[Federal Register Volume 81, Number 249 (Wednesday, December 28, 2016)]
[Proposed Rules]
[Pages 95810-95846]
[FR Doc No: 2016-30645]

Vol. 81

Wednesday,

No. 249

December 28, 2016

Part IV

 Environmental Protection Agency

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40 CFR Part 63

 National Emission Standards for Hazardous Air Pollutants: Nutritional
Yeast Manufacturing Risk and Technology Review; Proposed Rule

Federal Register / Vol. 81 , No. 249 / Wednesday, December 28, 2016 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2015-0730; FRL-9956-21-OAR]
RIN 2060-AS93

National Emission Standards for Hazardous Air Pollutants:
Nutritional Yeast Manufacturing Risk and Technology Review

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing
amendments to the National Emission Standards for Hazardous Air
Pollutants (NESHAP) for the Manufacturing of Nutritional Yeast source
category. The proposed amendments address the results of the residual
risk and technology reviews (RTRs) conducted as required under the
Clean Air Act (CAA) as well as other actions deemed appropriate during
the review of these standards. The proposed amendments include revising
the form of the fermenter volatile organic compounds (VOC) emission
limits, changing the testing and monitoring requirements, and updating
the reporting and recordkeeping requirements.

DATES: Comments. Comments must be received on or before February 13,
2017. Under the Paperwork Reduction Act (PRA), comments on the
information collection provisions are best assured of consideration if
the Office of Management and Budget (OMB) receives a copy of your
comments on or before January 27, 2017.
    Public Hearing. A public hearing will be held, if requested by
January 3, 2017.

ADDRESSES: Comments. Submit your comments, identified by Docket ID No.
EPA-HQ-OAR-2015-0730, at http://www.regulations.gov. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from Regulations.gov. The EPA may publish any
comment received to its public docket. Do not submit electronically any
information you consider to be Confidential Business Information (CBI)
or other information whose disclosure is restricted by statute.
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.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Allison Costa, Sector Policies and Programs Division
(Mail Code E140), 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 Chris Sarsony, Health
and Environmental Impacts Division (Mail Code C539-02), Office of Air
Quality Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; telephone number: (919)
541-4843; fax number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>For information about the applicability of the
NESHAP to a particular entity, contact Scott Throwe, Office of
Enforcement and Compliance Assurance, U.S. Environmental Protection
Agency, EPA WJC South Building (Mail Code 2227A), 1200 Pennsylvania
Avenue NW., Washington, DC 20460; telephone number:<PHONE_NUMBER>; fax
number:<PHONE_NUMBER>; and email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:
    Docket. The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2015-0730. All documents in the docket are
listed in the Regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, is not placed on the Internet and will be
publicly available only in hard copy. Publicly available docket
materials are available either electronically in Regulations.gov or in
hard copy at the EPA Docket Center, Room 3334, EPA WJC West Building,
1301 Constitution Avenue NW., Washington, DC. The Public Reading Room
is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding
legal holidays. The telephone number for the Public Reading Room is
(202) 566-1744, and the telephone number for the EPA Docket Center is
(202) 566-1742.
    Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-
2015-0730. The EPA's policy is that all comments received will be
included in the public docket without change and may be made available
online at http://www.regulations.gov, including any personal
information provided, unless the comment includes information claimed
to be CBI or other information whose disclosure is restricted by
statute. Do not submit information that you consider to be CBI or
otherwise protected through http://www.regulations.gov or email. The
http://www.regulations.gov Web site is an ``anonymous access'' system,
which means the EPA will not know your identity or contact information
unless you provide it in the body of your comment. If you send an email
comment directly to the EPA without going through http://www.regulations.gov, your email address will be automatically captured
and included as part of the comment that is placed in the public docket
and made available on the Internet. If you submit an electronic
comment, the EPA recommends that you include your name and other
contact information in the body of your comment and with any disk or
CD-ROM you submit. If the EPA cannot read your comment due to technical
difficulties and cannot contact you for clarification, the EPA may not
be able to consider your comment. Electronic files should not include
special characters or any form of encryption and be free of any defects
or viruses. For additional information about the EPA's public docket,
visit the EPA Docket Center homepage at https://www.epa.gov/dockets.
    Public Hearing. A public hearing will be held, if requested by
January 3, 2017, to accept oral comments on this proposed action. If a
hearing is requested, it will be held at the EPA's North Carolina
campus located at 109 T.W. Alexander Drive, Research Triangle Park, NC
27711. The hearing, if requested, will begin at 9:00 a.m. (local time)
and will conclude at 8:00 p.m. (local time). To request a hearing, to
register to speak at a hearing, or to inquire if a hearing will be
held, please contact Aimee St. Clair at<PHONE_NUMBER> or by email at
<EMAIL_ADDRESS>The last day to pre-register to speak at a
hearing, if one is held, will be January 10, 2017. Additionally,
requests to speak will be taken the day of the hearing at the hearing
registration desk, although preferences on speaking times may not be
able to be fulfilled. Please note that registration requests

received before the hearing will be confirmed by the EPA via email. The
EPA will make every effort to accommodate all speakers who arrive and
register. Because the hearing will be held at a U.S. governmental
facility, individuals planning to attend the hearing should be prepared
to show valid picture identification to the security staff in order to
gain access to the meeting room. Please note that the REAL ID Act,
passed by Congress in 2005, established new requirements for entering
federal facilities. If your driver's license is issued by Alaska,
American Samoa, Arizona, Kentucky, Louisiana, Maine, Massachusetts,
Minnesota, Montana, New York, Oklahoma or the state of Washington, you
must present an additional form of identification to enter the federal
building. Acceptable alternative forms of identification include:
federal employee badges, passports, enhanced driver's licenses and
military identification cards. In addition, you will need to obtain a
property pass for any personal belongings you bring with you. Upon
leaving the building, you will be required to return this property pass
to the security desk. No large signs will be allowed in the building,
cameras may only be used outside of the building and demonstrations
will not be allowed on federal property for security reasons.
    Please note that any updates made to any aspect of the hearing,
including whether or not a hearing will be held, will be posted online
at https://www.epa.gov/stationary-sources-air-pollution/manufacturing-nutritional-yeast-national-emission-standards. We ask that you contact
Aimee St. Clair at<PHONE_NUMBER> or by email at<EMAIL_ADDRESS>or monitor our Web site to determine if a hearing will be held. The EPA
does not intend to publish a notice in the Federal Register announcing
any such updates. Please go to https://www.epa.gov/stationary-sources-air-pollution/manufacturing-nutritional-yeast-national-emission-standards for more information on the public hearing.
    Preamble Acronyms and Abbreviations. We use multiple acronyms and
terms in this preamble. While this list may not be exhaustive, to ease
the reading of this preamble and for reference purposes, the EPA
defines the following terms and acronyms here:

AEGL Acute exposure guideline levels
AERMOD Air dispersion model used by the HEM-3 model
ATSDR Agency for Toxic Substances and Disease Registry
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CEMS Continuous emission monitoring system
CFR Code of Federal Regulations
EGU Electric generation unit
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guidelines
FR Federal Register
HAP Hazardous air pollutants
HCl Hydrochloric acid
HEM-3 Human Exposure Model, Version 1.1.0
HF Hydrogen fluoride
HI Hazard index
HQ Hazard quotient
ICR Information Collection Request
IRIS Integrated Risk Information System
km Kilometer
MACT Maximum achievable control technology
MATS Mercury Air Toxics Standard
mg/kg-day Milligrams per kilogram per day
mg/m\3\ Milligrams per cubic meter
MIR Maximum individual risk
MON Miscellaneous organic chemical manufacturing NESHAP
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NAS National Academy of Sciences
NATA National Air Toxics Assessment
NEI National Emissions Inventory
NESHAP National emissions standards for hazardous air pollutants
NOX Nitrogen oxides
NRC National Research Council
QA/QC Quality assurance/quality control
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PB-HAP Hazardous air pollutants known to be persistent and bio-
accumulative in the environment
POM Polycyclic organic matter
ppmv Parts per million by volume
PRA Paperwork Reduction Act
PS Performance Specification
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
SBA Small Business Administration
SOP Standing Operating Procedures
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
TTN Technology Transfer Network
UF Uncertainty factor
[micro]g/m\3\ Microgram per cubic meter
UMRA Unfunded Mandates Reform Act
URE Unit risk estimate
VOC Volatile organic compounds

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

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

I. General Information

A. Does this action apply to me?

    Table 1 of this preamble lists the NESHAP and the associated
regulated industrial source category that is the subject of this
proposal. Table 1 is not intended to be exhaustive, but rather provides
a guide for readers regarding the entities that this proposed action is
likely to affect. The proposed standards, once promulgated, will be
directly applicable to the affected sources. Federal, state, local, and
tribal government entities would not be affected by this proposed
action. 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), the Manufacturing of Nutritional Yeast source
category includes any facility engaged in the manufacture of baker's
yeast by fermentation (both active dry yeast and compressed yeast). The
category includes, but is not limited to, the following manufacturing
process units: fermentation vessels and the drying and packaging
system. The original source category was named Baker's Yeast
Manufacturing, but it was revised to Manufacturing of Nutritional Yeast
to provide clarity on the scope (63 FR 55812, October 19, 1998).

    Table 1--NESHAP and Industrial Source Categories Affected By This
                             Proposed Action
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               NESHAP and  source category                NAICS code \1\
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Manufacturing of Nutritional Yeast......................          311999
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\1\ North American Industry Classification System (NAICS).

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

    In addition to being available in the docket, an electronic copy of
this action is available on the Internet. Following signature by the
EPA Administrator, the EPA will post a copy of this proposed action at
https://www.epa.gov/stationary-sources-air-pollution/manufacturing-nutritional-yeast-national-emission-standards. Following publication in
the Federal Register, the EPA will post the Federal Register version of
the proposal and key technical documents at this same Web site.
Information on the overall RTR program is available at https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.

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

    Submitting CBI. Do not submit information containing CBI to the EPA
through http://www.regulations.gov or email. Clearly mark the part or
all of the information that you claim to be CBI. For CBI information on
a disk or CD-ROM that you mail to the EPA, mark the outside of the disk
or CD-ROM as CBI and then identify electronically within the disk or
CD-ROM the specific information that is claimed as CBI. In addition to
one complete version of the comments that includes information claimed
as CBI, you must submit a copy of the comments that does not contain
the information claimed as CBI for inclusion in the public docket. If
you submit a CD-ROM or disk that does not contain CBI, mark the outside
of the disk or CD-ROM clearly that it does not contain CBI. Information
not marked as CBI will be included in the public docket and the EPA's
electronic public docket without prior notice. Information marked as
CBI will not be disclosed except in accordance with procedures set
forth in 40 Code of Federal Regulations (CFR) part 2. Send or deliver
information identified as CBI only to the following address: OAQPS
Document Control Officer (C404-02), OAQPS, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina 27711,
Attention Docket ID No. EPA-HQ-OAR-2015-0730.

