[Federal Register Volume 79, Number 125 (Monday, June 30, 2014)]
[Proposed Rules]
[Pages 36879-37075]
[FR Doc No: 2014-12167]

Vol. 79

Monday,

No. 125

June 30, 2014

Part II

Environmental Protection Agency

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40 CFR Parts 60 and 63

Petroleum Refinery Sector Risk and Technology Review and New Source
Performance Standards; Proposed Rule

Federal Register / Vol. 79 , No. 125 / Monday, June 30, 2014 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 60 and 63

[EPA-HQ-OAR-2010-0682; FRL-9720-4]
RIN 2060-AQ75

Petroleum Refinery Sector Risk and Technology Review and New
Source Performance Standards

AGENCY: Environmental Protection Agency.

ACTION: Proposed rule.

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SUMMARY: This action proposes amendments to the national emission
standards for hazardous air pollutants for petroleum refineries to
address the risk remaining after application of the standards
promulgated in 1995 and 2002. This action also proposes amendments to
the national emission standards for hazardous air pollutants for
petroleum refineries based on the results of the Environmental
Protection Agency (EPA) review of developments in practices, processes
and control technologies and includes new monitoring, recordkeeping and
reporting requirements. The EPA is also proposing new requirements
related to emissions during periods of startup, shutdown and
malfunction to ensure that the standards are consistent with court
opinions issued since promulgation of the standards. This action also
proposes technical corrections and clarifications for new source
performance standards for petroleum refineries to improve consistency
and clarity and address issues raised after the 2008 rule promulgation.
Implementation of this proposed rule will result in projected
reductions of 1,760 tons per year (tpy) of hazardous air pollutants
(HAP), which will reduce cancer risk and chronic health effects.

DATES:
    Comments. Comments must be received on or before August 29, 2014. A
copy of comments on the information collection provisions should be
submitted to the Office of Management and Budget (OMB) on or before
July 30, 2014.
    Public Hearing. The EPA will hold public hearings on this proposed
rule on July 16, 2014, at Banning's Landing Community Center, 100 E.
Water Street, Wilmington, California 90744, and on August 5, 2014, at
the Alvin D. Baggett Recreation Building 1302 Keene Street in Galena
Park, Texas, 77547.

ADDRESSES:
    Comments. Submit your comments, identified by Docket ID Number EPA-
HQ-OAR-2010-0682, 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-HQ-OAR-2010-0682.
     Fax:<PHONE_NUMBER>. Attention Docket ID Number EPA-HQ-
OAR-2010-0682.
     Mail: U.S. Postal Service, send comments to: EPA Docket
Center, William Jefferson Clinton (WJC) West Building (Air Docket),
Attention Docket ID Number EPA-HQ-OAR-2010-0682, U.S. Environmental
Protection Agency, Mailcode: 28221T, 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 (OMB), Attn: Desk Officer for
EPA, 725 17th Street NW., Washington, DC 20503.
     Hand Delivery: U.S. Environmental Protection Agency, WJC
West Building (Air Docket), Room 3334, 1301 Constitution Ave. NW.,
Washington, DC 20004. Attention Docket ID Number EPA-HQ-OAR-2010-0682.
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-
2010-0682. 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-2010-0682. 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, WJC West Building, Room 3334, 1301
Constitution Ave. NW., Washington, DC. The Public Reading Room is open
from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal
holidays. The telephone number for the Public Reading Room is (202)
566-1744, and the telephone number for the EPA Docket Center is (202)
566-1742.
    Public Hearing. The public hearing will be held in Wilmington,
California on July 16, 2014 at Banning's Landing Community Center, 100
E. Water Street, Wilmington, California 90744. The hearing will convene
at 9 a.m. and end at 8 p.m. A lunch break will be held from 1 p.m.
until 2 p.m. A dinner break will be held from 5 p.m. until 6 p.m. The
public hearing in Galena Park, Texas will be held on August 5, 2014, at
the Alvin D. Baggett Recreation Building 1302 Keene Street Galena Park,
Texas 77547. The hearing will convene at 9 a.m. and will end at 8 p.m.
A lunch break will be held from noon until 1 p.m. A dinner break will
be held from 5 p.m. until 6 p.m. Please contact Ms. Virginia Hunt at
(919) 541-0832 or at<EMAIL_ADDRESS>to register to speak at the
hearing. The last day to pre-register in advance to speak at the
hearing is July 11, 2014, for the Wilmington, California hearing and
August 1, 2014, for the Galena Park, Texas hearing. Additionally,
requests to speak will be taken the day of the hearing at the hearing
registration desk, although preferences on speaking times may not be
able to be fulfilled. If you require the service of a translator or

special accommodations such as audio description, please let us know at
the time of registration.

FOR FURTHER INFORMATION CONTACT: For questions about this proposed
action, contact Ms. Brenda Shine, Sector Policies and Programs Division
(E143-01), Office of Air Quality Planning and Standards (OAQPS), 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. Ted Palma, Health
and Environmental Impacts Division (C539-02), Office of Air Quality
Planning and Standards (OAQPS), U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; telephone number: (919)
541-5470; fax number:<PHONE_NUMBER>; and email address:
<EMAIL_ADDRESS>For information about the applicability of the
National Emissions Standards for Hazardous Air Pollutants (NESHAP) or
the New Source Performance Standards (NSPS) to a particular entity,
contact Maria Malave, Office of Enforcement and Compliance Assurance
(OECA), telephone number:<PHONE_NUMBER>; fax number:<PHONE_NUMBER>;
and email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Preamble Acronyms and Abbreviations

    We use multiple acronyms and terms in this preamble. While this
list may not be exhaustive, to ease the reading of this preamble and
for reference purposes, the EPA defines the following terms and
acronyms here:

10/25 tpy emissions equal to or greater than 10 tons per year of a
single pollutant or 25 tons per year of cumulative pollutants
ACGIH American Conference of Governmental Industrial Hygienists
ADAF age-dependent adjustment factors
AEGL acute exposure guideline levels
AERMOD air dispersion model used by the HEM-3 model
APCD air pollution control devices
API American Petroleum Institute
BDT best demonstrated technology
BLD bag leak detectors
BSER best system of emission reduction
Btu/ft\2\ British thermal units per square foot
Btu/scf British thermal units per standard cubic foot
CAA Clean Air Act
CalEPA California EPA
CBI confidential business information
CCU catalytic cracking units
Ccz combustion zone combustibles concentration
CDDF chlorinated dibenzodioxins and furans
CDX Central Data Exchange
CEDRI Compliance and Emissions Data Reporting Interface
CEMS continuous emissions monitoring system
CFR Code of Federal Regulations
CO carbon monoxide
CO2 carbon dioxide
CO2e carbon dioxide equivalents
COMS continuous opacity monitoring system
COS carbonyl sulfide
CPMS continuous parameter monitoring system
CRU catalytic reforming units
CS2 carbon disulfide
DCU delayed coking units
DIAL differential absorption light detection and ranging
EBU enhanced biological unit
EPA Environmental Protection Agency
ERPG emergency response planning guidelines
ERT Electronic Reporting Tool
ESP electrostatic precipitator
FCCU fluid catalytic cracking units
FGCD fuel gas combustion devices
FR Federal Register
FTIR Fourier transform infrared spectroscopy
g PM/kg grams particulate matter per kilogram
GC gas chromatograph
GHG greenhouse gases
GPS global positioning system
H2S hydrogen sulfide
HAP hazardous air pollutants
HCl hydrogen chloride
HCN hydrogen cyanide
HEM-3 Human Exposure Model, Version 1.1.0
HF hydrogen fluoride
HFC highest fenceline concentration
HI hazard index
HQ hazard quotient
ICR Information Collection Request
IRIS Integrated Risk Information System
km kilometers
lb/day pounds per day
LDAR leak detection and repair
LFL lower flammability limit
LFLcz combustion zone lower flammability limit
LMC lowest measured concentration
LOAEL lowest-observed-adverse-effect level
LTD long tons per day
MACT maximum achievable control technology
mg/kg-day milligrams per kilogram per day
mg/L milligrams per liter
mg/m\3\ milligrams per cubic meter
Mg/yr megagrams per year
MFC measured fenceline concentration
MFR momentum flux ratio
MIR maximum individual risk
mph miles per hour
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NAS National Academy of Sciences
NATA National Air Toxics Assessment
NEI National Emissions Inventory
NESHAP National Emissions Standards for Hazardous Air Pollutants
NFS near-field interfering source
NHVcz combustion zone net heating value
Ni nickel
NIOSH National Institutes for Occupational Safety and Health
NOAEL no-observed-adverse-effect level
NOX nitrogen oxides
NRC National Research Council
NRDC Natural Resources Defense Council
NSPS new source performance standards
NTTAA National Technology Transfer and Advancement Act
OAQPS Office of Air Quality Planning and Standards
OECA Office of Enforcement and Compliance Assurance
OMB Office of Management and Budget
OSC off-site source contribution
OTM other test method
PAH polycyclic aromatic hydrocarbons
PB-HAP hazardous air pollutants known to be persistent and bio-
accumulative in the environment
PBT persistent, bioaccumulative, and toxic
PCB polychlorinated biphenyls
PEL probable effect level
PM particulate matter
PM2.5 particulate matter 2.5 micrometers in diameter and
smaller
POM polycyclic organic matter
ppm parts per million
ppmv parts per million by volume
ppmw parts per million by weight
psia pounds per square inch absolute
psig pounds per square inch gauge
REL reference exposure level
REM Model Refinery Emissions Model
RFA Regulatory Flexibility Act
RfC reference concentration
RfD reference dose
RTR residual risk and technology review
SAB Science Advisory Board
SBA Small Business Administration
SBAR Small Business Advocacy Review
SCR selective catalytic reduction
SISNOSE significant economic impact on a substantial number of small
entities
S/L/Ts state, local and tribal air pollution control agencies
SO2 sulfur dioxide
SRU sulfur recovery unit
SSM startup, shutdown and malfunction
STEL short-term exposure limit
TEQ toxicity equivalent
TLV threshold limit value
TOC total organic carbon
TOSHI target organ-specific hazard index
tpy tons per year
TRIM.FaTE Total Risk Integrated Methodology.Fate, Transport, and
Ecological Exposure model
UB uniform background
UF uncertainty factor
UMRA Unfunded Mandates Reform Act
URE unit risk estimate
UV-DOAS ultraviolet differential optical absorption spectroscopy
VCS voluntary consensus standards
VOC volatile organic compounds
WJC William Jefferson Clinton
[deg]F degrees Fahrenheit
[Delta]C the concentration difference between the highest measured
concentration and the lowest measured concentration
[mu]g/m\3\ micrograms per cubic meter

