[Federal Register Volume 78, Number 213 (Monday, November 4, 2013)]
[Proposed Rules]
[Pages 66107-66138]
[FR Doc No: 2013-24276]

Vol. 78

Monday,

No. 213

November 4, 2013

Part II

Environmental Protection Agency

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40 CFR Part 63

National Emissions Standards for Hazardous Air Pollutants Residual Risk
and Technology Review for Flexible Polyurethane Foam Production;
Proposed Rule

Federal Register / Vol. 78 , No. 213 / Monday, November 4, 2013 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2012-0510; FRL-9900-94-OAR]
RIN 2060-AR58

National Emissions Standards for Hazardous Air Pollutants
Residual Risk and Technology Review for Flexible Polyurethane Foam
Production

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The EPA is proposing amendments to the National Emissions
Standards for Hazardous Air Pollutants for Flexible Polyurethane Foam
Production to address the results of the residual risk and technology
review. In light of our review, we are proposing amendments that would
prohibit the use of hazardous air pollutant-based auxiliary blowing
agents for slabstock foam production facilities. In addition, the EPA
is proposing amendments to correct and clarify regulatory provisions
related to emissions during periods of startup, shutdown and
malfunction; to add provisions for affirmative defense; to add
requirements for reporting of performance testing through the
Electronic Reporting Tool; to revise compliance dates for applicable
proposed actions; to clarify the leak detection methods allowed for
diisocyanate storage vessels at slabstock foam production facilities;
and to revise the rule to add a schedule for delay of leak repairs for
valves and connectors.

DATES:
    Comments. Comments must be received on or before December 4, 2013.
A copy of comments on the information collection provisions should be
submitted to the Office of Management and Budget (OMB) on or before
December 4, 2013.
    Public Hearing. If anyone contacts the EPA requesting a public
hearing by November 14, 2013, the public hearing will be held on
November 20, 2013, from 10:00 a.m. to 4:00 p.m. on the EPA campus at
109 T.W. Alexander Drive in Research Triangle Park, North Carolina. If
EPA holds a public hearing, the EPA will keep the record of the hearing
open for 30 days after completion of the hearing to provide an
opportunity for submission of rebuttal and supplementary information.

ADDRESSES: Submit your comments, identified by Docket ID Number EPA-HQ-
OAR-2012-0510, by one of the following methods:
     http://www.regulations.gov: Follow the on-line
instructions for submitting comments.
     Email<EMAIL_ADDRESS>Attention Docket ID Number
EPA-EPA-HQ-OAR-2012-0510.
     Fax:<PHONE_NUMBER>, Attention Docket ID Number EPA-HQ-
OAR-2012-0510.
     Mail: U.S. Postal Service, send comments to: EPA Docket
Center, EPA West (Air Docket), Attention Docket ID Number EPA-HQ-OAR-
2012-0510, U.S. Environmental Protection Agency, Mailcode: 2822T, 1200
Pennsylvania Ave. NW., Washington, DC 20460. Please include a total of
two copies. In addition, please mail a copy of your comments on the
information collection provisions to the Office of Information and
Regulatory Affairs, Office of Management and Budget, Attn: Desk Officer
for EPA, 725 17th Street NW., Washington, DC 20503.
     Hand Delivery: U.S. Environmental Protection Agency, EPA
West (Air Docket), Room 3334, 1301 Constitution Ave. NW., Washington,
DC 20004, Attention Docket ID Number EPA-HQ-OAR-2012-0510. Such
deliveries are only accepted during the Docket's normal hours of
operation, and special arrangements should be made for deliveries of
boxed information.
    Instructions. Direct your comments to Docket ID Number EPA-HQ-OAR-
2012-0510. 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 confidential business information (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: http://www.epa.gov/dockets.
    Docket. The EPA has established a docket for this rulemaking under
Docket ID Number EPA-HQ-OAR-2012-0510. 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, EPA West, Room 3334, 1301
Constitution Ave. NW., Washington, DC. The Public Reading Room is open
from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal
holidays. The telephone number for the Public Reading Room is (202)
566-1744, and the telephone number for the EPA Docket Center is (202)
566-1742.
    Public Hearing. If anyone contacts the EPA requesting a public
hearing by November 14, 2013, the public hearing will be held on
November 20, 2013, from 10:00 a.m. to 4:00 p.m. on the EPA campus at
109 T.W. Alexander Drive in Research Triangle Park, North Carolina.
Persons interested in presenting oral testimony or inquiring as to
whether a public hearing will be held should contact Ms. Pamela
Garrett, Sector Policies and Programs Division (D243-01), Office of Air
Quality Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; telephone number: (919)
541-7966; fax number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>
FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Ms. Kaye Whitfield, Sector Policies and Programs
Division (D243-02), Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711; telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
and email address<EMAIL_ADDRESS>For specific information
regarding the risk modeling

methodology, contact Mr. Chris Sarsony, Health and Environmental
Impacts Division (C539-02), Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Research Triangle
Park, North Carolina 27711; telephone number:<PHONE_NUMBER>; fax
number:<PHONE_NUMBER>; and email address<EMAIL_ADDRESS>For
information about the applicability of the National Emission Standards
for Hazardous Air Pollutants (NESHAP) to a particular entity, contact
Mr. Scott Throwe, Office of Enforcement and Compliance Assurance;
telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>; and email
address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Preamble Acronyms and Abbreviations

    This preamble includes several acronyms and terms used to describe
industrial processes, data inventories and risk modeling. 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:

ABA auxiliary blowing agent
AEGL acute exposure guideline levels
AERMOD air dispersion model used by the HEM-3 model
BAAQMD Bay Area Air Quality Management District
CAA Clean Air Act
CalEPA California EPA
CBI Confidential Business Information
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CFR Code of Federal Regulations
EIS Emission Inventory System
EPA Environmental Protection Agency
ERPG Emergency Response Planning Guidelines
ERT Electronic Reporting Tool
FPUF Flexible Polyurethane Foam
FR Federal Register
HAP hazardous air pollutants
HCl hydrogen chloride
HEM-3 Human Exposure Model, Version 1.1.0
HI hazard index
HF hydrogen fluoride
HQ hazard quotient
ICR information collection request
IRIS Integrated Risk Information System
kg kilogram
km kilometer
lb pound
LDAR leak detection and repair
MACT maximum achievable control technology
MACT Code Code within the National Emissions Inventory used to
identify processes included in a source category
mg/kg-day milligrams per kilogram per day
mg/m\3\ milligrams per cubic meter
MIR maximum individual risk
NAICS North American Industry Classification System
NEI National Emissions Inventory
NESHAP National Emissions Standards for Hazardous Air Pollutants
NRC National Research Council
NRDC Natural Resources Defense Council
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
POM polycyclic organic matter
PFA Polyurethane Foam Association
ppm parts per million
QA quality assurance
REL reference exposure level
RCO recuperative thermal oxidizer
RfC reference concentration
RfD reference dose or daily oral exposure
RTO regenerative thermal oxidizer
RTR residual risk and technology review
SAB Science Advisory Board
SBA Small Business Administration
S/L/Ts State, local, and tribal air pollution control agencies
SOP standing operating procedures
SSM startup, shutdown and malfunction
TOSHI target organ-specific hazard index
tpy tons per year
TRI Toxics Release Inventory
TRIM Total Risk Integrated Methodology
TTN Technology Transfer Network
UF uncertainty factors
[micro]g/m\3\ microgram per cubic meter
UMRA Unfunded Mandates Reform Act
URE unit risk estimate
VCS voluntary consensus standards
WWW world wide web
    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 do the MACT standards
regulate its HAP emissions?
    C. What data collection activities were conducted to support
this action?
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?
    D. What other analyses and reviews were conducted in support of
this proposal and how did we conduct those analyses and reviews?
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
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    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
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 industrial source category that
is the subject of this proposal. Table 1 is not intended to be
exhaustive but rather to provide a guide for readers regarding the
entities that this proposed action is likely to affect. The proposed
standards, once finalized, will be directly applicable to the affected
sources. One federal entity is affected by this proposed action, and no
state, local or tribal government entities are 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 ``Flexible Polyurethane
Foam Production'' source category is any facility engaged in the

manufacture of foam made from a polymer containing a plurality of
carbamate linkages in the chain backbone (polyurethane).\1\
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    \1\ U.S. EPA, 1992. Documentation for Developing the Initial
Source Category List--Final Report. EPA-450/3-91-030.

Table 1--NESHAP and Industrial Source Category Affected by This Proposed
                                 Action
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                                                             NAICS code
         Source category                   NESHAP                \a\
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Flexible Polyurethane Foam        Flexible Polyurethane          326150
 Production.                       Foam Production.
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\a\ North American Industry Classification System

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

    In addition to being available in the docket, an electronic copy of
this action is available on the Internet through the EPA's Technology
Transfer Network (TTN) Web site, a forum for information and technology
exchange in various areas of air pollution control. Following signature
by the EPA Administrator, the EPA will post a copy of this proposed
action on the TTN's policy and guidance page for newly proposed or
promulgated rules at: http://www.epa.gov/ttn/oarpg/t3pfpr.html.
Following publication in the Federal Register, the EPA will post the
Federal Register version of the proposal and key technical documents on
the project Web site: http://www.epa.gov/ttn/atw/foam/foampg.html.
Information on the overall residual risk and technology review (RTR)
program is available at the following Web site: http://www.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: Roberto
Morales, OAQPS Document Control Officer (C404-02), OAQPS, U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711, Attention Docket ID Number EPA-HQ-OAR-2012-0510.

II. Background

A. What is the statutory authority for this action?

    Section 112 of the Clean Air Act (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
emissions 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
emissions 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 eight 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).
This provision requires, first, 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. Congress did
not act in response, thereby triggering the EPA's obligation under CAA
section 112(f)(2) to analyze and address residual risk.
    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 subsection 112(f)(2)
incorporates the standards 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 this process 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, which 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. Determining Acceptability
    The agency in the Benzene NESHAP concluded that ``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.''
Id. 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 38045. 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 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 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. 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.
    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,\2\ but must consider cost, energy, safety
and other relevant factors in doing so.
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    \2\ ``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 38044-38045, 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 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.