II. Background

A. What is the statutory authority for this action?

    Section 112 of the CAA establishes a two-stage regulatory process
to address emissions of hazardous air pollutants (HAP) from stationary
sources. In the first stage, after the EPA has identified categories of
sources emitting one or more of the HAP listed in CAA section 112(b),
CAA section 112(d) requires us to promulgate technology-based NESHAP
for those sources. ``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. For major sources, 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) and
are commonly referred to as maximum achievable control technology
(MACT) standards.
    MACT standards must reflect the maximum degree of emissions
reduction achievable through the application of measures, processes,
methods, systems or techniques, including, but not limited to, measures
that: (1) Reduce the volume of or eliminate pollutants through process
changes, substitution of materials, or other modifications; (2) enclose
systems or processes to eliminate emissions; (3) capture or treat
pollutants when released from a process, stack, storage, or fugitive
emissions point; (4) are design, equipment, work practice, or
operational standards (including requirements for operator training or
certification); or (5) are a combination of the above. CAA section
112(d)(2)(A)-(E). The MACT standards may take the form of design,
equipment, work practice, or operational standards where the EPA first
determines either that: (1) A pollutant cannot be emitted through a
conveyance designed and constructed to emit or capture the pollutant,
or that any requirement for, or use of, such a conveyance would be
inconsistent with law; or (2) the application of measurement
methodology to a particular class of sources is not practicable due to
technological and economic limitations. CAA section 112(h)(1)-(2).
    The MACT ``floor'' is the minimum control level allowed for MACT
standards promulgated under CAA section 112(d)(3) and may not be based
on cost considerations. For new sources, the MACT floor cannot be less
stringent than the emissions control that is achieved in practice by
the best-controlled similar source. The MACT floor for existing sources
can be less stringent than floors for new sources, but not less
stringent than the average emissions limitation achieved by the best-
performing 12 percent of existing sources in the category or
subcategory (or the best-performing five sources for categories or
subcategories with fewer than 30 sources). In developing MACT
standards, the EPA must also consider control options that are more
stringent than the floor. We may establish standards more stringent
than the floor based on considerations of the cost of achieving the
emission reductions, any non-air quality health and environmental
impacts, and energy requirements.
    The EPA is then required to review these technology-based standards
and revise them ``as necessary (taking into account developments in
practices, processes, and control technologies)'' no less frequently
than every 8 years. CAA section 112(d)(6). In conducting this 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 second stage in standard-setting focuses on reducing any
remaining (i.e., ``residual'') risk according to CAA section 112(f).
CAA section 112(f)(1) required that the EPA prepare a report to
Congress discussing (among other things) methods of calculating the
risks posed (or potentially posed) by sources after implementation of
the MACT standards, the public health significance of those risks, and
the EPA's recommendations as to legislation regarding such remaining
risk. The EPA prepared and submitted the ``Residual Risk Report to
Congress,'' EPA-453/R-99-001 (``Risk Report'') in March 1999. CAA
section 112(f)(2) then provides that if Congress does not act on any
recommendation in the Risk Report, the EPA must analyze and address
residual risk for each category or subcategory of sources 8 years after
promulgation of such standards pursuant to CAA section 112(d).
    Section 112(f)(2) of the CAA requires the EPA to determine for
source categories subject to MACT standards whether the emission
standards provide an ample margin of safety to protect public health.
Section 112(f)(2)(B) of the CAA expressly preserves the EPA's use of
the two-step process for developing standards to address any residual
risk and the Agency's interpretation of ``ample margin of safety''
developed in the National Emissions Standards for Hazardous Air
Pollutants: Benzene Emissions from Maleic Anhydride Plants,
Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment
Leaks, and Coke By-Product Recovery Plants (Benzene NESHAP) (54 FR
38044, September 14, 1989). The EPA notified Congress in the Risk
Report that the Agency intended to use the Benzene NESHAP approach in
making CAA section 112(f) residual risk determinations (EPA-453/R-99-
001, p. ES-11). The EPA subsequently adopted this approach in its
residual risk determinations and in a challenge to the risk review for
the Synthetic Organic Chemical Manufacturing source category, the
United States Court of Appeals for the District of Columbia Circuit
upheld as reasonable 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)(``[S]ubsection
112(f)(2)(B) expressly incorporates the EPA's interpretation of the
Clean Air Act from the Benzene standard, complete with a citation to
the Federal Register.''); see also, A Legislative History of the Clean
Air Act Amendments of 1990, vol. 1, p. 877 (Senate debate on Conference
Report).
    The first step in the process of evaluating residual risk is the
determination of acceptable risk. If risks are unacceptable, the EPA
cannot consider cost in identifying the emissions standards necessary
to bring risks to an acceptable level. The second step is the
determination of whether standards must be further revised in order to
provide an ample margin of safety to protect public health. The ample
margin of safety is the level at which the standards must be set,
unless an even more stringent standard is necessary to prevent, taking
into consideration costs, energy, safety, and other relevant factors,
an adverse environmental effect.
1. Step 1--Determination of Acceptability
    The Agency in the Benzene NESHAP concluded that ``the acceptability
of risk under section 112 is best judged on the basis of a broad set of
health risk measures and information'' and that the ``judgment on
acceptability cannot be reduced to any single factor.'' Benzene NESHAP
at 38046. The determination of what represents an ``acceptable'' risk
is based on a judgment of ``what risks are acceptable in the world in
which we live'' (Risk Report at 178, quoting NRDC v. EPA, 824 F.2d
1146, 1165 (D.C. Cir. 1987) (en banc) (``Vinyl Chloride''), recognizing
that our world is not risk-free.
    In the Benzene NESHAP, we stated that ``EPA will generally presume
that if the risk to [the maximum exposed] individual is no higher than
approximately one in 10 thousand, that risk level is considered
acceptable.'' 54 FR at 38045, September 14, 1989. We discussed the
maximum individual lifetime cancer risk (or maximum individual risk
(MIR)) as being ``the estimated risk that a person living near a plant
would have if he or she were exposed to the maximum pollutant
concentrations for 70 years.'' Id. We explained that this measure of
risk ``is an estimate of the upper bound of risk based on conservative
assumptions, such as continuous exposure for 24 hours per day for 70
years.'' Id. We acknowledged that maximum individual lifetime cancer
risk ``does not necessarily reflect the true risk, but displays a
conservative risk level which is an upper-bound that is unlikely to be
exceeded.'' Id.
    Understanding that there are both benefits and limitations to using
the MIR as a metric for determining acceptability, we acknowledged in
the Benzene NESHAP that ``consideration of maximum individual risk * *
* must take into account the strengths and weaknesses of this measure
of risk.'' Id. Consequently, the presumptive risk level of 100-in-1
million (1-in-10 thousand) provides a benchmark for judging the
acceptability of maximum individual lifetime cancer risk, but does not
constitute a rigid line for making that determination. Further, in the
Benzene NESHAP, we noted that:

    ``[p]articular attention will also be accorded to the weight of
evidence presented in the risk assessment of potential
carcinogenicity or other health effects of a pollutant. While the
same numerical risk may be estimated for an exposure to a pollutant
judged to be a known human carcinogen, and to a pollutant considered
a possible human carcinogen based on limited animal test data, the
same weight cannot be accorded to both estimates. In considering the
potential public health effects of the two pollutants, the Agency's
judgment on acceptability, including the MIR, will be influenced by
the greater weight of evidence for the known human carcinogen.''

Id. at 38046. The Agency also explained in the Benzene NESHAP that:

    ``[i]n establishing a presumption for MIR, rather than a rigid
line for acceptability, the Agency intends to weigh it with a series
of other health measures and factors. These include the overall
incidence of cancer or other serious health effects within the
exposed population, the numbers of persons exposed within each
individual lifetime risk range and associated incidence within,
typically, a 50 kilometers (km) exposure radius around facilities,
the science policy assumptions and estimation uncertainties
associated with the risk measures, weight of the scientific evidence
for human health effects, other quantified or unquantified health
effects, effects due to co-location of facilities, and co-emission
of pollutants.''

Id. at 38045. In some cases, these health measures and factors taken
together may provide a more realistic description of the magnitude of
risk in the exposed population than that provided by maximum individual
lifetime cancer risk alone.
    As noted earlier, in NRDC v. EPA, the Court held that CAA section
112(f)(2) ``incorporates the EPA's interpretation of the Clean Air Act
from the Benzene Standard.'' The Court further held that Congress'
incorporation of the Benzene standard applies equally to carcinogens
and non-carcinogens. 529 F.3d at 1081-82. Accordingly, we also consider
non-cancer risk metrics in our determination of risk acceptability and
ample margin of safety.
2. Step 2--Determination of Ample Margin of Safety
    CAA section 112(f)(2) requires the EPA to determine, for source
categories

subject to MACT standards, whether those standards provide an ample
margin of safety to protect public health. As explained in the Benzene
NESHAP, ``the second step of the inquiry, determining an `ample margin
of safety,' again includes consideration of all of the health factors,
and whether to reduce the risks even further. . . . Beyond that
information, additional factors relating to the appropriate level of
control will also be considered, including costs and economic impacts
of controls, technological feasibility, uncertainties, and any other
relevant factors. Considering all of these factors, the agency will
establish the standard at a level that provides an ample margin of
safety to protect the public health, as required by section 112.'' 54
FR 38046, September 14, 1989.
    According to CAA section 112(f)(2)(A), if the MACT standards for
HAP ``classified as a known, probable, or possible human carcinogen do
not reduce lifetime excess cancer risks to the individual most exposed
to emissions from a source in the category or subcategory to less than
one in one million,'' the EPA must promulgate residual risk standards
for the source category (or subcategory), as necessary to provide an
ample margin of safety to protect public health. In doing so, the EPA
may adopt standards equal to existing MACT standards if the EPA
determines that the existing standards (i.e., the MACT standards) are
sufficiently protective. NRDC v. EPA, 529 F.3d 1077, 1083 (D.C. Cir.
2008) (``If EPA determines that the existing technology-based standards
provide an 'ample margin of safety,' then the Agency is free to readopt
those standards during the residual risk rulemaking.'') The EPA must
also adopt more stringent standards, if necessary, to prevent an
adverse environmental effect,\1\ but must consider cost, energy,
safety, and other relevant factors in doing so.
---------------------------------------------------------------------------

    \1\ ``Adverse environmental effect'' is defined as any
significant and widespread adverse effect, which may be reasonably
anticipated to wildlife, aquatic life, or natural resources,
including adverse impacts on populations of endangered or threatened
species or significant degradation of environmental qualities over
broad areas. CAA section 112(a)(7).
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    The CAA does not specifically define the terms ``individual most
exposed,'' ``acceptable level,'' and ``ample margin of safety.'' In the
Benzene NESHAP, 54 FR 38044, September 14, 1989, we stated as an
overall objective:

    In protecting public health with an ample margin of safety under
section 112, EPA strives to provide maximum feasible protection
against risks to health from hazardous air pollutants by (1)
protecting the greatest number of persons possible to an individual
lifetime risk level no higher than approximately 1-in-1 million and
(2) limiting to no higher than approximately 1-in-10 thousand [i.e.,
100-in-1 million] the estimated risk that a person living near a
plant would have if he or she were exposed to the maximum pollutant
concentrations for 70 years.

