per million) or mg/m\3\ (milligrams per cubic meter)) of a
substance above which it is predicted that the general population,
including susceptible individuals, could experience notable discomfort,
irritation, or certain asymptomatic nonsensory effects. However, the
effects are not disabling and are transient and reversible upon
cessation of exposure.'' The document also notes that ``Airborne
concentrations below AEGL-1 represent exposure levels that can produce
mild and progressively increasing but transient and nondisabling odor,
taste, and sensory irritation or certain asymptomatic, nonsensory
effects.'' Id. AEGL-2 are defined as ``the airborne concentration
(expressed as parts per million or milligrams per cubic meter) of a
substance above which it is predicted that the general population,
including susceptible individuals, could experience irreversible or
other serious, long-lasting adverse health effects or an impaired
ability to escape.'' Id.
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    \14\ 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.
    \15\ National Academy of Sciences, 2001. Standing Operating
Procedures for Developing Acute Exposure Levels for Hazardous
Chemicals, page 2. Available at https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf. Note that the
National Advisory Committee for Acute Exposure Guideline Levels for
Hazardous Substances ended in October 2011, but the AEGL program
continues to operate at the EPA and works with the National
Academies to publish final AEGLs (https://www.epa.gov/aegl).
---------------------------------------------------------------------------

    ERPGs are ``developed for emergency planning and are intended as
health-based guideline concentrations for single exposures to
chemicals.'' \16\ 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.
---------------------------------------------------------------------------

    \16\ ERPGS Procedures and Responsibilities. March 2014. American
Industrial Hygiene Association. Available at: https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf.
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    An acute REL for 1-hour exposure durations is typically lower than
its corresponding AEGL-1 and ERPG-1. Even though their definitions are
slightly different, AEGL-1s are often the same as the corresponding
ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from
our acute inhalation screening risk assessment typically result when we
use the acute REL for a HAP. In cases where the maximum acute HQ
exceeds 1, we also report the HQ based on the next highest acute dose-
response value (usually the AEGL-1 and/or the ERPG-1).
    For these source categories, we did not have short term emissions
data; therefore, we developed source category-specific factors based on
information about each industry. We request comment on our assumptions
regarding hour-to-hour variation in emissions and our methods of
calculating the multiplier for estimating the peak 1-hour emissions for
each source category and any additional information that could help
refine our approach.
    The Surface Coating of Metal Cans source category process is a
continuous (non-batch) coating application and curing process that
results in consistent emission rates. The sources in this category
primarily roll-apply coatings onto the surface of the metal cans. The
sources employ the use of various compliance options, which include the
use of compliant coatings, coatings when averaged meet the emission
limits, and for facilities that cannot use these options, they employ
the use of add-on controls. We expect that the hourly variations in
emissions from these processes during routine operations to be minimal.
Thus, applying the default emission factor of 10 to estimate the worst-
case hourly emission rate is not reasonable for this category. We
expect that minimal variations in emissions occur due to variations in
the organic HAP content of the coatings. We calculated acute emissions
by developing a source category-specific multiplier of 1.1 that was
applied to the actual annual emissions, which were then divided by the
total number of hours in a year (8,760 hours). A further discussion of
why this factor was chosen can be found in Appendix 1 to the Metal Cans
Risk Assessment Report in the Metal Cans Docket.
    Similarly, for the Surface Coating of Metal Coil source category,
we expect to see minimal hour-to-hour variation in emissions during
routine operations because coil coating operations roll-apply coating
onto a moving metal strip (coil) in a continuous coating process. The
coil ends are seamed together in a continuous (non-batch) process that
achieves a consistent emission rate. Thus, the default emission factor
of 10 to estimate the worst-case hourly emission rate is not reasonable
for this category. We expect that minimal variation in emissions occur
due to variations in the organic HAP content of the coatings from batch
to batch. We calculated acute emissions by developing a source
category-specific multiplier of 1.1 that was applied to the actual
annual emissions, which were then divided by the total number of hours
in a year (8,760 hours). A further discussion of why this factor was
chosen can be found in Appendix 1 to the Metal Coil Risk Assessment
Report in the Metal Coil Docket.
    In our acute inhalation screening risk assessment, acute impacts
are deemed negligible for HAP for which acute HQs are less than or
equal to 1 (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 exposures of concern. For both
source categories in this action, the data refinements employed
consisted of plotting the HEM-3 polar grid results for each HAP with an
acute HQ value greater than 1 on aerial photographs of the facilities.