B. What is this source category and how do the MACT standards regulate
its HAP emissions?

    The MACT standards for Flexible Polyurethane Foam (FPUF) Production
were promulgated on October 7, 1998, (63 FR 53980) and codified at 40
CFR part 63, subpart III. The FPUF Production MACT standards apply to
each new and existing flexible polyurethane foam or rebond foam process
that produces flexible polyurethane foam or rebond foam, emits HAP, and
is located at a contiguous, major source plant site. The requirements
of the standards are the same for both new and existing sources.
    There are three types of FPUF producers in the source category:
Slabstock, molded and rebond. Slabstock foam is produced in large
continuous buns that are then cut into the desired size and shape.
Slabstock foam products are primarily used in furniture seat cushions
and bedding materials. Molded foam is produced by ``shooting'' the foam
mixture into a mold of the desired shape and size. Molded foam is
typically used in automotive seats, packaging and a range of specialty
products. Rebond foam is made from scrap foam that is converted into a
material primarily used for carpet underlay. Rebond foam production is
often co-located with slabstock foam production facilities.
    Slabstock and molded polyurethane foams are produced by mixing
three major ingredients: A polyol polymer, an isocyanate and water. The
polyol is either a polyether or polyester polymer with hydroxyl end
groups. Other ingredients are often added to modify the polymer, and
catalysts are used to balance the principal foam production reactions.
Auxiliary blowing agents (ABAs) may be used to produce specific
densities and grades of foam where the gases produced by the
isocyanate-water reaction are insufficient to achieve the desired
density. ABAs are more widely used in the production of slabstock foams
than in the production of molded foams. Rebond foam is produced from
scrap slabstock or molded polyurethane foam.
    The HAP emission points at FPUF production facilities depend on the
type of foam being produced. Prior to compliance with the original FPUF
Production MACT standards, the primary HAP emission point for slabstock
foam facilities was the foam production line, due to emissions of HAP
ABAs. Other HAP emission points at slabstock production facilities
include storage vessels and equipment leaks. At molded and rebond foam
facilities, the primary HAP emission points are storage vessels and
equipment leaks.
    Many facilities discontinued use of HAP ABAs before the rule's
October 2001 compliance date, allowing these facilities to be
designated as area sources. Based on the best information available,
slabstock production facilities using HAP ABAs on, or after, the rule's
October 2001 compliance date also have discontinued use of HAP-based
ABAs. We solicit comment on the use of HAP-based ABAs and whether any
facilities in the FPUF production source category currently use these
products.
    In the past decade, the FPUF production source category has
experienced plant closures and consolidations. Today, there are 13 FPUF
production facilities subject to the MACT standards: 7 slabstock, 6
molded and 2 rebond. One rebond facility is co-located with a slabstock
facility, and the other rebond facility is co-located with a molded
foam facility. A list of these facilities is included in the
memorandum, Development of the RTR

Emissions Dataset for the Flexible Polyurethane Foam Production Source
Category, which is available in the docket for this proposed
rulemaking.
    The FPUF Production MACT standards contain requirements specific
for each of the three types of foam production processes. For slabstock
foam production, the FPUF Production MACT standards include
diisocyanate and HAP ABA emissions reduction requirements. For molded
and rebond foam production, the FPUF Production MACT standards prohibit
the use of HAP in mold release agents and equipment cleaners, except in
very limited circumstances.
    For slabstock foam production, the FPUF Production MACT standards
regulate emissions of diisocyanates from storage vessels, transfer
pumps and equipment leaks. The storage vessel requirements include the
installation of either a vapor recovery system or a carbon adsorption
system. Transfer pumps are required to be either sealless pumps or
pumps submerged in a neutral oil, and submerged pumps must be visually
inspected periodically for leaks. All components in diisocyanate
service must be repaired when a leak is detected.
    Standards for HAP ABA emissions at slabstock facilities include
emission point requirements for the foam production line, storage
vessels, equipment leaks and equipment cleaning. For the slabstock
production line, the FPUF Production MACT standards contain
restrictions on the amount of HAP ABAs that can be used, based on the
grades of foam produced. The FPUF Production MACT standards also
regulate HAP ABAs by requiring installation of either a vapor recovery
system or a carbon adsorption system on storage vessels. For equipment
leaks, the FPUF Production MACT standards require a leak detection and
repair program (LDAR) for HAP ABAs. The use of HAP or HAP-based
products for equipment cleaning is prohibited at slabstock flexible
polyurethane foam production facilities. This proposed rule also
includes an alternative source-wide HAP ABA emission limit. The source-
wide emission limit allows slabstock facilities to comply by limiting
the total amount of a single HAP ABA used, rather than by complying
with the individual HAP ABA emission point requirements (e.g.,
production line, LDAR, equipment cleaning).
    For molded foam and rebond foam production, the FPUF Production
MACT standards prohibit the use of HAP-based products as mold release
agents and as equipment cleaners, except that diisocyanates may be used
to flush the mixhead and associated piping during startup and
maintenance if the diisocyanates are contained in a closed-loop system
and re-used in production.

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

    In 2011, we surveyed nine companies that own and operate foam
production facilities, as provided for under section 114 of the CAA. We
also conducted plant visits to four facilities in 2012 and 2013,
retrieved permit data from approximately 32 state agencies, and
obtained emissions inventory data from state agencies. Finally, we
reviewed data in four EPA emission inventory databases: National
Emissions Inventory (NEI), Emissions Inventory System (EIS), Toxics
Release Inventory (TRI) and Envirofacts to identify facilities that may
be part of the source category, emission sources and quantities of
emissions. The CAA section 114 questionnaire included requests for
available information regarding process equipment, control devices and
work practices for emission reductions, point and fugitive emissions
and other aspects of facility operations.
    The emissions data and risk assessment inputs for the FPUF
production source category are described further in the memorandum
Development of the RTR Emissions Dataset for the Flexible Polyurethane
Foam Production Source Category, which is available in the docket for
this proposed rulemaking.