    The Agency further stated that ``[t]he EPA also considers incidence
(the number of persons estimated to suffer cancer or other serious
health effects as a result of exposure to a pollutant) to be an
important measure of the health risk to the exposed population.
Incidence measures the extent of health risks to the exposed population
as a whole, by providing an estimate of the occurrence of cancer or
other serious health effects in the exposed population.'' Id. at 38045.
    In the ample margin of safety decision process, the Agency again
considers all of the health risks and other health information
considered in the first step, including the incremental risk reduction
associated with standards more stringent than the MACT standard or a
more stringent standard that the EPA has determined is necessary to
ensure risk is acceptable. In the ample margin of safety analysis, the
Agency considers additional factors, including costs and economic
impacts of controls, technological feasibility, uncertainties, and any
other relevant factors. Considering all of these factors, the Agency
will establish the standard at a level that provides an ample margin of
safety to protect the public health, as required by CAA section 112(f).
54 FR 38046, September 14, 1989.

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

    In the original 1992 list of sources under CAA section 112(c)(1),
the EPA defined the Baker's Yeast Manufacturing source category as
including any facility engaged in the manufacture of baker's yeast by
fermentation (both active dry yeast and compressed yeast) (57 FR
31576). The EPA explained that the category included, but was not
limited to, the following manufacturing process units: Fermentation
vessels and the drying and packaging system. The original source
category was renamed to Manufacturing of Nutritional Yeast in 1998 to
clarify that the source category covered the manufacturing of yeast,
not its use in facilities such as breweries or bakeries. Both ``baker's
yeast'' and ``nutritional yeast'' are common names for Saccharomyces
cerevisiae, which is a specific species of yeast that is used to
produce many common food and beverage products and whose manufacturing
process typically emits HAP. The 40 CFR part 63, subpart CCCC NESHAP,
which was finalized in 2001, defines a manufacturer of nutritional
yeast as a facility that makes yeast for the purpose of becoming an
ingredient in dough for bread or any other yeast-raised baked product,
or for becoming a nutritional food additive intended for consumption by
humans (66 FR 27876). Facilities that manufacture nutritional yeast
intended for consumption by animals, such as an additive for livestock
feed, are not included in the description of sources covered by this
subpart in 40 CFR 63.2131. In addition, the NESHAP clarifies that
fermenters are not subject to emission limits during the production of
specialty yeast (e.g., yeast for use in wine, champagne, whiskey, or
beer) in 40 CFR 63.2132. We are not proposing to amend the source
category definition in this action and are, therefore, not seeking
comment on the source category definition at this time.
    Only facilities that are located at or are part of a major source
of HAP emissions are subject to the Manufacturing of Nutritional Yeast
NESHAP; area sources of HAP are not subject to the rule. The HAP
emitted by nutritional yeast manufacturing facilities is acetaldehyde,
a probable carcinogen. In 2016, there are four nutritional yeast
manufacturing facilities that are subject to the NESHAP.
    The affected sources at nutritional yeast manufacturing facilities
are the collection of equipment used to manufacture Saccharomyces
cerevisiae yeast, including fermenters. The sizes of the fermenters
vary; generally smaller fermenters are used for earlier fermentation
stages and larger fermenters are used for later fermentation stages.
The initial, smaller fermenters, where the sugar source is added only
at the start of the batch (e.g., laboratory and pure culture
fermenters), are not subject to emission limits. The 40 CFR part 63,
subpart CCCC emission limits apply to the final three stages of the
fermentation process where the sugar source is added intermittently
throughout the process, which are often referred to as stock (third-to-
last stage), first generation (second-to-last stage), and trade (last
stage) fermentation.
    Currently, the fermenters are subject to batch average VOC emission
limits that differ for each fermentation stage, and which must be met
for 98 percent of all batches in each fermentation stage on a rolling
12-month basis. VOC is used as a surrogate for the HAP of interest,
acetaldehyde. The batch

average VOC limits are 300 parts per million by volume (ppmv) for stock
fermenters (third-to-last stage), 200 ppmv for first generation
fermenters (second-to-last stage), and 100 ppmv for trade fermenters
(last stage).
    In the current NESHAP, facilities can continuously monitor either
the VOC concentration in the fermenter exhaust or the brew ethanol
concentration in the fermenter liquid to determine compliance with the
emission limits. If a facility monitors brew ethanol concentration, it
must conduct an annual performance test to determine the correlation
between the brew ethanol concentration in the fermenter liquid and the
VOC concentration in the fermenter exhaust gas.

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

    The EPA visited three nutritional yeast manufacturing facilities
during the development of the NESHAP. Those facilities were the
American Yeast and AB Mauri Fleischmann's Yeast facilities in Memphis,
Tennessee, which we visited in December 2015, and the Red Star Yeast
facility in Cedar Rapids, Iowa, which we visited in June 2016. We also
held a conference call with the Minn-Dak Wahpeton facility, located in
Wahpeton, North Dakota, in May 2016. The EPA discussed the specific
yeast fermentation processes employed by each facility, including a
discussion of the number and design of their fermenters and associated
emission points, the process controls and monitors used, unregulated
emission sources, and other aspects of facility operations. The site
visits and conference call are documented in separate memoranda: ``Site
Visit Report--American Yeast Corporation, Memphis Plant,'' ``Site Visit
Report--AB Mauri Fleischmann's Yeast, Memphis Plant,'' ``Site Visit
Report--Red Star Yeast, Cedar Rapids, IA,'' and ``Notes from May 6,
2016 Conference Call Between the EPA and Minn-Dak Wahpeton,'' which are
available in the docket for this action.

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

    The EPA used information from the National Emissions Inventory
(NEI) and the RACT/BACT/LAER Clearinghouse (RBLC) to support this
proposed rulemaking. We used the NEI emissions and supporting data to
develop the modeling file for the risk review. The EPA utilized the
RBLC to identify additional control technologies for the technology
review. See sections III.A, III.C, and IV.C of this preamble for
further details on the use of these sources of information.

III. Analytical Procedures

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

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

    The EPA conducted 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 non-cancer health effects, and the hazard quotient (HQ) for
acute exposures to HAP with the potential to cause non-cancer health
effects. The assessment also provides estimates of the distribution of
cancer risks within the exposed populations, cancer incidence, and an
evaluation of the potential for adverse environmental effects. The
eight sections that follow this paragraph describe how we estimated
emissions and conducted the risk assessment. The docket for this
rulemaking contains the following document which provides more
information on the risk assessment inputs and models: ``Residual Risk
Assessment for the Manufacturing of Nutritional Yeast Source Category
in Support of the December 2016 Risk and Technology Review Proposed
Rule.'' The methods used to assess risks (as described in the eight
primary steps below) are consistent with those peer-reviewed by a panel
of the EPA's Science Advisory Board (SAB) in 2009 and described in
their peer review report issued in 2010; \2\ they are also consistent
with the key recommendations contained in that report.
---------------------------------------------------------------------------

    \2\ U.S. EPA SAB. Risk and Technology Review (RTR) Risk
Assessment Methodologies: For Review by the EPA's Science Advisory
Board with Case Studies--MACT I Petroleum Refining Sources and
Portland Cement Manufacturing, May 2010.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions
release characteristics?
    Fermenters are the primary emission source at nutritional yeast
facilities. Each fermenter emission source has a stack through which
the emissions are vented. The HAP emitted is acetaldehyde, which is a
by-product of the fermentation process. We used acetaldehyde emissions
data from the 2011 NEI and state emission reports (i.e., Iowa Emissions
Inventory Questionnaire reports) as the basis of the actual emission
estimates for each facility. The stack parameters used for each
fermenter were obtained from the 2011 NEI, title V permits, or were
provided to the Agency during site visits. We used default parameters
if site-specific information was not available. Additional details on
the data and methods used to develop actual emissions for the risk
modeling are provided in the memorandum, ``Emissions Data and Acute
Risk Factor Used in Residual Risk Modeling: Manufacturing of
Nutritional Yeast Source Category,'' which is available in the docket
for this action.
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 the specified annual time
period. In some cases, these ``actual'' emission levels are lower than
the emission levels required to comply with the current MACT standards.
The emissions level allowed to be emitted by the MACT standards is
referred to as the ``MACT-allowable'' emissions level. We discussed the
use of both MACT-allowable and actual emissions in the final Coke Oven
Batteries RTR (70 FR 19998-19999, April 15, 2005) and in the proposed
and final Hazardous Organic NESHAP RTRs (71 FR 34428, June 14, 2006,
and 71 FR 76609, December 21, 2006, respectively). In those actions, we
noted that assessing the risks at the MACT-allowable level is
inherently reasonable since these risks reflect the maximum level
facilities could emit and still comply with national emission
standards. We also explained that it is reasonable to consider actual
emissions, where such data are available, in both steps of the risk
analysis, in accordance with the Benzene NESHAP approach. (54 FR 38044,
September 14, 1989.)
    For nutritional yeast manufacturing facilities, we used the actual
emissions as the basis for the MACT-allowable emissions in the risk
assessment. We set allowable emissions equal to actual emissions based
on information gathered during the site visits that the facilities are
operating near maximum capacity and close to the level of emissions
allowed under the NESHAP. It is difficult to calculate a precise
allowable emissions level for this industry because the emission limits
are based on the average emissions concentration during each batch and
the absolute number of batches produced at a facility fluctuates each
year based on market demand for yeast.
    Furthermore, facilities are also unlikely to emit significantly
higher levels of HAP due to a business incentive to minimize
acetaldehyde

emissions and continuous monitoring requirements in the rule.
Acetaldehyde is a by-product of sub-optimal yeast production.
Increasing concentrations of acetaldehyde indicate decreases relative
to the potential amount and/or quality of yeast that can be produced
within a fermentation batch, resulting in a loss of profit for the
yeast manufacturer. Therefore, companies have a business incentive to
reduce HAP emissions as much as possible. Additionally, continuous
monitoring ensures that the facilities receive real-time information
about emissions throughout the yeast manufacturing process. These
monitoring systems have enabled facilities to set up control systems
that automatically adjust process parameters in real-time to reduce
emissions if they reach a specified level.
    As stated above, MACT-allowable emissions are used to develop
estimates of risk when actual emissions are lower than those required
to meet current emission standards. Due to the difficulties that limit
the calculation of allowable emissions (e.g., the current NESHAP
standard requirements) and the low likelihood of facilities emitting
significantly higher levels of HAP than current amounts, actual
emissions provide the most accurate estimate of emissions that will be
emitted from nutritional yeast manufacturing facilities. Therefore, we
determined that the use of actual emissions as the basis of the MACT-
allowable emissions in this risk assessment is the most appropriate
option for this subpart.
3. How did we conduct dispersion modeling, determine inhalation
exposures, and estimate individual and population inhalation risks?
    Both long-term and short-term inhalation exposure concentrations
and health risks from the source category addressed in this proposal
were estimated using the Human Exposure Model (Community and Sector
HEM-3 version 1.1.0). 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 km of
the modeled sources,\3\ and (3) estimating individual and population-
level inhalation risks using the exposure estimates and quantitative
dose-response information.
---------------------------------------------------------------------------