We then assessed whether the highest acute HQs were off-site and at
locations that may be accessible to the public (e.g., roadways and
public buildings). These refinements are discussed more fully in the
Metal Cans and Metal Coil Risk Assessment Reports, available in the
respective Metal Cans and Metal Coil Dockets.
4. How do we conduct the multipathway exposure and risk screening
assessment?
    The EPA conducts a tiered screening assessment examining the
potential for significant human health risks due to exposures via
routes other than inhalation (i.e., ingestion). We first determine
whether any sources in the source categories emit 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 https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Surface Coating of Metal Cans 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. For the Surface Coating of Metal Coil source
category, we identified PB-HAP emissions of lead, so we proceeded to
the next step of the evaluation. In this

step, we determine whether the facility-specific emission rates of the
emitted PB-HAP are large enough to create the potential for significant
human health risk through ingestion exposure under reasonable worst-
case conditions. To facilitate this step, we use previously developed
screening threshold emission rates for several PB-HAP that are based on
a hypothetical upper-end screening exposure scenario developed for use
in conjunction with the EPA's Total Risk Integrated Methodology.Fate,
Transport, and Ecological Exposure (TRIM.FaTE) model. The PB-HAP with
screening threshold emission rates are arsenic compounds, cadmium
compounds, chlorinated dibenzodioxins and furans, mercury compounds,
and polycyclic organic matter (POM). Based on the EPA estimates of
toxicity and bioaccumulation potential, the pollutants above represent
a conservative list for inclusion in multipathway risk assessments for
RTR rules. (See Volume 1, Appendix D at https://www.epa.gov/sites/production/files/201308/documents/volume_1_reflibrary.pdf). In this
assessment, we compare the facility-specific emission rates of these
PB-HAP to the screening threshold emission rates for each PB-HAP to
assess the potential for significant human health risks via the
ingestion pathway. We call this application of the TRIM.FaTE model the
Tier 1 screening assessment. The ratio of a facility's actual emission
rate to the Tier 1 screening threshold emission rate is a ``screening
value.''
    We derive the Tier 1 screening threshold emission rates for these
PB-HAP (other than lead compounds) to correspond to a maximum excess
lifetime cancer risk of 1-in-1 million (i.e., for arsenic compounds,
polychlorinated dibenzodioxins and furans and POM) or, for HAP that
cause noncancer health effects (i.e., cadmium compounds and mercury
compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP
or combination of carcinogenic PB-HAP in the Tier 1 screening
assessment exceeds the Tier 1 screening threshold emission rate for any
facility (i.e., the screening value is greater than 1), we conduct a
second screening assessment, which we call the Tier 2 screening
assessment.
    In the Tier 2 screening assessment, the location of each facility
that exceeds a Tier 1 screening threshold emission rate is used to
refine the assumptions associated with the Tier 1 fisher and farmer
exposure scenarios at that facility. A key assumption in the Tier 1
screening assessment is that a lake and/or farm is located near the
facility. As part of the Tier 2 screening assessment, we use a U.S.
Geological Survey (USGS) database to identify actual waterbodies within
50 km of each facility. We also examine the differences between local
meteorology near the facility and the meteorology used in the Tier 1
screening assessment. We then adjust the previously-developed Tier 1
screening threshold emission rates for each PB-HAP for each facility
based on an understanding of how exposure concentrations estimated for
the screening scenario change with the use of local meteorology and
USGS waterbody data. If the PB-HAP emission rates for a facility exceed
the Tier 2 screening threshold emission rates and data are available,
we may conduct a Tier 3 screening assessment. If PB-HAP emission rates
do not exceed a Tier 2 screening value of 1, we consider those PB-HAP
emissions to pose risks below a level of concern.
    There are several analyses that can be included in a Tier 3
screening assessment, depending upon the extent of refinement
warranted, including validating that the lakes are fishable,
considering plume-rise to estimate emissions lost above the mixing
layer, and considering hourly effects of meteorology and plume rise on
chemical fate and transport. If the Tier 3 screening assessment
indicates that risks above levels of concern cannot be ruled out, the
EPA may further refine the screening assessment through a site-specific
assessment.