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 provided 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 provided estimates of the distribution of
cancer risks within the exposed populations, cancer incidence and an
evaluation of the potential for adverse environmental effects for the
source category. The risk assessment consisted of eight primary steps,
as discussed below. The docket for this rulemaking contains the
following document, which provides more information on the risk
assessment inputs and models: Draft Residual Risk Assessment for the
Flexible Polyurethane Foam Production Source Category. 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; \3\ they are also consistent with the key
recommendations contained in that report.
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    \3\ U.S. EPA SAB. Risk and Technology Review (RTR) Risk
Assessment Methodologies: For Review by the EPA's Science Advisory
Board with Case Studies--MACT I Petroleum Refining Sources and
Portland Cement Manufacturing, May 2010.
---------------------------------------------------------------------------

1. How did we estimate actual emissions and identify the emissions
release characteristics?
    Data from the 13 existing FPUF production facilities were used to
create a dataset that is the basis for the risk assessment. We
estimated the amount of actual and allowable emissions using data
collected through the CAA section 114 request, emission inventories
(EIS, NEI and TRI) and site visits. We performed quality assurance (QA)
procedures for the emissions data and release characteristics to
identify any outliers, and then confirmed or corrected the data. For
facilities where speciated HAP data were unavailable or unreliable,
more recent inventory data were obtained from state or local permitting
agencies. In addition to the QA of the source data for the facilities
contained in the dataset, we also checked the coordinates of every
emission source in the dataset through visual observations using tools
such as Google Earth and ArcView, and made corrections, as necessary.
Further information about the development of the dataset is provided in
the technical document: Draft Development of the RTR Emissions Dataset
for the Flexible Polyurethane Foam Production 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 MACT 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 a facility is allowed to emit and still comply with the
MACT standards. The emissions level allowed to be emitted by the MACT
standards is referred to as the ``MACT-allowable'' emissions level.
This represents the highest emissions

level that could be emitted by facilities without violating the MACT
standards. We discussed the use of both MACT-allowable and actual
emissions in the final Coke Oven Batteries residual risk rule (70 FR
19998-19999, April 15, 2005) and in the proposed and final Hazardous
Organic NESHAP residual risk rules (71 FR 34428, June 14, 2006, and 71
FR 76609, December 21, 2006, respectively). In those previous 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. (54 FR 38044,
September 14, 1989.)
    For the FPUF production source category, we determined that actual
emissions are a reasonable estimate of the MACT-allowable emissions for
molded and rebond foam facilities. The MACT requirements for these
facilities are HAP use prohibitions, and both the actual and the MACT-
allowable emissions, while in compliance with these requirements, are
therefore zero.
    For slabstock foam production facilities, we estimate that the
level of diisocyanate actual emissions is a reasonable estimate of the
MACT-allowable diisocyanate emissions. The diisocyanate storage vessels
and other equipment are subject to equipment standards and work
practices. For equipment standards, sources subject to the standards
are required to install specific equipment. In order to comply with
this proposed rule, the equipment must be maintained properly and in
good working condition. Therefore, we do not expect any difference
between the actual emissions level and the level allowed by the MACT
standards because the level of control typically does not vary for
equipment standards. Similarly, we do not expect any difference between
actual and MACT-allowable emissions for emission sources subject to
work practice requirements, provided that facilities are not conducting
additional work practices proven to reduce emissions beyond those
required in this proposed rule. We are not aware of any such situations
at facilities in this source category. Therefore, for facilities
complying with the equipment and work practice standards, we believe
that the actual diisocyanate emission levels are a reasonable
estimation of the levels allowed by the standards.
    For HAP ABA emissions from slabstock facilities, we estimate that
MACT-allowable emissions are higher than actual emissions. While we
believe that all slabstock production facilities have discontinued use
of HAP-based ABAs, and they are reporting zero emissions of HAP ABA,
the MACT rule does not prohibit the use of HAP ABAs. Therefore, MACT-
allowable HAP ABA emissions were attributed to each slabstock facility
based on emissions information gathered during development of the MACT
standards. We assigned appropriate emissions release parameters for
each facility, and modeled using the same procedures and tools used for
modeling actual emissions, to obtain facility-specific maximum risk
values based on MACT-allowable emissions. The docket for this
rulemaking contains the following document which provides more
information on the development of estimated MACT-allowable emissions:
MACT-Allowable Emissions for the Flexible Polyurethane Foam Production
Source Category.
3. How did we conduct dispersion modeling, determine inhalation
exposure 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
kilometers (km) of the modeled sources,\4\ and (3) estimating
individual and population-level inhalation risks using the exposure
estimates and quantitative dose-response information.
---------------------------------------------------------------------------

    \4\ 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.\5\ 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 (2011) of
hourly surface and upper air observations for more than 824
meteorological stations, selected to provide coverage of the United
States and Puerto Rico. A second library of United States Census Bureau
census block \6\ 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:
http://www.epa.gov/ttn/atw/toxsource/summary.html and are discussed in
more detail later in this section.
---------------------------------------------------------------------------

    \5\ 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).
    \6\ 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), which 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 EPA 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 \7\) 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) and
the limitations of Gaussian dispersion models, including AERMOD.
---------------------------------------------------------------------------

    \7\ 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 Science Advisory Board (SAB) in their
2002 peer review of 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 either the EPA
reference concentration (RfC) (http://www.epa.gov/riskassessment/glossary.htm), 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,'' or, in cases where an RfC from the EPA's IRIS database is
not available, 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://www.oehha.ca.gov/air/hot_spots/pdf/HRAguidefinal.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.
    The EPA also evaluated screening estimates of acute exposures and
risks for each of the HAP at the point of highest off-site exposure for
each facility (i.e., not just the census block centroids), assuming
that a person is located at this spot at a time when both the peak
(hourly) emissions rate and worst-case dispersion conditions occur. 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 for our acute analysis.
    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://www.oehha.ca.gov/air/pdf/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 by 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 (http://www.epa.gov/oppt/aegl/pubs/sop.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.
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.
---------------------------------------------------------------------------