    \3\ This metric comes from the Benzene NESHAP. See 54 FR 38046.
---------------------------------------------------------------------------

    The air dispersion model used by the HEM-3 model (AERMOD) is one of
the EPA's preferred models for assessing pollutant concentrations from
industrial facilities.\4\ 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 (2014) of
hourly surface and upper air observations for more than 800
meteorological stations, selected to provide coverage of the United
States and Puerto Rico. A second library of United States Census Bureau
census block \5\ 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 unit risk factors and other
health benchmarks is used to estimate health risks. These risk factors
and health benchmarks are the latest values recommended by the EPA for
HAP and other toxic air pollutants. These values are available at
https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants and are discussed in
more detail later in this section.
---------------------------------------------------------------------------

    \4\ 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).
    \5\ A census block is the smallest geographic area for which
census statistics are tabulated.
---------------------------------------------------------------------------

    In developing the risk assessment for chronic exposures, we used
the estimated annual average ambient air concentrations of each HAP
emitted by each source for which we have emissions data in the source
category. The air concentrations at each nearby census block centroid
were used as a surrogate for the chronic inhalation exposure
concentration for all the people who reside in that census block. We
calculated the MIR for each facility as the cancer risk associated with
a continuous lifetime (24 hours per day, 7 days per week, and 52 weeks
per year for a 70-year period) exposure to the maximum concentration at
the centroid of inhabited census blocks. Individual cancer risks were
calculated by multiplying the estimated lifetime exposure to the
ambient concentration of each of the 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 probability of contracting cancer
over a lifetime of exposure to a concentration of 1 microgram of the
pollutant per cubic meter of air. For residual risk assessments, we
generally use URE values 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) URE values, where available. In cases where
new, scientifically credible dose response values have been developed
in a manner consistent with the EPA guidelines and have undergone a
peer review process similar to that used by the EPA, we may use such
dose-response values in place of, or in addition to, other values, if
appropriate.
    The EPA estimated incremental individual lifetime cancer risks
associated with emissions from the facilities in the source category as
the sum of the risks for each of the carcinogenic HAP (including those
classified as carcinogenic to humans, likely to be carcinogenic to
humans, and suggestive evidence of carcinogenic potential) \6\ emitted
by the modeled sources. Cancer incidence and the distribution of
individual cancer risks for the population within 50 km of the sources
were also estimated for the source category as part of this assessment
by summing individual risks. A distance of 50 km is consistent with
both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044,
September 14, 1989) and the limitations of Gaussian dispersion models,
including AERMOD.
---------------------------------------------------------------------------

    \6\ These classifications also coincide with the terms ``known
carcinogen, probable carcinogen, and possible carcinogen,''
respectively, which are the terms advocated in the EPA's previous
``Guidelines for Carcinogen Risk Assessment,'' published in 1986 (51
FR 33992, September 24, 1986). Summing the risks of these individual
compounds to obtain the cumulative cancer risks is an approach that
was recommended by the EPA's SAB in their 2002 peer review of the
EPA's National Air Toxics Assessment (NATA) titled, ``NATA--
Evaluating the National-scale Air Toxics Assessment 1996 Data--an
SAB Advisory,'' available at http://yosemite.epa.gov/sab/
sabproduct.nsf/214C6E915BB04E14852570CA007A682C/$File/
ecadv02001.pdf.
---------------------------------------------------------------------------

    To assess the risk of non-cancer health effects from chronic
exposures, we summed the HQ for each of the HAP that affects a common
target organ system to obtain the HI for that target organ system (or
target organ-specific HI, TOSHI). The HQ is the estimated exposure
divided by the chronic reference value, which is a value selected from
one of several sources. First, the chronic reference level can be the
EPA reference concentration (RfC) (https://ofmpub.epa.gov/sor_internet/
registry/termreg/searchandretrieve/glossariesandkeywordlists/
search.do?details=&glossaryName=Risk

%20Assessment%20Glossary), defined as ``an estimate (with uncertainty
spanning perhaps an order of magnitude) of a continuous inhalation
exposure to the human population (including sensitive subgroups) that
is likely to be without an appreciable risk of deleterious effects
during a lifetime.'' Alternatively, in cases where an RfC from the
EPA's IRIS database is not available or where the EPA determines that
using a value other than the RfC is appropriate, the chronic reference
level can be a value from the following prioritized sources: (1) The
Agency for Toxic Substances and Disease Registry Minimum Risk Level
(http://www.atsdr.cdc.gov/mrls/index.asp), which is defined as ``an
estimate of daily human exposure to a hazardous substance that is
likely to be without an appreciable risk of adverse non-cancer health
effects (other than cancer) over a specified duration of exposure'';
(2) the CalEPA Chronic Reference Exposure Level (REL) (http://oehha.ca.gov/media/downloads/crnr/2015guidancemanual.pdf), which is
defined as ``the concentration level (that is expressed in units of
micrograms per cubic meter ([mu]g/m\3\) for inhalation exposure and in
a dose expressed in units of milligram per kilogram-day (mg/kg-day) for
oral exposures), at or below which no adverse health effects are
anticipated for a specified exposure duration''; 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, in
place of or in concert with other values.
    As mentioned above, in order to characterize non-cancer chronic
effects, and in response to key recommendations from the SAB, the EPA
selects dose-response values that reflect the best available science
for all HAP included in RTR risk assessments.\7\ More specifically, for
a given HAP, the EPA examines the availability of inhalation reference
values from the sources included in our tiered approach (e.g., IRIS
first, Agency for Toxic Substances and Disease Registry (ATSDR) second,
CalEPA third) and determines which inhalation reference value
represents the best available science. Thus, as new inhalation
reference values become available, the EPA will typically evaluate them
and determine whether they should be given preference over those
currently being used in RTR risk assessments.
---------------------------------------------------------------------------

    \7\ The SAB peer review of RTR Risk Assessment Methodologies is
available at http://yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.
---------------------------------------------------------------------------

    The EPA also evaluated screening estimates of acute exposures and
risks for each of the HAP (for which appropriate acute dose-response
values are available) at the point of highest potential off-site
exposure for each facility. To do this, the EPA estimated the risks
when both the peak hourly emissions rate and worst-case dispersion
conditions occur. We also assume that a person is located at the point
of highest impact during that same time. In accordance with our mandate
in section 112 of the CAA, we use the point of highest off-site
exposure to assess the potential risk to the maximally exposed
individual. The acute HQ is the estimated acute exposure divided by the
acute dose-response value. In each case, the EPA calculated acute HQ
values using best available, short-term dose-response values. These
acute dose-response values, which are described below, include the
acute REL, acute exposure guideline levels (AEGL) and emergency
response planning guidelines (ERPG) for 1-hour exposure durations. As
discussed below, we used conservative assumptions for emissions rates,
meteorology, and exposure location.
    As described in the CalEPA's ``Air Toxics Hot Spots Program Risk
Assessment Guidelines, Part I, The Determination of Acute Reference
Exposure Levels for Airborne Toxicants,'' an acute REL value (http://oehha.ca.gov/media/downloads/crnr/acuterel.pdf) is defined as ``the
concentration level at or below which no adverse health effects are
anticipated for a specified exposure duration.'' Id. at page 2. Acute
REL values are based on the most sensitive, relevant, adverse health
effect reported in the peer-reviewed medical and toxicological
literature. Acute REL values 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.
    AEGL values were derived in response to recommendations from the
National Research Council (NRC). As described in ``Standing Operating
Procedures (SOP) of the National Advisory Committee on Acute Exposure
Guideline Levels for Hazardous Substances'' (https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf),\8\ ``the NRC's
previous name for acute exposure levels--community emergency exposure
levels was replaced by the term AEGL to reflect the broad application
of these values to planning, response, and prevention in the community,
the workplace, transportation, the military, and the remediation of
Superfund sites.'' Id. at 2. This document also states that AEGL values
``represent threshold exposure limits for the general public and are
applicable to emergency exposures ranging from 10 minutes to eight
hours.'' Id. at 2.
---------------------------------------------------------------------------

    \8\ National Academy of Sciences (NAS), 2001. Standing Operating
Procedures for Developing Acute Exposure Levels for Hazardous
Chemicals, page 2.
---------------------------------------------------------------------------

    The document lays out the purpose and objectives of AEGL by stating
that ``the primary purpose of the AEGL program and the National
Advisory Committee for Acute Exposure Guideline Levels for Hazardous
Substances is to develop guideline levels for once-in-a-lifetime,
short-term exposures to airborne concentrations of acutely toxic, high-
priority chemicals.'' Id. at 21. In detailing the intended application
of AEGL values, the document states that ``[i]t is anticipated that the
AEGL values will be used for regulatory and nonregulatory purposes by
U.S. Federal and state agencies and possibly the international
community in conjunction with chemical emergency response, planning,
and prevention programs. More specifically, the AEGL values will be
used for conducting various risk assessments to aid in the development
of emergency preparedness and prevention plans, as well as real-time
emergency response actions, for accidental chemical releases at fixed
facilities and from transport carriers.'' Id. at 31.
    The AEGL-1 value is then 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.'' Id. at 3. 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. Similarly, the document defines AEGL-2 values 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.
    ERPG values are derived for use in emergency response, as described
in the American Industrial Hygiene Association's ERP Committee document
titled, ``ERPGS Procedures and Responsibilities'' (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), which
states that, ``Emergency Response Planning Guidelines were developed
for emergency planning and are intended as health based guideline
concentrations for single exposures to chemicals.'' \9\ Id. at 1. The
ERPG-1 value 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 value 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.
---------------------------------------------------------------------------

    \9\ ERP Committee Procedures and Responsibilities. March 2014.
American Industrial Hygiene Association.
---------------------------------------------------------------------------

    As can be seen from the definitions above, the AEGL and ERPG values
include the similarly-defined severity levels 1 and 2. For many
chemicals, a severity level 1 value AEGL or ERPG has not been developed
because the types of effects for these chemicals are not consistent
with the AEGL-1/ERPG-1 definitions; in these instances, we compare
higher severity level AEGL-2 or ERPG-2 values to our modeled exposure
levels to screen for potential acute concerns. When AEGL-1/ERPG-1
values are available, they are used in our acute risk assessments.
    Acute REL values for 1-hour exposure durations are typically lower
than their corresponding AEGL-1 and ERPG-1 values. Even though their
definitions are slightly different, AEGL-1 values are often the same as
the corresponding ERPG-1 values, and AEGL-2 values are often equal to
ERPG-2 values. Maximum HQ values from our acute screening risk
assessments typically result when basing them on the acute REL value
for a particular pollutant. In cases where our maximum acute HQ value
exceeds 1, we also report the HQ value based on the next highest acute
dose-response value (usually the AEGL-1 and/or the ERPG-1 value).
    To develop screening estimates of acute exposures in the absence of
hourly emissions data, generally we first develop estimates of maximum
hourly emissions rates by multiplying the average actual annual hourly
emissions rates by a default factor to cover routinely variable
emissions. We choose the factor to use partially based on process
knowledge and engineering judgment. The factor chosen also reflects a
Texas study of short-term emissions variability, which showed that most
peak emission events in a heavily-industrialized four-county area
(Harris, Galveston, Chambers, and Brazoria Counties, Texas) were less
than twice the annual average hourly emissions rate. The highest peak
emissions event was 74 times the annual average hourly emissions rate,
and the 99th percentile ratio of peak hourly emissions rate to the
annual average hourly emissions rate was 9.\10\ Considering this
analysis, to account for more than 99 percent of the peak hourly
emissions, we apply a conservative screening multiplication factor of
10 to the average annual hourly emissions rate in our acute exposure
screening assessments as our default approach. However, we use a factor
other than 10 if we have information that indicates that a different
factor is appropriate for a particular source category.
---------------------------------------------------------------------------