    The EPA also defines the following abbreviations for regulations
cited within this preamble:

AWP Alternative Work Practice To Detect Leaks From Equipment (40 CFR
63.11(c), (d) and (e))
Benzene NESHAP National Emission 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 (40 CFR part
61, subpart L as of publication in the Federal Register at 54 FR
38044, September 14, 1989)
BWON National Emission Standard for Benzene Waste Operations (40 CFR
part 61, subpart FF)
Generic MACT National Emission Standards for Storage Vessels (40 CFR
part 63, subpart WW)
HON National Emission Standards for Organic Hazardous Air Pollutants
(40 CFR part 63, subparts F, G and H)
Marine Vessel MACT National Emission Standards for Marine Tank
Vessel Loading Operations (40 CFR part 63, subpart Y)
Refinery MACT 1 National Emission Standards for Hazardous Air
Pollutants From Petroleum Refineries (40 CFR part 63, subpart CC)
Refinery MACT 2 National Emission Standards for Hazardous Air
Pollutants for Petroleum Refineries: Catalytic Cracking Units,
Catalytic Reforming Units, and Sulfur Recovery Units (40 CFR part
63, subpart UUU)
Refinery NSPS J Standards of Performance for Petroleum Refineries
(40 CFR part 60, subpart J)
Refinery NSPS Ja Standards of Performance for Petroleum Refineries
for which Construction, Reconstruction, or Modification Commenced
After May 14, 2007 (40 CFR part 60, subpart Ja)

    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?
    D. Public Hearing
II. Background
    A. What is the statutory authority for this action?
    B. What are the source categories and how do the NESHAP and NSPS
regulate emissions?
    C. What data collection activities were conducted to support
this action?
    D. What other relevant background information and data are
available?
III. Analytical Procedures
    A. How did we estimate post-MACT risks posed by the source
categories?
    B. How did we consider the risk results in making decisions for
this proposal?
    C. How did we perform the technology review?
IV. Analytical Results and Proposed Decisions
    A. What actions are we taking pursuant to CAA sections 112(d)(2)
and 112(d)(3)?
    B. What are the results and proposed decisions based on our
technology review?
    C. What are the results of the risk assessment and analyses?
    D. What are our proposed decisions regarding risk acceptability,
ample margin of safety and adverse environmental effects?
    E. What other actions are we proposing?
    F. What compliance dates are we proposing?
V. Summary of Cost, Environmental and Economic Impacts
    A. What are the affected sources, the air quality impacts and
cost impacts?
    B. What are the economic impacts?
    C. 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

    A redline version of the regulatory language that incorporates the
proposed changes in this action is available in the docket for this
action (Docket ID No. EPA-HQ-OAR-2010-0682).

I. General Information

A. Does this action apply to me?

    Table 1 of this preamble lists the industries that are 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. These proposed standards, once
promulgated, will be directly applicable to the affected sources. Thus,
federal, state, local and tribal government entities would not be
affected by this proposed action. As defined in the ``Initial List of
Categories of Sources Under Section 112(c)(1) of the Clean Air Act
Amendments of 1990'' (see 57 FR 31576, July 16, 1992), the ``Petroleum
Refineries--Catalytic Cracking (Fluid and other) Units, Catalytic
Reforming Units, and Sulfur Plant Units'' source category and the
``Petroleum Refineries--Other Sources Not Distinctly Listed'' both
consist of any facility engaged in producing gasoline, naphthas,
kerosene, jet fuels, distillate fuel oils, residual fuel oils,
lubricants, or other products from crude oil or unfinished petroleum
derivatives. The first of these source categories includes process
vents associated with the following refinery process units: Catalytic
cracking (fluid and other) units, catalytic reforming units and sulfur
plant units. The second source category includes all emission sources
associated with refinery process units except the process vents listed
in the Petroleum Refineries--Catalytic Cracking (Fluid and Other)
Units, Catalytic Reforming Units, and Sulfur Plant Units Source
Category. The emission sources included in this source category
include, but are not limited to, miscellaneous process vents (vents
other than those listed in Petroleum Refineries--Catalytic Cracking
(Fluid and Other) Units, Catalytic Reforming Units, and Sulfur Plant
Units Source Category), equipment leaks, storage vessels, wastewater,
gasoline loading, marine vessel loading, and heat exchange systems.

                              Table 1--Industries Affected by This Proposed Action
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                                                                    NAICS\a\
                            Industry                                  Code       Examples of regulated entities
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Petroleum Refining Industry.....................................       324110  Petroleum refinery sources that
                                                                                are subject to 40 CFR part 60,
                                                                                subpart J and Ja and 40 CFR part
                                                                                63, subparts CC and UUU.
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\a\ North American Industry Classification System.

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

    Following signature by the EPA Administrator, the EPA will post a
copy of this proposed action at: http://www.epa.gov/ttn/atw/petref.html. Following publication in the Federal Register, the EPA
will post the Federal Register version of the proposal and key
technical documents at the Web site. 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-2010-0682.

D. Public Hearing

    The hearing will provide interested parties the opportunity to
present data, views or arguments concerning the proposed action. The
EPA will make every effort to accommodate all speakers who arrive and
register. The EPA may ask clarifying questions during the oral
presentations but will not respond to the presentations at that time.
Written statements and supporting information submitted during the
comment period will be considered with the same weight as oral comments
and supporting information presented at the public hearing. Written
comments on the proposed rule must be postmarked by August 29, 2014.
Commenters should notify Ms. Virginia Hunt if they will need specific
equipment, or if there are other special needs related to providing
comments at the hearing. Oral testimony will be limited to 5 minutes
for each commenter. The EPA encourages commenters to provide the EPA
with a copy of their oral testimony electronically (via email or CD) or
in hard copy form. Verbatim transcripts of the hearings and written
statements will be included in the docket for the rulemaking. The EPA
will make every effort to follow the schedule as closely as possible on
the day of the hearing; however, please plan for the hearing to run
either ahead of schedule or behind schedule. Information regarding the
hearing will be available at: http://www.epa.gov/ttnatw01/petrefine/petrefpg.html.

II. Background

A. What is the statutory authority for this action?

1. NESHAP
    Section 112 of the Clean Air Act (CAA) establishes a two-stage
regulatory process to address emissions of 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 national
emissions standards for hazardous air pollutants (NESHAP) for those
sources. ``Major sources'' are those that emit or have the potential to
emit 10 tpy or more of a single HAP or 25 tpy or more of any
combination of HAP. 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
emission reductions, any non-air quality health and environmental
impacts and energy requirements.
    The EPA is then required to review these technology-based standards
and revise them ``as necessary (taking into account developments in
practices, processes, and control technologies)'' no less frequently
than every 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).
Section 112(f)(1) required that the EPA by November 1996 prepare a
report to Congress discussing (among