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

    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 (http://sp4m.aiha.org/insideaiha/GuidelineDevelopment/ERPG/Documents/ERP-SOPs2006.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. November 1,
2006. 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, but also reflecting 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. For this source
category, however, there was no such information available and the
default factor of 10 was used in the acute screening process.
---------------------------------------------------------------------------

    \10\ See http://www.tceq.state.tx.us/compliance/field_ops/eer/index.html or docket to access the source of these data.
---------------------------------------------------------------------------

    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.
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. 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. However, we recognize that
having this level of data is rare; hence, our use of 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.
---------------------------------------------------------------------------

    \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. (2009) 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, and available on-line at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003.
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4. How did we conduct the multipathway 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 hazardous air pollutants 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://www.epa.gov/ttn/fera/risk_atra_vol1.html).
    For the FPUF production source category, we did not identify
emissions of any PB-HAP. Because we did not identify PB-HAP emissions,
no further

evaluation of multipathway risk was conducted for this source category.
5. How did we assess risks considering emissions control options?
    In addition to assessing baseline inhalation risks and screening
for potential multipathway risks, we also estimated risks considering
the potential emissions reductions that would be achieved by the
control options under consideration. In these cases, the expected
emissions reductions were applied to the specific HAP and emissions
points in the source category dataset to develop corresponding
estimates of risk and incremental risk reductions.
6. How did we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect
    The EPA developed a screening approach 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 persistent bioaccumulative HAP
(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. 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 (based on data 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
multipathway risk allows us to estimate concentrations of cadmium
compounds, dioxins/furans, POM and mercury in soil, sediment and water.
For lead, we currently do not have the ability to calculate these
concentrations using the TRIM.Fate model. Therefore, to evaluate the
potential for environmental effects from lead, we compare the estimated
chronic inhalation exposures from the source category emissions of lead
with the level of the secondary National Ambient Air Quality Standard
(NAAQS) for lead.\13\ We consider values below the level of the
secondary lead NAAQS as 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.''
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    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 of the total acid gas HAP emitted by
stationary sources. 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 multipathway exposure and risk
screening analysis using the HEM3-AERMOD air dispersion model, and we
are able to use the air dispersion modeling to estimate the potential
for an adverse environmental effect.
    For the FPUF production source category, the data do not show
emissions of any of the seven HAP (cadmium, dioxins/furans, POM,
mercury, HCL or HF) in the environmental risk screen. Because we did
not identify emissions of these seven HAP from the source category, we
did not conduct any further quantitative evaluation of environmental
risk.
    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.
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 emissions sources at the facility for which we have
data. The emissions data for estimating these ``facility-wide'' risks
were obtained from the 2005 NEI (available at http://www.epa.gov/ttn/atw/nata2005). We analyzed risks due to the inhalation of HAP that are
emitted ``facility-wide'' for the populations residing within 50 km of
each facility, consistent with the methods used for the source category
analysis described above. For these facility-wide risk analyses, the
modeled FPUF production source category risks were compared to the
facility-wide risks to determine the portion of facility-wide risks
that could be attributed to the FPUF production source category. We
specifically examined the facilities associated with the highest
estimates of risk and determined the percentage of that risk
attributable to the FPUF production source category. The Draft Residual
Risk Assessment for the Flexible Polyurethane Foam Production Source
Category, available through the docket for this action, provides all
the methodology and results of the facility-wide analyses, including
all facility-wide risks and the percentage of FPUF production source
category contribution to facility-wide risks.
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. A brief discussion of the
uncertainties in the emissions dataset, dispersion modeling, inhalation
exposure estimates and dose-response relationships follows below. A
more thorough discussion of these uncertainties is included in the
Draft Residual Risk Assessment for the Flexible Polyurethane Foam
Production Source Category, which is available in the docket for this
action.
a. Uncertainties in the Emissions Dataset
    Although the development of the RTR 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 emissions 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 emissions rates for the
acute effects screening assessment were based on an emission adjustment
factor applied to the average annual hourly emissions 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 estimated
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 over-estimate 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.\14\ 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).
---------------------------------------------------------------------------

    \14\ 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 receptors 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 emissions 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 overstatement of 25 to 30 percent of exposures.\15\
---------------------------------------------------------------------------

    \15\ 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 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 human
activity patterns. In this assessment, we assume that individuals
remain for 1 hour at the point of maximum ambient concentration as
determined by the co-occurrence of peak emissions and worst-case
meteorological conditions. 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 of worst-case impact.
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 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 Draft Residual Risk Assessment
for the Flexible Polyurethane Foam Production Source Category, 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).\16\ In some circumstances, the true risk could be as
low as zero; however, in other circumstances the risk could be
greater.\17\ 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).
---------------------------------------------------------------------------

    \16\ IRIS glossary (http://www.epa.gov/NCEA/iris/help_gloss.htm).
    \17\ 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.
---------------------------------------------------------------------------

    RfCs and reference doses (RfDs) represent chronic exposure levels
that provide an estimate (with uncertainty spanning perhaps an order of
magnitude) of a continuous inhalation exposure or a daily oral
exposure, respectively, 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, 1994) which
considers uncertainty, variability and gaps in the available data. The
UFs are applied to derive reference values that are intended to protect
against appreciable risk of deleterious effects. The UFs are commonly
default values,\18\ e.g., factors of 10 or 3, used in the absence of
compound-specific data; where data are available, UFs may also be
developed using compound-specific information. When data are limited,
more assumptions are needed and more UFs are used.
---------------------------------------------------------------------------

    \18\ 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 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, 2004, An Examination of EPA
Risk Assessment Principles and Practices, EPA/100/B-04/001 available
at: http://www.epa.gov/osa/pdfs/ratf-final.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.
e. Uncertainties in the Multipathway Assessment
    For each source category, we generally rely on site-specific levels
of PB-HAP emissions to determine whether a refined assessment of the
impacts from multipathway exposures is necessary. This determination is
based on the results of a two-tiered screening analysis that relies on
the outputs from models that estimate environmental pollutant
concentrations and human exposures for four PB-HAP. Two important types
of uncertainty associated with the use of these models in RTR risk
assessments and inherent to any assessment that relies on environmental
modeling are model uncertainty and input uncertainty.\19\
---------------------------------------------------------------------------

    \19\ In the context of this discussion, the term ``uncertainty''
as it pertains to exposure and risk encompasses both variability in
the range of expected inputs and screening results due to existing
spatial, temporal, and other factors, as well as uncertainty in
being able to accurately estimate the true result.