    \10\ Allen, et al., Variable Industrial VOC Emissions and their
impact on ozone formation in the Houston Galveston Area. Texas
Environmental Research Consortium, 2004, and available online at:
https://www.researchgate.net/publication/237593060_Variable_Industrial_VOC_Emissions
and_their_Impact_on_Ozone_Formation_in_the_Houston_Galveston_Area
---------------------------------------------------------------------------

    For this source category, we used an acute multiplication factor of
1.2 for all emission sources from nutritional yeast manufacturing
facilities. The factor equals the average peak-to-mean ratio developed
using 5 years of batch-averaged fermenter VOC concentration data from
the facility with the highest emissions in the 2011 NEI. While the
current rule requires continuous monitoring of emissions, facilities
are required to report whether the percentage of batches that meet
emission limits based on the average concentration of VOC emitted from
each batch meets the current compliance requirements; not the
continuous levels of emissions at the facility. Using the data above,
we developed a multiplier to estimate potential acute emissions from
each facility in this source category. A further discussion of why this
factor was chosen can be found in the memorandum, ``Emissions Data and
Acute Risk Factor Used in Residual Risk Modeling: Manufacturing of
Nutritional Yeast Source Category,'' available in the docket for this
rulemaking.
    As part of our acute risk assessment process, for cases where acute
HQ values from the screening step were less than or equal to 1 (even
under the conservative assumptions of the screening analysis), acute
impacts were deemed negligible and no further analysis was performed
for these HAP. In cases where an acute HQ from the screening step was
greater than 1, additional site-specific data were considered to
develop a more refined estimate of the potential for acute impacts of
concern. For this source category, all acute HQ screening values were
less than 1. Therefore, we did not employ additional data refinements.
    Ideally, we would prefer to have continuous measurements over time
to see how the emissions vary by each hour over an entire year. Having
a frequency distribution of hourly emissions rates over a year would
allow us to perform a probabilistic analysis to estimate potential
threshold exceedances and their frequency of occurrence. Such an
evaluation could include a more complete statistical treatment of the
key parameters and elements adopted in this screening analysis.
Recognizing that this level of data is rarely available, we instead
rely on the multiplier approach.
    To better characterize the potential health risks associated with
estimated acute exposures to HAP, and in response to a key
recommendation from the SAB's peer review of the EPA's RTR risk
assessment methodologies,\11\ we generally examine a wider range of
available acute health metrics (e.g., RELs, AEGLs) than we do for our
chronic risk assessments. This is in response to the SAB's
acknowledgement that there are generally more data gaps and
inconsistencies in acute reference values than there are in chronic
reference values. In some cases, when

Reference Value Arrays \12\ for HAP have been developed, we consider
additional acute values (i.e., occupational and international values)
to provide a more complete risk characterization.
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    \11\ The SAB peer review of RTR Risk Assessment Methodologies is
available at http://yosemite.epa.gov/sab/sabproduct.nsf/
4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.
    \12\ U.S. EPA. Chapter 2.9, Chemical Specific Reference Values
for Formaldehyde in Graphical Arrays of Chemical-Specific Health
Effect Reference Values for Inhalation Exposures (Final Report).
U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/
061, 2009, and available online at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003.
---------------------------------------------------------------------------

4. How did we conduct the multi-pathway exposure and risk screening?
    The EPA conducted a screening analysis examining the potential for
significant human health risks due to exposures via routes other than
inhalation (i.e., ingestion). We first determined whether any sources
in the source category emitted any HAP known to be persistent and
bioaccumulative in the environment (PB-HAP). The PB-HAP compounds or
compound classes are identified for the screening from the EPA's Air
Toxics Risk Assessment Library (available at http://www2.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library).
    For the Manufacturing of Nutritional Yeast source category, we did
not identify emissions of any PB-HAP. Because we did not identify PB-
HAP emissions, no further evaluation of multi-pathway risk was
conducted for this source category.
5. How did we assess risks considering emissions control options?
    The proposed rule amendments include changes to the form of the
current emission limits, additional testing requirements, changes to
the current monitoring requirements, and updates to the reporting and
recordkeeping requirements. The proposed amendments to the emission
limits may lead to a slight decrease in the overall emissions from the
facilities, but we are unable to quantify this reduction. Facilities
will continue to employ current process controls to comply with the
emission limits (i.e., they are not required to install additional
control technologies); however, the facilities may need to make minor
adjustments to the level of process controls to comply with the new
limits.
    The proposed amendments to testing and monitoring requirements will
increase the reliability of the emissions data that is monitored by
each facility to ensure that the current emission limits are being met
consistently. Therefore, risks considering the proposed amendments are
estimated to be the same as actual risks under the current MACT
standard.
6. How did we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect
    The EPA conducts a screening assessment to examine the potential
for adverse environmental effects as required under section
112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines ``adverse
environmental effect'' as ``any significant and widespread adverse
effect, which may reasonably be anticipated, to wildlife, aquatic life,
or other natural resources, including adverse impacts on populations of
endangered or threatened species or significant degradation of
environmental quality over broad areas.''
b. Environmental HAP
    The EPA focuses on seven HAP, which we refer to as ``environmental
HAP,'' in its screening analysis: Five PB-HAP and two acid gases. The
five PB-HAP are cadmium, dioxins/furans, polycyclic organic matter
(POM), mercury (both inorganic mercury and methyl mercury), and lead
compounds. The two acid gases are hydrogen chloride (HCl) and hydrogen
fluoride (HF). The rationale for including these seven HAP in the
environmental risk screening analysis is presented below.
    HAP that persist and bioaccumulate are of particular environmental
concern because they accumulate in the soil, sediment, and water. The
PB-HAP are taken up, through sediment, soil, water, and/or ingestion of
other organisms, by plants or animals (e.g., small fish) at the bottom
of the food chain. As larger and larger predators consume these
organisms, concentrations of the PB-HAP in the animal tissues increases
as does the potential for adverse effects. The five PB-HAP we evaluate
as part of our screening analysis account for 99.8 percent of all PB-
HAP emissions nationally from stationary sources (on a mass basis from
the 2005 NEI.
    In addition to accounting for almost all of the mass of PB-HAP
emitted, we note that the TRIM.FaTE model that we use to evaluate
multi-pathway risk allows us to estimate concentrations of cadmium
compounds, dioxins/furans, POM, and mercury in soil, sediment and
water. For lead compounds, we currently do not have the ability to
calculate these concentrations using the TRIM.FaTE model. Therefore, to
evaluate the potential for adverse environmental effects from lead
compounds, we compare the estimated HEM-modeled exposures from the
source category emissions of lead with the level of the secondary
National Ambient Air Quality Standards (NAAQS) for lead.\13\ We
consider values below the level of the secondary lead NAAQS to be
unlikely to cause adverse environmental effects.
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    \13\ The secondary lead NAAQS is a reasonable measure of
determining whether there is an adverse environmental effect since
it was established considering ``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.''
---------------------------------------------------------------------------

    Due to their well-documented potential to cause direct damage to
terrestrial plants, we include two acid gases, HCl, and HF in the
environmental screening analysis. According to the 2005 NEI, HCl, and
HF account for about 99 percent (on a mass basis) of the total acid gas
HAP emitted by stationary sources in the U.S. In addition to the
potential to cause direct damage to plants, high concentrations of HF
in the air have been linked to fluorosis in livestock. Air
concentrations of these HAP are already calculated as part of the human
multi-pathway exposure and risk screening analysis using the HEM3-
AERMOD air dispersion model, and we are able to use the air dispersion
modeling results to estimate the potential for an adverse environmental
effect.
    The EPA acknowledges that other HAP beyond the seven HAP discussed
above may have the potential to cause adverse environmental effects.
Therefore, the EPA may include other relevant HAP in its environmental
risk screening in the future, as modeling science and resources allow.
The EPA invites comment on the extent to which other HAP emitted by the
source category may cause adverse environmental effects. Such
information should include references to peer-reviewed ecological
effects benchmarks that are of sufficient quality for making regulatory
decisions, as well as information on the presence of organisms located
near facilities within the source category that such benchmarks
indicate could be adversely affected.
c. Screening Methodology
    For the environmental risk screening analysis, the EPA first
determined whether any facilities in the Manufacturing of Nutritional
Yeast source category emitted any of the seven environmental HAP. For
this source category, we did not identify emissions

of any of the seven environmental HAP included in the screen. Because
we did not identify environmental HAP emissions, we did not conduct a
further evaluation of environmental risk.
7. How did we conduct facility-wide assessments?
    To put the source category risks in context, we typically examine
the risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, we examine the HAP emissions not only from the
source category emission points of interest, but also emissions of HAP
from all other emission sources at the facility for which we have data.
The current NESHAP does not set emission limits for equipment other
than fermenters at the affected sources. There is a potential for
temporary wastewater storage tanks (e.g., pH adjustment tanks) and
dryers to emit small amounts of acetaldehyde at nutritional yeast
facilities covered by this subpart. The NEI does not include emissions
from wastewater storage tanks at any of the four facilities subject to
this rule. Only one of the four facilities has dryers; the NEI did
report estimated emissions from these dryers, which were included in
the risk assessment for this source category.
    We did not perform a separate facility-wide risk assessment for
facilities that manufacture nutritional yeast. One facility (American
Yeast) reported 43 pounds of additional HAP emissions, composed largely
of hexane and formaldehyde, from equipment sources not covered by 40
CFR part 63, subpart CCCC (e.g., boilers, equipment covered by other
NESHAP).\14\ However, because these emissions were so low and from
pollutants with low risk factors, we concluded that a facility-wide
risk assessment would yield the same or only very slightly different
results as the source category assessment.
---------------------------------------------------------------------------

    \14\ Because these emissions originate from sources outside the
manufacturing of nutritional yeast source category, they were also
excluded from the source category risk analysis.
---------------------------------------------------------------------------