other things) methods of calculating the risks posed (or potentially
posed) by sources after implementation of the MACT standards, the
public health significance of those risks and the EPA's recommendations
as to legislation regarding such remaining risk. The EPA prepared and
submitted the Residual Risk Report to Congress, EPA-453/R-99-001 (Risk
Report) in March 1999. CAA section 112(f)(2) then provides that if
Congress does not act on any recommendation in the Risk Report, the EPA
must analyze and address residual risk for each category or subcategory
of sources 8 years after promulgation of such standards pursuant to CAA
section 112(d).
    Section 112(f)(2) of the CAA requires the EPA to determine for
source categories subject to MACT standards whether the emission
standards provide an ample margin of safety to protect public health.
Section 112(f)(2)(B) of the CAA expressly preserves the EPA's use of
the two-step process for developing standards to address any residual
risk and the agency's interpretation of ``ample margin of safety''
developed in the National Emissions Standards for Hazardous Air
Pollutants: Benzene Emissions from Maleic Anhydride Plants,
Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment
Leaks, and Coke By-Product Recovery Plants (Benzene NESHAP) (54 FR
38044, September 14, 1989). The EPA notified Congress in the Risk
Report that the agency intended to use the Benzene NESHAP approach in
making CAA section 112(f) residual risk determinations (EPA-453/R-99-
001, p. ES-11). The EPA subsequently adopted this approach in its
residual risk determinations and in a challenge to the risk review for
the Synthetic Organic Chemical Manufacturing source category, the
United States Court of Appeals for the District of Columbia Circuit
upheld as reasonable the EPA's interpretation that 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 the process of evaluating residual risk is the
determination of acceptable risk. If risks are unacceptable, the EPA
cannot consider cost in identifying the emissions standards necessary
to bring risks to an acceptable level. The second step is the
determination of whether standards must be further revised in order to
provide an ample margin of safety to protect public health. The ample
margin of safety is the level at which the standards must be set,
unless an even more stringent standard is necessary to prevent, taking
into consideration costs, energy, safety and other relevant factors, an
adverse environmental effect.
a. Step 1--Determining Acceptability
    The agency in the Benzene NESHAP concluded ``that the acceptability
of risk under section 112 is best judged on the basis of a broad set of
health risk measures and information'' and that the ``judgment on
acceptability cannot be reduced to any single factor.'' 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 at 38045, September 14, 1989. We discussed the
maximum individual lifetime cancer risk (or maximum individual risk
(MIR)) as being ``the estimated risk that a person living near a plant
would have if he or she were exposed to the maximum pollutant
concentrations for 70 years.'' Id. We explained that this measure of
risk ``is an estimate of the upper bound of risk based on conservative
assumptions, such as continuous exposure for 24 hours per day for 70
years.'' Id. We acknowledged that maximum individual lifetime cancer
risk ``does not necessarily reflect the true risk, but displays a
conservative risk level which is an upper-bound that is unlikely to be
exceeded.'' Id.
    Understanding that there are both benefits and limitations to using
the MIR as a metric for determining acceptability, we acknowledged in
the Benzene NESHAP that ``consideration of maximum individual risk * *
* must take into account the strengths and weaknesses of this measure
of risk.'' Id. Consequently, the presumptive risk level of 100-in-1
million (1-in-10 thousand) provides a benchmark for judging the
acceptability of maximum individual lifetime cancer risk, but does not
constitute a rigid line for making that determination. Further, in the
Benzene NESHAP, we noted that:

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

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

[i]n establishing a presumption for MIR, rather than a rigid line
for acceptability, the Agency intends to weigh it with a series of
other health measures and factors. These include the overall
incidence of cancer or other serious health effects within the
exposed population, the numbers of persons exposed within each
individual lifetime risk range and associated incidence within,
typically, a 50 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.
b. Step 2--Determination of Ample Margin of Safety
    CAA section 112(f)(2) requires the EPA to determine, for source
categories subject to MACT standards, whether those standards provide
an ample margin of safety to protect public health. As explained in the
Benzene NESHAP, ``the second step of the inquiry, determining an `ample
margin of safety,' again includes consideration of all of the health
factors, and whether to reduce the risks even further. . . .

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

    \1\ ``Adverse environmental effect'' is defined as any
significant and widespread adverse effect, which may be reasonably
anticipated to wildlife, aquatic life or natural resources,
including adverse impacts on populations of endangered or threatened
species or significant degradation of environmental qualities over
broad areas. CAA section 112(a)(7).
---------------------------------------------------------------------------

    The CAA does not specifically define the terms ``individual most
exposed,'' ``acceptable level'' and ``ample margin of safety.'' In the
Benzene NESHAP, 54 FR at 38044-38045, September 14, 1989, we stated as
an overall objective:

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

The agency further stated that ``[t]he EPA also considers incidence
(the number of persons estimated to suffer cancer or other serious
health effects as a result of exposure to a pollutant) to be an
important measure of the health risk to the exposed population.
Incidence measures the extent of health risks to the exposed population
as a whole, by providing an estimate of the occurrence of cancer or
other serious health effects in the exposed population.'' Id. at 38045.
    In the ample margin of safety decision process, the agency again
considers all of the health risks and other health information
considered in the first step, including the incremental risk reduction
associated with standards more stringent than the MACT standard or a
more stringent standard that EPA has determined is necessary to ensure
risk is acceptable. In the ample margin of safety analysis, the agency
considers additional factors, including costs and economic impacts of
controls, technological feasibility, uncertainties and any other
relevant factors. Considering all of these factors, the agency will
establish the standard ``at a level that provides an ample margin of
safety to protect the public health,'' as required by CAA section
112(f). 54 FR 38046, September 14, 1989.
2. NSPS
    Section 111 of the CAA establishes mechanisms for controlling
emissions of air pollutants from stationary sources. Section 111(b) of
the CAA provides authority for the EPA to promulgate new source
performance standards (NSPS) which apply only to newly constructed,
reconstructed and modified sources. Once the EPA has elected to set
NSPS for new and modified sources in a given source category, CAA
section 111(d) calls for regulation of existing sources, with certain
exceptions explained below.
    Specifically, section 111(b) of the CAA requires the EPA to
establish emission standards for any category of new and modified
stationary sources that the Administrator, in his or her judgment,
finds ``causes, or contributes significantly to, air pollution which
may reasonably be anticipated to endanger public health or welfare.''
The EPA has previously made endangerment findings under this section of
the CAA for more than 60 stationary source categories and subcategories
that are now subject to NSPS.
    Section 111 of the CAA gives the EPA significant discretion to
identify the affected facilities within a source category that should
be regulated. To define the affected facilities, the EPA can use size
thresholds for regulation and create subcategories based on source
type, class or size. Emission limits also may be established either for
equipment within a facility or for an entire facility. For listed
source categories, the EPA must establish ``standards of performance''
that apply to sources that are constructed, modified or reconstructed
after the EPA proposes the NSPS for the relevant source category.\2\
---------------------------------------------------------------------------

    \2\ Specific statutory and regulatory provisions define what
constitutes a modification or reconstruction of a facility. 40 CFR
60.14 provides that an existing facility is modified and, therefore,
subject to an NSPS, if it undergoes ``any physical change in the
method of operation . . . which increases the amount of any air
pollutant emitted by such source or which results in the emission of
any air pollutant not previously emitted.'' 40 CFR 60.15, in turn,
provides that a facility is reconstructed if components are replaced
at an existing facility to such an extent that the capital cost of
the new equipment/components exceed 50 percent of what is believed
to be the cost of a completely new facility.
---------------------------------------------------------------------------

    The EPA also has significant discretion to determine the
appropriate level for the standards. Section 111(a)(1) of the CAA
provides that NSPS are to ``reflect the degree of emission limitation
achievable through the application of the best system of emission
reduction which (taking into account the cost of achieving such
reduction and any non-air quality health and environmental impact and
energy requirements) the Administrator determines has been adequately
demonstrated.'' This level of control is commonly referred to as best
demonstrated technology (BDT) or the best system of emission reduction
(BSER). The standard that the EPA develops, based on the BSER
achievable at that source, is commonly a numerical emission limit,
expressed as a performance level (i.e., a rate-based standard).
Generally, the EPA does not prescribe a particular technological system
that must be used to comply with a NSPS. Rather, sources remain free to
elect whatever combination of measures will achieve equivalent or
greater control of emissions.
    Costs are also considered in evaluating the appropriate standard of
performance for each category or subcategory. The EPA generally
compares control options and estimated costs and emission impacts of
multiple, specific emission standard options under consideration. As
part of this analysis, the EPA considers numerous factors relating to
the potential cost of the regulation, including industry organization
and market structure, control options available to reduce emissions of
the regulated pollutant(s) and costs of these controls.