---------------------------------------------------------------------------

    Model uncertainty concerns whether the selected models are
appropriate for the assessment being conducted and whether they
adequately represent the actual processes that might occur for that
situation. An example of model uncertainty is the question of whether
the model adequately describes the movement of a pollutant through the
soil. This type of uncertainty is difficult to quantify. However, based
on feedback received from previous EPA Science Advisory Board reviews
and other reviews, we are confident that the models used in the screen
are appropriate and state-of-the-art for the multipathway risk
assessments conducted in support of RTR.
    Input uncertainty is concerned with how accurately the models have
been configured and parameterized for the assessment at hand. For Tier
1 of the multipathway screen, we configured the models to avoid
underestimating exposure and risk to reduce the likelihood that the
results indicate the risks are lower than they actually are. This was
accomplished by selecting upper-end values from nationally-
representative data sets for the more influential parameters in the
environmental model, including selection and spatial configuration of
the area of interest, lake location and size, meteorology, surface
water and soil characteristics and structure of the aquatic food web.
We also assume an ingestion exposure scenario and values for human
exposure factors that represent reasonable maximum exposures.
    In Tier 2 of the multipathway assessment, we refine the model
inputs to account for meteorological patterns in the vicinity of the
facility versus using upper-end national values and we identify the
actual location of lakes near the facility rather than the default lake
location that we apply in Tier 1. By refining the screening approach in
Tier 2 to account for local geographical and meteorological data, we
decrease the likelihood that concentrations in environmental media are
overestimated, thereby increasing the usefulness of the screen. The
assumptions and the associated uncertainties regarding the selected
ingestion exposure scenario are the same for Tier 1 and Tier 2.
    For both Tiers 1 and 2 of the multipathway assessment, our approach
to addressing model input uncertainty is generally cautious. We choose
model inputs from the upper end of the range of possible values for the
influential parameters used in the models, and we assume that the
exposed individual exhibits ingestion behavior that would lead to a
high total exposure. This approach reduces the likelihood of not
identifying high risks for adverse impacts.
    Despite the uncertainties, when individual pollutants or facilities
do screen out, we are confident that the potential for adverse
multipathway impacts on human health is very low. On the other hand,
when individual pollutants or facilities do not screen out, it does not
mean that multipathway impacts are significant, only that we cannot
rule out that possibility and that a refined multipathway analysis for
the site might be necessary to obtain a more accurate risk
characterization for the source category.
    For further information on uncertainties and the Tier 1 and 2
screening methods, refer to the risk document Appendix 5, ``Technical
Support Document for TRIM-Based Multipathway Tiered Screening
Methodology for RTR.''

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 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. 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 tighter
emission standards if 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. 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; 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 Federal Register notice.
    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. 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 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.'

54 FR 38057. 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\
---------------------------------------------------------------------------

    \21\ 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 memo 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. 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 overlapping sources in the same category; and (3) for
some persistent and bioaccumulative pollutants, analyzing the ingestion
route of exposure. In addition, the RTR risk assessments have always
considered aggregate cancer risk from all carcinogens and aggregate
non-cancer hazard indices 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 emissions 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 FPUF Production 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 emissions 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.
     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).
    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 FPUF Production 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 emissions

sources in the FPUF production 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.

D. What other analyses and reviews were conducted in support of this
proposal and how did we conduct those analyses and reviews?

    In addition to the analyses described above, we reviewed the FPUF
Production MACT standards to determine whether we should make
additional amendments. From this review we have identified one
additional revision. We are proposing revisions to the startup,
shutdown and malfunction (SSM) provisions of the MACT rule in order to
ensure that they are consistent with the court decision in Sierra Club
v. EPA, 551 F.3d 1019 (D.C. Cir. 2008), which vacated two provisions
that exempted sources from the requirement to comply with otherwise
applicable section 112(d) emission standards during periods of SSM. Our
analyses and proposed changes related to these issues are presented in
section IV.D of this preamble.

IV. Analytical Results and Proposed Decisions

    This section of the preamble provides the results of our RTR
reviews of the FPUF Production MACT standards and our proposed
revisions to the FPUF Production MACT standards regarding the startup,
shutdown and malfunction provisions.

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

    As described above, for the FPUF production source category, we
conducted an inhalation risk assessment for all HAP emitted, a
multipathway screening analysis for PB-HAP emitted and an environmental
HAP screening analysis. We also performed a facility-wide risk
assessment for the facilities in the source category. Results of the
risk assessment are presented briefly below and in more detail in the
residual risk document: Draft Residual Risk Assessment for the Flexible
Polyurethane Foam Production Source Category, which is available in the
docket for this rulemaking.
1. FPUF Production Source Category Inhalation Risk Assessment Results
    Table 2 of this preamble provides a summary of the results of the
inhalation risk assessment for the source category.