8. How did we consider uncertainties in risk assessment?
    In the Benzene NESHAP, we concluded that risk estimation
uncertainty should be considered in our decision-making under the ample
margin of safety framework. 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 protective and environmentally protective. A brief
discussion of the uncertainties in the RTR emissions dataset,
dispersion modeling, inhalation exposure estimates, and dose-response
relationships follows below. A more thorough discussion of these
uncertainties is included in the ``Residual Risk Assessment for the
Manufacturing of Nutritional Yeast Source Category in Support of the
December 2016 Risk and Technology Review Proposed Rule,'' which is
available in the docket for this action.
a. Uncertainties in the RTR Emissions Dataset
    Although the development of the RTR emissions dataset involved
quality assurance/quality control processes, the accuracy of emissions
values will vary depending on the source of the data, the degree to
which data are incomplete or missing, the degree to which assumptions
made to complete the datasets are accurate, errors in emission
estimates, and other factors. The emission estimates considered in this
analysis generally are annual totals for certain years, and they do not
reflect short-term fluctuations during the course of a year or
variations from year to year. The estimates of peak hourly emission
rates for the acute effects screening assessment were based on an
emission adjustment factor applied to the average annual hourly
emission rates, which are intended to account for emission fluctuations
due to normal facility operations.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration
estimates associated with any model, including the EPA's recommended
regulatory dispersion model, AERMOD. In using a model to estimate
ambient pollutant concentrations, the user chooses certain options to
apply. For RTR assessments, we select some model options that have the
potential to overestimate ambient air concentrations (e.g., not
including plume depletion or pollutant transformation). We select other
model options that have the potential to underestimate ambient impacts
(e.g., not including building downwash). Other options that we select
have the potential to either under- or overestimate ambient levels
(e.g., meteorology and receptor locations). On balance, considering the
directional nature of the uncertainties commonly present in ambient
concentrations estimated by dispersion models, the approach we apply in
the RTR assessments should yield unbiased estimates of ambient HAP
concentrations.
c. Uncertainties in Inhalation Exposure
    The EPA did not include the effects of human mobility on exposures
in the assessment. Specifically, short-term mobility and long-term
mobility between census blocks in the modeling domain were not
considered.\15\ The approach of not considering short or long-term
population mobility does not bias the estimate of the theoretical MIR
(by definition), nor does it affect the estimate of cancer incidence
because the total population number remains the same. It does, however,
affect the shape of the distribution of individual risks across the
affected population, shifting it toward higher estimated individual
risks at the upper end and reducing the number of people estimated to
be at lower risks, thereby increasing the estimated number of people at
specific high risk levels (e.g., 1-in-10 thousand or 1-in-1 million).
---------------------------------------------------------------------------

    \15\ Short-term mobility is movement from one micro-environment
to another over the course of hours or days. Long-term mobility is
movement from one residence to another over the course of a
lifetime.
---------------------------------------------------------------------------

    In addition, the assessment predicted the chronic exposures at the
centroid of each populated census block as surrogates for the exposure
concentrations for all people living in that block. Using the census
block centroid to predict chronic exposures tends to over-predict
exposures for people in the census block who live farther from the
facility and under-predict exposures for people in the census block who
live closer to the facility. Thus, using the census block centroid to
predict chronic exposures may lead to a potential understatement or
overstatement of the true maximum impact, but is an unbiased estimate
of average risk and incidence. We reduce this uncertainty by analyzing
large census blocks near facilities using aerial imagery and adjusting
the location of the block centroid to better represent the population
in the block, as well as adding additional receptor locations where the
block population is not well represented by a single location.
    The assessment evaluates the cancer inhalation risks associated
with pollutant exposures over a 70-year period, which is the assumed
lifetime of an individual. In reality, both the length of time that
modeled emission sources at facilities actually operate (i.e., more or
less than 70 years) and the domestic growth or decline of the modeled
industry (i.e., the increase or decrease in the number or size of
domestic facilities) will influence the future risks

posed by a given source or source category. Depending on the
characteristics of the industry, these factors will, in most cases,
result in an overestimate both in individual risk levels and in the
total estimated number of cancer cases. However, in the unlikely
scenario where a facility maintains, or even increases, its emissions
levels over a period of more than 70 years, residents live beyond 70
years at the same location, and the residents spend most of their days
at that location, then the cancer inhalation risks could potentially be
underestimated. However, annual cancer incidence estimates from
exposures to emissions from these sources would not be affected by the
length of time an emissions source operates.
    The exposure estimates used in these analyses assume chronic
exposures to ambient (outdoor) levels of pollutants. Because most
people spend the majority of their time indoors, actual exposures may
not be as high, depending on the characteristics of the pollutants
modeled. For many of the HAP, indoor levels are roughly equivalent to
ambient levels, but for very reactive pollutants or larger particles,
indoor levels are typically lower. This factor has the potential to
result in an overestimate of 25 to 30 percent of exposures.\16\
---------------------------------------------------------------------------

    \16\ U.S. EPA. National-Scale Air Toxics Assessment for 1996.
(EPA 453/R-01-003; January 2001; page 85.)
---------------------------------------------------------------------------

    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 that
should be highlighted. The accuracy of an acute inhalation exposure
assessment depends on the simultaneous occurrence of independent
factors that may vary greatly, such as hourly emissions rates,
meteorology, and the presence of humans at the location of the maximum
concentration. In the acute screening assessment that we conduct under
the RTR program, we assume that peak emissions from the source category
and worst-case meteorological conditions co-occur, thus, resulting in
maximum ambient concentrations. These two events are unlikely to occur
at the same time, making these assumptions conservative. We then
include the additional assumption that a person is located at this
point during this same time period. For this source category, these
assumptions would tend to be worst-case actual exposures as it is
unlikely that a person would be located at the point of maximum
exposure during the time when peak emissions and worst-case
meteorological conditions occur simultaneously.
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 non-cancer effects from both chronic and acute
exposures. Some uncertainties may be considered quantitatively, and
others generally are expressed in qualitative terms. We note as a
preface to this discussion a point on dose-response uncertainty that is
brought out in the EPA's 2005 Cancer Guidelines; namely, that ``the
primary goal of EPA actions is protection of human health; accordingly,
as an Agency policy, risk assessment procedures, including default
options that are used in the absence of scientific data to the
contrary, should be health protective'' (EPA's 2005 Cancer Guidelines,
pages 1-7). This is the approach followed here as summarized in the
next several paragraphs. A complete detailed discussion of
uncertainties and variability in dose-response relationships is given
in the ``Residual Risk Assessment for the Manufacturing of Nutritional
Yeast Source Category in Support of the December 2016 Risk and
Technology Review Proposed Rule,'' which is available in the docket for
this action.
    Cancer URE values used in our risk assessments are those that have
been developed to generally provide an upper bound estimate of risk.
That is, they represent a ``plausible upper limit to the true value of
a quantity'' (although this is usually not a true statistical
confidence limit).\17\ In some circumstances, the true risk could be as
low as zero; however, in other circumstances the risk could be
greater.\18\ When developing an upper bound estimate of risk and to
provide risk values that do not underestimate risk, health-protective
default approaches are generally used. To err on the side of ensuring
adequate health protection, the EPA typically uses the upper bound
estimates rather than lower bound or central tendency estimates in our
risk assessments, an approach that may have limitations for other uses
(e.g., priority-setting or expected benefits analysis).
---------------------------------------------------------------------------

    \17\ IRIS glossary (https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \18\ 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.
---------------------------------------------------------------------------

    Chronic non-cancer RfC and reference dose (RfD) values represent
chronic exposure levels that are intended to be health-protective
levels. Specifically, these values provide an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure (RfC) or a daily oral exposure (RfD) to the human
population (including sensitive subgroups) that is likely to be without
an appreciable risk of deleterious effects during a lifetime. To derive
values that are intended to be ``without appreciable risk,'' the
methodology relies upon an uncertainty factor (UF) approach (U.S. EPA,
1993 and 1994), which considers uncertainty, variability, and gaps in
the available data. The UF are applied to derive reference values that
are intended to protect against appreciable risk of deleterious
effects. The UF are commonly default values,\19\ e.g., factors of 10 or
3, used in the absence of compound-specific data; where data are
available, UF may also be developed using compound-specific
information. When data are limited, more assumptions are needed and
more UF are used. Thus, there may be a greater tendency to overestimate
risk in the sense that further study might support development of
reference values that are higher (i.e., less potent) because fewer
default assumptions are needed. However, for some pollutants, it is
possible that risks may be underestimated.
---------------------------------------------------------------------------

    \19\ According to the NRC report, ``Science and Judgment in Risk
Assessment'' (NRC, 1994) ``[Default] options are generic approaches,
based on general scientific knowledge and policy judgment, that are
applied to various elements of the risk assessment process when the
correct scientific model is unknown or uncertain.'' The 1983 NRC
report, ``Risk Assessment in the Federal Government: Managing the
Process,'' defined default option as ``the option chosen on the
basis of risk assessment policy that appears to be the best choice
in the absence of data to the contrary'' (NRC, 1983a, p. 63).
Therefore, default options are not rules that bind the Agency;
rather, the Agency may depart from them in evaluating the risks
posed by a specific substance when it believes this to be
appropriate. In keeping with the EPA's goal of protecting public
health and the environment, default assumptions are used to ensure
that risk to chemicals is not underestimated (although defaults are
not intended to overtly overestimate risk). See EPA, ``An
Examination of EPA Risk Assessment Principles and Practices,'' EPA/
100/B-04/001, 2004, available at https://nctc.fws.gov/resources/course-resources/pesticides/Risk%20Assessment/Risk%20Assessment%20Principles%20and%20Practices.pdf.
---------------------------------------------------------------------------

    While collectively termed ``UF,'' these factors account for a
number of different quantitative considerations when using observed
animal (usually rodent) or human toxicity data in the development of
the RfC. The UF are intended to

account for: (1) Variation in susceptibility among the members of the
human population (i.e., inter-individual variability); (2) uncertainty
in extrapolating from experimental animal data to humans (i.e.,
interspecies differences); (3) uncertainty in extrapolating from data
obtained in a study with less-than-lifetime exposure (i.e.,
extrapolating from sub-chronic to chronic exposure); (4) uncertainty in
extrapolating the observed data to obtain an estimate of the exposure
associated with no adverse effects; and (5) uncertainty when the
database is incomplete or there are problems with the applicability of
available studies.
    Many of the UF used to account for variability and uncertainty in
the development of acute reference values are quite similar to those
developed for chronic durations, but they more often use individual UF
values that may be less than 10. The UF are applied based on chemical-
specific or health effect-specific information (e.g., simple irritation
effects do not vary appreciably between human individuals, hence a
value of 3 is typically used), or based on the purpose for the
reference value (see the following paragraph). The UF applied in acute
reference value derivation include: (1) Heterogeneity among humans; (2)
uncertainty in extrapolating from animals to humans; (3) uncertainty in
lowest observed adverse effect (exposure) level to no observed adverse
effect (exposure) level adjustments; and (4) uncertainty in accounting
for an incomplete database on toxic effects of potential concern.
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 reference value at another exposure duration
(e.g., 1 hour).
    Not all acute reference 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 reference value or
values being exceeded. Where relevant to the estimated exposures, the
lack of short-term dose-response values at different levels of severity
should be factored into the risk characterization as potential
uncertainties.
    For a group of compounds that are unspeciated (e.g., glycol
ethers), we conservatively use the most protective reference 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 reference value, we also apply the most
protective reference value from the other compounds in the group to
estimate risk.