B. What are the source categories and how do the NESHAP and NSPS
regulate emissions?

    The source categories include petroleum refineries engaged in
converting crude oil into refined products, including liquefied
petroleum gas, gasoline, kerosene, aviation fuel, diesel fuel, fuel
oils, lubricating oils and feedstocks for the petrochemical industry.
Petroleum refinery activities start with the receipt of crude oil for
storage at the refinery, include all petroleum handling and refining
operations, and terminate with loading of refined products into
pipelines, tank or rail cars, tank trucks, or ships or barges that take
products from the refinery to distribution centers. Petroleum refinery-
specific process units include fluid catalytic cracking units (FCCU)
and catalytic reforming units (CRU), as well as units and processes
found at many types of manufacturing facilities (including petroleum
refineries), such as storage vessels and wastewater treatment plants.
HAP emitted by this industry include organics (e.g., acetaldehyde,
benzene, formaldehyde, hexane, phenol, naphthalene, 2-
methylnaphthalene, dioxins, furans, ethyl benzene, toluene and xylene);
reduced sulfur compounds (i.e., carbonyl sulfide (COS), carbon
disulfide (CS2)); inorganics (e.g., hydrogen chloride (HCl),
hydrogen cyanide (HCN), chlorine, hydrogen fluoride (HF)); and metals
(e.g., antimony, arsenic, beryllium, cadmium, chromium, cobalt, lead,
mercury, manganese and nickel). Criteria pollutants and other non-
hazardous air pollutants that are also emitted include nitrogen oxides
(NOX), particulate matter (PM), sulfur dioxide
(SO2), volatile organic compounds (VOC), carbon monoxide
(CO), greenhouse gases (GHG), and total reduced sulfur.
    The federal emission standards that are the primary subject of this
proposed rulemaking are:
     National Emission Standards for Hazardous Air Pollutants
from Petroleum Refineries (40 CFR part 63, subpart CC) (Refinery MACT
1);
     National Emission Standards for Hazardous Air Pollutants
for Petroleum Refineries: Catalytic Cracking Units, Catalytic Reforming
Units, and Sulfur Recovery Units (40 CFR part 63, subpart UUU)
(Refinery MACT 2);
     Standards of Performance for Petroleum Refineries (40 CFR
part 60, subpart J) (Refinery NSPS J); and
     Standards of Performance for Petroleum Refineries for
which Construction, Reconstruction, or Modification Commenced After May
14, 2007 (40 CFR part 60, subpart Ja) (Refinery NSPS Ja).
1. Refinery MACT Standards
    The EPA promulgated MACT standards pursuant to CAA section
112(d)(2) and (3) for refineries located at major sources in three
separate rules. On August 18, 1995, the first Petroleum Refinery MACT
standard was promulgated in 40 CFR part 63, subpart CC (60 FR 43620).
This rule is known as ``Refinery MACT 1'' and covers the ``Sources Not
Distinctly Listed,'' meaning it includes all emission sources from
petroleum refinery process units, except those listed separately under
the section 112(c) source category list expected to be regulated by
other MACT standards. Some of the emission sources regulated in
Refinery MACT 1 include miscellaneous process vents, storage vessels,
wastewater, equipment leaks, gasoline loading racks, marine tank vessel
loading and heat exchange systems.
    Certain process vents that were listed as a separate source
category under CAA section 112(c) and that were not addressed as part
of the Refinery MACT 1 were subsequently regulated under a second MACT
standard specific to these petroleum refinery process vents, codified
as 40 CFR part 63, subpart UUU, which we promulgated on April 11, 2002
(67 FR 17762). This standard, which is referred to as ``Refinery MACT
2,'' covers process vents on catalytic cracking units (CCU) (including
FCCU), CRU and sulfur recovery units (SRU).
    Finally, on October 28, 2009, we promulgated MACT standards for
heat exchange systems, which the EPA had not addressed in the original
1995 Refinery MACT 1 rule (74 FR 55686). In this same 2009 action, we
updated cross-references to the General Provisions in 40 CFR part 63.
On June 20, 2013 (78 FR 37133), we promulgated minor revisions to the
heat exchange provisions of Refinery MACT 1.
    On September 27, 2012, Air Alliance Houston, California Communities
Against Toxics and other environmental and public health groups filed a
lawsuit alleging that the EPA missed statutory deadlines to review and
revise Refinery MACT 1 and 2.
    The EPA has reached an agreement to settle that litigation. In a
consent decree filed January 13, 2014 in the U.S. District Court for
the District of Columbia, the EPA commits to perform the risk and
technology review for Refinery MACT 1 and 2 and by May 15, 2014, either
propose any regulations or propose that additional regulations are not
necessary. Under the Consent Decree, the EPA commits to take final
action by April 17, 2015, establishing regulations pursuant to the risk
and technology review or to issue a final determination that revision
to the existing rules is not necessary.
2. Refinery NSPS
    Refinery NSPS subparts J and Ja regulate criteria pollutant
emissions, including PM, SO2, NOX and CO from
FCCU catalyst regenerators, fuel gas combustion devices (FGCD) and
sulfur recovery plants. Refinery NSPS Ja also regulates criteria
pollutant emissions from fluid coking units and delayed coking units
(DCU).
    The NSPS for petroleum refineries (40 CFR part 60, subpart J;
Refinery NSPS J) were promulgated in 1974, amended in 1976 and amended
again in 2008, following a review of the standards. As part of the
review that led to the 2008 amendments to Refinery NSPS J, the EPA
developed separate standards of performance for new process units (40
CFR part 60, subpart Ja; Refinery NSPS Ja). However, the EPA received
petitions for reconsideration and granted reconsideration on issues
related to those standards. On December 22, 2008, the EPA addressed
petition issues related to process heaters and flares by proposing
amendments to certain provisions. Final amendments to Refinery NSPS Ja
were promulgated on September 12, 2012 (77 FR 56422).
    In this action, we are proposing amendments to address technical
corrections and clarifications raised in a 2008 industry petition for
reconsideration applicable to Refinery NSPS Ja. We are addressing these
issues in this proposal because they also affect sources included
within these proposed amendments to Refinery MACT 1 and 2.

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

    In 2010, the EPA began a significant effort to gather additional
information and perform analyses to determine how to address statutory
obligations for the Refinery MACT standards and the NSPS. This effort
focused on gathering comprehensive information through an industry-wide
Information Collection Request (ICR) on petroleum refineries, conducted
under CAA section 114 authority. The information not claimed as CBI by
respondents is available in the docket (see Docket Item Nos. EPA-HQ-
OAR-2010-0682-0064 through 0069). The EPA issued a single ICR (OMB
Control Number 2060-0657) for sources covered under Refinery MACT 1 and
2 and Refinery NSPS J and Ja.
    On April 1, 2011, the ICR was sent out to the petroleum refining
industry. In a comprehensive manner, the ICR

collected information on processing characteristics, crude slate
characteristics, emissions inventories and source testing to fill known
data gaps. The ICR had four components: (1) A questionnaire on
processes and controls to be completed by all petroleum refineries
(Component 1); (2) an emissions inventory to be developed by all
petroleum refineries using the emissions estimation protocol developed
for this effort (Component 2); (3) distillation feed sampling and
analysis to be conducted by all petroleum refineries (Component 3); and
(4) emissions source testing to be completed in accordance with an EPA-
approved protocol for specific sources at specific petroleum refineries
(Component 4). We received responses from 149 refineries. We have since
learned that seven refineries are synthetic minor sources, bringing the
total number of major source refineries operating in 2010 to 142.
    Information collected through the ICR was used to establish the
baseline emissions and control levels for purposes of the regulatory
reviews, to identify the most effective control measures, and to
estimate the environmental and cost impacts associated with the
regulatory options considered. As part of the information collection
process, we provided a protocol for survey respondents to follow in
developing the emissions inventories under Component 2 (Emission
Estimation Protocol for Petroleum Refineries, available as Docket Item
Number EPA-HQ-OAR-2010-0682-0060). The protocol contained detailed
guidance for estimating emissions from typical refinery emission
sources and was intended to provide a measure of consistency and
replicability for emission estimates across the refining industry.
Prior to issuance of the ICR, the protocol was publicly disseminated
and underwent several revisions after public comments were received.
Draft and final versions of the emission estimation protocol are
provided in the docket to this rule (Docket ID Number EPA-HQ-OAR-2010-
0682). The protocol provided a hierarchy of methodologies available for
estimating emissions that corresponded to the level of information
available at refineries. For each emission source, the various emission
measurement or estimation methods specific to that source were ranked
in order of preference, with ``Methodology Rank 1'' being the preferred
method, followed by ``Methodology Rank 2,'' and so on. Refinery owners
and operators were requested through the ICR to use the highest ranked
method (with Methodology Rank 1 being the highest) for which data were
available. Methodology Ranks 1 or 2 generally relied on continuous
emission measurements. When continuous measurement data were not
available, engineering calculations or site-specific emission factors
(Methodology Ranks 3 and 4) were specified in the protocol by EPA;
these methods generally needed periodic, site-specific measurements.
When site-specific measurement or test data were not available, default
emission factors (Methodology Rank 5) were provided in the protocol by
EPA.
    As we reviewed the ICR-submitted emissions inventories, we
determined that, in some cases, refiners either did not follow the
protocol methodology or made an error in their calculations. This was
evident because pollutants that we expected to be reported from certain
emission sources were either not reported or were reported in amounts
that were not consistent with the protocol methodology. In these cases,
we contacted the refineries and, based on their replies, made
corrections to emission estimates. The original Component 2 submittals,
documentation of the changes as a result of our review, and the final
emissions inventories we relied on for our analyses are available in
the technical memorandum entitled Emissions Data Quality Memorandum and
Development of the Risk Model Input File, in Docket ID Number EPA-HQ-
OAR-2010-0682.
    Collected emissions test data (test reports, continuous emissions
monitoring system (CEMS) data and other continuous monitoring system
data) were used to assess the effectiveness of existing control
measures, to fill data gaps and to examine variability in emissions.
The ICR requested source testing for a total of 90 specific process
units at 75 particular refineries across the industry. We received a
total of 72 source tests; in some cases, refinery sources claimed that
units we requested to be tested were no longer in operation, did not
exist or did not have an emission point to the atmosphere (this was the
case for hydrocrackers). In other cases, refiners claimed they were not
able to conduct testing because of process characteristics. For
example, source testing of DCU proved to be difficult because the
moisture content of the steam vent required a significant amount of gas
to be sampled to account for dilution. Venting periods of less than 20
minutes did not accommodate this strategy and, therefore, if refiners
vented for less than 20 minutes, they did not sample their steam vent.
As a result, only two DCU tests out of eight requested were received as
part of Component 4. Results of the stack test data are compiled and
available in Docket ID Number EPA-HQ-OAR-2010-0682.

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

    Over the past several years, the EPA has worked with the Texas
Commission on Environmental Quality and industry representatives to
better characterize proper flare performance. Flares are used to
control emissions from various vents at refineries as well as at other
types of facilities not in the petroleum refinery source categories,
such as chemical and petrochemical manufacturing facilities. In April
2012, we released a technical report for peer review that discussed our
observations regarding the operation and performance of flares. The
report was a result of the analysis of several flare efficiency studies
and flare performance test reports. To provide an objective evaluation
of our analysis, we asked a third party to facilitate an ad hoc peer
review process of the technical report. This third party established a
balanced peer review panel of reviewers from outside the EPA. These
reviewers consisted of individuals that could be considered ``technical
combustion experts'' within four interest groups: the refinery
industry, industrial flare consultants, academia, and environmental
stakeholders.
    The EPA developed a charge statement with ten charge questions for
the review panel. The peer reviewers were asked to perform a thorough
review of the technical report and answer the charge questions to the
extent possible, based on their technical expertise. The details of the
peer review process and the charge questions, as well as comments
received from the peer review process, were posted online to the
Consolidated Petroleum Refinery Rulemaking Repository at the EPA's
Technology Transfer Network Air Toxics Web site (see http://www.epa.gov/ttn/atw/petref.html). These items are also provided in a
memorandum entitled Peer Review of ``Parameters for Properly Designed
and Operated Flares'' (see Docket ID Number EPA-HQ-OAR-2010-0682).
After considering the comments received from the peer review process,
we developed a final technical memorandum (see technical memorandum,
Flare Performance Data: Summary of Peer Review Comments and Additional
Data Analysis for Steam-

Assisted Flares, in Docket ID Number EPA-HQ-OAR-2010-0682).