                                                        Table 2--Flexible Polyurethane Foam Production Inhalation Risk Assessment Results
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                            Maximum individual     Estimated population      Estimated annual      Maximum chronic non-          Maximum screening acute non-cancer HQ \4\
                                            cancer risk  (in 1     at increased risk of      cancer incidence        cancer TOSHI \3\    -------------------------------------------------------
                                               million) \2\          cancer >= 1-in-1        (cases per year)    ------------------------
                                         ------------------------         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 actual emissions      Based on allowable
                                            actual     allowable    actual     allowable    actual     allowable   emissions   emissions             level                  emissions level
                                           emissions   emissions   emissions   emissions   emissions   emissions     level       level
                                           level \2\     level     level \2\     level     level \2\     level
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
13......................................         0.7           5           0         700     0.00004      0.0004         0.9         0.9  HQERPG	1 = 0.9              HQREL = 4
                                                                                HQERPG	1=0.9
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\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 FPUF production 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
level data, as shown in Table 2, indicate that the maximum lifetime
individual cancer risk could be up to 0.7-in-1 million, the maximum
chronic non-cancer TOSHI value could be up to 0.9, and the maximum off-
site acute HQ value could be up to 0.9. The total estimated national
cancer incidence from these facilities based on actual emission levels
is 0.00004 excess cancer cases per year or one case in every 25,000
years.
    As discussed in section III.A.2, we also determined that MACT-
allowable HAP ABA emissions levels at slabstock production facilities
are greater than actual HAP ABA emissions, while allowable emissions
from all other processes are equal to actual emissions. The inhalation
risk modeling using MACT-allowable HAP ABA emissions and the actual
emissions for the other processes at slabstock production facilities,
indicate that the maximum lifetime individual cancer risk could be up
to 5-in-1 million, the maximum chronic non-cancer TOSHI value could be
up to 0.9, and the maximum off-site acute HQ value could be up to 4,
based on the REL value for methylene chloride. The total estimated
national cancer incidence from these facilities based on the MACT-
allowable emission levels is 0.0004 excess cancer cases per year or one
case in every 2,500 years. For more detail about the MACT-allowable
emissions levels, see the memorandum, MACT-Allowable Emissions for the
Flexible Polyurethane Foam Production Source Category, in the docket
for this rulemaking.
2. Acute Risk Results
    Table 2 shows the acute risk results for the FPUF production source
category. The screening analysis for worst-case acute impacts was based
on a conservative default emissions multiplier of 10 to estimate the
peak hourly emission rates from the average rates. Refer to Appendix 6
of the draft residual risk document in the docket for the detailed
acute risk results.
3. Multipathway Risk Screening Results
    There are no PB-HAP emitted by facilities in this category.
Therefore, we do not expect there is a potential for human health
multipathway risks as a result of emissions of these HAP.
4. Ecological Risk Screening Results
    The emissions data for the FPUF 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. Based on the processes and materials used in
the source category, we do not expect any of the seven environmental
HAP to be emitted. Also, we are unaware of any adverse environmental
effect caused by emissions of HAP that are emitted by this source
category. Therefore, we do not expect an adverse environmental effect
as a result of HAP emissions from this source category.

5. Facility-Wide Inhalation Risk Assessment Results
    Table 3 displays the results of the facility-wide risk assessment.
This assessment is based on actual emission levels. For detailed
facility-specific results, see Appendix 6 of the Draft Residual Risk
Assessment for the Flexible Polyurethane Foam Production Source
Category in the docket for this rulemaking.

     Table 3--FPUF Production Facility-Wide Risk Assessment Results
------------------------------------------------------------------------

------------------------------------------------------------------------
Number of facilities analyzed..................................     13
Cancer Risk:
    Estimated maximum facility-wide individual cancer risk (in      20
     1 million)................................................
    Number of facilities with estimated facility-wide                0
     individual cancer risk of 100-in-1 million or more........
    Number of facilities at which the FPUF production source         0
     category contributes 50 percent or more to the facility-
     wide individual cancer risks of 100-in-1 million or more..
    Number of facilities with estimated facility-wide                3
     individual cancer risk of 1-in-1 million or more..........
    Number of facilities at which the FPUF production source         0
     category contributes 50 percent or more to the facility-
     wide individual cancer risk of 1-in-1 million or more.....
Chronic Non-cancer Risk:
    Maximum facility-wide chronic non-cancer TOSHI.............      0.9
    Number of facilities with facility-wide maximum non-cancer       0
     TOSHI greater than 1......................................
    Number of facilities at which the FPUF production source         0
     category contributes 50 percent or more to the facility-
     wide maximum non-cancer TOSHI of 1 or more................
------------------------------------------------------------------------

    The facility-wide MIR and TOSHI are based on actual emissions from
all emissions sources at the identified facilities. The results
indicate that 3 facilities have a facility-wide cancer MIR greater than
or equal to 1-in-1 million. The maximum facility-wide MIR is 20-in-1
million, with emission points from the FPUF production source category
contributing less than 10 percent of the maximum facility-wide risk.
The maximum facility-wide TOSHI is 0.9, with the FPUF production source
category contributing 100 percent to the facility-wide TOSHI.
6. What demographic groups might benefit from this regulation?
    To determine whether or not to conduct a demographics analysis, we
look at a combination of factors including the MIR, non-cancer TOSHI,
population around the facilities in the source category and other
relevant factors. For the FPUF production source category, our analyses
show that actual emissions result in no individuals being exposed to
cancer risk greater than 1-in-1 million or a non-cancer TOSHI greater
than 1. Therefore, we did not conduct an assessment of risks to
individual demographic groups for this rulemaking. However, we did
conduct a proximity analysis, which identifies any overrepresentation
of minority, low income or indigenous populations near facilities in
the source category. The results of this analysis are presented in the
section of this preamble titled, ``Executive Order 12898: Federal
Actions to Address Environmental Justice in Minority Populations and
Low-Income Populations.''