    In evaluating the potential multipathway risk from emissions of
lead compounds, rather than developing a screening threshold emission
rate, we compare maximum estimated chronic inhalation exposure
concentrations to the level of the current National Ambient Air Quality
Standards (NAAQS) for lead.\17\ Values below the level of the primary
(health-based) lead NAAQS are considered to have a low potential for
multipathway risk.
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    \17\ In doing so, the EPA notes that the legal standard for a
primary NAAQS--that a standard is requisite to protect public health
and provide an adequate margin of safety (CAA section 109(b))--
differs from the CAA section 112(f) standard (requiring, among other
things, that the standard provide an ``ample margin of safety to
protect public health''). However, the primary lead NAAQS is a
reasonable measure of determining risk acceptability (i.e., the
first step of the Benzene NESHAP analysis) since it is designed to
protect the most susceptible group in the human population--
children, including children living near major lead emitting
sources. 73 FR 67002/3; 73 FR 67000/3; 73 FR 67005/1. In addition,
applying the level of the primary lead NAAQS at the risk
acceptability step is conservative, since that primary lead NAAQS
reflects an adequate margin of safety.
---------------------------------------------------------------------------

    For further information on the multipathway assessment approach,
see the Metal Coil Risk Assessment Report, which is available in the
Metal Coil docket for this action.
5. How do we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect, Environmental HAP, and Ecological
Benchmarks
    The EPA conducts a screening assessment to examine the potential
for an adverse environmental effect as required under section
112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines ``adverse
environmental effect'' as ``any significant and widespread adverse
effect, which may reasonably be anticipated, to wildlife, aquatic life,
or other natural resources, including adverse impacts on populations of
endangered or threatened species or significant degradation of
environmental quality over broad areas.''
    The EPA focuses on eight HAP, which are referred to as
``environmental HAP,'' in its screening assessment: Six PB-HAP and two
acid gases. The PB-HAP included in the screening assessment are arsenic
compounds, cadmium compounds, dioxins/furans, (POM, mercury (both
inorganic mercury and methyl mercury), and lead compounds. The acid
gases included in the screening assessment are hydrochloric acid (HCl)
and hydrogen fluoride (HF).
    HAP that persist and bioaccumulate are of particular environmental
concern because they accumulate in the soil, sediment, and water. The
acid gases, HCl and HF, are included due to their well-documented
potential to cause direct damage to terrestrial plants. In the
environmental risk screening assessment, we evaluate the following four
exposure media: Terrestrial soils, surface water bodies (includes
water-column and benthic sediments), fish consumed by wildlife, and
air. Within these four exposure media, we evaluate nine ecological
assessment endpoints, which are defined by the ecological entity and
its attributes. For PB-HAP (other than lead), both community-level and
population-level endpoints are included. For acid gases, the ecological
assessment evaluated is terrestrial plant communities.
    An ecological benchmark represents a concentration of HAP that has
been linked to a particular environmental effect level. For each
environmental HAP, we identified the available ecological benchmarks
for each assessment endpoint. We identified, where possible, ecological
benchmarks at the following effect levels: Probable effect levels,
lowest-observed-adverse-

effect level, and no-observed-adverse-effect level. In cases where
multiple effect levels were available for a particular PB-HAP and
assessment endpoint, we use all of the available effect levels to help
us to determine whether ecological risks exist and, if so, whether the
risks could be considered significant and widespread.
    For further information on how the environmental risk screening
assessment was conducted, including a discussion of the risk metrics
used, how the environmental HAP were identified, and how the ecological
benchmarks were selected, see Appendix 9 of the Metal Cans Risk
Assessment Report and the Metal Coil Risk Assessment Report, in the
Metal Cans Docket and the Metal Coil Docket, respectively.
b. Environmental Risk Screening Methodology
    For the environmental risk screening assessment, the EPA first
determined whether any facilities in the Surface Coating of Metal Cans
and Surface Coating of Metal Coil source categories emitted any of the
environmental HAP. For the Surface Coating of Metal Cans source
category, we identified emissions of HCl and HF. For the Surface
Coating of Metal Coil source category, we identified emissions of HF
and lead.
    Because one or more of the environmental HAP evaluated are emitted
by at least one facility in the source categories, we proceeded to the
second step of the evaluation for both the Surface Coating of Metal
Cans and the Surface Coating of Metal Coil source categories.
c. PB-HAP Methodology
    The environmental screening assessment includes six PB-HAP: Arsenic
compounds, cadmium compounds, dioxins/furans, POM, mercury (both
inorganic mercury and methyl mercury), and lead compounds. With the
exception of lead, the environmental risk screening assessment for PB-
HAP consists of three tiers. The first tier of the environmental risk
screening assessment uses the same health-protective conceptual model
that is used for the Tier 1 human health screening assessment.