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 categories?

    The EPA conducted a risk assessment that provided estimates of the
MIR posed by the HAP emissions from each source in the source
categories, 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 each source category. The eight sections that follow this
paragraph describe how we estimated emissions and conducted the risk
assessment. The docket for this rulemaking (Docket ID Number EPA-HQ-
OAR-2010-0682) contains the following document which provides more
information on the risk assessment inputs and models: Draft Residual
Risk Assessment for the Petroleum Refining Source Sector. 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.
---------------------------------------------------------------------------

    \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?
    We compiled data sets using the ICR emission inventory submittals
as a starting point. The data sets were refined following an extensive
quality assurance check of source locations, emission release
characteristics, annual emission estimates and FCCU release parameters.
They were then updated based on additional information received from
refineries. In addition, we supplemented these data with results from
stack testing, which were required later than the inventories under the
ICR. As the stack test information was received, we compared these data
against the refined emission inventories and the default emission
factors provided in the Emission Estimation Protocol for Petroleum
Refineries (Docket Item Number EPA-HQ-OAR-2010-0682-0060).
    Based on the stack test data for FCCU, we calculated that, on
average, HCN emissions were a factor of 10 greater than the average
emission factor of 770 pounds per barrel FCCU feed provided in the
protocol. Therefore, we revised the HCN emissions for FCCU in the
emissions inventory used for the risk modeling runs (the results are
presented in this preamble). For the 10 facilities that performed a
stack test to determine HCN emissions from their FCCU, we used the
actual emissions measured during the stack tests in place of the
inventories originally supplied in response to the ICR. For those
facilities that did not perform a stack test, but reported HCN
emissions in the emissions inventory portion of the ICR, we increased
the emissions of HCN by a factor of 10, assuming the original emission
inventory estimates for FCCU HCN emissions were based on the default
emission factor in the protocol. The emissions inventory from the ICR
and documentation of the changes made to the file as a result of our
review are contained in the technical memorandum entitled Emissions
Data Quality Memorandum and Development of the Risk Model Input File,
in Docket ID Number EPA-HQ-OAR-2010-0682 and available on our Web
site.\4\
---------------------------------------------------------------------------

    \4\ The emissions inventory and the revised emissions modeling
file can also be found at http://www.epa.gov/ttn/atw/petref.htm.
---------------------------------------------------------------------------

2. How did we estimate MACT-allowable emissions?
    The available emissions data in the RTR dataset (i.e., the
emissions inventory) include estimates of the mass of HAP emitted
during the specified annual time period. In some cases, these
``actual'' emission levels are lower than the emission levels required
to comply with the MACT standards. The emissions level allowed to be
emitted by the MACT standards is referred to as the ``MACT-allowable''
emissions level. We discussed the use of both MACT-allowable and actual
emissions in the final Coke Oven Batteries 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 approach. (54 FR 38044,
September 14, 1989.)
    We requested allowable emissions data in the ICR. However, unlike
for actual emissions, where the ICR specified the use of the Emission
Estimation Protocol for Petroleum Refineries (available as Docket Item
Number EPA-HQ-OAR-2010-0682-0060), we did not specify a method to
calculate allowable emissions. As a result, in our review of these data
and when comparing estimates between facilities, we found that
facilities did not estimate allowable emissions consistently across the
industry. In addition, facilities failed to report allowable emissions
for many emission points, likely because they did not know how to
translate a work practice or performance standard into an allowable
emission estimate and they did not know how to speciate individual HAP
where the MACT standard is based on a surrogate, such as PM or VOC.
Therefore, the ICR-submitted information for allowable emissions did
not include emission estimates for all HAP and sources of interest.
Consequently, we used our Refinery Emissions Model (REM Model) to
estimate allowable emissions. The REM model relies on model plants that
vary based on throughput capacity. Each model plant contains process-
specific default emission factors, adjusted for compliance with the
Refinery MACT 1 and 2 emission standards.
    The risks associated with the allowable emissions were evaluated
using the same dispersion modeling practices, exposure assumptions and
health benchmarks as the actual risks. However, because each refinery's
allowable emissions were calculated by using model plants, selected
based on each refinery's actual capacities and throughputs, emission
estimates for point sources are not specific to a particular latitude/
longitude location. Therefore, for risk modeling purposes, all
allowable emissions were assumed to be released from the centroid of
the facility. (Note: for fugitive (area) sources, the surface area was
selected by the size of the model plant and the release point was
shifted to the southwest so the center of the fugitive area was near
the centroid of the facility). The emission and risk estimates for the
actual emission inventory were compared to the

allowable emissions and risk estimates. For most work practices, where
allowable emission estimates are difficult to predict, the actual risk
estimates were higher than those projected using the REM Model
estimates. Consequently, we post-processed the two risk files, taking
the higher risk estimates from the actual emissions inventory for
sources subject to work practice standards, such as process equipment
leaks, and sources that were not covered in the REM Model, combining
them with the risk estimates from sources with more readily determined
allowable emissions. The combined post-processed allowable risk
estimates provide a high estimate of the risk allowed under Refinery
MACT 1 and 2. The REM Model assumptions and emission estimates, along
with the post-processing of risk estimate results that produced the
final risk estimates for the allowable emissions, are provided in the
docket (see Refinery Emissions and Risk Estimates for Modeled
``Allowable'' Emissions in Docket ID Number EPA-HQ-OAR-2010-0682).
3. How did we conduct dispersion modeling, determine inhalation
exposures and estimate individual and population inhalation risks?
    Both long-term and short-term inhalation exposure concentrations
and health risks from the source categories 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 \5\, and (3) estimating
individual and population-level inhalation risks using the exposure
estimates and quantitative dose-response information.
---------------------------------------------------------------------------

    \5\ This metric comes from the Benzene NESHAP. See 54 FR 38046,
September 14, 1989.
---------------------------------------------------------------------------

    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.\6\ To perform the dispersion modeling and to
develop the preliminary risk estimates, HEM-3 draws on three data
libraries. The first is a library of meteorological data, which is used
for dispersion calculations. This library includes 1 year (2011) of
hourly surface and upper air observations for 824 meteorological
stations, selected to provide coverage of the United States and Puerto
Rico. A second library of United States Census Bureau census block \7\
internal point locations and populations provides the basis of human
exposure calculations (U.S. Census, 2010). In addition, for each census
block, the census library includes the elevation and controlling hill
height, which are also used in dispersion calculations. A third library
of pollutant 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.
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    \6\ U.S. EPA. Revision to the Guideline on Air Quality Models:
Adoption of a Preferred General Purpose (Flat and Complex Terrain)
Dispersion Model and Other Revisions (70 FR 68218, November 9,
2005).
    \7\ A census block is the smallest geographic area for which
census statistics are tabulated.
---------------------------------------------------------------------------

    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
([micro]g/m\3\)) by its unit risk estimate (URE). The URE is an upper
bound estimate of an individual's probability of contracting cancer
over a lifetime of exposure to a concentration of 1 microgram of the
pollutant per cubic meter of air. For residual risk assessments, we
generally use URE values from the EPA's Integrated Risk Information
System (IRIS). For carcinogenic pollutants without 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.
    We note here that several carcinogens emitted by facilities in
these source categories have a mutagenic mode of action. For these
compounds, we applied the age-dependent adjustment factors (ADAF)
described in the EPA's Supplemental Guidance for Assessing
Susceptibility from Early-Life Exposure to Carcinogens.\8\ This
adjustment has the effect of increasing the estimated lifetime risks
for these pollutants by a factor of 1.6. Although only a small fraction
of the total polycyclic organic matter (POM) emissions were reported as
individual compounds, the EPA expresses carcinogenic potency of POM
relative to the carcinogenic potency of benzo[a]pyrene, based on
evidence that carcinogenic POM have the same mutagenic mode of action
as does benzo[a]pyrene. The EPA's Science Policy Council recommends
applying the ADAF to all carcinogenic polycyclic aromatic hydrocarbons
(PAH) for which risk estimates are based on potency relative to
benzo[a]pyrene. Accordingly, we have applied the ADAF to the
benzo[a]pyrene-equivalent mass portion of all POM mixtures.
---------------------------------------------------------------------------

    \8\ Supplemental Guidance for Assessing Susceptibility from
Early-Life Exposure to Carcinogens. Risk Assessment Forum, U.S.
Environmental Protection Agency, Washington, DC. EPA/630/R-03/003F.
March 2005. Available at http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf.
---------------------------------------------------------------------------

    The EPA estimated incremental individual lifetime cancer risks
associated with emissions from the facilities in the source categories
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 \9\)
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 categories as part of this
assessment by summing individual risks. A distance of 50 km is
consistent with both the analysis supporting the

1989 Benzene NESHAP (54 FR 38044, September 14, 1989) and the
limitations of Gaussian dispersion models, including AERMOD.
---------------------------------------------------------------------------