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.C 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 FPUF production source category, the risk analysis
indicates that the cancer risks to the individual most exposed could be
up to 0.7-in-1 million due to actual emissions and 5-in-1 million based
on 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 (0.00004
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
emissions are all below an HQ of 1. Therefore, we find there is little
potential concern of acute non-cancer health impacts from actual
emissions. For acute non-cancer risks based on allowable emissions,
there was an HQ of 4 based on the REL for methylene chloride. Since the
acute modeling scenario is worst-case because of its confluence of peak
emission rates and worst-case dispersion conditions, and since the HQ
estimates for methylene chloride based on the AEGL-1 and ERPG-1 values
for this facility are below 1, we are proposing to find that acute non-
cancer health impacts of concern are unlikely.
    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 that the risks from the FPUF
production source category are acceptable.
2. Ample Margin of Safety Analysis and Proposed Controls
    Although we are proposing that the risks from the FPUF production
source category are acceptable, risk estimates for 700 individuals in
the exposed population are above 1-in-1 million at the MACT-allowable
emissions levels. Consequently, we further considered whether the FPUF
Production MACT standards provide an ample margin of safety to protect
public health at the MACT-allowable emissions levels. In this ample
margin of safety analysis, we investigated available emissions control
options that might reduce the risk associated with MACT-allowable
emissions 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.
    For HAP used as an ABA at slabstock foam production facilities, we
considered prohibiting facilities from using any HAP or HAP-based
product as an ABA, as an option to reduce risks from this source
category. Emissions of HAP ABA were shown to contribute

nearly 100 percent to the maximum individual cancer risks at the MACT-
allowable emissions level for this source category. This control option
would require facilities to use ABAs that do not contain HAP. We
estimate the HAP emissions reduction resulting from this control option
would be approximately 735 tpy from the baseline MACT-allowable
emissions level. We estimate there would be no costs associated with
implementation of this option, as all facilities in the source category
are reporting that they do not have HAP ABA emissions from the foam
production line, and industry representatives have confirmed that all
sources have already discontinued use of a HAP or HAP-based product as
an ABA. Furthermore, there are no additional costs associated with the
recordkeeping and reporting requirements for compliance. With this
control option, we estimate the maximum cancer risks based on allowable
emissions would be reduced from 5-in-1 million to less than 1-in-1
million, the annual cancer incidence would be reduced from 0.0004 to
0.00004, the acute HQ would be reduced from 4 to less than 1 and the
non-cancer TOSHI would remain unchanged. We believe this HAP ABA
prohibition is technically feasible for all slabstock FPUF production
operations and is a cost-effective measure to achieve emissions and
health risk reductions associated with the MACT-allowable level of
emissions. Therefore, based on this analysis, we are proposing under
section 112(f)(2) of the CAA to prohibit the use of HAP or HAP-based
products as ABAs.
    We are proposing that the existing MACT standards, as modified to
include the HAP-based ABA prohibition described above, will provide an
ample margin of safety to protect public health and prevent an adverse
environmental effect.
    For diisocyanate storage vessels, as discussed in section IV.C.2.
of this preamble, we identified one control option to further reduce
HAP emissions from these storage vessels, which were shown to
contribute approximately 1 percent to the maximum individual cancer
risks at the MACT-allowable emissions level for the source category.
This control option would require sources to increase storage vessel
HAP emissions control efficiencies to 98 percent, using technologies
such as regenerative thermal oxidizers (RTO) or recuperative thermal
oxidizers (RCO). We estimate the resulting HAP reduction would be
approximately 0.0026 tpy from the baseline MACT-allowable emissions
level. The estimated cost effectiveness per ton of HAP emissions
reduction would be $124 million and $269 million, based on using a RTO
and RCO, respectively. The additional control requirement would not
achieve a reduction in the maximum individual cancer risks or any of
the other risk metrics due to emissions at the MACT-allowable level.
Due to the minimal reductions in HAP emissions and risk, along with the
substantial costs associated with this option, we are proposing that
additional HAP emissions controls for FPUF production diisocyanate
storage vessels are not necessary to provide an ample margin of safety.
    For equipment leaks at slabstock foam production facilities, as
discussed in section IV.C.3. of this preamble, we identified several
control options to further address risks from leaking components. We
estimate that up to 3 percent of the emissions and associated risk at
the MACT-allowable levels could be attributed to equipment leaks.\22\
The control options identified include the use of ``leakless'' valves
in diisocyanate service at slabstock facilities and implementation of
an enhanced LDAR program for diisocyanate equipment leaks at slabstock
facilities. These control options would require sources to use
``leakless'' valve technology or implement a LDAR program that would
incorporate monitoring with EPA Method 21, specific leak definitions,
and possibly a limit on the total number of non-repairable equipment
allowed. We estimate the HAP reduction resulting from the ``leakless''
valve technology would be 1 tpy from the baseline MACT-allowable
emissions level, with a cost effectiveness of $305,000/ton HAP
reduction. The HAP emissions reduction resulting from an enhanced LDAR
program would be 0.38 tpy from the baseline MACT-allowable emissions
level, with a cost effectiveness of approximately $74,000/ton HAP
reduction. The HAP emissions reduction resulting from the portion of an
enhanced LDAR program that incorporates limits on the total number of
non-repairable equipment allowed would be 0.08 tpy from the baseline