TRIM.FaTE model simulations were used to back-calculate Tier 1
screening threshold emission rates. The screening threshold emission
rates represent the emission rate in tons per year that results in
media concentrations at the facility that equal the relevant ecological
benchmark. To assess emissions from each facility in the category, the
reported emission rate for each PB-HAP was compared to the Tier 1
screening threshold emission rate for that PB-HAP for each assessment
endpoint and effect level. If emissions from a facility do not exceed
the Tier 1 screening threshold emission rate, the facility ``passes''
the screening assessment, and, therefore, is not evaluated further
under the screening approach. If emissions from a facility exceed the
Tier 1 screening threshold emission rate, we evaluate the facility
further in Tier 2.
    In Tier 2 of the environmental screening assessment, the screening
threshold emission rates are adjusted to account for local meteorology
and the actual location of lakes in the vicinity of facilities that did
not pass the Tier 1 screening assessment. For soils, we evaluate the
average soil concentration for all soil parcels within a 7.5-km radius
for each facility and PB-HAP. For the water, sediment, and fish tissue
concentrations, the highest value for each facility for each pollutant
is used. If emission concentrations from a facility do not exceed the
Tier 2 screening threshold emission rate, the facility ``passes'' the
screening assessment and typically is not evaluated further. If
emissions from a facility exceed the Tier 2 screening threshold
emission rate, we evaluate the facility further in Tier 3.
    As in the multipathway human health risk assessment, in Tier 3 of
the environmental screening assessment, we examine the suitability of
the lakes around the facilities to support life and remove those that
are not suitable (e.g., lakes that have been filled in or are
industrial ponds), adjust emissions for plume-rise, and conduct hour-
by-hour time-series assessments. If these Tier 3 adjustments to the
screening threshold emission rates still indicate the potential for an
adverse environmental effect (i.e., facility emission rate exceeds the
screening threshold emission rate), we may elect to conduct a more
refined assessment using more site-specific information. If, after
additional refinement, the facility emission rate still exceeds the
screening threshold emission rate, the facility may have the potential
to cause an adverse environmental effect.
    To evaluate the potential for an adverse environmental effect from
lead, we compared the average modeled air concentrations (from HEM-3)
of lead around each facility in the source category to the level of the
secondary NAAQS for lead. The secondary lead NAAQS is a reasonable
means of evaluating environmental risk because it is set to provide
substantial protection against adverse welfare effects which can
include ``effects on soils, water, crops, vegetation, man-made
materials, animals, wildlife, weather, visibility and climate, damage
to and deterioration of property, and hazards to transportation, as
well as effects on economic values and on personal comfort and well-
being.''
d. Acid Gas Environmental Risk Methodology
    The environmental screening assessment for acid gases evaluates the
potential phytotoxicity and reduced productivity of plants due to
chronic exposure to HF and HCl. The environmental risk screening
methodology for acid gases is a single-tier screening assessment that
compares modeled ambient air concentrations (from AERMOD) to the
ecological benchmarks for each acid gas. To identify a potential
adverse environmental effect (as defined in section 112(a)(7) of the
CAA) from emissions of HF and HCl, we evaluate the following metrics:
The size of the modeled area around each facility that exceeds the
ecological benchmark for each acid gas, in acres and km\2\; the
percentage of the modeled area around each facility that exceeds the
ecological benchmark for each acid gas; and the area-weighted average
screening value around each facility (calculated by dividing the area-
weighted average concentration over the 50-km modeling domain by the
ecological benchmark for each acid gas). For further information on the
environmental screening assessment approach, see Appendix 9 of the
Metal Cans Risk Assessment Report and Metal Coil Risk Assessment
Report, which are available in each respective docket for this action.
6. How do we conduct facility-wide assessments?
    To put the source category risks in context, we typically examine
the risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, we examine the HAP emissions not only from the
source category emission points of interest, but also emissions of HAP
from all other emission sources at the facility for which we have data.