    \9\ These classifications also coincide with the terms ``known
carcinogen, probable carcinogen, and possible carcinogen,''
respectively, which are the terms advocated in the EPA's previous
Guidelines for Carcinogen Risk Assessment, published in 1986 (51 FR
33992, September 24, 1986). Summing the risks of these individual
compounds to obtain the cumulative cancer risks is an approach that
was recommended by the EPA's SAB in their 2002 peer review of EPA's
National Air Toxics Assessment (NATA) entitled, 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.
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    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 level, which is a value selected from
one of several sources. First, the chronic reference level can be 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.'' Alternatively, in cases where an RfC from the EPA's IRIS
database is not available or where the EPA determines that using a
value other than the RfC is appropriate, the chronic reference level
can be a value from the following prioritized sources: (1) The Agency
for Toxic Substances and Disease Registry Minimum Risk Level (http://www.atsdr.cdc.gov/mrls/index.asp), which is defined as ``an estimate of
daily human exposure to a hazardous substance that is likely to be
without an appreciable risk of adverse non-cancer health effects (other
than cancer) over a specified duration of exposure''; (2) the CalEPA
Chronic Reference Exposure Level (REL) (http://www.oehha.ca.gov/air/hot_spots/pdf/HRAguidefinal.pdf), which is defined as ``the
concentration level (that is expressed in units of [micro]g/m\3\ for
inhalation exposure and in a dose expressed in units of milligram per
kilogram per 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 realistic assumptions based on knowledge of the emission point
release characteristics for emission rates, and conservative
assumptions for 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 through the inclusion of margins of
safety. Because margins of safety are incorporated to address data gaps
and uncertainties, exceeding the REL value 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),\10\ ``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.
---------------------------------------------------------------------------

    \10\ National Academy of Sciences (NAS), 2001. Standing
Operating Procedures for Developing Acute Exposure Levels for
Hazardous Chemicals, page 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.
    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
entitled, ERPGS Procedures and Responsibilities, 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.'' \11\ 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.
---------------------------------------------------------------------------

    \11\ ERP Committee Procedures and Responsibilities. November 1,
2006. American Industrial Hygiene Association. Available at https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERP-SOPs2006.pdf.
---------------------------------------------------------------------------

    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. However, for the petroleum refineries category, we
incorporated additional information and process knowledge in order to
better characterize acute emissions, as described below. The ICR
included input fields for both annual emissions and maximum hourly
emissions. The maximum hourly emission values were often left blank or
appeared to be reported in units other than those required for this
emissions field (pounds per hour). Consequently, instead of relying on
the inadequate data provided in response to the ICR, we elected to
estimate the hourly emissions based on the reported annual emissions
(converted to average hourly emissions in terms of pounds per hour) and
then to apply an escalation factor, considering the different types of
emission sources and their inherent variability, in order to calculate
maximum hourly rates. For sources with relatively continuous operations
and steady state emissions, such as FCCU, sulfur recovery plants, and
continuous catalytic reformers, a factor of 2 was used to estimate the
maximum hourly rates from the average hourly emission rates. For
sources with relatively continuous emissions, but with more
variability, like storage tanks and wastewater systems, a factor of 4
was used to estimate the maximum hourly rates from the average hourly
emission rates. For non-continuous emission sources with more
variability, such as DCU, cyclic CRU, semi-regenerative CRU, and
transfer and loading operations, the number of hours in the venting
cycle and the variability of emissions expected in that cycle were used
to determine the escalation factor for each emissions source. The
escalation factors for these processes range from 10 to 60. For more
detail regarding escalation factors and the rationale for their
selection, see Derivation of Hourly Emission Rates for Petroleum
Refinery Emission Sources Used in the Acute Risk Analysis, available in
the docket for this rulemaking (Docket ID Number EPA-HQ-OAR-2010-0682).
    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. For these
source categories, the data refinements employed consisted of using the
site-specific facility layout to distinguish facility property from an
area where the public could be exposed. These refinements are discussed
more fully in the Draft Residual Risk Assessment for the Petroleum
Refining Source Sector, which is available in the docket for this
rulemaking (Docket ID Number EPA-HQ-OAR-2010-0682). Ideally, we would
prefer to have continuous measurements over time to see how the
emissions vary by each hour over an entire year. Having a frequency
distribution of hourly emissions rates over a year would allow us to
perform a probabilistic analysis to estimate potential threshold
exceedances and their frequency of occurrence. Such an evaluation could
include a more complete statistical treatment of the key parameters and
elements adopted in this screening analysis. Recognizing that this
level of data is rarely available, we instead rely on the multiplier
approach.
    To better characterize the potential health risks associated with
estimated acute exposures to HAP, and in response to a key
recommendation from the SAB's peer review of the EPA's RTR risk
assessment methodologies,\12\ we generally examine a wider range of
available acute health metrics (e.g., REL, AEGL) 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, e.g., when Reference Value Arrays \13\
for HAP have been developed, we consider additional acute values (i.e.,
occupational and international values) to provide a more complete risk
characterization.
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    \12\ 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.
    \13\ 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 categories emitted any hazardous air pollutants known to
be persistent and bio-accumulative 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 petroleum refinery source categories, we identified
emissions of cadmium compounds, chlorinated dibenzodioxins and furans
(CDDF), lead compounds, mercury compounds, polychlorinated biphenyls
(PCB), and polycylic organic matter (POM). Because PB-HAP are emitted
by at least one facility, we proceeded to the second step of the
evaluation. In this step, we determined whether the facility-specific
emission rates of each of the emitted PB-HAP were large enough to
create the potential for significant non-inhalation human health risks
under reasonable worst-case conditions. To facilitate this step, we
developed emissions rate screening levels for each PB-HAP using a
hypothetical upper-end screening exposure scenario developed for use in
conjunction with the EPA's ``Total Risk Integrated Methodology. Fate,
Transport, and Ecological Exposure'' (TRIM.FaTE) model. We conducted a
sensitivity analysis on the screening scenario to ensure that its key
design parameters would represent the upper end of the range of
possible values, such that it would represent a conservative but not
impossible scenario. The facility-specific emissions rates of each of
the PB-HAP were compared to their corresponding emission rate screening
values to assess the potential for significant human health risks via
non-inhalation pathways. We call this application of the TRIM.FaTE
model the Tier I TRIM- Screen or Tier I screen.
    For the purpose of developing emissions rates for our Tier I TRIM-
Screen, we derived emission levels for each PB-HAP (other than lead) at
which the maximum excess lifetime cancer risk would be 1-in-1 million
or, for HAP that cause non-cancer health effects, the maximum HQ would
be 1. If the emissions rate of any PB-HAP exceeds the Tier I screening
emissions rate for any facility, we conduct a second screen, which we
call the Tier II TRIM-screen or Tier II screen. In the Tier II screen,
the location of each facility that exceeded the Tier I emission rate is
used to refine the assumptions associated with the environmental
scenario while maintaining the exposure scenario assumptions. We then
adjust the risk-based Tier I screening level for each PB-HAP for each
facility based on an understanding of how exposure concentrations
estimated for the screening scenario change with meteorology and
environmental assumptions. PB-HAP emissions that do not exceed these
new Tier II screening levels are considered to pose no unacceptable
risks. When facilities exceed the Tier II screening levels, it does not
mean that multi-pathway impacts are significant, only that we cannot
rule out that possibility based on the results of the screen. These
facilities may be further evaluated for multi-pathway risks using the
TRIM.FaTE model.
    In evaluating the potential for multi-pathway risk from emissions
of lead compounds, rather than developing a screening emissions rate
for them, we compared modeled maximum estimated chronic inhalation
exposures with the level of the current National Ambient Air Quality
Standards (NAAQS) for lead.\14\ Values below the level of the primary
(health-based) lead NAAQS were considered to have a low potential for
multi-pathway risk.
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    \14\ In doing so, EPA notes that the legal standard for a
primary NAAQS--that a standard is requisite to protect public health
and provide an adequate margin of safety (CAA Section 109(b))--
differs from the Section 112(f) standard (requiring among other
things that the standard provide an ``ample margin of safety'').
However, the lead NAAQS is a reasonable measure of determining risk
acceptability (i.e., the first step of the Benzene NESHAP analysis)
since it is designed to protect the most susceptible group in the
human population--children, including children living near major
lead emitting sources. 73 FR 67002/3; 73 FR 67000/3; 73 FR 67005/1,
November 12, 2008. In addition, applying the level of the primary
lead NAAQS at the risk acceptability step is conservative, since
that primary lead NAAQS reflects an adequate margin of safety.
---------------------------------------------------------------------------