B. How did we consider the risk results in making decisions for this
proposal?

    As discussed in section II.A of this preamble, in evaluating and
developing standards under CAA section 112(f)(2), we apply a two-step
process to address residual risk. 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)
\20\ of approximately [1-in-10 thousand] [i.e., 100-in-1 million].'' 54
FR 38045, September 14, 1989. If risks are unacceptable, the EPA must
determine the emissions standards necessary to bring risks to an
acceptable level without considering costs. In the second step of the
process, the EPA considers whether the emissions standards provide an
ample margin of safety ``in consideration of all health information,
including the number of persons at risk levels higher than
approximately 1-in-1 million, as well as other relevant factors,
including costs and economic impacts, technological feasibility, and
other factors relevant to each particular decision.'' Id. The EPA must
promulgate emission standards necessary to provide an ample margin of
safety. 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.
---------------------------------------------------------------------------

    \20\ Although defined as ``maximum individual risk,'' MIR refers
only to cancer risk. MIR, one metric for assessing cancer risk, is
the estimated risk were an individual exposed to the maximum level
of a pollutant for a lifetime.
---------------------------------------------------------------------------

    In past residual risk actions, the EPA considered a number of human
health risk metrics associated with emissions from the categories under
review, including the MIR, the number of persons in various risk
ranges, cancer incidence, the maximum non-cancer HI and the maximum
acute non-cancer hazard. See, e.g., 72 FR 25138, May 3, 2007; and 71 FR
42724, July 27, 2006. The EPA considered this health information for
both actual and allowable emissions. See, e.g., 75 FR 65068, October
21, 2010; 75 FR 80220, December 21, 2010; 76 FR 29032, May 19, 2011.
The EPA also discussed risk estimation uncertainties and considered the
uncertainties in the determination of acceptable risk and ample margin
of safety in these past actions. The EPA considered this same type of
information in support of this action.
    The Agency is considering these various measures of health
information to inform our determinations of risk acceptability and
ample margin of safety under CAA section 112(f). As explained in the
Benzene NESHAP, ``the first step judgment on acceptability cannot be
reduced to any single factor'' and, thus, ``[t]he Administrator
believes that the acceptability of risk under [previous] section 112 is
best judged on the basis of a broad set of health risk measures and
information.'' 54 FR 38046, September 14, 1989. Similarly, with regard
to the ample margin of safety determination, ``the Agency again
considers all of the health risk and other health information
considered in the first step. Beyond that information, additional
factors relating to the appropriate level of control will also be
considered, including cost and economic impacts of controls,
technological feasibility, uncertainties, and any other relevant
factors.'' Id.
    The Benzene NESHAP approach provides flexibility regarding factors
the EPA may consider in making determinations and how the EPA may weigh
those factors for each source category. In responding to comment on our
policy under the Benzene NESHAP, the EPA explained that:

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

    See 54 FR at 38057, September 14, 1989. Thus, the level of the MIR
is only one factor to be weighed in determining acceptability of risks.
The Benzene NESHAP explained that ``an MIR of approximately one in 10
thousand should ordinarily be the upper end of the range of
acceptability. As risks increase above this benchmark, they become
presumptively less acceptable under CAA section 112, and would be
weighed with the other health risk

measures and information in making an overall judgment on
acceptability. Or, the Agency may find, in a particular case, that a
risk that includes MIR less than the presumptively acceptable level is
unacceptable in the light of other health risk factors.'' Id. at 38045.
Similarly, with regard to the ample margin of safety analysis, the EPA
stated in the Benzene NESHAP that: ``EPA believes the relative weight
of the many factors that can be considered in selecting an ample margin
of safety can only be determined for each specific source category.
This occurs mainly because technological and economic factors (along
with the health-related factors) vary from source category to source
category.'' Id. at 38061. We also consider the uncertainties associated
with the various risk analyses, as discussed earlier in this preamble,
in our determinations of acceptability and ample margin of safety.
    The EPA notes that it has not considered certain health information
to date in making residual risk determinations. At this time, we do not
attempt to quantify those HAP risks that may be associated with
emissions from other facilities that do not include the source
categories in question, mobile source emissions, natural source
emissions, persistent environmental pollution, or atmospheric
transformation in the vicinity of the sources in these categories.
    The Agency 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
non-cancer risks, where pollutant-specific exposure health reference
levels (e.g., RfCs) are based on the assumption that thresholds exist
for adverse health effects. For example, the Agency recognizes that,
although exposures attributable to emissions from a source category or
facility alone may not indicate the potential for increased risk of
adverse non-cancer health effects in a population, the exposures
resulting from emissions from the facility in combination with
emissions from all of the other sources (e.g., other facilities) to
which an individual is exposed may be sufficient to result in increased
risk of adverse non-cancer health effects. In May 2010, the 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.'' \21\
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    \21\ The EPA's responses to this and all other key
recommendations of the SAB's advisory on RTR risk assessment
methodologies (which is available at: http://yosemite.epa.gov/sab/
sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-
007-unsigned.pdf) are outlined in a memorandum to this rulemaking
docket from David Guinnup titled, ``EPA's Actions in Response to the
Key Recommendations of the SAB Review of RTR Risk Assessment
Methodologies.''
---------------------------------------------------------------------------

    In response to the SAB recommendations, the EPA is incorporating
cumulative risk analyses into its RTR risk assessments, including those
reflected in this proposal. The Agency is: (1) Conducting facility-wide
assessments, which include source category emission points, as well as
other emission points within the facilities; (2) considering sources in
the same category whose emissions result in exposures to the same
individuals; and (3) for some persistent and bioaccumlative pollutants,
analyzing the ingestion route of exposure. In addition, the RTR risk
assessments have always considered aggregate cancer risk from all
carcinogens and aggregate non-cancer HI from all non-carcinogens
affecting the same target organ system.
    Although we are interested in placing source category and facility-
wide HAP risks in the context of total HAP risks from all sources
combined in the vicinity of each source, we are concerned about the
uncertainties of doing so. Because of the contribution to total HAP
risk from emission sources other than those that we have studied in
depth during this RTR review, such estimates of total HAP risks would
have significantly greater associated uncertainties than the source
category or facility-wide estimates. Such aggregate or cumulative
assessments would compound those uncertainties, making the assessments
too unreliable.

C. How did we perform the technology review?

    Our technology review focused on the identification and evaluation
of developments in practices, processes, and control technologies that
have occurred since the MACT standards were promulgated. Where we
identified such developments, in order to inform our decision of
whether it is ``necessary'' to revise the emissions standards, we
analyzed the technical feasibility of applying these developments and
the estimated costs, energy implications, non-air environmental
impacts, as well as considering the emission reductions. We also
considered the appropriateness of applying controls to new sources
versus retrofitting existing sources.
    Based on our analyses of the available data and information, we
identified potential developments in practices, processes, and control
technologies. For this exercise, we considered any of the following to
be a ``development'':
     Any add-on control technology or other equipment that was
not identified and considered during development of the original MACT
standards;
     Any improvements in add-on control technology or other
equipment (that were identified and considered during development of
the original MACT standards) that could result in additional emissions
reduction;
     Any work practice or operational procedure that was not
identified or considered during development of the original MACT
standards;
     Any process change or pollution prevention alternative
that could be broadly applied to the industry and that was not
identified or considered during development of the original MACT
standards; and
     Any significant changes in the cost (including cost
effectiveness) of applying controls (including controls the EPA
considered during the development of the original MACT standards).
    In addition to reviewing the practices, processes, and control
technologies that were considered at the time we originally developed
(or last updated) the NESHAP, we reviewed a variety of data sources in
our investigation of potential practices, processes, or controls to
consider. Among the sources we reviewed were the NESHAP for various
industries that were promulgated since the MACT standards being
reviewed in this action. We reviewed the regulatory requirements and/or
technical analyses associated with these regulatory actions to identify
any practices, processes, and control technologies considered in these
efforts that could be applied to emission sources in the Manufacturing
of Nutritional Yeast source category, as well as the costs, non-air
impacts, and energy implications associated with the use of these
technologies. Additionally, we requested information from facilities
regarding developments in practices, processes, or control technology.
Finally, we reviewed information from other sources, such as state and/
or local permitting agency databases and industry-supported databases.

IV. Analytical Results and Proposed Decisions

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

    As described above, for the Manufacturing of Nutritional Yeast
source category, we conducted an inhalation risk assessment for all HAP
emitted. We present results of the risk assessment briefly below and in
more detail in the document: ``Residual Risk Assessment for the
Manufacturing of Nutritional Yeast Source Category in Support of the
December 2016 Risk and Technology Review Proposed Rule,'' which is
available in the docket for this action.
1. Inhalation Risk Assessment Results
    Table 2 of this preamble provides a summary of the results of the
inhalation risk assessment for the source category. As discussed in
section III.A.2 of this preamble, we set MACT-allowable HAP emission
levels at nutritional yeast manufacturing facilities equal to actual
emissions. For more detail about the MACT-allowable emission levels,
see the memorandum, ``Emissions Data and Acute Risk Factor Used in
Residual Risk Modeling: Manufacturing of Nutritional Yeast Source
Category,'' which is available in the docket for this action.

                                       Table 2--Nutritional Yeast Manufacturing Inhalation Risk Assessment Results
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                    Maximum individual     Estimated population      Estimated annual      Maximum chronic  non-     Maximum screening
                                    cancer risk  (in 1     at  increased risk of     cancer incidence        cancer  TOSHI \3\     acute non-cancer  HQ
                                       million) \2\          cancer >= 1-in-1        (cases per year)    ------------------------           \4\
                                 ------------------------         Million        ------------------------                        -----------------------
    Number of facilities \1\                             ------------------------                          Based on    Based on
                                   Based on    Based on    Based on    Based on    Based on    Based on     actual     allowable   Based on    Based on
                                    actual     allowable    actual     allowable    actual     allowable   emissions   emissions    actual     allowable
                                   emissions   emissions   emissions   emissions   emissions   emissions   level \2\     level     emissions   emissions
                                   level \2\     level     level \2\     level     level \2\     level                             level \2\     level
--------------------------------------------------------------------------------------------------------------------------------------------------------
4...............................          2           2         750         750      0.0009      0.0009        0.08        0.08     HQREL =     HQREL =
                                                                                0.2        0.2.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Number of facilities evaluated in the risk analysis.
\2\ Maximum individual excess lifetime cancer risk due to HAP emissions from the source category.
\3\ Maximum TOSHI. The target organ with the highest TOSHI for the Manufacturing of Nutritional Yeast source category is the respiratory system.
\4\ The maximum estimated acute exposure concentration was divided by available short-term threshold values to develop an array of HQ values. HQ values
  shown use the lowest available acute threshold value, which in most cases is the REL. When HQ values exceed 1, we also show HQ values using the next
  lowest available acute dose-response value. See section III.A.3 of this preamble for explanation of acute dose-response values.