For these source categories, we conducted the facility-wide assessment
using a dataset compiled from the 2014 NEI. The source category records
of that NEI dataset were removed, evaluated, and updated as described
in section II.C of this preamble: ``What data collection activities
were conducted to support this action?'' Once a quality assured source
category dataset was available, it was placed back with the remaining
records from the NEI for that facility.

The facility-wide file was then used to analyze risks due to the
inhalation of HAP that are emitted ``facility-wide'' for the
populations residing within 50 km of each facility, consistent with the
methods used for the source category analysis described above. For
these facility-wide risk analyses, the modeled source category risks
were compared to the facility-wide risks to determine the portion of
the facility-wide risks that could be attributed to the source
categories 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 Metal Cans Risk Assessment Report and the
Metal Coil Risk Assessment Report, available respectively in the Metal
Cans Docket and the Metal Coil Docket, provide the methodology and
results of the facility-wide analyses, including all facility-wide
risks and the percentage of source category contribution to facility-
wide risks.
7. How do we consider uncertainties in risk assessment?
    Uncertainty and the potential for bias are inherent in all risk
assessments, including those performed for this proposal. Although
uncertainty exists, we believe that our approach, which used
conservative tools and assumptions, ensures that our decisions are
health and environmentally protective. A brief discussion of the
uncertainties in the RTR emissions datasets, 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 Metal Cans Risk Assessment
Report and the Metal Coil Risk Assessment Report, available
respectively in the Metal Cans Docket and the Metal Coil Docket. 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 Datasets
    Although the development of the RTR emissions datasets involved
quality assurance/quality control processes, the accuracy of emissions
values will vary depending on the source of the data, the degree to
which data are incomplete or missing, the degree to which assumptions
made to complete the datasets are accurate, errors in emission
estimates, and other factors. The emission estimates considered in this
analysis generally are annual totals for certain years, and they do not
reflect short-term fluctuations during the course of a year or
variations from year to year. The estimates of peak hourly emission
rates for the acute effects screening assessment were based on an
emission adjustment factor applied to the average annual hourly
emission rates, which are intended to account for emission fluctuations
due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration
estimates associated with any model, including the EPA's recommended
regulatory dispersion model, AERMOD. In using a model to estimate
ambient pollutant concentrations, the user chooses certain options to
apply. For RTR assessments, we select some model options that have the
potential to overestimate ambient air concentrations (e.g., not
including plume depletion or pollutant transformation). We select other
model options that have the potential to underestimate ambient impacts
(e.g., not including building downwash). Other options that we select
have the potential to either under- or overestimate ambient levels
(e.g., meteorology and receptor locations). On balance, considering the
directional nature of the uncertainties commonly present in ambient
concentrations estimated by dispersion models, the approach we apply in
the RTR assessments should yield unbiased estimates of ambient HAP
concentrations. We also note that the selection of meteorology dataset
location could have an impact on the risk estimates. As we continue to
update and expand our library of meteorological station data used in
our risk assessments, we expect to reduce this variability.
c. Uncertainties in Inhalation Exposure Assessment
    Although every effort is made to identify all of the relevant
facilities and emission points, as well as to develop accurate
estimates of the annual emission rates for all relevant HAP, the
uncertainties in our emission inventory likely dominate the
uncertainties in the exposure assessment. Some uncertainties in our
exposure assessment include human mobility, using the centroid of each
census block, assuming lifetime exposure, and assuming only outdoor
exposures. For most of these factors, there is neither an under nor
overestimate when looking at the maximum individual risk or the
incidence, but the shape of the distribution of risks may be affected.
With respect to outdoor exposures, actual exposures may not be as high
if people spend time indoors, especially for very reactive pollutants
or larger particles. For all factors, we reduce uncertainty when
possible. For example, with respect to census-block centroids, we
analyze large blocks using aerial imagery and adjust locations of the
block centroids to better represent the population in the blocks. We
also add additional receptor locations where the population of a block
is not well represented by a single location.
d. Uncertainties in Dose-Response Relationships
    There are uncertainties inherent in the development of the dose-
response values used in our risk assessments for cancer effects from
chronic exposures and noncancer effects from both chronic and acute
exposures. Some uncertainties are generally expressed quantitatively,
and others are generally expressed in qualitative terms. We note, as a
preface to this discussion, a point on dose-response uncertainty that
is stated in the EPA's 2005 Guidelines for Carcinogen Risk Assessment;
namely, that ``the primary goal of EPA actions is protection of human
health; accordingly, as an Agency policy, risk assessment procedures,
including default options that are used in the absence of scientific
data to the contrary, should be health protective'' (the EPA's 2005
Guidelines for Carcinogen Risk Assessment, 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.\18\
That is, they represent a ``plausible upper limit to the true value of
a quantity'' (although this is usually not a true statistical
confidence limit). In some circumstances, the true risk could be as low
as zero; however, in other circumstances the risk could be greater.\19\
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,\20\ which considers
uncertainty, variability, and gaps in the available data. The UFs are
applied to derive dose-response values that are intended to protect
against appreciable risk of deleterious effects.