    For further information on the multi-pathway analysis approach, see
the Draft Residual Risk Assessment for the Petroleum Refining Source
Sector, which is available in the docket for this action (Docket ID
Number EPA-HQ-OAR-2010-0682).
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 emission reductions that would be achieved by the control
options under consideration. We used the same emissions inventory that
we used for the risk modeling and applied emission reduction estimates
for the control options we are proposing to calculate the post-control
risk. We note that for storage vessels, in response to the ICR some
facilities reported emissions for their tank farm or a group of storage
vessels rather than for each individual storage vessel. In order to
calculate emissions for each storage vessel, we used unit-specific data
from the ICR to estimate the pre- and post-control emissions based on
the operating characteristics and controls reported for each unit. For
example, HAP emissions from each storage vessel were estimated based on
the size, contents, and controls reported for that storage vessel. If
additional controls would be necessary to comply with proposed
requirements for storage vessels, the HAP emissions were again
estimated based on the upgraded controls. The pre- and post-control
emissions were summed across all storage vessels at the facility to
determine a facility-specific emission reduction factor. The facility-
specific emission reduction factor was then used to adjust the
emissions for each of the pollutants reported for storage vessels at
that facility to account for the post-control emissions. In this
manner, the expected emission reductions were applied to the specific
HAP and emission points in the source category dataset to develop
corresponding estimates of risk and incremental risk reductions. The
resulting emission file used for post-control risk analysis is
available in the docket for this action (Docket ID Number EPA-HQ-OAR-
2010-0682).
6. How did we conduct the environmental risk screening assessment?
a. Adverse Environmental Effect
    The EPA has 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 PB-HAP and two acid gases. The
five PB-HAP are cadmium, dioxins/furans, POM, mercury (both inorganic
mercury and methyl mercury) and lead compounds. The two acid gases are
HCl and HF. The rationale for including these seven HAP in the
environmental risk screening analysis is presented below.
    HAP that persist and bioaccumulate are of particular environmental
concern because they accumulate in the soil, sediment and water. The
PB-HAP are

taken up, through sediment, soil, water, and/or ingestion of other
organisms, by plants or animals (e.g., small fish) at the bottom of the
food chain. As larger and larger predators consume these organisms,
concentrations of the PB-HAP in the animal tissues increases as does
the potential for adverse effects. The five PB-HAP we evaluate as part
of our screening analysis account for 99.8 percent of all PB-HAP
emissions nationally from stationary sources (on a mass basis from the
2005 National Emissions Inventory (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 compounds, we currently do not have the ability to calculate
these concentrations using the TRIM.Fate model. Therefore, to evaluate
the potential for adverse environmental effects from lead, we compare
the estimated HEM-modeled exposures from the source category emissions
of lead with the level of the secondary NAAQS for lead.\15\ We consider
values below the level of the secondary lead NAAQS to be unlikely to
cause adverse environmental effects.
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    \15\ 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 (on a mass basis) of the total acid gas
HAP emitted by stationary sources in the U.S. In addition to the
potential to cause direct damage to plants, high concentrations of HF
in the air have been linked to fluorosis in livestock. Air
concentrations of these HAP are already calculated as part of the human
multipathway exposure and risk screening analysis using the HEM3-AERMOD
air dispersion model, and we are able to use the air dispersion
modeling results to estimate the potential for an adverse environmental
effect.
    The EPA acknowledges that other HAP beyond the seven HAP discussed
above may have the potential to cause adverse environmental effects.
Therefore, the EPA may include other relevant HAP in its environmental
risk screening in the future, as modeling science and resources allow.
The EPA invites comment on the extent to which other HAP emitted by the
source categories 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 categories that such benchmarks
indicate could be adversely affected.
c. Ecological Assessment Endpoints and Benchmarks for PB-HAP
    An important consideration in the development of the EPA's
screening methodology is the selection of ecological assessment
endpoints and benchmarks. Ecological assessment endpoints are defined
by the ecological entity (e.g., aquatic communities including fish and
plankton) and its attributes (e.g., frequency of mortality). Ecological
assessment endpoints can be established for organisms, populations,
communities or assemblages, and ecosystems.
    For PB-HAP, we evaluated the following community-level ecological
assessment endpoints to screen for organisms directly exposed to HAP in
soils, sediment and water:
     Local terrestrial communities (i.e., soil invertebrates,
plants) and populations of small birds and mammals that consume soil
invertebrates exposed to PB-HAP in the surface soil.
     Local benthic (i.e., bottom sediment dwelling insects,
amphipods, isopods and crayfish) communities exposed to PB-HAP in
sediment in nearby water bodies.
     Local aquatic (water-column) communities (including fish
and plankton) exposed to PB-HAP in nearby surface waters.
    For PB-HAP, we also evaluated the following population-level
ecological assessment endpoint to screen for indirect HAP exposures of
top consumers via the bioaccumulation of HAP in food chains.
     Piscivorous (i.e., fish-eating) wildlife consuming PB-HAP-
contaminated fish from nearby water bodies.
    For cadmium compounds, dioxins/furans, POM and mercury, we
identified the available ecological benchmarks for each assessment
endpoint. An ecological benchmark represents a concentration of HAP
(e.g., 0.77 micrograms of HAP per liter of water) that has been linked
to a particular environmental effect level (e.g., a no-observed-
adverse-effect level (NOAEL)) through scientific study. For PB-HAP we
identified, where possible, ecological benchmarks at the following
effect levels:
     Probable effect level (PEL): Level above which adverse
effects are expected to occur frequently.
     Lowest-observed-adverse-effect level (LOAEL): The lowest
exposure level tested at which there are biologically significant
increases in frequency or severity of adverse effects.
     No-observed-adverse-effect level (NOAEL): The highest
exposure level tested at which there are no biologically significant
increases in the frequency or severity of adverse effect.
    We established a hierarchy of preferred benchmark sources to allow
selection of benchmarks for each environmental HAP at each ecological
assessment endpoint. In general, the EPA sources that are used at a
programmatic level (e.g., Office of Water, Superfund Program) were
used, if available. If not, the EPA benchmarks used in regional
programs (e.g., Superfund) were used. If benchmarks were not available
at a programmatic or regional level, we used benchmarks developed by
other federal agencies (e.g., NOAA) or state agencies.
    Benchmarks for all effect levels are not available for all PB-HAP
and assessment endpoints. In cases where multiple effect levels were
available for a particular PB-HAP and assessment endpoint, we use all
of the available effect levels to help us to determine whether
ecological risks exist and, if so, whether the risks could be
considered significant and widespread.
d. Ecological Assessment Endpoints and Benchmarks for Acid Gases
    The environmental screening analysis also evaluated potential
damage and reduced productivity of plants due to direct exposure to
acid gases in the air. For acid gases, we evaluated the following
ecological assessment endpoint:
     Local terrestrial plant communities with foliage exposed
to acidic gaseous HAP in the air.
    The selection of ecological benchmarks for the effects of acid
gases on plants followed the same approach as for PB-HAP (i.e., we
examine all of the available chronic benchmarks). For HCl, the EPA
identified chronic benchmark concentrations. We note that the benchmark
for chronic HCl exposure to plants is greater than the reference
concentration for chronic inhalation exposure for human health. This
means

that where EPA includes regulatory requirements to prevent an
exceedance of the reference concentration for human health, additional
analyses for adverse environmental effects of HCl would not be
necessary.
    For HF, EPA identified chronic benchmark concentrations for plants
and evaluated chronic exposures to plants in the screening analysis.
High concentrations of HF in the air have also been linked to fluorosis
in livestock. However, the HF concentrations at which fluorosis in
livestock occur are higher than those at which plant damage begins.
Therefore, the benchmarks for plants are protective of both plants and
livestock.
e. Screening Methodology
    For the environmental risk screening analysis, the EPA first
determined whether any petroleum refineries emitted any of the seven
environmental HAP. For the petroleum refinery source categories, we
identified emissions of cadmium, dioxins/furans, POM, mercury (both
inorganic mercury and methyl mercury), lead, HCl and HF.
    Because one or more of the seven environmental HAP evaluated are
emitted by at least one petroleum refinery, we proceeded to the second
step of the evaluation.
f. PB-HAP Methodology
    For cadmium, mercury, POM and dioxins/furans, the environmental
screening analysis consists of two tiers, while lead is analyzed
differently as discussed earlier. In the first tier, we determined
whether the maximum facility-specific emission rates of each of the
emitted environmental HAP were large enough to create the potential for
adverse environmental effects under reasonable worst-case environmental
conditions. These are the same environmental conditions used in the
human multipathway exposure and risk screening analysis.
    To facilitate this step, TRIM.FaTE was run for each PB-HAP under
hypothetical environmental conditions designed to provide
conservatively high HAP concentrations. The model was set to maximize
runoff from terrestrial parcels into the modeled lake, which in turn,
maximized the chemical concentrations in the water, the sediments, and
the fish. The resulting media concentrations were then used to back-
calculate a screening threshold emission rate that corresponded to the
relevant exposure benchmark concentration value for each assessment
endpoint. To assess emissions from a facility, the reported emission
rate for each PB-HAP was compared to the screening threshold emission
rate for that PB-HAP for each assessment endpoint. If emissions from a
facility do not exceed the Tier I threshold, the facility ``passes''
the screen, and therefore, is not evaluated further under the screening
approach. If emissions from a facility exceed the Tier I threshold, we
evaluate the facility further in Tier II.
    In Tier II of the environmental screening analysis, the screening
emission thresholds are adjusted to account for local meteorology and
the actual location of lakes in the vicinity of facilities that did not
pass the Tier I screen. The modeling domain for each facility in the
Tier II analysis consists of eight octants. Each octant contains five
modeled soil concentrations at various distances from the facility (5
soil concentrations x 8 octants = total of 40 soil concentrations per
facility) and one lake with modeled concentrations for water, sediment
and fish tissue. In the Tier II environmental risk screening analysis,
the 40 soil concentration points are averaged to obtain an average soil
concentration for each facility for each PB-HAP. For the water,
sediment and fish tissue concentrations, the highest value for each
facility for each pollutant is used. If emission concentrations from a
facility do not exceed the Tier II threshold, the facility passes the
screen, and is typically not evaluated further. If emissions from a
facility exceed the Tier II threshold, the facility does not pass the
screen and, therefore, may have the potential to cause adverse
environmental effects. Such facilities are evaluated further to
investigate factors such as the magnitude and characteristics of the
area of exceedance.
g. Acid Gas Methodology
    The environmental screening analysis evaluates the potential
phytotoxicity and reduced productivity of plants due to chronic
exposure to acid gases. The environmental risk screening methodology
for acid gases is a single-tier screen that compares the average off-
site ambient air concentration over the modeling domain to ecological
benchmarks for each of the acid gases. Because air concentrations are
compared directly to the ecological benchmarks, emission-based
thresholds are not calculated for acid gases as they are in the
ecological risk screening methodology for PB-HAP.
    For purposes of ecological risk screening, EPA identifies a
potential for adverse environmental effects to plant communities from
exposure to acid gases when the average concentration of the HAP around
a facility exceeds the LOAEL ecological benchmark. In such cases, we
further investigate factors such as the magnitude and characteristics
of the area of exceedance (e.g., land use of exceedance area, size of
exceedance area) to determine if there is an adverse environmental
effect.
    For further information on the environmental screening analysis
approach, see section IV.C.5 of this preamble and the Draft Residual
Risk Assessment for the Petroleum Refining Source Sector, which is
available in the docket for this action (Docket ID Number EPA-HQ-OAR-
2010-0682).
7. How did we conduct facility-wide assessments?
    To put the source category risks in context, following the
assessment approach outlined in the SAB (2010) review, we examine the
risks from the entire ``facility,'' where the facility includes all
HAP-emitting operations within a contiguous area and under common
control. In other words, we examine the HAP emissions not only from the
source category emission points of interest, but also emissions of HAP
from all other emission sources at the facility for which we have data.
    The emissions inventories provided in response to the ICR included
emissions information for all emission sources at the facilities that
are part of the refineries source categories. Generally, only a few
emission sources located at refineries are not subject to either
Refinery MACT 1 or 2; the most notable are boilers, process heaters and
internal combustion engines, which are addressed by other MACT
standards.
    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 source category risks were compared to the facility-wide risks
to determine the portion of facility-wide risks that could be
attributed to each of the source categories addressed in this proposal.
We specifically examined the facility that was associated with the
highest estimates of risk and determined the percentage of that risk
attributable to the source category of interest. The Draft Residual
Risk Assessment for the Petroleum Refining Source Sector available
through the docket for this action (Docket ID Number EPA-HQ-OAR-2010-
0682) provides the methodology and results of the facility-wide
analyses, including all facility-wide risks and the percentage of
source category contribution to facility-wide risks.