    The results of the inhalation risk modeling using actual emissions
data, as shown in Table 2 of this preamble, indicate that the maximum
lifetime individual cancer risk could be up to 2-in-1 million, the
maximum chronic non-cancer TOSHI value could be up to 0.08, and the
maximum off-facility site acute HQ value could be up to 0.2. The total
estimated national cancer incidence from these facilities based on
actual emission levels is 0.0009 excess cancer cases per year or 1 case
in every 1,100 years.
2. Acute Risk Results
    Table 2 of this preamble shows the acute risk results for the
Manufacturing of Nutritional Yeast source category. The screening
analysis for acute impacts was based on an industry specific multiplier
of 1.2, to estimate the peak emission rates from the average rates. For
more detailed acute risk results, refer to the draft document:
``Residual Risk Assessment for the Manufacturing of Nutritional Yeast
Source Category in Support of the December 2016 Risk and Technology
Review Proposed Rule,'' which is available in the docket for this
action.
3. Multi-Pathway Risk Screening Results
    There are no PB-HAP emitted by facilities in this source category.
Therefore, we do not expect any human health multi-pathway risks as a
result of emissions from this source category.
4. Environmental Risk Screening Results
    The emissions data for the Manufacturing of Nutritional Yeast
source category indicate that sources within this source category do
not emit any of the seven pollutants that we identified as
``environmental HAP,'' as discussed earlier in this preamble.
Additionally, the processes and materials used in the source category
typically do not emit any of the seven environmental HAP. Also, we are
unaware of any adverse environmental effect caused by emissions of HAP
that are emitted by this source category (acetaldehyde). Therefore, we
do not expect an adverse environmental effect as a result of HAP
emissions from this source category.
5. Facility-Wide Risk Results
    As explained in section III.A.7 of this preamble, we did not
perform a separate facility-wide risk assessment because we expect
facility-wide risks to be equal to the risks we assessed for this
source category.
6. What demographic groups might benefit from this regulation?
    To examine the potential for any environmental justice issues that
might be associated with the source category, we performed a
demographic analysis, which is an assessment of risks to individual
demographic groups within the population near the four nutritional
yeast manufacturing facilities that are subject to the NESHAP. In this
analysis, we evaluated the distribution of HAP-related cancer risks and
non-cancer hazards from the nutritional yeast manufacturing facilities
across different social, demographic, and economic groups within the
populations living near facilities identified as having the highest
risks. The methodology and the results of the demographic analyses are
included in a technical report, ``Risk and Technology Review--Analysis
of Socio-Economic Factors for Populations Living Near Nutritional Yeast
Manufacturing Facilities,'' available in the docket for this action.
    The analysis indicates that the minority population living within
50 km (1,700,000 people, of whom 41 percent are minority) and within 5
km (131,567 people, of whom 68 percent are minority) of the four
nutritional yeast manufacturing facilities is greater than the minority
population found nationwide (28 percent). The specific

demographics of the population within 5 and 50 km of the facilities
indicate potential disparities in risks in certain demographic groups,
including the ``African American,'' ``Below the Poverty Level,'' and
``Over 25 and without high school diploma'' groups.
    When examining the risk levels of those exposed to emissions from
the four nutritional yeast manufacturing facilities, we find
approximately 750 persons are exposed to a cancer risk greater than or
equal to 1-in-1 million, and the highest cancer risk for these
individuals is less than 2-in-1 million. Of these 750 persons, 100
percent of them are defined as minority. When examining the noncancer
risks surrounding these facilities, no one is predicted to have a
chronic non-cancer TOSHI greater than 1.

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

1. Risk Acceptability
    As noted in section III.B of this preamble, we weigh all health
risk factors in our risk acceptability determination, including the
cancer MIR, the number of persons in various cancer and non-cancer risk
ranges, cancer incidence, the maximum non-cancer TOSHI, the maximum
acute non-cancer HQ, the extent of non-cancer risks, the potential for
adverse environmental effects, the distribution of cancer and non-
cancer risks in the exposed population, and risk estimation
uncertainties (54 FR 38044, September 14, 1989).
    For the Manufacturing of Nutritional Yeast source category, the
risk analysis indicates that the cancer risks to the individual most
exposed could be up to 2-in-1 million due to actual emissions and up to
2-in-1 million based on allowable emissions. As explained in section
III.A.2 of this preamble, we determined that actual emissions provide
an accurate representation of maximum emissions from the source
category and used the actual emissions in both steps of the risk
assessment (i.e., determination of risk based on actual and MACT-
allowable emissions). These risks are considerably less than 100-in-1
million, which is the presumptive upper limit of acceptable risk. The
risk analysis also shows very low cancer incidence (0.0009 cases per
year), as well as no potential for adverse chronic or multi-pathway
health effects. In addition, the risk assessment indicates no
significant potential for multi-pathway health effects or adverse
environmental effects. The acute non-cancer risks based on actual and
allowable emissions are all below an HQ of 1. Therefore, we find there
is little potential concern of acute non-cancer health impacts from
actual and allowable emissions.
    Considering all of the health risk information and factors
discussed above, including the uncertainties discussed in section
III.A.8 of this preamble, we propose to find that the risks from the
Manufacturing of Nutritional Yeast source category are acceptable.
2. Ample Margin of Safety Analysis
    Although we are proposing that the risks from the Manufacturing of
Nutritional Yeast source category are acceptable, risk estimates for
approximately 750 individuals in the exposed population are above 1-in-
1 million at the actual and MACT-allowable emissions levels.
Consequently, we further considered whether the MACT standards for the
Manufacturing of Nutritional Yeast source category provide an ample
margin of safety to protect public health. In this ample margin of
safety analysis, we investigated available emissions control options
that might reduce the risk from the source category. We considered this
information along with all of the health risks and other health
information considered in our determination of risk acceptability.
    As discussed in section IV.C of this preamble, during the
technology review for this source category, we evaluated two control
technologies for reducing acetaldehyde emissions from fermenters at
nutritional yeast facilities: Thermal oxidizers and wet (packed bed)
scrubbers. Thermal oxidizers have the potential to reduce total
acetaldehyde emissions from this source category by 11 tpy to 36 tpy,
for a total of 90 tpy for the industry, but would also lead to
increases in energy use and emissions of approximately 89 tpy of
nitrogen oxides (NOX) from these facilities. The cost
effectiveness for thermal oxidizers varied per facility, with an
average cost of $56,000 per ton of acetaldehyde reduced. The average
cost effectiveness for packed bed scrubbers was $74,000 per ton of
acetaldehyde per facility. The use of packed bed scrubbers would also
lead to additional environmental impacts, such as increased energy and
water usage, as well as the need to use and dispose of solvents. These
cost-effectiveness values are significantly higher than values that we
have historically deemed to be cost effective for organic HAP in other
NESHAP. Due to the additional environmental impacts that would be
imposed and the low level of current risk, along with the substantial
costs associated with these options, we are proposing that additional
emissions controls for this source category are not necessary to
provide an ample margin of safety.
3. Environmental Effects
    We did not identify emissions of any of the seven environmental HAP
included in our environmental risk screening, and are unaware of any
adverse environmental effects caused by HAP emitted by this source
category (acetaldehyde). Therefore, we do not expect there to be an
adverse environmental effect as a result of HAP emissions from this
source category and we are proposing that it is not necessary to set a
more stringent standard to prevent, taking into consideration costs,
energy, safety, and other relevant factors, an adverse environmental
effect.

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

    In order to fulfill our obligations under CAA section 112(d)(6), we
conducted a technology review to identify developments in practices,
processes, and control technologies that may advise revisions to the
current NESHAP standards applicable to the Manufacturing of Nutritional
Yeast source category (i.e., 40 CFR part 63, subpart CCCC). In
conducting our technology review, we utilized the RBLC database,
reviewed title V permits for each nutritional yeast facility, and
reviewed regulatory actions related to emissions controls at similar
sources that could be applicable to nutritional yeast manufacturing
facilities.
    After reviewing information from the sources above, we identified
two control technologies for further evaluation that are technically
feasible for use at nutritional yeast facilities: thermal oxidizers and
wet scrubbers.\22\ These control technologies were identified both in
the RBLC database and in a review of the miscellaneous organic chemical
manufacturing NESHAP (MON). The RBLC database contains multiple sources
with similar production processes as nutritional yeast manufacturing
facilities that employ thermal oxidizers or wet scrubbers, e.g.,
fermenters at ethanol facilities. We also identified the MON in
particular as being a potentially useful analog for manufacturing of
nutritional yeast because the MON regulates

emissions from ethanol fermenters (the same sources identified in the
RBLC) that are located at facilities that are major sources of HAP
emissions. Our review of this rule revealed that facilities use thermal
oxidizers as a control technology to comply with the process vent
emission limits in the MON.
---------------------------------------------------------------------------

    \22\ Additional information about this determination is
documented in the memorandum, ``Technology Review for the
Manufacturing of Nutritional Yeast Source Category,'' which is
available in the docket for this action.
---------------------------------------------------------------------------

    After identifying control technologies that are technically
feasible for reducing acetaldehyde emissions from nutritional yeast
fermenters, we then evaluated the costs and emissions reductions
associated with installing regenerative thermal oxidizers (RTOs) and
packed bed scrubbers at each of the four nutritional yeast facilities.
The total capital investment to install RTOs ranged from $2 million to
$6.9 million per facility for a total of approximately $14.9 million
for the industry. Annual costs for each facility were approximately
$0.8 million to $2.2 million, for a total of $5.2 million per year for
the industry. Applying a control efficiency of 98 percent, acetaldehyde
emissions for each facility would be reduced by approximately 11 tpy to
36 tpy, for a total of 90 tpy for the industry. To install RTOs at each
facility, the resulting cost effectiveness ranged from $32,000 to
$90,000 per ton of acetaldehyde reduced. Furthermore, use of RTOs would
result in increased energy use and NOX emissions of
approximately 89 tpy from nutritional yeast manufacturing facilities.
Additional information about the assumptions and methodologies used in
these calculations is documented in the memorandum, ``Technology Review
for the Manufacturing of Nutritional Yeast Source Category,'' which is
available in the docket for this action.
    The total capital investment to install packed bed scrubbers on
fermenters ranged from $3 million to $11.6 million per facility for a
total of about $24.5 million for the industry. Annual costs for each
facility were approximately $0.8 million to $2.5 million, for a total
of $5.8 million per year for the industry. Applying a control
efficiency of 85 percent, acetaldehyde emissions for each facility
would be reduced by approximately 9.4 tpy to 31 tpy, for a total of 78
tpy for the industry. To install packed bed scrubbers at each facility,
the resulting cost effectiveness ranged from $43,000 to $110,000 per
ton of acetaldehyde reduced. Furthermore, the use of packed bed
scrubbers would lead to increased energy usage and other environmental
impacts, such as the usage and disposal of water and caustic solutions
(e.g., sodium hydroxide). These cost-effectiveness values are
significantly higher than values that we have historically deemed to be
cost effective for organic HAP in other NESHAP. Additional information
about the assumptions and methodologies used in these calculation is
documented in the memorandum, ``Technology Review for the Manufacturing
of Nutritional Yeast Source Category,'' which is available in the
docket for this action.
    Considering the high costs per ton of acetaldehyde reduced and
potential adverse environmental impacts associated with the
installation of RTOs or packed bed scrubbers, we did not consider these
technologies to be cost effective for further reducing acetaldehyde
emissions from fermenters at nutritional yeast manufacturing
facilities. In light of the results of the technology review, we