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    \18\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \19\ 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.
    \20\ See A Review of the Reference Dose and Reference
Concentration Processes, U.S. EPA, December 2002, and Methods for
Derivation of Inhalation Reference Concentrations and Application of
Inhalation Dosimetry, U.S. EPA, 1994.
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    Many of the UFs used to account for variability and uncertainty in
the development of acute dose-response values are quite similar to
those developed for chronic durations. Additional adjustments are often
applied to account for uncertainty in extrapolation from observations
at one exposure duration (e.g., 4 hours) to derive an acute dose-
response value at another exposure duration (e.g., 1 hour). Not all
acute dose-response values are developed for the same purpose, and care
must be taken when interpreting the results of an acute assessment of
human health effects relative to the dose-response value or values
being exceeded. Where relevant to the estimated exposures, the lack of
acute dose-response values at different levels of severity should be
factored into the risk characterization as potential uncertainties.
    Uncertainty also exists in the selection of ecological benchmarks
for the environmental risk screening assessment. We established a
hierarchy of preferred benchmark sources to allow selection of
benchmarks for each environmental HAP at each ecological assessment
endpoint. We searched for benchmarks for three effect levels (i.e., no-
effects level, threshold-effect level, and probable effect level), but
not all combinations of ecological assessment/environmental HAP had
benchmarks for all three effect levels. Where multiple effect levels
were available for a particular HAP and assessment endpoint, we used
all of the available effect levels to help us determine whether risk
exists and whether the risk could be considered significant and
widespread.
    Although we make every effort to identify appropriate human health
effect dose-response values for all pollutants emitted by the sources
in this risk assessment, some HAP emitted by this source category are
lacking dose-response assessments. Accordingly, these pollutants cannot
be included in the quantitative risk assessment, which could result in
quantitative estimates understating HAP risk. To help to alleviate this
potential underestimate, where we conclude similarity with a HAP for
which a dose-response value is available, we use that value as a
surrogate for the assessment of the HAP for which no value is
available. To the extent use of surrogates indicates appreciable risk,
we may identify a need to increase priority for an IRIS assessment for
that substance. We additionally note that, generally speaking, HAP of
greatest concern due to environmental exposures and hazard are those
for which dose-response assessments have been performed, reducing the
likelihood of understating risk. Further, HAP not included in the
quantitative assessment are assessed qualitatively and considered in
the risk characterization that informs the risk management decisions,
including consideration of HAP reductions achieved by various control
options.
    For a group of compounds that are unspeciated (e.g., glycol
ethers), we conservatively use the most protective dose-response value
of an individual compound in that group to estimate risk. Similarly,
for an individual compound in a group (e.g., ethylene glycol diethyl
ether) that does not have a specified dose-response value, we also
apply the most protective dose-response value from the other compounds
in the group to estimate risk.
e. Uncertainties in Acute Inhalation Screening Assessments
    In addition to the uncertainties highlighted above, there are
several factors specific to the acute exposure assessment that the EPA
conducts as part of the risk review under section 112 of the CAA. The
accuracy of an acute inhalation exposure assessment depends on the
simultaneous occurrence of independent factors that may vary greatly,
such as hourly 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 these source categories, 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.
f. Uncertainties in the Multipathway and Environmental Risk Screening
Assessments
    For each source category, we generally rely on site-specific levels
of PB-HAP or environmental HAP emissions to determine whether a refined
assessment of the impacts from multipathway exposures is necessary or
whether it is necessary to perform an environmental screening
assessment. This determination is based on the results of a three-
tiered screening assessment that relies on the outputs from models--
TRIM.FaTE and AERMOD--that estimate environmental pollutant
concentrations and human exposures for five PB-HAP (dioxins, POM,
mercury, cadmium, and arsenic) and two acid gases (HF and HCl). For
lead, we use AERMOD to determine ambient air concentrations, which are
then compared to the secondary NAAQS standard for lead. Two important
types of uncertainty associated with the use of these models in RTR
risk assessments and inherent to any assessment that relies on
environmental modeling are model uncertainty and input uncertainty.\21\
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    \21\ In the context of this discussion, the term ``uncertainty''
as it pertains to exposure and risk encompasses both variability in
the range of expected inputs and screening results due to existing
spatial, temporal, and other factors, as well as uncertainty in
being able to accurately estimate the true result.