8. How did we consider uncertainties in risk assessment?
    In the Benzene NESHAP we concluded that risk estimation uncertainty
should be considered in our decision-making under the ample margin of
safety framework. Uncertainty and the potential for bias are inherent
in all risk assessments, including those performed for this proposal.
Although uncertainty exists, we believe that our approach, which used
conservative tools and assumptions, ensures that our decisions are
health protective and environmentally protective. A brief discussion of
the uncertainties in the emissions datasets, 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 Petroleum Refining Source
Sector, which is available in the docket for this action (Docket ID
Number EPA-HQ-OAR-2010-0682).
a. Uncertainties in the Emission Datasets
    Although the development of the RTR datasets involved quality
assurance/quality control processes, the accuracy of emissions values
will vary depending on the source of the data, the degree to which data
are incomplete or missing, the degree to which assumptions made to
complete the datasets are accurate, errors in emission estimates and
other factors. The emission estimates considered in this analysis are
annual totals for 2010, 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 emission adjustment factors applied
to the average annual hourly emission rates, which are intended to
account for emission fluctuations due to normal facility operations.
    As discussed previously, we attempted to provide a consistent
framework for reporting of emissions information by developing the
refinery emissions estimation protocol and requesting that refineries
follow the protocol when reporting emissions inventory data in response
to the ICR. This protocol, called Emission Estimation Protocol for
Petroleum Refineries, is available in the docket for this rulemaking
(Docket Item Number EPA-HQ-OAR-2010-0682-0060). Additionally, we
developed our own estimates of emissions that are based on the factors
provided in the protocol and the REM Model. We developed emission
estimates based on refinery unit capacities, which also provided an
estimate of allowable emissions. We then conducted risk modeling using
REM Model estimates and by locating emissions at the centroid of each
refinery in an attempt to understand the risk associated with emissions
from each refinery. Therefore, even if there were errors in the
emission inventories reported in the ICR, as was the case in many
instances, emissions for those facilities were also modeled using the
protocol emission factors. The risk modeling of allowable emissions
based on emission factors and unit capacities did not result in
significantly different risk results than the actual emissions modeling
runs. Results of the allowable emissions risk estimates are provided in
the Draft Residual Risk Assessment for the Petroleum Refining Source
Sector, which is available in Docket ID Number EPA-HQ-OAR-2010-0682.
b. Uncertainties in Dispersion Modeling
    We recognize there is uncertainty in ambient concentration
estimates associated with any model, including the EPA's recommended
regulatory dispersion model, AERMOD. In using a model to estimate
ambient pollutant concentrations, the user chooses certain options to
apply. For RTR assessments, we select some model options that have the
potential to overestimate ambient air concentrations (e.g., not
including plume depletion or pollutant transformation). We select other
model options that have the potential to underestimate ambient impacts
(e.g., not including building downwash). Other options that we select
have the potential to either under- or overestimate ambient levels
(e.g., meteorology and receptor locations). On balance, considering the
directional nature of the uncertainties commonly present in ambient
concentrations estimated by dispersion models, the approach we apply in
the RTR assessments should yield unbiased estimates of ambient HAP
concentrations.
c. Uncertainties in Inhalation Exposure
    The EPA did not include the effects of human mobility on exposures
in the assessment. Specifically, short-term mobility and long-term
mobility between census blocks in the modeling domain were not
considered.\16\ 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).
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    \16\ 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 further from the
facility and under-predict exposures for people in the census block who
live closer to the facility. Thus, using the census block centroid to
predict chronic exposures may lead to a potential understatement or
overstatement of the true maximum impact, but is an unbiased estimate
of average risk and incidence. We reduce this uncertainty by analyzing
large census blocks near facilities using aerial imagery and adjusting
the location of the block centroid to better represent the population
in the block, as well as adding additional receptor locations where the
block population is not well represented by a single location.
    The assessment evaluates the cancer inhalation risks associated
with pollutant exposures over a 70-year period, which is the assumed
lifetime of an individual. In reality, both the length of time that
modeled emission sources at facilities actually operate (i.e., more or
less than 70 years) and the domestic growth or decline of the modeled
industry (i.e., the increase or decrease in the number or size of
domestic facilities) will influence the future risks posed by a given
source or source category. Depending on the characteristics of the
industry, these factors will, in most cases, result in an overestimate
both in individual risk levels and in the total estimated number of
cancer cases. However, in the unlikely scenario where a facility
maintains, or even increases, its emissions levels over a period of
more than 70 years, residents live beyond 70 years at the same
location, and the residents spend most of their days at that location,
then the cancer inhalation risks could potentially be underestimated.
However, annual cancer incidence estimates from exposures to emissions
from these

sources would not be affected by the length of time an emissions source
operates.
    The exposure estimates used in these analyses assume chronic
exposures to ambient (outdoor) levels of pollutants. Because most
people spend the majority of their time indoors, actual exposures may
not be as high, depending on the characteristics of the pollutants
modeled. For many of the HAP, indoor levels are roughly equivalent to
ambient levels, but for very reactive pollutants or larger particles,
indoor levels are typically lower. This factor has the potential to
result in an overestimate of 25 to 30 percent of exposures.\17\
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    \17\ U.S. EPA. National-Scale Air Toxics Assessment for 1996.
(EPA 453/R-01-003; January 2001; page 85.)
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    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 when peak emissions
and worst-case meteorological conditions occur simultaneously.
d. Uncertainties in Dose-Response Relationships
    There are uncertainties inherent in the development of the dose-
response values used in our risk assessments for cancer effects from
chronic exposures and non-cancer effects from both chronic and acute
exposures. Some uncertainties may be considered quantitatively, and
others generally are expressed in qualitative terms. We note as a
preface to this discussion a point on dose-response uncertainty that is
brought out in the EPA's 2005 Cancer Guidelines; namely, that ``the
primary goal of EPA actions is protection of human health; accordingly,
as an Agency policy, risk assessment procedures, including default
options that are used in the absence of scientific data to the
contrary, should be health protective'' (EPA 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 Petroleum Refining Source
Sector, which is available in the docket for this action (Docket ID
Number EPA-HQ-OAR-2010-0682).
    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).\18\ In some circumstances, the true risk could be as
low as zero; however, in other circumstances, the risk could also be
greater.\19\ 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).
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    \18\ IRIS glossary (http://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary).
    \19\ An exception to this is the URE for benzene, which is
considered to cover a range of values, each end of which is
considered to be equally plausible, and which is based on maximum
likelihood estimates.
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    Chronic non-cancer RfC and reference dose (RfD) values represent
chronic exposure levels that are intended to be health-protective
levels. Specifically, these values provide an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure (RfC) or a daily oral exposure (RfD) to the human
population (including sensitive subgroups) that is likely to be without
an appreciable risk of deleterious effects during a lifetime. To derive
values that are intended to be ``without appreciable risk,'' the
methodology relies upon an uncertainty factor (UF) approach (U.S. EPA,
1993, 1994) which considers uncertainty, variability and gaps in the
available data. The UF are applied to derive reference values that are
intended to protect against appreciable risk of deleterious effects.
The UF are commonly default values,\20\ e.g., factors of 10 or 3, used
in the absence of compound-specific data; where data are available, UF
may also be developed using compound-specific information. When data
are limited, more assumptions are needed and more UF are used. Thus,