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    Model uncertainty concerns whether the model adequately represents
the actual processes (e.g., movement and accumulation) that might occur
in the environment. For example, does the model adequately describe the
movement of a pollutant through the soil? This type of uncertainty is
difficult to quantify. However, based on feedback received from
previous the EPA SAB reviews and other reviews, we are confident that
the models used in the screening assessments are appropriate and state-
of-the-art for the multipathway and environmental screening risk
assessments conducted in support of RTR.
    Input uncertainty is concerned with how accurately the models have
been configured and parameterized for the assessment at hand. For Tier
1 of the multipathway and environmental

screening assessments, we configured the models to avoid
underestimating exposure and risk. This was accomplished by selecting
upper-end values from nationally representative datasets for the more
influential parameters in the environmental model, including selection
and spatial configuration of the area of interest, lake location and
size, meteorology, surface water, soil characteristics, and structure
of the aquatic food web. We also assume an ingestion exposure scenario
and values for human exposure factors that represent reasonable maximum
exposures.
    In Tier 2 of the multipathway and environmental screening
assessments, we refine the model inputs to account for meteorological
patterns in the vicinity of the facility versus using upper-end
national values, and we identify the actual location of lakes near the
facility rather than the default lake location that we apply in Tier 1.
By refining the screening approach in Tier 2 to account for local
geographical and meteorological data, we decrease the likelihood that
concentrations in environmental media are overestimated, thereby
increasing the usefulness of the screening assessment. In Tier 3 of the
screening assessments, we refine the model inputs again to account for
hour-by-hour plume rise and the height of the mixing layer. We can also
use those hour-by-hour meteorological data in a TRIM.FaTE run using the
screening configuration corresponding to the lake location. These
refinements produce a more accurate estimate of chemical concentrations
in the media of interest, thereby reducing the uncertainty with those
estimates. The assumptions and the associated uncertainties regarding
the selected ingestion exposure scenario are the same for all three
tiers.
    For the environmental screening assessment for acid gases, we
employ a single-tiered approach. We use the modeled air concentrations
and compare those with ecological benchmarks.
    For all tiers of the multipathway and environmental screening
assessments, our approach to addressing model input uncertainty is
generally cautious. We choose model inputs from the upper end of the
range of possible values for the influential parameters used in the
models, and we assume that the exposed individual exhibits ingestion
behavior that would lead to a high total exposure. This approach
reduces the likelihood of not identifying high risks for adverse
impacts.
    Despite the uncertainties, when individual pollutants or facilities
do not exceed screening threshold emission rates (i.e., screen out), we
are confident that the potential for adverse multipathway impacts on
human health is very low. On the other hand, when individual pollutants
or facilities do exceed screening threshold emission rates, it does not
mean that impacts are significant, only that we cannot rule out that
possibility and that a refined assessment for the site might be
necessary to obtain a more accurate risk characterization for the
source category.
    The EPA evaluates the following HAP in the multipathway and/or
environmental risk screening assessments, where applicable: Arsenic,
cadmium, dioxins/furans, lead, mercury (both inorganic and methyl
mercury), POM, HCl, and HF. These HAP represent pollutants that can
cause adverse impacts either through direct exposure to HAP in the air
or through exposure to HAP that are deposited from the air onto soils
and surface waters and then through the environment into the food web.
These HAP represent those HAP for which we can conduct a meaningful
multipathway or environmental screening risk assessment. For other HAP
not included in our screening assessments, the model has not been
parameterized such that it can be used for that purpose. In some cases,
depending on the HAP, we may not have appropriate multipathway models
that allow us to predict the concentration of that pollutant. The EPA
acknowledges that other HAP beyond these that we are evaluating may
have the potential to cause adverse effects and, therefore, the EPA may
evaluate other relevant HAP in the future, as modeling science and
resources allow.